4,034 research outputs found
The Exotic Barium Bismuthates
We review the remarkable properties, including superconductivity,
charge-density-wave ordering, and metal-insulator transitions, of lead- and
potassium-doped barium bismuthate. We discuss some of the early theoretical
studies of these systems. Our recent theoretical work, on the negative-U\/,
extended-Hubbard model for these systems, is also described. Both the large-
and intermediate-U\/ regimes of this model are examined, using mean-field and
random-phase approximations, particularly with a view to fitting various
experimental properties of these bismuthates. On the basis of our studies, we
point out possibilities for exotic physics in these systems. We also emphasize
the different consequences of electronic and phonon-mediated mechanisms for the
negative U.\/ We show that, for an electronic mechanism, the \secin
\,\,phases of these bismuthates must be unique, with their transport properties
{\it dominated by charge Cooperon bound states}. This can explain the
observed difference between the optical and transport gaps. We propose other
experimental tests for this novel mechanism of charge transport and comment on
the effects of disorder.Comment: UUencoded LaTex file, 122 pages, figures available on request To
appear in Int. J. Mod. Phys. B as a review articl
Effect of shape anisotropy on transport in a 2-dimensional computational model: Numerical simulations showing experimental features observed in biomembranes
We propose a 2-d computational model-system comprising a mixture of spheres
and the objects of some other shapes, interacting via the Lennard-Jones
potential. We propose a reliable and efficient numerical algorithm to obtain
void statistics. The void distribution, in turn, determines the selective
permeability across the system and bears a remarkable similarity with features
reported in certain biological experiments.Comment: 1 tex file, 2 sty files and 5 figures. To appear in Proc. of StatPhys
conference held in Calcutta, Physica A 199
A simple method of obtaining pure microconidia in Neurospora crassa
In order to examine the nuclear types that may be carried in strains of Neurospora collected from nature, we desired a method of selectively inducing microconidiation in mycelia whereby uninucleate microconidia could be obtained for isolating homokaryotic derivatives. We have devised a simple and highly effective method of obtaining pure microconidia from wild-collected strains as well as from N. crassa 74-OR23-1VA
Coherent bremsstrahlung and GDR width from 252Cf cold fission
The energy spectrum of the high energy gamma-rays in coincidence with the
prompt gamma rays has been measured for the spontaneous fission of 252Cf. The
nucleus-nucleus coherent bremsstrahlung of the accelerating fission fragments
is observed and the result has been substantiated with a theoretical
calculation based on the coulomb acceleration model. The width of the giant
dipole resonance (GDR) decay from the excited fission fragments has been
extracted for the first time and compared with the thermal shape fluctuation
model (TSFM) in the liquid drop formalism. The extracted GDR width is
significantly smaller than the predictions of TSFM.Comment: 12 pages, 3 figures, accepted for publication in Phys. Lett.
Distribution-Free Tests for Two-Sample Location Problems Based on Subsamples
Nonparametric tests for location problems have received much attention in the literature.
Many nonparametric tests have been proposed for one, two and several samples location problems. In
this paper a class of test statistics is proposed for two sample location problem when the underlying
distributions of the samples are symmetric. The class of test statistics proposed is linear combination
of U-statistics whose kernel is based on subsamples extrema. The members of the new class are
shown to be asymptotically normal. The performance of the proposed class of tests is evaluated using
Pitman Asymptotic Relative Efficiency. It is observed that the members of the proposed class of tests
are better than the existing tests in the literature
Gunnery Surface Target
The functional and technical requirements of the Gunnery surface target for Naval firing practice are given. The design evolved, and the raw materials required for its various components are described and discussed in detail. The target designed can with stand the sea state of seven in all operating conditions while being towed at a speed of 15 knots in a wind speed of 25 knots. It is visible upto a distance of 18 km and has radar responsive characteristics upto 22 km
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