Weak Gravitational Field and Casimir Energy
NASA Astrophysics Data System (ADS)
Tanhayi, M. R.; Pirmoradian, R.
2016-02-01
In this paper we consider the effect of a weak gravitation field on the Casimir energy. Under a weak perturbation of a metric, we first obtain the linear energy-momentum tensor of a scalar field in a generic background and then the corrected energy of a scalar filed which satisfies the Dirichlet boundary condition is calculated up to first order of the metric perturbation. We show that our results coincide to the previous related works e.g., the Casimir effect when studied in Fermi coordinates.
NASA Astrophysics Data System (ADS)
Tsukamoto, Naoki; Kitamura, Takao; Nakajima, Koki; Asada, Hideki
2014-09-01
The gravitational lensing effects in the weak gravitational field by exotic lenses have been investigated intensively to find nonluminous exotic objects. Gravitational lensing based on 1/rn fall-off metric, as a one-parameter model that can treat by hand both the Schwarzschild lens (n =1) and the Ellis wormhole (n =2) in the weak field, has been recently studied. Only for n=1 case, however, it has been explicitly shown that effects of relativistic lens images by the strong field on the light curve can be neglected. We discuss whether relativistic images by the strong field can be neglected for n>1 in the Tangherlini spacetime which is one of the simplest models for our purpose. We calculate the divergent part of the deflection angle for arbitrary n and the regular part for n=1, 2 and 4 in the strong field limit, the deflection angle for arbitrary n under the weak gravitational approximation. We also compare the radius of the Einstein ring with the radii of the relativistic Einstein rings for arbitrary n. We conclude that the images in the strong gravitational field have little effect on the total light curve and that the time-symmetric demagnification parts in the light curve will appear even after taking account of the images in the strong gravitational field for n>1.
Weber's gravitational force as static weak field approximation
NASA Astrophysics Data System (ADS)
Tiandho, Yuant
2016-02-01
Weber's gravitational force (WGF) is one of gravitational model that can accommodate a non-static system because it depends not only on the distance but also on the velocity and the acceleration. Unlike Newton's law of gravitation, WGF can predict the anomalous of Mercury and gravitational bending of light near massive object very well. Then, some researchers use WGF as an alternative model of gravitation and propose a new mechanics theory namely the relational mechanics theory. However, currently we have known that the theory of general relativity which proposed by Einstein can explain gravity with very accurate. Through the static weak field approximation for the non-relativistic object, we also have known that the theory of general relativity will reduce to Newton's law of gravity. In this work, we expand the static weak field approximation that compatible with relativistic object and we obtain a force equation which correspond to WGF. Therefore, WGF is more precise than Newton's gravitational law. The static-weak gravitational field that we used is a solution of the Einstein's equation in the vacuum that satisfy the linear field approximation. The expression of WGF with ξ = 1 and satisfy the requirement of energy conservation are obtained after resolving the geodesic equation. By this result, we can conclude that WGF can be derived from the general relativity.
Interaction of Dirac and Majorana neutrinos with weak gravitational fields
Menon, A.; Thalapillil, Arun M.
2008-12-01
In this paper the interaction of high energy neutrinos with weak gravitational fields is briefly explored. The form of the graviton-neutrino vertex is motivated from Lorentz and gauge invariance and the nonrelativistic interpretations of the neutrino-gravitational form factors are obtained. We comment on the renormalization conditions, the preservation of the weak equivalence principle and the definition of the neutrino mass radius. We associate the neutrino-gravitational form factors with specific angular momentum states. Based on Feynman diagrams, spin-statistics, CP invariance and symmetries of the angular momentum states in the graviton-neutrino vertex, we deduce differences between the Majorana and Dirac cases. It is then proved that in spite of the theoretical differences between the two cases, as far as experiments are considered, they would be virtually indistinguishable for any space-time geometry satisfying the weak-field condition. We then calculate the transition gravitational form factors for the neutrino by evaluating the relevant Feynman diagrams at 1-loop and estimate a neutrino transition mass radius. The form factor is seen to depend on the momentum transfer very weakly. It is also seen that the neutrino transition mass radius is smaller than the typical neutrino charge radius by a couple of orders of magnitude.
Republication of: Quantum theory of weak gravitational fields
NASA Astrophysics Data System (ADS)
Bronstein, Matvei
2012-01-01
This is an English translation of a paper by Matvei Bronstein, first published in German in 1936 in a long-extinct Soviet journal, in which he presented the first attempt at quantizing a weak (linearized) gravitational field, rather modern in its approach. The paper has been selected by the Editors of General Relativity and Gravitation for re-publication in the Golden Oldies series of the journal. This republication is accompanied by an editorial note written by Stanley Deser and Alexei Starobinsky, and Bronstein's brief biography written by Stanley Deser.
Discreteness of space from GUP in a weak gravitational field
NASA Astrophysics Data System (ADS)
Deb, Soumen; Das, Saurya; Vagenas, Elias C.
2016-04-01
Quantum gravity effects modify the Heisenberg's uncertainty principle to a generalized uncertainty principle (GUP). Earlier work showed that the GUP-induced corrections to the Schrödinger equation, when applied to a non-relativistic particle in a one-dimensional box, led to the quantization of length. Similarly, corrections to the Klein-Gordon and the Dirac equations, gave rise to length, area and volume quantizations. These results suggest a fundamental granular structure of space. In this work, it is investigated how spacetime curvature and gravity might influence this discreteness of space. In particular, by adding a weak gravitational background field to the above three quantum equations, it is shown that quantization of lengths, areas and volumes continue to hold. However, it should be noted that the nature of this new quantization is quite complex and under proper limits, it reduces to cases without gravity. These results suggest that quantum gravity effects are universal.
Casimir effect of two conducting parallel plates in a general weak gravitational field
NASA Astrophysics Data System (ADS)
Nazari, Borzoo
2015-10-01
We calculate the finite vacuum energy density of the scalar and electromagnetic fields inside a Casimir apparatus made up of two conducting parallel plates in a general weak gravitational field. The metric of the weak gravitational field has a small deviation from flat spacetime inside the apparatus, and we find it by expanding the metric in terms of small parameters of the weak background. We show that the metric found can be transformed via a gauge transformation to the Fermi metric. We solve the Klein-Gordon equation exactly and find mode frequencies in Fermi spacetime. Using the fact that the electromagnetic field can be represented by two scalar fields in the Fermi spacetime, we find general formulas for the energy density and mode frequencies of the electromagnetic field. Some well-known weak backgrounds are examined and consistency of the results with the literature is shown.
Gravitational lensing beyond the weak-field approximation
Perlick, Volker
2014-01-14
Gravitational lensing is considered in the full spacetime formalism of general relativity, assuming that the light rays are lightlike geodesics in a Lorentzian manifold. The review consists of three parts. The first part is devoted to spherically symmetric and static spacetimes. In particular, an exact lens map for this situation is discussed. The second part is on axisymmetric and stationary spacetimes. It concentrates on the investigation of the photon region, i.e., the region filled by spherical lightlike geodesics, in the Kerr spacetime. The photon region is of crucial relevance for the formation of a shadow. Finally, the third part briefly addresses two topics that apply to spacetimes without symmetry, namely Fermat’s principle and the exact lens map of Frittelli and Newman.
NASA Astrophysics Data System (ADS)
Almosallami, Azzam
2011-03-01
In this paper we derived the relativistic Quantized force, where the force given as a function of frequency [1]. Where, in this paper we defined the relativistic momentum as a function of frequency equivalent to the energy held by a body, and time, and then the quantized force is given as the first derivative of the momentum with respect to time. Subsequently we introduce in section one Newton's second law as it is relativistic quantized, and in section two we introduce the relativistic quantized inertial force, and then the relativistic quantized gravitational force, and the quantized gravitational time dilation. At the end we shall generalize the Schwartzschild metric to describe the weak and strong gravitational field.
NASA Astrophysics Data System (ADS)
Harris, Edward G.
1991-05-01
Starting from the equations of general relativity, equations similar to those of electromagnetic theory are derived. It is assumed that the particles are slowly moving (v?c), and the gravitational field is sufficiently weak that nonlinear terms in Einstein's field equations can be neglected. For static fields, the analogy to electrostatics and magnetostatics is very close. Results are compared with those of a previous derivation by Braginsky, Caves, and Thorne [Phys. Rev. D 15, 2047-2068 (1977)]. These results lead to very simple derivations of the Lense-Thirring precession [Phys. Z. 19, 156-163 (1918)] and the spin-curvature force of Papepetrou [Proc. R. Soc. London Ser. A 209, 248-258 (1951)] and Pirani [Acta Phys. Pol. 15, 389-405 (1956)].
The generation of gravitational waves. 1. Weak-field sources: A plug-in-and-grind formalism
NASA Technical Reports Server (NTRS)
Thorne, K. S.; Kovacs, S. J.
1974-01-01
A plug-in-and-grind formalism is derived for calculating the gravitational waves emitted by any system with weak internal gravitational fields. If the internal fields have negligible influence on the system's motions, then the formalism reduces to standard linearized theory. Whether or not gravity affects the motions, if the motions are slow and internal stresses are weak, then the new formalism reduces to the standard quadrupole-moment formalism. In the general case the new formalism expresses the radiation in terms of a retarded Green's function for slightly curved spacetime, and then breaks the Green's-function integral into five easily understood pieces: direct radiation, produced directly by the motions of the sources; whump radiation, produced by the the gravitational stresses of the source; transition radiation, produced by a time-changing time delay (Shapiro effect) in the propagation of the nonradiative, 1/r field of the source; focussing radiation produced when one portion of the source focusses, in a time-dependent way, the nonradiative field of another portion of the source, and tail radiation, produced by backscatter of the nonradiative field in regions of focussing.
NASA Astrophysics Data System (ADS)
Schreck, M.
2015-12-01
In the current article, the classical analog of the minimal photon sector in the Lorentz-violating Standard-Model extension (SME) is investigated. The analysis is based on describing a photon classically by a geometric ray that satisfies the eikonal equation. The action principle, which leads to the eikonal equation in conventional optics, is demonstrated to work in most (but not all) Lorentz-violating cases as well. Furthermore it is found that the integrands of the action functional correspond to Finsler structures. Based on these results, Lorentz-violating light rays in a weak gravitational background are treated through the use of the minimal-coupling principle. This allows for obtaining sensitivities on Lorentz violation in the photon sector by measurements of light bending at massive bodies such as the Sun. The computations are carried out for the currently running ESA mission GAIA and the planned NASA/ESA mission LATOR. Finally, a range of aspects of explicit Lorentz violation for photons is discussed in the Finsler setting.
Bimonte, Giuseppe; Rosa, Luigi; Esposito, Giampiero
2008-07-15
This paper studies two perfectly conducting parallel plates in the weak gravitational field on the surface of the Earth. Since the appropriate line element, to first order in the constant gravity acceleration g, is precisely of the Rindler type, we can exploit the formalism for studying Feynman Green functions in Rindler spacetime. Our analysis does not reduce the electromagnetic potential to the transverse part before quantization. It is instead fully covariant and well suited for obtaining all components of the regularized and renormalized energy-momentum tensor to arbitrary order in the gravity acceleration g. The general structure of the calculation is therefore elucidated, and the components of the Maxwell energy-momentum tensor are evaluated up to second order in g, improving a previous analysis by the authors and correcting their old first-order formula for the Casimir energy.
NASA Astrophysics Data System (ADS)
Rowland, David R.
2015-06-01
Galaxy rotation curves are generally analyzed theoretically using Newtonian physics; however, two groups of authors have claimed that for self-gravitating dusts, general relativity (GR) makes significantly different predictions to Newtonian physics, even in the weak field, low velocity limit. One group has even gone so far as to claim that nonlinear general relativistic effects can explain flat galactic rotation curves without the need for cold dark matter. These claims seem to contradict the well-known fact that the weak field, low velocity, low pressure correspondence limit of GR is Newtonian gravity, as evidenced by solar system tests. Both groups of authors claim that their conclusions do not contradict this fact, with Cooperstock and Tieu arguing that the reason is that for the solar system, we have test particles orbiting a central gravitating body, whereas for a galaxy, each star is both an orbiting body and a contributor to the net gravitational field, and this supposedly makes a difference due to nonlinear general relativistic effects. Given the significance of these claims for analyses of the flat galactic rotation curve problem, this article compares the predictions of GR and Newtonian gravity for three cases of self-gravitating dusts for which the exact general relativistic solutions are known. These investigations reveal that GR and Newtonian gravity are in excellent agreement in the appropriate limits, thus supporting the conventional use of Newtonian physics to analyze galactic rotation curves. These analyses also reveal some sources of error in the referred to works.
Gravitational Thermodynamics for Interstellar Gas and Weakly Degenerate Quantum Gas
NASA Astrophysics Data System (ADS)
Zhu, Ding Yu; Shen, Jian Qi
2016-03-01
The temperature distribution of an ideal gas in gravitational fields has been identified as a longstanding problem in thermodynamics and statistical physics. According to the principle of entropy increase (i.e., the principle of maximum entropy), we apply a variational principle to the thermodynamical entropy functional of an ideal gas and establish a relationship between temperature gradient and gravitational field strength. As an illustrative example, the temperature and density distributions of an ideal gas in two simple but typical gravitational fields (i.e., a uniform gravitational field and an inverse-square gravitational field) are considered on the basis of entropic and hydrostatic equilibrium conditions. The effect of temperature inhomogeneity in gravitational fields is also addressed for a weakly degenerate quantum gas (e.g., Fermi and Bose gas). The present gravitational thermodynamics of a gas would have potential applications in quantum fluids, e.g., Bose–Einstein condensates in Earth’s gravitational field and the temperature fluctuation spectrum in cosmic microwave background radiation.
NASA Astrophysics Data System (ADS)
Doyen, G.; Drakova, D.
2015-08-01
We construct a world model consisting of a matter field living in 4 dimensional spacetime and a gravitational field living in 11 dimensional spacetime. The seven hidden dimensions are compactified within a radius estimated by reproducing the particle-wave characteristics of diffraction experiments. In the presence of matter fields the gravitational field develops localized modes with elementary excitations called gravonons which are induced by the sources (massive particles). The final world model treated here contains only gravonons and a scalar matter field. The gravonons are localized in the environment of the massive particles which generate them. The solution of the Schrdinger equation for the world model yields matter fields which are localized in the 4 dimensional subspace. The localization has the following properties: (i) There is a chooser mechanism for the selection of the localization site. (ii) The chooser selects one site on the basis of minor energy differences and differences in the gravonon structure between the sites, which at present cannot be controlled experimentally and therefore let the choice appear statistical. (iii) The changes from one localization site to a neighbouring one take place in a telegraph-signal like manner. (iv) The times at which telegraph like jumps occur depend on subtleties of the gravonon structure which at present cannot be controlled experimentally and therefore let the telegraph-like jumps appear statistical. (v) The fact that the dynamical law acts in the configuration space of fields living in 11 dimensional spacetime lets the events observed in 4 dimensional spacetime appear non-local. In this way the phenomenology of CQM is obtained without the need of introducing the process of collapse and a probabilistic interpretation of the wave function. Operators defining observables need not be introduced. All experimental findings are explained in a deterministic way as a consequence of the time development of the wave function in configuration space according to Schrdinger's equation without the need of introducing a probabilistic interpretation.
Gravitational anomaly and Hawking radiation near a weakly isolated horizon
Wu Xiaoning; Huang Chaoguang; Sun Jiarui
2008-06-15
Based on the idea of the work by Wilczek and his collaborators, we consider the gravitational anomaly near a weakly isolated horizon. We find that there exists a universal choice of tortoise coordinate for any weakly isolated horizon. Under this coordinate, the leading behavior of a quite arbitrary scalar field near a horizon is a 2-dimensional chiral scalar field. This means we can extend the idea of Wilczek and his collaborators to more general cases and show the relation between gravitational anomaly and Hawking radiation is a universal property of a black hole horizon.
Gravitational anomaly and Hawking radiation near a weakly isolated horizon
NASA Astrophysics Data System (ADS)
Wu, Xiaoning; Huang, Chao-Guang; Sun, Jia-Rui
2008-06-01
Based on the idea of the work by Wilczek and his collaborators, we consider the gravitational anomaly near a weakly isolated horizon. We find that there exists a universal choice of tortoise coordinate for any weakly isolated horizon. Under this coordinate, the leading behavior of a quite arbitrary scalar field near a horizon is a 2-dimensional chiral scalar field. This means we can extend the idea of Wilczek and his collaborators to more general cases and show the relation between gravitational anomaly and Hawking radiation is a universal property of a black hole horizon.
Weak Gravitational Lensing Systematics from Image Combination
NASA Astrophysics Data System (ADS)
Shapiro, C.; Rowe, B. T. P.; Goodsall, T.; Hirata, C.; Fucik, J.; Rhodes, J.; Seshadri, S.; Smith, R.
2013-12-01
Extremely accurate shape measurements of galaxy images are needed to probe dark energy properties with weak gravitational lensing surveys. To increase survey area with a fixed observing time and pixel count, images from surveys such as the Wide Field Infrared Survey Telescope (WFIRST) or Euclid will necessarily be undersampled and therefore distorted by aliasing. Oversampled, unaliased images can be obtained by combining multiple, dithered exposures of the same source with a suitable reconstruction algorithm. Any such reconstruction must minimally distort the reconstructed images for weak lensing analyses to be unbiased. In this paper, we use the image combination (IMCOM) algorithm of Rowe, Hirata, and Rhodes to investigate the effect of image combination on shape measurements (size and ellipticity). We simulate dithered images of sources with varying amounts of ellipticity and undersampling, reconstruct oversampled output images from them using IMCOM, and measure shape distortions in the output. Our simulations show that IMCOM creates no significant distortions when the relative offsets between dithered images are precisely known. Distortions increase with the uncertainty in those offsets, but become problematic only with relatively poor astrometric precision; e.g., for images similar to those from the Astrophysics Focused Telescope Asset (AFTA) implementation of WFIRST, combining eight undersampled images (sampling ratio Q = 1) with highly pessimistic uncertainty in astrometric registration (σd ~ 10-3 pixels) yields an rms shear error of O(10-4). Our analysis pipeline is adapted from that of the Precision Projector Laboratory—a joint project between NASA Jet Propulsion Laboratory and Caltech that characterizes image sensors using laboratory emulations of astronomical data.
Baryons, neutrinos, feedback and weak gravitational lensing
NASA Astrophysics Data System (ADS)
Harnois-Déraps, Joachim; van Waerbeke, Ludovic; Viola, Massimo; Heymans, Catherine
2015-06-01
The effect of baryonic feedback on the dark matter mass distribution is generally considered to be a nuisance to weak gravitational lensing. Measurements of cosmological parameters are affected as feedback alters the cosmic shear signal on angular scales smaller than a few arcminutes. Recent progress on the numerical modelling of baryon physics has shown that this effect could be so large that, rather than being a nuisance, the effect can be constrained with current weak lensing surveys, hence providing an alternative astrophysical insight on one of the most challenging questions of galaxy formation. In order to perform our analysis, we construct an analytic fitting formula that describes the effect of the baryons on the mass power spectrum. This fitting formula is based on three scenarios of the OverWhelmingly Large hydrodynamical simulations. It is specifically calibrated for z < 1.5, where it models the simulations to an accuracy that is better than 2 per cent for scales k < 10 h Mpc-1 and better than 5 per cent for 10 < k < 100 h Mpc-1. Equipped with this precise tool, this paper presents the first constraint on baryonic feedback models using gravitational lensing data, from the Canada France Hawaii Telescope Lensing Survey (CFHTLenS). In this analysis, we show that the effect of neutrino mass on the mass power spectrum is degenerate with the baryonic feedback at small angular scales and cannot be ignored. Assuming a cosmology precision fixed by WMAP9, we find that a universe with massless neutrinos is rejected by the CFHTLenS lensing data with 85-98 per cent confidence, depending on the baryon feedback model. Some combinations of feedback and non-zero neutrino masses are also disfavoured by the data, although it is not yet possible to isolate a unique neutrino mass and feedback model. Our study shows that ongoing weak gravitational lensing surveys (KiDS, HSC and DES) will offer a unique opportunity to probe the physics of baryons at galactic scales, in addition to the expected constraints on the total neutrino mass.
Probing satellite haloes with weak gravitational lensing
NASA Astrophysics Data System (ADS)
Gillis, Bryan R.; Hudson, Michael J.; Hilbert, Stefan; Hartlap, Jan
2013-02-01
We demonstrate the possibility of detecting tidal stripping of dark matter subhaloes within galaxy groups using weak gravitational lensing. We have run ray-tracing simulations on galaxy catalogues from the Millennium Simulation to generate mock shape catalogues. The ray-tracing catalogues assume a halo model for galaxies and groups using various models with different distributions of mass between galaxy and group haloes to simulate different stages of group evolution. Using these mock catalogues, we forecast the lensing signals that will be detected around galaxy groups and satellite galaxies, as well as test two different methods for isolating the satellites' lensing signals. A key challenge is to determine the accuracy to which group centres can be identified. We show that with current and ongoing surveys, it will possible to detect stripping in groups of mass 1012-1015 M⊙.
Atomic Inference from Weak Gravitational Lensing Data
Marshall, Phil; /KIPAC, Menlo Park
2005-12-14
We present a novel approach to reconstructing the projected mass distribution from the sparse and noisy weak gravitational lensing shear data. The reconstructions are regularized via the knowledge gained from numerical simulations of clusters, with trial mass distributions constructed from n NFW profile ellipsoidal components. The parameters of these ''atoms'' are distributed a priori as in the simulated clusters. Sampling the mass distributions from the atom parameter probability density function allows estimates of the properties of the mass distribution to be generated, with error bars. The appropriate number of atoms is inferred from the data itself via the Bayesian evidence, and is typically found to be small, reecting the quality of the data. Ensemble average mass maps are found to be robust to the details of the noise realization, and succeed in recovering the demonstration input mass distribution (from a realistic simulated cluster) over a wide range of scales. As an application of such a reliable mapping algorithm, we comment on the residuals of the reconstruction and the implications for predicting convergence and shear at specific points on the sky.
Octonic Gravitational Field Equations
NASA Astrophysics Data System (ADS)
Demir, Sleyman; Tani?li, Murat; Tolan, Tlay
2013-08-01
Generalized field equations of linear gravity are formulated on the basis of octons. When compared to the other eight-component noncommutative hypercomplex number systems, it is demonstrated that associative octons with scalar, pseudoscalar, pseudovector and vector values present a convenient and capable tool to describe the Maxwell-Proca-like field equations of gravitoelectromagnetism in a compact and simple way. Introducing massive graviton and gravitomagnetic monopole terms, the generalized gravitational wave equation and Klein-Gordon equation for linear gravity are also developed.
The general theory of secondary weak gravitational lensing
NASA Astrophysics Data System (ADS)
Clarkson, Chris
2015-09-01
Weak gravitational lensing is normally assumed to have only two principle effects: a magnification of a source and a distortion of the sources shape in the form of a shear. However, further distortions are actually present owing to changes in the gravitational field across the scale of the ray bundle of light propagating to us, resulting in the familiar arcs in lensed images. This is normally called the flexion, and is approximated by Taylor expanding the shear and magnification across the image plane. However, the physical origin of this effect arises from higher-order corrections in the geodesic deviation equation governing the gravitational force between neighbouring geodesics so involves derivatives of the Riemann tensor. We show that integrating the second-order geodesic deviation equation results in a `Hessian map' for gravitational lensing, which is a higher-order addition to the Jacobi map. We derive the general form of the Hessian map in an arbitrary spacetime paying particular attention to the separate effects of local Ricci versus non-local Weyl curvature. We then specialise to the case of a perturbed FLRW model, and give the general form of the Hessian for the first time. This has a host of new contributions which could in principle be used as tests for modified gravity.
NASA Astrophysics Data System (ADS)
Chen, Shao-Guang
According to f =d(mv)/dt=m(dv/dt)+ v(dm/dt), a same gravitational formula had been de-duced from the variance in physical mass of QFT and from the variance in mass of inductive energy-transfer of GR respectively: f QF T = f GR = -G (mM/r2 )((r/r)+(v/c)) when their interaction-constants are all taken the experimental values (H05-0029-08, E15-0039-08). f QF T is the quasi-Casimir pressure. f GR is equivalent to Einstein's equation, then more easy to solve it. The hypothesis of the equivalent principle is not used in f QF T , but required by f GR . The predictions of f QF T and f GR are identical except that f QF T has quantum effects but f GR has not and f GR has Lense-Thirring effect but f QF T has not. The quantum effects of gravitation had been verified by Nesvizhevsky et al with the ultracold neutrons falling in the earth's gravitational field in 2002. Yet Lense-Thirring effect had not been measured by GP-B. It shows that f QF T is essential but f GR is phenomenological. The macro-f QF T is the statistic average pressure collided by net virtual neutrinos ? 0 flux (after self-offset in opposite directions) and in direct proportion to the mass. But micro-f QF T is in direct proportion to the scattering section. The electric mass (in inverse proportion to de Broglie wavelength ?) far less than nucleonic mass and the electric scattering section (in direct proportion to ?2 ) far large than that of nucleon, then the net ? 0 flux pressure exerted to electron far large than that to nucleon and the electric displacement far large than that of nucleon, it causes the gravitational polarization of positive-negative charge center separation. Because the gravity far less than the electromagnetic binding force, in atoms the gravitational polarization only produces a little separation. But the net ? 0 flux can press a part freedom electrons in plasma of ionosphere into the earth's surface, the static electric force of redundant positive ions prevents electrons from further falling and till reach the equilibrium of stable spatial charge distribution, which is just the cause of the geomagnetic field and the geo-electric field (the observational value on the earth surface is about 120 V/m downward equivalent to 500000 Coulomb negative charges in the earth surface). All celestial bodies are gravitation sources and attract the molecules and ions in space to its circumference by the gravitation of own and other celestial bodies, e.g., all planets in the solar system have their own atmospheres. Therefore, the origin mechanism of geo-electric and geomagnetic fields caused by gravitation is very universal, at least it is appli-cable to all the planets in the solar system. For planets, the joint result of the gravitations of the planets and the sun makes the negative charges and dipolar charges distributed in the surfaces of the celestial bodies. The quicker the rotation is, the larger the angular momentum U is, then larger the accompanying current and magnetic moment P, it accord a experiential law found by subsistent observational data of all celestial bodies in solar system: P = -G 1/2 U cos ? / c (1), ? is the angle between the net ? 0 flux direction (mark by CMB) and the rotational axis of celestial body (Chen Shao-Guang, Chinese Science Bulletin, 26,233,1981). Uranian and Neptunian P predicted with Eq.(1) in 1981 are about -3.41028 Gscm3 and 1.91028 Gscm3 respectively (use new rotate speed measured by Voyager 2). The P measured by Voyager 2 in 1986 and 1989 are about -1.9 1028 Gscm3 and 1.51028 Gscm3 respectively (the contribution of quadrupole P is converted into the contribution of dipole P alone). The neutron star pos-sesses much high density and rotational speed because of the conservation of the mass and the angular momentum during the course of the formation, then has strong gravity and largerU. From Eq.(1) there is a larger P and extremely strong surface magnetic field in neutron star. The origin mechanism of basal electric and magnetic fields of celestial bodies will affect directly all fields refer
Caution: Strong Gravitational Field Present
ERIC Educational Resources Information Center
Reif, Marc
2014-01-01
I came up with a new way to introduce the concept of a constant gravitational field near the surface of the Earth. I made "g-field detectors" (see Fig. 1 ) and suspended them by strings from the ceiling in a regular spacing. The detectors are cardstock arrows with a hole punched out of them and the letter "g" in the center.
Particles, Fields, and Gravitation. Proceedings
Rembieli ski, J.
1998-11-01
These proceedings represent papers presented at the Conference on Particles, Fields, and Gravitation held in Lodz, Poland in April, 1998. The topics discussed included quantum deformations and noncommutative geometry, quantum mechanics, quantum and topological field theory, modern gravitation theory and geometrical methods in physics. Solvable and quasisolvable models were also disussed. The talks and the resulting papers provided a comprehensive coverage of the main aspects of contemporary theoretical and mathematical physics. The Conference was attended by more than 100 scientists from all over the world. There were 54 papers presented at the conference,out of which 1 paper has been abstracted for the Energy,Science and Technology database.(AIP)
The gravitational field of Phobos
Chao, B.F.; Rubincam, D.P. )
1989-08-01
The external gravitational field produced by a rigid body of uniform density but irregular shape is formulated in terms of spherical harmonics. The formalism is applied to the Martian satellite Phobos. Based on a 3-dimensional shape model of Phobos by Duxbury, the gravitational coefficients up to degree and order 4 for a homogeneous Phobos are computed. In particular, the authors find J{sub 2} = 0.105. The in-plane liberation amplitude of a homogeneous Phobos is predicted to be 0.97{degree}, within the rather large uncertainty of the observed value of 0.78 {plus minus} 0.4{degree}.
Combining Strong and Weak Gravitational Lensing in Abell 1689
NASA Astrophysics Data System (ADS)
Limousin, Marceau; Richard, Johan; Jullo, Eric; Kneib, Jean-Paul; Fort, Bernard; Soucail, Genevive; Elasdttir, rds; Natarajan, Priyamvada; Ellis, Richard S.; Smail, Ian; Czoske, Oliver; Smith, Graham P.; Hudelot, Patrick; Bardeau, Sbastien; Ebeling, Harald; Egami, Eiichi; Knudsen, Kirsten K.
2007-10-01
We present a reconstruction of the mass distribution of galaxy cluster Abell 1689 at z=0.18 using detected strong lensing features from deep ACS observations and extensive ground based spectroscopy. Earlier analyses have reported up to 32 multiply imaged systems in this cluster, of which only 3 were spectroscopically confirmed. In this work, we present a parametric strong lensing mass reconstruction using 34 multiply imaged systems of which 24 have newly determined spectroscopic redshifts, which is a major step forward in building a robust mass model. In turn, the new spectroscopic data allows a more secure identification of multiply imaged systems. The resultant mass model enables us to reliably predict the redshifts of additional multiply imaged systems for which no spectra are currently available, and to use the location of these systems to further constrain the mass model. Using our strong lensing mass model, we predict on larger scale a shear signal which is consistent with that inferred from our large scale weak lensing analysis derived using CFH12K wide field images. Thanks to a new method for reliably selecting a well defined background lensed galaxy population, we resolve the discrepancy found between the NFW concentration parameters derived from earlier strong and weak lensing analysis. The derived parameters for the best fit NFW profile is found to be c200=7.6+/-1.6 and r200=2.16+/-0.10 h-170 Mpc (corresponding to a 3D mass equal to M200=[1.32+/-0.2]1015 h70 Msolar). The large number of new constraints incorporated in this work makes Abell 1689 the most reliably reconstructed cluster to date. This well calibrated mass model, which we here make publicly available, will enable us to exploit Abell 1689 efficiently as a gravitational telescope, as well as to potentially constrain cosmology. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Also based on observations from the NASA/ESA Hubble Space Telescope (programs 9289 and 10150) obtained at the Space Telescope Science Institute, which is operated by AURA under NASA contract NAS5-26555.
Weak Gravitational Lensing from Regular Bardeen Black Holes
NASA Astrophysics Data System (ADS)
Ghaffarnejad, Hossein; niad, Hassan
2015-09-01
In this article we study weak gravitational lensing of regular Bardeen black hole which has scalar charge g and mass m. We investigate the angular position and magnification of non-relativistic images in two cases depending on the presence or absence of photon sphere. Defining dimensionless charge parameter q=g/2m we seek to disappear photon sphere in the case of |q|>{24?5}/{125} for which the space time metric encounters strongly with naked singularities. We specify the basic parameters of lensing in terms of scalar charge by using the perturbative method and found that the parity of images is different in two cases: (a) The strongly naked singularities is present in the space time. (b) singularity of space time is weak or is eliminated (the black hole lens).
Weak Gravitational Lensing from Regular Bardeen Black Holes
NASA Astrophysics Data System (ADS)
Ghaffarnejad, Hossein; niad, Hassan
2016-03-01
In this article we study weak gravitational lensing of regular Bardeen black hole which has scalar charge g and mass m. We investigate the angular position and magnification of non-relativistic images in two cases depending on the presence or absence of photon sphere. Defining dimensionless charge parameter q= {g}/{2m} we seek to disappear photon sphere in the case of |q|>{24√5}/{125} for which the space time metric encounters strongly with naked singularities. We specify the basic parameters of lensing in terms of scalar charge by using the perturbative method and found that the parity of images is different in two cases: (a) The strongly naked singularities is present in the space time. (b) singularity of space time is weak or is eliminated (the black hole lens).
NASA Astrophysics Data System (ADS)
Rueda, Jorge A.; Ruffini, R.; Xue, S.-S.
2011-12-01
The isothermal Tolman condition and the constancy of the Klein potentials originally expressed for the sole gravitational interaction in a single fluid are here generalized to the case of a three quantum fermion fluid duly taking into account the strong, electromagnetic, weak and gravitational interactions. The set of constitutive equations including the Einstein-Maxwell-Thomas-Fermi equations as well as the ones corresponding to the strong interaction description are here presented in the most general relativistic isothermal case. This treatment represents an essential step to correctly formulate a self-consistent relativistic field theoretical approach of neutron stars.
NASA Astrophysics Data System (ADS)
Krot, Alexander M.
2002-01-01
the framework of this model bodies have fuzzy outlines and are represented by means of spheroidal forms. The consistency of the statistical model with the Einstein general relativity3,4,5 has been shown. In the work6, which is a continuation of the paper2, it was investigated a slowly evolving in time process of a gravitational compression (contraction) of a spheroidal body close to an unstable mehanical equilibrium state (a low mass flow), therefore the process of the gravitational contraction appears slowly developing in time (the case of unobservable velocities of particles composing a spheroidal body). For this case in the work7 it has been shown that the strength and potential of the gravitational field of a slowly contracting spheroidal body satisfy a differential equation of the second order of the parabolic type for the case of unobservable velocities of particles. Therefore gravitational waves of a soliton type are propagated in a weakly gravitating spheroidal body if values of velocities are unobservable. body. In the connection with the above-given statements, in the present paper the following assumptions are used: 1.The spheroidal body under consideration is homogeneous in its chemical structure, i.e. it consists of identical particles with the mass m0. 2.The spheroidal body is not subjected to influence of external fields and bodies. 3.The spheroidal body is isothermal and has temperature close to the absolute zero. 4.The concentration gradient is not too large in the sense that interphase boundaries are absent inside the spheroidal body. 5. In view of low values of the temperature the heat conduction and viscosity processes are not important, which allows to describe the rotation of the spheroidal body as a whole, while movement of flows of particles inside the weakly gravitating spheroidal body is modeled by means of a motion of an ideal medium (the case of observable velocities of particles). 6.Since the process of the gravitational compression (contraction) of the spheroidal body is weak and viscosity is absent, we regard the motion of the continuous medium to be non-turbulent. modeled by means of an ideal liquid. It is determined the connection of this equation with an equation of motion of a particle in a noninertial frame of reference. A gravimagnetic field is introduced in this paper. It is obtained the scalar and vector potentials as well as the Lagrange function of a particle moving in a gravitational and gravimagnetic fields. It is derived the equations of hyperbolic type for the gravitational field of a weakly gravitating spheroidal body under observable values of velocities of particles composing it. 1. A.M.Krot, Achievements in Modern Radioelectronics, special issue "Cosmic Radiophysics", no.8, pp.66- 2. A.M.Krot, Proc. SPIE 13th Symp."AeroSense", Orlando, Florida, April 5-9,1999, vol.3710,pp.1248-1259. 3. L.D.Landau and E.M.Lifshitz, Classical Theory of Fields, Addison-Wesley, 1951. 4. S.Weinberg, Gravitation and Cosmology, John Wiley and Sons, New York, 1972. 5. C.W.Misner, K.S.Thorne, and J.A.Wheeler, Gravitation, W.H.Freeman and Co., San Francisco, 1973. 6. A.M.Krot, Proc. SPIE 14th Symp."AeroSense",Orlando,Florida,April 24-28,2000,vol.4038,pp.1318-1329. 7. A.M.Krot, Proc. SPIE 15th Symp."AeroSense",Orlando,Florida,April 16-20,2001,vol.4394,pp.1271-1282.
Gravitational failure of sea cliffs in weakly lithified sediment
Hampton, M.A.
2002-01-01
Gravitational failure of sea cliffs eroded into weakly lithified sediment at several sites in California involves episodic stress-release fracturing and cantilevered block falls. The principal variables that influence the gravitational stability are tensional stresses generated during the release of horizontal confining stress and weakening of the sediment with increased saturation levels. Individual failures typically comprise less than a cubic meter of sediment, but large areas of a cliff face can be affected by sustained instability over a period of several days. Typically, only the outer meter or so of sediment is removed during a failure episode. In-place sediment saturation levels vary over time and space, generally being higher during the rainy season but moderate to high year-round. Laboratory direct-shear tests show that sediment cohesion decreases abruptly with increasing saturation level; the decrease is similar for all tested sediment if the cohesion is normalized by the maximum, dry-sediment cohesion. Large failures that extend over most or all of the height of the sea cliff are uncommon, but a few large wedge-shaped failures sometimes occur, as does separation of large blocks at sea cliff-gully intersections.
Primordial magnetic seed field amplification by gravitational waves
Betschart, Gerold; Zunckel, Caroline; Dunsby, Peter K.S.; Marklund, Mattias
2005-12-15
Using second-order gauge-invariant perturbation theory, a self-consistent framework describing the nonlinear coupling between gravitational waves and a large-scale homogeneous magnetic field is presented. It is shown how this coupling may be used to amplify seed magnetic fields to strengths needed to support the galactic dynamo. In situations where the gravitational wave background is described by an 'almost' Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmology we find that the magnitude of the original magnetic field is amplified by an amount proportional to the magnitude of the gravitational wave induced shear anisotropy and the square of the field's initial comoving scale. We apply this mechanism to the case where the seed field and gravitational wave background are produced during inflation and find that the magnitude of the gravitational boost depends significantly on the manner in which the estimate of the shear anisotropy at the end of inflation is calculated. Assuming a seed field of 10{sup -34} G spanning a comoving scale of about 10 kpc today, the shear anisotropy at the end of inflation must be at least as large as 10{sup -40} in order to obtain a generated magnetic field of the same order of magnitude as the original seed. Moreover, contrasting the weak-field approximation to our gauge-invariant approach, we find that while both methods agree in the limit of high conductivity, their corresponding solutions are otherwise only compatible in the limit of infinitely long-wavelength gravitational waves.
Structure formation, backreaction and weak gravitational fields
Paranjape, Aseem; Singh, T P E-mail: tpsingh@tifr.res.in
2008-03-15
There is an ongoing debate in the literature as to whether the effects of averaging out inhomogeneities ('backreaction') in cosmology can be large enough to account for the acceleration of the scale factor in the Friedmann-Lemaitre-Robertson-Walker (FLRW) models. In particular, some simple models of structure formation studied in the literature seem to indicate that this is indeed possible, and it has also been suggested that the perturbed FLRW framework is no longer a good approximation during structure formation, when the density contrast becomes non-linear. In this work we attempt to clarify the situation to some extent, using a fully relativistic model of pressureless spherical collapse. We find that whereas averaging during structure formation can lead to acceleration via a selective choice of averaging domains, the acceleration is not present when more generic domains are used for averaging. Further, we show that for most of the duration of the collapse, matter velocities remain small, and the perturbed FLRW form of the metric can be explicitly recovered, in the structure formation phase. We also discuss the fact that the magnitude of the average effects of inhomogeneities depends on the scale of averaging, and while it may not be completely negligible on intermediate scales, it is expected to remain small when averaging on suitably large scales.
Classical field approach to quantum weak measurements.
Dressel, Justin; Bliokh, Konstantin Y; Nori, Franco
2014-03-21
By generalizing the quantum weak measurement protocol to the case of quantum fields, we show that weak measurements probe an effective classical background field that describes the average field configuration in the spacetime region between pre- and postselection boundary conditions. The classical field is itself a weak value of the corresponding quantum field operator and satisfies equations of motion that extremize an effective action. Weak measurements perturb this effective action, producing measurable changes to the classical field dynamics. As such, weakly measured effects always correspond to an effective classical field. This general result explains why these effects appear to be robust for pre- and postselected ensembles, and why they can also be measured using classical field techniques that are not weak for individual excitations of the field. PMID:24702338
Improving PSF modelling for weak gravitational lensing using new methods in model selection
NASA Astrophysics Data System (ADS)
Rowe, Barnaby
2010-05-01
A simple theoretical framework for the description and interpretation of spatially correlated modelling residuals is presented, and the resulting tools are found to provide a useful aid to model selection in the context of weak gravitational lensing. The description is focused upon the specific problem of modelling the spatial variation of a telescope point spread function (PSF) across the instrument field of view, a crucial stage in lensing data analysis, but the technique may be used to rank competing models wherever data are described empirically. As such it may, with further development, provide useful extra information when used in combination with existing model selection techniques such as the Akaike and Bayesian information criteria, or the Bayesian evidence. Two independent diagnostic correlation functions are described, and the interpretation of these functions is demonstrated by using a simulated PSF anisotropy field. The efficacy of these diagnostic functions as an aid to the correct choice of empirical model is then demonstrated by analysing results for a suite of Monte Carlo simulations of random PSF fields with varying degrees of spatial structure, and it is shown how the diagnostic functions can be related to requirements for precision cosmic shear measurement. The limitations of the technique, and opportunities for improvements and applications to fields other than weak gravitational lensing, are discussed.
On the consequences of the weak field approximation
NASA Astrophysics Data System (ADS)
Laubenstein, John
2013-04-01
General Relativity reduces to Newtonian gravity within the appropriate limit. But, what is that limit? The conventional response is that of the weak field approximation in which the gravitating source is weak and velocities are low. But, this is a far cry from a quantitative statement. In that regard, the weak field may be defined more quantitatively as one in which any error introduced is far beyond the level of precision required. Since the field can always be made incrementally weaker there is no limit as to the degree of precision that can be achieved. In this regard, GR reduces exactly to Newtonian gravity at the limit where velocity goes to zero. It is only out of convenience that we extend this to include those conditions where v << c with the argument that any error is arbitrarily small. However, in practice GR can be shown to reduce to an exact Newtonian expression at v > 0. How can this observation fit with the quantitative definition of the weak field? This paper explores the consequences of the weak field approximation and the fact that GR reduces directly to Newtonian gravity within the weak field as opposed to the more specific condition where v = zero.
Weak gravitational lensing systematic errors in the dark energy survey
NASA Astrophysics Data System (ADS)
Plazas, Andres Alejandro
Dark energy is one of the most important unsolved problems in modern Physics, and weak gravitational lensing (WL) by mass structures along the line of sight ("cosmic shear") is a promising technique to learn more about its nature. However, WL is subject to numerous systematic errors which induce biases in measured cosmological parameters and prevent the development of its full potential. In this thesis, we advance the understanding of WL systematics in the context of the Dark Energy Survey (DES). We develop a testing suite to assess the performance of the shapelet-based DES WL measurement pipeline. We determine that the measurement bias of the parameters of our Point Spread Function (PSF) model scales as (S/N )-2, implying that a PSF S/N > 75 is needed to satisfy DES requirements. PSF anisotropy suppression also satisfies the requirements for source galaxies with S/N ≳ 45. For low-noise, marginally-resolved exponential galaxies, the shear calibration errors are up to about 0.06% (for shear values ≲ 0.075). Galaxies with S/N ≳ 75 present about 1% errors, sufficient for first-year DES data. However, more work is needed to satisfy full-area DES requirements, especially in the high-noise regime. We then implement tests to validate the high accuracy of the map between pixel coordinates and sky coordinates (astrometric solution), which is crucial to detect the required number of galaxies for WL in stacked images. We also study the effect of atmospheric dispersion on cosmic shear experiments such as DES and the Large Synoptic Survey Telescope (LSST) in the four griz bands. For DES (LSST), we find systematics in the g and r (g, r, and i) bands that are larger than required. We find that a simple linear correction in galaxy color is accurate enough to reduce dispersion shear systematics to insignificant levels in the r ( i) band for DES (LSST). More complex corrections will likely reduce the systematic cosmic-shear errors below statistical errors for LSST r band. However, g-band dispersion effects remain large enough for induced systematics to dominate the statistical error of both surveys, so cosmic-shear measurements should rely on the redder bands.
Semiclassical limit for Dirac particles interacting with a gravitational field
Silenko, Alexander J.; Teryaev, Oleg V.
2005-03-15
The behavior of a spin-1/2 particle in a weak static gravitational field is considered. The Dirac Hamiltonian is diagonalized by the Foldy-Wouthuysen transformation providing also the simple form for the momentum and spin polarization operators. The operator equations of momentum and spin motion are derived for a first time. Their semiclassical limit is analyzed. The dipole spin-gravity coupling in the previously found (another) Hamiltonian does not lead to any observable effects. The general agreement between the quantum and classical approaches is established, contrary to several recent claims. The expression for the gravitational Stern-Gerlach force is derived. The helicity evolution in the gravitational field and corresponding accelerated frame coincides, being the manifestation of the equivalence principle.
String pair production in a time-dependent gravitational field
Tolley, Andrew J.; Wesley, Daniel H.
2005-12-15
We study the pair creation of point particles and strings in a time-dependent, weak gravitational field. We find that, for massive string states, there are surprising and significant differences between the string and point-particle results. Central to our approach is the fact that a weakly curved spacetime can be represented by a coherent state of gravitons, and therefore we employ standard techniques in string perturbation theory. String and point-particle pairs are created through tree-level interactions between the background gravitons. In particular, we focus on the production of excited string states and perform explicit calculations of the production of a set of string states of arbitrary excitation level. The differences between the string and point-particle results may contain important lessons for the pair production of strings in the strong gravitational fields of interest in cosmology and black hole physics.
The Equivalence of Time and Gravitational Field
NASA Astrophysics Data System (ADS)
Baruk?i?a, Ilija
The relationship between energy, time and space is still not solved in an appropriate manner. According to Newton's concept of time and space, both have to be taken as absolute. If we follow Leibniz and his arguments, space and time are relative. Since Einstein's theory of relativity we know at least that energy, time and space are deeply related. Albert Einstein originally predicted that time is nothing absolute but something relative, time changes and can change. Especially, time and gravitational field are related somehow even in detail if we still don't know how. According to the gravitational time dilation, the lower the gravitational potential, the more slowly time passes and vice versa. Somehow, it appears to be that the behaviour of time is directly linked to the behaviour of the gravitational field. The aim of this publication is to work out the interior logic between time and gravitational field and to make the proof that time is equivalent to the gravitational field and vice versa.
Numerical study of primordial magnetic field amplification by inflation-produced gravitational waves
Kuroyanagi, Sachiko; Tashiro, Hiroyuki; Sugiyama, Naoshi
2010-01-15
We numerically study the interaction of inflation-produced magnetic fields with gravitational waves, both of which originate from quantum fluctuations during inflation. The resonance between the magnetic field perturbations and the gravitational waves has been suggested as a possible mechanism for magnetic field amplification. However, some analytical studies suggest that the effect of the inflationary gravitational waves is too small to provide significant amplification. Our numerical study shows more clearly how the interaction affects the magnetic fields and confirms the weakness of the influence of the gravitational waves. We present an investigation based on the magnetohydrodynamic approximation and take into account the differences of the Alfven speed.
On the Bel radiative gravitational fields
NASA Astrophysics Data System (ADS)
Ferrando, Joan Josep; Sez, Juan Antonio
2012-04-01
We analyze the concept of intrinsic radiative gravitational fields defined by Bel and we show that the three radiative types, N, III and II, correspond with the three following different physical situations: pure radiation, asymptotic pure radiation and generic (non-pure, non-asymptotic pure) radiation. We introduce the concept of observer at rest with respect to the gravitational field and that of proper super-energy of the gravitational field and we show that, for non-radiative fields, the minimum value of the relative super-energy density is the proper super-energy density, which is acquired by the observers at rest with respect to the field. Several super-energy inequalities are also examined.
Physical optics in a uniform gravitational field
NASA Astrophysics Data System (ADS)
Hacyan, Shahen
2012-01-01
The motion of a (quasi-)plane wave in a uniform gravitational field is studied. It is shown that the energy of an elliptically polarized wave does not propagate along a geodesic, but in a direction that is rotated with respect to the gravitational force. The similarity with the walk-off effect in anisotropic crystals or the optical Magnus effect in inhomogeneous media is pointed out.
Gravitational waves induced by spinor fields
NASA Astrophysics Data System (ADS)
Feng, Kaixi; Piao, Yun-Song
2015-07-01
In realistic model building, spinor fields with various masses are present. During inflation, a spinor field may induce gravitational waves as a second order effect. In this paper, we calculate the contribution of a single massive spinor field to the power spectrum of primordial gravitational wave by using a retarded Green propagator. We find that the correction is scale invariant and of order H4/MP4 for arbitrary spinor mass m?. Additionally, we also observe that when m??H , the dependence of correction on m?/H is nontrivial.
Galilean-invariant scalar fields can strengthen gravitational lensing.
Wyman, Mark
2011-05-20
The mystery of dark energy suggests that there is new gravitational physics on long length scales. Yet light degrees of freedom in gravity are strictly limited by Solar System observations. We can resolve this apparent contradiction by adding a Galilean-invariant scalar field to gravity. Called Galileons, these scalars have strong self-interactions near overdensities, like the Solar System, that suppress their dynamical effect. These nonlinearities are weak on cosmological scales, permitting new physics to operate. In this Letter, we point out that a massive-gravity-inspired coupling of Galileons to stress energy can enhance gravitational lensing. Because the enhancement appears at a fixed scaled location for dark matter halos of a wide range of masses, stacked cluster analysis of weak lensing data should be able to detect or constrain this effect. PMID:21668215
Hyperbolic Octonion Formulation of Gravitational Field Equations
NASA Astrophysics Data System (ADS)
Demir, Sleyman
2013-01-01
In this paper, the Maxwell-Proca type field equations of linear gravity are formulated in terms of hyperbolic octonions (split octonions). A hyperbolic octonionic gravitational wave equation with massive gravitons and gravitomagnetic monopoles is proposed. The real gravitoelectromagnetic field equations are recovered and written in compact form from an octonionic potential. In the absence of charges, this reduces to the Klein-Gordon equation of motion for the massive graviton. The analogy between massive gravitational theory and electromagnetism is shown in terms of the present formulation.
Chameleon scalar fields in relativistic gravitational backgrounds
Tsujikawa, Shinji; Tamaki, Takashi; Tavakol, Reza E-mail: tamaki@gravity.phys.waseda.ac.jp
2009-05-15
We study the field profile of a scalar field {phi} that couples to a matter fluid (dubbed a chameleon field) in the relativistic gravitational background of a spherically symmetric spacetime. Employing a linear expansion in terms of the gravitational potential {Phi}{sub c} at the surface of a compact object with a constant density, we derive the thin-shell field profile both inside and outside the object, as well as the resulting effective coupling with matter, analytically. We also carry out numerical simulations for the class of inverse power-law potentials V({phi}) = M{sup 4+n}{phi}{sup -n} by employing the information provided by our analytical solutions to set the boundary conditions around the centre of the object and show that thin-shell solutions in fact exist if the gravitational potential {Phi}{sub c} is smaller than 0.3, which marginally covers the case of neutron stars. Thus the chameleon mechanism is present in the relativistic gravitational backgrounds, capable of reducing the effective coupling. Since thin-shell solutions are sensitive to the choice of boundary conditions, our analytic field profile is very helpful to provide appropriate boundary conditions for {Phi}{sub c}{approx}
Ren, Jing; Xianyu, Zhong-Zhi; He, Hong-Jian E-mail: xianyuzhongzhi@gmail.com
2014-06-01
We study gravitational interaction of Higgs boson through the unique dimension-4 operator ξH{sup †}HR, with H the Higgs doublet and R the Ricci scalar curvature. We analyze the effect of this dimensionless nonminimal coupling ξ on weak gauge boson scattering in both Jordan and Einstein frames. We explicitly establish the longitudinal-Goldstone equivalence theorem with nonzero ξ coupling in both frames, and analyze the unitarity constraints. We study the ξ-induced weak boson scattering cross sections at O(1−30) TeV scales, and propose to probe the Higgs-gravity coupling via weak boson scattering experiments at the LHC (14 TeV) and the next generation pp colliders (50-100 TeV). We further extend our study to Higgs inflation, and quantitatively derive the perturbative unitarity bounds via coupled channel analysis, under large field background at the inflation scale. We analyze the unitarity constraints on the parameter space in both the conventional Higgs inflation and the improved models in light of the recent BICEP2 data.
Rotation of the cosmic microwave background polarization from weak gravitational lensing.
Dai, Liang
2014-01-31
When a cosmic microwave background (CMB) photon travels from the surface of last scatter through spacetime metric perturbations, the polarization vector may rotate about its direction of propagation. This gravitational rotation is distinct from, and occurs in addition to, the lensing deflection of the photon trajectory. This rotation can be sourced by linear vector or tensor metric perturbations and is fully coherent with the curl deflection field. Therefore, lensing corrections to the CMB polarization power spectra as well as the temperature-polarization cross correlations due to nonscalar perturbations are modified. The rotation does not affect lensing by linear scalar perturbations, but needs to be included when calculations go to higher orders. We present complete results for weak lensing of the full-sky CMB power spectra by general linear metric perturbations, taking into account both deflection of the photon trajectory and rotation of the polarization. For the case of lensing by gravitational waves, we show that the B modes induced by the rotation largely cancel those induced by the curl component of deflection. PMID:24580435
Gravitational radiation from preheating with many fields
Jr, John T. Giblin; Price, Larry R.; Siemens, Xavier E-mail: larry@gravity.phys.uwm.edu
2010-08-01
Parametric resonances provide a mechanism by which particles can be created just after inflation. Thus far, attention has focused on a single or many inflaton fields coupled to a single scalar field. However, generically we expect the inflaton to couple to many other relativistic degrees of freedom present in the early universe. Using simulations in an expanding Friedmann-Lematre-Robertson-Walker spacetime, in this paper we show how preheating is affected by the addition of multiple fields coupled to the inflaton. We focus our attention on gravitational wave production an important potential observational signature of the preheating stage. We find that preheating and its gravitational wave signature is robust to the coupling of the inflaton to more matter fields.
Constraining modified gravitational theories by weak lensing with Euclid
Martinelli, Matteo; Calabrese, Erminia; De Bernardis, Francesco; Melchiorri, Alessandro; Pagano, Luca; Scaramella, Roberto
2011-01-15
Future proposed satellite missions such as Euclid can offer the opportunity to test general relativity on cosmic scales through mapping of the galaxy weak-lensing signal. In this paper we forecast the ability of these experiments to constrain modified gravity scenarios such as those predicted by scalar-tensor and f(R) theories. We find that Euclid will improve constraints expected from the Planck satellite on these modified theories of gravity by 2 orders of magnitude. We discuss parameter degeneracies and the possible biases introduced by modifications to gravity.
Shell sources of stationary axisymmetric gravitational fields
NASA Astrophysics Data System (ADS)
Babala, D.
1986-02-01
A number of solutions for material shell sources of stationary axisymmetric gravitational fields are presented. Explicit solutions are found for shells lying on equipotential hypersurfaces (gtt - const) and generating static 'monopole' fields in prolate and oblate spheroidal coordinates (Zipoy-Voorhees fields). Numerical solutions are found for shells lying on hypersurfaces of constant gphi-t/g sub phi-phi and generating Kerr- and Tomimatsu-Sato (delta = 2) fields. The shells have minimum areas allowed by the energy conditions of Hawking and Ellis.
Effect of quantum statistics on the gravitational weak equivalence principle
NASA Astrophysics Data System (ADS)
Mousavi, S. V.; Majumdar, A. S.; Home, D.
2015-11-01
We study the effect of quantum statistics on the arrival time distribution of quantum particles computed through the probability current density. It is shown that symmetrization or asymmetrization of the wave function affects the arrival time distribution for even freely propagating particles. In order to investigate the effect of statistics on the weak equivalence principle in quantum mechanics (WEQ), we then compute the mean arrival time for wavepackets in free fall. The violation of WEQ through the effect of statistics on the mass dependence of the mean arrival time is clearly exhibited. We finally evaluate the effect of spin on the violation of WEQ using a different approach by including an explicit spin-dependence in the probability current distribution, and compare it with the approach using particle statistics. Our results show WEQ re-emerges smoothly in the limit of large mass.
Gravitational Lensing by Kerr-Sen Dilaton-Axion Black Hole in the Weak Deflection Limit
Gyulchev, G. N.; Yazadjiev, S. S.
2010-11-25
We investigate analytically gravitational lensing by charged, stationary, axially symmetric Kerr-Sen dilaton-axion black hole in the weak deflection limit. Approximate solutions to the lightlike equations of motion are present up to and including third-order terms in M/b, a/b and r{sub {alpha}}/b, where M is the black hole mass, a is the angular momentum, r{sub {alpha}}= Q{sup 2}/M,Q being the charge and b is the impact parameter of the light ray. We compute the positions of the two weak field images up to post-Newtonian order. The shift of the critical curves as a function of the lens angular momentum is found, and it is shown that they decrease slightly with the increase of the charge. The lensing observables are compared to these characteristics for particular cases as Schwarzschild and Kerr black holes as well as the Gibbons-Maeda-Garfinkle-Horowitz-Strominger black hole.
Prolate spheroidal harmonic expansion of gravitational field
Fukushima, Toshio
2014-06-01
As a modification of the oblate spheroidal case, a recursive method is developed to compute the point value and a few low-order derivatives of the prolate spheroidal harmonics of the second kind, Q{sub nm} (y), namely the unnormalized associated Legendre function (ALF) of the second kind with its argument in the domain, 1 < y < ∞. They are required in evaluating the prolate spheroidal harmonic expansion of the gravitational field in addition to the point value and the low-order derivatives of P-bar {sub nm}(t), the 4π fully normalized ALF of the first kind with its argument in the domain, |t| ≤ 1. The new method will be useful in the gravitational field computation of elongated celestial objects.
Geometrical structure of gravitation and matter fields
NASA Astrophysics Data System (ADS)
Halpern, Leopold
1994-02-01
Einstein's requirement of a unified geometrical description of gravitational fields and their matter sources is shown to become possible (at least for certain matter sources) by relaxing his other requirement of a minimal interaction of gravitation with matter. Arguments are presented to demonstrate that Schrödinger's discovery of pair creation by gravitational fields and the associated effects of virtual pairs make the relaxation of the latter requirement inevitable in order to obtain a complete macroscopic description (which needs no separate insertion to take account of averaged quantum effects). The gravitational field equations in case of a nonminimal interaction need higher derivatives of the metric than the second. The author's gauge theory on the manifold of the anti-de Sitter group SO(3, 2) with the subgroup SO(3, 1) (proper Lorentz group) as gauge group and the factor space of the two group manifolds as space-time manifold gives rise to a Yang-Mills field which can be interpreted to be composed of Riemannian curvature and a tensor formed out of torsion. Einstein's equations with a cosmological member are satisfied by the Cartan-Killing metric on the group manifold so that the generalization to a Kaluza-Klein theory results in a minimal disturbance of the group symmetry. The separation of the Yang-Mills field results in a part of its energy-momentum tensor becoming purely Riemannian; this part may be interpreted to be due to the contribution of virtual matter, whereas the part with torsion is due to real matter and its interaction with curvature. The Yang-Mills field equations have a third-order derivative purely metric part, which is equivalent to the field equations suggested by Yang (in the latter, however, torsion should be inseparably present and has been ignored). The torsion part is the “matter source” of this term and it is tempting to relate it to elementary particle spin. The theory can be regarded as a gauge theory of space-time geometry. It needs generalizations to geometrize matter with an energy-momentum tensor of nonvanishing trace. The equations, however, already considerably modify the problem of gravitational collapse. Further developments should serve to eliminate the “absurdity of relativity”—the collapse to a point (of which Einstein himself never became convinced).
Weak gravity strongly constrains large-field axion inflation
NASA Astrophysics Data System (ADS)
Heidenreich, Ben; Reece, Matthew; Rudelius, Tom
2015-12-01
Models of large-field inflation based on axion-like fields with shift symmetries can be simple and natural, and make a promising prediction of detectable primordial gravitational waves. The Weak Gravity Conjecture is known to constrain the simplest case in which a single compact axion descends from a gauge field in an extra dimension. We argue that the Weak Gravity Conjecture also constrains a variety of theories of multiple compact axions including N-flation and some alignment models. We show that other alignment models entail surprising consequences for how the mass spectrum of the theory varies across the axion moduli space, and hence can be excluded if further conjectures hold. In every case that we consider, plausible assumptions lead to field ranges that cannot be parametrically larger than M Pl. Our results are strongly suggestive of a general inconsistency in models of large-field inflation based on compact axions, and possibly of a more general principle forbidding super-Planckian field ranges.
Reptation in a Weak Driving Field
NASA Astrophysics Data System (ADS)
Aalberts, Daniel; van Leeuwen, J. M. J.
1997-03-01
A simplified model of reptation is presented. The Master Equation of the model is systematically solved by expansion in powers of the strength of the driving field. From the explicit form of the probability distribution, exact conclusions can be drawn about the average shape of the polymer, its drift velocity, and the zero field diffusion constant. Correlations between segments of the chain are calculated and turn out to be large, even in the weak driving field limit. The results are compared with simulations of the model.
NASA Astrophysics Data System (ADS)
Dhiman, Joginder Singh; Sharma, Rajni
2016-03-01
The self-gravitating instability of an infinitely extending axisymmetric cylinder of viscoelastic medium permeated with non uniform magnetic field and rotation is studied for both the strongly coupled plasma (SCP) and weakly coupled plasma (WCP). The non uniform magnetic field and rotation are considered to act along the axial direction of the cylinder. The normal mode method of perturbations is applied to obtain the dispersion relation. The condition for the onset of gravitational instability has been derived from the dispersion relation under both strongly and weakly coupling limits. It is found that the Jeans criterion for gravitational collapse gets modified due to the presence of shear and bulk viscosities for the SCP, however, the magnetic field and rotation whether uniform or non uniform has no effect on the Jeans criterion of an infinitely extending axisymmetric cylinder of a self-gravitating viscoelastic medium.
Theory of microemulsions in a gravitational field
NASA Technical Reports Server (NTRS)
Jeng, J. F.; Miller, Clarence A.
1989-01-01
A theory of microemulsions developed previously is extended to include the effect of a gravitational field. It predicts variation with position of drop size, drop volume fraction, and area per molecule in the surfactant films within a microemulsion phase. Variation in volume fraction is greatest and occurs in such a way that oil content increases with increasing elevation, as has been found experimentally. Large composition variations are predicted within a middle phase microemulsion near optimal conditions because inversion from the water-continuous to the oil-continuous arrangement occurs with increasing elevation. Generally speaking, gravity reduces solubilization within microemulsions and promotes separation of excess phases.
NASA Astrophysics Data System (ADS)
Yahalom, Asher
2011-11-01
In this study, stability conditions of self-gravitating disc models are obtained. The self-gravitating disc models under study include known models such as the Maclaurin disc and the infinite, self-gravitating, rotating sheet. These models also include a new class of analytically solvable models denoted by 'generalized Maclaurin discs'. These self-gravitating, finite discs are differentially rotating with adiabatic index ? > 2 and have the property that the derivatives of densities go smoothly to zero at the boundary. Stability conditions of the various models are obtained through the 'weak energy principle' introduced by Katz, Inagaki & Yahalom. It is shown that necessary and sufficient conditions of stability are obtained when we have only pair coupling in the gyroscopic terms of the perturbed Lagrangian; otherwise, the 'weak energy principle' gives only sufficient conditions. All perturbations considered are in the same plane as the configurations. For differentially rotating discs, we consider only radial perturbations. The limits of stability are identical with those given by a dynamical analysis when available, and with the results of the strong energy principle analysis when given. Thus, although the 'weak energy' method is mathematically more simple than the 'strong energy' method of Katz et al., since it does not involve solving second-order partial differential equations, it is by no means less effective. Additional results also derived through the 'weak energy principle' include stability conditions for the 2D Rayleigh flows and Toomre's local criterion for the stability of rotating discs. Among the most interesting results is an exact extension of Toomre's criterion to the global stability of generalized Maclaurin discs, whereby a necessary condition for local stability becomes a sufficient condition for global stability.
On seasonal variations of Mars' gravitational field
NASA Technical Reports Server (NTRS)
Chao, B. Fong; Rubincam, David P.
1987-01-01
A great quantity of CO2 is exchanged between the Martian atmosphere and polar caps in the course of a Martian year. This exchange occurs in seasonal cycles: CO2 condenses to form the polar caps in winter and sublimes into the atmosphere in summer. The mass involved is about 25% of the total mass of the Martian atmosphere. This paper studies the effects of the CO2 mass redistribution on the Mars' gravitational field. Two mechanisms are examined: (1) the waxing and waning of solid CO2 in the polar caps, and (2) the geographical distribution of gaseous CO2 in the atmosphere. The maximum changes produced by (1) in the low-degree zonal J sub l harmonics in the Mars gravitational field are found to be as much as 7.5 x 10 to the-9 power for J sub 2 (corresponding to 1.1 cm change in the geoid), and about half as much for J sub 3. The effect of (2) on some most prominent low-degree harmonics (for l =1-3) in the effective topography (defined as the departure of the true topography from the geoid) is also evaluated. Their magnitudes are large by Earth standards. Whether they can be observed by the upcoming Mars Observer is still uncertain.
Large field inflation and gravitational entropy
NASA Astrophysics Data System (ADS)
Kaloper, Nemanja; Kleban, Matthew; Lawrence, Albion; Sloth, Martin S.
