Abstract: Locally rotationally symmetric (LRS) Bianchi type-I dark energy cosmological model with variable equation of state (EoS) parameter in (Nordtvedt 1970) general scalar tensor theory of gravitation with the help of a special case proposed by (Schwinger 1970) is obtained. It is observed that these anisotropic and isotropic dark energy cosmological models always represent an accelerated universe and are consistent with the recent observations of type-Ia supernovae. Some important features of the models, thus obtained, have been discussed. PubDate: Wed, 12 Jun 2013 16:25:39 +000
Abstract: A vacuum spacetime with a central mass is derived as a stationary solution to Einstein's equations. The vacuum metric has a geodesic, shear-free, expanding, and twisting null congruence k and thus is algebraically special. The properties of the metric are calculated. In particular, it is shown that the spacetime has an event horizon inside which there is a black hole. The metric is neither spherically nor axially symmetric. It is therefore in interesting contrast with the majority of metrics featuring a central mass which have one or more of these symmetry properties. The metric reduces to the Schwarzschild case when a certain parameter is set to zero. PubDate: Tue, 04 Jun 2013 15:03:10 +000
Abstract: The restricted 2+2 body problem was stated by Whipple (1984) as a particular case of the general n + v problem described by Whipple and Szebehely (1984). In this work we reconsider the problem by studying some aspects of the dynamics of the minor bodies, such as the parametric variation of their equilibrium positions, as well as the attracting regions formed by the initial approximations used for the numerical determination of these positions. In the latter case we describe the process to form these regions, and we numerically investigate their dependence on the parameters of the system. The results in many cases show a fractal-type structure of these regions. As test problems, we use the Sun-Jupiter-binary asteroids and the Earth-Moon-dual artificial satellites systems.
Abstract: The linear stability of equilibrium points of a test particle of infinitesimal mass in the framework of Robe's circular restricted three-body problem, as in Hallan and Rana, together with effect of variation in masses of the primaries with time according to the combined Meshcherskii law, is investigated. It is seen that, due to a small perturbation in the centrifugal force and an arbitrary constant of a particular integral of the Gylden-Meshcherskii problem, every point on the line joining the centers of the primaries is an equilibrium point provided they lie within the shell. Further, a number of pairs of equilibrium points lying on the -plane and forming triangles with the centers of the shell and the second primary exist, for some values of . The points collinear with the center of the shell are found to be stable under some conditions and the range of stability depends on the small perturbations and , while the triangular points are unstable. Illustrative numerical exploration is given to indicate significant improvement of the problem in Hallan and Rana.
Abstract: We examine the question of energy localization for an exact solution of Einstein's equations with a scalar field corresponding to the phantom energy interpretation of dark energy. We apply three different energy-momentum complexes, the Einstein, the Papapetrou, and the Møller prescriptions, to the exterior metric and determine the energy distribution for each. Comparing the results, we find that the three prescriptions yield identical energy distributions.
Abstract: It has been argued that the correct, that is, positive, sign of quantum vacuum energy density, or, more properly, negative sign of quantum vacuum pressure, requires not a very large, and to some extent model-independent, number,
for example, ∼100, of additional, undiscovered fundamental bosonic particle species, absent in the standard model. Interpretation of the new particle species in terms of dark matter ones permits to qualitatively, and even quantitatively, connect all the three concepts given in the title.
Abstract: We have presented a method of obtaining parametric classes of spherically symmetric analytic solutions of the general relativistic field equations in canonical coordinates. A number of previously known classes of solutions have been rediscovered which describe perfect fluid balls with infinite central pressure and infinite central density though their ratio is positively finite and less than one. From the solution of one of the newly discovered classes, we have constructed a causal model in which outmarch of pressure and density is positive and monotonically decreasing, and pressure-density ratio is positive and less than one throughout within the balls. Corresponding to this model, we have maximized the Neutron star mass 2.40ð‘€Θ
with the linear dimensions of 28.43 kms and surface red shift of 0.4142.
Abstract: In juxtaposition with the standard model of rotation-powered pulsar, the model of vibration-powered magnetar undergoing quake-induced torsional Alfvén vibrations in its own ultrastrong magnetic field experiencing decay is considered. The presented line of argument suggests that the gradual decrease of frequencies (lengthening of periods) of long-periodic-pulsed radiation detected from a set of X-ray sources can be attributed to magnetic-field-decay-induced energy conversion from seismic vibrations to magnetodipole radiation of quaking magnetar.
