Pizzo, Nick
2017-11-01
A simple criterion for water particles to surf an underlying surface gravity wave is presented. It is found that particles travelling near the phase speed of the wave, in a geometrically confined region on the forward face of the crest, increase in speed. The criterion is derived using the equation of John (Commun. Pure Appl. Maths, vol. 6, 1953, pp. 497-503) for the motion of a zero-stress free surface under the action of gravity. As an example, a breaking water wave is theoretically and numerically examined. Implications for upper-ocean processes, for both shallow- and deep-water waves, are discussed.
Liouville gravity on bordered surfaces
International Nuclear Information System (INIS)
Jaskolski, Z.
1991-11-01
The functional quantization of the Liouville gravity on bordered surfaces in the conformal gauge is developed. It was shown that the geometrical interpretation of the Polyakov path integral as a sum over bordered surfaces uniquely determines the boundary conditions for the fields involved. The gravitational scaling dimensions of boundary and bulk operators and the critical exponents are derived. In particular, the boundary Hausdorff dimension is calculated. (author). 21 refs
The measurement of surface gravity.
Crossley, David; Hinderer, Jacques; Riccardi, Umberto
2013-04-01
This review covers basic theory and techniques behind the use of ground-based gravimetry at the Earth's surface. The orientation is toward modern instrumentation, data processing and interpretation for observing surface, land-based, time-variable changes to the geopotential. The instrumentation side is covered in some detail, with specifications and performance of the most widely used models of the three main types: the absolute gravimeters (FG5, A10 from Micro-g LaCoste), superconducting gravimeters (OSG, iGrav from GWR instruments), and the new generation of spring instruments (Micro-g LaCoste gPhone, Scintrex CG5 and Burris ZLS). A wide range of applications is covered, with selected examples from tides and ocean loading, atmospheric effects on gravity, local and global hydrology, seismology and normal modes, long period and tectonics, volcanology, exploration gravimetry, and some examples of gravimetry connected to fundamental physics. We show that there are only a modest number of very large signals, i.e. hundreds of µGal (10(-8) m s(-2)), that are easy to see with all gravimeters (e.g. tides, volcanic eruptions, large earthquakes, seasonal hydrology). The majority of signals of interest are in the range 0.1-5.0 µGal and occur at a wide range of time scales (minutes to years) and spatial extent (a few meters to global). Here the competing effects require a careful combination of different gravimeter types and measurement strategies to efficiently characterize and distinguish the signals. Gravimeters are sophisticated instruments, with substantial up-front costs, and they place demands on the operators to maximize the results. Nevertheless their performance characteristics such as drift and precision have improved dramatically in recent years, and their data recording ability and ruggedness have seen similar advances. Many subtle signals are now routinely connected with known geophysical effects such as coseismic earthquake displacements, post
Free surface flows under compensated gravity conditions
Dreyer, Miachel E
2007-01-01
This book considers the behavior of fluids in a low-gravity environment with special emphasis on application in PMD (propellant management device) systems . In the compensated gravity environment of a spacecraft, the hydrostatic pressure decreases to very low values depending on the residual acceleration, and surface tension forces become dominant. Consequently, surface tension can be used to transport and position liquids if the residual acceleration and the resulting hydrostatic pressure are small compared to the capillary pressure. One prominent application is the use of PMDs in surface-tension satellite tanks. PMDs must ensure that the tank outlet is covered with liquid whenever outflow is demanded. Furthermore, PMDs are used to ensure expulsion and refilling of tanks for liquids and gases for life support, reactants, and experiment supplies. Since most of the PMD designs are not testable on ground and thus rely on analytical or numerical concepts, this book treats three different flow problems with analy...
