-> AERONAUTICS AND SPACE FLIGHT
(Total: 93 journals)
- The Mass of Graviton and Its Relation to the Number of Information
according to the Holographic Principle
Abstract: We investigate the relation of the mass of the graviton to the number of information in a flat universe. As a result we find that the mass of the graviton scales as . Furthermore, we find that the number of gravitons contained inside the observable horizon is directly proportional to the number of information ; that is, . Similarly, the total mass of gravitons that exist in the universe is proportional to the number of information ; that is, . In an effort to establish a relation between the graviton mass and the basic parameters of the universe, we find that the mass of the graviton is simply twice the Hubble mass as it is defined by Gerstein et al. (2003), times the square root of the quantity , where is the deceleration parameter of the universe. In relation to the geometry of the universe we find that the mass of the graviton varies according to the relation , and therefore obviously controls the geometry of the space time through a deviation of the geodesic spheres from the spheres of Euclidean metric.
PubDate: Wed, 29 Oct 2014 10:09:06 +000
- CCD SDSS Photometry of Poorly Studied Star Clusters in the Large
Abstract: We present for the first time CCD SDSS photometry, obtained at the Gemini South telescope with the GMOS attached, of stars in the field of the poorly studied star clusters NGC1768, HS 85, SL 676, NGC2107, NGC2190, and SL 866, which are distributed in the main body of the Large Magellanic Cloud. We applied a subtraction procedure to statistically clean the cluster CMDs from field star contamination. In order to disentangle cluster features from those belonging to their surrounding fields, we applied a subtraction procedure which makes use of variable cells to reproduce the field star color-magnitude diagrams (CMDs) as closely as possible. We then traced their stellar density radial profiles from star counts performed over the cleaned field stars dataset and derived their radii. Using the cleaned cluster CMDs, we estimated ages and metallicities from matching theoretical isochrones computed for the SDSS system. The studied star clusters have ages from 0.1 up to 2.0 Gyr and are of slightly metal-poor metal content ( dex).
PubDate: Sun, 11 May 2014 13:42:20 +000
- Retracted: On the Geoeffectiveness Structure of Solar Wind-Magnetosphere
Coupling Functions during Intense Storms
PubDate: Thu, 23 Jan 2014 14:18:20 +000
- A Statistical Study on DH CMEs and Its Geoeffectiveness
Abstract: A detailed investigation on geoeffectiveness of CMEs associated with DH-type-II bursts observed during 1997–2008 is presented. The collected sample events are divided into two groups based on their association with CMEs related to geomagnetic storms Dst ≤−50 nT, namely, (i) geoeffective events and (ii) nongeoeffective events. We found that the geoeffective events have high starting frequency, low ending frequency, long duration, wider bandwidth, energetic flares, and CMEs than nongeoeffective events. The geoeffective events are found to have intense geomagnetic storm with mean Dst index (−150 nT). There exists good correlation between the properties of CMEs and flares for geoeffective events, while no clear correlation exists for nongeoeffective events. There exists a weak correlation for geoeffective events between (i) CME speed and Dst index and good correlation between (i) CME speed and solar wind speed , (ii) Dst index and solar wind speed , and (iii) Dst index and southward magnetic field component () . From our study we conclude that the intense and long duration southward magnetic field component () and fast solar wind speed are responsible for geomagnetic storms, and the geomagnetic storms weakly depend on CME speed. About 22% (50/230) of the DH-type-II bursts are associated with geomagnetic storms. Therefore the DH-type-II bursts associated with energetic flares and CMEs are good indicator of geomagnetic storms.
PubDate: Tue, 24 Dec 2013 18:07:06 +000
- BVRcIc Observations and Analysis of the Near-Contact Solar Type Eclipsing
Binary, V530 Andromedae
Abstract: We present the first precision UBVRcIc light curves, an initial period study, and a simultaneous light curve solution for the near-contact solar type eclipsing binary V530 And. Our observations were taken with the 0.81 m Lowell reflector on 27 and 29 September, 2011, with time being granted from the National Undergraduate Research Observatory (NURO). Our Wilson Devinney Program solution yields a semidetached, V1010 Oph configuration: the more massive component is filling its Roche lobe. The system is apparently approaching contact for the first time. It is not a classic Algol.
