NASA Astrophysics Data System (ADS)
Tsukamoto, Naoki; Kitamura, Takao; Nakajima, Koki; Asada, Hideki
2014-09-01
The gravitational lensing effects in the weak gravitational field by exotic lenses have been investigated intensively to find nonluminous exotic objects. Gravitational lensing based on 1/rn fall-off metric, as a one-parameter model that can treat by hand both the Schwarzschild lens (n =1) and the Ellis wormhole (n =2) in the weak field, has been recently studied. Only for n=1 case, however, it has been explicitly shown that effects of relativistic lens images by the strong field on the light curve can be neglected. We discuss whether relativistic images by the strong field can be neglected for n>1 in the Tangherlini spacetime which is one of the simplest models for our purpose. We calculate the divergent part of the deflection angle for arbitrary n and the regular part for n=1, 2 and 4 in the strong field limit, the deflection angle for arbitrary n under the weak gravitational approximation. We also compare the radius of the Einstein ring with the radii of the relativistic Einstein rings for arbitrary n. We conclude that the images in the strong gravitational field have little effect on the total light curve and that the time-symmetric demagnification parts in the light curve will appear even after taking account of the images in the strong gravitational field for n>1.
Weber's gravitational force as static weak field approximation
NASA Astrophysics Data System (ADS)
Tiandho, Yuant
2016-02-01
Weber's gravitational force (WGF) is one of gravitational model that can accommodate a non-static system because it depends not only on the distance but also on the velocity and the acceleration. Unlike Newton's law of gravitation, WGF can predict the anomalous of Mercury and gravitational bending of light near massive object very well. Then, some researchers use WGF as an alternative model of gravitation and propose a new mechanics theory namely the relational mechanics theory. However, currently we have known that the theory of general relativity which proposed by Einstein can explain gravity with very accurate. Through the static weak field approximation for the non-relativistic object, we also have known that the theory of general relativity will reduce to Newton's law of gravity. In this work, we expand the static weak field approximation that compatible with relativistic object and we obtain a force equation which correspond to WGF. Therefore, WGF is more precise than Newton's gravitational law. The static-weak gravitational field that we used is a solution of the Einstein's equation in the vacuum that satisfy the linear field approximation. The expression of WGF with ξ = 1 and satisfy the requirement of energy conservation are obtained after resolving the geodesic equation. By this result, we can conclude that WGF can be derived from the general relativity.
Weak Gravitational Wave and Casimir Energy of a Scalar Field
NASA Astrophysics Data System (ADS)
Tavakoli, F.; Pirmoradian, R.; Parsabod, I.
2016-09-01
In this paper, we calculate the effect of a weak gravitational field on the Casimir force between two ideal plates subjected to a massless minimally coupled field. It is the aim of this work to study the Casimir energy under a weak perturbation of gravity. Moreover, the fluctuations of the stress-energy tensor for a scalar field in de Sitter space-time are computed as well.
[The use of a detector of the extremely weak radiation as a variometer of gravitation field].
Gorshkov, E S; Bondarenko, E G; Shapovalov, S N; Sokolovskiĭ, V V; Troshichev, O A
2001-01-01
It was shown that the detector of extremely weak radiation with selectively increased sensitivity to the nonelectromagnetic, including the gravitational component of the spectrum of active physical fields can be used as the basis for constructing a variometer of gravitational field of a new type.
NASA Astrophysics Data System (ADS)
Pires, Sandrine; Starck, Jean-Luc; Leonard, Adrienne; Réfrégier, Alexandre
2012-03-01
This chapter reviews the data mining methods recently developed to solve standard data problems in weak gravitational lensing. We detail the different steps of the weak lensing data analysis along with the different techniques dedicated to these applications. An overview of the different techniques currently used will be given along with future prospects. Until about 30 years ago, astronomers thought that the Universe was composed almost entirely of ordinary matter: protons, neutrons, electrons, and atoms. The field of weak lensing has been motivated by the observations made in the last decades showing that visible matter represents only about 4-5% of the Universe (see Figure 14.1). Currently, the majority of the Universe is thought to be dark, that is, does not emit electromagnetic radiation. The Universe is thought to be mostly composed of an invisible, pressure less matter - potentially relic from higher energy theories - called "dark matter" (20-21%) and by an even more mysterious term, described in Einstein equations as a vacuum energy density, called "dark energy" (70%). This "dark" Universe is not well described or even understood; its presence is inferred indirectly from its gravitational effects, both on the motions of astronomical objects and on light propagation. So this point could be the next breakthrough in cosmology. Today's cosmology is based on a cosmological model that contains various parameters that need to be determined precisely, such as the matter density parameter Omega_m or the dark energy density parameter Omega_lambda. Weak gravitational lensing is believed to be the most promising tool to understand the nature of dark matter and to constrain the cosmological parameters used to describe the Universe because it provides a method to directly map the distribution of dark matter (see [1,6,60,63,70]). From this dark matter distribution, the nature of dark matter can be better understood and better constraints can be placed on dark energy
Gravitational lensing beyond the weak-field approximation
NASA Astrophysics Data System (ADS)
Perlick, Volker
2014-01-01
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.
Gravitational lensing beyond the weak-field approximation
Perlick, Volker
2014-01-14
Gravitational lensing is considered in the full spacetime formalism of general relativity, assuming that the light rays are lightlike geodesics in a Lorentzian manifold. The review consists of three parts. The first part is devoted to spherically symmetric and static spacetimes. In particular, an exact lens map for this situation is discussed. The second part is on axisymmetric and stationary spacetimes. It concentrates on the investigation of the photon region, i.e., the region filled by spherical lightlike geodesics, in the Kerr spacetime. The photon region is of crucial relevance for the formation of a shadow. Finally, the third part briefly addresses two topics that apply to spacetimes without symmetry, namely Fermat’s principle and the exact lens map of Frittelli and Newman.
Localized electromagnetic and weak gravitational fields in the source-free space.
Borzdov, G N
2001-03-01
Localized electromagnetic and weak gravitational time-harmonic fields in the source-free space are treated using expansions in plane waves. The presented solutions describe fields having a very small (about several wavelengths) and clearly defined core region with maximum intensity of field oscillations. In a given Lorentz frame L, a set of the obtained exact time-harmonic solutions of the free-space homogeneous Maxwell equations consists of three subsets (storms, whirls, and tornados), for which time average energy flux is identically zero at all points, azimuthal and spiral, respectively. In any other Lorentz frame L', they will be observed as a kind of electromagnetic missile moving without dispersing at speed V
NASA Astrophysics Data System (ADS)
Harris, Edward G.
1991-05-01
Starting from the equations of general relativity, equations similar to those of electromagnetic theory are derived. It is assumed that the particles are slowly moving (v≪c), and the gravitational field is sufficiently weak that nonlinear terms in Einstein's field equations can be neglected. For static fields, the analogy to electrostatics and magnetostatics is very close. Results are compared with those of a previous derivation by Braginsky, Caves, and Thorne [Phys. Rev. D 15, 2047-2068 (1977)]. These results lead to very simple derivations of the Lense-Thirring precession [Phys. Z. 19, 156-163 (1918)] and the spin-curvature force of Papepetrou [Proc. R. Soc. London Ser. A 209, 248-258 (1951)] and Pirani [Acta Phys. Pol. 15, 389-405 (1956)].
The generation of gravitational waves. 1. Weak-field sources: A plug-in-and-grind formalism
NASA Technical Reports Server (NTRS)
Thorne, K. S.; Kovacs, S. J.
1974-01-01
A plug-in-and-grind formalism is derived for calculating the gravitational waves emitted by any system with weak internal gravitational fields. If the internal fields have negligible influence on the system's motions, then the formalism reduces to standard linearized theory. Whether or not gravity affects the motions, if the motions are slow and internal stresses are weak, then the new formalism reduces to the standard quadrupole-moment formalism. In the general case the new formalism expresses the radiation in terms of a retarded Green's function for slightly curved spacetime, and then breaks the Green's-function integral into five easily understood pieces: direct radiation, produced directly by the motions of the sources; whump radiation, produced by the the gravitational stresses of the source; transition radiation, produced by a time-changing time delay (Shapiro effect) in the propagation of the nonradiative, 1/r field of the source; focussing radiation produced when one portion of the source focusses, in a time-dependent way, the nonradiative field of another portion of the source, and tail radiation, produced by backscatter of the nonradiative field in regions of focussing.
NASA Astrophysics Data System (ADS)
Schreck, M.
2015-12-01
In the current article, the classical analog of the minimal photon sector in the Lorentz-violating Standard-Model extension (SME) is investigated. The analysis is based on describing a photon classically by a geometric ray that satisfies the eikonal equation. The action principle, which leads to the eikonal equation in conventional optics, is demonstrated to work in most (but not all) Lorentz-violating cases as well. Furthermore it is found that the integrands of the action functional correspond to Finsler structures. Based on these results, Lorentz-violating light rays in a weak gravitational background are treated through the use of the minimal-coupling principle. This allows for obtaining sensitivities on Lorentz violation in the photon sector by measurements of light bending at massive bodies such as the Sun. The computations are carried out for the currently running ESA mission GAIA and the planned NASA/ESA mission LATOR. Finally, a range of aspects of explicit Lorentz violation for photons is discussed in the Finsler setting.
Instrumental systematics and weak gravitational lensing
NASA Astrophysics Data System (ADS)
Mandelbaum, R.
2015-05-01
We present a pedagogical review of the weak gravitational lensing measurement process and its connection to major scientific questions such as dark matter and dark energy. Then we describe common ways of parametrizing systematic errors and understanding how they affect weak lensing measurements. Finally, we discuss several instrumental systematics and how they fit into this context, and conclude with some future perspective on how progress can be made in understanding the impact of instrumental systematics on weak lensing measurements.
NASA Astrophysics Data System (ADS)
Doyen, G.; Drakova, D.
2015-08-01
We construct a world model consisting of a matter field living in 4 dimensional spacetime and a gravitational field living in 11 dimensional spacetime. The seven hidden dimensions are compactified within a radius estimated by reproducing the particle-wave characteristics of diffraction experiments. In the presence of matter fields the gravitational field develops localized modes with elementary excitations called gravonons which are induced by the sources (massive particles). The final world model treated here contains only gravonons and a scalar matter field. The gravonons are localized in the environment of the massive particles which generate them. The solution of the Schrödinger equation for the world model yields matter fields which are localized in the 4 dimensional subspace. The localization has the following properties: (i) There is a chooser mechanism for the selection of the localization site. (ii) The chooser selects one site on the basis of minor energy differences and differences in the gravonon structure between the sites, which at present cannot be controlled experimentally and therefore let the choice appear statistical. (iii) The changes from one localization site to a neighbouring one take place in a telegraph-signal like manner. (iv) The times at which telegraph like jumps occur depend on subtleties of the gravonon structure which at present cannot be controlled experimentally and therefore let the telegraph-like jumps appear statistical. (v) The fact that the dynamical law acts in the configuration space of fields living in 11 dimensional spacetime lets the events observed in 4 dimensional spacetime appear non-local. In this way the phenomenology of CQM is obtained without the need of introducing the process of collapse and a probabilistic interpretation of the wave function. Operators defining observables need not be introduced. All experimental findings are explained in a deterministic way as a consequence of the time development of the wave
Gravitational anomaly and Hawking radiation near a weakly isolated horizon
Wu Xiaoning; Huang Chaoguang; Sun Jiarui
2008-06-15
Based on the idea of the work by Wilczek and his collaborators, we consider the gravitational anomaly near a weakly isolated horizon. We find that there exists a universal choice of tortoise coordinate for any weakly isolated horizon. Under this coordinate, the leading behavior of a quite arbitrary scalar field near a horizon is a 2-dimensional chiral scalar field. This means we can extend the idea of Wilczek and his collaborators to more general cases and show the relation between gravitational anomaly and Hawking radiation is a universal property of a black hole horizon.
Gravitational anomaly and Hawking radiation near a weakly isolated horizon
NASA Astrophysics Data System (ADS)
Wu, Xiaoning; Huang, Chao-Guang; Sun, Jia-Rui
2008-06-01
Based on the idea of the work by Wilczek and his collaborators, we consider the gravitational anomaly near a weakly isolated horizon. We find that there exists a universal choice of tortoise coordinate for any weakly isolated horizon. Under this coordinate, the leading behavior of a quite arbitrary scalar field near a horizon is a 2-dimensional chiral scalar field. This means we can extend the idea of Wilczek and his collaborators to more general cases and show the relation between gravitational anomaly and Hawking radiation is a universal property of a black hole horizon.
Baryons, neutrinos, feedback and weak gravitational lensing
NASA Astrophysics Data System (ADS)
Harnois-Déraps, Joachim; van Waerbeke, Ludovic; Viola, Massimo; Heymans, Catherine
2015-06-01
The effect of baryonic feedback on the dark matter mass distribution is generally considered to be a nuisance to weak gravitational lensing. Measurements of cosmological parameters are affected as feedback alters the cosmic shear signal on angular scales smaller than a few arcminutes. Recent progress on the numerical modelling of baryon physics has shown that this effect could be so large that, rather than being a nuisance, the effect can be constrained with current weak lensing surveys, hence providing an alternative astrophysical insight on one of the most challenging questions of galaxy formation. In order to perform our analysis, we construct an analytic fitting formula that describes the effect of the baryons on the mass power spectrum. This fitting formula is based on three scenarios of the OverWhelmingly Large hydrodynamical simulations. It is specifically calibrated for z < 1.5, where it models the simulations to an accuracy that is better than 2 per cent for scales k < 10 h Mpc-1 and better than 5 per cent for 10 < k < 100 h Mpc-1. Equipped with this precise tool, this paper presents the first constraint on baryonic feedback models using gravitational lensing data, from the Canada France Hawaii Telescope Lensing Survey (CFHTLenS). In this analysis, we show that the effect of neutrino mass on the mass power spectrum is degenerate with the baryonic feedback at small angular scales and cannot be ignored. Assuming a cosmology precision fixed by WMAP9, we find that a universe with massless neutrinos is rejected by the CFHTLenS lensing data with 85-98 per cent confidence, depending on the baryon feedback model. Some combinations of feedback and non-zero neutrino masses are also disfavoured by the data, although it is not yet possible to isolate a unique neutrino mass and feedback model. Our study shows that ongoing weak gravitational lensing surveys (KiDS, HSC and DES) will offer a unique opportunity to probe the physics of baryons at galactic scales, in
Gravitational force in weakly correlated particle spatial distributions.
Gabrielli, Andrea; Masucci, Adolfo Paolo; Labini, Francesco Sylos
2004-03-01
We study the statistics of the gravitational (Newtonian) force in a particular class of weakly correlated spatial distributions of pointlike and unitary mass particles generated by the so-called Gauss-Poisson point processes. In particular we extend to these distributions the analysis that Chandrasekhar introduced for purely Poisson processes. In this way we can find the explicit asymptotic behavior of the probability density function of the force for both large and small values of the field as a generalization of the Holtzmark statistics. In particular, we show how the modifications at large fields depend on the density correlations introduced at small scales. The validity of the introduced approximations is positively tested through a direct comparison with the analysis of the statistics of the gravitational force in numerical simulations of Gauss-Poisson processes.
Atomic Inference from Weak Gravitational Lensing Data
Marshall, Phil; /KIPAC, Menlo Park
2005-12-14
We present a novel approach to reconstructing the projected mass distribution from the sparse and noisy weak gravitational lensing shear data. The reconstructions are regularized via the knowledge gained from numerical simulations of clusters, with trial mass distributions constructed from n NFW profile ellipsoidal components. The parameters of these ''atoms'' are distributed a priori as in the simulated clusters. Sampling the mass distributions from the atom parameter probability density function allows estimates of the properties of the mass distribution to be generated, with error bars. The appropriate number of atoms is inferred from the data itself via the Bayesian evidence, and is typically found to be small, reecting the quality of the data. Ensemble average mass maps are found to be robust to the details of the noise realization, and succeed in recovering the demonstration input mass distribution (from a realistic simulated cluster) over a wide range of scales. As an application of such a reliable mapping algorithm, we comment on the residuals of the reconstruction and the implications for predicting convergence and shear at specific points on the sky.
The general theory of secondary weak gravitational lensing
Clarkson, Chris
2015-09-01
Weak gravitational lensing is normally assumed to have only two principle effects: a magnification of a source and a distortion of the sources shape in the form of a shear. However, further distortions are actually present owing to changes in the gravitational field across the scale of the ray bundle of light propagating to us, resulting in the familiar arcs in lensed images. This is normally called the flexion, and is approximated by Taylor expanding the shear and magnification across the image plane. However, the physical origin of this effect arises from higher-order corrections in the geodesic deviation equation governing the gravitational force between neighbouring geodesics— so involves derivatives of the Riemann tensor. We show that integrating the second-order geodesic deviation equation results in a 'Hessian map' for gravitational lensing, which is a higher-order addition to the Jacobi map. We derive the general form of the Hessian map in an arbitrary spacetime paying particular attention to the separate effects of local Ricci versus non-local Weyl curvature. We then specialise to the case of a perturbed FLRW model, and give the general form of the Hessian for the first time. This has a host of new contributions which could in principle be used as tests for modified gravity.
Testing Einstein's weak equivalence principle with gravitational waves
NASA Astrophysics Data System (ADS)
Wu, Xue-Feng; Gao, He; Wei, Jun-Jie; Mészáros, Peter; Zhang, Bing; Dai, Zi-Gao; Zhang, Shuang-Nan; Zhu, Zong-Hong
2016-07-01
A conservative constraint on Einstein's weak equivalence principle (WEP) can be obtained under the assumption that the observed time delay between correlated particles from astronomical sources is dominated by the gravitational fields through which they move. Current limits on the WEP are mainly based on the observed time delays of photons with different energies. It is highly desirable to develop more accurate tests that include the gravitational wave (GW) sector. The detection by the advanced LIGO/VIRGO systems of gravitational waves will provide attractive candidates for constraining the WEP, extending the tests to gravitational interactions with potentially higher accuracy. Considering the capabilities of the advanced LIGO/VIRGO network and the source direction uncertainty, we show that the joint detection of GWs and electromagnetic signals could probe the WEP to an accuracy down to 10-10 , which is one order of magnitude tighter than previous limits, and 7 orders of magnitude tighter than the multimessenger (photons and neutrinos) results by supernova 1987A.
NASA Astrophysics Data System (ADS)
Chen, Shao-Guang
According to f =d(mv)/dt=m(dv/dt)+ v(dm/dt), a same gravitational formula had been de-duced from the variance in physical mass of QFT and from the variance in mass of inductive energy-transfer of GR respectively: f QF T = f GR = -G (mM/r2 )((r/r)+(v/c)) when their interaction-constants are all taken the experimental values (H05-0029-08, E15-0039-08). f QF T is the quasi-Casimir pressure. f GR is equivalent to Einstein's equation, then more easy to solve it. The hypothesis of the equivalent principle is not used in f QF T , but required by f GR . The predictions of f QF T and f GR are identical except that f QF T has quantum effects but f GR has not and f GR has Lense-Thirring effect but f QF T has not. The quantum effects of gravitation had been verified by Nesvizhevsky et al with the ultracold neutrons falling in the earth's gravitational field in 2002. Yet Lense-Thirring effect had not been measured by GP-B. It shows that f QF T is essential but f GR is phenomenological. The macro-f QF T is the statistic average pressure collided by net virtual neutrinos ν 0 flux (after self-offset in opposite directions) and in direct proportion to the mass. But micro-f QF T is in direct proportion to the scattering section. The electric mass (in inverse proportion to de Broglie wavelength λ) far less than nucleonic mass and the electric scattering section (in direct proportion to λ2 ) far large than that of nucleon, then the net ν 0 flux pressure exerted to electron far large than that to nucleon and the electric displacement far large than that of nucleon, it causes the gravitational polarization of positive-negative charge center separation. Because the gravity far less than the electromagnetic binding force, in atoms the gravitational polarization only produces a little separation. But the net ν 0 flux can press a part freedom electrons in plasma of ionosphere into the earth's surface, the static electric force of redundant positive ions prevents electrons from further
Caution: Strong Gravitational Field Present
ERIC Educational Resources Information Center
Reif, Marc
2014-01-01
I came up with a new way to introduce the concept of a constant gravitational field near the surface of the Earth. I made "g-field detectors" (see Fig. 1 ) and suspended them by strings from the ceiling in a regular spacing. The detectors are cardstock arrows with a hole punched out of them and the letter "g" in the center.
Particles, Fields, and Gravitation. Proceedings
Rembieli ski, J.
1998-11-01
These proceedings represent papers presented at the Conference on Particles, Fields, and Gravitation held in Lodz, Poland in April, 1998. The topics discussed included quantum deformations and noncommutative geometry, quantum mechanics, quantum and topological field theory, modern gravitation theory and geometrical methods in physics. Solvable and quasisolvable models were also disussed. The talks and the resulting papers provided a comprehensive coverage of the main aspects of contemporary theoretical and mathematical physics. The Conference was attended by more than 100 scientists from all over the world. There were 54 papers presented at the conference,out of which 1 paper has been abstracted for the Energy,Science and Technology database.(AIP)
The gravitational field of Phobos
Chao, B.F.; Rubincam, D.P. )
1989-08-01
The external gravitational field produced by a rigid body of uniform density but irregular shape is formulated in terms of spherical harmonics. The formalism is applied to the Martian satellite Phobos. Based on a 3-dimensional shape model of Phobos by Duxbury, the gravitational coefficients up to degree and order 4 for a homogeneous Phobos are computed. In particular, the authors find J{sub 2} = 0.105. The in-plane liberation amplitude of a homogeneous Phobos is predicted to be 0.97{degree}, within the rather large uncertainty of the observed value of 0.78 {plus minus} 0.4{degree}.
Weak gravitational shear and flexion with polar shapelets
NASA Astrophysics Data System (ADS)
Massey, Richard; Rowe, Barnaby; Refregier, Alexandre; Bacon, David J.; Bergé, Joel
2007-09-01
We derive expressions, in terms of `polar shapelets', for the image distortion operations associated with weak gravitational lensing. Shear causes galaxy shapes to become elongated, and is sensitive to the second derivative of the projected gravitational potential along their line of sight; flexion bends galaxy shapes into arcs, and is sensitive to the third derivative. Polar shapelets provide a natural representation, in which both shear and flexion transformations are compact. Through this tool, we understand progress in several weak lensing methods. We then exploit various symmetries of shapelets to construct a range of shear estimators with useful properties. Through an analogous investigation, we also explore several flexion estimators. In particular, some of the estimators can be measured simultaneously and independently for every galaxy, and will provide unique checks for systematics in future weak lensing analyses. Using simulated images from the Shear TEsting Programme, we show that we can recover input shears with no significant bias. A complete software package to parametrize astronomical images in terms of polar shapelets, and to perform a full weak lensing analysis, is available on the Internet.
Combining Strong and Weak Gravitational Lensing in Abell 1689
NASA Astrophysics Data System (ADS)
Limousin, Marceau; Richard, Johan; Jullo, Eric; Kneib, Jean-Paul; Fort, Bernard; Soucail, Geneviève; Elíasdóttir, Árdís; Natarajan, Priyamvada; Ellis, Richard S.; Smail, Ian; Czoske, Oliver; Smith, Graham P.; Hudelot, Patrick; Bardeau, Sébastien; Ebeling, Harald; Egami, Eiichi; Knudsen, Kirsten K.
2007-10-01
We present a reconstruction of the mass distribution of galaxy cluster Abell 1689 at z=0.18 using detected strong lensing features from deep ACS observations and extensive ground based spectroscopy. Earlier analyses have reported up to 32 multiply imaged systems in this cluster, of which only 3 were spectroscopically confirmed. In this work, we present a parametric strong lensing mass reconstruction using 34 multiply imaged systems of which 24 have newly determined spectroscopic redshifts, which is a major step forward in building a robust mass model. In turn, the new spectroscopic data allows a more secure identification of multiply imaged systems. The resultant mass model enables us to reliably predict the redshifts of additional multiply imaged systems for which no spectra are currently available, and to use the location of these systems to further constrain the mass model. Using our strong lensing mass model, we predict on larger scale a shear signal which is consistent with that inferred from our large scale weak lensing analysis derived using CFH12K wide field images. Thanks to a new method for reliably selecting a well defined background lensed galaxy population, we resolve the discrepancy found between the NFW concentration parameters derived from earlier strong and weak lensing analysis. The derived parameters for the best fit NFW profile is found to be c200=7.6+/-1.6 and r200=2.16+/-0.10 h-170 Mpc (corresponding to a 3D mass equal to M200=[1.32+/-0.2]×1015 h70 Msolar). The large number of new constraints incorporated in this work makes Abell 1689 the most reliably reconstructed cluster to date. This well calibrated mass model, which we here make publicly available, will enable us to exploit Abell 1689 efficiently as a gravitational telescope, as well as to potentially constrain cosmology. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des
Weak Gravitational Lensing from Regular Bardeen Black Holes
NASA Astrophysics Data System (ADS)
Ghaffarnejad, Hossein; niad, Hassan
2016-03-01
In this article we study weak gravitational lensing of regular Bardeen black hole which has scalar charge g and mass m. We investigate the angular position and magnification of non-relativistic images in two cases depending on the presence or absence of photon sphere. Defining dimensionless charge parameter q= {g}/{2m} we seek to disappear photon sphere in the case of |q|>{24√5}/{125} for which the space time metric encounters strongly with naked singularities. We specify the basic parameters of lensing in terms of scalar charge by using the perturbative method and found that the parity of images is different in two cases: (a) The strongly naked singularities is present in the space time. (b) singularity of space time is weak or is eliminated (the black hole lens).
Gravitational failure of sea cliffs in weakly lithified sediment
Hampton, M.A.
2002-01-01
Gravitational failure of sea cliffs eroded into weakly lithified sediment at several sites in California involves episodic stress-release fracturing and cantilevered block falls. The principal variables that influence the gravitational stability are tensional stresses generated during the release of horizontal confining stress and weakening of the sediment with increased saturation levels. Individual failures typically comprise less than a cubic meter of sediment, but large areas of a cliff face can be affected by sustained instability over a period of several days. Typically, only the outer meter or so of sediment is removed during a failure episode. In-place sediment saturation levels vary over time and space, generally being higher during the rainy season but moderate to high year-round. Laboratory direct-shear tests show that sediment cohesion decreases abruptly with increasing saturation level; the decrease is similar for all tested sediment if the cohesion is normalized by the maximum, dry-sediment cohesion. Large failures that extend over most or all of the height of the sea cliff are uncommon, but a few large wedge-shaped failures sometimes occur, as does separation of large blocks at sea cliff-gully intersections.
Karhunen-Loeve Analysis for Weak Gravitational Lensing
NASA Astrophysics Data System (ADS)
Vanderplas, Jacob T.
In the past decade, weak gravitational lensing has become an important tool in the study of the universe at the largest scale, giving insights into the distribution of dark matter, the expansion of the universe, and the nature of dark energy. This thesis research explores several applications of Karhunen-Loève (KL) analysis to speed and improve the comparison of weak lensing shear catalogs to theory in order to constrain cosmological parameters in current and future lensing surveys. This work addresses three related aspects of weak lensing analysis: Three-dimensional Tomographic Mapping: (Based on work published in Vanderplas et al 2011) We explore a new fast approach to three-dimensional mass mapping in weak lensing surveys. The KL approach uses a KL-based filtering of the shear signal to reconstruct mass structures on the line-of-sight, and provides a unified framework to evaluate the efficacy of linear reconstruction techniques. We find that the KL-based filtering leads to near-optimal angular resolution, and computation times which are faster than previous approaches. We also use the KL formalism to show that linear non-parametric reconstruction methods are fundamentally limited in their ability to resolve lens redshifts. Shear Peak Statistics with Incomplete Data: (Based on work published in Vanderplas et al 2012) We explore the use of KL eigenmodes for interpolation across masked regions in observed shear maps. Mass mapping is an inherently non-local calculation, meaning gaps in the data can have a significant effect on the properties of the derived mass map. Our KL mapping procedure leads to improvements in the recovery of detailed statistics of peaks in the mass map, which holds promise of improved cosmological constraints based on such studies. Two-point parameter estimation with KL modes: The power spectrum of the observed shear can yield powerful cosmological constraints. Incomplete survey sky coverage, however, can lead to mixing of power between
Quantum states of neutrons in the Earth's gravitational field.
Nesvizhevsky, Valery V; Börner, Hans G; Petukhov, Alexander K; Abele, Hartmut; Baessler, Stefan; Ruess, Frank J; Stöferle, Thilo; Westphal, Alexander; Gagarski, Alexei M; Petrov, Guennady A; Strelkov, Alexander V
2002-01-17
The discrete quantum properties of matter are manifest in a variety of phenomena. Any particle that is trapped in a sufficiently deep and wide potential well is settled in quantum bound states. For example, the existence of quantum states of electrons in an electromagnetic field is responsible for the structure of atoms, and quantum states of nucleons in a strong nuclear field give rise to the structure of atomic nuclei. In an analogous way, the gravitational field should lead to the formation of quantum states. But the gravitational force is extremely weak compared to the electromagnetic and nuclear force, so the observation of quantum states of matter in a gravitational field is extremely challenging. Because of their charge neutrality and long lifetime, neutrons are promising candidates with which to observe such an effect. Here we report experimental evidence for gravitational quantum bound states of neutrons. The particles are allowed to fall towards a horizontal mirror which, together with the Earth's gravitational field, provides the necessary confining potential well. Under such conditions, the falling neutrons do not move continuously along the vertical direction, but rather jump from one height to another, as predicted by quantum theory.
The Equivalence of Time and Gravitational Field
NASA Astrophysics Data System (ADS)
Barukčića, Ilija
The relationship between energy, time and space is still not solved in an appropriate manner. According to Newton's concept of time and space, both have to be taken as absolute. If we follow Leibniz and his arguments, space and time are relative. Since Einstein's theory of relativity we know at least that energy, time and space are deeply related. Albert Einstein originally predicted that time is nothing absolute but something relative, time changes and can change. Especially, time and gravitational field are related somehow even in detail if we still don't know how. According to the gravitational time dilation, the lower the gravitational potential, the more slowly time passes and vice versa. Somehow, it appears to be that the behaviour of time is directly linked to the behaviour of the gravitational field. The aim of this publication is to work out the interior logic between time and gravitational field and to make the proof that time is equivalent to the gravitational field and vice versa.
Spin-2 particles in gravitational fields
Papini, G.
2007-02-15
We give a solution of the wave equation for massless, or massive spin-2 particles propagating in a gravitational background. The solution is covariant, gauge-invariant and exact to first order in the background gravitational field. The background contribution is confined to a phase factor from which geometrical and physical optics can be derived. The phase also describes Mashhoon's spin-rotation coupling and, in general, the spin-gravity interaction.
Physical optics in a uniform gravitational field
NASA Astrophysics Data System (ADS)
Hacyan, Shahen
2012-01-01
The motion of a (quasi-)plane wave in a uniform gravitational field is studied. It is shown that the energy of an elliptically polarized wave does not propagate along a geodesic, but in a direction that is rotated with respect to the gravitational force. The similarity with the walk-off effect in anisotropic crystals or the optical Magnus effect in inhomogeneous media is pointed out.
String pair production in a time-dependent gravitational field
Tolley, Andrew J.; Wesley, Daniel H.
2005-12-15
We study the pair creation of point particles and strings in a time-dependent, weak gravitational field. We find that, for massive string states, there are surprising and significant differences between the string and point-particle results. Central to our approach is the fact that a weakly curved spacetime can be represented by a coherent state of gravitons, and therefore we employ standard techniques in string perturbation theory. String and point-particle pairs are created through tree-level interactions between the background gravitons. In particular, we focus on the production of excited string states and perform explicit calculations of the production of a set of string states of arbitrary excitation level. The differences between the string and point-particle results may contain important lessons for the pair production of strings in the strong gravitational fields of interest in cosmology and black hole physics.
Initial Results from a Laboratory Emulation of Weak Gravitational Lensing Measurements
NASA Astrophysics Data System (ADS)
Seshadri, S.; Shapiro, C.; Goodsall, T.; Fucik, J.; Hirata, C.; Rhodes, J. D.; Rowe, B. T. P.; Smith, R. M.
2013-09-01
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 μm cut-off Teledyne HgCdTe/H2RG detector. We used a 0.88 μm 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.
Radiative processes in external gravitational fields
Papini, Giorgio
2010-07-15
Kinematically forbidden processes may be allowed in the presence of external gravitational fields. These can be taken into account by introducing generalized particle momenta. The corresponding transition probabilities can then be calculated to all orders in the metric deviation from the field-free expressions by simply replacing the particle momenta with their generalized counterparts. The procedure applies to particles of any spin and to any gravitational fields. Transition probabilities, emission power, and spectra are, to leading order, linear in the metric deviation. It is also shown how a small dissipation term in the particle wave equations can trigger a strong backreaction that introduces resonances in the radiative process and deeply affects the resulting gravitational background.
On the consequences of the weak field approximation
NASA Astrophysics Data System (ADS)
Laubenstein, John
2013-04-01
General Relativity reduces to Newtonian gravity within the appropriate limit. But, what is that limit? The conventional response is that of the weak field approximation in which the gravitating source is weak and velocities are low. But, this is a far cry from a quantitative statement. In that regard, the weak field may be defined more quantitatively as one in which any error introduced is far beyond the level of precision required. Since the field can always be made incrementally weaker there is no limit as to the degree of precision that can be achieved. In this regard, GR reduces exactly to Newtonian gravity at the limit where velocity goes to zero. It is only out of convenience that we extend this to include those conditions where v << c with the argument that any error is arbitrarily small. However, in practice GR can be shown to reduce to an exact Newtonian expression at v > 0. How can this observation fit with the quantitative definition of the weak field? This paper explores the consequences of the weak field approximation and the fact that GR reduces directly to Newtonian gravity within the weak field as opposed to the more specific condition where v = zero.
Neutrino optics and oscillations in gravitational fields
Lambiase, G.; Punzi, R.; Papini, G.; Scarpetta, G.
2005-04-01
We study the propagation of neutrinos in gravitational fields using wave functions that are exact to first order in the metric deviation. For illustrative purposes, the geometrical background is represented by the Lense-Thirring metric. We derive explicit expressions for neutrino deflection, helicity transitions, flavor oscillations, and oscillation Hamiltonian.
Gravitational radiation from preheating with many fields
Jr, John T. Giblin; Price, Larry R.; Siemens, Xavier E-mail: larry@gravity.phys.uwm.edu
2010-08-01
Parametric resonances provide a mechanism by which particles can be created just after inflation. Thus far, attention has focused on a single or many inflaton fields coupled to a single scalar field. However, generically we expect the inflaton to couple to many other relativistic degrees of freedom present in the early universe. Using simulations in an expanding Friedmann-Lemaître-Robertson-Walker spacetime, in this paper we show how preheating is affected by the addition of multiple fields coupled to the inflaton. We focus our attention on gravitational wave production — an important potential observational signature of the preheating stage. We find that preheating and its gravitational wave signature is robust to the coupling of the inflaton to more matter fields.
Ren, Jing; Xianyu, Zhong-Zhi; He, Hong-Jian E-mail: xianyuzhongzhi@gmail.com
2014-06-01
We study gravitational interaction of Higgs boson through the unique dimension-4 operator ξH{sup †}HR, with H the Higgs doublet and R the Ricci scalar curvature. We analyze the effect of this dimensionless nonminimal coupling ξ on weak gauge boson scattering in both Jordan and Einstein frames. We explicitly establish the longitudinal-Goldstone equivalence theorem with nonzero ξ coupling in both frames, and analyze the unitarity constraints. We study the ξ-induced weak boson scattering cross sections at O(1−30) TeV scales, and propose to probe the Higgs-gravity coupling via weak boson scattering experiments at the LHC (14 TeV) and the next generation pp colliders (50-100 TeV). We further extend our study to Higgs inflation, and quantitatively derive the perturbative unitarity bounds via coupled channel analysis, under large field background at the inflation scale. We analyze the unitarity constraints on the parameter space in both the conventional Higgs inflation and the improved models in light of the recent BICEP2 data.
Rotation of the cosmic microwave background polarization from weak gravitational lensing.
Dai, Liang
2014-01-31
When a cosmic microwave background (CMB) photon travels from the surface of last scatter through spacetime metric perturbations, the polarization vector may rotate about its direction of propagation. This gravitational rotation is distinct from, and occurs in addition to, the lensing deflection of the photon trajectory. This rotation can be sourced by linear vector or tensor metric perturbations and is fully coherent with the curl deflection field. Therefore, lensing corrections to the CMB polarization power spectra as well as the temperature-polarization cross correlations due to nonscalar perturbations are modified. The rotation does not affect lensing by linear scalar perturbations, but needs to be included when calculations go to higher orders. We present complete results for weak lensing of the full-sky CMB power spectra by general linear metric perturbations, taking into account both deflection of the photon trajectory and rotation of the polarization. For the case of lensing by gravitational waves, we show that the B modes induced by the rotation largely cancel those induced by the curl component of deflection. PMID:24580435
Prolate spheroidal harmonic expansion of gravitational field
Fukushima, Toshio
2014-06-01
As a modification of the oblate spheroidal case, a recursive method is developed to compute the point value and a few low-order derivatives of the prolate spheroidal harmonics of the second kind, Q{sub nm} (y), namely the unnormalized associated Legendre function (ALF) of the second kind with its argument in the domain, 1 < y < ∞. They are required in evaluating the prolate spheroidal harmonic expansion of the gravitational field in addition to the point value and the low-order derivatives of P-bar {sub nm}(t), the 4π fully normalized ALF of the first kind with its argument in the domain, |t| ≤ 1. The new method will be useful in the gravitational field computation of elongated celestial objects.
Some results of Moon's gravitational field investigations
NASA Astrophysics Data System (ADS)
Haigel, Y. I.; Zazulyak, P. M.
2016-10-01
The task of studying the gravitational field of the moon is important for long-term planning of its research using manned and robotic spacecrafts. Determination of harmonic expansion coefficients of selenopotential may not be reliable because of their construction based on different data and different methods of mathematical processing. With mutual comparative assessment of selenopotential models we can get some information about the reliability determination harmonic coefficients.
Constraining modified gravitational theories by weak lensing with Euclid
Martinelli, Matteo; Calabrese, Erminia; De Bernardis, Francesco; Melchiorri, Alessandro; Pagano, Luca; Scaramella, Roberto
2011-01-15
Future proposed satellite missions such as Euclid can offer the opportunity to test general relativity on cosmic scales through mapping of the galaxy weak-lensing signal. In this paper we forecast the ability of these experiments to constrain modified gravity scenarios such as those predicted by scalar-tensor and f(R) theories. We find that Euclid will improve constraints expected from the Planck satellite on these modified theories of gravity by 2 orders of magnitude. We discuss parameter degeneracies and the possible biases introduced by modifications to gravity.
Towards weakly constrained double field theory
NASA Astrophysics Data System (ADS)
Lee, Kanghoon
2016-08-01
We show that it is possible to construct a well-defined effective field theory incorporating string winding modes without using strong constraint in double field theory. We show that X-ray (Radon) transform on a torus is well-suited for describing weakly constrained double fields, and any weakly constrained fields are represented as a sum of strongly constrained fields. Using inverse X-ray transform we define a novel binary operation which is compatible with the level matching constraint. Based on this formalism, we construct a consistent gauge transform and gauge invariant action without using strong constraint. We then discuss the relation of our result to the closed string field theory. Our construction suggests that there exists an effective field theory description for massless sector of closed string field theory on a torus in an associative truncation.
NASA Astrophysics Data System (ADS)
Dhiman, Joginder Singh; Sharma, Rajni
2016-03-01
The self-gravitating instability of an infinitely extending axisymmetric cylinder of viscoelastic medium permeated with non uniform magnetic field and rotation is studied for both the strongly coupled plasma (SCP) and weakly coupled plasma (WCP). The non uniform magnetic field and rotation are considered to act along the axial direction of the cylinder. The normal mode method of perturbations is applied to obtain the dispersion relation. The condition for the onset of gravitational instability has been derived from the dispersion relation under both strongly and weakly coupling limits. It is found that the Jeans criterion for gravitational collapse gets modified due to the presence of shear and bulk viscosities for the SCP, however, the magnetic field and rotation whether uniform or non uniform has no effect on the Jeans criterion of an infinitely extending axisymmetric cylinder of a self-gravitating viscoelastic medium.
A Gravitational Experiment Involving Inhomogeneous Electric Fields
Datta, T.; Yin Ming; Vargas, Jose
2004-02-04
Unification of gravitation with other forms of interactions, particularly with electromagnetism, will have tremendous impacts on technology and our understanding of nature. The economic impact of such an achievement will also be unprecedented and far more extensive than the impact experienced in the past century due to the unification of electricity with magnetism and optics. Theoretical unification of gravitation with electromagnetism using classical differential geometry has been pursued since the late nineteen twenties, when Einstein and Cartan used teleparallelism for the task. Recently, Vargas and Torr have followed the same line of research with more powerful mathematics in a more general geometric framework, which allows for the presence of other interactions. Their approach also uses Kaehler generalization of Cartan's exterior calculus, which constitutes a language appropriate for both classical and quantum physics. Given the compelling nature of teleparallelism (path-independent equality of vectors at a distance) and the problems still existing with energy-momentum in general relativity, it is important to seek experimental evidence for such expectations. Such experimental programs are likely to provide quantitative guidance to the further development of current and future theories. We too, have undertaken an experimental search for potential electrically induced gravitational (EIG) effects. This presentation describes some of the practical concerns that relates to our investigation of electrical influences on laboratory size test masses. Preliminary results, appear to indicate a correlation between the application of a spatially inhomogeneous electric field and the appearance of an additional force on the test mass. If confirmed, the presence of such a force will be consistent with the predictions of Vargas-Torr. More importantly, proven results will shed new light and clearer understanding of the interactions between gravitational and electromagnetic
A Gravitational Experiment Involving Inhomogeneous Electric Fields
NASA Astrophysics Data System (ADS)
Datta, T.; Yin, Ming; Vargas, Jose
2004-02-01
Unification of gravitation with other forms of interactions, particularly with electromagnetism, will have tremendous impacts on technology and our understanding of nature. The economic impact of such an achievement will also be unprecedented and far more extensive than the impact experienced in the past century due to the unification of electricity with magnetism and optics. Theoretical unification of gravitation with electromagnetism using classical differential geometry has been pursued since the late nineteen twenties, when Einstein and Cartan used teleparallelism for the task. Recently, Vargas and Torr have followed the same line of research with more powerful mathematics in a more general geometric framework, which allows for the presence of other interactions. Their approach also uses Kähler generalization of Cartan's exterior calculus, which constitutes a language appropriate for both classical and quantum physics. Given the compelling nature of teleparallelism (path-independent equality of vectors at a distance) and the problems still existing with energy-momentum in general relativity, it is important to seek experimental evidence for such expectations. Such experimental programs are likely to provide quantitative guidance to the further development of current and future theories. We too, have undertaken an experimental search for potential electrically induced gravitational (EIG) effects. This presentation describes some of the practical concerns that relates to our investigation of electrical influences on laboratory size test masses. Preliminary results, appear to indicate a correlation between the application of a spatially inhomogeneous electric field and the appearance of an additional force on the test mass. If confirmed, the presence of such a force will be consistent with the predictions of Vargas-Torr. More importantly, proven results will shed new light and clearer understanding of the interactions between gravitational and electromagnetic
General relativistic theory of light propagation in the field of gravitational multipoles
NASA Astrophysics Data System (ADS)
Korobkov, Pavel
We consider propagation of electromagnetic signals through the time-dependent gravitational field of an isolated astronomical system emitting gravitational waves. The system is assumed to possess multipole moments of arbitrary order. Working in the linear, weak-field approximation of general relativity, we obtain analytical expressions for light-ray trajectory and observable effects of bending of light, time delay, and gravitational rotation of the polarization plane. The relative positions of the source of light, the isolated system, and the observer are not restricted, which makes our formalism quite general and applicable for most practical situations. Asymptotic expressions for observable effects are obtained in two limiting cases of arrangement of light source, observer, and the source of gravitational waves: the gravitational-lens approximation and the approximation of plane gravitational waves. It is shown that in the gravitational-lens approximation the leading contributions to the effects due to multipole moments of arbitrary order fall off with the impact parameter as 1/d2 and 1/d3 for time delay and deflection of light respectively. Such, stronger than it could be a priori expected, dependance on impact parameter hinders observation of time-dependent effects in gravitational lensing. In the plane-gravitational-wave approximation the expressions for observable effects due to gravitational waves of arbitrary multipolarity are obtained in terms of the transverse-traceless (TT) part of the spacial components of the metric tensor.
A weak combined magnetic field changes root gravitropism
NASA Astrophysics Data System (ADS)
Kordyum, E. L.; Bogatina, N. I.; Kalinina, Ja. M.; Sheykina, N. V.
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 μ-metal shields. Inside μ -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
Theory of microemulsions in a gravitational field
NASA Technical Reports Server (NTRS)
Jeng, J. F.; Miller, Clarence A.
1989-01-01
A theory of microemulsions developed previously is extended to include the effect of a gravitational field. It predicts variation with position of drop size, drop volume fraction, and area per molecule in the surfactant films within a microemulsion phase. Variation in volume fraction is greatest and occurs in such a way that oil content increases with increasing elevation, as has been found experimentally. Large composition variations are predicted within a middle phase microemulsion near optimal conditions because inversion from the water-continuous to the oil-continuous arrangement occurs with increasing elevation. Generally speaking, gravity reduces solubilization within microemulsions and promotes separation of excess phases.
Reptation in a Weak Driving Field
NASA Astrophysics Data System (ADS)
Aalberts, Daniel; van Leeuwen, J. M. J.
1997-03-01
A simplified model of reptation is presented. The Master Equation of the model is systematically solved by expansion in powers of the strength of the driving field. From the explicit form of the probability distribution, exact conclusions can be drawn about the average shape of the polymer, its drift velocity, and the zero field diffusion constant. Correlations between segments of the chain are calculated and turn out to be large, even in the weak driving field limit. The results are compared with simulations of the model.
Gravitational Descendants in Symplectic Field Theory
NASA Astrophysics Data System (ADS)
Fabert, Oliver
2011-02-01
It was pointed out by Y. Eliashberg in his ICM 2006 plenary talk that the rich algebraic formalism of symplectic field theory leads to a natural appearance of quantum and classical integrable systems, at least in the case when the contact manifold is the prequantization space of a symplectic manifold. In this paper we generalize the definition of gravitational descendants in SFT from circle bundles in the Morse-Bott case to general contact manifolds. After we have shown using the ideas in Okounkov and Pandharipande (Ann Math 163(2):517-560, 2006) that for the basic examples of holomorphic curves in SFT, that is, branched covers of cylinders over closed Reeb orbits, the gravitational descendants have a geometric interpretation in terms of branching conditions, we follow the ideas in Cieliebak and Latschev (
Weak Gravitational Lensing by Galaxy Troughs in the Dark Energy Survey
NASA Astrophysics Data System (ADS)
Gruen, Daniel; Dark Energy Survey Collaboration
2016-06-01
The Dark Energy Survey (DES) is in the process of imaging 5000 sq. deg. of the southern sky in five broad-band filters. Its primary purpose is to constrain cosmology and the physics of dark energy using weak gravitational lensing, galaxy clusters, baryonic acoustic oscillations, and supernova distance measurements.I will give an overview of weak gravitational lensing results from early DES data, with a focus on the newly developed galaxy trough statistics. Using the latter, we have made the highest signal-to-noise lensing measurements of the low density Universe to date, probing gravity and structure formation in the underdense regime. Besides these recent results, I will give an outlook on cosmological and astrophysical applications of the trough lensing signal.
Symmetries in tetrad theories. [of gravitational fields and general relativity
NASA Technical Reports Server (NTRS)
Chinea, F. J.
1988-01-01
The isometry conditions for gravitational fields are given directly at the tetrad level, rather than in terms of the metric. As an illustration, an analysis of the curvature collineations and Killing fields for a twisting type-N vacuum gravitational field is made.
Constraining stochastic gravitational wave background from weak lensing of CMB B-modes
NASA Astrophysics Data System (ADS)
Shaikh, Shabbir; Mukherjee, Suvodip; Rotti, Aditya; Souradeep, Tarun
2016-09-01
A stochastic gravitational wave background (SGWB) will affect the CMB anisotropies via weak lensing. Unlike weak lensing due to large scale structure which only deflects photon trajectories, a SGWB has an additional effect of rotating the polarization vector along the trajectory. We study the relative importance of these two effects, deflection & rotation, specifically in the context of E-mode to B-mode power transfer caused by weak lensing due to SGWB. Using weak lensing distortion of the CMB as a probe, we derive constraints on the spectral energy density (ΩGW) of the SGWB, sourced at different redshifts, without assuming any particular model for its origin. We present these bounds on ΩGW for different power-law models characterizing the SGWB, indicating the threshold above which observable imprints of SGWB must be present in CMB.
NASA Astrophysics Data System (ADS)
Belvedere, Riccardo; Pugliese, Daniela; Rueda, Jorge A.; Ruffini, Remo; Xue, She-Sheng
2012-06-01
We formulate the equations of equilibrium of neutron stars taking into account strong, weak, electromagnetic, and gravitational interactions within the framework of general relativity. The nuclear interactions are described by the exchange of the σ, ω, and ρ 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 ˜ℏ/(mec)˜102ℏ/(mπc) of opposite charge, as well as a neutral crust at lower densities. Inside the core there is a Coulomb potential well of depth ˜mπc2/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/(eℏ). The electron chemical potential and the density decrease, in the boundary interface, until values μecrust<μecore and ρ<ρ. For each central density, an entire family of core-crust interface boundaries and, correspondingly, an entire family of crusts with different mass and thickness, exist. The configuration with ρ=ρ˜4.3×1011 gcm separates neutron stars with and without inner crust. We present here the novel neutron star mass-radius for the especial case ρ=ρ and compare and contrast it with the one obtained from the traditional Tolman-Oppenheimer-Volkoff treatment.
Gravitational properties of light—the gravitational field of a laser pulse
NASA Astrophysics Data System (ADS)
Rätzel, Dennis; Wilkens, Martin; Menzel, Ralf
2016-02-01
The gravitational field of a laser pulse of finite lifetime, is investigated in the framework of linearized gravity. Although the effects are very small, they may be of fundamental physical interest. It is shown that the gravitational field of a linearly polarized light pulse is modulated as the norm of the corresponding electric field strength, while no modulations arise for circular polarization. In general, the gravitational field is independent of the polarization direction. It is shown that all physical effects are confined to spherical shells expanding with the speed of light, and that these shells are imprints of the spacetime events representing emission and absorption of the pulse. Nearby test particles at rest are attracted towards the pulse trajectory by the gravitational field due to the emission of the pulse, and they are repelled from the pulse trajectory by the gravitational field due to its absorption. Examples are given for the size of the attractive effect. It is recovered that massless test particles do not experience any physical effect if they are co-propagating with the pulse, and that the acceleration of massless test particles counter-propagating with respect to the pulse is four times stronger than for massive particles at rest. The similarities between the gravitational effect of a laser pulse and Newtonian gravity in two dimensions are pointed out. The spacetime curvature close to the pulse is compared to that induced by gravitational waves from astronomical sources.
Onthe static and spherically symmetric gravitational field
NASA Astrophysics Data System (ADS)
Gottlieb, Ioan; Maftei, Gheorghe; Mociutchi, Cleopatra
Starting from a generalization of Einstein 's theory of gravitation, proposed by one of the authors (Cleopatra Mociutchi), the authors study a particular spherical symmetric case. Among other one obtain the compatibility conditions for the existence of the static and spherically symmetruic gravitational filed in the case of extended Einstein equation.
Gravitational consequences of modern field theories
NASA Technical Reports Server (NTRS)
Horowitz, Gary T.
1989-01-01
Some gravitational consequences of certain extensions of Einstein's general theory of relativity are discussed. These theories are not alternative theories of gravity in the usual sense. It is assumed that general relativity is the appropriate description of all gravitational phenomena which were observed to date.
Wormholes, emergent gauge fields, and the weak gravity conjecture
Harlow, Daniel
2016-01-20
This paper revisits the question of reconstructing bulk gauge fields as boundary operators in AdS/CFT. In the presence of the ormhole dual to the thermo field double state of two CFTs, the existence of bulk gauge fields is in some tension with the microscopic tensor factorization of the Hilbert space. Here, I explain how this tension can be resolved by splitting the gauge field into charged constituents, and I argue that this leads to a new argument for the "principle of completeness", which states that the charge lattice of a gauge theory coupled to gravity must be fully populated. Imore » also claim that it leads to a new motivation for (and a clarification of) the "weak gravity conjecture", which I interpret as a strengthening of this principle. This setup gives a simple example of a situation where describing low-energy bulk physics in CFT language requires knowledge of high-energy bulk physics. Furthermore, this contradicts to some extent the notion of "effective conformal field theory", but in fact is an expected feature of the resolution of the black hole information problem. An analogous factorization issue exists also for the gravitational field, and I comment on several of its implications for reconstructing black hole interiors and the emergence of spacetime more generally.« less
NASA Astrophysics Data System (ADS)
Plazas, A. A.; Shapiro, C.; Kannawadi, A.; Mandelbaum, R.; Rhodes, J.; Smith, R.
2016-10-01
Weak gravitational lensing (WL) is one of the most powerful techniques to learn about the dark sector of the universe. To extract the WL signal from astronomical observations, galaxy shapes must be measured and corrected for the point-spread function (PSF) of the imaging system with extreme accuracy. Future WL missions—such as NASA’s Wide-Field Infrared Survey Telescope (WFIRST)—will use a family of hybrid near-infrared complementary metal-oxide-semiconductor detectors (HAWAII-4RG) that are untested for accurate WL measurements. Like all image sensors, these devices are subject to conversion gain nonlinearities (voltage response to collected photo-charge) that bias the shape and size of bright objects such as reference stars that are used in PSF determination. We study this type of detector nonlinearity (NL) and show how to derive requirements on it from WFIRST PSF size and ellipticity requirements. We simulate the PSF optical profiles expected for WFIRST and measure the fractional error in the PSF size (ΔR/R) and the absolute error in the PSF ellipticity (Δe) as a function of star magnitude and the NL model. For our nominal NL model (a quadratic correction), we find that, uncalibrated, NL can induce an error of ΔR/R = 1 × 10-2 and Δe 2 = 1.75 × 10-3 in the H158 bandpass for the brightest unsaturated stars in WFIRST. In addition, our simulations show that to limit the bias of ΔR/R and Δe in the H158 band to ˜10% of the estimated WFIRST error budget, the quadratic NL model parameter β must be calibrated to ˜1% and ˜2.4%, respectively. We present a fitting formula that can be used to estimate WFIRST detector NL requirements once a true PSF error budget is established.
Wormholes, emergent gauge fields, and the weak gravity conjecture
NASA Astrophysics Data System (ADS)
Harlow, Daniel
2016-01-01
This paper revisits the question of reconstructing bulk gauge fields as boundary operators in AdS/CFT. In the presence of the wormhole dual to the thermofield double state of two CFTs, the existence of bulk gauge fields is in some tension with the microscopic tensor factorization of the Hilbert space. I explain how this tension can be resolved by splitting the gauge field into charged constituents, and I argue that this leads to a new argument for the "principle of completeness", which states that the charge lattice of a gauge theory coupled to gravity must be fully populated. I also claim that it leads to a new motivation for (and a clarification of) the "weak gravity conjecture", which I interpret as a strengthening of this principle. This setup gives a simple example of a situation where describing low-energy bulk physics in CFT language requires knowledge of high-energy bulk physics. This contradicts to some extent the notion of "effective conformal field theory", but in fact is an expected feature of the resolution of the black hole information problem. An analogous factorization issue exists also for the gravitational field, and I comment on several of its implications for reconstructing black hole interiors and the emergence of spacetime more generally.
Field theoretic treatment of gravitational interaction in electrodynamics
NASA Astrophysics Data System (ADS)
Serdyukov, A. N.
2011-03-01
A theory of gravitational interaction in classical electrodynamics is developed on the basis of an earlier-proposed minimal relativistic model of gravitation. From the variation principle, a system of gaugeinvariant equations of the interacting electromagnetic and gravitational fields is deduced and their common energy-momentum tensor is constructed. A rigorous solution to the problem of regularizing the field mass of a point charge is given with consideration for the coupling energy of the gravitational interaction. The propagation of electromagnetic waves in the gravitational field is discussed. It is shown that, under the condition of the existing resonant ratio 2: 3 for the periods of Mercury's orbital revolution and daily rotation, tidal forces cause a regular shift in the planet's perihelion in an observable forward direction.
Interaction of gravitational waves with magnetic and electric fields
Barrabes, C.; Hogan, P. A.
2010-03-15
The existence of large-scale magnetic fields in the universe has led to the observation that if gravitational waves propagating in a cosmological environment encounter even a small magnetic field then electromagnetic radiation is produced. To study this phenomenon in more detail we take it out of the cosmological context and at the same time simplify the gravitational radiation to impulsive waves. Specifically, to illustrate our findings, we describe the following three physical situations: (1) a cylindrical impulsive gravitational wave propagating into a universe with a magnetic field, (2) an axially symmetric impulsive gravitational wave propagating into a universe with an electric field and (3) a 'spherical' impulsive gravitational wave propagating into a universe with a small magnetic field. In cases (1) and (3) electromagnetic radiation is produced behind the gravitational wave. In case (2) no electromagnetic radiation appears after the wave unless a current is established behind the wave breaking the Maxwell vacuum. In all three cases the presence of the magnetic or electric fields results in a modification of the amplitude of the incoming gravitational wave which is explicitly calculated using the Einstein-Maxwell vacuum field equations.
Lovelock gravitational field equations in cosmology
Deruelle, N. Laboratoire de Physique Theorique, Institut Henri Poincare, 11 rue Pierre et Marie Curie, 75005 Paris ); Farina-Busto, L. )
1990-06-15
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.
Computing Gravitational Fields of Finite-Sized Bodies
NASA Technical Reports Server (NTRS)
Quadrelli, Marco
2005-01-01
A computer program utilizes the classical theory of gravitation, implemented by means of the finite-element method, to calculate the near gravitational fields of bodies of arbitrary size, shape, and mass distribution. The program was developed for application to a spacecraft and to floating proof masses and associated equipment carried by the spacecraft for detecting gravitational waves. The program can calculate steady or time-dependent gravitational forces, moments, and gradients thereof. Bodies external to a proof mass can be moving around the proof mass and/or deformed under thermoelastic loads. An arbitrarily shaped proof mass is represented by a collection of parallelepiped elements. The gravitational force and moment acting on each parallelepiped element of a proof mass, including those attributable to the self-gravitational field of the proof mass, are computed exactly from the closed-form equation for the gravitational potential of a parallelepiped. The gravitational field of an arbitrary distribution of mass external to a proof mass can be calculated either by summing the fields of suitably many point masses or by higher-order Gauss-Legendre integration over all elements surrounding the proof mass that are part of a finite-element mesh. This computer program is compatible with more general finite-element codes, such as NASTRAN, because it is configured to read a generic input data file, containing the detailed description of the finiteelement mesh.
Fast Reconnection of Weak Magnetic Fields
NASA Technical Reports Server (NTRS)
Zweibel, Ellen G.
1998-01-01
Fast magnetic reconnection refers to annihilation or topological rearrangement of magnetic fields on a timescale that is independent (or nearly independent) of the plasma resistivity. The resistivity of astrophysical plasmas is so low that reconnection is of little practical interest unless it is fast. Yet, the theory of fast magnetic reconnection is on uncertain ground, as models must avoid the tendency of magnetic fields to pile up at the reconnection layer, slowing down the flow. In this paper it is shown that these problems can be avoided to some extent if the flow is three dimensional. On the other hand, it is shown that in the limited but important case of incompressible stagnation point flows, every flow will amplify most magnetic fields. Although examples of fast magnetic reconnection abound, a weak, disordered magnetic field embedded in stagnation point flow will in general be amplified, and should eventually modify the flow. These results support recent arguments against the operation of turbulent resistivity in highly conducting fluids.
