arXiv subjects

Soumyajyoti Biswas

Publications and source records attributed to Soumyajyoti Biswas.

71 records · Page 4Linked to original sources

arXiv2017

Critical noise can make the minority candidate win: The US Presidential Election cases

A national voting population, when segmented into groups like, for example, different states, can yield a counter-intuitive scenario where the winner may not necessarily get the most number of total votes. A recent example is the 2016 presidential election in the US. We model the situation by using interacting opinion dynamics models and look at the effect of coarse graining near the critical points where the spatial fluctuations are high. We establish that the sole effect of coarse graining, which mimics the `winner takes all' electoral college system in the US, can give rise to finite probabilities of such events of minority candidate winning even in the large size limit near the critical point. The overall probabilities of victory of the minority candidate can be predicted from the models which indicates that one may expect more instances of minority candidate winning in the future.

physics.soc-ph↗

arXiv2016

Interface propagation in fiber bundles: Local, mean-field and intermediate range-dependent statistics

The fiber bundle model is essentially an array of elements that break when sufficient load is applied on them. With a local loading mechanism, this can serve as a model for a one-dimensional interface separating the broken and unbroken parts of a solid in mode-I fracture. The interface can propagate through the system depending on the loading rate and disorder present in the failure thresholds of the fibers. In the presence of a quasi-static drive, the intermittent dynamics of the interface mimic front propagation in disordered media. Such situations appear in diverse physical systems such as mode-I crack propagation, domain wall dynamics in magnets, charge density waves, contact line in wetting etc. We study the effect of the range of interaction, i.e. the neighborhood of the interface affected following a local perturbation, on the statistics of the intermittent dynamics of the front. There exists a crossover from local to global behavior as the range of interaction grows and a continuously varying `universality' in the intermediate range. This means that the interaction range is a relevant parameter of any resulting physics. This is particularly relevant in view of the fact that there is a scatter in the experimental observations of the exponents, in even idealized experiments on fracture fronts, and also a possibility in changing the interaction range in real samples.

cond-mat.stat-mech↗

arXiv2016

Failure time in heterogeneous systems

We show that the failure time $τ_f$ in fiber bundle model, taken as a prototype of heterogeneous materials, depends crucially on the strength of the disorder $δ$ and the stress release range $R$ in the system. For $R$ beyond a critical value $R_c$ the distribution of $τ_f$ follows Weibull form. In this region, the average $τ_f$ shows the variation $τ_f \sim L^α$ where $L$ is the system size. For $R<R_c$, $τ_f\sim L/R$. We find that the crossover length scale has the scaling form $R_c \sim L^{1-α}$. This scaling has been found to be valid for various disorder distributions. For $δ<δ_c$, $α$ is an increasing function of $δ$. For all $δ\ge δ_c$, $α$=1/3.

cond-mat.dis-nn↗

arXiv2015

Maximizing the strength of fiber bundles under uniform loading

The collective strength of a system of fibers, each having a failure threshold drawn randomly from a distribution, indicates the maximum load carrying capacity of different disordered systems ranging from disordered solids, power-grid networks, to traffic in a parallel system of roads. In many of the cases where the redistribution of load following a local failure can be controlled, it is a natural requirement to find the most efficient redistribution scheme, i.e., following which system can carry the maximum load. We address the question here and find that the answer depends on the mode of loading. We analytically find the maximum strength and corresponding redistribution schemes for sudden and quasi static loading. The associated phase transition from partial to total failure by increasing the load has been studied. The universality class is found to be dependent on the redistribution mechanism.

cond-mat.stat-mech↗

arXiv2015

Nucleation versus percolation: Scaling criterion for failure in disordered solids

One of the major factors governing the mode of failure in disordered solids is the effective range $R$, over which the stress field is modified following a local rupture event. In random fiber bundle model, considered as a prototype of disordered solids, we show that the failure mode is nucleation dominated in the large system size limit, as long as $R$ scales slower than $L^ζ$, with $ζ=2/3$. For a faster increase in $R$, the failure properties are dominated by the mean-field critical point, where the damages are uncorrelated in space. In that limit, the precursory avalanches of all sizes are obtained even in the large system size limit. We expect these results to be valid for systems with finite (normalizable) disorder.

