A PRELIMINARY JUPITER MODEL

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

Hubbard, W. B.; Militzer, B.

In anticipation of new observational results for Jupiter's axial moment of inertia and gravitational zonal harmonic coefficients from the forthcoming Juno orbiter, we present a number of preliminary Jupiter interior models. We combine results from ab initio computer simulations of hydrogen–helium mixtures, including immiscibility calculations, with a new nonperturbative calculation of Jupiter's zonal harmonic coefficients, to derive a self-consistent model for the planet's external gravity and moment of inertia. We assume helium rain modified the interior temperature and composition profiles. Our calculation predicts zonal harmonic values to which measurements can be compared. Although some models fit the observed (pre-Juno) second-more » and fourth-order zonal harmonics to within their error bars, our preferred reference model predicts a fourth-order zonal harmonic whose absolute value lies above the pre-Juno error bars. This model has a dense core of about 12 Earth masses and a hydrogen–helium-rich envelope with approximately three times solar metallicity.« less

High-latitude filtering in a global grid-point model using model normal modes. [Fourier filters for synoptic weather forecasting

NASA Technical Reports Server (NTRS)

Takacs, L. L.; Kalnay, E.; Navon, I. M.

1985-01-01

A normal modes expansion technique is applied to perform high latitude filtering in the GLAS fourth order global shallow water model with orography. The maximum permissible time step in the solution code is controlled by the frequency of the fastest propagating mode, which can be a gravity wave. Numerical methods are defined for filtering the data to identify the number of gravity modes to be included in the computations in order to obtain the appropriate zonal wavenumbers. The performances of the model with and without the filter, and with a time tendency and a prognostic field filter are tested with simulations of the Northern Hemisphere winter. The normal modes expansion technique is shown to leave the Rossby modes intact and permit 3-5 day predictions, a range not possible with the other high-latitude filters.

Correlation of Experimental and Theoretical Steady-State Spinning Motion for a Current Fighter Airplane Using Rotation-Balance Aerodynamic Data

DTIC Science & Technology

1978-07-01

were input into the computer program. The program was numerically intergrated with time by using a fourth-order Runge-Kutta integration algorithm with...equations of motion are numerically intergrated to provide time histories of the aircraft spinning motion. A.2 EQUATIONS DEFINING THE FORCE AND MOMENT...by Cy or Cn. 50 AE DC-TR-77-126 A . 4 where EQUATIONS FOR TRANSFERRING AERODYNAMIC DATA INPUTS TO THE PROPER HORIZONTAL CENTER OF GRAVITY

Galaxy rotation curves in f(R,ϕ) gravity

NASA Astrophysics Data System (ADS)

Stabile, A.; Capozziello, S.

2013-03-01

We investigate the possibility of explaining theoretically the galaxy rotation curves by a gravitational potential in total absence of dark matter. To this aim an analytic fourth-order theory of gravity, nonminimally coupled with a massive scalar field, is considered. Specifically, the interaction term is given by an analytic function f(R,ϕ), where R is the Ricci scalar and ϕ is the scalar field. The gravitational potential is generated by a pointlike source and compared with the so-called Sanders’s potential that can be exactly reproduced in this case. This result means that the problem of dark matter in spiral galaxies could be fully addressed by revising general relativity at galactic scales and requiring further gravitational degrees of freedom instead of new material components that have not been found up to now.

Evaluation of gravitational curvatures of a tesseroid in spherical integral kernels

NASA Astrophysics Data System (ADS)

Deng, Xiao-Le; Shen, Wen-Bin

2018-04-01

Proper understanding of how the Earth's mass distributions and redistributions influence the Earth's gravity field-related functionals is crucial for numerous applications in geodesy, geophysics and related geosciences. Calculations of the gravitational curvatures (GC) have been proposed in geodesy in recent years. In view of future satellite missions, the sixth-order developments of the gradients are becoming requisite. In this paper, a set of 3D integral GC formulas of a tesseroid mass body have been provided by spherical integral kernels in the spatial domain. Based on the Taylor series expansion approach, the numerical expressions of the 3D GC formulas are provided up to sixth order. Moreover, numerical experiments demonstrate the correctness of the 3D Taylor series approach for the GC formulas with order as high as sixth order. Analogous to other gravitational effects (e.g., gravitational potential, gravity vector, gravity gradient tensor), numerically it is found that there exist the very-near-area problem and polar singularity problem in the GC east-east-radial, north-north-radial and radial-radial-radial components in spatial domain, and compared to the other gravitational effects, the relative approximation errors of the GC components are larger due to not only the influence of the geocentric distance but also the influence of the latitude. This study shows that the magnitude of each term for the nonzero GC functionals by a grid resolution 15^' } } × 15^' }} at GOCE satellite height can reach of about 10^{-16} m^{-1} s2 for zero order, 10^{-24 } or 10^{-23} m^{-1} s2 for second order, 10^{-29} m^{-1} s2 for fourth order and 10^{-35} or 10^{-34} m^{-1} s2 for sixth order, respectively.

Stability enhancement of high Prandtl number chaotic convection in an anisotropic porous layer with feedback control

NASA Astrophysics Data System (ADS)

Mahmud, M. N.

2018-04-01

The chaotic dynamical behaviour of thermal convection in an anisotropic porous layer subject to gravity, heated from below and cooled from above, is studied based on theory of dynamical system in the presence of feedback control. The extended Darcy model, which includes the time derivative has been employed in the momentum equation to derive a low dimensional Lorenz-like equation by using Galerkin-truncated approximation. The classical fourth-order Runge-Kutta method is used to obtain the numerical solution in order to exemplify the dynamics of the nonlinear autonomous system. The results show that stability enhancement of chaotic convection is feasible via feedback control.

Conservation Laws and Symmetry Properties of a Class of Higher Order Theories of Gravity

NASA Astrophysics Data System (ADS)

Barraco, D.; Dominguez, E.; Guibert, R.; Hamity, V.

1998-04-01

We consider a class of fourth order theories of gravity with arbitrary matter fields arising from a diffeomorphism invariant Lagrangian density mathcal{L}_T = mathcal{L}_G + mathcal{L}_M, with mathcal{L}_G = sqrt { - g} left[ {R + hleft( R right)} right]and mathcal{L}_Mthe phenomenological representation of the nongravitational fields. We derive first the generalization of the Einstein pseudotensor and the von Freud superpotential. We then show, using the arbitrariness that is always present in the choice of pseudotensor and superpotential, that we can choose these superpotentials to have the same form as those for the Hilbert Lagrangian of general relativity (GR). In particular we may introduce the Moller superpotential of GR as associated with a double-index differential conservation law. Similarly, using the Moller superpotential we prove that we can choose the Komar vector of GR to construct a conserved quantity for isolated asymptotically flat systems. For the example R + R2theory we prove then, that the active mass is equal to the total energy (or inertial mass) of the system.

Mass Anomalies on Ganymede

NASA Technical Reports Server (NTRS)

Schubert, G.; Anderson, J. D.; Jacobson, R. A.; Lau, E. L.; Moore, W. B.; Palguta, J.

2004-01-01

Radio Doppler data from two Ganymede encounters (G1 and G2) on the first two orbits in the Galileo mission have been analyzed previously for gravity information . For a satellite in hydrostatic equilibrium, its gravitational field can be modeled adequately by a truncated spherical harmonic series of degree two. However, a fourth degree field is required in order to fit the second Galileo flyby (G2). This need for a higher degree field strongly suggests that Ganymede s gravitational field is perturbed by a gravity anomaly near the G2 closest approach point (79.29 latitude, 123.68 west longitude). In fact, a plot of the Doppler residuals , after removal of the best-fit model for the zero degree term (GM) and the second degree moments (J2 and C22), suggests that if an anomaly exists, it is located downtrack of the closest approach point, closer to the equator.

S2 like Star Orbits near the Galactic Center in Rn and Yukawa Gravity

NASA Astrophysics Data System (ADS)

Borka, Dusko; Jovanović, Predrag; Jovanović Vesna Borka; Zakharov, Alexander F.

2015-01-01

In this chapter we investigate the possibility to provide theoretical explanation for the observed deviations of S2 star orbit around the Galactic Center using gravitational potentials derived from extended gravity models, but in absence of dark matter. Extended Theories of Gravity are alternative theories of gravitational interaction developed from the exact starting points investigated first by Einstein and Hilbert and aimed from one side to extend the positive results of General Relativity and, on the other hand, to cure its shortcomings. One of the aims of these theories is to explain galactic and extragalactic dynamics without introduction of dark matter. They are based on straightforward generalizations of the Einstein theory where the gravitational action (the Hilbert-Einstein action) is assumed to be linear in the Ricci curvature scalar R. The f(R) gravity is a type of modified gravity which generalizes Einstein's General Relativity, i.e. the simplest case is just the General Relativity. It is actually a family of models, each one defined by a different function of the Ricci scalar. Here, we consider Rn (power-law fourth-order theories of gravity) and Yukawa-like modified gravities in the weak field limit and discuss the constrains on these theories. For that purpose we simulate the orbit of S2 star around the Galactic Center in Rn and Yukawa-like gravity potentials and compare it with New Technology Telescope/Very Large Telescope (NTT/VLT) as well as by Keck telescope observations. Our simulations result in strong constraints on the range of gravity interaction and showed that both Rn and Yukawa gravity could satisfactorily explain the observed orbits of S2 star. However, we concluded that parameters of Rn and Yukawa gravity theories must be very close to those corresponding to the Newtonian limit of the theory. Besides, in contrast to Newtonian gravity, these two modified theories induce orbital precession, even in the case of point-like central mass. The approach we are proposing seems to be sufficiently reliable to constrain the modified gravity models from stellar orbits around Galactic Center.

Topographical scattering of gravity waves

NASA Astrophysics Data System (ADS)

Miles, J. W.; Chamberlain, P. G.

1998-04-01

A systematic hierarchy of partial differential equations for linear gravity waves in water of variable depth is developed through the expansion of the average Lagrangian in powers of [mid R:][nabla del, Hamilton operator][mid R:] (h=depth, [nabla del, Hamilton operator]h=slope). The first and second members of this hierarchy, the Helmholtz and conventional mild-slope equations, are second order. The third member is fourth order but may be approximated by Chamberlain & Porter's (1995) ‘modified mild-slope’ equation, which is second order and comprises terms in [nabla del, Hamilton operator]2h and ([nabla del, Hamilton operator]h)2 that are absent from the mild-slope equation. Approximate solutions of the mild-slope and modified mild-slope equations for topographical scattering are determined through an iterative sequence, starting from a geometrical-optics approximation (which neglects reflection), then a quasi-geometrical-optics approximation, and on to higher-order results. The resulting reflection coefficient for a ramp of uniform slope is compared with the results of numerical integrations of each of the mild-slope equation (Booij 1983), the modified mild-slope equation (Porter & Staziker 1995), and the full linear equations (Booij 1983). Also considered is a sequence of sinusoidal sandbars, for which Bragg resonance may yield rather strong reflection and for which the modified mild-slope approximation is in close agreement with Mei's (1985) asymptotic approximation.

Viability of Noether Symmetry of F( R) Theory of Gravity

NASA Astrophysics Data System (ADS)

Sarkar, Kaushik; Sk, Nayem; Debnath, Subhra; Sanyal, Abhik Kumar

2013-04-01

Recently, we have explored vices and virtues of R^{3/2} term in the action which has in-built Noether symmetry and anticipated that a linear term might improve the situation (Sarkar et al., arXiv:1201.2987 [astro-ph.CO], 2012). In the absence of a conserved current it is extremely difficult to obtain an analytical solution of the said fourth order theory of gravity in the presence of a linear term. Here, we therefore enlarge the configuration space by including a scalar field in addition and also taking some of the anisotropic models (in the absence of a scalar field) into account. We observe that Noether symmetry remains obscure and it does not even reproduce the one that already exists in the literature (Sanyal, Gen. Relativ. Gravit., 37:407, 2005). However, there exists in general, a conserved current for F( R) theory of gravity in the presence of a non-minimally coupled scalar field (Sanyal, Phys. Lett. B, 624:81, 2005; Mod. Phys. Lett. A, 25:2667, 2010), which simplifies the field equations considerably. Here, we briefly expatiate the non-Noether conserved current and show that indeed the situation is modified.

Polymer quantization, stability and higher-order time derivative terms

NASA Astrophysics Data System (ADS)

Cumsille, Patricio; Reyes, Carlos M.; Ossandon, Sebastian; Reyes, Camilo

2016-03-01

The possibility that fundamental discreteness implicit in a quantum gravity theory may act as a natural regulator for ultraviolet singularities arising in quantum field theory has been intensively studied. Here, along the same expectations, we investigate whether a nonstandard representation called polymer representation can smooth away the large amount of negative energy that afflicts the Hamiltonians of higher-order time derivative theories, rendering the theory unstable when interactions come into play. We focus on the fourth-order Pais-Uhlenbeck model which can be reexpressed as the sum of two decoupled harmonic oscillators one producing positive energy and the other negative energy. As expected, the Schrödinger quantization of such model leads to the stability problem or to negative norm states called ghosts. Within the framework of polymer quantization we show the existence of new regions where the Hamiltonian can be defined well bounded from below.

On the hyperbolicity and stability of 3+1 formulations of metric f( R) gravity

NASA Astrophysics Data System (ADS)

Mongwane, Bishop

2016-11-01

3+1 formulations of the Einstein field equations have become an invaluable tool in Numerical relativity, having been used successfully in modeling spacetimes of black hole collisions, stellar collapse and other complex systems. It is plausible that similar considerations could prove fruitful for modified gravity theories. In this article, we pursue from a numerical relativistic viewpoint the 3+1 formulation of metric f( R) gravity as it arises from the fourth order equations of motion, without invoking the dynamical equivalence with Brans-Dicke theories. We present the resulting system of evolution and constraint equations for a generic function f( R), subject to the usual viability conditions. We confirm that the time propagation of the f( R) Hamiltonian and Momentum constraints take the same Mathematical form as in general relativity, irrespective of the f( R) model. We further recast the 3+1 system in a form akin to the BSSNOK formulation of numerical relativity. Without assuming any specific model, we show that the ADM version of f( R) is weakly hyperbolic and is plagued by similar zero speed modes as in the general relativity case. On the other hand the BSSNOK version is strongly hyperbolic and hence a promising formulation for numerical simulations in metric f( R) theories.

Quantum Structure of Space and Time

NASA Astrophysics Data System (ADS)

Duff, M. J.; Isham, C. J.

2012-07-01

Foreword Abdus Salam; Preface; List of participants; Part I. Quantum Gravity, Fields and Topology: 1. Some remarks on gravity and quantum mechanics Roger Penrose; 2. An experimental test of quantum gravity Don N. Page and C. D. Geilker; 3. Quantum mechanical origin of the sandwich theorem in classical gravitation theory Claudio Teitelboim; 4. θ-States induced by the diffeomorphism group in canonically quantized gravity C. J. Isham; 5. Strong coupling quantum gravity: an introduction Martin Pilati; 6. Quantizing fourth order gravity theories S. M. Christensen; 7. Green's functions, states and renormalisation M. R. Brown and A. C. Ottewill; 8. Introduction to quantum regge calculus Martin Roček and Ruth Williams; 9. Spontaneous symmetry breaking in curved space-time D. J. Toms; 10. Spontaneous symmetry breaking near a black hole M. S. Fawcett and B. F. Whiting; 11. Yang-Mills vacua in a general three-space G. Kunstatter; 12. Fermion fractionization in physics R. Jackiw; Part II. Supergravity: 13. The new minimal formulation of N=1 supergravity and its tensor calculus M. F. Sohnius and P. C. West; 14. A new deteriorated energy-momentum tensor M. J. Duff and P. K. Townsend; 15. Off-shell N=2 and N=4 supergravity in five dimensions P. Howe; 16. Supergravity in high dimensions P. van Niewenhuizen; 17. Building linearised extended supergravities J. G. Taylor; 18. (Super)gravity in the complex angular momentum plane M. T. Grisaru; 19. The multiplet structure of solitons in the O(2) supergravity theory G. W. Gibbons; 20. Ultra-violet properties of supersymmetric gauge theory S. Ferrara; 21. Extended supercurrents and the ultra-violet finiteness of N=4 supersymmetric Yang-Mills theories K. S. Stelle; 22. Duality rotations B. Zumino; Part III. Cosmology and the Early Universe: 23. Energy, stability and cosmological constant S. Deser; 24. Phase transitions in the early universe T. W. B. Kibble; 25. Complete cosmological theories L. P. Grishchuk and Ya. B. Zeldovich; 26. The cosmological constant and the weak anthropic principle S. W. Hawking.

Static vacuum solutions on curved space-times with torsion

NASA Astrophysics Data System (ADS)

Shabani, Hamid; Ziaie, Amir Hadi

2018-06-01

The Einstein-Cartan-Kibble-Sciama (ECKS) theory of gravity naturally extends Einstein’s general relativity (GR) to include intrinsic angular momentum (spin) of matter. The main feature of this theory consists of an algebraic relation between space-time torsion and spin of matter, which indeed deprives the torsion of its dynamical content. The Lagrangian of ECKS gravity is proportional to the Ricci curvature scalar constructed out of a general affine connection so that owing to the influence of matter energy-momentum and spin, curvature and torsion are produced and interact only through the space-time metric. In the absence of spin, the space-time torsion vanishes and the theory reduces to GR. It is however possible to have torsion propagation in vacuum by resorting to a model endowed with a nonminimal coupling between curvature and torsion. In the present work we try to investigate possible effects of the higher order terms that can be constructed from space-time curvature and torsion, as the two basic constituents of Riemann-Cartan geometry. We consider Lagrangians that include fourth-order scalar invariants from curvature and torsion and then investigate the resulting field equations. The solutions that we find show that there could exist, even in vacuum, nontrivial static space-times that admit both black holes and naked singularities.

Space Manufacturing: The Next Great Challenge

NASA Technical Reports Server (NTRS)

Whitaker, Ann F.; Curreri, Peter; Sharpe, Jonathan B.; Colberg, Wendell R.; Vickers, John H.

1998-01-01

Space manufacturing encompasses the research, development and manufacture necessary for the production of any product to be used in near zero gravity, and the production of spacecraft required for transporting research or production devices to space. Manufacturing for space, and manufacturing in space will require significant breakthroughs in materials and manufacturing technology, as well as in equipment designs. This report reviews some of the current initiatives in achieving space manufacturing. The first initiative deals with materials processing in space, e.g., processing non-terrestrial and terrestrial materials, especially metals. Some of the ramifications of the United States Microgravity Payloads fourth (USMP-4) mission are discussed. Some problems in non-terrestrial materials processing are mentioned. The second initiative is structures processing in space. In order to accomplish this, the International Space Welding Experiment was designed to demonstrate welding technology in near-zero gravity. The third initiative is advancements in earth-based manufacturing technologies necessary to achieve low cost access to space. The advancements discussed include development of lightweight material having high specific strength, and automated fabrication and manufacturing methods for these materials.

Behavioral regulation of gravity - Schedule effects under escape-avoidance procedures

NASA Technical Reports Server (NTRS)

Clark, F. C.; Lange, K. O.; Belleville, R. E.

1973-01-01

Squirrel monkeys were restrained in a centrifuge capsule and trained to escape and avoid increases in artificial gravity. During escape-avoidance, lever responses reduced centrifugally simulated gravity or postponed scheduled increases. The effect of variation in the interval of postponement (equal to the duration of decrease produced by escape responses) was studied under a multiple schedule of four components. Three components were gravity escape-avoidance with postponement times of 20, 40, and 60 sec. The fourth component was extinction. Each component was associated with a different auditory stimulus. Rate of responding decreased with increasing postponement time and higher mean g-levels occurred at shorter intervals of postponement. Effects of the schedule parameter on response rate and mean g-level were similar to effects of the schedule on free-operant avoidance and on titration behavior maintained by shock.

Teaching Physics and Feeling Good about It.

ERIC Educational Resources Information Center

Prokop, Charles F.

1988-01-01

Describes a high school physics teaching sequence including more modern topics. The first quarter covers cosmology, astronomy, optics, wave mechanics, relativity, gravity, and quantum theory. The second quarter covers classical mechanics. The third quarter covers electromagnetism and electronics. The fourth quarter consists of thermodynamics and…

Behavioral regulation of gravity: schedule effects under escape-avoidance procedures1

PubMed Central

Clark, Fogle C.; Lange, Karl O.; Belleville, Richard E.

1973-01-01

Squirrel monkeys were restrained in a centrifuge capsule and trained to escape and avoid increases in artificial gravity. During escape-avoidance, lever responses reduced centrifugally simulated gravity or postponed scheduled increases. The effect of variation in the interval of postponement (equal to the duration of decrease produced by escape responses) was studied under a multiple schedule of four components. Three components were gravity escape-avoidance with postponement times of 20, 40, and 60 sec. The fourth component was extinction. Each component was associated with a different auditory stimulus. Rate of responding decreased with increasing postponement time and higher mean g-levels occurred at shorter intervals of postponement. Effects of the schedule parameter on response rate and mean g-level were similar to effects of the schedule on free-operant avoidance and on titration behavior maintained by shock. ImagesFig. 1. PMID:4202386

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Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-30

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EFTofPNG: a package for high precision computation with the effective field theory of post-Newtonian gravity

NASA Astrophysics Data System (ADS)

Levi, Michele; Steinhoff, Jan

2017-12-01

We present a novel public package ‘EFTofPNG’ for high precision computation in the effective field theory of post-Newtonian (PN) gravity, including spins. We created this package in view of the timely need to publicly share automated computation tools, which integrate the various types of physics manifested in the expected increasing influx of gravitational wave (GW) data. Hence, we created a free and open source package, which is self-contained, modular, all-inclusive, and accessible to the classical gravity community. The ‘EFTofPNG’ Mathematica package also uses the power of the ‘xTensor’ package, suited for complicated tensor computation, where our coding also strategically approaches the generic generation of Feynman contractions, which is universal to all perturbation theories in physics, by efficiently treating n-point functions as tensors of rank n. The package currently contains four independent units, which serve as subsidiaries to the main one. Its final unit serves as a pipeline chain for the obtainment of the final GW templates, and provides the full computation of derivatives and physical observables of interest. The upcoming ‘EFTofPNG’ package version 1.0 should cover the point mass sector, and all the spin sectors, up to the fourth PN order, and the two-loop level. We expect and strongly encourage public development of the package to improve its efficiency, and to extend it to further PN sectors, and observables useful for the waveform modelling.

Chicxulub multiring impact basin - Size and other characteristics derived from gravity analysis

NASA Technical Reports Server (NTRS)

Sharpton, Virgil L.; Burke, Kevin; Camargo-Zanoguera, Antonio; Hall, Stuart A.; Lee, D. S.; Marin, Luis E.; Suarez-Reynoso, Gerardo; Quezada-Muneton, Juan M.; Spudis, Paul D.; Urrutia-Fucugauchi, Jaime

1993-01-01

The buried Chicxulub impact structure in Mexico, which is linked to the Cretaceous-Tertiary (K-T) boundary layer, may be significantly larger than previously suspected. Reprocessed gravity data over Northern Yucatan reveal three major rings and parts of a fourth ring, spaced similarly to those observed at multiring impact basins on other planets. The outer ring, probably corresponding to the basin's topographic rim, is almost 300 kilometers in diameter, indicating that Chicxulub may be one of the largest impact structures produced in the inner solar system since the period of early bombardment ended nearly 4 billion years ago.

Complete characterization of fourth-order symplectic integrators with extended-linear coefficients.

PubMed

Chin, Siu A

2006-02-01

The structure of symplectic integrators up to fourth order can be completely and analytically understood when the factorization (split) coefficients are related linearly but with a uniform nonlinear proportional factor. The analytic form of these extended-linear symplectic integrators greatly simplified proofs of their general properties and allowed easy construction of both forward and nonforward fourth-order algorithms with an arbitrary number of operators. Most fourth-order forward integrators can now be derived analytically from this extended-linear formulation without the use of symbolic algebra.

Finding Coefficients of the Full Array of Motion-Independent N-Body Potentials of Metric Gravity from Gravity's Exterior and Interior Effacement Algebra

NASA Astrophysics Data System (ADS)

Nordtvedt, Kenneth

2018-01-01

In the author's previous publications, a recursive linear algebraic method was introduced for obtaining (without gravitational radiation) the full potential expansions for the gravitational metric field components and the Lagrangian for a general N-body system. Two apparent properties of gravity— Exterior Effacement and Interior Effacement—were defined and fully enforced to obtain the recursive algebra, especially for the motion-independent potential expansions of the general N-body situation. The linear algebraic equations of this method determine the potential coefficients at any order n of the expansions in terms of the lower-order coefficients. Then, enforcing Exterior and Interior Effacement on a selecedt few potential series of the full motion-independent potential expansions, the complete exterior metric field for a single, spherically-symmetric mass source was obtained, producing the Schwarzschild metric field of general relativity. In this fourth paper of this series, the complete spatial metric's motion-independent potentials for N bodies are obtained using enforcement of Interior Effacement and knowledge of the Schwarzschild potentials. From the full spatial metric, the complete set of temporal metric potentials and Lagrangian potentials in the motion-independent case can then be found by transfer equations among the coefficients κ( n, α) → λ( n, ɛ) → ξ( n, α) with κ( n, α), λ( n, ɛ), ξ( n, α) being the numerical coefficients in the spatial metric, the Lagrangian, and the temporal metric potential expansions, respectively.

Unitarity of spin-2 theories with linearized Weyl symmetry in D=2+1 dimensions

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

Dalmazi, D.

2009-10-15

Here we prove unitarity of the recently found fourth-order (in derivatives) self-dual model of spin-2 by investigating the analytic structure of its propagator. The model describes massive particles of helicity +2 (or -2) in D=2+1 dimensions and corresponds to the quadratic truncation of a higher derivative topologically massive gravity about a flat background. It is an intriguing example of a theory where a term in the propagator of the form 1/[{open_square}{sup 2}({open_square}-m{sup 2})] does not lead to ghosts. The crucial role of the linearized Weyl symmetry in getting rid of the ghosts is pointed out. We use a peculiar pairmore » of gauge conditions which fix the linearized reparametrizations and linearized Weyl symmetries separately.« less

A fourth-order box method for solving the boundary layer equations

NASA Technical Reports Server (NTRS)

Wornom, S. F.

1977-01-01

A fourth order box method for calculating high accuracy numerical solutions to parabolic, partial differential equations in two variables or ordinary differential equations is presented. The method is the natural extension of the second order Keller Box scheme to fourth order and is demonstrated with application to the incompressible, laminar and turbulent boundary layer equations. Numerical results for high accuracy test cases show the method to be significantly faster than other higher order and second order methods.

Cassini Maneuver Experience for the Fourth Year of the Solstice Mission

NASA Technical Reports Server (NTRS)

Vaquero, Mar; Hahn, Yungsun; Stumpf, Paul; Valerino, Powtawche; Wagner, Sean; Wong, Mau

2014-01-01

After sixteen years of successful mission operations and invaluable scientific discoveries, the Cassini orbiter continues to tour Saturn on the most complex gravity-assist trajectory ever flown. To ensure that the end-of-mission target of September 2017 is achieved, propellant preservation is highly prioritized over maneuver cycle minimization. Thus, the maneuver decision process, which includes determining whether a maneuver is performed or canceled, designing a targeting strategy and selecting the engine for execution, is being continuously re-evaluated. This paper summarizes the maneuver experience throughout the fourth year of the Solstice Mission highlighting 27 maneuvers targeted to nine Titan flybys.

Hoph Bifurcation in Viscous, Low Speed Flows About an Airfoil with Structural Coupling

DTIC Science & Technology

1993-03-01

8 2.1 Equations of Motion ...... ..................... 8 2.2 Coordinate Transformation ....................... 13 2.3 Aerodynamic...a-frame) f - Apparent body forces applied in noninertial system fL - Explicit fourth-order numerical damping term Ai - Implicit fourth-order...resulting airfoil motion . The equations describing the airfoil motion are integrated in time using a fourth-order Runge-Kutta algorithm. The

Some classes of gravitational shock waves from higher order theories of gravity

NASA Astrophysics Data System (ADS)

Oikonomou, V. K.

2017-02-01

We study the gravitational shock wave generated by a massless high energy particle in the context of higher order gravities of the form F(R,R_{μν}R^{μν},R_{μναβ}R^{μν αβ}). In the case of F(R) gravity, we investigate the gravitational shock wave solutions corresponding to various cosmologically viable gravities, and as we demonstrate the solutions are rescaled versions of the Einstein-Hilbert gravity solution. Interestingly enough, other higher order gravities result to the general relativistic solution, except for some specific gravities of the form F(R_{μν}R^{μν}) and F(R,R_{μν}R^{μν}), which we study in detail. In addition, when realistic Gauss-Bonnet gravities of the form R+F(G) are considered, the gravitational shock wave solutions are identical to the general relativistic solution. Finally, the singularity structure of the gravitational shock waves solutions is studied, and it is shown that the effect of higher order gravities makes the singularities milder in comparison to the general relativistic solutions, and in some particular cases the singularities seem to be absent.

Dual of the Janus solution: An interface conformal field theory

NASA Astrophysics Data System (ADS)

Clark, A. B.; Freedman, D. Z.; Karch, A.; Schnabl, M.

2005-03-01

We propose and study a specific gauge theory dual of the smooth, nonsupersymmetric (and apparently stable) Janus solution of Type IIB supergravity found in Bak et al. [J. High Energy Phys., JHEPFG, 1029-8479 05 (2003) 072]. The dual field theory is N=4 SYM theory on two half-spaces separated by a planar interface with different coupling constants in each half-space. We assume that the position dependent coupling multiplies the operator L' which is the fourth descendent of the primary TrX{IXJ} and closely related to the N=4 Lagrangian density. At the classical level supersymmetry is broken explicitly, but SO(3,2) conformal symmetry is preserved. We use conformal perturbation theory to study various correlation functions to first and second order in the discontinuity of g2YM, confirming quantum level conformal symmetry. Certain quantities such as the vacuum expectation value are protected to all orders in g2YMN, and we find perfect agreement between the weak coupling value in the gauge theory and the strong coupling gravity result. SO(3,2) symmetry requires vanishing vacuum energy, =0, and this is confirmed in first order in the discontinuity.

Precision gravity studies at Cerro Prieto: a progress report

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

Grannell, R.B.; Kroll, R.C.; Wyman, R.M.

A third and fourth year of precision gravity data collection and reduction have now been completed at the Cerro Prieto geothermal field. In summary, 66 permanently monumented stations were occupied between December and April of 1979 to 1980 and 1980 to 1981 by a LaCoste and Romberg gravity meter (G300) at least twice, with a minimum of four replicate values obtained each time. Station 20 alternate, a stable base located on Cerro Prieto volcano, was used as the reference base for the third year and all the stations were tied to this base, using four to five hour loops. Themore » field data were reduced to observed gravity values by (1) multiplication with the appropriate calibration factor; (2) removal of calculated tidal effects; (3) calculation of average values at each station, and (4) linear removal of accumulated instrumental drift which remained after carrying out the first three reductions. Following the reduction of values and calculation of gravity differences between individual stations and the base stations, standard deviations were calculated for the averaged occupation values (two to three per station). In addition, pooled variance calculations were carried out to estimate precision for the surveys as a whole.« less

Active member vibration control experiment in a KC-135 reduced gravity environment

NASA Technical Reports Server (NTRS)

Lawrence, C. R.; Lurie, B. J.; Chen, G.-S.; Swanson, A. D.

1991-01-01

An active member vibration control experiment in a KC-135 reduced gravity environment was carried out by the Air Force Flight Dynamics Laboratory and the Jet Propulsion Laboratory. Two active members, consisting of piezoelectric actuators, displacement sensors, and load cells, were incorporated into a 12-meter, 104 kg box-type test structure. The active member control design involved the use of bridge (compound) feedback concept, in which the collocated force and velocity signals are feedback locally. An impact-type test was designed to accommodate the extremely short duration of the reduced gravity testing window in each parabolic flight. The moving block analysis technique was used to estimate the modal frequencies and dampings from the free-decay responses. A broadband damping performance was demonstrated up to the ninth mode of 40 Hz. The best damping performance achieved in the flight test was about 5 percent in the fourth mode of the test structure.

Venus gravity and topography: 60th degree and order model

NASA Technical Reports Server (NTRS)

Konopliv, A. S.; Borderies, N. J.; Chodas, P. W.; Christensen, E. J.; Sjogren, W. L.; Williams, B. G.; Balmino, G.; Barriot, J. P.

1993-01-01

We have combined the most recent Pioneer Venus Orbiter (PVO) and Magellan (MGN) data with the earlier 1978-1982 PVO data set to obtain a new 60th degree and order spherical harmonic gravity model and a 120th degree and order spherical harmonic topography model. Free-air gravity maps are shown over regions where the most marked improvement has been obtained (Ishtar-Terra, Alpha, Bell and Artemis). Gravity versus topography relationships are presented as correlations per degree and axes orientation.

A spectral approach for the stability analysis of turbulent open-channel flows over granular beds

NASA Astrophysics Data System (ADS)

Camporeale, C.; Canuto, C.; Ridolfi, L.

2012-01-01

A novel Orr-Sommerfeld-like equation for gravity-driven turbulent open-channel flows over a granular erodible bed is here derived, and the linear stability analysis is developed. The whole spectrum of eigenvalues and eigenvectors of the complete generalized eigenvalue problem is computed and analyzed. The fourth-order eigenvalue problem presents singular non-polynomial coefficients with non-homogenous Robin-type boundary conditions that involve first and second derivatives. Furthermore, the Exner condition is imposed at an internal point. We propose a numerical discretization of spectral type based on a single-domain Galerkin scheme. In order to manage the presence of singular coefficients, some properties of Jacobi polynomials have been carefully blended with numerical integration of Gauss-Legendre type. The results show a positive agreement with the classical experimental data and allow one to relate the different types of instability to such parameters as the Froude number, wavenumber, and the roughness scale. The eigenfunctions allow two types of boundary layers to be distinguished, scaling, respectively, with the roughness height and the saltation layer for the bedload sediment transport.

Compensating amplitude-dependent tune-shift without driving fourth-order resonances

NASA Astrophysics Data System (ADS)

Ögren, J.; Ziemann, V.

2017-10-01

If octupoles are used in a ring to correct the amplitude-dependent tune-shift one normally tries to avoid that the octupoles drive additional resonances. Here we consider the optimum placement of octupoles that only affects the amplitude-dependent tune-shift, but does not drive fourth-order resonances. The simplest way turns out to place three equally powered octupoles with 60 ° phase advance between adjacent magnets. Using two such octupole triplets separated by a suitable phase advance cancels all fourth-order resonance driving terms and forms a double triplet we call a six-pack. Using three six-packs at places with different ratios of the beta functions allows to independently control all amplitude-dependent tune-shift terms without exciting additional fourth-order resonances in first order of the octupole excitation.

Somigliana-Pizzetti gravity: the international gravity formula accurate to the sub-nanoGal level

NASA Astrophysics Data System (ADS)

Ardalan, A. A.; Grafarend, E. W.

2001-09-01

The Somigliana-Pizzetti gravity field (the International gravity formula), namely the gravity field of the level ellipsoid (the International Reference Ellipsoid), is derived to the sub-nanoGal accuracy level in order to fulfil the demands of modern gravimetry (absolute gravimeters, super conducting gravimeters, atomic gravimeters). Equations (53), (54) and (59) summarise Somigliana-Pizzetti gravity o({,u) as a function of Jacobi spheroidal latitude { and height u to the order ™(10m10 Gal), and o(B,H) as a function of Gauss (surface normal) ellipsoidal latitude B and height H to the order ™(10m10 Gal) as determined by GPS (`global problem solver'). Within the test area of the state of Baden-Württemberg, Somigliana-Pizzetti gravity disturbances of an average of 25.452 mGal were produced. Computer programs for an operational application of the new international gravity formula with (L,B,H) or (u,{,u) coordinate inputs to a sub-nanoGal level of accuracy are available on the Internet.

Fourth-order numerical solutions of diffusion equation by using SOR method with Crank-Nicolson approach

NASA Astrophysics Data System (ADS)

Muhiddin, F. A.; Sulaiman, J.

2017-09-01

The aim of this paper is to investigate the effectiveness of the Successive Over-Relaxation (SOR) iterative method by using the fourth-order Crank-Nicolson (CN) discretization scheme to derive a five-point Crank-Nicolson approximation equation in order to solve diffusion equation. From this approximation equation, clearly, it can be shown that corresponding system of five-point approximation equations can be generated and then solved iteratively. In order to access the performance results of the proposed iterative method with the fourth-order CN scheme, another point iterative method which is Gauss-Seidel (GS), also presented as a reference method. Finally the numerical results obtained from the use of the fourth-order CN discretization scheme, it can be pointed out that the SOR iterative method is superior in terms of number of iterations, execution time, and maximum absolute error.

Use of GRACE determined secular gravity rates for glacial isostatic adjustment studies in North-America

NASA Astrophysics Data System (ADS)

van der Wal, Wouter; Wu, Patrick; Sideris, Michael G.; Shum, C. K.

2008-10-01

Monthly geopotential spherical harmonic coefficients from the GRACE satellite mission are used to determine their usefulness and limitations for studying glacial isostatic adjustment (GIA) in North-America. Secular gravity rates are estimated by unweighted least-squares estimation using release 4 coefficients from August 2002 to August 2007 provided by the Center for Space Research (CSR), University of Texas. Smoothing is required to suppress short wavelength noise, in addition to filtering to diminish geographically correlated errors, as shown in previous studies. Optimal cut-off degrees and orders are determined for the destriping filter to maximize the signal to noise ratio. The halfwidth of the Gaussian filter is shown to significantly affect the sensitivity of the GRACE data (with respect to upper mantle viscosity and ice loading history). Therefore, the halfwidth should be selected based on the desired sensitivity. It is shown that increase in water storage in an area south west of Hudson Bay, from the summer of 2003 to the summer of 2006, contributes up to half of the maximum estimated gravity rate. Hydrology models differ in the predictions of the secular change in water storage, therefore even 4-year trend estimates are influenced by the uncertainty in water storage changes. Land ice melting in Greenland and Alaska has a non-negligible contribution, up to one-fourth of the maximum gravity rate. The estimated secular gravity rate shows two distinct peaks that can possibly be due to two domes in the former Pleistocene ice cover: west and south east of Hudson Bay. With a limited number of models, a better fit is obtained with models that use the ICE-3G model compared to the ICE-5G model. However, the uncertainty in interannual variations in hydrology models is too large to constrain the ice loading history with the current data span. For future work in which GRACE will be used to constrain ice loading history and the Earth's radial viscosity profile, it is important to include realistic uncertainty estimates for hydrology models and land ice melting in addition to the effects of lateral heterogeneity.

A Two Colorable Fourth Order Compact Difference Scheme and Parallel Iterative Solution of the 3D Convection Diffusion Equation

NASA Technical Reports Server (NTRS)

Zhang, Jun; Ge, Lixin; Kouatchou, Jules

2000-01-01

A new fourth order compact difference scheme for the three dimensional convection diffusion equation with variable coefficients is presented. The novelty of this new difference scheme is that it Only requires 15 grid points and that it can be decoupled with two colors. The entire computational grid can be updated in two parallel subsweeps with the Gauss-Seidel type iterative method. This is compared with the known 19 point fourth order compact differenCe scheme which requires four colors to decouple the computational grid. Numerical results, with multigrid methods implemented on a shared memory parallel computer, are presented to compare the 15 point and the 19 point fourth order compact schemes.

Four-Photon Imaging with Thermal Light

NASA Astrophysics Data System (ADS)

Wen, Feng; Xue, Xinxin; Zhang, Xun; Yuan, Chenzhi; Sun, Jia; Song, Jianping; Zhang, Yanpeng

2014-10-01

In a near-field four-photon correlation measurement, ghost imaging with classical incoherent light is investigated. By applying the Klyshko advanced-wave picture, we consider the properties of four-photon spatial correlation and find that the fourth-order spatial correlation function can be decomposed into multiple lower-order correlation functions. On the basis of the spatial correlation properties, a proof-of-principle four-photon ghost imaging is proposed, and the effect of each part in a fourth-order correlation function on imaging is also analyzed. In addition, the similarities and differences among ghost imaging by fourth-, second-, and third-order correlations are also discussed. It is shown that the contrast and visibility of fourth-order correlated imaging are improved significantly, while the resolution is unchanged. Such studies can be very useful in better understanding multi photon interference and multi-channel correlation imaging.

Fourth-order convergence of a compact scheme for the one-dimensional biharmonic equation

NASA Astrophysics Data System (ADS)

Fishelov, D.; Ben-Artzi, M.; Croisille, J.-P.

2012-09-01

The convergence of a fourth-order compact scheme to the one-dimensional biharmonic problem is established in the case of general Dirichlet boundary conditions. The compact scheme invokes value of the unknown function as well as Pade approximations of its first-order derivative. Using the Pade approximation allows us to approximate the first-order derivative within fourth-order accuracy. However, although the truncation error of the discrete biharmonic scheme is of fourth-order at interior point, the truncation error drops to first-order at near-boundary points. Nonetheless, we prove that the scheme retains its fourth-order (optimal) accuracy. This is done by a careful inspection of the matrix elements of the discrete biharmonic operator. A number of numerical examples corroborate this effect. We also present a study of the eigenvalue problem uxxxx = νu. We compute and display the eigenvalues and the eigenfunctions related to the continuous and the discrete problems. By the positivity of the eigenvalues, one can deduce the stability of of the related time-dependent problem ut = -uxxxx. In addition, we study the eigenvalue problem uxxxx = νuxx. This is related to the stability of the linear time-dependent equation uxxt = νuxxxx. Its continuous and discrete eigenvalues and eigenfunction (or eigenvectors) are computed and displayed graphically.

Criticality in third order lovelock gravity and butterfly effect

NASA Astrophysics Data System (ADS)

Qaemmaqami, Mohammad M.

2018-01-01

We study third order Lovelock Gravity in D=7 at the critical point which three (A)dS vacua degenerate into one. We see there is not propagating graviton at the critical point. And also we compute the butterfly velocity for this theory at the critical point by considering the shock wave solutions near horizon, this is important to note that although there is no propagating graviton at the critical point, due to boundary gravitons the butterfly velocity is non-zero. Finally we observe that the butterfly velocity for third order Lovelock Gravity at the critical point in D=7 is less than the butterfly velocity for Einstein-Gauss-Bonnet Gravity at the critical point in D=7 which is less than the butterfly velocity in D = 7 for Einstein Gravity, vB^{E.H}>vB^{E.G.B}>vB^{3rd Lovelock} . Maybe we can conclude that by adding higher order curvature corrections to Einstein Gravity the butterfly velocity decreases.

Venus spherical harmonic gravity model to degree and order 60

NASA Technical Reports Server (NTRS)

Konopliv, Alex S.; Sjogren, William L.

1994-01-01

The Magellan and Pioneer Venus Orbiter radiometric tracking data sets have been combined to produce a 60th degree and order spherical harmonic gravity field. The Magellan data include the high-precision X-band gravity tracking from September 1992 to May 1993 and post-aerobraking data up to January 5, 1994. Gravity models are presented from the application of Kaula's power rule for Venus and an alternative a priori method using surface accelerations. Results are given as vertical gravity acceleration at the reference surface, geoid, vertical Bouguer, and vertical isostatic maps with errors for the vertical gravity and geoid maps included. Correlation of the gravity with topography for the different models is also discussed.

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.

Fourth-order partial differential equation noise removal on welding images

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

Halim, Suhaila Abd; Ibrahim, Arsmah; Sulong, Tuan Nurul Norazura Tuan

2015-10-22

Partial differential equation (PDE) has become one of the important topics in mathematics and is widely used in various fields. It can be used for image denoising in the image analysis field. In this paper, a fourth-order PDE is discussed and implemented as a denoising method on digital images. The fourth-order PDE is solved computationally using finite difference approach and then implemented on a set of digital radiographic images with welding defects. The performance of the discretized model is evaluated using Peak Signal to Noise Ratio (PSNR). Simulation is carried out on the discretized model on different level of Gaussianmore » noise in order to get the maximum PSNR value. The convergence criteria chosen to determine the number of iterations required is measured based on the highest PSNR value. Results obtained show that the fourth-order PDE model produced promising results as an image denoising tool compared with median filter.« less

Metric for strong intrinsic fourth-order phonon anharmonicity

NASA Astrophysics Data System (ADS)

Yue, Sheng-Ying; Zhang, Xiaoliang; Qin, Guangzhao; Phillpot, Simon R.; Hu, Ming

2017-05-01

Under the framework of Taylor series expansion for potential energy, we propose a simple and robust metric, dubbed "regular residual analysis," to measure the fourth-order phonon anharmonicity in crystals. The method is verified by studying the intrinsic strong higher-order anharmonic effects in UO2 and CeO2. Comparison of the thermal conductivity results, which calculated by the anharmonic lattice dynamics method coupled with the Boltzmann transport equation and the spectral energy density method coupled with ab initio molecular dynamics simulation further validates our analysis. Analysis of the bulk Si and Ge systems confirms that the fourth-order phonon anharmonicity is enhanced and cannot be neglected at high enough temperatures, which agrees with a previous study where the four-phonon scattering was explicitly determined. This metric will facilitate evaluating and interpreting the lattice thermal conductivity of crystals with strong fourth-order phonon anharmonicity.

Mars synthetic topographic mapping

USGS Publications Warehouse

Wu, S.S.C.

1978-01-01

Topographic contour maps of Mars are compiled by the synthesis of data acquired from various scientific experiments of the Mariner 9 mission, including S-band radio-occulation, the ultraviolet spectrometer (UVS), the infrared radiometer (IRR), the infrared interferometer spectrometer (IRIS) and television imagery, as well as Earth-based radar information collected at Goldstone, Haystack, and Arecibo Observatories. The entire planet is mapped at scales of 1:25,000,000 and 1:25,000,000 using Mercator, Lambert, and polar stereographic map projections. For the computation of map projections, a biaxial spheroid figure is adopted. The semimajor and semiminor axes are 3393.4 and 3375.7 km, respectively, with a polar flattening of 0.0052. For the computation of elevations, a topographic datum is defined by a gravity field described in terms of spherical harmonics of fourth order and fourth degree combined with a 6.1-mbar occulation pressure surface. This areoid can be approximated by a triaxial ellipsoid with semimajor axes of A = 3394.6 km and B = 3393.3 km and a semiminor axis of C = 3376.3 km. The semimajor axis A intersects the Martian surface at longitude 105??W. The dynamic flattening of Mars is 0.00525. The contour intercal of the maps is 1 km. For some prominent features where overlapping pictures from Mariner 9 are available, local contour maps at relatively larger scales were also compiled by photogrammetric methods on stereo plotters. ?? 1978.

Agenda of the Fourth Annual Summer Conference, NASA/USRA University Advanced Design Program

NASA Technical Reports Server (NTRS)

1988-01-01

Presentations given by the participants at the fourth annual summer conference of the NASA/USRA University Advanced Design Program are summarized. The study topics include potential space and aeronautics projects which could be undertaken during a 20 to 30 year period beginning with the Space Station Initial Operating Configuration (IOC) scheduled for the early to mid-1990's. This includes system design studies for both manned and unmanned endeavors; e.g., lunar launch and landing facilities and operations, variable artificial gravity facility for the Space Station, manned Mars aircraft and delivery system, long term space habitat, construction equipment for lunar bases, Mars oxygen production system, trans-Pacific high speed civil transport, V/STOL aircraft concepts, etc.

A Non-Dissipative Staggered Fourth-Order Accurate Explicit Finite Difference Scheme for the Time-Domain Maxwell's Equations

NASA Technical Reports Server (NTRS)

Yefet, Amir; Petropoulos, Peter G.

1999-01-01

We consider a divergence-free non-dissipative fourth-order explicit staggered finite difference scheme for the hyperbolic Maxwell's equations. Special one-sided difference operators are derived in order to implement the scheme near metal boundaries and dielectric interfaces. Numerical results show the scheme is long-time stable, and is fourth-order convergent over complex domains that include dielectric interfaces and perfectly conducting surfaces. We also examine the scheme's behavior near metal surfaces that are not aligned with the grid axes, and compare its accuracy to that obtained by the Yee scheme.

Numerical pricing of options using high-order compact finite difference schemes

NASA Astrophysics Data System (ADS)

Tangman, D. Y.; Gopaul, A.; Bhuruth, M.

2008-09-01

We consider high-order compact (HOC) schemes for quasilinear parabolic partial differential equations to discretise the Black-Scholes PDE for the numerical pricing of European and American options. We show that for the heat equation with smooth initial conditions, the HOC schemes attain clear fourth-order convergence but fail if non-smooth payoff conditions are used. To restore the fourth-order convergence, we use a grid stretching that concentrates grid nodes at the strike price for European options. For an American option, an efficient procedure is also described to compute the option price, Greeks and the optimal exercise curve. Comparisons with a fourth-order non-compact scheme are also done. However, fourth-order convergence is not experienced with this strategy. To improve the convergence rate for American options, we discuss the use of a front-fixing transformation with the HOC scheme. We also show that the HOC scheme with grid stretching along the asset price dimension gives accurate numerical solutions for European options under stochastic volatility.

A fourth order accurate finite difference scheme for the computation of elastic waves

NASA Technical Reports Server (NTRS)

Bayliss, A.; Jordan, K. E.; Lemesurier, B. J.; Turkel, E.

1986-01-01

A finite difference for elastic waves is introduced. The model is based on the first order system of equations for the velocities and stresses. The differencing is fourth order accurate on the spatial derivatives and second order accurate in time. The model is tested on a series of examples including the Lamb problem, scattering from plane interf aces and scattering from a fluid-elastic interface. The scheme is shown to be effective for these problems. The accuracy and stability is insensitive to the Poisson ratio. For the class of problems considered here it is found that the fourth order scheme requires for two-thirds to one-half the resolution of a typical second order scheme to give comparable accuracy.

Dual of the Janus solution: An interface conformal field theory

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

Clark, A.B.; Karch, A.; Freedman, D.Z.

2005-03-15

We propose and study a specific gauge theory dual of the smooth, nonsupersymmetric (and apparently stable) Janus solution of Type IIB supergravity found in Bak et al. [J. High Energy Phys. 05 (2003) 072]. The dual field theory is N=4 SYM theory on two half-spaces separated by a planar interface with different coupling constants in each half-space. We assume that the position dependent coupling multiplies the operator L{sup '} which is the fourth descendent of the primary TrX{sup {l_brace}}{sup I}X{sup J{r_brace}} and closely related to the N=4 Lagrangian density. At the classical level supersymmetry is broken explicitly, but SO(3,2) conformalmore » symmetry is preserved. We use conformal perturbation theory to study various correlation functions to first and second order in the discontinuity of g{sub YM}{sup 2}, confirming quantum level conformal symmetry. Certain quantities such as the vacuum expectation value are protected to all orders in g{sub YM}{sup 2}N, and we find perfect agreement between the weak coupling value in the gauge theory and the strong coupling gravity result. SO(3,2) symmetry requires vanishing vacuum energy, =0, and this is confirmed in first order in the discontinuity.« less

Low-degree gravity change from GPS data of COSMIC and GRACE satellite missions

NASA Astrophysics Data System (ADS)

Lin, Tingjung; Hwang, Cheinway; Tseng, Tzu-Pang; Chao, B. F.

2012-01-01

This paper demonstrates estimation of time-varying gravity harmonic coefficients from GPS data of COSMIC and GRACE satellite missions. The kinematic orbits of COSMIC and GRACE are determined to the cm-level accuracy. The NASA Goddard's GEODYN II software is used to model the orbit dynamics of COSMIC and GRACE, including the effect of a static gravity field. The surface forces are estimated per one orbital period. Residual orbits generated from kinematic and reference orbits serve as observables to determine the harmonic coefficients in the weighted-constraint least-squares. The monthly COSMIC and GRACE GPS data from September 2006 to December 2007 (16 months) are processed to estimate harmonic coefficients to degree 5. The geoid variations from the GPS and CSR RL04 (GRACE) solutions show consistent patterns over space and time, especially in regions of active hydrological changes. The monthly GPS-derived second zonal coefficient closely resembles the SLR-derived and CSR RL04 values, and third and fourth zonal coefficients resemble the CSR RL04 values.

Characteristics of the fourth order resonance in high intensity linear accelerators

NASA Astrophysics Data System (ADS)

Jeon, D.; Hwang, Kyung Ryun

2017-06-01

For the 4σ = 360° space-charge resonance in high intensity linear accelerators, the emittance growth is surveyed for input Gaussian beams, as a function of the depressed phase advance per cell σ and the initial tune depression (σo - σ). For each data point, the linac lattice is designed such that the fourth order resonance dominates over the envelope instability. The data show that the maximum emittance growth takes place at σ ≈ 87° over a wide range of the tune depression (or beam current), which confirms that the relevant parameter for the emittance growth is σ and that for the bandwidth is σo - σ. An interesting four-fold phase space structure is observed that cannot be explained with the fourth order resonance terms alone. Analysis attributes this effect to a small negative sixth order detuning term as the beam is redistributed by the resonance. Analytical studies show that the tune increases monotonically for the Gaussian beam which prevents the resonance for σ > 90°. Frequency analysis indicates that the four-fold structure observed for input Kapchinskij-Vladmirskij beams when σ < 90°, is not the fourth order resonance but a fourth order envelope instability because the 1/4 = 90°/360° component is missing in the frequency spectrum.

77 FR 17476 - Information Collections Being Reviewed by the Federal Communications Commission

Federal Register 2010, 2011, 2012, 2013, 2014

2012-03-26

... Rules for FM Broadcast Translator Stations, Fourth Report and Order and Third Order on Reconsideration... more than 4 pending translator applications) to request the dismissal of applications to comply with... Service and Eligibility Rules for FM Broadcast Translator Stations, Fourth Report and Order and Third...

Documentation of the Goddard Laboratory for atmospheres fourth-order two-layer shallow water model

NASA Technical Reports Server (NTRS)

Takacs, L. L. (Compiler)

1986-01-01

The theory and numerical treatment used in the 2-level GLA fourth-order shallow water model are described. This model was designed to emulate the horizontal finite differences used by the GLA Fourth-Order General Circulation Model (Kalnay et al., 1983) in addition to its grid structure, form of high-latitude and global filtering, and time-integration schemes. A user's guide is also provided instructing the user on how to create initial conditions, execute the model, and post-process the data history.

Eigenvalues of the Wentzell-Laplace operator and of the fourth order Steklov problems

NASA Astrophysics Data System (ADS)

Xia, Changyu; Wang, Qiaoling

2018-05-01

We prove a sharp upper bound and a lower bound for the first nonzero eigenvalue of the Wentzell-Laplace operator on compact manifolds with boundary and an isoperimetric inequality for the same eigenvalue in the case where the manifold is a bounded domain in a Euclidean space. We study some fourth order Steklov problems and obtain isoperimetric upper bound for the first eigenvalue of them. We also find all the eigenvalues and eigenfunctions for two kind of fourth order Steklov problems on a Euclidean ball.

Bilinear, trilinear forms, and exact solution of certain fourth order integrable difference equations

NASA Astrophysics Data System (ADS)

Sahadevan, R.; Rajakumar, S.

2008-03-01

A systematic investigation of finding bilinear or trilinear representations of fourth order autonomous ordinary difference equation, x(n +4)=F(x(n),x(n+1),x(n+2),x(n+3)) or xn +4=F(xn,xn +1,xn +2,xn +3), is made. As an illustration, we consider fourth order symplectic integrable difference equations reported by [Capel and Sahadevan, Physica A 289, 86 (2001)] and derived their bilinear or trilinear forms. Also, it is shown that the obtained bilinear representations admit exact solution of rational form.