Vacuum polarization in gravitational and electromagnetic fields around a superconducting string
Mankiewicz, L. ); Misiak, M.
1989-09-15
We have calculated the polarization current induced in the physical vacuum around a superconducting cosmic string taking into account the gravitational field of the string. The current can be calculated as an expansion in powers of the inverse of the electron mass. In the region far from the string, where it is justified to keep only the lowest term of this expansion, the polarization current turns out to screen the original current in the string, but the effect is very weak. A direct calculation of terms due to the presence of the gravitational field shows that they are dominated, for realistic string parameters, by the purely electromagnetic contribution.
Gravitational waves from self-ordering scalar fields
Fenu, Elisa; Durrer, Ruth; Figueroa, Daniel G.; García-Bellido, Juan E-mail: daniel.figueroa@uam.es E-mail: juan.garciabellido@uam.es
2009-10-01
Gravitational waves were copiously produced in the early Universe whenever the processes taking place were sufficiently violent. The spectra of several of these gravitational wave backgrounds on subhorizon scales have been extensively studied in the literature. In this paper we analyze the shape and amplitude of the gravitational wave spectrum on scales which are superhorizon at the time of production. Such gravitational waves are expected from the self ordering of randomly oriented scalar fields which can be present during a thermal phase transition or during preheating after hybrid inflation. We find that, if the gravitational wave source acts only during a small fraction of the Hubble time, the gravitational wave spectrum at frequencies lower than the expansion rate at the time of production behaves as Ω{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 (kη{sub *} << 1), enters the horizon, for kη ∼> 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.
Strong field gravitational lensing by a charged Galileon black hole
NASA Astrophysics Data System (ADS)
Zhao, Shan-Shan; Xie, Yi
2016-07-01
Strong field gravitational lensings are dramatically disparate from those in the weak field by representing relativistic images due to light winds one to infinity loops around a lens before escaping. We study such a lensing caused by a charged Galileon black hole, which is expected to have possibility to evade no-hair theorem. We calculate the angular separations and time delays between different relativistic images of the charged Galileon black hole. All these observables can potentially be used to discriminate a charged Galileon black hole from others. We estimate the magnitudes of these observables for the closest supermassive black hole Sgr A*. The strong field lensing observables of the charged Galileon black hole can be close to those of a tidal Reissner-Nordström black hole or those of a Reissner-Nordström black hole. It will be helpful to distinguish these black holes if we can separate the outermost relativistic images and determine their angular separation, brightness difference and time delay, although it requires techniques beyond the current limit.
Neutron interference in the gravitational field of a ring laser
NASA Astrophysics Data System (ADS)
Fischetti, Robert D.; Mallett, Ronald L.
2015-07-01
The neutron split-beam interferometer has proven to be particularly useful in measuring Newtonian gravitational effects such as those studied by Colella, Overhauser, and Werner (COW). The development of the ring laser has led to numerous applications in many areas of physics including a recent general relativistic prediction of frame dragging in the gravitational field produced by the electromagnetic radiation in a ring laser. This paper introduces a new general technique based on a canonical transformation of the Dirac equation for the gravitational field of a general linearized spacetime. Using this technique it is shown that there is a phase shift in the interference of two neutron beams due to the frame-dragging nature of the gravitational field of a ring laser.
Further Evidence for Weak Field Critical Adsorption
NASA Astrophysics Data System (ADS)
Franck, Carl; Peach, Sarah; Polak, Robert D.
1997-03-01
Following our unexpected discovery of weak short-range surface field effects on the critical mixing transition of a binary liquid,(N.S. Desai, S. Peach, and C. Franck, Phys. Rev. E52), 4129 (1995) we have directly addressed our concern that these results might have been affected by surface heterogeneity. We have used octadecyltrichlorosilane (OTS) to cover borosilicate glass surfaces with partial monolayers. Reference substrates with identical treatment had OTS patches no larger than the bulk correlation length within 40 mK of the critical transition. The present reflectivity experiment employs uncovered reference surfaces for comparison in a single sample cell. We confirm our earlier discovery of a persistent (down to 3 mK above the critical point) deviation of the degree of critical adsorption from the maximum value expected. We have also improved our earlier analysis in order to examine the scaling behavior. Supported by the NSF under DMR-9320910, and through central facilities of the Materials Science Center at Cornell Univ.
Magnetic Field in the Gravitationally Stratified Coronal Loops
NASA Astrophysics Data System (ADS)
Dwivedi, B. N.; Srivastava, A. K.
2015-03-01
We study the effect of gravitational stratification on the estimation of magnetic fields in the coronal loops. By using the method of MHD seismology of kink waves for the estimation of magnetic field of coronal loops, we derive a new formula for the magnetic field considering the effect of gravitational stratification. The fast-kink wave is a potential diagnostic tool for the estimation of magnetic field in fluxtubes. We consider the eleven kink oscillation cases observed by TRACE between July 1998 and June 2001. We calculate magnetic field in the stratified loops ( B str) and compare them with the previously calculated absolute magnetic field ( B abs). The gravitational stratification efficiently affects the magnetic field estimation in the coronal loops as it affects also the properties of kink waves. We find ≈22% increment in the magnetic field for the smallest ( L = 72 Mm) while ≈ 42% increment in the absolute magnetic field for the longest ( L = 406 Mm) coronal loops. The magnetic fields B str and B abs also increase with the number density, if the loop length does not vary much. The increment in the magnetic field due to gravitational stratification is small at the lower number densities, however, it is large at the higher number densities. We find that damping time of kink waves due to phase-mixing is less in the case of gravitationally stratified loops compared to nonstratified ones. This indicates the more rapid damping of kink waves in the stratified loops. In conclusion, we find that the gravitational stratification efficiently affects the estimation of magnetic field and damping time estimation especially in the longer coronal loops.
NASA Computational Case Study: Modeling Planetary Magnetic and Gravitational Fields
NASA Technical Reports Server (NTRS)
Simpson, David G.; Vinas, Adolfo F.
2014-01-01
In this case study, we model a planet's magnetic and gravitational fields using spherical harmonic functions. As an exercise, we analyze data on the Earth's magnetic field collected by NASA's MAGSAT spacecraft, and use it to derive a simple magnetic field model based on these spherical harmonic functions.
Weyl fluid dark matter model tested on the galactic scale by weak gravitational lensing
NASA Astrophysics Data System (ADS)
Wong, K. C.; Harko, T.; Cheng, K. S.; Gergely, L. Á.
2012-08-01
The higher-dimensional Weyl curvature induces on the brane a new source of gravity. This Weyl fluid of geometrical origin (reducing in the spherically symmetric, static configuration to a dark radiation and dark pressure) modifies spacetime geometry around galaxies and has been shown to explain the flatness of galactic rotation curves. Independent observations for discerning between the Weyl fluid and other dark matter models are necessary. Gravitational lensing could provide such a test. Therefore we study null geodesics and weak gravitational lensing in the dark radiation dominated region of galaxies in a class of spherically symmetric braneworld metrics. We find that the lensing profile in the braneworld scenario is distinguishable from dark matter lensing, despite both the braneworld scenario and dark matter models fitting the rotation curve data. In particular, in the asymptotic regions, light deflection is 18% enhanced as compared to dark matter halo predictions. For a linear equation of state of the Weyl fluid, we further find a critical radius below which braneworld effects reduce, while above it they amplify light deflection. This is in contrast to any dark matter model, the addition of which always increases the deflection angle.
An accurate and practical method for inference of weak gravitational lensing from galaxy images
NASA Astrophysics Data System (ADS)
Bernstein, Gary M.; Armstrong, Robert; Krawiec, Christina; March, Marisa C.
2016-07-01
We demonstrate highly accurate recovery of weak gravitational lensing shear using an implementation of the Bayesian Fourier Domain (BFD) method proposed by Bernstein & Armstrong, extended to correct for selection biases. The BFD formalism is rigorously correct for Nyquist-sampled, background-limited, uncrowded images of background galaxies. BFD does not assign shapes to galaxies, instead compressing the pixel data D into a vector of moments M, such that we have an analytic expression for the probability P(M|g) of obtaining the observations with gravitational lensing distortion g along the line of sight. We implement an algorithm for conducting BFD's integrations over the population of unlensed source galaxies which measures ≈10 galaxies s-1 core-1 with good scaling properties. Initial tests of this code on ≈109 simulated lensed galaxy images recover the simulated shear to a fractional accuracy of m = (2.1 ± 0.4) × 10-3, substantially more accurate than has been demonstrated previously for any generally applicable method. Deep sky exposures generate a sufficiently accurate approximation to the noiseless, unlensed galaxy population distribution assumed as input to BFD. Potential extensions of the method include simultaneous measurement of magnification and shear; multiple-exposure, multiband observations; and joint inference of photometric redshifts and lensing tomography.
Gravitational Fields with 2-Dimensional Killing Leaves and the Gravitational Interaction of Light
NASA Astrophysics Data System (ADS)
Vilasi, Gaetano
Gravitational fields invariant for a non Abelian Lie algebra generating a 2-dimensional distribution, are explicitly described. When the orthogonal distribution is integrable and the metric is not degenerate along the orbits, these solutions are parameterized either by solutions of a transcendental equation (the tortoise equation), or by solutions of Darboux equation. Metrics, corresponding to solutions of the tortoise equation, are characterized as those that admit a 3-dimensional Lie algebra of Killing fields with 2-dimensional leaves. It is shown that the remaining metrics represent nonlinear gravitational waves obeying to two nonlinearsuperposition laws. The energy and the polarization of this family of waves are explicitly evaluated; it is shown that they have spin-1 and their possible sources are also described. Old results by Tolman, Ehrenfest, Podolsky and Wheeler on the gravitational interaction of photons are naturally reinterpreted.
Residual symmetries of the gravitational field
NASA Astrophysics Data System (ADS)
Ayón-Beato, Eloy; Velázquez-Rodríguez, Gerardo
2016-02-01
We develop a geometric criterion that unambiguously characterizes the residual symmetries of a gravitational Ansatz. It also provides a systematic and effective computational procedure for finding all the residual symmetries of any gravitational Ansatz. We apply the criterion to several examples starting with the Collinson Ansatz for circular stationary axisymmetric spacetimes. We reproduce the residual symmetries already known for this Ansatz including their conformal symmetry, for which we identify the corresponding infinite generators spanning the two related copies of the Witt algebra. We also consider the noncircular generalization of this Ansatz and show how the noncircular contributions on the one hand break the conformal invariance and on the other hand enhance the standard translation symmetries of the circular Killing vectors to supertranslations depending on the direction along which the circularity is lost. As another application of the method, the well-known relation defining conjugate gravitational potentials introduced by Chandrasekhar, which makes possible the derivation of the Kerr black hole from a trivial solution of the Ernst equations, is deduced as a special point of the general residual symmetry of the Papapetrou Ansatz. In this derivation we emphasize how the election of Weyl coordinates, which determines the Papapetrou Ansatz, breaks also the conformal freedom of the stationary axisymmetric spacetimes. Additionally, we study AdS waves for any dimension generalizing the residual symmetries already known for lower dimensions and exhibiting a very complex infinite-dimensional Lie algebra containing three families: two of them span the semidirect sum of the Witt algebra and scalar supertranslations and the third generates vector supertranslations. Independently of this complexity we manage to comprehend the true meaning of the infinite connected group as the precise diffeomorphisms subgroup allowing to locally deform the AdS background into Ad
Constraining Horava-Lifshitz gravity by weak and strong gravitational lensing
Horvath, Zsolt; Gergely, Laszlo A.; Keresztes, Zoltan; Harko, Tiberiu; Lobo, Francisco S. N.
2011-10-15
We discuss gravitational lensing in the Kehagias-Sfetsos space-time emerging in the framework of Horava-Lifshitz gravity. In weak lensing, we show that there are three regimes, depending on the value of {lambda}=1/{omega}d{sup 2}, where {omega} is the Horava-Lifshitz parameter and d characterizes the lensing geometry. When {lambda} is close to zero, light deflection typically produces two images, as in Schwarzschild lensing. For very large {lambda}, the space-time approaches flatness, therefore there is only one undeflected image. In the intermediate range of {lambda}, only the upper focused image is produced due to the existence of a maximal deflection angle {delta}{sub max}, a feature inexistent in the Schwarzschild weak lensing. We also discuss the location of Einstein rings, and determine the range of the Horava-Lifshitz parameter compatible with present-day lensing observations. Finally, we analyze in the strong lensing regime the first two relativistic Einstein rings and determine the constraints on the parameter range to be imposed by forthcoming experiments.
Contributions of Spherical Harmonics to Magnetic and Gravitational Fields
NASA Technical Reports Server (NTRS)
Roithmayr, Carlos M.
2004-01-01
Gravitational forces are of cardinal importance in the dynamics of spacecraft; magnetic attractions sometime play a significant role also, as was the case with the Long Duration Exposure Facility, and as is now true for the first segment of Space Station Freedom. Both satellites depend on gravitational moment and a device known as a magnetic damper to stabilize their orientation. Magnetic fields are mathematically similar to gravitational fields in one important respect: each can be regarded as a gradient of a potential function that, in turn, can be described as an infinite series of spherical harmonics. Consequently, the two fields can be computed, in part, with quantities that need only be evaluated once, resulting in a savings of time when both fields are needed. The objective of this material is to present magnetic field and gravitational force expressions, and point out the terms that belong to both this is accomplished in Section 1 and 2. Section 3 contains the deductive reasoning with which one obtains the expressions of interest. Finally, examples in Section 4 show these equations can be used to reproduce others that arise in connection with special cases such as the magnetic field produced by a tilted dipole, and gravitational force exerted by an oblate spheroid. The mathematics are discussed in the context of terrestrial fields; however, by substituting appropriate constants, the results can be made applicable to fields belonging to other celestial bodies. The expressions presented here share the characteristics of algorithms set forth for computing gravitational force. In particular, computation is performed speedily by means of recursion formulae, and the expressions do not suffer from the shortcoming of a singularity when evaluated at points that lie on the polar axis.
Using Gravitational Analogies to Introduce Elementary Electrical Field Theory Concepts
ERIC Educational Resources Information Center
Saeli, Susan; MacIsaac, Dan
2007-01-01
Since electrical field concepts are usually unfamiliar, abstract, and difficult to visualize, conceptual analogies from familiar gravitational phenomena are valuable for teaching. Such analogies emphasize the underlying continuity of field concepts in physics and support the spiral development of student understanding. We find the following four…
Vacuum entanglement enhancement by a weak gravitational field
Cliche, M.; Kempf, A.
2011-02-15
Separate regions in space are generally entangled, even in the vacuum state. It is known that this entanglement can be swapped to separated Unruh-DeWitt detectors, i.e., that the vacuum can serve as a source of entanglement. Here, we demonstrate that, in the presence of curvature, the amount of entanglement that Unruh-DeWitt detectors can extract from the vacuum can be increased.
WEAK GRAVITATIONAL LENSING AS A PROBE OF PHYSICAL PROPERTIES OF SUBSTRUCTURES IN DARK MATTER HALOS
Shirasaki, Masato
2015-02-01
We propose a novel method to select satellite galaxies in outer regions of galaxy groups or clusters using weak gravitational lensing. The method is based on the theoretical expectation that the tangential shear pattern around satellite galaxies would appear with negative values at an offset distance from the center of the main halo. We can thus locate the satellite galaxies statistically with an offset distance of several lensing smoothing scales by using the standard reconstruction of surface mass density maps from weak lensing observation. We test the idea using high-resolution cosmological simulations. We show that subhalos separated from the center of the host halo are successfully located even without assuming the position of the center. For a number of such subhalos, the characteristic mass and offset length can be also estimated on a statistical basis. We perform a Fisher analysis to show how well upcoming weak lensing surveys can constrain the mass density profile of satellite galaxies. In the case of the Large Synoptic Survey Telescope with a sky coverage of 20,000 deg{sup 2}, the mass of the member galaxies in the outer region of galaxy clusters can be constrained with an accuracy of ∼0.1 dex for galaxy clusters with mass 10{sup 14} h {sup –1} M {sub ☉} at z = 0.15. Finally we explore the detectability of tidal stripping features for subhalos having a wide range of masses of 10{sup 11}-10{sup 13} h {sup –1} M {sub ☉}.
NASA Astrophysics Data System (ADS)
Harnois-Déraps, Joachim; van Waerbeke, Ludovic
2015-07-01
Numerical N-body simulations play a central role in the assessment of weak gravitational lensing statistics, residual systematics and error analysis. In this paper, we investigate and quantify the impact of finite simulation volume on weak lensing two- and four-point statistics. These finite support (FS) effects are modelled for several estimators, simulation box sizes and source redshifts, and validated against a new large suite of 500 N-body simulations. The comparison reveals that our theoretical model is accurate to better than 5 per cent for the shear correlation function ξ+(θ) and its error. We find that the most important quantities for FS modelling are the ratio between the measured angle θ and the angular size of the simulation box at the source redshift, θbox(zs), or the multipole equivalent ℓ/ℓbox(zs). When this ratio reaches 0.1, independently of the source redshift, the shear correlation function ξ+ is suppressed by 5, 10, 20 and 25 per cent for Lbox = 1000, 500, 250 and 147 h-1 Mpc, respectively. The same effect is observed in ξ-(θ), but at much larger angles. This has important consequences for cosmological analyses using N-body simulations and should not be overlooked. We propose simple semi-analytic correction strategies that account for shape noise and survey masks, generalizable to any weak lensing estimator. From the same simulation suite, we revisit the existing non-Gaussian covariance matrix calibration of the shear correlation function, and propose a new one based on the 9-year Wilkinson Microwave Anisotropy Probe)+baryon acoustic oscillations+supernova cosmology. Our calibration matrix is accurate at 20 per cent down to the arcminute scale, for source redshifts in the range 0 < z < 3, even for the far off-diagonal elements. We propose, for the first time, a parametrization for the full ξ- covariance matrix, also 20 per cent accurate for most elements.
Bats respond to very weak magnetic fields.
Tian, Lan-Xiang; Pan, Yong-Xin; Metzner, Walter; Zhang, Jin-Shuo; Zhang, Bing-Fang
2015-01-01
How animals, including mammals, can respond to and utilize the direction and intensity of the Earth's magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae) can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5th of the natural intensity (i.e., 10 μT; the lowest field strength tested here), the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 μT), despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (P<0.05). Hence, N. plancyi is able to detect the direction of a magnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth's magnetic field strength varied and the polarity reversed tens of times over the past fifty million years.
Using Jupiter's gravitational field to probe the Jovian convective dynamo.
Kong, Dali; Zhang, Keke; Schubert, Gerald
2016-03-23
Convective motion in the deep metallic hydrogen region of Jupiter is believed to generate its magnetic field, the strongest in the solar system. The amplitude, structure and depth of the convective motion are unknown. A promising way of probing the Jovian convective dynamo is to measure its effect on the external gravitational field, a task to be soon undertaken by the Juno spacecraft. We calculate the gravitational signature of non-axisymmetric convective motion in the Jovian metallic hydrogen region and show that with sufficiently accurate measurements it can reveal the nature of the deep convection.
Using Jupiter's gravitational field to probe the Jovian convective dynamo.
Kong, Dali; Zhang, Keke; Schubert, Gerald
2016-01-01
Convective motion in the deep metallic hydrogen region of Jupiter is believed to generate its magnetic field, the strongest in the solar system. The amplitude, structure and depth of the convective motion are unknown. A promising way of probing the Jovian convective dynamo is to measure its effect on the external gravitational field, a task to be soon undertaken by the Juno spacecraft. We calculate the gravitational signature of non-axisymmetric convective motion in the Jovian metallic hydrogen region and show that with sufficiently accurate measurements it can reveal the nature of the deep convection. PMID:27005472
Is the quantum Hall effect influenced by the gravitational field?
Hehl, Friedrich W; Obukhov, Yuri N; Rosenow, Bernd
2004-08-27
Most of the experiments on the quantum Hall effect (QHE) were made at approximately the same height above sea level. A future international comparison will determine whether the gravitational field g(x) influences the QHE. In the realm of (1+2)-dimensional phenomenological macroscopic electrodynamics, the Ohm-Hall law is metric independent ("topological"). This suggests that it does not couple to g(x). We corroborate this result by a microscopic calculation of the Hall conductance in the presence of a post-Newtonian gravitational field. PMID:15447125
Axisymmetric plasma equilibrium in gravitational and magnetic fields
Krasheninnikov, S. I.; Catto, P. J.
2015-12-15
Plasma equilibria in gravitational and open-ended magnetic fields are considered for the case of topologically disconnected regions of the magnetic flux surfaces where plasma occupies just one of these regions. Special dependences of the plasma temperature and density on the magnetic flux are used which allow the solution of the Grad–Shafranov equation in a separable form permitting analytic treatment. It is found that plasma pressure tends to play the dominant role in the setting the shape of magnetic field equilibrium, while a strong gravitational force localizes the plasma density to a thin disc centered at the equatorial plane.
Spin Hall effect of photons in a static gravitational field
Gosselin, Pierre; Berard, Alain; Mohrbach, Herve
2007-04-15
Starting from a Hamiltonian description of the photon within the set of Bargmann-Wigner equations we derive new semiclassical equations of motion for the photon propagating in a static gravitational field. These equations which are obtained in the representation diagonalizing the Hamiltonian at the order ({Dirac_h}/2{pi}), present the first order corrections to the geometrical optics. The photon Hamiltonian shows a new kind of helicity-torsion coupling. However, even for a torsionless space-time, photons do not follow the usual null geodesic as a consequence of an anomalous velocity term. This term is responsible for the gravitational birefringence phenomenon: photons with distinct helicity follow different geodesics in a static gravitational field.
Bats Respond to Very Weak Magnetic Fields
Tian, Lan-Xiang; Pan, Yong-Xin; Metzner, Walter; Zhang, Jin-Shuo; Zhang, Bing-Fang
2015-01-01
How animals, including mammals, can respond to and utilize the direction and intensity of the Earth’s magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae) can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5th of the natural intensity (i.e., 10 μT; the lowest field strength tested here), the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 μT), despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (P<0.05). Hence, N. plancyi is able to detect the direction of a magnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth’s magnetic field strength varied and the polarity reversed tens of times over the past fifty million years. PMID:25922944
Field theory on R× S 3 topology. VI: Gravitation
NASA Astrophysics Data System (ADS)
Carmeli, M.; Malin, S.
1987-04-01
We extend to curved space-time the field theory on R×S3 topology in which field equations were obtained for scalar particles, spin one-half particles, the electromagnetic field of magnetic moments, an SU2 gauge theory, and a Schrödinger-type equation, as compared to ordinary field equations that are formulated on a Minkowskian metric. The theory obtained is an angular-momentum representation of gravitation. Gravitational field equations are presented and compared to the Einstein field equations, and the mathematical and physical similarity and differences between them are pointed out. The problem of motion is discussed, and the equations of motion of a rigid body are developed and given explicitly. One result which is worth emphazing is that while general relativity theory yields Newton's law of motion in the lowest approximation, our theory gives Euler's equations of motion for a rigid body in its lowest approximation.
Probing Dark Energy via Weak Gravitational Lensing with the Supernova Acceleration Probe (SNAP)
Albert, J.; Aldering, G.; Allam, S.; Althouse, W.; Amanullah, R.; Annis, J.; Astier, P.; Aumeunier, M.; Bailey, S.; Baltay, C.; Barrelet, E.; Basa, S.; Bebek, C.; Bergstom, L.; Bernstein, G.; Bester, M.; Besuner, B.; Bigelow, B.; Blandford, R.; Bohlin, R.; Bonissent, A.; /Caltech /LBL, Berkeley /Fermilab /SLAC /Stockholm U. /Paris, IN2P3 /Marseille, CPPM /Marseille, Lab. Astrophys. /Yale U. /Pennsylvania U. /UC, Berkeley /Michigan U. /Baltimore, Space Telescope Sci. /Indiana U. /Caltech, JPL /Australian Natl. U., Canberra /American Astron. Society /Chicago U. /Cambridge U. /Saclay /Lyon, IPN
2005-08-08
SNAP is a candidate for the Joint Dark Energy Mission (JDEM) that seeks to place constraints on the dark energy using two distinct methods. The first, Type Ia SN, is discussed in a separate white paper. The second method is weak gravitational lensing, which relies on the coherent distortions in the shapes of background galaxies by foreground mass structures. The excellent spatial resolution and photometric accuracy afforded by a 2-meter space-based observatory are crucial for achieving the high surface density of resolved galaxies, the tight control of systematic errors in the telescope's Point Spread Function (PSF), and the exquisite redshift accuracy and depth required by this project. These are achieved by the elimination of atmospheric distortion and much of the thermal and gravity loads on the telescope. The SN and WL methods for probing dark energy are highly complementary and the error contours from the two methods are largely orthogonal. The nominal SNAP weak lensing survey covers 1000 square degrees per year of operation in six optical and three near infrared filters (NIR) spanning the range 350 nm to 1.7 {micro}m. This survey will reach a depth of 26.6 AB magnitude in each of the nine filters and allow for approximately 100 resolved galaxies per square arcminute, {approx} 3 times that available from the best ground-based surveys. Photometric redshifts will be measured with statistical accuracy that enables scientific applications for even the faint, high redshift end of the sample. Ongoing work aims to meet the requirements on systematics in galaxy shape measurement, photometric redshift biases, and theoretical predictions.
Zhang Pengjie
2010-09-10
The galaxy intrinsic alignment is a severe challenge to precision cosmic shear measurement. We propose self-calibrating the induced gravitational shear-galaxy intrinsic ellipticity correlation (the GI correlation) in weak lensing surveys with photometric redshift measurements. (1) We propose a method to extract the intrinsic ellipticity-galaxy density cross-correlation (I-g) from the galaxy ellipticity-density measurement in the same redshift bin. (2) We also find a generic scaling relation to convert the extracted I-g correlation to the necessary GI correlation. We perform a concept study under simplified conditions and demonstrate its capability to significantly reduce GI contamination. We discuss the impact of various complexities on the two key ingredients of the self-calibration technique, namely the method for extracting the I-g correlation and the scaling relation between the I-g and the GI correlation. We expect that none of them will likely be able to completely invalidate the proposed self-calibration technique.
Lorentz transformations in the presence of a uniform gravitational field.
NASA Technical Reports Server (NTRS)
Broucke, R.
1971-01-01
This article describes a Lorentz-like transformation between a fixed frame and an inertial frame that is free falling due to the presence of a uniform gravitation field. The application to the clock paradox problem and some connections with similar works are also discussed.
Gravitational collapse of massless scalar field and cosmic censorship
Goldwirth, D.S.; Piran, T.
1987-12-15
We present a numerical study of the gravitational collapse of a massless scalar field. We calculate the future evolution of new initial data, suggested by Christodoulou, and we show that in spite of the original expectations these data lead only to singularities engulfed by an event horizon.
Relativistic motion of spinning particles in a gravitational field
NASA Astrophysics Data System (ADS)
Chicone, C.; Mashhoon, B.; Punsly, B.
2005-08-01
The relative motion of a classical relativistic spinning test particle is studied with respect to a nearby free test particle in the gravitational field of a rotating source. The effects of the spin-curvature coupling force are elucidated and the implications of the results for the motion of rotating plasma clumps in astrophysical jets are discussed.
Teleportation of a Weak Coherent Cavity Field State
NASA Astrophysics Data System (ADS)
Cardoso, Wesley B.; Qiang, Wen-Chao; Avelar, Ardiley T.
2016-07-01
In this paper we propose a scheme to teleport a weak coherent cavity field state. The scheme relies on the resonant atom-field interaction inside a high-Q cavity. The mean photon-number of the cavity field is assumed much smaller than one, hence the field decay inside the cavity can be effectively suppressed.
Hydrodynamic representation of the Klein-Gordon-Einstein equations in the weak field limit
NASA Astrophysics Data System (ADS)
Suárez, Abril; Chavanis, Pierre-Henri
2015-11-01
Using a generalization of the Madelung transformation, we derive the hydrodynamic representation of the Klein-Gordon-Einstein equations in the weak field limit. We consider a complex self-interacting scalar field with an arbitrary potential of the form V(|ϕ|2). We compare the results with simplified models in which the gravitational potential is introduced by hand in the Klein-Gordon equation, and assumed to satisfy a (generalized) Poisson equation. Nonrelativistic hydrodynamic equations based on the Schrodinger-Poisson equations or on the Gross-Pitaevskii-Poisson equations are recovered in the limit c → +∞.
Gravitational Collapse with Negative Energy Fields
NASA Astrophysics Data System (ADS)
Narlikar, Jayant V.
2007-04-01
This paper re-examines the classical problem of the collapse of a dust ball, with the added input of a negative energy scalar field. It is shown that not only is the collapse halted prior to the singularity, but a black hole may not even form. The object bounces at a stage when it is still outside any event horizon.
Gravitational constant in multiple field gravity
Abedi, Habib; Abbassi, Amir M. E-mail: amabasi@khayam.ut.ac.ir
2015-05-01
In the present study, we consider general form of the Lagrangian f(R, φ{sup I}, X) , that is a function of the Ricci scalar, multiple scalar fields and non-canonical kinetic terms. We obtain the effective Newton's constant deep inside the Hubble radius. We use Jordan and Einstein frames, and study the conservation of energy-momentum tensor.
Nbody Simulations and Weak Gravitational Lensing using new HPC-Grid resources: the PI2S2 project
NASA Astrophysics Data System (ADS)
Becciani, U.; Antonuccio-Delogu, V.; Costa, A.; Comparato, M.
2008-08-01
We present the main project of the new grid infrastructure and the researches, that have been already started in Sicily and will be completed by next year. The PI2S2 project of the COMETA consortium is funded by the Italian Ministry of University and Research and will be completed in 2009. Funds are from the European Union Structural Funds for Objective 1 regions. The project, together with a similar project called Trinacria GRID Virtual Laboratory (Trigrid VL), aims to create in Sicily a computational grid for e-science and e-commerce applications with the main goal of increasing the technological innovation of local enterprises and their competition on the global market. PI2S2 project aims to build and develop an e-Infrastructure in Sicily, based on the grid paradigm, mainly for research activity using the grid environment and High Performance Computer systems. As an example we present the first results of a new grid version of FLY a tree Nbody code developed by INAF Astrophysical Observatory of Catania, already published in the CPC program Library, that will be used in the Weak Gravitational Lensing field.
A study of spin chemistry in weak magnetic fields.
Timmel, Christiane R; Henbest, Kevin B
2004-12-15
This paper reviews the latest developments in the field of spin chemistry with a particular focus on the effects of weak static and/or oscillating magnetic fields (typically smaller than the average hyperfine coupling) on radical recombination reactions. Anisotropic magnetic field effects and their significance in the debate about potential mechanisms controlling magnetoreception in birds are discussed.
Biological effects due to weak magnetic field on plants
NASA Astrophysics Data System (ADS)
Belyavskaya, N. A.
2004-01-01
Throughout the evolution process, Earth's magnetic field (MF, about 50 μT) was a natural component of the environment for living organisms. Biological objects, flying on planned long-term interplanetary missions, would experience much weaker magnetic fields, since galactic MF is known to be 0.1-1 nT. However, the role of weak magnetic fields and their influence on functioning of biological organisms are still insufficiently understood, and is actively studied. Numerous experiments with seedlings of different plant species placed in weak magnetic field have shown that the growth of their primary roots is inhibited during early germination stages in comparison with control. The proliferative activity and cell reproduction in meristem of plant roots are reduced in weak magnetic field. Cell reproductive cycle slows down due to the expansion of G 1 phase in many plant species (and of G 2 phase in flax and lentil roots), while other phases of cell cycle remain relatively stabile. In plant cells exposed to weak magnetic field, the functional activity of genome at early pre-replicate period is shown to decrease. Weak magnetic field causes intensification of protein synthesis and disintegration in plant roots. At ultrastructural level, changes in distribution of condensed chromatin and nucleolus compactization in nuclei, noticeable accumulation of lipid bodies, development of a lytic compartment (vacuoles, cytosegresomes and paramural bodies), and reduction of phytoferritin in plastids in meristem cells were observed in pea roots exposed to weak magnetic field. Mitochondria were found to be very sensitive to weak magnetic field: their size and relative volume in cells increase, matrix becomes electron-transparent, and cristae reduce. Cytochemical studies indicate that cells of plant roots exposed to weak magnetic field show Ca 2+ over-saturation in all organelles and in cytoplasm unlike the control ones. The data presented suggest that prolonged exposures of plants to weak
NASA Astrophysics Data System (ADS)
Kopeikin, Sergei; Mashhoon, Bahram
2002-03-01
The propagation of light in the gravitational field of self-gravitating spinning bodies moving with arbitrary velocities is discussed. The gravitational field is assumed to be ``weak'' everywhere. The equations of motion of a light ray are solved in the first post-Minkowskian approximation which is linear with respect to the universal gravitational constant G. We do not restrict ourselves to the approximation of a gravitational lens so that the solution of light geodesics is applicable for arbitrary locations of the source of light and the observer. This formalism is applied for studying corrections to the Shapiro time delay in binary pulsars caused by the rotation of the pulsar and its companion. We also derive the correction to the light deflection angle caused by the rotation of gravitating bodies in the solar system (Sun, planets) or a gravitational lens. The gravitational shift of frequency due to the combined translational and rotational motions of light-ray-deflecting bodies is analyzed as well. We give a general derivation of the formula describing the relativistic rotation of the plane of polarization of electromagnetic waves (Skrotskii effect). This formula is valid for arbitrary translational and rotational motion of gravitating bodies and greatly extends the results of previous researchers. Finally, we discuss the Skrotskii effect for gravitational waves emitted by localized sources such as a binary system. The theoretical results of this paper can be applied for studying various relativistic effects in microarcsecond space astrometry and developing corresponding algorithms for data processing in space astrometric missions such as FAME, SIM, and GAIA.
New symbolic tools for differential geometry, gravitation, and field theory
NASA Astrophysics Data System (ADS)
Anderson, I. M.; Torre, C. G.
2012-01-01
DifferentialGeometry is a Maple software package which symbolically performs fundamental operations of calculus on manifolds, differential geometry, tensor calculus, spinor calculus, Lie algebras, Lie groups, transformation groups, jet spaces, and the variational calculus. These capabilities, combined with dramatic recent improvements in symbolic approaches to solving algebraic and differential equations, have allowed for development of powerful new tools for solving research problems in gravitation and field theory. The purpose of this paper is to describe some of these new tools and present some advanced applications involving: Killing vector fields and isometry groups, Killing tensors, algebraic classification of solutions of the Einstein equations, and symmetry reduction of field equations.
Gravitational field calculations on a dynamic lattice by distributed computing.
NASA Astrophysics Data System (ADS)
Mähönen, P.; Punkka, V.
A new method of calculating numerically time evolution of a gravitational field in general relativity is introduced. Vierbein (tetrad) formalism, dynamic lattice and massively parallelized computation are suggested as they are expected to speed up the calculations considerably and facilitate the solution of problems previously considered too hard to be solved, such as the time evolution of a system consisting of two or more black holes or the structure of worm holes.
Gravitation Field Calculations on a Dynamic Lattice by Distributed Computing
NASA Astrophysics Data System (ADS)
Mähönen, Petri; Punkka, Veikko
A new method of calculating numerically time evolution of a gravitational field in General Relatity is introduced. Vierbein (tetrad) formalism, dynamic lattice and massively parallelized computation are suggested as they are expected to speed up the calculations considerably and facilitate the solution of problems previously considered too hard to be solved, such as the time evolution of a system consisting of two or more black holes or the structure of worm holes.
Stability of rotating self-gravitating filaments: effects of magnetic field
NASA Astrophysics Data System (ADS)
Sadhukhan, Shubhadeep; Mondal, Surajit; Chakraborty, Sagar
2016-07-01
We have performed systematic local linear stability analysis on a radially stratified infinite self-gravitating cylinder of rotating plasma under the influence of magnetic field. In order to render the system analytically tractable, we have focused solely on the axisymmetric modes of perturbations. Using cylindrical coordinate system, we have derived the critical linear mass density of a non-rotating filament required for gravitational collapse to ensue in the presence of azimuthal magnetic field. Moreover, for such filaments threaded by axial magnetic field, we show that the growth rates of the modes having non-zero radial wavenumber are reduced more strongly by the magnetic field than that of the modes having zero radial wavenumber. More importantly, our study contributes to the understanding of the stability property of rotating astrophysical filaments that are more often than not influenced by magnetic fields. In addition to complementing many relevant numerical studies reported the literature, our results on filaments under the influence of magnetic field generalize some of the very recent analytical works. For example, here we prove that even a weak magnetic field can play a dominant role in determining stability of the filament when the rotation time-scale is larger than the free-fall time-scale. A filamentary structure with faster rotation is, however, comparatively more stable for the same magnetic field. The results reported herein, due to strong locality assumption, are strictly valid for the modes for which one can ignore the radial variations in the density and the magnetic field profiles.
Improved routing strategy based on gravitational field theory
NASA Astrophysics Data System (ADS)
Song, Hai-Quan; Guo, Jin
2015-10-01
Routing and path selection are crucial for many communication and logistic applications. We study the interaction between nodes and packets and establish a simple model for describing the attraction of the node to the packet in transmission process by using the gravitational field theory, considering the real and potential congestion of the nodes. On the basis of this model, we propose a gravitational field routing strategy that considers the attractions of all of the nodes on the travel path to the packet. In order to illustrate the efficiency of proposed routing algorithm, we introduce the order parameter to measure the throughput of the network by the critical value of phase transition from a free flow phase to a congested phase, and study the distribution of betweenness centrality and traffic jam. Simulations show that, compared with the shortest path routing strategy, the gravitational field routing strategy considerably enhances the throughput of the network and balances the traffic load, and nearly all of the nodes are used efficiently. Project supported by the Technology and Development Research Project of China Railway Corporation (Grant No. 2012X007-D) and the Key Program of Technology and Development Research Foundation of China Railway Corporation (Grant No. 2012X003-A).
Apparatus and method for producing an artificial gravitational field
NASA Technical Reports Server (NTRS)
Mccanna, Jason (Inventor)
1993-01-01
An apparatus and method is disclosed for producing an artificial gravitational field in a spacecraft by rotating the same around a spin axis. The centrifugal force thereby created acts as an artificial gravitational force. The apparatus includes an engine which produces a drive force offset from the spin axis to drive the spacecraft towards a destination. The engine is also used as a counterbalance for a crew cabin for rotation of the spacecraft. Mass of the spacecraft, which may include either the engine or crew cabin, is shifted such that the centrifugal force acting on that mass is no longer directed through the center of mass of the craft. This off-center centrifugal force creates a moment that counterbalances the moment produced by the off-center drive force to eliminate unwanted rotation which would otherwise be precipitated by the offset drive force.
Novikov, V V; Ponomarev, V O; Novikov, G V; Kuvichkin, V V; Iablokova, E V; Fesenko, E E
2010-01-01
A number of effects of weak combined (static and alternating) magnetic fields with an alternating component of tens and hundreds nT at a collinear static field of 42 microT, which is equivalent to the geomagnetic field, have been found: the activation of fission and regeneration of planarians Dugesia tigrina, the inhibition of the growth of the Ehrlich ascites carcinoma in mice, the stimulation of the production of the tumor necrosis factor by macrophages, a decrease in the protection of chromatin against the action of DNase 1, and the enhancement of protein hydrolysis in systems in vivo and in vitro. The frequency and amplitude ranges for the alternating component of weak combined magnetic fields have been determined at which it affects various biological systems. Thus, the optimal amplitude at a frequency of 4.4 Hz is 100 nT (effective value); at a frequency of 16.5 Hz, the range of effective amplitudes is broader, 150-300 nT; and at a frequency of 1 (0.5) Hz, it is 300 nT. The sum of close frequencies (e.g., 16 and 17 Hz) produces a similar biological effect as the product of the modulating (0.5 Hz) and carrying frequencies (16.5 Hz), which is explained by the ratio A = A0sin omega1t + A0sin omega2t = A0sin(omega1 + omega2)t/2cos(omega1 - omega2)t/2. The efficiency of magnetic signals with pulsations (the sum of close frequencies) is more pronounced than that of sinusoidal frequencies. These data may indicate the presence of several receptors of weak magnetic fields in biological systems and, as a consequence, a higher efficiency of the effect at the simultaneous adjustment to these frequencies by the field. Even with consideration of these facts, the mechanism of the biological action of weak combined magnetic fields remains still poorly understood. PMID:20968074
NASA Astrophysics Data System (ADS)
Troxel, M. A.; Ishak, Mustapha
2015-02-01
The wealth of incoming and future cosmological observations will allow us to map out the structure and evolution of the observable universe to an unprecedented level of precision. Among these observations is the weak gravitational lensing of galaxies, e.g., cosmic shear that measures the minute distortions of background galaxy images by intervening cosmic structure. Weak lensing and cosmic shear promise to be a powerful probe of astrophysics and cosmology, constraining models of dark energy, measuring the evolution of structure in the universe, and testing theories of gravity on cosmic scales. However, the intrinsic alignment of galaxies-their shape and orientation before being lensed-may pose a great challenge to the use of weak gravitational lensing as an accurate cosmological probe, and has been identified as one of the primary physical systematic biases in cosmic shear studies. Correlations between this intrinsic alignment and the lensing signal can persist even for large physical separations, and isolating the effect of intrinsic alignment from weak lensing is not trivial. A great deal of work in the last two decades has been devoted to understanding and characterizing this intrinsic alignment, which is also a direct and complementary probe of structure formation and evolution in its own right. In this review, we report in a systematic way the state of our understanding of the intrinsic alignment of galaxies, with a particular emphasis on its large-scale impact on weak lensing measurements and methods for its isolation or mitigation. We begin with an introduction to the use of cosmic shear as a probe for cosmology and describe the various physical contributions by intrinsic alignment to the shear or convergence 2- and 3-point correlations. We then review developments in the modeling of the intrinsic alignment signal, including a trend toward attempting to incorporate more accurate nonlinear and single halo effects. The impact on cosmological constraints by the
Two-dimensional colloidal mixtures in magnetic and gravitational fields
NASA Astrophysics Data System (ADS)
Löwen, H.; Horn, T.; Neuhaus, T.; ten Hagen, B.
2013-11-01
This mini-review is concerned with two-dimensional colloidal mixtures exposed to various kinds of external fields. By a magnetic field perpendicular to the plane, dipole moments are induced in paramagnetic particles which give rise to repulsive interactions leading to complex crystalline alloys in the composition-asymmetry diagram. A quench in the magnetic field induces complex crystal nucleation scenarios. If exposed to a gravitational field, these mixtures exhibit a brazil-nut effect and show a boundary layering which is explained in terms of a depletion bubble picture. The latter persists for time-dependent gravity ("colloidal shaking"). Finally, we summarize crystallization effects when the second species is frozen in a disordered matrix which provides obstacles for the crystallizing component.
Weak, Quiet Magnetic Fields Seen in the Venus Atmosphere
Zhang, T. L.; Baumjohann, W.; Russell, C. T.; Luhmann, J. G.; Xiao, S. D.
2016-01-01
The existence of a strong internal magnetic field allows probing of the interior through both long term changes of and short period fluctuations in that magnetic field. Venus, while Earth’s twin in many ways, lacks such a strong intrinsic magnetic field, but perhaps short period fluctuations can still be used to probe the electrical conductivity of the interior. Toward the end of the Venus Express mission, an aerobraking campaign took the spacecraft below the ionosphere into the very weakly electrically conducting atmosphere. As the spacecraft descended from 150 to 140 km altitude, the magnetic field became weaker on average and less noisy. Below 140 km, the median field strength became steady but the short period fluctuations continued to weaken. The weakness of the fluctuations indicates they might not be useful for electromagnetic sounding of the atmosphere from a high altitude platform such as a plane or balloon, but possibly could be attempted on a lander. PMID:27009234
Weak, Quiet Magnetic Fields Seen in the Venus Atmosphere
NASA Astrophysics Data System (ADS)
Zhang, Tielong; Baumjohann, Wolfgang; Russell, Christopher; Luhmann, Janet
2016-04-01
The existence of a strong internal magnetic field allows probing of the interior through both long term changes of and short period fluctuations in that magnetic field. Venus, while Earth's twin in many ways, lacks such a strong intrinsic magnetic field, but perhaps short period fluctuations can still be used to probe the electrical conductivity of the interior. Toward the end of the Venus Express mission, an aerobraking campaign took the spacecraft below the ionosphere into the very weakly electrically conducting atmosphere. As the spacecraft descended from 150 to 140 km altitude, the magnetic field became weaker on average and less noisy. Below 140 km, the median field strength became steady but the short period fluctuations continued to weaken. The weakness of the fluctuations indicates they might not be useful for electromagnetic sounding of the atmosphere from a high altitude platform such as a plane or balloon, but possibly could be attempted on a lander.
Weak, Quiet Magnetic Fields Seen in the Venus Atmosphere
NASA Astrophysics Data System (ADS)
Zhang, T. L.; Baumjohann, W.; Russell, C. T.; Luhmann, J. G.; Xiao, S. D.
2016-03-01
The existence of a strong internal magnetic field allows probing of the interior through both long term changes of and short period fluctuations in that magnetic field. Venus, while Earth’s twin in many ways, lacks such a strong intrinsic magnetic field, but perhaps short period fluctuations can still be used to probe the electrical conductivity of the interior. Toward the end of the Venus Express mission, an aerobraking campaign took the spacecraft below the ionosphere into the very weakly electrically conducting atmosphere. As the spacecraft descended from 150 to 140 km altitude, the magnetic field became weaker on average and less noisy. Below 140 km, the median field strength became steady but the short period fluctuations continued to weaken. The weakness of the fluctuations indicates they might not be useful for electromagnetic sounding of the atmosphere from a high altitude platform such as a plane or balloon, but possibly could be attempted on a lander.
Weak, Quiet Magnetic Fields Seen in the Venus Atmosphere.
Zhang, T L; Baumjohann, W; Russell, C T; Luhmann, J G; Xiao, S D
2016-01-01
The existence of a strong internal magnetic field allows probing of the interior through both long term changes of and short period fluctuations in that magnetic field. Venus, while Earth's twin in many ways, lacks such a strong intrinsic magnetic field, but perhaps short period fluctuations can still be used to probe the electrical conductivity of the interior. Toward the end of the Venus Express mission, an aerobraking campaign took the spacecraft below the ionosphere into the very weakly electrically conducting atmosphere. As the spacecraft descended from 150 to 140 km altitude, the magnetic field became weaker on average and less noisy. Below 140 km, the median field strength became steady but the short period fluctuations continued to weaken. The weakness of the fluctuations indicates they might not be useful for electromagnetic sounding of the atmosphere from a high altitude platform such as a plane or balloon, but possibly could be attempted on a lander. PMID:27009234
Weak, Quiet Magnetic Fields Seen in the Venus Atmosphere.
Zhang, T L; Baumjohann, W; Russell, C T; Luhmann, J G; Xiao, S D
2016-03-24
The existence of a strong internal magnetic field allows probing of the interior through both long term changes of and short period fluctuations in that magnetic field. Venus, while Earth's twin in many ways, lacks such a strong intrinsic magnetic field, but perhaps short period fluctuations can still be used to probe the electrical conductivity of the interior. Toward the end of the Venus Express mission, an aerobraking campaign took the spacecraft below the ionosphere into the very weakly electrically conducting atmosphere. As the spacecraft descended from 150 to 140 km altitude, the magnetic field became weaker on average and less noisy. Below 140 km, the median field strength became steady but the short period fluctuations continued to weaken. The weakness of the fluctuations indicates they might not be useful for electromagnetic sounding of the atmosphere from a high altitude platform such as a plane or balloon, but possibly could be attempted on a lander.
E.coli in weak magnetic field in different media
NASA Astrophysics Data System (ADS)
Masood, Samina
We study the growth of E-coli in a weak magnetic field, both in a liquid and a solid medium. We use LB broth for that purpose at the room temperature and study the growth in different types of magnetic field. We grow it over the bar magnets and within the magnetic field generated by the Helmholtz coils. It has been clearly noticed that the growth of bacteria is clearly affected with the magnetic field and the different types of magnetic field affect differently.
Stationary axisymmetric fields in a teleparallel theory of gravitation
NASA Astrophysics Data System (ADS)
Saez, D.
1984-12-01
The stationary axisymmetric field in the tetrad theory of gravitation of Moller (1978) and hence (as shown by Meyre, 1982) in the teleparallel limit of the gauge theory of Hehl et al. (1978) is investigated analytically. A set of tetrads satisfying the Moller equations and giving a Kerr metric is defined, and its existence is proved. It is suggested that the introduction of suitable conditions could reduce the number of tetrads in the Kerr case to one or a small number, and that the present analytical techniques could be applied to other stationary axisymmetric metrics of general relativity.
Spin in stationary gravitational fields and rotating frames
Obukhov, Yuri N.; Silenko, Alexander J.; Teryaev, Oleg V.
2010-03-24
A spin motion of particles in stationary spacetimes is investigated in the framework of the classical gravity and relativistic quantum mechanics. We bring the Dirac equation for relativistic particles in nonstatic spacetimes to the Hamiltonian form and perform the Foldy-Wouthuysen transformation. We show the importance of the choice of tetrads for description of spin dynamics in the classical gravity. We derive classical and quantum mechanical equations of motion of the spin for relativistic particles in stationary gravitational fields and rotating frames and establish the full agreement between the classical and quantum mechanical approaches.
Boson stars: Gravitational equilibria of self-interacting scalar fields
Colpi, M.; Shapiro, S.L.; Wasserman, I.
1986-11-17
Spherically symmetric gravitational equilibria of self-interacting scalar fields phi with interaction potential V(phi) = (1/4)lambdachemically bondphichemically bond/sup 4/ are determined. Surprisingly, the resulting configurations may differ markedly from the noninteracting case even when lambda<<1. Contrary to generally accepted astrophysical folklore, it is found that the maximum masses of such boson stars may be comparable to the Chandrasekhar mass for fermions of mass m/sub fermion/--lambda/sup -1/4/m/sub boson/. .AE
Gravitational field of a spinning pencil of light
Mitskievic, N.V.; Kumaradtya, K.K.
1989-05-01
An exact solution of Einstein's equations in a vacuum (outside of singularities), belonging to Kundt's class and Petrov type N, is interpreted as the metric of a spinning pencil of light (a linear source infinitely extended in one direction and moving with the speed of light). It is shown that the gravitational fields of two parallel pencils of light do not interact with each other, i.e., the superposition of the metrics of two parallel pencils of light is an exact solution of Einstein's equations in a vacuum.
Numerical computation of gravitational field for general axisymmetric objects
NASA Astrophysics Data System (ADS)
Fukushima, Toshio
2016-10-01
We developed a numerical method to compute the gravitational field of a general axisymmetric object. The method (i) numerically evaluates a double integral of the ring potential by the split quadrature method using the double exponential rules, and (ii) derives the acceleration vector by numerically differentiating the numerically integrated potential by Ridder's algorithm. Numerical comparison with the analytical solutions for a finite uniform spheroid and an infinitely extended object of the Miyamoto-Nagai density distribution confirmed the 13- and 11-digit accuracy of the potential and the acceleration vector computed by the method, respectively. By using the method, we present the gravitational potential contour map and/or the rotation curve of various axisymmetric objects: (i) finite uniform objects covering rhombic spindles and circular toroids, (ii) infinitely extended spheroids including Sérsic and Navarro-Frenk-White spheroids, and (iii) other axisymmetric objects such as an X/peanut-shaped object like NGC 128, a power-law disc with a central hole like the protoplanetary disc of TW Hya, and a tear-drop-shaped toroid like an axisymmetric equilibrium solution of plasma charge distribution in an International Thermonuclear Experimental Reactor-like tokamak. The method is directly applicable to the electrostatic field and will be easily extended for the magnetostatic field. The FORTRAN 90 programs of the new method and some test results are electronically available.
5th International School on Field Theory and Gravitation
NASA Astrophysics Data System (ADS)
Following the philosophy that the International School on Field Theory and Gravitation must be held each three years in different Brazilian Universities and, if possible, in different brazilian states, the next meeting will take place at Physics Institute of Universidade Federal do Mato Grosso, UFMT, Cuiabá city on April, 20-24/2009 very close to the beautiful Pantanal and Chapada dos Guimarães area. The goal of the meeting is to promote a greater integration among many physicists from the local university, UFMT, Co-organizing institutions in Brasil and foreign countries such as Canada, USA, Italy, China, England, Swiss, Spain, Brazil and others; to stimulate the organization of scientific events in our physics Institute and thus contributing to local research activities; to exhibit different fields of physics and to stimulate new lines of theoretical research and technological developments in the Universidade Federal do Mato Grosso, UFMT. Finally, we make efforts to promote the development of advanced studies, taking it to the present core of research in a strong process of affirmation of new lines of theoretical studies in our Physics Institute. To this, we invite colleagues, collaborators, researchers, students, and friends to attend this fifth edition of International School on Field Theory and gravitation-2009.
Massive to gauge field reduction and gravitational wave zone information
NASA Astrophysics Data System (ADS)
Deser, S.
2016-07-01
I analyze the possible relevance of LIGO's gravitational wave detection to the viability of massive gravity models. In GR, a wave zone, where the linearized approximation holds, is guaranteed to exist and the observed wave's amplitude profile can be sufficiently related to the emitting strong field interior to verify that, in this case, it was due to an inspiraling black hole merger. After an excursion to massive spin 1's massless limit, linear massive tensor theory is shown explicitly to propagate only (retarded) maximal, helicity 2, modes to O( m) as m→ 0; however, we don't know if the full theory has a similar "wave zone" governed by the linear model. Even if it does, a much more serious obstacle for massive gravity is to construct a time-varying strong field event to compare with the strong field footprint of LIGO's observed signals.
Fate of Extended States and Localization Transition at Weak Fields
NASA Astrophysics Data System (ADS)
Yang, Kun
1997-03-01
The reconciliation between the nonexistence of extended states in two dimensions in zero magnetic field, and the existence of critical energies in the high field limit, first addressed qualitatively (D. E. Khmelnitskii, Phys. Lett. A 106), 182 (1984); R. B. Laughlin, Phys. Rev. Lett. 52, 2304 (1984). a decade ago, has reemerged as a subject of considerable interest and debate, following experimental investigations in the two dimensional electron gas at low fields. We have addressed the problem on two fronts. For strong magnetic fields, where Landau level mixing effects are weak, we have developed a systematic analytic expansion in powers of 1\\over B. (F. D. M. Haldane and Kun Yang, Phys. Rev. Lett. 78), to appear. We find the dominant level repulsion effect (of order 1\\over B^2), lowers the energies of typical states in a Landau band. The critical energies, however, are not affected at this order. In contrast, we find that, the extended state energies levitates to order 1\\over B^3, thus reconciling levitation of extended states with level repulsion due to Landau level mixing. In the regime of weak magnetic field and strong Landau level mixing, where the perturbative approach is not applicable, we have performed a numerical study on lattice models, (Kun Yang and R. N. Bhatt, Phys. Rev. Lett. 76), 1316 (1996). which provides evidence for this levitation at weak magnetic field. Furthermore, we obtain a localization transition to an insulating phase at weak field, and a finite size scaling analysis shows that the localization length diverges at this transition with an exponent that is the same as that of the plateau transitions in the strong field regime, ν≈ 2.3. Relations between our theoretical results and experimental findings will be discussed.
Reentering the Gravitational Fringe Field of the Solar System
NASA Astrophysics Data System (ADS)
Fisher, P. C.
A 1998 proposal to the National Aeronautics and Space Administration (NASA) described how to update an earlier proposal outline for an experiment involving a manned spacecraft that traveled to just outside the gravitational field of the solar system. The recent proposal briefly describes how to initiate a 25-year program to launch a seven-year mission. Very little thought has been given to astronomical/astrophysical investigations that might be carried out over seven years, but one or more generations of NASA's Terrestrial Planet Finder program might be included. Only a little serious thought has been given to how to reenter the solar system's gravitational fringe field, but access to several procedures and three-fold redundancy seems desirable. Some details of the proposed paper study will be given. Non-responsibility statement, from source document of calendar 1973. This document was prepared while the author was on an unpaid leave of absence from The Lockheed Missiles and Space Company (LMSC) of Palo Alto, California. The comments made herein are partly the results of experiments carried out over a number of years. For a portion of this time, both NASA and LMSC financed the author's space astronomy investigations. It may be that either or both these institutions may possess some proprietary rights to portions of the ideas and information presented. This work was supported by Ruffner Associates, Inc.
Gravitation field algorithm and its application in gene cluster
2010-01-01
Background Searching optima is one of the most challenging tasks in clustering genes from available experimental data or given functions. SA, GA, PSO and other similar efficient global optimization methods are used by biotechnologists. All these algorithms are based on the imitation of natural phenomena. Results This paper proposes a novel searching optimization algorithm called Gravitation Field Algorithm (GFA) which is derived from the famous astronomy theory Solar Nebular Disk Model (SNDM) of planetary formation. GFA simulates the Gravitation field and outperforms GA and SA in some multimodal functions optimization problem. And GFA also can be used in the forms of unimodal functions. GFA clusters the dataset well from the Gene Expression Omnibus. Conclusions The mathematical proof demonstrates that GFA could be convergent in the global optimum by probability 1 in three conditions for one independent variable mass functions. In addition to these results, the fundamental optimization concept in this paper is used to analyze how SA and GA affect the global search and the inherent defects in SA and GA. Some results and source code (in Matlab) are publicly available at http://ccst.jlu.edu.cn/CSBG/GFA. PMID:20854683
Gravitational waves and scalar perturbations from spectator fields
Biagetti, Matteo; Dimastrogiovanni, Emanuela; Peloso, Marco; Fasiello, Matteo E-mail: emanuela1573@gmail.com E-mail: peloso@physics.umn.edu
2015-04-01
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 ∼ 0.1) would indicate an inflationary expansion rate close to 10{sup 14} 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 [1], where a spectator field σ with a sound speed c{sub s} || 1 acts as a source for gw during inflation. In our formulation σ 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 σ and find that, in our realization, r is not enhanced with respect to the standard result but it is strongly sensitive to c{sub s}, thus breaking the direct r ↔ H connection.
NASA Technical Reports Server (NTRS)
Eby, P. B.
1978-01-01
The construction of a clock based on the beta decay process is proposed to test for any violations by the weak interaction of the strong equivalence principle bu determining whether the weak interaction coupling constant beta is spatially constant or whether it is a function of gravitational potential (U). The clock can be constructed by simply counting the beta disintegrations of some suitable source. The total number of counts are to be taken a measure of elapsed time. The accuracy of the clock is limited by the statistical fluctuations in the number of counts, N, which is equal to the square root of N. Increasing N gives a corresponding increase in accuracy. A source based on the electron capture process can be used so as to avoid low energy electron discrimination problems. Solid state and gaseous detectors are being considered. While the accuracy of this type of beta decay clock is much less than clocks based on the electromagnetic interaction, there is a corresponding lack of knowledge of the behavior of beta as a function of gravitational potential. No predictions from nonmetric theories as to variations in beta are available as yet, but they may occur at the U/sg C level.
Slowly and Rapidly Propagating "Liquid Flames" in Gravitational Fields
NASA Technical Reports Server (NTRS)
Shkadinsky, K. G.; Shkadinskaya, G. V.; Matkowsky, B. J.; Gokoglu, S. (Technical Monitor)
2000-01-01
We consider the combustion, in a gravitational field, of a heterogeneous powder mixture compressed into a solid sample, in which the high temperature ahead of the reaction zone destroys the solid, due, e.g. to melting of some of components of the mixture. Thus, a suspension is formed, consisting of a liquid bath containing solid or liquid particles. Processes such as heat and mass transfer as well as chemical reactions in the suspension determine the structure of the combustion wave and its propagation velocity. Under the influence of gravitational forces there is the possibility of relative motion of the liquid and solid. Previous theoretical analyses considered the rate of beat transfer between the solid and liquid phases to be sufficiently large that their two distinct temperatures rapidly equilibrated to a single temperature. In addition to this case, we also consider the case when the rate of heat transfer is not so large and the model involves the separate temperatures of the solid and liquid phases. We find that multiplicity of traveling wave structures is possible. In particular, in addition to a low velocity structure, which is essentially the same as that obtained from the one temperature description, we find a high velocity structure, which does not exist in the one temperature description, but rather depends on the fact that the solid and fluid temperatures differ from each other. Both structures can exist for the same parameter values in a given range. We describe the dependence of the combustion characteristics of the two structures on gravitational forces and other factors. In particular, we compare the characteristics in gravity and microgravity environments.