2016-02-01
Large field inflation can be sensitive to perturbative and nonperturbative quantum corrections that spoil slow roll. A large number N of light species in the theory, which occur in many string constructions, can amplify these problems. One might even worry that in a de Sitter background, light species will lead to a violation of the covariant entropy bound at large N . If so, requiring the validity of the covariant entropy bound could limit the number of light species and their couplings, which in turn could severely constrain axion-driven inflation. Here we show that there is no such problem when we correctly renormalize models with many light species, taking the physical Planck scale to be Mpl 2≳N MUV2 , where MUV is the cutoff for the quantum field theory coupled to semiclassical quantum gravity. The number of light species then cancels out of the gravitational entropy of de Sitter or near-de Sitter backgrounds at leading order. Working in detail with N scalar fields in de Sitter space, renormalized to one loop order, we show that the gravitational entropy automatically obeys the covariant entropy bound. Furthermore, while the axion decay constant is a strong coupling scale for the axion dynamics, we show that it is not in general the cutoff of 4d semiclassical gravity. After renormalizing the two point function of the inflaton, we note that it is also controlled by scales much below the cutoff. We revisit N -flation and Kachru-Kallosh-Linde-Trivedi-type compactifications in this light, and show that they are perfectly consistent with the covariant entropy bound. Thus, while quantum gravity might yet spoil large field inflation, holographic considerations in the semiclassical theory do not obstruct it.
Gravitational radiative corrections from effective field theory
NASA Astrophysics Data System (ADS)
Goldberger, Walter D.; Ross, Andreas
2010-06-01
In this paper we construct an effective field theory (EFT) that describes long wavelength gravitational radiation from compact systems. To leading order, this EFT consists of the multipole expansion, which we describe in terms of a diffeomorphism invariant point particle Lagrangian. The EFT also systematically captures post-Minkowskian corrections to the multipole expansion due to nonlinear terms in general relativity. Specifically, we compute long distance corrections from the coupling of the (mass) monopole moment to the quadrupole moment, including up to two mass insertions. Along the way, we encounter both logarithmic short distance (UV) and long wavelength (IR) divergences. We show that the UV divergences can be (1) absorbed into a renormalization of the multipole moments and (2) resummed via the renormalization group. The IR singularities are shown to cancel from properly defined physical observables. As a concrete example of the formalism, we use this EFT to reproduce a number of post-Newtonian corrections to the gravitational wave energy flux from nonrelativistic binaries, including long distance effects up to 3 post-Newtonian (v6) order. Our results verify that the factorization of scales proposed in the NRGR framework of Goldberger and Rothstein is consistent up to order 3PN.
Gravitational radiative corrections from effective field theory
Goldberger, Walter D.; Ross, Andreas
2010-06-15
In this paper we construct an effective field theory (EFT) that describes long wavelength gravitational radiation from compact systems. To leading order, this EFT consists of the multipole expansion, which we describe in terms of a diffeomorphism invariant point particle Lagrangian. The EFT also systematically captures 'post-Minkowskian' corrections to the multipole expansion due to nonlinear terms in general relativity. Specifically, we compute long distance corrections from the coupling of the (mass) monopole moment to the quadrupole moment, including up to two mass insertions. Along the way, we encounter both logarithmic short distance (UV) and long wavelength (IR) divergences. We show that the UV divergences can be (1) absorbed into a renormalization of the multipole moments and (2) resummed via the renormalization group. The IR singularities are shown to cancel from properly defined physical observables. As a concrete example of the formalism, we use this EFT to reproduce a number of post-Newtonian corrections to the gravitational wave energy flux from nonrelativistic binaries, including long distance effects up to 3 post-Newtonian (v{sup 6}) order. Our results verify that the factorization of scales proposed in the NRGR framework of Goldberger and Rothstein is consistent up to order 3PN.
Gravitational Descendants in Symplectic Field Theory
NASA Astrophysics Data System (ADS)
Fabert, Oliver
2011-02-01
It was pointed out by Y. Eliashberg in his ICM 2006 plenary talk that the rich algebraic formalism of symplectic field theory leads to a natural appearance of quantum and classical integrable systems, at least in the case when the contact manifold is the prequantization space of a symplectic manifold. In this paper we generalize the definition of gravitational descendants in SFT from circle bundles in the Morse-Bott case to general contact manifolds. After we have shown using the ideas in Okounkov and Pandharipande (Ann Math 163(2):517-560, 2006) that for the basic examples of holomorphic curves in SFT, that is, branched covers of cylinders over closed Reeb orbits, the gravitational descendants have a geometric interpretation in terms of branching conditions, we follow the ideas in Cieliebak and Latschev (
Wormholes, emergent gauge fields, and the weak gravity conjecture
NASA Astrophysics Data System (ADS)
Harlow, Daniel
2016-01-01
This paper revisits the question of reconstructing bulk gauge fields as boundary operators in AdS/CFT. In the presence of the wormhole dual to the thermofield double state of two CFTs, the existence of bulk gauge fields is in some tension with the microscopic tensor factorization of the Hilbert space. I explain how this tension can be resolved by splitting the gauge field into charged constituents, and I argue that this leads to a new argument for the "principle of completeness", which states that the charge lattice of a gauge theory coupled to gravity must be fully populated. I also claim that it leads to a new motivation for (and a clarification of) the "weak gravity conjecture", which I interpret as a strengthening of this principle. This setup gives a simple example of a situation where describing low-energy bulk physics in CFT language requires knowledge of high-energy bulk physics. This contradicts to some extent the notion of "effective conformal field theory", but in fact is an expected feature of the resolution of the black hole information problem. An analogous factorization issue exists also for the gravitational field, and I comment on several of its implications for reconstructing black hole interiors and the emergence of spacetime more generally.
Symmetries in tetrad theories. [of gravitational fields and general relativity
NASA Technical Reports Server (NTRS)
Chinea, F. J.
1988-01-01
The isometry conditions for gravitational fields are given directly at the tetrad level, rather than in terms of the metric. As an illustration, an analysis of the curvature collineations and Killing fields for a twisting type-N vacuum gravitational field is made.
NASA Astrophysics Data System (ADS)
Belvedere, Riccardo; Pugliese, Daniela; Rueda, Jorge A.; Ruffini, Remo; Xue, She-Sheng
2012-06-01
We formulate the equations of equilibrium of neutron stars taking into account strong, weak, electromagnetic, and gravitational interactions within the framework of general relativity. The nuclear interactions are described by the exchange of the ?, ?, and ? virtual mesons. The equilibrium conditions are given by our recently developed theoretical framework based on the Einstein-Maxwell-Thomas-Fermi equations along with the constancy of the general relativistic Fermi energies of particles, the "Klein potentials", throughout the configuration. The equations are solved numerically in the case of zero temperatures and for selected parameterizations of the nuclear models. The solutions lead to a new structure of the star: a positively charged core at supranuclear densities surrounded by an electronic distribution of thickness ?/(mec)102?/(m?c) of opposite charge, as well as a neutral crust at lower densities. Inside the core there is a Coulomb potential well of depth m?c2/e. The constancy of the Klein potentials in the transition from the core to the crust, imposes the presence of an overcritical electric field (Ec, the critical field being Ec=me2c3/(e?). The electron chemical potential and the density decrease, in the boundary interface, until values ?ecrust
Fast Reconnection of Weak Magnetic Fields
NASA Technical Reports Server (NTRS)
Zweibel, Ellen G.
1998-01-01
Fast magnetic reconnection refers to annihilation or topological rearrangement of magnetic fields on a timescale that is independent (or nearly independent) of the plasma resistivity. The resistivity of astrophysical plasmas is so low that reconnection is of little practical interest unless it is fast. Yet, the theory of fast magnetic reconnection is on uncertain ground, as models must avoid the tendency of magnetic fields to pile up at the reconnection layer, slowing down the flow. In this paper it is shown that these problems can be avoided to some extent if the flow is three dimensional. On the other hand, it is shown that in the limited but important case of incompressible stagnation point flows, every flow will amplify most magnetic fields. Although examples of fast magnetic reconnection abound, a weak, disordered magnetic field embedded in stagnation point flow will in general be amplified, and should eventually modify the flow. These results support recent arguments against the operation of turbulent resistivity in highly conducting fluids.
Consequences of Coupled Electromagnetic-Gravitational Fields
NASA Technical Reports Server (NTRS)
Smalley, Larry
2002-01-01
In the late 1980s there was a flurry of activities involving the newly discovered high Tc superconductors in the development of new devices such as more efficient current transmission, transformers, generators, and motors. One such developmental project by Podkletnov in 1992 noted some small, anomalous gravitational behaviors. A following unpublished paper by Podkletnov 1995 provided data with larger effects using a larger (approx. 25 cm) superconducting disk. Unfortunately this disk was extremely fragile and was broken beyond repair. To date, these experiments have not been successfully repeated because of the difficulties of producing stable, durable (and fired) superconducting disks. This problem with firing these disks has been solved by Li. What remains is to install the disk in "motor", at superconducting temperatures in the presence of appropriately tailored magnetic fields.
Quantum mechanics on the gravitational field
Teitelboim, C.
1982-06-15
An approach to the quantum theory of gravitation is developed by analogy with the quantum mechanics of the simplest generally covariant system: the relativistic point particle. The central object in the formalism is the transition amplitude from one three-geometry to another which is given by a path integral. In that path integral one sums over all possible histories which connect two three-geometries separated by a given local proper time and then integrates over all possible proper-time separations. The choice of the range of integration for the proper time fixes the boundary conditions for the transition amplitude. If only positive proper times are allowed, the resulting amplitude is causal. A perturbation theory is developed in which the expansion parameter is the signature which takes the value minus one when the field histories (spacetimes) have hperbolic signature and plus one for the Euclidean case. The ''free theory corresponds to zero signature and may be viewed as the result of replacing the Lorentz group as a symmetry group of the tangent spaces by one of its contractions, namely that one where the speed of light approaches zero. It is argued that besides that processes in which the universe starts or finishes at a singularity, there are also processes with a nonzero amplitude in which the universe starts and finishes in the same regular configuration without ever going through a singularity. These latter processes may be pictured as a loop in the configurtion space of the gravitational field. The work remains formal throughout in that no definite meaning is given to the functional integrals considered.
Gravitational properties of light—the gravitational field of a laser pulse
NASA Astrophysics Data System (ADS)
Rätzel, Dennis; Wilkens, Martin; Menzel, Ralf
2016-02-01
The gravitational field of a laser pulse of finite lifetime, is investigated in the framework of linearized gravity. Although the effects are very small, they may be of fundamental physical interest. It is shown that the gravitational field of a linearly polarized light pulse is modulated as the norm of the corresponding electric field strength, while no modulations arise for circular polarization. In general, the gravitational field is independent of the polarization direction. It is shown that all physical effects are confined to spherical shells expanding with the speed of light, and that these shells are imprints of the spacetime events representing emission and absorption of the pulse. Nearby test particles at rest are attracted towards the pulse trajectory by the gravitational field due to the emission of the pulse, and they are repelled from the pulse trajectory by the gravitational field due to its absorption. Examples are given for the size of the attractive effect. It is recovered that massless test particles do not experience any physical effect if they are co-propagating with the pulse, and that the acceleration of massless test particles counter-propagating with respect to the pulse is four times stronger than for massive particles at rest. The similarities between the gravitational effect of a laser pulse and Newtonian gravity in two dimensions are pointed out. The spacetime curvature close to the pulse is compared to that induced by gravitational waves from astronomical sources.
Weak gravitational lensing as a method to constrain unstable dark matter
Wang Meiyu; Zentner, Andrew R.
2010-12-15
The nature of the dark matter remains a mystery. The possibility of an unstable dark matter particle decaying to invisible daughter particles has been explored many times in the past few decades. Meanwhile, weak gravitational lensing shear has gained a lot of attention as a probe of dark energy, though it was previously considered a dark matter probe. Weak lensing is a useful tool for constraining the stability of the dark matter. In the coming decade a number of large galaxy imaging surveys will be undertaken and will measure the statistics of cosmological weak lensing with unprecedented precision. Weak lensing statistics are sensitive to unstable dark matter in at least two ways. Dark matter decays alter the matter power spectrum and change the angular diameter distance-redshift relation. We show how measurements of weak lensing shear correlations may provide the most restrictive, model-independent constraints on the lifetime of unstable dark matter. Our results rely on assumptions regarding nonlinear evolution of density fluctuations in scenarios of unstable dark matter and one of our aims is to stimulate interest in theoretical work on nonlinear structure growth in unstable dark matter models.
Gravitational consequences of modern field theories
NASA Technical Reports Server (NTRS)
Horowitz, Gary T.
1989-01-01
Some gravitational consequences of certain extensions of Einstein's general theory of relativity are discussed. These theories are not alternative theories of gravity in the usual sense. It is assumed that general relativity is the appropriate description of all gravitational phenomena which were observed to date.
On the super-energy radiative gravitational fields
NASA Astrophysics Data System (ADS)
Ferrando, Joan Josep; Sez, Juan Antonio
2013-05-01
We extend our recent analysis (Ferrando J J and Sez J A 2012 Class. Quantum Grav. 29 075012) on the Bel radiative gravitational fields to the super-energy radiative gravitational fields defined by Garca-Parrado (2008 Class. Quantum Grav. 25 015006). We give an intrinsic characterization of the new radiative fields and consider some distinguished classes of both radiative and non-radiative fields. Several super-energy inequalities are improved.
Vacuum polarization in gravitational and electromagnetic fields around a superconducting string
Mankiewicz, L. ); Misiak, M.
1989-09-15
We have calculated the polarization current induced in the physical vacuum around a superconducting cosmic string taking into account the gravitational field of the string. The current can be calculated as an expansion in powers of the inverse of the electron mass. In the region far from the string, where it is justified to keep only the lowest term of this expansion, the polarization current turns out to screen the original current in the string, but the effect is very weak. A direct calculation of terms due to the presence of the gravitational field shows that they are dominated, for realistic string parameters, by the purely electromagnetic contribution.
A gravitational field model for the earth.
NASA Technical Reports Server (NTRS)
Smith, D. E.; Lerch, F. J.; Wagner, C. A.
1973-01-01
Two models of the earth's gravitational field have been computed. The first, Goddard Earth Model 1 (GEM 1), has been derived from satellite tracking data. The second, Goddard Earth Model 2 (GEM 2), has been derived from a combination of satellite tracking and surface gravimetric data. The satellite data consisted primarily of optical data processed on 300 weekly orbital arcs for 25 close earth satellites. Surface gravity data were employed in the form of 5 x 5 deg mean free-air gravity anomalies providing about 70% world coverage. Station locations were obtained for 46 tracking sites by combining electronic, laser, and additional optical tracking data with the above satellite data. Analysis of the radial positions of these stations and a value of mean gravity on the geoid indicated a mean equatorial radius for the earth of about 6378.145 meters. Results of geopotential tests on satellite data not used in the solution show that better agreement was obtained with the GEM 1 and GEM 2 models than with the 1969 Smithsonian Standard Earth II model.
Interaction of gravitational waves with magnetic and electric fields
Barrabes, C.; Hogan, P. A.
2010-03-15
The existence of large-scale magnetic fields in the universe has led to the observation that if gravitational waves propagating in a cosmological environment encounter even a small magnetic field then electromagnetic radiation is produced. To study this phenomenon in more detail we take it out of the cosmological context and at the same time simplify the gravitational radiation to impulsive waves. Specifically, to illustrate our findings, we describe the following three physical situations: (1) a cylindrical impulsive gravitational wave propagating into a universe with a magnetic field, (2) an axially symmetric impulsive gravitational wave propagating into a universe with an electric field and (3) a 'spherical' impulsive gravitational wave propagating into a universe with a small magnetic field. In cases (1) and (3) electromagnetic radiation is produced behind the gravitational wave. In case (2) no electromagnetic radiation appears after the wave unless a current is established behind the wave breaking the Maxwell vacuum. In all three cases the presence of the magnetic or electric fields results in a modification of the amplitude of the incoming gravitational wave which is explicitly calculated using the Einstein-Maxwell vacuum field equations.
Computing Gravitational Fields of Finite-Sized Bodies
NASA Technical Reports Server (NTRS)
Quadrelli, Marco
2005-01-01
A computer program utilizes the classical theory of gravitation, implemented by means of the finite-element method, to calculate the near gravitational fields of bodies of arbitrary size, shape, and mass distribution. The program was developed for application to a spacecraft and to floating proof masses and associated equipment carried by the spacecraft for detecting gravitational waves. The program can calculate steady or time-dependent gravitational forces, moments, and gradients thereof. Bodies external to a proof mass can be moving around the proof mass and/or deformed under thermoelastic loads. An arbitrarily shaped proof mass is represented by a collection of parallelepiped elements. The gravitational force and moment acting on each parallelepiped element of a proof mass, including those attributable to the self-gravitational field of the proof mass, are computed exactly from the closed-form equation for the gravitational potential of a parallelepiped. The gravitational field of an arbitrary distribution of mass external to a proof mass can be calculated either by summing the fields of suitably many point masses or by higher-order Gauss-Legendre integration over all elements surrounding the proof mass that are part of a finite-element mesh. This computer program is compatible with more general finite-element codes, such as NASTRAN, because it is configured to read a generic input data file, containing the detailed description of the finiteelement mesh.
Quantum field theory methods in the study of gravitation
NASA Astrophysics Data System (ADS)
Toriumi, Reiko
Some further results that support the phase structure of quantum gravitation with a nontrivial ultraviolet fixed point are presented. The approaches explored here are based on quantum field theories and lattice discretization. Finally consequences of this phase structure in quantum gravitation are studied in the context of cosmology.
NASA Astrophysics Data System (ADS)
Ivanov, A. N.; Wellenzohn, M.
2015-09-01
We analyze a nonrelativistic approximation of the Dirac equation for slow fermions, coupled to the chameleon field and torsion in the spacetime with the Schwarzschild metric, taken in the weak gravitational field of the Earth approximation. We follow the analysis of the Dirac equation in the curved spacetime with torsion, proposed by Kostelecky [Phys. Rev. D 69, 105009 (2004)], and apply the Foldy-Wouthuysen transformations. We derive the effective low-energy gravitational potentials for slow fermions, coupled to the gravitational field of the Earth, the chameleon field and to torsion with minimal and nonminimal couplings.
Gravitational waves from self-ordering scalar fields
Fenu, Elisa; Durrer, Ruth; Figueroa, Daniel G.; Garca-Bellido, Juan E-mail: daniel.figueroa@uam.es E-mail: juan.garciabellido@uam.es
2009-10-01
Gravitational waves were copiously produced in the early Universe whenever the processes taking place were sufficiently violent. The spectra of several of these gravitational wave backgrounds on subhorizon scales have been extensively studied in the literature. In this paper we analyze the shape and amplitude of the gravitational wave spectrum on scales which are superhorizon at the time of production. Such gravitational waves are expected from the self ordering of randomly oriented scalar fields which can be present during a thermal phase transition or during preheating after hybrid inflation. We find that, if the gravitational wave source acts only during a small fraction of the Hubble time, the gravitational wave spectrum at frequencies lower than the expansion rate at the time of production behaves as ?{sub GW}(f) ? f{sup 3} with an amplitude much too small to be observable by gravitational wave observatories like LIGO, LISA or BBO. On the other hand, if the source is active for a much longer time, until a given mode which is initially superhorizon (k?{sub *} << 1), enters the horizon, for k? ?> 1, we find that the gravitational wave energy density is frequency independent, i.e. scale invariant. Moreover, its amplitude for a GUT scale scenario turns out to be within the range and sensitivity of BBO and marginally detectable by LIGO and LISA. This new gravitational wave background can compete with the one generated during inflation, and distinguishing both may require extra information.
WEAK GRAVITATIONAL LENSING AS A PROBE OF PHYSICAL PROPERTIES OF SUBSTRUCTURES IN DARK MATTER HALOS
Shirasaki, Masato
2015-02-01
We propose a novel method to select satellite galaxies in outer regions of galaxy groups or clusters using weak gravitational lensing. The method is based on the theoretical expectation that the tangential shear pattern around satellite galaxies would appear with negative values at an offset distance from the center of the main halo. We can thus locate the satellite galaxies statistically with an offset distance of several lensing smoothing scales by using the standard reconstruction of surface mass density maps from weak lensing observation. We test the idea using high-resolution cosmological simulations. We show that subhalos separated from the center of the host halo are successfully located even without assuming the position of the center. For a number of such subhalos, the characteristic mass and offset length can be also estimated on a statistical basis. We perform a Fisher analysis to show how well upcoming weak lensing surveys can constrain the mass density profile of satellite galaxies. In the case of the Large Synoptic Survey Telescope with a sky coverage of 20,000deg{sup 2}, the mass of the member galaxies in the outer region of galaxy clusters can be constrained with an accuracy of ?0.1 dex for galaxy clusters with mass 10{sup 14} h {sup 1} M {sub ?} at z = 0.15. Finally we explore the detectability of tidal stripping features for subhalos having a wide range of masses of 10{sup 11}-10{sup 13} h {sup 1} M {sub ?}.
NASA Astrophysics Data System (ADS)
Rhodes, Jason
The nature of dark energy, thought to be driving the accelerating expansion of the Universe, is one of the most compelling mysteries in all of science. Determining the equation-of-state of dark energy to 1% accuracy is currently a leading goal for many planned cosmological surveys and numerical simulations of structure formation are required to make predictions and help mitigate systematics for upcoming surveys such as NASA’s Wide-Field Infrared Survey Telescope (WFIRST), ESA’s Euclid and the Large Synoptic Survey Telescope (LSST). We propose to: 1) Enhance our weak lensing simulation pipeline, SUNGLASS, to include galaxy intrinsic alignments 2) Develop and test intrinsic alignment mitigation techniques 3) Generate high precision covariance matrices and determine the precision required to measure the equation-of-state of dark energy to 1% 4) Develop a covariance emulator Our SUNGLASS pipeline (Simulated UNiverses for Gravitational Lensing Analysis and Shear Surveys; Kiessling et al. 2011a) is able to produce Monte Carlo suites of numerical simulations and rapidly generates mock weak lensing galaxy shear catalogues. We propose to enhance the SUNGLASS pipeline to include realistic galaxy properties using the Galacticus software (Benson 2012). With the realistic galaxy properties made available from Galacticus, we will be able to place realistic intrinsic alignment (IA) signals, where galaxy shapes are correlated due to their physical proximity, into the mock catalogues. Using the SUNGLASS/Galacticus catalogues, we propose to reduce the degrees of freedom in a plausible IA model and find optimal methods of controlling IA through removal techniques and modeling. It is currently unknown how accurate a covariance matrix needs to be in order to measure the equation-of-state of dark energy to 1%. We will directly generate the matrices with 10^4 independent N-body realizations for a LCDM cosmology to test how errors propagate through the non-linear modes and compare results with Gaussian estimates. We will also determine how accurate the inverse covariance matrix needs to be to measure dark energy to 1%. Future missions will require cosmology dependent covariance matrices, so we will need simulations at up to 10^4 points in parameter space. The ~10^8 simulations needed (10^4 realizations at up to 10^4 points in parameter space) would take a prohibitively large amount of time and computing resources. To reduce the number of realizations required in the future, while sampling the plausible parameter space, we will develop and test an emulator that does not compromise on the accuracy of the inverse covariance matrix. The developments and investigations proposed here are absolutely essential for the success of future telescope missions in determining the dark energy equation-of-state to an accuracy of 1%. The SUNGLASS pipeline is uniquely placed to tackle all of these problems in a rapid and computationally efficient way and the developments proposed will result in a pipeline that is able to drive a cosmology telescope mission from the development phase all the way through to accurate data analysis.
Bats respond to very weak magnetic fields.
Tian, Lan-Xiang; Pan, Yong-Xin; Metzner, Walter; Zhang, Jin-Shuo; Zhang, Bing-Fang
2015-01-01
How animals, including mammals, can respond to and utilize the direction and intensity of the Earth's magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae) can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5th of the natural intensity (i.e., 10 ?T; the lowest field strength tested here), the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 ?T), despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (P<0.05). Hence, N. plancyi is able to detect the direction of a magnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth's magnetic field strength varied and the polarity reversed tens of times over the past fifty million years. PMID:25922944
Neutron interference in the gravitational field of a ring laser
NASA Astrophysics Data System (ADS)
Fischetti, Robert D.; Mallett, Ronald L.
2015-07-01
The neutron split-beam interferometer has proven to be particularly useful in measuring Newtonian gravitational effects such as those studied by Colella, Overhauser, and Werner (COW). The development of the ring laser has led to numerous applications in many areas of physics including a recent general relativistic prediction of frame dragging in the gravitational field produced by the electromagnetic radiation in a ring laser. This paper introduces a new general technique based on a canonical transformation of the Dirac equation for the gravitational field of a general linearized spacetime. Using this technique it is shown that there is a phase shift in the interference of two neutron beams due to the frame-dragging nature of the gravitational field of a ring laser.
Universality of Bubble-Jets in Gravitational Fields
NASA Astrophysics Data System (ADS)
Obreschkow, Danail; Tinguely, Marc; Dorsaz, Nicolas; Kobel, Philippe; de Bosset, Aurele; Farhat, Mohamed
2011-11-01
Gravity matters: for us, as well as for small vapor bubbles in liquids. When cavitation bubbles collapse, they feel the presence of a faint hydrostatic pressure gradient caused by gravity -- an effect, which is widely neglected for the experimental difficulty of uncovering the weak action of gravity. We faced this challenge by designing an experiment able to generate uniquely spherical cavitation bubbles. Captivating high-speed movies showing the collapse of those bubbles manifest beautiful jets caused solely by gravity. These jets were studied systematically by running the experiment aboard an acrobatic aircraft (52nd ESA parabolic flight campaign), able to simulate the gravitational fields of the smallest moons and the largest planets in the solar system. The data reveals a clear connection between the size of the jets and the level of gravity. Further reduction and theoretical developments led to a universal scaling law between the size of jets emitted by cavitation bubbles and a single parameter, which only depends on the pressure field and the bubble volume.
NASA Astrophysics Data System (ADS)
Zakharov, A.; De Paolis, F.; Ingrosso, G.; Nucita, A.
There are several well known GR tests in a weak gravitational field limit however some of these tests could could be fitted by alternative theories of gravitation On the other hand there is very little information about GR tests in the strong gravitational field We calculated shapes of shadows mirages forming just near BH horizons and discuss a possibility to evaluate inclination angle spin and charge of black hole In 2007 the Radioastron space telescope will be launched and it will be a generalization of VLBI technique using the space -- ground base Using this interferometer one could evaluate parameters parameters of the supermassive black holes in particular parameters of the black hole in the Galactic Centre
Bats Respond to Very Weak Magnetic Fields
Tian, Lan-Xiang; Pan, Yong-Xin; Metzner, Walter; Zhang, Jin-Shuo; Zhang, Bing-Fang
2015-01-01
How animals, including mammals, can respond to and utilize the direction and intensity of the Earth’s magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae) can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5th of the natural intensity (i.e., 10 μT; the lowest field strength tested here), the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 μT), despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (P<0.05). Hence, N. plancyi is able to detect the direction of a magnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth’s magnetic field strength varied and the polarity reversed tens of times over the past fifty million years. PMID:25922944
Nonlinear superposition of strong gravitational field of compact stars
NASA Astrophysics Data System (ADS)
Chen, Shao-Guang
According to QFT it is deduced that the gravitation is likely to originate from the polarization effect of Dirac vacuum fluctuation (Chen Shao-Guang, Nuovo Cimento B 104, 611, 1989) . In Dirac vacuum the lowest-energy virtual neutrinos nu possess most number, which exert isotropic colliding pressure to isolated mass-point A (m) , the net force on A is zero. For another mass-point B (M) near A to obstruct nu flux shooting to A, the nu number along the line connecting A and B will decrease and destroy isotropic distribution of nu , which leads to not only the change in momentum P (produces net nu flux and net force Fp) but also the change in energy E or rest mass m (produces net force Fm) because in QFT the rest mass is not the bare mass but the physical mass of renormalization which contains nu with energy. From the definition of force: F ≡ d (m v) /d t = m ( d v / d t ) + v (d m / d t ) = Fp + Fm (1) , on A (or B) net force (quasi-Casimir pressure of weak interaction) is: F Q = Fp + Fm = - K (m M /r 2 )((r /r ) + (v /c )) (2). According to the change in masses caused by Bondi's inductive transfer of energy in GR (H. Bondi, Proc. R. Soc. London A 427, 249, 1990) and Eq. (1) a new gravitational formula is deduced: F G = Fp +Fm = - G (m M /r 2 )( (r /r ) + (v /c )) (3). F G is equivalent to Einstein's equation. Then we can solve the multi-bodies gravitational problems. K calculated from the weak-electromagnetism unified theory (W-EUT) has the same order of magnitude as experimental gravitational constant G. F G and F Q as a bridge joins QFT and GR. If K ≡ G, gravitational theory would be merged into W-EUT. The gravitational laws predicted by FG and F Q are identical except that F Q has quantum effects but F G has not, F G has Lense-Thirring effect but F Q has not. The change in masses of A and B caused by the nonlinearity of Einstein's equation or by mass renormalization of QFT will influence their forces on third object C (as self-shielding effect of gravities among objects or each parts of a object): F = - G∞ m M (1 - q ) r / r 3 = - G (r ) m M r / r 3 (4). Here G (r ) = G∞ (1 - q ), q = k M / r 2 = k D L S / r 2 . q is a positive shielding coefficient, G∞ is the gravitational constant when infinite distance between mass-point A and object B (q = 0 ). M / r 2 is the gravitational field strength of B in the place of A, D and L are the density and the thickness respectively, S is the cross section of B. S / r 2 is the solid angle of B subtends to A , k is a constant determined by experiments and called as the section of unit mass. From Stacey et al's experimental results kmu of nucleons to virtual neutrino mu is 4.7×10-19 cm2 g-1 .The section of single nucleon to electronic neutrino obtained by nuclear physics experiments is about 1.1×10-43 cm2 which divided by nucleon-mass is the section of unit mass kmue ≈6.6×10-20 cm2 g-1 . For the earth (L ≈104 km) as a obstructing layer qmue = 4.6×10-10 ; qmu = 3.3×10-9 . Therefore, the self-shielding effect of gravity can be generally ignored, but can not for the compact stars: A spherical shell of neutron (D large than 1014 g cm-3 ) as obstructing layer, when S / r 2 =1 and L=1 km then qmue =1 and qmu large than 1 (completely obstruct mue and mu ), i.e., the gravity from its inside and exterior will be completely shielded. It makes that a neutron star likes a empty shell then it may rapidly rotating and has not upper limit of masses and radii, which will influence the mechanisms of pulsars, quasars and X-rays generated at the surface of cooling and/or rapidly rotating compact stars.
NASA Computational Case Study: Modeling Planetary Magnetic and Gravitational Fields
NASA Technical Reports Server (NTRS)
Simpson, David G.; Vinas, Adolfo F.
2014-01-01
In this case study, we model a planet's magnetic and gravitational fields using spherical harmonic functions. As an exercise, we analyze data on the Earth's magnetic field collected by NASA's MAGSAT spacecraft, and use it to derive a simple magnetic field model based on these spherical harmonic functions.
Vacuum entanglement enhancement by a weak gravitational field
Cliche, M.; Kempf, A.
2011-02-15
Separate regions in space are generally entangled, even in the vacuum state. It is known that this entanglement can be swapped to separated Unruh-DeWitt detectors, i.e., that the vacuum can serve as a source of entanglement. Here, we demonstrate that, in the presence of curvature, the amount of entanglement that Unruh-DeWitt detectors can extract from the vacuum can be increased.
NASA Astrophysics Data System (ADS)
Harnois-Draps, Joachim; van Waerbeke, Ludovic
2015-07-01
Numerical N-body simulations play a central role in the assessment of weak gravitational lensing statistics, residual systematics and error analysis. In this paper, we investigate and quantify the impact of finite simulation volume on weak lensing two- and four-point statistics. These finite support (FS) effects are modelled for several estimators, simulation box sizes and source redshifts, and validated against a new large suite of 500 N-body simulations. The comparison reveals that our theoretical model is accurate to better than 5 per cent for the shear correlation function ?+(?) and its error. We find that the most important quantities for FS modelling are the ratio between the measured angle ? and the angular size of the simulation box at the source redshift, ?box(zs), or the multipole equivalent ?/?box(zs). When this ratio reaches 0.1, independently of the source redshift, the shear correlation function ?+ is suppressed by 5, 10, 20 and 25 per cent for Lbox = 1000, 500, 250 and 147 h-1 Mpc, respectively. The same effect is observed in ?-(?), but at much larger angles. This has important consequences for cosmological analyses using N-body simulations and should not be overlooked. We propose simple semi-analytic correction strategies that account for shape noise and survey masks, generalizable to any weak lensing estimator. From the same simulation suite, we revisit the existing non-Gaussian covariance matrix calibration of the shear correlation function, and propose a new one based on the 9-year Wilkinson Microwave Anisotropy Probe)+baryon acoustic oscillations+supernova cosmology. Our calibration matrix is accurate at 20 per cent down to the arcminute scale, for source redshifts in the range 0 < z < 3, even for the far off-diagonal elements. We propose, for the first time, a parametrization for the full ?- covariance matrix, also 20 per cent accurate for most elements.
Equilibrium of self-gravitating tori in spherical gravitational and dipolar magnetic fields
NASA Astrophysics Data System (ADS)
Trova, A.; Karas, V.; Slan, P.; Kov?, J.
2015-12-01
We investigate a new model for equilibria of self-gravitating fluid tori with electric charge that are embedded in gravitational potential and a dipolar magnetic field produced by the central mass. We find that the shape and the vertical structure of the massive torus are influenced by effects of self-gravity which were neglected in our previous work tep{slany13}. We show the impact of self-gravity on the morphology of figures of equilibrium, depending on the rotation of the fluid and the strength of the magnetic field.
Gravitational Fields with 2-Dimensional Killing Leaves and the Gravitational Interaction of Light
NASA Astrophysics Data System (ADS)
Vilasi, Gaetano
Gravitational fields invariant for a non Abelian Lie algebra generating a 2-dimensional distribution, are explicitly described. When the orthogonal distribution is integrable and the metric is not degenerate along the orbits, these solutions are parameterized either by solutions of a transcendental equation (the tortoise equation), or by solutions of Darboux equation. Metrics, corresponding to solutions of the tortoise equation, are characterized as those that admit a 3-dimensional Lie algebra of Killing fields with 2-dimensional leaves. It is shown that the remaining metrics represent nonlinear gravitational waves obeying to two nonlinearsuperposition laws. The energy and the polarization of this family of waves are explicitly evaluated; it is shown that they have spin-1 and their possible sources are also described. Old results by Tolman, Ehrenfest, Podolsky and Wheeler on the gravitational interaction of photons are naturally reinterpreted.
Residual symmetries of the gravitational field
NASA Astrophysics Data System (ADS)
Ayón-Beato, Eloy; Velázquez-Rodríguez, Gerardo
2016-02-01
We develop a geometric criterion that unambiguously characterizes the residual symmetries of a gravitational Ansatz. It also provides a systematic and effective computational procedure for finding all the residual symmetries of any gravitational Ansatz. We apply the criterion to several examples starting with the Collinson Ansatz for circular stationary axisymmetric spacetimes. We reproduce the residual symmetries already known for this Ansatz including their conformal symmetry, for which we identify the corresponding infinite generators spanning the two related copies of the Witt algebra. We also consider the noncircular generalization of this Ansatz and show how the noncircular contributions on the one hand break the conformal invariance and on the other hand enhance the standard translation symmetries of the circular Killing vectors to supertranslations depending on the direction along which the circularity is lost. As another application of the method, the well-known relation defining conjugate gravitational potentials introduced by Chandrasekhar, which makes possible the derivation of the Kerr black hole from a trivial solution of the Ernst equations, is deduced as a special point of the general residual symmetry of the Papapetrou Ansatz. In this derivation we emphasize how the election of Weyl coordinates, which determines the Papapetrou Ansatz, breaks also the conformal freedom of the stationary axisymmetric spacetimes. Additionally, we study AdS waves for any dimension generalizing the residual symmetries already known for lower dimensions and exhibiting a very complex infinite-dimensional Lie algebra containing three families: two of them span the semidirect sum of the Witt algebra and scalar supertranslations and the third generates vector supertranslations. Independently of this complexity we manage to comprehend the true meaning of the infinite connected group as the precise diffeomorphisms subgroup allowing to locally deform the AdS background into AdS waves.
Magnetic field-aligned plasma currents in gravitational fields
NASA Astrophysics Data System (ADS)
Garcia, O. E.; Leer, E.; Pcseli, H. L.; Trulsen, J. K.
2015-03-01
Analytical models are presented for currents along vertical magnetic field lines due to slow bulk electron motion in plasmas subject to a gravitational force. It is demonstrated that a general feature of this problem is a singularity in the plasma pressure force that develops at some finite altitude when a plasma that is initially in static equilibrium is set into slow motion. Classical fluid models thus do not allow general steady-state solutions for field-aligned currents. General solutions have to be non-stationary, varying on time scales of many periods of a plasma equivalent to the Brunt-Visl frequency. Except for very special choices of parameters, a steady-state solution exists only in an average sense. The conditions at large altitudes turn out to be extremely sensitive to even small changes in parameters at low altitudes. Low frequency fluctuations detected at large altitudes in the polar regions need not be caused by local low frequency instabilities, but merely reflect small fluctuations in conditions at low altitudes.
Contributions of Spherical Harmonics to Magnetic and Gravitational Fields
NASA Technical Reports Server (NTRS)
Roithmayr, Carlos M.
2004-01-01
Gravitational forces are of cardinal importance in the dynamics of spacecraft; magnetic attractions sometime play a significant role also, as was the case with the Long Duration Exposure Facility, and as is now true for the first segment of Space Station Freedom. Both satellites depend on gravitational moment and a device known as a magnetic damper to stabilize their orientation. Magnetic fields are mathematically similar to gravitational fields in one important respect: each can be regarded as a gradient of a potential function that, in turn, can be described as an infinite series of spherical harmonics. Consequently, the two fields can be computed, in part, with quantities that need only be evaluated once, resulting in a savings of time when both fields are needed. The objective of this material is to present magnetic field and gravitational force expressions, and point out the terms that belong to both this is accomplished in Section 1 and 2. Section 3 contains the deductive reasoning with which one obtains the expressions of interest. Finally, examples in Section 4 show these equations can be used to reproduce others that arise in connection with special cases such as the magnetic field produced by a tilted dipole, and gravitational force exerted by an oblate spheroid. The mathematics are discussed in the context of terrestrial fields; however, by substituting appropriate constants, the results can be made applicable to fields belonging to other celestial bodies. The expressions presented here share the characteristics of algorithms set forth for computing gravitational force. In particular, computation is performed speedily by means of recursion formulae, and the expressions do not suffer from the shortcoming of a singularity when evaluated at points that lie on the polar axis.
Using Gravitational Analogies to Introduce Elementary Electrical Field Theory Concepts
ERIC Educational Resources Information Center
Saeli, Susan; MacIsaac, Dan
2007-01-01
Since electrical field concepts are usually unfamiliar, abstract, and difficult to visualize, conceptual analogies from familiar gravitational phenomena are valuable for teaching. Such analogies emphasize the underlying continuity of field concepts in physics and support the spiral development of student understanding. We find the following four
Using Gravitational Analogies to Introduce Elementary Electrical Field Theory Concepts
ERIC Educational Resources Information Center
Saeli, Susan; MacIsaac, Dan
2007-01-01
Since electrical field concepts are usually unfamiliar, abstract, and difficult to visualize, conceptual analogies from familiar gravitational phenomena are valuable for teaching. Such analogies emphasize the underlying continuity of field concepts in physics and support the spiral development of student understanding. We find the following four…
Hydrodynamic representation of the Klein-Gordon-Einstein equations in the weak field limit
NASA Astrophysics Data System (ADS)
Surez, Abril; Chavanis, Pierre-Henri
2015-11-01
Using a generalization of the Madelung transformation, we derive the hydrodynamic representation of the Klein-Gordon-Einstein equations in the weak field limit. We consider a complex self-interacting scalar field with an arbitrary potential of the form V(|?|2). We compare the results with simplified models in which the gravitational potential is introduced by hand in the Klein-Gordon equation, and assumed to satisfy a (generalized) Poisson equation. Nonrelativistic hydrodynamic equations based on the Schrodinger-Poisson equations or on the Gross-Pitaevskii-Poisson equations are recovered in the limit c ? +?.
Probing Dark Energy via Weak Gravitational Lensing with the Supernova Acceleration Probe (SNAP)
Albert, J.; Aldering, G.; Allam, S.; Althouse, W.; Amanullah, R.; Annis, J.; Astier, P.; Aumeunier, M.; Bailey, S.; Baltay, C.; Barrelet, E.; Basa, S.; Bebek, C.; Bergstom, L.; Bernstein, G.; Bester, M.; Besuner, B.; Bigelow, B.; Blandford, R.; Bohlin, R.; Bonissent, A.; /Caltech /LBL, Berkeley /Fermilab /SLAC /Stockholm U. /Paris, IN2P3 /Marseille, CPPM /Marseille, Lab. Astrophys. /Yale U. /Pennsylvania U. /UC, Berkeley /Michigan U. /Baltimore, Space Telescope Sci. /Indiana U. /Caltech, JPL /Australian Natl. U., Canberra /American Astron. Society /Chicago U. /Cambridge U. /Saclay /Lyon, IPN
2005-08-08
SNAP is a candidate for the Joint Dark Energy Mission (JDEM) that seeks to place constraints on the dark energy using two distinct methods. The first, Type Ia SN, is discussed in a separate white paper. The second method is weak gravitational lensing, which relies on the coherent distortions in the shapes of background galaxies by foreground mass structures. The excellent spatial resolution and photometric accuracy afforded by a 2-meter space-based observatory are crucial for achieving the high surface density of resolved galaxies, the tight control of systematic errors in the telescope's Point Spread Function (PSF), and the exquisite redshift accuracy and depth required by this project. These are achieved by the elimination of atmospheric distortion and much of the thermal and gravity loads on the telescope. The SN and WL methods for probing dark energy are highly complementary and the error contours from the two methods are largely orthogonal. The nominal SNAP weak lensing survey covers 1000 square degrees per year of operation in six optical and three near infrared filters (NIR) spanning the range 350 nm to 1.7 {micro}m. This survey will reach a depth of 26.6 AB magnitude in each of the nine filters and allow for approximately 100 resolved galaxies per square arcminute, {approx} 3 times that available from the best ground-based surveys. Photometric redshifts will be measured with statistical accuracy that enables scientific applications for even the faint, high redshift end of the sample. Ongoing work aims to meet the requirements on systematics in galaxy shape measurement, photometric redshift biases, and theoretical predictions.
Weak gravitation waves in vacuum and in media: Taking nonlinearity into account
NASA Astrophysics Data System (ADS)
Efroimsky, Michael
1994-06-01
The relevance of the nonlinear nature of gravity waves has been pointed out, in the astrophysical context, in recent publications by Christodoulou and by Thorne, who studied the nonlinear contribution to the memory effect. In the cosmological context, the role of nonlinearity has been discovered by Salopek, who studied the evolution of the primordial cosmological perturbations. In this article, we use the weak-field approximation to derive, in the perturbative approach, the wave equation for pure gravity waves with nonlinear correction terms.
Accurate modeling of weak lensing with the stochastic gravitational lensing method
NASA Astrophysics Data System (ADS)
Kainulainen, Kimmo; Marra, Valerio
2011-01-01
We revise and extend the stochastic gravitational lensing method (the sGL method) first introduced by Kainulainen and Marra [Phys. Rev. DPRVDAQ1550-7998 80, 123020 (2009)10.1103/PhysRevD.80.123020]. Here we include a realistic halo-mass function and density profiles to model the distribution of mass between and within galaxies, galaxy groups, and galaxy clusters. We also introduce a modeling of the filamentary large-scale structures and a method to embed halos into these structures. We show that the sGL method naturally reproduces the weak lensing results for the Millennium simulation. The strength of the sGL method is that a numerical code based on it can compute the lensing probability distribution function (PDF) for a given inhomogeneous model universe in a few seconds. This makes it a useful tool to study how lensing depends on cosmological parameters and its impact on observations. The sGL method can also be used to simulate the effect of a wide array of systematic biases on the observable lensing PDF. As an example we show how simple selection effects may reduce the variance of the observed PDF, which could possibly mask opposite effects from very large-scale structures. We also show how a survey like the Joint Dark Energy Mission could constrain the lensing PDF relative to a given cosmological model. The updated turboGL code is available at turboGL.org.
Zhang Pengjie
2010-09-10
The galaxy intrinsic alignment is a severe challenge to precision cosmic shear measurement. We propose self-calibrating the induced gravitational shear-galaxy intrinsic ellipticity correlation (the GI correlation) in weak lensing surveys with photometric redshift measurements. (1) We propose a method to extract the intrinsic ellipticity-galaxy density cross-correlation (I-g) from the galaxy ellipticity-density measurement in the same redshift bin. (2) We also find a generic scaling relation to convert the extracted I-g correlation to the necessary GI correlation. We perform a concept study under simplified conditions and demonstrate its capability to significantly reduce GI contamination. We discuss the impact of various complexities on the two key ingredients of the self-calibration technique, namely the method for extracting the I-g correlation and the scaling relation between the I-g and the GI correlation. We expect that none of them will likely be able to completely invalidate the proposed self-calibration technique.
Anisotropic parametrized post-Newtonian gravitational metric field
NASA Technical Reports Server (NTRS)
Nordtvedt, K., Jr.
1976-01-01
The anisotropic generalization of the parameterized post-Newtonian (PPN) gravitational metric field is made for the case of theories with energy and momentum conservation laws. Such an anisotropic metric field will generally result in two-tensor or bimetric theories of gravity in an anisotropic universe. New anisotropic 3 x 3 spatial PPN matrices are introduced into the general metric expansion. Earth gravimeter measurements strongly restrict some anisotropies, while anisotropic inertial and gravitational mass for celestial bodies result from other combinations of the PPN matrices.
Using Jupiter's gravitational field to probe the Jovian convective dynamo.
Kong, Dali; Zhang, Keke; Schubert, Gerald
2016-01-01
Convective motion in the deep metallic hydrogen region of Jupiter is believed to generate its magnetic field, the strongest in the solar system. The amplitude, structure and depth of the convective motion are unknown. A promising way of probing the Jovian convective dynamo is to measure its effect on the external gravitational field, a task to be soon undertaken by the Juno spacecraft. We calculate the gravitational signature of non-axisymmetric convective motion in the Jovian metallic hydrogen region and show that with sufficiently accurate measurements it can reveal the nature of the deep convection. PMID:27005472
Biological effects due to weak magnetic field on plants
NASA Astrophysics Data System (ADS)
Belyavskaya, N. A.
2004-01-01
Throughout the evolution process, Earth's magnetic field (MF, about 50 μT) was a natural component of the environment for living organisms. Biological objects, flying on planned long-term interplanetary missions, would experience much weaker magnetic fields, since galactic MF is known to be 0.1-1 nT. However, the role of weak magnetic fields and their influence on functioning of biological organisms are still insufficiently understood, and is actively studied. Numerous experiments with seedlings of different plant species placed in weak magnetic field have shown that the growth of their primary roots is inhibited during early germination stages in comparison with control. The proliferative activity and cell reproduction in meristem of plant roots are reduced in weak magnetic field. Cell reproductive cycle slows down due to the expansion of G 1 phase in many plant species (and of G 2 phase in flax and lentil roots), while other phases of cell cycle remain relatively stabile. In plant cells exposed to weak magnetic field, the functional activity of genome at early pre-replicate period is shown to decrease. Weak magnetic field causes intensification of protein synthesis and disintegration in plant roots. At ultrastructural level, changes in distribution of condensed chromatin and nucleolus compactization in nuclei, noticeable accumulation of lipid bodies, development of a lytic compartment (vacuoles, cytosegresomes and paramural bodies), and reduction of phytoferritin in plastids in meristem cells were observed in pea roots exposed to weak magnetic field. Mitochondria were found to be very sensitive to weak magnetic field: their size and relative volume in cells increase, matrix becomes electron-transparent, and cristae reduce. Cytochemical studies indicate that cells of plant roots exposed to weak magnetic field show Ca 2+ over-saturation in all organelles and in cytoplasm unlike the control ones. The data presented suggest that prolonged exposures of plants to weak magnetic field may cause different biological effects at the cellular, tissue and organ levels. They may be functionally related to systems that regulate plant metabolism including the intracellular Ca 2+ homeostasis. However, our understanding of very complex fundamental mechanisms and sites of interactions between weak magnetic fields and biological systems is still incomplete and still deserve strong research efforts.
NASA Astrophysics Data System (ADS)
Chen, Shao-Guang
According to f =d(mv)/dt=m(dv/dt)+ v(dm/dt), a same gravitational formula had been de-duced from the variance in physical mass of QFT and from the variance in mass of inductive energy-transfer of GR respectively: f QF T = f GR = -G (mM/r2 )((r/r)+(v/c)) when their interaction-constants are all taken the experimental values (H05-0029-08, E15-0039-08). f QF T is the quasi-Casimir pressure of net virtual neutrinos ν 0 flux (after counteract contrary direction ν 0 ). f GR is equivalent to Einstein's equation, then more easy to solve it. The hypothesis of the equivalent principle is not used in f QF T , but required by f GR . The predictions of f QF T and f GR are identical except that f QF T has quantum effects but f GR has not and f GR has Lense-Thirring effect but f QF T has not. The quantum effects of gravitation had been verified by Nesvizhevsky et al with the ultracold neutrons falling in the earth's gravitational field in 2002. Yet Lense-Thirring effect had not been measured by GP-B. It shows that f QF T is essential but f GR is phenomenological. The origin problem of the basis geo-electric and geomagnetic fields can be solved with the positive-negative charge center separation caused by f QF T , but cannot by f GR . The de Broglie wavelength of an electron is longer than that of a nucleon, and the section is larger, so is the net ν 0 flux pressure. The pressures difference between ν 0 flux on the electron and on the nucleon is as an extra pressure solely exerted on the electrons by ν 0 flux, which causes a gravitational polarization of the positive-negative charge center separation and increases the static electric force from the nucleus to the electrons along the opposite direction of ν 0 flux to offset the extra pressure on the electrons. At the same time, there must be a polarized static electric reaction force from the electrons to the nucleus along ν 0 flux direction, just like transferring the extra ν 0 flux pressure of the electrons to the nucleus. Therefore, the extra ν 0 flux pressure exerted on the whole atom is not actually offset by the static electric force from the positive-negative charge separation, i.e., the gravitation will be dependent of the com-position of matter. That is certainly true in the interaction between two isolated mass-points. But nothing can exist without environment. The masses tested in Cavendish's experiment, Eotvos's experiment and other precise gravitational experiments are not isolated mass-points. The electric polarization by ν 0 flux makes the testing mass and around (brackets, walls, houses) become the electric dipoles. In a way of relays the polarization of charge separation will be transported to the edge of the body, and make it become the electric dipole with the positive and negative charge on its two surfaces and the electric neutrality in the center. The interaction between the electric dipoles finally transfers the extra ν 0 flux pressure on the electrons from a body being tested onto the bodies around, i.e., the static electric force from the polarization of the bodies around offsets the extra ν 0 flux pressure on the electrons of testing mass. Because the electromagnetic force is 30 more orders of magnitude stronger than the ν 0 flux weak force, the slightly polarization of the bodies around can completely offset the extra ν 0 flux pressure on the electrons. The compensating action of the static forces between electric dipoles is equiv-alent to the equal section in unit mass of an electron and a nucleon. That is to say, the ν 0 flux pressure gives the same force and displacement to the electron and nucleon just like no positive-negative charge separation. Therefore, for gravitation, the mass of an electron can be converted to a proton, which makes the atom like a particle of absolutely electric neutrality comprising all neutrons, i.e., the macro-gravitation of non-isolated bodies is corresponding to the section only contributed by nucleons in atom. Then no matter how many electrons there are in the atom, the force is always in direct proportion to the number of nucleons in the atom or to the total mass of all the electrons and the nucleus of this atom, i.e., the gravitation to be independent of the composition of matter (or the kind of atom).
Field theory on R× S 3 topology. VI: Gravitation
NASA Astrophysics Data System (ADS)
Carmeli, M.; Malin, S.
1987-04-01
We extend to curved space-time the field theory on R×S3 topology in which field equations were obtained for scalar particles, spin one-half particles, the electromagnetic field of magnetic moments, an SU2 gauge theory, and a Schrödinger-type equation, as compared to ordinary field equations that are formulated on a Minkowskian metric. The theory obtained is an angular-momentum representation of gravitation. Gravitational field equations are presented and compared to the Einstein field equations, and the mathematical and physical similarity and differences between them are pointed out. The problem of motion is discussed, and the equations of motion of a rigid body are developed and given explicitly. One result which is worth emphazing is that while general relativity theory yields Newton's law of motion in the lowest approximation, our theory gives Euler's equations of motion for a rigid body in its lowest approximation.
The physical effects in the gravitational field of black holes
Markov, M.A.
1987-01-01
This book contains five sections each with several chapters. The section headings are: The Physical Effects in the Gravitational Field of Black Holes, Vacuum Polarization of Massless Fields in Black Holes, Certain Properties of a Nonsingular Model of a Black Hole, The Quantum Effect of Scalar Field Radiation by an Accerlerated Body with a Mirror Boundary, and One-Loop Calculations of Photon Splitting in Relativistic Quantum Plasma by Green's Function Technique.
Propagation of light in the stationary field of multipole gravitational lens
NASA Astrophysics Data System (ADS)
Kopeikin, S. M.
1997-05-01
A rigorous mathematical formalism for calculating the propagation of light rays in the stationary post-Newtonian field of an isolated celestial body (or system of bodies) considered as a gravitational lens having a complex multipole structure is developed. Symmetric trace-free tensors are used in the definition of gravitational multipoles instead of the less convenient (in general situations) scalar and vector spherical harmonics. Two types of perturbations of light rays, caused correspondingly by the mass and spin multipoles, are analyzed in full detail. A new simple method of integration for the equations of light propagation is proposed. This method enables us for the first time to obtain complete expressions both for the relativistic time delay and for the angle of the total deflection of light in any order of multipole perturbations without restriction. The results thus obtained can be applied to the interpretation of the secondary weak gravitational lens effects produced by the solar system bodies, stars, binary pulsars, and galaxies where the influence of higher-order multipoles on the propagation of null rays may be important and measurable. The methods developed in the paper can be also applied to physical optics of multipole electromagnetic lenses and for calculation of propagation of gravitational waves through the curved space-time. As a particular application of the method the generalized equation for a multipole gravitational lens is derived using Cartesian coordinates and symmetric transverse-traceless tensors.
Hirata, Christopher M.; Cutler, Curt
2010-06-15
Gravitational wave sources are a promising cosmological standard candle because their intrinsic luminosities are determined by fundamental physics (and are insensitive to dust extinction). They are, however, affected by weak lensing magnification due to the gravitational lensing from structures along the line of sight. This lensing is a source of uncertainty in the distance determination, even in the limit of perfect standard candle measurements. It is commonly believed that the uncertainty in the distance to an ensemble of gravitational wave sources is limited by the standard deviation of the lensing magnification distribution divided by the square root of the number of sources. Here we show that by exploiting the non-Gaussian nature of the lensing magnification distribution, we can improve this distance determination, typically by a factor of 2-3; we provide a fitting formula for the effective distance accuracy as a function of redshift for sources where the lensing noise dominates.
Scalar field as a time variable during gravitational evolution
NASA Astrophysics Data System (ADS)
Nakonieczna, Anna; Lewandowski, Jerzy
2015-09-01
Using a scalar field as an intrinsic "clock" while investigating the dynamics of gravitational systems has been successfully pursued in various researches on the border between classical and quantum gravity. The objective of our research was to check explicitly whether the scalar field can serve as a time variable during dynamical evolution of the matter-geometry system, especially in regions of high curvature, which are essential from the perspective of quantum gravity. For this purpose, we analyzed a gravitational collapse of a self-interacting scalar field within the framework of general relativity. The obtained results indicated that the hypersurfaces of constant scalar field are spacelike in dynamical regions nearby the singularities formed during the investigated process. The scalar field values change monotonically in the areas, in which the constancy hypersurfaces are spacelike.
Lorentz transformations in the presence of a uniform gravitational field.
NASA Technical Reports Server (NTRS)
Broucke, R.
1971-01-01
This article describes a Lorentz-like transformation between a fixed frame and an inertial frame that is free falling due to the presence of a uniform gravitation field. The application to the clock paradox problem and some connections with similar works are also discussed.
Nbody Simulations and Weak Gravitational Lensing using new HPC-Grid resources: the PI2S2 project
NASA Astrophysics Data System (ADS)
Becciani, U.; Antonuccio-Delogu, V.; Costa, A.; Comparato, M.
2008-08-01
We present the main project of the new grid infrastructure and the researches, that have been already started in Sicily and will be completed by next year. The PI2S2 project of the COMETA consortium is funded by the Italian Ministry of University and Research and will be completed in 2009. Funds are from the European Union Structural Funds for Objective 1 regions. The project, together with a similar project called Trinacria GRID Virtual Laboratory (Trigrid VL), aims to create in Sicily a computational grid for e-science and e-commerce applications with the main goal of increasing the technological innovation of local enterprises and their competition on the global market. PI2S2 project aims to build and develop an e-Infrastructure in Sicily, based on the grid paradigm, mainly for research activity using the grid environment and High Performance Computer systems. As an example we present the first results of a new grid version of FLY a tree Nbody code developed by INAF Astrophysical Observatory of Catania, already published in the CPC program Library, that will be used in the Weak Gravitational Lensing field.
Substructure in the Hubble Frontier Fields clusters from weak lensing flexion measurements
NASA Astrophysics Data System (ADS)
Rexroth, Markus
2015-08-01
Flexion is the second order weak gravitational lensing effect which is responsible for the arclike appearance of lensed sources. Its strong signal in the intermediate regime and the orthogonality to the shear field make flexion an ideal complement to today's strong and weak lensing measurements. Furthermore, its high sensitivity to local density peaks makes it a great tool for detecting substructure and increasing the resolution of mass maps. The strength of the Hubble Frontier Fields clusters and the high quality of the data make these objects a prime target for flexion measurements. We present an automated measurement pipeline and substructure constraints from its application to the clusters MACSJ0416.1-2403 and Abell 2744.
Novikov, V V; Ponomarev, V O; Novikov, G V; Kuvichkin, V V; Iablokova, E V; Fesenko, E E
2010-01-01
A number of effects of weak combined (static and alternating) magnetic fields with an alternating component of tens and hundreds nT at a collinear static field of 42 microT, which is equivalent to the geomagnetic field, have been found: the activation of fission and regeneration of planarians Dugesia tigrina, the inhibition of the growth of the Ehrlich ascites carcinoma in mice, the stimulation of the production of the tumor necrosis factor by macrophages, a decrease in the protection of chromatin against the action of DNase 1, and the enhancement of protein hydrolysis in systems in vivo and in vitro. The frequency and amplitude ranges for the alternating component of weak combined magnetic fields have been determined at which it affects various biological systems. Thus, the optimal amplitude at a frequency of 4.4 Hz is 100 nT (effective value); at a frequency of 16.5 Hz, the range of effective amplitudes is broader, 150-300 nT; and at a frequency of 1 (0.5) Hz, it is 300 nT. The sum of close frequencies (e.g., 16 and 17 Hz) produces a similar biological effect as the product of the modulating (0.5 Hz) and carrying frequencies (16.5 Hz), which is explained by the ratio A = A0sin omega1t + A0sin omega2t = A0sin(omega1 + omega2)t/2cos(omega1 - omega2)t/2. The efficiency of magnetic signals with pulsations (the sum of close frequencies) is more pronounced than that of sinusoidal frequencies. These data may indicate the presence of several receptors of weak magnetic fields in biological systems and, as a consequence, a higher efficiency of the effect at the simultaneous adjustment to these frequencies by the field. Even with consideration of these facts, the mechanism of the biological action of weak combined magnetic fields remains still poorly understood. PMID:20968074
Diffusion of relativistic gas mixtures in gravitational fields
NASA Astrophysics Data System (ADS)
Kremer, Gilberto M.
2014-01-01
A mixture of relativistic gases of non-disparate rest masses in a Schwarzschild metric is studied on the basis of a relativistic Boltzmann equation in the presence of gravitational fields. A BGK-type model equation of the collision operator of the Boltzmann equation is used in order to compute the non-equilibrium distribution functions by the Chapman-Enskog method. The main focus of this work is to obtain Ficks law without the thermal-diffusion cross-effect. Ficks law has four contributions, two of them are the usual terms proportional to the gradients of concentration and pressure. The other two are of the same nature as those which appear in Fouriers law in the presence of gravitational fields and are related to an acceleration and a gravitational potential gradient, but unlike Fouriers law these last two terms are of non-relativistic order. Furthermore, it is shown that the coefficients of diffusion depend on the gravitational potential and become smaller than those in its absence.
Weak, Quiet Magnetic Fields Seen in the Venus Atmosphere
Zhang, T. L.; Baumjohann, W.; Russell, C. T.; Luhmann, J. G.; Xiao, S. D.
2016-01-01
The existence of a strong internal magnetic field allows probing of the interior through both long term changes of and short period fluctuations in that magnetic field. Venus, while Earth’s twin in many ways, lacks such a strong intrinsic magnetic field, but perhaps short period fluctuations can still be used to probe the electrical conductivity of the interior. Toward the end of the Venus Express mission, an aerobraking campaign took the spacecraft below the ionosphere into the very weakly electrically conducting atmosphere. As the spacecraft descended from 150 to 140 km altitude, the magnetic field became weaker on average and less noisy. Below 140 km, the median field strength became steady but the short period fluctuations continued to weaken. The weakness of the fluctuations indicates they might not be useful for electromagnetic sounding of the atmosphere from a high altitude platform such as a plane or balloon, but possibly could be attempted on a lander. PMID:27009234
Weak, Quiet Magnetic Fields Seen in the Venus Atmosphere.
Zhang, T L; Baumjohann, W; Russell, C T; Luhmann, J G; Xiao, S D
2016-01-01
The existence of a strong internal magnetic field allows probing of the interior through both long term changes of and short period fluctuations in that magnetic field. Venus, while Earth's twin in many ways, lacks such a strong intrinsic magnetic field, but perhaps short period fluctuations can still be used to probe the electrical conductivity of the interior. Toward the end of the Venus Express mission, an aerobraking campaign took the spacecraft below the ionosphere into the very weakly electrically conducting atmosphere. As the spacecraft descended from 150 to 140 km altitude, the magnetic field became weaker on average and less noisy. Below 140 km, the median field strength became steady but the short period fluctuations continued to weaken. The weakness of the fluctuations indicates they might not be useful for electromagnetic sounding of the atmosphere from a high altitude platform such as a plane or balloon, but possibly could be attempted on a lander. PMID:27009234
NASA Astrophysics Data System (ADS)
Chiba, J.
1984-11-01
Gravitational wave is produced whenever massive bodies accelerate under gravitational or nongravitational driving forces. The equations of Einstein's general theory of relativity have solutions in the weak field approximations which are very similar to those of electrodynamics. Analogies may be made between gravitational radiation and the electromagnetic radiation from accelerated charges although care has to be taken to recognize the limitations of such analogies. Because of the weakness of the Einstein's qravitational constant, the rate of energy radiated is normally very small. It is very desirable to be able to generate dynamic Newtonian gravitational field with sufficient intensity to be detected in the small laboratory. Experimental techniques used in generation and detection of dynamic Newtonian gravitational fields are reviewed and their application to Morse code communication in very near zone, as one approach to the gravitational wave technology.
Constraints on the shapes of galaxy dark matter haloes from weak gravitational lensing
NASA Astrophysics Data System (ADS)
van Uitert, E.; Hoekstra, H.; Schrabback, T.; Gilbank, D. G.; Gladders, M. D.; Yee, H. K. C.
2012-09-01
We study the shapes of galaxy dark matter haloes by measuring the anisotropy of the weak gravitational lensing signal around galaxies in the second Red-sequence Cluster Survey (RCS2). We determine the average shear anisotropy within the virial radius for three lens samples: the "all" sample, which contains all galaxies with 19 < mr' < 21.5, and the "red" and "blue" samples, whose lensing signals are dominated by massive low-redshift early-type and late-type galaxies, respectively. To study the environmental dependence of the lensing signal, we separate each lens sample into an isolated and clustered part and analyse them separately. We address the impact of several complications on the halo ellipticity measurement, including PSF residual systematics in the shape catalogues, multiple deflections, and the clustering of lenses. We estimate that the impact of these is small for our lens selections. Furthermore, we measure the azimuthal dependence of the distribution of physically associated galaxies around the lens samples. We find that these satellites preferentially reside near the major axis of the lenses, and constrain the angle between the major axis of the lens and the average location of the satellites to ⟨θ⟩ = 43.7° ± 0.3° for the "all" lenses, ⟨θ⟩ = 41.7° ± 0.5° for the "red" lenses and ⟨θ⟩ = 42.0° ± 1.4° for the "blue" lenses. We do not detect a significant shear anisotropy for the average "red" and "blue" lenses, although for the most elliptical "red" and "blue" galaxies it is marginally positive and negative, respectively. For the "all" sample, we find that the anisotropy of the galaxy-mass cross-correlation function ⟨f - f45⟩ = 0.23 ± 0.12, providing weak support for the view that the average galaxy is embedded in, and preferentially aligned with, a triaxial dark matter halo. Assuming an elliptical Navarro-Frenk-White profile, we find that the ratio of the dark matter halo ellipticity and the galaxy ellipticity fh = eh/eg = 1.50-1.01+1.03, which for a mean lens ellipticity of 0.25 corresponds to a projected halo ellipticity of eh = 0.38-0.25+0.26 if the halo and the lens are perfectly aligned. For isolated galaxies of the "all" sample, the average shear anisotropy increases to ⟨f-f45⟩ = 0.51-0.25+0.26 and fh = 4.73-2.05+2.17, whilst for clustered galaxies the signal is consistent with zero. These constraints provide lower limits on the average dark matter halo ellipticity, as scatter in the relative position angle between the galaxies and the dark matter haloes is expected to reduce the shear anisotropy by a factor ~2.
