BibliographyType,ISBN,Identifier,Author,Title,Journal,Volume,Number,Month,Pages,Year,Address,Note,URL,Booktitle,Chapter,Edition,Series,Editor,Publisher,ReportType,Howpublished,Institution,Organizations,School,Annote,Custom1,Custom2,Custom3,Custom4,Custom5
5,"","statphys23_1109","Brilliantov, N.V.; Poeschel, T.; Kranz, W.T. & Zippelius, A.","Translations and Rotations Are Correlated in Granular Gases","",,,"9-13 July","",2007,"Genova, Italy","","http://st23.statphys23.org/webservices/abstract/preview_pop.php?ID_PAPER=1109","Abstract Book of the XXIII IUPAP International Conference on Statistical Physics","","","","Pietronero, Luciano; Loreto, Vittorio & Zapperi, Stefano","","","","","","","","In a granular gas of rough particles the axis of rotation is shown to be correlated with the translational velocity of the particles. The average relative orientation of angular and linear velocities depends on the restitution coefficients -- the parameters which characterize the dissipative nature of the collision [1,2]. Using the Boltzmann equation and pseudo-Liouville operator technique [1,3] we derive a simple analytical theory for these correlations. We also perform numerical simulations for a wide range of coefficients of normal and tangential restitution. Two different numerical methods were used: Direct simulation Monte Carlo (DSMC) [4] and event-driven molecular dynamics (MD). Surprisingly, the limit of smooth spheres was found to be singular: even an arbitrarily small roughness of the particles gives rise to orientational correlations. The results of the analytical theory are in a good agreement with the numerical simulations [5]. 

1) N.V. Brilliantov and T. Poeschel, Kinetic Theory of Granular Gases (Oxford University Press, Oxford, 2004).\\ 2) T. Poeschel, and N.V. Brilliantov (Eds.), Granular Gas Dynamics, Lecture Notes in Physics, vol. 624, Springer (2003).\\ 3) T. Aspelmeier, M. Huthmann, and A. Zippelius, in Granular Gases, S. Luding and T. Poeschel (Eds), Lecture Notes in Physics vol. 425, Springer, Berlin, (2000), p. 680.\\ 4) T. Poeschel and T. Schwager, Computational Granular Dynamics (Springer, New York, 2005).\\ 5) N.V. Brilliantov, T. Poeschel, W.T. Kranz, and A. Zippelius, Phys. Rev. Lett., 98, (2007) 128001.","","boltzmann coefficients dynamics equation gases granular kinetic molecular restitution statphys23 theory topic-7 ","",""
5,"","statphys23_0584","Kobayashi, M.U. & Fujisaka, H.F.","Time correlation functions and diffusion coefficients in chaotic sytems in terms of unstable periodic orbits","",,,"9-13 July","",2007,"Genova, Italy","","http://st23.statphys23.org/webservices/abstract/preview_pop.php?ID_PAPER=584","Abstract Book of the XXIII IUPAP International Conference on Statistical Physics","","","","Pietronero, Luciano; Loreto, Vittorio & Zapperi, Stefano","","","","","","","","\hskip 0.6cm Time correlation functions and diffusion coefficients are the most fundamental quantities for studying fluctuation statistics in chaotic systems. Although deriving time correlation functions and diffusion coefficients from fundamental equations of motion describing chaotic dynamics is an important and fundamental problem in statistical mechanics, it is generally quite difficult to do this, because of the nonlinearity of chaotic systems and the singular structure of the invariant measure. These can be obtained, in principle, by solving the eigenvalue problems of the time evolution operator. The eigenvalue problem is, however, generally meaningless, because the eigenfunctions of the time evolution operators in chaotic systems are singular almost everywhere in the state space, due to the fractal structure of the manifolds. In order to avoid this problem, one of the present authors proposed a new method of determining the time correlation functions that does not require solving the eigenvalue problem. This new method, called the {\it Markov method}, extends Mori's original projection operator approach in a more tractable way and can be used to associate the {\it dynamical} correlation functions with {\it static} quantities. Meanwhile {\it static} quantities are determined in terms of unstable periodic orbits. Thus the {\it dynamical} correlation functions can be obtained in terms of unstable periodic orbits.

\hskip 0.6cm Furthermore diffusion coefficients can be obtained by integrating time correlation functions. So we can determine diffusion coefficients in terms of unstable periodic orbits by using the above method.

\hskip 0.6cm In this presentation, applying this method to various chaotic dynamical systems, we prove the usefulness of the present approach.","","chaos coefficients correlation diffusion dynamical functions orbits periodic statphys23 topic-5 unstable ","",""
5,"","statphys23_0144","Reddy, K. Anki & Kumaran, V.","Rheology and Microstructure of Dense Granular Flows","",,,"9-13 July","",2007,"Genova, Italy","","http://st23.statphys23.org/webservices/abstract/preview_pop.php?ID_PAPER=144","Abstract Book of the XXIII IUPAP International Conference on Statistical Physics","","","","Pietronero, Luciano; Loreto, Vittorio & Zapperi, Stefano","","","","","","","","A granular material is a collection of discrete,solid paricles dispersed in an interstitial fluid, which is ubiquitous in nature.Apart from exhibiting fascinating properties because of dissipative ineractions ,their importance in geophysics and in various industrial processes,flows of granular materials are the focus of large amount of research involving physicists and engineers.A good understanding of the physics of granular materials is desired in order to design efficient processing and handling systems.Towards a better understanding of rheology of granular flows,we implemented numerical simulations of granular material flow in two different geomtries to investigate the bulk rheology, i) simple shear flow in the absence of gravity using Lees- Edwards boundary conditions with hard sphere collision rules as governing equations, ii) flow down an inclined plane using Discrete Element Method(DEM) that employ a linear spring-dashpot model for particle interactions.Bagnold coefficients, which are the ratios of the different components of the stress and the square of the strain rate, and dissipation rates were estimated and we found a good aggrement between the kinetic theory results and numerical simulation data over a wide range of parameters.

