2,173 research outputs found
Software correlators as testbeds for RFI algorithms
In-correlator techniques offer the possibility of identifying and/or excising
radio frequency interference (RFI) from interferometric observations at much
higher time and/or frequency resolution than is generally possible with the
final visibility dataset. Due to the considerable computational requirements of
the correlation procedure, cross-correlators have most commonly been
implemented using high-speed digital signal processing boards, which typically
require long development times and are difficult to alter once complete.
"Software" correlators, on the other hand, make use of commodity server
machines and a correlation algorithm coded in a high-level language. They are
inherently much more flexible and can be developed - and modified - much more
rapidly than purpose-built "hardware" correlators. Software correlators are
thus a natural choice for testing new RFI detection and mitigation techniques
for interferometers. The ease with which software correlators can be adapted to
test RFI detection algorithms is demonstrated by the addition of kurtosis
detection and plotting to the widely used DiFX software correlator, which
highlights previously unknown short -duration RFI at the Hancock VLBA station.Comment: 6 pages, 1 figure, accepted for publication in Proceedings of Science
[PoS(RFI2010)035]. Presented at RFI2010, the Third Workshop on RFI Mitigation
in Radio Astronomy, 29-31 March 2010, Groningen, The Netherland
Rooting a phylogenetic tree with nonreversible substitution models
BACKGROUND: We compared two methods of rooting a phylogenetic tree: the stationary and the nonstationary substitution processes. These methods do not require an outgroup. METHODS: Given a multiple alignment and an unrooted tree, the maximum likelihood estimates of branch lengths and substitution parameters for each associated rooted tree are found; rooted trees are compared using their likelihood values. Site variation in substitution rates is handled by assigning sites into several classes before the analysis. RESULTS: In three test datasets where the trees are small and the roots are assumed known, the nonstationary process gets the correct estimate significantly more often, and fits data much better, than the stationary process. Both processes give biologically plausible root placements in a set of nine primate mitochondrial DNA sequences. CONCLUSIONS: The nonstationary process is simple to use and is much better than the stationary process at inferring the root. It could be useful for situations where an outgroup is unavailable
Una amplia nómina de los hombres del comercio sevillano del S. XVII
Este trabajo fue presentado al IX Congreso Internacional de Americanistas celebrado en Badajoz en Septiembre de 2000
Stabilization of the alleged bishomoromatic bicyclo[3.2.1]octa-2,6-dienyl anion by counterion interactions and by hyperconjugation
Hyperconjugation and inductive effects, rather than homoaromaticity, are responsible for the stabilization of the title anion in the gas phase; interaction of the double bond with the Li+ gegenion in the endo geometry contributes additionally in solution
The use of photographic methods in contrast enhancement of ERTS-1 images
The contrast of ERTS 70mm positive images can be enhanced to varying degrees by rephotographing the images with different types of negative films, and by overdeveloping the films with different developers. A combination of high contrast copy film (Kodak 5069) and a high energy developer (Kodak D-11) yields high contrast. Still greater contrast may be otbained by using a film of higher contrast capability and a developer of higher energy capability. Contrast can also be enhanced in the printing process with the use of highcontrast photographic papers, or with the use of polycontrast photographic paper and filters. Contrast enhancement by photocopying delineates topographic boundaries and may aid in the objective measurement of topographic parameters
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