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At least 127 records · Page 7Linked to original sources
arXiv2007

Wet Sand flows better than dry sand

We investigated the yield stress and the apparent viscosity of sand with and without small amounts of liquid. By pushing the sand through a tube with an enforced Poiseuille like profile we minimize the effect of avalanches and shear localization. We find that the system starts to flow when a critical shear of the order of one particle diameter is exceeded. In contrast to common believe, we observe that the resistance against the flow of wet sand is much smaller than that of dry sand. For the dissipative flow we propose a non-equilibrium state equation for granular fluids.

cond-mat.stat-mech↗
arXiv2009

Quantifying Disorder in Point Patterns

Disorder in point patterns can be quantified by means of the complexity, rather than in terms of geometric attributes of pattern structure. A complexity-based disorder-quantifying statistic indicates the practical difficulties associated with modeling processes that produce jammed patterns, particularly with the assessment of model fit and with the simulation of high-intensity hard-core patterns.

cond-mat.stat-mech↗
arXiv2007

On Order, Disorder and Coherence

We provide a brief survey of quantum statistical characterisations of order, disorder and coherence in systems of many degrees of freedom. Here, order and coherence are described in terms of symmetry breakdown, while disorder is described in terms of entropy and algorithmic complexity, whose interconnection has been recently extended from the classical to the quantum domain. We see that, in the present physical context, the concepts of order and disorder are not mutually antithetical, but bear an interrelationship similar to that between signals and noise.

math-ph↗
arXiv2009

Random Bistochastic Matrices

Ensembles of random stochastic and bistochastic matrices are investigated. While all columns of a random stochastic matrix can be chosen independently, the rows and columns of a bistochastic matrix have to be correlated. We evaluate the probability measure induced into the Birkhoff polytope of bistochastic matrices by applying the Sinkhorn algorithm to a given ensemble of random stochastic matrices. For matrices of order N=2 we derive explicit formulae for the probability distributions induced by random stochastic matrices with columns distributed according to the Dirichlet distribution. For arbitrary $N$ we construct an initial ensemble of stochastic matrices which allows one to generate random bistochastic matrices according to a distribution locally flat at the center of the Birkhoff polytope. The value of the probability density at this point enables us to obtain an estimation of the volume of the Birkhoff polytope, consistent with recent asymptotic results.

nlin.SI↗
arXiv2007

Quantum anharmonic oscillator and its statistical properties

In the present article a family of quantum anharmonic oscillators is studied using Hermite's function basis (Fock's basis) in the Hilbert space. The numerical investigation of the eigenenergies of that family is presented. The statistical properties of the calculated eigenvalues are compared with the theoretical predictions derived from the Random Matrix Theory. Conclusions are inferred.

cond-mat.stat-mech↗
arXiv2008

Seismic Electric Signals and 1/f "noise" in natural time

By making use of the concept of natural time, a simple model is proposed which exhibits the $1/f^a$ behavior with $a$ close to unity. The properties of the model are compared to those of the Seismic Electric Signals (SES) activities that have been found to obey the ubiquitous $1/f^a$ behavior with $a \approx 1$. This comparison, which is made by using the most recent SES data, reveals certain similarities, but the following important difference is found: The model suggests that the entropy $S_-$ under time reversal becomes larger compared to the entropy $S$ in forward time, thus disagreeing with the experimental SES results which show that $S$ may be either smaller or larger than $S_-$. This might be due to the fact that SES activities exhibit {\em critical} dynamics, while the model cannot capture all the characteristics of such dynamics.

cond-mat.stat-mech↗
arXiv2007

The role of the Fox-Wright functions in fractional sub-diffusion of distributed order

The fundamental solution of the fractional diffusion equation of distributed order in time (usually adopted for modelling sub-diffusion processes) is obtained based on its Mellin-Barnes integral representation. Such solution is proved to be related via a Laplace-type integral to the Fox-Wright functions. A series expansion is also provided in order to point out the distribution of time-scales related to the distribution of the fractional orders. The results of the time fractional diffusion equation of a single order are also recalled and then re-obtained from the general theory.

