Shear viscosity from thermal fluctuations in relativistic conformal fluid dynamics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Evaporative respiratory cooling augments pit organ thermal detection in rattlesnakes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Noise and ultraviolet divergences in the dynamics of the chiral condensate in QCD

The time evolution of the matter produced in high energy heavy-ion collisions seems to be well described by relativistic viscous hydrodynamics. In addition to the hydrodynamic degrees of freedom related to energy-momentum conservation, degrees of freedom associated with order parameters of broken continuous symmetries must be considered because they are all coupled to each other. of particular interest is the coupling of degrees of freedom associated with the chiral symmetry of QCD. Quantum and thermal fluctuations of the chiral fields act as noise sources in the classical equations of motion, turning them into stochastic differential equations in the form of Ginzburg-Landau-Langevin (GLL) equations. Analytic solutions of GLL equations are attainable only in very special circumstances and extensive numerical simulations are necessary, usually by discretizing the equations on a spatial lattice. However, a not much appreciated issue in the numerical simulations of GLL equations is that ultraviolet divergences in the form of lattice-spacing dependence plague the solutions. The divergences are related to the well-known Rayleigh-Jeans catastrophe in classical field theory. In the present communication we present a systematic lattice renormalization method to control the catastrophe. We discuss the implementation of the method for a GLL equation derived in the context of a model for the QCD chiral phase transition and consider the nonequilibrium evolution of the chiral condensate during the hydrodynamic flow of the quark-gluon plasma.

Influence from the free volume on the photoinduced birefringence in azocompound-containing polymers

The photoinduced birefringence is analyzed in a guest-host azobenzene-containing polymer in the temperature range from 20 to 330 K. An anomalous behavior arises in the low-temperature range, suggesting strong influence from the free volume for the chromophores in the polymer. This influence is so strong that quenched samples have a photoinduced signal ca. 5 times greater than the annealed ones at room temperature. An extended free volume model is presented based on two assumptions about thermal fluctuations in the cavities and their size distribution. This model, which is an extension of the model by Mita et al., can explain the main features of the photoinduced birefringence as a function of time, temperature, and initial free volume state. To account for the influence of free volume on the photoorientation, the detailed reorientation model by Sekkat's was used. We show that Sekkat's model leads to an exponential behavior at small orientation regimes, which simplifies the mathematical treatment and allows the mean free volume to be obtained from the data fitting.

Influences of thermal and electric load fluctuations in the cogeneration attractiveness

The use of mean values of thermal and electric demand can be justifiable for synthesising the configuration and for estimating the economic results because it simplifies the analysis in a preliminary feasibility study of a cogeneration plant. For determining the cogeneration scheme that best fits the energetic needs of a process several cycles and combinations must be considered, and those technically feasible will be analysed according to economic models. Although interesting for a first approach, this procedure do not consider that the peaks and valleys present in the load patterns will impose additional constraints relatively to the equipment capacities. In this paper, the effects of thermal and electric load fluctuation to the cogeneration plant design were considered. An approach for modelling these load variability is proposed for comparing two competing thermal and electric parity competing schemes. A gas turbine associated to a heat recovery steam generator was then proposed and analysed for thermal- and electric-following operational strategies. Thermal-following option revealed to be more attractive for the technical and economic limits defined for this analysis. (c) 2006 Elsevier Ltd. All rights reserved.

THERMAL RADIATION FROM A FLUCTUATING EVENT HORIZON

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Zooplankton fluctuations in Jurumirim Reservoir (São Paulo, Brazil): a three-year study

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Superconducting vortex fluctuations in YBa2Cu3O7-δ

Measurements of magnetization in YBa2Cu3O7-δ single crystals were performed for applied fields H parallel and perpendicular to the ab planes. The data show a temperature T = T* at which the magnetization M(T*) is independent of the applied field. This result is interpreted as due to vortex fluctuations of an anisotropic 3-D superconductor.