16,427 research outputs found
Electron-positron annihilation into Dirac magnetic monopole and antimonopole: the string ambiguity and the discrete symmetries
We address the problem of string arbitrariness in the quantum field theory of
Dirac magnetic monopoles. Different prescriptions are shown to yield different
physical results. The constraints due to the discrete symmetries (C and P) are
derived for the process of electron- positron annihilation into the
monopole-antimonopole pair. In the case of the annihilation through the
one-photon channel, the production of spin 0 monopoles is absolutely forbidden;
spin 1/2 monopole and antimonopole should have the same helicities (or,
equivalently, the monopole-antimonopole state should be p-wave ).Comment: 14 pages, revtex, 3 figure
Genericity aspects in gravitational collapse to black holes and naked singularities
We investigate here the genericity and stability aspects for naked
singularities and black holes that arise as the final states for a complete
gravitational collapse of a spherical massive matter cloud. The form of the
matter considered is a general Type I matter field, which includes most of the
physically reasonable matter fields such as dust, perfect fluids and such other
physically interesting forms of matter widely used in gravitation theory. We
first study here in some detail the effects of small pressure perturbations in
an otherwise pressure-free collapse scenario, and examine how a collapse
evolution that was going to the black hole endstate would be modified and go to
a naked singularity, once small pressures are introduced in the initial data.
This allows us to understand the distribution of black holes and naked
singularities in the initial data space. Collapse is examined in terms of the
evolutions allowed by Einstein equations, under suitable physical conditions
and as evolving from a regular initial data. We then show that both black holes
and naked singularities are generic outcomes of a complete collapse, when
genericity is defined in a suitable sense in an appropriate space.Comment: 24 pages, 6 figures, some changes in text and figures to match the
version accepted for publication by IJMP
Effect of different planting geometry and herbicides for controlling the weeds in direct seeded rice
The efficacy of selected herbicides along with the planting geometry for weed control in direct seeded rice was evaluated under tropical conditions of Pantnagar during rainy season of 2013. Pendimethalin (1kg active ingredient (a.i.) ha-1 3 days after sowing) + bispyribac-Na (25g a.i. ha-1 28 days after sowing) + one hand weeding at 45 days after sowing and bispyribac-Na (25g a. i. ha-1 28 days after sowing) + one hand weeding at 45days after sowing had a mean grain yield of 47.95 and 37.68 while continuous drilling at 20cm and 20 x 10cm had a mean grain yield 34.72 and 34.14 qha-1 , respectively which is significantly superior than wider (25 x 25cm) spacing. Wider spacing (25 x 25cm) among planting geometry and weedy check among the weed control treatments resulted in higher uptake of nitrogen. Among the spacing, continuous drilling at 20cm and Pendimethalin (1kg a.i. ha-1) + bispyribac- Na (25g a.i. ha-1) + one hand weeding at 45 days after sowing among weed control practices proved most profitable with net returns of ` 40576 ha-1 and ` 40633 ha-1 and benefit:cost ratio of 1.7 and 1.8, respectively. It was revealed that all the weed control treatments were superior to weedy conditions
Observational Evidence of Sausage-Pinch Instability in Solar Corona by SDO/AIA
We present the first observational evidence of the evolution of sausage-pinch
instability in Active Region 11295 during a prominence eruption using data
recorded on 12 September 2011 by the Atmospheric Imaging Assembly (AIA) onboard
the Solar Dynamics Observatory (SDO). We have identified a magnetic flux tube
visible in AIA 304 \AA\ that shows curvatures on its surface with variable
cross-sections as well as enhanced brightness. These curvatures evolved and
thereafter smoothed out within a time-scale of a minute. The curved locations
on the flux tube exhibit a radial outward enhancement of the surface of about
1-2 Mm (factor of 2 larger than the original thickness of the flux tube) from
the equilibrium position. AIA 193 \AA\ snapshots also show the formation of
bright knots and narrow regions inbetween at the four locations as that of 304
\AA\ along the flux tube where plasma emission is larger compared to the
background. The formation of bright knots over an entire flux tube as well as
the narrow regions in < 60 s may be the morphological signature of the sausage
instability. We also find the flows of the confined plasma in these bright
knots along the field lines, which indicates the dynamicity of the flux tube
that probably causes the dominance of the longitudinal field component over
short temporal scales. The observed longitudinal motion of the plasma frozen in
the magnetic field lines further vanishes the formed curvatures and plasma
confinements as well as growth of instability to stablize the flux tube.Comment: 12 pages, 5 figure
Floral anatomy of Rivina humilis L., and the theory of carpel polymorphism
This article does not have an abstract
Strong curvature singularities in quasispherical asymptotically de Sitter dust collapse
We study the occurrence, visibility, and curvature strength of singularities
in dust-containing Szekeres spacetimes (which possess no Killing vectors) with
a positive cosmological constant. We find that such singularities can be
locally naked, Tipler strong, and develop from a non-zero-measure set of
regular initial data. When examined along timelike geodesics, the singularity's
curvature strength is found to be independent of the initial data.Comment: 16 pages, LaTeX, uses IOP package, 2 eps figures; accepted for
publication in Class. Quantum Gra
Magnetic and Transport Properties of Ternary Indides of type R2CoIn8 (R = Ce, Pr and Dy)
We have synthesized and investigated the magnetic and transport properties of
a series of compounds, R2CoIn8 (R = rare earth). Compounds form in single phase
with a tetragonal structure (space group P4/mmm, no. 162). The Ce compound
shows heavy fermion behavior. The magnetic susceptibility of Pr2CoIn8 shows a
marked deviation from the Curie-Weiss behavior at low temperatures, which is
attributed to the crystalline electric field effects. Heat capacity and
magnetization measurements show that Dy2CoIn8 undergoes a magnetic transition
at 17 K and a second transition near 5 K, the latter of which may be due to
spin reorientation. Magnetization of this compound shows two metamagnetic
transitions approximately at 3.6 T and 8.3 T.Comment: Total 7 pages of text and figure
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