PubDate: Thu, 12 Dec 2013 11:02:30 +000
- Axially Symmetric Bulk Viscous String Cosmological Models in GR and
Brans-Dicke Theory of Gravitation
Abstract: Axially symmetric string cosmological models with bulk viscosity in Brans-Dicke (1961) and general relativity (GR) have been studied. The field equations have been solved by using the anisotropy feature of the universe in the axially symmetric space-time. Some important features of the models, thus obtained, have been discussed. We noticed that the presence of scalar field does not affect the geometry of the space-time but changes the matter distribution, and as a special case, it is always possible to obtain axially symmetric string cosmological model with bulk viscosity in general relativity.
PubDate: Wed, 06 Nov 2013 13:31:13 +000
- LRS Bianchi Type-I Dark Energy Cosmological Models in General Scalar
Tensor Theory of Gravitation
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
- A Central Mass in a Stationary Vacuum without Spherical or Axial Symmetry
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
- The Restricted 2+2 Body Problem: Parametric Variation of the Equilibrium
States of the Minor Bodies and Their Attracting Regions
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.
PubDate: Thu, 04 Apr 2013 09:33:26 +000
- Robe's Restricted Three-Body Problem with Variable Masses and Perturbing
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.
PubDate: Mon, 25 Mar 2013 16:10:28 +000
- The Localized Energy Distribution of Dark Energy Star Solutions
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.
PubDate: Thu, 07 Mar 2013 13:03:03 +000
- Dark Energy Constraints on Red-Shift-Based Gravity
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.
PubDate: Tue, 19 Feb 2013 14:32:45 +000
- Dust Fluid Cosmological Model
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.
PubDate: Sun, 17 Feb 2013 13:41:55 +000
- History of the Tether Concept and Tether Missions: A Review
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.
PubDate: Thu, 14 Feb 2013 13:20:22 +000
- Phenomenological Description of Neutron Capture Cross Sections at
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.
PubDate: Wed, 30 Jan 2013 15:58:54 +000
- Bianchi Type II, VIII, and IX Perfect Fluid Dark Energy Cosmological
Models in Saez-Ballester and General Theory of Gravitation
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.
PubDate: Wed, 23 Jan 2013 10:23:21 +000
- Conformal Gravity and the Alcubierre Warp Drive Metric
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.
PubDate: Tue, 15 Jan 2013 10:08:27 +000
- Tilted Bianchi Type IX Dust Fluid Cosmological Model in General Relativity
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.
PubDate: Tue, 18 Dec 2012 10:27:51 +000
- Implications and Applications of Kinematic Galaxy Scaling Relations
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.
PubDate: Tue, 20 Nov 2012 11:25:05 +000
- Effect of Radiative Heat-Loss Function and Finite Larmor Radius
Corrections on Jeans Instability of Viscous Thermally Conducting
Self-Gravitating Astrophysical Plasma
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.
PubDate: Sat, 29 Sep 2012 15:33:12 +000
- Analytical Methods in Gravitational Microlensing
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.
PubDate: Tue, 25 Sep 2012 16:47:59 +000
- Long-Lived Positronium and AGN Jets
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.
PubDate: Mon, 24 Sep 2012 08:39:08 +000
- On the Magnetogravitational Instability of a Ferromagnetic Dust Cloud in
the Presence of Nonuniform Rotation
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.
PubDate: Thu, 16 Aug 2012 12:19:52 +000
- Three-Dimensional Filamentation Analysis of SDSS DR5 Survey
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.
PubDate: Wed, 27 Jun 2012 13:21:09 +000
- A Nonaxisymmetric Solution of Einstein’s Equations Featuring Pure
Radiation from a Rotating Source
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.
PubDate: Tue, 08 May 2012 09:43:05 +000
- An Endoreversible Thermodynamic Model Applied to the Convective Zone of
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‘…ð‘† up to ð‘…ð‘† being ð‘…ð‘† the 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.
PubDate: Mon, 26 Mar 2012 09:22:14 +000
- UBVRI Photometric Analysis of the Solar-Type Eclipsing Binary TYC
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.
