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1

NASA Astrophysics Data System (ADS)

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.

Tsukamoto, Naoki; Kitamura, Takao; Nakajima, Koki; Asada, Hideki

2014-09-01

2

Gravitational field fluctuations in weakly clustered systems

NASA Astrophysics Data System (ADS)

Stochastic fluctuations of the gravitational field in a collisionless, weakly clustered protogalactic system are induced by local fluctuations in the number density of small collapsed peaks. The probability distribution of the stochastic forces generated by these fluctuations is calculated, and a generalization of the Holtsmark distribution, previously studied in a stellar dynamical context by Chandrasekhar and Von Neumann and by Kandrup, is found. The probability distribution of the torques induced by these stochastic forces is also found, the analog of the Holtsmark law for the torque distribution is introduced, and different cases corresponding to different power laws are studied. These considerations are applied to realistic models of protogalactic and protocluster density perturbations. The force probability distribution is remarkably influenced by the clustering of substructure: the profile is more strongly peaked, and the asymptotic decay is almost suppressed, resulting in an enhanced probability near the average value.

Antonuccio-Delogu, V.; Atrio-Barandela, F.

1992-06-01

3

Coupling of Gravitation and Electromagnetism in the Weak Field Approximation

Using the weak field approximation, we can express the theory of general relativity in a Maxwell-type structure comparable to electromagnetism. We find that every electromagnetic field is coupled to a gravitoelectric and gravitomagnetic field. Acknowledging the fact that both fields originate from the same source, the particle, we can express the magnetic and electric field through their gravitational respective analogues using the proportionality coefficient k. This coefficient depends on the ratio of mass and charge and the ratio between the electromagnetic and gravitic-gravitomagnetic permittivity and permeability respectively. Although the coefficient is very small, the fact that electromagnetic fields in material media can be used to generate gravitational and gravitomagnetic fields and vice versa is not commonly known. We find that the coupling coefficient can be increased by massive ion currents, electron and nuclear spin-alignment. Advances in material sciences, cryogenic technology and high frequency electromagnetic fields in material media may lead to applications of the derived relationships.

M. Tajmar; C. de Matos

2000-03-03

4

The generation of gravitational waves. I - Weak-field sources

NASA Technical Reports Server (NTRS)

This paper derives and summarizes a 'plug-in-and-grind' formalism 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, the formalism reduces to standard 'linearized theory'. Independent of the effects of gravity on the motions, the formalism reduces to the standard 'quadrupole-moment formalism' if the motions are slow and internal stresses are weak. In the general case, the formalism expresses the radiation in terms of a retarded Green's function for slightly curved spacetime and breaks the Green's function integral into five easily understood pieces: direct radiation, produced directly by the motions of the source; whump radiation, produced by 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; focusing radiation, produced when one portion of the source focuses, in a time-dependent way, the nonradiative field of another portion of the source; and tail radiation, produced by 'back-scatter' of the nonradiative field in regions of focusing.

Thorne, K. S.; Kovacs, S. J.

1975-01-01

5

Casimir effect in a weak gravitational field and the spacetime index of refraction

In a recent paper [arXiv:0904.2904] using a conjecture it is shown how one can calculate the effect of a weak stationary gravitational field on vacuum energy in the context of Casimir effect in an external gravitational field treated in 1+3 formulation of spacetime decomposition.. In this article, employing quntum field theory in curved spacetime, we explicitly calculate the effect of a weak static gravitational field on virtual massless scalar particles in a Casimir apparatus. It is shown that, as expected from the proposed conjecture, both the frequency and renormalized energy of the virtual scalar field are affected by the gravitational field through its index of refraction. This could be taken as a strong evidence in favour of the proposed conjecture. Generalizations to weak {\\it stationary} spacetimes and virtual photons are also discussed.

B. Nazari; M. Nouri-Zonoz

2010-10-07

6

Gravitational lensing beyond the weak-field approximation

NASA Astrophysics Data System (ADS)

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.

Perlick, Volker

2014-01-01

7

Gravitational lensing beyond the weak-field approximation

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.

Perlick, Volker, E-mail: perlick@zarm.uni-bremen.de [ZARM, University of Bremen, 28359 Bremen (Germany)

2014-01-14

8

This review forms the Weak Lensing part of the Saas-Fee Advanced Course on Gravitational Lensing. It describes the basicsm applications and results of weak lensing. Contents: (1) Introduction (2) The principles of weak gravitational lensing (3) Observational issues and challenges (4) Clusters of galaxies: Introduction, and strong lensing (5) Mass reconstructions from weak lensing (6) Cosmic shear -- lensing by the LSS (7) Large-scale structure lensing: results (8) The mass of, and associated with galaxies (9) Additional issues in cosmic shear (10) Concluding remarks.

Peter Schneider

2005-09-09

9

Hard Thermal Loops, Weak Gravitational Fields and The Quark Gluon Energy Momentum Tensor

We use an auxiliary field construction to discuss the hard thermal loop effective action associated with massless thermal SU(N) QCD interacting with a weak gravitational field. It is demonstrated that the previous attempt to derive this effective action has only been partially successful and that it is presently only known to first order in the graviton coupling constant. This is still sufficient to enable a calculation of a symmetric traceless quark gluon plasma energy momentum tensor. Finally, we comment on the conserved currents and charges of the derived energy momentum tensor.

E. A. Gaffney

1994-09-13

10

On slow flows of a weakly stratified relativistic fluid in a static gravitational field

NASA Astrophysics Data System (ADS)

Simplified equations for slow flows of a weakly stratified (in entropy) fluid inside or near a massive astrophysical object have been derived from the variational formulation of ideal general relativistic hydrodynamics under the conditions that the gravitational field in the leading order is centrosymmetric and static and that the effect of a magnetic field is negligibly small. Internal waves and vortices in such systems are soft modes as compared to sound. This circumstance allows the formulation of a "soundproof" Hamiltonian model. This model is an analog of nonrelativistic hydrodynamic anelastic models, which are widely used in studies of internal waves and/or convection in spatially inhomogeneous compressible media in atmospheric physics, geophysics, and astrophysics.

Ruban, V. P.

2014-04-01

11

It is shown that weight operator of a composite quantum body in a weak external gravitational field in the post-Newtonian approximation of the General Relativity does not commute with its energy operator, taken in the absence of the field. Nevertheless, the weak equivalence between the expectations values of weight and energy is shown to survive at a macroscopic level for stationary quantum states for the simplest composite quantum body - a hydrogen atom. Breakdown of the weak equivalence between weight and energy at a microscopic level for stationary quantum states can be experimentally detected by studying unusual electromagnetic radiation, emitted by the atoms, supported and moved in the Earth gravitational field with constant velocity, using spacecraft or satellite. For superpositions of stationary quantum states, a breakdown of the above mentioned equivalence at a macroscopic level leads to time dependent oscillations of the expectation values of weight, where the equivalence restores after averaging over time procedure.

Andrei Lebed

2012-05-14

12

The generation of gravitational waves. 1. Weak-field sources: A plug-in-and-grind formalism

NASA Technical Reports Server (NTRS)

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.

Thorne, K. S.; Kovacs, S. J.

1974-01-01

13

Weak Gravitational Lensing by Voids

We consider the prospects for detecting weak gravitational lensing by underdensities (voids) in the large-scale matter distribution. We derive the basic expressions for magnification and distortion by spherical voids. Clustering of the background sources and cosmic variance are the main factors which limit in principle the detection of lensing by voids. We conclude that only voids with radii larger than $\\sim 100$ \\hm have lensing signal to noise larger than unity.

Luca Amendola; Joshua A. Frieman; Ioav Waga

1998-11-29

14

Weak gravitational lensing of the CMB

Weak gravitational lensing has several important effects on the cosmic microwave background (CMB): it changes the CMB power spectra, induces non-Gaussianities, and generates a B-mode polarization signal that is an important source of confusion for the signal from primordial gravitational waves. The lensing signal can also be used to help constrain cosmological parameters and lensing mass distributions. We review the

Antony Lewis; Anthony Challinor

2006-01-01

15

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 characteristic 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 solution of the Schroedinger 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 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 dependent on subtleties of the gravonon structure which 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 Copenhagen quantum mechanics 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 Schroedinger's equation.

Gerold Doyen; Deiana Drakova

2014-08-12

16

Weak gravitational lensing with DEIMOS

We introduce a novel method for weak-lensing measurements, which is based on a mathematically exact deconvolution of the moments of the apparent brightness distribution of galaxies from the telescope's point spread function (PSF). No assumptions on the shape of the galaxy or the PSF are made. The (de)convolution equations are exact for unweighted moments only, while in practice a compact

P. Melchior; M. Viola; B. M. Schäfer; M. Bartelmann

2011-01-01

17

Gravitational anomaly and Hawking radiation near a weakly isolated horizon

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.

Wu Xiaoning [Institute of Mathematics, Academy of Mathematics and Systems Science, Chinese Academy of Sciences, P.O. Box 2734, Beijing, 100080 (China); Kavli Institute for Theoretical Physics China at the Chinese Academy of Sciences (KITPC-CAS), P.O. Box 2732, Beijing, 100080 (China); Huang Chaoguang [Institute of High Energy Physics, Chinese Academy of Sciences, P.O. Box 918(4), Beijing, 100049 (China); Kavli Institute for Theoretical Physics China at the Chinese Academy of Sciences (KITPC-CAS), P.O. Box 2732, Beijing, 100080 (China); Sun Jiarui [Institute of High Energy Physics, Chinese Academy of Sciences, P.O. Box 918(4), Beijing, 100049 (China); Graduate School of Chinese Academy of Sciences, Beijing, 100049 (China)

2008-06-15

18

We present a tensorial relative of the familiar affine connection and argue that it should be regarded as the gravitational field tensor. Remarkably, the Lagrangian density expressed in terms of this tensor has a simple form, which depends only on the metric and its first derivatives and, moreover, is a true scalar quantity. The geodesic equation, moreover, shows that our tensor plays a role that is strongly reminiscent of the gravitational field in Newtonian mechanics and this, together with other evidence, which we present, leads us to identify it as the gravitational field tensor. We calculate the gravitational field tensor for the Schwarzschild metric. We suggest some of the advantages to be gained from applying our tensor to the study of gravitational waves.

Stephen M. Barnett

2014-12-05

19

Weak gravitational lensing with the Square Kilometre Array

We investigate the capabilities of various stages of the SKA to perform world-leading weak gravitational lensing surveys. We outline a way forward to develop the tools needed for pursuing weak lensing in the radio band. We identify the key analysis challenges and the key pathfinder experiments that will allow us to address them in the run up to the SKA. We identify and summarize the unique and potentially very powerful aspects of radio weak lensing surveys, facilitated by the SKA, that can solve major challenges in the field of weak lensing. These include the use of polarization and rotational velocity information to control intrinsic alignments, and the new area of weak lensing using intensity mapping experiments. We show how the SKA lensing surveys will both complement and enhance corresponding efforts in the optical wavebands through cross-correlation techniques and by way of extending the reach of weak lensing to high redshift.

Brown, M L; Camera, S; Harrison, I; Joachimi, B; Metcalf, R B; Pourtsidou, A; Takahashi, K; Zuntz, J A; Abdalla, F B; Bridle, S; Jarvis, M; Kitching, T D; Miller, L; Patel, P

2015-01-01

20

Atomic Inference from Weak Gravitational Lensing Data

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.

Marshall, Phil; /KIPAC, Menlo Park

2005-12-14

21

Studying the LSS through weak gravitational lensing maps

Weak gravitational lensing is a promising tool for the study of the mass distribution in the Universe. Here we report some partial results that show how lensing maps can be used to differentiate between cosmological models. We pay special attention to the role of noise and smoothing. As an application, we use mock convergence fields constructed from N-body simulations of the large-scale structure for three historically important cosmological models. Various map analyses are used, including Minkowski functionals, and their ability to differentiate the models is calculated and discussed.

Antonio C. C. Guimarães

2001-12-10

22

Entropy of the gravitational field

We derive a formula for the nonequilibrium entropy of a classical stochastic field in terms of correlation functions of this field. The formalism is then applied to define the entropy of gravitational perturbations (both gravitational waves and density fluctuations). We calculate this entropy in a specific cosmological model (the inflationary Universe) and find that on scales of interest in cosmology

R. Brandenberger; V. Mukhanov; T. Prokopec

1993-01-01

23

Weak Gravitational Lensing and Cluster Mass Estimates

Hierarchical theories of structure formation predict that clusters of galaxies should be embedded in a web like structure, with filaments emanating from them to large distances. The amount of mass contained within such filaments near a cluster can be comparable to the collapsed mass of the cluster itself. Diffuse infalling material also contains a large amount of mass. Both these components can contribute to the cluster weak lensing signal. This ``projection bias'' is maximized if a filament lies close to the line-of-sight to a cluster. Using large--scale numerical simulations of structure formation in a cosmological constant dominated cold dark matter model, we show that the projected mass typically exceeds the actual mass by several tens of percent. This effect is significant for attempts to estimate cluster masses through weak lensing observations, and will affect weak lensing surveys aimed at constructing the cluster mass function.

Christopher A. Metzler; Martin White; Michael Norman; Chris Loken

1999-04-13

24

Gravitational Collapse of Vacuum Gravitational Field Configurations

This paper proves a theorem about the existence of an apparent horizon in general relativity, which applies equally well to vacuum configurations and matter configurations. The theorem uses the reciprocal of the surface-to-volume ratio of a region on a space slice to measure the radius of the region, and uses the minimum value $K_{\\rm min}$ of certain components of the extrinsic curvature to measure the strengh of the gravitational field in the region. The theorem proves that, if the product of the radius times $K_{\\rm min}$ is larger than unity, then an apparent horizon must form, signalling the formation of a black hole.

Douglas M. Eardley

1994-11-08

25

Caution: Strong Gravitational Field Present

ERIC Educational Resources Information Center

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.

Reif, Marc

2014-01-01

26

Topological Defects in Gravitational Lensing Shear Fields

Shear fields due to weak gravitational lensing have characteristic coherent patterns. We describe the topological defects in shear fields in terms of the curvature of the surface described by the lensing potential. A simple interpretation of the characteristic defects is given in terms of the the umbilical points of the potential surface produced by ellipsoidal halos. We show simulated lensing shear maps and point out the typical defect configurations. Finally, we show how statistical properties such as the abundance of defects can be expressed in terms of the correlation function of the lensing potential.

Vitelli, Vincenzo; Kamien, Randall D

2009-01-01

27

Topological defects in gravitational lensing shear fields

Shear fields due to weak gravitational lensing have characteristic coherent patterns. We describe the topological defects in shear fields in terms of the curvature of the surface described by the lensing potential. A simple interpretation of the characteristic defects is given in terms of the the umbilical points of the potential surface produced by ellipsoidal halos. We show simulated lensing shear maps and point out the typical defect configurations. Finally, we show how statistical properties such as the abundance of defects can be expressed in terms of the correlation function of the lensing potential.

Vitelli, Vincenzo [Instituut-Lorentz, Universiteit Leiden, Postbus 9506, 2300 RA Leiden (Netherlands); Jain, Bhuvnesh; Kamien, Randall D., E-mail: vitelli@lorentz.leidenuniv.nl, E-mail: bjain@physics.upenn.edu, E-mail: kamien@physics.upenn.edu [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104 (United States)

2009-09-01

28

Entropy of the gravitational field

We derive a formula for the nonequilibrium entropy of a classical stochastic field in terms of correlation functions of this field. The formalism is then applied to define the entropy of gravitational perturbations (both gravitational waves and density fluctuations). We calculate this entropy in a specific cosmological model (the inflationary Universe) and find that on scales of interest in cosmology the entropy in both density perturbations and gravitational waves exceeds the entropy of statistical fluctuations of the microwave background. The nonequilibrium entropy discussed here is a measure of loss of information about the system. We discuss the origin of the entropy in our cosmological models and compare the definition of entropy in terms of correlation functions with the microcanonical definition in quantum statistical mechanics.

Brandenberger, R. (Department of Physics, Brown University, Providence, Rhode Island 02912 (United States)); Mukhanov, V. (Institute of Theoretical Physics, Eidgenoessische Technische Hochschule Hoenggerberg, CH-8093 Zuerich (Switzerland)); Prokopec, T. (Department of Physics, Brown University, Providence, Rhode Island 02912 (United States))

1993-09-15

29

Weak gravitational lensing as a tool for cosmology

NASA Astrophysics Data System (ADS)

I will speak about recent developments in the measurements of the weak gravitational signal from maps of the cosmic microwave background (CMB) radiation. This signal is regarded as a contaminant of the primordial signal, but simultaneously it contains information on the large-scale matter distribution. Weak lensing of the CMB results from the coupling of the CMB photons to the gravitational potential integrated along the line of sight. Whereas lensing of galaxy shapes probes up to z~2, lensing of the CMB probes up to the last-scattering surface at z~1000 thus being a powerful tool for cosmology. Weak lensing generates a non-Gaussian pattern on the CMB temperature, while conserving the surface brightness. Hence, estimators of the weak lensing signal are quadratic in the temperature maps. I will then speak about a novel estimator which acts in real space, contrary to conventional estimators which act in harmonic space. The novel estimator performs well in the presence of detector noise and cuts in the maps due to point source excisions. Time allowing, I will also speak about how to use weak lensing to study the nature of dark matter and constrain deviations from general relativity at cosmological scales.

Carvalho, C. S.

2012-01-01

30

Weakly-Interacting Massive Particles in Torsionally-Gravitating Dirac Theory

NASA Astrophysics Data System (ADS)

We shall consider the problem of Dark Matter (DM) in torsion gravity with Dirac matter fields; we will consider the fact that if Weakly-Interacting Massive Particles in a bath are allowed to form condensates then torsional effects may be relevant even at galactic scales: we show that torsionally-gravitating Dirac fields have interesting properties for the problem of DM. We discuss consequences.

Fabbri, Luca

2013-08-01

31

LIGHT ON DARK MATTER WITH WEAK GRAVITATIONAL LENSING 1 Light on Dark Matter

LIGHT ON DARK MATTER WITH WEAK GRAVITATIONAL LENSING 1 Light on Dark Matter with Weak Gravitational reviews statistical methods re- cently developed to reconstruct and analyze dark matter mass maps from decades showing that the visible matter represents only about 4-5% of the Universe, the rest being dark

Starck, Jean-Luc

32

Quantum Measurement Problem and the Possible Role of the Gravitational Field

The quantum measurement problem and various unsuccessful attempts to resolve it are reviewed. A suggestion by Diosi and Penrose for the half life of the quantum superposition of two Newtonian gravitational fields is generalized to an arbitrary quantum superposition of relativistic, but weak, gravitational fields. The nature of the ``collapse'' process of the wave function is examined.

Jeeva Anandan

1998-08-11

33

Quantum Measurement Problem and the Possible Role of the Gravitational Field

The quantum measurement problem and various unsuccessful attempts to resolve it are reviewed. A suggestion by Diosi and Penrose for the half life of the quantum superposition of two Newtonian gravitational fields is generalized to an arbitrary quantum superposition of relativistic, but weak, gravitational fields. The nature of the ``collapse'' process of the wave function is examined.

Anandan, Jeeva S

1999-01-01

34

Tomographic Weak Gravitational Lensing Magnification with the Deep Lens Survey

NASA Astrophysics Data System (ADS)

Using half a million galaxies from the Deep Lens Survey, we have measured the gravitational lensing-induced magnification of high redshift (z 4) Lyman Break Galaxies (LBGs) by foreground field galaxies at a S/N > 20, finding a signal consistent with the expected lensing behavior. Using photometric redshifts, we can further divide our foreground galaxies into 8 roughly equal sub-groups covering the redshift range 0.4 < z < 1.2, which spans the expected lensing efficiency peak. After accounting for the evolution in large scale bias, we find that the measured lensing signal for the 8 sub-samples is consistent with the expected tomographic signal in LambdaCDM with a sigma8 given by WMAP CMB data. We find that these results are robust against systematic effects from variations in survey depth, seeing, and extinction as well as cross-contamination between the photometric redshift-selected foreground and LBG samples.

Morrison, Christopher; Scranton, R.; Schmidt, S.; Tyson, J.; Wittman, D.

2012-01-01

35

Numerical study of primordial magnetic field amplification by inflation-produced gravitational waves

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.

Kuroyanagi, Sachiko [Department of Physics, Nagoya University, Chikusa, Nagoya 464-8602 (Japan); Tashiro, Hiroyuki [Institut d'Astrophysique Spatiale, Universite Paris-Sud XI and CNR, Orsay, F-91405 (France); Sugiyama, Naoshi [Department of Physics, Nagoya University, Chikusa, Nagoya 464-8602 (Japan); Institute for Physics and Mathematics of the Universe, University of Tokyo, 5-1-5 Kashiwa-no-ha, Kashiwa City, Chiba 277-8582 (Japan)

2010-01-15

36

Initial Results from a Laboratory Emulation of Weak Gravitational Lensing Measurements

NASA Astrophysics Data System (ADS)

Weak gravitational lensing observations are a key science driver for the NASA Wide Field Infrared Survey Telescope (WFIRST). To validate the performance of the WFIRST infrared detectors, we have performed a laboratory emulation of weak gravitational lensing measurements. Our experiments used a custom precision projector system to image a target mask composed of a grid of pinholes, emulating stellar point sources, onto a 1.7 ?m cut-off Teledyne HgCdTe/H2RG detector. We used a 0.88 ?m LED illumination source and f/22 pupil stop to produce undersampled point spread functions similar to those expected from WFIRST. We also emulated the WFIRST image reconstruction strategy, using the image combination (IMCOM) algorithm to derive oversampled images from dithered, undersampled input images. We created shear maps for this data and computed shear correlation functions to mimic a real weak lensing analysis. After removing only second-order polynomial fits to the shear maps, we found that the correlation functions could be reduced to O(10-6). This places a conservative upper limit on the detector-induced bias to the correlation function (under our test conditions). This bias is two orders of magnitude lower than the expected weak lensing signal. Restricted to scales relevant to dark energy analyses (sky separations >0.5'), the bias is O(10-7) - comparable to the requirement for future weak lensing missions to avoid biasing cosmological parameter estimates. Our experiment will need to be upgraded and repeated under different configurations to fully characterize the shape measurement performance of WFIRST IR detectors.

Seshadri, S.; Shapiro, C.; Goodsall, T.; Fucik, J.; Hirata, C.; Rhodes, J. D.; Rowe, B. T. P.; Smith, R. M.

2013-09-01

37

Most of the matter in the Universe is not luminous, and can be observed only through its gravitational influence on the appearance of luminous matter. Weak gravitational lensing is a technique that uses the distortions of the images of distant galaxies as a tracer of dark matter: such distortions are induced as the light passes through large-scale distributions of dark

J. Anthony Tyson; David Kirkman; Ian Dell'Antonio; Gary Bernstein; David M. Wittman

2000-01-01

38

The Equivalence of Time and Gravitational Field

NASA Astrophysics Data System (ADS)

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.

Baruk?i?a, Ilija

39

Galilean-invariant scalar fields can strengthen gravitational lensing.

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

Wyman, Mark

2011-05-20

40

Weighing the Cosmological Energy Contents with Weak Gravitational Lensing

NASA Astrophysics Data System (ADS)

Using perturbation theory, Bernardeau, Van Waerbeke, & Mellier show that the skewness of the large-scale lensing convergence, or projected mass density, could be used to constrain ?m, the matter content of the universe. However, deep weak-lensing field surveys in the near future will likely measure the convergence on small angular scales (<~10'), where the signal will be dominated by highly nonlinear fluctuations. We develop a method for computing the small-scale convergence skewness that gives predictions that agree well with existing results from ray-tracing N-body simulations but is significantly faster. We demonstrate that the small-scale convergence skewness is insensitive to the shape and normalization of the primordial (cold dark matter-type) power spectrum, making it dependent almost entirely on the cosmological energy contents. Moreover, nonlinear clustering appears to enhance the differences between predictions of the convergence skewness for a range of models. Hence, in addition to constraining ?m, the small-scale convergence skewness from future deep and several degrees wide surveys can be used to differentiate between curvature-dominated and cosmological constant (?)-dominated models, as well as to constrain the equation of state of a quintessence component, thereby distinguishing ? from quintessence. Finally, our method can be easily generalized to other measures such as the aperture mass statistics.

Hui, Lam

1999-07-01

41

Light clocks in strong gravitational fields

We argue that the time measured by a light clock operating with photons rather than classical light requires a refinement of the standard clock postulate in general relativity. In the presence of a gravitational field, already the one-loop quantum corrections to classical Maxwell theory affect light propagation and the construction of observers' frames of reference. Carefully taking into account these kinematic effects, a concise geometric expression for the time shown by a light clock is obtained. This result has far-reaching implications for physics in strong gravitational fields.

Raffaele Punzi; Frederic P. Schuller; Mattias N. R. Wohlfarth

2009-02-11

42

On the theory of gravitation field

We construct a general relativity formula for the law of gravity for material bodies. The formula contains three numeric parameters that are to be determined experimentally. If they are chosen from symmetry considerations, then the theory that appears is close to the theory of electrodynamics: the gravitational field is given by two vector fields, one can write the energy-momentum tensor, we give an answer on the question what a gravitational wave is. Going to infinity, this wave carries with it the negative energy.

N. N. Chaus

1999-03-12

43

A weak combined magnetic field changes root gravitropism

NASA Astrophysics Data System (ADS)

Immobile higher plants are oriented in the gravitational field due to gravitropim that is a physiological growth reaction and consists of three phases: reception of a gravitational signal by statocytes, its transduction to the elongation zone, and finally the organ bending. According to the starch-statolith hypothesis, amyloplasts in the specialized graviperceptive cells - statocytes sediment in the direction of a gravitational vector in the distal part of a cell. The polar arrangement of organelles is maintained by means of the cytoskeleton. On the Kholodny-Went's, theory the root bending is provided by the polar movement of auxin from a root cap to the elongation zone. It is also known that gravistimulation initiates a rapid Ca2+ redistribution in a root apex. Calcium ions modify an activity of many cytoskeletal proteins and clustering of calcium channels may be directed by actin microfilaments. Although the available data show the Ca2+ and cytoskeleton participation in graviperception and signal transduction, the clear evidence with regard to the participation of cytoskeletal elements and calcium ions in these processes is therefore substantial but still circumstantial and requires new experimental data. Roots are characterized with positive gravitropism, i. e. they grow in the direction of a gravitational vector. It was first shown by us that roots change the direction of a gravitropic reaction under gravistimulation in the weak combined magnetic field with a frequency of 32 Hz. 2-3-day old cress seedlings were gravistimulated in moist chambers, which are placed in ?-metal shields. Inside ? -metal shields, combined magnetic fields have been created. Experiments were performed in darkness at temperature 20±10C. Measurements of the magnitude of magnetic fields were carried out with a flux-gate magnetometer. Cress roots reveal negative gravitropism, i. e. they grow in the opposite direction to a gravitational vector, during 2 h of gravistimulation and then roots begin to grow more or less parallel to the Earth's surface, i.e. they reveal plagiotropism. Since such combined magnetic field is adjusted to the cyclotron frequency of Ca2+ ions, these observations demonstrate the participation of calcium ions in root gravitropism. Cyclotron frequency of Ca2+ ions is the formal frequency of ion rotation in the static magnetic field. Simultaneous applying the altering magnetic field with the same frequency can provoke auto-oscillation in the system and consequently change the rate and/or the direction of Ca2+ ion flow in a root under gravistimulation. The data of light, electron, and confocal laser microscopy and kinetics of a gravitropic reaction, which have been obtained on such the new original model, are discussed in the light of current concepts of root gravitropism.

Kordyum, E. L.; Bogatina, N. I.; Kalinina, Ja. M.; Sheykina, N. V.

44

We study gravitational interaction of Higgs boson through the unique dimension-4 operator $\\xi H^\\dag H R$, with $H$ the Higgs doublet and $R$ the Ricci scalar curvature. We analyze the effect of this dimensionless nonminimal coupling $\\xi$ on weak gauge boson scattering in both Jordan and Einstein frames. We explicitly establish the longitudinal-Goldstone boson equivalence theorem with nonzero $\\xi$ coupling in both frames, and analyze the unitarity constraints. We study the $\\xi$-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(14TeV) and the next generation pp colliders (50-100TeV). 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.

Jing Ren; Zhong-Zhi Xianyu; Hong-Jian He

2014-05-16

45

NASA Astrophysics Data System (ADS)

We study gravitational interaction of Higgs boson through the unique dimension-4 operator ?H†HScript R, with H the Higgs doublet and Script R the Ricci scalar curvature. We analyze the effect of this dimensionless nonminimal coupling ? on weak gauge boson scattering in both Jordan and Einstein frames. We explicitly establish the longitudinal-Goldstone equivalence theorem with nonzero ? coupling in both frames, and analyze the unitarity constraints. We study the ?-induced weak boson scattering cross sections at Script 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.

Ren, Jing; Xianyu, Zhong-Zhi; He, Hong-Jian

2014-06-01

46

Gravitational fields as generalized string models

We show that Einstein's main equations for stationary axisymmetric fields in vacuum are equivalent to the motion equations for bosonic strings moving on a special nonflat background. This new representation is based on the analysis of generalized harmonic maps in which the metric of the target space explicitly depends on the parametrization of the base space. It is shown that this representation is valid for any gravitational field which possesses two commuting Killing vector fields. We introduce the concept of dimensional extension which allows us to consider this type of gravitational fields as strings embedded in D-dimensional nonflat backgrounds, even in the limiting case where the Killing vector fields are hypersurface orthogonal.

Francisco J. Hernandez; Francisco Nettel; Hernando Quevedo

2008-09-25

47

Measures and metrics in uniform gravitational fields

A partially alternative derivation of the expression for the time dilation effect in a uniform static gravitational field is obtained by means of a thought experiment in which rates of clocks at rest at different heights are compared using as reference a clock bound to a free falling reference system (FFRS). Derivations along these lines have already been proposed, but

Marco Alberici

2005-01-01

48

MOND as the weak-field limit of an extended metric theory of gravity

NASA Astrophysics Data System (ADS)

We show that the Modified Newtonian Dynamics (MOND) regime can be fully recovered as the weak-field limit of a particular theory of gravity formulated in the metric approach. This is possible when Milgrom's acceleration constant is taken as a fundamental quantity which couples to the theory in a very consistent manner. As a consequence, the scale invariance of the gravitational interaction is naturally broken. In this sense, Newtonian gravity is the weak-field limit of general relativity and MOND is the weak-field limit of that particular extended theory of gravity.

Mendoza, S.; Bernal, T.; Hidalgo, J. C.; Capozziello, S.

2012-07-01

49

Generalized Gravitational Entropy of Interacting Scalar Field and Maxwell Field

The generalized gravitational entropy proposed by Lewkowycz and Maldacena in recent is extended to the interacting real scalar field and Maxwell field system. Using the BTZ geometry we first investigate the case of free real scalar field and then show a possible way to calculate the entropy of the interacting scalar field. Next, we investigate the Maxwell field system. We exactly solve the wave equation and calculate the analytic value of the generalized gravitational entropy. We also use the Einstein equation to find the effect of backreaction of the Maxwell field on the spacetime. The associated modified area law is consistent with the generalized gravitational entropy. Our investigations have not found the unexpected anomalous surface term.

Huang, Wung-Hong

2014-01-01

50

Rotation of the cosmic microwave background polarization from weak gravitational lensing.

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

Dai, Liang

2014-01-31

51

Statistical properties of filaments in weak gravitational lensing

NASA Astrophysics Data System (ADS)

We study the weak lensing properties of filaments that connect clusters of galaxies through large cosmological N-body simulations. We select 4639 halo pairs with masses higher than 1014 h-1 M? from the simulations and investigate dark matter distributions between two haloes with ray-tracing simulations. In order to classify filament candidates, we estimate convergence profiles and perform profile fitting. We find that matter distributions between haloes can be classified in a plane of fitting parameters, which allows us to select straight filaments from the ray-tracing simulations. We also investigate the statistical properties of these filaments, finding them to be consistent with previous studies. We find that 35 per cent of halo pairs possess straight filaments, 4 per cent of which can be detected directly at signal-to-noise ratio S/N ? 2 with weak lensing. Furthermore, we study the statistical properties of haloes at the edges of filaments. We find that haloes are preferentially elongated along filamentary structures and are less massive with increasing filament mass. However, the dependence of these halo properties on the masses of straight filaments is very weak.

Higuchi, Yuichi; Oguri, Masamune; Shirasaki, Masato

2014-06-01

52

Graphene transparency in weak magnetic fields

NASA Astrophysics Data System (ADS)

We carry out an explicit calculation of the vacuum polarization tensor for an effective low-energy model of monolayer graphene in the presence of a weak magnetic field of intensity B perpendicularly aligned to the membrane. By expanding the quasiparticle propagator in the Schwinger proper time representation up to order (eB)2, where e is the unit charge, we find an explicitly transverse tensor, consistent with gauge invariance. Furthermore, assuming that graphene is irradiated with monochromatic light of frequency ? along the external field direction, from the modified Maxwell equations we derive the intensity of transmitted light. Corrections to this quantity, both calculated and measured, are of the order of (eB)2/?4. Our findings generalize and complement previously known results reported in the literature regarding the light absorption problem in graphene from the experimental and theoretical points of view, with and without external magnetic fields.

Valenzuela, David; Hernández-Ortiz, Saúl; Loewe, Marcelo; Raya, Alfredo

2015-02-01

53

GRAVITATIONAL FIELD SHIELDING AND SUPERNOVA EXPLOSIONS

A new mechanism for supernova explosions called gravitational field shielding is proposed, in accord with a five-dimensional fully covariant Kaluza-Klein theory with a scalar field that unifies the four-dimensional Einsteinian general relativity and Maxwellian electromagnetic theory. It is shown that a dense compact collapsing core of a star will suddenly turn off or completely shield its gravitational field when the core collapses to a critical density, which is inversely proportional to the square of mass of the core. As the core suddenly turns off its gravity, the extremely large pressure immediately stops the core collapse and pushes the mantle material of supernova moving outward. The work done by the pressure in the expansion can be the order of energy released in a supernova explosion. The gravity will resume and stop the core from a further expansion when the core density becomes less than the critical density. Therefore, the gravitational field shielding leads a supernova to impulsively explode and form a compact object such as a neutron star as a remnant. It works such that a compressed spring will shoot the oscillator out when the compressed force is suddenly removed.

Zhang, T. X. [Physics Department, Alabama A and M University, Normal, AL 35762 (United States)

2010-12-20

54

Constraining modified gravitational theories by weak lensing with Euclid

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.

Martinelli, Matteo; Calabrese, Erminia; De Bernardis, Francesco; Melchiorri, Alessandro; Pagano, Luca [Physics Department and INFN, Universita di Roma 'La Sapienza', Ple Aldo Moro 2, 00185, Rome (Italy); Scaramella, Roberto [INAF, Osservatorio Astronomico di Roma, via Frascati 33, 0040 Monte Porzio Catone (Italy)

2011-01-15

55

Lyman Alpha Emitters in gravitational lensed fields

NASA Astrophysics Data System (ADS)

We study the luminosity function of Lyman Alpha Emitters (LAEs) at redshifts between z~6.5 in strong gravitational lensed (GL) fields by clusters of galaxies, using OSIRIS tunable filters (TFs) at the GTC. OSIRIS TFs enhance the emission line contrast, together with the total flux magnification produced by the lens, will be used to detect faint LAEs and to extend the low luminosity queue of the Luminosity Function (LF) of LAEs.

De Leo, M. A.; de Diego, J. A.; Verdugo, T.; Bongiovanni, A.; Cepa, J.; González-Serrano, J. I.

2013-05-01

56

Testing dark energy paradigms with weak gravitational lensing R. Ali Vanderveld,1

Testing dark energy paradigms with weak gravitational lensing R. Ali Vanderveld,1 Michael J all quintessence models, with or without early dark energy. We further explore how uncertainties a given dark energy paradigm, such as the standard CDM model of cold dark matter and a cosmological

Hu, Wayne

57

Constraints on the inner density profile of dark matter haloes from weak gravitational lensing

We construct two linear filtering techniques based on weak gravitational lensing to constrain the inner slope alpha of the density profile of dark matter haloes. Both methods combine all available information into an estimate of this single number. Under idealized assumptions, alpha is constrained to ~15 per cent if the halo concentration c is known, and to <~30 per cent

M. Viola; M. Maturi; M. Bartelmann

2010-01-01

58

Problems in field theoretical approach to gravitation

We consider gravitational self interaction in the lowest approximation and assume that graviton interacts with gravitational energy-momentum tensor in the same way as it interacts with particles. We show that, using gravitational vertex with a preferred gravitational energy-momentum tensor, it is possible to obtain a metric necessary for explaining perihelion precession. The preferred gravitational energy-momentum tensor gives positive gravitational energy density of Newtonian center. We show also that, employing "improvement" technique, any gravitational energy-momentum tensor can be made suitable for using in gravitational wave equation for obtaining metric which explains perihelion precession. Yet the "improvement" leads to negative gravitational energy density of the Newtonian center.

