Showing papers by "Ramakrishna Ramaswamy published in 1996"
TL;DR: In this paper, the steady state of a driven diffusive lattice gas was characterized using a quantum Hamiltonian formalism, and it was shown that for arbitrary transition rates the model has product invariant measure.
Abstract: We characterize the steady state of a driven diffusive lattice gas in which each site holds several particles, and the dynamics is activated and asymmetric. Using a quantum Hamiltonian formalism, we show that for arbitrary transition rates the model has product invariant measure. In the steady state, a pairwise balance condition is shown to hold. Configurations n 00 and n 0 leading respectively into and out of a given configuration n are matched in pairs so that the flux of transitions from n 00 to n is equal to the flux from n to n 0 . Pairwise balance is more general than the condition of detailed balance and holds in the non-equilibrium steady state of a number of stochastic models.
77 citations
TL;DR: The largest Lyapunov exponent has universal behavior, showing abrupt variation as a function of the control parameter as the system passes through the crisis point, either in the value itself, in the case of an attractsor-widening crisis, or in the slope, for an attractor-merging crisis.
Abstract: We study the variation of Lyapunov exponents of simple dynamical systems near attractor-widening and attractor-merging crises. The largest Lyapunov exponent has universal behavior, showing abrupt variation as a function of the control parameter as the system passes through the crisis point, either in the value itself, in the case of an attractor-widening crisis, or in the slope, for an attractor-merging crisis. The distribution of local Lyapunov exponents is very different for the two cases: the fluctuations remain constant through a merging crisis, but there is a dramatic increase in the fluctuations at a widening crisis.
26 citations
TL;DR: In this article, the authors analyzed the quasibounded spectrum of the transition state in collinear (He, H2+) collisions using time-dependent wave packet calculations.
Abstract: The quasibound spectrum of the transition state in collinear (He, H2+) collisions is obtained from time‐dependent wave packet calculations. Examination of short‐ and long‐range correlations in the eigenvalue spectra through a study of the nearest neighbor spacing distribution, P(s), and the spectral rigidity, Δ3(L), reveals signatures of quantum chaotic behavior. Analysis in the time domain is carried out by computing the survival probability 〈〈P(t)〉〉 averaged over initial states and Hamiltonian. All these indicators show intermediate behavior between regular and chaotic. A quantitative comparison of 〈〈P(t)〉〉 with the results of random matrix theory provides an estimate of the fraction of phase space exhibiting chaotic behavior, in reasonable agreement with the classical dynamics. We also analyse the dynamical evolution of coherent Gaussian wave packets located initially in different regions of phase space and compute the survival probability, power spectrum and the volume of phase space over which the wa...
20 citations
TL;DR: The fractal dimension and interparticle correlations on the backbone indicate a continous phase transition at density with critical exponent, which is characterized through simulations.
Abstract: We study the jam phase of the deterministic traffic model in two dimensions. Within the jam phase, there is a phase transition, from a self-organized jam (formed by initial synchronization followed by jamming), to a random-jam structure. The backbone of the jam is defined and used to analyse self-organization in the jam. The fractal dimension and interparticle correlations on the backbone indicate a continous phase transition at density with critical exponent , which are characterized through simulations.
7 citations
TL;DR: A model of biological resource management is cast as a problem of adaptive control in a nonlinear dynamical system and optimisation of harvest is achieved through a simple algorithmic procedure which is remarkably robust under a variety of perturbations.
6 citations
TL;DR: In this paper, the authors study three models of driven sandpile-type automata in the presence of quenched random defects, termed the random sites (A), random bonds (B), and random slopes (C), which self-organize into a critical state.
Abstract: We study three models of driven sandpile-type automata in the presence of quenched random defects. When the dynamics is conservative, all these models, termed the random sites (A), random bonds (B), and random slopes (C), self-organize into a critical state. For model C the concentration-dependent exponents are nonuniversal. In the case of nonconservative defects, the asymptotic state is subcritical. Possible defect-mediated nonequilibrium phase transitions are also discussed.
5 citations
TL;DR: In this paper, the power spectrum of fluctuations in the potential energy of atoms in small rare-gas clusters is studied and the origins of long-lived memory effects have their origins in hierarchical relaxation processes arising in the motion of the atoms from the surface to the core and vice versa.
Abstract: We study the power spectrum of fluctuations in the potential energy of atoms in small rare-gas clusters. At temperatures when the cluster is in a liquid-like state the spectra have a “1/f” dependence over a wide range of frequency f. This behavior is distinctly different from both the solid phase of clusters or bulk liquid, and is indicative of long-range temporal correlations. The origins of this phenomenon is explored by studying the individual potential-energy distributions in pure and mixed rare-gas clusters, Xe55 and ArXe54, via molecular dynamics simulations. Substitution of atomic impurities acts as an effective probe of the dynamics, and we observe that long-lived memory effects have their origins in hierarchical relaxation processes arising in the motion of the atoms from the surface to the core and vice-versa.