Abstract: Models in which the Lagrangian contains only a kinetic factor and does not depend explicitly
on the field itself in k-essence cosmology are considered. In the case of a constant potential, we
obtain an exact analytic solution of k-essence, ð‘¤ð‘˜=−(3ð›¼−2)/3ð›¼, under a simple hypothesis, ð‘Ž=ð‘Ž0(ð‘¡/ð‘¡0)ð›¼, but without any assumption about the form of ð¹(ð‘‹). In purely kinetic k-essence
model, the acceleration can only be induced after the matter-dominated epoch; the Universe is
about 33.5+4.2−3.4 Gyr old now and about 3.1 Gyr old at ð‘§=3.9 which is consistent with the fact of
quasar observation, while this observation contradicts with the prediction of ΛCDM model, and the
year where a transition from deceleration to acceleration expansion is about from 18.43 Gyr to 25.2 Gyr after the beginning of the Universe. These results may offer clues to test observationally the
k-essence scenario in the future.
Abstract: Lane-Emden's equation has fundamental importance in the recent analysis of many problems in relativity and astrophysics including some models of density profiles for dark matter halos. An efficient numerical method is presented for linear and nonlinear Lane-Emden-type equations using the Bernstein polynomial operational matrix of integration. The proposed approach is different from other numerical techniques as it is based on the Bernstein polynomial integration matrix. Some illustrative examples are given to demonstrate the efficiency and validity of the proposed algorithm.
Abstract: The geoeffectiveness of some coupling functions for the Solar Wind-Magnetosphere Interaction had been studied. 58 storms with peak Dst < −100 nT were used. The result showed that the interplanetary magnetic field ðµð‘§ appeared to be more relevant with the magnetic field ðµ (which agreed with previous results). However, both the 𑉠(solar wind flow speed) and ðµð‘§ factors in the interplanetary dawn-dusk electric field (ð‘‰×ðµð‘§) are effective in the generation of very intense storms (peak Dst < −250 nT) while “intense” storms (−250 nT ≤ peak Dst < −100 nT) are mostly enhanced by the ðµð‘§ factor alone (in most cases). The southward ðµð‘§ duration ðµð‘‡ seems to be more relevant for Dst < −250 nT class of storms and invariably determines the recovery phase duration. Most of the storms were observed to occur at midnight hours (i.e., 2100–0400 UT), having a 41.2% incidence rate, with high frequency between 2300 UT and 0000 UT. 62% of the events were generated as a result of Magnetic Cloud (MC), while 38% were generated by complex ejecta. The ðµ-ðµð‘§ relation for the magnetic cloud attained a correlation coefficient of 0.8922, while it is 0.7608 for the latter. Conclusively, ðµð‘§ appears to be the most geoeffective factor, and geoeffectiveness should be a factor that depends on methods of event identification and classification as well as the direction of event correlation.
Abstract: Gravity is one of the most inexplicable forces of nature, controlling
everything, from the expansion of the Universe to the ebb and flow
of ocean tides. The search for the laws of motion and gravitation
began more than two thousand years ago but still we do not have
the complete picture of it. In this paper, we have outlined how our
understanding of gravity is changing drastically with time and how
the previous explanations have shaped the most recent developments
in the field like superstrings and braneworlds.
Abstract: The way in which turbulent fluxes are usually represented in computations of large-scale flow in the convection zones of the sun and other stars is briefly described. A model of an ensemble of eddies that is capable of generalization to circumstances more complicated than the usual essentially spherically symmetrical convection zone is outlined. Generalization usually requires the introduction of new postulates, and, in so doing, also lays bare some of the assumptions, often implicit, in the usual mixing-length formalisms.
Abstract: The unusual morphology and internal structure of bubbles within lunar regolith impact glasses have been studied using traditional scanning electron microscopy and the novel technique transmission X-ray microscopy (TXM), with 3D tomography reconstruction. Here, we show the previously unknown phenomenon of building a highly porous cellular structure within bubbles in glassy particles of the dust fraction of lunar regolith. Vesicles within studied lunar glasses are filled in with submicron-sized particles as shown in the presented micrograph. These particles consist of glass nano in size elements. What is shown in the TXM tomography reconstruction anaglyph demonstrates cellular-like, 3D structure where oblique probably glassy fine particles down to 100 nm in diameter build chains of sophisticated network. It also may be suggested that submicron and nano-sized grains present in lunar regolith are the result of particle liberation from broken glassy vesicles. This liberation takes place when regolith is exposed to constant impact pulverisation. Liberated particles are permanently enriching lunar soil in the finest soil constituent. This constituent presence in lunar regolith may be responsible for the unusual behaviour of lunar material. This unusual constituent of lunar regolith and its properties have to be better understood before our permanent lunar exploration begins.
Abstract: TYC 3034-0299-1 (CVn) is a magnetically active, contact binary, ROTSE variable. UBVRcIc light curves are presented along with a period study and a simultaneous UBVRI light curve solution. Our light curves show eclipse amplitudes of 0.72 and 0.62 mags (V) in the primary and secondary eclipses. Modeled results include a dark spot region, found at longitude 51°, a 24% Roche lobe fill-out, and a mass ratio of 0.48. A total eclipse is found to occur in the secondary eclipse making TYC 3034-0299-1 a W-type (less massive star is hotter) W UMa variable.
