3,876 research outputs found
SPITZER observations of dust destruction in the Puppis A supernova remnant
The interaction of the Puppis A supernova remnant (SNR) with a neighboring molecular cloud provides a unique
opportunity to measure the amount of grain destruction in an SNR shock. Spitzer Space Telescope MIPS imaging
of the entire SNR at 24, 70, and 160 ÎŒm shows an extremely good correlation with X-ray emission, indicating
that the SNRâs IR radiation is dominated by the thermal emission of swept-up interstellar dust, collisionally
heated by the hot shocked gas. Spitzer IRS spectral observations targeted both the Bright Eastern Knot (BEK)
of the SNR where a small cloud has been engulfed by the supernova blast wave and outlying portions of the
associated molecular cloud that are yet to be hit by the shock front. Modeling the spectra from both regions
reveals the composition and the grain size distribution of the interstellar dust, both in front of and behind the
SNR shock front. The comparison shows that the ubiquitous polycyclic aromatic hydrocarbons of the interstellar
medium are destroyed within the BEK, along with nearly 25% of the mass of graphite and silicate dust grains
A human antibody against Zika virus crosslinks the E protein to prevent infection
The recent Zika virus (ZIKV) epidemic has been linked to unusual and severe clinical manifestations including microcephaly in fetuses of infected pregnant women and Guillian-BarrĂ© syndrome in adults. Neutralizing antibodies present a possible therapeutic approach to prevent and control ZIKV infection. Here we present a 6.2âĂ
resolution three-dimensional cryo-electron microscopy (cryoEM) structure of an infectious ZIKV (strain H/PF/2013, French Polynesia) in complex with the Fab fragment of a highly therapeutic and neutralizing human monoclonal antibody, ZIKV-117. The antibody had been shown to prevent fetal infection and demise in mice. The structure shows that ZIKV-117 Fabs cross-link the monomers within the surface E glycoprotein dimers as well as between neighbouring dimers, thus preventing the reorganization of E protein monomers into fusogenic trimers in the acidic environment of endosomes
Effects of Proton Center Closure on Pediatric Case Volume and Resident Education at an Academic Cancer Center
Purpose
To analyze effects of closure of an academic proton treatment center (PTC) on pediatric case volume, distribution, and resident education.
Methods and Materials
This was a review of 412 consecutive pediatric (age â€18 years) cases treated at a single institution from 2012 to 2016. Residents' Accreditation Council for Graduate Medical Education case logs for the same years were also analyzed. Characteristics of the patient population and resident case volumes before and after closure of the PTC are reported.
Results
Overall pediatric new starts declined by approximately 50%, from 35 to 70 per 6 months in 2012 to 2014 to 22 to 30 per 6 months in 2015 to 2016. Central nervous system (CNS) case volume declined sharply, from 121 patients treated in 2012 to 2015 to 18 patients in 2015 to 2016. In 2012 to 2014 our institution treated 36, 24, and 17 patients for medulloblastoma/intracranial primitive neuroectodermal tumor, ependymoma, and low-grade glioma, respectively, compared with 0, 1, and 1 patient(s) in 2015 to 2016. Forty-nine patients were treated with craniospinal radiation (CSI) from 2012 to 2014, whereas only 2 patients underwent CSI between 2015 and 2016. Hematologic malignancy patient volume and use of total body irradiation remained relatively stable. Patients treated when the PTC was open were significantly younger (9.1 vs 10.7 years, P=.010) and their radiation courses were longer (35.4 vs 20.9 days, P<.0001) than those treated after its closure. Resident case logs showed only a small decline in total pediatric cases, because the percentage of pediatric cases covered by residents increased after PTC closure; however, residents logged fewer CNS cases after PTC closure versus before.
