14,579 research outputs found
Computation of topside ionograms from N/h/ profiles
Computation of topside ionograms from electron concentration profile
Vibronic interactions in the visible and near-infrared spectra of C60− anions
Electron-phonon coupling is an important factor in understanding many properties of the C60 fullerides. However, there has been little success in quantifying the strength of the vibronic coupling in C60 ions, with considerable disagreement between experimental and theoretical results. We will show that neglect of quadratic coupling in previous models for C60- ions results in a significant overestimate of the linear coupling constants. Including quadratic coupling allows a coherent interpretation to be made of earlier experimental and theoretical results which at first sight are incompatible
The Rayleigh-Brillouin Spectrum in Special Relativistic Hydrodynamics
In this paper we calculate the Rayleigh-Brillouin spectrum for a relativistic
simple fluid according to three different versions available for a relativistic
approach to non-equilibrium thermodynamics. An outcome of these calculations is
that Eckart's version predicts that such spectrum does not exist. This provides
an argument to question its validity. The remaining two results, which differ
one from another, do provide a finite form for such spectrum. This raises the
rather intriguing question as to which of the two theories is a better
candidate to be taken as a possible version of relativistic non-equilibrium
thermodynamics. The answer will clearly require deeper examination of this
problem.Comment: 13 pages, no figures. Accepted for publication in Phys. Rev.
Gamma-ray emission from dark matter wakes of recoiled black holes
A new scenario for the emission of high-energy gamma-rays from dark matter
annihilation around massive black holes is presented. A black hole can leave
its parent halo, by means of gravitational radiation recoil, in a merger event
or in the asymmetric collapse of its progenitor star. A recoiled black hole
which moves on an almost-radial orbit outside the virial radius of its central
halo, in the cold dark matter background, reaches its apapsis in a finite time.
Near or at the apapsis passage, a high-density wake extending over a large
radius of influence, forms around the black hole. It is shown that significant
gamma-ray emission can result from the enhancement of neutralino annihilation
in these wakes. At its apapsis passage, a black hole is shown to produce a
flash of high-energy gamma-rays whose duration is determined by the mass of the
black hole and the redshift at which it is ejected. The ensemble of such black
holes in the Hubble volume is shown to produce a diffuse high-energy gamma-ray
background whose magnitude is compared to the diffuse emission from dark matter
haloes alone.Comment: version to appear in Astrophysical Journal letters (labels on Fig. 3
corrected
Derivation of the Zakharov equations
This paper continues the study of the validity of the Zakharov model
describing Langmuir turbulence. We give an existence theorem for a class of
singular quasilinear equations. This theorem is valid for well-prepared initial
data. We apply this result to the Euler-Maxwell equations describing
laser-plasma interactions, to obtain, in a high-frequency limit, an asymptotic
estimate that describes solutions of the Euler-Maxwell equations in terms of
WKB approximate solutions which leading terms are solutions of the Zakharov
equations. Because of transparency properties of the Euler-Maxwell equations,
this study is led in a supercritical (highly nonlinear) regime. In such a
regime, resonances between plasma waves, electromagnetric waves and acoustic
waves could create instabilities in small time. The key of this work is the
control of these resonances. The proof involves the techniques of geometric
optics of Joly, M\'etivier and Rauch, recent results of Lannes on norms of
pseudodifferential operators, and a semiclassical, paradifferential calculus
- …