Analysis of gravity data using trend surfaces
Asimopolos, Natalia-Silvia; Asimopolos, Laurentiu
2013-04-01
In this paper we have developed algorithms and related software programs for calculating of trend surfaces of higher order. These methods of analysis of trends, like mobile media applications are filtration systems for geophysical data in surface. In particular we presented few case studies for gravity data and gravity maps. Analysis with polynomial trend surfaces contributes to the recognition, isolation and measurement of trends that can be represented by surfaces or hyper-surfaces (in several sizes), thus achieving a separation in regional variations and local variations. This separation is achieved by adjusting the trend function at different values. Trend surfaces using the regression analysis satisfy the criterion of least squares. The difference between the surface of trend and the observed value in a certain point is the residual value. Residual sum of squares of these values should be minimal as the criterion of least squares. The trend surface is considered as regional or large-scale and the residual value will be regarded as local or small-scale component. Removing the regional trend has the effect of highlighting local components represented by residual values. Surface analysis and hyper-surfaces principles are applied to the surface trend and any number of dimensions. For hyper-surfaces we can work with polynomial functions with four or more variables (three variables of space and other variables for interest parameters) that have great importance in some applications. In the paper we presented the mathematical developments about generalized trend surfaces and case studies about gravimetric data. The trend surfaces have the great advantage that the effect of regional anomalies can be expressed as analytic functions. These tendency surfaces allows subsequent mathematical processing and interesting generalizations, with great advantage to work with polynomial functions compared with the original discrete data. For gravity data we estimate the depth of
Touching random surfaces and Liouville gravity
International Nuclear Information System (INIS)
Klebanov, I.R.
1995-01-01
Large N matrix models modified by terms of the form g(TrΦ n ) 2 generate random surfaces which touch at isolated points. Matrix model results indicate that, as g is increased to a special value g t , the string susceptibility exponent suddenly jumps from its conventional value γ to γ/(γ-1). We study this effect in Liouville gravity and attribute it to a change of the interaction term from Oe α + φ for g t to Oe α - φ for g=g t (α + and α - are the two roots of the conformal invariance condition for the Liouville dressing of a matter operator O). Thus, the new critical behavior is explained by the unconventional branch of Liouville dressing in the action
Vincent, S.; Marsh, J. G.
1973-01-01
A global detailed gravimetric geoid has been computed by combining the Goddard Space Flight Center GEM-4 gravity model derived from satellite and surface gravity data and surface 1 deg-by-1 deg mean free air gravity anomaly data. The accuracy of the geoid is + or - 2 meters on continents, 5 to 7 meters in areas where surface gravity data are sparse, and 10 to 15 meters in areas where no surface gravity data are available. Comparisons have been made with the astrogeodetic data provided by Rice (United States), Bomford (Europe), and Mather (Australia). Comparisons have also been carried out with geoid heights derived from satellite solutions for geocentric station coordinates in North America, the Caribbean, Europe, and Australia.
2D gravity, random surfaces and all that
International Nuclear Information System (INIS)
Ambjoern, J.
1990-11-01
I review the recent progress in 2d gravity and discuss the new numerical simulations for 2d gravity and for random surfaces in d>2. The random surface theories of interest in d>2 have extrinsic curvature terms, and for a finite value of the extrinsic curvature coupling there seems to be a second order phase transition where the string tension scales. (orig.)
2015-09-30
Interaction of Surface Gravity Waves with Nonlinear Internal Gravity Waves Lian Shen St. Anthony Falls Laboratory and Department of Mechanical...on studying surface gravity wave evolution and spectrum in the presence of surface currents caused by strongly nonlinear internal solitary waves...interaction of surface and internal gravity waves in the South China Sea. We will seek answers to the following questions: 1) How does the wind-wave
Surface singularities in Eddington-inspired Born-Infeld gravity.
Pani, Paolo; Sotiriou, Thomas P
2012-12-21
Eddington-inspired Born-Infeld gravity was recently proposed as an alternative to general relativity that offers a resolution of spacetime singularities. The theory differs from Einstein's gravity only inside matter due to nondynamical degrees of freedom, and it is compatible with all current observations. We show that the theory is reminiscent of Palatini f(R) gravity and that it shares the same pathologies, such as curvature singularities at the surface of polytropic stars and unacceptable Newtonian limit. This casts serious doubt on its viability.
Field verification of ADCP surface gravity wave elevation spectra
Hoitink, A.J.F.; Peters, H.C.; Schroevers, M.
2007-01-01
Acoustic Doppler current profilers (ADCPs) can measure orbital velocities induced by surface gravity waves, yet the ADCP estimates of these velocities are subject to a relatively high noise level. The present paper introduces a linear filtration technique to significantly reduce the influence of
Properties of surface waves in granular media under gravity
International Nuclear Information System (INIS)
Zheng He-Peng
2014-01-01
Acoustical waves propagating along the free surface of granular media under gravity are investigated in the framework of elasticity theory. The influence of stress on a surface wave is analyzed. The results have shown that two types of surface waves, namely sagittal and transverse modes exist depending on initial stress states, which may have some influence on the dispersion relations of surface waves, but the influence is not great. Considering that the present experimental accuracy is far from distinguishing this detail, the validity of elasticity theory on the surface waves propagating in granular media can still be maintained. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
Precise surface gravities of δ Scuti stars from asteroseismology
García Hernández, A.; Suárez, J. C.; Moya, A.; Monteiro, M. J. P. F. G.; Guo, Z.; Reese, D. R.; Pascual-Granado, J.; Barceló Forteza, S.; Martín-Ruiz, S.; Garrido, R.; Nieto, J.
