2022-01-17T08:04:12Z
http://ulir.ul.ie/oai/request
oai:ulir.ul.ie:10344/349
2017-01-26T14:57:31Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Gleeson, James P.
funder:SFI
2009
http://hdl.handle.net/10344/349
peer-reviewed
The motion of overdamped particles in a one-dimensional spatially-periodic potential is considered. The potential is also randomly-fluctuating in time, due to multiplicative colored noise terms, and has a deterministic tilt. Numerical simulations show two distinct parameter regimes, corresponding to free-running near-deterministic particles, and particles which are trapped in local minima of the potential with intermittent escape flights. Perturbation and asymptotic methods are developed to understand the drift velocity and diffusion coefficient in each parameter regime.
Science Foundation Ireland: 06/IN.1/366 and 05/RFP/MAT0016.
eng
Physica A;388/4
http://dx.doi.org/10.1016/j.physa.2008.10.013
05/RFP/MAT0016
random transport
colored noise
Transport in randomly-fluctuating spatially-periodic potentials
Journal Article
oai:ulir.ul.ie:10344/350
2015-04-30T14:31:10Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Khoury, Maria
Gleeson, James P.
Sancho, J. M.
Lacasta, A. M.
Lindenberg, Katja
funder:SFI
2009
http://hdl.handle.net/10344/350
peer-reviewed
Transport and diffusion of particles on modulated surfaces is a nonequilibrium problem which is receiving a great deal of attention due to its technological applications, but analytical calculations are scarce. In earlier work, we developed a perturbative approach to begin to provide an analytic platform for predictions about particle trajectories over such surfaces. In some temperature and forcing regimes, we successfully reproduced results for average particle velocities obtained from numerical simulations. In this paper, we extend the perturbation theory to the calculation of higher moments, in particular the diffusion tensor and the skewness. Numerical simulations are used to check the domain of validity of the perturbative approach.
eng
American Physical Society
Physical Review E;80 Art No. 021123
http://dx.doi.org/10.1103/PhysRevE.80.021123
06/IN.1/I366
MACSI
perturbation theory
surface diffusion
Diffusion coefficient in periodic and random potentials
Journal Article
oai:ulir.ul.ie:10344/347
2015-05-18T11:02:42Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Gleeson, James P.
2009
http://hdl.handle.net/10344/347
peer-reviewed
Analytical results are derived for the bond percolation threshold and the size of the giant connected component in a class of random networks with nonzero clustering. The network's degree distribution and clustering spectrum may be prescribed and theoretical results match well with numerical simulations on both synthetic and real-world networks.
Science Foundation Ireland: 06/IN.1/I366 and MACSI 06/MI/005
eng
American Physical Society
Physical Review E;80 Art No. 036107
http://dx.doi.org/10.1103/PhysRevE.80.036107
networks
percolation
Bond percolation on a class of clustered random networks
Journal Article
oai:ulir.ul.ie:10344/348
2020-12-02T12:55:22Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Gleeson, James P.
Melnik, Sergey
2009
http://hdl.handle.net/10344/348
peer-reviewed
An analytical approach to calculating bond percolation thresholds, sizes of k-cores, and sizes of giant connected components on structured random networks with nonzero clustering is presented. The networks are generated using a generalization of Trapman's [P. Trapman, Theor. Popul. Biol. 71, 160 (2007)] model of cliques embedded in treelike random graphs. The resulting networks have arbitrary degree distributions and tunable degree-dependent clustering. The effect of clustering on the bond percolation thresholds for networks of this type is examined and contrasted with some recent results in the literature. For very high levels of clustering the percolation threshold in these generalized Trapman networks is increased above the value it takes in a randomly wired (unclustered) network of the same degree distribution. In assortative scale-free networks, where the variance of the degree distribution is infinite, this clustering effect can lead to a nonzero percolation (epidemic) threshold.
SFI
American Physical Society
http://dx.doi.org/10.1103/PhysRevE.80.046121
Physical Review E;80 Art No. 046121
05/RFP/MAT0016
06/IN.1/I366
MACSI
05/RFP/MAT0016
network theory
percolation
Analytical results for bond percolation and k-core sizes on clustered networks
Journal Article
oai:ulir.ul.ie:10344/4444
2017-01-26T14:51:20Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Gleeson, James P.
funder:SFI
funder:ERC
2013
http://hdl.handle.net/10344/4444
peer-reviewed
A wide class of binary-state dynamics on networks-including, for example, the voter model, the Bass diffusion model, and threshold models-can be described in terms of transition rates (spin-flip probabilities) that depend on the number of nearest neighbors in each of the two possible states. High-accuracy approximations for the emergent dynamics of such models on uncorrelated, infinite networks are given by recently developed compartmental models or approximate master equations (AMEs). Pair approximations (PAs) and mean-field theories can be systematically derived from the AME. We show that PA and AME solutions can coincide under certain circumstances, and numerical simulations confirm that PA is highly accurate in these cases. For monotone dynamics (where transitions out of one nodal state are impossible, e.g., susceptible-infected disease spread or Bass diffusion), PA and the AME give identical results for the fraction of nodes in the infected (active) state for all time, provided that the rate of infection depends linearly on the number of infected neighbors. In the more general nonmonotone case, we derive a condition-that proves to be equivalent to a detailed balance condition on the dynamics-for PA and AME solutions to coincide in the limit t -> infinity. This equivalence permits bifurcation analysis, yielding explicit expressions for the critical (ferromagnetic or paramagnetic transition) point of such dynamics, that is closely analogous to the critical temperature of the Ising spin model. Finally, the AME for threshold models of propagation is shown to reduce to just two differential equations and to give excellent agreement with numerical simulations. As part of this work, the Octave or Matlab code for implementing and solving the differential-equation systems is made available for download.
PUBLISHED
peer-reviewed
eng
American Physical Society
317614
Physical Review X;3, 021004
http://dx.doi.org/10.1103/PhysRevX.3.021004
11/PI/1026
09/SR/E1780
317614
collective behavior
model
spread
recruitment
contagion
graphs
Binary-state dynamics on complex networks: pair approximation and beyond
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4445
2019-09-23T13:25:41Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Fennell, Peter G.
Gleeson, James P.
Cellai, Davide
funder:SFI
funder:ERC
2014
http://hdl.handle.net/10344/4445
peer-reviewed
Facilitated spin models were introduced some decades ago to mimic systems characterized by a glass transition. Recent developments have shown that a class of facilitated spin models is also able to reproduce characteristic signatures of the structural relaxation properties of glass-forming liquids. While the equilibrium phase diagram of these models can be calculated analytically, the dynamics are usually investigated numerically. Here we propose a network-based approach, called approximate master equation (AME), to the dynamics of the Fredrickson-Andersen model. The approach correctly predicts the critical temperature at which the glass transition occurs. We also find excellent agreement between the theory and the numerical simulations for the transient regime, except in close proximity of the liquid-glass transition. Finally, we analytically characterize the critical clusters of the model and show that the departures between our AME approach and the Monte Carlo can be related to the large interface between blocked and unblocked spins at temperatures close to the glass transition.
PUBLISHED
peer-reviewed
eng
American Physical Society
317614
Physical Review E;90, 032824
http://dx.doi.org/10.1103/PhysRevE.90.032824
11/P1/1026
317614
glass-transition
bootstrap percolation
bethe lattice
Analytical approach to the dynamics of facilitated spin models on random networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4453
2020-12-02T12:54:56Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Gleeson, James P.
Melnik, Sergey
Ward, Jonathan A
Porter, Mason A
Murcha, Peter J
funder:SFI
funder:INSPIRE
2012
http://hdl.handle.net/10344/4453
peer-reviewed
Mean-field analysis is an important tool for understanding dynamics on complex networks. However, surprisingly little attention has been paid to the question of whether mean-field predictions are accurate, and this is particularly true for real-world networks with clustering and modular structure. In this paper, we compare mean-field predictions to numerical simulation results for dynamical processes running on 21 real-world networks and demonstrate that the accuracy of such theory depends not only on the mean degree of the networks but also on the mean first-neighbor degree. We show that mean-field theory can give (unexpectedly) accurate results for certain dynamics on disassortative real-world networks even when the mean degree is as low as 4.
PUBLISHED
peer-reviewed
eng
American Physical Society
Physical Review E;85, 026106
http://dx.doi.org/10.1103/PhysRevE.85.026106
06/IN.1/I366
06/MI/005
09/SRC/EI780
220020177
EP/I016058/1
DMS-0645369
complex networks
heterogeneous networks
epidemics
spread
models
Accuracy of mean-field theory for dynamics on real-world networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4462
2020-12-02T16:01:43Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Gleeson, James P.
Ward, Jonathan A
O'Sullivan, Kevin P.
Lee, William T.
funder:SFI
2014
http://hdl.handle.net/10344/4462
peer-reviewed
Heavy-tailed distributions of meme popularity occur naturally in a model of meme diffusion on social networks. Competition between multiple memes for the limited resource of user attention is identified as the mechanism that poises the system at criticality. The popularity growth of each meme is described by a critical branching process, and asymptotic analysis predicts power-law distributions of popularity with very heavy tails (exponent alpha
PUBLISHED
peer-reviewed
eng
American Physical Society
Physical Review Letters;112, 048701
http://dx.doi.org/10.1103/PhysRevLett.112.048701
11/PI/1026
09/SRC/E1780
EP/I016048/1
self-organized criticality
evolution
distributions
extinction
emergence
systems
Competition-induced criticality in a model of meme popularity
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4463
2017-01-26T14:56:47Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Gleeson, James P.
funder:SFI
2011
http://hdl.handle.net/10344/4463
peer-reviewed
Binary-state dynamics (such as the susceptible-infected-susceptible (SIS) model of disease spread, or Glauber spin dynamics) on random networks are accurately approximated using master equations. Standard mean-field and pairwise theories are shown to result from seeking approximate solutions of the master equations. Applications to the calculation of SIS epidemic thresholds and critical points of nonequilibrium spin models are also demonstrated.
PUBLISHED
peer-reviewed
eng
American Physical Society
http://dx.doi.org/10.1103/PhysRevLett.107.068701
06/IN1/I366
06/MI/005
contact process
model
epidemics
lattice
spread
High-accuracy approximation of binary-state dynamics on networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4464
2019-09-13T10:23:04Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Cellai, Davide
López, Eduardo
Zhou, Jie
Gleeson, James P.
Bianconi, Ginestra
funder:SFI
2013
http://hdl.handle.net/10344/4464
peer-reviewed
From transportation networks to complex infrastructures, and to social and communication networks, a large variety of systems can be described in terms of multiplexes formed by a set of nodes interacting through different networks (layers). Multiplexes may display an increased fragility with respect to the single layers that constitute them. However, so far the overlap of the links in different layers has been mostly neglected, despite the fact that it is an ubiquitous phenomenon in most multiplexes. Here, we show that the overlap among layers can improve the robustness of interdependent multiplex systems and change the critical behavior of the percolation phase transition in a complex way.
PUBLISHED
peer-reviewed
eng
American Physical Society
Physical Review E;88, 052811
http://dx.doi.org/10.1103/PhysRevE.88.052811
11/PI/1026
interdependent networks
complex networks
systems
Percolation in multiplex networks with overlap
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4465
2020-12-02T12:59:29Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Melnik, Sergey
Hackett, Adam W.
Porter, Mason A
Mucha, Peter J
Gleeson, James P.
funder:SFI
2011
http://hdl.handle.net/10344/4465
peer-reviewed
We demonstrate that a tree-based theory for various dynamical processes operating on static, undirected networks yields extremely accurate results for several networks with high levels of clustering. We find that such a theory works well as long as the mean intervertex distance l is sufficiently small-that is, as long as it is close to the value of l in a random network with negligible clustering and the same degree-degree correlations. We support this hypothesis numerically using both real-world networks from various domains and several classes of synthetic clustered networks. We present analytical calculations that further support our claim that tree-based theories can be accurate for clustered networks, provided that the networks are "sufficiently small" worlds.
PUBLISHED
peer-reviewed
eng
American Physical Society
Physical Review E;83, 036112
http://dx.doi.org/10.1103/PhysRevE.83.036112
06/IN.1/I366
06/MI/005
complex networks
heterogeneous networks
random graphs
populations
epidemics
dynamics
disease
spread
The unreasonable effectiveness of tree-based theory for networks with clustering
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4466
2020-12-02T12:56:24Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Melnik, Sergey
Porter, Mason A
Mucha, Peter J
Gleeson, James P.
funder:IRC
funder:SFI
funder:ERC
2014
http://hdl.handle.net/10344/4466
peer-reviewed
We develop a new ensemble of modular random graphs in which degree-degree correlations can be different in each module, and the inter-module connections are defined by the joint degree-degree distribution of nodes for each pair of modules. We present an analytical approach that allows one to analyze several types of binary dynamics operating on such networks, and we illustrate our approach using bond percolation, site percolation, and the Watts threshold model. The new network ensemble generalizes existing models (e. g., the well-known configuration model and Lancichinetti-Fortunato-Radicchi networks) by allowing a heterogeneous distribution of degree-degree correlations across modules, which is important for the consideration of nonidentical interacting networks. (C) 2014 AIP Publishing LLC.
PUBLISHED
peer-reviewed
eng
American Institute of Physics
317614
Chaos;24, 023106
http://dx.doi.org/10.1063/1.4869983
11/PI/1026
317614
complex networks
interdependent networks
cascade
model
Dynamics on modular networks with heterogeneous correlations
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4467
2020-12-02T12:59:09Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Melnik, Sergey
Ward, Jonathan A
Gleeson, James P.
Porter, Mason A
2013
http://hdl.handle.net/10344/4467
peer-reviewed
The spread of ideas across a social network can be studied using complex contagion models, in which agents are activated by contact with multiple activated neighbors. The investigation of complex contagions can provide crucial insights into social influence and behavior-adoption cascades on networks. In this paper, we introduce a model of a multi-stage complex contagion on networks. Agents at different stages-which could, for example, represent differing levels of support for a social movement or differing levels of commitment to a certain product or idea-exert different amounts of influence on their neighbors. We demonstrate that the presence of even one additional stage introduces novel dynamical behavior, including interplay between multiple cascades, which cannot occur in single-stage contagion models. We find that cascades-and hence collective action-can be driven not only by high-stage influencers but also by low-stage influencers. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4790836]
PUBLISHED
peer-reviewed
eng
American Institute of Physics
Chaos;23, 013124
http://dx.doi.org/10.1063/1.4790836
social-influence
collective action
networks
behavior
diffusion
model
dynamics
spread
innovations
cascades
Multi-stage complex contagions
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4469
2019-05-01T14:56:45Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Hackett, Adam W.
Gleeson, James P.
funder:SFI
2013
http://hdl.handle.net/10344/4469
peer-reviewed
We present an analytical approach to determining the expected cascade size in a broad range of dynamical models on the class of highly clustered random graphs introduced by Gleeson [J. P. Gleeson, Phys. Rev. E 80, 036107 (2009)]. A condition for the existence of global cascades is also derived. Applications of this approach include analyses of percolation, and Watts's model. We show how our techniques can be used to study the effects of in-group bias in cascades on social networks.
PUBLISHED
peer-reviewed
eng
American Physical Society
Physical Review E;87, 062801
http://dx.doi.org/10.1103/PhysRevE.87.062801
06/IN.1/I366
11/PI/1026
06/MI/005
NETWORKS
field ising-model
collective dynamics
networks
hysteresis
robustness
Cascades on clique-based graphs
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4472
2020-12-02T12:55:42Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Hackett, Adam W.
Melnik, Sergey
Gleeson, James P.
funder:SFI
2011
http://hdl.handle.net/10344/4472
peer-reviewed
We present an analytical approach to determining the expected cascade size in a broad range of dynamical models on the class of random networks with arbitrary degree distribution and nonzero clustering introduced previously in [M.E.J. Newman, Phys. Rev. Lett. 103, 058701 (2009)]. A condition for the existence of global cascades is derived as well as a general criterion that determines whether increasing the level of clustering will increase, or decrease, the expected cascade size. Applications, examples of which are provided, include site percolation, bond percolation, and Watts' threshold model; in all cases analytical results give excellent agreement with numerical simulations.
PUBLISHED
peer-reviewed
eng
American Physical Society
Physical Review E;83, 056107
http://dx.doi.org/10.1103/PhysRevE.83.056107
061/IN.1/I366
06/M1/005
scale-free networks
random graphs
percolation
epidemics
Cascades on a class of clustered random networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4523
2017-01-26T14:54:32Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Gleeson, James P.
funder:SFI
2008
http://hdl.handle.net/10344/4523
peer-reviewed
The mean size of unordered binary avalanches on infinite directed random networks may be determined using the damage propagation function introduced by [B. Samuelsson and J. E. S. Socolar, Phys. Rev. E 74, 036113 (2006)]. The derivation of Samuelsson and Socolar explicitly assumes a Poisson distribution of out-degrees. It is shown here that the damage propagation function method may be used whenever the in-degree and out-degree of network nodes are independently distributed; in particular, it is not necessary that the out-degree distribution be Poisson. The general case of correlated in- and out-degrees is discussed and numerical simulations (on large finite networks) are compared with the theoretical predictions (for infinite networks).
PUBLISHED
peer-reviewed
eng
American Physical Society
Physical Review E;77, 057101
http://dx.doi.org/10.1103/PhysRevE.77.057101
06/IN.1/1366
05 RFPMAT0016
random networks
Mean size of avalanches on directed random networks with arbitrary degree distributions
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4547
2018-12-04T11:26:38Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Kyrke-Smith, T.M.
