15,574 research outputs found
Bounds for eigenvalue ratios of the Laplacian
For a bounded domain with a piecewise smooth boundary in an
-dimensional Euclidean space , we study eigenvalues of the
Dirichlet eigenvalue problem of the Laplacian. First we give a general
inequality for eigenvalues of the Laplacian. As an application, we study lower
order eigenvalues of the Laplacian and derive the ratios of lower order
eigenvalues of the Laplacian.Comment: 14 page
Electromagnetic Scattering and Statistic Analysis of Clutter from Oil Contaminated Sea Surface
In order to investigate the electromagnetic (EM) scattering characteristics of the three dimensional sea surface contaminated by oil, a rigorous numerical method multilevel fast multipole algorithm (MLFMA) is developed to preciously calculate the electromagnetic backscatter from the two-layered oil contaminated sea surface. Illumination window and resistive window are combined together to depress the edge current induced by artificial truncation of the sea surface. By using this combination, the numerical method can get a high efficiency at a less computation cost. The differences between backscatters from clean sea and oil contaminated sea are investigated with respect to various incident angles and sea states. Also, the distribution of the sea clutter is examined for the oil-spilled cases in this paper
Rotor-to-stator rub vibration in centrifugal compressor
One example of excessive vibration encountered during loading of a centrifugal compressor train (H type compressor with HP casing) is discussed. An investigation was made of the effects of the dynamic load on the bearing stiffness and the rotor-bearing system critical speed. The high vibration occurred at a "threshold load," but the machine didn't run smoothly due to rubs even when it had passed through the threshold load. The acquisition and discussion of the data taken in the field as well as a description of the case history which utilizes background information to identify the malfunction conditions is presented. The analysis shows that the failures, including full reverse precession rub and exact one half subharmonic vibration, were caused by the oversize bearings and displacement of the rotor center due to foundation deformation and misalignment between gear shafts, etc. The corrective actions taken to alleviate excessive vibration and the problems which remain to be solved are also presented
Symmetric vortices for two-component Ginzburg-Landau systems
We study Ginzburg--Landau equations for a complex vector order parameter
Psi=(psi_+,psi_-). We consider symmetric (equivariant) vortex solutions in the
plane R^2 with given degrees n_\pm, and prove existence, uniqueness, and
asymptotic behavior of solutions for large r. We also consider the monotonicity
properties of solutions, and exhibit parameter ranges in which both vortex
profiles |psi_+|, |psi_i| are monotone, as well as parameter regimes where one
component is non-monotone. The qualitative results are obtained by means of a
sub- and supersolution construction and a comparison theorem for elliptic
systems.Comment: 32 page
Chiral geometry of higher excited bands in triaxial nuclei with particle-hole configuration
The lowest six rotational bands have been studied in the particle-rotor model
with the particle-hole configuration
and different triaxiality parameter . Both constant and spin-dependent
variable moments of inertial (CMI and VMI) are introduced. The energy spectra,
electromagnetic transition probabilities, angular momentum components and
-distribution have been examined. It is shown that, besides the band 1 and
band 2, the predicted band 3 and band 4 in the calculations of both CMI and VMI
for atomic nuclei with could be interpreted as chiral doublet
bands.Comment: 4 pages, 4 figure
Compressive Channel Estimation and Multi-user Detection in C-RAN
This paper considers the channel estimation (CE) and multi-user detection
(MUD) problems in cloud radio access network (C-RAN). Assuming that active
users are sparse in the network, we solve CE and MUD problems with compressed
sensing (CS) technology to greatly reduce the long identification pilot
overhead. A mixed L{2,1}-regularization functional for extended sparse
group-sparsity recovery is proposed to exploit the inherently sparse property
existing both in user activities and remote radio heads (RRHs) that active
users are attached to. Empirical and theoretical guidelines are provided to
help choosing tuning parameters which have critical effect on the performance
of the penalty functional. To speed up the processing procedure, based on
alternating direction method of multipliers and variable splitting strategy, an
efficient algorithm is formulated which is guaranteed to be convergent.
Numerical results are provided to illustrate the effectiveness of the proposed
functional and efficient algorithm.Comment: 6 pages, 3 figure
Doublet bands in Cs in the triaxial rotor model coupled with two quasiparticles
The positive parity doublet bands based on the configuration in Cs have been investigated in the two
quasi-particles coupled with a triaxial rotor model. The energy spectra ,
energy staggering parameter , and
values, intraband ratios,
ratios, and orientation of the
angular momentum for the rotor as well as the valence proton and neutron are
calculated. After including the pairing correlation, good agreement has been
obtained between the calculated results and the data available, which supports
the interpretation of this positive parity doublet bands as chiral bands.Comment: Phys.Rev.C (accepted
Market timing with aggregate accruals
We propose a market-timing strategy that aims to exploit aggregate accruals' return forecasting power. Using several performance measures of the aggregate accruals-based market-timing strategy, such as excess portfolio return, Sharpe ratio, and Jensen's alpha, we find robust evidence that, relative to the passive investment strategy of buying and holding the stock market, the market-timing strategy delivers superior performance that is both statistically and economically significant. Specifically, on average, the market-timing strategy beats the SP500 index by 6 to 22 percentage points (annualized) after controlling for transaction costs over the 1980-2004 period.© 2009 Palgrave Macmillan.postprin
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