Changes In Gravitational Field Research Articles

Method of distinguishing between black holes and wormholes

Beginning with a brief review of the regular space-time with asymptotically Minkowski core, we can consider two copies of the space-time connected through a short-throat wormhole whose radius of mouth is equal to or larger than an extremal regular black hole with asymptotically Minkowski core's event horizon radius. If the wormhole is traversable and smooth, fluxes in these two space-times will interact with and flow into each other. On the cosmological scale, gravity is a candidate for the flux. As the gravitational field changes in one space-time, the behaviors of stars around the wormhole will be affected by the other space-time since we assume that there exists enough exotic matter to keep the wormhole open. The changes in a gravitational field can be quantized through the gauge invariant perturbations. The variances in orbits of stars can be reflected by changes in the kinematic shifts of photon frequencies. Then, we use this to distinguish between the black hole and wormhole generated by the same space-time line element, since a black hole cannot connect two space-times and is unaffected by another space-time.

Some features of an interaction of electromagnetic radiation quantums with a gravitational field and a problem of graviton

The problems connected to propagation of a gravitational field are considered. The law of electromagnetic radiation frequency change in gravitational field is shown. The problem of a gravitational field quantization is investigated. Energy of a graviton is found by two ways. First, on the basis of use quantum gravitational eikonal and Lagrangian of a gravitational field the energy of a solitary graviton is found. It is shown that graviton has the mass proportional to its frequency. Second, due to refusal from symmetric stresses tensor in structure of an energy-impulse tensor the quantum form of the energy-impulse tensor in Einstein's equation is found. It has allowed found the energy of a solitary graviton. Both ways of an energy graviton finding has given the identical result. It is shown that the solution of the Einsteins equation with use of the quantum form of an energy-impulse tensor for the certain direction represents the sum of a gravitational wave and a graviton. It is found out that at approach of a graviton to the massive bodies (double stars) radiating gravitational waves there is a resonant pumping of the gravitational field energy of these bodies to the gravitons with increase in their mass and frequency. It enables registration of the gravitons with the help of the detector located near to massive bodies. The assumption is made that dark energy of a gravitational field is all set of the graviton energies of a space.

Co-Seismic and Post-Seismic Temporal and Spatial Gravity Changes of the 2010 Mw 8.8 Maule Chile Earthquake Observed by GRACE and GRACE Follow-on

The Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-on (GRACE-FO) satellites are important for studying regional gravitational field changes caused by strong earthquakes. In this study, we chose Chile, one of Earth’s most active seismic zones to explore the co-seismic and post-seismic gravitational field changes of the 2010 Mw 8.8 Maule earthquake based on longer-term GRACE and the newest GRACE-FO data. We calculated the first-order co-seismic gravity gradient changes (GGCs) and probed the geodynamic characteristics of the earthquake. The earthquake caused significant positive gravity change on the footwall and negative gravity changes on the hanging wall of the seismogenic fault. The time series of gravity changes at typical points all clearly revealed an abrupt change caused by the earthquake. The first-order northern co-seismic GGCs had a strong suppressive effect on the north-south strip error. GRACE-FO results showed that the latest post-seismic gravity changes had obvious inherited development characteristics, and that the west coast of Chile maybe still affected by the post-seismic effect. The cumulative gravity changes simulated based on viscoelastic dislocation model is approximately consistent with the longer-term GRACE and the newest GRACE-FO observations. Our results provide important reference for understanding temporal and spatial gravity variations associated with the co-seismic and post-seismic processes of the 2010 Maule earthquake.

Discrete relativistic positioning systems

We discuss the design for a discrete, immediate, simple relativistic positioning system (rPS) which is potentially able of self-positioning (up to isometries) and operating without calibration or ground control assistance. The design is discussed in 1 + 1 spacetimes, in Minkowski and Schwarzschild solutions, as well as in 2 + 1 spacetimes in Minkowski. The system works without calibration, i.e. clock synchronizations, or prior knowledge about the motion of clocks, it is robust, i.e. it is able to test hypotheses break down (for example, if one or more clocks temporarily become not-freely falling, or the gravitational field changes), and then it is automatically back and operational when the assumed conditions are restored. In the Schwarzschild case, we also check that the system can best fit the gravitational mass of the source of the gravitational field. We stress that no weak field assumptions are made anywhere. In particular, the rPS we propose can work in a region close to the horizon since it does not use approximations or PPN expansions. More generally, the rPS can be adapted as detectors for the gravitational field and we shall briefly discuss their role in testing different theoretical settings for gravity. In fact, rPS is a natural candidate for a canonical method to extract observables out of a gravitational theory, an activity also known as designing experiments to test gravity.

