Statistical mechanical theory of an oscillating isolated system. The relaxation to equilibrium

In this contribution we show that a suitably defined nonequilibrium entropy of an N-body isolated system is not a constant of the motion in general and its variation is bounded, the bounds determined by the thermodynamic entropy, i.e., the equilibrium entropy. We define the nonequilibrium entropy as a convex functional of the set of n-particle reduced distribution functions (n=0,......., N) generalizing the Gibbs fine-grained entropy formula. Additionally, as a consequence of our microscopic analysis we find that this nonequilibrium entropy behaves as a free entropic oscillator. In the approach to the equilibrium regime we find relaxation equations of the Fokker-Planck type, particularly for the one-particle distribution function

Class of dilute granular Couette flows with uniform heat flux

In a recent paper [F. Vega Reyes et al., Phys. Rev. Lett. 104, 028001 (2010)] we presented a preliminary description of a special class of steady Couette flows in dilute granular gases. In all flows of this class the viscous heating is exactly balanced by inelastic cooling. This yields a uniform heat flux and a linear relationship between the local temperature and flow velocity. The class (referred to as the LTu class) includes the Fourier flow of ordinary gases and the simple shear flow of granular gases as special cases. In the present paper we provide further support for this class of Couette flows by following four different routes, two of them being theoretical (Grad's moment method of the Boltzmann equation and exact solution of a kinetic model) and the other two being computational (molecular dynamics and Monte Carlo simulations of the Boltzmann equation). Comparison between theory and simulations shows a very good agreement for the non-Newtonian rheological properties, even for quite strong inelasticity, and a good agreement for the heat flux coefficients in the case of Grad's method, the agreement being only qualitative in the case of the kinetic model.Comment: 15 pages, 10 figures; v2: change of title plus some other minor change

Long-Lived Superheavy Particles in Dynamical Supersymmetry-Breaking Models in Supergravity

Superheavy particles of masses $\simeq 10^{13}-10^{14} GeV$ with lifetimes $\simeq 10^{10}-10^{22} years$ are very interesting, since their decays may account for the ultra-high energy (UHE) cosmic rays discovered beyond the Greisen-Zatsepin-Kuzmin cut-off energy $E \sim 5 \times 10^{10} GeV$. We show that the presence of such long-lived superheavy particles is a generic prediction of QCD-like SU(N_c) gauge theories with N_f flavors of quarks and antiquarks and the large number of colors N_c. We construct explicit models based on supersymmetric SU(N_c) gauge theories and show that if the dynamical scale $\Lambda \simeq 10^{13}-10^{14} GeV$ and N_c = 6-10 the lightest composite baryons have the desired masses and lifetimes to explain the UHE cosmic rays. Interesting is that in these models the gaugino condensation necessarily occurs and hence these models may play a role of so-called hidden sector for supersymmetry breaking in supergravity.Comment: 13 pages, Late

Urban transportation: Perspectives on mobility and choice

A study of urban transportation systems are presented characterized by intensive scrutiny of many ideas, philosophies, and academic perspectives. This report is intended to communicate some dimensions of the urban transportation problem to the general public

Particle-Based Mesoscale Hydrodynamic Techniques

Dissipative particle dynamics (DPD) and multi-particle collision (MPC) dynamics are powerful tools to study mesoscale hydrodynamic phenomena accompanied by thermal fluctuations. To understand the advantages of these types of mesoscale simulation techniques in more detail, we propose new two methods, which are intermediate between DPD and MPC -- DPD with a multibody thermostat (DPD-MT), and MPC-Langevin dynamics (MPC-LD). The key features are applying a Langevin thermostat to the relative velocities of pairs of particles or multi-particle collisions, and whether or not to employ collision cells. The viscosity of MPC-LD is derived analytically, in very good agreement with the results of numerical simulations.Comment: 7 pages, 2 figures, 1 tabl

Determination of absolute neutrino masses from Z-bursts

Ultrahigh energy neutrinos (UHE\nu) scatter on relic neutrinos (R\nu) producing Z bosons, which can decay hadronically producing protons (Z-burst). We compare the predicted proton spectrum with the observed ultrahigh energy cosmic ray (UHECR) spectrum and determine the mass of the heaviest R\nu via a maximum likelihood analysis. Our prediction depends on the origin of the power-like part of the UHECR spectrum: m_\nu=2.75^{+1.28}_{-0.97} eV for Galactic halo and 0.26^{+0.20}_{-0.14} eV for extragalactic (EG) origin. The necessary UHE\nu flux should be detected in the near future.Comment: slight rewording, revised neutrino fluxes, conclusions unchanged, version to appear in Phys. Rev. Let

Hydrodynamic modes, Green-Kubo relations, and velocity correlations in dilute granular gases

It is shown that the hydrodynamic modes of a dilute granular gas of inelastic hard spheres can be identified, and calculated in the long wavelength limit. Assuming they dominate at long times, formal expressions for the Navier-Stokes transport coefficients are derived. They can be expressed in a form that generalizes the Green-Kubo relations for molecular systems, and it is shown that they can also be evaluated by means of $N$-particle simulation methods. The form of the hydrodynamic modes to zeroth order in the gradients is used to detect the presence of inherent velocity correlations in the homogeneous cooling state, even in the low density limit. They manifest themselves in the fluctuations of the total energy of the system. The theoretical predictions are shown to be in agreement with molecular dynamics simulations. Relevant related questions deserving further attention are pointed out

Correlation between Compact Radio Quasars and Ultra-High Energy Cosmic Rays

Some proposals to account for the highest energy cosmic rays predict that they should point to their sources. We study the five highest energy events (E>10^20 eV) and find they are all aligned with compact, radio-loud quasars. The probability that these alignments are coincidental is 0.005, given the accuracy of the position measurements and the rarity of such sources. The source quasars have redshifts between 0.3 and 2.2. If the correlation pointed out here is confirmed by further data, the primary must be a new hadron or one produced by a novel mechanism.Comment: 8 pages, 3 tables, revtex. with some versions of latex it's necessary to break out the tables and latex them separately using article.sty rather than revtex.st