Normal gravity field in relativistic geodesy

NASA Astrophysics Data System (ADS)

Kopeikin, Sergei; Vlasov, Igor; Han, Wen-Biao

2018-02-01

Modern geodesy is subject to a dramatic change from the Newtonian paradigm to Einstein's theory of general relativity. This is motivated by the ongoing advance in development of quantum sensors for applications in geodesy including quantum gravimeters and gradientometers, atomic clocks and fiber optics for making ultra-precise measurements of the geoid and multipolar structure of the Earth's gravitational field. At the same time, very long baseline interferometry, satellite laser ranging, and global navigation satellite systems have achieved an unprecedented level of accuracy in measuring 3-d coordinates of the reference points of the International Terrestrial Reference Frame and the world height system. The main geodetic reference standard to which gravimetric measurements of the of Earth's gravitational field are referred is a normal gravity field represented in the Newtonian gravity by the field of a uniformly rotating, homogeneous Maclaurin ellipsoid of which mass and quadrupole momentum are equal to the total mass and (tide-free) quadrupole moment of Earth's gravitational field. The present paper extends the concept of the normal gravity field from the Newtonian theory to the realm of general relativity. We focus our attention on the calculation of the post-Newtonian approximation of the normal field that is sufficient for current and near-future practical applications. We show that in general relativity the level surface of homogeneous and uniformly rotating fluid is no longer described by the Maclaurin ellipsoid in the most general case but represents an axisymmetric spheroid of the fourth order with respect to the geodetic Cartesian coordinates. At the same time, admitting a post-Newtonian inhomogeneity of the mass density in the form of concentric elliptical shells allows one to preserve the level surface of the fluid as an exact ellipsoid of rotation. We parametrize the mass density distribution and the level surface with two parameters which are intrinsically connected to the existence of the residual gauge freedom, and derive the post-Newtonian normal gravity field of the rotating spheroid both inside and outside of the rotating fluid body. The normal gravity field is given, similarly to the Newtonian gravity, in a closed form by a finite number of the ellipsoidal harmonics. We employ transformation from the ellipsoidal to spherical coordinates to deduce a more conventional post-Newtonian multipolar expansion of scalar and vector gravitational potentials of the rotating spheroid. We compare these expansions with that of the normal gravity field generated by the Kerr metric and demonstrate that the Kerr metric has a fairly limited application in relativistic geodesy as it does not match the normal gravity field of the Maclaurin ellipsoid already in the Newtonian limit. We derive the post-Newtonian generalization of the Somigliana formula for the normal gravity field measured on the surface of the rotating spheroid and employed in practical work for measuring Earth's gravitational field anomalies. Finally, we discuss the possible choice of the gauge-dependent parameters of the normal gravity field model for practical applications and compare it with the existing EGM2008 model of a gravitational field.

Rare-Earth Fourth-Order Multipole Moment in Cubic ErCo2 Probed by Linear Dichroism in Core-Level Photoemission

NASA Astrophysics Data System (ADS)

Abozeed, Amina A.; Kadono, Toshiharu; Sekiyama, Akira; Fujiwara, Hidenori; Higashiya, Atsushi; Yamasaki, Atsushi; Kanai, Yuina; Yamagami, Kohei; Tamasaku, Kenji; Yabashi, Makina; Ishikawa, Tetsuya; Andreev, Alexander V.; Wada, Hirofumi; Imada, Shin

2018-03-01

We developed a method to experimentally quantify the fourth-order multipole moment of the rare-earth 4f orbital. Linear dichroism (LD) in the Er 3d5/2 core-level photoemission spectra of cubic ErCo2 was measured using bulk-sensitive hard X-ray photoemission spectroscopy. Theoretical calculation reproduced the observed LD, and the result showed that the observed result does not contradict the suggested Γ 83 ground state. Theoretical calculation further showed a linear relationship between the LD size and the size of the fourth-order multipole moment of the Er3+ ion, which is proportional to the expectation value < O40 + 5O44> , where Onm are the Stevens operators. These analyses indicate that the LD in 3d photoemission spectra can be used to quantify the average fourth-order multipole moment of rare-earth atoms in a cubic crystal electric field.

Venus Gravity: 180th Degree and Order Model

NASA Technical Reports Server (NTRS)

Konopliv, A. S.; Banerdt, W. B.; Sjogren, W. L.

1998-01-01

The Megallan Doppler radiometric tracking data provides unprecedented precision for spacecraft based gravity measurements with the maximum resolution approaching spherical harmonic degree and order 180 in selected equatorial regions.

Sixth- and eighth-order Hermite integrator for N-body simulations

NASA Astrophysics Data System (ADS)

Nitadori, Keigo; Makino, Junichiro

2008-10-01

We present sixth- and eighth-order Hermite integrators for astrophysical N-body simulations, which use the derivatives of accelerations up to second-order ( snap) and third-order ( crackle). These schemes do not require previous values for the corrector, and require only one previous value to construct the predictor. Thus, they are fairly easy to implement. The additional cost of the calculation of the higher-order derivatives is not very high. Even for the eighth-order scheme, the number of floating-point operations for force calculation is only about two times larger than that for traditional fourth-order Hermite scheme. The sixth-order scheme is better than the traditional fourth-order scheme for most cases. When the required accuracy is very high, the eighth-order one is the best. These high-order schemes have several practical advantages. For example, they allow a larger number of particles to be integrated in parallel than the fourth-order scheme does, resulting in higher execution efficiency in both general-purpose parallel computers and GRAPE systems.

Characteristics of the fourth order resonance in high intensity linear accelerators

DOE PAGES

Jeon, D.; Hwang, Kyung Ryun

2017-06-19

For the 4σ = 360° space-charge resonance in high intensity linear accelerators, the emittance growth is surveyed for input Gaussian beams, as a function of the depressed phase advance per cell σ and the initial tune depression (σ o – σ). For each data point, the linac lattice is designed such that the fourth order resonance dominates over the envelope instability. Additionally, the data show that the maximum emittance growth takes place at σ ≈ 87° over a wide range of the tune depression (or beam current), which confirms that the relevant parameter for the emittance growth is σ andmore » that for the bandwidth is σ o – σ. An interesting four-fold phase space structure is observed that cannot be explained with the fourth order resonance terms alone. Analysis attributes this effect to a small negative sixth order detuning term as the beam is redistributed by the resonance. Analytical studies show that the tune increases monotonically for the Gaussian beam which prevents the resonance for σ > 90°. Lastly, frequency analysis indicates that the four-fold structure observed for input Kapchinskij-Vladmirskij beams when σ < 90°, is not the fourth order resonance but a fourth order envelope instability because the 1/4 = 90°/360° component is missing in the frequency spectrum.« less

Characteristics of the fourth order resonance in high intensity linear accelerators

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

Jeon, D.; Hwang, Kyung Ryun

For the 4σ = 360° space-charge resonance in high intensity linear accelerators, the emittance growth is surveyed for input Gaussian beams, as a function of the depressed phase advance per cell σ and the initial tune depression (σ o – σ). For each data point, the linac lattice is designed such that the fourth order resonance dominates over the envelope instability. Additionally, the data show that the maximum emittance growth takes place at σ ≈ 87° over a wide range of the tune depression (or beam current), which confirms that the relevant parameter for the emittance growth is σ andmore » that for the bandwidth is σ o – σ. An interesting four-fold phase space structure is observed that cannot be explained with the fourth order resonance terms alone. Analysis attributes this effect to a small negative sixth order detuning term as the beam is redistributed by the resonance. Analytical studies show that the tune increases monotonically for the Gaussian beam which prevents the resonance for σ > 90°. Lastly, frequency analysis indicates that the four-fold structure observed for input Kapchinskij-Vladmirskij beams when σ < 90°, is not the fourth order resonance but a fourth order envelope instability because the 1/4 = 90°/360° component is missing in the frequency spectrum.« less

Advanced reservoir characterization and evaluation of CO{sub 2} gravity drainage in the naturally fractured Spraberry Trend Area, Class III

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

Heckman, Tracy; Schechter, David S.

2000-04-11

The overall goal of this project was to assess the economic feasibility of CO{sub 2} flooding the naturally fractured Spraberry Trend Area in West Texas. This objective was accomplished by conducting research in four areas: (1) extensive characterization of the reservoirs, (2) experimental studies of crude oil/brine/rock (COBR) interaction in the reservoirs, (3) analytical and numerical simulation of Spraberry reservoirs, and, (4) experimental investigations on CO{sub 2} gravity drainage in Spraberry whole cores. This report provides results of the fourth year of the five-year project for each of the four areas including a status report of field activities leading upmore » to injection of CO{sub 2}.« less

Effects of gravity on the circadian period in rats

NASA Technical Reports Server (NTRS)

Murakami, Dean M.; Demaria, Victor H.; Fuller, Charles A.

1991-01-01

The effect of increased gravity force on the circadian period of body temperature and activity of rats was investigated using rats implanted with a small radio telemetry device and, after a 2-week recovery and a 3-week control period at 1G, rotated at for 4 weeks at a constant 2G field in a 18-ft-diam centrifuge. Measurements of the mean freerunning period of the temperature and activity rhythms after 10 days showed that the exposure to 2G led to a functional separation of the pacemakers that regulate the activity and the temperature in the animals. Each pacemaker reacted differently: the activity period increased and the temperature period decreased. By the third or the fourth week, the activity and the temperature periods have returned to 1G control levels.

ISMCR 1994: Topical Workshop on Virtual Reality. Proceedings of the Fourth International Symposium on Measurement and Control in Robotics

NASA Technical Reports Server (NTRS)

1994-01-01

This symposium on measurement and control in robotics included sessions on: (1) rendering, including tactile perception and applied virtual reality; (2) applications in simulated medical procedures and telerobotics; (3) tracking sensors in a virtual environment; (4) displays for virtual reality applications; (5) sensory feedback including a virtual environment application with partial gravity simulation; and (6) applications in education, entertainment, technical writing, and animation.

Einsteinian cubic gravity

NASA Astrophysics Data System (ADS)

Bueno, Pablo; Cano, Pablo A.

2016-11-01

We drastically simplify the problem of linearizing a general higher-order theory of gravity. We reduce it to the evaluation of its Lagrangian on a particular Riemann tensor depending on two parameters, and the computation of two derivatives with respect to one of those parameters. We use our method to construct a D -dimensional cubic theory of gravity which satisfies the following properties: (1) it shares the spectrum of Einstein gravity, i.e., it only propagates a transverse and massless graviton on a maximally symmetric background; (2) it is defined in the same way in general dimensions; (3) it is neither trivial nor topological in four dimensions. Up to cubic order in curvature, the only previously known theories satisfying the first two requirements are the Lovelock ones. We show that, up to cubic order, there exists only one additional theory satisfying requirements (1) and (2). Interestingly, this theory is, along with Einstein gravity, the only one which also satisfies (3).

Fourth-order acoustic torque in intense sound fields

NASA Technical Reports Server (NTRS)

Wang, T. G.; Kanber, H.; Olli, E. E.

1978-01-01

The observation of a fourth-order acoustic torque in intense sound fields is reported. The torque was determined by measuring the acoustically induced angular deflection of a polished cylinder suspended by a torsion fiber. This torque was measured in a sound field of amplitude greater than that in which first-order acoustic torque has been observed.

FAST TRACK COMMUNICATION: Born-Infeld extension of new massive gravity

NASA Astrophysics Data System (ADS)

Güllü, İbrahim; Çaǧri Şişman, Tahsin; Tekin, Bayram

2010-08-01

We present a three-dimensional gravitational Born-Infeld theory which reduces to the recently found new massive gravity (NMG) at the quadratic level in the small curvature expansion and at the cubic order reproduces the deformation of NMG obtained from AdS/CFT. Our action provides a remarkable extension of NMG to all orders in the curvature and might define a consistent quantum gravity.

Fourth-Order Spatial Correlation of Thermal Light

NASA Astrophysics Data System (ADS)

Wen, Feng; Zhang, Xun; Xue, Xin-Xin; Sun, Jia; Song, Jian-Ping; Zhang, Yan-Peng

2014-11-01

We investigate the fourth-order spatial correlation properties of pseudo-thermal light in the photon counting regime, and apply the Klyshko advanced-wave picture to describe the process of four-photon coincidence counting measurement. We deduce the theory of a proof-of-principle four-photon coincidence counting configuration, and find that if the four randomly radiated photons come from the same radiation area and are indistinguishable in principle, the fourth-order correlation of them is 24 times larger than that when four photons come from different radiation areas. In addition, we also show that the higher-order spatial correlation function can be decomposed into multiple lower-order correlation functions, and the contrast and visibility of low-order correlation peaks are less than those of higher orders, while the resolutions all are identical. This study may be useful for better understanding the four-photon interference and multi-channel correlation imaging.

Possibilities of the regional gravity field recovery from first-, second- and third-order radial derivatives of the disturbing gravitational potential measured on moving platforms

NASA Astrophysics Data System (ADS)

Pitonak, Martin; Sprlak, Michal; Novak, Pavel; Tenzer, Robert

2016-04-01

Recently realized gravity-dedicated satellite missions allow for measuring values of scalar, vectorial (Gravity Recovery And Climate Experiment - GRACE) and second-order tensorial (Gravity field and steady-state Ocean Circulation Explorer - GOCE) parameters of the Earth's gravitational potential. Theoretical aspects related to using moving sensors for measuring elements of the third-order gravitational tensor are currently under investigation, e.g., the gravity field-dedicated satellite mission OPTIMA (OPTical Interferometry for global Mass change detection from space) should measure third-order derivatives of the Earth's gravitational potential. This contribution investigates regional recovery of the disturbing gravitational potential on the Earth's surface from satellite and aerial observations of the first-, second- and third-order radial derivatives of the disturbing gravitational potential. Synthetic measurements along a satellite orbit at the altitude of 250 km and along an aircraft track at the altitude of 10 km are synthetized from the global gravitational model EGM2008 and polluted by the Gaussian noise. The process of downward continuation is stabilized by the Tikhonov regularization. Estimated values of the disturbing gravitational potential are compared with the same quantity synthesized directly from EGM2008.

Multi-scale Eulerian model within the new National Environmental Modeling System

NASA Astrophysics Data System (ADS)

Janjic, Zavisa; Janjic, Tijana; Vasic, Ratko

2010-05-01

The unified Non-hydrostatic Multi-scale Model on the Arakawa B grid (NMMB) is being developed at NCEP within the National Environmental Modeling System (NEMS). The finite-volume horizontal differencing employed in the model preserves important properties of differential operators and conserves a variety of basic and derived dynamical and quadratic quantities. Among these, conservation of energy and enstrophy improves the accuracy of nonlinear dynamics of the model. Within further model development, advection schemes of fourth order of formal accuracy have been developed. It is argued that higher order advection schemes should not be used in the thermodynamic equation in order to preserve consistency with the second order scheme used for computation of the pressure gradient force. Thus, the fourth order scheme is applied only to momentum advection. Three sophisticated second order schemes were considered for upgrade. Two of them, proposed in Janjic(1984), conserve energy and enstrophy, but with enstrophy calculated differently. One of them conserves enstrophy as computed by the most accurate second order Laplacian operating on stream function. The other scheme conserves enstrophy as computed from the B grid velocity. The third scheme (Arakawa 1972) is arithmetic mean of the former two. It does not conserve enstrophy strictly, but it conserves other quadratic quantities that control the nonlinear energy cascade. Linearization of all three schemes leads to the same second order linear advection scheme. The second order term of the truncation error of the linear advection scheme has a special form so that it can be eliminated by simply preconditioning the advected quantity. Tests with linear advection of a cone confirm the advantage of the fourth order scheme. However, if a localized, large amplitude and high wave-number pattern is present in initial conditions, the clear advantage of the fourth order scheme disappears. In real data runs, problems with noisy data may appear due to mountains. Thus, accuracy and formal accuracy may not be synonymous. The nonlinear fourth order schemes are quadratic conservative and reduce to the Arakawa Jacobian in case of non-divergent flow. In case of general flow the conservation properties of the new momentum advection schemes impose stricter constraint on the nonlinear cascade than the original second order schemes. However, for non-divergent flow, the conservation properties of the fourth order schemes cannot be proven in the same way as those of the original second order schemes. Therefore, nonlinear tests were carried out in order to check how well the fourth order schemes control the nonlinear energy cascade. In the tests nonlinear shallow water equations are solved in a rotating rectangular domain (Janjic, 1984). The domain is covered with only 17 x 17 grid points. A diagnostic quantity is used to monitor qualitative changes in the spectrum over 116 days of simulated time. All schemes maintained meaningful solutions throughout the test. Among the second order schemes, the best result was obtained with the scheme that conserved enstrophy as computed by the second order Laplacian of the stream function. It was closely followed by the Arakawa (1972) scheme, while the remaining scheme was distant third. The fourth order schemes ranked in the same order, and were competitive throughout the experiments with their second order counterparts in preventing accumulation of energy at small scales. Finally, the impact was examined of the fourth order momentum advection on global medium range forecasts. The 500 mb anomaly correlation coefficient is used as a measure of success of the forecasts. Arakawa, A., 1972: Design of the UCLA general circulation model. Tech. Report No. 7, Department of Meteorology, University of California, Los Angeles, 116 pp. Janjic, Z. I., 1984: Non-linear advection schemes and energy cascade on semi-staggered grids. Monthly Weather Review, 112, 1234-1245.

Gap solitons in PT-symmetric optical lattices with higher-order diffraction.

PubMed

Ge, Lijuan; Shen, Ming; Ma, Chunlan; Zang, Taocheng; Dai, Lu

2014-12-01

The existence and stability of gap solitons are investigated in the semi-infinite gap of a parity-time (PT)-symmetric periodic potential (optical lattice) with a higher-order diffraction. The Bloch bands and band gaps of this PT-symmetric optical lattice depend crucially on the coupling constant of the fourth-order diffraction, whereas the phase transition point of this PT optical lattice remains unchangeable. The fourth-order diffraction plays a significant role in destabilizing the propagation of dipole solitons. Specifically, when the fourth-order diffraction coupling constant increases, the stable region of the dipole solitons shrinks as new regions of instability appear. However, fundamental solitons are found to be always linearly stable with arbitrary positive value of the coupling constant. We also investigate nonlinear evolution of the PT solitons under perturbation.

Generation of localized patterns in anharmonic lattices with cubic-quintic nonlinearities and fourth-order dispersion via a variational approach

NASA Astrophysics Data System (ADS)

Wamba, Etienne; Tchakoutio Nguetcho, Aurélien S.

2018-05-01

We use the time-dependent variational method to examine the formation of localized patterns in dynamically unstable anharmonic lattices with cubic-quintic nonlinearities and fourth-order dispersion. The governing equation is an extended nonlinear Schrödinger equation known for modified Frankel-Kontorova models of atomic lattices and here derived from an extended Bose-Hubbard model of bosonic lattices with local three-body interactions. In presence of modulated waves, we derive and investigate the ordinary differential equations for the time evolution of the amplitude and phase of dynamical perturbation. Through an effective potential, we find the modulationally unstable domains of the lattice and discuss the effect of the fourth-order dispersion in the dynamics. Direct numerical simulations are performed to support our analytical results, and a good agreement is found. Various types of localized patterns, including breathers and solitonic chirped-like pulses, form in the system as a result of interplay between the cubic-quintic nonlinearities and the second- and fourth-order dispersions.

Interpretations of gravity and magnetic anomalies in the Songliao Basin with Wavelet Multi-scale Decomposition

NASA Astrophysics Data System (ADS)

Li, Changbo; Wang, Liangshu; Sun, Bin; Feng, Runhai; Wu, Yongjing

2015-09-01

In this paper, we introduce the method of Wavelet Multi-scale Decomposition (WMD) combined with Power Spectrum Analysis (PSA) for the separation of regional gravity and magnetic anomalies. The Songliao Basin is situated between the Siberian Plate and the North China Plate, and its main structural trend of gravity and magnetic anomaly fields is NNE. The study area shows a significant feature of deep collage-type construction. According to the feature of gravity field, the region was divided into five sub-regions. The gravity and magnetic fields of the Songliao Basin were separated using WMD with a 4th order separation. The apparent depth of anomalies in each order was determined by Logarithmic PSA. Then, the shallow high-frequency anomalies were removed and the 2nd-4th order wavelet detail anomalies were used to study the basin's major faults. Twenty-six faults within the basement were recognized. The 4th order wavelet approximate anomalies were used for the inversion of the Moho discontinuity and the Curie isothermal surface.

A Hermite WENO reconstruction for fourth order temporal accurate schemes based on the GRP solver for hyperbolic conservation laws

NASA Astrophysics Data System (ADS)

Du, Zhifang; Li, Jiequan

2018-02-01

This paper develops a new fifth order accurate Hermite WENO (HWENO) reconstruction method for hyperbolic conservation schemes in the framework of the two-stage fourth order accurate temporal discretization in Li and Du (2016) [13]. Instead of computing the first moment of the solution additionally in the conventional HWENO or DG approach, we can directly take the interface values, which are already available in the numerical flux construction using the generalized Riemann problem (GRP) solver, to approximate the first moment. The resulting scheme is fourth order temporal accurate by only invoking the HWENO reconstruction twice so that it becomes more compact. Numerical experiments show that such compactness makes significant impact on the resolution of nonlinear waves.

Integrating a Gravity Simulation and Groundwater Modeling on the Calibration of Specific Yield for Choshui Alluvial Fan

NASA Astrophysics Data System (ADS)

Chang, Liang Cheng; Tsai, Jui pin; Chen, Yu Wen; Way Hwang, Chein; Chung Cheng, Ching; Chiang, Chung Jung

2014-05-01

For sustainable management, accurate estimation of recharge can provide critical information. The accuracy of estimation is highly related to uncertainty of specific yield (Sy). Because Sy value is traditionally obtained by a multi-well pumping test, the available Sy values are usually limited due to high installation cost. Therefore, this information insufficiency of Sy may cause high uncertainty for recharge estimation. Because gravity is a function of a material mass and the inverse square of the distance, gravity measurement can assist to obtain the mass variation of a shallow groundwater system. Thus, the groundwater level observation data and gravity measurements are used for the calibration of Sy for a groundwater model. The calibration procedure includes four steps. First, gravity variations of three groundwater-monitoring wells, Si-jhou, Tu-ku and Ke-cuo, are observed in May, August and November 2012. To obtain the gravity caused by groundwater variation, this study filters the noises from other sources, such as ocean tide and land subsidence, in the collected data The refined data, which are data without noises, are named gravity residual. Second, this study develops a groundwater model using MODFLOW 2005 to simulate the water mass variation of the groundwater system. Third, we use Newton gravity integral to simulate the gravity variation caused by the simulated water mass variation during each of the observation periods. Fourth, comparing the ratio of the gravity variation between the two data sets, which are observed gravity residuals and simulated gravities. The values of Sy is continuously modified until the gravity variation ratios of the two data sets are the same. The Sy value of Si-jhou is 0.216, which is obtained by the multi-well pumping test. This Sy value is assigned to the simulation model. The simulation results show that the simulated gravity can well fit the observed gravity residual without parameter calibration. This result indicates that the proposed approach is correct and reasonable. In Tu-ku and Ke-cuo, the ratios of the gravity variation between observed gravity residuals and simulated gravities are approximate 1.8 and 50, respectively. The Sy values of these two stations are modified 1.8 and 50 times the original values. These modified Sy values are assigned to the groundwater morel. After the parameter re-assignment, the simulated gravities meet the gravity residuals in these two stations. In conclusion, the study results show that the proposed approach has the potential to identify Sy without installing wells. Therefore, the proposed approach can be used to increase the spatial density of Sy and can conduct the recharge estimation with low uncertainty.

Gravity model improvement investigation. [improved gravity model for determination of ocean geoid

NASA Technical Reports Server (NTRS)

Siry, J. W.; Kahn, W. D.; Bryan, J. W.; Vonbun, F. F.

1973-01-01

This investigation was undertaken to improve the gravity model and hence the ocean geoid. A specific objective is the determination of the gravity field and geoid with a space resolution of approximately 5 deg and a height resolution of the order of five meters. The concept of the investigation is to utilize both GEOS-C altimeter and satellite-to-satellite tracking data to achieve the gravity model improvement. It is also planned to determine the geoid in selected regions with a space resolution of about a degree and a height resolution of the order of a meter or two. The short term objectives include the study of the gravity field in the GEOS-C calibration area outlined by Goddard, Bermuda, Antigua, and Cape Kennedy, and also in the eastern Pacific area which is viewed by ATS-F.

Forward modelling of global gravity fields with 3D density structures and an application to the high-resolution ( 2 km) gravity fields of the Moon

NASA Astrophysics Data System (ADS)

Šprlák, M.; Han, S.-C.; Featherstone, W. E.

2017-12-01

Rigorous modelling of the spherical gravitational potential spectra from the volumetric density and geometry of an attracting body is discussed. Firstly, we derive mathematical formulas for the spatial analysis of spherical harmonic coefficients. Secondly, we present a numerically efficient algorithm for rigorous forward modelling. We consider the finite-amplitude topographic modelling methods as special cases, with additional postulates on the volumetric density and geometry. Thirdly, we implement our algorithm in the form of computer programs and test their correctness with respect to the finite-amplitude topography routines. For this purpose, synthetic and realistic numerical experiments, applied to the gravitational field and geometry of the Moon, are performed. We also investigate the optimal choice of input parameters for the finite-amplitude modelling methods. Fourth, we exploit the rigorous forward modelling for the determination of the spherical gravitational potential spectra inferred by lunar crustal models with uniform, laterally variable, radially variable, and spatially (3D) variable bulk density. Also, we analyse these four different crustal models in terms of their spectral characteristics and band-limited radial gravitation. We demonstrate applicability of the rigorous forward modelling using currently available computational resources up to degree and order 2519 of the spherical harmonic expansion, which corresponds to a resolution of 2.2 km on the surface of the Moon. Computer codes, a user manual and scripts developed for the purposes of this study are publicly available to potential users.

Geologic and geophysical maps of the eastern three-fourths of the Cambria 30' x 60' quadrangle, central California Coast Ranges

USGS Publications Warehouse

Graymer, R.W.; Langenheim, V.E.; Roberts, M.A.; McDougall, Kristin

2014-01-01

The Cambria 30´ x 60´ quadrangle comprises southwestern Monterey County and northwestern San Luis Obispo County. The land area includes rugged mountains of the Santa Lucia Range extending from the northwest to the southeast part of the map; the southern part of the Big Sur coast in the northwest; broad marine terraces along the southwest coast; and broadvalleys, rolling hills, and modest mountains in the northeast. This report contains geologic, gravity anomaly, and aeromagnetic anomaly maps of the eastern three-fourths of the 1:100,000-scale Cambria quadrangle and the associated geologic and geophysical databases (ArcMap databases), as well as complete descriptions of the geologic map units and the structural relations in the mapped area. A cross section is based on both the geologic map and potential-field geophysical data. The maps are presented as an interactive, multilayer PDF, rather than more traditional pre-formatted map-sheet PDFs. Various geologic, geophysical, paleontological, and base map elements are placed on separate layers, which allows the user to combine elements interactively to create map views beyond the traditional map sheets. Four traditional map sheets (geologic map, gravity map, aeromagnetic map, paleontological locality map) are easily compiled by choosing the associated data layers or by choosing the desired map under Bookmarks.

Superconducting tensor gravity gradiometer

NASA Technical Reports Server (NTRS)

Paik, H. J.

1981-01-01

The employment of superconductivity and other material properties at cryogenic temperatures to fabricate sensitive, low-drift, gravity gradiometer is described. The device yields a reduction of noise of four orders of magnitude over room temperature gradiometers, and direct summation and subtraction of signals from accelerometers in varying orientations are possible with superconducting circuitry. Additional circuits permit determination of the linear and angular acceleration vectors independent of the measurement of the gravity gradient tensor. A dewar flask capable of maintaining helium in a liquid state for a year's duration is under development by NASA, and a superconducting tensor gravity gradiometer for the NASA Geodynamics Program is intended for a LEO polar trajectory to measure the harmonic expansion coefficients of the earth's gravity field up to order 300.

Electroencephalography in ellipsoidal geometry with fourth-order harmonics.

PubMed

Alcocer-Sosa, M; Gutierrez, D

2016-08-01

We present a solution to the electroencephalographs (EEG) forward problem of computing the scalp electric potentials for the case when the head's geometry is modeled using a four-shell ellipsoidal geometry and the brain sources with an equivalent current dipole (ECD). The proposed solution includes terms up to the fourth-order ellipsoidal harmonics and we compare this new approximation against those that only considered up to second- and third-order harmonics. Our comparisons use as reference a solution in which a tessellated volume approximates the head and the forward problem is solved through the boundary element method (BEM). We also assess the solution to the inverse problem of estimating the magnitude of an ECD through different harmonic approximations. Our results show that the fourth-order solution provides a better estimate of the ECD in comparison to lesser order ones.

Spacetime encodings. IV. The relationship between Weyl curvature and Killing tensors in stationary axisymmetric vacuum spacetimes

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

Brink, Jeandrew

The problem of obtaining an explicit representation for the fourth invariant of geodesic motion (generalized Carter constant) of an arbitrary stationary axisymmetric vacuum spacetime generated from an Ernst potential is considered. The coupling between the nonlocal curvature content of the spacetime as encoded in the Weyl tensor, and the existence of a Killing tensor is explored and a constructive, algebraic test for a fourth-order Killing tensor suggested. The approach used exploits the variables defined for the Baecklund transformations to clarify the relationship between Weyl curvature, constants of geodesic motion, expressed as Killing tensors, and the solution-generation techniques. A new symmetricmore » noncovariant formulation of the Killing equations is given. This formulation transforms the problem of looking for fourth-order Killing tensors in 4D into one of looking for four interlocking two-manifolds admitting fourth-order Killing tensors in 2D.« less

Documentation of the GLAS fourth order general circulation model. Volume 1: Model documentation

NASA Technical Reports Server (NTRS)

Kalnay, E.; Balgovind, R.; Chao, W.; Edelmann, J.; Pfaendtner, J.; Takacs, L.; Takano, K.

1983-01-01

The volume 1, of a 3 volume technical memoranda which contains a documentation of the GLAS Fourth Order General Circulation Model is presented. Volume 1 contains the documentation, description of the stratospheric/tropospheric extension, user's guide, climatological boundary data, and some climate simulation studies.

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.;

Perturbative Quantum Gravity and its Relation to Gauge Theory.

PubMed

Bern, Zvi

2002-01-01

In this review we describe a non-trivial relationship between perturbative gauge theory and gravity scattering amplitudes. At the semi-classical or tree-level, the scattering amplitudes of gravity theories in flat space can be expressed as a sum of products of well defined pieces of gauge theory amplitudes. These relationships were first discovered by Kawai, Lewellen, and Tye in the context of string theory, but hold more generally. In particular, they hold for standard Einstein gravity. A method based on D -dimensional unitarity can then be used to systematically construct all quantum loop corrections order-by-order in perturbation theory using as input the gravity tree amplitudes expressed in terms of gauge theory ones. More generally, the unitarity method provides a means for perturbatively quantizing massless gravity theories without the usual formal apparatus associated with the quantization of constrained systems. As one application, this method was used to demonstrate that maximally supersymmetric gravity is less divergent in the ultraviolet than previously thought.

An efficient and accurate two-stage fourth-order gas-kinetic scheme for the Euler and Navier-Stokes equations

NASA Astrophysics Data System (ADS)

Pan, Liang; Xu, Kun; Li, Qibing; Li, Jiequan

2016-12-01

For computational fluid dynamics (CFD), the generalized Riemann problem (GRP) solver and the second-order gas-kinetic scheme (GKS) provide a time-accurate flux function starting from a discontinuous piecewise linear flow distributions around a cell interface. With the adoption of time derivative of the flux function, a two-stage Lax-Wendroff-type (L-W for short) time stepping method has been recently proposed in the design of a fourth-order time accurate method for inviscid flow [21]. In this paper, based on the same time-stepping method and the second-order GKS flux function [42], a fourth-order gas-kinetic scheme is constructed for the Euler and Navier-Stokes (NS) equations. In comparison with the formal one-stage time-stepping third-order gas-kinetic solver [24], the current fourth-order method not only reduces the complexity of the flux function, but also improves the accuracy of the scheme. In terms of the computational cost, a two-dimensional third-order GKS flux function takes about six times of the computational time of a second-order GKS flux function. However, a fifth-order WENO reconstruction may take more than ten times of the computational cost of a second-order GKS flux function. Therefore, it is fully legitimate to develop a two-stage fourth order time accurate method (two reconstruction) instead of standard four stage fourth-order Runge-Kutta method (four reconstruction). Most importantly, the robustness of the fourth-order GKS is as good as the second-order one. In the current computational fluid dynamics (CFD) research, it is still a difficult problem to extend the higher-order Euler solver to the NS one due to the change of governing equations from hyperbolic to parabolic type and the initial interface discontinuity. This problem remains distinctively for the hypersonic viscous and heat conducting flow. The GKS is based on the kinetic equation with the hyperbolic transport and the relaxation source term. The time-dependent GKS flux function provides a dynamic process of evolution from the kinetic scale particle free transport to the hydrodynamic scale wave propagation, which provides the physics for the non-equilibrium numerical shock structure construction to the near equilibrium NS solution. As a result, with the implementation of the fifth-order WENO initial reconstruction, in the smooth region the current two-stage GKS provides an accuracy of O ((Δx) 5 ,(Δt) 4) for the Euler equations, and O ((Δx) 5 ,τ2 Δt) for the NS equations, where τ is the time between particle collisions. Many numerical tests, including difficult ones for the Navier-Stokes solvers, have been used to validate the current method. Perfect numerical solutions can be obtained from the high Reynolds number boundary layer to the hypersonic viscous heat conducting flow. Following the two-stage time-stepping framework, the third-order GKS flux function can be used as well to construct a fifth-order method with the usage of both first-order and second-order time derivatives of the flux function. The use of time-accurate flux function may have great advantages on the development of higher-order CFD methods.

Using supercomputers for the time history analysis of old gravity dams

NASA Astrophysics Data System (ADS)

Rouve, G.; Peters, A.

Some of the old masonry dams that were built in Germany at the beginning of this century are a matter of concern today. In the course of time certain deterioration caused or amplified by aging has appeared and raised questions about the safety of these old dams. The Finite Element Method, which in the past two decades has found a widespread application, offers a suitable tool to re-evaluate the safety of these old gravity dams. The reliability of the results, however, strongly depends on the knowledge of the material parameters. Using historical records and observations a numerical back-analysis models has been developed to simulate the behaviour of these old masonry structures and to estimate their material properties by calibration. Only an implementation on a fourth generation vector computer made the application of this large model possible in practice.

Short-Arc Analysis of Intersatellite Tracking Data in a Gravity Mapping Mission

NASA Technical Reports Server (NTRS)

Rowlands, David D.; Ray, Richard D.; Chinn, Douglas S.; Lemoine, Frank G.; Smith, David E. (Technical Monitor)

2001-01-01

A technique for the analysis of low-low intersatellite range-rate data in a gravity mapping mission is explored. The technique is based on standard tracking data analysis for orbit determination but uses a spherical coordinate representation of the 12 epoch state parameters describing the baseline between the two satellites. This representation of the state parameters is exploited to allow the intersatellite range-rate analysis to benefit from information provided by other tracking data types without large simultaneous multiple data type solutions. The technique appears especially valuable for estimating gravity from short arcs (e.g., less than 15 minutes) of data. Gravity recovery simulations which use short arcs are compared with those using arcs a day in length. For a high-inclination orbit, the short-arc analysis recovers low-order gravity coefficients remarkably well, although higher order terms, especially sectorial terms, are less accurate. Simulations suggest that either long or short arcs of GRACE data are likely to improve parts of the geopotential spectrum by orders of magnitude.

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.

New classes of modified teleparallel gravity models

NASA Astrophysics Data System (ADS)

Bahamonde, Sebastian; Böhmer, Christian G.; Krššák, Martin

2017-12-01

New classes of modified teleparallel theories of gravity are introduced. The action of this theory is constructed to be a function of the irreducible parts of torsion f (Tax ,Tten ,Tvec), where Tax ,Tten and Tvec are squares of the axial, tensor and vector components of torsion, respectively. This is the most general (well-motivated) second order teleparallel theory of gravity that can be constructed from the torsion tensor. Different particular second order theories can be recovered from this theory such as new general relativity, conformal teleparallel gravity or f (T) gravity. Additionally, the boundary term B which connects the Ricci scalar with the torsion scalar via R = - T + B can also be incorporated into the action. By performing a conformal transformation, it is shown that the two unique theories which have an Einstein frame are either the teleparallel equivalent of general relativity or f (- T + B) = f (R) gravity, as expected.

Fourth order difference methods for hyperbolic IBVP's

NASA Technical Reports Server (NTRS)

Gustafsson, Bertil; Olsson, Pelle

1994-01-01

Fourth order difference approximations of initial-boundary value problems for hyperbolic partial differential equations are considered. We use the method of lines approach with both explicit and compact implicit difference operators in space. The explicit operator satisfies an energy estimate leading to strict stability. For the implicit operator we develop boundary conditions and give a complete proof of strong stability using the Laplace transform technique. We also present numerical experiments for the linear advection equation and Burgers' equation with discontinuities in the solution or in its derivative. The first equation is used for modeling contact discontinuities in fluid dynamics, the second one for modeling shocks and rarefaction waves. The time discretization is done with a third order Runge-Kutta TVD method. For solutions with discontinuities in the solution itself we add a filter based on second order viscosity. In case of the non-linear Burger's equation we use a flux splitting technique that results in an energy estimate for certain different approximations, in which case also an entropy condition is fulfilled. In particular we shall demonstrate that the unsplit conservative form produces a non-physical shock instead of the physically correct rarefaction wave. In the numerical experiments we compare our fourth order methods with a standard second order one and with a third order TVD-method. The results show that the fourth order methods are the only ones that give good results for all the considered test problems.

A fully Sinc-Galerkin method for Euler-Bernoulli beam models

NASA Technical Reports Server (NTRS)

Smith, R. C.; Bowers, K. L.; Lund, J.

1990-01-01

A fully Sinc-Galerkin method in both space and time is presented for fourth-order time-dependent partial differential equations with fixed and cantilever boundary conditions. The Sinc discretizations for the second-order temporal problem and the fourth-order spatial problems are presented. Alternate formulations for variable parameter fourth-order problems are given which prove to be especially useful when applying the forward techniques to parameter recovery problems. The discrete system which corresponds to the time-dependent partial differential equations of interest are then formulated. Computational issues are discussed and a robust and efficient algorithm for solving the resulting matrix system is outlined. Numerical results which highlight the method are given for problems with both analytic and singular solutions as well as fixed and cantilever boundary conditions.

Zero-gravity open-type urine receptacle

NASA Technical Reports Server (NTRS)

Girala, A. S.

1972-01-01

The development of the zero-gravity open-type urine receptacle used in the Apollo command module is described. This type receptacle eliminates the need for a cuff-type urine collector or for the penis to circumferentially contact the receptacle in order to urinate. This device may be used in a gravity environment, varying from zero gravity to earth gravity, such as may be experienced in a space station or space base.

Fourth order exponential time differencing method with local discontinuous Galerkin approximation for coupled nonlinear Schrodinger equations

DOE PAGES

Liang, Xiao; Khaliq, Abdul Q. M.; Xing, Yulong

2015-01-23

In this paper, we study a local discontinuous Galerkin method combined with fourth order exponential time differencing Runge-Kutta time discretization and a fourth order conservative method for solving the nonlinear Schrödinger equations. Based on different choices of numerical fluxes, we propose both energy-conserving and energy-dissipative local discontinuous Galerkin methods, and have proven the error estimates for the semi-discrete methods applied to linear Schrödinger equation. The numerical methods are proven to be highly efficient and stable for long-range soliton computations. Finally, extensive numerical examples are provided to illustrate the accuracy, efficiency and reliability of the proposed methods.

Marangoni bubble motion in zero gravity. [Lewis zero gravity drop tower

NASA Technical Reports Server (NTRS)

Thompson, R. L.; Dewitt, K. J.

1979-01-01

It was shown experimentally that the Marangoni phenomenon is a primary mechanism for the movement of a gas bubble in a nonisothermal liquid in a low gravity environment. A mathematical model consisting of the Navier-Stokes and thermal energy equations, together with the appropriate boundary conditions for both media, is presented. Parameter perturbation theory is used to solve this boundary value problem; the expansion parameter is the Marangoni number. The zeroth, first, and second order approximations for the velocity, temperature and pressure distributions in the liquid and in the bubble, and the deformation and terminal velocity of the bubble are determined. Experimental zero gravity data for a nitrogen bubble in ethylene glycol, ethanol, and silicone oil subjected to a linear temperature gradient were obtained using the NASA Lewis zero gravity drop tower. Comparison of the zeroth order analytical results for the bubble terminal velocity showed good agreement with the experimental measurements. The first and second order solutions for the bubble deformation and bubble terminal velocity are valid for liquids having Prandtl numbers on the order of one, but there is a lack of appropriate data to test the theory fully.

Very accurate upward continuation to low heights in a test of non-Newtonian theory

NASA Technical Reports Server (NTRS)

Romaides, Anestis J.; Jekeli, Christopher

1989-01-01

Recently, gravity measurements were made on a tall, very stable television transmitting tower in order to detect a non-Newtonian gravitational force. This experiment required the upward continuation of gravity from the Earth's surface to points as high as only 600 m above ground. The upward continuation was based on a set of gravity anomalies in the vicinity of the tower whose data distribution exhibits essential circular symmetry and appropriate radial attenuation. Two methods were applied to perform the upward continuation - least-squares solution of a local harmonic expansion and least-squares collocation. Both methods yield comparable results, and have estimated accuracies on the order of 50 microGal or better (1 microGal = 10(exp -8) m/sq s). This order of accuracy is commensurate with the tower gravity measurments (which have an estimated accuracy of 20 microGal), and enabled a definitive detection of non-Newtonian gravity. As expected, such precise upward continuations require very dense data near the tower. Less expected was the requirement of data (though sparse) up to 220 km away from the tower (in the case that only an ellipsoidal reference gravity is applied).

Design of a Low Gravity Simulator for Performing Non-Equilibrium Investigations near the Lambda Transition of ^4He

NASA Technical Reports Server (NTRS)

Israelsson, U. E.; Duncan, R. V.

1993-01-01

A design is presented of a low gravity simulator where a magnetic field gradient is employed to oppose the hydrostatic pressure effects of gravity. It appears feasible to reduce the effective gravity environment of the helium in the cell by about two orders of magnitude. The corresponding shift in transition temperature with vertical height would be reduced to 12.7 nK/cm. Methods for instrumenting the simulator to perform high resolution investigations of non-equilibrium phenomena near the lambda point are presented. The advantages of using a low gravity simulator in searching for the predicted change in character of the superfluid transition from continuous to first order in the presence of a heat current are also discussed.

A critical analysis of the numerical and analytical methods used in the construction of the lunar gravity potential model.

NASA Astrophysics Data System (ADS)

Tuckness, D. G.; Jost, B.

1995-08-01

Current knowledge of the lunar gravity field is presented. The various methods used in determining these gravity fields are investigated and analyzed. It will be shown that weaknesses exist in the current models of the lunar gravity field. The dominant part of this weakness is caused by the lack of lunar tracking data information (farside, polar areas), which makes modeling the total lunar potential difficult. Comparisons of the various lunar models reveal an agreement in the low-order coefficients of the Legendre polynomials expansions. However, substantial differences in the models can exist in the higher-order harmonics. The main purpose of this study is to assess today's lunar gravity field models for use in tomorrow's lunar mission designs and operations.

High order accurate solutions of viscous problems

NASA Technical Reports Server (NTRS)

Hayder, M. Ehtesham; Turkel, Eli

1993-01-01

We consider a fourth order extension to MacCormack's scheme. The original extension was fourth order only for the inviscid terms but was second order for the viscous terms. We show how to modify the viscous terms so that the scheme is uniformly fourth order in the spatial derivatives. Applications are given to some boundary layer flows. In addition, for applications to shear flows the effect of the outflow boundary conditions are very important. We compare the accuracy of several of these different boundary conditions for both boundary layer and shear flows. Stretching at the outflow usually increases the oscillations in the numerical solution but the addition of a filtered sponge layer (with or without stretching) reduces such oscillations. The oscillations are generated by insufficient resolution of the shear layer. When the shear layer is sufficiently resolved then oscillations are not generated and there is less of a need for a nonreflecting boundary condition.

Documentation of the Fourth Order Band Model

NASA Technical Reports Server (NTRS)

Kalnay-Rivas, E.; Hoitsma, D.

1979-01-01

A general circulation model is presented which uses quadratically conservative, fourth order horizontal space differences on an unstaggered grid and second order vertical space differences with a forward-backward or a smooth leap frog time scheme to solve the primitive equations of motion. The dynamic equations for motion, finite difference equations, a discussion of the structure and flow chart of the program code, a program listing, and three relevent papers are given.

All Male State-Funded Military Academies: Anachronism or Necessary Anomaly?

ERIC Educational Resources Information Center

Russo, Charles J.; Scollay, Susan J.

1993-01-01

The United States Court of Appeals for the Fourth District, although stopping short of ordering the Virginia Military Institute (VMI) to admit women, ordered VMI to implement a program which comports with the requirements of equal protection. Offers an analysis of the Fourth Circuit's ruling, a discussion of important educational questions, and a…

Resummed memory kernels in generalized system-bath master equations

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

Mavros, Michael G.; Van Voorhis, Troy, E-mail: tvan@mit.edu

2014-08-07

Generalized master equations provide a concise formalism for studying reduced population dynamics. Usually, these master equations require a perturbative expansion of the memory kernels governing the dynamics; in order to prevent divergences, these expansions must be resummed. Resummation techniques of perturbation series are ubiquitous in physics, but they have not been readily studied for the time-dependent memory kernels used in generalized master equations. In this paper, we present a comparison of different resummation techniques for such memory kernels up to fourth order. We study specifically the spin-boson Hamiltonian as a model system bath Hamiltonian, treating the diabatic coupling between themore » two states as a perturbation. A novel derivation of the fourth-order memory kernel for the spin-boson problem is presented; then, the second- and fourth-order kernels are evaluated numerically for a variety of spin-boson parameter regimes. We find that resumming the kernels through fourth order using a Padé approximant results in divergent populations in the strong electronic coupling regime due to a singularity introduced by the nature of the resummation, and thus recommend a non-divergent exponential resummation (the “Landau-Zener resummation” of previous work). The inclusion of fourth-order effects in a Landau-Zener-resummed kernel is shown to improve both the dephasing rate and the obedience of detailed balance over simpler prescriptions like the non-interacting blip approximation, showing a relatively quick convergence on the exact answer. The results suggest that including higher-order contributions to the memory kernel of a generalized master equation and performing an appropriate resummation can provide a numerically-exact solution to system-bath dynamics for a general spectral density, opening the way to a new class of methods for treating system-bath dynamics.« less

A mixed-order nonlinear diffusion compressed sensing MR image reconstruction.

PubMed

Joy, Ajin; Paul, Joseph Suresh

2018-03-07

Avoid formation of staircase artifacts in nonlinear diffusion-based MR image reconstruction without compromising computational speed. Whereas second-order diffusion encourages the evolution of pixel neighborhood with uniform intensities, fourth-order diffusion considers smooth region to be not necessarily a uniform intensity region but also a planar region. Therefore, a controlled application of fourth-order diffusivity function is used to encourage second-order diffusion to reconstruct the smooth regions of the image as a plane rather than a group of blocks, while not being strong enough to introduce the undesirable speckle effect. Proposed method is compared with second- and fourth-order nonlinear diffusion reconstruction, total variation (TV), total generalized variation, and higher degree TV using in vivo data sets for different undersampling levels with application to dictionary learning-based reconstruction. It is observed that the proposed technique preserves sharp boundaries in the image while preventing the formation of staircase artifacts in the regions of smoothly varying pixel intensities. It also shows reduced error measures compared with second-order nonlinear diffusion reconstruction or TV and converges faster than TV-based methods. Because nonlinear diffusion is known to be an effective alternative to TV for edge-preserving reconstruction, the crucial aspect of staircase artifact removal is addressed. Reconstruction is found to be stable for the experimentally determined range of fourth-order regularization parameter, and therefore not does not introduce a parameter search. Hence, the computational simplicity of second-order diffusion is retained. © 2018 International Society for Magnetic Resonance in Medicine.

Evolution of Control Programs for a Swarm of Autonomous Unmanned Aerial Vehicles

DTIC Science & Technology

2004-03-01

Game of Checkers,” IBM Journal of Research and Development , 3 (3):210–229 (July 1959). 91. Serway , R. A. Physics for Scientists and Engineers (Fourth...incomplete physics model is used for this research. Ignoring mass and the effects of gravity and friction greatly simplifies the model. At the same...of work on GAs [9, 60, 53]. The seminal work in GAs is the 1975 book Adaptation in Natural and Artificial Systems by John H. Holland [41]. In a GA

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.

Aspects of general higher-order gravities

NASA Astrophysics Data System (ADS)

Bueno, Pablo; Cano, Pablo A.; Min, Vincent S.; Visser, Manus R.

2017-02-01

We study several aspects of higher-order gravities constructed from general contractions of the Riemann tensor and the metric in arbitrary dimensions. First, we use the fast-linearization procedure presented in [P. Bueno and P. A. Cano, arXiv:1607.06463] to obtain the equations satisfied by the metric perturbation modes on a maximally symmetric background in the presence of matter and to classify L (Riemann ) theories according to their spectrum. Then, we linearize all theories up to quartic order in curvature and use this result to construct quartic versions of Einsteinian cubic gravity. In addition, we show that the most general cubic gravity constructed in a dimension-independent way and which does not propagate the ghostlike spin-2 mode (but can propagate the scalar) is a linear combination of f (Lovelock ) invariants, plus the Einsteinian cubic gravity term, plus a new ghost-free gravity term. Next, we construct the generalized Newton potential and the post-Newtonian parameter γ for general L (Riemann ) gravities in arbitrary dimensions, unveiling some interesting differences with respect to the four-dimensional case. We also study the emission and propagation of gravitational radiation from sources for these theories in four dimensions, providing a generalized formula for the power emitted. Finally, we review Wald's formalism for general L (Riemann ) theories and construct new explicit expressions for the relevant quantities involved. Many examples illustrate our calculations.

Parameterization of turbulence and the planetary boundary layer in the GLA Fourth Order GCM

NASA Technical Reports Server (NTRS)

Helfand, H. M.

1985-01-01

A new scheme has been developed to model the planetary boundary layer in the GLAS Fourth Order GCM through explicit resolution of its vertical structure into two or more vertical layers. This involves packing the lowest layers of the GCM close to the ground and developing new parameterization schemes that can express the turbulent vertical fluxes of heat, momentum and moisture at the earth's surface and between the layers that are contained with the PBL region. Offline experiments indicate that the combination of the modified level 2.5 second-order turbulent closure scheme and the 'extended surface layer' similarity scheme should work well to simulate the behavior of the turbulent PBL even at the coarsest vertical resolution with which such schemes will conceivably be used in the GLA Fourth Order GCM.

Time-varying sliding-coefficient-based decoupled terminal sliding-mode control for a class of fourth-order systems.

PubMed

Bayramoglu, Husnu; Komurcugil, Hasan

2014-07-01

A time-varying sliding-coefficient-based decoupled terminal sliding mode control strategy is presented for a class of fourth-order systems. First, the fourth-order system is decoupled into two second-order subsystems. The sliding surface of each subsystem was designed by utilizing time-varying coefficients. Then, the control target of one subsystem to another subsystem was embedded. Thereafter, a terminal sliding mode control method was utilized to make both subsystems converge to their equilibrium points in finite time. The simulation results on the inverted pendulum system demonstrate that the proposed method exhibits a considerable improvement in terms of a faster dynamic response and lower IAE and ITAE values as compared with the existing decoupled control methods. Copyright © 2014 ISA. Published by Elsevier Ltd. All rights reserved.

Generalized energy and potential enstrophy conserving finite difference schemes for the shallow water equations

NASA Technical Reports Server (NTRS)

Abramopoulos, Frank

1988-01-01

The conditions under which finite difference schemes for the shallow water equations can conserve both total energy and potential enstrophy are considered. A method of deriving such schemes using operator formalism is developed. Several such schemes are derived for the A-, B- and C-grids. The derived schemes include second-order schemes and pseudo-fourth-order schemes. The simplest B-grid pseudo-fourth-order schemes are presented.

Higher order explicit symmetric integrators for inseparable forms of coordinates and momenta

NASA Astrophysics Data System (ADS)

Liu, Lei; Wu, Xin; Huang, Guoqing; Liu, Fuyao

2016-06-01

Pihajoki proposed the extended phase-space second-order explicit symmetric leapfrog methods for inseparable Hamiltonian systems. On the basis of this work, we survey a critical problem on how to mix the variables in the extended phase space. Numerical tests show that sequent permutations of coordinates and momenta can make the leapfrog-like methods yield the most accurate results and the optimal long-term stabilized error behaviour. We also present a novel method to construct many fourth-order extended phase-space explicit symmetric integration schemes. Each scheme represents the symmetric production of six usual second-order leapfrogs without any permutations. This construction consists of four segments: the permuted coordinates, triple product of the usual second-order leapfrog without permutations, the permuted momenta and the triple product of the usual second-order leapfrog without permutations. Similarly, extended phase-space sixth, eighth and other higher order explicit symmetric algorithms are available. We used several inseparable Hamiltonian examples, such as the post-Newtonian approach of non-spinning compact binaries, to show that one of the proposed fourth-order methods is more efficient than the existing methods; examples include the fourth-order explicit symplectic integrators of Chin and the fourth-order explicit and implicit mixed symplectic integrators of Zhong et al. Given a moderate choice for the related mixing and projection maps, the extended phase-space explicit symplectic-like methods are well suited for various inseparable Hamiltonian problems. Samples of these problems involve the algorithmic regularization of gravitational systems with velocity-dependent perturbations in the Solar system and post-Newtonian Hamiltonian formulations of spinning compact objects.

Documentation of the GLAS fourth order general circulation model. Volume 2: Scalar code

NASA Technical Reports Server (NTRS)

Kalnay, E.; Balgovind, R.; Chao, W.; Edelmann, D.; Pfaendtner, J.; Takacs, L.; Takano, K.

1983-01-01

Volume 2, of a 3 volume technical memoranda contains a detailed documentation of the GLAS fourth order general circulation model. Volume 2 contains the CYBER 205 scalar and vector codes of the model, list of variables, and cross references. A variable name dictionary for the scalar code, and code listings are outlined.

Bounded Hamiltonian in the Fourth-Order Extension of the Chern-Simons Theory

NASA Astrophysics Data System (ADS)

Abakumova, V. A.; Kaparulin, D. S.; Lyakhovich, S. L.

2018-04-01

The problem of constructing alternative Hamiltonian formulations in the extended Chern-Simons theory with higher derivatives is considered. It is shown that the fourth-order extended theory admits a four-parameter series of alternative Hamiltonians which can be bounded from below, even if the canonical energy of the model is unbounded from below.

Exploratory and Higher-Order Factor Analyses of the Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) Adolescent Subsample

ERIC Educational Resources Information Center

Canivez, Gary L.; Watkins, Marley W.

2010-01-01

The factor structure of the Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV; Wechsler, 2008a) with the adolescent participants (ages 16-19 years; N = 400) in the standardization sample was assessed using exploratory factor analysis, multiple factor extraction criteria, and higher-order exploratory factor analyses. Results from…

Error Patterns in Ordering Fractions among At-Risk Fourth-Grade Students

ERIC Educational Resources Information Center

Malone, Amelia S.; Fuchs, Lynn S.

2017-01-01

The three purposes of this study were to (a) describe fraction ordering errors among at-risk fourth grade students, (b) assess the effect of part-whole understanding and accuracy of fraction magnitude estimation on the probability of committing errors, and (c) examine the effect of students' ability to explain comparing problems on the probability…

Stability and square integrability of derivatives of solutions of nonlinear fourth order differential equations with delay.

PubMed

Korkmaz, Erdal

2017-01-01

In this paper, we give sufficient conditions for the boundedness, uniform asymptotic stability and square integrability of the solutions to a certain fourth order non-autonomous differential equations with delay by using Lyapunov's second method. The results obtained essentially improve, include and complement the results in the literature.

Gravity field and shape of Ceres from Dawn

NASA Astrophysics Data System (ADS)

Park, Ryan; Konopliv, Alexander; Vaughan, Andrew; Bills, Bruce; Castillo-Rogez, Julie; Ermakov, Anton; Fu, Roger; Raymond, Carol; Russell, Chris; Zuber, Maria

2017-04-01

The Dawn gravity science investigation utilizes the DSN radio tracking of the spacecraft and on-board framing camera images to determine the gravity field and global shape of Ceres. The gravity science data collected during Approach, Survey, High-Altitude Mapping Orbit, and Low-Altitude Mapping Orbit phases were processed. The final gravity science solution yielded a degree and order 18 gravity field, called CERES18C, which is globally accurate to degree and order 14. Also, the final Ceres shape using the stereo-photoclinometry method is available with the height uncertainty better than 30 meters. The degree-2 gravity harmonics show that the rotation of Ceres is very nearly about a principal axis. Combining the gravity field and topography gives the bulk density of 2162.6±2.0 kg/m3. The estimated spin pole vector yields RA=(291.42744±0.00022)° and Dec=(66.76065±0.00022)° with the prime meridian and rotation rate of (170.374±0.012)° and (952.1532638±0.0000019)°/day, respectively. The low Bouguer gravity at high topographic areas, and vice versa, indicates that the topography of Ceres is compensated, which can be explained by a low-viscosity layer at depth. Further studies on Ceres interior show that low gravity-topography admittances are consistent with Airy isostasy and finite-element modeling require a decrease of viscosity with depth.