NASA Astrophysics Data System (ADS)
Jee, Myungkook James
2006-06-01
Clusters of galaxies, the largest gravitationally bound objects in the Universe, are useful tracers of cosmic evolution, and particularly detailed studies of still-forming clusters at high-redshifts can considerably enhance our understanding of the structure formation. We use two powerful methods that have become recently available for the study of these distant clusters: spaced- based gravitational weak-lensing and high-resolution X-ray observations. Detailed analyses of five high-redshift (0.8 < z < 1.3) clusters are presented based on the deep Advanced Camera for Surveys (ACS) and Chandra X-ray images. We show that, when the instrumental characteristics are properly understood, the newly installed ACS on the Hubble Space Telescope (HST) can detect subtle shape distortions of background galaxies down to the limiting magnitudes of the observations, which enables the mapping of the cluster dark matter in unprecedented high-resolution. The cluster masses derived from this HST /ACS weak-lensing study have been compared with those from the re-analyses of the archival Chandra X-ray data. We find that there are interesting offsets between the cluster galaxy, intracluster medium (ICM), and dark matter centroids, and possible scenarios are discussed. If the offset is confirmed to be uniquitous in other clusters, the explanation may necessitate major refinements in our current understanding of the nature of dark matter, as well as the cluster galaxy dynamics. CL0848+4452, the highest-redshift ( z = 1.27) cluster yet detected in weak-lensing, has a significant discrepancy between the weak- lensing and X-ray masses. If this trend is found to be severe and common also for other X-ray weak clusters at redshifts beyond the unity, the conventional X-ray determination of cluster mass functions, often inferred from their immediate X-ray properties such as the X-ray luminosity and temperature via the so-called mass-luminosity (M-L) and mass-temperature (M-T) relations, will become
Is there a weak mixed polarity background field? Theoretical arguments
NASA Technical Reports Server (NTRS)
Spruit, H. C.; Title, A. M.; Van Ballegooijen, A. A.
1987-01-01
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.
Tunneling Time and Weak Measurement in Strong Field Ionization
NASA Astrophysics Data System (ADS)
Zimmermann, Tomáš; Mishra, Siddhartha; Doran, Brent R.; Gordon, Daniel F.; Landsman, Alexandra S.
2016-06-01
Tunneling delays represent a hotly debated topic, with many conflicting definitions and little consensus on when and if such definitions accurately describe the physical observables. Here, we relate these different definitions to distinct experimental observables in strong field ionization, finding that two definitions, Larmor time and Bohmian time, are compatible with the attoclock observable and the resonance lifetime of a bound state, respectively. Both of these definitions are closely connected to the theory of weak measurement, with Larmor time being the weak measurement value of tunneling time and Bohmian trajectory corresponding to the average particle trajectory, which has been recently reconstructed using weak measurement in a two-slit experiment [S. Kocsis, B. Braverman, S. Ravets, M. J. Stevens, R. P. Mirin, L. K. Shalm, and A. M. Steinberg, Science 332, 1170 (2011)]. We demonstrate a big discrepancy in strong field ionization between the Bohmian and weak measurement values of tunneling time, and we suggest this arises because the tunneling time is calculated for a small probability postselected ensemble of electrons. Our results have important implications for the interpretation of experiments in attosecond science, suggesting that tunneling is unlikely to be an instantaneous process.
Tunneling Time and Weak Measurement in Strong Field Ionization.
Zimmermann, Tomáš; Mishra, Siddhartha; Doran, Brent R; Gordon, Daniel F; Landsman, Alexandra S
2016-06-10
Tunneling delays represent a hotly debated topic, with many conflicting definitions and little consensus on when and if such definitions accurately describe the physical observables. Here, we relate these different definitions to distinct experimental observables in strong field ionization, finding that two definitions, Larmor time and Bohmian time, are compatible with the attoclock observable and the resonance lifetime of a bound state, respectively. Both of these definitions are closely connected to the theory of weak measurement, with Larmor time being the weak measurement value of tunneling time and Bohmian trajectory corresponding to the average particle trajectory, which has been recently reconstructed using weak measurement in a two-slit experiment [S. Kocsis, B. Braverman, S. Ravets, M. J. Stevens, R. P. Mirin, L. K. Shalm, and A. M. Steinberg, Science 332, 1170 (2011)]. We demonstrate a big discrepancy in strong field ionization between the Bohmian and weak measurement values of tunneling time, and we suggest this arises because the tunneling time is calculated for a small probability postselected ensemble of electrons. Our results have important implications for the interpretation of experiments in attosecond science, suggesting that tunneling is unlikely to be an instantaneous process. PMID:27341232
NASA Astrophysics Data System (ADS)
Higuchi, Yuichi; Shirasaki, Masato
2016-07-01
We study the effect of f(R) gravity on the statistical properties of various large-scale structures which can be probed in weak gravitational lensing measurements. A set of ray-tracing simulations of gravitational lensing in f(R) gravity enables us to explore cosmological information on (i) stacking analyses of weak lensing observables and (ii) peak statistics in reconstructed lensing mass maps. For the f(R) model proposed by Hu & Sawicki, the measured lensing signals of dark matter haloes in the stacking analysis would show a ≲10 per cent difference between the standard Λcold dark matter and the f(R) model when the additional degree of freedom in f(R) model would be |fR0| ˜ 10-5. Among various large-scale structures to be studied in stacking analysis, troughs, i.e. underdensity regions in projected plane of foreground massive haloes, could be promising to constrain the model with |fR0| ˜ 10-5, while stacking analysis around voids is found to be difficult to improve the constraint of |fR0| even in future lensing surveys with a sky coverage of ˜1000 deg2. On the peak statistics, we confirm the correspondence between local maxima and dark matter haloes along the line of sight, regardless of the modification of gravity in our simulation. Thus, the number count of high significance local maxima would be useful to probe the mass function of dark matter haloes even in the f(R) model with |fR0| ≲ 10-5. We also find that including local minima in lensing mass maps would be helpful to improve the constant on f(R) gravity down to |fR0| = 10-5 in ongoing weak lensing surveys.
Constants of motion in stationary axisymmetric gravitational fields
NASA Astrophysics Data System (ADS)
Markakis, C.
2014-07-01
The motion of test particles in stationary axisymmetric gravitational fields is generally non-integrable unless a non-trivial constant of motion, in addition to energy and angular momentum along the symmetry axis, exists. The Carter constant in Kerr-de Sitter space-time is the only example known to date. Proposed astrophysical tests of the black hole no-hair theorem have often involved integrable gravitational fields more general than the Kerr family, but the existence of such fields has been a matter of debate. To elucidate this problem, we treat its Newtonian analogue by systematically searching for non-trivial constants of motion polynomial in the momenta and obtain two theorems. First, solving a set of quadratic integrability conditions, we establish the existence and uniqueness of the family of stationary axisymmetric potentials admitting a quadratic constant. As in Kerr-de Sitter space-time, the mass moments of this class satisfy a `no-hair' recursion relation M2l +2 = a2M2l, and the constant is Noether related to a second-order Killing-Stäckel tensor. Second, solving a new set of quartic integrability conditions, we establish non-existence of quartic constants. Remarkably, a subset of these conditions is satisfied when the mass moments obey a generalized `no-hair' recursion relation M2l +4 = (a2 + b2)M2l +2 - a2b2M2l. The full set of quartic integrability conditions, however, cannot be satisfied non-trivially by any stationary axisymmetric vacuum potential.
The Weak-Field Limit of the Magnetorotational Instability
NASA Astrophysics Data System (ADS)
Krolik, Julian H.; Zweibel, Ellen G.
2006-06-01
We investigate the behavior of the magnetorotational instability in the limit of extremely weak magnetic field, i.e., as the ratio of ion cyclotron frequency to orbital frequency (X) becomes small. Considered only in terms of cold two-fluid theory, instability persists to arbitrarily small values of X, and the maximum growth rate is of the order of the orbital frequency except for the range me/mi<|X|<1, where it can be rather smaller. In this range, field aligned with rotation (X>0) produces slower growth than antialigned field (X<0). The maximum growth rate is generally achieved at smaller and smaller wavelengths as |X| diminishes. When |X|
Neutron Interference in the Gravitational Field of a Ring Laser
NASA Astrophysics Data System (ADS)
Fischetti, Robert
2013-04-01
A number of analyses of neutron interference effects due to various metric perturbations have been found in the literature [1,2]. However, the approach of each author depends on a specific metric. I will present a new general technique giving the Foldy-Wouthuysen transformed Hamiltonian for a Dirac particle in the most general linearized space-time metric. I will then apply this new technique to calculate the phase shift on a neutron beam interferometer due to the gravitational field of a ring laser [3].[4pt] [1] D. M Greenberger and A. W. Overhauser, Rev. Mod. Phys. 51, 43--78 (1979).[0pt] [2] F. W. Hehl and W. T. Ni, Phys. Rev. D, vol 42, no. 6, pp. 2045-2048, 1990.[0pt] [3] R. L. Mallett, Phys. Lett. A 269, 214 (2000).
Geodesics in the field of a rotating deformed gravitational source
NASA Astrophysics Data System (ADS)
Boshkayev, K. A.; Quevedo, H.; Abutalip, M. S.; Kalymova, Zh. A.; Suleymanova, Sh. S.
2016-01-01
We investigate equatorial geodesics in the gravitational field of a rotating and deformed source described by the approximate Hartle-Thorne metric. In the case of massive particles, we derive within the same approximation analytic expressions for the orbital angular velocity, the specific angular momentum and energy, and the radii of marginally stable and marginally bound circular orbits. Moreover, we calculate the orbital angular velocity and the radius of lightlike circular geodesics. We study numerically the frame dragging effect and the influence of the quadrupolar deformation of the source on the motion of test particles. We show that the effects originating from the rotation can be balanced by the effects due to the oblateness of the source.
CHARGED TORI IN SPHERICAL GRAVITATIONAL AND DIPOLAR MAGNETIC FIELDS
Slany, P.; Kovar, J.; Stuchlik, Z.; Karas, V.
2013-03-01
A Newtonian model of non-conductive, charged, perfect fluid tori orbiting in combined spherical gravitational and dipolar magnetic fields is presented and stationary, axisymmetric toroidal structures are analyzed. Matter in such tori exhibits a purely circulatory motion and the resulting convection carries charges into permanent rotation around the symmetry axis. As a main result, we demonstrate the possible existence of off-equatorial charged tori and equatorial tori with cusps that also enable outflows of matter from the torus in the Newtonian regime. These phenomena qualitatively represent a new consequence of the interplay between gravity and electromagnetism. From an astrophysical point of view, our investigation can provide insight into processes that determine the vertical structure of dusty tori surrounding accretion disks.
Observable gravitational waves from inflation with small field excursions
Hotchkiss, Shaun; Mazumdar, Anupam; Nadathur, Seshadri E-mail: a.mazumdar@lancaster.ac.uk
2012-02-01
The detection of primordial gravitational waves, or tensor perturbations, would be regarded as compelling evidence for inflation. The canonical measure of this is the ratio of tensor to scalar perturbations, r. For single-field slow-roll models of inflation with small field excursions, the Lyth bound dictates that if the evolution of the slow-roll parameter ε is monotonic, the tensor-to-scalar ratio must be below observationally detectable levels. We describe how non-monotonic evolution of ε 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 ε 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.
Gravitational waves in bouncing cosmologies from gauge field production
NASA Astrophysics Data System (ADS)
Ben-Dayan, Ido
2016-09-01
We calculate the gravitational waves (GW) spectrum produced in various Early Universe scenarios from gauge field sources, thus generalizing earlier inflationary calculations to bouncing cosmologies. We consider generic couplings between the gauge fields and the scalar field dominating the energy density of the Universe. We analyze the requirements needed to avoid a backreaction that will spoil the background evolution. When the scalar is coupled only to Ftilde F term, the sourced GW spectrum is exponentially enhanced and parametrically the square of the vacuum fluctuations spectrum, Script PsT ~ (Script PvT)2, giving an even bluer spectrum than the standard vacuum one. When the scalar field is also coupled to F2 term, the amplitude is still exponentially enhanced, but the spectrum can be arbitrarily close to scale invariant (still slightly blue), nT gtrsim 0, that is distinguishable form the slightly red inflationary one. Hence, we have a proof of concept of observable GW on CMB scales in a bouncing cosmology.
Magnetophoresis of diamagnetic microparticles in a weak magnetic field.
Zhu, Gui-Ping; Hejiazan, Majid; Huang, Xiaoyang; Nguyen, Nam-Trung
2014-12-21
Magnetic manipulation is a promising technique for lab-on-a-chip platforms. The magnetic approach can avoid problems associated with heat, surface charge, ionic concentration and pH level. The present paper investigates the migration of diamagnetic particles in a ferrofluid core stream that is sandwiched between two diamagnetic streams in a uniform magnetic field. The three-layer flow is expanded in a circular chamber for characterisation based on imaging of magnetic nanoparticles and fluorescent microparticles. A custom-made electromagnet generates a uniform magnetic field across the chamber. In a relatively weak uniform magnetic field, the diamagnetic particles in the ferrofluid move and spread across the chamber. Due to the magnetization gradient formed by the ferrofluid, diamagnetic particles undergo negative magnetophoresis and move towards the diamagnetic streams. The effects of magnetic field strength and the concentration of diamagnetic particles are studied in detail. PMID:25325774
Rocha, Jorge V.; Cardoso, Vitor
2011-05-15
We analyze the gravitational perturbations induced by particles falling into a three dimensional, asymptotically AdS black hole geometry. More specifically, we solve the linearized perturbation equations obtained from the geodesic motion of a ringlike distribution of test particles in the BTZ background. This setup ensures that the U(1) symmetry of the background is preserved. The nonasymptotic flatness of the background raises difficulties in attributing the significance of energy and angular momentum to the conserved quantities of the test particles. This issue is well known but, to the best of our knowledge, has never been addressed in the literature. We confirm that the naive expressions for energy and angular momentum are the correct definitions. Finally, we put an asymptotically AdS version of the weak cosmic censorship to a test: by attempting to overspin the BTZ black hole with test particles it is found that the black hole cannot be spun-up past its extremal limit.
Gravitational spectra from direct measurements. [of surface field
NASA Technical Reports Server (NTRS)
Wagner, C. A.; Colombo, O. L.
1979-01-01
A simple rapid method is described for determining the spectrum of a surface field (in spherical harmonics) from harmonic analysis of direct (in situ) measurements along great circle arcs. The method is shown to give excellent overall trends (smoothed spectra) to very high degree from even a few short arcs of satellite data. Three examples are taken with perfect measurements of satellite tracking over a planet made up of hundreds of point masses using (1) altimetric heights from a low-orbiting spacecraft, (2) velocity (range rate) residuals between a low and a high satellite in circular orbits, and (3) range rate data between a station at infinity and a satellite in a highly eccentric orbit. In particular, the smoothed spectrum of the earth's gravitational field is determined to about degree 400(50-km half wavelength) from 1 x 1 deg gravimetry and the equivalent of 11 revolutions of GEOS 3 and Skylab altimetry. This measurement shows that there is about 46 cm of geoid height (rms worldwide) remaining in the field beyond degree 180.
Peters, Thomas; Klessen, Ralf S.; Federrath, Christoph; Smith, Rowan J.; Schleicher, Dominik R. G.; Banerjee, Robi; Sur, Sharanya
2012-12-01
Stars form by the gravitational collapse of interstellar gas. The thermodynamic response of the gas can be characterized by an effective equation of state. It determines how gas heats up or cools as it gets compressed, and hence plays a key role in regulating the process of stellar birth on virtually all scales, ranging from individual star clusters up to the galaxy as a whole. We present a systematic study of the impact of thermodynamics on gravitational collapse in the context of high-redshift star formation, but argue that our findings are also relevant for present-day star formation in molecular clouds. We consider a polytropic equation of state, P = k{rho}{sup {Gamma}}, with both sub-isothermal exponents {Gamma} < 1 and super-isothermal exponents {Gamma} > 1. We find significant differences between these two cases. For {Gamma} > 1, pressure gradients slow down the contraction and lead to the formation of a virialized, turbulent core. Weak magnetic fields are strongly tangled and efficiently amplified via the small-scale turbulent dynamo on timescales corresponding to the eddy-turnover time at the viscous scale. For {Gamma} < 1, on the other hand, pressure support is not sufficient for the formation of such a core. Gravitational contraction proceeds much more rapidly and the flow develops very strong shocks, creating a network of intersecting sheets and extended filaments. The resulting magnetic field lines are very coherent and exhibit a considerable degree of order. Nevertheless, even under these conditions we still find exponential growth of the magnetic energy density in the kinematic regime.
NASA Technical Reports Server (NTRS)
Dong, D.; Gross, R. S.; Dickey, J. O.
1994-01-01
Laser ranging measurements to single satellite are sensitive to the Earth's gravitational field and its temporal variations. Using 13 years (1980-1992) of LAGEOS I laser ranging data, we have recovered monthly mean linear combinations of even and odd degree zonal spherical harmonic coefficients of the Earth's gravitational field.
The emergence of weakly twisted magnetic fields in the sun
Archontis, V.; Hood, A. W.; Tsinganos, K.
2013-11-20
We have studied the emergence of a weakly twisted magnetic flux tube from the upper convection zone into the solar atmosphere. It is found that the rising magnetized plasma does not undergo the classical, single Ω-shaped loop emergence, but it becomes unstable in two places, forming two magnetic lobes that are anchored in small-scale bipolar structures at the photosphere, between the two main flux concentrations. The two magnetic lobes rise and expand into the corona, forming an overall undulating magnetic flux system. The dynamical interaction of the lobes results in the triggering of high-speed and hot jets and the formation of successive cool and hot loops that coexist in the emerging flux region. Although the initial emerging field is weakly twisted, a highly twisted magnetic flux rope is formed at the low atmosphere, due to shearing and reconnection. The new flux rope (hereafter post-emergence flux rope) does not erupt. It remains confined by the overlying field. Although there is no ejective eruption of the post-emergence rope, it is found that a considerable amount of axial and azimuthal flux is transferred into the solar atmosphere during the emergence of the magnetic field.
Differentiation of optical isomers through enhanced weak-field interactions
NASA Technical Reports Server (NTRS)
Aronowitz, S.
1980-01-01
The influence of weak field interaction terms due to the cooperative effects which arise from a macroscopic assemblage of interacting sites is studied. Differential adsorption of optical isomers onto an achiral surface is predicted to occur if the surface was continuous and sufficiently large. However, the quantity of discontinuous crystal surfaces did not enhance the percentage of differentiation and thus the procedure of using large quantities of small particles was not a viable technique for obtaining a detectable differentiation of optical isomers on an achiral surface.
Spherical collapse of dark matter haloes in tidal gravitational fields
NASA Astrophysics Data System (ADS)
Reischke, Robert; Pace, Francesco; Meyer, Sven; Schäfer, Björn Malte
2016-08-01
We study the spherical collapse model in the presence of external gravitational tidal shear fields for different dark energy scenarios and investigate the impact on the mass function and cluster number counts. While previous studies of the influence of shear and rotation on δc have been performed with heuristically motivated models, we try to avoid this model dependence and sample the external tidal shear values directly from the statistics of the underlying linearly evolved density field based on first order Lagrangian perturbation theory. Within this self-consistent approach, in the sense that we restrict our treatment to scales where linear theory is still applicable, only fluctuations larger than the scale of the considered objects are included into the sampling process which naturally introduces a mass dependence of δc. We find that shear effects are predominant for smaller objects and at lower redshifts, i. e. the effect on δc is at or below the percent level for the ΛCDM model. For dark energy models we also find small but noticeable differences, similar to ΛCDM. The virial overdensity ΔV is nearly unaffected by the external shear. The now mass dependent δc is used to evaluate the mass function for different dark energy scenarios and afterwards to predict cluster number counts, which indicate that ignoring the shear contribution can lead to biases of the order of 1σ in the estimation of cosmological parameters like Ωm, σ8 or w.
Spherical collapse of dark matter haloes in tidal gravitational fields
NASA Astrophysics Data System (ADS)
Reischke, Robert; Pace, Francesco; Meyer, Sven; Schäfer, Björn Malte
2016-11-01
We study the spherical collapse model in the presence of external gravitational tidal shear fields for different dark energy scenarios and investigate the impact on the mass function and cluster number counts. While previous studies of the influence of shear and rotation on δc have been performed with heuristically motivated models, we try to avoid this model dependence and sample the external tidal shear values directly from the statistics of the underlying linearly evolved density field based on first-order Lagrangian perturbation theory. Within this self-consistent approach, in the sense that we restrict our treatment to scales where linear theory is still applicable, only fluctuations larger than the scale of the considered objects are included into the sampling process which naturally introduces a mass dependence of δc. We find that shear effects are predominant for smaller objects and at lower redshifts, i. e. the effect on δc is at or below the percent level for the ΛCDM model. For dark energy models we also find small but noticeable differences, similar to ΛCDM. The virial overdensity ΔV is nearly unaffected by the external shear. The now mass dependent δc is used to evaluate the mass function for different dark energy scenarios and afterwards to predict cluster number counts, which indicate that ignoring the shear contribution can lead to biases of the order of 1σ in the estimation of cosmological parameters like Ωm, σ8 or w.
Probing Strong-field General Relativity with Gravitational Waves
NASA Astrophysics Data System (ADS)
Pretorius, Frans
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
NASA Technical Reports Server (NTRS)
Peng, Huei; Torr, Douglas G.
1990-01-01
This paper investigates the effect of gravitational waves on a superconductor. It is found that the key properties of a superconductor, namely zero resistance and perfect diamagnetism, give rise to an important new effect, the presence of an induced electric field E in the interior of the superconductor. The E field reacts with the ions and superelectrons. It is argued that the induced E field might provide a significantly more sensitive means of detecting gravitational waves. It appears likely that existing resonant-mass superconducting antennas with L about 3m, Q about 10 to the 8th could be readily modified to detect E fields induced by GWs of dimensionless amplitude h about 10 to the -24th.
Gravitational lensing from compact bodies: Analytical results for strong and weak deflection limits
Amore, Paolo; Cervantes, Mayra; De Pace, Arturo; Fernandez, Francisco M.
2007-04-15
We develop a nonperturbative method that yields analytical expressions for the deflection angle of light in a general static and spherically symmetric metric. The method works by introducing into the problem an artificial parameter, called {delta}, and by performing an expansion in this parameter to a given order. The results obtained are analytical and nonperturbative because they do not correspond to a polynomial expression in the physical parameters. Already to first order in {delta} the analytical formulas obtained using our method provide at the same time accurate approximations both at large distances (weak deflection limit) and at distances close to the photon sphere (strong deflection limit). We have applied our technique to different metrics and verified that the error is at most 0.5% for all regimes. We have also proposed an alternative approach which provides simpler formulas, although with larger errors.
Weak-field limit of Kaluza-Klein models with spherical compactification: Experimental constraints
NASA Astrophysics Data System (ADS)
Chopovsky, Alexey; Eingorn, Maxim; Zhuk, Alexander
2012-03-01
We investigate the classical gravitational tests for the six-dimensional Kaluza-Klein model with spherical (of a radius a) compactification of the internal space. The model contains also a bare multidimensional cosmological constant Λ6. The matter, which corresponds to this ansatz, can be simulated by a perfect fluid with the vacuum equation of state in the external space and an arbitrary equation of state with the parameter ω1 in the internal space. For example, ω1=1 and ω1=2 correspond to the monopole two-forms and the Casimir effect, respectively. In the particular case Λ6=0, the parameter ω1 is also absent: ω1=0. In the weak-field approximation, we perturb the background ansatz by a pointlike mass. We demonstrate that in the case ω1>0 the perturbed metric coefficients have the Yukawa-type corrections with respect to the usual Newtonian gravitational potential. The inverse square law experiments restrict the parameters of the model: a/ω1≲6×10-3cm. Therefore, in the Solar System the parameterized post-Newtonian parameter γ is equal to 1 with very high accuracy. Thus, our model satisfies the gravitational experiments (the deflection of light and the time delay of radar echoes) at the same level of accuracy as general relativity. We demonstrate also that our background matter provides the stable compactification of the internal space in the case ω1>0. However, if ω1=0, then the parameterized post-Newtonian parameter γ=1/3, which strongly contradicts the observations.
Weak-field general relativistic dynamics and the Newtonian limit
NASA Astrophysics Data System (ADS)
Cooperstock, F. I.
2016-01-01
We show that the generally held view that the gravity of weak-field nonrelativistic-velocity sources being invariably almost equivalent to Newtonian gravity (NG) (the “Newtonian limit” approach) is in some instances misleading and in other cases incorrect. A particularly transparent example is provided by comparing the Newtonian and general relativistic analyses of a simple variant of van Stockum’s infinite rotating dust cylinder. We show that some very recent criticisms of our work that had been motivated by the Newtonian limit approach were incorrect and note that no specific errors in our work were found in the critique. In the process, we underline some problems that arise from inappropriate coordinate transformations. As further support for our methodology, we note that our weak-field general relativistic treatment of a model galaxy was vindicated recently by the observations of Xu et al. regarding our prediction that the Milky Way was 19-21 kpc in radius as opposed to the commonly held view that the radius was 15 kpc.
Effective field theory of weakly coupled inflationary models
Gwyn, Rhiannon; Palma, Gonzalo A.; Sakellariadou, Mairi; Sypsas, Spyros E-mail: gpalmaquilod@ing.uchile.cl E-mail: spyridon.sypsas@kcl.ac.uk
2013-04-01
The application of Effective Field Theory (EFT) methods to inflation has taken a central role in our current understanding of the very early universe. The EFT perspective has been particularly useful in analyzing the self-interactions determining the evolution of co-moving curvature perturbations (Goldstone boson modes) and their influence on low-energy observables. However, the standard EFT formalism, to lowest order in spacetime differential operators, does not provide the most general parametrization of a theory that remains weakly coupled throughout the entire low-energy regime. Here we study the EFT formulation by including spacetime differential operators implying a scale dependence of the Goldstone boson self-interactions and its dispersion relation. These operators are shown to arise naturally from the low-energy interaction of the Goldstone boson with heavy fields that have been integrated out. We find that the EFT then stays weakly coupled all the way up to the cutoff scale at which ultraviolet degrees of freedom become operative. This opens up a regime of new physics where the dispersion relation is dominated by a quadratic dependence on the momentum ω ∼ 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.
Influence of strong field vacuum polarization on gravitational-electromagnetic wave interaction
Forsberg, M.; Brodin, G.; Papadopoulos, D.
2010-07-15
The interaction between gravitational and electromagnetic waves in the presence of a static magnetic field is studied. The field strength of the static field is allowed to surpass the Schwinger critical field, such that the QED effects of vacuum polarization and magnetization are significant. Equations governing the interaction are derived and analyzed. It turns out that the energy conversion from gravitational to electromagnetic waves can be significantly altered due to the QED effects. The consequences of our results are discussed.
Variable Field Analytical Ultracentrifugation: II. Gravitational Sweep Sedimentation Velocity.
Ma, Jia; Zhao, Huaying; Sandmaier, Julia; Alexander Liddle, J; Schuck, Peter
2016-01-01
Sedimentation velocity (SV) analytical ultracentrifugation is a classical biophysical technique for the determination of the size-distribution of macromolecules, macromolecular complexes, and nanoparticles. SV has traditionally been carried out at a constant rotor speed, which limits the range of sedimentation coefficients that can be detected in a single experiment. Recently we have introduced methods to implement experiments with variable rotor speeds, in combination with variable field solutions to the Lamm equation, with the application to expedite the approach to sedimentation equilibrium. Here, we describe the use of variable-field sedimentation analysis to increase the size-range covered in SV experiments by ∼100-fold with a quasi-continuous increase of rotor speed during the experiment. Such a gravitational-sweep sedimentation approach has previously been shown to be very effective in the study of nanoparticles with large size ranges. In the past, diffusion processes were not accounted for, thereby posing a lower limit of particle sizes and limiting the accuracy of the size distribution. In this work, we combine variable field solutions to the Lamm equation with diffusion-deconvoluted sedimentation coefficient distributions c(s), which further extend the macromolecular size range that can be observed in a single SV experiment while maintaining accuracy and resolution. In this way, approximately five orders of magnitude of sedimentation coefficients, or eight orders of magnitude of particle mass, can be probed in a single experiment. This can be useful, for example, in the study of proteins forming large assemblies, as in fibrillation process or capsid self-assembly, in studies of the interaction between very dissimilar-sized macromolecular species, or in the study of broadly distributed nanoparticles.
The effects of weak magnetic fields on radical pairs.
Barnes, Frank S; Greenebaum, Ben
2015-01-01
It is proposed that radical concentrations can be modified by combinations of weak, steady and alternating magnetic fields that modify the population distribution of the nuclear and electronic spin state, the energy levels and the alignment of the magnetic moments of the components of the radical pairs. In low external magnetic fields, the electronic and nuclear angular momentum vectors are coupled by internal forces that outweigh the external fields' interactions and are characterized in the Hamiltonian by the total quantum number F. Radical pairs form with their unpaired electrons in singlet (S) or triplet (T) states with respect to each other. At frequencies corresponding to the energy separation between the various states in the external magnetic fields, transitions can occur that change the populations of both electron and nuclear states. In addition, the coupling between the nuclei, nuclei and electrons, and Zeeman shifts in the electron and nuclear energy levels can lead to transitions with resonances spanning frequencies from a few Hertz into the megahertz region. For nuclear energy levels with narrow absorption line widths, this can lead to amplitude and frequency windows. Changes in the pair recombination rates can change radical concentrations and modify biological processes. The overall conclusion is that the application of magnetic fields at frequencies ranging from a few Hertz to microwaves at the absorption frequencies observed in electron and nuclear resonance spectroscopy for radicals can lead to changes in free radical concentrations and have the potential to lead to biologically significant changes. PMID:25399679
A weak combined magnetic field changes root gravitropism
NASA Astrophysics Data System (ADS)
Kordyum, E. L.; Bogatina, N. I.; Kalinina, Ya. M.; Sheykina, N. V.
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 μ-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.
Gravitational field models for the earth (GEM 1 and 2)
NASA Technical Reports Server (NTRS)
Lerch, F. J.; Wagner, C. A.; Smith, D. E.; Andson, M. L.; Brownd, J. E.; Richardson, J. A.
1972-01-01
Two models of the earth's gravitational field have been computed at Goddard Space Flight Center. The first, Goddard Earth Model 1 (GEM 1), has been derived from satellite tracking data. The second, Goddard Earth Model 2 (GEM 2), has been derived from a combination of satellite tracking and surface gravimetric data. The geopotential models are represented in spherical harmonics complete to degree and order 16 for the combined solution and complete to degree and order 12 for the satellite solution. Both solutions include zonal terms to degree 21 and related satellite resonant coefficients to degree 22. The satellite data consisted primarily of optical data processed on 300 weekly orbital arcs for 25 close earth satellites. Surface gravity data were employed in the form of 5 deg x 5 deg mean free-air gravity anomalies providing about 70% world coverage. Station locations were obtained for 46 tracking sites by combining electronic, laser, and additional optical tracking data with the above satellite data. Analysis of the radial positions of these stations and a value of mean gravity on the geoid indicated a mean equatorial radius for the earth of about 6378145 meters. Results of geopotential tests on satellite data not used in the solution show that better agreement was obtained with the GEM 1 and GEM 2 models than with the 1969 Smithsonian Standard Earth 2 model.
Improved Gravitation Field Algorithm and Its Application in Hierarchical Clustering
Zheng, Ming; Sun, Ying; Liu, Gui-xia; Zhou, You; Zhou, Chun-guang
2012-01-01
Background Gravitation field algorithm (GFA) is a new optimization algorithm which is based on an imitation of natural phenomena. GFA can do well both for searching global minimum and multi-minima in computational biology. But GFA needs to be improved for increasing efficiency, and modified for applying to some discrete data problems in system biology. Method An improved GFA called IGFA was proposed in this paper. Two parts were improved in IGFA. The first one is the rule of random division, which is a reasonable strategy and makes running time shorter. The other one is rotation factor, which can improve the accuracy of IGFA. And to apply IGFA to the hierarchical clustering, the initial part and the movement operator were modified. Results Two kinds of experiments were used to test IGFA. And IGFA was applied to hierarchical clustering. The global minimum experiment was used with IGFA, GFA, GA (genetic algorithm) and SA (simulated annealing). Multi-minima experiment was used with IGFA and GFA. The two experiments results were compared with each other and proved the efficiency of IGFA. IGFA is better than GFA both in accuracy and running time. For the hierarchical clustering, IGFA is used to optimize the smallest distance of genes pairs, and the results were compared with GA and SA, singular-linkage clustering, UPGMA. The efficiency of IGFA is proved. PMID:23173043
Electrodynamics of Radiating Charges in a Gravitational Field
NASA Astrophysics Data System (ADS)
Grøn, Øyvind
The electrodynamics of a radiating charge and its electromagnetic field based upon the Lorentz-Abraham-Dirac (LAD) equation are discussed both with reference to an inertial reference frame and a uniformly accelerated reference frame. It is demonstrated that energy and momentum are conserved during runaway motion of a radiating charge and during free fall of a charge in a field of gravity. This does not mean that runaway motion is really happening. It may be an unphysical solution of the LAD equation of motion of a radiating charge due to the unrealistic point particle model of the charge upon which it is based. However it demonstrates the consistency of classical electrodynamics, including the LAD equation which is deduced from Maxwell's equations and the principle of energy-momentum conservation applied to a radiating charge and its electromagnetic field. The decisive role of the Schott energy in this connection is made clear and an answer is given to the question: What sort of energy is the Schott energy and where is it found? It is the part of the electromagnetic field energy which is proportional to (minus) the scalar product of the velocity and acceleration of a moving accelerated charged particle. In the case of the electromagnetic field of a point charge it is localized at the particle. This energy is negative if the acceleration is in the same direction as the velocity and positive if it is in the opposite direction. During runaway motion the Schott energy becomes more and more negative and in the case of a charged particle with finite extension, it is localized in a region with increasing extension surrounding the particle. The Schott energy provides the radiated energy of a freely falling charge. Also it is pointed out that a proton and a neutron fall with the same acceleration in a uniform gravitational field, although the proton radiates and the neutron does not. It is made clear that the question as to whether or not a charge radiates has a reference
Weak scattering of scalar and electromagnetic random fields
NASA Astrophysics Data System (ADS)
Tong, Zhisong
This dissertation encompasses several studies relating to the theory of weak potential scattering of scalar and electromagnetic random, wide-sense statistically stationary fields from various types of deterministic or random linear media. The proposed theory is largely based on the first Born approximation for potential scattering and on the angular spectrum representation of fields. The main focus of the scalar counterpart of the theory is made on calculation of the second-order statistics of scattered light fields in cases when the scattering medium consists of several types of discrete particles with deterministic or random potentials. It is shown that the knowledge of the correlation properties for the particles of the same and different types, described with the newly introduced pair-scattering matrix, is crucial for determining the spectral and coherence states of the scattered radiation. The approach based on the pair-scattering matrix is then used for solving an inverse problem of determining the location of an "alien" particle within the scattering collection of "normal" particles, from several measurements of the spectral density of scattered light. Weak scalar scattering of light from a particulate medium in the presence of optical turbulence existing between the scattering centers is then approached using the combination of the Born's theory for treating the light interaction with discrete particles and the Rytov's theory for light propagation in extended turbulent medium. It is demonstrated how the statistics of scattered radiation depend on scattering potentials of particles and the power spectra of the refractive index fluctuations of turbulence. This theory is of utmost importance for applications involving atmospheric and oceanic light transmission. The second part of the dissertation includes the theoretical procedure developed for predicting the second-order statistics of the electromagnetic random fields, such as polarization and linear momentum
NASA Astrophysics Data System (ADS)
Fukushima, Toshio
2016-07-01
Using the analytical expressions of the Newtonian gravitational potential and the associated acceleration vector for an infinitely thin uniform rectangular plate, we developed a method to compute the gravitational field of a general infinitely thin object without assuming its axial symmetry when its surface mass density is known at evenly spaced rectangular grid points. We utilized the method in evaluating the gravitational field of the H I gas, dust, red stars, and blue stars components of M74 from its THINGS, 2MASS, PDSS1, and GALEX data. The non-axisymmetric feature of M74 including an asymmetric spiral structure is seen from (i) the contour maps of the determined gravitational potential, (ii) the vector maps of the associated acceleration vector, and (iii) the cross-section views of the gravitational field and the surface mass density along different directions. An x-mark pattern in the gravitational field is detected at the core of M74 from the analysis of its dust and red stars components. Meanwhile, along the east-west direction in the central region of the angular size of 1 arcmin, the rotation curve derived from the radial component of the acceleration vector caused by the red stars component matches well with that observed by the VENGA project. Thus the method will be useful in studying the dynamics of particles and fluids near and inside spiral galaxies with known photometry data. Electronically available are the table of the determined gravitational fields of M74 on its galactic plane as well as the FORTRAN 90 programs to produce them.
Unifying Self-Consistent Field Theory for Weak Polyelectrolytes
NASA Astrophysics Data System (ADS)
Witte, Kevin; Won, You-Yeon
2008-03-01
A self-consistent field (SCF) theory for weak polyelectrolytes has been derived from a grand canonical partition function. The formalism accounts for the location and mixing of the charged and uncharged polymer species, treating the local (spatially dependent) charge fraction as a field variable with which to minimize the total free energy. This method of the derivation gives the resulting equations, especially those governing the local charge fraction, that are identical to the results obtained by Szleifer and coworkers (J. Polym. Sci. B Polym. Phys., 2006) who built upon the mean-field ``annealed'' free energy expression proposed by Raphael and Joanny (Europhys. Lett., 1990). However, we show that these results are further identical to the ``two-state'' model of Borukhov, Andelman and Orland (Eur. Phys. J. B, 1998), namely, the potential field due to the polymer charges with which the chains interact and the local charge fraction are shown to be exactly equal. This annealed model is derived by averaging the partition function with regard to the monomer charges. The charged and uncharged states are weighted by their probabilities which is, in our notation, the bulk charge fraction and one minus the bulk charge fraction, respectively. The utility of this theory is demonstrated by comparing its predictions against various experimental results from bulk potentiometric measurements and also from polyelectrolyte brush compression studies.
Pollux: a stable weak dipolar magnetic field but no planet?
NASA Astrophysics Data System (ADS)
Aurière, Michel; Konstantinova-Antova, Renada; Espagnet, Olivier; Petit, Pascal; Roudier, Thierry; Charbonnel, Corinne; Donati, Jean-François; Wade, Gregg A.
2014-08-01
Pollux is considered as an archetype of a giant star hosting a planet: its radial velocity (RV) presents sinusoidal variations with a period of about 590 d, which have been stable for more than 25 years. Using ESPaDOnS and Narval we have detected a weak (sub-gauss) magnetic field at the surface of Pollux and followed up its variations with Narval during 4.25 years, i.e. more than for two periods of the RV variations. The longitudinal magnetic field is found to vary with a sinusoidal behaviour with a period close to that of the RV variations and with a small shift in phase. We then performed a Zeeman Doppler imaging (ZDI) investigation from the Stokes V and Stokes I least-squares deconvolution (LSD) profiles. A rotational period is determined, which is consistent with the period of variations of the RV. The magnetic topology is found to be mainly poloidal and this component almost purely dipolar. The mean strength of the surface magnetic field is about 0.7 G. As an alternative to the scenario in which Pollux hosts a close-in exoplanet, we suggest that the magnetic dipole of Pollux can be associated with two temperature and macroturbulent velocity spots which could be sufficient to produce the RV variations. We finally investigate the scenarii of the origin of the magnetic field which could explain the observed properties of Pollux.
Proton-Proton Weak Capture in Chiral Effective Field Theory
Marcucci, Laura Elisa; Schiavilla, Rocco; Viviani, MIchele
2013-05-01
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.
Proton-proton weak capture in chiral effective field theory.
Marcucci, L E; Schiavilla, R; Viviani, M
2013-05-10
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 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 β 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±0.006)×10(-23) MeV fm(2), with a P-wave contribution of 0.020×10(-23) MeV fm(2). The theoretical uncertainty is due to the fitting procedure of the low-energy constants and to the cutoff dependence.
Proton-proton weak capture in chiral effective field theory.
Marcucci, L E; Schiavilla, R; Viviani, M
2013-05-10
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 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 β 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±0.006)×10(-23) MeV fm(2), with a P-wave contribution of 0.020×10(-23) MeV fm(2). The theoretical uncertainty is due to the fitting procedure of the low-energy constants and to the cutoff dependence. PMID:23705703
NASA Astrophysics Data System (ADS)
Rivera, Susana
Throughout the last century, since the last decades of the XIX century, until present day, there had been many attempts to achieve the unification of the Forces of Nature. First unification was done by James Clerk Maxwell, with his Electromagnetic Theory. Then Max Plank developed his Quantum Theory. In 1905, Albert Einstein gave birth to the Special Relativity Theory, and in 1916 he came out with his General Relativity Theory. He noticed that there was an evident parallelism between the Gravitational Force, and the Electromagnetic Force. So, he tried to unify these forces of Nature. But Quantum Theory interposed on his way. On the 1940’s it had been developed the Quantum Electrodynamics (QED), and with it, the unified field theory had an arise interest. On the 60’s and 70’s there was developed the Quantum Chromodynamics (QCD). Along with these theories came the discovery of the strong interaction force and weak interaction force. And though there had been many attempts to unify all these forces of the nature, it could only be achieved the Unification of strong interaction, weak interaction and Electromagnetic Force. On the late 80”s and throughout the last two decades, theories such as “super-string theory”, “or the “M-theory”, among others, groups of Scientists, had been doing grand efforts and finally they came out with the unification of the forces of nature, being the only limitation the use of more than 11 dimensions. Using an ingenious mathematical tool known as the super symmetries, based on the Kaluza - Klein work, they achieve this goal. The strings of these theories are in the rank of 10-33 m. Which make them undetectable. There are many other string theories. The GEUFT theory is based on the existence of concentrated energy lines, which vibrates, expands and contracts, submitting and absorbing energy, matter and antimatter, and which yields a determined geometry, that gives as a result the formation of stars, galaxies, nebulae, clusters
Mapping Weak Crustal Magnetic Fields on Mars with Electron Reflectometry
NASA Technical Reports Server (NTRS)
Mitchell, D. L.; Lillis, R.; Lin, R. P.; Connerney, J. E. P.; Acuna, M. H.
2004-01-01
One of the great surprises of the Mars Global Surveyor (MGS) mission was the discovery of intensely magnetized crust. These magnetic sources are at least ten times stronger than their terrestrial counterparts, probably requiring large volumes of coherently magnetized material, very strong remanence, or both. Perhaps the most intriguing aspect of these fields is their large scale coherence and organization into east-west stripes thousands of kilometers long. The anomalies were almost certainly created by thermoremanent magnetization (TRM) in the presence of a strong Martian dynamo. With few exceptions, the crustal fields are associated with the oldest terrain on Mars. Much of the northern lowlands appears to be non-magnetic, except for the relatively weak north polar anomalies and a few sources adja-cent to the dichotomy boundary, which appear to be associated with strongly magnetized crust south of the boundary. There is clear evidence for impact demagnetization of the Hellas, Argyre, and Isidis basins. Thus, Mars' crustal magnetic fields are among the oldest preserved geologic features on the planet.
CFHTLenS: the relation between galaxy dark matter haloes and baryons from weak gravitational lensing
NASA Astrophysics Data System (ADS)
Velander, Malin; van Uitert, Edo; Hoekstra, Henk; Coupon, Jean; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Kitching, Thomas D.; Mellier, Yannick; Miller, Lance; Van Waerbeke, Ludovic; Bonnett, Christopher; Fu, Liping; Giodini, Stefania; Hudson, Michael J.; Kuijken, Konrad; Rowe, Barnaby; Schrabback, Tim; Semboloni, Elisabetta
2014-01-01
We present a study of the relation between dark matter halo mass and the baryonic content of their host galaxies, quantified through galaxy luminosity and stellar mass. Our investigation uses 154 deg2 of Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) lensing and photometric data, obtained from the CFHT Legacy Survey. To interpret the weak lensing signal around our galaxies, we employ a galaxy-galaxy lensing halo model which allows us to constrain the halo mass and the satellite fraction. Our analysis is limited to lenses at redshifts between 0.2 and 0.4, split into a red and a blue sample. We express the relationship between dark matter halo mass and baryonic observable as a power law with pivot points of 10^{11} h_{70}^{-2} L_{{⊙}} and 2× 10^{11} h_{70}^{-2} M_{{⊙}} for luminosity and stellar mass, respectively. For the luminosity-halo mass relation, we find a slope of 1.32 ± 0.06 and a normalization of 1.19^{+0.06}_{-0.07}× 10^{13} h_{70}^{-1} M_{{⊙}} for red galaxies, while for blue galaxies the best-fitting slope is 1.09^{+0.20}_{-0.13} and the normalization is 0.18^{+0.04}_{-0.05}× 10^{13} h_{70}^{-1} M_{{⊙}}. Similarly, we find a best-fitting slope of 1.36^{+0.06}_{-0.07} and a normalization of 1.43^{+0.11}_{-0.08}× 10^{13} h_{70}^{-1} M_{{⊙}} for the stellar mass-halo mass relation of red galaxies, while for blue galaxies the corresponding values are 0.98^{+0.08}_{-0.07} and 0.84^{+0.20}_{-0.16}× 10^{13} h_{70}^{-1} M_{{⊙ }}. All numbers convey the 68 per cent confidence limit. For red lenses, the fraction which are satellites inside a larger halo tends to decrease with luminosity and stellar mass, with the sample being nearly all satellites for a stellar mass of 2× 109 h_{70}^{-2} M_{{⊙}}. The satellite fractions are generally close to zero for blue lenses, irrespective of luminosity or stellar mass. This, together with the shallower relation between halo mass and baryonic tracer, is a direct confirmation from galaxy
Taylor, James E.; Massey, Richard J.; Leauthaud, Alexie; Tanaka, Masayuki; George, Matthew R.; Rhodes, Jason; Ellis, Richard; Scoville, Nick; Kitching, Thomas D.; Capak, Peter; Finoguenov, Alexis; Ilbert, Olivier; Kneib, Jean-Paul; Jullo, Eric; Koekemoer, Anton M.
2012-04-20
Gravitational lensing can provide pure geometric tests of the structure of spacetime, for instance by determining empirically the angular diameter distance-redshift relation. This geometric test has been demonstrated several times using massive clusters which produce a large lensing signal. In this case, matter at a single redshift dominates the lensing signal, so the analysis is straightforward. It is less clear how weaker signals from multiple sources at different redshifts can be stacked to demonstrate the geometric dependence. We introduce a simple measure of relative shear which for flat cosmologies separates the effect of lens and source positions into multiplicative terms, allowing signals from many different source-lens pairs to be combined. Applying this technique to a sample of groups and low-mass clusters in the COSMOS survey, we detect a clear variation of shear with distance behind the lens. This represents the first detection of the geometric effect using weak lensing by multiple, low-mass groups. The variation of distance with redshift is measured with sufficient precision to constrain the equation of state of the universe under the assumption of flatness, equivalent to a detection of a dark energy component {Omega}{sub X} at greater than 99% confidence for an equation-of-state parameter -2.5 {<=} w {<=} -0.1. For the case w = -1, we find a value for the cosmological constant density parameter {Omega}{sub {Lambda}} = 0.85{sup +0.044}{sub -}0{sub .19} (68% CL) and detect cosmic acceleration (q{sub 0} < 0) at the 98% CL. We consider the systematic uncertainties associated with this technique and discuss the prospects for applying it in forthcoming weak-lensing surveys.
Self-assembled aggregates in the gravitational field: Growth and nematic order
NASA Astrophysics Data System (ADS)
Baulin, Vladimir A.
2003-08-01
The influence of the gravitational field on the reversible process of assembly and disassembly of linear aggregates is the focus of this paper. Even the earth gravitational field can affect the equilibrium properties of heavy biological aggregates such as microtubules or actin filaments. The gravity gives rise to the concentration gradient which results in the distribution of aggregates of different lengths with height. Strong enough gravitational field induces the overall growth of the aggregates. The gravitational field facilitates the isotropic to nematic phase transition reflecting in a broader transition region. Coexisting phases have notedly different length distributions and the phase transition represents the interplay between the growth in the isotropic phase and the precipitation into nematic phase. The fields in an ultracentrifuge can only reinforce the effect of gravity, so the present description can be applied to a wider range of systems.
Light deflection and time delay in the solar gravitational field
Richter, G.W.
1983-01-01
The second nonvanishing order of contribution to light deflection and time delay in the solar gravitational field is studied for a realistic solar model and for a wide range of metric theories of gravity. It is shown that the second-order effects arise at order (GM/c/sup 2/R)/sup 2/ identical to epsilon/sup 4/. To calculate these effects, every component of the solar metric must be known to order epsilon/sup 4/. The parametrized post-Newtonian (PPN) metric provides most of those components. However, some extension of the PPN metric is required. This extension leads to the parametrized post-linear (PPL) metric, which is used in all calculations. To study light deflection to order epsilon/sup 4/ requires that the orbits of scattered photons be known to that order. These orbits are solved for, first in the equatorial plane and then in general, and are used to determine the deflection as measured by an observer at rest with respect to the sun. In the equatorial plane there is only a radial component to this deflection. In general, there is another component orthogonal to the radial plane, but knowledge of this component is not necessary to determine the total deflection to order epsilon/sup 4/. The total second-order deflection can be as large as 300..mu.. arcsec (for deflection by Jupiter). Measurements of some second-order terms are within the astrometric capabilities of experiments proposed for the 1990's. The time delay in the round-trip travel time of a radar beam reflected from a planet is due to the variable coordinate speed of the light signal and to the bending of the beam path. The delay is calculated to order epsilon/sup 4/. It is shown that the beam-bending gives a second-order contribution as large as the present-day uncertainties in time delay experiments with the Viking spacecraft.
Kinetic simulation of rarefied and weakly ionized hypersonic flow fields
NASA Astrophysics Data System (ADS)
Farbar, Erin D.
When a vehicle enters the Earth's atmosphere at the very large velocities associated with Lunar and Mars return, a strong bow shock is formed in front of the vehicle. The shock heats the air to very high temperatures, causing collisions that are sufficiently energetic to produce ionized particles. As a result, a weakly ionized plasma is formed in the region between the bow shock and the vehicle surface. The presence of this plasma impedes the transport of radio frequency waves to the vehicle, causing the phenomenon known as "communications black out". The plasma also interacts with the neutral particles in the flow field, and contributes to the heat flux at the vehicle surface. Since it is difficult to characterize these flow fields using flight or ground based experiments, computational tools play an important role in the design of reentry vehicles. It is important to include the physical phenomena associated with the presence of the plasma in the computational analysis of the flow fields about these vehicles. Physical models for the plasma phenomena are investigated using a state of the art, Direct Simulation Monte Carlo (DSMC) code. Models for collisions between charged particles, plasma chemistry, and the self-induced electric field that currently exist in the literature are implemented. Using these baseline models, steady state flow field solutions are computed for the FIRE II reentry vehicle at two different trajectory points. The accuracy of each baseline plasma model is assessed in a systematic fashion, using one flight condition of the FIRE II vehicle as the test case. Experimental collision cross section data is implemented to model collisions of electrons with neutral particles. Theoretical and experimental reaction cross section data are implemented to model chemical reactions that involve electron impact, and an associative ionization reaction. One-dimensional Particle-In-Cell (PIC) routines are developed and coupled to the DSMC code, to assess the
New exact solution for the exterior gravitational field of a charged spinning mass
Chamorro, A. ); Manko, V.S. ); Denisova, T.E. )
1991-11-15
An exact asymptotically flat solution of the Einstein-Maxwell equations describing the exterior gravitational field of a charged rotating axisymmetric mass possessing an arbitrary set of multipole moments is presented explicitly.
New exact solution for the exterior gravitational field of a spinning mass
Manko, V.S. Department of Theoretical Physics, Peoples' Friendship University, Ordzhonikidze Street 3, Moscow 117198, U.S.S.R. )
1990-04-02
An exact asymptotically flat solution of the vacuum Einstein equations representing the exterior gravitational field of a stationary axisymmetric mass with an arbitrary mass-multipole structure is presented.
Gederim, V V; Sokolovskiĭ, V V; Gorshkov, E S; Shapovalov, S N; Troshichev, O A
2001-01-01
Monitoring the content of lymphocytes and nucleated neutrophils (observation period 10.5 months) and the determination of the values of leucocytes coefficient and erythrocyte sedimentation rate in chronic patients revealed rhythms of oscillations of these parameters (from 3-5 to 33 days). The coincidence of these rhythms with the rhythms of variations of gravitational field indicates that gravitational field affects the quantitative blood cell composition and the rheological properties of blood.
Electromagnetic Waves in a Uniform Gravitational Field and Planck's Postulate
ERIC Educational Resources Information Center
Acedo, Luis; Tung, Michael M.
2012-01-01
The gravitational redshift forms the central part of the majority of the classical tests for the general theory of relativity. It could be successfully checked even in laboratory experiments on the earth's surface. The standard derivation of this effect is based on the distortion of the local structure of spacetime induced by large masses. The…
Deep HST imaging of distant weak radio and field galaxies
NASA Technical Reports Server (NTRS)
Windhorst, R. A.; Gordon, J. M.; Pascarelle, S. M.; Schmidtke, P. C.; Keel, W. C.; Burkey, J. M.; Dunlop, J. S.
1994-01-01
We present deep Hubble Space Telescope (HST) Wide-Field Camera (WFC) V- and I-band images of three distant weak radio galaxies with z = 0.311-2.390 and seven field galaxies with z = 0.131-0.58. The images were deconvolved with both the Lucy and multiresolution CLEAN methods, which yield a restoring Full Width at Half Maximum (FWHM) of less than or equal to 0.2 sec, (nearly) preserve photons and signal-to-noise ratio at low spatial frequencies, and produce consistent light profiles down to our 2 sigma surface brightness sensitivity limit of V approximately 27.2 and I approximately 25.9 mag/sq arcsec. Multi-component image modeling was used to provide deconvolution-independent estimates of structural parameters for symmetric galaxies. We present 12-band (m(sub 2750) UBVRIgriJHK) photometry for a subset of the galaxies and bootstrap the unknown FOC/48 zero point at 2750 A in three independent ways (yielding m(sub 2750) = 21.34 +/- 0.09 mag for 1.0 e(-)/s). Two radio galaxies with z = 0.311 and 0.528, as well as one field galaxy with z = 0.58, have the colors and spectra of early-type galaxies, and a(exp 1/4)-like light profiles in the HST images. The two at z greater than 0.5 have little or no color gradients in V - I and are likely giant ellipticals, while the z = 0.311 radio galaxy has a dim exponential disk and is likely an S0. Six of the seven field galaxies have light profiles that indicate (small) inner bulges following a(exp 1/4) laws and outer exponential disks, both with little or no color gradients. These are (early-type) spiral galaxies with z = 0.131-0.528. About half have faint companions or bars. One shows lumpy structure, possibly a merger. The compact narrow-line galaxy 53W002 at z = 2.390 has less than or = 30% +/- 10% of its HST V and I flux in the central kiloparsec (due to its weak Active Galactic Nucleus (AGN)). Most of its light (V approximately equal to 23.3) occurs in a symmetric envelope with a regular a(exp 1/4)-like profile of effective
Field theory and weak Euler-Lagrange equation for classical particle-field systems.
Qin, Hong; Burby, Joshua W; Davidson, Ronald C
2014-10-01
It is commonly believed as a fundamental principle that energy-momentum conservation of a physical system is the result of space-time symmetry. However, for classical particle-field systems, e.g., charged particles interacting through self-consistent electromagnetic or electrostatic fields, such a connection has only been cautiously suggested. It has not been formally established. The difficulty is due to the fact that the dynamics of particles and the electromagnetic fields reside on different manifolds. We show how to overcome this difficulty and establish the connection by generalizing the Euler-Lagrange equation, the central component of a field theory, to a so-called weak form. The weak Euler-Lagrange equation induces a new type of flux, called the weak Euler-Lagrange current, which enters conservation laws. Using field theory together with the weak Euler-Lagrange equation developed here, energy-momentum conservation laws that are difficult to find otherwise can be systematically derived from the underlying space-time symmetry.
Cosmological equivalence principle and the weak-field limit
Wiltshire, David L.
2008-10-15
The strong equivalence principle is extended in application to averaged dynamical fields in cosmology to include the role of the average density in the determination of inertial frames. The resulting cosmological equivalence principle is applied to the problem of synchronization of clocks in the observed universe. Once density perturbations grow to give density contrasts of order 1 on scales of tens of megaparsecs, the integrated deceleration of the local background regions of voids relative to galaxies must be accounted for in the relative synchronization of clocks of ideal observers who measure an isotropic cosmic microwave background. The relative deceleration of the background can be expected to represent a scale in which weak-field Newtonian dynamics should be modified to account for dynamical gradients in the Ricci scalar curvature of space. This acceleration scale is estimated using the best-fit nonlinear bubble model of the universe with backreaction. At redshifts z < or approx. 0.25 the scale is found to coincide with the empirical acceleration scale of modified Newtonian dynamics. At larger redshifts the scale varies in a manner which is likely to be important for understanding dynamics of galaxy clusters, and structure formation. Although the relative deceleration, typically of order 10{sup -10} ms{sup -2}, is small, when integrated over the lifetime of the universe it amounts to an accumulated relative difference of 38% in the rate of average clocks in galaxies as compared to volume-average clocks in the emptiness of voids. A number of foundational aspects of the cosmological equivalence principle are also discussed, including its relation to Mach's principle, the Weyl curvature hypothesis, and the initial conditions of the universe.
NASA Astrophysics Data System (ADS)
Wang, Wenting; White, Simon D. M.; Mandelbaum, Rachel; Henriques, Bruno; Anderson, Michael E.; Han, Jiaxin
2016-03-01
We use weak gravitational lensing to measure mean mass profiles around locally brightest galaxies (LBGs). These are selected from the Seventh Data Release of the Sloan Digital Sky Survey spectroscopic and photometric catalogues to be brighter than any neighbour projected within 1.0 Mpc and differing in redshift by <1000 km s-1. Most (>83 per cent) are expected to be the central galaxies of their dark matter haloes. Previous stacking analyses have used this LBG sample to measure mean Sunyaev-Zeldovich flux and mean X-ray luminosity as a function of LBG stellar mass. In both cases, a simulation of the formation of the galaxy population was used to estimate effective halo mass for LBGs of given stellar mass, allowing the derivation of scaling relations between the gas properties of haloes and their mass. By comparing results from a variety of simulations to our lensing data, we show that this procedure has significant model dependence reflecting: (i) the failure of any given simulation to reproduce observed galaxy abundances exactly; (ii) a dependence on the cosmology underlying the simulation; and (iii) a dependence on the details of how galaxies populate haloes. We use our lensing results to recalibrate the scaling relations, eliminating most of this model dependence and explicitly accounting both for residual modelling uncertainties and for observational uncertainties in the lensing results. The resulting scaling relations link the mean gas properties of dark haloes to their mass over an unprecedentedly wide range, 1012.5 < M500/M⊙ < 1014.5, and should fairly and robustly represent the full halo population.
NASA Astrophysics Data System (ADS)
Ghosh, Shaon; Bloemen, Steven; Nelemans, Gijs; Groot, Paul J.; Price, Larry R.
