The Myosuit: Bi-articular Anti-gravity Exosuit That Reduces Hip Extensor Activity in Sitting Transfers

PubMed Central

Schmidt, Kai; Duarte, Jaime E.; Grimmer, Martin; Sancho-Puchades, Alejandro; Wei, Haiqi; Easthope, Chris S.; Riener, Robert

2017-01-01

Muscle weakness—which can result from neurological injuries, genetic disorders, or typical aging—can affect a person's mobility and quality of life. For many people with muscle weakness, assistive devices provide the means to regain mobility and independence. These devices range from well-established technology, such as wheelchairs, to newer technologies, such as exoskeletons and exosuits. For assistive devices to be used in everyday life, they must provide assistance across activities of daily living (ADLs) in an unobtrusive manner. This article introduces the Myosuit, a soft, wearable device designed to provide continuous assistance at the hip and knee joint when working with and against gravity in ADLs. This robotic device combines active and passive elements with a closed-loop force controller designed to behave like an external muscle (exomuscle) and deliver gravity compensation to the user. At 4.1 kg (4.6 kg with batteries), the Myosuit is one of the lightest untethered devices capable of delivering gravity support to the user's knee and hip joints. This article presents the design and control principles of the Myosuit. It describes the textile interface, tendon actuators, and a bi-articular, synergy-based approach for continuous assistance. The assistive controller, based on bi-articular force assistance, was tested with a single subject who performed sitting transfers, one of the most gravity-intensive ADLs. The results show that the control concept can successfully identify changes in the posture and assist hip and knee extension with up to 26% of the natural knee moment and up to 35% of the knee power. We conclude that the Myosuit's novel approach to assistance using a bi-articular architecture, in combination with the posture-based force controller, can effectively assist its users in gravity-intensive ADLs, such as sitting transfers. PMID:29163120

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dehghani, M.H.; Department of Physics, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L 3G1; Perimeter Institute for Theoretical Physics, 35 Caroline Street North, Waterloo, Ontario

We investigate the existence of Taub-NUT (Newman-Unti-Tamburino) and Taub-bolt solutions in Gauss-Bonnet gravity and obtain the general form of these solutions in d dimensions. We find that for all nonextremal NUT solutions of Einstein gravity having no curvature singularity at r=N, there exist NUT solutions in Gauss-Bonnet gravity that contain these solutions in the limit that the Gauss-Bonnet parameter {alpha} goes to zero. Furthermore there are no NUT solutions in Gauss-Bonnet gravity that yield nonextremal NUT solutions to Einstein gravity having a curvature singularity at r=N in the limit {alpha}{yields}0. Indeed, we have nonextreme NUT solutions in 2+2k dimensions withmore » nontrivial fibration only when the 2k-dimensional base space is chosen to be CP{sup 2k}. We also find that the Gauss-Bonnet gravity has extremal NUT solutions whenever the base space is a product of 2-torii with at most a two-dimensional factor space of positive curvature. Indeed, when the base space has at most one positively curved two-dimensional space as one of its factor spaces, then Gauss-Bonnet gravity admits extreme NUT solutions, even though there a curvature singularity exists at r=N. We also find that one can have bolt solutions in Gauss-Bonnet gravity with any base space with factor spaces of zero or positive constant curvature. The only case for which one does not have bolt solutions is in the absence of a cosmological term with zero curvature base space.« less

Static solutions for fourth order gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nelson, William

2010-11-15

The Lichnerowicz and Israel theorems are extended to higher order theories of gravity. In particular it is shown that Schwarzschild is the unique spherically symmetric, static, asymptotically flat, black-hole solution, provided the spatial curvature is less than the quantum gravity scale outside the horizon. It is then shown that in the presence of matter (satisfying certain positivity requirements), the only static and asymptotically flat solutions of general relativity that are also solutions of higher order gravity are the vacuum solutions.

Mission Analysis for Multiple Rendezvous of Near-Earth Asteroids Using Earth Gravity Assist

DTIC Science & Technology

2010-03-01

devices. Finding solutions with this approach leads to a quicker timeline for possible missions since one does not have to wait for the propulsion...in this research. The discussion focuses on their approach to the problem and the applicability to this research. The headings are the titles of... approach the problem utilizing conventional impulsive thrust propulsion systems and utilize data presented from the JPL website for locating the

Effects of Gravity-Assist Timing on Outer-Planet Missions Using Solar-Electric Propulsion

NASA Technical Reports Server (NTRS)

Woo, Byoungsam; Coverstone, Victoria L.; Cupples, Michael

2004-01-01

Missions to the outer planets for spacecraft with a solar-electric propulsion system (SEPS) and that utilize a single Venus gravity assist are investigated. The trajectories maximize the delivered mass to the target planet for a range of flight times. A comparison of the trajectory characteristics (delivered mass, launch energy and onboard propulsive energy) is made for various Venus gravity assist opportunities. Methods to estimate the delivered mass to the outer planets are developed.

Gravity-assist engine for space propulsion

NASA Astrophysics Data System (ADS)

Bergstrom, Arne

2014-06-01

As a possible alternative to rockets, the present article describes a new type of engine for space travel, based on the gravity-assist concept for space propulsion. The new engine is to a great extent inspired by the conversion of rotational angular momentum to orbital angular momentum occurring in tidal locking between astronomical bodies. It is also greatly influenced by Minovitch's gravity-assist concept, which has revolutionized modern space technology, and without which the deep-space probes to the outer planets and beyond would not have been possible. Two of the three gravitating bodies in Minovitch's concept are in the gravity-assist engine discussed in this article replaced by an extremely massive ‘springbell' (in principle a spinning dumbbell with a powerful spring) incorporated into the spacecraft itself, and creating a three-body interaction when orbiting around a gravitating body. This makes gravity-assist propulsion possible without having to find suitably aligned astronomical bodies. Detailed numerical simulations are presented, showing how an actual spacecraft can use a ca 10-m diameter springbell engine in order to leave the earth's gravitational field and enter an escape trajectory towards interplanetary destinations.

Exploring plane-symmetric solutions in f(R) gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shamir, M. F., E-mail: farasat.shamir@nu.edu.pk

2016-02-15

The modified theories of gravity, especially the f(R) gravity, have attracted much attention in the last decade. This paper is devoted to exploring plane-symmetric solutions in the context of metric f(R) gravity. We extend the work on static plane-symmetric vacuum solutions in f(R) gravity already available in the literature [1, 2]. The modified field equations are solved using the assumptions of both constant and nonconstant scalar curvature. Some well-known solutions are recovered with power-law and logarithmic forms of f(R) models.

An Exact Solution of Einstein-Maxwell Gravity Coupled to a Scalar Field

NASA Technical Reports Server (NTRS)

Turyshev, S. G.

1995-01-01

The general solution to low-energy string theory representing static spherically symmetric solution of the Einstein-Maxwell gravity with a massless scalar field has been found. Some of the partial cases appear to coincide with known solutions to black holes, naked singularities, and gravity and electromagnetic fields.

Charged black holes in quartic quasi-topological gravity

NASA Astrophysics Data System (ADS)

Ghanaatian, M.; Naeimipour, F.; Bazrafshan, A.; Abkar, M.

2018-05-01

In this paper, we construct exact solutions of charged black holes in the presence of quartic quasi-topological gravity. We obtain thermodynamics and conserved quantities of the solutions and check the first law of thermodynamics. In studying the physical properties of the solutions, we consider anti-de Sitter, de Sitter, and flat solutions of charged black holes in quartic quasi-topological gravity and compare them with Einstein and third-order quasi-topological gravities. We also investigate the thermal stability of the solutions and show that thermal stability is just for anti-de Sitter solutions, not for de Sitter and flat ones.

Exact Solutions in Three-Dimensional Gravity

NASA Astrophysics Data System (ADS)

García-Díaz, Alberto A.

2017-09-01

Preface; 1. Introduction; 2. Point particles; 3. Dust solutions; 4. AdS cyclic symmetric stationary solutions; 5. Perfect fluid static stars; 6. Static perfect fluid stars with Λ; 7. Hydrodynamic equilibrium; 8. Stationary perfect fluid with Λ; 9. Friedmann–Robertson–Walker cosmologies; 10. Dilaton-inflaton FRW cosmologies; 11. Einstein–Maxwell solutions; 12. Nonlinear electrodynamics black hole; 13. Dilaton minimally coupled to gravity; 14. Dilaton non-minimally coupled to gravity; 15. Low energy 2+1 string gravity; 16. Topologically massive gravity; 17. Bianchi type spacetimes in TMG; 18. Petrov type N wave metrics; 19. Kundt spacetimes in TMG; 20. Cotton tensor in Riemannian spacetimes; References; Index.

The JPL Mars gravity field, Mars50c, based upon Viking and Mariner 9 Doppler tracking data

NASA Technical Reports Server (NTRS)

Konopliv, Alexander S.; Sjogren, William L.

1995-01-01

This report summarizes the current JPL efforts of generating a Mars gravity field from Viking 1 and 2 and Mariner 9 Doppler tracking data. The Mars 50c solution is a complete gravity field to degree and order 50 with solutions as well for the gravitational mass of Mars, Phobos, and Deimos. The constants and models used to obtain the solution are given and the method for determining the gravity field is presented. The gravity field is compared to the best current gravity GMM1 of Goddard Space Flight Center.

Exact solutions to quadratic gravity

NASA Astrophysics Data System (ADS)

Pravda, V.; Pravdová, A.; Podolský, J.; Švarc, R.

2017-04-01

Since all Einstein spacetimes are vacuum solutions to quadratic gravity in four dimensions, in this paper we study various aspects of non-Einstein vacuum solutions to this theory. Most such known solutions are of traceless Ricci and Petrov type N with a constant Ricci scalar. Thus we assume the Ricci scalar to be constant which leads to a substantial simplification of the field equations. We prove that a vacuum solution to quadratic gravity with traceless Ricci tensor of type N and aligned Weyl tensor of any Petrov type is necessarily a Kundt spacetime. This will considerably simplify the search for new non-Einstein solutions. Similarly, a vacuum solution to quadratic gravity with traceless Ricci type III and aligned Weyl tensor of Petrov type II or more special is again necessarily a Kundt spacetime. Then we study the general role of conformal transformations in constructing vacuum solutions to quadratic gravity. We find that such solutions can be obtained by solving one nonlinear partial differential equation for a conformal factor on any Einstein spacetime or, more generally, on any background with vanishing Bach tensor. In particular, we show that all geometries conformal to Kundt are either Kundt or Robinson-Trautman, and we provide some explicit Kundt and Robinson-Trautman solutions to quadratic gravity by solving the above mentioned equation on certain Kundt backgrounds.

Boundary stress tensor and asymptotically AdS3 non-Einstein spaces at the chiral point

NASA Astrophysics Data System (ADS)

Giribet, Gaston; Goya, Andrés; Leston, Mauricio

2011-09-01

Chiral gravity admits asymptotically AdS3 solutions that are not locally equivalent to AdS3; meaning that solutions do exist which, while obeying the strong boundary conditions usually imposed in general relativity, happen not to be Einstein spaces. In topologically massive gravity (TMG), the existence of non-Einstein solutions is particularly connected to the question about the role played by complex saddle points in the Euclidean path integral. Consequently, studying (the existence of) nonlocally AdS3 solutions to chiral gravity is relevant to understanding the quantum theory. Here, we discuss a special family of nonlocally AdS3 solutions to chiral gravity. In particular, we show that such solutions persist when one deforms the theory by adding the higher-curvature terms of the so-called new massive gravity. Moreover, the addition of higher-curvature terms to the gravity action introduces new nonlocally AdS3 solutions that have no analogues in TMG. Both stationary and time-dependent, axially symmetric solutions that asymptote AdS3 space without being locally equivalent to it appear. Defining the boundary stress tensor for the full theory, we show that these non-Einstein geometries have associated vanishing conserved charges.

Schwarzschild solution from Weyl transverse gravity

NASA Astrophysics Data System (ADS)

Oda, Ichiro

2017-01-01

We study classical solutions in the Weyl-transverse (WTDiff) gravity. The WTDiff gravity is invariant under both the local Weyl (conformal) transformation and the volume preserving diffeomorphisms (Diff) (transverse diffeomorphisms (TDiff)) and is known to be equivalent to general relativity at least at the classical level. In particular, we find that in a general spacetime dimension, the Schwarzschild metric is a classical solution in the WTDiff gravity when it is expressed in the Cartesian coordinate system.

Generalized Vaidya solutions and Misner-Sharp mass for n -dimensional massive gravity

NASA Astrophysics Data System (ADS)

Hu, Ya-Peng; Wu, Xin-Meng; Zhang, Hongsheng

2017-04-01

Dynamical solutions are always of interest to people in gravity theories. We derive a series of generalized Vaidya solutions in the n -dimensional de Rham-Gabadadze-Tolley massive gravity with a singular reference metric. Similar to the case of the Einstein gravity, the generalized Vaidya solution can describe shining/absorbing stars. Moreover, we also find a more general Vaidya-like solution by introducing a more generic matter field than the pure radiation in the original Vaidya spacetime. As a result, the above generalized Vaidya solution is naturally included in this Vaidya-like solution as a special case. We investigate the thermodynamics for this Vaidya-like spacetime by using the unified first law and present the generalized Misner-Sharp mass. Our results show that the generalized Minser-Sharp mass does exist in this spacetime. In addition, the usual Clausius relation δ Q =T d S holds on the apparent horizon, which implicates that the massive gravity is in a thermodynamic equilibrium state. We find that the work density vanishes for the generalized Vaidya solution, while it appears in the more general Vaidya-like solution. Furthermore, the covariant generalized Minser-Sharp mass in the n -dimensional de Rham-Gabadadze-Tolley massive gravity is also derived by taking a general metric ansatz into account.

EGSIEM: Combination of GRACE monthly gravity models on normal equation level

NASA Astrophysics Data System (ADS)

Meyer, Ulrich; Jean, Yoomin; Jäggi, Adrian; Mayer-Gürr, Torsten; Neumayer, Hans; Lemoine, Jean-Michel

2016-04-01

One of the three geodetic services to be realized in the frame of the EGSIEM project is a scientific combination service. Each associated processing center (AC) will follow a set of common processing standards but will apply its own, independent analysis method. Therefore the quality, robustness and reliability of the combined monthly gravity fields is expected to improve significantly compared to the individual solutions. The Monthly GRACE gravity fields of all ACs are combined on normal equation level. The individual normal equations are weighted depending on pairwise comparisons of the individual gravity field solutions. To derive these weights and for quality control of the individual contributions first a combination of the monthly gravity fields on solution level is performed. The concept of weighting and of the combination on normal equation level is introduced and the formats used for normal equation exchange and gravity field solutions is described. First results of the combination on normal equation level are presented and compared to the corresponding combinations on solution level. EGSIEM has an open data policy and all processing centers of GRACE gravity fields are invited to participate in the combination.

Designing of Multibody Gravity Assist Tours in Jovian System for the Satellite Landing

NASA Astrophysics Data System (ADS)

Grushevskii, Alexey; Koryanov, Victor; Tuchin, Andrey; Golubev, Yury

Space missions inside Jovian system are not possible without multiple gravity assists in modern times. The orbit design for real upcoming very complicated missions by NASA, ESA, RSA should be adaptive to mission parameters, such as: the time of system arrival, incomplete information about ephemeris of Galilean Moons and their gravitational fields, errors of flybys implementation. Limited dynamic capabilities, taking place in case of maneuvering around Jupiter's moons, demand multiple encounters (about 15-30 times) for these purposes. Mission design is complicated due to requirements of the Ganymede Orbit Insertion (GOI) ("JUICE" ESA) and also Ganymede Landing implementation ("Laplas-P" RSA [1]) comparing to the ordinary early “velocity gain" missions since “Pioneers” and "Voyagers”. Thus such scenario splits in two parts. Part 1(P1), as usually, would be used to reduce the spacecraft’s orbital energy with respect to Jupiter and set up the conditions for more frequent flybys. Part 2(P2) would be used to lower the spacecraft’s Ganymede relative velocity to set up the correct conditions for the GOI. The technique of P1 implementation is well known: it is the sequence of resonant same-body transfers “from Ganymede to Ganymede”(the solution based on the Lambert solution technique). But the P2 implementation couldn’t be the same (in requirements of quasi ballistic gravity assist with low cost propellant consumption). The cause is the invariance of Tisserand’s parameter in a circular restricted three-body system (CR3BP) [2]. Therefore it is impossible to change the magnitude of the V∞ velocity vector of the spacecraft with respect to the Ganymede. Furthermore, the same body flybys sequence on the Tisserand-Poincare (T-P) graph [2] falls according the V∞-isoline to the “Extra Radiation” zone with low altitude pericenter of spacecraft’s orbit. So regular expensive corrections of pericenter’s height increasing are demanding in this case. But the other implementation of P2 can be used. They are- “crossed” gravity assists from one small body G(“Ganymede”) to the second small body NG(“Not Ganymede”, generally for a not big TID it is Callisto) and then - in the opposite direction. We can “to outwit” the Tisserand’s criterion like this. It allows us to build special effective “phase beam”(PB) methods of orbit design synthesis for landing space mission in classes of encounter sequences-disjunctions G-NG-G (or modified G-…-G-NG-…-NG-G-…). As the result, the idea of adaptive synthesis of mission design was constructed by authors. Then it was implemented by effective algorithm. The corresponding numerical scheme was developed with using Tisserand-Poincare graph and the simulation of hundreds of thousands of options formation of the calculation. The DeltaV-low cost searching was utilized also for trajectory design with help of multiple rebounds of phase beams modeling. REFERENCES 1. Golubev Yu.F., Grushevskii A.V., Koryanov V.V., Tuchin A.G. A Method of Orbits Designing Using Gravity Assist Maneuvers To The Landing on the Jovian’s Moons // International Colloquium and Workshop Ganymede Lander: scientific goals and experiments, Moscow, March 4-8, 2013. URL: http://glcw2013.cosmos.ru/presentations 2. Campagnola S., Russell R.P. Endgame Problem. Part 2: Multi-Body Technique and TP Graph // Journal of Guidance, Control, and Dynamics, Vol. 33, No. 2, 2010, pp. 476-486, doi:10.2514/1.44290

Simulation study on combination of GRACE monthly gravity field solutions

NASA Astrophysics Data System (ADS)

Jean, Yoomin; Meyer, Ulrich; Jäggi, Adrian

2016-04-01

The GRACE monthly gravity fields from different processing centers are combined in the frame of the project EGSIEM. This combination is done on solution level first to define weights which will be used for a combination on normal equation level. The applied weights are based on the deviation of the individual gravity fields from the arithmetic mean of all involved gravity fields. This kind of weighting scheme relies on the assumption that the true gravity field is close to the arithmetic mean of the involved individual gravity fields. However, the arithmetic mean can be affected by systematic errors in individual gravity fields, which consequently results in inappropriate weights. For the future operational scientific combination service of GRACE monthly gravity fields, it is necessary to examine the validity of the weighting scheme also in possible extreme cases. To investigate this, we make a simulation study on the combination of gravity fields. Firstly, we show how a deviated gravity field can affect the combined solution in terms of signal and noise in the spatial domain. We also show the impact of systematic errors in individual gravity fields on the resulting combined solution. Then, we investigate whether the weighting scheme still works in the presence of outliers. The result of this simulation study will be useful to understand and validate the weighting scheme applied to the combination of the monthly gravity fields.

de Sitter and power-law solutions in some models of modified gravity

NASA Astrophysics Data System (ADS)

Zhong, Yi; Elizalde, Emilio

2016-11-01

Inspired by some recent works of Lovelock Brans-Dicke (BD) gravity and mimetic gravity, cosmology solutions in extensions of these two modified gravities are investigated. A nonlocal term is added to the Lovelock BD action and Gauss-Bonnet (GB) terms to the mimetic action, correspondingly. de Sitter and power scale factor solutions are then obtained in both theories. They can provide natural new approaches to a more accurate description of the unverse evolution.

Adjoint Sensitivity Analysis of Orbital Mechanics: Application to Computations of Observables' Partials with Respect to Harmonics of the Planetary Gravity Fields

NASA Technical Reports Server (NTRS)

Ustinov, Eugene A.; Sunseri, Richard F.

2005-01-01

An approach is presented to the inversion of gravity fields based on evaluation of partials of observables with respect to gravity harmonics using the solution of adjoint problem of orbital dynamics of the spacecraft. Corresponding adjoint operator is derived directly from the linear operator of the linearized forward problem of orbital dynamics. The resulting adjoint problem is similar to the forward problem and can be solved by the same methods. For given highest degree N of gravity harmonics desired, this method involves integration of N adjoint solutions as compared to integration of N2 partials of the forward solution with respect to gravity harmonics in the conventional approach. Thus, for higher resolution gravity models, this approach becomes increasingly more effective in terms of computer resources as compared to the approach based on the solution of the forward problem of orbital dynamics.

Solar Probe Plus: Mission design challenges and trades

NASA Astrophysics Data System (ADS)

Guo, Yanping

2010-11-01

NASA plans to launch the first mission to the Sun, named Solar Probe Plus, as early as 2015, after a comprehensive feasibility study that significantly changed the original Solar Probe mission concept. The original Solar Probe mission concept, based on a Jupiter gravity assist trajectory, was no longer feasible under the new guidelines given to the mission. A complete redesign of the mission was required, which called for developing alternative trajectories that excluded a flyby of Jupiter. Without the very powerful gravity assist from Jupiter it was extremely difficult to get to the Sun, so designing a trajectory to reach the Sun that is technically feasible under the new mission guidelines became a key enabler to this highly challenging mission. Mission design requirements and challenges unique to this mission are reviewed and discussed, including various mission scenarios and six different trajectory designs utilizing various planetary gravity assists that were considered. The V 5GA trajectory design using five Venus gravity assists achieves a perihelion of 11.8 solar radii ( RS) in 3.3 years without any deep space maneuver (DSM). The V 7GA trajectory design reaches a perihelion of 9.5 RS using seven Venus gravity assists in 6.39 years without any DSM. With nine Venus gravity assists, the V 9GA trajectory design shows a solar orbit at inclination as high as 37.9° from the ecliptic plane can be achieved with the time of flight of 5.8 years. Using combined Earth and Venus gravity assists, as close as 9 RS from the Sun can be achieved in less than 10 years of flight time at moderate launch C3. Ultimately the V 7GA trajectory was chosen as the new baseline mission trajectory. Its design allowing for science investigation right after launch and continuing for nearly 7 years is unprecedented for interplanetary missions. The redesigned Solar Probe Plus mission is not only feasible under the new guidelines but also significantly outperforms the original mission concept in both technical implementation and scientific returns.

Near real-time GRACE gravity field solutions for hydrological monitoring applications

NASA Astrophysics Data System (ADS)

Kvas, Andreas; Gouweleeuw, Ben; Mayer-Gürr, Torsten; Güntner, Andreas

2016-04-01

Within the EGSIEM (European Gravity Service for Improved Emergency Management) project, a demonstrator for a near real-time (NRT) gravity field service which provides daily GRACE gravity field solutions will be established. Compared to the official GRACE gravity products, these NRT solutions will increase the temporal resolution from one month to one day and reduce the latency from currently two months to five days. This fast availability allows the monitoring of total water storage variations and of hydrological extreme events as they occur, in contrast to a 'confirmation after occurrence' as is the situation today. The service will be jointly run by GFZ (German Research Centre for Geosciences) and Graz University of Technology, with each analysis center providing an independent solution. A Kalman filter framework, in which GRACE data is combined with prior information, serves as basis for the gravity field recovery in order to increase the redundancy of the gravity field estimates. The on-line nature of the NRT service necessitates a tailored smoothing algorithm as opposed to post-processing applications, where forward-backward smoothing can be applied. This contribution gives an overview on the near real-time processing chain and highlights differences between the computed NRT solutions and the standard GRACE products. We discuss the special characteristics of the Kalman filtered gravity field models as well as derived products and give an estimate of the expected error levels. Additionally, we show the added value of the NRT solutions through comparison of the first results of the pre-operational phase with in-situ data and monthly GRACE gravity field models.

NASA’s New “Gravity Assist” Podcast Debuts Nov. 15

NASA Image and Video Library

2017-10-27

Join us November 15 for the debut of the new NASA podcast, “Gravity Assist,” hosted by Dr. Jim Green, NASA’s director of planetary science. Gravity Assist is a virtual tour of the solar system and beyond with the top scientists in the world as your guides. The weekly podcast kicks off with a special 10-part series on the solar system that begins with the Sun, and takes you outward to Pluto and beyond.

Intercomparison and Assessment of GRACE Temporal Gravity Solutions Performance

NASA Astrophysics Data System (ADS)

Choe, J.; Nerem, R. S.; Leuliette, E. W.

2006-12-01

The GRACE mission has been producing monthly estimates of changes in the Earth's gravity field since April 2002. Converting the raw GRACE range, accelerometer, and GPS measurements into estimates of the gravity field is a complex process, and therefore different analysis groups use various "recipes" resulting in different models of the time-varying gravity field. We have intercompared the solutions generated by a number of groups: Center for Space Research (CSR), Jet Propulsion Laboratory (JPL), Goddard Space Flight Center (GSFC), Centre National d'Etudes Spatiales (CNES) and GeoForschungsZentrum (GFZ), to determine the characteristics of each group's solutions as applied to different scientific applications. For different scales of gaussian smoothing, we have examined the power spectrum of each model, the pattern of seasonal gravity variations, the residuals from a seasonal fit, and results from locations in the Sahara desert and Atlantic Ocean where the signals are known to be small. We have also characterized the level of "striping" in each center's solutions. In addition, we have compared each center's solutions for changes in Greenland and Antarctic ice mass, global ocean mass, and hydrologic changes over the continents. Using these tests and evaluations, we have been able to characterize the performance of each center's gravity solutions.

Quasilocal energy for three-dimensional massive gravity solutions with chiral deformations of AdS{sub 3} boundary conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garbarz, Alan, E-mail: alan-at@df.uba.ar; Giribet, Gaston, E-mail: gaston-at@df.uba.ar, E-mail: af.goya-at@df.uba.ar; Goya, Andrés, E-mail: gaston-at@df.uba.ar, E-mail: af.goya-at@df.uba.ar

2015-03-26

We consider critical gravity in three dimensions; that is, the New Massive Gravity theory formulated about Anti-de Sitter (AdS) space with the specific value of the graviton mass for which it results dual to a two-dimensional conformai field theory with vanishing central charge. As it happens with Kerr black holes in four-dimensional critical gravity, in three-dimensional critical gravity the Bañados-Teitelboim-Zanelli black holes have vanishing mass and vanishing angular momentum. However, provided suitable asymptotic conditions are chosen, the theory may also admit solutions carrying non-vanishing charges. Here, we give simple examples of exact solutions that exhibit falling-off conditions that are evenmore » weaker than those of the so-called Log-gravity. For such solutions, we define the quasilocal stress-tensor and use it to compute conserved charges. Despite the drastic deformation of AdS{sub 3} asymptotic, these solutions have finite mass and angular momentum, which are shown to be non-zero.« less

Plane Symmetric Solutions in f(G) Gravity

NASA Astrophysics Data System (ADS)

Shamir, M. Farasat; Saeed, Atrooba

2017-12-01

The purpose of this document is to investigate the universe in f(G) gravity. A wgeneral static plane symmetric space-time is chosen and exact solutions are explored using a viable f(G) gravity model. In particular, power and exponential law solutions are discussed. In addition, the physical relevance of the solutions with Taub's metric and anti-deSitter space-time is shown. Graphical analysis of energy density and pressure of the universe is done to substantiate the study.

Pressure Profiles in a Loop Heat Pipe Under Gravity Influence

NASA Technical Reports Server (NTRS)

Ku, Jentung

2015-01-01

During the operation of a loop heat pipe (LHP), the viscous flow induces pressure drops in various elements of the loop. The total pressure drop is equal to the sum of pressure drops in vapor grooves, vapor line, condenser, liquid line and primary wick, and is sustained by menisci at liquid and vapor interfaces on the outer surface of the primary wick in the evaporator. The menisci will curve naturally so that the resulting capillary pressure matches the total pressure drop. In ground testing, an additional gravitational pressure head may be present and must be included in the total pressure drop when LHP components are placed in a non-planar configuration. Under gravity-neutral and anti-gravity conditions, the fluid circulation in the LHP is driven solely by the capillary force. With gravity assist, however, the flow circulation can be driven by the combination of capillary and gravitational forces, or by the gravitational force alone. For a gravity-assist LHP at a given elevation between the horizontal condenser and evaporator, there exists a threshold heat load below which the LHP operation is gravity driven and above which the LHP operation is capillary force and gravity co-driven. The gravitational pressure head can have profound effects on the LHP operation, and such effects depend on the elevation, evaporator heat load, and condenser sink temperature. This paper presents a theoretical study on LHP operations under gravity neutral, anti-gravity, and gravity-assist modes using pressure diagrams to help understand the underlying physical processes. Effects of the condenser configuration on the gravitational pressure head and LHP operation are also discussed.

Pressure Profiles in a Loop Heat Pipe under Gravity Influence

NASA Technical Reports Server (NTRS)

Ku, Jentung

2015-01-01

During the operation of a loop heat pipe (LHP), the viscous flow induces pressure drops in various elements of the loop. The total pressure drop is equal to the sum of pressure drops in vapor grooves, vapor line, condenser, liquid line and primary wick, and is sustained by menisci at liquid and vapor interfaces on the outer surface of the primary wick in the evaporator. The menisci will curve naturally so that the resulting capillary pressure matches the total pressure drop. In ground testing, an additional gravitational pressure head may be present and must be included in the total pressure drop when LHP components are placed in a non-planar configuration. Under gravity-neutral and anti-gravity conditions, the fluid circulation in the LHP is driven solely by the capillary force. With gravity assist, however, the flow circulation can be driven by the combination of capillary and gravitational forces, or by the gravitational force alone. For a gravity-assist LHP at a given elevation between the horizontal condenser and evaporator, there exists a threshold heat load below which the LHP operation is gravity driven and above which the LHP operation is capillary force and gravity co-driven. The gravitational pressure head can have profound effects on the LHP operation, and such effects depend on the elevation, evaporator heat load, and condenser sink temperature. This paper presents a theoretical study on LHP operations under gravity-neutral, anti-gravity, and gravity-assist modes using pressure diagrams to help understand the underlying physical processes. Effects of the condenser configuration on the gravitational pressure head and LHP operation are also discussed.

General Relativity solutions in modified gravity

NASA Astrophysics Data System (ADS)

Motohashi, Hayato; Minamitsuji, Masato

2018-06-01

Recent gravitational wave observations of binary black hole mergers and a binary neutron star merger by LIGO and Virgo Collaborations associated with its optical counterpart constrain deviation from General Relativity (GR) both on strong-field regime and cosmological scales with high accuracy, and further strong constraints are expected by near-future observations. Thus, it is important to identify theories of modified gravity that intrinsically possess the same solutions as in GR among a huge number of theories. We clarify the three conditions for theories of modified gravity to allow GR solutions, i.e., solutions with the metric satisfying the Einstein equations in GR and the constant profile of the scalar fields. Our analysis is quite general, as it applies a wide class of single-/multi-field scalar-tensor theories of modified gravity in the presence of matter component, and any spacetime geometry including cosmological background as well as spacetime around black hole and neutron star, for the latter of which these conditions provide a necessary condition for no-hair theorem. The three conditions will be useful for further constraints on modified gravity theories as they classify general theories of modified gravity into three classes, each of which possesses i) unique GR solutions (i.e., no-hair cases), ii) only hairy solutions (except the cases that GR solutions are realized by cancellation between singular coupling functions in the Euler-Lagrange equations), and iii) both GR and hairy solutions, for the last of which one of the two solutions may be selected dynamically.

Gravity Gradient Tensor of Arbitrary 3D Polyhedral Bodies with up to Third-Order Polynomial Horizontal and Vertical Mass Contrasts

NASA Astrophysics Data System (ADS)

Ren, Zhengyong; Zhong, Yiyuan; Chen, Chaojian; Tang, Jingtian; Kalscheuer, Thomas; Maurer, Hansruedi; Li, Yang

2018-03-01

During the last 20 years, geophysicists have developed great interest in using gravity gradient tensor signals to study bodies of anomalous density in the Earth. Deriving exact solutions of the gravity gradient tensor signals has become a dominating task in exploration geophysics or geodetic fields. In this study, we developed a compact and simple framework to derive exact solutions of gravity gradient tensor measurements for polyhedral bodies, in which the density contrast is represented by a general polynomial function. The polynomial mass contrast can continuously vary in both horizontal and vertical directions. In our framework, the original three-dimensional volume integral of gravity gradient tensor signals is transformed into a set of one-dimensional line integrals along edges of the polyhedral body by sequentially invoking the volume and surface gradient (divergence) theorems. In terms of an orthogonal local coordinate system defined on these edges, exact solutions are derived for these line integrals. We successfully derived a set of unified exact solutions of gravity gradient tensors for constant, linear, quadratic and cubic polynomial orders. The exact solutions for constant and linear cases cover all previously published vertex-type exact solutions of the gravity gradient tensor for a polygonal body, though the associated algorithms may differ in numerical stability. In addition, to our best knowledge, it is the first time that exact solutions of gravity gradient tensor signals are derived for a polyhedral body with a polynomial mass contrast of order higher than one (that is quadratic and cubic orders). Three synthetic models (a prismatic body with depth-dependent density contrasts, an irregular polyhedron with linear density contrast and a tetrahedral body with horizontally and vertically varying density contrasts) are used to verify the correctness and the efficiency of our newly developed closed-form solutions. Excellent agreements are obtained between our solutions and other published exact solutions. In addition, stability tests are performed to demonstrate that our exact solutions can safely be used to detect shallow subsurface targets.

Daily GRACE gravity field solutions track major flood events in the Ganges-Brahmaputra Delta

NASA Astrophysics Data System (ADS)

Gouweleeuw, Ben T.; Kvas, Andreas; Gruber, Christian; Gain, Animesh K.; Mayer-Gürr, Thorsten; Flechtner, Frank; Güntner, Andreas

2018-05-01

Two daily gravity field solutions based on observations from the Gravity Recovery and Climate Experiment (GRACE) satellite mission are evaluated against daily river runoff data for major flood events in the Ganges-Brahmaputra Delta (GBD) in 2004 and 2007. The trends over periods of a few days of the daily GRACE data reflect temporal variations in daily river runoff during major flood events. This is especially true for the larger flood in 2007, which featured two distinct periods of critical flood level exceedance in the Brahmaputra River. This first hydrological evaluation of daily GRACE gravity field solutions based on a Kalman filter approach confirms their potential for gravity-based large-scale flood monitoring. This particularly applies to short-lived, high-volume floods, as they occur in the GBD with a 4-5-year return period. The release of daily GRACE gravity field solutions in near-real time may enable flood monitoring for large events.

Looking for empty topological wormhole spacetimes in F(R)-modified gravity

NASA Astrophysics Data System (ADS)

Di Criscienzo, R.; Myrzakulov, R.; Sebastiani, L.

2013-12-01

Much attention has been recently devoted to modified theories of gravity, the simplest models of which overcome General Relativity simply by replacing R with F(R) in the Einstein-Hilbert action. Unfortunately, such models typically lack most of the beautiful solutions discovered in Einstein’s gravity. Nonetheless, in F(R) gravity, it has been possible to get at least few black holes, but still we do not know any empty wormhole-like spacetime solution. This paper aims to explain why it is so hard to get such solutions (given that they exist!). Few solutions are derived in the simplest cases, while only an implicit form has been obtained in the non-trivial case.

Low energy trajectories to Mars via gravity assist from Venus to earth

NASA Technical Reports Server (NTRS)

Williams, S. N.; Longuski, J. M.

1991-01-01

The analytical determination of launch dates and proposed trajectories is reviewed with respect to the search for a low-energy trajectory to Mars with gravitational assist from Venus for the years 1995-2024. Both Ballistic and Venus-Earth gravity assist (VEGA) trajectories are calculated with an automated design tool by the authors (1990). The trajectories are modeled as conic sections from one gravitating body to the next, and gravity assist is considered to act impulsively. VEGA trajectories to Mars require similar launch energies for 6 years listed and have moderate arrival C3s, with the lowest C3 requirement in 2015. The flight time and arrival energies of the trajectories are found to be larger than those of ballistic trajectories, but the low-energy launch window makes them desirable for unmanned Mars missions, in particular.

Trajectory design for a rendezvous mission to Earth's Trojan asteroid 2010 TK7

NASA Astrophysics Data System (ADS)

Lei, Hanlun; Xu, Bo; Zhang, Lei

2017-12-01

In this paper a rendezvous mission to the Earth's Trojan asteroid 2010 TK7 is proposed, and preliminary transfer trajectories are designed. Due to the high inclination (∼ 20.9°) of the target asteroid relative to the ecliptic plane, direct transfers usually require large amounts of fuel consumption, which is beyond the capacity of current technology. As gravity assist technique could effectively change the inclination of spacecraft's trajectory, it is adopted to reduce the launch energy and rendezvous velocity maneuver. In practical computation, impulsive and low-thrust, gravity-assisted trajectories are considered. Among all the trajectories computed, the low-thrust gravity-assisted trajectory with Venus-Earth-Venus (V-E-V) swingby sequence performs the best in terms of propellant mass. For a spacecraft with initial mass of 800 kg , propellant mass of the best trajectory is 36.74 kg . Numerical results indicate that both the impulsive and low-thrust, gravity-assisted trajectories corresponding to V-E-V sequence could satisfy mission constraints, and can be applied to practical rendezvous mission.

On the Liouville 2D dilaton gravity models with sinh-Gordon matter

NASA Astrophysics Data System (ADS)

Frolov, Valeri P.; Zelnikov, Andrei

2018-02-01

We study 1 + 1 dimensional dilaton gravity models which take into account backreaction of the sinh-Gordon matter field. We found a wide class of exact solutions which generalizes black hole solutions of the Jackiw-Teitelboim gravity model and its hyperbolic deformation.

Global Mass Flux Solutions from GRACE: A Comparison of Parameter Estimation Strategies - Mass Concentrations Versus Stokes Coefficients

NASA Technical Reports Server (NTRS)

Rowlands, D. D.; Luthcke, S. B.; McCarthy J. J.; Klosko, S. M.; Chinn, D. S.; Lemoine, F. G.; Boy, J.-P.; Sabaka, T. J.

2010-01-01

The differences between mass concentration (mas con) parameters and standard Stokes coefficient parameters in the recovery of gravity infonnation from gravity recovery and climate experiment (GRACE) intersatellite K-band range rate data are investigated. First, mascons are decomposed into their Stokes coefficient representations to gauge the range of solutions available using each of the two types of parameters. Next, a direct comparison is made between two time series of unconstrained gravity solutions, one based on a set of global equal area mascon parameters (equivalent to 4deg x 4deg at the equator), and the other based on standard Stokes coefficients with each time series using the same fundamental processing of the GRACE tracking data. It is shown that in unconstrained solutions, the type of gravity parameter being estimated does not qualitatively affect the estimated gravity field. It is also shown that many of the differences in mass flux derivations from GRACE gravity solutions arise from the type of smoothing being used and that the type of smoothing that can be embedded in mas con solutions has distinct advantages over postsolution smoothing. Finally, a 1 year time series based on global 2deg equal area mascons estimated every 10 days is presented.

Low-thrust trajectory optimization in a full ephemeris model

NASA Astrophysics Data System (ADS)

Cai, Xing-Shan; Chen, Yang; Li, Jun-Feng

2014-10-01

The low-thrust trajectory optimization with complicated constraints must be considered in practical engineering. In most literature, this problem is simplified into a two-body model in which the spacecraft is subject to the gravitational force at the center of mass and the spacecraft's own electric propulsion only, and the gravity assist (GA) is modeled as an instantaneous velocity increment. This paper presents a method to solve the fuel-optimal problem of low-thrust trajectory with complicated constraints in a full ephemeris model, which is closer to practical engineering conditions. First, it introduces various perturbations, including a third body's gravity, the nonspherical perturbation and the solar radiation pressure in a dynamic equation. Second, it builds two types of equivalent inner constraints to describe the GA. At the same time, the present paper applies a series of techniques, such as a homotopic approach, to enhance the possibility of convergence of the global optimal solution.

Unattainable extended spacetime regions in conformal gravity

NASA Astrophysics Data System (ADS)

Chakrabarty, Hrishikesh; Benavides-Gallego, Carlos A.; Bambi, Cosimo; Modesto, Leonardo

2018-03-01

The Janis-Newman-Winicour metric is a solution of Einstein's gravity minimally coupled to a real massless scalar field. The γ-metric is instead a vacuum solution of Einstein's gravity. Both spacetimes have no horizon and possess a naked singularity at a finite value of the radial coordinate, where curvature invariants diverge and the spacetimes are geodetically incomplete. In this paper, we reconsider these solutions in the framework of conformal gravity and we show that it is possible to solve the spacetime singularities with a suitable choice of the conformal factor. Now curvature invariants remain finite over the whole spacetime. Massive particles never reach the previous singular surface and massless particles can never do it with a finite value of their affine parameter. Our results support the conjecture according to which conformal gravity can fix the singularity problem that plagues Einstein's gravity.

Analytic solutions for Long's equation and its generalization

NASA Astrophysics Data System (ADS)

Humi, Mayer

2017-12-01

Two-dimensional, steady-state, stratified, isothermal atmospheric flow over topography is governed by Long's equation. Numerical solutions of this equation were derived and used by several authors. In particular, these solutions were applied extensively to analyze the experimental observations of gravity waves. In the first part of this paper we derive an extension of this equation to non-isothermal flows. Then we devise a transformation that simplifies this equation. We show that this simplified equation admits solitonic-type solutions in addition to regular gravity waves. These new analytical solutions provide new insights into the propagation and amplitude of gravity waves over topography.

Gravity-assist trajectories to Venus, Mars, and the ice giants: Mission design with human and robotic applications

NASA Astrophysics Data System (ADS)

Hughes, Kyle M.

Gravity-assist trajectories to Uranus and Neptune are found (with the allowance of impulsive maneuvers using chemical propulsion) for launch dates ranging from 2024 to 2038 for Uranus and 2020 to 2070 for Neptune. Solutions are found using a patched conic model with analytical ephemeris via the Satellite Tour Design Program (STOUR), originally developed at the Jet Propulsion Laboratory (JPL). Delivered payload mass is computed for all solutions for select launch vehicles, and attractive solutions are identified as those that deliver a specified amount of payload mass into orbit at the target body in minimum time. The best cases for each launch year are cataloged for orbiter missions to Uranus and Neptune. Solutions with sufficient delivered payload for a multi-planet mission (e.g. sending a probe to Saturn on the way to delivering an orbiter at Uranus) become available when the Space Launch System (SLS) launch vehicle is employed. A set of possible approach trajectories are modeled at the target planet to assess what (if any) adjustments are needed for ring avoidance, and to determine the probe entry conditions. Mars free-return trajectories are found with an emphasis on short flight times for application to near-term human flyby missions (similar to that of Inspiration Mars). Venus free-returns are also investigated and proposed as an alternative to a human Mars flyby mission. Attractive Earth-Mars free-return opportunities are identified that use an intermediate Venus flyby. One such opportunity, in 2021, has been adopted by the Inspiration Mars Foundation as a backup to the currently considered 2018 Mars free-return opportunity. Methods to establish spacecraft into Earth-Mars cycler trajectories are also investigated to reduce the propellant cost required to inject a 95-metric ton spacecraft into a cycler orbit. The establishment trajectories considered use either a V-infinity leveraging maneuver or low thrust. The V-infinity leveraging establishment trajectories are validated using patched conics via the STOUR program. Establishment trajectories that use low-thrust were investigated with particular focus on validating the patched-conic based solutions at instances where Earth encounter times are not negligible.

On estimating gravity anomalies - A comparison of least squares collocation with conventional least squares techniques

NASA Technical Reports Server (NTRS)

Argentiero, P.; Lowrey, B.

1977-01-01

The least squares collocation algorithm for estimating gravity anomalies from geodetic data is shown to be an application of the well known regression equations which provide the mean and covariance of a random vector (gravity anomalies) given a realization of a correlated random vector (geodetic data). It is also shown that the collocation solution for gravity anomalies is equivalent to the conventional least-squares-Stokes' function solution when the conventional solution utilizes properly weighted zero a priori estimates. The mathematical and physical assumptions underlying the least squares collocation estimator are described.

On the feasibility of using satellite gravity observations for detecting large-scale solid mass transfer events

NASA Astrophysics Data System (ADS)

Peidou, Athina C.; Fotopoulos, Georgia; Pagiatakis, Spiros

2017-10-01

The main focus of this paper is to assess the feasibility of utilizing dedicated satellite gravity missions in order to detect large-scale solid mass transfer events (e.g. landslides). Specifically, a sensitivity analysis of Gravity Recovery and Climate Experiment (GRACE) gravity field solutions in conjunction with simulated case studies is employed to predict gravity changes due to past subaerial and submarine mass transfer events, namely the Agulhas slump in southeastern Africa and the Heart Mountain Landslide in northwestern Wyoming. The detectability of these events is evaluated by taking into account the expected noise level in the GRACE gravity field solutions and simulating their impact on the gravity field through forward modelling of the mass transfer. The spectral content of the estimated gravity changes induced by a simulated large-scale landslide event is estimated for the known spatial resolution of the GRACE observations using wavelet multiresolution analysis. The results indicate that both the Agulhas slump and the Heart Mountain Landslide could have been detected by GRACE, resulting in {\\vert }0.4{\\vert } and {\\vert }0.18{\\vert } mGal change on GRACE solutions, respectively. The suggested methodology is further extended to the case studies of the submarine landslide in Tohoku, Japan, and the Grand Banks landslide in Newfoundland, Canada. The detectability of these events using GRACE solutions is assessed through their impact on the gravity field.

Better Aircraft Positioning for Airborne Gravimetry: Results from GRAV-D's "Kinematic GPS Challenge" Issued to the GPS Community

NASA Astrophysics Data System (ADS)

Diehl, T. M.; Mader, G. L.; Preaux, S. A.; Weil, C.

2011-12-01

The National Geodetic Survey's (NGS's) Gravity for the Redefinition of the American Vertical Datum (GRAV-D) program plans to collect airborne gravity data across the entire U.S. and its holdings over the next decade. The goal is to build a geoid accurate to 1-2 cm, for which the airborne gravity data is key. The first phase is underway, with > 13% of data collection already completed across the U.S. To achieve the best airborne gravity data accuracy possible, the GPS position solutions must provide not just accurate positions, but also accurate velocities and accelerations to be used in calculating the gravity corrections. However, to our knowledge, no comparison has been done of available kinematic GPS processing techniques as they pertain to producing accurate airborne gravity results. So, in Fall 2010, NGS issued the "Kinematic GPS Challenge" to the GPS processing community, soliciting position solutions for GPS data of two GRAV-D airborne gravity flights done in Louisiana in 2008. Of the four lines on these two flights, one of the lines on the first flight was noisy (due to excessive turbulence) and was reflown on the second flight. These two flights of data allow the Challenge results to be tested on both good-quality and noisy data, as well as to be compared for repeatability along the reflown line, the assumption being that the solution producing the best fit between the reflown gravity data is the best. Fifteen position results from nine contributors were submitted from the GPS community for each of the two flights. We will present the results of the Kinematic GPS Challenge in an anonymous manner, to provide information to the airborne gravity community while protecting the identities of the GPS contributors while they incorporate the results into their research projects. Initial analyses show that the submitted position solutions are somewhat different, usually by +/- 0.25 m or less in X, Y, and Z. The shape and structure of these differences indicate significant differences in the derived velocities and accelerations. Those differences are easily identifiable in the gravity anomalies calculated with those solutions. Several gravity solutions computed produce differences from the ensemble average of 2-3 mGal in places, though most were within +/- 1 mGal. An additional comparison was done with the current preferred NGS GPS+IMU solution (a loosely-coupled differential GPS+IMU solution from commercial software) versus the Challenge GPS-only solutions. The loosely coupled solution fared better in the noisy flight than the GPS only, but there was less significant difference in the calm weather flight. Our presentation will provide a comprehensive analysis of the Challenge results.

(Compactified) black branes in four dimensional f(R)-gravity

NASA Astrophysics Data System (ADS)

Dimakis, N.; Giacomini, Alex; Paliathanasis, Andronikos

2018-02-01

A new family of analytical solutions in a four dimensional static spacetime is presented for f (R) -gravity. In contrast to General Relativity, we find that a non trivial black brane/string solution is supported in vacuum power law f (R) -gravity for appropriate values of the parameters characterizing the model and when axisymmetry is introduced in the line element. For the aforementioned solution, we perform a brief investigation over its basic thermodynamic quantities.

Noncommutative wormhole solutions in F(T, T𝒢) gravity

NASA Astrophysics Data System (ADS)

Sharif, M.; Nazir, Kanwal

2017-04-01

This paper is devoted to the study of static spherically symmetric wormhole solutions along with noncommutative geometry in the background of F(T, T𝒢) gravity. We assume a nonzero redshift function as well as two well-known models of this gravity and discuss the behavior of null/weak energy conditions graphically. We conclude that there does not exist any physically acceptable wormhole solution for the first model, but there is a chance to develop physically acceptable wormhole solution in a particular region for the second model.

Anisotropic cosmological solutions in R + R^2 gravity

NASA Astrophysics Data System (ADS)

Müller, Daniel; Ricciardone, Angelo; Starobinsky, Alexei A.; Toporensky, Aleksey

2018-04-01

In this paper we investigate the past evolution of an anisotropic Bianchi I universe in R+R^2 gravity. Using the dynamical system approach we show that there exists a new two-parameter set of solutions that includes both an isotropic "false radiation" solution and an anisotropic generalized Kasner solution, which is stable. We derive the analytic behavior of the shear from a specific property of f( R) gravity and the analytic asymptotic form of the Ricci scalar when approaching the initial singularity. Finally, we numerically check our results.

Testing the Dependence of Airborne Gravity Results on Three Variables in Kinematic GPS Processing

NASA Astrophysics Data System (ADS)

Weil, C.; Diehl, T. M.

2011-12-01

The National Geodetic Survey's Gravity for the Redefinition of the American Vertical Datum (GRAV-D) program plans to collect airborne gravity data across the entire U.S. and its holdings over the next decade. The goal is to build a geoid accurate to 1-2 cm, for which the airborne gravity data is key. The first phase is underway, with > 13% of data collection completed in: parts of Alaska, parts of California, most of the Gulf Coast, Puerto Rico, and the Virgin Islands. Obtaining accurate airborne gravity survey results depends on the quality of the GPS/IMU position solution used in the processing. There are many factors that could have an influence on the positioning results. First, we will investigate how an increased data sampling rate for the GPS/IMU affects the position solution and accelerations derived from those positions. Second we will test the hypothesis that, for differential kinematic processing a better solution is obtained using both a base and a rover GPS unit that contain an additional rubidium clock that is reported to sync better with GPS time. Finally, we will look at a few different GPS+IMU processing methods available in commercial software. This includes comparing GPS-only solutions with loosely coupled GPS/IMU solutions from the Applanix POSAV-510 system and tightly coupled solutions with our newly-acquired NovAtel SPAN system (micro-IRS IMU). Differential solutions are compared with PPP (Precise Point Positioning) solutions along with multi-pass and advanced tropospheric corrections available with the NovAtel Inertial Explorer software. Based on preliminary research, we expect that the tightly-coupled solutions with either better troposphere and/or multi-pass solutions will provide superior position (and gravity) results.

An overview and categorization of dynamic arm supports for people with decreased arm function.

PubMed

Van der Heide, Loek A; van Ninhuijs, Bob; Bergsma, Arjen; Gelderblom, Gert Jan; van der Pijl, Dick J; de Witte, Luc P

2014-08-01

Assistive devices that augment arm function were already introduced during the polio era. Devices are still being developed, but a review has not been performed thus far. To create an overview and categorize assistive devices facilitating arm function in activities of daily living for people with decreased arm function. Literature review. A systematic review in three scientific literature databases. Conference proceedings, assistive technology databases, and references were searched and experts consulted. This resulted in a database of dynamic arm supports. Product information was added, and the devices were categorized. A total of 104 dynamic arm supports were found. These could be categorized as nonactuated devices (N = 39), passively actuated devices (N = 24), actively actuated devices (N = 34), or devices using the functional electrical stimulation principle (N = 7). Functionality analysis resulted in second-level categorization: tremor suppression, facilitation of anti-gravity movement, and assistance of specific joint motion. All devices could be ordered in a categorization of low complexity. Many have been developed; most have disappeared and have been succeeded by similar devices. Limitations of the devices found mainly concern interfacing and the range of motion facilitated. Future devices could make use of whatever residual strength is available in the users' arm for control. The provided overview of devices in this article and the classification developed is relevant for practitioners seeking assistive solutions for their clients as it makes the range of developed solutions both accessible and comprehensible. © The International Society for Prosthetics and Orthotics 2013.

GRACE time-variable gravity field recovery using an improved energy balance approach

NASA Astrophysics Data System (ADS)

Shang, Kun; Guo, Junyi; Shum, C. K.; Dai, Chunli; Luo, Jia

2015-12-01

A new approach based on energy conservation principle for satellite gravimetry mission has been developed and yields more accurate estimation of in situ geopotential difference observables using K-band ranging (KBR) measurements from the Gravity Recovery and Climate Experiment (GRACE) twin-satellite mission. This new approach preserves more gravity information sensed by KBR range-rate measurements and reduces orbit error as compared to previous energy balance methods. Results from analysis of 11 yr of GRACE data indicated that the resulting geopotential difference estimates agree well with predicted values from official Level 2 solutions: with much higher correlation at 0.9, as compared to 0.5-0.8 reported by previous published energy balance studies. We demonstrate that our approach produced a comparable time-variable gravity solution with the Level 2 solutions. The regional GRACE temporal gravity solutions over Greenland reveals that a substantially higher temporal resolution is achievable at 10-d sampling as compared to the official monthly solutions, but without the compromise of spatial resolution, nor the need to use regularization or post-processing.

On the Resolvability of Steam Assisted Gravity Drainage Reservoirs Using Time-Lapse Gravity Gradiometry

NASA Astrophysics Data System (ADS)

Elliott, E. Judith; Braun, Alexander

2017-11-01

Unconventional heavy oil resource plays are important contributors to oil and gas production, as well as controversial for posing environmental hazards. Monitoring those reservoirs before, during, and after operations would assist both the optimization of economic benefits and the mitigation of potential environmental hazards. This study investigates how gravity gradiometry using superconducting gravimeters could resolve depletion areas in steam assisted gravity drainage (SAGD) reservoirs. This is achieved through modelling of a SAGD reservoir at 1.25 and 5 years of operation. Specifically, the density change structure identified from geological, petrological, and seismic observations is forward modelled for gravity and gradients. Three main parameters have an impact on the resolvability of bitumen depletion volumes and are varied through a suitable parameter space: well pair separation, depth to the well pairs, and survey grid sampling. The results include a resolvability matrix, which identifies reservoirs that could benefit from time-lapse gravity gradiometry monitoring. After 1.25 years of operation, during the rising phase, the resolvable maximum reservoir depth ranges between the surface and 230 m, considering a well pair separation between 80 and 200 m. After 5 years of production, during the spreading phase, the resolvability of depletion volumes around single well pairs is greatly compromised as the depletion volume is closer to the surface, which translates to a larger portion of the gravity signal. The modelled resolvability matrices were derived from visual inspection and spectral analysis of the gravity gradient signatures and can be used to assess the applicability of time-lapse gradiometry to monitor reservoir density changes.

A black hole with torsion in 5D Lovelock gravity

NASA Astrophysics Data System (ADS)

Cvetković, B.; Simić, D.

2018-03-01

We analyze static spherically symmetric solutions of five dimensional (5D) Lovelock gravity in the first order formulation. In the Riemannian sector, when torsion vanishes, the Boulware–Deser black hole represents a unique static spherically symmetric black hole solution for the generic choice of the Lagrangian parameters. We show that a special choice of the Lagrangian parameters, different from the Lovelock Chern–Simons gravity, leads to the existence of a static black hole solution with torsion, the metric of which is asymptotically anti-de Sitter (AdS). We calculate the conserved charges and thermodynamical quantities of this black hole solution.

Geometric scalar theory of gravity beyond spherical symmetry

NASA Astrophysics Data System (ADS)

Moschella, U.; Novello, M.

2017-04-01

We construct several exact solutions for a recently proposed geometric scalar theory of gravity. We focus on a class of axisymmetric geometries and a big-bang-like geometry and discuss their Lorentzian character. The axisymmetric solutions are parametrized by an integer angular momentum l . The l =0 (spherical) case gives rise to the Schwarzschild geometry. The other solutions have naked singular surfaces. While not a priori obvious, all the solutions that we present here are globally Lorentzian. The Lorentzian signature appears to be a robust property of the disformal geometries solving the vacuum geometric scalar theory of gravity equations.

Kundt solutions of minimal massive 3D gravity

NASA Astrophysics Data System (ADS)

Deger, Nihat Sadik; Sarıoǧlu, Ã.-zgür

2015-11-01

We construct Kundt solutions of minimal massive gravity theory and show that, similar to topologically massive gravity (TMG), most of them are constant scalar invariant (CSI) spacetimes that correspond to deformations of round and warped (A)dS. We also find an explicit non-CSI Kundt solution at the merger point. Finally, we give their algebraic classification with respect to the traceless Ricci tensor (Segre classification) and show that their Segre types match with the types of their counterparts in TMG.

Noether symmetry approach in f(G,T) gravity

NASA Astrophysics Data System (ADS)

Shamir, M. Farasat; Ahmad, Mushtaq

2017-01-01

We explore the recently introduced modified Gauss-Bonnet gravity (Sharif and Ikram in Eur Phys J C 76:640, 2016), f(G,T) pragmatic with G, the Gauss-Bonnet term, and T, the trace of the energy-momentum tensor. Noether symmetry approach has been used to develop some cosmologically viable f(G,T) gravity models. The Noether equations of modified gravity are reported for flat FRW universe. Two specific models have been studied to determine the conserved quantities and exact solutions. In particular, the well known deSitter solution is reconstructed for some specific choice of f(G,T) gravity model.

Born-Infeld Gravity Revisited

NASA Astrophysics Data System (ADS)

Setare, M. R.; Sahraee, M.

2013-12-01

In this paper, we investigate the behavior of linearized gravitational excitation in the Born-Infeld gravity in AdS3 space. We obtain the linearized equation of motion and show that this higher-order gravity propagate two gravitons, massless and massive, on the AdS3 background. In contrast to the R2 models, such as TMG or NMG, Born-Infeld gravity does not have a critical point for any regular choice of parameters. So the logarithmic solution is not a solution of this model, due to this one cannot find a logarithmic conformal field theory as a dual model for Born-Infeld gravity.

Identifying high frequency signals in the daily swath mascon solutions from GRACE

NASA Astrophysics Data System (ADS)

Save, H.

2016-12-01

The Gravity Recovery and Climate Experiment (GRACE) mission has provided us with unique information about the total water column in the Earth system over the past 14 years. The GRACE project provides a monthly mean time-variable gravity solution. There has been significant progress in the community over the years to develop shorter time-window gravity solutions. The daily swath mascon solutions, which are under development at the Center for Space Research (CSR), are computed using daily GRACE observation data. This paper discusses the development and the progress of this product. This paper summarizes the analysis of these solutions with special emphasis on identifying the higher frequency natural processes observed by GRACE using these daily swath mascon solutions.

Exact solutions in 3D gravity with torsion

NASA Astrophysics Data System (ADS)

González, P. A.; Vásquez, Yerko

2011-08-01

We study the three-dimensional gravity with torsion given by the Mielke-Baekler (MB) model coupled to gravitational Chern-Simons term, and that possess electric charge described by Maxwell-Chern-Simons electrodynamics. We find and discuss this theory's charged black holes solutions and uncharged solutions. We find that for vanishing torsion our solutions by means of a coordinate transformation can be written as three-dimensional Chern-Simons black holes. We also discuss a special case of this theory, Topologically Massive Gravity (TMG) at chiral point, and we show that the logarithmic solution of TMG is also a solution of the MB model at a fixed point in the space of parameters. Furthermore, we show that our solutions generalize Gödel type solutions in a particular case. Also, we recover BTZ black hole in Riemann-Cartan spacetime for vanishing charge.

Strong anti-gravity Life in the shock wave

NASA Astrophysics Data System (ADS)

Fabbrichesi, Marco; Roland, Kaj

1992-12-01

Strong anti-gravity is the vanishing of the net force between two massive particles at rest, to all orders in Newton's constant. We study this phenomenon and show that it occurs in any effective theory of gravity which is obtained from a higher-dimensional model by compactification on a manifold with flat directions. We find the exact solution of the Einstein equations in the presence of a point-like source of strong anti-gravity by dimensional reduction of a shock-wave solution in the higher-dimensional model.

Ocean gravity and geoid determination

NASA Technical Reports Server (NTRS)

Kahn, W. D.; Siry, J. W.; Brown, R. D.; Wells, W. T.

1977-01-01

Gravity anomalies have been recovered in the North Atlantic and the Indian Ocean regions. Comparisons of 63 2 deg x 2 deg mean free air gravity anomalies recovered in the North Atlantic area and 24 5 deg x 5 deg mean free air gravity anomalies in the Indian Ocean area with surface gravimetric measurements have shown agreement to + or - 8 mgals for both solutions. Geoids derived from the altimeter solutions are consistent with altimetric sea surface height data to within the precision of the data, about + or - 2 meters.

Exact vacuum solution to conformal Weyl gravity and galactic rotation curves

NASA Technical Reports Server (NTRS)

Mannheim, Philip D.; Kazanas, Demosthenes

1989-01-01

The complete, exact exterior solution for a static, spherically symmetric source in locally conformal invariant Weyl gravity is presented. The solution includes the familiar exterior Schwarzschild solution as a special case and contains an extra gravitational potential term which grows linearly with distance. The obtained solution provides a potential explanation for observed galactic rotation curves without the need for dark matter. The solution also has some interesting implications for cosmology.

