Searcharxiv⌕ Search

SEARCH · Searcharxiv

Results for “cond-mat.stat-mech”

Search indexed arXiv papers on artificial intelligence, large language models, computer vision and robotics. Read source abstracts and follow links to arXiv.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
arXiv2007

Spin Effects in Quantum Chromodynamics and Recurrence Lattices with Multi-Site Exchanges

In this thesis, we consider some spin effects in QCD and recurrence lattices with multi-site exchanges. Main topic of our manuscript are critical phenomena in spin systems defined on the recurrence lattices. Main tool of our approach is the method of recursive (hierarchical) lattices. We apply the method of dynamical mapping (or recursive lattices) for investigation of magnetic properties of the fluid and solid $^3$He, phase transitions in crystals and macromolecules. First, we analyze the helix-coil phase transition for polypeptides and proteins, and describe an quasi unfolding transition (like the cold denaturation process) for the degree of helicity (the order parameter for macromolecules). Next we consider the recurrent models of $^3$He defined on the square, Husimi and hexagon lattices. Using the method of dynamical mapping, the magnetization curves with plateaus, bifurcation point and one period doubling are obtained. Then we investigate the model with cubic symmetry defined on the Bethe lattice and containing both linear and quadratic spin-spin interactions. The magnetization of the system is calculated, and a complex structure of the phase transitions between the disordered, partially ordered and completely ordered states is observed. In the framework of QCD, we consider the azimuthal asymmetries in heavy flavor production in the lepton-nucleon deep inelastic scattering (DIS). We calculate the azimuthal (or $ϕ$-) dependence of the next-to-leading order heavy-quark-initiated contributions to DIS. It is shown that, contrary to the basic gluon-initiated component, the photon-quark scattering mechanism is practically $\cos2ϕ$-independent. We investigate the possibility of measuring both nonperturbative (intrinsic) and perturbative (CTEQ, MRST) charm distributions using the $\cos2ϕ$ asymmetry.

cond-mat.stat-mech↗
arXiv2007

On the long range correlations of thermodynamic systems out of equilibrium

Experiments show that macroscopic systems in a stationary nonequilibrium state exhibit long range correlations of the local thermodynamic variables. In previous papers we proposed a Hamilton-Jacobi equation for the nonequilibrium free energy as a basic principle of nonequilibrium thermodynamics. We show here how an equation for the two point correlations can be derived from the Hamilton-Jacobi equation for arbitrary transport coefficients for dynamics with both external fields and boundary reservoirs. In contrast with fluctuating hydrodynamics, this approach can be used to derive equations for correlations of any order. Generically, the solutions of the equation for the correlation functions are non-trivial and show that long range correlations are indeed a common feature of nonequilibrium systems. Finally, we establish a criterion to determine whether the local thermodynamic variables are positively or negatively correlated in terms of properties of the transport coefficients.

cond-mat.stat-mech↗
arXiv2007

Plastic Response of a 2D Amorphous Solid to Quasi-Static Shear : II - Dynamical Noise and Avalanches in a Mean Field Model

We build a minimal, mean-field, model of plasticity of amorphous solids, based upon a phenomenology of dissipative events derived, in a preceding paper [A. Lemaitre, C. Caroli, arXiv:0705.0823] from extensive molecular simulations. It reduces to the dynamics of an ensemble of identical shear transformation zones interacting via the dynamic noise due to the long ranged elastic fields induced by zone flips themselves. We find that these ingredients are sufficient to generate flip avalanches with a power-law scaling with system size, analogous to that observed in molecular simulations. We further show that the scaling properties of avalanches sensitively depend on the detailed shape of the noise spectrum. This points out the importance of developing a realistic coarse-grained description of elasticity in these systems.

cond-mat.dis-nn↗
arXiv2008

Non-local detection of resistance fluctuations of an open quantum dot

We investigate quantum fluctuations in the non-local resistance of an open quantum dot which is connected to four reservoirs via quantum point contacts. In this four-terminal quantum dot the voltage path can be separated from the current path. We measured non-local resistance fluctuations of several hundreds of Ohms, which have been characterized as a function of bias voltage, gate voltage and perpendicular magnetic field. The amplitude of the resistance fluctuations is strongly reduced when the coupling between the voltage probes and the dot is enhanced. Along with experimental results, we present a theoretical analysis based on the Landauer-Büttiker formalism. While the theory predicts non-local resistance fluctuations of considerably larger amplitude than what has been observed, agreement with theory is very good if an additional dephasing mechanism is assumed.

cond-mat.mes-hall↗
arXiv2007

Inflection point as a manifestation of tricritical point on the dynamic phase boundary in Ising meanfield dynamics

