1,653 research outputs found
Chemical Enrichment at High Redshifts
We have tried to understand the recent observations related to metallicity in
Ly forest clouds in the framework of the two component model suggested
by Chiba & Nath (1997). We find that even if the mini-halos were chemically
enriched by an earlier generation of stars, to have [C/H] -2.5, the
number of C IV lines with column density , contributed by the
mini-halos, at the redshift of 3, would be only about 10% of the total number
of lines, for a chemical enrichment rate of in the galaxies.
Recently reported absence of heavy element lines associated with most of the Ly
lines with H I column density between and by Lu et al (1998), if correct, gives an upper limit on [C/H]=-3.7,
not only in the mini-halos, but also in the outer parts of galactic halos. This
is consistent with the results of numerical simulations, according to which,
the chemical elements associated with the Ly clouds are formed in situ
in clouds, rather than in an earlier generation of stars. However, the mean
value of for the column density ratio of C IV and H I,
determined by Cowie and Songaila (1998) for low Lyman alpha optical depths,
implies an abundance of [C/H] =-2.5 in mini-halos as well as in most of the
region in galactic halos, presumably enriched by an earlier generation of
stars. The redshift and column density distribution of C IV has been shown to
be in reasonable agreement with the observations.Comment: 23 pages, 6 figures, To appear in Astrophysical Journa
THERMOGRAPHIC APPLICATIONS OF TEMPERATURE SENSITIVE FLUORESCENCE OF SrS:Cu PHOSPHORS
The present work aims at investigating the temperature sensitive fluoro-optic behaviour of Cu-activated strontium sulphide (SrS) phosphors and its possible application in thermography. Accordingly, SrS (Cu) phosphors have been synthesized and painted with the help of adhesive on silica substrate. The excitation and emission spectra of such phosphor coatings have been recorded at room temperature (25C). The temperature dependence of fluorescence intensity and the lifetime of phosphorescence have also been studied. From the systematic variation of these two parameters with temperature, it appears that these phosphors are good candidates for thermographic application, at least, in the temperature range of investigation (25-150C)
New Shape Invariant Potentials in Supersymmetric Quantum Mechanics
Quantum mechanical potentials satisfying the property of shape invariance are
well known to be algebraically solvable. Using a scaling ansatz for the change
of parameters, we obtain a large class of new shape invariant potentials which
are reflectionless and possess an infinite number of bound states. They can be
viewed as q-deformations of the single soliton solution corresponding to the
Rosen-Morse potential. Explicit expressions for energy eigenvalues,
eigenfunctions and transmission coefficients are given. Included in our
potentials as a special case is the self-similar potential recently discussed
by Shabat and Spiridonov.Comment: 8pages, Te
Spontaneous Symmetry Breaking and the Renormalization of the Chern-Simons Term
We calculate the one-loop perturbative correction to the coefficient of the
\cs term in non-abelian gauge theory in the presence of Higgs fields, with a
variety of symmetry-breaking structures. In the case of a residual
symmetry, radiative corrections do not change the coefficient of the \cs term.
In the case of an unbroken non-abelian subgroup, the coefficient of the
relevant \cs term (suitably normalized) attains an integral correction, as
required for consistency of the quantum theory. Interestingly, this coefficient
arises purely from the unbroken non-abelian sector in question; the orthogonal
sector makes no contribution. This implies that the coefficient of the \cs term
is a discontinuous function over the phase diagram of the theory.Comment: Version to be published in Phys Lett B., minor additional change
Detecting cold gas at intermediate redshifts: GMRT survey using Mg II systems
Intervening HI 21-cm absorption systems at z > 1.0 are very rare and only 4
confirmed detections have been reported in the literature. Despite their
scarcity, they provide interesting and unique insights into the physical
conditions in the interstellar medium of high-z galaxies. Moreover, they can
provide independent constraints on the variation of fundamental constants. We
report 3 new detections based on our ongoing Giant Metrewave Radio Telescope
(GMRT) survey for 21-cm absorbers at 1.10< z_abs< 1.45 from candidate damped
Lyman_alpha systems. The 21-cm lines are narrow for the z_abs = 1.3710 system
towards SDSS J0108-0037 and z_abs = 1.1726 system toward SDSS J2358-1020. Based
on line full-width at half maximum, the kinetic temperatures are <= 5200 K and
<=800 K, respectively. The 21-cm absorption profile of the third system, z_abs
=1.1908 system towards SDSS J0804+3012, is shallow, broad and complex,
extending up to 100 km/s. The centroids of the 21-cm lines are found to be
shifted with respect to the corresponding centroids of the metal lines derived
from SDSS spectra. This may mean that the 21-cm absorption is not associated
with the strongest metal line component.Comment: 13 pages with 5 figures. Accepted for publication in ApJ
Periodic Solutions of Nonlinear Equations Obtained by Linear Superposition
We show that a type of linear superposition principle works for several
nonlinear differential equations. Using this approach, we find periodic
solutions of the Kadomtsev-Petviashvili (KP) equation, the nonlinear
Schrodinger (NLS) equation, the model, the sine-Gordon
equation and the Boussinesq equation by making appropriate linear
superpositions of known periodic solutions. This unusual procedure for
generating solutions is successful as a consequence of some powerful, recently
discovered, cyclic identities satisfied by the Jacobi elliptic functions.Comment: 19 pages, 4 figure
Linear Superposition in Nonlinear Equations
Even though the KdV and modified KdV equations are nonlinear, we show that
suitable linear combinations of known periodic solutions involving Jacobi
elliptic functions yield a large class of additional solutions. This procedure
works by virtue of some remarkable new identities satisfied by the elliptic
functions.Comment: 7 pages, 1 figur
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