5,938 research outputs found
Nonthermal X-Rays from Supernova Remnant G330.2+1.0 and the Characteristics of its Central Compact Object
We present results from our X-ray data analysis of the SNR G330.2+1.0 and its
CCO, CXOU J160103.1--513353 (J1601). Using our XMM-Newton and Chandra
observations, we find that the X-ray spectrum of J1601 can be described by
neutron star atmosphere models (T ~ 2.5--3.7 MK). Assuming the distance of d ~
5 kpc for J1601 as estimated for SNR G330.2+1.0, a small emission region of R ~
1--2 km is implied. X-ray pulsations previously suggested by Chandra are not
confirmed by the XMM-Newton data, and are likely not real. However, our timing
analysis of the XMM-Newton data is limited by poor photon statistics, and thus
pulsations with a relatively low amplitude (i.e., an intrinsic pulsed-fraction
< 40%) cannot be ruled out. Our results indicate that J1601 is a CCO similar to
that in the Cassiopeia A SNR.X-ray emission from SNR G330.2+1.0 is dominated by
power law continuum (Gamma ~ 2.1--2.5) which primarily originates from thin
filaments along the boundary shell. This X-ray spectrum implies synchrotron
radiation from shock-accelerated electrons with an exponential roll-off
frequency ~ 2--3 x 10^17 Hz. For the measured widths of the X-ray filaments (D
~ 0.3 pc) and the estimated shock velocity (v_s ~ a few x 10^3 km s^-1), a
downstream magnetic field B ~ 10--50 G is derived. The estimated maximum
electron energy E_max ~ 27--38 TeV suggests that G330.2+1.0 is a candidate TeV
gamma-ray source. We detect faint thermal X-ray emission in G330.2+1.0. We
estimate a low preshock density n_0 ~ 0.1 cm^-3, which suggests a dominant
contribution from an inverse Compton mechanism (than the proton-proton
collision) to the prospective gamma-ray emission. Follow-up deep radio, X-ray,
and gamma-ray observations will be essential to reveal the details of the shock
parameters and the nature of particle accelerations in this SNR.Comment: 26 pages, 3 tables, 7 figures (4 color figures), Accepted by Ap
Spectral and Rotational Changes in the Isolated Neutron Star RX J0720.4-3125
RX J0720.4-3125 is an isolated neutron star that, uniquely in its class, has
shown changes in its thermal X-ray spectrum. We use new spectra taken with
Chandra's Low Energy Transmission Grating Spectrometer, as well as archival
observations, to try to understand the timescale and nature of these changes.
We construct lightcurves, which show both small, slow variations on a timescale
of years, and a larger event that occurred more quickly, within half a year.
From timing, we find evidence for a `glitch' coincident with this larger
event, with a fractional increase in spin frequency of 5x10^{-8}. We compare
the `before' and `after' spectra with those from RX J1308.6+2127, an isolated
neutron star with similar temperature and magnetic field strength, but with a
much stronger absorption feature in its spectrum. We find that the `after'
spectrum can be represented remarkably well by the superposition of the
`before' spectrum, scaled by two thirds, and the spectrum of RX J1308.6+2127,
thus suggesting that the event affected approximately one third of the surface.
We speculate the event reflects a change in surface composition caused by,
e.g., an accretion episode.Comment: 4 pages, 2 figures, 2 tables, emulateapj format. ApJL, accepte
How to Put a Heavier Higgs on the Lattice
Lattice work, exploring the Higgs mass triviality bound, seems to indicate
that a strongly interacting scalar sector in the minimal standard model cannot
exist while low energy QCD phenomenology seems to indicate that it could. We
attack this puzzle using the 1/N expansion and discover a simple criterion for
selecting a lattice action that is more likely to produce a heavy Higgs
particle. Our large calculation suggests that the Higgs mass bound might be
around , which is about 30% higher than previously obtained
An evaluation of risk factors for major adverse cardiovascular events during tocilizumab therapy
Objective:
To evaluate associations between lipid levels, inflammation, and rheumatoid arthritis (RA) disease activity, at baseline and during treatment, with the risk of major adverse cardiovascular events (MACE) in tocilizumabâtreated patients with RA.
