1,680 research outputs found
Catch assessment of indigenous and exotic carp species of Nasti baor
An investigation on length-weight relationship, length-frequency distribution, catch per unit of effort (CPUE) and stocking and harvesting status of three Indian major
carps: rohu Labeo rohita, catla Catla catla and mrigal Cirrhinus mrigala and three exotic carps: silver carp Hypophthalmichthys molitrix, grass carp Ctenopharyngodon idella) and common carp Cyprinus carpio was carried out in Nasti baor (oxbow lake) for the harvesting season from August to December 1995. The length-weight relationship for six carp species was established for the harvesting months of November and December 1995. The b values for different species respectively for the months of November and December were 2.95 and 2.58 for rohu, 3.06 and 2.98 for catla, 2,84 and 2.90 for mrigal, 2.75 and 2.60 for silver carp, 2.51 and 1.97 for grass carp and 2.38 and 2.50 for common carp. In CPUE study, the CPUE was 0.58 kg/ha/hr while the catch per gear was 0.08 kg/ha/hr/purse-seine. The recovery percentage of mrigal was highest (63.57%) and it was lowest (16.81%) in case of silver carp. The density of submerged macrophytes (Hydrilla, Utricularia, Ceratophyllum and Vallisneria) was highest (4.39 kg/sqm) in November and was lowest (0.76 kg/sqm) in September
On the energy-momentum tensor in non-commutative gauge theories
We study the properties of the energy-momentum tensor in non-commutative
gauge theories by coupling them to a weak external gravitational field. In
particular, we show that the stress tensor of such a theory coincides exactly
with that derived from a theory where a Seiberg-Witten map has been implemented
(namely, the procedure is commutative). Various other interesting features are
also discussed.Comment: 3 page
Condensation Transitions in Two Species Zero-Range Process
We study condensation transitions in the steady state of a zero-range process
with two species of particles. The steady state is exactly soluble -- it is
given by a factorised form provided the dynamics satisfy certain constraints --
and we exploit this to derive the phase diagram for a quite general choice of
dynamics. This phase diagram contains a variety of new mechanisms of condensate
formation, and a novel phase in which the condensate of one of the particle
species is sustained by a `weak' condensate of particles of the other species.
We also demonstrate how a single particle of one of the species (which plays
the role of a defect particle) can induce Bose-Einstein condensation above a
critical density of particles of the other species.Comment: 17 pages, 4 Postscript figure
Character Expansion Methods for Matrix Models of Dually Weighted Graphs
We consider generalized one-matrix models in which external fields allow
control over the coordination numbers on both the original and dual lattices.
We rederive in a simple fashion a character expansion formula for these models
originally due to Itzykson and Di Francesco, and then demonstrate how to take
the large N limit of this expansion. The relationship to the usual matrix model
resolvent is elucidated. Our methods give as a by-product an extremely simple
derivation of the Migdal integral equation describing the large limit of
the Itzykson-Zuber formula. We illustrate and check our methods by analyzing a
number of models solvable by traditional means. We then proceed to solve a new
model: a sum over planar graphs possessing even coordination numbers on both
the original and the dual lattice. We conclude by formulating equations for the
case of arbitrary sets of even, self-dual coupling constants. This opens the
way for studying the deep problem of phase transitions from random to flat
lattices.Comment: 22 pages, harvmac.tex, pictex.tex. All diagrams written directly into
the text in Pictex commands. (Two minor math typos corrected.
Acknowledgements added.
Coordinate noncommutativity in strong non-uniform magnetic fields
Noncommuting spatial coordinates are studied in the context of a charged
particle moving in a strong non-uniform magnetic field. We derive a relation
involving the commutators of the coordinates, which generalizes the one
realized in a strong constant magnetic field. As an application, we discuss the
noncommutativity in the magnetic field present in a magnetic mirror.Comment: 4 page
Bouncing cosmological solutions due to the self-gravitational corrections and their stability
In this paper we consider the bouncing braneworld scenario, in which the bulk
is given by a five-dimensional AdS black hole spacetime with matter field
confined in a brane. Exploiting the CFT/FRW-cosmology relation, we
consider the self-gravitational corrections to the first Friedmann-like
equation which is the equation of the brane motion. The self-gravitational
corrections act as a source of stiff matter contrary to standard FRW cosmology
where the charge of the black hole plays this role. Then, we study the
stability of solutions with respect to homogeneous and isotropic perturbations.