math-ph↗
arXiv2008

Potts models on hierarchical lattices and Renormalization Group dynamics II: examples and numerical results

We obtain the exact renormalization map and plots of Lee-Yang and Fisher zeros distributions for Potts models on a number of hierarchical lattices: the diamond hierarchical lattice, a lattice we call spider web, the Sierpinski gasket and cylinders. Such models are only examples among the ones we can study in the general framework of hierarchical lattices, developed in a previous paper.

cond-mat.stat-mech↗
arXiv2007

Theory of fluorescence correlation spectroscopy at variable observation area for two-dimensional diffusion on a meshgrid

It has recently been proposed, with the help of numerical investigations, that fluorescence correlation spectroscopy at variable observation area can reveal the existence of a meshgrid of semi-permeable barriers hindering the two-dimensional diffusion of tagged particles, such as plasmic membrane constituents. We present a complete theory confirming and accounting for these findings. It enables a reliable, quantitative exploitation of experimental data from which the sub-wavelength mesh size can be extracted. Time scales at which fluorescence correlation spectroscopy must be performed experimentally are discussed in detail.

cond-mat.stat-mech↗
arXiv2008

Complexity of hierarchical ensembles

Within the framework of generalized combinatorial approach, complexity is determined as a disorder measure for hierarchical statistical ensembles related to Cayley trees possessing arbitrary branching and number of levels. With strengthening hierarchical coupling, the complexity is shown to increase monotonically to the limit value that grows with tree branching. In contrast to the temperature dependence of thermodynamic entropy, the complexity is reduced by the variance of hierarchical statistical ensemble if the branching exponent does not exceed the gold mean. Time dependencies are found for both the probability distribution over ensemble states and the related complexity. The latter is found explicitly for self-similar ensemble and generalized for arbitrary hierarchical trees.

cond-mat.stat-mech↗
arXiv2008

Equilibria of culture contact derived from ingroup and outgroup attitudes

Modern societies feature an increasing contact between cultures, yet we have a poor understanding of what the outcomes might be. Here we consider a mathematical model of contact between social groups, grounded in social psychology and analyzed using tools from statistical physics. We use the model to study how a culture might be affected by immigration. We find that in some cases residents' culture is relatively unchanged, but in other cases residents may adopt the opinions and beliefs of immigrants. The decisive factors are each group's cultural legacy and its attitudes towards in- and out-groups. The model can also predict how social policies may influence the outcome of culture contact.

physics.soc-ph↗
arXiv2008

How to control nonlinear effects in Binder cumulants

We point out that ignoring nonlinear effects in finite size scaling may lead to errors in estimates of the critical temperature and Binder cumulants. We show that the order of magnitude of these effects can be estimated from data at relatively small volume. Using this estimate, we propose to use linear fits in increasingly small temperature regions as the volume is increased (rather than using a fixed temperature interval). The choice of the exact coefficient of proportionality can be optimized and reveals interesting crossing patterns among estimates. We show that the new procedure works very well for Dyson's hierarchical model. We discuss applications of the method for 3 dimensional spin models and finite temperature lattice gauge theories and comment on the nonlinear effects for existing calculations.