cond-mat.stat-mech↗

arXiv2013

Self-organized dynamics in local load sharing fiber bundle models

We study the dynamics of a local load sharing fiber bundle model in two dimensions, under an external load (which increases with time at a fixed slow rate) applied at a single point. Due to the local load sharing nature, the redistributed load remains localized along the boundary of the broken patch. The system then goes to a self-organized state with a stationary average value of load per fiber along the (increasing) boundary of the broken patch (damaged region) and a scale free distribution of avalanche sizes and other related quantities are observed. In particular, when the load redistribution is only among nearest surviving fiber(s), the numerical estimates of the exponent values are comparable with those of the Manna model. When the load redistribution is uniform along the patch boundary, the model shows a simple mean-field limit of this self-organizing critical behaviour, for which we give analytical estimates of the saturation load per fiber values and avalanche size distribution exponent. These are in good agreement with numerical simulation results.

cond-mat.stat-mech↗

arXiv2013

Kinetic exchange opinion model: solution in the single parameter map limit

We study a recently proposed kinetic exchange opinion model (Lallouache et. al., Phys. Rev E 82:056112, 2010) in the limit of a single parameter map. Although it does not include the essentially complex behavior of the multiagent version, it provides us with the insight regarding the choice of order parameter for the system as well as some of its other dynamical properties. We also study the generalized two- parameter version of the model, and provide the exact phase diagram. The universal behavior along this phase boundary in terms of the suitably defined order parameter is seen.

physics.soc-ph↗

arXiv2013

Equivalence of the train model of earthquake and boundary driven Edwards-Wilkinson interface

A discretized version of the Burridge-Knopoff train model with (non-linear friction force replaced by) random pinning is studied in one and two dimensions. A scale free distribution of avalanches and the Omori law type behaviour for after-shocks are obtained. The avalanche dynamics of this model becomes precisely similar (identical exponent values) to the Edwards-Wilkinson (EW) model of interface propagation. It also allows the complimentary observation of depinning velocity growth (with exponent value identical with that for EW model) in this train model and Omori law behaviour of after-shock (depinning) avalanches in the EW model.

cond-mat.stat-mech↗

arXiv2013

Crossover behaviors in one and two dimensional heterogeneous load sharing fiber bundle models

We study the effect of heterogeneous load sharing in the fiber bundle models of fracture. The system is divided into two groups of fibers (fraction $p$ and $1-p$) in which one group follow the completely local load sharing mechanism and the other group follow global load sharing mechanism. Patches of local disorders (weakness) in the loading plate can cause such a situation in the system. We find that in 2d a finite crossover (between global and local load sharing behaviours) point comes up at a finite value of the disorder concentration (near $p_c\sim 0.53$), which is slightly below the site percolation threshold. We numerically determine the phase diagrams (in 1d and 2d) and identify the critical behavior below $p_c$ with the mean field behavior (completely global load sharing) for both dimensions. This crossover can occur due to geometrical percolation of disorders in the loading plate. We also show how the critical point depends on the loading history, which is identified as a special property of local load sharing.

cond-mat.stat-mech↗

arXiv2012

Statistical Physics of Fracture, Friction and Earthquake

We review the present status of our research and understanding regarding the dynamics and the statistical properties of earthquakes, mainly from a statistical physical viewpoint. Emphasis is put both on the physics of friction and fracture, which provides a "microscopic" basis of our understanding of an earthquake instability, and on the statistical physical modelling of earthquakes, which provides "macroscopic" aspects of such phenomena. Recent numerical results on several representative models are reviewed, with attention to both their "critical" and "characteristic" properties. We highlight some of relevant notions and related issues, including the origin of power-laws often observed in statistical properties of earthquakes, apparently contrasting features of characteristic earthquakes or asperities, the nature of precursory phenomena and nucleation processes, the origin of slow earthquakes, etc.

cond-mat.stat-mech↗

arXiv2012

Continuous transition of social efficiencies in the stochastic strategy Minority Game

