Showing papers on "Gravitational field published in 1988"

Black holes in string-generated gravity models.

Abstract: Spherically symmetric solutions of d-dimensional Einstein-Maxwell theory with a Gauss-Bonnet term are classified. All spherically symmetric solutions of d-dimensional Einstein gravity coupled to the Gauss-Bonnet and Born-Infeld terms are derived, classified, and compared with the previous solutions. Thermodynamic properties of the black holes are discussed and the black-hole temperatures derived. Unlike the solutions of Einstein-Maxwell theory the solutions with a Born-Infeld term do not appear to have a stable end point with regard to thermal evaporation.

Model-independent constraints on possible modifications of Newtonian gravity.

Abstract: New model-independent constraints on possible modifications of Newtonian gravity over solar-system distance scales are presented, and their implications discussed. The constraints arise from the analysis of various planetary astrometric data sets. The results of the model-independent analysis are then applied to set limits on a variation in the l/r-squared behavior of gravity, on possible Yukawa-type interactions with ranges of the order of planetary distance scales, and on a deviation from Newtonian gravity of the type discussed by Milgrom (1983).

Geophysical Geodesy: The Slow Deformations of the Earth

Abstract: Part 1: An overview. Part 2 Geodetic concepts: gravity and gravitational potential elements of potential theory co-ordinate reference frames precession and nutation rotational motion of a deformable body - general formulation. Part 3 The geophysical setting: radial earth structure lateral variations the plate tectonics hypothesis some special loading problem. Part 4 The hydrosphere and atmosphere: sea-level late Pleistocene and Holocene sea-levels ocean tides the atmosphere the atmosphere in motion ground-water and the water balance. Part 5 Terrestrial geodetic methods: control surveys strain analysis gravity astronomical latitude, longitude, and time tilt and strain. Part 6 Satellite methods: orbital mechanics observing earth satellites estimating geodetic parameters estimating oceanographic parameters. Part 7 Lunar methods: motion of the moon lunar tides lunar laser ranging estimating selenodetic and geodetic constants. Part 8 Radio interferometric methods: principles of long-baseline interferometry estimating geodetic and geophysical parameters radio interferometric observations of satellites. Part 9 The Earth's gravity field: interpretation - general considerations gravity and tectonics - some examples the core-mantle boundary. Part 10 Crustal movements: stress in the crust and lithosphere instantaneous global tectonic motions vertical movements on geological time scales deformation at plate boundaries - some examples post-glacial rebound. Part 11 Tides and rotation of the Earth: the free rotational modes of the Earth the forced nutations of the Earth tidal estimates of Love numbers tidal accelerations, torques, and dissipation some rotational excitation mechanisms. Part 12: Epilogue. References. Index.

Tail Transported Temporal Correlations in the Dynamics of a Gravitating System

Abstract: The existence of retarded correlations over arbitrarily large time spans in the dynamics of a gravitating system, namely, the influence of the past evolution of a material system on its present gravitational internal dynamics, is investigated. This ''hereditary'' influence can be thought of as transported by the gravitational waves emitted by the system in the past and subsequently scattered off the curvature of spacetime back onto the system (''backscattered waves'' or ''tails''). The method used here applies to weakly self-gravitating slowly varying sources. It is a combination of a multipolar post-Minkowskian expansion for the metric in the weak-field region outside the system, and of a post-Newtonian-type expansion for the metric in the near zone. The two expansions are then ''matched'' in the weak-field-near-zone overlap region. The lowest-order nonlinear piece in the near-zone metric which depends on the full past history of the source (''hereditary'' term) is determined. This term arises at the fourth post-Newtonian (PN) level. The arising of this ''hereditary'' term signifies the breakdown of one of the fundamental tenets of the post-Newtonian approximation schemes. Indeed, at the 4PN level it becomes impossible to express the near-zone metric as a functional of the instantaneous state of the material source.more » This means also that there is a fundamental breakdown of the concept of near zone versus the concept of wave zone. The direct dynamical influence of the above-determined hereditary, or tail, term on the evolution of the material system is then studied. This term is found to modify the Burke-Thorne gravitational radiation quadrupole damping force.« less

