14,830 research outputs found
Low-energy quenching of positronium by helium
Very low-energy scattering of orthopositronium by helium has been
investigated for simultaneous study of elastic cross section and pick-off
quenching rate using a model exchange potential. The present calculational
scheme, while agrees with the measured cross section of Skalsey et al,
reproduces successfully the parameter ^ 1Z_{\makebox{eff}}, the effective
number of electrons per atom in a singlet state relative to the positron.
Together with the fact that this model potential also leads to an agreement
with measured medium energy cross sections of this system, this study seems to
resolve the long-standing discrepancy at low energies among different
theoretical calculations and experimental measurements.Comment: 4 latex pages, 3 postscript figure
Sensing Models and Its Impact on Network Coverage in Wireless Sensor Network
Network coverage of wireless sensor network (WSN) means how well an area of
interest is being monitored by the deployed network. It depends mainly on
sensing model of nodes. In this paper, we present three types of sensing models
viz. Boolean sensing model, shadow-fading sensing model and Elfes sensing
model. We investigate the impact of sensing models on network coverage. We also
investigate network coverage based on Poisson node distribution. A comparative
study between regular and random node placement has also been presented in this
paper. This study will be useful for coverage analysis of WSN.Comment: 5 pages, 5 figures, IEEE Region 10 Colloquium and the Third ICIIS,
Kharagpur, INDIA December 8-10, 200
Automorphisms of Moduli Spaces Associated to a Riemann Surface
We compute the automorphism groups of the Dolbeault, de Rham and Betti moduli
spaces for the multiplicative group associated to a compact
connected Riemann surface
Vector bundles trivialized by proper morphisms and the fundamental group scheme
Let X be a smooth projective variety defined over an algebraically closed
field k. Nori constructed a category of vector bundles on X, called essentially
finite vector bundles, which is reminiscent of the category of representations
of the fundamental group (in characteristic zero). In fact, this category is
equivalent to the category of representations of a pro--finite group scheme
which controls all finite torsors. We show that essentially finite vector
bundles coincide with those which become trivial after being pulled back by
some proper and surjective morphism to X.Comment: Final versio
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