3,104 research outputs found
Radial Surface Density Profiles of Gas and Dust in the Debris Disk around 49 Ceti
We present ~0.4 resolution images of CO(3-2) and associated continuum
emission from the gas-bearing debris disk around the nearby A star 49 Ceti,
observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). We
analyze the ALMA visibilities in tandem with the broad-band spectral energy
distribution to measure the radial surface density profiles of dust and gas
emission from the system. The dust surface density decreases with radius
between ~100 and 310 au, with a marginally significant enhancement of surface
density at a radius of ~110 au. The SED requires an inner disk of small grains
in addition to the outer disk of larger grains resolved by ALMA. The gas disk
exhibits a surface density profile that increases with radius, contrary to most
previous spatially resolved observations of circumstellar gas disks. While ~80%
of the CO flux is well described by an axisymmetric power-law disk in Keplerian
rotation about the central star, residuals at ~20% of the peak flux exhibit a
departure from axisymmetry suggestive of spiral arms or a warp in the gas disk.
The radial extent of the gas disk (~220 au) is smaller than that of the dust
disk (~300 au), consistent with recent observations of other gas-bearing debris
disks. While there are so far only three broad debris disks with well
characterized radial dust profiles at millimeter wavelengths, 49 Ceti's disk
shows a markedly different structure from two radially resolved gas-poor debris
disks, implying that the physical processes generating and sculpting the gas
and dust are fundamentally different.Comment: 20 pages, 8 figures, accepted for publication in ApJ March 31, 2017
(submitted Nov 2016
Expression of Drug Targets in Patients Treated with Sorafenib, Carboplatin and Paclitaxel
Introduction: Sorafenib, a multitarget kinase inhibitor, targets members of the mitogen-activated protein kinase (MAPK) pathway and VEGFR kinases. Here we assessed the association between expression of sorafenib targets and biomarkers of taxane sensitivity and response to therapy in pre-treatment tumors from patients enrolled in ECOG 2603, a phase III comparing sorafenib, carboplatin and paclitaxel (SCP) to carboplatin, paclitaxel and placebo (CP). Methods: Using a method of automated quantitative analysis (AQUA) of in situ protein expression, we quantified expression of VEGF-R2, VEGF-R1, VEGF-R3, FGF-R1, PDGF-Rβ, c-Kit, B-Raf, C-Raf, MEK1, ERK1/2, STMN1, MAP2, EB1 and Bcl-2 in pretreatment specimens from 263 patients. Results: An association was found between high FGF-R1 and VEGF-R1 and increased progression-free survival (PFS) and overall survival (OS) in our combined cohort (SCP and CP arms). Expression of FGF-R1 and VEGF-R1 was higher in patients who responded to therapy ((CR+PR) vs. (SD+PD+ un-evaluable)). Conclusions: In light of the absence of treatment effect associated with sorafenib, the association found between FGF-R1 and VEGF-R1 expression and OS, PFS and response might reflect a predictive biomarker signature for carboplatin/paclitaxel-based therapy. Seeing that carboplatin and pacitaxel are now widely used for this disease, corroboration in another cohort might enable us to improve the therapeutic ratio of this regimen. © 2013 Jilaveanu et al
Evaluation of Hypervelocity Carbon Dioxide Blunt Body Experiments in an Expansion Tube Facility
This work represents efforts to study high-enthalpy carbon dioxide flows in anticipation
of the upcoming Mars Science Laboratory (MSL) and future missions. The
current study extends the previous presentation of experimental results by the comparison
now with axisymmetric simulations incorporating detailed thermochemical
modeling. The work is motivated by observed anomalies between experimental
and numerical studies in hypervelocity impulse facilities. In this work, experiments
are conducted in the Hypervelocity Expansion Tube (HET) which, by virtue of its
flow acceleration process, exhibits minimal freestream dissociation in comparison
to reflected shock tunnels. This simplifies the comparison with computational result
as freestream dissociation and considerable thermochemical excitation can be
neglected. Shock shapes of the Laboratory aeroshell and spherical geometries are
compared with numerical simulations. In an effort to address surface chemistry
issues arising from high-enthalpy carbon dioxide ground-test based experiments,
spherical stagnation point and aeroshell heat transfer distributions are also compared
with simulation. The shock stand-off distance has been identified in the
past as sensitive to the thermochemical state and as such, is used here as an experimental
measureable for comparison with CFD and two different theoretical
models. For low-density, small-scale experiments it is seen that models based upon