Combustion of solid carbon rods in zero and normal gravity

NASA Technical Reports Server (NTRS)

Spuckler, C. M.; Kohl, F. J.; Miller, R. A.; Stearns, C. A.; Dewitt, K. J.

1979-01-01

In order to investigate the mechanism of carbon combustion, spectroscopic carbon rods were resistance ignited and burned in an oxygen environment in normal and zero gravity. Direct mass spectrometric sampling was used in the normal gravity tests to obtain concentration profiles of CO2, CO, and O2 as a function of distance from the carbon surface. The experimental concentrations were compared to those predicted by a stagnant film model. Zero gravity droptower tests were conducted in order to assess the effect of convection on the normal gravity combustion process. The ratio of flame diameter to rod diameter as a function of time for oxygen pressures of 5, 10, 15, and 20 psia was obtained for three different diameter rods. It was found that this ratio was inversely proportional to both the oxygen pressure and the rod diameter.

Venus - Global gravity and topography

NASA Technical Reports Server (NTRS)

Mcnamee, J. B.; Borderies, N. J.; Sjogren, W. L.

1993-01-01

A new gravity field determination that has been produced combines both the Pioneer Venus Orbiter (PVO) and the Magellan Doppler radio data. Comparisonsbetween this estimate, a spherical harmonic model of degree and order 21, and previous models show that significant improvements have been made. Results are displayed as gravity contours overlaying a topographic map. We also calculate a new spherical harmonic model of topography based on Magellan altimetry, with PVO altimetry included where gaps exist in the Magellan data. This model is also of degree and order 21, so in conjunction with the gravity model, Bouguer and isostatic anomaly maps can be produced. These results are very consistent with previous results, but reveal more spatial resolution in the higher latitudes.

Gravity data from the Sierra Vista Subwatershed, Upper San Pedro Basin, Arizona

USGS Publications Warehouse

Kennedy, Jeffrey R.

2015-01-01

This report (1) summarizes changes to the Sierra Vista Subwatershed regional time-lapse gravity network with respect to station locations and (2) presents 2014 and 2015 gravity measurements and gravity values at each station. A prior gravity network, established between 2000 and 2005, was revised in 2014 to cover a larger number of stations over a smaller geographic area in order to decrease measurement and interpolation uncertainty. The network currently consists of 59 gravity stations, including 14 absolute-gravity stations. Following above-average rainfall during summer 2014, gravity increased at all but one of the absolute-gravity stations that were observed in both June 2014 and January 2015. This increase in gravity indicates increased groundwater storage in the aquifer and (or) unsaturated zone as a result of rainfall and infiltration.

An improved model for the Earth's gravity field

NASA Technical Reports Server (NTRS)

Tapley, B. D.; Shum, C. K.; Yuan, D. N.; Ries, J. C.; Schutz, B. E.

1989-01-01

An improved model for the Earth's gravity field, TEG-1, was determined using data sets from fourteen satellites, spanning the inclination ranges from 15 to 115 deg, and global surface gravity anomaly data. The satellite measurements include laser ranging data, Doppler range-rate data, and satellite-to-ocean radar altimeter data measurements, which include the direct height measurement and the differenced measurements at ground track crossings (crossover measurements). Also determined was another gravity field model, TEG-1S, which included all the data sets in TEG-1 with the exception of direct altimeter data. The effort has included an intense scrutiny of the gravity field solution methodology. The estimated parameters included geopotential coefficients complete to degree and order 50 with selected higher order coefficients, ocean and solid Earth tide parameters, Doppler tracking station coordinates and the quasi-stationary sea surface topography. Extensive error analysis and calibration of the formal covariance matrix indicate that the gravity field model is a significant improvement over previous models and can be used for general applications in geodesy.

Numerical solution of the generalized, dissipative KdV-RLW-Rosenau equation with a compact method

NASA Astrophysics Data System (ADS)

Apolinar-Fernández, Alejandro; Ramos, J. I.

2018-07-01

The nonlinear dynamics of the one-dimensional, generalized Korteweg-de Vries-regularized-long wave-Rosenau (KdV-RLW-Rosenau) equation with second- and fourth-order dissipative terms subject to initial Gaussian conditions is analyzed numerically by means of three-point, fourth-order accurate, compact finite differences for the discretization of the spatial derivatives and a trapezoidal method for time integration. By means of a Fourier analysis and global integration techniques, it is shown that the signs of both the fourth-order dissipative and the mixed fifth-order derivative terms must be negative. It is also shown that an increase of either the linear drift or the nonlinear convection coefficients results in an increase of the steepness, amplitude and speed of the right-propagating wave, whereas the speed and amplitude of the wave decrease as the power of the nonlinearity is increased, if the amplitude of the initial Gaussian condition is equal to or less than one. It is also shown that the wave amplitude and speed decrease and the curvature of the wave's trajectory increases as the coefficients of the second- and fourth-order dissipative terms are increased, while an increase of the RLW coefficient was found to decrease both the damping and the phase velocity, and generate oscillations behind the wave. For some values of the coefficients of both the fourth-order dissipative and the Rosenau terms, it has been found that localized dispersion shock waves may form in the leading part of the right-propagating wave, and that the formation of a train of solitary waves that result from the breakup of the initial Gaussian conditions only occurs in the absence of both Rosenau's, Kortweg-de Vries's and second- and fourth-order dissipative terms, and for some values of the amplitude and width of the initial condition and the RLW coefficient. It is also shown that negative values of the KdV term result in steeper, larger amplitude and faster waves and a train of oscillations behind the wave, whereas positive values of that coefficient may result in negative phase and group velocities, no wave breakup and oscillations ahead of the right-propagating wave.

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.

A fourth-order Cartesian grid embeddedboundary method for Poisson’s equation

DOE PAGES

Devendran, Dharshi; Graves, Daniel; Johansen, Hans; ...

2017-05-08

In this paper, we present a fourth-order algorithm to solve Poisson's equation in two and three dimensions. We use a Cartesian grid, embedded boundary method to resolve complex boundaries. We use a weighted least squares algorithm to solve for our stencils. We use convergence tests to demonstrate accuracy and we show the eigenvalues of the operator to demonstrate stability. We compare accuracy and performance with an established second-order algorithm. We also discuss in depth strategies for retaining higher-order accuracy in the presence of nonsmooth geometries.

A fourth-order Cartesian grid embeddedboundary method for Poisson’s equation

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

Devendran, Dharshi; Graves, Daniel; Johansen, Hans

In this paper, we present a fourth-order algorithm to solve Poisson's equation in two and three dimensions. We use a Cartesian grid, embedded boundary method to resolve complex boundaries. We use a weighted least squares algorithm to solve for our stencils. We use convergence tests to demonstrate accuracy and we show the eigenvalues of the operator to demonstrate stability. We compare accuracy and performance with an established second-order algorithm. We also discuss in depth strategies for retaining higher-order accuracy in the presence of nonsmooth geometries.

Ineffective higher derivative black hole hair

NASA Astrophysics Data System (ADS)

Goldstein, Kevin; Mashiyane, James Junior

2018-01-01

Inspired by the possibility that the Schwarzschild black hole may not be the unique spherically symmetric vacuum solution to generalizations of general relativity, we consider black holes in pure fourth order higher derivative gravity treated as an effective theory. Such solutions may be of interest in addressing the issue of higher derivative hair or during the later stages of black hole evaporation. Non-Schwarzschild solutions have been studied but we have put earlier results on a firmer footing by finding a systematic asymptotic expansion for the black holes and matching them with known numerical solutions obtained by integrating out from the near-horizon region. These asymptotic expansions can be cast in the form of trans-series expansions which we conjecture will be a generic feature of non-Schwarzschild higher derivative black holes. Excitingly we find a new branch of solutions with lower free energy than the Schwarzschild solution, but as found in earlier work, solutions only seem to exist for black holes with large curvatures, meaning that one should not generically neglect even higher derivative corrections. This suggests that one effectively recovers the nonhair theorems in this context.

Empirical Foundations of the Relativistic Gravity

NASA Astrophysics Data System (ADS)

Ni, Wei-Tou

In 1859, Le Verrier discovered the mercury perihelion advance anomaly. This anomaly turned out to be the first relativistic-gravity effect observed. During the 141 years to 2000, the precisions of laboratory and space experiments, and astrophysical and cosmological observations on relativistic gravity have been improved by 3 orders of magnitude. In 1999, we envisaged a 3-6 order improvement in the next 30 years in all directions of tests of relativistic gravity. In 2000, the interferometric gravitational wave detectors began their runs to accumulate data. In 2003, the measurement of relativistic Shapiro time-delay of the Cassini spacecraft determined the relativistic-gravity parameter γ to be 1.000021 ± 0.000023 of general relativity — a 1.5-order improvement. In October 2004, Ciufolini and Pavlis reported a measurement of the Lense-Thirring effect on the LAGEOS and LAGEOS2 satellites to be 0.99 ± 0.10 of the value predicted by general relativity. In April 2004, Gravity Probe B (Stanford relativity gyroscope experiment to measure the Lense-Thirring effect to 1%) was launched and has been accumulating science data for more than 170 days now. μSCOPE (MICROSCOPE: MICRO-Satellite à trainée Compensée pour l'Observation du Principle d'Équivalence) is on its way for a 2008 launch to test Galileo equivalence principle to 10-15. LISA Pathfinder (SMART2), the technological demonstrator for the LISA (Laser Interferometer Space Antenna) mission is well on its way for a 2009 launch. STEP (Satellite Test of Equivalence Principle), and ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) are in good planning stage. Various astrophysical tests and cosmological tests of relativistic gravity will reach precision and ultra-precision stages. Clock tests and atomic interferometry tests of relativistic gravity will reach an ever-increasing precision. These will give revived interest and development both in experimental and theoretical aspects of gravity, and may lead to answers to some profound questions of gravity and the cosmos.

Regional Recovery of the Disturbing Gravitational Potential from Satellite Observations of First-, Second- and Third-order Radial Derivatives of the Disturbing Gravitational Potential

NASA Astrophysics Data System (ADS)

Novak, P.; Pitonak, M.; Sprlak, M.

2015-12-01

Recently realized gravity-dedicated satellite missions allow for measuring values of scalar, vectorial (Gravity Recovery And Climate Experiment - GRACE) and second-order tensorial (Gravity field and steady-state Ocean Circulation Explorer - GOCE) parameters of the Earth's gravitational potential. Theoretical aspects related to using moving sensors for measuring elements of a third-order gravitational tensor are currently under investigation, e.g. the gravity-dedicated satellite mission OPTIMA (OPTical Interferometry for global Mass change detection from space) should measure third-order derivatives of the Earth's gravitational potential. This contribution investigates regional recovery of the disturbing gravitational potential on the Earth's surface from satellite observations of first-, second- and third-order radial derivatives of the disturbing gravitational potential. Synthetic measurements along a satellite orbit at the altitude of 250 km are synthetized from the global gravitational model EGM2008 and polluted by the Gaussian noise. The process of downward continuation is stabilized by the Tikhonov regularization. Estimated values of the disturbing gravitational potential are compared with the same quantity synthesized directly from EGM2008. Finally, this contribution also discusses merging a regional solution into a global field as a patchwork.

Analysis and development of fourth order LCLC resonant based capacitor charging power supply for pulse power applications.

PubMed

Naresh, P; Hitesh, C; Patel, A; Kolge, T; Sharma, Archana; Mittal, K C

2013-08-01

A fourth order (LCLC) resonant converter based capacitor charging power supply (CCPS) is designed and developed for pulse power applications. Resonant converters are preferred t utilize soft switching techniques such as zero current switching (ZCS) and zero voltage switching (ZVS). An attempt has been made to overcome the disadvantages in 2nd and 3rd resonant converter topologies; hence a fourth order resonant topology is used in this paper for CCPS application. In this paper a novel fourth order LCLC based resonant converter has been explored and mathematical analysis carried out to calculate load independent constant current. This topology provides load independent constant current at switching frequency (fs) equal to resonant frequency (fr). By changing switching condition (on time and dead time) this topology has both soft switching techniques such as ZCS and ZVS for better switching action to improve the converter efficiency. This novel technique has special features such as low peak current through switches, DC blocking for transformer, utilizing transformer leakage inductance as resonant component. A prototype has been developed and tested successfully to charge a 100 μF capacitor to 200 V.

Plumes in the mantle. [free air and isostatic gravity anomalies for geophysical interpretation

NASA Technical Reports Server (NTRS)

Khan, M. A.

1973-01-01

Free air and isostatic gravity anomalies for the purposes of geophysical interpretation are presented. Evidence for the existance of hotspots in the mantle is reviewed. The prosposed locations of these hotspots are not always associated with positive gravity anomalies. Theoretical analysis based on simplified flow models for the plumes indicates that unless the frictional viscosities are several orders of magnitude smaller than the present estimates of mantle viscosity or alternately, the vertical flows are reduced by about two orders of magnitude, the plume flow will generate implausibly high temperatures.

Experimental study on line-of-sight (LOS) attitude control using control moment gyros under micro-gravity environment

NASA Astrophysics Data System (ADS)

Kojima, Hirohisa; Hiraiwa, Kana; Yoshimura, Yasuhiro

2018-02-01

This paper presents the results of line-of-sight (LOS) attitude control using control moment gyros under a micro-gravity environment generated by parabolic flight. The W-Z parameters are used to describe the spacecraft attitude. In order to stabilize the current LOS to the target LOS, backstepping-based feedback control is considered using the W-Z parameters. Numerical simulations and experiments under a micro-gravity environment are carried out, and their results are compared in order to validate the proposed control methods.

Unstructured High-Order Galerkin-Temporal- Boundary Methods for the Klein-Gordon Equation with Non-Reflecting Boundary Conditions

DTIC Science & Technology

2010-06-01

9 C. Conservation of Momentum . . . . . . . . . . . . . . . . . . . . . 11 1. Gravity Effects . . . . . . . . . . . . . . . . . . . . . . . . . 12 2...describe the high-order spectral element method used to discretize the problem in space (up to 16th order polynomials ) in Chapter IV. Chapter V discusses...inertial frame. Body forces are those acting on the fluid volume that are proportional to the mass. The body forces considered here are gravity and

Prompt gravity signal induced by the 2011 Tohoku-Oki earthquake

PubMed Central

Montagner, Jean-Paul; Juhel, Kévin; Barsuglia, Matteo; Ampuero, Jean Paul; Chassande-Mottin, Eric; Harms, Jan; Whiting, Bernard; Bernard, Pascal; Clévédé, Eric; Lognonné, Philippe

2016-01-01

Transient gravity changes are expected to occur at all distances during an earthquake rupture, even before the arrival of seismic waves. Here we report on the search of such a prompt gravity signal in data recorded by a superconducting gravimeter and broadband seismometers during the 2011 Mw 9.0 Tohoku-Oki earthquake. During the earthquake rupture, a signal exceeding the background noise is observed with a statistical significance higher than 99% and an amplitude of a fraction of μGal, consistent in sign and order of magnitude with theoretical predictions from a first-order model. While prompt gravity signal detection with state-of-the-art gravimeters and seismometers is challenged by background seismic noise, its robust detection with gravity gradiometers under development could open new directions in earthquake seismology, and overcome fundamental limitations of current earthquake early-warning systems imposed by the propagation speed of seismic waves. PMID:27874858

A distinguishing gravitational property for gravitational equation in higher dimensions

NASA Astrophysics Data System (ADS)

Dadhich, Naresh

2016-03-01

It is well known that Einstein gravity is kinematic (meaning that there is no non-trivial vacuum solution; i.e. the Riemann tensor vanishes whenever the Ricci tensor does so) in 3 dimension because the Riemann tensor is entirely given in terms of the Ricci tensor. Could this property be universalized for all odd dimensions in a generalized theory? The answer is yes, and this property uniquely singles out pure Lovelock (it has only one Nth order term in the action) gravity for which the Nth order Lovelock-Riemann tensor is indeed given in terms of the corresponding Ricci tensor for all odd, d=2N+1, dimensions. This feature of gravity is realized only in higher dimensions and it uniquely picks out pure Lovelock gravity from all other generalizations of Einstein gravity. It serves as a good distinguishing and guiding criterion for the gravitational equation in higher dimensions.

Prompt gravity signal induced by the 2011 Tohoku-Oki earthquake.

PubMed

Montagner, Jean-Paul; Juhel, Kévin; Barsuglia, Matteo; Ampuero, Jean Paul; Chassande-Mottin, Eric; Harms, Jan; Whiting, Bernard; Bernard, Pascal; Clévédé, Eric; Lognonné, Philippe

2016-11-22

Transient gravity changes are expected to occur at all distances during an earthquake rupture, even before the arrival of seismic waves. Here we report on the search of such a prompt gravity signal in data recorded by a superconducting gravimeter and broadband seismometers during the 2011 Mw 9.0 Tohoku-Oki earthquake. During the earthquake rupture, a signal exceeding the background noise is observed with a statistical significance higher than 99% and an amplitude of a fraction of μGal, consistent in sign and order of magnitude with theoretical predictions from a first-order model. While prompt gravity signal detection with state-of-the-art gravimeters and seismometers is challenged by background seismic noise, its robust detection with gravity gradiometers under development could open new directions in earthquake seismology, and overcome fundamental limitations of current earthquake early-warning systems imposed by the propagation speed of seismic waves.

Prompt gravity anomaly induced to the 2011Tohoku-Oki earthquake

NASA Astrophysics Data System (ADS)

Montagner, Jean-Paul; Juhel, Kevin; Barsuglia, Matteo; Ampuero, Jean-Paul; Harms, Jan; Chassande-Mottin, Eric; Whiting, Bernard; Bernard, Pascal; Clévédé, Eric; Lognonné, Philippe

2017-04-01

Transient gravity changes are expected to occur at all distances during an earthquake rupture, even before the arrival of seismic waves. Here we report on the search of such a prompt gravity signal in data recorded by a superconducting gravimeter and broadband seismometers during the 2011 Mw 9.0 Tohoku-Oki earthquake. During the earthquake rupture, a signal exceeding the background noise is observed with a statistical significance higher than 99% and an amplitude of a fraction of μGal, consistent in sign and order-of-magnitude with theoretical predictions from a first-order model. While prompt gravity signal detection with state-of-the-art gravimeters and seismometers is challenged by background seismic noise, its robust detection with gravity gradiometers under development could open new directions in earthquake seismology, and overcome fundamental limitations of current earthquake early-warning systems (EEWS) imposed by the propagation speed of seismic waves.

Gravity results from Pioneer 10 Doppler data. [during Jupiter encounter

NASA Technical Reports Server (NTRS)

Anderson, J. D.; Null, G. W.; Wong, S. K.

1974-01-01

Two-way Doppler data received from Pioneer 10 during its encounter with Jupiter have been analyzed, and preliminary results have been obtained on the mass and the gravity field of Jupiter and on the masses of the four Galilean satellites. The ratios of the masses of the satellites to the mass of Jupiter are approximately 0.00004696 for Io, 0.00002565 for Europa, 0.00007845 for Ganymede, and 0.00005603 for Callisto (all error estimates presented in this paper are standard errors; those for Pioneer 10 represent our evaluation of the real errors as distinguished from formal errors). The ratio of the mass of the sun to the mass of the Jupiter system is about 1047.342, which is in good agreement with recent determinations from the motions of asteroids. The second- and fourth-degree zonal harmonic coefficients in the gravity field of Jupiter are 0.014720 and -0.00065, respectively, based on an equatorial planetary radius of 71,400 km, and the derived dynamical oblateness is 0.0647 at the same radius. The Pioneer 10 data are consistent with the assumption that Jupiter is in hydrostatic equilibrium at all levels.

Perspectives from space: NASA classroom information and activities

NASA Technical Reports Server (NTRS)

1992-01-01

This booklet contains the information and classroom activities included on the backs of the eight poster series, 'Perspectives From Space'. The first series, Earth, An Integrated System, contains information on global ecology, remote sensing from space, data products, earth modeling, and international environmental treaties. The second series, Patterns Among Planets, contains information on the solar system, planetary processes, impacts and atmospheres, and a classroom activity on Jupiter's satellite system. The third series, Our Place In The Cosmos, contains information on the scale of the universe, origins of the universe, mission to the universe, and three classroom activities. The fourth series, Our Sun, The Nearest Star, contains information on the Sun. The fifth series, Oasis Of Life, contains information on the development of life, chemical and biological evolution on Earth and the search for other life in the universe. The sixth series, The Influence Of Gravity, contains information on Newton's Law of Gravity, space and microgravity, microgravity environment, and classroom activities on gravity. The seventh series, The Spirit Of Exploration, contains information on space exploration, the Apollo Program, future exploration activities, and two classroom activities. The eighth series, Global Cooperation, contains information on rocketry, the space race, and multi-nation exploration projects.

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.

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.

Gravity/Topography Admittances and Lithospheric Evolution on Mars: The Importance of Finite-Amplitude Topography

NASA Technical Reports Server (NTRS)

McGovern, Patrick J.; Solomon, Sean C.; Smith, David E.; Zuber, Maria T.; Neumann, Gregory A.; Head, J. W., III; Phillips, Roger J.; Simons, Mark

2001-01-01

We calculate localized gravity/topography admittances for Mars, in order to estimate elastic lithosphere thickness. A finite-amplitude correction to modeled gravity is required to properly interpret admittances in high-relief regions of Mars. Additional information is contained in the original extended abstract.

Fourth order Douglas implicit scheme for solving three dimension reaction diffusion equation with non-linear source term

NASA Astrophysics Data System (ADS)

Hasnain, Shahid; Saqib, Muhammad; Mashat, Daoud Suleiman

2017-07-01

This research paper represents a numerical approximation to non-linear three dimension reaction diffusion equation with non-linear source term from population genetics. Since various initial and boundary value problems exist in three dimension reaction diffusion phenomena, which are studied numerically by different numerical methods, here we use finite difference schemes (Alternating Direction Implicit and Fourth Order Douglas Implicit) to approximate the solution. Accuracy is studied in term of L2, L∞ and relative error norms by random selected grids along time levels for comparison with analytical results. The test example demonstrates the accuracy, efficiency and versatility of the proposed schemes. Numerical results showed that Fourth Order Douglas Implicit scheme is very efficient and reliable for solving 3-D non-linear reaction diffusion equation.

Lattice Boltzmann method for bosons and fermions and the fourth-order Hermite polynomial expansion.

PubMed

Coelho, Rodrigo C V; Ilha, Anderson; Doria, Mauro M; Pereira, R M; Aibe, Valter Yoshihiko

2014-04-01

The Boltzmann equation with the Bhatnagar-Gross-Krook collision operator is considered for the Bose-Einstein and Fermi-Dirac equilibrium distribution functions. We show that the expansion of the microscopic velocity in terms of Hermite polynomials must be carried to the fourth order to correctly describe the energy equation. The viscosity and thermal coefficients, previously obtained by Yang et al. [Shi and Yang, J. Comput. Phys. 227, 9389 (2008); Yang and Hung, Phys. Rev. E 79, 056708 (2009)] through the Uehling-Uhlenbeck approach, are also derived here. Thus the construction of a lattice Boltzmann method for the quantum fluid is possible provided that the Bose-Einstein and Fermi-Dirac equilibrium distribution functions are expanded to fourth order in the Hermite polynomials.

A freestream-preserving fourth-order finite-volume method in mapped coordinates with adaptive-mesh refinement

DOE PAGES

Guzik, Stephen M.; Gao, Xinfeng; Owen, Landon D.; ...

2015-12-20

We present a fourth-order accurate finite-volume method for solving time-dependent hyperbolic systems of conservation laws on mapped grids that are adaptively refined in space and time. Some novel considerations for formulating the semi-discrete system of equations in computational space are combined with detailed mechanisms for accommodating the adapting grids. Furthermore, these considerations ensure that conservation is maintained and that the divergence of a constant vector field is always zero (freestream-preservation property). The solution in time is advanced with a fourth-order Runge-Kutta method. A series of tests verifies that the expected accuracy is achieved in smooth flows and the solution ofmore » a Mach reflection problem demonstrates the effectiveness of the algorithm in resolving strong discontinuities.« less

(abstract) Venus Gravity Field

NASA Technical Reports Server (NTRS)

Konopliv, A. S.; Sjogren, W. L.

1995-01-01

A global gravity field model of Venus to degree and order 75 (5772 spherical harmonic coefficients) has been estimated from Doppler radio tracking of the orbiting spacecraft Pioneer Venus Orbiter (1979-1992) and Magellan (1990-1994). After the successful aerobraking of Magellan, a near circular polar orbit was attained and relatively uniform gravity field resolution (approximately 200 km) was obtained with formal uncertainties of a few milligals. Detailed gravity for several highland features are displayed as gravity contours overlaying colored topography. The positive correlation of typography with gravity is very high being unlike that of the Earth, Moon, and Mars. The amplitudes are Earth-like, but have significantly different gravity-topography ratios for different features. Global gravity, geoid, and isostatic anomaly maps as well as the admittance function are displayed.

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.

Holographic heat current as Noether current

NASA Astrophysics Data System (ADS)

Liu, Hai-Shan; Lü, H.; Pope, C. N.

2017-09-01

We employ the Noether procedure to derive a general formula for the radially conserved heat current in AdS planar black holes with certain transverse and traceless perturbations, for a general class of gravity theories. For Einstein gravity, the general higher-order Lovelock gravities and also a class of Horndeski gravities, we derive the boundary stress tensor and show that the resulting boundary heat current matches precisely the bulk Noether current.

Torus Approach in Gravity Field Determination from Simulated GOCE Gravity Gradients

NASA Astrophysics Data System (ADS)

Liu, Huanling; Wen, Hanjiang; Xu, Xinyu; Zhu, Guangbin

2016-08-01

In Torus approach, observations are projected to the nominal orbits with constant radius and inclination, lumped coefficients provides a linear relationship between observations and spherical harmonic coefficients. Based on the relationship, two-dimensional FFT and block-diagonal least-squares adjustment are used to recover Earth's gravity field model. The Earth's gravity field model complete to degree and order 200 is recovered using simulated satellite gravity gradients on a torus grid, and the degree median error is smaller than 10-18, which shows the effectiveness of Torus approach. EGM2008 is employed as a reference model and the gravity field model is resolved using the simulated observations without noise given on GOCE orbits of 61 days. The error from reduction and interpolation can be mitigated by iterations. Due to polar gap, the precision of low-order coefficients is lower. Without considering these coefficients the maximum geoid degree error and cumulative error are 0.022mm and 0.099mm, respectively. The Earth's gravity field model is also recovered from simulated observations with white noise 5mE/Hz1/2, which is compared to that from direct method. In conclusion, it is demonstrated that Torus approach is a valid method for processing massive amount of GOCE gravity gradients.

Semirational rogue waves for the three-coupled fourth-order nonlinear Schrödinger equations in an alpha helical protein

NASA Astrophysics Data System (ADS)

Du, Zhong; Tian, Bo; Qu, Qi-Xing; Chai, Han-Peng; Wu, Xiao-Yu

2017-12-01

Investigated in this paper are the three-coupled fourth-order nonlinear Schrödinger equations, which describe the dynamics of alpha helical protein with the interspine coupling at the higher order. We show that the representation of the Lax pair with Expressions (42) -(45) in Ref. [25] is not correct, because the three-coupled fourth-order nonlinear Schrödinger equations can not be reproduced by the Lax pair with Expressions (42) -(45) in Ref. [25] through the compatibility condition. Therefore, we recalculate the Lax pair. Based on the recalculated Lax pair, we construct the generalized Darboux transformation, and derive the first- and second-order semirational solutions. Through such solutions, dark-bright-bright soliton, breather-breather-bright soliton, breather soliton and rogue waves are analyzed. It is found that the rogue waves in the three components are mutually proportional. Moreover, three types of the semirational rogue waves consisting of the rogue waves and solitons are presented: (1) consisting of the first-order rogue wave and one soliton; (2) consisting of the first-order rogue wave and two solitons; (3) consisting of the second-order rogue wave and two solitons.

Data reduction and tying in regional gravity surveys—results from a new gravity base station network and the Bouguer gravity anomaly map for northeastern Mexico

NASA Astrophysics Data System (ADS)

Hurtado-Cardador, Manuel; Urrutia-Fucugauchi, Jaime

2006-12-01

Since 1947 Petroleos Mexicanos (Pemex) has conducted oil exploration projects using potential field methods. Geophysical exploration companies under contracts with Pemex carried out gravity anomaly surveys that were referred to different floating data. Each survey comprises observations of gravity stations along highways, roads and trails at intervals of about 500 m. At present, 265 separate gravimeter surveys that cover 60% of the Mexican territory (mainly in the oil producing regions of Mexico) are available. This gravity database represents the largest, highest spatial resolution information, and consequently has been used in the geophysical data compilations for the Mexico and North America gravity anomaly maps. Regional integration of gravimeter surveys generates gradients and spurious anomalies in the Bouguer anomaly maps at the boundaries of the connected surveys due to the different gravity base stations utilized. The main objective of this study is to refer all gravimeter surveys from Pemex to a single new first-order gravity base station network, in order to eliminate problems of gradients and spurious anomalies. A second objective is to establish a network of permanent gravity base stations (BGP), referred to a single base from the World Gravity System. Four regional loops of BGP covering eight States of Mexico were established to support the tie of local gravity base stations from each of the gravimeter surveys located in the vicinity of these loops. The third objective is to add the gravity constants, measured and calculated, for each of the 265 gravimeter surveys to their corresponding files in the Pemex and Instituto Mexicano del Petroleo database. The gravity base used as the common datum is the station SILAG 9135-49 (Latin American System of Gravity) located in the National Observatory of Tacubaya in Mexico City. We present the results of the installation of a new gravity base network in northeastern Mexico, reference of the 43 gravimeter surveys to the new network, the regional compilation of Bouguer gravity data and a new updated Bouguer gravity anomaly map for northeastern Mexico.

Implementation of the incremental scheme for one-electron first-order properties in coupled-cluster theory.

PubMed

Friedrich, Joachim; Coriani, Sonia; Helgaker, Trygve; Dolg, Michael

2009-10-21

A fully automated parallelized implementation of the incremental scheme for coupled-cluster singles-and-doubles (CCSD) energies has been extended to treat molecular (unrelaxed) first-order one-electron properties such as the electric dipole and quadrupole moments. The convergence and accuracy of the incremental approach for the dipole and quadrupole moments have been studied for a variety of chemically interesting systems. It is found that the electric dipole moment can be obtained to within 5% and 0.5% accuracy with respect to the exact CCSD value at the third and fourth orders of the expansion, respectively. Furthermore, we find that the incremental expansion of the quadrupole moment converges to the exact result with increasing order of the expansion: the convergence of nonaromatic compounds is fast with errors less than 16 mau and less than 1 mau at third and fourth orders, respectively (1 mau=10(-3)ea(0)(2)); the aromatic compounds converge slowly with maximum absolute deviations of 174 and 72 mau at third and fourth orders, respectively.

On Richardson extrapolation for low-dissipation low-dispersion diagonally implicit Runge-Kutta schemes

NASA Astrophysics Data System (ADS)

Havasi, Ágnes; Kazemi, Ehsan

2018-04-01

In the modeling of wave propagation phenomena it is necessary to use time integration methods which are not only sufficiently accurate, but also properly describe the amplitude and phase of the propagating waves. It is not clear if amending the developed schemes by extrapolation methods to obtain a high order of accuracy preserves the qualitative properties of these schemes in the perspective of dissipation, dispersion and stability analysis. It is illustrated that the combination of various optimized schemes with Richardson extrapolation is not optimal for minimal dissipation and dispersion errors. Optimized third-order and fourth-order methods are obtained, and it is shown that the proposed methods combined with Richardson extrapolation result in fourth and fifth orders of accuracy correspondingly, while preserving optimality and stability. The numerical applications include the linear wave equation, a stiff system of reaction-diffusion equations and the nonlinear Euler equations with oscillatory initial conditions. It is demonstrated that the extrapolated third-order scheme outperforms the recently developed fourth-order diagonally implicit Runge-Kutta scheme in terms of accuracy and stability.

Measurement of Shear Elastic Moduli in Quasi-Incompressible Soft Solids

NASA Astrophysics Data System (ADS)

Rénier, Mathieu; Gennisson, Jean-Luc; Barrière, Christophe; Catheline, Stefan; Tanter, Mickaël; Royer, Daniel; Fink, Mathias

2008-06-01

Recently a nonlinear equation describing the plane shear wave propagation in isotropic quasi-incompressible media has been developed using a new expression of the strain energy density, as a function of the second, third and fourth order shear elastic constants (respectively μ, A, D) [1]. In such a case, the shear nonlinearity parameter βs depends only from these last coefficients. To date, no measurement of the parameter D have been carried out in soft solids. Using a set of two experiments, acoustoelasticity and finite amplitude shear waves, the shear elastic moduli up to the fourth order of soft solids are measured. Firstly, this theoretical background is applied to the acoustoelasticity theory, giving the variations of the shear wave speed as a function of the stress applied to the medium. From such variations, both linear (μ) and third order shear modulus (A) are deduced in agar-gelatin phantoms. Experimentally the radiation force induced by a focused ultrasound beam is used to generate quasi-plane linear shear waves within the medium. Then the shear wave propagation is imaged with an ultrafast ultrasound scanner. Secondly, in order to give rise to finite amplitude plane shear waves, the radiation force generation technique is replaced by a vibrating plate applied at the surface of the phantoms. The propagation is also imaged using the same ultrafast scanner. From the assessment of the third harmonic amplitude, the nonlinearity parameter βS is deduced. Finally, combining these results with the acoustoelasticity experiment, the fourth order modulus (D) is deduced. This set of experiments provides the characterization, up to the fourth order, of the nonlinear shear elastic moduli in quasi-incompressible soft media. Measurements of the A moduli reveal that while the behaviors of both soft solids are close from a linear point of view, the corresponding nonlinear moduli A are quite different. In a 5% agar-gelatin phantom, the fourth order elastic constant D is found to be 30±10 kPa.

The use of staggered scheme and an absorbing buffer zone for computational aeroacoustics

NASA Technical Reports Server (NTRS)

Nark, Douglas M.

1995-01-01

Various problems from those proposed for the Computational Aeroacoustics (CAA) workshop were studied using second and fourth order staggered spatial discretizations in conjunction with fourth order Runge-Kutta time integration. In addition, an absorbing buffer zone was used at the outflow boundaries. Promising results were obtained and provide a basis for application of these techniques to a wider variety of problems.

An Evaluation of the Higher Order Thinking Skills Program with Fourth and Fifth Grade Students.

ERIC Educational Resources Information Center

Eisenman, J. Gordon, Jr.

The Higher Order Thinking Skills Program (HOTS) is a computer-based program for teaching thinking skills developed by Stanley Pogrow at the University of Arizona. It is now used in over 800 U.S. schools. This study investigated the effects of the HOTS program versus the traditional Chapter 1 program on fourth and fifth grade students'…

Representation of Renormalization Group Functions By Nonsingular Integrals in a Model of the Critical Dynamics of Ferromagnets: The Fourth Order of The ɛ-Expansion

NASA Astrophysics Data System (ADS)

Adzhemyan, L. Ts.; Vorob'eva, S. E.; Ivanova, E. V.; Kompaniets, M. V.

2018-04-01

Using the representation for renormalization group functions in terms of nonsingular integrals, we calculate the dynamical critical exponents in the model of critical dynamics of ferromagnets in the fourth order of the ɛ-expansion. We calculate the Feynman diagrams using the sector decomposition technique generalized to critical dynamics problems.

Holographic studies of Einsteinian cubic gravity

NASA Astrophysics Data System (ADS)

Bueno, Pablo; Cano, Pablo A.; Ruipérez, Alejandro

2018-03-01

Einsteinian cubic gravity provides a holographic toy model of a nonsupersymmetric CFT in three dimensions, analogous to the one defined by Quasi-topological gravity in four. The theory admits explicit non-hairy AdS4 black holes and allows for numerous exact calculations, fully nonperturbative in the new coupling. We identify several entries of the AdS/CFT dictionary for this theory, and study its thermodynamic phase space, finding interesting new phenomena. We also analyze the dependence of Rényi entropies for disk regions on universal quantities characterizing the CFT. In addition, we show that η/ s is given by a non-analytic function of the ECG coupling, and that the existence of positive-energy black holes strictly forbids violations of the KSS bound. Along the way, we introduce a new method for evaluating Euclidean on-shell actions for general higher-order gravities possessing second-order linearized equations on AdS( d+1). Our generalized action involves the very same Gibbons-Hawking boundary term and counterterms valid for Einstein gravity, which now appear weighted by the universal charge a * controlling the entanglement entropy across a spherical region in the CFT dual to the corresponding higher-order theory.

Middle Atmosphere Program. Handbook for MAP, volume 28

NASA Technical Reports Server (NTRS)

Liu, C. H. (Editor); Edwards, Belva (Editor)

1989-01-01

Extended abstracts from the fourth workshop on the technical and scientific aspects of MST (mesosphere stratosphere troposphere) radar are presented. Individual sessions addressed the following topics: meteorological applications of MST and ST radars, networks, and campaigns; dynamics of the equatorial middle atmosphere; interpretation of radar returns from clear air; techniques for studying gravity waves and turbulence; intercomparison and calibration of wind and wave measurements at various frequencies; progress in existing and planned MST and ST radars; hardware design for MST and ST radars and boundary layer/lower troposphere profilers; signal processing; and data management.

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.

Scattering of fermions in the Yukawa theory coupled to unimodular gravity

NASA Astrophysics Data System (ADS)

Gonzalez-Martin, S.; Martin, C. P.

2018-03-01

We compute the lowest order gravitational UV divergent radiative corrections to the S matrix element of the fermion + fermion→ fermion + fermion scattering process in the massive Yukawa theory, coupled either to Unimodular Gravity or to General Relativity. We show that both Unimodular Gravity and General Relativity give rise to the same UV divergent contribution in Dimensional Regularization. This is a nontrivial result, since in the classical action of Unimodular Gravity coupled to the Yukawa theory, the graviton field does not couple neither to the mass operator nor to the Yukawa operator. This is unlike the General Relativity case. The agreement found points in the direction that Unimodular Gravity and General Relativity give rise to the same quantum theory when coupled to matter, as long as the Cosmological Constant vanishes. Along the way we have come across another unexpected cancellation of UV divergences for both Unimodular Gravity and General Relativity, resulting in the UV finiteness of the one-loop and κ y^2 order of the vertex involving two fermions and one graviton only.

Assessment of Higher-Order RANS Closures in a Decelerated Planar Wall-Bounded Turbulent Flow

NASA Technical Reports Server (NTRS)

Jeyapaul, Elbert; Coleman, Gary N.; Rumsey, Christopher L.

2014-01-01

A reference DNS database is presented, which includes third- and fourth-order moment budgets for unstrained and strained planar channel flow. Existing RANS closure models for third- and fourth-order terms are surveyed, and new model ideas are introduced. The various models are then compared with the DNS data term by term using a priori testing of the higher-order budgets of turbulence transport, velocity-pressure-gradient, and dissipation for both the unstrained and strained databases. Generally, the models for the velocity-pressure-gradient terms are most in need of improvement.

On the recovery of gravity anomalies from high precision altimeter data

NASA Technical Reports Server (NTRS)

Lelgemann, D.

1976-01-01

A model for the recovery of gravity anomalies from high precision altimeter data is derived which consists of small correction terms to the inverse Stokes' formula. The influence of unknown sea surface topography in the case of meandering currents such as the Gulf Stream is discussed. A formula was derived in order to estimate the accuracy of the gravity anomalies from the known accuracy of the altimeter data. It is shown that for the case of known harmonic coefficients of lower order the range of integration in Stokes inverse formula can be reduced very much.

Monge-Ampére simulation of fourth order PDEs in two dimensions with application to elastic-electrostatic contact problems

NASA Astrophysics Data System (ADS)

DiPietro, Kelsey L.; Lindsay, Alan E.

2017-11-01

We present an efficient moving mesh method for the simulation of fourth order nonlinear partial differential equations (PDEs) in two dimensions using the Parabolic Monge-Ampére (PMA) equation. PMA methods have been successfully applied to the simulation of second order problems, but not on systems with higher order equations which arise in many topical applications. Our main application is the resolution of fine scale behavior in PDEs describing elastic-electrostatic interactions. The PDE system considered has multiple parameter dependent singular solution modalities, including finite time singularities and sharp interface dynamics. We describe how to construct a dynamic mesh algorithm for such problems which incorporates known self similar or boundary layer scalings of the underlying equation to locate and dynamically resolve fine scale solution features in these singular regimes. We find a key step in using the PMA equation for mesh generation in fourth order problems is the adoption of a high order representation of the transformation from the computational to physical mesh. We demonstrate the efficacy of the new method on a variety of examples and establish several new results and conjectures on the nature of self-similar singularity formation in higher order PDEs.

Time accurate application of the MacCormack 2-4 scheme on massively parallel computers

NASA Technical Reports Server (NTRS)

Hudson, Dale A.; Long, Lyle N.

1995-01-01

Many recent computational efforts in turbulence and acoustics research have used higher order numerical algorithms. One popular method has been the explicit MacCormack 2-4 scheme. The MacCormack 2-4 scheme is second order accurate in time and fourth order accurate in space, and is stable for CFL's below 2/3. Current research has shown that the method can give accurate results but does exhibit significant Gibbs phenomena at sharp discontinuities. The impact of adding Jameson type second, third, and fourth order artificial viscosity was examined here. Category 2 problems, the nonlinear traveling wave and the Riemann problem, were computed using a CFL number of 0.25. This research has found that dispersion errors can be significantly reduced or nearly eliminated by using a combination of second and third order terms in the damping. Use of second and fourth order terms reduced the magnitude of dispersion errors but not as effectively as the second and third order combination. The program was coded using Thinking Machine's CM Fortran, a variant of Fortran 90/High Performance Fortran, and was executed on a 2K CM-200. Simple extrapolation boundary conditions were used for both problems.

Test Equal Bending by Gravity for Space and Time

NASA Astrophysics Data System (ADS)

Sweetser, Douglas

2009-05-01

For the simplest problem of gravity - a static, non-rotating, spherically symmetric source - the solution for spacetime bending around the Sun should be evenly split between time and space. That is true to first order in M/R, and confirmed by experiment. At second order, general relativity predicts different amounts of contribution from time and space without a physical justification. I show an exponential metric is consistent with light bending to first order, measurably different at second order. All terms to all orders show equal contributions from space and time. Beautiful minimalism is Nature's way.

Efficient and accurate time-stepping schemes for integrate-and-fire neuronal networks.

PubMed

Shelley, M J; Tao, L

2001-01-01

To avoid the numerical errors associated with resetting the potential following a spike in simulations of integrate-and-fire neuronal networks, Hansel et al. and Shelley independently developed a modified time-stepping method. Their particular scheme consists of second-order Runge-Kutta time-stepping, a linear interpolant to find spike times, and a recalibration of postspike potential using the spike times. Here we show analytically that such a scheme is second order, discuss the conditions under which efficient, higher-order algorithms can be constructed to treat resets, and develop a modified fourth-order scheme. To support our analysis, we simulate a system of integrate-and-fire conductance-based point neurons with all-to-all coupling. For six-digit accuracy, our modified Runge-Kutta fourth-order scheme needs a time-step of Delta(t) = 0.5 x 10(-3) seconds, whereas to achieve comparable accuracy using a recalibrated second-order or a first-order algorithm requires time-steps of 10(-5) seconds or 10(-9) seconds, respectively. Furthermore, since the cortico-cortical conductances in standard integrate-and-fire neuronal networks do not depend on the value of the membrane potential, we can attain fourth-order accuracy with computational costs normally associated with second-order schemes.

Modeling of the Earth's gravity field using the New Global Earth Model (NEWGEM)

NASA Technical Reports Server (NTRS)

Kim, Yeong E.; Braswell, W. Danny

1989-01-01

Traditionally, the global gravity field was described by representations based on the spherical harmonics (SH) expansion of the geopotential. The SH expansion coefficients were determined by fitting the Earth's gravity data as measured by many different methods including the use of artificial satellites. As gravity data have accumulated with increasingly better accuracies, more of the higher order SH expansion coefficients were determined. The SH representation is useful for describing the gravity field exterior to the Earth but is theoretically invalid on the Earth's surface and in the Earth's interior. A new global Earth model (NEWGEM) (KIM, 1987 and 1988a) was recently proposed to provide a unified description of the Earth's gravity field inside, on, and outside the Earth's surface using the Earth's mass density profile as deduced from seismic studies, elevation and bathymetric information, and local and global gravity data. Using NEWGEM, it is possible to determine the constraints on the mass distribution of the Earth imposed by gravity, topography, and seismic data. NEWGEM is useful in investigating a variety of geophysical phenomena. It is currently being utilized to develop a geophysical interpretation of Kaula's rule. The zeroth order NEWGEM is being used to numerically integrate spherical harmonic expansion coefficients and simultaneously determine the contribution of each layer in the model to a given coefficient. The numerically determined SH expansion coefficients are also being used to test the validity of SH expansions at the surface of the Earth by comparing the resulting SH expansion gravity model with exact calculations of the gravity at the Earth's surface.

Gravity investigation of the Manson impact structure, Iowa

NASA Technical Reports Server (NTRS)

Plescia, J. B.

1993-01-01

The Manson crater, of probable Cretaceous/Tertiary age, is located in northwestern Iowa (center at 42 deg. 34.44 min N; 94 deg. 33.60 min W). A seismic reflection profile along an east west line across the crater and drill hole data indicate a crater about 35 km in diameter having the classic form for an impact crater, an uplifted central peak composed of uplifted Proterozoic crystalline bedrock, surrounded by a 'moat' filled with impact produced breccia and a ring graben zone composed of tilted fault blocks of the Proterozoic and Paleozoic country rocks. The structure has been significantly eroded. This geologic structure would be expected to produce a significant gravity signature and study of that signature would shed additional light on the details of the crater structure. A gravity study was undertaken to better resolve the crustal structure. The regional Bouguer gravity field is characterized by a southeastward decreasing field. To first order, the Bouguer gravity field can be understood in the context of the geology of the Precambrian basement. The high gravity at the southeast corner is associated with the mid-continent gravity high; the adjacent low to the northwest results from a basin containing low-density clastic sediments shed from the basement high. Modeling of a simple basin and adjacent high predicts much of the observed Bouguer gravity signature. A gravity signature due to structure associated with the Manson impact is not apparent in the Bouguer data. To resolve the gravity signature of the impact, a series of polynomial surfaces were fit to the Bouguer gravity field to isolate the small wavelength residual anomalies. The residual gravity obtained after subtracting a 5th- or 6th-order polynomial seems to remove most of the regional effects and isolate local anomalies. The pattern resolved in the residual gravity is one of a gravity high surrounded by gravity lows and in turn surrounded by isolated gravity highs. The central portion of the crater is characterized by two positive anomalies having amplitudes of about plus 4 mGal separated by a gentle saddle located approximately at the crater center.

Hierarchal Genetic Stratigraphy: A Framework for Paleoceanography

NASA Astrophysics Data System (ADS)

Busch, R. M.; West, R. R.

1987-04-01

A detailed, genetic stratigraphic framework for paleoceanographic studies can be derived by describing, correlating, interpreting, and predicting stratigraphic sequences relative to a hierarchy of their constituent time-stratigraphic transgressive-regressive units ("T-R units"). T-R unit hierarchies are defined and correlated using lithostratigraphic and paleoecologic data, but correlations can be enhanced or "checked" (tested to confirm or deny) with objective biostratigraphic, magnetostratigraphic, or chemostratigraphic data. Such chronostratigraphies can then be bracketed by radiometric ages, so that average periodicities for T-R units can be calculated and a hierarchal geochronology derived. T-R units are inferred to be the net depositional result of eustatic cycles of sea level change and can be differentiated from autocyclic deepening-shallowing units because the latter are noncorrelative intrabasinally. Boundaries between T-R units are conformable or unconformable "genetic surfaces" of two types: transgressive surfaces and "climate change surfaces". The latter are useful for correlating minor transgressive phases through nonmarine intervals, thereby deriving information linking paleoclimatic and paleoceanographic processes. Permo-Carboniferous sequences can be analyzed relative to a hierarchy of six scales of genetic T-R units having periodicities of 225-300 m.y. (first order), 20-90 m.y. (second order), 7-13 m.y. (third-order), 0.6-3.6 m.y. (fourth order), 300-500 × 10³ years (fifth order), and 50-130 × 10³ years or less (sixth-order). Paleogeographic maps for the time of maximum transgression ("transgressive apex") of successive fifth-order T-R units (5-25 m thick) in the Glenshaw Formation (Upper Pennsylvanian, Northern Appalachian Basin) delineate delta lobes, embayments, islands, and linear seaways. Relative extent of marine inundation on the fifth-order maps was used to delineate fourth-order T-R units, and the fourth-order T-R units constitute the transgressive half of a third-order T-R unit. This third-, fourth-, and fifth-order hierarchy is correlated more than 1200 km (750 miles) to the Western Interior "Basin," and is confirmed with limited objective biostratigraphy.

Cutoff for extensions of massive gravity and bi-gravity

NASA Astrophysics Data System (ADS)

Matas, Andrew

2016-04-01

Recently there has been interest in extending ghost-free massive gravity, bi-gravity, and multi-gravity by including non-standard kinetic terms and matter couplings. We first review recent proposals for this class of extensions, emphasizing how modifications of the kinetic and potential structure of the graviton and modifications of the coupling to matter are related. We then generalize existing no-go arguments in the metric language to the vielbein language in second-order form. We give an ADM argument to show that the most promising extensions to the kinetic term and matter coupling contain a Boulware-Deser ghost. However, as recently emphasized, we may still be able to view these extensions as effective field theories below some cutoff scale. To address this possibility, we show that there is a decoupling limit where a ghost appears for a wide class of matter couplings and kinetic terms. In particular, we show that there is a decoupling limit where the linear effective vielbein matter coupling contains a ghost. Using the insight we gain from this decoupling limit analysis, we place an upper bound on the cutoff for the linear effective vielbein coupling. This result can be generalized to new kinetic interactions in the vielbein language in second-order form. Combined with recent results, this provides a strong uniqueness argument on the form of ghost-free massive gravity, bi-gravity, and multi-gravity.

The Role of GRAIL Orbit Determination in Preprocessing of Gravity Science Measurements

NASA Technical Reports Server (NTRS)

Kruizinga, Gerhard; Asmar, Sami; Fahnestock, Eugene; Harvey, Nate; Kahan, Daniel; Konopliv, Alex; Oudrhiri, Kamal; Paik, Meegyeong; Park, Ryan; Strekalov, Dmitry;

Low-order aberration sensitivity of eighth-order coronagraph masks

NASA Technical Reports Server (NTRS)

Shaklan, Stuart B.; Green, Joseph J.

2005-01-01

In a recent paper, Kuchner, Crepp, and Ge describe new image-plane coronagraph mask designs that reject to eighth order the leakage of starlight caused by image motion at the mask, resulting in a substantial relaxation of image centroiding requirements compared to previous fourth-order and second-order masks. They also suggest that the new masks are effective at rejecting leakage caused by low-order aberrations (e.g., focus, coma, and astigmatism). In this paper, we derive the sensitivity of eighth-order masks to aberrations of any order and provide simulations of coronagraph behavior in the presence of optical aberrations.We find that the masks leak light as the fourth power of focus, astigmatism, coma, and trefoil. This has tremendous performance advantages for the Terrestrial Planet Finder Coronagraph.

Gapless topological order, gravity, and black holes

NASA Astrophysics Data System (ADS)

Rasmussen, Alex; Jermyn, Adam S.

2018-04-01

In this work we demonstrate that linearized gravity exhibits gapless topological order with an extensive ground state degeneracy. This phenomenon is closely related both to the topological order of the pyrochlore U (1 ) spin liquid and to recent work by Hawking and co-workers, who used the soft-photon and graviton theorems to demonstrate that the vacuum in linearized gravity is not unique. We first consider lattice models whose low-energy behavior is described by electromagnetism and linearized gravity, and then argue that the topological nature of these models carries over into the continuum. We demonstrate that these models can have many ground states without making assumptions about the topology of spacetime or about the high-energy nature of the theory, and show that the infinite family of symmetries described by Hawking and co-workers is simply the different topological sectors. We argue that in this context black holes appear as topological defects in the infrared theory, and that this suggests a potential approach to understanding both the firewall paradox and information encoding in gravitational theories. Finally, we use insights from the soft-boson theorems to make connections between deconfined gauge theories with continuous gauge groups and gapless topological order.

A high-order 3-D spectral-element method for the forward modelling and inversion of gravimetric data—Application to the western Pyrenees

NASA Astrophysics Data System (ADS)

Martin, Roland; Chevrot, Sébastien; Komatitsch, Dimitri; Seoane, Lucia; Spangenberg, Hannah; Wang, Yi; Dufréchou, Grégory; Bonvalot, Sylvain; Bruinsma, Sean

2017-04-01

We image the internal density structure of the Pyrenees by inverting gravity data using an a priori density model derived by scaling a Vp model obtained by full waveform inversion of teleseismic P-waves. Gravity anomalies are computed via a 3-D high-order finite-element integration in the same high-order spectral-element grid as the one used to solve the wave equation and thus to obtain the velocity model. The curvature of the Earth and surface topography are taken into account in order to obtain a density model as accurate as possible. The method is validated through comparisons with exact semi-analytical solutions. We show that the spectral-element method drastically accelerates the computations when compared to other more classical methods. Different scaling relations between compressional velocity and density are tested, and the Nafe-Drake relation is the one that leads to the best agreement between computed and observed gravity anomalies. Gravity data inversion is then performed and the results allow us to put more constraints on the density structure of the shallow crust and on the deep architecture of the mountain range.

Testing charm quark equilibration in ultrahigh-energy heavy ion collisions with fluctuations

NASA Astrophysics Data System (ADS)

Graf, Thorben; Steinheimer, Jan; Bleicher, Marcus; Herold, Christoph

2018-03-01

Recent lattice QCD data on higher order susceptibilities of charm quarks provide the opportunity to explore charm quark equilibration in the early quark gluon plasma (QGP) phase. Here, we propose to use the lattice data on second- and fourth-order net charm susceptibilities to infer the charm quark equilibration temperature and the corresponding volume, in the early QGP stage, via a combined analysis of experimentally measured multiplicity fluctuations. Furthermore, the first perturbative results for the second- and fourth-order charm quark susceptibilities and their ratio are presented.

Finite Differences and Collocation Methods for the Solution of the Two Dimensional Heat Equation

NASA Technical Reports Server (NTRS)

Kouatchou, Jules

1999-01-01

In this paper we combine finite difference approximations (for spatial derivatives) and collocation techniques (for the time component) to numerically solve the two dimensional heat equation. We employ respectively a second-order and a fourth-order schemes for the spatial derivatives and the discretization method gives rise to a linear system of equations. We show that the matrix of the system is non-singular. Numerical experiments carried out on serial computers, show the unconditional stability of the proposed method and the high accuracy achieved by the fourth-order scheme.

Characterizing interstate vibrational coherent dynamics of surface adsorbed catalysts by fourth-order 3D SFG spectroscopy

NASA Astrophysics Data System (ADS)

Li, Yingmin; Wang, Jiaxi; Clark, Melissa L.; Kubiak, Clifford P.; Xiong, Wei

2016-04-01

We report the first fourth-order 3D SFG spectroscopy of a monolayer of the catalyst Re(diCN-bpy)(CO)3Cl on a gold surface. Besides measuring the vibrational coherences of single vibrational modes, the fourth-order 3D SFG spectrum also measures the dynamics of interstate coherences and vibrational coherences states between two vibrational modes. By comparing the 3D SFG to the corresponding 2D and third-order 3D IR spectroscopy of the same molecules in solution, we found that the interstate coherences exist in both liquid and surface systems, suggesting that the interstate coherence is not disrupted by surface interactions. However, by analyzing the 3D spectral lineshape, we found that the interstate coherences also experience non-negligible homogenous dephasing dynamics that originate from surface interactions. This unique ability of determining interstate vibrational coherence dynamics of the molecular monolayer can help in understanding of how energy flows within surface catalysts and other molecular monolayers.