2016-08-01
Aims: Binary neutron stars are among the most promising candidates for joint gravitational-wave and electromagnetic astronomy. The goal of this work is to investigate various observing strategies that telescopes with wide field of view might incorporate while searching for electromagnetic counterparts of gravitational-wave triggers. Methods: We examined various strategies of scanning the gravitational-wave sky localizations on the mock 2015-16 gravitational-wave events. First, we studied the performance of the sky coverage using a naive tiling system that completely covers a given confidence interval contour using a fixed grid. Then we propose the ranked-tiling strategy where we sample the localization in discrete two-dimensional intervals that are equivalent to the telescope's field of view and rank them based on their sample localizations. We then introduce an optimization of the grid by iterative sliding of the tiles. Next, we conducted tests for all the methods on a large sample of sky localizations that are expected in the first two years of operation of the Laser interferometer Gravitational-wave Observatory (LIGO) and Virgo detectors. We investigated the performance of the ranked-tiling strategy for telescope arrays and compared their performance against monolithic telescopes with a giant field of view. Finally, we studied the ability of optical counterpart detection by various types of telescopes. Results: Our analysis reveals that the ranked-tiling strategy improves the localization coverage over the contour-covering method. The improvement is more significant for telescopes with larger fields of view. We also find that while optimizing the position of the tiles significantly improves the coverage compared to contour-covering tiles. For ranked-tiles the same procedure leads to negligible improvement in the coverage of the sky localizations. We observed that distributing the field of view of the telescopes into arrays of multiple telescopes significantly
NASA Astrophysics Data System (ADS)
Zhao, Xiao-Dong; Qian, Zheng
2015-10-01
The accurate measurement of dynamic characteristics in weak magnetic sensors is urgently required as a greater number of applications for these devices are found. In this paper, a novel weak pulsed magnetic field system is presented. The underlying principle is to drive a permanent magnet passing another magnet rapidly, producing a pulsed weak magnetic field. The magnitude of the field can be adjusted by changing the velocity and distance between the two magnets. The standard value of the pulsed dynamic magnetic field can be traced back to the accurate measurement of time, displacement, and static magnetic field. In this study a detailed procedure for producing a pulse magnetic field system using the above method is outlined after which a theoretical analysis of the permanent magnet movement is discussed. Using the described apparatus a milli-second level pulse-width with a milli-Tesla magnetic field magnitude is used to study the dynamic characteristics of a giant magnetoresistance sensor. We conclude by suggesting possible improvements to the described apparatus.
Biological effects due to weak magnetic fields on plants
NASA Astrophysics Data System (ADS)
Belyavskaya, N.
In the evolution process, living organisms have experienced the action of the Earth's magnetic field (MF) that is a natural component of our environment. It is known that a galactic MF induction does not exceed 0.1 nT, since investigations of weak magnetic field (WMF) effects on biological systems have attracted attention of biologists due to planning long-term space flights to other planets where the magnetizing force is near 10-5 Oe. However, the role of WMF and its influence on organisms' functioning are still insufficiently investigated. A large number of experiments with seedlings of different plant species placed in WMF has found that the growth of their primary roots is inhibited during the early terms of germination in comparison with control. The proliferation activity and cell reproduction are reduced in meristem of plant roots under WMF application. The prolongation of total cell reproductive cycle is registered due to the expansion of G phase in1 different plant species as well as of G phase in flax and lentil roots along with2 relative stability of time parameters of other phases of cell cycle. In plant cells exposed to WMF, the decrease in functional activity of genome at early prereplicate period is shown. WMF causes the intensification in the processes of proteins' synthesis and break-up in plant roots. Qualitative and quantitative changes in protein spectrum in growing and differentiated cells of plant roots exposed to WMF are revealed. At ultrastructural level, there are observed such ultrastructural peculiarities as changes in distribution of condensed chromatin and nucleolus compactization in nuclei, noticeable accumulation of lipid bodies, development of a lytic compartment (vacuoles, cytosegresomes and paramural bodies), and reduction of phytoferritin in plastids in meristem cells of pea roots exposed to WMF. Mitochondria are the most sensitive organelle to WMF application: their size and relative volume in cells increase, matrix is electron
Theory of monodispersion of liquids by gravitational and electric fields
Zemskov, A.A.; Shiryaeva, S.O.; Grigor'ev, A.I. )
1993-06-01
It is shown that the drop regime of the electrostatic monodispersion of liquid from the meniscus on the tip of the capillary through which the liquid is supplied takes place under the joint action of equally directed gravitational and electric forces with the gravitational forces playing a decisive role. With the increase of electric forces, with other conditions equal, the size of torn away drops decreases, while their charges and the frequency of emission increase. When the contribution of gravitational forces to the detachment of the drop from the tip of the capillary tube becomes negligible as compared to electric forces, the transition to the harmonic regime of the monodispersion of the fluid occurs. The parameters of drops simulated in this regime, as well as the existence of different zones of harmonic monodispersion, are subject to adequate physical theoretical analysis within the framework of the thermodynamic approach on the basis of the principle of the minimum scattering of energy in the stationary nonequilibrium process.
NASA Astrophysics Data System (ADS)
Linet, B.; Teyssandier, P.
2016-02-01
We present a complete analysis of the light rays within the linearized, weak-field approximation of a Schwarzschild-like metric describing the gravitational field of an isolated, spherically symmetric body. We prove in this context the existence of two time transfer functions and we obtain these functions in an exact closed-form. We are led to distinguish two regimes. In the first regime, the two time transfer functions correspond to rays which are confined in regions of spacetime where the weak-field approximation is valid. Such a regime occurs in gravitational lensing configurations with double images of a given source. We find the general expressions of the angular separation and the difference in light travel time between the two images. In the second regime, there exists only one time transfer function corresponding to a light ray remaining in a region of weak field. Performing a Taylor expansion of this function with respect to the gravitational constant, we obtain the Shapiro time delay completed by a series of so-called "enhanced terms." The enhanced terms beyond the third order are new.
Overconnections and the energy-tensors of gauge and gravitational fields
NASA Astrophysics Data System (ADS)
Canarutto, Daniel
2016-08-01
A geometric construction for obtaining a prolongation of a connection to a connection of a bundle of connections is presented. This determines a natural extension of the notion of canonical energy-tensor which suits gauge and gravitational fields, and shares the main properties of the energy-tensor of a matter field in the jet space formulation of Lagrangian field theory, in particular with regards to symmetries of the Poincaré-Cartan form. Accordingly, the joint energy-tensor for interacting matter and gauge fields turns out to be a natural geometric object, whose definition needs no auxiliary structures. Various topics related to energy-tensors, symmetries and the Einstein equations in a theory with interacting matter, gauge and gravitational fields can be viewed under a clarifying light. Finally, the symmetry determined by the "Komar superpotential" is expressed as a symmetry of the gravitational Poincaré-Cartan form.
Physics of Gravitational Interaction: Geometry of Space or Quantum Field in Space
NASA Astrophysics Data System (ADS)
Baryshev, Yurij
2006-03-01
Thirring-Feynman's tensor field approach to gravitation opens new understanding on the physics of gravitational interaction and stimulates novel experiments on the nature of gravity. According to Field Gravity, the universal gravity force is caused by exchange of gravitons - the quanta of gravity field. Energy of this field is well-defined and excludes the singularity. All classical relativistic effects are the same as in General Relativity. The intrinsic scalar (spin 0) part of gravity field corresponds to ``antigravity'' and only together with the pure tensor (spin 2) part gives the usual Newtonian force. Laboratory and astrophysical experiments which may test the predictions of FG, will be performed in near future. In particular, observations at gravity observatories with bar and interferometric detectors, like Explorer, Nautilus, LIGO and VIRGO, will check the predicted scalar gravitational waves from supernova explosions. New types of cosmological models in Minkowski space are possible too.
Escape of gravitational radiation from the field of massive bodies
NASA Technical Reports Server (NTRS)
Price, Richard H.; Pullin, Jorge; Kundu, Prasun K.
1993-01-01
We consider a compact source of gravitational waves of frequency omega in or near a massive spherically symmetric distribution of matter or a black hole. Recent calculations have led to apparently contradictory results for the influence of the massive body on the propagation of the waves. We show here that the results are in fact consistent and in agreement with the 'standard' viewpoint in which the high-frequency compact source produces the radiation as if in a flat background, and the background curvature affects the propagation of these waves.
Was Newton right? A search for non-Newtonian behavior of weak-field gravity
NASA Astrophysics Data System (ADS)
Boynton, Paul; Moore, Michael; Newman, Riley; Berg, Eric; Bonicalzi, Ricco; McKenney, Keven
2014-06-01
Empirical tests of Einstein's metric theory of gravitation, even in the non-relativistic, weak-field limit, could play an important role in judging theory-driven extensions of the current Standard Model of fundamental interactions. Guided by Galileo's work and his own experiments, Newton formulated a theory of gravity in which the force of attraction between two bodies is independent of composition and proportional to the inertia of each, thereby transparently satisfying Galileo's empirically informed conjecture regarding the Universality of Free Fall. Similarly, Einstein honored the manifest success of Newton's theory by assuring that the linearized equations of GTR matched the Newtonian formalism under "classical" conditions. Each of these steps, however, was explicitly an approximation raised to the status of principle. Perhaps, at some level, Newtonian gravity does not accurately describe the physical interaction between uncharged, unmagnetized, macroscopic bits of ordinary matter. What if Newton were wrong? Detecting any significant deviation from Newtonian behavior, no matter how small, could provide new insights and possibly reveal new physics. In the context of physics as an empirical science, for us this yet unanswered question constitutes sufficient motivation to attempt precision measurements of the kind described here. In this paper we report the current status of a project to search for violation of the Newtonian inverse square law of gravity.
Generalized crossing states in the interacting case: The uniform gravitational field
Villanueva, Anthony D.; Galapon, Eric A.
2010-11-15
We reconsider Baute et al.'s free crossing states [Phys. Rev. A 61, 022118 (2000)] and show that if we require a generalization in the interacting case that goes in complete parallel with the free-particle case, then this generalized crossing state cannot be arbitrary but is determined by the null space of the particle's quantum time-of-arrival operator. Nonetheless, the free crossing states appear as the leading term in the asymptotic expansion of our generalized crossing state in the limit of large momentum. We then examine the quantum time-of-arrival problem of a spinless particle in a uniform gravitational field. Mass-dependent time-of-arrival probability distributions emerge, signifying quantum departures from the weak equivalence principle. However, in the classical limit of large mass and vanishing uncertainty in position, the mass dependence of the quantum time-of-arrival distribution becomes exponentially small and the mean quantum time of arrival reduces to the classical time of arrival.
Spheroidal models of the exterior gravitational field of Asteroids Bennu and Castalia
NASA Astrophysics Data System (ADS)
Sebera, Josef; Bezděk, Aleš; Pešek, Ivan; Henych, Tomáš
2016-07-01
Gravitational field of small bodies can be modeled e.g. with mascons, a polyhedral model or in terms of harmonic functions. If the shape of a body is close to the spheroid, it is advantageous to employ the spheroidal basis functions for expressing the gravitational field. Spheroidal harmonic models, similarly to the spherical ones, may be used in navigation and geophysical tasks. We focus on modeling the exterior gravitational field of oblate-like Asteroid (101955) Bennu and prolate-like Asteroid (4769) Castalia with spheroidal harmonics. Using the Gauss-Legendre quadrature and the spheroidal basis functions, we converted the gravitational potential of a particular polyhedral model of a constant density into the spheroidal harmonics. The results consist of (i) spheroidal harmonic coefficients of the exterior gravitational field for the Asteroids Bennu and Castalia, (ii) spherical harmonic coefficients for Bennu, and (iii) the first and second-order Cartesian derivatives in the local spheroidal South-East-Up frame for both bodies. The spheroidal harmonics offer biaxial flexibility (compared with spherical harmonics) and low computational costs that allow high-degree expansions (compared with ellipsoidal harmonics). The obtained spheroidal models for Bennu and Castalia represent the exterior gravitational field valid on and outside the Brillouin spheroid but they can be used even under this surface. For Bennu, 5 m above the surface the agreement with point-wise integration was 1% or less, while it was about 10% for Castalia due to its more irregular shape. As the shape models may produce very high frequencies, it was crucial to use higher maximum degree to reduce the aliasing. We have used the maximum degree 360 to achieve 9-10 common digits (in RMS) when reconstructing the input (the gravitational potential) from the spheroidal coefficients. The physically meaningful maximum degree may be lower (≪ 360) but its particular value depends on the distance and/or on the
Palenzuela, Carlos; Lehner, Luis; Yoshida, Shin
2010-04-15
In addition to producing loud gravitational waves, the dynamics of a binary black hole system could induce emission of electromagnetic radiation by affecting the behavior of plasmas and electromagnetic fields in their vicinity. We study how the electromagnetic fields are affected by a pair of orbiting black holes through the merger. In particular, we show how the binary's dynamics induce a variability in possible electromagnetically induced emissions as well as an enhancement of electromagnetic fields during the late-merge and merger epochs. These time dependent features will likely leave their imprint in processes generating detectable emissions and can be exploited in the detection of electromagnetic counterparts of gravitational waves.
Short guide to direct gravitational field modelling with Hotine's equations
NASA Astrophysics Data System (ADS)
Sebera, Josef; Wagner, Carl A.; Bezděk, Aleš; Klokočník, Jaroslav
2013-03-01
This paper presents a unified approach to the least squares spherical harmonic analysis of the acceleration vector and Eötvös tensor (gravitational gradients) in an arbitrary orientation. The Jacobian matrices are based on Hotine's equations that hold in the Earth-fixed Cartesian frame and do not need any derivatives of the associated Legendre functions. The implementation was confirmed through closed-loop tests in which the simulated input is inverted in the least square sense using the rotated Hotine's equations. The precision achieved is at the level of rounding error with RMS about 10^{-12}{-}10^{-14} m in terms of the height anomaly. The second validation of the linear model is done with help from the standard ellipsoidal correction for the gravity disturbance that can be computed with an analytic expression as well as with the rotated equations. Although the analytic expression for this correction is only of a limited accuracy at the submillimeter level, it was used for an independent validation. Finally, the equivalent of the ellipsoidal correction, called the effect of the normal, has been numerically obtained also for other gravitational functionals and some of their combinations. Most of the numerical investigations are provided up to spherical harmonic degree 70, with degree 80 for the computation time comparison using real GRACE data. The relevant Matlab source codes for the design matrices are provided.
NASA Astrophysics Data System (ADS)
Roy, S. R.; Banerjee, S. K.
1992-11-01
A homogeneous Bianchi type VIh cosmological model filled with perfect fluid, null electromagnetic field and streaming neutrinos is obtained for which the free gravitational field is of the electric type. The barotropic equation of statep = (γ-1)ɛ is imposed in the particular case of Bianchi VI0 string models. Various physical and kinematical properties of the models are discussed.
Mapping Gravitational and Magnetic Fields with Children 9-11: Relevance, Difficulties and Prospects
ERIC Educational Resources Information Center
Bradamante, F.; Viennot, L.
2007-01-01
This paper presents an investigation centered on a guided conceptual path concerning magnetic and gravitational fields, proposed for children aged 9-11. The goal is to appreciate to what extent the idea of "mapping" two fields of interaction is accessible and fruitful for children of that age. The conceptual target is to link magnetic and…
Field theory and weak Euler-Lagrange equation for classical particle-field systems
Qin, Hong; Burby, Joshua W; Davidson, Ronald C
2014-10-01
It is commonly believed that energy-momentum conservation is the result of space-time symmetry. However, for classical particle-field systems, e.g., Klimontovich-Maxwell and Klimontovich- Poisson systems, such a connection hasn't been formally established. The difficulty is due to the fact that particles and the electromagnetic fields reside on different manifolds. To establish the connection, the standard Euler-Lagrange equation needs to be generalized to a weak form. Using this technique, energy-momentum conservation laws that are difficult to find otherwise can be systematically derived.
NASA Astrophysics Data System (ADS)
Abanov, Alexander G.; Gromov, Andrey
2014-07-01
We compute electromagnetic, gravitational, and mixed linear response functions of two-dimensional free fermions in an external quantizing magnetic field at an integer filling factor. The results are presented in the form of the effective action and as an expansion of currents and stresses in wave vectors and frequencies of the probing electromagnetic and metric fields. In addition to the well-studied U (1) Chern-Simons and Wen-Zee terms we find a gravitational Chern-Simons term that controls the correction to the Hall viscosity due to the background curvature. We relate the coefficient in front of the term with the chiral central charge.
Using Jupiter’s gravitational field to probe the Jovian convective dynamo
NASA Astrophysics Data System (ADS)
Kong, Dali; Zhang, Keke; Schubert, Gerald
2016-03-01
Convective motion in the deep metallic hydrogen region of Jupiter is believed to generate its magnetic field, the strongest in the solar system. The amplitude, structure and depth of the convective motion are unknown. A promising way of probing the Jovian convective dynamo is to measure its effect on the external gravitational field, a task to be soon undertaken by the Juno spacecraft. We calculate the gravitational signature of non-axisymmetric convective motion in the Jovian metallic hydrogen region and show that with sufficiently accurate measurements it can reveal the nature of the deep convection.
Using Jupiter’s gravitational field to probe the Jovian convective dynamo
Kong, Dali; Zhang, Keke; Schubert, Gerald
2016-01-01
Convective motion in the deep metallic hydrogen region of Jupiter is believed to generate its magnetic field, the strongest in the solar system. The amplitude, structure and depth of the convective motion are unknown. A promising way of probing the Jovian convective dynamo is to measure its effect on the external gravitational field, a task to be soon undertaken by the Juno spacecraft. We calculate the gravitational signature of non-axisymmetric convective motion in the Jovian metallic hydrogen region and show that with sufficiently accurate measurements it can reveal the nature of the deep convection. PMID:27005472
On axionic field ranges, loopholes and the weak gravity conjecture
Brown, Jon; Cottrell, William; Shiu, Gary; Soler, Pablo
2016-04-05
Here, we clarify some aspects of the impact that the Weak Gravity Conjecture has on models of (generalized) natural inflation. In particular we address certain technical and conceptual concerns recently raised regarding the stringent constraints and conclusions found in our previous work. We also point out the difficulties faced by attempts to evade these constraints. Furthermore, these new considerations improve the understanding of the quantum gravity constraints we found and further support the conclusion that it remains challenging for axions to drive natural inflation.
Net effect of many gravitational fields on the intensity of celestial light sources. Master's thesis
Cipperly, G.E.
1982-12-01
This thesis investigates the lens-like action of the gravitational fields of celestial bodies, which can alter the apparent intensity of more distant sources. Previous work in this area has shown that the chance of an individual body being sufficiently well aligned with a source to cause a very large gravitational intensity change is small. The issue addressed in this study is the possibility of there being a significant total change in the intensity of a source due to the combined effects of the gravitational fields of all celestial bodies, and in particular, the potential impact on intensity distance measurements, that is, determination of the distances of celestial light sources by means of intensity comparisons. It is first shown that the problem can be treated in flat space by associating an appropriate index of refraction with gravitational fields. A wave approach is taken in deriving the total deflection of a ray by the field of a single point mass. A statistical analysis is then performed to determine the expression for the mean total change in the intensity of celestial light sources due to the combined fields of all intervening bodies.
Magnetohydrodynamic channel flows with weak transverse magnetic fields.
Rothmayer, A P
2014-07-28
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.
NASA Astrophysics Data System (ADS)
Hawkins, L.; Anwar, T.; Scherbakova, V.; Biggin, A. J.; Kravchinsky, V. A.; Shatsillo, A.; Holt, J.; Pavlov, V.
2015-12-01
The ~50 million year transition from the peak in reversal frequency in the Middle Jurassic (~170Ma), associated with a weak geomagnetic field, to the stable and apparently strong field during the Cretaceous Normal Superchron (84-121Ma), represents a dramatic change in time-averaged geomagnetic field behaviour during the Mesozoic Era. New evidence from Siberian samples suggests there is a similar transition in geomagnetic field behaviour during the Palaeozoic, with a weak geomagnetic field in the Upper Devonian preceding the Permo-Carboniferous Superchron (262-318Ma). Both sites, the Viluy Traps and the Zharovsk complex of the Patom Margin, have seemingly reliable, published palaeomagnetic directions and new age constraints, 364.4 ± 1.7Ma (40Ar/39A) 371-377Ma (U-Pb) respectively. The samples were measured using the Thermal Thellier-Coe protocol with partial thermo-remanent magnetisation (pTRM) and tail checks and the Microwave Thellier-IZZI protocol with pTRM checks. Accepted Arai plots show positive pTRM checks, a clear relation between distinct primary directional and palaeointensity components and little to no zig-zagging. Three distinct magneto-mineralogical types were identified from SEM and rock magnetic techniques; low Ti- and intermediate Ti- titanomagnetite and possible maghemite, with mineral type affecting the success rate of samples but resulting in no significant variation in palaeointensity results. The Arai plots also commonly have a distinct two-slope concave-up shape, although non-heating, pseudo-Thellier experiments have supported this resulting from a strong overprint component rather than alteration or multi-domain effects. Results from these experiments give low site mean values between 2.3-29.9μT (Virtual Dipole Moments 4-50.6 ZAm2). The apparently periodic (~180 million years) transitions in geomagnetic field behaviour may indicate the influence of mantle convection changing heat flow across the Core Mantle Boundary.
Illustrating Some Principles of Separation Science through Gravitational Field-Flow Fractionation
ERIC Educational Resources Information Center
Beckett, Ronald; Sharma, Reshmi; Andric, Goja; Chantiwas, Rattikan; Jakmunee, Jaroon; Grudpan, Kate
2007-01-01
Particle separation is an important but often neglected topic in undergraduate curricula. This article discusses how the method of gravitational field-flow fractionation (GrFFF) can be used to illustrate many principles of separation science and some fundamental concepts of physical chemistry. GrFFF separates particles during their elution through…
[Physical essence of erythrocytic sedimentation rate in the gravitation field of the earth].
Cherniĭ, A N
2009-01-01
The erythrocytic sedimentation rate method has been long known in medicine and extensively used in laboratory practice in tuberculosis facilities. However, many authors note that the erythrocytic sedimentation rate phenomenon has not clearly understood. By applying the total theory of relativity and quantum mechanics, the author discloses the physical essence of erythrocytic sedimentation in the gravitation field of the Earth.
Where Else Is Null the Gravitational Field between Two Massive Spheres?
ERIC Educational Resources Information Center
Lima, F. M. S.
2009-01-01
To find the point between two massive spherical bodies at which their gravitational fields cancel is an apparently simple problem usually found in introductory physics textbooks. However, by noting that such a point does not exist when the distance between the spheres is small and one of the masses is much smaller than the other--e.g., between the…
Reply to 'Comment on 'Primordial magnetic seed field amplification by gravitational waves''
Betschart, Gerold; Zunckel, Caroline; Dunsby, Peter K S; Marklund, Mattias
2007-04-15
Here we respond to the comment by Tsagas on our earlier paper. We show that the results in that comment are flawed and cannot be used for drawing conclusions about the nature of magnetic field amplification by gravitational waves and give further support that the results of our earlier paper are correct.
Higgs and gravitational scalar fields together induce Weyl gauge
NASA Astrophysics Data System (ADS)
Scholz, Erhard
2015-02-01
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.
Field-induced vortices in weakly anisotropic ferroelectrics
NASA Astrophysics Data System (ADS)
Sené, A.; Baudry, L.; Luk'yanchuk, I.; Lahoche, L.; El Amraoui, Y.
2011-03-01
In microscale and nanoscale ferroelectric samples, the formation and growth of domains are the usual stages of the polarization switching mechanism. By assuming weak polarization anisotropy and by solving the Ginzburg-Landau-Khalatnikov equation we have explored an alternative mechanism which consists in ferroelectric switching induced by vortex formation. We have studied the polarization dynamics inside a ferroelectric circular capacitor where switching leads to the formation of a metastable vortex state with a rotational motion of the polarization. Our results are consistent with recent first-principle simulations [I.I. Naumov, H.X. Fu, Phys. Rev. Lett. 98, 077603 (2007)] and with experiments on PbZr 0.2Ti 0.8O 3 [A. Gruverman, D. Wu, H.J. Fan, I. Vrejoiu, M. Alexe, R.J. Harrison, J.F. Scott, J. Phys. Condens. Matter 20 342201(2008)] and demonstrate that vortex-induced polarization switching can be an effective mechanism for circular nanocapacitors.
The scaling of weak field phase-only control in Markovian dynamics
Am-Shallem, Morag; Kosloff, Ronnie
2014-07-28
We consider population transfer in open quantum systems, which are described by quantum dynamical semigroups (QDS). Using second order perturbation theory of the Lindblad equation, we show that it depends on a weak external field only through the field's autocorrelation function, which is phase independent. Therefore, for leading order in perturbation, QDS cannot support dependence of the population transfer on the phase properties of weak fields. We examine an example of weak-field phase-dependent population transfer, and show that the phase-dependence comes from the next order in the perturbation.
The scaling rule for environmental organizing systems in a gravitational field.
Fujiwara, Noboru
2004-02-01
A recent thermodynamics and information study examined the basis of a scaling rule for simple living organisms. The present paper examines a scaling rule for the relationship between the integrated scaled metabolic energy and the mass of a system for a wide range of masses, from animals to the 4He cores of main-sequence stars, considering the effect of gravitational energy. The expected specific scaled energy for animals and the 4He cores of main-sequence stars is 1600 times greater than the specific scaled energy for fundamental living organisms, such as unicellular organisms. This difference results from their organization in a gravitational field or the lack thereof.
NASA Astrophysics Data System (ADS)
Fukushima, Toshio
2016-08-01
We present a method to integrate the gravitational field for general three-dimensional objects. By adopting the spherical polar coordinates centered at the evaluation point as the integration variables, we numerically compute the volume integral representation of the gravitational potential and of the acceleration vector. The variable transformation completely removes the algebraic singularities of the original integrals. The comparison with exact solutions reveals around 15 digits accuracy of the new method. Meanwhile, the 6 digit accuracy of the integrated gravitational field is realized by around 106 evaluations of the integrand per evaluation point, which costs at most a few seconds at a PC with Intel Core i7-4600U CPU running at 2.10 GHz clock. By using the new method, we show the gravitational field of a grand design spiral arm structure as an example. The computed gravitational field shows not only spiral shaped details but also a global feature composed of a thick oblate spheroid and a thin disc. The developed method is directly applicable to the electromagnetic field computation by means of Coulomb's law, the Biot-Savart law, and their retarded extensions. Sample FORTRAN 90 programs and test results are electronically available.
Turner, E.L.
1988-07-01
For several years astronomers have devoted considerable effort to finding and studying a class of celestial phenomena whose very existence depends on rare cosmic accidents. These are gravitational-lens events, which occur when two or more objects at different distances from the earth happen to lie along the same line of sight and so coincide in the sky. The radiation from the more distant object, typically a quasar, is bent by the gravitational field of the foreground object. The bending creates a cosmic mirage: distorted or multiple images of the background object. Such phenomena may reveal many otherwise undetectable features of the image source, of the foreground object and of the space lying between them. Such observations could help to resolve several fundamental questions in cosmology. In the past decade theoretical and observational research on gravitational lenses has grown rapidly and steadily. At this writing at least 17 candidate lens systems have been discussed in the literature. Of the 17 lens candidates reported so far in professional literature, only five are considered to have been reliably established by subsequent observations. Another three are generally regarded as weak or speculative cases with less than 50 percent chance of actually being lens systems. In the remaining nine cases the evidence is mixed or is sparse enough so that the final judgment could swing either way. As might be concluded, little of the scientific promise of gravitational lenses has yet been realized. The work has not yielded a clear value for the proportionality constant or any of the other fundamental cosmological parameter. 7 figs.
Mechanosensory hairs in bumblebees (Bombus terrestris) detect weak electric fields
Sutton, Gregory P.; Clarke, Dominic; Morley, Erica L.; Robert, Daniel
2016-01-01
Bumblebees (Bombus terrestris) use information from surrounding electric fields to make foraging decisions. Electroreception in air, a nonconductive medium, is a recently discovered sensory capacity of insects, yet the sensory mechanisms remain elusive. Here, we investigate two putative electric field sensors: antennae and mechanosensory hairs. Examining their mechanical and neural response, we show that electric fields cause deflections in both antennae and hairs. Hairs respond with a greater median velocity, displacement, and angular displacement than antennae. Extracellular recordings from the antennae do not show any electrophysiological correlates to these mechanical deflections. In contrast, hair deflections in response to an electric field elicited neural activity. Mechanical deflections of both hairs and antennae increase with the electric charge carried by the bumblebee. From this evidence, we conclude that sensory hairs are a site of electroreception in the bumblebee. PMID:27247399
Mechanosensory hairs in bumblebees (Bombus terrestris) detect weak electric fields.
Sutton, Gregory P; Clarke, Dominic; Morley, Erica L; Robert, Daniel
2016-06-28
Bumblebees (Bombus terrestris) use information from surrounding electric fields to make foraging decisions. Electroreception in air, a nonconductive medium, is a recently discovered sensory capacity of insects, yet the sensory mechanisms remain elusive. Here, we investigate two putative electric field sensors: antennae and mechanosensory hairs. Examining their mechanical and neural response, we show that electric fields cause deflections in both antennae and hairs. Hairs respond with a greater median velocity, displacement, and angular displacement than antennae. Extracellular recordings from the antennae do not show any electrophysiological correlates to these mechanical deflections. In contrast, hair deflections in response to an electric field elicited neural activity. Mechanical deflections of both hairs and antennae increase with the electric charge carried by the bumblebee. From this evidence, we conclude that sensory hairs are a site of electroreception in the bumblebee.
Weak Lensing PSF Correction of Wide-field CCD Mosaic Images (SULI Paper)
Cevallos, Marissa; /Caltech /SLAC
2006-01-04
Gravitational lensing provides some of the most compelling evidence for the existence of dark matter. Dark matter on galaxy cluster scales can be mapped due to its weak gravitational lensing effect: a cluster mass distribution can be inferred from the net distortion of many thousands of faint background galaxies that it induces. Because atmospheric aberration and defects in the detector distort the apparent shape of celestial objects, it is of great importance to characterize accurately the point spread function (PSF) across an image. In this research, the PSF is studied in images from the Canada-France-Hawaii Telescope (CFHT), whose camera is divided into 12 CCD chips. Traditional weak lensing methodology involves averaging the PSF across the entire image: in this work we investigate the effects of measuring the PSF in each chip independently. This chip-by-chip analysis was found to reduce the strength of the correlation between star and galaxy shapes, and predicted more strongly the presence of known galaxy clusters in mass maps. These results suggest correcting the CFHT PSF on an individual chip basis significantly improves the accuracy of detecting weak lensing.
Temporal variations of the earth's gravitational field from satellite laser ranging to LAGEOS
NASA Technical Reports Server (NTRS)
Nerem, R. S.; Chao, B. F.; Au, A. Y.; Chan, J. C.; Klosko, S. M.; Pavlis, N. K.; Williamson, R. G.
1993-01-01
Monthly values of the J2 and J3 earth gravitational coefficients were estimated using LAGEOS satellite laser ranging data collected between 1980 and 1989. Monthly variations in gravitational coefficients caused by atmospheric mass redistribution were calculated using measurements of variations in surface atmospheric pressure. Results for correlation studies of the two time series are presented. The LAGEOS and atmospheric J2 time series agree well and it appears that variations in J2 can be attributed to the redistribution of atmospheric mass. Atmospheric and LAGEOS estimates for J3 show poorer agreement, J3 estimates appear to be very sensitive to unmodeled forces acting on the satellite. Results indicate that the LAGEOS data can be used to detect small variations in the gravitational field.
Next-to-leading order gravitational spin-orbit coupling in an effective field theory approach
Levi, Michele
2010-11-15
We use an effective field theory (EFT) approach to calculate the next-to-leading order (NLO) gravitational spin-orbit interaction between two spinning compact objects. The NLO spin-orbit interaction provides the most computationally complex sector of the NLO spin effects, previously derived within the EFT approach. In particular, it requires the inclusion of nonstationary cubic self-gravitational interaction, as well as the implementation of a spin supplementary condition (SSC) at higher orders. The EFT calculation is carried out in terms of the nonrelativistic gravitational field parametrization, making the calculation more efficient with no need to rely on automated computations, and illustrating the coupling hierarchy of the different gravitational field components to the spin and mass sources. Finally, we show explicitly how to relate the EFT derived spin results to the canonical results obtained with the Arnowitt-Deser-Misner (ADM) Hamiltonian formalism. This is done using noncanonical transformations, required due to the implementation of covariant SSC, as well as canonical transformations at the level of the Hamiltonian, with no need to resort to the equations of motion or the Dirac brackets.
Active Region Filaments Might Harbor Weak Magnetic Fields
NASA Astrophysics Data System (ADS)
Díaz Baso, C. J.; Martínez González, M. J.; Asensio Ramos, A.
2016-05-01
Recent spectropolarimetric observations of active region filaments have revealed polarization profiles with signatures typical of the strong field Zeeman regime. The conspicuous absence in those observations of scattering polarization and Hanle effect signatures was then pointed out by some authors. This was interpreted as either a signature of mixed “turbulent” field components or as a result of optical thickness. In this article, we present a natural scenario to explain these Zeeman-only spectropolarimetric observations of active region (AR) filaments. We propose a two-component model, one on top of the other. Both components have horizontal fields, with the azimuth difference between them being close to 90°. The component that lies lower in the atmosphere is permeated by a strong field of the order of 600 G, while the upper component has much weaker fields, of the order of 10 G. The ensuing scattering polarization signatures of the individual components have opposite signs, so its combination along the line of sight reduces—and even can cancel out—the Hanle signatures, giving rise to an apparent Zeeman-only profile. This model is also applicable to other chromospheric structures seen in absorption above ARs.
Gravitational collapse of scalar fields via spectral methods
Oliveira, H. P. de; Rodrigues, E. L.; Skea, J. E. F.
2010-11-15
In this paper we present a new numerical code based on the Galerkin method to integrate the field equations for the spherical collapse of massive and massless scalar fields. By using a spectral decomposition in terms of the radial coordinate, the field equations were reduced to a finite set of ordinary differential equations in the space of modes associated with the Galerkin expansion of the scalar field, together with algebraic sets of equations connecting modes associated with the metric functions. The set of ordinary differential equations with respect to the null coordinate is then integrated using an eighth-order Runge-Kutta method. The numerical tests have confirmed the high accuracy and fast convergence of the code. As an application we have evaluated the whole spectrum of black hole masses which ranges from infinitesimal to large values obtained after varying the amplitude of the initial scalar field distribution. We have found strong numerical evidence that this spectrum is described by a nonextensive distribution law.
Polarization and trapping of weakly bound atoms in penning trap fields.
Kuzmin, S G; O'Neil, T M
2004-06-18
The ATHENA and ATRAP groups at CERN recently reported the production 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. The atoms are polarized by the electric field and can be trapped radially in the edge region of the plasma where the electric field is maximum.
Gravitational field models for study of Earth mantle dynamics
NASA Technical Reports Server (NTRS)
1979-01-01
The tectonic forces or stresses due to the small scale mantle flow under the South American plate are detected and determined by utilizing the harmonics of the geopotential field model. The high degree harmonics are assumed to describe the small scale mantle convection patterns. The input data used in the derivation of this model is made up of 840,000 optical, electronic, and laser observations and 1,656 5 deg x 5 deg mean free air anomalies. Although there remain some statistically questionable aspects of the high degree harmonics, it seems appropriate now to explore their implications for the tectonic forces or stress field under the crust.
Abele, H.; Jenke, T.; Leeb, H.; Schmiedmayer, J.
2010-03-15
We propose to apply Ramsey's method of separated oscillating fields to the spectroscopy of the quantum states in the gravity potential above a horizontal mirror. This method allows a precise measurement of quantum mechanical phaseshifts of a Schroedinger wave packet bouncing off a hard surface in the gravitational field of the Earth. Measurements with ultracold neutrons will offer a sensitivity to Newton's law or hypothetical short-ranged interactions, which is about 21 orders of magnitude below the energy scale of electromagnetism.
Gravitational self-force in nonvacuum spacetimes: An effective field theory derivation
NASA Astrophysics Data System (ADS)
Zimmerman, Peter
2015-09-01
In this paper we investigate the motion of small compact objects in nonvacuum spacetimes using methods from effective field theory in curved spacetime. Although a vacuum formulation is sufficient in many astrophysical contexts, there are applications such as the role of the self-force in enforcing cosmic censorship in the context of the overcharging problem, which necessitate an extension into the nonvacuum regime. The defining feature of the self-force problem in nonvacuum spacetimes is the coupling between gravitational and nongravitational field perturbations. The formulation of the self-force problem for nonvacuum spacetimes was recently provided in simultaneous papers by Zimmerman and Poisson [Gravitational self-force in nonvacuum spacetimes, Phys. Rev. D 90, 084030 (2014)] and Linz, Friedmann, and Wiseman [Combined gravitational and electromagnetic self-force on charged particles in electrovac spacetimes, Phys. Rev. D 90, 084031 (2014)]. Here we distinguish ourselves by working with the effective action rather than the field equations. The formalism utilizes the multi-index notation developed by Zimmerman and Poisson [Gravitational self-force in nonvacuum spacetimes, Phys. Rev. D 90, 084030 (2014) to accommodate the coupling between the different fields. Using dimensional regularization, we arrive at a finite expression for the local self-force expressed in terms of multi-index quantities evaluated in the background spacetime. We then apply the formalism to compute the coupled gravitational self-force in two explicit cases. First, we calculate the self-force on a massive particle possessing scalar charge and moving in a scalarvac spacetime. We then derive an expression for the self-force on an electrically charged, massive particle moving in an electrovac spacetime. In both cases, the force is expressed as a sum of local terms involving tensors defined in the background spacetime and evaluated at the current position of the particle, as well as tail integrals
Locality of Gravitational Systems from Entanglement of Conformal Field Theories.
Lin, Jennifer; Marcolli, Matilde; Ooguri, Hirosi; Stoica, Bogdan
2015-06-01
The Ryu-Takayanagi formula relates the entanglement entropy in a conformal field theory to the area of a minimal surface in its holographic dual. We show that this relation can be inverted for any state in the conformal field theory to compute the bulk stress-energy tensor near the boundary of the bulk spacetime, reconstructing the local data in the bulk from the entanglement on the boundary. We also show that positivity, monotonicity, and convexity of the relative entropy for small spherical domains between the reduced density matrices of any state and of the ground state of the conformal field theory are guaranteed by positivity conditions on the bulk matter energy density. As positivity and monotonicity of the relative entropy are general properties of quantum systems, this can be interpreted as a derivation of bulk energy conditions in any holographic system for which the Ryu-Takayanagi prescription applies. We discuss an information theoretical interpretation of the convexity in terms of the Fisher metric.
Gravitation: Field theory par excellence Newton, Einstein, and beyond
Yilmaz, H.
1984-09-01
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.
NASA Astrophysics Data System (ADS)
Lucchesi, D. M.; Anselmo, L.; Bassan, M.; Pardini, C.; Peron, R.; Pucacco, G.; Visco, M.
2015-08-01
In this work, the Laser Ranged Satellites Experiment (LARASE) is presented. This is a research program that aims to perform new refined tests and measurements of gravitation in the field of the Earth in the weak field and slow motion (WFSM) limit of general relativity (GR). For this objective we use the free available data relative to geodetic passive satellite lasers tracked from a network of ground stations by means of the satellite laser ranging (SLR) technique. After a brief introduction to GR and its WFSM limit, which aims to contextualize the physical background of the tests and measurements that LARASE will carry out, we focus on the current limits of validation of GR and on current constraints on the alternative theories of gravity that have been obtained with the precise SLR measurements of the two LAGEOS satellites performed so far. Afterward, we present the scientific goals of LARASE in terms of upcoming measurements and tests of relativistic physics. Finally, we introduce our activities and we give a number of new results regarding the improvements to the modelling of both gravitational and non-gravitational perturbations to the orbit of the satellites. These activities are a needed prerequisite to improve the forthcoming new measurements of gravitation. An innovation with respect to the past is the specialization of the models to the LARES satellite, especially for what concerns the modelling of its spin evolution, the neutral drag perturbation and the impact of Earth's solid tides on the satellite orbit.
Cartographic generalization of urban street networks based on gravitational field theory
NASA Astrophysics Data System (ADS)
Liu, Gang; Li, Yongshu; Li, Zheng; Guo, Jiawei
2014-05-01
The automatic generalization of urban street networks is a constant and important aspect of geographical information science. Previous studies show that the dual graph for street-street relationships more accurately reflects the overall morphological properties and importance of streets than do other methods. In this study, we construct a dual graph to represent street-street relationship and propose an approach to generalize street networks based on gravitational field theory. We retain the global structural properties and topological connectivity of an original street network and borrow from gravitational field theory to define the gravitational force between nodes. The concept of multi-order neighbors is introduced and the gravitational force is taken as the measure of the importance contribution between nodes. The importance of a node is defined as the result of the interaction between a given node and its multi-order neighbors. Degree distribution is used to evaluate the level of maintaining the global structure and topological characteristics of a street network and to illustrate the efficiency of the suggested method. Experimental results indicate that the proposed approach can be used in generalizing street networks and retaining their density characteristics, connectivity and global structure.
Horizon thermodynamics and gravitational field equations in Horava-Lifshitz gravity
Cai Ronggen; Ohta, Nobuyoshi
2010-04-15
We explore the relationship between the first law of thermodynamics and gravitational field equation at a static, spherically symmetric black hole horizon in Horava-Lifshitz theory with/without detailed balance. It turns out that as in the cases of Einstein gravity and Lovelock gravity, the gravitational field equation can be cast to a form of the first law of thermodynamics at the black hole horizon. This way we obtain the expressions for entropy and mass in terms of black hole horizon, consistent with those from other approaches. We also define a generalized Misner-Sharp energy for static, spherically symmetric spacetimes in Horava-Lifshitz theory. The generalized Misner-Sharp energy is conserved in the case without matter field, and its variation gives the first law of black hole thermodynamics at the black hole horizon.
On the usefulness of relativistic space-times for the description of the Earth's gravitational field
NASA Astrophysics Data System (ADS)
Soffel, Michael; Frutos, Francisco
2016-07-01
The usefulness of relativistic space-times for the description of the Earth's gravitational field is investigated. A variety of exact vacuum solutions of Einstein's field equations (Schwarzschild, Erez and Rosen, Gutsunayev and Manko, Hernández-Pastora and Martín, Kerr, Quevedo, and Mashhoon) are investigated in that respect. It is argued that because of their multipole structure and influences from external bodies, all these exact solutions are not really useful for the central problem. Then, approximate space-times resulting from an MPM or post-Newtonian approximation are considered. Only in the DSX formalism that is of the first post-Newtonian order, all aspects of the problem can be tackled: a relativistic description (a) of the Earth's gravity field in a well-defined geocentric reference system (GCRS), (b) of the motion of solar system bodies in a barycentric reference system (BCRS), and (c) of inertial and tidal terms in the geocentric metric describing the external gravitational field. A relativistic SLR theory is also discussed with respect to our central problem. Orders of magnitude of many effects related to the Earth's gravitational field and SLR are given. It is argued that a formalism with accuracies better than of the first post-Newtonian order is not yet available.
Multiple D/p-branes in weak background fields
NASA Astrophysics Data System (ADS)
Taylor, Washington, IV; Van Raamsdonk, Mark
2000-05-01
We find the terms in the non-abelian world-volume action of a system of many Dp-branes which describe the leading coupling to all type II supergravity background fields. These results are found by T-dualizing earlier results for D0-branes, which in turn were determined from calculations of the M(atrix) theory description of the supercurrent of 11D supergravity. Our results are compatible with earlier results on the supersymmetric Born-Infeld action for a single D-brane in a general background and with Tseytlin's symmetrized trace proposal for extending the abelian Born-Infeld action to a non-abelian theory. In the case p=3, the operators we find on the D-brane world-volume are closely related to those which couple to supergravity fields in the AdS 5× S5 IIB supergravity background. This gives an explicit construction, including normalization, of some of the operators used in the celebrated AdS/CFT correspondence for 3-branes. We also discuss the S-duality of the action in the case p=3, finding that the S-duality of the action determines how certain operators in the N=4 4D SYM theory transform under S-duality. These S-duality results give some new insight into the puzzle of the transverse 5-brane in M(atrix) theory.
Impurity-assisted tunneling magnetoresistance under a weak magnetic field.
Txoperena, Oihana; Song, Yang; Qing, Lan; Gobbi, Marco; Hueso, Luis E; Dery, Hanan; Casanova, Fèlix
2014-10-01
Injection of spins into semiconductors is essential for the integration of the spin functionality into conventional electronics. Insulating layers are often inserted between ferromagnetic metals and semiconductors for obtaining an efficient spin injection, and it is therefore crucial to distinguish between signatures of electrical spin injection and impurity-driven effects in the tunnel barrier. Here we demonstrate an impurity-assisted tunneling magnetoresistance effect in nonmagnetic-insulator-nonmagnetic and ferromagnetic-insulator-nonmagnetic tunnel barriers. In both cases, the effect reflects on-off switching of the tunneling current through impurity channels by the external magnetic field. The reported effect is universal for any impurity-assisted tunneling process and provides an alternative interpretation to a widely used technique that employs the same ferromagnetic electrode to inject and detect spin accumulation. PMID:25325651
Thick branes from self-gravitating scalar fields
Novikov, Oleg O.; Andrianov, Vladimir A.; Andrianov, Alexander A.
2014-07-23
The formation of a domain wall ('thick brane') induced by scalar matter dynamics and triggered by a thin brane defect is considered in noncompact five-dimensional space-time with warped AdS type geometry. The scalar matter is composed of two fields with softly broken O(2) symmetry and minimal coupling to gravity. The nonperturbative effects in the invariant mass spectrum of light localized scalar states are investigated for different values of the tension of the thin brane defect. Especially interesting is the case of the thin brane with negative tension when the singular barriers form a potential well with two infinitely tall walls and the discrete spectrum of localized states arises completely isolated from the bulk.
Myers-Perry black hole in an external gravitational field
NASA Astrophysics Data System (ADS)
Abdolrahimi, Shohreh; Kunz, Jutta; Nedkova, Petya
2015-03-01
We obtain a new exact solution of the 5D Einstein equations in vacuum describing a distorted Myers-Perry black hole with a single angular momentum. Locally, the solution is interpreted as a black hole distorted by a stationary U (1 )×U (1 ) symmetric distribution of external matter. Technically, the solution is constructed by applying a twofold Bäcklund transformation on a 5D distorted Minkowski spacetime as a seed. The physical quantities of the solution are calculated, and a local Smarr-like relation on the black hole horizon is derived. It possesses the same form as the Smarr-like relation for the asymptotically flat Myers-Perry black hole. It is demonstrated that in contrast to the asymptotically flat Myers-Perry black hole, the ratio of the horizon angular momentum and the mass J2/M3 is unbounded, and can grow arbitrarily large. We study the properties of the ergoregion and the horizon surface. The external field does not influence the horizon topology. The horizon geometry however is distorted, and any regular axisymmetric geometry is possible.
BAYESIAN INFERENCE OF SOLAR AND STELLAR MAGNETIC FIELDS IN THE WEAK-FIELD APPROXIMATION
Asensio Ramos, A.
2011-04-10
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.
NASA Technical Reports Server (NTRS)
Voorhies, Coerte V.
2004-01-01
As Earth's main magnetic field weakens, our magnetic shield against the onslaught of the solar wind thins. And the field strength needed to fend off battering by solar coronal mass ejections is decreasing, just when the delicate complexity of modem, vulnerable, electro-technological systems is increasing at an unprecedented rate. Recently, a working group of distinguished scientist from across the nation has asked NASA's Solid Earth and Natural Hazards program a key question: What are the dynamics of Earth s magnetic field and its interactions with the Earth system? Paleomagnetic studies of crustal rocks magnetized in the geologic past reveal that polarity reversals have occurred many times during Earth s history. Networked super-computer simulations of core field and flow, including effects of gravitational, pressure, rotational Coriolis, magnetic and viscous forces, suggest how this might happen in detail. And space-based measurements of the real, time-varying magnetic field help constrain estimates of the speed and direction of fluid iron flowing near the top of the core and enable tests of some hypotheses about such flow. Now scientists at NASA s Goddard Space Flight Center have developed and applied methods to test the hypotheses of narrow scale flow and of a dynamically weak magnetic field near the top of Earth s core. Using two completely different methods, C. V. Voorhies has shown these hypotheses lead to specific theoretical forms for the "spectrum" of Earth s main magnetic field and the spectrum of its rate of change. Much as solar physicists use a prism to separate sunlight into its spectrum, from long wavelength red to short wavelength blue light, geophysicists use a digital prism, spherical harmonic analysis, to separate the measured geomagnetic field into its spectrum, from long to short wavelength fields. They do this for the rate of change of the field as well.
DOE R&D Accomplishments Database
Lee, T. D.
1970-07-01
While the phenomenon of beta-decay was discovered near the end of the last century, the notion that the weak interaction forms a separate field of physical forces evolved rather gradually. This became clear only after the experimental discoveries of other weak reactions such as muon-decay, muon-capture, etc., and the theoretical observation that all these reactions can be described by approximately the same coupling constant, thus giving rise to the notion of a universal weak interaction. Only then did one slowly recognize that the weak interaction force forms an independent field, perhaps on the same footing as the gravitational force, the electromagnetic force, and the strong nuclear and sub-nuclear forces.
The Effect of Weak Combined Magnetic Field on Root Gravitropism and a Role of Ca2+ Ions Therein
NASA Astrophysics Data System (ADS)
Kordyum, Elizabeth; Bogatina, Nina; Kondrachuk, A.
At present, magnetic fields of different types are widely used to study gravity sensing in plants. For instance, magnetic levitation of amyloplasts caused by high gradient magnetic field enables us to alter the effective gravity sensed by plant cells. For the first time we showed that a weak combined magnetic field (CMF), that is the sum of collinear permanent and alternating magnetic fields ( 0.5 gauss, 0-100 Hz), changes a cress and pea root positive gravitropic reaction on a negative one. This effect has the form of resonance and occurs at the frequency of cyclotron resonance of calcium ions. What is especially interesting is that under gravistimulation in the CMF, the displacement of amylopasts in the root cap statocytes is directed to the upper wall of a cell, i.e. in the direction opposite to the gravitational vector. The displacement of amyloplasts, which contain the abundance of free Ca2+ ions in the stroma, is accompanied by Ca2+ redistribution in the same direction, and increasing in the cytosol around amyloplasts near ten times in the CMF in comparison with the state magnetic field. Earlier, we also observed the Ca2+ accumulation in the upper site of a root curvature in the elongation zone in the CMF unlike a positive gravitropic reaction. Thus, it should be stressed that a root is bending in the same direction in which amyloplasts are displacing: downwards when gravitropism is positive and upwards when gravitropism is negative. The obtained data confirm the amyloplast statolithic function and give another striking demonstration of a leading role of Ca2+ ions in root gravitropism. But these data bring the question: what forces can promote amyloplast displacement against gravity? The possible explanation of the effect found is discussed. It is based on the ion cyclotron resonance in biosystems proposed by Liboff.. The original approach based on the use of a weak CMF may be helpful for understanding the mechanisms of plant gravisensing
Solar oscillations, gravitational multipole field of the sun and the solar neutrino paradox
Hill, H.A.; Rosenwald, R.D.
1986-11-04
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.
NASA Astrophysics Data System (ADS)
Suvorov, Arthur George; Melatos, Andrew
2016-08-01
The Ernst formulation of the Einstein equations is generalized to accommodate f (R ) theories of gravity. It is shown that, as in general relativity, the axisymmetric f (R ) field equations for a vacuum spacetime that is either stationary or cylindrically symmetric reduce to a single, nonlinear differential equation for a complex-valued scalar function. As a worked example, we apply the generalized Ernst equations to derive a f (R ) generalization of the Zipoy-Voorhees metric, which may be used to describe the gravitational field outside of an ellipsoidal neutron star. We also apply the theory to investigate the phase speed of large-amplitude gravitational waves in f (R ) gravity in the context of solitonlike solutions that display shock-wave behavior across the causal boundary.
Kantserova, N P; Lysenko, L A; Ushakova, N V; Krylov, V V; Nemova, N N
2015-01-01
The study aimed to determine the molecular targets of magnetic fields in living objects. Time-dependent effects of weak low-frequency magnetic field tuned to the parametric resonance for calcium ions were studied on model organisms (fish, whelk). The dynamics of Ca(2+)-dependent proteinase activity under the exposure to magnetic fields with given parameters was determined and minimal time of exposure in order to achieve inactivation of these proteinases was find out as well. As hyperactivation of Ca(2+)-dependent proteinases is a basis of degenerative pathology development the therapeutic potential of weak low-frequency magnetic fields enabling to modulate Ca(2+)-dependent proteinase activity is supported. PMID:27125027
Gravitational radiation from collapsing magnetized dust
Sotani, Hajime; Yoshida, Shijun; Kokkotas, Kostas D.
2007-04-15
In this article we study the influence of magnetic fields on the axial gravitational waves emitted during the collapse of a homogeneous dust sphere. We found that while the energy emitted depends weakly on the initial matter perturbations it has strong dependence on the strength and the distribution of the magnetic field perturbations. The gravitational wave output of such a collapse can be up to an order of magnitude larger or smaller calling for detailed numerical 3D studies of collapsing magnetized configurations.
Gravitational quantum states of Antihydrogen
Voronin, A. Yu.; Froelich, P.; Nesvizhevsky, V. V.
2011-03-15
We present a theoretical study of the motion of the antihydrogen atom (H) in the gravitational field of Earth above a material surface. We predict that the H atom, falling in the gravitational field of Earth above a material surface, would settle into long-lived quantum states. We point out a method of measuring the difference in the energy of H in such states. The method allows for spectroscopy of gravitational levels based on atom-interferometric principles. We analyze the general feasibility of performing experiments of this kind. We point out that such experiments provide a method of measuring the gravitational force (Mg) acting on H and that they might be of interest in the context of testing the weak equivalence principle for antimatter.
NASA Astrophysics Data System (ADS)
Suárez, Abril; Chavanis, Pierre-Henri
2015-07-01
Using a generalization of the Madelung transformation, we derive the hydrodynamic representation of the Klein-Gordon-Einstein equations in the weak field limit. We consider a complex self-interacting scalar field with a λ |φ |4 potential. We study the evolution of the spatially homogeneous background in the fluid representation and derive the linearized equations describing the evolution of small perturbations in a static and in an expanding Universe. We compare the results with simplified models in which the gravitational potential is introduced by hand in the Klein-Gordon equation, and assumed to satisfy a (generalized) Poisson equation. Nonrelativistic hydrodynamic equations based on the Schrödinger-Poisson equations or on the Gross-Pitaevskii-Poisson equations are recovered in the limit c →+∞. We study the evolution of the perturbations in the matter era using the nonrelativistic limit of our formalism. Perturbations whose wavelength is below the Jeans length oscillate in time while perturbations whose wavelength is above the Jeans length grow linearly with the scale factor as in the cold dark matter model. The growth of perturbations in the scalar field model is substantially faster than in the cold dark matter model. When the wavelength of the perturbations approaches the cosmological horizon (Hubble length), a relativistic treatment is mandatory. In that case, we find that relativistic effects attenuate or even prevent the growth of perturbations. This paper exposes the general formalism and provides illustrations in simple cases. Other applications of our formalism will be considered in companion papers.
On an analogy to the Steklov case for a balanced gyrostat in a Newtonian gravitational force field
NASA Astrophysics Data System (ADS)
Zlochevskii, S. I.
1982-12-01
New particular solutions are obtained for the equations of motion of a gyrostat about a fixed center of mass in a Newtonian gravitational force field. Arkhangel'skii's (1977) modification of Steklov's (1899) method is the basis of the investigation.
Nesvizhevsky, V V; Protasov, K V
2005-01-01
An upper limit to non-Newtonian attractive forces is obtained from the measurement of quantum states of neutrons in the Earth's gravitational field. This limit improves the existing constraints in the nanometer range.
NASA Astrophysics Data System (ADS)
Hirata, N.; Matsumoto, K.; Kimura, J.; Kitazato, K.
2014-07-01
The relationship between the global distribution of regolith deposits and the gravitational potential fields on small asteroids is investigated in this paper. It is expected that the global distribution of regolith deposits is controlled by the gravitational potential fields on small asteroids, because they are formed on low potential regions on a small asteroid by gravitational migration [1]. Regolith deposits would be formed on the polar regions of an oblate body with slow rotation, because gravitational potential is low on the polar regions. Smooth terrains found on the polar regions of asteroid Itokawa are representatives of this case [2, 3]. Oppositely, regolith deposits would be found on the equatorial region of a spherical body with fast rotation, where the latitudinal gradient of the centrifugal potential from the pole to the equator overcome the gravitational potential gradient. Equatorial bulges found on fast-rotating near-Earth asteroids with oblate shapes may have this kind of regolith deposit [4,5]. When two gradients are canceled by each other, an equipotential state over the whole surface of the body is achieved. The equilibrium rotation period is defined as the period at which the equipotential state is accomplished. In this case, local topographic features would affect the distribution of regolith deposits. We modeled the gravity potential on the spheroidal surface by considering a balance between the gravitational attraction and the centrifugal force. The figure represents equilibrium rotation periods for given axial ratios of spheroidal bodies and densities. Itokawa (density: 1950 kg/m^3, axial ratio: 2.5 for a/c and 1.2 for a/c) [3] is located above the equilibrium line of its rotation period 12.132 h, indicating that low potential regions and smooth terrains are formed on the polar region, whereas Bennu (density 1260 kg/m^3, axial ratio: 1.1) [6,7] is far below of its equilibrium line (P: 4.3 h), suggesting that its equatorial region has
NASA Astrophysics Data System (ADS)
Hong-bo, Wang; Chang-yin, Zhao; Wei, Zhang; Jin-wei, Zhan; Sheng-xian, Yu
2016-07-01
The Earth gravitational field model is one of the most important dynamic models in satellite orbit computation. Several space gravity missions made great successes in recent years, prompting the publishing of several gravitational filed models. In this paper, two classical (JGM3, EGM96) and four latest (EIGEN-CHAMP05S, GGM03S, GOCE02S, EGM2008) models are evaluated by employing them in the precision orbit determination (POD) and prediction. These calculations are performed based on the laser ranging observation of four Low Earth Orbit (LEO) satellites, including CHAMP, GFZ-1, GRACE-A, and SWARM-A. The residual error of observation in POD is adopted to describe the accuracy of six gravitational field models. The main results we obtained are as follows. (1) For the POD of LEOs, the accuracies of 4 latest models are at the same level, and better than those of 2 classical models; (2) Taking JGM3 as reference, EGM96 model's accuracy is better in most situations, and the accuracies of the 4 latest models are improved by 12%-47% in POD and 63% in prediction, respectively. We also confirm that the model's accuracy in POD is enhanced with the increasing degree and order if they are smaller than 70, and when they exceed 70, the accuracy keeps constant, implying that the model's degree and order truncated to 70 are sufficient to meet the requirement of LEO computation of centimeter precision.
An Investigation into Quantifying Micron-G Changes in a Gravitational Field of 1G
NASA Technical Reports Server (NTRS)
Gauthier, Richard R.; Gilbert, John A.
1997-01-01
This project called for the development of an accelerometer designed to be used in conjunction with gravity shielding experiments. The device had to measure local gravitational changes on the order of a few micro-G's (micron-G) with a spatial resolution greater than one measurement per ten square centimeters. Measurements had to be made at a minimum rate of two per second. Tasks included the design, development and demonstration of a prototype. The deliverable consisted of three copies of this final report. The study resulted in the development of a Transversely Suspended Accelerometer (TSA) which met all of the technical specifications. Different generations of the device were demonstrated to NASA/MSFC personnel as they were developed. The final prototype is available for further demonstration and future use. The study draws attention to the fact that the magnetic fields required to produce gravitational shielding may result in apparent decreases in the weights of suspended objects on the order of those attributed to the effect itself. This observation reinforces the need to quantify the influences of the magnetic field on any measurement device used to study gravitational shielding. This task was accomplished for the TSA.
On the gravitational field of a radiating, isothermal perfect gas cloud
NASA Astrophysics Data System (ADS)
Campos, L. M. B. C.