Black hole solutions in mimetic Born-Infeld gravity

NASA Astrophysics Data System (ADS)

Chen, Che-Yu; Bouhmadi-López, Mariam; Chen, Pisin

2018-01-01

The vacuum, static, and spherically symmetric solutions in the mimetic Born-Infeld gravity are studied. The mimetic Born-Infeld gravity is a reformulation of the Eddington-inspired-Born-Infeld (EiBI) model under the mimetic approach. Due to the mimetic field, the theory contains non-trivial vacuum solutions different from those in Einstein gravity. We find that with the existence of the mimetic field, the spacelike singularity inside a Schwarzschild black hole could be altered to a lightlike singularity, even though the curvature invariants still diverge at the singularity. Furthermore, in this case, the maximal proper time for a timelike radially-infalling observer to reach the singularity is found to be infinite.

Black hole solutions in mimetic Born-Infeld gravity.

PubMed

Chen, Che-Yu; Bouhmadi-López, Mariam; Chen, Pisin

2018-01-01

The vacuum, static, and spherically symmetric solutions in the mimetic Born-Infeld gravity are studied. The mimetic Born-Infeld gravity is a reformulation of the Eddington-inspired-Born-Infeld (EiBI) model under the mimetic approach. Due to the mimetic field, the theory contains non-trivial vacuum solutions different from those in Einstein gravity. We find that with the existence of the mimetic field, the spacelike singularity inside a Schwarzschild black hole could be altered to a lightlike singularity, even though the curvature invariants still diverge at the singularity. Furthermore, in this case, the maximal proper time for a timelike radially-infalling observer to reach the singularity is found to be infinite.

On estimating gravity anomalies: A comparison of least squares collocation with least squares techniques

NASA Technical Reports Server (NTRS)

Argentiero, P.; Lowrey, B.

1976-01-01

The least squares collocation algorithm for estimating gravity anomalies from geodetic data is shown to be an application of the well known regression equations which provide the mean and covariance of a random vector (gravity anomalies) given a realization of a correlated random vector (geodetic data). It is also shown that the collocation solution for gravity anomalies is equivalent to the conventional least-squares-Stokes' function solution when the conventional solution utilizes properly weighted zero a priori estimates. The mathematical and physical assumptions underlying the least squares collocation estimator are described, and its numerical properties are compared with the numerical properties of the conventional least squares estimator.

Black hole solutions in mimetic Born-Infeld gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Che-Yu; Bouhmadi-López, Mariam; Chen, Pisin

The vacuum, static, and spherically symmetric solutions in the mimetic Born-Infeld gravity are studied. The mimetic Born-Infeld gravity is a reformulation of the Eddington-inspired-Born-Infeld (EiBI) model under the mimetic approach. Due to the mimetic field, the theory contains non-trivial vacuum solutions different from those in Einstein gravity. Here, we find that with the existence of the mimetic field, the spacelike singularity inside a Schwarzschild black hole could be altered to a lightlike singularity, even though the curvature invariants still diverge at the singularity. Furthermore, in this case, the maximal proper time for a timelike radially-infalling observer to reach the singularitymore » is found to be infinite.« less

Black hole solutions in mimetic Born-Infeld gravity

DOE PAGES

Chen, Che-Yu; Bouhmadi-López, Mariam; Chen, Pisin

2018-01-23

The vacuum, static, and spherically symmetric solutions in the mimetic Born-Infeld gravity are studied. The mimetic Born-Infeld gravity is a reformulation of the Eddington-inspired-Born-Infeld (EiBI) model under the mimetic approach. Due to the mimetic field, the theory contains non-trivial vacuum solutions different from those in Einstein gravity. Here, we find that with the existence of the mimetic field, the spacelike singularity inside a Schwarzschild black hole could be altered to a lightlike singularity, even though the curvature invariants still diverge at the singularity. Furthermore, in this case, the maximal proper time for a timelike radially-infalling observer to reach the singularitymore » is found to be infinite.« less

Differentiation of naphthalene and paradichlorobenzene mothballs based on their difference in specific gravity.

PubMed

Fukuda, T; Koyama, K; Yamashita, M; Koichi, N; Takeda, M

1991-08-01

The present study was conducted to measure the specific gravities of paradichlorobenzene and naphthalene mothballs and compare them with the specific gravity of a saturated aqueous solution of sodium chloride (1.197). The specific gravities of 450 paradichlorobenzene mothballs from 5 manufactures and 150 naphthalene mothballs from 2 manufactures were measured with a specific gravity meter. The mean specific gravities of paradichlorobenzene mothballs were between 1.429 and 1.437 (p = 0.99). On the other hand, the mean specific gravities of naphthalene mothballs were between 1.094 and 1.100 (p = 0.99). Based on the fact that paradichlorobenzene mothballs sink in a saturated solution of salt whereas naphthalene mothballs float on it, these 2 kinds of mothballs ought to be rapidly and accurately distinguished in clinical settings.

Novel Applications of Magnetic Fields for Fluid Flow Control and for Simulating Variable Gravity Conditions

NASA Technical Reports Server (NTRS)

Ramachandran, N.

2005-01-01

Static and dynamic magnetic fields have been used to control convection in many materials processing applications. In most of the applications, convection control (damping or enhancement) is achieved through the Lorentz force that can be tailored to counteract/assist dominant system flows. This technique has been successfully applied to liquids that are electrically conducting, such as high temperature melts of semiconductors, metals and alloys, etc. In liquids with low electrical conductivity such as ionic solutions of salts in water, the Lorentz force is weak and hence not very effective and alternate ways of flow control are necessary. If the salt in solution is paramagnetic then the variation of magnetic susceptibility with temperature and/or concentration can be used for flow control. For thermal buoyancy driven flows this can be accomplished in a temperature range below the Curie point of the salt. The magnetic force is proportional to the magnetic susceptibility and the product of the magnetic field and its gradient. By suitably positioning the experiment cell in the magnet, system flows can be assisted or countered, as desired. A similar approach can be extended to diamagnetic substances and fluids but the required magnetic force is considerably larger than that required for paramagnetic substances. The presentation will provide an overview of work to date on a NASA fluid physics sponsored project that aims to test the hypothesis of convective flow control using strong magnetic fields in protein crystal growth. The objective is to understand the nature of the various forces that come into play, delineate causative factors for fluid flow and to quantify them through experiments, analysis, and numerical modeling. The seminar will report specifically on the experimental results using paramagnetic salts and solutions in magnetic fields and compare them to analytical predictions. Applications of the concept to protein crystallization studies will be discussed. The use of strong magnetic fields for terrestrially simulating variable gravity environments and applications supporting the NASA Exploration Initiative will also be briefly discussed.

Vacuum-assisted venous return reduces blood usage.

PubMed

Banbury, Michael K; White, Jennifer A; Blackstone, Eugene H; Cosgrove, Delos M

2003-09-01

To determine whether vacuum-assisted venous return has clinical advantages over conventional gravity drainage apart from allowing the use of smaller cannulas and shorter tubing. A total of 150 valve operations were performed at our institution between February and July 1999 using vacuum-assisted venous return with small venous cannulas connected to short tubing. These were compared with (1) 83 valve operations performed between April 1997 and January 1998 using the initial version of vacuum-assisted venous return, and (2) 124 valve operations performed between January and April of 1997 using conventional gravity drainage. Priming volume, hematocrit value, red blood cell usage, and total blood product usage were compared multivariably. These comparisons were covariate and propensity adjusted for dissimilarities between the groups and confirmed by propensity-matched pairs analysis. Priming volume was 1.4 +/- 0.4 L for small-cannula vacuum-assisted venous return, 1.7 +/- 0.4 L for initial vacuum-assisted venous return, and 2.0 +/- 0.4 L for gravity drainage (P <.0001). Smaller priming resulted in higher hematocrit values both at the beginning of cardiopulmonary bypass (27% +/- 5% compared with 26% +/- 4% and 25% +/- 4%, respectively, P <.0001) and at the end (30% +/- 4% compared with 28% +/- 4% and 27% +/- 4%, respectively, P <.0001). Red cell transfusions were used in 17% of the patients having small-cannula vacuum-assisted venous return, 27% of the initial patients having vacuum-assisted venous return, and 37% of the patients having gravity drainage (P =.001); total blood product usage was 19%, 27%, and 39%, respectively (P =.002). Although ministernotomy also was associated with reduced blood product usage (P <.004), propensity matching on type of sternotomy confirmed the association of vacuum-assisted venous return with lowered blood product usage. Vacuum-assisted venous return results in (1) higher hematocrit values during cardiopulmonary bypass and (2) decreased red cell and total blood product usage.

Causal properties of nonlinear gravitational waves in modified gravity

NASA Astrophysics Data System (ADS)

Suvorov, Arthur George; Melatos, Andrew

2017-09-01

Some exact, nonlinear, vacuum gravitational wave solutions are derived for certain polynomial f (R ) gravities. We show that the boundaries of the gravitational domain of dependence, associated with events in polynomial f (R ) gravity, are not null as they are in general relativity. The implication is that electromagnetic and gravitational causality separate into distinct notions in modified gravity, which may have observable astrophysical consequences. The linear theory predicts that tachyonic instabilities occur, when the quadratic coefficient a2 of the Taylor expansion of f (R ) is negative, while the exact, nonlinear, cylindrical wave solutions presented here can be superluminal for all values of a2. Anisotropic solutions are found, whose wave fronts trace out time- or spacelike hypersurfaces with complicated geometric properties. We show that the solutions exist in f (R ) theories that are consistent with Solar System and pulsar timing experiments.

Altimeter measurements for the determination of the Earth's gravity field

NASA Technical Reports Server (NTRS)

Tapley, B. D.; Schutz, B. E.; Shum, C. K.

1986-01-01

Progress in the following areas is described: refining altimeter and altimeter crossover measurement models for precise orbit determination and for the solution of the earth's gravity field; performing experiments using altimeter data for the improvement of precise satellite ephemerides; and analyzing an optimal relative data weighting algorithm to combine various data types in the solution of the gravity field.

Enhanced asymptotic BMS3 algebra of the flat spacetime solutions of generalized minimal massive gravity

NASA Astrophysics Data System (ADS)

Setare, M. R.; Adami, H.

2018-01-01

We apply the new fall of conditions presented in the paper [1] on asymptotically flat spacetime solutions of Chern-Simons-like theories of gravity. We show that the considered fall of conditions asymptotically solve equations of motion of generalized minimal massive gravity. We demonstrate that there exist two type of solutions, one of those is trivial and the others are non-trivial. By looking at non-trivial solutions, for asymptotically flat spacetimes in the generalized minimal massive gravity, in contrast to Einstein gravity, cosmological parameter can be non-zero. We obtain the conserved charges of the asymptotically flat spacetimes in generalized minimal massive gravity, and by introducing Fourier modes we show that the asymptotic symmetry algebra is a semidirect product of a BMS3 algebra and two U (1) current algebras. Also we verify that the BMS3 algebra can be obtained by a contraction of the AdS3 asymptotic symmetry algebra when the AdS3 radius tends to infinity in the flat-space limit. Finally we find energy, angular momentum and entropy for a particular case and deduce that these quantities satisfy the first law of flat space cosmologies.

Least squares collocation applied to local gravimetric solutions from satellite gravity gradiometry data

NASA Technical Reports Server (NTRS)

Robbins, J. W.

1985-01-01

An autonomous spaceborne gravity gradiometer mission is being considered as a post Geopotential Research Mission project. The introduction of satellite diometry data to geodesy is expected to improve solid earth gravity models. The possibility of utilizing gradiometer data for the determination of pertinent gravimetric quantities on a local basis is explored. The analytical technique of least squares collocation is investigated for its usefulness in local solutions of this type. It is assumed, in the error analysis, that the vertical gravity gradient component of the gradient tensor is used as the raw data signal from which the corresponding reference gradients are removed to create the centered observations required in the collocation solution. The reference gradients are computed from a high degree and order geopotential model. The solution can be made in terms of mean or point gravity anomalies, height anomalies, or other useful gravimetric quantities depending on the choice of covariance types. Selected for this study were 30 x 30 foot mean gravity and height anomalies. Existing software and new software are utilized to implement the collocation technique. It was determined that satellite gradiometry data at an altitude of 200 km can be used successfully for the determination of 30 x 30 foot mean gravity anomalies to an accuracy of 9.2 mgal from this algorithm. It is shown that the resulting accuracy estimates are sensitive to gravity model coefficient uncertainties, data reduction assumptions and satellite mission parameters.

Persistent hydrocephalus due to postural activation of a ventricular shunt anti-gravity device.

PubMed

Craven, Claudia L; Toma, Ahmed K; Watkins, Laurence D

2017-03-01

The ever present need to balance over drainage with under drainage in hydrocephalus has required innovations including adjustable valves with antigravity devices. These are activated in the vertical position to prevent siphoning. We describe a group of bedridden patients who presented with unexplained under drainage caused by activation of antigravity shunt components produced by peculiar head/body position. Retrospective single centre case series of hydrocephalus patients, treated with ventriculo-peritoneal (VP) shunt insertion between April 2014 - February 2016. These patients presented with clinical and radiological under drainage syndrome. Medical notes were reviewed for clinical picture and outcome. Radiological studies were reviewed assessing shunt placement and ventricular size. Seven patients presented with clinical and radiological under drainage syndrome. A consistent posturing of long term hyper-flexion of the neck whilst lying supine was observed. All patients had similar shunt construct (adjustable Miethke ProGAV valve and shunt assistant anti-gravity component). In each of those patients a hypothesis was formulated that neck flexion was activating the shunt assistance anti-gravity component in supine position. Five patients underwent shunt revision surgery removing the shunt assistant device from the cranium and adding an anti-gravity component to the shunt system at the chest. One had the shunt assistant completely removed and one patient was managed conservatively with mobilisation. All patients had clinical and radiological improvement. Antigravity shunt components implanted cranially in bedridden hydrocephalus patients will produce underdrainage due to head flexion induced anti-gravity device activation. In these patients, anti-gravity devices should be placed at the chest. Alternatively, special nursing attention should be paid to head-trunk angle. Copyright © 2016 Elsevier Ltd. All rights reserved.

5D Lovelock gravity: New exact solutions with torsion

NASA Astrophysics Data System (ADS)

Cvetković, B.; Simić, D.

2016-10-01

Five-dimensional Lovelock gravity is investigated in the first order formalism. A new class of exact solutions is constructed: the Bañados, Teitelboim, Zanelli black rings with and without torsion. We show that our solution with torsion exists in a different sector of the Lovelock gravity, as compared to the Lovelock Chern-Simons sector or the one investigated by Canfora et al. The conserved charges of the solutions are found using Nester's formula, and the results are confirmed by the canonical method. We show that the theory linearized around the background with torsion possesses two additional degrees of freedom with respect to general relativity.

New error calibration tests for gravity models using subset solutions and independent data - Applied to GEM-T3

NASA Technical Reports Server (NTRS)

Lerch, F. J.; Nerem, R. S.; Chinn, D. S.; Chan, J. C.; Patel, G. B.; Klosko, S. M.

1993-01-01

A new method has been developed to provide a direct test of the error calibrations of gravity models based on actual satellite observations. The basic approach projects the error estimates of the gravity model parameters onto satellite observations, and the results of these projections are then compared with data residual computed from the orbital fits. To allow specific testing of the gravity error calibrations, subset solutions are computed based on the data set and data weighting of the gravity model. The approach is demonstrated using GEM-T3 to show that the gravity error estimates are well calibrated and that reliable predictions of orbit accuracies can be achieved for independent orbits.

Generalized quasitopological gravity

NASA Astrophysics Data System (ADS)

Hennigar, Robie A.; KubizÅák, David; Mann, Robert B.

2017-05-01

We construct the most general, to cubic order in curvature, theory of gravity whose (most general) static spherically symmetric vacuum solutions are fully described by a single field equation. The theory possesses the following remarkable properties: (i) It has a well-defined Einstein gravity limit, (ii) it admits "Schwarzschild-like" solutions characterized by a single metric function, (iii) on maximally symmetric backgrounds it propagates the same degrees of freedom as Einstein's gravity, and (iv) Lovelock and quasitopological gravities, as well as the recently developed Einsteinian cubic gravity [Bueno and Cano Phys. Rev. D 94, 104005 (2016)., 10.1103/PhysRevD.94.104005] in four dimensions, are recovered as special cases. We perform a brief analysis of asymptotically flat black holes in this theory and study their thermodynamics.

Ballistic Mercury orbiter mission via Venus and Mercury gravity assists

NASA Astrophysics Data System (ADS)

Yen, Chen-Wan Liu

1989-09-01

This paper shows that it is possible to deliver a payload of 600 to 2000 kg to a 300-km circular orbit at Mercury, using the presently available NASA STS and a single-stage bipropellant chemical rocket. This superior payload performance is attained by swingbys of Venus, plus more importantly, the use of the reverse Delta-V/EGA process. In contrast to the familiar Delta-V/EGA process used to boost the launch energy by returning to earth for a gravity assist, the reverse process reduces the Mercury approach energy each time a spacecraft makes a near-resonant return to Mercury for a gravity assist and reduces the orbit-capture Delta-V requirement. The mission sequences for such high-performance missions are described, and example mission opportunities for the years 1990 to 2010 are presented.

Galileo 1989 VEEGA trajectory design. [Venus-Earth-Earth-Gravity-Assist

NASA Technical Reports Server (NTRS)

D'Amario, Louis A.; Byrnes, Dennis V.; Johannesen, Jennie R.; Nolan, Brian G.

1989-01-01

The new baseline for the Galileo Mission is a 1989 Venus-earth-earth gravity-assist (VEEGA) trajectory, which utilizes three gravity-assist planetary flybys in order to reduce launch energy requirements significantly compared to other earth-Jupiter transfer modes. The launch period occurs during October-November 1989. The total flight time is about 6 years, with November 1995 as the most likely choice for arrival at Jupiter. Optimal 1989 VEEGA trajectories have been generated for a wide range of earth launch dates and Jupiter arrival dates. Launch/arrival space contour plots are presented for various trajectory parameters, including propellant margin, which is used to measure mission performance. The accessible region of the launch/arrival space is defined by propellant margin and launch energy constraints; the available launch period is approximately 1.5 months long.

Mission Design for the Innovative Interstellar Explorer Vision Mission

NASA Technical Reports Server (NTRS)

Fiehler, Douglas I.; McNutt, Ralph L.

2005-01-01

The Innovative Interstellar Explorer, studied under a NASA Vision Mission grant, examined sending a probe to a heliospheric distance of 200 Astronomical Units (AU) in a "reasonable" amount of time. Previous studies looked at the use of a near-Sun propulsive maneuver, solar sails, and fission reactor powered electric propulsion systems for propulsion. The Innovative Interstellar Explorer's mission design used a combination of a high-energy launch using current launch technology, a Jupiter gravity assist, and electric propulsion powered by advanced radioisotope power systems to reach 200 AU. Many direct and gravity assist trajectories at several power levels were considered in the development of the baseline trajectory, including single and double gravity assists utilizing the outer planets (Jupiter, Saturn, Uranus, and Neptune). A detailed spacecraft design study was completed followed by trajectory analyses to examine the performance of the spacecraft design options.

Classical aspects of higher spin topologically massive gravity

NASA Astrophysics Data System (ADS)

Chen, Bin; Long, Jiang; Zhang, Jian-Dong

2012-10-01

We study the classical solutions of three-dimensional topologically massive gravity (TMG) and its higher spin generalization, in the first-order formulation. The action of higher spin TMG has been proposed by Chen and Long (2011 J. High Energy Phys. JHEP12(2011)114) to be of a Chern-Simons-like form. The equations of motion are more complicated than the ones in pure higher spin AdS3 gravity, but are still tractable. As all the solutions in higher spin gravity are automatically the solutions of higher spin TMG, we focus on other solutions. We manage to find the AdS pp-wave solutions with higher spin hair and find that the non-vanishing higher spin fields may or may not modify the pp-wave geometry. In order to discuss the warped spacetime, we introduce the notion of a special Killing vector, which is defined to be the symmetry on the frame-like fields. We reproduce various warped spacetimes of TMG in our framework, with the help of special Killing vectors.

Broad-search algorithms for the spacecraft trajectory design of Callisto-Ganymede-Io triple flyby sequences from 2024 to 2040, Part II: Lambert pathfinding and trajectory solutions

NASA Astrophysics Data System (ADS)

Lynam, Alfred E.

2014-01-01

Triple-satellite-aided capture employs gravity-assist flybys of three of the Galilean moons of Jupiter in order to decrease the amount of ΔV required to capture a spacecraft into Jupiter orbit. Similarly, triple flybys can be used within a Jupiter satellite tour to rapidly modify the orbital parameters of a Jovicentric orbit, or to increase the number of science flybys. In order to provide a nearly comprehensive search of the solution space of Callisto-Ganymede-Io triple flybys from 2024 to 2040, a third-order, Chebyshev's method variant of the p-iteration solution to Lambert's problem is paired with a second-order, Newton-Raphson method, time of flight iteration solution to the V∞-matching problem. The iterative solutions of these problems provide the orbital parameters of the Callisto-Ganymede transfer, the Ganymede flyby, and the Ganymede-Io transfer, but the characteristics of the Callisto and Io flybys are unconstrained, so they are permitted to vary in order to produce an even larger number of trajectory solutions. The vast amount of solution data is searched to find the best triple-satellite-aided capture window between 2024 and 2040.

Gravity model improvement using GEOS-3 (GEM 9 and 10)

NASA Technical Reports Server (NTRS)

Lerch, F. J.; Klosko, S. M.; Laubscher, R. E.; Wagner, C. A.

1977-01-01

The use of collocation permitted GEM 9 to be a larger field than previous derived satellite models, GEM 9 having harmonics complete to 20 x 20 with selected higher degree terms. The satellite data set has approximately 840,000 observations, of which 200,000 are laser ranges taken on 9 satellites equipped with retroreflectors. GEM 10 is complete to 22 x 22 with selected higher degree terms out to degree and order 30 amounting to a total of 592 coefficients. Comparisons with surface gravity and altimeter data indicate a substantial improvement in GEM 9 over previous satellite solutions; GEM 9 is in even closer agreement with surface data than the previously published GEM 6 solution which contained surface gravity. In particular the free air gravity anomalies calculated from GEM 9 and a surface gravity solution are in excellent agreement for the high degree terms.

Fluid density and concentration measurement using noninvasive in situ ultrasonic resonance interferometry

DOEpatents

Pope, Noah G.; Veirs, Douglas K.; Claytor, Thomas N.

1994-01-01

The specific gravity or solute concentration of a process fluid solution located in a selected structure is determined by obtaining a resonance response spectrum of the fluid/structure over a range of frequencies that are outside the response of the structure itself. A fast fourier transform (FFT) of the resonance response spectrum is performed to form a set of FFT values. A peak value for the FFT values is determined, e.g., by curve fitting, to output a process parameter that is functionally related to the specific gravity and solute concentration of the process fluid solution. Calibration curves are required to correlate the peak FFT value over the range of expected specific gravities and solute concentrations in the selected structure.

Fluid density and concentration measurement using noninvasive in situ ultrasonic resonance interferometry

DOEpatents

Pope, N.G.; Veirs, D.K.; Claytor, T.N.

1994-10-25

The specific gravity or solute concentration of a process fluid solution located in a selected structure is determined by obtaining a resonance response spectrum of the fluid/structure over a range of frequencies that are outside the response of the structure itself. A fast Fourier transform (FFT) of the resonance response spectrum is performed to form a set of FFT values. A peak value for the FFT values is determined, e.g., by curve fitting, to output a process parameter that is functionally related to the specific gravity and solute concentration of the process fluid solution. Calibration curves are required to correlate the peak FFT value over the range of expected specific gravities and solute concentrations in the selected structure. 7 figs.

Radial and tangential gravity rates from GRACE in areas of glacial isostatic adjustment

NASA Astrophysics Data System (ADS)

van der Wal, Wouter; Kurtenbach, Enrico; Kusche, Jürgen; Vermeersen, Bert

2011-11-01

In areas dominated by Glacial Isostatic Adjustment (GIA), the free-air gravity anomaly rate can be converted to uplift rate to good approximation by using a simple spectral relation. We provide quantitative comparisons between gravity rates derived from monthly gravity field solutions (GFZ Potsdam, CSR Texas, IGG Bonn) from the Gravity Recovery and Climate Experiment (GRACE) satellite mission with uplift rates measured by GPS in these areas. The band-limited gravity data from the GRACE satellite mission can be brought to very good agreement with the point data from GPS by using scaling factors derived from a GIA model (the root-mean-square of differences is 0.55 mm yr-1 for a maximum uplift rate signal of 10 mm yr-1). The root-mean-square of the differences between GRACE derived uplift rates and GPS derived uplift rates decreases with increasing GRACE time period to a level below the uncertainty that is expected from GRACE observations, GPS measurements and the conversion from gravity rate to uplift rate. With the current length of time-series (more than 8 yr) applying filters and a hydrology correction to the GRACE data does not reduce the root-mean-square of differences significantly. The smallest root-mean-square was obtained with the GFZ solution in Fennoscandia and with the CSR solution in North America. With radial gravity rates in excellent agreement with GPS uplift rates, more information on the GIA process can be extracted from GRACE gravity field solutions in the form of tangential gravity rates, which are equivalent to a rate of change in the deflection of the vertical scaled by the magnitude of gravity rate vector. Tangential gravity rates derived from GRACE point towards the centre of the previously glaciated area, and are largest in a location close to the centre of the former ice sheet. Forward modelling showed that present day tangential gravity rates have maximum sensitivity between the centre and edge of the former ice sheet, while radial gravity rates are most sensitive in the centre of the former ice sheet. As a result, tangential gravity rates offer constraints on a two-layer mantle viscosity profile that are different from radial gravity rates, which can be exploited in future GIA studies.

Progress towards CSR RL06 GRACE gravity solutions

NASA Astrophysics Data System (ADS)

Save, Himanshu

2017-04-01

The GRACE project plans to re-processes the GRACE mission data in order to be consistent with the first gravity products released by the GRACE-FO project. The next generation Release-06 (RL06) gravity products from GRACE will include the improvements in GRACE Level-1 data products, background gravity models and the processing methodology. This paper will outline the planned improvements for CSR - RL06 and discuss the preliminary results. This paper will discuss the evolution of the quality of the GRACE solutions, especially over the past few years. We will also discuss the possible challenges we may face in connecting/extending the measurements of mass fluxes from the GRACE era to the GRACE-FO era due quality of the GRACE solutions from recent years.

Gravity-induced stresses in finite slopes

USGS Publications Warehouse

Savage, W.Z.

1994-01-01

An exact solution for gravity-induced stresses in finite elastic slopes is presented. This solution, which is applied for gravity-induced stresses in 15, 30, 45 and 90?? finite slopes, has application in pit-slope design, compares favorably with published finite element results for this problem and satisfies the conditions that shear and normal stresses vanish on the ground surface. The solution predicts that horizontal stresses are compressive along the top of the slopes (zero in the case of the 90?? slope) and tensile away from the bottom of the slopes, effects which are caused by downward movement and near-surface horizontal extension in front of the slope in response to gravity loading caused by the additional material associated with the finite slope. ?? 1994.

Power law f(𝒢,T) gravity models supporting wormhole solutions

NASA Astrophysics Data System (ADS)

Shamir, M. Farasat; Ahmad, Mushtaq

This work provides some feasible regions for the existence of traversable wormhole geometries in modified f(𝒢,T) gravity. For this purpose, three different matter contents have been studied with special emphasis on anisotropic fluid by considering a specific f(𝒢,T) gravity power law model. It has been shown that the null energy conditions for the effective energy-momentum tensor are widely violated for the ordinary matter content. However, some small feasible regions to support the wormhole solutions have been noted. Furthermore, the stability of the anisotropic feasible regions for the wormhole solutions has been discussed. It is concluded that the wormhole geometries threaded by the ordinary matter actually exist and are well stable in f(𝒢,T) gravity.

Dark-energy cosmological models in f(G) gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shamir, M. F., E-mail: farasat.shamir@nu.edu.pk

We discuss dark-energy cosmological models in f(G) gravity. For this purpose, a locally rotationally symmetric Bianchi type I cosmological model is considered. First, exact solutions with a well-known form of the f(G) model are explored. One general solution is discussed using a power-law f(G) gravity model and physical quantities are calculated. In particular, Kasner’s universe is recovered and the corresponding f(G) gravity models are reported. Second, the energy conditions for the model under consideration are discussed using graphical analysis. It is concluded that solutions with f(G) = G{sup 5/6} support expansion of universe while those with f(G) = G{sup 1/2}more » do not favor the current expansion.« less

Gravitating Q-balls in the Affleck-Dine mechanism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tamaki, Takashi; Sakai, Nobuyuki; Department of Education, Yamagata University, Yamagata 990-8560

2011-04-15

We investigate how gravity affects ''Q-balls'' with the Affleck-Dine potential V{sub AD}({phi}):=(m{sup 2}/2){phi}{sup 2} [1+Kln(({phi}/M)){sup 2}]. Contrary to the flat case, in which equilibrium solutions exist only if K<0, we find three types of gravitating solutions as follows. In the case that K<0, ordinary Q-ball solutions exist; there is an upper bound of the charge due to gravity. In the case that K=0, equilibrium solutions called (mini-)boson stars appear due to gravity; there is an upper bound of the charge, too. In the case that K>0, equilibrium solutions appear, too. In this case, these solutions are not asymptotically flat butmore » surrounded by Q-matter. These solutions might be important in considering a dark matter scenario in the Affleck-Dine mechanism.« less

Magnetic solutions in Einstein-massive gravity with linear and nonlinear fields

NASA Astrophysics Data System (ADS)

Hendi, Seyed Hossein; Panah, Behzad Eslam; Panahiyan, Shahram; Momennia, Mehrab

2018-06-01

The solutions of U(1) gauge-gravity coupling is one of the interesting models for analyzing the semi-classical nature of spacetime. In this regard, different well-known singular and nonsingular solutions have been taken into account. The paper at hand investigates the geometrical properties of the magnetic solutions by considering Maxwell and power Maxwell invariant (PMI) nonlinear electromagnetic fields in the context of massive gravity. These solutions are free of curvature singularity, but have a conic one which leads to presence of deficit/surplus angle. The emphasize is on modifications that these generalizations impose on deficit angle which determine the total geometrical structure of the solutions, hence, physical/gravitational properties. It will be shown that depending on the background spacetime [being anti de Sitter (AdS) or de Sitter (dS)], these generalizations present different effects and modify the total structure of the solutions differently.

Existence of global weak solution for a reduced gravity two and a half layer model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Zhenhua, E-mail: zhenhua.guo.math@gmail.com; Li, Zilai, E-mail: lizilai0917@163.com; Yao, Lei, E-mail: yaolei1056@hotmail.com

2013-12-15

We investigate the existence of global weak solution to a reduced gravity two and a half layer model in one-dimensional bounded spatial domain or periodic domain. Also, we show that any possible vacuum state has to vanish within finite time, then the weak solution becomes a unique strong one.

Gravimetric investigations on the North American Datum (1972 - 1973)

NASA Technical Reports Server (NTRS)

Mather, R. S.

1975-01-01

All the available unclassified gravity data on the North American Datum (NAD) and in the surrounding oceans was assembled late in 1972 for the investigation of the gravity field in North America and its relation to North American Datum 1927 (NAD 27). The gravity data in Canada and the United States was compiled on a common datum compatible with the International Gravity Standardization Network 1971 (IGSN 71). The variation in the error of representation in the region is studied along with the correlation characteristics of gravity anomalies with elevation. A free air geoid (FAG 73) was computed from a combination of surface gravity data and Goddard Earth Model (GEM) 4 and this was used as the basis for the computation of the non-Stokesian contributions to the height anomaly. The geocentric orientation parameters obtained by this astrogravimetric method are compared with those obtained by satellite techniques. The differences are found to be no greater than those between individual satellite solutions. The differences between the astrogravimetric solution and satellite solutions GSFC 73 and GEM 6 are studied in detail with a view to obtaining a better understanding of these discrepancies.

Black holes in higher derivative gravity.

PubMed

Lü, H; Perkins, A; Pope, C N; Stelle, K S

2015-05-01

Extensions of Einstein gravity with higher-order derivative terms arise in string theory and other effective theories, as well as being of interest in their own right. In this Letter we study static black-hole solutions in the example of Einstein gravity with additional quadratic curvature terms. A Lichnerowicz-type theorem simplifies the analysis by establishing that they must have vanishing Ricci scalar curvature. By numerical methods we then demonstrate the existence of further black-hole solutions over and above the Schwarzschild solution. We discuss some of their thermodynamic properties, and show that they obey the first law of thermodynamics.

Exact solutions in 3D new massive gravity.

PubMed

Ahmedov, Haji; Aliev, Alikram N

2011-01-14

We show that the field equations of new massive gravity (NMG) consist of a massive (tensorial) Klein-Gordon-type equation with a curvature-squared source term and a constraint equation. We also show that, for algebraic type D and N spacetimes, the field equations of topologically massive gravity (TMG) can be thought of as the "square root" of the massive Klein-Gordon-type equation. Using this fact, we establish a simple framework for mapping all types D and N solutions of TMG into NMG. Finally, we present new examples of types D and N solutions to NMG.

Exact Solutions in 3D New Massive Gravity

NASA Astrophysics Data System (ADS)

Ahmedov, Haji; Aliev, Alikram N.

2011-01-01

We show that the field equations of new massive gravity (NMG) consist of a massive (tensorial) Klein-Gordon-type equation with a curvature-squared source term and a constraint equation. We also show that, for algebraic type D and N spacetimes, the field equations of topologically massive gravity (TMG) can be thought of as the “square root” of the massive Klein-Gordon-type equation. Using this fact, we establish a simple framework for mapping all types D and N solutions of TMG into NMG. Finally, we present new examples of types D and N solutions to NMG.

Gravity Survey of the Rye Patch KGRA, Rye Patch, Nevada

NASA Astrophysics Data System (ADS)

Mcdonald, M. R.; Gosnold, W. D.

2011-12-01

The Rye Patch Known Geothermal Resource Area (KGRA) is located in Pershing County Nevada on the west side of the Humboldt Range and east of the Rye Patch Reservoir approximately 200 km northeast of Reno, Nevada. Previous studies include an earlier gravity survey, 3-D seismic reflection, vertical seismic profiling (VSP) on a single well, 3-D seismic imaging, and a report of the integrated seismic studies. Recently, Presco Energy conducted an aeromagnetic survey and is currently in the process of applying 2-D VSP methods to target exploration and production wells at the site. These studies have indicated that geothermal fluid flow primarily occurs along faults and fractures and that two potential aquifers include a sandstone/siltstone member of the Triassic Natchez Pass Formation and a karst zone that occurs at the interface between Mesozoic limestone and Tertiary volcanics. We hypothesized that addition of a high-resolution gravity survey would better define the locations, trends, lengths, and dip angles of faults and possible solution cavity features. The gravity survey encompassed an area of approximately 78 km2 (30 mi2) within the boundary of the KGRA along with portions of 8 sections directly to the west and 8 sections directly to the east. The survey included 203 stations that were spaced at 400 m intervals. The simple Bouguer anomaly patterns were coincident with elevation, and those patterns remained after terrain corrections were performed. To remove this signal, the data were further processed using wave-length (bandpass) filtering techniques. The results of the filtering and comparison with the recent aeromagnetic survey indicate that the location and trend of major fault systems can be identified using this technique. Dip angles can be inferred by the anomaly contour gradients. By further reductions in the bandpass window, other features such as possible karst solution channels may also be recognizable. Drilling or other geophysical methods such as a magnetotelluric survey may assist in confirming the results. However, lengths of the features were difficult to interpret as the wavelength filtering tends to truncate features in accordance with the bandpass window. Additional gravity measurements would aid in providing higher resolution for the identification and interpretation of features, particularly in the vicinity of the Humboldt House to the north and in an area located to the south of the study area where a large feature was identified in both the aeromagnetic and gravity surveys.

Orbiting naked singularities in large-ω Brans-Dicke gravity

NASA Astrophysics Data System (ADS)

Chauvineau, Bertrand

2017-11-01

Brans-Dicke gravity admits spherical solutions describing naked singularities rather than black holes. Depending on some parameters entering such a solution, stable circular orbits exist for all radii. One shows that, despite the fact a naked singularity is an infinite redshift location, the far observed orbital motion frequency is unbounded for an adiabatically decreasing radius. We then argue that this feature remains true in a wide set of scalar(s)-tensor theories if gravity. This is a salient difference with general relativity, and the repercussion on the gravitational radiation by EMRI systems is stressed. Since this behaviour survives the ω \\longrightarrow ∞ limit, the possibility of such solutions is of utmost interest in the new gravitational wave astronomy context, despite the current constraints on scalar-tensor gravity.

Impact of tracking loop settings of the Swarm GPS receiver on gravity field recovery

NASA Astrophysics Data System (ADS)

Dahle, C.; Arnold, D.; Jäggi, A.

2017-06-01

The Swarm mission consists of three identical satellites equipped with GPS receivers and orbiting in near-polar low Earth orbits. Thus, they can be used to determine the Earth's gravity field by means of high-low satellite-to-satellite tracking (hl-SST). However, first results by several groups have revealed systematic errors both in precise science orbits and resulting gravity field solutions which are caused by ionospheric disturbances affecting the quality of Swarm GPS observations. Looking at gravity field solutions, the errors lead to systematic artefacts located in two bands north and south of the geomagnetic equator. In order to reduce these artefacts, erroneous GPS observations can be identified and rejected before orbit and gravity field processing, but this may also lead to slight degradations of orbit and low degree gravity field coefficient quality. Since the problems were believed to be receiver-specific, the GPS tracking loop bandwidths onboard Swarm have been widened several times starting in May 2015. The influence of these tracking loop updates on Swarm orbits and, particularly, gravity field solutions is investigated in this work. The main findings are that the first updates increasing the bandwidth from 0.25 Hz to 0.5 Hz help to significantly improve the quality of Swarm gravity fields and that the improvements are even larger than those achieved by GPS data rejection. It is also shown that these improvements are indeed due to an improved quality of GPS observations around the geomagnetic equator, and not due to missing observations in these regions. As the ionospheric activity is rather low in the most recent months, the effect of the tracking loop updates in summer 2016 cannot be properly assessed yet. Nevertheless, the quality of Swarm gravity field solutions has already improved after the first updates which is especially beneficial in view of filling the upcoming gap between the GRACE and GRACE Follow-on missions with hl-SST gravity products.

Electric Field Effects in Self-Propagating High-Temperature Synthesis under Microgravity Conditions

NASA Technical Reports Server (NTRS)

Unuvar, C.; Frederick, D. M.; Shaw, B. D.; Munir, Z. A.

2003-01-01

Self-propagating high-temperature synthesis (SHS) has been used to form many materials. SHS generally involves mixing reactants together (e.g., metal powders) and igniting the mixture such that a combustion (deflagration) wave passes though the mixture. The imposition of an electric field (AC or DC) across SHS reactants has been shown to have a marked effect on the dynamics of wave propagation and on the nature, composition, and homogeneity of the product . The use of an electric field with SHS has been termed "field-assisted SHS". Combustion wave velocities and temperatures are directly affected by the field, which is typically perpendicular to the average wave velocity. The degree of activation by the field (e.g., combustion rate) is related to the current density distribution within the sample, and is therefore related to the temperature-dependent spatial distribution of the effective electrical conductivity of reactants and products. Furthermore, the field can influence other important SHS-related phenomena including capillary flow, mass-transport in porous media, and Marangoni flows. These phenomena are influenced by gravity in conventional SHS processes (i.e., without electric fields). As a result the influence of the field on SHS under reduced gravity is expected to be different than under normal gravity. It is also known that heat loss rates from samples, which can depend significantly on gravity, can influence final products in SHS. This research program is focused on studying field-assisted SHS under reduced gravity conditions. The broad objective of this research program is to understand the role of an electric field in SHS reactions under conditions where gravity-related effects are suppressed. The research will allow increased understanding of fundamental aspects of field-assisted SHS processes as well as synthesis of materials that cannot be formed in normal gravity.

The processing of the Viking Orbiter range data and its contribution to Mars gravity solutions

NASA Technical Reports Server (NTRS)

Lemoine, Frank G.; Rosborough, George W.; Smith, David E.

1992-01-01

The processing of Doppler data has been the primary method for deriving models of the Mars gravity field. Since the Mariner 9 and Viking spacecraft were placed in orbit about Mars, many models from degree and order 6 to degree and order 50 have been developed. However, during the Viking mission, some 26,000 range measurements to the two Viking Orbiters were also obtained. These data have not previously been used in the derivation of Mars gravity models. A portion of these range data have been processed simultaneously with the Doppler data. Normal equations were generated for both sets of data and were used to create two solutions complete to degree and order 30: a nominal solution including both the range and the Doppler data (MGM-R100), and another solution including only the Doppler data (MGM-R101). Tests with the covariances of these solutions, as well as with orbit overlap tests indicate that the interplanetary range data can be used to improve the modeling of the Mars gravity field.

Four-dimensional black holes in Einsteinian cubic gravity

NASA Astrophysics Data System (ADS)

Bueno, Pablo; Cano, Pablo A.

2016-12-01

We construct static and spherically symmetric generalizations of the Schwarzschild- and Reissner-Nordström-(anti-)de Sitter [RN-(A)dS] black-hole solutions in four-dimensional Einsteinian cubic gravity (ECG). The solutions are characterized by a single function which satisfies a nonlinear second-order differential equation. Interestingly, we are able to compute independently the Hawking temperature T , the Wald entropy S and the Abbott-Deser mass M of the solutions analytically as functions of the horizon radius and the ECG coupling constant λ . Using these we show that the first law of black-hole mechanics is exactly satisfied. Some of the solutions have positive specific heat, which makes them thermodynamically stable, even in the uncharged and asymptotically flat case. Further, we claim that, up to cubic order in curvature, ECG is the most general four-dimensional theory of gravity which allows for nontrivial generalizations of Schwarzschild- and RN-(A)dS characterized by a single function which reduce to the usual Einstein gravity solutions when the corresponding higher-order couplings are set to zero.

The ITSG-Grace2014 Gravity Field Model

NASA Astrophysics Data System (ADS)

Kvas, Andreas; Mayer-Gürr, Torsten; Zehenter, Norbert; Klinger, Beate

2015-04-01

The ITSG-Grace2014 GRACE-only gravity field model consists of a high resolution unconstrained static model (up to degree 200) with trend and annual signal, monthly unconstrained solutions with different spatial resolutions as well as daily snapshots derived by using a Kalman smoother. Apart from the estimated spherical harmonic coefficients, full variance-covariance matrices for the monthly solutions and the static gravity field component are provided. Compared to the previous release, multiple improvements in the processing chain are implemented: updated background models, better ionospheric modeling for GPS observations, an improved satellite attitude by combination of star camera and angular accelerations, estimation of K-band antenna center variations within the gravity field recovery process as well as error covariance function determination. Furthermore, daily gravity field variations have been modeled in the adjustment process to reduce errors caused by temporal leakage. This combined estimation of daily gravity variations field variations together with the static gravity field component represents a computational challenge due to the significantly increased parameter count. The modeling of daily variations up to a spherical harmonic degree of 40 for the whole GRACE observation period results in a system of linear equations with over 6 million unknown gravity field parameters. A least squares adjustment of this size is not solvable in a sensible time frame, therefore measures to reduce the problem size have to be taken. The ITSG-Grace2014 release is presented and selected parts of the processing chain and their effect on the estimated gravity field solutions are discussed.

FLRW cosmological models with quark and strange quark matters in f(R,T) gravity

NASA Astrophysics Data System (ADS)

Nagpal, Ritika; Singh, J. K.; Aygün, S.

2018-06-01

In this paper, we have studied the magnetized quark matter (QM) and strange quark matter (SQM) distributions in the presence of f(R,T) gravity in the background of Friedmann-Lemaître-Robertson-Walker (FLRW) metric. To get exact solutions of modified field equations we have used f(R,T ) = R + 2 f(T) model given by Harko et al. with two different parametrization of geometrical parameters i.e. the parametrization of the deceleration parameter q , and the scale factor a in hybrid expansion form. Also, we have obtained Einstein Static Universe (ESU) solutions for QM and SQM distributions in f(R,T) gravity and General Relativity (GR). All models in f(R,T) gravity and GR for FRW and ESU Universes with QM also SQM distributions, we get zero magnetic field. These results agree with the solutions of Aktaş and Aygün in f(R,T) gravity. However, we have also discussed the physical consequences of our obtained models.

Non-Schwarzschild black-hole metric in four dimensional higher derivative gravity: Analytical approximation

NASA Astrophysics Data System (ADS)

Kokkotas, K. D.; Konoplya, R. A.; Zhidenko, A.

2017-09-01

Higher derivative extensions of Einstein gravity are important within the string theory approach to gravity and as alternative and effective theories of gravity. H. Lü, A. Perkins, C. Pope, and K. Stelle [Phys. Rev. Lett. 114, 171601 (2015), 10.1103/PhysRevLett.114.171601] found a numerical solution describing a spherically symmetric non-Schwarzschild asymptotically flat black hole in Einstein gravity with added higher derivative terms. Using the general and quickly convergent parametrization in terms of the continued fractions, we represent this numerical solution in the analytical form, which is accurate not only near the event horizon or far from the black hole, but in the whole space. Thereby, the obtained analytical form of the metric allows one to study easily all the further properties of the black hole, such as thermodynamics, Hawking radiation, particle motion, accretion, perturbations, stability, quasinormal spectrum, etc. Thus, the found analytical approximate representation can serve in the same way as an exact solution.

Energy-dependent topological anti-de Sitter black holes in Gauss-Bonnet Born-Infeld gravity

NASA Astrophysics Data System (ADS)

Hendi, S. H.; Behnamifard, H.; Bahrami-Asl, B.

2018-03-01

Employing higher-curvature corrections to Einstein-Maxwell gravity has garnered a great deal of attention motivated by the high-energy regime in the quantum nature of black hole physics. In addition, one may employ gravity's rainbow to encode quantum gravity effects into black hole solutions. In this paper, we regard an energy-dependent static spacetime with various topologies and study its black hole solutions in the context of Gauss-Bonnet Born-Infeld (GB-BI) gravity. We study the thermodynamic properties and examine the first law of thermodynamics. Using a suitable local transformation, we endow the Ricci-flat black hole solutions with a global rotation and study the effects of rotation on thermodynamic quantities. We also investigate thermal stability in a canonical ensemble by calculating the heat capacity. We obtain the effects of various parameters on the horizon radius of stable black holes. Finally, we discuss a second-order phase transition in the extended phase space thermodynamics and investigate the critical behavior.

C-metric solution for conformal gravity with a conformally coupled scalar field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meng, Kun, E-mail: mengkun@tjpu.edu.cn; Zhao, Liu, E-mail: lzhao@nankai.edu.cn

The C-metric solution of conformal gravity with a conformally coupled scalar field is presented. The solution belongs to the class of Petrov type D spacetimes and is conformal to the standard AdS C-metric appeared in vacuum Einstein gravity. For all parameter ranges, we identify some of the physically interesting static regions and the corresponding coordinate ranges. The solution may contain a black hole event horizon, an acceleration horizon, either of which may be cut by the conformal infinity or be hidden behind the conformal infinity. Since the model is conformally invariant, we also discussed the possible effects of the conformalmore » gauge choices on the structure of the spacetime.« less

Procedures and results related to the direct determination of gravity anomalies from satellite and terrestrial gravity data

NASA Technical Reports Server (NTRS)

Rapp, R. H.

1974-01-01

The equations needed for the incorporation of gravity anomalies as unknown parameters in an orbit determination program are described. These equations were implemented in the Geodyn computer program which was used to process optical satellite observations. The arc dependent parameter unknowns, 184 unknown 15 deg and coordinates of 7 tracking stations were considered. Up to 39 arcs (5 to 7 days) involving 10 different satellites, were processed. An anomaly solution from the satellite data and a combination solution with 15 deg terrestrial anomalies were made. The limited data samples indicate that the method works. The 15 deg anomalies from various solutions and the potential coefficients implied by the different solutions are reported.

Cosmological reconstruction and stability in F(T,TG) gravity

NASA Astrophysics Data System (ADS)

Sharif, M.; Nazir, Kanwal

This study investigates the reconstruction scheme and stability of some well-known cosmological models in F(T,TG) gravity, where T and TG represent the torsion scalar and Gauss-Bonnet invariant torsion term, respectively. For this purpose, we consider isotropic homogeneous universe model and develop the corresponding field equations. It is found that we can reproduce cosmological evolution for power-law, de Sitter solutions, phantom/nonphantom era and Λ cold dark matter by applying reconstruction scheme in this gravity. Finally, we discuss stability of the reconstructed power-law and de Sitter solutions as well as two well-known F(T,TG) models. It is concluded that all these models provide stable solutions for suitable choices of the constants except power-law solutions.

Observational Constraints on the Identification of Shallow Lunar Magmatism: Insights from Floor-Fractured Craters

NASA Technical Reports Server (NTRS)

Jozwiak, L. M.; Head, J. W., III; Neumann, G. A.; Wilson, L.

2016-01-01

Floor-fractured craters are a class of lunar crater hypothesized to form in response to the emplacement of a shallow magmatic intrusion beneath the crater floor. The emplacement of a shallow magmatic body should result in a positive Bouguer anomaly relative to unaltered complex craters, a signal which is observed for the average Bouguer anomaly interior to the crater walls. We observe the Bouguer anomaly of floor-fractured craters on an individual basis using the unfiltered Bouguer gravity solution from GRAIL and also a degree 100-600 band-filtered Bouguer gravity solution. The low-magnitude of anomalies arising from shallow magmatic intrusions makes identification using unfiltered Bouguer gravity solutions inconclusive. The observed anomalies in the degree 100-600 Bouguer gravity solution are spatially heterogeneous, although there is spatial correlation between volcanic surface morphologies and positive Bouguer anomalies. We interpret these observations to mean that the spatial heterogeneity observed in the Bouguer signal is the result of variable degrees of magmatic degassing within the intrusions.

High Degree and Order Gravity Fields of the Moon Derived from GRAIL Data

NASA Technical Reports Server (NTRS)

Lemoine, F. G.; Goossens, S. J.; Sabaka, T. J.; Nicholas, J. B.; Mazarico, E.; Rowlands, D. D.; Loomis, B. D.; Chinn, D. S.; Caprette, D. S.; McCarthy, J. J.;

Seasonal and Static Gravity Field of Mars from MGS, Mars Odyssey and MRO Radio Science

NASA Technical Reports Server (NTRS)

Genova, Antonio; Goossens, Sander; Lemoine, Frank G.; Mazarico, Erwan; Neumann, Gregory A.; Smith, David E.; Zuber, Maria T.

2016-01-01

We present a spherical harmonic solution of the static gravity field of Mars to degree and order 120, GMM-3, that has been calculated using the Deep Space Network tracking data of the NASA Mars missions, Mars Global Surveyor (MGS), Mars Odyssey (ODY), and the Mars Reconnaissance Orbiter (MRO). We have also jointly determined spherical harmonic solutions for the static and time-variable gravity field of Mars, and the Mars k 2 Love numbers, exclusive of the gravity contribution of the atmosphere. Consequently, the retrieved time-varying gravity coefficients and the Love number k 2 solely yield seasonal variations in the mass of the polar caps and the solid tides of Mars, respectively. We obtain a Mars Love number k 2 of 0.1697 +/-0.0027 (3- sigma). The inclusion of MRO tracking data results in improved seasonal gravity field coefficients C 30 and, for the first time, C 50 . Refinements of the atmospheric model in our orbit determination program have allowed us to monitor the odd zonal harmonic C 30 for approx.1.5 solar cycles (16 years). This gravity model shows improved correlations with MOLA topography up to 15% larger at higher harmonics ( l = 60–80) than previous solutions.

Seasonal and static Gravity Field of Mars from MGS, Mars Odyssey and MRO Radio Science

NASA Technical Reports Server (NTRS)

Genova, Antonio; Goossens, Sander; Lemoine, Frank G.; Mazarico, Erwan; Neumann, Gregory A.; Smith, David E.; Zuber, Maria T.

2016-01-01

We present a spherical harmonic solution of the static gravity field of Mars to degree and order 120, GMM-3, that has been calculated using the Deep Space Network tracking data of the NASA Mars missions, Mars Global Surveyor (MGS), Mars Odyssey (ODY), and the Mars Reconnaissance Orbiter (MRO). We have also jointly determined spherical harmonic solutions for the static and time-variable gravity field of Mars, and the Mars k(sub 2) Love numbers, exclusive of the gravity contribution of the atmosphere. Consequently, the retrieved time-varying gravity coefficients and the Love number k(sub 2) solely yield seasonal variations in the mass of the polar caps and the solid tides of Mars, respectively. We obtain a Mars Love number k(sub 2) of 0.1697 +/- 0.0027 (3- sigma). The inclusion of MRO tracking data results in improved seasonal gravity field coefficients C(sub 30) and, for the first time, C 50. Refinements of the atmospheric model in our orbit determination program have allowed us to monitor the odd zonal harmonic C(sub 30) for approximately 1.5 solar cycles (16 years). This gravity model shows improved correlations with MOLA topography up to 15% larger at higher harmonics ( l = 60-80) than previous solutions.

Annual, Seasonal, and Secular Changes in Time-Variable Gravity from GRACE

NASA Astrophysics Data System (ADS)

Lemoine, F. G.; Luthcke, S. B.; Klosko, S. M.; Rowlands, D. D.; Chinn, D. S.; McCarthy, J. J.; Ray, R. D.; Boy, J.

2007-12-01

The NASA/DLR GRACE mission, launched in 2002, has now operated for more than five years, producing monthly and ten-day snapshots of the variations of the gravity field of the Earth. The available solutions, either from spherical harmonics or from mascons, allow us new insights into the variations of surface gravity on the Earth at annual, inter-annual, and secular time scales. Our baseline time series, based on GGM02C, NCEP Atmospheric Gravity with IB, and GOT00 tides now is extended to July 2007, spanning four+ years, and we analyze both mascon and spherical harmonic solutions from this time series with respect to global hydrology variations. Our 4degx4deg mascon solutions are extended to cover all continental regions of the globe. Comparisons with hydrology (land-surface) models can offer insights into how these models might be improved. We compare our baseline time series, with new time series that include an updated Goddard Ocean Tide (GOT) model, ECMWF- 3hr atmosphere de-aliasing data, and the MOG-2D ocean dealiasing product. Finally, we intercompare the spherical harmonic solutions at low degree from GRACE from the various product centers (e.g., GFZ, CSR, GRGS), and look for secular signals in both the GSFC mascon and spherical harmonic solutions, taking care to compare the results for secular gravity field change with independent solutions developed over 25 years of independent tracking to geodetic satellites by Satellite Laser Ranging (SLR) and DORIS.

Stability of the Kasner universe in f (T ) gravity

NASA Astrophysics Data System (ADS)

Paliathanasis, Andronikos; Said, Jackson Levi; Barrow, John D.

2018-02-01

f (T ) gravity theory offers an alternative context in which to consider gravitational interactions where torsion, rather than curvature, is the mechanism by which gravitation is communicated. We investigate the stability of the Kasner solution with several forms of the arbitrary Lagrangian function examined within the f (T ) context. This is a Bianchi type-I vacuum solution with anisotropic expansion factors. In the f (T ) gravity setting, the solution must conform to a set of conditions in order to continue to be a vacuum solution of the generalized field equations. With this solution in hand, the perturbed field equations are determined for power-law and exponential forms of the f (T ) function. We find that the point which describes the Kasner solution is a saddle point which means that the singular solution is unstable. However, we find the de Sitter universe is a late-time attractor. In general relativity, the cosmological constant drives the isotropization of the spacetime while in this setting the extra f (T ) contributions now provide this impetus.

Cosmological bouncing solutions in extended teleparallel gravity theories

NASA Astrophysics Data System (ADS)

de la Cruz-Dombriz, Álvaro; Farrugia, Gabriel; Said, Jackson Levi; Gómez, Diego Sáez-Chillón

2018-05-01

In the context of extended teleparallel gravity theories with a 3 +1 -dimensional Gauss-Bonnet analog term, we address the possibility of these theories reproducing several well-known cosmological bouncing scenarios in a four-dimensional Friedmann-Lemaître-Robertson-Walker geometry. We study which types of gravitational Lagrangians are capable of reconstructing bouncing solutions provided by analytical expressions for symmetric, oscillatory, superbounce, matter bounce, and singular bounce. Some of the Lagrangians discovered are analytical at the origin, having both Minkowski and Schwarzschild vacuum solutions. All these results open up the possibility for such theories to be competitive candidates of extended theories of gravity in cosmological scales.

Scalar hair around charged black holes in Einstein-Gauss-Bonnet gravity

NASA Astrophysics Data System (ADS)

Grandi, Nicolás; Landea, Ignacio Salazar

2018-02-01

We explore charged black hole solutions in Einstein-Gauss-Bonnet gravity in five dimensions, with a charged scalar hair. We interpret such hairy black holes as the final state of the superradiant instability previously reported for this system. We explore the relation of the hairy black hole solutions with the nonbackreacting quasibound states and scalar clouds, as well as with the boson star solutions.

Probability Analysis for Accidental Impact on Mars by the Micro-Spacecraft Procyon

NASA Astrophysics Data System (ADS)

Funase, Ryu; Yano, Hajime; Kawakatsu, Yasuhiro; Ozaki, Naoya; Nakajima, Shintaro; Shimizu, Yukio

This paper analyzes the impact probability on Mars for the 50kg-class micro-spacecraft PROCYON (PRoximate Object Close flYby with Optical Navigation) in 50 years after its launch. PROCYON, which is mainly developed by the University of Tokyo and the Japan Aerospace Exploration Agency (JAXA), has two missions: the first is the technology demonstration of a micro-spacecraft bus system for deep space exploration and the second is proximity operation by Near-Earth asteroids (NEAs) as the closest flyby distance from a target asteroid is aimed around 30 kilometer. The spacecraft is scheduled to be launched together with Japan’s second asteroid sample return spacecraft "Hayabusa-2" at the end of 2014. Initially PROCYON will be inserted into an Earth resonant trajectory that allows the spacecraft to cruise back to the Earth by solar electric propulsion leveraging. The Earth gravity assist, which is scheduled at the end of 2015, will enable the spacecraft to expand a number of candidate NEAs for flyby operations. At the time of the writing, its candidate NEAs include "2000 DP107", "2010 LJ14" and "2002 AJ29". A miniature ion thruster is mounted on the spacecraft to provide 300muN of thrust with specific impulse of 1200 seconds for deep space maneuver before Earth gravity assist. Considering a small amount of its fuel (about 2 kg of Xenon propellant), PROCYON has no possibility to impact directly on Mars without Earth gravity assist. However, if PROCYON successfully obtains large enough delta-V by the Earth gravity assist at the end of 2015, a possibility of accidental impact on Mars cannot be neglected in order to comply the COSPAR planetary protection requirements for forward contamination. In this paper, we calculate the possibility of accidental impact on Mars after the Earth gravity assist. As the result we conclude that the possibility of Mars impact is negligible within 50 years after its launch.

Improvements in GRACE Gravity Fields Using Regularization

NASA Astrophysics Data System (ADS)

Save, H.; Bettadpur, S.; Tapley, B. D.

2008-12-01

The unconstrained global gravity field models derived from GRACE are susceptible to systematic errors that show up as broad "stripes" aligned in a North-South direction on the global maps of mass flux. These errors are believed to be a consequence of both systematic and random errors in the data that are amplified by the nature of the gravity field inverse problem. These errors impede scientific exploitation of the GRACE data products, and limit the realizable spatial resolution of the GRACE global gravity fields in certain regions. We use regularization techniques to reduce these "stripe" errors in the gravity field products. The regularization criteria are designed such that there is no attenuation of the signal and that the solutions fit the observations as well as an unconstrained solution. We have used a computationally inexpensive method, normally referred to as "L-ribbon", to find the regularization parameter. This paper discusses the characteristics and statistics of a 5-year time-series of regularized gravity field solutions. The solutions show markedly reduced stripes, are of uniformly good quality over time, and leave little or no systematic observation residuals, which is a frequent consequence of signal suppression from regularization. Up to degree 14, the signal in regularized solution shows correlation greater than 0.8 with the un-regularized CSR Release-04 solutions. Signals from large-amplitude and small-spatial extent events - such as the Great Sumatra Andaman Earthquake of 2004 - are visible in the global solutions without using special post-facto error reduction techniques employed previously in the literature. Hydrological signals as small as 5 cm water-layer equivalent in the small river basins, like Indus and Nile for example, are clearly evident, in contrast to noisy estimates from RL04. The residual variability over the oceans relative to a seasonal fit is small except at higher latitudes, and is evident without the need for de-striping or spatial smoothing.

The 3-5 semiconductor solid solution single crystal growth. [low gravity float zone growth experiments using gallium indium antimonides and cadmium tellurides

NASA Technical Reports Server (NTRS)

Gertner, E. R.

1980-01-01

Techniques used for liquid and vapor phase epitaxy of gallium indium arsenide are described and the difficulties encountered are examined. Results show that the growth of bulk III-V solid solution single crystals in a low gravity environment will not have a major technological impact. The float zone technique in a low gravity environment is demonstrated using cadmium telluride. It is shown that this approach can result in the synthesis of a class of semiconductors that can not be grown in normal gravity because of growth problems rooted in the nature of their phase diagrams.

Conformal gravity holography in four dimensions.

PubMed

Grumiller, Daniel; Irakleidou, Maria; Lovrekovic, Iva; McNees, Robert

2014-03-21

We formulate four-dimensional conformal gravity with (anti-)de Sitter boundary conditions that are weaker than Starobinsky boundary conditions, allowing for an asymptotically subleading Rindler term concurrent with a recent model for gravity at large distances. We prove the consistency of the variational principle and derive the holographic response functions. One of them is the conformal gravity version of the Brown-York stress tensor, the other is a "partially massless response". The on shell action and response functions are finite and do not require holographic renormalization. Finally, we discuss phenomenologically interesting examples, including the most general spherically symmetric solutions and rotating black hole solutions with partially massless hair.