2017-10-01
The work reported here demonstrates that it is possible to accurately determine surface gravities of δ Scuti (δ Sct) stars using the frequency content from high-precision photometry and a measurement of the parallax. Using a sample of 10 eclipsing binary systems with a δ Sct component and the unique δ Sct star discovered with a transiting planet, WASP-33, we were able to refine the Δν-\\bar{ρ } relation. Using this relation and parallaxes, we obtained independent values for the masses and radii, allowing us to calculate the surface gravities without any constraints from spectroscopic or binary analysis. A remarkably good agreement was found between our results and those published, extracted from the analysis of the radial velocities and light curves of the systems. This reinforces the potential of Δν as a valuable observable for δ Sct stars and settles the degeneracy problem for the log g determination through spectroscopy.
Normal Incidence for Graded Index Surfaces
Khankhoje, Uday K.; Van Zyl, Jakob
2011-01-01
A plane wave is incident normally from vacuum (eta(sub 0) = 1) onto a smooth surface. The substrate has three layers; the top most layer has thickness d(sub 1) and permittivity epsilon(sub 1). The corresponding numbers for the next layer are d(sub 2); epsilon(sub 2), while the third layer which is semi-in nite has index eta(sub 3). The Hallikainen model [1] is used to relate volumetric soil moisture to the permittivity. Here, we consider the relation for the real part of the permittivity for a typical loam soil: acute epsilon(mv) = 2.8571 + 3.9678 x mv + 118:85 x mv(sup 2).
Gravity current into an ambient fluid with an open surface
Ungarish, Marius
2017-11-01
Consider the steady-state gravity current of height h and density ρ1 that propagates into an ambient motionless fluid of height H and density ρ2 with an upper surface open to the atmosphere (open channel) at high Reynolds number. The current propagates with speed U and causes a depth decrease χ of the top surface. This is a significant extension of Benjamin's (1968) seminal solution for the fixed-top channel χ = 0 . Here the determination of χ is a part of the problem. The dimensionless parameters of the problem are a = h / H and r =ρ2 /ρ1 . We show that a control-volume analysis determines χ = χ / H and Fr = U / (g ' h)1/2 as functions of a , r , where g ' = (r-1 - 1) g is the reduced gravity. The system satisfies balance of volume and momentum (explicitly), and vorticity (implicitly). We present solutions. The predicted flows are in general dissipative, and thus physically valid only for a Frb (a) , but the reduction is not dramatic, typically a few percent. In the Boussinesq r 1 case, χ << 1 while Fr and dissipation are close to Benjamin's values.
Influence of World and Gravity Model Selection on Surface Interacting Vehicle Simulations
Madden, Michael M.
2007-01-01
A vehicle simulation is surface-interacting if the state of the vehicle (position, velocity, and acceleration) relative to the surface is important. Surface-interacting simulations perform ascent, entry, descent, landing, surface travel, or atmospheric flight. Modeling of gravity is an influential environmental factor for surface-interacting simulations. Gravity is the free-fall acceleration observed from a world-fixed frame that rotates with the world. Thus, gravity is the sum of gravitation and the centrifugal acceleration due to the world s rotation. In surface-interacting simulations, the fidelity of gravity at heights above the surface is more significant than gravity fidelity at locations in inertial space. A surface-interacting simulation cannot treat the gravity model separately from the world model, which simulates the motion and shape of the world. The world model's simulation of the world's rotation, or lack thereof, produces the centrifugal acceleration component of gravity. The world model s reproduction of the world's shape will produce different positions relative to the world center for a given height above the surface. These differences produce variations in the gravitation component of gravity. This paper examines the actual performance of world and gravity/gravitation pairs in a simulation using the Earth.
Gamow, George
2003-01-01
A distinguished physicist and teacher, George Gamow also possessed a special gift for making the intricacies of science accessible to a wide audience. In Gravity, he takes an enlightening look at three of the towering figures of science who unlocked many of the mysteries behind the laws of physics: Galileo, the first to take a close look at the process of free and restricted fall; Newton, originator of the concept of gravity as a universal force; and Einstein, who proposed that gravity is no more than the curvature of the four-dimensional space-time continuum.Graced with the author's own draw
Electronic structure of incident carbon ions on a graphite surface
International Nuclear Information System (INIS)
Kiuchi, Masato; Takeuchi, Takae; Yamamoto, Masao.
