145,615 research outputs found
On factorization of a subclass of 2-D digital FIR lossless matricesfor 2-D QMF bank applications
The role of one-dimensional (1-D) digital finite impulse response (FIR) lossless matrices in the design of FIR perfect reconstruction quadrature mirror filter (QMF) banks has been explored previously. Structures which can realize the complete family of FIR lossless transfer matrices, have also been developed, with QMF application in mind. For the case of 2-D QMF banks, the same concept of lossless polyphase matrix has been used to obtain perfect reconstruction. However, the problem of finding a structure to cover all 2-D FIR lossless matrices of a given degree has not been solved. Progress in this direction is reported. A structure which completely covers a well-defined subclass of 2-D digital FIR lossless matrices is obtained
Representations and classification of traveling wave solutions to Sinh-G{\"o}rdon equation
Two concepts named atom solution and combinatory solution are defined. The
classification of all single traveling wave atom solutions to Sinh-G{\"o}rdon
equation is obtained, and qualitative properties of solutions are discussed. In
particular, we point out that some qualitative properties derived intuitively
from dynamic system method aren't true. In final, we prove that our solutions
to Sinh-G{\"o}rdon equation include all solutions obtained in the paper[Fu Z T
et al, Commu. in Theor. Phys.(Beijing) 2006 45 55]. Through an example, we show
how to give some new identities on Jacobian elliptic functions.Comment: 12 pages. accepted by Communications in theoretical physics (Beijing
Role of Interlayer Coupling on the Evolution of Band Edges in Few-Layer Phosphorene
Using first-principles calculations, we have investigated the evolution of
band-edges in few-layer phosphorene as a function of the number of P layers.
Our results predict that monolayer phosphorene is an indirect band gap
semiconductor and its valence band edge is extremely sensitive to strain. Its
band gap could undergo an indirect-to-direct transition under a lattice
expansion as small as 1% along zigzag direction. A semi-empirical interlayer
coupling model is proposed, which can well reproduce the evolution of valence
band-edges obtained by first-principles calculations. We conclude that the
interlayer coupling plays a dominated role in the evolution of the band-edges
via decreasing both band gap and carrier effective masses with the increase of
phosphorene thickness. A scrutiny of the orbital-decomposed band structure
provides a better understanding of the upward shift of valence band maximum
surpassing that of conduction band minimum.Comment: 25 pages, 9 figure
Evaluation of absorption cycle for space station environmental control system application Interim report
Zero-gravity absorption refrigeration system design and performance testing for space station environmental control applicatio
Magnetothermopower and Magnetoresistivity of RuSr2Gd1-xLaxCu2O8 (x=0, 0.1)
We report measurements of magnetothermopower and magnetoresistivity as a
function of temperature on RuSr2Gd1-xLaxCu2O8 (x = 0, 0.1). The normal-state
thermopower shows a dramatic decrease after applying a magnetic field of 5 T,
whereas the resistivity shows only a small change after applying the same
field. Our results suggest that RuO2 layers are conducting and the magnetic
field induced decrease of the overall thermopower is caused by the decrease of
partial thermopower decrease associated with the spin entropy decrease of the
carriers in the RuO2 layers.Comment: 21 pages, 6 figure
Nonsequential Double Ionization with Polarization-gated Pulses
We investigate laser-induced nonsequential double ionization by a
polarization-gated laser pulse, constructed employing two counter-rotating
circularly polarized few cycle pulses with a time delay . We address the
problem within a classical framework, and mimic the behavior of the
quantum-mechanical electronic wave packet by means of an ensemble of classical
electron trajectories. These trajectories are initially weighted with the
quasi-static tunneling rate, and with suitably chosen distributions for the
momentum components parallel and perpendicular to the laser-field polarization,
in the temporal region for which it is nearly linearly polarized. We show that,
if the time delay is of the order of the pulse length, the
electron-momentum distributions, as functions of the parallel momentum
components, are highly asymmetric and dependent on the carrier-envelope (CE)
phase. As this delay is decreased, this asymmetry gradually vanishes. We
explain this behavior in terms of the available phase space, the quasi-static
tunneling rate and the recollision rate for the first electron, for different
sets of trajectories. Our results show that polarization-gating technique may
provide an efficient way to study the NSDI dynamics in the single-cycle limit,
without employing few-cycle pulses.Comment: 17 pages, 6 figure
Chemical abundance analysis of 19 barium stars
We aim at deriving accurate atmospheric parameters and chemical abundances of
19 barium (Ba) stars, including both strong and mild Ba stars, based on the
high signal-to-noise ratio and high resolution Echelle spectra obtained from
the 2.16 m telescope at Xinglong station of National Astronomical
Observatories, Chinese Academy of Sciences. The chemical abundances of the
sample stars were obtained from an LTE, plane-parallel and line-blanketed
atmospheric model by inputting the atmospheric parameters (effective
temperatures, surface gravities, metallicity and microturbulent velocity) and
equivalent widths of stellar absorption lines. These samples of Ba stars are
giants indicated by atmospheric parameters, metallicities and kinematic
analysis about UVW velocity. Chemical abundances of 17 elements were obtained
for these Ba stars. Their light elements (O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr,
Mn and Ni) are similar to the solar abundances. Our samples of Ba stars show
obvious overabundances of neutron-capture (n-capture) process elements relative
to the Sun. Their median abundances of [Ba/Fe], [La/Fe] and [Eu/Fe] are 0.54,
0.65 and 0.40, respectively. The YI and ZrI abundances are lower than Ba, La
and Eu, but higher than the light elements for the strong Ba stars and similar
to the iron-peak elements for the mild stars. There exists a positive
correlation between Ba intensity and [Ba/Fe]. For the n-capture elements (Y,
Zr, Ba, La), there is an anti-correlation between their [X/Fe] and [Fe/H]. We
identify nine of our sample stars as strong Ba stars with [Ba/Fe]>0.6 where
seven of them have Ba intensity Ba=2-5, one has Ba=1.5 and another one has
Ba=1.0. The remaining ten stars are classified as mild Ba stars with
0.17<[Ba/Fe]<0.54
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