Weakly chiral networks and two-dimensional delocalized states in a weak magnetic field
NASA Astrophysics Data System (ADS)
Mkhitaryan, V. V.; Kagalovsky, V.; Raikh, M. E.
2010-04-01
We study numerically the localization properties of two-dimensional electrons in a weak perpendicular magnetic field. For this purpose we construct weakly chiral network models on the square and triangular lattices. The prime idea is to separate in space the regions with phase action of magnetic field, where it affects interference in course of multiple disorder scattering, and the regions with orbital action of magnetic field, where it bends electron trajectories. In our models, the disorder mixes counterpropagating channels on the links, while scattering matrices at the nodes describe exclusively the bending of electron trajectories. By artificially introducing a strong spread in the scattering strengths on the links (but keeping the average strength constant), we eliminate the interference and reduce the electron propagation over a network to a classical percolation problem. In this limit we establish the form of the disorder-magnetic field phase diagram. This diagram contains the regions with and without edge states, i.e., the regions with zero and quantized Hall conductivities. Taking into account that, for a given disorder, the scattering strength scales as inverse electron energy, we find agreement of our phase diagram with levitation scenario: energy separating the Anderson and quantum-Hall insulating phases floats up to infinity upon decreasing magnetic field. From numerical study, based on the analysis of quantum transmission of the network with random phases on the links, we conclude that the positions of the weak-field quantum-Hall transitions on the phase diagram are very close to our classical-percolation results. We checked that, in accord with the Pruisken theory, presence or absence of time-reversal symmetry on the links has no effect on the line of delocalization transitions. We also find that floating up of delocalized states in energy is accompanied by doubling of the critical exponent of the localization radius. We establish the origin of this doubling within classical-percolation analysis.
Why are living things sensitive to weak magnetic fields?
Liboff, Abraham R
2014-09-01
There is evidence for robust interactions of weak ELF magnetic fields with biological systems. Quite apart from the difficulties attending a proper physical basis for such interactions, an equally daunting question asks why these should even occur, given the apparent lack of comparable signals in the long-term electromagnetic environment. We suggest that the biological basis is likely to be found in the weak (∼50 nT) daily swing in the geomagnetic field that results from the solar tidal force on free electrons in the upper atmosphere, a remarkably constant effect exactly in phase with the solar diurnal change. Because this magnetic change is locked into the solar-derived everyday diurnal response in living things, one can argue that it acts as a surrogate for the solar variation, and therefore plays a role in chronobiological processes. This implies that weak magnetic field interactions may have a chronodisruptive basis, homologous to the more familiar effects on the biological clock arising from sleep deprivation, phase-shift employment and light at night. It is conceivable that the widespread sensitivity of biological systems to weak ELF magnetic fields is vestigially derived from this diurnal geomagnetic effect. PMID:23915203
Gravitation Field Calculations on a Dynamic Lattice by Distributed Computing
NASA Astrophysics Data System (ADS)
Mhnen, Petri; Punkka, Veikko
A new method of calculating numerically time evolution of a gravitational field in General Relatity is introduced. Vierbein (tetrad) formalism, dynamic lattice and massively parallelized computation are suggested as they are expected to speed up the calculations considerably and facilitate the solution of problems previously considered too hard to be solved, such as the time evolution of a system consisting of two or more black holes or the structure of worm holes.
Gravitational field calculations on a dynamic lattice by distributed computing.
NASA Astrophysics Data System (ADS)
Mhnen, P.; Punkka, V.
A new method of calculating numerically time evolution of a gravitational field in general relativity is introduced. Vierbein (tetrad) formalism, dynamic lattice and massively parallelized computation are suggested as they are expected to speed up the calculations considerably and facilitate the solution of problems previously considered too hard to be solved, such as the time evolution of a system consisting of two or more black holes or the structure of worm holes.
A New Weak Field Double Resonance NMR Spectrometer
NASA Astrophysics Data System (ADS)
Akay, Cengiz; Yaliner, Ayta
1995-03-01
Weak field NMR and double resonance spectrometers are mostly homemade. In this work, some electronic units of such a spectrometer operating at 1.437 mT were designed and realized by including new integrated circuits: an audio generator, digital sweep generator, digital additional field and delay unit, Quartz generator, NMR detector(Q-meter), AF-narrowband amplifier, phase shifter and phase sensitive detector.
Improved routing strategy based on gravitational field theory
NASA Astrophysics Data System (ADS)
Song, Hai-Quan; Guo, Jin
2015-10-01
Routing and path selection are crucial for many communication and logistic applications. We study the interaction between nodes and packets and establish a simple model for describing the attraction of the node to the packet in transmission process by using the gravitational field theory, considering the real and potential congestion of the nodes. On the basis of this model, we propose a gravitational field routing strategy that considers the attractions of all of the nodes on the travel path to the packet. In order to illustrate the efficiency of proposed routing algorithm, we introduce the order parameter to measure the throughput of the network by the critical value of phase transition from a free flow phase to a congested phase, and study the distribution of betweenness centrality and traffic jam. Simulations show that, compared with the shortest path routing strategy, the gravitational field routing strategy considerably enhances the throughput of the network and balances the traffic load, and nearly all of the nodes are used efficiently. Project supported by the Technology and Development Research Project of China Railway Corporation (Grant No. 2012X007-D) and the Key Program of Technology and Development Research Foundation of China Railway Corporation (Grant No. 2012X003-A).
Endogenous Cortical Oscillations Constrain Neuromodulation by Weak Electric Fields
Schmidt, Stephen L.; Iyengar, Apoorva K.; Foulser, A. Alban; Boyle, Michael R.; Fröhlich, Flavio
2014-01-01
Background Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation modality that may modulate cognition by enhancing endogenous neocortical oscillations with the application of sine-wave electric fields. Yet, the role of endogenous network activity in enabling and shaping the effects of tACS has remained unclear. Objective We combined optogenetic stimulation and multichannel slice electrophysiology to elucidate how the effect of weak sine-wave electric field depends on the ongoing cortical oscillatory activity. We hypothesized that the structure of the response to stimulation depended on matching the stimulation frequency to the endogenous cortical oscillation. Methods We studied the effect of weak sine-wave electric fields on oscillatory activity in mouse neocortical slices. Optogenetic control of the network activity enabled the generation of in vivo like cortical oscillations for studying the temporal relationship between network activity and sine-wave electric field stimulation. Results Weak electric fields enhanced endogenous oscillations but failed to induce a frequency shift of the ongoing oscillation for stimulation frequencies that were not matched to the endogenous oscillation. This constraint on the effect of electric field stimulation imposed by endogenous network dynamics was limited to the case of weak electric fields targeting in vivo-like network dynamics. Together, these results suggest that the key mechanism of tACS may be enhancing but not overriding of intrinsic network dynamics. Conclusion Our results contribute to understanding the inconsistent tACS results from human studies and propose that stimulation precisely adjusted in frequency to the endogenous oscillations is key to rational design of non-invasive brain stimulation paradigms. PMID:25129402
The MOG weak field approximation and observational test of galaxy rotation curves
NASA Astrophysics Data System (ADS)
Moffat, J. W.; Rahvar, S.
2013-12-01
As an alternative to dark matter models, Modified Gravity (MOG) theory is a covariant modification of Einstein gravity. The theory introduces two additional scalar fields and one vector field. The aim is to explain the dynamics of astronomical systems based only on their baryonic matter. The effect of the vector field in the theory resembles a Lorentz force where each particle has a charge proportional to its inertial mass. The weak field approximation of MOG is derived by perturbing the metric and the fields around Minkowski space-time. We obtain an effective gravitational potential which yields the Newtonian attractive force plus a repulsive Yukawa force. This potential, in addition to the Newtonian gravitational constant, GN, has two additional constant parameters ? and ?. We use The H I Nearby Galaxy Survey catalogue of galaxies and fix the two parameters ? and ? of the theory to be ? = 8.89 0.34 and ? = 0.042 0.004 kpc-1. We then apply the effective potential with the fixed universal parameters to the Ursa Major catalogue of galaxies and obtain good fits to galaxy rotation curve data with an average value of
Apparatus and method for producing an artificial gravitational field
NASA Technical Reports Server (NTRS)
Mccanna, Jason (Inventor)
1993-01-01
An apparatus and method is disclosed for producing an artificial gravitational field in a spacecraft by rotating the same around a spin axis. The centrifugal force thereby created acts as an artificial gravitational force. The apparatus includes an engine which produces a drive force offset from the spin axis to drive the spacecraft towards a destination. The engine is also used as a counterbalance for a crew cabin for rotation of the spacecraft. Mass of the spacecraft, which may include either the engine or crew cabin, is shifted such that the centrifugal force acting on that mass is no longer directed through the center of mass of the craft. This off-center centrifugal force creates a moment that counterbalances the moment produced by the off-center drive force to eliminate unwanted rotation which would otherwise be precipitated by the offset drive force.
Quantum limit on time measurement in a gravitational field
NASA Astrophysics Data System (ADS)
Sinha, Supurna; Samuel, Joseph
2015-01-01
Good clocks are of importance both to fundamental physics and for applications in astronomy, metrology and global positioning systems. In a recent technological breakthrough, researchers at NIST have been able to achieve a stability of one part in 1018 using an ytterbium clock. This naturally raises the question of whether there are fundamental limits to time keeping. In this article we point out that gravity and quantum mechanics set a fundamental limit on the fractional frequency uncertainty of clocks. This limit comes from a combination of the uncertainty relation, the gravitational redshift and the relativistic time dilation effect. For example, a single ion aluminium clock in a terrestrial gravitational field cannot achieve a fractional frequency uncertainty better than one part in 1022. This fundamental limit explores the interaction between gravity and quantum mechanics on a laboratory scale.
Hubble Frontier Fields : ``A New Era for Gravitational Lensing''
NASA Astrophysics Data System (ADS)
Jauzac, Mathilde; Eckert, Dominique; Jullo, Eric; Richard, Johan; Ebeling, Harald; Kneib, Jean-Paul; Limousin, Marceau; Atek, Hakim; Natarajan, Priyamvada; Rexroth, Markus
2015-08-01
The Hubble Frontier Fields (HFF) initiative constitutes the largest commitment ever of HST time to the exploration of the distant Universe via gravitational lensing by massive galaxy clusters.I will present the new gravitational lensing pictures of the first HFF complex clusters. We have demonstrated that we are now able to `weight’ these clusters' cores down to the percent level precision (recently published works), serving our quest for the high-redshift Universe.However, while the depth of these dataset makes these clusters amazing Cosmic Telescopes, it also enables us to get an unprecedented understanding of the cluster physics.Therefore, presenting the case of MACSJ0416 and Abell 2744, I will demonstrate the importance of such high-quality data to analyse the merging/dynamical history of the cluster itself while comparing dark matter, light and gas distributions.
Nematic ordering of rigid rods in a gravitational field
NASA Astrophysics Data System (ADS)
Baulin, Vladimir A.; Khokhlov, Alexei R.
1999-09-01
The isotropic-to-nematic transition in an athermal solution of long rigid rods subject to a gravitational (or centrifugal) field is theoretically considered in the Onsager approximation. The new feature emerging in the presence of gravity is a concentration gradient that coupled with the nematic ordering. For rodlike molecules this effect becomes noticeable at centrifugal acceleration g~103-104 m/s2, while for biological rodlike objects, such as tobacco mosaic virus, the effect is important even for normal gravitational acceleration conditions. Rods are concentrated near the bottom of the vessel, which sometimes leads to gravity induced nematic ordering. The concentration range corresponding to phase separation increases with increasing g. In the region of phase separation the local rod concentration, as well as the order parameter, follow a step function with height.
Weak magnetic fields in central stars of planetary nebulae?
NASA Astrophysics Data System (ADS)
Steffen, M.; Hubrig, S.; Todt, H.; Schller, M.; Hamann, W.-R.; Sandin, C.; Schnberner, D.
2014-10-01
Context. It is not yet clear whether magnetic fields play an essential role in shaping planetary nebulae (PNe), or whether stellar rotation alone and/or a close binary companion, stellar or substellar, can account for the variety of the observed nebular morphologies. Aims: In a quest for empirical evidence verifying or disproving the role of magnetic fields in shaping planetary nebulae, we follow up on previous attempts to measure the magnetic field in a representative sample of PN central stars. Methods: We obtained low-resolution polarimetric spectra with FORS 2 installed on the Antu telescope of the VLT for a sample of 12 bright central stars of PNe with different morphologies, including two round nebulae, seven elliptical nebulae, and three bipolar nebulae. Two targets are Wolf-Rayet type central stars. Results: For the majority of the observed central stars, we do not find any significant evidence for the existence of surface magnetic fields. However, our measurements may indicate the presence of weak mean longitudinal magnetic fields of the order of 100 Gauss in the central star of the young elliptical planetary nebula IC 418 as well as in the Wolf-Rayet type central star of the bipolar nebula Hen 2-113 and the weak emission line central star of the elliptical nebula Hen 2-131. A clear detection of a 250 G mean longitudinal field is achieved for the A-type companion of the central star of NGC 1514. Some of the central stars show a moderate night-to-night spectrum variability, which may be the signature of a variable stellar wind and/or rotational modulation due to magnetic features. Conclusions: Since our analysis indicates only weak fields, if any, in a few targets of our sample, we conclude that strong magnetic fields of the order of kG are not widespread among PNe central stars. Nevertheless, simple estimates based on a theoretical model of magnetized wind bubbles suggest that even weak magnetic fields below the current detection limit of the order of 100 G may well be sufficient to contribute to the shaping of the surrounding nebulae throughout their evolution. Our current sample is too small to draw conclusions about a correlation between nebular morphology and the presence of stellar magnetic fields. Based on observations obtained at the European Southern Observatory, Paranal, Chile (ESO program No. 088.D-0425(A)).
Weak MHD discontinuities in a radiation-induced flow field
NASA Astrophysics Data System (ADS)
Ram, R.; Rai, A.; Upadhyay, R. P.
1984-07-01
The growth of MHD discontinuities in a radiation-induced flow field at very high temperature is studied. The growth and decay properties of the weak MHD discontinuities are discussed in terms of the influences of a time-dependent gasdynamic field, a radiation field, and a magnetic field with finite electrical conductivity. The effects of thermal radiation and conduction on the global behavior of the discontinuities is analyzed under a quasi-equilibrium and quasi-isotropic hypothesis concerning the differential approximation to a radiative heat transfer equation. It is shown that the time-dependent radiation field gives rise to a radiation-induced wave which has a small effect on the nonrelativistic flow properties of the gasdynamic field. Radiation stresses resist the steepening tendency of a compressive weak wave and stabilize it, whereas thermal conduction effects tend to destabilize the wave. The cases of diverging and converging waves are considered separately in order to determine when a shock discontinuity or a caustic will be formed or disallowed under curvature effects.
Weak-field quantum Hall transition: microscopic verification
NASA Astrophysics Data System (ADS)
Mkhitaryan, Vagharsh; Kagalovsky, Victor; Raikh, Mikhail
2010-03-01
Levitation scenario: the higher is the Fermi level the lower is the magnetic field at which transition into ?xy=1 quantum Hall phase takes place, was put forward by Khmelnitskii more than 25 years ago. It was based on field-theoretical arguments. While zero-field complete localization of 2D electron states even at high energies was confirmed by numerical treatment of the Anderson Hamiltonian, no microscopic description of low-field quantum Hall transition existed so far. We constructed a weakly-chiral network model [Phys. Rev. Lett. 103, 066801 (2009)] which, depending on node parameters, captures both the Anderson insulator (?xy=0 ) phase and the quantum Hall (?xy=1) phase. Numerical analysis of this model, as well as analytical treatment of its classical limit, are in full agreement with each other; they both reveal delocalization transition in non- quantizing magnetic field, where electron trajectories are only slightly curved. At low-field transition, electron states can be viewed as two weakly coupled by disorder Chalker-Coddington networks, with opposite chiralities.
Saturn's fast spin determined from its gravitational field and oblateness.
Helled, Ravit; Galanti, Eli; Kaspi, Yohai
2015-04-01
The alignment of Saturn's magnetic pole with its rotation axis precludes the use of magnetic field measurements to determine its rotation period. The period was previously determined from radio measurements by the Voyager spacecraft to be 10h39min22.4s (ref. 2). When the Cassini spacecraft measured a period of 10h 47min6s, which was additionally found to change between sequential measurements, it became clear that the radio period could not be used to determine the bulk planetary rotation period. Estimates based upon Saturn's measured wind fields have increased the uncertainty even more, giving numbers smaller than the Voyager rotation period, and at present Saturn's rotation period is thought to be between 10h32min and 10h47min, which is unsatisfactory for such a fundamental property. Here we report a period of 10h32min45s46s, based upon an optimization approach using Saturn's measured gravitational field and limits on the observed shape and possible internal density profiles. Moreover, even when solely using the constraints from its gravitational field, the rotation period can be inferred with a precision of several minutes. To validate our method, we applied the same procedure to Jupiter and correctly recovered its well-known rotation period. PMID:25807487
Analog of electric and magnetic fields in stationary gravitational systems
Embacher, F.
1984-08-01
Newtonian and Machian aspects of the stationary gravitational field are brought into formal analogy with a stationry electromagnetic field. The electromagnetic vector potential equals (up to a factor) the timelike Killing vector field. The current density is given by the contraction of the Killing vector with the Ricci tensor. A coordinate-dependent split in electric and magnetic field vectors is given, and some results of classical electrodynamics are used to illustrate the analogy. In the linearized theory, the usual Maxwell equations are obtained. The analogy also holds from the point of view of particle motion. The geodesic equation is brought into a special form that exhibits an analog to the Lorentz force. Two examples (which have played an important role in the theoretical discovery of Machian effects) are considered.
Two-dimensional colloidal mixtures in magnetic and gravitational fields
NASA Astrophysics Data System (ADS)
Löwen, H.; Horn, T.; Neuhaus, T.; ten Hagen, B.
2013-11-01
This mini-review is concerned with two-dimensional colloidal mixtures exposed to various kinds of external fields. By a magnetic field perpendicular to the plane, dipole moments are induced in paramagnetic particles which give rise to repulsive interactions leading to complex crystalline alloys in the composition-asymmetry diagram. A quench in the magnetic field induces complex crystal nucleation scenarios. If exposed to a gravitational field, these mixtures exhibit a brazil-nut effect and show a boundary layering which is explained in terms of a depletion bubble picture. The latter persists for time-dependent gravity ("colloidal shaking"). Finally, we summarize crystallization effects when the second species is frozen in a disordered matrix which provides obstacles for the crystallizing component.
NASA Technical Reports Server (NTRS)
Eby, P. B.
1978-01-01
The construction of a clock based on the beta decay process is proposed to test for any violations by the weak interaction of the strong equivalence principle bu determining whether the weak interaction coupling constant beta is spatially constant or whether it is a function of gravitational potential (U). The clock can be constructed by simply counting the beta disintegrations of some suitable source. The total number of counts are to be taken a measure of elapsed time. The accuracy of the clock is limited by the statistical fluctuations in the number of counts, N, which is equal to the square root of N. Increasing N gives a corresponding increase in accuracy. A source based on the electron capture process can be used so as to avoid low energy electron discrimination problems. Solid state and gaseous detectors are being considered. While the accuracy of this type of beta decay clock is much less than clocks based on the electromagnetic interaction, there is a corresponding lack of knowledge of the behavior of beta as a function of gravitational potential. No predictions from nonmetric theories as to variations in beta are available as yet, but they may occur at the U/sg C level.
Numerical Tests of Fast Reconnection in Weakly Stochastic Magnetic Fields
NASA Astrophysics Data System (ADS)
Kowal, Grzegorz; Lazarian, A.; Vishniac, E. T.; Otmianowska-Mazur, K.
2009-07-01
We study the effects of turbulence on magnetic reconnection using three-dimensional direct numerical simulations. This is the first attempt to test a model of fast magnetic reconnection in the presence of weak turbulence proposed by Lazarian & Vishniac. This model predicts that weak turbulence, which is generically present in most astrophysical systems, enhances the rate of reconnection by reducing the transverse scale for reconnection events and by allowing many independent flux reconnection events to occur simultaneously. As a result, the reconnection speed becomes independent of Ohmic resistivity and is determined by the magnetic field wandering induced by turbulence. We test the dependence of the reconnection speed on turbulent power, the energy injection scale, and resistivity. We apply the open and experiment with the outflow boundary conditions in our numerical model and discuss the advantages and drawbacks of various setups. To test our results, we also perform simulations of turbulence with the same outflow boundaries but without a large-scale field reversal, thus without large-scale reconnection. To quantify the reconnection speed we use both an intuitive definition, i.e., the speed of the reconnected flux inflow, and a more sophisticated definition based on a formally derived analytical expression. Our results confirm the predictions of the Lazarian and Vishniac model. In particular, we find that the reconnection speed is proportional to the square root of the injected power, as predicted by the model. The dependence on the injection scale for some of our models is a bit weaker than expected, i.e., l 3/4 inj, compared to the predicted linear dependence on the injection scale, which may require some refinement of the model or may be due to effects such as the finite size of the excitation region, which are not a part of the model. The reconnection speed was found to depend on the expected rate of magnetic field wandering and not on the magnitude of the guide field. In our models, we see no dependence on the guide field when its strength is comparable to the reconnected component. More importantly, while in the absence of turbulence we successfully reproduce the Sweet-Parker scaling of reconnection, in the presence of turbulence we do not observe any dependence on Ohmic resistivity, confirming that the reconnection of the weakly stochastic field is fast. We also do not observe a dependence on anomalous resistivity, which suggests that the presence of anomalous effects, e.g., Hall MHD effects, may be irrelevant for astrophysical systems with weakly stochastic magnetic fields.
Dynamics of extended spinning masses in a gravitational field
Mashhoon, Bahram; Singh, Dinesh
2006-12-15
We develop a first-order approximation method for the influence of spin on the motion of extended spinning test masses in a gravitational field. This approach is illustrated for approximately circular equatorial motion in the exterior Kerr spacetime. In this case, the analytic results for the first-order approximation are compared to the numerical integration of the exact system and the limitations of the first-order results are pointed out. Furthermore, we employ our analytic results to illustrate the gravitomagnetic clock effect for spinning particles.
The Gravitational Fields of the Galilean Satellites -- Revisited
NASA Astrophysics Data System (ADS)
Jacobson, Robert A.
2013-10-01
One of the major scientific results from the Galileo mission to the Jovian system was the determination of the gravitational fields of the Galilean satellites. Schubert et al. summarize those results in chapter 13 of Jupiter: The planet, satellites and magnetosphere (Bagenal, Dowling, and McKinnon, eds., Cambridge U. Press, 2004). As a part of our recent update of the ephemerides of the Galilean satellites, we redetermined the satellite gravitational fields from the Galileo data. Our reprocessing of the data included, for the first time, calibrations for the effects of Io's plasma torus. We also removed some close encounter data at Europa and Callisto which was corrupted by the encountered satellite ionosphere. In fitting the data we employed a data whitening algorithm, developed for Cassini gravity science data processing, which takes into account the effect of the solar plasma on the Doppler data. Our new results confirm the previous ones for Io and Europa; the Io torus has a negligible effect on the fit to the Io encounter data. However, for Ganymede we found that the data whitening removes the data signature which was previous attributed to mass anomalies (Palguta et al. 2006, Icarus 180), and for Callisto we found that removing the ionosphere corruption significantly reduced the J2. Our overall conclusion is that a quadrupole field in hydrostatic equilibrium is sufficient to fit the data for all four satellites.
5th International School on Field Theory and Gravitation
NASA Astrophysics Data System (ADS)
Following the philosophy that the International School on Field Theory and Gravitation must be held each three years in different Brazilian Universities and, if possible, in different brazilian states, the next meeting will take place at Physics Institute of Universidade Federal do Mato Grosso, UFMT, Cuiab city on April, 20-24/2009 very close to the beautiful Pantanal and Chapada dos Guimares area. The goal of the meeting is to promote a greater integration among many physicists from the local university, UFMT, Co-organizing institutions in Brasil and foreign countries such as Canada, USA, Italy, China, England, Swiss, Spain, Brazil and others; to stimulate the organization of scientific events in our physics Institute and thus contributing to local research activities; to exhibit different fields of physics and to stimulate new lines of theoretical research and technological developments in the Universidade Federal do Mato Grosso, UFMT. Finally, we make efforts to promote the development of advanced studies, taking it to the present core of research in a strong process of affirmation of new lines of theoretical studies in our Physics Institute. To this, we invite colleagues, collaborators, researchers, students, and friends to attend this fifth edition of International School on Field Theory and gravitation-2009.
NASA Astrophysics Data System (ADS)
Jee, Myungkook James
2006-06-01
Clusters of galaxies, the largest gravitationally bound objects in the Universe, are useful tracers of cosmic evolution, and particularly detailed studies of still-forming clusters at high-redshifts can considerably enhance our understanding of the structure formation. We use two powerful methods that have become recently available for the study of these distant clusters: spaced- based gravitational weak-lensing and high-resolution X-ray observations. Detailed analyses of five high-redshift (0.8 < z < 1.3) clusters are presented based on the deep Advanced Camera for Surveys (ACS) and Chandra X-ray images. We show that, when the instrumental characteristics are properly understood, the newly installed ACS on the Hubble Space Telescope (HST) can detect subtle shape distortions of background galaxies down to the limiting magnitudes of the observations, which enables the mapping of the cluster dark matter in unprecedented high-resolution. The cluster masses derived from this HST /ACS weak-lensing study have been compared with those from the re-analyses of the archival Chandra X-ray data. We find that there are interesting offsets between the cluster galaxy, intracluster medium (ICM), and dark matter centroids, and possible scenarios are discussed. If the offset is confirmed to be uniquitous in other clusters, the explanation may necessitate major refinements in our current understanding of the nature of dark matter, as well as the cluster galaxy dynamics. CL0848+4452, the highest-redshift ( z = 1.27) cluster yet detected in weak-lensing, has a significant discrepancy between the weak- lensing and X-ray masses. If this trend is found to be severe and common also for other X-ray weak clusters at redshifts beyond the unity, the conventional X-ray determination of cluster mass functions, often inferred from their immediate X-ray properties such as the X-ray luminosity and temperature via the so-called mass-luminosity (M-L) and mass-temperature (M-T) relations, will become highly unstable in this redshift regime. Therefore, the relatively unbiased weak-lensing measurements of the cluster mass properties can be used to adequately calibrate the scaling relations in future high-redshift cluster investigations.
Effects of the Interaction of a Rotating Ideal Liquid with a Vortical Gravitational Field
NASA Astrophysics Data System (ADS)
Krechet, V. G.; Oshurko, V. B.; Rodichev, S. V.
2015-07-01
Stationary configurations of self-gravitating, rotating liquids with barotropic equation of state are considered within the framework of GTR. It is shown that such a rotating self-gravitating continuous medium can induce the formation of a vortical gravitational field, which can lead to the appearance of a geometry of spacetime with nontrivial topology, for example wormholes.
Weak magnetic fields in early-type stars: failed fossils
NASA Astrophysics Data System (ADS)
Braithwaite, Jonathan; Cantiello, Matteo
2013-02-01
Weak magnetic fields have recently been detected in Vega and Sirius. Here, we explore the possibility that these fields are the remnants of some field inherited or created during or shortly after star formation and are still evolving dynamically as we observe them. The time-scale of this evolution is given in terms of the Alfvn time-scale and the rotation frequency by ?evol ?2A ?, which is then comparable to the age of the star. According to this theory, all intermediate- and high-mass stars should contain fields of at least the strength found so far in Vega and Sirius. Faster rotators are expected to have stronger magnetic fields. Stars may experience an increase in surface field strength during their early main sequence, but for most of their lives field strength will decrease slowly. The length scale of the magnetic structure on the surface may be small in very young stars but should quickly increase to at least very approximately a fifth of the stellar radius. The field strength may be higher at the poles than at the equator.
Gravitation field algorithm and its application in gene cluster
2010-01-01
Background Searching optima is one of the most challenging tasks in clustering genes from available experimental data or given functions. SA, GA, PSO and other similar efficient global optimization methods are used by biotechnologists. All these algorithms are based on the imitation of natural phenomena. Results This paper proposes a novel searching optimization algorithm called Gravitation Field Algorithm (GFA) which is derived from the famous astronomy theory Solar Nebular Disk Model (SNDM) of planetary formation. GFA simulates the Gravitation field and outperforms GA and SA in some multimodal functions optimization problem. And GFA also can be used in the forms of unimodal functions. GFA clusters the dataset well from the Gene Expression Omnibus. Conclusions The mathematical proof demonstrates that GFA could be convergent in the global optimum by probability 1 in three conditions for one independent variable mass functions. In addition to these results, the fundamental optimization concept in this paper is used to analyze how SA and GA affect the global search and the inherent defects in SA and GA. Some results and source code (in Matlab) are publicly available at http://ccst.jlu.edu.cn/CSBG/GFA. PMID:20854683
Variations in Gravitational Field, Tidal Force, Electromagnetic Waves and Earthquakes
NASA Astrophysics Data System (ADS)
Strasser, Valentino
2010-12-01
This paper is the report on an experiment carried out between the month of December 2009 and the month of April 2010 between the Venetian Lagoon and the Northern Apennines in Italy, to check on a potential relationship between earthquakes and variations in the local gravitational field, the effect on the tide exercised by the interaction between the moon and the Sun, the appearance of anomalous light effects in the atmosphere ("Earth lights"), and the emission of radio waves caused by stresses in the Earth's crust. The cases studied show that there is indeed some concomitance between the periodic rising and falling of the sea level and the terrestrial tide effect, due to the gravitational attraction of the moon and sun on the Earth. In fact, changes in the local force of gravity coincided with the cycle of high and low tides and, in certain cases, with a variation in the electromagnetic field that preceded the occurrence of a seismic event by just a few hours. The o! bservations in the article are limited to the magnitude range discussed in the paper.
Was the Earth's Magnetic Field Weak in the Late Devonian?
NASA Astrophysics Data System (ADS)
Anwar, T.; Biggin, A. J.; Kravchinsky, V. A.; Pavlov, V.
2014-12-01
Very few data exist to describe geomagnetic field behaviour in the Late Devonian (LD). Samples, which have recently been Ar-Ar dated to 364-377 Myr ago, of LD-aged volcanics and instrusives from the Viluy large igneous province in Siberia are investigated. These units have already demonstrated reliable, palaeomagnetic directions consistent with the retention of a primary remanence. Microwave Thellier-type palaeointensity experiments (mostly IZZI protocol with partial thermoremanent magnetization checks) were performed on 55 samples from 16 sites, of which, 12 samples from 4 sites provide satisfactory paleointensity data. Arai plots are strongly concave-up in shape but multiple lines of evidence support that this is caused by a strong component of magnetisation overprinting a weak primary magnetisation rather than by lab-induced alteration or multidomain behaviour. The samples display corresponding distinct directional components, positive pTRM checks and little or no zig-zagging of the Arai plot. Furthermore, the results of non-heating pseudo-Thellier experiments support the existence of a strong component overprinting a much weaker one. The site-mean paleointensities, ranging from 5.3-11.1 ?T and which correspond to a virtual axial dipole moments (VADMs) of (1.0-2.1) 1022 Am2, indicate that the LD was a time of extremely weak magnetic field intensity. It provides the evidence that the superchron state, between ~310 and 265 Myr ago, is preceded by very weak field in the LD (~60 Myr before the superchron). If low dipole moment can be considered an indicator of high reversal frequency (as appears to be the case in the mid-Jurassic) then our results support that rapid transitions between reversal hyperactivity and superchron states are a recurring feature in the palaeomagnetic record, potentially linked to simultaneous episodes of true polar wander.
The emergence of weakly twisted magnetic fields in the sun
Archontis, V.; Hood, A. W.; Tsinganos, K.
2013-11-20
We have studied the emergence of a weakly twisted magnetic flux tube from the upper convection zone into the solar atmosphere. It is found that the rising magnetized plasma does not undergo the classical, single ?-shaped loop emergence, but it becomes unstable in two places, forming two magnetic lobes that are anchored in small-scale bipolar structures at the photosphere, between the two main flux concentrations. The two magnetic lobes rise and expand into the corona, forming an overall undulating magnetic flux system. The dynamical interaction of the lobes results in the triggering of high-speed and hot jets and the formation of successive cool and hot loops that coexist in the emerging flux region. Although the initial emerging field is weakly twisted, a highly twisted magnetic flux rope is formed at the low atmosphere, due to shearing and reconnection. The new flux rope (hereafter post-emergence flux rope) does not erupt. It remains confined by the overlying field. Although there is no ejective eruption of the post-emergence rope, it is found that a considerable amount of axial and azimuthal flux is transferred into the solar atmosphere during the emergence of the magnetic field.
Weak gravitational lensing due to large-scale structure of the universe
NASA Technical Reports Server (NTRS)
Jaroszynski, Michal; Park, Changbom; Paczynski, Bohdan; Gott, J. Richard, III
1990-01-01
The effect of the large-scale structure of the universe on the propagation of light rays is studied. The development of the large-scale density fluctuations in the omega = 1 universe is calculated within the cold dark matter scenario using a smooth particle approximation. The propagation of about 10 to the 6th random light rays between the redshift z = 5 and the observer was followed. It is found that the effect of shear is negligible, and the amplification of single images is dominated by the matter in the beam. The spread of amplifications is very small. Therefore, the filled-beam approximation is very good for studies of strong lensing by galaxies or clusters of galaxies. In the simulation, the column density was averaged over a comoving area of approximately (1/h Mpc)-squared. No case of a strong gravitational lensing was found, i.e., no 'over-focused' image that would suggest that a few images might be present. Therefore, the large-scale structure of the universe as it is presently known does not produce multiple images with gravitational lensing on a scale larger than clusters of galaxies.
Differentiation of optical isomers through enhanced weak-field interactions
NASA Technical Reports Server (NTRS)
Aronowitz, S.
1980-01-01
The influence of weak field interaction terms due to the cooperative effects which arise from a macroscopic assemblage of interacting sites is studied. Differential adsorption of optical isomers onto an achiral surface is predicted to occur if the surface was continuous and sufficiently large. However, the quantity of discontinuous crystal surfaces did not enhance the percentage of differentiation and thus the procedure of using large quantities of small particles was not a viable technique for obtaining a detectable differentiation of optical isomers on an achiral surface.
Weak-field general relativistic dynamics and the Newtonian limit
NASA Astrophysics Data System (ADS)
Cooperstock, F. I.
2016-01-01
We show that the generally held view that the gravity of weak-field nonrelativistic-velocity sources being invariably almost equivalent to Newtonian gravity (NG) (the Newtonian limit approach) is in some instances misleading and in other cases incorrect. A particularly transparent example is provided by comparing the Newtonian and general relativistic analyses of a simple variant of van Stockums infinite rotating dust cylinder. We show that some very recent criticisms of our work that had been motivated by the Newtonian limit approach were incorrect and note that no specific errors in our work were found in the critique. In the process, we underline some problems that arise from inappropriate coordinate transformations. As further support for our methodology, we note that our weak-field general relativistic treatment of a model galaxy was vindicated recently by the observations of Xu etal. regarding our prediction that the Milky Way was 19-21kpc in radius as opposed to the commonly held view that the radius was 15kpc.
Effective field theory of weakly coupled inflationary models
Gwyn, Rhiannon; Palma, Gonzalo A.; Sakellariadou, Mairi; Sypsas, Spyros E-mail: gpalmaquilod@ing.uchile.cl E-mail: spyridon.sypsas@kcl.ac.uk
2013-04-01
The application of Effective Field Theory (EFT) methods to inflation has taken a central role in our current understanding of the very early universe. The EFT perspective has been particularly useful in analyzing the self-interactions determining the evolution of co-moving curvature perturbations (Goldstone boson modes) and their influence on low-energy observables. However, the standard EFT formalism, to lowest order in spacetime differential operators, does not provide the most general parametrization of a theory that remains weakly coupled throughout the entire low-energy regime. Here we study the EFT formulation by including spacetime differential operators implying a scale dependence of the Goldstone boson self-interactions and its dispersion relation. These operators are shown to arise naturally from the low-energy interaction of the Goldstone boson with heavy fields that have been integrated out. We find that the EFT then stays weakly coupled all the way up to the cutoff scale at which ultraviolet degrees of freedom become operative. This opens up a regime of new physics where the dispersion relation is dominated by a quadratic dependence on the momentum ? ? p{sup 2}. In addition, provided that modes crossed the Hubble scale within this energy range, the predictions of inflationary observables including non-Gaussian signatures are significantly affected by the new scales characterizing it.
Rocha, Jorge V.; Cardoso, Vitor
2011-05-15
We analyze the gravitational perturbations induced by particles falling into a three dimensional, asymptotically AdS black hole geometry. More specifically, we solve the linearized perturbation equations obtained from the geodesic motion of a ringlike distribution of test particles in the BTZ background. This setup ensures that the U(1) symmetry of the background is preserved. The nonasymptotic flatness of the background raises difficulties in attributing the significance of energy and angular momentum to the conserved quantities of the test particles. This issue is well known but, to the best of our knowledge, has never been addressed in the literature. We confirm that the naive expressions for energy and angular momentum are the correct definitions. Finally, we put an asymptotically AdS version of the weak cosmic censorship to a test: by attempting to overspin the BTZ black hole with test particles it is found that the black hole cannot be spun-up past its extremal limit.
The effects of weak magnetic fields on radical pairs.
Barnes, Frank S; Greenebaum, Ben
2015-01-01
It is proposed that radical concentrations can be modified by combinations of weak, steady and alternating magnetic fields that modify the population distribution of the nuclear and electronic spin state, the energy levels and the alignment of the magnetic moments of the components of the radical pairs. In low external magnetic fields, the electronic and nuclear angular momentum vectors are coupled by internal forces that outweigh the external fields' interactions and are characterized in the Hamiltonian by the total quantum number F. Radical pairs form with their unpaired electrons in singlet (S) or triplet (T) states with respect to each other. At frequencies corresponding to the energy separation between the various states in the external magnetic fields, transitions can occur that change the populations of both electron and nuclear states. In addition, the coupling between the nuclei, nuclei and electrons, and Zeeman shifts in the electron and nuclear energy levels can lead to transitions with resonances spanning frequencies from a few Hertz into the megahertz region. For nuclear energy levels with narrow absorption line widths, this can lead to amplitude and frequency windows. Changes in the pair recombination rates can change radical concentrations and modify biological processes. The overall conclusion is that the application of magnetic fields at frequencies ranging from a few Hertz to microwaves at the absorption frequencies observed in electron and nuclear resonance spectroscopy for radicals can lead to changes in free radical concentrations and have the potential to lead to biologically significant changes. PMID:25399679
Constants of motion in stationary axisymmetric gravitational fields
NASA Astrophysics Data System (ADS)
Markakis, C.
2014-07-01
The motion of test particles in stationary axisymmetric gravitational fields is generally non-integrable unless a non-trivial constant of motion, in addition to energy and angular momentum along the symmetry axis, exists. The Carter constant in Kerr-de Sitter space-time is the only example known to date. Proposed astrophysical tests of the black hole no-hair theorem have often involved integrable gravitational fields more general than the Kerr family, but the existence of such fields has been a matter of debate. To elucidate this problem, we treat its Newtonian analogue by systematically searching for non-trivial constants of motion polynomial in the momenta and obtain two theorems. First, solving a set of quadratic integrability conditions, we establish the existence and uniqueness of the family of stationary axisymmetric potentials admitting a quadratic constant. As in Kerr-de Sitter space-time, the mass moments of this class satisfy a `no-hair' recursion relation M2l +2 = a2M2l, and the constant is Noether related to a second-order Killing-Stäckel tensor. Second, solving a new set of quartic integrability conditions, we establish non-existence of quartic constants. Remarkably, a subset of these conditions is satisfied when the mass moments obey a generalized `no-hair' recursion relation M2l +4 = (a2 + b2)M2l +2 - a2b2M2l. The full set of quartic integrability conditions, however, cannot be satisfied non-trivially by any stationary axisymmetric vacuum potential.
Weak-field limit of Kaluza-Klein models with spherical compactification: Experimental constraints
NASA Astrophysics Data System (ADS)
Chopovsky, Alexey; Eingorn, Maxim; Zhuk, Alexander
2012-03-01
We investigate the classical gravitational tests for the six-dimensional Kaluza-Klein model with spherical (of a radius a) compactification of the internal space. The model contains also a bare multidimensional cosmological constant ?6. The matter, which corresponds to this ansatz, can be simulated by a perfect fluid with the vacuum equation of state in the external space and an arbitrary equation of state with the parameter ?1 in the internal space. For example, ?1=1 and ?1=2 correspond to the monopole two-forms and the Casimir effect, respectively. In the particular case ?6=0, the parameter ?1 is also absent: ?1=0. In the weak-field approximation, we perturb the background ansatz by a pointlike mass. We demonstrate that in the case ?1>0 the perturbed metric coefficients have the Yukawa-type corrections with respect to the usual Newtonian gravitational potential. The inverse square law experiments restrict the parameters of the model: a/?1?610-3cm. Therefore, in the Solar System the parameterized post-Newtonian parameter ? is equal to 1 with very high accuracy. Thus, our model satisfies the gravitational experiments (the deflection of light and the time delay of radar echoes) at the same level of accuracy as general relativity. We demonstrate also that our background matter provides the stable compactification of the internal space in the case ?1>0. However, if ?1=0, then the parameterized post-Newtonian parameter ?=1/3, which strongly contradicts the observations.
Weak scattering of scalar and electromagnetic random fields
NASA Astrophysics Data System (ADS)
Tong, Zhisong
This dissertation encompasses several studies relating to the theory of weak potential scattering of scalar and electromagnetic random, wide-sense statistically stationary fields from various types of deterministic or random linear media. The proposed theory is largely based on the first Born approximation for potential scattering and on the angular spectrum representation of fields. The main focus of the scalar counterpart of the theory is made on calculation of the second-order statistics of scattered light fields in cases when the scattering medium consists of several types of discrete particles with deterministic or random potentials. It is shown that the knowledge of the correlation properties for the particles of the same and different types, described with the newly introduced pair-scattering matrix, is crucial for determining the spectral and coherence states of the scattered radiation. The approach based on the pair-scattering matrix is then used for solving an inverse problem of determining the location of an "alien" particle within the scattering collection of "normal" particles, from several measurements of the spectral density of scattered light. Weak scalar scattering of light from a particulate medium in the presence of optical turbulence existing between the scattering centers is then approached using the combination of the Born's theory for treating the light interaction with discrete particles and the Rytov's theory for light propagation in extended turbulent medium. It is demonstrated how the statistics of scattered radiation depend on scattering potentials of particles and the power spectra of the refractive index fluctuations of turbulence. This theory is of utmost importance for applications involving atmospheric and oceanic light transmission. The second part of the dissertation includes the theoretical procedure developed for predicting the second-order statistics of the electromagnetic random fields, such as polarization and linear momentum, scattered from static media. The spatial distribution of these properties of scattered fields is shown to be substantially dependent on the correlation and polarization properties of incident fields and on the statistics of the refractive index distribution within the scatterers. Further, an example is considered which illustrates the usefulness of the electromagnetic scattering theory of random fields in the case when the scattering medium is a thin bio-tissue layer with the prescribed power spectrum of the refractive index fluctuations. The polarization state of the scattered light is shown to be influenced by correlation and polarization states of the illumination as well as by the particle size distribution of the tissue slice.
NASA Astrophysics Data System (ADS)
Leauthaud, Alexie; J. Benson, Andrew; Civano, Francesca; L. Coil, Alison; Bundy, Kevin; Massey, Richard; Schramm, Malte; Schulze, Andreas; Capak, Peter; Elvis, Martin; Kulier, Andrea; Rhodes, Jason
2015-01-01
Understanding the relationship between galaxies hosting active galactic nuclei (AGN) and the dark matter haloes in which they reside is key to constraining how black hole fuelling is triggered and regulated. Previous efforts have relied on simple halo mass estimates inferred from clustering, weak gravitational lensing, or halo occupation distribution modelling. In practice, these approaches remain uncertain because AGN, no matter how they are identified, potentially live a wide range of halo masses with an occupation function whose general shape and normalization are poorly known. In this work, we show that better constraints can be achieved through a rigorous comparison of the clustering, lensing, and cross-correlation signals of AGN hosts to the fiducial stellar-to-halo mass relation (SHMR) derived for all galaxies, irrespective of nuclear activity. Our technique exploits the fact that the global SHMR can be measured with much higher accuracy than any statistic derived from AGN samples alone. Using 382 moderate luminosity X-ray AGN at z < 1 from the COSMOS field, we report the first measurements of weak gravitational lensing from an X-ray-selected sample. Comparing this signal to predictions from the global SHMR, we find that, contrary to previous results, most X-ray AGN do not live in medium size groups - nearly half reside in relatively low mass haloes with M200b 1012.5 M?. The AGN occupation function is well described by the same form derived for all galaxies but with a lower normalization - the fraction of haloes with AGN in our sample is a few per cent. The number of AGN satellite galaxies scales as a power law with host halo mass with a power-law index ? = 1. By highlighting the relatively `normal' way in which moderate luminosity X-ray AGN hosts occupy haloes, our results suggest that the environmental signature of distinct fuelling modes for luminous quasars compared to moderate luminosity X-ray AGN is less obvious than previously claimed.
Comment on 'Primordial magnetic seed field amplification by gravitational waves'
Tsagas, Christos G.
2007-04-15
We consider the amplification of cosmological magnetic fields by gravitational waves as it was recently presented by Betschart et al. That study confined to infinitely conductive environments, arguing that on spatially flat Friedmann backgrounds the gravito-magnetic interaction proceeds always as if the Universe were a perfect conductor. We explain why this claim is not correct and then reexamine the Maxwell-Weyl coupling at the limit of ideal magnetohydrodynamics. We find that the scales of the main results of Betschart et al. were not properly assessed and that the incorrect scale assessment has compromised both the physical and the numerical results of the paper. This comment aims to clarify these issues on the one hand, while on the other it takes a closer look at the gauge invariance and the nonlinearity of the formalism proposed by Betschart et al.
Geodesics in the field of a rotating deformed gravitational source
NASA Astrophysics Data System (ADS)
Boshkayev, K. A.; Quevedo, H.; Abutalip, M. S.; Kalymova, Zh. A.; Suleymanova, Sh. S.
2016-01-01
We investigate equatorial geodesics in the gravitational field of a rotating and deformed source described by the approximate Hartle-Thorne metric. In the case of massive particles, we derive within the same approximation analytic expressions for the orbital angular velocity, the specific angular momentum and energy, and the radii of marginally stable and marginally bound circular orbits. Moreover, we calculate the orbital angular velocity and the radius of lightlike circular geodesics. We study numerically the frame dragging effect and the influence of the quadrupolar deformation of the source on the motion of test particles. We show that the effects originating from the rotation can be balanced by the effects due to the oblateness of the source.
On the Energy Source of the Gravitational Field
NASA Astrophysics Data System (ADS)
Mayer, Alexander
2011-11-01
According to the principles of special relativity, the systemic energy budget of a quantum harmonic oscillator exceeds canonical ``total energy" (E) by the difference between the 1?-norm and 2?-norm (E) of the complex number (mc^2 + ipc). This surplus energy manifests as a spatially unbounded continuous waveform centered on the source particle, having a phase velocity equal to the speed of light. In the immediate vicinity of a source particle and at corresponding high radial amplitude variation, the interaction between this waveform and spacetime induces various quantum effects. A kilogram of mass contains 0^27 subatomic harmonic oscillators (e.g., quarks); decoherent superposition of their momentum-driven (/?x) radiated waveforms provides an isotropic monotonically-decreasing space energy density. Spacetime response to the presence of this distributed energy manifests as the gravitational field in accord with the basic interpretation of general relativity: ``energy curves spacetime.'' Hypotheses put forward in this discussion are empirically testable with tabletop experiments.
CHARGED TORI IN SPHERICAL GRAVITATIONAL AND DIPOLAR MAGNETIC FIELDS
Slany, P.; Kovar, J.; Stuchlik, Z.; Karas, V.
2013-03-01
A Newtonian model of non-conductive, charged, perfect fluid tori orbiting in combined spherical gravitational and dipolar magnetic fields is presented and stationary, axisymmetric toroidal structures are analyzed. Matter in such tori exhibits a purely circulatory motion and the resulting convection carries charges into permanent rotation around the symmetry axis. As a main result, we demonstrate the possible existence of off-equatorial charged tori and equatorial tori with cusps that also enable outflows of matter from the torus in the Newtonian regime. These phenomena qualitatively represent a new consequence of the interplay between gravity and electromagnetism. From an astrophysical point of view, our investigation can provide insight into processes that determine the vertical structure of dusty tori surrounding accretion disks.
Pollux: a stable weak dipolar magnetic field but no planet?
NASA Astrophysics Data System (ADS)
Aurière, Michel; Konstantinova-Antova, Renada; Espagnet, Olivier; Petit, Pascal; Roudier, Thierry; Charbonnel, Corinne; Donati, Jean-François; Wade, Gregg A.
2014-08-01
Pollux is considered as an archetype of a giant star hosting a planet: its radial velocity (RV) presents sinusoidal variations with a period of about 590 d, which have been stable for more than 25 years. Using ESPaDOnS and Narval we have detected a weak (sub-gauss) magnetic field at the surface of Pollux and followed up its variations with Narval during 4.25 years, i.e. more than for two periods of the RV variations. The longitudinal magnetic field is found to vary with a sinusoidal behaviour with a period close to that of the RV variations and with a small shift in phase. We then performed a Zeeman Doppler imaging (ZDI) investigation from the Stokes V and Stokes I least-squares deconvolution (LSD) profiles. A rotational period is determined, which is consistent with the period of variations of the RV. The magnetic topology is found to be mainly poloidal and this component almost purely dipolar. The mean strength of the surface magnetic field is about 0.7 G. As an alternative to the scenario in which Pollux hosts a close-in exoplanet, we suggest that the magnetic dipole of Pollux can be associated with two temperature and macroturbulent velocity spots which could be sufficient to produce the RV variations. We finally investigate the scenarii of the origin of the magnetic field which could explain the observed properties of Pollux.
Observable gravitational waves from inflation with small field excursions
Hotchkiss, Shaun; Mazumdar, Anupam; Nadathur, Seshadri E-mail: a.mazumdar@lancaster.ac.uk
2012-02-01
The detection of primordial gravitational waves, or tensor perturbations, would be regarded as compelling evidence for inflation. The canonical measure of this is the ratio of tensor to scalar perturbations, r. For single-field slow-roll models of inflation with small field excursions, the Lyth bound dictates that if the evolution of the slow-roll parameter ? is monotonic, the tensor-to-scalar ratio must be below observationally detectable levels. We describe how non-monotonic evolution of ? can evade the Lyth bound and generate observationally large r, even with small field excursions. This has consequences for the scalar power spectrum as it necessarily predicts an enhancement in the spectrum at very small scales and significant scale-dependent running at CMB scales. This effect has not been appropriately accounted for in previous analyses. We describe a mechanism that will generically produce the required behaviour in ? and give an example of this mechanism arising in a well-motivated small-field model. This model can produce r ? 0.05 while satisfying all current observational constraints.
Singularity analysis of potential fields to enhance weak anomalies
NASA Astrophysics Data System (ADS)
Chen, G.; Cheng, Q.; Liu, T.
2013-12-01
Geoanomalies generally are nonlinear, non-stationary and weak, especially in the land cover areas, however, the traditional methods of geoanomaly identification are usually based on linear theory. In past two decades, many power-law function models have been developed based on fractal concept in mineral exploration and mineral resource assessment, such that the density-area (C-A) model and spectrum-area model (S-A) suggested by Qiuming Cheng have played important roles in extracting geophysical and geochemical anomalies. Several power-law relationships are evident in geophysical potential fields, such as field value-distance, power spectrum-wave number as well as density-area models. The singularity index based on density-area model involves the first derivative transformation of the measure. Hence, we introduce the singularity analysis to develop a novel high-pass filter for extracting gravity and magnetic anomalies with the advantage of scale invariance. Furthermore, we suggest that the statistics of singularity indices can provide a new edge detection scheme for the gravity or magnetic source bodies. Meanwhile, theoretical magnetic anomalies are established to verify these assertions. In the case study from Nanling mineral district in south China and Qikou Depression in east China, compared with traditional geophysical filtering methods including multiscale wavelet analysis and total horizontal gradient methods, the singularity method enhances and extracts the weak anomalies caused by buried magmatic rocks more effectively, and provides more distinct boundary information of rocks. Moreover, the singularity mapping results have good correspondence relationship with both the outcropping rocks and known mineral deposits to support future mineral resource exploration. The singularity method based on fractal analysis has potential to be a new useful theory and technique for processing gravity and magnetic anomaly data.
Peters, Thomas; Klessen, Ralf S.; Federrath, Christoph; Smith, Rowan J.; Schleicher, Dominik R. G.; Banerjee, Robi; Sur, Sharanya
2012-12-01
Stars form by the gravitational collapse of interstellar gas. The thermodynamic response of the gas can be characterized by an effective equation of state. It determines how gas heats up or cools as it gets compressed, and hence plays a key role in regulating the process of stellar birth on virtually all scales, ranging from individual star clusters up to the galaxy as a whole. We present a systematic study of the impact of thermodynamics on gravitational collapse in the context of high-redshift star formation, but argue that our findings are also relevant for present-day star formation in molecular clouds. We consider a polytropic equation of state, P = k{rho}{sup {Gamma}}, with both sub-isothermal exponents {Gamma} < 1 and super-isothermal exponents {Gamma} > 1. We find significant differences between these two cases. For {Gamma} > 1, pressure gradients slow down the contraction and lead to the formation of a virialized, turbulent core. Weak magnetic fields are strongly tangled and efficiently amplified via the small-scale turbulent dynamo on timescales corresponding to the eddy-turnover time at the viscous scale. For {Gamma} < 1, on the other hand, pressure support is not sufficient for the formation of such a core. Gravitational contraction proceeds much more rapidly and the flow develops very strong shocks, creating a network of intersecting sheets and extended filaments. The resulting magnetic field lines are very coherent and exhibit a considerable degree of order. Nevertheless, even under these conditions we still find exponential growth of the magnetic energy density in the kinematic regime.
Nonlinear gravitational self-force: Field outside a small body
NASA Astrophysics Data System (ADS)
Pound, Adam
2012-10-01
A small extended body moving through an external spacetime g?? creates a metric perturbation h??, which forces the body away from geodesic motion in g??. The foundations of this effect, called the gravitational self-force, are now well established, but concrete results have mostly been limited to linear order. Accurately modeling the dynamics of compact binaries requires proceeding to nonlinear orders. To that end, I show how to obtain the metric perturbation outside the body at all orders in a class of generalized wave gauges. In a small buffer region surrounding the body, the form of the perturbation can be found analytically as an expansion for small distances r from a representative worldline. Given only a specification of the bodys multipole moments, the field obtained in the buffer region suffices to find the metric everywhere outside the body via a numerical puncture scheme. Following this procedure at first and second order, I calculate the field in the buffer region around an arbitrarily structured compact body at sufficiently high order in r to numerically implement a second-order puncture scheme, including effects of the bodys spin. I also define nth-order (local) generalizations of the Detweiler-Whiting singular and regular fields and show that in a certain sense, the body can be viewed as a skeleton of multipole moments.
NASA Technical Reports Server (NTRS)
Dong, D.; Gross, R. S.; Dickey, J. O.
1994-01-01
Laser ranging measurements to single satellite are sensitive to the Earth's gravitational field and its temporal variations. Using 13 years (1980-1992) of LAGEOS I laser ranging data, we have recovered monthly mean linear combinations of even and odd degree zonal spherical harmonic coefficients of the Earth's gravitational field.
Model for the optimization of escape from two pursuers in a gravitational field
NASA Astrophysics Data System (ADS)
Novoselov, V. S.
A solution is obtained to the simplifed game-theoretic problem of determining the optimal encounter of three players in a gravitational field, assuming that two of the players form a coalition while the third is performing evasive maneuvers. The problem is one of determining coplanar impulse transfer in the gravitational field.
Atmospheric Gravitational Torque Variations Based on Various Gravity Fields
NASA Technical Reports Server (NTRS)
Sanchez, Braulio V.; Rowlands, David; Smith, David E. (Technical Monitor)
2001-01-01
Advancements in the study of the Earth's variable rate of rotation and the motion of its rotation axis have given impetus to the analysis of the torques between the atmosphere, oceans and solid Earth. The output from global general circulation models of the atmosphere (pressure, surface stress) is being used as input to the torque computations. Gravitational torque between the atmosphere, oceans and solid Earth is an important component of the torque budget. Computation of the gravitational torque involves the adoption of a gravitational model from a wide variety available. The purpose of this investigation is to ascertain to what extent this choice might influence the results of gravitational torque computations.
Neutron star mass-radius relation with gravitational field shielding by a scalar field
NASA Astrophysics Data System (ADS)
Zhang, Bo-Jun; Zhang, Tian-Xi; Guggilla, Padmaja; Dokhanian, Mostafa
2013-05-01
The currently well-developed models for equations of state (EoSs) have been severely impacted by recent measurements of neutron stars with a small radius and/or large mass. To explain these measurements, the theory of gravitational field shielding by a scalar field is applied. This theory was recently developed in accordance with the five-dimensional (5D) fully covariant Kaluza-Klein (KK) theory that has successfully unified Einstein's general relativity and Maxwell's electromagnetic theory. It is shown that a massive, compact neutron star can generate a strong scalar field, which can significantly shield or reduce its gravitational field, thus making it more massive and more compact. The mass-radius relation developed under this type of modified gravity can be consistent with these recent measurements of neutron stars. In addition, the effect of gravitational field shielding helps explain why the supernova explosions of some very massive stars (e.g., 40 Msolar as measured recently) actually formed neutron stars rather than black holes as expected. The EoS models, ruled out by measurements of small radius and/or large mass neutron stars according to the theory of general relativity, can still work well in terms of the 5D fully covariant KK theory with a scalar field.
Kinetic simulation of rarefied and weakly ionized hypersonic flow fields
NASA Astrophysics Data System (ADS)
Farbar, Erin D.
When a vehicle enters the Earth's atmosphere at the very large velocities associated with Lunar and Mars return, a strong bow shock is formed in front of the vehicle. The shock heats the air to very high temperatures, causing collisions that are sufficiently energetic to produce ionized particles. As a result, a weakly ionized plasma is formed in the region between the bow shock and the vehicle surface. The presence of this plasma impedes the transport of radio frequency waves to the vehicle, causing the phenomenon known as "communications black out". The plasma also interacts with the neutral particles in the flow field, and contributes to the heat flux at the vehicle surface. Since it is difficult to characterize these flow fields using flight or ground based experiments, computational tools play an important role in the design of reentry vehicles. It is important to include the physical phenomena associated with the presence of the plasma in the computational analysis of the flow fields about these vehicles. Physical models for the plasma phenomena are investigated using a state of the art, Direct Simulation Monte Carlo (DSMC) code. Models for collisions between charged particles, plasma chemistry, and the self-induced electric field that currently exist in the literature are implemented. Using these baseline models, steady state flow field solutions are computed for the FIRE II reentry vehicle at two different trajectory points. The accuracy of each baseline plasma model is assessed in a systematic fashion, using one flight condition of the FIRE II vehicle as the test case. Experimental collision cross section data is implemented to model collisions of electrons with neutral particles. Theoretical and experimental reaction cross section data are implemented to model chemical reactions that involve electron impact, and an associative ionization reaction. One-dimensional Particle-In-Cell (PIC) routines are developed and coupled to the DSMC code, to assess the limitations of the baseline electric field model. Interpretation of the DSMC-PIC results leads to the development of an improved electric field model that does not require the substantial computational resources needed to obtain DSMC-PIC solutions.
Standard electroweak interactions in gravitational theory with chameleon field and torsion
NASA Astrophysics Data System (ADS)
Ivanov, A. N.; Wellenzohn, M.
2015-04-01
We propose a version of a gravitational theory with a torsion field, induced by the chameleon field. Following Hojman et al. [Phys. Rev. D 17, 3141 (1976)], the results obtained in Phys. Rev. D 90, 045040 (2014) are generalized by extending Einstein gravity to Einstein-Cartan gravity with a torsion field as a gradient of the chameleon field through a modification of the local gauge invariance of minimal coupling in the Weinberg-Salam electroweak model. The contributions of the chameleon (torsion) field to the observables of electromagnetic and weak processes are calculated. Since in our approach the chameleon-photon coupling constant ?? is equal to the chameleon-matter coupling constant ? , i.e., ??=? , the experimental constraints on ? obtained in terrestrial laboratories by T. Jenke et al. [Phys. Rev. Lett. 112, 115105 (2014)] and by H. Lemmel et al. [Phys. Lett. B 743, 310 (2015)]can be used for the analysis of astrophysical sources of chameleons, proposed by C. Burrage et al. [Phys. Rev. D 79, 044028 (2009)], A.-C. Davis et al. [Phys. Rev. D 80, 064016 (2009)], and in references therein, where chameleons induce photons because of direct chameleon-photon transitions in the magnetic fields.
The HST Frontier Fields: Gravitational Lensing Models Release
NASA Astrophysics Data System (ADS)
Coe, Dan A.; Lotz, J.; Natarajan, P.; Richard, J.; Zitrin, A.; Kneib, J.; Ebeling, H.; Sharon, K.; Johnson, T.; Limousin, M.; Bradac, M.; Hoag, A.; Cain, B.; Merten, J.; Williams, L. L.; Sebesta, K.; Meneghetti, M.; Koekemoer, A. M.; Barker, E. A.
2014-01-01
The Hubble Frontier Fields (HFF) is a Director's Discretionary Time (DDT) program to deeply observe up to six massive strong-lensing galaxy clusters and six "blank" fields in parallel. These complementary observations will yield magnified and direct images of some of the most distant galaxies yet observed. The strongly lensed images will be our deepest views of our universe to date. Interpretation of some (but not all) observed properties of the strongly lensed galaxies requires gravitational lens modeling. In order to maximize the value of this public dataset to the extragalactic community, STScI commissioned five teams funded by NASA to derive the best possible lens models from existing data. After coordinating to share observational constraints, including measured redshifts of strongly lensed galaxies, the teams independently derived lens models using robust, established methodologies. STScI released these models to the community in October before HFF observations of the first cluster, Abell 2744. Here we describe these models as well as a web tool which allows users to extract magnification estimates with uncertainties from all models for any galaxy strongly lensed by a HFF cluster. Inputs are the galaxy's coordinates (RA and Dec), redshift, and (optionally) observed radius. We also discuss ongoing work to study lens model uncertainties by modeling simulated clusters.
Influence of strong field vacuum polarization on gravitational-electromagnetic wave interaction
Forsberg, M.; Brodin, G.; Papadopoulos, D.
2010-07-15
The interaction between gravitational and electromagnetic waves in the presence of a static magnetic field is studied. The field strength of the static field is allowed to surpass the Schwinger critical field, such that the QED effects of vacuum polarization and magnetization are significant. Equations governing the interaction are derived and analyzed. It turns out that the energy conversion from gravitational to electromagnetic waves can be significantly altered due to the QED effects. The consequences of our results are discussed.
Taylor, James E.; Massey, Richard J.; Leauthaud, Alexie; Tanaka, Masayuki; George, Matthew R.; Rhodes, Jason; Ellis, Richard; Scoville, Nick; Kitching, Thomas D.; Capak, Peter; Finoguenov, Alexis; Ilbert, Olivier; Kneib, Jean-Paul; Jullo, Eric; Koekemoer, Anton M.
2012-04-20
Gravitational lensing can provide pure geometric tests of the structure of spacetime, for instance by determining empirically the angular diameter distance-redshift relation. This geometric test has been demonstrated several times using massive clusters which produce a large lensing signal. In this case, matter at a single redshift dominates the lensing signal, so the analysis is straightforward. It is less clear how weaker signals from multiple sources at different redshifts can be stacked to demonstrate the geometric dependence. We introduce a simple measure of relative shear which for flat cosmologies separates the effect of lens and source positions into multiplicative terms, allowing signals from many different source-lens pairs to be combined. Applying this technique to a sample of groups and low-mass clusters in the COSMOS survey, we detect a clear variation of shear with distance behind the lens. This represents the first detection of the geometric effect using weak lensing by multiple, low-mass groups. The variation of distance with redshift is measured with sufficient precision to constrain the equation of state of the universe under the assumption of flatness, equivalent to a detection of a dark energy component {Omega}{sub X} at greater than 99% confidence for an equation-of-state parameter -2.5 {<=} w {<=} -0.1. For the case w = -1, we find a value for the cosmological constant density parameter {Omega}{sub {Lambda}} = 0.85{sup +0.044}{sub -}0{sub .19} (68% CL) and detect cosmic acceleration (q{sub 0} < 0) at the 98% CL. We consider the systematic uncertainties associated with this technique and discuss the prospects for applying it in forthcoming weak-lensing surveys.
Relativistic Mass Change in the Fields of Gravitation, Non-Holonomity, and Deformation
NASA Astrophysics Data System (ADS)
Rabounski, Dmitri
2010-10-01
This study targets solving the scalar geodesic equation (equation of energy) of a mass-bearing particle travelling in the gravitational field, the field of non-holonomity (rotation) of space, and the field of deformation of space, which are the only three external factors present in the equation. The obtained solutions manifest a change in the mass of the particle according to the distance travelled in the corresponding field. The mass defect due to the field of gravitation is known. The effects of the fields of space non-holonomity and space deformation have not been studied before. In contrast to the gravitational mass defect, registered in the gravitational field near the Earth, these two effects are much smaller: they reach the measurable limit 10-10 only in space travel within cosmological distances. A complete report of this study has been submitted to The Abraham Zelmanov Journal.