Pseudospectral collocation methods for fourth order differential equations

NASA Technical Reports Server (NTRS)

Malek, Alaeddin; Phillips, Timothy N.

1994-01-01

Collocation schemes are presented for solving linear fourth order differential equations in one and two dimensions. The variational formulation of the model fourth order problem is discretized by approximating the integrals by a Gaussian quadrature rule generalized to include the values of the derivative of the integrand at the boundary points. Collocation schemes are derived which are equivalent to this discrete variational problem. An efficient preconditioner based on a low-order finite difference approximation to the same differential operator is presented. The corresponding multidomain problem is also considered and interface conditions are derived. Pseudospectral approximations which are C1 continuous at the interfaces are used in each subdomain to approximate the solution. The approximations are also shown to be C3 continuous at the interfaces asymptotically. A complete analysis of the collocation scheme for the multidomain problem is provided. The extension of the method to the biharmonic equation in two dimensions is discussed and results are presented for a problem defined in a nonrectangular domain.

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.

Modified first-order Hořava-Lifshitz gravity: Hamiltonian analysis of the general theory and accelerating FRW cosmology in a power-law F(R) model

NASA Astrophysics Data System (ADS)

Carloni, Sante; Chaichian, Masud; Nojiri, Shin'Ichi; Odintsov, Sergei D.; Oksanen, Markku; Tureanu, Anca

2010-09-01

We propose the most general modified first-order Hořava-Lifshitz gravity, whose action does not contain time derivatives higher than the second order. The Hamiltonian structure of this theory is studied in all the details in the case of the spatially-flat Friedmann-Robertson-Walker (FRW) space-time, demonstrating many of the features of the general theory. It is shown that, with some plausible assumptions, including the projectability of the lapse function, this model is consistent. As a large class of such theories, the modified Hořava-Lifshitz F(R) gravity is introduced. The study of its ultraviolet properties shows that its z=3 version seems to be renormalizable in the same way as the original Hořava-Lifshitz proposal. The Hamiltonian analysis of the modified Hořava-Lifshitz F(R) gravity shows that it is in general a consistent theory. The F(R) gravity action is also studied in the fixed-gauge form, where the appearance of a scalar field is particularly illustrative. Then the spatially-flat FRW cosmology for this F(R) gravity is investigated. It is shown that a special choice of parameters for this theory leads to the same equations of motion as in the case of traditional F(R) gravity. Nevertheless, the cosmological structure of the modified Hořava-Lifshitz F(R) gravity turns out to be much richer than for its traditional counterpart. The emergence of multiple de Sitter solutions indicates the possibility of unification of early-time inflation with late-time acceleration within the same model. Power-law F(R) theories are also investigated in detail. It is analytically shown that they have a quite rich cosmological structure: early-/late-time cosmic acceleration of quintessence, as well as of phantom types. Also it is demonstrated that all the four known types of finite-time future singularities may occur in the power-law Hořava-Lifshitz F(R) gravity. Finally, a covariant proposal for (renormalizable) F(R) gravity within the Hořava-Lifshitz spirit is presented.

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.

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.

Numerical solution of the wave equation with variable wave speed on nonconforming domains by high-order difference potentials

NASA Astrophysics Data System (ADS)

Britt, S.; Tsynkov, S.; Turkel, E.

2018-02-01

We solve the wave equation with variable wave speed on nonconforming domains with fourth order accuracy in both space and time. This is accomplished using an implicit finite difference (FD) scheme for the wave equation and solving an elliptic (modified Helmholtz) equation at each time step with fourth order spatial accuracy by the method of difference potentials (MDP). High-order MDP utilizes compact FD schemes on regular structured grids to efficiently solve problems on nonconforming domains while maintaining the design convergence rate of the underlying FD scheme. Asymptotically, the computational complexity of high-order MDP scales the same as that for FD.

Critical study of higher order numerical methods for solving the boundary-layer equations

NASA Technical Reports Server (NTRS)

Wornom, S. F.

1978-01-01

A fourth order box method is presented for calculating numerical solutions to parabolic, partial differential equations in two variables or ordinary differential equations. The method, which is the natural extension of the second order box scheme to fourth order, was demonstrated with application to the incompressible, laminar and turbulent, boundary layer equations. The efficiency of the present method is compared with two point and three point higher order methods, namely, the Keller box scheme with Richardson extrapolation, the method of deferred corrections, a three point spline method, and a modified finite element method. For equivalent accuracy, numerical results show the present method to be more efficient than higher order methods for both laminar and turbulent flows.

Geologic interpretation of gravity data from the Date Creek basin and adjacent areas, west-central Arizona

USGS Publications Warehouse

Otton, James K.; Wynn, Jeffrey C.

1978-01-01

A gravity survey of the Date Creek Basin and adjacent areas was conducted in June 1977 to provide information for the interpretation of basin geology. A comparison of facies relations in the locally uraniferous Chapin Wash Formation and the position of the Anderson mine gravity anomaly in the Date Creek Basin suggested that a relationship between gravity lows and the development of thick lacustrine sections in the region might exist. A second-order residual gravity map derived from the complete Bouguer gravity map for the survey area (derived from survey data and pre-existing U.S. Department of Defense data) shows an excellent correspondence between gravity lows and sediment-filled basins and suggests considerable variation in basin-fill thickness. Using the Anderson mine anomaly as a model, gravity data and facies relations suggest that the southeastern flank of the Aguila Valley gravity low and the gravity low at the western end of the Hassayampa Plain are likely areas for finding thick sections of tuffaceous lacustrine rocks.

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.

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.

Model-independent constraints on possible modifications of Newtonian gravity

NASA Technical Reports Server (NTRS)

Talmadge, C.; Berthias, J.-P.; Hellings, R. W.; Standish, E. M.

1988-01-01

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

Gravity-Dependent Transport in Industrial Processes

NASA Technical Reports Server (NTRS)

Ostrach, Simon; Kamotani, Yasuhiro

1996-01-01

Gravity dependent transport phenomena in various industrial processes are investigated in order to indicate new directions for micro-gravity research that enhance the commercial success of the space program. The present article describes the commercialization possibilities of such topics associated with physicochemical transport phenomena. The topics are: coating flow, rotating electrochemical system, and convection in low Plandtl number fluids. The present study is directed to understand these phenomena, and to develop a knowledge base for their applications with emphasis to a micro-gravity environment.

An adaptive multiblock high-order finite-volume method for solving the shallow-water equations on the sphere

DOE PAGES

McCorquodale, Peter; Ullrich, Paul; Johansen, Hans; ...

2015-09-04

We present a high-order finite-volume approach for solving the shallow-water equations on the sphere, using multiblock grids on the cubed-sphere. This approach combines a Runge--Kutta time discretization with a fourth-order accurate spatial discretization, and includes adaptive mesh refinement and refinement in time. Results of tests show fourth-order convergence for the shallow-water equations as well as for advection in a highly deformational flow. Hierarchical adaptive mesh refinement allows solution error to be achieved that is comparable to that obtained with uniform resolution of the most refined level of the hierarchy, but with many fewer operations.

Where Does Wood Most Effectively Enhance Storage? Network-Scale Distribution of Sediment and Organic Matter Stored by Instream Wood

NASA Astrophysics Data System (ADS)

Pfeiffer, Andrew; Wohl, Ellen

2018-01-01

We used 48 reach-scale measurements of large wood and wood-associated sediment and coarse particulate organic matter (CPOM) storage within an 80 km2 catchment to examine spatial patterns of storage relative to stream order. Wood, sediment, and CPOM are not distributed uniformly across the drainage basin. Third- and fourth-order streams (23% of total stream length) disproportionately store wood and coarse and fine sediments: 55% of total wood volume, 78% of coarse sediment, and 49% of fine sediment, respectively. Fourth-order streams store 0.8 m3 of coarse sediment and 0.2 m3 of fine sediment per cubic meter of wood. CPOM storage is highest in first-order streams (60% of storage in 47% of total network stream length). First-order streams can store up to 0.3 m3 of CPOM for each cubic meter of wood. Logjams in third- and fourth-order reaches are primary sediment storage agents, whereas roots in small streams may be more important for storage of CPOM. We propose the large wood particulate storage index to quantify average volume of sediment or CPOM stored by a cubic meter of wood.

A 3D Unstructured Mesh Euler Solver Based on the Fourth-Order CESE Method

DTIC Science & Technology

2013-06-01

Form 298 (Rev. 8-98) Prescribed by ANSI Std. 239.18 A 3D Unstructured Mesh Euler Solver Based on the Fourth-Order CESE Method David L. Bilyeu ∗1,2...Similarly, the fluxes, f x,y,z i , and their derivatives inside a SE are also discretized by the Taylor series expansion: ∂ Cfx ,y,zi ∂xI∂yJ∂zK∂tL = A

Path-Integral Monte Carlo Determination of the Fourth-Order Virial Coefficient for a Unitary Two-Component Fermi Gas with Zero-Range Interactions

NASA Astrophysics Data System (ADS)

Yan, Yangqian; Blume, D.

2016-06-01

The unitary equal-mass Fermi gas with zero-range interactions constitutes a paradigmatic model system that is relevant to atomic, condensed matter, nuclear, particle, and astrophysics. This work determines the fourth-order virial coefficient b4 of such a strongly interacting Fermi gas using a customized ab initio path-integral Monte Carlo (PIMC) algorithm. In contrast to earlier theoretical results, which disagreed on the sign and magnitude of b4 , our b4 agrees within error bars with the experimentally determined value, thereby resolving an ongoing literature debate. Utilizing a trap regulator, our PIMC approach determines the fourth-order virial coefficient by directly sampling the partition function. An on-the-fly antisymmetrization avoids the Thomas collapse and, combined with the use of the exact two-body zero-range propagator, establishes an efficient general means to treat small Fermi systems with zero-range interactions.

Thermodynamic phase transition of a black hole in rainbow gravity

NASA Astrophysics Data System (ADS)

Feng, Zhong-Wen; Yang, Shu-Zheng

2017-09-01

In this letter, using the rainbow functions that were proposed by Magueijo and Smolin, we investigate the thermodynamics and the phase transition of rainbow Schwarzschild black hole. First, we calculate the rainbow gravity corrected Hawking temperature. From this modification, we then derive the local temperature, free energy, and other thermodynamic quantities in an isothermal cavity. Finally, we analyze the critical behavior, thermodynamic stability, and phase transition of the rainbow Schwarzschild black hole. The results show that the rainbow gravity can stop the Hawking radiation in the final stages of black holes' evolution and lead to the remnants of black holes. Furthermore, one can observe that the rainbow Schwarzschild black hole has one first-order phase transition, two second-order phase transitions, and three Hawking-Page-type phase transitions in the framework of rainbow gravity theory.

Matter scattering in quadratic gravity and unitarity

NASA Astrophysics Data System (ADS)

Abe, Yugo; Inami, Takeo; Izumi, Keisuke; Kitamura, Tomotaka

2018-03-01

We investigate the ultraviolet (UV) behavior of two-scalar elastic scattering with graviton exchanges in higher-curvature gravity theory. In Einstein gravity, matter scattering is shown not to satisfy the unitarity bound at tree level at high energy. Among some of the possible directions for the UV completion of Einstein gravity, such as string theory, modified gravity, and inclusion of high-mass/high-spin states, we take R_{μν}^2 gravity coupled to matter. We show that matter scattering with graviton interactions satisfies the unitarity bound at high energy, even with negative norm states due to the higher-order derivatives of metric components. The difference in the unitarity property of these two gravity theories is probably connected to that in another UV property, namely, the renormalizability property of the two.

Crustal flushing and its relationship to magnetic and hydrothermal processes on the East Pacific Rise crest

NASA Technical Reports Server (NTRS)

Wright, Dawn J.; Haymon, Rachel M.; Fornari, Daniel J.

1995-01-01

The deep-towed Argo I optical/acoustical vehicle and a geographic information system (GIS) have been used to establish the abundance, widths, and spatial distribution of fissures, as well as the relative age distribution of lavas along the narrow (less than 500 m wide) axial zone of the East Pacific Rise (EPR) from 9 deg 12 min to 9 deg 54 min N. On a second-order scale (approximately 78 km long), wider but less numerous fissures are found in the northern portion of the survey area; this changes to narrower, more abundant fissures in the south. A profile of the cumulative width added by fissures to the axial zone exhibits minima in three areas along strike (near 9 deg 49 min, 9 deg 35 min, and 9 deg 15 min N), where the most recent eruptions have occurred above sites of magmatic injection from the upper mantle, filling and covering older fissures. On a fourth-order scale (5-15 km long) the mean density of fissuring on a given segment is greater where relative axial lava age is greater. Fissure density also correlates with hydrothermal vent abundance and type. Increased cracking toward segment tips is observed at the second-order scale, whereas fourth-order segments tend to be more cracked in the middle. Cracking on a fourth-order scale may be driven by the propagation of dikes, rather than by the far-field plate stresses. The above relations constrain the model of Haymon et al. (1991) in which individual fourth-order segments are in different phases of a volcanic-hydrothermal-tectonic cycle.

Hierarchical clustering in chameleon f(R) gravity

NASA Astrophysics Data System (ADS)

Hellwing, Wojciech A.; Li, Baojiu; Frenk, Carlos S.; Cole, Shaun

2013-11-01

We use a suite of high-resolution state-of-the-art N-body dark matter simulations of chameleon f(R) gravity to study the higher order volume-averaged correlation functions overline{ξ _n} together with the hierarchical nth-order correlation amplitudes S_n=overline{ξ }_n/overline{ξ }_2^{n-1} and density distribution functions (PDF). We show that under the non-linear modifications of gravity the hierarchical scaling of the reduced cumulants is preserved. This is however characterized by significant changes in the values of both overline{ξ _n} and Sn and their scale dependence with respect to General Relativity gravity (GR). In addition, we measure a significant increase of the non-linear σ8 parameter reaching 14, 5 and 0.5 per cent in excess of the GR value for the three flavours of our f(R) models. We further note that the values of the reduced cumulants up to order n = 9 are significantly increased in f(R) gravity for all our models at small scales R ≲ 30 h-1 Mpc. In contrast, the values of the hierarchical amplitudes, Sn, are smaller in f(R) indicating that the modified gravity density distribution functions are deviating from the GR case. Furthermore, we find that the redshift evolution of relative deviations of the f(R) hierarchical correlation amplitudes is fastest at high and moderate redshifts 1 ≤ z ≤ 4. The growth of these deviations significantly slows down in the low-redshift universe. We also compute the PDFs and show that for scales below ˜20 h-1 Mpc, they are significantly shifted in f(R) gravity towards the low densities. Finally, we discuss the implications of our theoretical predictions for measurements of the hierarchical clustering in galaxy redshift surveys, including the important problems of the galaxy biasing and redshift space distortions.

Determination of the Threshold of Gravity for the Susceptibility to Kinetosis in Fish - a Centrifuge Experiment in the ZARM Drop-Tower employing gradually reduced Gravity

NASA Astrophysics Data System (ADS)

Anken, R.; Hilbig, R.

In the course of earlier experiments at diminished gravity conditions we have successfully used larval cichlid fish Oreochromis mossambicus as a vertebrate model system in investigating the basic cause of susceptibility to motion sickness kinetosis It was observed that most animals of a given batch reveal kinetoses i e performing looping responses LR or spinning movements SM at high quality microgravity 10-6g ZARM drop-tower whereas comparatively few individuals swim kinetotically at low quality microgravity LQM 0 03-0 05g during parabolic aircraft flights Anken and Hilbig Microgravity Sci Technol 15 52-57 2004 In order to gain further insights into a possible threshold of gravity for inducing motion sickness animals were subjected to drop-tower flights within a centrifuge The levels of gravity applied ranged from 0 009g until 0 3g The lowest level of gravity under which few normally swimming fish were observed ranged around 0 015g Since this is a very low level of gravity the normally swimming fish have to be considered to be either extremely sensitive to any force of gravity in order to use it as a cue for postural control or they use cues other than the residual gravity for maintaining equilibrium Most of the remaining kinetotically swimming animals showed LR whereas few exhibited SM With increasing gravity the ratio of normally swimming and spinning specimens increased accompanied by a decrease in the number of looping larvae Regarding the ratio a shift from LR to SM took place at around 0 02g At 0 3g all animals behaved

The OSIRIS-REx Radio Science Experiment at Bennu

NASA Astrophysics Data System (ADS)

McMahon, J. W.; Scheeres, D. J.; Hesar, S. G.; Farnocchia, D.; Chesley, S.; Lauretta, D.

2018-02-01

The OSIRIS-REx mission will conduct a Radio Science investigation of the asteroid Bennu with a primary goal of estimating the mass and gravity field of the asteroid. The spacecraft will conduct proximity operations around Bennu for over 1 year, during which time radiometric tracking data, optical landmark tracking images, and altimetry data will be obtained that can be used to make these estimates. Most significantly, the main Radio Science experiment will be a 9-day arc of quiescent operations in a 1-km nominally circular terminator orbit. The pristine data from this arc will allow the Radio Science team to determine the significant components of the gravity field up to the fourth spherical harmonic degree. The Radio Science team will also be responsible for estimating the surface accelerations, surface slopes, constraints on the internal density distribution of Bennu, the rotational state of Bennu to confirm YORP estimates, and the ephemeris of Bennu that incorporates a detailed model of the Yarkovsky effect.

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.

Cosmological models in energy-momentum-squared gravity

NASA Astrophysics Data System (ADS)

Board, Charles V. R.; Barrow, John D.

2017-12-01

We study the cosmological effects of adding terms of higher order in the usual energy-momentum tensor to the matter Lagrangian of general relativity. This is in contrast to most studies of higher-order gravity which focus on generalizing the Einstein-Hilbert curvature contribution to the Lagrangian. The resulting cosmological theories give rise to field equations of similar form to several particular theories with different fundamental bases, including bulk viscous cosmology, loop quantum gravity, k -essence, and brane-world cosmologies. We find a range of exact solutions for isotropic universes, discuss their behaviors with reference to the early- and late-time evolution, accelerated expansion, and the occurrence or avoidance of singularities. We briefly discuss extensions to anisotropic cosmologies and delineate the situations where the higher-order matter terms will dominate over anisotropies on approach to cosmological singularities.

Axion as a cold dark matter candidate: analysis to third order perturbation for classical axion

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

Noh, Hyerim; Hwang, Jai-chan; Park, Chan-Gyung, E-mail: hr@kasi.re.kr, E-mail: jchan@knu.ac.kr, E-mail: park.chan.gyung@gmail.com

2015-12-01

We investigate aspects of axion as a coherently oscillating massive classical scalar field by analyzing third order perturbations in Einstein's gravity in the axion-comoving gauge. The axion fluid has its characteristic pressure term leading to an axion Jeans scale which is cosmologically negligible for a canonical axion mass. Our classically derived axion pressure term in Einstein's gravity is identical to the one derived in the non-relativistic quantum mechanical context in the literature. We present the general relativistic continuity and Euler equations for an axion fluid valid up to third order perturbation. Equations for axion are exactly the same as thatmore » of a zero-pressure fluid in Einstein's gravity except for an axion pressure term in the Euler equation. Our analysis includes the cosmological constant.« less

Regression Models of Quarterly Overhead Costs for Six Government Aerospace Contractors.

DTIC Science & Technology

1986-03-01

34 Testing ,, for Serial Correlation After Least Squares %Regression, Econometrica, Vol. 36, No. 1, pp. 133-150, January 1968. Intrili8ator M.D., Econometric ...to be superior. These two estimators are both two-stage estimators that are calculated utilizing Wallis’s test statistic for fourth-order...utilizing Wallis’s test statistic for fourth-order autocorrelation. NTIS C F’,& D tI1C T - .1 I -. . . ..- rJ ,. *p J • - DA 3

Harmonic analysis of the DTU10 global gravity anomalies

NASA Astrophysics Data System (ADS)

Abrykosov, O.; Förste, Ch.; Gruber, Ch.; Shako, R.; Barthelmes, F.

2012-04-01

We have computed the Earth's gravity models to degree/order 5400 and 10800 (in terms of the ellipsoidal and spherical harmonics) from a rigorous integration of the 2'x2' and 1'x1' global grids of gravity anomalies provided by the Danish Technical University (DTU). The gravity signal recovered from the DTU10 data shows 1) a strong dependency on the truncation of the EGM2008 gravity model which were used to fill-in land areas in the DTU10 grids and 2) an irregular behaviour at frequencies behind the resolution of the EGM2008. We discuss the gravity signal and its accuracy estimation computed from the complete DTU10 grids as well as separately from the data over land and ocean areas.

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.

Theoretical regime diagrams for thermally driven flows in a beta-plane channel in the presence of variable gravity

NASA Technical Reports Server (NTRS)

Geisler, J. E.; Fowlis, W. W.

1980-01-01

The effect of a power law gravity field on baroclinic instability is examined, with a focus on the case of inverse fifth power gravity, since this is the power law produced when terrestrial gravity is simulated in spherical geometry by a dielectric force. Growth rates are obtained of unstable normal modes as a function of parameters of the problem by solving a second order differential equation numerically. It is concluded that over the range of parameter space explored, there is no significant change in the character of theoretical regime diagrams if the vertically averaged gravity is used as parameter.

Hamiltonian structure of three-dimensional gravity in Vielbein formalism

NASA Astrophysics Data System (ADS)

Hajihashemi, Mahdi; Shirzad, Ahmad

2018-01-01

Considering Chern-Simons like gravity theories in three dimensions as first order systems, we analyze the Hamiltonian structure of three theories Topological massive gravity, New massive gravity, and Zwei-Dreibein Gravity. We show that these systems demonstrate a new feature of the constrained systems in which a new kind of constraints emerge due to factorization of determinant of the matrix of Poisson brackets of constraints. We find the desired number of degrees of freedom as well as the generating functional of local Lorentz transformations and diffeomorphism through canonical structure of the system. We also compare the Hamiltonian structure of linearized version of the considered models with the original ones.

Teleparallel equivalent of Lovelock gravity

NASA Astrophysics Data System (ADS)

González, P. A.; Vásquez, Yerko

2015-12-01

There is a growing interest in modified gravity theories based on torsion, as these theories exhibit interesting cosmological implications. In this work inspired by the teleparallel formulation of general relativity, we present its extension to Lovelock gravity known as the most natural extension of general relativity in higher-dimensional space-times. First, we review the teleparallel equivalent of general relativity and Gauss-Bonnet gravity, and then we construct the teleparallel equivalent of Lovelock gravity. In order to achieve this goal, we use the vielbein and the connection without imposing the Weitzenböck connection. Then, we extract the teleparallel formulation of the theory by setting the curvature to null.

Numerical simulation analysis of four-stage mutation of solid-liquid two-phase grinding

NASA Astrophysics Data System (ADS)

Li, Junye; Liu, Yang; Hou, Jikun; Hu, Jinglei; Zhang, Hengfu; Wu, Guiling

2018-03-01

In order to explore the numerical simulation of solid-liquid two-phase abrasive grain polishing and abrupt change tube, in this paper, the fourth order abrupt change tube was selected as the research object, using the fluid mechanics software to simulate,based on the theory of solid-liquid two-phase flow dynamics, study on the mechanism of AFM micromachining a workpiece during polishing.Analysis at different inlet pressures, the dynamic pressure distribution pipe mutant fourth order abrasive flow field, turbulence intensity, discuss the influence of the inlet pressure of different abrasive flow polishing effect.

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 ).

Receiver design, performance analysis, and evaluation for space-borne laser altimeters and space-to-space laser ranging systems

NASA Technical Reports Server (NTRS)

Davidson, Frederic M.; Sun, Xiaoli

1993-01-01

This interim report consists of four separate reports from our research on the receivers of NASA's Gravity And Magnetic Experiment Satellite (GAMES). The first report is entitled 'Analysis of phase estimation bias of GAMES receiver due to Doppler shift.' The second report is 'Background radiation on GAMES fine ranging detector from the moon, the planets, and the stars.' The third report is 'Background radiation on GAMES receivers from the ocean sun glitter and the direct sun.' The fourth report is 'GAMES receiver performance versus background radiation power on the detectors.'

Higher Curvature Gravity from Entanglement in Conformal Field Theories.

PubMed

Haehl, Felix M; Hijano, Eliot; Parrikar, Onkar; Rabideau, Charles

2018-05-18

By generalizing different recent works to the context of higher curvature gravity, we provide a unifying framework for three related results: (i) If an asymptotically anti-de Sitter (AdS) spacetime computes the entanglement entropies of ball-shaped regions in a conformal field theory using a generalized Ryu-Takayanagi formula up to second order in state deformations around the vacuum, then the spacetime satisfies the correct gravitational equations of motion up to second order around the AdS background. (ii) The holographic dual of entanglement entropy in higher curvature theories of gravity is given by the Wald entropy plus a particular correction term involving extrinsic curvatures. (iii) Conformal field theory relative entropy is dual to gravitational canonical energy (also in higher curvature theories of gravity). Especially for the second point, our novel derivation of this previously known statement does not involve the Euclidean replica trick.

Higher Curvature Gravity from Entanglement in Conformal Field Theories

NASA Astrophysics Data System (ADS)

Haehl, Felix M.; Hijano, Eliot; Parrikar, Onkar; Rabideau, Charles

2018-05-01

By generalizing different recent works to the context of higher curvature gravity, we provide a unifying framework for three related results: (i) If an asymptotically anti-de Sitter (AdS) spacetime computes the entanglement entropies of ball-shaped regions in a conformal field theory using a generalized Ryu-Takayanagi formula up to second order in state deformations around the vacuum, then the spacetime satisfies the correct gravitational equations of motion up to second order around the AdS background. (ii) The holographic dual of entanglement entropy in higher curvature theories of gravity is given by the Wald entropy plus a particular correction term involving extrinsic curvatures. (iii) Conformal field theory relative entropy is dual to gravitational canonical energy (also in higher curvature theories of gravity). Especially for the second point, our novel derivation of this previously known statement does not involve the Euclidean replica trick.

Interacting spin-2 fields in the Stückelberg picture

NASA Astrophysics Data System (ADS)

Noller, Johannes; Scargill, James H. C.; Ferreira, Pedro G.

2014-02-01

We revisit and extend the `Effective field theory for massive gravitons' constructed by Arkani-Hamed, Georgi and Schwartz in the light of recent progress in constructing ghost-free theories with multiple interacting spin-2 fields. We show that there exist several dual ways of restoring gauge invariance in such multi-gravity theories, find a generalised Fierz-Pauli tuning condition relevant in this context and highlight subtleties in demixing tensor and scalar modes. The generic multi-gravity feature of scalar mixing and its consequences for higher order interactions are discussed. In particular we show how the decoupling limit is qualitatively changed in theories of interacting spin-2 fields. We relate this to dRGT (de Rham, Gabadadze, Tolley) massive gravity, Hassan-Rosen bigravity and the multi-gravity constructions by Hinterbichler and Rosen. As an additional application we show that EBI (Eddington-Born-Infeld) bigravity and higher order generalisations thereof possess ghost-like instabilities.

The reconstruction of f(ϕ)R and mimetic gravity from viable slow-roll inflation

NASA Astrophysics Data System (ADS)

Odintsov, S. D.; Oikonomou, V. K.

2018-04-01

In this work, we extend the bottom-up reconstruction framework of F (R) gravity to other modified gravities, and in particular for f (ϕ) R and mimetic F (R) gravities. We investigate which are the important conditions in order for the method to work, and we study several viable cosmological evolutions, focusing on the inflationary era. Particularly, for the f (ϕ) R theory case, we specify the functional form of the Hubble rate and of the scalar-to-tensor ratio as a function of the e-foldings number and accordingly, the rest of the physical quantities and also the slow-roll and the corresponding observational indices can be calculated. The same method is applied in the mimetic F (R) gravity case, and in both cases we thoroughly analyze the resulting free parameter space, in order to show that the viability of the models presented is guaranteed and secondly that there is a wide range of values of the free parameters for which the viability of the models occurs. In addition, the reconstruction method is also studied in the context of mimetic F (R) = R gravity. As we demonstrate, the resulting theory is viable, and also in this case, only the scalar-to-tensor ratio needs to be specified, since the rest follow from this condition. Finally, we discuss in brief how the reconstruction method could function for other modified gravities.

Vestibular convergence patterns in vestibular nuclei neurons of alert primates

NASA Technical Reports Server (NTRS)

Dickman, J. David; Angelaki, Dora E.

2002-01-01

Sensory signal convergence is a fundamental and important aspect of brain function. Such convergence may often involve complex multidimensional interactions as those proposed for the processing of otolith and semicircular canal (SCC) information for the detection of translational head movements and the effective discrimination from physically congruent gravity signals. In the present study, we have examined the responses of primate rostral vestibular nuclei (VN) neurons that do not exhibit any eye movement-related activity using 0.5-Hz translational and three-dimensional (3D) rotational motion. Three distinct neural populations were identified. Approximately one-fourth of the cells exclusively encoded rotational movements (canal-only neurons) and were unresponsive to translation. The canal-only central neurons encoded head rotation in SCC coordinates, exhibited little orthogonal canal convergence, and were characterized with significantly higher sensitivities to rotation as compared to primary SCC afferents. Another fourth of the neurons modulated their firing rates during translation (otolith-only cells). During rotations, these neurons only responded when the axis of rotation was earth-horizontal and the head was changing orientation relative to gravity. The remaining one-half of VN neurons were sensitive to both rotations and translations (otolith + canal neurons). Unlike primary otolith afferents, however, central neurons often exhibited significant spatiotemporal (noncosine) tuning properties and a wide variety of response dynamics to translation. To characterize the pattern of SCC inputs to otolith + canal neurons, their rotational maximum sensitivity vectors were computed using exclusively responses during earth-vertical axis rotations (EVA). Maximum sensitivity vectors were distributed throughout the 3D space, suggesting strong convergence from multiple SCCs. These neurons were also tested with earth-horizontal axis rotations (EHA), which would activate both vertical canals and otolith organs. However, the recorded responses could not be predicted from a linear combination of EVA rotational and translational responses. In contrast, one-third of the neurons responded similarly during EVA and EHA rotations, although a significant response modulation was present during translation. Thus this subpopulation of otolith + canal cells, which included neurons with either high- or low-pass dynamics to translation, appear to selectively ignore the component of otolith-selective activation that is due to changes in the orientation of the head relative to gravity. Thus contrary to primary otolith afferents and otolith-only central neurons that respond equivalently to tilts relative to gravity and translational movements, approximately one-third of the otolith + canal cells seem to encode a true estimate of the translational component of the imposed passive head and body movement.

Investigations on vertical crustal movements in the Venezuelan Andes by gravimetric methods

NASA Technical Reports Server (NTRS)

Drewes, H.

1978-01-01

A precise gravimetric network has been installed in the Venezuelan Andes to study eventual gravity changes due to vertical tectonic movements. The design and the measurements of the network are described and the accuracy is estimated. In the center of the region a local gravity network has been reobserved three times. The detected variations are discussed. In order to obtain a genuine statement as far as possible about the significance of observed gravity changes, requirements for the procedure of monitoring precise gravity networks are pointed out.

Influence of gravity level and interfacial energies on dispersion-forming tendencies in hypermonotectic Cu-Pb-Al alloys

NASA Technical Reports Server (NTRS)

Andrews, J. B.; Curreri, P. A.; Sandlin, A. C.

1988-01-01

Results on the nondirectional solidification of several hypermonotectic Cu-Pb-Al alloys were obtained aboard NASA's KC-135 zero-gravity aircraft in order to determine the influence of interfacial energies and gravity levels on dispersion-forming tendencies. The Al content was systematially varied in the alloys. The dispersion-forming ability is correlated with gravity level during solidification, the interfacial energy between the immiscible phases, and the tendency for the minority immiscible phase to wet the walls of the crucible.

Establishment of National Gravity Base Network of Iran

NASA Astrophysics Data System (ADS)

Hatam Chavari, Y.; Bayer, R.; Hinderer, J.; Ghazavi, K.; Sedighi, M.; Luck, B.; Djamour, Y.; Le Moign, N.; Saadat, R.; Cheraghi, H.

2009-04-01

A gravity base network is supposed to be a set of benchmarks uniformly distributed across the country and the absolute gravity values at the benchmarks are known to the best accessible accuracy. The gravity at the benchmark stations are either measured directly with absolute devices or transferred by gravity difference measurements by gravimeters from known stations. To decrease the accumulation of random measuring errors arising from these transfers, the number of base stations distributed across the country should be as small as possible. This is feasible if the stations are selected near to the national airports long distances apart but faster accessible and measurable by a gravimeter carried in an airplane between the stations. To realize the importance of such a network, various applications of a gravity base network are firstly reviewed. A gravity base network is the required reference frame for establishing 1st , 2nd and 3rd order gravity networks. Such a gravity network is used for the following purposes: a. Mapping of the structure of upper crust in geology maps. The required accuracy for the measured gravity values is about 0.2 to 0.4 mGal. b. Oil and mineral explorations. The required accuracy for the measured gravity values is about 5 µGal. c. Geotechnical studies in mining areas for exploring the underground cavities as well as archeological studies. The required accuracy is about 5 µGal and better. d. Subsurface water resource explorations and mapping crustal layers which absorb it. An accuracy of the same level of previous applications is required here too. e. Studying the tectonics of the Earth's crust. Repeated precise gravity measurements at the gravity network stations can assist us in identifying systematic height changes. The accuracy of the order of 5 µGal and more is required. f. Studying volcanoes and their evolution. Repeated precise gravity measurements at the gravity network stations can provide valuable information on the gradual upward movement of lava. g. Producing precise mean gravity anomaly for precise geoid determination. Replacing precise spirit leveling by the GPS leveling using precise geoid model is one of the forth coming application of the precise geoid. A gravity base network of 28 stations established over Iran. The stations were built mainly at bedrocks. All stations were measured by an FG5 absolute gravimeter, at least 12 hours at each station, to obtain an accuracy of a few micro gals. Several stations were repeated several times during recent years to estimate the gravity changes.

Structural design of a large deformable primary mirror for a space telescope

NASA Astrophysics Data System (ADS)

Hansen, J. G. R.

A 4 meter aperture deformable primary mirror is designed with the mirror and its supports integrated into a single structure. The integrated active mirror's minimal weight makes it desirable for a space telescope as well as a terrestrial application. Utilizing displacement actuators, the active controls at the mirror's surface include position control and slope control in both the radial and tangential directions at each of the 40 control points. Influence functions for each of the controls are nearly independent, reducing the complexity of the control system. Experiments with breadboard models verify the structural concept and the techniques used in the finite element method of computer structural analysis. The majority of this paper is a description of finite element analysis results. Localization of influence functions is exhaustively treated. For gravity loads, a thermal gradient through the mirror thickness, and a uniform thermal soak, diffraction limited performance of the 4m design is evaluated. Loads are applied to defocus the mirror and to cause fourth-order astigmatism. Mirror scallop, instigated by a focus shift, has been virtually eliminated with the 40-actuator design. The structural concept is so effective that it should be considered for uncontrolled primary mirrors as well as active mirrors.

Geodynamics and temporal variations in the gravity field

NASA Technical Reports Server (NTRS)

Mcadoo, D. C.; Wagner, C. A.

1989-01-01

Just as the Earth's surface deforms tectonically, so too does the gravity field evolve with time. Now that precise geodesy is yielding observations of these deformations it is important that concomitant, temporal changes in the gravity field be monitored. Although these temporal changes are minute they are observable: changes in the J2 component of the gravity field were inferred from satellite (LAGEOS) tracking data; changes in other components of the gravity field would likely be detected by Geopotential Research Mission (GRM), a proposed but unapproved NASA gravity field mission. Satellite gradiometers were also proposed for high-precision gravity field mapping. Using simple models of geodynamic processes such as viscous postglacial rebound of the solid Earth, great subduction zone earthquakes and seasonal glacial mass fluctuations, we predict temporal changes in gravity gradients at spacecraft altitudes. It was found that these proposed gravity gradient satellite missions should have sensitivities equal to or better than 10(exp -4) E in order to reliably detect these changes. It was also found that satellite altimetry yields little promise of useful detection of time variations in gravity.

Inelastic black hole scattering from charged scalar amplitudes

NASA Astrophysics Data System (ADS)

Luna, Andrés; Nicholson, Isobel; O'Connell, Donal; White, Chris D.

2018-03-01

We explain how the lowest-order classical gravitational radiation produced during the inelastic scattering of two Schwarzschild black holes in General Relativity can be obtained from a tree scattering amplitude in gauge theory coupled to scalar fields. The gauge calculation is related to gravity through the double copy. We remove unwanted scalar forces which can occur in the double copy by introducing a massless scalar in the gauge theory, which is treated as a ghost in the link to gravity. We hope these methods are a step towards a direct application of the double copy at higher orders in classical perturbation theory, with the potential to greatly streamline gravity calculations for phenomenological applications.

Tackling non-linearities with the effective field theory of dark energy and modified gravity

NASA Astrophysics Data System (ADS)

Frusciante, Noemi; Papadomanolakis, Georgios

2017-12-01

We present the extension of the effective field theory framework to the mildly non-linear scales. The effective field theory approach has been successfully applied to the late time cosmic acceleration phenomenon and it has been shown to be a powerful method to obtain predictions about cosmological observables on linear scales. However, mildly non-linear scales need to be consistently considered when testing gravity theories because a large part of the data comes from those scales. Thus, non-linear corrections to predictions on observables coming from the linear analysis can help in discriminating among different gravity theories. We proceed firstly by identifying the necessary operators which need to be included in the effective field theory Lagrangian in order to go beyond the linear order in perturbations and then we construct the corresponding non-linear action. Moreover, we present the complete recipe to map any single field dark energy and modified gravity models into the non-linear effective field theory framework by considering a general action in the Arnowitt-Deser-Misner formalism. In order to illustrate this recipe we proceed to map the beyond-Horndeski theory and low-energy Hořava gravity into the effective field theory formalism. As a final step we derived the 4th order action in term of the curvature perturbation. This allowed us to identify the non-linear contributions coming from the linear order perturbations which at the next order act like source terms. Moreover, we confirm that the stability requirements, ensuring the positivity of the kinetic term and the speed of propagation for scalar mode, are automatically satisfied once the viability of the theory is demanded at linear level. The approach we present here will allow to construct, in a model independent way, all the relevant predictions on observables at mildly non-linear scales.

Global Gravity Field Determination by Combination of terrestrial and Satellite Gravity Data

NASA Astrophysics Data System (ADS)

Fecher, T.; Pail, R.; Gruber, T.

2011-12-01

A multitude of impressive results document the success of the satellite gravity field mission GOCE with a wide field of applications in geodesy, geophysics and oceanography. The high performance of GOCE gravity field models can be further improved by combination with GRACE data, which is contributing the long wavelength signal content of the gravity field with very high accuracy. An example for such a consistent combination of satellite gravity data are the satellite-only models GOCO01S and GOCO02S. However, only the further combination with terrestrial and altimetric gravity data enables to expand gravity field models up to very high spherical harmonic degrees and thus to achieve a spatial resolution down to 20-30 km. First numerical studies for high-resolution global gravity field models combining GOCE, GRACE and terrestrial/altimetric data on basis of the DTU10 model have already been presented. Computations up to degree/order 600 based on full normal equations systems to preserve the full variance-covariance information, which results mainly from different weights of individual terrestrial/altimetric data sets, have been successfully performed. We could show that such large normal equations systems (degree/order 600 corresponds to a memory demand of almost 1TByte), representing an immense computational challenge as computation time and memory requirements put high demand on computational resources, can be handled. The DTU10 model includes gravity anomalies computed from the global model EGM08 in continental areas. Therefore, the main focus of this presentation lies on the computation of high-resolution combined gravity field models based on real terrestrial gravity anomaly data sets. This is a challenge due to the inconsistency of these data sets, including also systematic error components, but a further step to a real independent gravity field model. This contribution will present our recent developments and progress by using independent data sets at certain land areas, which are combined with DTU10 in the ocean areas, as well as satellite gravity data. Investigations have been made concerning the preparation and optimum weighting of the different data sources. The results, which should be a major step towards a GOCO-C model, will be validated using external gravity field data and by applying different validation methods.

Documentation of the GLAS fourth order general calculation model. Volume 3: Vectorized code for the Cyber 205

NASA Technical Reports Server (NTRS)

Kalnay, E.; Balgovind, R.; Chao, W.; Edelmann, D.; Pfaendtner, J.; Takacs, L.; Takano, K.

1983-01-01

Volume 3 of a 3-volume technical memoranda which contains documentation of the GLAS fourth order genera circulation model is presented. The volume contains the CYBER 205 scalar and vector codes of the model, list of variables, and cross references. A dictionary of FORTRAN variables used in the Scalar Version, and listings of the FORTRAN Code compiled with the C-option, are included. Cross reference maps of local variables are included for each subroutine.

Fiber pulling apparatus modification

NASA Technical Reports Server (NTRS)

Smith, Guy A.; Workman, Gary L.

1992-01-01

A reduced gravity fiber pulling apparatus (FPA) was constructed in order to study the effects of gravity on glass fiber formation. The apparatus was specifically designed and built for use on NASA's KC-135 aircraft. Four flights have been completed to date during which E-glass fiber was successfully produced in simulated zero, high, and lunar gravity environments. In addition simulated lunar soil samples were tested for their fiber producing properties using the FPA.

Anomaly-free cosmological perturbations in effective canonical quantum gravity

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

Barrau, Aurelien; Bojowald, Martin; Kagan, Mikhail

2015-05-01

This article lays out a complete framework for an effective theory of cosmological perturbations with corrections from canonical quantum gravity. Since several examples exist for quantum-gravity effects that change the structure of space-time, the classical perturbative treatment must be rethought carefully. The present discussion provides a unified picture of several previous works, together with new treatments of higher-order perturbations and the specification of initial states.

The Effects of Gravity on Combustion and Structure Formation During Combustion Synthesis in Gasless Systems

NASA Technical Reports Server (NTRS)

Varma, Arvind; Mukasyan, Alexander; Pelekh, Aleksey

1997-01-01

There have been relatively few publications examining the role of gravity during combustion synthesis (CS), mostly involving thermite systems. The main goal of this research was to study the influence of gravity on the combustion characteristics of heterogeneous gasless systems. In addition, some aspects of microstructure formation processes which occur during gasless CS were also studied. Four directions for experimental investigation have been explored: (1) the influence of gravity force on the characteristic features of heterogeneous combustion wave propagation (average velocity, instantaneous velocities, shape of combustion front); (2) the combustion of highly porous mixtures (with porosity greater than that for loose powders), which cannot be obtained in normal gravity; (3) the effect of gravity on sample expansion during combustion, in order to produce highly porous materials under microgravity conditions; and (4) the effect of gravity on the structure formation mechanism during the combustion synthesis of poreless composite materials.

On the capability of SWARM for estimating time-variable gravity fields and mass variations

NASA Astrophysics Data System (ADS)

Reubelt, Tilo; Baur, Oliver; Weigelt, Matthias; Sneeuw, Nico

2013-04-01

Recently, the implementation of the GRACE Follow-On mission has been approved. However, this successor of GRACE is planned to become operational in 2017 at the earliest. In order to fill the impending gap of 3-4 years between GRACE and GRACE-FO, the capability of the magnetic field mission SWARM as a gap filler for time-variable gravity field determination has to be investigated. Since the three SWARM satellites, where two of them fly on a pendulum formation, are equipped with high-quality GPS receivers and accelerometers, orbit analysis from high-low Satellite-to-Satellite Tracking (hl-SST) can be applied for geopotential recovery. As data analysis from CHAMP and GRACE has shown, the detection of annual gravity signals and gravity trends from hl-SST is possible for long-wavelength features corresponding to a Gaussian radius of 1000 km, although the accuracy of a low-low SST mission like GRACE cannot be reached. However, since SWARM is a three-satellite constellation and might provide GPS data of higher quality compared to previous missions, improved gravity field recovery can be expected. We present detailed closed-loop simulation studies for a 5 years period based on time-variable gravity caused by mass changes in the hydrosphere, cryosphere and solid Earth. Models for these variations are used to simulate the SWARM satellite orbits. We recover time-variable gravity from orbit analysis adopting the acceleration approach. Finally, we convert time-variable gravity to mass change in order to compare with the a priori model input.

Frozen-wave instability in near-critical hydrogen subjected to horizontal vibration under various gravity fields.

PubMed

Gandikota, G; Chatain, D; Amiroudine, S; Lyubimova, T; Beysens, D

2014-01-01

The frozen-wave instability which appears at a liquid-vapor interface when a harmonic vibration is applied in a direction tangential to it has been less studied until now. The present paper reports experiments on hydrogen (H2) in order to study this instability when the temperature is varied near its critical point for various gravity levels. Close to the critical point, a liquid-vapor density difference and surface tension can be continuously varied with temperature in a scaled, universal way. The effect of gravity on the height of the frozen waves at the interface is studied by performing the experiments in a magnetic facility where effective gravity that results from the coupling of the Earth's gravity and magnetic forces can be varied. The stability diagram of the instability is obtained. The experiments show a good agreement with an inviscid model [Fluid Dyn. 21 849 (1987)], irrespective of the gravity level. It is observed in the experiments that the height of the frozen waves varies weakly with temperature and increases with a decrease in the gravity level, according to a power law with an exponent of 0.7. It is concluded that the wave height becomes of the order of the cell size as the gravity level is asymptotically decreased to zero. The interface pattern thus appears as a bandlike pattern of alternate liquid and vapor phases, a puzzling phenomenon that was observed with CO2 and H2 near their critical point in weightlessness [Acta Astron. 61 1002 (2007); Europhys. Lett. 86 16003 (2009)].

ARISTOTELES: A European approach for an Earth gravity field recovery mission

NASA Technical Reports Server (NTRS)

Benz, R.; Faulks, H.; Langemann, M.

1989-01-01

Under contract of the European Space Agency a system study for a spaceborne gravity field recovery mission was performed, covering as a secondary mission objective geodetic point positioning in the cm range as well. It was demonstrated that under the given programmatic constraints including dual launch and a very tight development schedule, a six months gravity field mission in a 200 km near polar, dawn-dusk orbit is adequate to determine gravity anomalies to better than 5 mgal with a spatial resolution of 100 x 100 km half wavelength. This will enable scientists to determine improved spherical harmonic coefficients of the Earth gravity field equation to the order and degree of 180 or better.

COLA with scale-dependent growth: applications to screened modified gravity models

NASA Astrophysics Data System (ADS)

Winther, Hans A.; Koyama, Kazuya; Manera, Marc; Wright, Bill S.; Zhao, Gong-Bo

2017-08-01

We present a general parallelized and easy-to-use code to perform numerical simulations of structure formation using the COLA (COmoving Lagrangian Acceleration) method for cosmological models that exhibit scale-dependent growth at the level of first and second order Lagrangian perturbation theory. For modified gravity theories we also include screening using a fast approximate method that covers all the main examples of screening mechanisms in the literature. We test the code by comparing it to full simulations of two popular modified gravity models, namely f(R) gravity and nDGP, and find good agreement in the modified gravity boost-factors relative to ΛCDM even when using a fairly small number of COLA time steps.

Chromogravity explains {open_quotes}strong gravity{close_quotes}

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

Ne`eman, Y.; Sijacki, D.

1993-03-01

In this paper the authors deal with the question of gravitational type interactions in the case of strong interaction phenomena. They present arguments which indicate that it is not necessary to invoke a gravity type interaction into QCD in order to account for observed phenomena. They argue that the gravitational type phenomena discussed in previous work is a manifestation of a class of Feynmann diagrams. These seem to generate an analog to gravity, a J=2 {open_quotes}chromograviton{close_quotes} or {open_quotes}pseudo-graviton{close_quotes} whose action effectively generates Salam`s {open_quotes}Strong Gravity{close_quotes} or {open_quotes}f-gravity{close_quotes}, withthough having to introduce the theory as an additional input.

Action Research and Differentiating Reading Instruction in Mississippi: Fourth-Grade Students' Reading Success

ERIC Educational Resources Information Center

Mims, Wyn, M.; Lockley, Jeannie

2017-01-01

A fourth-grade teacher utilized action research in order to make data-driven decisions about reading interventions with her students. The teacher decided on a broad intervention, which was differentiating reading instruction, implemented differentiated instruction, collected data and continuously adjusted interventions based on monitoring data.…

Dense Gravity Currents with Breaking Internal Waves

NASA Astrophysics Data System (ADS)

Tanimoto, Yukinobu; Hogg, Charlie; Ouellette, Nicholas; Koseff, Jeffrey

2017-11-01

Shoaling and breaking internal waves along a pycnocline may lead to mixing and dilution of dense gravity currents, such as cold river inflows into lakes or brine effluent from desalination plants in near-coastal environments. In order to explore the interaction between gravity currents and breaking interfacial waves a series of laboratory experiments was performed in which a sequence of internal waves impinge upon a shelf-slope gravity current. The waves are generated in a two-layer thin-interface ambient water column under a variety of conditions characterizing both the waves and the gravity currents. The mixing of the gravity current is measured through both intrusive (CTD probe) and nonintrusive (Planar-laser inducted fluorescence) techniques. We will present results over a full range of Froude number (characterizing the waves) and Richardson number (characterizing the gravity current) conditions, and will discuss the mechanisms by which the gravity current is mixed into the ambient environment including the role of turbulence in the process. National Science Foundation.

Mars - Crustal structure inferred from Bouguer gravity anomalies.

NASA Technical Reports Server (NTRS)

Phillips, R. J.; Saunders, R. S.; Conel, J. E.

1973-01-01

Bouguer gravity has been computed for the equatorial region of Mars by differencing free air gravity and the gravity predicted from topographic variations. The free air gravity was generated from an eighth-order set of spherical harmonic coefficients. The gravity from topographic variations was generated by integrating a two-dimensional Green's function over each contour level. The Bouguer gravity indicates crustal inhomogeneities on Mars that are postulated to be variations in crustal thickness. The Tharsis ridge is a region of thick continental type crust. The gravity data, structural patterns, topography, and surface geology of this region lead to the interpretation of the Tharsis topographic high as a broad crustal upwarp possibly associated with local formation of lower-density crustal material and subsequent rise of a thicker crust. The Amazonis region is one of several basins of relatively thin crust, analogous to terrestrial ocean basins. The Libya and Hellas basins, which are probable impact features, are also underlain by thin crust and are possible regions of mantle upwelling.

Clear and Measurable Signature of Modified Gravity in the Galaxy Velocity Field

NASA Astrophysics Data System (ADS)

Hellwing, Wojciech A.; Barreira, Alexandre; Frenk, Carlos S.; Li, Baojiu; Cole, Shaun

2014-06-01

The velocity field of dark matter and galaxies reflects the continued action of gravity throughout cosmic history. We show that the low-order moments of the pairwise velocity distribution v12 are a powerful diagnostic of the laws of gravity on cosmological scales. In particular, the projected line-of-sight galaxy pairwise velocity dispersion σ12(r) is very sensitive to the presence of modified gravity. Using a set of high-resolution N-body simulations, we compute the pairwise velocity distribution and its projected line-of-sight dispersion for a class of modified gravity theories: the chameleon f(R) gravity and Galileon gravity (cubic and quartic). The velocities of dark matter halos with a wide range of masses would exhibit deviations from general relativity at the (5-10)σ level. We examine strategies for detecting these deviations in galaxy redshift and peculiar velocity surveys. If detected, this signature would be a "smoking gun" for modified gravity.

Path integral Monte Carlo determination of the fourth-order virial coefficient for unitary two-component Fermi gas with zero-range interactions

NASA Astrophysics Data System (ADS)

Yan, Yangqian; Blume, D.

2016-05-01

The unitary equal-mass Fermi gas with zero-range interactions constitutes a paradigmatic model system that is relevant to atomic, condensed matter, nuclear, particle, and astro physics. This work determines the fourth-order virial coefficient b4 of such a strongly-interacting Fermi gas using a customized ab inito path integral Monte Carlo (PIMC) algorithm. In contrast to earlier theoretical results, which disagreed on the sign and magnitude of b4, our b4 agrees with the experimentally determined value, thereby resolving an ongoing literature debate. Utilizing a trap regulator, our PIMC approach determines the fourth-order virial coefficient by directly sampling the partition function. An on-the-fly anti-symmetrization avoids the Thomas collapse and, combined with the use of the exact two-body zero-range propagator, establishes an efficient general means to treat small Fermi systems with zero-range interactions. We gratefully acknowledge support by the NSF.

Path-Integral Monte Carlo Determination of the Fourth-Order Virial Coefficient for a Unitary Two-Component Fermi Gas with Zero-Range Interactions.

PubMed

Yan, Yangqian; Blume, D

2016-06-10

The unitary equal-mass Fermi gas with zero-range interactions constitutes a paradigmatic model system that is relevant to atomic, condensed matter, nuclear, particle, and astrophysics. This work determines the fourth-order virial coefficient b_{4} of such a strongly interacting Fermi gas using a customized ab initio path-integral Monte Carlo (PIMC) algorithm. In contrast to earlier theoretical results, which disagreed on the sign and magnitude of b_{4}, our b_{4} agrees within error bars with the experimentally determined value, thereby resolving an ongoing literature debate. Utilizing a trap regulator, our PIMC approach determines the fourth-order virial coefficient by directly sampling the partition function. An on-the-fly antisymmetrization avoids the Thomas collapse and, combined with the use of the exact two-body zero-range propagator, establishes an efficient general means to treat small Fermi systems with zero-range interactions.

Variational path integral molecular dynamics and hybrid Monte Carlo algorithms using a fourth order propagator with applications to molecular systems

NASA Astrophysics Data System (ADS)

Kamibayashi, Yuki; Miura, Shinichi

2016-08-01

In the present study, variational path integral molecular dynamics and associated hybrid Monte Carlo (HMC) methods have been developed on the basis of a fourth order approximation of a density operator. To reveal various parameter dependence of physical quantities, we analytically solve one dimensional harmonic oscillators by the variational path integral; as a byproduct, we obtain the analytical expression of the discretized density matrix using the fourth order approximation for the oscillators. Then, we apply our methods to realistic systems like a water molecule and a para-hydrogen cluster. In the HMC, we adopt two level description to avoid the time consuming Hessian evaluation. For the systems examined in this paper, the HMC method is found to be about three times more efficient than the molecular dynamics method if appropriate HMC parameters are adopted; the advantage of the HMC method is suggested to be more evident for systems described by many body interaction.

Gravity field error analysis: Applications of GPS receivers and gradiometers on low orbiting platforms

NASA Technical Reports Server (NTRS)

Schrama, E.

1990-01-01

The concept of a Global Positioning System (GPS) receiver as a tracking facility and a gradiometer as a separate instrument on a low orbiting platform offers a unique tool to map the Earth's gravitational field with unprecedented accuracies. The former technique allows determination of the spacecraft's ephemeris at any epoch to within 3 to 10 cm, the latter permits the measurement of the tensor of second order derivatives of the gravity field to within 0.01 to 0.0001 Eotvos units depending on the type of gradiometer. First, a variety of error sources in gradiometry where emphasis is placed on the rotational problem pursuing as well a static as a dynamic approach is described. Next, an analytical technique is described and applied for an error analysis of gravity field parameters from gradiometer and GPS observation types. Results are discussed for various configurations proposed on Topex/Poseidon, Gravity Probe-B, and Aristoteles, indicating that GPS only solutions may be computed up to degree and order 35, 55, and 85 respectively, whereas a combined GPS/gradiometer experiment on Aristoteles may result in an acceptable solution up to degree and order 240.

Development and analysis of a twelfth degree and order gravity model for Mars

NASA Technical Reports Server (NTRS)

Christensen, E. J.; Balmino, G.

1979-01-01

Satellite geodesy techniques previously applied to artificial earth satellites have been extended to obtain a high-resolution gravity field for Mars. Two-way Doppler data collected by 10 Deep Space Network (DSN) stations during Mariner 9 and Viking 1 and 2 missions have been processed to obtain a twelfth degree and order spherical harmonic model for the martian gravitational potential. The quality of this model was evaluated by examining the rms residuals within the fit and the ability of the model to predict the spacecraft state beyond the fit. Both indicators show that more data and higher degree and order harmonics will be required to further refine our knowledge of the martian gravity field. The model presented shows much promise, since it resolves local gravity features which correlate highly with the martian topography. An isostatic analysis based on this model, as well as an error analysis, shows rather complete compensation on a global (long wavelength) scale. Though further model refinements are necessary to be certain, local (short wavelength) features such as the shield volcanos in Tharsis appear to be uncompensated. These are interpreted to place some bounds on the internal structure of Mars.

