arXiv subjects

Syed Rashid Ahmad

Publications and source records attributed to Syed Rashid Ahmad.

6 recordsLinked to original sources

arXiv2025

Universal Aging Dynamics and Scaling Laws in Three-Dimensional Driven Granular Gases

We establish universal scaling laws and quantify aging in three-dimensional uniformly heated hard sphere granular gases through large-scale event-driven molecular dynamics ($N=500{,}000$). We report three primary quantitative discoveries: (i) The characteristic energy decay time exhibits a universal inverse scaling $τ_0 \propto ε^{-1.03 \pm 0.02}$ with the dissipation parameter $ε= 1 - e^2$. (ii) The steady-state temperature follows a precise power-law $T_{\mathrm{steady}} \propto ε^{-1.51 \pm 0.03}$, reflecting the non-linear balance between thermostat heating and collisional dissipation. (iii) The velocity autocorrelation function $\bar{A}(τ_w, τ)$ demonstrates pronounced aging, with decay rates $λ$ following a power-law slowing down $λ(τ_w) \propto τ_w^{-0.82 \pm 0.05}$. These results establish the first 3D quantitative benchmarks for aging in driven dissipative gases, where near-Gaussian statistics persist despite extreme structural clustering.

cond-mat.stat-mech↗

arXiv2025

Temporal Correlations and Inelastic Dynamics in a Vibrated Binary Granular Mixture

We investigate the dynamics of binary mixtures of inelastic particles through event-driven molecular dynamics simulations, focusing on velocity autocorrelation functions (VACFs). The study examines two distinct particle types under varying inelasticity conditions, systematically analyzing coefficients of restitution (CoR) ranging from 0.80 to 0.95. Like-particle interactions (AA and BB) maintain equal CoR values, while unlike-particle interactions (AB) are assigned the average CoR. The simulation framework incorporates a vibrating base system to maintain energy input and system stability. Our analysis reveals significant differences in VACF decay rates between Type 1 and Type 2 particles, demonstrating non-equipartition of energy within the binary mixture. The degree of this disparity is strongly influenced by the coefficient of restitution, with lower CoR values leading to more pronounced differences between particle types. These findings provide insights into the complex dynamics of granular gases and the role of inelasticity in energy distribution within binary mixtures. Our study contributes to the understanding of non-equilibrium statistical mechanics in granular systems and has potential implications for industrial processes involving particulate materials, such as fluidized beds and pneumatic conveying systems.

cond-mat.soft↗

arXiv2025

Velocity Distribution of a Uniformly Heated Hard Sphere Granular Gas

This paper presents a molecular dynamics simulation of an inelastic gas, where collisions between molecules are characterized by a coefficient of restitution less than unity. The simulation employs an event-driven algorithm to efficiently propagate the system in time, tracking molecular positions and velocities. A thermostat mechanism is incorporated to maintain the system's temperature by applying Gaussian white noise to the molecular velocities. The system's kinetic energy evolves towards a non-equilibrium steady state, with the initial dynamics governed by the interplay between energy input from the thermostat and energy dissipation through inelastic collisions. This steady state emerges when the energy gain from the thermostat balances the energy loss due to inelastic collisions. We calculate the coefficients of the Sonine polynomial expansion of the velocity distribution function to show that the velocity distribution exhibits a departure from the Maxwell-Boltzmann distribution in the steady state.

physics.comp-ph↗

arXiv2025

Aging Dynamics and Velocity Field Correlations in Three-Dimensional Uniformly Heated Granular Gases: A Molecular Dynamics Study

We conduct a molecular dynamics simulation of an inelastic gas system utilizing an event-driven algorithm combined with a thermostat mechanism. Initially, the kinetic energy of the system experiences a decay before settling into a non-equilibrium steady state. To explore the aging characteristics, we analyze the velocity autocorrelation function, denoted as $ C(t_w, t) $. Our findings indicate that $ C(t_w, t) $ exhibits a dependence on both waiting time $ t_w $ and correlation time $ t $ in an independent manner. At the outset, $ C(t_w, t) $ demonstrates an exponential decay pattern. With increasing $ t_w $, a slower decay is observed, which can be attributed to the development of correlations in the velocity field. The explicit relationship of $ C(t_w, t) $ with respect to $ t_w $ serves as compelling evidence of the aging properties present in the system. These results deepen our comprehension of non-equilibrium statistical mechanics and the dynamics of dissipative systems. Our research has significant implications for a range of applications involving inelastic collisions, extending from granular materials to phenomena observed in astrophysics. The simulation methodology and the insights gained contribute to the wider field of complex systems, shedding light on the behavior of systems that are far from equilibrium, particularly those characterized by energy dissipation due to inelastic interactions.

physics.comp-ph↗

arXiv2024

Probing 3D Velocity Distributions Insights from a Vibrated Dual-Species Granular System

We explore the velocity distributions in a vibrated binary granular gas system, focusing on how these distributions are influenced by the coefficient of restitution (CoR) and the inelasticity of particle collisions. Through molecular dynamics simulations, we examine the system's behavior for a range of CoR values below unity: specifically, 0.80, 0.85, 0.90, and 0.95. We track the evolution of velocity distributions as the system approaches a non-equilibrium steady state. Our findings reveal a clear departure from the classical Maxwell-Boltzmann distribution, with increasing deviations as CoR decreases, indicating non-equipartition of energy between the two particle types. This behavior underscores the intricate dynamics inherent in inelastic collisions and highlights the significance of particle inelasticity in determining the system's velocity distributions. These results provide insight into non-equilibrium statistical mechanics and have implications for real-world applications where granular materials are subject to external vibrations.

cond-mat.soft↗

arXiv2017

Critical behaviour in two-dimensional Coulomb Glass at zero temperature

The lattice model of Coulomb Glass in two dimensions with box-type random field distribution is studied at zero temperature for system size upto $96^{2}$. To obtain the minimum energy state we annealed the system using Monte Carlo simulation followed by further minimization using cluster-flipping. The values of the critical exponents are determined using the standard finite size scaling. We found that the correlation length $ξ$ diverges with an exponent $ν=1.0$ at the critical disorder $W_{c} = 0.2253$ and that $χ_{dis} \approx ξ^{4-\barη}$ with $\barη=2$ for the disconnected susceptibility. The staggered magnetization behaves discontinuously around the transition and the critical exponent of magnetization $β=0$. The probability distribution of the staggered magnetization shows a three peak structure which is a characteristic feature for the phase coexistence at first-order phase transition. In addition to this, at the critical disorder we have also studied the properties of the domain for different system sizes. In contradiction with the Imry-Ma arguments, we found pinned and non-compact domains where most of the random field energy was contained in the domain wall. Our results are also inconsistent with Binder's roughening picture.

cond-mat.dis-nn↗