We studied the dynamical phase transition in kinetic Ising ferromagnet driven by oscillating magnetic field in meanfield approximation. The meanfield differential equation was solved by sixth order Runge-Kutta-Felberg method. We calculated the transition temperature as a function of amplitude and frequency of the oscillating field. This was plotted against field amplitude taking frequency as a parameter. As frequency increases the phase boundary is observed to become inflated. The phase boundary shows an inflection point which separates the nature of the transition. On the dynamic phase boundary a tricritical point (TCP) was found, which separates the nature (continuous/discontinuous) of the dynamic transition across the phase boundary. The inflection point is identified as the TCP and hence a simpler method of determining the position of TCP was found. TCP was observed to shift towards high field for higher frequency. As frequency decreases the dynamic phase boundary is observe to shrink. In the zero frequency limit this boundary shows a tendency to merge to the temperature variation of the coercive field.

cond-mat.stat-mech↗
arXiv2007

Isoconfigurational thermostat

A holonomic constraint is used to enforce a constant instantaneous configurational temperature on an equilibrium system. Three sets of equations of motion are obtained, differing according to the way in which the holonomic constraint is introduced and the phase space distribution function that is preserved by the dynamics. Firstly, Gauss' principle of least constraint is used, and it is shown that it does not preserve the canonical distribution. Secondly, a modified Hamiltonian is used to find a dynamics that provides a restricted microcanonical distribution. Lastly, we provide equations that are specifically designed to both satisfy the temperature constraint and produce a restricted canonical ensemble.

cond-mat.stat-mech↗
arXiv2007

Cellular automata for traffic flow simulation with safety embedded notions

In this paper a cellular automata model for one-lane traffic flow is presented. A new set of rules is proposed to better capture driver reactions to traffic that are intended to preserve safety on the highway. As a result, drivers behavior is derived from an analysis that determines the most appropriate action for a vehicle based on the distance from the vehicle ahead of it and the velocities of the two neighbor vehicles. The model preserves simplicity of CA rules and at the same time makes the results closer to real highway behavior. Simulation results exhibit the three states observed in real traffic flow: Free-flow states, synchronized states, and stop-and-go states.

cond-mat.stat-mech↗
arXiv2007

Information functionals and the notion of (un)certainty: RMT - inspired case

Information functionals allow to quantify the degree of randomness of a given probability distribution, either absolutely (through min/max entropy principles) or relative to a prescribed reference one. Our primary aim is to analyze the "minimum information" assumption, which is a classic concept (R. Balian, 1968) in the random matrix theory. We put special emphasis on generic level (eigenvalue) spacing distributions and the degree of their randomness, or alternatively - information/organization deficit.

quant-ph↗
arXiv2007

Group Testing with Random Pools: optimal two-stage algorithms

We study Probabilistic Group Testing of a set of N items each of which is defective with probability p. We focus on the double limit of small defect probability, p<<1, and large number of variables, N>>1, taking either p->0 after $N\to\infty$ or $p=1/N^β$ with $β\in(0,1/2)$. In both settings the optimal number of tests which are required to identify with certainty the defectives via a two-stage procedure, $\bar T(N,p)$, is known to scale as $Np|\log p|$. Here we determine the sharp asymptotic value of $\bar T(N,p)/(Np|\log p|)$ and construct a class of two-stage algorithms over which this optimal value is attained. This is done by choosing a proper bipartite regular graph (of tests and variable nodes) for the first stage of the detection. Furthermore we prove that this optimal value is also attained on average over a random bipartite graph where all variables have the same degree, while the tests have Poisson-distributed degrees. Finally, we improve the existing upper and lower bound for the optimal number of tests in the case $p=1/N^β$ with $β\in[1/2,1)$.

cs.DS↗
arXiv2008

Random Boolean Networks

This review explains in a self-contained way the properties of random Boolean networks and their attractors, with a special focus on critical networks. Using small example networks, analytical calculations, phenomenological arguments, and problems to solve, the basic concepts are introduced and important results concerning phase diagrams, numbers of relevant nodes and attractor properties are derived.

cond-mat.stat-mech↗
arXiv2007

Two-dimensional phase transition models and λϕ^4 field theory

The overview is given of the results obtained recently in the course of renormalization-group (RG) study of two-dimensional (2D) models. RG functions of the two-dimensional n-vector λϕ^4 Euclidean field theory are written down up to the five-loop terms and perturbative series are resummed by the Pade-Borel-Leroy techniques. An account for the five-loop term is shown to shift the Wilson fixed point only briefly, leaving it outside the segment formed by the results of the lattice calculations. This is argued to reflect the influence of the non-analytical contribution to the β-function. The evaluation of the critical exponents for n = 1, n = 0 and n = -1 in the five-loop approximation and comparison of the results with known exact values confirm the conclusion that non-analytical contributions are visible in two dimensions. The estimates obtained on the base of pseudo-εexpansions originating from the 5-loop 2D RG series are also discussed.

