Status of the Clausius inequality in classical thermodynamics

We present an analysis of the foundations of the well known Clausius inequality. It is shown that, strictly speaking, the inequality is not a logical consequence of the Kelvin-Planck formulation of the second law of thermodynamics. Some thought experiments demonstrating the violation of the Clausius inequality are considered. Also, a reformulation of the Landauer's principle in terms of the Clausius inequality is proposed. This version of the inequality may be considered a consequence of the fluctuation theorem.Comment: 29 pages, 9 figure

On the sigma function identity

We consider the known functional identity on the Weierstrass sigma function. A complete classification of odd entire functions which satisfy the same identity is obtained.Comment: This result turns out to be very old (see Whittaker,Watson,"A Course of Modern Analysis", ch. 20, Exercise 38). Two proofs are essentially differen

On the Clausius theorem

We show that for a metastable system there exists a theoretical possibility of a violation of the Clausius inequality without a violation of the second law. Possibilities of experimental detection of this hypothetical violation are pointed out

The Clausius inequality does not follow from the second law of thermodynamics

The example of macroscopic thermodynamical system violating the Clausius inequality is presented

Is the Clausius inequality a consequence of the second law?

We present an analysis of the foundations of the well known Clausius inequality. It is shown that, in general, the inequality is not a logical consequence of the Kelvin-Planck formulation of the second law of thermodynamics. Some thought experiments demonstrating the violation of the Clausius inequality are considered. The possibility of experimental detection of the violation is pointed out.Comment: 14 pages, 5 figure

X-fluid and viscous fluid in D-dimensional anisotropic integrable cosmology

D-dimensional cosmological model describing the evolution of a perfect fluid with negative pressure (x-fluid) and a fluid possessing both shear and bulk viscosity in n Ricci-flat spaces is investigated. The second equations of state are chosen in some special form of metric dependence of the shear and bulk viscosity coefficients. The equations of motion are integrated and the dynamical properties of the exact solutions are studied. It is shown the possibility to resolve the cosmic coincidence problem when the x-fluid plays role of quintessence and the viscous fluid is used as cold dark matter.Comment: 11 pages, Latex 2.0

Toda Chains with Type Am Lie Algebra for Multidimensional Classical Cosmology with Intersecting p-Branes

We consider a D-dimensional cosmological model describing an evolution of (n+1) Einstein factor spaces in the theory with several dilatonic scalar fields and generalized electro-magnetic forms, admitting an interpretation in terms of intersecting p-branes. The equations of motion of the model are reduced to the Euler-Lagrange equations for the so called pseudo-Euclidean Toda-like system. We consider the case, when characteristic vectors of the model, related to p-branes configuration and their couplings to the dilatonic fields, may be interpreted as the root vectors of a Lie algebra of the type Am. The model is reduced to the open Toda chain and integrated. The exact solution is presented in the Kasner-like form.Comment: 13 pages, Late

Multidimensional Cosmology with Multicomponent Perfect Fluid and Toda Lattices

The integration procedure for multidimensional cosmological models with multicomponent perfect fluid in spaces of constant curvature is developed. Reduction of pseudo-Euclidean Toda-like systems to the Euclidean ones is done. Some known solutions are singled out from those obtained. The existence of the wormholes is proved.Comment: 21 page

Exact Solutions in Multidimensional Cosmology with Shear and Bulk Viscosity

Multidimensional cosmological model describing the evolution of a fluid with shear and bulk viscosity in $n$ Ricci-flat spaces is investigated. The barotropic equation of state for the density and the pressure in each space is assumed. The second equation of state is chosen in the form when the bulk and the shear viscosity coefficients are inversely proportional to the volume of the Universe. The integrability of Einstein equations reads as a colinearity constraint between vectors which are related to constant parameters in the first and second equations of state. We give exact solutions in a Kasner-like form. The processes of dynamical compactification and the entropy production are discussed. The non-singular $D$-dimensional isotropic viscous solution is singled out.Comment: 18 pages, Latex 2.0

General solutions for flat Friedmann universe filled by perfect fluid and scalar field with exponential potential

We study integrability by quadrature of a spatially flat Friedmann model containing both a minimally coupled scalar field $\phi$ with an exponential potential $V(\phi)\sim\exp[-\sqrt{6}\sigma\kappa\phi]$, $\kappa=\sqrt{8\pi G_N}$, of arbitrary sign and a perfect fluid with barotropic equation of state $p=(1-h)\rho$. From the mathematical view point the model is pseudo-Euclidean Toda-like system with 2 degrees of freedom. We apply the methods developed in our previous papers, based on the Minkowsky-like geometry for 2 characteristic vectors depending on the parameters $\sigma$ and $h$. In general case the problem is reduced to integrability of a second order ordinary differential equation known as the generalized Emden-Fowler equation, which was investigated by discrete-group methods. We present 4 classes of general solutions for the parameters obeying the following relations: {\bf A}. $\sigma$ is arbitrary, $h=0$; {\bf B}. $\sigma=1-h/2$, $0<h<2$; {\bf C1}. $\sigma=1-h/4$, $0<h\leq 2$; {\bf C2}. $\sigma=|1-h|$, $0<h\leq 2$, $h\neq 1,4/3$. We discuss the properties of the exact solutions near the initial singularity and at the final stage of evolution.Comment: 13 pages, Latex, 1 figure, submit. to Class. Quantum Gra