A. I. Nikishov

2004-10-20

59

Gravitational collapse of charged scalar fields

In order to study the gravitational collapse of charged matter we analyze the simple model of an self-gravitating massless scalar field coupled to the electromagnetic field in spherical symmetry. The evolution equations for the Maxwell-Klein-Gordon sector are derived in the 3+1 formalism, and coupled to gravity by means of the stress-energy tensor of these fields. To solve consistently the full system we employ a generalized Baumgarte-Shapiro-Shibata-Nakamura (BSSN) formulation of General Relativity that is adapted to spherical symmetry. We consider two sets of initial data that represent a time symmetric spherical thick shell of charged scalar field, and differ by the fact that one set has zero global electrical charge while the other has non-zero global charge. For compact enough initial shells we find that the configuration doesn't disperse and approaches a final state corresponding to a sub-extremal Reissner-N\\"ordstrom black hole with $|Q|

Jose M. Torres; Miguel Alcubierre

2014-07-29

60

Competition Between Gravitational and Scalar Field Radiation

NASA Astrophysics Data System (ADS)

Recent astrophysical observations have provided strong evidence that the present expansion of the universe is accelerating, powered by the energy density associated with a cosmological term. Assuming the latter to be not simply a constant term but a ``quintessence'' field, we study the radiation of quanta of such a quintessence field (``quintons'') by binary systems of different types and compare intensities to those of standard tensor gravitational wave emission. We consider both the case in which the quintessence field varies only over cosmological distances and the case in which it is modified spatially by (strong) gravitational fields, a condition that results in bounds on the gradient of the scalar field. We show that, in both the first case and, because of a bound we derive from the Hulse-Taylor pulsar, in the second, there is not sufficient quinton radiation to affect expected LISA and LIGO gravity wave signals from binary systems. We show that in the second case, the Large Hadron Collider is capable of setting a bound similar to that from the binary pulsar.

Kazanas, Demosthenes; Teplitz, Vigdor L.

2004-02-01

61

Fast Reconnection of Weak Magnetic Fields

NASA Technical Reports Server (NTRS)

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.

Zweibel, Ellen G.

1998-01-01

62

Mapping the dark matter with weak gravitational lensing

We consider the problem of reconstructing the projected mass distribution in clusters from coherent distortions of background galaxies. The ellipticity of a background galaxy provides an estimate of the trace-free components of the tidal field. We present a technique for inverting this problem. The resulting surface density contains a strong, but incoherent, random component arising from the random intrinsic galaxy

Nick Kaiser; Gordon Squires

1993-01-01

63

Graphene transparency in weak magnetic fields

We carry out an explicit calculation of the vacuum polarization tensor for an effective low-energy model of monolayer graphene in the presence of a weak magnetic field of intensity $B$ perpendicularly aligned to the membrane. By expanding the quasiparticle propagator in the Schwinger proper time representation up to order $(eB)^2$, where $e$ is the unit charge, we find an explicitly transverse tensor, consistent with gauge invariance. Furthermore, assuming that graphene is radiated with monochromatic light of frequency $\\omega$ along the external field direction, from the modified Maxwell's equations we derive the intensity of transmitted light and the angle of polarization rotation in terms of the longitudinal ($\\sigma_{xx}$) and transverse ($\\sigma_{xy}$) conductivities. Corrections to these quantities, both calculated and measured, are of order $(eB)^2/\\omega^4$. Our findings generalize and complement previously known results reported in literature regarding the light absorption problem in graphene from the experimental and theoretical points of view, with and without external magnetic fields.

David Valenzuela; Saúl Hernández-Ortiz; Marcelo Loewe; Alfredo Raya

2014-10-20

64

On seasonal variations of Mars' gravitational field

NASA Technical Reports Server (NTRS)

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.

Chao, B. Fong; Rubincam, David P.

1987-01-01

65

Symmetries in tetrad theories. [of gravitational fields and general relativity

NASA Technical Reports Server (NTRS)

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.

Chinea, F. J.

1988-01-01

66

NASA Astrophysics Data System (ADS)

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

Belvedere, Riccardo; Pugliese, Daniela; Rueda, Jorge A.; Ruffini, Remo; Xue, She-Sheng

2012-06-01

67

Gravitational Descendants in Symplectic Field Theory

NASA Astrophysics Data System (ADS)

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 (

Fabert, Oliver

2011-02-01

68

Consequences of Coupled Electromagnetic-Gravitational Fields

NASA Technical Reports Server (NTRS)

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.

Smalley, Larry

2002-01-01

69

Vacuum polarization in gravitational and electromagnetic fields around a superconducting string

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.

Mankiewicz, L. (Nicolaus Copernicus Astronomical Centre, Polish Academy of Sciences, 00-716 Warsaw, ul. Bartycka 18, Poland (PL)); Misiak, M. (Institute for Theoretical Physics, University of Warsaw, 00-681 Warsaw, ul. Hoza 69, Poland)

1989-09-15

70

Weak Lensing of the Cosmic Microwave Background by Foreground Gravitational Waves

Weak lensing distortion of the background cosmic microwave background (CMB) temperature and polarization patterns by the foreground density fluctuations is well studied in the literature. We discuss the gravitational lensing modification to CMB anisotropies and polarization by a stochastic background of primordial gravitational waves between us and the last scattering surface. While density fluctuations perturb CMB photons via gradient-type deflections only, foreground gravitational waves distort CMB anisotropies via both gradient- and curl-type displacements. The latter is a rotation of background images, while the former is related to the lensing convergence. For a primordial background of inflationary gravitational waves, with an amplitude corresponding to a tensor-to-scalar ratio below the current upper limit of $\\sim$ 0.3, the resulting modifications to the angular power spectra of CMB temperature anisotropy and polarization are below the cosmic variance limit. At tens of arcminute angular scales and below, these corrections, however, are above the level at which systematics must be controlled in all-sky anisotropy and polarization maps with no instrumental noise and other secondary and foreground signals.

Chao Li; Asantha Cooray

2006-04-07

71

We propose the almost-geodesic motion of self-gravitating test bodies as a possible selection rule among metric theories of gravity. Starting from a heuristic statement, the "gravitational weak equivalence principle", we build a formal, operative test able to probe the validity of the principle for any metric theory of gravity, in an arbitrary number of spacetime dimensions. We show that, if the theory admits a well-posed variational formulation, this test singles out only the purely metric theories of gravity. This conclusion reproduces known results in the cases of general relativity (also with a cosmological constant term), and scalar-tensor theories, but extends also to debated or unknown scenarios, such as f(R) and Lanczos-Lovelock theories. We thus provide new tools going beyond the standard methods, where the latter turn out to be inconclusive or inapplicable.

Eolo Di Casola; Stefano Liberati; Sebastiano Sonego

2013-12-30

72

NASA Astrophysics Data System (ADS)

We propose the almost-geodesic motion of self-gravitating test bodies as a possible selection rule among metric theories of gravity. Starting from a heuristic statement, the "gravitational weak equivalence principle," we build a formal operative test able to probe the validity of the principle for any metric theory of gravity in an arbitrary number of spacetime dimensions. We show that, if the theory admits a well-posed variational formulation, this test singles out only the purely metric theories of gravity. This conclusion reproduces known results in the cases of general relativity (as well as with a cosmological constant term) and scalar-tensor theories, but extends also to debated or unknown scenarios, such as the f(R) and Lanczos-Lovelock theories. We thus provide new tools going beyond the standard methods, where the latter turn out to be inconclusive or inapplicable.

Di Casola, Eolo; Liberati, Stefano; Sonego, Sebastiano

2014-04-01

73

We report the first confirmation of colour-selected galaxy cluster candidates by means of weak gravitational lensing. Significant lensing signals were identified in the course of the shear-selection programme of dark matter haloes in the Garching-Bonn Deep Survey, which currently covers 20 square degrees of deep, high-quality imaging data on the southern sky. The detection was made in a field that was previously covered by the ESO Imaging Survey (EIS) in 1997. A highly significant shear-selected mass-concentration perfectly coincides with the richest EIS cluster candidate at z~0.2, thus confirming its cluster nature. Several other shear patterns in the field can also be identified with cluster candidates, one of which could possibly be part of a filament at z~0.45.

Mischa Schirmer; Thomas Erben; Peter Schneider; Christian Wolf; Klaus Meisenheimer

2004-01-12

74

Weak gravitational lensing as a method to constrain unstable dark matter

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.

Wang Meiyu; Zentner, Andrew R. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)

2010-12-15

75

Fermat principle in arbitrary gravitational fields

The Fermat principle is reviewed and used to derive the zigzag path constructed for massive and massless particles in order to determine if these paths are a suitable approximation to the first order of the gravitational lens effect. It is found that such paths are suitable for thin comoving gravitational lenses to the first order in the lens effect, and

Israel Kovner

1990-01-01

76

Gravitational consequences of modern field theories

NASA Technical Reports Server (NTRS)

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.

Horowitz, Gary T.

1989-01-01

77

The Effect of Weak Gravitational Lensing on the Angular Distribution of Gamma-Ray Bursts

If Gamma-Ray Bursts (GRBs) are cosmologically distributed standard candles and are associated with the luminous galaxies, then the observed angular distribution of all GRBs is altered due to weak gravitational lensing of bursts by density inhomogeneities. The amplitude of the effect is generally small. For example, if the current catalogs extend to $z_{max}\\sim 1$ and we live in a flat $\\Omega=1$ Universe, the angular auto-correlation function of GRBs will be enhanced by $\\sim 8\\%$ due to lensing, on all angular scales. For an extreme case of $z_{max}= 1.5$ and ($\\Omega$, $\\Lambda$)=(0.2, 0.8), an enhancement of $\\sim 33\\%$ is predicted. If the observed distribution of GRBs is used in the future to derive power spectra of mass density fluctuations on large angular scales, the effect of weak lensing should probably be taken into account.

L. L. R. Williams

1996-06-10

78

Interaction of gravitational waves with magnetic and electric fields

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.

Barrabes, C.; Hogan, P. A.

2010-03-15

79

Lensing by Distant Clusters: HST Observations of Weak Shear in the Field of 3C324

We present the detection of weak gravitational lensing in the field of the radio galaxy 3C324 (z=1.206) using deep HST imaging. ~From an analysis of the shapes of faint R=24.5-27.5 galaxies in the field we measure a weak, coherent distortion centered close to the radio source. This shear field most likely arises from gravitational lensing of distant field galaxies by a foreground mass concentration. In the light of previous observations of this region, which indicate the presence of a rich cluster around the radio source, we suggest that the most likely candidate for the lens is the cluster associated with the radio galaxy at z=1.2. If so, this is the most distant cluster to have been detected by weak shear observations. Such a statement has two important consequences. Firstly, it shows that massive, collapsed structures exist in the high redshift Universe, and secondly that a significant fraction of the R=24.5-27.5 field galaxy population lies beyond z=1.2.

Ian Smail; Mark Dickinson

1995-10-08

80

Lovelock gravitational field equations in cosmology

We present a systematic study of cosmological solutions in the Lovelock theory of gravitation, including maximally symmetric space-times, Robertson-Walker universes, and product manifolds of symmetric subspaces.

Deruelle, N. (CERN, Theory Division, CH-1211 Geneve 23 (France) Laboratoire de Physique Theorique, Institut Henri Poincare, 11 rue Pierre et Marie Curie, 75005 Paris (France)); Farina-Busto, L. (School of Mathematical Sciences, Queen Mary College, Mile End Road, London E1 4NS (England))

1990-06-15

81

A search for weak stellar magnetic fields

The magnetic fields of normal main sequence stars, supergiants, and mercury-manganese stars were measured in metal lines with the magnetometer of the main stellar spectrograph and in hydrogen lines with the spectropolarimeter at the 6-meter telescope. These data were analyzed statistically with data obtained by other authors. It is concluded that the dipole magnetic fields of the stars studied hardly

Yu. V. Glagolevskij; I. I. Romanyuk; I. D. Najdenov; V. G. Shtol

1991-01-01

82

Search for weak magnetic fields of stars

The magnetic fields of some normal stars of the main sequence, supergiants and Hg-Mn stars have been measured from metallic and hydrogen lines on the 6-m telescope with the Fabry-Perot magnetometer and spectropolarimeter. These results and the data of other authors are statistically analysed. A conclusion is drawn that the studied types of stars hardly contain a magnetic field exceeding

Yu. V. Glagolevskij; I. I. Romanyuk; I. D. Najdenov; V. G. Shtol

1989-01-01

83

Gravitational waves from self-ordering scalar fields

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.

Fenu, Elisa; Durrer, Ruth [Institute de Physique Théorique, Université de Genève, 24 quai E. Ansermet, 1211 Genève 4 (Switzerland); Figueroa, Daniel G.; García-Bellido, Juan, E-mail: elisa.fenu@unige.ch, E-mail: daniel.figueroa@uam.es, E-mail: ruth.durrer@unige.ch, E-mail: juan.garciabellido@uam.es [Instituto de Física Teórica CSIC-UAM and Departamento de Física Teórica, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid (Spain)

2009-10-01

84

Weak lensing studies with GOODS/ACS fields

NASA Astrophysics Data System (ADS)

The main goal of this thesis is to improve current understanding of structure formation in the universe at z ~ 1--2 through weak lensing studies with the Hubble Space Telescope ( HST ) Advanced Camera for Surveys (ACS) data, obtained as part of the Great Observatories Origin Deep Survey (GOODS) project. In this thesis, we present a uniform approach to describes light propagation in both isotropic universe and weakly perturbed universe to discuss the effects of gravitational lensing, apply it to two prime applications of gravitational lensing to cosmology; lensing by dark matter halos and lensing by the large- scale structure, investigate the expected weak lensing effects from the applications and discuss how the effects can be measured through galaxy shape. We describe how galaxy shapes are measured from the GOODS data. We present preliminary measurements of galaxy-galaxy lensing and detection of cosmic shear. We detect a clear galaxy-galaxy lensing signal for lens galaxies at z ~ 0.5 at projected separations ranging from 10" to 200". The detected shear is compatible with ground-based measurements obtained for low-redshift galaxies. We also detect a clear cosmic shear signal using source galaxies at z ~ 1.0. The detected shear is generally consistent with other observations that measured s 8 ~= 0.7.

Park, Yousin

2006-06-01

85

Weak Gravitational Lensing as a Probe of Physical Properties of Substructures in Dark Matter Halos

NASA Astrophysics Data System (ADS)

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 20,000 deg2, 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 1014 h –1 M ? at z = 0.15. Finally we explore the detectability of tidal stripping features for subhalos having a wide range of masses of 1011-1013 h –1 M ?.

Shirasaki, Masato

2015-02-01

86

NASA Astrophysics Data System (ADS)

The electronic energy of H2+ in magnetic fields of up to B=0.2{{B}0} (or 4.7× {{10}4} T) is investigated. Numerical values of the magnetic susceptibility for both the diamagnetic and paramagnetic contributions are reported for arbitrary orientations of the molecule in the magnetic field. It is shown that both diamagnetic and paramagnetic susceptibilities grow with inclination, while paramagnetic susceptibility is systematically much smaller than the diamagnetic one. Accurate two-dimensional Born–Oppenheimer surfaces are obtained with special trial functions. Using these surfaces, vibrational and rotational states are computed and analyzed for the isotopologues H2+ and D2+.

Medel Cobaxin, Héctor; Alijah, Alexander; López Vieyra, Juan Carlos; Turbiner, Alexander V.

2015-02-01

87

Fermat principle in arbitrary gravitational fields

The Fermat principle is reviewed and used to derive the zigzag path constructed for massive and massless particles in order to determine if these paths are a suitable approximation to the first order of the gravitational lens effect. It is found that such paths are suitable for thin comoving gravitational lenses to the first order in the lens effect, and also if there is a nonstationary perturbation. As an example, the Fermat principle is applied to a perturbation by gravitational waves, and the transverse velocity of the caustic motion is derived. This velocity creates difficulty for the proposal by McBreen and Metcalfe (1988) that gamma-ray bursts come from small, hot BL Lac cores crossed by microcaustics. 23 refs.

Kovner, I. (Weizmann Institute of Science, Rehovot (Israel))

1990-03-01

88

In December 1911, Max Abraham published a paper on gravitation at the basis of which was Albert Einstein's 1911 June conclusion about a relationship between the velocity of light and the gravitational potential. In February 1912, Einstein published his work on static gravitational fields, which was based on his 1911 June theory. In March 1912, Einstein corrected his paper, but Abraham claimed that Einstein borrowed his equations; however, it was actually Abraham who needed Einstein's ideas and not the other way round. Einstein thought that Abraham converted to his theory of static fields while Abraham presumed exactly the opposite. Einstein then moved to Zurich and switched to new mathematical tools. He examined various candidates for generally covariant field equations, and already considered the field equations of his general theory of relativity about three years before he published them in November 1915. However, he discarded these equations only to return to them more than three years later. Einstein's 1...

Weinstein, Galina

2012-01-01

89

Unification of Gravitation, Gauge Field and Dark Energy

This paper is composed of two correlated topics: 1. unification of gravitation with gauge fields; 2. the coupling between the daor field and other fields and the origin of dark energy. After introducing the concept of ``daor field" and discussing the daor geometry, we indicate that the complex daor field has two kinds of symmetry transformations. Hence the gravitation and SU(1,3) gauge field are unified under the framework of the complex connection. We propose a first-order nonlinear coupling equation of the daor field, which includes the coupling between the daor field and SU(1,3) gauge field and the coupling between the daor field and the curvature, and from which Einstein's gravitational equation can be deduced. The cosmological observations imply that dark energy cannot be zero, and which will dominate the doom of our Universe. The real part of the daor field self-coupling equation can be regarded as Einstein's equation endowed with the cosmological constant. It shows that dark energy originates from the self-coupling of the space-time curvature, and the energy-momentum tensor is proportional to the square of coupling constant \\lambda. The dark energy density given by our scenario is in agreement with astronomical observations. Furthermore, the Newtonian gravitational constant G and the coupling constant \\epsilon of gauge field satisfy G= \\lambda^{2}\\epsilon^{2}.

Xin-Bing Huang

2005-08-26

90

Gravitational radiation generated by cosmological phase transition magnetic fields

We study gravitational waves generated by the cosmological magnetic fields induced via bubble collisions during the electroweak (EW) and QCD phase transitions. The magnetic field generation mechanisms considered here are based on the use of the fundamental EW minimal supersymmetric and QCD Lagrangians. The gravitational waves spectrum is computed using a magnetohydrodynamic turbulence model. We find that the gravitational wave spectrum amplitude generated by the EW phase transition peaks at a frequency of approximately 1-2 mHz, and is of the order of 10{sup -20}-10{sup -21}; thus this signal is possibly detectable by the Laser Interferometer Space Antenna (LISA). The gravitational waves generated during the QCD phase transition, however, are outside the LISA sensitivity bands.

Kahniashvili, Tina [McWilliams Center for Cosmology and Department of Physics, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213 (United States); Department of Physics, Laurentian University, Sudbury, Ontario P3E 2C6 (Canada); National Astrophysical Observatory, Ilia Chavchavadze State University, Tbilisi, GE-0160 (Georgia); Kisslinger, Leonard [McWilliams Center for Cosmology and Department of Physics, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213 (United States); Stevens, Trevor [Department of Physics, West Virginia Wesleyan College, Buckhannon, West Virginia 26201 (United States)

2010-01-15

91

Gravitational radiation in d>4 from effective field theory

NASA Astrophysics Data System (ADS)

Some years ago, a new powerful technique, known as the classical effective field theory, was proposed to describe classical phenomena in gravitational systems. Here we show how this approach can be useful to investigate theoretically important issues, such as gravitational radiation in any spacetime dimension. In particular, we derive for the first time the Einstein-Infeld-Hoffman Lagrangian and we compute Einstein’s quadrupole formula for any number of flat spacetime dimensions.

Cardoso, Vitor; Dias, Óscar J. C.; Figueras, Pau

2008-11-01

92

Contributions of Spherical Harmonics to Magnetic and Gravitational Fields

NASA Technical Reports Server (NTRS)

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.

Roithmayr, Carlos M.

2004-01-01

93

Using Gravitational Analogies to Introduce Elementary Electrical Field Theory Concepts

ERIC Educational Resources Information Center

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…

Saeli, Susan; MacIsaac, Dan

2007-01-01

94

On the gravitational scattering of gravitational waves

NASA Astrophysics Data System (ADS)

We discuss the scattering of weak gravitational waves from a slowly rotating gravitational source, having mass M and angular momentum J. We start considering the dynamics of a massless spin-2 field {{? }? ? } propagating in the weak gravitational field of the source, writing down the Fierz-Pauli in the presence of a slightly curved background. We adopt a semiclassical framework, where the gravitational background is described as a classical external field; meanwhile, the spin-2 field is treated quantum mechanically. In the weak-coupling limit, in which the typical wavelength of {{? }? ? } satisfies {{? }? }\\gg {{R}s} (where Rs is the Schwarzschild radius of the source), we obtain the cross-section for the scattering process in the Born approximation. We also discuss helicity asymmetry, showing its relationship with the spin-2 field coupling to the derivatives of the background metric. We finally consider the transition to the case of gravitational wave scattering, showing that—under reasonable assumptions—gravitational waves are expected to follow the same behavior. Our results partly agree with those presented through the years by various authors. The present analysis suggests that the scattering of weak gravitational waves in the field of a macroscopic gravitational source still represents an interesting open issue for further careful investigation.

Sorge, Francesco

2015-02-01

95

Probing Dark Energy via Weak Gravitational Lensing with the Supernova Acceleration Probe (SNAP)

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.

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

2005-08-08

96

Field theory on R× S 3 topology. VI: Gravitation

NASA Astrophysics Data System (ADS)

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.

Carmeli, M.; Malin, S.

1987-04-01

97

Geometric Boundary Data for the Gravitational Field

An outstanding issue in the treatment of boundaries in general relativity is the lack of a local geometric interpretation of the necessary boundary data. For the Cauchy problem, the initial data is supplied by the 3-metric and extrinsic curvature of the initial Cauchy hypersurface.. This Cauchy data determines a solution to Einstein's equations which is unique up to a diffeomorphism. Here, we show how three pieces of boundary data, which are associated locally with the geometry of the boundary, likewise determine a solution of the initial-boundary value problem which is unique up to a diffeomorphism. One piece of this data, constructed from the extrinsic curvature of the boundary, determines the dynamical evolution of the boundary. The other two pieces constitute a conformal class of rank-2, positive definite metrics, which represent the two gravitational degrees of freedom.

H-O. Kreiss; J. Winicour

2014-02-25

98

Why are living things sensitive to weak magnetic fields?

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

Liboff, Abraham R

2014-09-01

99

Stochastic quantization of the linearized gravitational field

Stochastic field equations for linearized gravity are presented. The theory is compared with the usual quantum field theory and questions of Lorentz covariance are discussed. The classical radiation approximation is also presented.

Mark P. Davidson

2001-12-13

100

Cosmological electromagnetic fields due to gravitational wave perturbations Mattias Marklund*

Cosmological electromagnetic fields due to gravitational wave perturbations Mattias Marklund and Applied Mathematics, University of Cape Town, Rondebosch 7701, Cape Town, South Africa; and Department of Electromagnetics, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden Peter K. S. Dunsby Department

Dunsby, Peter

101

The MOG weak field approximation and observational test of galaxy rotation curves

NASA Astrophysics Data System (ADS)

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

Moffat, J. W.; Rahvar, S.

2013-12-01

102

Tail terms in gravitational radiation reaction via effective field theory

NASA Astrophysics Data System (ADS)

Gravitational radiation reaction affects the dynamics of gravitationally bound binary systems. Here we focus on the leading “tail” term which modifies binary dynamics at fourth post-Newtonian order, as first computed by Blanchet and Damour. We reproduce this result using effective field theory techniques in the framework of the Lagrangian formalism suitably extended to include dissipation effects. We recover the known logarithmic tail term, consistently with the recent interpretation of the logarithmic tail term in the mass parameter, as a renormalization group effect of the Bondi mass of the system.

Foffa, Stefano; Sturani, Riccardo

2013-02-01

103

Is there a weak mixed polarity background field? Theoretical arguments

NASA Technical Reports Server (NTRS)

A number of processes associated with the formation of active regions produce 'U-loops': fluxtubes having two ends at the photosphere but otherwise still embedded in the convection zone. The mass trapped on the field lines of such loops makes them behave in a qualitatively different way from the 'omega-loops' that form active regions. It is shown that U-loops will disperse though the convection zone and form a weak (down to a few gauss) field that covers a significant fraction of the solar surface. This field is tentatively identified with the inner-network fields observed at Kitt Peak and Big Bear. The process by which these fields escape through the surface is described; a remarkable property is that it can make active region fields apparently disappear in situ. The mixed polarity moving magnetic features near sunspots are interpreted as a locally intense form of this disappearance by escape of U-loops.

Spruit, H. C.; Title, A. M.; Van Ballegooijen, A. A.

1987-01-01

104

Field Equations and Conservation Laws in the Nonsymmetric Gravitational Theory

The field equations in the nonsymmetric gravitational theory are derived from a Lagrangian density using a first-order formalism. Using the general covariance of the Lagrangian density, conservation laws and tensor identities are derived. Among these are the generalized Bianchi identities and the law of energy-momentum conservation. The Lagrangian density is expanded to second-order, and treated as an ``Einstein plus fields'' theory. From this, it is deduced that the energy is positive in the radiation zone.

J. Legare; J. W. Moffat

1994-12-02

105

Gravitational Interaction of Higher Spin Massive Fields and String Theory

We discuss the problem of consistent description of higher spin massive\\u000afields coupled to external gravity. As an example we consider massive field of\\u000aspin 2 in arbitrary gravitational field. Consistency requires the theory to\\u000ahave the same number of degrees of freedom as in flat spacetime and to describe\\u000acausal propagation. By careful analysis of lagrangian structure of the

I. L. Buchbinder; V. D. Pershin

2000-01-01

106

Weighing the Giants: Galaxy Cluster Cosmology Anchored by Weak Gravitational Lensing

NASA Astrophysics Data System (ADS)

The gas mass fractions and the distribution in mass and redshift of the galaxy cluster population provide powerful probes of cosmology, constraining the cosmic matter density (?m), the amplitude of the matter power spectrum (?8), properties of dark energy, and the mass of neutrinos, among other parameters. Historically, these tests have been limited by the absolute accuracy of cluster mass determinations. Here, mass measurements from weak lensing (made in the right way) have an advantage over estimates based on observations of the intracluster medium (ICM), because the former are nearly unbiased and can be straightforwardly tested against simulations. I will report new cosmological constraints obtained from an analysis of X-ray selected cluster samples, incorporating extensive gravitational lensing data from the Weighing the Giants project -- the first cluster cosmology study to consistently integrate a lensing mass calibration, including a rigorous quantification of all systematic uncertainties. Compared with earlier work, which had to incorporate larger systematic allowances associated with an ICM-based mass calibration, our joint constraints on ?m and ?8 are improved by a factor of 2. Including Cosmic Microwave Background and other cosmological probes in the analysis, we find no evidence for non-zero neutrino mass in the current data. This result is directly dependent on the absolute cluster mass calibration, and conflicts with some recent cluster results using ICM-based masses, highlighting the need for an accurate mass calibration (such as lensing provides). We also obtain tight constraints on dark energy models; for flat models with a constant equation of state (w), the cluster data alone yield w=-0.98±0.15. Our data, and their combination with other leading cosmological data sets, remain consistent with the concordance model of cosmology, with zero global curvature, dark energy as a non-evolving cosmological constant (w=-1), minimal neutrino mass, and gravity described by General Relativity.

Mantz, Adam; Von Der Linden, Anja; Allen, Steven W.; Applegate, Douglas; Kelly, Patrick; Morris, Glenn; Rapetti, David; Schmidt, Robert; Ebeling, Harald

2014-08-01

107

A Michelson interferometer in the field of a plane gravitational wave

We treat the problem of a Michelson interferometer in the field of a plane gravitational wave in the framework of general relativity. The arms of the interferometer are regarded as the world lines of the light beams, whose motion is determined by the Hamilton-Jacobi equation for a massless particle. In the case of a weak monochromatic wave we find that the formula for the delay of a light beam agrees with the result obtained by solving the linearized coupled Einstein-Maxwell equations. We also calculate this delay in the next (quadratic) approximation.

Nikodem J. Poplawski

2005-03-16

108

A weak combined magnetic field changes root gravitropism

NASA Astrophysics Data System (ADS)

Although gravitropism has been studied for many decades, many questions on plant gravitropism, including the participation of Ca 2+ ions in graviperception and signal transduction, remain open and require new experiments. We have studied gravistimulation and root gravitropism in the presence of the weak, alternating magnetic field that consisted of a sinusoidal frequency of 32 Hz inside a ?-metal shield. We discovered that this field changes normally positively gravitropic cress root to exhibit negative gravitropism. Because the combined magnetic field was adjusted to the cyclotron frequency of Ca 2+ ions, the obtained data suggest that calcium ion participate in root gravitropism. Simultaneous application of the oscillating magnetic field of the same frequency ion induce oscillation of Ca 2+ ions and can change the rate and/or the direction of Ca 2+ ion flux in roots. Control and magnetic field-exposed roots were examined for change in the distribution of amyloplasts and cellular organelles by light, electron, and confocal laser microscopy.

Kordyum, E. L.; Bogatina, N. I.; Kalinina, Ya. M.; Sheykina, N. V.

109

Anisotropy of magnetic susceptibility measured in variable weak magnetic fields

NASA Astrophysics Data System (ADS)

Theory of the low-field anisotropy of magnetic susceptibility (AMS) of rocks is based on the assumption of the linear relationship between magnetization and magnetizing field, resulting in field independent susceptibility. This relationship is by definition valid in diamagnetic and paramagnetic minerals, while in ferrimagnetic and antiferromagnetic minerals this relationship is in general non-linear (represented by hysteresis loop), being linear only in very weak fields in which the initial susceptibility is measured. Among these minerals, magnetite shows no field variation of susceptibility and its anisotropy in the low fields used in common AMS meters. In pyrrhotite, hematite and titanomagnetite bearing rocks, in which these minerals are very fine-grained, the field variation of susceptibility is insignificant. Using linear theory in calculating the AMS is fully legitimate in all these cases. In pyrrhotite, hematite, and titanomagnetite bearing rocks, in which these minerals are relatively coarse-grained (typically hundreds of micrometers), clear field variation of magnetic susceptibility may exist even in the low fields used in common AMS meters, often resulting in bad fit of the susceptibility tensor to the measured data. Strictly speaking, linear theory in calculating the AMS is in general incorrect in this case. The KLY-3S Kappabridge has been modified in such a way to enable AMS measurement also in the fields down to 3 A/m. Examples are shown of the effect of this field decrease on the measured data.

Pokorny, J.; Suza, P.; Hrouda, F.

2003-04-01

110

NASA Astrophysics Data System (ADS)

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.

Chiba, J.

1984-11-01

111

Gravitational wave in Lorentz violating gravity

By making use of the weak gravitational field approximation, we obtain a linearized solution of the gravitational vacuum field equation in an anisotropic spacetime. The plane-wave solution and dispersion relation of gravitational wave is presented explicitly. There is possibility that the speed of gravitational wave is larger than the speed of light and the casuality still holds. We show that the energy-momentum of gravitational wave in the ansiotropic spacetime is still well defined and conserved.

Xin Li; Zhe Chang

2011-11-06

112

Nonrelativistic field theoretic setting for gravitational self-interactions

It is shown that a recently proposed model for the gravitational interaction in non relativistic quantum mechanics is the instantaneous action at a distance limit of a field theoretic model containing a negative energy field. It reduces to the Schroedinger-Newton theory in a suitable mean field approximation. While both the exact model and its approximation lead to estimates for localization lengths, only the former gives rise to an explicit non unitary dynamics accounting for the emergence of the classical behavior of macroscopic bodies.

Sergio De Filippo

2001-07-09

113

Dynamics of dark energy in the gravitational fields of matter inhomogeneities

NASA Astrophysics Data System (ADS)

We study the dynamical properties and space distribution of dark energy in the weak and strong gravitational fields caused by inhomogeneities of matter in the static world of galaxies and clusters. We show that the dark energy in the weak gravitational fields of matter density perturbations can condense or dilute, but amplitudes of its perturbations remain very small on all scales. We illustrate also how the "accretion" of the phantom dark energy onto the matter overdensity forms the dark energy underdensity. We analyze the behavior of dark energy in the gravitational fields of stars and black holes with the Schwarzschild metric. It is shown that, in the case of stars, the static solution of the differential equations for energy-momentum conservation exists and describes the distribution of density of dark energy inside and outside of a star. We have found that for stars and galaxies its value differs slightly from the average and is a bit higher for the quintessential scalar field as dark energy and a bit lower for the phantom one. The difference grows with the decrease of the effective sound speed of dark energy and is large in the neighborhood of neutron stars. We obtain and analyze also the solutions of equations that describe the stationary accretion of the dark energy as a test component onto the Schwarzschild black hole. It is shown that the rate of change of mass of the dark energy is positive in the case of quintessential dark energy and is negative in the case of the phantom one.

Novosyadlyj, Bohdan; Kulinich, Yurij; Tsizh, Maksym

2014-09-01

114

Gravitational Field Measurements for Understanding Planetary Internal Structures

NASA Astrophysics Data System (ADS)

A powerful tool of investigating the interior structures of planets and their satellites in our solar system is the precision measurement of their gravitational fields. Spacecraft missions to the planets are equipped with quality radio systems for communications and navigation. Along with precision instrumentation at ground stations, the end-to-end radio links provide for very precise tracking of the Doppler effect resulting from the gravity signals. Detailed and proven mathematical formulations are used to construct gravitational fields of various sizes (degree and order) and resolution depending on the length of the mission and coverage of the target body. This has been applied at practically every planet and large satellite in the solar system. Recently, extensive work has been done on the asteroid Vesta and the Moon. This paper will summarize the techniques and methodologies and results from recent missions, such as GRAIL and Dawn, and the implications for interior structure.

Asmar, Sami; Konopliv, Alex

115

Electromagnetic waves in the gravitational field of massive dark halos

The propagation of plane electromagnetic waves in the gravitational field inside a rotating cloud of dark matter is analyzed. Formulas for the deflection and absorption of light, and the rotation of the polarization plane are obtained in closed form in terms of the mass density and the angular velocity of the cloud. It is shown that the formulas can be considerably simplified for axisymmetric configurations. As an example, the formalism is applied to a rotating massive cloud described by a Plummer potential.

Shahen Hacyan

2014-01-31

116

NASA Astrophysics Data System (ADS)

After some historical remarks, we consider observational data on the gravitational lensing, different types of lensing: strong, weak, and microlensing, discovery of planets around distant stars by microlensing. We consider lensing with large deviation angles, when light passes close to the gravitational radius of the lens, and formation of weak relativistic rings. In the last part we consider an influence of plasma on the gravitational lensing. When a gravitating body is surrounded by a plasma, the lensing angle depends on the frequency of the electromagnetic wave, due to dispersion properties of plasma, in presence of a plasma inhomogeneity, and due to a gravity. The second effect leads, even in a uniform plasma, to a difference of the gravitational photon deflection angle from the vacuum case, and to its dependence on the photon frequency. Both effects are taken into account. Dependence of the lensing angle on the photon frequency in a homogeneous plasma resembles the properties of a refractive prism spectrometer, which strongest action is for longest radiowaves. We have shown that the gravitational effect could be detected in the case of a hot gas in the gravitational field of a galaxy cluster.

Bisnovatyi-Kogan, G. S.; Tsupko, O. Yu.

117

BPS Dyon in a Weak Electromagnetic Field: Equations of Motion and Radiation Fields

Dynamics of a BPS dyon in a weak, constant, electromagnetic field is studied through a perturbative analysis of appropriate non-linear field equations. The full Lorentz force law for a BPS dyon is established. Also derived are the radiation fields accompanying the motion.

Dongsu Bak; Choonkyu Lee

1994-02-09

118

Gravitational waves from stochastic relativistic sources: primordial turbulence and magnetic fields

Gravitational waves from stochastic relativistic sources: primordial turbulence and magnetic fields the gravitational waves induced by an incompressible turbulent fluid and by a causal magnetic field present in the early universe. The gravitational wave power spectra show common features: they are both blue on large

Durrer, Ruth

119

The Gravitational Field of a Radiating Electromagnetic Dipole

We begin with the time-dependent electric and magnetic dipole solution of Maxwell's equations in Minkowski space. This Maxwell field is then used to determine the behavior of the gravitational field (the Weyl tensor) as a second-order perturbation off of the Minkowski background. From the Weyl tensor we go on and find the spin-coefficients and the full metric in this approximation. The physical meaning of many of the relations is discussed. In particular we can identify the conservation law of angular momentum that contains an angular momentum flux term.

Tim Adamo; Ezra T Newman

2008-07-22

120

Vacuum Effects in Gravitational Fields: Theory and Detectability

In this thesis, we investigate quantum vacuum effects in the presence of gravitational fields. After discussing the general theory of vacuum effects in strong fields we apply it to the relevant issue of the interaction of the quantum vacuum with black hole geometries. In particular we consider the long-standing problem of the interpretation of gravitational entropy. After these investigations, we discuss the possible experimental tests of particle creation from the quantum vacuum. This leads us to study acoustic geometries and their way of ``simulating'' gravitational structures, such as horizons and black holes. We study the stability of these structures and the problems related to setting up experimental detection of ``phonon Hawking flux'' from acoustic horizons. This line of research then leads us to propose a new model for explaining the emission of light in the phenomenon of Sonoluminescence, based on the dynamical Casimir effect. This is possibly amenable to experimental investigation. Finally we consider high energy phenomena in the early universe. In particular we discuss inflation and possible alternative frameworks for solving the cosmological puzzles.

