871 research outputs found
Gallavotti-Cohen theorem, Chaotic Hypothesis and the zero-noise limit
The Fluctuation Relation for a stationary state, kept at constant energy by a
deterministic thermostat - the Gallavotti-Cohen Theorem -- relies on the
ergodic properties of the system considered. We show that when perturbed by an
energy-conserving random noise, the relation follows trivially for any system
at finite noise amplitude. The time needed to achieve stationarity may stay
finite as the noise tends to zero, or it may diverge. In the former case the
Gallavotti-Cohen result is recovered, while in the latter case, the crossover
time may be computed from the action of `instanton' orbits that bridge
attractors and repellors. We suggest that the `Chaotic Hypothesis' of
Gallavotti can thus be reformulated as a matter of stochastic stability of the
measure in trajectory space. In this form this hypothesis may be directly
tested
A Non-Associative Deformation of Yang-Mills Gauge Theory
An ansatz is presented for a possible non-associative deformation of the
standard Yang-Mills type gauge theories. An explicit algebraic structure for
the deformed gauge symmetry is put forward and the resulting gauge theory
developed. The non-associative deformation is constructed in such a way that an
apparently associative Lie algebraic structure is retained modulo a closure
problem for the generators. It is this failure to close which leads to new
physics in the model as manifest in the gauge field kinetic term in the
resulting Lagrangian. A possible connection between this model and quantum
group gauge theories is also investigated.Comment: 18 pages, RevTeX, also uses aps.st
Magnetic Charge in a Nonassociative Field Theory
The violation of the Jacobi identity by the presence of magnetic charge is
accomodated by using an explicitly nonassociative theory of octonionic fields.
It is found that the dynamics of this theory is simplified if the Lagrangian
contains only dyonic charges, but certain problems in the constrained
quantisation remain. The extension of these concepts to string theory may
however resolve these difficulties.Comment: 10 pages, REVTeX, no figure
TGFÎČ inhibition stimulates collagen maturation to enhance bone repair and fracture resistance in a murine myeloma model
Multiple myeloma is a plasma cell malignancy that causes debilitating bone disease and fractures, in which TGFÎČ plays a central role. Current treatments do not repair existing damage and fractures remain a common occurrence. We developed a novel low tumour phase murine model mimicking the plateau phase in patients, as we hypothesized this would be an ideal time to treat with a bone anabolic. Using in vivo microCT we show substantial and rapid bone lesion repair (and prevention) driven by SDâ208 (TGFÎČ receptor I kinase inhibitor) and chemotherapy (bortezomib and lenalidomide) in mice with human U266âGFPâluc myeloma. We discovered that lesion repair occurred via an intramembranous fracture repairâlike mechanism and that SDâ208 enhanced collagen matrix maturation to significantly improve fracture resistance. Lesion healing was associated with VEGFA expression in woven bone, reduced osteocyteâderived PTHrP, increased osteoblasts, decreased osteoclasts and lower serum TRACPâ5b. SDâ208 also completely prevented bone lesion development mice with aggressive JJN3 tumors, and was more effective than an antiâTGFÎČ neutralizing antibody (1D11). We also discovered that SDâ208 promoted osteoblastic differentiation (and overcame the TGFÎČâinduced block in osteoblastogenesis) in myeloma patient bone marrow stromal cells in vitro, comparable to normal donors. The improved bone quality and fractureâresistance with SDâ208 provides incentive for clinical translation to improve myeloma patient quality of life by reducing fracture risk and fatality
Drag and jet quenching of heavy quarks in a strongly coupled N=2* plasma
The drag of a heavy quark and the jet quenching parameter are studied in the
strongly coupled N=2* plasma using the AdS/CFT correspondence. Both increase in
units of the spatial string tension as the theory departs from conformal
invariance. The description of heavy quark dynamics using a Langevin equation
is also considered. It is found that the difference between the velocity
dependent factors of the transverse and longitudinal momentum broadening of the
quark admit an interpretation in terms of relativistic effects, so the
distribution is spherical in the quark rest frame. When conformal invariance is
broken there is a broadening of the longitudinal momentum distribution. This
effect may be useful in understanding the jet distribution observed in
experiments.Comment: 30 pages, 5 figures, references added, minor corrections. To be
published in JHE
Modeling phase behavior for quantifying micro-pervaporation experiments
We present a theoretical model for the evolution of mixture concentrations in
a micro-pervaporation device, similar to those recently presented
experimentally. The described device makes use of the pervaporation of water
through a thin PDMS membrane to build up a solute concentration profile inside
a long microfluidic channel. We simplify the evolution of this profile in
binary mixtures to a one-dimensional model which comprises two
concentration-dependent coefficients. The model then provides a link between
directly accessible experimental observations, such as the widths of dense
phases or their growth velocity, and the underlying chemical potentials and
phenomenological coefficients. It shall thus be useful for quantifying the
thermodynamic and dynamic properties of dilute and dense binary mixtures.Comment: to be published in EPJ-
Is weak temperature dependence of electron dephasing possible?