Abstract: Within the context of finite-time thermodynamics (FTTs) some models of convective atmospheric cells have been proposed to calculate the efficiency of the conversion of solar energy into wind energy and also for calculating the surface temperature of the planets of the solar system. One of these models is the Gordon and Zarmi (GZ) model, which consists in taking the sun-earth-wind system as a FTT-cyclic heat engine where the heat input is solar radiation, the working fluid is the earth's atmosphere and the energy in the winds is the work produced. The cold reservoir to which the engine rejects heat is the 3K surrounding universe. In the present work we apply the GZ-model to investigate some features of the convective zone of the sun by means of a possible structure of successive convective cells along the well-established convective region of the sun. That is, from 0.714 ð‘…𑆠up to ð‘…𑆠being ð‘…𑆠the radius of the sun. Besides, we estimate the number of cells of the model, the possible size of the cells, their thermal efficiency, and also their average power output. Our calculations were made by means of two FTT regimes of performance: the maximum power regime and the maximum ecological function regime. Our results are in reasonable agreement with others reported in the literature.
Abstract: We introduce a new method to calculate the multiscale 3D filamentation of SDSS DR5 galaxy clusters and also applied it to N-body simulations. We compared the filamentation of the observed versus mock samples in metric space on scales from 8 Mpc to 30 Mpc. Mock samples are closer to the observed sample than random samples, and one of the mock samples behaves better than another one. We also find that the observed sample has a large filamentation value at a scale of 10 Mpc, which is not found from either mock samples or random samples.
Abstract: A special nonaxisymmetric solution of Einstein’s equations is derived, representing pure radiation from a rotating isolated source. The spacetime is assumed to be algebraically special having a multiple null eigenvector of the Weyl tensor forming a geodesic, shear-free, diverging, and twisting congruence ð¤. Employing a complex null tetrad involving the vector ð¤, the Ricci tensor, density of the radiation, divergence, and twist are calculated for the derived metric. A particular (nonaxisymmetric) subcase is shown to be flat at infinity and to contain the axisymmetric radiating Kerr metric, derived by Kramer and separately by Vaidya and Patel, as a special case. The spacetime is of Petrov type II and without Killing vectors.
Abstract: We suggest that stable states of positronium might exist in the jets of active galactic nuclei (AGN). Electrons and positrons are created near the accretion
disks of supermassive black holes at the centers of AGN and are accelerated along magnetic field lines while within the Alfvèn radius. The conditions in this region are ideal for the creation of bound states of positronium which are stable against annihilation. Traveling at relativistic speeds along the jet, the helical magnetic field enables the atoms to survive for great distances.
Abstract: The effect of a nonuniform magnetic field on the gravitational instability of a nonuniformly rotating infinitely extending axisymmetric cylinder in a homogenous ferromagnetic medium has been studied. The propagation of the wave is allowed along radial direction. A general dispersion relation, using the normal mode analysis method on the perturbation equations of the problem, is obtained. It is found that Bel and Schatzman criterion determines the gravitational instability of this general problem. Thus, it appears that the effect of non-uniform magnetic field on the gravitational instability as discussed by (Dhiman and Dadwal, 2010) is marginalized by the magnetic polarizability of ferrofluid.
Abstract: We discuss analytical results dealing with photometric and astrometric gravitational microlensing. The first two sections concern approximation methods that allow us to get solutions of the general lens equation near fold caustics and cusp points up to any prescribed accuracy. Two methods of finding approximate solutions near the fold are worked out. The results are applied to derive new corrections to total amplifications of critical source images. Analytic expressions are obtained in case of the Gaussian, power-law, and limb-darkening extended source models; here we present the first nonzero corrections to the well-known linear caustic approximation. Possibilities to distinguish different source models in observations are discussed on the basis of statistical simulations of microlensed light curves. In the next section, we discuss astrometric microlensing effects in various cases of extended sources and extended lenses, including a simple model of weak statistical microlensing by extended dark matter clumps. Random walks of a distant source image microlensed by stochastic masses are estimated. We note that the bulk motion of foreground stars induces a small apparent rotation of the extragalactic reference frame. Compact analytical relations describing the statistics of such motions are presented.
Abstract: The effect of radiative heat-loss function and finite ion Larmor radius (FLR) corrections on the self-gravitational instability of infinite homogeneous viscous plasma has been investigated incorporating the effects of thermal conductivity and finite electrical resistivity for the formation of a star in astrophysical plasma. The general dispersion relation is derived using the normal mode analysis method with the help of relevant linearized perturbation equations of the problem. Furthermore the wave propagation along and perpendicular to the direction of external magnetic field has been discussed. Stability of the medium is discussed by applying Routh Hurwitz’s criterion. We find that the presence of radiative heat-loss function and thermal conductivity modify the fundamental Jeans criterion of gravitational instability into radiative instability criterion. From the curves we see that temperature dependent heat-loss function, FLR corrections and viscosity have stabilizing effect, while density dependent heat-loss function has destabilizing effect on the growth rate of self-gravitational instability. Our result shows that the FLR corrections and radiative heat-loss functions affect the star formation.