S. Liberati

2000-09-14

121

Quantum limit on time measurement in a gravitational field

NASA Astrophysics Data System (ADS)

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.

Sinha, Supurna; Samuel, Joseph

2015-01-01

122

Quantum Limit on Stability of Clocks in a Gravitational Field

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 1 part in $10^{18}$ using an Ytterbium clock. This naturally raises the question of whether there are fundamental limits to the stability of clocks. In this paper we point out that gravity and quantum mechanics set a fundamental limit on the stability 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 hydrogen maser clock in a terrestrial gravitational field cannot achieve a stability better than one part in $10^{22}$. This observation has implications for laboratory experiments involving both gravity and quantum theory.

Supurna Sinha; Joseph Samuel

2014-03-21

123

Apparatus and method for producing an artificial gravitational field

NASA Technical Reports Server (NTRS)

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.

Mccanna, Jason (inventor)

1993-01-01

124

Effective field theory of weakly coupled inflationary models

NASA Astrophysics Data System (ADS)

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 ? ~ p2. 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.

Gwyn, Rhiannon; Palma, Gonzalo A.; Sakellariadou, Mairi; Sypsas, Spyros

2013-04-01

125

Effective field theory of weakly coupled inflationary models

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.

Gwyn, Rhiannon [Max-Planck-Institut für Gravitationsphysik, Albert-Einstein-Institut, Am Mühlenberg 1, D-14476 Potsdam (Germany); Palma, Gonzalo A. [Physics Department, FCFM, Universidad de Chile, Blanco Encalada 2008, Santiago (Chile); Sakellariadou, Mairi; Sypsas, Spyros, E-mail: rhiannon.gwyn@aei.mpg.de, E-mail: gpalmaquilod@ing.uchile.cl, E-mail: mairi.sakellariadou@kcl.ac.uk, E-mail: spyridon.sypsas@kcl.ac.uk [Department of Physics, King's College London, Strand, London WC2R 2LS (United Kingdom)

2013-04-01

126

The MOG weak field approximation - II. Observational test of Chandra X-ray clusters

NASA Astrophysics Data System (ADS)

We apply the weak field approximation limit of the covariant scalar-tensor-vector gravity theory, so-called MOdified gravity (MOG), to the dynamics of clusters of galaxies by using only baryonic matter. The MOG effective gravitational potential in the weak field approximation is composed of an attractive Newtonian term and a repulsive Yukawa term with two parameters ? and ?. The numerical values of these parameters have been obtained by fitting the predicted rotation curves of galaxies to observational data, yielding the best-fitting result: ? = 8.89 ± 0.34 and ? = 0.042 ± 0.004 kpc-1. We extend the observational test of this theory to clusters of galaxies, using data for the ionized gas and the temperature profile of nearby clusters obtained by the Chandra X-ray telescope. Using the MOG virial theorem for clusters, we compare the mass profiles of clusters from observation and theory for 11 clusters. The theoretical mass profiles for the inner parts of clusters exceed the observational data. However, the observational data for the inner parts of clusters (i.e. r < 0.1r500) is scattered, but at distances larger than ˜300 kpc, the observed and predicted mass profiles converge. Our results indicate that MOG as a theory of modified gravity is compatible with the observational data from the Solar system to megaparsec scales without invoking dark matter.

Moffat, J. W.; Rahvar, S.

2014-07-01

127

Proton-Proton Weak Capture in Chiral Effective Field Theory

The astrophysical $S$-factor for proton-proton weak capture is calculated in chiral effective field theory over the center-of-mass relative-energy range 0--100 keV. The chiral two-nucleon potential derived up to next-to-next-to-next-to leading order is augmented by the full electromagnetic interaction including, beyond Coulomb, two-photon and vacuum-polarization corrections. The low-energy constants (LEC's) entering the weak current operators are fixed so as to reproduce the $A=3$ binding energies and magnetic moments, and the Gamow-Teller matrix element in tritium $\\beta$ decay. Contributions from $S$ and $P$ partial waves in the incoming two-proton channel are retained. The $S$-factor at zero energy is found to be $S(0)=(4.030 \\pm 0.006)\\times 10^{-23}$ MeV fm$^2$, with a $P$-wave contribution of $0.020\\times 10^{-23}$ MeV fm$^2$. The theoretical uncertainty is due to the fitting procedure of the LEC's and to the cutoff dependence. It is shown that polynomial fits to parametrize the energy dependence of the $S$-factor are inherently unstable.

Marcucci, Laura Elisa [Pisa U., INFN-Pisa; Schiavilla, Rocco [Old Dominion U., JLAB; Viviani, MIchele [INFN-Pisa

2013-05-01

128

Polarization modes for strong-field gravitational waves

Strong-field gravitational plane waves are often represented in either the Rosen or Brinkmann forms. These forms are related by a coordinate transformation, so they should describe essentially the same physics, but the two forms treat polarization states quite differently. Both deal well with linear polarizations, but there is a qualitative difference in the way they deal with circular, elliptic, and more general polarization states. In this article we will describe a general algorithm for constructing arbitrary polarization states in the Rosen form.

Bethan Cropp; Matt Visser

2010-11-25

129

Constants of motion in stationary axisymmetric gravitational fields

The motion of test particles in stationary axisymmetric gravitational fields is generally nonintegrable unless a nontrivial constant of motion, in addition to energy and angular momentum along the symmetry axis, exists. The Carter constant in Kerr-de Sitter spacetime 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 nontrivial 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 spacetime, the mass moments of this class satisfy a "no-hair" recursion relation $M_{2l+2}=a^2 M_{2l}$, and the constant is Noether-related to a second-order Killing-St\\"ackel tensor. Second, solving a new set of quartic integrability conditions, we establish nonexistence of quartic constants. Remarkably, a subset of these conditions is satisfied when the mass moments obey a generalized "no-hair" recursion relation $M_{2l+4}=(a^2+b^2)M_{2l+2}-a^2b^2 M_{2l}$. The full set of quartic integrability conditions, however, cannot be satisfied nontrivially by any stationary axisymmetric vacuum potential.

Charalampos Markakis

2014-05-29

130

NASA Technical Reports Server (NTRS)

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.

Eby, P. B.

1978-01-01

131

Singularity analysis of potential fields to enhance weak anomalies

NASA Astrophysics Data System (ADS)

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.

Chen, G.; Cheng, Q.; Liu, T.

2013-12-01

132

Electromagnetic signatures of far-field gravitational radiation in the 1+3 approach

Gravitational waves from astrophysical sources can interact with background electromagnetic fields, giving rise to distinctive and potentially detectable electromagnetic signatures. In this paper, we study such interactions for far-field gravitational radiation using the 1+3 approach to relativity. Linearised equations for the electromagnetic field on perturbed Minkowski space are derived and solved analytically. The inverse Gertsenshtein conversion of gravitational waves in a static electromagnetic field is rederived, and the resultant electromagnetic radiation is shown to be significant for highly magnetised pulsars in compact binary systems. We also obtain a variety of nonlinear interference effects for interacting gravitational and electromagnetic waves, although wave-wave resonances previously described in the literature are absent when the electric-magnetic self-interaction is taken into account. The fluctuation and amplification of electromagnetic energy flux as the gravitational wave strength increases towards the gravitational-electromagnetic frequency ratio is a possible signature of gravitational radiation from extended astrophysical sources.

Alvin J. K. Chua; Priscilla Cañizares; Jonathan R. Gair

2014-06-14

133

Far fields, from electrodynamics to gravitation, and the dark matter problem

Far fields, from electrodynamics to gravitation, and the dark matter problem A. Carati1 , S. The main idea is that the missing gravitational action may be due to the external far galaxies of electrodynamics and those of gravitation theory, in order to understand the dominant role of the far galaxies. 1

Carati, Andrea

134

NASA Astrophysics Data System (ADS)

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 (?), 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. ? = F [Er(?), Ep(?), Ef(?), Em(?)] (1) This work is an attempt to achieve the unification of the forces of nature, based on the existence of a four dimension Universe.

Rivera, Susana

135

Gravitational Waves and Scalar Perturbations from Spectator Fields

The most conventional mechanism for gravitational waves (gw) production during inflation is the amplification of vacuum metric fluctuations. In this case the gw production can be uniquely related to the inflationary expansion rate $H$. For example, a gw detection close to the present experimental limit (tensor-to-scalar ratio $r \\sim 0.1$) would indicate an inflationary expansion rate close to $10^{14} \\, {\\rm GeV}$. This conclusion, however, would be invalid if the observed gw originated from a different source. We construct and study one of the possible covariant formulations of the mechanism suggested in [43], where a spectator field $\\sigma$ with a sound speed $c_{s} \\ll 1$ acts as a source for gw during inflation. In our formulation $\\sigma$ is described by a so-called $P(X)$ Lagrangian and a non-minimal coupling to gravity. This field interacts only gravitationally with the inflaton, which has a standard action. We compute the amount of scalar and tensor density fluctuations produced by $\\sigma$ and find that, in our realization, $r$ is not enhanced with respect to the standard result but it is strongly sensitive to $c_s$, thus breaking the direct $r \\leftrightarrow H$ connection.

Matteo Biagetti; Emanuela Dimastrogiovanni; Matteo Fasiello; Marco Peloso

2014-11-12

136

Variations in Gravitational Field, Tidal Force, Electromagnetic Waves and Earthquakes

NASA Astrophysics Data System (ADS)

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.

Strasser, Valentino

2010-12-01

137

Equilibrium of multi-phase systems in gravitational fields.

Four necessary conditions for equilibrium of an isolated solid-liquid-vapor system in a gravitational field were derived by Ward and Sasges (1998) in a unified setting, by using an entropy maximization approach, and under the assumption that the liquid-vapor surface tension does not depend on elevation. These are thermal equilibrium, the Laplace and Young equations, and a condition on the chemical potentials of the components present in the system. Gibbs (1876) had obtained the Young equation in a derivation separate from the derivation of the other three conditions and by using an energy minimization approach. However, Gibbs had derived a more general form of the Laplace equation than Ward and Sasges's. Gibbs's equation contained a term expressing the contribution of the variation of surface tension with elevation. This equation has since been neglected by most of the scientific community. In the present paper, the same approach as Ward and Sasges's is used to derive, in an unified setting, the conditions for equilibrium of an isolated solid-liquid-vapor system in a gravitational field but under the assumption that the liquid-vapor surface tension may depend on elevation. The four well-known conditions for equilibrium are obtained, with Gibbs's generalized Laplace equation instead of the classical Laplace equation. The derivations in this paper were carried out for two different system geometries, namely, for a sessile drop and for a conical capillary tube, and similar conditions for equilibrium were obtained. PMID:18729502

Voitcu, Ovidiu; Elliott, Janet A W

2008-09-25

138

Gravitational Waves and Scalar Perturbations from Spectator Fields

The most conventional mechanism for gravitational waves (gw) production during inflation is the amplification of vacuum metric fluctuations. In this case the gw production can be uniquely related to the inflationary expansion rate $H$. For example, a gw detection close to the present experimental limit (tensor-to-scalar ratio $r \\sim 0.1$) would indicate an inflationary expansion rate close to $10^{14} \\, {\\rm GeV}$. This conclusion, however, would be invalid if the observed gw originated from a different source. We construct and study one of the possible covariant formulations of the mechanism suggested in [43], where a spectator field $\\sigma$ with a sound speed $c_{s} \\ll 1$ acts as a source for gw during inflation. In our formulation $\\sigma$ is described by a so-called $P(X)$ Lagrangian and a non-minimal coupling to gravity. This field interacts only gravitationally with the inflaton, which has a standard action. We compute the amount of scalar and tensor density fluctuations produced by $\\sigma$ and fin...

Biagetti, Matteo; Fasiello, Matteo; Peloso, Marco

2014-01-01

139

Field theory and weak Euler-Lagrange equation for classical particle-field systems

NASA Astrophysics Data System (ADS)

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.

Qin, Hong; Burby, Joshua W.; Davidson, Ronald C.

2014-10-01

140

Field theory and weak Euler-Lagrange equation for classical particle-field systems.

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

Qin, Hong; Burby, Joshua W; Davidson, Ronald C

2014-10-01

141

Gravitational waves from neutron stars with large toroidal B fields

NASA Astrophysics Data System (ADS)

We show that NS's with large toroidal B fields tend naturally to evolve into potent gravitational-wave (GW) emitters. The toroidal field Bt tends to distort the NS into a prolate shape, and this magnetic distortion dominates over the oblateness ``frozen into'' the NS crust for Bt>~3.4×1012 G (?s/300 Hz)2. An elastic NS with frozen-in B field of this magnitude is clearly secularly unstable: the wobble angle between the NS's angular momentum Ji and the star's magnetic axis niB grows on a dissipation time scale until Ji and niB are orthogonal. This final orientation is clearly the optimal one for GW emission. The basic cause of the instability is quite general, so we conjecture that the same final state is reached for a realistic NS, with superfluid core. Assuming this, we show that for LMXB's with Bt~2×1012-2×1014 G, the spindown from GW's is sufficient to balance the accretion torque-supporting a suggestion by Bildsten. The spindown rates of most millisecond pulsars can also be attributed to GW emission sourced by toroidal B fields, and both these sources could be observed by LIGO II. While the first-year spindown of a newborn NS is most likely dominated by electromagnetic processes, reasonable values of Bt and the (external) dipolar field Bd can lead to detectable levels of GW emission, for a newborn NS in our own Galaxy.

Cutler, Curt

2002-10-01

142

Constants of motion in stationary axisymmetric gravitational fields

NASA Astrophysics Data System (ADS)

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.

Markakis, C.

2014-07-01

143

Shape and gravitational field of the ellipsoidal satellites

NASA Astrophysics Data System (ADS)

The shape and gravitational field of ellipsoidal satellites are studied by using the tidal theory. For ellipsoidal satellites, the following conclusions were obtained: Firstly, in the early stage of the satellite formation, strong tidal friction allowed the satellites move in a synchronous orbit and evolve into a triaxial ellipsoidal shape. Because the tidal potential from the associated primary and the centrifugal potential from the satellite spin are nearly fixed at the surface, the early satellites are the viscoelastic celestial body, and their surfaces are nearly in the hydrostatic equilibrium state. The deformation is fixed in the surface of the satellite. By using the related parameters of primary and satellite, the tidal height and the theoretical lengths of three primary radii of the ellipsoidal satellite are calculated. Secondly, the current ellipsoidal satellites nearly maintain their ellipsoidal shape from solidification, which happened a few billion years ago. According to the satellite shape, we estimated the orbital period and spinning angular velocity, and then determined the evolution of the orbit. Lastly, assuming an ellipsoidal satellite originated in the hydrostatic equilibrium state, the surface shape could be determined by tidal, rotation, and additional potentials. However, the shape of the satellite's geoid differs from its surface shape. The relationship between these shapes is discussed and a formula for the gravitational harmonic coefficients is presented.

Gao, BuXi; Huang, Yong

2014-10-01

144

NASA Astrophysics Data System (ADS)

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.

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

145

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.

Peters, Thomas; Klessen, Ralf S.; Federrath, Christoph; Smith, Rowan J. [Zentrum fuer Astronomie, Institut fuer Theoretische Astrophysik, Universitaet Heidelberg, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany); Schleicher, Dominik R. G. [Institut fuer Astrophysik, Georg-August-Universitaet, Friedrich-Hund-Platz 1, D-37077 Goettingen (Germany); Banerjee, Robi [Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg (Germany); Sur, Sharanya, E-mail: tpeters@physik.uzh.ch [Raman Research Institute, C. V. Raman Avenue, Sadashivnagar, Bangalore 560080 (India)

2012-12-01

146

Deep HST imaging of distant weak radio and field galaxies

NASA Astrophysics Data System (ADS)

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 (m2750 UBVRIgriJHK) photometry for a subset of the galaxies and bootstrap the unknown FOC/48 zero point at 2750 A in three independent ways (yielding m2750 = 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 a1/4-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 a1/4 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 a1/4-like profile of effective radius a approximately equal to 1.1 sec (approximately equal to 12 kpc for H0 = 50, q0 = 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.

Windhorst, R. A.; Gordon, J. M.; Pascarelle, S. M.; Schmidtke, P. C.; Keel, W. C.; Burkey, J. M.; Dunlop, J. S.

1994-11-01

147

Deep HST imaging of distant weak radio and field galaxies

NASA Technical Reports Server (NTRS)

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.

Windhorst, R. A.; Gordon, J. M.; Pascarelle, S. M.; Schmidtke, P. C.; Keel, W. C.; Burkey, J. M.; Dunlop, J. S.

1994-01-01

148

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.

Rocha, Jorge V. [CENTRA, Departamento de Fisica, Instituto Superior Tecnico, Universidade Tecnica de Lisboa, Av. Rovisco Pais 1, 1049 Lisboa (Portugal); Cardoso, Vitor [CENTRA, Departamento de Fisica, Instituto Superior Tecnico, Universidade Tecnica de Lisboa, Av. Rovisco Pais 1, 1049 Lisboa (Portugal); Department of Physics and Astronomy, University of Mississippi, University, Mississippi 38677 (United States)

2011-05-15

149

Cosmological equivalence principle and the weak-field limit

NASA Astrophysics Data System (ADS)

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?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 10-10ms-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.

Wiltshire, David L.

2008-10-01

150

Observable gravitational waves from inflation with small field excursions

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.

Hotchkiss, Shaun [Department of Physics, University of Helsinki and Helsinki Institute of Physics, P.O. Box 64, FIN-00014 University of Helsinki (Finland); Mazumdar, Anupam [Physics Department, Lancaster University, Keble Rd, Lancaster LA1 4YB (United Kingdom); Nadathur, Seshadri, E-mail: shaun.hotchkiss@helsinki.fi, E-mail: a.mazumdar@lancaster.ac.uk, E-mail: seshadri@thphys.ox.ac.uk [Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3NP (United Kingdom)

2012-02-01

151

Comment on 'Primordial magnetic seed field amplification by gravitational waves'

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.

Tsagas, Christos G. [Section of Astrophysics, Astronomy and Mechanics, Department of Physics, Aristotle University of Thessaloniki, Thessaloniki 54124 (Greece)

2007-04-15

152

CHARGED TORI IN SPHERICAL GRAVITATIONAL AND DIPOLAR MAGNETIC FIELDS

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.

Slany, P.; Kovar, J.; Stuchlik, Z. [Institute of Physics, Faculty of Philosophy and Science, Silesian University in Opava Bezrucovo nam. 13, CZ-746 01 Opava (Czech Republic)] [Institute of Physics, Faculty of Philosophy and Science, Silesian University in Opava Bezrucovo nam. 13, CZ-746 01 Opava (Czech Republic); Karas, V., E-mail: petr.slany@fpf.slu.cz [Astronomical Institute, Academy of Sciences, Bocni II, Prague CZ-141 31 (Czech Republic)

2013-03-01

153

Evolution of external magnetic fields of the stars during their gravitational collapse

NASA Astrophysics Data System (ADS)

The evolution of external electromagnetic field of the stars during their gravitational collapse has been considered. As follows from the calculations, the external magnetic and electrical field of the stars grows very strong during the gravitational collapse. By decreasing radius more than by three orders, the magnetic field increases by millions of times. The external magnetic field of a star increases by billions of times at the final stage of gravitation collapse, reaching values of 1012 Gs near stellar surface. During the collapse the electrical field also increases. At the final stage of the collapse, the electric field increases by billions of times.

Kryvdyk, V.

2015-02-01

154

Relativistic Manifestations of gravitational fields in gravimetry and geodesy

NASA Astrophysics Data System (ADS)

The theoretical principles and methods of the relativistic gravimetry and geodesy are established in the framework of General Relativity. A gravitational field and properties of geocentric and topocentric coordinate systems are described by the specific form of metric tensor, which is obtained from the Einstein equations with the help of the post-Newtonian iterations. By matching of asymptotic, post-Newtonian expansions of the metric tensor in the geocentric and topocentric coordinates we have derived the relationship between these reference systems as well as relativistic corrections to the Earth's gravity force and its gradient. Besides, a new term in the Newtonian definition of the Earth's gravity force was discovered. Two possible definitions of relativistic geoid are considered, namely: 1) the surface, formed by imaginary infinite set of ideal clocks, which have a constant rate of proper time with respect to geocentric coordinate time (u-geoid); 2) the surface, which is orthogonal to the vector field of the directions of plumb line (a-geoid). The equation of surface of the relativistic geoid is obtained. It is shown, that u- and a- geoids coincide under condition of constant rigid-body rotation of the Earth. The notion of relativistic level surface of the self-gravitating perfect fluid, taken as a model of the Earth's matter, is considered. It is proved, that under conditions of constant rigid rotation of the fluid and hydrostatic behavior of tides, the post-Newtonian equation of the level surface is the same as the one of the relativistic geoid. In conclusion, relativistic generalization of the Clairaut's equation is obtained.

Kopejkin, S. M.

1991-01-01

155

On the Field-Redefinition Theorem in Gravitational Theories

NASA Astrophysics Data System (ADS)

The gravitational sector of classical Lagrangian theories can generally be expressed in the form of a power series L = sqrt {-g} [-1 over 2 kappa -2 R+ sum n=2infty (an Rn+tilde an partial 2 Rn ) ], where kappa 2 is the gravitational coupling and R is the Ricci scalar. By means of a metric field-redefinition gij rightarrow (1+beta R)gij + gamma Rij+ delta RikRjk + . . . , the quadratic terms R2 can be removed completely (due to the Gauss-Bonnet identity) and the cubic and higher-order terms Rn partially, only those terms constructed solely from the Riemann tensor Rijkl remaining invariant. It has been shown by Lawrence, however, that the implementation of this procedure at a specific order n inevitably gives rise to ghosts at the next and higher orders n'ge n+1, in the sense that a term Rn in L is replaced by terms Rn-m(partial 2R)m, for example. Classically, these ghosts may lead to instabilities, and it is therefore necessary to investigate the stability of the theory to linear perturbations, both before and after the metric has been transformed. In the cosmological Friedmann space-time ds2=dt2-a02 e2alpha (t) dx2 which describes the Universe, where t is comoving time and a0 ealpha (t) is the radius function of the three-space dx2, assumed flat, we find, by examining the characteristic equation, that the low-energy solution invariably possesses exponentially growing (and decaying) modes, after carrying out the field redefinition, irrespective of whether such modes were present initially. Therefore, it is not expedient to redefine the metric in this background, which, rather, should be considered as fixed. We discuss the relevance of this result for the heterotic superstring theory, particularly with regard to the vacuum solutions obtained previously from the effective Lagrangian including terms n le 4, and to the terms R2.

Pollock, M. D.

2008-06-01

156

The effects of strong magnetic and gravitational fields on emission properties of neutron stars

Neutron stars offer us a unique medium to study the physics of intense magnetic and gravitational fields. They can be magnetized so strongly that exotic quantum electrodynamical processes become important. With their strong gravity, they can gravitationally lens radiation from their own surfaces. In this thesis, I study how these fields affect the physical processes and the interactions of photons

Feryal Ozel

2002-01-01

157

In this work the collapsing process of a spherically symmetric star, made of dust cloud, in the background of dark energy is studied for two different gravity theories separately, i.e., DGP Brane gravity and Loop Quantum gravity. Two types of dark energy fluids, namely, Modified Chaplygin gas and Generalised Cosmic Chaplygin gas are considered for each model. Graphs are drawn to characterize the nature and the probable outcome of gravitational collapse. A comparative study is done between the collapsing process in the two different gravity theories. It is found that in case of dark matter, there is a great possibility of collapse and consequent formation of Black hole. In case of dark energy possibility of collapse is far lesser compared to the other cases, due to the large negative pressure of dark energy component. There is an increase in mass of the cloud in case of dark matter collapse due to matter accumulation. The mass decreases considerably in case of dark energy due to dark energy accretion on the cloud. In case of collapse with a combination of dark energy and dark matter, it is found that in the absence of interaction there is a far better possibility of formation of black hole in DGP brane model compared to Loop quantum cosmology model.

Prabir Rudra; Ritabrata Biswas; Ujjal Debnath

2012-04-03

158

Influence of strong field vacuum polarization on gravitational-electromagnetic wave interaction

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.

Forsberg, M.; Brodin, G. [Department of Physics, Umeaa University, SE-901 87 Umeaa (Sweden); Papadopoulos, D. [Department of Physics, Section of Astrophysics, Astronomy and Mechanics, 54124 Thessaloniki (Greece)

2010-07-15

159

Electromagnetic signatures of far-field gravitational radiation in the 1 + 3 approach

NASA Astrophysics Data System (ADS)

Gravitational waves (GWs) from astrophysical sources can interact with background electromagnetic fields, giving rise to distinctive and potentially detectable electromagnetic signatures. In this paper, we study such interactions for far-field gravitational radiation using the 1 + 3 approach to relativity. Linearized equations for the electromagnetic field on perturbed Minkowski space are derived and solved analytically. The inverse Gertsenshte?n conversion of GWs in a static electromagnetic field is rederived, and the resultant electromagnetic radiation is shown to be significant for highly magnetized pulsars in compact binary systems. We also obtain a variety of nonlinear interference effects for interacting gravitational and electromagnetic waves, although wave–wave resonances previously described in the literature are absent when the electric–magnetic self-interaction is taken into account. The fluctuation and amplification of electromagnetic energy flux as the GW strength increases towards the gravitational–electromagnetic frequency ratio is a possible signature of gravitational radiation from extended astrophysical sources.

Chua, Alvin J. K.; Cañizares, Priscilla; Gair, Jonathan R.

2015-01-01

160

Probing Strong-field General Relativity with Gravitational Waves

NASA Astrophysics Data System (ADS)

We are on the verge of a new era in astrophysics as a world-wide effort to observe the universe with gravitational waves takes hold---ground based laser interferometers (Hz to kHz), pulsar timing (micro to nano Hz), measurements of polarization of the cosmic microwave background (sub-nano Hz), and the planned NASA/ESA mission LISA (.1 mHz to .1 Hz). This project will study the theoretical nature of gravitational waves (GWs) emitted by two sources in the LISA band, namely supermassive-black-hole (SMBH) binary mergers, and extreme-mass-ratio-inspirals (EMRI's)---the merger of a stellar mass black hole, neutron star, or white dwarf with a SMBH. The primary goal will be to ascertain how well LISA, by observing these sources, could answer the following related questions about the fundamental nature of strong-field gravity: Does Einstein's theory of general relativity (GR) describe the geometry of black holes in the universe? What constraints can GW observations of SMBH mergers and EMRIs place on alternative theories of gravity? If there are deviations from GR, are there statistics that could give indications of a deviation if sources are detected using a search strategy based solely on GR waveforms? The primary reasons for focusing on LISA sources to answer these questions are (a) binary SMBH mergers could be detected by LISA with exquisitely high signal-to- noise, allowing enough parameters of the system to be accurately extracted to perform consistency checks of the underlying theory, (b) EMRIs will spend numerous orbits close to the central black hole, and thus will be quite sensitive to even small near-horizon deviations from GR. One approach to develop the requisite knowledge and tools to answer these questions is to study a concrete, theoretically viable alternative to GR. We will focus on the dynamical variant of Chern-Simons modified gravity (CSMG), which is interesting for several reasons, chief among which are (1) that CSMG generically arises in both string theory and loop quantum gravity, and (2) that although CSMG is consistent with all present day tests of GR, it still allows for significant, near-horizon deformations in the geometry of rotating (Kerr) black holes. Here is a brief list of the steps and research methodology we will employ:?(i) Obtain the equivalent of the full Kerr solution in CSMG using numerical methods. (ii) Explore the structure of GWs emitted by EMRIs about the CS rotating black hole solution. Given simulated LISA noise curves, we can then address the questions posed above within the context of CSMG. (iii) Simulate the latter stages of comparable mass SMBH binary mergers in CSMG by numerically solving the full CSMG field equations to learn about highly dynamical, non- linear GR deformations. We can then repeat the analysis of (ii). (iv) Study whether CSMG GWs fit in the recently proposed parameterized post- Einsteinian (ppE) framework, to study generic deviations from GR in a statistical fashion. One can then repeat the analysis of (ii) but within the ppE scheme. We believe this proposed work is of significance and import to both the objectives of this solicitation, and the interests of NASA---knowing the nature of strong-field gravity will be one of the keys to unraveling the origin of the universe, and will tell us how black holes behave and interact with their environs, the details of which are important in understanding the formation and evolution of structure in the universe. Furthermore, these questions are best suited to be answered by LISA, a planned joint NASA-ESA mission. The ultimate success of LISA is very much dependent on (amongst other things) how well the community understands the complete nature of gravitational wave sources.

Pretorius, Frans

161

Was Newton right? A search for non-Newtonian behavior of weak-field gravity

NASA Astrophysics Data System (ADS)

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.

Boynton, Paul; Moore, Michael; Newman, Riley; Berg, Eric; Bonicalzi, Ricco; McKenney, Keven

2014-06-01

162

Effective Field Theory Methods in Gravitational Physics and Tests of Gravity

NASA Astrophysics Data System (ADS)

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.

Cannella, Umberto

2011-03-01

163

Field Methods for Characterizing Weak Rock for Engineering

that describe weak rock units, based on a review of technical literature. Some of these properties, particularly near the ground surface or along fractures.'' Santi and Doyle (1997) also note, ``although systems, Chapman and others (1976) note that shale classification systems have fallen into three

164

Baryon masses in the three-state Potts field theory in a weak magnetic field

NASA Astrophysics Data System (ADS)

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 particles—the 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.

Rutkevich, S. B.

2015-01-01

165

Do the constants of nature couple to strong gravitational fields?

Recently, white dwarf stars have found a new use in the fundamental physics community. Many prospective theories of the fundamental interactions of Nature allow traditional constants, like the fine structure constant $\\alpha$, to vary in some way. A study by Berengut et al. (2013) used the Fe/Ni V line measurements made by Preval et al. (2013) from the hot DA white dwarf G191-B2B, in an attempt to detect any variation in $\\alpha$. It was found that the Fe V lines indicated an increasing alpha, whereas the Ni V lines indicated a decreasing alpha. Possible explanations for this could be misidentification of the lines, inaccurate atomic data, or wavelength dependent distortion in the spectrum. We examine the first two cases by using a high S/N reference spectrum from the hot sdO BD+28$^{\\circ}$4211 to calibrate the Fe/Ni V atomic data. With this new data, we re-evaluate the work of Berengut et al. (2013) to derive a new constraint on the variation of alpha in a gravitational field.

S. P. Preval; M. A. Barstow; J. B. Holberg; J. D. Barrow; J. C. Berengut; J. K. Webb; D. Dougan; J. Hu

2014-10-13

166

Constants of motion in stationary axisymmetric gravitational fields

The motion of a test particle in a stationary axisymmetric gravitational field is generally nonintegrable unless, in addition to the energy and angular momentum about the symmetry axis, an extra nontrivial constant of motion exists. We use a direct approach to systematically search for a nontrivial constant of motion polynomial in the momenta. By solving a set of quadratic integrability conditions, we establish the existence and uniqueness of the family of stationary axisymmetric Newtonian potentials admitting a nontrivial constant quadratic in the momenta. Although such constants do not arise from a group of diffeomorphisms, they are Noether-related to symmetries of the action and associated with irreducible rank-2 Killing-St\\"ackel tensors. The multipole moments of this class of potentials satisfy a no-hair recursion relation $M_{2l+2}=a^2 M_{2l}$ and the associated quadratic constant is the Newtonian analogue of the Carter constant in a Kerr-de Sitter spacetime. We further explore the possibility of invari...

Markakis, Charalampos

2012-01-01

167

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.

Taylor, James E. [Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1 (Canada); Massey, Richard J. [Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE (United Kingdom); Leauthaud, Alexie; Tanaka, Masayuki [Institute for the Physics and Mathematics of the Universe, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8583 (Japan); George, Matthew R. [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Rhodes, Jason; Ellis, Richard; Scoville, Nick [California Institute of Technology, MC 249-17, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Kitching, Thomas D. [Institute for Astronomy, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Capak, Peter [Spitzer Science Center, 314-6 Caltech, 1201 East California Boulevard, Pasadena, CA 91125 (United States); Finoguenov, Alexis [Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse, 85748 Garching (Germany); Ilbert, Olivier; Kneib, Jean-Paul [LAM, CNRS-UNiv Aix-Marseille, 38 rue F. Joliot-Curis, 13013 Marseille (France); Jullo, Eric [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Koekemoer, Anton M., E-mail: taylor@uwaterloo.ca [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2012-04-20

168

Chiral Imprint of a Cosmic Gauge Field on Primordial Gravitational Waves

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.

Bielefeld, Jannis

2014-01-01

169

Constraints on Gravitational Scaling Dimensions from Non-Local Effective Field Equations

Quantum corrections to the classical field equations, induced by a scale dependent gravitational constant, are analyzed in the case of the static isotropic metric. The requirement of general covariance for the resulting non-local effective field equations puts severe restrictions on the nature of the solutions that can be obtained. In general the existence of vacuum solutions to the effective field equations restricts the value of the gravitational scaling exponent $\

Herbert W. Hamber; Ruth M. Williams

2006-07-28

170

General Relativistic Theory of Light Propagation in the Field of Radiative Gravitational Multipoles

The extremely high precision of current astronomical observations demands a much better theoretical treatment of relativistic effects in the propagation of electromagnetic signals through variable gravitational fields of isolated astronomical systems emitting gravitational waves. This paper presents a consistent approach giving a complete and exhaustive solution of this problem in the first post-Minkowskian approximation of general relativity.

Sergei Kopeikin; Pavel Korobkov

2005-10-18

171

Local Determination of the Light Deflection in the Sperically Symmetric Static Gravitational Field

The new method of invariant definition of the measurable angle of light deflection in the static central symmetric gravitational field is suggested. The predicted pure gravitational contribution to the deflection angle slightly differs from its classical estimate and one may hope that this discrepancy could be experimentally detected in the near future. (uuencoded,compressed PostScript, 23 p. inc. 2 fig.)

S. Tertychniy

1993-11-02

172

Scalar-Tensor Theory and Gravitational Waves

An analysis of general scalar-tensor gravitation theory, containing two arbitrary functions of the scalar field, is presented. The weak-field limit is considered in detail, and predictions for the classical tests of gravitation theory are derived. A definite relationship between the light propagation and perihelion shift effects is found to hold under very general conditions. The theory of the detection of

Robert V. Wagoner

1970-01-01

173

Gravitational waves from Abelian gauge fields and cosmic strings at preheating

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.

Dufaux, Jean-Francois [APC, UMR 7164 (CNRS-Universite Paris 7), 10 rue Alice Domon et Leonie Duquet, 75205 Paris Cedex 13 (France); Instituto de Fisica Teorica UAM/CSIC, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Figueroa, Daniel G. [Instituto de Fisica Teorica UAM/CSIC, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Department of Physics, CERN-Theory Division, CH-1211 Geneva 23 (Switzerland); Garcia-Bellido, Juan [Instituto de Fisica Teorica UAM/CSIC, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Departement de Physique Theorique, Universite de Geneve, CH-1211 Geneve 4 (Switzerland)

2010-10-15

174

On the basis of the field concept of gravitation and gravitational analogue of the Faradays induction law the difference of inertial mass of a body at its accelerated movement in horizontal and vertical directions relative to the Earth is shown. For an illustration of such a distinction the results of comparison of a motion of balance mechanical watch at horizontal and vertical orientations of balance axis are given. The expediency of statement of precision mechanical experiments with measurement of anisotropy of the inertial mass is noted, allowing to estimate the validity of the field approach in the description of gravitation.

Alexander L. Dmitriev

2009-03-25

175

Magnetohydrodynamic channel flows with weak transverse magnetic fields.

Magnetohydrodynamic flow of an incompressible fluid through a plane channel with slowly varying walls and a magnetic field applied transverse to the channel is investigated in the high Reynolds number limit. It is found that the magnetic field can first influence the hydrodynamic flow when the Hartmann number reaches a sufficiently large value. The magnetic field is found to suppress the steady and unsteady viscous flow near the channel walls unless the wall shapes become large. PMID:24936018

Rothmayer, A P

2014-07-28

176

Acceleration of low energy charged particles by gravitational waves

The acceleration of charged particles in the presence of a magnetic field and gravitational waves is under consideration. It is shown that the weak gravitational waves can cause the acceleration of low energy particles under appropriate conditions. Such conditions may be satisfied close to the source of the gravitational waves if the magnetized plasma is in a turbulent state.

G. Voyatzis; L. Vlahos; S. Ichtiaroglou; D. Papadopoulos

2005-12-07

177

Gravitational field of a spinning sigma-model cosmic string

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.

Simanek, E. [Department of Physics, University of California, Riverside, California 92521 (United States)

2008-08-15

178

[Research under reduced gravity. Part II: experiments in variable gravitational fields].

