977 research outputs found
Evaluation of an entraining droplet activation parameterization using in situ cloud data
This study investigates the ability of a droplet activation parameterization (which considers the effects of entrainment and mixing) to reproduce observed cloud droplet
number concentration (CDNC) in ambient clouds. Predictions of the parameterization are compared against cloud averages of CDNC from ambient cumulus and stratocumulus clouds sampled during CRYSTAL‐FACE (Key West, Florida, July 2002) and CSTRIPE (Monterey, California, July 2003), respectively. The entrainment parameters required by the
parameterization are derived from the observed liquid water content profiles. For the cumulus clouds considered in the study, CDNC is overpredicted by 45% with the adiabatic
parameterization. When entrainment is accounted for, the predicted CDNC agrees within 3.5%. Cloud‐averaged CDNC for stratocumulus clouds is well captured when entrainment is
not considered. In all cases considered, the entraining parameterization compared favorably against a statistical correlation developed from observations to treat entrainment effects on droplet number. These results suggest that including entrainment effects in the calculation of CDNC, as presented here, could address important overprediction biases associated with using adiabatic CDNC to represent cloud‐scale average values
The QSO HE0450-2958: Scantily dressed or heavily robed? A normal quasar as part of an unusual ULIRG
(Abridged) The luminous z=0.286 quasar HE0450-2958 is interacting with a
companion galaxy at 6.5 kpc distance and the whole system is a ULIRG. A so far
undetected host galaxy triggered the hypothesis of a mostly "naked" black hole
(BH) ejected from the companion by three-body interaction. We present new
HST/NICMOS 1.6micron imaging data at 0.1" resolution and VLT/VISIR 11.3micron
images at 0.35" resolution that for the first time resolve the system in the
near- and mid-infrared. We combine these with existing optical HST and CO maps.
(i) At 1.6micron we find an extension N-E of the quasar nucleus that is
likely a part of the host galaxy, though not its main body. If true, this
places HE0450-2958 directly onto the M_BH-M_bulge-relation for nearby galaxies.
(ii) HE0450-2958 is consistent with lying at the high-luminosity end of
Narrow-Line Seyfert 1 Galaxies, and more exotic explanations like a "naked
quasar" are unlikely. (iii) All 11.3micron radiation in the system is emitted
by the quasar nucleus, which is radiating at super-Eddington rate,
L/L_Edd=6.2+3.8-1.8, or 12 M_sun/yr. (iv) The companion galaxy is covered in
optically thick dust and is not a collisional ring galaxy. It emits in the far
infrared at ULIRG strength, powered by Arp220-like star formation (strong
starburst-like). An M82-like SED is ruled out. (v) With its black hole
accretion rate HE0450-2958 produces not enough new stars to maintain its
position on the M_BH-M_bulge-relation, and star formation and black hole
accretion are spatially disjoint; the bulge has to grow by redistribution of
preexisting stars. (vi) Systems similar to HE0450-2958 with spatially disjoint
ULIRG-strength star formation and quasar activity are rare. At z<0.43 we only
find <4% (3/77) candidates for a similar configuration.Comment: 12 pages, 6 figures, accepted for publication in Ap
Structure–property relationship of defect-trapped Pt single-site electrocatalysts for the hydrogen evolution reaction
Single-site catalysts (SSCs) have attracted significant research interest due to their high metal atom utilization. Platinum single sites trapped in the defects of carbon substrates (trapped Pt-SSCs) have been proposed as efficient and stable electrocatalysts for the hydrogen evolution reaction (HER). However, the correlation between Pt bonding environment, its evolution during operation, and catalytic activity is still unclear. Here, a trapped Pt-SSC is synthesized by pyrolysis of H2PtCl6 chemisorbed on a polyaniline substrate. In situ heated scanning transmission electron microscopy and temperature-dependent X-ray photoelectron spectroscopy clarify the thermally induced structural evolution of Pt during pyrolysis. The results show that the nitrogen in polyaniline coordinates with Pt ions and atomically disperses them before pyrolysis and traps Pt sites at pyridinic N defects generated during the substrate graphitization. Operando X-ray absorption spectroscopy confirms that the trapped Pt-SSC is stable at the HER working potentials but with inferior electrocatalytic activity compared with metallic Pt nanoparticles. First principle calculations suggest that the inferior activity of trapped Pt-SSCs is due to their unfavorable hydrogen chemisorption energy relative to metallic Pt(111) surfaces. These results further the understanding of the structure–property relationship in trapped Pt-SSCs and motivate a detailed techno-economic analysis to evaluate their commercial applicability