2016-04-01
The paper considers a static isotropic self-gravitating perfect gas in the presence of thermal radiation. The gravitational field is specified in terms of the radiation and gas pressures. Assuming that the thermodynamic internal energy is small compared with relativistic rest energy, it is shown that the gas pressure satisfies the Lane-Emden equation; the assumption of dominant intrinsic relativistic rest energy is satisfied by the hottest stars. Six-solutions of the Lane-Enden equation are obtained together with the corresponding gravitational fields. The basis for comparison is the singular solution I decaying like the inverse square of the radius, that is the leading term of the asymptotic solution V. Two semi-linear solutions are obtained using as variables nonlinear functions of the gas pressure, leading to nonlinear second-order differential equations that can be linearized; one solution II holds for small radius and leads to zero, finite or infinite central pressure, and the other solution III holds asymptomatically and exhibits pressure oscillations. The singular solution I for large radius is matched to a power series solution IV for small radius leading to a solution valid for all radii. The asymptotic solutions III and V: (i) coincide in their common domain of validity; (ii) can be truncated with good accuracy leading to the solution VI.
NASA Astrophysics Data System (ADS)
Ye, Jun; He, Wei; Wu, Qiong; Hu, Bo; Tang, Jin; Zhang, Xiang-Qun; Chen, Zi-Yu; Cheng, Zhao-Hua
2014-03-01
The weak bias field applied on perpendicular direction of the external field provides an excellent opportunity to investigate the in-plane magnetization reversal process of Fe/Si(001) film. In this work, we present the magneto-optical Kerr effect test of Fe single crystal film grown on Si(001) substrate with ultrathin p(2 × 2) iron silicide as buffer layer. Owing to the weak bias field, both 180° and 90° domain wall displacements were observed in one hysteresis loop between the easy axis and hard axis of iron film. Furthermore, both the 180° and 90° domain wall pinning energies can be derived from one hysteresis loop with weak bias field.
Alternatives to Schwarzschild in the weak field limit of General Relativity
Bozza, V.; Postiglione, A. E-mail: postiglione@fis.uniroma3.it
2015-06-01
The metric outside an isolated object made up of ordinary matter is bound to be the classical Schwarzschild vacuum solution of General Relativity. Nevertheless, some solutions are known (e.g. Morris-Thorne wormholes) that do not match Schwarzschild asymptotically. On a phenomenological point of view, gravitational lensing in metrics falling as 1/r{sup q} has recently attracted great interest. In this work, we explore the conditions on the source matter for constructing static spherically symmetric metrics exhibiting an arbitrary power-law as Newtonian limit. For such space-times we also derive the expressions of gravitational redshift and force on probe masses, which, together with light deflection, can be used in astrophysical searches of non-Schwarzschild objects made up of exotic matter. Interestingly, we prove that even a minimally coupled scalar field with a power-law potential can support non-Schwarzschild metrics with arbitrary asymptotic behaviour.
Legreneur, Pierre; Bels, Vincent; Monteil, Karine; Laurin, Michel
2013-05-01
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.
Inflationary gravitational waves in the effective field theory of modified gravity
NASA Astrophysics Data System (ADS)
De Felice, Antonio; Tsujikawa, Shinji
2015-05-01
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., Hořava-Lifshitz gravity). We obtain the inflationary power spectrum of tensor modes 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 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.
The deflection of light induced by the Sun's gravitational field and measured with geodetic VLBI
NASA Astrophysics Data System (ADS)
Titov, O.; Girdiuk, A.
2015-08-01
The Sun's gravitational field deflects the apparent positions of close objects in accordance with the formulae of general relativity. Optical astrometry is used to test the prediction, but only with the stars close to the Sun and only during total Solar eclipses. Geodetic Very Long Baseline Interferometry (VLBI) is capable of measuring the deflection of the light from distant radio sources anytime and across the whole sky. We show that the effect of light deflection is equivalent to the gravitational delay calculated during the reduction of VLBI data. All reference radio sources display an annual circular motion with the magnitude proportional to their ecliptic latitude. In particular, radio sources near the ecliptic pole draw an annual circle with magnitude of 4~mas. This effect could be easily measured with the current precision of the geodetic VLBI data.
Radiative degrees of freedom of the gravitational field in exact general relativity
NASA Astrophysics Data System (ADS)
Ashtekar, Abhay
1981-12-01
The radiative degrees of freedom of the gravitational field are isolated by analyzing the structure available at null infinity, JIt is shown thay they are coded in certain equivalence classes {D} of connections; all information about gravitational radiation can be extracted from the curvature tensors of these connections directly on J without any reference to the interior of space-time. The space of classical vacua—i.e., of {D} with trivial curvature—is analyzed. It is shown that the quotient ST/T of the BMS supertranslation group by its translation subgroup acts simply and transitively on this space. The available structure is compared with that of gauge theories. Since the entire discussion can be carried out onJ without any reference to the interior, it suggests a new approach to quantum gravity. This approach will be presented in detail in a subsequent paper.
NASA Astrophysics Data System (ADS)
Okura, Yuki; Futamase, Toshifumi
2016-08-01
We improve the ellipticity of re-smeared artificial image (ERA) method of point-spread function (PSF) correction in a weak lensing shear analysis in order to treat the realistic shape of galaxies and the PSF. This is done by re-smearing the PSF and the observed galaxy image using a re-smearing function (RSF) and allows us to use a new PSF with a simple shape and to correct the PSF effect without any approximations or assumptions. We perform a numerical test to show that the method applied for galaxies and PSF with some complicated shapes can correct the PSF effect with a systematic error of less than 0.1%. We also apply the ERA method for real data of the Abell 1689 cluster to confirm that it is able to detect the systematic weak lensing shear pattern. The ERA method requires less than 0.1 or 1 s to correct the PSF for each object in a numerical test and a real data analysis, respectively.
Paramagnetic relaxation in anisotropic materials in zero and weak constant fields
Fokina, N. P.; Khalvashi, E. Kh.; Khutsishvili, K. O.
2014-12-21
Paramagnetic relaxation in strongly anisotropic materials is analytically investigated in zero and weak constant magnetic fields. The objectives of the microscopic analytical investigation are (i) the weak-field electron paramagnetic resonance (EPR) linewidth and (ii) the electron spin relaxation rates given by a calorimetric Gorter type experiment in the zero constant field at the arbitrary low-frequency field directions, respectively, to the sample crystallographic axes. The EPR linewidth is calculated under the suggestion of its spin-phonon nature at the one-phonon mechanism of the spin-lattice relaxation in the case of the strong isotropic exchange interaction for the arbitrary direction Z of the constant magnetic field. The EPR linewidth is presented as the half sum of the zero-field relaxation rates, measured by the Gorter experiment with the low-frequency field oriented along the X, Y axes. With the help of the macroscopic consideration, it is shown that the zero-field relaxation rates describe the relaxation of the X and Y magnetization components in a zero or weak constant magnetic field. The relaxation rates of the magnetizations created along a,b,c crystallographic axes by a low-frequency field in a Gorter type experiment follow the obtained expressions in the particular cases and are in the experimentally confirmed relations with the EPR linewidth.
NASA Astrophysics Data System (ADS)
Schillaci, Michael Jay
2016-03-01
After providing a very short review of Classical gravito-magnetism I will present a novel framework for the development and extension of the Classical theory of gravity. Specifically, I will first discuss the proposed, Lorentz-like force experienced by a moving mass in the presence of a rotating gravitational source, and then I will provide a first principles definition of the proposed Frenetic Field. Of note this field has units of frequency and so provides for straight-forward comparison with previous Classical results. i.e., The Lens-Thirring Effect. I then continue with a discussion of a general gauge constraint of the Frenetic field in terms of a velocity field which depends upon both the mass and rotational velocity of and the distance to the source. This framework allows for direct comparison with Relativistic predictions where I find (minimally) first-order agreement for the refraction of light by a rotating gravitational source, and provide for a robust description of the temporal character of these ``lenses'' in terms of an absolute time parameter. I will conclude by extending the theoretical framework to the case of many sources and discuss implications for the evolution of accretion disks due to possible gravito-frenetic wave phenomena.
Guo, Shuang; Zhu, Chenqi; Gao-Yang, Yaya; Qiu, Bailing; Wu, Di; Liang, Qihui; He, Jiayuan; Han, Nanyin
2016-02-01
Gravitational field-flow fractionation is the simplest field-flow fractionation technique in terms of principle and operation. The earth' s gravity is its external field. Different sized particles are injected into a thin channel and carried by carrier fluid. The different velocities of the carrier liquid in different places results in a size-based separation. A gravitational field-flow fractionation (GrFFF) instrument was designed and constructed. Two kinds of polystyrene (PS) particles with different sizes (20 µm and 6 µm) were chosen as model particles. In this work, the separation of the sample was achieved by changing the concentration of NaN3, the percentage of mixed surfactant in the carrier liquid and the flow rate of carrier liquid. Six levels were set for each factor. The effects of these three factors on the retention ratio (R) and plate height (H) of the PS particles were investigated. It was found that R increased and H decreased with increasing particle size. On the other hand, the R and H increased with increasing flow rate. The R and H also increased with increasing NaN3 concentration. The reason was that the electrostatic repulsive force between the particles and the glass channel wall increased. The force allowed the samples approach closer to the channel wall. The results showed that the resolution and retention time can be improved by adjusting the experimental conditions. These results can provide important values to the further applications of GrFFF technique. PMID:27382718
NASA Astrophysics Data System (ADS)
Guerci, Daniele; Borge, Juan; Raimondi, Roberto
2016-08-01
We evaluate the spin polarization (Edelstein or inverse spin galvanic effect) and the spin Hall current induced by an applied electric field by including the weak localization corrections for a two-dimensional electron gas. We show that the weak localization effects yield logarithmic corrections to both the spin polarization conductivity relating the spin polarization and the electric field and to the spin Hall angle relating the spin and charge currents. The renormalization of both the spin polarization conductivity and the spin Hall angle combine to produce a zero correction to the total spin Hall conductivity as required by an exact identity. Suggestions for the experimental observation of the effect are given.
The ionospheric effects of a weak intrinsic magnetic field at Mars
NASA Technical Reports Server (NTRS)
Shinagawa, H.; Cravens, T. E.
1992-01-01
An improved model of the Martian ionosphere which allows the magnetic field to have any direction in the horizontal plane is presented, as well as results of calculations for several different intrinsic magnetic field strengths and directions. When the solar wind dynamic pressure exceeds the Martian ionospheric thermal pressure, the plasma motion is weakly downward throughout the ionosphere for the case of no intrinsic magnetic field, but when the intrinsic and induced fields are in opposite directions, the plasma flow tends to converge toward the current sheet. As a consequence of this convergence, the plasma density is somewhat enhanced near the current sheet, which is located near an altitude of 170 km. The ionosphere above an altitude of about 190 km is not significantly affected by the existence of an intrinsic field as weak as 60 nT.
Conductivity of molten sodium chloride in an arbitrarily weak dc electric field.
Delhommelle, Jerome; Cummings, Peter T; Petravic, Janka
2005-09-15
We use nonequilibrium molecular-dynamics (NEMD) simulations to characterize the response of a fluid subjected to an electric field. We focus on the response for very weak fields. Fields accessible by conventional NEMD methods are typically of the order of 10(9) V m(-1), i.e., several orders of magnitude larger than those typically used in experiments. Using the transient time-correlation function, we show how NEMD simulations can be extended to study systems subjected to a realistic dc electric field. We then apply this approach to study the response of molten sodium chloride for a wide range of dc electric fields.
NASA Astrophysics Data System (ADS)
Grunskaya, Lubov; Isakevich, Valiriy; Efimov, Vladislav; Zakirov, Alexander
Experimental investigations of electromagnetic fields in the atmosphere boundary layer are done at the distance spaced stations, situated on VSU test ground, at Main Geophysical Observa-tory(St. Petersburg), on Kamchatka pen., on Lake Baikal. The distance spaced reception of electrical and magnetic fields will allow to analyze more widely the nature of the investigated interactions. Monitoring of electromagnetic fields in the ELF range is being realized. The work is connected with search of interconnection of the electromagnetic field of the atmosphere boundary layer with the gravitational Compact Binaries wave fields. For analyzing Compact Binaries were taken with ELF of GW-radiation: J 0700+6418, J 1012+5307, J 1537+1155, J 1959+2048, J 2130+1210, J 1915+1606, J 1910+0004, J 1910+0004, J 1748-2446A.For analyz-ing the spectrum of the magnetic fields there was used the information of VSU station and the monitoring information of Japanese geomagnetic stations Kakioka and Mambetsu. The aim of such investigations is connected with displaying tide processes (the Moon tides) and gravita-tional wave influence of Compact Binaries in the electromagnetic fields.On the first stage of the investigations a correlative spectral analysis of the experimental data was being carried out. There was factually extracted the influence of the atmosphere lower layer electromagnetic field of the thermogravitational solar tides and a number of gravitational: M1, M2, N2. It was ob-tained that astrophysical sources GV-6, GV-3,GV-4, GV-8, GV-9 have the most probability of non-casual of events. The subsequent investigations are connected with search of main features accompanying such influences. They are signal modulations by diurnal and year's rotation of the Earth. Such modulations are peculiar to sources of non-terrestrial origin. We are planning an extraction of the radiation frequency change of the source because of energy loss for the radiation of GW. Such investigations turned out to be
Traveling-wave tubes and backward-wave oscillators with weak external magnetic fields.
Abu-elfadl, T M; Nusinovich, G S; Shkvarunets, A G; Carmel, Y; Antonsen, T M; Goebel, D
2001-06-01
Recent development of plasma-assisted slow-wave oscillators [Goebel et al. IEEE Trans. Plasma Sci. 22, 547 (1994)], microwave sources that operate without guiding magnetic fields, has stimulated interest in the theoretical analysis of such tubes. In principle, in the absence of guiding magnetic fields, due to the space charge forces and the radial electric field of the wave, the electrons may propagate radially outward which increases electron coupling to the slow wave whose field is localized near the slow-wave structure (SWS). This increases the wave growth rate and efficiency, and hence allows one to shorten the interaction region. So the radial electron motion can be beneficial for operation if it does not lead to interception of electrons by the SWS. To avoid this interception a weak external magnetic field can be applied. The theory developed describes the effect of weak magnetic fields on the operation of traveling-wave tubes and backward-wave oscillators with electrons moving not only axially but also transversely. This theory allows one to estimate the magnetic field required for protecting the SWS from electron bombardment at different power levels. Theoretical predictions of the efficiency enhancement due to the weak magnetic field are confirmed in experiments.
Traveling-wave tubes and backward-wave oscillators with weak external magnetic fields
Abu-elfadl, T. M.; Nusinovich, G. S.; Shkvarunets, A. G.; Carmel, Y.; Antonsen, T. M.; Goebel, D.
2001-06-01
Recent development of plasma-assisted slow-wave oscillators [Goebel IEEE Trans. Plasma Sci. >22, 547 (1994)], microwave sources that operate without guiding magnetic fields, has stimulated interest in the theoretical analysis of such tubes. In principle, in the absence of guiding magnetic fields, due to the space charge forces and the radial electric field of the wave, the electrons may propagate radially outward which increases electron coupling to the slow wave whose field is localized near the slow-wave structure (SWS). This increases the wave growth rate and efficiency, and hence allows one to shorten the interaction region. So the radial electron motion can be beneficial for operation if it does not lead to interception of electrons by the SWS. To avoid this interception a weak external magnetic field can be applied. The theory developed describes the effect of weak magnetic fields on the operation of traveling-wave tubes and backward-wave oscillators with electrons moving not only axially but also transversely. This theory allows one to estimate the magnetic field required for protecting the SWS from electron bombardment at different power levels. Theoretical predictions of the efficiency enhancement due to the weak magnetic field are confirmed in experiments.
NASA Astrophysics Data System (ADS)
Lu, Xu; Yang, Feng-Wei; Xie, Yi
2016-07-01
We analyze strong gravitational field time delay for photons coupled to the Weyl tensor in a Schwarzschild black hole. By making use of the method of strong deflection limit, we find that these time delays between relativistic images are significantly affected by polarization directions of such a coupling. A practical problem about determination of the polarization direction by observations is investigated. It is found that if the first and second relativistic images can be resolved, the measurement of time delay can more effectively improve detectability of the polarization direction.
Metric-Field Approach to Gravitation and the Problem of the Universe Acceleration
NASA Astrophysics Data System (ADS)
Verozub, Leonid V.
2002-07-01
A metric-field approach to gravitation is presented. It is based on an idea of dependency of space-time properties on measuring instruments. Some bimetric equations that realize this idea are considered. They were tested by the binary pulsar PSR1913+16. The spherically - symmetric solution of the equations has no event horizon and no physical singularity in the center. The proper energy of a point particle is finite. There can exist supermassive compact configurations of the degenerated Fermi-gas which can be identified with observed objects in galactic centers. The problem of the Universe acceleration has a natural explanation.
Global surface-water-induced seasonal variations in the earth's rotation and gravitational field
NASA Technical Reports Server (NTRS)
Chao, B. F.; O'Connor, William P.
1988-01-01
The effects of seasonal changes in continental surface-water storage on the low-degree gravitational-field coefficients (J), the annual wobble excitation (Psi), and the seasonal length-of-day (LOD) variations are investigated by means of numerical simulations based on compiled meteorological data (Willmott et al., 1985) and satellite snow-load estimates (Chao et al., 1987). The formulation of the model equations and the overall characteristics of the data sets are discussed in detail, and the computation results are presented in tables and graphs. The effect on Psi is found to be relatively small due to longitudinal cancellation, but those on LOD and J are considered significant.
Quantum fog and the degradation of information by the gravitational field
Sciffer, M. )
1993-07-01
In this paper the authors discuss how information transferred optically through a gravitational field is degraded as the quanta interact with the medium (vacuum state). The authors quantify information by means of Shannon's entropy, and consider information carriers that are quanta of some field. Next, the authors obtain the quantum noise ([open quote]quantum fog[close quote]) produced by the gravitational field and derive the appropriate [open quote]channel capacity[close quote] formula, which quantifies the maximum amount of information that can be transmitted per pulse, in the face of this noise. It is shown that the channel capacity formula vanishes if the source of information is a space-time singularity because a very intense noise is produced in the vicinity of the singularity. In other words, space-time singularities are hidden behind a very intense [open quote]quantum fog[close quote] and cannot be optically observed. A second consequence is that information is degraded as anisotropies (lumpiness) develop in the universe. 32 refs., 9 figs., 5 figs.
Relativistic weak lensing from a fully non-linear cosmological density field
Thomas, D.B.; Bruni, M.; Wands, D. E-mail: marco.bruni@port.ac.uk
2015-09-01
In this paper we examine cosmological weak lensing on non-linear scales and show that there are Newtonian and relativistic contributions and that the latter can also be extracted from standard Newtonian simulations. We use the post-Friedmann formalism, a post-Newtonian type framework for cosmology, to derive the full weak-lensing deflection angle valid on non-linear scales for any metric theory of gravity. We show that the only contributing term that is quadratic in the first order deflection is the expected Born correction and lens-lens coupling term. We use this deflection angle to analyse the vector and tensor contributions to the E- and B- mode cosmic shear power spectra. In our approach, once the gravitational theory has been specified, the metric components are related to the matter content in a well-defined manner. Specifying General Relativity, we write down a complete set of equations for a GR+ΛCDM universe for computing all of the possible lensing terms from Newtonian N-body simulations. We illustrate this with the vector potential and show that, in a GR+ΛCDM universe, its contribution to the E-mode is negligible with respect to that of the conventional Newtonian scalar potential, even on non-linear scales. Thus, under the standard assumption that Newtonian N-body simulations give a good approximation of the matter dynamics, we show that the standard ray tracing approach gives a good description for a ΛCDM cosmology.
Magnetite in human tissues: A mechanism for the biological effects of weak ELF magnetic fields
Kirschvink, J.L.; Kobayashi-Kirschvink, A.; Diaz-Ricci, J.C.; Kirschvink, S.J. )
1992-01-01
Due to the apparent lack of a biophysical mechanism, the question of whether weak, low-frequency magnetic fields are able to influence living organisms has long been one of the most controversial subjects in any field of science. However, two developments during the past decade have changed this perception dramatically, the first being the discovery that many organisms, including humans, biochemically precipitate the ferrimagnetic mineral magnetite (Fe3O4). In the magnetotactic bacteria, the geomagnetic response is based on either biogenic magnetite or greigite (Fe3S4), and reasonably good evidence exists that this is also the case in higher animals such as the honey bee. Second, the development of simple behavioral conditioning experiments for training honey bees to discriminate magnetic fields demonstrates conclusively that at least one terrestrial animal is capable of detecting earth-strength magnetic fields through a sensory process. In turn, the existence of this ability implies the presence of specialized receptors which interact at the cellular level with weak magnetic fields in a fashion exceeding thermal noise. A simple calculation shows that magnetosomes moving in response to earth-strength ELF fields are capable of opening trans-membrane ion channels, in a fashion similar to those predicted by ionic resonance models. Hence, the presence of trace levels of biogenic magnetite in virtually all human tissues examined suggests that similar biophysical processes may explain a variety of weak field ELF bioeffects. 61 refs.
NASA Technical Reports Server (NTRS)
Kumar, Vinod; Kumar, Nagendra; Srivastava, Krishna M.; Mittal, R. C.
1993-01-01
The problem of gravitational instability of an infinite homogeneous self-gravitating medium carrying a uniform magnetic field in the presence of Hall effect has been investigated to include the effect due to rotation. The dispersion relation has been obtained. It has been found that the Jeans's criterion for the instability remains unaffected even when the effect due to rotation is considered in the presence of Hall effect carrying a uniform magnetic.
On observation of neutron quantum states in the Earth's gravitational field
NASA Astrophysics Data System (ADS)
Vankov, Anatoli Andrei
2010-03-01
Observation of neutron gravitational quantum states En=mgzn in the peV energy range (z1 is about 10μm 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(za), namely, a horizontal flux of relatively fast neutrons (k≫kz in wavelength terms) passing through a slit of variable height za 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(za) and the probability density distribution P(z,za) 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(za) 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 105 times greater than eigenvalues En. The latter are related to the neutron transverse mode kz 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
Mantle convection and the large scale structures of the Earth's gravitational field
NASA Technical Reports Server (NTRS)
Peltier, W. R.
1985-01-01
The connection between the observed large scale structure of the Earths' gravitational field, as represented by the GEM10 model, and the surface kinematic manifestations of plate tectonics, as represented by the absolute plate motion model of Minster and Jordan, is explored using a somewhat novel method of analysis. Two scalar derivatives of the field of surface plate velocities, namely the horizontal divergence and the radial vorticity, are computed from the plate motion data. These two scalars are respectively determined by the poloidal and toroidal scalars in terms of which any essentially solenoidal vector field may be completely represented. They provide a compact summary of the observed plate boundary types in nature, with oceanic ridges and trenches being essentially boundaries of divergence, and transform faults being essentially boundaries of vorticity.
Weak electromagnetic field admitting integrability in Kerr-NUT-(A)dS spacetimes
NASA Astrophysics Data System (ADS)
Kolář, Ivan; Krtouš, Pavel
2015-06-01
We investigate properties of higher-dimensional generally rotating black-hole spacetimes, so-called Kerr-NUT-(anti)-de Sitter spacetimes, as well as a family of related spaces which share the same explicit and hidden symmetries. In these spaces, we study a particle motion in the presence of a weak electromagnetic field and compare it with its operator analogies. First, we find general commutativity conditions for classical observables and for their operator counterparts, then we investigate a fulfillment of these conditions in the Kerr-NUT-(anti)-de Sitter and related spaces. We find the most general form of the weak electromagnetic field compatible with the complete integrability of the particle motion and the comutativity of the field operators. For such a field we solve the charged Hamilton-Jacobi and Klein-Gordon equations by separation of variables.
Magnetic fields and fluctuations in weakly Mn doped ZnGeP{sub 2}
Mengyan, P. W.; Lichti, R. L.; Baker, B. B.; Celebi, Y. G.; Catak, E.; Carroll, B. R.; Zawilski, K. T.; Schunemann, P. G.
2014-02-21
We report on our measurements of local and bulk magnetic features in weakly Mn doped ZnGeP{sub 2}. Utilizing muon spin rotation and relaxation measurements, we identify local ferromagnetic order and fluctuations in the local fields as sampled by an implanted muon (μ{sup +}). We also report on field induced ferromagnetism occurring above the claimed paramagnetic to ferromagnetic transition temperature (T{sub c} = 312 K)
Biasing a ferronematic - a new way to detect weak magnetic field.
Tomašovičová, Natália; Kováč, Jozef; Raikher, Yuriy; Éber, Nándor; Tóth-Katona, Tibor; Gdovinová, Veronika; Jadżyn, Jan; Pinčák, Richard; Kopčanský, Peter
2016-06-29
The magnetic properties of a ferronematic, i.e., a nematic liquid crystal doped with magnetic nanoparticles in low volume concentration are studied, with the focus on the ac magnetic susceptibility. A weak dc bias magnetic field (a few Oe) applied to the ferronematic in its isotropic phase increases the ac magnetic susceptibility considerably. Passage of the isotropic-to-nematic phase transition resets this enhancement irreversibly (unless the dc bias field is applied again in the isotropic phase). PMID:27296792
Leeuwen-Segarceanu, Elena M. van; Dorresteijn, Lucille D.A.; Pillen, Sigrid; Biesma, Douwe H.; Vogels, Oscar J.M.; Alfen, Nens van
2012-02-01
Purpose: To describe the damage to the muscles and propose a pathophysiologic mechanism for muscle atrophy and weakness after mantle field radiotherapy in Hodgkin lymphoma (HL) survivors. Methods and Materials: We examined 12 patients treated by mantle field radiotherapy between 1969 and 1998. Besides evaluation of their symptoms, the following tests were performed: dynamometry; ultrasound of the sternocleidomastoid, biceps, and antebrachial flexor muscles; and needle electromyography of the neck, deltoid, and ultrasonographically affected arm muscles. Results: Ten patients (83%) experienced neck complaints, mostly pain and muscle weakness. On clinical examination, neck flexors were more often affected than neck extensors. On ultrasound, the sternocleidomastoid was severely atrophic in 8 patients, but abnormal echo intensity was seen in only 3 patients. Electromyography of the neck muscles showed mostly myogenic changes, whereas the deltoid, biceps, and antebrachial flexor muscles seemed to have mostly neurogenic damage. Conclusions: Many patients previously treated by mantle field radiotherapy develop severe atrophy and weakness of the neck muscles. Neck muscles within the radiation field show mostly myogenic damage, and muscles outside the mantle field show mostly neurogenic damage. The discrepancy between echo intensity and atrophy suggests that muscle damage is most likely caused by an extrinsic factor such as progressive microvascular fibrosis. This is also presumed to cause damage to nerves within the radiated field, resulting in neurogenic damage of the deltoid and arm muscles.
Ermakov, A M; Lednev, V V
2010-01-01
The effects of weak combined magnetic fields adjusted to the parametric resonance for Ca2+ and K+ and extremely weak alternating magnetic field on the metamorphosis of the meal-worm beetle Tenebrio molitor have been studied. It was shown that the exposure of pupas of insects to all above-indicated types of fields stimulates the metamorphosis. However, after the exposure to weak combined magnetic fields adjusted to the parametric resonance for Ca2+ and K+, the number of insects with anomalies increases, which is not observed by the action of the weak alternating magnetic field.
Ishikawa, Kazuhiro; Behrens, Manja; Eriksson, Stefanie; Topgaard, Daniel; Olsson, Ulf; Wennerström, Håkan
2016-07-01
It is shown that the ternary system heavy water-heptane-hexadecyl hexaethylene oxide (C16E6) has a stable bicontinuous microemulsion phase down to an exceptionally low concentration at the balanced temperature of 26.8 °C. It is further demonstrated that the ambient gravitational field has an influence on the observed phase equilibria for typical sample sizes (∼1 cm). Direct measurements using a nuclear magnetic resonance imaging technique demonstrate that sample compositions vary with the height in the vials. It is furthermore found that some samples show four phases at equilibrium in apparent violation of Gibbs' phase rule. It is pointed out that Gibbs' phase rule strictly applies only when effects of gravity are negligible. A further consequence of the ambient gravitational field is that, for the system studied, the microemulsion one-phase samples are not observed, when using standard size vials, that is, sample heights on the order of a centimeter. Quantitative determinations of concentration profiles can be used to determine parameters of the free-energy density for the system.
Formation of graded vanadium oxide (V–O compound) under strong gravitational field
Khandaker, Jahirul Islam; Tokuda, Makoto; Ogata, Yudai; Januszko, Kamila; Mashimo, Tsutomu; Nishiyama, Tadao; Yoshiasa, Akira
2015-05-14
Sedimentation of atoms induced under strong gravitational field gives a tool for controlling elemental compositions in condensed matter. We performed a strong-gravity experiment (0.397 × 10{sup 6 }G at 400 °C for 24 h) on a V{sub 2}O{sub 5} polycrystal using the high-temperature ultracentrifuge to examine the composition change and further the structure change. The graded composition structure of V and O was formed along gravity direction, where V increases and O decreases with gravity. It was found by the x-ray diffraction and Raman scattering method that VO{sub 2} and V{sub 2}O{sub 3} phases appeared and the amounts increased, while one of the V{sub 2}O{sub 5} phase decreased gradually along gravity direction. The X-ray absorption near edge structure spectra analysis identified the chemical valency decrease (+5 to +3). The UV-Vis absorption spectroscopy addressed the shifting in center of major absorption peak to longer wavelength (red shift) with the increase in gravitational field. The tail absorption peak (band gap 2.09 eV) at strong gravity region in the graded structure showed transparent conductive oxide.
Diffusion phenomenon at the interface of Cu-brass under a strong gravitational field
Ogata, Yudai; Tokuda, Makoto; Januszko, Kamila; Khandaker, Jahirul Islam; Mashimo, Tsutomu; Iguchi, Yusuke; Ono, Masao
2015-03-28
To investigate diffusion phenomenon at the interface between Cu and brass under a strong gravitational field generated by ultracentrifuge apparatus, we performed gravity experiments on samples prepared by electroplating with interfaces normal and parallel to the direction of gravity. For the parallel-mode sample, for which sedimentation cannot occur thorough the interface, the concentration change was significant within the lower gravity region; many pores were observed in this region. Many vacancies arising from crystal strain due to the strong gravitational field moved into the lower gravity region, and enhanced the atoms mobilities. For the two normal-mode samples, which have interface normal to the direction of gravity, the composition gradient of the brass-on-Cu sample was steeper than that for Cu-on-brass. This showed that the atoms of denser Cu diffuse in the direction of gravity, whereas Zn atoms diffuse in the opposite direction by sedimentation. The interdiffusion coefficients became higher in the Cu-on-brass sample, and became lower in the brass-on-Cu sample. This rise may be related to the behavior of the vacancies.
Formation of graded vanadium oxide (V-O compound) under strong gravitational field
NASA Astrophysics Data System (ADS)
Khandaker, Jahirul Islam; Tokuda, Makoto; Ogata, Yudai; Januszko, Kamila; Nishiyama, Tadao; Yoshiasa, Akira; Mashimo, Tsutomu
2015-05-01
Sedimentation of atoms induced under strong gravitational field gives a tool for controlling elemental compositions in condensed matter. We performed a strong-gravity experiment (0.397 × 106 G at 400 °C for 24 h) on a V2O5 polycrystal using the high-temperature ultracentrifuge to examine the composition change and further the structure change. The graded composition structure of V and O was formed along gravity direction, where V increases and O decreases with gravity. It was found by the x-ray diffraction and Raman scattering method that VO2 and V2O3 phases appeared and the amounts increased, while one of the V2O5 phase decreased gradually along gravity direction. The X-ray absorption near edge structure spectra analysis identified the chemical valency decrease (+5 to +3). The UV-Vis absorption spectroscopy addressed the shifting in center of major absorption peak to longer wavelength (red shift) with the increase in gravitational field. The tail absorption peak (band gap 2.09 eV) at strong gravity region in the graded structure showed transparent conductive oxide.
Inferring Gene Regulatory Networks by Singular Value Decomposition and Gravitation Field Algorithm
Zheng, Ming; Wu, Jia-nan; Huang, Yan-xin; Liu, Gui-xia; Zhou, You; Zhou, Chun-guang
2012-01-01
Reconstruction of gene regulatory networks (GRNs) is of utmost interest and has become a challenge computational problem in system biology. However, every existing inference algorithm from gene expression profiles has its own advantages and disadvantages. In particular, the effectiveness and efficiency of every previous algorithm is not high enough. In this work, we proposed a novel inference algorithm from gene expression data based on differential equation model. In this algorithm, two methods were included for inferring GRNs. Before reconstructing GRNs, singular value decomposition method was used to decompose gene expression data, determine the algorithm solution space, and get all candidate solutions of GRNs. In these generated family of candidate solutions, gravitation field algorithm was modified to infer GRNs, used to optimize the criteria of differential equation model, and search the best network structure result. The proposed algorithm is validated on both the simulated scale-free network and real benchmark gene regulatory network in networks database. Both the Bayesian method and the traditional differential equation model were also used to infer GRNs, and the results were used to compare with the proposed algorithm in our work. And genetic algorithm and simulated annealing were also used to evaluate gravitation field algorithm. The cross-validation results confirmed the effectiveness of our algorithm, which outperforms significantly other previous algorithms. PMID:23226565
Ishikawa, Kazuhiro; Behrens, Manja; Eriksson, Stefanie; Topgaard, Daniel; Olsson, Ulf; Wennerström, Håkan
2016-07-01
It is shown that the ternary system heavy water-heptane-hexadecyl hexaethylene oxide (C16E6) has a stable bicontinuous microemulsion phase down to an exceptionally low concentration at the balanced temperature of 26.8 °C. It is further demonstrated that the ambient gravitational field has an influence on the observed phase equilibria for typical sample sizes (∼1 cm). Direct measurements using a nuclear magnetic resonance imaging technique demonstrate that sample compositions vary with the height in the vials. It is furthermore found that some samples show four phases at equilibrium in apparent violation of Gibbs' phase rule. It is pointed out that Gibbs' phase rule strictly applies only when effects of gravity are negligible. A further consequence of the ambient gravitational field is that, for the system studied, the microemulsion one-phase samples are not observed, when using standard size vials, that is, sample heights on the order of a centimeter. Quantitative determinations of concentration profiles can be used to determine parameters of the free-energy density for the system. PMID:27035803
Zonal Toroidal Harmonic Expansions of External Gravitational Fields for Ring-like Objects
NASA Astrophysics Data System (ADS)
Fukushima, Toshio
2016-08-01
We present an expression of the external gravitational field of a general ring-like object with axial and plane symmetries such as oval toroids or annular disks with an arbitrary density distribution. The main term is the gravitational field of a uniform, infinitely thin ring representing the limit of zero radial width and zero vertical height of the object. The additional term is derived from a zonal toroidal harmonic expansion of a general solution of Laplace’s equation outside the Brillouin toroid of the object. The special functions required are the point value and the first-order derivative of the zonal toroidal harmonics of the first kind, namely, the Legendre function of the first kind of half integer degree and an argument that is not less than unity. We developed a recursive method to compute them from two pairs of seed values explicitly expressed by some complete elliptic integrals. Numerical experiments show that appropriately truncated expansions converge rapidly outside the Brillouin toroid. The truncated expansion can be evaluated so efficiently that, for an oval toroid with an exponentially damping density profile, it is 3000–10,000 times faster than the two-dimensional numerical quadrature. A group of the Fortran 90 programs required in the new method and their sample outputs are available electronically.
Inferring gene regulatory networks by singular value decomposition and gravitation field algorithm.
Zheng, Ming; Wu, Jia-nan; Huang, Yan-xin; Liu, Gui-xia; Zhou, You; Zhou, Chun-guang
2012-01-01
Reconstruction of gene regulatory networks (GRNs) is of utmost interest and has become a challenge computational problem in system biology. However, every existing inference algorithm from gene expression profiles has its own advantages and disadvantages. In particular, the effectiveness and efficiency of every previous algorithm is not high enough. In this work, we proposed a novel inference algorithm from gene expression data based on differential equation model. In this algorithm, two methods were included for inferring GRNs. Before reconstructing GRNs, singular value decomposition method was used to decompose gene expression data, determine the algorithm solution space, and get all candidate solutions of GRNs. In these generated family of candidate solutions, gravitation field algorithm was modified to infer GRNs, used to optimize the criteria of differential equation model, and search the best network structure result. The proposed algorithm is validated on both the simulated scale-free network and real benchmark gene regulatory network in networks database. Both the Bayesian method and the traditional differential equation model were also used to infer GRNs, and the results were used to compare with the proposed algorithm in our work. And genetic algorithm and simulated annealing were also used to evaluate gravitation field algorithm. The cross-validation results confirmed the effectiveness of our algorithm, which outperforms significantly other previous algorithms.
Gas-Phase Influence on Quasisteady "Liquid Flames" in Gravitational Fields
NASA Technical Reports Server (NTRS)
Shkadinsky, K. G.; Shkadinskaya, G. V.; Matkowsky, B. J.; Gokoglu, S. (Technical Monitor)
2000-01-01
We consider the SHS (self-propagating high-temperature synthesis) process for synthesizing materials. In this process a powder mixture of reactants is cold pressed into a sample, which is ignited at one end. A high temperature combustion wave then propagates through the sample converting reactants to the desired product material. In this process, melting of some or all the components is often observed. Therefore, we study combustion waves propagating through a high caloricity inorganic powder mixture whose combustion temperature exceeds the melting temperatures of many components. The solid matrix is thus destroyed by the propagating combustion wave due to melting ahead of the reaction zone, and a liquid bath is formed which contains gaseous bubbles. The waves propagate in the presence of a gravitational field. Due to the effect of gravity, there is relative motion between the rising bubbles and the descending bath, which affects the composition of the medium, its thermophysical properties, the 'liquid flame' structure, and the propagation velocity. To enhance our understanding of phenomena associated with the interaction of the relative motion with the propagating combustion wave we formulate and analyze a relatively simple mathematical model of liquid flames in a gravitational field. We describe the wave structure and combustion characteristics including the combustion velocity. We compare our results to existing experimental observations and suggest new experiments to be performed. We consider the effects of gravity and, in particular, examine both microgravity and large gravity conditions.
Zonal Toroidal Harmonic Expansions of External Gravitational Fields for Ring-like Objects
NASA Astrophysics Data System (ADS)
Fukushima, Toshio
2016-08-01
We present an expression of the external gravitational field of a general ring-like object with axial and plane symmetries such as oval toroids or annular disks with an arbitrary density distribution. The main term is the gravitational field of a uniform, infinitely thin ring representing the limit of zero radial width and zero vertical height of the object. The additional term is derived from a zonal toroidal harmonic expansion of a general solution of Laplace’s equation outside the Brillouin toroid of the object. The special functions required are the point value and the first-order derivative of the zonal toroidal harmonics of the first kind, namely, the Legendre function of the first kind of half integer degree and an argument that is not less than unity. We developed a recursive method to compute them from two pairs of seed values explicitly expressed by some complete elliptic integrals. Numerical experiments show that appropriately truncated expansions converge rapidly outside the Brillouin toroid. The truncated expansion can be evaluated so efficiently that, for an oval toroid with an exponentially damping density profile, it is 3000-10,000 times faster than the two-dimensional numerical quadrature. A group of the Fortran 90 programs required in the new method and their sample outputs are available electronically.
Dust acoustic shock wave in electronegative dusty plasma: Roles of weak magnetic field
Ghosh, Samiran; Ehsan, Z.; Murtaza, G.
2008-02-15
The effects of nonsteady dust charge variations and weak magnetic field on small but finite amplitude nonlinear dust acoustic wave in electronegative dusty plasma are investigated. The dynamics of the nonlinear wave are governed by a Korteweg-de Vries Burger equation that possesses dispersive shock wave. The weak magnetic field is responsible for the dispersive term, whereas nonsteady dust charge variation is responsible for dissipative term, i.e., the Burger term. The coefficient of dissipative term depends only on the obliqueness of the magnetic field. It is found that for parallel propagation the dynamics of the nonlinear wave are governed by the Burger equation that possesses monotonic shock wave. The relevances of the findings to cometary dusty plasma, e.g., Comet Halley are briefly discussed.
Novikov, V V; Sheĭman, I M; Iablokova, E V; Fesenko, E E
2014-01-01
It is shown that an exposure of pupae of the mealworm beetle Tenebrio molitor to the combined static (42 μT) and very weak alternating (250 nT) magnetic fields exerts different influence, depending on the frequency of the alternating magnetic field, on duration of metamorphosis processes in these insects. For instance, an exposure of pupae to weak combined magnetic fields, adjusted to the frequency of ion cyclotron resonance for glutaminic acid (4,4 Hz), stimulates metamorphosis process--a transitional stage from pupae to imago lasts shorter. An inhibiting effect was observed when adjusted to the frequency of ion cyclotron resonance for Ca2 (32,2 Hz). At some frequencies this effect is not seen. For instance, an exposure at a frequency of ion cyclotron resonance for K+ (16,5 Hz) exerts no noticeable effect on the duration of the pupal metamorphosis stage.
Novikov, V V; Sheĭman, I M; Iablokova, E V; Fesenko, E E
2014-01-01
It is shown that an exposure of pupae of the mealworm beetle Tenebrio molitor to the combined static (42 μT) and very weak alternating (250 nT) magnetic fields exerts different influence, depending on the frequency of the alternating magnetic field, on duration of metamorphosis processes in these insects. For instance, an exposure of pupae to weak combined magnetic fields, adjusted to the frequency of ion cyclotron resonance for glutaminic acid (4,4 Hz), stimulates metamorphosis process--a transitional stage from pupae to imago lasts shorter. An inhibiting effect was observed when adjusted to the frequency of ion cyclotron resonance for Ca2 (32,2 Hz). At some frequencies this effect is not seen. For instance, an exposure at a frequency of ion cyclotron resonance for K+ (16,5 Hz) exerts no noticeable effect on the duration of the pupal metamorphosis stage. PMID:25715625
NASA Astrophysics Data System (ADS)
Wang, H. B.; Zhao, C. Y.; Zhang, W.; Zhan, J. W.; Yu, S. X.
2015-09-01
The Earth gravitational filed model is a kind of important dynamic model in satellite orbit computation. In recent years, several space gravity missions have obtained great success, prompting a lot of gravitational filed models to be published. In this paper, 2 classical models (JGM3, EGM96) and 4 latest models, including EIGEN-CHAMP05S, GGM03S, GOCE02S, and EGM2008 are evaluated by being employed in the precision orbit determination (POD) and prediction, based on the laser range observation of four low earth orbit (LEO) satellites, including CHAMP, GFZ-1, GRACE-A, and SWARM-A. The residual error of observation in POD is adopted to describe the accuracy of six gravitational field models. We show the main results as follows: (1) for LEO POD, the accuracies of 4 latest models (EIGEN-CHAMP05S, GGM03S, GOCE02S, and EGM2008) are at the same level, and better than those of 2 classical models (JGM3, EGM96); (2) If taking JGM3 as reference, EGM96 model's accuracy is better in most situations, and the accuracies of the 4 latest models are improved by 12%-47% in POD and 63% in prediction, respectively. We also confirm that the model's accuracy in POD is enhanced with the increasing degree and order if they are smaller than 70, and when they exceed 70 the accuracy keeps stable, and is unrelated with the increasing degree, meaning that the model's degree and order truncated to 70 are sufficient to meet the requirement of LEO orbit computation with centimeter level precision.
Orbit determination and gravitational field accuracy for a Mercury transponder satellite
NASA Technical Reports Server (NTRS)
Vincent, Mark A.; Bender, Pater L.
1990-01-01
Covariance studies were performed to investigate the orbit determination problem for a small transponder satellite in a nearly circular polar orbit with 4-hour period around Mercury. With X band and Ka band Doppler and range measurements, the analysis indicates that the gravitational field through degree and order 10 can be solved for from as few as 40 separate 8-hour arcs of tracking data. In addition, the earth-Mercury distance can be determined during each ranging period with about 6-cm accuracy. The expected geoid accuracy is 10 cm up through degree 5, and 1 m through degree 8. The main error sources were the geocentric range measurement error, the uncertainties in higher degree gravity field terms, which were not solved for, and the solar radiation pressure uncertainty.
NASA Technical Reports Server (NTRS)
Sjogren, W. L.; Wollenhaupt, W. R.; Wimberly, R. N.
1973-01-01
The purpose of this experiment was to measure the variations in the lunar gravitational field near the trajectory of orbiting space vehicles (the command and service module (CSM) and the small particles and fields subsatellites ejected from the Apollo 15 and 16 spacecraft). New information has been obtained from all Apollo orbiting spacecraft; however, this report shall be limited to the results from the Apollo 17 CSM and the Apollo 16 subsatellite. The data acquired are precise speed measurements of the orbiting spacecraft from which accelerations or gravity profiles may be inferred. Feature resolution is controlled by the spacecraft altitude and is almost a direct relationship (i.e., data taken from a 50-km altitude will resolve approximately a 50-km feature). Therefore, revolutions 3 to 12, when the CSM was in the low-altitude orbits, provided the clearest information.
A null-tetrad approach to Kerr{endash}Schild gravitational fields in matter
Udeschini, E.B.; Magli, G.
1996-11-01
The null tetrad formalism is used to investigate the structure of the Einstein field equations for Kerr{endash}Schild gravitational fields in the presence of an elastic solid source. It is shown that such equations may be reduced to five nonlinear partial differential equations for five variables. It turns out that, when the interior solutions admit the same preferred null congruence of the vacuum ones and some compatibility conditions hold, it is possible to reduce them to a linear system and to develop a method of solution which closely resembles the {open_quote}{open_quote}variation of the arbitrary constants{close_quote}{close_quote} for ordinary differential equations. In the present paper, the above technical framework is developed in general and applied to two simple examples, deferring to future work the approach to the Kerr{endash}interior problem. {copyright} {ital 1996 American Institute of Physics.}
Conversion of relic gravitational waves into photons in cosmological magnetic fields
Dolgov, Alexander D.; Ejlli, Damian E-mail: ejlli@fe.infn.it
2012-12-01
Conversion of gravitational waves into electromagnetic radiation is discussed. The probability of transformations of gravitons into photons in presence of cosmological background magnetic field is calculated at the recombination epoch and during subsequent cosmological stages. The produced electromagnetic radiation is concentrated in the X-ray part of the spectrum. It is shown that if the early Universe was dominated by primordial black holes (PBHs) prior to Big Bang Nucleosynthesis (BBN), the relic gravitons emitted by PBHs would transform to an almost isotropic background of electromagnetic radiation due to conversion of gravitons into photons in cosmological magnetic fields. Such extragalactic radiation could be noticeable or even dominant component of Cosmic X-ray Background.
Three-dimensional magnetized and rotating hot plasma equilibrium in a gravitational field
NASA Astrophysics Data System (ADS)
Catto, Peter J.; Krasheninnikov, Sergei I.; Pusztai, Istvan
2015-11-01
We present analytic and numerical solutions for three-dimensional magnetized axisymmetric equilibria confining rotating hot plasma in a gravitational field. Our solution to the full Shafranov-Grad equation can exhibit strong equatorial plane localization of the plasma density and current, resulting in disk equilibria for the plasma density. We find that a toriodal magnetic field is sometimes necessary to find a equilibrium in the presence of gravity for many cases of interest. Work supported by the US Department of Energy grants DE-FG02-91ER-54109 at MIT and DE-FG02-04ER54739 at UCSD & by an International Career Grant from Vetenskapsrådet.
Weak cosmic censorship, dyonic Kerr-Newman black holes and Dirac fields
NASA Astrophysics Data System (ADS)
Zsolt Tóth, Gábor
2016-06-01
It was investigated recently, with the aim of testing the weak cosmic censorship conjecture, whether an extremal Kerr black hole can be converted into a naked singularity by interaction with a massless classical Dirac test field, and it was found that this is possible. We generalize this result to electrically and magnetically charged rotating extremal black holes (i.e. extremal dyonic Kerr-Newman black holes) and massive Dirac test fields, allowing magnetically or electrically uncharged or nonrotating black holes and the massless Dirac field as special cases. We show that the possibility of the conversion is a direct consequence of the fact that the Einstein-Hilbert energy-momentum tensor of the classical Dirac field does not satisfy the null energy condition, and is therefore not in contradiction with the weak cosmic censorship conjecture. We give a derivation of the absence of superradiance of the Dirac field without making use of the complete separability of the Dirac equation in the dyonic Kerr-Newman background, and we determine the range of superradiant frequencies of the scalar field. The range of frequencies of the Dirac field that can be used to convert a black hole into a naked singularity partially coincides with the superradiant range of the scalar field. We apply horizon-penetrating coordinates, as our arguments involve calculating quantities at the event horizon. We describe the separation of variables for the Dirac equation in these coordinates, although we mostly avoid using it.
NASA Astrophysics Data System (ADS)
Clevenson, Hannah; Chen, Edward H.; Dolde, Florian; Teale, Carson; Englund, Dirk; Braje, Danielle
2016-08-01
We report on detailed studies of electronic and nuclear spin states in the diamond-nitrogen-vacancy (NV) center under weak transverse magnetic fields. We numerically predict and experimentally verify a previously unobserved NV hyperfine level anticrossing (LAC) occurring at bias fields of tens of gauss—two orders of magnitude lower than previously reported LACs at ˜500 and ˜1000 G axial magnetic fields. We then discuss how the NV ground-state Hamiltonian can be manipulated in this regime to tailor the NV's sensitivity to environmental factors and to map into the nuclear spin state.
Extinction of photoemission of Mn-Doped ZnS nanofluid in weak magnetic field
NASA Astrophysics Data System (ADS)
Vu, Anh-Tuan; Bui, Hong-Van; Pham, Van-Ben; Le, Van-Hong; Hoang, Nam-Nhat
2016-08-01
The observation of extinction of photoluminescence of Mn-doped ZnS nanofluid under applying of weak magnetic field is reported. At a constant field of 270 Gauss and above, the exponential decays of photoluminescent intensity was observed in disregard of field direction. About 50% extinction was achieved after 30 minute magnetization and a total extinction after 1 hour. The memory effect preserved for more than 2 hours at room temperature. This extinction was observed in a system with no clear ferromagnetic behavior.
Detection of ultra-weak magnetic fields in Am stars: β Ursae Majoris and θ Leonis
NASA Astrophysics Data System (ADS)
Blazère, A.; Petit, P.; Lignières, F.; Aurière, M.; Ballot, J.; Böhm, T.; Folsom, C. P.; Gaurat, M.; Jouve, L.; Lopez Ariste, A.; Neiner, C.; Wade, G. A.
2016-02-01
Context. An extremely weak circularly polarized signature was recently discovered in spectral lines of the chemically peculiar Am star Sirius A. A weak surface magnetic field was proposed to account for the observed polarized signal, but the shape of the phase-averaged signature, dominated by a prominent positive lobe, is not expected in the standard theory of the Zeeman effect. Aims: We aim at verifying the presence of weak circularly polarized signatures in two other bright Am stars, β UMa and θ Leo, and investigating the physical origin of Sirius-like polarized signals further. Methods: We present here a set of deep spectropolarimetric observations of β UMa and θ Leo, observed with the NARVAL spectropolarimeter. We analyzed all spectra with the least squares deconvolution multiline procedure. To improve the signal-to-noise ratio and detect extremely weak signatures in Stokes V profiles, we co-added all available spectra of each star (around 150 observations each time). Finally, we ran several tests to evaluate whether the detected signatures are consistent with the behavior expected from the Zeeman effect. Results: The line profiles of the two stars display circularly polarized signatures similar in shape and amplitude to the observations previously gathered for Sirius A. Our series of tests brings further evidence of a magnetic origin of the recorded signal. Conclusions: These new detections suggest that very weak magnetic fields may well be present in the photospheres of a significant fraction of intermediate-mass stars. The strongly asymmetric Zeeman signatures measured so far in Am stars (featuring a dominant single-sign lobe) are not expected in the standard theory of the Zeeman effect and may be linked to sharp vertical gradients in photospheric velocities and magnetic field strengths.
The Decay of a Weak Large-scale Magnetic Field in Two-dimensional Turbulence
NASA Astrophysics Data System (ADS)
Kondić, Todor; Hughes, David W.; Tobias, Steven M.
2016-06-01
We investigate the decay of a large-scale magnetic field in the context of incompressible, two-dimensional magnetohydrodynamic turbulence. It is well established that a very weak mean field, of strength significantly below equipartition value, induces a small-scale field strong enough to inhibit the process of turbulent magnetic diffusion. In light of ever-increasing computer power, we revisit this problem to investigate fluids and magnetic Reynolds numbers that were previously inaccessible. Furthermore, by exploiting the relation between the turbulent diffusion of the magnetic potential and that of the magnetic field, we are able to calculate the turbulent magnetic diffusivity extremely accurately through the imposition of a uniform mean magnetic field. We confirm the strong dependence of the turbulent diffusivity on the product of the magnetic Reynolds number and the energy of the large-scale magnetic field. We compare our findings with various theoretical descriptions of this process.
NASA Astrophysics Data System (ADS)
Monarkha, V. Yu.; Paschenko, V. A.; Timofeev, V. P.
2013-02-01
The dynamics of Abrikosov vortices and their bundles was experimentally investigated in weak constant magnetic fields, in the range of Earth's magnetic field. Characteristics of the isothermal magnetization relaxation in YBCO single-crystal samples with strong pinning centers were studied for different sample-field orientation. The obtained values of normalized relaxation rate S allowed us to estimate the effective pinning potential U in the bulk of the YBCO sample and its temperature dependence, as well as the critical current density Jc. A comparison between the data obtained and the results of similar measurements in significantly higher magnetic fields was performed. To compare different techniques for evaluation of Jc, the magnetization loop measurements M(H), which relate the loop width to the critical current, were carried out. These measurements provided important parameters of the samples under study (penetration field Hp and first critical field Hc1), which involve the geometrical configuration of the samples.
TESTING WEAK-LENSING MAPS WITH REDSHIFT SURVEYS: A SUBARU FIELD
Kurtz, Michael J.; Geller, Margaret J.; Fabricant, Daniel G.; Utsumi, Yousuke; Miyazaki, Satoshi; Dell'Antonio, Ian P. E-mail: mgeller@cfa.harvard.edu E-mail: yousuke.utsumi@nao.ac.jp E-mail: ian@het.brown.edu
2012-05-10
We use a dense redshift survey in the foreground of the Subaru GTO2deg{sup 2} weak-lensing field (centered at {alpha}{sub 2000} = 16{sup h}04{sup m}44{sup s}; {delta}{sub 2000} = 43 Degree-Sign 11'24'') to assess the completeness and comment on the purity of massive halo identification in the weak-lensing map. The redshift survey (published here) includes 4541 galaxies; 4405 are new redshifts measured with the Hectospec on the MMT. Among the weak-lensing peaks with a signal-to-noise greater than 4.25, 2/3 correspond to individual massive systems; this result is essentially identical to the Geller et al. test of the Deep Lens Survey (DLS) field F2. The Subaru map, based on images in substantially better seeing than the DLS, enables detection of less massive halos at fixed redshift as expected. We demonstrate that the procedure adopted by Miyazaki et al. for removing some contaminated peaks from the weak-lensing map improves agreement between the lensing map and the redshift survey in the identification of candidate massive systems.
Size-dependent nonlinear weak-field magnetic behavior of maghemite nanoparticles.
de Montferrand, Caroline; Lalatonne, Yoann; Bonnin, Dominique; Lièvre, Nicole; Lecouvey, Marc; Monod, Philippe; Russier, Vincent; Motte, Laurence
2012-06-25
The magnetic behavior at room temperature of maghemite nanoparticles of variable sizes (from 7 to 20 nm) is compared using a conventional super quantum interference device (SQUID) and a recently patented technology, called MIAplex. The SQUID usually measures the magnetic response versus an applied magnetic field in a quasi-static mode until high field values (from -4000 to 4000 kA m(-1)) to determine the field-dependence and saturation magnetization of the sample. The MIAplex is a handheld portable device that measures a signal corresponding to the second derivative of the magnetization around zero field (between -15 and 15 kA m(-1)). In this paper, the magnetic response of the size series is correlated, both in diluted and powder form, between the SQUID and MIAplex. The SQUID curves are measured at room temperature in two magnetic field ranges from -4000 to 4000 kA m(-1) (-5T to 5T) and from -15 to 15 kA m(-1). Nonlinear behavior at weak fields is highlighted and the magnetic curves for diluted solutions evolve from quasi-paramagnetic to superparamagnetic behavior when the size of the nanoparticles increases. For the 7-nm sample, the fit of the magnetization with the Langevin model weighted with log-normal distribution corresponds closely to the magnetic size. This confirms the accuracy of the model of non-interacting superparamagnetic particles with a magnetically frustrated surface layer of about 0.5 nm thickness. For the other samples (10-nm to 21-nm), the experimental weak-field magnetization curves are modeled by more than one population of magnetically responding species. This behavior is consistent with a chemically uniform but magnetically distinct structure composed of a core and a magnetically active nanoparticle canted shell. Accordingly the weak-field signature corresponds to the total assembly of the nanoparticles. The impact of size polydispersity is also discussed.
Thermoelectric Magnetohydrodynamic Flow During Crystal Growth with a Moderate or Weak Magnetic Field
NASA Technical Reports Server (NTRS)
Khine, Y. Y.; Walker, John S.; Szofran, Frank R.; Rose, M. Franklin (Technical Monitor)
2000-01-01
This paper treats a steady, axisymmetric melt motion in a cylindrical ampoule with a uniform, axial magnetic field and with an electric current due to a radial temperature variation along the crystal-melt interface, where the values of the absolute thermoelectric power for the crystal and melt are different. The radial component of the thermoelectric current in the melt produces an azimuthal body force, and the axial variation of the centrifugal force due to the azimuthal motion drives a meridional circulation with radial and axial velocities. For moderate magnetic field strengths, the azimuthal velocity and magnetic field produce a radial induced electric field which partially cancels the Seebeck electromotive force in the melt, so that the thermoelectric current and the melt motion are coupled. For weak magnetic fields, the thermoelectric current is decoupled from the melt motion, which is an ordinary hydrodynamic flow driven by a known azimuthal body force. The results show how the flow varies with the strength of the magnetic field and with the magnitude of the temperature variation along the crystal-melt interface. They also define the parameter ranges for which the simpler weak-field decoupled analysis gives accurate predictions.
On the equilibrium shape of a heavily charged drop suspended in a weak electrostatic field
NASA Astrophysics Data System (ADS)
Shiryaeva, S. O.; Petrushov, N. A.; Grigor'ev, A. I.
2015-08-01
The object of investigation is the shape of a heavily charged drop placed in a weak electrostatic field. Calculations were carried out in the fourth order of smallness in the eccentricity, through which the steady-state deformation of the drop is measured. It is shown that the equilibrium shape of such a drop can be approximated by a prolate spheroid. This shape is due to the self-charge of the drop rather than to the external field, which is very weak and merely specifies a preferred direction. In an electrostatic suspension, where such a situation may take place, the deformation-related measurement inaccuracy of the critical charge can be totally eliminated if fine droplets are used.
Weak Solutions of the Cohomological Equation on ℝ 2 {mathbb {R}}(2) for Regular Vector Fields
NASA Astrophysics Data System (ADS)
De Leo, Roberto
2015-12-01
In a recent article (De Leo, R., Ann. Glob. Anal. Geom., 39, 3, 231-248 2011), we studied the global solvability of the so-called cohomological equation L ξ f = g in , where ξ is a regular vector field on the plane and L ξ the corresponding Lie derivative operator. In a joint article with T. Gramchev and A. Kirilov (2011), we studied the existence of global weak solutions of the cohomological equation for planar vector fields depending only on one coordinate. Here we generalize the results of both articles by providing explicit conditions for the existence of global weak solutions to the cohomological equation when ξ is intrinsically Hamiltonian or of finite type.