Abstract: Some tilted Bianchi type IX dust fluid cosmological model is investigated. To get a deterministic model we assume that , where and are metric potentials and the fluid is pressureless, that is, . Some physical and geometric properties of the model are discussed. Also, we have discussed a special model in terms of only.
Abstract: Galaxy scaling relations, which describe a connection between ostensibly unrelated physical characteristics, testify to an underlying order in galaxy formation that requires understanding. I review the development of a scaling relation that (1) unites the well-known fundamental plane (FP) relation of giant elliptical galaxies and Tully-Fisher (TF) relation of disk galaxies, (2) fits low
mass spheroidal galaxies, including the ultrafaint satellites of our galaxy, (3) explains the apparent shift of lenticular galaxies relative to both FP or TF, (4) describes all stellar dynamical systems, including systems with no dark matter (stellar clusters), (5) associates explicitly the numerical coefficients that account for the apparent tilt of the FP away from the expectation drawn from the virial theorem with variations in the total mass-to-light ratio of galaxies within the half-light radius, (6) connects with results that demonstrate the robustness of mass estimators when applied at the half-light radius, and (7) results in smaller scatter for disk galaxies than the TF relation. I review two applications: (1) the cross-calibration of distance measurement methods and (2) the determination of mass-to-light ratios of simple stellar populations and implications for the stellar initial mass function.
Abstract: We present an analysis of the classic Alcubierre metric based on conformal gravity, rather than
standard general relativity. The main characteristics of the resulting warp drive remain the same as in the original study by Alcubierre, that is, effective superluminal motion is a viable outcome of the metric. We show that for particular choices of the shaping function, the Alcubierre metric in the context of conformal gravity does not violate the weak energy condition, as was the case of the original solution. In particular, the resulting warp drive does not require the use of exotic matter. Therefore, if conformal gravity is a correct extension of general relativity, superluminal motion via an Alcubierre metric might be a realistic solution, thus allowing faster-than-light interstellar travel.
Abstract: Studying the published values of Maxwellian-averaged neutron capture cross sections, we found simple phenomenological rules obeyed by the cross sections as a function of proton and neutron numbers. We use these rules to make predictions for cross sections of neutron capture on nuclei with proton number above 83, where very few MACS data are available. These predictions may be useful in certain models of nucleosynthesis of heavy nuclei in stars.
Abstract: The paper deals with spatially homogeneous anisotropic Bianchi type II, VIII , and IX dark energy cosmological models filled with perfect fluid in the framework of Saez-Ballester (1986) theory, and Einstein's general relativity. Assuming that the two sources interact minimally and therefore their energy momentum tensors are conserved separately, we have considered different cases and presented anisotropic as well as isotropic cosmological models. Some important physical and geometrical features of the models, thus obtained, have been discussed.
Abstract: This paper introduces history of space tethers, including tether concepts and tether missions, and attempts to provide a source of references for historical understanding of space tethers. Several concepts of space tethers since the original concept has been conceived are listed in the literature, as well as a summary of interesting applications, and a research of space tethers is given. With the aim of implementing scientific experiments in aerospace, several space tether missions which have been delivered for aerospace application are introduced in the literature.
Abstract: We have studied cosmological dynamics in gravity theory via cosmographic parameters. We have changed variables of field equations from time to red-shift and solved the achieved differential equation analytically for . Then we have used Taylor expansion to find general form of function around the present day value of scalar curvature. By introducing we would simplify our calculations; if we consider as a given function we would restrict our answers of . In this paper we offer a linear form of which leads us to a specific function, where is a constant which depends on the present day value of deceleration parameter. As an example, using Taylor expansion coefficients, we have compared our analytically calculated function with reconstructed function for Dark Energy models. To reconstruct action for Dark Energy models, we have used corresponding of each Dark Energy model for calculating Taylor expansion coefficients. As our function is linear, the Taylor expansion coefficients would be a function of present day value of deceleration parameter.
Abstract: Bianchi type I tilted bulk viscous fluid cosmological model filled with dust fluid is investigated. We assume that (constant), where is the coefficient of bulk viscosity and is the expansion in the model. It has been assumed that the expansion in the model is only in two directions; that is, one of the components of Hubble parameters is zero. The physical and geometrical aspects of the model in the presence and absence of bulk viscosity are also discussed. Also, we have discussed two special models and their physical properties. From this, we present a particular example based on dust fluid.
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