cond-mat.stat-mech↗
arXiv2011

Thermodynamic properties of magneto-anisotropic nanoparticles

The purpose of this paper is to study the thermodynamic equilibrium properties of a collection of non-interacting three-dimensional (3D) magnetically anisotropic nanoparticles in the light of classical statistical physics. Pertaining to the angular dependence ($α$) of the magnetic field with the anisotropy axis, energy landscape plots are obtained which reveal a continuous transition from a double well to a single well for $α=\fracπ{2}$ and show asymmetric bistable shape for other values of $α$. The present analysis is related with the interpretation of equilibrium magnetization and static susceptibility of nanomagnetic system as a function of external magnetic field, $B$, and temperature, $T$. The magnetization and susceptibility confirms the non Langevin behaviour of magneto-anisotropic monodomain particles. The susceptibility analysis establishes the ferromagnetic, antiferromagnetic and paramagnetic like coupling for various $α$. This study reveals the essential role of magneto anisotropic energy in the interpretation of the magnetic behaviour of a collection of noninteracting single domain nanoparticles.

cond-mat.stat-mech↗
arXiv2008

Flux enhancement and multistability induced by time delays in a feedback controlled flashing ratchet

Feedback controlled ratchets are thermal rectifiers that use information on the state of the system to operate. We study the effects of time delays in the feedback for a protocol that performs an instantaneous maximization of the center-of-mass velocity in the many particle case. For small delays the center-of-mass velocity decreases for increasing delays (although not as fast as in the few particle case). However, for large delays we find the surprising result that the presence of a delay can improve the flux performance of the ratchet. In fact, the maximum flux obtained with the optimal periodic protocol is attained. This implies that the delayed feedback protocol considered can perform better than its non-delayed counterpart. The improvement of the flux observed in the presence of large delays is the result of the emergence of a new dynamical regime where the presence of the delayed feedback stabilizes quasiperiodic solutions that resemble the solutions obtained in a certain closed-loop protocol with thresholds. In addition, in this new regime the system presents multistability, i.e. several quasiperiodic solutions can be stable for a fixed time delay.

cond-mat.stat-mech↗
arXiv2007

Statistical field theory for a multicomponent fluid: The collective variables approach

Using the collective variables (CV) method the basic relations of statistical field theory of a multicomponent non-homogeneous fluids are reconsidered. The corresponding CV action depends on two sets of scalar fields - fields $ρ_α$ connected to the local density fluctuations of the $α$th species of particles and fields $ω_α$ conjugated to $ρ_α$. The explicit expressions for the CV field correlations and their relation to the density correlation functions are found. The perturbation theory is formulated and a mean field level (MF) of the theory is considered in detail.

cond-mat.soft↗
arXiv2008

Perturbation method to model enamel caries progress

We develop a theoretical model of the carious lesion progress caused by acids diffusing into the tooth enamel from the dental plaque. The acids react with static hydroxyapatite, which leads to demineralization of the enamel, and consequently to the development of the carious lesion. The model utilizes the diffusion-reaction equations with one static and one mobile reactant where the reaction term is proportional to the product of concentrations of acids and of mineral. The changes of concentrations are calculated approximately by means of a perturbation method. The analytical approximate solutions are compared with the numerical ones and experimental data.

cond-mat.stat-mech↗
arXiv2007

Fourier's Law for a Granular Fluid

Newton' viscosity law for the momentum flux and Fourier's law for the heat flux define Navier-Stokes hydrodynamics for a simple, one component fluid. There is ample evidence that a hydrodynamic description applies as well to a mesoscopic granular fluid with the same form for Newton's viscosity law. However, theory predicts a qualitative difference for Fourier's law with an additional contribution from density gradients even at uniform temperature. The reasons for the absence of such terms for normal fluids are indicated, and a related microscopic explanation for their existence in granular fluids is presented.

cond-mat.stat-mech↗
arXiv2007

Transition temperature of the homogeneous and dilute Bose gas in D-dimensions

The phase transition temperature of the homogeneous and dilute Bose gas in D-dimensions ($2 \le D \le 3$) is calculated by a mean field-based statistical method. The shift of the phase transition temperature is written up to the leading order as $ΔT_c/T_c^0 = c \gam^{\al}$, where $\gam=n^{1/3}a$. We derived Huang's result of the phase transition temperature in the generalized dimensions. We show that $ c(D)$ is positive and $\al(D)=2(D/2-1)^2$ in the short-wavelength range. The origin of the difference between $\al=1/2$ and $\al=1$ at D=3 is discussed. The $T_c$ at D=2 is calculated in the same scheme. The result is compared with Fisher and Hohenberg's KT temperature.

cond-mat.stat-mech↗