hep-lat↗
arXiv2007

On quantum cosmology as field theory of bosonic string mass groundstate

The Quantum Cosmology can be understand as the theory of an one object that is the Universe described in terms of fundamental mass groundstate of the free boson string, that is a tachyon - a hypothetical particle with negative mass square, which has linear velocity more than the velocity of light c. From this fact it is clear that whole information about physics of our Universe is focused on studying of this untypical particle physics. In this paper this point of view is touched up on. As the general-relativistic model of our Universe we study the Einstein-Friedmann Spacetime. Firstly, the way of canonical quantization beginning from first quantization of the Dirac Hamiltonian constraints up to the second quantization by the Von Neumann-Araki-Woods quantization in the Fock space is briefly discussed. We show that using of the Bogoliubov-Heinsenberg static operator basis leads to formulation of the second quantization of the considered free boson string in terms of the monodromy in the Fock space. Finally, we propose some specific model of the Universe - the extremal tachyon mass model, and in frames of its the Hubble evolution parameter, the equation of state for Dark Matter in the Universe, and the temperature of our Universe are concluded.

gr-qc↗
arXiv2007

Facilitated spin models: recent and new results

Facilitated or kinetically constrained spin models (KCSM) are a class of interacting particle systems reversible w.r.t. to a simple product measure. Each dynamical variable (spin) is re-sampled from its equilibrium distribution only if the surrounding configuration fulfills a simple local constraint which \emph{does not involve} the chosen variable itself. Such simple models are quite popular in the glass community since they display some of the peculiar features of glassy dynamics, in particular they can undergo a dynamical arrest reminiscent of the liquid/glass transitiom. Due to the fact that the jumps rates of the Markov process can be zero, the whole analysis of the long time behavior becomes quite delicate and, until recently, KCSM have escaped a rigorous analysis with the notable exception of the East model. In these notes we will mainly review several recent mathematical results which, besides being applicable to a wide class of KCSM, have contributed to settle some debated questions arising in numerical simulations made by physicists. We will also provide some interesting new extensions. In particular we will show how to deal with interacting models reversible w.r.t. to a high temperature Gibbs measure and we will provide a detailed analysis of the so called one spin facilitated model on a general connected graph.

math.PR↗
arXiv2011

From Boltzmann-Gibbs ensemble to generalized ensembles

We reconsider the Boltzmann-Gibbs statistical ensemble in thermodynamics using the multinomial coefficient approach. We show that an ensemble is defined by the determination of four statistical quantities, the element probabilities $p_i$, the configuration probabilities $P_j$, the entropy $S$ and the extremum constraints (EC). This distinction is of central importance for the understanding of the conditions under which a microcanonical, canonical and macrocanonical ensemble is defined. These three ensembles are characterized by the conservation of their sizes. A variation of the ensemble size creates difficulties in the definitions of the quadruplet $\{p_i, P_j, S, \mt{EC}\}$, giving rise for a generalization of the Boltzmann-Gibbs formalism, such one as introduced by Tsallis. We demonstrate that generalized thermodynamics represent a transformation of ordinary thermodynamics in such a way that the energy of the system remains conserved. From our results it becomes evident that Tsallis's formalism is a very specific generalization, however, not the only one. We also revisit the Jaynes's Maximum Entropy Principle, showing that in general it can lead to incorrect results and consider the appropriate corrections.

cond-mat.stat-mech↗
arXiv2007

High-order perturbative expansions of multi-parameter Phi^4 quantum field theories

We present high-order pertubative expansions of multi-parameter Phi^4 quantum field theories with an N-component fundamental field, containing up to 4th-order polynomials of the field. Multi-parameter Phi^4 theories generalize the simplest O(N)-symmetric Phi^4 theories, and describe more complicated symmetry breaking patterns. These notes collect several high-order perturbative series of physically interesting multi-parameter Phi^4 theories, to five or six loops. We consider the O(M)XO(N)-symmetric Phi^4 model, the so-called MN model, and a spin-density-wave Phi^4 model containing five quartic terms.

hep-th↗
arXiv2008

The model of interacting spatial permutations and its relation to the Bose gas

The model of spatial permutations is related to the Feynman-Kac representation of the Bose gas. The transition to infinite cycles corresponds to Bose-Einstein condensation. We review the general setting and some results, and we derive a multi-body interaction between permutation jumps, that is due to the original interactions between quantum particles.

cond-mat.stat-mech↗