PubDate: Sun, 11 Mar 2012 18:05:36 +000
- On Estimating Fluxes due to Small-Scale Turbulent Convection in a Rotating
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.
PubDate: Wed, 29 Feb 2012 13:15:41 +000
- Discovery of Discrete Structured Bubbles within Lunar Regolith Impact
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.
PubDate: Thu, 26 Jan 2012 18:06:30 +000
- Understanding Gravity: Some Extra-Dimensional Perspectives
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.
PubDate: Wed, 18 Jan 2012 14:45:36 +000
- On the Geoeffectiveness Structure of Solar Wind-Magnetosphere Coupling
Functions during Intense Storms
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 ð‘‰ (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.
PubDate: Tue, 17 Jan 2012 11:03:02 +000
- Solution of the Lane-Emden Equation Using the Bernstein Operational Matrix
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.
PubDate: Wed, 11 Jan 2012 15:23:15 +000
- An Old Universe in K-Essence Cosmology
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.
PubDate: Mon, 09 Jan 2012 14:08:54 +000
- Vibration-Powered Radiation of Quaking Magnetar
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.
PubDate: Thu, 05 Jan 2012 17:21:17 +000
- Vacuum Pressure, Dark Energy, and Dark Matter
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.
PubDate: Wed, 04 Jan 2012 15:20:27 +000
- Varieties of Parametric Classes of Exact Solutions in General Relativity
Representing Static Fluid Balls
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.
PubDate: Tue, 03 Jan 2012 07:58:08 +000
- On Some Properties of SEP Effective CMEs
Abstract: Solar energetic particles (SEP) are believed to originate from two different sources, solar flares and coronal mass ejections (CMEs). The large SEP events constitute a serious radiation hazard. The high-energy solar proton data obtained from NOAA Space Environment Services Center are used to investigate some statistical properties such as speed, apparent width, acceleration, latitude, mass, kinetic energy, and occurrence rate of SEP effective CMEs observed during the period 1997–2006 covering the solar cycle 23. It is found that SEP effective CMEs are nearly halo in nature, and they follow solar cycle variation. Such CMEs have higher speeds than those of non-SEP effective CMEs.
PubDate: Sun, 25 Dec 2011 10:47:48 +000
- New Black Holes Solutions in a Modified Gravity
Abstract: We present some basic concepts of a theory of modified gravity, inspired by the gauge
theories, where the commutator algebra of covariant derivative gives us an added term with respect to the General Relativity, which represents the interaction of gravity with a substratum. New spherically symmetric solutions of this theory are obtained and can be viewed as solutions that reproduce the mass, the charge, the cosmological constant, and the Rindler acceleration, without coupling with the matter content, that is, in the vacuum.
PubDate: Wed, 21 Dec 2011 15:18:49 +000
- LRS Bianchi Type II Inflationary Universe with Massless Scalar Field
Abstract: Inflationary scenario in locally rotationally symmetric (LRS) Bianchi Type II space-time with massless scalar field with flat potential is discussed. To get the deterministic solution in terms of cosmic time ð‘¡, we have assumed that the scale factor ∼ð‘’3ð»ð‘¡, that is, ð‘…2ð‘†∼ð‘’3ð»ð‘¡ and ð‘‰(ðœ™) = constant where ð‘‰ is effective potential and ðœ™ is Higg's field. We find that spatial volume increases with time and the model isotropizes for large value of ð‘¡ under special condition. The Higg's field decreases slowly and tends to a constant value when ð‘¡→∞. The model represents uniform expansion but accelerating universe and leads to de-Sitter type metric.
PubDate: Sun, 18 Dec 2011 09:35:41 +000
- Pulsars: Cosmic Permanent “Neutromagnets”'
Abstract: We argue that pulsars may be spin-polarized neutron stars, that is,
cosmic permanent magnets. This would simply explain several observational facts about pulsars, including the “beacon effect” itself, that is, the static/stable misalignment of rotational and magnetic axes, the extreme temporal stability of the pulses, and the existence of an upper
limit for the magnetic field strength, coinciding with the one observed
in “magnetars.” Although our model admittedly is speculative, this
latter fact seems to us unlikely to be pure coincidence.
