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Bikas K. Chakrabarti

Publications and source records attributed to Bikas K. Chakrabarti.

At least 55 records · Page 3Linked to original sources
arXiv2019

Inequality in Death from Social Conflicts: A Gini & Kolkata indices-based Study

Human deaths caused by individual man-made conflicts (e.g., wars, armed-conflicts, terrorist-attacks etc.) occur unequally across the events (conflicts) and such inequality (in deaths) have been studied here using Lorenz curve and values of the inequality indices Gini ($g$) and Kolkata ($k$) have been estimated from it. The data are taken from various well-known databases maintained by some Universities and Peace Research Institutes. The inequality measures for man-made conflicts are found to have very high values ($g$ = $0.82 ~\pm~ $0.02, $k$ = $0.84~ \pm~ $0.02), which is rarely seen in economic (income or wealth) inequality measures across the world ($g \leq 0.4$, $k \leq 0.6$; presumably because of various welfare measures). We also investigated the inequalities in human deaths from natural disasters (like earthquakes, floods, etc.). Interestingly, we observe that the social inequality measures ($g$ and $k$ values) from man-made conflicts compare well with those of academic centers (inequality in citations; found in earlier studies) of different institutions of the world, while those for natural disasters can be even higher. We discuss about the `similarity classes' of social inequality (similar higher values of $g$ and $k$ indices) for man-made competitive societies like academic institutions and man-made social conflicts, and connect our observations with that of the growing recent trend of economic inequality across the world (with rapid disappearance of welfare strategies).

physics.soc-ph↗
arXiv2018

Econophysics as conceived by Meghnad Saha

We trace the initiative by Professor Meghnad Saha to develop a (statistical) physics model of market economy and his search for the mechanism to constrain the entropy maximized width of the income distribution in a society such that the spread of inequality can be minimized.

q-fin.GN↗
arXiv2018

International Centre for Social Complexity, Econophysics & Sociophysics Studies: A Proposal

In the concluding session of the Joint International Conference titled Econophys-2017 and Asia Pacific Econophysics Conference (APEC)-2017, held in Jawaharlal Nehru University and Delhi University during November 15-18, 2017, a brief version of this Proposal was presented. Several important and enthusiastic comments were received from the participants. This note is based on these comments and discussions.

physics.soc-ph↗
arXiv2017

Story of the Developments in Statistical Physics of Fracture, Breakdown \& Earthquake: A Personal Account

We review the developments of the statistical physics of fracture and earthquake over the last four decades. We argue that major progress has been made in this field and that the key concepts should now become integral part of the (under-) graduate level text books in condensed matter physics. For arguing in favor of this, we compare the development (citations) with the same for some other related topics in condensed matter, for which Nobel prizes have already been awarded.

physics.hist-ph↗
arXiv2016

Can Economics Afford Not To Become Natural Science?

The 'Discussion & Debate' issue of this Euro. Phys. J. Special Topic volume is: 'Can economics be a Physical Science?' I would rather address a more general question: 'Can economics or sociology avoid joining Natural Science?' and argue that mainstream or core economics or sociology can not escape joining natural science.

physics.hist-ph↗
arXiv2016

Inequality measures in kinetic exchange models of wealth distributions

In this paper, we study the inequality indices for some models of wealth exchange. We calculated Gini index and newly introduced k-index and compare the results with reported empirical data available for different countries. We have found lower and upper bounds for the indices and discuss the efficiencies of the models. Some exact analytical calculations are given for a few cases. We also exactly compute the quantities for Gamma and double Gamma distributions.

physics.soc-ph↗
arXiv2015

Social inequality: from data to statistical physics modeling

Social inequality is a topic of interest since ages, and has attracted researchers across disciplines to ponder over it origin, manifestation, characteristics, consequences, and finally, the question of how to cope with it. It is manifested across different strata of human existence, and is quantified in several ways. In this review we discuss the origins of social inequality, the historical and commonly used non-entropic measures such as Lorenz curve, Gini index and the recently introduced $k$ index. We also discuss some analytical tools that aid in understanding and characterizing them. Finally, we argue how statistical physics modeling helps in reproducing the results and interpreting them.

physics.soc-ph↗
arXiv2015

Quantum phase transitions in transverse field spin models: from statistical physics to quantum information

We review quantum phase transitions of spin systems in transverse magnetic fields taking the examples of the spin-1/2 Ising and XY models in a transverse field. Beginning with an overview of quantum phase transitions, we introduce a number of model Hamiltonians. We provide exact solutions in one spatial dimension connecting them to conformal field theoretical studies. We also discuss Kitaev models and some other exactly solvable spin systems. Studies of quantum phase transitions in the presence of quenched randomness and with frustrating interactions are presented in detail. We discuss novel phenomena like Griffiths-McCoy singularities. We then turn to more recent topics like information theoretic measures of the quantum phase transitions in these models such as concurrence, entanglement entropy, quantum discord and quantum fidelity. We then focus on non-equilibrium dynamics of a variety of transverse field systems across quantum critical points and lines. After mentioning rapid quenching studies, we dwell on slow dynamics and discuss the Kibble-Zurek scaling for the defect density following a quench across critical points and its modifications for quenching across critical lines, gapless regions and multicritical points. Topics like the role of different quenching schemes, local quenching, quenching of models with random interactions and quenching of a spin chain coupled to a heat bath are touched upon. The connection between non-equilibrium dynamics and quantum information theoretic measures is presented at some length. We indicate the connection between Kibble-Zurek scaling and adiabatic evolution of a state as well as the application of adiabatic dynamics as a tool of a quantum optimization technique known as quantum annealing. The final section is dedicated to a detailed discussion on recent experimental studies of transverse Ising-like systems.

