229 research outputs found
Infrared Emission from Supernova Remnants: Formation and Destruction of Dust
We review the observations of dust emission in supernova rem- nants (SNRs)
and supernovae (SNe). Theoretical calculations suggest that SNe, particularly
core-collapse, should make significant quantities of dust, perhaps as much as a
solar mass. Observations of extragalactic SNe have yet to find anywhere near
this amount, but this may be the result of observa- tional limitations. SN
1987A, in the process of transitioning from a SN to an SNR, does show signs of
a significant amount of dust forming in its ejecta, but whether this dust will
survive the passage of the reverse shock to be injected into the ISM is
unknown. IR observations of SNRs have not turned up significant quantities of
dust, and the dust that is observed is generally swept-up by the forward shock,
rather than created in the ejecta. Because the shock waves also destroy dust in
the ISM, we explore the question of whether SNe might be net destroyers, rather
than net creators of dust in the universe.Comment: Published in the Springer Handbook of Supernova
The 30 micron emission band in carbon-rich pre-planetary nebulae
The 16-48 μm spectra of five carbon-rich post-AGB objects (pre-planetary nebulae, PPNs) known to have an unidentified 21 μm emission feature in their IRAS LRS spectra have been obtained using the Kuiper Airborne Observatory. A broad emission band extending from 24 to ∼45 μm is present in the spectra of these objects. Peaking at ∼30 μm, the intensity of the band is variable from source to source, accounting in one case (IRAS 22272 + 5435) for ∼20% of its bolometric luminosity. However, its strength is not correlated with that of the 21 μm feature. The 30 μm band is similar to the feature previously found in other carbon-rich AGB stars and planetary nebulae. It is thus seen in a wide variety of objects, while the 21 μm band is seen only in a subset of PPNs. It was suggested for AGB stars that the 30 μm band could be carried by solid MgS particles. The observed 30 μm emission is modeled combining distributions of carbon grains and MgS grains. The required MgS abundance with respect to H nuclei is roughly estimated to be less than ∼7 × 10 -6, i.e., representing about 50% and 25% of the total abundances of S and Mg, respectively. Despite the relatively good fit with MgS, the possibility of alternative models especially with carbon-related compounds should still be addressed.published_or_final_versio
A supernova origin for dust in a high-redshift quasar
Interstellar dust plays a crucial role in the evolution of the Universe by
assisting the formation of molecules, by triggering the formation of the first
low-mass stars, and by absorbing stellar ultraviolet-optical light and
subsequently re-emitting it at infrared/millimetre wavelengths. Dust is thought
to be produced predominantly in the envelopes of evolved (age >1 Gyr), low-mass
stars. This picture has, however, recently been brought into question by the
discovery of large masses of dust in the host galaxies of quasars at redshift
z>6, when the age of the Universe was less than 1 Gyr. Theoretical studies,
corroborated by observations of nearby supernova remnants, have suggested that
supernovae provide a fast and efficient dust formation environment in the early
Universe. Here we report infrared observations of a quasar at redshift 6.2,
which are used to obtain directly its dust extinction curve. We then show that
such a curve is in excellent agreement with supernova dust models. This result
demonstrates a supernova origin for dust in this high-redshift quasar, from
which we infer that most of the dust at high redshifts has probably the same
origin.Comment: To Appear in Nature, September 30, 200
Formin 1-Isoform IV Deficient Cells Exhibit Defects in Cell Spreading and Focal Adhesion Formation
Background: Regulation of the cytoskeleton is a central feature of cell migration. The formin family of proteins controls the rate of actin nucleation at its barbed end. Thus, formins are predicted to contribute to several important cell processes such as locomotion, membrane ruffling, vesicle endocytosis, and stress fiber formation and disassociation. Methodology/Principal Findings: In this study we investigated the functional role of Formin1-isoform4 (Fmn1-IV) by using genetically null primary cells that displayed augmented protrusive behaviour during wound healing and delayed cell spreading. Cells deficient of Fmn1-IV also showed reduced efficiency of focal adhesion formation. Additionally, we generated an enhanced green fluorescence protein (EGFP)-fused Fmn1-IV knock-in mouse to monitor the endogenous subcellular localization of Fmn1-IV. Its localization was found within the cytoplasm and along microtubules, yet it was largely excluded from adherens junctions. Conclusions/Significance: It was determined that Fmn1-IV, as an actin nucleator, contributes to protrusion of the cell’s leading edge and focal adhesion formation, thus contributing to cell motility
