1,663 research outputs found
Quantum Macrostates, Equivalence of Ensembles and an H-Theorem
Before the thermodynamic limit, macroscopic averages need not commute for a
quantum system. As a consequence, aspects of macroscopic fluctuations or of
constrained equilibrium require a careful analysis, when dealing with several
observables. We propose an implementation of ideas that go back to John von
Neumann's writing about the macroscopic measurement. We apply our scheme to the
relation between macroscopic autonomy and an H-theorem, and to the problem of
equivalence of ensembles. In particular, we show how the latter is related to
the asymptotic equipartition theorem. The main point of departure is an
expression of a law of large numbers for a sequence of states that start to
concentrate, as the size of the system gets larger, on the macroscopic values
for the different macroscopic observables. Deviations from that law are
governed by the entropy.Comment: 16 pages; v1 -> v2: Sec. 3 slightly rewritten, 2 references adde
Irreversible thermodynamics of open chemical networks I: Emergent cycles and broken conservation laws
In this and a companion paper we outline a general framework for the
thermodynamic description of open chemical reaction networks, with special
regard to metabolic networks regulating cellular physiology and biochemical
functions. We first introduce closed networks "in a box", whose thermodynamics
is subjected to strict physical constraints: the mass-action law, elementarity
of processes, and detailed balance. We further digress on the role of solvents
and on the seemingly unacknowledged property of network independence of free
energy landscapes. We then open the system by assuming that the concentrations
of certain substrate species (the chemostats) are fixed, whether because
promptly regulated by the environment via contact with reservoirs, or because
nearly constant in a time window. As a result, the system is driven out of
equilibrium. A rich algebraic and topological structure ensues in the network
of internal species: Emergent irreversible cycles are associated to
nonvanishing affinities, whose symmetries are dictated by the breakage of
conservation laws. These central results are resumed in the relation between the number of fundamental affinities , that of broken
conservation laws and the number of chemostats . We decompose the
steady state entropy production rate in terms of fundamental fluxes and
affinities in the spirit of Schnakenberg's theory of network thermodynamics,
paving the way for the forthcoming treatment of the linear regime, of
efficiency and tight coupling, of free energy transduction and of thermodynamic
constraints for network reconstruction.Comment: 18 page
Marching to a different drummer : a cross-cultural comparison of young adolescents who challenge gender norms
Purpose: Little is known about how gender norms regulate adolescents' lives across different cultural settings. This study aims to illustrate what is considered as violating gender norms for boys and girls in four urban poor sites as well as the consequences that follow the challenging of gender norms.
Methods: Data were collected as part of the Global Early Adolescent Study, a 15-country collaboration to explore gender norms and health in early adolescence. The current study analyzed narrative and in-depth interviews conducted in urban poor sites in two middle-income (Shanghai, China; and New Delhi, India) and two high-income countries (Baltimore, U.S.; and Ghent, Belgium). A total of 238 participants, 59 boys and 70 girls aged 11-13 years old and 109 of their parents/guardians (28 male adults and 81 female adults), were interviewed. A thematic analysis was conducted across sites using Atlas. Ti 7.5 software.
Results: Findings revealed that although most perceptions and expressions about gender were regulated by stereotypical norms, there was a growing acceptability for girls to wear boyish clothes and engage in stereotypical masculine activities such as playing soccer/football. However, there was no comparable acceptance of boys engaging in traditional feminine behaviors. Across all sites, challenging gender norms was often found to lead to verbal, physical, and/or psychological retribution.
Conclusions: While it is sometimes acceptable for young adolescents to cross gender boundaries, once it becomes clear that a behavior is socially defined as typical for the other sex, and the adolescent will face more resistance. Researchers, programmers, and clinicians working in the field of adolescent health need not only attend to those who are facing the consequences of challenging prevailing gender norms, but also to address the environment that fosters exclusion and underscores differences
Derivation of the Planck Spectrum for Relativistic Classical Scalar Radiation from Thermal Equilibrium in an Accelerating Frame
The Planck spectrum of thermal scalar radiation is derived suggestively
within classical physics by the use of an accelerating coordinate frame. The
derivation has an analogue in Boltzmann's derivation of the Maxwell velocity
distribution for thermal particle velocities by considering the thermal
equilibrium of noninteracting particles in a uniform gravitational field. For
the case of radiation, the gravitational field is provided by the acceleration
of a Rindler frame through Minkowski spacetime. Classical zero-point radiation
and relativistic physics enter in an essential way in the derivation which is
based upon the behavior of free radiation fields and the assumption that the
field correlation functions contain but a single correlation time in thermal
equilibrium. The work has connections with the thermal effects of acceleration
found in relativistic quantum field theory.Comment: 23 page
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
You Can't Get Through Szekeres Wormholes - or - Regularity, Topology and Causality in Quasi-Spherical Szekeres Models
The spherically symmetric dust model of Lemaitre-Tolman can describe
wormholes, but the causal communication between the two asymptotic regions
through the neck is even less than in the vacuum
(Schwarzschild-Kruskal-Szekeres) case. We investigate the anisotropic
generalisation of the wormhole topology in the Szekeres model. The function
E(r, p, q) describes the deviation from spherical symmetry if \partial_r E \neq
0, but this requires the mass to be increasing with radius, \partial_r M > 0,
i.e. non-zero density. We investigate the geometrical relations between the
mass dipole and the locii of apparent horizon and of shell-crossings. We
present the various conditions that ensure physically reasonable
quasi-spherical models, including a regular origin, regular maxima and minima
in the spatial sections, and the absence of shell-crossings. We show that
physically reasonable values of \partial_r E \neq 0 cannot compensate for the
effects of \partial_r M > 0 in any direction, so that communication through the
neck is still worse than the vacuum.
We also show that a handle topology cannot be created by identifying
hypersufaces in the two asymptotic regions on either side of a wormhole, unless
a surface layer is allowed at the junction. This impossibility includes the
Schwarzschild-Kruskal-Szekeres case.Comment: zip file with LaTeX text + 6 figures (.eps & .ps). 47 pages. Second
replacement corrects some minor errors and typos. (First replacement prints
better on US letter size paper.
Cosmology with torsion: An alternative to cosmic inflation
We propose a simple scenario which explains why our Universe appears
spatially flat, homogeneous and isotropic. We use the
Einstein-Cartan-Kibble-Sciama (ECKS) theory of gravity which naturally extends
general relativity to include the spin of matter. The torsion of spacetime
generates gravitational repulsion in the early Universe filled with quarks and
leptons, preventing the cosmological singularity: the Universe expands from a
state of minimum but finite radius. We show that the dynamics of the closed
Universe immediately after this state naturally solves the flatness and horizon
problems in cosmology because of an extremely small and negative torsion
density parameter, . Thus the ECKS gravity provides
a compelling alternative to speculative mechanisms of standard cosmic
inflation. This scenario also suggests that the contraction of our Universe
preceding the bounce at the minimum radius may correspond to the dynamics of
matter inside a collapsing black hole existing in another universe, which could
explain the origin of the Big Bang.Comment: 8 pages; published versio
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