Katz, R.F
Fowler, Andrew C.
2013
http://hdl.handle.net/10344/4547
peer-reviewed
One challenge in improving our understanding of ice-stream dynamics is to develop models of the spatial and temporal transition from ice-sheet to ice-stream flow. We address this with a new, vertically integrated, higher-order formulation for ice-sheet dynamics that captures the leading-order physics of low aspect ratio, viscous fluid flow, regardless of the amount of slip at the bed. The theory introduces a parameter, lambda, which approximates the ratio of the basal stress to the shear stress scale, providing a measure of the relative importance of sliding and internal deformation. Our model is able to simultaneously describe the dynamics of both a slow-moving sheet and rapidly flowing ice streams. To test the formulation, we apply a triple-valued sliding law as the basal boundary condition and obtain numerical solutions that can be compared with previous work. We investigate the sensitivity of flow regimes and shear margin width to parameter variation, deriving a scaling for the latter. We also consider a double-valued sliding law, which enforces a constant, low basal stress beneath the ice stream. Comparisons of the resultant stress fields illustrate the different stress balances that can maintain ice-stream flow.
PUBLISHED
peer-reviewed
eng
International Glaciological Society
Journal of Glaciology;519, (215), pp. 449-466
http://dx.doi.org/10.3189/2013JoG12J140
glacier surge mechanism
sheet model pism
West Antarctica
till deformation
Stress balances of ice streams in a vertically integrated, higher-order formulation
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4557
2015-07-24T00:20:23Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Vynnycky, Michael
Masuda, Y
funder:SFI
2013
http://hdl.handle.net/10344/4557
peer-reviewed
The problem of fast viscous steady Rayleigh-Bénard convection in a rectangular
enclosure is revisited using asymptotic and numerical methods. There are two generic
cases: in the first, there is zero shear stress at all boundaries; in the second, there is
zero shear stress at the vertical boundaries, but no slip at the horizontal ones. For
the first case, we reconcile our new numerical solutions to the full equations with
earlier asymptotic results for large Rayleigh number and effectively infinite Prandtl
number. For the second case, we first derive the corresponding asymptotic theory and
then reconcile it also with the relevant full numerical solutions. However, the latter
also indicate behavior which the asymptotic theory does not predict, for Rayleigh
numbers in excess of just over 106 and aspect ratios in excess of around 1.1. C 2013
AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4829450
eng
American Institute of Physics
Physics of Fluids;25, 113602
http://dx.doi.org/10.1063/1.4829450
Rayleigh-Bénard convection
numerical methods
Rayleigh-Bénard convection at high Rayleigh number and infinite Prandtl number: asymptotics and numerics
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4688
2018-05-04T09:11:02Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Dassios, Ioannis K.
Zimbidis, Alexandros
Kontzalis, Charalambos
funder:SFI
2014
http://hdl.handle.net/10344/4688
peer-reviewed
This paper extends the classical Samuelson multiplier–accelerator model
for national economy. Actually, this new modeling structure removes the basic shortcoming of the original model producing stable business cycles when realistic values
of the parameters (multiplier, accelerator) are entered into the system of equations.
Under this new approach, we introduce some kind of randomness and memory into
the system. We assume that consumption, private investment and governmental expenditure depend upon the national income values of the last n (n > 1) years and
further assume that multiplier and accelerator factors are stochastic variables. Then
stochastic delayed difference equations of higher order are employed to describe the
model, while the respective solutions of higher order polynomials for the expectation
of national income variables correspond to the typical observed business cycles of
real economy. Stability and controllability conditions are investigated while numerical
examples provide further insight and better understanding as regards the control
actions, system design, and produced business cycles.
eng
Springer
Journal of Economic Structures;3 (7), pp. 1-24
http://dx.doi.org/10.1186/s40008-014-0007-y
SFI/09/SRC/E1780
Samuelson model
stochastic
difference equations
stability
control
state feedback
The delay effect in a sochastic multiplier–accelerator model
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/4689
2018-05-04T09:11:18Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Dassios, Ioannis K.
Cuffe, Paul
Keane, Andrew
funder:SFI
funder:ERC
2015
http://hdl.handle.net/10344/4689
n/a
Electrical power system calculations rely heavily on the Y_{bus} matrix,
which is the Laplacian matrix of the network under study, weighted by the
complex-valued admittance of each branch. It is often useful to partition the
Y_{bus} into four submatrices, to separately quantify the connectivity
between and among the load and generation nodes in the network. Simple
manipulation of these submatrices gives the F_{LG} matrix, which offers
useful insights on how voltage deviations propagate through a power system and
on how energy losses may be minimized. Various authors have observed that in
practice the elements of F_{LG} are real-valued and its rows sum close to
one: the present paper explains and proves these properties.
eng
608732
09/SRC/E1780
FP7/2007-2013
Laplacian matrix
power ow
admittance matrix
On the unity row summation and real valued nature of the F_{LG} matrix
info:eu-repo/semantics/report
oai:ulir.ul.ie:10344/4919
2018-07-06T12:36:29Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_4612
hdl_10344_4609
hdl_10344_4613
hdl_10344_73
hdl_10344_20
Kieran, Jennifer Ann
Norris, Suzanne
O'Leary, Aisling
Walsh, Cathal Dominic
Merriman, Raphael
Houlihan, D.
McCormick, Aiden
McKiernan, Susan
Bergin, Colm
Barry, Michael
2015
http://hdl.handle.net/10344/4919
peer-reviewed
Background: Recent advances in Hepatitis C therapeutics offer the possibility of cure but will be expensive. The cost of treatment may be partially offset by the avoidance of advanced liver disease. We performed a micro-costing study of the ambulatory healthcare utilisation of patients with Hepatitis C supplemented with inpatient diagnosis related group costs.Methods: The staff utilisation costs associated with a Hepatitis C ambulatory visit were measured and combined with the costs of investigations to establish a mean cost per consultation. An annualised estimate of cost was produced by multiplying this by the number of consultations accessed, stratified by degree of liver impairment. Inpatient costs were established by identifying the number of inpatient episodes and multiplying by Irish diagnosis related group costs. Non-parametric bootstrapping was performed to derive mean and 95% CI values.Results: Two hundred and twenty-five patients were identified. The cost of an outpatient medical review was (sic) 136 ((sic)3.60 SD). The cost of a Hepatitis C nursing review was (sic) 128 ((sic)7.30 SD). The annual mean costs of care were as follows (95% CI): Mild (sic) 398 ((sic) 336, (sic) 482), Moderate (sic) 417((sic) 335, (sic) 503), Compensated cirrhosis (sic) 1790 ((sic) 990, (sic) 3164), Decompensated cirrhosis (sic) 8302 ((sic) 3945, (sic) 14,637), Transplantation Year 1 (sic) 137,176 ((sic) 136,024, (sic) 138,306), Transplantation after Year 1 (sic) 5337 ((sic) 4942, (sic) 5799), Hepatocellular carcinoma (sic)21,992 ((sic)15,222, (sic)29,467), Sustained virological response (sic)44 ((sic)16, (sic)73).Conclusions: The direct medical cost associated with Hepatitis C care in Ireland is substantial and increases exponentially with progression of liver disease. The follow-up costs of patients with a sustained virological response in this cohort were low in comparison to patients with chronic infection.
PUBLISHED
peer-reviewed
eng
BioMed Central
BMC Infectious Diseases;15:471
Ireland
health economics
direct medical cost
hepatitis C
Hepatitis C in the era of direct-acting antivirals: real-world costs of untreated chronic hepatitis C; a cross-sectional study
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5034
2021-12-15T11:50:36Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Lee, William T.
Fowler, Andrew C.
Power, O.
Healy, Sandra
Browne, J.
funder:SFI
2010
http://hdl.handle.net/10344/5034
peer-reviewed
Polycrystalline silicon fuses are one time programmable memory elements which allow the calibration of integrated circuits at wafer and package level. We present a zero-dimensional lumped parameter model of the programming of fuses made from a combination of tungsten silicide and polycrystalline silicon. The components of the model are an electrical model, a thermal model, and a flow model. The model generates quantitatively accurate results and reproduces trends with applied voltage and fuse size. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3457469]
PUBLISHED
peer-reviewed
eng
American Institute of Physics
Applied Physics;97, 023502
http://dx.doi.org/10.1063/1.3457469
06/MI/005
charge injection
diffraction
electrodes
gold
organic semiconductors
point contacts
thin film transistors
Blowing of polycrystalline silicon fuses
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5036
2018-02-21T09:38:51Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Khaleque, Tania S
Fowler, Andrew C.
Howell, P D
Vynnycky, Michael
funder:SFI
2015
http://hdl.handle.net/10344/5036
peer-reviewed
Motivated by convection of planetary mantles, we consider a mathematical model for Rayleigh-Benard convection in a basally heated layer of a fluid whose viscosity depends strongly on temperature and pressure, defined in an Arrhenius form. The model is solved numerically for extremely large viscosity variations across a unit aspect ratio cell, and steady solutions for temperature, isotherms, and streamlines are obtained. To improve the efficiency of numerical computation, we introduce a modified viscosity law with a low temperature cutoff. We demonstrate that this simplification results in markedly improved numerical convergence without compromising accuracy. Continued numerical experiments suggest that narrow cells are preferred at extreme viscosity contrasts, and this conclusion is supported by a linear stability analysis. (C) 2015 AIP Publishing LLC.
PUBLISHED
peer-reviewed
eng
American Institute of Physics
Physics of Fluids;27, 076603
http://dx.doi.org/10.1063/1.4923061
12/1A/1683
stagnant lid convection
mantle convection
variable-viscosity
plate-tectonics
generation
Numerical studies of thermal convection with temperature-and pressure-dependent viscosity at extreme viscosity contrasts
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5037
2018-12-04T11:26:54Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Kyrke-Smith, T.M.
Katz, R.F
Fowler, Andrew C.
funder:SFI
funder:Natural Environment Research Council
2015
http://hdl.handle.net/10344/5037
peer-reviewed
Observations have long associated ice streams with the presence of meltwater at the bed. More recently, theoretical models have been able to reproduce ice stream behavior as a consequence of the coupled dynamics of ice and subglacial meltwater. In this paper we analyze the properties of ice streams that form in a coupled model of ice flow and subglacial hydrology. We see that there is a natural length scale defining ice stream separation and width. This arises as a result of the balance between effective pressure gradients driving meltwater away from ice streams and the enhanced water production in the streams due to the fast ice flow. We further discuss how the model interacts with topography, and we show that small perturbations to a uniform bed have a strong effect on where ice streams emerge in the model. However, in many cases ice streams then evolve to be closer to the dimensions defined by the natural length scale of the unperturbed system. The nondimensional parameter that defines this length scale is therefore of fundamental importance in the model.
PUBLISHED
peer-reviewed
eng
American Geophysical Union
Journal of Geophyical Research: Earth Surface;120, pp. 1501-1504
http://dx.doi.org/10.1002/2015JF003505
12/1A/1683
NE/I528485/1
West Antractica
East Antarctica
layer beneath
water piracy
sheet
flow
glacier
system
onset
Subglacial hydrology as a control on emergence, scale, and spacing of ice streams
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5038
2018-08-08T15:32:35Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Zammett, R.J
Fowler, Andrew C.
funder:SFI
2010
http://hdl.handle.net/10344/5038
peer-reviewed
Spiral-shaped canyons on the polar ice caps of Mars are striking morphological features whose explanation is still mysterious. We pose a model for the kinetics at the ice-atmosphere interface based on the positive feedback properties of both dust and ice albedo within the north polar ice cap, together with katabatic wind transport of exposed dust. Analysis of this model indicates that traveling waves are possible, but only solitary waves are found in the numerical solution. This suggests that the traveling wave hypothesis for trough formation may not be an appropriate explanation.
PUBLISHED
peer-reviewed
eng
Society for Industrial and Applied Mathematics
SIAM Journal on Applied Mathematics;70 (7), pp. 2409-2433
http://www.siam.org/journals/siap/70-7/73455.html
06/MI/005
polar ice caps
spiral waves
phase plane analysis
Mars
climate
water
The morphology of the Martian ice caps: a mathematical model of ice-dust kinetics
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5039
2019-09-18T11:36:27Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Robinson, Marguerite
Fowler, Andrew C.
Alexander, A.J.
O'Brien, Stephen B.G.
funder:EI
funder:SFI
2008
http://hdl.handle.net/10344/5039
peer-reviewed
We describe a simple model of a bubbly two-phase flow which is able to explain why waves propagate downward when a pint of Guinness is poured, and also how the waves are generated. Our theory involves a physically based regularization of the basic equations of the two-phase flow, using interphasic pressure difference and virtual mass terms, together with bulk or eddy viscosity terms. We show that waves can occur through an instability analogous to that which forms roll waves in inclined fluid flows, and we provide a description of the form of these waves, and compare them to observations. Our theory provides a platform for the description of waves in more general bubbly two-phase flows, and the way in which the flow breaks down to form slug flow. (C) 2008 American Institute of Physics.
PUBLISHED
peer-reviewed
eng
American Institute of Physics
Physics of Fluids;20, 067101
http://dx.doi.org/10.1063/1.2929369
SC/2001/188
06/MI/005
stability
averaged multifield model
void fraction waves
2-phase flow
kinematic waves
bubbly flows
roll waves
Waves in Guinness
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5040
2018-02-21T09:37:50Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Fowler, Andrew C.
Kopteva, Natalia
Oakley, Charles
2006
http://hdl.handle.net/10344/5040
peer-reviewed
We consider a deterministic model of landscape evolution through the mechanism of overland flow over an erodible substrate, using the St. Venant equations of hydraulics together with the Exner equation for hillslope erosion. A novelty in the model is the allowance for a nonzero bedload layer thickness, which is necessary to distinguish between transport limited and detachment limited sediment removal. It has long been known that transport limited uniform flow is unstable when the hillslope topography is geomorphologically concave (i.e., the center of curvature is above ground). In this paper, we show how finite amplitude development of the consequent channel flow leads to an evolution equation for its depth h of the form h(t) = h(3/2) + (h(3/2))(YY), where Y is the cross-stream space variable. We show that solutions of compact support exist but that, despite appearances, blow up does not occur because of an associated integral constraint, and the channel equation admits a unique and apparently globally stable steady state. The consequences for hillslope evolution models are discussed.
PUBLISHED
peer-reviewed
eng
Society for Industrial and Applied Mathematics
SIAM Journal on Applied Mathematics;67 (4), pp. 1016-1040
http://dx.doi.org/10.1137/050629264
river networks
mathematical geomorphology
channel formation
nonlinear diffusion
drainage-basin evolution
elementary theory
stability
inception
model
The formation of river channels
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5084
2018-05-04T09:11:34Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Dassios, Ioannis K.
Fountoulakis, Kimon
Gondzio, Jacek
funder:Engineering and Physical Sciences Research Council
2016
http://hdl.handle.net/10344/5084
peer-reviewed
In this paper we are concerned with the solution of Compressed Sensing (CS) problems where the signals to be recovered are sparse in coherent and redundant dictionaries. We extend the primal-dual Newton Conjugate Gradients (pdNCG) method for CS problems. We provide an inexpensive and provably effective preconditioning technique for linear systems using pdNCG. Numerical results are presented on CS problems which demonstrate the performance of pdNCG with the proposed preconditioner compared to state-of-the-art existing solvers.
PUBLISHED
peer-reviewed
eng
Society for Industrial and Applied Mathematics
SIAM Journal on Scientific Computing;37 (6), pp. A2783-A2812
https://ioannisdassios.wordpress.com/research-visits-talks-2/
EP/I017127/1
compressed sensing
total-variation
second-order methods
A preconditioner for a primal-dual Newton conjugate gradients method for compressed sensing problems
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5156
2022-01-12T09:25:05Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Hackett, Adam W.
Cellai, Davide
Gomez, S.
Arenas, Alex
Gleeson, James P.
funder:ERC
funder:ICREA Academia, Generalitat de Catalunya
funder:James S. McDonnell Foundation
funder:SFI
2016
http://hdl.handle.net/10344/5156
peer-reviewed
We present an analytical approach for bond percolation on multiplex networks and use it to determine the expected size of the giant connected component and the value of the critical bond occupation probability in these networks. We advocate the relevance of these tools to the modeling of multilayer robustness and contribute to the debate on whether any benefit is to be yielded from studying a full multiplex structure as opposed to its monoplex projection, especially in the seemingly irrelevant case of a bond occupation probability that does not depend on the layer. Although we find that in many cases the predictions of our theory for multiplex networks coincide with previously derived results for monoplex networks, we also uncover the remarkable result that for a certain class of multiplex networks, well described by our theory, new critical phenomena occur as multiple percolation phase transitions are present. We provide an instance of this phenomenon in a multiplex network constructed from London rail and European air transportation data sets.
PUBLISHED
peer-reviewed
eng
American Physical Society
Grant No 317614
Physical Review X;6, 021002
http://dx.doi.org/10.1103/PhysRevX.6.021002
317614
11/PI/1026
09/SRC/E1780
14/IF/2461
interdependent networks
failures
Bond percolation on multiplex networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5185
2021-12-03T14:29:47Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Livingstone, Stephen J.
Utting, Daniel J.
Ruffell, Alastair
Clark, Chris D.