cond-mat.stat-mech↗
arXiv2014

Statistical Mechanics of Competitive Resource Allocation using Agent-based Models

Demand outstrips available resources in most situations, which gives rise to competition, interaction and learning. In this article, we review a broad spectrum of multi-agent models of competition (El Farol Bar problem, Minority Game, Kolkata Paise Restaurant problem, Stable marriage problem, Parking space problem and others) and the methods used to understand them analytically. We emphasize the power of concepts and tools from statistical mechanics to understand and explain fully collective phenomena such as phase transitions and long memory, and the mapping between agent heterogeneity and physical disorder. As these methods can be applied to any large-scale model of competitive resource allocation made up of heterogeneous adaptive agent with non-linear interaction, they provide a prospective unifying paradigm for many scientific disciplines.

physics.soc-ph↗
arXiv2014

Multivariable Optimization: Quantum Annealing & Computation

Recent developments in quantum annealing techniques have been indicating potential advantage of quantum annealing for solving NP-hard optimization problems. In this article we briefly indicate and discuss the beneficial features of quantum annealing techniques and compare them with those of simulated annealing techniques. We then briefly discuss the quantum annealing studies of some model spin glass and kinetically constrained systems.

cond-mat.stat-mech↗
arXiv2014

Measuring social inequality with quantitative methodology: analytical estimates and empirical data analysis by Gini and $k$ indices

Social inequality manifested across different strata of human existence can be quantified in several ways. Here we compute non-entropic measures of inequality such as Lorenz curve, Gini index and the recently introduced $k$ index analytically from known distribution functions. We characterize the distribution functions of different quantities such as votes, journal citations, city size, etc. with suitable fits, compute their inequality measures and compare with the analytical results. A single analytic function is often not sufficient to fit the entire range of the probability distribution of the empirical data, and fit better to two distinct functions with a single crossover point. Here we provide general formulas to calculate these inequality measures for the above cases. We attempt to specify the crossover point by minimizing the gap between empirical and analytical evaluations of measures. Regarding the $k$ index as an `extra dimension', both the lower and upper bounds of the Gini index are obtained as a function of the $k$ index. This type of inequality relations among inequality indices might help us to check the validity of empirical and analytical evaluations of those indices.

physics.soc-ph↗
arXiv2014

Inequality in Societies, Academic Institutions and Science Journals: Gini and k-indices

Social inequality is traditionally measured by the Gini-index ($g$). The $g$-index takes values from $0$ to $1$ where $g=0$ represents complete equality and $g=1$ represents complete inequality. Most of the estimates of the income or wealth data indicate the $g$ value to be widely dispersed across the countries of the world: \textit{g} values typically range from $0.30$ to $0.65$ at a particular time (year). We estimated similarly the Gini-index for the citations earned by the yearly publications of various academic institutions and the science journals. The ISI web of science data suggests remarkably strong inequality and universality ($g=0.70\pm0.07$) across all the universities and institutions of the world, while for the journals we find $g=0.65\pm0.15$ for any typical year. We define a new inequality measure, namely the $k$-index, saying that the cumulative income or citations of ($1-k$) fraction of people or papers exceed those earned by the fraction ($k$) of the people or publications respectively. We find, while the $k$-index value for income ranges from $0.60$ to $0.75$ for income distributions across the world, it has a value around $0.75\pm0.05$ for different universities and institutions across the world and around $0.77\pm0.10$ for the science journals. Apart from above indices, we also analyze the same institution and journal citation data by measuring Pietra index and median index.

physics.soc-ph↗
arXiv2013

Response of Two-dimensional Kinetic Ising Model under Stochastic Field

We study, using Monte Carlo dynamics, the time ($t$) dependent average magnetization per spin $m(t)$ behavior of 2-D kinetic Ising model under a binary ($\pm h_0$) stochastic field $h(t)$. The time dependence of the stochastic field is such that its average over each successive time interval $τ$ is assured to be zero (without any fluctuation). The average magnetization $Q=(1/τ)\int_{0}^τ m(t) dt$ is considered as order parameter of the system. The phase diagram in ($h_0,τ$) plane is obtained. Fluctuations in order parameter and their scaling properties are studied across the phase boundary. These studies indicate that the nature of the transition is Ising like (static Ising universality class) for field amplitudes $h_0$ below some threshold value $h_0^c(τ)$ (dependent on $τ$ values; $h_0^c\rightarrow0$ as $τ\rightarrow\infty$ across the phase boundary) . Beyond these $h_0^c (τ)$, the transition is no longer continuous.

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

Noise induced rupture process: Phase boundary and scaling of waiting time distribution

A bundle of fibers has been considered here as a model for composite materials, where breaking of the fibers occur due to a combined influence of applied load (stress) and external noise. Through numerical simulation and a mean-field calculation we show that there exists a robust phase boundary between continuous (no waiting time) and intermittent fracturing regimes. In the intermittent regime, throughout the entire rupture process avalanches of different sizes are produced and there is a waiting time between two consecutive avalanches. The statistics of waiting times follows a Gamma distribution and the avalanche distribution shows power law scaling, similar to what have been observed in case of earthquake events and bursts in fracture experiments. We propose a prediction scheme that can tell when the system is expected to reach the continuous fracturing point from the intermittent phase.

cond-mat.stat-mech↗