Nonequilibrium Stefan-Boltzmann law

We study thermal radiation outside equilibrium. The situation considered consists of two bodies emitting photons at two different temperatures. We show that the system evolves to a stationary state characterized by an energy current which satisfies a Stefan-Boltzmann-like law expressing it as the difference of the temperatures to the fourth power of the emitters . The results obtained show how the classical laws governing the thermal radiation at equlibrium can be generalized away from equilibrium situations.Comment: 9 pages, 1 figure. To be published in J. Noneq. Ther

Issue Brief: European Americans and Native Americans

This issue brief examines the relationship between European/White Americans and Native Americans. Complicated even to the present day, the relationship between these two groups has historically been one of oppressor versus oppressed, a dichotomy that has since evolved but which serves to shed light on the intricacies of the contemporary Native American experience in comparison to that of white America

Failure of the work-Hamiltonian connection for free energy calculations

Extensions of statistical mechanics are routinely being used to infer free energies from the work performed over single-molecule nonequilibrium trajectories. A key element of this approach is the ubiquitous expression dW/dt=\partial H(x,t)/ \partial t which connects the microscopic work W performed by a time-dependent force on the coordinate x with the corresponding Hamiltonian H(x,t) at time t. Here we show that this connection, as pivotal as it is, cannot be used to estimate free energy changes. We discuss the implications of this result for single-molecule experiments and atomistic molecular simulations and point out possible avenues to overcome these limitations

Entropic Stochastic Resonance

We present a novel scheme for the appearance of Stochastic Resonance when the dynamics of a Brownian particle takes place in a confined medium. The presence of uneven boundaries, giving rise to an entropic contribution to the potential, may upon application of a periodic driving force result in an increase of the spectral amplification at an optimum value of the ambient noise level. This Entropic Stochastic Resonance (ESR), characteristic of small-scale systems, may constitute a useful mechanism for the manipulation and control of single-molecules and nano-devices.Comment: 4 pages, 3 figure

Simulation of the Onset turbulent flow around a Isothermal Complex Geometries: an analysis of thermofluid dynamic flow

In this work, in the area of Computational Fluid Dynamics (CFD), more specifically in the area of thermofluid dynamics for two-dimensional flows (2D), and also considering, the fluid-body interaction, allied to the phenomena of heat-transfer by mixed convection and the beginning of processes of the turbulent flow phenomenon in the fluid-body interaction, a study is proposed that demonstrates the efficiency in the analysis and simulation of these complex phenomena. We adopt an Eulerian approach for a fixed mesh, which is intended to represent the thermofluid dynamic movement, working together with a Lagrangian mesh, the latter being intended to discretize the immersed body. The strategy, in this work, allows approaching complex isothermal geometries, which present a certain aerodynamic degree on their surface, being popularly known as blunt body, where this, in turn, is immersed in an incompressible Newtonian fluid. One of the contributions of this work is the introduction of a simple but efficient method to calculate the Nusselt number. Regarding the process of validation and modeling of the physical phenomena of interest, that is, regarding the effectiveness of the methodology, called the Immersed Frontier, an implementation with low computational cost was carried out for the transfer of mixed convection heat, as well as for modeling the turbulence, namely, making use of the Spalart-Allmaras model, in the context of the URANS (Unsteady Reynolds Average Navier -Stokes) methodology. Numerical results showed good convergence with data available in the literature, which confirms the numerical precision and reliability of the adopted model

Damage spreading in the mode-coupling equations for glasses

We examine the problem of damage spreading in the off-equilibrium mode coupling equations. The study is done for the spherical $p$-spin model introduced by Crisanti, Horner and Sommers. For $p>2$ we show the existence of a temperature transition $T_0$ well above any relevant thermodynamic transition temperature. Above $T_0$ the asymptotic damage decays to zero while below $T_0$ it decays to a finite value independent of the initial damage. This transition is stable in the presence of asymmetry in the interactions. We discuss the physical origin of this peculiar phase transition which occurs as a consequence of the non-linear coupling between the damage and the two-time correlation functions.Comment: 5 pages, 2 figures, Revtex fil