CFHTLenS: the relation between galaxy dark matter haloes and baryons from weak gravitational lensing
NASA Astrophysics Data System (ADS)
Velander, Malin; van Uitert, Edo; Hoekstra, Henk; Coupon, Jean; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Kitching, Thomas D.; Mellier, Yannick; Miller, Lance; Van Waerbeke, Ludovic; Bonnett, Christopher; Fu, Liping; Giodini, Stefania; Hudson, Michael J.; Kuijken, Konrad; Rowe, Barnaby; Schrabback, Tim; Semboloni, Elisabetta
2014-01-01
We present a study of the relation between dark matter halo mass and the baryonic content of their host galaxies, quantified through galaxy luminosity and stellar mass. Our investigation uses 154 deg2 of Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) lensing and photometric data, obtained from the CFHT Legacy Survey. To interpret the weak lensing signal around our galaxies, we employ a galaxy-galaxy lensing halo model which allows us to constrain the halo mass and the satellite fraction. Our analysis is limited to lenses at redshifts between 0.2 and 0.4, split into a red and a blue sample. We express the relationship between dark matter halo mass and baryonic observable as a power law with pivot points of 10^{11} h_{70}^{-2} L_{{⊙}} and 2× 10^{11} h_{70}^{-2} M_{{⊙}} for luminosity and stellar mass, respectively. For the luminosity-halo mass relation, we find a slope of 1.32 ± 0.06 and a normalization of 1.19^{+0.06}_{-0.07}× 10^{13} h_{70}^{-1} M_{{⊙}} for red galaxies, while for blue galaxies the best-fitting slope is 1.09^{+0.20}_{-0.13} and the normalization is 0.18^{+0.04}_{-0.05}× 10^{13} h_{70}^{-1} M_{{⊙}}. Similarly, we find a best-fitting slope of 1.36^{+0.06}_{-0.07} and a normalization of 1.43^{+0.11}_{-0.08}× 10^{13} h_{70}^{-1} M_{{⊙}} for the stellar mass-halo mass relation of red galaxies, while for blue galaxies the corresponding values are 0.98^{+0.08}_{-0.07} and 0.84^{+0.20}_{-0.16}× 10^{13} h_{70}^{-1} M_{{⊙ }}. All numbers convey the 68 per cent confidence limit. For red lenses, the fraction which are satellites inside a larger halo tends to decrease with luminosity and stellar mass, with the sample being nearly all satellites for a stellar mass of 2× 109 h_{70}^{-2} M_{{⊙}}. The satellite fractions are generally close to zero for blue lenses, irrespective of luminosity or stellar mass. This, together with the shallower relation between halo mass and baryonic tracer, is a direct confirmation from galaxy-galaxy lensing that blue galaxies reside in less clustered environments than red galaxies. We also find that the halo model, while matching the lensing signal around red lenses well, is prone to overpredicting the large-scale signal for faint and less massive blue lenses. This could be a further indication that these galaxies tend to be more isolated than assumed.
Deep HST imaging of distant weak radio and field galaxies
NASA Technical Reports Server (NTRS)
Windhorst, R. A.; Gordon, J. M.; Pascarelle, S. M.; Schmidtke, P. C.; Keel, W. C.; Burkey, J. M.; Dunlop, J. S.
1994-01-01
We present deep Hubble Space Telescope (HST) Wide-Field Camera (WFC) V- and I-band images of three distant weak radio galaxies with z = 0.311-2.390 and seven field galaxies with z = 0.131-0.58. The images were deconvolved with both the Lucy and multiresolution CLEAN methods, which yield a restoring Full Width at Half Maximum (FWHM) of less than or equal to 0.2 sec, (nearly) preserve photons and signal-to-noise ratio at low spatial frequencies, and produce consistent light profiles down to our 2 sigma surface brightness sensitivity limit of V approximately 27.2 and I approximately 25.9 mag/sq arcsec. Multi-component image modeling was used to provide deconvolution-independent estimates of structural parameters for symmetric galaxies. We present 12-band (m(sub 2750) UBVRIgriJHK) photometry for a subset of the galaxies and bootstrap the unknown FOC/48 zero point at 2750 A in three independent ways (yielding m(sub 2750) = 21.34 +/- 0.09 mag for 1.0 e(-)/s). Two radio galaxies with z = 0.311 and 0.528, as well as one field galaxy with z = 0.58, have the colors and spectra of early-type galaxies, and a(exp 1/4)-like light profiles in the HST images. The two at z greater than 0.5 have little or no color gradients in V - I and are likely giant ellipticals, while the z = 0.311 radio galaxy has a dim exponential disk and is likely an S0. Six of the seven field galaxies have light profiles that indicate (small) inner bulges following a(exp 1/4) laws and outer exponential disks, both with little or no color gradients. These are (early-type) spiral galaxies with z = 0.131-0.528. About half have faint companions or bars. One shows lumpy structure, possibly a merger. The compact narrow-line galaxy 53W002 at z = 2.390 has less than or = 30% +/- 10% of its HST V and I flux in the central kiloparsec (due to its weak Active Galactic Nucleus (AGN)). Most of its light (V approximately equal to 23.3) occurs in a symmetric envelope with a regular a(exp 1/4)-like profile of effective radius a approximately equal to 1.1 sec (approximately equal to 12 kpc for H(sub 0) = 50, q(sub 0) = 0.1. Its (HST) V - I color varies at most from approximately 0.3 mag at a approximately equal to 0.2 sec to approximately 1.2 mag at a approximately greater than 0.4 sec, and possibly to approximately greater than 2.2 mag at a approximately greater than 1.2 sec. Together with its I - K color (approximately equal to 2.5 mag for a approximately greater than 1.0 sec-2.0 sec), this is consistent with an aging stellar population approximately 0.3-0.5 Gyr old in the galaxy center (a approx. less than 2 kpc radius), and possibly approximately 0.5-1.0 Gyr old at a approximately greater than 10 kpc radius. While its outer part may thus have started to collapse at z = 2.5-4, its inner part still is aligned with its redshifted Ly(alpha) cloud and its radio axis, possibly caused by star formation associated with the radio jet, or by reflection from its AGN cone.
Cosmological equivalence principle and the weak-field limit
Wiltshire, David L.
2008-10-15
The strong equivalence principle is extended in application to averaged dynamical fields in cosmology to include the role of the average density in the determination of inertial frames. The resulting cosmological equivalence principle is applied to the problem of synchronization of clocks in the observed universe. Once density perturbations grow to give density contrasts of order 1 on scales of tens of megaparsecs, the integrated deceleration of the local background regions of voids relative to galaxies must be accounted for in the relative synchronization of clocks of ideal observers who measure an isotropic cosmic microwave background. The relative deceleration of the background can be expected to represent a scale in which weak-field Newtonian dynamics should be modified to account for dynamical gradients in the Ricci scalar curvature of space. This acceleration scale is estimated using the best-fit nonlinear bubble model of the universe with backreaction. At redshifts z < or approx. 0.25 the scale is found to coincide with the empirical acceleration scale of modified Newtonian dynamics. At larger redshifts the scale varies in a manner which is likely to be important for understanding dynamics of galaxy clusters, and structure formation. Although the relative deceleration, typically of order 10{sup -10} ms{sup -2}, is small, when integrated over the lifetime of the universe it amounts to an accumulated relative difference of 38% in the rate of average clocks in galaxies as compared to volume-average clocks in the emptiness of voids. A number of foundational aspects of the cosmological equivalence principle are also discussed, including its relation to Mach's principle, the Weyl curvature hypothesis, and the initial conditions of the universe.
Field theory and weak Euler-Lagrange equation for classical particle-field systems.
Qin, Hong; Burby, Joshua W; Davidson, Ronald C
2014-10-01
It is commonly believed as a fundamental principle that energy-momentum conservation of a physical system is the result of space-time symmetry. However, for classical particle-field systems, e.g., charged particles interacting through self-consistent electromagnetic or electrostatic fields, such a connection has only been cautiously suggested. It has not been formally established. The difficulty is due to the fact that the dynamics of particles and the electromagnetic fields reside on different manifolds. We show how to overcome this difficulty and establish the connection by generalizing the Euler-Lagrange equation, the central component of a field theory, to a so-called weak form. The weak Euler-Lagrange equation induces a new type of flux, called the weak Euler-Lagrange current, which enters conservation laws. Using field theory together with the weak Euler-Lagrange equation developed here, energy-momentum conservation laws that are difficult to find otherwise can be systematically derived from the underlying space-time symmetry. PMID:25375609
Improved Gravitation Field Algorithm and Its Application in Hierarchical Clustering
Zheng, Ming; Sun, Ying; Liu, Gui-xia; Zhou, You; Zhou, Chun-guang
2012-01-01
Background Gravitation field algorithm (GFA) is a new optimization algorithm which is based on an imitation of natural phenomena. GFA can do well both for searching global minimum and multi-minima in computational biology. But GFA needs to be improved for increasing efficiency, and modified for applying to some discrete data problems in system biology. Method An improved GFA called IGFA was proposed in this paper. Two parts were improved in IGFA. The first one is the rule of random division, which is a reasonable strategy and makes running time shorter. The other one is rotation factor, which can improve the accuracy of IGFA. And to apply IGFA to the hierarchical clustering, the initial part and the movement operator were modified. Results Two kinds of experiments were used to test IGFA. And IGFA was applied to hierarchical clustering. The global minimum experiment was used with IGFA, GFA, GA (genetic algorithm) and SA (simulated annealing). Multi-minima experiment was used with IGFA and GFA. The two experiments results were compared with each other and proved the efficiency of IGFA. IGFA is better than GFA both in accuracy and running time. For the hierarchical clustering, IGFA is used to optimize the smallest distance of genes pairs, and the results were compared with GA and SA, singular-linkage clustering, UPGMA. The efficiency of IGFA is proved. PMID:23173043
Gravitational field models for the earth (GEM 1 and 2)
NASA Technical Reports Server (NTRS)
Lerch, F. J.; Wagner, C. A.; Smith, D. E.; Andson, M. L.; Brownd, J. E.; Richardson, J. A.
1972-01-01
Two models of the earth's gravitational field have been computed at Goddard Space Flight Center. The first, Goddard Earth Model 1 (GEM 1), has been derived from satellite tracking data. The second, Goddard Earth Model 2 (GEM 2), has been derived from a combination of satellite tracking and surface gravimetric data. The geopotential models are represented in spherical harmonics complete to degree and order 16 for the combined solution and complete to degree and order 12 for the satellite solution. Both solutions include zonal terms to degree 21 and related satellite resonant coefficients to degree 22. The satellite data consisted primarily of optical data processed on 300 weekly orbital arcs for 25 close earth satellites. Surface gravity data were employed in the form of 5 deg x 5 deg mean free-air gravity anomalies providing about 70% world coverage. Station locations were obtained for 46 tracking sites by combining electronic, laser, and additional optical tracking data with the above satellite data. Analysis of the radial positions of these stations and a value of mean gravity on the geoid indicated a mean equatorial radius for the earth of about 6378145 meters. Results of geopotential tests on satellite data not used in the solution show that better agreement was obtained with the GEM 1 and GEM 2 models than with the 1969 Smithsonian Standard Earth 2 model.
NASA Astrophysics Data System (ADS)
de La Fuente, Alberto; Shimizu, Kenji; NiO, Yarko; Imberger, JRg
2010-12-01
The energy transfer in a large deep lake, from the largest wind-excited basin-scale waves down to solitary-type waves, was investigated through a combination of inviscid nonlinear modal analysis and numerical simulations on the basis of weakly nonhydrostatic equations for internal gravitational waves. Data from four thermistor chains deployed in Lake Constance in 2003 revealed a Kelvin wave as the dominant primary basin-scale wave that transferred its energy, through nonlinear energy cascade, to waves with smaller spatial scales. The simulation results showed that the Kelvin wave excited higher azimuthal Kelvin wave modes whose phases were locked to the parent Kelvin wave to build a steepened wave front associated with the tail of solitary-type waves and large flow velocity in the wake of the steepened wave front. It is shown that it is the nonlinear and nonhydrostatic inviscid evolution of basin-scale waves that shifts the flow conditions from a basinwide coherent linear flow to a flow dominated by strong currents in localized regions where damping and mixing mechanisms may act efficiently.
Effective Field Theory Methods in Gravitational Physics and Tests of Gravity
NASA Astrophysics Data System (ADS)
Cannella, Umberto
2011-03-01
In this PhD thesis I make use of the "Effective Field Theory of Gravity for Extended Objects" by Goldberger and Rothstein in order to investigate theories of gravity and to take a different point of view on the physical information that can be extracted from experiments. In the first work I present, I study a scalar-tensor theory of gravity and I address the renormalization of the energy-momentum tensor for point-like and string-like sources. The second and third study I report are set in the context of testing gravity. So far experiments have probed dynamical regimes only up to order (v/c)^5 in the post-Newtonian expansion, which corresponds to the very first term of the radiative sector in General Relativity. In contrast, by means of gravitational-wave astronomy, one aims at testing General Relativity up to (v/c)^(12)! It is then relevant to envisage testing frameworks which are appropriate to this strong-field/radiative regime. In the last two chapters of this thesis a new such framework is presented. Using the effective field theory approach, General Relativity non-linearities are described by Feynman diagrams in which classical gravitons interact with matter sources and among themselves. Tagging the self-interaction vertices of gravitons with parameters it is possible, for example, to translate the measure of the period decay of Hulse-Taylor pulsar in a constraint on the three-graviton vertex at the 0.1% level; for comparison, LEP constraints on the triple-gauge-boson couplings of weak interactions are accurate at 3%. With future observations of gravitational waves, higher order graviton vertices can in principle be constrained through a Fisher matrix analysis.
NASA Astrophysics Data System (ADS)
Zhao, Xiao-Dong; Qian, Zheng
2015-10-01
The accurate measurement of dynamic characteristics in weak magnetic sensors is urgently required as a greater number of applications for these devices are found. In this paper, a novel weak pulsed magnetic field system is presented. The underlying principle is to drive a permanent magnet passing another magnet rapidly, producing a pulsed weak magnetic field. The magnitude of the field can be adjusted by changing the velocity and distance between the two magnets. The standard value of the pulsed dynamic magnetic field can be traced back to the accurate measurement of time, displacement, and static magnetic field. In this study a detailed procedure for producing a pulse magnetic field system using the above method is outlined after which a theoretical analysis of the permanent magnet movement is discussed. Using the described apparatus a milli-second level pulse-width with a milli-Tesla magnetic field magnitude is used to study the dynamic characteristics of a giant magnetoresistance sensor. We conclude by suggesting possible improvements to the described apparatus.
Zhao, Xiao-Dong; Qian, Zheng
2015-10-01
The accurate measurement of dynamic characteristics in weak magnetic sensors is urgently required as a greater number of applications for these devices are found. In this paper, a novel weak pulsed magnetic field system is presented. The underlying principle is to drive a permanent magnet passing another magnet rapidly, producing a pulsed weak magnetic field. The magnitude of the field can be adjusted by changing the velocity and distance between the two magnets. The standard value of the pulsed dynamic magnetic field can be traced back to the accurate measurement of time, displacement, and static magnetic field. In this study a detailed procedure for producing a pulse magnetic field system using the above method is outlined after which a theoretical analysis of the permanent magnet movement is discussed. Using the described apparatus a milli-second level pulse-width with a milli-Tesla magnetic field magnitude is used to study the dynamic characteristics of a giant magnetoresistance sensor. We conclude by suggesting possible improvements to the described apparatus. PMID:26520987
Biological effects due to weak magnetic fields on plants
NASA Astrophysics Data System (ADS)
Belyavskaya, N.
In the evolution process, living organisms have experienced the action of the Earth's magnetic field (MF) that is a natural component of our environment. It is known that a galactic MF induction does not exceed 0.1 nT, since investigations of weak magnetic field (WMF) effects on biological systems have attracted attention of biologists due to planning long-term space flights to other planets where the magnetizing force is near 10-5 Oe. However, the role of WMF and its influence on organisms' functioning are still insufficiently investigated. A large number of experiments with seedlings of different plant species placed in WMF has found that the growth of their primary roots is inhibited during the early terms of germination in comparison with control. The proliferation activity and cell reproduction are reduced in meristem of plant roots under WMF application. The prolongation of total cell reproductive cycle is registered due to the expansion of G phase in1 different plant species as well as of G phase in flax and lentil roots along with2 relative stability of time parameters of other phases of cell cycle. In plant cells exposed to WMF, the decrease in functional activity of genome at early prereplicate period is shown. WMF causes the intensification in the processes of proteins' synthesis and break-up in plant roots. Qualitative and quantitative changes in protein spectrum in growing and differentiated cells of plant roots exposed to WMF are revealed. At ultrastructural level, there are observed such ultrastructural peculiarities as changes in distribution of condensed chromatin and nucleolus compactization in nuclei, noticeable accumulation of lipid bodies, development of a lytic compartment (vacuoles, cytosegresomes and paramural bodies), and reduction of phytoferritin in plastids in meristem cells of pea roots exposed to WMF. Mitochondria are the most sensitive organelle to WMF application: their size and relative volume in cells increase, matrix is electron-transparent, and cristae reduce. Cytochemical studies indicate that cells of plant roots exposed to WMF show the Ca2 + oversaturation both in all organelles and in a hyaloplasm of the cells unlike the control ones. The data presented suggest that prolonged plant exposures to WMF may cause different biological effects at the cellular, tissue and organ level. They may be functionally related to systems that regulate plant metabolism including the intracellular Ca 2 + homeostasis. The understanding of the fundamental mechanisms and sites of interactions between WMF and biological systems are complex and still deserve strong efforts, particular addressed to basic principles of coupling between field energy and biomolecules.
NASA Astrophysics Data System (ADS)
Rivera, Susana
Throughout the last century, since the last decades of the XIX century, until present day, there had been many attempts to achieve the unification of the Forces of Nature. First unification was done by James Clerk Maxwell, with his Electromagnetic Theory. Then Max Plank developed his Quantum Theory. In 1905, Albert Einstein gave birth to the Special Relativity Theory, and in 1916 he came out with his General Relativity Theory. He noticed that there was an evident parallelism between the Gravitational Force, and the Electromagnetic Force. So, he tried to unify these forces of Nature. But Quantum Theory interposed on his way. On the 1940’s it had been developed the Quantum Electrodynamics (QED), and with it, the unified field theory had an arise interest. On the 60’s and 70’s there was developed the Quantum Chromodynamics (QCD). Along with these theories came the discovery of the strong interaction force and weak interaction force. And though there had been many attempts to unify all these forces of the nature, it could only be achieved the Unification of strong interaction, weak interaction and Electromagnetic Force. On the late 80”s and throughout the last two decades, theories such as “super-string theory”, “or the “M-theory”, among others, groups of Scientists, had been doing grand efforts and finally they came out with the unification of the forces of nature, being the only limitation the use of more than 11 dimensions. Using an ingenious mathematical tool known as the super symmetries, based on the Kaluza - Klein work, they achieve this goal. The strings of these theories are in the rank of 10-33 m. Which make them undetectable. There are many other string theories. The GEUFT theory is based on the existence of concentrated energy lines, which vibrates, expands and contracts, submitting and absorbing energy, matter and antimatter, and which yields a determined geometry, that gives as a result the formation of stars, galaxies, nebulae, clusters on the Macrocosmic level, and that allows the formation of fundamental particles on the Microcosmic level. The strings are described by a function named Symbiosis (σ), which depends on four energetic contributions: (1) Radiation Energy (2) Plasma Energy (3) Conducted Flux Energy and (4) Mass Energy. There is an intimate relation between them, and depending on the value they have at a certain moment and at a certain time, the string dynamics and its geometry are settled. That means that symbiosis describes the strings state in any point of the geometer - energy field. σ = F [Er(σ), Ep(σ), Ef(σ), Em(σ)] (1) This work is an attempt to achieve the unification of the forces of nature, based on the existence of a four dimension Universe.
Chiral imprint of a cosmic gauge field on primordial gravitational waves
NASA Astrophysics Data System (ADS)
Bielefeld, Jannis; Caldwell, Robert R.
2015-06-01
A cosmological gauge field with isotropic stress-energy introduces parity violation into the behavior of gravitational waves. We show that a primordial spectrum of inflationary gravitational waves develops a preferred handedness, left or right circularly polarized, depending on the abundance and coupling of the gauge field during the radiation era. A modest abundance of the gauge field would induce parity-violating correlations of the cosmic microwave background temperature and polarization patterns that could be detected by current and future experiments.
Gravitational waves from Abelian gauge fields and cosmic strings at preheating
Dufaux, Jean-Francois; Garcia-Bellido, Juan
2010-10-15
Primordial gravitational waves provide a very important stochastic background that could be detected soon with interferometric gravitational wave antennas or indirectly via the induced patterns in the polarization anisotropies of the cosmic microwave background. The detection of these waves will open a new window into the early Universe, and therefore it is important to characterize in detail all possible sources of primordial gravitational waves. In this paper we develop theoretical and numerical methods to study the production of gravitational waves from out-of-equilibrium gauge fields at preheating. We then consider models of preheating after hybrid inflation, where the symmetry breaking field is charged under a local U(1) symmetry. We analyze in detail the dynamics of the system in both momentum and configuration space. We show that gauge fields leave specific imprints in the resulting gravitational wave spectra, mainly through the appearance of new peaks at characteristic frequencies that are related to the mass scales in the problem. We also show how these new features in the spectra correlate with stringlike spatial configurations in both the Higgs and gauge fields that arise due to the appearance of topological winding numbers of the Higgs around Nielsen-Olesen strings. We study in detail the time evolution of the spectrum of gauge fields and gravitational waves as these strings evolve and decay before entering a turbulent regime where the gravitational wave energy density saturates.
NASA Astrophysics Data System (ADS)
Linet, B.; Teyssandier, P.
2016-02-01
We present a complete analysis of the light rays within the linearized, weak-field approximation of a Schwarzschild-like metric describing the gravitational field of an isolated, spherically symmetric body. We prove in this context the existence of two time transfer functions and we obtain these functions in an exact closed-form. We are led to distinguish two regimes. In the first regime, the two time transfer functions correspond to rays which are confined in regions of spacetime where the weak-field approximation is valid. Such a regime occurs in gravitational lensing configurations with double images of a given source. We find the general expressions of the angular separation and the difference in light travel time between the two images. In the second regime, there exists only one time transfer function corresponding to a light ray remaining in a region of weak field. Performing a Taylor expansion of this function with respect to the gravitational constant, we obtain the Shapiro time delay completed by a series of so-called "enhanced terms." The enhanced terms beyond the third order are new.
NASA Astrophysics Data System (ADS)
Taylor, James E.; Massey, Richard J.; Leauthaud, Alexie; George, Matthew R.; Rhodes, Jason; Kitching, Thomas D.; Capak, Peter; Ellis, Richard; Finoguenov, Alexis; Ilbert, Olivier; Jullo, Eric; Kneib, Jean-Paul; Koekemoer, Anton M.; Scoville, Nick; Tanaka, Masayuki
2012-04-01
Gravitational lensing can provide pure geometric tests of the structure of spacetime, for instance by determining empirically the angular diameter distance-redshift relation. This geometric test has been demonstrated several times using massive clusters which produce a large lensing signal. In this case, matter at a single redshift dominates the lensing signal, so the analysis is straightforward. It is less clear how weaker signals from multiple sources at different redshifts can be stacked to demonstrate the geometric dependence. We introduce a simple measure of relative shear which for flat cosmologies separates the effect of lens and source positions into multiplicative terms, allowing signals from many different source-lens pairs to be combined. Applying this technique to a sample of groups and low-mass clusters in the COSMOS survey, we detect a clear variation of shear with distance behind the lens. This represents the first detection of the geometric effect using weak lensing by multiple, low-mass groups. The variation of distance with redshift is measured with sufficient precision to constrain the equation of state of the universe under the assumption of flatness, equivalent to a detection of a dark energy component ? X at greater than 99% confidence for an equation-of-state parameter -2.5 <= w <= -0.1. For the case w = -1, we find a value for the cosmological constant density parameter ?? = 0.85+0.044 -0.19 (68% CL) and detect cosmic acceleration (q 0 < 0) at the 98% CL. We consider the systematic uncertainties associated with this technique and discuss the prospects for applying it in forthcoming weak-lensing surveys. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by AURA Inc. under the NASA contract NAS 5-26555; the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; the European Southern Observatory under the Large Program 175.A-0839, Chile; Kitt Peak National Observatory, Cerro Tololo Inter-American Observatory, and the National Optical Astronomy Observatory, which are operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.
NASA Astrophysics Data System (ADS)
Wang, Wenting; White, Simon D. M.; Mandelbaum, Rachel; Henriques, Bruno; Anderson, Michael E.; Han, Jiaxin
2016-03-01
We use weak gravitational lensing to measure mean mass profiles around locally brightest galaxies (LBGs). These are selected from the Seventh Data Release of the Sloan Digital Sky Survey spectroscopic and photometric catalogues to be brighter than any neighbour projected within 1.0 Mpc and differing in redshift by <1000 km s-1. Most (>83 per cent) are expected to be the central galaxies of their dark matter haloes. Previous stacking analyses have used this LBG sample to measure mean Sunyaev-Zeldovich flux and mean X-ray luminosity as a function of LBG stellar mass. In both cases, a simulation of the formation of the galaxy population was used to estimate effective halo mass for LBGs of given stellar mass, allowing the derivation of scaling relations between the gas properties of haloes and their mass. By comparing results from a variety of simulations to our lensing data, we show that this procedure has significant model dependence reflecting: (i) the failure of any given simulation to reproduce observed galaxy abundances exactly; (ii) a dependence on the cosmology underlying the simulation; and (iii) a dependence on the details of how galaxies populate haloes. We use our lensing results to recalibrate the scaling relations, eliminating most of this model dependence and explicitly accounting both for residual modelling uncertainties and for observational uncertainties in the lensing results. The resulting scaling relations link the mean gas properties of dark haloes to their mass over an unprecedentedly wide range, 1012.5 < M500/M⊙ < 1014.5, and should fairly and robustly represent the full halo population.
NASA Astrophysics Data System (ADS)
Rhodes, Jason D.; Massey, Richard J.; Albert, Justin; Collins, Nicholas; Ellis, Richard S.; Heymans, Catherine; Gardner, Jonathan P.; Kneib, Jean-Paul; Koekemoer, Anton; Leauthaud, Alexie; Mellier, Yannick; Refregier, Alexander; Taylor, James E.; Van Waerbeke, Ludovic
2007-09-01
We examine the spatial and temporal stability of the Hubble Space Telescope's Advanced Camera for Surveys (ACS) Wide Field Camera (WFC) point-spread function (PSF) using the 2 deg2 COSMOS survey. This is important for studies of weak gravitational lensing, where the ability to deconvolve the PSF from galaxy shapes is of paramount importance. We show that stochastic aliasing of the PSF necessarily occurs during ``drizzling.'' This aliasing is maximal if the output-pixel scale is equal to the input-pixel scale. This source of PSF variation can be significantly reduced by choosing a Gaussian drizzle kernel with a size of 0.8 input pixels and by reducing the output-pixel scale. We show that the PSF is temporally unstable, resulting in an overall slow periodic focus change in the COSMOS images. Using a modified version of the Tiny Tim PSF modeling software, we create grids of undistorted stars over a range of telescope focus values. We then use the approximately 10 well-measured stars in each COSMOS field to pick the best-fit focus value for each field. The Tiny Tim model stars can then be used to perform PSF corrections for weak lensing. We derive a parametric correction for the effect of charge transfer efficiency (CTE) degradation on the shapes of objects in the COSMOS field as a function of observation date, position within the ACS WFC field, and object flux. Finally, we discuss future plans to improve the CTE correction. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555 also based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; the XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and NASA; the European Southern Observatory, Chile; Kitt Peak National Observatory, Cerro Tololo Inter-American Observatory, and the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation; the National Radio Astronomy Observatory, which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.; and the Canada-France-Hawaii Telescope, operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France, and the University of Hawaii.
Was Newton right? A search for non-Newtonian behavior of weak-field gravity
NASA Astrophysics Data System (ADS)
Boynton, Paul; Moore, Michael; Newman, Riley; Berg, Eric; Bonicalzi, Ricco; McKenney, Keven
2014-06-01
Empirical tests of Einstein's metric theory of gravitation, even in the non-relativistic, weak-field limit, could play an important role in judging theory-driven extensions of the current Standard Model of fundamental interactions. Guided by Galileo's work and his own experiments, Newton formulated a theory of gravity in which the force of attraction between two bodies is independent of composition and proportional to the inertia of each, thereby transparently satisfying Galileo's empirically informed conjecture regarding the Universality of Free Fall. Similarly, Einstein honored the manifest success of Newton's theory by assuring that the linearized equations of GTR matched the Newtonian formalism under "classical" conditions. Each of these steps, however, was explicitly an approximation raised to the status of principle. Perhaps, at some level, Newtonian gravity does not accurately describe the physical interaction between uncharged, unmagnetized, macroscopic bits of ordinary matter. What if Newton were wrong? Detecting any significant deviation from Newtonian behavior, no matter how small, could provide new insights and possibly reveal new physics. In the context of physics as an empirical science, for us this yet unanswered question constitutes sufficient motivation to attempt precision measurements of the kind described here. In this paper we report the current status of a project to search for violation of the Newtonian inverse square law of gravity.
Gravitational field of a spinning sigma-model cosmic string
Simanek, E.
2008-08-15
We study the effect of internal space rotation on the gravitational properties of infinite straight and stationary cosmic strings. From the approximate solution of Einstein equations for the spinning Q-lump string, we obtain long-range gravitational acceleration resembling that of a rotating massive cylindrical shell. We also compute the angular velocity of the inertial frame dragging and the angle of light deflection by the Q-lump string. Matter accretion onto spinning strings can play a role in galaxy formation when the angular velocity times the string width is comparable to the speed of light.
Factorization of the relativistic Pauli equation in the presence of a gravitational field
NASA Astrophysics Data System (ADS)
Melek, M.
1988-08-01
Attention is called to a possible solution to the problem of the ambiguity in the numerical coefficient of the correction term (h(2) R) that occurs in the Klein-Gordon and relativistic Pauli equations in the presence of a gravitational field. This solution is based on the possibility of factorizing the relativistic Pauli equation for the propagator of the spin 1/2 particle, defined by a path integral, to obtain the Dirac equation in the presence of a gravitational field.
Electromagnetic Waves in a Uniform Gravitational Field and Planck's Postulate
ERIC Educational Resources Information Center
Acedo, Luis; Tung, Michael M.
2012-01-01
The gravitational redshift forms the central part of the majority of the classical tests for the general theory of relativity. It could be successfully checked even in laboratory experiments on the earth's surface. The standard derivation of this effect is based on the distortion of the local structure of spacetime induced by large masses. The
Electromagnetic Waves in a Uniform Gravitational Field and Planck's Postulate
ERIC Educational Resources Information Center
Acedo, Luis; Tung, Michael M.
2012-01-01
The gravitational redshift forms the central part of the majority of the classical tests for the general theory of relativity. It could be successfully checked even in laboratory experiments on the earth's surface. The standard derivation of this effect is based on the distortion of the local structure of spacetime induced by large masses. The…
Chiral symmetry breaking in {ital d}=3 NJL model in external gravitational and magnetic fields
Gitman, D.M.; Odintsov, S.D.; Shilnov, Y.I.
1996-08-01
The phase structure of the {ital d}=3 Nambu{endash}Jona-Lasinio model in curved spacetime with a magnetic field is investigated in leading order of the 1/{ital N} expansion and in the linear curvature approximation (an external magnetic field is treated exactly). The possibility of chiral symmetry breaking under the combined action of the external gravitational and magnetic fields is shown explicitly. In some circumstances the chiral symmetry may be restored due to the compensation of the magnetic field by the gravitational field. {copyright} {ital 1996 The American Physical Society.}
Field theory and weak Euler-Lagrange equation for classical particle-field systems
Qin, Hong; Burby, Joshua W; Davidson, Ronald C
2014-10-01
It is commonly believed that energy-momentum conservation is the result of space-time symmetry. However, for classical particle-field systems, e.g., Klimontovich-Maxwell and Klimontovich- Poisson systems, such a connection hasn't been formally established. The difficulty is due to the fact that particles and the electromagnetic fields reside on different manifolds. To establish the connection, the standard Euler-Lagrange equation needs to be generalized to a weak form. Using this technique, energy-momentum conservation laws that are difficult to find otherwise can be systematically derived.
Baryon masses in the three-state Potts field theory in a weak magnetic field
NASA Astrophysics Data System (ADS)
Rutkevich, S. B.
2015-01-01
The 3-state Potts field theory describes the scaling limit of the 3-state Potts model on the two-dimensional lattice near its continuous phase transition point. In the presence of thermal and magnetic field perturbations, the 3-state Potts field theory in the ordered phase exhibits confinement of kinks, which allows both mesons and baryons. We calculate the masses of light baryons in this model in the weak confinement regime in leading order of the small magnetic field. In leading order of perturbation theory, the light baryons can be viewed as bound states of three quantum particlesthe kinks, which move on a line and interact via a linear potential. We determine the masses of the lightest baryons by numerical solution of the associated non-relativistic one-dimensional quantum three-body problem.
Novikov, V V; Karnaukhov, A V
1997-01-01
To analyze the mechanisms of action of weak electric and magnetic fields on ion motion in solution, a new approach is outlined allowing for collective interactions of large ionic ensembles with the external field. PMID:9125229
Dynamics of a Fabry-Perot cavity in the field of a plane gravitational wave
Tarabrin, S P
2007-12-31
The interaction of a weak gravitational wave with a Fabry-Perot cavity is analysed beyond the long-wavelength approximation in the input-mirror locally Lorentzian frame of reference taking the light pressure into account. The generalised expressions are obtained for the coefficient of pondermotive optical rigidity, the motion law of the moving mirror of the cavity and the response function of the cavity. It is shown that the latter is a sum of two phase shifts of a circulating light wave: the phase incursion after reflection from the moving mirror and the phase incursion due to the direct interaction of gravitational and light waves in the cavity. The possibility of the resonance detection of high-frequency gravitational waves by using the optical rigidity effect is considered. (fifth seminar in memory of d.n. klyshko)
Physics of Gravitational Interaction: Geometry of Space or Quantum Field in Space
NASA Astrophysics Data System (ADS)
Baryshev, Yurij
2006-03-01
Thirring-Feynman's tensor field approach to gravitation opens new understanding on the physics of gravitational interaction and stimulates novel experiments on the nature of gravity. According to Field Gravity, the universal gravity force is caused by exchange of gravitons - the quanta of gravity field. Energy of this field is well-defined and excludes the singularity. All classical relativistic effects are the same as in General Relativity. The intrinsic scalar (spin 0) part of gravity field corresponds to ``antigravity'' and only together with the pure tensor (spin 2) part gives the usual Newtonian force. Laboratory and astrophysical experiments which may test the predictions of FG, will be performed in near future. In particular, observations at gravity observatories with bar and interferometric detectors, like Explorer, Nautilus, LIGO and VIRGO, will check the predicted scalar gravitational waves from supernova explosions. New types of cosmological models in Minkowski space are possible too.
Quasistationary solutions of self-gravitating scalar fields around collapsing stars
NASA Astrophysics Data System (ADS)
Sanchis-Gual, Nicolas; Degollado, Juan Carlos; Montero, Pedro J.; Font, Jos A.; Mewes, Vassilios
2015-10-01
Recent work has shown that scalar fields around black holes can form long-lived, quasistationary configurations surviving for cosmological time scales. Scalar fields thus cannot be discarded as viable candidates for dark matter halo models in galaxies around central supermassive black holes (SMBHs). One hypothesized formation scenario of most SMBHs at high redshift is the gravitational collapse of supermassive stars (SMSs) with masses of 105 M? . Any such scalar field configurations must survive the gravitational collapse of a SMS in order to be a viable model of physical reality. To check for the postcollapse survival of these configurations and to follow the dynamics of the black hole-scalar field system we present in this paper the results of a series of numerical relativity simulations of gravitationally collapsing, spherically symmetric stars surrounded by self-gravitating scalar fields. We use an ideal fluid equation of state with adiabatic index ? =4 /3 which is adequate to simulate radiation-dominated isentropic SMSs. Our results confirm the existence of oscillating, long-lived, self-gravitating scalar field configurations around nonrotating black holes after the collapse of the stars.
The study on the coefficients of Earth's gravitational field using Scaled Sensitivity Matrix method
NASA Astrophysics Data System (ADS)
Qu, Weijing; Dong, Danan; Wu, Bin
2015-04-01
The estimated monthly mean gravitational field parameters from one or two satellites only represent the linear combinations of a few primary spherical harmonic coefficients due to the limited sensitivity to the Earth's gravitational field. Using multiple satellites at various altitudes and inclinations increase the sensitivity and mitigate the non-unique problem. In practice, however, the explorations with a few satellites are still inevitable, such as the moon and deep space missions. Furthermore, the problem of the estimated parameters contaminated by the other un-estimated parameters due to the high correlation exists widely among various disciplines. Thus the quantitative assessment of the influence of un-estimated parameters on the estimated parameters provides important insight into the nature of the obtained solutions. In this paper, we study the estimated monthly mean, uncorrelated gravitational field parameters ( , , and ) from the Lageos1 and Lageos2 Satellite Laser Ranging (SLR) data for the 10 years period (2004-2013). Using the Scaled Sensitivity Matrix (SSM) method, we investigate the contributions from the other 73 un-estimated gravitational coefficients from degrees and orders 2 through 8 to the 4 estimated gravitational parameters. Our results confirm the reasonableness of the previous zonal combination coefficients from the orbital node analysis. Meanwhile our results reveal time-dependent correlations between the estimated non-zonal parameters and the un-estimated gravitational coefficients.
Newton's Law of Universal Gravitation
NASA Astrophysics Data System (ADS)
Grn, yvind
For a spherical mass distribution, V(?c r)=-mGM/r, with zero potential infinitely far from the centre of M. Newton's law of gravitation is valid for "small" velocities, i.e. velocities much smaller than the velocity of light and "weak" fields. Weak fields are fields in which the gravitational potential energy of a test particle is very small compared to its rest mass energy. (Note that here one is interested only in the absolute values of the above quantities and not their sign.)
The scaling of weak field phase-only control in Markovian dynamics
Am-Shallem, Morag; Kosloff, Ronnie
2014-07-28
We consider population transfer in open quantum systems, which are described by quantum dynamical semigroups (QDS). Using second order perturbation theory of the Lindblad equation, we show that it depends on a weak external field only through the field's autocorrelation function, which is phase independent. Therefore, for leading order in perturbation, QDS cannot support dependence of the population transfer on the phase properties of weak fields. We examine an example of weak-field phase-dependent population transfer, and show that the phase-dependence comes from the next order in the perturbation.
Escape of gravitational radiation from the field of massive bodies
NASA Technical Reports Server (NTRS)
Price, Richard H.; Pullin, Jorge; Kundu, Prasun K.
1993-01-01
We consider a compact source of gravitational waves of frequency omega in or near a massive spherically symmetric distribution of matter or a black hole. Recent calculations have led to apparently contradictory results for the influence of the massive body on the propagation of the waves. We show here that the results are in fact consistent and in agreement with the 'standard' viewpoint in which the high-frequency compact source produces the radiation as if in a flat background, and the background curvature affects the propagation of these waves.
NASA Astrophysics Data System (ADS)
Masalovich, S.
2014-11-01
An extraordinary focusing property of a parabolic mirror for ultracold neutrons in the presence of the gravitational field was first reported by Steyerl and co-authors. It was shown that all neutrons emitted from the focus of the mirror will be reflected back upon the same focus passing a point of return in the gravitational field in between. The present note offers a complementary geometric proof of this feature and discusses its application to many-mirror systems. The results can also be applied to electrons and ions in an electric field.
Palenzuela, Carlos; Lehner, Luis; Yoshida, Shin
2010-04-15
In addition to producing loud gravitational waves, the dynamics of a binary black hole system could induce emission of electromagnetic radiation by affecting the behavior of plasmas and electromagnetic fields in their vicinity. We study how the electromagnetic fields are affected by a pair of orbiting black holes through the merger. In particular, we show how the binary's dynamics induce a variability in possible electromagnetically induced emissions as well as an enhancement of electromagnetic fields during the late-merge and merger epochs. These time dependent features will likely leave their imprint in processes generating detectable emissions and can be exploited in the detection of electromagnetic counterparts of gravitational waves.
Weak Lensing PSF Correction of Wide-field CCD Mosaic Images (SULI Paper)
Cevallos, Marissa; /Caltech /SLAC
2006-01-04
Gravitational lensing provides some of the most compelling evidence for the existence of dark matter. Dark matter on galaxy cluster scales can be mapped due to its weak gravitational lensing effect: a cluster mass distribution can be inferred from the net distortion of many thousands of faint background galaxies that it induces. Because atmospheric aberration and defects in the detector distort the apparent shape of celestial objects, it is of great importance to characterize accurately the point spread function (PSF) across an image. In this research, the PSF is studied in images from the Canada-France-Hawaii Telescope (CFHT), whose camera is divided into 12 CCD chips. Traditional weak lensing methodology involves averaging the PSF across the entire image: in this work we investigate the effects of measuring the PSF in each chip independently. This chip-by-chip analysis was found to reduce the strength of the correlation between star and galaxy shapes, and predicted more strongly the presence of known galaxy clusters in mass maps. These results suggest correcting the CFHT PSF on an individual chip basis significantly improves the accuracy of detecting weak lensing.
Mapping Gravitational and Magnetic Fields with Children 9-11: Relevance, Difficulties and Prospects
ERIC Educational Resources Information Center
Bradamante, F.; Viennot, L.
2007-01-01
This paper presents an investigation centered on a guided conceptual path concerning magnetic and gravitational fields, proposed for children aged 9-11. The goal is to appreciate to what extent the idea of "mapping" two fields of interaction is accessible and fruitful for children of that age. The conceptual target is to link magnetic and
The interaction of a gravitational wave with a pure radiation field
NASA Astrophysics Data System (ADS)
Astefanoaiei, Iordana; Maftei, Gheorghe
We analyse the cosmological model, proposed by K. A. Bronnikov [1] in what concern the interaction of pure radiation field with gravitational waves, taking account of cylindrical symmetry of the configuration. We use the Newman-Penrose formalism, we calcultae in the null-tetradic base the spin coefficients, the directional derivatives, and we verify the commutation relations, the Bianchi identities, and we obtain the tetradic components of the Ricci and Weyl tensors for the c=d case using the Newman-Penrose formalism. We analyse the behavior of the gravitational waves, interacting with pure radiation field, by assuming that the energy-momentum pseudotensor has null components, while the gravitational field itself is of N Petrov type.
Computable Fields and Weak Truth-Table Reducibility
NASA Astrophysics Data System (ADS)
Steiner, Rebecca M.
For a computable field F, the splitting set S F of F is the set of polynomials with coefficients in F which factor over F, and the root set R F of F is the set of polynomials with coefficients in F which have a root in F.
On the possibility of detecting weak magnetic fields in variable white dwarfs
NASA Technical Reports Server (NTRS)
Jones, Philip W.; Hansen, Carl J.; Pesnell, W. Dean; Kawaler, Steven D.
1989-01-01
It is suggested that 'weak' magnetic fields of strengths less than 10 to the 6th G may be detectable in some variable white dwarfs. Weak fields can cause subtle changes in the Fourier power spectra of these stars in the form of 'splitting' in frequency of otherwise degenerate signals. Present-day observational and analysis techniques are capable of detecting these changes. It is suggested suggested, by listing some well-studied candidate stars, that perhaps the magnetic signature of splitting has already been observed in at least one object and that the difficult task of intensive measurements of weak fields should now be undertaken of those candidates.
Lichnerowicz-type theorems for self-gravitating systems with nonlinear electromagnetic fields
NASA Astrophysics Data System (ADS)
Cao, Li-Ming; Peng, Yuxuan; Xu, Jianfei
2014-07-01
We consider a self-gravitating system containing a globally timelike Killing vector and a nonlinear Born-Infeld electromagnetic field and scalar fields. We prove that under certain boundary conditions (asymptotically flat/anti-de Sitter) there cannot be any nontrivial field configurations in the spacetime. To explore nontrivial solutions, one should break any of the conditions we imposed. The case with another type of nonlinear electromagnetic field is also analyzed, and similar conclusions have been obtained under certain conditions.
Bi-local field in gravitational shockwave background
NASA Astrophysics Data System (ADS)
Kanda, N.; Naka, S.
2015-03-01
Particles with almost light velocity are able to be sources of shockwave gravity (SWG). Then, for ultra-high-energy particles, there exist two-body scatterings such that one particle is scattered from the gravitational background produced by another particle. Since the spacetime of SWG is closely related to a pp-wave solution of the AdS-type background, this type of interaction is also interesting in AdS dual gauge theories. From those viewpoints, the scattering of point particles or strings by SWG were studied. In this paper, we study the case of the bi-local models, which are simple relativistic bound systems having a close relation with specific modes of open strings. In particular, we analyze the bound-state effect on the scattering amplitudes, which describe the interaction between this model and SWG.
The Global Gravitational Anomaly of the Self-dual Field Theory
NASA Astrophysics Data System (ADS)
Monnier, Samuel
2014-01-01
We derive a formula for the global gravitational anomaly of the self-dual field theory on an arbitrary compact oriented Riemannian manifold. Along the way, we uncover interesting links between the theory of determinant line bundles of Dirac operators, Siegel theta functions and a functor constructed by Hopkins and Singer. We apply our result to type IIB supergravity and show that in the naive approximation where the Ramond-Ramond fields are treated as differential cohomology classes, the global gravitational anomaly vanishes on all 10-dimensional spin manifolds. We sketch a few other important physical applications.
Using Jupiter’s gravitational field to probe the Jovian convective dynamo
Kong, Dali; Zhang, Keke; Schubert, Gerald
2016-01-01
Convective motion in the deep metallic hydrogen region of Jupiter is believed to generate its magnetic field, the strongest in the solar system. The amplitude, structure and depth of the convective motion are unknown. A promising way of probing the Jovian convective dynamo is to measure its effect on the external gravitational field, a task to be soon undertaken by the Juno spacecraft. We calculate the gravitational signature of non-axisymmetric convective motion in the Jovian metallic hydrogen region and show that with sufficiently accurate measurements it can reveal the nature of the deep convection. PMID:27005472
Lifetime and decay of unstable particles in strong gravitational fields
Fregolente, Douglas; Saa, Alberto
2008-05-15
We consider here the decay of unstable particles in geodesic circular motion around compact objects. For the neutron, in particular, strong and weak decay are calculated by means of a semiclassical approach. Noticeable effects are expected to occur as one approaches the photonic circular orbit of realistic black holes. We argue that, in such a limit, the quasithermal spectrum inherent to extremely relativistic observers in circular motion plays a role similar to the Unruh radiation for uniformly accelerated observers.
Impurity-Assisted Tunneling Magnetoresistance under a Weak Magnetic Field
NASA Astrophysics Data System (ADS)
Txoperena, Oihana; Song, Yang; Qing, Lan; Gobbi, Marco; Hueso, Luis E.; Dery, Hanan; Casanova, Flix
2014-10-01
Injection of spins into semiconductors is essential for the integration of the spin functionality into conventional electronics. Insulating layers are often inserted between ferromagnetic metals and semiconductors for obtaining an efficient spin injection, and it is therefore crucial to distinguish between signatures of electrical spin injection and impurity-driven effects in the tunnel barrier. Here we demonstrate an impurity-assisted tunneling magnetoresistance effect in nonmagnetic-insulator-nonmagnetic and ferromagnetic-insulator-nonmagnetic tunnel barriers. In both cases, the effect reflects on-off switching of the tunneling current through impurity channels by the external magnetic field. The reported effect is universal for any impurity-assisted tunneling process and provides an alternative interpretation to a widely used technique that employs the same ferromagnetic electrode to inject and detect spin accumulation.
Impurity-assisted tunneling magnetoresistance under a weak magnetic field.
Txoperena, Oihana; Song, Yang; Qing, Lan; Gobbi, Marco; Hueso, Luis E; Dery, Hanan; Casanova, Flix
2014-10-01
Injection of spins into semiconductors is essential for the integration of the spin functionality into conventional electronics. Insulating layers are often inserted between ferromagnetic metals and semiconductors for obtaining an efficient spin injection, and it is therefore crucial to distinguish between signatures of electrical spin injection and impurity-driven effects in the tunnel barrier. Here we demonstrate an impurity-assisted tunneling magnetoresistance effect in nonmagnetic-insulator-nonmagnetic and ferromagnetic-insulator-nonmagnetic tunnel barriers. In both cases, the effect reflects on-off switching of the tunneling current through impurity channels by the external magnetic field. The reported effect is universal for any impurity-assisted tunneling process and provides an alternative interpretation to a widely used technique that employs the same ferromagnetic electrode to inject and detect spin accumulation. PMID:25325651
Mean-field universality class induced by weak hyperbolic curvatures
NASA Astrophysics Data System (ADS)
Gendiar, Andrej; Daniška, Michal; Krčmár, Roman; Nishino, Tomotoshi
2014-07-01
Order-disorder phase transition of the ferromagnetic Ising model is investigated on a series of two-dimensional lattices that have negative Gaussian curvatures. Exceptional lattice sites of coordination number seven are distributed on the triangular lattice, where the typical distance between the nearest exceptional sites is proportional to an integer parameter n. Thus, the corresponding curvature is asymptotically proportional to -n-2. Spontaneous magnetization and specific heat are calculated by means of the corner transfer matrix renormalization group method. For all the finite n cases, we observe the mean-field-like phase transition. It is confirmed that the entanglement entropy at the transition temperature is linear in (c/6)lnn, where c =1/2 is the central charge of the Ising model. The fact agrees with the presence of the typical length scale n being proportional to the curvature radius.
NASA Astrophysics Data System (ADS)
Lahav, Ofer; Terlevich, Elena; Terlevich, Roberto J.
1996-07-01
Preface; Part I. Galactic Structure: 1. Dynamics of triaxial systems P. T. de Zeeuw; 2. The mass of the galactic halo D. N. C. Lin; 3. Negative specific heat in clusters of atoms R. M. Lynden-Bell; 4. Dynamical evolution of globular clusters J. P. Ostriker; 5. Disc stability J. C. B. Papaloizou; 6. Protostellar discs J. E. Pringle; 7. Dynamics of warped galaxies S. D. Tremaine; Part II. Quasars, Galaxy Formation and Evolution: 8. Jets and cooling flows J. J. Binney; 9. Galactic nuclei M. J. Rees; 10. Optical quasar surveys M. Schmidt; 11. Violent relaxation in hierarchical clustering S. D. M. White; Part III. Cosmology: 12. Observational tests of general relativity R. D. Blandford; 13. A reconsideration of the peculiar velocity field within the local supercluster D. Burnstein; 14. Cosmology with the APM G. P. Efstathiou; 15. Geometric algebra, spacetime physics and gravitation S. F. Gull; 16. Weak gravitational lensing N. Kaiser; 17. Energy in general relativity J. Katz; 18. Gravitational dynamics in an expanding universe T. Padmanabhan; 19. Dynamics of the relative motions of the galaxies in and near the local group P. J. E. Peebles; 20. Inertia D. Lynden-Bell; Epilogue V. C. Rubin; Appendices Donald Lynden-Bell and D. J. D. Earn.
Net effect of many gravitational fields on the intensity of celestial light sources. Master's thesis
Cipperly, G.E.
1982-12-01
This thesis investigates the lens-like action of the gravitational fields of celestial bodies, which can alter the apparent intensity of more distant sources. Previous work in this area has shown that the chance of an individual body being sufficiently well aligned with a source to cause a very large gravitational intensity change is small. The issue addressed in this study is the possibility of there being a significant total change in the intensity of a source due to the combined effects of the gravitational fields of all celestial bodies, and in particular, the potential impact on intensity distance measurements, that is, determination of the distances of celestial light sources by means of intensity comparisons. It is first shown that the problem can be treated in flat space by associating an appropriate index of refraction with gravitational fields. A wave approach is taken in deriving the total deflection of a ray by the field of a single point mass. A statistical analysis is then performed to determine the expression for the mean total change in the intensity of celestial light sources due to the combined fields of all intervening bodies.
GMM-1: A 50 degree and order gravitational field model for Mars
NASA Technical Reports Server (NTRS)
Smith, D. E.; Lerch, F. J.; Nerem, R. S.; Zuber, M. T.; Patel, G. B.; Fricke, S. K.; Lemoine, F. G.
1993-01-01
Knowledge of the gravitational field, in combination with surface topography, provides one of the principal means of inferring the internal structure of a planetary body. The highest resolution gravitational field for Mars published thus far was derived from Doppler tracking data from the Mariner 9 and Viking 1 and 2 spacecraft and is complete to degree and order 18 corresponding to a half wavelength resolution of approximately 600 km. This field, which is characterized by a spatial resolution that is slightly better than that of the highest resolution (16x16) topographic model, has been utilized extensively in analyses of the state of stress and isostatic compensation of the Martian lithosphere. However, the resolution and quality of current gravity and topographic fields are such that the origin and evolution of even the major physiographic features on Mars, such as the hemispheric dichotomy and Tharsis rise, are not well understood. We have re-analyzed the Viking and Mariner data sets and have derived a new gravitational field, which we designated GMM-1 (Goddard Mars Model-1). This model is complete to spherical harmonic degree and order 50 with a corresponding (half wavelength) spatial resolution of 200-300 km where the data permit. In contrast to previous models, GMM-1 was solved to as high degree and order as necessary to nearly exhaust the attenuated gravitational signal contained in the tracking data.
Reheating signature in the gravitational wave spectrum from self-ordering scalar fields
NASA Astrophysics Data System (ADS)
Kuroyanagi, Sachiko; Hiramatsu, Takashi; Yokoyama, Jun'ichi
2016-02-01
We investigate the imprint of reheating on the gravitational wave spectrum produced by self-ordering of multi-component scalar fields after a global phase transition. The equation of state of the Universe during reheating, which usually has different behaviour from that of a radiation-dominated Universe, affects the evolution of gravitational waves through the Hubble expansion term in the equations of motion. This gives rise to a different power-law behavior of frequency in the gravitational wave spectrum. The reheating history is therefore imprinted in the shape of the spectrum. We perform 5123 lattice simulations to investigate how the ordering scalar field reacts to the change of the Hubble expansion and how the reheating effect arises in the spectrum. We also compare the result with inflation-produced gravitational waves, which has a similar spectral shape, and discuss whether it is possible to distinguish the origin between inflation and global phase transition by detecting the shape with future direct detection gravitational wave experiments such as DECIGO.
DOE R&D Accomplishments Database
Lee, T. D.
1970-07-01
While the phenomenon of beta-decay was discovered near the end of the last century, the notion that the weak interaction forms a separate field of physical forces evolved rather gradually. This became clear only after the experimental discoveries of other weak reactions such as muon-decay, muon-capture, etc., and the theoretical observation that all these reactions can be described by approximately the same coupling constant, thus giving rise to the notion of a universal weak interaction. Only then did one slowly recognize that the weak interaction force forms an independent field, perhaps on the same footing as the gravitational force, the electromagnetic force, and the strong nuclear and sub-nuclear forces.
NASA Astrophysics Data System (ADS)
Blake, Chris; Joudaki, Shahab; Heymans, Catherine; Choi, Ami; Erben, Thomas; Harnois-Deraps, Joachim; Hildebrandt, Hendrik; Joachimi, Benjamin; Nakajima, Reiko; van Waerbeke, Ludovic; Viola, Massimo
2016-03-01
The unknown nature of `dark energy' motivates continued cosmological tests of large-scale gravitational physics. We present a new consistency check based on the relative amplitude of non-relativistic galaxy peculiar motions, measured via redshift-space distortion, and the relativistic deflection of light by those same galaxies traced by galaxy-galaxy lensing. We take advantage of the latest generation of deep, overlapping imaging and spectroscopic data sets, combining the Red Cluster Sequence Lensing Survey, the Canada-France-Hawaii Telescope Lensing Survey, the WiggleZ Dark Energy Survey and the Baryon Oscillation Spectroscopic Survey. We quantify the results using the `gravitational slip' statistic EG, which we estimate as 0.48 ± 0.10 at z = 0.32 and 0.30 ± 0.07 at z = 0.57, the latter constituting the highest redshift at which this quantity has been determined. These measurements are consistent with the predictions of General Relativity, for a perturbed Friedmann-Robertson-Walker metric in a Universe dominated by a cosmological constant, which are EG = 0.41 and 0.36 at these respective redshifts. The combination of redshift-space distortion and gravitational lensing data from current and future galaxy surveys will offer increasingly stringent tests of fundamental cosmology.
Embryological changes induced by weak, extremely low frequency electromagnetic fields.
Delgado, J M; Leal, J; Monteagudo, J L; Gracia, M G
1982-01-01
Fertilized chicken eggs were incubated for 48 hours while exposed to extremely low frequency magnetic fields (ELMF) of 10 Hz, 100 Hz and 1000 Hz with intensities of 0.12, 1.2 and 12 micro T. Gross morphological and histological analysis of the exposed embryos revealed the following effects: (1) ELMF of 100 Hz/1.2 micro T had the most consistent and powerful inhibitory effect on embryogenesis. Development of embryos was reduced to the formation of the three primitive layers. Brain vesicles, auditory pit, neural tube, foregut, heart, vessels, and somites were not developed. Glycosaminoglycans were almost absent. (2) The above results demonstrate a window effect because embryos exposed to 100 Hz/1.2 micro T were less developed than embryos exposed at lower and higher intensities and frequencies. (3) Developing organs reacted with different sensitivity to ELMF of specific frequencies and intensities. Somites were not disturbed by exposure to 10 Hz with any of the intensities used. Formation of blood vessels was completely blocked by ELMF of 1000 Hz/12 micro T while traces of other organs were present. (4) The drastic embryological disturbances described were obtained with much lower intensities (1 micro T = 0.01 Gauss) than those used in studies by other investigators. (5) Embryological alterations induced by ELMF may depend on disturbances in the presence and structure of glycosaminoglycans which are essential elements in cellular activities, including cell migration. (6) The use of ELMF of low intensity may be a powerful method to investigate embryogenetic mechanisms and may also be a useful technique for investigation of other biological systems. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 PMID:7107514
The Effect of Weak Combined Magnetic Field on Root Gravitropism and a Role of Ca2+ Ions Therein
NASA Astrophysics Data System (ADS)
Kordyum, Elizabeth; Bogatina, Nina; Kondrachuk, A.
At present, magnetic fields of different types are widely used to study gravity sensing in plants. For instance, magnetic levitation of amyloplasts caused by high gradient magnetic field enables us to alter the effective gravity sensed by plant cells. For the first time we showed that a weak combined magnetic field (CMF), that is the sum of collinear permanent and alternating magnetic fields ( 0.5 gauss, 0-100 Hz), changes a cress and pea root positive gravitropic reaction on a negative one. This effect has the form of resonance and occurs at the frequency of cyclotron resonance of calcium ions. What is especially interesting is that under gravistimulation in the CMF, the displacement of amylopasts in the root cap statocytes is directed to the upper wall of a cell, i.e. in the direction opposite to the gravitational vector. The displacement of amyloplasts, which contain the abundance of free Ca2+ ions in the stroma, is accompanied by Ca2+ redistribution in the same direction, and increasing in the cytosol around amyloplasts near ten times in the CMF in comparison with the state magnetic field. Earlier, we also observed the Ca2+ accumulation in the upper site of a root curvature in the elongation zone in the CMF unlike a positive gravitropic reaction. Thus, it should be stressed that a root is bending in the same direction in which amyloplasts are displacing: downwards when gravitropism is positive and upwards when gravitropism is negative. The obtained data confirm the amyloplast statolithic function and give another striking demonstration of a leading role of Ca2+ ions in root gravitropism. But these data bring the question: what forces can promote amyloplast displacement against gravity? The possible explanation of the effect found is discussed. It is based on the ion cyclotron resonance in biosystems proposed by Liboff.. The original approach based on the use of a weak CMF may be helpful for understanding the mechanisms of plant gravisensing
NASA Technical Reports Server (NTRS)
Voorhies, Coerte V.
2004-01-01
As Earth's main magnetic field weakens, our magnetic shield against the onslaught of the solar wind thins. And the field strength needed to fend off battering by solar coronal mass ejections is decreasing, just when the delicate complexity of modem, vulnerable, electro-technological systems is increasing at an unprecedented rate. Recently, a working group of distinguished scientist from across the nation has asked NASA's Solid Earth and Natural Hazards program a key question: What are the dynamics of Earth s magnetic field and its interactions with the Earth system? Paleomagnetic studies of crustal rocks magnetized in the geologic past reveal that polarity reversals have occurred many times during Earth s history. Networked super-computer simulations of core field and flow, including effects of gravitational, pressure, rotational Coriolis, magnetic and viscous forces, suggest how this might happen in detail. And space-based measurements of the real, time-varying magnetic field help constrain estimates of the speed and direction of fluid iron flowing near the top of the core and enable tests of some hypotheses about such flow. Now scientists at NASA s Goddard Space Flight Center have developed and applied methods to test the hypotheses of narrow scale flow and of a dynamically weak magnetic field near the top of Earth s core. Using two completely different methods, C. V. Voorhies has shown these hypotheses lead to specific theoretical forms for the "spectrum" of Earth s main magnetic field and the spectrum of its rate of change. Much as solar physicists use a prism to separate sunlight into its spectrum, from long wavelength red to short wavelength blue light, geophysicists use a digital prism, spherical harmonic analysis, to separate the measured geomagnetic field into its spectrum, from long to short wavelength fields. They do this for the rate of change of the field as well.
Variations of the gravitational field as a motive power for rhythmics of biochemical processes
NASA Astrophysics Data System (ADS)
Troshichev, O. A.; Gorshkov, E. S.; Shapovalov, S. N.; Sokolovskii, V. V.; Ivanov, V. V.; Vorobeitchikov, V. M.
2004-01-01
Variations of the gravitational field affected by the Sun and the Moon while the Earth's moving along the orbit seem to be a powerful source of many rhythmical processes typical of biochemical processes. Studies carried out in AARI revealed the obvious relationships between the dynamics of some biochemical reactions and ?D- function describing the regular variations of the gravitational field under combined influence of the Sun and the Moon. The following of them are examined as examples: the rate of the unithiol oxidation in vitro, concentration of the thiol compounds in human urine, some hematological indicators (rate of the erythrocytes sedimentation, hemoglobin content). Compatibility of run of the biochemical indicators and ?D-function is indicative of essential influence of the regular variations of the gravitational field on rhythmics of the biochemical processes. As this takes place, the solar activity acts like to the instability factor. Balance of the solar activity effects and the varying gravitational field effect alter in time depending on location in the solar activity cycle.
Where Else Is Null the Gravitational Field between Two Massive Spheres?
ERIC Educational Resources Information Center
Lima, F. M. S.
2009-01-01
To find the point between two massive spherical bodies at which their gravitational fields cancel is an apparently simple problem usually found in introductory physics textbooks. However, by noting that such a point does not exist when the distance between the spheres is small and one of the masses is much smaller than the other--e.g., between the…
Where Else Is Null the Gravitational Field between Two Massive Spheres?
ERIC Educational Resources Information Center
Lima, F. M. S.
2009-01-01
To find the point between two massive spherical bodies at which their gravitational fields cancel is an apparently simple problem usually found in introductory physics textbooks. However, by noting that such a point does not exist when the distance between the spheres is small and one of the masses is much smaller than the other--e.g., between the
Illustrating Some Principles of Separation Science through Gravitational Field-Flow Fractionation
ERIC Educational Resources Information Center
Beckett, Ronald; Sharma, Reshmi; Andric, Goja; Chantiwas, Rattikan; Jakmunee, Jaroon; Grudpan, Kate
2007-01-01
Particle separation is an important but often neglected topic in undergraduate curricula. This article discusses how the method of gravitational field-flow fractionation (GrFFF) can be used to illustrate many principles of separation science and some fundamental concepts of physical chemistry. GrFFF separates particles during their elution through…
[Physical essence of erythrocytic sedimentation rate in the gravitation field of the earth].
Cherniĭ, A N
2009-01-01
The erythrocytic sedimentation rate method has been long known in medicine and extensively used in laboratory practice in tuberculosis facilities. However, many authors note that the erythrocytic sedimentation rate phenomenon has not clearly understood. By applying the total theory of relativity and quantum mechanics, the author discloses the physical essence of erythrocytic sedimentation in the gravitation field of the Earth. PMID:19514457
Reply to 'Comment on 'Primordial magnetic seed field amplification by gravitational waves''
Betschart, Gerold; Zunckel, Caroline; Dunsby, Peter K S; Marklund, Mattias
2007-04-15
Here we respond to the comment by Tsagas on our earlier paper. We show that the results in that comment are flawed and cannot be used for drawing conclusions about the nature of magnetic field amplification by gravitational waves and give further support that the results of our earlier paper are correct.
Illustrating Some Principles of Separation Science through Gravitational Field-Flow Fractionation
ERIC Educational Resources Information Center
Beckett, Ronald; Sharma, Reshmi; Andric, Goja; Chantiwas, Rattikan; Jakmunee, Jaroon; Grudpan, Kate
2007-01-01
Particle separation is an important but often neglected topic in undergraduate curricula. This article discusses how the method of gravitational field-flow fractionation (GrFFF) can be used to illustrate many principles of separation science and some fundamental concepts of physical chemistry. GrFFF separates particles during their elution through
Effect of a uniform sea-level change on the earth's rotation and gravitational field
NASA Technical Reports Server (NTRS)
Chao, B. Fong; O'Connor, William P.