1997-01-01
The electronic structure of an incident carbon ion on a graphite surface is discussed on the basis of ab initio molecular orbital calculations. A carbon cation forms a covalent bond with the graphite, and a carbon nonion is attracted to the graphite surface through van der Waals interaction. A carbon anion has no stable state on a graphite surface. The charge effects of incident ions become clear upon detailed examination of the electronic structure. (author)
Indian Academy of Sciences (India)
We study the cosmological dynamics for R p exp( λ R ) gravity theory in the metric formalism, using dynamical systems approach. Considering higher-dimensional FRW geometries in case of an imperfect fluid which has two different scale factors in the normal and extra dimensions, we find the exact solutions, and study its ...
The behavior of surface tension on steady-state rotating fluids in the low gravity environments
Hung, R. J.; Leslie, Fred W.
1987-01-01
The effect of surface tension on steady-state rotating fluids in a low gravity environment is studied. All the values of the physical parameters used in these calculations, except in the low gravity environments, are based on the measurements carried out by Leslie (1985) in the low gravity environment of a free-falling aircraft. The profile of the interface of two fluids is derived from Laplace's equation relating the pressure drop across an interface to the radii of curvature which has been applied to a low gravity rotating bubble that contacts the container boundary. The interface shape depends on the ratio of gravity to surface tension forces, the ratio of centrifugal to surface tension forces, the contact radius of the interface to the boundary, and the contact angle. The shape of the bubble is symmetric about its equator in a zero-gravity environment. This symmetry disappears and gradually shifts to parabolic profiles as the gravity environment becomes non-zero. The location of the maximum radius of the bubble moves upward from the center of the depth toward the top boundary of the cylinder as gravity increases. The contact radius of interface to the boundary r0 at the top side of cylinder increases and r0 at the bottom side of the cylinder decreases as the gravity environment increases from zero to 1 g.
ASTEROSEISMIC-BASED ESTIMATION OF THE SURFACE GRAVITY FOR THE LAMOST GIANT STARS
International Nuclear Information System (INIS)
Liu, Chao; Wu, Yue; Deng, Li-Cai; Wang, Liang; Wang, Wei; Li, Guang-Wei; Fang, Min; Fu, Jian-Ning; Hou, Yong-Hui; Zhang, Yong
2015-01-01
Asteroseismology is one of the most accurate approaches to estimate the surface gravity of a star. However, most of the data from the current spectroscopic surveys do not have asteroseismic measurements, which is very expensive and time consuming. In order to improve the spectroscopic surface gravity estimates for a large amount of survey data with the help of the small subset of the data with seismic measurements, we set up a support vector regression (SVR) model for the estimation of the surface gravity supervised by 1374 Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) giant stars with Kepler seismic surface gravity. The new approach can reduce the uncertainty of the estimates down to about 0.1 dex, which is better than the LAMOST pipeline by at least a factor of 2, for the spectra with signal-to-noise ratio higher than 20. Compared with the log g estimated from the LAMOST pipeline, the revised log g values provide a significantly improved match to the expected distribution of red clump and red giant branch stars from stellar isochrones. Moreover, even the red bump stars, which extend to only about 0.1 dex in log g, can be discriminated from the new estimated surface gravity. The method is then applied to about 350,000 LAMOST metal-rich giant stars to provide improved surface gravity estimates. In general, the uncertainty of the distance estimate based on the SVR surface gravity can be reduced to about 12% for the LAMOST data
ASTEROSEISMIC-BASED ESTIMATION OF THE SURFACE GRAVITY FOR THE LAMOST GIANT STARS
Energy Technology Data Exchange (ETDEWEB)
Liu, Chao; Wu, Yue; Deng, Li-Cai; Wang, Liang; Wang, Wei; Li, Guang-Wei [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, 20 A Datun Road, Beijing 100012 (China); Fang, Min [Departamento de Física Teórica, Facultad de Ciencias, Universidad Autonóma de Madrid, E-28049 Cantoblanco, Madrid (Spain); Fu, Jian-Ning [Department of Astronomy, Beijing Normal University, 19 Avenue Xinjiekouwai, Beijing 100875 (China); Hou, Yong-Hui; Zhang, Yong, E-mail: liuchao@nao.cas.cn [Nanjing Institute of Astronomical Optics and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042 (China)
2015-07-01
Asteroseismology is one of the most accurate approaches to estimate the surface gravity of a star. However, most of the data from the current spectroscopic surveys do not have asteroseismic measurements, which is very expensive and time consuming. In order to improve the spectroscopic surface gravity estimates for a large amount of survey data with the help of the small subset of the data with seismic measurements, we set up a support vector regression (SVR) model for the estimation of the surface gravity supervised by 1374 Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) giant stars with Kepler seismic surface gravity. The new approach can reduce the uncertainty of the estimates down to about 0.1 dex, which is better than the LAMOST pipeline by at least a factor of 2, for the spectra with signal-to-noise ratio higher than 20. Compared with the log g estimated from the LAMOST pipeline, the revised log g values provide a significantly improved match to the expected distribution of red clump and red giant branch stars from stellar isochrones. Moreover, even the red bump stars, which extend to only about 0.1 dex in log g, can be discriminated from the new estimated surface gravity. The method is then applied to about 350,000 LAMOST metal-rich giant stars to provide improved surface gravity estimates. In general, the uncertainty of the distance estimate based on the SVR surface gravity can be reduced to about 12% for the LAMOST data.
Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey
International Nuclear Information System (INIS)
Martin, Emily C.; Mace, Gregory N.; McLean, Ian S.; Logsdon, Sarah E.; Rice, Emily L.; Kirkpatrick, J. Davy; Burgasser, Adam J.; McGovern, Mark R.; Prato, Lisa
2017-01-01
We combine 131 new medium-resolution ( R ∼ 2000) J -band spectra of M, L, and T dwarfs from the Keck NIRSPEC Brown Dwarf Spectroscopic Survey (BDSS) with 97 previously published BDSS spectra to study surface-gravity-sensitive indices for 228 low-mass stars and brown dwarfs spanning spectral types M5–T9. Specifically, we use an established set of spectral indices to determine surface gravity classifications for all of the M6–L7 objects in our sample by measuring the equivalent widths (EW) of the K i lines at 1.1692, 1.1778, and 1.2529 μ m, and the 1.2 μ m FeH J absorption index. Our results are consistent with previous surface gravity measurements, showing a distinct double peak—at ∼L5 and T5—in K i EW as a function of spectral type. We analyze the K i EWs of 73 objects of known ages and find a linear trend between log(Age) and EW. From this relationship, we assign age ranges to the very low gravity, intermediate gravity, and field gravity designations for spectral types M6–L0. Interestingly, the ages probed by these designations remain broad, change with spectral type, and depend on the gravity-sensitive index used. Gravity designations are useful indicators of the possibility of youth, but current data sets cannot be used to provide a precise age estimate.
Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey
Energy Technology Data Exchange (ETDEWEB)
Martin, Emily C.; Mace, Gregory N.; McLean, Ian S.; Logsdon, Sarah E. [Department of Physics and Astronomy, University of California Los Angeles, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547 (United States); Rice, Emily L. [Department of Engineering Science and Physics, College of Staten Island, 2800 Victory Boulevard, Staten Island, NY 10301 (United States); Kirkpatrick, J. Davy [Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Burgasser, Adam J. [Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States); McGovern, Mark R. [Math and Sciences Division, Antelope Valley College, 3041 West Avenue K, Lancaster, CA 93536 (United States); Prato, Lisa, E-mail: emartin@astro.ucla.edu [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States)
2017-03-20
We combine 131 new medium-resolution ( R ∼ 2000) J -band spectra of M, L, and T dwarfs from the Keck NIRSPEC Brown Dwarf Spectroscopic Survey (BDSS) with 97 previously published BDSS spectra to study surface-gravity-sensitive indices for 228 low-mass stars and brown dwarfs spanning spectral types M5–T9. Specifically, we use an established set of spectral indices to determine surface gravity classifications for all of the M6–L7 objects in our sample by measuring the equivalent widths (EW) of the K i lines at 1.1692, 1.1778, and 1.2529 μ m, and the 1.2 μ m FeH{sub J} absorption index. Our results are consistent with previous surface gravity measurements, showing a distinct double peak—at ∼L5 and T5—in K i EW as a function of spectral type. We analyze the K i EWs of 73 objects of known ages and find a linear trend between log(Age) and EW. From this relationship, we assign age ranges to the very low gravity, intermediate gravity, and field gravity designations for spectral types M6–L0. Interestingly, the ages probed by these designations remain broad, change with spectral type, and depend on the gravity-sensitive index used. Gravity designations are useful indicators of the possibility of youth, but current data sets cannot be used to provide a precise age estimate.