PubDate: Tue, 06 Dec 2011 16:09:36 +000
- Locations of Satellite Galaxies in the Two-Degree Field Galaxy Redshift
Abstract: We compute the locations of satellite galaxies in the Two-Degree Field Galaxy Redshift Survey using two sets of selection criteria and three sources of photometric data. Using the SuperCOSMOS ð‘Ÿð¹ photometry, we find that the satellites are located preferentially near the major axes of their hosts, and the anisotropy is detected at a highly significant level (confidence levels of 99.6% to 99.9%). The locations of satellites that have high velocities relative to their hosts are statistically indistinguishable from the locations of satellites that have low velocities relative to their hosts. Additionally, satellites with passive star formation are distributed anisotropically about their hosts (99% confidence level), while the locations of star-forming satellites are consistent with an isotropic distribution. These two distributions are, however, statistically indistinguishable. Therefore it is not correct to interpret this as evidence that the locations of the star-forming satellites are intrinsically different from those of the passive satellites.
PubDate: Mon, 24 Oct 2011 08:05:01 +000
- A New Galactic Wolf-Rayet Star in Centaurus
Abstract: I communicate the detection of a new Galactic Wolf-Rayet star (WR60a) in Centaurus. The H- and
K-band spectra of WR60a show strong carbon near-infrared emission lines, characteristic of Wolf-Rayet stars of the
WC5-7 subtype. Adopting mean absolute magnitude MK and mean intrinsic (ð½-ð¾ð‘†) and (ð»-ð¾ð‘†) colours, it was found that WR60a suffers a mean visual extinction of 3.8±1.3 magnitudes, being located at a probable heliocentric
distance of 5.2±0.8 Kpc, which for the related Galactic longitude (l=312) puts this star probably in the Carina-Sagittarius arm at about 5.9 kpc from the Galactic center. I searched for clusters in the vicinity of WR60a
and in principle found no previously known clusters in a search radius region of several tens arcminutes. The detection of a
well-isolated WR star induced us to seek for some still unknown cluster, somewhere in the vicinity of WR60a. From
inspection of 5.8 μm and 8.0 μm Spitzer/IRAC GLIMPSE images of the region around the new WR star,
strong mid-infrared extended emission at about 13.5 arcmin south-west of WR60a was found.
The study of the H-KS colour
distribution of point sources associated with the extended emission reveals the presence of a new Galactic cluster
candidate probably formed by at least 85 stars.
PubDate: Wed, 14 Sep 2011 15:29:48 +000
- Kinematical Conformal Cosmology: Fundamental Parameters from Astrophysical
Abstract: We continue the presentation of an alternative cosmology based on conformal
gravity, following our kinematical approach to the subject introduced in a
recent paper. In line with the assumptions of our model, which proposes a
closed-form expression for the cosmic scale factor ð‘…(ð‘¡), we revise the
Hubble and deceleration parameters and introduce modified cosmological
distances, analyzing in particular the case of the luminosity distance. Our kinematical conformal cosmology is then able to explain the anomalous
acceleration of the Pioneer spacecraft, as due to a local region of gravitational blueshift. From the reported data of the Pioneer anomaly, we also
compute the current value of our first fundamental parameter, ð›¾0=1.94×10−28cm−1, in line with the original estimate by P. Mannheim of this quantity. Our second fundamental parameter, ð›¿0=3.83×10−5, interpreted
as the current value of a cosmological time variable, is derived from a
detailed fitting of type Ia supernovae “gold-silver” data, producing Hubble plots of the same
quality of those obtained by standard cosmology, but without requiring any
dark matter or dark energy contribution. If further experiments will confirm the presence of an anomalous frequency
blueshift in the outer region of the solar system, as described by our model,
kinematical conformal cosmology might become a viable alternative to standard
PubDate: Wed, 17 Aug 2011 14:21:41 +000
- Why the Sunspot Cycle Is Double Peaked
Abstract: Many sunspot cycles are double peaked. In 1967, Gnevyshev suggested that actually all cycles have two peaks generated by different physical mechanisms, but sometimes the gap between them is too short for the maxima to be distinguished in indices of the total sunspot activity. Here, we show that indeed all cycles have two peaks easily identified in sunspot activity in different latitudinal bands. We study the double peaks in the last 12 sunspot cycles and show that they are manifestation of the two surges of toroidal field—the one generated from the poloidal field advected all the way on the surface to the poles, down to the tachocline and equatorward to sunspot latitudes, and another one generated from the poloidal field diffused at mid-latitudes from the surface to the tachocline and transformed there into toroidal field. The existence of these two surges of toroidal field is due to the relative magnitudes of the speed of the large-scale solar meridional circulation and the diffusivity in the solar convection zone which are estimated from geomagnetic data.