1988-01-01
Global water redistriburtion between the oceans, atmosphere and continents causes changes in the earth's rotation and gravitational field. To conserve water mass, the effect of the small uniform change in sea-level must be considered. Explicit formulas are provided for these sea-level corrections to the gravitational Stokes coefficients, polar motion and length of day. In two recent publications, this sea-level correction term for polar motion was given incorrectly. These errors which arose from normalization conventions with the ocean function are corrected.
Turner, E.L.
1988-07-01
For several years astronomers have devoted considerable effort to finding and studying a class of celestial phenomena whose very existence depends on rare cosmic accidents. These are gravitational-lens events, which occur when two or more objects at different distances from the earth happen to lie along the same line of sight and so coincide in the sky. The radiation from the more distant object, typically a quasar, is bent by the gravitational field of the foreground object. The bending creates a cosmic mirage: distorted or multiple images of the background object. Such phenomena may reveal many otherwise undetectable features of the image source, of the foreground object and of the space lying between them. Such observations could help to resolve several fundamental questions in cosmology. In the past decade theoretical and observational research on gravitational lenses has grown rapidly and steadily. At this writing at least 17 candidate lens systems have been discussed in the literature. Of the 17 lens candidates reported so far in professional literature, only five are considered to have been reliably established by subsequent observations. Another three are generally regarded as weak or speculative cases with less than 50 percent chance of actually being lens systems. In the remaining nine cases the evidence is mixed or is sparse enough so that the final judgment could swing either way. As might be concluded, little of the scientific promise of gravitational lenses has yet been realized. The work has not yielded a clear value for the proportionality constant or any of the other fundamental cosmological parameter. 7 figs.
Next-to-leading order gravitational spin-orbit coupling in an effective field theory approach
Levi, Michele
2010-11-15
We use an effective field theory (EFT) approach to calculate the next-to-leading order (NLO) gravitational spin-orbit interaction between two spinning compact objects. The NLO spin-orbit interaction provides the most computationally complex sector of the NLO spin effects, previously derived within the EFT approach. In particular, it requires the inclusion of nonstationary cubic self-gravitational interaction, as well as the implementation of a spin supplementary condition (SSC) at higher orders. The EFT calculation is carried out in terms of the nonrelativistic gravitational field parametrization, making the calculation more efficient with no need to rely on automated computations, and illustrating the coupling hierarchy of the different gravitational field components to the spin and mass sources. Finally, we show explicitly how to relate the EFT derived spin results to the canonical results obtained with the Arnowitt-Deser-Misner (ADM) Hamiltonian formalism. This is done using noncanonical transformations, required due to the implementation of covariant SSC, as well as canonical transformations at the level of the Hamiltonian, with no need to resort to the equations of motion or the Dirac brackets.
Gravitational collapse of scalar fields via spectral methods
Oliveira, H. P. de; Rodrigues, E. L.; Skea, J. E. F.
2010-11-15
In this paper we present a new numerical code based on the Galerkin method to integrate the field equations for the spherical collapse of massive and massless scalar fields. By using a spectral decomposition in terms of the radial coordinate, the field equations were reduced to a finite set of ordinary differential equations in the space of modes associated with the Galerkin expansion of the scalar field, together with algebraic sets of equations connecting modes associated with the metric functions. The set of ordinary differential equations with respect to the null coordinate is then integrated using an eighth-order Runge-Kutta method. The numerical tests have confirmed the high accuracy and fast convergence of the code. As an application we have evaluated the whole spectrum of black hole masses which ranges from infinitesimal to large values obtained after varying the amplitude of the initial scalar field distribution. We have found strong numerical evidence that this spectrum is described by a nonextensive distribution law.
Abele, H.; Jenke, T.; Leeb, H.; Schmiedmayer, J.
2010-03-15
We propose to apply Ramsey's method of separated oscillating fields to the spectroscopy of the quantum states in the gravity potential above a horizontal mirror. This method allows a precise measurement of quantum mechanical phaseshifts of a Schroedinger wave packet bouncing off a hard surface in the gravitational field of the Earth. Measurements with ultracold neutrons will offer a sensitivity to Newton's law or hypothetical short-ranged interactions, which is about 21 orders of magnitude below the energy scale of electromagnetism.
Ponomarev, V O; Novikov, V V; Karnaukhov, A V; Ponomarev, O A
2008-01-01
A theoretical model of the mechanism of action of weak electromagnetic fields on water solutions has been constructed. The model predicts the redistribution of protons on spatial inhomogeneities in water medium. It is shown that an external field leads to the phasing of ions on the standing wave, which is considered as an inhomogeneity. As a result of an inhomogeneous distribution of hydrogen ions, local regions with a higher and lower acidity arise. The acidity of medium substantially affects the rate of chemical reactions; therefore, the exposure to a weak external field can change this parameter. The effect of local changes in acidity on the rate of hydrogen peroxide production was considered. It was predicted that the exposure to a weak electromagnetic field with particular parameters can increase the rate and, as a consequence, the concentration of hydrogen peroxide in solution. PMID:18543761
NASA Astrophysics Data System (ADS)
Lucchesi, D. M.; Anselmo, L.; Bassan, M.; Pardini, C.; Peron, R.; Pucacco, G.; Visco, M.
2015-08-01
In this work, the Laser Ranged Satellites Experiment (LARASE) is presented. This is a research program that aims to perform new refined tests and measurements of gravitation in the field of the Earth in the weak field and slow motion (WFSM) limit of general relativity (GR). For this objective we use the free available data relative to geodetic passive satellite lasers tracked from a network of ground stations by means of the satellite laser ranging (SLR) technique. After a brief introduction to GR and its WFSM limit, which aims to contextualize the physical background of the tests and measurements that LARASE will carry out, we focus on the current limits of validation of GR and on current constraints on the alternative theories of gravity that have been obtained with the precise SLR measurements of the two LAGEOS satellites performed so far. Afterward, we present the scientific goals of LARASE in terms of upcoming measurements and tests of relativistic physics. Finally, we introduce our activities and we give a number of new results regarding the improvements to the modelling of both gravitational and non-gravitational perturbations to the orbit of the satellites. These activities are a needed prerequisite to improve the forthcoming new measurements of gravitation. An innovation with respect to the past is the specialization of the models to the LARES satellite, especially for what concerns the modelling of its spin evolution, the neutral drag perturbation and the impact of Earth's solid tides on the satellite orbit.
Gravitational self-force in nonvacuum spacetimes: An effective field theory derivation
NASA Astrophysics Data System (ADS)
Zimmerman, Peter
2015-09-01
In this paper we investigate the motion of small compact objects in nonvacuum spacetimes using methods from effective field theory in curved spacetime. Although a vacuum formulation is sufficient in many astrophysical contexts, there are applications such as the role of the self-force in enforcing cosmic censorship in the context of the overcharging problem, which necessitate an extension into the nonvacuum regime. The defining feature of the self-force problem in nonvacuum spacetimes is the coupling between gravitational and nongravitational field perturbations. The formulation of the self-force problem for nonvacuum spacetimes was recently provided in simultaneous papers by Zimmerman and Poisson [Gravitational self-force in nonvacuum spacetimes, Phys. Rev. D 90, 084030 (2014)] and Linz, Friedmann, and Wiseman [Combined gravitational and electromagnetic self-force on charged particles in electrovac spacetimes, Phys. Rev. D 90, 084031 (2014)]. Here we distinguish ourselves by working with the effective action rather than the field equations. The formalism utilizes the multi-index notation developed by Zimmerman and Poisson [Gravitational self-force in nonvacuum spacetimes, Phys. Rev. D 90, 084030 (2014) to accommodate the coupling between the different fields. Using dimensional regularization, we arrive at a finite expression for the local self-force expressed in terms of multi-index quantities evaluated in the background spacetime. We then apply the formalism to compute the coupled gravitational self-force in two explicit cases. First, we calculate the self-force on a massive particle possessing scalar charge and moving in a scalarvac spacetime. We then derive an expression for the self-force on an electrically charged, massive particle moving in an electrovac spacetime. In both cases, the force is expressed as a sum of local terms involving tensors defined in the background spacetime and evaluated at the current position of the particle, as well as tail integrals that depend on the past history of the particle.
Nonminimally coupled gravitational and electromagnetic fields: pp-wave solutions
Dereli, Tekin; Sert, Oezcan
2011-03-15
We give the Lagrangian formulation of a generic nonminimally extended Einstein-Maxwell theory with an action that is linear in the curvature and quadratic in the electromagnetic field. We derive the coupled field equations by a first-order variational principle using the method of Lagrange multipliers. We look for solutions describing plane-fronted Einstein-Maxwell waves with parallel rays. We give a family of exact pp-wave solutions associated with a partially massless spin-2 photon and a partially massive spin-2 graviton.
Gravitational field models for study of Earth mantle dynamics
NASA Technical Reports Server (NTRS)
1979-01-01
The tectonic forces or stresses due to the small scale mantle flow under the South American plate are detected and determined by utilizing the harmonics of the geopotential field model. The high degree harmonics are assumed to describe the small scale mantle convection patterns. The input data used in the derivation of this model is made up of 840,000 optical, electronic, and laser observations and 1,656 5 deg x 5 deg mean free air anomalies. Although there remain some statistically questionable aspects of the high degree harmonics, it seems appropriate now to explore their implications for the tectonic forces or stress field under the crust.
NASA Astrophysics Data System (ADS)
Suárez, Abril; Chavanis, Pierre-Henri
2015-07-01
Using a generalization of the Madelung transformation, we derive the hydrodynamic representation of the Klein-Gordon-Einstein equations in the weak field limit. We consider a complex self-interacting scalar field with a λ |φ |4 potential. We study the evolution of the spatially homogeneous background in the fluid representation and derive the linearized equations describing the evolution of small perturbations in a static and in an expanding Universe. We compare the results with simplified models in which the gravitational potential is introduced by hand in the Klein-Gordon equation, and assumed to satisfy a (generalized) Poisson equation. Nonrelativistic hydrodynamic equations based on the Schrödinger-Poisson equations or on the Gross-Pitaevskii-Poisson equations are recovered in the limit c →+∞. We study the evolution of the perturbations in the matter era using the nonrelativistic limit of our formalism. Perturbations whose wavelength is below the Jeans length oscillate in time while perturbations whose wavelength is above the Jeans length grow linearly with the scale factor as in the cold dark matter model. The growth of perturbations in the scalar field model is substantially faster than in the cold dark matter model. When the wavelength of the perturbations approaches the cosmological horizon (Hubble length), a relativistic treatment is mandatory. In that case, we find that relativistic effects attenuate or even prevent the growth of perturbations. This paper exposes the general formalism and provides illustrations in simple cases. Other applications of our formalism will be considered in companion papers.
NASA Astrophysics Data System (ADS)
Schubert, G.; Zhang, K.; Kong, D.; Anderson, J. D.; Helled, R.
2010-12-01
The shapes and gravitational fields of rotationally and tidally distorted planets and satellites depend on their interior mass distributions. Measurements of these observable characteristics are therefore used to infer the internal structure of planetary bodies. Interpretations are based on approximate formulae such as the Radau-Darwin relation derivable from the theory of figures or more accurate evaluations of the theory. The exact solution for the shape and gravitational field of the rotationally distorted constant density Maclaurin spheroid has, until now, provided one of the only ways to assess the accuracy and range of validity of approximate theory of figure predictions. We generalize the Maclaurin spheroid solution to a 2-layer core-envelope body, a more realistic model of a real planet or moon. The exact 2-layer Maclaurin spheroid solution, e. g., the shapes of the surface and core-envelope interface, depend on 3 parameters, the core-envelope density ratio, the fractional volume of the core, and ?2/2?G?2, where ? is the rotation rate, G is the gravitational constant, and ?2 is the envelope density. For realistic parameter values, the flattening of the interface is smaller than that of the surface. Results of the exact solution are compared with predictions of the theory of figures up to order 3 in the small rotational parameter of the theory. The exact solution serves as a benchmark for numerical models that attempt to invert gravitational and shape data to infer internal planetary structure.
Cartographic generalization of urban street networks based on gravitational field theory
NASA Astrophysics Data System (ADS)
Liu, Gang; Li, Yongshu; Li, Zheng; Guo, Jiawei
2014-05-01
The automatic generalization of urban street networks is a constant and important aspect of geographical information science. Previous studies show that the dual graph for street-street relationships more accurately reflects the overall morphological properties and importance of streets than do other methods. In this study, we construct a dual graph to represent street-street relationship and propose an approach to generalize street networks based on gravitational field theory. We retain the global structural properties and topological connectivity of an original street network and borrow from gravitational field theory to define the gravitational force between nodes. The concept of multi-order neighbors is introduced and the gravitational force is taken as the measure of the importance contribution between nodes. The importance of a node is defined as the result of the interaction between a given node and its multi-order neighbors. Degree distribution is used to evaluate the level of maintaining the global structure and topological characteristics of a street network and to illustrate the efficiency of the suggested method. Experimental results indicate that the proposed approach can be used in generalizing street networks and retaining their density characteristics, connectivity and global structure.
Alternatives to Schwarzschild in the weak field limit of General Relativity
NASA Astrophysics Data System (ADS)
Bozza, V.; Postiglione, A.
2015-06-01
The metric outside an isolated object made up of ordinary matter is bound to be the classical Schwarzschild vacuum solution of General Relativity. Nevertheless, some solutions are known (e.g. Morris-Thorne wormholes) that do not match Schwarzschild asymptotically. On a phenomenological point of view, gravitational lensing in metrics falling as 1/rq has recently attracted great interest. In this work, we explore the conditions on the source matter for constructing static spherically symmetric metrics exhibiting an arbitrary power-law as Newtonian limit. For such space-times we also derive the expressions of gravitational redshift and force on probe masses, which, together with light deflection, can be used in astrophysical searches of non-Schwarzschild objects made up of exotic matter. Interestingly, we prove that even a minimally coupled scalar field with a power-law potential can support non-Schwarzschild metrics with arbitrary asymptotic behaviour.
Locality of Gravitational Systems from Entanglement of Conformal Field Theories.
Lin, Jennifer; Marcolli, Matilde; Ooguri, Hirosi; Stoica, Bogdan
2015-06-01
The Ryu-Takayanagi formula relates the entanglement entropy in a conformal field theory to the area of a minimal surface in its holographic dual. We show that this relation can be inverted for any state in the conformal field theory to compute the bulk stress-energy tensor near the boundary of the bulk spacetime, reconstructing the local data in the bulk from the entanglement on the boundary. We also show that positivity, monotonicity, and convexity of the relative entropy for small spherical domains between the reduced density matrices of any state and of the ground state of the conformal field theory are guaranteed by positivity conditions on the bulk matter energy density. As positivity and monotonicity of the relative entropy are general properties of quantum systems, this can be interpreted as a derivation of bulk energy conditions in any holographic system for which the Ryu-Takayanagi prescription applies. We discuss an information theoretical interpretation of the convexity in terms of the Fisher metric. PMID:26196612
Horizon thermodynamics and gravitational field equations in Horava-Lifshitz gravity
Cai Ronggen; Ohta, Nobuyoshi
2010-04-15
We explore the relationship between the first law of thermodynamics and gravitational field equation at a static, spherically symmetric black hole horizon in Horava-Lifshitz theory with/without detailed balance. It turns out that as in the cases of Einstein gravity and Lovelock gravity, the gravitational field equation can be cast to a form of the first law of thermodynamics at the black hole horizon. This way we obtain the expressions for entropy and mass in terms of black hole horizon, consistent with those from other approaches. We also define a generalized Misner-Sharp energy for static, spherically symmetric spacetimes in Horava-Lifshitz theory. The generalized Misner-Sharp energy is conserved in the case without matter field, and its variation gives the first law of black hole thermodynamics at the black hole horizon.
Radiation reaction and gravitational waves in the effective field theory approach
NASA Astrophysics Data System (ADS)
Galley, Chad R.; Tiglio, Manuel
2009-06-01
We compute the contribution to the Lagrangian from the leading order (2.5 post-Newtonian) radiation reaction and the quadrupolar gravitational waves emitted from a binary system using the effective field theory (EFT) approach of Goldberger and Rothstein. We use an initial value formulation of the underlying (quantum) framework to implement retarded boundary conditions and describe these real-time dissipative processes. We also demonstrate why the usual scattering formalism of quantum field theory inadequately accounts for these. The methods discussed here should be useful for deriving real-time quantities (including radiation reaction forces and gravitational wave emission) and hereditary terms in the post-Newtonian approximation (including memory, tail and other causal, history-dependent integrals) within the EFT approach. We also provide a consistent formulation of the radiation sector in the equivalent effective field theory approach of Kol and Smolkin.
Radiation reaction and gravitational waves in the effective field theory approach
Galley, Chad R.; Tiglio, Manuel
2009-06-15
We compute the contribution to the Lagrangian from the leading order (2.5 post-Newtonian) radiation reaction and the quadrupolar gravitational waves emitted from a binary system using the effective field theory (EFT) approach of Goldberger and Rothstein. We use an initial value formulation of the underlying (quantum) framework to implement retarded boundary conditions and describe these real-time dissipative processes. We also demonstrate why the usual scattering formalism of quantum field theory inadequately accounts for these. The methods discussed here should be useful for deriving real-time quantities (including radiation reaction forces and gravitational wave emission) and hereditary terms in the post-Newtonian approximation (including memory, tail and other causal, history-dependent integrals) within the EFT approach. We also provide a consistent formulation of the radiation sector in the equivalent effective field theory approach of Kol and Smolkin.
Paramagnetic relaxation in anisotropic materials in zero and weak constant fields
NASA Astrophysics Data System (ADS)
Fokina, N. P.; Khalvashi, E. Kh.; Khutsishvili, K. O.
2014-12-01
Paramagnetic relaxation in strongly anisotropic materials is analytically investigated in zero and weak constant magnetic fields. The objectives of the microscopic analytical investigation are (i) the weak-field electron paramagnetic resonance (EPR) linewidth and (ii) the electron spin relaxation rates given by a calorimetric Gorter type experiment in the zero constant field at the arbitrary low-frequency field directions, respectively, to the sample crystallographic axes. The EPR linewidth is calculated under the suggestion of its spin-phonon nature at the one-phonon mechanism of the spin-lattice relaxation in the case of the strong isotropic exchange interaction for the arbitrary direction Z of the constant magnetic field. The EPR linewidth is presented as the half sum of the zero-field relaxation rates, measured by the Gorter experiment with the low-frequency field oriented along the X, Y axes. With the help of the macroscopic consideration, it is shown that the zero-field relaxation rates describe the relaxation of the X and Y magnetization components in a zero or weak constant magnetic field. The relaxation rates of the magnetizations created along a,b,c crystallographic axes by a low-frequency field in a Gorter type experiment follow the obtained expressions in the particular cases and are in the experimentally confirmed relations with the EPR linewidth.
Paramagnetic relaxation in anisotropic materials in zero and weak constant fields
Fokina, N. P.; Khalvashi, E. Kh.; Khutsishvili, K. O.
2014-12-21
Paramagnetic relaxation in strongly anisotropic materials is analytically investigated in zero and weak constant magnetic fields. The objectives of the microscopic analytical investigation are (i) the weak-field electron paramagnetic resonance (EPR) linewidth and (ii) the electron spin relaxation rates given by a calorimetric Gorter type experiment in the zero constant field at the arbitrary low-frequency field directions, respectively, to the sample crystallographic axes. The EPR linewidth is calculated under the suggestion of its spin-phonon nature at the one-phonon mechanism of the spin-lattice relaxation in the case of the strong isotropic exchange interaction for the arbitrary direction Z of the constant magnetic field. The EPR linewidth is presented as the half sum of the zero-field relaxation rates, measured by the Gorter experiment with the low-frequency field oriented along the X, Y axes. With the help of the macroscopic consideration, it is shown that the zero-field relaxation rates describe the relaxation of the X and Y magnetization components in a zero or weak constant magnetic field. The relaxation rates of the magnetizations created along a,b,c crystallographic axes by a low-frequency field in a Gorter type experiment follow the obtained expressions in the particular cases and are in the experimentally confirmed relations with the EPR linewidth.
Gravitational research. Gravitational waves
NASA Astrophysics Data System (ADS)
Amaldi, E.; Pizzella, G.
1985-04-01
Gravitational wave research is reviewed. Gravitational theory, relativity theory, experiments in general relativity, sources of gravitational waves, the Rome gravitational experiment, quantic limits of gravitational waves measurements and how to avoid those limits are discussed.
Dynamical stability of a self-gravitating rotating cylinder in a helical magnetic field
NASA Astrophysics Data System (ADS)
Luyten, P. J.
1989-03-01
The effect of a helical magnetic field on the oscillations and the stability of a homogeneous self-gravitating rotating cylinder is investigated. The axial field has a tendency to stabilize long wave numbers and to destabilize small wave numbers so that maximum instability occurs for a finite wave number. If the toroidal and the axial component of the field have the same sign, the instability associated with the toroidal field can be removed by the rotation or by the axial field. Rotational instability is reduced but cannot be removed by the field. If the components of the field have the opposite sign, rotational instability is increased. The maximum growth rate of the magnetic instability is reduced by a small axial field and tends to a finite value for large axial fields.
Thick branes from self-gravitating scalar fields
Novikov, Oleg O.; Andrianov, Vladimir A.; Andrianov, Alexander A.
2014-07-23
The formation of a domain wall ('thick brane') induced by scalar matter dynamics and triggered by a thin brane defect is considered in noncompact five-dimensional space-time with warped AdS type geometry. The scalar matter is composed of two fields with softly broken O(2) symmetry and minimal coupling to gravity. The nonperturbative effects in the invariant mass spectrum of light localized scalar states are investigated for different values of the tension of the thin brane defect. Especially interesting is the case of the thin brane with negative tension when the singular barriers form a potential well with two infinitely tall walls and the discrete spectrum of localized states arises completely isolated from the bulk.
Weak Solutions of the Cohomological Equation on ? 2 {mathbb {R}}(2) for Regular Vector Fields
NASA Astrophysics Data System (ADS)
De Leo, Roberto
2015-12-01
In a recent article (De Leo, R., Ann. Glob. Anal. Geom., 39, 3, 231-248 2011), we studied the global solvability of the so-called cohomological equation L ? f = g in , where ? is a regular vector field on the plane and L ? the corresponding Lie derivative operator. In a joint article with T. Gramchev and A. Kirilov (2011), we studied the existence of global weak solutions of the cohomological equation for planar vector fields depending only on one coordinate. Here we generalize the results of both articles by providing explicit conditions for the existence of global weak solutions to the cohomological equation when ? is intrinsically Hamiltonian or of finite type.
Spin polarization induced by an electric field in the presence of weak localization effects
NASA Astrophysics Data System (ADS)
Guerci, Daniele; Borge, Juan; Raimondi, Roberto
2016-01-01
We evaluate the spin polarization (Edelstein or inverse spin galvanic effect) and the spin Hall current induced by an applied electric field by including the weak localization corrections for a two-dimensional electron gas. We show that the weak localization effects yield logarithmic corrections to both the spin polarization conductivity relating the spin polarization and the electric field and to the spin Hall angle relating the spin and charge currents. The renormalization of both the spin polarization conductivity and the spin Hall angle combine to produce a zero correction to the total spin Hall conductivity as required by an exact identity. Suggestions for the experimental observation of the effect are given.
Dark sector impact on gravitational collapse of an electrically charged scalar field
NASA Astrophysics Data System (ADS)
Nakonieczna, Anna; Rogatko, Marek; Nakonieczny, Łukasz
2015-11-01
Dark matter and dark energy are dominating components of the Universe. Their presence affects the course and results of processes, which are driven by the gravitational interaction. The objective of the paper was to examine the influence of the dark sector on the gravitational collapse of an electrically charged scalar field. A phantom scalar field was used as a model of dark energy in the system. Dark matter was modeled by a complex scalar field with a quartic potential, charged under a U(1)-gauge field. The dark components were coupled to the electrically charged scalar field via the exponential coupling and the gauge field-Maxwell field kinetic mixing, respectively. Complete non-linear simulations of the investigated process were performed. They were conducted from regular initial data to the end state, which was the matter dispersal or a singularity formation in a spacetime. During the collapse in the presence of dark energy dynamical wormholes and naked singularities were formed in emerging spacetimes. The wormhole throats were stabilized by the violation of the null energy condition, which occurred due to a significant increase of a value of the phantom scalar field function in its vicinity. The square of mass parameter of the dark matter scalar field potential controlled the formation of a Cauchy horizon or wormhole throats in the spacetime. The joint impact of dark energy and dark matter on the examined process indicated that the former decides what type of an object forms, while the latter controls the amount of time needed for the object to form. Additionally, the dark sector suppresses the natural tendency of an electrically charged scalar field to form a dynamical Reissner-Nordström spacetime during the gravitational collapse.
NASA Astrophysics Data System (ADS)
Ortaggio, Marcello
2004-03-01
We investigate the ultrarelativistic boost of a Schwarzschild black hole immersed in an external electromagnetic field, described by an exact solution of the Einstein-Maxwell equations found by Ernst (the Schwarzschild-Melvin metric). Following the classical method of Aichelburg and Sexl, the gravitational field generated by a black hole moving with the speed of light and the transformed electromagnetic field are determined. The corresponding exact solution describes an impulsive gravitational wave propagating in the static, cylindrically symmetric, electrovac universe of Melvin, and for a vanishing electromagnetic field it reduces to the well known Aichelburg-Sexl pp?wave. In the boosting process, the original Petrov type I of the Schwarzschild-Melvin solution simplifies to type II on the impulse, and to type D elsewhere. The geometry of the wave front is studied, in particular its nonconstant Gauss curvature. In addition, a more general class of impulsive waves in the Melvin universe is constructed by means of a six-dimensional embedding formalism adapted to the background. A coordinate system is also presented in which all the impulsive metrics take a continuous form. Finally, it is shown that these solutions are a limiting case of a family of exact gravitational waves with an arbitrary profile. This family is identified with a solution previously found by Garfinkle and Melvin. We thus complement their analysis, in particular demonstrating that such spacetimes are of type II and belong to the Kundt class.
Gravitational radiation from collapsing magnetized dust
Sotani, Hajime; Yoshida, Shijun; Kokkotas, Kostas D.
2007-04-15
In this article we study the influence of magnetic fields on the axial gravitational waves emitted during the collapse of a homogeneous dust sphere. We found that while the energy emitted depends weakly on the initial matter perturbations it has strong dependence on the strength and the distribution of the magnetic field perturbations. The gravitational wave output of such a collapse can be up to an order of magnitude larger or smaller calling for detailed numerical 3D studies of collapsing magnetized configurations.
Myers-Perry black hole in an external gravitational field
NASA Astrophysics Data System (ADS)
Abdolrahimi, Shohreh; Kunz, Jutta; Nedkova, Petya
2015-03-01
We obtain a new exact solution of the 5D Einstein equations in vacuum describing a distorted Myers-Perry black hole with a single angular momentum. Locally, the solution is interpreted as a black hole distorted by a stationary U (1 )U (1 ) symmetric distribution of external matter. Technically, the solution is constructed by applying a twofold Bcklund transformation on a 5D distorted Minkowski spacetime as a seed. The physical quantities of the solution are calculated, and a local Smarr-like relation on the black hole horizon is derived. It possesses the same form as the Smarr-like relation for the asymptotically flat Myers-Perry black hole. It is demonstrated that in contrast to the asymptotically flat Myers-Perry black hole, the ratio of the horizon angular momentum and the mass J2/M3 is unbounded, and can grow arbitrarily large. We study the properties of the ergoregion and the horizon surface. The external field does not influence the horizon topology. The horizon geometry however is distorted, and any regular axisymmetric geometry is possible.
Can Surface Flux Transport Account for the Weak Polar Field in Cycle 23?
NASA Astrophysics Data System (ADS)
Jiang, Jie; Cameron, Robert H.; Schmitt, Dieter; Schssler, Manfred
2013-06-01
To reproduce the weak magnetic field on the polar caps of the Sun observed during the declining phase of cycle 23 poses a challenge to surface flux transport models since this cycle has not been particularly weak. We use a well-calibrated model to evaluate the parameter changes required to obtain simulated polar fields and open flux that are consistent with the observations. We find that the low polar field of cycle 23 could be reproduced by an increase of the meridional flow by 55% in the last cycle. Alternatively, a decrease of the mean tilt angle of sunspot groups by 28% would also lead to a similarly low polar field, but cause a delay of the polar field reversals by 1.5 years in comparison to the observations.
Nonlocal effective gravitational field equations and the running of Newton's constant G
Hamber, H.W.; Williams, R.M.
2005-08-15
Nonperturbative studies of quantum gravity have recently suggested the possibility that the strength of gravitational interactions might slowly increase with distance. Here a set of generally covariant effective field equations are proposed, which are intended to incorporate the gravitational, vacuum-polarization induced, running of Newton's constant G. One attractive feature of this approach is that, from an underlying quantum gravity perspective, the resulting long-distance (or large time) effective gravitational action inherits only one adjustable parameter {xi}, having the units of a length, arising from dimensional transmutation in the gravitational sector. Assuming the above scenario to be correct, some simple predictions for the long-distance corrections to the classical standard model Robertson-Walker metric are worked out in detail, with the results formulated as much as possible in a model-independent framework. It is found that the theory, even in the limit of vanishing renormalized cosmological constant, generally predicts an accelerated power-law expansion at later times t{approx}{xi}{approx}1/H.
General Relativistic Theory of the VLBI Time Delay in the Gravitational Field of Moving Bodies
NASA Technical Reports Server (NTRS)
Kopeikin, Sergei
2003-01-01
The general relativistic theory of the gravitational VLBI experiment conducted on September 8, 2002 by Fomalont and Kopeikin is explained. Equations of radio waves (light) propagating from the quasar to the observer are integrated in the time-dependent gravitational field of the solar system by making use of either retarded or advanced solutions of the Einstein field equations. This mathematical technique separates explicitly the effects associated with the propagation of gravity from those associated with light in the integral expression for the relativistic VLBI time delay of light. We prove that the relativistic correction to the Shapiro time delay, discovered by Kopeikin (ApJ, 556, L1, 2001), changes sign if one retains direction of the light propagation but replaces the retarded for the advanced solution of the Einstein equations. Hence, this correction is associated with the propagation of gravity. The VLBI observation measured its speed, and that the retarded solution is the correct one.
The forthcoming Radioastron Mission as a tool for GR tests in the strong gravitational field limit
NASA Astrophysics Data System (ADS)
Zakharov, A.; De Paolis, F.; Nucita, A.; Ingrosso, G.
In 2007 the Radioastron satellite will be launched As a result 10-meter radio telescope will be located at a high orbit around the Earth Actually it will be a generalization of VLBI technique using space -- ground base The interferometer will have extraordinary angular resolution namely at the shortest wavelengths angular resolution is about 10 -5 -10 -6 as These angular sizes are comparable with angular sizes of shadows mirages around nearest supermassive black holes For example the size of the shadow around the black hole in the Galactic Centre is about 50 mu as it means that in principle such a tool like the Radioastron interferometer could resolve the shadow Analyzing the shapes of shadows mirages one could evaluate parameters of a black hole such as spin a inclination angle theta and a black hole charge or magnetic monopole and test GR in the strong gravitational field limit corresponding gravitational fields near black hole horizons
Conductivity of molten sodium chloride in an arbitrarily weak dc electric field
NASA Astrophysics Data System (ADS)
Delhommelle, Jerome; Cummings, Peter T.; Petravic, Janka
2005-09-01
We use nonequilibrium molecular-dynamics (NEMD) simulations to characterize the response of a fluid subjected to an electric field. We focus on the response for very weak fields. Fields accessible by conventional NEMD methods are typically of the order of 109Vm-1, i.e., several orders of magnitude larger than those typically used in experiments. Using the transient time-correlation function, we show how NEMD simulations can be extended to study systems subjected to a realistic dc electric field. We then apply this approach to study the response of molten sodium chloride for a wide range of dc electric fields.
Conductivity of molten sodium chloride in an arbitrarily weak dc electric field.
Delhommelle, Jerome; Cummings, Peter T; Petravic, Janka
2005-09-15
We use nonequilibrium molecular-dynamics (NEMD) simulations to characterize the response of a fluid subjected to an electric field. We focus on the response for very weak fields. Fields accessible by conventional NEMD methods are typically of the order of 10(9) V m(-1), i.e., several orders of magnitude larger than those typically used in experiments. Using the transient time-correlation function, we show how NEMD simulations can be extended to study systems subjected to a realistic dc electric field. We then apply this approach to study the response of molten sodium chloride for a wide range of dc electric fields. PMID:16392571
Fast Gravitational Field Model Using Adaptive Orthogonal Finite Element Approximation
NASA Astrophysics Data System (ADS)
Younes, A.; Macomber, B.; Woollands, R.; Probe, A.; Bai, X.; Junkins, J.
2013-09-01
Recent research has addressed the issue that high degree and order gravity expansions involve tens of thousands of terms in a theoretically infinite order spherical harmonic expansion (some gravity models extend to degree and order 200 with over 30,000 terms) which in principle must be computed at every integration step to obtain the acceleration consistent with the gravity model. We propose to evaluate these gravity model interpolation models and use them in conjunction with the modified Picard path approximation methods. It was decided to consider analogous orthogonal approximation methods to interpolate, an FEM model, high (degree, order) gravity fields, by replacing the global spherical harmonic series by a family of locally precise orthogonal polynomial approximations for efficient computation. Our preliminary results showed that time to compute the state of the art (degree and order 200) spherical harmonic gravity is reduced by 4 to 5 orders of magnitude while maintaining > 9 digits of accuracy. Most of the gain is due to adopting the orthogonal FEM approach, but radial adaptation of the approximation degree gains an additional order of magnitude speedup. The efficient data base storage/access of the local coefficients is studied, which utilizes porting the algorithm to the NVIDIA GPU. This paper will address the accuracy and efficiency in both a C++ serial PC architecture as well as a PC/GPU architecture. The Adaptive Orthogonal Finite Element Gravity Model (AOFEGM) is expected to have broad potential for speeding the trajectory propagation algorithms; for example, used in conjunction with orthogonal Finite Element Model (FEM) gravity approximations, the Chebyshev-Picard path approximation enables truly revolutionary speedups in orbit propagation without accuracy loss.
Diffusion of Scalar Particles in Janis-Newman-Winicour-Wyman Gravitational Field and GRBs
NASA Astrophysics Data System (ADS)
Lambiase, G.; Capozziello, S.; Carloni, S.
The propagation of a boson particle in the Janis-Newman-Winicour-Wyman (JNWW) gravitational field is analyzed. We derive the wave function of the scalar particle, and the effective potential experienced by quantum particles. Besides, we show that the probability to find the scalar particle near the region where the naked singularity is finite. Finally, these results are proposed as a model to study the gamma ray bursts (GRBs) physics.
Energy-momentum complex of gravitational field in the Palatini formalism
NASA Astrophysics Data System (ADS)
Novotn, Jan
1993-06-01
It is shown that Murphy's energy-momentum complex of the gravitational field, derived from the Hilbert Lagrangian by use of the Palatini formalism, is identical to the complex derived from the same Lagrangian in a standard way by Mitskievic. The explicitly tensorial formulation of conservation laws in general relativity is eflectively used and some properties of the complex in question are discussed in connection with Murphy's article.
Gravitational quantum states of Antihydrogen
Voronin, A. Yu.; Froelich, P.; Nesvizhevsky, V. V.
2011-03-15
We present a theoretical study of the motion of the antihydrogen atom (H) in the gravitational field of Earth above a material surface. We predict that the H atom, falling in the gravitational field of Earth above a material surface, would settle into long-lived quantum states. We point out a method of measuring the difference in the energy of H in such states. The method allows for spectroscopy of gravitational levels based on atom-interferometric principles. We analyze the general feasibility of performing experiments of this kind. We point out that such experiments provide a method of measuring the gravitational force (Mg) acting on H and that they might be of interest in the context of testing the weak equivalence principle for antimatter.
Dynamo Models Incorporating Iron "Snow Zones" Consistent with Mercury's Weak Observed Magnetic Field
NASA Astrophysics Data System (ADS)
Vilim, R.; Stanley, S.; Hauck, S. A.
2009-12-01
The Mariner 10 and MESSENGER probes have revealed that Mercury possesses a field of internal origin, with a dipole moment between 230 and 290 nT-Rm3 (Rm is the mean radius of Mercury). The field is dominated by an axial dipole, and is approximately 100 times weaker than expected. Although it is likely caused by a planetary dynamo, a field as weak as Mercury's is difficult to produce with an Earth-like dynamo. This disparity in field strengths implies that the core dynamics of Mercury differ markedly from Earth's, and that an exotic internal field partitioning should be expected. Recent experimental work by Chen et al. (2008) indicates that convection in Mercury's outer core may be compositionally driven at multiple points by an iron precipitate, or "snow". Using the Kuang-Bloxham numerical dynamo model, we find that models which include a snow state midway through the convecting region can produce weak fields on the same order as those observed for Mercury. We present the observable features of our model and discuss the mechanism responsible for generating these weak fields.
Magnetite in human tissues: a mechanism for the biological effects of weak ELF magnetic fields.
Kirschvink, J L; Kobayashi-Kirschvink, A; Diaz-Ricci, J C; Kirschvink, S J
1992-01-01
Due to the apparent lack of a biophysical mechanism, the question of whether weak, low-frequency magnetic fields are able to influence living organisms has long been one of the most controversial subjects in any field of science. However, two developments during the past decade have changed this perception dramatically, the first being the discovery that many organisms, including humans, biochemically precipitate the ferrimagnetic mineral magnetite (Fe3O4). In the magnetotactic bacteria, the geomagnetic response is based on either biogenic magnetite or greigite (Fe3S4), and reasonably good evidence exists that this is also the case in higher animals such as the honey bee. Second, the development of simple behavioral conditioning experiments for training honey bees to discriminate magnetic fields demonstrates conclusively that at least one terrestrial animal is capable of detecting earth-strength magnetic fields through a sensory process. In turn, the existence of this ability implies the presence of specialized receptors which interact at the cellular level with weak magnetic fields in a fashion exceeding thermal noise. A simple calculation shows that magnetosomes moving in response to earth-strength ELF fields are capable of opening trans-membrane ion channels, in a fashion similar to those predicted by ionic resonance models. Hence, the presence of trace levels of biogenic magnetite in virtually all human tissues examined suggests that similar biophysical processes may explain a variety of weak field ELF bioeffects. PMID:1285705
Magnetite in human tissues: A mechanism for the biological effects of weak ELF magnetic fields
Kirschvink, J.L.; Kobayashi-Kirschvink, A.; Diaz-Ricci, J.C.; Kirschvink, S.J. )
1992-01-01
Due to the apparent lack of a biophysical mechanism, the question of whether weak, low-frequency magnetic fields are able to influence living organisms has long been one of the most controversial subjects in any field of science. However, two developments during the past decade have changed this perception dramatically, the first being the discovery that many organisms, including humans, biochemically precipitate the ferrimagnetic mineral magnetite (Fe3O4). In the magnetotactic bacteria, the geomagnetic response is based on either biogenic magnetite or greigite (Fe3S4), and reasonably good evidence exists that this is also the case in higher animals such as the honey bee. Second, the development of simple behavioral conditioning experiments for training honey bees to discriminate magnetic fields demonstrates conclusively that at least one terrestrial animal is capable of detecting earth-strength magnetic fields through a sensory process. In turn, the existence of this ability implies the presence of specialized receptors which interact at the cellular level with weak magnetic fields in a fashion exceeding thermal noise. A simple calculation shows that magnetosomes moving in response to earth-strength ELF fields are capable of opening trans-membrane ion channels, in a fashion similar to those predicted by ionic resonance models. Hence, the presence of trace levels of biogenic magnetite in virtually all human tissues examined suggests that similar biophysical processes may explain a variety of weak field ELF bioeffects. 61 refs.
NASA Astrophysics Data System (ADS)
Wo?oszyn, M.; Spisak, B. J.
2012-01-01
Influence of the weak electric field on the electronic structure of the Fibonacci superlattice is considered. The electric field produces a nonlinear dynamics of the energy spectrum of the aperiodic superlattice. Mechanism of the nonlinearity is explained in terms of energy levels anticrossings. The multifractal formalism is applied to investigate the effect of weak electric field on the statistical properties of electronic eigenfunctions. It is shown that the applied electric field does not remove the multifractal character of the electronic eigenfunctions, and that the singularity spectrum remains non-parabolic, however with a modified shape. Changes of the distances between energy levels of neighbouring eigenstates lead to the changes of the inverse participation ratio of the corresponding eigenfunctions in the weak electric field. It is demonstrated, that the local minima of the inverse participation ratio in the vicinity of the anticrossings correspond to discontinuity of the first derivative of the difference between marginal values of the singularity strength. Analysis of the generalized dimension as a function of the electric field shows that the electric field correlates spatial fluctuations of the neighbouring electronic eigenfunction amplitudes in the vicinity of anticrossings, and the nonlinear character of the scaling exponent confirms multifractality of the corresponding electronic eigenfunctions.
Relativistic weak lensing from a fully non-linear cosmological density field
NASA Astrophysics Data System (ADS)
Thomas, D. B.; Bruni, M.; Wands, D.
2015-09-01
In this paper we examine cosmological weak lensing on non-linear scales and show that there are Newtonian and relativistic contributions and that the latter can also be extracted from standard Newtonian simulations. We use the post-Friedmann formalism, a post-Newtonian type framework for cosmology, to derive the full weak-lensing deflection angle valid on non-linear scales for any metric theory of gravity. We show that the only contributing term that is quadratic in the first order deflection is the expected Born correction and lens-lens coupling term. We use this deflection angle to analyse the vector and tensor contributions to the E- and B- mode cosmic shear power spectra. In our approach, once the gravitational theory has been specified, the metric components are related to the matter content in a well-defined manner. Specifying General Relativity, we write down a complete set of equations for a GR+ΛCDM universe for computing all of the possible lensing terms from Newtonian N-body simulations. We illustrate this with the vector potential and show that, in a GR+ΛCDM universe, its contribution to the E-mode is negligible with respect to that of the conventional Newtonian scalar potential, even on non-linear scales. Thus, under the standard assumption that Newtonian N-body simulations give a good approximation of the matter dynamics, we show that the standard ray tracing approach gives a good description for a ΛCDM cosmology.
Weak electromagnetic field admitting integrability in Kerr-NUT-(A)dS spacetimes
NASA Astrophysics Data System (ADS)
Kol?, Ivan; Krtou, Pavel
2015-06-01
We investigate properties of higher-dimensional generally rotating black-hole spacetimes, so-called Kerr-NUT-(anti)-de Sitter spacetimes, as well as a family of related spaces which share the same explicit and hidden symmetries. In these spaces, we study a particle motion in the presence of a weak electromagnetic field and compare it with its operator analogies. First, we find general commutativity conditions for classical observables and for their operator counterparts, then we investigate a fulfillment of these conditions in the Kerr-NUT-(anti)-de Sitter and related spaces. We find the most general form of the weak electromagnetic field compatible with the complete integrability of the particle motion and the comutativity of the field operators. For such a field we solve the charged Hamilton-Jacobi and Klein-Gordon equations by separation of variables.
Magnetic fields and fluctuations in weakly Mn doped ZnGeP{sub 2}
Mengyan, P. W.; Lichti, R. L.; Baker, B. B.; Celebi, Y. G.; Catak, E.; Carroll, B. R.; Zawilski, K. T.; Schunemann, P. G.
2014-02-21
We report on our measurements of local and bulk magnetic features in weakly Mn doped ZnGeP{sub 2}. Utilizing muon spin rotation and relaxation measurements, we identify local ferromagnetic order and fluctuations in the local fields as sampled by an implanted muon (?{sup +}). We also report on field induced ferromagnetism occurring above the claimed paramagnetic to ferromagnetic transition temperature (T{sub c} = 312 K)
Leeuwen-Segarceanu, Elena M. van; Dorresteijn, Lucille D.A.; Pillen, Sigrid; Biesma, Douwe H.; Vogels, Oscar J.M.; Alfen, Nens van
2012-02-01
Purpose: To describe the damage to the muscles and propose a pathophysiologic mechanism for muscle atrophy and weakness after mantle field radiotherapy in Hodgkin lymphoma (HL) survivors. Methods and Materials: We examined 12 patients treated by mantle field radiotherapy between 1969 and 1998. Besides evaluation of their symptoms, the following tests were performed: dynamometry; ultrasound of the sternocleidomastoid, biceps, and antebrachial flexor muscles; and needle electromyography of the neck, deltoid, and ultrasonographically affected arm muscles. Results: Ten patients (83%) experienced neck complaints, mostly pain and muscle weakness. On clinical examination, neck flexors were more often affected than neck extensors. On ultrasound, the sternocleidomastoid was severely atrophic in 8 patients, but abnormal echo intensity was seen in only 3 patients. Electromyography of the neck muscles showed mostly myogenic changes, whereas the deltoid, biceps, and antebrachial flexor muscles seemed to have mostly neurogenic damage. Conclusions: Many patients previously treated by mantle field radiotherapy develop severe atrophy and weakness of the neck muscles. Neck muscles within the radiation field show mostly myogenic damage, and muscles outside the mantle field show mostly neurogenic damage. The discrepancy between echo intensity and atrophy suggests that muscle damage is most likely caused by an extrinsic factor such as progressive microvascular fibrosis. This is also presumed to cause damage to nerves within the radiated field, resulting in neurogenic damage of the deltoid and arm muscles.
An Investigation into Quantifying Micron-G Changes in a Gravitational Field of 1G
NASA Technical Reports Server (NTRS)
Gauthier, Richard R.; Gilbert, John A.
1997-01-01
This project called for the development of an accelerometer designed to be used in conjunction with gravity shielding experiments. The device had to measure local gravitational changes on the order of a few micro-G's (micron-G) with a spatial resolution greater than one measurement per ten square centimeters. Measurements had to be made at a minimum rate of two per second. Tasks included the design, development and demonstration of a prototype. The deliverable consisted of three copies of this final report. The study resulted in the development of a Transversely Suspended Accelerometer (TSA) which met all of the technical specifications. Different generations of the device were demonstrated to NASA/MSFC personnel as they were developed. The final prototype is available for further demonstration and future use. The study draws attention to the fact that the magnetic fields required to produce gravitational shielding may result in apparent decreases in the weights of suspended objects on the order of those attributed to the effect itself. This observation reinforces the need to quantify the influences of the magnetic field on any measurement device used to study gravitational shielding. This task was accomplished for the TSA.
Empirical model of the gravitational field generated by the oceanic lithosphere
NASA Astrophysics Data System (ADS)
Tenzer, Robert; Chen, Wenjin; Ye, Zhourun
2015-01-01
We present an empirical model of the gravitational field generated by the oceanic lithosphere computed over the world's oceans with a spectral resolution complete to a spherical harmonic degree of 180. This gravity model is compiled based on applying methods for a spherical harmonic analysis and synthesis of the global gravity and crustal structure models. The in situ seawater densities and the density samples from ocean-floor drilling sites are utilized in the gravimetric forward modeling of bathymetry and marine sediments. The gravitational signal attributed to the oceanic lithosphere density structure is described empirically in terms of the ocean-floor age and depth. The former is explained by the increasing density with age due to conductive cooling of the oceanic lithosphere. The latter describes the gravitational signature of thermal lithospheric contraction, which is isostatically compensated by ocean deepening. The long-wavelength gravity spectrum reflects mainly the compositional and thermal structures within the sub-lithospheric mantle. We demonstrate that this empirical gravity model reproduces realistically most of the long-to-medium wavelength features of the actual gravity field, except for some systematic discrepancies, especially along continental slopes and large sedimentary accumulations, which cannot be described accurately by applied empirical models.
Recent results on the mass, gravitational field and moments of inertia of the moon.
NASA Technical Reports Server (NTRS)
Michael, W. H., Jr.; Blackshear, W. T.
1972-01-01
Use of Doppler tracking data from the Lunar Orbiter series of spacecraft in an analysis of the spherical harmonic coefficients of the lunar gravitational field through thirteenth degree and order. The value obtained for the mass of the moon, GM = 4902.84 cu km/sec/sec, is in good agreement with previous results and with results obtained by alternate procedures. Acceleration contour plots, derived from the gravitational coefficients, show correlations with surface features on the near side of the moon, but are of questionable validity for the far side because of the lack of direct tracking data on the far side. Based on the most recent gravitational field data, the current estimate for the polar moment of inertia of the moon is C/Ma squared = 0.4019 super + 0.004 sub - 0.002. This value indicates that the interior of the moon can be homogeneous, but some results presented strongly suggest that the moon is differentiated, with an excess of mass in the direction toward the earth.
Hydrodynamical wind on vertically self-gravitating ADAFs in the presence of toroidal magnetic field
NASA Astrophysics Data System (ADS)
Ghasemnezhad, Maryam; Abbassi, Shahram
2016-02-01
We present the effect of a hydrodynamical wind on the structure and the surface temperature of a vertically self-gravitating magnetized advection-dominated accretion flows (ADAFs) using self-similar solutions. Also a model for an axisymmetric, steady-state, vertically self-gravitating hot accretion flow threaded by a toroidal magnetic field has been formulated. The model is based on α-prescription for turbulence viscosity. It is found that the thickness and radial velocity of the disc are reduced significantly as wind gets stronger. In particular, the solutions indicated that the wind and advection have the same effects on the structure of the disc. We also find that the thin ADAF becomes hotter by including the wind parameter and the self-gravity parameter.
The deflection of light induced by the Sun's gravitational field and measured with geodetic VLBI
NASA Astrophysics Data System (ADS)
Titov, O.; Girdiuk, A.
2015-08-01
The Sun's gravitational field deflects the apparent positions of close objects in accordance with the formulae of general relativity. Optical astrometry is used to test the prediction, but only with the stars close to the Sun and only during total Solar eclipses. Geodetic Very Long Baseline Interferometry (VLBI) is capable of measuring the deflection of the light from distant radio sources anytime and across the whole sky. We show that the effect of light deflection is equivalent to the gravitational delay calculated during the reduction of VLBI data. All reference radio sources display an annual circular motion with the magnitude proportional to their ecliptic latitude. In particular, radio sources near the ecliptic pole draw an annual circle with magnitude of 4~mas. This effect could be easily measured with the current precision of the geodetic VLBI data.
The prevalence of weak magnetic fields in Herbig Ae stars: the case of PDS 2
NASA Astrophysics Data System (ADS)
Hubrig, S.; Carroll, T. A.; Schller, M.; Ilyin, I.
2015-04-01
Models of magnetically driven accretion and outflows reproduce many observational properties of T Tauri stars, but the picture is much less clear for the Herbig Ae/Be stars, due to the poor knowledge of their magnetic field strength and topology. The Herbig Ae star PDS 2 was previously included in two magnetic studies based on low-resolution spectropolarimetric observations. Only in one of these studies the presence of a weak mean longitudinal magnetic field was reported. In the present study, for the first time, high-resolution high accuracy radial velocity planet searcher (HARPS) spectropolarimetric observations of PDS 2 are used to investigate the presence of a magnetic field. A firm detection of a weak longitudinal magnetic field is achieved using the multiline singular value decomposition method for Stokes profile reconstruction (
Dust acoustic shock wave in electronegative dusty plasma: Roles of weak magnetic field
Ghosh, Samiran; Ehsan, Z.; Murtaza, G.
2008-02-15
The effects of nonsteady dust charge variations and weak magnetic field on small but finite amplitude nonlinear dust acoustic wave in electronegative dusty plasma are investigated. The dynamics of the nonlinear wave are governed by a Korteweg-de Vries Burger equation that possesses dispersive shock wave. The weak magnetic field is responsible for the dispersive term, whereas nonsteady dust charge variation is responsible for dissipative term, i.e., the Burger term. The coefficient of dissipative term depends only on the obliqueness of the magnetic field. It is found that for parallel propagation the dynamics of the nonlinear wave are governed by the Burger equation that possesses monotonic shock wave. The relevances of the findings to cometary dusty plasma, e.g., Comet Halley are briefly discussed.
Novikov, V V; She?man, I M; Iablokova, E V; Fesenko, E E
2014-01-01
It is shown that an exposure of pupae of the mealworm beetle Tenebrio molitor to the combined static (42 ?T) and very weak alternating (250 nT) magnetic fields exerts different influence, depending on the frequency of the alternating magnetic field, on duration of metamorphosis processes in these insects. For instance, an exposure of pupae to weak combined magnetic fields, adjusted to the frequency of ion cyclotron resonance for glutaminic acid (4,4 Hz), stimulates metamorphosis process--a transitional stage from pupae to imago lasts shorter. An inhibiting effect was observed when adjusted to the frequency of ion cyclotron resonance for Ca2 (32,2 Hz). At some frequencies this effect is not seen. For instance, an exposure at a frequency of ion cyclotron resonance for K+ (16,5 Hz) exerts no noticeable effect on the duration of the pupal metamorphosis stage. PMID:25715625
Ultra-weak magnetic fields in Am stars: ? UMa and ? Leo
NASA Astrophysics Data System (ADS)
Blazre, A.; Petit, P.; Lignires, F.; Aurire, M.; Bhm, T.; Wade, G.
2014-12-01
An extremely weak circularly-polarized signature was recently discovered in spectral lines of the chemically peculiar Am star Sirius A (Petit et al. 2011). This signal was interpreted as a Zeeman signature related to a sub-gauss longitudinal magnetic field, constituting the first detection of a surface magnetic field in an Am star. We present here ultra-deep spectropolarimetric observations of two other bright Am stars, ? UMa and ? Leo, observed with the NARVAL spectropolarimeter. The line profiles of the two stars display circularly-polarized signatures similar in shape to the observations gathered for Sirius A. These new detections suggest that very weak magnetic fields may be present in the photospheres of a significant fraction of intermediate-mass stars, although the strongly asymmetric Zeeman signatures measured so far in Am stars (featuring a prominent positive lobe and no detected negative lobe) are not expected in the standard theory of the Zeeman effect.
Jenrow, K A; Smith, C H; Liboff, A R
1996-01-01
We recently reported that cephalic regeneration in the planarian Dugesia tigrina was significantly delayed in populations exposed continuously to combined parallel DC and AC magnetic fields. This effect was consistent with hypotheses suggesting an underlying resonance phenomenon. We report here, in a parallel series of investigations on the same model system, that the incidence of regeneration anomalies presenting as tumor-like protuberances also increases significantly (P < .001) in association with exposure to weak 60 Hz magnetic fields, with peak intensities ranging between 1.0 and 80.0 microT. These anomalies often culminate in the complete disaggregation of the organism. Similar to regeneration rate effects, the incidence of regeneration anomalies is specifically dependent upon the planaria possessing a fixed orientation with respect to the applied magnetic field vectors. However, unlike the regeneration rate effects, the AC magnetic field alone, in the absence of any measurable DC field, is capable of producing these anomalies. Moreover, the incidence of regeneration anomalies follows a clear dose-response relationship as a function of AC magnetic field intensity, with the threshold for induced electric field intensity estimated at 5 microV/m. The addition of either 51.1 or 78.4 microT DC magnetic fields, applied in parallel combination with the AC field, enhances the appearance of anomalies relative to the 60 Hz AC field alone, but only at certain AC field intensities. Thus, whereas our previous study of regeneration rate effects appeared to involve exclusively resonance interactions, the regeneration anomalies reported here appear to result primarily from Faraday induction coupling. These results together with those reported previously point to two distinct physiological effects produced in regenerating planaria by exposure to weak extremely-low-frequency (ELF) magnetic fields. They further suggest that the planarian, which has recently been identified elsewhere as an excellent system for use in teratogenic investigations involving chemical teratogens, might be used similarly in teratogenic investigations involving ELF magnetic fields. PMID:8986364
Detection of ultra-weak magnetic fields in Am stars: β Ursae Majoris and θ Leonis
NASA Astrophysics Data System (ADS)
Blazère, A.; Petit, P.; Lignières, F.; Aurière, M.; Ballot, J.; Böhm, T.; Folsom, C. P.; Gaurat, M.; Jouve, L.; Lopez Ariste, A.; Neiner, C.; Wade, G. A.
2016-02-01
Context. An extremely weak circularly polarized signature was recently discovered in spectral lines of the chemically peculiar Am star Sirius A. A weak surface magnetic field was proposed to account for the observed polarized signal, but the shape of the phase-averaged signature, dominated by a prominent positive lobe, is not expected in the standard theory of the Zeeman effect. Aims: We aim at verifying the presence of weak circularly polarized signatures in two other bright Am stars, β UMa and θ Leo, and investigating the physical origin of Sirius-like polarized signals further. Methods: We present here a set of deep spectropolarimetric observations of β UMa and θ Leo, observed with the NARVAL spectropolarimeter. We analyzed all spectra with the least squares deconvolution multiline procedure. To improve the signal-to-noise ratio and detect extremely weak signatures in Stokes V profiles, we co-added all available spectra of each star (around 150 observations each time). Finally, we ran several tests to evaluate whether the detected signatures are consistent with the behavior expected from the Zeeman effect. Results: The line profiles of the two stars display circularly polarized signatures similar in shape and amplitude to the observations previously gathered for Sirius A. Our series of tests brings further evidence of a magnetic origin of the recorded signal. Conclusions: These new detections suggest that very weak magnetic fields may well be present in the photospheres of a significant fraction of intermediate-mass stars. The strongly asymmetric Zeeman signatures measured so far in Am stars (featuring a dominant single-sign lobe) are not expected in the standard theory of the Zeeman effect and may be linked to sharp vertical gradients in photospheric velocities and magnetic field strengths.
Discovery of a very weak magnetic field on the Am star Alhena
NASA Astrophysics Data System (ADS)
Blazère, A.; Neiner, C.; Petit, P.
2016-03-01
Alhena (γ Gem) was observed in the frame of the BRITE (BRIght Target Explorer) spectropolarimetric survey, which gathers high resolution, high signal-to-noise, high sensitivity, spectropolarimetric observations of all stars brighter than V=4 to combine seismic and spectropolarimetric studies of bright stars. We present here the discovery of a very weak magnetic field on the Am star Alhena, thanks to very high signal-to-noise spectropolarimetric data obtained with Narval at Télescope Bernard Lyot (TBL). All previously studied Am stars show the presence of ultra-weak (sub-Gauss) fields with Zeeman signatures with an unexpected prominent positive lobe. However, Alhena presents a slightly stronger (but still very weak, only a few Gauss) field with normal Zeeman signatures with a positive and negative lobe, as found in stronger field (hundreds or thousands of Gauss) stars. It is the first detection of a normal magnetic signature in an Am star. Alhena is thus a very interesting object, which might provide the clue to understanding the peculiar shapes of the magnetic signatures of the other Am stars.
Thermoelectric Magnetohydrodynamic Flow During Crystal Growth with a Moderate or Weak Magnetic Field
NASA Technical Reports Server (NTRS)
Khine, Y. Y.; Walker, John S.; Szofran, Frank R.; Rose, M. Franklin (Technical Monitor)
2000-01-01
This paper treats a steady, axisymmetric melt motion in a cylindrical ampoule with a uniform, axial magnetic field and with an electric current due to a radial temperature variation along the crystal-melt interface, where the values of the absolute thermoelectric power for the crystal and melt are different. The radial component of the thermoelectric current in the melt produces an azimuthal body force, and the axial variation of the centrifugal force due to the azimuthal motion drives a meridional circulation with radial and axial velocities. For moderate magnetic field strengths, the azimuthal velocity and magnetic field produce a radial induced electric field which partially cancels the Seebeck electromotive force in the melt, so that the thermoelectric current and the melt motion are coupled. For weak magnetic fields, the thermoelectric current is decoupled from the melt motion, which is an ordinary hydrodynamic flow driven by a known azimuthal body force. The results show how the flow varies with the strength of the magnetic field and with the magnitude of the temperature variation along the crystal-melt interface. They also define the parameter ranges for which the simpler weak-field decoupled analysis gives accurate predictions.
NASA Astrophysics Data System (ADS)
Luyten, P. J.
1988-02-01
The oscillations and stability of a homogeneous self-gravitating rotating cylinder in a toroidal magnetic field are investigated. It is assumed that the field is proportional to the distance to the axis of the cylinder. We show the existence of four infinite discreta spectra of magnetic (or rotational) modes. Rotation stabilizes the magnetic m = 1 instability. The magnetic field decreases the growth rate of rotational instability and reduces the interval of unstable wavenumbers. If m = 1, instability always occurs with the exception of the equipartition state. If m> 1, the instability can be suppressed by a sufficiently large magnetic field. Resistivity decreases the growth rate of magnetic instability, but increases the growth rate of rotational instability. For zero wavenumber perturbations secular instability occurs due to the action of resistivity before a neutral point is attained where a second secular instabiliity initiates due to the action of resistivity
Callebout, D.; Mikeladze, S.V.; Tsintsadze, N.L.; Shatashvili, N.L.
1993-02-01
The process of heat transport by electrons under the influence of a strong electromagnetic wave in a weakly ionized plasma is studied. It is shown that the electron temperature rapidly approaches a new equilibrium whose form depends only on the wave profile of the heat source. Using as an example the D layer of the earth`s ionosphere it is shown that an external field can give rise to considerable heating of the neutral particles. 11 refs., 3 figs.
[Effects of weak magnetic fields on different phases of planarian regeneration].
Tiras, Kh P; Petrova, O N; Miakisheva, S N; Popova, S S; Aslanidi, K B
2015-01-01
We analyzed the effects of weak combined magnetic fields, tuned to the cyclotron resonance condition for calcium ions, obtained in different phases of planarian regeneration. We showed that the result of regeneration in 72 hours after decapitation depends on the length of exposure, and the time between decapitation and initiation of a half-hour exposure. The experimental dependence can be explained by a multiplicity of enzymatic targets activated in different phases of the regeneration process. PMID:25868354
NASA Astrophysics Data System (ADS)
Grunskaya, Lubov; Isakevich, Valiriy; Efimov, Vladislav; Zakirov, Alexander
Experimental investigations of electromagnetic fields in the atmosphere boundary layer are done at the distance spaced stations, situated on VSU test ground, at Main Geophysical Observa-tory(St. Petersburg), on Kamchatka pen., on Lake Baikal. The distance spaced reception of electrical and magnetic fields will allow to analyze more widely the nature of the investigated interactions. Monitoring of electromagnetic fields in the ELF range is being realized. The work is connected with search of interconnection of the electromagnetic field of the atmosphere boundary layer with the gravitational Compact Binaries wave fields. For analyzing Compact Binaries were taken with ELF of GW-radiation: J 0700+6418, J 1012+5307, J 1537+1155, J 1959+2048, J 2130+1210, J 1915+1606, J 1910+0004, J 1910+0004, J 1748-2446A.For analyz-ing the spectrum of the magnetic fields there was used the information of VSU station and the monitoring information of Japanese geomagnetic stations Kakioka and Mambetsu. The aim of such investigations is connected with displaying tide processes (the Moon tides) and gravita-tional wave influence of Compact Binaries in the electromagnetic fields.On the first stage of the investigations a correlative spectral analysis of the experimental data was being carried out. There was factually extracted the influence of the atmosphere lower layer electromagnetic field of the thermogravitational solar tides and a number of gravitational: M1, M2, N2. It was ob-tained that astrophysical sources GV-6, GV-3,GV-4, GV-8, GV-9 have the most probability of non-casual of events. The subsequent investigations are connected with search of main features accompanying such influences. They are signal modulations by diurnal and year's rotation of the Earth. Such modulations are peculiar to sources of non-terrestrial origin. We are planning an extraction of the radiation frequency change of the source because of energy loss for the radiation of GW. Such investigations turned out to be possible after developing the method of scanning experimental signal of electromagnetic field into non-correlated components. There is shown efficiency of using latent vectors of covariance matrixes to expose complex periodical component of time series, including the ease when such components don't have energetic dom-inate in time series.The work was carried out with supporting of grants RFBR 09-05-08176, Program DSPHS 2.1.1/5660.
NASA Astrophysics Data System (ADS)
Colombeau, M.
2015-06-01
We construct a family of classical continuous functions S(x, y, z, t, ɛ) which tend to satisfy asymptotically the system of selfgravitating pressureless fluids when ɛ → 0. This produces a weak asymptotic method in the sense of Danilov, Omel'yanov, and Shelkovich. The construction is based on a family of two ordinary differential equations (ODEs) (one for the continuity equation and one for the Euler equation) in classical Banach spaces of continuous functions. This construction applies to 3-D self-gravitating pressureless fluids even in presence of point and string concentrations of matter. The method is constructive which permits to check numerically from standard methods for ODEs that these functions tend to the known or admitted solutions when the latter exist. As a direct application, we present a simulation of formation and evolution of a planetary system from a rotating disk of dust: a theorem in this paper asserts that the observed results are a depiction of functions that satisfy the system with arbitrary precision.
Direct measurements of electric fields in weak OH · · π hydrogen bonds
Saggu, Miguel; Levinson, Nicholas M.; Boxer, Steven G.
2011-01-01
Hydrogen bonds and aromatic interactions are of widespread importance in chemistry, biology and materials science. Electrostatics play a fundamental role in these interactions, but the magnitude of the electric fields that support them has not been quantified experimentally. Phenol forms a weak hydrogen bond complex with the π-cloud of benzene and we used this as a model system to study the role of electric fields in weak OH · · π hydrogen bonds. The effects of complex formation on the vibrational frequency of the phenol OH or OD stretches were measured in a series of benzene-based aromatic solvents. Large shifts are observed and these can be converted into electric fields via the measured vibrational Stark effect. A comparison of the measured fields with quantum chemical calculations demonstrates that calculations performed in the gas-phase are surprisingly effective at capturing the electrostatics observed in solution. The results provide quantitative measurements of the magnitude of electric fields and electrostatic binding energies in these interactions and suggest that electrostatics dominate them. The combination of vibrational Stark effect (VSE) measurements of electric fields and high-level quantum chemistry calculations is a general strategy for quantifying and characterizing the origins of intermolecular interactions. PMID:21936553
Direct measurements of electric fields in weak OH···π hydrogen bonds.
