1,097 research outputs found
Photoproduction of the meson on the proton at large momentum transfer
The differential cross section, for meson exclusive
photoproduction on the proton above the resonance region ( GeV) was
measured up to a momentum transfer GeV using the CLAS detector at
Jefferson Laboratory. The channel was identified by detecting a proton
and in the final state and using the missing mass technique. While the
low momentum transfer region shows the typical diffractive pattern expected
from Pomeron and Reggeon exchange, at large the differential cross section
has a flat behavior. This feature can be explained by introducing quark
interchange processes in addition to the QCD-inspired two-gluon exchange.Comment: 5 pages, 5 figure
Motor-sensory cortex-corticospinal system and developing locomotion and placing in rats
Normal and abnormal development of movement in the rat were studied by investigating the growth and organization of the motor-sensory cortexcorticospinal tract system (MSC-CST) and the functional and morphologic effects of ablating the MSC or quadrants of it at different ages. Major growth of the MSC outflow, the CST, in the brain stem and rostral cord occurred in the second and third weeks postnatally, coinciding approximately with the normal mid-third week transition from infantile to mature locomotion. Ablation of the MSC at birth revealed that while the MSC-CST was not essential for ordinary locomotion on flat terrain, its presence hastened normal development of this kind of movement, and that it was absolutely essential for locomotion on difficult terrain. The MSC quadrants showed quite different, and in some domains mutually exclusive, CST projection patterns to forebrain, diencephalon, brain stem, and spinal destinations (determined by Fink-Heimer-Nauta fiber degeneration studies). Ablation of some quadrants produced distinctive syndromes of disordered movement: the posterolateral quadrant related to active grasping in positioning limbs, while the posteromedial quadrant related to tactile motorsensory positioning of limbs. Thus in addition to the classic somatotopic organization of the MSC, there was another kind of organization into regions concerned with components of integrated movement of a number of parts of the body. Several forms of aberrant circuitry developed after MSC ablations in infants, but their possible roles in functional adaptation remain to be determined.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49673/1/1001430102_ftp.pd
Composition of Near-Earth Asteroid 2008 EV5: Potential target for Robotic and Human Exploration
We observed potentially hazardous asteroid (PHA) 2008 EV5 in the visible
(0.30-0.92 microns) and near-IR (0.75-2.5 microns) wavelengths to determine its
surface composition. This asteroid is especially interesting because it is a
potential target for two sample return mission proposals (Marco Polo-R and
Hayabusa-2) and human exploration due to its low delta-v for rendezvous. The
spectrum of 2008 EV5 is essentially featureless with exception of a weak
0.48-microns spin-forbidden Fe3+ absorption band. The spectrum also has an
overall blue slope. The albedo of 2008 EV5 remains uncertain with a lower limit
at 0.05 and a higher end at 0.20 based on thermal modeling. The Busch et al.
(2011) albedo estimate of 0.12 is consistent with our thermal modeling results.
The albedo and composition of 2008 EV5 are also consistent with a C-type
taxonomic classification (Somers et al. 2008). The best spectral match is with
CI carbonaceous chondrites similar to Orgueil, which also have a weak
0.48-microns feature and an overall blue slope. This 0.48-microns feature is
also seen in the spectrum of magnetite. The albedo of CI chondrites is at the
lower limit of our estimated range for the albedo of 2008 EV5.Comment: Pages: 19 Figures: 6 Tables:
A Statistical Survey of Ohio Winter Bird Life
Author Institution: Ohio State Universit
Discovery of a New Nearby Star
We report the discovery of a nearby star with a very large proper motion of
5.06 +/- 0.03 arcsec/yr. The star is called SO025300.5+165258 and referred to
herein as HPMS (high proper motion star). The discovery came as a result of a
search of the SkyMorph database, a sensitive and persistent survey that is well
suited for finding stars with high proper motions. There are currently only 7
known stars with proper motions > 5 arcsec/yr. We have determined a preliminary
value for the parallax of 0.43 +/- 0.13 arcsec. If this value holds our new
star ranks behind only the Alpha Centauri system (including Proxima Centauri)
and Barnard's star in the list of our nearest stellar neighbors. The spectrum
and measured tangential velocity indicate that HPMS is a main-sequence star
with spectral type M6.5. However, if our distance measurement is correct, the
HPMS is underluminous by 1.2 +/- 0.7 mag.Comment: 5 pages, 3 figures. Submitted to ApJ Letter
P-Selectin or Intercellular Adhesion Molecule (Icam)-1 Deficiency Substantially Protects against Atherosclerosis in Apolipoprotein E–Deficient Mice