assumptions of large binary scaling values are unable to match the experimental
and numerical results. Very good agreement between experiment and CFD is seen
for all shock shapes and heat transfer distributions fall within the non-catalytic and
super-catalytic solutions
Experimental and Numerical Investigation of Hypervelocity Carbon Dioxide Flow over Blunt Bodies
This paper represents ongoing efforts to study high-enthalpy carbon dioxide flows in anticipation of the upcoming
Mars Science Laboratory and future missions. The work is motivated by observed anomalies between experimental
and numerical studies in hypervelocity impulse facilities. In this study, experiments are conducted in the
hypervelocity expansion tube that, by virtue of its flow acceleration process, exhibits minimal freestream dissociation
in comparison with reflected shock tunnels, simplifying comparison with simulations. Shock shapes of the laboratory
aeroshell at angles of attack of 0, 11, and 16 deg and spherical geometries are in very good agreement with simulations
incorporating detailed thermochemical modeling. Laboratory shock shapes at a 0 deg of attack are also in good
agreement with data from the LENS X expansion tunnel facility, confirming results are facility-independent for the
same type of flow acceleration. The shock standoff distance is sensitive to the thermochemical state and is used as an
experimental measurable for comparison with simulations and two different theoretical models. For low-density
small-scale experiments, it is seen that models based upon assumptions of large binary scaling values do not match the
experimental and numerical results. In an effort to address surface chemistry issues arising in high-enthalpy groundtest
experiments, spherical stagnation point and aeroshell heat transfer distributions are also compared with the
simulation. Heat transfer distributions over the aeroshell at the three angles of attack are in reasonable agreement
with simulations, and the data fall within the noncatalytic and supercatalytic solutions
Molecular hydrogen jets and outflows in the Serpens south filamentary cloud
We aimed to map the jets and outflows from the Serpens South star forming
region and find an empirical relationship between the magnetic field and
outflow orientation. Near-infrared H2 v=1-0 S(1) 2.122{\mu}m -line imaging of
the \sim 30'-long filamentary shaped Serpens South star forming region was
carried out. K s broadband imaging of the same region was used for continuum
subraction. Candidate driving sources of the mapped jets/outflows are
identified from the list of known protostars and young stars in this region,
which was derived from studies using recent Spitzer and Herschel telescope
observations. 14 Molecular Hydrogen emission-line objects(MHOs) are identified
using our continuum-subtracted images. They are found to constitute ten
individual flows. Out of these, nine flows are located in the
lower-half(southern) part of the Serpens South filament, and one flow is
located at the northern tip of the filament. Four flows are driven by
well-identified Class 0 protostars, while the remaining six flows are driven by
candidate protostars mostly in the Class I stage, based on the Spitzer and
Herschel observations. The orientation of the outflows is systematically
perpendicular to the direction of the near-infrared polarization vector,
recently published in the literature. No significant correlation was observed
between the orientation of the flows and the axis of the filamentary cloud.Comment: Accepted by A&A for publication. 7 pages, 5 figure
Spitzer-IRAC GLIMPSE of high mass protostellar objects. I Infrared point sources and nebulae
The GLIMPSE archive was used to obtain 3.6--8.0micron, point source
photometry and images for 381 massive protostellar candidates lying in the
Galactic mid-plane. The colours, magnitudes and spectral indicies of sources in
each of the 381 target fields were analysed and compared with the predictions
of 2D radiative transfer model simulations. Although no discernable embedded
clusters were found in any targets, multiple sources or associations of
redenned young stellar objects were found in many sources indicating
multiplicity at birth. The spectral index () of these point sources in
3.6--8.0mum bands display large values of =2--5. A color-magnitude
analog plot was used to identify 79 infrared counterparts to the HMPOs. Compact
nebulae are found in 75% of the detected sources with morphologies that can be
well described by core-halo, cometary, shell-like and bipolar geometries
similar to those observed in ultra-compact HII regions. The IRAC band SEDs of
the IR counterparts of HMPOs are best described to represent YSOs with a mass
range of 8--20\msun in their Class I stages when compared with 2D radiative
transfer models. They also suggest that the high values represent
reprocessed star/star+disk emission that is arising in the dense envelopes.