Rapid Evaluation of Potential Fields in Three Dimensions

Abstract: : This paper describes a three dimensional version of the fast multipole algorithm for the rapid evaluation of the potential and force fields in systems of particles whose interactions are Coulombic or gravitational in nature. For a system of N particles, an amount of work of the order O(N-square) has traditionally been required to evaluate all pairwise interactions, unless some approximation or truncation method is used. The algorithm presented here requires an amount of work proportional to N to evaluate all interactions to within roundoff error, making it considerably more practical for large scale problems encountered in plasma physics, fluid dynamics, molecular dynamics and celestial mechanics.

A new gravitational model for the earth from satellite tracking data - GEM-T1

Abstract: A computation of a terrestrial gravitational field model called the Goddard Earth Model GEM-T1 is discussed and compared to previous models, including the GEM-L2. The software tools were redesigned for the model, allowing for the optimization of the technique of relative data weighting and model estimation used in GEM solutions. The GEM-T1 model provides a simultaneous solution for a gravity model in spherical harmonics complete to degree and order 36, a subset of 66 ocean tidal coefficients for the long-wavelength components of 12 major tides, and 5-day averaged earth rotation and polar motion parameters for the 1980 period on. GEM-T1 was derived from satellite tracking data acquired on 17 different satellites whose inclinations ranged from 15 degrees to polar. A simulation of the TOPEX/POSEIDON orbit using the covariances of the GEM-T1 model was made. Estimated radial error for the simulation was reduced to less than 30 cm rms.

Testing the principle of equivalence with neutrino oscillations.

Abstract: If the equivalence principle is violated, and gravity is not universally coupled to all leptonic flavors, a gravitational field may contribute to neutrino oscillations. The laboratory limits on the oscillation process can thus be interpreted as tests of the equivalence principle in the quantum-relativistic regime, and put severe constraints on a maximal violation of this principle in the case of massless neutrinos coupled to the Earth's gravitational field.

New precision tests of the Einstein equivalence principle from SN1987A

Abstract: The serendipitous observation of neutrinos and light from the recent supernova in the Large Magellanic Cloud has provided a wealth of new information about stellar collapse and about neutrinos. It is pointed out that, in addition, the nearly simultaneous arrival of the photons and neutrinos after a journey of some 160 000 yr provides a new, stringent test of the Einstein equivalence principle on intergalactic distance scales. The relativistic time delays of the photons and neutrinos from SN1987A caused by the gravitational field of our Galaxy are compared, and it is shown that they are equal, to an accuracy of approximately 0.2% of the predicted delay.

Optimum expression for computation of the gravity field of a homogeneous polyhedral body1

Abstract: The formula for the computation of the gravity field of a homogeneous polyhedral body is derived and transformed into the form which is most suitable when considering speed and simplicity of numerical calculation.

Action principle and partition function for the gravitational field in black-hole topologies.

Abstract: Statistical mechanics of gravitational fields describing the black-hole topological sector, and the correspondence to thermodynamics, are considered. The Euclidean action is evaluated on the constraint hypersurface and a measure is obtained, resulting in a path-integral form of the canonical partition function. We obtain the usual black-hole entropy plus quantum corrections when the temperature and size of the system are appropriate. Under other conditions, we give evidence for the existence of a phase transition (change of topology).

Quantum gravitational effects near cosmic strings

Abstract: The gravitational field associated with cosmic strings can produce a variety of quantum field effects, such as vacuum polarisation and particle production. The authors investigate the behaviour of particle detectors near straight strings in free space, immersed in thermal radiation, and passing through black holes. The expectation values of the stress-energy-momentum tensor for a scalar field near straight strings through black holes and in Robertson-Walker cosmological spacetimes are also calculated.

