34,458 research outputs found
Role of atrial receptors in the control of sodium excretion
Responses of an innervated and a contralateral chronically denervated kidney to mild positive pressure breathing are compared for saline volume expansions in chloralose anesthetized dogs. It is shown that mild pressure breathing significantly reduces sodium excretion, urine flow, free water clearance, and PAH clearance. After 20 minutes of positive pressure breathing, both kidney responses are identical suggesting the release of natriuretic hormone which reduces renal function in addition to the demonstrated change in renal nerve activity. Increase of the left atrial pressure through balloon obstruction of the mitral orifice increases urine flow, sodium excretion and PAH clearance; inflation of the balloon and positive pressure breathing again depresses renal function. Preliminary evidence indicates that receptors in the right atrium are more severely affected by pressure breathing than those in the left atrium
The Origin of the Spatial Distribution of X-ray luminous AGN in Massive Galaxy Clusters
We study the spatial distribution of a 95% complete sample of 508 X-ray point
sources (XPS) detected in the 0.5-2.0 keV band in Chandra ACIS-I observations
of 51 massive galaxy clusters found in the MACS survey. Covering the redshift
range z=0.3-0.7, our cluster sample is statistically complete and comprises all
MACS clusters with X-ray luminosities in excess of 4.5 x 10^44 erg/s (0.1-2.4
keV, h_0=0.7, LCDM). Also studied are 20 control fields that do not contain
clusters. We find the XPS surface density, computed in the cluster restframe,
to exhibit a pronounced excess within 3.5 Mpc of the cluster centers. The
excess, believed to be caused by AGN in the cluster, is significant at the 8.0
sigma confidence level compared to the XPS density observed at the field edges.
No significant central excess is found in the control fields. To investigate
the physical origin of the AGN excess, we study the radial AGN density profile
for a subset of 24 virialized clusters. We find a pronounced central spike
(r<0.5 Mpc), followed by a depletion region at about 1.5 Mpc, and a broad
secondary excess centered at approximately the virial radius of the host
clusters (~2.5 Mpc). We present evidence that the central AGN excess reflects
increased nuclear activity triggered by close encounters between infalling
galaxies and the giant cD-type elliptical occupying the very cluster center. By
contrast, the secondary excess at the cluster-field interface is likely due to
black holes being fueled by galaxy mergers. In-depth spectroscopic and
photometric follow-up observations of the optical counterparts of the XPS in a
subset of our sample are being conducted to confirm this picture.Comment: ApJ Letters, accepted (4 pages, 3 figures, uses emulateapj
Carbocations and the Complex Flavor and Bouquet of Wine: Mechanistic Aspects of Terpene Biosynthesis in Wine Grapes.
Computational chemistry approaches for studying the formation of terpenes/terpenoids in wines are presented, using five particular terpenes/terpenoids (1,8-cineole, α-ylangene, botrydial, rotundone, and the wine lactone), volatile compounds (or their precursors) found in wine and/or wine grapes, as representative examples. Through these examples, we show how modern computational quantum chemistry can be employed as an effective tool for assessing the validity of proposed mechanisms for terpene/terpenoid formation
Investigation to determine the effects of long-term bed rest on G-tolerance and on psychomotor performance Final report
Prolonged bed rest effects on gravity tolerance and psychomotor performance of human
XMM-Newton and Gemini Observations of Eight RASSCALS Galaxy Groups
We study the distribution of gas pressure and entropy in eight groups of
galaxies belonging to the ROSAT All-Sky Survey / Center for Astrophysics Loose
Systems (RASSCALS). We use archival and proprietary XMM-Newton observations,
supplementing the X-ray data with redshifts derived from the literature; we
also list 127 new redshifts measured with the Gemini North telescope. The
groups show remarkable self-similarity in their azimuthally averaged entropy
and temperature profiles. The entropy increases with radius; the behavior of
the entropy profiles is consistent with an increasing broken power law with
inner and outer slope 0.92+0.04-0.05 and 0.42+0.05-0.04 (68% confidence),
respectively. There is no evidence of a central, isentropic core, and the
entropy distribution in most of the groups is flatter at large radii than in
the inner region, challenging earlier reports as well as theoretical models
predicting large isentropic cores or asymptotic slopes of 1.1 at large radii.
The pressure profiles are consistent with a self-similar decreasing broken
power law in radius; the inner and outer slopes are -0.78+0.04-0.03 and
-1.7+0.1-0.3, respectively. The results suggest that the larger scatter in the
entropy distribution reflects the varied gasdynamical histories of the groups;
the regularity and self-similarity of the pressure profiles is a sign of a
similarity in the underlying dark matter distributions.Comment: Accepted for publication in the Astrophysical Journa
Structural anomalies, spin transitions and charge disproportionation in LnCoO3
The diamagnetic-paramagnetic and insulator-metal transitions in LnCoO3
perovskites (Ln = La, Y, rare earths) are reinterpreted and modeled as a
two-level excitation process. In distinction to previous models, the present
approach can be characterized as a LS-HS-IS (low-high-intermediate spin)
scenario. The first level is the local excitation of HS Co3+ species in the LS
ground state. The second excitation is based on the interatomic electron
transfer between the LS/HS pairs, leading finally to a stabilization of the
metallic phase based on IS Co3+. The model parameters have been quantified for
Ln = La, Pr and Nd samples using the powder neutron diffraction on the thermal
expansion of Co-O bonds, that is associated with the two successive spin
transitions. The same model is applied to interpret the magnetic susceptibility
of LaCoO3 and YCoO3.Comment: 52.Conference on Magnetism and Magnetic Materials, November 2007,
Tamp
Spot activity of the RS CVn star {\sigma} Geminorum
We model the photometry of RS CVn star Geminorum to obtain new
information on the changes of the surface starspot distribution, i.e., activity
cycles, differential rotation and active longitudes. We use the previously
published Continuous Periods Search-method (CPS) to analyse V-band differential
photometry obtained between the years 1987 and 2010 with the T3 0.4 m Automated
Telescope at the Fairborn Observatory. The CPS-method divides data into short
subsets and then models the light curves with Fourier-models of variable orders
and provides estimates of the mean magnitude, amplitude, period and light curve
minima. These light curve parameters are then analysed for signs of activity
cycles, differential rotation and active longitudes. We confirm the presence of
two previously found stable active longitudes, synchronised with the orbital
period d and find eight events where the active longitudes
are disrupted. The epochs of the primary light curve minima rotate with a
shorter period d than the orbital motion. If the
variations in the photometric rotation period were to be caused by differential
rotation, this would give a differential rotation coefficient of . The presence of two slightly different periods of active regions may
indicate a superposition of two dynamo modes, one stationary in the orbital
frame and the other one propagating in the azimuthal direction. Our estimate of
the differential rotation is much higher than previous results. However,
simulations show that this can be caused by insufficient sampling in our data.Comment: 10 pages, 6 figures. Submitted to A&
Identification of the X-ray pulsar in Hercules: A new optical pulsar
A series of photographic, photoelectric, and spectroscopic observations beginning June 1, 1972 has led to the optical identification of Her X-1 (2U 1705 + 34), a pulsed X-ray source in an eclipsing binary system, with the thirteenth magnitude blue variable star HZ Herculis. The detection of optical pulses at the frequency of the X-ray pulsar on three nights makes the identification conclusive and establishes HZ Her as the second known optical pulsar. The strength of the optical pulses may be correlated with the orbital phase but is not obviously related to the high or low intensity states of the X-ray source
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