Pawley, Steven
Atkinson, Nigel
Fowler, Andrew C.
funder:NERC
funder:SFI
2016
http://hdl.handle.net/10344/5185
peer-reviewed
Recent proxy measurements reveal that subglacial lakes beneath modern ice sheets periodically store and release large volumes of water, providing an important but poorly understood influence on contemporary ice dynamics and mass balance. This is because direct observations of how lake drainage initiates and proceeds are lacking. Here we present physical evidence of the mechanism and geometry of lake drainage from the discovery of relict subglacial lakes formed during the last glaciation in Canada. These palaeo-subglacial lakes comprised shallow (
PUBLISHED
peer-reviewed
eng
Nature Publishing Group
Nature Communications;7: 11767
http://dx.doi.org/10.1038/ncomms11767
NE/H015256/1
12/1A/1683
West Antarctica
glacier
beneath
Greenland
Discovery of relict subglacial lakes and their geometry and mechanism of drainage
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5195
2020-12-02T12:11:27Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Moroney, Kevin M.
Lee, William T.
O'Brien, Stephen B.G.
Suijver, Freek
Marra, Johan
funder:SFI
2016
http://hdl.handle.net/10344/5195
peer-reviewed
The extraction of coffee solubles from roasted and ground coffee is a complex operation, the understanding of which is key to the brewing of high quality coffee. This complexity stems from the fact that brewing of coffee is achieved through a wide variety of techniques each of which depends on a large number of process variables. In this paper, we consider a recent, experimentally validated model of coffee extraction, which describes extraction from a coffee bed using a double porosity model. The model incorporates dissolution and transport of coffee in the coffee bed. The model was shown to accurately describe extraction of coffee solubles from grains in two situations: extraction from a dilute suspension of coffee grains and extraction from a packed coffee bed. The full model equations can only be solved numerically. In this work we consider asymptotic solutions, based on the dominant mechanisms, in the case of coffee extraction from a dilute suspension of coffee grains. Extraction in this well mixed system, can be described by a set of ordinary differential equations. This allows analysis of the extraction kinetics from the coffee grains independent of transport processes associated with flow through packed coffee beds. Coffee extraction for an individual grain is controlled by two processes: a rapid dissolution of coffee from the grain surfaces in conjunction with a much slower diffusion of coffee through the tortuous intragranular pore network to the grain surfaces. Utilising a small parameter resulting from the ratio of these two timescales, we construct asymptotic solutions using the method of matched asymptotic expansions. The asymptotic solutions are compared with numerical solutions and data from coffee extraction experiments. The asymptotic solutions depend on a small number of dimensionless parameters, so the solutions facilitate quick investigation of the influence of various process parameters on the coffee extraction curves.
PUBLISHED
peer-reviewed
eng
SpringerOpen
Journal of Mathematics in Industry;7:3
http://dx.doi.org/10.1186/s13362-016-0024-6
12/IA/1683
double porosity model
coffee extraction kinetics
leaching
solid-liquid extraction
matched asymptotic expansions
Coffee extraction kinetics in a well mixed system
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5204
2018-02-21T09:36:55Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Ward, Jonathan A
Fowler, Andrew C.
funder:SFI
2016
http://hdl.handle.net/10344/5204
peer-reviewed
Purpose: The polishing of cut lead glass crystal is effected through the
dowsing of the glass in a mixture of two separate acids, which between them etch
the surface and as a result cause it to be become smooth. In order to characterise the
resultant polishing the rate of surface etching must be known, but when this involves
multicomponent surface reactions it becomes unclear what this rate actually is.
Methods: We develop a differential equation based discrete model to determine the
effective etching rate by means of an atomic scale model of the etching process.
Results: We calculate the etching rate numerically and provide an approximate
asymptotic estimate.
Conclusions: The natural extension of this work would be to develop a continuum
advection-diffusion model.
eng
SpringerOpen
Journal of Mathematics in Industry;1:1
06/MI/005
07/SK/I1190
09/IN.1/I2645
etching rate multi-component
crystal glass
mathematical model
ordinary differential equation
asymptotics
numerics
laplace transform
Acid polishing of lead glass
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5286
2019-10-17T09:11:41Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Haynes, Matthew
O'Brien, Stephen B.G.
Benilov, Eugene
funder:SFI
2016
http://hdl.handle.net/10344/5286
peer-reviewed
This paper uses asymptotic techniques to find the shape of a two dimensional liquid bridge suspended between two vertical walls. We model the equilibrium bridge shape using the Laplace-Young equation. We use the Bond number as a small parameter to deduce an asymptotic solution which is then compared with numerical solutions. The perturbation approach demonstrates that equilibrium is only possible if the contact angle lies within a hysteresis interval and the analysis relates the width of this interval to the Bond number. This result is verified by comparison with a global force balance. In addition, we examine the quasi-static evolution of such a two dimensional bridge. Published by AIP Publishing.
PUBLISHED
peer-reviewed
eng
AIP Publishing
Physics of Fluids;28: 042107
http://dx.doi.org/10.1063/1.4946001
12/IA/1683
pendant drops
contact-angle
small sessile
shape
equations
Asymptotics of a horizontal liquid bridge
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5476
2020-12-02T12:58:48Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Fennell, Peter G.
Melnik, Sergey
Gleeson, James P.
funder:SFI
funder:ERC
2016
http://hdl.handle.net/10344/5476
peer-reviewed
Continuous-time Markov process models of contagions are widely studied, not least because of their utility in predicting the evolution of real-world contagions and in formulating control measures. It is often the case, however, that discrete-time approaches are employed to analyze such models or to simulate them numerically. In such cases, time is discretized into uniform steps and transition rates between states are replaced by transition probabilities. In this paper, we illustrate potential limitations to this approach. We show how discretizing time leads to a restriction on the values of the model parameters that can accurately be studied. We examine numerical simulation schemes employed in the literature, showing how synchronous-type updating schemes can bias discrete-time formalisms when compared against continuous-time formalisms. Event-based simulations, such as the Gillespie algorithm, are proposed as optimal simulation schemes both in terms of replicating the continuous-time process and computational speed. Finally, we show how discretizing time can affect the value of the epidemic threshold for large values of the infection rate and the recovery rate, even if the ratio between the former and the latter is small.
PUBLISHED
peer-reviewed
eng
American Physical Society
FP7-ICT-2011-8
Physical Review E;E94, 052125
11/PI/1026
12/PI/1683
317614
complext networks
model
behavior
science
spread
Limitations of discrete-time approaches to continuous-time contagion dynamics
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5477
2019-09-13T10:22:16Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Cellai, Davide
Dorogovtsev, Sergey N.
Bianconi, Ginestra
funder:SFI
funder:ERC
2016
http://hdl.handle.net/10344/5477
peer-reviewed
Multiplex networks describe a large variety of complex systems, including infrastructures, transportation networks, and biological systems. Most of these networks feature a significant link overlap. It is therefore of particular importance to characterize the mutually connected giant component in these networks. Here we provide a message passing theory for characterizing the percolation transition in multiplex networks with link overlap and an arbitrary number of layers M. Specifically we propose and compare two message passing algorithms that generalize the algorithm widely used to study the percolation transition in multiplex networks without link overlap. The first algorithm describes a directed percolation transition and admits an epidemic spreading interpretation. The second algorithm describes the emergence of the mutually connected giant component, that is the percolation transition, but does not preserve the epidemic spreading interpretation. We obtain the phase diagrams for the percolation and directed percolation transition in simple representative cases. We demonstrate that for the same multiplex network structure, in which the directed percolation transition has nontrivial tricritical points, the percolation transition has a discontinuous phase transition, with the exception of the trivial case in which all the layers completely overlap.
PUBLISHED
peer-reviewed
eng
Ameriican Physical Society
FET-Proactive project Plexmath
Physical Review E;E94, 032301
14/IF/2461
317532
317614
interdependent networks
complex networks
Message passing theory for percolation models on multiplex networks with link overlap
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5543
2019-09-13T10:22:41Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Cellai, Davide
Bianconi, Ginestra
funder:SFI
funder:ERC
2016
http://hdl.handle.net/10344/5543
peer-reviewed
In multiplex networks with a large number of layers, the nodes can have different activities, indicating the total number of layers in which the nodes are present. Here we model multiplex networks with heterogeneous activity of the nodes and we study their robustness properties. We introduce a percolation model where nodes need to belong to the giant component only on the layers where they are active (i.e., their degree on that layer is larger than zero). We show that when there are enough nodes active only in one layer, the multiplex becomes more resilient and the transition becomes continuous. We find that multiplex networks with a power-law distribution of node activities are more fragile if the distribution of activity is broader. We also show that while positive correlations between node activity and degree can enhance the robustness of the system, the phase transition may become discontinuous, making the system highly unpredictable.
PUBLISHED
peer-reviewed
eng
American Physical Society
PLEXMATH
Physical Review E;93, 032302
14/IF/2461
11/PI/1026
317614
interdependent networks
Multiplex networks with heterogeneous activities of the nodes
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5544
2021-12-08T09:26:25Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Baxter, Gareth J.
Dorogovtsev, Sergey N.
Mendes, José F.F.
Cellai, Davide
funder:SFI
funder:ERC
funder:Portuguese Foundation for Science and Technology
2014
http://hdl.handle.net/10344/5544
peer-reviewed
Bootstrap percolation is a simple but nontrivial model. It has applications in many areas of science and has been explored on random networks for several decades. In single-layer (simplex) networks, it has been recently observed that bootstrap percolation, which is defined as an incremental process, can be seen as the opposite of pruning percolation, where nodes are removed according to a connectivity rule. Here we propose models of both bootstrap and pruning percolation for multiplex networks. We collectively refer to these two models with the concept of "weak" percolation, to distinguish them from the somewhat classical concept of ordinary ("strong") percolation. While the two models coincide in simplex networks, we show that they decouple when considering multiplexes, giving rise to a wealth of critical phenomena. Our bootstrap model constitutes the simplest example of a contagion process on a multiplex network and has potential applications in critical infrastructure recovery and information security. Moreover, we show that our pruning percolation model may provide a way to diagnose missing layers in a multiplex network. Finally, our analytical approach allows us to calculate critical behavior and characterize critical clusters.
PUBLISHED
peer-reviewed
eng
Americann Physical Society
PLEXMATH
Physical Review E;89, 042801
http://dx.doi.org/10.1103/PhysRevE.89.042801
11/PI/1026
317614
PEst-C/CTM/LA0025/2011
SFRH/BPD/74040/2010
interdependent networks
restoration
failures
Weak percolation on multiplex networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5545
2019-09-13T10:19:21Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Baxter, Gareth J.
Cellai, Davide
Dorogovtsev, Sergey N.
Mendes, José F.F.
2016
http://hdl.handle.net/10344/5545
peer-reviewed
In multiplex networks, cycles cannot be characterized only by their length, as edges may occur in different layers in different combinations. We define a classification of cycles by the number of edges in each layer and the number of switches between layers. We calculate the expected number of cycles of each type in the configuration model of a large sparse multiplex network. Our method accounts for the full degree distribution including correlations between degrees in different layers. In particular, we obtain the numbers of cycles of length 3 of all possible types. Using these, we give a complete set of clustering coefficients and their expected values. We show that correlations between the degrees of a vertex in different layers strongly affect the number of cycles of a given type, and the number of switches between layers. Both increase with assortative correlations and are strongly decreased by disassortative correlations. The effect of correlations on clustering coefficients is equally pronounced.
PUBLISHED
peer-reviewed
eng
American Chemical Society
Physical Review E;94, 062308
https://doi.org/10.1103/PhysRevE.94.062308
edge-colored graphs
failures
Cycles and clustering in multiplex networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5549
2020-12-02T12:56:46Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Faqeeh, Ali
Melnik, Sergey
Colomer-deSimón, Pol
Gleeson, James P.
2016
http://hdl.handle.net/10344/5549
peer-reviewed
It is commonly assumed in percolation theories that at most one percolating cluster can exist in a network. We show that several coexisting percolating clusters (CPCs) can emerge in networks due to limited mixing, i.e., a finite and sufficiently small number of interlinks between network modules. We develop an approach called modular message passing (MMP) to describe and verify these observations. We demonstrate that the appearance of CPCs is an important source of inaccuracy in previously introduced percolation theories, such as the message passing (MP) approach, which is a state-of-the-art theory based on the belief propagation method. Moreover, we show that the MMP theory improves significantly over the predictions of MP for percolation on synthetic networks with limited mixing and also on several real-world networks. These findings have important implications for understanding the robustness of networks and in quantifying epidemic outbreaks in the susceptible-infected-recovered (SIR) model of disease spread.
PUBLISHED
peer-reviewed
eng
American Physical Society
Physical Review E;93, 062308
http://dx.doi.org/10.1103/PhysRevE.93.062308
complext networks
random graphs
Emergence of coexisting percolating clusters in networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5550
2020-12-02T12:56:03Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Hurd, Thomas R
Cellai, Davide
Melnik, Sergey
Shao, Quentin, H
funder:Global Risk Institute for Financial Services in Toronto
funder:Natural Sciences and Engineering Research Council of Canada
funder:IRC
funder:ERC
2016
http://hdl.handle.net/10344/5550
peer-reviewed
The full text of this article will not be available on ULIR until the embargo expires on the 25/7/2017
The scope of financial systemic risk research encompasses a wide range of interbank channels and effects, including asset correlation shocks, default contagion, illiquidity contagion, and asset fire sales. This paper introduces a financial network model that combines the default and liquidity stress mechanisms into a "double cascade mapping". The progress and eventual result of the crisis is obtained by iterating this mapping to its fixed point. Unlike simpler models, this model can therefore quantify how illiquidity or default of one bank influences the overall level of liquidity stress and default in the system. Large-network asymptotic cascade mapping formulas are derived that can be used for efficient network computations of the double cascade. Numerical experiments then demonstrate that these asymptotic formulas agree qualitatively with Monte Carlo results for large finite networks, and quantitatively except when the initial system is placed in an exceptional "knife-edge" configuration. The experiments clearly support the main conclusion that when banks respond to liquidity stress by hoarding liquidity, then in the absence of asset fire sales, the level of defaults in a financial network is negatively related to the strength of bank liquidity hoarding and the eventual level of stress in the network.
ACCEPTED
peer-reviewed
eng
Plexmath
International Journal of Theoretical and Applied Finance;19, (5)
http://dx.doi.org/10.1142/S0219024916500412
11/PI/1026
banking network
contagion
random graph
default
funding liquidity
liquidity hoarding
systemic risk
Double cascade model of financial crises
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5580
2017-05-11T10:16:59Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_242
hdl_10344_240
hdl_10344_480
hdl_10344_504
hdl_10344_20
hdl_10344_73
hdl_10344_243
Gleeson, James P.
Faqeeh, Ali
funder:SFI
funder:ERC
2016
http://hdl.handle.net/10344/5580
peer-reviewed
Many of the systems we observe in nature, in societies, or in infrastructures are in the
form of a network of interacting units. This underlying network structure shapes the
behavior of such systems and is an indispensable factor in maintaining their correct
function. Likewise, the processes that operate on these systems are largely influenced
by their network structure. In this thesis, we investigate the theoretical approaches for
investigation of the properties of percolation processes on networks.
Percolation processes investigate the alteration of network connectivity. Two such
processes that constitute the main focus of this thesis are bond and site percolation,
which are simple models for the robustness of a network to random failures of (or
intentional attacks to) its constituting units. They also have been used to provide better
insight on some other more complicated processes such as spread of epidemic diseases
or stability of genetic networks, because some important features of these processes
can be mapped to percolation properties.
In this thesis, we first consider the so-called Aij theories developed for percolation
and several other processes that operate on networks. We investigate the e ect of
the presence of high density of short loops (a property observed in many real-world
networks) on the accuracy of Aij theories and show its impact on the performance of
these theories. We then show that another phenomenon, the emergence of coexisting
percolating clusters, can also cause significant inaccuracy in the Aij theory for bond
percolation on certain synthetic and real-world networks. Moreover, we introduce a
new theoretical approach that takes into account this phenomenon and improves upon
the state-of-the-art Aij theory. Then, we develop a theoretical framework for calculation
of percolation cluster sizes and discuss its potential applications in studying the
properties of neuronal avalanches.
eng
University of Limerick
percolation processes
network structure
Percolation and its relations to other processes in networks
info:eu-repo/semantics/doctoralThesis
11/PI/1026
12/IA/1683
317614
oai:ulir.ul.ie:10344/5791
2020-12-02T12:57:09Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Hurd, Thomas R
Gleeson, James P.
Melnik, Sergey
funder:Natural Sciences and Engineering Research Council of Canada
funder:Global Risk Institute for Financial Services of Canada
funder:SFI
funder:IRC
2017
http://hdl.handle.net/10344/5791
peer-reviewed
We introduce a probabilistic framework that represents stylized banking networks with the aim of predicting the size of contagion events. Most previous work on random financial networks assumes independent connections between banks, whereas our framework explicitly allows for (dis) assortative edge probabilities (i.e., a tendency for small banks to link to large banks). We analyze default cascades triggered by shocking the network and find that the cascade can be understood as an explicit iterated mapping on a set of edge probabilities that converges to a fixed point. We derive a cascade condition, analogous to the basic reproduction number R-0 in epidemic modelling, that characterizes whether or not a single initially defaulted bank can trigger a cascade that extends to a finite fraction of the infinite network. This cascade condition is an easily computed measure of the systemic risk inherent in a given banking network topology. We use percolation theory for random networks to derive a formula for the frequency of global cascades. These analytical results are shown to provide limited quantitative agreement with Monte Carlo simulation studies of finite-sized networks. We show that edge-assortativity, the propensity of nodes to connect to similar nodes, can have a strong effect on the level of systemic risk as measured by the cascade condition. However, the effect of assortativity on systemic risk is subtle, and we propose a simple graph theoretic quantity, which we call the graph-assortativity coefficient, that can be used to assess systemic risk.
