5,981 research outputs found
Investigation of vehicle glow in the far ultraviolet
To data, all vehicle glow observations have been conducted in the visible and near infrared wavelength regions. As the Space Telescope's wavelength coverage extends to the far ultraviolet range and current plasma theory of the spacecraft glow phenomena predicts bright glow intensities, a study of the ram glow effects in the 800-1400 angstrom region was undertaken. The data were collected between March 21-28, 1979, from 600 km altitude near local midnight by the University of California, Berkeley's extreme ultraviolet spectrometer on board the polar orbiting STP78-1 satellite. Data from several nighttime orbits obtained outside the South Atlantic Anomaly region and within + or - 30 deg magnetic latitude range were separated into forward (south viewing) and backward (north viewing) bins. Each of these binds was subdivided into three directional categories: (1) up (zenith angles 30-80 deg), (2) side (zenith angles 80-100 deg), and (3) down (zenith angles 120-150 deg). The maximum ram glow effects are expected in the side viewing directions. Our data include possible effects of ram glow signatures in the 800-1400 angstrom wavelength region
Mass Outflow Rate From Accretion Discs around Compact Objects
We compute mass outflow rates from accretion disks around compact objects,
such as neutron stars and black holes. These computations are done using
combinations of exact transonic inflow and outflow solutions which may or may
not form standing shock waves. Assuming that the bulk of the outflow is from
the effective boundary layers of these objects, we find that the ratio of the
outflow rate and inflow rate varies anywhere from a few percent to even close
to a hundred percent (i.e., close to disk evacuation case) depending on the
initial parameters of the disk, the degree of compression of matter near the
centrifugal barrier, and the polytropic index of the flow. Our result, in
general, matches with the outflow rates obtained through a fully time-dependent
numerical simulation. In some region of the parameter space when the standing
shock does not form, our results indicate that the disk may be evacuated and
may produce quiescence states.Comment: 30 Latex pages and 13 figures. crckapb.sty; Published in Class.
Quantum Grav. Vol. 16. No. 12. Pg. 387
Satellite observations of thought experiments close to a black hole
Since black holes are `black', methods of their identification must
necessarily be indirect. Due to very special boundary condition on the horizon,
the advective flow behaves in a particular way, which includes formation of
centrifugal pressure dominated boundary layer or CENBOL where much of the
infall energy is released and outflows are generated. The observational aspects
of black holes must depend on the steady and time-dependent properties of this
boundary layer. Several observational results are written down in this review
which seem to support the predictions of thought experiments based on this
advective accretion/outflow model. In future, when gravitational waves are
detected, some other predictions of this model could be tested as well.Comment: Published in Classical and Quantum Gravity, v. 17, No. 12, p. 2427,
200
Fluctuation Cumulant Behavior for the Field-Pulse Induced Magnetisation-Reversal Transition in Ising Models
The universality class of the dynamic magnetisation-reversal transition,
induced by a competing field pulse, in an Ising model on a square lattice,
below its static ordering temperature, is studied here using Monte Carlo
simulations. Fourth order cumulant of the order parameter distribution is
studied for different system sizes around the phase boundary region. The
crossing point of the cumulant (for different system sizes) gives the
transition point and the value of the cumulant at the transition point
indicates the universality class of the transition. The cumulant value at the
crossing point for low temperature and pulse width range is observed to be
significantly less than that for the static transition in the same
two-dimensional Ising model. The finite size scaling behaviour in this range
also indicates a higher correlation length exponent value. For higher
temperature and pulse width range, the transition seems to fall in a mean-field
like universality class.Comment: 5 pages, 8 eps figures, thoroughly revised manuscript with new
figures, accepted in Phys. Rev. E (2003
Staggered and extreme localization of electron states in fractal space
We present exact analytical results revealing the existence of a countable
infinity of unusual single particle states, which are localized with a
multitude of localization lengths in a Vicsek fractal network with diamond
shaped loops as the 'unit cells'. The family of localized states form clusters
of increasing size, much in the sense of Aharonov-Bohm cages [J. Vidal et al.,
Phys. Rev. Lett. 81, 5888 (1998)], but now without a magnetic field. The length
scale at which the localization effect for each of these states sets in can be
uniquely predicted following a well defined prescription developed within the
framework of real space renormalization group. The scheme allows an exact
evaluation of the energy eigenvalue for every such state which is ensured to
remain in the spectrum of the system even in the thermodynamic limit. In
addition, we discuss the existence of a perfectly conducting state at the band
center of this geometry and the influence of a uniform magnetic field threading
each elementary plaquette of the lattice on its spectral properties. Of
particular interest is the case of extreme localization of single particle
states when the magnetic flux equals half the fundamental flux quantum.Comment: 9 pages, 8 figure
X-ray Observation of SS 433 with RXTE
Apart from regular monitoring by ASM, the compact object SS 433 was observed
with RXTE several times last two/three years. We present the first analysis of
these observations. We also include the results of the recent exciting TOO
campaign made during donour inferior (orbital phase ) and superior
() conjunctions which took place on Oct. 2nd, 2003, and on March
13th, 2004 respectively, when the jet itself was directly pointing towards us
(i.e., precessional phase ). Generally, we found that two distinct
lines fit the spectra taken on all these days. We present some of the
light-curves and the X-ray spectra, and show that the Doppler shifts of the
emitted lines roughly match those predicted by the kinematic model for the
jets. We find that the line with a higher energy can be best identified with a
FeXXVI Ly- transition while the line with lower energy can be
identified with a FeXXV (1s2p - 1s) transition. We observe that the X-ray
flux on March 13th, 2004 (when the base of the jet is exposed) is more than
twice compared to that on Oct. 2nd, 2003 (when the base is covered by the
companion). We find the flux to continue to remain high at least till another
orbital period. We believe that this is because SS 433 was undergoing a weak
flaring activity during the recent observation.Comment: 15 pages, 6 figures, submitted for publication in MNRAS (April, 2004
Problem and Prospects of Urban Agriculture in Some Wards of Chandernagore Municipal Corporation
In twenty first century, urban agriculture has been gaining importance and potential in developing countries. The objective of the present study was to investigate the developments and problems of urban agriculture on the special emphasis on ward numbers 28,29 and 30 of Chandernagore Municipal Corporation (CMC) of Hooghly district of West Bengal. These three wards have been chosen due to the fact that all the said three wards were composed of areas that were rural before 1995, the years in which these wards were added to CMC to provide for expansion of the town. The significant part of population still dependent on agriculture. Particular crops, especially fruits and vegetables to ensure food security to the urban consumers
Majorana Fermions in Strongly Interacting Helical Liquids
Majorana fermions were proposed to occur at edges and interfaces of gapped
one-dimensional systems where phases with different topological character meet
due to an interplay of spin-orbit coupling, proximity-induced superconductivity
and external magnetic fields. Here we investigate the effect of strong particle
interactions, and show that the helical liquid offers a mechanism that protects
the very existence of Majorana edge states: whereas moderate interactions close
the proximity gap which supports the edge states, in helical liquids the gap
re-opens due to two-particle processes. However, gapless fermionic excitations
occur at spatial proximity to the Majorana states at interfaces and may
jeopardize their long term Majorana coherence.Comment: 7 pages, 4 figure
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