12,753 research outputs found
Single chain elasticity and thermoelasticity of polyethylene
Single-chain elasticity of polyethylene at point up to 90% of
stretching with respect to its contour length is computed by Monte-Carlo
simulation of an atomistic model in continuous space. The elasticity law
together with the free-energy and the internal energy variations with
stretching are found to be very well represented by the wormlike chain model up
to 65% of the chain elongation, provided the persistence length is treated as a
temperature dependent parameter. Beyond this value of elongation simple ideal
chain models are not able to describe the Monte Carlo data in a thermodynamic
consistent way. This study reinforces the use of the wormlike chain model to
interpret experimental data on the elasticity of synthetic polymers in the
finite extensibility regime, provided the chain is not yet in its fully
stretched regime. Specific solvent effects on the elasticity law and the
partition between energetic and entropic contributions to single chain
elasticity are investigated.Comment: 32 pages with 5 figures included. Accepted as a regular paper on The
Journal of Chemical Physics, August 2002. This article may be downloaded for
personal use only. Any other use requires prior permission of the author and
the American Institute of Physic
First Double-Chooz Results and the Reactor Antineutrino Anomaly
We investigate the possible effects of short-baseline antinu_e disappearance
implied by the reactor antineutrino anomaly on the Double-Chooz determination
of theta_{13} through the normalization of the initial antineutrino flux with
the Bugey-4 measurement. We show that the effects are negligible and the value
of theta_{13} obtained by the Double-Chooz collaboration is accurate only if
Delta m^2_{41} is larger than about 3 eV^2. For smaller values of Delta
m^2_{41} the short-baseline oscillations are not fully averaged at Bugey-4 and
the uncertainties due to the reactor antineutrino anomaly can be of the same
order of magnitude of the intrinsic Double-Chooz uncertainties.Comment: 4 page
Physical effects of the Immirzi parameter
The Immirzi parameter is a constant appearing in the general relativity
action used as a starting point for the loop quantization of gravity. The
parameter is commonly believed not to show up in the equations of motion,
because it appears in front of a term in the action that vanishes on shell. We
show that in the presence of fermions, instead, the Immirzi term in the action
does not vanish on shell, and the Immirzi parameter does appear in the
equations of motion. It determines the coupling constant of a four-fermion
interaction. Therefore the Immirzi parameter leads to effects that are
observable in principle, even independently from nonperturbative quantum
gravity.Comment: 3 pages. Substantial revision from the first versio
Emergent Quantum Mechanics and Emergent Symmetries
Quantum mechanics is 'emergent' if a statistical treatment of large scale
phenomena in a locally deterministic theory requires the use of quantum
operators. These quantum operators may allow for symmetry transformations that
are not present in the underlying deterministic system. Such theories allow for
a natural explanation of the existence of gauge equivalence classes (gauge
orbits), including the equivalence classes generated by general coordinate
transformations. Thus, local gauge symmetries and general coordinate invariance
could be emergent symmetries, and this might lead to new alleys towards
understanding the flatness problem of the Universe.Comment: 10 pages, 1 figure. Presented at PASCOS 13, Imperial College, London,
July 6, 200
Public Libraries and the Internet 2006
Examines the capability of public libraries to provide and sustain public access Internet services and resources that meet community needs, including serving as the first choice for content, resources, services, and technology infrastructure
Monolithic zirconia and digital impression: case report
The aim of this study is to present a clinical case of a full arch prosthetic rehabilitation on natural teeth, combining both digital work-flow and monolithic zirconi
On approximate solutions of semilinear evolution equations II. Generalizations, and applications to Navier-Stokes equations
In our previous paper [12] (Rev. Math. Phys. 16, 383-420 (2004)), a general
framework was outlined to treat the approximate solutions of semilinear
evolution equations; more precisely, a scheme was presented to infer from an
approximate solution the existence (local or global in time) of an exact
solution, and to estimate their distance. In the first half of the present work
the abstract framework of \cite{uno} is extended, so as to be applicable to
evolutionary PDEs whose nonlinearities contain derivatives in the space
variables. In the second half of the paper this extended framework is applied
to theincompressible Navier-Stokes equations, on a torus T^d of any dimension.
In this way a number of results are obtained in the setting of the Sobolev
spaces H^n(T^d), choosing the approximate solutions in a number of different
ways. With the simplest choices we recover local existence of the exact
solution for arbitrary data and external forces, as well as global existence
for small data and forces. With the supplementary assumption of exponential
decay in time for the forces, the same decay law is derived for the exact
solution with small (zero mean) data and forces. The interval of existence for
arbitrary data, the upper bounds on data and forces for global existence, and
all estimates on the exponential decay of the exact solution are derived in a
fully quantitative way (i.e., giving the values of all the necessary constants;
this makes a difference with most of the previous literature). Nextly, the
Galerkin approximate solutions are considered and precise, still quantitative
estimates are derived for their H^n distance from the exact solution; these are
global in time for small data and forces (with exponential time decay of the
above distance, if the forces decay similarly).Comment: LaTeX, 84 pages. The final version published in Reviews in
Mathematical Physic
Quantum Monte Carlo Simulation of the High-Pressure Molecular-Atomic Crossover in Fluid Hydrogen
A first-order liquid-liquid phase transition in high-pressure hydrogen
between molecular and atomic fluid phases has been predicted in computer
simulations using ab initio molecular dynamics approaches. However, experiments
indicate that molecular dissociation may occur through a continuous crossover
rather than a first-order transition. Here we study the nature of molecular
dissociation in fluid hydrogen using an alternative simulation technique in
which electronic correlation is computed within quantum Monte Carlo, the
so-called Coupled Electron Ion Monte Carlo (CEIMC) method. We find no evidence
for a first-order liquid-liquid phase transition.Comment: 4 pages, 5 figures; content changed; accepted for publication in
Phys. Rev. Let
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