PUBLISHED
peer-reviewed
eng
Public Library of Science
PLoS ONe;12 (2), e0170579
http://dx.doi.org/10.1371/journal.pone.0170579
11/PI/1026
topology
market
model
A framework for analyzing contagion in assortative banking networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5879
2020-12-02T12:13:13Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Cregan, Vincent
Lee, William T.
Clune, Louise
funder:SFI
funder:Embark Initiative postgraduate Award
2017
http://hdl.handle.net/10344/5879
peer-reviewed
A soft sensor for measuring product quality in the Bayer process has been developed.
The soft sensor uses a combination of historical process data recorded from online
sensors and laboratory measurements to predict a key quality indicator, namely
particle strength. Stepwise linear regression is used to select the relevant variables
from a large dataset composed of monitored properties and laboratory data. The
developed sensor is employed successfully by RUSAL Aughinish Alumina Ltd to
predict product strength five days into the future with R-squared equal to 0.75 and to
capture deviations from standard operating conditions
eng
SpringerOpen
Journal of Mathematics in Industry;7:7
http://dx.doi.org/10.1186/s13362-017-0037-9
06/MI/005
RS/2006/41
Bayer process
soft sensor
stepwise multiple linear regression
A soft sensor for the Bayer process
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/5922
2017-07-28T00:01:45Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Starnini, Michele
Gleeson, James P.
Boguna, Marián
funder:Generalitat de Catalunya
funder:SFI
funder:SFI
2017
http://hdl.handle.net/10344/5922
peer-reviewed
A general formalism is introduced to allow the steady state of non-Markovian processes on networks to be reduced to equivalent Markovian processes on the same substrates. The example of an epidemic spreading process is considered in detail, where all the non-Markovian aspects are shown to be captured within a single parameter, the effective infection rate. Remarkably, this result is independent of the topology of the underlying network, as demonstrated by numerical simulations on two-dimensional lattices and various types of random networks. Furthermore, an analytic approximation for the effective infection rate is introduced, which enables the calculation of the critical point and of the critical exponents for the non-Markovian dynamics.
PUBLISHED
peer-reviewed
eng
American Physical Society
Physical Review Letters;118,128301
http://dx.doi.org/10.1103/PhysRevLett.118.128301
FIS2013-47282-C2-1-P
FIS2016-76830-C2-2-P
2014SGR608
11/PI/1026
networks
smalpox
patterns
bursts
Equivalence between non-Markovian and Markovian dynamics in epidemic spreading processes
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/6066
2021-11-30T11:22:18Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Vynnycky, Michael
Saleem, S.
Devine, Kevin M.
Florio, B. J.
Mitchell, Sarah L.
O'Brien, Stephen B.G.
funder:Swedish Energy Agency
funder:SFI
funder:IRC
2017
http://hdl.handle.net/10344/6066
peer-reviewed
Asymptotic methods are employed to revisit an earlier model for oscillation-mark formation in the continuous casting of steel. A systematic non-dimensionalization of the governing equations, which was not carried out previously, leads to a model with 12 dimensionless parameters. Analysis is provided in the same parameter regime as for the earlier model, and surprisingly simple analytical solutions are found for the oscillation-mark profiles; these are found to agree reasonably well with the numerical solution in the earlier model and very well with fold-type oscillation marks that have been obtained in more recent experimental work. The benefits of this approach, when compared with time-consuming numerical simulations, are discussed in the context of auxiliary models for
macrosegregation and thermomechanical stresses and strains.
eng
The Royal Society
Royal Society Open Science;4:170062
37976-1
12/IA/1683
GOIPG/2014/1147
continuous casting
oscillation marks
asymptotic analysis
On the formation of fold-type oscillation marks in the continuous casting of steel
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/6058
2018-03-22T16:33:01Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
O'Sullivan, David J.P.
Garduño-Hernández, Guillermo
Gleeson, James P.
Beguerisse-Díaz, Mariano
funder:SFI
funder:Oxford-Emirates Data Science Lab
funder:James S. McDonnell Foundation
2017
http://hdl.handle.net/10344/6058
peer-reviewed
We examine the relationship between social structure and sentiment through the analysis of a large collection of tweets about the Irish Marriage Referendum of 2015. We obtain the
sentiment of every tweet with the hashtags #marref and #marriageref that was posted in the days leading to the referendum, and construct networks to aggregate sentiment
and use it to study the interactions among users. Our analysis shows that the sentiment of outgoing mention tweets is correlated with the sentiment of incoming mentions, and there are significantly more connections between users with similar sentiment scores than among users with opposite scores in the mention and follower networks. We combine the community structure of the follower and mention networks with the activity level of the users and sentiment scores to find groups that support voting ‘yes’ or ‘no’ in the referendum. There were numerous conversations between users on opposing sides
of the debate in the absence of follower connections, which suggests that there were efforts by some users to establish dialogue and debate across ideological divisions. Our analysis shows that social structure can be integrated successfully with sentiment to analyse and understand the disposition of social media users around controversial or polarizing issues. These results have potential applications in the integration of data and
metadata to study opinion dynamics, public opinion modelling and polling.
eng
The Royal Society
Royal Society Open Science;4:170154
11/PI/1026 2/IA/I683
220020349-CS
online social media
networks
text analysis
sentiment
public opinion
homophily
Integrating sentiment and social structure to determine preference alignments: the Irish marriage referendum
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/6086
2021-12-02T09:34:07Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_11
hdl_10344_73
hdl_10344_3077
hdl_10344_3104
Castro-Dominguez, Bernardo
Moroney, Kevin M.
Schaller, Barbara E.
O'Connor, S.
Cloonan, Aidan J.
Vo, Tuoi T.N.
Walker, Gavin M.
O'Reilly, Emmet J.
funder:SFI
2017
http://hdl.handle.net/10344/6086
peer-reviewed
The development of biocompatible membrane materials capable of delivering active pharmaceutical ingredients (APIs) over a fixed time period offers significant advantages to the pharmaceutical and biomedical industries alike. In addition the incorporation of APIs within polymeric materials potentially allows for the formation of amorphous solid dispersions (ASDs), which have shown enhanced bioavailability, increased dissolution profiles and enhanced adsorption into the blood stream. Mixed matrix membranes (MMMs) have been at the forefront of such developments, however manufacturing
MMMs with consistent batch to batch physical characteristics has proved challenging thereby significantly impeding the use of such materials by the pharmaceutical sector. This article describes the development, for the first time, of API and molecular sieve loaded mixed matrix membranes (MMMs) via electro spinning techniques. The developed membranes displayed consistent and controllable physical properties and more efficient API release relative to membranes prepared using traditional casting techniques. Mathematical modelling disclosed that the membranes generated via electrospinning show excellent correlation between experimental and predicted API release kinetics thereby paving the way for the development of MMMs for both pharmaceutical and biomedical applications.
eng
Royal Society of Chemistry
RSC Advances;7 : 43300-43309
14/SP/2750
12/IA/1683
electrospun
api-loaded
mixed
matrix
membranes
controlled
release
Electrospun API-loaded mixed matrix membranes for controlled release
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/6112
2018-08-08T14:56:19Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_242
hdl_10344_240
hdl_10344_480
hdl_10344_504
hdl_10344_20
hdl_10344_73
hdl_10344_243
Kopteva, Natalia
Timoney, Catherine M.
2017
http://hdl.handle.net/10344/6112
peer-reviewed
This work is concerned with finding accurate numerical approximations to
nonlinear reaction-diffusion problems that exhibit layer phenomena. It considers
three variations of problems of this type. These are; a two-dimensional
steady state equation with Dirichlet boundary conditions exhibiting interior
layer solutions; a time-dependent equation with singularly perturbed Neumann
boundary conditions with boundary layer solutions; and a steady state
equation with singularly perturbed Neumann boundary conditions exhibiting
boundary layer solutions.
Asymptotic analysis is called upon from previous literature in order to
obtain upper and lower solutions to the problems. The theory of Z-fields are
then used along with discrete upper and lower solutions to prove existence
of a discrete solution and obtain accuracy bounds. Discretisations in the finite
difference method and the finite element method are presented on layer
adapted meshes such as the Shishkin and Bakhvalov mesh. In cases where
incorrect computed solutions are obtained from a conventional discretisation
the stabilised method by Kopteva and Savescu [16] is employed, giving solutions
of the correct form.
It is found that the problems have second-order convergence in space in
the maximum norm, with a logarithmic factor for the Shishkin mesh, and,
for the time-dependent problem, first order convergence in time in the maximum
norm, again with a logarithmic factor for the Shishkin mesh. Finally,
numerical examples are given to support the theoretical results.
eng
University of Limerick
mathematics
Neumann boundary
finite element method
Numerical analysis of singularly perturbed nonlinear reaction-diffusion equations
info:eu-repo/semantics/doctoralThesis
oai:ulir.ul.ie:10344/6369
2018-03-06T20:05:39Z
hdl_10344_21
hdl_10344_9
hdl_10344_73
Gleeson, James P.
Durrett, Rick
funder:SFI
2017
http://hdl.handle.net/10344/6369
peer-reviewed
An avalanche or cascade occurs when one event causes one or more subsequent events,
which in turn may cause further events in a chain reaction. Avalanching dynamics are studied in many disciplines, with a recent focus on average avalanche shapes, i.e., the temporal profiles of avalanches of fixed duration. At the critical point of the dynamics, the rescaled average avalanche shapes for different durations collapse onto a single universal curve. We apply Markov branching process theory to derive an equation governing the average avalanche shape for cascade dynamics on networks. Analysis of the equation at criticality demonstrates that nonsymmetric average avalanche shapes (as observed in some experiments) occur for certain combinations of dynamics and network topology. We give examples using numerical simulations of models for information spreading, neural dynamics, and behavior adoption and we propose simple experimental tests to quantify whether cascading systems are in the critical state.
eng
Nature Publishing Group
Nature Communications;8: 1227
http://dx.doi.org/10.1038/s41467-017-01212-0
11/PI/1026
09/SRC/E1780
15/SPP/E3125
16/IA/4470
temporal profiles
avalanches
networks
cascade
Temporal profiles of avalanches on networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/6547
2018-02-10T01:02:32Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Ward, Michael J.
Moyles, Iain R.
funder:SFI
2017
http://hdl.handle.net/10344/6547
peer-reviewed
We analyze a singularly perturbed reaction-diffusion system in the semi-strong diffusion regime in two spatial dimensions where an activator species is localized to a closed curve, while the inhibitor species exhibits long range behavior over the domain. In the limit of small activator diffusivity we derive a new moving boundary problem characterizing the slow time evolution of the curve, which is defined in terms of a quasi steady-state inhibitor diffusion field and its properties on the curve. Numerical results from this curve evolution problem are illustrated for the Gierer-Meinhardt model (GMS) with saturation in the activator kinetics. A detailed analysis of the existence, stability, and dynamics of ring and near-ring solutions for the GMS model is given, whereby the activator concentrates on a thin ring concentric within a circular domain. A key new result for this ring geometry is that by including activator saturation there is a qualitative change in the phase portrait of ring equilibria, in that there is an S-shaped bifurcation diagram for ring equilibria, which allows for hysteresis behavior. In contrast, without saturation, it is well-known that there is a saddle-node bifurcation for the ring equilibria. For a near-circular ring, we develop an asymptotic expansion up to quadratic order to fully characterize the normal
velocity perturbations from our curve-evolution problem. In addition,
we also analyze the linear stability of the ring solution to both
breakup instabilities, leading to the disintegration of a ring into
localized spots, and zig-zag instabilities, leading to the slow shape
deformation of the ring. We show from a nonlocal eigenvalue problem
that activator saturation can stabilize breakup patterns that
otherwise would be unstable. Through a detailed matched asymptotic
analysis, we derive a new explicit formula for the small eigenvalues
associated with zig-zag instabilities, and we show that they are
equivalent to the velocity perturbations induced by the near-circular
ring geometry. Finally, we present full numerical simulations from
the GMS PDE system that confirm the predictions of the analysis.
peer-reviewed
eng
Society for Industrial and Applied Mathematics
Siam Journal on Applied Dynamical Systems;16 (1), pp. 597-639
https://doi.org/10.1137/16M1060327
SFI/13/IA/1923
homoclinic orbits
zig-zag instability
nonlocal eigenvalue problem
WKB stability
hysteresis
Existence, stability, and dynamics of ring and near-ring solutions to the saturated Gierer--Meinhardt model in the semistrong regime
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/6764
2019-03-28T11:51:28Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Kartun-Giles, Alexander P.
Krioukov, Dmitri
Gleeson, James P.
Moreno, Yamir
Bianconi, Ginestra
funder:SFI
funder:Government of Aragón, Spain
funder:FENOL
funder:MINECO
funder:FEDER
2018
http://hdl.handle.net/10344/6764
peer-reviewed
A projective network model is a model that enables predictions to be made based on a
subsample of the network data, with the predictions remaining unchanged if a larger sample is taken into consideration. An exchangeable model is a model that does not depend on the order in which nodes are sampled. Despite a large variety of non-equilibrium (growing) and equilibrium (static) sparse complex network models that are widely used in network science, how to reconcile sparseness (constant average degree) with the desired statistical properties of projectivity and exchangeability is currently an outstanding scientific problem. Here we propose a network process with hidden
variables which is projective and can generate sparse power-law networks. Despite the model not being exchangeable, it can be closely related to exchangeable uncorrelated networks as indicated by its information theory characterization and its network entropy. The use of the proposed network process as a null model is here tested on real data, indicating that the model offers a promising avenue for statistical network modelling.
eng
MDPI
Entropy;20, 257
http://dx.doi.org/10.3390/e20040257
ARO W911NF-16-1-0391
NSF IIS-1741355
16/IA/4470
FIS2014-55867-P
networks models
projectivity and exchangeability
network entropy
information theory of networks
Sparse power-law network model for reliable statistical predictions based on sampled data
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/6814
2019-11-20T14:12:54Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Dassios, Ioannis K.
funder:SFI
2018
http://hdl.handle.net/10344/6814
peer-reviewed
In this article, we focus on a generalized problem of linear non-autonomous fractional nabla difference equations. Firstly, we define the equations and describe how this family of problems covers other linear fractional difference equations that appear in the literature. Then, by using matrix theory we provide a new practical formula of solutions for these type of equations. Finally, numerical examples are given to justify our theory.
eng
Elsevier
Journal of Computational and Applied Mathematics;339, pp. 317-328
https://doi.org/10.1016/j.cam.2017.09.030
SFI/15/SPP/E3125
non-autonomous
matrix
nabla
fractional
difference equations
A practical formula of solutions for a family of linear non-autonomous fractional nabla difference equations
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/7083
2019-10-21T15:31:56Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_22
hdl_10344_20
Zeglinski, Jacek
Kuhs, Manuel
Khamar, Dikshitkumar
Hegarty, Avril C.
Devi, Renuka K.
Rasmuson, Åke C.
funder:SFI
funder:HEA
funder:Swedish Research Council
2018
http://hdl.handle.net/10344/7083
peer-reviewed
The influence of the solvent in nucleation of tolbutamide, a
medium-sized, flexible and polymorphic organic molecule, has been
explored by measuring nucleation induction times, estimating
solvent-solute interaction enthalpies using molecular modelling and
calorimetric data, probing interactions and clustering with
spectroscopy, and modelling solvent-dependence of molecular
conformation in solution. The nucleation driving force required to
reach the same induction time is strongly solvent-dependent,
increasing in the order: acetonitrile < ethyl acetate < n-propanol <
toluene. The combined DFT and MD modelling results show that in
acetonitrile, ethyl acetate and n-propanol the nucleation difficulty is a
function of the strength of solvent-solute interaction, with emphasis
on the interaction with specific H-bonding polar sites of importance in
the crystal structure. A clear exception from this rule is the most
difficult nucleation in toluene despite the weakest solvent-solute
interactions. However molecular dynamics modelling predicts that
tolbutamide assumes an intramolecularly H-bonded conformation in
toluene, substantially different from and more stable than the
conformation in the crystal structure, and thus presenting an
additional barrier to nucleation. This explains why nucleation in
toluene is the most difficult and why the relatively higher propensity
for aggregation of tolbutamide molecules in toluene solution, as
observed with FTIR spectroscopy, does not translate into easier
nucleation. Thus, our combined experimental and molecular
modelling study suggests that the solvent can influence on the
nucleation not only via differences in the desolvation but also
through the influence on molecular conformation.
eng
Wiley and Sons Ltd
Chemistry: A European Journal;24 (19), pp. 4916-3926
https://doi.org/10.1002/chem.201705954
10/IN.1/B3038
621-2010-5391
12/IA/1683
crystallization processes
product crystal structure
Crystal nucleation of tolbutamide in solution: relationship to solvent, solute conformation, and solution structure
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/7175
2018-09-28T00:01:23Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Faqeeh, Ali
Osat, Saeed
Radicchi, Filippo
2018
http://hdl.handle.net/10344/7175
peer-reviewed
We show that the community structure of a network can be used as a coarse version of its embedding in a
hidden space with hyperbolic geometry. The finding emerges from a systematic analysis of several real-world
and synthetic networks. We take advantage of the analogy for reinterpreting results originally obtained through
network hyperbolic embedding in terms of community structure only. First, we show that the robustness of a
multiplex network can be controlled by tuning the correlation between the community structures across di erent
layers. Second, we deploy an e cient greedy protocol for network navigability that makes use of routing tables
based on community structure.
eng
American Physical Society
Physical Review Letters;121 (9), 098301
https://doi.org/10.1103/PhysRevLett.121.098301
networks
community structure
Characterizing the analogy between hyperbolic embedding and community structure of complex networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/7193
2021-04-22T10:50:27Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Lee, William T.