Recently, the reduced gravitational field of space laboratories, rockets, or satellites in Earth orbits offers a gravitational field which is variable from 10(-4) g to 1 g by the use of centrifuges. Especially with plants, data concerning gravisensitivity are based on experiments with clinostats. First experiments in reduced gravitational fields, however, demonstrate the uncertainty of these results. Thus, the main task of gravitational biologists is to test the validity of results obtained with the aid of clinostats. On this basis it should be possible to find a common mechanism to explain the influence of gravity on organisms. Experiments under reduced gravity in sounding rockets provided new knowledge on the perception of the gravity stimulus in plant cells. PMID:11536495

Volkmann, D; Sievers, A

1992-03-01

179

Nuclear magnetic absorption line widths in weak magnetic fields with a Robinson oscillator

NUCLEAR MAGNETIC ABSORPTION LINE WIDTHS IN WEAK MAGNETIC FIELDS WITH A ROBINSON OSCILLATOR A Thesis by TIMOTHY LEE FLUGUM Subnntted to the Graduate College of Texas ARM University in partial fulfillment of the requirement for the degree... of MASTER OF SCIENCE August 19SI Major Subject: Physics NUCLEAR MAGNETIC ABSORPTION LINE WIDTHS IN WEAK MAGNETIC FIELDS WITH A ROBINSON OSCILLATOR A Thesis TIMOTHY LEE FLUGUM Approved as to style and content by: Nelson M. Duller (Chairman...

Flugum, Timothy Lee

2012-06-07

180

Chaotic attitude motion of satellites in the central gravitational field

NASA Astrophysics Data System (ADS)

New developments in nonlinear dynamics in the last two decades, especially chaos theory, make it possible to study various dynamic phenomena of nonlinear systems. In the present thesis, the nonlinear attitude motion of a satellite consisting of a single rigid body, or of two rigid bodies in gyrostat configuration, in a central gravitational field, on a circular or an elliptic orbit, is studied with particular attention given to the understanding of long-time dynamic behavior for a wide range of parameters. For the attitude motion of satellites in their orbital plane, it is shown that there exists chaotic motion for satellites with or without internal damping, in an elliptic orbit. It is shown that the system which describes the dynamic behavior of satellites without internal damping is nonintegrable. Thus chaotic motion and regular motion coexist. The connection between periodic motion and chaotic motion for satellites without internal damping is investigated numerically by studying the local bifurcations of periods motion. For satellites with internal damping, analytic criteria based on the Melnikov method are presented to determine whether chaotic motion might occur, and to reveal the connection between periodic motion and chaotic motion. The transition from periodic motion to chaotic motion for satellites with internal damping is studied by three means: phase planes, Poincare maps, and Lyapunov exponents. For the attitude motion of spinning axisymmetric single-body satellites or spinning axisymmetric gyrostat satellites without internal damping in a circular orbit, the Hamiltonians for the attitude motion are established and then used to reveal the characteristics of different types of motion, i.e. periodic motion, quasiperiodic motion, and chaotic motion. It is shown that except for the integrable cases where the attitude motion is either confined to small attitude angles around the equilibrium attitude positions, or the satellites are free of external torques, regular (periodic and quasiperiodic) and chaotic motion coexist depending on initial conditions, and the transition between the two types of motion is complicated. The global characteristics of the chaotic motion are obtained via the Poincare map technique. It is found that for gyrostat satellites with the axes of symmetry of the platform and the rotor coinciding, the rotor has a significant effect not only on the stability of equilibrium attitude positions, but also on the general dynamic behavior of the motion, e.g. a chaotic motion will become more and more regular as the spin velocity of the rotor increases. This is obviously of great importance in the design of gyrostat satellites.

Tong, Xiaohua

181

Iron snow zones as a mechanism for generating Mercury's weak observed magnetic field

to be responsible for the magnetic fields of other planets in the solar system. One possible explanation implies an estimated magnetic field strength of BIron snow zones as a mechanism for generating Mercury's weak observed magnetic field R. Vilim,1 S

Hauck II, Steven A.

182

Electromagnetic Waves in a Uniform Gravitational Field and Planck's Postulate

ERIC Educational Resources Information Center

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…

Acedo, Luis; Tung, Michael M.

2012-01-01

183

the presence of a weak interplanetary magnetic field may lead to the ; formation of a collision-free shock wave upstream from the boundary of the ; geomagnetic field and to a transition region characterized by an irregular ; magnetic field in the intervening space. Previous calculations of the ; coordinates of the shock wave are improved upon by application of

John R. Spreiter; Wm. Prichard Jones

1963-01-01

184

BAYESIAN INFERENCE OF SOLAR AND STELLAR MAGNETIC FIELDS IN THE WEAK-FIELD APPROXIMATION

The weak-field approximation is one of the simplest models that allows us to relate the observed polarization induced by the Zeeman effect with the magnetic field vector present on the plasma of interest. It is usually applied for diagnosing magnetic fields in the solar and stellar atmospheres. A fully Bayesian approach to the inference of magnetic properties in unresolved structures is presented. The analytical expression for the marginal posterior distribution is obtained, from which we can obtain statistically relevant information about the model parameters. The role of a priori information is discussed and a hierarchical procedure is presented that gives robust results that are almost insensitive to the precise election of the prior. The strength of the formalism is demonstrated through an application to IMaX data. Bayesian methods can optimally exploit data from filter polarimeters given the scarcity of spectral information as compared with spectro-polarimeters. The effect of noise and how it degrades our ability to extract information from the Stokes profiles is analyzed in detail.

Asensio Ramos, A., E-mail: aasensio@iac.es [Instituto de Astrofisica de Canarias, 38205, La Laguna, Tenerife (Spain); Departamento de Astrofisica, Universidad de La Laguna, E-38205 La Laguna, Tenerife (Spain)

2011-04-10

185

Computing the Influence of a Gravitational Wave on an Electromagnetic Field

NASA Astrophysics Data System (ADS)

General Relativity applied to electromagnetism: what happens to an electromagnetic field when the spacetime it is embedded in is oscillating? I present a numerical model that answers this question for any arbitrary boundary conditions and properties of the gravitational wave. This is particularly useful as this problem cannot be solved analytically for all but the simplest boundary conditions. The model can be used to determine a gravitational wave’s signature without being restricted to simple boundary conditions like LIGO's interferometers.

Srinivasan, Varadarajan

2015-01-01

186

NASA Technical Reports Server (NTRS)

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.

Voorhies, Coerte V.

2004-01-01

187

The Effect of Weak Combined Magnetic Field on Root Gravitropism and a Role of Ca2+ Ions Therein

NASA Astrophysics Data System (ADS)

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

Kordyum, Elizabeth; Bogatina, Nina; Kondrachuk, A.

188

Impurity-assisted tunneling magnetoresistance under a weak magnetic field.

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

Txoperena, Oihana; Song, Yang; Qing, Lan; Gobbi, Marco; Hueso, Luis E; Dery, Hanan; Casanova, Fèlix

2014-10-01

189

Mean-field universality class induced by weak hyperbolic curvatures.

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)ln n, 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. PMID:25122266

Gendiar, Andrej; Daniška, Michal; Kr?már, Roman; Nishino, Tomotoshi

2014-07-01

190

Solitary waves in two-dimensional dusty plasma crystal: Effects of weak magnetic field

It is shown that in the presence of weak magnetic field, the dust lattice solitary wave in two-dimensional (2D) hexagonal dusty plasma crystal is governed by a gyration-modified 2D Korteweg-de Vries equation due to the action of Lorentz force on the dust particles. Numerical solutions reveal that only for weak magnetic field an apparently single hump solitary wave solution exist. But, for strong magnetic field dust lattice solitary wave becomes unstable showing repetitive solitary hump of increasing magnitude with time.

Ghosh, Samiran [Department of Applied Mathematics, University of Calcutta, 92, Acharya Prafulla Chandra Road, Kolkata-700 009 (India); Gupta, M. R. [Department of Instrumentation Science, Jadavpur University, Kolkata-700 032 (India)

2010-03-15

191

Attempt at demonstrating the effect of a weak magnetic field on Taraxacum officinale

The exposure ofTaraxacum officinale L. at flowering time to a weak magnetic field resulted in (1) retarded opening and the closing of the inflorescence, (2)\\u000a wilting and death after prolonged exposure. Controls were unchanged. Plants exposed to the effect of magnetic fields were\\u000a degenerated in subsequent year.

Josef Novák; Ladislav Válek

1965-01-01

192

Gravitational field-flow fractionation (GFFF) is the simplest and cheapest of field-flow fractionation (FFF) techniques, although it is still at an early development stage. The application of GFFF to the determination of particle size distribution (PSD) of silica particles used as chromatographic supports is described. The accuracy of the method is evaluated by comparing PSDs obtained by GFFF with those obtained

P. Reschiglian; G. Torsi

1995-01-01

193

Embryological changes induced by weak, extremely low frequency electromagnetic fields.

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

Delgado, J M; Leal, J; Monteagudo, J L; Gracia, M G

1982-01-01

194

Lichnerowicz-Type Theorems for Self-gravitating Systems with Nonlinear Electromagnetic Fields

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/AdS) there can't 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.

Li-Ming Cao; Yuxuan Peng; Jianfei Xu

2014-04-26

195

Polarization and Trapping of Weakly Bound Atoms in Penning Trap Fields S. G. Kuzmin and T. M. O'Neil

Polarization and Trapping of Weakly Bound Atoms in Penning Trap Fields S. G. Kuzmin and T. M. O of weakly bound antihydrogen atoms in a non-neutral positron-antiproton plasma. This Letter derives an equation of motion for weakly bound atoms in the electric and magnetic fields of the plasma and trap

California at San Diego, University of

196

Wiggly tails: A gravitational wave signature of massive fields around black holes

NASA Astrophysics Data System (ADS)

Massive fields can exist in long-lived configurations around black holes. We examine how the gravitational wave signal of a perturbed black hole is affected by such "dirtiness" within linear theory. As a concrete example, we consider the gravitational radiation emitted by the infall of a massive scalar field into a Schwarzschild black hole. Whereas part of the scalar field is absorbed/scattered by the black hole and triggers gravitational wave emission, another part lingers in long-lived quasibound states. Solving numerically the Teukolsky master equation for gravitational perturbations coupled to the massive Klein-Gordon equation, we find a characteristic gravitational wave signal, composed by a quasinormal ringing followed by a late time tail. In contrast to "clean" black holes, however, the late time tail contains small amplitude wiggles with the frequency of the dominating quasibound state. Additionally, an observer dependent beating pattern may also be seen. These features were already observed in fully nonlinear studies; our analysis shows they are present at linear level, and, since it reduces to a 1+1 dimensional numerical problem, allows for cleaner numerical data. Moreover, we discuss the power law of the tail and that it only becomes universal sufficiently far away from the dirty black hole. The wiggly tails, by constrast, are a generic feature that may be used as a smoking gun for the presence of massive fields around black holes, either as a linear cloud or as fully nonlinear hair.

Degollado, Juan Carlos; Herdeiro, Carlos A. R.

2014-09-01

197

Gravitational waves from stochastic relativistic sources: primordial turbulence and magnetic fields

The power spectrum of a homogeneous and isotropic stochastic variable, characterized by a finite correlation length, does in general not vanish on scales larger than the correlation scale. If the variable is a divergence free vector field, we demonstrate that its power spectrum is blue on large scales. Accounting for this fact, we compute the gravitational waves induced by an incompressible turbulent fluid and by a causal magnetic field present in the early universe. The gravitational wave power spectra show common features: they are both blue on large scales, and peak at the correlation scale. However, the magnetic field can be treated as a coherent source and it is active for a long time. This results in a very effective conversion of magnetic energy in gravitational wave energy at horizon crossing. Turbulence instead acts as a source for gravitational waves over a time interval much shorter than a Hubble time, and the conversion into gravitational wave energy is much less effective. We also derive a strong constraint on the amplitude of a primordial magnetic field when the correlation length is much smaller than the horizon.

Chiara Caprini; Ruth Durrer

2006-03-17

198

A Test to Verify the Speed Change of Light in the Gravitational Field of the Earth

Based on the Schwarzschild solution of the Einstein equation of gravitational field, it is proved that the speed of light speed would change and isotropy of light speed would be violated in gravitational field with spherical symmetry. On the surface of the earth, the speed of light vertical to the surface is 0.2m/s less than that parallel to the surface. It is suggested to use the method of the Michelson Morley interference to verify the change of light speed and the violation of isotropy in the gravitational field of the earth. In the proposed experiment, one arm of interferometer is vertical to the earth surface while another is parallel to the surface. When two arms are turned over 90 degree, the shift of about 0.07 interference stripe would be caused which can be observed directly. So this experiment can be considered as a new verification for general relativity in the gravitational field with spherical symmetry. If the experiment shows that gravitation would change the speed of light and violate the isotropy of light speed, the result would cause great effects on foundational physics, astrophysics and cosmolo

Mei Xiaochun

2006-11-30

199

Gravitation and electromagnetism in theory of a unified four-vector field

A four-vector field in flat space-time, satisfying a gauge-invariant set of second-order differential equations, is considered as a unified field. The model variational principle corresponds to the general covariance idea and gives rise to nonlinear Born-Infeld electrodynamics. Thus the four-vector field is considered as an electromagnetic potential. It is suggested that space-localized (particle) solutions of the nonlinear field model correspond to material particles. Electromagnetic and gravitational interactions between field particles appear naturally when a many-particle solution is investigated with the help of a perturbation method. The electromagnetic interaction appears in the first order in the small field of distant particles. In the second order, there is an effective Riemannian space induced by the field of distant particles. This Riemannian space can be connected with gravitation.

Alexander A. Chernitskii

2006-09-28

200

Paramagnetic relaxation in anisotropic materials in zero and weak constant fields

NASA Astrophysics Data System (ADS)

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.

Fokina, N. P.; Khalvashi, E. Kh.; Khutsishvili, K. O.

2014-12-01

201

Weak field magnetoresistance of narrow-gap semiconductors InSb

The magnetoresistance of InSb has been intensively investigated. The experiments we perform here focus on weak field magnetoresistance of InSb thin film. We investigate the magnetoresistance of InSb films in perpendicular, tilted as well as parallel magnetic field. Our results verify the previous observations concerning weak localization effect in InSb thin film. Moreover, we systematically study the anisotropy of magnetoresistance of InSb. We find that the existence of in-plane field can effectively suppress the weak localization effect of InSb film. We fit the experimental data with two types of models, the match between data and model is excellent. From the fitting procedure, we get information about phase coherence time, spin-orbit scattering time. The information about Zeeman effect and sample roughness are also extracted from the fitting procedure.

Yang, R; Zhang, Yanhui; Chen, P P

2010-01-01

202

Weak field magnetoresistance of narrow-gap semiconductors InSb

The magnetoresistance of InSb has been intensively investigated. The experiments we perform here focus on weak field magnetoresistance of InSb thin film. We investigate the magnetoresistance of InSb films in perpendicular, tilted as well as parallel magnetic field. Our results verify the previous observations concerning weak localization effect in InSb thin film. Moreover, we systematically study the anisotropy of magnetoresistance of InSb. We find that the existence of in-plane field can effectively suppress the weak localization effect of InSb film. We fit the experimental data with two types of models, the match between data and model is excellent. From the fitting procedure, we get information about phase coherence time, spin-orbit scattering time. The information about Zeeman effect and sample roughness are also extracted from the fitting procedure.

R. Yang; G. L. Yu; Yanhui Zhang; P. P. Chen

2010-05-25

203

Lifetime and decay of unstable particles in strong gravitational fields

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 quasi-thermal spectrum inherent to extremely relativistic observers in circular motion plays a role similar to the Unruh radiation for uniformly accelerated observers.

Douglas Fregolente; Alberto Saa

2007-12-17

204

Universal Scaling and Echoing in Gravitational Collapse of a Complex Scalar Field

This paper studies gravitational collapse of a complex scalar field at the threshold for black hole formation, assuming that the collapse is spherically symmetric and continuously self-similar. A new solution of the coupled Einstein-scalar field equations is derived, after a small amount of numerical work with ordinary differential equations. The universal scaling and echoing behavior discovered by Choptuik in spherically symmetrical gravitational collapse appear in a somewhat different form. Properties of the endstate of the collapse are derived: The collapse leaves behind an irregular outgoing pulse of scalar radiation, with exactly flat spacetime within it.

Eric W. Hirschmann; Douglas M. Eardley

1994-12-21

205

Electromgnetic-gravitational cross-sections in external elctromagnetic fields

The classical processes: the conversion of photons into gravitons in the static electromagnetic fields are considered by using Feynman perturbation techniques. The differential cross sections are presented for the conversion in the electric field of the flat condesor and the magnetic field of the selenoid. A numerical evaluation shows that the cross sections may have the observable value in the present technical scenario.

Hoang Ngoc Long; Dang Van Soa; Tuan A. Tran

1994-10-03

206

K0 meson physics in the gravitation field: a constraint on the equivalence principle

K0-K0bar oscillations are extremely sensitive to the K0 and K0bar energy at rest. Even assuming m_K0=m_K0bar, the energy is not granted to be the same if gravitational effects on K0 and K0bar slightly differ. We consider various gravitation fields present and, in particular, galactic fields, which provide a negligible acceleration, but relatively large gravitational potential energy. A constraint from a possible effect of this potential energy on the kaon oscillations isfound to be |(m_g/m_i)_K0-(m_g/m_i)_K0bar| < 8 x 10^-13 atCL=90%. The derived constraint is competitive with other tests of universality of the free fall. Other applications are also discussed.

Savely G. Karshenboim

2008-11-06

207

Analytical solution from vector potentials for the gravitational field of a general polyhedron

NASA Astrophysics Data System (ADS)

Closed form solutions in terms of elementary functions are given for the Newtonian gravitational field and potential of a general constant density polyhedron, using a gravitational vector potential formulation. The solution constants are given in terms of scalar and vector products involving the position vectors of the field point and the polyhedron's vertices, giving one analytical expression for each edge of the polyhedron. It is shown that in this vector potential formulation, the gravitational problem is related to the point-in-polygon problem of computational geometry. The solution is derived using a new vector theorem giving the integral over a flat surface of a scalar potential as a line integral of a vector potential around its boundary. The method is also valid in the interior of the polyhedron and can be extended to polyhedra with linear spatial variation of the density. Numerical results are compared with results in the literature and detailed results are given for the five regular Platonic polyhedra.

Conway, John T.

2015-01-01

208

Magnetite in human tissues: A mechanism for the biological effects of weak ELF magnetic fields

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.

Kirschvink, J.L.; Kobayashi-Kirschvink, A.; Diaz-Ricci, J.C.; Kirschvink, S.J. (California Institute of Technology, Pasadena (United States))

1992-01-01

209

Stellar explosion in the weak field approximation of the Brans Dicke theory

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

Victor H. Hamity; Daniel E. Barraco

2005-01-01

210

Stellar explosion in the weak field approximation of the Brans–Dicke theory

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

Victor H. Hamity; Daniel E. Barraco

2005-01-01

211

Weak-field magnetoresistance coefficients and the related magnetoresistance skewness effect

49 Weak-field magnetoresistance coefficients and the related magnetoresistance skewness effect D. S the magnetoresistance skewness effect. A comparison with the classical method is also presented to indicate simplified and a new effect is risen, the magnetoresistance skewness (MRS) effect. This effect is expected

Paris-Sud XI, UniversitÃ© de

212

Highly polar states of Rydberg atoms in strong magnetic and weak electric fields

NASA Astrophysics Data System (ADS)

We study the spectra of diamagnetic rubidium Rydberg atoms in strong magnetic and weak electric parallel fields, in the n-mixing regime. Our emphasis is on isolated pairs of near-degenerate, opposite-parity, diamagnetic states that become mixed by the weak electric field. Such level pairs allow for the generation of nondegenerate states with large, tunable permanent electric dipole moments and large optical excitation cross sections from the atomic ground state. We investigate how the dipole moments and the zero-electric-field energy defects of these level pairs can be tuned using small variations of the electric and magnetic fields. Using calculations, we explore the abundance of such level pairs over wide spectral regions for several magnetic quantum numbers. Applications of polar, diamagnetic Rydberg states in Rydberg-atom interaction experiments are briefly discussed.

Paradis, E.; Zigo, S.; Raithel, G.

2013-01-01

213

Detecting weak magnetic fields in the central stars of planetary nebulae

NASA Astrophysics Data System (ADS)

We have carried out low-resolution spectropolarimetric observations with FORS 2, installed on the VLT, ESO, of a representative sample of 12 bright central stars of Planetary Nebulae (PNe) with different morphology. Two of the sample are hydrogen-deficient (Wolf-Rayet type) stars. Our measurements rule out the existence of strong global magnetic fields of the order of kG in any of the PN central stars of our sample. Even so, our data may indicate the presence of weak mean longitudinal magnetic fields of a few hundred Gauss in the central stars of two elliptical nebulae, IC 418 and NGC 2392, and a very weak magnetic field of about 100 G in the Wolf-Rayet type central star Hen 2-113. However, the significance of these marginal detections depends on the method adopted for estimating the uncertainties in the magnetic-field measurements.

Steffen, M.; Hubrig, S.; Todt, H.; Schöller, M.; Sandin, C.; Hamann, W.-R.; Schönberner, D.

2014-11-01

214

NASA Astrophysics Data System (ADS)

In this paper COX’s superpotential is extended to double complex form firstly, then how to get hyperbolic complex superpotential from the known ordinary complex superpotential is discussed, finally, new solutions of stationary axisymmetric gravitational fields are shown with a few specific cases.

Fang, Ge-Liang; Lyu, Yan; Zhang, Guo-Ying

2008-04-01

215

Variations of the gravitational field as a motive power for rhythmics of biochemical processes

NASA Astrophysics Data System (ADS)

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.

Troshichev, O. A.; Gorshkov, E. S.; Shapovalov, S. N.; Sokolovskii, V. V.; Ivanov, V. V.; Vorobeitchikov, V. M.

2004-01-01

216

The general equations describing the equilibrium shapes of self-gravitating gas clouds containing axisymmetric magnetic fields are presented. The general equations admit of a large class of solutions. It is shown that if one additional (ad hoc) asumption is made that the mass be spherically symmetrically distributed, then the gas pressure and the boundary conditions are sufficiently constraining that the general

I. Lerche; B. C. Low

1980-01-01

217

Zonal Harmonics of the Earth's Gravitational Field and the Basic Hypothesis of Geodesy

The basic hypothesis of geodesy as stated by Vening Meinesz and Heiskanen calls for an extremely smooth gravitational field for the earth as a whole, apart from local irregu- larities. From satellite measurements of zonal harmonics of orders 2, 3, and 4 it is shown that the actual roughness is about an order of magnitude greater than that demanded by

John A. O'Keefe

1959-01-01

218

Higgs and gravitational scalar fields together induce Weyl gauge

NASA Astrophysics Data System (ADS)

A common biquadratic potential for the Higgs field and an additional scalar field , non minimally coupled to gravity, is considered in a locally scale symmetric approach to standard model fields in curved spacetime. A common ground state of the two scalar fields exists and couples both fields to gravity, more precisely to Weyl geometric scalar curvature . In Einstein gauge (, often called "Einstein frame"), also is scaled to a constant. This condition makes perfect sense, even in the general case, in the Weyl geometric approach. There it has been called Weyl gauge, because it was first considered by Weyl in the different context of his original scale geometric theory of gravity of 1918. Now it may get new meaning as a combined effect of electroweak theory and gravity, and their common influence on atomic frequencies.

Scholz, Erhard

2015-02-01

219

Higgs and gravitational scalar fields together induce Weyl gauge

A common biquadratic potential for the Higgs field $h$ and an additional scalar field $\\phi$, non minimally coupled to gravity, is considered in locally scale symmetric approaches to standard model fields in curved spacetime. A common ground state of the two scalar fields exists and couples both fields to gravity, more precisely to scalar curvature $R$. In Einstein gauge ($\\phi = const$, often called "Einstein frame"), also $R$ is scaled to a constant. This condition makes perfect sense, even in the general case, in the Weyl geometric approach. There it has been called {\\em Weyl gauge}, because it was first considered by Weyl in the different context of his original scale geometric theory of gravity of 1918. Now it seems to get new meaning as a combined effect of electroweak theory and gravity, and their common influence on atomic frequencies.

Erhard Scholz

2014-07-25

220

Magnetic fields and fluctuations in weakly Mn doped ZnGeP{sub 2}

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)

Mengyan, P. W.; Lichti, R. L.; Baker, B. B. [Texas Tech University, Lubbock, TX 79407-1051 (United States); Celebi, Y. G.; Catak, E. [Istanbul University, Beyazit, 34459 Istanbul (Turkey); Carroll, B. R. [Arkansas State University, Jonesboro, AR 72467 (United States); Zawilski, K. T.; Schunemann, P. G. [BAE Systems, Advanced Systems and Technology, Nashua, NH 03061-0868 (United States)

2014-02-21

221

Study of weak solar magnetic fields. Final report, 1 December 1987-30 November 1988

There have been two major gains in this period: completion and analysis of round-the-clock observations in cooperation with the Huairou Observatory in the People's Republic of China, which enabled the author to obtain the first long-term observations of weak solar magnetic fields, and the application of the magneto-optic filter to the measurement of magnetic fields. The observations in collaboration with

Zirin

1989-01-01

222

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.

Leeuwen-Segarceanu, Elena M. van, E-mail: e.segarceanu@antoniusziekenhuis.nl [Department of Internal Medicine, St. Antonius Hospital, Nieuwegein (Netherlands); Dorresteijn, Lucille D.A. [Department of Neurology, Medisch Spectrum Twente, Enschede (Netherlands); Pillen, Sigrid [Department of Neurology and Clinical Neurophysiology, Donders Center for Neuroscience, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands); Biesma, Douwe H. [Department of Internal Medicine, University Medical Center Utrecht (Netherlands); Vogels, Oscar J.M. [Department of Neurology and Clinical Neurophysiology, St. Antonius Hospital, Nieuwegein (Netherlands); Alfen, Nens van [Department of Neurology and Clinical Neurophysiology, Donders Center for Neuroscience, Radboud University Nijmegen Medical Center, Nijmegen (Netherlands)

2012-02-01

223

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.

Azzam Almosallami

2011-01-01

224

Gravitational Anomaly and Transport

Quantum anomalies give rise to new transport phenomena. In particular a magnetic field can induce an anomalous current via the chiral magnetic effect and a vortex in the relativistic fluid can also induce a current via the chiral vortical effect. The related transport coefficients can be calculated via Kubo formulas. We evaluate the Kubo formula for the anomalous vortical conductivity at weak coupling and show that it receives contributions proportional to the gravitational anomaly coefficient. The gravitational anomaly gives rise to an anomalous vortical effect even for an uncharged fluid.

Karl Landsteiner; Eugenio Megias; Francisco Pena-Benitez

2011-03-25

225

Gravitational Anomaly and Transport

Quantum anomalies give rise to new transport phenomena. In particular a magnetic field can induce an anomalous current via the chiral magnetic effect and a vortex in the relativistic fluid can also induce a current via the chiral vortical effect. The related transport coefficients can be calculated via Kubo formulas. We evaluate the Kubo formula for the anomalous vortical conductivity at weak coupling and show that it receives contributions proportional to the gravitational anomaly coefficient. The gravitational anomaly gives rise to an anomalous vortical effect even for an uncharged fluid.

Landsteiner, Karl; Pena-Benitez, Francisco

2011-01-01

226

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.

Abele, H.; Jenke, T.; Leeb, H.; Schmiedmayer, J. [Technische Universitaet Wien, Atominstitut, Stadionallee 2, 1020 Wien (Austria)

2010-03-15

227

NASA Astrophysics Data System (ADS)

The gravitational collapse of a wide class of self-interacting homogeneous scalar fields models is analyzed. The class is characterized by certain general conditions on the scalar field potential, which, in particular, include both asymptotically polynomial and exponential behaviors. Within this class, we show that the generic evolution is always divergent in a finite time, and then make use of this result to construct radiating star models of the Vaidya type. It turns out that blackholes are generically formed in such models.

Giambò, Roberto; Giannoni, Fabio; Magli, Giulio

2008-04-01

228

Inflationary gravitational waves in the effective field theory of modified gravity

In the approach of the effective field theory of modified gravity, we derive the second-order action and the equation of motion for tensor perturbations on the flat isotropic cosmological background. This analysis accommodates a wide range of gravitational theories including Horndeski theories, its generalization, and the theories with spatial derivatives higher than second order (e.g., Horava-Lifshitz gravity). We obtain the inflationary power spectrum of gravitational waves by taking into account corrections induced by higher-order spatial derivatives and slow-roll corrections to the de Sitter background. We also show that the leading-order tensor spectrum in concrete modified gravitational theories can be mapped on to that in General Relativity under a disformal transformation. Our general formula will be useful to constrain inflationary models from the future precise measurement of the B-mode polarization in the cosmic microwave background.

De Felice, Antonio

2014-01-01

229

Gravitational collapse of scalar fields via spectral methods

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.

Oliveira, H. P. de; Rodrigues, E. L.; Skea, J. E. F. [Universidade do Estado do Rio de Janeiro, Instituto de Fisica-Departamento de Fisica Teorica, CEP 20550-013 Rio de Janeiro, RJ (Brazil)

2010-11-15

230

Breakdown of Weak-Field Magnetotransport at a Metallic Quantum Critical Point

NASA Astrophysics Data System (ADS)

We show how the collapse of an energy scale in a quantum critical metal can lead to physics beyond the weak-field limit usually used to compute transport quantities. For a density-wave transition we show that the presence of a finite magnetic field at the critical point leads to discontinuities in the transport coefficients as temperature tends to zero. The origin of these discontinuities lies in the breakdown of the weak-field Jones-Zener expansion which has previously been used to argue that magnetotransport coefficients are continuous at simple quantum critical points. The presence of potential scattering and magnetic breakdown rounds the discontinuities over a window determined by ??<1 where ? is the order parameter and ? is the quasiparticle elastic lifetime.

Fenton, J.; Schofield, A. J.

2005-12-01

231

Ultra-weak magnetic fields in Am stars: ? UMa and ? Leo

NASA Astrophysics Data System (ADS)

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.

Blazère, A.; Petit, P.; Lignières, F.; Aurière, M.; Böhm, T.; Wade, G.

2014-12-01

232

Dust acoustic shock wave in electronegative dusty plasma: Roles of weak magnetic field

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.

Ghosh, Samiran [Government College of Engineering and Textile Technology, 4, Cantonment Road, Berhampore, Murshidabad 742101, West Bengal (India); Ehsan, Z.; Murtaza, G. [Salam Chair and Department of Physics, G. C. University Lahore, 54000 Lahore (Pakistan)

2008-02-15

233

Ultra weak magnetic fields in Am stars: Beta UMa and theta Leo

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, $\\beta$ UMa and $\\theta$ 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.

Blazère, Aurore; Lignières, François; Aurière, Michel; Böhm, Torsten; Wade, Gregg

2014-01-01

234

Gravitational radiation from collapsing magnetized dust

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.

Sotani, Hajime [Department of Physics, Aristotle University of Thessaloniki, Thessaloniki 54124 (Greece); Yoshida, Shijun [Science and Engineering, Waseda University, Okubo, Shinjuku, Tokyo 169-8555 (Japan); Kokkotas, Kostas D. [Department of Physics, Aristotle University of Thessaloniki, Thessaloniki 54124 (Greece); Theoretical Astrophysics, University of Tuebingen, Auf der Morgenstelle 10, 72076, Tuebingen (Germany)

2007-04-15

235

Horizon thermodynamics and gravitational field equations in Horava-Lifshitz gravity

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.

Cai Ronggen [Key Laboratory of Frontiers in Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, P.O. Box 2735, Beijing 100190 (China); Department of Physics, Kinki University, Higashi-Osaka, Osaka 577-8502 (Japan); Ohta, Nobuyoshi [Department of Physics, Kinki University, Higashi-Osaka, Osaka 577-8502 (Japan)

2010-04-15

236

Resonant amplification of magnetic seed fields by gravitational waves in the early universe

Inflation is known to produce both gravitational waves and seed magnetic fields on scales well beyond the size of the horizon. The general relativistic study of the interaction between these two sources after the end of inflation, showed a significant amplification of the initial magnetic seed which brought the latter within the currently accepted dynamo limits. In the present article we revisit this gravitomagnetic interaction and argue that the observed strong growth of the field is the result of resonance. More specifically, we show that the maximum magnetic boost always occurs when the wavelength of the inducing gravitational radiation and the scale of the original seed field coincide. We also look closer at the physics of the proposed Maxwell-Weyl coupling, consider the implications of finite electrical conductivity for the efficiency of the amplification mechanism and clarify further the mathematics of the analysis.

Tsagas, Christos G. [Section of Astrophysics, Astronomy and Mechanics, Department of Physics, Aristotle University of Thessaloniki, Thessaloniki 54124 (Greece); DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA (United Kingdom)

2005-12-15

237

Charge Separation within Superconductors in the Presence of Tidal Gravitational Fields

Tidal gravitational fields affect the Cooper-pair electrons and lattice ions of a type I superconductor differently. The quantum nonlocalizability of the Cooper pairs, which will remain coherent in the presence of interacting fields corresponding to frequencies less than that of the Bardeen-Cooper-Schrieffer (BCS) gap frequency, causes the superconducting electrons to undergo non-classical, non-geodesic motion, in contrast to the classical, geodesic motion of the lattice ions. The ensuing relative motion between the electrons and the ionic lattice causes a charge separation that leads to a measurable voltage potential when a macroscopic, quantum-coherent superconducting system undergoes free fall in the Earth's inhomogeneous gravitational field. Theoretical and experimental implications will be discussed.

Minter, Stephen J. [University of California, Merced, Department of Natural Sciences, 5200 N. Lake Rd., Merced, CA 95343 (United States); Wegter-McNelly, Kirk [Boston University, School of Theology, 745 Commonwealth Ave., Boston, MA 02215 (United States); Chiao, Raymond Y. [University of California, Merced, Departments of Natural Sciences and Engineering, 5200N Lake Rd, Merced, CA 95343 (United States)

2009-09-09

238

Gravitation: Field theory par excellence Newton, Einstein, and beyond

Newtonian gravity satifies the two principles of equivalence m/sub i/ = m/sub p/ (the passive principle) and m/sub a/ = m/sub p/ (the active principle). A relativistic gauge field concept in D = s+1 dimensional curved-space will, in general, violate these two principles as in m/sub p/ = ..cap alpha..m/sub i/, m/sub a/ = lambdam/sub p/ where ..cap alpha.. = D: 3 and lambda measures the presence of the field stress-energy t/sup ..nu..//sub ..mu../ in the field equations. It is shown that ..cap alpha.. = 1, lambda = 0 corresponds to general relativity and ..cap alpha.. = 1, lambda = 1 to the theory of the author. It is noted that the correspondence limit of general relativity is not Newton's theory but a theory suggested by Robert Hooke a few years before Newton published his in Principia. The gauge is independent of the two principles but had to do with local special relativistic correspondence and compatibility with quantum mechanics. It is shown that unless ..cap alpha.. = 1, lambda = 1 the generalized theory cannot predict correctly many observables effects, including the 532'' per century Newtonian part in Mercury's perihelion advance.

Yilmaz, H.

1984-09-01

239

Piecewise Flat Gravitational Waves

We examine the continuum limit of the piecewise flat locally finite gravity model introduced by 't Hooft. In the linear weak field limit we find the energy--momentum tensor and metric perturbation of an arbitrary configuration of defects. The energy--momentum turns out to be restricted to satisfy certain conditions. The metric perturbation is mostly fixed by the energy--momentum except for its lightlike modes which reproduce linear gravitational waves, despite no such waves being present at the microscopic level.

Maarten van de Meent

2011-02-22

240

The effects of strong magnetic and gravitational fields on emission properties of neutron stars

NASA Astrophysics Data System (ADS)

Neutron stars offer us a unique medium to study the physics of intense magnetic and gravitational fields. They can be magnetized so strongly that exotic quantum electrodynamical processes become important. With their strong gravity, they can gravitationally lens radiation from their own surfaces. In this thesis, I study how these fields affect the physical processes and the interactions of photons with matter on the surfaces of neutron stars and shape their observable properties. Confining magnetic fields alter the properties of electrons, protons, and atoms present in the atmospheres of neutron stars. Therefore, they modify the interactions and propagation of photons through this medium. In particular, strong fields render the interactions anisotropic and polarization-dependent. In addition, the magnetic vacuum becomes polarized due to the presence of virtual electron-positron pairs in strong fields. I study the transfer of radiation in the atmospheres of neutron stars taking into account the resonances that arise because of the polarization of vacuum and the presence of the protons and electron in the plasma. The emission from the surface of neutron stars is also modified by general relativistic effects in strong gravitational fields. I determine the signatures of gravitational lensing and identify new effects introduced by the stellar gravity on the observable properties of neutron stars. I study the uncertainties these effects introduce to the inferred properties of such sources and discuss the importance of timing studies in constraining the processes that occur in the stellar interiors and surfaces. There are several classes of neutron star sources that are thought to show thermal emission from their surfaces, offering us a window into these extreme processes. Of these, I study in detail the intriguing anomalous X-ray pulsars, the young isolated neutron stars, and the accreting stars that show thermonuclear bursts on their surfaces, in an attempt to reveal the nature of these sources and understand the physical processes that take place on the surfaces of neutron stars.

