30,294 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
Neutrino masses, leptogenesis and dark matter in hybrid seesaw
We suggest a hybrid seesaw model where relatively ``light''right-handed
neutrinos give no contribution to the neutrino mass matrix due to a special
symmetry. This allows their Yukawa couplings to the standard model particles to
be relatively strong, so that the standard model Higgs boson can decay
dominantly to a left and a right-handed neutrino, leaving another stable
right-handed neutrino as cold dark matter. In our model neutrino masses arise
via the type-II seesaw mechanism, the Higgs triplet scalars being also
responsible for the generation of the matter-antimatter asymmetry via the
leptogenesis mechanism.Comment: 4 page
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
Spectral Analyses of the Nearest Persistent Ultraluminous X-Ray Source M33 X-8
We provide a detailed analysis of 12 XMM observations of the nearest
persistent extragalactic ultraluminous X-ray source (ULX), M33 X-8. No
significant spectral evolution is detected between the observations, therefore
we combine the individual observations to increase the signal-to-noise ratio
for spectral fitting. The combined spectra are best fitted by the
self-consistent p-free disk plus power-law component model with p =
0.571_{-0.030}^{+0.032}, kT_{in} = 1.38_{-0.08}^{+0.09} keV, and the flux ratio
of the p-free disk component to the power-law component being 0.63:0.37 in the
0.3 -- 10 keV band. The fitting indicates that the black hole in M33 X-8 is of
\sim 10 M_{\odot} and accretes at a super-Eddington rate (\sim 1.5 L_{Edd}),
and the phase of the accretion disk is close to a slim disk (p = 0.5). We
report, for the first time, that an extra power-law component is required in
addition to the p-free disk model for ULXs. In super-Eddington cases, the
power-law component may possibly result from the optically thin inner region f
the disk or a comptonized corona similar to that of a standard thin disk.Comment: 11 pages, 1 table, 2 figures, accepted by PAS
Low frequency elastic wave propagation in 2D locally resonant phononic crystal with asymmetric resonator
The resonance modes and the related effects to the transmission of elastic
waves in a two dimensional phononic crystal formed by periodic arrangements of
a two blocks unit cell in one direction are studied. The unit cell consists of
two asymmetric elliptic cylinders coated with silicon rubber and embedded in a
rigid matrix. The modes are obtained by the semi-analytic method in the least
square collocation scheme and confirmed by the finite element method
simulations. Two resonance modes, corresponding to the vibration of the
cylinder along the long and short axes, give rise to resonance reflections of
elastic waves. One mode in between the two modes, related to the opposite
vibration of the two cylinders in the unit cell in the direction along the
layer, results in the total transmission of elastic waves due to zero effective
mass density at the frequency. The resonance frequency of this new mode changes
continuously with the orientation angle of the elliptic resonator.Comment: 17 pages, 7 figure
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