Gravity field, geoid and ocean surface by space techniques

NASA Technical Reports Server (NTRS)

Anderle, R. J.

1978-01-01

Knowledge of the earth's gravity field continued to increase during the last four years. Altimetry data from the GEOS-3 satellite has provided the geoid over most of the ocean to an accuracy of about one meter. Increasing amounts of laser data has permitted the solution for 566 terms in the gravity field with which orbits of the GEOS-3 satellite have been computed to an accuracy of about one to two meters. The combination of satellite tracking data, altimetry and gravimetry has yielded a solution for 1360 terms in the earth's gravity field. A number of problems remain to be solved to increase the accuracy of the gravity field determination. New satellite systems would provide gravity data in unsurveyed areas and correction for topographic features of the ocean and improved computational procedures together with a more extensive laser network will considerably improve the accuracy of the results.

MIDACO on MINLP space applications

NASA Astrophysics Data System (ADS)

Schlueter, Martin; Erb, Sven O.; Gerdts, Matthias; Kemble, Stephen; Rückmann, Jan-J.

2013-04-01

A numerical study on two challenging mixed-integer non-linear programming (MINLP) space applications and their optimization with MIDACO, a recently developed general purpose optimization software, is presented. These applications are the optimal control of the ascent of a multiple-stage space launch vehicle and the space mission trajectory design from Earth to Jupiter using multiple gravity assists. Additionally, an NLP aerospace application, the optimal control of an F8 aircraft manoeuvre, is discussed and solved. In order to enhance the optimization performance of MIDACO a hybridization technique, coupling MIDACO with an SQP algorithm, is presented for two of these three applications. The numerical results show, that the applications can be solved to their best known solution (or even new best solution) in a reasonable time by the considered approach. Since using the concept of MINLP is still a novelty in the field of (aero)space engineering, the demonstrated capabilities are seen as very promising.

A numerical solution for thermoacoustic convection of fluids in low gravity

NASA Technical Reports Server (NTRS)

Spradley, L. W.; Bourgeois, S. V., Jr.; Fan, C.; Grodzka, P. G.

1973-01-01

A finite difference numerical technique for solving the differential equations which describe thermal convection of compressible fluids in low gravity are reported. Results of one-dimensional calculations are presented, and comparisons are made to previous solutions. The primary result presented is a one-dimensional radial model of the Apollo 14 heat flow and convection demonstration flight experiment. The numerical calculations show that thermally induced convective motion in a confined fluid can have significant effects on heat transfer in a low gravity environment.

Action growth for black holes in modified gravity

NASA Astrophysics Data System (ADS)

Sebastiani, Lorenzo; Vanzo, Luciano; Zerbini, Sergio

2018-02-01

The general form of the action growth for a large class of static black hole solutions in modified gravity which includes F (R ) -gravity models is computed. The cases of black hole solutions with nonconstant Ricci scalar are also considered, generalizing the results previously found and valid only for black holes with constant Ricci scalar. An argument is put forward to provide a physical interpretation of the results, which seem tightly connected with the generalized second law of black hole thermodynamics.

Models for the dynamics of dust-like matter in the self-gravity field: The method of hydrodynamic substitutions

NASA Astrophysics Data System (ADS)

Zhuravlev, V. M.

2017-09-01

Models for the dynamics of a dust-like medium in the self-gravity field are investigated. Solutions of the corresponding problems are constructed by the method of hydrodynamic substitutions generalizing the Cole-Hopf substitutions. The method is extended to multidimensional ideal and viscous fluid flows with cylindrical and spherical symmetries for which exact solutions are constructed. Solutions for the dynamics of self-gravitating dust with arbitrary initial distributions of both fluid density and velocity are constructed using special coordinate transformations. In particular, the problem of cosmological expansion is considered in terms of Newton's gravity theory. Models of a one-dimensional viscous dust fluid flow and some problems of gas hydrodynamics are considered. Examples of exact solutions and their brief analysis are provided.

Black hole solutions in d = 5 Chern-Simons gravity

NASA Astrophysics Data System (ADS)

Brihaye, Yves; Radu, Eugen

2013-11-01

The five dimensional Einstein-Gauss-Bonnet gravity with a negative cosmological constant becomes, for a special value of the Gauss-Bonnet coupling constant, a Chern-Simons (CS) theory of gravity. In this work we discuss the properties of several different types of black object solutions of this model. Special attention is paid to the case of spinning black holes with equal-magnitude angular momenta which posses a regular horizon of spherical topology. Closed form solutions are obtained in the small angular momentum limit. Nonperturbative solutions are constructed by solving numerically the equations of the model. Apart from that, new exact solutions describing static squashed black holes and black strings are also discussed. The action and global charges of all configurations studied in this work are obtained by using the quasilocal formalism with boundary counterterms generalized for the case of a d = 5 CS theory.

Retrograde and Direct Powered Aero-Gravity-Assist Trajectories around Mars

NASA Astrophysics Data System (ADS)

Murcia, J. O.; Prado, A. F. B. A.; Gomes, V. M.

2018-04-01

A Gravity-Assist maneuver is used to reduce fuel consumption and/or trip times in interplanetary missions. It is based in a close approach of a spacecraft to a celestial body. Missions like Voyager and Ulysses used this concept. The present paper performs a study of a maneuver that combines three effects: the gravity of the planet, the application of an impulsive maneuver when the spacecraft is passing by the periapsis and the effects of the atmosphere of the planet. Direct and retrograde trajectories are considered, with particular attention to the differences due to the higher relative velocity between the spacecraft and the atmosphere, which increases the effects of the atmosphere. The planet Mars is used for the numerical examples.

Effect of Gravity Level on the Particle Shape and Size During Zeolite Crystal Growth

NASA Technical Reports Server (NTRS)

Song, Hong-Wei; Ilebusi, Olusegun J.; Sacco, Albert, Jr.

2003-01-01

A microscopic diffusion model is developed to represent solute transport in the boundary layer of a growing zeolite crystal. This model is used to describe the effect of gravity on particle shape and solute distribution. Particle dynamics and crystal growth kinetics serve as the boundary conditions of flow and convection-diffusion equations. A statistical rate theory is used to obtain the rate of solute transport across the growing interface, which is expressed in terms of concentration and velocity of solute species. Microgravity can significantly decrease the solute velocity across the growing interface compared to its earth-based counterpart. The extent of this reduction highly depends on solute diffusion constant in solution. Under gravity, the flow towards the crystal enhances solute transport rate across the growing interface while the flow away from crystals reduces this rate, suggesting a non-uniform growth rate and thus an elliptic final shape. However, microgravity can significantly reduce the influence of flow and obtain a final product with perfect spherical shape. The model predictions compare favorably with the data of space experiment of zeolites grown in space.

GRACE Solutions for the Gravity Field over Central Europe Compared to the Surface Field as Recorded by the GGP Network.

NASA Astrophysics Data System (ADS)

Crossley, D. J.; de Linage, C.; Hinderer, J.; Boy, J.

2007-12-01

As the number of different solutions from the GRACE satellite gravity project evolves, we can make more meaningful comparisons between the satellite-derived field and the surface field as recorded by superconducting gravimeters. On the GRACE side, we use CSR Level 2 products RL01 and the recent RL04 solutions, GFZ RL04 solutions, and the CNES/GRGS 10-day solutions, all for the time periods these are available. On the GGP side, we take advantage of the 10 years of SG data since July 1997 from 6-8 ground stations in Europe, allowing for the change in the network configuration as stations begin and end recording. Only data since 2002 can be compared directly to GRACE. Our primary measure of variability is the first principal component of the EOF analysis of all the fields. Unsurprisingly, the seasonal components for all the comparisons are similar in phase, but different in amplitude, to the predictions from a global hydrology model (GLDAS), provided allowance is made for the location of the SG stations above or below the soil moisture horizon that controls the gravity signature. We use detailed modeling at the Strasbourg station, as well as published results for Moxa and Membach, to confirm the gravity effect of hydrology. Good agreement is found between the GGP and the CNES/GRGS 10-day solutions, indicating the higher temporal resolution of this satellite solution is valid for our limited geographical area. We also synthesize the gravity field over the sub-group of GGP stations in N.E. Asia to see how the GRACE variability compares to that for the European array and to assess future ground validation using new GGP stations in that part of the world.

Stealth configurations in vector-tensor theories of gravity

NASA Astrophysics Data System (ADS)

Chagoya, Javier; Tasinato, Gianmassimo

2018-01-01

Studying the physics of compact objects in modified theories of gravity is important for understanding how future observations can test alternatives to General Relativity. We consider a subset of vector-tensor Galileon theories of gravity characterized by new symmetries, which can prevent the propagation of the vector longitudinal polarization, even in absence of Abelian gauge invariance. We investigate new spherically symmetric and slowly rotating solutions for these systems, including an arbitrary matter Lagrangian. We show that, under certain conditions, there always exist stealth configurations whose geometry coincides with solutions of Einstein gravity coupled with the additional matter. Such solutions have a non-trivial profile for the vector field, characterized by independent integration constants, which extends to asymptotic infinity. We interpret our findings in terms of the symmetries and features of the original vector-tensor action, and on the number of degrees of freedom that it propagates. These results are important to eventually describe gravitationally bound configurations in modified theories of gravity, such as black holes and neutron stars, including realistic matter fields forming or surrounding the object.

Renormalization of Einstein gravity through a derivative-dependent field redefinition

NASA Astrophysics Data System (ADS)

Slovick, Brian

2018-01-01

This work explores an alternative solution to the problem of renormalizability in Einstein gravity. In the proposed approach, Einstein gravity is transformed into the renormalizable theory of four-derivative gravity by applying a local field redefinition containing an infinite number of higher derivatives. It is also shown that the current-current amplitude is invariant with the field redefinition, and thus the unitarity of Einstein gravity is preserved.

Feeling Gravity's Pull: Gravity Modeling. The Gravity Field of Mars

NASA Technical Reports Server (NTRS)

Lemoine, Frank; Smith, David; Rowlands, David; Zuber, Maria; Neumann, G.; Chinn, Douglas; Pavlis, D.

2000-01-01

Most people take the constant presence of gravitys pull for granted. However, the Earth's gravitational strength actually varies from location to location. This variation occurs because mass, which influences an object's gravitational pull, is not evenly distributed within the planet. Changes in topography, such as glacial movement, an earthquake, or a rise in the ocean level, can subtly affect the gravity field. An accurate measurement of the Earth's gravity field helps us understand the distribution of mass beneath the surface. This insight can assist us in locating petroleum, mineral deposits, ground water, and other valuable substances. Gravity mapping can also help notice or verify changes in sea surface height and other ocean characteristics. Such changes may indicate climate change from polar ice melting and other phenomena. In addition, gravity mapping can indicate how land moves under the surface after earthquakes and other plate tectonic processes. Finally, changes in the Earth's gravity field might indicate a shift in water distribution that could affect agriculture, water supplies for population centers, and long-term weather prediction. Scientists can map out the Earth's gravity field by watching satellite orbits. When a satellite shifts in vertical position, it might be passing over an area where gravity changes in strength. Gravity is only one factor that may shape a satellite's orbital path. To derive a gravity measurement from satellite movement, scientists must remove other factors that might affect a satellite's position: 1. Drag from atmospheric friction. 2. Pressure from solar radiation as it heads toward Earth and. as it is reflected off the surface of the Earth 3. Gravitational pull from the Sun, the Moon, and other planets in the Solar System. 4. The effect of tides. 5. Relativistic effects. Scientists must also correct for the satellite tracking process. For example, the tracking signal must be corrected for refraction through the atmosphere of the Earth. Supercomputers can calculate the effect of gravity for specific locations in space following a mathematical process known as spherical harmonics, which quantifies the gravity field of a planetary body. The process is based on Laplace's fundamental differential equation of gravity. The accuracy of a spherical harmonic solution is rated by its degree and order. Minute variations in gravity are measured against the geoid, a surface of constant gravity acceleration at mean sea level. The geoid reference gravity model strength includes the central body gravitational attraction (9.8 m/sq s) and a geopotential variation in latitude partially caused by the rotation of the Earth. The rotational effect modifies the shape of the geoid to be more like an ellipsoid, rather than a perfect, circle. Variations of gravity strength from the ellipsoidal reference model are measured in units called milli-Galileos (mGals). One mGal equals 10(exp -5) m/sq s. Research projects have also measured the gravity fields of other planetary bodies, as noted in the user profile that follows. From this information, we may make inferences about our own planet's internal structure and evolution. Moreover, mapping the gravity fields of other planets can help scientists plot the most fuel-efficient course for spacecraft expeditions to those planets.

Thermodynamics of "exotic" Bañados-Teitelboim-Zanelli black holes.

PubMed

Townsend, Paul K; Zhang, Baocheng

2013-06-14

A number of three-dimensional (3D) gravity models, such as 3D conformal gravity, admit "exotic" black hole solutions: the metric is the same as the Bañados-Teitelboim-Zanelli metric of 3D Einstein gravity but with reversed roles for mass and angular momentum, and an entropy proportional to the length of the inner horizon instead of the event horizon. Here we show that the Bañados-Teitelboim-Zanelli solutions of the exotic 3D Einstein gravity (with parity-odd action but Einstein field equations) are exotic black holes, and we investigate their thermodynamics. The first and second laws of black hole thermodynamics still apply, and the entropy still has a statistical interpretation.

Gravity model improvement using GEOS 3 /GEM 9 and 10/. [and Seasat altimetry data

NASA Technical Reports Server (NTRS)

Lerch, F. J.; Wagner, C. A.; Klosko, S. M.; Laubscher, R. E.

1979-01-01

Although errors in previous gravity models have produced large uncertainties in the orbital position of GEOS 3, significant improvement has been obtained with new geopotential solutions, Goddard Earth Model (GEM) 9 and 10. The GEM 9 and 10 solutions for the potential coefficients and station coordinates are presented along with a discussion of the new techniques employed. Also presented and discussed are solutions for three fundamental geodetic reference parameters, viz. the mean radius of the earth, the gravitational constant, and mean equatorial gravity. Evaluation of the gravity field is examined together with evaluation of GEM 9 and 10 for orbit determination accuracy. The major objectives of GEM 9 and 10 are achieved. GEOS 3 orbital accuracies from these models are about 1 m in their radial components for 5-day arc lengths. Both models yield significantly improved results over GEM solutions when compared to surface gravimetry, Skylab and GEOS 3 altimetry, and highly accurate BE-C (Beacon Explorer-C) laser ranges. The new values of the parameters discussed are given.

Clarifying the interplate main tectonic elements of Western Anatolia, Turkey by using GNSS velocities and Bouguer gravity anomalies

NASA Astrophysics Data System (ADS)

Çırmık, Ayça; Pamukçu, Oya

2017-10-01

In this study, the GNSS and gravity data were processed and compared together for examining the continental structures of the Western Anatolia region which has very complicated tectonism. The GNSS data of three national projects were processed and GNSS velocities were found as approximately 25 mm per year towards southwest with respect to the Eurasia fixed frame. In order to investigate the interplate motions of the region, the Anatolian and Aegean block solutions were calculated and the differences in directions and amplitudes of velocities were observed particularly in the Anatolian block solution. Due to the Anatolian block solutions, the study area was grouped into three regions and compared with the tectonic structures as the first time for Western Anatolia by this study. Additionally, W-E and N-S relative GNSS solutions were obtained for observing the possible tectonic borders of the study area. Besides, 2nd order horizontal derivative and low-pass filter methods were applied to Bouguer gravity anomalies and the results of the gravity applications and the changes on crustal-mantle interface were compared with the GNSS horizontal velocities.

Influence of heterogeneity on second-kind self-similar solutions for viscous gravity currents

DOE PAGES

Zheng, Zhong; Christov, Ivan  C.; Stone, Howard  A.

2014-05-01

We report experimental, theoretical and numerical results on the effects of horizontal heterogeneities on the propagation of viscous gravity currents. We use two geometries to highlight these effects: (a) a horizontal channel (or crack) whose gap thickness varies as a power-law function of the streamwise coordinate; (b) a heterogeneous porous medium whose permeability and porosity have power-law variations. We demonstrate that two types of self-similar behaviours emerge as a result of horizontal heterogeneity: (a) a first-kind self-similar solution is found using dimensional analysis (scaling) for viscous gravity currents that propagate away from the origin (a point of zero permeability); (b)more » a second-kind self-similar solution is found using a phase-plane analysis for viscous gravity currents that propagate toward the origin. These theoretical predictions, obtained using the ideas of self-similar intermediate asymptotics, are compared with experimental results and numerical solutions of the governing partial differential equation developed under the lubrication approximation. All three results are found to be in good agreement.« less

Mercury's gravity field, tidal Love number k2, and spin axis orientation revealed with MESSENGER radio tracking data

NASA Astrophysics Data System (ADS)

Verma, A. K.; Margot, J. L.

2015-12-01

We are conducting an independent analysis of two-way Doppler and two-way range radio tracking data from the MESSENGER spacecraft in orbit around Mercury from 2011 to 2015. Our goals are to estimate Mercury's gravity field and to obtain independent estimates of the tidal Love number k2 and spin axis orientation. Our gravity field solution reproduces existing values with high fidelity, and prospects for recovery of the other quantities are excellent. The tidal Love number k2 provides powerful constraints on interior models of Mercury, including the mechanical properties of the mantle and the possibility of a solid FeS layer at the top of the core. Current gravity analyses cannot rule out a wide range of values (k2=43-0.50) and a variety of plausible interior models. We are seeking an independent estimate of tidal Love number k2 with improved errors to further constrain these models. Existing gravity-based solutions for Mercury's spin axis orientation differ from those of Earth-based radar and topography-based solutions. This difference may indicate an error in one of the determinations, or a real difference between the orientations about which the gravity field and the crust rotate, which can exist in a variety of plausible configuration. Securing an independent estimate of the spin axis orientation is vital because this quantity has a profound impact on the determination of the moment of inertia and interior models. We have derived a spherical harmonic solution of the gravity field to degree and order 40 as well as estimates of the tidal Love number k2 and spin axis orientation.

Mercury’s gravity field, tidal Love number k2, and spin axis orientation revealed with MESSENGER radio tracking data

NASA Astrophysics Data System (ADS)

Verma, Ashok Kumar; Margot, Jean-Luc

2015-11-01

We are conducting an independent analysis of two-way Doppler and two-way range radio tracking data from the MESSENGER spacecraft in orbit around Mercury from 2011 to 2015. Our goals are to estimate Mercury’s gravity field and to obtain independent estimates of the tidal Love number k2 and spin axis orientation. Our gravity field solution reproduces existing values with high fidelity, and prospects for recovery of the other quantities are excellent.The tidal Love number k2 provides powerful constraints on interior models of Mercury, including the mechanical properties of the mantle and the possibility of a solid FeS layer at the top of the core. Current gravity analyses cannot rule out a wide range of values (k2=43-0.50) and a variety of plausible interior models. We are seeking an independent estimate of tidal Love number k2 with improved errors to further constrain these models.Existing gravity-based solutions for Mercury's spin axis orientation differ from those of Earth-based radar and topography-based solutions. This difference may indicate an error in one of the determinations, or a real difference between the orientations about which the gravity field and the crust rotate, which can exist in a variety of plausible configuration. Securing an independent estimate of the spin axis orientation is vital because this quantity has a profound impact on the determination of the moment of inertia and interior models.We have derived a spherical harmonic solution of the gravity field to degree and order 40 as well as estimates of the tidal Love number k2 and spin axis orientation

Rotating black hole solutions in relativistic analogue gravity

NASA Astrophysics Data System (ADS)

Giacomelli, Luca; Liberati, Stefano

2017-09-01

Simulation and experimental realization of acoustic black holes in analogue gravity systems have lead to a novel understanding of relevant phenomena such as Hawking radiation or superradiance. We explore here the possibility of using relativistic systems for simulating rotating black hole solutions and possibly get an acoustic analogue of a Kerr black hole. In doing so, we demonstrate a precise relation between nonrelativistic and relativistic solutions and provide a new class of vortex solutions for relativistic systems. Such solutions might be used in the future as a test bed in numerical simulations as well as concrete experiments.

Using gravity as a proxy for stress accumulation in complex fault systems

NASA Astrophysics Data System (ADS)

Hayes, Tyler Joseph

The gravity signal contains information regarding changes in density at all depths and can be used as a proxy for the strain accumulation in fault networks. A general method for calculating the total, dilatational, and free-air gravity for fault systems with arbitrary geometry, slip motion, and number of fault segments is presented. The technique uses a Green's function approach for a fault buried within an elastic half-space with an underlying driver plate forcing the system. A stress-evolution time-dependent earthquake fault model was used to create simulated slip histories over the San Andreas Fault network in California. Using a sum of the gravity signals from each fault segment in the model, via coseismic gravity Green's functions, a time-dependent gravity model was created. The steady-state gravity from the long term plate motion generates a signal over five years with magnitudes of +/- ˜2 muGal; the current limit of portable instrument observations. Moderate to large events generate signal magnitudes in the range of ˜10 muGal to ˜80 muGal, well within the range of ground based observations. The complex fault network geometry of California significantly affects the spatial extent of the gravity signal from the three events studied. Statistical analysis of 55 000 years of simulated slip histories were used to investigate the use of the dilatational gravity signal as a proxy for precursory stress and strain changes. Results indicate that the precursory dilatational gravity signal is dependent upon the fault orientation with respect the tectonic loading plate velocity. This effect is interpreted as a consequence of preferential amplification of the shear stress or reduction of the normal stress, depending on the steady-state regime investigated. Finally, solutions for the corresponding gravity gradients of the coseismic dilatational gravity signals are developed for a vertical strike-slip fault. Gravity gradient solutions exhibit similar spatial distributions as those calculated for Coulomb stress changes, reflecting their physical relationship to the stress changes. The magnitude of the signals, on the order of 1 x 10-4 E, are beyond the resolution of typical exploration instruments at the present time. Keywords. numerical solutions; seismic cycle; gravity; gravity gradients; time variable gravity; earthquake interaction; forecasting; and prediction

Quasi-local conserved charges in Lorenz-diffeomorphism covariant theory of gravity

NASA Astrophysics Data System (ADS)

Adami, H.; Setare, M. R.

2016-04-01

In this paper, using the combined Lorenz-diffeomorphism symmetry, we find a general formula for the quasi-local conserved charge of the covariant gravity theories in a first order formalism of gravity. We simplify the general formula for the Lovelock theory of gravity. Afterwards, we apply the obtained formula on BHT gravity to obtain the energy and angular momentum of the rotating OTT black hole solution in the context of this theory.

Impact of orbit design choices on the gravity field retrieval of Next Generation Gravity Missions - Insights on the ESA-ADDCON project

NASA Astrophysics Data System (ADS)

Daras, Ilias; Visser, Pieter; Sneeuw, Nico; van Dam, Tonie; Pail, Roland; Gruber, Thomas; Tabibi, Sajad; Chen, Qiang; Liu, Wei; Tourian, Mohammad; Engels, Johannes; Saemian, Peyman; Siemes, Christian; Haagmans, Roger

2017-04-01

Next Generation Gravity Missions (NGGMs) expected to be launched in the mid-term future have set high anticipations for an enhanced monitoring of mass transport in the Earth system, establishing their products applicable to new scientific fields and serving societal needs. The European Space Agency (ESA) has issued several studies on concepts of NGGMs. Following this tradition, the project "Additional Constellations & Scientific Analysis Studies of the Next Generation Gravity Mission" picks up where the previous study ESA-SC4MGV left off. One of the ESA-ADDCON project objectives is to investigate the impact of different orbit configurations and parameters on the gravity field retrieval. Given a two-pair Bender-type constellation, consisting of a polar and an inclined pair, choices for orbit design such as the altitude profile during mission lifetime, the length of retrieval period, the value of sub-cycles and the choice of a prograde over a retrograde orbit are investigated. Moreover, the problem of aliasing due to ocean tide model inaccuracies, as well as methods for mitigating their effect on gravity field solutions are investigated in the context of NGGMs. The performed simulations make use of the gravity field processing approach where low-resolution gravity field solutions are co-parameterized in short-term periods (e.g. daily) together with the long-term solutions (e.g. 11-day solution). This method proved to be beneficial for NGGMs (ESA-SC4MGV project) since the enhanced spatio-temporal sampling enables a self-de-aliasing of high-frequency atmospheric and oceanic signals, which may now be a part of the retrieved signal. The potential added value of having such signals for the first time in near real-time is assessed within the project. This paper demonstrates the preliminary results of the ESA-ADDCON project focusing on aspects of orbit design choices for NGGMs.

The effect of Earth's oblateness on the seismic moment estimation from satellite gravimetry

NASA Astrophysics Data System (ADS)

Dai, Chunli; Guo, Junyi; Shang, Kun; Shum, C. K.; Wang, Rongjiang

2018-05-01

Over the last decade, satellite gravimetry, as a new class of geodetic sensors, has been increasingly studied for its use in improving source model inversion for large undersea earthquakes. When these satellite-observed gravity change data are used to estimate source parameters such as seismic moment, the forward modelling of earthquake seismic deformation is crucial because imperfect modelling could lead to errors in the resolved source parameters. Here, we discuss several modelling issues and focus on one modelling deficiency resulting from the upward continuation of gravity change considering the Earth's oblateness, which is ignored in contemporary studies. For the low degree (degree 60) time-variable gravity solutions from Gravity Recovery and Climate Experiment mission data, the model-predicted gravity change would be overestimated by 9 per cent for the 2011 Tohoku earthquake, and about 6 per cent for the 2010 Maule earthquake. For high degree gravity solutions, the model-predicted gravity change at degree 240 would be overestimated by 30 per cent for the 2011 Tohoku earthquake, resulting in the seismic moment to be systematically underestimated by 30 per cent.

Mimetic compact stars

NASA Astrophysics Data System (ADS)

Momeni, D.; Moraes, P. H. R. S.; Gholizade, H.; Myrzakulov, R.

Modified gravity models have been constantly proposed with the purpose of evading some standard gravity shortcomings. Recently proposed by Chamseddine and Mukhanov, the Mimetic Gravity arises as an optimistic alternative. Our purpose in this work is to derive Tolman-Oppenheimer-Volkoff equations and solutions for such a gravity theory. We solve them numerically for quark star and neutron star cases. The results are carefully discussed.

Effect of gravity field on the nonequilibrium/nonlinear chemical oscillation reactions

NASA Astrophysics Data System (ADS)

Fujieda, S.; Mori, Y.; Nakazawa, A.; Mogami, Y.

2001-01-01

Biological systems have evolved for a long time under the normal gravity. The Belousov-Zhabotinsky (BZ) reaction is a nonlinear chemical system far from the equilibrium that may be considered as a simplified chemical model of the biological systems so as to study the effect of gravity. The reaction solution is comprised of bromate in sulfuric acid as an oxidizing agent, 1,4-cyclohexanedione as an organic substrate, and ferroin as a metal catalyst. Chemical waves in the BZ reaction-diffusion system are visualized as blue and red patterns of ferriin and ferroin, respectively. After an improvement to the tubular reaction vessels in the experimental setup, the traveling velocity of chemical waves in aqueous solutions was measured in time series under normal gravity, microgravity, hyper-gravity, and normal gravity using the free-fall facility of JAMIC (Japan Microgravity Center), Hokkaido, Japan. Chemical patterns were collected as image data via CCD camera and analyzed by the software of NIH image after digitization. The estimated traveling velocity increased with increasing gravity as expected. It was clear experimentally that the traveling velocity of target patterns in reaction diffusion system was influenced by the effect of convection and correlated closely with the gravity field.

2006 Compilation of Alaska Gravity Data and Historical Reports

USGS Publications Warehouse

Saltus, Richard W.; Brown, Philip J.; Morin, Robert L.; Hill, Patricia L.

2008-01-01

Gravity anomalies provide fundamental geophysical information about Earth structure and dynamics. To increase geologic and geodynamic understanding of Alaska, the U.S. Geological Survey (USGS) has collected and processed Alaska gravity data for the past 50 years. This report introduces and describes an integrated, State-wide gravity database and provides accompanying gravity calculation tools to assist in its application. Additional information includes gravity base station descriptions and digital scans of historical USGS reports. The gravity calculation tools enable the user to reduce new gravity data in a consistent manner for combination with the existing database. This database has sufficient resolution to define the regional gravity anomalies of Alaska. Interpretation of regional gravity anomalies in parts of the State are hampered by the lack of local isostatic compensation in both southern and northern Alaska. However, when filtered appropriately, the Alaska gravity data show regional features having geologic significance. These features include gravity lows caused by low-density rocks of Cenozoic basins, flysch belts, and felsic intrusions, as well as many gravity highs associated with high-density mafic and ultramafic complexes.

Low launch-energy trajectories to the outer solar system via Venus and earth gravity-assist flybys

NASA Technical Reports Server (NTRS)

Diehl, Roger; Belbruno, Edward; Bender, David; Myers, Mark; Stetson, Douglas

1988-01-01

Recent cancellation of the program to develop a Centaur upper stage for use in the Space Transportation System (STS) has motivated considerable interest in trajectory modes with low launch-energy requirements to the outer solar system. Flyby encounters of the inner planets, especially Venus and earth, may be used to enable missions to Jupiter, Saturn, and a restricted class of comets. An examination of mission opportunities to these targets is presented through the end of this century using gravity-assist trajectories.

The Feasibility of a Galileo-Style Tour of the Uranian Satellites

NASA Technical Reports Server (NTRS)

Heaton, Andrew F.; Longuski, James M.; Vanhooser, Teresa B. (Technical Monitor)

2001-01-01

Gravity-assist trajectories have been a key to outer Solar System exploration. In particular, the gravity-assist tour of the Jovian satellites has contributed significantly to the success of the Galileo mission. A comparison of the Jovian system to the Uranian system reveals that the two possess similar satellite/planet mass ratios. Tisserand graphs of the Uranian system also indicate the potential for tours at Uranus. In this paper. We devise tour strategies and design a prototypical tour of the Uranian satellites, proving that tours at Uranus are feasible.

Gravitation. [consideration of black holes in gravity theories

NASA Technical Reports Server (NTRS)

Fennelly, A. J.

1978-01-01

Investigations of several problems of gravitation are discussed. The question of the existence of black holes is considered. While black holes like those in Einstein's theory may not exist in other gravity theories, trapped surfaces implying such black holes certainly do. The theories include those of Brans-Dicke, Lightman-Lee, Rosen, and Yang. A similar two-tensor theory of Yilmaz is investigated and found inconsistent and nonviable. The Newman-Penrose formalism for Riemannian geometries is adapted to general gravity theories and used to implement a search for twisting solutions of the gravity theories for empty and nonempty spaces. The method can be used to find the gravitational fields for all viable gravity theories. The rotating solutions are of particular importance for strong field interpretation of the Stanford/Marshall gyroscope experiment. Inhomogeneous cosmologies are examined in Einstein's theory as generalizations of homogeneous ones by raising the dimension of the invariance groups by one more parameter. The nine Bianchi classifications are extended to Rosen's theory of gravity for homogeneous cosmological models.

Combination of monthly gravity field solutions from different processing centers

NASA Astrophysics Data System (ADS)

Jean, Yoomin; Meyer, Ulrich; Jäggi, Adrian

2015-04-01

Currently, the official GRACE Science Data System (SDS) monthly gravity field solutions are generated independently by the Centre for Space Research (CSR) and the German Research Centre for Geosciences (GFZ). Additional GRACE SDS monthly fields are provided by the Jet Propulsion Laboratory (JPL) for validation and outside the SDS by a number of other institutions worldwide. Although the adopted background models and processing standards have been harmonized more and more by the various processing centers during the past years, notable differences still exist and the users are more or less left alone with a decision which model to choose for their individual applications. Combinations are well-established in the area of other space geodetic techniques, such as the Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Very Long Baseline Interferometry (VLBI), where regular comparisons and combinations of space-geodetic products have tremendously increased the usefulness of the products in a wide range of disciplines and scientific applications. In the frame of the recently started Horizon 2020 project European Gravity Service for Improved Emergency Management (EGSIEM), a scientific combination service shall therefore be established to deliver the best gravity products for applications in Earth and environmental science research based on the unified knowledge of the European GRACE community. In a first step the large variety of available monthly GRACE gravity field solutions shall be mutually compared spatially and spectrally. We assess the noise of the raw as well as filtered solutions and compare the secular and seasonal periodic variations fitted to the monthly solutions. In a second step we will explore ways to generate combined solutions, e.g., based on a weighted average of the individual solutions using empirical weights derived from pair-wise comparisons. We will also assess the quality of such a combined solution and discuss the potential benefits for the GRACE and GRACE-FO user community.

21 CFR 864.9320 - Copper sulfate solution for specific gravity determinations.

Code of Federal Regulations, 2010 CFR

2010-04-01

... used to determine whether the hemoglobin content of a potential donor's blood meets the required level (12.5 grams per 100 milliliters of blood for women and 13.5 grams per 100 milliliters of blood for men... Establishments That Manufacture Blood and Blood Products § 864.9320 Copper sulfate solution for specific gravity...

On singularities of capillary surfaces in the absence of gravity

DOE PAGES

Roytburd, V.

1983-01-01

We smore » tudy numerical solutions to the equation of capillary surfaces in trapezoidal domains in the absence of gravity when the boundary contact angle declines from 90 ° to some critical value. We also discuss a result on the behavior of solutions in more general domains that confirms numerical calculations.« less

Microgravity

NASA Image and Video Library

2001-06-06

Gravity or density-driven convection occurs as protein molecules incorporate into a crystal lattice from the surrounding solution. The layer bordering the crystal (the depletion zone) then contains a less-dense protein concentration, causing the layer to rise. The remaining, denser solution sinks because of gravity, creating eddies that make it difficult for more protein molecules to attach to the crystal in an ordered way.

Radiation and the classical double copy for color charges

NASA Astrophysics Data System (ADS)

Goldberger, Walter D.; Ridgway, Alexander K.

2017-06-01

We construct perturbative classical solutions of the Yang-Mills equations coupled to dynamical point particles carrying color charge. By applying a set of color to kinematics replacement rules first introduced by Bern, Carrasco and Johansson, these are shown to generate solutions of d -dimensional dilaton gravity, which we also explicitly construct. Agreement between the gravity result and the gauge theory double copy implies a correspondence between non-Abelian particles and gravitating sources with dilaton charge. When the color sources are highly relativistic, dilaton exchange decouples, and the solutions we obtain match those of pure gravity. We comment on possible implications of our findings to the calculation of gravitational waveforms in astrophysical black hole collisions, directly from computationally simpler gluon radiation in Yang-Mills theory.

Butterfly effect in 3D gravity

NASA Astrophysics Data System (ADS)

Qaemmaqami, Mohammad M.

2017-11-01

We study the butterfly effect by considering shock wave solutions near the horizon of the anti-de Sitter black hole in some three-dimensional gravity models including 3D Einstein gravity, minimal massive 3D gravity, new massive gravity, generalized massive gravity, Born-Infeld 3D gravity, and new bigravity. We calculate the butterfly velocities of these models and also we consider the critical points and different limits in some of these models. By studying the butterfly effect in the generalized massive gravity, we observe a correspondence between the butterfly velocities and right-left moving degrees of freedom or the central charges of the dual 2D conformal field theories.

Regularized GRACE monthly solutions by constraining the difference between the longitudinal and latitudinal gravity variations

NASA Astrophysics Data System (ADS)

Chen, Qiujie; Chen, Wu; Shen, Yunzhong; Zhang, Xingfu; Hsu, Houze

2016-04-01

The existing unconstrained Gravity Recovery and Climate Experiment (GRACE) monthly solutions i.e. CSR RL05 from Center for Space Research (CSR), GFZ RL05a from GeoForschungsZentrum (GFZ), JPL RL05 from Jet Propulsion Laboratory (JPL), DMT-1 from Delft Institute of Earth Observation and Space Systems (DEOS), AIUB from Bern University, and Tongji-GRACE01 as well as Tongji-GRACE02 from Tongji University, are dominated by correlated noise (such as north-south stripe errors) in high degree coefficients. To suppress the correlated noise of the unconstrained GRACE solutions, one typical option is to use post-processing filters such as decorrelation filtering and Gaussian smoothing , which are quite effective to reduce the noise and convenient to be implemented. Unlike these post-processing methods, the CNES/GRGS monthly GRACE solutions from Centre National d'Etudes Spatiales (CNES) were developed by using regularization with Kaula rule, whose correlated noise are reduced to such a great extent that no decorrelation filtering is required. Actually, the previous studies demonstrated that the north-south stripes in the GRACE solutions are due to the poor sensitivity of gravity variation in east-west direction. In other words, the longitudinal sampling of GRACE mission is very sparse but the latitudinal sampling of GRACE mission is quite dense, indicating that the recoverability of the longitudinal gravity variation is poor or unstable, leading to the ill-conditioned monthly GRACE solutions. To stabilize the monthly solutions, we constructed the regularization matrices by minimizing the difference between the longitudinal and latitudinal gravity variations and applied them to derive a time series of regularized GRACE monthly solutions named RegTongji RL01 for the period Jan. 2003 to Aug. 2011 in this paper. The signal powers and noise level of RegTongji RL01 were analyzed in this paper, which shows that: (1) No smoothing or decorrelation filtering is required for RegTongji RL01 anymore. (2) The signal powers of RegTongji RL01 are obviously stronger than those of the filtered solutions but the noise levels of the regularized and filtered solutions are consistent, suggesting that RegTongji RL01 has the higher signal-to-noise ratio.

The earth's C21 and S21 gravity coefficients and the rotation of the core

NASA Technical Reports Server (NTRS)

Wahr, John M.

1987-01-01

Observational results for the earth's C21 and S21 gravity coefficients can be used to constrain the mean equatorial rotation of the core with respect to the mantle. Current satellite gravity solutions suggest the equatorial rotation rate is no larger than 1 x 10 to the -7th times the earth's diurnal spin rate, a limit more than one order of magnitude smaller than the polar rotation rate inferred from the westward drift of the earth's magnetic field. The next generation gravity solutions should improve this constraint by more than one order of magnitude. Implications for the fluid pressure at the core-mantle boundary and for the shape of that boundary are discussed.

(2 + 1)-dimensional interacting model of two massless spin-2 fields as a bi-gravity model

NASA Astrophysics Data System (ADS)

Hoseinzadeh, S.; Rezaei-Aghdam, A.

2018-06-01

We propose a new group-theoretical (Chern-Simons) formulation for the bi-metric theory of gravity in (2 + 1)-dimensional spacetime which describe two interacting massless spin-2 fields. Our model has been formulated in terms of two dreibeins rather than two metrics. We obtain our Chern-Simons gravity model by gauging mixed AdS-AdS Lie algebra and show that it has a two dimensional conformal field theory (CFT) at the boundary of the anti de Sitter (AdS) solution. We show that the central charge of the dual CFT is proportional to the mass of the AdS solution. We also study cosmological implications of our massless bi-gravity model.

One-loop quantum gravity repulsion in the early Universe.

PubMed

Broda, Bogusław

2011-03-11

Perturbative quantum gravity formalism is applied to compute the lowest order corrections to the classical spatially flat cosmological Friedmann-Lemaître-Robertson-Walker solution (for the radiation). The presented approach is analogous to the approach applied to compute quantum corrections to the Coulomb potential in electrodynamics, or rather to the approach applied to compute quantum corrections to the Schwarzschild solution in gravity. In the framework of the standard perturbative quantum gravity, it is shown that the corrections to the classical deceleration, coming from the one-loop graviton vacuum polarization (self-energy), have (UV cutoff free) opposite to the classical repulsive properties which are not negligible in the very early Universe. The repulsive "quantum forces" resemble those known from loop quantum cosmology.

High-resolution Local Gravity Model of the South Pole of the Moon from GRAIL Extended Mission Data

NASA Technical Reports Server (NTRS)

Goossens, Sander Johannes; Sabaka, Terence J.; Nicholas, Joseph B.; Lemoine, Frank G.; Rowlands, David D.; Mazarico, Erwan; Neumann, Gregory A.; Smith, David E.; Zuber, Maria T.

2014-01-01

We estimated a high-resolution local gravity field model over the south pole of the Moon using data from the Gravity Recovery and Interior Laboratory's extended mission. Our solution consists of adjustments with respect to a global model expressed in spherical harmonics. The adjustments are expressed as gridded gravity anomalies with a resolution of 1/6deg by 1/6deg (equivalent to that of a degree and order 1080 model in spherical harmonics), covering a cap over the south pole with a radius of 40deg. The gravity anomalies have been estimated from a short-arc analysis using only Ka-band range-rate (KBRR) data over the area of interest. We apply a neighbor-smoothing constraint to our solution. Our local model removes striping present in the global model; it reduces the misfit to the KBRR data and improves correlations with topography to higher degrees than current global models.

Thermodynamic instability of topological black holes in Gauss-Bonnet gravity with a generalized electrodynamics

NASA Astrophysics Data System (ADS)

Hendi, S. H.; Panahiyan, S.

2014-12-01

Motivated by the string corrections on the gravity and electrodynamics sides, we consider a quadratic Maxwell invariant term as a correction of the Maxwell Lagrangian to obtain exact solutions of higher dimensional topological black holes in Gauss-Bonnet gravity. We first investigate the asymptotically flat solutions and obtain conserved and thermodynamic quantities which satisfy the first law of thermodynamics. We also analyze thermodynamic stability of the solutions by calculating the heat capacity and the Hessian matrix. Then, we focus on horizon-flat solutions with an anti-de Sitter (AdS) asymptote and produce a rotating spacetime with a suitable transformation. In addition, we calculate the conserved and thermodynamic quantities for asymptotically AdS black branes which satisfy the first law of thermodynamics. Finally, we perform thermodynamic instability criterion to investigate the effects of nonlinear electrodynamics in canonical and grand canonical ensembles.

Non-linear regime of the Generalized Minimal Massive Gravity in critical points

NASA Astrophysics Data System (ADS)

Setare, M. R.; Adami, H.

2016-03-01

The Generalized Minimal Massive Gravity (GMMG) theory is realized by adding the CS deformation term, the higher derivative deformation term, and an extra term to pure Einstein gravity with a negative cosmological constant. In the present paper we obtain exact solutions to the GMMG field equations in the non-linear regime of the model. GMMG model about AdS_3 space is conjectured to be dual to a 2-dimensional CFT. We study the theory in critical points corresponding to the central charges c_-=0 or c_+=0, in the non-linear regime. We show that AdS_3 wave solutions are present, and have logarithmic form in critical points. Then we study the AdS_3 non-linear deformation solution. Furthermore we obtain logarithmic deformation of extremal BTZ black hole. After that using Abbott-Deser-Tekin method we calculate the energy and angular momentum of these types of black hole solutions.

MGA trajectory planning with an ACO-inspired algorithm

NASA Astrophysics Data System (ADS)

Ceriotti, Matteo; Vasile, Massimiliano

2010-11-01

Given a set of celestial bodies, the problem of finding an optimal sequence of swing-bys, deep space manoeuvres (DSM) and transfer arcs connecting the elements of the set is combinatorial in nature. The number of possible paths grows exponentially with the number of celestial bodies. Therefore, the design of an optimal multiple gravity assist (MGA) trajectory is a NP-hard mixed combinatorial-continuous problem. Its automated solution would greatly improve the design of future space missions, allowing the assessment of a large number of alternative mission options in a short time. This work proposes to formulate the complete automated design of a multiple gravity assist trajectory as an autonomous planning and scheduling problem. The resulting scheduled plan will provide the optimal planetary sequence and a good estimation of the set of associated optimal trajectories. The trajectory model consists of a sequence of celestial bodies connected by two-dimensional transfer arcs containing one DSM. For each transfer arc, the position of the planet and the spacecraft, at the time of arrival, are matched by varying the pericentre of the preceding swing-by, or the magnitude of the launch excess velocity, for the first arc. For each departure date, this model generates a full tree of possible transfers from the departure to the destination planet. Each leaf of the tree represents a planetary encounter and a possible way to reach that planet. An algorithm inspired by ant colony optimization (ACO) is devised to explore the space of possible plans. The ants explore the tree from departure to destination adding one node at the time: every time an ant is at a node, a probability function is used to select a feasible direction. This approach to automatic trajectory planning is applied to the design of optimal transfers to Saturn and among the Galilean moons of Jupiter. Solutions are compared to those found through more traditional genetic-algorithm techniques.

Solar Electric Propulsion Triple-Satellite-Aided Capture With Mars Flyby

NASA Astrophysics Data System (ADS)

Patrick, Sean

Triple-Satellite-aided-capture sequences use gravity-assists at three of Jupiter's four massive Galilean moons to reduce the DeltaV required to enter into Jupiter orbit. A triple-satellite-aided capture at Callisto, Ganymede, and Io is proposed to capture a SEP spacecraft into Jupiter orbit from an interplanetary Earth-Jupiter trajectory that employs low-thrust maneuvers. The principal advantage of this method is that it combines the ISP efficiency of ion propulsion with nearly impulsive but propellant-free gravity assists. For this thesis, two main chapters are devoted to the exploration of low-thrust triple-flyby capture trajectories. Specifically, the design and optimization of these trajectories are explored heavily. The first chapter explores the design of two solar electric propulsion (SEP), low-thrust trajectories developed using the JPL's MALTO software. The two trajectories combined represent a full Earth to Jupiter capture split into a heliocentric Earth to Jupiter Sphere of Influence (SOI) trajectory and a Joviocentric capture trajectory. The Joviocentric trajectory makes use of gravity assist flybys of Callisto, Ganymede, and Io to capture into Jupiter orbit with a period of 106.3 days. Following this, in chapter two, three more SEP low-thrust trajectories were developed based upon those in chapter one. These trajectories, devised using the high-fidelity Mystic software, also developed by JPL, improve upon the original trajectories developed in chapter one. Here, the developed trajectories are each three separate, full Earth to Jupiter capture orbits. As in chapter one, a Mars gravity assist is used to augment the heliocentric trajectories. Gravity-assist flybys of Callisto, Ganymede, and Io or Europa are used to capture into Jupiter Orbit. With between 89.8 and 137.2-day periods, the orbits developed in chapters one and two are shorter than most Jupiter capture orbits achieved using low-thrust propulsion techniques. Finally, chapter 3 presents an original trajectory design for a Very-Long-Baseline Interferometry (VLBI) satellite constellation. The design was created for the 8th Global Trajectory Optimization Competition (GTOC8) in which participants are tasked with creating and optimizing low-thrust trajectories to place a series of three space craft into formation to map given radio sources.

Hydrostatic factors affect the gravity responses of algae and roots

NASA Technical Reports Server (NTRS)

Staves, Mark P.; Wayne, Randy; Leopold, A. C.

1991-01-01

The hypothesis of Wayne et al. (1990) that plant cells perceive gravity by sensing a pressure differential between the top and the bottom of the cell was tested by subjecting rice roots and cells of Caracean algae to external solutions of various densities. It was found that increasing the density of the external medium had a profound effect on the polar ratio (PR, the ratio between velocities of the downwardly and upwardly streaming cytoplasm) of the Caracean algae cells. When these cells were placed in solutions of denser compound, the PR decreased to less than 1, as the density of the external medium became higher than that of the cell; thus, the normal gravity-induced polarity was reversed, indicating that the osmotic pressure of the medium affects the cell's ability to respond to gravity. In rice roots, an increase of the density of the solution inhibited the rate of gravitropism. These results agree with predictions of a hydrostatic model for graviperception.

Instabilities of Internal Gravity Wave Beams

NASA Astrophysics Data System (ADS)

Dauxois, Thierry; Joubaud, Sylvain; Odier, Philippe; Venaille, Antoine

2018-01-01

Internal gravity waves play a primary role in geophysical fluids: They contribute significantly to mixing in the ocean, and they redistribute energy and momentum in the middle atmosphere. Until recently, most studies were focused on plane wave solutions. However, these solutions are not a satisfactory description of most geophysical manifestations of internal gravity waves, and it is now recognized that internal wave beams with a confined profile are ubiquitous in the geophysical context. We discuss the reason for the ubiquity of wave beams in stratified fluids, which is related to the fact that they are solutions of the nonlinear governing equations. We focus more specifically on situations with a constant buoyancy frequency. Moreover, in light of recent experimental and analytical studies of internal gravity beams, it is timely to discuss the two main mechanisms of instability for those beams: (a) the triadic resonant instability generating two secondary wave beams and (b) the streaming instability corresponding to the spontaneous generation of a mean flow.

An exact solution for a rotating black hole in modified gravity

NASA Astrophysics Data System (ADS)

Filippini, Francesco; Tasinato, Gianmassimo

2018-01-01

Exact solutions describing rotating black holes can offer important tests for alternative theories of gravity, motivated by the dark energy and dark matter problems. We present an analytic rotating black hole solution for a class of vector-tensor theories of modified gravity, valid for arbitrary values of the rotation parameter. The new configuration is characterised by parametrically large deviations from the Kerr-Newman geometry, controlled by non-minimal couplings between vectors and gravity. It has an oblate horizon in Boyer-Lindquist coordinates, and it can rotate more rapidly and have a larger ergosphere than black holes in General Relativity (GR) with the same asymptotic properties. We analytically investigate the features of the innermost stable circular orbits for massive objects on the equatorial plane, and show that stable orbits lie further away from the black hole horizon with respect to rotating black holes in GR. We also comment on possible applications of our findings for the extraction of rotational energy from the black hole.

Cohomogeneity-one solutions in Einstein-Maxwell-dilaton gravity

NASA Astrophysics Data System (ADS)

Lim, Yen-Kheng

2017-05-01

The field equations for Einstein-Maxwell-dilaton gravity in D dimensions are reduced to an effective one-dimensional system under the influence of exponential potentials. Various cases where exact solutions can be found are explored. With this procedure, we present interesting solutions such as a one-parameter generalization of the dilaton-Melvin spacetime and a three-parameter solution that interpolates between the Reissner-Nordström and Bertotti-Robinson solutions. This procedure also allows simple, alternative derivations of known solutions such as the Lifshitz spacetime and the planar anti-de Sitter naked singularity. In the latter case, the metric is cast in a simpler form which reveals the presence of an additional curvature singularity.

Study of static wormhole solutions in F(T ,TG) gravity

NASA Astrophysics Data System (ADS)

Sharif, M.; Nazir, Kanwal

2018-06-01

In this paper, we investigate static spherically symmetric wormhole solutions in the background of F(T ,TG) gravity (T is the torsion scalar and TG represents teleparallel equivalent of the Gauss-Bonnet term). We study the wormhole solutions by assuming four different matter contents, a specific redshift function and a particular F(T ,TG) model. The behavior of null/weak energy conditions for these fluids is analyzed graphically. It turns out that wormhole solutions can be obtained in the absence of exotic matter for some particular regions of spacetime. We also explore stability of wormhole solutions through equilibrium condition. It is concluded that there exist physically acceptable wormhole solutions for anisotropic, isotropic and traceless fluids.

Space-time slicing in Horndeski theories and its implications for non-singular bouncing solutions

NASA Astrophysics Data System (ADS)

Ijjas, Anna

2018-02-01

In this paper, we show how the proper choice of gauge is critical in analyzing the stability of non-singular cosmological bounce solutions based on Horndeski theories. We show that it is possible to construct non-singular cosmological bounce solutions with classically stable behavior for all modes with wavelengths above the Planck scale where: (a) the solution involves a stage of null-energy condition violation during which gravity is described by a modification of Einstein's general relativity; and (b) the solution reduces to Einstein gravity both before and after the null-energy condition violating stage. Similar considerations apply to galilean genesis scenarios.

Three dimensional magnetic solutions in massive gravity with (non)linear field

NASA Astrophysics Data System (ADS)

Hendi, S. H.; Eslam Panah, B.; Panahiyan, S.; Momennia, M.

2017-12-01

The Noble Prize in physics 2016 motivates one to study different aspects of topological properties and topological defects as their related objects. Considering the significant role of the topological defects (especially magnetic strings) in cosmology, here, we will investigate three dimensional horizonless magnetic solutions in the presence of two generalizations: massive gravity and nonlinear electromagnetic field. The effects of these two generalizations on properties of the solutions and their geometrical structure are investigated. The differences between de Sitter and anti de Sitter solutions are highlighted and conditions regarding the existence of phase transition in geometrical structure of the solutions are studied.

Techniques for Solution- Assisted Optical Contacting

NASA Technical Reports Server (NTRS)

DeVine, Glenn; Ware, Brent; Wuchenich, Danielle M.; Spero, Robert E.; Klipstein, William M.; McKenzie, Kirk

2012-01-01

A document discusses a solution-assisted contacting technique for optical contacting. An optic of surface flatness Lambda/20 was successfully contacted with one of moderate surface quality, or Lambda/4. Optics used were both ultra-low expansion (ULE) glass (Lambda/4 and Lambda/20) and fused silica (Lambda/20). A stainless steel template of the intended interferometer layout was designed and constructed with three contact points per optic. The contact points were all on a common side of the template. The entire contacting jig was tilted at about 30 . Thus, when the isopropanol was applied, each optic slid due to gravity, resting on the contact points. All of the contacting was performed in a relatively dusty laboratory. A number of successful contacts were achieved where up to two or three visible pieces of dust could be seen. These were clearly visible due to refraction patterns between the optic and bench. On a number of optics, the final step of dropping isopropyl between the surfaces was repeated until a successful contact was achieved. The new procedures realized in this work represent a simplification for optical contacting in the laboratory. They will both save time and money spent during the contacting process, and research and development phases. The techniques outlined are suitable for laboratory experiments, research, and initial development stages.

Exploiting the Modified Colombo-Nyquist Rule for Co-estimating Sub-monthly Gravity Field Solutions from a GRACE-like Mission

NASA Astrophysics Data System (ADS)

Devaraju, B.; Weigelt, M.; Mueller, J.

2017-12-01

In order to suppress the impact of aliasing errors on the standard monthly GRACE gravity-field solutions, co-estimating sub-monthly (daily/two-day) low-degree solutions has been suggested as a solution. The maximum degree of the low-degree solutions is chosen via the Colombo-Nyquist rule of thumb. However, it is now established that the sampling of satellites puts a restriction on the maximum estimable order and not the degree - modified Colombo-Nyquist rule. Therefore, in this contribution, we co-estimate low-order sub-monthly solutions, and compare and contrast them with the low-degree sub-monthly solutions. We also investigate their efficacies in dealing with aliasing errors.

SU(2) Yang-Mills solitons in R2 gravity

NASA Astrophysics Data System (ADS)

Perapechka, I.; Shnir, Ya.

2018-05-01

We construct new family of spherically symmetric regular solutions of SU (2) Yang-Mills theory coupled to pure R2 gravity. The particle-like field configurations possess non-integer non-Abelian magnetic charge. A discussion of the main properties of the solutions and their differences from the usual Bartnik-McKinnon solitons in the asymptotically flat case is presented. It is shown that there is continuous family of linearly stable non-trivial solutions in which the gauge field has no nodes.

A new two-metric theory of gravity with prior geometry

NASA Technical Reports Server (NTRS)

Lightman, A. P.; Lee, D. L.

1972-01-01

A theory is presented of gravity which has the same post-Newtonian (PN) as that of general relativity. The field equations, and a calculation of the PN limit of the theory are discussed along with the equations of stellar structure for static spherically symmetric stars. A special exterior spherically symmetric solution, time dependent solutions, conservations, and gravitational waves are analyzed.

Gaussian black holes in Rastall gravity

NASA Astrophysics Data System (ADS)

Spallucci, Euro; Smailagic, Anais

In this short note we present the solution of Rastall gravity equations sourced by a Gaussian matter distribution. We find that the black hole metric shares all the common features of other regular, General Relativity BH solutions discussed in the literature: there is no curvature singularity and the Hawking radiation leaves a remnant at zero temperature in the form of a massive ordinary particle.

Estimating the Earth's geometry, rotation and gravity field using a multi-satellite SLR solution

NASA Astrophysics Data System (ADS)

Stefka, V.; Blossfeld, M.; Mueller, H.; Gerstl, M.; Panafidina, N.

2012-12-01

Satellite Laser Ranging (SLR) is the unique technique to determine station coordinates, Earth Orientation Parameter (EOP) and Stokes coefficients of the Earth's gravity field in one common adjustment. These parameters form the so called "three pillars" (Plag & Pearlman, 2009) of the Global Geodetic Observing System (GGOS). In its function as official analysis center of the International Laser Ranging Service (ILRS), DGFI is developing and maintaining software to process SLR observations called "DGFI Orbit and Geodetic parameter estimation Software" (DOGS). The software is used to analyze SLR observations and to compute multi-satellite solutions. To take benefit of different orbit performances (e.g. inclination and altitude), a solution using ten different spherical satellites (ETALON1/2, LAGEOS1/2, STELLA, STARLETTE, AJISAI, LARETS, LARES, BLITS) covering the period of 12 years of observations is computed. The satellites are relatively weighted using a variance component estimation (VCE). The obtained weights are analyzed w.r.t. the potential of the satellite to monitor changes in the Earths geometry, rotation and gravity field. The estimated parameters (station coordinates and EOP) are validated w.r.t. official time series of the IERS. The Stokes coefficients are compared to recent gravity field solutions.

Estimating the Earth's gravity field using a multi-satellite SLR solution

NASA Astrophysics Data System (ADS)

Bloßfeld, Mathis; Stefka, Vojtech; Müller, Horst; Gerstl, Michael

2013-04-01

Satellite Laser Ranging (SLR) is the unique technique to determine station coordinates, Earth Orientation Parameter (EOP) and Stokes coefficients of the Earth's gravity field in one common adjustment. These parameters form the so called "three pillars" (Plag & Pearlman, 2009) of the Global Geodetic Observing System (GGOS). In its function as official analysis center of the International Laser Ranging Service (ILRS), DGFI is developing and maintaining software to process SLR observations called "DGFI Orbit and Geodetic parameter estimation Software" (DOGS). The software is used to analyze SLR observations and to compute multi-satellite solutions. To take benefit of different orbit performances (e.g. inclination and altitude), a solution using ten different spherical satellites (ETALON1/2, LAGEOS1/2, STELLA, STARLETTE, AJISAI, LARETS, LARES, BLITS) covering 12 years of observations is computed. The satellites are relatively weighted using a variance component estimation (VCE). The obtained weights are analyzed w.r.t. the potential of the satellite to monitor changes in the Earths geometry, rotation and gravity field. The estimated parameters (station coordinates and EOP) are validated w.r.t. official time series of the IERS. The obtained Stokes coefficients are compared to recent gravity field solutions and discussed in detail.

New and Topologically Massive Gravity, from the Outside In

NASA Astrophysics Data System (ADS)

Cunliff, Colin

This thesis examines the asymptotically anti-de Sitter solutions of higher-derivative gravity in 2+1 dimensions, using a Fefferman-Graham-like approach that expands solutions from the boundary (at infinity) into the interior. First, solutions of topologically massive gravity (TMG) are analyzed for values of the mass parameter in the range mu ≥ 1. The traditional Fefferman-Graham expansion fails to capture the dynamics of TMG, and new terms in the asymptotic expansion are needed to include the massive graviton modes. The linearized modes of Carlip, Deser, Waldron and Wise map onto the non-Einstein solutions for all μ, with nonlinear corrections appearing at higher order in the expansion. A similar result is found for new massive gravity (NMG), where the asymptotic behavior of massive gravitons is found to depend on the coupling parameter m2. Additionally, new boundary conditions are discovered for a range of values -1 < 2m2 l2 < 1 at which non-Einstein modes decay more slowly than the rate required for Brown-Henneaux boundary conditions. The holographically renormalized stress tensor is computed for these modes, and the relevant counterterms are identified up to unphysical ambiguities.

Local Lunar Gravity Field Analysis over the South Pole-aitken Basin from SELENE Farside Tracking Data

NASA Technical Reports Server (NTRS)

Goossens, Sander Johannes; Ishihara, Yoshiaki; Matsumoto, Koji; Sasaki, Sho

2012-01-01

We present a method with which we determined the local lunar gravity field model over the South Pole-Aitken (SPA) basin on the farside of the Moon by estimating adjustments to a global lunar gravity field model using SELENE tracking data. Our adjustments are expressed in localized functions concentrated over the SPA region in a spherical cap with a radius of 45deg centered at (191.1 deg E, 53.2 deg S), and the resolution is equivalent to a 150th degree and order spherical harmonics expansion. The new solution over SPA was used in several applications of geophysical analysis. It shows an increased correlation with high-resolution lunar topography in the frequency band l = 40-70, and admittance values are slightly different and more leveled when compared to other, global gravity field models using the same data. The adjustments expressed in free-air anomalies and differences in Bouguer anomalies between the local solution and the a priori global solution correlate with topographic surface features. The Moho structure beneath the SPA basin is slightly modified in our solution, most notably at the southern rim of the Apollo basin and around the Zeeman crater

Theoretical and lidar studies of the density response of the mesospheric sodium layer to gravity wave perturbations

NASA Technical Reports Server (NTRS)

Shelton, J. D.; Gardner, C. S.

1981-01-01

The density response of atmospheric layers to gravity waves is developed in two forms, an exact solution and a perturbation series solution. The degree of nonlinearity in the layer density response is described by the series solution whereas the exact solution gives insight into the nature of the responses. Density perturbation in an atmospheric layer are shown to be substantially greater than the atmospheric density perturbation associated with the propagation of a gravity wave. Because of the density gradients present in atmospheric layers, interesting effects were observed such as a phase reversal in the linear layer response which occurs near the layer peak. Once the layer response is understood, the sodium layer can be used as a tracer of atmospheric wave motions. A two dimensional digital signal processing technique was developed. Both spatial and temporal filtering are utilized to enhance the resolution by decreasing shot noise by more han 10 dB. Many of the features associated with a layer density response to gravity waves were observed in high resolution density profiles of the mesospheric sodium layer. These include nonlinearities as well as the phase reversal in the linear layer response.