Comparisons of global topographic/isostatic models to the Earth's observed gravity field

Abstract: The Earth's gravitational potential, as described by a spherical harmonic expansion to degree 180, was compared to the potential implied by the topography and its isostatic compensation using five different hypothesis. Initially, series expressions for the Airy/Heiskanen topographic isostatic model were developed to the third order in terms of (h/R), where h is equivalent rock topography and R is a mean Earth radius. Using actual topographic developments for the Earth, it was found that the second and third terms of the expansion contributed 30 and 3 percents, of the first of the expansion. With these new equations it is possible to compute depths (D) of compensation, by degree, using 3 different criteria. The results show that the average depth implied by criterion I is 60 km while it is about 33 km for criteria 2 and 3 with smaller compensation depths at the higher degrees. Another model examined was related to the Vening-Meinesz regional hypothesis implemented in the spectral domain. Finally, oceanic and continental response functions were derived for the global data sets and comparisons made to locally determined values.

Three‐dimensional infinite Prandtl number convection in one and two layers with implications for the Earth's gravity field

Abstract: The three-dimensional planform of infinite Prandtl number convection is studied in one and two layers, with a numerical code which combines spectral and finite difference methods. The equations are solved in rectangular cavities supposing mirror symmetry on the sides. The one-layer experiments serve mainly for testing the code. These experiments reveal the outstanding importance of the initial and boundary conditions in the evolution of the flow pattern. The main emphasis of this paper is on two-layer convection models, with implications for the Earth's mantle and its gravity anomaly field. In this case, the interface between the two layers is fixed at a given depth, and coupling of the two circulations is ensured by the continuity of velocities and horizontal stress across the interface. The two-layer cases have been run with Rayleigh numbers up to 130 times the critical value, the thickness of the lower layer being twice that of the upper one. The ratio of the lower layer viscosity to the upper one is gradually increased. When this ratio is small (between 1 and 10), viscous coupling prevails, and bimodal or square cells formed in the lower layer induce similar, but counterrotating cells in the thin upper layer. When the viscosity ratio is high (several hundred), thermal coupling becomes dominant: again, the convective structure of the lower layer is more or less duplicated in the upper layer, but now the flows of both layers rotate in the same sense. In these situations the gravity anomalies are positively correlated with the topography of the upper surface. When the viscosity ratio is moderate (e.g., 25), the flow direction of the rolls in the thin upper layer becomes perpendicular to that observed in the lower layer, leading to a balance between the conflicting effects of the viscous and thermal couplings. This allows the upper rolls to have an aspect ratio close to 1. In this case, gravity is positevely correlated with deflection of the interface, but no more correlation can be seen with surface topography, which is determined by small-scale flow of the upper layer. These results suggest that the gravity and bathymetry anomalies of the Earth should be either positively correlated or not correlated at all. This has to be contrasted with earlier findings of two-dimensional modeling [Cserepes and Rabinowicz, 1985] which allow the possibility of having anticorrelation between gravity and topography.

Morphological Diversity of Equilibrium Receptor Systems in Aquatic Invertebrates

Abstract: For proper behavior and orientation in space, any organism with the capacity to move needs information about its attitude and movement. This information is provided by equilibrium receptor systems. These enable the organism to control its position and motor activities in the three dimensions of space, using the gravitational field as a reference system. Compared with all other reference systems, such as light, sound, odor, and taste, the gravitational field is characterized by a unique feature: during the life span of an organism it is nearly constant in both magnitude and direction. Thus, the gravitational field is an ideal reference system, and during the course of evolution all organisms that use locomotion have developed specialized receptor systems for equilibrium orientation that make use of this reference system.