Saggu, Miguel; Levinson, Nicholas M; Boxer, Steven G
2011-11-01
Hydrogen bonds and aromatic interactions are of widespread importance in chemistry, biology, and materials science. Electrostatics play a fundamental role in these interactions, but the magnitude of the electric fields that support them has not been quantified experimentally. Phenol forms a weak hydrogen bond complex with the π-cloud of benzene, and we used this as a model system to study the role of electric fields in weak OH···π hydrogen bonds. The effects of complex formation on the vibrational frequency of the phenol OH or OD stretches were measured in a series of benzene-based aromatic solvents. Large shifts are observed and these can be converted into electric fields via the measured vibrational Stark effect. A comparison of the measured fields with quantum chemical calculations demonstrates that calculations performed in the gas phase are surprisingly effective at capturing the electrostatics observed in solution. The results provide quantitative measurements of the magnitude of electric fields and electrostatic binding energies in these interactions and suggest that electrostatics dominate them. The combination of vibrational Stark effect (VSE) measurements of electric fields and high-level quantum chemistry calculations is a general strategy for quantifying and characterizing the origins of intermolecular interactions. PMID:21936553
Global surface-water-induced seasonal variations in the earth's rotation and gravitational field
NASA Technical Reports Server (NTRS)
Chao, B. F.; O'Connor, William P.
1988-01-01
The effects of seasonal changes in continental surface-water storage on the low-degree gravitational-field coefficients (J), the annual wobble excitation (Psi), and the seasonal length-of-day (LOD) variations are investigated by means of numerical simulations based on compiled meteorological data (Willmott et al., 1985) and satellite snow-load estimates (Chao et al., 1987). The formulation of the model equations and the overall characteristics of the data sets are discussed in detail, and the computation results are presented in tables and graphs. The effect on Psi is found to be relatively small due to longitudinal cancellation, but those on LOD and J are considered significant.
Fregolente, Douglas; Matsas, George E. A.; Vanzella, Daniel A. T.
2006-08-15
We investigate the possible decay of protons in geodesic circular motion around neutral compact objects. Weak and strong decay rates and the associated emitted powers are calculated using a semiclassical approach. Our results are discussed with respect to distinct ones in the literature, which consider the decay of accelerated protons in electromagnetic fields. A number of consistency checks are presented along the paper.
TASI Lectures on Holographic Space-Time, SUSY, and Gravitational Effective Field Theory
NASA Astrophysics Data System (ADS)
Banks, Tom
2012-11-01
I argue that the conventional field theoretic notion of vacuum state is not valid in quantum gravity. The arguments use gravitational effective field theory, as well as results from string theory, particularly the AdS/CFT correspondence. Different solutions of the same low energy gravitational field equations correspond to different quantum systems, rather than different states in the same system. I then introduce holographic space-time a quasi-local quantum mechanical construction based on the holographic principle. I argue that models of quantum gravity in asymptotically flat space-time will be exactly super-Poincare invariant, because the natural variables of holographic space-time for such a system, are the degrees of freedom of massless superparticles. The formalism leads to a non-singular quantum Big Bang cosmology, in which the asymptotic future is required to be a de Sitter space, with cosmological constant (c.c.) determined by cosmological initial conditions. It is also approximately SUSic in the future, with the gravitino mass K?1/4.
Quantum fog and the degradation of information by the gravitational field
Sciffer, M. )
1993-07-01
In this paper the authors discuss how information transferred optically through a gravitational field is degraded as the quanta interact with the medium (vacuum state). The authors quantify information by means of Shannon's entropy, and consider information carriers that are quanta of some field. Next, the authors obtain the quantum noise ([open quote]quantum fog[close quote]) produced by the gravitational field and derive the appropriate [open quote]channel capacity[close quote] formula, which quantifies the maximum amount of information that can be transmitted per pulse, in the face of this noise. It is shown that the channel capacity formula vanishes if the source of information is a space-time singularity because a very intense noise is produced in the vicinity of the singularity. In other words, space-time singularities are hidden behind a very intense [open quote]quantum fog[close quote] and cannot be optically observed. A second consequence is that information is degraded as anisotropies (lumpiness) develop in the universe. 32 refs., 9 figs., 5 figs.
Time evolution and decay of an excited atom in a weak electric field
Wang, J.B.
1996-07-01
A Mathematica notebook for describing the time evolution and decay of the hydrogen {ital n}=2 states in the presence of a weak external electric field is presented. The work involves (1) solving a set of differential equations coupled by the Hamiltonian of the external electric field and (2) deriving a set of formulas for a complete description of the polarization state of the emitted photons. It is demonstrated how problems with such complexity can be treated with ease and in an error-free manner by using symbolic software such as Mathematica. {copyright} {ital 1996 American Institute of Physics.}
Dark-field hyperlens: Super-resolution imaging of weakly scattering objects
NASA Astrophysics Data System (ADS)
Repn, Taavi; Lavrinenko, Andrei V.; Zhukovsky, Sergei V.
2015-09-01
We propose and numerically demonstrate a technique for subwavelength imaging based on a metal-dielectric multilayer hyperlens designed in such a way that only the large-wavevector waves are transmitted while all propagating waves from the image area are blocked by the hyperlens. As a result, the image plane only contains scattered light from subwavelength features of the objects and is free from background illumination. Similar in spirit to conventional dark-field microscopy, the proposed dark-field hyperlens is promising for optical imaging of weakly scattering subwavelength objects, such as optical nanoscopy of label-free biological objects.
Small-x QCD evolution of 2 n Wilson line correlator: The weak field limit
NASA Astrophysics Data System (ADS)
Ayala, Alejandro; Cazaroto, Erike R.; Hernndez, Luis Alberto; Jalilian-Marian, Jamal; Tejeda-Yeomans, Maria Elena
2014-10-01
We write down explicit expressions for the x evolution (equivalent to energy or rapidity evolution) of 2 n (n =1 ,2 ,⋯) Wilson lines using the JIMWLK equation and the color glass condensate formalism. We investigate the equation in the weak gluon field limit (linear regime) by expanding the Wilson lines in powers of the gluon field and show that it reduces to the BJKP equation describing the evolution of a state of 2 n Reggeized gluons with energy. We also make available for download a Mathematica program which provides this expression for any value of n .
Properties of Weak Lensing Clusters Detected on Hyper Suprime-Cams 2.3 deg2 field
NASA Astrophysics Data System (ADS)
Miyazaki, Satoshi; Oguri, Masamune; Hamana, Takashi; Tanaka, Masayuki; Miller, Lance; Utsumi, Yousuke; Komiyama, Yutaka; Furusawa, Hisanori; Sakurai, Junya; Kawanomoto, Satoshi; Nakata, Fumiaki; Uraguchi, Fumihiro; Koike, Michitaro; Tomono, Daigo; Lupton, Robert; Gunn, James E.; Karoji, Hiroshi; Aihara, Hiroaki; Murayama, Hitoshi; Takada, Masahiro
2015-07-01
We present properties of moderately massive clusters of galaxies detected by the newly developed Hyper Suprime-Cam on the Subaru telescope using weak gravitational lensing. Eight peaks exceeding a signal-to-noise ratio (S/N) of 4.5 are identified on the convergence S/N map of a 2.3 deg2 field observed during the early commissioning phase of the camera. Multi-color photometric data are used to generate optically selected clusters using the Cluster finding algorithm based on the Multiband Identification of Red-sequence galaxies algorithm. The optical cluster positions were correlated with the peak positions from the convergence map. All eight significant peaks have optical counterparts. The velocity dispersion of clusters is evaluated by adopting the Singular Isothemal Sphere fit to the tangential shear profiles, yielding virial mass estimates, {M}{500c}, of the clusters which range from 2.7 1013 to 4.4 10 {}14 {M}? . The number of peaks is considerably larger than the average number expected from ?CDM cosmology but this is not extremely unlikely if one takes the large sample variance in the small field into account. We could, however, safely argue that the peak count strongly favors the recent Planck result suggesting a high {? }8 value of 0.83. The ratio of stellar mass to the dark matter halo mass shows a clear decline as the halo mass increases. If the gas mass fraction, fg, in halos is universal, as has been suggested in the literature, the observed baryon mass in stars and gas shows a possible deficit compared with the total baryon density estimated from the baryon oscillation peaks in anisotropy of the cosmic microwave background.
Weak ac field-induced patterns in vertical deposition of colloids at various evaporation rates
NASA Astrophysics Data System (ADS)
Aslam, R.; Pichumani, M.; Gonzlez-Vias, W.
2015-03-01
Pattern formation in colloids by weak ac fields in vertical deposition-like configuration at different temperatures has been studied experimentally. At low evaporation (room temperature), the effect of the field leads to the evolution of a one-dimensional array of clusters along the contact line and columnar colloidal dried deposits are obtained at higher evaporation. We investigate the flow dynamics involved in this pattern formation. Homogeneous variation of the contact angle by electrowetting effect becomes unstable and breaks the translational symmetry at the meniscus. Electrokinetic forces together with capillary forces result in the accumulation of particles for pattern formation. The movement of electrically charged colloidal particles is controlled by weak ac electric field even at higher temperatures. We observe the effect of increasing initial particle concentration on the behavior of the clusters for various field frequencies. The average distance between clusters increase monotonically with an increase in the initial particle concentration. We also observe that the average width of columns increases according to the applied field strength.
On deflection fields, weak-focusing and strong-focusing storage rings for polar molecules.
de Nijs, Adrian J; Bethlem, Hendrick L
2011-11-14
In this paper, we analyze electric deflection fields for polar molecules in terms of a multipole expansion and derive a simple but rather insightful expression for the force on the molecules. Ideally, a deflection field exerts a strong, constant force in one direction, while the force in the other directions is zero. We show how, by a proper choice of the expansion coefficients, this ideal can be best approximated. We present a design for a practical electrode geometry based on this analysis. By bending such a deflection field into a circle, a simple storage ring can be created; the direct analog of a weak-focusing cyclotron for charged particles. We show that for realistic parameters a weak-focusing ring is only stable for molecules with a very low velocity. A strong-focusing (alternating-gradient) storage ring can be created by arranging many straight deflection fields in a circle and by alternating the sign of the hexapole term between adjacent deflection fields. The acceptance of this ring is numerically calculated for realistic parameters. Such a storage ring might prove useful in experiments looking for an EDM of elementary particles. PMID:21979152
Mssbauer spectra of single-domain particles in a weak magnetic field
NASA Astrophysics Data System (ADS)
Chuev, M. A.
2008-12-01
A three-level stochastic model taking into account the magnetic anisotropy, precession and diffusion of uniform magnetization of single-domain particles is developed in order to describe the Mssbauer absorption spectra of an ensemble of magnetic nanoparticles in a weak magnetic field. In contrast to conventional approaches searching for a distribution of the hyperfine field at nuclei, this model allows one to take into consideration physical mechanisms of formation of the magnetic hyperfine structure within the magnetic dynamics inherent to such materials. A number of qualitative effects observed in experimental Mssbauer spectra taken on small magnetic particles even in zero magnetic field can be self-consistently explained within the model in terms of the mean-field interparticle interaction. In particular, this model predicts the appearance of 57Fe magnetic sextets with a small hyperfine splitting slightly dependent on the particle size and temperature in a weak magnetic field and at high temperature, which look like effective 'doublets' of lines often observed in experimental spectra.
On observation of neutron quantum states in the Earth's gravitational field
Vankov, Anatoli Andrei
2010-03-01
Observation of neutron gravitational quantum states E{sub n}=mgz{sub n} in the peV energy range (z{sub 1} is about 10 {mu}m in the vertical direction) in the experiment conducted at Laue-Langevin Institute, Grenoble, with ultracold neutrons was recently reported in a series of publications. The purpose of the present work is to analyze the experiment. The experimental apparatus is designed to measure a transmission function T(z{sub a}), namely, a horizontal flux of relatively fast neutrons (k>>k{sub z} in wavelength terms) passing through a slit of variable height z{sub a} of upper absorbing wall. The quantum states in question are defined by the so-called Airy functions, which are solutions to the stationary 1D equation for a neutron 'bouncing' above the perfect mirror in a linear potential field. The Airy functions describe the quantum bouncer (QB), the concept of which is subject to theoretical study of toy 1D models of gravitationally bound particles in nonrelativistic quantum mechanics (QM). This is essentially different from the 3D nonstationary QM object, 'the running QB', investigated in the experiment. The authors assume that there is a connection between T(z{sub a}) and the probability density distribution P(z,z{sub a}) for QB states. They devised the 'phenomenological model', in which the quantum pattern should be visible in the transmission curve. We argue, however, that the measured curve T(z{sub a}) is not sensitive to QB states. Instead, it is sensitive to dynamics of neutron horizontal transport inside the absorbing slit for neutrons of energy values about 10{sup 5} times greater than eigenvalues E{sub n}. The latter are related to the neutron transverse mode k{sub z} and cannot be termed ''energies of neutron gravitational quantum states.'' We conclude that the experiment setup and real conditions are not adequate to the claimed objective, and the methodology of measured data treatment is flawed. The authors' claim that 'neutron gravitational quantum states are observed' is neither theoretically nor experimentally substantiated. Final, statistically significant results of the experiment are consistent with our physical reasoning that the experiment is not sensitive to 'neutron gravitational quantum states' (in terms of Airy mode) and does not prove even their existence in rigorous quantum-mechanical terms.
Quark deconfinement and gluon condensate in a weak magnetic field from QCD sum rules
NASA Astrophysics Data System (ADS)
Ayala, Alejandro; Dominguez, C. A.; Hernandez, L. A.; Loewe, M.; Rojas, Juan Cristobal; Villavicencio, Cristian
2015-07-01
We study QCD finite energy sum rules (FESR) for the axial-vector current correlator in the presence of a magnetic field, in the weak field limit and at zero temperature. We find that the perturbative QCD and the hadronic contribution to the sum rules get explicit magnetic-field-dependent corrections and that these in turn induce a magnetic field dependence on the deconfinement phenomenological parameter s0 and on the gluon condensate. The leading corrections turn out to be quadratic in the field strength. We find from the dimension d =2 first FESR that the magnetic field dependence of s0 is proportional to the absolute value of the light-quark condensate. Hence, it increases with increasing field strength. This implies that the parameters describing chiral symmetry restoration and deconfinement behave similarly as functions of the magnetic filed. Thus, at zero temperature the magnetic field is a catalyzing agent of both chiral symmetry breaking and confinement. From the dimension d =4 second FESR we obtain the behavior of the gluon condensate in the presence of the external magnetic field. This condensate also increases with increasing field strength.
Unveiling chameleon fields in tests of the gravitational inverse-square law
Upadhye, Amol; Gubser, Steven S.; Khoury, Justin
2006-11-15
Scalar self-interactions are known to weaken considerably the current constraints on scalar-mediated fifth forces. We consider a scalar field with a quartic self-interaction and gravitation-strength Yukawa couplings to matter particles. After discussing the phenomenology of this scalar field, we assess the ability of ongoing and planned experiments to detect the fifth force mediated by such a field. Assuming that the quartic and matter couplings are of order unity, the current-generation Eoet-Wash experiment at the University of Washington will be able to explore an interesting subset of parameter space. The next-generation Eoet-Wash experiment is expected to be able to detect, or to rule out, the fifth force due to such a scalar with unit quartic and matter couplings at the 3{sigma} confidence level.
Inhomogeneous magnetic seed fields and gravitational waves within the magnetohydrodynamic limit
Zunckel, Caroline; Betschart, Gerold; Dunsby, Peter K.S.; Marklund, Mattias
2006-05-15
In this paper we apply second-order gauge-invariant perturbation theory to investigate the possibility that the coupling between gravitational waves (GWs) and a large-scale inhomogeneous magnetic field acts as an amplification mechanism in an 'almost' Friedmann-Lemaitre-Robertson-Walker Universe. The spatial inhomogeneities in the magnetic field are consistently implemented using the magnetohydrodynamic (MHD) approximation, which yields an additional source term due to the interaction of the magnetic field with velocity perturbations in the plasma. Comparing the solutions with the corresponding results in our previous work indicates that, on superhorizon scales, the interaction with the spatially inhomogeneous field in the dust regime induces the same boost as the case of a homogeneous field, at least in the ideal MHD approximation. This is attributed to the observation that the MHD induced part of the generated field effectively only contributes on scales where the coherence length of the initial field is less than the Hubble scale. At subhorizon scales, the GW induced magnetic field is completely negligible in relation to the MHD induced field. Moreover, there is no amplification found in the long-wavelength limit.
Self-gravitating Body with an Internal Magnetic Field. I. New Analytical Equilibria
NASA Astrophysics Data System (ADS)
Aly, J.-J.; Amari, T.
2012-05-01
We construct exact analytical solutions of the equations describing the equilibrium of a self-gravitating magnetized fluid body, possibly rigidly rotating, by superposing two solutions of finite energy defined in the whole space, one describing a non-magnetized gravitating equilibrium (ST1) and the other describing a magnetized non-gravitating equilibrium (ST2). A large number of ST1s can be found in the literature and directly used for our constructions, and we thus concentrate on ST2s, which are difficult to obtain. We derive some of their general properties and exhibit two explicit classes of axisymmetric "elementary" such equilibria. The first one is extracted from the stellar models proposed by Prendergast and by Kutvitskii & Solov'ev, respectively. The second one is constructed by using Palumbo's theory of isodynamic equilibria, for which the magnetic pressure is constant on each flux surface. Both types of ST2s have their magnetic field confined within a bounded region, respectively, of spherical and toroidal shapes. A much more general ST2 can be obtained by juxtaposing n+q elementary ST2s, with n of the first type and q of the second type, in such a way that the magnetic regions do not pairwise overlap. The specific equilibria we obtain by superposition thus have no external field extending to infinity, and may be three dimensional (3D), which invalidates a recent nonexistence conjecture. Moreover, they may be arranged to contain force-free regions. Our superposition method can be considered as a 3D generalization of the axisymmetric splitting method previously developed by Kutvitskii & Solov'ev.
SELF-GRAVITATING BODY WITH AN INTERNAL MAGNETIC FIELD. I. NEW ANALYTICAL EQUILIBRIA
Aly, J.-J.; Amari, T.
2012-05-01
We construct exact analytical solutions of the equations describing the equilibrium of a self-gravitating magnetized fluid body, possibly rigidly rotating, by superposing two solutions of finite energy defined in the whole space, one describing a non-magnetized gravitating equilibrium (ST1) and the other describing a magnetized non-gravitating equilibrium (ST2). A large number of ST1s can be found in the literature and directly used for our constructions, and we thus concentrate on ST2s, which are difficult to obtain. We derive some of their general properties and exhibit two explicit classes of axisymmetric 'elementary' such equilibria. The first one is extracted from the stellar models proposed by Prendergast and by Kutvitskii and Solov'ev, respectively. The second one is constructed by using Palumbo's theory of isodynamic equilibria, for which the magnetic pressure is constant on each flux surface. Both types of ST2s have their magnetic field confined within a bounded region, respectively, of spherical and toroidal shapes. A much more general ST2 can be obtained by juxtaposing n+q elementary ST2s, with n of the first type and q of the second type, in such a way that the magnetic regions do not pairwise overlap. The specific equilibria we obtain by superposition thus have no external field extending to infinity, and may be three dimensional (3D), which invalidates a recent nonexistence conjecture. Moreover, they may be arranged to contain force-free regions. Our superposition method can be considered as a 3D generalization of the axisymmetric splitting method previously developed by Kutvitskii and Solov'ev.
Detecting the presence of weak magnetic fields using nitrogen-vacancy centers
NASA Astrophysics Data System (ADS)
Chaudhry, Adam Zaman
2015-06-01
We show how nitrogen-vacancy centers can be used to detect the presence of weak magnetic fields, that is, to find out whether a magnetic field, about which we may not have complete information, is actually present or not. The solution to this problem comes from quantum state discrimination theory. The effect of decoherence is taken into account to optimize the time over which the nitrogen-vacancy center is allowed to interact with the magnetic field before making a measurement. We also find the optimum measurement that should be performed. We then show how multiple measurements reduce the error in detecting the magnetic field. Finally, a major limitation of the measurement process, namely, limited photon detection efficiency, is taken into account. Our proposals should be implementable with current experimental technology.
Antimatter gravity and the weak equivalence principle
NASA Astrophysics Data System (ADS)
Holzscheiter, M. H.; Brown, R. E.; Camp, J.; Darling, T.; Dyer, P.; Holtkamp, D. B.; Jarmie, N.; King, N. S. P.; Schauer, M. M.; Cornford, S.; Hosea, K.; Kenefick, R. A.; Midzor, M.; Oakley, D.; Ristinen, R.; Witteborn, F. C.
1991-08-01
Ideas are presented for an experiment to compare the acceleration, g, of antiprotons in the Earth's gravitational field with that of particles of normed matter, such as protons or hydrogen ions. The experiments will test whether antiprotons obey the weak equivalence principle.(AIP)
Weak interactions from 1950-1960: a quantitative bibliometric study of the formation of a field
White, D.H.; Sullivan, D.
1986-01-01
A quantitative technique is illustrated which uses publication statistics from a bibliography of citations in the area of weak interactions to provide a view of trends and patterns in the development of the field during the period from 1950 to 1960. An overview is given of what the physicists working in weak interactions during this period were doing as indicated by an analysis of the subjects of their papers. The dominant problems and concerns are discussed. Focus is then turned to the events surrounding the emergence of the tau/theta particle puzzle, the discovery of parity nonconservation, and the resolution offered by the V-A theory. Displaying the data from the citation index in unusual ways highlights dominant issues of the period, especially the close relationship between theory and experiment in the latter half of the decade. 64 refs., 14 figs. (LEW)
Inferring Gene Regulatory Networks by Singular Value Decomposition and Gravitation Field Algorithm
Zheng, Ming; Wu, Jia-nan; Huang, Yan-xin; Liu, Gui-xia; Zhou, You; Zhou, Chun-guang
2012-01-01
Reconstruction of gene regulatory networks (GRNs) is of utmost interest and has become a challenge computational problem in system biology. However, every existing inference algorithm from gene expression profiles has its own advantages and disadvantages. In particular, the effectiveness and efficiency of every previous algorithm is not high enough. In this work, we proposed a novel inference algorithm from gene expression data based on differential equation model. In this algorithm, two methods were included for inferring GRNs. Before reconstructing GRNs, singular value decomposition method was used to decompose gene expression data, determine the algorithm solution space, and get all candidate solutions of GRNs. In these generated family of candidate solutions, gravitation field algorithm was modified to infer GRNs, used to optimize the criteria of differential equation model, and search the best network structure result. The proposed algorithm is validated on both the simulated scale-free network and real benchmark gene regulatory network in networks database. Both the Bayesian method and the traditional differential equation model were also used to infer GRNs, and the results were used to compare with the proposed algorithm in our work. And genetic algorithm and simulated annealing were also used to evaluate gravitation field algorithm. The cross-validation results confirmed the effectiveness of our algorithm, which outperforms significantly other previous algorithms. PMID:23226565
Diffusion phenomenon at the interface of Cu-brass under a strong gravitational field
NASA Astrophysics Data System (ADS)
Ogata, Yudai; Iguchi, Yusuke; Tokuda, Makoto; Januszko, Kamila; Khandaker, Jahirul Islam; Ono, Masao; Mashimo, Tsutomu
2015-03-01
To investigate diffusion phenomenon at the interface between Cu and brass under a strong gravitational field generated by ultracentrifuge apparatus, we performed gravity experiments on samples prepared by electroplating with interfaces normal and parallel to the direction of gravity. For the parallel-mode sample, for which sedimentation cannot occur thorough the interface, the concentration change was significant within the lower gravity region; many pores were observed in this region. Many vacancies arising from crystal strain due to the strong gravitational field moved into the lower gravity region, and enhanced the atoms mobilities. For the two normal-mode samples, which have interface normal to the direction of gravity, the composition gradient of the brass-on-Cu sample was steeper than that for Cu-on-brass. This showed that the atoms of denser Cu diffuse in the direction of gravity, whereas Zn atoms diffuse in the opposite direction by sedimentation. The interdiffusion coefficients became higher in the Cu-on-brass sample, and became lower in the brass-on-Cu sample. This rise may be related to the behavior of the vacancies.
Gravitational field of a hedgehog and the evolution of vacuum bubbles
NASA Astrophysics Data System (ADS)
Guendelman, E. I.; Rabinowitz, A.
1991-11-01
The gravitational field produced by a spherically symmetric ``hedgehog'' configuration in scalar field theories with global SO(3) symmetry (or higher) is studied in the limit in which these models become nonlinear ? models. The same gravitational effect can be generated by a set of cosmic strings intersecting at a point, in the limit that one considers a continuous distribution of such intersecting strings in a spherically symmetric configuration (to be referred to as the ``string hedgehog''). When the energy densities associated with the hedgehog are small, we obtain a static geometry, but for higher values, the resulting geometry is that of an anisotropic cosmology. The evolution of bubbles joining two phases, one of which contains a hedgehog (as defined above) is investigated. The role of such configurations in processes that lead to classical false-vacuum destabilization and in the evolution of inflationary bubbles is discussed. The generalization of our results to the gauged case, i.e., to magnetic-monopole hedgehogs, is discussed.
Gas-Phase Influence on Quasisteady "Liquid Flames" in Gravitational Fields
NASA Technical Reports Server (NTRS)
Shkadinsky, K. G.; Shkadinskaya, G. V.; Matkowsky, B. J.; Gokoglu, S. (Technical Monitor)
2000-01-01
We consider the SHS (self-propagating high-temperature synthesis) process for synthesizing materials. In this process a powder mixture of reactants is cold pressed into a sample, which is ignited at one end. A high temperature combustion wave then propagates through the sample converting reactants to the desired product material. In this process, melting of some or all the components is often observed. Therefore, we study combustion waves propagating through a high caloricity inorganic powder mixture whose combustion temperature exceeds the melting temperatures of many components. The solid matrix is thus destroyed by the propagating combustion wave due to melting ahead of the reaction zone, and a liquid bath is formed which contains gaseous bubbles. The waves propagate in the presence of a gravitational field. Due to the effect of gravity, there is relative motion between the rising bubbles and the descending bath, which affects the composition of the medium, its thermophysical properties, the 'liquid flame' structure, and the propagation velocity. To enhance our understanding of phenomena associated with the interaction of the relative motion with the propagating combustion wave we formulate and analyze a relatively simple mathematical model of liquid flames in a gravitational field. We describe the wave structure and combustion characteristics including the combustion velocity. We compare our results to existing experimental observations and suggest new experiments to be performed. We consider the effects of gravity and, in particular, examine both microgravity and large gravity conditions.
Formation of graded vanadium oxide (V–O compound) under strong gravitational field
Khandaker, Jahirul Islam; Tokuda, Makoto; Ogata, Yudai; Januszko, Kamila; Mashimo, Tsutomu; Nishiyama, Tadao; Yoshiasa, Akira
2015-05-14
Sedimentation of atoms induced under strong gravitational field gives a tool for controlling elemental compositions in condensed matter. We performed a strong-gravity experiment (0.397 × 10{sup 6 }G at 400 °C for 24 h) on a V{sub 2}O{sub 5} polycrystal using the high-temperature ultracentrifuge to examine the composition change and further the structure change. The graded composition structure of V and O was formed along gravity direction, where V increases and O decreases with gravity. It was found by the x-ray diffraction and Raman scattering method that VO{sub 2} and V{sub 2}O{sub 3} phases appeared and the amounts increased, while one of the V{sub 2}O{sub 5} phase decreased gradually along gravity direction. The X-ray absorption near edge structure spectra analysis identified the chemical valency decrease (+5 to +3). The UV-Vis absorption spectroscopy addressed the shifting in center of major absorption peak to longer wavelength (red shift) with the increase in gravitational field. The tail absorption peak (band gap 2.09 eV) at strong gravity region in the graded structure showed transparent conductive oxide.
Diffusion phenomenon at the interface of Cu-brass under a strong gravitational field
Ogata, Yudai; Tokuda, Makoto; Januszko, Kamila; Khandaker, Jahirul Islam; Mashimo, Tsutomu; Iguchi, Yusuke; Ono, Masao
2015-03-28
To investigate diffusion phenomenon at the interface between Cu and brass under a strong gravitational field generated by ultracentrifuge apparatus, we performed gravity experiments on samples prepared by electroplating with interfaces normal and parallel to the direction of gravity. For the parallel-mode sample, for which sedimentation cannot occur thorough the interface, the concentration change was significant within the lower gravity region; many pores were observed in this region. Many vacancies arising from crystal strain due to the strong gravitational field moved into the lower gravity region, and enhanced the atoms mobilities. For the two normal-mode samples, which have interface normal to the direction of gravity, the composition gradient of the brass-on-Cu sample was steeper than that for Cu-on-brass. This showed that the atoms of denser Cu diffuse in the direction of gravity, whereas Zn atoms diffuse in the opposite direction by sedimentation. The interdiffusion coefficients became higher in the Cu-on-brass sample, and became lower in the brass-on-Cu sample. This rise may be related to the behavior of the vacancies.
Formation of graded vanadium oxide (V-O compound) under strong gravitational field
NASA Astrophysics Data System (ADS)
Khandaker, Jahirul Islam; Tokuda, Makoto; Ogata, Yudai; Januszko, Kamila; Nishiyama, Tadao; Yoshiasa, Akira; Mashimo, Tsutomu
2015-05-01
Sedimentation of atoms induced under strong gravitational field gives a tool for controlling elemental compositions in condensed matter. We performed a strong-gravity experiment (0.397 106 G at 400 C for 24 h) on a V2O5 polycrystal using the high-temperature ultracentrifuge to examine the composition change and further the structure change. The graded composition structure of V and O was formed along gravity direction, where V increases and O decreases with gravity. It was found by the x-ray diffraction and Raman scattering method that VO2 and V2O3 phases appeared and the amounts increased, while one of the V2O5 phase decreased gradually along gravity direction. The X-ray absorption near edge structure spectra analysis identified the chemical valency decrease (+5 to +3). The UV-Vis absorption spectroscopy addressed the shifting in center of major absorption peak to longer wavelength (red shift) with the increase in gravitational field. The tail absorption peak (band gap 2.09 eV) at strong gravity region in the graded structure showed transparent conductive oxide.
Gravitational field of a hedgehog and the evolution of vacuum bubbles
Guendelman, E.I. ); Rabinowitz, A. )
1991-11-15
The gravitational field produced by a spherically symmetric hedgehog'' configuration in scalar field theories with global SO(3) symmetry (or higher) is studied in the limit in which these models become nonlinear {sigma} models. The same gravitational effect can be generated by a set of cosmic strings intersecting at a point, in the limit that one considers a continuous distribution of such intersecting strings in a spherically symmetric configuration (to be referred to as the string hedgehog''). When the energy densities associated with the hedgehog are small, we obtain a static geometry, but for higher values, the resulting geometry is that of an anisotropic cosmology. The evolution of bubbles joining two phases, one of which contains a hedgehog (as defined above) is investigated. The role of such configurations in processes that lead to classical false-vacuum destabilization and in the evolution of inflationary bubbles is discussed. The generalization of our results to the gauged case, i.e., to magnetic-monopole hedgehogs, is discussed.
Spinning gravitating objects in the effective field theory in the post-Newtonian scheme
NASA Astrophysics Data System (ADS)
Levi, Michele; Steinhoff, Jan
2015-09-01
We introduce a formulation for spinning gravitating objects in the effective field theory in the post-Newtonian scheme in the context of the binary inspiral problem. We aim at an effective action, where all field modes below the orbital scale are integrated out. We spell out the relevant degrees of freedom, in particular the rotational ones, and the associated symmetries. Building on these symmetries, we introduce the minimal coupling part of the point particle action in terms of gauge rotational variables, and construct the spin-induced nonminimal couplings, where we obtain the leading order couplings to all orders in spin. We specify the gauge for the rotational variables, where the unphysical degrees of freedom are eliminated already from the Feynman rules, and all the orbital field modes are integrated out. The equations of motion of the spin can be directly obtained via a proper variation of the action, and Hamiltonians may be straightforwardly derived. We implement this effective field theory for spin to derive all spin dependent potentials up to next-to-leading order to quadratic level in spin, namely up to the third post-Newtonian order for rapidly rotating compact objects. In particular, the proper next-to-leading order spin-squared potential and Hamiltonian for generic compact objects are also derived. For the implementations we use the nonrelativistic gravitational field decomposition, which is found here to eliminate higher-loop Feynman diagrams also in spin dependent sectors, and facilitates derivations. This formulation for spin is thus ideal for treatment of higher order spin dependent sectors.
Gravitational instabilities in a proto-planetary disk including the effects of magnetic fields
NASA Technical Reports Server (NTRS)
Noh, Hyerim; Vishniac, Ethan T.; Cochran, William D.
1994-01-01
We investigate the gravitational instability of a thin, Keplerian protoplanetary disk including the effects of a largely azimuthal magnetic field. The model follows that of our previous work (Noh, Vishniac, & Cochran 1991) except for the inclusion of a magnetic field. The disk is assumed to consist of neutral and ionized gas and neutral dust which are coupled by gravity and friction. The growth rates and eigenfunctions are calculated numerically using nonaxisymmetric linear perturbation methods. The results show that the growth rate has a maximum at some intermediate azimuthal number m, but for each value of m it is reduced relative to the unmagnetized case. The effects of the magnetic field appear more strongly on small scales. As the strength of the equilibrium magnetic field increases the growth rates decrease, and the maximum instability occurs at a lower value on m due to the increasing magnetic pressure. The response of each component to the magnetic field is discussed using the behavior of the eigenfunctions in the radial direction. With the inclusion of the magnetic field, the effects of the ionization fraction and friction on the growth rates also appear to be important for high m modes. Increasing the ionization fraction or the friction suppresses instability, but only slightly changes the maximally unstable azimuthal scales. The enhanced growth rates due to a dust component for which thermal pressure is negligible are somewhat reduced by the inclusion of a magnetic field. The effects of different boundary conditions (reflecting and transmitting) on the growth rates are also shown.
A null-tetrad approach to Kerr{endash}Schild gravitational fields in matter
Udeschini, E.B.; Magli, G.
1996-11-01
The null tetrad formalism is used to investigate the structure of the Einstein field equations for Kerr{endash}Schild gravitational fields in the presence of an elastic solid source. It is shown that such equations may be reduced to five nonlinear partial differential equations for five variables. It turns out that, when the interior solutions admit the same preferred null congruence of the vacuum ones and some compatibility conditions hold, it is possible to reduce them to a linear system and to develop a method of solution which closely resembles the {open_quote}{open_quote}variation of the arbitrary constants{close_quote}{close_quote} for ordinary differential equations. In the present paper, the above technical framework is developed in general and applied to two simple examples, deferring to future work the approach to the Kerr{endash}interior problem. {copyright} {ital 1996 American Institute of Physics.}
Conversion of relic gravitational waves into photons in cosmological magnetic fields
Dolgov, Alexander D.; Ejlli, Damian E-mail: ejlli@fe.infn.it
2012-12-01
Conversion of gravitational waves into electromagnetic radiation is discussed. The probability of transformations of gravitons into photons in presence of cosmological background magnetic field is calculated at the recombination epoch and during subsequent cosmological stages. The produced electromagnetic radiation is concentrated in the X-ray part of the spectrum. It is shown that if the early Universe was dominated by primordial black holes (PBHs) prior to Big Bang Nucleosynthesis (BBN), the relic gravitons emitted by PBHs would transform to an almost isotropic background of electromagnetic radiation due to conversion of gravitons into photons in cosmological magnetic fields. Such extragalactic radiation could be noticeable or even dominant component of Cosmic X-ray Background.
Late-time tails of a self-gravitating massless scalar field, revisited
NASA Astrophysics Data System (ADS)
Bizo?, Piotr; Chmaj, Tadeusz; Rostworowski, Andrzej
2009-09-01
We discuss the nonlinear origin of the power-law tail in the long-time evolution of a spherically symmetric self-gravitating massless scalar field in even-dimensional spacetimes. Using the third-order perturbation method, we derive explicit expressions for the tail (the decay rate and the amplitude) for solutions starting from small initial data, and we verify this prediction via numerical integration of the Einstein-scalar field equations in four and six dimensions. Our results show that the coincidence of decay rates of linear and nonlinear tails in four dimensions (which has misguided some tail hunters in the past) is in a sense accidental and does not hold in higher dimensions.
Equilibrium of a system of superconducting rings in a uniform gravitational field
NASA Astrophysics Data System (ADS)
Bishaev, A. M.; Bush, A. A.; Gavrikov, M. B.; Gordeev, I. S.; Denisyuk, A. I.; Kamentsev, K. E.; Kozintseva, M. V.; Savel'ev, V. V.; Sigov, A. S.
2013-05-01
To construct a plasma trap with levitating magnetic coils in the thin ring approximation, we derive the expression for the potential energy of a system of several superconducting rings (one of which is fixed) capturing the preset flows in the uniform gravitational field as a function of the coordinates of the free ring (or rings). Calculations performed in the Mathcad system show that the potential energy of such a system has a local minimum for certain values of parameters. Stable levitation of a superconducting ring in the position corresponding to calculations is realized in the field of another superconducting ring, and this leads to the conclusion that a magnetic Galatea trap can be prepared on the basis of a levitating quadrupole.
NASA Astrophysics Data System (ADS)
Wang, H. B.; Zhao, C. Y.; Zhang, W.; Zhan, J. W.; Yu, S. X.
2015-09-01
The Earth gravitational filed model is a kind of important dynamic model in satellite orbit computation. In recent years, several space gravity missions have obtained great success, prompting a lot of gravitational filed models to be published. In this paper, 2 classical models (JGM3, EGM96) and 4 latest models, including EIGEN-CHAMP05S, GGM03S, GOCE02S, and EGM2008 are evaluated by being employed in the precision orbit determination (POD) and prediction, based on the laser range observation of four low earth orbit (LEO) satellites, including CHAMP, GFZ-1, GRACE-A, and SWARM-A. The residual error of observation in POD is adopted to describe the accuracy of six gravitational field models. We show the main results as follows: (1) for LEO POD, the accuracies of 4 latest models (EIGEN-CHAMP05S, GGM03S, GOCE02S, and EGM2008) are at the same level, and better than those of 2 classical models (JGM3, EGM96); (2) If taking JGM3 as reference, EGM96 model's accuracy is better in most situations, and the accuracies of the 4 latest models are improved by 12%-47% in POD and 63% in prediction, respectively. We also confirm that the model's accuracy in POD is enhanced with the increasing degree and order if they are smaller than 70, and when they exceed 70 the accuracy keeps stable, and is unrelated with the increasing degree, meaning that the model's degree and order truncated to 70 are sufficient to meet the requirement of LEO orbit computation with centimeter level precision.
NASA Astrophysics Data System (ADS)
Schubert, Gerald; Anderson, John; Zhang, Keke; Kong, D.; Helled, Ravit
2011-08-01
The exact solution for the shape and gravitational field of a rotating two-layer Maclaurin ellipsoid of revolution is compared with predictions of the theory of figures up to third order in the small rotational parameter of the theory of figures. An explicit formula is derived for the external gravitational coefficient J2 of the exact solution. A new approach to the evaluation of the theory of figures based on numerical integration of ordinary differential equations is presented. The classical Radau-Darwin formula is found not to be valid for the rotational parameter ?2 = ?2/(2 ?G ?2) ? 0.17 since the formula then predicts a surface eccentricity that is smaller than the eccentricity of the core-envelope boundary. Interface eccentricity must be smaller than surface eccentricity. In the formula for ?2, ? is the angular velocity of the two-layer body, ?2 is the density of the outer layer, and G is the gravitational constant. For an envelope density of 3000 kg m -3 the failure of the Radau-Darwin formula corresponds to a rotation period of about 3 h. Application of the exact solution and the theory of figures is made to models of Earth, Mars, Uranus, and Neptune. The two-layer model with constant densities in the layers can provide realistic approximations to terrestrial planets and icy outer planet satellites. The two-layer model needs to be generalized to allow for a continuous envelope (outer layer) radial density profile in order to realistically model a gas or ice giant planet.
Non-Langevin high-temperature magnetization of nanoparticles in a weak magnetic field
Chuev, M. A.
2009-02-15
Experimental evidence and theoretical substantiation are presented for the asymptotic behavior of high-temperature magnetization of an ensemble of nanoparticles in a weak magnetic field, which was predicted earlier and which differs qualitatively from the 'Langevin' limit for ideal superparamagnetic particles. It is shown that the physical reason for the new asymptotic behavior is the temperature-independent 'positive' tilt of the uniform magnetization vector at local energy minima in the direction of the field; this asymptotic behavior is associated with the nonstandard thermodynamics of single-domain particles, which depends on the ratio of characteristic frequencies of regular precession and random diffusion of this vector. An alternative approach is proposed for describing the magnetic dynamics of an ensemble of nanoparticles in a magnetic field, and the precession orbits of the magnetization vector are considered as stochastic states of each particle, whereas each state is characterized by the trajectory-averaged value of magnetization.
Computer study of convection of weakly ionized plasma in a nonuniform magnetic field.
NASA Technical Reports Server (NTRS)
Shiau, J. N.
1972-01-01
A weakly ionized plasma in a strong and nonuniform magnetic field exhibits an instability analogous to the flute instability in a fully ionized plasma. The instability sets in at a critical magnetic field. To study the final state of the plasma after the onset of the instability, the plasma equations are integrated numerically assuming a certain initial spectrum of small disturbances. In the regime studied, numerical results indicate a final steadily oscillating state consisting of a single finite amplitude mode together with a time-independent modification of the original equilibrium. These results agree with the analytic results obtained by Simon in the slightly supercritical regime. As the magnetic field is increased further, the wavelength of the final oscillation becomes nonunique. There exists a subinterval in the unstable wave band. Final stable oscillation with a wavelength in this subinterval can be established if the initial disturbance has a sufficiently strong component at the particular wavelength.
Cosmology with weak lensing surveys.
Munshi, Dipak; Valageas, Patrick
2005-12-15
Weak gravitational lensing is responsible for the shearing and magnification of the images of high-redshift sources due to the presence of intervening mass. Since the lensing effects arise from deflections of the light rays due to fluctuations of the gravitational potential, they can be directly related to the underlying density field of the large-scale structures. Weak gravitational surveys are complementary to both galaxy surveys and cosmic microwave background observations as they probe unbiased nonlinear matter power spectra at medium redshift. Ongoing CMBR experiments such as WMAP and a future Planck satellite mission will measure the standard cosmological parameters with unprecedented accuracy. The focus of attention will then shift to understanding the nature of dark matter and vacuum energy: several recent studies suggest that lensing is the best method for constraining the dark energy equation of state. During the next 5 year period, ongoing and future weak lensing surveys such as the Joint Dark Energy Mission (JDEM; e.g. SNAP) or the Large-aperture Synoptic Survey Telescope will play a major role in advancing our understanding of the universe in this direction. In this review article, we describe various aspects of probing the matter power spectrum and the bi-spectrum and other related statistics with weak lensing surveys. This can be used to probe the background dynamics of the universe as well as the nature of dark matter and dark energy. PMID:16286284
NASA Astrophysics Data System (ADS)
Kirschvink, Joseph L.
1992-08-01
In a recent paper, Adair [Phys. Rev. A 43, 1039 (1991)] concludes that weak extremely-low-frequency (ELF) electromagnetic fields cannot affect biology on the cell level. However, Adair's assertion that few cells of higher organisms contain magnetite (Fe3O4) and his blanket denial of reproducible ELF effects on animals are both wrong. Large numbers of single-domain magnetite particles are present in a variety of animal tissues, including up to a hundred million per gram in human brain tissues, organized in clusters of tens to hundreds of thousand per gram. This is far more than a ``few cells.'' Similarly, a series of reproducible behavioral experiments on honeybees, Apis mellifera, have shown that they are capable of responding to weak ELF magnetic fields that are well within the bounds of Adair's criteria. A biologically plausible model of the interaction of single-domain magnetosomes with a mechanically activated transmembrane ion channel shows that ELF fields on the order of 0.1 to 1 mT are capable of perturbing the open-closed state by an energy of kT. As up to several hundred thousand such structures could fit within a eukaryotic cell, and the noise should go as the square root of the number of independent channels, much smaller ELF sensitivities at the cellular level are possible. Hence, the credibility of weak ELF magnetic effects on living systems must stand or fall mainly on the merits and reproducibility of the biological or epidemiological experiments that suggest them, rather than on dogma about physical implausibility.
Weak lensing calibrated M-T scaling relation of galaxy groups in the cosmos field
Kettula, K.; Finoguenov, A.; Massey, R.; Rhodes, J.; Hoekstra, H.; Taylor, J. E.; Spinelli, P. F.; Tanaka, M.; Ilbert, O.; Capak, P.; McCracken, H. J.; Koekemoer, A.
2013-11-20
The scaling between X-ray observables and mass for galaxy clusters and groups is instrumental for cluster-based cosmology and an important probe for the thermodynamics of the intracluster gas. We calibrate a scaling relation between the weak lensing mass and X-ray spectroscopic temperature for 10 galaxy groups in the COSMOS field, combined with 55 higher-mass clusters from the literature. The COSMOS data includes Hubble Space Telescope imaging and redshift measurements of 46 source galaxies per arcminute{sup 2}, enabling us to perform unique weak lensing measurements of low-mass systems. Our sample extends the mass range of the lensing calibrated M-T relation an order of magnitude lower than any previous study, resulting in a power-law slope of 1.48{sub ?0.09}{sup +0.13}. The slope is consistent with the self-similar model, predictions from simulations, and observations of clusters. However, X-ray observations relying on mass measurements derived under the assumption of hydrostatic equilibrium have indicated that masses at group scales are lower than expected. Both simulations and observations suggest that hydrostatic mass measurements can be biased low. Our external weak lensing masses provide the first observational support for hydrostatic mass bias at group level, showing an increasing bias with decreasing temperature and reaching a level of 30%-50% at 1 keV.
Novitskii, Yurii I; Novitskaya, Galina V; Serdyukov, Yurii A
2014-02-01
Composition and content of lipids were studied in 5-day-old radish seedlings (Raphanus sativus L. var. radicula DC.) grown in lowlight and darkness in an extremely low frequency (ELF) magnetic field characterized by 50?Hz frequency and ?500?T flux density. The control seedlings were grown under the same conditions, but without exposure to the magnetic field. The products of lipid metabolism were compared with lipid composition in seeds. In control seedlings, reserve neutral lipids, mostly triacylglycerides, were utilized for the formation of polar lipids (PL). As a result, the amount of the latter doubled, particularly due to glycolipids (GL) and phospholipids (PhL) compared to their content in seeds. At 20-22?C in light, magnetic field exposure increased the production of PL by threefold specifically, GL content increased fourfold and PhL content rose 2.5 times, compared to seeds. In darkness, the effect of magnetic field on lipids was weaker. At the lower temperature of 13-16?C in light, the effect of the magnetic field was weak, but in the darkness, no magnetic field action was recorded. It is concluded that ELF magnetic field stimulated lipid synthesis in chloroplast, mitochondrial, and other cell membranes in radish seedlings grown in light at 20-22?C and 13-16?C. PMID:24123065
Robust ground state and artificial gauge in DQW exciton condensates under weak magnetic field
NASA Astrophysics Data System (ADS)
Hakio?lu, T.; zgn, Ege; Gnay, Mehmet
2014-08-01
An exciton condensate is a vast playground in studying a number of symmetries that are of high interest in the recent developments in topological condensed matter physics. In double quantum wells (DQWs) they pose highly nonconventional properties due to the pairing of non-identical fermions with a spin dependent order parameter. Here, we demonstrate a new feature in these systems: the robustness of the ground state to weak external magnetic field and the appearance of the artificial spinor gauge fields beyond a critical field strength where negative energy pair-breaking quasi particle excitations, i.e. de-excitation pockets (DX-pockets), are created in certain k regions. The DX-pockets are the Kramers symmetry broken analogs of the negative energy pockets examined in the 1960s by Sarma. They respect a disk or a shell-topology in k-space or a mixture between them depending on the magnetic field strength and the electron-hole density mismatch. The Berry connection between the artificial spinor gauge field and the TKNN number is made. This field describes a collection of pure spin vortices in real space when the magnetic field has only inplane components.
Weak-field, multiple-cycle carrier envelope phase effects in laser excitation.
Renziehausen, Klaus; Hader, Kilian; Jakubetz, Werner; Engel, Volker
2013-05-10
Although the absolute or carrier envelope phase (CEP) of a laser pulse is usually assumed to be effective for ultrashort and/or ultrastrong pulses only, it is demonstrated that these limitations can eventually be removed. Therefore, the excitation of a model positively charged homonuclear diatomic molecule, in which four electronic states are coupled by the laser field, is studied. In an initial step, nuclear wave packets in two dissociative states are prepared. Upon reaching the fragment channel, a weak pulse interacts with the system and prepares CEP-dependent asymmetries associated with electron density localized on one or the other fragmentation product. PMID:23436555
Random fields and the weakly first-order phase transition in superconductors
Busiello, G.; De Cesare, L.; Uzunov, D.I.
1986-10-01
We study the influence of random fields with short-range and long-range correlations on the weakly first-order phase transition in superconductors. Renormalization-group (RG) analysis near the upper critical dimensionality d/sub u/ = 6 (short-range correlations) reveals a new critical behavior which holds if the number of the order-parameter components is n>10. In the long-range case, the RG transformation is self-consistent only if the parameter theta of the long-range correlations is assumed of order epsilon, epsilon = 6-d.
Dislocation scatterings in p-type Si1-x Ge x under weak electric field.
Hur, Ji-Hyun; Jeon, Sanghun
2015-12-11
We present a theoretical model which describes hole mobility degradation by charged dislocations in p-type Si1-x Ge x . The complete analytical expression of the dislocation mobility is calculated from the momentum relaxation time of hole carriers under weak electric field. The obtained dislocation mobility shows a T (3/2)/? relation and is proportional to the germanium density x. We also suggest a criterion for negating scatterings by dislocations in terms of the controllable parameters such as acceptor dopant density, dislocation density, temperature, and Ge density x, etc. PMID:26567870
Weak-Field Hall Effect in Graphene with Long-Range Scatterers
NASA Astrophysics Data System (ADS)
Noro, Masaki; Ando, Tsuneya
2016-01-01
The weak-field Hall conductivity is calculated in graphene containing scatterers with long-range potential within a self-consistent Born approximation. In the clean limit, the diagonal conductivity and the Hall conductivity are shown to agree with the Boltzmann results. Explicit numerical calculations are performed for scatterers with a Gaussian potential with the range d, showing that the Hall conductivity as well as the density of states and the diagonal conductivity becomes universal when the energy is scaled by 1/d. For more realistic charged impurities, the singularity appearing in the Hall coefficient near the charge neutrality point is shown to be sensitive to environmental dielectric material.
Jenrow, K.A.; Smith, C.H.; Liboff, A.R.
1996-12-31
The authors recently reported that cephalic regeneration in the planarian Dugesia tigrina was significantly delayed in populations exposed continuously to combined parallel DC and AC magnetic fields. This effect was consistent with hypotheses suggesting an underlying resonance phenomenon. The authors report here, in a parallel series of investigations on the same model system, that the incidence of regeneration anomalies presenting as tumor-like protuberances also increases significantly (P < .001) in association with exposure to weak 60 Hz magnetic fields, with peak intensities ranging between 1.0 and 80.0 {micro}T. These anomalies often culminate in the complete disaggregation of the organism. Similar to regeneration rate effects, the incidence of regeneration anomalies is specifically dependent upon the planaria possessing a fixed orientation with respect to the applied magnetic field vectors. However, unlike the regeneration rate effects, the AC magnetic field alone, in the absence of any measurable DC field, is capable of producing these anomalies. Moreover, the incidence of regeneration anomalies follows a clear dose-response relationship as a function of AC magnetic field intensity, with the threshold for induced electric field intensity estimated at 5 {micro} V/m. The addition of either 51.1 or 78.4 {micro}T DC magnetic fields, applied in parallel combination with the AC field, enhances the appearance of anomalies relative to the 60 Hz AC field alone, but only at certain AC field intensities. Thus, whereas the previous study of regeneration rate effects appeared to involve exclusively resonance interactions, the regeneration anomalies reported here appear to result primarily from Faraday induction coupling.
Classical and quantum decay of oscillations: Oscillating self-gravitating real scalar field solitons
NASA Astrophysics Data System (ADS)
Page, Don N.
2004-07-01
The oscillating gravitational field of an oscillaton of finite mass M causes it to lose energy by emitting classical scalar field waves, but at a rate that is nonperturbatively tiny for small ??GMm/?c, where m is the scalar field mass: dM/dt?-3 797 437.776(c3/G)?-2e-39.433 795 197/?[1+O(?)]. Oscillatons also decay by the quantum process of the annihilation of scalarons into gravitons, which is only perturbatively small in ?, giving by itself dM/dt?-0.008 513 223 935(m2c2/?)?5[1+O(?2)]. Thus the quantum decay is faster than the classical one for ??39.4338/[ln(?c/Gm2)+7 ln(1/?)+19.9160]. The time for an oscillaton to decay away completely into free scalarons and gravitons is tdecay2?6c3/G5m1110324 yr(1 meV/mc2)11. Oscillatons of more than one real scalar field of the same mass generically asymptotically approach a static-geometry U(1) boson star configuration with ?=?0, at the rate d(GM/c3)/dt?[(C/?4)e-?/?+Q(m/mPl)2?3](?2-?20), with ?0 depending on the magnitudes and relative phases of the oscillating fields, and with the same constants C, ?, and Q given numerically above for the single-field case that is equivalent to ?0=0.
NASA Astrophysics Data System (ADS)
Troshichev, O. A.; Gorshkov, E. S.; Shapovalov, S. N.; Sokolovskii, V. V.; Vorobeichikov, V. M.
2003-04-01
It is commonly accepted that linkage between the Earths biosphere and space environment is realized by means of electromagnetic fields. Meanwhile, the Earth is constantly subjected to influence of changeable gravitational field. Variations of the gravitational field affected by the Sun and the Moon while the Earths moving along the orbit seem to be a powerful source of many rhythmical processes typical of physics-chemical and biological systems. Studies carried out in AARI revealed the obvious relationships between the dynamics of physics-chemical and biological processes and variations in velocity of the Earths headway and rotary motion under the gravitational influence of the Sun and the Moon. The following of them are examined as an example: the rate of oxidation for the thiol compounds, the hematological signatures (rate of the erythrocytes sedimentation, and leukocytary ratio), influence of the lunar and solar eclipses on dynamics of growth of E.coli, and others.
Doppler shifting of a distant light source in a Schwarzschild gravitational field
NASA Astrophysics Data System (ADS)
Kislik, M. D.
1985-10-01
Correlations characterizing chromatic properties of a gravitational lens for different cases of reciprocal disposition of the observer, the source and the gravitating body have been analysed. The obtained results may be used directly for the experimental check-up of General Relativity and for the discovery of gravitating bodies in the Universe.
Electric-field-induced weakly chaotic transients in ferroelectric liquid crystals
NASA Astrophysics Data System (ADS)
Śliwa, I.; JeŻewski, W.; Kuczyński, W.
2016-01-01
Nonlinear dynamics induced in surface stabilized ferroelectric liquid crystals by strong alternating external electric fields is studied both theoretically and experimentally. As has already been shown, molecular reorientations induced by sufficiently strong fields of high-enough frequencies can reveal a long transient behavior that has a weakly chaotic character. The resulting complex dynamics of ferroelectric liquid crystals can be considered not only as a consequence of irregular motions of particular molecules but also as a repercussion of a surface-enforced partial decorrelation of nonlinear molecular motions within smectic layers. To achieve more insight into the nature of this phenomenon and to show that the underlying complex field-induced behavior of smectic liquid crystals is not exceptional, ranges of system parameters for which the chaotic behavior occurs are determined. It is proved that there exists a large enough set of initial phase trajectory points, for which weakly chaotic long-time transitory phenomena occur, and, thereby, it is demonstrated that such a chaotic behavior can be regarded as being typical for strongly field-driven thin liquid crystal systems. Additionally, the influence of low-amplitude random noise on the duration of the transient processes is numerically studied. The strongly nonlinear contribution to the electro-optic response, experimentally determined for liquid crystal samples at frequencies lower than the actual field frequency, is also analyzed for long-time signal sequences. Using a statistical approach to distinguish numerically response signals of samples from noise generated by measuring devices, it is shown that the distribution of sample signals distinctly differs from the device noise. This evidently corroborates the occurrence of the nonlinear low-frequency effect, found earlier for different surface stabilized liquid crystal samples.
NASA Astrophysics Data System (ADS)
Vizgin, Vladimir P.
2001-12-01
This article describes the history of discovery of the equations of gravitational field by Albert Einstein and David Hilbert in November 1915. The proof sheet of Hilbert's lecture report, made on 20 November 1915 and published in March 1916, rediscovered in 1997 in the archive of the university of Gttingen, throws new light on the history of this discovery. We also discuss the early history of the general theory of relativity that led to the expression of the general covariant equations of gravitational field.
NASA Astrophysics Data System (ADS)
Zschocke, Sven
2015-09-01
The light-trajectory in the gravitational field of N extended bodies in arbitrary motion is determined in the first post-Newtonian approximation. According to the theory of reference systems, the gravitational fields of these massive bodies are expressed in terms of their intrinsic multipoles, allowing for the arbitrary shape and inner structure of these bodies. The results of this investigation aim towards a consistent general-relativistic theory of light propagation in the Solar System for high-precision astrometry at the sub-microarcsecond level of accuracy.
Magnetic field mapping of the UCNTau magneto-gravitational trap: design study
Libersky, Matthew Murray
2014-09-04
The beta decay lifetime of the free neutron is an important input to the Standard Model of particle physics, but values measured using different methods have exhibited substantial disagreement. The UCN r experiment in development at Los Alamos National Laboratory (LANL) plans to explore better methods of measuring the neutron lifetime using ultracold neutrons (UCNs). In this experiment, UCNs are confined in a magneto-gravitational trap formed by a curved, asymmetric Halbach array placed inside a vacuum vessel and surrounded by holding field coils. If any defects present in the Halbach array are sufficient to reduce the local field near the surface below that needed to repel the desired energy level UCNs, loss by material interaction can occur at a rate similar to the loss by beta decay. A map of the magnetic field near the surface of the array is necessary to identify any such defects, but the array's curved geometry and placement in a vacuum vessel make conventional field mapping methods difficult. A system consisting of computer vision-based tracking and a rover holding a Hall probe has been designed to map the field near the surface of the array, and construction of an initial prototype has begun at LANL. The design of the system and initial results will be described here.
Improved mapping of planetary gravitational field with an electrostatic accelerometer/gradiometer
NASA Astrophysics Data System (ADS)
Foulon, Bernard; Huynh, Phuong-Anh; Liorzou, Francoise; Christophe, Bruno; Hardy, Emilie; Boulanger, Damien; Lebat, Vincent; Perrot, Eddy
2015-04-01
ONERA has a proven record spanning several years in developing the most accurate accelerometers for geodesy missions. They are still operational in the GRACE mission and their successors for the GRACE-FO mission will fly in 2017. Finally, the GOCE mission has shown the benefit of using a gradiometer for the direct measurement of the gravity field. Now, ONERA proposes a new accelerometer design, MicroSTAR, for interplanetary missions. This design based on the same technology as for the GRACE and GOCE space missions, with the notable addition of a bias rejection system, has a reduced mass and consumption. The accelerometer is embarked on Uranus Pathfinder (mission proposal for Cosmic M4) as up-scope instrument to achieve two scientific objectives: 1) to determine the gravity fields of Uranus and the satellites, allowing for a better understanding of the planet interior composition, 2) to test gravity at the largest possible length scales to search for deviations from General Relativity. The success of using accelerometer for geodesy mission could be imported in the planetary science field. The poster details the accuracy which can be achieved on the gravity potential field according to different accelerometer configurations. It describes the instrument and its integration inside an interplanetary probe. Finally, it explains the benefit of using this electrostatic accelerometer complementary to radio science technology for improved planetary gravitational field measurements.
Enhancing weak magnetic fabrics using field-impressed anisotropy: application to the Chinese loess
NASA Astrophysics Data System (ADS)
Liu, Qingsong; Yu, Yongjae; Deng, Chenglong; Pan, Yongxin; Zhu, Rixiang
2005-08-01
The anisotropy of the low-field magnetic susceptibility (AMS), alternating-field-treated AMS (AF-AMS), and anisotropy of anhysteretic remanent magnetization (AARM) have been systematically examined for a sandwich sequence of loess/palaeosols crossing the upper loess unit L2 (Marine Oxygen Isotope Stage 6, MIS6) to the last interglacial maximum (palaeosol unit S1S3, MIS5e) from the Yuanbao section, northwestern China. Results show that a weak, but detectable, magnetic lineation is controlled by coarse-grained aeolian Fe3O4 (magnetite). Because the long axes of the coarse-grained magnetites are statistically parallel to the palaeowind directions, the declination of the maximum susceptibility principal axis of AMS can be used as an indicator of palaeowind direction. In contrast, fine-grained pedogenic magnetic particles are responsible for the magnetic foliation. We found that AF-AMS can indicate the domain state of the magnetic particles, which is consistent with Potter & Stephenson's earlier model. We also found that AF demagnetization can significantly alter the AMS. In conclusion, the angular dependence of AF-AMS can enhance the weak AMS fabrics.
NASA Astrophysics Data System (ADS)
del Moral, A.; Azanza, Mara J.
2015-03-01
A biomagnetic-electrical model is presented that explains rather well the experimentally observed synchronization of the bioelectric potential firing rate ("frequency"), f, of single unit neurons of Helix aspersa mollusc under the application of extremely low frequency (ELF) weak alternating (AC) magnetic fields (MF). The proposed model incorporates to our widely experimentally tested model of superdiamagnetism (SD) and Ca2+ Coulomb explosion (CE) from lipid (LP) bilayer membrane (SD-CE model), the electrical quadrupolar long range interaction between the bilayer LP membranes of synchronized neuron pairs, not considered before. The quadrupolar interaction is capable of explaining well the observed synchronization. Actual extension of our SD-CE-model shows that the neuron firing frequency field, B, dependence becomes not modified, but the bioelectric frequency is decreased and its spontaneous temperature, T, dependence is modified. A comparison of the model with synchronization experimental results of pair of neurons under weak (B0 ?0.2-15 mT) AC-MF of frequency fM=50 Hz is reported. From the deduced size of synchronized LP clusters under B, is suggested the formation of small neuron networks via the membrane lipid correlation.
Control by decoherence: weak field control of an excited state objective
Katz, Gil; Ratner, Mark A.; Kosloff, Ronnie
2010-01-01
Coherent control employing a broadband excitation is applied to a branching reaction in the excited state. In a weak field for an isolated molecule, a control objective is only frequency dependent. This means that phase control of the pulse cannot improve the objective beyond the best frequency selection. Once the molecule is put into a dissipative environment a new timescale emerges. In this study, we demonstrate that the dissipation allows us to achieve coherent control of branching ratios in the excited state. The model studied contains a nuclear coordinate and three electronic states: the ground and two coupled diabatic excited states. The influence of the environment is modeled by the stochastic surrogate Hamiltonian. The excitation is generated by a Gaussian pulse where the phase control introduced a chirp to the pulse. For sufficient relaxation, we find significant control in the weak field depending on the chirp rate. The observed control is rationalized by a timing argument caused by a focused wavepacket. The initial non-adiabatic crossing is enhanced by the chirp. This is followed by energy relaxation which stabilizes the state by having an energy lower than the crossing point.
MagnetoSperm: A microrobot that navigates using weak magnetic fields
NASA Astrophysics Data System (ADS)
Khalil, Islam S. M.; Dijkslag, Herman C.; Abelmann, Leon; Misra, Sarthak
2014-06-01
In this work, a propulsion system similar in motion to a sperm-cell is investigated. This system consists of a structure resembling a sperm-cell with a magnetic head and a flexible tail of 42 μm and 280 μm in length, respectively. The thickness, length, and width of this structure are 5.2 μm, 322 μm, and 42 μm, respectively. The magnetic head includes a 200 nm-thick cobalt-nickel layer. The cobalt-nickel layer provides a dipole moment and allows the flexible structure to align along oscillating weak (less than 5 mT) magnetic field lines, and hence generates a propulsion thrust force that overcomes the drag force. The frequency response of this system shows that the propulsion mechanism allows for swimming at an average speed of 158 ± 32 μm/s at alternating weak magnetic field of 45 Hz. In addition, we experimentally demonstrate controlled steering of the flexible structure towards reference positions.
Nonlinear ion acoustic wave in a pair-ion plasma in a uniform weak magnetic field
NASA Astrophysics Data System (ADS)
Maity, Biplab; Ghosh, Samiran; Bharuthram, R.
2015-04-01
The dynamics of the nonlinear ion acoustic waves are investigated in the presence of an external weak magnetic field in pair-ion plasma in which the mass (temperature) of the positive ions are smaller (larger) than that of the negative ions. The linear dispersion relation of the ion acoustic wave is found to be modified by the externally applied magnetic field. The standard perturbative approach leads to a modified form of Korteweg-de Vries equation. The analytical as well as numerical solutions reveal that the localized (solitary wave) solutions decay slowly algebraically due to the Lorentz force by radiating energy to the tails of the dispersive ion acoustic waves. The results are discussed in the context of the lower region of D-layer ionospheric plasma.
Control of Optical Transitions with Magnetic Fields in Weakly Bound Molecules
NASA Astrophysics Data System (ADS)
McGuyer, B. H.; McDonald, M.; Iwata, G. Z.; Skomorowski, W.; Moszynski, R.; Zelevinsky, T.