High-order finite-volume solutions of the steady-state advection-diffusion equation with nonlinear Robin boundary conditions

NASA Astrophysics Data System (ADS)

Lin, Zhi; Zhang, Qinghai

2017-09-01

We propose high-order finite-volume schemes for numerically solving the steady-state advection-diffusion equation with nonlinear Robin boundary conditions. Although the original motivation comes from a mathematical model of blood clotting, the nonlinear boundary conditions may also apply to other scientific problems. The main contribution of this work is a generic algorithm for generating third-order, fourth-order, and even higher-order explicit ghost-filling formulas to enforce nonlinear Robin boundary conditions in multiple dimensions. Under the framework of finite volume methods, this appears to be the first algorithm of its kind. Numerical experiments on boundary value problems show that the proposed fourth-order formula can be much more accurate and efficient than a simple second-order formula. Furthermore, the proposed ghost-filling formulas may also be useful for solving other partial differential equations.

Boundary Closures for Fourth-order Energy Stable Weighted Essentially Non-Oscillatory Finite Difference Schemes

NASA Technical Reports Server (NTRS)

Fisher, Travis C.; Carpenter, Mark H.; Yamaleev, Nail K.; Frankel, Steven H.

2009-01-01

A general strategy exists for constructing Energy Stable Weighted Essentially Non Oscillatory (ESWENO) finite difference schemes up to eighth-order on periodic domains. These ESWENO schemes satisfy an energy norm stability proof for both continuous and discontinuous solutions of systems of linear hyperbolic equations. Herein, boundary closures are developed for the fourth-order ESWENO scheme that maintain wherever possible the WENO stencil biasing properties, while satisfying the summation-by-parts (SBP) operator convention, thereby ensuring stability in an L2 norm. Second-order, and third-order boundary closures are developed that achieve stability in diagonal and block norms, respectively. The global accuracy for the second-order closures is three, and for the third-order closures is four. A novel set of non-uniform flux interpolation points is necessary near the boundaries to simultaneously achieve 1) accuracy, 2) the SBP convention, and 3) WENO stencil biasing mechanics.

Atom interferometric gravity gradiometer: Disturbance compensation and mobile gradiometry

NASA Astrophysics Data System (ADS)

Mahadeswaraswamy, Chetan

First ever mobile gravity gradient measurement based on Atom Interferometric sensors has been demonstrated. Mobile gravity gradiometers play a significant role in high accuracy inertial navigation systems in order to distinguish inertial acceleration and acceleration due to gravity. The gravity gradiometer consists of two atom interferometric accelerometers. In each of the accelerometer an ensemble of laser cooled Cesium atoms is dropped and using counter propagating Raman pulses (pi/2-pi-pi/2) the ensemble is split into two states for carrying out atom interferometry. The interferometer phase is proportional to the specific force experienced by the atoms which is a combination of inertial acceleration and acceleration due to gravity. The difference in phase between the two atom interferometric sensors is proportional to gravity gradient if the platform does not undergo any rotational motion. However, any rotational motion of the platform induces spurious gravity gradient measurements. This apparent gravity gradient due to platform rotation is considerably different for an atom interferometric sensor compared to a conventional force rebalance type sensor. The atoms are in free fall and are not influenced by the motion of the case except at the instants of Raman pulses. A model for determining apparent gravity gradient due to rotation of platform was developed and experimentally verified for different frequencies. This transfer function measurement also lead to the development of a new technique for aligning the Raman laser beams with the atom clusters to within 20 mu rad. This gravity gradiometer is situated in a truck for the purpose of undertaking mobile surveys. A disturbance compensation system was designed and built in order to compensate for the rotational disturbances experienced on the floor of a truck. An electric drive system was also designed specifically to be able to move the truck in a uniform motion at very low speeds of about 1cm/s. A 250 x10-9 s-2 gravity gradient signature due to an underground void at Hansen Experimental Physics Building at Stanford was successfully measured using this mobile gradiometer.

Gravity waves

NASA Technical Reports Server (NTRS)

Fritts, David

1987-01-01

Gravity waves contributed to the establishment of the thermal structure, small scale (80 to 100 km) fluctuations in velocity (50 to 80 m/sec) and density (20 to 30%, 0 to peak). Dominant gravity wave spectrum in the middle atmosphere: x-scale, less than 100 km; z-scale, greater than 10 km; t-scale, less than 2 hr. Theorists are beginning to understand middle atmosphere motions. There are two classes: Planetary waves and equatorial motions, gravity waves and tidal motions. The former give rise to variability at large scales, which may alter apparent mean structure. Effects include density and velocity fluctuations, induced mean motions, and stratospheric warmings which lead to the breakup of the polar vortex and cooling of the mesosphere. On this scale are also equatorial quasi-biennial and semi-annual oscillations. Gravity wave and tidal motions produce large rms fluctuations in density and velocity. The magnitude of the density fluctuations compared to the mean density is of the order of the vertical wavelength, which grows with height. Relative density fluctuations are less than, or of the order of 30% below the mesopause. Such motions may cause significant and variable convection, and wind shear. There is a strong seasonal variation in gravity wave amplitude. Additional observations are needed to address and quantify mean and fluctuation statistics of both density and mean velocity, variability of the mean and fluctuations, and to identify dominant gravity wave scales and sources as well as causes of variability, both temporal and geographic.

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.

Tensor Galileons and gravity

NASA Astrophysics Data System (ADS)

Chatzistavrakidis, Athanasios; Khoo, Fech Scen; Roest, Diederik; Schupp, Peter

2017-03-01

The particular structure of Galileon interactions allows for higher-derivative terms while retaining second order field equations for scalar fields and Abelian p-forms. In this work we introduce an index-free formulation of these interactions in terms of two sets of Grassmannian variables. We employ this to construct Galileon interactions for mixed-symmetry tensor fields and coupled systems thereof. We argue that these tensors are the natural generalization of scalars with Galileon symmetry, similar to p-forms and scalars with a shift-symmetry. The simplest case corresponds to linearised gravity with Lovelock invariants, relating the Galileon symmetry to diffeomorphisms. Finally, we examine the coupling of a mixed-symmetry tensor to gravity, and demonstrate in an explicit example that the inclusion of appropriate counterterms retains second order field equations.

Scale hierarchy in Hořava-Lifshitz gravity: strong constraint from synchrotron radiation in the Crab Nebula.

PubMed

Liberati, Stefano; Maccione, Luca; Sotiriou, Thomas P

2012-10-12

Hořava-Lifshitz gravity models contain higher-order operators suppressed by a characteristic scale, which is required to be parametrically smaller than the Planck scale. We show that recomputed synchrotron radiation constraints from the Crab Nebula suffice to exclude the possibility that this scale is of the same order of magnitude as the Lorentz breaking scale in the matter sector. This highlights the need for a mechanism that suppresses the percolation of Lorentz violation in the matter sector and is effective for higher-order operators as well.

Evaluation of GOCE-based Global Geoid Models in Finnish Territory

NASA Astrophysics Data System (ADS)

Saari, Timo; Bilker-Koivula, Mirjam

2015-04-01

The gravity satellite mission GOCE made its final observations in the fall of 2013. By then it had exceeded its expected lifespan of one year with more than three additional years. Thus, the mission collected more data from the Earth's gravitational field than expected, and more comprehensive global geoid models have been derived ever since. The GOCE High-level Processing Facility (HPF) by ESA has published GOCE global gravity field models annually. We compared all of the 12 HPF-models as well as 3 additional GOCE, 11 GRACE and 6 combined GOCE+GRACE models with GPS-levelling data and gravity observations in Finland. The most accurate models were compared against high resolution global geoid models EGM96 and EGM2008. The models were evaluated up to three different degrees and order: 150 (the common maximum for the GRACE models), 240 (the common maximum for the GOCE models) and maximum. When coefficients up to degree and order 150 are used, the results of the GOCE models are comparable with the results of the latest GRACE models. Generally, all of the latest GOCE and GOCE+GRACE models give standard deviations of the height anomaly differences of around 15 cm and of gravity anomaly differences of around 10 mgal over Finland. The best solutions were not always achieved with the highest maximum degree and order of the satellite gravity field models, since the highest coefficients (above 240) may be less accurately determined. Over Finland, the latest GOCE and GOCE+GRACE models give similar results as the high resolution models EGM96 and EGM2008 when coefficients up to degree and order 240 are used. This is mainly due to the high resolution terrestrial data available in the area of Finland, which was used in the high resolution models.

Spectral asymptotics of Euclidean quantum gravity with diff-invariant boundary conditions

NASA Astrophysics Data System (ADS)

Esposito, Giampiero; Fucci, Guglielmo; Kamenshchik, Alexander Yu; Kirsten, Klaus

2005-03-01

A general method is known to exist for studying Abelian and non-Abelian gauge theories, as well as Euclidean quantum gravity, at 1-loop level on manifolds with boundary. In the latter case, boundary conditions on metric perturbations h can be chosen to be completely invariant under infinitesimal diffeomorphisms, to preserve the invariance group of the theory and BRST symmetry. In the de Donder gauge, however, the resulting boundary-value problem for the Laplace-type operator acting on h is known to be self-adjoint but not strongly elliptic. The latter is a technical condition ensuring that a unique smooth solution of the boundary-value problem exists, which implies, in turn, that the global heat-kernel asymptotics yielding 1-loop divergences and 1-loop effective action actually exists. The present paper shows that, on the Euclidean 4-ball, only the scalar part of perturbative modes for quantum gravity is affected by the lack of strong ellipticity. Further evidence for lack of strong ellipticity, from an analytic point of view, is therefore obtained. Interestingly, three sectors of the scalar-perturbation problem remain elliptic, while lack of strong ellipticity is 'confined' to the remaining fourth sector. The integral representation of the resulting ζ-function asymptotics on the Euclidean 4-ball is also obtained; this remains regular at the origin by virtue of a spectral identity here obtained for the first time.

Cognitive Development of Fourth Graders in a High-Stakes State.

ERIC Educational Resources Information Center

Aagaard, Lola; Boram, Robert

Jean Piaget's classic theory of cognitive development would imply that the higher-order items on the Kentucky state assessment would only be possible for students well into concrete operations or beginning formal operations. The implication would be that Kentucky fourth graders who are not fully concrete yet may be hitting a developmental ceiling…

Peace and World Order Studies: A Curriculum Guide. Fourth Edition.

ERIC Educational Resources Information Center

Wien, Barbara J., Ed.

The fourth edition of this curriculum guide will help college, university, and secondary school educators design and update courses, familiarize themselves with new literature and resources, and plan and justify new academic programs in the study of global problems. While syllabus categories remain the same as in previous editions, several new…

Bifactor Structure of the Wechsler Preschool and Primary Scale of Intelligence-Fourth Edition

ERIC Educational Resources Information Center

Watkins, Marley W.; Beaujean, A. Alexander

2014-01-01

The Wechsler Preschool and Primary Scale of Intelligence-Fourth Edition (WPPSI-IV; Wechsler, 2012) represents a substantial departure from its predecessor, including omission of 4 subtests, addition of 5 new subtests, and modification of the contents of the 5 retained subtests. Wechsler (2012) explicitly assumed a higher-order structure with…

Intricacies of cosmological bounce in polynomial metric f(R) gravity for flat FLRW spacetime

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

Bhattacharya, Kaushik; Chakrabarty, Saikat, E-mail: kaushikb@iitk.ac.in, E-mail: snilch@iitk.ac.in

2016-02-01

In this paper we present the techniques for computing cosmological bounces in polynomial f(R) theories, whose order is more than two, for spatially flat FLRW spacetime. In these cases the conformally connected Einstein frame shows up multiple scalar potentials predicting various possibilities of cosmological evolution in the Jordan frame where the f(R) theory lives. We present a reasonable way in which one can associate the various possible potentials in the Einstein frame, for cubic f(R) gravity, to the cosmological development in the Jordan frame. The issue concerning the energy conditions in f(R) theories is presented. We also point out themore » very important relationships between the conformal transformations connecting the Jordan frame and the Einstein frame and the various instabilities of f(R) theory. All the calculations are done for cubic f(R) gravity but we hope the results are sufficiently general for higher order polynomial gravity.« less

Geophysical Interpretation of Venus Gravity Data

NASA Technical Reports Server (NTRS)

Reasenberg, R. D.

1985-01-01

The subsurface distribution of Venus was investigated through the analysis of the data from Pioneer Venus Orbiter (PVO). In particular, the Doppler tracking data were used to map the gravitational potential. These were compared to the topographic data from the PVO radar (ORAD). In order to obtain an unbiased comparison, the topography data obtained from the PVO-ORAD were filtered to introduce distortions which are the same as those of the gravity models. Both the gravity and filtered topography maps are derived by two stage processes with a common second stage. In the first stage, the topography was used to calculate a corresponding spacecraft acceleration under the assumptions that the topography has a uniform given density and no compensation. In the second stage, the acceleration measures found in the first stage were passed through a linear inverter to yield maps of gravity and topography. Because these maps are the result of the same inversion process, they contain the same distortion; a comparison between them is unbiased to first order.

1/ r potential in higher dimensions

NASA Astrophysics Data System (ADS)

Chakraborty, Sumanta; Dadhich, Naresh

2018-01-01

In Einstein gravity, gravitational potential goes as 1/r^{d-3} in d non-compactified spacetime dimensions, which assumes the familiar 1 / r form in four dimensions. On the other hand, it goes as 1/r^{α }, with α =(d-2m-1)/m, in pure Lovelock gravity involving only one mth order term of the Lovelock polynomial in the gravitational action. The latter offers a novel possibility of having 1 / r potential for the non-compactified dimension spectrum given by d=3m+1. Thus it turns out that in the two prototype gravitational settings of isolated objects, like black holes and the universe as a whole - cosmological models, the Einstein gravity in four and mth order pure Lovelock gravity in 3m+1 dimensions behave in a similar fashion as far as gravitational interactions are considered. However propagation of gravitational waves (or the number of degrees of freedom) does indeed serve as a discriminator because it has two polarizations only in four dimensions.

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.

Interacting spin-2 fields in the Stückelberg picture

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

Noller, Johannes; Ferreira, Pedro G.; Scargill, James H.C., E-mail: noller@physics.ox.ac.uk, E-mail: james.scargill@physics.ox.ac.uk, E-mail: p.ferreira1@physics.ox.ac.uk

2014-02-01

We revisit and extend the 'Effective field theory for massive gravitons' constructed by Arkani-Hamed, Georgi and Schwartz in the light of recent progress in constructing ghost-free theories with multiple interacting spin-2 fields. We show that there exist several dual ways of restoring gauge invariance in such multi-gravity theories, find a generalised Fierz-Pauli tuning condition relevant in this context and highlight subtleties in demixing tensor and scalar modes. The generic multi-gravity feature of scalar mixing and its consequences for higher order interactions are discussed. In particular we show how the decoupling limit is qualitatively changed in theories of interacting spin-2 fields.more » We relate this to dRGT (de Rham, Gabadadze, Tolley) massive gravity, Hassan-Rosen bigravity and the multi-gravity constructions by Hinterbichler and Rosen. As an additional application we show that EBI (Eddington-Born-Infeld) bigravity and higher order generalisations thereof possess ghost-like instabilities.« less

Symmetry Reductions of Fourth-Order Nonlinear Diffusion Equations: Lubrication Model and Some Generalizations

NASA Astrophysics Data System (ADS)

Gandarias, M. L.; Medina, E.

Fourth-order nonlinear diffusion equations appear frequently in the description of physical processes, among these, the lubrication equation ut = (unuxxxx)x or the corresponding modified version ut = unuxxxx play an important role in the study of the interface movements. In this work we analyze the generalizations of the above equations given by ut = (f(u)uxxxx)x, ut = (f(u)uxxxx, and we find that if f(u) = un or f(u) = e-u the equations admit extra classical symmetries. The corresponding reductions are performed and some solutions are characterized.

Global solutions and finite time blow-up for fourth order nonlinear damped wave equation

NASA Astrophysics Data System (ADS)

Xu, Runzhang; Wang, Xingchang; Yang, Yanbing; Chen, Shaohua

2018-06-01

In this paper, we study the initial boundary value problem and global well-posedness for a class of fourth order wave equations with a nonlinear damping term and a nonlinear source term, which was introduced to describe the dynamics of a suspension bridge. The global existence, decay estimate, and blow-up of solution at both subcritical (E(0) < d) and critical (E(0) = d) initial energy levels are obtained. Moreover, we prove the blow-up in finite time of solution at the supercritical initial energy level (E(0) > 0).

The use of absolute gravity data for the validation of Global Geopotential Models and for improving quasigeoid heights determined from satellite-only Global Geopotential Models

NASA Astrophysics Data System (ADS)

Godah, Walyeldeen; Krynski, Jan; Szelachowska, Malgorzata

2018-05-01

The objective of this paper is to demonstrate the usefulness of absolute gravity data for the validation of Global Geopotential Models (GGMs). It is also aimed at improving quasigeoid heights determined from satellite-only GGMs using absolute gravity data. The area of Poland, as a unique one, covered with a homogeneously distributed set of absolute gravity data, has been selected as a study area. The gravity anomalies obtained from GGMs were validated using the corresponding ones determined from absolute gravity data. The spectral enhancement method was implemented to overcome the spectral inconsistency in data being validated. The quasigeoid heights obtained from the satellite-only GGM as well as from the satellite-only GGM in combination with absolute gravity data were evaluated with high accuracy GNSS/levelling data. Estimated accuracy of gravity anomalies obtained from GGMs investigated is of 1.7 mGal. Considering omitted gravity signal, e.g. from degree and order 101 to 2190, satellite-only GGMs can be validated at the accuracy level of 1 mGal using absolute gravity data. An improvement up to 59% in the accuracy of quasigeoid heights obtained from the satellite-only GGM can be observed when combining the satellite-only GGM with absolute gravity data.

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.

Time-variable and static gravity field of Mars from MGS, Mars Odyssey, and MRO

NASA Astrophysics Data System (ADS)

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

2016-04-01

The Mars Global Surveyor (MGS), Mars Odyssey (ODY), and Mars Reconnaissance Orbiter (MRO) missions have significantly contributed to the determination of global high-resolution global gravity fields of Mars for the last 16 years. All three spacecraft were located in sun-synchronous, near-circular polar mapping orbits for their primary mission phases at different altitudes and Local Solar Time (LST). X-Band tracking data have been acquired from the NASA Deep Space Network (DSN) providing information on the time-variable and static gravity field of Mars. MGS operated between 1999 and 2006 at 390 km altitude. ODY and MRO are still orbiting Mars with periapsis altitudes of 400 km and 255 km, respectively. Before entering these mapping phases, all three spacecraft collected radio tracking data at lower altitudes (˜170-200 km) that help improve the resolution of the gravity field of Mars in specific regions. We analyzed the entire MGS radio tracking data set, and ODY and MRO radio data until 2015. These observations were processed using a batch least-squares filter through the NASA GSFC GEODYN II software. We combined all 2- and 3-way range rate data to estimate the global gravity field of Mars to degree and order 120, the seasonal variations of gravity harmonic coefficients C20, C30, C40 and C50 and the Love number k2. The gravity contribution of Mars atmospheric pressures on the surface of the planet has been discerned from the time-varying and static gravity harmonic coefficients. Surface pressure grids computed using the Mars-GRAM 2010 atmospheric model, with 2.5° x2.5° spatial and 2-h resolution, are converted into gravity spherical harmonic coefficients. Consequently, the estimated gravity and tides provide direct information on the solid planet. We will present the new Goddard Mars Model (GMM-3) of Mars gravity field in spherical harmonics to degree and order 120. The solution includes the Love number k2 and the 3-frequencies (annual, semi-annual, and tri-annual) time-variable coefficients of the gravity zonal harmonics C20, C30, C40 and C50. The seasonal gravity coefficients led us to determine the inter-annual mass exchange between the polar caps over ˜11 years from October 2002 to November 2014.

On processed splitting methods and high-order actions in path-integral Monte Carlo simulations.

PubMed

Casas, Fernando

2010-10-21

Processed splitting methods are particularly well adapted to carry out path-integral Monte Carlo (PIMC) simulations: since one is mainly interested in estimating traces of operators, only the kernel of the method is necessary to approximate the thermal density matrix. Unfortunately, they suffer the same drawback as standard, nonprocessed integrators: kernels of effective order greater than two necessarily involve some negative coefficients. This problem can be circumvented, however, by incorporating modified potentials into the composition, thus rendering schemes of higher effective order. In this work we analyze a family of fourth-order schemes recently proposed in the PIMC setting, paying special attention to their linear stability properties, and justify their observed behavior in practice. We also propose a new fourth-order scheme requiring the same computational cost but with an enlarged stability interval.

Gravity field of Jupiter’s moon Amalthea and the implication on a spacecraft trajectory

NASA Astrophysics Data System (ADS)

Weinwurm, Gudrun

2006-01-01

Before its final plunge into Jupiter in September 2003, GALILEO made a last 'visit' to one of Jupiter's moons - Amalthea. This final flyby of the spacecraft's successful mission occurred on November 5, 2002. In order to analyse the spacecraft data with respect to Amalthea's gravity field, interior models of the moon had to be provided. The method used for this approach is based on the numerical integration of infinitesimal volume elements of a three-axial ellipsoid in elliptic coordinates. To derive the gravity field coefficients of the body, the second method of Neumann was applied. Based on the spacecraft trajectory data provided by the Jet Propulsion Laboratory, GALILEO's velocity perturbations at closest approach could be calculated. The harmonic coefficients of Amalthea's gravity field have been derived up to degree and order six, for both homogeneous and reasonable heterogeneous cases. Founded on these numbers the impact on the trajectory of GALILEO was calculated and compared to existing Doppler data. Furthermore, predictions for future spacecraft flybys were derived. No two-way Doppler-data was available during the flyby and the harmonic coefficients of the gravity field are buried in the one-way Doppler-noise. Nevertheless, the generated gravity field models reflect the most likely interior structure of the moon and can be a basis for further exploration of the Jovian system.

New algorithms for solving high even-order differential equations using third and fourth Chebyshev-Galerkin methods

NASA Astrophysics Data System (ADS)

Doha, E. H.; Abd-Elhameed, W. M.; Bassuony, M. A.

2013-03-01

This paper is concerned with spectral Galerkin algorithms for solving high even-order two point boundary value problems in one dimension subject to homogeneous and nonhomogeneous boundary conditions. The proposed algorithms are extended to solve two-dimensional high even-order differential equations. The key to the efficiency of these algorithms is to construct compact combinations of Chebyshev polynomials of the third and fourth kinds as basis functions. The algorithms lead to linear systems with specially structured matrices that can be efficiently inverted. Numerical examples are included to demonstrate the validity and applicability of the proposed algorithms, and some comparisons with some other methods are made.

Is it possible that a gravity increase of 20 μGal yr-1 in southern Tibet comes from a wide-range density increase?

NASA Astrophysics Data System (ADS)

Yi, Shuang; Wang, Qiuyu; Sun, Wenke

2016-02-01

With absolute gravimetric observations from 2010 to 2013 in the southern Tibet, Chen et al. (2016) reported a gravity increase of up to 20 μGal/yr and concluded that it is possible if there was a density increase in a disk range of 580 km in diameter. Here we used observations from the gravity satellites Gravity Recovery and Climate Experiment (GRACE) over 12 years to evaluate whether the model was practical, because a mass accumulation in such a large spatial range is well within the detectability ability of GRACE. The gravity trend based on their model is orders of magnitude larger than the GRACE observation, thus negating its conclusions. We then evaluated contributions from seasonal variation, lakes, glaciers, rivers, precipitation, and snowfall and concluded that these factors cannot cause such a large gravity signal. Finally, we discussed some possible explanations for the gravity increase of 40 μGal in two years.

Biomedical results of the Skylab Program.

PubMed

Michel, E L; Johnston, R S; Dietlein, L F

1976-01-01

Skylab, the fourth in a logical sequence of USA manned space flight projects following Mercury, Gemini and Apollo, presented life scientists with their first opportunity for an in-depth study of man's response to the space environment. Extensive medical investigations were undertaken to increase our understanding of man's adaptation to the space environment and his readaptation to gravity upon return to earth. The flight durations of the three Skylab missions were progressively increased from 28 days to 59 days and, finally, 84 days. The results of these investigations of the various body systems clearly demonstrated that man can adapt to zero gravity and perform useful work during long-duration space flight. However, definite changes (some unexpected) in the vestibular, cardiovascular, musculo-skeletal, renal and electrolyte areas were documented. The most significant were: the occurrence of space motion sickness early in the missions; diminished orthostatic tolerance, both in-flight and post-flight; moderate losses of calcium, phosphorus and nitrogen; and decreased tolerance for exercise post-flight. The mechanisms responsible for these physiological responses must be understood and, if necessary, effective countermeasures developed before man can endure unlimited exposure to space flight.

Space manufacturing III; Proceedings of the Fourth Conference, Princeton University, Princeton, N.J., May 14-17, 1979

NASA Technical Reports Server (NTRS)

Grey, J. (Editor); Krop, C.

1979-01-01

Papers are presented on the various technological, political, economic, environmental and social aspects of large manufacturing facilities in space. Specific topics include the potential global market for satellite solar power stations in 2025, the electrostatic separation of lunar soil, methods for extraterrestrial materials processing, the socio-political status of efforts toward the development of space manufacturing facilities, the financing of space industrialization, the optimization of space manufacturing systems, the design and project status of Mass Driver Two, and the use of laser-boosted lighter-than-air-vehicles as heavy-lift launch vehicles. Attention is also given to systems integration in the development of controlled ecological life support systems, the design of a space manufacturing facility to use lunar materials, high performance solar sails, the environmental effects of the satellite power system reference design, the guidance, trajectory and capture of lunar materials ejected from the moon by mass driver, the relative design merits of zero-gravity and one-gravity space environments, consciousness alteration in space and the prospecting and retrieval of asteroids.

An Experimental Study of Boiling in Reduced and Zero Gravity Fields

NASA Technical Reports Server (NTRS)

Usiskin, C. M.; Siegel, R.

1961-01-01

A pool boiling apparatus was mounted on a counterweighted platform which could be dropped a distance of nine feet. By varying the size of the counterweight, the effective gravity field on the equipment was adjusted between zero and unity. A study of boiling burnout in water indicated that a variation in the critical heat flux according to the one quarter power of gravity was reasonable. A consideration of the transient burnout process was necessary in order to properly interpret the data. A photographic study of nucleate boiling showed how the velocity of freely rising vapor bubbles decreased as gravity was reduced. The bubble diameters at the time of breakoff from the heated surface were found to vary inversely as gravity to the 1/3.5 power. Motion pictures were taken to illustrate both nucleate and film boiling in the low gravity range.

Measuring gravity currents in the Chicago River, Chicago, Illinois

USGS Publications Warehouse

Oberg, K.A.; Czuba, J.A.; Johnson, K.K.

2008-01-01

Recent studies of the Chicago River have determined that gravity currents are responsible for persistent bidirectional flows that have been observed in the river. A gravity current is the flow of one fluid within another caused by a density difference between the fluids. These studies demonstrated how acoustic Doppler current profilers (ADCP) can be used to detect and characterize gravity currents in the field. In order to better understand the formation and evolution of these gravity currents, the U.S. Geological Survey (USGS) has installed ADCPs and other instruments to continuously measure gravity currents in the Chicago River and the North Branch Chicago River. These instruments include stage sensors, thermistor strings, and both upward-looking and horizontal ADCPs. Data loggers and computers installed at gaging stations along the river are used to collect data from these instruments and transmit them to USGS offices. ?? 2008 IEEE.

Note: Planetary gravities made simple: Sample test of a Mars rover wheel.

PubMed

Viera-López, G; Serrano-Muñoz, A; Amigó-Vega, J; Cruzata, O; Altshuler, E

2017-08-01

We introduce an instrument for a wide spectrum of experiments on gravities other than our planet's. It is based on a large Atwood machine where one of the loads is a bucket equipped with a single board computer and different sensors. The computer is able to detect the falling (or rising) and then the stabilization of the effective gravity and to trigger actuators depending on the experiment. Gravities within the range 0.4 g-1.2 g are easily achieved with acceleration noise of the order of 0.01 g. Under Martian gravity, we are able to perform experiments of approximately 1.5 s duration. The system includes features such as WiFi and a web interface with tools for the setup, monitoring, and data analysis of the experiment. We briefly show a case study in testing the performance of a model Mars rover wheel in low gravities.

Note: Planetary gravities made simple: Sample test of a Mars rover wheel

NASA Astrophysics Data System (ADS)

Viera-López, G.; Serrano-Muñoz, A.; Amigó-Vega, J.; Cruzata, O.; Altshuler, E.

2017-08-01

We introduce an instrument for a wide spectrum of experiments on gravities other than our planet's. It is based on a large Atwood machine where one of the loads is a bucket equipped with a single board computer and different sensors. The computer is able to detect the falling (or rising) and then the stabilization of the effective gravity and to trigger actuators depending on the experiment. Gravities within the range 0.4 g-1.2 g are easily achieved with acceleration noise of the order of 0.01 g. Under Martian gravity, we are able to perform experiments of approximately 1.5 s duration. The system includes features such as WiFi and a web interface with tools for the setup, monitoring, and data analysis of the experiment. We briefly show a case study in testing the performance of a model Mars rover wheel in low gravities.

On solvability of boundary value problems for hyperbolic fourth-order equations with nonlocal boundary conditions of integral type

NASA Astrophysics Data System (ADS)

Popov, Nikolay S.

2017-11-01

Solvability of some initial-boundary value problems for linear hyperbolic equations of the fourth order is studied. A condition on the lateral boundary in these problems relates the values of a solution or the conormal derivative of a solution to the values of some integral operator applied to a solution. Nonlocal boundary-value problems for one-dimensional hyperbolic second-order equations with integral conditions on the lateral boundary were considered in the articles by A.I. Kozhanov. Higher-dimensional hyperbolic equations of higher order with integral conditions on the lateral boundary were not studied earlier. The existence and uniqueness theorems of regular solutions are proven. The method of regularization and the method of continuation in a parameter are employed to establish solvability.

Mass-induced instability of SAdS black hole in Einstein-Ricci cubic gravity

NASA Astrophysics Data System (ADS)

Myung, Yun Soo

2018-05-01

We perform the stability analysis of Schwarzschild-AdS (SAdS) black hole in the Einstein-Ricci cubic gravity. It shows that the Ricci tensor perturbations exhibit unstable modes for small black holes. We call this the mass-induced instability of SAdS black hole because the instability of small black holes arises from the massiveness in the linearized Einstein-Ricci cubic gravity, but not a feature of higher-order derivative theory giving ghost states. Also, we point out that the correlated stability conjecture holds for the SAdS black hole by computing the Wald entropy of SAdS black hole in Einstein-Ricci cubic gravity.

Stochastic Geometry and Quantum Gravity: Some Rigorous Results

NASA Astrophysics Data System (ADS)

Zessin, H.

The aim of these lectures is a short introduction into some recent developments in stochastic geometry which have one of its origins in simplicial gravity theory (see Regge Nuovo Cimento 19: 558-571, 1961). The aim is to define and construct rigorously point processes on spaces of Euclidean simplices in such a way that the configurations of these simplices are simplicial complexes. The main interest then is concentrated on their curvature properties. We illustrate certain basic ideas from a mathematical point of view. An excellent representation of this area can be found in Schneider and Weil (Stochastic and Integral Geometry, Springer, Berlin, 2008. German edition: Stochastische Geometrie, Teubner, 2000). In Ambjørn et al. (Quantum Geometry Cambridge University Press, Cambridge, 1997) you find a beautiful account from the physical point of view. More recent developments in this direction can be found in Ambjørn et al. ("Quantum gravity as sum over spacetimes", Lect. Notes Phys. 807. Springer, Heidelberg, 2010). After an informal axiomatic introduction into the conceptual foundations of Regge's approach the first lecture recalls the concepts and notations used. It presents the fundamental zero-infinity law of stochastic geometry and the construction of cluster processes based on it. The second lecture presents the main mathematical object, i.e. Poisson-Delaunay surfaces possessing an intrinsic random metric structure. The third and fourth lectures discuss their ergodic behaviour and present the two-dimensional Regge model of pure simplicial quantum gravity. We terminate with the formulation of basic open problems. Proofs are given in detail only in a few cases. In general the main ideas are developed. Sufficiently complete references are given.

Ricci polynomial gravity

NASA Astrophysics Data System (ADS)

Hao, Xin; Zhao, Liu

2017-12-01

We study a novel class of higher-curvature gravity models in n spacetime dimensions which we call Ricci polynomial gravity. The action consists purely of a polynomial in Ricci curvature of order N . In the absence of the second-order terms in the action, the models are ghost free around the Minkowski vacuum. By appropriately choosing the coupling coefficients in front of each term in the action, it is shown that the models can have multiple vacua with different effective cosmological constants, and can be made free of ghost and scalar degrees of freedom around at least one of the maximally symmetric vacua for any n >2 and any N ≥4 . We also discuss some of the physical implications of the existence of multiple vacua in the contexts of black hole physics and cosmology.

Primordial fluctuations from inflation in dRGT bimetric theory of gravity

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

Sakakihara, Yuki; Research Center for the Early Universe; Tanaka, Takahiro

2016-09-19

We investigate primordial gravitational waves and curvature perturbations in de Rham-Gabadadze-Tolley (dRGT) bimetric gravity. We evaluate the power-spectra in the leading order in slow roll. Taking into account the decay of massive graviton, we find that the action up to the second order reduces to the Einstein theory with a non-minimally coupled scalar field, which is simplified to a minimally coupled model by conformal transformation. We also find that the tensor to scalar ratio for large field inflation with power law potential is larger than the general relativity counterpart for any choice of parameters in dRGT bimetric gravity. In addition,more » we confirm that the usual consistency relation holds and we have a steeper spectrum for gravitational waves.« less

Utilizing the Upcoming Gravity Measurements from Cassini's Proximal Orbits for Studying the Atmospheric Dynamics of Saturn - How Deep Do the Winds Penetrate?

NASA Astrophysics Data System (ADS)

Kaspi, Y.; Galanti, E.

2014-12-01

At the end of the Cassini mission, the spacecraft will descend into close-by proximal orbits around Saturn. During those proximal orbits, Cassini will obtain high precision gravity measurements of the planet. In this talk, we will discuss how this data can be used to estimate the depth of the observed flows on the planet. This can be done in several ways: 1. measurements of the high order even harmonics which beyond J10 are dominated by the dynamics; 2. measurements of odd gravity harmonics which have no contribution from a static planet, and therefore are a pure signature of dynamics; 3. upper limits on the depth can be obtained by comparing low order even harmonics from dynamical models to the difference between the measured low order even harmonics and the largest possible values of a static planet; 4. direct latitudinally varying measurements of the gravity field exerted on the spacecraft. We will discuss how these methods may be applied and show that given the expected sensitivity of Cassini the odd harmonics J3 and J5 will have the best sensitivity to deep dynamics, allowing detection of winds reaching only O(100km) deep, if those exist on Saturn. We use a hierarchy of dynamical models ranging from full 3D dynamical circulation models to simplified dynamical models where the sensitivity of the gravity field to the dynamics can be explored. In order to invert the gravity field to be measured by Cassini into the depth dependent circulation, an adjoint inverse model is constructed for the dynamical models, thus allowing backward integration of the dynamical model. This tool can be used for examination of various scenarios, including cases in which the depth of the wind depends on latitudinal position. In summary, we expect that the very end of Cassini's tour holds an opportunity for gravity measurements that may finally allow answering one of the long-lasting puzzles in planetary science regarding the depth of the zonal jets on the gas giants. In fact, as Juno will be performing similar measurements we hope to be able to build a picture of the dynamics for both Jupiter and Saturn. Answering this puzzle, will likely help explain the origin of the multiple jet streams and strong equatorial superrotation on the gas giants.

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.

Absolute Gravity Datum in the Age of Cold Atom Gravimeters

NASA Astrophysics Data System (ADS)

Childers, V. A.; Eckl, M. C.

2014-12-01

The international gravity datum is defined today by the International Gravity Standardization Net of 1971 (IGSN-71). The data supporting this network was measured in the 1950s and 60s using pendulum and spring-based gravimeter ties (plus some new ballistic absolute meters) to replace the prior protocol of referencing all gravity values to the earlier Potsdam value. Since this time, gravimeter technology has advanced significantly with the development and refinement of the FG-5 (the current standard of the industry) and again with the soon-to-be-available cold atom interferometric absolute gravimeters. This latest development is anticipated to provide improvement in the range of two orders of magnitude as compared to the measurement accuracy of technology utilized to develop ISGN-71. In this presentation, we will explore how the IGSN-71 might best be "modernized" given today's requirements and available instruments and resources. The National Geodetic Survey (NGS), along with other relevant US Government agencies, is concerned about establishing gravity control to establish and maintain high order geodetic networks as part of the nation's essential infrastructure. The need to modernize the nation's geodetic infrastructure was highlighted in "Precise Geodetic Infrastructure, National Requirements for a Shared Resource" National Academy of Science, 2010. The NGS mission, as dictated by Congress, is to establish and maintain the National Spatial Reference System, which includes gravity measurements. Absolute gravimeters measure the total gravity field directly and do not involve ties to other measurements. Periodic "intercomparisons" of multiple absolute gravimeters at reference gravity sites are used to constrain the behavior of the instruments to ensure that each would yield reasonably similar measurements of the same location (i.e. yield a sufficiently consistent datum when measured in disparate locales). New atomic interferometric gravimeters promise a significant increase in accuracy. Our presentation will also explore the impact of such an instrument on our theory of how to constrain the gravity datum and on how to ensure stability, repeatability, and reproducibility across different absolute gravimeter systems.

Killing vector fields in three dimensions: a method to solve massive gravity field equations

NASA Astrophysics Data System (ADS)

Gürses, Metin

2010-10-01

Killing vector fields in three dimensions play an important role in the construction of the related spacetime geometry. In this work we show that when a three-dimensional geometry admits a Killing vector field then the Ricci tensor of the geometry is determined in terms of the Killing vector field and its scalars. In this way we can generate all products and covariant derivatives at any order of the Ricci tensor. Using this property we give ways to solve the field equations of topologically massive gravity (TMG) and new massive gravity (NMG) introduced recently. In particular when the scalars of the Killing vector field (timelike, spacelike and null cases) are constants then all three-dimensional symmetric tensors of the geometry, the Ricci and Einstein tensors, their covariant derivatives at all orders, and their products of all orders are completely determined by the Killing vector field and the metric. Hence, the corresponding three-dimensional metrics are strong candidates for solving all higher derivative gravitational field equations in three dimensions.

Simulations of four-dimensional simplicial quantum gravity as dynamical triangulation

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

Agishtein, M.E.; Migdal, A.A.

1992-04-20

In this paper, Four-Dimensional Simplicial Quantum Gravity is simulated using the dynamical triangulation approach. The authors studied simplicial manifolds of spherical topology and found the critical line for the cosmological constant as a function of the gravitational one, separating the phases of opened and closed Universe. When the bare cosmological constant approaches this line from above, the four-volume grows: the authors reached about 5 {times} 10{sup 4} simplexes, which proved to be sufficient for the statistical limit of infinite volume. However, for the genuine continuum theory of gravity, the parameters of the lattice model should be further adjusted to reachmore » the second order phase transition point, where the correlation length grows to infinity. The authors varied the gravitational constant, and they found the first order phase transition, similar to the one found in three-dimensional model, except in 4D the fluctuations are rather large at the transition point, so that this is close to the second order phase transition. The average curvature in cutoff units is large and positive in one phase (gravity), and small negative in another (antigravity). The authors studied the fractal geometry of both phases, using the heavy particle propagator to define the geodesic map, as well as with the old approach using the shortest lattice paths.« less

Search and Seizure of Students in Public Schools: 2002 Update of Fourth Amendment Cases.

ERIC Educational Resources Information Center

Stefkovich, Jacqueline A.

This paper presents court cases for the purpose of updating current knowledge on search and seizure of students in the school setting. These cases focus on the balance and interplay between students' Fourth Amendment rights and school administrators' obligations to maintain order and discipline in the schools. Part of this obligation implies…

Increasing the Responsibility Levels of Fourth Grade Gifted Children by Promoting Positive Character Traits and Caring Behaviors.

ERIC Educational Resources Information Center

Hogan, Marliese G.

This paper describes a project to improve the responsibility levels of 16 gifted students in fourth grade attending a daily 2-hour language arts gifted education class. Students had become inconsistent about completing assignments, maintaining an orderly environment, and communicating necessary information to parents. A teacher-developed checklist…

"Researching" with Third- and Fourth-Graders.

ERIC Educational Resources Information Center

Liston, Barbara

1970-01-01

In order to instill in children the skills which will be basic to their school experience, words implying a process (such as "hemp,""parasite," and "vanilla") may be "researched" by third and fourth graders through the use of a dictionary, an encyclopedia, a supplementary book on the subject, and an interview with an adult. The child makes a…

Departmentalized Classroom Environments versus Traditional Classroom Environments in Second through Fourth Grades: A Quantitative Analysis

ERIC Educational Resources Information Center

Ray, Staci Janelle

2017-01-01

Since No Child Left Behind was introduced, kindergarten through 12th-grade educators have seen a dramatic increase in accountability, rigor of standards, and responsibilities in the classroom (New America Foundation, 2015). In order to meet the increased demands of federal education regulations in second through fourth grades, many administrators…

The Fourth Grade Experience: Insights toward the Transition to Middle School

ERIC Educational Resources Information Center

Reynolds, Kelly A.

2005-01-01

The transition from elementary to middle school can be an exciting as well as scary time for young adolescents. The stress of this transition can be decreased by incorporating transition programs that address student needs and concerns. This qualitative research study was designed to gain an overall sense of fourth grade in order to better…

Venus gravity: Summary and coming events

NASA Technical Reports Server (NTRS)

Sjogren, W. L.

1992-01-01

The first significant dataset to provide local measures of venusian gravity field variations was that acquired from the Pioneer Venus Orbiter (PVO) during the 1979-1981 period. These observations were S-band Doppler radio signals from the orbiting spacecraft received at Earth-based tracking stations. Early reductions of these data were performed using two quite different techniques. Estimates of the classical spherical harmonics were made to various degrees and orders up to 10. At that time, solutions of much higher degree and order were very difficult due to computer limitations. These reductions, because of low degree and order, revealed only the most prominent features with poor spatial resolution and very reduced peak amplitudes.

Gravity-dependent transport in industrial processes

NASA Technical Reports Server (NTRS)

Ostrach, Simon; Kamotani, Yasuhiro

1994-01-01

Gravity-dependent transport phenomena in various industrial processes are investigated in order to address a broader range of microgravity phenomena and to develop new applications of microgravity. A number of important topics are identified and analyzed in detail. The present article describes results on coating flow, zeolite growth, and rotating electrochemical system.

SL(2,C) gravity on noncommutative space with Poisson structure

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

Miao Yangang; Zhang Shaojun

2010-10-15

The Einstein's gravity theory can be formulated as an SL(2,C) gauge theory in terms of spinor notations. In this paper, we consider a noncommutative space with the Poisson structure and construct an SL(2,C) formulation of gravity on such a space. Using the covariant coordinate technique, we build a gauge invariant action in which, according to the Seiberg-Witten map, the physical degrees of freedom are expressed in terms of their commutative counterparts up to the first order in noncommutative parameters.

Cautionary tales for reduced-gravity particle research

NASA Technical Reports Server (NTRS)

Marshall, John R.; Greeley, Ronald; Tucker, D. W.

1987-01-01

Failure of experiments conducted on the KC-135 aircraft in zero gravity are discussed. Tests that were a total failure are reported. Why the failure occurred and the sort of questions that potential researchers should ask in order to avoid the appearance of abstracts such as this are discussed. Many types of aggregation studies were proposed for the Space Station, and it is hoped that the following synopsis of events will add a touch of reality to experimentation proposed for this zero-gravity environment.

Atmospheric gravity waves with small vertical-to-horizotal wavelength ratios

NASA Astrophysics Data System (ADS)

Song, I. S.; Jee, G.; Kim, Y. H.; Chun, H. Y.

2017-12-01

Gravity wave modes with small vertical-to-horizontal wavelength ratios of an order of 10-3 are investigated through the systematic scale analysis of governing equations for gravity wave perturbations embedded in the quasi-geostrophic large-scale flow. These waves can be categorized as acoustic gravity wave modes because their total energy is given by the sum of kinetic, potential, and elastic parts. It is found that these waves can be forced by density fluctuations multiplied by the horizontal gradients of the large-scale pressure (geopotential) fields. These theoretical findings are evaluated using the results of a high-resolution global model (Specified Chemistry WACCM with horizontal resolution of 25 km and vertical resolution of 600 m) by computing the density-related gravity-wave forcing terms from the modeling results.

Neutron stars in Horndeski gravity

NASA Astrophysics Data System (ADS)

Maselli, Andrea; Silva, Hector O.; Minamitsuji, Masato; Berti, Emanuele

2016-06-01

Horndeski's theory of gravity is the most general scalar-tensor theory with a single scalar whose equations of motion contain at most second-order derivatives. A subsector of Horndeski's theory known as "Fab Four" gravity allows for dynamical self-tuning of the quantum vacuum energy, and therefore it has received particular attention in cosmology as a possible alternative to the Λ CDM model. Here we study compact stars in Fab Four gravity, which includes as special cases general relativity ("George"), Einstein-dilaton-Gauss-Bonnet gravity ("Ringo"), theories with a nonminimal coupling with the Einstein tensor ("John"), and theories involving the double-dual of the Riemann tensor ("Paul"). We generalize and extend previous results in theories of the John class and were not able to find realistic compact stars in theories involving the Paul class.

Understanding linkages between global climate indices and terrestrial water storage changes over Africa using GRACE products.

PubMed

Anyah, R O; Forootan, E; Awange, J L; Khaki, M

2018-09-01

Africa, a continent endowed with huge water resources that sustain its agricultural activities is increasingly coming under threat from impacts of climate extremes (droughts and floods), which puts the very precious water resource into jeopardy. Understanding the relationship between climate variability and water storage over the continent, therefore, is paramount in order to inform future water management strategies. This study employs Gravity Recovery And Climate Experiment (GRACE) satellite data and the higher order (fourth order cumulant) statistical independent component analysis (ICA) method to study the relationship between terrestrial water storage (TWS) changes and five global climate-teleconnection indices; El Niño-Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Madden-Julian Oscillation (MJO), Quasi-Biennial Oscillation (QBO) and the Indian Ocean Dipole (IOD) over Africa for the period 2003-2014. Pearson correlation analysis is applied to extract the connections between these climate indices (CIs) and TWS, from which some known strong CI-rainfall relationships (e.g., over equatorial eastern Africa) are found. Results indicate unique linear-relationships and regions that exhibit strong linkages between CIs and TWS. Moreover, unique regions having strong CI-TWS connections that are completely different from the typical ENSO-rainfall connections over eastern and southern Africa are also identified. Furthermore, the results indicate that the first dominant independent components (IC) of the CIs are linked to NAO, and are characterized by significant reductions of TWS over southern Africa. The second dominant ICs are associated with IOD and are characterized by significant increases in TWS over equatorial eastern Africa, while the combined ENSO and MJO are apparently linked to the third ICs, which are also associated with significant increase in TWS changes over both southern Africa, as well as equatorial eastern Africa. Copyright © 2018 Elsevier B.V. All rights reserved.

Comparison of volatility function technique for risk-neutral densities estimation

NASA Astrophysics Data System (ADS)

Bahaludin, Hafizah; Abdullah, Mimi Hafizah

2017-08-01

Volatility function technique by using interpolation approach plays an important role in extracting the risk-neutral density (RND) of options. The aim of this study is to compare the performances of two interpolation approaches namely smoothing spline and fourth order polynomial in extracting the RND. The implied volatility of options with respect to strike prices/delta are interpolated to obtain a well behaved density. The statistical analysis and forecast accuracy are tested using moments of distribution. The difference between the first moment of distribution and the price of underlying asset at maturity is used as an input to analyze forecast accuracy. RNDs are extracted from the Dow Jones Industrial Average (DJIA) index options with a one month constant maturity for the period from January 2011 until December 2015. The empirical results suggest that the estimation of RND using a fourth order polynomial is more appropriate to be used compared to a smoothing spline in which the fourth order polynomial gives the lowest mean square error (MSE). The results can be used to help market participants capture market expectations of the future developments of the underlying asset.

Field estimates of gravity terrain corrections and Y2K-compatible method to convert from gravity readings with multiple base stations to tide- and long-term drift-corrected observations

USGS Publications Warehouse

Plouff, Donald

2000-01-01

Gravity observations are directly made or are obtained from other sources by the U.S. Geological Survey in order to prepare maps of the anomalous gravity field and consequently to interpret the subsurface distribution of rock densities and associated lithologic or geologic units. Observations are made in the field with gravity meters at new locations and at reoccupations of previously established gravity "stations." This report illustrates an interactively-prompted series of steps needed to convert gravity "readings" to values that are tied to established gravity datums and includes computer programs to implement those steps. Inasmuch as individual gravity readings have small variations, gravity-meter (instrument) drift may not be smoothly variable, and acommodations may be needed for ties to previously established stations, the reduction process is iterative. Decision-making by the program user is prompted by lists of best values and graphical displays. Notes about irregularities of topography, which affect the value of observed gravity but are not shown in sufficient detail on topographic maps, must be recorded in the field. This report illustrates ways to record field notes (distances, heights, and slope angles) and includes computer programs to convert field notes to gravity terrain corrections. This report includes approaches that may serve as models for other applications, for example: portrayal of system flow; style of quality control to document and validate computer applications; lack of dependence on proprietary software except source code compilation; method of file-searching with a dwindling list; interactive prompting; computer code to write directly in the PostScript (Adobe Systems Incorporated) printer language; and high-lighting the four-digit year on the first line of time-dependent data sets for assured Y2K compatibility. Computer source codes provided are written in the Fortran scientific language. In order for the programs to operate, they first must be converted (compiled) into an executable form on the user's computer. Although program testing was done in a UNIX (tradename of American Telephone and Telegraph Company) computer environment, it is anticipated that only a system-dependent date-and-time function may need to be changed for adaptation to other computer platforms that accept standard Fortran code.d del iliscipit volorer sequi ting etue feum zzriliquatum zzriustrud esenibh ex esto esequat.

Possibilities of inversion of satellite third-order gravitational tensor onto gravity anomalies: a case study for central Europe

NASA Astrophysics Data System (ADS)

Pitoňák, Martin; Šprlák, Michal; Tenzer, Robert

2017-05-01

We investigate a numerical performance of four different schemes applied to a regional recovery of the gravity anomalies from the third-order gravitational tensor components (assumed to be observable in the future) synthetized at the satellite altitude of 200 km above the mean sphere. The first approach is based on applying a regional inversion without modelling the far-zone contribution or long-wavelength support. In the second approach we separate integral formulas into two parts, that is, the effects of the third-order disturbing tensor data within near and far zones. Whereas the far-zone contribution is evaluated by using existing global geopotential model (GGM) with spectral weights given by truncation error coefficients, the near-zone contribution is solved by applying a regional inversion. We then extend this approach for a smoothing procedure, in which we remove the gravitational contributions of the topographic-isostatic and atmospheric masses. Finally, we apply the remove-compute-restore (r-c-r) scheme in order to reduce the far-zone contribution by subtracting the reference (long-wavelength) gravity field, which is computed for maximum degree 80. We apply these four numerical schemes to a regional recovery of the gravity anomalies from individual components of the third-order gravitational tensor as well as from their combinations, while applying two different levels of a white noise. We validated our results with respect to gravity anomalies evaluated at the mean sphere from EGM2008 up to the degree 250. Not surprisingly, better fit in terms of standard deviation (STD) was attained using lower level of noise. The worst results were gained applying classical approach, STD values of our solution from Tzzz are 1.705 mGal (noise value with a standard deviation 0.01 × 10 - 15m - 1s - 2) and 2.005 mGal (noise value with a standard deviation 0.05 × 10 - 15m - 1s - 2), while the superior from r-c-r up to the degree 80, STD fit of gravity anomalies from Tzzz with respect to the same counterpart from EGM2008 is 0.510 mGal (noise value with a standard deviation 0.01 × 10 - 15m - 1s - 2) and 1.190 mGal (noise value with a standard deviation 0.05 × 10 - 15m - 1s - 2).

Importance of curvature evaluation scale for predictive simulations of dynamic gas-liquid interfaces

NASA Astrophysics Data System (ADS)

Owkes, Mark; Cauble, Eric; Senecal, Jacob; Currie, Robert A.

2018-07-01

The effect of the scale used to compute the interfacial curvature on the prediction of dynamic gas-liquid interfaces is investigated. A new interface curvature calculation methodology referred to herein as the Adjustable Curvature Evaluation Scale (ACES) is proposed. ACES leverages a weighted least squares regression to fit a polynomial through points computed on the volume-of-fluid representation of the gas-liquid interface. The interface curvature is evaluated from this polynomial. Varying the least squares weight with distance from the location where the curvature is being computed, adjusts the scale the curvature is evaluated on. ACES is verified using canonical static test cases and compared against second- and fourth-order height function methods. Simulations of dynamic interfaces, including a standing wave and oscillating droplet, are performed to assess the impact of the curvature evaluation scale for predicting interface motions. ACES and the height function methods are combined with two different unsplit geometric volume-of-fluid (VoF) schemes that define the interface on meshes with different levels of refinement. We find that the results depend significantly on curvature evaluation scale. Particularly, the ACES scheme with a properly chosen weight function is accurate, but fails when the scale is too small or large. Surprisingly, the second-order height function method is more accurate than the fourth-order variant for the dynamic tests even though the fourth-order method performs better for static interfaces. Comparing the curvature evaluation scale of the second- and fourth-order height function methods, we find the second-order method is closer to the optimum scale identified with ACES. This result suggests that the curvature scale is driving the accuracy of the dynamics. This work highlights the importance of studying numerical methods with realistic (dynamic) test cases and that the interactions of the various discretizations is as important as the accuracy of one part of the discretization.

Gravity gradient preprocessing at the GOCE HPF

NASA Astrophysics Data System (ADS)

Bouman, J.; Rispens, S.; Gruber, T.; Schrama, E.; Visser, P.; Tscherning, C. C.; Veicherts, M.

2009-04-01

One of the products derived from the GOCE observations are the gravity gradients. These gravity gradients are provided in the Gradiometer Reference Frame (GRF) and are calibrated in-flight using satellite shaking and star sensor data. In order to use these gravity gradients for application in Earth sciences and gravity field analysis, additional pre-processing needs to be done, including corrections for temporal gravity field signals to isolate the static gravity field part, screening for outliers, calibration by comparison with existing external gravity field information and error assessment. The temporal gravity gradient corrections consist of tidal and non-tidal corrections. These are all generally below the gravity gradient error level, which is predicted to show a 1/f behaviour for low frequencies. In the outlier detection the 1/f error is compensated for by subtracting a local median from the data, while the data error is assessed using the median absolute deviation. The local median acts as a high-pass filter and it is robust as is the median absolute deviation. Three different methods have been implemented for the calibration of the gravity gradients. All three methods use a high-pass filter to compensate for the 1/f gravity gradient error. The baseline method uses state-of-the-art global gravity field models and the most accurate results are obtained if star sensor misalignments are estimated along with the calibration parameters. A second calibration method uses GOCE GPS data to estimate a low degree gravity field model as well as gravity gradient scale factors. Both methods allow to estimate gravity gradient scale factors down to the 10-3 level. The third calibration method uses high accurate terrestrial gravity data in selected regions to validate the gravity gradient scale factors, focussing on the measurement band. Gravity gradient scale factors may be estimated down to the 10-2 level with this method.

Bismuth ferrite dielectric nanoparticles excited at telecom wavelengths as multicolor sources by second, third, and fourth harmonic generation.

PubMed

Riporto, Jérémy; Demierre, Alexis; Kilin, Vasyl; Balciunas, Tadas; Schmidt, Cédric; Campargue, Gabriel; Urbain, Mathias; Baltuska, Andrius; Le Dantec, Ronan; Wolf, Jean-Pierre; Mugnier, Yannick; Bonacina, Luigi

2018-05-03

We demonstrate the simultaneous generation of second, third, and fourth harmonics from a single dielectric bismuth ferrite nanoparticle excited using a telecom fiber laser at 1560 nm. We first characterize the signals associated with different nonlinear orders in terms of spectrum, excitation intensity dependence, and relative signal strengths. Successively, on the basis of the polarization-resolved emission curves of the three harmonics, we discuss the interplay of susceptibility tensor components at different orders and show how polarization can be used as an optical handle to control the relative frequency conversion properties.

