182 research outputs found
Cylindrically Symmetric Inhomogeneous Universes with a Cloud of Strings
Cylindrically symmetric inhomogeneous string cosmological models are
investigated in presence of string fluid as a source of matter. To get the
three types of exact solutions of Einstein's field equations we assume , and . Some physical and geometric
aspects of the models are discussed.Comment: 9 page
Some Bianchi Type III String Cosmological Models with Bulk Viscosity
We investigate the integrability of cosmic strings in Bianchi III space-time
in presence of a bulk viscous fluid by applying a new technique. The behaviour
of the model is reduced to the solution of a single second order nonlinear
differential equation. We show that this equation admits an infinite family of
solutions. Some physical consequences from these results are also discussed.Comment: 12 pages, no figure. To appear in Int. J. Theor. Phy
Bulk Viscous LRS Biachi-I Universe with variable and decaying
The present study deals with spatially homogeneous and totally anisotropic
locally rotationally symmetric (LRS) Bianchi type I cosmological model with
variable and in presence of imperfect fluid. To get the
deterministic model of Universe, we assume that the expansion in the
model is proportional to shear . This condition leads to , where ,\; are metric potential. The cosmological constant
is found to be decreasing function of time and it approaches a small
positive value at late time which is supported by recent Supernovae Ia (SN Ia)
observations. Also it is evident that the distance modulus curve of derived
model matches with observations perfectly.Comment: 11 pages, 4 figures and 1 table, Accepted for publication in
Astrophysics and Space Scienc
Synthesis, Characterization and Antimicrobial Screening of Novel Hydrazide Ligand & It’s Transition Metal Complexes
Published ArticleDifferent transition metal complexes were synthesized from novel 3-bromo-2-[1-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-
yl)ethylidene]hydrazide ligand (H2L) and characterized by spectral techniques. The synthesized ligand was found to act mono as well as
di deprotonated (OH, NH) manner and stoichiometry of the ligand to metal ions was confirmed to be 1:1 in case of complex using metal
chloride salts, whereas 1:2 in case of metal(II) complexes using metal acetate(II) salt. Structures of metal complexes were confirmed by
IR, 1H NMR, TGA, XRD, elemental analysis and UV technique which revealed that Mn(II), Co(II), Ni(II), Cu(II) complexes were
octahedral geometry and those of Cu(II), Zn(II) showed square planner and tetrahedral geometry around metal ion respectively. Furthermore
H2L and its metal complexes were screened for antimicrobial activity which showed that ligand enhanced its biological activity after
coordination with metal ions. In particular, Cd(II) and Mn(II) complexes exhibited excellent antifungal activity
A New Class of Inhomogeneous String Cosmological Models in General Relativity
A new class of solutions of Einstein field equations has been investigated
for inhomogeneous cylindrically symmetric space-time with string source. To get
the deterministic solution, it has been assumed that the expansion ()
in the model is proportional to the eigen value of the shear
tensor . Certain physical and geometric properties of the
models are also discussed.Comment: 12 pages, no figure. Submitted to Astrophys. Space Sci. arXiv admin
note: substantial text overlap with arXiv:0705.090
Dissipative Future Universe without Big Rip
The present study deals with dissipative future universe without big rip in
context of Eckart formalism. The generalized chaplygin gas, characterized by
equation of state , has been considered as
a model for dark energy due to its dark-energy-like evolution at late time. It
is demonstrated that, if the cosmic dark energy behaves like a fluid with
equation of state ; , as well as chaplygin gas
simultaneously then the big rip problem does not arises and the scale factor is
found to be regular for all time.Comment: 6 pages, 2 figures, To appear in Int. J. Theor. Phy
Lyra's Cosmology of Massive String in Anisotropic Bianchi-II Space-time
The paper deals with a spatially homogeneous and totally anisotropic Bianchi
II cosmological models representing massive strings in normal gauge for Lyra's
manifold. The modified Einstein's field equations have been solved by applying
variation law for Hubble's parameter. This law generates two type of solutions
for average scale factor, one is of power law type and other is of exponential
law type. The power law describes the dynamics of Universe from big bang to
present epoch while exponential law seems reasonable to project dynamics of
future Universe. It has been found that the displacement actor is a
decreasing function of time and it approaches to small positive value at late
time, which is collaborated with Halford (1970) as well as recent observations
of SN Ia. The study reveals that massive strings dominate in early Universe and
eventually disappear from Universe for sufficiently large time, which is in
agreement with the current astronomical observations.Comment: 12 pages, 5 figure
Constraining Running Non-Gaussianity
The primordial non-Gaussian parameter fNL has been shown to be
scale-dependent in several models of inflation with a variable speed of sound.
Starting from a simple ansatz for a scale-dependent amplitude of the primordial
curvature bispectrum for two common phenomenological models of primordial
non-Gaussianity, we perform a Fisher matrix analysis of the bispectra of the
temperature and polarization of the Cosmic Microwave Background (CMB) radiation
and derive the expected constraints on the parameter nNG that quantifies the
running of fNL(k) for current and future CMB missions such as WMAP, Planck and
CMBPol. We find that CMB information alone, in the event of a significant
detection of the non-Gaussian component, corresponding to fNL = 50 for the
local model and fNL = 100 for the equilateral model of non-Gaussianity, is able
to determine nNG with a 1-sigma uncertainty of Delta nNG = 0.1 and Delta nNG =
0.3, respectively, for the Planck mission. In addition, we consider a Fisher
matrix analysis of the galaxy power spectrum to determine the expected
constraints on the running parameter nNG for the local model and of the galaxy
bispectrum for the equilateral model from future photometric and spectroscopic
surveys. We find that, in both cases, large-scale structure observations should
achieve results comparable to or even better than those from the CMB, while
showing some complementarity due to the different distribution of the
non-Gaussian signal over the relevant range of scales. Finally, we compare our
findings to the predictions on the amplitude and running of non-Gaussianity of
DBI inflation, showing how the constraints on a scale-dependent fNL(k)
translate into constraints on the parameter space of the theory.Comment: 37 pages, 14 figure
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