1,434 research outputs found
Gravity from the entropy of light
The holographic principle, considered in a semiclassical setting, is shown to
have direct consequences on physics at a fundamental level. In particular, a
certain relation is pointed out to be the expression of holography in basic
thermodynamics. It is argued moreover that through this relation holography can
be recognized to induce gravity, and an expression for the gravitational
lensing is obtained in terms of entropy over wavelength of black-body
radiation, or, at a deeper level, in terms of maximum entropy over associated
space to the elementary bit of information.Comment: 7 pages; v2: completion of the list of references; v3: the discussion
is divided in Sections and the argument is described in more detail; v4: a
statement is added (below eq.13) on what is the supposed difference between
Jacobson's work in ref.21 and this attempt; addition of a paragraph in last
Sectio
A proof of the Bekenstein bound for any strength of gravity through holography
The universal entropy bound of Bekenstein is considered, at any strength of
the gravitational interaction. A proof of it is given, provided the considered
general-relativistic spacetimes allow for a meaningful and inequivocal
definition of the quantities which partecipate to the bound (such as system's
energy and radius). This is done assuming as starting point that, for assigned
statistical-mechanical local conditions, a lower-limiting scale l* to system's
size definitely exists, being it required by holography through its
semiclassical formulation as given by the generalized covariant entropy bound.
An attempt is made also to draw some possible general consequences of the l*
assumption with regards to the proliferation of species problem and to the
viscosity to entropy density ratio. Concerning the latter, various fluids are
considered including systems potentially relevant, to some extent, to the
quark-gluon plasma case.Comment: 13 pages. v2: the title is modified; the discussion is strengthened
and made more concise (10pp). v3: some short clarifications adde
Relative entropy and the Bekenstein bound
Elaborating on a previous work by Marolf et al, we relate some exact results
in quantum field theory and statistical mechanics to the Bekenstein universal
bound on entropy. Specifically, we consider the relative entropy between the
vacuum and another state, both reduced to a local region. We propose that, with
the adequate interpretation, the positivity of the relative entropy in this
case constitutes a well defined statement of the bound in flat space. We show
that this version arises naturally from the original derivation of the bound
from the generalized second law when quantum effects are taken into account. In
this formulation the bound holds automatically, and in particular it does not
suffer from the proliferation of the species problem. The results suggest that
while the bound is relevant at the classical level, it does not introduce new
physical constraints semiclassically.Comment: 12 pages, 1 figure, minor changes and references adde
Time varying gravitational constant G via the entropic force
If the uncertainty principle applies to the Verlinde entropic idea, it leads
to a new term in the Newton's second law of mechanics in the Planck's scale.
This curious velocity dependence term inspires a frictional feature of the
gravity. In this short letter we address that this new term modifies the
effective mass and the Newtonian constant as the time dependence quantities.
Thus we must have a running on the value of the effective mass on the particle
mass near the holographic screen and the . This result has a nigh
relation with the Dirac hypothesis about the large numbers hypothesis (L.N.H.)
[1]. We propose that the corrected entropic terms via Verlinde idea can be
brought as a holographic evidence for the authenticity of the Dirac idea.Comment: Accepted for publication in "Communications in Theoretical Physics
(CTP)",Major revisio
Experimental and numerical analysis of the martensitic transformation in AISI 304 steel sheets subjected to perforation by conical and hemispherical projectiles
In this work, an experimental and numerical analysis of the martensitic transformation in AISI 304 steel sheets subjected to perforation by conical and hemispherical projectiles is conducted. Experiments are performed using a pneumatic gas gun for with the impact velocities in the range of 35 m/s < V-0 < 200 m/s. Two target thicknesses are examined, t(1) = 0.5 mm and t(2) = 1.0 mm. The experimental setup enabled the determination of the impact velocity, the residual velocity and the failure mode of the steel sheets. The effect of the projectile nose shape on the target's capacity for energy absorption is evaluated. Moreover, martensite is detected in all the impacted samples, and the role played by the projectile nose shape on the transformation is highlighted. A three-dimensional model is developed in ABAQUS/Explicit to simulate the perforation tests. The material is defined via the constitutive model developed by Zaera et al. (2012) to describe the strain-induced martensitic transformation occurring in metastable austenitic steels at high strain rates. The finite element results are compared with the experimental evidence, and satisfactory matching is observed over the entire range of impact velocities tested and for both projectile configurations and target thicknesses considered. The numerical model succeeds in describing the perforation mechanisms associated with each projectile-target configuration analyzed. The roles played by impact velocity, target thickness and projectile nose shape on the martensitic transformation are properly captured.The researchers of the University Carlos III of Madrid are in
debted to the Comunidad Autónoma de Madrid (Project CCG10
UC3M/DPI 5596) and to the Ministerio de Ciencia e Innovación
de España (DPI2011 24068) for the financial support received
which allowed conducting part of this work
From Unruh temperature to generalized Bousso bound
In a classical spacetime satisfying Einstein's equation and the null