Conclusions
Overall pediatric case volume decreased after PTC closure, as did the number of patients treated for potentially curable CNS tumors. Our findings raise important questions regarding resident training in pediatric radiation oncology as these cases become increasingly concentrated at specialized centers
Chandra ACIS Survey of M33 (ChASeM33): X-ray Imaging Spectroscopy of M33SNR21, the Brightest X-ray Supernova Remnant in M33
We present and interpret new X-ray data for M33SNR21, the brightest X-ray
supernova remnant (SNR) in M33. The SNR is in seen projection against (and
appears to be interacting with) the bright HII region NGC592. Data for this
source were obtained as part of the Chandra ACIS Survey of M33 (ChASeM33) Very
Large Project. The nearly on-axis Chandra data resolve the SNR into a ~5"
diameter (20 pc at our assumed M33 distance of 817+/-58 kpc) slightly
elliptical shell. The shell is brighter in the east, which suggests that it is
encountering higher density material in that direction. The optical emission is
coextensive with the X-ray shell in the north, but extends well beyond the
X-ray rim in the southwest. Modeling the X-ray spectrum with an absorbed sedov
model yields a shock temperature of 0.46(+0.01,-0.02) keV, an ionization
timescale of n_e t = cm s, and
half-solar abundances (0.45 (+0.12, -0.09)). Assuming Sedov dynamics gives an
average preshock H density of 1.7 +/- 0.3 cm. The dynamical age estimate
is 6500 +/- 600 yr, while the best fit value and derived gives
8200 +/- 1700 yr; the weighted mean of the age estimates is 7600 +/- 600 yr. We
estimate an X-ray luminosity (0.25-4.5 keV) of (1.2 +/- 0.2) times
ergs s (absorbed), and (1.7 +/- 0.3) times ergs s
(unabsorbed), in good agreement with the recent XMM-Newton determination. No
significant excess hard emission was detected; the luminosity ergs s (2-8 keV) for any hard point source.Comment: 27 pages, 6 figures (3 color). ApJ (in press
Estimating a common period for a set of irregularly sampled functions with applications to periodic variable star data
We consider the problem of estimating a common period for a set of functions sampled at irregular intervals. The motivating problem arises in astronomy, where the functions represent a starâs observed brightness over time through different photometric filters. While current methods perform well when the brightness is sampled densely enough in at least one filter, they break down when no brightness function is densely sampled. In this paper we introduce two new methods for period estimation in this important latter case. The first, multiband generalized LombâScargle (MGLS), extends the frequently used LombâScargle method to naĂŻvely combine information across filters. The second, penalized generalized LombâScargle (PGLS), builds on MGLS by more intelligently borrowing strength across filters. Specifically, we incorporate constraints on the phases and amplitudes across the different functions using a nonconvex penalized likelihood function. We develop a fast algorithm to optimize the penalized likelihood that combines block coordinate descent with the majorizationâminimization (MM) principle. We test and validate our methods on synthetic and real astronomy data. Both PGLS and MGLS improve period estimation accuracy over current methods based on using a single function; moreover, PGLS outperforms MGLS and other leading methods when the functions are sparsely sampled
HST/FOS Eclipse Observations of the Nova-like Cataclysmic Variable UX Ursae Majoris
[abridged abstract]
We present and analyze Hubble Space Telescope observations of the eclipsing
nova-like cataclysmic variable UX UMa obtained with the Faint Object
Spectrograph. Two eclipses each were observed with the G160L grating (covering
the ultraviolet waveband) in August of 1994 and with the PRISM (covering the
near-ultraviolet to near-infrared) in November of the same year. The system was
50% brighter in November than in August, which, if due to a change in the
accretion rate, indicates a fairly substantial increase in Mdot_acc by >~ 50%.
Model disk spectra constructed as ensembles of stellar atmospheres provide
poor descriptions of the observed post-eclipse spectra, despite the fact that
UX UMa's light should be dominated by the disk at this time. Suitably scaled
single temperature model stellar atmospheres with T_eff = 12,500-14,500 K
actually provide a better match to both the ultraviolet and optical
post-eclipse spectra. Evidently, great care must be taken in attempts to derive
accretion rates from comparisons of disk models to observations.
One way to reconcile disk models with the observed post-eclipse spectra is to
postulate the presence of a significant amount of optically thin material in
the system. Such an optically thin component might be associated with the
transition region (``chromosphere'') between the disk photosphere and the fast
wind from the system, whose presence has been suggested by Knigge & Drew
(1997).Comment: 35 pages, including 12 figures; to appear in the ApJ (Vol. 499
A Large-Scale Synthesis and Characterization of Quaternary CuIn\u3csub\u3e\u3cem\u3ex\u3c/em\u3e\u3c/sub\u3eGa\u3csub\u3e1â\u3cem\u3ex\u3c/em\u3e\u3c/sub\u3eS\u3csub\u3e2\u3c/sub\u3e Chalcopyrite Nanoparticles via Microwave Batch Reactions
Various quaternary CuInxGa1âxS2 (0 †x †1) chalcopyrite nanoparticles have been prepared from molecular single-source precursors via microwave decomposition. We were able to control the nanoparticle size, phase, stoichiometry, and solubility. Depending on the choice of surface modifiers used, we were able to tune the solubility of the resulting nanoparticles. This method has been used to generate up to 5 g of nanoparticles and up to 150 g from multiple batch reactions with excellent reproducibility. Data from UV-Vis, photoluminescence, X-ray diffraction, TEM, DSC/TGA-MS, and ICP-OES analyses have shown high reproducibility in nanoparticle size, composition, and bandgap
A Large-scale Synthesis and Characterization of Quaternary CuInâGaâââSâ Chalcopyrite Nanoparticles via Microwave Batch Reactions
Various quaternary CuInxGa1-xS2 (0â€xâ€1) chalcopyrite nanoparticles have been prepared from molecular single-source precursors via microwave decomposition. We were able to control the nanoparticle size, phase, stoichiometry, and solubility. Depending on the choice of surface modifiers used, we were able to tune the solubility of the resulting nanoparticles. This method has been used to generate up to 5g of nanoparticles and up to 150g from multiple batch reactions with excellent reproducibility. Data from UV-Vis, photoluminescence, X-ray diffraction, TEM, DSC/TGA-MS, and ICP-OES analyses have shown high reproducibility in nanoparticle size, composition, and bandgap
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