Cosmic strings and the microwave sky. I - Anisotropy from moving strings

Abstract: A method is developed for calculating the component of the microwave anisotropy around cosmic string loops due to their rapidly changing gravitational fields. The method is only valid for impact parameters from the string much smaller than the horizon size at the time the photon passes the string. The method makes it possible to calculate the temperature pattern around arbitrary string configurations numerically in terms of one-dimensional integrals. This method is applied to temperature jump across a string, confirming and extending previous work. It is also applied to cusps and kinks on strings, and to determining the temperature pattern far from a strong loop. The temperature pattern around a few loop configurations is explicitly calculated. Comparisons with the work of Brandenberger et al. (1986) indicates that they have overestimated the MBR anisotropy from gravitational radiation emitted from loops.

Relativistic Theory of Gravity

Abstract: This paper presents a brief critical analysis of General Relativity Theory (GRT). It is shown that the theory, if accepted, leads to repudiation of a number of fundamental principles underlying physics. The article also presents the construction of Relativistic Theory of Gravitation (RTG) in which the gravitational field possesses all the attributes of physical fields and which concurs completely with the fundamental physical principles as well as with the available experimental and observational facts. It also considers the consequences of RTG, dealing, in particular, with the development of collapse and Universe evolution.

A new constraint on Saturn's zonal gravity harmonics from Voyager observations of an eccentric ringlet

Abstract: The results obtained by Porco et al. (1984) from an analysis of the kinematics of an eccentric ringlet in Saturn's inner ring are used to add an additional constraint to the gravity solution of Null et al. (1981) and thus to derive the first experimental estimate of the Saturn's J6 gravitational field. On the assumption that the eccentricity of this ringlet is forced by the satellite Titan, the location of the Titan apsidal resonance is determined to an accuracy of + or - 13 km, which in turn provides a strong constraint on Saturn's zonal gravity harmonics. Combining this constraint with the results of Null et all. and adopting a priori values for J8, J10, and J12 based on interior models, new estimates are obtained for the first three zonal gravity coefficients J2, J4, and J6.

Existence of the Gravitomagnetic Interaction

Abstract: The point of view expressed in the literature that gravitomagnetism has not yet been observed or measured is not entirely correct. Observations of gravitational phenomena are reviewed in which the gravitomagnetic interaction—a post-Newtonian gravitational force between moving matter—has participated and which has been measured to 1 part in 1000. Gravitomagnetism is shown to be ubiquitous in gravitational phenomena and is a necessary ingredient in the equations of motion, without which the most basic gravitational dynamical effects (including Newtonian gravity) could not be consistently calculated by different inertial observers.

Gravitational measurements, fundamental metrology and constants

Abstract: Can we Calculate the Fundamental Dimensionless Constants of Physics?.- Observables in General Relativity.- The Quantum Hall Effect Part I: Basic Experiments.- Quantum Hall Effect Part II: Metrological Applications.- Fundamental Physical Constants.- Variability of the Physical Constants.- The Measurement Problem of the General Matter Field Theory as Required by the Copenhagen School.- On the Relations between Fundamental Constants.- Quantum Electrodynamics and Fundamental Constants.- Searching for the Source of the Fifth Force.- Lorentz noninvariance and the Universality of free fall in Quasi-Riemannian Gravity.- Status of the Newtonian Gravitational Constant.- Time Variation of the Gravitational Constant.- The Supernova SN 1987A and the Neutrino Mass.- The Fifth Force Experiment at the TIFR.- Analysis of Ground States of General Relativity Theory and Relativistic Theory of Gravitation.- Gravitational-Relativistic Metrology.- Gravitational Waves.- The Gravitational Wave Experiment of the Rome Group. Data Recorded during SN1987A.- Solar-System Tests of General Relativity, the Transition to Second Order.- The Weyl-Dirac Theory and the Variation of the Gravitational Constant.- Selected Problems of Gravitational Wave Experiment.- Introductory Lectures on the Physics of High Energy Densities: Theories, Models, Measurements.- Detectors of Laboratory Gravitation Experiments and a new Method of Measuring G.- to the Theory of Fields in Finsler Spaces.- Neutrinos, Gravitons, Metrology and Gravitational Radiation.- On Quirino Majorana's Papers Regarding Gravitational Absorption.- I: Quelques Recherches sur l'Absorption de la Gravitation par la Matiere.- II: Theoretical and Experimental Researches on Gravitation.