Magnetic field mapping of the UCNTau magneto-gravitational trap: design study
Libersky, Matthew Murray
2014-09-04
The beta decay lifetime of the free neutron is an important input to the Standard Model of particle physics, but values measured using different methods have exhibited substantial disagreement. The UCN r experiment in development at Los Alamos National Laboratory (LANL) plans to explore better methods of measuring the neutron lifetime using ultracold neutrons (UCNs). In this experiment, UCNs are confined in a magneto-gravitational trap formed by a curved, asymmetric Halbach array placed inside a vacuum vessel and surrounded by holding field coils. If any defects present in the Halbach array are sufficient to reduce the local field near the surface below that needed to repel the desired energy level UCNs, loss by material interaction can occur at a rate similar to the loss by beta decay. A map of the magnetic field near the surface of the array is necessary to identify any such defects, but the array's curved geometry and placement in a vacuum vessel make conventional field mapping methods difficult. A system consisting of computer vision-based tracking and a rover holding a Hall probe has been designed to map the field near the surface of the array, and construction of an initial prototype has begun at LANL. The design of the system and initial results will be described here.
Astronomers Use X-Rays To Probe Gravitational Field Of A Neutron Star
NASA Astrophysics Data System (ADS)
2002-06-01
With NASA's Chandra X-ray Observatory, astronomers have detected features that may be the first direct evidence of the effect of gravity on radiation from a neutron star. This finding, if confirmed, could enable scientists to measure the gravitational field of neutron stars and determine whether they contain exotic forms of matter not seen on Earth. A team led by George Pavlov of Penn State University in University Park observed 1E 1207.4-5209, a neutron star in the center of a supernova remnant about 7,000 light years from Earth. The results were presented on June 6, 2002, at the American Astronomical Society in Albuquerque, NM. Pavlov's group found two dips, or absorption features, in the spectrum of X-rays from the star. If these dips are due to the absorption of X-rays near the star by helium ions in a strong magnetic field, they indicate that the gravitational field reduces the energies of X-rays escaping from near the surface of a neutron star. "This interpretation is consistent with the data," said Pavlov, "but the features may be a blend of many other features. More precise measurements, preferably with Chandra's grating spectrometer, are needed." "These absorption features may be the first evidence of the effect of gravity on radiation near the surface of an isolated neutron star," said Pavlov. "This is particularly important because it would allow us to set limits on the type of matter that comprises this star." Neutron stars are formed when a massive star runs out of fuel and its core collapses. A supernova explosion occurs and the collapsed core is compressed to a hot object about 12 miles in diameter, with a thin atmosphere of hydrogen and possibly heavier ions in a gravitational field 100 billion times as strong as Earth's. These objects, which have a density of more than 1 billion tons per teaspoonful, are called neutron stars because they have been thought to be composed mostly of neutrons. Although neutron stars have been studied extensively for
Probing gravitational dark matter
NASA Astrophysics Data System (ADS)
Ren, Jing; He, Hong-Jian
2015-03-01
So far all evidences of dark matter (DM) come from astrophysical and cosmological observations, due to the gravitational interactions of DM. It is possible that the true DM particle in the universe joins gravitational interactions only, but nothing else. Such a Gravitational DM (GDM) may act as a weakly interacting massive particle (WIMP), which is conceptually simple and attractive. In this work, we explore this direction by constructing the simplest scalar GDM particle χs. It is a Bbb Z2 odd singlet under the standard model (SM) gauge group, and naturally joins the unique dimension-4 interaction with Ricci curvature, ξsχs2Script R, where ξs is the dimensionless nonminimal coupling. We demonstrate that this gravitational interaction ξsχs2Script R, together with Higgs-curvature nonminimal coupling term ξhH†HScript R, induces effective couplings between χs2 and SM fields, and can account for the observed DM thermal relic abundance. We analyze the annihilation cross sections of GDM particles and derive the viable parameter space for realizing the DM thermal relic density. We further study the direct/indirect detections and the collider signatures of such a scalar GDM. These turn out to be highly predictive and testable.
Probing gravitational dark matter
Ren, Jing; He, Hong-Jian
2015-03-27
So far all evidences of dark matter (DM) come from astrophysical and cosmological observations, due to the gravitational interactions of DM. It is possible that the true DM particle in the universe joins gravitational interactions only, but nothing else. Such a Gravitational DM (GDM) may act as a weakly interacting massive particle (WIMP), which is conceptually simple and attractive. In this work, we explore this direction by constructing the simplest scalar GDM particle χ{sub s}. It is a ℤ{sub 2} odd singlet under the standard model (SM) gauge group, and naturally joins the unique dimension-4 interaction with Ricci curvature, ξ{sub s}χ{sub s}{sup 2}R, where ξ{sub s} is the dimensionless nonminimal coupling. We demonstrate that this gravitational interaction ξ{sub s}χ{sub s}{sup 2}R, together with Higgs-curvature nonminimal coupling term ξ{sub h}H{sup †}HR, induces effective couplings between χ{sub s}{sup 2} and SM fields, and can account for the observed DM thermal relic abundance. We analyze the annihilation cross sections of GDM particles and derive the viable parameter space for realizing the DM thermal relic density. We further study the direct/indirect detections and the collider signatures of such a scalar GDM. These turn out to be highly predictive and testable.
Improved model of the Earth's gravitational field: GEM-T1
Marsh, J.G.; Lerch, F.J.; Christodoulidis, D.C.; Putney, B.H.; Felsentreger, T.L.; Sanchez, B.V.; Smith, D.E.; Klosko, S.M.; Martin, T.V.; Pavlis, E.C.
1987-07-01
Goddard Earth Model T1 (GEM-T1), which was developed from an analysis of direct satellite tracking observations, is the first in a new series of such models. GEM-T1 is complete to degree and order 36. It was developed using consistent reference parameters and extensive earth and ocean tidal models. It was simultaneously solved for gravitational and tidal terms, earth orientation parameters, and the orbital parameters of 580 individual satellite arcs. The solution used only satellite tracking data acquired on 17 different satellites and is predominantly based upon the precise laser data taken by third generation systems. In all, 800,000 observations were used. A major improvement in field accuracy was obtained. For marine geodetic applications, long wavelength geoidal modeling is twice as good as in earlier satellite-only GEM models. Orbit determination accuracy has also been substantially advanced over a wide range of satellites that have been tested.
Mechanism of Partial Flame Propagation and Extinction in a Strong Gravitational Field.
Kazakov, Kirill A
2015-12-31
A theory of partial flame propagation driven by the gravitational field is developed. Using the on-shell approach, equations for the gas velocity distributions and the front shape of a steady flame are obtained and solved numerically. It is found that the solutions describing upward flame propagation come in pairs having close propagation speeds, and that the effect of strong gravity is to reverse the burnt gas velocity profile generated by the flame. On the basis of these results, a complete explanation is given of the intricate observed behavior of flames near the limits of inflammability, including the dependence of the inflammability range on the size of the combustion domain, the large distances of partial flame propagation, and the progression of flame extinction.
An improved model of the Earth's gravitational field: GEM-T1
NASA Technical Reports Server (NTRS)
Marsh, J. G.; Lerch, F. J.; Christodoulidis, D. C.; Putney, B. H.; Felsentreger, T. L.; Sanchez, B. V.; Smith, D. E.; Klosko, S. M.; Martin, T. V.; Pavlis, E. C.
1987-01-01
Goddard Earth Model T1 (GEM-T1), which was developed from an analysis of direct satellite tracking observations, is the first in a new series of such models. GEM-T1 is complete to degree and order 36. It was developed using consistent reference parameters and extensive earth and ocean tidal models. It was simultaneously solved for gravitational and tidal terms, earth orientation parameters, and the orbital parameters of 580 individual satellite arcs. The solution used only satellite tracking data acquired on 17 different satellites and is predominantly based upon the precise laser data taken by third generation systems. In all, 800,000 observations were used. A major improvement in field accuracy was obtained. For marine geodetic applications, long wavelength geoidal modeling is twice as good as in earlier satellite-only GEM models. Orbit determination accuracy has also been substantially advanced over a wide range of satellites that have been tested.
Semiclassical and quantum description of an ideal Bose gas in a uniform gravitational field
NASA Astrophysics Data System (ADS)
Bhaduri, Rajat K.; van Dijk, Wytse
2016-07-01
We consider an ideal Bose gas contained in a cylinder in three spatial dimensions, subjected to a uniform gravitational field. It has been claimed by some authors that there is discrepancy between the semiclassical and quantum calculations in the thermal properties of such a system. To check this claim, we calculate the heat capacity and isothermal compressibility of this system semiclassically as well as from the quantum spectrum of the density of states. The quantum calculation is done for a finite number of particles. We find good agreement between the two calculations when the number of particles are taken to be large. We also find that this system has the same thermal properties as an ideal five dimensional Bose gas.
NASA Astrophysics Data System (ADS)
Petrovskaya, M. S.
The conventional approach to the recovery of the Earth's gravitational field from satellite gradiometry observations is based on constructing, from the start, several boundary value (BV) relations, each of them corresponding to a separate observable component of the gravity gradient (GG) tensor or a certain combination of them. In particular, one of such projects, the ARISTOTELES mission, assumes that only the radial and across-track components are accessible (by technical reasons). The purpose of the present paper is mainly to discuss the principle aspects of the problem of the Earth's potential recovering from satellite gradiometry, to give an optimal formulation of the problem and derive the basic boundary value equation in different forms.
NASA Technical Reports Server (NTRS)
Nisbet, John S.
1989-01-01
General equations for the Reynolds number of a variety of types of ice crystals and water drops are given in terms of the Davies, Bond, and Knudsen numbers. The equations are in terms of the basic physical parameters of the system and are valid for calculating velocities in gravitational and electric fields over a very wide range of sizes and atmospheric conditions. The equations are asymptotically matched at the bottom and top of the size spectrum, useful when checking large computer codes. A numerical system for specifying the dimensional properties of ice crystals is introduced. Within the limits imposed by such variables as particle density, which have large deviations, the accuracy of velocities appears to be within 10 percent over the entire range of sizes of interest.
Variations of Mars gravitational field and rotation due to seasonal CO sub 2 exchange
Chao, B.F.; Rubincam, D.P. )
1990-08-30
About a quarter of the Martian atmospheric mass is exchanged between the atmosphere and the polar caps in the course of a Martian year: CO{sub 2} condenses to form (or add to) the polar caps in winter and sublimes into the atmosphere in summer. This paper studies the effect of this CO{sub 2} mass redistribution on Martian rotation and gravitational field. Two mechanisms are examined: (1) the waxing and waning of solid CO{sub 2} in the polar caps and (2) the geographical distribution of gaseous CO{sub 2} in the atmosphere. In particular, the net peak-to-peak changes in J{sub 2} and J{sub 3} over a Martian year are both found to be as much as {approximately}6 {times} 10{sup {minus}9}. A simulation suggests that these changes may be detected by the upcoming Mars Observer under favorable but realistic conditions.
Mechanism of Partial Flame Propagation and Extinction in a Strong Gravitational Field
NASA Astrophysics Data System (ADS)
Kazakov, Kirill A.
2015-12-01
A theory of partial flame propagation driven by the gravitational field is developed. Using the on-shell approach, equations for the gas velocity distributions and the front shape of a steady flame are obtained and solved numerically. It is found that the solutions describing upward flame propagation come in pairs having close propagation speeds, and that the effect of strong gravity is to reverse the burnt gas velocity profile generated by the flame. On the basis of these results, a complete explanation is given of the intricate observed behavior of flames near the limits of inflammability, including the dependence of the inflammability range on the size of the combustion domain, the large distances of partial flame propagation, and the progression of flame extinction.
NASA Technical Reports Server (NTRS)
Nisbet, John S.
1988-01-01
General equations for the Reynolds number of a variety of types of ice crystals and water drops are given in terms of the Davies, Bond, and Knudsen numbers. The equations are in terms of the basic physical parameters of the system and are valid for calculating velocities in gravitational and electric fields over a very wide range of sizes and atmospheric conditions. The equations are asymptotically matched at the bottom and top of the size spectrum, useful when checking large computer codes. A numerical system for specifying the dimensional properties of ice crystals is introduced. Within the limits imposed by such variables as particle density, which have large deviations, the accuracy of velocities appears to be within 10 percent over the entire range of sizes of interest.
Searching for Complex, Weak or Tangled Magnetic Fields in the Blue Supergiant Rigel
NASA Astrophysics Data System (ADS)
Shultz, M.; Wade, G. A.; Neiner, C.; Manset, N.; Petit, V.; Grunhut, J.; Guinan, E.; Hanes, D.; Mimes Collaboration
Seventy-eight high-resolution Stokes V, Q and U spectra of the B8 Iae supergiant Rigel were obtained with the ESPaDOnS instrument at the CFHT, and its clone NARVAL at the TBL in the context of the Magnetism in Massive Stars (MiMeS) Large Program, with the aim of scrutinizing this core-collapse supernova progenitor for direct evidence of weak and/or complex magnetic fields. In this paper we describe the reduction and analysis of the data, the constraints obtained on any magnetic field present in the stellar photosphere, and the variability of photospheric and wind lines.
Searching for weak or complex magnetic fields in polarized spectra of Rigel
NASA Astrophysics Data System (ADS)
Shultz, Matthew; Wade, Gregg A.; Neiner, Coralie; Manset, Nadine; Petit, Véronique; Grunhut, Jason H.; Guinan, Edward; Hanes, David A.; Hanes
2011-07-01
Seventy-eight high-resolution Stokes V, Q and U spectra of the B8Iae supergiant Rigel were obtained with the ESPaDOnS spectropolarimeter at CFHT and its clone NARVAL at TBL in the context of the Magnetism in Massive Stars (MiMeS) Large Program, in order to scrutinize this core-collapse supernova progenitor for evidence of weak and/or complex magnetic fields. In this paper we describe the reduction and analysis of the data, the constraints obtained on any photospheric magnetic field, and the variability of photospheric and wind lines.
Influence of a weak magnetic field on microplasticity of silicon crystals
NASA Astrophysics Data System (ADS)
Makara, V. A.; Steblenko, L. P.; Plyushchai, I. V.; Kurylyuk, A. N.; Kalinichenko, D. V.; Krit, A. N.; Naumenko, S. N.
2014-08-01
The possibility of magnetic ordering at dangling bonds in dislocation cores has been investigated theoretically. It has been experimentally shown that magnetic ordering in dislocations affects the spin-dependent effects occurring in dislocation crystals of silicon. It has been found that preliminary magnetic treatment of silicon crystals in a weak magnetic field leads to the suppression of the electroplastic effect induced in silicon crystals excited by an electric current. It has been assumed that a change in the microplasticity under the combined action of a magnetic field and an electric current is caused by a weakening of spin-dependent recombination at dislocation dangling bonds.
NASA Astrophysics Data System (ADS)
Shi, Pengpeng; Jin, Ke; Zheng, Xiaojing
2016-04-01
Weak magnetic nondestructive testing (e.g., metal magnetic memory method) concerns the magnetization variation of ferromagnetic materials due to its applied load and a weak magnetic surrounding them. One key issue on these nondestructive technologies is the magnetomechanical effect for quantitative evaluation of magnetization state from stress-strain condition. A representative phenomenological model has been proposed to explain the magnetomechanical effect by Jiles in 1995. However, the Jiles' model has some deficiencies in quantification, for instance, there is a visible difference between theoretical prediction and experimental measurements on stress-magnetization curve, especially in the compression case. Based on the thermodynamic relations and the approach law of irreversible magnetization, a nonlinear coupled model is proposed to improve the quantitative evaluation of the magnetomechanical effect. Excellent agreement has been achieved between the predictions from the present model and previous experimental results. In comparison with Jiles' model, the prediction accuracy is improved greatly by the present model, particularly for the compression case. A detailed study has also been performed to reveal the effects of initial magnetization status, cyclic loading, and demagnetization factor on the magnetomechanical effect. Our theoretical model reveals that the stable weak magnetic signals of nondestructive testing after multiple cyclic loads are attributed to the first few cycles eliminating most of the irreversible magnetization. Remarkably, the existence of demagnetization field can weaken magnetomechanical effect, therefore, significantly reduces the testing capability. This theoretical model can be adopted to quantitatively analyze magnetic memory signals, and then can be applied in weak magnetic nondestructive testing.
Transient effect of weak electromagnetic fields on calcium ion concentration in Arabidopsis thaliana
Pazur, Alexander; Rassadina, Valentina
2009-01-01
Background Weak magnetic and electromagnetic fields can influence physiological processes in animals, plants and microorganisms, but the underlying way of perception is poorly understood. The ion cyclotron resonance is one of the discussed mechanisms, predicting biological effects for definite frequencies and intensities of electromagnetic fields possibly by affecting the physiological availability of small ions. Above all an influence on Calcium, which is crucial for many life processes, is in the focus of interest. We show that in Arabidopsis thaliana, changes in Ca2+-concentrations can be induced by combinations of magnetic and electromagnetic fields that match Ca2+-ion cyclotron resonance conditions. Results An aequorin expressing Arabidopsis thaliana mutant (Col0-1 Aeq Cy+) was subjected to a magnetic field around 65 microtesla (0.65 Gauss) and an electromagnetic field with the corresponding Ca2+ cyclotron frequency of 50 Hz. The resulting changes in free Ca2+ were monitored by aequorin bioluminescence, using a high sensitive photomultiplier unit. The experiments were referenced by the additional use of wild type plants. Transient increases of cytosolic Ca2+ were observed both after switching the electromagnetic field on and off, with the latter effect decreasing with increasing duration of the electromagnetic impact. Compared with this the uninfluenced long-term loss of bioluminescence activity without any exogenic impact was negligible. The magnetic field effect rapidly decreased if ion cyclotron resonance conditions were mismatched by varying the magnetic fieldstrength, also a dependence on the amplitude of the electromagnetic component was seen. Conclusion Considering the various functions of Ca2+ as a second messenger in plants, this mechanism may be relevant for perception of these combined fields. The applicability of recently hypothesized mechanisms for the ion cyclotron resonance effect in biological systems is discussed considering it's operating at
[Mechanism of action of combined extremely weak magnetic field on aqueous solution of amino acid].
Zhadin, M N; Bakharev, B V; Bobkova, N V
2014-01-01
The fundamental physical mechanisms of resonance action of an extremely weak (40 nT) alternating magnetic field at the cyclotron frequency combined with a weak (40 μT) static magnetic field, on living systems are analyzed in the present work. The experimental effects of such sort of magnetic fields were described in different papers: the very narrow resonant peaks in electrical conductivity of the aqueous solutions in the in vitro experiments and the biomedical in vivo effects on living animals of magnetic fields with frequencies tuned to some amino acids. The existing experimental in vitro data had a good repeatability in different laboratories and countries. Unfortunately, for free ions such sort of effects are absolutely impossible because the dimensions of an ion rotation radius should be measured by meters at room temperature and at very low static magnetic fields used in all the above experiments. Even for bound ions these effects should be also absolutely impossible from the positions of classic physics because of rather high viscosity of biological liquid media (blood plasma, cerebrospinal liquid, cytoplasm). Only modern quantum electrodynamics of condensed media opens the new ways for solving these problems. The proposed article is devoted to analysis of quantum mechanisms of these effects. PMID:25707253
Bawin, S M; Adey, W R
1976-01-01
Weak sinusoidal electric fields modify the calcium efflux from freshly isolated chick and cat cerebral tissues bathed in Ringer's solution, at 36 degrees. Following incubation (30 min) with radioactive calcium (45Ca2+), each sample, immersed in fresh solution, was exposed for 20 min to fields at 1, 6, 16, 32, or 75 Hz, with electric gradients of 5, 10, 56, and 100 V/m in air. 45Ca2+ efflux in the solution was then measured in 0.2 ml aliquots and compared with efflux from unexposed control samples. Field exposures resulted in a general trend toward a reduction in the release of the preincubated 45Ca2+. Both frequency and amplitude sensitivities were observed. Maximum decreases occurred at 6 and 16 Hz (12-15%). Thresholds were around 10 and 56 V/m for chick and cat tissues, respectively. Similar but nonsignificant trends occurred during other field exposures. All results were statistically compared with matched samples of controls. Tissue gradients could not be measured, but estimates were of the order of 0.1 muV/cm. The susceptibility of the electrochemical equilibrium in the neuronal membrane to small extracellular perturbations is discussed and a possible role for weak intrinsic cerebral fields in neuronal excitability is suggested. Images PMID:1064869
A new high-integrated weak field sensor for automotive applications
NASA Astrophysics Data System (ADS)
Thiessen, T.; Prochaska, M.
2009-05-01
Especially in the field of automotive applications smart sensor systems for magnetic field sensing face increasing requirements concerning low cost, low power consumption and high magnetic performance. Over the past years AMR sensors play a decisive role in this application area because of their robustness and stability. In the following a high-integrated smart sensor system for magnetic field sensing is presented. A novel approach for the detection of weak magnetic fields is shown, which is based on an AC-excitation of AMR elements. In contrast to common used sensors this concept is based on a nonlinear AMR element without Barber pole construction. By means of this methodology sensitivity as well as temperature and life time stability is significantly improved, while the production costs compared to common-used sensors are reduced. Within this novel approach new signal conditioning algorithms and analog circuit topologies are presented, which are able to meet low offset and low noise requirements.
Rectification and signal averaging of weak electric fields by biological cells.
Astumian, R D; Weaver, J C; Adair, R K
1995-01-01
Oscillating electric fields can be rectified by proteins in cell membranes to give rise to a dc transport of a substance across the membrane or a net conversion of a substrate to a product. This provides a basis for signal averaging and may be important for understanding the effects of weak extremely low frequency (ELF) electric fields on cellular systems. We consider the limits imposed by thermal and "excess" biological noise on the magnitude and exposure duration of such electric field-induced membrane activity. Under certain circumstances, the excess noise leads to an increase in the signal-to-noise ratio in a manner similar to processes labeled "stochastic resonance." Numerical results indicate that it is difficult to reconcile biological effects with low field strengths. PMID:7731976
Weak interactions from 1950-1960: a quantitative bibliometric study of the formation of a field
White, D.H.; Sullivan, D.
1986-01-01
A quantitative technique is illustrated which uses publication statistics from a bibliography of citations in the area of weak interactions to provide a view of trends and patterns in the development of the field during the period from 1950 to 1960. An overview is given of what the physicists working in weak interactions during this period were doing as indicated by an analysis of the subjects of their papers. The dominant problems and concerns are discussed. Focus is then turned to the events surrounding the emergence of the tau/theta particle puzzle, the discovery of parity nonconservation, and the resolution offered by the V-A theory. Displaying the data from the citation index in unusual ways highlights dominant issues of the period, especially the close relationship between theory and experiment in the latter half of the decade. 64 refs., 14 figs. (LEW)
The role of gravitational potential energy in the Martian lithospheric stress field
NASA Astrophysics Data System (ADS)
Naliboff, J. B.; Lithgow-Bertelloni, C.
2006-12-01
Understanding the lithospheric stress field on Mars is essential in interpreting patterns of surface faulting and geomorphologic features, as well as assessing the accuracy of different lithospheric models. We compute the portion of the lithospheric stress field on Mars produced by variations in crustal density and thickness using data described in Neumann et al. (2004). Our computation consists of two parts: calculation of the gravitational potential energy (GPE) at 1 degree intervals followed by calculation of the stress field derived from variations in the GPE using the commercial finite element program ABAQUS. When calculating the GPE, we consider both Airy and Pratt isostatic compensation models, as well as scenarios where no compensation model is invoked or the Martian crust acts as the Martian lithosphere. The lithosphere is treated as an elastic body and the full 3-D equations for conservation of mass and momentum are solved. In future models variations in lithologic properties and a viscoselastic rheology for the lithosphere will be incorporated. Preliminary results show gradations in the GPE between the southern highland and northern lowland regions of Mars relating to variations in crustal thickness between the two regions. For example, when the crust is assumed to behave as the elastic lithosphere, the southern highlands of Mars exhibit a much higher GPE as a result of their higher on average crustal thickness. If the lithosphere is assumed to contain both crust and mantle sections and a uniform compensation depth is assigned, however, the variation in GPE between the two regions is significantly altered.
The R.I. Pimenov unified gravitation and electromagnetism field theory as semi-Riemannian geometry
Gromov, N. A.
2009-05-15
More than forty years ago R.I. Pimenov introduced a new geometry-semi-Riemannian one-as a set of geometrical objects consistent with a fibering pr: M{sub n} {yields} M{sub m}. He suggested the heuristic principle according to which the physically different quantities (meter, second, Coulomb, etc.) are geometrically modelled as space coordinates that are not superposed by automorphisms. As there is only one type of coordinates in Riemannian geometry and only three types of coordinates in pseudo-Riemannian one, a multiple-fibered semi-Riemannian geometry is the most appropriate one for the treatment of more than three different physical quantities as unified geometrical field theory. Semi-Euclidean geometry {sup 3}R{sub 5}{sup 4} with 1-dimensional fiber x{sup 5} and 4-dimensional Minkowski space-time as a base is naturally interpreted as classical electrodynamics. Semi-Riemannian geometry {sup 3}V{sub 5}{sup 4} with the general relativity pseudo-Riemannian space-time {sup 3}V{sub 4}, and 1-dimensional fiber x{sup 5}, responsible for the electromagnetism, provides the unified field theory of gravitation and electromagnetism. Unlike Kaluza-Klein theories, where the fifth coordinate appears in nondegenerate Riemannian or pseudo-Riemannian geometry, the theory based on semi-Riemannian geometry is free from defects of the former. In particular, scalar field does not arise.
Charged perfect fluid tori in strong central gravitational and dipolar magnetic fields
NASA Astrophysics Data System (ADS)
Kovář, Jiří; Slaný, Petr; Cremaschini, Claudio; Stuchlík, Zdeněk; Karas, Vladimír; Trova, Audrey
2016-06-01
We study electrically charged perfect fluid toroidal structures encircling a spherically symmetric gravitating object with Schwarzschild spacetime geometry and endowed with a dipole magnetic field. The work represents a direct continuation of our previous general-relativistic studies of electrically charged fluid in the approximation of zero conductivity, which formed tori around a Reissner-Nordström black hole or a Schwarzschild black hole equipped with a test electric charge and immersed in an asymptotically uniform magnetic field. After a general introduction of the zero-conductivity charged fluid model, we discuss a variety of possible topologies of the toroidal fluid configurations. Along with the charged equatorial tori forming interesting coupled configurations, we demonstrate the existence of the off-equatorial tori, for which the dipole type of magnetic field seems to be necessary. We focus on orbiting structures with constant specific angular momentum and on those in permanent rigid rotation. We stress that the general analytical treatment developed in our previous works is enriched here by the integrated form of the pressure equations. To put our work into an astrophysical context, we identify the central object with an idealization of a nonrotating magnetic neutron star. Constraining ranges of its parameters and also parameters of the circling fluid, we discuss a possible relevance of the studied toroidal structures, presenting along with their topology also pressure, density, temperature and charge profiles.
Novikov, V V; Sheĭman, I M; Fesenko, E E
2002-01-01
It was shown that the exposure to combined weak and extraweak magnetic fields (permanent component 42 microT; variable component of an amplitude of 100 nT, frequency 1-60 Hz) increases the intensity of asexual propagation of planarians Dugesia tigrina. The effect of combined magnetic fields is most pronounced at frequencies of 1, 3.7, and 32 Hz. The presence of concomitant technogeneous fields (50 Hz, 30 nT) does not markedly influence the effects of weak magnetic fields with a small variable component. Upon realization of effects of weak magnetic fields, their both components are of great importance; the absence of one (permanent) component changes the sing of the effect to the opposite. The transfer of the effect to planarians through water pretreated with magnetic fields probably indicates that aqueous medium is involved in the realization of biological effects of weak magnetic fields.
Discovery of a very weak magnetic field on the Am star Alhena
NASA Astrophysics Data System (ADS)
Blazère, A.; Neiner, C.; Petit, P.
2016-06-01
Alhena (γ Gem) was observed in the frame of the BRIght Target Explorer spectropolarimetric survey, which gathers high resolution, high signal-to-noise, high sensitivity, spectropolarimetric observations of all stars brighter than V = 4 to combine seismic and spectropolarimetric studies of bright stars. We present here the discovery of a very weak magnetic field on the Am star Alhena, thanks to very high signal-to-noise spectropolarimetric data obtained with Narval at Télescope Bernard Lyot. All previously studied Am stars show the presence of ultraweak (sub-Gauss) fields with Zeeman signatures with an unexpected prominent positive lobe. However, Alhena presents a slightly stronger (but still very weak, only a few Gauss) field with normal Zeeman signatures with a positive and negative lobe, as found in stronger field (hundreds or thousands of Gauss) stars. It is the first detection of a normal magnetic signature in an Am star. Alhena is thus a very interesting object, which might provide the clue to understanding the peculiar shapes of the magnetic signatures of the other Am stars.
Quantum interference control of an isolated resonance lifetime in the weak-field limit.
García-Vela, A
2015-11-21
Resonance states play an important role in a large variety of physical and chemical processes. Thus, controlling the resonance behavior, and particularly a key property like the resonance lifetime, opens up the possibility of controlling those resonance mediated processes. While such a resonance control is possible by applying strong-field approaches, the development of flexible weak-field control schemes that do not alter significantly the system dynamics still remains a challenge. In this work, one such control scheme within the weak-field regime is proposed for the first time in order to modify the lifetime of an isolated resonance state. The basis of the scheme suggested is quantum interference between two pathways induced by laser fields, that pump wave packet amplitude to the target resonance under control. The simulations reported here show that the scheme allows for both enhancement and quenching of the resonance survival lifetime, being particularly flexible to achieve large lifetime enhancements. Control effects on the resonance lifetime take place only while the pulse is operating. In addition, the conditions required to generate the two interfering quantum pathways are found to be rather easy to meet for general systems, which makes the experimental implementation straightforward and implies the wide applicability of the control scheme.
The Optical Gravitational Lensing Experiment. Gaia South Ecliptic Pole Field as Seen by OGLE-IV
NASA Astrophysics Data System (ADS)
Soszyński, I.; Udalski, A.; Poleski, R.; Kozłowski, S.; Wyrzykowski, Ł.; Pietrukowicz, P.; Szymański, M. K.; Kubiak, M.; Pietrzyński, G.; Ulaczyk, K.; Skowron, J.
2012-09-01
We present a comprehensive analysis of the Gaia South Ecliptic Pole (GSEP) field, 5.3 square degrees area around the South Ecliptic Pole on the outskirts of the LMC, based on the data collected during the fourth phase of the Optical Gravitational Lensing Experiment, OGLE-IV. The GSEP field will be observed during the commissioning phase of the ESA Gaia space mission for testing and calibrating the Gaia instruments. We provide the photometric maps of the GSEP region containing the mean VI photometry of all detected stellar objects and their equatorial coordinates. We show the quality and completeness of the OGLE-IV photometry and color-magnitude diagrams of this region. We conducted an extensive search for variable stars in the GSEP field leading to the discovery of 6789 variable stars. In this sample we found 132 classical Cepheids, 686 RR Lyr type stars, 2819 long-period, and 1377 eclipsing variables. Several objects deserving special attention were also selected, including a new classical Cepheid in a binary eclipsing system. To provide empirical data for the Gaia Science Alert system we also conducted a search for optical transients. We discovered two firm type Ia supernovae and nine additional supernova candidates. To facilitate future Gaia supernovae detections we prepared a list of more than 1900 galaxies to redshift about 0.1 located in the GSEP field. Finally, we present the results of astrometric study of the GSEP field. With the 26 months time base of the presented here OGLE-IV data, proper motions of stars could be detected with the accuracy reaching 2 mas/yr. Astrometry allowed to distinguish galactic foreground variable stars detected in the GSEP field from LMC objects and to discover about 50 high proper motion stars (proper motion ≥ 100 mas/yr). Among them three new nearby white dwarfs were found. All data presented in this paper are available to the astronomical community from the OGLE Internet archive.
NASA Astrophysics Data System (ADS)
Devyatisil'nyi, A. S.
2016-09-01
A model for recognizing inertial and satellite data on an object's motion that are delivered by a set of distributed onboard sensors (newtonmeters, gyros, satellite receivers) has been described. Specifically, the model is capable of estimating the parameters of the gravitational field.
Cellular target of weak magnetic fields: ionic conduction along actin filaments of microvilli.
Gartzke, Joachim; Lange, Klaus
2002-11-01
The interaction of weak electromagnetic fields (EMF) with living cells is a most important but still unresolved biophysical problem. For this interaction, thermal and other types of noise appear to cause severe restrictions in the action of weak signals on relevant components of the cell. A recently presented general concept of regulation of ion and substrate pathways through microvilli provides a possible theoretical basis for the comprehension of physiological effects of even extremely low magnetic fields. The actin-based core of microfilaments in microvilli is proposed to represent a cellular interaction site for magnetic fields. Both the central role of F-actin in Ca2+ signaling and its polyelectrolyte nature eliciting specific ion conduction properties render the microvillar actin filament bundle an ideal interaction site for magnetic and electric fields. Ion channels at the tip of microvilli are connected with the cytoplasm by a bundle of microfilaments forming a diffusion barrier system. Because of its polyelectrolyte nature, the microfilament core of microvilli allows Ca2+ entry into the cytoplasm via nonlinear cable-like cation conduction through arrays of condensed ion clouds. The interaction of ion clouds with periodically applied EMFs and field-induced cation pumping through the cascade of potential barriers on the F-actin polyelectrolyte follows well-known physical principles of ion-magnetic field (MF) interaction and signal discrimination as described by the stochastic resonance and Brownian motor hypotheses. The proposed interaction mechanism is in accord with our present knowledge about Ca2+ signaling as the biological main target of MFs and the postulated extreme sensitivity for coherent excitation by very low field energies within specific amplitude and frequency windows. Microvillar F-actin bundles shielded by a lipid membrane appear to function like electronic integration devices for signal-to-noise enhancement; the influence of coherent signals
Cosmology with weak lensing surveys.
Munshi, Dipak; Valageas, Patrick
2005-12-15
Weak gravitational lensing is responsible for the shearing and magnification of the images of high-redshift sources due to the presence of intervening mass. Since the lensing effects arise from deflections of the light rays due to fluctuations of the gravitational potential, they can be directly related to the underlying density field of the large-scale structures. Weak gravitational surveys are complementary to both galaxy surveys and cosmic microwave background observations as they probe unbiased nonlinear matter power spectra at medium redshift. Ongoing CMBR experiments such as WMAP and a future Planck satellite mission will measure the standard cosmological parameters with unprecedented accuracy. The focus of attention will then shift to understanding the nature of dark matter and vacuum energy: several recent studies suggest that lensing is the best method for constraining the dark energy equation of state. During the next 5 year period, ongoing and future weak lensing surveys such as the Joint Dark Energy Mission (JDEM; e.g. SNAP) or the Large-aperture Synoptic Survey Telescope will play a major role in advancing our understanding of the universe in this direction. In this review article, we describe various aspects of probing the matter power spectrum and the bi-spectrum and other related statistics with weak lensing surveys. This can be used to probe the background dynamics of the universe as well as the nature of dark matter and dark energy.
Cosmology with weak lensing surveys.
Munshi, Dipak; Valageas, Patrick
2005-12-15
Weak gravitational lensing is responsible for the shearing and magnification of the images of high-redshift sources due to the presence of intervening mass. Since the lensing effects arise from deflections of the light rays due to fluctuations of the gravitational potential, they can be directly related to the underlying density field of the large-scale structures. Weak gravitational surveys are complementary to both galaxy surveys and cosmic microwave background observations as they probe unbiased nonlinear matter power spectra at medium redshift. Ongoing CMBR experiments such as WMAP and a future Planck satellite mission will measure the standard cosmological parameters with unprecedented accuracy. The focus of attention will then shift to understanding the nature of dark matter and vacuum energy: several recent studies suggest that lensing is the best method for constraining the dark energy equation of state. During the next 5 year period, ongoing and future weak lensing surveys such as the Joint Dark Energy Mission (JDEM; e.g. SNAP) or the Large-aperture Synoptic Survey Telescope will play a major role in advancing our understanding of the universe in this direction. In this review article, we describe various aspects of probing the matter power spectrum and the bi-spectrum and other related statistics with weak lensing surveys. This can be used to probe the background dynamics of the universe as well as the nature of dark matter and dark energy. PMID:16286284
NASA Astrophysics Data System (ADS)
Dunning, Madeline; Bailey, Christopher; Voevodin, Anastasia; Tondiglia, Vincent; Natarajan, Lalgudi; White, Timothy; Bunning, Timothy
2011-03-01
We report on a new, low field electro-optical effect in weakly polymer stabilized cholesteric liquid crystals with negative dielectric anisotropy. By applying low DC electric fields (3 V / μm), a symmetric broadening of the cholesteric reflection band can be seen, resulting in band width increases by factors of two or more. An intensive study of the various experimental parameters combined with numerical calculations of the transmission spectra, indicate that the polymer interacts with the electric fields resulting in an approximately constant pitch gradient across the cell thickness. Our results show that the maximum pitch distortions reach values of approximately 15% the zero voltage value for notches in the visible range (pitches of 300-400nm), but increase along with the pitch. Possible physical mechanisms will be explored and discussed that might explain this interesting electro-optical effect.
Computer study of convection of weakly ionized plasma in a nonuniform magnetic field.
NASA Technical Reports Server (NTRS)
Shiau, J. N.
1972-01-01
A weakly ionized plasma in a strong and nonuniform magnetic field exhibits an instability analogous to the flute instability in a fully ionized plasma. The instability sets in at a critical magnetic field. To study the final state of the plasma after the onset of the instability, the plasma equations are integrated numerically assuming a certain initial spectrum of small disturbances. In the regime studied, numerical results indicate a final steadily oscillating state consisting of a single finite amplitude mode together with a time-independent modification of the original equilibrium. These results agree with the analytic results obtained by Simon in the slightly supercritical regime. As the magnetic field is increased further, the wavelength of the final oscillation becomes nonunique. There exists a subinterval in the unstable wave band. Final stable oscillation with a wavelength in this subinterval can be established if the initial disturbance has a sufficiently strong component at the particular wavelength.
Novitskii, Yurii I; Novitskaya, Galina V; Serdyukov, Yurii A
2014-02-01
Composition and content of lipids were studied in 5-day-old radish seedlings (Raphanus sativus L. var. radicula DC.) grown in lowlight and darkness in an extremely low frequency (ELF) magnetic field characterized by 50 Hz frequency and ∼500 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
Robust ground state and artificial gauge in DQW exciton condensates under weak magnetic field
NASA Astrophysics Data System (ADS)
Hakioğlu, T.; Özgün, Ege; Günay, Mehmet
2014-08-01
An exciton condensate is a vast playground in studying a number of symmetries that are of high interest in the recent developments in topological condensed matter physics. In double quantum wells (DQWs) they pose highly nonconventional properties due to the pairing of non-identical fermions with a spin dependent order parameter. Here, we demonstrate a new feature in these systems: the robustness of the ground state to weak external magnetic field and the appearance of the artificial spinor gauge fields beyond a critical field strength where negative energy pair-breaking quasi particle excitations, i.e. de-excitation pockets (DX-pockets), are created in certain k regions. The DX-pockets are the Kramers symmetry broken analogs of the negative energy pockets examined in the 1960s by Sarma. They respect a disk or a shell-topology in k-space or a mixture between them depending on the magnetic field strength and the electron-hole density mismatch. The Berry connection between the artificial spinor gauge field and the TKNN number is made. This field describes a collection of pure spin vortices in real space when the magnetic field has only inplane components.
NASA Astrophysics Data System (ADS)
Kirschvink, Joseph L.
1992-08-01
In a recent paper, Adair [Phys. Rev. A 43, 1039 (1991)] concludes that weak extremely-low-frequency (ELF) electromagnetic fields cannot affect biology on the cell level. However, Adair's assertion that few cells of higher organisms contain magnetite (Fe3O4) and his blanket denial of reproducible ELF effects on animals are both wrong. Large numbers of single-domain magnetite particles are present in a variety of animal tissues, including up to a hundred million per gram in human brain tissues, organized in clusters of tens to hundreds of thousand per gram. This is far more than a ``few cells.'' Similarly, a series of reproducible behavioral experiments on honeybees, Apis mellifera, have shown that they are capable of responding to weak ELF magnetic fields that are well within the bounds of Adair's criteria. A biologically plausible model of the interaction of single-domain magnetosomes with a mechanically activated transmembrane ion channel shows that ELF fields on the order of 0.1 to 1 mT are capable of perturbing the open-closed state by an energy of kT. As up to several hundred thousand such structures could fit within a eukaryotic cell, and the noise should go as the square root of the number of independent channels, much smaller ELF sensitivities at the cellular level are possible. Hence, the credibility of weak ELF magnetic effects on living systems must stand or fall mainly on the merits and reproducibility of the biological or epidemiological experiments that suggest them, rather than on dogma about physical implausibility.
Tomanova, K; Vacha, M
2016-06-01
Studies on weak man-made radiofrequency (RF) electromagnetic fields affecting animal magnetoreception aim for a better understanding of the reception mechanism and also point to a new phenomenon having possible consequences in ecology and environmental protection. RF impacts on magnetic compasses have recently been demonstrated in migratory birds and other vertebrates. We set out to investigate the effect of RF on the magnetic orientation of the Antarctic krill species Gondogeneia antarctica, a small marine crustacean widespread along the Antarctic littoral line. Here, we show that upon release, G. antarctica (held under laboratory conditions) escaped in the magnetically seaward direction along the magnetic sea-land axis (y-axis) of the home beach. However, the animals were disoriented after being exposed to RF. Orientation was lost not only in an RF field with a magnetic flux density of 20 nT, as expected according to the literature, but even under the 2 nT originally intended as a control. Our results extend recent findings of the extraordinary sensitivity of animal magnetoreception to weak RF fields in marine invertebrates.
Jenrow, K.A.; Smith, C.H.; Liboff, A.R.
1996-12-31
The authors recently reported that cephalic regeneration in the planarian Dugesia tigrina was significantly delayed in populations exposed continuously to combined parallel DC and AC magnetic fields. This effect was consistent with hypotheses suggesting an underlying resonance phenomenon. The authors report here, in a parallel series of investigations on the same model system, that the incidence of regeneration anomalies presenting as tumor-like protuberances also increases significantly (P < .001) in association with exposure to weak 60 Hz magnetic fields, with peak intensities ranging between 1.0 and 80.0 {micro}T. These anomalies often culminate in the complete disaggregation of the organism. Similar to regeneration rate effects, the incidence of regeneration anomalies is specifically dependent upon the planaria possessing a fixed orientation with respect to the applied magnetic field vectors. However, unlike the regeneration rate effects, the AC magnetic field alone, in the absence of any measurable DC field, is capable of producing these anomalies. Moreover, the incidence of regeneration anomalies follows a clear dose-response relationship as a function of AC magnetic field intensity, with the threshold for induced electric field intensity estimated at 5 {micro} V/m. The addition of either 51.1 or 78.4 {micro}T DC magnetic fields, applied in parallel combination with the AC field, enhances the appearance of anomalies relative to the 60 Hz AC field alone, but only at certain AC field intensities. Thus, whereas the previous study of regeneration rate effects appeared to involve exclusively resonance interactions, the regeneration anomalies reported here appear to result primarily from Faraday induction coupling.
Weak lensing calibrated M-T scaling relation of galaxy groups in the cosmos field
Kettula, K.; Finoguenov, A.; Massey, R.; Rhodes, J.; Hoekstra, H.; Taylor, J. E.; Spinelli, P. F.; Tanaka, M.; Ilbert, O.; Capak, P.; McCracken, H. J.; Koekemoer, A.
2013-11-20
The scaling between X-ray observables and mass for galaxy clusters and groups is instrumental for cluster-based cosmology and an important probe for the thermodynamics of the intracluster gas. We calibrate a scaling relation between the weak lensing mass and X-ray spectroscopic temperature for 10 galaxy groups in the COSMOS field, combined with 55 higher-mass clusters from the literature. The COSMOS data includes Hubble Space Telescope imaging and redshift measurements of 46 source galaxies per arcminute{sup 2}, enabling us to perform unique weak lensing measurements of low-mass systems. Our sample extends the mass range of the lensing calibrated M-T relation an order of magnitude lower than any previous study, resulting in a power-law slope of 1.48{sub −0.09}{sup +0.13}. The slope is consistent with the self-similar model, predictions from simulations, and observations of clusters. However, X-ray observations relying on mass measurements derived under the assumption of hydrostatic equilibrium have indicated that masses at group scales are lower than expected. Both simulations and observations suggest that hydrostatic mass measurements can be biased low. Our external weak lensing masses provide the first observational support for hydrostatic mass bias at group level, showing an increasing bias with decreasing temperature and reaching a level of 30%-50% at 1 keV.
Black holes and fundamental fields: Hair, kicks, and a gravitational Magnus effect
NASA Astrophysics Data System (ADS)
Okawa, Hirotada; Cardoso, Vitor
2014-11-01
Scalar fields pervade theoretical physics and are a fundamental ingredient to solve the dark matter problem, to realize the Peccei-Quinn mechanism in QCD or the string-axiverse scenario. They are also a useful proxy for more complex matter interactions, such as accretion disks or matter in extreme conditions. Here, we study the collision between scalar "clouds" and rotating black holes. For the first time we are able to compare analytic estimates and strong field, nonlinear numerical calculations for this problem. As the black hole pierces through the cloud it accretes according to the Bondi-Hoyle prediction, but is deflected through a purely kinematic gravitational "anti-Magnus" effect, which we predict to be present also during the interaction of black holes with accretion disks. After the interaction is over, we find large recoil velocities in the transverse direction. The end-state of the process belongs to the vacuum Kerr family if the scalar is massless, but can be a hairy black hole when the scalar is massive.
Wide-field X-ray afterglow searches for gravitational wave events
NASA Astrophysics Data System (ADS)
Shawhan, Peter; Tervala, Justin
2015-04-01
The Advanced LIGO and Virgo gravitational wave (GW) detectors are on track to begin collecting science data soon and to reach full sensitivity by 2019. Low-latency analysis of the GW data will provide triggers for astronomers to seek electromagnetic transient counterparts. Many instruments will contribute to that effort, but instruments with very large fields of view will have a natural advantage for following up the typically large GW error regions. In particular, we consider ISS-Lobster, a proposed NASA mission to be deployed on the International Space Station, which features a focusing imager for soft X-rays with a field of view of over 800 square degrees. Our study using binary neutron star coalescence simulations from Singer et al. shows that a single ISS-Lobster pointing will, on average, cover over 95% of a LIGO-Virgo 3-detector sky map, while even a 2-detector sky map can be over 85% covered (on average) by a sequence of four pointings. We gratefully acknowledge the support of NSF Grants PHY-1068549 and PHY-1404121.
Advances in Magnetic and Gravitational Potential Field Data in the Arctic
NASA Astrophysics Data System (ADS)
Olesen, Odleiv; Saltus, Rick
2010-10-01
Integration of Magnetics and Gravity in Northern Exploration (iMAGINE); Tromsø, Norway, 1-2 June 2010; Magnetic and gravitational potential field data are crucial components of regional tectonic framework studies and resource exploration in the Arctic. Special data acquisition difficulties at high latitudes include extreme weather conditions, ice-covered waters, and magnetic disturbances from the aurora borealis. Improved techniques in sub-ice, sub-salt, and sub-basalt exploration are required. The Integration of Magnetics and Gravity in Northern Exploration (iMAGINE) meeting (part of Arctic Days 2010) featured discussion of the most recent advances in potential field methods with particular attention to Arctic challenges. Presentations concentrated on regional interpretations in the Arctic Ocean, Barents Sea, Siberia, and northeastern Atlantic Ocean. Talks also touched on regional petroleum exploration and on the interpretation of weathered bedrock in Norway. In addition, a group of talks dealt with geomagnetic disturbances and their effect on magnetic data collection and in magnetic orientation for directional drilling.
Gravitational collapse of a homogeneous scalar field in deformed phase space
NASA Astrophysics Data System (ADS)
Rasouli, S. M. M.; Ziaie, A. H.; Marto, J.; Moniz, P. V.
2014-02-01
We study the gravitational collapse of a homogeneous scalar field, minimally coupled to gravity, in the presence of a particular type of dynamical deformation between the canonical momenta of the scale factor and of the scalar field. In the absence of such a deformation, a class of solutions can be found in the literature [R. Goswami and P. S. Joshi], whereby a curvature singularity occurs at the collapse end state, which can be either hidden behind a horizon or be visible to external observers. However, when the phase space is deformed, as implemented herein this paper, we find that the singularity may be either removed or instead, attained faster. More precisely, for negative values of the deformation parameter, we identify the emergence of a negative pressure term, which slows down the collapse so that the singularity is replaced with a bounce. In this respect, the formation of a dynamical horizon can be avoided depending on the suitable choice of the boundary surface of the star. Whereas for positive values, the pressure that originates from the deformation effects assists the collapse toward the singularity formation. In this case, since the collapse speed is unbounded, the condition on the horizon formation is always satisfied and furthermore the dynamical horizon develops earlier than when the phase-space deformations are absent. These results are obtained by means of a thoroughly numerical discussion.
Badent, R.; Kist, K.; Schwab, A.J.
1996-12-31
This paper deals with the investigation of prebreakdown phenomenon in insulating oil in weakly non-uniform fields of rod-plane geometries with gaps up to 100 mm under impulse voltages of both polarities up to 700 kV. As with the point-plane configuration, the rod-plane geometry shows a decrease of the time to breakdown with increasing voltage rate-of-rise. At a specific rate, a significantly shorter breakdown time is observed both for positive and negative polarities. Beyond this discontinuity range breakdown time decreases again but with lower rates.
Jiménez-Aquino, J I; Romero-Bastida, M
2011-07-01
The detection of weak signals through nonlinear relaxation times for a Brownian particle in an electromagnetic field is studied in the dynamical relaxation of the unstable state, characterized by a two-dimensional bistable potential. The detection process depends on a dimensionless quantity referred to as the receiver output, calculated as a function of the nonlinear relaxation time and being a characteristic time scale of our system. The latter characterizes the complete dynamical relaxation of the Brownian particle as it relaxes from the initial unstable state of the bistable potential to its corresponding steady state. The one-dimensional problem is also studied to complement the description.
Weakly nonlinear study of normal-field instability in confined ferrofluids.
Lira, Sérgio A; Miranda, José A
2011-07-01
Similar to the classic three-dimensional Rosensweig instability, a ferrofluid confined in a vertical Hele-Shaw cell subjected to an in-plane normal magnetic field develops a periodic array of peaked interfacial structures. We perform a weakly nonlinear analysis that is able to reproduce the morphology of such pattern formation phenomenon at lowest nonlinear order. A mode-coupling theory is applied to compare the early nonlinear evolution of the interface with static shapes obtained when relevant forces equilibrate. Our nonlinear results indicate that the time-evolving shapes tend to approach stable stationary solutions. PMID:21867300
Electric-field-induced weakly chaotic transients in ferroelectric liquid crystals.
Śliwa, I; Jeżewski, W; Kuczyński, W
2016-01-01
Nonlinear dynamics induced in surface stabilized ferroelectric liquid crystals by strong alternating external electric fields is studied both theoretically and experimentally. As has already been shown, molecular reorientations induced by sufficiently strong fields of high-enough frequencies can reveal a long transient behavior that has a weakly chaotic character. The resulting complex dynamics of ferroelectric liquid crystals can be considered not only as a consequence of irregular motions of particular molecules but also as a repercussion of a surface-enforced partial decorrelation of nonlinear molecular motions within smectic layers. To achieve more insight into the nature of this phenomenon and to show that the underlying complex field-induced behavior of smectic liquid crystals is not exceptional, ranges of system parameters for which the chaotic behavior occurs are determined. It is proved that there exists a large enough set of initial phase trajectory points, for which weakly chaotic long-time transitory phenomena occur, and, thereby, it is demonstrated that such a chaotic behavior can be regarded as being typical for strongly field-driven thin liquid crystal systems. Additionally, the influence of low-amplitude random noise on the duration of the transient processes is numerically studied. The strongly nonlinear contribution to the electro-optic response, experimentally determined for liquid crystal samples at frequencies lower than the actual field frequency, is also analyzed for long-time signal sequences. Using a statistical approach to distinguish numerically response signals of samples from noise generated by measuring devices, it is shown that the distribution of sample signals distinctly differs from the device noise. This evidently corroborates the occurrence of the nonlinear low-frequency effect, found earlier for different surface stabilized liquid crystal samples.
Electric-field-induced weakly chaotic transients in ferroelectric liquid crystals
NASA Astrophysics Data System (ADS)
Śliwa, I.; JeŻewski, W.; Kuczyński, W.
2016-01-01
Nonlinear dynamics induced in surface stabilized ferroelectric liquid crystals by strong alternating external electric fields is studied both theoretically and experimentally. As has already been shown, molecular reorientations induced by sufficiently strong fields of high-enough frequencies can reveal a long transient behavior that has a weakly chaotic character. The resulting complex dynamics of ferroelectric liquid crystals can be considered not only as a consequence of irregular motions of particular molecules but also as a repercussion of a surface-enforced partial decorrelation of nonlinear molecular motions within smectic layers. To achieve more insight into the nature of this phenomenon and to show that the underlying complex field-induced behavior of smectic liquid crystals is not exceptional, ranges of system parameters for which the chaotic behavior occurs are determined. It is proved that there exists a large enough set of initial phase trajectory points, for which weakly chaotic long-time transitory phenomena occur, and, thereby, it is demonstrated that such a chaotic behavior can be regarded as being typical for strongly field-driven thin liquid crystal systems. Additionally, the influence of low-amplitude random noise on the duration of the transient processes is numerically studied. The strongly nonlinear contribution to the electro-optic response, experimentally determined for liquid crystal samples at frequencies lower than the actual field frequency, is also analyzed for long-time signal sequences. Using a statistical approach to distinguish numerically response signals of samples from noise generated by measuring devices, it is shown that the distribution of sample signals distinctly differs from the device noise. This evidently corroborates the occurrence of the nonlinear low-frequency effect, found earlier for different surface stabilized liquid crystal samples.
NASA Astrophysics Data System (ADS)
Dimant, Y. S.; Oppenheim, M. M.; Fletcher, A. C.
2016-08-01
In weakly ionized plasmas neutral flows drag plasma across magnetic field lines generating intense electric fields and currents. An example occurs in the Earth's ionosphere near the geomagnetic equator. Similar processes take place in the Solar chromosphere and magnetohydrodynamic generators. This paper argues that not all convective neutral flows generate electric fields and currents and it introduces the corresponding universal criterion for their formation, ∇×(U ×B )≠∂B /∂t , where U is the neutral flow velocity, B is the magnetic field, and t is time. This criterion does not depend on the conductivity tensor, σ ̂ . For many systems, the displacement current, ∂B /∂t , is negligible making the criterion even simpler. This theory also shows that the neutral-dynamo driver that generates E-fields and currents plays the same role as the DC electric current plays for the generation of the magnetic field in the Biot-Savart law.
Imshennik, V. S.
2010-04-15
The standard problem of a radial motion of test particles in the stationary gravitational field of a spherically symmetric celestial body is solved and is used to determine the time features of this motion. The problem is solved for the equations of motion of general relativity (GR), and the time features are obtained in the post-Newtonian approximation, with linear GR corrections proportional to r{sub g}/r and {beta}{sup 2} (in the solution being considered, they are of the same order of smallness) being taken rigorously into account. Total times obtained by integrating the time differentials along the trajectories of motion are considered as the time features in question. It is shown that, for any parameters of the motion, the proper time (which corresponds to watches comoving with a test particle) exceeds the time of watches at rest (watches at the surface of the celestial body being considered). The mass and the radius of the celestial body, as well as the initial velocity of the test particle, serve as arbitrary parameters of the motion. The time difference indicated above implies a leading role of the gravitational redshift, which decreases somewhat because of the opposite effect of the Doppler shift. The results are estimated quantitatively for the important (from the experimental point of view) case of vertical flights of rockets starting from the Earth's surface. In this case, the GR corrections, albeit being extremely small (a few microseconds for several hours of the flight), aremeasurable with atomic (quantum) watches.
NASA Astrophysics Data System (ADS)
del Moral, A.; Azanza, María J.
2015-03-01
A biomagnetic-electrical model is presented that explains rather well the experimentally observed synchronization of the bioelectric potential firing rate ("frequency"), f, of single unit neurons of Helix aspersa mollusc under the application of extremely low frequency (ELF) weak alternating (AC) magnetic fields (MF). The proposed model incorporates to our widely experimentally tested model of superdiamagnetism (SD) and Ca2+ Coulomb explosion (CE) from lipid (LP) bilayer membrane (SD-CE model), the electrical quadrupolar long range interaction between the bilayer LP membranes of synchronized neuron pairs, not considered before. The quadrupolar interaction is capable of explaining well the observed synchronization. Actual extension of our SD-CE-model shows that the neuron firing frequency field, B, dependence becomes not modified, but the bioelectric frequency is decreased and its spontaneous temperature, T, dependence is modified. A comparison of the model with synchronization experimental results of pair of neurons under weak (B0 ≅0.2-15 mT) AC-MF of frequency fM=50 Hz is reported. From the deduced size of synchronized LP clusters under B, is suggested the formation of small neuron networks via the membrane lipid correlation.
MagnetoSperm: A microrobot that navigates using weak magnetic fields
NASA Astrophysics Data System (ADS)
Khalil, Islam S. M.; Dijkslag, Herman C.; Abelmann, Leon; Misra, Sarthak
2014-06-01
In this work, a propulsion system similar in motion to a sperm-cell is investigated. This system consists of a structure resembling a sperm-cell with a magnetic head and a flexible tail of 42 μm and 280 μm in length, respectively. The thickness, length, and width of this structure are 5.2 μm, 322 μm, and 42 μm, respectively. The magnetic head includes a 200 nm-thick cobalt-nickel layer. The cobalt-nickel layer provides a dipole moment and allows the flexible structure to align along oscillating weak (less than 5 mT) magnetic field lines, and hence generates a propulsion thrust force that overcomes the drag force. The frequency response of this system shows that the propulsion mechanism allows for swimming at an average speed of 158 ± 32 μm/s at alternating weak magnetic field of 45 Hz. In addition, we experimentally demonstrate controlled steering of the flexible structure towards reference positions.
Trombetta, F.; Basile, S.; Ferrante, G.
1989-04-01
A nonperturbative treatment of the multiphoton ionization of the hydrogen atom based on the S matrix and devised for nonresonant strong-field situations is analyzed in the weak-field limit. Comparisons are presented with other S matrices as well as other nonperturbative approaches. Our treatment is found to perform generally better than similar S-matrix treatments. The usual perturbative results are recovered provided that the photon wavelengths are sufficiently short and are off resonance with the atomic transitions. Important indications are obtained as to the role of the atomic structure, the relevance of the gauge consistency, and the reliability and improvement of the present nonperturbative treatment. The results represent a significant step toward an assessment of the S-matrix-based treatments of multiphoton ionization.
Cell Wall Regeneration by Protoplasts in the Weak Combined Magnetic Field
NASA Astrophysics Data System (ADS)
Nedukha, Olena; Bogatina, Nina; Kordyum, Elizabeth; Ovcharenko, Yu.; Vorobyeva, T.
2008-06-01
Role of gravity on growth of high plants has been studied for many years, but many questions on biogenesis of plant cell wall are investigated insufficiently, and require new experiments. We have studied regeneration of cell wall in the fused and separate protoplasts of tobacco and soyabean in the presence of the weak, alternating magnetic field that consisted of frequency of 32 Hz (for Ca2+ ; F=40 μT) or 75 Hz (for Mg2+; F=60 μT) in side μ-metal shield. We discovered that the combined magnetic field that was adjusted to the cyclotron frequency of Ca2+ or Mg2+ is changed the rate of cell wall regeneration. Light and confocal laser microscopy were used for the investigations.
Gravitation as a Composite Particle Effect in a Unified Spinor-Isospinor Preon Field Model I
NASA Astrophysics Data System (ADS)
Stumpf, H.
1988-04-01
The model is defined by a selfregularizing nonlinear preon field equation, and all observable (elementary and non-elementary) particles are assumed to be bound (quantum) states of fermionic preon fields. Electroweak gauge bosons, leptons, quarks, gluons as preon composites and their effective dynamics etc. were studied in preceding papers. In this paper gravitons are introduced as four-preon composites and their effective interactions are discussed. This discussion is performed by the application of functional quantum theory to the model under consideration and subsequent evaluation of a weak mapping procedure, both introduced in preceding papers. In the low energy limit it is demonstrated that the effective graviton dynamics lead to the complete homogeneous Einstein equations in tetrad formulation.