convergence condition, the same quantum mechanical effects that cause black
holes to have a temperature are found to imply, if joined to the macroscopic
nature of entropy, the covariant entropy bound in its generalized form. This is
obtained from thermodynamics, as applied across the local Rindler causal
horizon through every point p of the null hypersurfaces L the covariant entropy
bound refers to, in the direction of the null geodesics generating L.Comment: 5 pages. v2: some changes to clarify the path to the obtained
results; two (final) paragraphs, the acknowledgments and a reference adde
A constitutive model for analyzing martensite formation in austenitic steels deforming at high strain rates
This study presents a constitutive model for steels exhibiting SIMT, based on previous sem inal works, and the corresponding methodology to estimate their parameters. The model includes temperature effects in the phase transformation kinetics, and in the softening of each solid phase through the use of a homogenization technique. The model was validated with experimental results of dynamic tensile tests on AISI 304 sheet steel specimens, and their predictions correlate well with the experimental evidence in terms of macroscopic stress strain curves and martensite volume fraction formed at high strain rates. The work shows the value of considering temperature effects in the modeling of metastable austen itic steels submitted to impact conditions. Regarding most of the works reported in the lit erature on SIMT, modeling of the martensitic transformation at high strain rates is the distinctive feature of the present paper.The researchers of the University Carlos III of Madrid are indebted to the Comunidad Autónoma de Madrid (Project CCG10 UC3M/DPI 5596)) and to the Ministerio de Ciencia e Innovación de España (Project DPI/2008 06408) for the financial support received which allowed conducting part of this work. The authors express their thanks to Mr. Philippe and Mr. Tobisch from the company Zwick for the facilities provided to perform the tensile tests at high strain rates.Publicad
Reproductive patterns in deep versus shallow populations of the precious Mediterranean gorgonian Corallium rubrum ( Linnaeus, 1758) ( Sardinia, Central-Western Mediterranean)
This study quanti es the main reproductive features of the long-lived red coral Corallium rubrum, an octocoral endemic to the Mediterranean Sea and neighbouring Atlantic areas and one of the most valuable of all marine species, at different depths (38-40 m versus 96-115 m) in the north-western Sardinian waters (Central-Western Mediterranean Sea). Different population structures were observed with shallow colonies smaller (in basal diameter and height) than deeper ones. Both populations were all gonochoric at polyp and colony level and fertile. The sex-ratio was balanced in the deep red corals while in the shallow ones it was signi cantly biased towards female. Deep and shallow colonies were found to have a synchronous female sexual products development in the two depth ranges investigated. C. rubrum produced large female sexual products in both depth intervals in relationship with its reproductive mode, con rming a long oogenic development. In contrast to reproductive timing, the volume occupied by female sexual products per polyp was different between the populations, being higher in the deep than in the shallow populations. C. rubrum exhibited a reproductive strategy characterized by a relative low number of female sexual products per polyp revealing signi cant differences among the two depth ranges analyzed with a lower mean value of sexual products in the shallow colonies (mean fecundity per polyp: 1.14) than in the deeper ones (mean fecundity per polyp: 2.09). These results indicate differences in reproductive parameters such as sexual products distribution and reproductive output (fecundity) which were observed between shallow and deep populations of C. rubrum, in particular within deep dwelling populations
On the statistical-mechanical meaning of the Bousso bound
The Bousso entropy bound, in its generalized form, is investigated for the
case of perfect fluids at local thermodynamic equilibrium and evidence is found
that the bound is satisfied if and only if a certain local thermodynamic
property holds, emerging when the attempt is made to apply the bound to thin
layers of matter. This property consists in the existence of an ultimate lower
limit l* to the thickness of the slices for which a statistical-mechanical
description is viable, depending l* on the thermodynamical variables which
define the state of the system locally. This limiting scale, found to be in
general much larger than the Planck scale (so that no Planck scale physics must
be necessarily invoked to justify it), appears not related to gravity and this
suggests that the generalized entropy bound is likely to be rooted on
conventional flat-spacetime statistical mechanics, with the maximum admitted
entropy being however actually determined also by gravity.
Some examples of ideal fluids are considered in order to identify the
mechanisms which can set a lower limit to the statistical-mechanical
description and these systems are found to respect the lower limiting scale l*.
The photon gas, in particular, appears to seemingly saturate this limiting
scale and the consequence is drawn that for systems consisting of a single
slice of a photon gas with thickness l*, the generalized Bousso bound is
saturated. It is argued that this seems to open the way to a peculiar
understanding of black hole entropy: if an entropy can meaningfully (i.e. with
a second law) be assigned to a black hole, the value A/4 for it (where A is the
area of the black hole) is required simply by (conventional) statistical
mechanics coupled to general relativity.Comment: 6 pages. Some editing and the addition of a reference. This version,
ideally corresponding to the published one, contains 4 corrections to it,
with two of them (p.3, line 19 and p.6, line 10 of this version) with
semantic relevanc
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