Kaar, Simon
O'Brien, Stephen B.G.
2018
http://hdl.handle.net/10344/7193
peer-reviewed
A surprising phenomenon witnessed by many is the sinking bubbles seen in a settling pint of stout beer. Bubbles are less dense than the surrounding fluid so how does this happen? Previous work has shown that the explanation lies in a circulation of fluid promoted by the tilted sides of the glass. However, this work has relied heavily on computational fluid dynamics (CFD) simulations. Here, we show that the phenomenon of sinking bubbles can be predicted using a simple analytic model. To make the model analytically tractable, we work in the limit of small bubbles and consider a simplified geometry. The model confirms both the existence of sinking bubbles and the previously proposed mechanism.
eng
American Assocation of Physics Teachers
American Journal of Physics;86 (4)
https://doi.org/10.1119/1.5021361
sinking bubbles
stout beer
Sinking bubbles in stout beers
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/7213
2021-05-06T13:54:58Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_4612
hdl_10344_4609
hdl_10344_73
hdl_10344_4613
hdl_10344_20
Leahy, Joe
O'Leary, Aisling
Afdhal, Nezam
Gray, Emma
Milligan, Scott
Wehmeyer, Malte H.
Walsh, Cathal Dominic
2018
http://hdl.handle.net/10344/7213
peer-reviewed
The use of individual patient data (IPD) in network meta-analysis (NMA) is
becoming increasingly popular. However, as most studies do not report IPD,
most NMAs are performed using aggregate data for at least some, if not all, of
the studies. We investigate the benefits of including varying proportions of IPD
studies in an NMA.
Several models have previously been developed for including both aggregate
data and IPD in the same NMA.We performed a simulation study based on these
models to examine the impact of additional IPD studies on the accuracy and
precision of the estimates of both the treatment effect and the covariate effect.
We also compared the deviance information criterion (DIC) between models to
assess model fit. An increased proportion of IPD resulted in more accurate and
precise estimates for most models and datasets. However, the coverage probability
sometimes decreased when the model was misspecified. The use of IPD leads
to greater differences in DIC, which allows us choose the correct model more
often.
We analysed a Hepatitis C network consisting of 3 IPD observational studies.
The ranking of treatments remained the same for all models and datasets. We
observed similar results to the simulation study: The use of IPD leads to differences
in DIC and more precise estimates for the covariate effect. However, IPD
sometimes increased the posterior SD of the treatment effect estimate, which
may indicate between study heterogeneity. We recommend that IPD should be
used where possible, especially for assessing model fit.
eng
Wiley and Sons Ltd
Research Synthesis Methods;9 (3), ppp. 441-469
https://doi.org/10.1002/jrsm.1305
Individual Patient Data (IPD)
impact
The impact of individual patient data in a network meta-analysis: an investigation into parameter estimation and model selection
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/7226
2021-11-30T11:59:41Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_4612
hdl_10344_4609
hdl_10344_73
hdl_10344_4613
hdl_10344_20
Lawlor, Brian
Segurado, Ricardo
Kennelly, Sean
Olde Rikkert, Marcel G. M.
Howard, Robert
Pasquier, Florence
Borjesson-Hanson, Anne
Tsolaki, Magda
Lucca, Ugo
Molloy, D. William
Coen, Robert
Riepe, Matthias W.
Kálmán, János
Kenny, Rose Anne
Cregg, Fiona
O'Dwyer, Sarah
Walsh, Cathal Dominic
Adams, Jessica
Banzi, Rita
Breuilh, Laetitia
funder:European Commission
funder:UCLH NIHR Biomedical Research Centre, UK (RH)
funder:Hauts-de-Freance Region, France (FP)
2018
http://hdl.handle.net/10344/7226
peer-reviewed
Background
This study reports the findings of the first large-scale Phase III investigator-driven clinical trial to slow the rate of cognitive decline in Alzheimer disease with a dihydropyridine (DHP) calcium channel blocker, nilvadipine. Nilvadipine, licensed to treat hypertension, reduces amyloid production, increases regional cerebral blood flow, and has demonstrated anti-inflammatory and anti-tau activity in preclinical studies, properties that could have diseasemodifying effects for Alzheimer disease. We aimed to determine if nilvadipine was effective in slowing cognitive decline in subjects with mild to moderate Alzheimer disease.
Methods and findings
NILVAD was an 18-month, randomised, placebo-controlled, double-blind trial that randomised participants between 15 May 2013 and 13 April 2015. The study was conducted at 23 academic centres in nine European countries. Of 577 participants screened, 511 were eligible and were randomised (258 to placebo, 253 to nilvadipine). Participants took a trial treatment capsule once a day after breakfast for 78 weeks. Participants were aged >50 years, meeting National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer's disease Criteria (NINCDS-ADRDA) for diagnosis of probable Alzheimer disease, with a Standardised Mini-Mental State Examination (SMMSE) score of 12 and <27. Participants were randomly assigned to 8 mg sustained-release nilvadipine or matched placebo. The a priori defined primary outcome was progression on the Alzheimer's Disease Assessment Scale Cognitive Subscale-12 (ADAS-Cog 12) in the modified intention-to-treat (mITT) population (n = 498), with the Clinical Dementia Rating Scale sum of boxes (CDR-sb) as a gated co-primary outcome, eligible to be promoted to primary end point conditional on a significant
effect on the ADAS-Cog 12. The analysis set had a mean age of 73 years and was 62% female. Baseline demographic and Alzheimer disease_specific characteristics were similar between treatment groups, with reported mean of 1.7 years since diagnosis and mean SMMSE of 20.4. The prespecified primary analyses failed to show any treatment benefit for nilvadipine on the co-primary outcome (p = 0.465). Decline from baseline in ADASCog 12 on placebo was 0.79 (95% CI, −0.07-1.64) at 13 weeks, 6.41 (5.33-7.49) at 52 weeks, and 9.63 (8.33-10.93) at 78 weeks and on nilvadipine was 0.88 (0.02-1.74) at 13 weeks, 5.75 (4.66-6.85) at 52 weeks, and 9.41 (8.09-10.73) at 78 weeks. Exploratory analyses of the planned secondary outcomes showed no substantial effects, including on the CDR-sb or the Disability Assessment for Dementia. Nilvadipine appeared to be safe and well tolerated. Mortality was similar between groups (3 on nilvadipine, 4 on placebo); higher counts of adverse events (AEs) on nilvadipine (1,129 versus 1,030), and serious adverse events (SAEs; 146 versus 101), were observed. There were 14 withdrawals because of AEs. Major limitations of this study were that subjects had established dementia and the likelihood that non-Alzheimer subjects were included because of the lack of biomarker confirmation of the presence of brain amyloid.
Conclusions
The results do not suggest benefit of nilvadipine as a treatment in a population spanning mild to moderate Alzheimer disease.
eng
Public Library of Science
PLoS Medicine;15(9):e1002660
https://doi.org/10.1371/journal.pmed.1002660
279093
nilvadipine
mild
moderate
alzheimer
randomised controlled trial
Nilvadipine in mild to moderate alzheimer disease: a randomised controlled trial
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/7236
2018-10-19T00:02:35Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Cuffe, Paul
Dassios, Ioannis K.
Keane, Andrew
funder:SFI
funder:ERC
2016
http://hdl.handle.net/10344/7236
peer-reviewed
Abstract—Loss minimizing generator dispatch profiles for
power systems are usually derived using optimization techniques.
However, some authors have noted that a system’s KGL matrix
can be used to analytically determine a loss minimizing dispatch.
This letter draws on recent research on the characterization of
transmission system losses to demonstrate how the KGL matrix
achieves this. A new proof of the observed zero row summation
property of the YGGM matrix is provided to this end.
peer-reviewed
eng
IEEE Computer Society
n608732A
IEEE Transactions on Power Systems;31 (4), pp. 3322-3323
n608732A
09/SRC/E1780
software technology
transmission system
Analytic loss minimization: a proof
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/7239
2021-12-13T15:35:23Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Moroney, Kevin M.
Lee, William T.
O'Brien, Stephen B.G.
Suijver, Freek
Marra, Johan
funder:SFI
2016
http://hdl.handle.net/10344/7239
peer-reviewed
Extraction of coffee solubles from roast and ground coffee is a highly complex process, depending on a large number of brewing parameters. We consider a recent, experimentally validated, model of coffee extraction, describing extraction from a coffee bed using a double porosity model, which includes dissolution and transport of coffee. It was shown that this model can accurately describe coffee extraction in two situations: extraction from a dilute suspension of coffee grains and extraction from a packed coffee bed. Despite being based on some simplifying assumptions, this model can only be solved numerically. In this paper we consider asymptotic solutions of the model describing extraction from a packed coffee bed. Such solutions can explicitly relate coffee concentration to the process parameters. For an individual coffee grain, extraction is controlled by a rapid dissolution of coffee from the surface of the grain, in conjunction with a slower diffusion of coffee through the intragranular pore network to the grain surface. Extraction of coffee from the bed also depends on the speed of advection of coffee from the bed. We utilize the small parameter resulting from the ratio of the advection timescale to the grain diffusion timescale to construct asymptotic solutions using the method of matched asymptotic expansions. The asymptotic solutions are compared to numerical solutions and data from coffee extraction experiments. The asymptotic solutions depend on a small number of dimensionless parameters and so are useful to quickly fit extraction curves and investigate the influence of various process parameters on the extraction.
PUBLISHED
peer-reviewed
eng
Society for Industrial and Applied Mathematics
Siam Journal on Applied Mathematics;76 (6), pp. 2196-2217
12/IA/1683
double porosity model
coffee brewing process
coffee extraction kinetics
solid liquid extraction
asymptotic analysis
matched asymptotic expansions
Asymptotic analysis of the dominant mechanisms in the coffee extraction process
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/7280
2018-11-07T01:02:42Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Erkol, Şirag
Faqeeh, Ali
Radicchi, Filippo
funder:SFI
funder:National Science Foundation
funder:US Army Research Office
2018
http://hdl.handle.net/10344/7280
peer-reviewed
The full text of this article will not be available in ULIR until the embargo expires on the 05/10/2019
We consider the problem of identifying the most influential nodes for a spreading process on a network when prior knowledge about structure and dynamics of the system is incomplete or erroneous. Specifically, we perform a numerical analysis where the set of top spreaders is determined on the basis of prior information that is artificially altered by a certain level of noise. We then measure the optimality of the chosen set by measuring its spreading impact in the true system. Whereas we find that the identification of top spreaders is optimal when prior knowledge is complete and free of mistakes, we also find that the quality of the top spreaders identified using noisy information does not necessarily decrease as the noise level increases. For instance, we show that it is generally possible to compensate for erroneous information about dynamical parameters by adding synthetic errors in the structure of the network. Further, we show that, in some dynamical regimes, even completely losing prior knowledge on network structure may be better than relying on certain but incomplete information
eng
IOP Publishing
1552487
EPL (Europhysics Letters);123 (5)
http://dx.doi.org/10.1209/0295-5075/123/58007
16/IA/4470
W911NF-16-1-0104
CMMI-1552487
numerical analysis
knowledge
network
Influence maximization in noisy networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/7382
2018-12-05T01:01:55Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Kyrke-Smith, T.M.
Fowler, Andrew C.
funder:Natural Environment Research Council
funder:SFI
2014
http://hdl.handle.net/10344/7382
peer-reviewed
The existence of both water and sediment at the bed of ice streams is well documented, but there is a lack of fundamental understanding about the mechanisms of ice, water and sediment interaction. We pose a model to describe subglacial water flow below ice sheets, in the presence of a deformable sediment layer. Water flows in a rough-bedded film; the ice is supported by larger clasts, but there is a millimetric water layer submerging the smaller particles. Partial differential equations describing the water film are derived from a description of the dynamics of ice, water and mobile sediment. We assume that sediment transport is possible, either as fluvial bedload, but more significantly by ice-driven shearing and by internal squeezing. This provides an instability mechanism for rivulet formation; in the model, downstream sediment transport is compensated by lateral squeezing of till towards the incipient streams. We show that the model predicts the formation of shallow, swamp-like streams, with a typical depth of the order of centimetres. The swamps are stable features, typically with a width of the order of tens to hundreds of metres.
PUBLISHED
peer-reviewed
eng
121A1683
Proceedings of the Royal Society A;470:20140340
NE/I528485/1
12/1A/1683
subglacial hydrology
canals
Smith-Bretherton instability
sediment-floored channels
Subglacial swamps
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/7394
2021-01-13T16:06:53Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Davoren, Martin P.
Hayes, Kevin
Horgan, Mary
Shiely, Frances
funder:SFI
2014
http://hdl.handle.net/10344/7394
peer-reviewed
Objective The burden of sexually transmitted
infections (STIs) rests with young people, yet in
Ireland there has been very little research into
this population. The purpose of this study was to
determine the incidence rate and establish risk
factors that predict STI occurrence among
adolescents in Ireland.
Design Routine diagnostic, demographic and
behavioural data from first-time visits to three
screening centres in the southwest of Ireland
were obtained. Univariate and multivariable
logistic regression models were used to assess
risk factors that predict STI occurrence among
adolescents.
Results A total of 2784 first-time patients, aged
13–19 years, received 3475 diagnoses between
January 1999 and September 2009; 1168 (42%)
of adolescents had notifiable STIs. The incidence
rate of STIs is 225/100 000 person-years.
Univariate analysis identified eligible risk factors
(p<0.2) for inclusion in the multivariable model.
Multivariable logistic regression showed the
dominant risk factors for STI diagnosis to be:
males who sometimes [odds ratio (OR) 2.02] or
never (OR 1.83) use condoms; and females
18–19 years (OR 2.26) and 16–18 years (OR 1.8),
with 2 (OR 1.33) or 3+ (OR 1.56) partners in the
last 12 months, who are non-intravenous drug
users (OR 0.72), are most likely to receive a
positive STI diagnosis.
Conclusions STI diagnosis has become
increasingly common in Ireland. The proportion
of notifications among those aged under
20 years is increasing. These data illustrate the
significance of age, condom use and number of
sexual partners as risk factors for STI diagnosis.
Furthermore, providing data for the first time, we
report on the high incidence rate of STIs among
adolescents in Ireland. The high levels of risktaking
behaviour and STI acquisition are
highlighted and suggest that there is a need
for an integrated public health approach to
combat this phenomenon in the adolescent
population.
PUBLISHED
peer-reviewed
eng
BMJ Publishing Group
12IA1683
Journal of Family Planning and Reproductive Health Care;40, pp. 276-282
12/IA/1683
risk-factors
United States
young adults
prevalence
disease
Sexually transmitted infection incidence among adolescents in Ireland
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/7602
2020-10-06T14:43:51Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Fannon, James S.
Fowler, Andrew C.
Moyles, Iain R.
funder:SFI
2017
http://hdl.handle.net/10344/7602
peer-reviewed
We summarize the present form of the instability theory for drumlin formation, which describes the coupled subglacial flow of ice, water and sediment. This model has evolved over the last 20 years, and is now at the point where it can predict instabilities corresponding to ribbed moraine, drumlins and mega-scale glacial lineations, but efforts to provide numerical solutions of the model have been limited. The present summary adds some slight nuances to previously published versions of the theory, notably concerning the constitutive description of the subglacial water film and its flow. A new numerical method is devised to solve the model, and we show that it can be solved for realistic values of most of the parameters, with the exception of that corresponding to the water film thickness. We show that evolved bedforms can be three-dimensional and of the correct sizes, and we explore to some extent the variation of the solutions with the model’s parameters.
eng
The Royal Society Publishing
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences;473
http://dx.doi.org/10.1098/rspa.2017.0220
SFI/12/IA/1683
SFI/13/IA/1923
drumlins
ribbed moraine
mega-scale glacial lineations
instabiity
Numerical simulations of drumlin formations
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/7603
2020-10-06T14:42:27Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Fannon, James S.
Moyles, Iain R.
Fowler, Andrew C.
funder:SFI
2019
http://hdl.handle.net/10344/7603
peer-reviewed
The full text of this article will not be available in ULIR until the embargo expires on the 14/08/2019
We consider the instability properties of dense granular flow in inclined plane and plane shear geometries as tests for the compressible inertial-dependent rheology. The model, which is a recent generalisation of the incompressible 𝜇
𝜇(I)
rheology, constitutes a hydrodynamical description of dense granular flow which allows for variability in the solids volume fraction. We perform a full linear stability analysis of the model and compare its predictions to existing experimental data for glass beads on an inclined plane and discrete element simulations of plane shear in the absence of gravity. In the case of the former, we demonstrate that the compressible model can quantitatively predict the instability properties observed experimentally, and, in particular, we find that it performs better than its incompressible counterpart. For the latter, the qualitative behaviour of the plane shear instability is also well captured by the compressible model.
eng
Cambridge University Press
Journal of Fluid Mechanics;864, pp. 1026-1057
https://doi.org/10.1017/jfm.2019.43
SFI/12/IA/1683
SFI/13/IA/1923
rheology
linear stability
Application of the compressible I-dependent rheology to chute and shear flow instabilities
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/7714
2019-03-23T01:02:23Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Fowler, Andrew C.
funder:SFI
2019
http://hdl.handle.net/10344/7714
peer-reviewed
In this paper we revisit the problem of explaining phase transition by a study of a form of
the Boltzmann equation, where inter-molecular attraction is included by means of a Vlasov
term in the evolution equation for the one particle distribution function.We are able to show
that for typical gas densities, a uniform state is unstable if the inter-molecular attraction is
large enough. Our analysis relies strongly on the assumption, essential to the derivation of
the Boltzmann equation, that ν ≪ 1, where ν = d/l is the ratio of the molecular diameter
to the mean inter-particle distance; in this case, for fluctuations on the scale of the molecular
spacing, the collision term is small, and an explicit approximate solution is possible. We
give reasons why we think the resulting approximation is valid, and in conclusion offer some
possibilities for extension of the results to finite amplitude.
eng
Springer
12IA1683
Journal of Statistical Physics; 174, pp. 1011-1026
https://doi.org/10.1007/s10955-019-02222-6
12/IA/1683
phase transition
Boltzmann equation
stabiity theory
Phase transition in the Boltzmann–Vlasov equation
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/7732
2021-08-25T13:09:15Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
O'Brien, Joseph D.
