376 research outputs found
Relativistic linear stability equations for the nonlinear Dirac equation in Bose-Einstein condensates
We present relativistic linear stability equations (RLSE) for
quasi-relativistic cold atoms in a honeycomb optical lattice. These equations
are derived from first principles and provide a method for computing
stabilities of arbitrary localized solutions of the nonlinear Dirac equation
(NLDE), a relativistic generalization of the nonlinear Schr\"odinger equation.
We present a variety of such localized solutions: skyrmions, solitons,
vortices, and half-quantum vortices, and study their stabilities via the RLSE.
When applied to a uniform background, our calculations reveal an experimentally
observable effect in the form of Cherenkov radiation. Remarkably, the Berry
phase from the bipartite structure of the honeycomb lattice induces a
boson-fermion transmutation in the quasi-particle operator statistics.Comment: 6 pages, 3 figure
Bogoliubov-Cerenkov radiation in a Bose-Einstein condensate flowing against an obstacle
We study the density modulation that appears in a Bose-Einstein condensate
flowing with supersonic velocity against an obstacle. The experimental density
profiles observed at JILA are reproduced by a numerical integration of the
Gross-Pitaevskii equation and then interpreted in terms of Cerenkov emission of
Bogoliubov excitations by the defect. The phonon and the single-particle
regions of the Bogoliubov spectrum are respectively responsible for a conical
wavefront and a fan-shaped series of precursors
Finite temperature Cherenkov radiation in the presence of a magnetodielectric medium
A canonical approach to Cherenkov radiation in the presence of a
magnetodielectric medium is presented in classical, nonrelativistic and
relativistic quantum regimes. The equations of motion for the canonical
variables are solved explicitly for both positive and negative times. Maxwell
and related constitute equations are obtained. In the large-time limit, the
vector potential operator is found and expressed in terms of the medium
operators. The energy loss of a charged particle, emitted in the form of
radiation, in finite temperature is calculated. A Dirac equation concerning the
relativistic motion of the particle in presence of the magnetodielectric medium
is derived and the relativistic Cherenkov radiation at zero and finite
temperature is investigated. Finally, it is shown that the Cherenkov radiation
in nonrelativistic and relativistic quantum regimes, unlike its classical
counterpart, introduces automatically a cutoff for higher frequencies beyond
which the power of radiation emission is zero.Comment: To be appear in PR
Self-amplified Cherenkov radiation from a relativistic electron in a waveguide partially filled with a laminated material
The radiation from a relativistic electron uniformly moving along the axis of
cylindrical waveguide filled with laminated material of finite length is
investigated. Expressions for the spectral distribution of radiation passing
throw the transverse section of waveguide at large distances from the laminated
material are derived with no limitations on the amplitude and variation profile
of the layered medium permittivity and permeability. Numerical results for
layered material consisting of dielectric plates alternated with vacuum gaps
are given. It is shown that at a special choice of problem parameters,
Cherenkov radiation generated by the relativistic electron inside the plates is
self-amplified. The visual explanation of this effect is given and a possible
application is discussed.Comment: 8 pages, 4 figures,1 table, the paper is accepted for publication in
the Journal of Physics: Conference Serie
Observation of Resonant Diffusive Radiation in Random Multilayered Systems
Diffusive Radiation is a new type of radiation predicted to occur in randomly
inhomogeneous media due to the multiple scattering of pseudophotons. This
theoretical effect is now observed experimentally. The radiation is generated
by the passage of electrons of energy 200KeV-2.2MeV through a random stack of
films in the visible light region. The radiation intensity increases resonantly
provided the Cherenkov condition is satisfied for the average dielectric
constant of the medium. The observed angular dependence and electron resonance
energy are in agreement with the theoretical predictions. These observations
open a road to application of diffusive radiation in particle detection,
astrophysics, soft X-ray generation and etc.. `Comment: 4pages, 4figure
Slow group velocity and Cherenkov radiation
We theoretically study the effect of ultraslow group velocities on the
emission of Vavilov-Cherenkov radiation in a coherently driven medium. We show
that in this case the aperture of the group cone on which the intensity of the
radiation peaks is much smaller than that of the usual wave cone associated
with the Cherenkov coherence condition. We show that such a singular behaviour
may be observed in a coherently driven ultracold atomic gas.Comment: 4 pages, 4 figure
Unexpected prolonged presentation of influenza antigens promotes CD4 T cell memory generation
The kinetics of presentation of influenza virus–derived antigens (Ags), resulting in CD4 T cell effector and memory generation, remains undefined. Naive influenza-specific CD4 T cells were transferred into mice at various times after influenza infection to determine the duration and impact of virus-derived Ag presentation. Ag-specific T cell responses were generated even when the donor T cells were transferred 3–4 wk after viral clearance. Transfer of naive CD4 T cells during early phases of infection resulted in a robust expansion of highly differentiated effectors, which then contracted to a small number of memory T cells. Importantly, T cell transfer during later phases of infection resulted in a modest expansion of effectors with intermediate phenotypes, which were capable of persisting as memory with high efficiency. Thus, distinct stages of pathogen-derived Ag presentation may provide a mechanism by which T cell heterogeneity is generated and diverse memory subsets are maintained
Formation of hard VHE gamma-ray spectra of blazars due to internal photon-photon absorption
The energy spectra of TeV gamma-rays from blazars, after being corrected for
intergalatic absorption in the Extragalactic Background Light (EBL), appear
unusually hard, a fact that poses challenges to the conventional models of
particle acceleration in TeV blazars and/or to the EBL models. In this paper we
show that the internal absorption of gamma-rays caused by interactions with
dense narrow-band radiation fields in the vicinity of compact gamma-ray
production regions can lead to the formation of gamma-ray spectra of an almost
arbitrary hardness. This allows significant relaxation of the current tight
constraints on particle acceleration and radiation models, although at the
expense of enhanced requirements to the available nonthermal energy budget. The
latter, however, is not a critical issue, as long as it can be largely
compensated by the Doppler boosting, assuming very large () Doppler
factors of the relativistically moving gamma-ray production regions. The
suggested scenario of formation of hard gamma-ray spectra predicts detectable
synchrotron radiation of secondary electron-positron pairs which might require
a revision of the current ``standard paradigm'' of spectral energy
distributions of gamma-ray blazars. If the primary gamma-rays are of hadronic
origin related to or interactions, the ``internal gamma-ray
absorption'' model predicts neutrino fluxes close to the detection threshold of
the next generation high energy neutrino detectors.Comment: 10 pages, 8 figures, submitted to MNRA
Effects of rater priming and incentives on rating accuracy
We investigated the effects of two manipulations - incentives and rater priming - on performance appraisal accuracy. In contrast with previous studies, our results did not support the hypotheses that priming and incentives would improve Cronbach’s (1955) differential accuracy, a type of accuracy that is most relevant to employee feedback
Characterization of neutrino signals with radiopulses in dense media through the LPM effect
We discuss the possibilities of detecting radio pulses from high energy
showers in ice, such as those produced by PeV and EeV neutrino interactions. It
is shown that the rich radiation pattern structure in the 100 MHz to few GHz
allows the separation of electromagnetic showers induced by photons or
electrons above 100 PeV from those induced by hadrons. This opens up the
possibility of measuring the energy fraction transmitted to the electron in a
charged current electron neutrino interaction with adequate sampling of the
angular distribution of the signal. The radio technique has the potential to
complement conventional high energy neutrino detectors with flavor information.Comment: 5 pages, 4 ps figures. Submitted to Phys. Rev. Let
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