3,755 research outputs found
Convergence rates of the DPG method with reduced test space degree
This paper presents a duality theorem of the Aubin-Nitsche type for
discontinuous Petrov Galerkin (DPG) methods. This explains the numerically
observed higher convergence rates in weaker norms. Considering the specific
example of the mild-weak (or primal) DPG method for the Laplace equation, two
further results are obtained. First, the DPG method continues to be solvable
even when the test space degree is reduced, provided it is odd. Second, a
non-conforming method of analysis is developed to explain the numerically
observed convergence rates for a test space of reduced degree
Spatial Distribution of Metal Emissions in SNR 3C 397 Viewed with Chandra and XMM
We present X-ray equivalent width imaging of the supernova remnant (SNR) 3C
397 for Mg He\alpha, Si He\alpha, S He\alpha, and Fe K\alpha complex lines with
the Chandra and XMM-Newton observations. The images reveal that the heavier the
element is, the smaller the extent of the element distribution is. The Mg
emission is evidently enhanced in the southeastern blow-out region, well along
the radio boundary there, and appears to partially envelope the eastern Fe
knot. Two bilateral hat-like Si line-emitting structures are along the northern
and southern borders, roughly symmetric with respect to the southeast-northwest
elongation axis. An S line-emitting shell is located just inner to the northern
radio and IR shell, indicating of a layer of reversely shocked sulphur in the
ejecta. A few enhanced Fe features are basically aligned along the diagonal of
the rectangular shape of the SNR, which implicates an early asymmetric SN
explosion.Comment: 4 pages, 4 figures, appears in Science China Physics, Mechanics &
Astronomy, 2010, 53 (Suppl.1), 267-27
The Connection between Supernova Remnants and the Galactic Magnetic Field: A Global Radio Study of the Axisymmetric Sample
The study of supernova remnants (SNRs) is fundamental to understanding the
chemical enrichment and magnetism in galaxies, including our own Milky Way. In
an effort to understand the connection between the morphology of SNRs and the
Galactic magnetic field (GMF), we have examined the radio images of all known
SNRs in our Galaxy and compiled a large sample that have an "axisymmetric"
morphology, which we define to mean SNRs with a "bilateral" or "barrel"-shaped
morphology, in addition to one-sided shells. We selected the cleanest examples
and model each of these at their appropriate Galactic position using two GMF
models, those of Jansson & Farrar (2012a), which includes a vertical halo
component, and Sun et al. (2008) that is oriented entirely parallel to the
plane. Since the magnitude and relative orientation of the magnetic field
changes with distance from the sun, we analyse a range of distances, from 0.5
to 10 kpc in each case. Using a physically motivated model of a SNR expanding
into the ambient GMF, we find the models using Jansson & Farrar (2012a) are
able to reproduce observed morphologies of many SNRs in our sample. These
results strongly support the presence of an off-plane, vertical component to
the GMF, and the importance of the Galactic field on SNR morphology. Our
approach also provides a potential new method for determining distances to
SNRs, or conversely, distances to features in the large-scale GMF if SNR
distances are known.Comment: 24 pages, 8 figures plus one 5-page appendix figure, 3 tables,
accepted to A&
Multiplexed communication over a high-speed quantum channel
In quantum information systems it is of particular interest to consider the
best way in which to use the non-classical resources consumed by that system.