Dassios, Ioannis K.
Gleeson, James P.
funder:SFI
2019
http://hdl.handle.net/10344/7732
peer-reviewed
A model for the spreading of online information or ‘memes’ on multiplex networks is introduced and
analyzed using branching-process methods. The model generalizes that of (Gleeson et al 2016 Phys.
Rev.X) in two ways. First, even for a monoplex (single-layer) network, the model is defined for any
specific network defined by its adjacency matrix, instead of being restricted to an ensemble of random
networks. Second, a multiplex version of the model is introduced to capture the behavior of users who
post information from one social media platform to another. In both cases the branching process
analysis demonstrates that the dynamical system is, in the limit of low innovation, poised near a critical
point, which is known to lead to heavy-tailed distributions of meme popularity similar to those
observed in empirical data.
eng
IOP Publishing
New Journal of Physics;21: 025001
https://doi.org/10.1088/1367-2630/ab05ef
16/IA/4470
16/RC/3918
15/IA/3074
multiplex networks
branching processes
Spreading of memes on multiplex networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/8225
2020-10-29T15:29:15Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Nicoletti, Sara
Fanelli, Duccio
Zagli, Niccolò
Asllani, Malbor
Battistelli, Giorgio
Carletti, Timoteo
Chisci, Luigi
Innocenti, Giacomo
Livi, Roberto
2019
http://hdl.handle.net/10344/8225
peer-reviewed
A stochastic reaction-diffusion model is studied on a networked support. In each patch of the network, two species are assumed to interact
following a non-normal reaction scheme. When the interaction unit is replicated on a directed linear lattice, noise gets amplified via a selfconsistent
process,whichwe trace back to the degenerate spectrum of the embedding support. The same phenomenon holdswhen the system is
bound to explore a quasidegenerate network. In this case, the eigenvalues of the Laplacian operator,which governs species diffusion, accumulate
over a limited portion of the complex plane. The larger the network, the more pronounced the amplification. Beyond a critical network size, a
system deemed deterministically stable, hence resilient, can develop seemingly regular patterns in the concentration amount. Non-normality
and quasidegenerate networks may, therefore, amplify the inherent stochasticity and so contribute to altering the perception of resilience, as
quantified via conventional deterministic methods.
eng
AIP Publishing
Chaos;29, 083123
https://doi.org/10.1063/1.5099538
network
Resilience for stochastic systems interacting via a quasi-degenerate network
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/8323
2021-04-27T10:49:17Z
hdl_10344_21
hdl_10344_9
hdl_10344_73
hdl_10344_22
hdl_10344_3104
Schaller, Barbara E.
Moroney, Kevin M.
Castro-Dominguez, Bernardo
Cronin, Patrick
Belen-Girona, Jorge
Ruane, Patrick
Croker, Denise M.
Walker, Gavin M.
funder:SFI
2019
http://hdl.handle.net/10344/8323
peer-reviewed
In this work, the transfer of oral solid dosage forms, currently manufactured via wet granulation, to a continuous direct compression process was considered. Two main challenges were addressed: (1) a poorly flowing API (Canagliflozin) and (2) high drug loading (51 wt%). A scientific approach was utilised for formulation development, targeting flow and compaction behaviour suitable for manufacturing scale. This was achieved through systematic screening of excipients to identify feasible formulations. Targeted design of experiments based on factors such as formulation mixture and processing parameters were utilised to investigate key responses for tablet properties, flow and compaction behaviour. Flow behaviour was primarily evaluated from percentage compressibility and shear cell testing on a powder flow rheometer (FT4). The compaction behaviour was studied using a compaction simulator (Gamlen). The relationships between tablet porosity, tensile strength and compaction pressure were used to evaluate tabletability, compactibility and compressibility to assess scale-up. The success of this design procedure is illustrated by scaling up from the compaction simulator to a Riva Piccola rotary tablet press, while maintaining critical quality attributes (CQAs). Compactibility was identified as a suitable scale-up relationship. The developed procedure should allow accelerated development of formulations for continuous direct compression.
eng
Elsevier
14SP2750
International Journal of Pharmaceutics;566, pp. 615-630
https://doi.org/10.1016/j.ijpharm.2019.05.073
14/SP/2750
continuous direct compression
raw material characterization
systematic formulation development
high dosage formulation
compactibility
flow and compaction behaviour
Systematic development of a high dosage formulation to enable direct compression of a poorly flowing API: a case study
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/8521
2021-06-03T10:37:54Z
hdl_10344_21
hdl_10344_9
hdl_10344_73
da Cunha, Bruno Requião
MacCarron, Pádraig
Passold, Jean Fernando
dos Santos, Luiz Walmocyr
Oliveira, Kleber A.
Gleeson, James P.
funder:SFI
funder:ERC
funder:European Union (EU)
2020
http://hdl.handle.net/10344/8521
peer-reviewed
The networked nature of criminals using the dark web is poorly understood and infrequently studied,
mostly due to a lack of data. Rarer still are studies on the topological effectiveness of police interventions.
Between 2014 and 2016, the Brazilian Federal Police raided a child pornography ring acting inside the
dark web. With these data, we build a topic-view network and compare network disruption strategies
with the real police work. Only 7.4% of the forum users share relevant content, and the topological
features of this core differ markedly from other clandestine networks. Approximately 60% of the core
users need to be targeted to fully break the network connectivity, while the real effect of the arrests was
similar to random failure. Despite this topological robustness, the overall “viewership network” was still
well disrupted by the arrests, because only 10 users contributed to almost 1/3 of the total post views and 8
of these were apprehended. Moreover, the users who were arrested provided a total of 60% of the viewed
content. These results indicate that for similar online systems, aiming at the users that concentrate the
views may lead to more efficient police interventions than focusing on the overall connectivity.
eng
802421
Scientific Reports;10:73
16/IA/4470
12/RC/2289P2
802421
police topological
dark web
criminals
Assessing police topological efficiency in a major sting operation on the dark web
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/8597
2021-06-25T08:15:59Z
hdl_10344_21
hdl_10344_9
hdl_10344_73
Fowler, Andrew C.
McGuinness, Mark J.
2019
http://hdl.handle.net/10344/8597
peer-reviewed
We provide an analytic estimate for the size of the bulbs adjoining the main cardioid of the Mandelbrot set. The bulbs are approximate circles, and are associated with the stability regions in the complex parameter μ-space of period- q orbits of the underlying map z → z 2 −μ. For the ( p , q ) orbit with winding number p / q , the associated
stability bulb is an approximate circle with radius 1 q 2 sin πp q .
eng
Elsevier
Chaos, Solitons & Fractals: X;100019
Mandelbrot set
Mandelbrot bulbs
The size of mandelbrot bulbs
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/8784
2021-05-07T13:35:31Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Devine, Kevin M.
Vynnycky, Michael
Mitchell, Sarah L.
O’Brien, Stephen B. G.
funder:SFI
funder:IRC
funder:Fundação de Amparo à Pesquisa do Estado de São Paulo
2020
http://hdl.handle.net/10344/8784
peer-reviewed
This paper investigates the different possible behaviours of a recent asymptotic model for oscillation-mark formation in the continuous casting of steel, with particular focus on how the results obtained vary when the heat transfer coefficient (m), the thermal resistance (Rmf ) and the dependence of the viscosity of the flux powder as a function of temperature, μf (T) , are changed. It turns out that three different outcomes are possible: (I) the flux remains in molten state and no solid flux ever forms; (II) both molten and solid
flux are present, and the profile of the oscillation mark is continuous with respect to the space variable in the casting direction; (III) both molten and solid flux are present, and the profile of the oscillation mark is discontinuous with respect to the space variable in the casting direction. Although (I) gave good agreement with experimental data, it suffered the drawback that solid flux is typically observed during actual continuous casting; this has been rectified in this work via alternative (II). On the other hand, alternative (III) can occur as a result of hysteresis-type phenomenon that is encountered in other flows
that involve temperature-dependent viscosity; in the present case, this manifests itself via the possibility of multiple states for the oscillation-mark profile at the instants in time when solid flux begins to form and when it ceases to form.
eng
Oxford University Press
TD1409
IMA Journal of Applied Mathematics;00, pp. 1–36
12/IA/1683
GOIPG/2014/1147
continuous casting
oscillation marks
asymptotic analysis
Analysis of a model for the formation of fold-type oscillation marks in the continuous casting of steel
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/8894
2021-03-18T15:55:18Z
hdl_10344_21
hdl_10344_9
hdl_10344_73
MacCarron, Pádraig
Maher, Paul J.
Fennell, Susan C.
Burke, Kevin
Gleeson, James P.
Durrheim, Kevin
Quayle, Michael
funder:ERC
funder:IRC
funder:SFI
2020
http://hdl.handle.net/10344/8894
peer-reviewed
Shared opinions are an important feature in the formation of social groups. In this paper, we use the Axelrod model of cultural dissemination to represent opinion-based groups. In the Axelrod model, each agent has a set of features which each holds one of a set of nominally related traits. Survey data has a similar structure, where each participant answers each of a set of items with responses from a fixed list. We present an alternative method of displaying the Axelrod model by representing it as a bipartite graph, i.e., participants and their responses as separate nodes. This allows us to see which feature-trait combinations are selected in the final state. This visualisation is particularly useful when representing survey data as it illustrates the co-evolution of attitudes and opinion-based groups in Axelrod’s model of cultural diffusion. We also present a modification to the Axelrod model. A standard finding of the Axelrod model with many features is for all agents to fully agree in one cluster. We introduce an agreement threshold and allow nodes to interact only with those neighbours who are within this threshold (i.e., those with similar opinions) rather than those with any opinion. This method reliably yields a large number of clusters for small agreement thresholds and, importantly, does not limit to single cluster when the number of features grows large. This potentially provides a method for modelling opinion-based groups where as opinions are added, the number of clusters increase.
eng
Public Library of Science
PLoS ONE;15(6) e0233995
802421
16/IA/4470
12/RC/2289P2
Survey data
cultural diffusion
social groups
Agreement threshold on axelrod’s model of cultural dissemination
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/8906
2020-06-09T00:02:32Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_4612
hdl_10344_4609
hdl_10344_4613
hdl_10344_73
hdl_10344_20
Leahy, Joe
Thom, Howard
Jansen, Jeroen P
Gray, Emma
O'Leary, Aisling
White, Arthur
Walsh, Cathal Dominic
funder:HRB
funder:SFI
2019
http://hdl.handle.net/10344/8906
peer-reviewed
Increasingly, single-armed evidence is included in health technology assessment submissions when companies are seeking reimbursement for new drugs. While it is recognized that randomized controlled trials provide a higher standard of evidence, these are not available for many new agents that have been granted licenses in recent years. Therefore, it is important to examine whether alternative strategies for assessing this evidence may be used. In this work, we examine approaches to incorporating single-armed evidence formally in the evaluation process. We consider matching aggregate level covariates to comparator arms or trials and including this evidence in a network meta-analysis. We consider two methods of matching: (i) we include the chosen matched arm in the data set itself as a comparator for the single-arm trial; (ii) we use the baseline odds of an event in a chosen matched trial to use as a plug-in estimator for the single-arm trial. We illustrate that the synthesis of evidence resulting from such a setup is sensitive to the between-study variability, formulation of the prior for the between-design effect, weight given to the single-arm evidence, and extent of the bias in single-armed evidence. We provide a flowchart for the process involved in such a synthesis and highlight additional sensitivity analyses that should be carried out. This work was motivated by a hepatitis C data set, where many agents have only been examined in single-arm studies. We present the results of our methods applied to this data set.
ACCEPTED
peer-reviewed
eng
Wiley and Sons Ltd
Statistics in Medicine;38 (14), pp. 2505-2523
https://doi.org/10.1002/sim.8139
RL2013/4
08/IN.1/I1879
hepatitis C
hierarchical model
matched arms
network meta-analysis
single arm
Incorporating single-arm evidence into a network meta-analysis using aggregate level matching: assessing the impact
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/8947
2021-08-25T13:08:47Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
O'Brien, Joseph D.
Aleta, Alberto
Moreno, Yamir
Gleeson, James P.
funder:SFI
2020
http://hdl.handle.net/10344/8947
peer-reviewed
The Hawkes process has garnered attention in recent years for its suitability to describe the behavior of online information cascades. Here we present a fully tractable approach to analytically describe the distribution of the number of events in a Hawkes process, which, in contrast to purely empirical studies or simulation-based models, enables the effect of process parameters on cascade dynamics to be analyzed.We show that the presented
theory also allows predictions regarding the future distribution of events after a given number of events have been observed during a time window. Our results are derived through a differential-equation approach to attain the governing equations of a general branching process. We confirm our theoretical findings through extensive simulations of such processes. This work provides the basis for more complete analyses of the self-exciting processes that govern the spreading of information through many communication platforms, including the potential to predict cascade dynamics within confidence limits.
eng
American Physical Society
ECOST/STSM/TD1409/290216/071429
Physical Review E.;101, 062311
16/IA/4470
16/RC/3918
12/RC/2289P2
18/CRT/6049
Hawkes
information cascades.
Quantifying uncertainty in a predictive model for popularity dynamics
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/8968
2021-12-08T09:36:04Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
Asllani, Malbor
da Cunha, Bruno Requião
Estrada, Ernesto
Gleeson, James P.
funder:SFI
funder:ERC
2020
http://hdl.handle.net/10344/8968
peer-reviewed
Networks are universally considered as complex structures of interactions of large multi-component systems. To determine the role that each node has inside a complex network, several centrality measures have been developed. Such topological features are also crucial for their role in the dynamical processes occurring in networked systems. In this paper, we argue that the dynamical activity of the nodes may strongly reshape their relevance inside the network, making centrality measures in many cases, misleading. By proposing a generalisation of the communicability function, we show that when the dynamics taking place at the local level of the node is slower than the global one between the nodes, then the system may lose track of the structural features. On the contrary, hidden global properties such as the shortest path distances can be recovered only in the limit where network-level dynamics are negligible compared to node-level dynamics. From the perspective of network inference, this constitutes an uncertainty condition, in the sense that it limits the extraction of multi-resolution information about the structure, particularly in the presence of noise. For illustration purposes, we show that for networks with different time-scale structures such as strong modularity, the existence of fast global dynamics can imply that precise inference of the community structure is impossible.
eng
IOP Publishing
New Journal of Physics;22, 063037
16/IA/4470
16/RC/3918
12/RC/2289 P2
complex networks
dynamics on networks
inference methods
communicability measure
spreading dynamics
Dynamics impose limits to detectability of network structure
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/8974
2021-08-25T13:06:23Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
O'Brien, Joseph D.
Burke, Kevin
Burke, Mark E.
Barmish, Ross B.
funder:SFI
2020
http://hdl.handle.net/10344/8974
peer-reviewed
For sequential betting games, Kelly’s theory, aimed at maximization of the logarithmic growth of one’s account value, involves optimization of the so-called betting fraction K. In this Letter, we extend the classical formulation to allow for temporal correlation among bets. To demonstrate the potential of this new paradigm, for simplicity of exposition, we mainly address the case of a coin-flipping game with even-money payoff. To this end, we solve a problem with memory depth m. By this, we mean that the outcomes of coin flips are no longer assumed to be i.i.d. random variables. Instead, the probability of heads on flip k depends on previous flips k-1,k-2,...,k-m. For the simplest case of n flips, with m=1, we obtain a closed form solution Kn for the optimal betting fraction. This generalizes the classical result for the memoryless case. That is, instead of fraction K*=2p-1 which pervades the literature for a coin with probability of heads p≥1/2, our new fraction Kn depends on both n and the parameters associated with the temporal correlation. Generalizations of these results for m>1 and numerical simulations are also included. Finally, we indicate how the theory extends to time-varying feedback and alternative payoff distributions.
eng
IEEE Computer Society
16IA4470
IEEE Control Systems Letters;
http://dx.doi.org/ 10.1109/LCSYS.2020.3004029
16/1A/4470
stochastic systems
Markov processes
Finance
control applications
A generalization of the classical Kelly betting formula to the case of temporal correlation
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/8996
2020-07-11T00:08:38Z
hdl_10344_26
hdl_10344_25
hdl_10344_21
hdl_10344_9
hdl_10344_73
hdl_10344_34
Maher, Paul J.
