1,325 research outputs found
3-D Models of Embedded High-Mass Stars: Effects of a Clumpy Circumstellar Medium
We use 3-D radiative transfer models to show the effects of clumpy
circumstellar material on the observed infrared colors of high mass stars
embedded in molecular clouds. We highlight differences between 3-D clumpy and
1-D smooth models which can affect the interpretation of data. We discuss
several important properties of the emergent spectral energy distribution
(SED): More near-infrared light (scattered and direct from the central source)
can escape than in smooth 1-D models. The near- and mid-infrared SED of the
same object can vary significantly with viewing angle, depending on the clump
geometry along the sightline. Even the wavelength-integrated flux can vary with
angle by more than a factor of two. Objects with the same average circumstellar
dust distribution can have very different near-and mid-IR SEDs depending on the
clump geometry and the proximity of the most massive clump to the central
source.
Although clumpiness can cause similar objects to have very different SEDs,
there are some observable trends. Near- and mid-infrared colors are sensitive
to the weighted average distance of clumps from the central source and to the
magnitude of clumpy density variations (smooth-to-clumpy ratio). Far-infrared
emission remains a robust measure of the total dust mass. We present simulated
SEDs, colors, and images for 2MASS and Spitzer filters. We compare to
observations of some UCHII regions and find that 3-D clumpy models fit better
than smooth models. In particular, clumpy models with fractal dimensions in the
range 2.3-2.8, smooth to clumpy ratios of <50%, and density distributions with
shallow average radial density profiles fit the SEDs best.Comment: accepted to ApJ; version with full-res figures:
http://www.astro.virginia.edu/~ri3e/clumpy3d.pd
High Mass Star Formation. II. The Mass Function of Submillimeter Clumps in M17
We have mapped an approximately 5.5 by 5.5 pc portion of the M17 massive
star-forming region in both 850 and 450 micron dust continuum emission using
the Submillimeter Common-User Bolometer Array (SCUBA) on the James Clerk
Maxwell Telescope (JCMT). The maps reveal more than 100 dusty clumps with
deconvolved linear sizes of 0.05--0.2 pc and masses of 0.8--120 solar masses,
most of which are not associated with known mid-infrared point sources. Fitting
the clump mass function with a double power law gives a mean power law exponent
of alpha_high = -2.4 +/- 0.3 for the high-mass power law, consistent with the
exponent of the Salpeter stellar mass function. We show that a lognormal clump
mass distribution with a peak at about 4 solar masses produces as good a fit to
the clump mass function as does a double power law. This 4 solar mass peak mass
is well above the peak masses of both the stellar initial mass function and the
mass function of clumps in low-mass star-forming regions. Despite the
difference in intrinsic mass scale, the shape of the M17 clump mass function
appears to be consistent with the shape of the core mass function in low-mass
star-forming regions. Thus, we suggest that the clump mass function in
high-mass star-forming regions may be a scaled-up version of that in low-mass
regions, instead of its extension to higher masses.Comment: 33 pages, 6 figures, 3 tables. Accepted for publication in the
Astrophysical Journa
The Multi-faceted Ecto-enzyme CD38: Roles in Immunomodulation, Cancer, Aging, and Metabolic Diseases
CD38 (Cluster of Differentiation 38) is a multifunctional ecto-enzyme that metabolizes NAD+ and mediates nicotinamide dinucleotide (NAD+) and extracellular nucleotide homeostasis as well as intracellular calcium. CD38 is also an emerging therapeutic target under conditions in which metabolism is altered including infection, aging, and tumorigenesis. We describe multiple enzymatic activities of CD38, which may explain the breadth of biological roles observed for this enzyme. Of greatest significance is the role of CD38 as an ecto-enzyme capable of modulating extracellular NAD+ precursor availability: 1 to bacteria unable to perform de novo synthesis of NAD+; and 2 in aged parenchyma impacted by the accumulation of immune cells during the process of ‘inflammaging’. We also discuss the paradoxical role of CD38 as a modulator of intracellular NAD+, particularly in tumor immunity. Finally, we provide a summary of therapeutic approaches to CD38 inhibition and ‘NAD+ boosting’ for treatment of metabolic dysfunction observed during aging and in tumor immunity. The present review summarizes the role of CD38 in nicotinamide nucleotide homeostasis with special emphasis on the role of CD38 as an immunomodulator and druggable target
Limits on the Optical Brightness of the Epsilon Eridani Dust Ring
The STIS/CCD camera on the {\em Hubble Space Telescope (HST)} was used to
take deep optical images near the K2V main-sequence star Eridani in
an attempt to find an optical counterpart of the dust ring previously imaged by
sub-mm observations. Upper limits for the optical brightness of the dust ring
are determined and discussed in the context of the scattered starlight expected
from plausible dust models. We find that, even if the dust is smoothly
distributed in symmetrical rings, the optical surface brightness of the dust,
as measured with the {\em HST}/STIS CCD clear aperture at 55 AU from the star,
cannot be brighter than about 25 STMAG/". This upper limit excludes some
solid grain models for the dust ring that can fit the IR and sub-mm data.
