1,369 research outputs found
Geometric approach to sampling and communication
Relationships that exist between the classical, Shannon-type, and
geometric-based approaches to sampling are investigated. Some aspects of coding
and communication through a Gaussian channel are considered. In particular, a
constructive method to determine the quantizing dimension in Zador's theorem is
provided. A geometric version of Shannon's Second Theorem is introduced.
Applications to Pulse Code Modulation and Vector Quantization of Images are
addressed.Comment: 19 pages, submitted for publicatio
On the origin of extinction in the Coma cluster of galaxies
Visual extinction of distant clusters seen through the Coma cluster seem to suggest that dust may be present in the hot x ray emitting intracluster gas. However, the Infrared Astronomy Satellite (IRAS) failed to detect any infrared emission from the cluster at the level expected from the extinction measurements. Researchers carried out a detailed analysis of the properties of intracluster dust in the context of a model which includes continuous injection of dust by the cluster galaxies, grain destruction by sputtering, and transient grain heating by the hot plasma. Computed infrared fluxes are in agreement with the upper limit obtained from the IRAS. The calculations, and the constraint implied by the IRAS observations, suggest that the intracluster dust must be significantly depleted compared to interstellar abundances. Researchers discuss possible explanations for the discrepancy between the observed visual extinction and the IRAS upper limit
Analytical Continuation Approaches to Electronic Transport: The Resonant Level Model
The analytical continuation average spectrum method (ASM) and maximum entropy
(MaxEnt) method are applied to the dynamic response of a noninteracting
resonant level model within the framework of the Kubo formula for electric
conductivity. The frequency dependent conductivity is inferred from the
imaginary time current-current correlation function for a wide range of
temperatures, gate voltages and spectral densities representing the leads, and
compared with exact results. We find that the MaxEnt provides more accurate
results compared to the ASM over the full spectral range.Comment: 6 pages, 5 figure
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