Assessment of Surface Water Contamination from Coalbed Methane Fracturing-Derived Volatile Contaminants in Sullivan County, Indiana, USA
There is a growing concern over the contamination of surface water and the associated environmental and public health consequences from the recent proliferation in hydraulic fracturing in the USA. Petroleum hydrocarbon-derived contaminants of concern [benzene, toluene, ethylbenzene, and xylene (BTEX)] and various dissolved cations and anions were spatially determined in surface waters around 14 coalbed methane fracking wells in Sullivan County, IN, USA. At least one BTEX was detected in 69% of sampling sites (n=13) and 23% of sampling sites were found to be contaminated with all of the BTEX. Toluene was the most common BTEX compound detected across all sites, both upstream and downstream from coalbed methane fracking sites. The calcium (~60 ppm) and sulfates (~175 ppm) were the dominant cations and anions, respectively, in surface water around the fracking sites. This study represents the first report of BTEX contamination in surface water from coalbed methane hydraulic fracturing wells
Spectroscopic Study of SU UMa-type Dwarf Nova YZ Cnc during its 2002 Superoutburst
We report time-resolved spectroscopic observations of the SU Ursae Majoris
dwarf nova, YZ Cnc, for 2 nights over 11 hrs during its 2002 January
superoutburst. The spectra only show absorption-line profiles in the first day.
But the lines display blue and red troughs, with ``W'' profiles in the second
day. The radial velocity curve of the absorption troughs and emission peaks of
H has an amplitude of km s and a phase offset of
, which are very similar to those measured in quiescence;
however, the velocity deviates strongly from the systemic velocity
measured in quiescence, showing variation of the order of 60 km s.
And large shifts of 70 km s and 0.09, for the
orbital-averaged velocity and phase respectively, are also found in our
observations. All these phenomena can be well explained with a precession of an
eccentric disk and we conclude that these phenomena are the characteristic
products of an eccentric accretion disk.Comment: 11 pages, 4 figures, accepted for publication in ChJA
Neurochemical Changes in the Mouse Hippocampus Underlying the Antidepressant Effect of Genetic Deletion of P2X7 Receptors.
Recent investigations have revealed that the genetic deletion of P2X7 receptors (P2rx7) results in an antidepressant phenotype in mice. However, the link between the deficiency of P2rx7 and changes in behavior has not yet been explored. In the present study, we studied the effect of genetic deletion of P2rx7 on neurochemical changes in the hippocampus that might underlie the antidepressant phenotype. P2X7 receptor deficient mice (P2rx7-/-) displayed decreased immobility in the tail suspension test (TST) and an attenuated anhedonia response in the sucrose preference test (SPT) following bacterial endotoxin (LPS) challenge. The attenuated anhedonia was reproduced through systemic treatments with P2rx7 antagonists. The activation of P2rx7 resulted in the concentration-dependent release of [3H]glutamate in P2rx7+/+ but not P2rx7-/- mice, and the NR2B subunit mRNA and protein was upregulated in the hippocampus of P2rx7-/- mice. The brain-derived neurotrophic factor (BDNF) expression was higher in saline but not LPS-treated P2rx7-/- mice; the P2rx7 antagonist Brilliant blue G elevated and the P2rx7 agonist benzoylbenzoyl ATP (BzATP) reduced BDNF level. This effect was dependent on the activation of NMDA and non-NMDA receptors but not on Group I metabotropic glutamate receptors (mGluR1,5). An increased 5-bromo-2-deoxyuridine (BrdU) incorporation was also observed in the dentate gyrus derived from P2rx7-/- mice. Basal level of 5-HT was increased, whereas the 5HIAA/5-HT ratio was lower in the hippocampus of P2rx7-/- mice, which accompanied the increased uptake of [3H]5-HT and an elevated number of [3H]citalopram binding sites. The LPS-induced elevation of 5-HT level was absent in P2rx7-/- mice. In conclusion there are several potential mechanisms for the antidepressant phenotype of P2rx7-/- mice, such as the absence of P2rx7-mediated glutamate release, elevated basal BDNF production, enhanced neurogenesis and increased 5-HT bioavailability in the hippocampus
Double quasars: probes of black hole scaling relationships and merger scenarios
We analyze the available sample of double quasars, and investigate their
physical properties. Our sample comprises 85 pairs, selected from the Sloan