Magnitudes and positions for 59 discrete objects between 12.5" to 58"
from Eri are reported. Most if not all of these objects are likely
to be background stars and galaxies.Comment: Revision corrects author lis
Infrared to millimetre photometry of ultra-luminous IR galaxies: new evidence favouring a 3-stage dust model
Infrared to millimetre spectral energy distributions have been obtained for
41 bright ultra-luminous infrared galaxies. The observations were carried out
with ISOPHOT between 10 and 200 micron and supplemented for 16 sources with
SCUBA at 450 and 850 micron and with SEST at 1.3 mm. In addition, seven sources
were observed at 1.2 and 2.2 m with the 2.2 m telescope on Calar Alto.
These new SEDs represent the most complete set of infrared photometric
templates obtained so far on ULIRGs in the local universe.Comment: 23 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
Multi-wavelength observations of IGR J17544-2619 from quiescence to outburst
In this paper we report on a long multi-wavelength observational campaign of
the supergiant fast X-ray transient prototype IGR J17544-2619. A 150 ks-long
observation was carried out simultaneously with XMM-Newton and NuSTAR, catching
the source in an initial faint X-ray state and then undergoing a bright X-ray
outburst lasting about 7 ks. We studied the spectral variability during
outburst and quiescence by using a thermal and bulk Comptonization model that
is typically adopted to describe the X-ray spectral energy distribution of
young pulsars in high mass X-ray binaries. Although the statistics of the
collected X-ray data were relatively high we could neither confirm the presence
of a cyclotron line in the broad-band spectrum of the source (0.5-40 keV), nor
detect any of the previously reported tentative detection of the source spin
period. The monitoring carried out with Swift/XRT during the same orbit of the
system observed by XMM-Newton and NuSTAR revealed that the source remained in a
low emission state for most of the time, in agreement with the known property
of all supergiant fast X-ray transients being significantly sub-luminous
compared to other supergiant X-ray binaries. Optical and infrared observations
were carried out for a total of a few thousands of seconds during the
quiescence state of the source detected by XMM-Newton and NuSTAR. The measured
optical and infrared magnitudes were slightly lower than previous values
reported in the literature, but compatible with the known micro-variability of
supergiant stars. UV observations obtained with the UVOT telescope on-board
Swift did not reveal significant changes in the magnitude of the source in this
energy domain compared to previously reported values.Comment: Accepted for publication on A&A. V2: few typos correcte
Otimização de metodologia para estimar a emissão de amônia no processo de compostagem de dejetos de suÃnos.
Proojeto: 01.09.01.001
Influence of two different solid-liquid separation processes on the settling characteristics of swine effluent.
ABSTRACT: Solid-liquid separation (SLS) in swine manure treatment is an important step due to a substantial amount of organic and inorganic solids that can be removed from liquid wastewater. The aim of this study was to evaluate the efficiency of two mechanical separation processes (screw press and rotary screen) followed by settling and to analyze the composition of liquid fractions. In this sense, total solids (TS), volatile solids (VS), fixed solids (FS), total phosphorous (TP), total Kjeldahl nitrogen (TKN) and total organic carbon (TOC) were analyzed. By combining mechanical separation with settling, the average of TS, VS and FS removal was 75%, 80% and 69%, respectively. Phosphorus removal reached 86%, and TKN achieved a reduction up to 45%. There was no statistical difference among the results obtained using SLS by screw press and rotary screen. It was possible to conclude that SLS process with mechanical devices, followed by settling, generates a suitable effluent to be used on nitrification and denitrification process, producing an effluent with a C/N ratio of 2.6, and the solid fraction is useful to anaerobic digestion
Volcanic Ash and SO2 retrievals using synthetic MODIS TIR data: comparison between inversion procedures and sensitivity analysis
In this work the volcanic ash and SO2 retrievals obtained by applying three different procedures (LUT - Look Up Table, NN - Neural Network and VPR - Volcanic Plume Removal) on MODIS Thermal InfraRed (TIR)
synthetic measurements have been compared. The synthetic measurements are generated using MODTRAN Radiative Transfer Model (RTM) for defined volcanic cloud configurations. The results, presented as the percentage
difference between the retrieved ash and SO2 total masses and the true values used for the synthetic data generation, indicate maximum differences of +/- 15% and +/- 10% for all the procedures and for ash and
SO2 retrievals respectively. A sensitivity analysis has been also realized to investigate the influence of volcanic
cloud altitude and water vapour profile on SO2 retrievals at 7.3 and 8.6 mm. Results confirm the high sensitivity of the 7.3 mm retrieval to the volcanic cloud altitude and show that the SO2 total masses estimated at
7.3 and 8.6 mm separately can be used to improve the information on the plume height. Finally, the water vapour profile is used to compute the minimum altitude over which the 7.3 mm retrieval is effective
- …