1,454 research outputs found
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
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
Exact Solutions of the Saturable Discrete Nonlinear Schrodinger Equation
Exact solutions to a nonlinear Schr{\"o}dinger lattice with a saturable
nonlinearity are reported. For finite lattices we find two different
standing-wave-like solutions, and for an infinite lattice we find a localized
soliton-like solution. The existence requirements and stability of these
solutions are discussed, and we find that our solutions are linearly stable in
most cases. We also show that the effective Peierls-Nabarro barrier potential
is nonzero thereby indicating that this discrete model is quite likely
nonintegrable
Element Abundances at High-redshift: Magellan MIKE Observations of sub-Damped Lyman-alpha Absorbers at 1.7 < z <2.4
We present chemical abundance measurements from high-resolution observations
of 5 sub-damped Lyman-alpha absorbers at 1.7 < z < 2.4 observed with the
Magellan Inamori Kyocera Echelle (MIKE) spectrograph on the 6.5-m Magellan II
Clay telescope. Lines of Zn II, Mg I, Mg II, Al II, Al III, S II, Si II, Si IV,
C II, C II*, C IV, Ni II, Mn II and Fe II were detected and column densities
were determined. The metallicity of the absorbing gas, inferred from the nearly
undepleted element Zn, is in the range of < -0.95 to +0.25 dex for the five
absorbers in our sample, with three of the systems being near-solar or
super-solar. We also investigate the effect of ionisation on the observed
abundances using photoionisation modelling. Combining our data with other
sub-DLA and DLA data from the literature, we report the most complete existing
determination of the metallicity vs. redshift relation for sub-DLAs and DLAs.
We confirm the suggestion from previous investigations that sub-DLAs are, on
average, more metal-rich than DLAs and evolve faster. We also discuss relative
abundances and abundance ratios in these absorbers. The more metal-rich systems
show significant dust depletion levels, as suggested by the ratios [Zn/Cr] and
[Zn/Fe]. For the majority of the systems in our sample, the [Mn/Fe] vs. [Zn/H]
trend is consistent with that seen previously for lower-redshift sub-DLAs. We
also measure the velocity width values for the sub-DLAs in our sample from
unsaturated absorption lines of Fe II 2344, 2374, 2600 A, and examine where
these systems lie in a plot of metallicity vs. velocity dispersion. Finally, we
examine cooling rate vs. H I column density in these sub-DLAs, and compare this
with the data from DLAs and the Milky Way ISM. We find that most of the systems
in our sample show higher cooling rate values compared to those seen in the
DLAs.Comment: Accepted for publication in the Monthly Notices of The Royal
Astronomical Societ
Superposition in nonlinear wave and evolution equations
Real and bounded elliptic solutions suitable for applying the Khare-Sukhatme
superposition procedure are presented and used to generate superposition
solutions of the generalized modified Kadomtsev-Petviashvili equation (gmKPE)
and the nonlinear cubic-quintic Schroedinger equation (NLCQSE).Comment: submitted to International Journal of Theoretical Physics, 23 pages,
2 figures, style change
Stability Check of Escarpment Using Finite Element Method
The valve house of the Tons Hydel Project, Madhya Pradesh, India is located just adjacent to a steep escarpment. The stability analysis of scarp near the valve house was made by the Central Water and Power Research Station, using finite element method. The problem was treated as a plain strain case. The analysis under self weight and with seepage forces indicated tensile stresses less than 4 kg/cm2 in the scarp. A proposal by the project authorities namely removing rock in the area above R.L.230 m at 74 degrees and filling lean concrete below the overhang was found to provide a stable condition. The state of stress in the scarp near the valve house was obtained under different conditions. The finite element method thus proved to be a very useful tool in analysing problem
Barrier Penetration for Supersymmetric Shape-Invariant Potentials
Exact reflection and transmission coefficients for supersymmetric
shape-invariant potentials barriers are calculated by an analytical
continuation of the asymptotic wave functions obtained via the introduction of
new generalized ladder operators. The general form of the wave function is
obtained by the use of the F-matrix formalism of Froman and Froman which is
related to the evolution of asymptotic wave function coefficients
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