Quantum communication protocols are integral to quantum information systems and
are amongst the most promising near-term applications of quantum information
science. Here we show that a multiplexed, digital quantum communications system
supported by comb of vacuum squeezing has a greater channel capacity per photon
than a source of broadband squeezing with the same analogue bandwidth. We
report on the time-resolved, simultaneous observation of the first dozen teeth
in a 2.4 GHz comb of vacuum squeezing produced by a sub-threshold OPO, as
required for such a quantum communications channel. We also demonstrate
multiplexed communication on that channel
Quality and biochemical changes of sweet cherries cv. Regina stored in modified atmosphere packaging
Biochemical and quality changes of sweet cherries cv. Regina were assessed over three consecutive years after storage in different modified atmosphere packaging (MAP) liners, with or without hydrocooling, compared to regular atmosphere (RA) storage. All plastic liners used in the experiment resulted in CO2-enrichment and O2-reduction inside packages, with the following impact on fruit quality after five weeks of storage: improved retention of fruit firmness and red color of skin, no significant effect on acidity and total soluble solids, and minimal loss of fruit weight. Fruit decay was absent under both storage conditions (RA and MAP), probably due to rain-protected cultivation of cherry trees. Stalks of MAP-fruits remained fresher than control fruits, obviously due to higher relative humidity condition inside packages. MA-packaged cherries were preferred by the taste panel, while cold-stored fruits were criticized due to flat and slightly bitter taste. The ATP concentration in air stored fruits was higher than in MA-packaged fruits, while ADP level was higher in MA-packaged fruits. Further, MA-packed sweet cherries exhibited higher antioxidant potential and ascorbic acid content than air-stored fruits. Moreover, hydrocooling did not cause any significant effect compared to nontreated fruits
Chandra Confirmation of a Pulsar Wind Nebula in DA 495
As part of a multiwavelength study of the unusual radio supernova remnant DA
495, we present observations made with the Chandra X-ray Observatory. Imaging
and spectroscopic analysis confirms the previously detected X-ray source at the
heart of the annular radio nebula, establishing the radiative properties of two
key emission components: a soft unresolved source with a blackbody temperature
of 1 MK consistent with a neutron star, surrounded by a nonthermal nebula 40''
in diameter exhibiting a power-law spectrum with photon index Gamma =
1.6+/-0.3, typical of a pulsar wind nebula. The implied spin-down luminosity of
the neutron star, assuming a conversion efficiency to nebular flux appropriate
to Vela-like pulsars, is ~10^{35} ergs/s, again typical of objects a few tens
of kyr old. Morphologically, the nebular flux is slightly enhanced along a
direction, in projection on the sky, independently demonstrated to be of
significance in radio polarization observations; we argue that this represents
the orientation of the pulsar spin axis. At smaller scales, a narrow X-ray
feature is seen extending out 5'' from the point source, a distance consistent
with the sizes of resolved wind termination shocks around many Vela-like
pulsars. Finally, we argue based on synchrotron lifetimes in the estimated
nebular magnetic field that DA 495 represents a rare pulsar wind nebula in
which electromagnetic flux makes up a significant part, together with particle
flux, of the neutron star's wind, and that this high magnetization factor may
account for the nebula's low luminosity.Comment: 26 pages, 5 figures, AASTeX preprint style. Accepted for publication
in The Astrophysical Journa
Socioeconomic and demographic factors associated with failure in Helicobacter pylori eradication using the standard triple therapy
Aim: To evaluate the influence of socioeconomic and demographic factors on the eradication rate of H. pylori, using standard triple therapy Background: the efficacy of the standard triple therapy (STT) for H. pylori eradication has decreased with the rise of antibiotic resistance. Other factors could influence the eradication failure, although available results are conflicting. Methods: Retrospective study, including adults with H. pylori infection treated de novo with STT (proton pump inhibitor, amoxicillin and clarithromycin). Eradication success was assessed by 13C-urea breath test. Demographic and socioeconomics variables were evaluated and correlated with eradication treatment outcome. The confounder variables were controlled by logistic regression analysis. Results: Out of 902 patients with H. pylori diagnosis, 693 met inclusion criteria (average age 53 years; females 55.2%). Nonsignificant differences were observed in relation to economics income between rural and urban areas (p=0.316). The eradication rate of H. pylori was 71.1%: male 78.9% vs female 65.9%, urban area 73.4% vs rural area 64.1%. With reference to age, income and nationality, the eradication rates were similar in all groups. According to logistic regression analysis, females had almost twice more likelihood of eradication failure in relation to males (OR 1.92; 95%CI: 1.38-2.72); and rural residents had OR 1.55 (95%CI: 1.03- 2.33) for having eradication failure in contrast with urban population. Conclusion: Female gender and rural residence are factors associated with H. Pylori eradication failure with standard triple therapy
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