379 research outputs found
Particle transport in evolving protoplanetary disks: Implications for results from Stardust
Samples returned from comet 81P/Wild 2 by Stardust confirm that substantial
quantities of crystalline silicates were incorporated into the comet at
formation. We investigate the constraints that this observation places upon
protoplanetary disk physics, assuming that outward transport of particles
processed at high temperatures occurs via advection and turbulent diffusion in
an evolving disk. We also look for constraints on particle formation locations.
Our results are based upon 1D disk models that evolve with time under the
action of viscosity and photoevaporation, and track solid transport using an
ensemble of individual particle trajectories. We find that two classes of disk
model are consistent with the Stardust findings. One class features a high
particle diffusivity (a Schmidt number Sc < 1), which suffices to diffuse
particles up to 20 microns in size outward against the mean gas flow. For Sc >
1, such models are unlikely to be viable, and significant outward transport
requires that the particles of interest settle into a midplane layer that
experiences an outward gas flow. In either class of models, the mass of inner
disk material that reaches the outer disk is a strong function of the disk's
initial compactness. Hence, models of grain transport within steady-state disks
underestimate the efficiency of outward transport. Neither model results in
sustained outward transport of very large particles exceeding a mm in size. We
show that the transport efficiency generally falls off rapidly with time.
Hence, high-temperature material must be rapidly incorporated into icy bodies
to avoid fallback, and significant radial transport may only occur during the
initial phase of rapid disk evolution. It may also vary substantially between
disks depending upon their initial mass distributions. We discuss implications
for Spitzer observations of crystalline silicates in T Tauri disks.Comment: ApJ, in pres
Spectral structure near the 11.3 micron emission feature
If the 11.3 micron emission feature seen in the spectra of many planetary nebulae, H II regions, and reflection nebulae is attributable to polycyclic aromatic hydrocarbons (PAHs), then additional features should be present between 11.3 and 13.0 microns. Moderate resolution spectra of NGC 7027, HD 44179, BD+30 deg 3639, and IRAS 21282+5050 are presented which show evidence for new emission features centered near 12.0 and 12.7 microns. These are consistent with an origin from PAHs and can be used to constrain the molecular structure of the family of PAHs responsible for the infrared features. There is an indication that coronene-like PAHs contribute far more to the emission from NGC 7027 than to the emission from HD 44179. The observed asymmetric profile of the 11.3 micron band in all the spectra is consistent with the slight anharmonicity expected in the C-H out-of-plane bending mode in PAHs. A series of repeating features between 10 and 11 microns in the spectrum of HD 44179 suggests a simple hydride larger than 2 atoms is present in the gas phase in this object
Patient-Reported Outcomes and Factors Associated With Patient Satisfaction After Surgical Treatment of Facial Nonmelanoma Skin Cancer
The origin of crystalline silicates in the Herbig Be star HD100546 and in comet Hale-Bopp
We have investigated the spatial distribution, and the properties and
chemical composition of the dust orbiting HD 100546. This system is remarkably
different from other isolated Herbig Ae/Be stars in both the strength of the
mid-IR excess and the composition of the circumstellar dust. We speculate that
the formation and spatial distribution of the crystalline dust observed in the
HD 100546 system may be linked to the formation of a proto-Jupiter in the disk
around HD 100546. Such a proto-Jupiter could gravitationally stir the disk
leading to a collisional cascade of asteroidal sized objects producing small
crystalline grains, or it could cause shocks by tidal interaction with the disk
which might produce crystalline dust grains through flash heating. As shown by
Malfait et al. (1998), the infrared spectrum of HD 100546 is very similar to
that of C/1995 O1 Hale-Bopp (Crovisier et al. 1997). Using an identical
methodology, we have therefore also studied this solar system comet. Both
objects have an almost identical grain composition, but with the important
difference that the individual dust species in Hale-Bopp are in thermal contact
with each other, while this is not the case in HD 100546. This suggests that if
similar processes leading to the dust composition as seen in HD 100546 also
occurred in our own solar system, that Hale-Bopp formed after the formation of