Thus we are witnessing the luminous envelopes around the protostars rather than
their photospheres or disks. We argue that the compact infrared nebulae likely
reflect the underlying physical structure of the dense cores and are found to
imitate the morphologies of known UCHII regions. Our results favour models of
continuuing accretion involving both molecular and ionised accretion components
to build the most massive stars rather than purely molecular rapid accretion
flows.Comment: 13 pages, 7 figures, accepted by A&
Infrared Variability of Evolved Protoplanetary Disks: Evidence for Scale Height Variations in the Inner Disk
We present the results of a multi-wavelength multi-epoch survey of five
evolved protoplanetary disks in the IC 348 cluster that show significant
infrared variability. Using 3-8micron and 24micron photometry along with
5-40micron spectroscopy from the Spitzer Space Telescope, as well as
ground-based 0.8-5micron spectroscopy, optical spectroscopy and near-infrared
photometry, covering timescales of days to years, we examine the variability in
the disk, stellar and accretion flux. We find substantial variations (10-60%)
at all infrared wavelengths on timescales of weeks to months for all of these
young stellar objects. This behavior is not unique when compared to other
cluster members and is consistent with changes in the structure of the inner
disk, most likely scale height fluctuations on a dynamical timescale. Previous
observations, along with our near-infrared photometry, indicate that the
stellar fluxes are relatively constant; stellar variability does not appear to
drive the large changes in the infrared fluxes. Based on our near-infrared
spectroscopy of the Pa-beta and Br-gamma lines we find that the accretion rates
are variable in most of the evolved disks but the overall rates are probably
too small to cause the infrared variability. We discuss other possible physical
causes for the variability, including the influence of a companion, magnetic
fields threading the disk, and X-ray flares.Comment: Accepted to ApJ. 33 pages, emulate apj forma
Galactic bulge giants: probing stellar and galactic evolution I. Catalogue of Spitzer IRAC and MIPS sources
Aims: We aim at measuring mass-loss rates and the luminosities of a
statistically large sample of Galactic bulge stars at several galactocentric
radii. The sensitivity of previous infrared surveys of the bulge has been
rather limited, thus fundamental questions for late stellar evolution, such as
the stage at which substantial mass-loss begins on the red giant branch and its
dependence on fundamental stellar properties, remain unanswered. We aim at
providing evidence and answers to these questions. Methods: To this end, we
observed seven 15 times 15 arcmin^2 fields in the nuclear bulge and its
vicinity with unprecedented sensitivity using the IRAC and MIPS imaging
instruments on-board the Spitzer Space Telescope. In each of the fields, tens
of thousands of point sources were detected. Results: In the first paper based
on this data set, we present the observations, data reduction, the final
catalogue of sources, and a detailed comparison to previous mid-IR surveys of
the Galactic bulge, as well as to theoretical isochrones. We find in general
good agreement with other surveys and the isochrones, supporting the high
quality of our catalogue.Comment: 21 pages, accepted for publication in A&A. A version with
high-resolution figures, as well as the data catalogues (including cross-id
with GLIMPSE and GALCEN) and image mosaics are available at the anonymous
ftp://ftp.ster.kuleuven.be/dist/stefan/Spitzer
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