6,111 research outputs found
Calcium-binding proteins immunoreactivity in the human subcortical and cortical visual structures
The distribution of neurons and fibers immunoreactive (ir) to the three calcium-binding proteins parvalbumin (PV), calbindin D-28k (CB), and calretinin (CR) was studied in the human lateral geniculate nucleus (LGN), lateral inferior pulvinar, and optic radiation, and related to that in the visual cortex. In the LGN, PV, CR, and CB immunoreactivity was present in all laminae, slightly stronger in the magnocellular than in the parvocellular laminae for CB and CR. PV-ir puncta, representing transversally cut axons, and CR-ir fibers were revealed within the laminae and interlaminar zones, and just beyond the outer border of lamina 6 in the geniculate capsule. In the optic radiation both PV- and CR-immunoreactive neurons, puncta, and fibers were present. CB immunoreactivity was revealed in neurons of all laminae of the lateral geniculate nucleus, including S lamina and interlaminar zones. There were hardly any CB-ir puncta or fibers in the laminae, interlaminar zones, geniculate capsule, or optic radiation. In the lateral inferior pulvinar, immunoreactive neurons for the three calcium-binding proteins were present in smaller number than in the LGN, as well as PV-ir puncta and CR-ir fibers within the nucleus and in the pulvinar capsule. In the white matter underlying area 17, fibers intermingled with a few scattered neurons were stained for both PV and CR, but very rarely for CB. These fibers stopped at the limit between areas 17 and 18. Area 17 showed a dense plexus of PV-ir puncta and neurons in the thalamo-receptive layer IV and CR-ir puncta and neurons both in the superficial layers I-II, IIIC, and in layer VA. Cajal-Retzius CR-ir neurons were present in layer I. CB-ir puncta were almost confined to layer I-III and CB-ir neurons to layer II. Finally the superior colliculus exhibited mostly populations of PV and CR pyramidal-like immunoreactive neurons, mainly in the intermediate tier. These data suggest that in the visual thalamus most calcium-binding protein immunoreactive neurons project to the visual cortex, while in the superior colliculus a smaller immunoreactive population represent projection neuron
Constraints on the Growth and Spin of the Supermassive Black Hole in M32 From High Cadence Visible Light Observations
We present 1-second cadence observations of M32 (NGC221) with the CHIMERA
instrument at the Hale 200-inch telescope of the Palomar Observatory. Using
field stars as a baseline for relative photometry, we are able to construct a
light curve of the nucleus in the g-prime and r-prime band with 1sigma=36
milli-mag photometric stability. We derive a temporal power spectrum for the
nucleus and find no evidence for a time-variable signal above the noise as
would be expected if the nuclear black hole were accreting gas. Thus, we are
unable to constrain the spin of the black hole although future work will use
this powerful instrument to target more actively accreting black holes. Given
the black hole mass of (2.5+/-0.5)*10^6 Msun inferred from stellar kinematics,
the absence of a contribution from a nuclear time-variable signal places an
upper limit on the accretion rate which is 4.6*10^{-8} of the Eddington rate, a
factor of two more stringent than past upper limits from HST. The low mass of
the black hole despite the high stellar density suggests that the gas liberated
by stellar interactions was primarily at early cosmic times when the low-mass
black hole had a small Eddington luminosity. This is at least partly driven by
a top-heavy stellar initial mass function at early cosmic times which is an
efficient producer of stellar mass black holes. The implication is that
supermassive black holes likely arise from seeds formed through the coalescence
of 3-100 Msun mass black holes that then accrete gas produced through stellar
interaction processes.Comment: 8 pages, 3 figures, submitted to the Astrophysical Journal, comments
welcom
Geomechanical Studies for a Himalayan Tunnel in Jointed Dolomites: A Case History
Reported case history of Himalayan tunnel reveals that Barton\u27s and Bieniawski\u27s classification systems provide better assessment of the rock mass behavior. The design and shear strength parameters derived from these classifications provided a preliminary design of the tunnel, which has been critically evaluated with the design, adopted at site. Based on the structural feature and ground water conditions, a number of tunnelling conditions have been predicted. The studies indicated the loosening rock pressures would be occuring at site with an estimated range of 0. 25 kg/cm2 to 3. 58 kg/cm2. Problems of roof collapse, flowing ground condition and cavity formation may occur during the excavation. Multiple drift excavation method is suggested for extremely poor conditions
Soft x-rays absorption and high-resolution powder x-ray diffraction study of superconducting CaxLa(1-x)Ba(1.75-x)La(0.25+x)Cu3Oy system
We have studied the electronic structure of unoccupied states measured by O
K-edge and Cu L-edge x-ray absorption spectroscopy (XAS), combined with crystal
structure studied by high resolution powder x-ray diffraction (HRPXRD), of
charge-compensated layered superconducting CaxLa(1-x)Ba(1.75-x)La(0.25+x)Cu3Oy
(0<x<0.4, 6.4<y<7.3) cuprate. A detailed analysis shows that, apart from hole
doping, chemical pressure on the electronically active CuO2 plane due to the
lattice mismatch with the spacer layers greatly influences the superconducting
properties of this system. The results suggest chemical pressure to be the most
plausible parameter to control the maximum critical temperatures (Tcmax) in
different cuprate families at optimum hole density.Comment: 14 pages, 11 figures, accepted for publication in Journal of Physics
and Chemistry of Solid
Direct Visualization of Laser-Driven Focusing Shock Waves
Cylindrically or spherically focusing shock waves have been of keen interest
for the past several decades. In addition to fundamental study of materials
under extreme conditions, cavitation, and sonoluminescence, focusing shock
waves enable myriad applications including hypervelocity launchers, synthesis
of new materials, production of high-temperature and high-density plasma
fields, and a variety of medical therapies. Applications in controlled
thermonuclear fusion and in the study of the conditions reached in laser fusion
are also of current interest. Here we report on a method for direct real-time
visualization and measurement of laser-driven shock generation, propagation,
and 2D focusing in a sample. The 2D focusing of the shock front is the
consequence of spatial shaping of the laser shock generation pulse into a ring
pattern. A substantial increase of the pressure at the convergence of the
acoustic shock front is observed experimentally and simulated numerically.