A Protective Role by Interleukin-17F in Colon Tumorigenesis
Interleukin-17F (IL-17F), produced by Th17 cells and other immune cells, is a member of IL-17 cytokine family with highest homology to IL-17A. IL-17F has been shown to have multiple functions in inflammatory responses. While IL-17A plays important roles in cancer development, the function of IL-17F in tumorigenesis has not yet been elucidated. In the current study, we found that IL-17F is expressed in normal human colonic epithelial cells, but this expression is greatly decreased in colon cancer tissues. To examine the roles of IL-17F in colon cancer, we have used IL-17F over-expressing colon cancer cell lines and IL-17F-deficient mice. Our data showed decreased tumor growth of IL-17F-transfected HCT116 cells comparing to mock transfectants when transplanted in nude mice. Conversely, there were increased colonic tumor numbers and tumor areas in Il-17f−/− mice than those from wild-type controls after colon cancer induction. These results indicate that IL-17F plays an inhibitory role in colon tumorigenesis in vivo. In IL-17F over-expressing tumors, there was no significant change in leukocyte infiltration; instead, we found decreased VEGF levels and CD31+ cells. While the VEGF levels were increased in the colon tissues of Il-17f−/− mice with colon cancer. Together, our findings demonstrate a protective role for IL-17F in colon cancer development, possibly via inhibiting tumor angiogenesis
The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope II. Multi-object spectroscopy (MOS)
We provide an overview of the capabilities and performance of the
Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST)
when used in its multi-object spectroscopy (MOS) mode employing a novel Micro
Shutter Array (MSA) slit device. The MSA consists of four separate 98 arcsec
91 arcsec quadrants each containing individually
addressable shutters whose open areas on the sky measure 0.20 arcsec
0.46 arcsec on a 0.27 arcsec 0.53 arcsec pitch. This is the first time
that a configurable multi-object spectrograph has been available on a space
mission. The levels of multiplexing achievable with NIRSpec MOS mode are
quantified and we show that NIRSpec will be able to observe typically fifty to
two hundred objects simultaneously with the pattern of close to a quarter of a
million shutters provided by the MSA. This pattern is fixed and regular, and we
identify the specific constraints that it yields for NIRSpec observation
planning. We also present the data processing and calibration steps planned for
the NIRSpec MOS data. The significant variation in size of the mostly
diffraction-limited instrument point spread function over the large wavelength
range of 0.6-5.3 m covered by the instrument, combined with the fact that
most targets observed with the MSA cannot be expected to be perfectly centred
within their respective slits, makes the spectrophotometric and wavelength
calibration of the obtained spectra particularly complex. These challenges
notwithstanding, the sensitivity and multiplexing capabilities anticipated of
NIRSpec in MOS mode are unprecedented, and should enable significant progress
to be made in addressing a wide range of outstanding astrophysical problems
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The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope II. Multi-object spectroscopy (MOS)
We provide an overview of the capabilities and performance of the
Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST)
when used in its multi-object spectroscopy (MOS) mode employing a novel Micro
Shutter Array (MSA) slit device. The MSA consists of four separate 98 arcsec
91 arcsec quadrants each containing individually
addressable shutters whose open areas on the sky measure 0.20 arcsec
0.46 arcsec on a 0.27 arcsec 0.53 arcsec pitch. This is the first time
that a configurable multi-object spectrograph has been available on a space
mission. The levels of multiplexing achievable with NIRSpec MOS mode are
quantified and we show that NIRSpec will be able to observe typically fifty to
two hundred objects simultaneously with the pattern of close to a quarter of a
million shutters provided by the MSA. This pattern is fixed and regular, and we
identify the specific constraints that it yields for NIRSpec observation
planning. We also present the data processing and calibration steps planned for
the NIRSpec MOS data. The significant variation in size of the mostly
diffraction-limited instrument point spread function over the large wavelength
range of 0.6-5.3 m covered by the instrument, combined with the fact that
most targets observed with the MSA cannot be expected to be perfectly centred
within their respective slits, makes the spectrophotometric and wavelength
