30,050 research outputs found
Impulsive cylindrical gravitational wave: one possible radiative form emitted from cosmic strings and corresponding electromagnetic response
The cosmic strings(CSs) may be one important source of gravitational
waves(GWs), and it has been intensively studied due to its special properties
such as the cylindrical symmetry. The CSs would generate not only usual
continuous GW, but also impulsive GW that brings more concentrated energy and
consists of different GW components broadly covering low-, intermediate- and
high-frequency bands simultaneously. These features might underlie interesting
electromagnetic(EM) response to these GWs generated by the CSs. In this paper,
with novel results and effects, we firstly calculate the analytical solutions
of perturbed EM fields caused by interaction between impulsive cylindrical GWs
(would be one of possible forms emitted from CSs) and background celestial high
magnetic fields or widespread cosmological background magnetic fields, by using
rigorous Einstein - Rosen metric. Results show: perturbed EM fields are also in
the impulsive form accordant to the GW pulse, and asymptotic behaviors of the
perturbed EM fields are fully consistent with the asymptotic behaviors of the
energy density, energy flux density and Riemann curvature tensor of
corresponding impulsive cylindrical GWs. The analytical solutions naturally
give rise to the accumulation effect which is proportional to the term of
distance^1/2, and based on it, we for the first time predict potentially
observable effects in region of the Earth caused by the EM response to GWs from
the CSs.Comment: 34 pages, 12 figure
Weak coupling d-wave BCS superconductivity and unpaired electrons in overdoped La_{2-x}Sr_{x}CuO_{4} single crystals
The low-temperature specific heat (SH) of overdoped La_{2-x}Sr_{x}CuO_{4}
single crystals (0.178=<x=<0.290) has been measured. For the superconducting
samples (0.178=<x=<0.238), the derived gap values (without any adjusting
parameters) approach closely onto the theoretical prediction
\Delta_{0}=2.14k_{B}T_{c} for the weak-coupling d-wave BCS superconductivity.
In addition, the residual term \gamma(0) of SH at H=0 increases with x
dramatically when beyond x~0.22, and finally evolves into the value of a
complete normal metallic state at higher doping levels, indicating growing
amount of unpaired electrons. We argue that this large \gamma(0) cannot be
simply attributed to the pair breaking induced by the impurity scattering,
instead the phase separation is possible.Comment: 6 pages, 6 figures; Contents added; Accepted for publication in Phys.
Rev.
Superconductivity at 36 K in Gadolinium-arsenide Oxides GdOFFeAs
In this paper we report the fabrication and superconducting properties of
GdOFFeAs. It is found that when x is equal to 0.17,
GdOFFeAs is a superconductor with the onset transition
temperature T 36.6K. Resistivity anomaly near 130K was
observed for all samples up to x = 0.17, such a phenomenon is similar to that
of LaOFFeAs. Hall coefficient indicates that
GdOFFeAs is conducted by electron-like charge carriers.Comment: 3 pages, 4 figure
Improved three-dimensional color-gradient lattice Boltzmann model for immiscible multiphase flows
In this paper, an improved three-dimensional color-gradient lattice Boltzmann
(LB) model is proposed for simulating immiscible multiphase flows. Compared
with the previous three-dimensional color-gradient LB models, which suffer from
the lack of Galilean invariance and considerable numerical errors in many cases
owing to the error terms in the recovered macroscopic equations, the present
model eliminates the error terms and therefore improves the numerical accuracy
and enhances the Galilean invariance. To validate the proposed model, numerical
simulation are performed. First, the test of a moving droplet in a uniform flow
field is employed to verify the Galilean invariance of the improved model.
Subsequently, numerical simulations are carried out for the layered two-phase
flow and three-dimensional Rayleigh-Taylor instability. It is shown that, using
the improved model, the numerical accuracy can be significantly improved in
comparison with the color-gradient LB model without the improvements. Finally,
the capability of the improved color-gradient LB model for simulating dynamic
multiphase flows at a relatively large density ratio is demonstrated via the
simulation of droplet impact on a solid surface.Comment: 9 Figure
TEM investigation of YBa2Cu3O7 thin films on SrTiO3 bicrystals
YBa2Cu3O7 films in c-axis orientation on bicrystalline SrTiO3 substrates are investigated by TEM. The films and the substrates are examined in cross-section and in plane view. The grain boundary of the bicrystal substrate contains (110) faceted voids, but is otherwise straight on a nanometer scale. Contrary to this, the film grain boundary is not straight grain boundary can be up to 100 nm for a 100 nm thick film. The deviation from the intended position of the YBCO grain boundary can already occur at the film/substrate interface where it can be as much as ±50 nm
Temperature dependence and resonance effects in Raman scattering of phonons in NdFeAsOF single crystals
We report plane-polarized Raman scattering spectra of iron oxypnictide
superconductor NdFeAsOF single crystals with varying fluorine
content. The spectra exhibit sharp and symmetrical phonon lines with a weak
dependence on fluorine doping . The temperature dependence does not show any
phonon anomaly at the superconducting transition. The Fe related phonon
intensity shows a strong resonant enhancement below 2 eV. We associate the
resonant enhancement to the presence of an interband transition around 2 eV
observed in optical conductivity. Our results point to a rather weak coupling
between Raman-active phonons and electronic excitations in iron oxypnictides
superconductors.Comment: 4 pages, 3 figures, to appear in Phys. Rev.
High-Efficient Parallel CAVLC Encoders on Heterogeneous Multicore Architectures
This article presents two high-efficient parallel realizations of the context-based adaptive variable length coding (CAVLC) based on heterogeneous multicore processors. By optimizing the architecture of the CAVLC encoder, three kinds of dependences are eliminated or weaken, including the context-based data dependence, the memory accessing dependence and the control dependence. The CAVLC pipeline is divided into three stages: two scans, coding, and lag packing, and be implemented on two typical heterogeneous multicore architectures. One is a block-based SIMD parallel CAVLC encoder on multicore stream processor STORM. The other is a component-oriented SIMT parallel encoder on massively parallel architecture GPU. Both of them exploited rich data-level parallelism. Experiments results show that compared with the CPU version, more than 70 times of speedup can be obtained for STORM and over 50 times for GPU. The implementation of encoder on STORM can make a real-time processing for 1080p @30fps and GPU-based version can satisfy the requirements for 720p real-time encoding. The throughput of the presented CAVLC encoders is more than 10 times higher than that of published software encoders on DSP and multicore platforms
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