Single-shot acquisitions using a streak camera reveal that at the convergence
of the shock wave in liquid water the supersonic speed reaches Mach 6,
corresponding to the multiple gigapascal pressure range 30 GPa
Cosmology with decaying tachyon matter
We investigate the case of a homogeneous tachyon field coupled to gravity in
a spatially flat Friedman-Robertson-Walker spacetime. Assuming the field
evolution to be exponentially decaying with time we solve the field equations
and show that, under certain conditions, the scale factor represents an
accelerating universe, following a phase of decelerated expansion. We make use
of a model of dark energy (with p=-\rho) and dark matter (p=0) where a single
scalar field (tachyon) governs the dynamics of both the dark components. We
show that this model fits the current supernova data as well as the canonical
\LambdaCDM model. We give the bounds on the parameters allowed by the current
data.Comment: 14 pages, 6 figures, v2, Discussions and references addede
Eccentricity-induced systematic error on parametrized tests of general relativity: hierarchical Bayesian inference applied to a binary black hole population
One approach to testing general relativity (GR) introduces free parameters in
the post-Newtonian (PN) expansion of the gravitational-wave (GW) phase. If
systematic errors on these testing GR (TGR) parameters exceed the statistical
errors, this may signal a false violation of GR. Here, we consider systematic
errors produced by unmodeled binary eccentricity. Since the eccentricity of GW
events in ground-based detectors is expected to be small or negligible, the use
of quasicircular waveform models for testing GR may be safe when analyzing a
small number of events. However, as the catalog size of GW detections
increases, more stringent bounds on GR deviations can be placed by combining
information from multiple events. In that case, even small systematic biases
may become significant. We apply the approach of hierarchical Bayesian
inference to model the posterior probability distributions of the TGR
parameters inferred from a population of eccentric binary black holes (BBHs).
We assume each TGR parameter value varies across the BBH population according
to a Gaussian distribution. We compute the posterior distributions for these
Gaussian hyperparameters. This is done for LIGO and Cosmic Explorer (CE). We
find that systematic biases from unmodeled eccentricity can signal false GR
violations for both detectors when considering constraints set by a catalog of
events. We also compute the projected bounds on the TGR parameters when
eccentricity is included as a parameter in the waveform model. We find that the
first four dimensionless TGR deformation parameters can be bounded at
confidence to for LIGO and for CE [where ]. In comparison to the circular orbit
case, the combined bounds on the TGR parameters worsen by a modest factor of
when eccentricity is included in the waveform.Comment: 23 pages, 9 figures, 1 tabl
Effect of Pt substitution on the electronic structure of AuTe2
We report a photoemission and x-ray absorption study on Au1-xPtxTe2 (x = 0
and 0.35) triangular lattice in which superconductivity is induced by Pt
substitution for Au. Au 4f and Te 3d core-level spectra of AuTe2 suggests a
valence state of Au2+(Te2)2-, which is consistent with its distorted crystal
structure with Te-Te dimers and compressed AuTe6 otahedra. On the other hand,
valence-band photoemission spectra and pre-edge peaks of Te 3d absorption edge
indicate that Au 5d bands are almost fully occupied and that Te 5p holes govern
the transport properties and the lattice distortion. The two apparently
conflicting pictures can be reconciled by strong Au 5d/Au 6s-Te 5p
hybridization. Absence of a core-level energy shift with Pt substitution is
inconsistent with the simple rigid band picture for hole doping. The Au 4f
core-level spectrum gets slightly narrow with Pt substitution, indicating that
the small Au 5d charge modulation in distorted AuTe2 is partially suppressed.Comment: 13 pages, 4 figures, accepted by Physical Review
HI Fluctuations at Large Redshifts: II - the Signal Expected for GMRT
For the GMRT, we calculate the expected signal from redshifted HI emission at
two frequency bands centered at 610 and 325 MHz. The study focuses on the
visibility-visibility cross-correlations, proposed earlier as the optimal
statistical estimator for detecting and analyzing this signal. These
correlations directly probe the power spectrum of density fluctuations at the
redshift where the radiation originated, and thereby provide a method for
studying the large scale structures at large redshifts. We present detailed
estimates of the correlations expected between the visibilities measured at
different baselines and frequencies. Analytic fitting formulas representing the
salient features of the expected signal are also provided. These will be useful
in planning observations and deciding an optimal strategy for detecting this
signal.Comment: 16 pages including 7 figures, published in JAp
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