173,015 research outputs found
Jet conversions in a quark-gluon plasma
Quark and gluon jets traversing through a quark-gluon plasma not only lose
their energies but also can undergo flavor conversions. The conversion rates
via the elastic and the inelastic scatterings are evaluated in the lowest order in QCD.
Including both jet energy loss and conversions in the expanding quark-gluon
plasma produced in relativistic heavy ion collisions, we have found a net
conversion of quark to gluon jets. This reduces the difference between the
nuclear modification factors for quark and gluon jets in central heavy ion
collisions and thus enhances the and ratios at high
transverse momentum. However, a much larger net quark to gluon jet conversion
rate than the one given by the lowest-order QCD is needed to account for the
observed similar ratios in central Au+Au and p+p collisions at same energy.
Implications of our results are discussed.Comment: version to appear in PR
Helium star evolutionary channel to super-Chandrasekhar mass type Ia supernovae
Recent discovery of several overluminous type Ia supernovae (SNe Ia)
indicates that the explosive masses of white dwarfs may significantly exceed
the canonical Chandrasekhar mass limit. Rapid differential rotation may support
these massive white dwarfs. Based on the single-degenerate scenario, and
assuming that the white dwarfs would differentially rotate when the accretion
rate , employing Eggleton's
stellar evolution code we have performed the numerical calculations for
1000 binary systems consisting of a He star and a CO white dwarf (WD). We
present the initial parameters in the orbital period - helium star mass plane
(for WD masses of and , respectively), which
lead to super-Chandrasekhar mass SNe Ia. Our results indicate that, for an
initial massive WD of , a large number of SNe Ia may result from
super-Chandrasekhar mass WDs, and the highest mass of the WD at the moment of
SNe Ia explosion is 1.81 , but very massive () WDs
cannot be formed. However, when the initial mass of WDs is , the
explosive masses of SNe Ia are nearly uniform, which is consistent with the
rareness of super-Chandrasekhar mass SNe Ia in observations.Comment: 6 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Strain-mediated metal-insulator transition in epitaxial ultra-thin films of NdNiO3
We have synthesized epitaxial NdNiO ultra-thin films in a
layer-by-layer growth mode under tensile and compressive strain on SrTiO
(001) and LaAlO (001), respectively. A combination of X-ray diffraction,
temperature dependent resistivity, and soft X-ray absorption spectroscopy has
been applied to elucidate electronic and structural properties of the samples.
In contrast to the bulk NdNiO, the metal-insulator transition under
compressive strain is found to be completely quenched, while the transition
remains under the tensile strain albeit modified from the bulk behavior.Comment: 4 pages, 4 figure
Entropy of the FRW universe based on the generalized uncertainty principle
The statistical entropy of the FRW universe described by time-dependent
metric is newly calculated using the brick wall method based on the general
uncertainty principle with the minimal length. We can determine the minimal
length with the Plank scale to obtain the entropy proportional to the area of
the cosmological apparent horizon.Comment: 10 pages, accepted in Modern Physics Letters
A Study of Linear Approximation Techniques for SAR Azimuth Processing
The application of the step transform subarray processing techniques to synthetic aperture radar (SAR) was studied. The subarray technique permits the application of efficient digital transform computational techniques such as the fast Fourier transform to be applied while offering an effective tool for range migration compensation. Range migration compensation is applied at the subarray level, and with the subarray size based on worst case range migration conditions, a minimum control system is achieved. A baseline processor was designed for a four-look SAR system covering approximately 4096 by 4096 SAR sample field every 2.5 seconds. Implementation of the baseline system was projected using advanced low power technologies. A 20 swath is implemented with approximately 1000 circuits having a power dissipation of from 70 to 195 watts. The baseline batch step transform processor is compared to a continuous strip processor, and variations of the baseline are developed for a wide range of SAR parameters
Quantum Statistical Entropy and Minimal Length of 5D Ricci-flat Black String with Generalized Uncertainty Principle
In this paper, we study the quantum statistical entropy in a 5D Ricci-flat
black string solution, which contains a 4D Schwarzschild-de Sitter black hole
on the brane, by using the improved thin-layer method with the generalized
uncertainty principle. The entropy is the linear sum of the areas of the event
horizon and the cosmological horizon without any cut-off and any constraint on
the bulk's configuration rather than the usual uncertainty principle. The
system's density of state and free energy are convergent in the neighborhood of
horizon. The small-mass approximation is determined by the asymptotic behavior
of metric function near horizons. Meanwhile, we obtain the minimal length of
the position which is restrained by the surface gravities and the
thickness of layer near horizons.Comment: 11pages and this work is dedicated to the memory of Professor Hongya
Li
Pulse generation without gain-bandwidth limitation in a laser with self-similar evolution
With existing techniques for mode-locking, the bandwidth of ultrashort pulses from a laser is determined primarily by the spectrum of the gain medium. Lasers with self-similar evolution of the pulse in the gain medium can tolerate strong spectral breathing, which is stabilized by nonlinear attraction to the parabolic self-similar pulse. Here we show that this property can be exploited in a fiber laser to eliminate the gain-bandwidth limitation to the pulse duration. Broad (̃200 nm) spectra are generated through passive nonlinear propagation in a normal-dispersion laser, and these can be dechirped to ̃20-fs duration
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Reaction Mechanisms for Long-Life Rechargeable Zn/MnO 2 Batteries
Rechargeable aqueous Zn-ion batteries (ZIBs) are very promising for large-scale grid energy storage applications owing to their low cost, environmentally benign constituents, excellent safety, and relatively high energy density. Their usage, however, is largely hampered by the fast capacity fade. The complexity of the reactions has resulted in long-standing ambiguities of the chemical pathways of Zn/MnO 2 system. In this study, we find that both H + /Zn 2+ intercalation and conversion reactions occur at different voltages and that the rapid capacity fading can clearly be ascribed to the rate-limiting and irreversible conversion reactions at a lower voltage. By limiting the irreversible conversion reactions at â1.26 V, we successfully demonstrate ultrahigh power and long life that are superior to most of the reported ZIBs or even some lithium-ion batteries
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