Abort Options for Human Missions to Earth-Moon Halo Orbits

NASA Technical Reports Server (NTRS)

Jesick, Mark C.

2013-01-01

Abort trajectories are optimized for human halo orbit missions about the translunar libration point (L2), with an emphasis on the use of free return trajectories. Optimal transfers from outbound free returns to L2 halo orbits are numerically optimized in the four-body ephemeris model. Circumlunar free returns are used for direct transfers, and cislunar free returns are used in combination with lunar gravity assists to reduce propulsive requirements. Trends in orbit insertion cost and flight time are documented across the southern L2 halo family as a function of halo orbit position and free return flight time. It is determined that the maximum amplitude southern halo incurs the lowest orbit insertion cost for direct transfers but the maximum cost for lunar gravity assist transfers. The minimum amplitude halo is the most expensive destination for direct transfers but the least expensive for lunar gravity assist transfers. The on-orbit abort costs for three halos are computed as a function of abort time and return time. Finally, an architecture analysis is performed to determine launch and on-orbit vehicle requirements for halo orbit missions.

New 2D dilaton gravity for nonsingular black holes

NASA Astrophysics Data System (ADS)

Kunstatter, Gabor; Maeda, Hideki; Taves, Tim

2016-05-01

We construct a two-dimensional action that is an extension of spherically symmetric Einstein-Lanczos-Lovelock (ELL) gravity. The action contains arbitrary functions of the areal radius and the norm squared of its gradient, but the field equations are second order and obey Birkhoff’s theorem. In complete analogy with spherically symmetric ELL gravity, the field equations admit the generalized Misner-Sharp mass as the first integral that determines the form of the vacuum solution. The arbitrary functions in the action allow for vacuum solutions that describe a larger class of interesting nonsingular black hole spacetimes than previously available.

Baroclinic instability with variable gravity: A perturbation analysis

NASA Technical Reports Server (NTRS)

Giere, A. C.; Fowliss, W. W.; Arias, S.

1980-01-01

Solutions for a quasigeostrophic baroclinic stability problem in which gravity is a function of height were obtained. Curvature and horizontal shear of the basic state flow were omitted and the vertical and horizontal temperature gradients of the basic state were taken as constant. The effect of a variable dielectric body force, analogous to gravity, on baroclinic instability for the design of a spherical, baroclinic model for Spacelab was determined. Such modeling could not be performed in a laboratory on the Earth's surface because the body force could not be made strong enough to dominate terrestrial gravity. A consequence of the body force variation and the preceding assumptions was that the potential vorticity gradient of the basic state vanished. The problem was solved using a perturbation method. The solution gives results which are qualitatively similar to Eady's results for constant gravity; a short wavelength cutoff and a wavelength of maximum growth rate were observed. The averaged values of the basic state indicate that both the wavelength range of the instability and the growth rate at maximum instability are increased. Results indicate that the presence of the variable body force will not significantly alter the dynamics of the Spacelab experiment. The solutions are also relevant to other geophysical fluid flows where gravity is constant but the static stability or Brunt-Vaisala frequency is a function of height.

Reconstruction of cosmological matter perturbations in modified gravity

NASA Astrophysics Data System (ADS)

Gonzalez, J. E.

2017-12-01

The analysis of perturbative quantities is a powerful tool to distinguish between different dark energy models and gravity theories degenerated at the background level. In this work, we generalize the integral solution of the matter density contrast for general relativity gravity [V. Sahni and A. Starobinsky, Int. J. Mod. Phys. D 15, 2105 (2006)., 10.1142/S0218271806009704, U. Alam, V. Sahni, and A. A. Starobinsky, Astrophys. J. 704, 1086 (2009)., 10.1088/0004-637X/704/2/1086] to a wide class of modified gravity (MG) theories. To calculate this solution, it is necessary to have prior knowledge of the Hubble rate, the density parameter at the present epoch (Ωm 0), and the functional form of the effective Newton's constant that characterizes the gravity theory. We estimate in a model-independent way the Hubble expansion rate by applying a nonparametric reconstruction method to model-independent cosmic chronometer data and high-z quasar data. In order to compare our generalized solution of the matter density contrast, using the nonparametric reconstruction of H (z ) from observational data, with a purely theoretical one, we choose a parametrization of the screened modified gravity and the Ωm 0 from WMAP-9 Collaborations. Finally, we calculate the growth index for the analyzed cases, finding very good agreement between theoretical values and the obtained ones using the approach presented in this work.

Analytic solutions in nonlinear massive gravity.

PubMed

Koyama, Kazuya; Niz, Gustavo; Tasinato, Gianmassimo

2011-09-23

We study spherically symmetric solutions in a covariant massive gravity model, which is a candidate for a ghost-free nonlinear completion of the Fierz-Pauli theory. There is a branch of solutions that exhibits the Vainshtein mechanism, recovering general relativity below a Vainshtein radius given by (r(g)m(2))(1/3), where m is the graviton mass and r(g) is the Schwarzschild radius of a matter source. Another branch of exact solutions exists, corresponding to de Sitter-Schwarzschild spacetimes where the curvature scale of de Sitter space is proportional to the mass squared of the graviton.

Time Changes of the European Gravity Field from GRACE: A Comparison with Ground Measurements from Superconducting Gravimeters and with Hydrology Model Predictions

NASA Technical Reports Server (NTRS)

Hinderer, J.; Lemoine, Frank G.; Crossley, D.; Boy, J.-P.

2004-01-01

We investigate the time-variable gravity changes in Europe retrieved from the initial GRACE monthly solutions spanning a 18 month duration from April 2002 to October 2003. Gravity anomaly maps are retrieved in Central Europe from the monthly satellite solutions we compare the fields according to various truncation levels (typically between degree 10 and 20) of the initial fields (expressed in spherical harmonics to degree 120). For these different degrees, an empirical orthogonal function (EOF) decomposition of the time-variable gravity field leads us to its main spatial and temporal characteristics. We show that the dominant signal is found to be annual with an amplitude and a phase both in agreement with predictions in Europe modeled using snow and soil-moisture variations from recent hydrology models. We compare these GRACE gravity field changes to surface gravity observations from 6 superconducting gravimeters of the GGP (Global Geodynamics Project) European sub-network, with a special attention to loading corrections. Initial results suggest that all 3 data sets (GRACE, hydrology and GGP) are responding to annual changes in near-surface water in Europe of a few microGal (at length scales of approx.1000 km) that show a high value in winter and a summer minimum. We also point out that the GRACE gravity field evolution seems to indicate that there is a trend in gravity between summer 2002 and summer 2003 which can be related to the 2003 heatwave in Europe and its hydrological consequences (drought). Despite the limited time span of our analysis and the uncertainties in retrieving a regional solution from the network of gravimeters, the calibration and validation aspects of the GRACE data processing based on the annual hydrology cycle in Europe are in progress.

Combination of GRACE monthly gravity field solutions from different processing strategies

NASA Astrophysics Data System (ADS)

Jean, Yoomin; Meyer, Ulrich; Jäggi, Adrian

2018-02-01

We combine the publicly available GRACE monthly gravity field time series to produce gravity fields with reduced systematic errors. We first compare the monthly gravity fields in the spatial domain in terms of signal and noise. Then, we combine the individual gravity fields with comparable signal content, but diverse noise characteristics. We test five different weighting schemes: equal weights, non-iterative coefficient-wise, order-wise, or field-wise weights, and iterative field-wise weights applying variance component estimation (VCE). The combined solutions are evaluated in terms of signal and noise in the spectral and spatial domains. Compared to the individual contributions, they in general show lower noise. In case the noise characteristics of the individual solutions differ significantly, the weighted means are less noisy, compared to the arithmetic mean: The non-seasonal variability over the oceans is reduced by up to 7.7% and the root mean square (RMS) of the residuals of mass change estimates within Antarctic drainage basins is reduced by 18.1% on average. The field-wise weighting schemes in general show better performance, compared to the order- or coefficient-wise weighting schemes. The combination of the full set of considered time series results in lower noise levels, compared to the combination of a subset consisting of the official GRACE Science Data System gravity fields only: The RMS of coefficient-wise anomalies is smaller by up to 22.4% and the non-seasonal variability over the oceans by 25.4%. This study was performed in the frame of the European Gravity Service for Improved Emergency Management (EGSIEM; http://www.egsiem.eu) project. The gravity fields provided by the EGSIEM scientific combination service (ftp://ftp.aiub.unibe.ch/EGSIEM/) are combined, based on the weights derived by VCE as described in this article.

Validation of the EGSIEM combined monthly GRACE gravity fields

NASA Astrophysics Data System (ADS)

Li, Zhao; van Dam, Tonie; Chen, Qiang; Weigelt, Matthias; Güntner, Andreas; Jäggi, Adrian; Meyer, Ulrich; Jean, Yoomin; Altamimi, Zuheir; Rebischung, Paul

2016-04-01

Observations indicate that global warming is affecting the water cycle. Here in Europe predictions are for more frequent high precipitation events, wetter winters, and longer and dryer summers. The consequences of these changes include the decreasing availability of fresh water resources in some regions as well as flooding and erosion of coastal and low-lying areas in other regions. These weather related effects impose heavy costs on society and the economy. We cannot stop the immediate effects global warming on the water cycle. But there may be measures that we can take to mitigate the costs to society. The Horizon2020 supported project, European Gravity Service for Improved Emergency Management (EGSIEM), will add value to EO observations of variations in the Earth's gravity field. In particular, the EGSIEM project will interpret the observations of gravity field changes in terms of changes in continental water storage. The project team will develop tools to alert the public water storage conditions could indicate the onset of regional flooding or drought. As part of the EGSIEM project, a combined GRACE gravity product is generated, using various monthly GRACE solutions from associated processing centers (ACs). Since each AC follows a set of common processing standards but applies its own independent analysis method, the quality, robustness, and reliability of the monthly combined gravity fields should be significantly improved as compared to any individual solution. In this study, we present detailed and updated comparisons of the combined EGSIEM GRACE gravity product with GPS position time series, hydrological models, and existing GRACE gravity fields. The GPS residuals are latest REPRO2 station position residuals, obtained by rigorously stacking the IGS Repro 2 , daily solutions, estimating, and then restoring the annual and semi-annual signals.

Impact of GNSS orbit modeling on LEO orbit and gravity field determination

NASA Astrophysics Data System (ADS)

Arnold, Daniel; Meyer, Ulrich; Sušnik, Andreja; Dach, Rolf; Jäggi, Adrian

2017-04-01

On January 4, 2015 the Center for Orbit Determination in Europe (CODE) changed the solar radiation pressure modeling for GNSS satellites to an updated version of the empirical CODE orbit model (ECOM). Furthermore, since September 2012 CODE operationally computes satellite clock corrections not only for the 3-day long-arc solutions, but also for the non-overlapping 1-day GNSS orbits. This provides different sets of GNSS products for Precise Point Positioning, as employed, e.g., in the GNSS-based precise orbit determination of low Earth orbiters (LEOs) and the subsequent Earth gravity field recovery from kinematic LEO orbits. While the impact of the mentioned changes in orbit modeling and solution strategy on the GNSS orbits and geophysical parameters was studied in detail, their implications on the LEO orbits were not yet analyzed. We discuss the impact of the update of the ECOM and the influence of 1-day and 3-day GNSS orbit solutions on zero-difference LEO orbit and gravity field determination, where the GNSS orbits and clock corrections, as well as the Earth rotation parameters are introduced as fixed external products. Several years of kinematic and reduced-dynamic orbits for the two GRACE LEOs are computed with GNSS products based on both the old and the updated ECOM, as well as with 1- and 3-day GNSS products. The GRACE orbits are compared by means of standard validation measures. Furthermore, monthly and long-term GPS-only and combined GPS/K-band gravity field solutions are derived from the different sets of kinematic LEO orbits. GPS-only fields are validated by comparison to combined GPS/K-band solutions, while the combined solutions are validated by analysis of the formal errors, as well as by comparing them to the combined GRACE solutions of the European Gravity Service for Improved Emergency Management (EGSIEM) project.

Holographic thermalization and generalized Vaidya-AdS solutions in massive gravity

NASA Astrophysics Data System (ADS)

Hu, Ya-Peng; Zeng, Xiao-Xiong; Zhang, Hai-Qing

2017-02-01

We investigate the effect of massive graviton on the holographic thermalization process. Before doing this, we first find out the generalized Vaidya-AdS solutions in the de Rham-Gabadadze-Tolley (dRGT) massive gravity by directly solving the gravitational equations. Then, we study the thermodynamics of these Vaidya-AdS solutions by using the Misner-Sharp energy and unified first law, which also shows that the massive gravity is in a thermodynamic equilibrium state. Moreover, we adopt the two-point correlation function at equal time to explore the thermalization process in the dual field theory, and to see how the graviton mass parameter affects this process from the viewpoint of AdS/CFT correspondence. Our results show that the graviton mass parameter will increase the holographic thermalization process.

Bernese advances towards a global analysis of Lunar geodesy

NASA Astrophysics Data System (ADS)

Bertone, S.; Girardin, V.; Bourgoin, A.; Arnold, D.; Jaeggi, A.

2017-12-01

In this presentation we discuss our latest GRAIL-based lunar gravity fields generated with the Celestial Mechanics Approach using the planetary extension of the Bernese GNSS Software (BSW) developed at the Astronomical Institute of the University of Bern (AIUB).Based on one-way X band and two-way S-band Doppler data, we perform orbit determination by solving six initial orbital elements, dynamical parameters, and stochastic parameters in daily arcs using a least-squares adjustment. Significative improvements to our solutions come from the recent implementation of an accurate modeling of non-gravitational forces, including accelerations due to solar and planetary (albedo and IR) radiation pressure, based on the 28-plate macromodel to represent the GRAIL satellites. Also, as suggested in previous works, we deal with imperfections in the modeling of solar eclipses by both an accurate data screening at mid-latitudes and by taking into account solar panel voltage data in our processing. Empirical and pseudo-stochastic parameters are estimated on top of our dynamical modeling to absorb its deficiencies. We analyze the impact of different parametrizations using either pulses (i.e., instantaneous velocity changes) and piecewise constant accelerations (PCA) on our orbits.Based on these improved orbits, one- and two-way Doppler and KBRR data are then used together with an appropriate weighting for a combined orbit and gravity field determination process.We present our latest solutions of the lunar gravity field, based on the recent GRAIL GRGM900C gravity field (as validation of our modeling and parametrization) and on iterations from the SELENE SGM150J gravity field (to check the independence of our solution). We detail our procedure to gradually enlarge the parameter space while adding new data to our gravity field solution. In addition, we present our latest solution for the Moon tidal Love number k_2.Moreover, some important lunar geophysical parameters are best obtained by processing data from Lunar Laser Ranging (LLR) stations. We analyze the impact of a combined processing on the recovery of a set of parameters and we provide some preliminary results.Finally, we compare all of our results with the most recent solutions of the lunar gravity field and of other geodetic parameters released by other groups.

Overload control of artificial gravity facility using spinning tether system for high eccentricity transfer orbits

NASA Astrophysics Data System (ADS)

Gou, Xing-wang; Li, Ai-jun; Tian, Hao-chang; Wang, Chang-qing; Lu, Hong-shi

2018-06-01

As the major part of space life supporting systems, artificial gravity requires further study before it becomes mature. Spinning tether system is a good alternative solution to provide artificial gravity for the whole spacecraft other than additional devices, and its longer tether length could significantly reduce spinning velocity and thus enhance comfortability. An approximated overload-based feedback method is proposed to provide estimated spinning velocity signals for controller, so that gravity level could be accurately controlled without complicated GPS modules. System behavior in high eccentricity transfer orbits is also studied to give a complete knowledge of the spinning stabilities. The application range of the proposed method is studied in various orbit cases and spinning velocities, indicating that it is accurate and reliable for most of the mission phases especially for the final constant gravity level phase. In order to provide stable gravity level for transfer orbit missions, a sliding mode controller based on estimated angular signals is designed for closed-loop control. Numerical results indicate that the combination of overload-based feedback and sliding mode controller could satisfy most of the long-term artificial gravity missions. It is capable of forming flexible gravity environment in relatively good accuracy even in the lowest possible orbital radiuses and high eccentricity orbits of crewed space missions. The proposed scheme provides an effective tether solution for the artificial gravity construction in interstellar travel.

Advanced simulation and analysis of a geopotential research mission

NASA Technical Reports Server (NTRS)

Schutz, B. E.

1988-01-01

Computer simulations have been performed for an orbital gradiometer mission to assist in the study of high degree and order gravity field recovery. The simulations were conducted for a satellite in near-circular, frozen orbit at a 160-km altitude using a gravitational field complete to degree and order 360. The mission duration is taken to be 32 days. The simulation provides a set of measurements to assist in the evaluation of techniques developed for the determination of the gravity field. Also, the simulation provides an ephemeris to study available tracking systems to satisfy the orbit determination requirements of the mission.

Calculation of gravity and magnetic anomalies along profiles with end corrections and inverse solutions for density and magnetization

USGS Publications Warehouse

Cady, John W.

1977-01-01

A computer program is presented which performs, for one or more bodies, along a profile perpendicular to strike, both forward calculations for the magnetic and gravity anomaly fields and independent gravity and magnetic inverse calculations for density and susceptibility or remanent magnetization.

The interaction of Dirac particles with non-abelian gauge fields and gravity - bound states

NASA Astrophysics Data System (ADS)

Finster, Felix; Smoller, Joel; Yau, Shing-Tung

2000-09-01

We consider a spherically symmetric, static system of a Dirac particle interacting with classical gravity and an SU(2) Yang-Mills field. The corresponding Einstein-Dirac-Yang-Mills equations are derived. Using numerical methods, we find different types of soliton-like solutions of these equations and discuss their properties. Some of these solutions are stable even for arbitrarily weak gravitational coupling.

Solution to the spectral filter problem of residual terrain modelling (RTM)

NASA Astrophysics Data System (ADS)

Rexer, Moritz; Hirt, Christian; Bucha, Blažej; Holmes, Simon

2018-06-01

In physical geodesy, the residual terrain modelling (RTM) technique is frequently used for high-frequency gravity forward modelling. In the RTM technique, a detailed elevation model is high-pass-filtered in the topography domain, which is not equivalent to filtering in the gravity domain. This in-equivalence, denoted as spectral filter problem of the RTM technique, gives rise to two imperfections (errors). The first imperfection is unwanted low-frequency (LF) gravity signals, and the second imperfection is missing high-frequency (HF) signals in the forward-modelled RTM gravity signal. This paper presents new solutions to the RTM spectral filter problem. Our solutions are based on explicit modelling of the two imperfections via corrections. The HF correction is computed using spectral domain gravity forward modelling that delivers the HF gravity signal generated by the long-wavelength RTM reference topography. The LF correction is obtained from pre-computed global RTM gravity grids that are low-pass-filtered using surface or solid spherical harmonics. A numerical case study reveals maximum absolute signal strengths of ˜ 44 mGal (0.5 mGal RMS) for the HF correction and ˜ 33 mGal (0.6 mGal RMS) for the LF correction w.r.t. a degree-2160 reference topography within the data coverage of the SRTM topography model (56°S ≤ φ ≤ 60°N). Application of the LF and HF corrections to pre-computed global gravity models (here the GGMplus gravity maps) demonstrates the efficiency of the new corrections over topographically rugged terrain. Over Switzerland, consideration of the HF and LF corrections reduced the RMS of the residuals between GGMplus and ground-truth gravity from 4.41 to 3.27 mGal, which translates into ˜ 26% improvement. Over a second test area (Canada), our corrections reduced the RMS of the residuals between GGMplus and ground-truth gravity from 5.65 to 5.30 mGal (˜ 6% improvement). Particularly over Switzerland, geophysical signals (associated, e.g. with valley fillings) were found to stand out more clearly in the RTM-reduced gravity measurements when the HF and LF correction are taken into account. In summary, the new RTM filter corrections can be easily computed and applied to improve the spectral filter characteristics of the popular RTM approach. Benefits are expected, e.g. in the context of the development of future ultra-high-resolution global gravity models, smoothing of observed gravity data in mountainous terrain and geophysical interpretations of RTM-reduced gravity measurements.

Prima facie questions in quantum gravity

NASA Astrophysics Data System (ADS)

Isham, C. J.

The long history of the study of quantum gravity has thrown up a complex web of ideas and approaches. The aim of this article is to unravel this web a little by analysing some of the {\\em prima facie\\/} questions that can be asked of almost any approach to quantum gravity and whose answers assist in classifying the different schemes. Particular emphasis is placed on (i) the role of background conceptual and technical structure; (ii) the role of spacetime diffeomorphisms; and (iii) the problem of time.

High-resolution CSR GRACE RL05 mascons

NASA Astrophysics Data System (ADS)

Save, Himanshu; Bettadpur, Srinivas; Tapley, Byron D.

2016-10-01

The determination of the gravity model for the Gravity Recovery and Climate Experiment (GRACE) is susceptible to modeling errors, measurement noise, and observability issues. The ill-posed GRACE estimation problem causes the unconstrained GRACE RL05 solutions to have north-south stripes. We discuss the development of global equal area mascon solutions to improve the GRACE gravity information for the study of Earth surface processes. These regularized mascon solutions are developed with a 1° resolution using Tikhonov regularization in a geodesic grid domain. These solutions are derived from GRACE information only, and no external model or data is used to inform the constraints. The regularization matrix is time variable and will not bias or attenuate future regional signals to some past statistics from GRACE or other models. The resulting Center for Space Research (CSR) mascon solutions have no stripe errors and capture all the signals observed by GRACE within the measurement noise level. The solutions are not tailored for specific applications and are global in nature. This study discusses the solution approach and compares the resulting solutions with postprocessed results from the RL05 spherical harmonic solutions and other global mascon solutions for studies of Arctic ice sheet processes, ocean bottom pressure variation, and land surface total water storage change. This suite of comparisons leads to the conclusion that the mascon solutions presented here are an enhanced representation of the RL05 GRACE solutions and provide accurate surface-based gridded information that can be used without further processing.

Advanced methods of low cost mission design for Jovian moons exploration

NASA Astrophysics Data System (ADS)

Grushevskii, Alexey; Koryanov, Victor; Tuchin, Andrey; Golubev, Yury; Tuchin, Denis

2016-07-01

DeltaV-low-cost gravity assists tours mission design of for the Jovian Moons exploration is considered (orbiters and probes around Io, Europa, Ganymede, Callisto), taking radiation hazard into account. Limited dynamic opportunities of using flybys require multiple gravity assists. Relevance of regular creation of optimum scenarios - sequences of passing of celestial bodies with definition of conditions of their execution is obvious. This work is devoted to the description of criteria for creation of such chains. New Multi-Tisserand coordinates [1,2] for this purpose are introduced for the best study of features for the radiation hazard decrease and the spacecraft asymptotic velocity reduction. One of main problems of the Jovian system mission design (JIMO, JUICE, Laplas P) is that the reduction of the asymptotic velocity of the spacecraft with respect to the satellite for the Jovian moon's capture is impossible. A valid reason is in the invariance of Jacobi integral and Tisserand parameter in a restricted three-body model (RTBP) [3]. Furthermore, the same-body flybys tour falls into the hazard radiation zone according the Tisserand-Poincaré graph. Formalized beam's algorithm to overcome this "problem of the ballistic destiny" with using full ephemeris model and with several coupled RTBP engaging has been implemented. Withal low-cost reduction of the spacecraft asymptotic velocity for the capture of the moon is required. The corresponding numerical scheme was developed with using Tisserand-Poincaré graph and the simulation of tens of millions of options. The Delta V-low cost searching was utilized also with help of the modeling of the multiple rebounds (cross gravity assists) of the beam of trajectories. The techniques are developed by the authors specifically to the needs of the mission "Laplas P" of Roscosmos. If we have answers to the questions "what kind of gravity assists", we need answer on the question "when". New Multi-Tisserand coordinates for this purpose are introduced. They are Tisserand parameters of SC relative some small bodies in several local RTBP. The Multi-Tisserand graph built based on them. It is shown that the "cross" gravity assists at the early stage of SC orbital energy reduction for TID-comfortable tour are required. As a result, a reasonable increase in the duration of the missions of the Jovian Moons exploration can be exchanged on a sharp decline TID and "comfortable" (in TID) tours scenario can be found in the Jovian system (less than 200-300 Krad for the "light" SC with the 4-5 mm Al shield, or less than 70 Krad for standard SC protection 8-10 mm Al). References 1. Grushevskii, A. et al. Adaptive low radiation multibody gravity assist tours design in Jovian system for the landing on Jovian's moons // Proceedings 65th International Astronautical Congress - IAC 2014, Toronto, Canada, 2014. 2. Golubev Yu.F., Grushevskii A.V., Koryanov V.V., Tuchin A.G., and Tuchin D.A. Bifurcation Points during Gravity Assist Tours in the Jovian System// Doklady Physics, Pleiades Publishing, Ltd., 2015. Vol. 60, No. 5, pp. 210-213. DOI: 10.1134/S1028335815050043. 3. Campagnola, S. and Russell, R. "Endgame Problem. Part 2: Multi-Body Technique and TP Graph," Journal of Guidance, Control, and Dynamics," Vol. 33, No. 2, pp. 476-486, 2010.

Comment on the Exterior Solutions and Their Geometry in Scalar-Tensor Theories of Gravity

NASA Astrophysics Data System (ADS)

Tsuchida, T.; Watanabe, K.

1999-01-01

We study series of stationary solutions with asymptotic flatness properties in the Einstein-Maxwell-free scalar system because they are locally equivalent to the exterior solutions in some class of scalar-tensor theories of gravity. First, we classify spherical exterior solutions into two types of solutions, an apparently black hole type solution and an apparently worm hole type solution. The solutions contain three parameters, and we clarify their physical significance. Second, we reduce the field equations for the axisymmetric exterior solutions. We find that the reduced equations are partially the same as the Ernst equations. As simple examples, we derive new series of static, axisymmetric exterior solutions, which correspond to Voorhees's solutions. We then establish a non-trivial relation between the spherical exterior solutions and our new solutions. Finally, since null geodesics have conformally invariant properties, we study the local geometry of the exterior solutions by using the optical scalar equations and find some anomalous behavior of the null geodesics.

Interplay between gravity and quintessence: a set of new GR solutions

NASA Astrophysics Data System (ADS)

Chernin, Arthur D.; Santiago, David I.; Silbergleit, Alexander S.

2002-02-01

A set of new exact analytical general relativity (GR) solutions with time-dependent and spatially inhomogeneous quintessence demonstrate (1) a static non-empty space-time with a horizon-type singular surface; (2) time-dependent spatially homogeneous `spheres' which are completely different in geometry from the Friedmann isotropic models; (3) infinitely strong anti-gravity at a `true' singularity where the density is infinitely large. It is also found that (4) the GR solutions allow for an extreme `density-free' form of energy that can generate regular space-time geometries.

New universal attractor in nonminimally coupled gravity: Linear inflation

NASA Astrophysics Data System (ADS)

Racioppi, Antonio

2018-06-01

Once quantum corrections are taken into account, the strong coupling limit of the ξ -attractor models (in metric gravity) might depart from the usual Starobinsky solution and move into linear inflation. Furthermore, it is well known that the metric and Palatini formulations of gravity lead to different inflationary predictions in presence of nonminimally couplings between gravity and the inflaton. In this paper, we show that for a certain class of nonminimally coupled models, loop corrections will lead to a linear inflation attractor regardless of the adopted gravity formulation.

Lifshitz gravity for Lifshitz holography.

PubMed

Griffin, Tom; Hořava, Petr; Melby-Thompson, Charles M

2013-02-22

We argue that Hořava-Lifshitz (HL) gravity provides the minimal holographic dual for Lifshitz-type field theories with anisotropic scaling and a dynamical exponent z. First we show that Lifshitz spacetimes are vacuum solutions of HL gravity, without need for additional matter. Then we perform holographic renormalization of HL gravity, and show how it reproduces the full structure of the z=2 anisotropic Weyl anomaly in dual field theories in 2+1 dimensions, while its minimal relativistic gravity counterpart yields only one of two independent central charges in the anomaly.

Modeling and estimation of a low degree geopotential model from terrestrial gravity data

NASA Technical Reports Server (NTRS)

Pavlis, Nikolaos K.

1988-01-01

The development of appropriate modeling and adjustment procedures for the estimation of harmonic coefficients of the geopotential, from surface gravity data was studied, in order to provide an optimum way of utilizing the terrestrial gravity information in combination solutions currently developed at NASA/Goddard Space Flight Center, for use in the TOPEX/POSEIDON mission. The mathematical modeling was based on the fundamental boundary condition of the linearized Molodensky boundary value problem. Atmospheric and ellipsoidal corrections were applied to the surface anomalies. Terrestrial gravity solutions were found to be in good agreement with the satellite ones over areas which are well surveyed (gravimetrically), such as North America or Australia. However, systematic differences between the terrestrial only models and GEMT1, over extended regions in Africa, the Soviet Union, and China were found. In Africa, gravity anomaly differences on the order of 20 mgals and undulation differences on the order of 15 meters, over regions extending 2000 km in diameter, occur. Comparisons of the GEMT1 implied undulations with 32 well distributed Doppler derived undulations gave an RMS difference of 2.6 m, while corresponding comparison with undulations implied by the terrestrial solution gave RMS difference on the order of 15 m, which implies that the terrestrial data in that region are substantially in error.

Geophysical parameters from the analysis of laser ranging to starlette

NASA Technical Reports Server (NTRS)

Schutz, B. E.; Shum, C. K.

1987-01-01

Starlette Satellite Laser Ranging (SLR) data were used, along with several other satellite data sets, for the solution of a preliminary gravity field model for TOPEX, PTGF1. A further improvement in the earth gravity model was accomplished using data collected by 12 satellites to solve another preliminary gravity model for TOPEX, designated PTGF2. The solution for the Earth Rotation Parameter (ERP) was derived from the analysis of SLR data to Starlette during the MERIT Campaign. Starlette orbits in 1976 and 1983 were analyzed for the mapping of the tidal response of the earth. Publications and conference presentations pertinent to research are listed.

A unified picture of cosmological entropy on apparent horizon in F(R, G) gravity

NASA Astrophysics Data System (ADS)

Keskin, Ali Ihsan; Acikgoz, Irfan

2017-10-01

In this study, the validity of the generalized second law of thermodynamics (GSLT) has been investigated in F(R, G) gravity. We consider that the boundary of the universe is surrounded by an apparent horizon in the spatially flat Friedmann-Robertson-Walker (FRW) universe, and we take into account the Hawking temperature on the horizons. The unified solutions of the field equations corresponding to gravity theory have been applied to the validity of the GSLT frame, and in this way, both the solutions have been verified and all the expansion history of the universe has been shown in a unified picture.

Geometric actions for three-dimensional gravity

NASA Astrophysics Data System (ADS)

Barnich, G.; González, H. A.; Salgado-Rebolledo, P.

2018-01-01

The solution space of three-dimensional asymptotically anti-de Sitter or flat Einstein gravity is given by the coadjoint representation of two copies of the Virasoro group in the former and the centrally extended BMS3 group in the latter case. Dynamical actions that control these solution spaces are usually constructed by starting from the Chern–Simons formulation and imposing all boundary conditions. In this note, an alternative route is followed. We study in detail how to derive these actions from a group-theoretical viewpoint by constructing geometric actions for each of the coadjoint orbits, including the appropriate Hamiltonians. We briefly sketch relevant generalizations and potential applications beyond three-dimensional gravity.

Gravity receptors in a microcrustacean water flea - Sensitivity of antennal-socket setae in Daphnia magna

NASA Technical Reports Server (NTRS)

Meyers, D. G.; Farmer, J. M.

1982-01-01

Gravity receptors of Dephnia magna were discovered on the basal segment of the swimming antennae and were shown to respond to upward water currents that pass the animal as it sinks between swimming strokes. Sensitivity of the gravity perceiving mechanism was tested by subjecting daphnids to a series of five decreasingly dense aqueous solutions (neutral density to water) in darkness (to avoid visual cues). Three-dimensional, video analysis of body position (pitch, yaw and roll) and swimming path (hop and sink, vertical and horizontal patterns) revealed a gradual threshold that occurred near a density difference between the animal and its environment of less than 0.25%. Because daphnids do not sink but continue to slide after stroking in the increased density solutions, gravity perception appears to occur during a vertical swing of the longitudinal body axis to the vertical plane, about their center of gravity, and, thereby, implies a multidirectional sensitivity for the antennal-socket setae.

Earth's gravity field to the eighteenth degree and geocentric coordinates for 104 stations from satellite and terrestrial data

NASA Technical Reports Server (NTRS)

Gaposchkin, E. M.

1973-01-01

Geodetic parameters describing the earth's gravity field and the positions of satellite-tracking stations in a geocentric reference frame were computed. These parameters were estimated by means of a combination of five different types of data: routine and simultaneous satellite observations, observations of deep-space probes, measurements of terrestrial gravity, and surface-triangulation data. The combination gives better parameters than does any subset of data types. The dynamic solution used precision-reduced Baker-Nunn observations and laser range data of 25 satellites. Data from the 49-station National Oceanic and Atmospheric Administration BC-4 network, the 19-station Smithsonian Astrophysical Observatory Baker-Nunn network, and independent camera stations were employed in the geometrical solution. Data from the tracking of deep-space probes were converted to relative longitudes and distances to the earth's axis of rotation of the tracking stations. Surface-gravity data in the form of 550-km squares were derived from 19,328 1 deg X 1 deg mean gravity anomalies.

Unitarity problems in 3D gravity theories

NASA Astrophysics Data System (ADS)

Alkac, Gokhan; Basanisi, Luca; Kilicarslan, Ercan; Tekin, Bayram

2017-07-01

We revisit the problem of the bulk-boundary unitarity clash in 2 +1 -dimensional gravity theories, which has been an obstacle in providing a viable dual two-dimensional conformal field theory for bulk gravity in anti-de Sitter (AdS) spacetime. Chiral gravity, which is a particular limit of cosmological topologically massive gravity (TMG), suffers from perturbative log-modes with negative energies inducing a nonunitary logarithmic boundary field theory. We show here that any f (R ) extension of TMG does not improve the situation. We also study the perturbative modes in the metric formulation of minimal massive gravity—originally constructed in a first-order formulation—and find that the massive mode has again negative energy except in the chiral limit. We comment on this issue and also discuss a possible solution to the problem of negative-energy modes. In any of these theories, the infinitesimal dangerous deformations might not be integrable to full solutions; this suggests a linearization instability of AdS spacetime in the direction of the perturbative log-modes.

Modified gravity in Arnowitt-Deser-Misner formalism

NASA Astrophysics Data System (ADS)

Gao, Changjun

2010-02-01

Motivated by Hořava-Lifshitz gravity theory, we propose and investigate two kinds of modified gravity theories, the f(R) kind and the K-essence kind, in the Arnowitt-Deser-Misner (ADM) formalism. The f(R) kind includes one ultraviolet (UV) term and one infrared (IR) term together with the Einstein-Hilbert action. We find that these two terms naturally present the ultraviolet and infrared modifications to the Friedmann equation. The UV and IR modifications can avoid the past Big-Bang singularity and the future Big-Rip singularity, respectively. Furthermore, the IR modification can naturally account for the current acceleration of the Universe. The Lagrangian of K-essence kind modified gravity is made up of the three-dimensional Ricci scalar and an arbitrary function of the extrinsic curvature term. We find the cosmic acceleration can also be naturally interpreted without invoking any kind of dark energy. The static, spherically symmetry and vacuum solutions of both theories are Schwarzschild or Schwarzschild-de Sitter solution. Thus these modified gravity theories are viable for solar system tests.

Regular black holes in f(T) Gravity through a nonlinear electrodynamics source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Junior, Ednaldo L.B.; Rodrigues, Manuel E.; Houndjo, Mahouton J.S., E-mail: ednaldobarrosjr@gmail.com, E-mail: esialg@gmail.com, E-mail: sthoundjo@yahoo.fr

2015-10-01

We seek to obtain a new class of exact solutions of regular black holes in f(T) Gravity with non-linear electrodynamics material content, with spherical symmetry in 4D. The equations of motion provide the regaining of various solutions of General Relativity, as a particular case where the function f(T)=T. We developed a powerful method for finding exact solutions, where we get the first new class of regular black holes solutions in the f(T) Theory, where all the geometrics scalars disappear at the origin of the radial coordinate and are finite everywhere, as well as a new class of singular black holes.

Black holes in six-dimensional conformal gravity

NASA Astrophysics Data System (ADS)

Lü, H.; Pang, Yi; Pope, C. N.

2013-05-01

We study conformally invariant theories of gravity in six dimensions. In four dimensions, there is a unique such theory that is polynomial in the curvature and its derivatives, namely, Weyl-squared, and furthermore all solutions of Einstein gravity are also solutions of the conformal theory. By contrast, in six dimensions there are three independent conformally invariant polynomial terms one could consider. There is a unique linear combination (up to overall scale) for which Einstein metrics are also solutions, and this specific theory forms the focus of our attention in this paper. We reduce the equations of motion for the most general spherically symmetric black hole to a single fifth-order differential equation. We obtain the general solution in the form of an infinite series, characterized by five independent parameters, and we show how a finite three-parameter truncation reduces to the already known Schwarzschild-AdS metric and its conformal scaling. We derive general results for the thermodynamics and the first law for the full five-parameter solutions. We also investigate solutions in extended theories coupled to conformally invariant matter, and in addition we derive some general results for conserved charges in cubic-curvature theories in arbitrary dimensions.

Skyrmions, Skyrme stars and black holes with Skyrme hair in five spacetime dimension

NASA Astrophysics Data System (ADS)

Brihaye, Yves; Herdeiro, Carlos; Radu, Eugen; Tchrakian, D. H.

2017-11-01

We consider a class of generalizations of the Skyrme model to five spacetime dimensions ( d = 5), which is defined in terms of an O(5) sigma model. A special ansatz for the Skyrme field allows angular momentum to be present and equations of motion with a radial dependence only. Using it, we obtain: 1) everywhere regular solutions describing localised energy lumps ( Skyrmions); 2) Self-gravitating, asymptotically flat, everywhere non-singular solitonic solutions ( Skyrme stars), upon minimally coupling the model to Einstein's gravity; 3) both static and spinning black holes with Skyrme hair, the latter with rotation in two orthogonal planes, with both angular momenta of equal magnitude. In the absence of gravity we present an analytic solution that satisfies a BPS-type bound and explore numerically some of the non-BPS solutions. In the presence of gravity, we contrast the solutions to this model with solutions to a complex scalar field model, namely boson stars and black holes with synchronised hair. Remarkably, even though the two models present key differences, and in particular the Skyrme model allows static hairy black holes, when introducing rotation, the synchronisation condition becomes mandatory, providing further evidence for its generality in obtaining rotating hairy black holes.

Wave equations in conformal gravity

NASA Astrophysics Data System (ADS)

Du, Juan-Juan; Wang, Xue-Jing; He, You-Biao; Yang, Si-Jiang; Li, Zhong-Heng

2018-05-01

We study the wave equation governing massless fields of all spins (s = 0, 1 2, 1, 3 2 and 2) in the most general spherical symmetric metric of conformal gravity. The equation is separable, the solution of the angular part is a spin-weighted spherical harmonic, and the radial wave function may be expressed in terms of solutions of the Heun equation which has four regular singular points. We also consider various special cases of the metric and find that the angular wave functions are the same for all cases, the actual shape of the metric functions affects only the radial wave function. It is interesting to note that each radial equation can be transformed into a known ordinary differential equation (i.e. Heun equation, or confluent Heun equation, or hypergeometric equation). The results show that there are analytic solutions for all the wave equations of massless spin fields in the spacetimes of conformal gravity. This is amazing because exact solutions are few and far between for other spacetimes.

Spacetime-bridge solutions in vacuum gravity

NASA Astrophysics Data System (ADS)

Sengupta, Sandipan

2017-11-01

Vacuum spacetime solutions, which are representations of a bridgelike geometry, are constructed as purely geometric sources of curvature in gravity theory. These configurations satisfy the first-order equations of motion everywhere. Each of them consists of two identical sheets of asymptotically flat geometry, connected by a region of finite extension where the tetrad is noninvertible. The solutions can be classified into nonstatic and static spacetimes. The first class represents a single causal universe equipped (locally) with a timelike coordinate everywhere. The latter, on the other hand, could be interpreted as a sum of two self-contained universes which are causally disconnected. These geometries, even though they have different metrical dimensions in the regions within and away from the bridge, are regular. This is reflected through the associated gauge-covariant fields, which are continuous across the hypersurfaces connecting the invertible and noninvertible phases of the tetrad and are finite everywhere. These vacuum bridge solutions have no analogue in the Einsteinian theory of gravity.

Downward continuation of the free-air gravity anomalies to the ellipsoid using the gradient solution and terrain correction: An attempt of global numerical computations

NASA Technical Reports Server (NTRS)

Wang, Y. M.

1989-01-01

The formulas for the determination of the coefficients of the spherical harmonic expansion of the disturbing potential of the earth are defined for data given on a sphere. In order to determine the spherical harmonic coefficients, the gravity anomalies have to be analytically downward continued from the earth's surface to a sphere-at least to the ellipsoid. The goal is to continue the gravity anomalies from the earth's surface downward to the ellipsoid using recent elevation models. The basic method for the downward continuation is the gradient solution (the g sub 1 term). The terrain correction was also computed because of the role it can play as a correction term when calculating harmonic coefficients from surface gravity data. The fast Fourier transformation was applied to the computations.

Gravitational stresses in anisotropic rock masses

USGS Publications Warehouse

Amadei, B.; Savage, W.Z.; Swolfs, H.S.

1987-01-01

This paper presents closed-form solutions for the stress field induced by gravity in anisotropic rock masses. These rocks are assumed to be laterally restrained and are modelled as a homogeneous, orthotropic or transversely isotropic, linearly elastic material. The analysis, constrained by the thermodynamic requirement that strain energy be positive definite, gives the following important result: inclusion of anisotropy broadens the range of permissible values of gravity-induced horizontal stresses. In fact, for some ranges of anisotropic rock properties, it is thermodynamically admissible for gravity-induced horizontal stresses to exceed the vertical stress component; this is not possible for the classical isotropic solution. Specific examples are presented to explore the nature of the gravity-induced stress field in anisotropic rocks and its dependence on the type, degree and orientation of anisotropy with respect to the horizontal ground surface. ?? 1987.

Analysis of capillary drainage from a flat solid strip

NASA Astrophysics Data System (ADS)

Ramé, Enrique; Zimmerli, Gregory A.

2014-06-01

A long and narrow solid strip coated with a thin liquid layer is used as a model of a generic fluid mass probe in a spacecraft propellant tank just after a small thruster firing. The drainage dynamics of the initial coating layer into the settled bulk fluid affects the interpretation of probe measurements as the sensors' signal depends strongly on whether a sensor is in contact with vapor or with liquid. We analyze the drainage under various conditions of zero-gravity (i.e., capillary drainage) and with gravity aligned with the strip length, corresponding to the thruster acceleration. Long-time analytical solutions are found for zero and non-zero gravity. In the case with gravity, an approximate solution is found using matched asymptotics. Estimates show that a thrust of 10-3g0 significantly reduces drainage times.

Gravity model development for precise orbit computations for satellite altimetry

NASA Technical Reports Server (NTRS)

Marsh, James G.; Lerch, Francis, J.; Smith, David E.; Klosko, Steven M.; Pavlis, Erricos

1986-01-01

Two preliminary gravity models developed as a first step in reaching the TOPEX/Poseidon modeling goals are discussed. They were obtained by NASA-Goddard from an analysis of exclusively satellite tracking observations. With the new Preliminary Gravity Solution-T2 model, an improved global estimate of the field is achieved with an improved description of the geoid.

Application of Newtonian Physics to Predict the Speed of a Gravity Racer

ERIC Educational Resources Information Center

Driscoll, H. F.; Bullas, A. M.; King, C. E.; Senior, T.; Haake, S. J.; Hart, J.

2016-01-01

Gravity racing can be studied using numerical solutions to the equations of motion derived from Newton's second law. This allows students to explore the physics of gravity racing and to understand how design and course selection influences vehicle speed. Using Euler's method, we have developed a spreadsheet application that can be used to predict…

Results from a U.S. Absolute Gravity Survey,

DTIC Science & Technology

1982-01-01

National Bureau of Standards. La . ... ,., 831A08 NOV -2- 1. Introduction We have recently completed an absolute gravity survey at twelve sites in the...Air Force Geophysics Laboratory (AFGL) and the Istituto di Metrologia -7- "G. Colonnetti" (IMGC) [Marson and Alasia, 1978, 19801. All three...for ab- solute measurements of the earth’s gravity, Metrologia , in press, 1982. L 4 !" Table 1. Gravity values transferred to the floor in gal (cm

Gsolve, a Python computer program with a graphical user interface to transform relative gravity survey measurements to absolute gravity values and gravity anomalies

NASA Astrophysics Data System (ADS)

McCubbine, Jack; Tontini, Fabio Caratori; Stagpoole, Vaughan; Smith, Euan; O'Brien, Grant

2018-01-01

A Python program (Gsolve) with a graphical user interface has been developed to assist with routine data processing of relative gravity measurements. Gsolve calculates the gravity at each measurement site of a relative gravity survey, which is referenced to at least one known gravity value. The tidal effects of the sun and moon, gravimeter drift and tares in the data are all accounted for during the processing of the survey measurements. The calculation is based on a least squares formulation where the difference between the absolute gravity at each surveyed location and parameters relating to the dynamics of the gravimeter are minimized with respect to the relative gravity observations, and some supplied gravity reference site values. The program additionally allows the user to compute free air gravity anomalies, with respect to the GRS80 and GRS67 reference ellipsoids, from the determined gravity values and calculate terrain corrections at each of the surveyed sites using a prism formula and a user supplied digital elevation model. This paper reviews the mathematical framework used to reduce relative gravimeter survey observations to gravity values. It then goes on to detail how the processing steps can be implemented using the software.

Singular boundary method for global gravity field modelling

NASA Astrophysics Data System (ADS)

Cunderlik, Robert

2014-05-01

The singular boundary method (SBM) and method of fundamental solutions (MFS) are meshless boundary collocation techniques that use the fundamental solution of a governing partial differential equation (e.g. the Laplace equation) as their basis functions. They have been developed to avoid singular numerical integration as well as mesh generation in the traditional boundary element method (BEM). SBM have been proposed to overcome a main drawback of MFS - its controversial fictitious boundary outside the domain. The key idea of SBM is to introduce a concept of the origin intensity factors that isolate singularities of the fundamental solution and its derivatives using some appropriate regularization techniques. Consequently, the source points can be placed directly on the real boundary and coincide with the collocation nodes. In this study we deal with SBM applied for high-resolution global gravity field modelling. The first numerical experiment presents a numerical solution to the fixed gravimetric boundary value problem. The achieved results are compared with the numerical solutions obtained by MFS or the direct BEM indicating efficiency of all methods. In the second numerical experiments, SBM is used to derive the geopotential and its first derivatives from the Tzz components of the gravity disturbing tensor observed by the GOCE satellite mission. A determination of the origin intensity factors allows to evaluate the disturbing potential and gravity disturbances directly on the Earth's surface where the source points are located. To achieve high-resolution numerical solutions, the large-scale parallel computations are performed on the cluster with 1TB of the distributed memory and an iterative elimination of far zones' contributions is applied.

Effect of Gravity on Robot-Assisted Motor Training After Chronic Stroke: A Randomized Trial

PubMed Central

Conroy, Susan S.; Whitall, Jill; Dipietro, Laura; Jones-Lush, Lauren M.; Zhan, Min; Finley, Margaret A.; Wittenberg, George F.; Krebs, Hermano I.; Bever, Christopher T.

2015-01-01

Objectives To determine the efficacy of 2 distinct 6-week robot-assisted reaching programs compared with an intensive conventional arm exercise program (ICAE) for chronic, stroke-related upper-extremity (UE) impairment. To examine whether the addition of robot-assisted training out of the horizontal plane leads to improved outcomes. Design Randomized controlled trial, single-blinded, with 12-week follow-up. Setting Research setting in a large medical center. Participants Adults (N=62) with chronic, stroke-related arm weakness stratified by impairment severity using baseline UE motor assessments. Interventions Sixty minutes, 3 times a week for 6 weeks of robot-assisted planar reaching (gravity compensated), combined planar with vertical robot-assisted reaching, or intensive conventional arm exercise program. Main Outcome Measure UE Fugl-Meyer Assessment (FMA) mean change from baseline to final training. Results All groups showed modest gains in the FMA from baseline to final with no significant between group differences. Most change occurred in the planar robot group (mean change ± SD, 2.94± 0.77; 95% confidence interval [CI], 1.40 – 4.47). Participants with greater motor impairment (n=41) demonstrated a larger difference in response (mean change ± SD, 2.29±0.72; 95% CI, 0.85–3.72) for planar robot-assisted exercise compared with the intensive conventional arm exercise program (mean change ± SD, 0.43±0.72; 95% CI, −1.00 to 1.86). Conclusions Chronic UE deficits because of stroke are responsive to intensive motor task training. However, training outside the horizontal plane in a gravity present environment using a combination of vertical with planar robots was not superior to training with the planar robot alone. PMID:21849168

ARTEMIS Mission Overview: From Concept to Operations

NASA Technical Reports Server (NTRS)

Folta, David; Sweetser, Theodore

2011-01-01

ARTEMIS (Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun) repurposed two spacecraft to extend their useful science (Angelopoulos, 2010) by moving them via lunar gravity assists from elliptical Earth orbits to L1 and L2 Earth-Moon libration orbits and then to lunar orbits by exploiting the Earth-Moon-Sun dynamical environment. This paper describes the complete design from conceptual plans using weak stability transfer options and lunar gravity assist to the implementation and operational support of the Earth-Moon libration and lunar orbits. The two spacecraft of the ARTEMIS mission will have just entered lunar orbit at this paper's presentation.

Low-thrust trajectory optimization of asteroid sample return mission with multiple revolutions and moon gravity assists

NASA Astrophysics Data System (ADS)

Tang, Gao; Jiang, FanHuag; Li, JunFeng

2015-11-01

Near-Earth asteroids have gained a lot of interest and the development in low-thrust propulsion technology makes complex deep space exploration missions possible. A mission from low-Earth orbit using low-thrust electric propulsion system to rendezvous with near-Earth asteroid and bring sample back is investigated. By dividing the mission into five segments, the complex mission is solved separately. Then different methods are used to find optimal trajectories for every segment. Multiple revolutions around the Earth and multiple Moon gravity assists are used to decrease the fuel consumption to escape from the Earth. To avoid possible numerical difficulty of indirect methods, a direct method to parameterize the switching moment and direction of thrust vector is proposed. To maximize the mass of sample, optimal control theory and homotopic approach are applied to find the optimal trajectory. Direct methods of finding proper time to brake the spacecraft using Moon gravity assist are also proposed. Practical techniques including both direct and indirect methods are investigated to optimize trajectories for different segments and they can be easily extended to other missions and more precise dynamic model.

The U.S. Rosetta Project: Mars Gravity Assist

NASA Technical Reports Server (NTRS)

Alexander, Claudia; Holmes, Dwight P.; Goldstein, R.; Parker, Joel

2008-01-01

Since launch on March 2, 2004, the International Rosetta Mission has flown by the Earth/Moon system one time and conducted several distant observations of comets, including support for the Deep Impact measurements of comet 9 P/Tempel 1. In 2007, Rosetta flew by Mars for a gravity assist, and conducted observations of the Martian upper atmosphere as well as extended observations, in support of the New Horizons Jupiter encounter, of the Jovian magnetotail and Io torus. In late 2007 Rosetta had its second encounter with the Earth/Moon system. NASA's contribution to the Rosetta mission consists of three hardware experiments, and the portion of the electronics package for a fourth, as well as the participation of an Interdisciplinary Scientist (IDS); backup tracking, telecommunications, and navigation assurance provided by the Deep Space Network (DSN); support for the scientific participation of U.S. investigators on non-U.S. PI-led experiments. Collectively these elements are known as the U.S. Rosetta Project. In this paper we will update the status of the instruments following the both the Mars and Earth/Moon gravity assists. In addition, we will present a summary of the science observations for both Mars and Jupiter. 12.

Temporal gravity field modeling based on least square collocation with short-arc approach

NASA Astrophysics Data System (ADS)

ran, jiangjun; Zhong, Min; Xu, Houze; Liu, Chengshu; Tangdamrongsub, Natthachet

2014-05-01

After the launch of the Gravity Recovery And Climate Experiment (GRACE) in 2002, several research centers have attempted to produce the finest gravity model based on different approaches. In this study, we present an alternative approach to derive the Earth's gravity field, and two main objectives are discussed. Firstly, we seek the optimal method to estimate the accelerometer parameters, and secondly, we intend to recover the monthly gravity model based on least square collocation method. The method has been paid less attention compared to the least square adjustment method because of the massive computational resource's requirement. The positions of twin satellites are treated as pseudo-observations and unknown parameters at the same time. The variance covariance matrices of the pseudo-observations and the unknown parameters are valuable information to improve the accuracy of the estimated gravity solutions. Our analyses showed that introducing a drift parameter as an additional accelerometer parameter, compared to using only a bias parameter, leads to a significant improvement of our estimated monthly gravity field. The gravity errors outside the continents are significantly reduced based on the selected set of the accelerometer parameters. We introduced the improved gravity model namely the second version of Institute of Geodesy and Geophysics, Chinese Academy of Sciences (IGG-CAS 02). The accuracy of IGG-CAS 02 model is comparable to the gravity solutions computed from the Geoforschungszentrum (GFZ), the Center for Space Research (CSR) and the NASA Jet Propulsion Laboratory (JPL). In term of the equivalent water height, the correlation coefficients over the study regions (the Yangtze River valley, the Sahara desert, and the Amazon) among four gravity models are greater than 0.80.

Theory of Metastable State Relaxation in a Gravitational Field for Non-Critical Binary Systems with Non-Conserved Order Parameter

NASA Technical Reports Server (NTRS)

Izmailov, Alexander F.; Myerson, Allan S.

1993-01-01

A new mathematical ansatz is developed for solution of the time-dependent Ginzburg-Landau nonlinear partial differential equation describing metastable state relaxation in binary (solute+solvent) non-critical solutions with non-conserved scalar order parameter in presence of a gravitational field. It has been demonstrated analytically that in such systems metastability initiates heterogeneous solute redistribution which results in the formation of a non-equilibrium singly-periodic spatial solute structure in the new solute-rich phase. The critical radius of nucleation and the induction time in these systems are gravity-dependent. It has also been proved that metastable state relaxation in vertical columns of supersaturated non-critical binary solutions leads to formation of the solute concentration gradient. Analytical expression for this concentration gradient is found and analysed. It is concluded that gravity can initiate phase separation (nucleation or spinodal decomposition).

Sub-basin-scale sea level budgets from satellite altimetry, Argo floats and satellite gravimetry: a case study in the North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Kleinherenbrink, Marcel; Riva, Riccardo; Sun, Yu

2016-11-01

In this study, for the first time, an attempt is made to close the sea level budget on a sub-basin scale in terms of trend and amplitude of the annual cycle. We also compare the residual time series after removing the trend, the semiannual and the annual signals. To obtain errors for altimetry and Argo, full variance-covariance matrices are computed using correlation functions and their errors are fully propagated. For altimetry, we apply a geographically dependent intermission bias [Ablain et al.(2015)], which leads to differences in trends up to 0.8 mm yr-1. Since Argo float measurements are non-homogeneously spaced, steric sea levels are first objectively interpolated onto a grid before averaging. For the Gravity Recovery And Climate Experiment (GRACE), gravity fields full variance-covariance matrices are used to propagate errors and statistically filter the gravity fields. We use four different filtered gravity field solutions and determine which post-processing strategy is best for budget closure. As a reference, the standard 96 degree Dense Decorrelation Kernel-5 (DDK5)-filtered Center for Space Research (CSR) solution is used to compute the mass component (MC). A comparison is made with two anisotropic Wiener-filtered CSR solutions up to degree and order 60 and 96 and a Wiener-filtered 90 degree ITSG solution. Budgets are computed for 10 polygons in the North Atlantic Ocean, defined in a way that the error on the trend of the MC plus steric sea level remains within 1 mm yr-1. Using the anisotropic Wiener filter on CSR gravity fields expanded up to spherical harmonic degree 96, it is possible to close the sea level budget in 9 of 10 sub-basins in terms of trend. Wiener-filtered Institute of Theoretical geodesy and Satellite Geodesy (ITSG) and the standard DDK5-filtered CSR solutions also close the trend budget if a glacial isostatic adjustment (GIA) correction error of 10-20 % is applied; however, the performance of the DDK5-filtered solution strongly depends on the orientation of the polygon due to residual striping. In 7 of 10 sub-basins, the budget of the annual cycle is closed, using the DDK5-filtered CSR or the Wiener-filtered ITSG solutions. The Wiener-filtered 60 and 96 degree CSR solutions, in combination with Argo, lack amplitude and suffer from what appears to be hydrological leakage in the Amazon and Sahel regions. After reducing the trend, the semiannual and the annual signals, 24-53 % of the residual variance in altimetry-derived sea level time series is explained by the combination of Argo steric sea levels and the Wiener-filtered ITSG MC. Based on this, we believe that the best overall solution for the MC of the sub-basin-scale budgets is the Wiener-filtered ITSG gravity fields. The interannual variability is primarily a steric signal in the North Atlantic Ocean, so for this the choice of filter and gravity field solution is not really significant.

Temperature Oscillation in a Loop Heat Pipe with Gravity Assist

NASA Technical Reports Server (NTRS)

Ku, Jentung; Garrison, Matt; Patel, Deepak; Ottenstein, Laura; Robinson, Frank

2014-01-01

ATLAS Laser Thermal Control System (LTCS) thermal vacuum testing where the condenser-radiator was placed in a vertical position, it was found that the loop heat pipe (LHP) reservoir required much more control heater power than the analytical model had predicted. The required control heater power was also higher than the liquid subcooling entering the reservoir using the measured temperatures and the calculated mass flow rate based on steady state LHP operation. This presentation describes the investigation of the LHP behaviors under a gravity assist mode with a very cold radiator sink temperature and a large thermal mass attached to the evaporator. It is concluded that gravity caused the cold liquid to drop from the condenser-radiator to the reservoir, resulting in a rapid decrease of the reservoir temperature. When the reservoir temperature was increasing, a reverse flow occurred in the liquid line, carrying warm liquid to the condenser-radiator. Both events consumed the reservoir control heater power. The fall and rise of the reservoir temperature also caused the net heat input to the evaporator to vary due to the release and storage of the sensible heat of the thermal mass. The combination of these effects led to a persistent reservoir temperature oscillation and a repeated influx of cold liquid from the condenser. This was the root cause of the extraordinary high control heater power requirement in the LTCS TV test. Without gravity assist, such a persistent temperature oscillation will not be present.

Novel Control Scheme of Power Assisted Wheelchair for Preventing Overturn (Part II)-Variable Assistance Ratio Control Based on Estimation of Center-of-Gravity Angle and Phase Plane-

NASA Astrophysics Data System (ADS)

Hata, Naoki; Seki, Hirokazu; Koyasu, Yuichi; Hori, Yoichi

Aged people and disabled people who have difficulty in walking are increasing. As one of mobility support, significance of a power assisted wheelchair which assists driving force using electric motors and spreads their living areas has been enhanced. However, the increased driving force often causes a dangerous overturn of wheelchair. This paper proposes a novel control method to prevent power assisted wheelchair from overturning. The man-wheelchair system can be regarded as an inverse pendulum model when the front wheels are rising. The center-of-gravity (COG) angle of the model is the most important information directly-linked to overturn. Behavior of the system can be analyzed using phase plane as shown in this paper. The COG angle cannot be directly measured using a sensor, therefore, COG observer based on its velocity is proposed. On the basis of the analysis on phase plane, a novel control method with variable assistance ratio to prevent a dangerous overturn is proposed. The effectiveness of the proposed method is verified by the practical experiments on the flat ground and uphill slope.

DORIS-based point mascons for the long term stability of precise orbit solutions

NASA Astrophysics Data System (ADS)

Cerri, L.; Lemoine, J. M.; Mercier, F.; Zelensky, N. P.; Lemoine, F. G.

2013-08-01

In recent years non-tidal Time Varying Gravity (TVG) has emerged as the most important contributor in the error budget of Precision Orbit Determination (POD) solutions for altimeter satellites' orbits. The Gravity Recovery And Climate Experiment (GRACE) mission has provided POD analysts with static and time-varying gravity models that are very accurate over the 2002-2012 time interval, but whose linear rates cannot be safely extrapolated before and after the GRACE lifespan. One such model based on a combination of data from GRACE and Lageos from 2002-2010, is used in the dynamic POD solutions developed for the Geophysical Data Records (GDRs) of the Jason series of altimeter missions and the equivalent products from lower altitude missions such as Envisat, Cryosat-2, and HY-2A. In order to accommodate long-term time-variable gravity variations not included in the background geopotential model, we assess the feasibility of using DORIS data to observe local mass variations using point mascons. In particular, we show that the point-mascon approach can stabilize the geographically correlated orbit errors which are of fundamental interest for the analysis of regional Mean Sea Level trends based on altimeter data, and can therefore provide an interim solution in the event of GRACE data loss. The time series of point-mass solutions for Greenland and Antarctica show good agreement with independent series derived from GRACE data, indicating a mass loss at rate of 210 Gt/year and 110 Gt/year respectively.

Global detailed gravimetric geoid. [based on gravity model derived from satellite tracking and surface gravity data

NASA Technical Reports Server (NTRS)

Vincent, S.; Marsh, J. G.

1973-01-01

A global detailed gravimetric geoid has been computed by combining the Goddard Space Flight Center GEM-4 gravity model derived from satellite and surface gravity data and surface 1 deg-by-1 deg mean free air gravity anomaly data. The accuracy of the geoid is + or - 2 meters on continents, 5 to 7 meters in areas where surface gravity data are sparse, and 10 to 15 meters in areas where no surface gravity data are available. Comparisons have been made with the astrogeodetic data provided by Rice (United States), Bomford (Europe), and Mather (Australia). Comparisons have also been carried out with geoid heights derived from satellite solutions for geocentric station coordinates in North America, the Caribbean, Europe, and Australia.

