10,333 research outputs found
Statistical Evidence for Three classes of Gamma-ray Bursts
Two different multivariate clustering techniques, the K-means partitioning
method and the Dirichlet process of mixture modeling, have been applied to the
BATSE Gamma-ray burst (GRB) catalog, to obtain the optimum number of coherent
groups. In the standard paradigm, GRB are classified in only two groups, the
long and short bursts. However, for both the clustering techniques, the optimal
number of classes was found to be three, a result which is consistent with
previous statistical analysis. In this classification, the long bursts are
further divided into two groups which are primarily differentiated by their
total fluence and duration and hence are named low and high fluence GRB.
Analysis of GRB with known red-shifts and spectral parameters suggests that low
fluence GRB have nearly constant isotropic energy output of 10^{52} ergs while
for the high fluence ones, the energy output ranges from 10^{52} to 10^{54}
ergs. It is speculated that the three kinds of GRBs reflect three different
origins: mergers of neutron star systems, mergers between white dwarfs and
neutron stars, and collapse of massive stars.Comment: 7 pages, accepted for publication in the Astrophysical Journal. Minor
editorial change
Contrasting the magnetic response between magnetic-glass and reentrant spin-glass
Magnetic-glass is a recently identified phenomenon in various classes of
magnetic systems undergoing a first order magnetic phase transition. We shall
highlight here a few experimentally determined characteristics of
magnetic-glass and the relevant set of experiments, which will enable to
distinguish a magnetic-glass unequivocally from the well known phenomena of
spin-glass and reentrant spin-glass.Comment: 10 pages and 4 figures. The preprint has been amended after taking
care of various typographical errors, some errors in Figs.2 and 4 and with
the addition of some new references. This version has been accepted for
publication in Physical Review
Fluctuation Effects And Order Parameter Symmetry In The Cuprate Superconductors
Effect of phase fluctuations on superconducting states with anisotropic order
parameters is studied in a BCS like lattice model of cuprate superconductors.
The degradation of the mean field transition temperature due to phase
fluctuations is estimated within a Kosterlitz-Thouless scenario. Values of the
interaction parameters for optimal doping, corresponding to a stable
superconducting state of symmetry, which fit the nodal structure of
the superconducting order parameter in the Bi2212 compound, are obtained. The
angular position of the node is found to be insensitive to the dopant
concentration.Comment: Latex file, 8 output pages, 5 figures (available from Authors on
request), to appear in Europhysics Letter
Morphogenetic prepattern during embryonic development—a nonlinear analysis
AbstractBy considering a nonlinear reaction-diffusion negative feedback epigenetic control system, involving synthesis of the mitotic-inducing and inhibiting proteins simultaneously with intercellular self-diffusion and negative cross-diffusion of the latter only, Tapaswi and Saha [1] have showed the system generates a Turing structure during embryonic development. In this paper, we have observed, by using Lyapunov's direct method, that the pattern, thus generated, is globally asymptotically stable
Pseudorandom Generators for Width-3 Branching Programs
We construct pseudorandom generators of seed length that -fool ordered read-once branching programs
(ROBPs) of width and length . For unordered ROBPs, we construct
pseudorandom generators with seed length . This is the first improvement for pseudorandom
generators fooling width ROBPs since the work of Nisan [Combinatorica,
1992].
Our constructions are based on the `iterated milder restrictions' approach of
Gopalan et al. [FOCS, 2012] (which further extends the Ajtai-Wigderson
framework [FOCS, 1985]), combined with the INW-generator [STOC, 1994] at the
last step (as analyzed by Braverman et al. [SICOMP, 2014]). For the unordered
case, we combine iterated milder restrictions with the generator of
Chattopadhyay et al. [CCC, 2018].
Two conceptual ideas that play an important role in our analysis are: (1) A
relabeling technique allowing us to analyze a relabeled version of the given
branching program, which turns out to be much easier. (2) Treating the number
of colliding layers in a branching program as a progress measure and showing
that it reduces significantly under pseudorandom restrictions.
In addition, we achieve nearly optimal seed-length
for the classes of: (1) read-once polynomials on
variables, (2) locally-monotone ROBPs of length and width
(generalizing read-once CNFs and DNFs), and (3) constant-width ROBPs of length
having a layer of width in every consecutive
layers.Comment: 51 page
Dynamical Mean Field Theory of Double Perovskite Ferrimagnets
The dynamical mean field method is used to analyze the magnetic transition
temperature and optical conductivity of a model for the ferrimagnetic double
perovskites such as . The calculated transition temperatures and
optical conductivities are found to depend sensitively on the band structure.
For parameters consistent with local spin density approximation band
calculations, the computed transition temperatures are lower than observed, and
in particular decrease dramatically as band filling is increased, in
contradiction to experiment. Band parameters which would increase the
transition temperature are identified.Comment: Supercedes cond-mat/000628 (PRB64 024424/1-4 (2001
A ratio-dependent eco-epidemiological model of the Salton sea
Ratio-dependent models set up a challenging issue for their rich dynamics incomparison to prey-dependent models. Little attention has been paid so far to describe the importance of transmissible disease in ecological situation by considering ratio-dependent models. In this paper, by assuming the predator response function as ratio-dependent, we consider a model of a system of three non-linear differential equations describing the time evolution of susceptible and infected Tilapia fish population and their predator, the Pelican. Existence and stability analysis of different equilibria of the system lead to different realistic thresholds in terms of system parameters. The condition for extinction of the species is also worked out. Our analytical and numerical studies may be helpful to chalk out suitable control strategies for minimizing the extinction of the Pelicans. We also suggest that supply of alternative food source for predator population may be used as a possible solution to save the predator from their extinction
Structural domain and spin ordering induced glassy magnetic phase in single layered manganite PrSrMnO
The single layered manganite PrSrMnO undergoes
structural transition from high temperature tetragonal phase to low temperature
orthorhombic phase below room temperature. The orthorhombic phase was reported
to have two structural variants with slightly different lattice parameters and
Mn-3 levels show orbital ordering within both the variants, albeit having
mutually perpendicular ordering axis. In addition to orbital ordering, the
orthorhombic variants also order antiferromagnetically with different N\'eel
temperatures. Our magnetic investigation on the polycrystalline sample of
PrSrMnO shows large thermal hysteresis indicating the
first order nature of the tetragonal to orthorhombic transition. We observe
magnetic memory, large relaxation, frequency dependent ac susceptbility and
aging effects at low temperature, which indicate spin glass like magnetic
ground state in the sample. The glassy magnetic state presumably arises from
the interfacial frustration of orthorhombic domains with orbital and spin
orderings playing crucial role toward the competing magnetic interactions.Comment: 6 pages, 4 figures, Accepted in Europhysics Letter
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