40,794 research outputs found
Nonthermal X-Ray Emission from G266.2-1.2 (RX J0852.0-4622)
The newly discovered supernova remnant G266.2-1.2 (RX J0852.0-4622), along
the line of sight to the Vela SNR, was observed with ASCA for 120 ks. We find
that the X-ray spectrum is featureless, and well described by a power law,
extending to three the class of shell-type SNRs dominated by nonthermal X-ray
emission. Although the presence of the Vela SNR compromises our ability to
accurately determine the column density, the GIS data appear to indicate
absorption considerably in excess of that for Vela itself, indicating that
G266.2-1.2 may be several times more distant. An unresolved central source may
be an associated neutron star, though difficulties with this interpretation
persist.Comment: 4 pages, 5 figures, uses aipproc.sty & epsfig.sty. To appear in
"Young Supernova Remnants" (11th Annual Astrophysics Conference in Maryland),
S. S. Holt & U. Hwang (eds), AIP, New York (2001
GpsTunes: controlling navigation via audio feedback
We combine the functionality of a mobile Global Positioning System (GPS) with that of an MP3 player, implemented on a PocketPC, to produce a handheld system capable of guiding a user to their desired target location via continuously adapted music feedback. We illustrate how the approach to presentation of the audio display can benefit from insights from control theory, such as predictive 'browsing' elements to the display, and the appropriate representation of uncertainty or ambiguity in the display. The probabilistic interpretation of the navigation task can be generalised to other context-dependent mobile applications. This is the first example of a completely handheld location- aware music player. We discuss scenarios for use of such systems
The Extraordinarily Rapid Expansion of the X-ray Remnant of Kepler's Supernova (SN1604)
Four individual high resolution X-ray images from ROSAT and the Einstein
Observatory have been used to measure the expansion rate of the remnant of
Kepler's supernova (SN 1604). Highly significant measurements of the expansion
have been made for time baselines varying from 5.5 yrs to 17.5 yrs. All
measurements are consistent with a current expansion rate averaged over the
entire remnant of 0.239 (+/-0.015) (+0.017,-0.010) % per yr, which, when
combined with the known age of the remnant, determines the expansion parameter
m, defined as , to be 0.93 (+/-0.06) (+0.07,-0.04). The error
bars on these results include both statistical (first set of errors) and
systematic (second set) uncertainty. According to this result the X-ray remnant
is expanding at a rate that is remarkably close to free expansion and nearly
twice as fast as the mean expansion rate of the radio remnant. The expansion
rates as a function of radius and azimuthal angle are also presented based on
two ROSAT images that were registered to an accuracy better than 0.5
arcseconds. Significant radial and azimuthal variations that appear to arise
from the motion of individual X-ray knots are seen. The high expansion rate of
the X-ray remnant appears to be inconsistent with currently accepted dynamical
models for the evolution of Kepler's SNR.Comment: 14 pages, including 7 postscript figs, LaTeX, emulateapj. Accepted by
Ap
Large-scale and significant expression from pseudogenes in Sodalis glossinidius â a facultative bacterial endosymbiont
The majority of bacterial genomes have high coding efficiencies, but there are some genomes of intracellular bacteria that have low gene density. The genome of the endosymbiont Sodalis glossinidius contains almost 50â% pseudogenes containing mutations that putatively silence them at the genomic level. We have applied multiple âomicâ strategies, combining Illumina and Pacific Biosciences Single-Molecule Real-Time DNA sequencing and annotation, stranded RNA sequencing and proteome analysis to better understand the transcriptional and translational landscape of Sodalis pseudogenes, and potential mechanisms for their control. Between 53 and 74â% of the Sodalis transcriptome remains active in cell-free culture. The mean sense transcription from coding domain sequences (CDSs) is four times greater than that from pseudogenes. Comparative genomic analysis of six Illumina-sequenced Sodalis isolates from different host Glossina species shows pseudogenes make up ~40â% of the 2729 genes in the core genome, suggesting that they are stable and/or that Sodalis is a recent introduction across the genus Glossina as a facultative symbiont. These data shed further light on the importance of transcriptional and translational control in deciphering hostâmicrobe interactions. The combination of genomics, transcriptomics and proteomics gives a multidimensional perspective for studying prokaryotic genomes with a view to elucidating evolutionary adaptation to novel environmental niches
Liquid drops on a surface: using density functional theory to calculate the binding potential and drop profiles and comparing with results from mesoscopic modelling
The contribution to the free energy for a film of liquid of thickness on
a solid surface, due to the interactions between the solid-liquid and
liquid-gas interfaces is given by the binding potential, . The precise
form of determines whether or not the liquid wets the surface. Note that
differentiating gives the Derjaguin or disjoining pressure. We develop a
microscopic density functional theory (DFT) based method for calculating
, allowing us to relate the form of to the nature of the molecular
interactions in the system. We present results based on using a simple lattice
gas model, to demonstrate the procedure. In order to describe the static and
dynamic behaviour of non-uniform liquid films and drops on surfaces, a
mesoscopic free energy based on is often used. We calculate such
equilibrium film height profiles and also directly calculate using DFT the
corresponding density profiles for liquid drops on surfaces. Comparing
quantities such as the contact angle and also the shape of the drops, we find
good agreement between the two methods. We also study in detail the effect on
of truncating the range of the dispersion forces, both those between the
fluid molecules and those between the fluid and wall. We find that truncating
can have a significant effect on and the associated wetting behaviour of
the fluid.Comment: 16 pages, 13 fig
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