Fourth order scheme for wavelet based solution of Black-Scholes equation

NASA Astrophysics Data System (ADS)

Finěk, Václav

2017-12-01

The present paper is devoted to the numerical solution of the Black-Scholes equation for pricing European options. We apply the Crank-Nicolson scheme with Richardson extrapolation for time discretization and Hermite cubic spline wavelets with four vanishing moments for space discretization. This scheme is the fourth order accurate both in time and in space. Computational results indicate that the Crank-Nicolson scheme with Richardson extrapolation significantly decreases the amount of computational work. We also numerically show that optimal convergence rate for the used scheme is obtained without using startup procedure despite the data irregularities in the model.

Applications of acoustic-gravity waves numerical modeling to tsunami signals observed by gravimetry satellites in very low orbit

NASA Astrophysics Data System (ADS)

Brissaud, Q.; Garcia, R.; Sladen, A.; Martin, R.; Komatitsch, D.

2016-12-01

Acoustic and gravity waves propagating in planetary atmospheres have been studied intensively as markers of specific phenomena (tectonic events, explosions) or as contributors to atmosphere dynamics. To get a better understanding of the physics behind these dynamic processes, both acoustic and gravity waves propagation should be modeled in an attenuating and windy 3D atmosphere from the ground all the way to the upper thermosphere. Thus, in order to provide an efficient numerical tool at the regional or global scale we introduce a high-order finite-difference time domain (FDTD) approach that relies on the linearized compressible Navier-Stokes equations with spatially non constant physical parameters (density, viscosities and speed of sound) and background velocities (wind). We present applications of these simulations to the propagation of gravity waves generated by tsunamis for realistic cases for which atmospheric models are extracted from empirical models including variations with altitude of atmospheric parameters, and tsunami forcing at the ocean surface is extracted from shallow water simulations. We describe the specific difficulties induced by the size of the simulation, the boundary conditions and the spherical geometry and compare the simulation outputs to data gathered by gravimetric satellites crossing gravity waves generated by tsunamis.

The effects of gravity level during directional solidification on the microstructure of hypermonotectic Al-In-Sn alloys

NASA Technical Reports Server (NTRS)

Curreri, P. A.; Kaukler, W. F.

1986-01-01

Five hypermonotectic Al-In-Sn compositions were directionally solidified in a Bridgman-type furnace at normal gravity and during aircraft low-gravity maneuvers. The tendency of the Al-30In alloy to form an indium-rich band at the start of unidirectional growth (SUG) made it difficult to study the integration of L sub 2 into the solidification interface. Hypermonotectic compositions closer to monotectic slightly hypermonotectic caused only a partial band on L sub 2 to form at SUG and allowed the study of such variables as gravity, composition, and monotectic dome height on integration of excess L sub 2 into the solid plus L sub 2 interface. It was found that formation of aligned composite structures for the Al-In-Sn system is not only a function of G and R but also of the degree to which the composition varies from monotectic. Most of the aligned fibrous structures formed from hypermonotectic Al-In-Sn had spacings that were of the order of irregular fibrous structures reported for on monotectic Al-In-Sn. The spacings for the large fibers and aligned globules found for ground and low-gravity processed Al-In-18-Sn-22, respectively, were significantly larger than the others measured and were of the order expected for cell spacings under the growth conditions utilized. It was found that the integration into the solidification front of excess L sub 2 in low gravity was a function of the Sn composition of the alloy.

Jacobi-Gauss-Lobatto collocation method for the numerical solution of 1+1 nonlinear Schrödinger equations

NASA Astrophysics Data System (ADS)

Doha, E. H.; Bhrawy, A. H.; Abdelkawy, M. A.; Van Gorder, Robert A.

2014-03-01

A Jacobi-Gauss-Lobatto collocation (J-GL-C) method, used in combination with the implicit Runge-Kutta method of fourth order, is proposed as a numerical algorithm for the approximation of solutions to nonlinear Schrödinger equations (NLSE) with initial-boundary data in 1+1 dimensions. Our procedure is implemented in two successive steps. In the first one, the J-GL-C is employed for approximating the functional dependence on the spatial variable, using (N-1) nodes of the Jacobi-Gauss-Lobatto interpolation which depends upon two general Jacobi parameters. The resulting equations together with the two-point boundary conditions induce a system of 2(N-1) first-order ordinary differential equations (ODEs) in time. In the second step, the implicit Runge-Kutta method of fourth order is applied to solve this temporal system. The proposed J-GL-C method, used in combination with the implicit Runge-Kutta method of fourth order, is employed to obtain highly accurate numerical approximations to four types of NLSE, including the attractive and repulsive NLSE and a Gross-Pitaevskii equation with space-periodic potential. The numerical results obtained by this algorithm have been compared with various exact solutions in order to demonstrate the accuracy and efficiency of the proposed method. Indeed, for relatively few nodes used, the absolute error in our numerical solutions is sufficiently small.

Empirical performance of interpolation techniques in risk-neutral density (RND) estimation

NASA Astrophysics Data System (ADS)

Bahaludin, H.; Abdullah, M. H.

2017-03-01

The objective of this study is to evaluate the empirical performance of interpolation techniques in risk-neutral density (RND) estimation. Firstly, the empirical performance is evaluated by using statistical analysis based on the implied mean and the implied variance of RND. Secondly, the interpolation performance is measured based on pricing error. We propose using the leave-one-out cross-validation (LOOCV) pricing error for interpolation selection purposes. The statistical analyses indicate that there are statistical differences between the interpolation techniques:second-order polynomial, fourth-order polynomial and smoothing spline. The results of LOOCV pricing error shows that interpolation by using fourth-order polynomial provides the best fitting to option prices in which it has the lowest value error.

Higher Order, Multisample, Confirmatory Factor Analysis of the Wechsler Intelligence Scale for Children--Fourth Edition: What Does It Measure?

ERIC Educational Resources Information Center

Keith, Timothy Z.; Fine, Jodene Goldenring; Taub, Gordon E.; Reynolds, Matthew R.; Kranzler, John H.

2006-01-01

The recently published fourth edition of the Wechsler Intelligence Scale for Children (WISC-IV) represents a considerable departure from previous versions of the scale. The structure of the instrument has changed, and some subtests have been added and others deleted. The technical manual for the WISC-IV provided evidence supporting this new…

Higher-order formulas of amplitude-dependent tune shift caused by a sextupole magnetic field distribution

NASA Astrophysics Data System (ADS)

Soutome, Kouichi; Tanaka, Hitoshi

2017-06-01

Nowadays, designs for ring-based light sources use multibend lattices for achieving a very small emittance of around 100 pmrad. In this type of storage ring, the chromaticity correcting sextupoles generally have greater strengths than those used in typical third-generation light sources. Therefore, controlling lattice nonlinearity such as amplitude-dependent tune shift (ADTS) is important for enabling stable operations and smooth beam commissioning. As the strength of the sextupoles increases, their higher-order terms contribute significantly to ADTS, rendering well-known lowest-order formulas inadequate for describing tune variations at large horizontal amplitudes. In response, we have derived explicit expressions of ADTS up to the fourth order in sextupole strength based on the canonical perturbation theory, assuming that the amplitude of a vertical betatron oscillation is smaller compared with the horizontal one. The new formulas express the horizontal and vertical betatron tune variations as functions of the action variables: Jx and Jy up to O (Jx2) and O (Jy) . The derived formulas were applied to a five-bend achromat lattice designed for the SPring-8 upgrade. By comparing the calculated results with the tracking simulations, we found that (1) the formulas accurately express ADTS around a horizontal amplitude of ˜10 mm and (2) the nonlinear terms of the fourth order in sextupole strength govern the behaviors of circulating electrons at large horizontal amplitudes. In this paper, we present explicit expressions of fourth-order formulas of ADTS and provide some examples to illustrate their effectiveness.

Weyl gravity revisited

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

Álvarez, Enrique; González-Martín, Sergio, E-mail: enrique.alvarez@uam.es, E-mail: sergio.gonzalez.martin@csic.es

2017-02-01

The on shell equivalence of first order and second order formalisms for the Einstein-Hilbert action does not hold for those actions quadratic in curvature. It would seem that by considering the connection and the metric as independent dynamical variables, there are no quartic propagators for any dynamical variable. This suggests that it is possible to get both renormalizability and unitarity along these lines. We have studied a particular instance of those theories, namely Weyl gravity. In this first paper we show that it is not possible to implement this program with the Weyl connection alone.

Higher curvature gravities, unlike GR, cannot be bootstrapped from their (usual) linearizations

NASA Astrophysics Data System (ADS)

Deser, S.

2017-12-01

We show that higher curvature order gravities, in particular the propagating quadratic curvature models, cannot be derived by self-coupling from their linear, flat space, forms, except through an unphysical version of linearization; only GR can. Separately, we comment on an early version of the self-coupling bootstrap.

Graviton propagator from background-independent quantum gravity.

PubMed

Rovelli, Carlo

2006-10-13

We study the graviton propagator in Euclidean loop quantum gravity. We use spin foam, boundary-amplitude, and group-field-theory techniques. We compute a component of the propagator to first order, under some approximations, obtaining the correct large-distance behavior. This indicates a way for deriving conventional spacetime quantities from a background-independent theory.

Cartan gravity, matter fields, and the gauge principle

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

Westman, Hans F., E-mail: hwestman74@gmail.com; Zlosnik, Tom G., E-mail: t.zlosnik@imperial.ac.uk

Gravity is commonly thought of as one of the four force fields in nature. However, in standard formulations its mathematical structure is rather different from the Yang–Mills fields of particle physics that govern the electromagnetic, weak, and strong interactions. This paper explores this dissonance with particular focus on how gravity couples to matter from the perspective of the Cartan-geometric formulation of gravity. There the gravitational field is represented by a pair of variables: (1) a ‘contact vector’ V{sup A} which is geometrically visualized as the contact point between the spacetime manifold and a model spacetime being ‘rolled’ on top ofmore » it, and (2) a gauge connection A{sub μ}{sup AB}, here taken to be valued in the Lie algebra of SO(2,3) or SO(1,4), which mathematically determines how much the model spacetime is rotated when rolled. By insisting on two principles, the gauge principle and polynomial simplicity, we shall show how one can reformulate matter field actions in a way that is harmonious with Cartan’s geometric construction. This yields a formulation of all matter fields in terms of first order partial differential equations. We show in detail how the standard second order formulation can be recovered. In particular, the Hodge dual, which characterizes the structure of bosonic field equations, pops up automatically. Furthermore, the energy–momentum and spin-density three-forms are naturally combined into a single object here denoted the spin-energy–momentum three-form. Finally, we highlight a peculiarity in the mathematical structure of our first-order formulation of Yang–Mills fields. This suggests a way to unify a U(1) gauge field with gravity into a SO(1,5)-valued gauge field using a natural generalization of Cartan geometry in which the larger symmetry group is spontaneously broken down to SO(1,3)×U(1). The coupling of this unified theory to matter fields and possible extensions to non-Abelian gauge fields are left as open questions. -- Highlights: •Develops Cartan gravity to include matter fields. •Coupling to gravity is done using the standard gauge prescription. •Matter actions are manifestly polynomial in all field variables. •Standard equations recovered on-shell for scalar, spinor and Yang–Mills fields. •Unification of a U(1) field with gravity based on the orthogonal group SO(1,5)« less

A contrastive study on the influences of radial and three-dimensional satellite gravity gradiometry on the accuracy of the Earth's gravitational field recovery

NASA Astrophysics Data System (ADS)

Zheng, Wei; Hsu, Hou-Tse; Zhong, Min; Yun, Mei-Juan

2012-10-01

The accuracy of the Earth's gravitational field measured from the gravity field and steady-state ocean circulation explorer (GOCE), up to 250 degrees, influenced by the radial gravity gradient Vzz and three-dimensional gravity gradient Vij from the satellite gravity gradiometry (SGG) are contrastively demonstrated based on the analytical error model and numerical simulation, respectively. Firstly, the new analytical error model of the cumulative geoid height, influenced by the radial gravity gradient Vzz and three-dimensional gravity gradient Vij are established, respectively. In 250 degrees, the GOCE cumulative geoid height error measured by the radial gravity gradient Vzz is about 2½ times higher than that measured by the three-dimensional gravity gradient Vij. Secondly, the Earth's gravitational field from GOCE completely up to 250 degrees is recovered using the radial gravity gradient Vzz and three-dimensional gravity gradient Vij by numerical simulation, respectively. The study results show that when the measurement error of the gravity gradient is 3 × 10-12/s2, the cumulative geoid height errors using the radial gravity gradient Vzz and three-dimensional gravity gradient Vij are 12.319 cm and 9.295 cm at 250 degrees, respectively. The accuracy of the cumulative geoid height using the three-dimensional gravity gradient Vij is improved by 30%-40% on average compared with that using the radial gravity gradient Vzz in 250 degrees. Finally, by mutual verification of the analytical error model and numerical simulation, the orders of magnitude from the accuracies of the Earth's gravitational field recovery make no substantial differences based on the radial and three-dimensional gravity gradients, respectively. Therefore, it is feasible to develop in advance a radial cold-atom interferometric gradiometer with a measurement accuracy of 10-13/s2-10-15/s2 for precisely producing the next-generation GOCE Follow-On Earth gravity field model with a high spatial resolution.

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.

Cosmological perturbations in mimetic Horndeski gravity

NASA Astrophysics Data System (ADS)

Arroja, Frederico; Bartolo, Nicola; Karmakar, Purnendu; Matarrese, Sabino

2016-04-01

We study linear scalar perturbations around a flat FLRW background in mimetic Horndeski gravity. In the absence of matter, we show that the Newtonian potential satisfies a second-order differential equation with no spatial derivatives. This implies that the sound speed for scalar perturbations is exactly zero on this background. We also show that in mimetic G3 theories the sound speed is equally zero. We obtain the equation of motion for the comoving curvature perturbation (first order differential equation) and solve it to find that the comoving curvature perturbation is constant on all scales in mimetic Horndeski gravity. We find solutions for the Newtonian potential evolution equation in two simple models. Finally we show that the sound speed is zero on all backgrounds and therefore the system does not have any wave-like scalar degrees of freedom.

Immirzi parameter and Noether charges in first order gravity

NASA Astrophysics Data System (ADS)

Durka, Remigiusz

2012-02-01

The framework of SO(3,2) constrained BF theory applied to gravity makes it possible to generalize formulas for gravitational diffeomorphic Noether charges (mass, angular momentum, and entropy). It extends Wald's approach to the case of first order gravity with a negative cosmological constant, the Holst modification and the topological terms (Nieh-Yan, Euler, and Pontryagin). Topological invariants play essential role contributing to the boundary terms in the regularization scheme for the asymptotically AdS spacetimes, so that the differentiability of the action is automatically secured. Intriguingly, it turns out that the black hole thermodynamics does not depend on the Immirzi parameter for the AdS-Schwarzschild, AdS-Kerr, and topological black holes, whereas a nontrivial modification appears for the AdS-Taub-NUT spacetime, where it impacts not only the entropy, but also the total mass.

Probing Modified Gravity with Double Pulsars

NASA Astrophysics Data System (ADS)

Deng, Xue-Mei; Xie, Yi; Huang, Tian-Yi

2015-01-01

Although Einstein's general relativity has passed all the tests so far, alternative theories are still required for deeper understanding of the nature of gravity. Double pulsars provide us a significant opportunity to test them. In order to probe some modified gravities which try to explain some astrophysical phenomena without dark matter, we use periastron advance dot ω of four binary pulsars (PSR B1913+16, PSR B1534+12, PSR J0737-3039 and PSR B2127+11C) to constrain their Yukawa parameters: λ = (3.97 ± 0.01) × 108m and α = (2.40 ± 0.02) × 10-8. It might help us to distinguish different gravity theories and get closer to the new physics.

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

Winther, Hans A.; Koyama, Kazuya; Wright, Bill S.

We present a general parallelized and easy-to-use code to perform numerical simulations of structure formation using the COLA (COmoving Lagrangian Acceleration) method for cosmological models that exhibit scale-dependent growth at the level of first and second order Lagrangian perturbation theory. For modified gravity theories we also include screening using a fast approximate method that covers all the main examples of screening mechanisms in the literature. We test the code by comparing it to full simulations of two popular modified gravity models, namely f ( R ) gravity and nDGP, and find good agreement in the modified gravity boost-factors relative tomore » ΛCDM even when using a fairly small number of COLA time steps.« less

PENTACLE: Parallelized particle-particle particle-tree code for planet formation

NASA Astrophysics Data System (ADS)

Iwasawa, Masaki; Oshino, Shoichi; Fujii, Michiko S.; Hori, Yasunori

2017-10-01

We have newly developed a parallelized particle-particle particle-tree code for planet formation, PENTACLE, which is a parallelized hybrid N-body integrator executed on a CPU-based (super)computer. PENTACLE uses a fourth-order Hermite algorithm to calculate gravitational interactions between particles within a cut-off radius and a Barnes-Hut tree method for gravity from particles beyond. It also implements an open-source library designed for full automatic parallelization of particle simulations, FDPS (Framework for Developing Particle Simulator), to parallelize a Barnes-Hut tree algorithm for a memory-distributed supercomputer. These allow us to handle 1-10 million particles in a high-resolution N-body simulation on CPU clusters for collisional dynamics, including physical collisions in a planetesimal disc. In this paper, we show the performance and the accuracy of PENTACLE in terms of \\tilde{R}_cut and a time-step Δt. It turns out that the accuracy of a hybrid N-body simulation is controlled through Δ t / \\tilde{R}_cut and Δ t / \\tilde{R}_cut ˜ 0.1 is necessary to simulate accurately the accretion process of a planet for ≥106 yr. For all those interested in large-scale particle simulations, PENTACLE, customized for planet formation, will be freely available from https://github.com/PENTACLE-Team/PENTACLE under the MIT licence.

Simulations of Dissipative Circular Restricted Three-body Problems Using the Velocity-scaling Correction Method

NASA Astrophysics Data System (ADS)

Wang, Shoucheng; Huang, Guoqing; Wu, Xin

2018-02-01

In this paper, we survey the effect of dissipative forces including radiation pressure, Poynting–Robertson drag, and solar wind drag on the motion of dust grains with negligible mass, which are subjected to the gravities of the Sun and Jupiter moving in circular orbits. The effect of the dissipative parameter on the locations of five Lagrangian equilibrium points is estimated analytically. The instability of the triangular equilibrium point L4 caused by the drag forces is also shown analytically. In this case, the Jacobi constant varies with time, whereas its integral invariant relation still provides a probability for the applicability of the conventional fourth-order Runge–Kutta algorithm combined with the velocity scaling manifold correction scheme. Consequently, the velocity-only correction method significantly suppresses the effects of artificial dissipation and a rapid increase in trajectory errors caused by the uncorrected one. The stability time of an orbit, regardless of whether it is chaotic or not in the conservative problem, is apparently longer in the corrected case than in the uncorrected case when the dissipative forces are included. Although the artificial dissipation is ruled out, the drag dissipation leads to an escape of grains. Numerical evidence also demonstrates that more orbits near the triangular equilibrium point L4 escape as the integration time increases.

Wave Dynamics and Transport in the Stratosphere

NASA Technical Reports Server (NTRS)

Holton, James R.; Alexander, M. Joan

1999-01-01

The report discusses: (1) Gravity waves generated by tropical convection: A study in which a two-dimensional cloud-resolving model was used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation was completed. (2) Gravity wave ray tracing studies:It was developed a linear ray tracing model of gravity wave propagation to extend the nonlinear storm model results into the mesosphere and thermosphere. (3) tracer filamentation: Vertical soundings of stratospheric ozone often exhibit laminated tracer structures characterized by strong vertical tracer gradients. (4) Mesospheric gravity wave modeling studies: Although our emphasis in numerical simulation of gravity waves generated by convection has shifted from simulation of idealized two-dimensional squall lines to the most realistic (and complex) study of wave generation by three-dimensional storms. (5) Gravity wave climatology studies: Mr. Alexander applied a linear gravity wave propagation model together with observations of the background wind and stability fields to compute climatologies of gravity wave activity for comparison to observations. (6) Convective forcing of gravity waves: Theoretical study of gravity wave forcing by convective heat sources has completed. (7) Gravity waves observation from UARS: The objective of this work is to apply ray tracing, and other model technique, in order to determine to what extend the horizontal and vertical variation in satellite observed distribution of small-scale temperature variance can be attributed to gravity waves from particular sources. (8) The annual and interannual variations in temperature and mass flux near the tropical tropopause. and (9) Three dimensional cloud model.

Predicting gravity and sediment thickness in Afghanistan

NASA Astrophysics Data System (ADS)

Jung, W.; Brozena, J.; Peters, M.

2013-02-01

The US Naval Research Laboratory conducted comprehensive high-altitude (7 km above mean sea level) aero-geophysical surveys over Afghanistan in 2006 (Rampant Lion I). The surveys were done in collaboration with the US Geological Survey and upon the request of Islamic Republic of Afghanistan Ministry of Mines. In this study, we show that a best fitting admittance between topography and airborne gravity in western Afghanistan can be used to predict airborne gravity for the no-data area of eastern Afghanistan where the mountains are too high to conduct airborne surveys, due to the threat of ground fire. The differences between the airborne and the predicted gravity along a tie-track through the no-data area were found to be within ±12 mGal range with rms difference 7.3 mGal, while those between the predicted gravity from a simple Airy model (with compensation depth of 32 km and crustal density of 2.67 g cm-3) and the airborne gravity were within ±22 mGal range with rms difference 10.3 mGal. A combined airborne free-air anomaly has been constructed by merging the predicted gravity with the airborne data. We also demonstrate that sediment thickness can be estimated for basin areas where surface topography and airborne free-air anomaly profiles do not show a correlation presumably because of thick sediments. In order to estimate sediment thickness, we first determine a simple linear relationship from a scatter plot of the airborne gravity points and the interpolated Shuttle Radar Topography Mission (SRTM) topography along the Rampant Lion I tracks, and computed corresponding quasi-topography tracks by multiplying the linear relationship with the airborne free-air anomalies. We then take the differences between the SRTM and quasi-topography as a first-order estimate of sediment thickness. A global gravity model (GOCO02S), upward continued to the same altitude (7 km above mean sea level) as the data collection, was compared with the low-pass filtered (with cutoff wavelength 132 km which is approximately equivalent to the reported safe degree and order 250 of GOCO02S at 34º N) combined airborne free-air anomalies. The rms difference between the two data sets was 12.4 mGal. The observed admittance in the western Afghanistan mountains appears to be best fit to a theoretical elastic plate compensation model (with an effective elastic thickness of 5 km and crustal thickness of 22 km) where the ratio between surface load and subsurface load is equal.

Sparse Method for Direction of Arrival Estimation Using Denoised Fourth-Order Cumulants Vector.

PubMed

Fan, Yangyu; Wang, Jianshu; Du, Rui; Lv, Guoyun

2018-06-04

Fourth-order cumulants (FOCs) vector-based direction of arrival (DOA) estimation methods of non-Gaussian sources may suffer from poor performance for limited snapshots or difficulty in setting parameters. In this paper, a novel FOCs vector-based sparse DOA estimation method is proposed. Firstly, by utilizing the concept of a fourth-order difference co-array (FODCA), an advanced FOCs vector denoising or dimension reduction procedure is presented for arbitrary array geometries. Then, a novel single measurement vector (SMV) model is established by the denoised FOCs vector, and efficiently solved by an off-grid sparse Bayesian inference (OGSBI) method. The estimation errors of FOCs are integrated in the SMV model, and are approximately estimated in a simple way. A necessary condition regarding the number of identifiable sources of our method is presented that, in order to uniquely identify all sources, the number of sources K must fulfill K ≤ ( M 4 - 2 M 3 + 7 M 2 - 6 M ) / 8 . The proposed method suits any geometry, does not need prior knowledge of the number of sources, is insensitive to associated parameters, and has maximum identifiability O ( M 4 ) , where M is the number of sensors in the array. Numerical simulations illustrate the superior performance of the proposed method.

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.

f(R) gravity on non-linear scales: the post-Friedmann expansion and the vector potential

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

Thomas, D.B.; Bruni, M.; Koyama, K.

2015-07-01

Many modified gravity theories are under consideration in cosmology as the source of the accelerated expansion of the universe and linear perturbation theory, valid on the largest scales, has been examined in many of these models. However, smaller non-linear scales offer a richer phenomenology with which to constrain modified gravity theories. Here, we consider the Hu-Sawicki form of f(R) gravity and apply the post-Friedmann approach to derive the leading order equations for non-linear scales, i.e. the equations valid in the Newtonian-like regime. We reproduce the standard equations for the scalar field, gravitational slip and the modified Poisson equation in amore » coherent framework. In addition, we derive the equation for the leading order correction to the Newtonian regime, the vector potential. We measure this vector potential from f(R) N-body simulations at redshift zero and one, for two values of the f{sub R{sub 0}} parameter. We find that the vector potential at redshift zero in f(R) gravity can be close to 50% larger than in GR on small scales for |f{sub R{sub 0}}|=1.289 × 10{sup −5}, although this is less for larger scales, earlier times and smaller values of the f{sub R{sub 0}} parameter. Similarly to in GR, the small amplitude of this vector potential suggests that the Newtonian approximation is highly accurate for f(R) gravity, and also that the non-linear cosmological behaviour of f(R) gravity can be completely described by just the scalar potentials and the f(R) field.« less

Gravity monitoring of Tatun Volcanic Group activities and inference for underground fluid circulations

NASA Astrophysics Data System (ADS)

Mouyen, Maxime; Chao, Benjamin Fong; Hwang, Cheinway; Hsieh, Wen-Chi

2016-12-01

The Tatun Volcano Group (TVG), located on the northern coast of Taiwan adjacent to the city of Taipei, experiences active hydrothermalism but has no historical record of volcanic eruption. Yet recent studies suggest that TVG is dormant-active rather than extinct. To monitor mass transfers and to gain further understanding of this volcanic area, gravity variations have been recorded continuously since 2012 using a superconducting gravimeter, and once every few months since 2005 using absolute gravimeters. We analyze the continuous gravity time series and propose a model that best explains the gravity variations due to local groundwater redistribution. By correcting these variations, we identify gravity changes as large as 35 μGal that occurred concomitantly to fluid pressure-induced earthquakes and changes in the gas composition at Dayoukeng, one of TVG's fumaroles, over 2005-2007. We examine several fluid movements that can match the gravity observations, yet too few additional constraints exist to favor any of them. In particular, no significant ground displacements are observed when these gravity variations occurred. On the other hand, the model of gravity changes due to local groundwater redistribution can be routinely computed and removed from the ongoing time gravity measurements in order to quickly identify any unusual mass transfer occurring beneath TVG.

Gravity monitoring of Tatun Volcanic Group activities and inference for underground fluid circulations

NASA Astrophysics Data System (ADS)

Mouyen, Maxime; Chao, Benjamin; Hwang, Cheinway; Hsieh, Wen-Chi

2017-04-01

The Tatun Volcano Group (TVG), located on the northern coast of Taiwan adjacent to the city of Taipei, experiences active hydrothermalism but has no historical record of volcanic eruption. Yet recent studies suggest that TVG is dormant-active rather than extinct. To monitor mass transfers and to gain further understanding of this volcanic area, gravity variations have been recorded continuously since 2012 using a superconducting gravimeter, and once every few months since 2005 using absolute gravimeters. We analyze the continuous gravity time series and propose a model that best explain the gravity variations due to local groundwater redistribution. By correcting these variations, we identify gravity changes as large as 35 µGal that occurred concomitantly to fluid pressure-induced earthquakes and changes in the gas composition at Dayoukeng, one of TVG's fumaroles, over 2005-2007. We examine several fluid movements that can match the gravity observations, yet too few additional constraints exist to favor any of them. In particular, no significant ground displacements are observed when these gravity variations occurred. On the other hand, the model of gravity changes due to local groundwater redistribution can be routinely computed and removed from the ongoing time gravity measurements in order to quickly identify any unusual mass transfer occurring beneath TVG.

Emergence of gravity, fermion, gauge and Chern-Simons fields during formation of N-dimensional manifolds from joining point-like ones

NASA Astrophysics Data System (ADS)

Sepehri, Alireza; Shoorvazi, Somayyeh

In this paper, we will consider the birth and evolution of fields during formation of N-dimensional manifolds from joining point-like ones. We will show that at the beginning, only there are point-like manifolds which some strings are attached to them. By joining these manifolds, 1-dimensional manifolds are appeared and gravity, fermion, and gauge fields are emerged. By coupling these manifolds, higher dimensional manifolds are produced and higher orders of fermion, gauge fields and gravity are emerged. By decaying N-dimensional manifold, two child manifolds and a Chern-Simons one are born and anomaly is emerged. The Chern-Simons manifold connects two child manifolds and leads to the energy transmission from the bulk to manifolds and their expansion. We show that F-gravity can be emerged during the formation of N-dimensional manifold from point-like manifolds. This type of F-gravity includes both type of fermionic and bosonic gravity. G-fields and also C-fields which are produced by fermionic strings produce extra energy and change the gravity.

Height system unification based on the Fixed Geodetic Boundary Value Problem with limited availability of gravity data

NASA Astrophysics Data System (ADS)

Porz, Lucas; Grombein, Thomas; Seitz, Kurt; Heck, Bernhard; Wenzel, Friedemann

2017-04-01

Regional height reference systems are generally related to individual vertical datums defined by specific tide gauges. The discrepancies of these vertical datums with respect to a unified global datum cause height system biases that range in an order of 1-2 m at a global scale. One approach for unification of height systems relates to the solution of a Geodetic Boundary Value Problem (GBVP). In particular, the fixed GBVP, using gravity disturbances as boundary values, is solved at GNSS/leveling benchmarks, whereupon height datum offsets can be estimated by least squares adjustment. In spherical approximation, the solution of the fixed GBVP is obtained by Hotine's spherical integral formula. However, this method relies on the global availability of gravity data. In practice, gravity data of the necessary resolution and accuracy is not accessible globally. Thus, the integration is restricted to an area within the vicinity of the computation points. The resulting truncation error can reach several meters in height, making height system unification without further consideration of this effect unfeasible. This study analyzes methods for reducing the truncation error by combining terrestrial gravity data with satellite-based global geopotential models and by modifying the integral kernel in order to accelerate the convergence of the resulting potential. For this purpose, EGM2008-derived gravity functionals are used as pseudo-observations to be integrated numerically. Geopotential models of different spectral degrees are implemented using a remove-restore-scheme. Three types of modification are applied to the Hotine-kernel and the convergence of the resulting potential is analyzed. In a further step, the impact of these operations on the estimation of height datum offsets is investigated within a closed loop simulation. A minimum integration radius in combination with a specific modification of the Hotine-kernel is suggested in order to achieve sub-cm accuracy for the estimation of height datum offsets.

Non-analyticity of holographic Rényi entropy in Lovelock gravity

NASA Astrophysics Data System (ADS)

Puletti, V. Giangreco M.; Pourhasan, Razieh

2017-08-01

We compute holographic Rényi entropies for spherical entangling surfaces on the boundary while considering third order Lovelock gravity with negative cosmological constant in the bulk. Our study shows that third order Lovelock black holes with hyperbolic event horizon are unstable, and at low temperatures those with smaller mass are favoured, giving rise to first order phase transitions in the bulk. We determine regions in the Lovelock parameter space in arbitrary dimensions, where bulk phase transitions happen and where boundary causality constraints are met. We show that each of these points corresponds to a dual boundary conformal field theory whose Rényi entropy exhibits a kink at a certain critical index n.

Modular Extended-Stay HyperGravity Facility Design Concept: An Artificial-Gravity Space-Settlement Ground Analogue

NASA Technical Reports Server (NTRS)

Dorais, Gregory A.

2015-01-01

This document defines the design concept for a ground-based, extended-stay hypergravity facility as a precursor for space-based artificial-gravity facilities that extend the permanent presence of both human and non-human life beyond Earth in artificial-gravity settlements. Since the Earth's current human population is stressing the environment and the resources off-Earth are relatively unlimited, by as soon as 2040 more than one thousand people could be living in Earthorbiting artificial-gravity habitats. Eventually, the majority of humanity may live in artificialgravity habitats throughout this solar system as well as others, but little is known about the longterm (multi-generational) effects of artificial-gravity habitats on people, animals, and plants. In order to extend life permanently beyond Earth, it would be useful to create an orbiting space facility that generates 1g as well as other gravity levels to rigorously address the numerous challenges of such an endeavor. Before doing so, developing a ground-based artificial-gravity facility is a reasonable next step. Just as the International Space Station is a microgravity research facility, at a small fraction of the cost and risk a ground-based artificial-gravity facility can begin to address a wide-variety of the artificial-gravity life-science questions and engineering challenges requiring long-term research to enable people, animals, and plants to live off-Earth indefinitely.

The Development Of Drosophila Melanogaster under Different Duration Space Flight and Subsequent Adaptation to Earth Gravity.

PubMed

Ogneva, Irina V; Belyakin, Stepan N; Sarantseva, Svetlana V

2016-01-01

In prospective human exploration of outer space, the need to preserve a species over several generations under changed gravity conditions may arise. This paper demonstrates our results in the creation of the third generation of fruit fly Drosophila melanogaster (third-stage larvae) during the 44.5-day space flight (Foton-M4 satellite (2014, Russia)), then the fourth generation on Earth and the fifth generation again in conditions of the 12-day space flight (2014, in the Russian Segment of the ISS). The species preserves fertility despite a number of changes in the level of expression and content of cytoskeletal proteins, which are the key components of the cleavage spindle and the contractile ring of cells. The results of transcriptome screening and space analysis of cytoskeletal proteins show that the exposure to weightless conditions leads to the increased transcription of metabolic genes, cuticle components and the decreased transcription of genes involved in morphogenesis, cell differentiation, cytoskeletal organization and genes associated with the plasma membrane. "Subsequent" exposure to the microgravity for 12 days resulted in an even more significant increase/decrease in the transcription of the same genes. On the contrary, the transition from the microgravity conditions to the gravity of Earth leads to the increased transcription of genes whose products are involved in the morphogenesis, cytoskeletal organization, motility of cells and transcription regulation, and to the decreased transcription of cuticle genes and proteolytic processes.

The Development Of Drosophila Melanogaster under Different Duration Space Flight and Subsequent Adaptation to Earth Gravity

PubMed Central

Belyakin, Stepan N.; Sarantseva, Svetlana V.

2016-01-01

In prospective human exploration of outer space, the need to preserve a species over several generations under changed gravity conditions may arise. This paper demonstrates our results in the creation of the third generation of fruit fly Drosophila melanogaster (third-stage larvae) during the 44.5-day space flight (Foton-M4 satellite (2014, Russia)), then the fourth generation on Earth and the fifth generation again in conditions of the 12-day space flight (2014, in the Russian Segment of the ISS). The species preserves fertility despite a number of changes in the level of expression and content of cytoskeletal proteins, which are the key components of the cleavage spindle and the contractile ring of cells. The results of transcriptome screening and space analysis of cytoskeletal proteins show that the exposure to weightless conditions leads to the increased transcription of metabolic genes, cuticle components and the decreased transcription of genes involved in morphogenesis, cell differentiation, cytoskeletal organization and genes associated with the plasma membrane. “Subsequent” exposure to the microgravity for 12 days resulted in an even more significant increase/decrease in the transcription of the same genes. On the contrary, the transition from the microgravity conditions to the gravity of Earth leads to the increased transcription of genes whose products are involved in the morphogenesis, cytoskeletal organization, motility of cells and transcription regulation, and to the decreased transcription of cuticle genes and proteolytic processes. PMID:27861601

Effects of high gravity on amphibian development.

PubMed

Kashiwagi, Akihiko; Hanada, Hideki; Kawakami, Satomi; Kubo, Hideo; Shinkai, Tadashi; Fujii, Hirotada; Kashiwagi, Keiko

2003-10-01

In order to clarify the possible effects of high gravity environments on eggs and developing embryos, Rana rugosa and Xenopus laevis fertilized eggs and early embryos were raised in 2 G, 5 G, 7 G and 10 G up to the hatched tadpole stage. The results showed that: (1) High gravity significantly retarded the development of eggs and embryos beginning treatment before the blastula stage and induced various abnormalities, including two heads and microcephally suggesting that high gravity is apt to disrupt the animal-vegital axis. On the other hand, embryos beginning treatment after the gastrula stage showed a striking increase in the number of normal-appearing feeding tadpoles. (2) Autopsy revealed that brains, notochords and muscles were reduced in development and differentiation for embryos and tadpoles developed in high gravity. (3) It seems likely that the system for hydrogen peroxide detoxification develops abnormally in high gravity-treated embryos and tadpoles, which probably results in oxidative stress, leading to considerable cell damage.

Mean gravity anomalies from a combination of Apollo/ATS 6 and GEOS 3/ATS 6 SST tracking campaigns. [Satellite to Satellite Tracking

NASA Technical Reports Server (NTRS)

Kahn, W. D.; Klosko, S. M.; Wells, W. T.

1982-01-01

Advances in satellite tracking data accuracy and coverage over the past 15 years have led to major improvements in global geopotential models. But the spacial resolution of the gravity field obtained solely from satellite dynamics sensed by tracking data is still of the order of 1000 km. Attention is given to an approach which will provide information regarding the fine structure of the gravity field on the basis of an application of local corrections to the global field. According to this approach, a basic satellite to satellite tracked (SST) range-rate measurement is constructed from the link between a ground station, a geosynchronous satellite (ATS 6), and a near-earth satellite (Apollo or GEOS 3). Attention is given to a mathematical model, the simulation of SST gravity anomaly estimation accuracies, a gravity anomaly estimation from GEOS 3/ATS 6 and Apollo/ATS 6 SST observations, and an evaluation of the mean gravity anomalies determined from SST.

Constraining modified gravitational theories by weak lensing with Euclid

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

Martinelli, Matteo; Calabrese, Erminia; De Bernardis, Francesco

2011-01-15

Future proposed satellite missions such as Euclid can offer the opportunity to test general relativity on cosmic scales through mapping of the galaxy weak-lensing signal. In this paper we forecast the ability of these experiments to constrain modified gravity scenarios such as those predicted by scalar-tensor and f(R) theories. We find that Euclid will improve constraints expected from the Planck satellite on these modified theories of gravity by 2 orders of magnitude. We discuss parameter degeneracies and the possible biases introduced by modifications to gravity.

Ultrafine particle and fiber production in micro-gravity

NASA Technical Reports Server (NTRS)

Webb, George W.

1987-01-01

The technique of evaporation and condensation of material in an inert gas is investigated for the purpose of preparing ultrafine particles (of order 10 nm in diameter) with a narrow distribution of sizes. Gravity-driven convection increases the rate of coalescence of the particles, leading to larger sizes and a broader distribution. Analysis and experimental efforts to investigate coalescence of particles are presented. The possibility of reducing coalescence in microgravity is discussed. An experimental test in reduced gravity to be performed in a KC135 aircraft is described briefly.

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.

Astrophysical flows near [Formula: see text] gravity black holes.

PubMed

Ahmed, Ayyesha K; Azreg-Aïnou, Mustapha; Bahamonde, Sebastian; Capozziello, Salvatore; Jamil, Mubasher

In this paper, we study the accretion process for fluids flowing near a black hole in the context of f ( T ) teleparallel gravity. Specifically, by performing a dynamical analysis by a Hamiltonian system, we are able to find the sonic points. After that, we consider different isothermal test fluids in order to study the accretion process when they are falling onto the black hole. We find that these flows can be classified according to the equation of state and the black hole features. Results are compared in f ( T ) and f ( R ) gravity.

Handbook for MAP, volume 32. Part 1: MAP summary. Part 2: MAPSC minutes, reading, August 1989. MAP summaries from nations. Part 3: MAP data catalogue

NASA Technical Reports Server (NTRS)

Vincent, R. A. (Editor); Edwards, B. (Editor); Hirota, I. (Editor)

1991-01-01

Extended abstracts from the fourth workshop on the technical and scientific aspects of mesosphere stratosphere troposphere (MST) radar are presented. Individual sessions addressed the following topics: meteorological applications of MST and ST radars, networks, and campaigns; the dynamics of the equatorial middle atmosphere; interpretation of radar returns from clear air; techniques for studying gravity waves and turbulence, intercomparison and calibration of wind and wave measurements at various frequencies; progress in existing and planned MST and ST radars; hardware design for MST and ST radars and boundary layer/lower troposphere profilers; signal processing; and data management.

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

Broda, Jill Terese

The neutron flux across the nuclear reactor core is of interest to reactor designers and others. The diffusion equation, an integro-differential equation in space and energy, is commonly used to determine the flux level. However, the solution of a simplified version of this equation when automated is very time consuming. Since the flux level changes with time, in general, this calculation must be made repeatedly. Therefore solution techniques that speed the calculation while maintaining accuracy are desirable. One factor that contributes to the solution time is the spatial flux shape approximation used. It is common practice to use the samemore » order flux shape approximation in each energy group even though this method may not be the most efficient. The one-dimensional, two-energy group diffusion equation was solved, for the node average flux and core k-effective, using two sets of spatial shape approximations for each of three reactor types. A fourth-order approximation in both energy groups forms the first set of approximations used. The second set used combines a second-order approximation with a fourth-order approximation in energy group two. Comparison of the results from the two approximation sets show that the use of a different order spatial flux shape approximation results in considerable loss in accuracy for the pressurized water reactor modeled. However, the loss in accuracy is small for the heavy water and graphite reactors modeled. The use of different order approximations in each energy group produces mixed results. Further investigation into the accuracy and computing time is required before any quantitative advantage of the use of the second-order approximation in energy group one and the fourth-order approximation in energy group two can be determined.« less

A Comparison of the Influences of Verbal-Successive and Spatial-Simultaneous Factors on Achieving Readers in Fourth and Fifth Grade: A Multivariate Correlational Study.

ERIC Educational Resources Information Center

Solan, Harold A.

1987-01-01

This study involving 38 normally achieving fourth and fifth grade children confirmed previous studies indicating that both spatial-simultaneous (in which perceived stimuli are totally available at one point in time) and verbal-successive (information is presented in serial order) cognitive processing are important in normal learning. (DB)

Monochromatic plane-fronted waves in conformal gravity are pure gauge

NASA Astrophysics Data System (ADS)

Fabbri, Luca; Paranjape, M. B.

2011-05-01

We consider plane-fronted, monochromatic gravitational waves on a Minkowski background, in a conformally invariant theory of general relativity. By this we mean waves of the form: gμν=ημν+γμνF(k·x), where γμν is a constant polarization tensor, and kμ is a lightlike vector. We also assume the coordinate gauge condition |g|-1/4∂τ(|g|1/4gστ)=0 which is the conformal analog of the harmonic gauge condition gμνΓμνσ=-|g|-1/2∂τ(|g|1/2gστ)=0, where det⁡[gμν]≡g. Requiring additionally the conformal gauge condition g=-1 surprisingly implies that the waves are both transverse and traceless. Although the ansatz for the metric is eminently reasonable when considering perturbative gravitational waves, we show that the metric is reducible to the metric of Minkowski space-time via a sequence of coordinate transformations which respect the gauge conditions, without any perturbative approximation that γμν be small. This implies that we have, in fact, exact plane-wave solutions; however, they are simply coordinate/conformal artifacts. As a consequence, they carry no energy. Our result does not imply that conformal gravity does not have gravitational wave phenomena. A different, more generalized ansatz for the deviation, taking into account the fourth-order nature of the field equation, which has the form gμν=ημν+Bμν(n·x)G(k·x), indeed yields waves which carry energy and momentum [P. D. Mannheim, Gen. Relativ. Gravit.GRGVA80001-7701 43, 703 (2010)10.1007/s10714-010-1088-z]. It is just surprising that transverse, traceless, plane-fronted gravitational waves, those that would be used in any standard, perturbative, quantum analysis of the theory, simply do not exist.

Enceladus's crust as a non-uniform thin shell: I tidal deformations

NASA Astrophysics Data System (ADS)

Beuthe, Mikael

2018-03-01

The geologic activity at Enceladus's south pole remains unexplained, though tidal deformations are probably the ultimate cause. Recent gravity and libration data indicate that Enceladus's icy crust floats on a global ocean, is rather thin, and has a strongly non-uniform thickness. Tidal effects are enhanced by crustal thinning at the south pole, so that realistic models of tidal tectonics and dissipation should take into account the lateral variations of shell structure. I construct here the theory of non-uniform viscoelastic thin shells, allowing for depth-dependent rheology and large lateral variations of shell thickness and rheology. Coupling to tides yields two 2D linear partial differential equations of the fourth order on the sphere which take into account self-gravity, density stratification below the shell, and core viscoelasticity. If the shell is laterally uniform, the solution agrees with analytical formulas for tidal Love numbers; errors on displacements and stresses are less than 5% and 15%, respectively, if the thickness is less than 10% of the radius. If the shell is non-uniform, the tidal thin shell equations are solved as a system of coupled linear equations in a spherical harmonic basis. Compared to finite element models, thin shell predictions are similar for the deformations due to Enceladus's pressurized ocean, but differ for the tides of Ganymede. If Enceladus's shell is conductive with isostatic thickness variations, surface stresses are approximately inversely proportional to the local shell thickness. The radial tide is only moderately enhanced at the south pole. The combination of crustal thinning and convection below the poles can amplify south polar stresses by a factor of 10, but it cannot explain the apparent time lag between the maximum plume brightness and the opening of tiger stripes. In a second paper, I will study the impact of a non-uniform crust on tidal dissipation.

Learning geosciences from science fictions movies: A quantitative analysis of Pando-magnetism in Avatar.

NASA Astrophysics Data System (ADS)

Martin-Hernandez, F.; Negredo, A. M.; Salguero, J. M.

2015-12-01

Many storylines presenting a geoscientific background are portrayed in science fiction movies. However, this background is often discussed only in qualitative terms in outreach books and forums. Here we report a mentoring experience of an end of degree project carried out in the fourth year of the degree in Physics in the Complutense University of Madrid (Spain). The supervisors intended to take advantage of the students' passion for science fiction movies to foster learning by assessing a robust, quantitative and critical analysis of the main geoscientific phenomena appearing in Avatar movie by James Cameron (2009). The student was supposed to consult abundant scientific literature. Much interest was paid to analyze the conditions for the levitation of Hallelujah floating mountains in Pandora, the imaginary satellite where the movie action takes place. Pandora was assumed to be an Earth-like astronomical object where the same physical laws as in the Earth could be applied. Hallelujah Mountains are made of unobtanium, an electrical superconductor at room-temperature and therefore diamagnetic material and they are assumed to be located over a magnetic field pole. The numerical values of the magnetic susceptibility and the required field to make the material levitate at the Pandora's gravity conditions were estimated. For this purpose, the magnetic susceptibility of the superconductor with the highest critical temperature existing today on Earth, the cuprate YBa2Cu3O7 was estimated. Results were compared with the magnetic susceptibility of two diamagnetic and abundant materials in the Earth's crust, namely quartz and calcite, and with the water susceptibility. The magnetic field required to levitate cuprates was almost 9 T, about six orders of magnitude higher than the Earth's magnetic field. On the basis of the quantitative analysis of magnetic and gravity field in Pandora, the student provided a list of suggestions to improve the scientific basis for futures releases.

Progress in the development of the GMM-2 gravity field model for Mars

NASA Technical Reports Server (NTRS)

Lemoine, F. G.; Smith, D. E.; Lerch, F. J.; Zuber, M. T.; Patel, G. B.

1994-01-01

Last year we published the GMM-1 (Goddard Mars Model-1) gravity model for Mars. We have completely re-analyzed the Viking and Mariner 9 tracking data in the development of the new field, designated GMM-2. The model is complete to degree and order 70. Various aspects of the model are discussed.

15 CFR 754.2 - Crude oil.

Code of Federal Regulations, 2013 CFR

2013-01-01

... gravity of 20.0 degrees API or lower, at an average volume not to exceed 25 MB/D, will be authorized as... that the California heavy crude oil: (i) Has a gravity of 20.0 degrees API or lower; (ii) Was produced... least 2,000 meters water depth). Exceptions can be made at the discretion of the captain only in order...

15 CFR 754.2 - Crude oil.

Code of Federal Regulations, 2012 CFR

2012-01-01

... gravity of 20.0 degrees API or lower, at an average volume not to exceed 25 MB/D, will be authorized as... that the California heavy crude oil: (i) Has a gravity of 20.0 degrees API or lower; (ii) Was produced... least 2,000 meters water depth). Exceptions can be made at the discretion of the captain only in order...

15 CFR 754.2 - Crude oil.

Code of Federal Regulations, 2014 CFR

2014-01-01

... gravity of 20.0 degrees API or lower, at an average volume not to exceed 25 MB/D, will be authorized as... that the California heavy crude oil: (i) Has a gravity of 20.0 degrees API or lower; (ii) Was produced... least 2,000 meters water depth). Exceptions can be made at the discretion of the captain only in order...

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.

Energy scale of Lorentz violation in Rainbow Gravity

NASA Astrophysics Data System (ADS)

Nilsson, Nils A.; Dąbrowski, Mariusz P.

2017-12-01

We modify the standard relativistic dispersion relation in a way which breaks Lorentz symmetry-the effect is predicted in a high-energy regime of some modern theories of quantum gravity. We show that it is possible to realise this scenario within the framework of Rainbow Gravity which introduces two new energy-dependent functions f1(E) and f2(E) into the dispersion relation. Additionally, we assume that the gravitational constant G and the cosmological constant Λ also depend on energy E and introduce the scaling function h(E) in order to express this dependence. For cosmological applications we specify the functions f1 and f2 in order to fit massless particles which allows us to derive modified cosmological equations. Finally, by using Hubble+SNIa+BAO(BOSS+Lyman α)+CMB data, we constrain the energy scale ELV to be at least of the order of 1016 GeV at 1 σ which is the GUT scale or even higher 1017 GeV at 3 σ. Our claim is that this energy can be interpreted as the decoupling scale of massless particles from spacetime Lorentz violating effects.

Moyal deformations of Clifford gauge theories of gravity

NASA Astrophysics Data System (ADS)

Castro, Carlos

2016-12-01

A Moyal deformation of a Clifford Cl(3, 1) Gauge Theory of (Conformal) Gravity is performed for canonical noncommutativity (constant Θμν parameters). In the very special case when one imposes certain constraints on the fields, there are no first-order contributions in the Θμν parameters to the Moyal deformations of Clifford gauge theories of gravity. However, when one does not impose constraints on the fields, there are first-order contributions in Θμν to the Moyal deformations in variance with the previous results obtained by other authors and based on different gauge groups. Despite that the generators of U(2, 2),SO(4, 2),SO(2, 3) can be expressed in terms of the Clifford algebra generators this does not imply that these algebras are isomorphic to the Clifford algebra. Therefore one should not expect identical results to those obtained by other authors. In particular, there are Moyal deformations of the Einstein-Hilbert gravitational action with a cosmological constant to first-order in Θμν. Finally, we provide a mechanism which furnishes a plausible cancellation of the huge vacuum energy density.

Some spectral approximation of one-dimensional fourth-order problems

NASA Technical Reports Server (NTRS)

Bernardi, Christine; Maday, Yvon

1989-01-01

Some spectral type collocation method well suited for the approximation of fourth-order systems are proposed. The model problem is the biharmonic equation, in one and two dimensions when the boundary conditions are periodic in one direction. It is proved that the standard Gauss-Lobatto nodes are not the best choice for the collocation points. Then, a new set of nodes related to some generalized Gauss type quadrature formulas is proposed. Also provided is a complete analysis of these formulas including some new issues about the asymptotic behavior of the weights and we apply these results to the analysis of the collocation method.

Large scale structure constraints for a class of f(R) theories of gravity

NASA Astrophysics Data System (ADS)

Abebe, Amare; de la Cruz-Dombriz, Álvaro; Dunsby, Peter K. S.

2013-08-01

Over the past few years much attention has been given to the study of modified gravity theories in order to find a more natural explanation for the late time acceleration of the Universe. Nevertheless, a comparison of the matter power spectrum predictions made by these theories with available data has not yet been subjected to a detailed analysis. In the context of f(R) theories of gravity we study the predicted power spectra using both a dynamical systems approach for the background and solving for the matter perturbations without using the quasistatic approximation, comparing the theoretical results with several Sloan Digital Sky Survey data. The importance of studying the first order perturbed equations by assuming the correct background evolution and the relevance of the initial conditions are also stressed. We determine the statistical significance in relation to the observational data and demonstrate their conflict with existing observations.

Neutron stars structure in the context of massive gravity

NASA Astrophysics Data System (ADS)

Hendi, S. H.; Bordbar, G. H.; Eslam Panah, B.; Panahiyan, S.

2017-07-01

Motivated by the recent interests in spin-2 massive gravitons, we study the structure of neutron star in the context of massive gravity. The modifications of TOV equation in the presence of massive gravity are explored in 4 and higher dimensions. Next, by considering the modern equation of state for the neutron star matter (which is extracted by the lowest order constrained variational (LOCV) method with the AV18 potential), different physical properties of the neutron star (such as Le Chatelier's principle, stability and energy conditions) are investigated. It is shown that consideration of the massive gravity has specific contributions into the structure of neutron star and introduces new prescriptions for the massive astrophysical objects. The mass-radius relation is examined and the effects of massive gravity on the Schwarzschild radius, average density, compactness, gravitational redshift and dynamical stability are studied. Finally, a relation between mass and radius of neutron star versus the Planck mass is extracted.

Teleparallel theories of gravity as analogue of nonlinear electrodynamics

NASA Astrophysics Data System (ADS)

Hohmann, Manuel; Järv, Laur; Krššák, Martin; Pfeifer, Christian

2018-05-01

The teleparallel formulation of gravity theories reveals close structural analogies to electrodynamics, which are more hidden in their usual formulation in terms of the curvature of spacetime. We show how every locally Lorentz invariant teleparallel theory of gravity with second-order field equations can be understood as built from a gravitational field strength and excitation tensor which are related to each other by a constitutive relation, analogous to the premetric construction of theories of electrodynamics. We demonstrate how the previously studied models of f (T ) and f (Tax,Tten,Tvec) gravity as well as teleparallel dark energy can be formulated in this language. The advantage of this approach to gravity is that the field equations for different models all take the same compact form and general results can be obtained. An important new such result we find is a constraint which relates the field equations of the tetrad and the spin connection.

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.

New observational constraints on f ( T ) gravity from cosmic chronometers

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

Nunes, Rafael C.; Pan, Supriya; Saridakis, Emmanuel N., E-mail: nunes@ecm.ub.edu, E-mail: span@iiserkol.ac.in, E-mail: Emmanuel_Saridakis@baylor.edu

2016-08-01

We use the local value of the Hubble constant recently measured with 2.4% precision, as well as the latest compilation of cosmic chronometers data, together with standard probes such as Supernovae Type Ia and Baryon Acoustic Oscillation distance measurements, in order to impose constraints on the viable and most used f ( T ) gravity models, where T is the torsion scalar in teleparallel gravity. In particular, we consider three f ( T ) models with two parameters, out of which one is independent, and we quantify their deviation from ΛCDM cosmology through a sole parameter. Our analysis reveals thatmore » for one of the models a small but non-zero deviation from ΛCDM cosmology is slightly favored, while for the other models the best fit is very close to ΛCDM scenario. Clearly, f ( T ) gravity is consistent with observations, and it can serve as a candidate for modified gravity.« less

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.

Human evaluation in association to the mathematical analysis of arch forms: Two-dimensional study.

PubMed

Zabidin, Nurwahidah; Mohamed, Alizae Marny; Zaharim, Azami; Marizan Nor, Murshida; Rosli, Tanti Irawati

2018-03-01

To evaluate the relationship between human evaluation of the dental-arch form, to complete a mathematical analysis via two different methods in quantifying the arch form, and to establish agreement with the fourth-order polynomial equation. This study included 64 sets of digitised maxilla and mandible dental casts obtained from a sample of dental arch with normal occlusion. For human evaluation, a convenient sample of orthodontic practitioners ranked the photo images of dental cast from the most tapered to the less tapered (square). In the mathematical analysis, dental arches were interpolated using the fourth-order polynomial equation with millimetric acetate paper and AutoCAD software. Finally, the relations between human evaluation and mathematical objective analyses were evaluated. Human evaluations were found to be generally in agreement, but only at the extremes of tapered and square arch forms; this indicated general human error and observer bias. The two methods used to plot the arch form were comparable. The use of fourth-order polynomial equation may be facilitative in obtaining a smooth curve, which can produce a template for individual arch that represents all potential tooth positions for the dental arch. Copyright © 2018 CEO. Published by Elsevier Masson SAS. All rights reserved.

