Components Of Gravitational Field Research Articles

Effect of Pressure and Gravitational Field on the Distribution of Cu during the Directed Growth of a Single Crystal of the Alloy Al–0.005 wt % Cu

Abstract—Using quantitative X-ray spectral analysis and metallography, the distribution of copper concentration in the α-solid solution of Al and the dislocation density in single crystals of the Al alloy–0.005 wt % Cu, grown from the melt at different values of argon pressure (Ar) and the gravitational field component (gmg) directed along the surface of the crystallization front. A strong inhomogeneity in the copper concentration measured in adjacent areas of the cross-sectional surface of the crystal and its correlation with the inhomogeneity of the distribution of dislocations in single crystals of the alloy, which depends on pressure and the gravitational field component, were discovered. The mechanism of relaxation of the excess free volume of the phase transformation released in the region of the interphase boundary during crystal growth is considered.

Highly relativistic spin-gravity- Λ coupling

The effects of highly relativistic spin-gravity coupling in the Schwarzschild-de Sitter background which follow from the Mathisson-Papapetrou equations are investigated. The dependence of gravitoelectric and gravitomagnetic components of gravitational field on the velocity of an observer which is moving in Schwarzschild-de Sitter's background is estimated. The action of gravitomagnetic components on a fast moving spinning particle is considered. Different cases of the highly relativistic circular orbits of a spinning particle which essentially differ from the corresponding geodesic orbits are described.

Black holes in modified gravity (MOG)

The field equations for Scalar-Tensor-Vector-Gravity (STVG) or modified gravity (MOG) have a static, spherically symmetric black hole solution determined by the mass $M$ with two horizons. The strength of the gravitational constant is $G=G_N(1+\alpha)$ where $\alpha$ is a parameter. A regular singularity-free MOG solution is derived using a nonlinear field dynamics for the repulsive gravitational field component and a reasonable physical energy-momentum tensor. The Kruskal-Szekeres completion of the MOG black hole solution is obtained. The Kerr-MOG black hole solution is determined by the mass $M$, the parameter $\alpha$ and the spin angular momentum $J=Ma$. The equations of motion and the stability condition of a test particle orbiting the MOG black hole are derived, and the radius of the black hole photosphere and the shadows cast by the Schwarzschild-MOG and Kerr-MOG black holes are calculated. A traversable wormhole solution is constructed with a throat stabilized by the repulsive component of the gravitational field.

Next-to-leading order gravitational spin-orbit coupling in an effective field theory approach

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 non-stationary 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 non-relativistic 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 ADM Hamiltonian formalism. This is done using non-canonical 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.

Effect of pressure on the copper redistribution in a solid solution and on the parameters of the dendritic structure of Al-4% Cu single crystals upon crystallization in a gravitational field

Using electron microprobe analysis (EMA), copper concentration in the aluminum α solid solution has been determined; its distribution has been studied in Al-4% Cu single crystals obtained at different pressures under the conditions of the existence of a gravitational-field component oriented tangentially relative to the growth direction. Parameters of a dendrite structure have been determined. Their relationship with a change in the chemical composition of the alloy induced by an inhomogeneous redistribution of the second component in the process of crystallization under the effect of both the pressure and the gravitational-field component has been demonstrated.

The lunar gravity mission MAGIA: preliminary design and performances

The importance of an accurate model of the Moon gravity field has been assessed for future navigation missions orbiting and/or landing on the Moon, in order to use our natural satellite as an intermediate base for next solar system observations and exploration as well as for lunar resources mapping and exploitation. One of the main scientific goals of MAGIA mission, whose Phase A study has been recently funded by the Italian Space Agency (ASI), is the mapping of lunar gravitational anomalies, and in particular those on the hidden side of the Moon, with an accuracy of 1 mGal RMS at lunar surface in the global solution of the gravitational field up to degree and order 80. MAGIA gravimetric experiment is performed into two phases: the first one, along which the main satellite shall perform remote sensing of the Moon surface, foresees the use of Precise Orbit Determination (POD) data available from ground tracking of the main satellite for the determination of the long wavelength components of gravitational field. Improvement in the accuracy of POD results are expected by the use of ISA, the Italian accelerometer on board the main satellite. Additional gravitational data from recent missions, like Kaguya/Selene, could be used in order to enhance the accuracy of such results. In the second phase the medium/short wavelength components of gravitational field shall be obtained through a low-to-low (GRACE-like) Satellite-to-Satellite Tracking (SST) experiment. POD data shall be acquired during the whole mission duration, while the SST data shall be available after the remote sensing phase, when the sub-satellite shall be released from the main one and both satellites shall be left in a free-fall dynamics in the gravity field of the Moon. SST range-rate data between the two satellites shall be measured through an inter-satellite link with accuracy compliant with current state of art space qualified technology. SST processing and gravitational anomalies retrieval shall benefit from a second ISA accelerometer on the sub-satellite in order to decouple lunar gravitational signal from other accelerations. Experiment performance analysis shows that the stated scientific requirements can be achieved with a low mass and low cost sub-satellite, with a SST gravimetric mission of just few months.