one or more proto-gas giants.Comment: 17 pages, 10 figures, Accepted for publication in Astronomy and
Astrophysic
Testing models of Laramide orogenic initiation by investigation of Late Cretaceous magmatic-tectonic evolution of the central Mojave sector of the California arc
The Mojave Desert region is in a critical position for assessing models of Laramide orogenesis, which is hypothesized to have initiated as one or more seamounts subducted beneath the Cretaceous continental margin. Geochronological and geochemical characteristics of Late Cretaceous magmatic products provide the opportunity to test the validity of Laramide orogenic models. Laramide-aged plutons are exposed along a transect across the Cordilleran Mesozoic magmatic system from Joshua Tree National Park in the Eastern Transverse Ranges eastward into the central Mojave Desert. A transect at latitude âŒ33.5°N to 34.5°N includes: (1) the large upper-crustal Late Cretaceous Cadiz Valley batholith, (2) a thick section of Proterozoic to Jurassic host rocks, (3) Late Cretaceous stock to pluton-sized bodies at mesozonal depths, and (4) a Jurassic to Late Cretaceous midcrustal sheeted complex emplaced at âŒ20 km depth that transitions into a migmatite complex truncated along the San Andreas fault. This magmatic section is structurally correlative with the Big Bear Lake intrusive suite in the San Bernardino Mountains and similar sheeted rocks recovered in the Cajon Pass Deep Scientific Drillhole. Zircon U-Pb geochronology of 12 samples via secondary ionization mass spectrometry (SIMS) (six from the Cadiz Valley batholith and six from the Cajon Pass Deep Scientific Drillhole) indicates that all Cretaceous igneous units investigated were intruded between 83 and 74 Ma, and Cajon Pass samples include a Jurassic age component. A compilation of new and published SIMS geochronological data demonstrates that voluminous magmatism in the Eastern Transverse Ranges and central Mojave Desert was continuous throughout the period suggested for the intersection and flat-slab subduction of the Shatsky Rise conjugate deep into the interior of western North America. Whole-rock major-element, trace-element, and isotope geochemistry data from samples from a suite of 106 igneous rocks represent the breadth of Late Cretaceous units in the transect. Geochemistry indicates an origin in a subduction environment and intrusion into a crust thick enough to generate residual garnet. The lack of significant deflections of compositional characteristics and isotopic ratios in igneous products through space and time argues against a delamination event prior to 74 Ma. We argue that Late Cretaceous plutonism from the Eastern Transverse Ranges to the central Mojave Desert represents subduction zone arc magmatism that persisted until ca. 74 Ma. This interpretation is inconsistent with the proposed timing of the docking of the Shatsky Rise conjugate with the margin of western North America, particularly models in which the leading edge of the Shatsky Rise was beneath Wyoming at 74 Ma. Alternatively, the timing of cessation of plutonism precedes the timing of the passage of the Hess Rise conjugate beneath western North America at ca. 70â65 Ma. The presence, geochemical composition, and age of arc products in the Eastern Transverse Ranges and central Mojave Desert region must be accounted for in any tectonic model of the transition from Sevier to Laramide orogenesis.Published versio
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Transcriptome-based repurposing of apigenin as a potential anti-fibrotic agent targeting hepatic stellate cells
We have used a computational approach to identify anti-fibrotic therapies by querying a transcriptome. A transcriptome signature of activated hepatic stellate cells (HSCs), the primary collagen-secreting cell in liver, and queried against a transcriptomic database that quantifies changes in gene expression in response to 1,309 FDA-approved drugs and bioactives (CMap). The flavonoid apigenin was among 9 top-ranked compounds predicted to have anti-fibrotic activity; indeed, apigenin dose-dependently reduced collagen I in the human HSC line, TWNT-4. To identify proteins mediating apigeninâs effect, we next overlapped a 122-gene signature unique to HSCs with a list of 160 genes encoding proteins that are known to interact with apigenin, which identified C1QTNF2, encoding for Complement C1q tumor necrosis factor-related protein 2, a secreted adipocytokine with metabolic effects in liver. To validate its disease relevance, C1QTNF2 expression is reduced during hepatic stellate cell activation in culture and in a mouse model of alcoholic liver injury in vivo, and its expression correlates with better clinical outcomes in patients with hepatitis C cirrhosis (n = 216), suggesting it may have a protective role in cirrhosis progression.These findings reinforce the value of computational approaches to drug discovery for hepatic fibrosis, and identify C1QTNF2 as a potential mediator of apigeninâs anti-fibrotic activity