Ozel, Feryal

2002-10-01

241

Cartographic generalization of urban street networks based on gravitational field theory

NASA Astrophysics Data System (ADS)

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.

Liu, Gang; Li, Yongshu; Li, Zheng; Guo, Jiawei

2014-05-01

242

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.

Turner, E.L.

1988-07-01

243

Thermoelectric Magnetohydrodynamic Flow During Crystal Growth with a Moderate or Weak Magnetic Field

NASA Technical Reports Server (NTRS)

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.

Khine, Y. Y.; Walker, John S.; Szofran, Frank R.; Rose, M. Franklin (Technical Monitor)

2000-01-01

244

Molecular alignment and filamentation: Comparison between weak- and strong-field models

NASA Astrophysics Data System (ADS)

The impact of nonadiabatic laser-induced molecular alignment on filamentation is numerically studied. Weak- and strong-field models of impulsive molecular alignment are compared in the context of nonlinear pulse propagation. It is shown that the widely used weak-field model describing the refractive index modification induced by impulsive molecular alignment accurately reproduces the propagation dynamics providing that only a single pulse is involved during the experiment. On the contrary, it fails at reproducing the nonlinear propagation experienced by an intense laser pulse traveling in the wake of a second strong laser pulse. The discrepancy depends on the relative delay between the two pulses and is maximal for delays corresponding to half the rotational period of the molecule.

Berti, N.; Béjot, P.; Wolf, J.-P.; Faucher, O.

2014-11-01

245

Vibrational spectra of free and intracellular DNA in the weak electromagnetic field

NASA Astrophysics Data System (ADS)

Vibrational bands of DNA molecules from birds' erythrocytes, as well as Dunaliella viridis alga cells and Escherichia coli bacteria clinical strains in the weak microwave field were investigated with IR spectroscopy. Drastic changes were detected in the intensities and fine structure of C equals O and PL2 bands for polarized spectra of irradiated samples of DNA molecules as compared with the reference samples in the 1700-1000 cm-1 region. No essential changes were detected in the IR spectra in the region of PO2 bands of DNA for the Escherichia coli, irradiated by the weak electromagnetic field, but essential redistribution of intensities and change in halfwidths of the PO2 symmetrical bonds were detected for Dunaliella viridis alga cells.

Dovbeshko, Galina I.

1998-09-01

246

We perform a series of two-dimensional, axisymmetric, magnetohydrodynamic simulations of the rotational collapse of a supernova core. In order to calculate the waveforms of the gravitational wave, we derive the quadrupole formula including the contributions from the electromagnetic fields. Recent stellar evolution calculations imply that the magnetic fields of the toroidal components are much stronger than those of the poloidal ones at the presupernova stage. Thus, we systematically investigate the effects of the toroidal magnetic fields on the amplitudes and waveforms. Furthermore, we employ the two kinds of the realistic equation of states, which are often used in the supernova simulations. Then, we investigate the effects of the equation of states on the gravitational wave signals. With these computations, we find that the peak amplitudes are lowered by an order of 10% for the models with the strongest toroidal magnetic fields. However, the peak amplitudes are mostly within sensitivity range of laser interferometers such as TAMA and the first LIGO for a source at a distance of 10 kpc. Furthermore, we point out that the amplitudes of second peaks are still within the detection limit of the first LIGO for the source, although the characteristics of second peaks are reduced by the magnetic fields. We stress the importance of the detection, since it will give us information about the angular momentum distribution of massive evolved stars. When we compare the gravitational waves from the two realistic equation of states, significant differences are not found, except that the typical frequencies of the gravitational wave become slightly higher for the softer equation of state.

Kei Kotake; Shoichi Yamada; Katsuhiko Sato; Kohsuke Sumiyoshi; Hiroyuki Ono; Hideyuki Suzuki

2004-01-27

247

On the weak field approximation of Brans-Dicke theory of gravity

It is shown that in the weak field approximation solutions of Brans-Dicke equations are simply related to the solutions of General Relativity equations for the same matter distribution. A simple method is developed which permits to obtain Brans-Dicke solutions from Einstein solutions when both theories are considered in their linearized forms. To illustrate the method some examples found in the literature are discussed.

A. Barros; C. Romero

1997-12-18

248

A Weak Lensing Survey in the Fields of z~1 Luminous Radio Sources

In this paper we present weak lensing observations of the fields around 8 z~1 luminous radio sources. These data are searched for the lensing signatures of clusters that are either physically associated with the radio objects, or are foreground systems projected along the line of sight. The radio sources were all imaged with WFPC-2/HST providing high quality shape information on large numbers of faint galaxies around them. Statistical analysis of the coherent shear field visible in the shapes of the faint galaxies indicates that we have detected a weak lensing signal close to one of the targets, 3C336 at z=0.927, with a high level of confidence. A second, independent WFPC-2 observation of this target reinforces this detection. Our results support the earlier suggestion of weak lensing in this field by Fort et al (1996) using ground-based data. We also combined the shear distributions in the remaining 7 field to improve our sensitivity to weak shear signals from any structure typically associated with these sources. We find no detectable signal and estimate an upper limit on the maximum shear allowed by our observations. Using an N(z) estimated from lensing analyses we convert our observed lensing signal and limits into estimates of the masses of the various structures. We suggest that further lensing observations of distant radio sources and their host environments may allow the cluster L_X-mass relationship to be mapped at high-z. This is crucial for interpreting the results of the next generation of deep X-ray surveys, and thus constraining the redshift evolution of the cluster mass function out to z=1.

Richard G. Bower; Ian Smail

1996-12-16

249

Interhemispheric conjugate auroral features during a weak substorm interval were investigated using simultaneous all-sky camera (ASC) measurements at the northern and southern geomagnetic conjugate points at Tjörnes (TJO; 66.2°N, 342.9°E) in Iceland and Syowa Station (SYO; 69.0°S, 39.6°E) in Antarctica. Around postmidnight, just after the substorm onset, the ASC field of view (FOV) at TJO was first filled with dynamic

T. Motoba; K. Hosokawa; N. Sato; A. Kadokura; G. Bjornsson

2010-01-01

250

Thick branes from self-gravitating scalar fields

NASA Astrophysics Data System (ADS)

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.

Novikov, Oleg O.; Andrianov, Alexander A.; Andrianov, Vladimir A.

2014-07-01

251

General Relativistic Theory of the VLBI Time Delay in the Gravitational Field of Moving Bodies

NASA Technical Reports Server (NTRS)

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.

Kopeikin, Sergei

2003-01-01

252

Small-x QCD evolution of 2 n Wilson line correlator: The weak field limit

NASA Astrophysics Data System (ADS)

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 .

Ayala, Alejandro; Cazaroto, Erike R.; Hernández, Luis Alberto; Jalilian-Marian, Jamal; Tejeda-Yeomans, Maria Elena

2014-10-01

253

The thermodynamic functions of plasma under the influence of a weak magnetic field

NASA Astrophysics Data System (ADS)

The aim of this paper is to calculate the quantum thermodynamic functions until the third virial coefficient of plasma under the influence of a weak magnetic field. The calculation is based on the binary Slater sum in the case of a low density plasma, which is exact in a quadratic order with respect to the magnetic field. The method which was used is based on the Bloch equation. The second virial coefficient is obtained in the form of a convergent series expansion in terms of the interaction plasma parameter ?={eaeb}/{KT?} where ? being the thermal de Broglie wavelength between two particles. We compared our results with others.

Hussein, N. A.; Eisa, D. A.; Eldin, M. G.

2012-12-01

254

Weak-Field Spherically Symmetric Solutions in $f(T)$ gravity

We study weak-field solutions having spherical symmetry in $f(T)$ gravity; to this end, we solve the field equations for a non diagonal tetrad, starting from Lagrangian in the form $f(T)=T+\\alpha T^{n}$, where $\\alpha$ is a small constant, parameterizing the departure of the theory from GR. We show that the classical spherically symmetric solutions of GR, i.e. the Schwarzschild and Schwarzschild-de Sitter solutions, are perturbed by terms in the form $\\propto r^{2-2n}$ and discuss the impact of these perturbations in observational tests.

Ruggiero, Matteo Luca

2015-01-01

255

Hamiltonian dynamics of a rigid body in a central gravitational field

This paper concerns the dynamics of a rigid body of finite extent moving under the influence of a central gravitational field.\\u000a A principal motivation behind this paper is to reveal the hamiltonian structure of the n-body problem for masses of finite\\u000a extent and to understand the approximation inherent to modeling the system as the motion of point masses. To this

LI-SttENG WANG; P. S. Krishnaprasad; J. H. Maddocks

1990-01-01

256

The strong field gravitational lensing in the Schwarzschild black hole pierced by a cosmic string

In this work the gravitational lensing in the strong field limit around the Schwarzschild black hole pierced by a cosmic string is studied. We find the angular position and magnification of the relativistic images depending on the tension of cosmic string. It is interesting that the angular separation $s$ increases and the relative magnification $r$ decreases when the tension of string is greater. It is also interesting that the deflection angle is greater when the tension of cosmic string is stronger.

Hongbo Cheng; Huawen Wang; Jingyun Man

2010-10-12

257

One of the elements for the NEES-GC project on Seismic Risk Reduction for Port Facilities involves validation of numerical models against physical experiments using the geotechnical centrifuge. For example, tests have been performed to demonstrate the effectiveness of Prefabricated Vertical (PV) drains in mitigating liquefaction risks. This paper examines the effect of the non-uniform gravitational field on the seismically-induced ground

Antonios Vytiniotis; Andrew J. Whittle

258

Dark matter annihilation in the gravitational field of a black hole

In this paper we consider dark matter particle annihilation in the gravitational field of black holes. We obtain exact distribution function of the infalling dark matter particles, and compute the resulting flux and spectra of gamma rays coming from the objects. It is shown that the dark matter density significantly increases near a black hole. Particle collision energy becomes very high affecting relative cross-sections of various annihilation channels. We also discuss possible experimental consequences of these effects.

A. N. Baushev

2009-10-08

259

Gravitational resonance spectroscopy consists in measuring the energy spectrum of bouncing ultracold neutrons above a mirror by inducing resonant transitions between different discrete quantum levels. We discuss how to induce the resonances with a flow through arrangement in the GRANIT spectrometer, excited by an oscillating magnetic field gradient. The spectroscopy could be realized in two distinct modes (so called DC and AC) using the same device to produce the magnetic excitation. We present calculations demonstrating the feasibility of the newly proposed AC mode.

G. Pignol; S. Baessler; V. V. Nesvizhevsky; K. Protasov; D. Rebreyend; A. Yu. Voronin

2014-08-05

260

Solar oscillations, gravitational multipole field of the sun and the solar neutrino paradox

The visual solar oblateness work and the solar seismological work on the internal rotation of the sun are reviewed and their implications concerning the static gravitational multipole moments of the sun are discussed. The results of this work are quite deviant which is indicative of the complexity encountered and of the necessity for continued studies based on a diverse set of observing techniques. The evidence for phase-locked internal gravity modes of the sun is reviewed and the implications for the solar neutrino paradox are discussed. The rather unique possibility for testing the relevance which the phase-locked gravity modes have to this paradox is also noted. The oscillating perturbations in the sun's gravitational field produced by the classified internal gravity modes and the phase-locked modes are inferred from the observed temperature eigenfunctions. Strains of the order of 10/sup -18/ in gravitational radiation detectors based on free masses are inferred for frequencies near 100 ..mu..Hz. The relevance of these findings is discussed in terms of a new technique for use in solar seismological studies and of producing background signals in studies of low-frequency gravitational radiation. 64 refs., 2 figs.

Hill, H.A.; Rosenwald, R.D.

1986-11-04

261

Nonlocal Effective Gravitational Field Equations and the Running of Newton's G

Non-perturbative 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 $t \\sim \\xi \\sim 1/H$.

Herbert W. Hamber; Ruth M. Williams

2005-07-01

262

The authors prove that the dynamics of spin 1/2 particles in stationary gravitational fields can be described using an approach, which builds upon the formalism of pseudo-Hermitian Hamiltonians. The proof consists in the analysis of three expressions for Hamiltonians, which are derived from the Dirac equation and describe the dynamics of spin 1/2 particles in the gravitational field of the Kerr solution. The Hamiltonians correspond to different choices of tetrad vectors and differ from each other. The differences between the Hamiltonians confirm the conclusion known from many studies that the Hamiltonians derived from the Dirac equation are nonunique. Application of standard pseudo-Hermitian quantum mechanics rules to each of these Hamiltonians produces the same Hermitian Hamiltonian. The eigenvalue spectrum of the resulting Hamiltonian is the same as that of the Hamiltonians derived from the Dirac equation with any chosen system of tetrad vectors. For description of the dynamics of spin 1/2 particles in stationary gravitational fields can be used not only the formalism of pseudo-Hermitian Hamiltonians but also an alternative approach, which employs the Parker scalar product. The authors show that the alternative approach is equivalent to the formalism of pseudo-Hermitian Hamiltonians.

Gorbatenko, M. V.; Neznamov, V. P. [Russian Federal Nuclear Center - All-Russian Research Institute of Experimental Physics, Sarov, Mira 37, Nizhni Novgorod region, 607188 (Russian Federation)

2010-11-15

263

K0 meson physics in the gravitation field: a constraint on the equivalence principle

K0-K0bar oscillations are extremely sensitive to the K0 and K0bar energy at\\u000arest. Even assuming m_K0=m_K0bar, the energy is not granted to be the same if\\u000agravitational effects on K0 and K0bar slightly differ. We consider various\\u000agravitation fields present and, in particular, galactic fields, which provide a\\u000anegligible acceleration, but relatively large gravitational potential energy. A\\u000aconstraint from a

Savely G. Karshenboim; D. I. Mendeleev

2008-01-01

264

An Investigation into Quantifying Micron-G Changes in a Gravitational Field of 1G

NASA Technical Reports Server (NTRS)

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.

Gauthier, Richard R.; Gilbert, John A.

1997-01-01

265

Empirical model of the gravitational field generated by the oceanic lithosphere

NASA Astrophysics Data System (ADS)

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.

Tenzer, Robert; Chen, Wenjin; Ye, Zhourun

2015-01-01

266

Apparent velocities of sources moving in the gravitational field of a Kerr black hole

NASA Astrophysics Data System (ADS)

The apparent velocity of sources moving in the gravitational field of a Kerr black hole, as seen by a distant observer is investigated. A full, general relativity treatment is used, and the velocity is calculated for several combinations of the positions of the source and the observer. The calculations show that, on the whole, the Kerr-field velocity, when superluminal, is greater or smaller than the no-field, 'special relativity' velocity according as the source is located on the approaching or receding side. For a source located on the axis at radial distance r(e) the Kerr-field velocity is defined only for observers outside a certain angle from the axis, and is generally smaller than the no-field velocity, when both are superluminal.

Xiang, Shou-Ping; Kiang, Tao; Zhang, Jia-Lu

1988-07-01

267

The direct detection of gravitational waves with upcoming second-generation gravitational wave observatories such as Advanced LIGO and Advanced Virgo will allow us to probe the genuinely strong-field dynamics of general ...

Agathos, M.

268

In this paper, we demonstrated that interarticular coordination of terrestrial tetrapods emerges from an environment highly constrained by friction and the gravitational field. We briefly review recent works on the jumping behavior in squamates, lemurs and amphibians. We then explore previously published work as well as some unpublished experimental data on human jumping. Finally, we end by inferring locomotion in some of the first limbed vertebrates using a simulation procedure. All these data show that despite changes in shape, structure, and motor controls of taxa, the same spatio-temporal sequence of joint displacements always occurs when the movement is executed in a terrestrial environment. Comparison with aquatic locomotion argues for the hypothesis that this pattern emerged in early terrestrial tetrapods as a response to the gravitational constraint and the terrestrial frictional environment. PMID:23677448

Legreneur, Pierre; Bels, Vincent; Monteil, Karine; Laurin, Michel

2013-05-01

269

Application of the weak-field asymptotic theory to tunneling ionization of H2O

NASA Astrophysics Data System (ADS)

The weak-field asymptotic theory of tunneling ionization in a static electric field is applied to H2O. The orientation dependence of the ionization rate is studied. The use of polarization-consistent basis sets with up to heptuble-zeta accuracy and variationally optimized exponents improves the asymptotic form of the wave function and allows for an accurate extraction of the structure factor defining the ionization rate. The results are presented based on Hartree-Fock wave functions and density functional theory. The density functional theory reproduces closely the experimental vertical ionization potential. We find that the rate peaks at an angle of 81? between the field and molecular principal inertial axis through the O atom. The predictions for the orientation dependence of the rate are compared to available theoretical results.

Madsen, Lars Bojer; Jensen, Frank; Tolstikhin, Oleg I.; Morishita, Toru

2014-03-01

270

Recovery of the Cosmological Peculiar Velocity from the Density Field in the Weakly Nonlinear Regime

Using third-order perturbation theory, we derive a relation between the mean divergence of the peculiar velocity given density and the density itself. Our calculations assume Gaussian initial conditions and are valid for Gaussian filtering of the evolved density and velocity fields. The mean velocity divergence turns out to be a third-order polynomial in the density contrast. We test the power spectrum dependence of the coefficients of the polynomial for scale-free and standard CDM spectra and find it rather weak. Over scales larger than about 5 megaparsecs, the scatter in the relation is small compared to that introduced by random errors in the observed density and velocity fields. The relation can be useful for recovering the peculiar velocity from the associated density field, and also for non-linear analyses of the anisotropies of structure in redshift surveys.

Michal Chodorowski; Ewa Lokas; Agnieszka Pollo; Adi Nusser

1998-08-14

271

Floating-zone growth of silicon in magnetic fields. I. Weak static axial fields

NASA Astrophysics Data System (ADS)

Silicon floating-zone experiments, employing P- and Sb-doped crystals of 8 mm diameter and zones of 10-12 mm length, were carried out in a mirror furnace under static axial magnetic fields (magnetic induction B ? 500 mT). A strong influence of the magnetic field on the formation of dopant striations could be detected: Whereas crystals grown without field show an irregular striation pattern implying a broad frequency range of the melt flows (0.1-5 Hz), fields as small as 60 mT already show an influence by reducing the frequency spectrum to a range of 0.1-1.5 Hz. Higher fields reduce the spectrum even further and at fields of 220 mT only one frequency remains, producing a periodic striation pattern. Above 240 mT, nearly striation-free crystals could be obtained. In addition to changes in the microsegregation, the transient part of the axial macrosegregation is steeper because of the reduced mixing of the melt. The radial segregation is changed by a flattening of the interface curvature and the formation of a core region in the crystal. The core diameter is directly dependent on the magnetic induction.

Dold, P.; Cröll, A.; Benz, K. W.

1998-02-01

272

NASA Astrophysics Data System (ADS)

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.

Kirschvink, Joseph L.

1992-08-01

273

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?µT 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

Novitskii, Yurii I; Novitskaya, Galina V; Serdyukov, Yurii A

2014-02-01

274

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.

Jenrow, K.A.; Smith, C.H.; Liboff, A.R. [Oakland Univ., Rochester, MI (United States). Dept. of Physics] [Oakland Univ., Rochester, MI (United States). Dept. of Physics

1996-12-31

275

NASA Astrophysics Data System (ADS)

The objective of this paper is to obtain the analytical solutions which satisfy the differential Ginzburg-Landau equations and some boundary conditions. Based on the linear deformation theory, the effects of prestrain on the wave function and magnetic potential of deformable superconductors have been investigated in the presence of a weak magnetic field. The results show that for the superconductors with a linearly elastic deformation, the wave function in the materials should be considered for two different cases, i.e., type I and type II. The prestrain effect in deformable superconductors should not be neglected in determining the superconductivity in superconductors.

Yong, Huadong; Liu, Fangzhong; Zhou, Youhe

2010-10-01

276

Shear Viscosity in Weakly Coupled N-Component Scalar Field Theories

The rich phenomena of the shear viscosity (eta) to entropy density (s) ratio, eta/s, in weakly coupled N-component scalar field theories are studied. eta/s can have a "double dip" behavior due to resonances and the phase transition. If an explicit goldstone mass term is added, then eta/s can either decrease monotonically in temperature or, as seen in many other systems, reach a minimum at the phase transition. We also show how to go beyond the original variational approach to make the Boltzmann equation computation of eta systematic.

Jiunn-Wei Chen; Mei Huang; Chang-Tse Hsieh; Han-Hsin Lin

2010-11-18

277

NASA Astrophysics Data System (ADS)

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.

Grunskaya, Lubov; Isakevich, Valiriy; Efimov, Vladislav; Zakirov, Alexander

278

NASA Astrophysics Data System (ADS)

The existence of a special gravitational vacuum is considered in this paper. A phenomenological method differing from the traditional Einsteinian formalization is utilized. Vacuum, metric and matter form a complex determined by field equations and at great distances from gravitational masses vacuum effects are small but could be large in powerful fields. Singularities and black holes justify the approach as well as the Ambartsmyan theory concerning the existence of supermassive and superdense prestallar bodies that then disintegrate. A theory for these superdense bodies is developed involving gravitational field equations that describe the vacuum by an energy momentum tensor and define the field and mass distribution. Computations based on the theory for gravitational radii with incompressible liquid models adequately reflecting real conditions indicate that a gravitational vacuum could have considerable effects on superdense stars and could have radical effects for very large masses.

Grigoryan, L. S.; Saakyan, G. S.

1984-09-01

279

An analytic study of the ionization from an ultrathin quantum well in a weak electrostatic field

We consider the time evolution of a particle bound by an attractive one-dimensional delta-function potential (at x = 0) when a uniform electrostatic field (F) is applied. We explore explicit expressions for the time-dependent wavefunction \\psi_F(x,t) and the ionization probability {\\mathcal{P}}(t), respectively, in the weak-field limit. In doing so, \\psi_F(0,t) is a key element to their evaluation. We obtain a closed expression for \\psi_F(0,t) which is an excellent approximation of the exact result being a numerical solution of the Lippmann-Schwinger integral equation. The resulting probability density |\\psi_F(0,t)|^2, as a simple alternative to {\\mathcal{P}}(t), is also in good agreement to its counterpart from the exact one. In doing this, we also find a new and useful integral identity of the Airy function.

Ilki Kim

2007-06-12

280

Separation of polystyrene microbeads using dielectrophoretic/gravitational field-flow-fractionation.

The characterization of a dielectrophoretic/gravitational field-flow-fractionation (DEP/G-FFF) system using model polystyrene (PS) microbeads is presented. Separations of PS beads of different surface functionalization (COOH and none) and different sizes (6, 10, and 15 microm in diameter) are demonstrated. To investigate the factors influencing separation performance, particle elution times were determined as a function of particle suspension conductivity, fluid flow rate, and applied field frequency and voltage. Experimental data were analyzed using a previously reported theoretical model and good agreement between theory and experiment was found. It was shown that separation of PS beads was based on the differences in their effective dielectric properties. Particles possessing different dielectric properties were positioned at different heights in a fluid-flow profile in a thin chamber by the balance of DEP and gravitational forces, transported at different velocities under the influence of the fluid flow, and thereby separated. To explore hydrodynamic (HD) lift effects, velocities of PS beads were determined as a function of fluid flow rate in the separation chamber when no DEP field was applied. In this case, particle equilibrium height positions were governed solely by the balance of HD lift and gravitational forces. It was concluded that under the experimental conditions reported here, the DEP force was the dominant factor in controlling particle equilibrium height and that HD lift force played little role in DEP/G-FFF operation. Finally, the influence of various experimental parameters on separation performance was discussed for the optimization of DEP/G-FFF. PMID:9591693

Wang, X B; Vykoukal, J; Becker, F F; Gascoyne, P R

1998-01-01

281

Microcanonical mean-field thermodynamics of self-gravitating and rotating systems.

We derive the global phase diagram of a self-gravitating N-body system enclosed in a finite three-dimensional spherical volume V as a function of total energy and angular momentum, employing a microcanonical mean-field approach. At low angular momenta (i.e., for slowly rotating systems) the known collapse from a gas cloud to a single dense cluster is recovered. At high angular momenta, instead, rotational symmetry can be spontaneously broken and rotationally asymmetric structures (double clusters) appear. PMID:12144383

Votyakov, E V; Hidmi, H I; De Martino, A; Gross, D H E

2002-07-15

282

A new line element derived from the variable rest mass in gravitational field

This paper presents a new line element based on the assumption of the variable rest mass in gravitational field, and explores some its implications. This line element is not a vacuum solution of Einstein's equations, yet it is sufficiently close to Schwarzschild's line element to be compatible with all of the experimental and observational measurements made so far to confirm the three Einstein's predictions. The theory allows radiation and fast particles to escape from all massive bodies, even from those that in Einstein's general relativity framework will be black holes. The striking feature of this line element is the non-existence of black holes.

N. Ben-Amots

2008-08-19

283

Effect of the Earth's time-retarded transverse gravitational field on the motion of the Moon

Classical Newtonian gravitational theory does not satisfy the causality principle because it is based on instantaneous action-at-a-distance. A causal version of Newtonian theory for a large rotating sphere is derived herein by time-retarding the distance between interior circulating point-mass sources and an exterior field-point. The resulting causal theory explains exactly the flyby anomaly reported by NASA scientists in 2008. It also explains exactly an anomalous decrease in the Moon's orbital speed. No other known theory can make both of these claims.

J. C. Hafele

2012-02-27

284

NASA Astrophysics Data System (ADS)

In weakly collisional plasmas such as the intracluster medium (ICM), the viscous stress and the rate of change of the magnetic energy are proportional to the local pressure anisotropy, so subject to constraints imposed by the pressure-anisotropy-driven microinstabilities (mirror and firehose) and controlled by the local instantaneous plasma ?. The dynamics of such plasmas can be dramatically different from a conventional magnetohydrodynamic fluid. The plasma is expected to stay locally marginal with respect to the instabilities, but how it does this remains an open question. Two models of magnetic field evolution are investigated. In the first, marginality is achieved via suppression of the rate of change of the field. In the second, the instabilities give rise to anomalous collisionality, reducing pressure anisotropy to marginal - at the same time decreasing viscosity and so increasing the turbulent rate of strain. Implications of these two models are studied in a simplified zero-dimensional setting. In the first model, the field grows explosively but on a time-scale that scales with the initial ?, while in the second, dynamical field strength can be reached in one large-scale turbulence turnover time regardless of the initial seed. Both models produce very intermittent fields. Both also suffer from fairly strong constraints on their applicability: for typical cluster-core conditions, scale separation between the fluid motions (with account of suppressed viscous stress) and the miscoscale fluctuations break down at ? ˜ 104-105. At larger ? (weaker fields), a fully collisionless plasma dynamo theory is needed to justify field growth from a tiny primordial seed. However, the models discussed here are appropriate for studying the structure of the currently observed field as well as large-scale dynamics and thermodynamics of the magnetized ICM or similarly dilute astrophysical plasmas.

Mogavero, Federico; Schekochihin, Alexander A.

2014-06-01

285

NASA Technical Reports Server (NTRS)

The general equations describing the equilibrium shapes of self-gravitating gas clouds containing axisymmetric magnetic fields are presented. The general equations admit of a large class of solutions. It is shown that if one additional (ad hoc) asumption is made that the mass be spherically symmetrically distributed, then the gas pressure and the boundary conditions are sufficiently constraining that the general topological structure of the solution is effectively determined. The further assumption of isothermal conditions for this case demands that all solutions possess force-free axisymmetric magnetic fields. It is also shown how the construction of aspherical (but axisymmetric) configurations can be achieved in some special cases, and it is demonstrated that the detailed form of the possible equilibrium shapes depends upon the arbitrary choice of the functional form of the variation of the gas pressure along the field lines.

Lerche, I.; Low, B. C.

1980-01-01

286

On observation of neutron quantum states in the Earth's gravitational field

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.

Vankov, Anatoli Andrei [Institute of Physics and Power Engineering, 1 Bondarenko Square, Obninsk, Kaluga Region, 249020 (Russian Federation); Bethany College, 335 E. Swensson Street, Lindsborg, Kansas 67456 (United States)

2010-03-01

287

Chaotic transport in Hamiltonian systems perturbed by a weak turbulent wave field

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.

Abdullaev, S. S. [Institute for Energy and Climate Research-Plasma Physics, Forschungszentrum Juelich GmbH, Association EURATOM-FZJ, Partner in the Trilateral Euregio Cluster, D-52425 Juelich (Germany)

2011-08-15

288

Gravitational anomaly and transport phenomena.

Quantum anomalies give rise to new transport phenomena. In particular, a magnetic field can induce an anomalous current via the chiral magnetic effect and a vortex in the relativistic fluid can also induce a current via the chiral vortical effect. The related transport coefficients can be calculated via Kubo formulas. We evaluate the Kubo formula for the anomalous vortical conductivity at weak coupling and show that it receives contributions proportional to the gravitational anomaly coefficient. The gravitational anomaly gives rise to an anomalous vortical effect even for an uncharged fluid. PMID:21797593

Landsteiner, Karl; Megías, Eugenio; Pena-Benitez, Francisco

2011-07-01

289

Gravitational field of a hedgehog and the evolution of vacuum bubbles

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.

Guendelman, E.I. (Department of Nuclear Physics, Weizmann Institute of Science, Rehovot 76100 (Israel)); Rabinowitz, A. (Department of Physics, Ben Gurion University of the Negev, Beer Sheva 84105 (Israel))

1991-11-15

290

Gravitational field of a hedgehog and the evolution of vacuum bubbles

NASA Astrophysics Data System (ADS)

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.

Guendelman, E. I.; Rabinowitz, A.

1991-11-01

291

Weak gravity conjecture constraints on inflation

We consider the gravitational correction to the coupling of the scalar fields. Weak gravity conjecture says that the gravitational correction to the running of scalar coupling should be less than the contribution from scalar fields. For instance, a new scale $\\Lambda=\\lambda_4^{1/2}M_p$ sets a UV cutoff on the validity of the effective $\\lambda_4 \\phi^4$ theory. Furthermore, this conjecture implies a possible constraint on the inflation model, e.g. the chaotic inflation model might be in the swampland.

Qing-Guo Huang

2007-05-26

292

Observing optical coherence across Fock layers with weak-field homodyne detectors

NASA Astrophysics Data System (ADS)

Quantum properties of optical modes are typically assessed by observing their photon statistics or the distribution of their quadratures. Both particle- and wave-like behaviours deliver important information and each may be used as a resource in quantum-enhanced technologies. Weak-field homodyne (WFH) detection provides a scheme that combines the wave- and particle-like descriptions. Here we show that it is possible to observe a wave-like property such as the optical coherence across Fock basis states in the detection statistics derived from discrete photon counting. We experimentally demonstrate these correlations using two WHF detectors on each mode of two classes of two-mode entangled states. Furthermore, we theoretically describe the response of WHF detection on a two-mode squeezed state in the context of generalized Bell inequalities. Our work demonstrates the potential of this technique as a tool for hybrid continuous/discrete-variable protocols on a phenomenon that explicitly combines both approaches.

Donati, Gaia; Bartley, Tim J.; Jin, Xian-Min; Vidrighin, Mihai-Dorian; Datta, Animesh; Barbieri, Marco; Walmsley, Ian A.

2014-11-01

293

We have investigated modifications of magneto-optical properties in the weak-field annealed Co-based amorphous ribbons. It is found that spectral and magnetic field dependences of the transverse Kerr effect significantly change with the time of annealing in air and the magnetic field magnitude. The analysis reveals the existence of two anisotropies, one in low fields up to 300Oe and another in

E. A Ga?shina; N. S Perov; M. Yu Kochneva; P. M Sheverdyaeva; C. G Kim; C. O Kim

2003-01-01

294

Horizon Thermodynamics and Gravitational Field Equations in Quasi-Topological Gravity

In this paper we show that the gravitational field equations of $(n+1)$% -dimensional topological black holes with constant horizon curvature, in cubic and quartic quasi-topological gravity, can be recast in the form of the first law of thermodynamics, $dE=TdS-PdV$, at the black hole horizon. This procedure leads to extract an expression for the horizon entropy as well as the energy (mass) in terms of the horizon radius, which coincide exactly with those obtained in quasi-topological gravity by solving the field equations and using the Wald's method. We also argue that this approach is powerful and can be extended to all higher order quasi-topological gravity for extracting the corresponding entropy and energy in terms of horizon radius.

A. Sheykhi; M. H. Dehghani; R. Dehghani

2014-03-31

295

Conversion of relic gravitational waves into photons in cosmological magnetic fields

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.

Dolgov, Alexander D.; Ejlli, Damian, E-mail: dolgov@fe.infn.it, E-mail: ejlli@fe.infn.it [Dipartimento di Fisica e Scienze della Terra, Polo Scientifico e Tecnologico-Edificio C, Università degli Studi di Ferrara, Via Saragat 1, 44122 Ferrara (Italy)

2012-12-01

296

Horizon thermodynamics and gravitational field equations in quasi-topological gravity

NASA Astrophysics Data System (ADS)

In this paper we show that the gravitational field equations of -dimensional topological black holes with constant horizon curvature, in cubic and quartic quasi-topological gravity, can be recast in the form of the first law of thermodynamics, , at the black hole horizon. This procedure leads to extract an expression for the horizon entropy as well as the energy (mass) in terms of the horizon radius, which coincide exactly with those obtained in quasi-topological gravity by solving the field equations and using the Wald's method. We also argue that this approach is powerful enough to be extended to all higher order quasi-topological gravity for extracting the corresponding entropy and energy in terms of horizon radius.

Sheykhi, A.; Dehghani, M. H.; Dehghani, R.

2014-04-01

297

A null-tetrad approach to Kerr{endash}Schild gravitational fields in matter

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.}

Udeschini, E.B.; Magli, G. [Dipartimento di Matematica del Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy)] [Dipartimento di Matematica del Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy)

1996-11-01

298

Stochastic mean-field dynamics for fermions in the weak-coupling limit

NASA Astrophysics Data System (ADS)

Assuming that the effect of the residual interaction beyond the mean field is weak and has a short memory time, two approximate treatments of correlation in fermionic systems by means of the Markovian quantum jump are presented. A simplified scenario for the introduction of fluctuations beyond the mean field is presented first. In this theory, part of the quantum correlations between the residual interaction and the one-body density matrix are neglected and jumps occur between many-body densities formed of pairs of states D=|?a>, where |?a> and |?b> are antisymmetrized products of single-particle states. The underlying stochastic mean-field theory is discussed and is applied to the monopole vibration of a spherical Ca40 nucleus under the influence of a statistical ensemble of two-body contact interactions. This framework is however too simplistic to account for both fluctuation and dissipation. In the second part of this work, an alternative quantum jump method is obtained without making the approximation on quantum correlations. By restricting to two-particle two-hole residual interactions, the evolution of the one-body density matrix of a correlated system is transformed into a Lindblad equation. The associated dissipative dynamics can be simulated by quantum jumps between densities written as D=|?> is a normalized Slater determinant. The associated stochastic Schrödinger equation for single-particle wave functions is given.

Lacroix, Denis

2006-04-01

299

Three types of liposomes in aqueous solution were subjected to a low frequency switched weak magnetic field. A differential non-linear dielectric spectroscopy (DNLDS) was performed at 40 degrees C with two planar orthogonal electrodes, positioned parallel and vertical to the earth surface. The difference of the free voltage release (FVR) signals for the two orthogonal directions following electric pulses with an amplitude of 1.0 V and a duration of 25 ms, were Fourier-transformed. An additional magnetic field was switched with a period of 400 ms and a variable amplitude from 0 to 100 G, whose direction was parallel to the vertical electrode plane. With two of the liposomes (egg yolk lecithin (EY), asolectin doped with cholesterol (ASCO)) a decrease of the signal amplitude with increasing magnetic fields could be seen in most of the 25 observed harmonic frequencies (relative to the electric pulse frequency f(0) = 40 Hz). For EY liposomes this decrease was highly significant and not linear for the 1.-5., and above the 20. harmonic frequency, ASCO liposomes showed a similar effect. Asolectin liposomes showed the reverse response. Quantum mechanical conditions of charges on the liposome surface are discussed as a possible origin of these effects PMID:12872934

Pazur, Alexander

2003-01-01

300

Hanle effect in the solar Ba II D2 line: a diagnostic tool for chromospheric weak magnetic fields

The physics of the solar chromosphere depends in a crucial way on its magnetic structure. However there are presently very few direct magnetic field diagnostics available for this region. Here we investigate the diagnostic potential of the Hanle effect on the Ba II D2 line resonance polarization for the determination of weak chromospheric turbulent magnetic fields......

M. Faurobert; M. Derouich; V. Bommier; J. Arnaud

2009-01-03

301

We present an experiment of nonclassical interference between an intrinsically pure heralded single-photon state and a weak coherent state. Our experiment demonstrates that, without the use of bandpass filters, spectrally pure single photons can have high-visibility (89.4{+-}0.5%) interference with photons from a weak coherent field. Our scheme lays the groundwork for future experiments requiring quantum interference between photons in nonclassical states and those in coherent states.

