27,291 research outputs found
A systematic study of Rayleigh-Brillouin scattering in air, N2 and O2 gases
Spontaneous Rayleigh-Brillouin scattering experiments in air, N2 and O2 have
been performed for a wide range of temperatures and pressures at a wavelength
of 403 nm and at a 90 degrees scattering angle. Measurements of the
Rayleigh-Brillouin spectral scattering profile were conducted at high
signal-to-noise ratio for all three species, yielding high-quality spectra
unambiguously showing the small differences between scattering in air, and its
constituents N2 and O2. Comparison of the experimental spectra with
calculations using the Tenti S6 model, developed in 1970s based on linearized
kinetic equations for molecular gases, demonstrates that this model is valid to
high accuracy. After previous measurements performed at 366 nm, the Tenti S6
model is here verified for a second wavelength of 403 nm. Values for the bulk
viscosity for the gases are derived by optimizing the model to the
measurements. It is verified that the bulk viscosity parameters obtained from
previous experiments at 366 nm, are valid for wavelengths of 403 nm. Also for
air, which is treated as a single-component gas with effective gas transport
coefficients, the Tenti S6 treatment is validated for 403 nm as for the
previously used wavelength of 366 nm, yielding an accurate model description of
the scattering profiles for a range of temperatures and pressures, including
those of relevance for atmospheric studies. It is concluded that the Tenti S6
model, further verified in the present study, is applicable to LIDAR
applications for exploring the wind velocity and the temperature profile
distributions of the Earth's atmosphere. Based on the present findings,
predictions can be made on the spectral profiles for a typical LIDAR
backscatter geometry, which deviate by some 7 percent from purely Gaussian
profiles at realistic sub-atmospheric pressures occurring at 3-5 km altitude in
the Earth's atmosphere
Efficient electronic entanglement concentration assisted with single mobile electron
We present an efficient entanglement concentration protocol (ECP) for mobile
electrons with charge detection. This protocol is quite different from other
ECPs for one can obtain a maximally entangled pair from a pair of
less-entangled state and a single mobile electron with a certain probability.
With the help of charge detection, it can be repeated to reach a higher success
probability. It also does not need to know the coefficient of the original
less-entangled states. All these advantages may make this protocol useful in
current distributed quantum information processing.Comment: 6pages, 3figure
Fluctuations and scaling of inverse participation ratios in random binary resonant composites
We study the statistics of local field distribution solved by the
Green's-function formalism (GFF) [Y. Gu et al., Phys. Rev. B {\bf 59} 12847
(1999)] in the disordered binary resonant composites. For a percolating
network, the inverse participation ratios (IPR) with are illustrated, as
well as the typical local field distributions of localized and extended states.
Numerical calculations indicate that for a definite fraction the
distribution function of IPR has a scale invariant form. It is also shown
the scaling behavior of the ensemble averaged described by the
fractal dimension . To relate the eigenvectors correlations to resonance
level statistics, the axial symmetry between and the spectral
compressibility is obtained.Comment: 7 pages, 6 figures, accepted by Physical Review
Fast Monte Carlo Simulation for Patient-specific CT/CBCT Imaging Dose Calculation
Recently, X-ray imaging dose from computed tomography (CT) or cone beam CT
(CBCT) scans has become a serious concern. Patient-specific imaging dose
calculation has been proposed for the purpose of dose management. While Monte
Carlo (MC) dose calculation can be quite accurate for this purpose, it suffers
from low computational efficiency. In response to this problem, we have
successfully developed a MC dose calculation package, gCTD, on GPU architecture
under the NVIDIA CUDA platform for fast and accurate estimation of the x-ray
imaging dose received by a patient during a CT or CBCT scan. Techniques have
been developed particularly for the GPU architecture to achieve high
computational efficiency. Dose calculations using CBCT scanning geometry in a
homogeneous water phantom and a heterogeneous Zubal head phantom have shown
good agreement between gCTD and EGSnrc, indicating the accuracy of our code. In
terms of improved efficiency, it is found that gCTD attains a speed-up of ~400
times in the homogeneous water phantom and ~76.6 times in the Zubal phantom
compared to EGSnrc. As for absolute computation time, imaging dose calculation
for the Zubal phantom can be accomplished in ~17 sec with the average relative
standard deviation of 0.4%. Though our gCTD code has been developed and tested
in the context of CBCT scans, with simple modification of geometry it can be
used for assessing imaging dose in CT scans as well.Comment: 18 pages, 7 figures, and 1 tabl
Trapped interacting two-component bosons
In this paper we solve one dimensional trapped SU(2) bosons with repulsive
-function interaction by means of Bethe-ansatz method. The features of
ground state and low-lying excited states are studied by numerical and analytic
methods. We show that the ground state is an isospin "ferromagnetic" state
which differs from spin-1/2 fermions system. There exist three quasi-particles
in the excitation spectra, and both holon-antiholon and holon-isospinon
excitations are gapless for large systems. The thermodynamics equilibrium of
the system at finite temperature is studied by thermodynamic Bethe ansatz. The
thermodynamic quantities, such as specific heat etc. are obtained for the case
of strong coupling limit.Comment: 15 pages, 9 figure
Arbitrary Dimensional Schwarzschild-FRW Black Holes
The metric of arbitrary dimensional Schwarzschild black hole in the
background of Friedman-Robertson-Walker universe is presented in the cosmic
coordinates system. In particular, the arbitrary dimensional Schwarzschild-de
Sitter metric is rewritten in the Schwarzschild coordinates system and basing
on which the even more generalized higher dimensional Schwarzschild-de Sitter
metric with another extra dimensions is found. The generalized solution shows
that the cosmological constant may roots in the extra dimensions of space.Comment: 10 page
The Hard X-ray emission of the blazar PKS 2155--304
The synchrotron peak of the X-ray bright High Energy Peaked Blazar (HBL) PKS
2155304 occurs in the UV-EUV region and hence its X-ray emission (0.6--10
keV) lies mostly in the falling part of the synchrotron hump. We aim to study
the X-ray emission of PKS 2155304 during different intensity states in
20092014 using XMMNewton satellite. We studied the spectral curvature of
all of the observations to provide crucial information on the energy
distribution of the non-thermal particles. Most of the observations show
curvature or deviation from a single power-law and can be well modeled by a log
parabola model. In some of the observations, we find spectral flattening after
6 keV. In order to find the possible origin of the X-ray excess, we built the
Multi-band Spectral Energy distribution (SED). We find that the X-ray excess in
PKS 2155--304 is difficult to fit in the one zone model but, could be easily
reconciled in the spine/layer jet structure. The hard X-ray excess can be
explained by the inverse Comptonization of the synchrotron photons (from the
layer) by the spine electrons.Comment: 14 pages, 7 Figures, Accepted for publication in Ap
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