2,306 research outputs found
Two-stream instability in quasi-one-dimensional Bose-Einstein condensates
We apply a kinetic model to predict the existence of an instability mechanism in elongated Bose-Einstein condensates. Our kinetic description, based on the Wigner formalism, is employed to highlight the existence of unstable Bogoliubov waves that may be excited in the counterpropagation configuration. We identify a dimensionless parameter, the Mach number at T=0, that tunes different regimes of stability. We also estimate the magnitude of the main parameters at which two-stream instability is expected to be observed under typical experimental conditions
Eosinophilic fasciitis (Shulman's disease): review and comparative evaluation of seven patients.
OBJECTIVES:
Eosinophilic fasciitis (EF) was described in 1974 by Shulman as a rare fibrosing connective tissue disease of unknown etiology. An undetermined trigger is thought to lead to the degranulation of eosinophils that interact with fibroblasts and express fibrogenic cytokines including the transforming factor of tumor growth a and b and interleukins 1 and 6. The purpose of this study was to summarize seven cases of EF in a central hospital.
MATERIAL AND METHODS:
This was a retrospective and descriptive study of a population with EF of a central hospital. All patients diagnosed with EF in a hospital unit were admitted to the study between January 1, 2005, and April 30, 2018.
RESULTS:
A total of seven patients diagnosed with EF were analyzed. The median age of the population at the time of diagnosis was 56 years, and 57% of the patients were women. All patients had elevated peripheral eosinophilia and sedimentation rate, and only one patient had hypergammaglobulinemia. All patients had edema and cutaneous thickening of the limbs, 57% had constitutional symptoms, and 57% had inflammatory arthritis with joint contracture. Prednisolone (PDN) therapy was initiated in all patients, and only in two was the association of PDN with methotrexate (MTX) initially performed. In one patient triple therapy of PDN, MTX, and cyclosporine was required. At the time of this publication, only one patient maintains active disease, and tocilizumab has been initiated.
CONCLUSIONS:
Recent studies show a more favorable response from the combination of PDN and MTX than from PDN alone. Considering the rarity of the disease, more long-term studies are needed regarding the etiopathogenetics, progression, recurrence of EF, and new effective therapies.info:eu-repo/semantics/publishedVersio
Modulational instability of spatially broadband nonlinear optical pulses in four-state atomic systems
The modulational instability of broadband optical pulses in a four-state
atomic system is investigated. In particular, starting from a recently derived
generalized nonlinear Schr\"odinger equation, a wave-kinetic equation is
derived. A comparison between coherent and random phase wave states is made. It
is found that the spatial spectral broadening can contribute to the nonlinear
stability of ultra-short optical pulses. In practical terms, this could be
achieved by using random phase plate techniques.Comment: 9 pages, 3 figures, to appear in Phys. Rev.
Cascaded Nondegenerate Four-Wave Mixing Technique for High-Power Single-Cycle Pulse Synthesis in the Visible and Ultraviolet Ranges
We present a new technique to synthesize high-power single-cycle pulses in
the visible and ultraviolet ranges by coherent superposition of a multiband
octave-spanning spectrum obtained by highly-nondegenerate cascaded four-wave
mixing of femtosecond pulses in bulk isotropic nonresonant media. The
generation of coherent spectra spanning over two octaves in bandwidth is
experimentally demonstrated using a thin fused silica slide. Full
characterization of the intervening multicolored fields using
frequency-resolved optical gating, where multiple cascaded orders have been
measured simultaneously for the first time, supports the possibility of direct
synthesis of near-single-cycle 2.2 fs visible-UV pulses without recurring to
complex amplitude or phase control, which should enable many applications in
science and technology.Comment: 13 pages, 4 figures. Submitted to Physical Review
A new approach to the Sachs-Wolfe effect
We present a new approach to the Sachs-Wolfe effect, which is based on the
dynamics of photons in a space and time varying gravitational field. We
consider the influence of plasma dispersion effects on photon propagation, and
establish the limits of validity of the usual results of the standard
cosmological approach, for the large scale temperature anisotropies of the
cosmic microwave background. New dynamical contributions to the integrated
Sachs-Wolfe effect are also discussed.Comment: 5 page
A new approach to the Sachs-Wolfe effect
We present a new approach to the Sachs-Wolfe effect, which is based on the
dynamics of photons in a space and time varying gravitational field. We
consider the influence of plasma dispersion effects on photon propagation, and
establish the limits of validity of the usual results of the standard
cosmological approach, for the large scale temperature anisotropies of the
cosmic microwave background. New dynamical contributions to the integrated
Sachs-Wolfe effect are also discussed.Comment: 5 page
A phonon laser in ultra-cold matter
We show the possible excitation of a phonon laser instability in an
ultra-cold atomic gas confined in a magneto-optical trap. Such an effect
results from a negative Landau damping of the collective density perturbations
in the gas, leading to the coherent emission of phonons. This laser instability
can be driven by a blue-detuned laser superimposed to the usual red-detuning
laser beams which usually provide the cooling mechanism. Threshold conditions,
instability growth rates and saturation levels are derived. This work
generalizes, on theoretical grounds, the recent results obtained with single
ion phonon laser, to an ultra-cold atomic gas, where real phonons can be
excited. Future phonon lasers could thus adequately be called phasers.Comment: 4 pages, submitted to PR
Entanglement versus Quantum Discord in Two Coupled Double Quantum Dots
We study the dynamics of quantum correlations of two coupled double quantum
dots containing two excess electrons. The dissipation is included through the
contact with an oscillator bath. We solve the Redfield master equation in order
to determine the dynamics of the quantum discord and the entanglement of
formation. Based on our results, we find that the quantum discord is more
resistant to dissipation than the entanglement of formation for such a system.
We observe that this characteristic is related to whether the oscillator bath
is common to both qubits or not and to the form of the interaction Hamiltonian.
Moreover, our results show that the quantum discord might be finite even for
higher temperatures in the asymptotic limit.Comment: 14 pages, 8 figures (new version is the final version to appear in
NJP
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