16,647 research outputs found
Gene expression during mouse development and teratocarcinoma differentiation
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Speckle interferometry at the Blanco and SOAR telescopes in 2008 and 2009
The results of speckle interferometric measurements of binary and multiple
stars conducted in 2008 and 2009 at the Blanco and SOAR 4-m telescopes in Chile
are presented. A total of 1898 measurements of 1189 resolved pairs or
sub-systems and 394 observations of 285 un-resolved targets are listed. We
resolved for the first time 48 new pairs, 21 of which are new sub-systems in
close visual multiple stars. Typical internal measurement precision is 0.3 mas
in both coordinates, typical companion detection capability is at 0\farcs15 separation. These data were obtained with a new
electron-multiplication CCD camera; data processing is described in detail,
including estimation of magnitude difference, observational errors, detection
limits, and analysis of artifacts. We comment on some newly discovered pairs
and objects of special interest.Comment: Accepted for publication in Astronomical Journal. Tables 4,5,7 will
be published electronically, they are available in full from the author
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A Study of the Relationship Between Antivirus Regressions and Label Changes
AntiVirus (AV) products use multiple components to detect malware. A component which is found in virtually all AVs is the signature-based detection engine: this component assigns a particular signature label to a malware that the AV detects. In previous analysis [1-3], we observed cases of regressions in several different AVs: i.e. cases where on a particular date a given AV detects a given malware but on a later date the same AV fails to detect the same malware. We studied this aspect further by analyzing the only externally observable behaviors from these AVs, namely whether AV engines detect a malware and what labels they assign to the detected malware. In this paper we present the results of the analysis about the relationship between the changing of the labels with which AV vendors recognize malware and the AV regressions
Cross-correlation of the unresolved X-ray background with faint galaxies
At the faint end of the deepest X-ray surveys, a population of X-ray luminous
galaxies is seen. In this paper, we present the results of a cross-correlation
between the residual, unresolved X-ray photons in a very deep X-ray survey and
the positions of faint galaxies, in order to examine the importance of these
objects at even fainter flux levels. We measure a significant correlation on
all angular scales up to ~1 arcmin. This signal could account for a significant
fraction of the unresolved X-ray background, approximately 35 per cent if the
clustering is similar to optically selected galaxies. However, the angular form
of the correlation is seen to be qualitatively similar to that expected for
clusters of galaxies and the X-ray emission could be associated with hot gas in
clusters or with QSOs within galaxy clusters rather than emission from
individual faint galaxies. The relative contribution from each of these
possibilities cannot be determined with the current data.Comment: 7 pages LaTeX including 9 EPS figures. Uses mn.sty. Accepted for
publication by MNRA
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Dissociative Electron Attachment Cross Sections for H<sub>2</sub> and D<sub>2</sub>
New measurements of the absolute cross sections for dissociative electron attachment (DEA) in
molecular hydrogen and deuterium are presented which resolve previous ambiguities and provide a
test bed for theory. The experimental methodology is based upon a momentum imaging time-of-flight
spectrometer that allowed us to eliminate any contributions due to electronically excited metastable
neutrals and ultraviolet light while ensuring detection of all the ions. The isotope effect in the DEA
process in the two molecules is found to be considerably larger than previously observed. More
importantly, it is found to manifest in the polar dissociation process (also known as ion pair production)
as well
The discovery of very red counterparts to faint X-ray sources
We present deep K-band imaging at the positions of four very faint X-ray
sources found in the UK ROSAT Deep Survey to have no optical counterpart
brighter than R~23. Likely identifications are found within the ROSAT error
circle in all four fields with R-K colours of between 3.2 +/- 0.4 and 6.4 +/-
0.6. From a consideration of the R-K colours and X-ray to optical luminosity
ratios of the candidate identifications, we tentatively classify two of the
X-ray sources as very distant (z ~ 1) clusters of galaxies, one as a narrow
emission line galaxy and one as an obscured QSO.Comment: 7 pages, LaTeX, 7 figures (1 postscript file each). Uses mn.sty and
epsf.sty. Accepted by MNRAS. For more information see
http://www.astro.soton.ac.uk/~amn/UKdee
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