Teaching Curiosity to do gravimetry

Martian Geology![Figure][1] Self-portrait of Curiosity rover in Gale crater created using images taken by Curiosity’s Mars Hands Lens Imager, June 2018 PHOTO: NASA/JPL-CALTECH/MSSS Gravimetry—the measurement of tiny changes in gravitational fields—can be used to weigh mountains. Large-scale gravimetric mapping can be done from orbit, but examining small details requires a vehicle on the ground. The Curiosity rover on Mars carries several accelerometers used for routine navigation. Lewis et al. recalibrated these accelerometers to allow them to be used for gravimetry. They measured how the local gravitational field changed as the rover moved through Gale crater and began to climb Aeolis Mons (Mount Sharp). The resulting density of material under Gale crater shows that it is relativity porous, disproving a theory that the crater floor was once buried under several kilometers of rock. Science , this issue p. [535][2] [1]: pending:yes [2]: /lookup/doi/10.1126/science.aat0738

Earth\u2019s Subdecadal Angular Momentum Balance from Deformation and Rotation Data

Length-of-Day (LOD) measurements represent variations in the angular momentum of the solid Earth (crust and mantle). There is a known ~6-year LOD signal suspected to be due to core-mantle coupling. If it is, then the core flow associated with the 6-year LOD signal may also deform the mantle, causing a 6-year signal in the deformation of the Earth’s surface. Stacking of Global Positioning System (GPS) data is found to contain a ~6-year radial deformation signal. We inverted the deformation signal for the outer core’s flow and equivalent angular momentum changes, finding good agreement with the LOD signal in some cases. These results support the idea of subdecadal core-mantle coupling, but are not robust. Interpretation of the results must also take into account methodological limitations. Gravitational field changes resulting from solid Earth deformation were also computed and found to be smaller than the errors in the currently available data.

Changes in the effective gravitational field strength affect the state of phosphorylation of stress-related proteins in callus cultures of Arabidopsis thaliana.

In a recent study it was shown that callus cell cultures of Arabidopsis thaliana respond to changes in gravitational field strengths by changes in protein expression. Using ESI-MS/MS for proteins with differential abundance after separation by 2D-PAGE, 28 spots which changed reproducibly and significantly in amount (P <0.05) after 2 h of hypergravity (18 up-regulated, 10 down-regulated) could be identified. The corresponding proteins were largely involved in stress responses, including the detoxification of reactive oxygen species (ROS). In the present study, these investigations are extended to phosphorylated proteins. For this purpose, callus cell cultures of Arabidopsis thaliana were exposed to hypergravity (8 g) and simulated weightlessness (random positioning; RP) for up to 30 min, a period of time which yielded the most reliable data. The first changes, however, were visible as early as 10 min after the start of treatment. In comparison to 1 g controls, exposure to hypergravity resulted in 18 protein spots, and random positioning in 25, respectively, with increased/decreased signal intensity by at least 2-fold (P <0.05). Only one spot (alanine aminotransferase) responded the same way under both treatments. After 30 min of RP, four spots appeared, which could not be detected in control samples. Among the protein spots altered in phosphorylation, it was possible to identify 24 from those responding to random positioning and 12 which responded to 8 g. These 12 proteins (8 g) are partly (5 out of 12) the same as those changed in expression after exposure to 2 h of hypergravity. The respective proteins are involved in scavenging and detoxification of ROS (32%), primary metabolism (20.5%), general signalling (14.7%), protein translation and proteolysis (14.7%), and ion homeostasis (8.8%). Together with our recent data on protein expression, it is assumed that changes in gravitational fields induce the production of ROS. Our data further indicate that responses toward RP are more by post-translational protein modulation (most changes in the degree of phosphorylation occur under RP-treatment) than by protein expression (hypergravity).