Jin Ruibo; Zhang Jun; Matsuda, Nobuyuki; Mitsumori, Yasuyoshi; Kosaka, Hideo; Edamatsu, Keiichi [Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Shimizu, Ryosuke [PRESTO, Japan Science and Technology Agency, Kawaguchi 332-0012 (Japan)

2011-03-15

302

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 ?-potential and overcharging the particle surface; changes in the ?-potential are more pronounced for samples with higher CD. In mixtures of cationic and anionic PEs, in a wide range of their composition, the ?-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 (Vef) of polystyrene, graphite and aluminium-oxide particles in strong fields (100-400V/cm). This is in contrast to the electrophoresis in weak fields (5-20V/cm) in which adsorption of these polymers gives a drop in Vef 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

Barany, Sandor

2014-11-18

303

Gravitational Anomaly and Hydrodynamics

We study the anomalous induced current of a vortex in a relativistic fluid via the chiral vortical effect, which is analogous to the anomalous current induced by a magnetic field via the chiral magnetic effect. We perform this analysis at weak and strong coupling. We discuss inequivalent implementations to the chemical potential for an anomalous symmetry. At strong coupling we use a holographic model with a pure gauge and mixed gauge-gravitational Chern-Simons term in the action. We discuss the holographic renormalization and show that the Chern-Simons terms do not induce new divergences. Strong and weak coupling results agree precisely. We also point out that the holographic calculation can be done without a singular gauge field configuration on the horizon of the black hole.

Landsteiner, Karl; Melgar, Luis; Pena-Benitez, Francisco

2011-01-01

304

Gravitational Anomaly and Hydrodynamics

We study the anomalous induced current of a vortex in a relativistic fluid via the chiral vortical effect, which is analogous to the anomalous current induced by a magnetic field via the chiral magnetic effect. We perform this analysis at weak and strong coupling. We discuss inequivalent implementations to the chemical potential for an anomalous symmetry. At strong coupling we use a holographic model with a pure gauge and mixed gauge-gravitational Chern-Simons term in the action. We discuss the holographic renormalization and show that the Chern-Simons terms do not induce new divergences. Strong and weak coupling results agree precisely. We also point out that the holographic calculation can be done without a singular gauge field configuration on the horizon of the black hole.

Karl Landsteiner; Eugenio Megias; Luis Melgar; Francisco Pena-Benitez

2011-11-11

305

A search for weak or complex magnetic fields in the B3V star ? Herculis

NASA Astrophysics Data System (ADS)

We obtained 128 high signal-to-noise ratio Stokes V spectra of the B3V star ? 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 ? 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.

Wade, G. A.; Folsom, C. P.; Petit, P.; Petit, V.; Lignières, F.; Aurière, M.; Böhm, T.

2014-11-01

306

NASA Astrophysics Data System (ADS)

A new experiment named MTV-G, probing a large electron spin-precession due to a possible strong gravitational field, which predicted by large extra dimension model, is started at TRIUMF from 2011. In an electron-nuclear scattering experiment, a strong gravitational field is tested as a large spin precession effect caused by geodetic precession predicted by general relativity theory as a result of a warped space-time around nuclei. Experimental design using spin polarized electron source and Mott-spin analyzer, commissioning experiment and the preliminary results are described.

Tanaka, Saki; Nakaya, Yusuke; Ninomiya, Kazufumi; Nishio, Hironori; Onishi, Junichi; Openshaw, Robert; Pearson, Matthew; Totsuka, Yumi; Murata, Jiro

2014-01-01

307

Optical response of a quantum dot-metal nanoparticle hybrid interacting with a weak probe field.

We study optical effects in a hybrid system composed of a semiconductor quantum dot and a spherical metal nanoparticle that interacts with a weak probe electromagnetic field. We use modified nonlinear density matrix equations for the description of the optical properties of the system and obtain a closed-form expression for the linear susceptibilities of the quantum dot, the metal nanoparticle, and the total system. We then investigate the dependence of the susceptibility on the interparticle distance as well as on the material parameters of the hybrid system. We find that the susceptibility of the quantum dot exhibits optical transparency for specific frequencies. In addition, we show that there is a range of frequencies of the applied field for which the susceptibility of the semiconductor quantum dot leads to gain. This suggests that in such a hybrid system quantum coherence can reverse the course of energy transfer, allowing flow of energy from the metallic nanoparticle to the quantum dot. We also explore the susceptibility of the metal nanoparticle and show that it is strongly influenced by the presence of the quantum dot. PMID:23257986

Kosionis, Spyridon G; Terzis, Andreas F; Sadeghi, Seyed M; Paspalakis, Emmanuel

2013-01-30

308

Enhanced paramagnetic Cu(2+) ions removal by coupling a weak magnetic field with zero valent iron.

A weak magnetic field (WMF) was proposed to enhance paramagnetic Cu(2+) ions removal by zero valent iron (ZVI). The rate constants of Cu(2+) removal by ZVI with WMF at pH 3.0-6.0 were -10.8 to -383.7 fold greater than those without WMF. XRD and XPS analyses revealed that applying a WMF enhanced both the Cu(2+) adsorption to the ZVI surface and the transformation of Cu(2+) to Cu(0) by ZVI. The enhanced Cu(2+) sequestration by ZVI with WMF was accompanied with expedited ZVI corrosion and solution ORP drop. The uneven distribution of paramagnetic Cu(2+) along an iron wire in an inhomogeneous MF verified that the magnetic field gradient force would accelerate the paramagnetic Cu(2+) transportation toward the ZVI surface due to the WMF-induced sharp decay of magnetic flux intensity from ZVI surface to bulk Cu(2+) solution. The paramagnetic Fe(2+) ions generated by ZVI corrosion would also accumulate at the position with the highest magnetic flux intensity on the ZVI surface, causing uneven distribution of Fe(2+), and facilitate the local galvanic corrosion of ZVI, and thus, Cu(2+) reduction by ZVI. The electrochemical analysis verified that the accelerated ZVI corrosion in the presence of WMF partly arose from the Lorentz force-enhanced mass transfer. PMID:25464332

Jiang, Xiao; Qiao, Junlian; Lo, Irene M C; Wang, Lei; Guan, Xiaohong; Lu, Zhanpeng; Zhou, Gongming; Xu, Chunhua

2015-02-11

309

Weak nonlinear analysis of magneto-convection under magnetic field modulation

NASA Astrophysics Data System (ADS)

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.

Bhadauria, B. S.; Kiran, Palle

2014-09-01

310

NASA Astrophysics Data System (ADS)

This study is related to the physics of a snowflake divertor [1]. One of its features is a large size of the zone of a very weak poloidal magnetic field in the divertor area. In this zone, the poloidal plasma beta (defined as a ratio of the plasma pressure to the pressure of a poloidal magnetic field) significantly exceeds unity. This brings up some interesting new features to the equilibrium and convective stability of the divertor plasma. It has recently been suggested [2] that convective instability can spread the heat over a larger area than normally assumed and ``activate'' all four divertor legs of a snowflake divertor, thereby significantly reducing the divertor heat load, especially during the ELM events. A quantitative analysis of the convective instability and/or loss of equilibrium at high poloidal betas will be presented and related to the heat flux reduction for a simplified geometry. Experimentally detectable signatures of plasma convection in the divertor zone will be considered. Work performed for U.S. DoE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344[4pt] [1] D.D. Ryutov, Phys. Plas., 14, 064502, 2007;[0pt] [2] D.D. Ryutov et al., Contrib. Plasma Phys., to be published, 2012.

Ryutov, Dmitri

2012-03-01

311

Classical gauge gravitation theory

Classical gravitation theory is formulated as gauge theory on natural bundles where gauge symmetries are general covariant transformations and a gravitational field is a Higgs field responsible for their spontaneous symmetry breaking.

G. Sardanashvily

2011-10-06

312

Astronomers Use X-Rays To Probe Gravitational Field Of A Neutron Star

NASA Astrophysics Data System (ADS)

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

2002-06-01

313

An effective field theory for gravitating spinning objects in the post-Newtonian scheme

An effective field theory for gravitating spinning objects in the post-Newtonian approximation is formulated 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. We then proceed to construct the spin-induced nonminimal couplings, where we obtain the leading order couplings to all orders in spin for the first time. We specify to a 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 conveniently integrated out. The equations of motion of spin are then directly obtained via a proper variation of the action, and they take on a simple form. We implement this effective field ...

Levi, Michele

2015-01-01

314

A 660 D&O Gravitational Field of the Moon from the GRAIL Primary Mission

NASA Astrophysics Data System (ADS)

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.

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

315

NASA Astrophysics Data System (ADS)

Some new interesting solutions, the dynamics, behaviour and phenomena of rotating charged perfect fluid models are investigated, and their physical and geometrical properties are studied in order to substantiate the possibility of the existence of such astrophysical bodies in this Universe. The nature and role of the metric rotation ?( r, t) as well as that of the matter rotation ?( r, t) are studied for uniform and non-uniform motions. The reactions of the gravitational and charged fields with respect to the rotational motion are studied and possible results are explored for real astrophysical situations, and in some solutions we find the spatial restrictions on the models for realistic conditions. Rotating models which are expanding are obtained in which the rotational motions are decaying with time.

Singh, Koijam Manihar

2010-01-01

316

Evolution of geodesic congruences in a gravitationally collapsing scalar field background

NASA Astrophysics Data System (ADS)

The evolution of timelike geodesic congruences in a spherically symmetric, nonstatic, inhomogeneous spacetime representing gravitational collapse of a massless scalar field is studied. We delineate how initial values of the expansion, rotation, and shear of a congruence, as well as the spacetime curvature, influence the global behavior and focusing properties of a family of trajectories. Under specific conditions, the expansion scalar is shown to exhibit a finite jump (from negative to positive value) before focusing eventually occurs. This nonmonotonic behavior of the expansion, observed in our numerical work, is successfully explained through an analysis of the equation for the expansion. Finally, we bring out the role of the metric parameters (related to nonstaticity and spatial inhomogeneity) in shaping the overall behavior of geodesic congruences.

Shaikh, Rajibul; Kar, Sayan; DasGupta, Anirvan

2014-12-01

317

Capture of cosmic objects by central gravitational field of a galaxy cluster

The effect of capture of a cosmic object by the central gravitational field of a galaxy cluster is described in the expanding Universe. The cosmic evolution can be the origin of the capture explaining formation of galaxies and their clusters from the homogenous distribution of matter in the Universe. The Newton-like equation of the capture is derived for arbitrary equations of state in terms of the red shift parameter, and the influence of the Hubble velocities on the rotational curves is studied. The obtained rotational curves show us that the deficit of the visible matter for superclusters $M\\sim 10^{15}M_{\\odot}$ can be increased in the version of cosmology where observational quantities are identified with the conformal ones.

Piotr Flin; Victor Pervushin; Andrey Zorin

2004-06-02

318

An improved model of the Earth's gravitational field: GEM-T1

NASA Technical Reports Server (NTRS)

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.

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

319

Improved model of the Earth's gravitational field: GEM-T1

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.

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

320

Wave convection regimes in a binary mixture in a modulated gravitational field

Nonlinear wave convection regimes are studied in a horizontal layer of an incompressible binary mixture with anomalous thermal diffusion in the gravitational field modulated with an arbitrary amplitude and finite frequency. Oscillation regimes are numerically simulated by the finite difference method for the case of a layer with impenetrable rigid boundaries, which better corresponds to experimental laboratory conditions. A qualitative difference is found in the dynamics of nonlinear quasi-periodic and subharmonic oscillations appearing in the initially stratified mixture and behaving as modulated and regular standing waves. The dependences of the intensity of convective flows on the modulation amplitude are obtained. The results of nonlinear calculations are compared with data on the boundaries of the equilibrium stability found from the linear theory. It is shown that a region of parameters exists where alternating action suppresses the convective motion.

Myznikova, B. I. [Russian Academy of Sciences, Institute of Mechanics of Continuous Media, Ural Branch (Russian Federation); Smorodin, B. L., E-mail: bsmorodin@yandex.ru [Perm State University (Russian Federation)

2011-03-15

321

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

Plocková, J; Chmelík, J

2001-05-25

322

Fermions in Gravitation Theory

In gravitation theory, a fermion field must be regarded only in a pair with a certain tetrad gravitational field. These pairs can be represented by sections of the composite spinor bundle $S\\to\\Si\\to X^4$ where values of gravitational fields play the role of parameter coordinates, besides the familiar world coordinates.

G. Sardanashvily

1995-08-21

323

Probing Gravitational Dark Matter

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) acts 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 $\\chi_s$. It is a $\\mathbb{Z}_2$ odd singlet under the standard model (SM) gauge group, and naturally joins the unique dimension-4 interaction with Ricci curvature, $\\xi_s\\chi_s^2{\\cal R}$, where $\\xi_s$ is the dimensionless nonminimal coupling. We demonstrate that this gravitational interaction $\\xi_s\\chi_s^2{\\cal R}$, together with Higgs-curvature nonminimal coupling term $\\xi_h H^\\dag H {\\cal R}$, induces effective couplings between $\\chi_s^2$ and SM fields which 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.

Jing Ren; Hong-Jian He

2014-10-23

324

Gravitational Shielding Effects in Gauge Theory of Gravity

In 1992, E.E.Podkletnov and R.Nieminen find that, under certain conditions, ceramic superconductor with composite structure has revealed weak shielding properties against gravitational force. In classical Newton's theory of gravity and even in Einstein's general theory of gravity, there are no grounds of gravitational shielding effects. But in quantum gauge theory of gravity, the gravitational shielding effects can be explained in a simple and natural way. In quantum gauge theory of gravity, gravitational gauge interactions of complex scalar field can be formulated based on gauge principle. After spontaneous symmetry breaking, if the vacuum of the complex scalar field is not stable and uniform, there will be a mass term of gravitational gauge field. When gravitational gauge field propagates in this unstable vacuum of the complex scalar field, it will decays exponentially, which is the nature of gravitational shielding effects. The mechanism of gravitational shielding effects is studied in this paper, and some main properties of gravitational shielding effects are discussed.

Ning Wu

2003-07-23

325

The R.I. Pimenov unified gravitation and electromagnetism field theory as semi-Riemannian geometry

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.

Gromov, N. A., E-mail: gromov@dm.komisc.r [Komi Science Center UrD RAS, Department of Mathematics (Russian Federation)

2009-05-15

326

Mean-field modeling of the encapsulation of weakly acidic molecules in polyelectrolyte dendrimers.

The unique architecture of dendrimers has attracted interest in a wide variety of biomedical applications such as drug delivery. In order to gain insight into the solubilization of drugs inside dendrimer architectures, we have developed and numerically implemented a self-consistent field theory model for the equilibrium characteristics of charged dendrimer molecules in the presence of weakly acidic drug molecules. Using such a model, we examine the relative influence of excluded volume, electrostatic, and local enthalpic interactions upon the solubilization of drugs in dendrimers. When only excluded volume interactions are accounted, there is no driving force for drug solubilization inside the dendrimer, and hence depletion of the drug from the dendrimer molecule (relative to the bulk drug concentration) is observed. The inclusion of electrostatic interactions within the model results in solubilization of drugs within the dendrimer. The solubilization of the drugs is shown to increase with increasing drug charge density and increasing dendrimer generation number. We probe the effect of enthalpic interactions and demonstrate that the number of drug molecules encapsulated through enthalpic interaction is dependent upon the number of dendrimer monomers, the enthalpic interaction parameters between the dendrimer and drug (?PD), and the drug and solvent (?DS). We also analyze the combined effects of the preceding interactions to identify the synergism in their influence and delineate the relative importance of different parameters such as pOH, size of the drugs, and the Bjerrum length of the solution in influencing the encapsulation of drugs by dendrimer molecules. PMID:22708899

Lewis, Thomas; Ganesan, Venkat

2012-07-19

327

NASA Astrophysics Data System (ADS)

We develop an analytical device model for graphene bilayer field-effect transistors (GBL-FETs) with the back and top gates. The model is based on the Boltzmann equation for the electron transport and the Poisson equation in the weak nonlocality approximation for the potential in the GBL-FET channel. The potential distributions in the GBL-FET channel are found analytically. The source-drain current in GBL-FETs and their transconductance are expressed in terms of the geometrical parameters and applied voltages by analytical formulas in the most important limiting cases. These formulas explicitly account for the short-gate effect and the effect of drain-induced barrier lowering. The parameters characterizing the strength of these effects are derived. It is shown that the GBL-FET transconductance exhibits a pronounced maximum as a function of the top-gate voltage swing. The interplay of the short-gate effect and the electron collisions results in a nonmonotonic dependence of the transconductance on the top-gate length.

Ryzhii, V.; Ryzhii, M.; Satou, A.; Otsuji, T.; Mitin, V.

2011-03-01

328

Non-thermal mechanism of weak microwave fields influence on neurons

NASA Astrophysics Data System (ADS)

A non-thermal mechanism of weak microwave field impact on a nerve fiber is proposed. It is shown that in the range of about 30-300 GHz, there are strongly pronounced resonances associated with the excitation of ultrasonic vibrations in the membrane as a result of interaction with electromagnetic radiation. The viscous dissipation limits the resonances and results in their broadening. These forced vibrations create acoustic pressure, which may lead to the redistribution of the protein transmembrane channels, and thus changing the threshold of the action potential excitation in the axons of the neural network. The influence of the electromagnetic microwave radiation on various specific areas of myelin nerve fibers was analyzed: the nodes of Ranvier, and the initial segment—the area between the neuron hillock and the first part of the axon covered with the myelin layer. It was shown that the initial segment is the most sensitive area of the myelined neurons from which the action potential normally starts.

Shneider, M. N.; Pekker, M.

2013-09-01

329

hal-00022129,version3-2Apr2007 Semiclassical Dynamics of Dirac particles interacting with a Static Gravitational Field Pierre Gosselin1 , Alain BÂ´erard2 and HervÂ´e Mohrbach2 1 UniversitÂ´e Grenoble I, InstitutÂ´eculaire et des Collisions, 1, boulevard Arago, 57078 Metz, France The semiclassical limit for Dirac particles

Boyer, Edmond

330

Weak magnetic field significantly enhances selenite removal kinetics by zero valent iron.

The effect of weak magnetic field (WMF) on Se(IV) removal by zero valent iron (ZVI) was investigated as functions of pH and initial Se(IV) concentrations. The presence of WMF significantly accelerated Se(IV) removal and extended the working pH range of ZVI from 4.0-6.0 to 4.0-7.2. The WMF induced greater enhancement in Se(IV) removal by ZVI at lower initial Se(IV) concentrations. The influence of WMF on Se(IV) removal by ZVI was associated with a more dramatic drop in ORP and a more rapid release of Fe(2+) compared to the case without WMF. SEM and XRD analysis revealed that WMF accelerated the corrosion of ZVI and the transformation of amorphous iron (hdyr)oxides to lepidocrocite. XANES analyses showed that WMF expedited the reduction of Se(IV) to Se(0) by ZVI at pH 6.0 when its initial concentration was ?20.0 mg L(-1). Se(IV) dosed at 40.0 mg L(-1) was removed by ZVI via adsorption followed by reduction to Se(0) at pH 7.0 but via adsorption at 7.2 in the presence of WMF. Regardless of WMF, Se(IV) applied at 40.0 mg L(-1) was removed by reduction at pH 4.0-6.0. The WMF-induced improvement in Se(IV) removal by ZVI may be mainly attributable to the Lorentz force and magnetic field gradient force. Employing WMF to enhance Se(IV) removal by ZVI is a promising and environmental-friendly method since it does not need extra energy and costly reagents. PMID:24199999

Liang, Liping; Sun, Wu; Guan, Xiaohong; Huang, Yuying; Choi, Wonyong; Bao, Hongliang; Li, Lina; Jiang, Zheng

2014-02-01

331

Neuroprotective effect of weak static magnetic fields in primary neuronal cultures.

Low intensity static magnetic fields (SMFs) interact with various biological tissues including the CNS, thereby affecting key biological processes such as gene expression, cell proliferation and differentiation, as well as apoptosis. Previous studies describing the effect of SMFs on apoptotic cell death in several non-neuronal cell lines, emphasize the importance of such a potential modulation in the case of neurodegenerative disorders, where apoptosis constitutes a major route via which neurons degenerate and die. In this study, we examine the effect of SMFs on neuronal survival in primary cortical and hippocampal neurons that constitute a suitable experimental system for modeling the neurodegenerative state in vitro. We show that weak SMF exposure interferes with the apoptotic programing in rat primary cortical and hippocampal neurons, thereby providing protection against etoposide-induced apoptosis in a dose- and time-dependent manner. Primary cortical neurons exposed to SMF (50G) for 7days exhibited a 57.1±6.3% decrease in the percentage of cells undergoing apoptosis induced by etoposide (12?M), accompanied by a marked decrease in the expression of the pro-apoptotic markers: cleaved poly ADP ribose polymerase-1, cleaved caspase-3, active caspase-9 and the phospho-histone H2A variant (Ser139) by 41.0±5.0%, 81.2±5.0%, 72.9±6.4%, 42.75±2.9%, respectively, and by a 57.2±1.0% decrease in the extent of mitochondrial membrane potential collapse. Using the L-type voltage-gated Ca(2+) channel inhibitor nifedipine, which is selective to Ca(2+) influx through Cav1.2, we found that the anti-apoptotic effect of SMFs was mediated by Ca(2+) influx through these channels. Our findings demonstrating altered Ca(2+)-influx in response to thapsigargin stimulation in SMF-exposed cortical neurons, along with enhanced inhibition of KCl-induced Ca(2+)-influx through Cav1.2 channels and enhanced expression of Cav1.2 and Cav1.3 channels, allude to the involvement of voltage- and store-operated Ca(2+) channels in various aspects of the protective effect exerted by SMFs. These findings show the potential susceptibility of the CNS to weak SMF exposure and have implications for the design of novel strategies for the treatment and/or prevention of neurodegenerative diseases. PMID:25171788

Ben Yakir-Blumkin, M; Loboda, Y; Schächter, L; Finberg, J P M

2014-10-10

332

An analysis of a variety of existing experimental data leads to the conclusion on the existence of a resonance mechanism allowing weak magnetic fields to affect biological processes. These fields may either be static magnetic fields comparable in magnitude with the magnetic field of the earth or weak ultra-low frequency time-dependent fields. So far, a generally accepted theoretical model allowing one to understand the effect of magnetic and electric fields on biological processes is not available. By this reason, it is not clear which characteristics of the fields, like magnetic and electric field strength, frequency of change of the field, shape of the electromagnetic wave, the duration of the magnetic or electric influence or some particular combination of them, are responsible for the biological effect. In the present analysis it is shown that external time-independent magnetic fields may cause a resonance amplification of ionic electric currents in biological tissues and, in particular, in the vasculature system due to a Brownian motion of charges. These resonance electric currents may cause necrotic changes in the tissues or blood circulation and in this way significantly affect the biological organism. The magnitude of the magnetic fields leading to resonance effects is estimated, it is shown that it depends significantly on the radius of the blood capillaries.

Zakirjon Kanokov; Juern W. P. Schmelzer; Avazbek K. Nasirov

2009-04-07

333

NASA Technical Reports Server (NTRS)

Semiconductor crystals such as Hg(1-x)CD(x)Te grown by unidirectional solidification Bridgmann method have shown compositional segregations in both the axial and radial directions. Due to the wide separation between the liquidus and the solidus of its pseudobinary phase diagram, there is a diffusion layer of higher HgTe content built up in the melt near the melt-solid interface which gives a solute concentration gradient in the axial direction. The value of effective diffusion coefficient calculated from fitting of the data to 1D model varies with Hg(1-x)Cd(x)Te growth conditions. This indicates that the growth condition of the Hg(1-x)Cd(x)Te is not purely diffusion controlled. Because of the higher thermal conductivity in the melt than that in the crystal in the growth system, there is a thermal leakage through the fused silica crucible wall near the melt-solid interface. This gives a thermal gradient in the radial direction. Hart, and Thorpe, Hutt and Soulsby have shown that under such conditon a fluid will become convectively unstable as a result of different diffusitivities of temperature and solute. It is quite important to understand the effects of this thermosolute convection on the compositonal segregation in both axial and radial directions in the unidirectionally solidified crystals under various gravitational directions. To reach this goal, we start with a simplified problem to study the effects of thermal-solutal convection on the temperature and solutal fields under various gravitional orientations. We begin by reviewing model governing equations.

Wang, Jai-Ching

1993-01-01

334

NASA Astrophysics Data System (ADS)

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.

Solovyov, A. V.; Talipov, D. V.; Borodin, A. S.; Tuzhilkin, D. A.; Baklykova, E. S.; Pobachenko, S. V.

2014-11-01

335

Four-Field Equations: a New Model for Weakly Compressible MHD Turbulence in the Solar Wind Flight Center Turbulent plasmas in the solar wind and the interstellar medium of- ten contain a large to be in agreement. The scaling of density uctuations with Mach number are compared with solar wind data from Helios

Ng, Chung-Sang

336

Error-field induced electromagnetic torques in a large aspect-ratio, low- , weakly shaped tokamak March 2009 The toroidal electromagnetic braking torques exerted at the various internal rational localized toroidal electromagnetic torques which brake the plasma rotation. Moreover, if the error

Fitzpatrick, Richard

337

Doubly excited circular Ba(6pj, 21c) states : e-e interaction effects in weak external fields

The behaviour of doubly excited circular atoms in weak parallel electric and magnetic fields has been studied. The Hamiltonian, including the e-e interaction between the two excited electrons, Stark and Zeeman effects, is diagonalized in a truncated basis. The Rydberg electron, initially in a circular state, experiences a mixing of its orbital and magnetic quantum numbers, due to the presence

L. Chen; M. Chéret; M. Poirier; F. Roussel; T. Bolzinger; G. Spiess

1992-01-01

338

Probing Yukawian gravitational potential by numerical simulations. I. Changing N-body codes

NASA Astrophysics Data System (ADS)

In the weak field limit general relativity reduces, as is well known, to the Newtonian gravitation. Alternative theories of gravity, however, do not necessarily reduce to Newtonian gravitation; some of them, for example, reduce to Yukawa-like potentials instead of the Newtonian potential. Since the Newtonian gravitation is largely used to model with success the structures of the universe, such as for example galaxies and clusters of galaxies, a way to probe and constrain alternative theories, in the weak field limit, is to apply them to model the structures of the universe. In the present study, we consider how to probe Yukawa-like potentials using N-body numerical simulations.

Brandao, C. S. S.; de Araujo, J. C. N.

2010-04-01

339

Probing Yukawian gravitational potential by numerical simulations. II. Elliptical galaxies

NASA Astrophysics Data System (ADS)

Since the Newtonian gravitation is largely used to model with success the structures of the universe, such as galaxies and clusters of galaxies, for example, a way to probe and constrain alternative theories, in the weak field limit, is to apply them to model the structures of the universe. We then modified the well known Gadget-2 code to probe alternative theories of gravitation through galactic dynamics. In particular, we modified the Gadget-2 code to probe alternatives theories whose weak field limits have a Yukawa-like gravitational potential. As a first application of this modified Gadget-2 code we simulate the evolution of elliptical galaxies. These simulations show that galactic dynamics can be used to constrain the parameters associated with alternative theories of gravitation.

Brandao, C. S. S.; de Araujo, J. C. N.

2010-03-01

340

Black holes and fundamental fields: Hair, kicks, and a gravitational Magnus effect

NASA Astrophysics Data System (ADS)

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.

Okawa, Hirotada; Cardoso, Vitor

2014-11-01

341

Black holes and fundamental fields: hair, kicks and a gravitational "Magnus" effect

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 fundamental scalar is massive.

Hirotada Okawa; Vitor Cardoso

2014-05-19

342

Activating persulfate by Fe? coupling with weak magnetic field: performance and mechanism.

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

Xiong, Xinmei; Sun, Bo; Zhang, Jing; Gao, Naiyun; Shen, Jimin; Li, Jialing; Guan, Xiaohong

2014-10-01

343

Dynamics of Fermat potentials in non-perturbative gravitational lensing

We present a framework, based on the null-surface formulation of general relativity, for discussing the dynamics of Fermat potentials for gravitational lensing in a generic situation without approximations of any kind. Additionally, we derive two lens equations: one for the case of thick compact lenses and the other one for lensing by gravitational waves. These equations in principle generalize the astrophysical scheme for lensing by removing the thin-lens approximation while retaining the weak fields.

Simonetta Frittelli; Ezra T. Newman

2002-05-03

344

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.

Imshennik, V. S., E-mail: imshennik@itep.r [Institute of Theoretical and Experimental Physics (Russian Federation)

2010-04-15

345

Bound states of spin-half particles in a static gravitational field close to the black hole field

NASA Astrophysics Data System (ADS)

We consider the bound-state energy levels of a spin-1/2 fermion in the gravitational field of a near-black hole object. In the limit that the metric of the body becomes singular, all binding energies tend to the rest-mass energy (i.e. total energy approaches zero). We present calculations of the ground state energy for three specific interior metrics (Florides, Soffel and Schwarzschild) for which the spectrum collapses and becomes quasi-continuous in the singular metric limit. The lack of zero or negative energy states prior to this limit being reached prevents particle pair production occurring. Therefore, in contrast to the Coulomb case, no pairs are produced in the non-singular static metric. For the Florides and Soffel metrics the singularity occurs in the black hole limit, while for the Schwarzschild interior metric it corresponds to infinite pressure at the centre. The behaviour of the energy level spectrum is discussed in the context of the semi-classical approximation and using general properties of the metric.

Spencer-Smith, A. F.; Gossel, G. H.; Berengut, J. C.; Flambaum, V. V.

2013-03-01

346

A Dust-Penetrated Classification Scheme for Bars as Inferred from their Gravitational Force Fields

NASA Astrophysics Data System (ADS)

The division of galaxies into barred (SB) and normal (S) spirals is a fundamental aspect of the Hubble galaxy classification system. This tuning fork view was revised by de Vaucouleurs, whose classification volume recognized apparent bar strength (SA, SAB, SB) as a continuous property of galaxies called the ``family.'' However, the SA, SAB, and SB families are purely visual judgments that can have little bearing on the actual bar strength in a given galaxy. Until recently, published bar judgments were based exclusively on blue light images, where internal extinction or star formation can completely mask a bar. Near-infrared camera arrays, which principally trace the old stellar population in both normal and barred galaxies, now facilitate a quantification of bar strength in terms of gravitational potentials and force fields. In this paper, we show that the maximum value of the ratio of the tangential force to the mean axisymmetric radial force is a quantitative measure of the strength of a bar that can be straightforwardly derived for many galaxies. We show that a wide range of true bar strengths characterizes the category SB, while category SAB corresponds to a narrower range of bar strengths. Based on the force ratio, we define seven classes of bar strength and incorporate these classes into a dust-penetrated classification system for spiral galaxies. This work was supported by NSF grant AST 9617154 and the Anglo-American Chairman's Fund, Mrs. M. Keeton, CEO.

Buta, R.; Block, D. L.

2001-05-01

347

Light deflection in the post-linear gravitational field of bounded point-like masses

Light deflection in the post-linear gravitational field of two bounded point-like masses is treated. Both the light source and the observer are assumed to be located at infinity in an asymptotically flat space. The equations of light propagation are explicitly integrated to the second order in $G/c^2$. Some of the integrals are evaluated by making use of an expansion in powers of the ratio of the relative separation distance to the impact parameter $(r_{12}/\\xi)$. A discussion of which orders must be retained to be consistent with the expansion in terms of $G/c^2$ is given. It is shown that the expression obtained in this paper for the angle of light deflection is fully equivalent to the expression obtained by Kopeikin and Sch\\"afer up to the order given there. The deflection angle takes a particularly simple form for a light ray originally propagating orthogonal to the orbital plane of a binary with equal masses. Application of the formulae for the deflection angle to the double pulsar PSR J0737-3039 for an impact parameter five times greater than the relative separation distance of the binary's components shows that the corrections to the Epstein-Shapiro light deflection angle of about $10^{-6}$ arcsec lie between $10^{-7}$ and $10^{-8}$ arcsec.

Michael H. Brügmann

2005-05-27

348

The self-consistent field theory (SCFT) is employed to numerically study the response of weak polybase type polymer chains grafted on a sphere to electric fields generated by the uniform positive or negative charges on the grafting substrate in the planar polyelectrolyte brush limit. Also the effect of curvature of the grafting sphere on the brush height of weak polybase brushes in the absence of surface charges is investigated. The numerical study reveals interesting and nontrivial dependence of the brush height on the radius of the grafting substrate. Consistent with experimental results, in the parameter range of the surface charge density examined, the brush height is found to be independent of the applied electric field at intermediate and high grafting densities. At relatively low grafting density, the applied negative surface charge which is termed as negative bias in this study results in a reduction of the brush height. At rather low grafting density, the positive bias corresponding to applied positive surface charges can lead to a slight increase in the brush height. The underlining mechanism governing the response of weak polybase brushes to the applied electric field is elucidated. PMID:25459349

Tong, Chaohui

2014-12-23

349

Detection of weak magnetic fields induced by neuronal electrical activities using magnetic-resonance imaging is a potentially effective method for functional imaging of the brain. In this study, we performed a numerical analysis of the theoretical limit of sensitivity for detecting weak magnetic fields induced in the human brain. The limit of sensitivity was estimated from the intensities of signal and

Tomohisa Hatada; Masaki Sekino; Shoogo Ueno

2005-01-01

350

Multiparameter investigation of gravitational slip

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.

Daniel, Scott F.; Caldwell, Robert R. [Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire 03755 (United States); Cooray, Asantha; Serra, Paolo [Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Melchiorri, Alessandro [Physics Department and Sezione INFN, University of Rome, 'La Sapienza', Piazzale Aldo Moro 2, 00185 Rome (Italy)

2009-07-15

351

ON THE GRAVITATIONAL FIELDS OF MACLAURIN SPHEROID MODELS OF ROTATING FLUID PLANETS

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.

Kong, Dali; Zhang, Keke [Center for Geophysical and Astrophysical Fluid Dynamics and Department of Mathematical Sciences, University of Exeter, Exeter EX4 4QF (United Kingdom)] [Center for Geophysical and Astrophysical Fluid Dynamics and Department of Mathematical Sciences, University of Exeter, Exeter EX4 4QF (United Kingdom); Schubert, Gerald, E-mail: D.Kong@exeter.ac.uk, E-mail: kzhang@ex.ac.uk, E-mail: schubert@ucla.edu [Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA (United States)] [Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA (United States)

2013-02-10

352

REVIEW ARTICLE: Experiments on gravitation

The theoretical setting of the experimental study of gravitation is indicated and a brief account is given of experiments on gravitation from Newton onwards. The main content of the review comprises surveys of three groups of experiment: the investigation of the inverse square law, studies of the weak equivalence principle and determinations of the constant of gravitation. Attention is called

A. Cook

1988-01-01

353

A measurement of weak lensing by large scale structure in RCS fields

We have analysed ~24 square degrees of R_C-band imaging data from the Red-Sequence Cluster Survey (RCS), and measured the excess correlations between galaxy ellipticities on scales ranging from 1 to 30 arcminutes. We have used data from two different telescopes: ~16.4 square degrees of CFHT data and ~7.6 square degrees of CTIO 4-meter data, distributed over 13 widely separated patches. For the first time, a direct comparison can be made of the lensing signal measured using different instruments, which provides an important test of the weak lensing analysis itself. The measurements obtained from the two telescopes agree well. For the lensing analysis we use galaxies down to a limiting magnitude of R_C=24, for which the redshift distribution is known relatively well. This allows us to constrain some cosmological parameters. For the currently favored $\\Lambda$CDM model $(\\Omega_m=0.3, \\Omega_\\Lambda=0.7, \\Gamma=0.21)$ we obtain $\\sigma_8=0.81^{+0.14}_{-0.19}$ (95% confidence), in agreement with the results from Van Waerbeke et al. (2001) which used fainter galaxies (and consequently higher redshift galaxies). The good agreement between these two very different weak lensing studies demonstrates that weak lensing is a useful tool in observational cosmology.

Henk Hoekstra; Howard K. C. Yee; Michael D. Gladders; L. Felipe Barrientos; Patrick B. Hall; Leopoldo Infante

2002-02-14

354

Relativistic Transverse Gravitational Redshift

NASA Astrophysics Data System (ADS)

The parametrized post-Newtonian (PPN) formalism is a tool for quantitative analysis of the weak gravitational field based on the field equations of general relativity. This formalism and its ten parameters provide the practical theoretical foundation for the evaluation of empirical data produced by space-based missions designed to map and better understand the gravitational field (e.g., GRAIL, GRACE, GOCE). Accordingly, mission data is interpreted in the context of the canonical PPN formalism; unexpected, anomalous data are explained as similarly unexpected but apparently real physical phenomena, which may be characterized as ``gravitational anomalies," or by various sources contributing to the total error budget. Another possibility, which is typically not considered, is a small modeling error in canonical general relativity. The concept of the idealized point-mass spherical equipotential surface, which originates with Newton's law of gravity, is preserved in Einstein's synthesis of special relativity with accelerated reference frames in the form of the field equations. It was not previously realized that the fundamental principles of relativity invalidate this concept and with it the idea that the gravitational field is conservative (i.e., zero net work is done on any closed path). The ideal radial free fall of a material body from arbitrarily-large range to a point on such an equipotential surface (S) determines a unique escape-velocity vector of magnitude v collinear to the acceleration vector of magnitude g at this point. For two such points on S separated by angle d? , the Equivalence Principle implies distinct reference frames experiencing inertial acceleration of identical magnitude g in different directions in space. The complete equivalence of these inertially-accelerated frames to their analogous frames at rest on S requires evaluation at instantaneous velocity v relative to a local inertial observer. Because these velocity vectors are not parallel, a symmetric energy potential exists between the frames that is quantified by the instantaneous ? {v} = v\\cdot{d}? between them; in order for either frame to become indistinguishable from the other, such that their respective velocity and acceleration vectors are parallel, a change in velocity is required. While the qualitative features of general relativity imply this phenomenon (i.e., a symmetric potential difference between two points on a Newtonian `equipotential surface' that is similar to a friction effect), it is not predicted by the field equations due to a modeling error concerning time. This is an error of omission; time has fundamental geometric properties implied by the principles of relativity that are not reflected in the field equations. Where b is the radius and g is the gravitational acceleration characterizing a spherical geoid S of an ideal point-source gravitational field, an elegant derivation that rests on first principles shows that for two points at rest on S separated by a distance d << b, a symmetric relativistic redshift exists between these points of magnitude z = gd2/bc^2, which over 1 km at Earth sea level yields z ˜{10-17}. It can be tested with a variety of methods, in particular laser interferometry. A more sophisticated derivation yields a considerably more complex predictive formula for any two points in a gravitational field.

