394 research outputs found
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
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
Bianchi Type V Viscous Fluid Cosmological Models in Presence of Decaying Vacuum Energy
Bianchi type V viscous fluid cosmological model for barotropic fluid
distribution with varying cosmological term is investigated. We have
examined a cosmological scenario proposing a variation law for Hubble parameter
in the background of homogeneous, anisotropic Bianchi type V space-time.
The model isotropizes asymptotically and the presence of shear viscosity
accelerates the isotropization. The model describes a unified expansion history
of the universe indicating initial decelerating expansion and late time
accelerating phase. Cosmological consequences of the model are also discussed.Comment: 10 pages, 3 figure
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
Bianchi Type-II String Cosmological Models in Normal Gauge for Lyra's Manifold with Constant Deceleration Parameter
The present study deals with a spatially homogeneous and anisotropic
Bianchi-II cosmological models representing massive strings in normal gauge for
Lyra's manifold by applying the variation law for generalized Hubble's
parameter that yields a constant value of deceleration parameter. The variation
law for Hubble's parameter generates two types of solutions for the average
scale factor, one is of power-law type and other is of the exponential form.
Using these two forms, Einstein's modified field equations are solved
separately that correspond to expanding singular and non-singular models of the
universe respectively. The energy-momentum tensor for such string as formulated
by Letelier (1983) is used to construct massive string cosmological models for
which we assume that the expansion () in the model is proportional to
the component of the shear tensor . This
condition leads to , where A, B and C are the metric coefficients
and m is proportionality constant. Our models are in accelerating phase which
is consistent to the recent observations. It has been found that the
displacement vector behaves like cosmological term in the
normal gauge treatment and the solutions are consistent with recent
observations of SNe Ia. It has been found that massive strings dominate in the
decelerating universe whereas strings dominate in the accelerating universe.
Some physical and geometric behaviour of these models are also discussed.Comment: 24 pages, 10 figure
Observing Long Colour Flux Tubes in SU(2) Lattice Gauge Theory
We present results of a high statistics study of the chromo field
distribution between static quarks in SU(2) gauge theory on lattices of volumes
16^4, 32^4, and 48^3*64, with physical extent ranging from 1.3 fm up to 2.7 fm
at beta=2.5, beta=2.635, and beta=2.74. We establish string formation over
physical distances as large as 2 fm. The results are tested against Michael's
sum rules. A detailed investigation of the transverse action and energy flux
tube profiles is provided. As a by-product, we obtain the static lattice
potential in unpreceded accuracy.Comment: 66 pages, 29 figures, uuencoded latex file with epsfigures (450 K),
supplementary full colour figures are available via ftp, CERN-TH.7413/94
(extended version
A microscopic semiclassical confining field equation for lattice gauge theory in 2+1 dimensions
We present a semiclassical nonlinear field equation for the confining field
in 2+1--dimensional lattice gauge theory (compact QED). The equation is
derived directly from the underlying microscopic quantum Hamiltonian by means
of truncation. Its nonlinearities express the dynamic creation of magnetic
monopole currents leading to the confinement of the electric field between two
static electric charges. We solve the equation numerically and show that it can
be interpreted as a London relation in a dual superconductor.Comment: 21 pages, epsf postscript figures included, full postscript available
at ftp://ftp.th.physik.uni-frankfurt.de/pub/cbest/micro.ps.Z or
http://www.th.physik.uni-frankfurt.de/~cbest/pub.htm
A Critical Assessment of the Congruency between Environmental DNA and Palaeoecology for the Biodiversity Monitoring and Palaeoenvironmental Reconstruction
The present study suggests that standardized methodology, careful site selection, and stratigraphy are essential for investigating ancient ecosystems in order to evaluate biodiversity and DNA-based time series. Based on specific keywords, this investigation reviewed 146 publications using the SCOPUS, Web of Science (WoS), PUBMED, and Google Scholar databases. Results indicate that environmental deoxyribose nucleic acid (eDNA) can be pivotal for assessing and conserving ecosystems. Our review revealed that in the last 12 years (January 2008–July 2021), 63% of the studies based on eDNA have been reported from aquatic ecosystems, 25% from marine habitats, and 12% from terrestrial environments. Out of studies conducted in aquatic systems using the environmental DNA (eDNA) technique, 63% of the investigations have been reported from freshwater ecosystems, with an utmost focus on fish diversity (40%). Further analysis of the literature reveals that during the same period, 24% of the investigations using the environmental DNA technique were carried out on invertebrates, 8% on mammals, 7% on plants, 6% on reptiles, and 5% on birds. The results obtained clearly indicate that the environmental DNA technique has a clear-cut edge over other biodiversity monitoring methods. Furthermore, we also found that eDNA, in conjunction with different dating techniques, can provide better insight into deciphering eco-evolutionary feedback. Therefore, an attempt has been made to offer extensive information on the application of dating methods for different taxa present in diverse ecosystems. Last, we provide suggestions and elucidations on how to overcome the caveats and delineate some of the research avenues that will likely shape this field in the near future. This paper aims to identify the gaps in environmental DNA (eDNA) investigations to help researchers, ecologists, and decision-makers to develop a holistic understanding of environmental DNA (eDNA) and its utility as a palaeoenvironmental contrivance
A Critical Assessment of the Congruency between Environmental DNA and Palaeoecology for the Biodiversity Monitoring and Palaeoenvironmental Reconstruction
The present study suggests that standardized methodology, careful site selection, and stratigraphy are essential for investigating ancient ecosystems in order to evaluate biodiversity and DNA-based time series. Based on specific keywords, this investigation reviewed 146 publications using the SCOPUS, Web of Science (WoS), PUBMED, and Google Scholar databases. Results indicate that environmental deoxyribose nucleic acid (eDNA) can be pivotal for assessing and conserving ecosystems. Our review revealed that in the last 12 years (January 2008–July 2021), 63% of the studies based on eDNA have been reported from aquatic ecosystems, 25% from marine habitats, and 12% from terrestrial environments. Out of studies conducted in aquatic systems using the environmental DNA (eDNA) technique, 63% of the investigations have been reported from freshwater ecosystems, with an utmost focus on fish diversity (40%). Further analysis of the literature reveals that during the same period, 24% of the investigations using the environmental DNA technique were carried out on invertebrates, 8% on mammals, 7% on plants, 6% on reptiles, and 5% on birds. The results obtained clearly indicate that the environmental DNA technique has a clear-cut edge over other biodiversity monitoring methods. Furthermore, we also found that eDNA, in conjunction with different dating techniques, can provide better insight into deciphering eco-evolutionary feedback. Therefore, an attempt has been made to offer extensive information on the application of dating methods for different taxa present in diverse ecosystems. Last, we provide suggestions and elucidations on how to overcome the caveats and delineate some of the research avenues that will likely shape this field in the near future. This paper aims to identify the gaps in environmental DNA (eDNA) investigations to help researchers, ecologists, and decision-makers to develop a holistic understanding of environmental DNA (eDNA) and its utility as a palaeoenvironmental contrivance
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