Some aspects of reconstruction using a scalar field in f( T) gravity

NASA Astrophysics Data System (ADS)

Chakrabarti, Soumya; Said, Jackson Levi; Farrugia, Gabriel

2017-12-01

General relativity characterizes gravity as a geometric property exhibited on spacetime by massive objects, while teleparallel gravity achieves the same results at the level of equations, by taking a torsional perspective of gravity. Similar to the f( R) theory teleparallel gravity can also be generalized to f( T), with the resulting field equations being inherently distinct from f( R) gravity in that they are second order, while in the former case they turn out to be fourth order. In the present case, a minimally coupled scalar field is investigated in the f( T) gravity context for several forms of the scalar field potential. A number of new f( T) solutions are found for these potentials. Their respective state parameters are also being examined.

Testing local Lorentz invariance with short-range gravity

DOE PAGES

Kostelecký, V. Alan; Mewes, Matthew

2017-01-10

The Newton limit of gravity is studied in the presence of Lorentz-violating gravitational operators of arbitrary mass dimension. The linearized modified Einstein equations are obtained and the perturbative solutions are constructed and characterized. We develop a formalism for data analysis in laboratory experiments testing gravity at short range and demonstrate that these tests provide unique sensitivity to deviations from local Lorentz invariance.

Gravity Gradiometry and Map Matching: An Aid to Aircraft Inertial Navigation Systems

DTIC Science & Technology

2010-03-01

improve its performance. In all of these cases, because information from two or more different navigation systems feeds into a navigation solution...GRAVITY GRADIOMETRY AND MAP MATCHING: AN AID TO AIRCRAFT INERTIAL NAVIGATION SYSTEMS THESIS...M06 GRAVITY GRADIOMETRY AND MAP MATCHING: AN AID TO AIRCRAFT INERTIAL NAVIGATION SYSTEMS THESIS Presented to the Faculty Department of

On the breakdown of asymptotic Poincare invariance in D = 3 Einstein gravity

NASA Technical Reports Server (NTRS)

Deser, S.

1985-01-01

It is shown through a series of calculations that neither momentum nor boosts are definable for finite energy solutions of Einstein gravity in D = 3. The contrast between the effects of Lorentz transformations on the corresponding metrics for D = 3 and D = 4 gravity is demonstrated, and some comparisons with the vector gauge treatment of the problem are offered.

High-resolution local gravity model of the south pole of the Moon from GRAIL extended mission data.

PubMed

Goossens, Sander; Sabaka, Terence J; Nicholas, Joseph B; Lemoine, Frank G; Rowlands, David D; Mazarico, Erwan; Neumann, Gregory A; Smith, David E; Zuber, Maria T

2014-05-28

We estimated a high-resolution local gravity field model over the south pole of the Moon using data from the Gravity Recovery and Interior Laboratory's extended mission. Our solution consists of adjustments with respect to a global model expressed in spherical harmonics. The adjustments are expressed as gridded gravity anomalies with a resolution of 1/6° by 1/6° (equivalent to that of a degree and order 1080 model in spherical harmonics), covering a cap over the south pole with a radius of 40°. The gravity anomalies have been estimated from a short-arc analysis using only Ka-band range-rate (KBRR) data over the area of interest. We apply a neighbor-smoothing constraint to our solution. Our local model removes striping present in the global model; it reduces the misfit to the KBRR data and improves correlations with topography to higher degrees than current global models. We present a high-resolution gravity model of the south pole of the Moon Improved correlations with topography to higher degrees than global models Improved fits to the data and reduced striping that is present in global models.

High-resolution local gravity model of the south pole of the Moon from GRAIL extended mission data

PubMed Central

Goossens, Sander; Sabaka, Terence J; Nicholas, Joseph B; Lemoine, Frank G; Rowlands, David D; Mazarico, Erwan; Neumann, Gregory A; Smith, David E; Zuber, Maria T

2014-01-01

We estimated a high-resolution local gravity field model over the south pole of the Moon using data from the Gravity Recovery and Interior Laboratory's extended mission. Our solution consists of adjustments with respect to a global model expressed in spherical harmonics. The adjustments are expressed as gridded gravity anomalies with a resolution of 1/6° by 1/6° (equivalent to that of a degree and order 1080 model in spherical harmonics), covering a cap over the south pole with a radius of 40°. The gravity anomalies have been estimated from a short-arc analysis using only Ka-band range-rate (KBRR) data over the area of interest. We apply a neighbor-smoothing constraint to our solution. Our local model removes striping present in the global model; it reduces the misfit to the KBRR data and improves correlations with topography to higher degrees than current global models. Key Points We present a high-resolution gravity model of the south pole of the Moon Improved correlations with topography to higher degrees than global models Improved fits to the data and reduced striping that is present in global models PMID:26074637

Homogeneous anisotropic solutions of topologically massive gravity with a cosmological constant and their homogeneous deformations

NASA Astrophysics Data System (ADS)

Moutsopoulos, George

2013-06-01

We solve the equations of topologically massive gravity (TMG) with a potentially non-vanishing cosmological constant for homogeneous metrics without isotropy. We only reproduce known solutions. We also discuss their homogeneous deformations, possibly with isotropy. We show that de Sitter space and hyperbolic space cannot be infinitesimally homogeneously deformed in TMG. We clarify some of their Segre-Petrov types and discuss the warped de Sitter spacetime.

Einstein gravity with torsion induced by the scalar field

NASA Astrophysics Data System (ADS)

Özçelik, H. T.; Kaya, R.; Hortaçsu, M.

2018-06-01

We couple a conformal scalar field in (2+1) dimensions to Einstein gravity with torsion. The field equations are obtained by a variational principle. We could not solve the Einstein and Cartan equations analytically. These equations are solved numerically with 4th order Runge-Kutta method. From the numerical solution, we make an ansatz for the rotation parameter in the proposed metric, which gives an analytical solution for the scalar field for asymptotic regions.

Analytical general solutions for static wormholes in f(R,T) gravity

NASA Astrophysics Data System (ADS)

Moraes, P. H. R. S.; Correa, R. A. C.; Lobato, R. V.

2017-07-01

Originally proposed as a tool for teaching the general theory of relativity, wormholes are today approached in many different ways and are seeing as an efficient alternative for interstellar and time travel. Attempts to achieve observational signatures of wormholes have been growing as the subject has become more and more popular. In this article we investigate some f(R,T) theoretical predictions for static wormholes, i.e., wormholes whose throat radius can be considered a constant. Since the T-dependence in f(R,T) gravity is due to the consideration of quantum effects, a further investigation of wormholes in such a theory is well motivated. We obtain the energy conditions of static wormholes in f(R,T) gravity and apply an analytical approach to find their physical and geometrical solutions. We highlight that our results are in agreement with previous solutions and assumptions presented in the literature.

Analytical general solutions for static wormholes in f ( R , T ) gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moraes, P.H.R.S.; Correa, R.A.C.; Lobato, R.V., E-mail: moraes.phrs@gmail.com, E-mail: fis04132@gmail.com, E-mail: ronaldo.lobato@icranet.org

Originally proposed as a tool for teaching the general theory of relativity, wormholes are today approached in many different ways and are seeing as an efficient alternative for interstellar and time travel. Attempts to achieve observational signatures of wormholes have been growing as the subject has become more and more popular. In this article we investigate some f ( R , T ) theoretical predictions for static wormholes, i.e., wormholes whose throat radius can be considered a constant. Since the T -dependence in f ( R , T ) gravity is due to the consideration of quantum effects, a furthermore » investigation of wormholes in such a theory is well motivated. We obtain the energy conditions of static wormholes in f ( R , T ) gravity and apply an analytical approach to find their physical and geometrical solutions. We highlight that our results are in agreement with previous solutions and assumptions presented in the literature.« less

Low-gravity fluid physics: A program overview

NASA Technical Reports Server (NTRS)

1990-01-01

An overview is presented of the microgravity fluid physics program at Lewis Research Center. One of the main reasons for conducting low gravity research in fluid physics is to study phenomena such as surface tension, interfacial contact angles, and diffusion independent of such gravitationally induced effects as buoyant convection. Fluid physics is at the heart of many space-based technologies including power systems, thermal control systems, and life support systems. Fundamental understanding of fluid physics is a key ingredient to successful space systems design. In addition to describing ground-based and space-based low-gravity facilities, selected experiments are presented which highlight Lewis work in fluid physics. These experiments can be categorized into five theme areas which summarize the work being conducted at Lewis for OSSA: (1) isothermal/iso-solutal capillary phenomena; (2) capillary phenomena with thermal/solutal gradients; (3) thermal-solutal convection; (4) first- and second-order phase transitions in a static fluid; and (5) multiphase flow.

Sparse Reconstruction of Regional Gravity Signal Based on Stabilized Orthogonal Matching Pursuit (SOMP)

NASA Astrophysics Data System (ADS)

Saadat, S. A.; Safari, A.; Needell, D.

2016-06-01

The main role of gravity field recovery is the study of dynamic processes in the interior of the Earth especially in exploration geophysics. In this paper, the Stabilized Orthogonal Matching Pursuit (SOMP) algorithm is introduced for sparse reconstruction of regional gravity signals of the Earth. In practical applications, ill-posed problems may be encountered regarding unknown parameters that are sensitive to the data perturbations. Therefore, an appropriate regularization method needs to be applied to find a stabilized solution. The SOMP algorithm aims to regularize the norm of the solution vector, while also minimizing the norm of the corresponding residual vector. In this procedure, a convergence point of the algorithm that specifies optimal sparsity-level of the problem is determined. The results show that the SOMP algorithm finds the stabilized solution for the ill-posed problem at the optimal sparsity-level, improving upon existing sparsity based approaches.

Biological patterns: Novel indicators for pharmacological assays

NASA Technical Reports Server (NTRS)

Johnson, Jacqueline U.

1991-01-01

Variable gravity testing using the KC-135 demonstrated clearly that biological pattern formation was definitely shown to result from gravity alone, and not from oxygen gradients in solution. Motile pattern formation of spermatozoa are driven by alternate mechanisms, and apparently not affected by short-term changes in gravity. The chemical effects found appear to be secondary to the primary effect of gravity. Cryopreservation may be the remedy to the problem of 'spare' or 'standing order' biological samples for testing of space lab investigations, but further studies are necessary.

Noether symmetry approach in f(T, B) teleparallel cosmology.

PubMed

Bahamonde, Sebastian; Capozziello, Salvatore

2017-01-01

We consider the cosmology derived from f ( T ,  B ) gravity where T is the torsion scalar and [Formula: see text] a boundary term. In particular we discuss how it is possible to recover, under the same standard, the teleparallel f ( T ) gravity, the curvature f ( R ) gravity, and the teleparallel-curvature f ( R ,  T ) gravity, which are particular cases of f ( T ,  B ). We adopt the Noether Symmetry Approach to study the related dynamical systems and to find cosmological solutions.

Flat space (higher spin) gravity with chemical potentials

NASA Astrophysics Data System (ADS)

Gary, Michael; Grumiller, Daniel; Riegler, Max; Rosseel, Jan

2015-01-01

We introduce flat space spin-3 gravity in the presence of chemical potentials and discuss some applications to flat space cosmology solutions, their entropy, free energy and flat space orbifold singularity resolution. Our results include flat space Einstein gravity with chemical potentials as special case. We discover novel types of phase transitions between flat space cosmologies with spin-3 hair and show that the branch that continuously connects to spin-2 gravity becomes thermodynamically unstable for sufficiently large temperature or spin-3 chemical potential.

New post-Newtonian parameter to test Chern-Simons gravity.

PubMed

Alexander, Stephon; Yunes, Nicolas

2007-12-14

We study Chern-Simons (CS) gravity in the parametrized post-Newtonian (PPN) framework through a weak-field solution of the modified field equations. We find that CS gravity possesses the same PPN parameters as general relativity, except for the inclusion of a new term, proportional to the CS coupling and the curl of the PPN vector potential. This new term leads to a modification of frame dragging and gyroscopic precession and we provide an estimate of its size. This correction might be used in experiments, such as Gravity Probe B, to bound CS gravity and test string theory.

Generalized Vaidya spacetime for cubic gravity

NASA Astrophysics Data System (ADS)

Ruan, Shan-Ming

2016-03-01

We present a kind of generalized Vaidya solution of a new cubic gravity in five dimensions whose field equations in spherically symmetric spacetime are always second order like the Lovelock gravity. We also study the thermodynamics of its spherically symmetric apparent horizon and get its entropy expression and generalized Misner-Sharp energy. Finally, we present the first law and second law hold in this gravity. Although all the results are analogous to those in Lovelock gravity, we in fact introduce the contribution of a new cubic term in five dimensions where the cubic Lovelock term is just zero.

Gravity-induced stresses near a vertical cliff

USGS Publications Warehouse

Savage, W.Z.

1993-01-01

The exact solution for gravity-induced stresses beneath a vertical cliff presented here has application to the design of cut slopes in rock, compares favorably with published photoelastic and finite-element results for this problem, and satisfies the condition that shear and normal stresses vanish on the ground surface, except at the bottom corner where stress concentrations exist. The solution predicts that horizontal stresses are tensile away from the bottom of the cliff-effects caused by movement below the cliff in response to the gravity loading of the cliff. Also, it is shown that along the top of the cliff normal stresses reduce to those predicted for laterally constrained flat-lying topography. ?? 1993.

Seamless geoids across coastal zones - a comparison of satellite-derived gravity to airborne gravity across the seven continents

NASA Astrophysics Data System (ADS)

Forsberg, R.; Olesen, A. V.; Barnes, D.; Ingalls, S. E.; Minter, C. F.; Presicci, M. R.

2017-12-01

An accurate coastal geoid model is important for determination of near-shore ocean dynamic topography and currents, as well as for land GPS surveys and global geopotential models. Since many coastal regions across the globe are regions of intense development and coastal protection projects, precise geoid models at cm-level accuracy are essential. The only way to secure cm-geoid accuracies across coastal regions is to acquire more marine gravity data; here airborne gravity is the obvious method of choice due to the uniform accuracy, and the ability to provide a seamless geoid accuracy across the coastline. Current practice for gravity and geoid models, such as EGM2008 and many national projects, is to complement land gravity data with satellite radar altimetry at sea, a procedure which can give large errors in regions close to the coast. To quantify the coastal errors in satellite gravity, we compare results of a large set of recent airborne gravity surveys, acquired across a range of coastal zones globally from polar to equatorial regions, and quantify the errors as a function of distance from the coast line for a number of different global altimetry gravity solutions. We find that accuracy in satellite altimetry solutions depend very much on the availability of gravity data along the coast-near land regions in the underlying reference fields (e.g., EGM2008), with satellite gravity accuracy in the near-shore zone ranging from anywhere between 5 to 20 mGal r.m.s., with occasional large outliers; we also show how these errors may typically propagate into coastal geoid errors of 5-10 cm r.m.s. or more. This highlight the need for airborne (land) gravity surveys to be extended at least 20-30 km offshore, especially for regions of insufficient marine gravity coverage; we give examples of a few such recent surveys and associated marine geoid impacts.

Changes in gravitational parameters inferred from time variable GRACE data-A case study for October 2005 Kashmir earthquake

NASA Astrophysics Data System (ADS)

Hussain, Matloob; Eshagh, Mehdi; Ahmad, Zulfiqar; Sadiq, M.; Fatolazadeh, Farzam

2016-09-01

The earth's gravity changes are attributed to the redistribution of masses within and/or on the surface of the earth, which are due to the frictional sliding, tensile cracking and/or cataclastic flow of rocks along the faults and detectable by earthquake events. Inversely, the gravity changes are useful to describe the earthquake seismicity over the active orogenic belts. The time variable gravimetric data are hardly available to the public domain. However, Gravity Recovery and Climatic Experiment (GRACE) is the only satellite mission dedicated to model the variation of the gravity field and an available source to the science community. Here, we have tried to envisage gravity changes in terms of gravity anomaly (Δg), geoid (N) and the gravity gradients over the Indo-Pak plate with emphasis upon Kashmir earthquake of October 2005. For this purpose, we engaged the spherical harmonic coefficients of monthly gravity solutions from the GRACE satellite mission, which have good coverage over the entire globe with unprecedented accuracy. We have analysed numerically the solutions after removing the hydrological signals, during August to November 2005, in terms of corresponding monthly differentials of gravity anomaly, geoid and the gradients. The regional structures like Main Mantle Thrust (MMT), Main Karakoram Thrust (MKT), Herat and Chaman faults are in closed association with topography and with gravity parameters from the GRACE gravimetry and EGM2008 model. The monthly differentials of these quantities indicate the stress accumulation in the northeast direction in the study area. Our numerical results show that the horizontal gravity gradients seem to be in good agreement with tectonic boundaries and differentials of the gravitational elements are subtle to the redistribution of rock masses and topography caused by 2005 Kashmir earthquake. Moreover, the gradients are rather more helpful for extracting the coseismic gravity signatures caused by seismicity over the area. Higher positive values of gravity components having higher terrain elevations are more vulnerable to the seismicity and lower risk of diastrophism otherwise.

Two Phase Flow Modeling: Summary of Flow Regimes and Pressure Drop Correlations in Reduced and Partial Gravity

NASA Technical Reports Server (NTRS)

Balasubramaniam, R.; Rame, E.; Kizito, J.; Kassemi, M.

2006-01-01

The purpose of this report is to provide a summary of state-of-the-art predictions for two-phase flows relevant to Advanced Life Support. We strive to pick out the most used and accepted models for pressure drop and flow regime predictions. The main focus is to identify gaps in predictive capabilities in partial gravity for Lunar and Martian applications. Following a summary of flow regimes and pressure drop correlations for terrestrial and zero gravity, we analyze the fully developed annular gas-liquid flow in a straight cylindrical tube. This flow is amenable to analytical closed form solutions for the flow field and heat transfer. These solutions, valid for partial gravity as well, may be used as baselines and guides to compare experimental measurements. The flow regimes likely to be encountered in the water recovery equipment currently under consideration for space applications are provided in an appendix.

Solar system constraints on disformal gravity theories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ip, Hiu Yan; Schmidt, Fabian; Sakstein, Jeremy, E-mail: iphys@mpa-garching.mpg.de, E-mail: jeremy.sakstein@port.ac.uk, E-mail: fabians@mpa-garching.mpg.de

Disformal theories of gravity are scalar-tensor theories where the scalar couples derivatively to matter via the Jordan frame metric. These models have recently attracted interest in the cosmological context since they admit accelerating solutions. We derive the solution for a static isolated mass in generic disformal gravity theories and transform it into the parameterised post-Newtonian form. This allows us to investigate constraints placed on such theories by local tests of gravity. The tightest constraints come from preferred-frame effects due to the motion of the Solar System with respect to the evolving cosmological background field. The constraints we obtain improve uponmore » the previous solar system constraints by two orders of magnitude, and constrain the scale of the disformal coupling for generic models to ℳ ∼> 100 eV. These constraints render all disformal effects irrelevant for cosmology.« less

Evaluation of global satellite gravity models using terrestrial gravity observations over the Kingdom of Saudi Arabia A. Alothman and B. Elsaka

NASA Astrophysics Data System (ADS)

Alothman, Abdulaziz; Elsaka, Basem

The gravity field models from the GRACE and GOCE missions have increased the knowledge of the earth’s global gravity field. The latter GOCE mission has provided accuracies of about 1-2 cm and 1milli-Gal level in the global geoid and gravity anomaly, respectively. However, determining all wavelength ranges of the gravity field spectrum cannot be only achieved from satellite gravimetry but from the allowed terrestrial gravity data. In this contribution, we use a gravity network of 42 first-order absolute gravity stations, observed by LaCosta Romberg gravimeter during the period 1967-1969 by Ministry of Petroleum and Mineral Resources, to validate the GOCE gravity models in order to gain more detailed regional gravity information. The network stations are randomly distributed all over the country with a spacing of about 200 km apart. The results show that the geoid height and gravity anomaly determined from terrestrial gravity data agree with the GOCE based models and give additional information to the satellite gravity solutions.

Chern-Simons Modified Gravity

NASA Astrophysics Data System (ADS)

Efstratiou, P.

2013-09-01

This presentation will be based on my, undergraduate, thesis at Aristotle University of Thessoliniki with the same subject, supervised by Professor Demetrios Papadopoulos. I will first present the general mathematical formulation of the Chern-Simons (CS) modified gravity, which is split in a dynamical and a non-dynamical context, and the different physical theories which suggest this modification. Then proceed by examing the possibility that the CS theory shares solutions with General Relativity in both contexts. In the non-dynamical context I will present a new, undocumented solution as well as all the other possible solutions found to date. I will conclude by arguing that General Relativity and CS Theory share any solutions in the dynamical context.

Gravitational waves in ghost free bimetric gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohseni, Morteza, E-mail: m-mohseni@pnu.ac.ir

2012-11-01

We obtain a set of exact gravitational wave solutions for the ghost free bimetric theory of gravity. With a flat reference metric, the theory admits the vacuum Brinkmann plane wave solution for suitable choices of the coefficients of different terms in the interaction potential. An exact gravitational wave solution corresponding to a massive scalar mode is also admitted for arbitrary choice of the coefficients with the reference metric being proportional to the spacetime metric. The proportionality factor and the speed of the wave are calculated in terms of the parameters of the theory. We also show that a F(R) extensionmore » of the theory admits similar solutions but in general is plagued with ghost instabilities.« less

Exact solutions and phenomenological constraints from massive scalars in a gravity's rainbow spacetime

NASA Astrophysics Data System (ADS)

Bezerra, V. B.; Christiansen, H. R.; Cunha, M. S.; Muniz, C. R.

2017-07-01

We obtain the exact (confluent Heun) solutions to the massive scalar field in a gravity's rainbow Schwarzschild metric. With these solutions at hand, we study the Hawking radiation resulting from the tunneling rate through the event horizon. We show that the emission spectrum obeys nonextensive statistics and is halted when a certain mass remnant is reached. Next, we infer constraints on the rainbow parameters from recent LHC particle physics experiments and Hubble STIS astrophysics measurements. Finally, we study the low frequency limit in order to find the modified energy spectrum around the source.

A special class of solutions in F( R)-gravity

NASA Astrophysics Data System (ADS)

Calzà, Marco; Rinaldi, Massimiliano; Sebastiani, Lorenzo

2018-03-01

We consider a special class of vacuum F( R)-modified gravity models. The form of their Lagrangian is such that the field equations are trivially satisfied when the Ricci scalar is constant. There are many interesting F( R)-models for inflation and dark energy that fall in this class. However, little is known outside the domain of cosmology therefore we aim to explore the class of solutions that are static and spherically symmetric. After some general considerations, we investigate in more detail black hole solutions, traversable wormhole metrics and, finally, configurations that can match the anomalous rotation curves of galaxies.

Constant curvature black holes in Einstein AdS gravity: Euclidean action and thermodynamics

NASA Astrophysics Data System (ADS)

Guilleminot, Pablo; Olea, Rodrigo; Petrov, Alexander N.

2018-03-01

We compute the Euclidean action for constant curvature black holes (CCBHs), as an attempt to associate thermodynamic quantities to these solutions of Einstein anti-de Sitter (AdS) gravity. CCBHs are gravitational configurations obtained by identifications along isometries of a D -dimensional globally AdS space, such that the Riemann tensor remains constant. Here, these solutions are interpreted as extended objects, which contain a (D -2 )-dimensional de-Sitter brane as a subspace. Nevertheless, the computation of the free energy for these solutions shows that they do not obey standard thermodynamic relations.

Time-variable gravity fields and ocean mass change from 37 months of kinematic Swarm orbits

NASA Astrophysics Data System (ADS)

Lück, Christina; Kusche, Jürgen; Rietbroek, Roelof; Löcher, Anno

2018-03-01

Measuring the spatiotemporal variation of ocean mass allows for partitioning of volumetric sea level change, sampled by radar altimeters, into mass-driven and steric parts. The latter is related to ocean heat change and the current Earth's energy imbalance. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) mission has provided monthly snapshots of the Earth's time-variable gravity field, from which one can derive ocean mass variability. However, GRACE has reached the end of its lifetime with data degradation and several gaps occurred during the last years, and there will be a prolonged gap until the launch of the follow-on mission GRACE-FO. Therefore, efforts focus on generating a long and consistent ocean mass time series by analyzing kinematic orbits from other low-flying satellites, i.e. extending the GRACE time series. Here we utilize data from the European Space Agency's (ESA) Swarm Earth Explorer satellites to derive and investigate ocean mass variations. For this aim, we use the integral equation approach with short arcs (Mayer-Gürr, 2006) to compute more than 500 time-variable gravity fields with different parameterizations from kinematic orbits. We investigate the potential to bridge the gap between the GRACE and the GRACE-FO mission and to substitute missing monthly solutions with Swarm results of significantly lower resolution. Our monthly Swarm solutions have a root mean square error (RMSE) of 4.0 mm with respect to GRACE, whereas directly estimating constant, trend, annual, and semiannual (CTAS) signal terms leads to an RMSE of only 1.7 mm. Concerning monthly gaps, our CTAS Swarm solution appears better than interpolating existing GRACE data in 13.5 % of all cases, when artificially removing one solution. In the case of an 18-month artificial gap, 80.0 % of all CTAS Swarm solutions were found closer to the observed GRACE data compared to interpolated GRACE data. Furthermore, we show that precise modeling of non-gravitational forces acting on the Swarm satellites is the key for reaching these accuracies. Our results have implications for sea level budget studies, but they may also guide further research in gravity field analysis schemes, including satellites not dedicated to gravity field studies.

Radiating black hole solutions in Einstein-Gauss-Bonnet gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dominguez, Alfredo E.; Instituto Universitario Aeronautico, Avenida Fuerza Aerea km 6.5.; Gallo, Emanuel

2006-03-15

In this paper, we find some new exact solutions to the Einstein-Gauss-Bonnet equations. First, we prove a theorem which allows us to find a large family of solutions to the Einstein-Gauss-Bonnet gravity in n-dimensions. This family of solutions represents dynamic black holes and contains, as particular cases, not only the recently found Vaidya-Einstein-Gauss-Bonnet black hole, but also other physical solutions that we think are new, such as the Gauss-Bonnet versions of the Bonnor-Vaidya (de Sitter/anti-de Sitter) solution, a global monopole, and the Husain black holes. We also present a more general version of this theorem in which less restrictive conditionsmore » on the energy-momentum tensor are imposed. As an application of this theorem, we present the exact solution describing a black hole radiating a charged null fluid in a Born-Infeld nonlinear electrodynamics.« less

Quadratic curvature terms and deformed Schwarzschild-de Sitter black hole analogues in the laboratory

NASA Astrophysics Data System (ADS)

da Rocha, R.; Sobreiro, R. F.; Tomaz, A. A.

2017-12-01

Sound waves on a fluid stream, in a de Laval nozzle, are shown to correspond to quasinormal modes emitted by black holes that are physical solutions in a quadratic curvature gravity with cosmological constant. Sound waves patterns in transsonic regimes at a laboratory are employed here to provide experimental data regarding generalized theories of gravity, comprised by the exact de Sitter-like solution and a perturbative solution around the Schwarzschild-de Sitter standard solution as well. Using the classical tests of General Relativity to bound free parameters in these solutions, acoustic perturbations on fluid flows in nozzles are then regarded, to study quasinormal modes of these black holes solutions, providing deviations of the de Laval nozzle cross-sectional area, when compared to the Schwarzschild solution. The fluid sonic point in the nozzle, for sound waves in the fluid, is shown to implement the acoustic event horizon corresponding to quasinormal modes.

Some exact velocity profiles for granular flow in converging hoppers

NASA Astrophysics Data System (ADS)

Cox, Grant M.; Hill, James M.

2005-01-01

Gravity flow of granular materials through hoppers occurs in many industrial processes. For an ideal cohesionless granular material, which satisfies the Coulomb-Mohr yield condition, the number of known analytical solutions is limited. However, for the special case of the angle of internal friction δ equal to ninety degrees, there exist exact parametric solutions for the governing coupled ordinary differential equations for both two-dimensional wedges and three-dimensional cones, both of which involve two arbitrary constants of integration. These solutions are the only known analytical solutions of this generality. Here, we utilize the double-shearing theory of granular materials to determine the velocity field corresponding to these exact parametric solutions for the two problems of gravity flow through converging wedge and conical hoppers. An independent numerical solution for other angles of internal friction is shown to coincide with the analytical solution.

Can chaos be observed in quantum gravity?

NASA Astrophysics Data System (ADS)

Dittrich, Bianca; Höhn, Philipp A.; Koslowski, Tim A.; Nelson, Mike I.

2017-06-01

Full general relativity is almost certainly 'chaotic'. We argue that this entails a notion of non-integrability: a generic general relativistic model, at least when coupled to cosmologically interesting matter, likely possesses neither differentiable Dirac observables nor a reduced phase space. It follows that the standard notion of observable has to be extended to include non-differentiable or even discontinuous generalized observables. These cannot carry Poisson-algebraic structures and do not admit a standard quantization; one thus faces a quantum representation problem of gravitational observables. This has deep consequences for a quantum theory of gravity, which we investigate in a simple model for a system with Hamiltonian constraint that fails to be completely integrable. We show that basing the quantization on standard topology precludes a semiclassical limit and can even prohibit any solutions to the quantum constraints. Our proposed solution to this problem is to refine topology such that a complete set of Dirac observables becomes continuous. In the toy model, it turns out that a refinement to a polymer-type topology, as e.g. used in loop gravity, is sufficient. Basing quantization of the toy model on this finer topology, we find a complete set of quantum Dirac observables and a suitable semiclassical limit. This strategy is applicable to realistic candidate theories of quantum gravity and thereby suggests a solution to a long-standing problem which implies ramifications for the very concept of quantization. Our work reveals a qualitatively novel facet of chaos in physics and opens up a new avenue of research on chaos in gravity which hints at deep insights into the structure of quantum gravity.

Study of the convective fluid flows with evaporation on the basis of the exact solution in a three-dimensional infinite channel

NASA Astrophysics Data System (ADS)

Bekezhanova, V. B.; Goncharova, O. N.

2017-09-01

The solution of special type of the Boussinesq approximation of the Navier - Stokes equations is used to simulate the two-layer evaporative fluid flows. This solution is the 3D generalization of the Ostroumov - Birikh solution of the equations of free convection. Modeling of the 3D fluid flows is performed in an infinite channel of the rectangular cross section without assumption of the axis-symmetrical character of the flows. Influence of gravity and evaporation on the dynamic and thermal phenomena in the system is studied. The fluid flow patterns are determined by various thermal, mechanical and structural effects. Numerical investigations are performed for the liquid - gas system like ethanol - nitrogen and HFE-7100 - nitrogen under conditions of normal and low gravity. The solution allows one to describe a formation of the thermocapillary rolls and multi-vortex structures in the system. Alteration of topology and character of the flows takes place with change of the intensity of the applied thermal load, thermophysical properties of working media and gravity action. Flows with translational, translational-rotational or partially reverse motion can be formed in the system.

Spherically symmetric conformal gravity and ''gravitational bubbles''

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berezin, V.A.; Dokuchaev, V.I.; Eroshenko, Yu.N., E-mail: berezin@inr.ac.ru, E-mail: dokuchaev@inr.ac.ru, E-mail: eroshenko@inr.ac.ru

2016-01-01

The general structure of the spherically symmetric solutions in the Weyl conformal gravity is described. The corresponding Bach equations are derived for the special type of metrics, which can be considered as the representative of the general class. The complete set of the pure vacuum solutions is found. It consists of two classes. The first one contains the solutions with constant two-dimensional curvature scalar of our specific metrics, and the representatives are the famous Robertson-Walker metrics. One of them we called the ''gravitational bubbles'', which is compact and with zero Weyl tensor. Thus, we obtained the pure vacuum curved space-timesmore » (without any material sources, including the cosmological constant) what is absolutely impossible in General Relativity. Such a phenomenon makes it easier to create the universe from ''nothing''. The second class consists of the solutions with varying curvature scalar. We found its representative as the one-parameter family. It appears that it can be conformally covered by the thee-parameter Mannheim-Kazanas solution. We also investigated the general structure of the energy-momentum tensor in the spherical conformal gravity and constructed the vectorial equation that reveals clearly some features of non-vacuum solutions. Two of them are explicitly written, namely, the metrics à la Vaidya, and the electrovacuum space-time metrics.« less

Application of the gravity search algorithm to multi-reservoir operation optimization

NASA Astrophysics Data System (ADS)

Bozorg-Haddad, Omid; Janbaz, Mahdieh; Loáiciga, Hugo A.

2016-12-01

Complexities in river discharge, variable rainfall regime, and drought severity merit the use of advanced optimization tools in multi-reservoir operation. The gravity search algorithm (GSA) is an evolutionary optimization algorithm based on the law of gravity and mass interactions. This paper explores the GSA's efficacy for solving benchmark functions, single reservoir, and four-reservoir operation optimization problems. The GSA's solutions are compared with those of the well-known genetic algorithm (GA) in three optimization problems. The results show that the GSA's results are closer to the optimal solutions than the GA's results in minimizing the benchmark functions. The average values of the objective function equal 1.218 and 1.746 with the GSA and GA, respectively, in solving the single-reservoir hydropower operation problem. The global solution equals 1.213 for this same problem. The GSA converged to 99.97% of the global solution in its average-performing history, while the GA converged to 97% of the global solution of the four-reservoir problem. Requiring fewer parameters for algorithmic implementation and reaching the optimal solution in fewer number of functional evaluations are additional advantages of the GSA over the GA. The results of the three optimization problems demonstrate a superior performance of the GSA for optimizing general mathematical problems and the operation of reservoir systems.

The effect of anti-gravity treadmill training for prosthetic rehabilitation of a case with below-knee amputation.

PubMed

Mikami, Yukio; Fukuhara, Kouki; Kawae, Toshihiro; Kimura, Hiroaki; Ochi, Mitsuo

2015-12-01

The aim of this case study was to verify the efficacy and safety of anti-gravity treadmill training for prosthetic rehabilitation following below-knee amputation. The patient underwent left below-knee amputation as a result of diabetic foot gangrene. Since his physical strength and vitality had declined during the perioperative period, anti-gravity treadmill training was introduced for his outpatient prosthetic rehabilitation. Stable prosthetic gait exercise could be carried out under guidance on the anti-gravity treadmill, quickly resulting in improved gait. Furthermore, the patient's self-efficacy and exercise tolerance were elevated after the period of anti-gravity treadmill training. At the final evaluation following 6 weeks of rehabilitation with the anti-gravity treadmill, he had acquired prosthetic gait with the assistance of a T-cane. The anti-gravity treadmill was found to be a useful instrument for prosthetic rehabilitation following below-knee amputation. Anti-gravity treadmill training has the potential to support the prosthetic rehabilitation of below-knee amputees, especially for patients whose physical strength and vitality are decreased. © The International Society for Prosthetics and Orthotics 2014.

Exploring Lovelock theory moduli space for Schrödinger solutions

NASA Astrophysics Data System (ADS)

Jatkar, Dileep P.; Kundu, Nilay

2016-09-01

We look for Schrödinger solutions in Lovelock gravity in D > 4. We span the entire parameter space and determine parametric relations under which the Schrödinger solution exists. We find that in arbitrary dimensions pure Lovelock theories have Schrödinger solutions of arbitrary radius, on a co-dimension one locus in the Lovelock parameter space. This co-dimension one locus contains the subspace over which the Lovelock gravity can be written in the Chern-Simons form. Schrödinger solutions do not exist outside this locus and on this locus they exist for arbitrary dynamical exponent z. This freedom in z is due to the degeneracy in the configuration space. We show that this degeneracy survives certain deformation away from the Lovelock moduli space.

The effect of the external medium on the gravitropic curvature of rice (Oryza sativa, Poaceae) roots

NASA Technical Reports Server (NTRS)

Staves, M. P.; Wayne, R.; Leopold, A. C.

1997-01-01

The roots of rice seedlings, growing in artificial pond water, exhibit robust gravitropic curvature when placed perpendicular to the vector of gravity. To determine whether the statolith theory (in which intracellular sedimenting particles are responsible for gravity sensing) or the gravitational pressure theory (in which the entire protoplast acts as the gravity sensor) best accounts for gravity sensing in rice roots, we changed the physical properties of the external medium with impermeant solutes and examined the effect on gravitropism. As the density of the external medium is increased, the rate of gravitropic curvature decreases. The decrease in the rate of gravicurvature cannot be attributed to an inhibition of growth, since rice roots grown in 100 Osm/m3 (0.248 MPa) solutions of different densities all support the same root growth rate but inhibit gravicurvature increasingly with increasing density. By contrast, the sedimentation rate of amyloplasts in the columella cells is unaffected by the external density. These results are consistent with the gravitational pressure theory of gravity sensing, but cannot be explained by the statolith theory.

Phase-field modelling of β(Ti) solidification in Ti-45at.%Al: columnar dendrite growth at various gravity levels

NASA Astrophysics Data System (ADS)

Viardin, A.; Berger, R.; Sturz, L.; Apel, M.; Hecht, U.

2016-03-01

The effect of solutal convection on the solidification of γ titanium aluminides, specifically on β(Ti) dendrite growth, is not well known. With the aim of supporting directional solidification experiments under hyper-gravity using a large diameter centrifuge, 2D-phase field simulations of β(Ti) dendrite growth have been performed for the binary alloy Ti-45at.%Al and various gravity scenarios. Both, the direction and magnitude of the gravity vector were varied systematically in order to reveal the subtle interplay between the convective flow pattern and mushy zone characteristics. In this presentation, gravity effects are discussed for early dendrite growth. For selected cases the evolution on longer timescales is also analyse of and oscillatory modes leading to dynamically stable steady state growth are outlined. In a dedicated simulation series forced flow is superimposed, as to mimic thermally driven fluid flow expected to establish on the macroscopic scale (sample size) in the centrifugal experiments. Above a certain threshold this flow turns dominant and precludes solutally driven convective effects.

A Rationale for System-Dependent Advantages and Disadvantages of Solution Crystal Growth at Low Gravity

NASA Technical Reports Server (NTRS)

Rosenberger, Franz; Vekilov, Peter G.; Lin, Hong; Alexander, J. Iwan D.

1997-01-01

Protein crystallization experiments at reduced gravity have yielded crystals that, depending on the specific material, are either superior or inferior in their structural perfection compared to counterparts grown at normal gravity. A reduction of the crystals' quality due to their growth at low gravity cannot be understood from existing models. Our experimental investigations of the ground-based crystallization of the protein lysozyme have revealed pronounced unsteady growth layer dynamics and associated defect formation under steady external conditions. Through scaling analysis and numerical simulations we show that the observed fluctuations originate from the coupling of bulk transport with non-linear interface kinetics under mixed kinetics-transport control of the growth rate. The amplitude of the fluctuations is smallest when either transport or interfacial kinetics dominate the control of the crystallization process. Thus, depending on the specific system, crystal quality may be improved by either enhancing or suppressing the transport in the solution. These considerations provide, for the first time, a material-dependent rationale for the advantages, as well as the disadvantages, of reduced gravity for (protein) crystallization.

Gödel metrics with chronology protection in Horndeski gravities

NASA Astrophysics Data System (ADS)

Geng, Wei-Jian; Li, Shou-Long; Lü, H.; Wei, Hao

2018-05-01

Gödel universe, one of the most interesting exact solutions predicted by General Relativity, describes a homogeneous rotating universe containing naked closed time-like curves (CTCs). It was shown that such CTCs are the consequence of the null energy condition in General Relativity. In this paper, we show that the Gödel-type metrics with chronology protection can emerge in Einstein-Horndeski gravity. We construct such exact solutions also in Einstein-Horndeski-Maxwell and Einstein-Horndeski-Proca theories.

Black holes in loop quantum gravity: the complete space-time.

PubMed

Gambini, Rodolfo; Pullin, Jorge

2008-10-17

We consider the quantization of the complete extension of the Schwarzschild space-time using spherically symmetric loop quantum gravity. We find an exact solution corresponding to the semiclassical theory. The singularity is eliminated but the space-time still contains a horizon. Although the solution is known partially numerically and therefore a proper global analysis is not possible, a global structure akin to a singularity-free Reissner-Nordström space-time including a Cauchy horizon is suggested.

Inverse scattering method and soliton double solution family for the general symplectic gravity model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao Yajun

A previously established Hauser-Ernst-type extended double-complex linear system is slightly modified and used to develop an inverse scattering method for the stationary axisymmetric general symplectic gravity model. The reduction procedures in this inverse scattering method are found to be fairly simple, which makes the inverse scattering method applied fine and effective. As an application, a concrete family of soliton double solutions for the considered theory is obtained.

Horndeski extension of the minimal theory of quasidilaton massive gravity

NASA Astrophysics Data System (ADS)

De Felice, Antonio; Mukohyama, Shinji; Oliosi, Michele

2017-11-01

The minimal theory of quasidilaton massive gravity allows for a stable self-accelerating de Sitter solution in a wide range of parameters. On the other hand, in order for the theory to be compatible with local gravity tests, the fifth force due to the quasidilaton scalar needs to be screened at local scales. The present paper thus extends the theory by inclusion of a cubic Horndeski term in a way that (i) respects the quasidilaton global symmetry, that (ii) maintains the physical degrees of freedom in the theory being 3, that (iii) can accommodate the Vainshtein screening mechanism, and that (iv) still allows for a stable self-accelerating de Sitter solution. After adding the Horndeski term (and a k -essence type nonlinear kinetic term as well) to the precursor action, we switch to the Hamiltonian language and find a complete set of independent constraints. We then construct the minimal theory with 3 physical degrees of freedom by carefully adding a pair of constraints to the total Hamiltonian of the precursor theory. Switching back to the Lagrangian language, we study cosmological solutions and their stability in the minimal theory. In particular, we show that a self-accelerating de Sitter solution is stable for a wide range of parameters. Furthermore, as in the minimal theory of massive gravity, the propagation speed of the massive gravitational waves in the high momentum limit precisely agrees with the speed of light.

Holographic self-tuning of the cosmological constant

NASA Astrophysics Data System (ADS)

Charmousis, Christos; Kiritsis, Elias; Nitti, Francesco

2017-09-01

We propose a brane-world setup based on gauge/gravity duality in which the four-dimensional cosmological constant is set to zero by a dynamical self-adjustment mechanism. The bulk contains Einstein gravity and a scalar field. We study holographic RG flow solutions, with the standard model brane separating an infinite volume UV region and an IR region of finite volume. For generic values of the brane vacuum energy, regular solutions exist such that the four-dimensional brane is flat. Its position in the bulk is determined dynamically by the junction conditions. Analysis of linear fluctuations shows that a regime of 4-dimensional gravity is possible at large distances, due to the presence of an induced gravity term. The graviton acquires an effective mass, and a five-dimensional regime may exist at large and/or small scales. We show that, for a broad choice of potentials, flat-brane solutions are manifestly stable and free of ghosts. We compute the scalar contribution to the force between brane-localized sources and show that, in certain models, the vDVZ discontinuity is absent and the effective interaction at short distances is mediated by two transverse graviton helicities.

Effect of the improved accelerometer calibration method on AIUB's GRACE monthly gravity field solution

NASA Astrophysics Data System (ADS)

Jean, Yoomin; Meyer, Ulrich; Arnold, Daniel; Bentel, Katrin; Jäggi, Adrian

2017-04-01

The monthly global gravity field solutions derived using the measurements from the GRACE (Gravity Recovery and Climate Experiment) satellites have been continuously improved by the processing centers. One of the improvements in the processing method is a more detailed calibration of the on-board accelerometers in the GRACE satellites. The accelerometer data calibration is usually restricted to the scale factors and biases. It has been assumed that the three different axes are perfectly orthogonal in the GRACE science reference frame. Recently, it was shown by Klinger and Mayer-Gürr (2016) that a fully-populated scale matrix considering the non-orthogonality of the axes and the misalignment of the GRACE science reference frame and the GRACE accelerometer frame improves the quality of the C20 coefficient in the GRACE monthly gravity field solutions. We investigate the effect of the more detailed calibration of the GRACE accelerometer data on the C20 coefficient in the case of the AIUB (Astronomical Institute of the University of Bern) processing method using the Celestial Mechanics Approach. We also investigate the effect of the new calibration parameters on the stochastic parameters in the Celestial Mechanics Approach.

Bouncing cosmological solutions from f(R,T) gravity

NASA Astrophysics Data System (ADS)

Shabani, Hamid; Ziaie, Amir Hadi

2018-05-01

In this work we study classical bouncing solutions in the context of f(R,T)=R+h(T) gravity in a flat FLRW background using a perfect fluid as the only matter content. Our investigation is based on introducing an effective fluid through defining effective energy density and pressure; we call this reformulation as the " effective picture". These definitions have been already introduced to study the energy conditions in f(R,T) gravity. We examine various models to which different effective equations of state, corresponding to different h(T) functions, can be attributed. It is also discussed that one can link between an assumed f(R,T) model in the effective picture and the theories with generalized equation of state ( EoS). We obtain cosmological scenarios exhibiting a nonsingular bounce before and after which the Universe lives within a de-Sitter phase. We then proceed to find general solutions for matter bounce and investigate their properties. We show that the properties of bouncing solution in the effective picture of f(R,T) gravity are as follows: for a specific form of the f(R,T) function, these solutions are without any future singularities. Moreover, stability analysis of the nonsingular solutions through matter density perturbations revealed that except two of the models, the parameters of scalar-type perturbations for the other ones have a slight transient fluctuation around the bounce point and damp to zero or a finite value at late times. Hence these bouncing solutions are stable against scalar-type perturbations. It is possible that all energy conditions be respected by the real perfect fluid, however, the null and the strong energy conditions can be violated by the effective fluid near the bounce event. These solutions always correspond to a maximum in the real matter energy density and a vanishing minimum in the effective density. The effective pressure varies between negative values and may show either a minimum or a maximum.

Europe's Preparation For GOCE Gravity Field Recovery

NASA Astrophysics Data System (ADS)

Suenkel, H.; Suenkel, H.

2001-12-01

The European Space Agency ESA is preparing for its first dedicated gravity field mission GOCE (Gravity Field and Steady-state Ocean Circulation Explorer) with a proposed launch in fall 2005. The mission's goal is the mapping of the Earth's static gravity field with very high resolution and utmost accuracy on a global scale. GOCE is a drag-free mission, flown in a circular and sun-synchronous orbit at an altitude between 240 and 250 km. Each of the two operational phases will last for 6 months. GOCE is based on a sensor fusion concept combining high-low satellite-to-satellite tracking (SST) and satellite gravity gradiometry (SGG). The transformation of the GOCE sensor data into a scientific product of utmost quality and reliability requires a well-coordinated effort of experts in satellite geodesy, applied mathematics and computer science. Several research groups in Europe do have this expertise and decided to form the "European GOCE Gravity Consortium (EGG-C)". The EGG-C activities are subdivided into tasks such as standard and product definition, data base and data dissemination, precise orbit determination, global gravity field model solutions and regional solutions, solution validation, communication and documentation, and the interfacing to level 3 product scientific users. The central issue of GOCE data processing is, of course, the determination of the global gravity field model using three independent mathematical-numerical techniques which had been designed and pre-developed in the course of several scientific preparatory studies of ESA: 1. The direct solution which is a least squares adjustment technique based on a pre-conditioned conjugated gradient method (PCGM). The method is capable of efficiently transforming the calibrated and validated SST and SGG observations directly or via lumped coefficients into harmonic coefficients of the gravitational potential. 2. The time-wise approach considers both SST and SGG data as a time series. For an idealized repeat mission such a time series can be very efficiently transformed into lumped coefficients using fast Fourier techniques. For a realistic mission scenario this transformation has to be extended by an iteration process. 3. The space-wise approach which, after having transformed the original observations onto a spatial geographical grid, transforms the pseudo-observations into harmonic coefficients using a fast collocation technique. A successful mission presupposed, GOCE will finally deliver the Earth's gravity field with a resolution of about 70 km half wavelength and a global geoid with an accuracy of about 1 cm.

Extremal black holes in dynamical Chern-Simons gravity

NASA Astrophysics Data System (ADS)

McNees, Robert; Stein, Leo C.; Yunes, Nicolás

2016-12-01

Rapidly rotating black hole (BH) solutions in theories beyond general relativity (GR) play a key role in experimental gravity, as they allow us to compute observables in extreme spacetimes that deviate from the predictions of GR. Such solutions are often difficult to find in beyond-general-relativity theories due to the inclusion of additional fields that couple to the metric nonlinearly and non-minimally. In this paper, we consider rotating BH solutions in one such theory, dynamical Chern-Simons (dCS) gravity, where the Einstein-Hilbert action is modified by the introduction of a dynamical scalar field that couples to the metric through the Pontryagin density. We treat dCS gravity as an effective field theory and work in the decoupling limit, where corrections are treated as small perturbations from GR. We perturb about the maximally rotating Kerr solution, the so-called extremal limit, and develop mathematical insight into the analysis techniques needed to construct solutions for generic spin. First we find closed-form, analytic expressions for the extremal scalar field, and then determine the trace of the metric perturbation, giving both in terms of Legendre decompositions. Retaining only the first three and four modes in the Legendre representation of the scalar field and the trace, respectively, suffices to ensure a fidelity of over 99% relative to full numerical solutions. The leading-order mode in the Legendre expansion of the trace of the metric perturbation contains a logarithmic divergence at the extremal Kerr horizon, which is likely to be unimportant as it occurs inside the perturbed dCS horizon. The techniques employed here should enable the construction of analytic, closed-form expressions for the scalar field and metric perturbations on a background with arbitrary rotation.

Assessment of motion of a swing leg and gait rehabilitation with a gravity balancing exoskeleton.

PubMed

Agrawal, Sunil K; Banala, Sai K; Fattah, Abbas; Sangwan, Vivek; Krishnamoorthy, Vijaya; Scholz, John P; Hsu, Wei-Li

2007-09-01

The gravity balancing exoskeleton, designed at University of Delaware, Newark, consists of rigid links, joints and springs, which are adjustable to the geometry and inertia of the leg of a human subject wearing it. This passive exoskeleton does not use any motors but is designed to unload the human leg joints from the gravity load over its range-of-motion. The underlying principle of gravity balancing is to make the potential energy of the combined leg-machine system invariant with configuration of the leg. Additionally, parameters of the exoskeleton can be changed to achieve a prescribed level of gravity assistance, from 0% to 100%. The goal of the results reported in this paper is to provide preliminary quantitative assessment of the changes in kinematics and kinetics of the walking gait when a human subject wears such an exoskeleton. The data on kinematics and kinetics were collected on four healthy and three stroke patients who wore this exoskeleton. These data were computed from the joint encoders and interface torque sensors mounted on the exoskeleton. This exoskeleton was also recently used for a six-week training of a chronic stroke patient, where the gravity assistance was progressively reduced from 100% to 0%. The results show a significant improvement in gait of the stroke patient in terms of range-of-motion of the hip and knee, weight bearing on the hemiparetic leg, and speed of walking. Currently, training studies are underway to assess the long-term effects of such a device on gait rehabilitation of hemiparetic stroke patients.

The role of invariant manifolds in lowthrust trajectory design (part III)

NASA Technical Reports Server (NTRS)

Lo, Martin W.; Anderson, Rodney L.; Lam, Try; Whiffen, Greg

2006-01-01

This paper is the third in a series to explore the role of invariant manifolds in the design of low thrust trajectories. In previous papers, we analyzed an impulsive thrust resonant gravity assist flyby trajectory to capture into Europa orbit using the invariant manifolds of unstable resonant periodic orbits and libration orbits. The energy savings provided by the gravity assist may be interpreted dynamically as the result of a finite number of intersecting invariant manifolds. In this paper we demonstrate that the same dynamics is at work for low thrust trajectories with resonant flybys and low energy capture. However, in this case, the flybys and capture are effected by continuous families of intersecting invariant manifolds.

Gravity assisted recovery of liquid xenon at large mass flow rates

NASA Astrophysics Data System (ADS)

Virone, L.; Acounis, S.; Beaupère, N.; Beney, J.-L.; Bert, J.; Bouvier, S.; Briend, P.; Butterworth, J.; Carlier, T.; Chérel, M.; Crespi, P.; Cussonneau, J.-P.; Diglio, S.; Manzano, L. Gallego; Giovagnoli, D.; Gossiaux, P.-B.; Kraeber-Bodéré, F.; Ray, P. Le; Lefèvre, F.; Marty, P.; Masbou, J.; Morteau, E.; Picard, G.; Roy, D.; Staempflin, M.; Stutzmann, J.-S.; Visvikis, D.; Xing, Y.; Zhu, Y.; Thers, D.

2018-06-01

We report on a liquid xenon gravity assisted recovery method for nuclear medical imaging applications. The experimental setup consists of an elevated detector enclosed in a cryostat connected to a storage tank called ReStoX. Both elements are part of XEMIS2 (XEnon Medical Imaging System): an innovative medical imaging facility for pre-clinical research that uses pure liquid xenon as detection medium. Tests based on liquid xenon transfer from the detector to ReStoX have been successfully performed showing that an unprecedented mass flow rate close to 1 ton per hour can be reached. This promising achievement as well as future areas of improvement will be discussed in this paper.

Global Optimization of N-Maneuver, High-Thrust Trajectories Using Direct Multiple Shooting

NASA Technical Reports Server (NTRS)

Vavrina, Matthew A.; Englander, Jacob A.; Ellison, Donald H.

2016-01-01

The performance of impulsive, gravity-assist trajectories often improves with the inclusion of one or more maneuvers between flybys. However, grid-based scans over the entire design space can become computationally intractable for even one deep-space maneuver, and few global search routines are capable of an arbitrary number of maneuvers. To address this difficulty a trajectory transcription allowing for any number of maneuvers is developed within a multi-objective, global optimization framework for constrained, multiple gravity-assist trajectories. The formulation exploits a robust shooting scheme and analytic derivatives for computational efficiency. The approach is applied to several complex, interplanetary problems, achieving notable performance without a user-supplied initial guess.

Acausality of massive gravity.

PubMed

Deser, S; Waldron, A

2013-03-15

We show, by analyzing its characteristics, that the ghost-free, 5 degree of freedom, Wess-Zumino massive gravity model admits superluminal shock wave solutions and thus is acausal. Ironically, this pathology arises from the very constraint that removes the (sixth) Boulware-Deser ghost mode.

Instability-induced ordering, universal unfolding and the role of gravity in granular Couette flow

NASA Astrophysics Data System (ADS)

Alam, Meheboob; Arakeri, V. H.; Nott, P. R.; Goddard, J. D.; Herrmann, H. J.

2005-01-01

Linear stability theory and bifurcation analysis are used to investigate the role of gravity in shear-band formation in granular Couette flow, considering a kinetic-theory rheological model. We show that the only possible state, at low shear rates, corresponds to a "plug" near the bottom wall, in which the particles are densely packed and the shear rate is close to zero, and a uniformly sheared dilute region above it. The origin of such plugged states is shown to be tied to the spontaneous symmetry-breaking instabilities of the gravity-free uniform shear flow, leading to the formation of ordered bands of alternating dilute and dense regions in the transverse direction, via an infinite hierarchy of pitchfork bifurcations. Gravity plays the role of an "imperfection", thus destroying the "perfect" bifurcation structure of uniform shear. The present bifurcation problem admits universal unfolding of pitchfork bifurcations which subsequently leads to the formation of a sequence of a countably infinite number of "isolas", with the solution structures being a modulated version of their gravity-free counterpart. While the solution with a plug near the bottom wall looks remarkably similar to the shear-banding phenomenon in dense slow granular Couette flows, a "floating" plug near the top wall is also a solution of these equations at high shear rates. A two-dimensional linear stability analysis suggests that these floating plugged states are unstable to long-wave travelling disturbances.The unique solution having a bottom plug can also be unstable to long waves, but remains stable at sufficiently low shear rates. The implications and realizability of the present results are discussed in the light of shear-cell experiments under "microgravity" conditions.

Application of Newtonian physics to predict the speed of a gravity racer

NASA Astrophysics Data System (ADS)

Driscoll, H. F.; Bullas, A. M.; King, C. E.; Senior, T.; Haake, S. J.; Hart, J.

2016-07-01

Gravity racing can be studied using numerical solutions to the equations of motion derived from Newton’s second law. This allows students to explore the physics of gravity racing and to understand how design and course selection influences vehicle speed. Using Euler’s method, we have developed a spreadsheet application that can be used to predict the speed of a gravity powered vehicle. The application includes the effects of air and rolling resistance. Examples of the use of the application for designing a gravity racer are presented and discussed. Predicted speeds are compared to the results of an official world record attempt.

A model of the general ocean circulation determined from a joint solution for the Earth's gravity field

NASA Technical Reports Server (NTRS)

Nerem, R. S.; Tapley, B. D.; Shum, C. K.; Yuan, D. N.

1989-01-01

If the geoid and the satellite position are known accurately, satellite altimetry can be used to determine the geostrophic velocity of the surface ocean currents. The purpose of this investigation is to simultaneously estimate the sea surface topography, zeta, the model for the gravity field, and the satellite orbit. Satellite tracking data from fourteen satellites were used; along with Seasat and Geosat altimeter data as well as surface gravity data for the solution. The estimated model of zeta compares well at long wavelengths with the hydrographic model of zeta. Covariance studies show that the geoid is separable from zeta up to degree 9, at which point geoid error becomes comparable to the signal of zeta.

Stability of Einstein static universe in gravity theory with a non-minimal derivative coupling

NASA Astrophysics Data System (ADS)

Huang, Qihong; Wu, Puxun; Yu, Hongwei

2018-01-01

The emergent mechanism provides a possible way to resolve the big-bang singularity problem by assuming that our universe originates from the Einstein static (ES) state. Thus, the existence of a stable ES solution becomes a very crucial prerequisite for the emergent scenario. In this paper, we study the stability of an ES universe in gravity theory with a non-minimal coupling between the kinetic term of a scalar field and the Einstein tensor. We find that the ES solution is stable under both scalar and tensor perturbations when the model parameters satisfy certain conditions, which indicates that the big-bang singularity can be avoided successfully by the emergent mechanism in the non-minimally kinetic coupled gravity.

Nonsingular rainbow universes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Awad, Adel; Ali, Ahmed Farag; Majumder, Barun, E-mail: aawad@zewailcity.edu.eg, E-mail: ahmed.ali@fsc.bu.edu.eg, E-mail: barunbasanta@iitgn.ac.in

2013-10-01

In this work, we study FRW cosmologies in the context of gravity rainbow. We discuss the general conditions for having a nonsingular FRW cosmology in gravity rainbow. We propose that gravity rainbow functions can be fixed using two known modified dispersion relation (MDR), which have been proposed in literature. The first MDR was introduced by Amelino-Camelia, et el. in [9] and the second was introduced by Magueijo and Smolin in [24]. Studying these FRW-like cosmologies, after fixing the gravity rainbow functions, leads to nonsingular solutions which can be expressed in exact forms.

Improvement of the Earth's gravity field from terrestrial and satellite data

NASA Technical Reports Server (NTRS)

Rapp, Richard H.

1992-01-01

The determination of the Earth's gravitational potential can be done through the analysis of satellite perturbations, the analysis of surface gravity data, or both. The combination of the two data types yields a solution that combines the strength of each method: the longer wavelength strength in the satellite analysis with the better high frequency information from surface gravity data. Since 1972, Ohio State has carried out activities that have provided surface gravity data to a number of organizations who have developed combination potential coefficient models that describe the Earth's gravitational potential.

A hydroponic design for microgravity and gravity installations

NASA Technical Reports Server (NTRS)

Fielder, Judith; Leggett, Nickolaus

1990-01-01

A hydroponic system is presented that is designed for use in microgravity or gravity experiments. The system uses a sponge-like growing medium installed in tubular modules. The modules contain the plant roots and manage the flow of the nutrient solution. The physical design and materials considerations are discussed, as are modifications of the basic design for use in microgravity or gravity experiments. The major external environmental requirements are also presented.

Aqueous Solution Heat Pipe Transport: Qu-Tube vs. Capillary-Pumped Heat Pipe

DTIC Science & Technology

2013-07-01

independently of gravity , exhibit very high conductivity, work over large distances and temperature ranges, and operate at a lower pressure than...tubes” or “Qu-tubes.” These purportedly superior tubes were claimed to have such desirable qualities as entirely dry operation, gravity -independence... gravity -dependent. Our detailed and quantitative findings suggest that the devices we purchased are not revolutionary in performance, and may in fact

Revisiting the analogue of the Jebsen-Birkhoff theorem in Brans-Dicke gravity

NASA Astrophysics Data System (ADS)

Faraoni, Valerio; Hammad, Fayçal; Cardini, Adriana M.; Gobeil, Thomas

2018-04-01

We report the explicit form of the general static, spherically symmetric, and asymptotically flat solution of vacuum Brans-Dicke gravity in the Jordan frame, assuming that the Brans-Dicke scalar field has no singularities or zeros (except possibly for a central singularity). This general solution is conformal to the Fisher-Wyman geometry of Einstein theory and its nature depends on a scalar charge parameter. Apart from the Schwarzschild black hole, only wormhole throats and central naked singularities are possible.

Explicit solutions of a gravity-induced film flow along a convectively heated vertical wall.

PubMed

Raees, Ammarah; Xu, Hang

2013-01-01

The gravity-driven film flow has been analyzed along a vertical wall subjected to a convective boundary condition. The Boussinesq approximation is applied to simplify the buoyancy term, and similarity transformations are used on the mathematical model of the problem under consideration, to obtain a set of coupled ordinary differential equations. Then the reduced equations are solved explicitly by using homotopy analysis method (HAM). The resulting solutions are investigated for heat transfer effects on velocity and temperature profiles.