calibration of the obtained spectra particularly complex. These challenges
notwithstanding, the sensitivity and multiplexing capabilities anticipated of
NIRSpec in MOS mode are unprecedented, and should enable significant progress
to be made in addressing a wide range of outstanding astrophysical problems
The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope: IV. Capabilities and predicted performance for exoplanet characterization
The Near-Inrared Spectrograph (NIRSpec) on the James Webb Space Telescope
(JWST) is a very versatile instrument, offering multiobject and integral field
spectroscopy with varying spectral resolution (30 to 3000) over a
wide wavelength range from 0.6 to 5.3 micron, enabling scientists to study many
science themes ranging from the first galaxies to bodies in our own Solar
System. In addition to its integral field unit and support for multiobject
spectroscopy, NIRSpec features several fixed slits and a wide aperture
specifically designed to enable high precision time-series and transit as well
as eclipse observations of exoplanets. In this paper we present its
capabilities regarding time-series observations, in general, and transit and
eclipse spectroscopy of exoplanets in particular. Due to JWST's large
collecting area and NIRSpec's excellent throughput, spectral coverage, and
detector performance, this mode will allow scientists to characterize the
atmosphere of exoplanets with unprecedented sensitivity
Peptide Array X-Linking (PAX): A New Peptide-Protein Identification Approach
Many protein interaction domains bind short peptides based on canonical sequence consensus motifs. Here we report the development of a peptide array-based proteomics tool to identify proteins directly interacting with ligand peptides from cell lysates. Array-formatted bait peptides containing an amino acid-derived cross-linker are photo-induced to crosslink with interacting proteins from lysates of interest. Indirect associations are removed by high stringency washes under denaturing conditions. Covalently trapped proteins are subsequently identified by LC-MS/MS and screened by cluster analysis and domain scanning. We apply this methodology to peptides with different proline-containing consensus sequences and show successful identifications from brain lysates of known and novel proteins containing polyproline motif-binding domains such as EH, EVH1, SH3, WW domains. These results suggest the capacity of arrayed peptide ligands to capture and subsequently identify proteins by mass spectrometry is relatively broad and robust. Additionally, the approach is rapid and applicable to cell or tissue fractions from any source, making the approach a flexible tool for initial protein-protein interaction discovery.National Institutes of Health (U.S.) (Grant R21-CA-140030-01
Post-treatment skin reactions reported by cancer patients differ by race, not by treatment or expectations
Cancer patients may experience skin problems while undergoing chemotherapy and radiation therapy. Frequency of skin reactions may be influenced by skin pigmentation and psychological factors. A Symptom Inventory completed by 656 cancer patients nationwide before and after chemotherapy, radiation therapy, or chemotherapy plus radiation therapy was analysed to determine if treatment type, race (Black vs White), and pretreatment expectations influenced post-treatment skin reactions. Subsequent analysis of a local Symptom Inventory completed weekly for 5 weeks by 308 patients receiving radiation therapy examined severity of reported skin reactions. Significantly more patients receiving radiation therapy had stronger expectations of skin problems (62%) than patients receiving chemotherapy (40%, P=0.001) or chemotherapy plus radiation therapy (45%, P=0.003). Overall, expectations did not correlate with patient reported post-treatment skin problems in white (r=0.014, P=0.781) or black (r=0.021, P=0.936) patients. Although no significant difference was found between black and white patients in their pretreatment expectations of skin problems (P=0.32), black patients (10 out of 18, 56%) reported more skin problems than white patients (90 out of 393, 23%, P=0.001). Similarly, the local study showed that significantly more black patients (1 out of 5, 20%) reported severe skin reactions at the treatment site than white patients (12 out of 161, 8%). A direct correlation was observed between severity of skin problems and pain at the treatment site (r=0.541, P<0.001). Total radiation exposure did not significantly correlate with the report of skin problems at the treatment site for white or black patients. Overall, black patients reported more severe post-treatment skin problems than white patients. Our results suggest that symptom management for post-treatment skin reactions in cancer patients receiving radiation treatment could differ depending on their racial background
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