Analysis of the depletion of a stored aerosol in low gravity

NASA Technical Reports Server (NTRS)

Squires, P.

1977-01-01

The depletion of an aerosol stored in a container has been studied in l-g and in low gravity. Models were developed for sedimentation, coagulation and diffusional losses to the walls. The overall depletion caused by these three mechanisms is predicted to be of order 5 to 8 percent per hour in terrestrial conditions, which agrees with laboratory experience. Applying the models to a low gravity situation indicates that there only coagulation will be significant. (Gravity influences diffusional losses because of convection currents caused by random temperature gradients). For the types of aerosol studied, the rate of depletion of particles should be somewhat less than 0.001 N percent per hour, where N is the concentration per cu cm.

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.

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.

Feynman propagator for spin foam quantum gravity.

PubMed

Oriti, Daniele

2005-03-25

We link the notion causality with the orientation of the spin foam 2-complex. We show that all current spin foam models are orientation independent. Using the technology of evolution kernels for quantum fields on Lie groups, we construct a generalized version of spin foam models, introducing an extra proper time variable. We prove that different ranges of integration for this variable lead to different classes of spin foam models: the usual ones, interpreted as the quantum gravity analogue of the Hadamard function of quantum field theory (QFT) or as inner products between quantum gravity states; and a new class of causal models, the quantum gravity analogue of the Feynman propagator in QFT, nontrivial function of the orientation data, and implying a notion of "timeless ordering".

Engineering applications and analysis of vibratory motion fourth order fluid film over the time dependent heated flat plate

NASA Astrophysics Data System (ADS)

Mohmand, Muhammad Ismail; Mamat, Mustafa Bin; Shah, Qayyum

2017-07-01

This article deals with the time dependent analysis of thermally conducting and Magneto-hydrodynamic (MHD) liquid film flow of a fourth order fluid past a vertical and vibratory plate. In this article have been developed for higher order complex nature fluids. The governing-equations have been modeled in the terms of nonlinear partial differential equations with the help of physical boundary circumstances. Two different analytical approaches i.e. Adomian decomposition method (ADM) and the optimal homotopy asymptotic method (OHAM), have been used for discoveryof the series clarification of the problems. Solutions obtained via two diversemethods have been compared using the graphs, tables and found an excellent contract. Variants of the embedded flow parameters in the solution have been analysed through the graphical diagrams.

Fourth-order self-energy contribution to the Lamb shift

NASA Astrophysics Data System (ADS)

Mallampalli, S.; Sapirstein, J.

1998-03-01

Two-loop self-energy contributions to the fourth-order Lamb shift of ground-state hydrogenic ions are treated to all orders in Zα by using exact Dirac-Coulomb propagators. A rearrangement of the calculation into four ultraviolet finite parts, the M, P, F, and perturbed orbital (PO) terms, is made. Reference-state singularities present in the M and P terms are shown to cancel. The most computationally intensive part of the calculation, the M term, is evaluated for hydrogenlike uranium and bismuth, the F term is evaluated for a range of Z values, but the P term is left for a future calculation. For hydrogenlike uranium, previous calculations of the PO term give -0.971 eV: the contributions from the M and F terms calculated here sum to -0.325 eV.

Space Geodesy, VLBI, and the Fourth Pillar of Geodesy - Spacetime Curvature

NASA Astrophysics Data System (ADS)

Combrinck, Ludwig

2014-12-01

Typically geodesy is described as having ``three pillars'': the variations in Earth's shape, gravity field, and rotation. These pillars form the conceptual and observational basis for the celestial and terrestrial reference frames required for Earth and space observations. However, it is no longer adequate to base the conceptual and observational basis on only three pillars. Spacetime curvature as described by the General Theory of Relativity (GTR) is an integral component of all space geodesy techniques and influences all measurements, techniques, and data reduction. Spacetime curvature is therefore the fourth pillar. It is the measurement of the shape of spacetime and its variations. Due to accuracies of Very Long Baseline Interferometry (VLBI) and optical celestial reference frame measurements reaching the tens of micro-arcsecond level in the near future, it is essential to recognize the impact of spacetime seeing on the accuracy objectives of the Global Geodetic Observing System. Spacetime seeing (resulting from spacetime curvature) is analogous to astronomical seeing (resulting from atmospheric conditions), as all of spacetime is affected by microlensing/weak lensing to some extent as a result of mass (normal baryonic and darkmatter) distribution, placing a limit on the realization of the celestial reference frame.

An atlas of Rapp's 180-th order geopotential.

NASA Astrophysics Data System (ADS)

Melvin, P. J.

1986-08-01

Deprit's 1979 approach to the summation of the spherical harmonic expansion of the geopotential has been modified to spherical components and normalized Legendre polynomials. An algorithm has been developed which produces ten fields at the users option: the undulations of the geoid, three anomalous components of the gravity vector, or six components of the Hessian of the geopotential (gravity gradient). The algorithm is stable to high orders in single precision and does not treat the polar regions as a special case. Eleven contour maps of components of the anomalous geopotential on the surface of the ellipsoid are presented to validate the algorithm.

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.

Connection between quantum systems involving the fourth Painlevé transcendent and k-step rational extensions of the harmonic oscillator related to Hermite exceptional orthogonal polynomial

NASA Astrophysics Data System (ADS)

Marquette, Ian; Quesne, Christiane

2016-05-01

The purpose of this communication is to point out the connection between a 1D quantum Hamiltonian involving the fourth Painlevé transcendent PIV, obtained in the context of second-order supersymmetric quantum mechanics and third-order ladder operators, with a hierarchy of families of quantum systems called k-step rational extensions of the harmonic oscillator and related with multi-indexed Xm1,m2,…,mk Hermite exceptional orthogonal polynomials of type III. The connection between these exactly solvable models is established at the level of the equivalence of the Hamiltonians using rational solutions of the fourth Painlevé equation in terms of generalized Hermite and Okamoto polynomials. We also relate the different ladder operators obtained by various combinations of supersymmetric constructions involving Darboux-Crum and Krein-Adler supercharges, their zero modes and the corresponding energies. These results will demonstrate and clarify the relation observed for a particular case in previous papers.

Computer simulation results for bounds on the effective conductivity of composite media

NASA Astrophysics Data System (ADS)

Smith, P. A.; Torquato, S.

1989-02-01

This paper studies the determination of third- and fourth-order bounds on the effective conductivity σe of a composite material composed of aligned, infinitely long, identical, partially penetrable, circular cylinders of conductivity σ2 randomly distributed throughout a matrix of conductivity σ1. Both bounds involve the microstructural parameter ζ2 which is a multifold integral that depends upon S3, the three-point probability function of the composite. This key integral ζ2 is computed (for the possible range of cylinder volume fraction φ2) using a Monte Carlo simulation technique for the penetrable-concentric-shell model in which cylinders are distributed with an arbitrary degree of impenetrability λ, 0≤λ≤1. Results for the limiting cases λ=0 (``fully penetrable'' or randomly centered cylinders) and λ=1 (``totally impenetrable'' cylinders) compare very favorably with theoretical predictions made by Torquato and Beasley [Int. J. Eng. Sci. 24, 415 (1986)] and by Torquato and Lado [Proc. R. Soc. London Ser. A 417, 59 (1988)], respectively. Results are also reported for intermediate values of λ: cases which heretofore have not been examined. For a wide range of α=σ2/σ1 (conductivity ratio) and φ2, the third-order bounds on σe significantly improve upon second-order bounds which just depend upon φ2. The fourth-order bounds are, in turn, narrower than the third-order bounds. Moreover, when the cylinders are highly conducting (α≫1), the fourth-order lower bound provides an excellent estimate of the effective conductivity for a wide range of volume fractions.

Possible correlation between annual gravity change and shallow background seismicity rate at subduction zone by surface load

NASA Astrophysics Data System (ADS)

Mitsui, Yuta; Yamada, Kyohei

2017-12-01

The Gravity Recovery and Climate Experiment (GRACE) has monitored global gravity changes since 2002. Gravity changes are considered to represent hydrological water mass movements around the surface of the globe, although fault slip of a large earthquake also causes perturbation of gravity. Since surface water movements are expected to affect earthquake occurrences via elastic surface load or pore-fluid pressure increase, correlation between gravity changes and occurrences of small (not large) earthquakes may reflect the effects of surface water movements. In the present study, we focus on earthquakes smaller than magnitude 7.5 and examine the relation between annual gravity changes and earthquake occurrences at worldwide subduction zones. First, we extract amplitudes of annual gravity changes from GRACE data for land. Next, we estimate background seismicity rates in the epidemic-type aftershock sequence model from shallow seismicity data having magnitudes of over 4.5. Then, we perform correlation analysis of the amplitudes of the annual gravity changes and the shallow background seismicity rates, excluding source areas of large earthquakes, and find moderate positive correlation. It implies that annual water movements can activate shallow earthquakes, although the surface load elastostatic stress changes are on the order of or below 1 kPa, as small as a regional case in a previous study. We speculate that periodic stress perturbation is amplified through nonlinear responses of frictional faults.[Figure not available: see fulltext.

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.

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.

An improved rotated staggered-grid finite-difference method with fourth-order temporal accuracy for elastic-wave modeling in anisotropic media

DOE PAGES

Gao, Kai; Huang, Lianjie

2017-08-31

The rotated staggered-grid (RSG) finite-difference method is a powerful tool for elastic-wave modeling in 2D anisotropic media where the symmetry axes of anisotropy are not aligned with the coordinate axes. We develop an improved RSG scheme with fourth-order temporal accuracy to reduce the numerical dispersion associated with prolonged wave propagation or a large temporal step size. The high-order temporal accuracy is achieved by including high-order temporal derivatives, which can be converted to high-order spatial derivatives to reduce computational cost. Dispersion analysis and numerical tests show that our method exhibits very low temporal dispersion even with a large temporal step sizemore » for elastic-wave modeling in complex anisotropic media. Using the same temporal step size, our method is more accurate than the conventional RSG scheme. In conclusion, our improved RSG scheme is therefore suitable for prolonged modeling of elastic-wave propagation in 2D anisotropic media.« less

Rogue waves generation in a left-handed nonlinear transmission line with series varactor diodes

NASA Astrophysics Data System (ADS)

Onana Essama, B. G.; Atangana, J.; Biya Motto, F.; Mokhtari, B.; Cherkaoui Eddeqaqi, N.; Kofane, Timoleon C.

2014-07-01

We investigate the electromagnetic wave behavior and its characterization using collective variables technique. Second-order dispersion, first- and second-order nonlinearities, which strongly act in a left-handed nonlinear transmission line with series varactor diodes, are taken into account. Four frequency ranges have been found. The first one gives the so-called energetic soliton due to a perfect combination of second-order dispersion and first-order nonlinearity. The second frequency range presents a dispersive soliton leading to the collapse of the electromagnetic wave at the third frequency range. But the fourth one shows physical conditions which are able to provoke the appearance of wave trains generation with some particular waves, the rogue waves. Moreover, we demonstrate that the number of rogue waves increases with frequency. The soliton, thereafter, gains a relative stability when second-order nonlinearity comes into play with some specific values in the fourth frequency range. Furthermore, the stability conditions of the electromagnetic wave at high frequencies have been also discussed.

An improved rotated staggered-grid finite-difference method with fourth-order temporal accuracy for elastic-wave modeling in anisotropic media

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

Gao, Kai; Huang, Lianjie

The rotated staggered-grid (RSG) finite-difference method is a powerful tool for elastic-wave modeling in 2D anisotropic media where the symmetry axes of anisotropy are not aligned with the coordinate axes. We develop an improved RSG scheme with fourth-order temporal accuracy to reduce the numerical dispersion associated with prolonged wave propagation or a large temporal step size. The high-order temporal accuracy is achieved by including high-order temporal derivatives, which can be converted to high-order spatial derivatives to reduce computational cost. Dispersion analysis and numerical tests show that our method exhibits very low temporal dispersion even with a large temporal step sizemore » for elastic-wave modeling in complex anisotropic media. Using the same temporal step size, our method is more accurate than the conventional RSG scheme. In conclusion, our improved RSG scheme is therefore suitable for prolonged modeling of elastic-wave propagation in 2D anisotropic media.« less

Investigation of the factor structure of the Wechsler Adult Intelligence Scale--Fourth Edition (WAIS-IV): exploratory and higher order factor analyses.

PubMed

Canivez, Gary L; Watkins, Marley W

2010-12-01

The present study examined the factor structure of the Wechsler Adult Intelligence Scale--Fourth Edition (WAIS-IV; D. Wechsler, 2008a) standardization sample using exploratory factor analysis, multiple factor extraction criteria, and higher order exploratory factor analysis (J. Schmid & J. M. Leiman, 1957) not included in the WAIS-IV Technical and Interpretation Manual (D. Wechsler, 2008b). Results indicated that the WAIS-IV subtests were properly associated with the theoretically proposed first-order factors, but all but one factor-extraction criterion recommended extraction of one or two factors. Hierarchical exploratory analyses with the Schmid and Leiman procedure found that the second-order g factor accounted for large portions of total and common variance, whereas the four first-order factors accounted for small portions of total and common variance. It was concluded that the WAIS-IV provides strong measurement of general intelligence, and clinical interpretation should be primarily at that level.

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.

Estimating Jupiter’s Gravity Field Using Juno Measurements, Trajectory Estimation Analysis, and a Flow Model Optimization

NASA Astrophysics Data System (ADS)

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

2017-07-01

The upcoming Juno spacecraft measurements have the potential of improving our knowledge of Jupiter’s gravity field. The analysis of the Juno Doppler data will provide a very accurate reconstruction of spatial gravity variations, but these measurements will be very accurate only over a limited latitudinal range. In order to deduce the full gravity field of Jupiter, additional information needs to be incorporated into the analysis, especially regarding the Jovian flow structure and its depth, which can influence the measured gravity field. In this study we propose a new iterative method for the estimation of the Jupiter gravity field, using a simulated Juno trajectory, a trajectory estimation model, and an adjoint-based inverse model for the flow dynamics. We test this method both for zonal harmonics only and with a full gravity field including tesseral harmonics. The results show that this method can fit some of the gravitational harmonics better to the “measured” harmonics, mainly because of the added information from the dynamical model, which includes the flow structure. Thus, it is suggested that the method presented here has the potential of improving the accuracy of the expected gravity harmonics estimated from the Juno and Cassini radio science experiments.

Estimating Jupiter’s Gravity Field Using Juno Measurements, Trajectory Estimation Analysis, and a Flow Model Optimization

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

Galanti, Eli; Kaspi, Yohai; Durante, Daniele

The upcoming Juno spacecraft measurements have the potential of improving our knowledge of Jupiter’s gravity field. The analysis of the Juno Doppler data will provide a very accurate reconstruction of spatial gravity variations, but these measurements will be very accurate only over a limited latitudinal range. In order to deduce the full gravity field of Jupiter, additional information needs to be incorporated into the analysis, especially regarding the Jovian flow structure and its depth, which can influence the measured gravity field. In this study we propose a new iterative method for the estimation of the Jupiter gravity field, using a simulatedmore » Juno trajectory, a trajectory estimation model, and an adjoint-based inverse model for the flow dynamics. We test this method both for zonal harmonics only and with a full gravity field including tesseral harmonics. The results show that this method can fit some of the gravitational harmonics better to the “measured” harmonics, mainly because of the added information from the dynamical model, which includes the flow structure. Thus, it is suggested that the method presented here has the potential of improving the accuracy of the expected gravity harmonics estimated from the Juno and Cassini radio science experiments.« less

Advanced Multivariate Inversion Techniques for High Resolution 3D Geophysical Modeling (Invited)

NASA Astrophysics Data System (ADS)

Maceira, M.; Zhang, H.; Rowe, C. A.

2009-12-01

We focus on the development and application of advanced multivariate inversion techniques to generate a realistic, comprehensive, and high-resolution 3D model of the seismic structure of the crust and upper mantle that satisfies several independent geophysical datasets. Building on previous efforts of joint invesion using surface wave dispersion measurements, gravity data, and receiver functions, we have added a fourth dataset, seismic body wave P and S travel times, to the simultaneous joint inversion method. We present a 3D seismic velocity model of the crust and upper mantle of northwest China resulting from the simultaneous, joint inversion of these four data types. Surface wave dispersion measurements are primarily sensitive to seismic shear-wave velocities, but at shallow depths it is difficult to obtain high-resolution velocities and to constrain the structure due to the depth-averaging of the more easily-modeled, longer-period surface waves. Gravity inversions have the greatest resolving power at shallow depths, and they provide constraints on rock density variations. Moreover, while surface wave dispersion measurements are primarily sensitive to vertical shear-wave velocity averages, body wave receiver functions are sensitive to shear-wave velocity contrasts and vertical travel-times. Addition of the fourth dataset, consisting of seismic travel-time data, helps to constrain the shear wave velocities both vertically and horizontally in the model cells crossed by the ray paths. Incorporation of both P and S body wave travel times allows us to invert for both P and S velocity structure, capitalizing on empirical relationships between both wave types’ seismic velocities with rock densities, thus eliminating the need for ad hoc assumptions regarding the Poisson ratios. Our new tomography algorithm is a modification of the Maceira and Ammon joint inversion code, in combination with the Zhang and Thurber TomoDD (double-difference tomography) program.

Probing hybrid modified gravity by stellar motion around Galactic Center

NASA Astrophysics Data System (ADS)

Borka, D.; Capozziello, S.; Jovanović, P.; Borka Jovanović, V.

2016-06-01

We consider possible signatures for the so called hybrid gravity within the Galactic Central Parsec. This modified theory of gravity consists of a superposition of the metric Einstein-Hilbert Lagrangian with an f(R) term constructed à la Palatiniand can be easily reduced to an equivalent scalar-tensor theory. Such an approach is introduced in order to cure the shortcomings related to f(R) gravity, in general formulated either in metric or in metric-affine frameworks. Hybrid gravity allows to disentangle the further gravitational degrees of freedom with respect to those of standard General Relativity. The present analysis is based on the S2 star orbital precession around the massive compact dark object at the Galactic Center where the simulated orbits in hybrid modified gravity are compared with astronomical observations. These simulations result with constraints on the range of hybrid gravity interaction parameter ϕ0, showing that in the case of S2 star it is between -0.0009 and -0.0002. At the same time, we are also able to obtain the constraints on the effective mass parameter mϕ, and found that it is between -0.0034 and -0.0025 AU-1 for S2 star. Furthermore, the hybrid gravity potential induces precession of S2 star orbit in the same direction as General Relativity. In previous papers, we considered other types of extended gravities, like metric power law f(R)∝Rn gravity, inducing Yukawa and Sanders-like gravitational potentials, but it seems that hybrid gravity is the best among these models to explain different gravitational phenomena at different astronomical scales.

Hybrid gravity survey to search for submarine ore deposit

NASA Astrophysics Data System (ADS)

Araya, A.; Kanazawa, T.; Fujimoto, H.; Shinohara, M.; Yamada, T.; Mochizuki, K.; Iizasa, K.; Ishihara, T.; Omika, S.

2011-12-01

Along with seismic surveys, gravity survey is a useful method to profile the underground density structure. We propose a hybrid gravity survey using gravimeters and gravity gradiometers to detect submarine ore deposits as density anomalies by towing the instruments using an AUV (Autonomous Underwater Vehicle) or an ROV (Remotely Operated Vehicle). Gravimeters measure the regional density structure below the seafloor, whereas gravity gradiometers are sensitive to localized mass distribution. A gravity gradiometer comprises two accelerometers arranged with a vertical separation, and a gravity gradient can be obtained from the acceleration difference. Compared to gravimeters, gravity gradiometers are insensitive to common disturbances such as parallel acceleration, thermal drift, and apparent gravity effect (Eötvös effect). We made two accelerometers using astatic pendulums, and obtained common acceleration reduction more than two orders of magnitude. With these pendulums of 500-mm separation, resolution of 7E (=7x10^{-9}(1/s^2)), enough to detect a typical ore deposit buried 50m below the seafloor, was evaluated. During measurements using a submersible mobile object, instrument orientation is required to be controlled to keep verticality and to reduce centrifugal force associated with rotation of the instrument. Using a gyro and a tiltmeter, angular rotation was shown to be controlled within 0.001deg/s which corresponds to 0.3E in effective gravity gradient due to the centrifugal force. In this paper, target of this research, details of the instruments and their performance, and development for the submarine gravity survey using an AUV will be presented.

Test Review: Abidin, R. R. (2012) "Parenting Stress Index, Fourth Edition" ("PSI-4"). Lutz, Florida: Psychological Assessment Resources

ERIC Educational Resources Information Center

Johnson, Alyce O.

2015-01-01

The "Parenting Stress Index, Fourth Edition" (PSI-4) is a 120-item measure used to explore parental stress levels considering a parent's relationship with one of his or her children between the ages of 1 month and 12 years. The main purpose of the test is to define these stress levels and from where they originate in order to identify…

Acceleration levels on board the Space Station and a tethered elevator for micro and variable-gravity applications

NASA Technical Reports Server (NTRS)

Lorenzini, E. C.; Cosmo, M.; Vetrella, S.; Moccia, A.

1988-01-01

This paper investigates the dynamics and acceleration levels of a new tethered system for micro and variable-gravity applications. The system consists of two platforms tethered on opposite sides to the Space Station. A fourth platform, the elevator, is placed in between the Space Station and the upper platform. Variable-g levels on board the elevator are obtained by moving this facility along the upper tether, while micro-g experiments are carried out on board the Space Station. By controlling the length of the lower tether the position of the system CM can be maintained on board the Space Station despite variations of the station's distribution of mass. The paper illustrates the mathematical model, the environmental perturbations and the control techniques which have been adopted for the simulation and control of the system dynamics. Two sets of results from two different simulation runs are shown. The first set shows the system dynamics and the acceleration spectra on board the Space Station and the elevator during station-keeping. The second set of results demonstrates the capability of the elevator to attain a preselected g-level.

A surface spherical harmonic expansion of gravity anomalies on the ellipsoid

NASA Astrophysics Data System (ADS)

Claessens, S. J.; Hirt, C.

2015-10-01

A surface spherical harmonic expansion of gravity anomalies with respect to a geodetic reference ellipsoid can be used to model the global gravity field and reveal its spectral properties. In this paper, a direct and rigorous transformation between solid spherical harmonic coefficients of the Earth's disturbing potential and surface spherical harmonic coefficients of gravity anomalies in ellipsoidal approximation with respect to a reference ellipsoid is derived. This transformation cannot rigorously be achieved by the Hotine-Jekeli transformation between spherical and ellipsoidal harmonic coefficients. The method derived here is used to create a surface spherical harmonic model of gravity anomalies with respect to the GRS80 ellipsoid from the EGM2008 global gravity model. Internal validation of the model shows a global RMS precision of 1 nGal. This is significantly more precise than previous solutions based on spherical approximation or approximations to order or , which are shown to be insufficient for the generation of surface spherical harmonic coefficients with respect to a geodetic reference ellipsoid. Numerical results of two applications of the new method (the computation of ellipsoidal corrections to gravimetric geoid computation, and area means of gravity anomalies in ellipsoidal approximation) are provided.

The dynamic representation of gravity is suspended when the idiotropic vector is misaligned with gravity.

PubMed

De Sá Teixeira, Nuno Alexandre; Hecht, Heiko

2014-01-01

When people are asked to indicate the vanishing location of a moving target, errors in the direction of motion (representational momentum) and in the direction of gravity (representational gravity) are usually found. These errors possess a temporal course wherein the memory for the location of the target drifts downwards with increasing temporal intervals between target's disappearance and participant's responses (representational trajectory). To assess if representational trajectory is a body-referenced or a world-referenced phenomenon. A behavioral localization method was employed with retention times between 0 and 1400 ms systematically imposed after the target's disappearance. The target could move horizontally (rightwards or leftwards) or vertically (upwards or downwards). Body posture was varied in a counterbalanced order between sitting upright and lying on the side (left lateral decubitus position). In the upright task, the memory for target location drifted downwards with time in the direction of gravity. This time course did not emerge for the decubitus task, where idiotropic dominance was found. The dynamic visual representation of gravity is neither purely body-referenced nor world-referenced. It seems to be modulated instead by the relationship between the idiotropic vector and physical gravity.

Woods from the Miocene Bakate Formation, Ethiopia : anatomical characteristics, estimates of original specific gravity and ecological inferences

Treesearch

E.A. Wheeler; M.C. Wiemann; J.G. Fleagle

2007-01-01

An assemblage of permineralized woods from the Miocene Bakate Formation, Fejej Plain, Ethiopia, is described. This assemblage of twelve wood types differs from other Miocene wood assemblages known from Ethiopia. Cell wall percentages of the woods were determined to estimate the original specific gravities of the woods in order to better understand the Miocene...

g--Acceleration of Gravity: Its Measurement from the Shape of Water by Using a Computerized Rotational System

ERIC Educational Resources Information Center

Pintao, Carlos A. F.; de Souza Filho, Moacir P.

2007-01-01

This paper proposes a different experimental setup compared with the traditional ones, in order to determine the acceleration of gravity, which is carried out by using a fluid at a constant rotation. A computerized rotational system--by using a data acquisition system with specific software, a power amplifier and a rotary motion sensor--is…

Cosmology based on f(R) gravity admits 1 eV sterile neutrinos.

PubMed

Motohashi, Hayato; Starobinsky, Alexei A; Yokoyama, Jun'ichi

2013-03-22

It is shown that the tension between recent neutrino oscillation experiments, favoring sterile neutrinos with masses of the order of 1 eV, and cosmological data which impose stringent constraints on neutrino masses from the free streaming suppression of density fluctuations, can be resolved in models of the present accelerated expansion of the Universe based on f(R) gravity.

Altitude valve for railway suspension control system

NASA Astrophysics Data System (ADS)

Zhang, Xuan; Zhang, Lihao; Li, Qingxuan; Chen, WanSong

2017-09-01

With the variation of people and material during vehicle service, the gravity of vehicle could be unbalanced. As a result it might cause accident. In order to solve this problem, altitude valve is assembled on board. It can adjust the gravity of vehicle by the intake and outlet progress of the spring in the altitude valve to prevent the tilt of vehicles.

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.

Experiments to ensure Space Station fire safety - A challenge

NASA Technical Reports Server (NTRS)

Youngblood, W. W.; Seiser, K. M.

1988-01-01

Three experiments have been formulated in order to address prominent fire safety requirements aboard the NASA Space Shuttle; these experiments are to be conducted as part of a Space Station-based Technology Development Mission for the growth phase of Space Station construction and operation. The experiments are: (1) an investigation of the flame-spread rate and combustion-product evolution in the burning of typical spacecraft materials in low gravity; (2) an evaluation of the interaction of fires and candidate fire extinguishers in low gravity; and (3) an investigation of the persistence and propagation of smoldering and deep-seated combustion in low gravity.

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.

From SL(5, ℝ) Yang-Mills theory to induced gravity

NASA Astrophysics Data System (ADS)

Assimos, T. S.; Pereira, A. D.; Santos, T. R. S.; Sobreiro, R. F.; Tomaz, A. A.; Otoya, V. J. Vasquez

From pure Yang-Mills action for the SL(5, ℝ) group in four Euclidean dimensions we obtain a gravity theory in the first order formalism. Besides the Einstein-Hilbert term, the effective gravity has a cosmological constant term, a curvature squared term, a torsion squared term and a matter sector. To obtain such geometrodynamical theory, asymptotic freedom and the Gribov parameter (soft BRST symmetry breaking) are crucial. Particularly, Newton and cosmological constant are related to these parameters and they also run as functions of the energy scale. One-loop computations are performed and the results are interpreted.

Stellar and Circumstellar Properties of the Pre-Main-Sequence Binary GV Tau From Infrared Spectroscopy

DTIC Science & Technology

2008-09-20

surface gravity . With ourL-band spectra in order 25 (3.0450Y3.0865m;Fig. 1e), we detect strong HCN absorption (10% deep) and weaker C2H2 absorption in...Doppmann et al. 2005). The absorption lines of Na i and Mg i are particularly gravity and temperature sensitive, but in the opposite sense from each...other. For example, at cool effective temperatures (3200Y4500 K) and subdwarf surface gravities (3:5 log g 4:5) Na andMg lines both grow stronger as

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.

The Geoid Slope Validation Survey 2014 and GRAV-D airborne gravity enhanced geoid comparison results in Iowa

NASA Astrophysics Data System (ADS)

Wang, Y. M.; Becker, C.; Mader, G.; Martin, D.; Li, X.; Jiang, T.; Breidenbach, S.; Geoghegan, C.; Winester, D.; Guillaume, S.; Bürki, B.

2017-10-01

Three Geoid Slope Validation Surveys were planned by the National Geodetic Survey for validating geoid improvement gained by incorporating airborne gravity data collected by the "Gravity for the Redefinition of the American Vertical Datum" (GRAV-D) project in flat, medium and rough topographic areas, respectively. The first survey GSVS11 over a flat topographic area in Texas confirmed that a 1-cm differential accuracy geoid over baseline lengths between 0.4 and 320 km is achievable with GRAV-D data included (Smith et al. in J Geod 87:885-907, 2013). The second survey, Geoid Slope Validation Survey 2014 (GSVS14) took place in Iowa in an area with moderate topography but significant gravity variation. Two sets of geoidal heights were computed from GPS/leveling data and observed astrogeodetic deflections of the vertical at 204 GSVS14 official marks. They agree with each other at a {± }1.2 cm level, which attests to the high quality of the GSVS14 data. In total, four geoid models were computed. Three models combined the GOCO03/5S satellite gravity model with terrestrial and GRAV-D gravity with different strategies. The fourth model, called xGEOID15A, had no airborne gravity data and served as the benchmark to quantify the contribution of GRAV-D to the geoid improvement. The comparisons show that each model agrees with the GPS/leveling geoid height by 1.5 cm in mark-by-mark comparisons. In differential comparisons, all geoid models have a predicted accuracy of 1-2 cm at baseline lengths from 1.6 to 247 km. The contribution of GRAV-D is not apparent due to a 9-cm slope in the western 50-km section of the traverse for all gravimetric geoid models, and it was determined that the slopes have been caused by a 5 mGal bias in the terrestrial gravity data. If that western 50-km section of the testing line is excluded in the comparisons, then the improvement with GRAV-D is clearly evident. In that case, 1-cm differential accuracy on baselines of any length is achieved with the GRAV-D-enhanced geoid models and exhibits a clear improvement over the geoid models without GRAV-D data. GSVS14 confirmed that the geoid differential accuracies are in the 1-2 cm range at various baseline lengths. The accuracy increases to 1 cm with GRAV-D gravity when the west 50 km line is not included. The data collected by the surveys have high accuracy and have the potential to be used for validation of other geodetic techniques, e.g., the chronometric leveling. To reach the 1-cm height differences of the GSVS data, a clock with frequency accuracy of 10^{-18} is required. Using the GSVS data, the accuracy of ellipsoidal height differences can also be estimated.

A new formula of the Gravitational Curvature for the prism

NASA Astrophysics Data System (ADS)

Grazia D'Urso, Maria

2017-04-01

Gravitational Curvatures (GC) are the components of the third-order gravitational tensor and physically represent the rate of change of the gravity gradient. While scalar, vector and second-order tensor quantities of the Earth's gravitational field have extensively been studied and their properties have been well understood [1], the first successful terrestrial measurements of the third-order vertical gravitational gradients have been recently performed in [2] by atom interferometry sensors in laboratory environment. Possible benefits of the airborne third-order gravitational gradients for exploration geophysics are discussed in [3] while Brieden et al. (2010) [4] have proposed a new satellite mission called OPTical Interferometry for global Mass change detection from space (OPTIMA) sensing the third-order gravitational gradients in space. Moreover, exploitation of GC for modelling the Earth's gravitational field has been object of recent studies [5-7]. We extend the approach presented by the author in previous papers [8-10] by evaluating the algebraic expression of the third-order gravitational tensor for a prism. Comparisons with previous results [11-12] are also included. [1] Freeden W, Schreiner M (2009) Spherical functions of mathematical geosciences. A scalar, vectorial, and tensorial setup. In: Advances in geophysical and environmental mechanics and mathematics. Springer, Berlin [2] Rosi G, Cacciapuoti L, Sorrentino F, Menchetti M, Prevedelli M, Tino GM (2015) Measurements of the gravity-field curvature by atom interferometry. Phys Rev Lett 114:013001 [3] Di Francesco D, Meyer T, Christensen A, FitzGerald D (2009) Gravity gradiometry - today and tomorrow. In: 11th SAGA Biennial technical meeting and exhibition, 13-18 September 2009, Switzerland, pp 80-83 [4] Brieden P, Müller J, Flury J, Heinzel G (2010) The mission OPTIMA - novelties and benefit. In: Geotechnologien science report No. 17, Potsdam, pp 134-139 [5] Šprlák M, Novák P (2015) Integral formulas for computing a third-order gravitational tensor from volumetric mass density, disturbing gravitational potential, gravity anomaly and gravity disturbance. J Geod 89:141-157 [6] Šprlák M, Novák P (2016) Spherical gravitational curvature boundary-value problem. J Geod 90:727-739 [7] Hamáčková E, Šprlák M , Pitoňák M, Novák P (2016) Non-singular expressions for the spherical harmonic synthesis of gravitational curvatures in a local north-oriented reference frame. Comp & Geosc 88: 152-162 [8] D'Urso MG (2012) New expressions of the gravitational potential and its derivates for the prism. In Hotine-Marussi International Symposium on Mathematical Geodesy, 7rd. Sneeuw N, Novak P, Crespi M, Sansò F. Springer-Verlag, Berlin Heidelberg pp. 251-256 [9] D'Urso MG (2013) On the evaluation of the gravity effects of polyhedral bodies and a consistent treatment of related singularities. J Geod 87:239-252 [10] D'Urso MG (2014)Analytical computation of gravity effects for polyhedral bodies. J Geod 88:13-29 [11] Nagy D, Papp G, Benedek J (2000) The gravitational potential and its derivatives for the prism. J Geod 74:552-560 [12] Holstein H, Fitzgerald DJ, H. Stefanov H (2013) Gravimagnetic similarity for homogeneous rectangular prisms. 75th EAGE Conference & Exhibition, London

Integrated Analysis on Gravity and Magnetic Fields of the Hailar Basin, NE China: Implications for Basement Structure and Deep Tectonics

NASA Astrophysics Data System (ADS)

Sun, Bin; Wang, Liangshu; Dong, Ping; Wu, YongJing; Li, Changbo; Hu, Bo; Wang, Chong

2012-11-01

The Hailar Basin is one of the typical basins among the NE China Basin Groups, which is situated in the east of East Asia Orogene between the Siberia Plate and the North China Plate. Based on the detailed analysis of magnetic, gravity, petrophysical, geothermal and seismological data, we separate the Gravity and Magnetic Anomalies (GMA) into four orders using Wavelet Multi-scale Decomposition (WMD). The apparent depths of causative sources were then assessed by Power Spectrum Analysis (PSA) of each order. Low-order wavelet detail anomalies were used to study the basin's basement structure such as major faults, the basement lithology, uplifts and depressions. High-order ones were used for the inversion of Moho and Curie discontinuities using the Parker method. The results show that the Moho uplifting area of the Hailar Basin is located at the NE part of the basin, the Curie uplifting area is at the NW part, and neither of them is consistent with the basin's sedimentary center. This indicates that the Hailar Basin may differ in basin building pattern from other middle and eastern basins of the basin groups, and the Hailar Basin might be of a passive type. When the Pacific Plate was subducting to NE China, the frontier of the plate lying on the mantle transition zone didn't pass through the Great Khingan Mountains region, so there is not an obvious magma upwelling or lithospheric extension in the Hailar Basin area. Finally, based on the seismological data and results of WMD, a probable 2D crust model is derived from an across-basin profile using the 2D forward modeling of the Bouguer gravity anomaly. The results agree with those from seismic inversion, suggesting WMD is suitable for identifying major crustal density interfaces.

Predictive simulation of gait at low gravity reveals skipping as the preferred locomotion strategy

PubMed Central

Ackermann, Marko; van den Bogert, Antonie J.

2012-01-01

The investigation of gait strategies at low gravity environments gained momentum recently as manned missions to the Moon and to Mars are reconsidered. Although reports by astronauts of the Apollo missions indicate alternative gait strategies might be favored on the Moon, computational simulations and experimental investigations have been almost exclusively limited to the study of either walking or running, the locomotion modes preferred under Earth's gravity. In order to investigate the gait strategies likely to be favored at low gravity a series of predictive, computational simulations of gait are performed using a physiological model of the musculoskeletal system, without assuming any particular type of gait. A computationally efficient optimization strategy is utilized allowing for multiple simulations. The results reveal skipping as more efficient and less fatiguing than walking or running and suggest the existence of a walk-skip rather than a walk-run transition at low gravity. The results are expected to serve as a background to the design of experimental investigations of gait under simulated low gravity. PMID:22365845

Predictive simulation of gait at low gravity reveals skipping as the preferred locomotion strategy.

PubMed

Ackermann, Marko; van den Bogert, Antonie J

2012-04-30

The investigation of gait strategies at low gravity environments gained momentum recently as manned missions to the Moon and to Mars are reconsidered. Although reports by astronauts of the Apollo missions indicate alternative gait strategies might be favored on the Moon, computational simulations and experimental investigations have been almost exclusively limited to the study of either walking or running, the locomotion modes preferred under Earth's gravity. In order to investigate the gait strategies likely to be favored at low gravity a series of predictive, computational simulations of gait are performed using a physiological model of the musculoskeletal system, without assuming any particular type of gait. A computationally efficient optimization strategy is utilized allowing for multiple simulations. The results reveal skipping as more efficient and less fatiguing than walking or running and suggest the existence of a walk-skip rather than a walk-run transition at low gravity. The results are expected to serve as a background to the design of experimental investigations of gait under simulated low gravity. Copyright © 2012 Elsevier Ltd. All rights reserved.

The hidden flat like universe. Starobinsky-like inflation induced by f (T) gravity

NASA Astrophysics Data System (ADS)

El Hanafy, W.; Nashed, G. G. L.

2015-06-01

We study a single-fluid component in a flat like universe (FLU) governed by f( T) gravity theories, where T is the teleparallel torsion scalar. The FLU model, regardless of the value of the spatial curvature k, identifies a special class of f( T) gravity theories. Remarkably, FLU f( T) gravity does not reduce to teleparallel gravity theory. In large Hubble spacetime the theory is consistent with the inflationary universe scenario and respects the conservation principle. The equation of state evolves similarly in all models . We study the case when the torsion tensor consists of a scalar field, which enables to derive a quintessence potential from the obtained f( T) gravity theory. The potential produces Starobinsky-like model naturally without using a conformal transformation, with higher orders continuously interpolate between Starobinsky and quadratic inflation models. The slow-roll analysis shows double solutions, so that for a single value of the scalar tilt (spectral index) the theory can predict double tensor-to-scalar ratios r of E-mode and B-mode polarizations.

Venus Gravity Handbook

NASA Technical Reports Server (NTRS)

Konopliv, Alexander S.; Sjogren, William L.

1996-01-01

This report documents the Venus gravity methods and results to date (model MGNP90LSAAP). It is called a handbook in that it contains many useful plots (such as geometry and orbit behavior) that are useful in evaluating the tracking data. We discuss the models that are used in processing the Doppler data and the estimation method for determining the gravity field. With Pioneer Venus Orbiter and Magellan tracking data, the Venus gravity field was determined complete to degree and order 90 with the use of the JPL Cray T3D Supercomputer. The gravity field shows unprecedented high correlation with topography and resolution of features to the 2OOkm resolution. In the procedure for solving the gravity field, other information is gained as well, and, for example, we discuss results for the Venus ephemeris, Love number, pole orientation of Venus, and atmospheric densities. Of significance is the Love number solution which indicates a liquid core for Venus. The ephemeris of Venus is determined to an accuracy of 0.02 mm/s (tens of meters in position), and the rotation period to 243.0194 +/- 0.0002 days.

Gravity and geoid anomalies of the Philippine Sea: Evidence on the depth of compensation for the negative residual water depth anomaly

NASA Technical Reports Server (NTRS)

Bowin, C.

1982-01-01

A negative free-air gravity anomaly which occurs in the central part of the Philippine Sea was examined to determine the distribution and nature of possible regional mass excesses or deficiencies. Geoid anomalies from GEOS-3 observation were positive. A negative residual geoid anomaly consistent with the area of negative free-air gravity anomalies were found. Theoretical gravity-topography and geoid-topography admittance functions indicated that high density mantle at about 60 km dept could account for the magnitudes of the gravity and residual geoid anomaly and the 1 km residual water depth anomaly in the Philippine Sea. The negative residual depth anomaly may be compensated for by excess density in the uppermost mantle, but the residual geoid and regional free-air gravity anomalies and a slow surface wave velocity structure might result from low-density warm upper mantle material lying beneath the zone of high-density uppermost mantle. From a horizontal disk approximation, the depth of the low-density warm mantle was estimated to be on the order of 200 km.

Equation of state in the presence of gravity

NASA Astrophysics Data System (ADS)

Kim, Hyeong-Chan; Kang, Gungwon

2016-11-01

We investigate how an equation of state for matter is affected when a gravity is present. For this purpose, we consider a box of ideal gas in the presence of Newtonian gravity. In addition to the ordinary thermodynamic quantities, a characteristic variable that represents a weight per unit area relative to the average pressure is required in order to describe a macroscopic state of the gas. Although the density and the pressure are not uniform due to the presence of gravity, the ideal gas law itself is satisfied for the thermodynamic quantities when averaged over the system. Assuming that the system follows an adiabatic process further, we obtain a new relation between the averaged pressure and density, which differs from the conventional equation of state for the ideal gas in the absence of gravity. Applying our results to a small volume in a Newtonian star, however, we find that the conventional one is reliable for most astrophysical situations when the characteristic scale is small. On the other hand, gravity effects become significant near the surface of a Newtonian star.

Clustering of galaxies with f(R) gravity

NASA Astrophysics Data System (ADS)

Capozziello, Salvatore; Faizal, Mir; Hameeda, Mir; Pourhassan, Behnam; Salzano, Vincenzo; Upadhyay, Sudhaker

2018-02-01

Based on thermodynamics, we discuss the galactic clustering of expanding Universe by assuming the gravitational interaction through the modified Newton's potential given by f(R) gravity. We compute the corrected N-particle partition function analytically. The corrected partition function leads to more exact equations of state of the system. By assuming that the system follows quasi-equilibrium, we derive the exact distribution function that exhibits the f(R) correction. Moreover, we evaluate the critical temperature and discuss the stability of the system. We observe the effects of correction of f(R) gravity on the power-law behaviour of particle-particle correlation function also. In order to check the feasibility of an f(R) gravity approach to the clustering of galaxies, we compare our results with an observational galaxy cluster catalogue.

Chapter 3: Circum-Arctic mapping project: New magnetic and gravity anomaly maps of the Arctic

USGS Publications Warehouse

Gaina, C.; Werner, S.C.; Saltus, R.; Maus, S.; Aaro, S.; Damaske, D.; Forsberg, R.; Glebovsky, V.; Johnson, Kevin; Jonberger, J.; Koren, T.; Korhonen, J.; Litvinova, T.; Oakey, G.; Olesen, O.; Petrov, O.; Pilkington, M.; Rasmussen, T.; Schreckenberger, B.; Smelror, M.

2011-01-01

New Circum-Arctic maps of magnetic and gravity anomalies have been produced by merging regional gridded data. Satellite magnetic and gravity data were used for quality control of the long wavelengths of the new compilations. The new Circum-Arctic digital compilations of magnetic, gravity and some of their derivatives have been analyzed together with other freely available regional and global data and models in order to provide a consistent view of the tectonically complex Arctic basins and surrounding continents. Sharp, linear contrasts between deeply buried basement blocks with different magnetic properties and densities that can be identified on these maps can be used, together with other geological and geophysical information, to refine the tectonic boundaries of the Arctic domain. ?? 2011 The Geological Society of London.

Approaches to Validation of Models for Low Gravity Fluid Behavior

NASA Technical Reports Server (NTRS)

Chato, David J.; Marchetta, Jeffery; Hochstein, John I.; Kassemi, Mohammad

2005-01-01

This paper details the author experiences with the validation of computer models to predict low gravity fluid behavior. It reviews the literature of low gravity fluid behavior as a starting point for developing a baseline set of test cases. It examines authors attempts to validate their models against these cases and the issues they encountered. The main issues seem to be that: Most of the data is described by empirical correlation rather than fundamental relation; Detailed measurements of the flow field have not been made; Free surface shapes are observed but through thick plastic cylinders, and therefore subject to a great deal of optical distortion; and Heat transfer process time constants are on the order of minutes to days but the zero-gravity time available has been only seconds.

Effects of fourth-order dispersion in very high-speed optical time-division multiplexed transmission.

PubMed

Capmany, J; Pastor, D; Sales, S; Ortega, B

2002-06-01

We present a closed-form expression for computation of the output pulse's rms time width in an optical fiber link with up to fourth-order dispersion (FOD) by use of an optical source with arbitrary linewidth and chirp parameters. We then specialize the expression to analyze the effect of FOD on the transmission of very high-speed linear optical time-division multiplexing systems. By suitable source chirping, FOD can be compensated for to an upper link-length limit above which other techniques must be employed. Finally, a design formula to estimate the maximum attainable bit rate limited by FOD as a function of the link length is also presented.

Pure perceptual-based learning of second-, third-, and fourth-order sequential probabilities.

PubMed

Remillard, Gilbert

2011-07-01

There is evidence that sequence learning in the traditional serial reaction time task (SRTT), where target location is the response dimension, and sequence learning in the perceptual SRTT, where target location is not the response dimension, are handled by different mechanisms. The ability of the latter mechanism to learn sequential contingencies that can be learned by the former mechanism was examined. Prior research has established that people can learn second-, third-, and fourth-order probabilities in the traditional SRTT. The present study reveals that people can learn such probabilities in the perceptual SRTT. This suggests that the two mechanisms may have similar architectures. A possible neural basis of the two mechanisms is discussed.

Unification of Intercontinental Height Systems based on the Fixed Geodetic Boundary Value Problem - A Case Study in Spherical Approximation

NASA Astrophysics Data System (ADS)

Grombein, T.; Seitz, K.; Heck, B.

2013-12-01

In general, national height reference systems are related to individual vertical datums defined by specific tide gauges. The discrepancy of these vertical datums causes height system biases that range in an order of 1-2 m at a global scale. Continental height systems can be connected by spirit leveling and gravity measurements along the leveling lines as performed for the definition of the European Vertical Reference Frame. In order to unify intercontinental height systems, an indirect connection is needed. For this purpose, global geopotential models derived from recent satellite missions like GOCE provide an important contribution. However, to achieve a highly-precise solution, a combination with local terrestrial gravity data is indispensable. Such combinations result in the solution of a Geodetic Boundary Value Problem (GBVP). In contrast to previous studies, mostly related to the traditional (scalar) free GBVP, the present paper discusses the use of the fixed GBVP for height system unification, where gravity disturbances instead of gravity anomalies are applied as boundary values. The basic idea of our approach is a conversion of measured gravity anomalies to gravity disturbances, where unknown datum parameters occur that can be associated with height system biases. In this way, the fixed GBVP can be extended by datum parameters for each datum zone. By evaluating the GBVP at GNSS/leveling benchmarks, the unknown datum parameters can be estimated in a least squares adjustment. Beside the developed theory, we present numerical results of a case study based on the spherical fixed GBVP and boundary values simulated by the use of the global geopotential model EGM2008. In a further step, the impact of approximations like linearization as well as topographic and ellipsoidal effects is taken into account by suitable reduction and correction terms.

Extended Gravity: State of the Art and Perspectives

NASA Astrophysics Data System (ADS)

Capozziello, Salvatore; de Laurentis, Mariafelicia

2015-01-01

Several issues coming from Cosmology, Astrophysics and Quantum Field Theory suggest to extend the General Relativity in order to overcome several shortcomings emerging at conceptual and experimental level. From one hand, standard Einstein theory fails as soon as one wants to achieve a full quantum description of space-time. In fact, the lack of a final self-consistent Quantum Gravity Theory can be considered one of the starting points for alternative theories of gravity. Specifically, the approach based on corrections and enlargements of the Einstein scheme, have become a sort of paradigm in the study of gravitational interaction. On the other hand, such theories have acquired great interest in cosmology since they "naturally" exhibit inflationary behaviours which can overcome the shortcomings of standard cosmology. From an astrophysical point of view, Extended Theories of Gravity do not require to find candidates for dark energy and dark matter at fundamental level; the approach starts from taking into account only the "observed" ingredients (i.e., gravity, radiation and baryonic matter); it is in full agreement with the early spirit of General Relativity but one has to relax the strong hypothesis that gravity acts at same way at all scales. Several scalar-tensor and f(R)-models agree with observed cosmology, extragalactic and galactic observations and Solar System tests, and give rise to new effects capable of explaining the observed acceleration of cosmic fluid and the missing matter effect of self-gravitating structures. Despite these preliminary results, no final model addressing all the open issues is available at the moment, however the paradigm seems promising in order to achieve a complete and self-consistent theory working coherently at all interaction scales.

I-Love-Q relations for neutron stars in dynamical Chern Simons gravity

NASA Astrophysics Data System (ADS)

Gupta, Toral; Majumder, Barun; Yagi, Kent; Yunes, Nicolás

2018-01-01

Neutron stars are ideal to probe, not only nuclear physics, but also strong-field gravity. Approximate universal relations insensitive to the star’s internal structure exist among certain observables and are useful in testing general relativity, as they project out the uncertainties in the equation of state. One such set of universal relations between the moment of inertia (I), the tidal Love number and the quadrupole moment (Q) has been studied both in general relativity and in modified theories. In this paper, we study the relations in dynamical Chern–Simons gravity, a well-motivated, parity-violating effective field theory, extending previous work in various ways. First, we study how projected constraints on the theory using the I-Love relation depend on the measurement accuracy of I with radio observations and that of the Love number with gravitational-wave observations. Provided these quantities can be measured with future observations, we find that the latter could place bounds on dynamical Chern–Simons gravity that are six orders of magnitude stronger than current bounds. Second, we study the I–Q and Q-Love relations in this theory by constructing slowly-rotating neutron star solutions to quadratic order in spin. We find that the approximate universality continues to hold in dynamical Chern–Simons gravity, and in fact, it becomes stronger than in general relativity, although its existence depends on the normalization of the dimensional coupling constant of the theory. Finally, we study the variation of the eccentricity of isodensity contours inside a star and its relation to the degree of universality. We find that, in most cases, the eccentricity variation is smaller in dynamical Chern–Simons gravity than in general relativity, providing further support to the idea that the approximate self-similarity of isodensity contours is responsible for universality.

The gravity field and orientation of Mercury after the MESSENGER mission

NASA Astrophysics Data System (ADS)

Mazarico, E.; Genova, A.; Goossens, S. J.; Lemoine, F. G.; Neumann, G. A.; Zuber, M. T.; Smith, D. E.; Solomon, S. C.

2015-12-01

After more than four years in orbit about Mercury, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft impacted the planet's surface north of Shakespeare crater (54.44° N, 210.12° E,) on 30 April 2015. One of the main goals of the mission was to determine the gravity field of Mercury in order to learn about Mercury's interior. Together with ground-based radar measurements of the obliquity and forced librations, MESSENGER-derived gravity models helped revise models of Mercury's interior. Nevertheless, the refinement of Mercury's orientation with the latest data from MESSENGER can further improve the interior modeling of the planet. The last eight months of the mission provided a special opportunity to conduct low-altitude measurements, with extensive radio tracking coverage below 200 km altitude north of ~30°N. MESSENGER's Mercury Laser Altimeter (MLA) mapped the topography of Mercury's northern hemisphere with a sub-meter vertical precision, an along-track sampling of ~500 m, and a longitudinal resolution (~0.1°) limited by the number of spacecraft orbits (~4,000). The combination of gravity and topography helps determine crustal thickness and interior properties. Altimetric ranges provide geodetic constraints to improve the spacecraft orbit determination, and thus the gravity field model. In particular, whereas the MESSENGER spacecraft was not tracked at each periapsis passage, MLA operated nearly continuously (outside of thermally challenging periods). From an analysis of the entire radiometric and altimetric datasets acquired by MESSENGER, a new gravity field to degree and order 100 has been obtained, resolving features down to ~75 km horizontal scale. The altimetric data help reduce the uncertainties in the determination of the pole position. A reanalysis of the Mercury flybys also constrains the spin rate over the longest available time span.

AIUB-RL02: an improved time-series of monthly gravity fields from GRACE data

NASA Astrophysics Data System (ADS)

Meyer, U.; Jäggi, A.; Jean, Y.; Beutler, G.

2016-05-01

The new release AIUB-RL02 of monthly gravity models from GRACE GPS and K-Band range-rate data is based on reprocessed satellite orbits referring to the reference frame IGb08. The release is consistent with the IERS2010 conventions. Improvements with respect to its predecessor AIUB-RL01 include the use of reprocessed (RL02) GRACE observations, new atmosphere and ocean dealiasing products (RL05), an upgraded ocean tide model (EOT11A), and the interpolation of shallow ocean tides (admittances). The stochastic parametrization of AIUB-RL02 was adapted to include daily accelerometer scale factors, which drastically reduces spurious signal at the 161 d period in C20 and at other low degree and order gravity field coefficients. Moreover, the correlation between the noise in the monthly gravity models and solar activity is considerably reduced in the new release. The signal and the noise content of the new AIUB-RL02 monthly gravity fields are studied and calibrated errors are derived from their non-secular and non-seasonal variability. The short-period time-variable signal over the oceans, mostly representing noise, is reduced by 50 per cent with respect to AIUB-RL01. Compared to the official GFZ-RL05a and CSR-RL05 monthly models, the AIUB-RL02 stands out by its low noise at high degrees, a fact emerging from the estimation of seasonal variations for selected river basins and of mass trends in polar regions. Two versions of the monthly AIUB-RL02 gravity models, with spherical harmonics resolution of degree and order 60 and 90, respectively, are available for the time period from March 2003 to March 2014 at the International Center for Global Earth Models or from ftp://ftp.unibe.ch/aiub/GRAVITY/GRACE (last accessed 22 March 2016).

Disformally self-tuning gravity

NASA Astrophysics Data System (ADS)

Emond, William T.; Saffin, Paul M.

2016-03-01

We extend a previous self-tuning analysis of the most general scalar-tensor theory of gravity in four dimensions with second order field equations by considering a generalized coupling to the matter sector. Through allowing a disformal coupling to matter we are able to extend the Fab Four model and construct a new class of theories that are able to tune away the cosmological constant on Friedmann-Lemaitre-Robertson-Walker backgrounds.

Entirely passive heat pipe apparatus capable of operating against gravity

DOEpatents

Koenig, Daniel R.

1982-01-01

The disclosure is directed to an entirely passive heat pipe apparatus capable of operating against gravity for vertical distances in the order of 3 to 7 meters and more. A return conduit into which an inert gas is introduced is used to lower the specific density of the working fluid so that it may be returned a greater vertical distance from condenser to evaporator.

Entirely passive heat-pipe apparatus capable of operating against gravity

DOEpatents

Koenig, D.R.

1981-02-11

The disclosure is directed to an entirely passive heat pipe apparatus capable of operating against gravity for vertical distances in the order of 3 to 7 and more. A return conduit into which an inert gas is introduced is used to lower the specific density of the working fluid so that it may be returned a greater vertical distance from condenser to evaporator.

Mercury's Interior from MESSENGER Radio Science Data

NASA Astrophysics Data System (ADS)

Genova, A.; Mazarico, E.; Goossens, S. J.; Lemoine, F. G.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

2017-12-01

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft provided precise radio tracking data in orbit about Mercury for more than 4 years, from March 2011 to April 2015. These geodetic measurements enable us to investigate the interior structure of the planet from the inner core to the crust. The first three years of radio data allowed us to determine the gravity field of Mercury with a resolution of 150 km in the northern hemisphere (degree and order 50 in spherical harmonics) since the periapsis was located at higher latitudes (>65˚N) and 200-500 km altitudes. The comparison of this gravity solution with Mercury's topography, which was retrieved by using over 25 million individual measurements of the Mercury Laser Altimeter (MLA), resulted in a preliminary map of the crustal thickness of the planet. However, those results were limited by the resolution of the gravity field since the topography was defined in spherical harmonics up to degree and order 125. The last year of the MESSENGER extended mission was dedicated to a low-altitude campaign, where the spacecraft periapsis was maintained at altitudes between 25 and 100 km. The radio data collected during this mission phase allowed us to significantly improve the resolution of the gravity field locally in the northern hemisphere up to degree and order 100 in spherical harmonics. We present the gravity anomalies and crustal thickness maps that lead to a better understanding on the formation and evolution of specific regions. We present our estimated orientation model, which slightly differs from the solutions that were obtained by using Earth-based radar measurements and the co-registration of MESSENGER imaging and altimetry data. These previous estimates provide a direct measurement of the surface response, whereas the orientation model from gravity is more sensitive to the inner and outer core. A discrepancy between core and surface obliquities may provide fundamental information on the status of the outer core and the presence of a solid inner core. We also present the latest solution of the tidal Love number k2 that enables us to constrain the basal temperature and rigidity of the outer molten core.