The expression of leukocyte and endothelial cell adhesion molecules (CAMs) is essential for the emigration of leukocytes during an inflammatory response. The importance of the inflammatory response in the development of atherosclerosis is indicated by the increased expression of adhesion molecules, proinflammatory cytokines, and growth factors in lesions and lesion-prone areas and by protection in mice deficient in various aspects of the inflammatory response. We have quantitated the effect of deficiency for intercellular adhesion molecule (ICAM)-1, P-selectin, or E-selectin on atherosclerotic lesion formation at 20 wk of age in apolipoprotein (apo) E−/− (deficient) mice fed a normal chow diet. All mice were apo E−/− and CAM+/+ or CAM−/− littermates, and no differences were found in body weight or cholesterol levels among the various genotypes during the study. ICAM-1−/− mice had significantly less lesion area than their ICAM-1+/+ littermates: 4.08 ± 0.70 mm2 for −/− males vs. 5.87 ± 0.66 mm2 for +/+ males, and 3.95 ± 0.65 mm2 for −/− females vs. 5.59 ± 1.131 mm2 for +/+ females, combined P < 0.0001. An even greater reduction in lesion area was observed in P-selectin−/− mice: 3.06 ± 1.04 mm2 for −/− males vs. 5.09 ± 1.22 mm2 for +/+ males, and 2.85 ± 1.26 mm2 for −/− females compared with 5.60 ± 1.19 mm2 for +/+ females, combined P < 0.001. The reduction in lesion area for the E-selectin null mice, although less than that seen for ICAM-1 or P-selectin, was still significant (4.54 ± 2.14 mm2 for −/− males vs. 5.92 ± 0.63 mm2 for +/+ males, and 4.38 ± 0.85 mm2 for −/− females compared with 5.94 ± 1.44 mm2 for +/+ females, combined P < 0.01). These results, coupled with the closely controlled genetics of this study, indicate that reductions in the expression of P-selectin, ICAM-1, or E-selectin provide direct protection from atherosclerotic lesion formation in this model
Radiation-driven Fountain and Origin of Torus around Active Galactic Nuclei
We propose a plausible mechanism to explain the formation of the so-called
"obscuring tori" around active galactic nuclei (AGNs) based on
three-dimensional hydrodynamic simulations including radiative feedback from
the central source. The X-ray heating and radiation pressure on the gas are
explicitly calculated using a ray-tracing method. This radiation feedback
drives a "fountain", that is, a vertical circulation of gas in the central a
few to tens parsecs. Interaction between the non-steady outflows and inflows
causes the formation of a geometrically thick torus with internal turbulent
motion. As a result, the AGN is obscured for a wide range of solid angles. In a
quasi-steady state, the opening angles for the column density toward a black
hole < 10^23 cm^-2 are approximately +-30 deg and +-50 deg for AGNs with 10%
and 1% Eddington luminosity, respectively. Mass inflows through the torus
coexist with the outflow and internal turbulent motion, and the average mass
accretion rate to the central parsec region is 2x10^-4 ~ 10^-3, M_sun/yr this
is about ten times smaller than accretion rate required to maintain the AGN
luminosity. This implies that relatively luminous AGN activity is intrinsically
intermittent or that there are other mechanisms, such as stellar energy
feedback, that enhance the mass accretion to the center.Comment: 12 pages, 9 figures, accepted publication in Ap
The Nuclear Stellar Disk in Andromeda: A Fossil from the Era of Black Hole Growth
The physics of angular momentum transport from galactic scales (~10-100 pc)
to much smaller radii is one of the oustanding problems in our understanding of
the formation and evolution of super-massive black holes (BHs). Seemingly
unrelated observations have discovered that there is a lopsided stellar disk of
unknown origin orbiting the BH in M31, and possibly many other systems. We show
that these nominally independent puzzles are in fact closely related.
Multi-scale simulations of gas inflow from galactic to BH scales show that when
sufficient gas is driven towards a BH, gravitational instabilities form a
lopsided, eccentric disk that propagates inwards from larger radii. The
lopsided stellar disk exerts a strong torque on the remaining gas, driving
inflows that fuel the growth of the BH and produce quasar-level luminosities.
The same disk can produce significant obscuration along many sightlines and
thus may be the putative 'torus' invoked to explain obscured active galactic
nuclei and the cosmic X-ray background. The stellar relic of this disk is long
lived and retains the eccentric pattern. Simulations that yield quasar-level
accretion rates produce relic stellar disks with kinematics, eccentric
patterns, precession rates, and surface density profiles in reasonable
agreement with observations of M31. The observed properties of nuclear stellar
disks can thus be used to constrain the formation history of super-massive BHs.Comment: 6 pages, 4 figures, accepted to MNRAS Letters (matches published
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