We show that in a variant of the Minority Game problem, the agents can reach a state of maximum social efficiency, where the fluctuation between the two choices is minimum, by following a simple stochastic strategy. By imagining a social scenario where the agents can only guess about the number of excess people in the majority, we show that as long as the guess value is sufficiently close to the reality, the system can reach a state of full efficiency or minimum fluctuation. A continuous transition to less efficient condition is observed when the guess value becomes worse. Hence, people can optimize their guess value for excess population to optimize the period of being in the majority state. We also consider the situation where a finite fraction of agents always decide completely randomly (random trader) as opposed to the rest of the population that follow a certain strategy (chartist). For a single random trader the system becomes fully efficient with majority-minority crossover occurring every two-days interval on average. For just two random traders, all the agents have equal gain with arbitrarily small fluctuations.

physics.soc-ph↗

arXiv2012

Disorder induced phase transition in kinetic models of opinion dynamics

We propose a model of continuous opinion dynamics, where mutual interactions can be both positive and negative. Different types of distributions for the interactions, all characterized by a single parameter $p$ denoting the fraction of negative interactions, are considered. Results from exact calculation of a discrete version and numerical simulations of the continuous version of the model indicate the existence of a universal continuous phase transition at p=p_c below which a consensus is reached. Although the order-disorder transition is analogous to a ferromagnetic-paramagnetic phase transition with comparable critical exponents, the model is characterized by some distinctive features relevant to a social system.

physics.soc-ph↗

arXiv2011

Mean field solutions of kinetic exchange opinion models

We present here the exact solution of an infinite range, discrete, opinion formation model. The model shows an active-absorbing phase transition, similar to that numerically found in its recently proposed continuous version (Lallouache et al., Phys. Rev E 82, 056112 (2010)). Apart from the two-agent interactions here we also report the effect of having three agent interactions. The phase diagram has a continuous transition line (two agent interaction dominated) and a discontinuous transition line (three agent interaction dominated) separated by a tricritical point.

physics.soc-ph↗

arXiv2011

Depinning transitions in elastic strings

We study the depinning transitions of elastic strings in disordered media in two different cases. We consider the elastic forces to be of infinite range in one case, where the magnitude is proportional to the extension of the string. The critical points and elastic behavior can be estimated to some extent in this case. The exponents are estimated numerically and scaling relations are found to be obeyed. We have also considered a model where the elastic force is constant in magnitude. The critical points can again be argued and the critical exponents are numerically estimated. The scaling relations are well obeyed. Both of these models do not fall into known universality classes.

cond-mat.stat-mech↗

arXiv2011

Phase transitions and non-equilibrium relaxation in kinetic models of opinion formation

We review in details some recently proposed kinetic models of opinion dynamics. We discuss the several variants including a generalised model. We provide mean field estimates for the critical points, which are numerically supported with reasonable accuracy. Using non-equilibrium relaxation techniques, we also investigate the nature of phase transitions observed in these models. We study the nature of correlations as the critical points are approached, and comment on the universality of the phase transitions observed.

physics.soc-ph↗

arXiv2011

Dynamical percolation transition in the Ising model studied using a pulsed magnetic field

We study the dynamical percolation transition of the geometrical clusters in the two-dimensional Ising model when it is subjected to a pulsed field below the critical temperature. The critical exponents are independent of the temperature and pulse width and are different from the (static) percolation transition associated with the thermal transition. For a different model that belongs to the Ising universality class, the exponents are found to be same, confirming that the behavior is a common feature of the Ising class. These observations, along with a universal critical Binder cumulant value, characterize the dynamical percolation of the Ising universality class.

cond-mat.stat-mech↗

arXiv2010

Effect of fractal disorder on static friction in the Tomlinson model

We propose a modified version of the Tomlinson model for static friction between two chains of beads. We introduce disorder in terms of vacancies in the chain, and distribute the remaining beads in a scale invariant way. For this we utilize a generalized random Cantor set. We relate the static friction force, to the overlap distribution of the chains, and discuss how the distribution of the static friction force depends on the distribution of the remaining beads. For the random Cantor set we find a scaled distribution which is independent on the generation of the set.

cond-mat.stat-mech↗