11,271 research outputs found
Parametric instability in dark molecular clouds
The present work investigates the parametric instability of parallel
propagating circularly polarized Alfven(pump) waves in a weakly ionized
molecular cloud. It is shown that the relative drift between the plasma
particles gives rise to the Hall effect resulting in the modified pump wave
characteristics. Although the linearized fluid equations with periodic
coefficients are difficult to solve analytically, it is shown that a linear
transformation can remove the periodic dependence. The resulting linearized
equations with constant coefficients are used to derive an algebraic dispersion
relation. The growth rate of the parametric instability is a sensitive function
of the amplitude of the pump wave as well as to the ratio of the pump and the
modified dust-cyclotron frequencies. The instability is insensitive to the
plasma-beta The results are applied to the molecular clouds.Comment: 27 page, 5 figures, accepted in Ap
The repulsion between localization centers in the Anderson model
In this note we show that, a simple combination of deep results in the theory
of random Schr\"odinger operators yields a quantitative estimate of the fact
that the localization centers become far apart, as corresponding energies are
close together
Generalized kinetic equations for charge carriers in graphene
A system of generalized kinetic equations for the distribution functions of
two-dimensional Dirac fermions scattered by impurities is derived in the Born
approximation with respect to short-range impurity potential. It is proven that
the conductivity following from classical Boltzmann equation picture, where
electrons or holes have scattering amplitude reduced due chirality, is
justified except for an exponentially narrow range of chemical potential near
the conical point. When in this range, creation of infinite number of
electron-hole pairs related to quasi-relativistic nature of electrons in
graphene results in a renormalization of minimal conductivity as compared to
the Boltzmann term and logarithmic corrections in the conductivity similar to
the Kondo effect.Comment: final version, Phys. Rev. B, accepte
Light Baryon Resonances: Restrictions and Perspectives
The problem of nucleon resonances N' with masses below the Delta is
considered. We derive bounds for the properties of such states. Some of these
are new, while others improve upon existing limits. We discuss the nature of N'
states, and their unitary partners, assuming their existence can be verified.Comment: 11 pages, 11 figur
Supermassive Black Holes and Galaxy Formation
The formation of supermassive black holes (SMBH) is intimately related to
galaxy formation, although precisely how remains a mystery. I speculate that
formation of, and feedback from, SMBH may alleviate problems that have arisen
in our understanding of the cores of dark halos of galaxies.Comment: Talk at conference on Matter in the Universe, March 2001, ISSI Ber
Gauge Problem in the Gravitational Self-Force II. First Post Newtonian Force under Regge-Wheeler Gauge
We discuss the gravitational self-force on a particle in a black hole
space-time. For a point particle, the full (bare) self-force diverges. It is
known that the metric perturbation induced by a particle can be divided into
two parts, the direct part (or the S part) and the tail part (or the R part),
in the harmonic gauge, and the regularized self-force is derived from the R
part which is regular and satisfies the source-free perturbed Einstein
equations. In this paper, we consider a gauge transformation from the harmonic
gauge to the Regge-Wheeler gauge in which the full metric perturbation can be
calculated, and present a method to derive the regularized self-force for a
particle in circular orbit around a Schwarzschild black hole in the
Regge-Wheeler gauge. As a first application of this method, we then calculate
the self-force to first post-Newtonian order. We find the correction to the
total mass of the system due to the presence of the particle is correctly
reproduced in the force at the Newtonian order.Comment: Revtex4, 43 pages, no figure. Version to be published in PR
Multi-Zone Shell Model for Turbulent Wall Bounded Flows
We suggested a \emph{Multi-Zone Shell} (MZS) model for wall-bounded flows
accounting for the space inhomogeneity in a "piecewise approximation", in which
cross-section area of the flow, , is subdivided into "-zones". The area
of the first zone, responsible for the core of the flow, , and
areas of the next -zones, , decrease towards the wall like . In each -zone the statistics of turbulence is assumed to be space
homogeneous and is described by the set of "shell velocities" for
turbulent fluctuations of the scale . The MZS-model includes a
new set of complex variables, , , describing the
amplitudes of the near wall coherent structures of the scale
and responsible for the mean velocity profile. Suggested MZS-equations of
motion for and preserve the actual conservations laws
(energy, mechanical and angular momenta), respect the existing symmetries
(including Galilean and scale invariance) and account for the type of the
non-linearity in the Navier-Stokes equation, dimensional reasoning, etc. The
MZS-model qualitatively describes important characteristics of the wall bounded
turbulence, e.g., evolution of the mean velocity profile with increasing
Reynolds number, \RE, from the laminar profile towards the universal
logarithmic profile near the flat-plane boundary layer as \RE\to \infty.Comment: 27 pages, 17 figs, included, PRE, submitte
Multiscale theory of turbulence in wavelet representation
We present a multiscale description of hydrodynamic turbulence in
incompressible fluid based on a continuous wavelet transform (CWT) and a
stochastic hydrodynamics formalism. Defining the stirring random force by the
correlation function of its wavelet components, we achieve the cancellation of
loop divergences in the stochastic perturbation expansion. An extra
contribution to the energy transfer from large to smaller scales is considered.
It is shown that the Kolmogorov hypotheses are naturally reformulated in
multiscale formalism. The multiscale perturbation theory and statistical
closures based on the wavelet decomposition are constructed.Comment: LaTeX, 27 pages, 3 eps figure
Pseudoaneurysm of a branch of the femoral circumflex artery as a complication of revision arthroscopic release of the iliopsoas tendon
Treatment of painful internal snapping hip via arthroscopic release of the iliopsoas tendon is becoming the preferred option over open techniques because of the benefits of minimal dissection and fewer complications. However, complications do occur with arthroscopic techniques as well. We present the case of a 33-year-old woman who presented with painful internal snapping of her right hip and underwent arthroscopic release of the iliopsoas tendon. Following the procedure she continued to complain of pain in her groin and was therefore investigated further with a magnetic resonance imaging (MRI) which revealed a swelling near the femoral circumflex vessels. A computed tomography (CT) angiogram revealed a 15 mm pseudoaneurysm of the femoral circumflex artery, which was successfully treated by selective catheterisation and embolisation. Hip arthroscopists should be sufficiently familiar with the vascular anatomy around the hip and keep this complication in mind when releasing the iliopsoas tendon arthroscopically especially in revision cases with adhesions
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