275,771 research outputs found
Mechanical Proof of the Second Law of Thermodynamics Based on Volume Entropy
In a previous work (M. Campisi. Stud. Hist. Phil. M. P. 36 (2005) 275-290) we
have addressed the mechanical foundations of equilibrium thermodynamics on the
basis of the Generalized Helmholtz Theorem. It was found that the volume
entropy provides a good mechanical analogue of thermodynamic entropy because it
satisfies the heat theorem and it is an adiabatic invariant. This property
explains the ``equal'' sign in Clausius principle () in a purely
mechanical way and suggests that the volume entropy might explain the ``larger
than'' sign (i.e. the Law of Entropy Increase) if non adiabatic transformations
were considered. Based on the principles of microscopic (quantum or classical)
mechanics here we prove that, provided the initial equilibrium satisfy the
natural condition of decreasing ordering of probabilities, the expectation
value of the volume entropy cannot decrease for arbitrary transformations
performed by some external sources of work on a insulated system. This can be
regarded as a rigorous quantum mechanical proof of the Second Law. We discuss
how this result relates to the Minimal Work Principle and improves over
previous attempts. The natural evolution of entropy is towards larger values
because the natural state of matter is at positive temperature. Actually the
Law of Entropy Decrease holds in artificially prepared negative temperature
systems.Comment: 17 pages, 1 figur
The transition to irreversibility in sheared suspensions: An analysis based on a mesoscopic entropy production
We study the shear-induced diffusion effect and the transition to
irreversibility in suspensions under oscillatory shear flow by performing an
analysis of the entropy production associated to the motion of the particles.
We show that the Onsager coupling between different contributions to the
entropy production is responsible for the scaling of the mean square
displacement on particle diameter and applied strain. We also show that the
shear-induced effective diffusion coefficient depends on the volume fraction
and use Lattice-Boltzmann simulations to characterize the effect through the
power spectrum of particle positions for different Reynolds numbers and volume
fractions. Our study gives a thermodynamic explanation of the the transition to
irreversibility through a pertinent analysis of the second law of
thermodynamics.Comment: 17 pages, 3 figures, paper submitted tp phys rev
Lifshitz entanglement entropy from holographic cMERA
We study entanglement entropy in free Lifshitz scalar field theories
holographically by employing the metrics proposed by Nozaki, Ryu and Takayanagi
in \cite{Nozaki:2012zj} obtained from a continuous multi-scale entanglement
renormalisation ansatz (cMERA). In these geometries we compute the minimal
surface areas governing the entanglement entropy as functions of the dynamical
exponent and we exhibit a transition from an area law to a volume law
analytically in the limit of large . We move on to explore the effects of a
massive deformation, obtaining results for any in arbitrary dimension. We
then trigger a renormalisation group flow between a Lifshitz theory and a
conformal theory and observe a monotonic decrease in entanglement entropy along
this flow. We focus on strip regions but also consider a disc in the undeformed
theory.Comment: 17 pages, v2: references added and improved discussions, v3:
published versio
Raman study of the Verwey transition in Magnetite at high-pressure and low-temperature; effect of Al doping
We report high-pressure low-temperature Raman studies of the Verwey
transition in pure and Al-doped magnetite (Fe_3O_4). The low temperature phase
of magnetite displays a number of additional Raman modes that serve as
transition markers. These transition markers allow one to investigate the
effect of hydrostatic pressure on the Verwey transition temperature. Al-doped
magnetite Fe_2.8Al_0.2O_4 (TV=116.5K) displays a nearly linear decrease of the
transition temperature with an increase of pressure yielding dP/dT_V = -0.096
GPa/K. In contrast pure magnetite displays a significantly steeper slope of the
PT equilibrium line with dP/dT_V = -0.18 GPa/K. The slope of the PT equilibrium
lines is related to the changes of the molar entropy and molar volume at the
transition. We compare our spectroscopic data with that obtained from the
ambient pressure specific heat measurements and find a good agreement in the
optimally doped magnetite. Our data indicates that Al doping leads to a smaller
entropy change and larger volume expansion at the transition. Our data displays
the trends that are consistent with the mean field model of the transition that
assumes charge ordering in magnetite.Comment: 17 pages, 3 figure
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