16,081 research outputs found
Lorentz Violation for Photons and Ultra-High Energy Cosmic Rays
Lorentz symmetry breaking at very high energies may lead to photon dispersion
relations of the form omega^2=k^2+xi_n k^2(k/M_Pl)^n with new terms suppressed
by a power n of the Planck mass M_Pl. We show that first and second order terms
of size xi_1 > 10^(-14) and xi_2 < -10^(-6), respectively, would lead to a
photon component in cosmic rays above 10^(19) eV that should already have been
detected, if corresponding terms for electrons and positrons are significantly
smaller. This suggests that Lorentz invariance breakings suppressed up to
second order in the Planck scale are unlikely to be phenomenologically viable
for photons.Comment: 4 revtex pages, 3 postscript figures included, version published in
PR
Purification and characterization of digestive amylase from the tasar silkworm, Antheraea mylitta (Lepidoptera: Saturniidae)
Digestive amylase was purified from larvae of Indian tasar silkworm, Antheraea mylitta using ammonium sulphate precipitation, glycogen complex precipitation and gel filtration chromatography. Specific activity increased from 0.673 AU/mg in the crude digestive juice to 94.80 AU/mg in the final purified sample. Activity of the purified enzyme was 15-fold less than that of the digestive amylase of silkworm. Bombyx mori. The zymogram pattern of the purified amylase was similar to that of crude digestive juice on 7.5% native PAGE. The purified enzyme exhibited five bands on native PAGE. IEF of the purified enzyme also revealed five bands with pls of 6.5, 6.15, 5.9, 5.8 and 4.7, respectively. The purified enzyme is a single polypeptide chain with a Mr of 58 kDa. The amylase is most active at pH 9.5 and is a Ca2+ dependent endoenzyme which hydrolyses starch into maltose, maltotriose and maltotetrose and hence behaves as an α-amylase (EC 3.2.1.1). The enzyme was unaffected by the presence or absence of CI-, with Km for soluble starch of 0.113%
Stepping up food production in Kerala-Problems, Perspectives and Strategies
A disturbing factor of the agricultural scenario in Kerala is that in spite of significant developments in agricultural technology, the productivity of rice has remained stagnant during the past over two decades. The annual rice production in the State has been stagnant, at about 1.3 million tonnes for nearly a decade' as against the present requirement of 2.8 million tonnes per year, while the population bas been growing at an annual rate of 1.79 per cent, resulting in a progressively widening gap between internal production and requirements
Cosmological Origin of the Stellar Velocity Dispersions in Massive Early-Type Galaxies
We show that the observed upper bound on the line-of-sight velocity
dispersion of the stars in an early-type galaxy, sigma<400km/s, may have a
simple dynamical origin within the LCDM cosmological model, under two main
hypotheses. The first is that most of the stars now in the luminous parts of a
giant elliptical formed at redshift z>6. Subsequently, the stars behaved
dynamically just as an additional component of the dark matter. The second
hypothesis is that the mass distribution characteristic of a newly formed dark
matter halo forgets such details of the initial conditions as the stellar
"collisionless matter" that was added to the dense parts of earlier generations
of halos. We also assume that the stellar velocity dispersion does not evolve
much at z<6, because a massive host halo grows mainly by the addition of
material at large radii well away from the stellar core of the galaxy. These
assumptions lead to a predicted number density of ellipticals as a function of
stellar velocity dispersion that is in promising agreement with the Sloan
Digital Sky Survey data.Comment: ApJ, in press (2003); matches published versio
Casimir interactions in Ising strips with boundary fields: exact results
An exact statistical mechanical derivation is given of the critical Casimir
forces for Ising strips with arbitrary surface fields applied to edges. Our
results show that the strength as well as the sign of the force can be
controled by varying the temperature or the fields. An interpretation of the
results is given in terms of a linked cluster expansion. This suggests a
systematic approach for deriving the critical Casimir force which can be used
in more general models.Comment: 10 pages, 4 figure
Observational evidence of spin-induced precession in active galactic nuclei
We show that it is possible to explain the physical origin of jet precession
in active galactic nuclei (AGNs) through the misalignment between the rotation
axes of the accretion disk and of the Kerr black hole. We apply this scenario
to quasars, Seyfert galaxies and also to the Galactic Center black hole Sgr A*,
for which signatures of either jet or disk precession have been found. The
formalism adopted is parameterized by the ratio of the precession period to the
black hole mass and can be used to put constraints to the physical properties
of the accretion disk as well as to the black hole spin in those systems.Comment: 10 pages, 1 figure, accepted for publication in ApJ Letter
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