Atom Interferometer Measurement of the Newtonian Constant of Gravity

We measured the Newtonian constant of gravity, G, using a gravity gradiometer based on atom interferometry. The gradiometer measures the differential acceleration of two samples of laser-cooled Cs atoms. The change in gravitational field along one dimension is measured when a well-characterized Pb mass is displaced. Here, we report a value of G = 6.693 x 10(-11) cubic meters per kilogram second squared, with a standard error of the mean of +/-0.027 x 10(-11) and a systematic error of +/-0.021 x 10(-11) cubic meters per kilogram second squared. The possibility that unknown systematic errors still exist in traditional measurements makes it important to measure G with independent methods.

Nontidal oceanic contributions to gravitational field changes: Predictions of the Parallel Ocean Climate Model

This study examines the nontidal contributions of the oceans to the Earth's gravitational field variations as predicted by a global ocean general circulation model: the Parallel Ocean Climate Model. Such variations in the gravitational field Stokes coefficient are determined up to spherical harmonic degree and order 20 and compared with satellite laser ranging (SLR) data from LAGEOS I and LAGEOS II. For most Stokes coefficients except the lowest‐degree ones, this investigation indicates that the application of sea level adjustment to reduce the effects of the model's lack of mass conservation due to the Boussinesq approximation has a negligible effect on timescales less than a few years. Predicted gravitational changes show strong seasonal variability and account for a portion of the variations estimated from SLR. We conclude that, in addition to the atmosphere, the oceans are an important contributor to the temporal variations in the Earth's gravitational field. The Stokes coefficients are useful in examining oceanic mass transport between hemispheres and ocean basins. The estimated oceanic power spectrum has a spectral shape similar to the atmosphere and is well above the noise level of planned satellite missions like the Gravity Recovery and Climate Experiment (GRACE).

Immediate Early Gene Expression in the Vestibular Nuclei and Related Vegetative Areas in Rats During Space Flight

Changes in neuronal activity resulting in somatic and vegetative deficits occur during different space flight conditions. Immediate early genes (IEGs: c-fos and Fos-related antigen [FRA]) are useful indicators of changes in neuronal activity and plasticity. They are induced within minutes of several extracellular stimulations, while the corresponding proteins persist for hours (Fos) or days (FRAs). Changes in IEG expression are likely to contribute to adaptation to microgravity and readaptation to the terrestrial environment. During the NASA Neurolab Mission (STS-90), changes in IEG expression were studied in adult male albino rats (Fisher 344) sacrificed at flight day (FD) 2 (24 h after launch), FD14 and at similar time points after re-entry (R + 1, 24 h after re-entry, and R + 13). These time points were chosen to maximize the probability of detecting changes in IEG expression related to changes in gravitational fields occurring during the mission, e.g. (i) increase in gravitational force from 1 to 3 g during the launch, before reaching about 0 g at FD2; (ii) adaptation to 0 g at FD14; (iii) increase in gravity from 0 to , 1.5-1.8 g before reaching 1 g at R + 1; and (iv) readaptation to 1 g at R + 13. Fos- and FRA-positive cells were identified in the brainstem of flight rats and ground-based controls using immunocytochemistry. With respect to control rats, the number of labeled cells increased in flight animals in the medial and spinal vestibular nuclei (but not in the lateral vestibular nucleus) at FD2, decreased at FD14, greatly increased at R + 1 and returned to baseline levels at R + 13. Similar changes in IEG expression were also observed in the nucleus of the solitary tract, the area postrema and the central nucleus of the amygdala. In particular, in these vegetative areas the number of Fos-positive cells decreased in flight rats with respect to controls at FD14, i.e. after exposure to 0 g , but significantly increased at R + 1, i.e. after return to 1 g . Thus, altered gravitational fields produced molecular changes in vestibular nuclei controlling somatic functions, as well as in related medullary and basal forebrain structures regulating vegetative functions.