Gravity-driven pH adjustment for site-specific protein pKa measurement by solution-state NMR

NASA Astrophysics Data System (ADS)

Li, Wei

2017-12-01

To automate pH adjustment in site-specific protein pKa measurement by solution-state NMR, I present a funnel with two caps for the standard 5 mm NMR tube. The novelty of this simple-to-build and inexpensive apparatus is that it allows automatic gravity-driven pH adjustment within the magnet, and consequently results in a fully automated NMR-monitored pH titration without any hardware modification on the NMR spectrometer.

Addendum to ''Thin-shell wormholes supported by ordinary matter in Einstein-Gauss-Bonnet gravity''

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simeone, Claudio

2011-04-15

Thin-shell wormholes are constructed starting from the exotic branch of the Wiltshire spherically symmetric solution of Einstein-Gauss-Bonnet gravity. The energy-momentum tensor of the shell is studied, and it is shown that configurations supported by matter satisfying the energy conditions exist for certain values of the parameters. Differing from the previous result associated with the normal branch of the Wiltshire solution, this is achieved for small positive values of the Gauss-Bonnet parameter and for vanishing charge.

Stability of cylindrical thin shell wormholes supported by MGCG in f(R) gravity

NASA Astrophysics Data System (ADS)

Eid, A.

2018-02-01

In the framework of f(R) modified theory of gravity, the dynamical equations of motion of a cylindrical thin shell wormholes supported by a modified generalized Chaplygin gas are constructed, using the cut and paste scheme (Darmois Israel formalism). The mechanical stability analysis of a cylindrical thin shell wormhole is discussed using a linearized radial perturbation around static solutions at the wormhole throat. The presence of stable static solutions depends on the suitable values of some parameters of dynamical shell.

On the role of covariance information for GRACE K-band observations in the Celestial Mechanics Approach

NASA Astrophysics Data System (ADS)

Bentel, Katrin; Meyer, Ulrich; Arnold, Daniel; Jean, Yoomin; Jäggi, Adrian

2017-04-01

The Astronomical Institute at the University of Bern (AIUB) derives static and time-variable gravity fields by means of the Celestial Mechanics Approach (CMA) from GRACE (level 1B) data. This approach makes use of the close link between orbit and gravity field determination. GPS-derived kinematic GRACE orbit positions, inter-satellite K-band observations, which are the core observations of GRACE, and accelerometer data are combined to rigorously estimate orbit and spherical harmonic gravity field coefficients in one adjustment step. Pseudo-stochastic orbit parameters are set up to absorb unmodeled noise. The K-band range measurements in along-track direction lead to a much higher correlation of the observations in this direction compared to the other directions and thus, to north-south stripes in the unconstrained gravity field solutions, so-called correlated errors. By using a full covariance matrix for the K-band observations the correlation can be taken into account. One possibility is to derive correlation information from post-processing K-band residuals. This is then used in a second iteration step to derive an improved gravity field solution. We study the effects of pre-defined covariance matrices and residual-derived covariance matrices on the final gravity field product with the CMA.

Analytic solutions for single and multiple cylinders of gravitating polytropes in magnetostatic equilibrium

NASA Technical Reports Server (NTRS)

Lerche, I.; Low, B. C.

1980-01-01

Exact analytic solutions for the static equilibrium of a gravitating plasma polytrope in the presence of magnetic fields are presented. The means of generating various equilibrium configurations to illustrate directly the complex physical relationships between pressure, magnetic fields, and gravity in self-gravitating systems is demonstrated. One of the solutions is used to model interstellar clouds suspended by magnetic fields against the galactic gravity such as may be formed by the Parker (1966) instability. It is concluded that the pinching effect of closed loops of magnetic fields in the clouds may be a dominant agent in further collapsing the clouds following their formation.

Rapid Generation of Optimal Asteroid Powered Descent Trajectories Via Convex Optimization

NASA Technical Reports Server (NTRS)

Pinson, Robin; Lu, Ping

2015-01-01

This paper investigates a convex optimization based method that can rapidly generate the fuel optimal asteroid powered descent trajectory. The ultimate goal is to autonomously design the optimal powered descent trajectory on-board the spacecraft immediately prior to the descent burn. Compared to a planetary powered landing problem, the major difficulty is the complex gravity field near the surface of an asteroid that cannot be approximated by a constant gravity field. This paper uses relaxation techniques and a successive solution process that seeks the solution to the original nonlinear, nonconvex problem through the solutions to a sequence of convex optimal control problems.

Propulsion Technology Assessment: Science and Enabling Technologies to Explore the Interstellar Medium

NASA Technical Reports Server (NTRS)

Hopkins, Randall C.; Thomas, Herbert D.; Wiegmann, Bruce M.; Heaton, Andrew F.; Johnson, Les; Beers, Benjamin R.

2015-01-01

The Advanced Concepts Office at NASA’s George C. Marshall Space Flight Center conducted a study to assess what low-thrust advanced propulsion system candidates, existing and near term, could deliver a small, Voyager-like satellite to our solar system’s heliopause, approximately 100 AU from the sun, within 10 years. The advanced propulsion system trade study consisted of three candidates, including a Magnetically Shielded Miniature Hall thruster, a solar sail and an electric sail. A second analysis was conducted to determine which solid rocket motor kick stage(s) would be required to provide additional thrust at various points in the trajectory, assuming a characteristic energy capability provided by a Space Launch System Block 1B vehicle architecture carrying an 8.4 meter payload fairing. Two trajectory profiles were considered, including an escape trajectory using a Jupiter gravity assist and an escape trajectory first performing a Jupiter gravity assist followed by an Oberth maneuver around the sun and an optional Saturn gravity assist. Results indicated that if the Technology Readiness Level of an electric sail could be increased in time, this technology could not only enable a satellite to reach 100 AU in 10 years but it could potentially do so in even less time.

LETTER TO THE EDITOR: A theorem on topologically massive gravity

NASA Astrophysics Data System (ADS)

Aliev, A. N.; Nutku, Y.

1996-03-01

We show that for three dimensional spacetimes admitting a hypersurface orthogonal Killing vector field, Deser, Jackiw and Templeton's vacuum field equations of topologically massive gravity allow only the trivial flat spacetime solution. Thus spin is necessary to support topological mass.

Forced Gravity Waves and the Tropospheric Response to Convection

NASA Astrophysics Data System (ADS)

Halliday, O. J.; Griffiths, S. D.; Parker, D. J.; Stirling, A.

2017-12-01

It has been known for some time that gravity waves facilitate atmospheric adjustment to convective heating. Further, convectively forced gravity waves condition the neighboring atmosphere for the initiation and / or suppression of convection. Despite this, the radiation of gravity waves in macro-scale models (which are typically forced at the grid-scale, by existing parameterization schemes) is not well understood. We present here theoretical and numerical work directed toward improving our understanding of convectively forced gravity wave effects at the mesoscale. Using the linear hydrostatic equations of motion for an incompressible (but non-Boussinesq) fluid with vertically varying buoyancy frequency, we find a radiating solution to prescribed sensible heating. We then interrogate the spatial and temporal sensitivity of the vertical velocity and potential temperature response to different heating functions, considering the remote and near-field forced response both to steady and pulsed heating. We find that the meso-scale tropospheric response to convection is significantly dependent on the upward radiation characteristics of the gravity waves, which are in turn dependent upon the temporal and spatial structure of the source, and stratification of the domain. Moving from a trapped to upwardly-radiating solution there is a 50% reduction in tropospherically averaged vertical velocity, but significant perturbations persist for up to 4 hours in the far-field. We find the tropospheric adjustment to be sensitive to the horizontal length scale which characterizes the heating, observing a 20% reduction in vertical velocity when comparing the response from a 10 km to a 100 km heat source. We assess the implications for parameterization of convection in coarse-grained models in the light of these findings. We show that an idealized `full-physics' nonlinear simulation of deep convection in the UK Met Office Unified Model is qualitatively described by the linear solution: departures are quantified and explored.

Electromagnetic fields of slowly rotating magnetized compact stars in conformal gravity

NASA Astrophysics Data System (ADS)

Turimov, Bobur; Ahmedov, Bobomurat; Abdujabbarov, Ahmadjon; Bambi, Cosimo

2018-06-01

In this paper we investigate the exterior vacuum electromagnetic fields of slow-rotating magnetized compact stars in conformal gravity. Assuming the dipolar magnetic field configuration, we obtain an analytical solution of the Maxwell equations for the magnetic and the electric fields outside a slowly rotating magnetized star in conformal gravity. Furthermore, we study the dipolar electromagnetic radiation and energy losses from a rotating magnetized star in conformal gravity. In order to get constraints on the L parameter of conformal gravity, the theoretical results for the magnetic field of a magnetized star in conformal gravity are combined with the precise observational data of radio pulsar period slowdown, and it is found that the maximum value of the parameter of conformal gravity is less than L ≲9.5 ×105 cm (L /M ≲5 ).

Time varying G and \\varLambda cosmology in f(R,T) gravity theory

NASA Astrophysics Data System (ADS)

Tiwari, R. K.; Beesham, A.; Singh, Rameshwar; Tiwari, L. K.

2017-08-01

We have studied the time dependence of the gravitational constant G and cosmological constant Λ by taking into account an anisotropic and homogeneous Bianchi type-I space-time in the framework of the modified f(R,T) theory of gravity proposed by Harko et al. (Phys. Rev. D 84:024020, 2011). For a specific choice of f(R,T)=R+2f(T) where f(T)=-λ T, two solutions of the modified gravity field equations have been generated with the help of a variation law between the expansion anisotropy ({σ}/{θ}) and the scale factor (S), together with a general non-linear equation of state. The solution for m≠3 corresponds to singular model of the universe whereas the solution for m=3 represents a non-singular model. We infer that the models entail a constant value of the deceleration parameter. A careful analysis of all the physical parameters of the models has also been carried out.

On holographic Rényi entropy in some modified theories of gravity

NASA Astrophysics Data System (ADS)

Dey, Anshuman; Roy, Pratim; Sarkar, Tapobrata

2018-04-01

We perform a detailed analysis of holographic entanglement Rényi entropy in some modified theories of gravity with four dimensional conformal field theory duals. First, we construct perturbative black hole solutions in a recently proposed model of Einsteinian cubic gravity in five dimensions, and compute the Rényi entropy as well as the scaling dimension of the twist operators in the dual field theory. Consistency of these results are verified from the AdS/CFT correspondence, via a corresponding computation of the Weyl anomaly on the gravity side. Similar analyses are then carried out for three other examples of modified gravity in five dimensions that include a chemical potential, namely Born-Infeld gravity, charged quasi-topological gravity and a class of Weyl corrected gravity theories with a gauge field, with the last example being treated perturbatively. Some interesting bounds in the dual conformal field theory parameters in quasi-topological gravity are pointed out. We also provide arguments on the validity of our perturbative analysis, whenever applicable.

Gravity compensation in a Strapdown Inertial Navigation System to improve the attitude accuracy

NASA Astrophysics Data System (ADS)

Zhu, Jing; Wang, Jun; Wang, Xingshu; Yang, Shuai

2017-10-01

Attitude errors in a strapdown inertial navigation system due to gravity disturbances and system noises can be relatively large, although they are bound within the Schuler and the Earth rotation period. The principal objective of the investigation is to determine to what extent accurate gravity data can improve the attitude accuracy. The way the gravity disturbances affect the attitude were analyzed and compared with system noises by the analytic solution and simulation. The gravity disturbances affect the attitude accuracy by introducing the initial attitude error and the equivalent accelerometer bias. With the development of the high precision inertial devices and the application of the rotation modulation technology, the gravity disturbance cannot be neglected anymore. The gravity compensation was performed using the EGM2008 and simulations with and without accurate gravity compensation under varying navigation conditions were carried out. The results show that the gravity compensation improves the horizontal components of attitude accuracy evidently while the yaw angle is badly affected by the uncompensated gyro bias in vertical channel.

Structure formation in f(T) gravity and a solution for H0 tension

NASA Astrophysics Data System (ADS)

Nunes, Rafael C.

2018-05-01

We investigate the evolution of scalar perturbations in f(T) teleparallel gravity and its effects on the cosmic microwave background (CMB) anisotropy. The f(T) gravity generalizes the teleparallel gravity which is formulated on the Weitzenböck spacetime, characterized by the vanishing curvature tensor (absolute parallelism) and the non-vanishing torsion tensor. For the first time, we derive the observational constraints on the modified teleparallel gravity using the CMB temperature power spectrum from Planck's estimation, in addition to data from baryonic acoustic oscillations (BAO) and local Hubble constant measurements. We find that a small deviation of the f(T) gravity model from the ΛCDM cosmology is slightly favored. Besides that, the f(T) gravity model does not show tension on the Hubble constant that prevails in the ΛCDM cosmology. It is clear that f(T) gravity is also consistent with the CMB observations, and undoubtedly it can serve as a viable candidate amongst other modified gravity theories.

Human-Centered Design for the Personal Satellite Assistant

NASA Technical Reports Server (NTRS)

Bradshaw, Jeffrey M.; Sierhuis, Maarten; Gawdiak, Yuri; Thomas, Hans; Greaves, Mark; Clancey, William J.; Swanson, Keith (Technical Monitor)

2000-01-01

The Personal Satellite Assistant (PSA) is a softball-sized flying robot designed to operate autonomously onboard manned spacecraft in pressurized micro-gravity environments. We describe how the Brahms multi-agent modeling and simulation environment in conjunction with a KAoS agent teamwork approach can be used to support human-centered design for the PSA.

ARTEMIS: The First Mission to the Lunar Libration Orbits

NASA Technical Reports Server (NTRS)

Woodward, Mark; Folta, David; Woodfork, Dennis

2009-01-01

The ARTEMIS mission will be the first to navigate to and perform stationkeeping operations around the Earth-Moon L1 and L2 Lagrangian points. The NASA Goddard Space Flight Center (GSFC) has previous mission experience flying in the Sun-Earth L1 (SOHO, ACE, WIND, ISEE-3) and L2 regimes (WMAP) and have maintained these spacecraft in libration point orbits by performing regular orbit stationkeeping maneuvers. The ARTEMIS mission will build on these experiences, but stationkeeping in Earth-Moon libration orbits presents new challenges since the libration point orbit period is on the order of two weeks rather than six months. As a result, stationkeeping maneuvers to maintain the Lissajous orbit will need to be performed frequently, and the orbit determination solutions between maneuvers will need to be quite accurate. The ARTEMIS mission is a collaborative effort between NASA GSFC, the University of California at Berkeley (UCB), and the Jet Propulsion Laboratory (JPL). The ARTEMIS mission is part of the THEMIS extended mission. ARTEMIS comprises two of the five THEMIS spacecraft that will be maneuvered from near-Earth orbits into lunar libration orbits using a sequence of designed orbital maneuvers and Moon & Earth gravity assists. In July 2009, a series of orbit-raising maneuvers began the proper orbit phasing of the two spacecraft for the first lunar flybys. Over subsequent months, additional propulsive maneuvers and gravity assists will be performed to move each spacecraft though the Sun-Earth weak stability regions and eventually into Earth-Moon libration point orbits. We will present the overall orbit designs for the two ARTEMIS spacecraft and provide analysis results of the 3/4-body dynamics, and the sensitivities of the trajectory design to both · maneuver errors and orbit determination errors. We will present results from the. initial orbit-raising maneuvers.

The Coupling of Gravity to Spin and Electromagnetism

NASA Astrophysics Data System (ADS)

Finster, Felix; Smoller, Joel; Yau, Shing-Tung

The coupled Einstein-Dirac-Maxwell equations are considered for a static, spherically symmetric system of two fermions in a singlet spinor state. Stable soliton-like solutions are shown to exist, and we discuss the regularizing effect of gravity from a Feynman diagram point of view.

Zero-gravity aerosol behavior

NASA Technical Reports Server (NTRS)

Edwards, H. W.

1981-01-01

The feasibility and scientific benefits of a zero gravity aerosol study in an orbiting laboratory were examined. A macroscopic model was devised to deal with the simultaneous effects of diffusion and coagulation of particles in the confined aerosol. An analytical solution was found by treating the particle coagulation and diffusion constants as ensemble parameters and employing a transformation of variables. The solution was used to carry out simulated zero gravity aerosol decay experiments in a compact cylindrical chamber. The results demonstrate that the limitations of physical space and time imposed by the orbital situation are not prohibitive in terms of observing the history of an aerosol confined under zero gravity conditions. While the absence of convective effects would be a definite benefit for the experiment, the mathematical complexity of the problem is not greatly reduced when the gravitational term drops out of the equation. Since the model does not deal directly with the evolution of the particle size distribution, it may be desirable to develop more detailed models before undertaking an orbital experiment.

Synthesis of regional crust and upper-mantle structure from seismic and gravity data

NASA Technical Reports Server (NTRS)

Alexander, S. S.; Lavin, P. M.

1979-01-01

Available seismic and ground based gravity data are combined to infer the three dimensional crust and upper mantle structure in selected regions. This synthesis and interpretation proceeds from large-scale average models suitable for early comparison with high-altitude satellite potential field data to more detailed delineation of structural boundaries and other variations that may be significant in natural resource assessment. Seismic and ground based gravity data are the primary focal point, but other relevant information (e.g. magnetic field, heat flow, Landsat imagery, geodetic leveling, and natural resources maps) is used to constrain the structure inferred and to assist in defining structural domains and boundaries. The seismic data consists of regional refraction lines, limited reflection coverage, surface wave dispersion, teleseismic P and S wave delay times, anelastic absorption, and regional seismicity patterns. The gravity data base consists of available point gravity determinations for the areas considered.

Linearization instability for generic gravity in AdS spacetime

NASA Astrophysics Data System (ADS)

Altas, Emel; Tekin, Bayram

2018-01-01

In general relativity, perturbation theory about a background solution fails if the background spacetime has a Killing symmetry and a compact spacelike Cauchy surface. This failure, dubbed as linearization instability, shows itself as non-integrability of the perturbative infinitesimal deformation to a finite deformation of the background. Namely, the linearized field equations have spurious solutions which cannot be obtained from the linearization of exact solutions. In practice, one can show the failure of the linear perturbation theory by showing that a certain quadratic (integral) constraint on the linearized solutions is not satisfied. For non-compact Cauchy surfaces, the situation is different and for example, Minkowski space having a non-compact Cauchy surface, is linearization stable. Here we study, the linearization instability in generic metric theories of gravity where Einstein's theory is modified with additional curvature terms. We show that, unlike the case of general relativity, for modified theories even in the non-compact Cauchy surface cases, there are some theories which show linearization instability about their anti-de Sitter backgrounds. Recent D dimensional critical and three dimensional chiral gravity theories are two such examples. This observation sheds light on the paradoxical behavior of vanishing conserved charges (mass, angular momenta) for non-vacuum solutions, such as black holes, in these theories.

Robust Vision-Based Pose Estimation Algorithm for AN Uav with Known Gravity Vector

NASA Astrophysics Data System (ADS)

Kniaz, V. V.

2016-06-01

Accurate estimation of camera external orientation with respect to a known object is one of the central problems in photogrammetry and computer vision. In recent years this problem is gaining an increasing attention in the field of UAV autonomous flight. Such application requires a real-time performance and robustness of the external orientation estimation algorithm. The accuracy of the solution is strongly dependent on the number of reference points visible on the given image. The problem only has an analytical solution if 3 or more reference points are visible. However, in limited visibility conditions it is often needed to perform external orientation with only 2 visible reference points. In such case the solution could be found if the gravity vector direction in the camera coordinate system is known. A number of algorithms for external orientation estimation for the case of 2 known reference points and a gravity vector were developed to date. Most of these algorithms provide analytical solution in the form of polynomial equation that is subject to large errors in the case of complex reference points configurations. This paper is focused on the development of a new computationally effective and robust algorithm for external orientation based on positions of 2 known reference points and a gravity vector. The algorithm implementation for guidance of a Parrot AR.Drone 2.0 micro-UAV is discussed. The experimental evaluation of the algorithm proved its computational efficiency and robustness against errors in reference points positions and complex configurations.

Anamorphic quasiperiodic universes in modified and Einstein gravity with loop quantum gravity corrections

NASA Astrophysics Data System (ADS)

Amaral, Marcelo M.; Aschheim, Raymond; Bubuianu, Laurenţiu; Irwin, Klee; Vacaru, Sergiu I.; Woolridge, Daniel

2017-09-01

The goal of this work is to elaborate on new geometric methods of constructing exact and parametric quasiperiodic solutions for anamorphic cosmology models in modified gravity theories, MGTs, and general relativity, GR. There exist previously studied generic off-diagonal and diagonalizable cosmological metrics encoding gravitational and matter fields with quasicrystal like structures, QC, and holonomy corrections from loop quantum gravity, LQG. We apply the anholonomic frame deformation method, AFDM, in order to decouple the (modified) gravitational and matter field equations in general form. This allows us to find integral varieties of cosmological solutions determined by generating functions, effective sources, integration functions and constants. The coefficients of metrics and connections for such cosmological configurations depend, in general, on all spacetime coordinates and can be chosen to generate observable (quasi)-periodic/aperiodic/fractal/stochastic/(super) cluster/filament/polymer like (continuous, stochastic, fractal and/or discrete structures) in MGTs and/or GR. In this work, we study new classes of solutions for anamorphic cosmology with LQG holonomy corrections. Such solutions are characterized by nonlinear symmetries of generating functions for generic off-diagonal cosmological metrics and generalized connections, with possible nonholonomic constraints to Levi-Civita configurations and diagonalizable metrics depending only on a time like coordinate. We argue that anamorphic quasiperiodic cosmological models integrate the concept of quantum discrete spacetime, with certain gravitational QC-like vacuum and nonvacuum structures. And, that of a contracting universe that homogenizes, isotropizes and flattens without introducing initial conditions or multiverse problems.

Magnetized string cosmological models of accelerated expansion of the Universe in f(R,T) theory of gravity

NASA Astrophysics Data System (ADS)

Pradhan, Anirudh; Jaiswal, Rekha

A class of spatially homogeneous and anisotropic Bianchi-V massive string models have been studied in the modified f(R,T)-theory of gravity proposed by Harko et al. [Phys. Rev. D 84:024020, 2011] in the presence of magnetic field. For a specific choice of f(R,T)=f1(R) + f2(T), where f1(R) = ν1R and f2(T) = ν2T; ν1, ν2 being arbitrary parameters, solutions of modified gravity field equations have been generated. To find the deterministic solution of the field equations, we have considered the time varying deceleration parameter which is consistent with observational data of standard cosmology (SNIa, BAO and CMB). As a result to study the transit behavior of Universe, we consider a law of variation for the specifically chosen scale factor, which yields a time-dependent deceleration parameter comprising a class of models that depicts a transition of the Universe from the early decelerated phase to the recent accelerating phase. In this context, for the model of the Universe, the field equations are solved and corresponding cosmological aspects have been discussed. The Energy conditions in this modified gravity theory are also studied. Stability analysis of the solutions through cosmological perturbation is performed and it is concluded that the expanding solution is stable against the perturbation with respect to anisotropic spatial direction. Some physical and geometric properties of the models are also discussed.

Multiexponential models of (1+1)-dimensional dilaton gravity and Toda-Liouville integrable models

NASA Astrophysics Data System (ADS)

de Alfaro, V.; Filippov, A. T.

2010-01-01

We study general properties of a class of two-dimensional dilaton gravity (DG) theories with potentials containing several exponential terms. We isolate and thoroughly study a subclass of such theories in which the equations of motion reduce to Toda and Liouville equations. We show that the equation parameters must satisfy a certain constraint, which we find and solve for the most general multiexponential model. It follows from the constraint that integrable Toda equations in DG theories generally cannot appear without accompanying Liouville equations. The most difficult problem in the two-dimensional Toda-Liouville (TL) DG is to solve the energy and momentum constraints. We discuss this problem using the simplest examples and identify the main obstacles to solving it analytically. We then consider a subclass of integrable two-dimensional theories where scalar matter fields satisfy the Toda equations and the two-dimensional metric is trivial. We consider the simplest case in some detail. In this example, we show how to obtain the general solution. We also show how to simply derive wavelike solutions of general TL systems. In the DG theory, these solutions describe nonlinear waves coupled to gravity and also static states and cosmologies. For static states and cosmologies, we propose and study a more general one-dimensional TL model typically emerging in one-dimensional reductions of higher-dimensional gravity and supergravity theories. We especially attend to making the analytic structure of the solutions of the Toda equations as simple and transparent as possible.

Actions for particles and strings and Chern-Simons gravity

NASA Astrophysics Data System (ADS)

Jiusi, Lei; Nair, V. P.

2017-09-01

We consider actions for particles and strings, including twistorial descriptions on 4D Minkowski and AdS5 spacetimes from the point of view of coadjoint orbits for the isometry group. We also consider the collective coordinate dynamics of singular solutions in Chern-Simons (CS) theories and CS theories of gravity. This is a generalization of the work of Einstein, Infeld, and Hoffmann and also has potential points of contact with fluid-gravity correspondence.

Consequences of energy conservation violation: late time solutions of Λ (T) CDM subclass of f(R,T) gravity using dynamical system approach

NASA Astrophysics Data System (ADS)

Shabani, Hamid; Ziaie, Amir Hadi

2017-05-01

Very recently, Josset and Perez (Phys. Rev. Lett. 118:021102, 2017) have shown that a violation of the energy-momentum tensor ( EMT) could result in an accelerated expansion state via the appearance of an effective cosmological constant, in the context of unimodular gravity. Inspired by this outcome, in this paper we investigate cosmological consequences of a violation of the EMT conservation in a particular class of f(R,T) gravity when only the pressure-less fluid is present. In this respect, we focus on the late time solutions of models of the type f(R,T)=R+β Λ (-T). As the first task, we study the solutions when the conservation of EMT is respected, and then we proceed with those in which violation occurs. We have found, provided that the EMT conservation is violated, that there generally exist two accelerated expansion solutions of which the stability properties depend on the underlying model. More exactly, we obtain a dark energy solution for which the effective equation of state depends on the model parameters and a de Sitter solution. We present a method to parametrize the Λ (-T) function, which is useful in a dynamical system approach and has been employed in the model. Also, we discuss the cosmological solutions for models with Λ (-T)=8π G(-T)^{α } in the presence of ultra-relativistic matter.

Lunar gravity derived from long-period satellite motion, a proposed method

NASA Technical Reports Server (NTRS)

Ferrari, A. J.

1971-01-01

A method was devised to determine the spherical harmonic coefficients of the lunar gravity field. The method consists of a two-step data reduction and estimation process. Pseudo-Doppler data were generated simulating two different lunar orbits. The analysis included the perturbing effects of the L1 lunar gravity field, the earth, the sun, and solar radiation pressure. Orbit determinations were performed on these data and long-period orbital elements were obtained. The Kepler element rates from these solutions were used to recover L1 lunar gravity coefficients. Overall results of the experiment show that lunar gravity coefficients can be accurately determined and that the method is dynamically consistent with long-period perturbation theory.

Nonlocal teleparallel cosmology.

PubMed

Bahamonde, Sebastian; Capozziello, Salvatore; Faizal, Mir; Nunes, Rafael C

2017-01-01

Even though it is not possible to differentiate general relativity from teleparallel gravity using classical experiments, it could be possible to discriminate between them by quantum gravitational effects. These effects have motivated the introduction of nonlocal deformations of general relativity, and similar effects are also expected to occur in teleparallel gravity. Here, we study nonlocal deformations of teleparallel gravity along with its cosmological solutions. We observe that nonlocal teleparallel gravity (like nonlocal general relativity) is consistent with the present cosmological data obtained by SNe Ia + BAO + CC + [Formula: see text] observations. Along this track, future experiments probing nonlocal effects could be used to test whether general relativity or teleparallel gravity gives the most consistent picture of gravitational interaction.

Quasi-topological Ricci polynomial gravities

NASA Astrophysics Data System (ADS)

Li, Yue-Zhou; Liu, Hai-Shan; Lü, H.

2018-02-01

Quasi-topological terms in gravity can be viewed as those that give no contribution to the equations of motion for a special subclass of metric ansätze. They therefore play no rôle in constructing these solutions, but can affect the general perturbations. We consider Einstein gravity extended with Ricci tensor polynomial invariants, which admits Einstein metrics with appropriate effective cosmological constants as its vacuum solutions. We construct three types of quasi-topological gravities. The first type is for the most general static metrics with spherical, toroidal or hyperbolic isometries. The second type is for the special static metrics where g tt g rr is constant. The third type is the linearized quasitopological gravities on the Einstein metrics. We construct and classify results that are either dependent on or independent of dimensions, up to the tenth order. We then consider a subset of these three types and obtain Lovelock-like quasi-topological gravities, that are independent of the dimensions. The linearized gravities on Einstein metrics on all dimensions are simply Einstein and hence ghost free. The theories become quasi-topological on static metrics in one specific dimension, but non-trivial in others. We also focus on the quasi-topological Ricci cubic invariant in four dimensions as a specific example to study its effect on holography, including shear viscosity, thermoelectric DC conductivities and butterfly velocity. In particular, we find that the holographic diffusivity bounds can be violated by the quasi-topological terms, which can induce an extra massive mode that yields a butterfly velocity unbound above.

Dynamically controlled crystallization method and apparatus and crystals obtained thereby

NASA Technical Reports Server (NTRS)

Arnowitz, Leonard (Inventor); Steinberg, Emanuel (Inventor)

2003-01-01

A method and apparatus for dynamically controlling the crystallization of molecules including a crystallization chamber (14) or chambers for holding molecules in a precipitant solution, one or more precipitant solution reservoirs (16, 18), communication passages (17, 19) respectively coupling the crystallization chamber(s) with each of the precipitant solution reservoirs, and transfer mechanisms (20, 21, 22, 24, 26, 28) configured to respectively transfer precipitant solution between each of the precipitant solution reservoirs and the crystallization chamber(s). The transfer mechanisms are interlocked to maintain a constant volume of precipitant solution in the crystallization chamber(s). Precipitant solutions of different concentrations are transferred into and out of the crystallization chamber(s) to adjust the concentration of precipitant in the crystallization chamber(s) to achieve precise control of the crystallization process. The method and apparatus can be used effectively to grow crystals under reduced gravity conditions such as microgravity conditions of space, and under conditions of reduced or enhanced effective gravity as induced by a powerful magnetic field.

3D Gravity Inversion using Tikhonov Regularization

NASA Astrophysics Data System (ADS)

Toushmalani, Reza; Saibi, Hakim

2015-08-01

Subsalt exploration for oil and gas is attractive in regions where 3D seismic depth-migration to recover the geometry of a salt base is difficult. Additional information to reduce the ambiguity in seismic images would be beneficial. Gravity data often serve these purposes in the petroleum industry. In this paper, the authors present an algorithm for a gravity inversion based on Tikhonov regularization and an automatically regularized solution process. They examined the 3D Euler deconvolution to extract the best anomaly source depth as a priori information to invert the gravity data and provided a synthetic example. Finally, they applied the gravity inversion to recently obtained gravity data from the Bandar Charak (Hormozgan, Iran) to identify its subsurface density structure. Their model showed the 3D shape of salt dome in this region.

Effects of Humidity and Temperature on Orange Dye-Based Organic Field Effect Transistors Fabricated at Different Gravity

NASA Astrophysics Data System (ADS)

Fatima, N.; Ahmed, M. M.; Karimov, Kh. S.

2017-11-01

This study reports the fabrication of organic field effect transistors (OFETs) using 3-[ethyl[4-[(4-nitrophenyl)azo]phenyl]amino]propanenitrile, usually known as Orange-Dye 25 (OD) and its composite with sugar. The study investigated the heat- and humidity-dependent electrical characteristics of the fabricated devices. Fabrication was carried out from the aqueous solution of the materials using different gravity conditions, i.e., at positive (normal) gravity (+1 g) and at negative gravity (-1 g). A thin layer (10-15 μm) of OD or OD:sugar was deposited by drop-casting on pre-fabricated drain and source silver (Ag) electrodes having 30 μm separation and 2 mm length followed by aluminum (Al) thermal evaporation to achieve a Schottky barrier. Devices fabricated using OD at -1 g were more sensitive in capacitance-temperature and impedance-humidity relationships than those fabricated at +1 g. Moreover, OFETs fabricated at -1 g using OD:sugar offered capacitance-temperature sensitivity much higher than the devices fabricated at +1 g. It has been observed that, in the drop-casting method, the properties of OFETs are dependent upon gravity as well as the solution composition employed for channel definition.

Quintic quasi-topological gravity

NASA Astrophysics Data System (ADS)

Cisterna, Adolfo; Guajardo, Luis; Hassaïne, Mokhtar; Oliva, Julio

2017-04-01

We construct a quintic quasi-topological gravity in five dimensions, i.e. a theory with a Lagrangian containing {\\mathcal{R}}^5 terms and whose field equations are of second order on spherically (hyperbolic or planar) symmetric spacetimes. These theories have recently received attention since when formulated on asymptotically AdS spacetimes might provide for gravity duals of a broad class of CFTs. For simplicity we focus on five dimensions. We show that this theory fulfils a Birkhoff's Theorem as it is the case in Lovelock gravity and therefore, for generic values of the couplings, there is no s-wave propagating mode. We prove that the spherically symmetric solution is determined by a quintic algebraic polynomial equation which resembles Wheeler's polynomial of Lovelock gravity. For the black hole solutions we compute the temperature, mass and entropy and show that the first law of black holes thermodynamics is fulfilled. Besides of being of fourth order in general, we show that the field equations, when linearized around AdS are of second order, and therefore the theory does not propagate ghosts around this background. Besides the class of theories originally introduced in arXiv:1003.4773, the general geometric structure of these Lagrangians remains an open problem.

Tests and comparisons of gravity models.

NASA Technical Reports Server (NTRS)

Marsh, J. G.; Douglas, B. C.

1971-01-01

Optical observations of the GEOS satellites were used to obtain orbital solutions with different sets of geopotential coefficients. The solutions were compared before and after modification to high order terms (necessary because of resonance) and were then analyzed by comparing subsequent observations with predicted trajectories. The most important source of error in orbit determination and prediction for the GEOS satellites is the effect of resonance found in most published sets of geopotential coefficients. Modifications to the sets yield greatly improved orbits in most cases. The results of these comparisons suggest that with the best optical tracking systems and gravity models, satellite position error due to gravity model uncertainty can reach 50-100 m during a heavily observed 5-6 day orbital arc. If resonant coefficients are estimated, the uncertainty is reduced considerably.

The relativistic gravity train

NASA Astrophysics Data System (ADS)

Seel, Max

2018-05-01

The gravity train that takes 42.2 min from any point A to any other point B that is connected by a straight-line tunnel through Earth has captured the imagination more than most other applications in calculus or introductory physics courses. Brachystochron and, most recently, nonlinear density solutions have been discussed. Here relativistic corrections are presented. It is discussed how the corrections affect the time to fall through Earth, the Sun, a white dwarf, a neutron star, and—the ultimate limit—the difference in time measured by a moving, a stationary and the fiducial observer at infinity if the density of the sphere approaches the density of a black hole. The relativistic gravity train can serve as a problem with approximate and exact analytic solutions and as numerical exercise in any introductory course on relativity.

Nonlocal Galileons and self-acceleration

NASA Astrophysics Data System (ADS)

Gabadadze, Gregory; Yu, Siqing

2017-05-01

A certain class of nonlocal theories eliminates an arbitrary cosmological constant (CC) from a universe that can be perceived as our world. Dark energy then cannot be explained by a CC; it could however be due to massive gravity. We calculate the new corrections, which originate from the nonlocal terms that eliminate the CC, to the decoupling limit Lagrangian of massive gravity. The new nonlocal terms also have internal field space Galilean symmetry and are referred here as ;nonlocal Galileons.; We then study a self-accelerated solution and show that the new nonlocal terms change the perturbative stability analysis. In particular, small fluctuations are now stable and non-superluminal for some simple parameter choices, whereas for the same choices the pure massive gravity fluctuations are unstable. We also study stable spherically symmetric solutions on this background.

A Combined Gravity Compensation Method for INS Using the Simplified Gravity Model and Gravity Database.

PubMed

Zhou, Xiao; Yang, Gongliu; Wang, Jing; Wen, Zeyang

2018-05-14

In recent decades, gravity compensation has become an important way to reduce the position error of an inertial navigation system (INS), especially for a high-precision INS, because of the extensive application of high precision inertial sensors (accelerometers and gyros). This paper first deducts the INS's solution error considering gravity disturbance and simulates the results. Meanwhile, this paper proposes a combined gravity compensation method using a simplified gravity model and gravity database. This new combined method consists of two steps all together. Step 1 subtracts the normal gravity using a simplified gravity model. Step 2 first obtains the gravity disturbance on the trajectory of the carrier with the help of ELM training based on the measured gravity data (provided by Institute of Geodesy and Geophysics; Chinese Academy of sciences), and then compensates it into the error equations of the INS, considering the gravity disturbance, to further improve the navigation accuracy. The effectiveness and feasibility of this new gravity compensation method for the INS are verified through vehicle tests in two different regions; one is in flat terrain with mild gravity variation and the other is in complex terrain with fierce gravity variation. During 2 h vehicle tests, the positioning accuracy of two tests can improve by 20% and 38% respectively, after the gravity is compensated by the proposed method.

A Combined Gravity Compensation Method for INS Using the Simplified Gravity Model and Gravity Database

PubMed Central

Zhou, Xiao; Yang, Gongliu; Wang, Jing; Wen, Zeyang

2018-01-01

In recent decades, gravity compensation has become an important way to reduce the position error of an inertial navigation system (INS), especially for a high-precision INS, because of the extensive application of high precision inertial sensors (accelerometers and gyros). This paper first deducts the INS’s solution error considering gravity disturbance and simulates the results. Meanwhile, this paper proposes a combined gravity compensation method using a simplified gravity model and gravity database. This new combined method consists of two steps all together. Step 1 subtracts the normal gravity using a simplified gravity model. Step 2 first obtains the gravity disturbance on the trajectory of the carrier with the help of ELM training based on the measured gravity data (provided by Institute of Geodesy and Geophysics; Chinese Academy of sciences), and then compensates it into the error equations of the INS, considering the gravity disturbance, to further improve the navigation accuracy. The effectiveness and feasibility of this new gravity compensation method for the INS are verified through vehicle tests in two different regions; one is in flat terrain with mild gravity variation and the other is in complex terrain with fierce gravity variation. During 2 h vehicle tests, the positioning accuracy of two tests can improve by 20% and 38% respectively, after the gravity is compensated by the proposed method. PMID:29757983

Simulating nonlinear steady-state traveling waves on the falling liquid film entrained by a gas flow

NASA Astrophysics Data System (ADS)

Tsvelodub, O. Yu; Bocharov, A. A.

2017-09-01

The article is devoted to the simulation of nonlinear waves on a liquid film flowing under gravity in the known stress field at the interface. The paper studies nonlinear waves on a liquid film, flowing under the action of gravity in a known stress field at the interface. In the case of small Reynolds numbers the problem is reduced to the consideration of solutions of the nonlinear integral-differential equation for film thickness deviation from the undisturbed level. The periodic and soliton steady-state traveling solutions of this equation have been numerically found. The analysis of branching of new families of steady-state traveling solutions has been performed. In particular, it is shown that this model equation has solutions in the form of solitons-humps.

Rheology and physical-chemical characteristics of the solutions of the medicines

NASA Astrophysics Data System (ADS)

Urakov, A.; Urakova, N.

2015-04-01

In the laboratory studied the dynamics of rheology of water solutions with plasma- inflammatory and antiseptic funds when mixing them with blood, plasma and pus under the influence of the following physical and chemical factors of local interaction: gravity, specific gravity, temperature, relative viscosity, internal pressure, sparkling water, total concentration of the ingredients, surface activity, volume of acid and osmotic activity of medicines. Found that the rheology of biological liquids improve hyperthermic, highly alkaline and highly carbonated solution medicines. For the dilution of pus, dense festering mass of sulfur plugs and tear stones invited to apply heated to +39 - +42°C with aqueous solution of 0.5 - 3% hydrogen peroxide and 0.5 - 10% sodium bicarbonate saturated with carbon dioxide to excess pressure 0.2 ATM.

Nonminimal coupling for the gravitational and electromagnetic fields: Traversable electric wormholes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balakin, Alexander B.; Zayats, Alexei E.; Lemos, Jose P. S.

2010-04-15

We discuss new exact solutions of a three-parameter nonminimal Einstein-Maxwell model. The solutions describe static spherically symmetric objects with and without center, supported by an electric field nonminimally coupled to gravity. We focus on a unique one-parameter model, which admits an exact solution for a traversable electrically charged wormhole connecting two universes, one asymptotically flat the other asymptotically de Sitter ones. The relation between the asymptotic mass and charge of the wormhole and its throat radius is analyzed. The wormhole solution found is thus a nonminimal realization of Wheeler's idea about charge without charge and shows that, if the worldmore » is somehow nonminimal in the coupling of gravity to electromagnetism, then wormhole appearance, or perhaps construction, is possible.« less

Nonsingular universe in massive gravity's rainbow

NASA Astrophysics Data System (ADS)

Hendi, S. H.; Momennia, M.; Eslam Panah, B.; Panahiyan, S.

2017-06-01

One of the fundamental open questions in cosmology is whether we can regard the universe evolution without singularity like a Big Bang or a Big Rip. This challenging subject stimulates one to regard a nonsingular universe in the far past with an arbitrarily large vacuum energy. Considering the high energy regime in the cosmic history, it is believed that Einstein gravity should be corrected to an effective energy dependent theory which could be acquired by gravity's rainbow. On the other hand, employing massive gravity provided us with solutions to some of the long standing fundamental problems of cosmology such as cosmological constant problem and self acceleration of the universe. Considering these aspects of gravity's rainbow and massive gravity, in this paper, we initiate studying FRW cosmology in the massive gravity's rainbow formalism. At first, we show that although massive gravity modifies the FRW cosmology, but it does not itself remove the big bang singularity. Then, we generalize the massive gravity to the case of energy dependent spacetime and find that massive gravity's rainbow can remove the early universe singularity. We bring together all the essential conditions for having a nonsingular universe and the effects of both gravity's rainbow and massive gravity generalizations on such criteria are determined.

Space artificial gravity facilities - An approach to their construction

NASA Technical Reports Server (NTRS)

Wercinski, P. F.; Searby, N. D.; Tillman, B. W.

1988-01-01

In the course of adaptation to a space microgravity environment, humans experience cardiovascular deconditioning, loss of muscle mass, and loss of bone minerals. One possible solution to these space adaptation problems is to simulate earth's gravity using the centripetal acceleration created by a rotating system. The design and construction of rotating space structures pose many challenges. Before committing to the use of artificial gravity in future space missions, a man-rated Variable Gravity Research Facility (VGRF) should be developed in earth orbit as a gravitational research tool and testbed. This paper addresses the requirements and presents preliminary concepts for such a facility.

Holographic dark energy from fluid/gravity duality constraint by cosmological observations

NASA Astrophysics Data System (ADS)

Pourhassan, Behnam; Bonilla, Alexander; Faizal, Mir; Abreu, Everton M. C.

2018-06-01

In this paper, we obtain a holographic model of dark energy using the fluid/gravity duality. This model will be dual to a higher dimensional Schwarzschild black hole, and we would use fluid/gravity duality to relate to the parameters of this black hole to such a cosmological model. We will also analyze the thermodynamics of such a solution, and discuss the stability model. Finally, we use cosmological data to constraint the parametric space of this dark energy model. Thus, we will use observational data to perform cosmography for this holographic model based on fluid/gravity duality.

On static black holes solutions in Einstein and Einstein-Gauss-Bonnet gravity with topology [Formula: see text].

PubMed

Dadhich, Naresh; Pons, Josep M

We study static black hole solutions in Einstein and Einstein-Gauss-Bonnet gravity with the topology of the product of two spheres, [Formula: see text], in higher dimensions. There is an unusual new feature of the Gauss-Bonnet black hole: the avoidance of a non-central naked singularity prescribes a mass range for the black hole in terms of [Formula: see text]. For an Einstein-Gauss-Bonnet black hole a limited window of negative values for [Formula: see text] is also permitted. This topology encompasses black strings, branes, and generalized Nariai metrics. We also give new solutions with the product of two spheres of constant curvature.

Multiparticle Solutions in 2+1 Gravity and Time Machines

NASA Astrophysics Data System (ADS)

Steif, Alan R.

Multiparticle solutions for sources moving at the speed of light and corresponding to superpositions of single-particle plane-wave solutions are constructed in 2+1 gravity. It is shown that the two-particle spacetimes admit closed timelike curves provided the center-of-momentum energy exceeds a certain critical value. This occurs, however, at the cost of unphysical boundary conditions which are analogous to those affecting Gott’s time machine. As the energy exceeds the critical value, the closed timelike curves first occur at spatial infinity, then migrate inward as the energy is further increased. The total mass of the system also becomes imaginary for particle energies greater than the critical value.

Exact Schwarzschild-like solution in a bumblebee gravity model

NASA Astrophysics Data System (ADS)

Casana, R.; Cavalcante, A.; Poulis, F. P.; Santos, E. B.

2018-05-01

We obtain an exact vacuum solution from the gravity sector contained in the minimal standard-model extension. The theoretical model assumes a Riemann spacetime coupled to the bumblebee field which is responsible for the spontaneous Lorentz symmetry breaking. The solution achieved in a static and spherically symmetric scenario establishes a Schwarzschild-like black hole. In order to study the effects of the spontaneous Lorentz symmetry breaking we investigate some classic tests, including the advance of perihelion, the bending of light, and Shapiro's time delay. Furthermore, we compute some upper bounds, among which the most stringent associated with existing experimental data provides a sensitivity at the 10-15 level and that for future missions at the 10-19 level.

Gravity discharge vessel revisited: An explicit Lambert W function solution

NASA Astrophysics Data System (ADS)

Digilov, Rafael M.

2017-07-01

Based on the generalized Poiseuille equation modified by a kinetic energy correction, an explicit solution for the time evolution of a liquid column draining under gravity through an exit capillary tube is derived in terms of the Lambert W function. In contrast to the conventional exponential behavior, as implied by the Poiseuille law, a new analytical solution gives a full account for the volumetric flow rate of a fluid through a capillary of any length and improves the precision of viscosity determination. The theoretical consideration may be of interest to students as an example of how implicit equations in the field of physics can be solved analytically using the Lambert function.

Automated MALDI Matrix Coating System for Multiple Tissue Samples for Imaging Mass Spectrometry

NASA Astrophysics Data System (ADS)

Mounfield, William P.; Garrett, Timothy J.

2012-03-01

Uniform matrix deposition on tissue samples for matrix-assisted laser desorption/ionization (MALDI) is key for reproducible analyte ion signals. Current methods often result in nonhomogenous matrix deposition, and take time and effort to produce acceptable ion signals. Here we describe a fully-automated method for matrix deposition using an enclosed spray chamber and spray nozzle for matrix solution delivery. A commercial air-atomizing spray nozzle was modified and combined with solenoid controlled valves and a Programmable Logic Controller (PLC) to control and deliver the matrix solution. A spray chamber was employed to contain the nozzle, sample, and atomized matrix solution stream, and to prevent any interference from outside conditions as well as allow complete control of the sample environment. A gravity cup was filled with MALDI matrix solutions, including DHB in chloroform/methanol (50:50) at concentrations up to 60 mg/mL. Various samples (including rat brain tissue sections) were prepared using two deposition methods (spray chamber, inkjet). A linear ion trap equipped with an intermediate-pressure MALDI source was used for analyses. Optical microscopic examination showed a uniform coating of matrix crystals across the sample. Overall, the mass spectral images gathered from tissues coated using the spray chamber system were of better quality and more reproducible than from tissue specimens prepared by the inkjet deposition method.

Automated MALDI matrix coating system for multiple tissue samples for imaging mass spectrometry.

PubMed

Mounfield, William P; Garrett, Timothy J

2012-03-01

Uniform matrix deposition on tissue samples for matrix-assisted laser desorption/ionization (MALDI) is key for reproducible analyte ion signals. Current methods often result in nonhomogenous matrix deposition, and take time and effort to produce acceptable ion signals. Here we describe a fully-automated method for matrix deposition using an enclosed spray chamber and spray nozzle for matrix solution delivery. A commercial air-atomizing spray nozzle was modified and combined with solenoid controlled valves and a Programmable Logic Controller (PLC) to control and deliver the matrix solution. A spray chamber was employed to contain the nozzle, sample, and atomized matrix solution stream, and to prevent any interference from outside conditions as well as allow complete control of the sample environment. A gravity cup was filled with MALDI matrix solutions, including DHB in chloroform/methanol (50:50) at concentrations up to 60 mg/mL. Various samples (including rat brain tissue sections) were prepared using two deposition methods (spray chamber, inkjet). A linear ion trap equipped with an intermediate-pressure MALDI source was used for analyses. Optical microscopic examination showed a uniform coating of matrix crystals across the sample. Overall, the mass spectral images gathered from tissues coated using the spray chamber system were of better quality and more reproducible than from tissue specimens prepared by the inkjet deposition method.

Observed changes in the Earth's dynamic oblateness from GRACE data and geophysical models.

PubMed

Sun, Y; Ditmar, P; Riva, R

A new methodology is proposed to estimate changes in the Earth's dynamic oblateness ([Formula: see text] or equivalently, [Formula: see text]) on a monthly basis. The algorithm uses monthly Gravity Recovery and Climate Experiment (GRACE) gravity solutions, an ocean bottom pressure model and a glacial isostatic adjustment (GIA) model. The resulting time series agree remarkably well with a solution based on satellite laser ranging (SLR) data. Seasonal variations of the obtained time series show little sensitivity to the choice of GRACE solutions. Reducing signal leakage in coastal areas when dealing with GRACE data and accounting for self-attraction and loading effects when dealing with water redistribution in the ocean is crucial in achieving close agreement with the SLR-based solution in terms of de-trended solutions. The obtained trend estimates, on the other hand, may be less accurate due to their dependence on the GIA models, which still carry large uncertainties.

A new approach for estimating the Jupiter and Saturn gravity fields using Juno and Cassini measurements, trajectory estimation analysis, and a dynamical wind model optimization

NASA Astrophysics Data System (ADS)

Galanti, Eli; Durante, Daniele; Iess, Luciano; Kaspi, Yohai

2017-04-01

The ongoing Juno spacecraft measurements are improving our knowledge of Jupiter's gravity field. Similarly, the Cassini Grand Finale will improve the gravity estimate of Saturn. The analysis of the Juno and Cassini Doppler data will provide a very accurate reconstruction of spacial gravity variations, but these measurements will be very accurate only over a limited latitudinal range. In order to deduce the full gravity fields of Jupiter and Saturn, additional information needs to be incorporated into the analysis, especially with regards to the planets' wind structures. In this work we propose a new iterative approach for the estimation of Jupiter and Saturn gravity fields, using simulated measurements, a trajectory estimation model, and an adjoint based inverse thermal wind model. Beginning with an artificial gravitational field, the trajectory estimation model is used to obtain the gravitational moments. The solution from the trajectory model is then used as an initial guess for the thermal wind model, and together with an optimization method, the likely penetration depth of the winds is computed, and its uncertainty is evaluated. As a final step, the gravity harmonics solution from the thermal wind model is given back to the trajectory model, along with an estimate of their uncertainties, to be used as a priori for a new calculation of the gravity field. We test this method both for zonal harmonics only and with a full gravity field including tesseral harmonics. The results show that by using this method some of the gravitational moments are fitted better to the `observed' ones, mainly due to the added information from the dynamical model which includes the wind structure and its depth. Thus, it is suggested that the method presented here has the potential of improving the accuracy of the expected gravity moments estimated from the Juno and Cassini radio science experiments.

Differences in energy expenditure for conventional and femtosecond-assisted cataract surgery using 2 different phacoemulsification systems.

PubMed

Yesilirmak, Nilufer; Diakonis, Vasilios F; Sise, Adam; Waren, Daniel P; Yoo, Sonia H; Donaldson, Kendall E

2017-01-01

To compare the mean cumulative dissipated energy (CDE) in patients having femtosecond laser-assisted or conventional phacoemulsification cataract surgery using 2 different phacoemulsification platforms. Bascom Palmer Eye Institute, Miami, Florida, USA. Prospective comparative nonrandomized clinical study. Consecutive patients were scheduled to have femtosecond laser-assisted cataract surgery with the Lensx laser or conventional phacoemulsification using an active-fluidics torsional platform (Centurion) or torsional platform (Infiniti). The mean CDE and cataract grade were recorded. The study comprised 570 eyes (570 patients). There was no statistically significant difference in mean age (P = .41, femtosecond group; P = .33, conventional group) or cataract grade (P = .78 and P = .45, respectively) between the active-fluidics and gravity-fluidics platforms. In femtosecond cases (145 eyes), the mean CDE (percent-seconds) was 5.18 ± 4.58 (SD) with active fluidics and 7.00 ± 6.85 with gravity fluidics; in conventional cases (425 eyes), the mean CDE was 7.77 ± 6.97 and 11.43 ± 9.12, respectively. In both femtosecond cases and conventional cases, the CDE was lower with the active-fluidics platform than with the gravity-fluidics platform (P = .029, femtosecond group; P < .001 conventional group). With both fluidics platforms, the mean CDE was significantly lower in the femtosecond group than in the conventional group (both P < .001). The active-fluidics phacoemulsification platform achieved lower CDE values than the gravity-fluidics platform for conventional cataract extraction. Femtosecond laser pretreatment with the active-fluidics platform further reduced CDE. Copyright © 2017 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

On 3D minimal massive gravity

NASA Astrophysics Data System (ADS)

Alishahiha, Mohsen; Qaemmaqami, Mohammad M.; Naseh, Ali; Shirzad, Ahmad

2014-12-01

We study linearized equations of motion of the newly proposed three dimensional gravity, known as minimal massive gravity, using its metric formulation. By making use of a redefinition of the parameters of the model, we observe that the resulting linearized equations are exactly the same as that of TMG. In particular the model admits logarithmic modes at critical points. We also study several vacuum solutions of the model, specially at a certain limit where the contribution of Chern-Simons term vanishes.

Mass Redistribution in the Core and Time-varying Gravity at the Earth's Surface

NASA Technical Reports Server (NTRS)

Kuang, Wei-Jia; Chao, Benjamin F.; Fang, Ming

2003-01-01

The Earth's liquid outer core is in convection, as suggested by the existence of the geomagnetic field in much of the Earth's history. One consequence of the convection is the redistribution of mass resulting from relative motion among fluid parcels with slightly different densities. This time dependent mass redistribution inside the core produces a small perturbation on the gravity field of the Earth. With our numerical dynamo solutions, we find that the mass redistribution (and the resultant gravity field) symmetric about the equator is much stronger than that anti-symmetric about the equator. In particular, J(sub 2) component is the strongest. In addition, the gravity field variation increases with the Rayleigh number that measures the driving force for the geodynamo in the core. With reasonable scaling from the current dynamo solutions, we could expect that at the surface of the Earth, the J(sub 2) variation from the core is on the order of l0(exp -16)/year relative to the mean (i.e. spherically symmetric) gravity field of the Earth. The possible shielding effect due to core-mantle boundary pressure variation loading is likely much smaller and is therefore negligible. Our results suggest that time-varying gravity field perturbation due to core mass redistribution may be measured with modem space geodetic observations, which will result a new means of detecting dynamical processes in the Earth's deep interior.

Antigravity: Spin-gravity coupling in action

NASA Astrophysics Data System (ADS)

Plyatsko, Roman; Fenyk, Mykola

2016-08-01

The typical motions of a spinning test particle in Schwarzschild's background which show the strong repulsive action of the highly relativistic spin-gravity coupling are considered using the exact Mathisson-Papapetrou equations. An approximated approach to choice solutions of these equations which describe motions of the particle's proper center of mass is developed.

Big Mysteries: Extra Dimensions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lincoln, Don

2014-06-10

The weakness of gravity compared to the other subatomic forces is a real mystery. While nobody knows the answer, one credible solution is that gravity has access to more spatial dimensions than the other three known forces. In this video, Fermilab's Dr. Don Lincoln describes this idea, with the help of some very urbane characters.

Big Mysteries: Extra Dimensions

ScienceCinema

Lincoln, Don

2018-01-16

The weakness of gravity compared to the other subatomic forces is a real mystery. While nobody knows the answer, one credible solution is that gravity has access to more spatial dimensions than the other three known forces. In this video, Fermilab's Dr. Don Lincoln describes this idea, with the help of some very urbane characters.

A gravitational test of wave reinforcement versus fluid density models

NASA Technical Reports Server (NTRS)

Johnson, Jacqueline Umstead

1990-01-01

Spermatozoa, protozoa, and algae form macroscopic patterns somewhat analogous to thermally driven convection cells. These bioconvective patterns have attracted interest in the fluid dynamics community, but whether in all cases these waves were gravity driven was unknown. There are two conflicting theories, one gravity dependent (fluid density model), the other gravity independent (wave reinforcement theory). The primary objectives of the summer faculty fellows were to: (1) assist in sample collection (spermatozoa) and preparation for the KC-135 research airplane experiment; and (2) to collaborate on ground testing of bioconvective variables such as motility, concentration, morphology, etc., in relation to their macroscopic patterns. Results are very briefly given.

Effect of Numerical Error on Gravity Field Estimation for GRACE and Future Gravity Missions

NASA Astrophysics Data System (ADS)

McCullough, Christopher; Bettadpur, Srinivas

2015-04-01

In recent decades, gravity field determination from low Earth orbiting satellites, such as the Gravity Recovery and Climate Experiment (GRACE), has become increasingly more effective due to the incorporation of high accuracy measurement devices. Since instrumentation quality will only increase in the near future and the gravity field determination process is computationally and numerically intensive, numerical error from the use of double precision arithmetic will eventually become a prominent error source. While using double-extended or quadruple precision arithmetic will reduce these errors, the numerical limitations of current orbit determination algorithms and processes must be accurately identified and quantified in order to adequately inform the science data processing techniques of future gravity missions. The most obvious numerical limitation in the orbit determination process is evident in the comparison of measured observables with computed values, derived from mathematical models relating the satellites' numerically integrated state to the observable. Significant error in the computed trajectory will corrupt this comparison and induce error in the least squares solution of the gravitational field. In addition, errors in the numerically computed trajectory propagate into the evaluation of the mathematical measurement model's partial derivatives. These errors amalgamate in turn with numerical error from the computation of the state transition matrix, computed using the variational equations of motion, in the least squares mapping matrix. Finally, the solution of the linearized least squares system, computed using a QR factorization, is also susceptible to numerical error. Certain interesting combinations of each of these numerical errors are examined in the framework of GRACE gravity field determination to analyze and quantify their effects on gravity field recovery.

f(T) teleparallel gravity and cosmology.

PubMed

Cai, Yi-Fu; Capozziello, Salvatore; De Laurentis, Mariafelicia; Saridakis, Emmanuel N

2016-10-01

Over recent decades, the role of torsion in gravity has been extensively investigated along the main direction of bringing gravity closer to its gauge formulation and incorporating spin in a geometric description. Here we review various torsional constructions, from teleparallel, to Einstein-Cartan, and metric-affine gauge theories, resulting in extending torsional gravity in the paradigm of f (T) gravity, where f (T) is an arbitrary function of the torsion scalar. Based on this theory, we further review the corresponding cosmological and astrophysical applications. In particular, we study cosmological solutions arising from f (T) gravity, both at the background and perturbation levels, in different eras along the cosmic expansion. The f (T) gravity construction can provide a theoretical interpretation of the late-time universe acceleration, alternative to a cosmological constant, and it can easily accommodate with the regular thermal expanding history including the radiation and cold dark matter dominated phases. Furthermore, if one traces back to very early times, for a certain class of f (T) models, a sufficiently long period of inflation can be achieved and hence can be investigated by cosmic microwave background observations-or, alternatively, the Big Bang singularity can be avoided at even earlier moments due to the appearance of non-singular bounces. Various observational constraints, especially the bounds coming from the large-scale structure data in the case of f (T) cosmology, as well as the behavior of gravitational waves, are described in detail. Moreover, the spherically symmetric and black hole solutions of the theory are reviewed. Additionally, we discuss various extensions of the f (T) paradigm. Finally, we consider the relation with other modified gravitational theories, such as those based on curvature, like f (R) gravity, trying to illuminate the subject of which formulation, or combination of formulations, might be more suitable for quantization ventures and cosmological applications.

Gravity dependency of the gramicidin A channel conductivity. A model for gravity perception on the cellular level.

PubMed

Schatz, A; Linke-Hommes, A; Neubert, J

1996-01-01

Theoretical investigations involving the membrane-solution interface have revealed that the density of the solution varies appreciably within interfacial layers adjacent to charged membrane surfaces. The hypothesis that gravity interacts with this configuration and modifies transport rates across horizontal and vertical membranes differently was supported by initial experiments with gramicidin A channels in phosphatidylserine (PS) membranes in 0.1 M KCl. Channel conductivity was found to be about 1.6 times higher in horizontal membranes than in vertical membranes. Here we present the results of further experiments with gramicidin A channels (incorporated into charged PS- and uncharged phosphatidylcholine (PC) membranes in KCl- and CsCl-solutions) to demonstrate that the hypothesis is more generally applicable. Again, channel conductivity was found to be higher in horizontal PS membranes by a factor of between 1.20 and 1.75 in 0.1 M CsCl. No difference in channel conductivity was found for uncharged PC membranes in 0.1 M KCl and in 0.1 M CsCl. However, for PC membranes in 0.05 M KCl the channel conductivity was significantly higher in horizontal membranes by a factor of between 1.07 and 1.14. These results are consistent with the results of our model calculations of layer density and extension, which showed that the layer formation is enhanced by increasing membrane surface charge and decreasing electrolyte ion concentration. The mechanism of gravity interaction with membrane transport processes via interface reactions might be utilized by biological systems for orientational behaviour in the gravity field, which has been observed even for cellular systems.