Effect of pressure and gravitational field on the dendritic structure and distribution of solutes in Al-4% Cu single crystals

Peculiarities of the formation of the dendritic structure and the development of alloying-component sedimentation in the Al-4% Cu alloy during its directional solidification under conditions of the earth gravitational field under pressure have been studied. It has been found that pressure substantially affects the development of alloy-component sedimentation in the two-phase zone in the case of the dendritic growth of a solid as well. The increase in the copper concentration near the lateral surface of the single crystal along the gravitational-field component, which was revealed when analyzing the nonuniformity of the solute distribution in transverse sections of a eutectic-phase sample, as well as the changes in the lattice parameter of the α solid solution, were found to be maximum during the solidification of the melt under a pressure of 0.25 and minimum under a pressure of 0.15 MPa.

Formation of a dislocation structure of aluminum single crystals under the action of pressure and gravitational field on the melt

The distribution of dislocation density has been investigated experimentally in aluminum single crystals with various concentrations of copper impurity (∼0.0002, 0.005, and 0.05 wt %) that were obtained upon the crystallization of the melt under the action of a pressure and the gravitational-field component directed along the surface of the crystallization front. It has been found that a strong nonuniformity in the dislocation distribution arises in cross sections of the crystals in the direction of the field and this nonuniformity increases with increasing gravitational-field component and decreasing in the impurity concentration and rate of crystallization of the melt. It has been found that the degree of nonuniformity of the dislocation distribution in the crystals substantially depends on the magnitude of pressure at which the crystallization of the melt is realized and reaches a maximum at a certain pressure that is “optimum” for given conditions of the process of phase transformation.

Triaxial stellar systems following the r1/n luminosity law: an analytical mass-density expression, gravitational torques and the bulge/disc interplay

We have investigated the structural and dynamical properties of triaxial stellar systems whose surface brightness profiles follow the r 1 / n luminosity law - extending the analysis by Ciotti, who explored the propertiesof spherical r 1 / n systems. A new analytical expression that accurately reproduces the spatial (i.e., deprojected) luminosity density profiles (error less than 0.1 per cent) is presented for detailed modelling of the Sersic family of luminosity profiles. We evaluate both the symmetric and the non-axisymmetric components of the gravitational potential and force, and compute the torques as a function of position. For a given triaxiality, stellar systems with smaller values of n have a greater non-axisymmetric gravitational field component. We also explore the strength of the non-axisymmetric forces produced by bulges with differing n and triaxiality on systems having a range of bulge-to-disc ratios. The increasing disc-to-bulge ratio with increasing galaxy type (decreasing n) is found to greatly reduce the amplitude of the non-axisymmetric terms, and therefore reduce the possibility that triaxial bulges in late-type systems may be the mechanism or perturbation for non-symmetric structures in the disc. Using seeing-convolved r 1 / n -bulge plus exponential-disc fits to the K-band data from a sample of 80 nearby disc galaxies, we probe the relations between galaxy type, Sersic index n and the bulge-to-disc luminosity ratio. These relations are shown to be primarily a consequence of the relation between n and the total bulge luminosity. In the K band, the trend of decreasing bulge-to-disc luminosity ratio along the spiral Hubble sequence is predominantly, though not entirely, a consequence of the change in the total bulge luminosity; the trend between the total disc luminosity and Hubble type is much weaker.

Computing three-dimensional gravitational fields with equivalent sources

Existing techniques for computing the gravitational field due to a homogeneous polyhedron all transform the required volume integral, expressing the field due to a volume distribution of mass, into a surface integral, expressing the potential due to a surface mass distribution over the boundary of the source body. An alternative representation is also possible and results in a surface integral expressing the potential due to a variable-strength double layer located on the polyhedral source boundary. Manipulation of this integral ultimately allows the gravitational field component in an arbitrary direction to be expressed as a weighted sum of the potentials due to two basic source distributions. These are a uniform-strength double layer located on all faces and a uniform-strength line source located along all edges. The derivatives of the gravitational field components can also be expressed in a similar form as can the magnetic field components due to a homogeneous magnetic polyhedron. It follows that the present approach can be used to generate a universal program capable of modelling all the commonly used potential field responses due to 3D bodies of arbitrary shape.

Quantum graviton creation in a model universe

Quantization in the spatially inhomogeneous, anisotropic, Gowdy three-torus solution of Einstein's equations leads to the production of gravitons from empty space. The creation of pairs of gravitons occurs only in wave modes with wavelength exceeding the horizon size at an initial time. The final number of created gravitons in any mode is proportional to the number of causally unconnected regions at the initial time over the wavelength of that mode. At large times, graviton number is well defined since the solution is in WKB form. The creation process produces the anisotropic collisionless radiation identical to that discussed by Doroshkevich, Zel'dovich, and Novikov which characterizes the large time classical solution. Near the singularity, the model behaves like an empty Bianchi Type I universe at each point in space (local Kasner). The canonical methods of Arnowitt, Deser, and Misner yield a reduced Hamiltonian from which the classical equations of motion are obtained. The quantization of the rapidly varying gravitational field component resembles the procedures used by Parker or Zel'dovich et al. to study particle creation in curved spacetime.