2015-07-01
In weakly bound diatomic molecules, energy levels are closely spaced and thus more susceptible to mixing by magnetic fields than in the constituent atoms. We use this effect to control the strengths of forbidden optical transitions in 88Sr2 over 5 orders of magnitude with modest fields by taking advantage of the intercombination-line threshold. The physics behind this remarkable tunability is accurately explained with both a simple model and quantum chemistry calculations, and suggests new possibilities for molecular clocks. We show how mixed quantization in an optical lattice can simplify molecular spectroscopy. Furthermore, our observation of formerly inaccessible f -parity excited states offers an avenue for improving theoretical models of divalent-atom dimers.
Dark-field hyperlens: Super-resolution imaging of weakly scattering objects.
Repn, Taavi; Lavrinenko, Andrei V; Zhukovsky, Sergei V
2015-09-21
We propose a device for subwavelength optical imaging based on a metal-dielectric multilayer hyperlens designed in such a way that only large-wavevector (evanescent) waves are transmitted while all propagating (small-wavevector) waves from the object area are blocked by the hyper-lens. We numerically demonstrate that as the result of such filtering, the image plane only contains scattered light from subwavelength features of the objects and is completely free from background illumination. Similar in spirit to conventional dark-field microscopy, the proposed dark-field hyperlens is shown to enhance the subwavelength image contrast by more than two orders of magnitude. These findings are essential for optical imaging of weakly scattering subwavelength objects, such as real-time dynamic nanoscopy of label-free biological objects. PMID:26406731
Spectral response of magnetically trapped Bose gases to weak microwave fields
NASA Astrophysics Data System (ADS)
Federsel, P.; Rogulj, C.; Menold, T.; Fortgh, J.; Gnther, A.
2015-09-01
Microwave fields can be used to drive local spin transitions in quantum gases and for outcoupling of cold atomic beams from magnetic traps. In this paper, we derive an analytic theory for the outcoupling rate as a response to weak microwave fields of varying frequency and power. The theory holds for thermal clouds and Bose-Einstein condensates. It allows for calculating transition rates in arbitrary magnetic trap geometries and includes the effect of gravity. We verify our theory by measuring the flux of outcoupled atoms at the single-particle level. The derived spectral response is important for magnetic noise spectroscopy with quantum gases, and for probing quantum gas dynamics with single atom detectors in real time.
Landau pole in the Standard Model with weakly interacting scalar fields
NASA Astrophysics Data System (ADS)
Hamada, Yuta; Kawana, Kiyoharu; Tsumura, Koji
2015-07-01
We consider the Standard Model with a new scalar field X which is an nX representation of the SU (2)L with a hypercharge YX. The renormalization group running effects on the new scalar quartic coupling constants are evaluated. Even if we set the scalar quartic coupling constants to be zero at the scale of the new scalar field, the coupling constants are induced by the one-loop effect of the weak gauge bosons. Once non-vanishing couplings are generated, the couplings rapidly increase by renormalization group effect of the quartic coupling constant itself. As a result, the Landau pole appears below Planck scale if nX ≥ 4. We find that the scale of the obtained Landau pole is much lower than that evaluated by solving the one-loop beta function of the gauge coupling constants.
Astronomers Use X-Rays To Probe Gravitational Field Of A Neutron Star
NASA Astrophysics Data System (ADS)
2002-06-01
With NASA's Chandra X-ray Observatory, astronomers have detected features that may be the first direct evidence of the effect of gravity on radiation from a neutron star. This finding, if confirmed, could enable scientists to measure the gravitational field of neutron stars and determine whether they contain exotic forms of matter not seen on Earth. A team led by George Pavlov of Penn State University in University Park observed 1E 1207.4-5209, a neutron star in the center of a supernova remnant about 7,000 light years from Earth. The results were presented on June 6, 2002, at the American Astronomical Society in Albuquerque, NM. Pavlov's group found two dips, or absorption features, in the spectrum of X-rays from the star. If these dips are due to the absorption of X-rays near the star by helium ions in a strong magnetic field, they indicate that the gravitational field reduces the energies of X-rays escaping from near the surface of a neutron star. "This interpretation is consistent with the data," said Pavlov, "but the features may be a blend of many other features. More precise measurements, preferably with Chandra's grating spectrometer, are needed." "These absorption features may be the first evidence of the effect of gravity on radiation near the surface of an isolated neutron star," said Pavlov. "This is particularly important because it would allow us to set limits on the type of matter that comprises this star." Neutron stars are formed when a massive star runs out of fuel and its core collapses. A supernova explosion occurs and the collapsed core is compressed to a hot object about 12 miles in diameter, with a thin atmosphere of hydrogen and possibly heavier ions in a gravitational field 100 billion times as strong as Earth's. These objects, which have a density of more than 1 billion tons per teaspoonful, are called neutron stars because they have been thought to be composed mostly of neutrons. Although neutron stars have been studied extensively for more than three decades, their exact nature is still unknown. "We are not even sure that neutron stars are composed of neutrons," said Divas Sanwal, also of Penn State, and lead author on a paper describing the team's results. "They could be largely composed of subatomic particles called pions or kaons, or even free quarks." One key to narrow the range of possibilities is to measure the strength of gravity on the surface of a neutron star by observing its effect on X-rays from very near the surface of the star. According to Einstein's theory of General Relativity, attraction of photons by a star's gravitational field results in a lower energy of the photon (longer wavelength of radiation) when detected by a distant observer. The measurement of this gravitational redshift relates the mass to the radius of the star, and it will test the theories for the various possible forms of dense matter. The team, which also includes Slava Zavlin of Max Plank Institute for Extraterrestrial Physics, Germany, and Marcus Teter of Penn State, considered several possible explanations for the absorption features observed from 1E 1207. The strength and X-ray energy of the features make it improbable that they are due to intervening interstellar material or absorption due to electrons or ions circling in a strong magnetic field. The most likely hypothesis, they conclude, is that the features are due to absorption by helium ions in a magnetic field about a hundred trillion times more intense than the Earth's magnetic field. In this case, the gravitational redshift reduces the energy of the X-rays by 17 percent. Pavlov and his colleagues observed 1E 1027 with Chandra's Advanced CCD Imaging Spectrometer on January 6, 2000, and again on January 5, 2002, each time for approximately 30,000 seconds. The ACIS instrument was built for NASA by Penn State and the Massachusetts Institute of Technology, Cambridge, Mass. under the leadership of Gordon Garmire of Penn State. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the
Probing gravitational dark matter
NASA Astrophysics Data System (ADS)
Ren, Jing; He, Hong-Jian
2015-03-01
So far all evidences of dark matter (DM) come from astrophysical and cosmological observations, due to the gravitational interactions of DM. It is possible that the true DM particle in the universe joins gravitational interactions only, but nothing else. Such a Gravitational DM (GDM) may act as a weakly interacting massive particle (WIMP), which is conceptually simple and attractive. In this work, we explore this direction by constructing the simplest scalar GDM particle χs. It is a Bbb Z2 odd singlet under the standard model (SM) gauge group, and naturally joins the unique dimension-4 interaction with Ricci curvature, ξsχs2Script R, where ξs is the dimensionless nonminimal coupling. We demonstrate that this gravitational interaction ξsχs2Script R, together with Higgs-curvature nonminimal coupling term ξhH†HScript R, induces effective couplings between χs2 and SM fields, and can account for the observed DM thermal relic abundance. We analyze the annihilation cross sections of GDM particles and derive the viable parameter space for realizing the DM thermal relic density. We further study the direct/indirect detections and the collider signatures of such a scalar GDM. These turn out to be highly predictive and testable.
Probing gravitational dark matter
Ren, Jing; He, Hong-Jian
2015-03-27
So far all evidences of dark matter (DM) come from astrophysical and cosmological observations, due to the gravitational interactions of DM. It is possible that the true DM particle in the universe joins gravitational interactions only, but nothing else. Such a Gravitational DM (GDM) may act as a weakly interacting massive particle (WIMP), which is conceptually simple and attractive. In this work, we explore this direction by constructing the simplest scalar GDM particle χ{sub s}. It is a ℤ{sub 2} odd singlet under the standard model (SM) gauge group, and naturally joins the unique dimension-4 interaction with Ricci curvature, ξ{sub s}χ{sub s}{sup 2}R, where ξ{sub s} is the dimensionless nonminimal coupling. We demonstrate that this gravitational interaction ξ{sub s}χ{sub s}{sup 2}R, together with Higgs-curvature nonminimal coupling term ξ{sub h}H{sup †}HR, induces effective couplings between χ{sub s}{sup 2} and SM fields, and can account for the observed DM thermal relic abundance. We analyze the annihilation cross sections of GDM particles and derive the viable parameter space for realizing the DM thermal relic density. We further study the direct/indirect detections and the collider signatures of such a scalar GDM. These turn out to be highly predictive and testable.
NASA Technical Reports Server (NTRS)
Yuan, C.
1983-01-01
Under the influence of a spiral gravitational field, there should be differences among the mean motions of different types of objects with different dispersion velocities in a spiral galaxy. The old stars with high dispersion velocity should have essentially no mean motion normal to the galactic rotation. On the other hand, young objects and interstellar gas may be moving relative to the old stars at a velocity of a few kilometer per second in both the radial (galacto-centric), and circular directions, depending on the spiral model adopted. Such a velocity is usually referred as the systematic motion or the streaming motion. The conventionally adopted local standard of rest is indeed co-moving with the young objects of the solar vicinity. Therefore, it has a net systematic motion with respect to the circular motion of an equilibrium galactic model, defined by the old stars. Previously announced in STAR as N83-24443
Mechanism of Partial Flame Propagation and Extinction in a Strong Gravitational Field
NASA Astrophysics Data System (ADS)
Kazakov, Kirill A.
2015-12-01
A theory of partial flame propagation driven by the gravitational field is developed. Using the on-shell approach, equations for the gas velocity distributions and the front shape of a steady flame are obtained and solved numerically. It is found that the solutions describing upward flame propagation come in pairs having close propagation speeds, and that the effect of strong gravity is to reverse the burnt gas velocity profile generated by the flame. On the basis of these results, a complete explanation is given of the intricate observed behavior of flames near the limits of inflammability, including the dependence of the inflammability range on the size of the combustion domain, the large distances of partial flame propagation, and the progression of flame extinction.
Variations of Mars gravitational field and rotation due to seasonal CO sub 2 exchange
Chao, B.F.; Rubincam, D.P. )
1990-08-30
About a quarter of the Martian atmospheric mass is exchanged between the atmosphere and the polar caps in the course of a Martian year: CO{sub 2} condenses to form (or add to) the polar caps in winter and sublimes into the atmosphere in summer. This paper studies the effect of this CO{sub 2} mass redistribution on Martian rotation and gravitational field. Two mechanisms are examined: (1) the waxing and waning of solid CO{sub 2} in the polar caps and (2) the geographical distribution of gaseous CO{sub 2} in the atmosphere. In particular, the net peak-to-peak changes in J{sub 2} and J{sub 3} over a Martian year are both found to be as much as {approximately}6 {times} 10{sup {minus}9}. A simulation suggests that these changes may be detected by the upcoming Mars Observer under favorable but realistic conditions.
NASA Technical Reports Server (NTRS)
Nisbet, John S.
1989-01-01
General equations for the Reynolds number of a variety of types of ice crystals and water drops are given in terms of the Davies, Bond, and Knudsen numbers. The equations are in terms of the basic physical parameters of the system and are valid for calculating velocities in gravitational and electric fields over a very wide range of sizes and atmospheric conditions. The equations are asymptotically matched at the bottom and top of the size spectrum, useful when checking large computer codes. A numerical system for specifying the dimensional properties of ice crystals is introduced. Within the limits imposed by such variables as particle density, which have large deviations, the accuracy of velocities appears to be within 10 percent over the entire range of sizes of interest.
Mechanism of Partial Flame Propagation and Extinction in a Strong Gravitational Field.
Kazakov, Kirill A
2015-12-31
A theory of partial flame propagation driven by the gravitational field is developed. Using the on-shell approach, equations for the gas velocity distributions and the front shape of a steady flame are obtained and solved numerically. It is found that the solutions describing upward flame propagation come in pairs having close propagation speeds, and that the effect of strong gravity is to reverse the burnt gas velocity profile generated by the flame. On the basis of these results, a complete explanation is given of the intricate observed behavior of flames near the limits of inflammability, including the dependence of the inflammability range on the size of the combustion domain, the large distances of partial flame propagation, and the progression of flame extinction. PMID:26764992
An improved model of the Earth's gravitational field: GEM-T1
NASA Technical Reports Server (NTRS)
Marsh, J. G.; Lerch, F. J.; Christodoulidis, D. C.; Putney, B. H.; Felsentreger, T. L.; Sanchez, B. V.; Smith, D. E.; Klosko, S. M.; Martin, T. V.; Pavlis, E. C.
1987-01-01
Goddard Earth Model T1 (GEM-T1), which was developed from an analysis of direct satellite tracking observations, is the first in a new series of such models. GEM-T1 is complete to degree and order 36. It was developed using consistent reference parameters and extensive earth and ocean tidal models. It was simultaneously solved for gravitational and tidal terms, earth orientation parameters, and the orbital parameters of 580 individual satellite arcs. The solution used only satellite tracking data acquired on 17 different satellites and is predominantly based upon the precise laser data taken by third generation systems. In all, 800,000 observations were used. A major improvement in field accuracy was obtained. For marine geodetic applications, long wavelength geoidal modeling is twice as good as in earlier satellite-only GEM models. Orbit determination accuracy has also been substantially advanced over a wide range of satellites that have been tested.
NASA Astrophysics Data System (ADS)
Petrovskaya, M. S.
The conventional approach to the recovery of the Earth's gravitational field from satellite gradiometry observations is based on constructing, from the start, several boundary value (BV) relations, each of them corresponding to a separate observable component of the gravity gradient (GG) tensor or a certain combination of them. In particular, one of such projects, the ARISTOTELES mission, assumes that only the radial and across-track components are accessible (by technical reasons). The purpose of the present paper is mainly to discuss the principle aspects of the problem of the Earth's potential recovering from satellite gradiometry, to give an optimal formulation of the problem and derive the basic boundary value equation in different forms.
Variations of Mars gravitational field and rotation due to seasonal CO2 exchange
NASA Technical Reports Server (NTRS)
Chao, B. Fong; Rubincam, David Parry
1990-01-01
About a quarter of the Martian atmospheric mass is exchanged between the atmosphere and the polar caps in the course of a Martian year: CO2 condenses to form (or add to) the polar caps in winter and sublimes into the atmosphere in summer. This paper studies the effect of this CO2 mass redistribution on Martian rotation and gravitational field. Two mechanisms are examined: (1) the waxing and waning of solid CO2 in the polar caps and (2) the geographical distribution of gaseous CO2 in the atmosphere. In particular, the net peak-to-peak changes in J2 and J3 over a Martian year are both found to be as much as about 6 x 10 to the -9th. A simulation suggests that these changes may be detected by the upcoming Mars Observer under favorable but realistic conditions.
NASA Technical Reports Server (NTRS)
Nisbet, John S.
1988-01-01
General equations for the Reynolds number of a variety of types of ice crystals and water drops are given in terms of the Davies, Bond, and Knudsen numbers. The equations are in terms of the basic physical parameters of the system and are valid for calculating velocities in gravitational and electric fields over a very wide range of sizes and atmospheric conditions. The equations are asymptotically matched at the bottom and top of the size spectrum, useful when checking large computer codes. A numerical system for specifying the dimensional properties of ice crystals is introduced. Within the limits imposed by such variables as particle density, which have large deviations, the accuracy of velocities appears to be within 10 percent over the entire range of sizes of interest.
NASA Astrophysics Data System (ADS)
Sampson, Laura; Cornish, Neil; Yunes, Nicolas
2013-04-01
We study generic tests of strong-field General Relativity with gravitational waves emitted during the inspiral of compact binaries. We construct waveforms that deviate from the General Relativistic expectation through a series of post-Newtonian terms (instead of a single phase term); we find that these higher-order terms can affect our ability to test GR, in some cases by making it easier to detect a deviation, and in some cases by making it more difficult. We find that more complicated, parameterized post-Einsteinian families, with multiple phase terms, are suboptimal at detecting deviations from General Relativity; the simplest family still reigns supreme when trying to identify whether a deviation from Einstein's theory is present in the data.
Strong field limit analysis of gravitational lensing in Kerr-Taub-NUT spacetime
Wei, Shao-Wen; Liu, Yu-Xiao; Fu, Chun-E; Yang, Ke E-mail: liuyx@lzu.edu.cn E-mail: yangke09@lzu.edu.cn
2012-10-01
In this paper, we study numerically the quasi-equatorial lensing by the stationary, axially-symmetric black hole in Kerr-Taub-NUT spacetime in the strong field limit. The deflection angle of light ray and other strong deflection limit coefficients are obtained numerically and they are found to be closely dependent on the NUT charge n and spin a. We also compute the magnification and the positions of the relativistic images. The caustics are studied and the results show that these caustics drift away from the optical axis, which is quite different from the Schwarzschild black hole case. Moreover, the intersections of the critical curves on the equatorial plane are obtained and it is shown that they increase with the NUT charge. These results show that there is a significant effect of the NUT charge on the strong gravitational lensing.
Improved model of the Earth's gravitational field: GEM-T1
Marsh, J.G.; Lerch, F.J.; Christodoulidis, D.C.; Putney, B.H.; Felsentreger, T.L.; Sanchez, B.V.; Smith, D.E.; Klosko, S.M.; Martin, T.V.; Pavlis, E.C.
1987-07-01
Goddard Earth Model T1 (GEM-T1), which was developed from an analysis of direct satellite tracking observations, is the first in a new series of such models. GEM-T1 is complete to degree and order 36. It was developed using consistent reference parameters and extensive earth and ocean tidal models. It was simultaneously solved for gravitational and tidal terms, earth orientation parameters, and the orbital parameters of 580 individual satellite arcs. The solution used only satellite tracking data acquired on 17 different satellites and is predominantly based upon the precise laser data taken by third generation systems. In all, 800,000 observations were used. A major improvement in field accuracy was obtained. For marine geodetic applications, long wavelength geoidal modeling is twice as good as in earlier satellite-only GEM models. Orbit determination accuracy has also been substantially advanced over a wide range of satellites that have been tested.
Resonantly enhanced and diminished strong-field gravitational-wave fluxes
NASA Astrophysics Data System (ADS)
Flanagan, anna E.; Hughes, Scott A.; Ruangsri, Uchupol
2014-04-01
The inspiral of a stellar mass (1-100M?) compact body into a massive (105-107M?) black hole has been a focus of much effort, both for the promise of such systems as astrophysical sources of gravitational waves, and because they are a clean limit of the general relativistic two-body problem. Our understanding of this problem has advanced significantly in recent years, with much progress in modeling the "self-force" arising from the small body's interaction with its own spacetime deformation. Recent work has shown that this self-interaction is especially interesting when the frequencies associated with the orbit's ? and r motions are in an integer ratio: ??/?r=??/?r, with ?? and ?r both integers. In this paper, we show that key aspects of the self-interaction for such "resonant" orbits can be understood with a relatively simple Teukolsky-equation-based calculation of gravitational-wave fluxes. We show that fluxes from resonant orbits depend on the relative phase of radial and angular motions. The purpose of this paper is to illustrate in simple terms how this phase dependence arises using tools that are good for strong-field orbits, and to present a first study of how strongly the fluxes vary as a function of this phase and other orbital parameters. Future work will use the full dissipative self-force to examine resonant and near resonant strong-field effects in greater depth, which will be needed to characterize how a binary evolves through orbital resonances.
NASA Astrophysics Data System (ADS)
Asmar, S.; Konopliv, A. S.; Williams, J. G.; Watkins, M. M.; Zuber, M. T.; Smith, D. E.; Park, R. S.
2012-12-01
The Gravity Recovery and Interior Laboratory (GRAIL) dual-spacecraft mission has completed its primary three-month tour that resulted in a gravitational field of 420 degree-and-order or equivalent surface resolution of 13 km. The primary measurement for the gravity field is the inter-spacecraft K-Band Range Rate (KBRR) measurement derived from dual spacecraft one-way range. Advanced system calibrations and measurement timing have resulted in unprecedented data quality of better than 0.1 microns/sec. The gravity field solution using KBRR and Deep Space Network tracking data shows an error spectrum with several orders of magnitude improvement for all wavelengths when compared to previous missions. Nearly uniform correlations with topography exist through higher harmonic degrees and are a good measure of field integrity. The results of the mission satisfy the scientific objectives of determining the structure of the lunar interior from crust to core and advancing the understanding of the thermal evolution of the Moon. They also directly address the mission's investigations that include mapping the structure of the crust and lithosphere, understanding the Moon's asymmetric thermal evolution, determining the subsurface structure of impact basins and the origin of mascons, ascertaining the temporal evolution of the crustal brecciation and magmatism, and constrain deep interior structure from tides. Place limits on the size of a possible solid inner core.
A 660 D&O Gravitational Field of the Moon from the GRAIL Primary Mission
NASA Astrophysics Data System (ADS)
Yuan, Dah-Ning; Konopliv, Alex; Asmar, Sami; Park, Ryan; Williams, James; Watkins, Michael; Fahnestock, Eugene; Kruizinga, Gerhard; Paik, Meegyeong; Strekalov, Dmitry; Harvey, Nate; Zuber, Maria; Smith, David
2013-04-01
The Gravity Recovery and Interior Laboratory (GRAIL) mission has completed its primary three-month tour that resulted in a gravitational field of 660 degree-and-order or equivalent surface resolution of 8 km. The primary measurement for the gravity field is the inter-spacecraft K-Band Range Rate (KBRR) measurement derived from dual spacecraft one-way range. Direct Doppler tracking at X-band from the Deep Space Network for Ebb and Flow supplemented The KBRR. Advanced system calibrations and measurement timing have resulted in unprecedented data quality of better than 0.1 microns/sec. The gravity field solution shows an error spectrum with several orders of magnitude improvement for all wavelengths when compared to previous missions. Nearly uniform correlations with topography exist through higher harmonic degrees and are a good measure of field integrity. The results of the mission satisfy the scientific objectives of determining the structure of the lunar interior from crust to core and advancing the understanding of the thermal evolution of the Moon. They also directly address the mission's investigations that include mapping the structure of the crust and lithosphere, understanding the Moon's asymmetric thermal evolution, determining the subsurface structure of impact basins and the origin of mascons, ascertaining the temporal evolution of the crustal brecciation and magmatism, constrain deep interior structure from tides, and place limits on the size of a possible solid inner core.
Weakly perturbed Schwarzschild lens in the strong deflection limit
Bozza, V.; Sereno, M.
2006-05-15
We investigate the strong deflection limit of gravitational lensing by a Schwarzschild black hole embedded in an external gravitational field. The study of this model, analogous to the Chang and Refsdal lens in the weak deflection limit, is important to evaluate the gravitational perturbations on the relativistic images that appear in proximity of supermassive black holes hosted in galactic centers. By a simple dimensional argument, we prove that the tidal effect on the light ray propagation mainly occurs in the weak field region far away from the black hole and that the external perturbation can be treated as a weak field quadrupole term. We provide a description of relativistic critical curves and caustics and discuss the inversion of the lens mapping. Relativistic caustics are shifted and acquire a finite diamond shape. Sources inside the caustics produce four sequences of relativistic images. On the other hand, retro-lensing caustics are only shifted while remaining pointlike to the lowest order.
NASA Astrophysics Data System (ADS)
Tsybul'nik, V. A.; Roshchupkin, S. P.
2013-10-01
The gain coefficient for a weak electromagnetic field in the scattering of electrons by ions in an elliptically polarized light wave is theoretically studied in the general relativistic case. A simple analytical expression for the field amplification constant in a logarithmic approach is obtained. It is shown that the gain coefficient for ultrarelativistic electron energies depends on the energy as a cubic power of energy and can be significantly large. This effect results in an increase of the gain coefficient up to quantities of order ? (1-10) cm-1 for electron energies Ei (10-20) GeV. The obtained results may be experimentally verified, for example, by the scientific facilities at the SLAC National Accelerator Laboratory and the Facility for Antiproton and Ion Research (FAIR; Darmstadt, Germany).
Chaotic transport in Hamiltonian systems perturbed by a weak turbulent wave field
Abdullaev, S. S.
2011-08-15
Chaotic transport in a Hamiltonian system perturbed by a weak turbulent wave field is studied. It is assumed that a turbulent wave field has a wide spectrum containing up to thousands of modes whose phases are fluctuating in time with a finite correlation time. To integrate the Hamiltonian equations a fast symplectic mapping is derived. It has a large time-step equal to one full turn in angle variable. It is found that the chaotic transport across tori caused by the interactions of small-scale resonances have a fractal-like structure with the reduced or zero values of diffusion coefficients near low-order rational tori thereby forming transport barriers there. The density of rational tori is numerically calculated and its properties are investigated. It is shown that the transport barriers are formed in the gaps of the density of rational tori near the low-order rational tori. The dependencies of the depth and width of transport barriers on the wave field spectrum and the correlation time of fluctuating turbulent field (or the Kubo number) are studied. These numerical findings may have importance in understanding the mechanisms of transport barrier formation in fusion plasmas.
Chaotic transport in hamiltonian systems perturbed by a weak turbulent wave field.
Abdullaev, S S
2011-08-01
Chaotic transport in a hamiltonian system perturbed by a weak turbulent wave field is studied. It is assumed that a turbulent wave field has a wide spectrum containing up to thousands of modes whose phases are fluctuating in time with a finite correlation time. To integrate the hamiltonian equations a fast symplectic mapping is derived. It has a large time-step equal to one full turn in angle variable. It is found that the chaotic transport across tori caused by the interactions of small-scale resonances have a fractal-like structure with the reduced or zero values of diffusion coefficients near low-order rational tori thereby forming transport barriers there. The density of rational tori is numerically calculated and its properties are investigated. It is shown that the transport barriers are formed in the gaps of the density of rational tori near the low-order rational tori. The dependencies of the depth and width of transport barriers on the wave field spectrum and the correlation time of fluctuating turbulent field (or the Kubo number) are studied. These numerical findings may have importance in understanding the mechanisms of transport barrier formation in fusion plasmas. PMID:21929078
Unified quantum jump superoperator for optical fields from the weak- to the strong-coupling limit
Haeyrynen, Teppo; Oksanen, Jani; Tulkki, Jukka
2010-06-15
We derive a generalized quantum jump superoperator that can be used in the quantum trajectory description of single photon detectors, light-emitting diodes (LEDs), and lasers. Our model describes an optical single-mode cavity field coupled to a reservoir through a two-state quantum system and includes three physical parameters: the coupling of the field to the two-state system, the coupling of the two-state system to the reservoir, and the cavity loss rate. In this setup, the two-state system can act as a photodetector or as an energy-adding mechanism. In the first case, we assume that the reservoir acts as a damping mechanism for an ideal cavity and derive reduced field operators describing the photon detection events. Our model coincides with the commonly known quantum trajectory based photon counting models at the weak- and strong-coupling limits and is, furthermore, also applicable between their validity regimes. In the second case, we assume that the reservoir injects energy into a lossy cavity through the two-state system. Again we derive the reduced field operators describing photon creation events into the lossy cavity. We show that this setup can act as an LED or as a laser depending on the strength of the injection. We also investigate how the setup operates at the close proximity of the lasing threshold.
Resolution of partial cataplexy in multiple sclerosis by treatment with weak electromagnetic fields.
Sandyk, R
1996-02-01
Cataplexy, an ancillary symptom of narcolepsy, involves the sudden loss of muscle tone without altered consciousness usually brought on by sudden excitement or emotional influence and extreme exertions (Guilleminault et al., 1974; Parks et al., 1974; Guilleminault, 1976; Aldrich, 1992; 1993; Scrima, 1981; Baker, 1985). Attacks of generalized cataplexy produce complete atonic, areflexic partial or complete paralysis of striated muscles commonly involving the leg muscles resulting in collapse of the knees and falling while milder forms often termed partial cataplexy may manifest by sagging of the face, eyelid, or jaw, dysarthria, blurred vision, drooping of the head, weakness of an arm or leg, buckling at the knees, or simply a momentary sensation of weakness that is imperceptible to observers (Guilleminault, 1976; Aldrich, 1993). The duration of cataplexy is usually a few seconds, although severe episodes can last several minutes and rarely several hours or days in the case of "status cataplecticus" (Parkes et al., 1974; Guilleminault, 1976; Billiard & Cadilhac, 1985; Aldrich, 1992; 1993). This report concerns a 51 year old man with chronic progressive multiple sclerosis who exhibited daily episodes of partial cataplexy which resolved within 3 weeks after he received treatment with picotesla electromagnetic fields. PMID:8707478
Weak edge enhancement based on contextual modulation of non-classical receptive field
NASA Astrophysics Data System (ADS)
Xiao, Jie; Cai, Chao
2015-12-01
Edges and contours of an object contain a lot of information, so the detection and extraction of saliency edges and contours in the image become one of the most active issues in the research field of automatic target recognition. Weak edge enhancement plays an important role in contour detection. Based on psychophysical and physiological findings, a contour detection method which focuses on weak edge enhancement and inspired by the visual mechanism in the primary visual cortex (V1) is proposed in this paper. The method is divided in three steps. Firstly, the response of every single visual neuron in V1 is computed by local energy. Secondly, the local contrast which corresponds to the CRF is computed. If the local contrast in the image is below the low contrast threshold, expand NCRF to change the spatially modulatory range by increasing the NCRF radius. Thirdly, the facilitation and suppression (the contextual influence) on a neuron through horizontal interactions are obtained by using a spatially unified modulating function. We tested it on synthetic images and encouraging results were acquired.
Ultra-weak magnetic fields in Am stars: ? UMa and ? Leo
NASA Astrophysics Data System (ADS)
Blazre, A.; Petit, P.; Lignires, F.; Aurire, M.; Ballot, J.; Bhm, T.; Folsom, C.; Ariste, A. Lpez; Wade, G. A.
2015-10-01
An extremely weak circularly-polarized signature was recently detected in the spectral lines of the Am star Sirius A. With a prominent positive lobe, the shape of the phase-averaged Stokes V line profile is atypical of stellar Zeeman signatures, casting doubts on its magnetic origin. We report here on ultra-deep spectropolarimetric observations of two more bright Am stars: ? Uma and ? Leo. Stokes V line signatures are detected in both objects, with a shape and amplitude similar to the one observed on Sirius A. We demonstrate that the amplitude of the Stokes V line profiles depend on various line parameters (Land factor, wavelength, depth) as expected from a Zeeman signature, confirming that extremely weak magnetic fields are likely present in a large fraction of Am stars. We suggest that the strong asymmetry of the polarized signatures, systematically observed so far in Am stars and never reported in strongly magnetic Ap stars, bears unique information about the structure and dynamics of the thin surface convective shell of Am stars.
Gravitational field equations near an arbitrary null surface expressed as a thermodynamic identity
NASA Astrophysics Data System (ADS)
Chakraborty, Sumanta; Parattu, Krishnamohan; Padmanabhan, T.
2015-10-01
Previous work has demonstrated that the gravitational field equations in all Lanczos-Lovelock models imply a thermodynamic identity T δλ S = δλ E + P δλ V (where the variations are interpreted as changes due to virtual displacement along the affine parameter λ) in the near-horizon limit in static spacetimes. Here we generalize this result to any arbitrary null surface in an arbitrary spacetime and show that certain components of the Einstein's equations can be expressed in the form of the above thermodynamic identity. We also obtain an explicit expression for the thermodynamic energy associated with the null surface. Under appropriate limits, our expressions reduce to those previously derived in the literature. The components of the field equations used in obtaining the current result are orthogonal to the components used previously to obtain another related result, viz. that some components of the field equations reduce to a Navier-Stokes equation on any null surface, in any spacetime. We also describe the structure of Einstein's equations near a null surface in terms of three well-defined projections and show how the different results complement each other.
The R.I. Pimenov unified gravitation and electromagnetism field theory as semi-Riemannian geometry
Gromov, N. A.
2009-05-15
More than forty years ago R.I. Pimenov introduced a new geometry-semi-Riemannian one-as a set of geometrical objects consistent with a fibering pr: M{sub n} {yields} M{sub m}. He suggested the heuristic principle according to which the physically different quantities (meter, second, Coulomb, etc.) are geometrically modelled as space coordinates that are not superposed by automorphisms. As there is only one type of coordinates in Riemannian geometry and only three types of coordinates in pseudo-Riemannian one, a multiple-fibered semi-Riemannian geometry is the most appropriate one for the treatment of more than three different physical quantities as unified geometrical field theory. Semi-Euclidean geometry {sup 3}R{sub 5}{sup 4} with 1-dimensional fiber x{sup 5} and 4-dimensional Minkowski space-time as a base is naturally interpreted as classical electrodynamics. Semi-Riemannian geometry {sup 3}V{sub 5}{sup 4} with the general relativity pseudo-Riemannian space-time {sup 3}V{sub 4}, and 1-dimensional fiber x{sup 5}, responsible for the electromagnetism, provides the unified field theory of gravitation and electromagnetism. Unlike Kaluza-Klein theories, where the fifth coordinate appears in nondegenerate Riemannian or pseudo-Riemannian geometry, the theory based on semi-Riemannian geometry is free from defects of the former. In particular, scalar field does not arise.
NASA Astrophysics Data System (ADS)
Christophe, B.; Lebat, V.; Foulon, B.; Liorzou, F.; Perrot, E.; Boulanger, D.; Hardy, E.
2014-12-01
ONERA has developed since several years the most accurate accelerometers for the geodesy mission. The accelerometers are still operational in the GRACE mission. Their successors for the GRACE-FO mission are under manufacturing and will fly in 2017. Finally, the GOCE mission has proved the interest of gradiometer for a direct measurement of the gravity field.Now, ONERA proposes a new design of accelerometer, MicroSTAR, for interplanetary mission. It inherits of the same technology but with reduced mass and consumption. It has been proposed in several missions towards outer planets in order to test the deviation to the relativity general over large distance to the sun (with the addition of a bias rejection system). But the same instrument could be interesting to improve our knowledge of the planetary gravitational potential field, allowing a better understanding of the planet interior composition. The success of using accelerometer for geodesy mission could be imported in the planetary science.The paper will present the accuracy achievable on the gravity potential field according to different accelerometer configurations (one accelerometer, one gradiometer arm or a complete 3-axis gradiometer). Then, the instrument will be described and the integration of the instrument inside an interplanetary probe will be evoked.
Magnetic interactions, weak ferromagnetism, and field-induced transitions in Nd2NiO4
NASA Astrophysics Data System (ADS)
Batlle, X.; Obradors, X.; Martnez, B.
1992-02-01
The magnetic properties of stoichiometric Nd2NiO4 have been investigated by means of dc- and ac-magnetic-susceptibility and isothermal-magnetization measurements. Five different magnetic phase transitions have been identified and characterized. A collinear antiferromagnetic ordering of Ni2+ magnetic moments exists between TN1~=320 K and Tc1~=130 K (gx mode) where an orthorhombic-to-tetragonal (Bmab to P42/ncm) structural phase transition occurs. In this temperature range, the Nd3+ ions behave as a paramagnet being polarized by the effect of an internal magnetic field associated with the Ni-Nd antiferromagnetic superexchange interaction. A weak ferromagnetic component appears below 130 K, which is consistent with the gxcyfz and gx+cyfz magnetic modes for Ni2+ proposed from a neutron-powder-diffraction experiment. An additional out-of-plane component of the internal magnetic field on the Nd3+ ions develops with this structural phase transition and strongly polarizes these ions. Two additional transitions are observed at Tc2~=68 K (very prominent) and Tc3~=45 K (very smooth), which are characterized by a sudden increase in the internal magnetic field acting on the Nd ions. This internal magnetic field is evaluated and an antiparallel ordering between the Ni and Nd weak ferromagnetic spin components is inferred. A field-induced transition has been identified. A peak on both the differential susceptibility and the real part of the ac susceptibility at TN2~=11 K marks a long-range antiferromagnetic ordering of the Nd3+ ions. The out-of-plane component of the Ni2+ magnetic moments is attributed to the antisymmetric interaction DNi-Ni, which turns out to be quite important (DNi-Ni~=-16.0 meV) as compared to La2NiO4 and La2CuO4, probably because of a greater tilting angle of the octahedra. Finally, the magnetocrystalline anisotropy associated with Nd ions is found to be high below 20 K.
Effect of weak permanent magnetic field on lipid composition and content in perilla leaves.
Novitskii, Yurii; Novitskaya, Galina; Serdyukov, Yurii
2016-02-01
Composition and content of lipids were studied in leaves of red perilla plants (Perilla nankinensis [Lour.] Decne.) grown in weak permanent horizontal magnetic field (PMF) of 500?T flux density under controlled illumination, temperature, and humidity in the phytothron chamber. Control plants were grown under similar conditions, but without PMF exposure. Exposure of perilla plants for a month to PMF retarded plant flowering as compared to control. PMF treatment increased total lipid content, including polar lipids, among them glycolipids and phospholipids. PMF did not affect content of neutral lipids. It is concluded that PMF stimulated synthesis of membrane lipids of chloroplasts, mitochondria, and cytoplasm in perilla leaves. A possible role of PMF as a factor imitating the additional light source retarding flowering of a short-day perilla plants is discussed. Bioelectromagnetics. 37:108-115, 2016. 2016 Wiley Periodicals, Inc. PMID:26866720
Numerical study on the stability of weakly collisional plasma in EB fields
Hork, M.
2015-02-15
Plasma stability in weakly collisional plasmas in the presence of EB fields is studied with numerical simulations. Different types of ion-neutral collisions are considered in a fully magnetized regime. We study the influence of ion-neutral collisions and the role of collision types on the stability of plasma. It is found that the stability of plasma depends on the type of ion-neutral collisions, with the plasma being unstable for charge exchange collisions, and stable for the elastic scattering. The analysis focuses on the temporal evolution of the velocity phase space, RMS values of the potential fluctuations, and coherent structures in potential densities. For the unstable case, we observe growth and propagation of electrostatic waves. Simulations are performed with a three-dimensional electrostatic particle in cell code.
Magnetoresistive memory with recording by electric field: Is the weak ferromagnetism necessary?
NASA Astrophysics Data System (ADS)
Morosov, A. I.; Sigov, A. S.
2015-06-01
Possible approaches to creating a magnetoresistive memory with recording by electric field (MERAM) are considered. The memory based on a particular geometry of multiferroic BiFeO3 is shown to be the most promising. The relatively small values of the weak ferromagnetic moment and linear magnetoelectric coupling constant in BiFeO3 are not significant obstructions for creation of such a MERAM. The key factors are the coupling between electrical polarization and the antiferromagnetism vector in the multiferroic (not between polarization and magnetization vectors), as well as the exchange coupling between the antiferromagnetism vector and the ferromagnet layer magnetization caused by the spin-flop orientation of the latter two vectors at the interface. This is inherently an antiferromagnetic-ferroelectric device mechanism.
Reduction of degenerate four-wave mixing spectra to relative populations I. Weak-field limit
Williams, S.; Zare, R.N. ); Rahn, L.A. , Sandia National Laboratories, Livermore, California 94551 )
1994-07-15
Diagrammatic perturbation theory combined with a spherical tensor treatment allows the degenerate four-wave mixing (DFWM) signal resulting from an isotropic molecular sample to be decomposed into a sum of three multipole moments in the weak-field (no saturation) limit. The zeroth moment gives the relative internal-state population contribution, the first moment the orientation contribution, and the second moment the alignment contribution to the DFWM spectra. This treatment makes explicit how the magnitude of the DFWM signal depends on the polarizations of the other three beams and the collisional relaxation caused by the environment. A general expression is derived for the DFWM signal for an arbitrary geometric configuration of the beams (arbitrary phase matching geometry). Under the assumption that the rates of collisional relaxation of the population, the orientation, and the alignment are the same, simple analytic expressions are found for the most commonly used experimental configurations, which should facilitate the practical analysis of DFWM spectra.
Application of a weak magnetic field to improve microbial fuel cell performance.
Tong, Zhong-Hua; Yu, Han-Qing; Li, Wen-Wei; Wang, Yun-Kun; Sun, Min; Liu, Xian-Wei; Sheng, Guo-Ping
2015-12-01
Microbial fuel cells (MFCs) have emerged as a promising technology for wastewater treatment with concomitant energy production but the performance is usually limited by low microbial activities. This has spurred intensive research interest for microbial enhancement. This study demonstrated an interesting stimulation effect of a static magnetic field (MF) on sludge-inoculated MFCs and explored into the mechanisms. The implementation of a 100-mT MF accelerated the reactor startup and led to increased electricity generation. Under the MF exposure, the activation loss of the MFC was decreased, but there was no increased secretion of redox mediators. Thus, the MF effect was mainly due to enhanced bioelectrochemical activities of anodic microorganisms, which are likely attributed to the oxidative stress and magnetohydrodynamic effects under an MF exposure. This work implies that weak MF may be applied as a simple and effective approach to stimulate microbial activities for various bioelectrochemical energy production and decontamination applications. PMID:26410373
Temperature and magnetic field dependence of a Kondo system in the weak coupling regime
Zhang, Yong-hui; Kahle, Steffen; Herden, Tobias; Stroh, Christophe; Mayor, Marcel; Schlickum, Uta; Ternes, Markus; Wahl, Peter; Kern, Klaus
2013-01-01
The Kondo effect arises due to the interaction between a localized spin and the electrons of a surrounding host. Studies of individual magnetic impurities by scanning tunneling spectroscopy have renewed interest in Kondo physics; however, a quantitative comparison with theoretical predictions remained challenging. Here we show that the zero-bias anomaly detected on an organic radical weakly coupled to a Au (111) surface can be described with astonishing agreement by perturbation theory as originally developed by Kondo 60 years ago. Our results demonstrate that Kondo physics can only be fully conceived by studying both temperature and magnetic field dependence of the resonance. The identification of a spin 1/2 Kondo system is of relevance not only as a benchmark for predictions for Kondo physics but also for correlated electron materials in general. PMID:23817525
Temperature and magnetic field dependence of a Kondo system in the weak coupling regime.
Zhang, Yong-hui; Kahle, Steffen; Herden, Tobias; Stroh, Christophe; Mayor, Marcel; Schlickum, Uta; Ternes, Markus; Wahl, Peter; Kern, Klaus
2013-01-01
The Kondo effect arises due to the interaction between a localized spin and the electrons of a surrounding host. Studies of individual magnetic impurities by scanning tunneling spectroscopy have renewed interest in Kondo physics; however, a quantitative comparison with theoretical predictions remained challenging. Here we show that the zero-bias anomaly detected on an organic radical weakly coupled to a Au (111) surface can be described with astonishing agreement by perturbation theory as originally developed by Kondo 60 years ago. Our results demonstrate that Kondo physics can only be fully conceived by studying both temperature and magnetic field dependence of the resonance. The identification of a spin 1/2 Kondo system is of relevance not only as a benchmark for predictions for Kondo physics but also for correlated electron materials in general. PMID:23817525
Garca-Vela, Alberto; Henriksen, Niels E
2015-03-01
The possibility of quantum interference control of the final state distributions of photodissociation fragments by means of pure phase modulation of the pump laser pulse in the weak-field regime is demonstrated theoretically for the first time. The specific application involves realistic wave packet calculations of the transient vibrational populations of the Br2(B, v(f)) fragment produced upon predissociation of the Ne-Br2(B) complex, which is excited to a superposition of resonance states using pulses with different linear chirps. Transient phase effects on the fragment populations are found to persist for long times (about 200 ps) after the pulse is over due to interference between overlapping resonances in Ne-Br2(B). PMID:26262659
Gravitational Lens Modeling of Fields Containing Multiple Projected Cluster-Scale Halos
NASA Astrophysics Data System (ADS)
Raney, Catie Ann; Wong, Kenneth C.; Umetsu, Keiichi; Keeton, Charles R.; Ammons, S. Mark; Zabludoff, Ann I.; French, K. Decker
2016-01-01
We have identified new lines of sight that are promising places to search for high-redshift galaxies. These beams contain a total mass well above 1015 M⊙ distributed among multiple group- and cluster-scale halos. The field J085007.6+360428 includes the massive cluster Zwicky 1953 plus a second massive halo in the foreground, and it features two candidate lensed images of a galaxy with a photometric redshift z=5.03. We present results from a joint weak and strong lensing analysis of the field that accounts for the full three-dimensional mass distribution and uses a full pixel reconstruction of the lensed images. We find that constraints on various field parameters, specifically cluster mass and concentration, are considerably improved with the joint approach.
Plocková, J; Chmelík, J
2001-05-25
Gravitational field-flow fractionation (GFFF) utilizes the Earth's gravitational field as an external force that causes the settlement of particles towards the channel accumulation wall. Hydrodynamic lift forces oppose this action by elevating particles away from the channel accumulation wall. These two counteracting forces enable modulation of the resulting force field acting on particles in GFFF. In this work, force-field programming based on modulating the magnitude of hydrodynamic lift forces was implemented via changes of flow-rate, which was accomplished by a programmable pump. Several flow-rate gradients (step gradients, linear gradients, parabolic, and combined gradients) were tested and evaluated as tools for optimization of the separation of a silica gel particle mixture. The influence of increasing amount of sample injected on the peak resolution under flow-rate gradient conditions was also investigated. This is the first time that flow-rate gradients have been implemented for programming of the resulting force field acting on particles in GFFF. PMID:11407583
Stellar explosion in the weak field approximation of the Brans Dicke theory
NASA Astrophysics Data System (ADS)
Hamity, Victor H.; Barraco, Daniel E.
2005-10-01
We treat a very crude model of an exploding star, in the weak field approximation of the Brans Dicke theory, in a scenario that resembles some characteristic data of a type Ia supernova. The most noticeable feature, in the electromagnetic component, is the relationship between the absolute magnitude at maximum brightness of the star and the decline rate in one magnitude from that maximum. This characteristic has become one of the most accurate methods to measure luminosity distances to objects at cosmological distances (Phillips M M 1993 Astrophys. J. 413 L105; see www.all-science-fair-projects.com/science_fair_projects_encyclopedia/Supernova, for a brief description of supernovae types). An interesting result is that the active mass associated with the scalar field is totally radiated to infinity, representing a mass loss in the ratio of the 'tensor' component to the scalar component of 1 to (2? + 3) (? is the Brans Dicke parameter), in agreement with a general result of Hawking (1972 Commun. Math. Phys. 25 167). Then, this model shows explicitly, in a dynamical case, the mechanism of the radiation of a scalar field, which is necessary to understand the Hawking result.
Weak Pion and Photon Production from Nuclei in a Chiral Effective Field Theory (Update)
NASA Astrophysics Data System (ADS)
Zhang, Xilin; Serot, Brian D.
2011-04-01
Neutrino-induced pion and photon production from nucleons and nuclei are important for the interpretation of neutrino-oscillation experiments. [A. A. Aquilar-Arevalo et al. (MiniBooNE Collaboration), Phys. Rev. Lett. 100, 032301 (2008)]. We have been working on these problems in a Lorentz-covariant effective field theory (known as QHD EFT), which contains nucleons, pions, Deltas (Δ), isoscalar scalar (σ) and vector (ω) fields, and isovector vector (ρ) fields and has nonlinear chiral symmetry built in. Here we update our results on weak pion and photon production from nuclei, including both incoherent and coherent scattering. Connections between our results and the background analysis from MiniBooNE will be presented. In particular, coherent production of photons will be emphasized, and the possible relevance to the low-energy excess events at MiniBooNE will be explored. To justify our approximation scheme, we compare our results with data for inclusive electron scattering off nuclei up to the Δ peak and with coherent photoproduction of pions. Finally, we focus on the approximation scheme used and discuss the important Δ dynamics in the medium. An interesting mechanism to generate the Δ's spin-orbit coupling in the nucleus will be introduced, together with its possible consequences. Supported in part by the Department of Energy under Contract No. DE-FG02-87ER40365.
Modification of the classical Heisenberg helimagnet by weak uniaxial anisotropy and magnetic field
Zaliznyak, I.A.; Zhitomirsky, M.E.
1995-09-01
A classical ground state of the isotropic Heisenberg spin Hamiltonian on a primitive Bravais lattice is known to be a single-Q plane helix. Additional uniaxial anisotropy and external magnetic field can greatly distort this structure by generating higher-order (at the wave vectors nQ) Fourier harmonics in the spatial spin configuration. These features are not captured within the usual formalism based on the Luttinger-Tisza theorem, when the classical ground state energy is minimized under the {open_quotes}weak{close_quotes} condition on the lengths of the spins. We discuss why the correct solution is lost in that approach and present another microscopic treatment of the problem. For easy-axis and easy-plane quadratic uniaxial anisotropy it allows one to find the classical ground state for general Q and for any orientation of the magnetic field considering the effect of anisotropy (but not the field) as a perturbation of the exchange structure. As a result, the classical ground state energy, the uniform magnetization, and the magnetic Bragg peak intensities that are measured in the experiments are calculated. 21 refs., 1 fig.
Electrodiffusiophoresis of a large-zeta-potential particle in weak fields
NASA Astrophysics Data System (ADS)
Tricoli, Vincenzo; Orsini, Gabriele
2015-10-01
The electrodiffusiophoresis of a large-zeta-potential (ζ) particle in weak fields is investigated. In this large-ζ regime, Debye-layer kinetics determines O(1) perturbations to the electric- and concentration fields in the surrounding electroneutral solution. Taking these effects into account, the expressions of the slip-flow coefficient and the effective surface boundary-conditions for the electric- and concentration fields are derived. For binary and symmetric electrolyte where only one ion species carries the current in the electroneutral domain, the far-field salt gradient as related to the electric field is determined. The electrodiffusiophoretic mobility is obtained for three particle geometries: sphere, cylinder and spheroid arbitrarily oriented with respect to the externally applied field. Strong departure from Smoluchowskian behavior is found. If co-ion is the current carrier, the mobility is independent of ζ, regardless of the body shape. Also, the hydrodynamic flow-field is irrotational. If counter-ion is the current carrier, the problem formulated in terms of a properly-defined scalar field (Ω), which embodies both the electric potential (Ψ) and the salt concentration, becomes formally identical to the one addressed in our previous work, concerning the small-ζ regime, with negligible salt gradients. Then, all the results obtained in that study are extended and applied even to the large-ζ regime considered here, provided the new expressions now derived for the surface boundary conditions and the slip-flow coefficient are employed and Ω is used in place of Ψ. The present results are discussed also in comparison with the classical studies of Dukhin et al and O’Brien et al concerning electrophoresis of highly charged particles with no salt gradient at infinity, and with recent studies of electrodiffusiophoresis, which, however, neglected the fields perturbations caused by Debye-layer kinetics. It is found that the effects addressed and incorporated in the present study determine remarkably different mobility-versus-ζ behaviour as compared to those previous theories.
Barany, Sandor
2015-08-01
A review on the effects of adsorbed non-ionic polymers and polyelectrolytes on the electrophoresis of dispersed particles is given. The variety of changes in the electrical double layer (EDL) structure and, in particular, electrokinetic potential in weak electric fields as a result of polymer adsorption is discussed. Examples on the dependence of zeta potential of particles on the adsorbed amount of polymers are described. An analysis of the influence of various complicating factors, namely polarization of the EDL, curvature of the surface and the presence of electrolytes, on the calculation of polymer layer thickness from electrophoretic data has been performed. Results of electrophoretic measurements in suspensions of non-conventional particles (TiC, SiC and Si3N4) having adsorbed polyethylene oxide are presented. Regularities of the effect of anionic and cationic polyelectrolytes (PEs) and their binary mixtures on the electrokinetic potential of dispersed particles (polystyrene, silica, bentonite and kaolin) as a function of the polymer dose, pH, charge density (CD) of the polyelectrolyte, as well as the mixture composition and the sequence of component addition are described. It has been shown that addition of increasing amount of anionic PEs increases the absolute value of the negative zeta potential of particles, while adsorption of cationic PEs results in a significant decrease in the negative ζ-potential and overcharging the particle surface; changes in the ζ-potential are more pronounced for samples with higher CD. In mixtures of cationic and anionic PEs, in a wide range of their composition, the ζ-potential of negatively charged particles is determined by the adsorbed amount of the anionic polymer independently of the CD of polyelectrolyte and the sequence of the mixture component addition. The role of coulombic and non-coulombic forces in the mechanism of polyelectrolyte adsorption and structure of adsorbed layers formed is discussed. The results of comparative investigations on the effect of adsorbed polymers on the electrophoresis of dispersed particles in weak and strong electric fields are presented. It is shown that adsorption of non-ionic polymers only slightly (by about 20-50%) decreases the electrophoretic velocity (V(ef)) of polystyrene, graphite and aluminium-oxide particles in strong fields (100-400 V/cm). This is in contrast to the electrophoresis in weak fields (5-20 V/cm) in which adsorption of these polymers gives a drop in V(ef) by an order of magnitude or even more. In line with our theoretical predictions, it means that the non-linear ("cubic") electrophoresis, that arises in strong electric fields, is independent of the position of the shear plane, i.e. the zeta potential value. It is determined mainly by the surface conductivity of particles, i.e. by the Dukhin number that characterizes the polarization of the electric double layer. PMID:25456453
Black holes and fundamental fields: Hair, kicks, and a gravitational Magnus effect
NASA Astrophysics Data System (ADS)
Okawa, Hirotada; Cardoso, Vitor
2014-11-01
Scalar fields pervade theoretical physics and are a fundamental ingredient to solve the dark matter problem, to realize the Peccei-Quinn mechanism in QCD or the string-axiverse scenario. They are also a useful proxy for more complex matter interactions, such as accretion disks or matter in extreme conditions. Here, we study the collision between scalar "clouds" and rotating black holes. For the first time we are able to compare analytic estimates and strong field, nonlinear numerical calculations for this problem. As the black hole pierces through the cloud it accretes according to the Bondi-Hoyle prediction, but is deflected through a purely kinematic gravitational "anti-Magnus" effect, which we predict to be present also during the interaction of black holes with accretion disks. After the interaction is over, we find large recoil velocities in the transverse direction. The end-state of the process belongs to the vacuum Kerr family if the scalar is massless, but can be a hairy black hole when the scalar is massive.
Wide-field X-ray afterglow searches for gravitational wave events
NASA Astrophysics Data System (ADS)
Shawhan, Peter; Tervala, Justin
2015-04-01
The Advanced LIGO and Virgo gravitational wave (GW) detectors are on track to begin collecting science data soon and to reach full sensitivity by 2019. Low-latency analysis of the GW data will provide triggers for astronomers to seek electromagnetic transient counterparts. Many instruments will contribute to that effort, but instruments with very large fields of view will have a natural advantage for following up the typically large GW error regions. In particular, we consider ISS-Lobster, a proposed NASA mission to be deployed on the International Space Station, which features a focusing imager for soft X-rays with a field of view of over 800 square degrees. Our study using binary neutron star coalescence simulations from Singer et al. shows that a single ISS-Lobster pointing will, on average, cover over 95% of a LIGO-Virgo 3-detector sky map, while even a 2-detector sky map can be over 85% covered (on average) by a sequence of four pointings. We gratefully acknowledge the support of NSF Grants PHY-1068549 and PHY-1404121.
NASA Technical Reports Server (NTRS)
Chao, Benjamin F.; Chen, J. L.; Johnson, T.; Au, A. Y.
1998-01-01
Hydrological mass transport in the geophysical fluids of the atmosphere-hydrosphere-solid Earth surface system can excite Earth's rotational variations in both length-of-day and polar motion. These effects can be computed in terms of the hydrological angular momentum by proper integration of global meteorological data. We do so using the 40-year NCEP data and the 18-year NASA GEOS-1 data, where the precipitation and evapotranspiration budgets are computed via the water mass balance of the atmosphere based on Oki et al.'s (1995) algorithm. This hydrological mass redistribution will also cause geocenter motion and changes in Earth's gravitational field, which are similarly computed using the same data sets. Corresponding geodynamic effects due to the oceanic mass transports (i.e. oceanic angular momentum and ocean-induced geocenter/gravity changes) have also been computed in a similar manner. We here compare two independent sets of the result from: (1) non-steric ocean surface topography observations based on Topex/Poseidon, and (2) the model output of the mass field by the Parallel Ocean Climate Model. Finally, the hydrological and the oceanic time series are combined in an effort to better explain the observed non-atmospheric effects. The latter are obtained by subtracting the atmospheric angular momentum from Earth rotation observations, and the atmosphere- induced geocenter/gravity effects from corresponding geodetic observations, both using the above-mentioned atmospheric data sets.
Advances in Magnetic and Gravitational Potential Field Data in the Arctic
NASA Astrophysics Data System (ADS)
Olesen, Odleiv; Saltus, Rick
2010-10-01
Integration of Magnetics and Gravity in Northern Exploration (iMAGINE); Troms, Norway, 1-2 June 2010; Magnetic and gravitational potential field data are crucial components of regional tectonic framework studies and resource exploration in the Arctic. Special data acquisition difficulties at high latitudes include extreme weather conditions, ice-covered waters, and magnetic disturbances from the aurora borealis. Improved techniques in sub-ice, sub-salt, and sub-basalt exploration are required. The Integration of Magnetics and Gravity in Northern Exploration (iMAGINE) meeting (part of Arctic Days 2010) featured discussion of the most recent advances in potential field methods with particular attention to Arctic challenges. Presentations concentrated on regional interpretations in the Arctic Ocean, Barents Sea, Siberia, and northeastern Atlantic Ocean. Talks also touched on regional petroleum exploration and on the interpretation of weathered bedrock in Norway. In addition, a group of talks dealt with geomagnetic disturbances and their effect on magnetic data collection and in magnetic orientation for directional drilling.
Doppler shifting of a distant light source in a Schwarzschild gravitational field
Kislik, M.D.
1985-10-01
For three limiting cases of relative placement of a light source, a gravitational lens, and the observer, equations are established that describe the lens chromatic properties. The results have direct applications to experimental tests of general relativity and to the discovery of dark gravitating bodies.
A search for weak or complex magnetic fields in the B3V star ι Herculis
NASA Astrophysics Data System (ADS)
Wade, G. A.; Folsom, C. P.; Petit, P.; Petit, V.; Lignières, F.; Aurière, M.; Böhm, T.
2014-11-01
We obtained 128 high signal-to-noise ratio Stokes V spectra of the B3V star ι Her on five consecutive nights in 2012 with the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope, with the aim of searching for the presence of weak and/or complex magnetic fields. Least-squares deconvolution (LSD) mean profiles were computed from individual spectra, averaged over individual nights and over the entire run. No Zeeman signatures are detected in any of the profiles. The longitudinal magnetic field in the grand average profile was measured to be -0.24 ± 0.32 G, as compared to -0.22 ± 0.32 G in the null profile. Our observations therefore provide no evidence for the presence of Zeeman signatures analogous to those observed in the A0V star Vega by Lignières et al. We interpret these observations in three ways. First, we compare the LSD profiles with synthetic Stokes V profiles corresponding to organized (dipolar) magnetic fields, for which we find an upper limit of about 8 G on the polar strength of any surface dipole present. Secondly, we compare the grand average profile with calculations corresponding to the random magnetic spot topologies of Kochukhov & Sudnik, inferring that spots, if present, of 2° radius with strengths of 2-4 G and a filling factor of 50 per cent should have been detected in our data. Finally, we compare the observations with synthetic V profiles corresponding to the surface magnetic maps of Vega (Petit et al.) computed for the spectral characteristics of ι Her. We conclude that while it is unlikely we would have detected a magnetic field identical to Vega's, we would have likely detected one with a peak strength of about 30 G, i.e. approximately four times as strong as that of Vega.
Weak nonlinear analysis of magneto-convection under magnetic field modulation
NASA Astrophysics Data System (ADS)
Bhadauria, B. S.; Kiran, Palle
2014-09-01
An analytic study of heat transport in an electrically conducting fluid layer is performed under a non-uniform time-dependent magnetic field. The applied vertical magnetic field consists of two parts: a constant part and a time-dependent periodic part, which varies sinusoidally with time. A weakly nonlinear theory has been considered to investigate heat transfer in the fluid layer. The heat transfer coefficient is obtained by deriving the non-autonomous Ginzburg-Landau equation for an amplitude of convection. This amplitude of convection is derived by using NDSolve Mathematica 8, and the results are verified using Runge-Kutta-Fehlberg method. The Nusselt number is obtained in terms of various system parameters and the effect of each parameter on heat transport is reported in detail. The effect of magnetic Prandtl number Pm, amplitude of modulation ? is to enhance the heat transfer. The Chandrasekhar number Q, modulation frequency ? is to stabilize the system. Further, it is found that magnetic modulation can be used effectively in either enhancing the heat transfer or diminishing it.
Charge Density Wave in a Two-Dimensional Electron Liquid in a Weak Magnetic Field
NASA Astrophysics Data System (ADS)
Fogler, M. M.; Koulakov, A. A.; Shklovskii, B. I.
1996-03-01
We study the ground state of a clean two-dimensional electron liquid in a weak magnetic field where N >> 1 lower Landau levels are completely filled and the upper level is partially filled. It is shown that the electrons at the upper Landau level form domains with filling factor equal to one and zero. The domains alternate with a spatial period of the order of the cyclotron radius, which is much larger than the interparticle distance at the upper Landau level. At half-fillings the domains have the shape of stripes; away from the half-fillings, they turn into large ``bubbles''. We discuss two experimentally relevant consequences of the proposed picture. One is the one-particle density of states, which can be probed by tunneling experiments. It is shown to have a pseudogap linear in the magnetic field in the limit of large N. The other is the narrowing of the quantum Hall conductivity peaks in high-mobility samples with decreasing temperature. It can be explained by the pinning of the CDW.
Plasma waves around separatrix in collisionless magnetic reconnection with weak guide field
NASA Astrophysics Data System (ADS)
Chen, Yangao; Fujimoto, Keizo; Xiao, Chijie; Ji, Hantao
2015-08-01
Electrostatic and electromagnetic waves excited by electron beam around the separatrix region are analyzed in detail during the collisionless magnetic reconnection with a weak guide field by using 2-D particle-in-cell simulation with the adaptive mesh refinement. Broadband electrostatic waves are excited both in the inflow and outflow regions around the separatrices due to the electron bump-on-tail, two-stream, and Buneman instabilities. In contrast, the quasi-monochromatic electromagnetic waves are excited only in the inflow side of the separatrices due to a beam-driven whistler instability. The localization of the whistler waves is attributed to the nonuniformity of the out-of-plane magnetic field By. The whistler instability is suppressed in the outflow side where By is too small for the oblique propagation. The electrostatic waves with distinct speeds can explain the in situ spacecraft observations. From the causality point of view, the waves are generated as the consequence of the electron bulk acceleration to thermalize the particles through wave-particle interactions. These simulation results provide guidance to analyze high-resolution wave observations during reconnection in the ongoing and upcoming satellite missions, as well as in dedicated laboratory experiments.
Morozov, Darya; Bar, Leah; Sochen, Nir; Cohen, Yoram
2013-04-01
NMR diffusion-diffraction patterns observed in compartments in which restricted diffusion occurs are a useful tool for direct extraction of compartment sizes. Such diffusion-diffraction patterns may be observed when the signal intensity E(q,?) is plotted against the wave-vector q (when q=(2?)(-1)??G). However, the smaller the compartment sizes are, the higher are the q-values needed to observe such diffractions. Moreover, these q-values should be achieved using short gradient pulses requiring extremely strong gradient systems. The angular double-pulsed-field gradient (d-PFG) NMR methodology has been proposed as a tool to extract compartment sizes using relatively low q-values. In this study, we have used single-PFG (s-PFG) NMR and angular d-PFG NMR to characterize the size of microcapillaries of about 21?m in diameter. We found that these microcapillaries are characterized by relatively strong background gradients that completely masked the effects of the microscopic anisotropy (?A) of the sample, resulting in a completely unexpected E(?) profile in the angular d-PFG NMR experiments. We also show that bipolar angular d-PFG NMR experiments can largely suppress the effect of these background gradients resulting in the expected E(?) profile from which the compartment dimensions could be obtained with relatively weak gradient pulses. These results demonstrate that the above methodology provides a quick, reliable, non-invasive means for estimating small pore sizes with relatively weak gradients in the presence of large magnetic susceptibility. PMID:23102951
Bhardwaj, S; Mkhitaryan, V V; Gruzberg, I A
2014-06-01
We consider a recently proposed network model of the integer quantum Hall (IQH) effect in a weak magnetic field. Using a supersymmetry approach, we reformulate the network model in terms of a superspin ladder. A subsequent analysis of the superspin ladder and the corresponding supersymmetric nonlinear sigma model allows us to establish the phase diagram of the network model, and the form of the critical line of the weak-field IQH transition. Our results confirm the universality of the IQH transition, which is described by the same sigma model in strong and weak magnetic fields. We apply the suspersymmetry method to several related network models that were introduced in the literature to describe the quantum Hall effect in graphene, the spin-degenerate Landau levels, and localization of electrons in a random magnetic field.
Adair, R K
1994-01-01
Previous calculations of limits imposed by thermal noise on the effects of weak 60-Hz magnetic fields on biological magnetite are generalized and extended to consider multiple signals, the possibility of anomalously large magnetosome structures, and the possibility of anomalously small cytoplasm viscosities. The results indicate that the energies transmitted to the magnetite elements by fields less than 5 microT, characteristic of the electric power distribution system, will be much less than thermal noise energies. Hence, the effects of such weak fields will be masked by that noise and cannot be expected to affect biology or, therefore, the health of populations. PMID:8159681
Gravitation as a Composite Particle Effect in a Unified Spinor-Isospinor Preon Field Model I
NASA Astrophysics Data System (ADS)
Stumpf, H.