Methods:
In retrospective post hoc analyses, data were pooled for 3,986 adult patients with moderate to severe RA who received â„1 dose of tocilizumab (4 mg/kg or 8 mg/kg) intravenously every 4 weeks in randomized controlled trials and extension studies. Cox proportional hazards modeling was used to evaluate associations between baseline characteristics and posttreatment changes in laboratory and disease characteristics (week 24) and change in disease activity and laboratory values from baseline to week 24 with the risk of future MACE during extended followup.
Results:
We identified 50 independently adjudicated cases of MACE during 14,683 patientâyears of followup (0.34 MACE cases/100 patientâyears). At baseline, age, a history of cardiac disorders, the Disease Activity Score in 28 joints (DAS28), and the total cholesterol:highâdensity lipoprotein cholesterol ratio were independently associated with MACE in multivariable models (P < 0.05 for all). During treatment, a higher DAS28 and higher swollen and tender joint counts at week 24 were associated with future MACE. In separate models, greater reductions in the DAS28 and joint counts from baseline to week 24 were inversely associated with future MACE; changes in lipid parameters were not statistically significantly associated with the risk of MACE.
Conclusion:
In this population of patients treated with tocilizumab, an association was observed between the baseline total cholesterol:highâdensity lipoprotein cholesterol ratio and an increased risk of MACE. The risk of MACE while receiving treatment, however, was associated with control of disease activity but not lipid changes. Larger studies are needed to confirm these findings
MST construction in O
We consider a simple model for overlay networks, where all n processes are connected to all other processes, and each message contains at most O(log n) bits. For this model, we present a distributed algorithm that constructs a minimumweight spanning tree in O(log log n) communication rounds, where in each round any process can send a message to each other process. This result is the first to break the âŠ(log n) parallel time complexity barrier with small message sizes. Categories and Subject Descriptors F.2 [theory of computation]: analysis of algorithms and problem complexity; G.2.2 [mathematics of computing]: discrete mathematicsâgraph theor
Multimodal Intrinsic Speckle-Tracking (MIST) to extract rapidly-varying diffuse X-ray scatter
Speckle-based phase-contrast X-ray imaging (SB-PCXI) can reconstruct
high-resolution images of weakly-attenuating materials that would otherwise be
indistinguishable in conventional attenuation-based imaging. The experimental
setup of SB-PCXI requires only a sufficiently coherent source and spatially
random mask, positioned between the source and detector. The technique can
extract sample information at length scales smaller than the imaging system's
spatial resolution; this enables multimodal signal reconstruction. ``Multimodal
Intrinsic Speckle-Tracking'' (MIST) is a rapid and deterministic formalism
derived from the paraxial-optics form of the Fokker-Planck equation. MIST
simultaneously extracts attenuation, refraction, and small-angle scattering
(diffusive-dark-field) signals from a sample and is more computationally
efficient compared to alternative speckle-tracking approaches. Hitherto,
variants of MIST have assumed the diffusive-dark-field signal to be spatially
slowly varying. Although successful, these approaches have been unable to
well-describe unresolved sample microstructure whose statistical form is not
spatially slowly varying. Here, we extend the MIST formalism such that there is
no such restriction, in terms of a sample's rotationally-isotropic
diffusive-dark-field signal. We reconstruct multimodal signals of two samples,
each with distinct X-ray attenuation and scattering properties. The
reconstructed diffusive-dark-field signals have superior image quality compared
to our previous approaches which assume the diffusive-dark-field to be a slowly
varying function of transverse position. Our generalisation may assist
increased adoption of SB-PCXI in applications such as engineering and
biomedical disciplines, forestry, and palaeontology, and is anticipated to aid
the development of speckle-based diffusive-dark-field tensor tomography.Comment: 18 pages, 7 figure
High-Flow Nasal Cannula Failure Odds Is Largely Independent of Duration of Use in COVID-19
Nasal Cannula; COVID-19CĂĄnula nasal; COVID-19CĂ nula nasal; COVID-1
-manifolds with eventual identities, bidifferential calculus and twisted Lenard-Magri chains
Given an -manifold with eventual identities we examine what this structure
entails from the point of view of integrable PDEs of hydrodynamic type. In
particular, we show that in the semisimple case the characterization of
eventual identities recently given by David and Strachan is equivalent to the
requirement that has vanishing Nijenhuis torsion. Moreover, after