Motion of the Three Viscoelastic Planets in Gravitational Field of the Mutual Attraction
NASA Astrophysics Data System (ADS)
Vilke, V. G.; Shatina, A. V.; Shatina, L. S.
2009-04-01
The translational-rotational motion of the three viscoelastic planets in gravitational field of the mutual attraction is studied. We model the planets by the homogeneous isotropic viscoelastic bodies, which in the natural non-deformed state occupy the spherical regions in the three-dimensional Eucliden space. The problem is being solved within the framework of the linear model of the theory of elasticity. The functional of the inner dissipative forces corresponds to the Kelvin-Voigt model. Each of the planets deforms due to its rotation around its mass center and its movement relative to the system's mass centre: the planet is being compressed endwise its axis of rotation and tidal humps appear aloud the lines binding the planet's mass centers. The changes in the planet's shape in their turn alter its translational-rotational movement. The system of equations of motion of the considered mechanical system is deduced from the D'Alembert-Lagrange variational principle and represents a complicated integro-differential system of equations in the banach space. The method of separation of motions is applied to the obtained system of equations and an approximate system of ordinary differential equations is deduced witch describes the translational-rotational motion of the planets, taking into account the perturbations caused by elasticity and dissipation. Unperturbed system of equations corresponds to the problem of the motion of the three rigid spheres interacting under the law of universal gravitation. Boundary problem of finding the vector of elastic displacement, describing forced oscillation of the planet under the influence of external forces and inertial forces of the translational motion is solved for each of the planets. Due to the planets' sphericity in their natural non-deformed state, the solutions of the boundary problems can be represented analytically as a sum of finite number of spherical functions. The solutions of the boundary problems are used to form
The effects of weak extremely low frequency magnetic fields on calcium/calmodulin interactions.
Hendee, S P; Faour, F A; Christensen, D A; Patrick, B; Durney, C H; Blumenthal, D K
1996-01-01
Mechanisms by which weak electromagnetic fields may affect biological systems are of current interest because of their potential health effects. Lednev has proposed an ion parametric resonance hypothesis (Lednev, 1991, Bioelectromagnetics, 12:71-75), which predicts that when the ac, frequency of a combined dc-ac magnetic field equals the cyclotron frequency of calcium, the affinity of calcium for calcium-binding proteins such as calmodulin will be markedly affected. The present study evaluated Lednev's theory using two independent systems, each sensitive to changes in the affinity of calcium for calmodulin. One of the systems used was the calcium/calmodulin-dependent activation of myosin light chain kinase, a system similar to that previously used by Lednev. The other system monitored optical changes in the binding of a fluorescent peptide to the calcium/calmodulin complex. Each system was exposed to a 20.9 microT static field superimposed on a 20.9 microT sinusoidal field over a narrow frequency range centered at 16 Hz, the cyclotron frequency of the unhydrated calcium ion. In contrast to Lednev's predictions, no significant effect of combined dc-ac magnetic fields on calcium/calmodulin interactions was indicated in either experimental system. PMID:8744329
Gravitational wave production from the decay of the standard model Higgs field after inflation
NASA Astrophysics Data System (ADS)
Figueroa, Daniel G.; García-Bellido, Juan; Torrentí, Francisco
2016-05-01
During or towards the end of inflation, the Standard Model (SM) Higgs forms a condensate with a large amplitude. Following inflation, the condensate oscillates, decaying nonperturbatively into the rest of the SM species. The resulting out-of-equilibrium dynamics converts a fraction of the energy available into gravitational waves (GWs). We study this process using classical lattice simulations in an expanding box, following the energetically dominant electroweak gauge bosons W± and Z . We characterize the GW spectrum as a function of the running couplings, Higgs initial amplitude, and postinflationary expansion rate. As long as the SM is decoupled from the inflationary sector, the generation of this background is universally expected, independently of the nature of inflation. Our study demonstrates the efficiency of GW emission by gauge fields undergoing parametric resonance. The initial energy of the Higgs condensate represents, however, only a tiny fraction of the inflationary energy. Consequently, the resulting background is highly suppressed, with an amplitude h2ΩGW(o )≲1 0-29 today. The amplitude can be boosted to h2ΩGW(o )≲1 0-16 , if following inflation the universe undergoes a kination-domination stage; however, the background is shifted in this case to high frequencies fp≲1011 Hz . In all cases the signal is out of the range of current or planned GW detectors. This background will therefore remain, most likely, as a curiosity of the SM.
Analysis of network traffic flow dynamics based on gravitational field theory
NASA Astrophysics Data System (ADS)
Liu, Gang; Li, Yong-Shu; Zhang, Xi-Ping
2013-06-01
For further research on the gravity mechanism of the routing protocol in complex networks, we introduce the concept of routing awareness depth, which is represented by ρ. On this basis, we define the calculation formula of the gravity of the transmission route for the packet, and propose a routing strategy based on the gravitational field of the node and the routing awareness depth. In order to characterize the efficiency of the method, we introduce an order parameter, ζ, to measure the throughput of the network by the critical value of phase transition from free flow to congestion, and use the node betweenness centrality, B, to test the transmission efficiency of the network and congestion distribution. We simulate the network transmission performance under different values of the routing awareness depth, ρ. Simulation results show that if the value of the routing awareness depth ρ is too small, then the gravity of the route is composed of the attraction of very few nodes on the route, which cannot improve the capacity of the network effectively. If the value of the routing awareness depth ρ is greater than the network's average distance
Hubble Space Telescope Wide Field Camera imaging of the gravitational lens 2237 + 0305
NASA Technical Reports Server (NTRS)
Rix, Hans-Walter; Schneider, Donald P.; Bahcall, John N.
1992-01-01
Images of the gravitational lens system 2237 + 0305, taken with the HST Wide Field Camera, are analyzed. Positions for the four quasar images, accurate to +/-0.015 arcsec, and relative magnitudes in U and R, accurate to +/-0.06 and 0.04 mag, respectively, are determined. The upper limits on the observed brightness of the fifth image are found to be less than or approximately equal to 7 percent of the brightest quasar image. The mass of the lens inside 0.9 arcsec is found to be 1.08 +/-0.02 x 10 exp 10 solar masses/h100 corresponding to a mass-to-light ratio in B of 12.3h100. This solar mass/solar luminosity estimate agrees with values obtained from stellar dynamics for other elliptical galaxies. A comparison of predictions from this mass model with the measured central velocity dispersion yields a distance-independent agreement to within 10 percent, assuming isotropic velocity dispersions.
Satellite motion in the gravitational field of a viscoelastic planet with a core
NASA Astrophysics Data System (ADS)
Shatina, A. V.; Sherstnyov, E. V.
2015-03-01
The motion of a "planet-satellite" system in a gravitational field of mutual attraction forces is investigated. The planet is modeled by a body consisting of a solid core and a viscoelastic shell made of Kelvin-Voigt material. The satellite is modeled by a material point. A system of integro-differential equations of motion of a mechanical system is derived from the variational d'Alembert-Lagrange principle within the linear model of the theory of elasticity. Using the asymptotic method of separation of motions, an approximate system of equations of motion is constructed in vector form. This system describes the dynamics of a system with allowance for disturbances caused by elasticity and dissipation. The solution of the quasistatic problem of elasticity theory for the deformable shell of a planet is obtained in the explicit form. An averaged system of differential equations describing the evolution of satellite's orbital parameters is derived. For partial cases phase trajectories are constructed, stationary solutions are found, and their stability is investigated. As examples, some planets of the Solar system and their satellites are considered. This problem is a model for studying the tidal theory of planetary motion.
The Distribution of Galaxies’ Gravitational Field Stemming from Their Tidal Interaction
NASA Astrophysics Data System (ADS)
Stephanovich, Vladimir; Godłowski, Włodzimierz
2015-09-01
We calculate the distribution function of astronomical objects’ (like galaxies and/or smooth halos of different kinds) gravitational fields due to their tidal interaction. For that we apply the statistical method of Chandrasekhar, used originally to calculate the famous Holtzmark distribution. We show that in our approach the distribution function is never Gaussian, its form being dictated by the potential of interaction between objects. This calculation permits us to perform a theoretical analysis of the relation between angular momentum and mass (richness) of the galaxy clusters. To do so, we follow the ideas of Catelan & Theuns and Heavens & Peacock. The main difference is that here we reduce the problem to a discrete many-body case, where all physical properties of the system are determined by the interaction potential V({{\\boldsymbol{r}}}{ij}). The essence of reduction is that we use the multipole (up to quadrupole here) expansion of Newtonian potential so that all hydrodynamic, “extended” characteristics of an object, such as its density mass, are “integrated out,” leaving its “point-like” characteristics, such as mass and quadrupole moment. In that sense we do not distinguish between galaxies and smooth components such as halos. We compare our theoretical results with observational data.
NASA Astrophysics Data System (ADS)
Mikhailovskii, A. B.; Fridman, A. M.; Churikov, A. P.; Pustovitov, V. D.; Smolyakov, A. I.
2009-04-01
Magnetohydrodynamic (MHD) theory of ideal instabilities in a high-β rotating cylindrical plasma with an azimuthal magnetic field and a radial gravitational field is developed (β is the ratio of the plasma and magnetic field pressures). The basis of this theory is a system of two first-order differential equations for the Frieman-Rotenberg variable (the sum of the perturbed plasma and magnetic field pressures) and the radial plasma displacement, which leads to the second-order differential equation for the displacement. The sausage instability criterion is derived which generalizes the earlier results for a plasma without gravitation. It is shown that this instability can occur for both the decreasing and increasing plasma pressures. The non-axisymmetric modes are also considered. This analysis is related to the MHD instability theory in a nonrotating plasma dealing with snake instabilities. A number of rotational and gravitational effects on both the m = 1 and m > 1 modes are revealed, where m is the azimuthal mode number. The eigenmode equation describing the Suydam modes in the presence of rotational and gravitational effects is derived. These modes can be responsible, in particular, for the Velikhov and rotational-convective instabilities.
The weak magnetic field of the O9.7 supergiant ζOrionisA
NASA Astrophysics Data System (ADS)
Bouret, J.-C.; Donati, J.-F.; Martins, F.; Escolano, C.; Marcolino, W.; Lanz, T.; Howarth, I. D.
2008-09-01
We report here the detection of a weak magnetic field of 50-100G on the O9.7 supergiant ζOrionisA (ζOriA), using spectropolarimetric observations obtained with NARVAL at the 2-m Télescope Bernard Lyot atop Pic du Midi (France). ζOriA is the third O star known to host a magnetic field (along with θ1OriC and HD191612), and the first detection on a `normal' rapidly rotating O star. The magnetic field of ζOriA is the weakest magnetic field ever detected on a massive star. The measured field is lower than the thermal equipartition limit (about 100G). By fitting non-local thermodynamic equilibrium (NLTE) model atmospheres to our spectra, we determined that ζOriA is a 40Msolar star with a radius of 25Rsolar and an age of about 5-6Myr, showing no surface nitrogen enhancement and losing mass at a rate of about 2 × 10-6Msolaryr-1. The magnetic topology of ζOriA is apparently more complex than a dipole and involves two main magnetic polarities located on both sides of the same hemisphere; our data also suggest that ζOriA rotates in about 7.0d and is about 40° away from pole-on to an Earth-based observer. Despite its weakness, the detected magnetic field significantly affects the wind structure; the corresponding Alfvén radius is however very close to the surface, thus generating a different rotational modulation in wind lines than that reported on the two other known magnetic O stars. The rapid rotation of ζOriA with respect to θ1OriC appears as a surprise, both stars having similar unsigned magnetic fluxes (once rescaled to the same radius); it may suggest that the subequipartition field detected on ζOriA is not a fossil remnant (as opposed to that of θ1 OriC and HD191612), but the result of an exotic dynamo action produced through magnetohydrodynamics (MHD) instabilities. Based on observations obtained at the Télescope Bernard Lyot (TBL), operated by the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique of France
Approximation methods in gravitational-radiation theory
NASA Technical Reports Server (NTRS)
Will, C. M.
1986-01-01
The observation of gravitational-radiation damping in the binary pulsar PSR 1913 + 16 and the ongoing experimental search for gravitational waves of extraterrestrial origin have made the theory of gravitational radiation an active branch of classical general relativity. In calculations of gravitational radiation, approximation methods play a crucial role. Recent developments are summarized in two areas in which approximations are important: (a) the quadrupole approxiamtion, which determines the energy flux and the radiation reaction forces in weak-field, slow-motion, source-within-the-near-zone systems such as the binary pulsar; and (b) the normal modes of oscillation of black holes, where the Wentzel-Kramers-Brillouin approximation gives accurate estimates of the complex frequencies of the modes.
Effect of weak static magnetic fields on the development of cultured skeletal muscle cells.
Surma, Sergei V; Belostotskaya, Galina B; Shchegolev, Boris F; Stefanov, Vasily E
2014-12-01
We studied the effect produced on the development and functional activity of skeletal muscle cells from newborn Wistar rats in primary culture by weak static magnetic fields (WSMF; 60-400 µT) with a high capacity of penetrating the biological media. To reduce the impact of external magnetic fields, cells were cultured at 37 °C in a multilayered shielding chamber with the attenuation coefficient equal to 160. WSMF inside the chamber was created by a circular permanent magnet. We found that the application of WSMF with the magnetic field strength only a few times that of the geomagnetic field can accelerate the development of skeletal muscle cells, resulting in the formation of multinuclear hypertrophied myotubes. WSMF was shown to induce 1.5- to 3.5-fold rise in the concentration of intracellular calcium [Ca(2+)]i due to the release of Ca(2+) from the sarcoplasmic reticulum (SR) through ryanodine receptors (RyR), which increases in the maturation of myotubes. We also found that fully differentiated myotubes at late stages of development were less sensitive to WSMF, manifesting a gradual decrease in the frequency of contractions. However, myotubes at the stage when electromechanical coupling was forming dramatically reduced the frequency of contractions during the first minutes of their exposure to WSMF.
Chaotic transport in Hamiltonian systems perturbed by a weak turbulent wave field
Abdullaev, S. S.
2011-08-15
Chaotic transport in a Hamiltonian system perturbed by a weak turbulent wave field is studied. It is assumed that a turbulent wave field has a wide spectrum containing up to thousands of modes whose phases are fluctuating in time with a finite correlation time. To integrate the Hamiltonian equations a fast symplectic mapping is derived. It has a large time-step equal to one full turn in angle variable. It is found that the chaotic transport across tori caused by the interactions of small-scale resonances have a fractal-like structure with the reduced or zero values of diffusion coefficients near low-order rational tori thereby forming transport barriers there. The density of rational tori is numerically calculated and its properties are investigated. It is shown that the transport barriers are formed in the gaps of the density of rational tori near the low-order rational tori. The dependencies of the depth and width of transport barriers on the wave field spectrum and the correlation time of fluctuating turbulent field (or the Kubo number) are studied. These numerical findings may have importance in understanding the mechanisms of transport barrier formation in fusion plasmas.
Inferring the 3D gravitational field of the Milky Way with stellar streams
NASA Astrophysics Data System (ADS)
Price-Whelan, Adrian Michael
2016-06-01
We develop two new methods to measure the structure of matter around the Milky Way using stellar tidal streams from disrupting dwarf galaxies and globular clusters. The dark matter halo of the Milky Way is expected to be triaxial and filled with substructure, but measurements of the shape and profile of dark matter around the Galaxy are highly uncertain and often contradictory. We demonstrate that kinematic data from near-future surveys for stellar streams or shells produced by tidal disruption of stellar systems around the Milky Way will provide precise measures of the gravitational potential to test these predictions. We develop a probabilistic method for inferring the Galactic potential with tidal streams based on the idea that the stream stars were once close in phase space and test this method on synthetic datasets generated from N-body simulations of satellite disruption with observational uncertainties chosen to mimic current and near-future surveys of various stars. We find that with just four well-measured stream stars, we can infer properties of a triaxial potential with precisions of order 5--7 percent. We then demonstrate that, if the Milky Way's dark matter halo is triaxial and is not fully integrable (as is expected), an appreciable fraction of orbits will be chaotic. We examine the influence of chaos on the phase-space morphology of cold tidal streams and show that streams even in weakly chaotic regions look very different from those in regular regions. We discuss the implications of this fact given that we see several long, thin streams in the Galactic halo; our results suggest that long, cold streams around our Galaxy must exist only on regular (or very nearly regular) orbits and potentially provide a map of the regular regions of the Milky Way potential. We then apply this understanding of stream formation along chaotic orbits to the interpretation of a newly-discovered, puzzling stellar stream near the Galactic bulge. We conclude that the
Ultra-weak magnetic fields in Am stars: β UMa and θ Leo
NASA Astrophysics Data System (ADS)
Blazère, A.; Petit, P.; Lignières, F.; Aurière, M.; Ballot, J.; Böhm, T.; Folsom, C.; Ariste, A. López; Wade, G. A.
2015-10-01
An extremely weak circularly-polarized signature was recently detected in the spectral lines of the Am star Sirius A. With a prominent positive lobe, the shape of the phase-averaged Stokes V line profile is atypical of stellar Zeeman signatures, casting doubts on its magnetic origin. We report here on ultra-deep spectropolarimetric observations of two more bright Am stars: β Uma and θ Leo. Stokes V line signatures are detected in both objects, with a shape and amplitude similar to the one observed on Sirius A. We demonstrate that the amplitude of the Stokes V line profiles depend on various line parameters (Landé factor, wavelength, depth) as expected from a Zeeman signature, confirming that extremely weak magnetic fields are likely present in a large fraction of Am stars. We suggest that the strong asymmetry of the polarized signatures, systematically observed so far in Am stars and never reported in strongly magnetic Ap stars, bears unique information about the structure and dynamics of the thin surface convective shell of Am stars.
Exact Relativistic Newtonian Representation of Gravitational static Spacetime Geometries
NASA Astrophysics Data System (ADS)
Ghosh, Shubhrangshu; Sarkar, Tamal; Bhadra, Arunava
2016-09-01
We construct a self-consistent relativistic Newtonian analogue corresponding to gravitational static spherical symmetric spacetime geometries, starting directly from a generalized scalar relativistic gravitational action in a Newtonian framework, which gives geodesic equations of motion identical to those of the parent metric. Consequently, the derived velocity-dependent relativistic scalar potential, which is a relativistic generalization of the Newtonian gravitational potential, exactly reproduces the relativistic gravitational features corresponding to any static spherical symmetric spacetime geometry in its entirety, including all the experimentally tested gravitational effects in the weak field up to the present. This relativistic analogous potential is expected to be quite useful in studying a wide range of astrophysical phenomena, especially in strong field gravity.
Numerical study on the stability of weakly collisional plasma in E×B fields
Horký, M.
2015-02-15
Plasma stability in weakly collisional plasmas in the presence of E×B fields is studied with numerical simulations. Different types of ion-neutral collisions are considered in a fully magnetized regime. We study the influence of ion-neutral collisions and the role of collision types on the stability of plasma. It is found that the stability of plasma depends on the type of ion-neutral collisions, with the plasma being unstable for charge exchange collisions, and stable for the elastic scattering. The analysis focuses on the temporal evolution of the velocity phase space, RMS values of the potential fluctuations, and coherent structures in potential densities. For the unstable case, we observe growth and propagation of electrostatic waves. Simulations are performed with a three-dimensional electrostatic particle in cell code.
Application of a weak magnetic field to improve microbial fuel cell performance.
Tong, Zhong-Hua; Yu, Han-Qing; Li, Wen-Wei; Wang, Yun-Kun; Sun, Min; Liu, Xian-Wei; Sheng, Guo-Ping
2015-12-01
Microbial fuel cells (MFCs) have emerged as a promising technology for wastewater treatment with concomitant energy production but the performance is usually limited by low microbial activities. This has spurred intensive research interest for microbial enhancement. This study demonstrated an interesting stimulation effect of a static magnetic field (MF) on sludge-inoculated MFCs and explored into the mechanisms. The implementation of a 100-mT MF accelerated the reactor startup and led to increased electricity generation. Under the MF exposure, the activation loss of the MFC was decreased, but there was no increased secretion of redox mediators. Thus, the MF effect was mainly due to enhanced bioelectrochemical activities of anodic microorganisms, which are likely attributed to the oxidative stress and magnetohydrodynamic effects under an MF exposure. This work implies that weak MF may be applied as a simple and effective approach to stimulate microbial activities for various bioelectrochemical energy production and decontamination applications.
Reis, Wieland G.; Weitz, R. Thomas; Kettner, Michel; Kraus, Alexander; Schwab, Matthias Georg; Tomović, Željko; Krupke, Ralph; Mikhael, Jules
2016-01-01
The identification of scalable processes that transfer random mixtures of single-walled carbon nanotubes (SWCNTs) into fractions featuring a high content of semiconducting species is crucial for future application of SWCNTs in high-performance electronics. Herein we demonstrate a highly efficient and simple separation method that relies on selective interactions between tailor-made amphiphilic polymers and semiconducting SWCNTs in the presence of low viscosity separation media. High purity individualized semiconducting SWCNTs or even self-organized semiconducting sheets are separated from an as-produced SWCNT dispersion via a single weak field centrifugation run. Absorption and Raman spectroscopy are applied to verify the high purity of the obtained SWCNTs. Furthermore SWCNT - network field-effect transistors were fabricated, which exhibit high ON/OFF ratios (105) and field-effect mobilities (17 cm2/Vs). In addition to demonstrating the feasibility of high purity separation by a novel low complexity process, our method can be readily transferred to large scale production. PMID:27188435
NASA Astrophysics Data System (ADS)
Reis, Wieland G.; Weitz, R. Thomas; Kettner, Michel; Kraus, Alexander; Schwab, Matthias Georg; Tomović, Željko; Krupke, Ralph; Mikhael, Jules
2016-05-01
The identification of scalable processes that transfer random mixtures of single-walled carbon nanotubes (SWCNTs) into fractions featuring a high content of semiconducting species is crucial for future application of SWCNTs in high-performance electronics. Herein we demonstrate a highly efficient and simple separation method that relies on selective interactions between tailor-made amphiphilic polymers and semiconducting SWCNTs in the presence of low viscosity separation media. High purity individualized semiconducting SWCNTs or even self-organized semiconducting sheets are separated from an as-produced SWCNT dispersion via a single weak field centrifugation run. Absorption and Raman spectroscopy are applied to verify the high purity of the obtained SWCNTs. Furthermore SWCNT - network field-effect transistors were fabricated, which exhibit high ON/OFF ratios (105) and field-effect mobilities (17 cm2/Vs). In addition to demonstrating the feasibility of high purity separation by a novel low complexity process, our method can be readily transferred to large scale production.
NASA Astrophysics Data System (ADS)
Samal, M. K.; Seshu, P.
2009-06-01
Piezoceramic materials exhibit different types of nonlinearities depending upon the magnitude of the mechanical and electric field strength in the continuum. Some of the nonlinearities observed under weak electric fields are: presence of superharmonics in the response spectra and jump phenomena etc. especially if the system is excited near resonance. In this paper, an analytical solution (in 2D plane stress domain) for the nonlinear response of a rectangular piezoceramic slab has been obtained by use of Rayleigh-Ritz method and perturbation technique. The eigenfunction obtained from solution of the differential equation of the linear problem has been used as the shape function in the Rayleigh-Ritz method. Forced vibration experiments have been conducted on a rectangular piezoceramic slab by applying varying electric field strengths across the thickness and the results have been compared with those of analytical solution. The analytical solutions compare well with those of experimental results. These solutions should serve as a method to validate the FE formulations as well as help in the determination of nonlinear material property coefficients for these materials.
Reis, Wieland G; Weitz, R Thomas; Kettner, Michel; Kraus, Alexander; Schwab, Matthias Georg; Tomović, Željko; Krupke, Ralph; Mikhael, Jules
2016-01-01
The identification of scalable processes that transfer random mixtures of single-walled carbon nanotubes (SWCNTs) into fractions featuring a high content of semiconducting species is crucial for future application of SWCNTs in high-performance electronics. Herein we demonstrate a highly efficient and simple separation method that relies on selective interactions between tailor-made amphiphilic polymers and semiconducting SWCNTs in the presence of low viscosity separation media. High purity individualized semiconducting SWCNTs or even self-organized semiconducting sheets are separated from an as-produced SWCNT dispersion via a single weak field centrifugation run. Absorption and Raman spectroscopy are applied to verify the high purity of the obtained SWCNTs. Furthermore SWCNT - network field-effect transistors were fabricated, which exhibit high ON/OFF ratios (10(5)) and field-effect mobilities (17 cm(2)/Vs). In addition to demonstrating the feasibility of high purity separation by a novel low complexity process, our method can be readily transferred to large scale production. PMID:27188435
Weak Pion and Photon Production from Nuclei in a Chiral Effective Field Theory (Update)
NASA Astrophysics Data System (ADS)
Zhang, Xilin; Serot, Brian D.
2011-04-01
Neutrino-induced pion and photon production from nucleons and nuclei are important for the interpretation of neutrino-oscillation experiments. [A. A. Aquilar-Arevalo et al. (MiniBooNE Collaboration), Phys. Rev. Lett. 100, 032301 (2008)]. We have been working on these problems in a Lorentz-covariant effective field theory (known as QHD EFT), which contains nucleons, pions, Deltas (Δ), isoscalar scalar (σ) and vector (ω) fields, and isovector vector (ρ) fields and has nonlinear chiral symmetry built in. Here we update our results on weak pion and photon production from nuclei, including both incoherent and coherent scattering. Connections between our results and the background analysis from MiniBooNE will be presented. In particular, coherent production of photons will be emphasized, and the possible relevance to the low-energy excess events at MiniBooNE will be explored. To justify our approximation scheme, we compare our results with data for inclusive electron scattering off nuclei up to the Δ peak and with coherent photoproduction of pions. Finally, we focus on the approximation scheme used and discuss the important Δ dynamics in the medium. An interesting mechanism to generate the Δ's spin-orbit coupling in the nucleus will be introduced, together with its possible consequences. Supported in part by the Department of Energy under Contract No. DE-FG02-87ER40365.
Electrodiffusiophoresis of a large-zeta-potential particle in weak fields.
Tricoli, Vincenzo; Orsini, Gabriele
2015-10-21
The electrodiffusiophoresis of a large-zeta-potential (ζ) particle in weak fields is investigated. In this large-ζ regime, Debye-layer kinetics determines O(1) perturbations to the electric- and concentration fields in the surrounding electroneutral solution. Taking these effects into account, the expressions of the slip-flow coefficient and the effective surface boundary-conditions for the electric- and concentration fields are derived. For binary and symmetric electrolyte where only one ion species carries the current in the electroneutral domain, the far-field salt gradient as related to the electric field is determined. The electrodiffusiophoretic mobility is obtained for three particle geometries: sphere, cylinder and spheroid arbitrarily oriented with respect to the externally applied field. Strong departure from Smoluchowskian behavior is found. If co-ion is the current carrier, the mobility is independent of ζ, regardless of the body shape. Also, the hydrodynamic flow-field is irrotational. If counter-ion is the current carrier, the problem formulated in terms of a properly-defined scalar field (Ω), which embodies both the electric potential (Ψ) and the salt concentration, becomes formally identical to the one addressed in our previous work, concerning the small-ζ regime, with negligible salt gradients. Then, all the results obtained in that study are extended and applied even to the large-ζ regime considered here, provided the new expressions now derived for the surface boundary conditions and the slip-flow coefficient are employed and Ω is used in place of Ψ. The present results are discussed also in comparison with the classical studies of Dukhin et al and O'Brien et al concerning electrophoresis of highly charged particles with no salt gradient at infinity, and with recent studies of electrodiffusiophoresis, which, however, neglected the fields perturbations caused by Debye-layer kinetics. It is found that the effects addressed and incorporated
A new method to measure galaxy bias by combining the density and weak lensing fields
NASA Astrophysics Data System (ADS)
Pujol, Arnau; Chang, Chihway; Gaztañaga, Enrique; Amara, Adam; Refregier, Alexandre; Bacon, David J.; Carretero, Jorge; Castander, Francisco J.; Crocce, Martin; Fosalba, Pablo; Manera, Marc; Vikram, Vinu
2016-10-01
We present a new method to measure redshift-dependent galaxy bias by combining information from the galaxy density field and the weak lensing field. This method is based on the work of Amara et al., who use the galaxy density field to construct a bias-weighted convergence field κg. The main difference between Amara et al.'s work and our new implementation is that here we present another way to measure galaxy bias, using tomography instead of bias parametrizations. The correlation between κg and the true lensing field κ allows us to measure galaxy bias using different zero-lag correlations, such as <κgκ>/<κκ> or <κgκg>/<κgκ>. Our method measures the linear bias factor on linear scales, under the assumption of no stochasticity between galaxies and matter. We use the Marenostrum Institut de Ciències de l'Espai (MICE) simulation to measure the linear galaxy bias for a flux-limited sample (i < 22.5) in tomographic redshift bins using this method. This article is the first that studies the accuracy and systematic uncertainties associated with the implementation of the method and the regime in which it is consistent with the linear galaxy bias defined by projected two-point correlation functions (2PCF). We find that our method is consistent with a linear bias at the per cent level for scales larger than 30 arcmin, while non-linearities appear at smaller scales. This measurement is a good complement to other measurements of bias, since it does not depend strongly on σ8 as do the 2PCF measurements. We will apply this method to the Dark Energy Survey Science Verification data in a follow-up article.
A search for weak or complex magnetic fields in the B3V star ι Herculis
NASA Astrophysics Data System (ADS)
Wade, G. A.; Folsom, C. P.; Petit, P.; Petit, V.; Lignières, F.; Aurière, M.; Böhm, T.
2014-11-01
We obtained 128 high signal-to-noise ratio Stokes V spectra of the B3V star ι Her on five consecutive nights in 2012 with the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope, with the aim of searching for the presence of weak and/or complex magnetic fields. Least-squares deconvolution (LSD) mean profiles were computed from individual spectra, averaged over individual nights and over the entire run. No Zeeman signatures are detected in any of the profiles. The longitudinal magnetic field in the grand average profile was measured to be -0.24 ± 0.32 G, as compared to -0.22 ± 0.32 G in the null profile. Our observations therefore provide no evidence for the presence of Zeeman signatures analogous to those observed in the A0V star Vega by Lignières et al. We interpret these observations in three ways. First, we compare the LSD profiles with synthetic Stokes V profiles corresponding to organized (dipolar) magnetic fields, for which we find an upper limit of about 8 G on the polar strength of any surface dipole present. Secondly, we compare the grand average profile with calculations corresponding to the random magnetic spot topologies of Kochukhov & Sudnik, inferring that spots, if present, of 2° radius with strengths of 2-4 G and a filling factor of 50 per cent should have been detected in our data. Finally, we compare the observations with synthetic V profiles corresponding to the surface magnetic maps of Vega (Petit et al.) computed for the spectral characteristics of ι Her. We conclude that while it is unlikely we would have detected a magnetic field identical to Vega's, we would have likely detected one with a peak strength of about 30 G, i.e. approximately four times as strong as that of Vega.
NASA Astrophysics Data System (ADS)
Khait, Yu. L.
1996-08-01
Novel experimentally verifiable and theoretically explained effects of weak static magnetic fields (WSMFs) acting during ion implantation of semiconductors and superconducting ceramics (SCC) at 300 K, moderate ion energies (e.g. 200-400 keV) and low dosage (e.g. 10 11-10 13 m -2) on the post-implantation radiation damage (PIRD) and material parameters are discussed. The WSMF of strength of H ≈ 1 kOe reduces, as previously reported, the PIRD in Hg 08Cd 02Te and InSb by factors of 2 and 1.54, respectively, and can increase the PIRD and change material parameters in SCCs. The WSMF effects on the radiation damage is a generic consequence of the kinetic electron-related theory of atomic rate processes in solids which shows that local electron transitions (LETs) in the nanometer vicinity of hopping atoms (defects) influence exponentially defect formation and migration rates. The magnetic field changing the LET number affects exponentially the rates of formation, migration and agglomeration of point defects and thus change the radiation damage.
Plasma Waves Around Separatrix in Collisionless Magnetic Reconnection with Weak Guide Field
NASA Astrophysics Data System (ADS)
Chen, Y.; Fujimoto, K.; Xiao, C.; Ji, H.
2015-12-01
Electrostatic and electromagnetic waves excited by electron beam around the separatrix region are analyzed in detail during the collisionless magnetic reconnection with a weak guide field by using 2D particle-in-cell simulation with the adaptive mesh refinement. Broadband electrostatic waves are excited both in the inflow and outflow regions around the separatrices due to the electron bump-on-tail, two-stream, and Buneman instabilities. In contrast, the quasi-monochromatic electromagnetic waves are excited only in the inflow side of the separatrices due to a beam-driven Whistler instability. The localization of the Whistler waves is attributed to the non-uniformity of the out-of-plane magnetic field By. The Whistler instability is suppressed in the outflow side where By is too small for the oblique propagation. The electrostatic waves with distinct speeds can explain the in situ spacecraft observations. From the causality point of view, the waves are generated as the consequence of the electron bulk acceleration to thermalize the particles through wave-particle interactions. These simulation results provide guidance to analyze high-resolution wave observations during reconnection in the ongoing and upcoming satellite missions, as well as in dedicated laboratory experiments.
Optical response of a quantum dot-metal nanoparticle hybrid interacting with a weak probe field.
Kosionis, Spyridon G; Terzis, Andreas F; Sadeghi, Seyed M; Paspalakis, Emmanuel
2013-01-30
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.
General relativistic N-body simulations in the weak field limit
NASA Astrophysics Data System (ADS)
Adamek, Julian; Daverio, David; Durrer, Ruth; Kunz, Martin
2013-11-01
We develop a formalism for general relativistic N-body simulations in the weak field regime, suitable for cosmological applications. The problem is kept tractable by retaining the metric perturbations to first order, the first derivatives to second order, and second derivatives to all orders, thus taking into account the most important nonlinear effects of Einstein gravity. It is also expected that any significant “backreaction” should appear at this order. We show that the simulation scheme is feasible in practice by implementing it for a plane-symmetric situation and running two test cases, one with only cold dark matter, and one which also includes a cosmological constant. For these plane-symmetric situations, the deviations from the usual Newtonian N-body simulations remain small and, apart from a nontrivial correction to the background, can be accurately estimated within the Newtonian framework. The correction to the background scale factor, which is a genuine backreaction effect, can be robustly obtained with our algorithm. Our numerical approach is also naturally suited for the inclusion of extra relativistic fields and thus for dark energy or modified gravity simulations.
Bhardwaj, S; Mkhitaryan, V V; Gruzberg, I A
2014-06-01
We consider a recently proposed network model of the integer quantum Hall (IQH) effect in a weak magnetic field. Using a supersymmetry approach, we reformulate the network model in terms of a superspin ladder. A subsequent analysis of the superspin ladder and the corresponding supersymmetric nonlinear sigma model allows us to establish the phase diagram of the network model, and the form of the critical line of the weak-field IQH transition. Our results confirm the universality of the IQH transition, which is described by the same sigma model in strong and weak magnetic fields. We apply the suspersymmetry method to several related network models that were introduced in the literature to describe the quantum Hall effect in graphene, the spin-degenerate Landau levels, and localization of electrons in a random magnetic field.
NASA Astrophysics Data System (ADS)
Zheng, Sheng Ming
2012-10-01
In the natural world, people have discovered four kinds of forces: electromagnetic force, gravitation, weak force, and strong force. Although the gravitation has been discovered more than three hundred years, its mechanism of origin is unclear until today. While investigating the origin of gravitation, I do some experiments discover the moving photons produce gravitation. This discovery shows the origin of gravitation. Meanwhile I do some experiments discover the light interference fringes are produced by the gravitation: my discovery demonstrate light is a particle, but is not a wave-particle duality. Furthermore, applications of this discovery to other moving particles show a similar effect. In a word: the micro particle moving produce gravitation and electromagnetic force. Then I do quantity experiment get a general formula: Reveal the essence of gravitational mass and the essence of electric charge; reveal the origin of gravitation and the essence of matter wave. Along this way, I unify the gravitation and electromagnetic force. Namely I find a natural law that from atomic world to star world play in moving track. See website: https://www.lap-publishing.com/catalog/details/store/gb/book/978-3-8473-2658-8/mechanism-of-interaction-in-moving-matter
Endothelial Cell Morphology and Migration are Altered by Changes in Gravitational Fields
NASA Technical Reports Server (NTRS)
Melhado, Caroline; Sanford, Gary; Harris-Hooker, Sandra
1997-01-01
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.
Non-thermal mechanism of weak microwave fields influence on neurons
NASA Astrophysics Data System (ADS)
Shneider, M. N.; Pekker, M.
2013-09-01
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.
Weak Ligand-Field Effect from Ancillary Ligands on Enhancing Single-Ion Magnet Performance.
Meng, Yin-Shan; Zhang, Yi-Quan; Wang, Zhe-Ming; Wang, Bing-Wu; Gao, Song
2016-08-26
A series of bis-pentamethylcyclopentadienyl-supported Dy complexes containing different ancillary ligands were synthesized and characterized. Magnetic studies showed that 1 Dy [Cp*2 DyCl(THF)], 1 Dy' [Cp*2 DyCl2 K(THF)]n , 2 Dy [Cp*2 DyBr(THF)], 3 Dy [Cp*2 DyI(THF)] and 4 Dy [Cp*2 DyTp] (Tp=hydrotris(1-pyrazolyl)borate) were single-ion magnets (SIMs). The 1D dysprosium chain 1 Dy' exhibited a hysteresis at up to 5 K. Furthermore, 3 Dy featured the highest energy barrier (419 cm(-1) ) among the complexes. The effects of ancillary ligands on single-ion magnetic properties were studied by experimental, ab initio calculations and electrostatic analysis methods in detail. These results demonstrated that the QTM rate was strongly dependent on the ancillary ligands and that a weak equatorial ligand field could be beneficial for constructing Dy-SIMs. PMID:27417884
Nedeljkovic, N.N.; Nedeljkovic, Lj.D.
2005-09-15
The ionization distances R{sub c}{sup I} of slow hydrogenlike Rydberg atoms approaching solid surfaces in the presence of a weak external electric field are calculated. The ionization is treated as resonant electron tunneling in the very vicinity of the top of the potential barrier, created between the ionic core and polarized solid. We obtain both the complex energies and the ionization distances by solving the energy eigenvalue problem under the outgoing wave boundary condition towards the solid. The eigenvalue problem is studied in parabolic coordinates within the framework of an etalon equation method adapted to include the confluence of turning points. It is demonstrated that in a critical region R{approx_equal}R{sub c}{sup I}>>1 a.u. of ion-surface distances R, parabolic quantum numbers n{sub 1}, n{sub 2}, and m can serve as approximate, but 'sufficiently good' quantum numbers, at least for lower n{sub 1} values. The method offers asymptotically exact analytical expressions for the ionization rates and energies, which follow the theoretical predictions of the complex scaling method (CSM). It is also found that the resulting ionization distances R{sub c}{sup I} are in very good agreement with the results of CSM. The implications of using obtained results in analyzing the recent xenon experimental data for R{sub c}{sup I} are briefly discussed.
NASA Astrophysics Data System (ADS)
Louthain, James A.; Welsh, Byron M.
1998-09-01
A new atmospheric screen generator is developed for use in performance calculations of adaptive optics and imaging systems. The generator is valid over a wide range of atmospheric turbulence parameters and incorporates both phase and amplitude effects. The new screen generator accounts for diffraction effects caused by turbulence and incorporates the phase, amplitude, and cross statistics of a weak turbulence model. The second order statistics of the phase and amplitude perturbations are based on the auto- correlation functions developed by Lee and Harp and the cross-correlation of the phase and amplitude perturbations derived in this paper. The correlations are derived by modeling the turbulence as a number of layers of randomly varying refractivity perpendicular to the propagation path. As the field propagates through the medium, diffraction occurs at each of the layers. A Fourier series expansion of the wavefront phase and amplitude is used. The screen generator uses the power and cross spectral densities of the phase and amplitude perturbations. The mean square value and the structure functions of the wavefront phase and amplitude are calculated in a Monte Carlo experiment and shown to be within 1% of the theoretical value.
Transitions among H Stark substates induced by time-varying, weak static electric fields
NASA Astrophysics Data System (ADS)
Butz, A.; Koch, P. M.; Schultz, K. D.; Wilson, J.
2002-05-01
Our laboratory produces H Rydberg atoms (typically 14 keV) with a collision/laser method. H^+-Xe collisions produce H(n) atoms. A 100 kV/cm field ionizes n>9. In F1 near 30 kV/cm, a CO2 laser transfers 50% of (n,n_1,|m|)=(7,0,0) atoms to (10,0,0) (or other chosen substate). They fly through F2 and are excited in F3 with a CO2 laser from n=10 substates to n>24 substates. Each F is transverse between parallel plates, but we separately control the voltage to all six plates. If all Fi are parallel and F_2, F3 exceed a few V/cm, population stays on the (10,0,0) substate, and we get a `simple' excitation spectrum in F_3. If F2 or F3 (or both) is too weak or antiparallel, we detect new excitation peaks in F3 from atoms moved into other n=10 substates. Our experimental goal is careful, quantitative measurements and interpretation of these excitation spectra to understand where the population goes. Our theoretical goal is a model for this process similar to that for Majorana depolarization of magnetic substates in Lamb-shift polarized ion sourcesfootnote G.G. Ohlsen, Los Alamos Report LA-3949 (1968); W.J. Thompson, Nucl. Instr. Meth. A 333, 443 (1993). .
Subtle consequences of exposure to weak microwave fields: Are there non-thermal effects?
NASA Astrophysics Data System (ADS)
Lovely, R. H.; Mizumori, S. J. Y.; Johnson, R. B.; Guy, A. W.
When we speak of subtle consequences of exposure we mean only that the effects were observed in the absence of changes in core temperature due to microwave exposure. When we measure + delta T degree C in core temperature consequent to microwave exposure, we are witnessing a breakdown of thermoregulatory mechanisms. Short of this event, the exposed subject makes a number of thermoregulatory and metabolic accommodations to maintain a constant body temperature and to deal effectively with the energy being deposited in its tissues. These latter changes should interest us for they are the subtle consequences exposure to weak microwave fields. The long-term accommodations, which accompany subchronic exposure, can lead to a number of interesting effects some of which are described below. Two fundamentally different types of experimental protocol were employed. In Experiment 1A, independent groups of male rats were either exposed or sham-exposed to 915 MHz microwaves for 10 hr/night for up to 4 mo. In Experiment 1B, independent groups of rats were similarly exposed, or sham-exposed, to 2450 MHz microwaves for 10 hr/night for 4 mo. In Experiment 2, using a different type of protocol, pregnant female rats were exposed for 20 hr/day for 19 days of gestation. Control groups were either sham-exposed or served as caged controls. The main focus of the study attended to assessment of various functions and the developmental status of the gravid rats' progeny.
NASA Astrophysics Data System (ADS)
Nath, G.; Vishwakarma, J. P.
2016-11-01
Similarity solutions are obtained for the flow behind a spherical shock wave in a non-ideal gas under gravitational field with conductive and radiative heat fluxes, in the presence of a spatially decreasing azimuthal magnetic field. The shock wave is driven by a piston moving with time according to power law. The radiation is considered to be of the diffusion type for an optically thick grey gas model and the heat conduction is expressed in terms of Fourier's law for heat conduction. Similarity solutions exist only when the surrounding medium is of constant density. The gas is assumed to have infinite electrical conductivity and to obey a simplified van der Waals equation of state. It is shown that an increase of the gravitational parameter or the Alfven-Mach number or the parameter of the non-idealness of the gas decreases the compressibility of the gas in the flow-field behind the shock, and hence there is a decrease in the shock strength. The pressure and density vanish at the inner surface (piston) and hence a vacuum is formed at the center of symmetry. The shock waves in conducting non-ideal gas under gravitational field with conductive and radiative heat fluxes can be important for description of shocks in supernova explosions, in the study of a flare produced shock in the solar wind, central part of star burst galaxies, nuclear explosion etc. The solutions obtained can be used to interpret measurements carried out by space craft in the solar wind and in neighborhood of the Earth's magnetosphere.
Weak magnetic field significantly enhances selenite removal kinetics by zero valent iron.
Liang, Liping; Sun, Wu; Guan, Xiaohong; Huang, Yuying; Choi, Wonyong; Bao, Hongliang; Li, Lina; Jiang, Zheng
2014-02-01
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.
Weak magnetic field significantly enhances selenite removal kinetics by zero valent iron.
Liang, Liping; Sun, Wu; Guan, Xiaohong; Huang, Yuying; Choi, Wonyong; Bao, Hongliang; Li, Lina; Jiang, Zheng
2014-02-01
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
Modeling weakly-ionized plasmas in magnetic field: A new computationally-efficient approach
NASA Astrophysics Data System (ADS)
Parent, Bernard; Macheret, Sergey O.; Shneider, Mikhail N.
2015-11-01
Despite its success at simulating accurately both non-neutral and quasi-neutral weakly-ionized plasmas, the drift-diffusion model has been observed to be a particularly stiff set of equations. Recently, it was demonstrated that the stiffness of the system could be relieved by rewriting the equations such that the potential is obtained from Ohm's law rather than Gauss's law while adding some source terms to the ion transport equation to ensure that Gauss's law is satisfied in non-neutral regions. Although the latter was applicable to multicomponent and multidimensional plasmas, it could not be used for plasmas in which the magnetic field was significant. This paper hence proposes a new computationally-efficient set of electron and ion transport equations that can be used not only for a plasma with multiple types of positive and negative ions, but also for a plasma in magnetic field. Because the proposed set of equations is obtained from the same physical model as the conventional drift-diffusion equations without introducing new assumptions or simplifications, it results in the same exact solution when the grid is refined sufficiently while being more computationally efficient: not only is the proposed approach considerably less stiff and hence requires fewer iterations to reach convergence but it yields a converged solution that exhibits a significantly higher resolution. The combined faster convergence and higher resolution is shown to result in a hundredfold increase in computational efficiency for some typical steady and unsteady plasma problems including non-neutral cathode and anode sheaths as well as quasi-neutral regions.
Frilot, C; Carrubba, S; Marino, A A
2014-01-31
Subliminal electromagnetic fields (EMFs) triggered nonlinear evoked potentials in awake but not anesthetized animals, and increased glucose metabolism in the hindbrain. Field detection occurred somewhere in the head and possibly was an unrecognized function of sensory neurons in facial skin, which synapse in the trigeminal nucleus and project to the thalamus via glutamate-dependent pathways. If so, anesthetic agents that antagonize glutamate neurotransmission would be expected to degrade EMF-evoked potentials (EEPs) to a greater extent than agents having different pharmacological effects. We tested the hypothesis using ketamine which blocks N-methyl-d-aspartate (NMDA) receptors (NMDARs), and xylazine which is an α₂-adrenoreceptor agonist. Electroencephalograms (EEGs) of rats were examined using recurrence analysis to observe EEPs in the presence and absence of ketamine and/or xylazine anesthesia. Auditory evoked potentials (AEPs) served as positive controls. The frequency of observation of evoked potentials in a given condition (wake or anesthesia) was compared with that due to chance using the Fisher's exact test. EEPs were observed in awake rats but not while they were under anesthesia produced using a cocktail of xylazine and ketamine. In another experiment each rat was measured while awake and while under anesthesia produced using either xylazine or ketamine. EEPs and AEPs were detected during wake and under xylazine (P<0.05 in each of the four measurements). In contrast, neither EEPs nor AEPs were observed when anesthesia was produced partly or wholly using ketamine. The duration and latency of the EEPs was unaltered by xylazine anesthesia. The afferent signal triggered by the transduction of weak EMFs was likely mediated by NMDAR-mediated glutamate neurotransmission.
Frilot, C; Carrubba, S; Marino, A A
2014-01-31
Subliminal electromagnetic fields (EMFs) triggered nonlinear evoked potentials in awake but not anesthetized animals, and increased glucose metabolism in the hindbrain. Field detection occurred somewhere in the head and possibly was an unrecognized function of sensory neurons in facial skin, which synapse in the trigeminal nucleus and project to the thalamus via glutamate-dependent pathways. If so, anesthetic agents that antagonize glutamate neurotransmission would be expected to degrade EMF-evoked potentials (EEPs) to a greater extent than agents having different pharmacological effects. We tested the hypothesis using ketamine which blocks N-methyl-d-aspartate (NMDA) receptors (NMDARs), and xylazine which is an α₂-adrenoreceptor agonist. Electroencephalograms (EEGs) of rats were examined using recurrence analysis to observe EEPs in the presence and absence of ketamine and/or xylazine anesthesia. Auditory evoked potentials (AEPs) served as positive controls. The frequency of observation of evoked potentials in a given condition (wake or anesthesia) was compared with that due to chance using the Fisher's exact test. EEPs were observed in awake rats but not while they were under anesthesia produced using a cocktail of xylazine and ketamine. In another experiment each rat was measured while awake and while under anesthesia produced using either xylazine or ketamine. EEPs and AEPs were detected during wake and under xylazine (P<0.05 in each of the four measurements). In contrast, neither EEPs nor AEPs were observed when anesthesia was produced partly or wholly using ketamine. The duration and latency of the EEPs was unaltered by xylazine anesthesia. The afferent signal triggered by the transduction of weak EMFs was likely mediated by NMDAR-mediated glutamate neurotransmission. PMID:24239718
NASA Astrophysics Data System (ADS)
Mema, Ensela; Cummings, Linda J.; Kondic, Lou
We consider a mathematical model that consists of a NLC layer sandwiched between two parallel bounding plates, across which an external field is applied. We investigate its effect on the director orientation by considering the dielectric and flexoelectric contributions and varying parameters that represent the anchoring conditions and the electric field strength. In particular, we investigate possible director configurations that occur in weakly anchored and non-planar systems. We observe that non-planar anchoring angles destroy any hysteresis seen in a planar system by eliminating the fully vertical director configuration and the ''saturation threshold'' seen in weakly anchored planar Freedericksz cells. Supported by NSF Grant No. DMS-1211713.
NASA Astrophysics Data System (ADS)
Pitonak, Martin; Sprlak, Michal; Novak, Pavel; Tenzer, Robert
2016-04-01
Recently realized gravity-dedicated satellite missions allow for measuring values of scalar, vectorial (Gravity Recovery And Climate Experiment - GRACE) and second-order tensorial (Gravity field and steady-state Ocean Circulation Explorer - GOCE) parameters of the Earth's gravitational potential. Theoretical aspects related to using moving sensors for measuring elements of the third-order gravitational tensor are currently under investigation, e.g., the gravity field-dedicated satellite mission OPTIMA (OPTical Interferometry for global Mass change detection from space) should measure third-order derivatives of the Earth's gravitational potential. This contribution investigates regional recovery of the disturbing gravitational potential on the Earth's surface from satellite and aerial observations of the first-, second- and third-order radial derivatives of the disturbing gravitational potential. Synthetic measurements along a satellite orbit at the altitude of 250 km and along an aircraft track at the altitude of 10 km are synthetized from the global gravitational model EGM2008 and polluted by the Gaussian noise. The process of downward continuation is stabilized by the Tikhonov regularization. Estimated values of the disturbing gravitational potential are compared with the same quantity synthesized directly from EGM2008.
Omnidirectional Gravitational Radiation Observatory: Proceedings of the First International Workshop
NASA Astrophysics Data System (ADS)
Velloso, W. F.; Aguiar, O. D.; Magalhães, N. S.
1997-08-01
neutron star coalescence, bar-mode instability and core colapse events by spherical antennas * Interaction of high energy muons and hadrons with a large aluminum spherical resonant detector * Optimal detection of pulsed GW signals correlated with cosmic gamma-bursts * Preliminary results of searching of joint gravity-neutrinos-gamma events * Next Generation Resonant-Mass Antennas * A 100 TON 10mK spherical gravitational wave detector * Experimental study of spherical resonators at very low temperatures * Thermal convective cooling of gravitational radiation antennas * Very low temperature measurements of quality factors of copper alloys for resonant gravitational wave antennae * Real life TIGA measurements: results from the LSU prototype * Simulation of a spherical resonant-mass gravitational wave antenna * DEFOSP: the gravitational wave detector for a space laboratory * The resonator problem in a spherical GW antenna * On the use of the Finite Elements Method to design the structures of mechanical isolation to resonant mass antennas * Transducers and Amplification Techniques * Low-loss sapphire transducers for resonant-mass Gravitational Wave detectors and quantum non-demolition readouts * Improvement of an inductive tripode transducer electrical Q * Tests of a resonant capacitive transducer with integrated readout on the cryogenic gravitational wave antenna ALTAIR * Development of an optical transducer * Noise measurements on two-squid gravitational wave transducer systems * Resonant/Free Mass Omnidirectional Network * The present status of VIRGO Project * The supernova cosmological background of gravitational waves * LIGO: status and prospects * The ring interferometer in the field of a weak gravitational wave * List of Participants
NASA Astrophysics Data System (ADS)
Burdaev, M. N.
2011-10-01
The paper presents the derivation of two new equations for calculating the time of transfer between two points of the central gravitational field: for hyperbolic orbits and the universal equation for elliptical and hyperbolic orbits. In the paper we have used as an independent variable, instead of the linear elements (semimajor axis, focal parameter of orbit or a chord connecting the ends of boundary radii of transfer), the angular parameter—the angle between the radius vector of an initial point of transfer and the vector of initial velocity of transfer. Paper's material is a continuation of that presented in the "Space research" Journal, vol. 2, March-April, 2009.
NASA Astrophysics Data System (ADS)
Herrera, L.; Magli, G.; Malafarina, D.
2005-08-01
A new, globally regular model describing a static, non spherical gravitating object in General Relativity is presented. The model is composed by a vacuum Weyl-Levi-Civita special field - the so called gamma metric - generated by a regular static distribution of mass-energy. Standard requirements of physical reasonableness such as, energy, matching and regularity conditions are satisfied. The model is used as a toy in investigating various issues related to the directional behavior of naked singularities in static spacetimes and the black hole (Schwarzschild) limit.
NASA Astrophysics Data System (ADS)
Wendt, Kyle
2016-03-01
How large is the 48Ca nucleus? While the electric charge distribution of this nucleus was accurately measured decades ago, both experimental and ab initio descriptions of the neutron distribution are deficient. We address this question using ab initio calculations of the electric charge, neutron, and weak distributions of 48Ca based on chiral effective field theory. Historically, chiral effective field theory calculations of systems larger than 4 nucleons have been plagued by strong systematic errors which result in theoretical descriptions that are too dense and over bound. We address these errors using a novel approach that permits us to accurately reproduce binding energy and charge radius of 48Ca, and to constrain electroweak observables such as the neutron radius, electric dipole polarizability, and the weak form factor. For a full list of contributors to this work, please see ``Neutron and weak-charge distributions of the 48Ca nucleus,'' Nature Physics (2015) doi:10.1038/nphys3529.
Activating persulfate by Fe⁰ coupling with weak magnetic field: performance and mechanism.
Xiong, Xinmei; Sun, Bo; Zhang, Jing; Gao, Naiyun; Shen, Jimin; Li, Jialing; Guan, Xiaohong
2014-10-01
Weak magnetic field (WMF) and Fe(0) were proposed to activate PS synergistically (WMF-Fe(0)/PS) to degrade dyes and aromatic contaminants. The removal rates of orange G (OG) by WMF-Fe(0)/PS generally decreased with increasing initial pH (3.0-10.0) and increased with increasing Fe(0) (0.5-3.0 mM) or PS dosages (0.5-3.0 mM). Compared to its counterpart without WMF, the WMF-Fe(0)/PS process could induce a 5.4-28.2 fold enhancement in the removal rate of OG under different conditions. Moreover, the application of WMF significantly enhanced the decolorization rate and the mineralization of OG. The degradation rates of caffeine, 4-nitrophenol, benzotriazole and diuron by Fe(0)/PS were improved by 2.1-11.1 fold due to the superimposed WMF. Compared to many other sulfate radical-based advanced oxidation technologies under similar reaction conditions, WMF-Fe(0)/PS technology could degrade selected organic contaminants with much greater rates. Sulfate radical was identified to be the primary radical species responsible for the OG degradation at pH 7.0 in WMF-Fe(0)/PS process. This study unraveled that the presence of WMF accelerated the corrosion rate of Fe(0) and thus promoted the release of Fe(2+), which induced the increased production of sulfate radicals from PS and promoted the degradation of organic contaminants. Employing WMF to enhance oxidation capacity of Fe(0)/PS is a novel, efficient, promising and environmental-friendly method since it does not need extra energy and costly reagents.
Effects of oxygen and weak magnetic field on Fe(0)/bisulfite system: performance and mechanisms.
Xiong, Xinmei; Gan, Jinhong; Zhan, Wei; Sun, Bo
2016-08-01
The performance and mechanisms of 4-nitrophenol (4-NP) degradation by the Fe(0)/bisulfite system were systematically investigated for the first time. The evidences presented in this study verified that O2 was a crucial factor that affected the mechanism of Fe(0)/bisulfite-driven 4-NP degradation. In the Fe(0)/bisulfite/O2 system, Fe(0) acted as a supplier of Fe(2+) to catalyze bisulfite oxidation that induced a chain reaction to produce reactive radicals for 4-NP degradation. While under N2 purging condition, bisulfite worked as a specified reductant that facilitated the transformation of Fe(3+) to nascent Fe(2+) ions, which principally accounted for the reductive removal of 4-NP. The application of a weak magnetic field (WMF) efficiently improved the removal rate of 4-NP and did not alter the mechanisms in both Fe(0)/bisulfite/O2 and Fe(0)/bisulfite/N2 processes. The secondary radicals, HO(·), SO4 (·-), and SO5 (·-), were considered as the most possible active oxidants contributing to the oxidative removal of 4-NP and even partial mineralization under an oxic condition. Compared with anoxic conditions, the performance removal of 4-NP by the WMF-Fe(0)/bisulfite/O2 system showed less pHini dependence. To facilitate the application of WMF-Fe(0)/bisulfite/O2 technology in real practice, premagnetization of Fe(0) was employed to combine with bisulfite/O2 and proved to be an effective and applicable method for 4-NP removal. PMID:27184150
NASA Astrophysics Data System (ADS)
Wyrzykowski, Ł.; Moniez, M.; Horne, K.; Street, R.
2012-04-01
Gravitational microlensing is a well established and unique field of time-domain astrophysics. For two decades microlensing surveys have been regularly observing millions of stars to detect elusive events that follow a characteristic Paczyński lightcurve. This workshop reviewed the current state of the field, and covered the major topics related to microlensing: searches for extrasolar planets, and studies of dark matter. There were also discussions of issues relating to the organisation of follow-up observations for microlensing, as well as serendipitous scientific outcomes resulting from extensive microlensing data.
Su, Ying; Wang, C.; Avishai, Y.; Meir, Yigal; Wang, X. R.
2016-01-01
The one-parameter scaling theory of localization predicts that all states in a disordered two-dimensional system with broken time reversal symmetry are localized even in the presence of strong spin-orbit coupling. While at constant strong magnetic fields this paradigm fails (recall the quantum Hall effect), it is believed to hold at weak magnetic fields. Here we explore the nature of quantum states at weak magnetic field and strongly fluctuating spin-orbit coupling, employing highly accurate numerical procedure based on level spacing distribution and transfer matrix technique combined with one parameter finite-size scaling hypothesis. Remarkably, the metallic phase, (known to exist at zero magnetic field), persists also at finite (albeit weak) magnetic fields, and eventually crosses over into a critical phase, which has already been confirmed at high magnetic fields. A schematic phase diagram drawn in the energy-magnetic field plane elucidates the occurrence of localized, metallic and critical phases. In addition, it is shown that nearest-level statistics is determined solely by the symmetry parameter β and follows the Wigner surmise irrespective of whether states are metallic or critical. PMID:27628694
Su, Ying; Wang, C; Avishai, Y; Meir, Yigal; Wang, X R
2016-01-01
The one-parameter scaling theory of localization predicts that all states in a disordered two-dimensional system with broken time reversal symmetry are localized even in the presence of strong spin-orbit coupling. While at constant strong magnetic fields this paradigm fails (recall the quantum Hall effect), it is believed to hold at weak magnetic fields. Here we explore the nature of quantum states at weak magnetic field and strongly fluctuating spin-orbit coupling, employing highly accurate numerical procedure based on level spacing distribution and transfer matrix technique combined with one parameter finite-size scaling hypothesis. Remarkably, the metallic phase, (known to exist at zero magnetic field), persists also at finite (albeit weak) magnetic fields, and eventually crosses over into a critical phase, which has already been confirmed at high magnetic fields. A schematic phase diagram drawn in the energy-magnetic field plane elucidates the occurrence of localized, metallic and critical phases. In addition, it is shown that nearest-level statistics is determined solely by the symmetry parameter β and follows the Wigner surmise irrespective of whether states are metallic or critical.
