414 research outputs found
Identification of Shocks in the Spectra from Black Holes
We study the spectral properties of a low angular momentum flow as a function
of the shock strength, compression ratio, accretion rate and flow geometry. In
the absence of a satisfactory description of magnetic fields inside the
advective disk, we consider the presence of only stochastic fields and use the
ratio of the field energy to the gravitational energy density as a parameter.
We not only include `conventional' synchrotron emission and Comptonization by
Maxwell-Bolzmann electrons in the gas, but we also compute these effects due to
power-law electrons. For strong shocks, a bump is produced due to the
post-shock flow. A power-law spectral components due to the thermal and
non-thermal electrons appear after this bump.Comment: 8 pages, 5 figures, Astronomy and Space Science (in press),
Proceedings of the Hong Kong Conference (2004) Edited by Cheng and Romer
Gravitational Wave Emission From a Binary Black Hole System in Presence of an Accretion Disk
We study time evolution and gravitational wave emission properties of a black
hole orbiting {\it inside} an accretion disk surrounding a massive black hole.
We simultaneously solve the structure equations of the accretion disk in
presence of heating, cooling and viscosity as well as the equations governing
the companion orbit. The deviation from Keplerian distribution of angular
momentum of the disk due to pressure and advection effects causes a significant
exchange of angular momentum between the disk and the companion. This
significantly affects the gravitational wave emission properties from the
binary system. We show that when the companion is light, the effect is
extremely important and must be taken into account while interpreting
gravitational wave signals from such systems.Comment: 8 pages of Latex plus postscript fil
Cellular organisation and functions of the olfactory epithelium of pearl spot Etroplus suratensis (Bloch): a light and scanning electron microscopic study
The cellular organisation of the olfactory rosettes of Etroplus suratensis was
studied by light and scanning electron microscopy. The oval shaped olfactory
rosette of the fish consists of 12 lamellae radiating from a central raphe. The
olfactory lamellae are comprised of restricted areas of sensory epithelium and
broad areas of non-sensory epithelium in the apical, middle, and basal regions.
The sensory epithelium contains three types of receptor cells: microvillus, ciliated,
and rod cells, as well as labyrinth cells and supporting cells. The non-sensory
epithelium consists of stratified epithelial and mucous cells. The transitional
region between the sensory and non-sensory epithelium consists of ciliated
receptor cells, mucous cells, and stratified epithelial cells. The different cells on
the olfactory epithelium were discussed regarding the functional significance
of the fish concerned. (Folia Morphol 2010; 69, 3: 154-159
Histological and ultrastructural studies of the olfactory epithelium of spotted butter fish Scatophagus argus (Linnaeus)
The olfactory epithelium of Scatophagus argus (Linnaeus) was investigated by
light and scanning electron microscopy. The elongated olfactory organ is made
up of 20 to 22 primary lamellae arranged on both sides of the narrow median
raphe. Sensory and non-sensory regions are located separately on each lamella.
The sensory epithelium occupies the upper apical broad half and extreme
basal part of the olfactory lamellae whereas the middle slender part is covered
with non-sensory epithelium. The sensory epithelium consists of ciliated, microvillus,
and crypt cells. The non-sensory epithelium is made up of stratified
epithelial cells having different patterns of finger-like micro-ridges and mucous
cells. Different cells lining the olfactory epithelium have been correlated with
the functional views of the fish concerned. (Folia Morphol 2011; 70, 2: 74–79
Magneto-transport in a quantum network: Evidence of a mesoscopic switch
We investigate magneto-transport properties of a shaped three-arm
mesoscopic ring where the upper and lower sub-rings are threaded by
Aharonov-Bohm fluxes and , respectively, within a
non-interacting electron picture. A discrete lattice model is used to describe
the quantum network in which two outer arms are subjected to binary alloy
lattices while the middle arm contains identical atomic sites. It is observed
that the presence of the middle arm provides localized states within the band
of extended regions and lead to the possibility of switching action from a high
conducting state to a low conducting one and vice versa. This behavior is
justified by studying persistent current in the network. Both the total current
and individual currents in three separate branches are computed by using
second-quantized formalism and our idea can be utilized to study magnetic
response in any complicated quantum network. The nature of localized
eigenstates are also investigated from probability amplitudes at different
sites of the quantum device.Comment: 7 pages, 9 figure
Fast Transition between High-soft and Low-soft States in GRS 1915+105: Evidence for a Critically Viscous Accretion Flow
We present the results of a detailed analysis of RXTE observations of class
which show an unusual state transition between high-soft and low-soft
states in the microquasar GRS 1915+105. Out of about 600 pointed RXTE
observations, the source was found to exhibit such state transition only on 16
occasions. An examination of the RXTE/ASM data in conjunction with the pointed
observations reveals that these events appeared as a series of quasi-regular
dips in two stretches of long duration (about 20 days during each occasions)
when hard X-ray and radio flux were very low. The X-ray light curve and
color-color diagram of the source during these observations are found to be
different from any reported so far. The duration of these dips is found to be
of the order of a few tens of seconds with a repetition time of a few hundred
seconds. The transition between these dips and non-dips which differ in
intensity by a factor of ~ 3.5, is observed to be very fast (~ a few seconds).