2 citations
Journal Article•
TL;DR: Genes coding for proteins is a very important pattern recognition problem in bioinformatics and this lecture focuses on some computational issues in gene identification.
Abstract: The ultimate goal of molecular cell biology is to understand the physiology of living cells in terms of the information that is encoded in the genome of the cell – and we would like to address the question how computational biology can help in achieving this goal. Genes coding for proteins is a very important pattern recognition problem in bioinformatics and this lecture focuses on some computational issues in gene identification.
2 citations
TL;DR: A directed coupled map lattice model in d52 dimensions, with two degrees of freedom associated with each lattice site, that reaches a self-organized critical state at any concentration of defects and is driven out of the critical state in the case of nonconservative dynamics.
Abstract: We study a directed coupled map lattice model in d=2 dimensions, with two degrees of freedom associated with each lattice site. The two freedoms are coupled at a fraction c of lattice bonds acting as quenched random defects. The system is driven (by adding ``energy,'' say) in one of the degrees of freedom at the top of the lattice, and the relaxation rules depend on the local difference between the two variables at a lattice site. In the case of conservative dynamics, at any concentration of defects the system reaches a self-organized critical state with universal critical exponents close to the mean-field values ${\mathrm{\ensuremath{\tau}}}_{\mathit{t}}$=1, ${\mathrm{\ensuremath{\tau}}}_{\mathit{s}}$=2/3, and ${\mathrm{\ensuremath{\tau}}}_{\mathit{n}}$=1/2, for the integrated distributions of avalanche durations (t), size (s), and released energy (n), respectively. The probability distributions follow the general scaling form P(X,L)=${\mathit{L}}^{\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\alpha}}}$P(${\mathit{XL}}^{\mathrm{\ensuremath{-}}{\mathit{D}}_{\mathit{X}}}$), where \ensuremath{\alpha}\ensuremath{\approxeq}1 is the scaling exponent for the distribution of avalanche lengths, X stands for t, s, or n, and ${\mathit{D}}_{\mathit{X}}$ is the (independently determined) fractal dimension with respect to X. The distribution of current through the system is, however, nonuniversal, and does not show any apparent scaling form. In the case of nonconservative dynamics---obtained by incomplete energy transfer at the defect bonds---the system is driven out of the critical state. In the scaling region close to c=0 the probability distributions exhibit the general scaling form P(X,c,L)=${\mathit{X}}^{\mathrm{\ensuremath{-}}{\mathrm{\ensuremath{\tau}}}_{\mathit{X}}}$P[X/${\ensuremath{\xi}}_{\mathit{X}}$(c),${\mathit{XL}}^{\mathrm{\ensuremath{-}}{\mathit{D}}_{\phantom{\rule{0ex}{0ex}}}\mathrm{X}}$], where ${\mathrm{\ensuremath{\tau}}}_{\mathit{X}}$=\ensuremath{\alpha}/${\mathit{D}}_{\mathit{X}}$ and the corresponding coherence length ${\ensuremath{\xi}}_{\mathit{X}}$(c) depends on the concentration of defect bonds c as ${\ensuremath{\xi}}_{\mathit{X}}$(c)\ensuremath{\sim}${\mathit{c}}^{\mathrm{\ensuremath{-}}{\mathit{D}}_{\mathit{X}}}$. \textcopyright{} 1996 The American Physical Society.
2 citations
TL;DR: In this paper, the authors studied the dynamics of a hamiltonian system with two degrees of freedom coupled to a Nose-Hoover thermostat and showed that the system is quasi-integrable: at low energies, most of the motion is on two-dimensional tori, while at higher energies, the motion was mainly chaotic.
Abstract: We study the dynamics of a hamiltonian system with two degrees of freedom coupled to a Nose-Hoover thermostat. In the absence of the thermostat, the system is quasi-integrable: at low energies, most of the motion is on two-dimensional tori, while at higher energies, the motion is mainly chaotic. Upon coupling to the thermostat the system becomes more chaotic, as evidenced by the magnitude of the largest Lyapunov exponent. In contrast to the case of isotropic oscillator systems coupled to thermostats, there is no evidence for a regime of integrable behaviour, even for large values of Q.
2 citations
TL;DR: In this paper, the stability, energetics and dynamics of small model hydrogen fluoride clusters (HF) n were studied using isoergic molecular dynamics simulations. And the largest Lyapunov exponent was computed over the energy range when the clusters melted, and was found to be more useful in defining the onset of melting than Lindemann's index.
Abstract: We study the stability, energetics and dynamics of small model hydrogen fluoride clusters (HF) n using isoergic molecular dynamics simulations. The largest Lyapunov exponent is computed over the energy range when the clusters melt, and is found to be more useful in defining the onset of melting than Lindemann's index. We also examine the power spectrum of potential energy fluctuations of clusters in the liquid state, which show 1/f dependence over a smaller frequency range than rare-gas clusters of comparable size.