having defined new equivalence relations for connections compatible with
respect to the -product , namely hydrodynamically almost equivalent
and hydrodynamically equivalent connections, we show how these two concepts
manifest themselves in several specific situations. In particular, in the case
of an -manifold endowed with eventual identity and two almost
hydrodynamically equivalent flat connections we are able to derive the
recurrence relations for the flows of the associated integrable hierarchy. If
the two connections originate from a flat pencil of metrics these reduce to the
standard bi-Hamiltonian recursion. Furthermore, using the geometric set-up
proposed here we show how the recurrence relations of the principal hierarchy
introduced by Dubrovin arise in this general framework and we provide a general
cohomological set-up for the conservation laws of the semihamiltonian hierarchy
associated to a semisimple -manifold with compatible connection and eventual
identity. Therefore, the point of view we propose, not only highlight the
conceptual unity of two well-known recursive schemes (principal hierarchy and
classical bi-Hamiltonian) but it also provides a far reaching generalization of
these recursions that relies on the presence of an eventual identity.Comment: 40 page
Spatial Variation of the X-ray spectrum of the Crab Nebula
We present spectral analysis of the Crab Nebula obtained with the {\it
Chandra} X-ray observatory. The X-ray spectrum is characterized by a power-law
whose index varies across the nebula. The variation can be discussed in terms
of the particle injection from the pulsar in two different directions: the
equatorial plane containing the torus and the symmetry axis along the jet. In
the equatorial plane, spectra within the torus are the hardest, with photon
index , and are almost independent of the surface
brightness. At the periphery of the torus, the spectrum gradually softens in
the outer, lower surface brightness regions, up to . This
indicates that synchrotron losses become significant to X-ray emitting
particles at the outer boundary of the torus. We discuss the nature of the
torus, incorporating information from observations at other wavelengths.
Spectral variations are also seen within the southern jet. The core of the jet
is the hardest with 2.0, and the outer sheath surrounding the
core becomes softer with up to 2.5 at the outermost part. Based on the
similarity between the spectra of the jet core and the torus, we suggest that
the electron spectra of the particles injected from the pulsar are also similar
in these two different directions. The brightness ratio between the near and
far sides of the torus can be explained by Doppler boosting and relativistic
aberration; however, the observed ratio cannot be derived from the standard
weakly magnetized pulsar wind model. We also found a site where an optical
filament comprised of supernova ejecta is absorbing the soft X-ray emission
( 2 keV).Comment: 21 pages, 5 figures, 2 tables, AASTeX preprint. Accepted for
publication in the Astrophysical Journal (scheduled on July 1, 2004
An X-Ray Study of Supernova Remnant N49 and Soft Gamma-Ray Repeater 0526-66 in the Large Magellanic Cloud
We report on the results from our deep Chandra observation (120 ks) of the
supernova remnant (SNR) N49 and soft Gamma-ray repeater (SGR) 0526-66 in the
Large Magellanic Cloud. We firmly establish the detection of an ejecta "bullet"
beyond the southwestern boundary of N49. The X-ray spectrum of the bullet is
distinguished from that of the main SNR shell, showing significantly enhanced
Si and S abundances. We also detect an ejecta feature in the eastern shell,
which shows metal overabundances similar to those of the bullet. If N49 was
produced by a core-collapse explosion of a massive star, the detected Si-rich
ejecta may represent explosive O-burning or incomplete Si-burning products from
deep interior of the supernova. On the other hand, the observed Si/S abundance
ratio in the ejecta may favor Type Ia origin for N49. We refine the Sedov age
of N49, tau_Sed ~ 4800 yr, with the explosion energy E_0 ~ 1.8 x 10^51 erg. Our
blackbody (BB) + power law (PL) model for the quiescent X-ray emission from SGR
0526-66 indicates that the PL photon index (Gamma ~ 2.5) is identical to that
of PSR 1E1048.1-5937, the well-known candidate transition object between
anomalous X-ray pulsars and SGRs. Alternatively, the two-component BB model
implies X-ray emission from a small (R ~ 1 km) hot spot(s) (kT ~ 1 keV) in
addition to emission from the neutron star's cooler surface (R ~ 10 km, kT ~
0.4 keV). There is a considerable discrepancy in the estimated column toward
0526-66 between BB+PL and BB+BB model fits. Discriminating these spectral
models would be crucial to test the long-debated physical association between
N49 and 0526-66.Comment: Accepted by ApJ, 27 pages in total (aastex preprint format) including
5 figures (4 in color) and 5 table
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