 We investigated quantitatively on the three dimensional structure by decomposing the pair distribution function into spherical harmonics , by using Voronoi cell volume distribution and Bond Orientational Order Parameter Analysis.","","bagnold coefficients dense flows granular kinetic micro rheology statphys23 structure theory topic-7 ","",""
5,"","statphys23_0005","Shibata, H.","Turbulent Viscosity Coefficient in Low-Reynolds-Number Turbulence","",,,"9-13 July","",2007,"Genova, Italy","","http://st23.statphys23.org/webservices/abstract/preview_pop.php?ID_PAPER=5","Abstract Book of the XXIII IUPAP International Conference on Statistical Physics","","","","Pietronero, Luciano; Loreto, Vittorio & Zapperi, Stefano","","","","","","","","The turbulent transport coefficients have been studied extensively for long years[1]. Recently, the turbulent transport coefficients have been calculated on the basis of statistical mechanics[2]. Above all, the divergence of the turbulent viscosity coefficient was found in the Rayleigh-B{\' e}nard convection by numerical calculation. These results are going to be confirmed. E. Helfand represented the statistical mechanical expression of the transport coefficients[3]. He assumed that fluids satisfied the Navier-Stokes equation with the molecular viscosity coefficient. In addition, the velocity components were assumed to be subject to the Maxwell distribution. His expression holds for the quiescent fluids, i.e., the fluids in a microscale. However, the concepts of the turbulent viscosity coefficients are necessary for us to characterize fluids in the state of turbulence. It should be noticed that the turbulent transport coefficients are quantities in the scales much larger than the microscale. So, we assume the Navier-Stokes equation with the turbulent viscosity coefficient for a fluid parcel. In addition, the velocity components of the fluid parcel are assumed to satisfy the Gaussian statistics. Then it is possible for us to describe the same formulas for the turbulent transport coefficients as the ones by Helfand for the transport coefficients. Here we take up the turbulent viscosity coefficient. The formula for the turbulent viscosity coefficient is expressed as $$ \nu ={V \over kT}\int_0^{\infty} dt C(t), \eqno(1) $$ $$ C(t) \equiv <J_{xy}(t)J_{xy}(0)> -<J_{xy}(t)><J_{xy}(0)>, \eqno(2) $$ and $$ J_{xy}(t) \equiv \int_V d \vec r \rho (\vec r, t) v_x (\vec r, t) v_y(\vec r,t), \eqno(3) $$ where $V$ is the volume where the turbulent viscosity coefficient is calculated. $k$ is a constant and $T$ is the effective temperature. $<\cdots >$ means the long time average along the long trajectory of a solution. The behavior of the turbulent viscosity coefficient in 3-dimensional turbulence is shown here. The lattice Boltzmann method is used in order to simulate the homogeneous turbulence and to calculate the turbulent viscosity coefficient of it. It is clearly shown that the turbulent viscosity coefficient becomes large as the Reynolds number of the homogeneous turbulence becomes large. The dependency of the turbulent viscosity coefficient on the Reynolds number will be shown.\\
1) S.B. Pope, Turbulent Flows, Cambridge Univ. Press, Cambridge, 2000.\\ 2) H. Shibata, Physica A 333, 71(2004).\\ 3) E. Helfand, Phys. Rev. 119, 1(1960).","","boltzmann coefficient coefficients equation homogeneous lattice method navier-stokes statphys23 topic-5 transport turbulence turbulent viscosity ","",""
5,"","statphys23_0904","Urrutia, I.","Configuration Integral and Thermodynamic properties for small systems of confined Hard Spheres","",,,"9-13 July","",2007,"Genova, Italy","","http://st23.statphys23.org/webservices/abstract/preview_pop.php?ID_PAPER=904","Abstract Book of the XXIII IUPAP International Conference on Statistical Physics","","","","Pietronero, Luciano; Loreto, Vittorio & Zapperi, Stefano","","","","","","","","Exact results for the inhomogeneous Hard Sphere (HS) fluid systems are of great theoretical interest. In this work we analyze the configuration integral (CI) of the canonical partition function for two and three HS constrained to move on closed volumes of simple geometrical shape. We present the exact analytical expressions of such CI for some simple shaped pores. The dependence of thermodynamic properties of these systems over a wide range of pore size parameter are studied focusing on low and high density limits.","","analytic coefficients configuration exact hard integral results spheres statphys23 topic-1 virial ","",""