Su, Ying; Wang, C; Avishai, Y; Meir, Yigal; Wang, X R
2016-01-01
The one-parameter scaling theory of localization predicts that all states in a disordered two-dimensional system with broken time reversal symmetry are localized even in the presence of strong spin-orbit coupling. While at constant strong magnetic fields this paradigm fails (recall the quantum Hall effect), it is believed to hold at weak magnetic fields. Here we explore the nature of quantum states at weak magnetic field and strongly fluctuating spin-orbit coupling, employing highly accurate numerical procedure based on level spacing distribution and transfer matrix technique combined with one parameter finite-size scaling hypothesis. Remarkably, the metallic phase, (known to exist at zero magnetic field), persists also at finite (albeit weak) magnetic fields, and eventually crosses over into a critical phase, which has already been confirmed at high magnetic fields. A schematic phase diagram drawn in the energy-magnetic field plane elucidates the occurrence of localized, metallic and critical phases. In addition, it is shown that nearest-level statistics is determined solely by the symmetry parameter β and follows the Wigner surmise irrespective of whether states are metallic or critical. PMID:27628694
NASA Astrophysics Data System (ADS)
Su, Ying; Wang, C.; Avishai, Y.; Meir, Yigal; Wang, X. R.
2016-09-01
The one-parameter scaling theory of localization predicts that all states in a disordered two-dimensional system with broken time reversal symmetry are localized even in the presence of strong spin-orbit coupling. While at constant strong magnetic fields this paradigm fails (recall the quantum Hall effect), it is believed to hold at weak magnetic fields. Here we explore the nature of quantum states at weak magnetic field and strongly fluctuating spin-orbit coupling, employing highly accurate numerical procedure based on level spacing distribution and transfer matrix technique combined with one parameter finite-size scaling hypothesis. Remarkably, the metallic phase, (known to exist at zero magnetic field), persists also at finite (albeit weak) magnetic fields, and eventually crosses over into a critical phase, which has already been confirmed at high magnetic fields. A schematic phase diagram drawn in the energy-magnetic field plane elucidates the occurrence of localized, metallic and critical phases. In addition, it is shown that nearest-level statistics is determined solely by the symmetry parameter β and follows the Wigner surmise irrespective of whether states are metallic or critical.
NASA Astrophysics Data System (ADS)
Nakonieczna, Anna; Yeom, Dong-han
2016-05-01
Investigating the dynamics of gravitational systems, especially in the regime of quantum gravity, poses a problem of measuring time during the evolution. One of the approaches to this issue is using one of the internal degrees of freedom as a time variable. The objective of our research was to check whether a scalar field or any other dynamical quantity being a part of a coupled multi-component matter-geometry system can be treated as a `clock' during its evolution. We investigated a collapse of a self-gravitating electrically charged scalar field in the Einstein and Brans-Dicke theories using the 2+2 formalism. Our findings concentrated on the spacetime region of high curvature existing in the vicinity of the emerging singularity, which is essential for the quantum gravity applications. We investigated several values of the Brans-Dicke coupling constant and the coupling between the Brans-Dicke and the electrically charged scalar fields. It turned out that both evolving scalar fields and a function which measures the amount of electric charge within a sphere of a given radius can be used to quantify time nearby the singularity in the dynamical spacetime part, in which the apparent horizon surrounding the singularity is spacelike. Using them in this respect in the asymptotic spacetime region is possible only when both fields are present in the system and, moreover, they are coupled to each other. The only nonzero component of the Maxwell field four-potential cannot be used to quantify time during the considered process in the neighborhood of the whole central singularity. None of the investigated dynamical quantities is a good candidate for measuring time nearby the Cauchy horizon, which is also singular due to the mass inflation phenomenon.
NASA Astrophysics Data System (ADS)
Pervishko, A. A.; Kibis, O. V.; Shelykh, I. A.
2016-08-01
We investigate theoretically the effect of a magnetic field on intersubband polaritons in an asymmetric quantum well placed inside an optical resonator. It is demonstrated that the field-induced diamagnetic shift of electron subbands in the well increases the broadening of optical lines corresponding to intersubband electron transitions. As a consequence, the magnetic field can switch the polariton system from the regime of strong light-matter coupling to the regime of weak one. This effect paves a way to the effective control of polaritonic devices with a magnetic field.
On the unreasonable effectiveness of the post-Newtonian approximation in gravitational physics.
Will, Clifford M
2011-04-12
The post-Newtonian approximation is a method for solving Einstein's field equations for physical systems in which motions are slow compared to the speed of light and where gravitational fields are weak. Yet it has proven to be remarkably effective in describing certain strong-field, fast-motion systems, including binary pulsars containing dense neutron stars and binary black hole systems inspiraling toward a final merger. The reasons for this effectiveness are largely unknown. When carried to high orders in the post-Newtonian sequence, predictions for the gravitational-wave signal from inspiraling compact binaries will play a key role in gravitational-wave detection by laser-interferometric observatories.
Resonance of Gaussian Electromagnetic Field to the High Frequency Gravitational Waves
NASA Astrophysics Data System (ADS)
Li, Jin; Zhang, Lu; Lin, Kai; Wen, Hao
2016-08-01
We consider a Gaussian Beam (GB) resonant system for high frequency gravitational waves (HFGWs) detection. At present, we find the optimal signal strength in theory through setting the magnetic component of GB in a standard gaussian form. Under the synchro-resonance condition, we study the signal strength (i.e., transverse perturbative photon fluxes) from the relic HFGWs (predicted by ordinary inflationary model) and the braneworld HFGWs (from braneworld scenarios). Both of them would generate potentially detectable transverse perturbative photon fluxes (PPFs). Furthermore we find optimal system parameters and the relationship between frequency and effective width of energy fluxes accumulation.
NASA Astrophysics Data System (ADS)
Fontana, Giorgio
2005-02-01
There is only one experimental proof that gravitational waves exist. With such a limitation, it may seem premature to suggest the possibility that gravitational waves can became a preferred space propulsion technique. The present understanding of the problem indicates that this is not the case. The emission of gravitational waves from astrophysical sources has been confirmed by observation, the respective detection at large distance from the source is difficult and actually we have no confirmation of a successful detection. Therefore the required preliminary discovery has been already made. This opinion is enforced by many different proposals for building the required powerful gravitational wave generators that have recently appeared in the literature and discussed at conferences. It is no longer reasonable to wait for additional confirmation of the existence of gravitational waves to start a program for building generators and testing their possible application to space travel. A vast literature shows that gravitational waves can be employed for space propulsion. Gravitational wave rockets have been proposed, non-linearity of Einstein equations allows the conversion of gravitational waves to a static gravitational field and ``artificial gravity assist'' may become a new way of travelling in space-time. Different approaches to gravitational wave propulsion are reviewed and compared. Gravitational wave propulsion is also compared to traditional rocket propulsion and an undeniable advantage can be demonstrated in terms of efficiency and performance. Testing the predictions will require gravitational wave generators with high power and wavelength short enough for producing high energy densities. Detectors designed for the specific application must be developed, taking into account that non-linearity effects are expected. The study and development of Gravitational wave propulsion is a very challenging endeavor, involving the most complex theories, sophisticated
Bambi, Cosimo
2014-03-01
In extensions of general relativity and in theories aiming at unifying gravity with the forces of the Standard Model, the value of the ''fundamental constants'' is often determined by the vacuum expectation value of new fields, which may thus change in different backgrounds. Variations of fundamental constants with respect to the values measured today in laboratories on Earth are expected to be more evident on cosmological timescales and/or in strong gravitational fields. In this paper, I show that the analysis of the Kα iron line observed in the X-ray spectrum of black holes can potentially be used to probe the fine structure constant α in gravitational potentials relative to Earth of Δφ ≈ 0.1. At present, systematic effects not fully under control prevent to get robust and stringent bounds on possible variations of the value of α with this technique, but the fact that current data can be fitted with models based on standard physics already rules out variations of the fine structure constant larger than some percent.
NASA Technical Reports Server (NTRS)
Dong, D,; Gross, R.S.; Dickey, J.
1996-01-01
Monthly mean gravitational field parameters (denoted here as C(sub even)) that represent linear combinations of the primarily even degree zonal spherical harmonic coefficients of the Earth's gravitational field have been recovered using LAGEOS I data and are compared with those derived from gridded global surface pressure data of the National meteorological center (NMC) spanning 1983-1992. The effect of equilibrium ocean tides and surface water variations are also considered. Atmospheric pressure and surface water fluctuations are shown to be the dominant cause of observed annual C(sub even) variations. Closure with observations is seen at the 1sigma level when atmospheric pressure, ocean tide and surface water effects are include. Equilibrium ocean tides are shown to be the main source of excitation at the semiannual period with closure at the 1sigma level seen when both atmospheric pressure and ocean tide effects are included. The inverted barometer (IB) case is shown to give the best agreement with the observation series. The potential of the observed C(sub even) variations for monitoring mass variations in the polar regions of the Earth and the effect of the land-ocean mask in the IB calculation are discussed.
Schlaufman, K
2004-10-11
Atmospheric turbulence can mimic the effects of weak lensing in astronomical images, so it is necessary to understand to what degree turbulence affects weak lensing measurements. In particular, we studied the ellipticity induced upon the point-spread functions (PSFs) of a grid of simulated stars separated by distances (d {approx} 1{prime}) that will be characteristic of Large Synoptic Survey Telescope (LSST) images. We observe that atmospherically induced ellipticity changes on small scales (d < 0.5{prime}) and use linear interpolation between stars separated by d = 0.5{prime} to determine the induced ellipticity everywhere in the field-of-view.
Weak Lie symmetry and extended Lie algebra
Goenner, Hubert
2013-04-15
The concept of weak Lie motion (weak Lie symmetry) is introduced. Applications given exhibit a reduction of the usual symmetry, e.g., in the case of the rotation group. In this context, a particular generalization of Lie algebras is found ('extended Lie algebras') which turns out to be an involutive distribution or a simple example for a tangent Lie algebroid. Riemannian and Lorentz metrics can be introduced on such an algebroid through an extended Cartan-Killing form. Transformation groups from non-relativistic mechanics and quantum mechanics lead to such tangent Lie algebroids and to Lorentz geometries constructed on them (1-dimensional gravitational fields).
Effect of an atom on a quantum guided field in a weakly driven fiber-Bragg-grating cavity
Le Kien, Fam; Hakuta, K.
2010-02-15
We study the interaction of an atom with a quantum guided field in a weakly driven fiber-Bragg-grating (FBG) cavity. We present an effective Hamiltonian and derive the density-matrix equations for the combined atom-cavity system. We calculate the mean photon number, the second-order photon correlation function, and the atomic excited-state population. We show that due to the confinement of the guided cavity field in the fiber cross-section plane and in the space between the FBG mirrors, the presence of the atom in the FBG cavity can significantly affect the mean photon number and the photon statistics even though the cavity finesse is moderate, the cavity is long, and the probe field is weak.
Shape, zonal winds and gravitational field of Jupiter: a fully self-consistent, multi-layered model
NASA Astrophysics Data System (ADS)
Schubert, Gerald; Kong, Dali; Zhang, Keke
2016-10-01
We construct a three-dimensional, finite-element, fully self-consistent, multi-layered,non-spheroidal model of Jupiter consisting of an inner core, a metallic electrically conducting dynamo region and an outer molecular electrically insulating envelope. We assume that the Jovian zonal winds are on cylinders parallel to the rotation axis but, due to the effect of magnetic braking, are confined within the outer molecular envelope. Two related calculations are carried out. The first provides an accurate description of the shape and internal density profile of Jupiter; the effect of rotational distortion is not treated as a small perturbation on a spherically symmetric state. This calculation determines the density, size and shape of the inner core, the irregular shape of the 1-bar pressure level, and the internal structure of Jupiter; the full effect of rotational distortion, without the influence of the zonal winds, is accounted for. Our multi-layered model is able to produce the known mass, the known equatorial and polar radii, and the known zonal gravitational coefficient J2 of Jupiter within their error bars; it also yields the coefficients J4 and J6 within about 5% accuracy, and the core equatorial radius 0.09RJ containing 3.73 Earth masses.The second calculation determines the variation of the gravitational field caused solely by the effect of the zonal winds on the rotationally distorted non-spheroidal Jupiter. Four different cases, ranging from a deep wind profile to a very shallow profile, are considered and implications for accurate interpretation of the zonal gravitational coefficients expected from the Juno mission are discussed.
Gravitational waves from inflation
NASA Astrophysics Data System (ADS)
Guzzetti, M. C.; Bartolo, N.; Liguori, M.; Matarrese, S.
2016-09-01
The production of a stochastic background of gravitational waves is a fundamental prediction of any cosmological inflationary model. The features of such a signal encode unique information about the physics of the Early Universe and beyond, thus representing an exciting, powerful window on the origin and evolution of the Universe. We review the main mechanisms of gravitational-wave production, ranging from quantum fluctuations of the gravitational field to other mechanisms that can take place during or after inflation. These include e.g. gravitational waves generated as a consequence of extra particle production during inflation, or during the (p)reheating phase. Gravitational waves produced in inflation scenarios based on modified gravity theories and second-order gravitational waves are also considered. For each analyzed case, the expected power spectrum is given. We discuss the discriminating power among different models, associated with the validity/violation of the standard consistency relation between tensor-to-scalar ratio r and tensor spectral index nT. In light of the prospects for (directly/indirectly) detecting primordial gravitational waves, we give the expected present-day gravitational radiation spectral energy-density, highlighting the main characteristics imprinted by the cosmic thermal history, and we outline the signatures left by gravitational waves on the Cosmic Microwave Background and some imprints in the Large-Scale Structure of the Universe. Finally, current bounds and prospects of detection for inflationary gravitational waves are summarized.
Hanna, Chad; Mandel, Ilya; Vousden, Will E-mail: imandel@star.sr.bham.ac.uk
2014-03-20
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 deg{sup 2}; 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
Ayala, Alejandro; Bashir, Adnan; Raya, Alfredo; Sanchez, Angel
2009-08-01
Working in the linear sigma model with quarks, we compute the finite-temperature effective potential in the presence of a weak magnetic field, including the contribution of the pion ring diagrams and considering the sigma as a classical field. In the approximation where the pion self-energy is computed perturbatively, we show that there is a region of the parameter space where the effect of the ring diagrams is to preclude the phase transition from happening. Inclusion of the magnetic field has small effects that however become more important as the system evolves to the lowest temperatures allowed in the analysis.
Discharge of a copper-magnesium galvanic cell in the presence of a weak electromagnetic field
NASA Astrophysics Data System (ADS)
Kolesnikov, A. A.; Zarembo, Ya. V.; Zarembo, V. I.
2007-07-01
The effect of weak periodic electromagnetic pulses with a repetition rate of 250 kHz on the discharge of a copper-magnesium galvanic cell is studied experimentally. Comparative characteristics of the electrochemical process and scanning electron microscopy images of electrode reaction products are presented.
Light scalar field constraints from gravitational-wave observations of compact binaries
NASA Astrophysics Data System (ADS)
Berti, Emanuele; Gualtieri, Leonardo; Horbatsch, Michael; Alsing, Justin
2012-06-01
Scalar-tensor theories are among the simplest extensions of general relativity. In theories with light scalars, deviations from Einstein’s theory of gravity are determined by the scalar mass ms and by a Brans-Dicke-like coupling parameter ωBD. We show that gravitational-wave observations of nonspinning neutron star-black hole binary inspirals can be used to set lower bounds on ωBD and upper bounds on the combination ms/ωBD. We estimate via a Fisher matrix analysis that individual observations with signal-to-noise ratio ρ would yield (ms/ωBD)(ρ/10)≲10-15, 10-16, and 10-19eV for Advanced LIGO, ET, and eLISA, respectively. A statistical combination of multiple observations may further improve these bounds.
NASA Astrophysics Data System (ADS)
Vil'ke, V. G.; Shatina, A. V.
2004-01-01
We study the translational-rotational motion of a planet modeled by a viscoelastic sphere in the gravitational fields of an immovable attracting center and a satellite modeled as material points. The satellite and the planet move with respect to their common center of mass that, in turn, moves with respect to the attracting center. The exact system of equations of motion of the considered mechanical system is deduced from the D'Alembert-Lagrange variational principle. The method of separation of motions is applied to the obtained system of equations and an approximate system of ordinary differential equations is deduced which describes the translational-rotational motion of the planet and its satellite, taking into account the perturbations caused by elasticity and dissipation. An analysis of the deformed state of the viscoelastic planet under the action of gravitational forces and forces of inertia is carried out. It is demonstrated that in the steady-state motion, when energy dissipation vanishes, the planet's center of mass and the satellite move along circular orbits with respect to the attracting center, being located on a single line with it. The viscoelastic planet in its steady-state motion is immovable in the orbital frame of reference. It is demonstrated that this steady-state motion is unstable.
Modeling a nonperturbative spinor vacuum interacting with a strong gravitational wave
NASA Astrophysics Data System (ADS)
Dzhunushaliev, Vladimir; Folomeev, Vladimir
2015-07-01
We consider the propagation of strong gravitational waves interacting with a nonperturbative vacuum of spinor fields. To described the latter, we suggest an approximate model. The corresponding Einstein equation has the form of the Schrödinger equation. Its gravitational-wave solution is analogous to the solution of the Schrödinger equation for an electron moving in a periodic potential. The general solution for the periodic gravitational waves is found. The analog of the Kronig-Penney model for gravitational waves is considered. It is shown that the suggested gravitational-wave model permits the existence of weak electric charge and current densities concomitant with the gravitational wave. Based on this observation, a possible experimental verification of the model is suggested.
NASA Astrophysics Data System (ADS)
Chen, Biao; Yin, Chun-lin
1980-12-01
We discuss the dispersion relation of local linear waves in a compressible and perfectly conducting gas possessing magnetic and gravitational fields in a slowly rotating frame of reference. Instead of the full energy equation and a gas law, a not necessarily adiabatic equation of state p= p( ϱ) is used to close the system of equations, — an arguably flexible way of treatment when we are not clear about the contributions by radiation and conductivity to the energy transport. We give a general dimensionless dispersion relation, (8). This reduces to (9) if the magnetic field B is zero; to (10) if, further, rotation φ is zero; to the relation for accoustic waves (11), if further the gravitational field G is zero. When B is not zero, we consider various cases with the propagation vector K always perpendicular to B: the relation now reduces to (13) if K is not perpendicular to φ; to (14) if, further, K is parallel to G; to (15) if φ=0; to the relation for last magneto-accoustic waves (16) if G=0. It reduces to (17) if K is perpendicular to G; to the fast magneto-accoustic waves (18), if, further, φ=0. It reduces to (19) if K is perpendicular to φ and to (20), if, further, K is parallel to G. Our study shows that, in general, there are no pure modes, only hybrids. In particular, a rotation gives rise to modes that are dependent on the latitude, which we call "physico-geometrical" waves. The present study is preliminary, and we may expect even more interesting results when we take into consideration the energy equation and the effects of radiation.
Hatada, Tomohisa; Sekino, Masaki; Ueno, Shoogo
2004-01-01
Detection of weak magnetic fields induced by neuronal electrical activities with magnetic resonance imaging (MRI) is a potentially effective method for functional imaging of the brain. In this study, we compared the theoretical and practical limits of sensitivity for detecting weak magnetic fields with a columnar phantom. The theoretical limit of sensitivity was estimated from signal and noise intensities in magnetic resonance images. The theoretical limit of sensitivity was approximately 10(-8)T. The practical limit was 10 times the theoretical limit. The dependence of the theoretical limit of sensitivity on acquisition parameters, such as the repetition time (TR), echo time (TE), number of pixels, and spectral width, was quantitatively evaluated. The results indicated the existence of an optimal value in T(E)/T2*.
Faraday rotation due to quadratic gravitation
NASA Astrophysics Data System (ADS)
Chen, Yihan; Liu, Liping; Tian, Wen-Xiu
2011-01-01
The linearized field equations of quadratic gravitation in stationary space-time are written in quasi-Maxwell form. The rotation of the polarization plane for an electromagnetic wave propagating in the gravito-electromagnetic field caused by a rotating gravitational lens is discussed. The influences of the Yukawa potential in quadratic gravitation on the gravitational Faraday rotation are investigated.
Modeling Gravitational Radiation Waveforms from Black Hole Mergers
NASA Technical Reports Server (NTRS)
Baker, J. G.; Centrelia, J. M.; Choi, D.; Koppitz, M.; VanMeter, J.
2006-01-01
Gravitational radiation from merging binary black hole systems is anticipated as a key source for gravitational wave observations. Ground-based instruments, such as the Laser Interferometer Gravitational-wave Observatory (LIGO) may observe mergers of stellar-scale black holes, while the space-based Laser Interferometer Space Antenna (LISA) observatory will be sensitive to mergers of massive galactic-center black holes over a broad range of mass scales. These cataclysmic events may emit an enormous amount of energy in a brief time. Gravitational waves from comparable mass mergers carry away a few percent of the system's mass-energy in just a few wave cycles, with peak gravitational wave luminosities on the order of 10^23 L_Sun. Optimal analysis and interpretation of merger observation data will depend on developing a detailed understanding, based on general relativistic modeling, of the radiation waveforms. We discuss recent progress in modeling radiation from equal mass mergers using numerical simulations of Einstein's gravitational field equations, known as numerical relativity. Our simulations utilize Adaptive Mesh Refinement (AMR) to allow high-resolution near the black holes while simultaneously keeping the outer boundary of the computational domain far from the black holes, and making it possible to read out gravitational radiation waveforms in the weak-field wave zone. We discuss the results from simulations beginning with the black holes orbiting near the system's innermost stable orbit, comparing the recent simulations with earlier "Lazarus" waveform estimates based on an approximate hybrid numerical/perturbative technique.
Lee, Min-Hyong; Choi, Seong Wook
2008-12-01
We investigated the evolution of the electron energy distribution function (EEDF) in a solenoidal inductively coupled plasma surrounded by an axial dc magnetic field. The increase in the dc magnetic field caused the EEDF to evolve from a bi-Maxwellian to a Maxwellian distribution. At the discharge center, the number of low energy electrons was significantly reduced while the high energy electron population showed little change when a weak dc magnetic field was present. However, at the discharge radial boundary, the high energy electron population decreased significantly with the magnetic field while the change in low energy population was not prominent compared to the discharge boundary. These changes in EEDFs at the boundary and center of the discharge are due to the radial confinement and the restriction of radial transport of electrons by dc magnetic field.
The perturbation of gravitational waves in plasma in the FRW space-time
NASA Astrophysics Data System (ADS)
Youssef, Manal H.
2016-01-01
In this paper we study the perturbation of gravitational waves in plasma,using the relativistic hydro-magnetic equation in the so-called Cowling approximation considering a Friedman-Robertson-Walker (FRW) cosmological model. It has been assumed the gravitational field and the weak magnetic field do not break the homogeneity and isotropy of the considered FRW space time. Applying the formalism proposed for Zel'dovich and Novikov (The structure and evolution of the universe, Volume II, 1983), Brandenburg et al. (Phys. Rev. D 54:1291, 1996) and Weinberg (Gravitation and Cosmology, 1972). We verify that density fluctuation may be obtained.
NASA Technical Reports Server (NTRS)
Chao, B. Fong; Au, Andrew Y.
1991-01-01
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.
NASA Astrophysics Data System (ADS)
Sharaf, Mohamed Adel; Awad, Mervat El-Sayed; Banaja, Mona A.
1987-05-01
In this paper, economical and stable recurrence formulas for the earth's zonal potential and its gradient for the KS regularized theory will be established for any number N of the zonal harmonic coefficient. A general recursive computational algorithm based on these formulas is also established for the initial value problem of the KS theory for the prediction of artificial satellites in the earth's gravitational field with axial symmetry. Applications of the algorithm for the problem of the final state prediction are illustrated by numerical examples of three test orbits each for two geopotential models corresponding to N = 2 and N = 36. A final state of any desired accuracy is obtained for each case study, a result which shows the flexibility of the algorithm.
Cosmic matter-antimatter asymmetry and gravitational force
NASA Technical Reports Server (NTRS)
Hsu, J. P.
1980-01-01
Cosmic matter-antimatter asymmetry due to the gravitational interaction alone is discussed, considering the gravitational coupling of fermion matter related to the Yang-Mills (1954) gauge symmetry with the unique generalization of the four-dimensional Poincare group. Attention is given to the case of weak static fields which determines the space-time metric where only large source terms are retained. In addition, considering lowest-order Feynman diagrams, there are presented gravitational potential energies between fermions, between antifermions, and between a fermion and an antifermion. It is concluded that the gravitational force between matter is different from that between antimatter; implications from this concerning the evolution of the universe are discussed.
NASA Astrophysics Data System (ADS)
Trinh, Vinh H.; Tolstikhin, Oleg I.; Morishita, Toru
2016-10-01
The many-electron weak-field asymptotic theory of tunneling ionization including the first-order correction terms in the asymptotic expansion of the ionization rate in field strength was highlighted in our recent fast track communication (Trinh et al 2015 J. Phys. B: At. Mol. Opt. Phys. 48 061003) by demonstrating its performance for two-electron atoms. Here we present a thorough derivation of the first-order terms omitted in the previous publication and provide additional numerical illustrations of the theory.
Robertson, Brant E.; Stark, Dan P.; Ellis, Richard S.; Dunlop, James S.; McLure, Ross J.; McLeod, Derek
2014-12-01
Strong gravitational lensing provides a powerful means for studying faint galaxies in the distant universe. By magnifying the apparent brightness of background sources, massive clusters enable the detection of galaxies fainter than the usual sensitivity limit for blank fields. However, this gain in effective sensitivity comes at the cost of a reduced survey volume and, in this Letter, we demonstrate that there is an associated increase in the cosmic variance uncertainty. As an example, we show that the cosmic variance uncertainty of the high-redshift population viewed through the Hubble Space Telescope Frontier Field cluster Abell 2744 increases from ∼35% at redshift z ∼ 7 to ≳ 65% at z ∼ 10. Previous studies of high-redshift galaxies identified in the Frontier Fields have underestimated the cosmic variance uncertainty that will affect the ultimate constraints on both the faint-end slope of the high-redshift luminosity function and the cosmic star formation rate density, key goals of the Frontier Field program.
Prediction of horizontal gas-solid flows under different gravitational fields
NASA Astrophysics Data System (ADS)
Laín, Santiago; Sommerfeld, Martin
2014-11-01
In this paper the performance of horizontal pneumatic conveying under different gravity environments is evaluated. An Euler-Lagrange approach validated versus ground experiments is employed to predict the relevant particle variables such as particle mass flux, mean conveying and fluctuating velocities in terrestrial, lunar and micro-gravity conditions. Gravity reduced computations predict a reduction in the global particle-wall collision frequency. Also, in the case of low wall roughness and small particle mass loading, reduction of gravity acceleration implies an increase of particle-wall collision frequency with the upper wall of the channel affecting greatly the particle mass flux profile. In the case of high wall roughness and/or high particle-to-fluid mass loading (i.e., around 1.0) particle conveying characteristics are similar in the three gravity conditions evaluated. This is due to the fact that both, wall roughness and inter-particle collisions reduce gravitational settling. However, the influence of gravity on the additional pressure loss along the channel due to the conveying of the particles is much reduced.
Periodic Orbit Families in the Gravitational Field of Irregular-shaped Bodies
NASA Astrophysics Data System (ADS)
Jiang, Yu; Baoyin, Hexi
2016-11-01
The discovery of binary and triple asteroids in addition to the execution of space missions to minor celestial bodies in the past several years have focused increasing attention on periodic orbits around irregular-shaped celestial bodies. In the present work, we adopt a polyhedron shape model for providing an accurate representation of irregular-shaped bodies and employ the model to calculate their corresponding gravitational and effective potentials. We also investigate the characteristics of periodic orbit families and the continuation of periodic orbits. We prove a fact, which provides a conserved quantity that permits restricting the number of periodic orbits in a fixed energy curved surface about an irregular-shaped body. The collisions of Floquet multipliers are maintained during the continuation of periodic orbits around the comet 1P/Halley. Multiple bifurcations in the periodic orbit families about irregular-shaped bodies are also discussed. Three bifurcations in the periodic orbit family have been found around the asteroid 216 Kleopatra, which include two real saddle bifurcations and one period-doubling bifurcation.
NASA Astrophysics Data System (ADS)
Hu, Xuanyu
2016-06-01
The spherical and ellipsoidal harmonic series of the external gravitational potential for a given mass distribution are equivalent in their mutual region of uniform convergence. In an instructive case, the equality of the two series on the common coordinate surface of an infinitely large sphere reveals the exact correspondence between the spherical and ellipsoidal harmonic coefficients. The transformation between the two sets of coefficients can be accomplished via the numerical methods by Walter (Celest Mech 2:389-397, 1970) and Dechambre and Scheeres (Astron Astrophys 387:1114-1122, 2002), respectively. On the other hand, the harmonic coefficients are defined by the integrals of mass density moments in terms of the respective solid harmonics. This paper presents general algebraic formulas for expressing the solid ellipsoidal harmonics as a linear combination of the corresponding solid spherical harmonics. An exact transformation from spherical to ellipsoidal harmonic coefficients is found by incorporating these connecting expressions into the density integral. A computational procedure is proposed for the transformation. Numerical results based on the nearly ellipsoidal Martian moon, Phobos, are presented for validation of the method.
Okura, Yuki; Futamase, Toshifumi E-mail: tof@astr.tohoku.ac.jp
2014-09-10
Highly accurate weak lensing analysis is urgently required for planned cosmic shear observations. For this purpose we have eliminated various systematic noises in the measurement. The point-spread function (PSF) effect is one of them. A perturbative approach for correcting the PSF effect on the observed image ellipticities has been previously employed. Here we propose a new non-perturbative approach for PSF correction that avoids the systematic error associated with the perturbative approach. The new method uses an artificial image for measuring shear which has the same ellipticity as the lensed image. This is done by re-smearing the observed galaxy images and observed star images (PSF) with an additional smearing function to obtain the original lensed galaxy images. We tested the new method with simple simulated objects that have Gaussian or Sérsic profiles smeared by a Gaussian PSF with sufficiently large size to neglect pixelization. Under the condition of no pixel noise, it is confirmed that the new method has no systematic error even if the PSF is large and has a high ellipticity.
NASA Astrophysics Data System (ADS)
Varela, J.; Pantellini, F.; Moncuquet, M.
2016-01-01
The aim of this study is to simulate the interaction of the solar wind with the Hermean magnetosphere when the interplanetary magnetic field is weak, performing a parametric study for all the range of hydrodynamic values of the solar wind predicted on Mercury for the ENLIL + GONG WSA + Cone SWRC model: density from 12 to 180 cm-3, velocity from 200 to 500 km/s and temperatures from 2 ·104 to 18 ·104 K, and compare the results with a real MESSENGER orbit as reference case. We use the code PLUTO in spherical coordinates and an asymmetric multipolar expansion for the Hermean magnetic field. The study shows for all simulations a stand off distance larger than the Mercury radius and the presence of close magnetic field lines on the day side of the planet, so the dynamic pressure of the solar wind is not high enough to push the magnetopause on the planet surface if the interplanetary magnetic field is weak. The simulations with large dynamic pressure lead to a large compression of the Hermean magnetic field modifying its topology in the inner magnetosphere as well as the plasma flows from the magnetosheath towards the planet surface.
NASA Astrophysics Data System (ADS)
LeFloch, Philippe G.; Ma, Yue
2016-09-01
The Hyperboloidal Foliation Method (introduced by the authors in 2014) is extended here and applied to the Einstein equations of general relativity. Specifically, we establish the nonlinear stability of Minkowski spacetime for self-gravitating massive scalar fields, while existing methods only apply to massless scalar fields. First of all, by analyzing the structure of the Einstein equations in wave coordinates, we exhibit a nonlinear wave-Klein-Gordon model defined on a curved background, which is the focus of the present paper. For this model, we prove here the existence of global-in-time solutions to the Cauchy problem, when the initial data have sufficiently small Sobolev norms. A major difficulty comes from the fact that the class of conformal Killing fields of Minkowski space is significantly reduced in the presence of a massive scalar field, since the scaling vector field is not conformal Killing for the Klein-Gordon operator. Our method relies on the foliation (of the interior of the light cone) of Minkowski spacetime by hyperboloidal hypersurfaces and uses Lorentz-invariant energy norms. We introduce a frame of vector fields adapted to the hyperboloidal foliation and we establish several key properties: Sobolev and Hardy-type inequalities on hyperboloids, as well as sup-norm estimates, which correspond to the sharp time decay for the wave and the Klein-Gordon equations. These estimates allow us to control interaction terms associated with the curved geometry and the massive field by distinguishing between two levels of regularity and energy growth and by a successive use of our key estimates in order to close a bootstrap argument.
Theory of weak scattering of stochastic electromagnetic fields from deterministic and random media
Tong Zhisong; Korotkova, Olga
2010-09-15
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.
Childhood leukemia and residential exposure to weak extremely low frequency magnetic fields
Feychting, M.; Ahlbom, A.
1995-03-01
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.
Numerical Simulation of Gel Electrophoresis of DNA Knots in Weak and Strong Electric Fields
Weber, C.; Stasiak, A.; De Los Rios, P.; Dietler, G.
2006-01-01
Gel electrophoresis allows one to separate knotted DNA (nicked circular) of equal length according to the knot type. At low electric fields, complex knots, being more compact, drift faster than simpler knots. Recent experiments have shown that the drift velocity dependence on the knot type is inverted when changing from low to high electric fields. We present a computer simulation on a lattice of a closed, knotted, charged DNA chain drifting in an external electric field in a topologically restricted medium. Using a Monte Carlo algorithm, the dependence of the electrophoretic migration of the DNA molecules on the knot type and on the electric field intensity is investigated. The results are in qualitative and quantitative agreement with electrophoretic experiments done under conditions of low and high electric fields. PMID:16473912
Weak lensing and cosmological investigation
NASA Astrophysics Data System (ADS)
Acquaviva, Viviana
2005-03-01
In the last few years the scientific community has been dealing with the challenging issue of identifying the dark energy component. We regard weak gravitational lensing as a brand new, and extremely important, tool for cosmological investigation in this field. In fact, the features imprinted on the Cosmic Microwave Background radiation by the lensing from the intervening distribution of matter represent a pretty unbiased estimator, and can thus be used for putting constraints on different dark energy models. This is true in particular for the magnetic-type B-modes of CMB polarization, whose unlensed spectrum at large multipoles (l ~= 1000) is very small even in presence of an amount of gravitational waves as large as currently allowed by the experiments: therefore, on these scales the lensing phenomenon is the only responsible for the observed power, and this signal turns out to be a faithful tracer of the dark energy dynamics. We first recall the formal apparatus of the weak lensing in extended theories of gravity, introducing the physical observables suitable to cast the bridge between lensing and cosmology, and then evaluate the amplitude of the expected effect in the particular case of a Non-Minimally-Coupled model, featuring a quadratic coupling between quintessence and Ricci scalar.
Levi, Michele; Steinhoff, Jan E-mail: jan.steinhoff@aei.mpg.de
2016-01-01
We implement the effective field theory for gravitating spinning objects in the post-Newtonian scheme at the next-to-next-to-leading order level to derive the gravitational spin-orbit interaction potential at the third and a half post-Newtonian order for rapidly rotating compact objects. From the next-to-next-to-leading order interaction potential, which we obtain here in a Lagrangian form for the first time, we derive straightforwardly the corresponding Hamiltonian. The spin-orbit sector constitutes the most elaborate spin dependent sector at each order, and accordingly we encounter a proliferation of the relevant Feynman diagrams, and a significant increase of the computational complexity. We present in detail the evaluation of the interaction potential, going over all contributing Feynman diagrams. The computation is carried out in terms of the ''nonrelativistic gravitational'' fields, which are advantageous also in spin dependent sectors, together with the various gauge choices included in the effective field theory for gravitating spinning objects, which also optimize the calculation. In addition, we automatize the effective field theory computations, and carry out the automated computations in parallel. Such automated effective field theory computations would be most useful to obtain higher order post-Newtonian corrections. We compare our Hamiltonian to the ADM Hamiltonian, and arrive at a complete agreement between the ADM and effective field theory results. Finally, we provide Hamiltonians in the center of mass frame, and complete gauge invariant relations among the binding energy, angular momentum, and orbital frequency of an inspiralling binary with generic compact spinning components to third and a half post-Newtonian order. The derivation presented here is essential to obtain further higher order post-Newtonian corrections, and to reach the accuracy level required for the successful detection of gravitational radiation.
Aspects of the Gravitational and Thermal Physics of Solitons in Field Theory.
NASA Astrophysics Data System (ADS)
O'Neill, Christopher M.
We numerically study classical soliton solutions to two physically relevant field theories in an astrophysical setting, and through the Euclidean path integral formalism of finite-temperature field theory, we develop a new analytical method to study solitons semiclassically in a cosmological setting. By carefully considering non-Abelian gauge theories coupled to classical Einstein gravity, we demonstrate how black hole solutions to such theories can have nontrivial field structure outside the event horizon, despite the widely held belief to the contrary known as the "no-hair" conjecture. We next obtain numerical particle-like soliton and black hole solutions in the spontaneously broken phase of the Einstein-Yang-Mills-Higgs system, which consists of an SU(2) gauge field coupled to a Higgs doublet (the electroweak standard model without hypercharge). We also obtain such solutions to the related Einstein-Non-Abelian -Proca theory as a prelude to the gauge field case. Using the bosonic part of the low-energy heterotic string action, we then construct string-inspired regular and black hole solutions to Einstein-Yang-Mills theory coupled to massive dilaton and axion fields. Though we present numerical solutions only for the case of a trivial axion field, we analyze the full system and discuss the feasibility of additional solutions. Shifting from classical to quantum field theory, we next develop a general method utilizing collective coordinates and Euclidean functional constraints to study solitons semiclassically in the path integral formulation of Euclidean quantum field theory. Our method is an extension of the existing semiclassical method, which does not accomodate Euclidean time or the usual canonical Euclidean formalism, and applies to both time-independent solitons and solitons with time-dependence arising from global charge symmetries. We illustrate the method through an example finite-temperature field theory calculation: the one-loop partition function for
Initiation and blocking of the action potential in an axon in weak ultrasonic or microwave fields.
Shneider, M N; Pekker, M
2014-05-01
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
Electric-field domain boundary instability in weakly coupled semiconductor superlattices
NASA Astrophysics Data System (ADS)
Rasulova, G. K.; Pentin, I. V.; Brunkov, P. N.; Egorov, A. Yu.
2016-05-01
Damped oscillations of the current were observed in the transient current pulse characteristics of a 30-period weakly coupled GaAs/AlGaAs superlattice (SL). The switching time of the current is exponentially decreased as the voltage is verged towards the current discontinuity region indicating that the space charge necessary for the domain boundary formation is gradually accumulated in a certain SL period in a timescale of several hundreds ns. The spectral features in the electroluminescence spectra of two connected in parallel SL mesas correspond to the energy of the intersubband transitions and the resonance detuning of subbands caused by charge trapping in the quantum wells (QWs) residing in a region of the expanded domain boundary. The obtained results support our understanding of the origin of self-oscillations as a cyclic dynamics of the subband structure in the QWs forming the expanded domain boundary.
Initiation and blocking of the action potential in an axon in weak ultrasonic or microwave fields
NASA Astrophysics Data System (ADS)
Shneider, M. N.; Pekker, M.
2014-05-01
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.
Four Poission-Laplace Theory of Gravitation (I)
NASA Astrophysics Data System (ADS)
Nyambuya, Golden Gadzirayi
2015-08-01
The Poisson-Laplace equation is a working and acceptable equation of gravitation which is mostly used or applied in its differential form in Magneto-Hydro-Dynamic (MHD) modelling of e.g. molecular clouds. From a general relativistic standpoint, it describes gravitational fields in the region of low spacetime curvature as it emerges in the weak field limit. For non-static gravitational fields, this equation is not generally covariant. On the requirements of general covariance, this equation can be extended to include a time-dependent component, in which case one is led to the Four Poisson-Laplace equation. We solve the Four Poisson-Laplace equation for radial solutions, and apart from the Newtonian gravitational component, we obtain four new solutions leading to four new gravitational components capable (in-principle) of explaining e.g. the Pioneer anomaly, the Titius-Bode Law and the formation of planetary rings. In this letter, we focus only on writing down these solutions. The task showing that these new solutions might explain the aforesaid gravitational anomalies has been left for separate future readings.
Discovery of an extremely weak magnetic field in the white dwarf LTT 16093 = WD 2047+372
NASA Astrophysics Data System (ADS)
Landstreet, J. D.; Bagnulo, S.; Martin, A.; Valyavin, G.
2016-06-01
Context. Magnetic fields have been detected in several hundred white dwarfs, with strengths ranging from a few kG to several hundred MG. Only a few of the known fields have a mean magnetic field modulus below about 1 MG. Aims: We are searching for new examples of magnetic white dwarfs with very weak fields, and trying to model the few known examples. Our search is intended to be sensitive enough to detect fields at the few kG level. Methods: We have been surveying bright white dwarfs for very weak fields using spectropolarimeters at the Canada-France-Hawaii telescope, the William Herschel Telescope (WHT), the European Southern Observatory, and the Russian Special Astrophysical Observatory. We discuss in some detail tests of the WHT spectropolarimeter ISIS using the known magnetic strong-field Ap star HD 215441 (Babcock's star) and the long-period Ap star HD 201601 (γ Equ). Results: We report the discovery of a field with a mean field modulus of about 57 kG in the white dwarf LTT 16093 = WD 2047+372. The field is clearly detected through the Zeeman splitting of Hα seen in two separate circularly polarised spectra from two different spectropolarimeters. Zeeman circular polarisation is also detected, but only barely above the 3σ level. Conclusions: The discovery of this field is significant because it is the third weakest field ever unambiguously discovered in a white dwarf, while still being large enough that we should be able to model the field structure in some detail with future observations. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, and on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and
Sampoorna, M.; Nagendra, K. N. E-mail: knn@iiap.res.in
2015-10-10
The dynamical state of the solar and stellar atmospheres depends on the macroscopic velocity fields prevailing within them. The presence of such velocity fields in the line formation regions strongly affects the polarized radiation field emerging from these atmospheres. Thus it becomes necessary to solve the radiative transfer equation for polarized lines in moving atmospheres. Solutions based on the “observer’s frame method” are computationally expensive to obtain, especially when partial frequency redistribution (PRD) in line scattering and large-amplitude velocity fields are taken into account. In this paper we present an efficient alternative method of solution, namely, the comoving frame technique, to solve the polarized PRD line formation problems in the presence of velocity fields. We consider one-dimensional planar isothermal atmospheres with vertical velocity fields. We present a study of the effect of velocity fields on the emergent linear polarization profiles formed in optically thick moving atmospheres. We show that the comoving frame method is far superior when compared to the observer’s frame method in terms of the computational speed and memory requirements.
The Optical Gravitational Lensing Experiment. OGLE-III Photometric Maps of the Galactic Disk Fields
NASA Astrophysics Data System (ADS)
Szymański, M. K.; Udalski, A.; Soszyński, I.; Kubiak, M.; Pietrzyński, G.; Poleski, R.; Wyrzykowski, Ł.; Ulaczyk, K.
2010-12-01
We present OGLE-III Photometric Maps of the Galactic disk fields observed during the OGLE-III campaigns for low luminosity transiting objects that led to the discovery of the first transitng exoplanets. The maps contain precise, calibrated VI photometry of about 9 million stars from 21 OGLE-III fields in the Galactic disk observed in the years 2002-2009 and covering more than 7 square degrees in the sky. Precise astrometry of these objects is also provided. We discuss quality of the data and present a few color-magnitude diagrams of the observed fields. All photometric data are available to the astronomical community from the OGLE Internet archive.
Dilute plasma coupling currents to a high voltage solar array in weak magnetic fields
NASA Technical Reports Server (NTRS)
Grier, N. T.
1984-01-01
The plasma coupling current to an approximately 2000 sq cm array was measured for externally biased positive and negative voltages on the array to 1000 V in applied magnetic field strengths from 0 to 0.93 G. The plasma density varied from 2,000 to 1.3 million electrons/cu cm. It was found that the magnetic field primarily increased the plasma coupling current for negative biases. For positive bias, the current could increase or decrease depending on the voltage, field strength, and plasma density. It was also found that the plasma coupling current was not very sensitive to how the plane of the array was oriented relative to the magnetic field.
Vaughan, Timothy E; Weaver, James C
2005-05-01
We describe an approach to aiding the design and interpretation of experiments involving biological effects of weakly interacting electromagnetic fields that range from steady (dc) to microwave frequencies. We propose that if known biophysical mechanisms cannot account for an inferred, underlying molecular change signal-to-noise ratio, (S/N)gen, of a observed result, then there are two interpretation choices: (1) there is an unknown biophysical mechanism with stronger coupling between the field exposure and the ongoing biochemical process, or (2) the experiment is responding to something other than the field exposure. Our approach is based on classical detection theory, the recognition that weakly interacting fields cannot break chemical bonds, and the consequence that such fields can only alter rates of ongoing, metabolically driven biochemical reactions, and transport processes. The approach includes both fundamental chemical noise (molecular shot noise) and other sources of competing chemical change, to be compared quantitatively to the field induced change for the basic case that the field alters a single step in a biochemical network. Consistent with pharmacology and toxicology, we estimate the molecular dose (mass associated with field induced molecular change per mass tissue) resulting from illustrative low frequency field exposures for the biophysical mechanism of voltage gated channels. For perspective, we then consider electric field-mediated delivery of small molecules across human skin and into individual cells. Specifically, we consider the examples of iontophoretic and electroporative delivery of fentanyl through skin and electroporative delivery of bleomycin into individual cells. The total delivered amount corresponds to a molecular change signal and the delivery variability corresponds to generalized chemical noise. Viewed broadly, biological effects due to nonionizing fields may include animal navigation, medical applications, and environmental
The dichotomy between strong and ultra-weak magnetic fields among intermediate-mass stars
NASA Astrophysics Data System (ADS)
Lignières, François; Petit, Pascal; Aurière, Michel; Wade, Gregg A.; Böhm, Torsten
2014-08-01
Until recently, the detection of magnetic fields at the surface of intermediate-mass main-sequence stars has been limited to Ap/Bp stars, a class of chemically peculiar stars. This class represents no more than 5-10% of the stars in this mass range. This small fraction is not explained by the fossil field paradigm that describes the Ap/Bp type magnetism as a remnant of an early phase of the star-life. Also, the limitation of the field measurements to a small and special group of stars is obviously a problem to study the effect of the magnetic fields on the stellar evolution of a typical intermediate-mass star. Thanks to the improved sensitivity of a new generation of spectropolarimeters, a lower bound to the magnetic fields of Ap/Bp stars, a two orders of magnitude desert in the longitudinal magnetic field and a new type of sub-gauss magnetism first discovered on Vega have been identified. These advances provide new clues to understand the origin of intermediate-mass magnetism as well as its influence on stellar evolution. In particular, a scenario has been proposed whereby the magnetic dichotomy between Ap/Bp and Vega-like magnetism originate from the bifurcation between stable and unstable large scale magnetic configurations in differentially rotating stars. In this paper, we review these recent observational findings and discuss this scenario.
Goodman, Michael L.
2011-04-10
A Harris sheet magnetic field with maximum magnitude B{sub 0} and length scale L is combined with the anisotropic electrical conductivity, viscosity, and thermoelectric tensors for an electron-proton plasma to define a magnetohydrodynamic model that determines the steady state of the plasma. The transport tensors are functions of temperature, density, and magnetic field strength, and are computed self-consistently as functions of position x normal to the current sheet. The flow velocity, magnetic field, and gravitational force lie along the z-axis. The plasma is supported against gravity by the viscous force. Analytic solutions are obtained for temperature, density, and velocity. They are valid over a broad range of temperature, density, and magnetic field strength, and so may be generally useful in astrophysical applications. Numerical examples of solutions in the parameter range of the solar atmosphere are presented. The objective is to compare Joule and viscous heating rates, determine the velocity shear that generates viscous forces that support the plasma and are self-consistent with a mean outward mass flux comparable to the solar wind mass flux, and compare the thermoelectric and conduction current contributions to the Joule heating rate. The ratio of the viscous to Joule heating rates per unit mass can exceed unity by orders of magnitude, and increases rapidly with L. The viscous heating rate can be concentrated outside the region where the current density is localized, corresponding to a resistively heated layer of plasma bounded by viscously heated plasma. The temperature gradient drives a thermoelectric current density that can have a magnitude greater than that of the electric-field-driven conduction current density, so thermoelectric effects are important in determining the Joule heating rate.
Momot, A. I.
2013-07-15
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.
Stuchlík, Zdeněk; Schee, Jan E-mail: jan.schee@fpf.slu.cz
2011-09-01
Using the pseudo-Newtonian (PN) potential reflecting properties of the Schwarz-schild-de Sitter spacetime, we estimate the influence of the repulsive cosmological constant Λ ∼ 1.3 × 10{sup −56}cm{sup −2} implied by recent cosmological tests onto the motion of both Small and Large Magellanic Clouds (SMC and LMC) in the gravitational field of the Milky Way. Considering detailed modelling of the gravitational field of the Galaxy disc, bulge and cold dark matter halo, the trajectories of SMC and LMC constructed for the PN potential with the cosmological constant are confronted to those given for Λ = 0. In the realistic model of the extended cold dark matter halo its edge and related total mass are taken at typical values reflecting recent diversity in the total Galaxy mass estimates. In all cases, strong influence of the cosmological constant, on 10% level or higher, has been found for motion of both SMC and LMC. Inside the halo, the Newtonian part of the PN potential is exact enough, while outside the halo the PN potential can give relevant relativistic corrections. The role of the cosmological constant is most conspicuous when binding mass is estimated for the satellite galaxies. We have found a strong influence of cosmic repulsion on the total binding mass for both galaxies. For SMC there is the binding mass M{sub SMC}{sup Λ=0} = 7.07 × 10{sup 11}M{sub ⨀} and M{sub SMC}{sup Λ>0} = 8.61 × 10{sup 11}M{sub ⨀}, while even much higher increase is found for LMC, where M{sub LMC}{sup Λ=0} = 1.50 × 10{sup 12}M{sub ⨀} and M{sub LMC}{sup Λ} {sup >0} = 2.21 × 10{sup 12}M{sub ⨀}, putting serious doubts on the possibility that the LMC is bounded by the Milky Way. However, the estimates of binding masses are strongly influenced by initial velocity of SMC and LMC; we took the values inferred for the IAU MW rotation velocity ∼ 220 km/s. Our results indicate very important role of the cosmic repulsion in the motion of interacting galaxies, clearly
Constraints on gravitational properties of antimatter from cyclotron-frequency measurements
NASA Astrophysics Data System (ADS)
Holzscheiter, Michael H.
2014-05-01
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.
KCNJ15/Kir4.2 couples with polyamines to sense weak extracellular electric fields in galvanotaxis
Nakajima, Ken-ichi; Zhu, Kan; Sun, Yao-Hui; Hegyi, Bence; Zeng, Qunli; Murphy, Christopher J.; Small, J. Victor; Chen-Izu, Ye; Izumiya, Yoshihiro; Penninger, Josef M.; Zhao, Min
2015-01-01
Weak electric fields guide cell migration, known as galvanotaxis/electrotaxis. The sensor(s) cells use to detect the fields remain elusive. Here we perform a large-scale screen using an RNAi library targeting ion transporters in human cells. We identify 18 genes that show either defective or increased galvanotaxis after knockdown. Knockdown of the KCNJ15 gene (encoding inwardly rectifying K+ channel Kir4.2) specifically abolishes galvanotaxis, without affecting basal motility and directional migration in a monolayer scratch assay. Depletion of cytoplasmic polyamines, highly positively charged small molecules that regulate Kir4.2 function, completely inhibits galvanotaxis, whereas increase of intracellular polyamines enhances galvanotaxis in a Kir4.2-dependent manner. Expression of a polyamine-binding defective mutant of KCNJ15 significantly decreases galvanotaxis. Knockdown or inhibition of KCNJ15 prevents phosphatidylinositol 3,4,5-triphosphate (PIP3) from distributing to the leading edge. Taken together these data suggest a previously unknown two-molecule sensing mechanism in which KCNJ15/Kir4.2 couples with polyamines in sensing weak electric fields. PMID:26449415
Malkemper, E. Pascal; Eder, Stephan H. K.; Begall, Sabine; Phillips, John B.; Winklhofer, Michael; Hart, Vlastimil; Burda, Hynek
2015-01-01
The mammalian magnetic sense is predominantly studied in species with reduced vision such as mole-rats and bats. Far less is known about surface-dwelling (epigeic) rodents with well-developed eyes. Here, we tested the wood mouse Apodemus sylvaticus for magnetoreception using a simple behavioural assay in which mice are allowed to build nests overnight in a visually symmetrical, circular arena. The tests were performed in the ambient magnetic field or in a field rotated by 90°. When plotted with respect to magnetic north, the nests were bimodally clustered in the northern and southern sectors, clearly indicating that the animals used magnetic cues. Additionally, mice were tested in the ambient magnetic field with a superimposed radio frequency magnetic field of the order of 100 nT. Wood mice exposed to a 0.9 to 5 MHz frequency sweep changed their preference from north-south to east-west. In contrast to birds, however, a constant frequency field tuned to the Larmor frequency (1.33 MHz) had no effect on mouse orientation. In sum, we demonstrated magnetoreception in wood mice and provide first evidence for a radical-pair mechanism in a mammal. PMID:25923312
NASA Astrophysics Data System (ADS)
Sharma, Navneet; Rawat, Tarun Kumar; Parthasarathy, Harish; Gautam, Kumar
2016-06-01
The aim of this paper is to design a current source obtained as a representation of p information symbols \\{I_k\\} so that the electromagnetic (EM) field generated interacts with a quantum atomic system producing after a fixed duration T a unitary gate U( T) that is as close as possible to a given unitary gate U_g. The design procedure involves calculating the EM field produced by \\{I_k\\} and hence the perturbing Hamiltonian produced by \\{I_k\\} finally resulting in the evolution operator produced by \\{I_k\\} up to cubic order based on the Dyson series expansion. The gate error energy is thus obtained as a cubic polynomial in \\{I_k\\} which is minimized using gravitational search algorithm. The signal to noise ratio (SNR) in the designed gate is higher as compared to that using quadratic Dyson series expansion. The SNR is calculated as the ratio of the Frobenius norm square of the desired gate to that of the desired gate error.
NASA Astrophysics Data System (ADS)
Elaeva, M. S.; Zhukov, M. Yu.; Shiryaeva, E. V.
2016-08-01
The hodograph method is used to construct a solution describing the interaction of weak discontinuities (rarefaction waves) for the problem of mass transfer by an electric field (zonal electrophoresis). Mathematically, the problem is reduced to the study of a system of two first-order quasilinear hyperbolic partial differential equations with data on characteristics (Goursat problem). The solution is constructed analytically in the form of implicit relations. An efficient numerical algorithm is described that reduces the system of quasilinear partial differential equations to ordinary differential equations. For the zonal electrophoresis equations, the Riemann problem with initial discontinuities specified at two different spatial points is completely solved.
Lemaitre-Tolman-Bondi solutions in the Newtonian gauge: from strong to weak fields
Van Acoleyen, Karel
2008-10-15
Lemaitre-Tolman-Bondi (LTB) solutions are used frequently to describe the collapse or expansion of spherically symmetric inhomogeneous mass distributions in the Universe. These exact solutions are obtained in the synchronous gauge where non-linear dynamics (with respect to the Friedmann-Lemaitre-Roberston-Walker (FLRW) background) induce large deviations from the FLRW metric. In this paper we show explicitly that this is a gauge artefact (for realistic sub-horizon inhomogeneities). We write down the non-linear gauge transformation from synchronous to Newtonian gauge for a general LTB solution using the fact that the peculiar velocities are small. In the latter gauge we recover the solution in the form of a weakly perturbed FLRW metric that is assumed in standard cosmology. Furthermore we show how to obtain the LTB solutions directly in Newtonian gauge and illustrate how the Newtonian approximation remains valid in the non-linear regime where cosmological perturbation theory breaks down. Finally we discuss the implications of our results for the backreaction scenario.
Quantum Opportunities in Gravitational Wave Detectors
Mavalvala, Negris
2012-03-14
Direct observation of gravitational waves should open a new window into the Universe. Gravitational wave detectors are the most sensitive position meters ever constructed. The quantum limit in gravitational wave detectors opens up a whole new field of study. Quantum opportunities in gravitational wave detectors include applications of quantum optics techniques and new tools for quantum measurement on truly macroscopic (human) scales.
Weak extremely-low-frequency magnetic fields and regeneration in the planarian Dugesia tigrina
Jenrow, K.A.; Smith, C.H.; Liboff, A.R.
1995-06-01
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.
The Optical Gravitational Lensing Experiment. OGLE-III Photometric Maps of the Galactic Bulge Fields
NASA Astrophysics Data System (ADS)
Szymański, M. K.; Udalski, A.; Soszyński, I.; Kubiak, M.; Pietrzyński, G.; Poleski, R.; Wyrzykowski, Ł.; Ulaczyk, K.
2011-06-01
We present OGLE-III Photometric Maps of the Galactic bulge fields observed during the third phase of the OGLE project. This paper describes the last, concluding set of maps based on OGLE-III data. The maps contain precise, calibrated VI photometry of about 340 million stars from 267 fields in the Galactic bulge observed during entire OGLE-III phase (2002-2009), covering about 92 square degrees in the sky. Precise astrometry of these objects is also provided. We briefly discuss the photometry procedures and the quality of the data. We also present sample data and color-magnitude diagrams of the observed fields. All photometric data are available to the astronomical community from the OGLE Internet archive.
The mass-zero spin-two field and gravitational theory.
NASA Technical Reports Server (NTRS)
Coulter, C. A.
1972-01-01
Demonstration that the conventional theory of the mass-zero spin-two field with sources introduces extraneous nonspin-two field components in source regions and fails to be covariant under the full or restricted conformal group. A modified theory is given, expressed in terms of the physical components of mass-zero spin-two field rather than in terms of 'potentials,' which has no extraneous components inside or outside sources, and which is covariant under the full conformal group. For a proper choice of source term, this modified theory has the correct Newtonian limit and automatically implies that a symmetric second-rank source tensor has zero divergence. It is shown that possibly a generally covariant form of the spin-two theory derived here can be constructed to agree with general relativity in all currently accessible experimental situations.
Registration of weak ULF/ELF oscillations of the surface electric field strength
NASA Astrophysics Data System (ADS)
Boldyrev, A. I.; Vyazilov, A. E.; Ivanov, V. N.; Kemaev, R. V.; Korovin, V. Ya.; Melyashinskii, A. V.; Pamukhin, K. V.; Panov, V. N.; Shvyrev, Yu. N.
2016-07-01
Measurements of the atmospheric electric field strength made by an electrostatic fluxmeter with a unique threshold sensitivity for such devices (6 × 10-2-10-3 V m-1 Hz-1/2 in the 10-3-25 Hz frequency range) and wide dynamic (120 dB) and spectral (0-25 Hz) ranges, are presented. The device parameters make it possible to observe the electric component of global electromagnetic Schumann resonances and long-period fluctuations in the atmospheric electric field strength.