MacCarron, Pádraig
Quayle, Michael
funder:ERC
2020
http://hdl.handle.net/10344/8996
peer-reviewed
Partisan patterns of compliance with public health measures are a feature of early COVID-19responses. In many cases, these differences in behaviour relate to pre-existing group
identities. However, in times of rapid societal change, novel opinion-based groups can
emerge and provide a new basis for partisan identification and divergent collective
behaviour. Here, we use network methods to map the emergence of opposing opinion based groups and assess their implications for public health behaviour. In a longitudinal study, we tracked public health attitudes and self-reported behaviour ina sample of UK participants over four time points. Network visualisation reveal a rift in attitudinal alignment over time and the genesisof twodistinct groups characterised by trust,ordistrust, in science (Study1a; N = 253). These groups also diverge in public health behaviour. In a brief follow-up study (N = 206),we find that this opinion polarization partially reflects underlying societal divides. We discuss implications for opinion-based group research and public health campaigns
eng
Wiley
802421
British Journal of Social Psychology;
802421
Partisan
societal divides
Mapping public health responses with attitude networks: the emergence of opinion-based groups in the UK’s early COVID-19 response phase
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/9096
2021-08-25T13:06:52Z
hdl_10344_21
hdl_10344_9
hdl_10344_73
O'Brien, Joseph D.
Burke, Mark E.
Burke, Kevin
funder:SFI
2020
http://hdl.handle.net/10344/9096
peer-reviewed
—We present a generalization of the Simultaneous Long-Short (SLS) trading strategy described in recent control literature wherein we allow for different parameters across the short and long sides of the controller; we refer to this new strategy as Generalized SLS (GSLS). Furthermore, we investigate the conditions under which positive gain can be assured within the GSLS setup for both deterministic stock price evolution and geometric Brownian motion. In contrast to existing literature in this area (which places little emphasis on the practical application of SLS strategies), we suggest optimization procedures for selecting the control parameters based on historical data, and we extensively test these procedures across a large number of real stock price trajectories (495 in total). We ﬁnd that the implementation of such optimization procedures greatly improves the performance compared with ﬁxing control parameters, and, indeed, the GSLS strategy outperforms the simpler SLS strategy in general.
eng
IEEE Computer Society
16IA4470
IEEE Transactions on Automatic Control;
http://dx.doi.org/10.1109/TAC.2020.3011914
16/IA/4470
feedback-based stock trading
parameter optimization
simultaneous long-short strategy
S&P500
A generalized framework for simultaneous long-short feedback trading
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/9489
2021-12-06T14:38:47Z
hdl_10344_21
hdl_10344_9
hdl_10344_73
Gessey-Jones, Thomas
Connaughton, Colm
Dunbard, Robin
Kenna, Ralph
MacCarron, Pádraig
O'Conchobhaire, Cathal
Yose, Joseph
funder:Coventry University
funder:ERC
2020
http://hdl.handle.net/10344/9489
peer-reviewed
Network science and data analytics are used to quantify static and dynamic structures in George R. R. Martin’s epic novels, A Song of Ice and Fire, works noted for their scale and complexity. By tracking the network of character interactions as the story unfolds, it is found that structural properties remain approximately stable and comparable to real-world social networks. Furthermore, the degrees of the most connected characters reflect a cognitive limit on the number of concurrent social connections that humans tend to maintain. We also analyze the distribution of time intervals between significant deaths measured with respect to the in-story timeline. These are consistent with power-law distributions commonly found in interevent times for a range of nonviolent human activities in the real world. We propose that structural features in the narrative that are reflected in our actual social world help readers to follow and to relate to the story, despite its sprawling extent. It is also found that the distribution of intervals between significant deaths in chapters is different to that for the in-story timeline; it is geometric rather than power law. Geometric distributions are memoryless in that the time since the last death does not inform as to the time to the next. This provides measurable support for the widely held view that significant deaths in A Song of Ice and Fire are unpredictable chapter by chapter
eng
National Academy of Sciences
612707
PNAS;117 (46),pp. 28582-28588
802421
Ice and Fire
dynamic structures
Narrative structure of a song of ice and fire creates a fictional world with realistic measures of social complexity
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/9590
2021-11-30T12:45:59Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Muolo, Riccardo
Carletti, Timoteo
Gleeson, James P.
Asllani, Malbor
funder:SFI
2021
http://hdl.handle.net/10344/9590
peer-reviewed
Synchronization is an important behavior that characterizes many natural and human made systems that are composed by several interacting units. It can be found in a broad spectrum of applications, ranging from neuroscience to power-grids, to mention a few. Such systems synchronize because of the complex set of coupling they exhibit, with the latter being modeled by complex networks. The dynamical behavior of the system and the topology of the underlying network are strongly intertwined, raising the question of the optimal architecture that makes synchronization robust. The Master Stability Function (MSF) has been proposed and extensively studied as a generic framework for tackling synchronization problems. Using this method, it has been shown that, for a class of models, synchronization in strongly directed networks is robust to external perturbations.
Recent findings indicate that many real-world networks are strongly directed, being potential candidates for optimal synchronization. Moreover, many empirical networks are also strongly non-normal. Inspired by this latter fact in this work, we address the role of the non-normality in the synchronization dynamics by pointing out that standard techniques, such as the MSF, may fail to predict the stability of synchronized states. We demonstrate that, due to a transient growth that is induced by the structure’s non normality, the system might lose synchronization, contrary to the spectral prediction.
These results lead to a trade-off between non-normality and directedness that should be properly considered when designing an optimal network, enhancing the robustness of synchronization.
eng
MDPI
Entropy;23,(36)
FC 33443
16/IA/4470
16/RC/3918
12/RC/2289 P2
18/CRT/6049
non-normal networks
synchronization
optimal networks
Synchronization dynamics in non-normal networks: the trade-off for optimality
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/9595
2021-12-14T14:16:42Z
hdl_10344_21
hdl_10344_9
hdl_10344_73
Unicomb, Samuel
Iñiguez, Gerardo
Gleeson, James P.
Karsai, Márton
funder:SFI
funder:ERD
funder:European Union (EU)
funder:Horizon 2020
2021
http://hdl.handle.net/10344/9595
peer-reviewed
Burstiness, the tendency of interaction events to be heterogeneously distributed in time, is
critical to information diffusion in physical and social systems. However, an analytical framework capturing the effect of burstiness on generic dynamics is lacking. Here we develop a master equation formalism to study cascades on temporal networks with burstiness modelled by renewal processes. Supported by numerical and data-driven simulations, we describe the interplay between heterogeneous temporal interactions and models of threshold-driven and epidemic spreading. We find that increasing interevent time variance can both accelerate and decelerate spreading for threshold models, but can only decelerate epidemic spreading. When accounting for the skewness of different interevent time distributions, spreading times collapse onto a universal curve. Our framework uncovers a deep yet subtle connection between generic diffusion mechanisms and underlying temporal network structures that impacts a broad class of networked phenomena, from spin interactions to epidemic contagion and language dynamics.
eng
Nature Research
Nature Communications;12,(133)
16/IA/4470
16/RC/3918
12/RC/2289
18/CRT/6049
761758
epidemic contagion
Burstiness
Dynamics of cascades on burstiness-controlled temporal networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/9625
2021-01-21T01:01:01Z
hdl_10344_21
hdl_10344_9
hdl_10344_73
Carletti, Timoteo
Asllani, Malbor
Fanelli, Duccio
Latora, Vito
2020
http://hdl.handle.net/10344/9625
peer-reviewed
Random walks are the simplest way to explore or search a graph and have revealed a very useful tool to investigate and characterize the structural properties of complex networks from the real world. For instance, they have been used to identify the modules of a given network, its most central nodes and paths, or to determine the typical times to reach a target. Although various types of random walks whose motion is biased on node
properties, such as the degree, have been proposed, which are still amenable to analytical solution, most if not all of them rely on the assumption of linearity and independence of the walkers. In this work we introduce a class of nonlinear stochastic processes describing a system of interacting random walkers moving over networks with
finite node capacities. The transition probabilities that rule the motion of the walkers in our model are modulated by nonlinear functions of the available space at the destination node, with a bias parameter that allows to tune the tendency of the walkers to avoid nodes occupied by other walkers. First, we derive the master equation governing the dynamics of the system, and we determine an analytical expression for the occupation probability
of the walkers at equilibrium in the most general case and under different level of network congestions. Then we study different types of synthetic and real-world networks, presenting numerical and analytical results for the entropy rate, a proxy for the network exploration capacities of the walkers. We find that, for each level of the nonlinear bias, there is an optimal crowding that maximizes the entropy rate in a given network topology. The analysis suggests that a large fraction of real-world networks are organized in such a way as to favor exploration under congested conditions. Our work provides a general and versatile framework to model nonlinear stochastic processes whose transition probabilities vary in time depending on the current state of the system.
eng
American Physical Society
Physical Review Research;2, 033012
Random walks
complex networks
Nonlinear walkers and efficient exploration of congested networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/9640
2021-01-23T01:01:07Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_380
hdl_10344_379
hdl_10344_73
hdl_10344_383
hdl_10344_20
Mitchell, Sarah L.
McInerney, N.P.
O'Brien, Stephen B.G.
funder:SFI
2021
http://hdl.handle.net/10344/9640
peer-reviewed
This study examines a one-dimensional Stefan problem describing the sorption of a finite amount of swelling solvent in a glassy polymer. The polymer is initially in a dry non-swollen state, where the polymer network is dense. The polymer is then injected with a critical concentration of a swelling solvent, causing polymer chain relaxation to occur. A moving boundary separating the swollen rubbery polymer from the dry glassy polymer is created, whose speed is defined by a kinetic law. The form of the kinetic law is typically assumed to be linear, but this is a nonphysical restriction, and thus we consider the case for a general exponent. We present formal asymptotic expansions, for both small and large times as well as for small and large values of the control parameter, as well as considering the heat balance integral method. These approximations are compared with a numerical scheme, which uses a boundary immobilisation technique and correctly identifies the appropriate starting solution.
eng
Elsevier
SFI12IA/1683
Applied Mathematical Modelling;92, pp. 624-650
SFI/12/IA/1683
mathematical modelling
moving boundary problem
Stefan problem
swelling polymer
asymptotics
heat balance integral method
Approximate solution techniques for the sorption of a finite amount of swelling solvent in a glassy polymer
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/9872
2021-08-25T13:08:12Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
O'Brien, Joseph D.
Gleeson, James P.
O'Sullivan, David J.P.
funder:SFI
funder:European Union (EU)
2021
http://hdl.handle.net/10344/9872
peer-reviewed
In all competitions where results are based upon an individual’s performance the question of whether the outcome is a consequence of skill or luck arises. We explore this question
through an analysis of a large dataset of approximately one million contestants playing Fantasy Premier League, an online fantasy sport where managers choose players from the English football (soccer) league. We show that managers’ ranks over multiple seasons are correlated and we analyse the actions taken by managers to increase their likelihood of success. The prime factors in determining a manager’s success are found to be long-term planning and consistently good decision-making in the face of the noisy contests upon which this game is based. Similarities between managers’ decisions over time that result in the emergence of ‘template’ teams, suggesting a form of herding dynamics taking place within the game, are also observed. Taken together, these findings indicate common strategic considerations and consensus among successful managers on crucial decision points over an extended temporal period.
eng
Public Library of Science
PLoS ONE;16(3), e0246698
16/IA/4470
16/RC/3918
12/RC/2289
18/CRT/6049
English football
managers
Identification of skill in an online game: The case of fantasy premier league
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/9873
2021-08-25T13:05:58Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
O'Brien, Joseph D.
Gleeson, James P.
funder:SFI
2021
http://hdl.handle.net/10344/9873
peer-reviewed
A detailed analysis of matches played in the sport of Snooker during the period 1968–2020 is used to calculate a directed and weighted dominance network based upon the corresponding results. We consider a ranking procedure based upon the well-studied PageRank algorithm that incorporates details of not only the number of wins a player has had over their career but also the quality of opponent faced in these wins. Through this study, we find that John Higgins is the highest performing Snooker player of all time with
Ronnie O’Sullivan appearing in second place. We demonstrate how this approach can be applied across a variety of temporal periods in each of which we may identify the strongest player in the corresponding era. This procedure is then compared with more classical ranking schemes. Furthermore, a visualization tool known as the rank-clock is introduced to the sport which allows for immediate analysis of the career trajectory of individual competitors. These results further demonstrate the use of network science in the quantification of success within the field of sport.
eng
Oxford University Press
Journal of Complex Networks;00, pp.1–16
16/IA/4470
16/RC/3918
12/RC/2289P2
network analysis
Page Rank
sports
A complex networks approach to ranking professional snooker players
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/9894
2021-03-19T01:01:09Z
hdl_10344_10
hdl_10344_9
hdl_10344_26
hdl_10344_25
hdl_10344_21
hdl_10344_73
hdl_10344_34
hdl_10344_20
Fennell, Susan C.
Burke, Kevin
Quayle, Michael
Gleeson, James P.
funder:IRC
funder:SFI
funder:ERC
funder:European Union (EU)
funder:Horizon 2020
2021
http://hdl.handle.net/10344/9894
peer-reviewed
When the interactions of agents on a network are assumed to follow the Deffuant opinion dynamics model, the
outcomes are known to depend on the structure of the underlying network. This behavior cannot be captured by
existing mean-field approximations for the Deffuant model. In this paper, a generalized mean-field approximation
is derived that accounts for the effects of network topology on Deffuant dynamics through the degree distribution
or community structure of the network. The accuracy of the approximation is examined by comparison with
large-scale Monte Carlo simulations on both synthetic and real-world networks.
eng
American Chemical Society
802421
Physical Review E;103, 012314
http://dx.doi.org/10.1103/PhysRevE.103.012314
16/IA/4470
16/RC/3918
18/CRT/6049
802421
mathematics
Generalized mean-field approximation for the Deffuant opinion dynamics model on networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/9949
2021-04-01T07:58:31Z
hdl_10344_21
hdl_10344_9
hdl_10344_242
hdl_10344_240
hdl_10344_480
hdl_10344_243
hdl_10344_504
hdl_10344_73
Fowler, Andrew C.
Kanppe, Jan
2019
http://hdl.handle.net/10344/9949
peer-reviewed
Soil treatment units (STUs) are an integral component of most domestic on-site wastewater
treatment systems. Understanding their long-term environmental impacts and performance
will help to improve design guidelines and operational procedures. In this study, the first
systematic tracing of primary and secondary treated effluent percolating into the unsaturated
subsoil below shallow gravel trenches in STUs was undertaken using a three-dimensional
network of soil sensors continuously recording volumetric water content, soil temperature,
and electric conductivity in the pore water. Three full-scale on-site systems were constructed
to treat the domestic effluent of individual households (2 to 4 PE) at field sites in rural Ireland.
Following a conventional two-chamber septic tank, the partially treated effluent was, then, split
equally into two streams for (i) direct discharge of primary effluent into one half of the STU,
and (ii) further treatment in a secondary treatment unit before final discharge to soil in the
other half of the STU. Data obtained from the sensor network and chemical analysis of effluent
as it percolated through the vadose zone serve as proxy for determining the existence and
extent of zones of effective percolation and biomat spread at the base of percolation trenches.
From results of the field measurements and numerical modeling using HYDRUS 2D, it can be
inferred that soil moisture retention within a biological clogging zone at the infiltrative layer
– also known as a microbial biomat – expressed distinct responses to hydraulic and organic
loading patterns, and environmental factors such as periods of extended drought or temporarily
saturated conditions following heavy rainfall events. The results of this study, in turn, will
contribute to a more insightful assessment of existing guidelines and regulations governing
the design and operation of on-site treatment systems in Ireland and internationally.
eng
University of Limerick
biomat
on-site wastewater treatment
septic system
soil treatment unit
vadose
The influence of a growing microbial biomat on water retention and pollutant attenuation in soil treatment units receiving domestic effluent
info:eu-repo/semantics/doctoralThesis
oai:ulir.ul.ie:10344/10008
2021-05-21T11:06:45Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Gleeson, James P.
Onaga, Tomokatsu
Fennell, Peter
Cotter, James
Burke, Raymond
O'Sullivan, David J.P.
funder:SFI
funder:European Union (EU)
2021
http://hdl.handle.net/10344/10008
peer-reviewed
A detailed analysis of Twitter-based information cascades is performed, and it is demonstrated that branching process hypotheses are approximately satisfied. Using a branching process framework, models of agent-to-agent transmission are compared to conclude that a limited attention model better reproduces the relevant characteristics of the data than the more common independent cascade model. Existing and new analytical results for branching processes are shown to match well to the important statistical characteristics of the empirical information cascades, thus demonstrating the power of branching process descriptions for understanding social information spreading.
eng
Oxford University Press
Journal of Complex Networks; 8 (6)
16/IA/4470
16/RC/3918
12/RC/2289
18/CRT/6049
JP19K14618
branching processes
networks
cascades
Branching process descriptions of information cascades on twitter
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/10031
2021-05-07T13:53:20Z
hdl_10344_21
hdl_10344_9
hdl_10344_73
hdl_10344_3104
Moroney, Kevin M.
Kotamarthy, Lalith
Muthancheri, Indu
Ramachandran, Rohit
Vynnycky, Michael
funder:SFI
2021
http://hdl.handle.net/10344/10031
peer-reviewed
The published OA version of this article was added to ULIR on the 07/05/2021
Accurate mechanistic in vitro dissolution models can deliver insight into drug release behaviour and guide formulation development. Drug release profiles from drug-excipient granules can be impacted by variation of porosity and drug load within granules, which may arise from inherent variability in granulation processes. Here, we analyse and validate a recent model of drug release from a single spherical granule with a matrix of insoluble excipient, incorporating radial variation of porosity and drug load. The model is presented and specialised to the case where the initial drug load is large compared to the capacity of the granule's pores at solubility. In this limit, the model reduces to a single ordinary differential equation describing depletion of a shrinking, drug-saturated core. Model validation is performed using drug release data from the literature for a granule system consisting of acetaminophen and microcrystalline cellulose. A new extended model to describe dissolution from a polydisperse collection of granules is derived. The performance is compared to single particle models using equivalent spherical diameters. The developed model provides a new tool to explore the dissolution parameter space for these systems and for considering the impact of radial variation of granule porosity and drug load arising from manufacturing processes.