Dust Formation In Early Galaxies
We investigate the sources and amount of dust in early galaxies. We discuss
dust nucleation in stellar atmospheres using published extended atmosphere
models, stellar evolution tracks and nucleation conditions and conclude that
the (TPAGB) phase of intermediate mass stars is likely to be the most promising
site for dust formation in stellar winds. The implications of chemical
evolution models for high redshift galaxies are investigated and we show there
is no difficulty in producing dusty galaxies at redshifts above 5 if supernovae
are a dominant source of interstellar dust. If dust does not condense
efficiently in SNe then significant dust masses can only be generated at by
galaxies with a high star formation efficiency. We find the visual optical
depth for individual star forming clouds can reach values greater than 1 at
very low metallicity (1/100 solar) provided that the mass-radius exponent of
molecular clouds is less than two. Most of the radiation from star formation
will emerge at IR wavelengths in the early universe provided that dust is
present. The (patchy) visual optical depth through a typical early galaxy will
however, remain less than 1 on average until a metallicity of 1/10 solar is
reached.Comment: in press MNRAS, 17 pages with 19 figs, corrected typo
Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV
The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of âs = 7TeV corresponding to an integrated luminosity of 38 pb-1. Jets are reconstructed with the anti-kt algorithm with distance parameters R=0. 4 or R=0. 6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pTâ„20 GeV and pseudorapidities {pipe}η{pipe}<4. 5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2. 5 % in the central calorimeter region ({pipe}η{pipe}<0. 8) for jets with 60â€pT<800 GeV, and is maximally 14 % for pT<30 GeV in the most forward region 3. 2â€{pipe}η{pipe}<4. 5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pT, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pT jets recoiling against a high-pT jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pT jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined. © 2013 CERN for the benefit of the ATLAS collaboration
Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector
The inclusive and dijet production cross-sections have been measured for jets
containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass
energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The
measurements use data corresponding to an integrated luminosity of 34 pb^-1.
The b-jets are identified using either a lifetime-based method, where secondary
decay vertices of b-hadrons in jets are reconstructed using information from
the tracking detectors, or a muon-based method where the presence of a muon is
used to identify semileptonic decays of b-hadrons inside jets. The inclusive
b-jet cross-section is measured as a function of transverse momentum in the
range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet
cross-section is measured as a function of the dijet invariant mass in the
range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets
and the angular variable chi in two dijet mass regions. The results are
compared with next-to-leading-order QCD predictions. Good agreement is observed
between the measured cross-sections and the predictions obtained using POWHEG +
Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet
cross-section. However, it does not reproduce the measured inclusive
cross-section well, particularly for central b-jets with large transverse
momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final
version published in European Physical Journal
Observation of associated near-side and away-side long-range correlations in âsNN=5.02ââTeV proton-lead collisions with the ATLAS detector
Two-particle correlations in relative azimuthal angle (ÎÏ) and pseudorapidity (Îη) are measured in âsNN=5.02ââTeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1ââÎŒb-1 of data as a function of transverse momentum (pT) and the transverse energy (ÎŁETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Îη|<5) ânear-sideâ (ÎÏâŒ0) correlation that grows rapidly with increasing ÎŁETPb. A long-range âaway-sideâ (ÎÏâŒÏ) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ÎŁETPb, is found to match the near-side correlation in magnitude, shape (in Îη and ÎÏ) and ÎŁETPb dependence. The resultant ÎÏ correlation is approximately symmetric about Ï/2, and is consistent with a dominant cosâĄ2ÎÏ modulation for all ÎŁETPb ranges and particle pT
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