1988-04-01
The model is defined by a selfregularizing nonlinear preon field equation, and all observable (elementary and non-elementary) particles are assumed to be bound (quantum) states of fermionic preon fields. Electroweak gauge bosons, leptons, quarks, gluons as preon composites and their effective dynamics etc. were studied in preceding papers. In this paper gravitons are introduced as four-preon composites and their effective interactions are discussed. This discussion is performed by the application of functional quantum theory to the model under consideration and subsequent evaluation of a weak mapping procedure, both introduced in preceding papers. In the low energy limit it is demonstrated that the effective graviton dynamics lead to the complete homogeneous Einstein equations in tetrad formulation.
Imshennik, V. S.
2010-04-15
The standard problem of a radial motion of test particles in the stationary gravitational field of a spherically symmetric celestial body is solved and is used to determine the time features of this motion. The problem is solved for the equations of motion of general relativity (GR), and the time features are obtained in the post-Newtonian approximation, with linear GR corrections proportional to r{sub g}/r and {beta}{sup 2} (in the solution being considered, they are of the same order of smallness) being taken rigorously into account. Total times obtained by integrating the time differentials along the trajectories of motion are considered as the time features in question. It is shown that, for any parameters of the motion, the proper time (which corresponds to watches comoving with a test particle) exceeds the time of watches at rest (watches at the surface of the celestial body being considered). The mass and the radius of the celestial body, as well as the initial velocity of the test particle, serve as arbitrary parameters of the motion. The time difference indicated above implies a leading role of the gravitational redshift, which decreases somewhat because of the opposite effect of the Doppler shift. The results are estimated quantitatively for the important (from the experimental point of view) case of vertical flights of rockets starting from the Earth's surface. In this case, the GR corrections, albeit being extremely small (a few microseconds for several hours of the flight), aremeasurable with atomic (quantum) watches.
Motion of the Three Viscoelastic Planets in Gravitational Field of the Mutual Attraction
NASA Astrophysics Data System (ADS)
Vilke, V. G.; Shatina, A. V.; Shatina, L. S.
2009-04-01
The translational-rotational motion of the three viscoelastic planets in gravitational field of the mutual attraction is studied. We model the planets by the homogeneous isotropic viscoelastic bodies, which in the natural non-deformed state occupy the spherical regions in the three-dimensional Eucliden space. The problem is being solved within the framework of the linear model of the theory of elasticity. The functional of the inner dissipative forces corresponds to the Kelvin-Voigt model. Each of the planets deforms due to its rotation around its mass center and its movement relative to the system's mass centre: the planet is being compressed endwise its axis of rotation and tidal humps appear aloud the lines binding the planet's mass centers. The changes in the planet's shape in their turn alter its translational-rotational movement. The system of equations of motion of the considered mechanical system is deduced from the D'Alembert-Lagrange variational principle and represents a complicated integro-differential system of equations in the banach space. The method of separation of motions is applied to the obtained system of equations and an approximate system of ordinary differential equations is deduced witch describes the translational-rotational motion of the planets, taking into account the perturbations caused by elasticity and dissipation. Unperturbed system of equations corresponds to the problem of the motion of the three rigid spheres interacting under the law of universal gravitation. Boundary problem of finding the vector of elastic displacement, describing forced oscillation of the planet under the influence of external forces and inertial forces of the translational motion is solved for each of the planets. Due to the planets' sphericity in their natural non-deformed state, the solutions of the boundary problems can be represented analytically as a sum of finite number of spherical functions. The solutions of the boundary problems are used to form the perturbing additives to the equations of motion. As a result of this procedure we get a vectorial perturbated system of ordinary differential equations on the radius of the planets' mass centers and the vectors of the planets' angular momentums. The stationary motion of the system of the three viscoelastic planets when the dissipative functional is equal to zero (the analogue of the triangular libration points in the classical three-body problem) is founded. According to this movement, the spheres move as one solid body with constant angular velocity, and the spheres' mass centers lie on a plan, orthogonal to the vector of angular velocity. If in unperturbed problem the mass centers of the planets form an equilateral triangle, the presence of perturbations leads to the emergence of the additives to stationary values of the triangle's side lengths, as the result of which the triangular in general case becomes inequilaterally. Due to the presence of dissipation of the system, the stationary triangular configuration is unsteady. This work is an extension of the series of articles [1-4] devoted to the problem of the viscoelastic spheres motion in gravitational field, the model problem for investigating the tidal evolution of the planets motion. The work is supported by RFBR, project 08-02-00367. References 1) Vilke V.G. The Motion of a Spherical Viscoelastic Body in the Central Newtonian Field of Forces // Appl. Math. Mech., 1980, Vol. 44, No 3, pp. 395-402. 2) Vilke V.G. Analytical and qualitative methods in the dynamics of the systems with infinite number of degrees of freedom. Moscow: Moscow State University, 1986. 3) Shatina A.V. Evolution of the Motion of a Viscoelastic Sphere in a Central Newtonian Field // Cosmic Research, 2001, Vol. 39, No 3, pp. 282-294. 4) Vilke V.G., Shatina A.V. Translational-Rotational Motion of a Viscoelastic Sphere in Gravitational Field of an Attracting Center and a Satellite // Cosmic Research, 2004, Vol. 42, No 1, pp. 95-106.
NASA Technical Reports Server (NTRS)
Walker, M.; Will, C. M.
1980-01-01
An argument is presented to determine the accuracy with which a solution of Einstein's field equations of gravitation must be approximated in order to describe the dominant effects of gravitational radiation emission from weak-field systems. Several previous calculations are compared in the light of this argument, and some apparent discrepancies among them are resolved. The majority of these calculations support the 'quadrupole formulae' for gravitational radiation energy loss and radiation reaction.
Frontier Fields: Subaru Weak-Lensing Analysis of the Merging Galaxy Cluster A2744
NASA Astrophysics Data System (ADS)
Medezinski, Elinor; Umetsu, Keiichi; Okabe, Nobuhiro; Nonino, Mario; Molnar, Sandor; Massey, Richard; Dupke, Renato; Merten, Julian
2016-01-01
We present a weak-lensing analysis of the merging Frontier Fields (FF) cluster Abell 2744 using new Subaru/Suprime-Cam imaging. The wide-field lensing mass distribution reveals this cluster is comprised of four distinct substructures. Simultaneously modeling the two-dimensional reduced shear field using a combination of a Navarro-Frenk-White (NFW) model for the main core and truncated NFW models for the subhalos, we determine their masses and locations. The total mass of the system is constrained as {M}200{{c}}=(2.06+/- 0.42) {10}15 {M}? . The most massive clump is the southern component with {M}200{{c}}=(7.7+/- 3.4) {10}14 {M}? , followed by the western substructure ({M}200{{c}}=(4.5+/- 2.0) {10}14 {M}? ) and two smaller substructures to the northeast ({M}200{{c}}=(2.8+/- 1.6) {10}14 {M}? ) and northwest ({M}200{{c}}=(1.9+/- 1.2) {10}14 {M}? ). The presence of the four substructures supports the picture of multiple mergers. Using a composite of hydrodynamical binary simulations we explain this complicated system without the need for a slingshot effect to produce the northwest X-ray interloper, as previously proposed. The locations of the substructures appear to be offset from both the gas ({87}-28+34 arcsec, 90% CL) and the galaxies ({72}-53+34 arcsec, 90% CL) in the case of the northwestern and western subhalos. To confirm or refute these findings, high resolution space-based observations extending beyond the current FF limited coverage to the west and northwestern area are essential. Based in part on data collected at the Subaru Telescope, which is operated by the National Astronomical Society of Japan.
Field equation of the correlation function of mass-density fluctuations for self-gravitating systems
NASA Astrophysics Data System (ADS)
Zhang, Yang; Chen, Qing
2015-09-01
We study the mass-density distribution of Newtonian self-gravitating systems. Modeling the system as a fluid in hydrostatical equilibrium, we obtain from first principles the field equation and its solution of the correlation function ?(r) of the mass-density fluctuation itself. We apply this to studies of the large-scale structure of the Universe within a small redshift range. The equation shows that ?(r) depends on the point mass m and the Jeans wavelength scale ?0, which are different for galaxies and clusters. It explains several long-standing prominent features of the observed clustering: that the profile of ?cc(r) of clusters is similar to ?gg(r) of galaxies, but with a higher amplitude and a longer correlation length, and that the correlation length increases with the mean separation between clusters as a universal scaling r0 ? 0.4d. Our solution ?(r) also shows that the observed power-law correlation function of galaxies ?gg(r) ? (r0/r)1.7 is only valid in a range 1
The Distribution of Galaxies’ Gravitational Field Stemming from Their Tidal Interaction
NASA Astrophysics Data System (ADS)
Stephanovich, Vladimir; Godłowski, Włodzimierz
2015-09-01
We calculate the distribution function of astronomical objects’ (like galaxies and/or smooth halos of different kinds) gravitational fields due to their tidal interaction. For that we apply the statistical method of Chandrasekhar, used originally to calculate the famous Holtzmark distribution. We show that in our approach the distribution function is never Gaussian, its form being dictated by the potential of interaction between objects. This calculation permits us to perform a theoretical analysis of the relation between angular momentum and mass (richness) of the galaxy clusters. To do so, we follow the ideas of Catelan & Theuns and Heavens & Peacock. The main difference is that here we reduce the problem to a discrete many-body case, where all physical properties of the system are determined by the interaction potential V({{\\boldsymbol{r}}}{ij}). The essence of reduction is that we use the multipole (up to quadrupole here) expansion of Newtonian potential so that all hydrodynamic, “extended” characteristics of an object, such as its density mass, are “integrated out,” leaving its “point-like” characteristics, such as mass and quadrupole moment. In that sense we do not distinguish between galaxies and smooth components such as halos. We compare our theoretical results with observational data.
Satellite motion in the gravitational field of a viscoelastic planet with a core
NASA Astrophysics Data System (ADS)
Shatina, A. V.; Sherstnyov, E. V.
2015-03-01
The motion of a "planet-satellite" system in a gravitational field of mutual attraction forces is investigated. The planet is modeled by a body consisting of a solid core and a viscoelastic shell made of Kelvin-Voigt material. The satellite is modeled by a material point. A system of integro-differential equations of motion of a mechanical system is derived from the variational d'Alembert-Lagrange principle within the linear model of the theory of elasticity. Using the asymptotic method of separation of motions, an approximate system of equations of motion is constructed in vector form. This system describes the dynamics of a system with allowance for disturbances caused by elasticity and dissipation. The solution of the quasistatic problem of elasticity theory for the deformable shell of a planet is obtained in the explicit form. An averaged system of differential equations describing the evolution of satellite's orbital parameters is derived. For partial cases phase trajectories are constructed, stationary solutions are found, and their stability is investigated. As examples, some planets of the Solar system and their satellites are considered. This problem is a model for studying the tidal theory of planetary motion.
Improved dynamics and gravitational collapse of tachyon field coupled with a barotropic fluid
NASA Astrophysics Data System (ADS)
Marto, João; Tavakoli, Yaser; Moniz, Paulo Vargas
2015-01-01
We consider a spherically symmetric gravitational collapse of a tachyon field with an inverse square potential, which is coupled with a barotropic fluid. By employing an holonomy correction imported from loop quantum cosmology (LQC), we analyze the dynamics of the collapse within a semiclassical description. Using a dynamical system approach, we find that the stable fixed points given by the standard general relativistic setting turn into saddle points in the present context. This provides a new dynamics in contrast to the black hole and naked singularities solutions appearing in the classical model. Our results suggest that classical singularities can be avoided by quantum gravity effects and are replaced by a bounce. By a thorough numerical studies we show that, depending on the barotropic parameter γ, there exists a class of solutions corresponding to either a fluid or a tachyon dominated regimes. Furthermore, for the case γ 1, we find an interesting tracking behavior between the tachyon and the fluid leading to a dust-like collapse. In addition, we show that, there exists a threshold scale which determines when an outward energy flux emerges, as a nonsingular black hole is forming, at the corresponding collapse final stages.
NASA Technical Reports Server (NTRS)
Press, W. H.; Thorne, K. S.
1972-01-01
Discussion of the nature and origin of gravitational waves in the light of current theories and data, stating the concept of gravitational waves as a field of relative gravitational forces that propagate with the speed of light. The topics include the generation of gravitational waves, their astrophysical sources, pulsars, supernovae, the birth of neutron stars, explosions in quasars and nuclei of galaxies, and atomic and molecular processes. Also considered are gravitational wave reception techniques, covering free-mass antennas, nonmechanical displacement sensors, almost free antennas, mechanical displacement sensors, acoustic systems, resonant antennas, Weber's detectors, and natural antennas. Future developments in gravitational wave astronomy are considered.
Approximation methods in gravitational-radiation theory
NASA Technical Reports Server (NTRS)
Will, C. M.
1986-01-01
The observation of gravitational-radiation damping in the binary pulsar PSR 1913 + 16 and the ongoing experimental search for gravitational waves of extraterrestrial origin have made the theory of gravitational radiation an active branch of classical general relativity. In calculations of gravitational radiation, approximation methods play a crucial role. Recent developments are summarized in two areas in which approximations are important: (a) the quadrupole approxiamtion, which determines the energy flux and the radiation reaction forces in weak-field, slow-motion, source-within-the-near-zone systems such as the binary pulsar; and (b) the normal modes of oscillation of black holes, where the Wentzel-Kramers-Brillouin approximation gives accurate estimates of the complex frequencies of the modes.
Multiparameter investigation of gravitational slip
Daniel, Scott F.; Caldwell, Robert R.; Cooray, Asantha; Serra, Paolo; Melchiorri, Alessandro
2009-07-15
A detailed analysis of gravitational slip, a new post-general relativity cosmological parameter characterizing the degree of departure of the laws of gravitation from general relativity on cosmological scales, is presented. This phenomenological approach assumes that cosmic acceleration is due to new gravitational effects; the amount of spacetime curvature produced per unit mass is changed in such a way that a universe containing only matter and radiation begins to accelerate as if under the influence of a cosmological constant. Changes in the law of gravitation are further manifest in the behavior of the inhomogeneous gravitational field, as reflected in the cosmic microwave background, weak lensing, and evolution of large-scale structure. The new parameter {pi}{sub 0} is naively expected to be of order unity. However, a multiparameter analysis, allowing for variation of all of the standard cosmological parameters, finds that {pi}{sub 0}=0.09{sub -0.59}{sup +0.74}(2{sigma}), where {pi}{sub 0}=0 corresponds to a cosmological constant plus cold dark matter universe under general relativity. Future probes of the cosmic microwave background (Planck) and large-scale structure (Euclid) may improve the limits by a factor of 4.
Chemical reactions induced by oscillating external fields in weak thermal environments
NASA Astrophysics Data System (ADS)
Craven, Galen T.; Bartsch, Thomas; Hernandez, Rigoberto
2015-02-01
Chemical reaction rates must increasingly be determined in systems that evolve under the control of external stimuli. In these systems, when a reactant population is induced to cross an energy barrier through forcing from a temporally varying external field, the transition state that the reaction must pass through during the transformation from reactant to product is no longer a fixed geometric structure, but is instead time-dependent. For a periodically forced model reaction, we develop a recrossing-free dividing surface that is attached to a transition state trajectory [T. Bartsch, R. Hernandez, and T. Uzer, Phys. Rev. Lett. 95, 058301 (2005)]. We have previously shown that for single-mode sinusoidal driving, the stability of the time-varying transition state directly determines the reaction rate [G. T. Craven, T. Bartsch, and R. Hernandez, J. Chem. Phys. 141, 041106 (2014)]. Here, we extend our previous work to the case of multi-mode driving waveforms. Excellent agreement is observed between the rates predicted by stability analysis and rates obtained through numerical calculation of the reactive flux. We also show that the optimal dividing surface and the resulting reaction rate for a reactive system driven by weak thermal noise can be approximated well using the transition state geometry of the underlying deterministic system. This agreement persists as long as the thermal driving strength is less than the order of that of the periodic driving. The power of this result is its simplicity. The surprising accuracy of the time-dependent noise-free geometry for obtaining transition state theory rates in chemical reactions driven by periodic fields reveals the dynamics without requiring the cost of brute-force calculations.
Chemical reactions induced by oscillating external fields in weak thermal environments.
Craven, Galen T; Bartsch, Thomas; Hernandez, Rigoberto
2015-02-21
Chemical reaction rates must increasingly be determined in systems that evolve under the control of external stimuli. In these systems, when a reactant population is induced to cross an energy barrier through forcing from a temporally varying external field, the transition state that the reaction must pass through during the transformation from reactant to product is no longer a fixed geometric structure, but is instead time-dependent. For a periodically forced model reaction, we develop a recrossing-free dividing surface that is attached to a transition state trajectory [T. Bartsch, R. Hernandez, and T. Uzer, Phys. Rev. Lett. 95, 058301 (2005)]. We have previously shown that for single-mode sinusoidal driving, the stability of the time-varying transition state directly determines the reaction rate [G. T. Craven, T. Bartsch, and R. Hernandez, J. Chem. Phys. 141, 041106 (2014)]. Here, we extend our previous work to the case of multi-mode driving waveforms. Excellent agreement is observed between the rates predicted by stability analysis and rates obtained through numerical calculation of the reactive flux. We also show that the optimal dividing surface and the resulting reaction rate for a reactive system driven by weak thermal noise can be approximated well using the transition state geometry of the underlying deterministic system. This agreement persists as long as the thermal driving strength is less than the order of that of the periodic driving. The power of this result is its simplicity. The surprising accuracy of the time-dependent noise-free geometry for obtaining transition state theory rates in chemical reactions driven by periodic fields reveals the dynamics without requiring the cost of brute-force calculations. PMID:25702003
ON THE GRAVITATIONAL FIELDS OF MACLAURIN SPHEROID MODELS OF ROTATING FLUID PLANETS
Kong, Dali; Zhang, Keke; Schubert, Gerald E-mail: kzhang@ex.ac.uk
2013-02-10
Hubbard recently derived an important iterative equation for calculating the gravitational coefficients of a Maclaurin spheroid that does not require an expansion in a small distortion parameter. We show that this iterative equation, which is based on an incomplete solution of the Poisson equation, diverges when the distortion parameter is not sufficiently small. We derive a new iterative equation that is based on a complete solution of the Poisson equation and, hence, always converges when calculating the gravitational coefficients of a Maclaurin spheroid.
Can Malin's gravitational-field equations be modified to obtain a viable theory of gravity
NASA Technical Reports Server (NTRS)
Smalley, L. L.; Prestage, J.
1976-01-01
Malin's (1975) gravitational theory, which was recently shown by Lindblom and Nester (1975) to be incorrect, is modified by means of a recently proposed method for obtaining viable gravitational theories. The resulting self-consistent theory, which is in effect a Rastall-type modification of the Einstein theory, exhibits nonconservation of momentum, yet agrees with all experimental limits known to date within the post-Newtonian approximation framework.
Gravitational lensing in quasar samples
NASA Astrophysics Data System (ADS)
Claeskens, Jean-François; Surdej, Jean
The first cosmic mirage was discovered approximately 20 years ago as the double optical counterpart of a radio source. This phenomenon had been predicted some 70 years earlier as a consequence of General Relativity. We present here a summary of what we have learnt since. The applications are so numerous that we had to concentrate on a few selected aspects of this new field of research. This review is focused on strong gravitational lensing, i.e. the formation of multiple images, in QSO samples. It is intended to give the reader an up-to-date status of the observations and to present an overview of its most interesting potential applications in cosmology and astrophysics, as well as numerous important results achieved so far. The first section follows an intuitive approach to the basics of gravitational lensing and is developed in view of our interest in multiply imaged quasars. The astrophysical and cosmological applications of gravitational lensing are outlined in Sect. 2 and the most important results are presented in Sect. 5. Sections 3 and 4 are devoted to the observations. Finally, conclusions are summarized in the last section. We have tried to avoid duplication with existing (and excellent) introductions to the field of gravitational lensing. For this reason, we did not concentrate on the individual properties of specific lens models, as these are already well presented in Narayan and Bartelmann (1996) and on a more intuitive ground in Refsdal and Surdej (1994). Wambsganss (1998) proposes a broad view on gravitational lensing in astronomy; the reviews by Fort and Mellier (1994) and Hattori et al. (1999) deal with lensing by galaxy clusters; microlensing in the Galaxy and the local group is reviewed by Paczynski (1996) and a general panorama on weak lensing is given by Bartelmann and Schneider (1999) and Mellier (1999). The monograph on the theory of gravitational lensing by Schneider, Ehlers and Falco (1992) also remains a reference in the field.
NASA Astrophysics Data System (ADS)
Xue, She-Sheng
2015-10-01
We study a quantum field theory for the Einstein-Cartan gravity and the domain of its ultraviolet unstable (stable) fixed point ?c ? 0 (Gc ? GN) of running gravitational constant G, where inflationary (low-redshift) universe can be realized as the basic space-time cutoff approaching to the Planck length apl. Because the fundamental operators of quantum gravitational field theory are dimension-2 area operators, the cosmological constant is inversely proportional to the squared correlation length ? ? ?-2. The correlation length ? characterizes an infrared size of a causally correlate patch of the universe. The quantitative description of low-redshift universe in the scaling-invariant region of fixed point Gc is given, and its deviation from the ?CDM can be examined by recent cosmological observations, such as supernova Type Ia.
Statistics of Gravitational Lensing by a Galaxy in Cluster or in Field
NASA Astrophysics Data System (ADS)
Yoon, So-Yoon; Park, Myeong-Gu
1996-10-01
To examine the effect of neighboring galaxies on the gravitational lensing statistics, we performed numerical simulations of lensing by many galaxies. The models consist of a galaxy in the rich cluster like Coma, or a galaxy surrounded by field galaxies in Omega_0=1 universe with Omega_gal=0.1, Omega_gal=0.3 or Omega_gal=1.0, where Omega_gal is the total mass in galaxies. Field galaxies either have the same mass or follow Schechter luminosity function and luminosity-velocity relation. Each lensing galaxy is assumed to be singular isothermal sphere (SIS) with finite cutoff radius. In most simulations, the lensing is mainly due to the single galaxy. But in Omega_gal=0.3 universe, one out of five simulations have `collective lensing' event in which more than two galaxies collectively produce multiple images. These cases cannot be incorporated into the simple `standard' lensing statistics calculations. In cases where `collective lensing' does not occur, distribution of image separation changes from delta function to bimodal distribution due to shear induced by the surrounding galaxies. The amount of spread in the distribution is from a few % up to about 50% of the mean image separation in case when the galaxy is in the Coma-like cluster or when the galaxy is in the field with Omega_gal=0.1 or Omega_gal=0.3. The mean of the image separation changes less than 5% compared with a single lens case. Cross section for multiple image lensing turns out to be relatively insensitive to the presence of the neighboring galaxies, changing less than 5% for Coma-like cluster and Omega_gal=0.1, 0.3 universe cases. So we conclude that Coma-like cluster or field galaxies whose total mass density Omega_gal < 0.3 do not significantly affect the probability of multiple image lensing if we exclude the `collective lensing' cases. However, the distribution of the image separations can be significantly affected especially if the `collective lensing' cases are included. Therefore, the effects of surrounding galaxies may not be negligible when statistics of lensing is used to deduce the cosmological informations.
Four-hair relations for differentially rotating neutron stars in the weak-field limit
NASA Astrophysics Data System (ADS)
Bretz, Joseph; Yagi, Kent; Yunes, Nicols
2015-10-01
The opportunity to study physics at supra-nuclear densities through x-ray observations of neutron stars has led to in-depth investigations of certain approximately universal relations that can remove degeneracies in pulse profile models. One such set of relations determines all of the multipole moments of a neutron star just from the first three (the mass monopole, the current dipole and the mass quadrupole moment) approximately independently of the equation of state. These three-hair relations were found to hold in neutron stars that rotate rigidly, as is the case in old pulsars, but neutron stars can also rotate differentially, as is the case for proto-neutron stars and hypermassive transient remnants of binary mergers. We here extend the three-hair relations to differentially rotating stars for the first time with a generic rotation law using two approximations: a weak-field scheme (an expansion in powers of the neutron star compactness) and a perturbative differential rotation scheme (an expansion about rigid rotation). These approximations allow us to analytically derive approximately universal relations that allow us to determine all of the multipole moments of a (perturbative) differentially rotating star in terms of only the first four moments. These new four-hair relations for differentially rotating neutron stars are found to be approximately independent of the equation of state to a higher degree than the three-hair relations for uniformly rotating stars. Our results can be instrumental in the development of four-hair relations for rapidly differentially rotating stars in full general relativity using numerical simulations.
Weak magnetic field accelerates chromate removal by zero-valent iron.
Feng, Pian; Guan, Xiaohong; Sun, Yuankui; Choi, Wonyong; Qin, Hejie; Wang, Jianmin; Qiao, Junlian; Li, Lina
2015-05-01
Weak magnetic field (WMF) was employed to improve the removal of Cr(VI) by zero-valent iron (ZVI) for the first time. The removal rate of Cr(VI) was elevated by a factor of 1.12-5.89 due to the application of a WMF, and the WMF-induced improvement was more remarkable at higher Cr(VI) concentration and higher pH. Fe2+ was not detected until Cr(VI) was exhausted, and there was a positive correlation between the WMF-induced promotion factor of Cr(VI) removal rate and that of Fe2+ release rate in the absence of Cr(VI) at pH4.0-5.5. These phenomena imply that ZVI corrosion with Fe2+ release was the limiting step in the process of Cr(VI) removal. The superimposed WMF had negligible influence on the apparent activation energy of Cr(VI) removal by ZVI, indicating that WMF accelerated Cr(VI) removal by ZVI but did not change the mechanism. The passive layer formed with WMF was much more porous than without WMF, thereby facilitating mass transport. Therefore, WMF could accelerate ZVI corrosion and alleviate the detrimental effects of the passive layer, resulting in more rapid removal of Cr(VI) by ZVI. Exploiting the magnetic memory of ZVI, a two-stage process consisting of a small reactor with WMF for ZVI magnetization and a large reactor for removing contaminants by magnetized ZVI can be employed as a new method of ZVI-mediated remediation. PMID:25968271
NASA Astrophysics Data System (ADS)
Yang, Ningjiang; Zhang, Changmin
1994-05-01
The physical effect produced by the ultraworking frequency alternating weaking magnetic field (UWFAWM) is demagnetization. We used two methods to study the influence of UWFAWM on the microvasculture of Kunmin mice. Method 1 (in vivo) included 21 mice (the experimental group 11 and the control group 10). Method 2 (in vitro) included 25 mice (the experimental group 13, the control group 12). Each group was put in the coil of the JDM-1 Type Demagnetometer which produced UWFAWM. The coil was electrified for the experimental groups, but not for the control groups, for 20 min, once a day. (1) Method 1. On the 10th day of demagnetization, the surface microvascultural diameters of liver and mesenterium were measured in two groups.1 The results showed that those in the experimental group (25.053.92 ?m and 24.444. 7 ?m, respectively) were markedly greater than those in the control group (10.701.72 ?m and 18.371.93 ?m, respectively. (2) Method 2. On the 40th day of demagnetizing, we killed all mice and immediately preserved the brain, heart, lung, liver, kidney, stomach, intestine, and submandibular gland in 10% formalin, then used continuous paraffin sections of 5 ?m and HE stain, and measured the microvascular diameter of each group.2 The results showed that mean diameters of the organs in the experimental group were also significantly greater than those in the control group (p<0.01). This study confirms that UWFAWM can dilate the microvascultures of various organs, resulting in local aterial hyperemia of the organ, advance local tissue metabolism, and an increase in organic function, thus providing a basis for treating some diseases and for health care.
Activating persulfate by Fe? coupling with weak magnetic field: performance and mechanism.
Xiong, Xinmei; Sun, Bo; Zhang, Jing; Gao, Naiyun; Shen, Jimin; Li, Jialing; Guan, Xiaohong
2014-10-01
Weak magnetic field (WMF) and Fe(0) were proposed to activate PS synergistically (WMF-Fe(0)/PS) to degrade dyes and aromatic contaminants. The removal rates of orange G (OG) by WMF-Fe(0)/PS generally decreased with increasing initial pH (3.0-10.0) and increased with increasing Fe(0) (0.5-3.0 mM) or PS dosages (0.5-3.0 mM). Compared to its counterpart without WMF, the WMF-Fe(0)/PS process could induce a 5.4-28.2 fold enhancement in the removal rate of OG under different conditions. Moreover, the application of WMF significantly enhanced the decolorization rate and the mineralization of OG. The degradation rates of caffeine, 4-nitrophenol, benzotriazole and diuron by Fe(0)/PS were improved by 2.1-11.1 fold due to the superimposed WMF. Compared to many other sulfate radical-based advanced oxidation technologies under similar reaction conditions, WMF-Fe(0)/PS technology could degrade selected organic contaminants with much greater rates. Sulfate radical was identified to be the primary radical species responsible for the OG degradation at pH 7.0 in WMF-Fe(0)/PS process. This study unraveled that the presence of WMF accelerated the corrosion rate of Fe(0) and thus promoted the release of Fe(2+), which induced the increased production of sulfate radicals from PS and promoted the degradation of organic contaminants. Employing WMF to enhance oxidation capacity of Fe(0)/PS is a novel, efficient, promising and environmental-friendly method since it does not need extra energy and costly reagents. PMID:24934323
Collision induced two-pulsed photon echo at the transition 01 in a weak longitudinal magnetic field
NASA Astrophysics Data System (ADS)
Rubtsova, N. N.; Goldort, V. G.; Ishchenko, V. N.; Khvorostov, E. B.; Kochubei, S. A.; Reshetov, V. A.
2015-12-01
It was shown experimentally in ytterbium vapour at the transition (6s2) 1S0 ?ftrightarrow (6s6p) 3P1 (type 0?ftrightarrow 1 ), that the weak longitudinal magnetic field destroys the collision induced two-pulsed photon echo generated in a gas mixture with heavy atomic buffer; in agreement with theoretical prediction.
NASA Astrophysics Data System (ADS)
Solovyov, A. V.; Talipov, D. V.; Borodin, A. S.; Tuzhilkin, D. A.; Baklykova, E. S.; Pobachenko, S. V.
2014-11-01
The results of experimental studies on the cardiovascular system response to the impact of weak low-frequency acoustic fields using ERG characteristics are presented. The slowing of the heart rate under the impact of frequencies 10Hz and 100Hz is shown.
Materniak, S; Patrykiejew, A; Soko?owski, S
2011-06-01
Using Monte Carlo simulation methods in the grand canonical and semigrand canonical ensembles, we study the phase behavior of two-dimensional symmetrical binary mixtures of Lennard-Jones particles subjected to a weakly corrugated external field of a square symmetry. It is shown that the both vapor-liquid condensation and demixing transition in the liquid phase are not appreciably affected by a weakly corrugated external field. On the other hand, even a weakly corrugated external field considerably influences the structure of solid phases and the liquid-solid transition. In particular, the solid phases are found to exhibit uniaxially ordered distorted hexagonal structure. The triple point temperature increases with the corrugation of the external field, while the triple point density becomes lower when the surface corrugation increases. The changes in the location of the triple point are shown to lead to the changes of the phase diagram topology. It is also demonstrated that the solid phase undergoes a demixing transition, which is also very slightly affected by the weakly corrugated external potential. The demixing transition in the solid phase is shown to belong to the universality class of the Ising model. PMID:21663373
NASA Technical Reports Server (NTRS)
Kuznetsova, M. M.; Sibeck, D. G.; Hesse, M.; Wang, Y.; Rastaetter, L.; Toth, G.; Ridley, A.
2009-01-01
We use the global magnetohydrodynamic (MHD) code BATS-R-US to model multipoint observations of Flux Transfer Event (FTE) signatures. Simulations with high spatial and temporal resolution predict that cavities of weak magnetic field strength protruding into the magnetosphere trail FTEs. These predictions are consistent with recently reported multi-point Cluster observations of traveling magnetopause erosion regions (TMERs).
NASA Astrophysics Data System (ADS)
Giulini, Domenico; Groardt, Andr
2012-11-01
In this paper, we show that the Schrdinger-Newton equation for spherically symmetric gravitational fields can be derived in a WKB-like expansion in 1/c from the Einstein-Klein-Gordon and Einstein-Dirac systems.
Motion of massive bodies: Testing the nonsymmetric gravitation theory
Moffat, J.W.; Woolgar, E.
1988-02-15
We derive the equations of motion for massive extended bodies in the first post-Newtonian approximation to the nonsymmetric gravitation theory. The results are applied to the problem of the perihelion shift of Mercury and the periastron shifts of binary stars. We prove the equivalence of gravitational and inertial masses in the theory at the first post-Newtonian level. Hence, the theory predicts no Nordtvedt effect in the Moon's orbit about Earth. Other weak-field tests of the nonsymmetric gravitation theory are discussed.
NASA Astrophysics Data System (ADS)
Cheng, J. L.; Vermeulen, N.; Sipe, J. E.
2015-12-01
Numerically solving the semiconductor Bloch equations within a phenomenological relaxation time approximation, we extract both the linear and nonlinear optical conductivities of doped graphene and gapped graphene under excitation by a laser pulse. We discuss in detail the dependence of second harmonic generation, third harmonic generation, and the Kerr effects on the doping level, the gap, and the electric field amplitude. The numerical results for weak electric fields agree with those calculated from available analytic perturbation formulas. For strong electric fields when saturation effects are important, all the effective third order nonlinear response coefficients show a strong field dependence.
Lossless Kerr-phase gate in a quantum-well system via tunneling interference effect for weak fields
NASA Astrophysics Data System (ADS)
Shi, Y. L.; Huang, Y. C.; Wu, J. X.; Zhu, C. J.; Xu, J. P.; Yang, Y. P.
2015-06-01
We examine a lossless Kerr-phase gate in a semiconductor quantum-well system via the tunneling interference effect for weak fields. We show that there exists a magic detuning for the signal field, at which the absorption or amplification for the probe field can be eliminated by increasing the tunneling interference effect. Simultaneously, the probe field will acquire a -? phase shift at the exit of the medium. We demonstrate with numerical simulations that a lossless Kerr-phase gate is achieved, which may result in many applications in information science and telecommunication.
NASA Astrophysics Data System (ADS)
Weinberg, Nevin Nachum
The studies presented herein are on three distinct topics in astrophysics: I. We solve for the evolution of the vertical extent of the convective region of a neutron star atmosphere during a type I X-ray burst. The convective region is well-mixed with ashes of nuclear burning, and its extent determines the burst rise time. We show that the maximum extent of the convective region during photospheric radius expansion (PRE) bursts can be sufficiently great that some ashes of burning are: (1) ejected by the radiation-driven wind during the PRE phase and, (2) exposed at the neutron star surface following the PRE phase. We calculate the expected column density of ashes in hydrogen-like states and find that the resulting photoionization edges should be detectable with current high spectral resolution X-ray telescopes. A detection would probe the burst nuclear burning processes and might enable a measurement of the neutron star gravitational redshift. II. We discuss physical experiments achievable via the monitoring of stellar dynamics near the massive black hole (MBH) at the Galactic center with a next- generation, extremely large telescope (ELT). We use the Markov Chain Monte Carlo method to evaluate the constraints that the monitoring of these orbits will place on the matter content at the Galactic center. We compare these future constraints with those obtained with the current data. We also describe how the monitoring of stellar proper motions can be used to probe directly the masses of isolated stellar remnants near the MBH. III. We calculate the abundance of dark-matter concentrations that are sufficiently overdense to produce a detectable weak-gravitational-lensing signal. Most of these overdensities are virialized halos containing identifiable X-ray and/or optical clusters. However, a significant fraction are nonvirialized, cluster-mass overdensities still in the process of gravitational collapse---these should produce significantly weaker or no X-ray emission. Our predicted abundance of such dark clusters is consistent with the abundance implied by the detection of apparent dark lenses. We also examine the prospect of using weak gravitational lenses to constrain the dark energy equation-of- state.
NASA Astrophysics Data System (ADS)
Zheng, Sheng Ming
2012-10-01
In the natural world, people have discovered four kinds of forces: electromagnetic force, gravitation, weak force, and strong force. Although the gravitation has been discovered more than three hundred years, its mechanism of origin is unclear until today. While investigating the origin of gravitation, I do some experiments discover the moving photons produce gravitation. This discovery shows the origin of gravitation. Meanwhile I do some experiments discover the light interference fringes are produced by the gravitation: my discovery demonstrate light is a particle, but is not a wave-particle duality. Furthermore, applications of this discovery to other moving particles show a similar effect. In a word: the micro particle moving produce gravitation and electromagnetic force. Then I do quantity experiment get a general formula: Reveal the essence of gravitational mass and the essence of electric charge; reveal the origin of gravitation and the essence of matter wave. Along this way, I unify the gravitation and electromagnetic force. Namely I find a natural law that from atomic world to star world play in moving track. See website: https://www.lap-publishing.com/catalog/details/store/gb/book/978-3-8473-2658-8/mechanism-of-interaction-in-moving-matter
NASA Astrophysics Data System (ADS)
Qin, Ying-Mei; Wang, Jiang; Men, Cong; Zhao, Jia; Wei, Xi-Le; Deng, Bin
2012-07-01
Both external and endogenous electrical fields widely exist in the environment of cortical neurons. The effects of a weak alternating current (AC) field on a neural network model with synaptic plasticity are studied. It is found that self-sustained rhythmic firing patterns, which are closely correlated with the cognitive functions, are significantly modified due to the self-organizing of the network in the weak AC field. The activities of the neural networks are affected by the synaptic connection strength, the external stimuli, and so on. In the presence of learning rules, the synaptic connections can be modulated by the external stimuli, which will further enhance the sensitivity of the network to the external signal. The properties of the external AC stimuli can serve as control parameters in modulating the evolution of the neural network.
Effect of an atom on a quantum guided field in a weakly driven fiber-Bragg-grating cavity
Le Kien, Fam; Hakuta, K.
2010-02-15
We study the interaction of an atom with a quantum guided field in a weakly driven fiber-Bragg-grating (FBG) cavity. We present an effective Hamiltonian and derive the density-matrix equations for the combined atom-cavity system. We calculate the mean photon number, the second-order photon correlation function, and the atomic excited-state population. We show that due to the confinement of the guided cavity field in the fiber cross-section plane and in the space between the FBG mirrors, the presence of the atom in the FBG cavity can significantly affect the mean photon number and the photon statistics even though the cavity finesse is moderate, the cavity is long, and the probe field is weak.
Weak Lie symmetry and extended Lie algebraa)
NASA Astrophysics Data System (ADS)
Goenner, Hubert
2013-04-01
The concept of weak Lie motion (weak Lie symmetry) is introduced. Applications given exhibit a reduction of the usual symmetry, e.g., in the case of the rotation group. In this context, a particular generalization of Lie algebras is found ("extended Lie algebras") which turns out to be an involutive distribution or a simple example for a tangent Lie algebroid. Riemannian and Lorentz metrics can be introduced on such an algebroid through an extended Cartan-Killing form. Transformation groups from non-relativistic mechanics and quantum mechanics lead to such tangent Lie algebroids and to Lorentz geometries constructed on them (1-dimensional gravitational fields).
Weak Lie symmetry and extended Lie algebra
Goenner, Hubert
2013-04-15
The concept of weak Lie motion (weak Lie symmetry) is introduced. Applications given exhibit a reduction of the usual symmetry, e.g., in the case of the rotation group. In this context, a particular generalization of Lie algebras is found ('extended Lie algebras') which turns out to be an involutive distribution or a simple example for a tangent Lie algebroid. Riemannian and Lorentz metrics can be introduced on such an algebroid through an extended Cartan-Killing form. Transformation groups from non-relativistic mechanics and quantum mechanics lead to such tangent Lie algebroids and to Lorentz geometries constructed on them (1-dimensional gravitational fields).
Endothelial Cell Morphology and Migration are Altered by Changes in Gravitational Fields
NASA Technical Reports Server (NTRS)
Melhado, Caroline; Sanford, Gary; Harris-Hooker, Sandra
1997-01-01
Many of the physiological changes of the cardiovascular system during space flight may originate from the dysfunction of basic biological mechanisms caused by microgravity. The weightlessness affects the system when blood and other fluids move to the upper body causing the heart to enlarge to handle the increased blood flow to the upper extremities and decrease circulating volume. Increase arterial pressure triggers baroreceptors which signal the brain to adjust heart rate. Hemodynarnic studies indicate that the microgravity-induced headward fluid redistribution results in various cardiovascular changes such as; alteration of vascular permeability resulting in lipid accumulation in the lumen of the vasculature and degeneration of the the vascular wall, capillary alteration with extensive endothelial invagination. Achieving a true microgravity environment in ground based studies for prolonged periods is virtually impossible. The application of vector-averaged gravity to mammalian cells using horizontal clinostat produces alterations of cellular behavior similar to those observed in microgravity. Similarly, the low shear, horizontally rotating bioreactor (originally designed by NASA) also duplicates several properties of microgravity. Additionally, increasing gravity, i.e., hypcrgravity is easily achieved. Hypergravity has been found to increase the proliferation of several different cell lines (e.g., chick embryo fibroblasts) while decreasing cell motility and slowing liver regeneration following partial hepatectomy. The effect of altered gravity on cells maybe similar to those of other physical forces, i.e. shear stress. Previous studies examining laminar flow and shear stress on endothelial cells found that the cells elongate, orient with the direction of flow, and reorganize their F-actin structure, with concomitant increase in cell stiffness. These studies suggest that alterations in the gravity environment will change the behavior of most cells, including vascular cells. However, few studies have been directed at assessing the effect of altered gravitational field on vascular cell fiction and metabolism, Using image analysis we examined how bovine aortic endothelial cells altered their morphological characteristics and their response to a denudation injury when cells were subjected to simulated microgravity and hypergravity.
Ideal gas in a strong gravitational field: Area dependence of entropy
Kolekar, Sanved; Padmanabhan, T.
2011-03-15
We study the thermodynamic parameters like entropy, energy etc. of a box of gas made up of indistinguishable particles when the box is kept in various static background spacetimes having a horizon. We compute the thermodynamic variables using both statistical mechanics as well as by solving the hydrodynamical equations for the system. When the box is far away from the horizon, the entropy of the gas depends on the volume of the box except for small corrections due to background geometry. As the box is moved closer to the horizon with one (leading) edge of the box at about Planck length (L{sub p}) away from the horizon, the entropy shows an area dependence rather than a volume dependence. More precisely, it depends on a small volume A{sub perpendicular}L{sub p}/2 of the box, up to an order O(L{sub p}/K){sup 2} where A{sub perpendicular} is the transverse area of the box and K is the (proper) longitudinal size of the box related to the distance between leading and trailing edge in the vertical direction (i.e. in the direction of the gravitational field). Thus the contribution to the entropy comes from only a fraction O(L{sub p}/K) of the matter degrees of freedom and the rest are suppressed when the box approaches the horizon. Near the horizon all the thermodynamical quantities behave as though the box of gas has a volume A{sub perpendicular}L{sub p}/2 and is kept in a Minkowski spacetime. These effects are: (i) purely kinematic in their origin and are independent of the spacetime curvature (in the sense that the Rindler approximation of the metric near the horizon can reproduce the results) and (ii) observer dependent. When the equilibrium temperature of the gas is taken to be equal to the horizon temperature, we get the familiar A{sub perpendicular}/L{sub p}{sup 2} dependence in the expression for entropy. All these results hold in a D+1 dimensional spherically symmetric spacetime. The analysis based on methods of statistical mechanics and the one based on thermodynamics applied to the gas treated as a fluid in static geometry, lead to the same results showing the consistency. The implications are discussed.
Ayala, Alejandro; Bashir, Adnan; Raya, Alfredo; Sanchez, Angel
2009-08-01
Working in the linear sigma model with quarks, we compute the finite-temperature effective potential in the presence of a weak magnetic field, including the contribution of the pion ring diagrams and considering the sigma as a classical field. In the approximation where the pion self-energy is computed perturbatively, we show that there is a region of the parameter space where the effect of the ring diagrams is to preclude the phase transition from happening. Inclusion of the magnetic field has small effects that however become more important as the system evolves to the lowest temperatures allowed in the analysis.
Scalar Gravitational Theory with Variable Rest Mass
NASA Astrophysics Data System (ADS)
Froedge, D. T.
2007-04-01
In this paper we will present the mechanical dynamics of a gravitational system resulting from a specific, rest mass, scalar potential relation, that is equivalent in predicting orbital and photon motion to that of General Relativity in the weak field solutions. The weak solutions of General Relativity do not appear to be contradicted by this development, and in this range the physical difference may not be measurable. The strong field solutions will be significantly different, however since, in this scalar relation, the rest mass goes to zero at Schwarzschild boundary. The consequences of the mass dependence gravitational potential results, for large masses, not in the prediction of black holes, but rather mass to Gamma ray converters. The theory would suggest that the defined gamma ray sources emissions of the galactic center imaged by the ESA/INTEGRAL spacecraft could be from bodies close to the maximum mass.
NASA Astrophysics Data System (ADS)
Li, Hanxiao; Fautrelle, Yves; Hou, Long; Du, Dafan; Zhang, Yikun; Ren, Zhongming; Lu, Xionggang; Moreau, Rene; Li, Xi
2016-02-01
The influence of a weak transverse magnetic field on the morphology and orientation of Al3Ni dendrites in directionally solidified Al-12 wt% Ni alloys was investigated. The experimental results indicated that the magnetic field caused segregation. It was also found that the application of a magnetic field decreased the primary dendrite spacing. By means of electronic backscatter diffraction (EBSD) analysis, the orientation of the Al3Ni dendrite was studied. In the case of no magnetic field, the <010> crystal direction of the Al3Ni crystal was oriented along the solidification direction. When a transverse magnetic field was applied, the <001> crystal direction rotated to the magnetic field direction, whereas the <010> crystal direction remained oriented along the solidification direction. The above experimental results are discussed in the context of thermoelectric magnetic convection (TEMC) and crystal anisotropy.
NASA Astrophysics Data System (ADS)
Robertson, Brant E.; Ellis, Richard S.; Dunlop, James S.; McLure, Ross J.; Stark, Dan P.; McLeod, Derek
2014-12-01
Strong gravitational lensing provides a powerful means for studying faint galaxies in the distant universe. By magnifying the apparent brightness of background sources, massive clusters enable the detection of galaxies fainter than the usual sensitivity limit for blank fields. However, this gain in effective sensitivity comes at the cost of a reduced survey volume and, in this Letter, we demonstrate that there is an associated increase in the cosmic variance uncertainty. As an example, we show that the cosmic variance uncertainty of the high-redshift population viewed through the Hubble Space Telescope Frontier Field cluster Abell 2744 increases from ~35% at redshift z ~ 7 to >~ 65% at z ~ 10. Previous studies of high-redshift galaxies identified in the Frontier Fields have underestimated the cosmic variance uncertainty that will affect the ultimate constraints on both the faint-end slope of the high-redshift luminosity function and the cosmic star formation rate density, key goals of the Frontier Field program.
THREE-DIMENSIONAL RECONSTRUCTION OF THE DENSITY FIELD: AN SVD APPROACH TO WEAK-LENSING TOMOGRAPHY
VanderPlas, J. T.; Connolly, A. J.; Jain, B.; Jarvis, M.
2011-02-01
We present a new method for constructing three-dimensional mass maps from gravitational lensing shear data. We solve the lensing inversion problem using truncation of singular values (within the context of generalized least-squares estimation) without a priori assumptions about the statistical nature of the signal. This singular value framework allows a quantitative comparison between different filtering methods: we evaluate our method beside the previously explored Wiener-filter approaches. Our method yields near-optimal angular resolution of the lensing reconstruction and allows cluster sized halos to be de-blended robustly. It allows for mass reconstructions which are two to three orders of magnitude faster than the Wiener-filter approach; in particular, we estimate that an all-sky reconstruction with arcminute resolution could be performed on a timescale of hours. We find however that linear, non-parametric reconstructions have a fundamental limitation in the resolution achieved in the redshift direction.
NASA Astrophysics Data System (ADS)
Nakonieczna, Anna; Yeom, Dong-han
2016-02-01
There does not exist a notion of time which could be transferred straightforwardly from classical to quantum gravity. For this reason, a method of time quantification which would be appropriate for gravity quantization is being sought. One of the existing proposals is using the evolving matter as an intrinsic `clock' while investigating the dynamics of gravitational systems. The objective of our research was to check whether scalar fields can serve as time variables during a dynamical evolution of a coupled multicomponent matter-geometry system. We concentrated on a neutral case, which means that the elaborated system was not charged electrically nor magnetically. For this purpose, we investigated a gravitational collapse of a self-interacting complex and real scalar fields in the Brans-Dicke theory using the 2+2 spacetime foliation. We focused mainly on the region of high curvature appearing nearby the emerging singularity, which is essential from the perspective of quantum gravity. We investigated several formulations of the theory for various values of the Brans-Dicke coupling constant and the coupling between the Brans-Dicke field and the matter sector of the theory. The obtained results indicated that the evolving scalar fields can be treated as time variables in close proximity of the singularity due to the following reasons. The constancy hypersurfaces of the Brans-Dicke field are spacelike in the vicinity of the singularity apart from the case, in which the equation of motion of the field reduces to the wave equation due to a specific choice of free evolution parameters. The hypersurfaces of constant complex and real scalar fields are spacelike in the regions nearby the singularities formed during the examined process. The values of the field functions change monotonically in the areas, in which the constancy hypersurfaces are spacelike.
Omnidirectional Gravitational Radiation Observatory: Proceedings of the First International Workshop
NASA Astrophysics Data System (ADS)
Velloso, W. F.; Aguiar, O. D.; Magalhães, N. S.
1997-08-01
The Table of Contents for the full book PDF is as follows: * Foreword * Introduction: The OMNI-1 Workshop and the beginning of the International Gravitational Radiation Observatory * Opening Talks * Gravitational radiation sources for Acoustic Detectors * The scientific and technological benefits of gravitational wave research * Operating Second and Third Generation Resonant-Mass Antennas * Performance of the ALLEGRO detector -- and what our experience tells us about spherical detectors * The Perth Niobium resonant mass antenna with microwave parametric transducer * The gravitational wave detectors EXPLORER and NAUTILUS * Gravitational Waves and Astrophysical Sources for the Next Generation Observatory * What is the velocity of gravitational waves? * Superstring Theory: how it change our ideas about the nature of Gravitation * Statistical approach to the G.W. emission from radio pulsars * Gravitational waves from precessing millisecond pulsars * The production rate of compact binary G.W. sources in elliptical galaxies * On the possibility to detect Gravitational Waves from precessing galactic neutron stars * Gravitational wave output of the head-on collision of two black holes * SN as a powerfull source of gravitational radiation * Long thick cosmic strings radiating gravitational waves and particles * Non-Parallel Electric and Magnetic Fields in a gravitational background, stationary G.W. and gravitons * Exact solutions of gravitational waves * Factorization method for linearized quantum gravity at tree-level. Graviton, photon, electron processes * Signal Detection with Resonant-Mass Antennas * Study of coalescing binaries with spherical gravitational waves detectors * Influence of transducer asymmetries on the isotropic response of a spherical gravitational wave antenna * Performances and preliminary results of the cosmic-ray detector associated with NAUTILUS * Possible transducer configurations for a spherical gravitational wave antenna * Detectability of neutron star coalescence, bar-mode instability and core colapse events by spherical antennas * Interaction of high energy muons and hadrons with a large aluminum spherical resonant detector * Optimal detection of pulsed GW signals correlated with cosmic gamma-bursts * Preliminary results of searching of joint gravity-neutrinos-gamma events * Next Generation Resonant-Mass Antennas * A 100 TON 10mK spherical gravitational wave detector * Experimental study of spherical resonators at very low temperatures * Thermal convective cooling of gravitational radiation antennas * Very low temperature measurements of quality factors of copper alloys for resonant gravitational wave antennae * Real life TIGA measurements: results from the LSU prototype * Simulation of a spherical resonant-mass gravitational wave antenna * DEFOSP: the gravitational wave detector for a space laboratory * The resonator problem in a spherical GW antenna * On the use of the Finite Elements Method to design the structures of mechanical isolation to resonant mass antennas * Transducers and Amplification Techniques * Low-loss sapphire transducers for resonant-mass Gravitational Wave detectors and quantum non-demolition readouts * Improvement of an inductive tripode transducer electrical Q * Tests of a resonant capacitive transducer with integrated readout on the cryogenic gravitational wave antenna ALTAIR * Development of an optical transducer * Noise measurements on two-squid gravitational wave transducer systems * Resonant/Free Mass Omnidirectional Network * The present status of VIRGO Project * The supernova cosmological background of gravitational waves * LIGO: status and prospects * The ring interferometer in the field of a weak gravitational wave * List of Participants
Saroka, Kevin S; Persinger, Michael A
2013-09-01
Exotic experiences such as the sensing of another consciousness or the detachment of consciousness from the body are occasionally reported by individuals with partial seizures from a temporal lobe focus. The experiences display the characteristics of Hughlings Jackson's "parasitic consciousness". We have hypothesized that these experiences are encouraged by slight discrepancies in hemispheric activity that can be simulated by application of weak, physiologically-patterned magnetic fields across the cerebral hemispheres. Electroencephalographic and Low Resolution Electromagnetic Tomography (sLORETA) data revealed altered activity bands within specific regions within the cerebral cortices during these experiences. The clear changes in power of brain activity were discerned after consistent durations of exposure to specifically patterned weak magnetic fields. Millisecond range point durations were required. The technology may be useful to explore the subjective components associated with complex partial seizures. PMID:23872082
Novitskii, Yu I; Novitskaya, G V; Molokanov, D R; Serdyukov, Yu A; Yusupova, I U
2015-01-01
The lipid composition and content were analyzed in lettuce Lactica sativa L. (variety Stone head) leaves grown in a weak horizontal permanent magnetic field (PMF) produced by Helmholtz coils of 400 A/m strength under controlled conditions of illumination and temperature in phytothrone. Control plants were grown under the same conditions in a geomagnetic field. PMF decreased the total lipid content by 40% due to a significant decrease in polar and neutral lipids. Among polar lipids, the fractions of glycolipids and phospholipids diminished. Among glycolipids, the content of monogalactosyldiacylglycerols was lower by 25-52%. The content of phospholipids decreased, too, namely phosphatidylglycerols were lower by 17-51%, phosphatidylcholines by 21-24%, phosphatidylethanolamines by 12-20%, and phosphatidylinositols by 12-41%. Therefore, weak PMF reduced the content of lipids in membranes, including the chloroplast, mitochondrial, and cytoplasmic membranes. PMID:26638236
NASA Astrophysics Data System (ADS)
Ishiyama, U.; Thanh Cuong, Nguyen; Okada, Susumu
2016-04-01
Using density functional theory, we studied the electronic properties of carbon nanotube (CNT) thin films under an electric field. The carrier accumulation due to the electric field depends strongly on the CNT species forming the thin films. Under a low electron concentration, the injected electrons are distributed throughout the CNTs, leading to an unusual electric field between CNTs, the direction of which is opposite to that of the applied field. This unusual field response of CNT thin films to an external electric field is ascribed to the internal electric field arising from the electrostatic potential difference between the constituent CNTs.
NASA Astrophysics Data System (ADS)
de Bom, C. R.; Furlanetto, C.; More, A.; Brandt, C.; Makler, M.; Santiago, B.
2015-01-01
Strongly Lensed systems, and in particular gravitational arcs, are useful tools for a variety of astrophysical applications. Finding arcs in wide-field surveys such as the Dark Energy Survey (DES) requires automated algorithms to select arc candidates due to the large amount of data. In this contribution we present a new arcfinding method that uses the Mediatrix filamentation method coupled to a neural network to select arc candidates. We carry out a systematic comparison between this method and three other arcfinders available in the literature -- Lenzen et al. (2004), Horesh et al. (2005), and More et al. (2012) -- on a sample of arc simulated with the PaintArcs method.
NASA Astrophysics Data System (ADS)
Wilson, Michelle; Zabludoff, Ann I.; Wong, Kenneth C.; Keeton, Charles R.; French, Katheryn Decker; Momcheva, Ivelina G.; Williams, Kurtis A.
2016-01-01
Galaxy-scale strong gravitational lensing has long been used to measure cosmological parameters such as the Hubble constant as well as the dark matter properties of galaxy halos. Additional mass around the lens galaxy or projected in the line-of-sight affects the light bending and needs to be incorporated into lensing analyses. We present new results from a spectroscopic survey to characterize the environmental and line-of-sight mass for 28 galaxy-scale lens fields. We show how the external convergence, number of lensed images, and lensed image separation are altered by groups at the lens and along the sightline.
Gravitational Radiation in a Nonsymmetric Gravitational Theory.
NASA Astrophysics Data System (ADS)
Krisher, Timothy Philip
We analyze the properties of gravitational radiation in a nonsym- metric gravitational theory (NGT) proposed by Moffat that is based on a nonsymmetric metric and affine connection. A generalized formalism is developed for determining the physically observable polarization modes of weak, plane gravitational waves in nonsym- metric theories of gravitation. For the case of NGT, we find that a Lorentz-invariant description of gravitational waves is possible if a "transposition -invariant" definition of measurable geodesic deviation is adopted for the theory. We then analyze the generation of gravitational radiation and show that NGT predicts the emission of dipole gravitational radiation from a binary system. The source of the dipole radiation is a vector density S postulated to be proportional to the number density of fermion particles in the components of the system. This radiation is shown to result in a secular decrease in the orbital period of a binary system in addition to that predicted by general relativity. The size of the effect is proportional to the reduced mass of the system and to the square of the difference in L('2)/ mass between the two compo- nents of the system, where L is a parameter having units of length that is related to the number of fermion particles in each component. We discuss how the theory might be constrained by observations of the binary pulsar PSR 1913+16 and the cataclysmic binary AM CVn.
Gravitational radiation in a nonsymmetric gravitational theory
NASA Astrophysics Data System (ADS)
Krisher, T. P.
The properties of gravitational radiation in a nonsymmetric gravitational theory (NGT) proposed by Moffat that is based on a nonsymmetric metric and affine connection were analyzed. A generalized formalism is developed for determining the physically observable polarization modes of weak, plane gravitational waves in nonsymmetric theories of gravitation. For the case of NGT, it is found that a Lorentz-invariant description of gravitational waves is possible if a transposition-invariant definition of measurable geodesic deviation is adopted for the theory. The generation of gravitational radiation is examined and it is shown that NGT predicts the emission of dipole gravitational radiation from a binary system. The source of the dipole radiation is a vector density S postulated to be proportional to the number density of fermion particles in the components of the system. This radiation results in a secular decrease in the orbital period of a binary system in addition to that predicted by general relativity. Constriction of the theory might be constrained by observations of the binary pulsar PSR 1913 + 16 and the cataclysmic binary AM CVn.
NASA Astrophysics Data System (ADS)
Varela, J.; Pantellini, F.; Moncuquet, M.
2016-01-01
The aim of this study is to simulate the interaction of the solar wind with the Hermean magnetosphere when the interplanetary magnetic field is weak, performing a parametric study for all the range of hydrodynamic values of the solar wind predicted on Mercury for the ENLIL + GONG WSA + Cone SWRC model: density from 12 to 180 cm-3, velocity from 200 to 500 km/s and temperatures from 2 ·104 to 18 ·104 K, and compare the results with a real MESSENGER orbit as reference case. We use the code PLUTO in spherical coordinates and an asymmetric multipolar expansion for the Hermean magnetic field. The study shows for all simulations a stand off distance larger than the Mercury radius and the presence of close magnetic field lines on the day side of the planet, so the dynamic pressure of the solar wind is not high enough to push the magnetopause on the planet surface if the interplanetary magnetic field is weak. The simulations with large dynamic pressure lead to a large compression of the Hermean magnetic field modifying its topology in the inner magnetosphere as well as the plasma flows from the magnetosheath towards the planet surface.
NASA Astrophysics Data System (ADS)
Madsen, Lars Bojer; Tolstikhin, Oleg I.; Morishita, Toru
2012-05-01
The recently developed weak-field asymptotic theory [Phys. Rev. A1050-294710.1103/PhysRevA.84.053423 84, 053423 (2011)] is applied to the analysis of tunneling ionization of a molecular ion (H2+), several homonuclear (H2, N2, O2) and heteronuclear (CO, HF) diatomic molecules, and a linear triatomic molecule (CO2) in a static electric field. The dependence of the ionization rate on the angle between the molecular axis and the field is determined by a structure factor for the highest occupied molecular orbital. This factor is calculated using a virtually exact discrete variable representation wave function for H2+, very accurate Hartree-Fock wave functions for the diatomics, and a Hartree-Fock quantum chemistry wave function for CO2. The structure factors are expanded in terms of standard functions and the associated structure coefficients, allowing the determination of the ionization rate for any orientation of the molecule with respect to the field, are tabulated. Our results, which are exact in the weak-field limit for H2+ and, in addition, under the Hartree-Fock approximation for the diatomics, are compared with results from the recent literature.
NASA Astrophysics Data System (ADS)
Stuchlk, Zden?k; Kolo, Martin
2016-01-01
To test the role of large-scale magnetic fields in accretion processes, we study the dynamics of the charged test particles in the vicinity of a black hole immersed into an asymptotically uniform magnetic field. Using the Hamiltonian formalism of the charged particle dynamics, we examine chaotic scattering in the effective potential related to the black hole gravitational field combined with the uniform magnetic field. Energy interchange between the translational and oscillatory modes of the charged particle dynamics provides a mechanism for charged particle acceleration along the magnetic field lines. This energy transmutation is an attribute of the chaotic charged particle dynamics in the combined gravitational and magnetic fields only, the black hole rotation is not necessary for such charged particle acceleration. The chaotic scatter can cause a transition to the motion along the magnetic field lines with small radius of the Larmor motion or vanishing Larmor radius, when the speed of the particle translational motion is largest and it can be ultra-relativistic. We discuss the consequences of the model of ionization of test particles forming a neutral accretion disc, or heavy ions following off-equatorial circular orbits, and we explore the fate of heavy charged test particles after ionization where no kick of heavy ions is assumed and only the switch-on effect of the magnetic field is relevant. We demonstrate that acceleration and escape of the ionized particles can be efficient along the Kerr black hole symmetry axis parallel to the magnetic field lines. We show that a strong acceleration of the ionized particles to ultra-relativistic velocities is preferred in the direction close to the magnetic field lines. Therefore, the process of ionization of Keplerian discs around the Kerr black holes can serve as a model of relativistic jets.
Possibility of realizing weak gravity in redshift space distortion measurements
NASA Astrophysics Data System (ADS)
Tsujikawa, Shinji
2015-08-01
We study the possibility of realizing a growth rate of matter density perturbations lower than that in general relativity. Using the approach of the effective field theory of modified gravity encompassing theories beyond Horndeski, we derive the effective gravitational coupling Geff and the gravitational slip parameter η for perturbations deep inside the Hubble radius. In Horndeski theories we derive a necessary condition for achieving weak gravity associated with tensor perturbations, but this is not a sufficient condition due to the presence of a scalar-matter interaction that always enhances Geff. Beyond the Horndeski domain it is possible to realize Geff smaller than Newton's gravitational constant G , while the scalar and tensor perturbations satisfy no-ghost and stability conditions. We present a concrete dark energy scenario with varying ct and numerically study the evolution of perturbations to confront the model with the observations of redshift-space distortions and weak lensing.
NASA Astrophysics Data System (ADS)
Bambi, Cosimo
2014-03-01
In extensions of general relativity and in theories aiming at unifying gravity with the forces of the Standard Model, the value of the ``fundamental constants'' is often determined by the vacuum expectation value of new fields, which may thus change in different backgrounds. Variations of fundamental constants with respect to the values measured today in laboratories on Earth are expected to be more evident on cosmological timescales and/or in strong gravitational fields. In this paper, I show that the analysis of the K? iron line observed in the X-ray spectrum of black holes can potentially be used to probe the fine structure constant ? in gravitational potentials relative to Earth of ?phi ? 0.1. At present, systematic effects not fully under control prevent to get robust and stringent bounds on possible variations of the value of ? with this technique, but the fact that current data can be fitted with models based on standard physics already rules out variations of the fine structure constant larger than some percent.
Bambi, Cosimo
2014-03-01
In extensions of general relativity and in theories aiming at unifying gravity with the forces of the Standard Model, the value of the ''fundamental constants'' is often determined by the vacuum expectation value of new fields, which may thus change in different backgrounds. Variations of fundamental constants with respect to the values measured today in laboratories on Earth are expected to be more evident on cosmological timescales and/or in strong gravitational fields. In this paper, I show that the analysis of the Kα iron line observed in the X-ray spectrum of black holes can potentially be used to probe the fine structure constant α in gravitational potentials relative to Earth of Δφ ≈ 0.1. At present, systematic effects not fully under control prevent to get robust and stringent bounds on possible variations of the value of α with this technique, but the fact that current data can be fitted with models based on standard physics already rules out variations of the fine structure constant larger than some percent.
NASA Technical Reports Server (NTRS)
Dong, D,; Gross, R.S.; Dickey, J.
1996-01-01
Monthly mean gravitational field parameters (denoted here as C(sub even)) that represent linear combinations of the primarily even degree zonal spherical harmonic coefficients of the Earth's gravitational field have been recovered using LAGEOS I data and are compared with those derived from gridded global surface pressure data of the National meteorological center (NMC) spanning 1983-1992. The effect of equilibrium ocean tides and surface water variations are also considered. Atmospheric pressure and surface water fluctuations are shown to be the dominant cause of observed annual C(sub even) variations. Closure with observations is seen at the 1sigma level when atmospheric pressure, ocean tide and surface water effects are include. Equilibrium ocean tides are shown to be the main source of excitation at the semiannual period with closure at the 1sigma level seen when both atmospheric pressure and ocean tide effects are included. The inverted barometer (IB) case is shown to give the best agreement with the observation series. The potential of the observed C(sub even) variations for monitoring mass variations in the polar regions of the Earth and the effect of the land-ocean mask in the IB calculation are discussed.