ACCEPTED
peer-reviewed
eng
Elsevier
International Journal of Pharmaceutics;599, 120219
https://doi.org/10.1016/j.ijpharm.2021.120219
12/RC/2275 P2
drug dissolution
granule microstructure
moving boundary models
porosity
A moving-boundary model of dissolution from binary drug-excipient granules incorporating microstructure.
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/10059
2021-05-07T08:03:20Z
hdl_10344_21
hdl_10344_9
hdl_10344_4612
hdl_10344_4609
hdl_10344_73
hdl_10344_4613
Allen, Niamh
Ni Riain, Una
Conlon, Niall
Ferenczi, Annamaria
Martin, Antonio Isidro Carrion
Domegan, Lisa
Walsh, Cathal Dominic
Doherty, Lorraine
O'Farrelly, Cliona
Higgins, Eibhlin
Kerr, Colm
McGrath, Jonathan
Fleming, Catherine
Bergin, Colm
funder:HRB
2021
http://hdl.handle.net/10344/10059
peer-reviewed
no abstract available
eng
Cambridge University Press
Epidemiology and Infection;
http://dx.doi.org/ 10.1017/S0950268821000984
antibodies
hospital care workers
Prevalence of antibodies to SARS-CoV-2 in Irish Hospital Healthcare Workers
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/10115
2021-06-29T07:49:16Z
hdl_10344_21
hdl_10344_9
hdl_10344_4612
hdl_10344_4609
hdl_10344_73
hdl_10344_4613
McConnell, David
Hickey, Conor
Bargary, Norma
Trela-Larsen, Lea
Walsh, Cathal Dominic
Barry, Michael
Adams, Roisin
funder:Trinity College Dublin
2021
http://hdl.handle.net/10344/10115
peer-reviewed
SARS-CoV-2 continues to widely circulate in populations globally. Under detection is
acknowledged and is problematic when attempting to capture the true prevalence. Seroprevalence studies, where blood samples from a population sample are tested for SARS-CoV-2 antibodies that react to the SARS-CoV-2 virus, are a common method for estimating the proportion of people previously infected with the virus in a given population. However, obtaining reliable estimates from seroprevalence studies is challenging for a number of reasons, and the uncertainty in the results is often overlooked by scientists, policy makers, and the media. This paper reviews the methodological issues that arise in designing these studies, and the main sources of uncertainty that affect the results. We discuss the choice of study population, recruitment of subjects, uncertainty surrounding
the accuracy of antibody tests, and the relationship between antibodies and infection over time. Understanding these issues can help the reader to interpret and critically evaluate the results of seroprevalence studies.
eng
MDPI
Int. Journal of Environmental Research and Public Health;18, 4640
COVID-19
SARS-CoV-2
coronavirus
Understanding the challenges and uncertainties of seroprevalence studies for SARS-CoV-2
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/10328
2021-09-15T15:02:40Z
hdl_10344_21
hdl_10344_9
hdl_10344_73
Reddy, Gujji Murali Mohan
Nanda, P.
Vynnycky, Michael
Cuminato, J.A.
funder:SERB, India
2021
http://hdl.handle.net/10344/10328
peer-reviewed
In this article, we study a novel computational technique for the efficient numerical solution of the inverse boundary identification problem with uncertain data in two dimensions.
The method essentially relies on a posteriori error indicators consisting of the Tikhonov
regularized solutions obtained by the method of fundamental solutions (MFS) and the
given data for the problem in hand. For a desired accuracy, the a posteriori error estimator chooses the best possible combination of a complete set of fundamental solutions
determined by the location of the sources that are arranged in a particular manner on
a pseudo-boundary at each iteration. Also, since we are interested in a stable solution,
an adaptive stochastic optimization strategy based on an error-balancing criterion is used,
so as to avoid unstable regions where the stability contributions may be relatively large.
These ideas are applied to two benchmark problems and are found to produce efficient
and accurate results.
eng
Elsevier
Applied Mathematics and Computation;409, 126402
SRG/2019/001973
A posteriori error estimator
Fundamental solutions
Efficient numerical solution of boundary identification problems: MFS with adaptive stochastic optimization
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/10467
2021-08-25T13:07:44Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_73
hdl_10344_20
O'Brien, Joseph D.
Oliveira, Kleber A.
Gleeson, James P.
Asllani, Malbor
funder:SFI
2021
http://hdl.handle.net/10344/10467
peer-reviewed
A large number of complex systems, naturally emerging in various domains, are well described by directed networks, resulting in numerous interesting features that are absent from their undirected counterparts. Among these properties is a strong non-normality, inherited by a strong asymmetry that characterizes such systems and guides their underlying hierarchy. In this work, we consider an extensive collection of empirical networks and analyze their structural properties using information-theoretic tools. A ubiquitous feature is observed amongst such systems as the level of non-normality increases. When the non-normality reaches a given threshold, highly directed substructures aiming towards terminal (sink or source) nodes, denoted here as leaders, spontaneously emerge. Furthermore, the relative number of leader nodes describe the level of anarchy that characterizes the networked systems. Based on the structural analysis, we develop a null model to capture features such as the aforementioned transition in the networks' ensemble. We also demonstrate that the role of leader nodes at the pinnacle of the hierarchy is crucial in driving dynamical processes in these systems. This work paves the way for a deeper understanding of the architecture of empirical complex systems and the processes taking place on them.
eng
American Physical Society
Physical Review Research;3 (2) 023117
16/RC/3918
16/IA/4470
12/RC/2289P2
18/CRT/6049
complex systems
mathematics
Hierarchical route to the emergence of leader nodes in real-world networks
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/10549
2021-09-09T00:01:06Z
hdl_10344_21
hdl_10344_9
hdl_10344_73
Fowler, Andrew C.
funder:SFI
2021
http://hdl.handle.net/10344/10549
peer-reviewed
This paper addresses the problem of extinction in continuous models of population
dynamics associated with small numbers of individuals. We begin with an extended
discussion of extinction in the particular case of a stochastic logistic model, and how
it relates to the corresponding continuous model. Two examples of ‘small number
dynamics’ are then considered. The first is what Mollison calls the ‘atto-fox’ problem
(in a model of fox rabies), referring to the problematic theoretical occurrence of a
predicted rabid fox density of 10−18 (atto-) per square kilometre. The second is how the
production of large numbers of eggs by an individual can reliably lead to the eventual
survival of a handful of adults, as it would seem that extinction then becomes a likely
possibility. We describe the occurrence of the atto-fox problem in other contexts, such
as the microbial ‘yocto-cell’ problem, and we suggest that the modelling resolution
is to allow for the existence of a reservoir for the extinctively challenged individuals.
This is functionally similar to the concept of a ‘refuge’ in predator–prey systems and
represents a state for the individuals in which they are immune from destruction. For
what I call the ‘frogspawn’ problem, where only a few individuals survive to adulthood
from a large number of eggs, we provide a simple explanation based on a Holling type
3 response and elaborate it by means of a suitable nonlinear age-structured model.
eng
Springer
Bulletin of Mathematical Biology;83, 104
SFI/13/IA/1923
Atto-foxes
Boom-and-bust
Extinction
Atto-Foxes and other minutiae
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/10634
2021-10-02T00:01:10Z
hdl_10344_21
hdl_10344_9
hdl_10344_4612
hdl_10344_4609
hdl_10344_73
hdl_10344_4613
Allen, Niamh
Brady, Melissa
Carrion Martin, Antonio Isidro
Domegan, Lisa
Walsh, Cathal Dominic
Doherty, Lorraine
Ni Riain, Una
Bergin, Colm
Fleming, Catherine
Conlon, Niall
2021
http://hdl.handle.net/10344/10634
peer-reviewed
The full text of this article will not be available in ULIR until the embargo expires on the 05/08/2022
Dear Editor,
We write in response to correspondence from Whitaker et al. in this Journal (1). The authors
demonstrate increases in seropositivity for SARS-CoV-2 antibodies against the spike protein
as the roll out of COVID-19 vaccines continues, whilst parallel assessment of nucleocapsid
antibodies remained stable. This study is an example of the use of parallel assessment of
spike (S) and nucleocapsid (N) antibodies to discriminate between natural infection and
vaccine related seropositivity (2) (3). This approach remains attractive, but as the pandemic
rolls on it is worth considering the paucity of evidence about the impact of vaccination on
antibody production in response to a subsequent natural infection
eng
Elsevier
Journal of Infection;83 (4), pp. e9-e10
https://doi.org/10.1016/j.jinf.2021.08.012
SARS-CoV-2
Serological markers of SARS-CoV-2 infection; anti-nucleocapsid antibody positivity may not be the ideal marker of natural infection in vaccinated individuals
info:eu-repo/semantics/contributionToPeriodical
oai:ulir.ul.ie:10344/10652
2021-10-08T00:01:07Z
hdl_10344_21
hdl_10344_9
hdl_10344_73
Dubber, Donata
Knappe, Jan
Gill, Laurence W.
funder:SFI
2021
http://hdl.handle.net/10344/10652
peer-reviewed
This research has used fluorescence spectroscopy and parallel factor analysis (PARAFAC)
in order to characterize dissolved organic matter in septic tank effluent, as it passes through the
biomat/biozone, infiltrating into the unsaturated zone beneath domestic wastewater treatment
systems (DWWTSs). Septic tank effluent and soil moisture samples from the percolation areas of
two DWWTSs have been analyzed using fluorescence excitation–emission spectroscopy. Using
PARAFAC analysis, a six-component model was obtained whereby individual model components
could be assigned to humified organic matter, fluorescent whitening compounds (FWCs), and protein-like compounds. This has shown that fluorescent dissolved organic matter (FDOM) in domestic wastewater was dominated by protein-like compounds and FWCs and that, with treatment in the percolation area, protein-like compounds and FWCs are removed and contributions from terrestrially derived (soil) organic decomposition compounds increase, leading to a higher degree of humification and aromaticity. The results also suggest that the biomat is the most important element determining FDOM removal and consequently affecting DOM composition. Furthermore, no significant difference was found in the FDOM composition of samples from the percolation area irrespective of whether they received primary or secondary effluent. Overall, the tested fluorometric methods were shown to provide information about structural and functional properties of organic matter which can be useful for further studies concerning bacterial and/or virus transport from DWWTSs.
eng
MDPI
Water;13, 2627
15/ERC/B3128
13/IA/1923
on-site wastewater
organics
fluorescence
Characterisation of organic matter and its transformation processes in on-site wastewater effluent percolating through soil using fluorescence spectroscopic methods and parallel factor analysis (PARAFAC)
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/10724
2021-11-02T01:01:06Z
hdl_10344_21
hdl_10344_9
hdl_10344_73
Davis, Arran J.
MacCarron, Pádraig
Cohen, Emma
funder:SFI
funder:University of Oxford
funder:British Academy
2021
http://hdl.handle.net/10344/10724
peer-reviewed
There is growing academic, civic and policy interest in the public health benefits of community-based exercise events. Shifting the emphasis from competitive sport to communal activity, these events have wide appeal. In addition to physical health benefits, regular participation can reduce social isolation and loneliness through opportunities for social connection. Taking a broad evolutionary and social psychological perspective, we suggest that social factors warrant more attention in current approaches to physical (in)activity and exercise behavior. We develop and test the hypothesis that social reward and support in exercise are associated with positive exercise experiences and greater performance outputs. Using a repeated-measures design, we examine the influence of social perceptions and behavior on subjective enjoyment, energy, fatigue, effort, and objective performance (run times) among a UK sample of parkrun participants. Social factors were associated with greater subjective enjoyment and energy. Higher subjective energy, in turn, was associated with faster run times, without any corresponding increase in perceived effort. No significant main effects of social factors on fatigue, performance or effort were detected. The role of social structural factors has long been recognized in public health approaches to physical activity. Our results indicate that there should be greater research attention on how positive and rewarding social behaviors and experiences—particularly subjective enjoyment and energy, and perceptions of community social support and belonging—influence exercise-related behavior, psychology and physiology, and promote health through collective physical activity. The research also supplements traditional emphases on social facilitation and team sport that have dominated sport and exercise psychology and offers new avenues for understanding the deep connections among psychological, social and physical function in everyday health
eng
Public Library of Science
MD130076
PLoS ONE;16(9), e0256546
16/IA/4470
fatigue
energy
Social reward and support effects on exercise experiences and performance: evidence from parkrun
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/10742
2021-11-05T01:01:17Z
hdl_10344_21
hdl_10344_9
hdl_10344_242
hdl_10344_240
hdl_10344_480
hdl_10344_73
hdl_10344_504
hdl_10344_243
Burke, Kevin
Gleeson, James P.
Quayle, Michael
Fennell, Susan C.
funder:IRC
2021
http://hdl.handle.net/10344/10742
peer-reviewed
Individuals’ opinions, beliefs and behaviours are formed through social
interaction. In this thesis we are interested in the influence of social
interaction on (i) how opinions spread and (ii) the emergence of social
norms.
In the first part of this thesis we derive a generalised mean-field ap proximation that accounts for the effect of network topology on Def fuant opinion dynamics through the degree distribution or community
structure of the network. We examine the accuracy of the approxima tion by comparing with Monte Carlo simulations on both synthetic
and real-world networks. We carry out a mathematical analysis of the
mean-field equations to understand the early-time behaviour and to
locate the clusters in steady state. We obtain analytic results on fully
connected networks and networks with two degree classes.
In the second part of this thesis we outline a modelling methodology
for analysing social interaction data. We apply our method to data
collected using the Virtual Interaction Application (VIAPPL) — a
software platform for conducting experiments that reveal how social
norms and identities emerge through social interaction. We apply our
model to show that ingroup favouritism and reciprocity are present
in the experiments, and to quantify the strengthening of these be haviours over time. Our method enables us to identify participants
whose behaviour is markedly different from the norm. We use the
method to provide a visualisation of the data that highlights the level
of ingroup favouritism, the strong reciprocal relationships, and the
different behaviour of participants in the game. While our method ology was developed with VIAPPL in mind, its usage extends to any
type of social interaction data.
eng
University of Limerick
social interaction
mathematics
connected networks
Mathematical and statistical models for studying social interaction
info:eu-repo/semantics/doctoralThesis
oai:ulir.ul.ie:10344/10748
2021-11-06T01:01:07Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
Kohlstädt, Sebastian
Vynnycky, Michael
Goeke, Stephan
Gebauer-Teichmann, Andreas
2021
http://hdl.handle.net/10344/10748
peer-reviewed
This paper investigates the critical plunger velocity in high-pressure die casting during the
slow phase of the piston motion and how it can be determined with computational fluid dynamics (CFD) in open source software. The melt-air system is modelled via an Eulerian volume-of-fluid approach, treating the air as a compressible perfect gas. The turbulence is treated via a Reynold saveraged Navier Stokes (RANS) approach that uses the Menter SST k-w model. Two different strategies for mesh motion are presented and compared against each other. The solver is validated via analytical models and empirical data. A method is then presented to determine the optimal velocity using a two-dimensional (2D) mesh. As a second step, it is then discussed how the results are in line with those obtained for an actual, industrially relevant, three-dimensional (3D) geometry that also includes the ingate system of the die.
eng
MDPI
Fluids;6, 386
(3D) geometry
compressible two-phase flow
high-pressure die casting
On determining the critical velocity in the shot sleeve of a high-pressure die casting machine using open source CFD
info:eu-repo/semantics/article
oai:ulir.ul.ie:10344/10786
2021-11-17T01:01:05Z
hdl_10344_10
hdl_10344_9
hdl_10344_21
hdl_10344_20
hdl_10344_73
O'Brien, Joseph D.
Gleeson, James P.
funder:SFI
2021
http://hdl.handle.net/10344/10786
peer-reviewed
Simon’s classical random-copying model, introduced in 1955, has garnered much attention for its ability, in spite of an apparent simplicity, to produce characteristics similar to those observed across the spectrum of complex systems. Through a discrete-time mechanism in which items are added to a sequence based upon rich-gets-richer dynamics, Simon demonstrated that the resulting size distributions of such sequences exhibit power-law tails. The simplicity of this model arises from the approach by which copying occurs uniformly over all previous elements in the sequence. Here we propose a generalization of this model which moves away from this uniform assumption, instead incorporating memory effects that allow the copying event to occur via an arbitrary age-dependent kernel. Through this approach, we first demonstrate the potential to determine further information regarding the structure of sequences from the classical model before illustrating, via analytical study and numeric simulation, the flexibility offered by the arbitrary choice of memory. Furthermore, we demonstrate how previously proposed memory-dependent models can be further studied as specific cases of the proposed
framework.
eng
American Physical Society
Physical Review Research;3, 043057
16/IA/4470
16/RC/3918
12/RC/2289P2
mechanism
Simon’s classical random-copying model
Memory-cognizant generalization to Simon’s random-copying neutral model
info:eu-repo/semantics/article
MToxMDB8MjpoZGxfMTAzNDRfNzN8Mzp8NDp8NTpyaWFuX2Rj