It is observed that the low-frequency narrow QPOs are absent in the power
density spectrum (PDS) of the dip and non-dip regions of class and the
PDS is a power law in 0.1 - 10 Hz frequency range. There is a remarkable
similarity in the spectral and timing properties of the source during the dip
and non-dip regions in these set of observations. These properties of the
source are distinctly different from those seen in the observations of other
classes. This indicates that the basic accretion disk structure during both dip
and non-dip regions of class is similar, but differ only in intensity.
To explain these observations, we invoke a model in which the viscosity is very
close to critical viscosity and the shock wave is weak or absent.Comment: Replaced with correct figures, Jour. of Astrophysics and Astronomy
(accepted
An experimental study of Primary Cosmic Rays at the knee energy region by observation of Extensive Air Showers (EAS)
Simultaneous measurements have been made of the radial (lateral) electron density distribution and the radial muon density distribution at various measured muon energies in the range 2.5–100 GeV in vertically incident EAS in the
size range 3.153104 –1.793106 (primary energy range 2.431014 –8.331015 eV) particles detected near sea level. The characteristics of these radial distributions in terms of the measured shower parameters have been determined and used to draw conclusions about the average nuclear mass of the primaries of these EAS
Viscosity in spherically symmetric accretion
The influence of viscosity on the flow behaviour in spherically symmetric
accretion, has been studied here. The governing equation chosen has been the
Navier-Stokes equation. It has been found that at least for the transonic
solution, viscosity acts as a mechanism that detracts from the effectiveness of
gravity. This has been conjectured to set up a limiting scale of length for
gravity to bring about accretion, and the physical interpretation of such a
length-scale has been compared with the conventional understanding of the
so-called "accretion radius" for spherically symmetric accretion. For a
perturbative presence of viscosity, it has also been pointed out that the
critical points for inflows and outflows are not identical, which is a
consequence of the fact that under the Navier-Stokes prescription, there is a
breakdown of the invariance of the stationary inflow and outflow solutions --
an invariance that holds good under inviscid conditions. For inflows, the
critical point gets shifted deeper within the gravitational potential well.
Finally, a linear stability analysis of the stationary inflow solutions, under
the influence of a perturbation that is in the nature of a standing wave, has
indicated that the presence of viscosity induces greater stability in the
system, than has been seen for the case of inviscid spherically symmetric
inflows.Comment: 7 pages. Minor changes made in the version published in MNRA
Absorption cross section in warped AdS_3 black hole revisited
We investigate the absorption cross section for minimal-coupled scalars in
the warped AdS_3 black hole. According to our calculation, the cross section
reduces to the horizon area in the low energy limit as usually expected in
contrast to what was previously found. We also calculate the greybody factor
and find that the effective temperatures for the two chiral CFT's are
consistent with that derived from the quasinormal modes. Observing the
conjectured warped AdS/CFT correspondence, we suspect that a specific sector of
the CFT operators with the desired conformal dimension could be responsible for
the peculiar thermal behaviour of the warped AdS_3 black hole.Comment: 16+1 pages, typos corrected, references and footnotes adde
Spin 0 and spin 1/2 particles in a spherically symmetric static gravity and a Coulomb field
A relativistic particle in an attractive Coulomb field as well as a static
and spherically symmetric gravitational field is studied. The gravitational
field is treated perturbatively and the energy levels are obtained for both
spin 0 (Klein-Gordon) and spin 1/2 (Dirac) particles. The results are shown to
coincide with each other as well as the result of the nonrelativistic
(Schrodinger) equation in the nonrelativistic limit.Comment: 12 page
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