Pareto joint inversion of 2D magnetotelluric and gravity data

NASA Astrophysics Data System (ADS)

Miernik, Katarzyna; Bogacz, Adrian; Kozubal, Adam; Danek, Tomasz; Wojdyła, Marek

2015-04-01

In this contribution, the first results of the "Innovative technology of petrophysical parameters estimation of geological media using joint inversion algorithms" project were described. At this stage of the development, Pareto joint inversion scheme for 2D MT and gravity data was used. Additionally, seismic data were provided to set some constrains for the inversion. Sharp Boundary Interface(SBI) approach and description model with set of polygons were used to limit the dimensionality of the solution space. The main engine was based on modified Particle Swarm Optimization(PSO). This algorithm was properly adapted to handle two or more target function at once. Additional algorithm was used to eliminate non- realistic solution proposals. Because PSO is a method of stochastic global optimization, it requires a lot of proposals to be evaluated to find a single Pareto solution and then compose a Pareto front. To optimize this stage parallel computing was used for both inversion engine and 2D MT forward solver. There are many advantages of proposed solution of joint inversion problems. First of all, Pareto scheme eliminates cumbersome rescaling of the target functions, that can highly affect the final solution. Secondly, the whole set of solution is created in one optimization run, providing a choice of the final solution. This choice can be based off qualitative data, that are usually very hard to be incorporated into the regular inversion schema. SBI parameterisation not only limits the problem of dimensionality, but also makes constraining of the solution easier. At this stage of work, decision to test the approach using MT and gravity data was made, because this combination is often used in practice. It is important to mention, that the general solution is not limited to this two methods and it is flexible enough to be used with more than two sources of data. Presented results were obtained for synthetic models, imitating real geological conditions, where interesting density distributions are relatively shallow and resistivity changes are related to deeper parts. This kind of conditions are well suited for joint inversion of MT and gravity data. In the next stage of the solution development of further code optimization and extensive tests for real data will be realized. Presented work was supported by Polish National Centre for Research and Development under the contract number POIG.01.04.00-12-279/13

Simulation gravity modeling to spacecraft-tracking data - Analysis and application

NASA Technical Reports Server (NTRS)

Phillips, R. J.; Sjogren, W. L.; Abbott, E. A.; Zisk, S. H.

1978-01-01

It is proposed that line-of-sight gravity measurements derived from spacecraft-tracking data can be used for quantitative subsurface density modeling by suitable orbit simulation procedures. Such an approach avoids complex dynamic reductions and is analogous to the modeling of conventional surface gravity data. This procedure utilizes the vector calculations of a given gravity model in a simplified trajectory integration program that simulates the line-of-sight gravity. Solutions from an orbit simulation inversion and a dynamic inversion on Doppler observables compare well (within 1% in mass and size), and the error sources in the simulation approximation are shown to be quite small. An application of this technique is made to lunar crater gravity anomalies by simulating the complete Bouguer correction to several large young lunar craters. It is shown that the craters all have negative Bouguer anomalies.

Gravity-Off-loading System for Large-Displacement Ground Testing of Spacecraft Mechanisms

NASA Technical Reports Server (NTRS)

Han, Olyvia; Kienholz, David; Janzen, Paul; Kidney, Scott

2010-01-01

Gravity-off-loading of deployable spacecraft mechanisms during ground testing is a long-standing problem. Deployable structures which are usually too weak to support their own weight under gravity require a means of gravity-off-loading as they unfurl. Conventional solutions to this problem have been helium-filled balloons or mechanical pulley/counterweight systems. These approaches, however, suffer from the deleterious effects of added inertia or friction forces. The changing form factor of the deployable structure itself and the need to track the trajectory of the center of gravity also pose a challenge to these conventional technologies. This paper presents a novel testing apparatus for high-fidelity zero-gravity simulation for special application to deployable space structures such as solar arrays, magnetometer booms, and robotic arms in class 100,000 clean room environments

Generating a Reduced Gravity Environment on Earth

NASA Technical Reports Server (NTRS)

Dungan, Larry K.; Cunningham, Tom; Poncia, Dina

2010-01-01

Since the 1950s several reduced gravity simulators have been designed and utilized in preparing humans for spaceflight and in reduced gravity system development. The Active Response Gravity Offload System (ARGOS) is the newest and most realistic gravity offload simulator. ARGOS provides three degrees of motion within the test area and is scalable for full building deployment. The inertia of the overhead system is eliminated by an active motor and control system. This presentation will discuss what ARGOS is, how it functions, and the unique challenges of interfacing to the human. Test data and video for human and robotic systems will be presented. A major variable in the human machine interaction is the interface of ARGOS to the human. These challenges along with design solutions will be discussed.

Optimum data weighting and error calibration for estimation of gravitational parameters

NASA Technical Reports Server (NTRS)

Lerch, Francis J.

1989-01-01

A new technique was developed for the weighting of data from satellite tracking systems in order to obtain an optimum least-squares solution and an error calibration for the solution parameters. Data sets from optical, electronic, and laser systems on 17 satellites in GEM-T1 Goddard Earth Model-T1 (GEM-T1) were employed toward application of this technique for gravity field parameters. Also GEM-T2 (31 satellites) was recently computed as a direct application of the method and is summarized. The method employs subset solutions of the data associated with the complete solution to agree with their error estimates. With the adjusted weights the process provides for an automatic calibration of the error estimates for the solution parameters. The data weights derived are generally much smaller than corresponding weights obtained from nominal values of observation accuracy or residuals. Independent tests show significant improvement for solutions with optimal weighting. The technique is general and may be applied to orbit parameters, station coordinates, or other parameters than the gravity model.

Magnetic levitation-based Martian and Lunar gravity simulator

NASA Technical Reports Server (NTRS)

Valles, J. M. Jr; Maris, H. J.; Seidel, G. M.; Tang, J.; Yao, W.

2005-01-01

Missions to Mars will subject living specimens to a range of low gravity environments. Deleterious biological effects of prolonged exposure to Martian gravity (0.38 g), Lunar gravity (0.17 g), and microgravity are expected, but the mechanisms involved and potential for remedies are unknown. We are proposing the development of a facility that provides a simulated Martian and Lunar gravity environment for experiments on biological systems in a well controlled laboratory setting. The magnetic adjustable gravity simulator will employ intense, inhomogeneous magnetic fields to exert magnetic body forces on a specimen that oppose the body force of gravity. By adjusting the magnetic field, it is possible to continuously adjust the total body force acting on a specimen. The simulator system considered consists of a superconducting solenoid with a room temperature bore sufficiently large to accommodate small whole organisms, cell cultures, and gravity sensitive bio-molecular solutions. It will have good optical access so that the organisms can be viewed in situ. This facility will be valuable for experimental observations and public demonstrations of systems in simulated reduced gravity. c2005 Published by Elsevier Ltd on behalf of COSPAR.

Magnetic levitation-based Martian and Lunar gravity simulator.

PubMed

Valles, J M; Maris, H J; Seidel, G M; Tang, J; Yao, W

2005-01-01

Missions to Mars will subject living specimens to a range of low gravity environments. Deleterious biological effects of prolonged exposure to Martian gravity (0.38 g), Lunar gravity (0.17 g), and microgravity are expected, but the mechanisms involved and potential for remedies are unknown. We are proposing the development of a facility that provides a simulated Martian and Lunar gravity environment for experiments on biological systems in a well controlled laboratory setting. The magnetic adjustable gravity simulator will employ intense, inhomogeneous magnetic fields to exert magnetic body forces on a specimen that oppose the body force of gravity. By adjusting the magnetic field, it is possible to continuously adjust the total body force acting on a specimen. The simulator system considered consists of a superconducting solenoid with a room temperature bore sufficiently large to accommodate small whole organisms, cell cultures, and gravity sensitive bio-molecular solutions. It will have good optical access so that the organisms can be viewed in situ. This facility will be valuable for experimental observations and public demonstrations of systems in simulated reduced gravity. c2005 Published by Elsevier Ltd on behalf of COSPAR.

AdS charged black holes in Einstein-Yang-Mills gravity's rainbow: Thermal stability and P - V criticality

NASA Astrophysics Data System (ADS)

Hendi, Seyed Hossein; Momennia, Mehrab

2018-02-01

Motivated by the interesting non-abelian gauge field, in this paper, we look for the analytical solutions of Yang-Mills theory in the context of gravity's rainbow. Regarding the trace of quantum gravity in black hole thermodynamics, we examine the first law of thermodynamics and also thermal stability in the canonical ensemble. We show that although the rainbow functions and Yang-Mills charge modify the solutions, the first law of thermodynamics is still valid. Based on the phenomenological similarities between the adS black holes and van der Waals liquid/gas systems, we study the critical behavior of the Yang-Mills black holes in the extended phase space thermodynamics. We also investigate the effects of various parameters on thermal instability as well as critical properties by using appropriate figures.

Analysis of the fluid flow and heat transfer in a thin liquid film in the presence and absence of gravity

NASA Technical Reports Server (NTRS)

Rahman, M. M.; Hankey, W. L.; Faghri, A.

1991-01-01

The hydrodynamic and thermal behavior of a thin liquid film flowing over a solid horizontal surface is analyzed for both plane and radially spreading flows. The situations where the gravitational force is completely absent and where it is significant are analyzed separately and their practical relevance to a micro-gravity environment is discussed. In the presence of gravity, in addition to Reynolds number, the Froude number of the film is found to be an important parameter that determines the supercritical and subcritical flow regimes and any associated hydraulic jump. A closed-form solution is possible under some flow situations, whereas others require numerical integration of ordinary differential equations. The approximate analytical results are found to compare well with the available two-dimensional numerical solutions.

Large charged drop levitation against gravity

NASA Technical Reports Server (NTRS)

Rhim, Won-Kyu; Chung, Sang Kun; Hyson, Michael T.; Trinh, Eugene H.; Elleman, Daniel D.

1987-01-01

A hybrid electrostatic-acoustic levitator that can levitate and manipulate a large liquid drop in one gravity is presented. To the authors' knowledge, this is the first time such large drops (up to 4 mm in diameter in the case of water) have been levitated against 1-gravity. This makes possible, for the first time, many new experiments both in space and in ground-based laboratories, such as 1)supercooling and superheating, 2) containerless crystal growth from various salt solutions or melts, 3) drop dynamics of oscillating or rotating liquid drops, 4) drop evaporation and Rayleigh bursting, and 5) containerless material processing in space. The digital control system, liquid drop launch process, principles of electrode design, and design of a multipurpose room temperature levitation chamber are described. Preliminary results that demonstrate drop oscillation and rotation, and crystal growth from supersaturated salt solutions are presented.

AdS 2 holographic dictionary

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cvetic, Mirjam; Papadimitriou, Ioannis

Here, we construct the holographic dictionary for both running and constant dilaton solutions of the two dimensional Einstein-Maxwell-Dilaton theory that is obtained by a circle reduction from Einstein-Hilbert gravity with negative cosmological constant in three dimensions. This specific model ensures that the dual theory has a well defined ultraviolet completion in terms of a two dimensional conformal field theory, but our results apply qualitatively to a wider class of two dimensional dilaton gravity theories. For each type of solutions we perform holographic renormalization, compute the exact renormalized one-point functions in the presence of arbitrary sources, and derive the asymptotic symmetriesmore » and the corresponding conserved charges. In both cases we find that the scalar operator dual to the dilaton plays a crucial role in the description of the dynamics. Its source gives rise to a matter conformal anomaly for the running dilaton solutions, while its expectation value is the only non trivial observable for constant dilaton solutions. The role of this operator has been largely overlooked in the literature. We further show that the only non trivial conserved charges for running dilaton solutions are the mass and the electric charge, while for constant dilaton solutions only the electric charge is non zero. However, by uplifting the solutions to three dimensions we show that constant dilaton solutions can support non trivial extended symmetry algebras, including the one found by Compère, Song and Strominger, in agreement with the results of Castro and Song. Finally, we demonstrate that any solution of this specific dilaton gravity model can be uplifted to a family of asymptotically AdS 2 × S 2 or conformally AdS 2 × S 2 solutions of the STU model in four dimensions, including non extremal black holes. As a result, the four dimensional solutions obtained by uplifting the running dilaton solutions coincide with the so called ‘subtracted geometries’, while those obtained from the uplift of the constant dilaton ones are new.« less

AdS 2 holographic dictionary

DOE PAGES

Cvetic, Mirjam; Papadimitriou, Ioannis

2016-12-02

Here, we construct the holographic dictionary for both running and constant dilaton solutions of the two dimensional Einstein-Maxwell-Dilaton theory that is obtained by a circle reduction from Einstein-Hilbert gravity with negative cosmological constant in three dimensions. This specific model ensures that the dual theory has a well defined ultraviolet completion in terms of a two dimensional conformal field theory, but our results apply qualitatively to a wider class of two dimensional dilaton gravity theories. For each type of solutions we perform holographic renormalization, compute the exact renormalized one-point functions in the presence of arbitrary sources, and derive the asymptotic symmetriesmore » and the corresponding conserved charges. In both cases we find that the scalar operator dual to the dilaton plays a crucial role in the description of the dynamics. Its source gives rise to a matter conformal anomaly for the running dilaton solutions, while its expectation value is the only non trivial observable for constant dilaton solutions. The role of this operator has been largely overlooked in the literature. We further show that the only non trivial conserved charges for running dilaton solutions are the mass and the electric charge, while for constant dilaton solutions only the electric charge is non zero. However, by uplifting the solutions to three dimensions we show that constant dilaton solutions can support non trivial extended symmetry algebras, including the one found by Compère, Song and Strominger, in agreement with the results of Castro and Song. Finally, we demonstrate that any solution of this specific dilaton gravity model can be uplifted to a family of asymptotically AdS 2 × S 2 or conformally AdS 2 × S 2 solutions of the STU model in four dimensions, including non extremal black holes. As a result, the four dimensional solutions obtained by uplifting the running dilaton solutions coincide with the so called ‘subtracted geometries’, while those obtained from the uplift of the constant dilaton ones are new.« less

Long-term and seasonal Caspian Sea level change from satellite gravity and altimeter measurements

NASA Astrophysics Data System (ADS)

Chen, J. L.; Wilson, C. R.; Tapley, B. D.; Save, H.; Cretaux, Jean-Francois

2017-03-01

We examine recent Caspian Sea level change by using both satellite radar altimetry and satellite gravity data. The altimetry record for 2002-2015 shows a declining level at a rate that is approximately 20 times greater than the rate of global sea level rise. Seasonal fluctuations are also much larger than in the world oceans. With a clearly defined geographic region and dominant signal magnitude, variations in the sea level and associated mass changes provide an excellent way to compare various approaches for processing satellite gravity data. An altimeter time series derived from several successive satellite missions is compared with mass measurements inferred from Gravity Recovery and Climate Experiment (GRACE) data in the form of both spherical harmonic (SH) and mass concentration (mascon) solutions. After correcting for spatial leakage in GRACE SH estimates by constrained forward modeling and accounting for steric and terrestrial water processes, GRACE and altimeter observations are in complete agreement at seasonal and longer time scales, including linear trends. This demonstrates that removal of spatial leakage error in GRACE SH estimates is both possible and critical to improving their accuracy and spatial resolution. Excellent agreement between GRACE and altimeter estimates also provides confirmation of steric Caspian Sea level change estimates. GRACE mascon estimates (both the Jet Propulsion Laboratory (JPL) coastline resolution improvement version 2 solution and the Center for Space Research (CSR) regularized) are also affected by leakage error. After leakage corrections, both JPL and CSR mascon solutions also agree well with altimeter observations. However, accurate quantification of leakage bias in GRACE mascon solutions is a more challenging problem.

The family of anisotropically scaled equatorial waves

NASA Astrophysics Data System (ADS)

RamíRez GutiéRrez, Enver; da Silva Dias, Pedro Leite; Raupp, Carlos; Bonatti, Jose Paulo

2011-04-01

In the present work we introduce the family of anisotropic equatorial waves. This family corresponds to equatorial waves at intermediate states between the shallow water and the long wave approximation model. The new family is obtained by using anisotropic time/space scalings on the linearized, unforced and inviscid shallow water model. It is shown that the anisotropic equatorial waves tend to the solutions of the long wave model in one extreme and to the shallow water model solutions in the other extreme of the parameter dependency. Thus, the problem associated with the completeness of the long wave model solutions can be asymptotically addressed. The anisotropic dispersion relation is computed and, in addition to the typical dependency on the equivalent depth, meridional quantum number and zonal wavenumber, it also depends on the anisotropy between both zonal to meridional space and velocity scales as well as the fast to slow time scales ratio. For magnitudes of the scales compatible with those of the tropical region, both mixed Rossby-gravity and inertio-gravity waves are shifted to a moderately higher frequency and, consequently, not filtered out. This draws attention to the fact that, for completeness of the long wave like solutions, it is necessary to include both the anisotropic mixed Rossby-gravity and inertio-gravity waves. Furthermore, the connection of slow and fast manifolds (distinguishing feature of equatorial dynamics) is preserved, though modified for the equatorial anisotropy parameters used δ ∈ < 1]. New possibilities of horizontal and vertical scale nonlinear interactions are allowed. Thus, the anisotropic shallow water model is of fundamental importance for understanding multiscale atmosphere and ocean dynamics in the tropics.

A geopotential model from satellite tracking, altimeter, and surface gravity data: GEM-T3

NASA Technical Reports Server (NTRS)

Lerch, F. J.; Nerem, R. S.; Putney, B. H.; Felsentreger, T. L.; Sanchez, B. V.; Marshall, J. A.; Klosko, S. M.; Patel, G. B.; Williamson, R. G.; Chinn, D. S.

1994-01-01

An improved model of Earth's gravitational field, Goddard Earth Model T-3 (GEM-T3), has been developed from a combination of satellite tracking, satellite altimeter, and surface gravimetric data. GEM-T3 provides a significant improvement in the modeling of the gravity field at half wavelengths of 400 km and longer. This model, complete to degree and order 50, yields more accurate satellite orbits and an improved geoid representation than previous Goddard Earth Models. GEM-T3 uses altimeter data from GEOS 3 (1975-1976), Seasat (1978) and Geosat (1986-1987). Tracking information used in the solution includes more than 1300 arcs of data encompassing 31 different satellites. The recovery of the long-wavelength components of the solution relies mostly on highly precise satellite laser ranging (SLR) data, but also includes Tracking Network (TRANET) Doppler, optical, and satellite-to-satellite tracking acquired between the ATS 6 and GEOS 3 satellites. The main advances over GEM-T2 (beyond the inclusion of altimeter and surface gravity information which is essential for the resolution of the shorter wavelength geoid) are some improved tracking data analysis approaches and additional SLR data. Although the use of altimeter data has greatly enhanced the modeling of the ocean geoid between 65 deg N and 60 deg S latitudes in GEM-T3, the lack of accurate detailed surface gravimetry leaves poor geoid resolution over many continental regions of great tectonic interest (e.g., Himalayas, Andes). Estimates of polar motion, tracking station coordinates, and long-wavelength ocean tidal terms were also made (accounting for 6330 parameters). GEM-T3 has undergone error calibration using a technique based on subset solutions to produce reliable error estimates. The calibration is based on the condition that the expected mean square deviation of a subset gravity solution from the full set values is predicted by the solutions' error covariances. Data weights are iteratively adjusted until this condition for the error calibration is satisfied. In addition, gravity field tests were performed on strong satellite data sets withheld from the solution (thereby ensuring their independence). In these tests, the performance of the subset models on the withheld observations is compared to error projections based on their calibrated error covariances. These results demonstrate that orbit accuracy projections are reliable for new satellites which were not included in GEM-T3.

Main methods of trajectory synthesis for scenarios of space missions with gravity assist maneuvers in the system of Jupiter and with landing on one of its satellites

NASA Astrophysics Data System (ADS)

Golubev, Yu. F.; Tuchin, A. G.; Grushevskii, A. V.; Koryanov, V. V.; Tuchin, D. A.; Morskoy, I. M.; Simonov, A. V.; Dobrovolskii, V. S.

2016-12-01

The development of a methodology for designing trajectories of spacecraft intended for the contact and remote studies of Jupiter and its natural satellites is considered. This methodology should take into account a number of specific features. Firstly, in order to maintain the propellant consumption at an acceptable level, the flight profile, ensuring the injection of the spacecraft into orbit around the Jovian moon, should include a large number of gravity assist maneuvers both in the interplanetary phase of the Earth-to-Jupiter flight and during the flight in the system of the giant planet. Secondly, the presence of Jupiter's powerful radiation belts also imposes fairly strict limitations on the trajectory parameters.

Detection of groundwater conduits in limestones with gravity surveys: data from the area of the Chicxulub Impact crater, Yucatan Peninsula, Mexico.

PubMed

Kinsland, G L; Hurtado, M; Pope, K O

2000-04-15

Small negative gravity anomalies are found in gravity data from along the northwestern shoreline of the Yucatan Peninsula. These anomalies are shown to be due to elongate, shallow anomalous porosity zones in the Tertiary carbonates. These zones are caused primarily by groundwater solution and are presently active conduits for groundwater flow. The association of these small gravity anomalies with known topographic and structural features of the area, which partially overlies the Chicxulub Impact crater, indicates their development was influenced by structures, faults and/or fractures, within the Tertiary and pre-Tertiary carbonates.

Detection of groundwater conduits in limestones with gravity surveys: data from the area of the Chicxulub Impact crater, Yucatan Peninsula, Mexico

NASA Technical Reports Server (NTRS)

Kinsland, G. L.; Hurtado, M.; Pope, K. O.; Ocampo, A. C. (Principal Investigator)

2000-01-01

Small negative gravity anomalies are found in gravity data from along the northwestern shoreline of the Yucatan Peninsula. These anomalies are shown to be due to elongate, shallow anomalous porosity zones in the Tertiary carbonates. These zones are caused primarily by groundwater solution and are presently active conduits for groundwater flow. The association of these small gravity anomalies with known topographic and structural features of the area, which partially overlies the Chicxulub Impact crater, indicates their development was influenced by structures, faults and/or fractures, within the Tertiary and pre-Tertiary carbonates.

Hairy black holes in scalar extended massive gravity

NASA Astrophysics Data System (ADS)

Tolley, Andrew J.; Wu, De-Jun; Zhou, Shuang-Yong

2015-12-01

We construct static, spherically symmetric black hole solutions in scalar extended ghost-free massive gravity and show the existence of hairy black holes in this class of extension. While the existence seems to be a generic feature, we focus on the simplest models of this extension and find that asymptotically flat hairy black holes can exist without fine-tuning the theory parameters, unlike the bi-gravity extension, where asymptotical flatness requires fine-tuning in the parameter space. Like the bi-gravity extension, we are unable to obtain asymptotically dS regular black holes in the simplest models considered, but it is possible to obtain asymptotically AdS black holes.

Development and Optimization of Gas-Assisted Gravity Drainage (GAGD) Process for Improved Light Oil Recovery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dandina N. Rao; Subhash C. Ayirala; Madhav M. Kulkarni

This is the final report describing the evolution of the project ''Development and Optimization of Gas-Assisted Gravity Drainage (GAGD) Process for Improved Light Oil Recovery'' from its conceptual stage in 2002 to the field implementation of the developed technology in 2006. This comprehensive report includes all the experimental research, models developments, analyses of results, salient conclusions and the technology transfer efforts. As planned in the original proposal, the project has been conducted in three separate and concurrent tasks: Task 1 involved a physical model study of the new GAGD process, Task 2 was aimed at further developing the vanishing interfacialmore » tension (VIT) technique for gas-oil miscibility determination, and Task 3 was directed at determining multiphase gas-oil drainage and displacement characteristics in reservoir rocks at realistic pressures and temperatures. The project started with the task of recruiting well-qualified graduate research assistants. After collecting and reviewing the literature on different aspects of the project such gas injection EOR, gravity drainage, miscibility characterization, and gas-oil displacement characteristics in porous media, research plans were developed for the experimental work to be conducted under each of the three tasks. Based on the literature review and dimensional analysis, preliminary criteria were developed for the design of the partially-scaled physical model. Additionally, the need for a separate transparent model for visual observation and verification of the displacement and drainage behavior under gas-assisted gravity drainage was identified. Various materials and methods (ceramic porous material, Stucco, Portland cement, sintered glass beads) were attempted in order to fabricate a satisfactory visual model. In addition to proving the effectiveness of the GAGD process (through measured oil recoveries in the range of 65 to 87% IOIP), the visual models demonstrated three possible multiphase mechanisms at work, namely, Darcy-type displacement until gas breakthrough, gravity drainage after breakthrough and film-drainage in gas-invaded zones throughout the duration of the process. The partially-scaled physical model was used in a series of experiments to study the effects of wettability, gas-oil miscibility, secondary versus tertiary mode gas injection, and the presence of fractures on GAGD oil recovery. In addition to yielding recoveries of up to 80% IOIP, even in the immiscible gas injection mode, the partially-scaled physical model confirmed the positive influence of fractures and oil-wet characteristics in enhancing oil recoveries over those measured in the homogeneous (unfractured) water-wet models. An interesting observation was that a single logarithmic relationship between the oil recovery and the gravity number was obeyed by the physical model, the high-pressure corefloods and the field data.« less

Extended DBI massive gravity with generalized fiducial metric

NASA Astrophysics Data System (ADS)

Chullaphan, Tossaporn; Tannukij, Lunchakorn; Wongjun, Pitayuth

2015-06-01

We consider an extended model of DBI massive gravity by generalizing the fiducial metric to be an induced metric on the brane corresponding to a domain wall moving in five-dimensional Schwarzschild-Anti-de Sitter spacetime. The model admits all solutions of FLRW metric including flat, closed and open geometries while the original one does not. The background solutions can be divided into two branches namely self-accelerating branch and normal branch. For the self-accelerating branch, the graviton mass plays the role of cosmological constant to drive the late-time acceleration of the universe. It is found that the number degrees of freedom of gravitational sector is not correct similar to the original DBI massive gravity. There are only two propagating degrees of freedom from tensor modes. For normal branch, we restrict our attention to a particular class of the solutions which provides an accelerated expansion of the universe. It is found that the number of degrees of freedom in the model is correct. However, at least one of them is ghost degree of freedom which always present at small scale implying that the theory is not stable.

Phase structure of higher spin black hole

NASA Astrophysics Data System (ADS)

Chen, Bin; Long, Jiang; Wang, Yi-Nan

2013-03-01

In this paper, we investigate the phase structure of the black holes with one single higher spin hair, focusing specifically on the spin 3 and spin widetilde{4} black holes. Based on dimensional analysis and the requirement of thermodynamic consistency, we derive a universal formula relating the entropy with the conserved charges for arbitrary AdS 3 higher spin black holes. Then we use it to study the phase structure of the higher spin black holes. We find that there are six branches of solutions in the spin 3 gravity, eight branches of solutions in the spin widetilde{4} gravity and twelve branches of solutions in the G 2 gravity. In each case, all the branches are related by a simple angle shift in the entropy functions. In the spin 3 case, we reproduce all the results found before. In the spin widetilde{4} case, we find that at low temperature it lies in the BTZ branch while at high temperature it undergoes a phase transition to one of the two other branches, depending on the signature of the chemical potential, a reflection of charge conjugate asymmetry found before.

Lifshitz black branes and DC transport coefficients in massive Einstein-Maxwell-dilaton gravity

NASA Astrophysics Data System (ADS)

Kuang, Xiao-Mei; Papantonopoulos, Eleftherios; Wu, Jian-Pin; Zhou, Zhenhua

2018-03-01

We construct analytical Lifshitz massive black brane solutions in massive Einstein-Maxwell-dilaton gravity theory. We also study the thermodynamics of these black brane solutions and obtain the thermodynamical stability conditions. On the dual nonrelativistic boundary field theory with Lifshitz symmetry, we analytically compute the DC transport coefficients, including the electric conductivity, thermoelectric conductivity, and thermal conductivity. The novel property of our model is that the massive term supports the Lifshitz black brane solutions with z ≠1 in such a way that the DC transport coefficients in the dual field theory are finite. We also find that the Wiedemann-Franz law in this dual boundary field theory is violated, which indicates that it may involve strong interactions.

Binary Mixture of Perfect Fluid and Dark Energy in Modified Theory of Gravity

NASA Astrophysics Data System (ADS)

Shaikh, A. Y.

2016-07-01

A self consistent system of Plane Symmetric gravitational field and a binary mixture of perfect fluid and dark energy in a modified theory of gravity are considered. The gravitational field plays crucial role in the formation of soliton-like solutions, i.e., solutions with limited total energy, spin, and charge. The perfect fluid is taken to be the one obeying the usual equation of state, i.e., p = γρ with γ∈ [0, 1] whereas, the dark energy is considered to be either the quintessence like equation of state or Chaplygin gas. The exact solutions to the corresponding field equations are obtained for power-law and exponential volumetric expansion. The geometrical and physical parameters for both the models are studied.

Fluctuations, ghosts, and the cosmological constant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirayama, T.; Holdom, B.

2004-12-15

For a large region of parameter space involving the cosmological constant and mass parameters, we discuss fluctuating spacetime solutions that are effectively Minkowskian on large time and distance scales. Rapid, small amplitude oscillations in the scale factor have a frequency determined by the size of a negative cosmological constant. A field with modes of negative energy is required. If it is gravity that induces a coupling between the ghostlike and normal fields, we find that this results in stochastic rather than unstable behavior. The negative energy modes may also permit the existence of Lorentz invariant fluctuating solutions of finite energymore » density. Finally we consider higher derivative gravity theories and find oscillating metric solutions in these theories without the addition of other fields.« less

Conformal Weyl Gravity and Perihelion Precession

NASA Technical Reports Server (NTRS)

Sultana, Joseph; Kazanas, Demosthenes; Said, Jakson, Levi

2012-01-01

We investigate the perihelion shift of planetary motion in conformal Weyl gravity using the metric of the static, spherically symmetric solution discovered by Mannheim and Kazanas. To this end we employ a procedure similar to that used by Weinberg for the Schwarzschild solution, which has also been used recently to study the solar system effects of the cosmological constant Lambda. We show that besides the general relativistic terms obtained earlier from the Schwarzschild-de Sitter solution, the expression for the perihelion shift includes a negative contribution which arises from the linear term gamma ray in the metric. Using data for perihelion shift observations, we obtain constraints on the value of the constant gammma similar to that obtained earlier using galactic rotational curves.

Brane f(R) gravity cosmologies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balcerzak, Adam; DaPbrowski, Mariusz P.

2010-06-15

By the application of the generalized Israel junction conditions we derive cosmological equations for the fourth-order f(R) brane gravity and study their cosmological solutions. We show that there exists a nonstatic solution which describes a four-dimensional de Sitter (dS{sub 4}) brane embedded in a five-dimensional anti-de Sitter (AdS{sub 5}) bulk for a vanishing Weyl tensor contribution. On the other hand, for the case of a nonvanishing Weyl tensor contribution, there exists a static brane solution only. We claim that in order to get some more general nonstatic f(R) brane configurations, one needs to admit a dynamical matter energy-momentum tensor inmore » the bulk rather than just a bulk cosmological constant.« less

Intravenous Fluid Mixing in Normal Gravity, Partial Gravity, and Microgravity: Down-Selection of Mixing Methods

NASA Technical Reports Server (NTRS)

Niederhaus, Charles E.; Miller, Fletcher J.

2008-01-01

The missions envisioned under the Vision for Space Exploration will require development of new methods to handle crew medical care. Medications and intravenous (IV) fluids have been identified as one area needing development. Storing certain medications and solutions as powders or concentrates can both increase the shelf life and reduce the overall mass and volume of medical supplies. The powders or concentrates would then be mixed in an IV bag with Sterile Water for Injection produced in situ from the potable water supply. Fluid handling in microgravity is different than terrestrial settings, and requires special consideration in the design of equipment. This document describes the analyses and down-select activities used to identify the IV mixing method to be developed that is suitable for ISS and exploration missions. The chosen method is compatible with both normal gravity and microgravity, maintains sterility of the solution, and has low mass and power requirements. The method will undergo further development, including reduced gravity aircraft experiments and computations, in order to fully develop the mixing method and associated operational parameters.

Gravity wave forcing in the middle atmosphere due to reduced ozone heating during a solar eclipse

NASA Technical Reports Server (NTRS)

Fritts, David C.; Luo, Zhangai

1993-01-01

We present an analysis of the gravity wave structure and the associated forcing of the middle atmosphere induced by the screening of the ozone layer from solar heating during a solar eclipse. Fourier integral techniques and numerical evaluation of the integral solutions were used to assess the wave field structure and to compute the gravity wave forcing of the atmosphere at greater heights. Our solutions reveal dominant periods of a few hours, characteristic horizontal and vertical scales of about 5000 to 10,000 km and 200 km, respectively, and an integrated momentum flux in the direction of eclipse motion of about 5.6 x 10 exp 8 N at each height above the forcing level. These results suggest that responses to solar eclipses may be difficult to detect above background gravity wave and tidal fluctuations until well into the thermosphere. Conversely, the induced body forces may penetrate to considerable heights because of the large wave scales and will have significant effects at levels where the wave field is dissipated.

Topologically nontrivial black holes in Lovelock-Born-Infeld gravity

NASA Astrophysics Data System (ADS)

Farhangkhah, N.

2018-04-01

We present the black hole solutions possessing horizon with nonconstant-curvature and additional scalar restrictions on the base manifold in Lovelock gravity coupled to Born-Infeld (BI) nonlinear electrodynamics. The asymptotic and near origin behavior of the metric is presented and we analyze different behaviors of the singularity. We find that, in contrast to the case of black hole solutions of BI-Lovelock gravity with constant curvature horizon and Maxwell-Lovelock gravity with non constant horizon which have only timelike singularities, spacelike, and timelike singularities may exist for BI-Lovelock black holes with nonconstant curvature horizon. By calculating the thermodynamic quantities, we study the effects of nonlinear electrodynamics via the Born-Infeld action. Stability analysis shows that black holes with positive sectional curvature, κ , possess an intermediate unstable phase and large and small black holes are stable. We see that while Ricci flat Lovelock-Born-Infeld black holes having exotic horizons are stable in the presence of Maxwell field or either Born Infeld field with large born Infeld parameter β , unstable phase appears for smaller values of β , and therefore nonlinearity brings in the instability.

Gravity-induced stresses in stratified rock masses

USGS Publications Warehouse

Amadei, B.; Swolfs, H.S.; Savage, W.Z.

1988-01-01

This paper presents closed-form solutions for the stress field induced by gravity in anisotropic and stratified rock masses. These rocks are assumed to be laterally restrained. The rock mass consists of finite mechanical units, each unit being modeled as a homogeneous, transversely isotropic or isotropic linearly elastic material. The following results are found. The nature of the gravity induced stress field in a stratified rock mass depends on the elastic properties of each rock unit and how these properties vary with depth. It is thermodynamically admissible for the induced horizontal stress component in a given stratified rock mass to exceed the vertical stress component in certain units and to be smaller in other units; this is not possible for the classical unstratified isotropic solution. Examples are presented to explore the nature of the gravity induced stress field in stratified rock masses. It is found that a decrease in rock mass anisotropy and a stiffening of rock masses with depth can generate stress distributions comparable to empirical hyperbolic distributions previously proposed in the literature. ?? 1988 Springer-Verlag.

EGSIEM combination service: combination of GRACE monthly K-band solutions on normal equation level

NASA Astrophysics Data System (ADS)

Meyer, Ulrich; Jean, Yoomin; Arnold, Daniel; Jäggi, Adrian

2017-04-01

The European Gravity Service for Improved Emergency Management (EGSIEM) project offers a scientific combination service, combining for the first time monthly GRACE gravity fields of different analysis centers (ACs) on normal equation (NEQ) level and thus taking all correlations between the gravity field coefficients and pre-eliminated orbit and instrument parameters correctly into account. Optimal weights for the individual NEQs are commonly derived by variance component estimation (VCE), as is the case for the products of the International VLBI Service (IVS) or the DTRF2008 reference frame realisation that are also derived by combination on NEQ-level. But variance factors are based on post-fit residuals and strongly depend on observation sampling and noise modeling, which both are very diverse in case of the individual EGSIEM ACs. These variance factors do not necessarily represent the true error levels of the estimated gravity field parameters that are still governed by analysis noise. We present a combination approach where weights are derived on solution level, thereby taking the analysis noise into account.

Spherically symmetric vacuum in covariant F (T )=T +α/2 T2+O (Tγ) gravity theory

NASA Astrophysics Data System (ADS)

DeBenedictis, Andrew; Ilijić, Saša

2016-12-01

Recently, a fully covariant version of the theory of F (T ) torsion gravity has been introduced by M. Kršśák and E. Saridakis [Classical Quantum Gravity 33, 115009 (2016)]. In covariant F (T ) gravity, the Schwarzschild solution is not a vacuum solution for F (T )≠T , and therefore determining the spherically symmetric vacuum is an important open problem. Within the covariant framework, we perturbatively solve the spherically symmetric vacuum gravitational equations around the Schwarzschild solution for the scenario with F (T )=T +(α /2 )T2 , representing the dominant terms in theories governed by Lagrangians analytic in the torsion scalar. From this, we compute the perihelion shift correction to solar system planetary orbits as well as perturbative gravitational effects near neutron stars. This allows us to set an upper bound on the magnitude of the coupling constant, α , which governs deviations from general relativity. We find the bound on this nonlinear torsion coupling constant by specifically considering the uncertainty in the perihelion shift of Mercury. We also analyze a bound from a similar comparison with the periastron orbit of the binary pulsar PSR J0045-7319 as an independent check for consistency. Setting bounds on the dominant nonlinear coupling is important in determining if other effects in the Solar System or greater universe could be attributable to nonlinear torsion.

The measurement of solute diffusion coefficients in dilute liquid alloys: the influence of unit gravity and g-jitter on buoyancy convection.

PubMed

Smith, R W; Yang, B J; Huang, W D

2004-11-01

Liquid diffusion experiments conducted on the MIR space station using the Canadian Space Agency QUELD II processing facility and the microgravity isolation mount (MIM) showed that g-jitter significantly increased the measured solute diffusion coefficients. In some experiments, milli-g forced vibration was superimposed on the sample when isolated from the ambient g-jitter; this resulted in markedly increased solute transport. To further explore the effects arising in these long capillary diffusion couples from the absence of unit-gravity and the presence of the forced g-jitter, the effects of a 1 milli-g forcing vibration on the mass transport in a 1.5 mm diameter long capillary diffusion couple have been simulated. In addition, to increase understanding of the role of unit gravity in determining the extent to which gravity can influence measured diffusion coefficient values, comparative experiments involving gold, silver, and antimony diffusing in liquid lead have been carried out using a similar QUELD II facility to that employed in the QUELD II/MIM/MIR campaign but under terrestrial conditions. It was found that buoyancy-driven convection may still persist in the liquid even when conditions are arranged for a continuously decreasing density gradient up the axis of a vertical long capillary diffusion couple due to the presence of small radial temperature gradients.

Higher-order gravity in higher dimensions: geometrical origins of four-dimensional cosmology?

NASA Astrophysics Data System (ADS)

Troisi, Antonio

2017-03-01

Determining the cosmological field equations is still very much debated and led to a wide discussion around different theoretical proposals. A suitable conceptual scheme could be represented by gravity models that naturally generalize Einstein theory like higher-order gravity theories and higher-dimensional ones. Both of these two different approaches allow one to define, at the effective level, Einstein field equations equipped with source-like energy-momentum tensors of geometrical origin. In this paper, the possibility is discussed to develop a five-dimensional fourth-order gravity model whose lower-dimensional reduction could provide an interpretation of cosmological four-dimensional matter-energy components. We describe the basic concepts of the model, the complete field equations formalism and the 5-D to 4-D reduction procedure. Five-dimensional f( R) field equations turn out to be equivalent, on the four-dimensional hypersurfaces orthogonal to the extra coordinate, to an Einstein-like cosmological model with three matter-energy tensors related with higher derivative and higher-dimensional counter-terms. By considering the gravity model with f(R)=f_0R^n the possibility is investigated to obtain five-dimensional power law solutions. The effective four-dimensional picture and the behaviour of the geometrically induced sources are finally outlined in correspondence to simple cases of such higher-dimensional solutions.

Twins Image

NASA Image and Video Library

2005-08-02

NASA MESSENGER Earth flyby on Aug. 2, 2005, not only adjusted the spacecraft path to Mercury - the gravity assist maneuver allowed the spacecraft team to test several MESSENGER science instruments by observing its home planet.

Exact solutions with AdS asymptotics of Einstein and Einstein-Maxwell gravity minimally coupled to a scalar field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cadoni, Mariano; Serra, Matteo; Mignemi, Salvatore

We propose a general method for solving exactly the static field equations of Einstein and Einstein-Maxwell gravity minimally coupled to a scalar field. Our method starts from an ansatz for the scalar field profile, and determines, together with the metric functions, the corresponding form of the scalar self-interaction potential. Using this method we prove a new no-hair theorem about the existence of hairy black-hole and black-brane solutions and derive broad classes of static solutions with radial symmetry of the theory, which may play an important role in applications of the AdS/CFT correspondence to condensed matter and strongly coupled QFTs. Thesemore » solutions include: (1) four- or generic (d+2)-dimensional solutions with planar, spherical or hyperbolic horizon topology; (2) solutions with anti-de Sitter, domain wall and Lifshitz asymptotics; (3) solutions interpolating between an anti-de Sitter spacetime in the asymptotic region and a domain wall or conformal Lifshitz spacetime in the near-horizon region.« less

Solute transport along preferential flow paths in unsaturated fractures

USGS Publications Warehouse

Su, Grace W.; Geller, Jil T.; Pruess, Karsten; Hunt, James R.

2001-01-01

Laboratory experiments were conducted to study solute transport along preferential flow paths in unsaturated, inclined fractures. Qualitative aspects of solute transport were identified in a miscible dye tracer experiment conducted in a transparent replica of a natural granite fracture. Additional experiments were conducted to measure the breakthrough curves of a conservative tracer introduced into an established preferential flow path in two different fracture replicas and a rock‐replica combination. The influence of gravity was investigated by varying fracture inclination. The relationship between the travel times of the solute and the relative influence of gravity was substantially affected by two modes of intermittent flow that occurred: the snapping rivulet and the pulsating blob modes. The measured travel times of the solute were evaluated with three transfer function models: the axial dispersion, the reactors‐in‐series, and the lognormal models. The three models described the solute travel times nearly equally well. A mechanistic model was also formulated to describe transport when the pulsating blob mode occurred which assumed blobs of water containing solute mixed with residual pools of water along the flow path.

Black string in dRGT massive gravity

NASA Astrophysics Data System (ADS)

Tannukij, Lunchakorn; Wongjun, Pitayuth; Ghosh, Suchant G.

2017-12-01

We present a cylindrically symmetric solution, both charged and uncharged, which is known as a black string solution to the nonlinear ghost-free massive gravity found by de Rham, Gabadadze, and Tolley (dRGT). This "dRGT black string" can be thought of as a generalization of the black string solution found by Lemos. Moreover, the dRGT black string solution includes other classes of black string solution such as the monopole-black string ones since the graviton mass contributes to the global monopole term as well as the cosmological-constant term. To investigate the solution, we compute mass, temperature, and entropy of the dRGT black string. We found that the existence of the graviton mass drastically affects the thermodynamics of the black string. Furthermore, the Hawking-Page phase transition is found to be possible for the dRGT black string as well as the charged dRGT black string. The dRGT black string solution is thermodynamically stable for r>r_c with negative thermodynamical potential and positive heat capacity while it is unstable for r

Low Gravity Guidance System for Airborne Microgravity Research

NASA Technical Reports Server (NTRS)

Rieke, W. J.; Emery, E. F.; Boyer, E. O.; Hegedus, C.; ODonoghue, D. P.

1996-01-01

Microgravity research techniques have been established to achieve a greater understanding of the role of gravity in the fundamentals of a variety of physical phenomena and material processing. One technique in use at the NASA Lewis Research Center involves flying Keplarian trajectories with a modified Lear Jet and DC-9 aircraft to achieve a highly accurate Microgravity environment by neutralizing accelerations in all three axis of the aircraft. The Low Gravity Guidance System (LGGS) assists the pilot and copilot in flying the trajectories by displaying the aircraft acceleration data in a graphical display format. The Low Gravity Guidance System is a microprocessor based system that acquires and displays the aircraft acceleration information. This information is presented using an electroluminescent display mounted over the pilot's instrument panel. The pilot can select the Microgravity range that is required for a given research event. This paper describes the characteristics, design, calibration and testing of the Low Gravity Guidance System Phase 3, significant lessons from earlier systems and the developmental work on future systems.

Mars Gravity Field and Upper Atmosphere from MGS, Mars Odyssey, and MRO

NASA Astrophysics Data System (ADS)

Genova, A.; Goossens, S. J.; Lemoine, F. G.; Mazarico, E.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

2015-12-01

The NASA orbital missions Mars Global Surveyor (MGS), Mars Odyssey (ODY), and Mars Reconnaissance Orbiter (MRO) have been exploring and monitoring the planet Mars since 1997. MGS executed its mapping mission between 1999 and 2006 in a frozen sun-synchronous, near-circular, polar orbit with the periapsis altitude at ~370 km and the dayside equatorial crossing at 2 pm Local Solar Time (LST). The spacecraft was equipped with onboard instrumentation to acquire radio science data and to measure spacecraft ranges to the Martian surface (Mars Orbiter Laser Altimeter). These measurements resulted in static and time-varying gravity field and high-resolution global topography of the planet. ODY and MRO are still orbiting about Mars in two different sun-synchronous orbits, providing radio tracking data that indirectly measure both the static and time-varying gravity field and the atmospheric density. The orbit of ODY has its periapsis at ~390 km altitude and descending node at 4-5 pm LST. However, the spacecraft also collected measurements at lower altitudes (~220 km) in 2002 prior to the mapping phase. Since November 2006, MRO is in a low-altitude orbit with a periapsis altitude of 255 km and descending node at 3 pm LST. Radio data from MRO help improve the resolution of the static gravity field and measure the mass distribution of the polar caps, but the atmospheric drag at those altitudes may limit the benefits of these radio tracking observations. We present a combined solution of the Martian gravity field to degree and order 110 and atmospheric density profiles with radio tracking data from MGS, ODY and MRO. The gravity field solution is combined with the MOLA topography yielding an updated map of Mars crustal thickness. We also show our solution of the Love number k2 and time-variable gravity zonal harmonics (C20 and C30, in particular). The recovered atmospheric density profiles may be used in atmospheric models to constrain the long-term variability of the constituents in the upper atmosphere.

Thin-shell wormholes in rainbow gravity

NASA Astrophysics Data System (ADS)

Amirabi, Z.; Halilsoy, M.; Mazharimousavi, S. Habib

2018-03-01

At the Planck scale of length ˜10‑35 m where the energy is comparable with the Planck energy, the quantum gravity corrections to the classical background spacetime results in gravity’s rainbow or rainbow gravity. In this modified theory of gravity, geometry depends on the energy of the test particle used to probe the spacetime, such that in the low energy limit, it yields the standard general relativity. In this work, we study the thin-shell wormholes in the spherically symmetric rainbow gravity. We find the corresponding properties in terms of the rainbow functions which are essential in the rainbow gravity and the stability of such thin-shell wormholes are investigated. Particularly, it will be shown that there are exact solutions in which high energy particles crossing the throat will encounter less amount of total exotic matter. This may be used as an advantage over general relativity to reduce the amount of exotic matter.

Off-diagonal ekpyrotic scenarios and equivalence of modified, massive and/or Einstein gravity

NASA Astrophysics Data System (ADS)

Vacaru, Sergiu I.

2016-01-01

Using our anholonomic frame deformation method, we show how generic off-diagonal cosmological solutions depending, in general, on all spacetime coordinates and undergoing a phase of ultra-slow contraction can be constructed in massive gravity. In this paper, there are found and studied new classes of locally anisotropic and (in)homogeneous cosmological metrics with open and closed spatial geometries. The late time acceleration is present due to effective cosmological terms induced by nonlinear off-diagonal interactions and graviton mass. The off-diagonal cosmological metrics and related Stückelberg fields are constructed in explicit form up to nonholonomic frame transforms of the Friedmann-Lamaître-Robertson-Walker (FLRW) coordinates. We show that the solutions include matter, graviton mass and other effective sources modeling nonlinear gravitational and matter fields interactions in modified and/or massive gravity, with polarization of physical constants and deformations of metrics, which may explain certain dark energy and dark matter effects. There are stated and analyzed the conditions when such configurations mimic interesting solutions in general relativity and modifications and recast the general Painlevé-Gullstrand and FLRW metrics. Finally, we elaborate on a reconstruction procedure for a subclass of off-diagonal cosmological solutions which describe cyclic and ekpyrotic universes, with an emphasis on open issues and observable signatures.

Modeling wormholes in f (R ,T ) gravity

NASA Astrophysics Data System (ADS)

Moraes, P. H. R. S.; Sahoo, P. K.

2017-08-01

In this work, we propose the modeling of static wormholes within the f (R ,T ) extended theory of gravity perspective. We present some models of wormholes, which are constructed from different hypotheses for their matter content, i.e., different relations for their pressure components (radial and lateral) and different equations of state. The solutions obtained for the shape function of the wormholes obey the necessary metric conditions. They show a behavior similar to those found in previous references about wormholes, which also happens to our solutions for the energy density of such objects. We also apply the energy conditions for the wormholes' physical content.

Traversable wormholes without exotic matter in multimetric repulsive gravity

NASA Astrophysics Data System (ADS)

Hohmann, Manuel

2014-04-01

We present a static, spherically symmetric, traversable wormhole solution to multimetric gravity which is sustained by only nonexotic matter, i.e., matter which satisfies all energy conditions. The possibility of this solution arises from the fact that under certain conditions the multimetric gravitational field equations reduce to the Einstein equations, but with a negative effective gravitational constant. We show that the Arnowitt-Deser-Misner mass of this wormhole vanishes, so that it appears massless to observers in the asymptotically flat spacetime. We finally speculate on the feasibility of creating and maintaining this type of wormhole by an advanced civilization.

Gravity dependent processes and intracellular motion

NASA Technical Reports Server (NTRS)

Todd, Paul

1991-01-01

Most organelles large enough to sediment or to undergo isothermal settling within eukaryotic cells are held in position by one or more components of the cytoskeleton. The interior of eukaryotic cells is considered to be very crowded, and the evaluation of natural-convective processes is very difficult. In a most simple view, the cell may be considered as consisting of four immiscible phases among which solutes are exchanged causing steep concentration gradients and thermodynamic conditions far from equilibrium. Extracellular gravity-related forces may include natural convection due to solute gradients external to single cells or the work performed by swimming, ciliated, or elongating cells.

Probing quantum gravity through exactly soluble midi-superspaces I

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ashtekar, A.; Pierri, M.

1996-12-01

It is well-known that the Einstein-Rosen solutions to the 3+1- dimensional vacuum Einstein{close_quote}s equations are in one to one correspondence with solutions of 2+1-dimensional general relativity coupled to axi-symmetric, zero rest mass scalar fields. We first re-examine the quantization of this midi-superspace paying special attention to the asymptotically flat boundary conditions and to certain functional analytic subtleties associated with regularization. We then use the resulting quantum theory to analyze several conceptual and technical issues of quantum gravity. {copyright} {ital 1996 American Institute of Physics.}

On a more rigorous gravity field processing for future LL-SST type gravity satellite missions

NASA Astrophysics Data System (ADS)

Daras, I.; Pail, R.; Murböck, M.

2013-12-01

In order to meet the augmenting demands of the user community concerning accuracies of temporal gravity field models, future gravity missions of low-low satellite-to-satellite tracking (LL-SST) type are planned to carry more precise sensors than their precedents. A breakthrough is planned with the improved LL-SST measurement link, where the traditional K-band microwave instrument of 1μm accuracy will be complemented by an inter-satellite ranging instrument of several nm accuracy. This study focuses on investigations concerning the potential performance of the new sensors and their impact in gravity field solutions. The processing methods for gravity field recovery have to meet the new sensor standards and be able to take full advantage of the new accuracies that they provide. We use full-scale simulations in a realistic environment to investigate whether the standard processing techniques suffice to fully exploit the new sensors standards. We achieve that by performing full numerical closed-loop simulations based on the Integral Equation approach. In our simulation scheme, we simulate dynamic orbits in a conventional tracking analysis to compute pseudo inter-satellite ranges or range-rates that serve as observables. Each part of the processing is validated separately with special emphasis on numerical errors and their impact in gravity field solutions. We demonstrate that processing with standard precision may be a limiting factor for taking full advantage of new generation sensors that future satellite missions will carry. Therefore we have created versions of our simulator with enhanced processing precision with primarily aim to minimize round-off system errors. Results using the enhanced precision show a big reduction of system errors that were present at the standard precision processing even for the error-free scenario, and reveal the improvements the new sensors will bring into the gravity field solutions. As a next step, we analyze the contribution of individual error sources to the system's error budget. More specifically we analyze sensor noise from the laser interferometer and the accelerometers, errors in the kinematic orbits and the background fields as well as temporal and spatial aliasing errors. We give special care on the assessment of error sources with stochastic behavior, such as the laser interferometer and the accelerometers, and their consistent stochastic modeling in frame of the adjustment process.

Mercury's lithospheric thickness and crustal density, as inferred from MESSENGER observations

NASA Astrophysics Data System (ADS)

James, P. B.; Mazarico, E.; Genova, A.; Smith, D. E.; Neumann, G. A.; Solomon, S. C.

2015-12-01

The gravity field and topography of Mercury measured by the MESSENGER spacecraft have provided insights into the thickness of the planet's elastic lithosphere, Te. We localized the HgM006 free-air gravity anomaly and gtmes_125v03 shape datasets to search for theoretical elastic thickness solutions that best fit a variety of localized coherence spectra between Bouguer gravity anomaly and topography. We adopted a crustal density of ρcrust =2700 kg m-3 for the Bouguer gravity correction, but density uncertainty did not markedly affect the elastic thickness estimates. A best-fit solution in the northern smooth plains (NSP) gives an elastic thickness of Te =30-60 km at the time of formation of topography for a range of ratios of top to bottom loading from 1 to 5. For a mechanical lithosphere with a thickness of ~2Te and a temperature of 1600 °C at the base, this solution is consistent with a geothermal gradient of 9-18 K km-1. A similar coherence analysis exterior to the NSP produces an elastic thickness estimate of Te =20-50 km, albeit with a poorer fit. Coherence in the northern hemisphere as a whole does not approach zero at any wavelength, because of the presence of variations in crustal thickness that are unassociated with elastic loading. The ratios and correlations of gravity and topography at intermediate wavelengths (harmonic degree l between 30 and 50) also constrain regional crustal densities. We localized gravity and topography with a moving Slepian taper and calculated regionally averaged crustal densities with the approximation ρcrust=Zl/(2πG), where Zl is the localized admittance and G is the gravitational constant. The only regional density estimates greater than 2000 kg m-3 for l=30 correspond to the NSP. Density estimates outside of the NSP were unreasonably low, even for highly porous crust. We attribute these low densities to the confounding effects of crustal thickness variations and Kaula filtering of the gravity dataset at the highest harmonic degrees, both of which tend to introduce a downward bias to crustal density estimation. An alternative analysis—which corrected for crustal thickness variability and was restricted to regions with gravity/topography coherence greater than 0.6—yielded an aggregate crustal density of ρcrust=2602 ± 470 kg m-3 for Mercury's high northern latitudes.

Forward modeling of gravity data using geostatistically generated subsurface density variations

USGS Publications Warehouse

Phelps, Geoffrey

2016-01-01

Using geostatistical models of density variations in the subsurface, constrained by geologic data, forward models of gravity anomalies can be generated by discretizing the subsurface and calculating the cumulative effect of each cell (pixel). The results of such stochastically generated forward gravity anomalies can be compared with the observed gravity anomalies to find density models that match the observed data. These models have an advantage over forward gravity anomalies generated using polygonal bodies of homogeneous density because generating numerous realizations explores a larger region of the solution space. The stochastic modeling can be thought of as dividing the forward model into two components: that due to the shape of each geologic unit and that due to the heterogeneous distribution of density within each geologic unit. The modeling demonstrates that the internally heterogeneous distribution of density within each geologic unit can contribute significantly to the resulting calculated forward gravity anomaly. Furthermore, the stochastic models match observed statistical properties of geologic units, the solution space is more broadly explored by producing a suite of successful models, and the likelihood of a particular conceptual geologic model can be compared. The Vaca Fault near Travis Air Force Base, California, can be successfully modeled as a normal or strike-slip fault, with the normal fault model being slightly more probable. It can also be modeled as a reverse fault, although this structural geologic configuration is highly unlikely given the realizations we explored.

Infinite derivative gravity: non-singular cosmology & blackhole solutions

NASA Astrophysics Data System (ADS)

Mazumdar, A.

Both Einstein’s theory of General Relativity and Newton’s theory of gravity possess a short distance and small time scale catastrophe. The blackhole singularity and cosmological Big Bang singularity problems highlight that current theories of gravity are incomplete description at early times and small distances. I will discuss how one can potentially resolve these fundamental problems at a classical level and quantum level. In particular, I will discuss infinite derivative theories of gravity, where gravitational interactions become weaker in the ultraviolet, and therefore resolving some of the classical singularities, such as Big Bang and Schwarzschild singularity for compact non-singular objects with mass up to 1025 grams. In this lecture, I will discuss quantum aspects of infinite derivative gravity and discuss few aspects which can make the theory asymptotically free in the UV.

Interplanetary Program to Optimize Simulated Trajectories (IPOST). Volume 1: User's guide

NASA Technical Reports Server (NTRS)

Hong, P. E.; Kent, P. D.; Olson, D. W.; Vallado, C. A.

1992-01-01

IPOST is intended to support many analysis phases, from early interplanetary feasibility studies through spacecraft development and operations. The IPOST output provides information for sizing and understanding mission impacts related to propulsion, guidance, communications, sensor/actuators, payload, and other dynamic and geometric environments. IPOST models three degree of freedom trajectory events, such as launch/ascent, orbital coast, propulsive maneuvering (impulsive and finite burn), gravity assist, and atmospheric entry. Trajectory propagation is performed using a choice of Cowell, Encke, Multiconic, Onestep, or Conic methods. The user identifies a desired sequence fo trajectory events, and selects which parameters are independent (controls) and dependent (targets), as well as other constraints and the coat function. Targeting and optimization is performed using the Stanford NPSOL algorithm. IPOST structure allows sub-problems within a master optimization problem to aid in the general constrained parameter optimization solution. An alternate optimization method uses implicit simulation and collocation techniques.

Interplanetary Program to Optimize Simulated Trajectories (IPOST). Volume 2: Analytic manual

NASA Technical Reports Server (NTRS)

Hong, P. E.; Kent, P. D.; Olson, D. W.; Vallado, C. A.

1992-01-01

The Interplanetary Program to Optimize Space Trajectories (IPOST) is intended to support many analysis phases, from early interplanetary feasibility studies through spacecraft development and operations. The IPOST output provides information for sizing and understanding mission impacts related to propulsion, guidance, communications, sensor/actuators, payload, and other dynamic and geometric environments. IPOST models three degree of freedom trajectory events, such as launch/ascent, orbital coast, propulsive maneuvering (impulsive and finite burn), gravity assist, and atmospheric entry. Trajectory propagation is performed using a choice of Cowell, Encke, Multiconic, Onestep, or Conic methods. The user identifies a desired sequence of trajectory events, and selects which parameters are independent (controls) and dependent (targets), as well as other constraints and the cost function. Targeting and optimization is performed using the Stanford NPSOL algorithm. IPOST structure allows subproblems within a master optimization problem to aid in the general constrained parameter optimization solution. An alternate optimization method uses implicit simulation and collocation techniques.

Orbit Determination and Navigation of the Solar Terrestrial Relations Observatory (STEREO)

NASA Technical Reports Server (NTRS)

Mesarch, Michael A.; Robertson, Mika; Ottenstein, Neil; Nicholson, Ann; Nicholson, Mark; Ward, Douglas T.; Cosgrove, Jennifer; German, Darla; Hendry, Stephen; Shaw, James

2007-01-01

This paper provides an overview of the required upgrades necessary for navigation of NASA's twin heliocentric science missions, Solar TErestrial RElations Observatory (STEREO) Ahead and Behind. The orbit determination of the STEREO spacecraft was provided by the NASA Goddard Space Flight Center's (GSFC) Flight Dynamics Facility (FDF) in support of the mission operations activities performed by the Johns Hopkins University Applied Physics Laboratory (APL). The changes to FDF's orbit determination software included modeling upgrades as well as modifications required to process the Deep Space Network X-band tracking data used for STEREO. Orbit results as well as comparisons to independently computed solutions are also included. The successful orbit determination support aided in maneuvering the STEREO spacecraft, launched on October 26, 2006 (00:52 Z), to target the lunar gravity assists required to place the spacecraft into their final heliocentric drift-away orbits where they are providing stereo imaging of the Sun.

Orbit Determination and Navigation of the Solar Terrestrial Relations Observatory (STEREO)

NASA Technical Reports Server (NTRS)

Mesarch, Michael; Robertson, Mika; Ottenstein, Neil; Nicholson, Ann; Nicholson, Mark; Ward, Douglas T.; Cosgrove, Jennifer; German, Darla; Hendry, Stephen; Shaw, James

2007-01-01

This paper provides an overview of the required upgrades necessary for navigation of NASA's twin heliocentric science missions, Solar TErestrial RElations Observatory (STEREO) Ahead and Behind. The orbit determination of the STEREO spacecraft was provided by the NASA Goddard Space Flight Center's (GSFC) Flight Dynamics Facility (FDF) in support of the mission operations activities performed by the Johns Hopkins University Applied Physics Laboratory (APL). The changes to FDF s orbit determination software included modeling upgrades as well as modifications required to process the Deep Space Network X-band tracking data used for STEREO. Orbit results as well as comparisons to independently computed solutions are also included. The successful orbit determination support aided in maneuvering the STEREO spacecraft, launched on October 26, 2006 (00:52 Z), to target the lunar gravity assists required to place the spacecraft into their final heliocentric drift-away orbits where they are providing stereo imaging of the Sun.

Evaluation of rapid readout biological indicators for 132 degrees C gravity and 132 degrees C vacuum-assisted steam sterilization cycles using a new automated fluorescent reader.