The first-principle theory of electron dephasing by disorder-induced two
state fluctuators is developed. There exist two mechanisms of dephasing. First,
dephasing occurs due to direct transitions between the defect levels caused by
inelastic electron-defect scattering. The second mechanism is due to violation
of the time reversal symmetry caused by time-dependent fluctuations of the
scattering potential. These fluctuations originate from an interaction between
the dynamic defects and conduction electrons forming a thermal bath. The first
contribution to the dephasing rate saturates as temperature decreases. The
second contribution does not saturate, although its temperature dependence is
rather weak, . The quantitative estimates based on the
experimental data show that these mechanisms considered can explain the weak
temperature dependence of the dephasing rate in some temperature interval.
However, below some temperature dependent on the model of dynamic defects the
dephasing rate tends rapidly to zero. The relation to earlier studies of the
dephasing caused by the dynamical defects is discussed.Comment: 14 pages, 6 figures, submitted to PR
Generalized empty-interval method applied to a class of one-dimensional stochastic models
In this work we study, on a finite and periodic lattice, a class of
one-dimensional (bimolecular and single-species) reaction-diffusion models
which cannot be mapped onto free-fermion models.
We extend the conventional empty-interval method, also called
{\it interparticle distribution function} (IPDF) method, by introducing a
string function, which is simply related to relevant physical quantities.
As an illustration, we specifically consider a model which cannot be solved
directly by the conventional IPDF method and which can be viewed as a
generalization of the {\it voter} model and/or as an {\it epidemic} model. We
also consider the {\it reversible} diffusion-coagulation model with input of
particles and determine other reaction-diffusion models which can be mapped
onto the latter via suitable {\it similarity transformations}.
Finally we study the problem of the propagation of a wave-front from an
inhomogeneous initial configuration and note that the mean-field scenario
predicted by Fisher's equation is not valid for the one-dimensional
(microscopic) models under consideration.Comment: 19 pages, no figure. To appear in Physical Review E (November 2001
Exact Hypersurface-Homogeneous Solutions in Cosmology and Astrophysics
A framework is introduced which explains the existence and similarities of
most exact solutions of the Einstein equations with a wide range of sources for
the class of hypersurface-homogeneous spacetimes which admit a Hamiltonian
formulation. This class includes the spatially homogeneous cosmological models
and the astrophysically interesting static spherically symmetric models as well
as the stationary cylindrically symmetric models. The framework involves
methods for finding and exploiting hidden symmetries and invariant submanifolds
of the Hamiltonian formulation of the field equations. It unifies, simplifies
and extends most known work on hypersurface-homogeneous exact solutions. It is
shown that the same framework is also relevant to gravitational theories with a
similar structure, like Brans-Dicke or higher-dimensional theories.Comment: 41 pages, REVTEX/LaTeX 2.09 file (don't use LaTeX2e !!!) Accepted for
publication in Phys. Rev.
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