12,421 research outputs found
On the remote sensing of cloud properties from satellite infrared sounder data
A method for remote sensing of cloud parameters by using infrared sounder data has been developed on the basis of the parameterized infrared transfer equation applicable to cloudy atmospheres. The method is utilized for the retrieval of the cloud height, amount, and emissivity in 11 micro m region. Numerical analyses and retrieval experiments have been carried out by utilizing the synthetic sounder data for the theoretical study. The sensitivity of the numerical procedures to the measurement and instrument errors are also examined. The retrieved results are physically discussed and numerically compared with the model atmospheres. Comparisons reveal that the recovered cloud parameters agree reasonably well with the pre-assumed values. However, for cases when relatively thin clouds and/or small cloud fractional cover within a field of view are present, the recovered cloud parameters show considerable fluctuations. Experiments on the proposed algorithm are carried out utilizing High Resolution Infrared Sounder (HIRS/2) data of NOAA 6 and TIROS-N. Results of experiments show reasonably good comparisons with the surface reports and GOES satellite images
Data fusion with artificial neural networks (ANN) for classification of earth surface from microwave satellite measurements
A data fusion system with artificial neural networks (ANN) is used for fast and accurate classification of five earth surface conditions and surface changes, based on seven SSMI multichannel microwave satellite measurements. The measurements include brightness temperatures at 19, 22, 37, and 85 GHz at both H and V polarizations (only V at 22 GHz). The seven channel measurements are processed through a convolution computation such that all measurements are located at same grid. Five surface classes including non-scattering surface, precipitation over land, over ocean, snow, and desert are identified from ground-truth observations. The system processes sensory data in three consecutive phases: (1) pre-processing to extract feature vectors and enhance separability among detected classes; (2) preliminary classification of Earth surface patterns using two separate and parallely acting classifiers: back-propagation neural network and binary decision tree classifiers; and (3) data fusion of results from preliminary classifiers to obtain the optimal performance in overall classification. Both the binary decision tree classifier and the fusion processing centers are implemented by neural network architectures. The fusion system configuration is a hierarchical neural network architecture, in which each functional neural net will handle different processing phases in a pipelined fashion. There is a total of around 13,500 samples for this analysis, of which 4 percent are used as the training set and 96 percent as the testing set. After training, this classification system is able to bring up the detection accuracy to 94 percent compared with 88 percent for back-propagation artificial neural networks and 80 percent for binary decision tree classifiers. The neural network data fusion classification is currently under progress to be integrated in an image processing system at NOAA and to be implemented in a prototype of a massively parallel and dynamically reconfigurable Modular Neural Ring (MNR)
Robustness of One-Dimensional Photonic Bandgaps Under Random Variations of Geometrical Parameters
The supercell method is used to study the variation of the photonic bandgaps
in one-dimensional photonic crystals under random perturbations to thicknesses
of the layers. The results of both plane wave and analytical band structure and
density of states calculations are presented along with the transmission
cofficient as the level of randomness and the supercell size is increased. It
is found that higher bandgaps disappear first as the randomness is gradually
increased. The lowest bandgap is found to persist up to a randomness level of
55 percent.Comment: Submitted to Physical Review B on April 8 200
Pattern Competition in the Photorefractive Semiconductors
We analytically study the photorefractive Gunn effect in n-GaAs subjected to
two external laser beams which form a moving interference pattern (MIP) in the
semiconductor. When the intensity of the spatially independent part of the MIP,
denoted by , is small, the system has a periodic domain train (PDT),
consistent with the results of linear stability analysis. When is large,
the space-charge field induced by the MIP will compete with the PDT and result
in complex dynamics, including driven chaos via quasiperiodic route
Analysis of B-> \phi K Decays in QCD Factorization
We analyze the decay within the framework of QCD-improved
factorization. We found that although the twist-3 kaon distribution amplitude
dominates the spectator interactions, it will suppress the decay rates
slightly. The weak annihilation diagrams induced by penguin
operators, which are formally power-suppressed by order , are
chirally and logarithmically enhanced. Therefore, these annihilation
contributions are not subject to helicity suppression and can be sizable. The
predicted branching ratio of is in
the absence of annihilation contributions and it becomes
when annihilation effects are taken into
account. The prediction is consistent with CLEO and BaBar data but smaller than
the BELLE result.Comment: 13 pages, 3 figures. A major change for the presentation of
branching-ratio predictions. Experimental data are update
Branching ratios of decays in perturbative QCD approach
We study the rare decays , which can occur only via
annihilation type diagrams in the standard model. We calculate all of the four
modes, , in the framework of perturbative QCD approach
and give the branching ratios of the order about .Comment: 18 pages, 1 figure, Revte
Possible Large Direct CP Violations in Charmless B-Decays
We discuss the perturbative QCD approach for the exclusive two body B-meson
decays to light mesons. We briefly review its ingredients and some important
theoretical issues on factorization approach. We show numerical results which
are compatible with present experimantal data for the charmless B-meson decays.
Specailly we predict the possibility of large direct CP violation effects in
and .
In the last section we investigate two methods to determine the weak phases
and from processes. We obtain bounds on
and from present experimental measurements.Comment: 18 pages, latex, 8 figures and 8 tables, typos corrected and added
more tables and references. Presented at the 3rd workshop on Higher
Luminosity B Factory, 6-7 August 2002, Kanagawa, Japan; Submitted to Phys.
Rev.
Direct CP Violation in Hadronic B Decays
There are different approaches for the hadronic B decay calculations,
recently. In this paper, we upgrade three of them, namely factorization, QCD
factorization and the perturbative QCD approach based on factorization,
by using new parameters and full wave functions.
Although they get similar results for many of the branching ratios, the
direct CP asymmetries predicted by them are different, which can be tested by
recent experimental measurements of B factories.Comment: 11 pages, 3 figures, revtex4, Talk given at the Workshop on the
Frontiers of Theoretical Physics and Cross-Disciplinary, NSFC, Beijing, March
200
Scattering of slow-light gap solitons with charges in a two-level medium
The Maxwell-Bloch system describes a quantum two-level medium interacting
with a classical electromagnetic field by mediation of the the population
density. This population density variation is a purely quantum effect which is
actually at the very origin of nonlinearity. The resulting nonlinear coupling
possesses particularly interesting consequences at the resonance (when the
frequency of the excitation is close to the transition frequency of the
two-level medium) as e.g. slow-light gap solitons that result from the
nonlinear instability of the evanescent wave at the boundary. As nonlinearity
couples the different polarizations of the electromagnetic field, the
slow-light gap soliton is shown to experience effective scattering whith
charges in the medium, allowing it for instance to be trapped or reflected.
This scattering process is understood qualitatively as being governed by a
nonlinear Schroedinger model in an external potential related to the charges
(the electrostatic permanent background component of the field).Comment: RevTex, 14 pages with 5 figures, to appear in J. Phys. A: Math. Theo
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