Mayer, A. F.

2012-12-01

355

A special-relativistic scalar-vector theory of gravitation is presented which mimics an important class of solutions of Einstein's gravitational field equations. The theory includes solutions equivalent to Schwarzschild, Kerr, Reissner-Nordstroem, and Friedman metrics as well as to gravitational waves. In fact, all the empirical tests until now due to general relativity can be explained within this flat spacetime theory.

H. Goenner; M. Leclerc

2000-11-29

356

Contribution of gravitational potential energy differences to the global stress field

NASA Astrophysics Data System (ADS)

Modelling the lithospheric stress field has proved to be an efficient means of determining the role of lithospheric versus sublithospheric buoyancies and also of constraining the driving forces behind plate tectonics. Both these sources of buoyancies are important in generating the lithospheric stress field. However, these sources and the contribution that they make are dependent on a number of variables, such as the role of lateral strength variation in the lithosphere, the reference level for computing the gravitational potential energy per unit area (GPE) of the lithosphere, and even the definition of deviatoric stress. For the mantle contribution, much depends on the mantle convection model, including the role of lateral and radial viscosity variations, the spatial distribution of density buoyancies, and the resolution of the convection model. GPE differences are influenced by both lithosphere density buoyancies and by radial basal tractions that produce dynamic topography. The global lithospheric stress field can thus be divided into (1) stresses associated with GPE differences (including the contribution from radial basal tractions) and (2) stresses associated with the contribution of horizontal basal tractions. In this paper, we investigate only the contribution of GPE differences, both with and without the inferred contribution of radial basal tractions. We use the Crust 2.0 model to compute GPE values and show that these GPE differences are not sufficient alone to match all the directions and relative magnitudes of principal strain rate axes, as inferred from the comparison of our depth integrated deviatoric stress tensor field with the velocity gradient tensor field within the Earth's plate boundary zones. We argue that GPE differences calibrate the absolute magnitudes of depth integrated deviatoric stresses within the lithosphere; shortcomings of this contribution in matching the stress indicators within the plate boundary zones can be corrected by considering the contribution from horizontal tractions associated with density buoyancy driven mantle convection. Deviatoric stress magnitudes arising from GPE differences are in the range of 1-4 TN m-1, a part of which is contributed by dynamic topography. The EGM96 geoid data set is also used as a rough proxy for GPE values in the lithosphere. However, GPE differences from the geoid fail to yield depth integrated deviatoric stresses that can provide a good match to the deformation indicators. GPE values inferred from the geoid have significant shortcomings when used on a global scale due to the role of dynamically support of topography. Another important factor in estimating the depth integrated deviatoric stresses is the use of the correct level of reference in calculating GPE. We also elucidate the importance of understanding the reference pressure for calculating deviatoric stress and show that overestimates of deviatoric stress may result from either simplified 2-D approximations of the thin sheet equations or the assumption that the mean stress is equal to the vertical stress.

Ghosh, Attreyee; Holt, William E.; Flesch, Lucy M.

2009-11-01

357

The first order perturbations of the energy levels of a stationary hydrogen atom in static external gravitational field, with Schwarzschild metric, are investigated. The energy shifts are calculated for the relativistic 1S, 2S, 2P, 3S, 3P, 3D, 4S, 4P, 4D and 4F levels. The results show that the energy-level shifts of the states with total angular momentum quantum number 1/2 are all zero, and the ratio of absolute energy shifts with total angular momentum quantum number 5/2 is 1:4:5. This feature can be used to help us to distinguish the gravitational effect from other effect.

Zhen-Hua Zhao; Yu-Xiao Liu; Xi-Guo Li

2007-09-17

358

First scalar magnetic anomaly map from CHAMP satellite data indicates weak lithospheric field

Satellite magnetic anomaly maps derived by different techniques from Magsat\\/POGO data vary by more than a factor of 2 in the deduced strength of the lithospheric magnetic field. Here, we present a first anomaly map from new CHAMP scalar magnetic field data. After subtracting a recent Ørsted main and external field model, we remove remaining unmodeled large-scale external contributions from

S. Maus; M. Rother; R. Holme; H. Lühr; N. Olsen; V. Haak

2002-01-01

359

Kinetic theory of low-frequency cross-field instability in a weakly ionized plasma. I

A consistent kinetic theory is developed for the description of electrons under conditions of a low-frequency two-stream {bold E}{times}{bold B} instability in collisionally dominated, weakly ionized plasmas. Starting from the Boltzmann collision integral, a simplified kinetic equation for the electron distribution function has been derived, which takes into account strong pitch-angle scattering of electrons by neutrals, velocity dependence of the electron--neutral collision frequency, etc. Linearized equations describing small oscillations of the electron distribution function and ion density are presented. For the asymptotic case of short waves, the dispersion relation of the {bold E}{times}{bold B} instability has been obtained and analyzed under conditions typical for the lower ionosphere. Under certain conditions, the rigorous kinetic consideration yields substantial changes in results compared to previous theories. The general approach may be applied to other linear and nonlinear low-frequency processes in a weakly ionized plasma. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Dimant, Y.S.; Sudan, R.N. [Laboratory of Plasma Studies, Cornell University, Ithaca, New York 14853 (United States)] [Laboratory of Plasma Studies, Cornell University, Ithaca, New York 14853 (United States)

1995-04-01

360

Constraints on Omega_m and sigma_8 from weak lensing in RCS fields

We have analysed 53 square degrees of imaging data from the Red-Sequence Cluster Survey (RCS), and measured the excess correlations in the shapes of galaxies on scales out to ~1.5 degrees. We separate the signal into an ``E''- (lensing) and ``B''-mode (systematics), which allows us to study residual systematics. On scales larger than 10 arcminutes, we find no ``B''-mode. On smaller scales we find a small, but significant ``B''-mode. This signal is also present when we select a sample of bright galaxies. These galaxies are rather insensitive to observational distortions, and we therefore conclude that the oberved ``B''-mode is likely to be caused by intrinsic alignments. We therefore limit the cosmic shear analysis to galaxies with 220.1+0.16\\Omega_m$ (95% confidence). Comparison of the RCS results with three other recent cosmic shear measurements shows excellent agreement. The current weak lensing results are also in good agreement with CMB measurements, when we allow the reionization optical depth tau and the spectral index n_s to vary. We present a simple demonstration of how the weak lensing results can be used as a prior in the parameter estimation from CMB measurements to derive constraints on the reionization optical depth tau. (abridged)

Henk Hoekstra; Howard Yee; Mike Gladders

2002-06-03

361

The problem of grain screening is solved numerically for the case of weakly ionized plasma in the presence of an external magnetic field. The plasma dynamics is described within the drift-diffusion approximation under the assumption that the grain absorbs all encountered electrons and ions. We also assume that the plasma current through the grain surface is equal to zero in the stationary state. This condition is used to perform self-consistent calculations of the grain charge. The spatial distribution of the screened grain potential is studied and compared with the analytical estimates. It is shown that at the distances larger than the Debye length such potential has the Coulomb-like asymptotics with the effective charge dependent on the angle between the radius vector and the external magnetic field direction. The numerical solutions show that in the direction parallel to the external magnetic field the effective potential can have nonmonotonic behavior.

Momot, A. I. [Faculty of Physics, Taras Shevchenko National University of Kyiv, 64, Volodymyrs'ka St., Kyiv 01601 (Ukraine) [Faculty of Physics, Taras Shevchenko National University of Kyiv, 64, Volodymyrs'ka St., Kyiv 01601 (Ukraine); M.M. Bogolubov Institute for Theoretical Physics, Nat. Acad. Sci. of Ukraine, 14b, Metrologichna Str., Kyiv, 03680 (Ukraine)

2013-07-15

362

In two separate experiments a total of 71 volunteers were asked to generate spontaneous narratives that were scored automatically by the Whissell Dictionary of Affect. During the narratives, weak (1 microT; 10 mG) magnetic fields were applied briefly through the temporal planes. In Experiment I, subjects who were exposed to simple sine wave or pulsed fields generated more scorable words that indicated lower activation and evaluation than sham-field conditions. In Experiment II subjects exposed to a computer-generated wave form, designed to simulate neuronal burst firing, generated narratives dominated by more pleasantness and less activation than a reference group. The possibility that this approach could be utilized to study the affective dimension of language selection was indicated. PMID:8407157

Richards, P M; Persinger, M A; Koren, S A

1993-01-01

363

The toroidal electromagnetic braking torques exerted at the various internal rational surfaces of a large aspect-ratio, low-{beta}, weakly shaped, tokamak plasma by a nonaxisymmetric error field are investigated using a semianalytic approach. It is found that there is an optimal error-field spectrum for exerting a torque at a given rational surface. This spectrum is dominated by the resonant harmonic, but also contains sideband harmonics induced by plasma toroidicity, pressure, ellipticity, and triangularity. These sidebands couple back to the resonant harmonic in such a manner as to reduce its amplitude. Provided that there is significant coupling to a (stable) ideal external kink mode which is close to its marginal stability boundary, the optimal error field predominately contains sideband harmonics whose poloidal mode numbers are more positive than the resonant mode number (which is assumed to be positive), and also tends to balloon on the outboard side of the plasma.

Fitzpatrick, Richard [Department of Physics, Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712 (United States)

2009-03-15

364

Weak magnetic field effects on chiral critical temperature in a nonlocal Nambu--Jona-Lasinio model

In this article we study the nonlocal Nambu--Jona-Lasinio model with a Gaussian regulator in the chiral limit. Finite temperature effects and the presence of a homogeneous magnetic field are considered. The magnetic evolution of the critical temperature for chiral symmetry restoration is then obtained. Here we restrict ourselves to the case of low magnetic field values, being this a complementary discussion to the exisiting analysis in nonlocal models in the strong magnetic field regime.

M. Loewe; F. Marquez; C. Villavicencio; R. Zamora

2014-10-27

365

Endothelial Cell Morphology and Migration are Altered by Changes in Gravitational Fields

NASA Technical Reports Server (NTRS)

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.

Melhado, Caroline; Sanford, Gary; Harris-Hooker, Sandra

1997-01-01

366

Ideal gas in a strong gravitational field: Area dependence of entropy

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.

Kolekar, Sanved; Padmanabhan, T. [IUCAA, Pune University Campus, Ganeshkhind, Pune 411007 (India)

2011-03-15

367

Theory of weak scattering of stochastic electromagnetic fields from deterministic and random media

The theory of scattering of scalar stochastic fields from deterministic and random media is generalized to the electromagnetic domain under the first-order Born approximation. The analysis allows for determining the changes in spectrum, coherence, and polarization of electromagnetic fields produced on their propagation from the source to the scattering volume, interaction with the scatterer, and propagation from the scatterer to the far field. An example of scattering of a field produced by a {delta}-correlated partially polarized source and scattered from a {delta}-correlated medium is provided.

Tong Zhisong; Korotkova, Olga [Department of Physics, University of Miami, 1320 Campo Sano Drive, Coral Gables, Florida 33146 (United States)

2010-09-15

368

Since extremely low frequency (i.e., 50- or 60-Hz) magnetic fields (MFs) from overhead power lines and other electromagnetic sources are ubiquitous in modern societies, the possible carcinogenic effect of such fields recently suggested by epidemiological studies has engendered much concern. However, in view of various unknown and uncontrolled variables which may bias epidemiological studies on MF interactions, a causal relationship

Wolfgang Löscher; Ulrich Wahnschaffe; Meike Mevissen; Alexander Lerchl; Andreas Stamm

1994-01-01

369

Childhood leukemia and residential exposure to weak extremely low frequency magnetic fields

There is no known mechanism by which magnetic fields of the type generated by high voltage power lines can play a role in cancer development. Nevertheless, epidemiologic research has rather consistently found associations between residential magnetic field exposure and cancer. This is most evident for leukemia in children. 18 refs., 1 tab.

Feychting, M.; Ahlbom, A. [Karolinska Institute, Stockholm (Sweden)

1995-03-01

370

Effects of a weak DC electric field on root growth in Arundo donax (Poaceae)

Electric fields can determine changes at the morphological and the physiological level in plants. Plants of Arundo donax L. (giant reed), obtained by set, grown on organic substrate were exposed to a DC electric field. A significant increase in growth rate was observed in the shoots and roots of treated plants. Treated roots also showed a modification in their morphology

Antonio Scopa; Carmine Colacino; Maria Rosaria Barone Lumaga; Luigi Pariti; Giuseppe Martelli

2009-01-01

371

Kinetic theory of low-frequency cross-field instability in a weakly ionized plasma. II

The consistent kinetic approach developed in Paper I [Ya. S. Dimant and R. N. Sudan, Phys. Plasmas {bold 2}, 1157 (1995)] is applied to obtain the general dispersion relation of the two-stream {bold E}{times}{bold B} instability in collisionally dominated weakly ionized plasmas for wave frequencies small compared to the ion--neutral collision frequency. This dispersion relation covers the whole low-frequency band from the asymptotic short-wave limit studied in Paper I to the long-wave limit. Previous theories employing simplified kinetic theory or fluid equations for electron behavior are only correct in the long-wave limit. The principal new results are that the threshold conditions for this instability and the growth rates are altered from those predicted by earlier simplified theories. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Dimant, Y.S.; Sudan, R.N. [Laboratory of Plasma Studies, Cornell University, Ithaca, New York 14853 (United States)] [Laboratory of Plasma Studies, Cornell University, Ithaca, New York 14853 (United States)

1995-04-01

372

Initiation and blocking of the action potential in an axon in weak ultrasonic or microwave fields.

In this paper, we analyze the effect of the redistribution of the transmembrane ion channels in an axon caused by longitudinal acoustic vibrations of the membrane. These oscillations can be excited by an external source of ultrasound and weak microwave radiation interacting with the charges sitting on the surface of the lipid membrane. It is shown, using the Hodgkin-Huxley model of the axon, that the density redistribution of transmembrane sodium channels may reduce the threshold of the action potential, up to its spontaneous initiation. At the significant redistribution of sodium channels in the membrane, the rarefaction zones of the transmembrane channel density are formed, blocking the propagation of the action potential. Blocking the action potential propagation along the axon is shown to cause anesthesia in the example case of a squid axon. Various approaches to experimental observation of the effects considered in this paper are discussed. PMID:25353835

Shneider, M N; Pekker, M

2014-05-01

373

Energetic plasma-beam propagation in weak and strong magnetic fields

Dynamical aspects of a relativistic plasma beam propagating across a magnetic field are investigated through two- and three-dimensional particle-in-cell numerical simulations. In the two-dimensional simulations, different aspects of the physics are revealed by placing the initial ambient field perpendicular to and within the plane of calculation. In the former case the expected beam polarization appears at early times in the simulations but is quickly dominated by collectively induced heating. In the second geometry effects of magnetic field deformation appear. The consequences of allowing variation in the third dimension are briefly discussed.

Shanahan, W.R.

1983-01-01

374

An experimental setup is proposed for the precise measurement of the quantum states of ultracold neutrons bound in the earth's gravitational field. The experiment utilizes a CCD-based pixel sensor and magnification system to observe the fine structure of the neutron distribution. In this work, we analyzed the sensor's deposited energy measurement capability and found that its spatial resolution was 5.3 um. A magnifying power of two orders of magnitude was realized by using a cylindrical rod as a convex mirror.

T. Sanuki; S. Komamiya; S. Kawasaki; S. Sonoda

2009-01-05

375

Bianchi Type-II String Cosmological Model with Magnetic Field in Scalar-tensor Theory of Gravitation

NASA Astrophysics Data System (ADS)

The spatially homogeneous and totally anisotropic Bianchi type-II cosmological solutions of massive strings have been investigated in the presence of the magnetic field in the framework of scalar-tensor theory of gravitation formulated by Saez and Ballester (Phys. Lett. A 113:467, 1986). With the help of special law of variation for Hubble's parameter proposed by Berman (Nuovo Cimento B 74:182, 1983) string cosmological model is obtained in this theory. Some physical and kinematical properties of the model are also discussed.

Sharma, N. K.; Singh, J. K.

2014-07-01

376

Global dynamical behavior of a three-body system with flexible connection in the gravitational field

Summary In this paper, the global behavior of relative equilibrium states of a three-body satellite with flexible connection under\\u000a the action of the gravitational torque is studied. With geometric method, the conditions of existence of nontrivial solutions\\u000a to the relative equilibrium equations are determined. By using reduction method and singularity theory, the conditions of\\u000a occurrence of bifurcation from trivial solutions

G. Cheng; Y. Z. Liu

1999-01-01

377

Criticality and Bifurcation in the Gravitational Collapse of a Self-Coupled Scalar Field

We examine the gravitational collapse of a non-linear sigma model in spherical symmetry. There exists a family of continuously self-similar solutions parameterized by the coupling constant of the theory. These solutions are calculated together with the critical exponents for black hole formation of these collapse models. We also find that the sequence of solutions exhibits a Hopf-type bifurcation as the continuously self-similar solutions become unstable to perturbations away from self-similarity.

Eric W. Hirschmann; Douglas M. Eardley

1995-11-18

378

Gravitational forces in the Randall-Sundrum model with a scalar stabilizing field

We consider the problem of gravitational forces between point particles on the branes in a five-dimensional (5D) Randall-Sundrum model with two branes (at y1 and y2) and S1\\/Z2 symmetry of the fifth dimension. The matter on the branes is viewed as a perturbation on the vacuum metric and treated to linear order. In a previous work [R. Arnowitt and J.

R. Arnowitt; J. Dent

2007-01-01

379

Gravitational forces in the Randall-Sundrum model with a scalar stabilizing field

We consider the problem of gravitational forces between point particles on the branes in a five-dimensional (5D) Randall-Sundrum model with two branes (at yâ and yâ) and SÂ¹\\/Zâ symmetry of the fifth dimension. The matter on the branes is viewed as a perturbation on the vacuum metric and treated to linear order. In a previous work [R. Arnowitt and J.

R. Arnowitt; J. Dent

2007-01-01

380

The design of ion drivers for warm dense matter and high energy density physics applications and heavy ion fusion involves transverse focusing and longitudinal compression of intense ion beams to a small spot size on the target. To facilitate the process, the compression occurs in a long drift section filled with a dense background plasma, which neutralizes the intense beam self-fields. Typically, the ion bunch charge is better neutralized than its current, and as a result a net self-pinching (magnetic) force is produced. The self-pinching effect is of particular practical importance, and is used in various ion driver designs in order to control the transverse beam envelope. In the present work we demonstrate that this radial self-focusing force can be significantly enhanced if a weak (B {approx} 100 G) solenoidal magnetic field is applied inside the neutralized drift section, thus allowing for substantially improved transport. It is shown that in contrast to magnetic self-pinching, the enhanced collective self-focusing has a radial electric field component and occurs as a result of the overcompensation of the beam charge by plasma electrons, whereas the beam current becomes well-neutralized. As the beam leaves the neutralizing drift section, additional transverse focusing can be applied. For instance, in the neutralized drift compression experiments (NDCX) a strong (several Tesla) final focus solenoid is used for this purpose. In the present analysis we propose that the tight final focus in the NDCX experiments may possibly be achieved by using a much weaker (few hundred Gauss) magnetic lens, provided the ion beam carries an equal amount of co-moving neutralizing electrons from the preceding drift section into the lens. In this case the enhanced focusing is provided by the collective electron dynamics strongly affected by a weak applied magnetic field.

Dorf, Mikhail A. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Davidson, Ronald C.; Kaganovich, Igor D.; Startsev, Edward A. [Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

2012-05-15

381

Gravitation and electromagnetism

Maxwell's equations comprise both electromagnetic and gravitational fields. The transverse part of the vector potential belongs to magnetism, the longitudinal one is concerned with gravitation. The Coulomb gauge indicates that longitudinal components of the fields propagate instantaneously. The delta-function singularity of the field of the divergence of the vector potential, referred to as the dilatation center, represents an elementary agent of gravitation. Viewing a particle as a source or a scattering center of the point dilatation, the Newton's gravitation law can be reproduced.

V. P. Dmitriyev

2002-07-23

382

Molecular gyroscopes and biological effects of weak extremely low-frequency magnetic fields

NASA Astrophysics Data System (ADS)

Extremely low-frequency magnetic fields are known to affect biological systems. In many cases, biological effects display ``windows'' in biologically effective parameters of the magnetic fields: most dramatic is the fact that the relatively intense magnetic fields sometimes do not cause appreciable effect, while smaller fields of the order of 10-100 ?T do. Linear resonant physical processes do not explain the frequency windows in this case. Amplitude window phenomena suggest a nonlinear physical mechanism. Such a nonlinear mechanism has been proposed recently to explain those ``windows.'' It considers the quantum-interference effects on the protein-bound substrate ions. Magnetic fields cause an interference of ion quantum states and change the probability of ion-protein dissociation. This ion-interference mechanism predicts specific magnetic-field frequency and amplitude windows within which the biological effects occur. It agrees with a lot of experiments. However, according to the mechanism, the lifetime ?-1 of ion quantum states within a protein cavity should be of unrealistic value, more than 0.01 s for frequency band 10-100 Hz. In this paper, a biophysical mechanism has been proposed, which (i) retains the attractive features of the ion interference mechanism, i.e., predicts physical characteristics that might be experimentally examined and (ii) uses the principles of gyroscopic motion and removes the necessity to postulate large lifetimes. The mechanism considers the dynamics of the density matrix of the molecular groups, which are attached to the walls of protein cavities by two covalent bonds, i.e., molecular gyroscopes. Numerical computations have shown almost free rotations of the molecular gyroscopes. The relaxation time due to van der Waals forces was about 0.01 s for the cavity size of 28 Å.

Binhi, V. N.; Savin, A. V.

2002-05-01

383

Weak extremely-low-frequency magnetic fields and regeneration in the planarian Dugesia tigrina

Extremely-low-frequency (ELF), low-intensity magnetic fields have been shown to influence cell signaling processes in a variety of systems, both in vivo and in vitro. Similar effects have been demonstrated for nervous system development and neurite outgrowth. The authors report that regeneration in planaria, which incorporates many of these processes, is also affected by ELF magnetic fields. The rate of cephalic regeneration, reflected by the mean regeneration time (MRT), for planaria populations regenerating under continuous exposure to combined DC (78.4 {mu}T) and AC (60.0 Hz at 10.0 {mu}T{sub peak}) magnetic fields applied in parallel was found to be significantly delayed (P {much_lt} 0.001) by 48 {+-} 1 h relative to two different types of control populations (MRT {minus}140 {+-} 12 h). One control population was exposed to only the AC component of this field combination, while the other experienced only the ambient geomagnetic field. All measurements were conducted in a low-gradient, low-noise magnetics laboratory under well-maintained temperature conditions. This delay in regeneration was shown to be dependent on the planaria having a fixed orientation with respect to the magnetic field vectors. Results also indicate that this orientation-dependent transduction process does not result from Faraday induction but is consistent with a Ca{sup 2+} cyclotron resonance mechanism. Data interpretation also permits the tentative conclusion that the effect results from an inhibition of events at an early stage in the regeneration process before the onset of proliferation and differentiation.

Jenrow, K.A.; Smith, C.H.; Liboff, A.R. [Oakland Univ., Rochester, MI (United States). Dept. of Physics

1995-06-01

384

Measurement of weak magnetic field of corrosion current of isolated corrosion center

NASA Astrophysics Data System (ADS)

A very small magnetic field of corrosion current, of the order of 10-4 Oe, generated by isolated zinc inclusion in a copper platelet placed in electrolyte has been measured for the first time with a highly sensitive giant magneto-impedance magnetometer. The total corrosion current of the inclusion is estimated comparing the measured magnetic field distribution with corresponding theoretical calculation. The estimated value of the total corrosion current turns out to be in reasonable agreement with that one obtained in the standard gravimetric measurement.

Bardin, I. V.; Bautin, V. A.; Gudoshnikov, S. A.; Ljubimov, B. Ya.; Usov, N. A.

2015-01-01

385

Evidence for Weak Crustal Magnetic Fields over the Hellas, Chryse, and Acidalia Planitiae

NASA Astrophysics Data System (ADS)

The Electron Reflectometer (ER) onboard Mars Global Surveyor (MGS) detected a plasma boundary between the ionosphere and the solar wind as the latter is diverted around and past the planet [Mitchell et al., GRL, 27, 1871, 2000; Mitchell et al., JGR, 106, 23419, 2001]. Above this boundary the 10-1000 eV electron population is dominated by solar wind electrons, while below the boundary it is dominated by ionospheric photoelectrons. This "photoelectron boundary", or PEB, is sensitive to pressure variations and moves vertically in response to changes in the ionospheric pressure from below and the solar wind pressure from above. The PEB is also sensitive to crustal magnetic fields, which locally increase the total ionospheric pressure and positively bias the PEB altitude. We have empirically modeled and removed systematic variations in the PEB altitude associated with the solar wind interaction, thus isolating perturbations caused by crustal magnetic fields. A map of the PEB altitude perturbations closely resembles maps of the horizontal component of the crustal magnetic field measured at 400 km by the MGS Magnetometer (MAG). We find a PEB altitude bias over the Hellas basin that is consistent with a horizontal magnetic field with an intensity of several nanotesla at 400 km altitude. This is compatible with upper limits to the horizontal crustal field strength set by MGS MAG measurements. Since there is no evidence for significant crustal magnetic sources within the basin from MAG data obtained during aerobraking [Acuna et al. Science, 284, 790, 1999] or from electron reflection data obtained in the mapping orbit [Lillis et al., this conference], the most likely explanation is that the observed horizontal field originates from sources around the Hellas perimeter. No detectable PEB or magnetic signature is observed over the younger Argyre and Isidis Basins. There is also evidence for a significant enhancement (several nanoteslas) in the crustal field strength over Chryse Planitia and much of Acidalia Planitia, which are thought to contain hundreds of meters of material from the main outflow channels on Mars [Carr, Lunar Planetary Sci., 18, 155, 1987]. These fields appear to extend northward from a group of crustal magnetic sources along the dichotomy boundary that were mapped by the MGS Magnetometer.

Lee, C. O.; Mitchell, D. L.; Lillis, R.; Lin, R. P.; Reme, H.; Cloutier, P. A.; Acuna, M. H.

2003-04-01

386

Reversing the weak measurement of an arbitrary field with finite photon number

into the cavity. The diagram of the scheme is shown in Fig. 1. Two classical fields transversely propa- gate through two sides of the cavity. They are both resonant to the transition #6;b#7;? #6;a#7; and have space-dependent Rabi fre- quencies #5;#1;z#2... #1;?#5; /g#2;n is neglected here because it will be cancelled after the reversal. Step #1;II#2;: we add two other classical fields to the middle of the cavity. They have the same detuning #12;1? ab=#12;2 ? ac=#14; and same Rabi frequency #5...

Sun, Qingqing; Al-Amri, M.; Zubairy, M. Suhail.

2009-01-01

387

Gravitational form factors of the neutrino

The gravitational properties of the neutrino is studied in the weak field approximation. By imposing the hermiticity condition, CPT and CP invariance on the \\em tensor matrix element, we shown that the allowed gravitational form factors for Dirac and Majorana neutrinos are very different. In a CPT and CP invariant theory, the \\em tensor for a Dirac neutrino of the same specie is characterized by four gravitational form factors. As a result of CPT invariance, the \\em tensor for a Majorana neutrino of the same specie has five form factors. In a CP invariant theory, if the initial and final Majorana neutrinos have the same (opposite) CP parity, then only tensor (pseudo-tensor) type transition are allowed.

K. L. Ng

1993-05-03

388

Phase space structure of the electron diffusion region in reconnection with weak guide fields

Kinetic simulations of magnetic reconnection provide detailed information about the electric and magnetic structure throughout the simulation domain, as well as high resolution profiles of the essential fluid parameters including the electron and ion densities, flows, and pressure tensors. However, the electron distribution function, f(v), within the electron diffusion region becomes highly structured in the three dimensional velocity space and is not well resolved by the data available from the particle-in-cell (PIC) simulations. Here, we reconstruct the electron distribution function within the diffusion region at enhanced resolution. This is achieved by tracing electron orbits in the fields taken from PIC simulations back to the inflow region where an analytic form of the magnetized electron distribution is known. For antiparallel reconnection, the analysis reveals the highly structured nature of f(v), with striations corresponding to the number of times electrons have been reflected within the reconnection current layer, and exposes the origin of gradients in the electron pressure tensor important for momentum balance. The structure of the reconnection region is strongly tied to the pressure anisotropy that develops in the electrons upstream of the reconnection region. The addition of a guide field changes the nature of the electron distributions, and the differences are accounted for by studying the motion of single particles in the field geometry. Finally, the geometry of small guide field reconnection is shown to be highly sensitive to the ion/electron mass ratio applied in the simulation.

Ng, J.; Egedal, J.; Le, A. [Department of Physics, and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Daughton, W. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2012-11-15

389

NASA Technical Reports Server (NTRS)

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.

Dong, D,; Gross, R.S.; Dickey, J.

1996-01-01

390

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$\\alpha$ iron line observed in the X-ray spectrum of black holes can potentially be used to probe the fine structure constant $\\alpha$ in gravitational potentials relative to Earth of $\\Delta \\phi \\approx 0.1$. At present, systematic effects not fully under control prevent to get robust and stringent bounds on possible variations of the value of $\\alpha$ 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.

Cosimo Bambi

2014-03-13

391

NASA Astrophysics Data System (ADS)

There are many tasks, which are required simultaneously to measure value and direction of gravitation field vector in 3D space. For instance, the task of flying objects navigation by measurement of full gravitation field vector horizontal gradient. To solve this problem is suggested the system, consists of two remote fiber-optic gravimeters, situated in different ends of flying object. Fiber-optic gravimeter based on effect of influence of longitudinal strains of silicon single-mode fibers on lightwave phase shift. Fiber-optic gravimeter includes fiber-optic interferometers Mach-Zehnder and electronic scheme for measurement of phase shift. Sensitivity of this fiber-optic gravimeter is 10-7 g, where g-acceleration of free fall, if resolution of electronic scheme is 10-3 rad. As source of radiation for fiber-optic gravimeter is employed tunable diode laser on GaAlAs-GaAs with external dispertial cavity and frequency modulation of radiation. Frequency modulation of radiation is applied for measurement of phase shift in fiber-optic interferometers.

Bykovsky, Yuri A.; Scvorchevsky, Constantin A.; Beskurnikov, Andrey Y.; Poljakova, Olga V.; Grachev, Alexander P.; Shutov, Alexander V.

1997-06-01

392

Contrary to the belief that paleomagnetic reversals are not biologically significant, we find good reason to think otherwise. Attention is drawn to polarity transitions, time intervals a few thousand years long that follow the collapse of the existing geomagnetic dipole moment and precede the establishment of the new, oppositely directed moment. The geomagnetic field during transitions is reduced to a maximal mean intensity about 10% of the stable field and can exhibit low-frequency perturbations comparable to numerous laboratory-based extremely low frequency (ELF) studies reporting biological interactions, making it very likely that similar interactions must occur over the course of a polarity transition. This conclusion is strengthened by reports of medical problems that significantly correlate with intense solar winds, events that also generate ELF perturbations similar to those that can occur during polarity transitions. PMID:23323742

Liboff, Abraham R

2013-12-01

393

Effects of Nonlinear Micromagnetic Coupling on a Weak-Field Magnetoimpedance Sensor

We present a general harmonic formulation that takes into account, explicitly, the effects of micromagnetics for modeling the magnetic fields in a magnetoimpedance (MI) sensor element. We first relax assumptions commonly made to derive closed form solutions from a decoupled set of linear equations. We then solve numerically (using a meshless method formulated in point-collocation) the Maxwell and the Landau-Lifshitz-Gilbert

Kwaku Eason; Kok-Meng Lee

2008-01-01

394

An order-by-disorder process in the cyclic phase of spin-2 condensate with a weak magnetic field

We present in this paper a model study on the “order-by-disorder” process in the cyclic phase of spin-2 condensate, which forms a family of incommensurable, spiral degenerate ground states. On the basis of the ordering mechanism of entropic splitting, it is demonstrated that the energy corrections resulting from quantum fluctuations of disorder lift the accidental degeneracy of the cyclic configurations and thus lead to an eventual spiral order called the cyclic order. The order-by-disorder phenomenon is then realized even if the magnetic field exists. Finally, we show that our theoretic observations can be verified experimentally by direct detection of the cyclic order in the {sup 87}Rb condensate of a spin-2 manifold with a weak magnetic field. -- Highlights: •A model for the order-by-disorder process in the cyclic phase of spin-2 condensate is presented. •The second-order quantum fluctuations of the mean-field states are studied. •The energy corrections lift the accidental degeneracy of the cyclic configurations. •The order-by-disorder phenomenon is realized even if a magnetic field exists. •The theoretic observations can be verified experimentally for {sup 87}Rb condensate.

Zheng, Gong-Ping, E-mail: zhenggongping@yahoo.com.cn [Department of Physics, Henan Normal University, Xinxiang, Henan 453007 (China)] [Department of Physics, Henan Normal University, Xinxiang, Henan 453007 (China); Xu, Lei-Kuan; Qin, Shuai-Feng; Jian, Wen-Tian [Department of Physics, Henan Normal University, Xinxiang, Henan 453007 (China)] [Department of Physics, Henan Normal University, Xinxiang, Henan 453007 (China); Liang, J.-Q. [Institute of Theoretical Physics and Department of Physics, Shanxi University, Taiyuan, Shanxi 030006 (China)] [Institute of Theoretical Physics and Department of Physics, Shanxi University, Taiyuan, Shanxi 030006 (China)

2013-07-15

395

The Gravitational and Electrostatic Fields Far from an Isolated Einstein-Maxwell Source

The exterior solution for an arbitrary charged, massive source, is studied as a static deviation from the Reissner-Nordstr\\o m metric. This is reduced to two coupled ordinary differential equations for the gravitational and electrostatic potential functions. The homogeneous equations are explicitly solved in the particular case $q^2=m^2$, obtaining a multipole expansion with radial hypergeometric dependence for both potentials. In the limiting case of a neutral source, the equations are shown to coincide with recent results by Bondi and Rindler.

J. Ocariz; H. Rago

2000-03-17

396

A Signal-adaptive Method for Sparse Global and Regional Modeling of the Gravitational Field

NASA Astrophysics Data System (ADS)

We propose a novel algorithm to solve inverse problems appearing in the geosciences by taking the example of downward continuation of the gravitational potential. The method expands the signal in terms of trial functions which are iteratively picked from a large redundant set containing different types of functions. In particular, we are able to combine spherical harmonics of low degrees as well as wavelets and/or scaling functions for the reconstruction of global trends and regional details, respectively. The outcome is adapted to the data density and also to the detail structure of the signal which yields a certain sparsity of the solution. Numerical experiments are presented.

Telschow, R.

2013-12-01

397

Use of Langmuir probes in a weakly ionized, steady-state plasma with strong magnetic field

This article describes the use of Langmuir probes to measure plasma parameters in low density, low temperature plasmas with a strong applied magnetic field. The experiment has been performed at the Physics Department of Milan{close_quote}s University on the steady-state toroidal machine {open_quotes}Thorello.{close_quotes} Results have been analyzed by taking into account instrumental and ionic sheath effects. Finally, experimental results have been compared with direct measurements of the electron distribution function in Thorello. {copyright} {ital 1997 American Institute of Physics.}

Batani, D.; Alba, S.; Lombardi, P.; Galassi, A. [Dipartimento di Fisica, Universita di Milano, and Istituto Nazionale di Fisica della Materia, Unita di Milano, Via Celoria 16, 20133 Milano (Italy)] [Dipartimento di Fisica, Universita di Milano, and Istituto Nazionale di Fisica della Materia, Unita di Milano, Via Celoria 16, 20133 Milano (Italy)

1997-11-01

398

Non-mesonic weak decay of hypernuclei with effective field theory

NASA Astrophysics Data System (ADS)

The ?N ? NN interaction, the main responsible for the decay of heavy hypernuclei, is described within the effective field theory (EFT) framework. The EFT is developed up to (vec q2), where vec q is the transferred momentum between the interacting baryons. Numerical values for the leading order low-energy constants are obtained by two means. First, from a fit to the hypernuclear decay observables, and second, by comparing the EFT to the one-meson-exchange model describing the same interaction. All the two-pion exchange diagrams entering at the next-to-leading in the EFT have been calculated.