Spherically Symmetric Gravitational Collapse of a Dust Cloud in Third-Order Lovelock Gravity

NASA Astrophysics Data System (ADS)

Zhou, Kang; Yang, Zhan-Ying; Zou, De-Cheng; Yue, Rui-Hong

We investigate the spherically symmetric gravitational collapse of an incoherent dust cloud by considering a LTB-type spacetime in third-order Lovelock Gravity without cosmological constant, and give three families of LTB-like solutions which separately corresponding to hyperbolic, parabolic and elliptic. Notice that the contribution of high-order curvature corrections have a profound influence on the nature of the singularity, and the global structure of spacetime changes drastically from the analogous general relativistic case. Interestingly, the presence of high order Lovelock terms leads to the formation of massive, naked and timelike singularities in the 7D spacetime, which is disallowed in general relativity. Moveover, we point out that the naked singularities in the 7D case may be gravitational weak therefore may not be a serious threat to the cosmic censorship hypothesis, while the naked singularities in the D ≥ 8 inhomogeneous collapse violate the cosmic censorship hypothesis seriously.

Satellite tour design for the Cassini mission. [Saturn

NASA Technical Reports Server (NTRS)

Diehl, R. E.

1985-01-01

The mission design for the Cassini satellite tour of Saturn is described. The use of Titan encounters for gravity-assisted trajectory shaping to satisfy atmosphere, magnetosphere, and satellite science requirements is discussed. Three candidate satellite tours that illustrate the tradeoffs between different strategies to satisfy the science objectives are presented. Tour characteristics for a 4yr mission include at least 30 Titan encounters to provide a minimum of 90 deg orbit rotation for either a magnetotail petal orbit or noon petal orbit; evenly distributed Titan ground tracks for radar mapping coverage; at least 2 Iapetus and 1 Enceladus close flybys; inclined orbits during the first 3 yr to provide Earth and Sun occultations by Saturn and its rings; and Polar orbits during the fourth year.

The coolest DA white dwarfs detected at soft X-ray wavelengths

NASA Technical Reports Server (NTRS)

Kidder, K. M.; Holberg, J. B.; Barstow, M. A.; Tweedy, R. W.; Wesemael, F.

1992-01-01

New soft X-ray/EUV photometric observations of the DA white dwarfs KPD 0631 + 1043 = WD 0631 + 107 and PG 1113 + 413 = WD 1113 + 413 are analyzed. Previously reported soft X-ray detections of three other DAs and the failure to detect a fourth DA in deep Exosat observations are investigated. New ground-based spectra are presented for all of the objects, with IUE Ly-alpha spectra for some. These data are used to constrain the effective temperatures and surface gravities. The improved estimates of these parameters are employed to refer a photospheric He abundance for the hotter objects and to elucidate an effective observational low-temperature threshold for the detection of pure hydrogen DA white dwarfs at soft X-ray wavelengths.

Magellan project

NASA Technical Reports Server (NTRS)

Scott, J. F.; Griffith, D. G.; Gunn, J. M.; Piereson, R. G.; Stewart, J. M.; Tavormina, A. M.; Thompson, T. W.

1992-01-01

The Magellan spacecraft was placed into orbit around Venus on 10 Aug. 1990 and started radar data acquisition on 15 Sep. 1990. Since then, Magellan has completed mapping over 2.75 rotations of the planet (as of mid-July 1992). Synthetic aperture radar (SAR), altimetry, and radiometry observations have covered 84 percent of the surface during the first mission cycle from mid-Sep. 1990 through mid-May 1991. Operations in the second mission cycle from mid-May 1991 through mid-Jan. 1992 emphasized filling the larger gaps (the south polar region and a superior conjunction) from that first cycle. Planned observations in the fourth mission cycle from mid-Sep. 1992 through mid-May 1993 will emphasize high-resolution gravity observations of the equatorial regions of Venus.

Microgravity Combustion Research: 1999 Program and Results

NASA Technical Reports Server (NTRS)

Friedman, Robert (Editor); Gokoglu, Suleyman A. (Editor); Urban, David L. (Editor)

1999-01-01

The use of the microgravity environment of space to expand scientific knowledge and to enable the commercial development of space for enhancing the quality of life on Earth is particularly suitable to the field of combustion. This document reviews the current status of microgravity combustion research and derived information. It is the fourth in a series of timely surveys, all published as NASA Technical Memoranda, and it covers largely the period from 1995 to early 1999. The scope of the review covers three program areas: fundamental studies, applications to fire safety and other fields. and general measurements and diagnostics. The document also describes the opportunities for Principal Investigator participation through the NASA Research Announcement program and the NASA Glenn Research Center low-gravity facilities available to researchers.

Flight performance of bumble bee as a possible pollinator in space agriculture under partial gravity

NASA Astrophysics Data System (ADS)

Yamashita, Masamichi; Hashimoto, Hirofumi; Mitsuhata, Masahiro; Sasaki, Masami; Space Agriculture Task Force, J.

Space agriculture is an advanced life support concept for habitation on extraterrestrial bodies based on biological and ecological function. Flowering plant species are core member of space agriculture to produce food and revitalize air and water. Selection of crop plant species is made on the basis of nutritional requirements to maintain healthy life of space crew. Species selected for space agriculture have several mode of reproduction. For some of plant species, insect pollination is effective to increase yield and quality of food. In terrestrial agriculture, bee is widely introduced to pollinate flower. For pollinator insect on Mars, working environment is different from Earth. Magnitude of gravity is 0.38G on Mars surface. In order to confirm feasibility of insect pollination for space agriculture, capability of flying pollinator insect under such exotic condition should be examined. Even bee does not possess evident gravity sensory system, gravity dominates flying performance and behavior. During flight or hovering, lifting force produced by wing beat sustains body weight, which is the product of body mass and gravitational acceleration. Flying behavior of bumble bee, Bombus ignitus, was documented under partial or micro-gravity produced by parabolic flight of jet plane. Flying behavior at absence of gravity differed from that under normal gravity. Ability of bee to fly under partial gravity was examined at the level of Mars, Moon and the less, to determine the threshold level of gravity for bee flying maneuver. Adaptation process of bee flying under different gravity level was evaluated as well by successive documentation of parabolic flight experiment.

Convective Formation of Pileus Cloud Near the Tropopause

NASA Technical Reports Server (NTRS)

Garrett, Timothy J.; Dean-Day, Jonathan; Liu, Chuntao; Barnett, Brian K.; Mace, Gerald G.; Baumgardner, Darrel G.; Webster, Christopher R.; Bui, T. Paul; Read, William G.; Minnis, Patrick

2005-01-01

Pileus clouds form where humid, stably stratified air is mechanically displaced vertically ahead of rising convection. This paper describes convective formation of pileus cloud in the tropopause transition layer (TTL), and explores a possible link to the formation of long-lasting cirrus at cold temperatures. In-situ measurements from off the coast of Honduras during the July 2002 CRYSTALFACE experiment show an example of TTL cirrus associated with, and penetrated by, deep convection. The cirrus was enriched with total water compared to its surroundings, but composed of extremely small ice crystals with effective radii between 2 and 4 m. Through gravity wave analysis, and intercomparison of measured and simulated cloud microphysics, it is argued that the TTL cirrus in this case originated neither from convectively-forced gravity wave motions nor environmental mixing alone. Rather, it is hypothesized that some combination was involved in which, first, convection forced pileus cloud to form from TTL air; second, it punctured the pileus layer, contributing larger ice crystals through interfacial mixing; third, the addition of condensate inhibited evaporation of the original pileus ice crystals in the warm phase of the ensuing gravity wave; fourth, through successive pulses, deep convection formed the observed layer of TTL cirrus. While the general incidence and longevity of pileus cloud remains unknown, in-situ measurements, and satellite-based Microwave Limb Sounder retrievals, suggest that much of the tropical TTL is sufficiently humid to be susceptible to its formation. Where these clouds form and persist, there is potential for an irreversible repartition from water vapor to ice at cold temperatures.

Holographic Rényi entropy in AdS3/LCFT2 correspondence

NASA Astrophysics Data System (ADS)

Chen, Bin; Song, Feng-yan; Zhang, Jia-ju

2014-03-01

The recent study in AdS3/CFT2 correspondence shows that the tree level contribution and 1-loop correction of holographic Rényi entanglement entropy (HRE) exactly match the direct CFT computation in the large central charge limit. This allows the Rényi entanglement entropy to be a new window to study the AdS/CFT correspondence. In this paper we generalize the study of Rényi entanglement entropy in pure AdS3 gravity to the massive gravity theories at the critical points. For the cosmological topological massive gravity (CTMG), the dual conformal field theory (CFT) could be a chiral conformal field theory or a logarithmic conformal field theory (LCFT), depending on the asymptotic boundary conditions imposed. In both cases, by studying the short interval expansion of the Rényi entanglement entropy of two disjoint intervals with small cross ratio x, we find that the classical and 1-loop HRE are in exact match with the CFT results, up to order x 6. To this order, the difference between the massless graviton and logarithmic mode can be seen clearly. Moreover, for the cosmological new massive gravity (CNMG) at critical point, which could be dual to a logarithmic CFT as well, we find the similar agreement in the CNMG/LCFT correspondence. Furthermore we read the 2-loop correction of graviton and logarithmic mode to HRE from CFT computation. It has distinct feature from the one in pure AdS3 gravity.

The Biomechanics of Exercise Countermeasures

NASA Technical Reports Server (NTRS)

Cavanagh, Peter R.; Arnold, Steven; Derr, Janice; Sharkey, Neil; Wu, Ge

1999-01-01

The Penn State Zero-gravity Simulator (PSZS) is a device developed by the Center for Locomotion Studies (CELOS) to enable ground studies of exercise countermeasures for the bone loss that has been shown to occur during long-term exposure to zero gravity (0G). The PSZS simulates 0G exercise by providing a suspension system that holds an individual in a horizontal (supine) position above the floor in order to enable exercise on a wall-mounted treadmill. Due to this orientation, exercise performed in the PSZS is free of the force of -ravity in the direction that would normally contribute to ground reaction forces. In order for movements to be more similar to those in 0G, a constant force suspension of each segment (equal to the segment weight) is provided regardless of limb position. During the preliminary development of the PSZS, CELOS researchers also designed an optional gravity-replacement simulation feature for the PSZS. This feature was a prototype tethering system that consisted of a spring tension system to pull an exercising individual toward the treadmill. The immediate application of the tethering system was to be the provision of gravity-replacement loading so that exercise in 0G- and 1G-loading conditions could be compared, and the PSZS could then be used to evaluate exercise countermeasures for bone loss during space flight. This tethering system would also be a model for the further refinement of gravity-replacement systems provided for astronaut usage while performing prescribed exercise countermeasures for bone loss during long-term space flights.

Microvibration and Centre-of-Gravity Shift Measurements on Thermally Stressed Thermal-Control Blankets

NASA Astrophysics Data System (ADS)

Magg, Manfred; Grillenbeck, Anton, , Dr.

2004-08-01

Several samples of thermal control blankets were subjected to transient thermal loads in a thermal vacuum chamber in order to study their ability to excite micro- vibrations on a carrier structure and to cause tiny centre- of-gravity shifts. The reason for this investigation was driven by the GOCE project in order to minimize micro- vibrations on-board of the spacecraft while on-orbit. The objectives of this investigation were to better understand the mechanism which may produce micro- vibrations induced by the thermal control blankets, and to identify thermal control blanket lay-ups with minimum micro-vibration activity.

An Improved 360 Degree and Order Model of Venus Topography

NASA Technical Reports Server (NTRS)

Rappaport, Nicole J.; Konopliv, Alex S.; Kucinskas, Algis B.; Ford, Peter G.

1999-01-01

We present an improved 360 degree and order spherical harmonic solution for Venus' topography. The new model uses the most recent set of Venus altimetry data with spacecraft positions derived from a recent high resolution gravity model. Geometric analysis indicates that the offset between the center of mass and center of figure of Venus is about 10 times smaller than that for the Earth, the Moon, or Mars. Statistical analyses confirm that the RMS topography follows a power law over the central part of the spectrum. Compared to the previous topography model, the new model is more highly correlated with Venus' harmonic gravity field.

Variations on holography from modifications of gravity in anti-de sitter

NASA Astrophysics Data System (ADS)

Apolo Velez, Luis Alberto

In this thesis we study aspects of the AdS/CFT correspondence that result from modifications of gravity in the bulk and lead to novel features in the dual theories at the boundary. The variations on the holographic theme studied in this thesis are model-independent since we have not assumed a particular UV-completion of gravity. Our results can be applied to a wide class of models that include higher-spin theories and compactifications of string theory on AdS backgrounds. The modifications of the bulk physics studied in this thesis include massive gravitons, higher-derivative terms in the Einstein-Hilbert action, and new boundary conditions for gravity. We begin by showing that it is possible to construct duals with a massive graviton in the bulk by deforming the dual theory at the boundary. This procedure does not break the translation invariance of the dual theory and might be useful in the study of certain condensed matter systems. We then construct the most general class of parity-even tricritical gravities in three and four dimensions. These higher-derivative theories are not unitary and characterized by the logarithmic fall-off of their linearized perturbations. They are conjectured to be dual to rank-3 logarithmic conformal field theories. We will show that, at linear order in the equations of motion, it is possible to truncate the theory to a unitary subsector. We also show that tricritical gravities in three and four dimensions suffer from a linearization instability that forbids unitary truncations beyond linear order. Finally we consider the role of boundary conditions in the AdS3/CFT2 correspondence. We show that free boundary conditions that lead to enhanced asymptotic symmetry groups are dual to 2D theories of quantum gravity in either the conformal or lightcone gauges. In particular we match the generators of symmetries in the bulk and boundary theories and show that a proper identification of the generator of Virasoro transformations in the bulk leads to a vanishing total central charge. We also show that this identification is consistent with the constraint equations of 2D gravity.

First-order discrete Faddeev gravity at strongly varying fields

NASA Astrophysics Data System (ADS)

Khatsymovsky, V. M.

2017-11-01

We consider the Faddeev formulation of general relativity (GR), which can be characterized by a kind of d-dimensional tetrad (typically d = 10) and a non-Riemannian connection. This theory is invariant w.r.t. the global, but not local, rotations in the d-dimensional space. There can be configurations with a smooth or flat metric, but with the tetrad that changes abruptly at small distances, a kind of “antiferromagnetic” structure. Previously, we discussed a first-order representation for the Faddeev gravity, which uses the orthogonal connection in the d-dimensional space as an independent variable. Using the discrete form of this formulation, we considered the spectrum of (elementary) area. This spectrum turns out to be physically reasonable just on a classical background with large connection like rotations by π, that is, with such an “antiferromagnetic” structure. In the discrete first-order Faddeev gravity, we consider such a structure with periodic cells and large connection and strongly changing tetrad field inside the cell. We show that this system in the continuum limit reduces to a generalization of the Faddeev system. The action is a sum of related actions of the Faddeev type and is still reduced to the GR action.

A higher-order conservation element solution element method for solving hyperbolic differential equations on unstructured meshes

NASA Astrophysics Data System (ADS)

Bilyeu, David

This dissertation presents an extension of the Conservation Element Solution Element (CESE) method from second- to higher-order accuracy. The new method retains the favorable characteristics of the original second-order CESE scheme, including (i) the use of the space-time integral equation for conservation laws, (ii) a compact mesh stencil, (iii) the scheme will remain stable up to a CFL number of unity, (iv) a fully explicit, time-marching integration scheme, (v) true multidimensionality without using directional splitting, and (vi) the ability to handle two- and three-dimensional geometries by using unstructured meshes. This algorithm has been thoroughly tested in one, two and three spatial dimensions and has been shown to obtain the desired order of accuracy for solving both linear and non-linear hyperbolic partial differential equations. The scheme has also shown its ability to accurately resolve discontinuities in the solutions. Higher order unstructured methods such as the Discontinuous Galerkin (DG) method and the Spectral Volume (SV) methods have been developed for one-, two- and three-dimensional application. Although these schemes have seen extensive development and use, certain drawbacks of these methods have been well documented. For example, the explicit versions of these two methods have very stringent stability criteria. This stability criteria requires that the time step be reduced as the order of the solver increases, for a given simulation on a given mesh. The research presented in this dissertation builds upon the work of Chang, who developed a fourth-order CESE scheme to solve a scalar one-dimensional hyperbolic partial differential equation. The completed research has resulted in two key deliverables. The first is a detailed derivation of a high-order CESE methods on unstructured meshes for solving the conservation laws in two- and three-dimensional spaces. The second is the code implementation of these numerical methods in a computer code. For code development, a one-dimensional solver for the Euler equations was developed. This work is an extension of Chang's work on the fourth-order CESE method for solving a one-dimensional scalar convection equation. A generic formulation for the nth-order CESE method, where n ≥ 4, was derived. Indeed, numerical implementation of the scheme confirmed that the order of convergence was consistent with the order of the scheme. For the two- and three-dimensional solvers, SOLVCON was used as the basic framework for code implementation. A new solver kernel for the fourth-order CESE method has been developed and integrated into the framework provided by SOLVCON. The main part of SOLVCON, which deals with unstructured meshes and parallel computing, remains intact. The SOLVCON code for data transmission between computer nodes for High Performance Computing (HPC). To validate and verify the newly developed high-order CESE algorithms, several one-, two- and three-dimensional simulations where conducted. For the arbitrary order, one-dimensional, CESE solver, three sets of governing equations were selected for simulation: (i) the linear convection equation, (ii) the linear acoustic equations, (iii) the nonlinear Euler equations. All three systems of equations were used to verify the order of convergence through mesh refinement. In addition the Euler equations were used to solve the Shu-Osher and Blastwave problems. These two simulations demonstrated that the new high-order CESE methods can accurately resolve discontinuities in the flow field.For the two-dimensional, fourth-order CESE solver, the Euler equation was employed in four different test cases. The first case was used to verify the order of convergence through mesh refinement. The next three cases demonstrated the ability of the new solver to accurately resolve discontinuities in the flows. This was demonstrated through: (i) the interaction between acoustic waves and an entropy pulse, (ii) supersonic flow over a circular blunt body, (iii) supersonic flow over a guttered wedge. To validate and verify the three-dimensional, fourth-order CESE solver, two different simulations where selected. The first used the linear convection equations to demonstrate fourth-order convergence. The second used the Euler equations to simulate supersonic flow over a spherical body to demonstrate the scheme's ability to accurately resolve shocks. All test cases used are well known benchmark problems and as such, there are multiple sources available to validate the numerical results. Furthermore, the simulations showed that the high-order CESE solver was stable at a CFL number near unity.

FDTD simulation of EM wave propagation in 3-D media

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

Wang, T.; Tripp, A.C.

1996-01-01

A finite-difference, time-domain solution to Maxwell`s equations has been developed for simulating electromagnetic wave propagation in 3-D media. The algorithm allows arbitrary electrical conductivity and permittivity variations within a model. The staggered grid technique of Yee is used to sample the fields. A new optimized second-order difference scheme is designed to approximate the spatial derivatives. Like the conventional fourth-order difference scheme, the optimized second-order scheme needs four discrete values to calculate a single derivative. However, the optimized scheme is accurate over a wider wavenumber range. Compared to the fourth-order scheme, the optimized scheme imposes stricter limitations on the time stepmore » sizes but allows coarser grids. The net effect is that the optimized scheme is more efficient in terms of computation time and memory requirement than the fourth-order scheme. The temporal derivatives are approximated by second-order central differences throughout. The Liao transmitting boundary conditions are used to truncate an open problem. A reflection coefficient analysis shows that this transmitting boundary condition works very well. However, it is subject to instability. A method that can be easily implemented is proposed to stabilize the boundary condition. The finite-difference solution is compared to closed-form solutions for conducting and nonconducting whole spaces and to an integral-equation solution for a 3-D body in a homogeneous half-space. In all cases, the finite-difference solutions are in good agreement with the other solutions. Finally, the use of the algorithm is demonstrated with a 3-D model. Numerical results show that both the magnetic field response and electric field response can be useful for shallow-depth and small-scale investigations.« less

Partial gravity reaction experiment sysytem on graund using multi-Copter

NASA Astrophysics Data System (ADS)

Hasegawa, Katsuya; Maeda, Naoko

2016-07-01

In order to enable further space exploration into the space, Moon, Mars, and other planets, it is essential to understand the physiological response to low gravity environments. However, We made low gravity environment for studies using the satellite parabolic flight and drop tower. It is very expensive experiment that low gravity physiological response. Because, it requires rockets and airplanes and dedicated Tower, low gravity conditions test have not been conducted sufficiently due to the extraordinary high cost for conducting experiments. The study present is to develop the radio-controlled multicopter system that is used for the controlled falling flight vehicle (not free fall). During the controlled falling, the payload is exposed to a certain level of low gravity. 1) G profile: low gravity from 0 g to 1 g that will last approximately 5seconds, 50 kg. 2) Supply limited imaging techniques, high-speed or normal video and X ray images. 3) Wireless transmission of up to 64 channels of analog and digital signals. This vehicle is designed for experimentation on various model organisms, from cells to animals and plants. The multicopter flight system enables conducting experiments in low gravity conditions with less than 1% of the budget for spaceflight or parabolic flights. Experiment is possible to perform repeated many times in one day. We can expect reproducible results from many repeated trials at the lowest cost.

Major Fault Patterns in Zanjan State of Iran Based of GECO Global Geoid Model

NASA Astrophysics Data System (ADS)

Beheshty, Sayyed Amir Hossein; Abrari Vajari, Mohammad; Raoufikelachayeh, SeyedehSusan

2016-04-01

A new Earth Gravitational Model (GECO) to degree 2190 has been developed incorporates EGM2008 and the latest GOCE based satellite solutions. Satellite gradiometry data are more sensitive information of the long- and medium- wavelengths of the gravity field than the conventional satellite tracking data. Hence, by utilizing this new technique, more accurate, reliable and higher degrees/orders of the spherical harmonic expansion of the gravity field can be achieved. Gravity gradients can also be useful in geophysical interpretation and prospecting. We have presented the concept of gravity gradients with some simple interpretations. A MATLAB based computer programs were developed and utilized for determining the gravity and gradient components of the gravity field using the GGMs, followed by a case study in Zanjan State of Iran. Our numerical studies show strong (more than 72%) correlations between gravity anomalies and the diagonal elements of the gradient tensor. Also, strong correlations were revealed between the components of the deflection of vertical and the off-diagonal elements as well as between the horizontal gradient and magnitude of the deflection of vertical. We clearly distinguished two big faults in North and South of Zanjan city based on the current information. Also, several minor faults were detected in the study area. Therefore, the same geophysical interpretation can be stated for gravity gradient components too. Our mathematical derivations support some of these correlations.

Ceiling Fires Studied to Simulate Low-Gravity Fires

NASA Technical Reports Server (NTRS)

Olson, Sandra L.

2001-01-01

A unique new way to study low-gravity flames in normal gravity has been developed. To study flame structure and extinction characteristics in low-stretch environments, a normal gravity low-stretch diffusion flame was generated using a cylindrical PMMA sample of varying large radii, as shown in the photograph. These experiments have demonstrated that low-gravity flame characteristics can be generated in normal gravity through the proper use of scaling. On the basis of this work, it is feasible to apply this concept toward the development of an Earth-bound method of evaluating material flammability in various gravitational environments from normal gravity to microgravity, including the effects of partial gravity low-stretch rates such as those found on the Moon (1/6g) or Mars (1/3g). During these experiments, the surface regression rates for PMMA were measured for the first time over the full range of flammability in air, from blowoff at high stretch, to quenching at low stretch, as plotted in the graph. The solid line drawn through the central portion of the data (3

``Dressing'' lines and vertices in calculations of matrix elements with the coupled-cluster method and determination of Cs atomic properties

NASA Astrophysics Data System (ADS)

Derevianko, Andrei; Porsev, Sergey G.

2005-03-01

We consider evaluation of matrix elements with the coupled-cluster method. Such calculations formally involve infinite number of terms and we devise a method of partial summation (dressing) of the resulting series. Our formalism is built upon an expansion of the product C†C of cluster amplitudes C into a sum of n -body insertions. We consider two types of insertions: particle (hole) line insertion and two-particle (two-hole) random-phase-approximation-like insertion. We demonstrate how to “dress” these insertions and formulate iterative equations. We illustrate the dressing equations in the case when the cluster operator is truncated at single and double excitations. Using univalent systems as an example, we upgrade coupled-cluster diagrams for matrix elements with the dressed insertions and highlight a relation to pertinent fourth-order diagrams. We illustrate our formalism with relativistic calculations of the hyperfine constant A(6s) and the 6s1/2-6p1/2 electric-dipole transition amplitude for the Cs atom. Finally, we augment the truncated coupled-cluster calculations with otherwise omitted fourth order diagrams. The resulting analysis for Cs is complete through the fourth order of many-body perturbation theory and reveals an important role of triple and disconnected quadruple excitations.

Quality assessment of remote sensing image fusion using feature-based fourth-order correlation coefficient

NASA Astrophysics Data System (ADS)

Ma, Dan; Liu, Jun; Chen, Kai; Li, Huali; Liu, Ping; Chen, Huijuan; Qian, Jing

2016-04-01

In remote sensing fusion, the spatial details of a panchromatic (PAN) image and the spectrum information of multispectral (MS) images will be transferred into fused images according to the characteristics of the human visual system. Thus, a remote sensing image fusion quality assessment called feature-based fourth-order correlation coefficient (FFOCC) is proposed. FFOCC is based on the feature-based coefficient concept. Spatial features related to spatial details of the PAN image and spectral features related to the spectrum information of MS images are first extracted from the fused image. Then, the fourth-order correlation coefficient between the spatial and spectral features is calculated and treated as the assessment result. FFOCC was then compared with existing widely used indices, such as Erreur Relative Globale Adimensionnelle de Synthese, and quality assessed with no reference. Results of the fusion and distortion experiments indicate that the FFOCC is consistent with subjective evaluation. FFOCC significantly outperforms the other indices in evaluating fusion images that are produced by different fusion methods and that are distorted in spatial and spectral features by blurring, adding noise, and changing intensity. All the findings indicate that the proposed method is an objective and effective quality assessment for remote sensing image fusion.

Gravity and crustal movements: The canadian experience

NASA Astrophysics Data System (ADS)

Tanner, J. G.; Lambert, A.

1987-07-01

Repeated high precision gravity measurement have already played an important role in the detection of crustal deformation in Canada and elsewhere, but even more useful results can be expected through more widespread use of gravity in combination with other techniques. The crucial element in the process is the development of a good physical model on which the experiment can be based. Otherwise, considerable time and effort can be spent on determining the most appropriate field strategy. New technical developments on the horizon appear to offer enhanced opportunities for gravity studies of crustal processes. The coming availability of the Global Positioning System and transportable absolute gravimeters will open up the possibility of regional studies (i.e., areas of the order of 100 km or perhaps greater) of crustal movements at reasonable cost. Within Africa the development of an African Gravity Standardization Net will be a major first step in any program to provide a better understanding of the neo-tectonic framework of this vast continent.

Equivalent mechanical model of large-amplitude liquid sloshing under time-dependent lateral excitations in low-gravity conditions

NASA Astrophysics Data System (ADS)

Nan, Miao; Junfeng, Li; Tianshu, Wang

2017-01-01

Subjected to external lateral excitations, large-amplitude sloshing may take place in propellant tanks, especially for spacecraft in low-gravity conditions, such as landers in the process of hover and obstacle avoidance during lunar soft landing. Due to lateral force of the order of gravity in magnitude, the amplitude of liquid sloshing becomes too big for the traditional equivalent model to be accurate. Therefore, a new equivalent mechanical model, denominated the "composite model", that can address large-amplitude lateral sloshing in partially filled spherical tanks is established in this paper, with both translational and rotational excitations considered. The hypothesis of liquid equilibrium position following equivalent gravity is first proposed. By decomposing the large-amplitude motion of a liquid into bulk motion following the equivalent gravity and additional small-amplitude sloshing, a better simulation of large-amplitude liquid sloshing is presented. The effectiveness and accuracy of the model are verified by comparing the slosh forces and moments to results of the traditional model and CFD software.

An Online Gravity Modeling Method Applied for High Precision Free-INS

PubMed Central

Wang, Jing; Yang, Gongliu; Li, Jing; Zhou, Xiao

2016-01-01

For real-time solution of inertial navigation system (INS), the high-degree spherical harmonic gravity model (SHM) is not applicable because of its time and space complexity, in which traditional normal gravity model (NGM) has been the dominant technique for gravity compensation. In this paper, a two-dimensional second-order polynomial model is derived from SHM according to the approximate linear characteristic of regional disturbing potential. Firstly, deflections of vertical (DOVs) on dense grids are calculated with SHM in an external computer. And then, the polynomial coefficients are obtained using these DOVs. To achieve global navigation, the coefficients and applicable region of polynomial model are both updated synchronously in above computer. Compared with high-degree SHM, the polynomial model takes less storage and computational time at the expense of minor precision. Meanwhile, the model is more accurate than NGM. Finally, numerical test and INS experiment show that the proposed method outperforms traditional gravity models applied for high precision free-INS. PMID:27669261

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.

An Online Gravity Modeling Method Applied for High Precision Free-INS.

PubMed

Wang, Jing; Yang, Gongliu; Li, Jing; Zhou, Xiao

2016-09-23

For real-time solution of inertial navigation system (INS), the high-degree spherical harmonic gravity model (SHM) is not applicable because of its time and space complexity, in which traditional normal gravity model (NGM) has been the dominant technique for gravity compensation. In this paper, a two-dimensional second-order polynomial model is derived from SHM according to the approximate linear characteristic of regional disturbing potential. Firstly, deflections of vertical (DOVs) on dense grids are calculated with SHM in an external computer. And then, the polynomial coefficients are obtained using these DOVs. To achieve global navigation, the coefficients and applicable region of polynomial model are both updated synchronously in above computer. Compared with high-degree SHM, the polynomial model takes less storage and computational time at the expense of minor precision. Meanwhile, the model is more accurate than NGM. Finally, numerical test and INS experiment show that the proposed method outperforms traditional gravity models applied for high precision free-INS.

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.

Prospects for Probing Strong Gravity with a Pulsar-Black Hole System

NASA Technical Reports Server (NTRS)

Wex, N.; Liu, K.; Eatough, R. P.; Kramer, M.; Cordes, J. M.; Lazio, T. J. W.

2012-01-01

The discovery of a pulsar (PSR) in orbit around a black hole (BH) is expected to provide a superb new probe of relativistic gravity and BH properties. Apart from a precise mass measurement for the BH, one could expect a clean verification of the dragging of space-time caused by the BH spin. In order to measure the quadrupole moment of the BH for testing the no-hair theorem of general relativity (GR), one has to hope for a sufficiently massive BH. In this respect, a PSR orbiting the super-massive BH in the center of our Galaxy would be the ultimate laboratory for gravity tests with PSRs. But even for gravity theories that predict the same properties for BHs as GR, a PSR-BH system would constitute an excellent test system, due to the high grade of asymmetry in the strong field properties of these two components. Here we highlight some of the potential gravity tests that one could expect from different PSR-BH systems.

Observational constraints on transverse gravity: A generalization of unimodular gravity

NASA Astrophysics Data System (ADS)

Lopez-Villarejo, J. J.

2010-04-01

We explore the hypothesis that the set of symmetries enjoyed by the theory that describes gravity is not the full group of diffeomorphisms (Diff(M)), as in General Relativity, but a maximal subgroup of it (TransverseDiff(M)), with its elements having a jacobian equal to unity; at the infinitesimal level, the parameter describing the coordinate change xμ → xμ + ξμ(x) is transverse, i.e., δμξμ = 0. Incidentally, this is the smaller symmetry one needs to propagate consistently a graviton, which is a great theoretical motivation for considering these theories. Also, the determinant of the metric, g, behaves as a "transverse scalar", so that these theories can be seen as a generalization of the better-known unimodular gravity. We present our results on the observational constraints on transverse gravity, in close relation with the claim of equivalence with general scalar-tensor theory. We also comment on the structure of the divergences of the quantum theory to the one-loop order.

Baryogenesis in Lorentz-violating gravity theories

NASA Astrophysics Data System (ADS)

Sakstein, Jeremy; Solomon, Adam R.

2017-10-01

Lorentz-violating theories of gravity typically contain constrained vector fields. We show that the lowest-order coupling of such vectors to U (1)-symmetric scalars can naturally give rise to baryogenesis in a manner akin to the Affleck-Dine mechanism. We calculate the cosmology of this new mechanism, demonstrating that a net B - L can be generated in the early Universe, and that the resulting baryon-to-photon ratio matches that which is presently observed. We discuss constraints on the model using solar system and astrophysical tests of Lorentz violation in the gravity sector. Generic Lorentz-violating theories can give rise to the observed matter-antimatter asymmetry without violating any current bounds.

Separation of biogenic materials by electrophoresis under zero gravity (L-3)

NASA Technical Reports Server (NTRS)

Kuroda, Masao

1993-01-01

Electrophoresis separates electrically charged materials by imposing a voltage between electrodes. Though free-flow electrophoresis is used without carriers such as colloids to separate and purify biogenic materials including biogenic cells and proteins in blood, its resolving power and separation efficiency is very low on Earth due to sedimentation, flotation, and thermal convection caused by the specific gravity differences between separated materials and buffer solutions. The objective of this experiment is to make a comparative study of various electrophoresis conditions on the ground and in zero-gravity in order to ultimately develop a method for separating various important 'vial' components which are difficult to separate on the ground.

The Two-Phase Flow Separator Experiment Breadboard Model: Reduced Gravity Aircraft Results

NASA Technical Reports Server (NTRS)

Rame, E; Sharp, L. M.; Chahine, G.; Kamotani, Y.; Gotti, D.; Owens, J.; Gilkey, K.; Pham, N.

2015-01-01

Life support systems in space depend on the ability to effectively separate gas from liquid. Passive cyclonic phase separators use the centripetal acceleration of a rotating gas-liquid mixture to carry out phase separation. The gas migrates to the center, while gas-free liquid may be withdrawn from one of the end plates. We have designed, constructed and tested a breadboard that accommodates the test sections of two independent principal investigators and satisfies their respective requirements, including flow rates, pressure and video diagnostics. The breadboard was flown in the NASA low-gravity airplane in order to test the system performance and design under reduced gravity conditions.

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.

Effects of the Higher Order Thinking Skills Program on At-Risk Young Adolescents' Self-Concept, Reading Achievement, and Thinking Skills.

ERIC Educational Resources Information Center

Eisenman, Gordon; Payne, Beverly D.

1997-01-01

Contrasted effects of Higher Order Thinking Skills (HOTS) program to those of Chapter 1 programs on fourth and fifth graders' reading achievement, self-concept, and higher-order thinking skills. Found that HOTS is more effective in raising self-concept and some higher-order thinking skills in fifth grade and after two years of treatment, with…

Rotating solutions in critical Lovelock gravities

DOE PAGES

Cvetič, M.; Feng, Xing -Hui; Lü, H.; ...

2016-12-12

For appropriate choices of the coupling constants, the equations of motion of Lovelock gravities up to order n in the Riemann tensor can be factorized such that the theories admits a single (A)dS vacuum. In this paper we construct two classes of exact rotating metrics in such critical Lovelock gravities of order n in d = 2n + 1 dimensions. In one class, the n angular momenta in the n orthogonal spatial 2-planes are equal, and hence the metric is of cohomogeneity one. We construct these metrics in a Kerr-Schild form, but they can then be recast in terms ofmore » Boyer-Lindquist coordinates. The other class involves metrics with only a single non-vanishing angular momentum. Again we construct them in a Kerr-Schild form, but in this case it does not seem to be possible to recast them in Boyer-Lindquist form. Furthermore, both classes of solutions have naked curvature singularities, arising because of the over rotation of the configurations.« less

Global correlation of topographic heights and gravity anomalies

NASA Technical Reports Server (NTRS)

Roufosse, M. C.

1977-01-01

The short wavelength features were obtained by subtracting a calculated 24th-degree-and-order field from observed data written in 1 deg x 1 deg squares. The correlation between the two residual fields was examined by a program of linear regression. When run on a worldwide scale over oceans and continents separately, the program did not exhibit any correlation; this can be explained by the fact that the worldwide autocorrelation function for residual gravity anomalies falls off much faster as a function of distance than does that for residual topographic heights. The situation was different when the program was used in restricted areas, of the order of 5 deg x 5 deg square. For 30% of the world,fair-to-good correlations were observed, mostly over continents. The slopes of the regression lines are proportional to apparent densities, which offer a large spectrum of values that are being interpreted in terms of features in the upper mantle consistent with available heat-flow, gravity, and seismic data.

Rotating solutions in critical Lovelock gravities

NASA Astrophysics Data System (ADS)

Cvetič, M.; Feng, Xing-Hui; Lü, H.; Pope, C. N.

2017-02-01

For appropriate choices of the coupling constants, the equations of motion of Lovelock gravities up to order n in the Riemann tensor can be factorized such that the theories admit a single (A)dS vacuum. In this paper we construct two classes of exact rotating metrics in such critical Lovelock gravities of order n in d = 2 n + 1 dimensions. In one class, the n angular momenta in the n orthogonal spatial 2-planes are equal, and hence the metric is of cohomogeneity one. We construct these metrics in a Kerr-Schild form, but they can then be recast in terms of Boyer-Lindquist coordinates. The other class involves metrics with only a single non-vanishing angular momentum. Again we construct them in a Kerr-Schild form, but in this case it does not seem to be possible to recast them in Boyer-Lindquist form. Both classes of solutions have naked curvature singularities, arising because of the over rotation of the configurations.

Rotating solutions in critical Lovelock gravities

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

Cvetič, M.; Feng, Xing -Hui; Lü, H.

For appropriate choices of the coupling constants, the equations of motion of Lovelock gravities up to order n in the Riemann tensor can be factorized such that the theories admits a single (A)dS vacuum. In this paper we construct two classes of exact rotating metrics in such critical Lovelock gravities of order n in d = 2n + 1 dimensions. In one class, the n angular momenta in the n orthogonal spatial 2-planes are equal, and hence the metric is of cohomogeneity one. We construct these metrics in a Kerr-Schild form, but they can then be recast in terms ofmore » Boyer-Lindquist coordinates. The other class involves metrics with only a single non-vanishing angular momentum. Again we construct them in a Kerr-Schild form, but in this case it does not seem to be possible to recast them in Boyer-Lindquist form. Furthermore, both classes of solutions have naked curvature singularities, arising because of the over rotation of the configurations.« less

Detailed gravity anomalies from Geos 3 satellite altimetry data

NASA Technical Reports Server (NTRS)

Gopalapillai, G. S.; Mourad, A. G.

1979-01-01

Detailed gravity anomalies are computed from a combination of Geos 3 satellite altimeter and terrestrial gravity data using least-squares principles. The mathematical model used is based on the Stokes' equation modified for a nonglobal solution. Using Geos 3 data in the calibration area, the effects of several anomaly parameter configurations and data densities/distributions on the anomalies and their accuracy estimates are studied. The accuracy estimates for 1 deg x 1 deg mean anomalies from low density altimetry data are of the order of 4 mgal. Comparison of these anomalies with the terrestrial data and also with Rapp's data derived using collocation techniques show rms differences of 7.2 and 4.9 mgal, respectively. Indications are that the anomaly accuracies can be improved to about 2 mgal with high density data. Estimation of 30 in. x 30 in. mean anomalies indicates accuracies of the order of 5 mgal. Proper verification of these results will be possible only when accurate ground truth data become available.

The effect of the external medium on the gravity-induced polarity of cytoplasmic streaming in Chara corallina (Characeae).

PubMed

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

1997-11-01

Gravity induces a polarity of cytoplasmic streaming in vertical internodal cells of Chara such that the downwardly directed stream moves faster than the upwardly directed stream. In order 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 explain the gravity response in Chara internodal cells, we controlled the physical properties of the external medium, including density and osmolarity, with impermeant solutes and examined the effect on the polarity of cytoplasmic streaming. As the density of the external medium is increased, the polarity of cytoplasmic streaming decreases and finally disappears when the density of the external medium is equal to that of the cell (1015 kg/m3). A further increase in the density of the external medium causes a reversal of the gravity response. These results are consistent with the gravitational pressure theory of gravity sensing since the buoyancy of the protoplast is dependent on the difference between the density of the protoplast and the external medium, and are inconsistent with the statolith theory since the buoyancy of intracellular particles are unaffected by changes in the external medium.

The effect of the external medium on the gravity-induced polarity of cytoplasmic streaming in Chara corallina (Characeae)

NASA Technical Reports Server (NTRS)

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

1997-01-01

Gravity induces a polarity of cytoplasmic streaming in vertical internodal cells of Chara such that the downwardly directed stream moves faster than the upwardly directed stream. In order 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 explain the gravity response in Chara internodal cells, we controlled the physical properties of the external medium, including density and osmolarity, with impermeant solutes and examined the effect on the polarity of cytoplasmic streaming. As the density of the external medium is increased, the polarity of cytoplasmic streaming decreases and finally disappears when the density of the external medium is equal to that of the cell (1015 kg/m3). A further increase in the density of the external medium causes a reversal of the gravity response. These results are consistent with the gravitational pressure theory of gravity sensing since the buoyancy of the protoplast is dependent on the difference between the density of the protoplast and the external medium, and are inconsistent with the statolith theory since the buoyancy of intracellular particles are unaffected by changes in the external medium.

Inertia-gravity wave radiation from the merging of two co-rotating vortices in the f-plane shallow water system

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

Sugimoto, Norihiko, E-mail: nori@phys-h.keio.ac.jp

Inertia-gravity wave radiation from the merging of two co-rotating vortices is investigated numerically in a rotating shallow water system in order to focus on cyclone–anticyclone asymmetry at different values of the Rossby number (Ro). A numerical study is conducted on a model using a spectral method in an unbounded domain to estimate the gravity wave flux with high accuracy. Continuous gravity wave radiation is observed in three stages of vortical flows: co-rotating of the vortices, merging of the vortices, and unsteady motion of the merged vortex. A cyclone–anticyclone asymmetry appears at all stages at smaller Ro (≤20). Gravity waves frommore » anticyclones are always larger than those from cyclones and have a local maximum at smaller Ro (∼2) compared with that for an idealized case of a co-rotating vortex pair with a constant rotation rate. The source originating in the Coriolis acceleration has a key role in cyclone–anticyclone asymmetry in gravity waves. An additional important factor is that at later stages, the merged axisymmetric anticyclone rotates faster than the elliptical cyclone due to the effect of the Rossby deformation radius, since a rotation rate higher than the inertial cutoff frequency is required to radiate gravity waves.« less

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.

The Charles F. Prentice Award Lecture 2005: optics of the human eye: progress and problems.

PubMed

Charman, W Neil

2006-06-01

The history of measurements of ocular aberration is briefly reviewed and recent work using much-improved aberrometers and large samples of eyes is summarized. When on-axis, higher-order, monochromatic aberrations are averaged, undercorrected, positive, fourth-order spherical aberration dominates; other Zernike wavefront aberration coefficients have average values near zero. Individually, however, many eyes show substantial amounts of third-order and other fourth-order aberrations; the value of these varies idiosyncratically about zero. Most normal eyes show only small amounts of axial monochromatic aberration for photopic pupils up to around 3 mm; the limits to retinal image quality are then usually set by diffraction, uncorrected or imperfectly corrected spherocylindrical refractive error, accommodation error, and chromatic aberration. Longitudinal chromatic aberration varies very little across the population. With larger mesopic and scotopic pupils, monochromatic aberration plays a more important optical role, but overall visual performance is increasingly dominated by neural factors. Some remaining problems in measuring and modeling the eye's optical performance are discussed.

Runge-Kutta Methods for Linear Ordinary Differential Equations

NASA Technical Reports Server (NTRS)

Zingg, David W.; Chisholm, Todd T.

1997-01-01

Three new Runge-Kutta methods are presented for numerical integration of systems of linear inhomogeneous ordinary differential equations (ODES) with constant coefficients. Such ODEs arise in the numerical solution of the partial differential equations governing linear wave phenomena. The restriction to linear ODEs with constant coefficients reduces the number of conditions which the coefficients of the Runge-Kutta method must satisfy. This freedom is used to develop methods which are more efficient than conventional Runge-Kutta methods. A fourth-order method is presented which uses only two memory locations per dependent variable, while the classical fourth-order Runge-Kutta method uses three. This method is an excellent choice for simulations of linear wave phenomena if memory is a primary concern. In addition, fifth- and sixth-order methods are presented which require five and six stages, respectively, one fewer than their conventional counterparts, and are therefore more efficient. These methods are an excellent option for use with high-order spatial discretizations.

Astrophysical black holes in screened modified gravity

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

Davis, Anne-Christine; Jha, Rahul; Muir, Jessica

2014-08-01

Chameleon, environmentally dependent dilaton, and symmetron gravity are three models of modified gravity in which the effects of the additional scalar degree of freedom are screened in dense environments. They have been extensively studied in laboratory, cosmological, and astrophysical contexts. In this paper, we present a preliminary investigation into whether additional constraints can be provided by studying these scalar fields around black holes. By looking at the properties of a static, spherically symmetric black hole, we find that the presence of a non-uniform matter distribution induces a non-constant scalar profile in chameleon and dilaton, but not necessarily symmetron gravity. Anmore » order of magnitude estimate shows that the effects of these profiles on in-falling test particles will be sub-leading compared to gravitational waves and hence observationally challenging to detect.« less

Compact stars in Eddington-inspired Born-Infeld gravity: Anomalies associated with phase transitions

NASA Astrophysics Data System (ADS)

Sham, Y.-H.; Leung, P. T.; Lin, L.-M.

2013-03-01

We study how generic phase transitions taking place in compact stars constructed in the framework of the Eddington-inspired Born-Infeld (EiBI) gravity can lead to anomalous behavior of these stars. For the case with first-order phase transitions, compact stars in EiBI gravity with a positive coupling parameter κ exhibit a finite region with constant pressure, which is absent in general relativity. However, for the case with a negative κ, an equilibrium stellar configuration cannot be constructed. Hence EiBI gravity seems to impose stricter constraints on the microphysics of stellar matter. Besides, in the presence of spatial discontinuities in the sound speed cs due to phase transitions, the Ricci scalar is spatially discontinuous and contains δ-function singularities proportional to the jump in cs2 acquired in the associated phase transition.

New observational constraints on f ( R ) gravity from cosmic chronometers

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

Nunes, Rafael C.; Pan, Supriya; Saridakis, Emmanuel N.

We use the recently released cosmic chronometer data and the latest measured value of the local Hubble parameter, combined with the latest joint light curves of Supernovae Type Ia, and Baryon Acoustic Oscillation distance measurements, in order to impose constraints on the viable and most used f ( R ) gravity models. We consider four f ( R ) models, namely the Hu-Sawicki, the Starobinsky, the Tsujikawa, and the exponential one, and we parametrize them introducing a distortion parameter b that quantifies the deviation from ΛCDM cosmology. Our analysis reveals that a small but non-zero deviation from ΛCDM cosmology ismore » slightly favored, with the corresponding fittings exhibiting very efficient AIC and BIC Information Criteria values. Clearly, f ( R ) gravity is consistent with observations, and it can serve as a candidate for modified gravity.« less

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.

Perturbative quantum gravity as a double copy of gauge theory.

PubMed

Bern, Zvi; Carrasco, John Joseph M; Johansson, Henrik

2010-08-06

In a previous paper we observed that (classical) tree-level gauge-theory amplitudes can be rearranged to display a duality between color and kinematics. Once this is imposed, gravity amplitudes are obtained using two copies of gauge-theory diagram numerators. Here we conjecture that this duality persists to all quantum loop orders and can thus be used to obtain multiloop gravity amplitudes easily from gauge-theory ones. As a nontrivial test, we show that the three-loop four-point amplitude of N=4 super-Yang-Mills theory can be arranged into a form satisfying the duality, and by taking double copies of the diagram numerators we obtain the corresponding amplitude of N=8 supergravity. We also remark on a nonsupersymmetric two-loop test based on pure Yang-Mills theory resulting in gravity coupled to an antisymmetric tensor and dilaton.

Surface settling in partially filled containers upon step reduction in gravity

NASA Technical Reports Server (NTRS)

Weislogel, Marl M.; Ross, Howard D.

1990-01-01

A large literature exists concerning the equilibrium configurations of free liquid/gas surfaces in reduced gravity environments. Such conditions generally yield surfaces of constant curvature meeting the container wall at a particular (contact) angle. The time required to reach and stabilize about this configuration is less studied for the case of sudden changes in gravity level, e.g. from normal- to low-gravity, as can occur in many drop tower experiments. The particular interest here was to determine the total reorientation time for such surfaces in cylinders (mainly), as a function primarily of contact angle and kinematic viscosity, in order to aid in the development of drop tower experiment design. A large parametric range of tests were performed and, based on an accompanying scale analysis, the complete data set was correlated. The results of other investigations are included for comparison.

Nonlinear behavior of solar gravity modes driven by He-3 in the core. I - Bifurcation analysis

NASA Technical Reports Server (NTRS)

Merryfield, William J.; Gough, Douglas; Toomre, Juri

1990-01-01

The nonlinear development of solar gravity modes driven by He-3 burning in the solar core is investigated by means of an idealized dynamical model. Possible outcomes that have been suggested in the literature include the triggering of subcritical direct convection, leading to core mixing, and the saturation of the excitation processes, leading to sustained finite-amplitude oscillations. The present simple model suggests that the latter is the more likely. The limiting amplitude of the oscillations is estimated, ignoring possible resonances with other gravity modes, to be of order 10 km/s at the solar surface. Such oscillations would be easily observable. That large-amplitude gravity modes have not been observed suggests either that these modes are not unstable in the present era or that they are limited to much smaller amplitudes by resonant coupling.

Dark Coulomb binding of heavy neutrinos of fourth family

NASA Astrophysics Data System (ADS)

Belotsky, K. M.; Esipova, E. A.; Khlopov, M. Yu.; Laletin, M. N.

2015-11-01

Direct dark matter searches put severe constraints on the weakly interacting massive particles (WIMPs). These constraints cause serious troubles for the model of stable neutrino of fourth generation with mass around 50GeV. Though the calculations of primordial abundance of these particles make them in the charge symmetric case a sparse subdominant component of the modern dark matter, their presence in the universe would exceed the current upper limits by several orders of the magnitude. However, if quarks and leptons of fourth generation possess their own Coulomb-like y-interaction, recombination of pairs of heavy neutrinos and antineutrinos and their annihilation in the “neutrinium” atoms can play important role in their cosmological evolution, reducing their modern abundance far below the experimental upper limits. The model of stable fourth generation assumes that the dominant part of dark matter is explained by excessive Ū antiquarks, forming (ŪŪŪ)-- charged clusters, bound with primordial helium in nuclear-interacting O-helium (OHe) dark atoms. The y charge conservation implies generation of the same excess of fourth generation neutrinos, potentially dangerous WIMP component of this scenario. We show that due to y-interaction recombination of fourth neutrinos with OHe hides these WIMPs from direct WIMP searches, leaving the negligible fraction of free neutrinos, what makes their existence compatible with the experimental constraints.

The dynamics and control of large-flexible space structures, part 10

NASA Technical Reports Server (NTRS)

Bainum, Peter M.; Reddy, A. S. S. R.

1988-01-01

A mathematical model is developed to predict the dynamics of the proposed orbiting Spacecraft Control Laboratory Experiment (SCOLE) during the station keeping phase. The equations of motion are derived using a Newton-Euler formulation. The model includes the effects of gravity, flexibility, and orbital dynamics. The control is assumed to be provided to the system through the Shuttle's three torquers, and through six actuators located by pairs at two points on the mast and at the mass center of the reflector. The modal shape functions are derived using the fourth order beam equation. The generic mode equations are derived to account for the effects of the control forces on the modal shape and frequencies. The equations are linearized about a nominal equilibrium position. The linear regulator theory is used to derive control laws for both the linear model of the rigidized SCOLE as well as that of the actual SCOLE including the first four flexible modes. The control strategy previously derived for the linear model of the rigidized SCOLE is applied to the nonlinear model of the same configuration of the system and preliminary single axis slewing maneuvers conducted. The results obtained confirm the applicability of the intuitive and appealing two-stage control strategy which would slew the SCOLE system, as if rigid to its desired position and then concentrate on damping out the residual flexible motions.

The role of collective self-gravity in the nonlinear evolution of viscous overstability in Saturn's rings

NASA Astrophysics Data System (ADS)

Lehmann, M.; Schmidt, J.; Salo, H.

2017-09-01

Observational evidence for the presence of axisymmetric periodic micro-structure on length scales of 100m - 200m in Saturn's A and B rings was revealed by several instruments onboard the Cassini mission to Saturn. The structure was seen in radio occultations performed by the Radio Science Subsystem (RSS) (Thomson et al. (2007)) and stellar occultations carried out with the Ultraviolet Imaging Spectrograph (UVIS) (Colwell et al. (2007)), and the Visual and Infrared Mapping Spectrometer (VIMS) (Hedman et al. (2014)). Up to date, this micro-structure is best explained by the viscous overstability, which arises as a spontaneous oscillatory instability in a dense ring, if certain conditions are met, leading to the formation of axisymmetric density waves with wavelengths on the order of 100m. We investigate the influence of collective self-gravity forces on the nonlinear, large scale evolution of the viscous overstability in Saturn's rings. To this end we numerically solve the nonlinear hydrodynamic model equations for a dense ring, including radial self-gravity and employing values for the transport coefficients (such as the ring's viscosity and heat conductivity) derived by salo et al. (2001). We concentrate on ring optical depths of order unity, which are appropriate to model Saturn's dense rings. Furthermore, local N-body simulations, incorporating vertical and radial collective self-gravity forces are performed. Direct particle-particle forces are omitted, which prevents small scale gravitational instabilities (self-gravity wakes) from forming, an approximation that allows us to study long radial scales of some 10 kilometers and to compare directly the hydrodynamic model and the N-body simulations. Our hydrodynamic model results, in the limit of vanishing self-gravity, compare very well with the studies of Latter & Ogilvie (2010) and Rein & Latter (2013). In contrast, for rings with non-vanishing radial self-gravity we find that the wavelengths of saturated overstable wave trains tend to settle close to the frequency minimum of the nonlinear dispersion relation, i.e. the saturation wavelengths decrease with increasing surface mass density of the ring. Good agreement between hydrodynamics and N-body simulations is found for disks with strong radial self-gravity, while the largest deviations occur in the limit of weak self-gravity. The resulting saturation wavelengths of the viscous overstability for moderate and strong radial self-gravity (100m-300m) agree reasonably well with the length scale of the axisymmetric periodic micro structure in Saturn's inner A ring and the B ring, as found by Cassini.

Embeddings of the "New Massive Gravity"

NASA Astrophysics Data System (ADS)

Dalmazi, D.; Mendonça, E. L.

2016-07-01

Here we apply different types of embeddings of the equations of motion of the linearized "New Massive Gravity" in order to generate alternative and even higher-order (in derivatives) massive gravity theories in D=2+1. In the first part of the work we use the Weyl symmetry as a guiding principle for the embeddings. First we show that a Noether gauge embedding of the Weyl symmetry leads to a sixth-order model in derivatives with either a massive or a massless ghost, according to the chosen overall sign of the theory. On the other hand, if the Weyl symmetry is implemented by means of a Stueckelberg field we obtain a new scalar-tensor model for massive gravitons. It is ghost-free and Weyl invariant at the linearized level around Minkowski space. The model can be nonlinearly completed into a scalar field coupled to the NMG theory. The elimination of the scalar field leads to a nonlocal modification of the NMG. In the second part of the work we prove to all orders in derivatives that there is no local, ghost-free embedding of the linearized NMG equations of motion around Minkowski space when written in terms of one symmetric tensor. Regarding that point, NMG differs from the Fierz-Pauli theory, since in the latter case we can replace the Einstein-Hilbert action by specific f(R,Box R) generalizations and still keep the theory ghost-free at the linearized level.