Specifically, if we do not consider the self-gravitational corrections, the AdS
black hole with zero ADM mass, and open horizon is an attractor, while, if we
consider the self-gravitational corrections, the AdS black hole with zero ADM
mass and flat horizon, is a repellerComment: 9 pages, no figure
On Black Holes and Cosmological Constant in Noncommutative Gauge Theory of Gravity
Deformed Reissner-Nordstr\"om, as well as Reissner-Nordstr\"om de Sitter,
solutions are obtained in a noncommutative gauge theory of gravitation. The
gauge potentials (tetrad fields) and the components of deformed metric are
calculated to second order in the noncommutativity parameter. The solutions
reduce to the deformed Schwarzschild ones when the electric charge of the
gravitational source and the cosmological constant vanish. Corrections to the
thermodynamical quantities of the corresponding black holes and to the radii of
different horizons have been determined. All the independent invariants, such
as the Ricci scalar and the so-called Kretschmann scalar, have the same
singularity structure as the ones of the usual undeformed case and no smearing
of singularities occurs. The possibility of such a smearing is discussed. In
the noncommutative case we have a local disturbance of the geometry around the
source, although asymptotically at large distances it becomes flat.Comment: Based on a talk given at the International Conference on Fundamental
and Applied Research in Physics "Farphys 2007", 25-28 October 2007, Iasi,
Romani
Towards an explicit expression of the Seiberg-Witten map at all orders
The Seiberg-Witten map links noncommutative gauge theories to ordinary gauge
theories, and allows to express the noncommutative variables in terms of the
commutative ones. Its explicit form can be found order by order in the
noncommutative parameter theta and the gauge potential A by the requirement
that gauge orbits are mapped on gauge orbits. This of course leaves
ambiguities, corresponding to gauge transformations, and there is an infinity
of solutions. Is there one better, clearer than the others ? In the abelian
case, we were able to find a solution, linked by a gauge transformation to
already known formulas, which has the property of admitting a recursive
formulation, uncovering some pattern in the map. In the special case of a pure
gauge, both abelian and non-abelian, these expressions can be summed up, and
the transformation is expressed using the parametrisation in terms of the gauge
group.Comment: 17 pages. Latex, 1 figure. v2: minor changes, published versio
Kontsevich product and gauge invariance
We analyze the question of gauge invariance in a flat
non-commutative space where the parameter of non-commutativity,
, is a local function satisfying Jacobi identity (and
thereby leading to an associative Kontsevich product). We show that in this
case, both gauge transformations as well as the definitions of covariant
derivatives have to modify so as to have a gauge invariant action. We work out
the gauge invariant actions for the matter fields in the fundamental and the
adjoint representations up to order while we discuss the gauge
invariant Maxwell theory up to order . We show that despite the
modifications in the gauge transformations, the covariant derivative and the
field strength, Seiberg-Witten map continues to hold for this theory. In this
theory, translations do not form a subgroup of the gauge transformations
(unlike in the case when is a constant) which is reflected in
the stress tensor not being conserved.Comment: 7 page
Quantum Gravitational Corrections to the Real Klein-Gordon Field in the Presence of a Minimal Length
The (D+1)-dimensional -two-parameter Lorentz-covariant
deformed algebra introduced by Quesne and Tkachuk [C. Quesne and V. M. Tkachuk,
J. Phys. A: Math. Gen. \textbf {39}, 10909 (2006).], leads to a nonzero minimal
uncertainty in position (minimal length). The Klein-Gordon equation in a
(3+1)-dimensional space-time described by Quesne-Tkachuk Lorentz-covariant
deformed algebra is studied in the case where up to first order
over deformation parameter . It is shown that the modified Klein-Gordon
equation which contains fourth-order derivative of the wave function describes
two massive particles with different masses. We have shown that physically
acceptable mass states can only exist for which
leads to an isotropic minimal length in the interval . Finally, we have shown that the above estimation of
minimal length is in good agreement with the results obtained in previous
investigations.Comment: 10 pages, no figur
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