Drag Force and Slip Correction of Aggregate Aerosols

Abstract: The drag force on aggregate particles of uniform spheres was measured in a Millikan apparatus as a function of Knudsen number. Our experiment was designed to study the effect of particle orientation on the slip correction factor of nonspherical particles. The velocities of charged particles in a gravitational field with and without an applied electrical field were measured. An electrical field strength of 2000 V/cm was used to align doublet and triplet particles. Results showed that an aggregate particle moved in random orientation while in the gravitational field. The same particle moved with its polar axis parallel to the electric field (doublets) or with its plane of centers parallel to the electrical field (triangular triplets). Using a nonlinear regression method, both the dynamic shape factor and slip correction factor could be determined separately from the data. The dynamic shape factors at different orientations were in good agreement with those obtained previously in a sedimentation tank. The sl...

Approximation scheme for constructing a clumpy universe in general relativity.

Abstract: We shall develop an approximation scheme to construct the metric representing a realistic clumpy universe in general relativity. Spatial averaging is used to express the fact that the expansion of the universe is generated collectively by the clumps of matter. The dynamics of the clumps is treated by the post-Newtonian-type approximation. The scheme allows one to calculate the back reaction due to the growth of clumps on the expansion and vice versa. An expression for the deviation from homogeneous and isotropic expansion is derived in terms of inhomogeneities of the gravitational field generated by clumps. It should also be used as the correct interpretation of the observation of gravitational lenses.

Gravitational field of a global string.

Abstract: The gravitational field of a straight global string is derived in the linear approximation to general relativity, and the resulting trajectories of test particles are found. Part of the gravitational effect of global strings is a deficit angle which increases logarithmically with the distance to the string core. In this regard, a global string resembles a gauge string. A new feature, not present for gauge strings, is a repulsive gravitational potential outside the core. The lensing properties of the global string, as well as other classical effects, are studied.

Effect of a uniform sea-level change on the Earth's rotation and gravitational field

Abstract: Global water redistriburtion between the oceans, atmosphere and continents causes changes in the earth's rotation and gravitational field. To conserve water mass, the effect of the small uniform change in sea-level must be considered. Explicit formulas are provided for these sea-level corrections to the gravitational Stokes coefficients, polar motion and length of day. In two recent publications, this sea-level correction term for polar motion was given incorrectly. These errors which arose from normalization conventions with the ocean function are corrected.

On a family of solutions of the Einstein-Maxwell equations

Abstract: A family of axisymmetric asymptotically flat solutions of the Einstein-Maxwell field equations is presented. In a particular case we obtain a magnetostatic solution which reduces to the well-known Schwarzschild metric in the absence of a magnetic field and describes the exterior gravitational field of a massive magnetic dipole moment.

First Order Actions for Gravitational Systems, Strings and Membranes

Abstract: We discuss first order actions in general and the construction of first order actions by eliminating Lagrange multipliers in particular. A number of first order actions for gravitational theories are presented. Part of the article reviews first order actions, some of them well-known and some lesser known. New examples of first order actions include Weyl-invariant actions for membranes, with and without rigidity terms, as well as for Abelian and non-Abelian Born-Infeld actions in two dimensions.

Solutions to Einstein's field equations with Kantowski-Sachs symmetry and string dust source

Abstract: Einstein's field equations are solved with a two-parameter family of classical strings as the source for the gravitational field. The solutions have Kantowski-Sachs symmetry. The singularities of the solutions and the kinematical properties of the string world sheets are discussed.