Digital Sky Survey (SDSS). We derive physical parameters for the engine and the
host, and model the dynamical evolution of the pair. First, we compare
different scaling relationships between massive black holes and their hosts
(bulge mass, velocity dispersion, and their possible redshift dependences), and
discuss their consistency. We then compute dynamical friction timescales for
the double quasar systems to investigate their frequency and their agreement
with scenarios for quasar triggering. Comparing typical merging timescales to
expected quasar lifetimes, the fraction of double quasars should be roughly a
factor of 10 larger than observed. Additionally, we find that, depending on the
correlations between black holes and their hosts, the occurrence of double
quasars could be redshift-dependent. Comparison of our models to the SDSS
quasar catalog suggests that double quasars should be more common at high
redshift. We compare the typical separations at which double quasars are
observed to the predictions of merger simulations. We find that the
distribution of physical separations peaks at ~30 kpc, with a tail at larger
separations (~100-200 kpc). These large separation pairs are instead consistent
with unequal mass mergers where gas is dynamically perturbed during the first
pericentric passage, but the gas reaches the black hole only at the next
apocenter, where the pair is observed.Comment: ApJ in pres
PTH Signaling During Exercise Contributes to Bone Adaptation
Improving the structural integrity of bone reduces fracture risk and development of osteoporosis later in life. Exercise can increase the mechanical properties of bone, and this increase is often attributed to the dynamic loading created during exercise. However, the increase in systemic parathyroid hormone (PTH) levels during exercise gives reason to hypothesize that PTH signaling also regulates bone adaptation in response to exercise. Therefore, the first aim of this study was to establish the impact PTH signaling has on bone adaptation during exercise by inhibiting PTH signaling with PTH(7‐34); the second aim was to determine whether increasing PTH levels during exercise with PTH(1‐34) can augment bone adaptation. Thirty minutes after a single bout of running on a treadmill, mice exhibited a twofold increase in systemic PTH levels. Under the same exercise regimen, the influence of PTH signaling on bone adaptation during exercise was then evaluated in mice after 21 consecutive days of exercise and treatment with PTH(7‐34), PTH(1‐34), or vehicle. Exercise alone caused a significant increase in trabecular bone volume with adaptation to a more platelike structure, which was inhibited with PTH(7‐34) during exercise. Changes in structural‐level and tissue‐level mechanical properties during exercise occurred in the absence of significant changes to cortical bone geometry. Inhibition of PTH signaling during exercise attenuated the changes in structural‐level mechanical properties, but not tissue‐level properties. Enhanced PTH signaling during exercise with PTH(1‐34) increased trabecular and cortical bone volume, but had little effect on the structural‐level and tissue‐level mechanical properties compared to exercise alone. Our study is the first to demonstrate that bone adaptation during exercise is not only a function of dynamic loading, but also PTH release, and that PTH signaling contributes differently at the structural and tissue levels. © 2015 American Society for Bone and Mineral Research.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111785/1/jbmr2432.pd
Advancing Research on the Complex Interrelations Between Atrial Fibrillation and Heart Failure A Report From a US National Heart, Lung, and Blood Institute Virtual Workshop
The interrelationships between atrial fibrillation (AF) and heart failure (HF) are complex and poorly understood, yet the number of patients with AF and HF continues to increase worldwide. Thus, there is a need for initiatives that prioritize research on the intersection between AF and HF. This article summarizes the proceedings of a virtual workshop convened by the US National Heart, Lung, and Blood Institute to identify important research opportunities in AF and HF. Key knowledge gaps were reviewed and research priorities were proposed for characterizing the pathophysiological overlap and deleterious interactions between AF and HF; preventing HF in people with AF; preventing AF in individuals with HF; and addressing symptom burden and health status outcomes in AF and HF. These research priorities will hopefully help inform, encourage, and stimulate innovative, cost-efficient, and transformative studies to enhance the outcomes of patients with AF and HF
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