PubDate: Tue, 31 May 2011 15:03:55 +000
- On the Cosmic Ray-Induced Ionization Rate in Molecular Clouds
Abstract: The transformation of the energy dependence of the cosmic ray proton flux in the keV to GeV region is investigated theoretically when penetrating inside molecular clouds (Av>5 mag). The computations suggest that energy losses of the cosmic ray particles by interaction with the matter of the molecular cloud are principally caused by the inelastic (electronic) interaction potential; the transformed energy distribution of energetic protons is determined mainly by the column density of the absorbing medium. A cutoff of the cosmic ray spectrum inside clouds by their magnetic fields is also phenomenologically taken into account. This procedure allows a determination of environment-dependent ionization rates of molecular clouds. The theoretically predicted ionization rates are in good agreement with those derived from astronomical observations of H3+ absorption lines in the spectrum of the cloud connected with the Herbig Be star LkHð›¼ 101.
PubDate: Wed, 27 Apr 2011 15:27:42 +000
- The Dark Matter Halo Density Profile, Spiral Arm Morphology, and
Supermassive Black Hole Mass of M33
Abstract: We investigate the dark matter halo density profile of M33. We find that the HI rotation curve of M33 is best described by an NFW dark matter halo density profile model, with a halo concentration of ð‘vir=4.0±1.0 and a virial mass of ð‘€vir=(2.2±0.1)×1011M⊙. We go on to use the NFW concentration (ð‘vir) of M33, along with the values derived for other galaxies (as found in the literature), to show that ð‘vir correlates with both spiral arm pitch angle and supermassive black hole mass.
PubDate: Wed, 27 Apr 2011 10:23:05 +000
- Luminosity Function of Some Open Clusters
Abstract: We investigated the luminosity function (LF) and initial mass function (IMF) of some open clusters having different ages. To calculate the LF, we followed the classical definition by van Rhijn (1936). Statistical investigation of the dispersion around a range of magnitudes concerning what is called Wielen dip revealed that the dip is unreal. To confirm the unreality of the dip, we computed the IMF for these open clusters, the statistical investigation of the IMF confirmed the results obtained using the LF, that is, there is no dip for these open clusters under study.
PubDate: Tue, 26 Apr 2011 12:55:22 +000
- Statistical Effects in the Solar Activity Cycles during AD 1823–1996
Abstract: General statistical properties of solar activity cycles during the period AD 1823–1996—including the Gnevyshev-Ohl and Waldmeier effects as well as an amplitude-period effect—were analyzed using Wolf number, group sunspot number, and extended total sunspot area series. It was found out that the Gnevyshev-Ohl effect GO2 (the positive correlation between intensity of the even cycles 2ð‘ and intensity of the odd cycles 2ð‘+1) and the Waldmeier effect W2 (the anticorrelation between rise times of sunspot cycles and their amplitudes) are the most universal and robust features of the solar cycle. Other statistical relations were found appreciably sensitive to the selection of solar index, the interval of analysis, and the way of the cycle feature determination.
PubDate: Tue, 26 Apr 2011 09:23:34 +000
- Lie Group of Spacetime
Abstract: A brief review is presented of de Sitter-Fantappiè relativity, and we
propose some cosmological reflections suggested by this theory. Compared
to the original works, some deductions have been very simplified, and only
the physical meaning of the equations has been analyzed.
PubDate: Sun, 10 Apr 2011 15:05:36 +000