PubMed

Alfa, Michelle J; Olson, Nancy; DeGagne, Pat; Jackson, Michele

2002-07-01

The primary objective of this study was to evaluate fluorescent readout results of Attest 1291 Biological Indicators (BIs) (3M Health Care, St. Paul, MN) and Attest 1296 BI test packs (containing Attest 1292 BIs) using full and fractional cycles compared with the growth data when prolonged incubation (7 days) was included. Gravity displacement and vacuum-assisted steam sterilization cycles were evaluated. A secondary objective of this study was to evaluate the new automated rapid fluorescent reader (Attest 290 Auto Reader). The rapid readout BIs for gravity displacement and vacuum-assisted steam autoclave cycles at 132 degrees C were processed using full (4 minutes) and four fractional cycles that provided 30% to 80% positive results for growth after 24 hours of incubation (48 hours of incubation for Attest 1292 BIs from the Attest 1296 test packs). Sixty of each type of BI were tested for each cycle (300 of each BI type in total). For all full steam sterilization cycles, results of the rapid fluorescent readout and the 24-hour, 48-hour, and 7-day growth tests were negative for all Attest 1291 and 1292 BIs tested. For all fractional cycles, the 24- and 48-hour growth results for the Attest 1291 and 1292 BIs, respectively, were the same as the 7-day growth results. The fractional cycle data indicated that fluorescent rapid readout was a more sensitive indicator than growth. There were rare (0.9%) false-negative results for BIs under fractional cycle conditions and these all correlated with short fractional cycle exposure times. The fluorescent rapid readout results of the 1291 BIs and 1296 BI test packs reliably predict both 24- and 48-hour and 7-day growth. These data support the value of rapid readout BIs for sterilizer monitoring for both the vacuum-assisted and the gravity displacement steam sterilization cycles. The new automated reader requires less manipulation of the BI and makes monitoring user friendly and less prone to user errors.

Coherent states, quantum gravity, and the Born-Oppenheimer approximation. I. General considerations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stottmeister, Alexander, E-mail: alexander.stottmeister@gravity.fau.de; Thiemann, Thomas, E-mail: thomas.thiemann@gravity.fau.de

2016-06-15

This article, as the first of three, aims at establishing the (time-dependent) Born-Oppenheimer approximation, in the sense of space adiabatic perturbation theory, for quantum systems constructed by techniques of the loop quantum gravity framework, especially the canonical formulation of the latter. The analysis presented here fits into a rather general framework and offers a solution to the problem of applying the usual Born-Oppenheimer ansatz for molecular (or structurally analogous) systems to more general quantum systems (e.g., spin-orbit models) by means of space adiabatic perturbation theory. The proposed solution is applied to a simple, finite dimensional model of interacting spin systems,more » which serves as a non-trivial, minimal model of the aforesaid problem. Furthermore, it is explained how the content of this article and its companion affect the possible extraction of quantum field theory on curved spacetime from loop quantum gravity (including matter fields).« less

Horizon fluffs: In the context of generalized minimal massive gravity

NASA Astrophysics Data System (ADS)

Setare, Mohammad Reza; Adami, Hamed

2018-02-01

We consider a metric which describes Bañados geometries and show that the considered metric is a solution of the generalized minimal massive gravity (GMMG) model. We consider the Killing vector field which preserves the form of the considered metric. Using the off-shell quasi-local approach we obtain the asymptotic conserved charges of the given solution. Similar to the Einstein gravity in the presence of negative cosmological constant, for the GMMG model, we also show that the algebra among the asymptotic conserved charges is isomorphic to two copies of the Virasoro algebra. Eventually, we find a relation between the algebra of the near-horizon and the asymptotic conserved charges. This relation shows that the main part of the horizon fluffs proposed by Afshar et al., Sheikh-Jabbari and Yavartanoo appear for generic black holes in the class of Bañados geometries in the context of the GMMG model.

No hair theorem in quasi-dilaton massive gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, De-Jun; Zhou, Shuang-Yong

We investigate the static, spherically symmetric black hole solutions in the quasi-dilaton model and its generalizations, which are scalar extended dRGT massive gravity with a shift symmetry. We show that, unlike generic scalar extended massive gravity models, these theories do not admit static, spherically symmetric black hole solutions until the theory parameters in the dRGT potential are fine-tuned. When fine-tuned, the geometry of the static, spherically symmetric black hole is necessarily that of general relativity and the quasi-dilaton field is constant across the spacetime. The fine-tuning and the no hair theorem apply to black holes with flat, anti-de Sitter ormore » de Sitter asymptotics. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).« less

Transport phenomena of growth-in-gel zeolite crystallization in microgravity

NASA Technical Reports Server (NTRS)

Zhang, H.; Ostrach, S.; Kamotani, Y.

1993-01-01

Secondary nucleation (SN) due to crystal sedimentation has been believed to be one of the major effects that causes smaller sizes of final zeolite crystals. The present investigation indicates that, in a reactor, this gravity-induced SN occurs only within a white opaque column termed the gel portion. Under normal gravity this portion shrinks to the bottom of the hydrothermal reactor, leaving a clear portion of solution at the top, due to depletion of the flocculated gel particles. Solution phase nucleation and crystallization is assumed and a correlation for the shrinkage is therefore derived, which shows good agreement with experimental observations. A non-dimensional parameter is suggested as a criterion for the occurrence of SN. Based on the parameter whether or not microgravity is beneficial to zeolite growth is discussed. Also, the growth mechanism and the transport phenomena in the absence of gravity are discussed.

Shadows, signals, and stability in Einsteinian cubic gravity

NASA Astrophysics Data System (ADS)

Hennigar, Robie A.; Jahani Poshteh, Mohammad Bagher; Mann, Robert B.

2018-03-01

We conduct a preliminary investigation into the phenomenological implications of Einsteinian cubic gravity (ECG), a four-dimensional theory of gravity cubic in curvature of interest for its unique formulation and properties. We find an analytic approximation for a spherically symmetric black hole solution to this theory using a continued fraction ansatz. This approximate solution is valid everywhere outside of the horizon and we use it to study the orbit of massive test bodies near a black hole, specifically computing the innermost stable circular orbit. We compute constraints on the ECG coupling parameter imposed by Shapiro time delay. We then compute the shadow of an ECG black hole and find it to be larger than its Einsteinian counterpart in general relativity for the same value of the mass. Applying our results to Sgr A*, we find that departures from general relativity are small but in principle distinguishable.

Extrema of mass, first law of black hole mechanics, and a staticity theorem in Einstein-Maxwell-axion-dilaton gravity

NASA Astrophysics Data System (ADS)

Rogatko, Marek

1998-08-01

Using the ADM formulation of the Einstein-Maxwell axion-dilaton gravity we derive the formulas for the variation of mass and other asymptotic conserved quantities in the theory under consideration. Generalizing this kind of reasoning to the initial data for the manifold with an interior boundary we get the generalized first law of black hole mechanics. We consider an asymptotically flat solution to the Einstein-Maxwell axion-dilaton gravity describing a black hole with a Killing vector field timelike at infinity, the horizon of which comprises a bifurcate Killing horizon with a bifurcate surface. Supposing that the Killing vector field is asymptotically orthogonal to the static hypersurface with boundary S and a compact interior, we find that the solution is static in the exterior world, when the timelike vector field is normal to the horizon and has vanishing electric and axion-electric fields on static slices.

No hair theorem in quasi-dilaton massive gravity

DOE PAGES

Wu, De-Jun; Zhou, Shuang-Yong

2016-04-11

We investigate the static, spherically symmetric black hole solutions in the quasi-dilaton model and its generalizations, which are scalar extended dRGT massive gravity with a shift symmetry. We show that, unlike generic scalar extended massive gravity models, these theories do not admit static, spherically symmetric black hole solutions until the theory parameters in the dRGT potential are fine-tuned. When fine-tuned, the geometry of the static, spherically symmetric black hole is necessarily that of general relativity and the quasi-dilaton field is constant across the spacetime. The fine-tuning and the no hair theorem apply to black holes with flat, anti-de Sitter ormore » de Sitter asymptotics. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).« less

Utilization of Low Gravity Environment for Measuring Liquid Viscosity

NASA Technical Reports Server (NTRS)

Antar, Basil N.; Ethridge, Edwin

1998-01-01

The method of drop coalescence is used for determining the viscosity of highly viscous undercooled liquids. Low gravity environment is necessary in order to allow for examining large volumes affording much higher accuracy for the viscosity calculations than possible for smaller volumes available under 1 - g conditions. The drop coalescence method is preferred over the drop oscillation technique since the latter method can only be applied for liquids with vanishingly small viscosities. The technique developed relies on both the highly accurate solution of the Navier-Stokes equations as well as on data from experiments conducted in near zero gravity environment. Results are presented for method validation experiments recently performed on board the NASA/KC-135 aircraft. While the numerical solution was produced using the Boundary Element Method. In these tests the viscosity of a highly viscous liquid, glycerine at room temperature, was determined using the liquid coalescence method. The results from these experiments will be discussed.

The IfE Global Gravity Field Model Recovered from GOCE Orbit and Gradiometer Data

NASA Astrophysics Data System (ADS)

Wu, Hu; Muiller, Jurgen; Brieden, Phillip

2015-03-01

An independent global gravity field model is computed from the GOCE orbit and gradiometer data using our own IfE software. We analysed the same data period that were considered for the first released GOCE models. The Acceleration Approach is applied to process the orbit data. The gravity gradients are processed in the framework of the remove-restore technique by which the low-frequency noise of the original gradients are removed. For the combined solution, the normal equations are summed by the Variance Component Estimation Approach. The result in terms of accumulated geoid height error calculated from the coefficient difference w.r.t. EGM2008 is about 11 cm at D/O 200, which corresponds to the accuracy level of the first released TIM and DIR solutions. This indicates that our IfE model has a comparable performance as the other official GOCE models.

Unified theory of nonlinear electrodynamics and gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Torres-Gomez, Alexander; Krasnov, Kirill; Scarinci, Carlos

2011-01-15

We describe a class of unified theories of electromagnetism and gravity. The Lagrangian is of the BF type, with a potential for the B field, the gauge group is U(2) (complexified). Given a choice of the potential function the theory is a deformation of (complex) general relativity and electromagnetism, and describes just two propagating polarizations of the graviton and two of the photon. When gravity is switched off the theory becomes the usual nonlinear electrodynamics with a general structure function. The Einstein-Maxwell theory can be recovered by sending some of the parameters of the defining potential to zero, but formore » any generic choice of the potential the theory is indistinguishable from Einstein-Maxwell at low energies. A real theory is obtained by imposing suitable reality conditions. We also study the spherically-symmetric solution and show how the usual Reissner-Nordstrom solution is recovered.« less

The Kadomtsev-Petviashvili equation under rapid forcing

NASA Astrophysics Data System (ADS)

Moroz, Irene M.

1997-06-01

We consider the initial value problem for the forced Kadomtsev-Petviashvili equation (KP) when the forcing is assumed to be fast compared to the evolution of the unforced equation. This suggests the introduction of two time scales. Solutions to the forced KP are sought by expanding the dependent variable in powers of a small parameter, which is inversely related to the forcing time scale. The unforced system describes weakly nonlinear, weakly dispersive, weakly two-dimensional wave propagation and is studied in two forms, depending upon whether gravity dominates surface tension or vice versa. We focus on the effect that the forcing has on the one-lump solution to the KPI equation (where surface tension dominates) and on the one- and two-line soliton solutions to the KPII equation (when gravity dominates). Solutions to second order in the expansion are computed analytically for some specific choices of the forcing function, which are related to the choice of initial data.

Topologically massive gravity and Ricci-Cotton flow

NASA Astrophysics Data System (ADS)

Lashkari, Nima; Maloney, Alexander

2011-05-01

We consider topologically massive gravity (TMG), which is three-dimensional general relativity with a cosmological constant and a gravitational Chern-Simons term. When the cosmological constant is negative the theory has two potential vacuum solutions: anti-de Sitter space and warped anti-de Sitter space. The theory also contains a massive graviton state which renders these solutions unstable for certain values of the parameters and boundary conditions. We study the decay of these solutions due to the condensation of the massive graviton mode using Ricci-Cotton flow, which is the appropriate generalization of Ricci flow to TMG. When the Chern-Simons coupling is small the AdS solution flows to warped AdS by the condensation of the massive graviton mode. When the coupling is large the situation is reversed, and warped AdS flows to AdS. Minisuperspace models are constructed where these flows are studied explicitly.

Generalized teleparallel cosmology and initial singularity crossing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Awad, Adel; Nashed, Gamal, E-mail: Adel.Awad@bue.edu.eg, E-mail: gglnashed@sci.asu.edu.eg

We present a class of cosmological solutions for a generalized teleparallel gravity with f ( T )= T +α̃ (− T ) {sup n} , where α̃ is some parameter and n is an integer or half-integer. Choosing α̃ ∼ G {sup n} {sup −1}, where G is the gravitational constant, and working with an equation of state p = w ρ, one obtains a cosmological solution with multiple branches. The dynamics of the solution describes standard cosmology at late times, but the higher-torsion correction changes the nature of the initial singularity from big bang to a sudden singularity. Themore » milder behavior of the sudden singularity enables us to extend timelike or lightlike curves, through joining two disconnected branches of solution at the singularity, leaving the singularity traversable. We show that this extension is consistent with the field equations through checking the known junction conditions for generalized teleparallel gravity. This suggests that these solutions describe a contracting phase a prior to the expanding phase of the universe.« less

[Spread of spinal anesthesia with 3 different hyperbaric solutions used in Japan].

PubMed

Masuda, R; Yokoyama, K; Inoue, T

1998-12-01

We studied the spread of spinal anesthesia with 3 different hyperbaric solutions commercially available in Japan. Percamin-S [0.3% dibucaine in 5% hyperbaric saline] (P), Neo-Percamin.S [0.24% dibucaine with 0.12% T-caine in 9.5% glucose] (N) and 0.5% Tetcaine [tetracaine] in 10% glucose (T) were studied. Two ml of each solution was administered intrathecally using a 25 gauge Quincke needle. Patients (n = 90) were allocated to one of 9 groups receiving 2 ml of P, N or T at L 2-3, L 3-4 or L 4-5 interspace. Both N and T produced significantly higher spread of analgesia than P at any of L 3-4 and L 4-5 interspaces. P and N have the same specific gravity, even though significant differences were found in spread of segmental analgesia. Local anesthesic agents and solvent solutions themselves are considered to influence the spread of spinal anesthesia as the specific gravity of hyperbaric solution does.

49 CFR 178.965 - Drop test.

Code of Federal Regulations, 2012 CFR

2012-10-01

.... Water/anti-freeze solutions with a minimum specific gravity of 0.95 for testing at −18 °C (0 °F) or... of 0.45 cubic meters (15.9 cubic feet) or less must be subject to an additional drop test. (e) Drop... having essentially the same physical characteristics. (3) The specific gravity and viscosity of a...

49 CFR 178.965 - Drop test.

Code of Federal Regulations, 2014 CFR

2014-10-01

.... Water/anti-freeze solutions with a minimum specific gravity of 0.95 for testing at −18 °C (0 °F) or... of 0.45 cubic meters (15.9 cubic feet) or less must be subject to an additional drop test. (e) Drop... having essentially the same physical characteristics. (3) The specific gravity and viscosity of a...

49 CFR 178.810 - Drop test.

Code of Federal Regulations, 2012 CFR

2012-10-01

... solutions with a minimum specific gravity of 0.95 for testing at −18 °C (0 °F) or lower are considered... with a capacity of 0.45 cubic meters (15.9 cubic feet) or less must be subject to an additional drop... material having essentially the same physical characteristics. (3) The specific gravity and viscosity of a...

49 CFR 178.810 - Drop test.

Code of Federal Regulations, 2011 CFR

2011-10-01

... solutions with a minimum specific gravity of 0.95 for testing at −18 °C (0 °F) or lower are considered... with a capacity of 0.45 cubic meters (15.9 cubic feet) or less must be subject to an additional drop... material having essentially the same physical characteristics. (3) The specific gravity and viscosity of a...

49 CFR 178.965 - Drop test.

Code of Federal Regulations, 2011 CFR

2011-10-01

.... Water/anti-freeze solutions with a minimum specific gravity of 0.95 for testing at −18 °C (0 °F) or... of 0.45 cubic meters (15.9 cubic feet) or less must be subject to an additional drop test. (e) Drop... having essentially the same physical characteristics. (3) The specific gravity and viscosity of a...

49 CFR 178.810 - Drop test.

Code of Federal Regulations, 2014 CFR

2014-10-01

... solutions with a minimum specific gravity of 0.95 for testing at −18 °C (0 °F) or lower are considered... with a capacity of 0.45 cubic meters (15.9 cubic feet) or less must be subject to an additional drop... material having essentially the same physical characteristics. (3) The specific gravity and viscosity of a...

What have we gained from GOCE, and what is still to be expected?

NASA Astrophysics Data System (ADS)

Pail, R.; Fecher, T.; Mayer-Gürr, T.; Rieser, D.; Schuh, W. D.; Brockmann, J. M.; Jäggi, A.; Höck, E.

2012-04-01

So far three releases of GOCE-only gravity field models applying the time-wise method have been computed in the frame of the ESA project "GOCE High-Level Processing Facility". They have been complemented by satellite-only combination models generated by the GOCO ("Gravity Observation Combination") consortium. Due to the fact that the processing strategy has remained practically unchanged for all releases, the continuous improvement by including more and more GOCE data can be analyzed. One of the basic features of the time-wise gravity field models (GOCE_TIM) is the fact, that no gravity field prior information is used, neither as reference model nor for constraining the solution. Therefore, the gain of knowledge on the Earth's gravity field derived purely from the GOCE mission can be evaluated. The idea of the complementary GOCO models is to improve the long to medium wavelengths of the gravity field solutions, which are rather weakly defined by GOCE orbit information, by inclusion of additional data from satellite sources such as GRACE, CHAMP and SLR, taking benefit from the individual strengths and favourable features of the individual data types. In this contribution, we will review which impact GOCE has achieved so far on global and regional gravity field modelling. Besides the gravity field modelling itself, the contributions of GOCE to several application fields, such as the computation of geodetic mean dynamic topography (MDT), and also for geophysical modelling of the lithosphere, will be highlighted. Special emphasis shall be given to the discussion to what extent the full variance-covariance information, representing very realistic error estimates of the gravity field accuracy, can be utilized. Finally, also a GOCE performance prediction shall be given. After the end of the extended mission phase by December 2012, currently several mission scenarios are discussed, such as either extending the mission period further as long as possible at the same altitude, or lowering the satellite by 10-20 km for a shorter period. Based on numerical simulation studies the pros and cons of several scenarios regarding the achievable gravity field accuracy shall be evaluated and quantified.

Electrochemical energy storage by polyaniline nanofibers: high gravity assisted oxidative polymerization vs. rapid mixing chemical oxidative polymerization.

PubMed

Zhao, Yibo; Wei, Huige; Arowo, Moses; Yan, Xingru; Wu, Wei; Chen, Jianfeng; Wang, Yiran; Guo, Zhanhu

2015-01-14

Polyaniline (PANI) nanofibers prepared by high gravity chemical oxidative polymerization in a rotating packed bed (RPB) have demonstrated a much higher specific capacitance of 667.6 F g(-1) than 375.9 F g(-1) of the nanofibers produced by a stirred tank reactor (STR) at a gravimetric current of 10 A g(-1). Meanwhile, the cycling stability of the electrode is 62.2 and 65.9% for the nanofibers from RPB and STR after 500 cycles, respectively.

Gravity controlled anti-reverse rotation device

DOEpatents

Dickinson, Robert J.; Wetherill, Todd M.

1983-01-01

A gravity assisted anti-reverse rotation device for preventing reverse rotation of pumps and the like. A horizontally mounted pawl is disposed to mesh with a fixed ratchet preventing reverse rotation when the pawl is advanced into intercourse with the ratchet by a vertically mounted lever having a lumped mass. Gravitation action on the lumped mass urges the pawl into mesh with the ratchet, while centrifugal force on the lumped mass during forward, allowed rotation retracts the pawl away from the ratchet.

GOCE Precise Science Orbits for the Entire Mission and their Use for Gravity Field Recovery

NASA Astrophysics Data System (ADS)

Jäggi, Adrian; Bock, Heike; Meyer, Ulrich; Weigelt, Matthias

The Gravity field and steady-state Ocean Circulation Explorer (GOCE), ESA's first Earth Explorer Core Mission, was launched on March 17, 2009 into a sun-synchronous dusk-dawn orbit and re-entered into the Earth's atmosphere on November 11, 2013. It was equipped with a three-axis gravity gradiometer for high-resolution recovery of the Earth's gravity field, as well as with a 12-channel, dual-frequency Global Positioning System (GPS) receiver for precise orbit determination (POD), instrument time-tagging, and the determination of the long wavelength part of the Earth’s gravity field. A precise science orbit (PSO) product was provided during the entire mission by the GOCE High-level Processing Facility (HPF) from the GPS high-low Satellite-to-Satellite Tracking (hl-SST) data. We present the reduced-dynamic and kinematic PSO results for the entire mission period. Orbit comparisons and validations with independent Satellite Laser Ranging (SLR) measurements demonstrate the high quality of both orbit products being close to 2 cm 1-D RMS, but also reveal a correlation between solar activity, GPS data availability, and the quality of the orbits. We use the 1-sec kinematic positions of the GOCE PSO product for gravity field determination and present GPS-only solutions covering the entire mission period. The generated gravity field solutions reveal severe systematic errors centered along the geomagnetic equator, which may be traced back to the GPS carrier phase observations used for the kinematic orbit determination. The nature of the systematic errors is further investigated and reprocessed orbits free of systematic errors along the geomagnetic equator are derived. Eventually, the potential of recovering time variable signals from GOCE kinematic positions is assessed.

First independent lunar gravity field solution in the framework of project GRAZIL

NASA Astrophysics Data System (ADS)

Wirnsberger, Harald; Krauss, Sandro; Klinger, Beate; Mayer-Gürr, Torsten

2017-04-01

The twin satellite mission Gravity Recovery and Interior Laboratory (GRAIL) aims to recovering the lunar gravity field by means of intersatellite Ka-band ranging (KBR) observations. In order to exploit the potential of KBR data, absolute position information of the two probes is required. Hitherto, the Graz lunar gravity field models (GrazLGM) relies on the official orbit products provided by NASA. In this contribution, we present for the first time a completely independent Graz lunar gravity field model to spherical harmonic degree and order 420. The reduced dynamic orbits of the two probes are determined using variational equations following a batch least squares differential adjustment process. These orbits are based on S-band radiometric tracking data collected by the Deep Space Network and are used for the independent GRAIL gravity field recovery. To reveal a highly accurate lunar gravity field, an integral equation approach using short orbital arcs is adopted to process the KBR data. A comparison to state-of-the-art lunar gravity models computed at NASA-GSFC, NASA-JPL and AIUB demonstrate the progress of Graz lunar gravity field models derived within the project GRAZIL.

Reconstruction from scalar-tensor theory and the inhomogeneous equation of state in f( T) gravity

NASA Astrophysics Data System (ADS)

Said, Jackson Levi

2017-12-01

General relativity (GR) characterizes gravity as a geometric properly exhibited as curvature on spacetime. Teleparallelism describes gravity through torsional properties, and can reproduce GR at the level of equations. Similar to f( R) gravity, on taking a generalization, f( T) gravity can produce various modifications its gravitational mechanism. The resulting field equations are inherently distinct to f( R) gravity in that they are second order. In the present work, f( T) gravity is examined in the cosmological context with a number of solutions reconstructed by means of an auxiliary scalar field. To do this, various forms of the Hubble parameter are considered with an f( T) Lagrangian emerging for each instance. In addition, the inhomogeneous equation of state (EoS) is investigated with a particular Hubble parameter model used to show how this can be used to reconstruct the f( T) Lagrangian. Observationally, the auxiliary scalar field and the exotic terms in the FRW field equations give the same results, meaning that the variation in the Hubble parameter may be interpreted as the need to reformulate gravity in some way, as in f( T) gravity.

Analytical Study of Gravity Effects on Laminar Diffusion Flames

NASA Technical Reports Server (NTRS)

Edelman, R. B.; Fortune, O.; Weilerstein, G.

1972-01-01

A mathematical model is presented for the description of axisymmetric laminar-jet diffusion flames. The analysis includes the effects of inertia, viscosity, diffusion, gravity and combustion. These mechanisms are coupled in a boundary layer type formulation and solutions are obtained by an explicit finite difference technique. A dimensional analysis shows that the maximum flame width radius, velocity and thermodynamic state characterize the flame structure. Comparisons with experimental data showed excellent agreement for normal gravity flames and fair agreement for steady state low Reynolds number zero gravity flames. Kinetics effects and radiation are shown to be the primary mechanisms responsible for this discrepancy. Additional factors are discussed including elipticity and transient effects.

Superbounce and loop quantum ekpyrotic cosmologies from modified gravity: F(R) , F(G) and F(T) theories

NASA Astrophysics Data System (ADS)

Odintsov, S. D.; Oikonomou, V. K.; Saridakis, Emmanuel N.

2015-12-01

We investigate the realization of two bouncing paradigms, namely of the superbounce and the loop quantum cosmological ekpyrosis, in the framework of various modified gravities. In particular, we focus on the F(R) , F(G) and F(T) gravities, and we reconstruct their specific subclasses which lead to such universe evolutions. These subclasses constitute from power laws, polynomials, or hypergeometric ansatzes, which can be approximated by power laws. The qualitative similarity of the different effective gravities which realize the above two bouncing cosmologies, indicates that a universality might be lying behind the bounce. Finally, performing a linear perturbation analysis, we show that the obtained solutions are conditionally or fully stable.

Quantum solitonic wave-packet of a meso-scopic system in singularity free gravity

NASA Astrophysics Data System (ADS)

Buoninfante, Luca; Lambiase, Gaetano; Mazumdar, Anupam

2018-06-01

In this paper we will discuss how to localise a quantum wave-packet due to self-gravitating meso-scopic object by taking into account gravitational self-interaction in the Schrödinger equation beyond General Relativity. In particular, we will study soliton-like solutions in infinite derivative ghost free theories of gravity, which resolves the gravitational 1 / r singularity in the potential. We will show a unique feature that the quantum spread of such a gravitational system is larger than that of the Newtonian gravity, therefore enabling us a window of opportunity to test classical and quantum properties of such theories of gravity in the near future at a table-top experiment.

An improved GRACE monthly gravity field solution by modeling the non-conservative acceleration and attitude observation errors

NASA Astrophysics Data System (ADS)

Chen, Qiujie; Shen, Yunzhong; Chen, Wu; Zhang, Xingfu; Hsu, Houze

2016-06-01

The main contribution of this study is to improve the GRACE gravity field solution by taking errors of non-conservative acceleration and attitude observations into account. Unlike previous studies, the errors of the attitude and non-conservative acceleration data, and gravity field parameters, as well as accelerometer biases are estimated by means of weighted least squares adjustment. Then we compute a new time series of monthly gravity field models complete to degree and order 60 covering the period Jan. 2003 to Dec. 2012 from the twin GRACE satellites' data. The derived GRACE solution (called Tongji-GRACE02) is compared in terms of geoid degree variances and temporal mass changes with the other GRACE solutions, namely CSR RL05, GFZ RL05a, and JPL RL05. The results show that (1) the global mass signals of Tongji-GRACE02 are generally consistent with those of CSR RL05, GFZ RL05a, and JPL RL05; (2) compared to CSR RL05, the noise of Tongji-GRACE02 is reduced by about 21 % over ocean when only using 300 km Gaussian smoothing, and 60 % or more over deserts (Australia, Kalahari, Karakum and Thar) without using Gaussian smoothing and decorrelation filtering; and (3) for all examples, the noise reductions are more significant than signal reductions, no matter whether smoothing and filtering are applied or not. The comparison with GLDAS data supports that the signals of Tongji-GRACE02 over St. Lawrence River basin are close to those from CSR RL05, GFZ RL05a and JPL RL05, while the GLDAS result shows the best agreement with the Tongji-GRACE02 result.

Rapid Design of Gravity Assist Trajectories

NASA Technical Reports Server (NTRS)

Carrico, J.; Hooper, H. L.; Roszman, L.; Gramling, C.

1991-01-01

Several International Solar Terrestrial Physics (ISTP) missions require the design of complex gravity assisted trajectories in order to investigate the interaction of the solar wind with the Earth's magnetic field. These trajectories present a formidable trajectory design and optimization problem. The philosophy and methodology that enable an analyst to design and analyse such trajectories are discussed. The so called 'floating end point' targeting, which allows the inherently nonlinear multiple body problem to be solved with simple linear techniques, is described. The combination of floating end point targeting with analytic approximations with a Newton method targeter to achieve trajectory design goals quickly, even for the very sensitive double lunar swingby trajectories used by the ISTP missions, is demonstrated. A multiconic orbit integration scheme allows fast and accurate orbit propagation. A prototype software tool, Swingby, built for trajectory design and launch window analysis, is described.

An adaptive filter method for spacecraft using gravity assist

NASA Astrophysics Data System (ADS)

Ning, Xiaolin; Huang, Panpan; Fang, Jiancheng; Liu, Gang; Ge, Shuzhi Sam

2015-04-01

Celestial navigation (CeleNav) has been successfully used during gravity assist (GA) flyby for orbit determination in many deep space missions. Due to spacecraft attitude errors, ephemeris errors, the camera center-finding bias, and the frequency of the images before and after the GA flyby, the statistics of measurement noise cannot be accurately determined, and yet have time-varying characteristics, which may introduce large estimation error and even cause filter divergence. In this paper, an unscented Kalman filter (UKF) with adaptive measurement noise covariance, called ARUKF, is proposed to deal with this problem. ARUKF scales the measurement noise covariance according to the changes in innovation and residual sequences. Simulations demonstrate that ARUKF is robust to the inaccurate initial measurement noise covariance matrix and time-varying measurement noise. The impact factors in the ARUKF are also investigated.

Some Mechanical and Ballistic Properties of Titanium and Titanium Alloys

DTIC Science & Technology

1950-03-07

treated alloy steel armor, Justifies high expectations that titanium alloys may make excellent armor meterials . The corrosion resistant properties of...Fur* Metal Beat Treated -7-4 - -I-re Tensile Strength in pot 13,000 5 0,oo 230,000 203400 speifict Gravity 2.71 7.87 4.54 2.9 7.9 4.6 Stroe4cth-Vleight...solution of HCI: 50 parts by volume ECl-specific gravity 1.19 (37.6%) 50 parts by volume H2 0 2. Concentrated RIP: Hl-specific gravity 1.15 (14%) 3. 5

Causality and a -theorem constraints on Ricci polynomial and Riemann cubic gravities

NASA Astrophysics Data System (ADS)

Li, Yue-Zhou; Lü, H.; Wu, Jun-Bao

2018-01-01

In this paper, we study Einstein gravity extended with Ricci polynomials and derive the constraints on the coupling constants from the considerations of being ghost-free, exhibiting an a -theorem and maintaining causality. The salient feature is that Einstein metrics with appropriate effective cosmological constants continue to be solutions with the inclusion of such Ricci polynomials and the causality constraint is automatically satisfied. The ghost-free and a -theorem conditions can only be both met starting at the quartic order. We also study these constraints on general Riemann cubic gravities.

Dilution refrigeration for space applications

NASA Technical Reports Server (NTRS)

Israelsson, U. E.; Petrac, D.

1990-01-01

Dilution refrigerators are presently used routinely in ground based applications where temperatures below 0.3 K are required. The operation of a conventional dilution refrigerator depends critically on the presence of gravity. To operate a dilution refrigerator in space many technical difficulties must be overcome. Some of the anticipated difficulties are identified in this paper and possible solutions are described. A single cycle refrigerator is described conceptually that uses forces other than gravity to function and the stringent constraints imposed on the design by requiring the refrigerator to function on the earth without using gravity are elaborated upon.

Do massive compact objects without event horizon exist in infinite derivative gravity?

NASA Astrophysics Data System (ADS)

Koshelev, Alexey S.; Mazumdar, Anupam

2017-10-01

Einstein's general theory of relativity is plagued by cosmological and black-hole type singularities Recently, it has been shown that infinite derivative, ghost free, gravity can yield nonsingular cosmological and mini-black hole solutions. In particular, the theory possesses a mass-gap determined by the scale of new physics. This paper provides a plausible argument, not a no-go theorem, based on the Area-law of gravitational entropy that within infinite derivative, ghost free, gravity nonsingular compact objects in the static limit need not have horizons.

Benefits of Objective Collapse Models for Cosmology and Quantum Gravity

NASA Astrophysics Data System (ADS)

Okon, Elias; Sudarsky, Daniel

2014-02-01

We display a number of advantages of objective collapse theories for the resolution of long-standing problems in cosmology and quantum gravity. In particular, we examine applications of objective reduction models to three important issues: the origin of the seeds of cosmic structure, the problem of time in quantum gravity and the information loss paradox; we show how reduction models contain the necessary tools to provide solutions for these issues. We wrap up with an adventurous proposal, which relates the spontaneous collapse events of objective collapse models to microscopic virtual black holes.

Design and optimization of interplanetary spacecraft trajectories

NASA Astrophysics Data System (ADS)

McConaghy, Thomas Troy

Scientists involved in space exploration are always looking for ways to accomplish more with their limited budgets. Mission designers can decrease operational costs by crafting trajectories with low launch costs, short time-of-flight, or low propellant requirements. Gravity-assist maneuvers and low-thrust, high-efficiency ion propulsion can be of great help. This dissertation describes advances in methods to design and optimize interplanetary spacecraft trajectories. particularly for missions using gravity-assist maneuvers or low-thrust engines (or both). The first part of this dissertation describes a new, efficient, two-step methodology to design and optimize low-thrust gravity-assist trajectories. Models for the launch vehicle, solar arrays, and engines are introduced and several examples of optimized trajectories are presented. For example, a 3.7-year Earth-Venus-Earth-Mars-Jupiter flyby trajectory with maximized final mass is described. The way that the parameterization of the optimization problem affects convergence speed and reliability is also investigated. The choice of coordinate system is shown to make a significant difference. The second part of this dissertation describes a way to construct Earth-Mars cycler trajectories---periodic orbits that repeatedly encounter Earth and Mars, yet require little or no propellant. We find that well-known cyclers, such as the Aldrin cycler, are special cases of a much larger family of cyclers. In fact, so many new cyclers are found that a comprehensive naming system (nomenclature) is proposed. One particularly promising new cycler, the "ballistic S1L1 cycler" is analyzed in greater detail.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Serpa, L.F.; Cook, K.L.

Aeromagnetic and gravity surveys were conducted during 1978 in the Black Rock Desert, Utah over an area of about 2400 km/sup 2/ between the north-trending Pavant and Cricket Mountains. The surveys assisted in evaluating the geothermal resources in the Meadow-Hatton Known Geothermal Resource Area (KGRA) and vicinity by delineating geophysical characteristics of the subsurface. The gravity measurements from approximately 700 new stations were reduced to complete Bouguer gravity anomaly values with the aid of a computerized terrain-correction program and contoured at an interval of 1 milligal. The aeromagnetic survey was drape flown at an altitude of 305 m (1000 ft)more » and a total intensity residual aeromagnetic map with a contour interval of 20 gammas was produced. Two gravity and aeromagnetic east-west profiles and one north-south profile were modeled using a simultaneous 2 1/2-dimensional modeling technique to provide a single model satisfying both types of geophysical data.« less

Exploring the Tomlin-Varadarajan quantum constraints in U (1 )3 loop quantum gravity: Solutions and the Minkowski theorem

NASA Astrophysics Data System (ADS)

Lewandowski, Jerzy; Lin, Chun-Yen

2017-03-01

We explicitly solved the anomaly-free quantum constraints proposed by Tomlin and Varadarajan for the weak Euclidean model of canonical loop quantum gravity, in a large subspace of the model's kinematic Hilbert space, which is the space of the charge network states. In doing so, we first identified the subspace on which each of the constraints acts convergingly, and then by explicitly evaluating such actions we found the complete set of the solutions in the identified subspace. We showed that the space of solutions consists of two classes of states, with the first class having a property that involves the condition known from the Minkowski theorem on polyhedra, and the second class satisfying a weaker form of the spatial diffeomorphism invariance.

Monitoring And Controlling Hydroponic Flow

NASA Technical Reports Server (NTRS)

Dreschel, Thomas W.

1992-01-01

Pressure-monitoring and -controlling apparatus maintains slight suction required on nutrient solution in apparatus described in "Tubular Membrane Plant-Growth Unit" (KSC-11375), while overcoming gravity effects on operation of system on Earth. Suction helps to hold solution in tubular membrane.

Reduction of Effective Acceleration to Microgravity Levels

NASA Technical Reports Server (NTRS)

Downey, James P.

2000-01-01

Acceleration due to earth's gravity causes buoyancy driven convection and sedimentation in solutions. In addition. pressure gradients occur as a function of the height within a liquid column. Hence gravity effects both equilbria conditions and phase transitions as a result of hydrostatic pressure gradients. The affect of gravity on the rate of heat and man transfer in solutal processes can be particularly important in polymer processing due to the high sensitivity of polymeric materials to processing conditions. The term microgravity has been coined to describe an environment in which the affects of gravitational acceleration am greatly reduced. It may seem odd to talk in term of reducing the effects of gravitational acceleration since gravitational attraction is a basic property of matter. However, die presence of gravity on in situ processing or measurements can be negated by achieving conditions in which the laboratory, or more specifically the container of the experimental materials, a subjected to the same acceleration as the materials themselves. With regard to the laboratory reference frame, there is virtually no force on the experimental solutions. This is difficult to achieve but can be done. A short review of Newtonian physics provides an explanation on both how processes we affected by gravity and how microgravity conditions are achieved. The fact that fluids deform when subject to a force bid solids do not indicates that solids have a structure able to exert an opposing force that negates an externally applied force. Liquids deform when a force is applied, indicating that a liquid structure cannot completely negate an applied force. Just how easily a liquid resists deformation is related to its viscosity. Spaceflight provides an environment in which the laboratory reference frame i.e. the spacecraft and all the equipment therein an experiencing virtually identical forces. There is no solid foundation underneath such a laboratory, so the laboratory accelerates according to the force of gravity as do the experimental fluids within the lab. Hence, the magnitude of the form excited by the laboratory on the experimental solutions within are greatly reduced. When compared with a laboratory on the ground and averaged over time, the fluids in a spaceflight laboratory experience approximately a 10 (sup -6)decrease in acceleration relative to their laboratory reference frame hence the term microgravity.

Homogeneous, anisotropic three-manifolds of topologically massive gravity

NASA Astrophysics Data System (ADS)

Nutku, Y.; Baekler, P.

1989-10-01

We present a new class of exact solutions of Deser, Jackiw, and Templeton's theory (DJT) of topologically massive gravity which consists of homogeneous, anisotropic manifolds. In these solutions the coframe is given by the left-invariant 1-forms of 3-dimensional Lie algebras up to constant scale factors. These factors are fixed in terms of the DJT coupling constant μ which is the constant of proportionality between the Einstein and Cotton tensors in 3-dimensions. Differences between the scale factors result in anisotropy which is a common feature of topologically massive 3-manifolds. We have found that only Bianchi Types VI, VIII, and IX lead to nontrivial solutions. Among these, a Bianchi Type IX, squashed 3-sphere solution of the Euclideanized DJT theory has finite action. Bianchi Type VIII, IX solutions can variously be embedded in the de Sitter/anti-de Sitter space. That is, some DJT 3-manifolds that we shall present here can be regarded as the basic constituent of anti-de Sitter space which is the ground state solution in higher dimensional generalization of Einstein's general relativity.

Homogeneous, anisotropic three-manifolds of topologically massive gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nutku, Y.; Baekler, P.

1989-10-01

We present a new class of exact solutions of Deser, Jackiw, and Templeton's theory (DJT) of topologically massive gravity which consists of homogeneous, anisotropic manifolds. In these solutions the coframe is given by the left-invariant 1-forms of 3-dimensional Lie algebras up to constant scale factors. These factors are fixed in terms of the DJT coupling constant {mu}m which is the constant of proportionality between the Einstein and Cotton tensors in 3-dimensions. Differences between the scale factors result in anisotropy which is a common feature of topologically massive 3-manifolds. We have found that only Bianchi Types VI, VIII, and IX leadmore » to nontrivial solutions. Among these, a Bianchi Type IX, squashed 3-sphere solution of the Euclideanized DJT theory has finite action, Bianchi Type VIII, IX solutions can variously be embedded in the de Sitter/anti-de Sitter space. That is, some DJT 3-manifolds that we shall present here can be regarded as the basic constitent of anti-de Sitter space which is the ground state solution in higher dimensional generalizations of Einstein's general relativity. {copyright} 1989 Academic Press, Inc.« less

Magnetic Control of Solutal Buoyancy Driven Convection

NASA Technical Reports Server (NTRS)

Ramachandran, N.; Leslie, F. W.

2003-01-01

Volumetric forces resulting from local density variations and gravitational acceleration cause buoyancy induced convective motion in melts and solutions. Solutal buoyancy is a result of concentration differences in an otherwise isothermal fluid. If the fluid also exhibits variations in magnetic susceptibility with concentration then convection control by external magnetic fields can be hypothesized. Magnetic control of thermal buoyancy induced convection in ferrofluids (dispersions of ferromagnetic particles in a carrier fluid) and paramagnetic fluids have been demonstrated. Here we show the nature of magnetic control of solutal buoyancy driven convection of a paramagnetic fluid, an aqueous solution of Manganese Chloride hydrate. We predict the critical magnetic field required for balancing gravitational solutal buoyancy driven convection and validate it through a simple experiment. We demonstrate that gravity driven flow can be completely reversed by a magnetic field but the exact cancellation of the flow is not possible. This is because the phenomenon is unstable. The technique can be applied to crystal growth processes in order to reduce convection and to heat exchanger devices for enhancing convection. The method can also be applied to impose a desired g-level in reduced gravity applications.

Analytical expression for a class of spherically symmetric solutions in Lorentz-breaking massive gravity

NASA Astrophysics Data System (ADS)

Li, Ping; Li, Xin-zhou; Xi, Ping

2016-06-01

We present a detailed study of the spherically symmetric solutions in Lorentz-breaking massive gravity. There is an undetermined function { F }(X,{w}1,{w}2,{w}3) in the action of Stückelberg fields {S}φ ={{{Λ }}}4\\int {{{d}}}4x\\sqrt{-g}{ F }, which should be resolved through physical means. In general relativity, the spherically symmetric solution to the Einstein equation is a benchmark and its massive deformation also plays a crucial role in Lorentz-breaking massive gravity. { F } will satisfy the constraint equation {T}01=0 from the spherically symmetric Einstein tensor {G}01=0, if we maintain that any reasonable physical theory should possess the spherically symmetric solutions. The Stückelberg field {φ }i is taken as a ‘hedgehog’ configuration {φ }i=φ (r){x}i/r, whose stability is guaranteed by the topological one. Under this ansätz, {T}01=0 is reduced to d{ F }=0. The functions { F } for d{ F }=0 form a commutative ring {R}{ F }. We obtain an expression of the solution to the functional differential equation with spherical symmetry if { F }\\in {R}{ F }. If { F }\\in {R}{ F } and \\partial { F }/\\partial X=0, the functions { F } form a subring {S}{ F }\\subset {R}{ F }. We show that the metric is Schwarzschild, Schwarzschild-AdS or Schwarzschild-dS if { F }\\in {S}{ F }. When { F }\\in {R}{ F } but { F }\

Equivalent off-diagonal cosmological models and ekpyrotic scenarios in -modified, massive, and einstein gravity

NASA Astrophysics Data System (ADS)

Vacaru, Sergiu I.

2015-04-01

We reinvestigate how generic off-diagonal cosmological solutions depending, in general, on all spacetime coordinates can be constructed in massive and -modified gravity using the anholonomic frame deformation method. New classes of locally anisotropic and (in-) homogeneous cosmological metrics are constructed with open and closed spatial geometries. By resorting to such solutions, we show that they describe the late time acceleration due to effective cosmological terms induced by nonlinear off-diagonal interactions, possible modifications of the gravitational action and graviton mass. The cosmological metrics and related Stückelberg fields are constructed in explicit form up to nonholonomic frame transforms of the Friedmann-Lamaître-Robertson-Walker (FLRW) coordinates. The solutions include matter, graviton mass, and other effective sources modeling nonlinear gravitational and matter field interactions with polarization of physical constants and deformations of metrics, which may explain dark energy and dark matter effects. However, we argue that it is not always necessary to modify gravity if we consider the effective generalized Einstein equations with nontrivial vacuum and/or non-minimal coupling with matter. Indeed, we state certain conditions when such configurations mimic interesting solutions in general relativity and modifications, for instance, when we can extract the general Painlevé-Gullstrand and FLRW metrics. In a more general context, we elaborate on a reconstruction procedure for off-diagonal cosmological solutions which describe cyclic and ekpyrotic universes. Finally, open issues and further perspectives are discussed.

Principal Facts of Gravity data in the Northern Willamette Valley and Vicinity, Northwestern Oregon and Southwestern Washington

USGS Publications Warehouse

Morin, Robert L.; Wheeler, Karen L.; McPhee, Darcy K.; Dinterman, Philip A.; Watt, Janet T.

2007-01-01

Gravity data were collected from 2004 through 2006 to assist in mapping subsurface geology in the northern Willamette Valley and vicinity, northwestern Oregon and southwestern Washington. Prior to this effort to improve the gravity data coverage in the study area, very little regional data were available. This report gives the principle facts for 2710 new gravity stations and 1446 preexisting gravity stations. Much of the study area is now covered with data of sufficient density to define basin boundaries and correlate with many of the larger fault systems. ,p> The study area lies between 44? 52.5 and 46? N latitude and between 122? 15 and 123? 37.5 W longitude. Although this is a continuing project and more gravity data is expected to be collected, this report is being published to show the progress of the data collection. The majority of these data are spaced at about 1.6 km (1 mile), but three closely spaced profiles were measured in the Portland area across several faults. To obtain a 1.6 km grid of data points would require about 5120 gravity stations. To date we have collected 2710 stations. Including the preexisting data points, the total number of stations is 4156, and complete regional coverage is about 80 percent at this time.

Design and Validation of Exoskeleton Actuated by Soft Modules toward Neurorehabilitation-Vision-Based Control for Precise Reaching Motion of Upper Limb.

PubMed

Oguntosin, Victoria W; Mori, Yoshiki; Kim, Hyejong; Nasuto, Slawomir J; Kawamura, Sadao; Hayashi, Yoshikatsu

2017-01-01

We demonstrated the design, production, and functional properties of the Exoskeleton Actuated by the Soft Modules (EAsoftM). Integrating the 3D printed exoskeleton with passive joints to compensate gravity and with active joints to rotate the shoulder and elbow joints resulted in ultra-light system that could assist planar reaching motion by using the vision-based control law. The EAsoftM can support the reaching motion with compliance realized by the soft materials and pneumatic actuation. In addition, the vision-based control law has been proposed for the precise control over the target reaching motion within the millimeter scale. Aiming at rehabilitation exercise for individuals, typically soft actuators have been developed for relatively small motions, such as grasping motion, and one of the challenges has been to extend their use for a wider range reaching motion. The proposed EAsoftM presented one possible solution for this challenge by transmitting the torque effectively along the anatomically aligned with a human body exoskeleton. The proposed integrated systems will be an ideal solution for neurorehabilitation where affordable, wearable, and portable systems are required to be customized for individuals with specific motor impairments.

Design and Validation of Exoskeleton Actuated by Soft Modules toward Neurorehabilitation—Vision-Based Control for Precise Reaching Motion of Upper Limb

PubMed Central

Oguntosin, Victoria W.; Mori, Yoshiki; Kim, Hyejong; Nasuto, Slawomir J.; Kawamura, Sadao; Hayashi, Yoshikatsu

2017-01-01

We demonstrated the design, production, and functional properties of the Exoskeleton Actuated by the Soft Modules (EAsoftM). Integrating the 3D printed exoskeleton with passive joints to compensate gravity and with active joints to rotate the shoulder and elbow joints resulted in ultra-light system that could assist planar reaching motion by using the vision-based control law. The EAsoftM can support the reaching motion with compliance realized by the soft materials and pneumatic actuation. In addition, the vision-based control law has been proposed for the precise control over the target reaching motion within the millimeter scale. Aiming at rehabilitation exercise for individuals, typically soft actuators have been developed for relatively small motions, such as grasping motion, and one of the challenges has been to extend their use for a wider range reaching motion. The proposed EAsoftM presented one possible solution for this challenge by transmitting the torque effectively along the anatomically aligned with a human body exoskeleton. The proposed integrated systems will be an ideal solution for neurorehabilitation where affordable, wearable, and portable systems are required to be customized for individuals with specific motor impairments. PMID:28736514

On the ratio of dynamic topography and gravity anomalies in a dynamic Earth

NASA Astrophysics Data System (ADS)

Colli, L.; Ghelichkhan, S.; Bunge, H. P.

2016-12-01

Growing evidence from a variety of geologic indicators points to significant topography maintained convectively by viscous stresses in the mantle. However, while gravity is sensitive to dynamically supported topography, there are only small free-air gravity anomalies (<30 mGal) associated with Earth's long-wavelength topography. This has been used to suggest that surface heights computed assuming a complete isostatic equilibrium provide a good approximation to observed topography. Here we show that the apparent paradox is resolved by the well-established formalism of global, self-gravitating, viscously stratified Earth models. The models predict a complex relation between dynamic topography, mass, and gravity anomalies that is not summarized by a constant admittance—i.e., ratio of gravity anomalies to surface deflections—as one would infer from analytic flow solutions formulated in a half-space.

Black hole thermodynamics in Lovelock gravity's rainbow with (A)dS asymptote

NASA Astrophysics Data System (ADS)

Hendi, Seyed Hossein; Dehghani, Ali; Faizal, Mir

2017-01-01

In this paper, we combine Lovelock gravity with gravity's rainbow to construct Lovelock gravity's rainbow. Considering the Lovelock gravity's rainbow coupled to linear and also nonlinear electromagnetic gauge fields, we present two new classes of topological black hole solutions. We compute conserved and thermodynamic quantities of these black holes (such as temperature, entropy, electric potential, charge and mass) and show that these quantities satisfy the first law of thermodynamics. In order to study the thermal stability in canonical ensemble, we calculate the heat capacity and determinant of the Hessian matrix and show in what regions there are thermally stable phases for black holes. Also, we discuss the dependence of thermodynamic behavior and thermal stability of black holes on rainbow functions. Finally, we investigate the critical behavior of black holes in the extended phase space and study their interesting properties.

Impact of nonlinear effective interactions on group field theory quantum gravity condensates

NASA Astrophysics Data System (ADS)

Pithis, Andreas G. A.; Sakellariadou, Mairi; Tomov, Petar

2016-09-01

We present the numerical analysis of effectively interacting group field theory models in the context of the group field theory quantum gravity condensate analog of the Gross-Pitaevskii equation for real Bose-Einstein condensates including combinatorially local interaction terms. Thus, we go beyond the usually considered construction for free models. More precisely, considering such interactions in a weak regime, we find solutions for which the expectation value of the number operator N is finite, as in the free case. When tuning the interaction to the strongly nonlinear regime, however, we obtain solutions for which N grows and eventually blows up, which is reminiscent of what one observes for real Bose-Einstein condensates, where a strong interaction regime can only be realized at high density. This behavior suggests the breakdown of the Bogoliubov ansatz for quantum gravity condensates and the need for non-Fock representations to describe the system when the condensate constituents are strongly correlated. Furthermore, we study the expectation values of certain geometric operators imported from loop quantum gravity in the free and interacting cases. In particular, computing solutions around the nontrivial minima of the interaction potentials, one finds, already in the weakly interacting case, a nonvanishing condensate population for which the spectra are dominated by the lowest nontrivial configuration of the quantum geometry. This result indicates that the condensate may indeed consist of many smallest building blocks giving rise to an effectively continuous geometry, thus suggesting the interpretation of the condensate phase to correspond to a geometric phase.

Treatment of temporal aliasing effects in the context of next generation satellite gravimetry missions

NASA Astrophysics Data System (ADS)

Daras, Ilias; Pail, Roland

2017-09-01

Temporal aliasing effects have a large impact on the gravity field accuracy of current gravimetry missions and are also expected to dominate the error budget of Next Generation Gravimetry Missions (NGGMs). This paper focuses on aspects concerning their treatment in the context of Low-Low Satellite-to-Satellite Tracking NGGMs. Closed-loop full-scale simulations are performed for a two-pair Bender-type Satellite Formation Flight (SFF), by taking into account error models of new generation instrument technology. The enhanced spatial sampling and error isotropy enable a further reduction of temporal aliasing errors from the processing perspective. A parameterization technique is adopted where the functional model is augmented by low-resolution gravity field solutions coestimated at short time intervals, while the remaining higher-resolution gravity field solution is estimated at a longer time interval. Fine-tuning the parameterization choices leads to significant reduction of the temporal aliasing effects. The investigations reveal that the parameterization technique in case of a Bender-type SFF can successfully mitigate aliasing effects caused by undersampling of high-frequency atmospheric and oceanic signals, since their most significant variations can be captured by daily coestimated solutions. This amounts to a "self-dealiasing" method that differs significantly from the classical dealiasing approach used nowadays for Gravity Recovery and Climate Experiment processing, enabling NGGMs to retrieve the complete spectrum of Earth's nontidal geophysical processes, including, for the first time, high-frequency atmospheric and oceanic variations.

Towards combined global monthly gravity field solutions

NASA Astrophysics Data System (ADS)

Jaeggi, Adrian; Meyer, Ulrich; Beutler, Gerhard; Weigelt, Matthias; van Dam, Tonie; Mayer-Gürr, Torsten; Flury, Jakob; Flechtner, Frank; Dahle, Christoph; Lemoine, Jean-Michel; Bruinsma, Sean

2014-05-01

Currently, official GRACE Science Data System (SDS) monthly gravity field solutions are generated independently by the Centre for Space Research (CSR) and the German Research Centre for Geosciences (GFZ). Additional GRACE SDS monthly fields are provided by the Jet Propulsion Laboratory (JPL) for validation and outside the SDS by a number of other institutions worldwide. Although the adopted background models and processing standards have been harmonized more and more by the various processing centers during the past years, notable differences still exist and the users are more or less left alone with a decision which model to choose for their individual applications. This procedure seriously limits the accessibility of these valuable data. Combinations are well established in the area of other space geodetic techniques, such as the Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Very Long Baseline Interferometry (VLBI). Regularly comparing and combining space-geodetic products has tremendously increased the usefulness of the products in a wide range of disciplines and scientific applications. Therefore, we propose in a first step to mutually compare the large variety of available monthly GRACE gravity field solutions, e.g., by assessing the signal content over selected regions, by estimating the noise over the oceans, and by performing significance tests. We make the attempt to assign different solution characteristics to different processing strategies in order to identify subsets of solutions, which are based on similar processing strategies. Using these subsets we will in a second step explore ways to generate combined solutions, e.g., based on a weighted average of the individual solutions using empirical weights derived from pair-wise comparisons. We will also assess the quality of such a combined solution and discuss the potential benefits for the GRACE and GRACE-FO user community, but also address minimum processing requirements to be met by each analysis centre to enable a meaningful combination (either performed on the solution level or, preferably, on the normal equation level).

Tethered gravity laboratories study

NASA Technical Reports Server (NTRS)

Lucchetti, F.

1990-01-01

The scope of the study is to investigate ways of controlling the microgravity environment of the International Space Station by means of a tethered system. Four main study tasks were performed. First, researchers analyzed the utilization of the tether systems to improve the lowest possible steady gravity level on the Space Station and the tether capability to actively control the center of gravity position in order to compensate for activities that would upset the mass distribution of the Station. The purpose of the second task was to evaluate the whole of the experiments performable in a variable gravity environment and the related beneficial residual accelerations, both for pure and applied research in the fields of fluid, materials, and life science, so as to assess the relevance of a variable g-level laboratory. The third task involves the Tethered Variable Gravity Laboratory. The use of the facility that would crawl along a deployed tether and expose experiments to varying intensities of reduced gravity is discussed. Last, a study performed on the Attitude Tether Stabilizer concept is discussed. The stabilization effect of ballast masses tethered to the Space Station was investigated as a means of assisting the attitude control system of the Station.

Gravity and Nonconservative Force Model Tuning for the GEOSAT Follow-On Spacecraft

NASA Technical Reports Server (NTRS)

Lemoine, Frank G.; Zelensky, Nikita P.; Rowlands, David D.; Luthcke, Scott B.; Chinn, Douglas S.; Marr, Gregory C.; Smith, David E. (Technical Monitor)

2000-01-01

The US Navy's GEOSAT Follow-On spacecraft was launched on February 10, 1998 and the primary objective of the mission was to map the oceans using a radar altimeter. Three radar altimeter calibration campaigns have been conducted in 1999 and 2000. The spacecraft is tracked by satellite laser ranging (SLR) and Doppler beacons and a limited amount of data have been obtained from the Global Positioning Receiver (GPS) on board the satellite. Even with EGM96, the predicted radial orbit error due to gravity field mismodelling (to 70x70) remains high at 2.61 cm (compared to 0.88 cm for TOPEX). We report on the preliminary gravity model tuning for GFO using SLR, and altimeter crossover data. Preliminary solutions using SLR and GFO/GFO crossover data from CalVal campaigns I and II in June-August 1999, and January-February 2000 have reduced the predicted radial orbit error to 1.9 cm and further reduction will be possible when additional data are added to the solutions. The gravity model tuning has improved principally the low order m-daily terms and has reduced significantly the geographically correlated error present in this satellite orbit. In addition to gravity field mismodelling, the largest contributor to the orbit error is the non-conservative force mismodelling. We report on further nonconservative force model tuning results using available data from over one cycle in beta prime.

Black holes in quasi-topological gravity and conformal couplings

NASA Astrophysics Data System (ADS)

Chernicoff, Mariano; Fierro, Octavio; Giribet, Gaston; Oliva, Julio

2017-02-01

Lovelock theory of gravity provides a tractable model to investigate the effects of higher-curvature terms in the context of AdS/CFT. Yielding second order, ghost-free field equations, this theory represents a minimal setup in which higher-order gravitational couplings in asymptotically Anti-de Sitter (AdS) spaces, including black holes, can be solved analytically. This however has an obvious limitation as in dimensions lower than seven, the contribution from cubic or higher curvature terms is merely topological. Therefore, in order to go beyond quadratic order and study higher terms in AdS5 analytically, one is compelled to look for other toy models. One such model is the so-called quasi-topological gravity, which, despite being a higher-derivative theory, provides a tractable setup with R 3 and R 4 terms. In this paper, we investigate AdS5 black holes in quasi-topological gravity. We consider the theory conformally coupled to matter and in presence of Abelian gauge fields. We show that charged black holes in AdS5 which, in addition, exhibit a backreaction of the matter fields on the geometry can be found explicitly in this theory. These solutions generalize the black hole solution of quasi-topological gravity and exist in a region of the parameter spaces consistent with the constraints coming from causality and other consistency conditions. They have finite conserved charges and exhibit non-trivial thermodynamical properties.

A Test Run of the EGSIEM Near Real-Time Service Based on GRACE Mission Data

NASA Astrophysics Data System (ADS)

Kvas, A.; Gruber, C.; Gouweleeuw, B.; Guntner, A.; Mayer-Gürr, T.; Flechtner, F. M.

2017-12-01

To enable the use of GRACE and GRACE-FO data for rapid monitoring applications, the EGSIEM (European Gravity Service for Improved Emergency Management) project, funded by the Horizon 2020 Framework Program for Research and Innovation of the European Union, has implemented a demonstrator for a near real-time (NRT) gravity field service. The goal of this service is to provide daily gravity field solutions with a maximum latency of five days. For this purpose, two independent approaches were developed at the German Research Centre for Geosciences (GFZ) and Graz University of Technology (TUG). Based on these daily gravity field solutions, statistical flood and drought indicators are derived by the EGSIEM Hydrological Service, developed at GFZ. The NRT products are subsequently provided to the Center for Satellite based Crisis Information (ZKI) at the German Aerospace Center as well as the Global Flood Awareness System (GloFAS) at the Joint Research Center of the European Commission. In the first part of this contribution, the performance of the service based on a statistical analysis of historical flood events during the GRACE period is evaluated. Then, results from the six month long operational test run of the service which started on April 1st 2017 are presented and a comparison between historical and operational gravity products and flood indicators is made.

Glacial isostatic adjustment on the Northern Hemisphere - new results from GRACE

NASA Astrophysics Data System (ADS)

Mueller, J.; Steffen, H.; Gitlein, O.; Denker, H.; Timmen, L.

2007-12-01

The Earth's gravity field mapped by the Gravity Recovery and Climate Experiment (GRACE) satellite mission shows variations due to the integral effect of mass variations in the atmosphere, hydrosphere and geosphere. The Earth's gravity field is provided in form of monthly solutions by several institutions, e.~g. GFZ Potsdam, CSR and JPL. During the GRACE standard processing of these analysis centers, oceanic and atmospheric contributions as well as tidal effects are reduced. The solutions of the analysis centers differ slightly, which is due the application of different reduction models and center-specific processing schemes. We present our investigation of mass variations in the areas of glacial isostatic adjustment (GIA) in North America and Northern Europe from GRACE data. One key issue is the separation of GIA parts and the reduction of the observed quantities by applying dedicated filters (e.~g. isotropic, non-isotropic, and destriping filters) and global models of hydrological variations (e.~g. WGHM, LaDWorld, GLDAS). In a further step, we analyze the results of both regions regarding their reliability, and finally present a comparison to results of a geodynamical modeling and absolute gravity measurements. Our results clearly show that the quality of the GRACE-derived gravity- change signal benefits from improved reduction models and chosen analysis techniques. Nevertheless, the comparison to results of geodynamic models still reveals differences, and thus further studies are in progress.