On Mechanosensation in Bone Under Microgravity

Recent research has illuminated the biological response of bone to mechanical loading at the cellular level, but the precise mechanosensory system that signals bone cells to deposit or resorb tissue has not been identified. The purpose of this paper is to describe the current status of this research and to suggest some possible mechanosensory systems by which bone cells might sense environmental loads. The question of whether the mechanosensory system in bone tissue is at the level of the cell or whether it is at the tissue level and involving the cells is considered here. More precisely, the following question is addressed: can an osteocyte or an osteoblast read the gravitational field changes directly (and independent of changes in its environment), or does it detect those changes indirectly from its environment by contact stresses as it must detect other changes in mechanical loading on the surface of the earth? Our strategies for coping with the decay of the musculoskeletal system in long term space flight are somewhat dependent upon the answer to this question.

Bifurcation of a capillary minimal surface in a weak gravitational field

In this paper we study a variational elliptic boundary-value problem on a convex region with Bond parameter that arises in hydromechanics and is closely related to the Plateau problem. It describes the behaviour of an elastic surface separating two liquid or gaseous media as the gravitational field changes. In the absence of gravitational force we have and the solution to the problem is a minimal surface. Here we study the behaviour of this surface (loss of stability, bifurcations) when gravity is introduced. The method of analysis is based on reducing the problem to an operator equation in Hölder or Sobolev spaces with a non-linear Fredholm operator of index 0 that depends on the parameter , and applying the Crandall-Rabinowitz theorem on simple bifurcation points, the Lyapunov-Schmidt method of reduction to finite dimensions, and the key function method due to Sapronov. We obtain both necessary and sufficient general conditions for bifurcation, and study in detail the situation when is a circle or a square.

Linear and nonlinear system identification of autonomic heart-rate modulation.

The authors' findings show that system identification provides a useful, noninvasive, and quantitative means for evaluating cardiovascular regulatory mechanisms. With combinations of linear and nonlinear identification, new insights about the cardiovascular regulatory dynamics were obtained. System identification provides a new way of studying and monitoring cardiovascular function. Instead of just studying the signals generated by the cardiovascular regulatory system, the signals are analyzed to characterize quantitatively the mechanisms that generate them. System identification is a type of inverse modelingin which the physiologic signals are used to create a model of cardiovascular regulation for the specific individual from whom the data are obtained. As such, system identification would appear to be a desirable means for evaluating effects of physiologic alterations resulting from pharmacological interventions, changes in environment such as changes in gravitational field, physiologic stresses such as hypoxia and exercise, and disease processes. System identification may also prove to be an attractive means to study closed-loop regulation in other physiologic systems, ranging in size from biochemical pathways to intact multi-organ systems.

Search for an intermediate-range composition-dependent force coupling to N-Z.

We report a search for composition dependence in the forces acting on two test masses made primarily of lead and copper, due to an attracting mass made primarily of lead. The test masses are mounted on a torsion balance of high symmetry. The attracting mass is a 320-kg lead ring in an aluminum shell, positioned so that the torsion balance lies on the ring's axis at a distance from its center approximately equal to $\sqrt{\frac{3}{2}}$ times the ring's mean radius. When the ring is moved periodically between symmetric positions on opposite sides of the balance, the resulting change in gravitational field experienced by the balance is spatially uniform to a very high degree: all derivatives of the change in field at the center of the balance vanish through third order. We find the apparent gravitational force per unit mass on the two test masses due to the attracting ring mass to be equal to within 1.1\ifmmode\pm\else\textpm\fi{}1.2 ppm. Assuming a parametrization of a composition-dependent force in the notation of Fischbach, we find $\ensuremath{\xi}=(5.7\ifmmode\pm\else\textpm\fi{}6.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ for ${\ensuremath{\theta}}_{5}=90\ifmmode^\circ\else\textdegree\fi{}$ ($N\ensuremath{-}Z$ coupling), $\ensuremath{\xi}=(\ensuremath{-}1.2\ifmmode\pm\else\textpm\fi{}1.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ for ${\ensuremath{\theta}}_{5}=0\ifmmode^\circ\else\textdegree\fi{}$ ($B$ coupling).