Pérez-Obiol, A.; Entem, D. R.; Juliá-Díaz, B.; Parreño, A.

2014-04-01

399

We completely clarify the feature of primordial non-Gaussianities of tensor perturbations in the most general single-field inflation model with second-order field equations. It is shown that the most general cubic action for the tensor perturbation h(ij) is composed only of two contributions, one with two spacial derivatives and the other with one time derivative on each h(ij). The former is essentially identical to the cubic term that appears in Einstein gravity and predicts a squeezed shape, while the latter newly appears in the presence of the kinetic coupling to the Einstein tensor and predicts an equilateral shape. Thus, only two shapes appear in the graviton bispectrum of the most general single-field inflation model, which could open a new clue to the identification of inflationary gravitational waves in observations of cosmic microwave background anisotropies as well as direct detection experiments. PMID:22181868

Gao, Xian; Kobayashi, Tsutomu; Yamaguchi, Masahide; Yokoyama, Jun'ichi

2011-11-18

400

The mantra about gravitation as curvature is a misnomer. The curvature tensor for a standard of rest does not describe acceleration in a gravitational field but the \\underline{gradient} of the acceleration (e.g. geodesic deviation). The gravitational field itself (Einstein 1907) is essentially an accelerated reference system. It is characterized by a field of orthonormal four-legs in a Riemann space with Lorentz metric. By viewing vectors at different events having identical leg-components as parallel (teleparallelism) the geometry in a gravitational field defines torsion. This formulation of Einstein's 1907 principle of equivalence uses the same Riemannian metric and the same 1916 field equations for his theory of gravitation and fulfills his vision of General Relativity.

Engelbert L. Schucking

2008-03-28

401

NASA Astrophysics Data System (ADS)

The first detections of gravitational waves from binary neutron star mergers with advanced LIGO and Virgo observatories are anticipated in the next five years. These detections could pave the way for multi-messenger gravitational-wave (GW) and electromagnetic (EM) astronomy if GW triggers are successfully followed up with targeted EM observations. However, GW sky localization is relatively poor, with expected localization areas of ~10-100 deg2; this presents a challenge for following up GW signals from compact binary mergers. Even for wide-field instruments, tens or hundreds of pointings may be required. Prioritizing pointings based on the relative probability of successful imaging is important since it may not be possible to tile the entire gravitational-wave localization region in a timely fashion. Galaxy catalogs were effective at narrowing down regions of the sky to search in initial attempts at joint GW/EM observations. The relatively limited range of initial GW instruments meant that few galaxies were present per pointing and galaxy catalogs were complete within the search volume. The next generation of GW detectors will have a 10-fold increase in range thereby increasing the expected number of galaxies per unit solid angle by a factor of ~1000. As an additional complication, catalogs will be highly incomplete. Nevertheless, galaxy catalogs can still play an important role in prioritizing pointings for the next era of GW searches. We show how to quantify the advantages of using galaxy catalogs to prioritize wide-field follow-ups as a function of only two parameters: the three-dimensional volume within the field of view of a telescope after accounting for the GW distance measurement uncertainty, and the fraction of the GW sky localization uncertainty region that can be covered with telescope pointings. We find that the use of galaxy catalogs can improve the probability of successful imaging by ~10% to ~300% relative to follow-up strategies that do not utilize such catalogs for the scenarios we considered. We determine that catalogs with a 75% completeness perform comparably to complete catalogs in most cases, while 33%-complete catalogs can lead to lower follow-up success rates than complete catalogs for small fields of view, though still providing an advantage over strategies that do not use a catalog at all.

Hanna, Chad; Mandel, Ilya; Vousden, Will

2014-03-01

402

Background Previous reports indicate altered metabolism and enzyme kinetics for various organisms, as well as changes of neuronal functions and behaviour of higher animals, when they were exposed to specific combinations of weak static and alternating low frequency electromagnetic fields. Field strengths and frequencies, as well as properties of involved ions were related by a linear equation, known as the formula of ion cyclotron resonance (ICR, abbreviation mentioned first by Liboff). Under certain conditions already a aqueous solution of the amino acid and neurotransmitter glutamate shows this effect. Methods An aqueous solution of glutamate was exposed to a combination of a static magnetic field of 40 ?T and a sinusoidal electromagnetic magnetic field (EMF) with variable frequency (2–7 Hz) and an amplitude of 50 nT. The electric conductivity and dielectric properties of the solution were investigated by voltammetric techniques in combination with non linear dielectric spectroscopy (NLDS), which allow the examination of the dielectric properties of macromolecules and molecular aggregates in water. The experiments target to elucidate the biological relevance of the observed EMF effect on molecular level. Results An ion cyclotron resonance (ICR) effect of glutamate previously reported by the Fesenko laboratory 1998 could be confirmed. Frequency resolution of the sample currents was possible by NLDS techniques. The spectrum peaks when the conditions for ion cyclotron resonance (ICR) of glutamate are matched. Furthermore, the NLDS spectra are different under ICR- and non-ICR conditions: NLDS measurements with rising control voltages from 100–1100 mV show different courses of the intensities of the low order harmonics, which could possibly indicate "intensity windows". Furthermore, the observed magnetic field effects are pH dependent with a narrow optimum around pH 2.85. Conclusions Data will be discussed in the context with recent published models for the interaction of weak EMF with biological matter including ICR. A medical and health relevant aspect of such sensitive effects might be given insofar, because electromagnetic conditions for it occur at many occasions in our electromagnetic all day environment, concerning ion involvement of different biochemical pathways. PMID:15571630

Pazur, Alexander

2004-01-01

403

NASA Technical Reports Server (NTRS)

Numerical solutions are presented for the equations of radiative transfer for astrophysical masers in a magnetic field to describe the observed weak circular polarization of H2O and SiO masers. Previously unrecognized intensity-dependent effects are found to produce circular polarization which resembles that of the usual Zeeman effect. Astrophysical H2O, SiO, and perhaps other masers are likely to be radiatively saturated with rates for stimulated emission that are within 1-2 orders of magnitude of the Zeeman frequency. Under these conditions, the circular polarization found here tends to be larger (but can be smaller) and may be of opposite sign from that given by the standard treatment for polarized Zeeman spectra.

Nedoluha, Gerald E.; Watson, William D.

1990-01-01

404

NASA Astrophysics Data System (ADS)

This is the third in a series of papers aimed at developing a practical time-domain method for self-force calculations in Kerr spacetime. The key elements of the method are (i) removal of a singular part of the perturbation field with a suitable analytic “puncture,” (ii) decomposition of the perturbation equations in azimuthal (m-)modes, taking advantage of the axial symmetry of the Kerr background, (iii) numerical evolution of the individual m-modes in 2+1 dimensions with a finite difference scheme, and (iv) reconstruction of the local self-force from the mode sum. Here we report a first implementation of the method to compute the gravitational self-force. We work in the Lorenz gauge, solving directly for the metric perturbation in 2+1 dimensions, for the case of circular geodesic orbits. The modes m=0, 1 contain nonradiative pieces, whose time-domain evolution is hampered by certain gauge instabilities. We study this problem in detail and propose ways around it. In the current work we use the Schwarzschild geometry as a platform for development; in a forthcoming paper—the fourth in the series—we apply our method to the gravitational self-force in Kerr geometry.

Dolan, Sam R.; Barack, Leor

2013-04-01

405

Dark Energy Constraints from Weak-Lensing Cross-Correlation Cosmography

We present a method for implementing the idea of Jain & Taylor for constraining cosmological parameters with weak gravitational lensing. Photometric redshift information on foreground galaxies is used to produce templates of the mass structure at foreground slices zl, and the predicted distortion field is cross-correlated with the measured shapes of sources at redshift zs. The variation of the cross-correlation

G. M. Bernstein; B. Jain

2004-01-01

406

NASA Astrophysics Data System (ADS)

It is well established by now that transient luminous events (TLEs) observed at different altitudes above thunderstorms commonly consist of large numbers of needle-shaped filaments of ionization, called streamers [e.g., Gerken and Inan, JASTP, 65, 567, 2003; Su et al., Nature, 423, 974, 2003; Pasko, Nature, 423, 927, 2003; and references cited therein]. One of the important questions of the current TLEs research, which directly relates to the evaluation of the total volumes of atmosphere affected by these phenomena and possible role of some of the TLEs (i.e., sprites, jets and gigantic jets) in establishing a direct path of electrical contact between the tropospheric and mesospheric/lower ionospheric regions, is related to the determination of the minimum electric fields required for the propagation of streamers in air at different pressures [Pasko and George, JGR, 107, 1458, 2002]. The minimum field required for the propagation of positive streamers in air at ground pressure has been extensively documented experimentally and usually stays close to the value 4.4 kV/cm [Allen and Ghaffar, J. Phys. D Appl. Phys., 28, 331, 1995], in agreement with recent results of numerical simulations of positive streamers [Babaeva and Naidis, IEEE Trans. Plasma Sci., 25, 375, 1997; Morrow and Lowke, J. Phys. D Appl. Phys., 30, 614, 1997]. The information about the absolute value of the similar field for the negative streamers at present is very limited. The existing sources indicate that this field is a factor of 2-3 higher than the corresponding field for the positive streamers [e.g., Raizer, Gas Discharge Physics, 1991, p. 361; Babaeva and Naidis, 1997]. We note that although from the streamer similarity laws one generally would expect the minimum fields required for streamer propagation to scale with altitude proportionally to the air neutral density N, the actual scaling for the altitude range of sprites, jets and gigantic jets has not yet been verified experimentally, and a limited amount of data currently available in the literature [Griffiths and Phelps, Q.J.R. Meteorol. Soc., 102, 419, 1976; Bazelyan and Raizer, Spark Discharge, 1998, p. 216] indicate possible deviations from the N scaling. In this talk we will discuss conditions required for the propagation of streamers in air at different pressures and will present corresponding results from a new two-dimensional model, which has recently been developed at Penn State for studies of dynamics of streamers in weak uniform electric fields, documenting the minimum electric field magnitudes required for the propagation of positive and negative streamers at TLE altitudes.

Liu, N.; Pasko, V. P.

2003-12-01

407

NASA Astrophysics Data System (ADS)

Several groups produce estimates of the Earth's time-varying gravitational field with data provided by the GRACE mission. While the gravity fields are similar, differences in processing strategies and tuning parameters result in solutions with regionally specific variations and error patterns. This study analyzed the spatial, temporal, and spectral variations between four different gravity field products. The knowledge gained in this analysis was used to develop an ensemble solution that harnesses the best characteristics of each individual field to create an optimal model. Multiple methods were used to combine and analyze the individual and ensemble solutions. First a simple mean model was created; then the different solutions were weighted based on the formal error estimates as well as the monthly deviation from the arithmetic mean ensemble. These ensemble models as well as the four individual data center solutions were evaluated statistically, compared to independent hydrological models, and analyzed as to how well each solution fit the original orbit data. Therefore, the form and cause of the deviations between the models, as well as the impact of these variations, is characterized. Initial results show that the three ensemble solutions are all effective at reducing noise in the models and better correlate to hydrological processes than any individual solution.

Sakumura, C.; Bettadpur, S. V.; Bruinsma, S.

2013-12-01

408

NASA Astrophysics Data System (ADS)

While solving the main problem of the project related to the investigations of the interaction of the ELF electromagnetic fields in the atmosphere lower surface layer with the moon and solar tides and astrophysical gravitational and wave sources, a number of important results was got. In this direction the experimental and theoretical investigations got by the group of scientists of VSU, IZMIRAN, KSU, Voyeikov GGO,MSU GAISh and USU are united. From 2004 to 2006 monitoring of ELF electromagnetic fields with the equipment designed during doing this project, was carried out on the 6 stations, spaced in distance: on the VSU ground; in VSU building; in GGO, on Lake Baikal (Listvyanka) and a mountain station Mondy (the Institute of solar and Earth physics RAS, Irkutsk). 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 obtained that astrophysical sources GV-6, GV-3, GV-4, GV-8, GV-9 have the most probability of non-casual of events. There was carried out the analysis of the structure of the signals according to the covariance matrix vectors according to the atmosphere lower layer electrical field data, which allowed to extract a deep modulation with the period of day and night in the signal scanning corresponding to the astrophysical GW-sources which is one of the most important features of non-Earth mature signal origin on the given frequencies. The Work is carried out with RFFI grant supporting 04-05-64895.

Grunskaya, Lubov V.; Efimov, V. A.; Isakevich, V. V.

2007-08-01

409

Light and scanning electron microscopy was used to study the morphological parameters and ultrastructure of Helix lucorum statocysts and statoliths in Pomatias rivulare statocysts after 56, 93 and 110-day exposure to microgravity aboard the ISS. Increased gravity was simulated by 30-d centrifugation at 6 g. On the first day of recovery, many statoconia and statoliths were found to carry numerous warts. Moreover, statoconia grew in number significantly as compared with the ground control. On the contrary centrifugation caused massive destruction of statoconia. In a month after orbital flight and centrifugation morphology of both statoconia and stastoliths was nearly normal. These results evidence, that the gravitational field is an important factor for the abiotic medium responsible for building up the inertial mass in the equilibrium organ of animals. PMID:22312858

Gorgiladze, G I; Bukiia, R D; Kalandarishvili, É L; Korotkova, E V; Taktakishvili, A D; Davitashvili, M T; Gelashvili, N Sh

2011-01-01

410

NASA Technical Reports Server (NTRS)

Temporal variations in the low-degree zonal harmonics of the earth's gravitational field have recently been observed by satellite laser ranging. A host of geophysical processes contribute to these variations. The present paper studies quantitatively a prime contributor, atmospheric mass redistribution, using ECMWF global surface pressure data for the period of 1980-1988. The annual and semiannual amplitudes and phases of the zonal J(l) coefficient with degree l = 2-6 with and without the oceanic inverted-barometer (IB) effect are computed to obtain the predicted effects on the orbit nodal residuals of Lageos and Starlette. These predicted values are then compared with observations. It is found that the atmospheric influence, combined with the hydrological influence agree well with the Lageos observation for the annual term. The corresponding match appears poorer for Starlette.

Chao, B. Fong; Au, Andrew Y.

1991-01-01

411

The influence of extremely weak alternating magnetic fields (EW AMF) directed colinearly to the static Earth magnetic field on the rate of regeneration of planarians and the rate of gravitropic response in the stem segments of flax has been studied. The value of bioeffects of EW AMF is determined by the parameter gamma B(AC)/f, where y is the gyromagnetic ratio of the magnetic moments induced by the orbital movements of electrons in atoms, and B(AC) and f correspond to magnetic induction and frequency of the alternating magnetic component. It was shown that the magnitude of bioeffects depends on the amplitude (at fixed 1000 Hz - frequency) and frequency (at fixed 192 nT - amplitude) of the alternating component. Maxima of bioeffects are observed at gamma B(AC)/f = 0.9; 2.75, and minor maxima gamma B(AC)/f = 4.5; 6.1. The bioeffects are absent at gamma B(AC)/f = 1.8, 3.8, 5.3, 6.7. The positions of the maxima and minima of bioeffects correspond to the theoretical prediction (at gamma = 14000 Hz/microT). Primary targets for the EW AMF of this type are the magnetic moments induced by the orbital movements of electrons in atoms. PMID:20968085

Belova, N A; Ermakov, A M; Znobishcheva, A V; Skrebnitskaia, L K; Lednev, V V

2010-01-01

412

We consider stability of regimes of hydromagnetic thermal convection in a rotating horizontal layer with free electrically conducting boundaries, to perturbations involving large spatial and temporal scales. Equations governing the evolution of weakly nonlinear mean perturbations are derived under the assumption that the alpha-effect is insignificant in the leading order (e.g., due to a symmetry of the system). The mean-field equations generalise the standard equations of hydromagnetic convection: New terms emerge -- a second-order linear operator representing the combined eddy diffusivity, and quadratic terms associated with the eddy advection. If the perturbed CHM regime is non-steady and insignificance of the alpha-effect in the system does not rely on the presence of a spatial symmetry, the combined eddy diffusivity operator also involves a non-local pseudodifferential operator. If the perturbed CHM state is almost symmetric, alpha-effect terms appear in the mean-field equations as well. Near a point of a symmetry-breaking bifurcation, cubic nonlinearity emerges in the equations. All the new terms are in general anisotropic. A method for evaluation of their coefficients is presented; it requires solution of a significantly smaller number of auxiliary problems than in a straightforward approach.

V. Zheligovsky

2008-04-15

413

The application of a weak static B0 magnetic field (less than 1 mT) may produce a well-defined splitting of the (14)N Quadrupole Resonance line when the electric field gradient tensor at the nitrogen nucleus level is of axial symmetry. It is theoretically shown and experimentally confirmed that the actual splitting (when it exists) as well as the line-shape and the signal intensity depends on three factors: (i) the amplitude of B0, (ii) the amplitude and pulse duration of the radio-frequency field, B1, used for detecting the NQR signal, and (iii) the relative orientation of B0 and B1. For instance, when B0 is parallel to B1 and regardless of the B0 value, the signal intensity is three times larger than when B0 is perpendicular to B1. This point is of some importance in practice since NQR measurements are almost always performed in the earth field. Moreover, in the course of this study, it has been recognized that important pieces of information regarding line-shape are contained in data points at the beginning of the free induction decay (fid) which, in practice, are eliminated for avoiding spurious signals due to probe ringing. It has been found that these data points can generally be retrieved by linear prediction (LP) procedures. As a further LP benefit, the signal intensity loss (by about a factor of three) is regained. PMID:24183810

Guendouz, Laouès; Aissani, Sarra; Marêché, Jean-François; Retournard, Alain; Marande, Pierre-Louis; Canet, Daniel

2013-01-01

414

Explicit expressions are derived for the rectified radiative forces (RRFs) related to the action of a weak interfering optical\\u000a field of an arbitrary three-dimensional (3D) configuration upon resonance particles featuring the J=0 ? J=1 quantum transition. It is shown that, in contrast to the case of a monochromatic field, there are simple 3D biharmonic\\u000a field configurations for which the ratio

S. A. Gavrilyuk; I. V. Krasnov; S. P. Polyutov

2001-01-01

415

NASA Astrophysics Data System (ADS)

Numerical experiments are performed in order to investigate an MHD dynamo in a rotating spherical shell with stress-free top and no-slip bottom boundaries. The Ekman number, the Prandtl number, and the ratio of inner to outer radii are fixed as 10-3, 1, and 0.35, respectively. The magnetic Prandtl number is varied from 5 to 50, and the modified Rayleigh number is increased from 1.5 to 10 times the critical Rayleigh number. The initial imposed magnetic field is either a weak or strong magnetic field, where the magnetic energy of the initial field is approximately two orders of magnitude smaller or larger than the kinetic energy of the quasi-steady state of non-magnetic thermal convection. For cases involving a weak initial magnetic field, self-sustained dynamo solutions are established when the magnetic Prandtl number is larger than or equal to 5, and the modified Rayleigh number is larger than or equal to 5 times the critical Rayleigh number. The solutions are categorized as a weak field-dynamo, where the mean magnetic energy is one order of magnitude smaller than the mean kinetic energy. The dynamo solutions are characterized by a radially two-layer spatial structure. The upper layer is dominated by a strong prograde zonal mean zonal flow with large-scale prograde propagating spiral vortices having a longitudinal wavenumber of 3. Toroidal kinetic energy is converted to toroidal magnetic energy through stretching of the field lines by large-scale prograde propagating spiral vortices. On the other hand, the lower layer contains small-scale retrograde propagating columnar convective vortices having a longitudinal wavenumber of 8. The magnetic field lines are not concentrated in the vortices, but rather wind around the vortices in each layer. Poloidal kinetic energy is converted to poloidal magnetic energy through winding of the field lines around small-scale retrograde propagating columnar convective vortices. For cases involving a strong initial magnetic field, self-sustained dynamo solutions are established when the magnetic Prandtl number is greater than or equal to 4 and the modified Rayleigh number is greater than or equal to 3 times the critical Rayleigh number. In contrast with the cases involving a weak initial magnetic field, all of the dynamo solutions are strong-field solutions. Bistability is observed when the magnetic Prandtl number is 5, and the modified Rayleigh number is approximately equal to 10 times the critical Rayleigh number, where weak-field and strong-field dynamo solutions coexist. However, transition between the weak- and strong-field solutions does not occur in this case.

Sasaki, Y.; Takehiro, S.; Kuramoto, K.; Hayashi, Y.

2011-12-01

416

NASA Astrophysics Data System (ADS)

Numerical experiments are performed in order to investigate an MHD dynamo in a rotating spherical shell with stress-free top and no-slip bottom boundaries. The Ekman number, the Prandtl number, and the ratio of inner to outer radii are fixed as 10 -3, 1, and 0.35, respectively. The magnetic Prandtl number is varied from 5 to 50, and the modified Rayleigh number is increased from 1.5 to 10 times the critical Rayleigh number. The initial imposed magnetic field is either a weak or strong magnetic field, where the magnetic energy of the initial field is approximately two orders of magnitude smaller or larger than the kinetic energy of the quasi-steady state of non-magnetic thermal convection. For cases involving a weak initial magnetic field, self-sustained dynamo solutions are established when the magnetic Prandtl number is larger than or equal to 5, and the modified Rayleigh number is larger than or equal to 5 times the critical Rayleigh number. The solutions are categorized as a weak field-dynamo, where the mean magnetic energy is one order of magnitude smaller than the mean kinetic energy. The dynamo solutions are characterized by a radially two-layer spatial structure. The upper layer is dominated by a strong prograde zonal mean zonal flow with large-scale prograde propagating spiral vortices having a longitudinal wavenumber of 3. Toroidal kinetic energy is converted to toroidal magnetic energy through stretching of the field lines by large-scale prograde propagating spiral vortices. On the other hand, the lower layer contains small-scale retrograde propagating columnar convective vortices having a longitudinal wavenumber of 8. The magnetic field lines are not concentrated in the vortices, but rather wind around the vortices in each layer. Poloidal kinetic energy is converted to poloidal magnetic energy through winding of the field lines around small-scale retrograde propagating columnar convective vortices. For cases involving a strong initial magnetic field, self-sustained dynamo solutions are established when the magnetic Prandtl number is greater than or equal to 4 and the modified Rayleigh number is greater than or equal to 3 times the critical Rayleigh number. In contrast with the cases involving a weak initial magnetic field, all of the dynamo solutions are strong-field solutions. Bistability is observed when the magnetic Prandtl number is 5, and the modified Rayleigh number is approximately equal to 10 times the critical Rayleigh number, where weak-field and strong-field dynamo solutions coexist. However, transition between the weak- and strong-field solutions does not occur in this case.

Sasaki, Youhei; Takehiro, Shin-ichi; Kuramoto, Kiyoshi; Hayashi, Yoshi-Yuki

2011-10-01

417

Quantum gravitational anomaly as a dark matter

The general properties of a perfect relativistic fluid resulting from the quantum gravitational anomaly are investigated. It is found that, in the limit of a weak gravitational field, this fluid possesses a polytropic equation of state characterized by two universal constants: the polytropic constant and the natural polytropic index. Based on the astrophysical data, the estimates for the polytropic constant are given. It is shown that this fluid can describe a considerable part of the cold dark matter. The quantum theory of such a fluid is constructed in the framework of the background field method. The Ward identities associated with the entropy and vorticity conservation laws are derived. The leading gradient corrections to the pressure of the perfect fluid are found and the restrictions on their form are obtained. These restrictions guarantee, in particular, the absence of ghosts in the model. The second order nonlinear corrections to the equations of motion of a perfect relativistic fluid are analyzed and...

Kazinski, P O

2015-01-01

418

NASA Astrophysics Data System (ADS)

Detection of weak magnetic fields induced by neuronal electrical activities using magnetic-resonance imaging is a potentially effective method for functional imaging of the brain. In this study, we performed a numerical analysis of the theoretical limit of sensitivity for detecting weak magnetic fields induced in the human brain. The limit of sensitivity was estimated from the intensities of signal and noise in the magnetic-resonance images. The signal intensity was calculated with parameters which are commonly used in measurements of the human brain. The noise due to the head was calculated using the finite element method. The theoretical limit of sensitivity was approximately 10-8T.

Hatada, Tomohisa; Sekino, Masaki; Ueno, Shoogo

2005-05-01

419

The gravitational lens as a radiospectrometer

NASA Astrophysics Data System (ADS)

Gravitational lensing is predicted by general relativity and is found in observations. Weak lensing and observational examples of lenses, as well as strong lensing with relativistic rings, are considered. When a gravitating body is surrounded by a plasma, the lensing angle depends on a frequency of the electromagnetic wave due to refraction properties, and the dispersion properties of the light propagation in plasma. We consider here the effects of weak and strong gravitational lensing, observations of gravitational lenses, and spectrometric properties of a gravitational lens in a plasma.

Bisnovatyi-Kogan, G.

420

Constraints on gravitational properties of antimatter from cyclotron-frequency measurements

NASA Astrophysics Data System (ADS)

A fundamental question in physics that has yet to be addressed experimentally is whether particles of antimatter, such as the antiproton or positron, obey the weak equivalence principle (WEP). Several theoretical arguments have been put forward arguing limits for possible violations of WEP. No direct `classical' gravitational experiment, the measurement of the free fall of an antiparticle, has been performed to date to determine if a particle of antimatter would experience a force in the gravitational potential of a normal matter body that is different from normal gravity. 30 years ago we proposed a free fall experiment using protons and antiprotons, modeled after the experiment to measure the gravitational acceleration of a free electron. At that time we gave consideration to yet another possible observation of gravitational differences between matter and antimatter based on the gravitational red shift of clocks. I will recall the original arguments and make a number of comments pertaining to the technical problems and other issues that prevented the execution of the antiproton free fall measurement. Note that a different gravitational force on antimatter in the gravitational field of matter would not constitute a violation of CPT, as this is only concerned with the gravitational acceleration of antimatter in the gravitational field of an antimatter body.

Holzscheiter, Michael H.

2014-05-01

421

Gravitational Excitons as Dark Matter

In earlier work it was pointed out that for warped product spacetimes the conformal (geometrical moduli) excitations of the internal compactified factor spaces should be observable as massive scalar fields in the external spacetime. Here we show that these scalar fields (gravitational excitons) describe weakly interacting particles and can be considered as dark matter component. Masses of the gravexcitons are defined by the form of the effective potential of the theory and the stabilization scales of the internal space. This implies that different stabilization scales result in different types of DM. An essential role is played by the effective potential. On the one hand, its minima fix possible stabilization scales of the internal spaces; on the other hand, they provide possible values for the effective cosmological constant.

U. Guenther; A. Zhuk

2000-11-01

422

NASA Astrophysics Data System (ADS)

Since its launch in 2002, the Gravity Recovery and Climate Experiment (GRACE) has yielded tremendous insights into the spatio-temporal changes of mass redistribution in the Earth system. Such changes occur on widely varying spatial and temporal scales and take place both on Earth's surface, e.g., atmospheric mass fluctuations and the exchange of water, snow and ice, as well as in its interior, e.g., glacial isostatic adjustment and earthquakes. Each of these processes causes changes in the Earth's gravitational potential field which GRACE observes. One example is the Antarctic and Greenland ice mass changes inferred from GRACE observations of the changing geopotential as well as the associated time rate of change of its degree 2 and 4 zonal harmonics observed by satellite laser ranging. Deforming the Earth's surface and interior both co- and post-seismically, with some of the deformation permanent, earthquakes can affect the geopotential at a spatial scale up to thousands of kilometers and at temporal scales from seconds to months. Traditional measurements of earthquakes, e.g., by seismometers, GPS and inSAR, observe the co- and post-seismic surface displacements and are invaluable in understanding earthquake triggering mechanisms, slip distributions, rupture dynamics and slow post-seismic changes. Space-based observations of geopotential changes can add a whole new dimension to this as such observations are also sensitive to changes in the Earth's interior, over a larger area affected by the earthquake, over longer timescales, beyond that of Earth's longest period normal mode, and because they have global sensitivity including over sparsely instrumented oceanic domains. We use a joint seismic and gravitational normal-mode formalism to quantify changes in the gravitational potential due to different types of earthquakes, comparing them to predictions from dislocation models. We discuss the inverse problem of estimating the source parameters of large earthquakes, from the perspective of benchmarking the method and gaining insights into its sensitivities to earthquake hypocenter, focal mechanism and magnitude. We apply our procedure to several previously well-characterized earthquakes using GRACE data and discuss the additional information that can be obtained on earthquakes, that suffer poor traditional data coverage, by combining GRACE and seismic data in a joint estimation.

Sterenborg, G.; Simons, F. J.; Welch, E.; Morrow, E.; Mitrovica, J. X.

2013-12-01

423

Spherical Gravitational Waves in Relativistic Theory of Gravitation

Within the framework of relativistic theory of gravitation the exact spherically-symmetric wave solution is received. It is shown that this solution possesses the positive-definite energy and momentum deriving with the Fock energy-momentum density tensor of gravitational field. In this connection the sense of Birkhoff theorem in Relativistic Theory of Gravitation is discussed.

A. A. Leonovich; Yu. P. Vyblyi

2012-11-13

424

The three dimensional theory of gravitation based on a temporal scalar field in Riemanian geometry

A new approach to the model of the universe based on work by Rippl, Romero, Tavakol is presented. We have used the scheme for relating the vacuum (D + 1) dimensional theories to D dimensional theories for setting up a correspondence between vacuum 4-dimensional Einstein theory with 3-dimensional gravity theory with temporal scalar field. These ideas we continued by using the 3-dimensional analog of Jordan, Brans-Dicke theory with temporal scalar field. As the result space and time are treated in completely different ways. For the case of a static spherically symmetric field new vacuum static solutions are found.

S. Kozyrev

2004-06-21

425

Gauge theory, under the framework of quantum field theory, has successfully described three fundamental interactions: electromagnetic, weak, and strong interactions. Problems of describing the gravitational interaction in a similar manner has not been satisfied yet until now. Teleparallel gravity (TG) is one proposal describing gravitational field as a gauge field. This theory is quite new and it is equivalent to Einstein's general relativity. But as gravitational field in TG is expressed by torsion, rather than curvature, it gives an alternative framework for solving problems on gravity. This paper will present solution of the dynamical equation of abelian vector fields under the framework of TG in the Bianchi type I spacetime.

Triyanta; Zen, F. P. [Theoretical High Energy Physics and Instrumentation Division, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Indonesian Center for Theoretical and Mathematical Physics (ICTMP) (Indonesia); Supardi [Theoretical High Energy Physics and Instrumentation Division, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Indonesian Center for Theoretical and Mathematical Physics (ICTMP), Department of Physics, Faculty of Mathematics and Natural Sciences, Sriwijaya University (Indonesia); Wardaya, A. Y. [Theoretical High Energy Physics and Instrumentation Division, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung Indonesian Center for Theoretical and Mathematical Physics (ICTMP), Department of Physics, Faculty of Mathematics and Natural Sciences, Diponegoro University (Indonesia)

2010-12-23

426

In this study, a weak magnetic field (WMF), superimposed with a permanent magnet, was utilized to improve ZVI corrosion and thereby enhance As(V)/As(III) removal by ZVI at pHini 3.0-9.0. The experiment with real arsenic-bearing groundwater revealed that WMF could greatly improve arsenic removal by ZVI even in the presence of various cations and anions. The WMF-induced improvement in As(V)/As(III) removal by ZVI should be primarily associated with accelerated ZVI corrosion, as evidenced by the pH variation, Fe(2+) release, and the formation of corrosion products as characterized with X-ray absorption fine structure spectroscopy. The arsenic species analysis in solution/solid phases at pHini 3.0 revealed that As(III) oxidation to As(V) in aqueous phase preceded its subsequent sequestration by the newly formed iron (hydr)oxides. However, both As(V) adsorption following As(III) oxidation to As(V) in solution and As(III) adsorption preceding its conversion to As(V) in solid phase were observed at pHini 5.0-9.0. The application of WMF accelerated the transformation of As(III) to As(V) in both aqueous and solid phases at pHini 5.0-9.0 and enhanced the oxidation of As(III) to As(V) in solution at pHini 3.0. PMID:24870265

Sun, Yuankui; Guan, Xiaohong; Wang, Jianmin; Meng, Xiaoguang; Xu, Chunhua; Zhou, Gongming

2014-06-17

427

Impacts of electric and magnetic fields (EFs and MFs) on a biological organism vary depending on their application style, time, and intensities. High intensity MF and EF have destructive effects on plants. However, at low intensities, these phenomena are of special interest because of the complexity of plant responses. This study reports the effects of continuous, low-intensity static MF (7 mT) and EF (20 kV/m) on growth and antioxidant status of shallot (Allium ascalonicum L.) leaves, and evaluates whether shifts in antioxidant status of apoplastic and symplastic area help plants to adapt a new environment. Growth was induced by MF but EF applied emerged as a stress factor. Despite a lack of visible symptoms of injury, lipid peroxidation and H?O? levels increased in EF applied leaves. Certain symplastic antioxidant enzyme activities and non-enzymatic antioxidant levels increased in response to MF and EF applications. Antioxidant enzymes in the leaf apoplast, by contrast, were found to show different regulation responses to EF and MF. Our results suggest that apoplastic constituents may work as potentially important redox regulators sensing and signaling environmental changes. Static continuous MF and EF at low intensities have distinct impacts on growth and the antioxidant system in plant leaves, and weak MF is involved in antioxidant-mediated reactions in the apoplast, resulting in overcoming a possible redox imbalance. PMID:22647960

Cakmak, Turgay; Cakmak, Zeynep E; Dumlupinar, Rahmi; Tekinay, Turgay

2012-07-15

428

Weak lensing goes bananas: What flexion really measures

In weak gravitational lensing, the image distortion caused by shear measures the projected tidal gravitational field of the deflecting mass distribution. To lowest order, the shear is proportional to the mean image ellipticity. If the image sizes are not small compared to the scale over which the shear varies, higher-order distortions occur, called flexion. For ordinary weak lensing, the observable quantity is not the shear, but the reduced shear, owing to the mass-sheet degeneracy. Likewise, the flexion itself is unobservable. Rather, higher-order image distortions measure the reduced flexion, i.e., derivatives of the reduced shear. We derive the corresponding lens equation in terms of the reduced flexion and calculate the resulting relation between brightness moments of source and image. Assuming an isotropic distribution of source orientations, estimates for the reduced shear and flexion are obtained; these are then tested with simulations. In particular, the presence of flexion affects the determination o...

Schneider, Peter

2007-01-01

429

In the last years a lot of papers were published treating general relativity as an effective field theory. We are dealing with general relativity and the combination of general relativity and scalar QED as effective field theories. For effective field theories the quantization is well known therefore we are able to quantize general relativity and the combination of general relativity and scalar QED. The vertex rules can be extracted from the action and the non-analytical contributions to the 1-loop scattering matrix of scalars and charged scalars are calculated in the non-relativistic limit. The non-analytical parts of the scattering amplitudes yield the long range, low energy, leading quantum corrections. From the general relativity as an effective field theory the leading quantum corrections to the Newtonian gravity is constructed. General relativity combined with scalar QED yield the post-Newtonian and quantum corrections to the two-particle non-relativistic scattering matrix potential for charged scalar p...

Faller, Sven

2007-01-01

430

Gravitational Wave Verification Sources

NASA Astrophysics Data System (ADS)

Ultra-compact binary systems containing white dwarfs dominate the gravitational wave foreground in the mHz frequency range. Many of these binaries are weak gravitational wave sources. However, there are nine systems where the gravitational wave strain is strong enough to make them verification sources for gravitational wave missions, e.g. the evolved Laser Interferometer Space Antenna (eLISA). Here we present a summary of the physical characteristics of these nine systems, including the observed rate of orbital decay. In addition, we present the recent discoveries from the ELM Survey, which identified two verification sources in the last 3 years. We also discuss the future prospects for increasing the sample of verification binaries.

Kilic, Mukremin; Brown, Warren R.; Hermes, J. J.; Gianninas, A.

431

Gravitational waves in the spectral action of noncommutative geometry

The spectral triple approach to noncommutative geometry allows one to develop the entire standard model (and supersymmetric extensions) of particle physics from a purely geometry standpoint and thus treats both gravity and particle physics on the same footing. The bosonic sector of the theory contains a modification to Einstein-Hilbert gravity, involving a nonconformal coupling of curvature to the Higgs field and conformal Weyl term (in addition to a nondynamical topological term). In this paper we derive the weak-field limit of this gravitational theory and show that the production and dynamics of gravitational waves are significantly altered. In particular, we show that the graviton contains a massive mode that alters the energy lost to gravitational radiation, in systems with evolving quadrupole moment. We explicitly calculate the general solution and apply it to systems with periodically varying quadrupole moments, focusing, in particular, on the well-known energy loss formula for circular binaries.

Nelson, William; Ochoa, Joseph; Sakellariadou, Mairi [Institute of Gravitation and the Cosmos, Penn State University, State College, Pennsylvania 16801 (United States); Department of Physics, King's College, University of London, Strand WC2R 2LS, London (United Kingdom)

2010-10-15