Extra Low-Gear: A Micro-Gravity Laboratory to Simulate Asteroid Surfaces
Scheeres, D. J.; Sánchez, P.; Dissly, R. W.; Asphaug, E. I.; Housen, K. R.; Swift, M. R.; Yano, H.; Roark, S. E.; Soto, J. C.
2009-03-01
The conceptual design and application of a low-speed centrifuge for carrying out milli to micro-G gravity experiments to simulate the granular nature of the surface and interiors of asteroids and comets is described.
Recent progress in the theory of random surfaces and simplicial quantum gravity
International Nuclear Information System (INIS)
Ambjoern, J.
1995-01-01
Some of the recent developments in the theory of random surfaces and simplicial quantum gravity is reviewed. For 2d quantum gravity this includes the failure of Regge calculus, our improved understanding of the c>1 regime, some surprises for q-state Potts models with q>4, attempts to use renormalization group techniques, new critical behavior of random surface models with extrinsic curvature and improved algorithms. For simplicial quantum gravity in higher dimensions it includes a discussion of the exponential entropy bound needed for the models to be well defined, the question of ''computational ergodicity'' and the question of how to extract continuum behavior from the lattice simulations. ((orig.))
Review of Electrical and Gravity Methods of Near-Surface ...
African Journals Online (AJOL)
USER
ABSTRACT: The theory and practice of electrical and gravity methods of geophysics for groundwater exploration was reviewed with illustrations and data examples. With the goal of reducing cases of borehole/water-well failure attributed to the lack of the knowledge of the methods of geophysics for groundwater exploration ...
Review of Electrical and Gravity Methods of Near-Surface ...
African Journals Online (AJOL)
USER
In every big city, dozen of new boreholes or hand-dug wells are .... This paper is a review of the electrical and gravity methods of ... audience/readership. II. ..... W. W. Northon and Company, New York. Butler ... McGraw Hill Books Co. New York ...
Surface tension of the horizon and Archimedes' principle for gravity
Shu, Liangsuo; Cui, Kaifeng; Liu, Xiaokang; Liu, Zhichun; Liu, Wei
2018-01-01
In this letter, by combining the holographic principle with the graviton Bose-Einstein condensates hypothesis of gravitational backgrounds, we provide a theory of gravity, which provides some kinetic details of how the gravitational coupling between matter and spacetime works. The effective radial potential energy of an object in a gravitational field is found to be the sum of the interfacial energy caused by its micro horizon and the energy required to make room for it by displacing graviton...
DEFF Research Database (Denmark)
Zhdanov, Michael; Cai, Hongzhu
2014-01-01
We introduce a new method of modeling and inversion of potential field data generated by a density contrast surface. Our method is based on 3D Cauchy-type integral representation of the potential fields. Traditionally, potential fields are calculated using volume integrals of the domains occupied...
Near-surface characterization for seismic exploration based on gravity and resistivity data
Czech Academy of Sciences Publication Activity Database
Mrlina, Jan
(2016), č. článku 41892. [Middle East Geoscience Conference and Exhibition /12./. Manama, 07.03.2016-10.03.2016] Institutional support: RVO:67985530 Keywords : gravity and resistivity surveys * near-surface formations * seismic velocity Subject RIV: DC - Siesmology, Volcanology, Earth Structure
Computation of 3D steady Navier-Stokes flow with free-surface gravity waves
Lewis, M.R.; Koren, B.; Raven, H.C.; Armfield, S.; Morgan, P.; Srinivas, K,
2003-01-01
In this paper an iterative method for the computation of stationary gravity-wave solutions is investigated, using a novel formulation of the free-surface (FS) boundary-value problem. This method requires the solution of a sequence of stationary Reynolds-Averaged Navier-Stokes subproblems employing
Computation of 3D steady Navier-Stokes flow with free-surface gravity waves
M.R. Lewis; B. Koren (Barry); H.C. Raven
2003-01-01
textabstractIn this paper an iterative method for the computation of stationary gravity-wave solutions is investigated, using a novel formulation of the free-surface (FS) boundary-value problem. This method requires the solution of a sequence of stationary Reynolds-Averaged Navier-Stokes subproblems
Signal and noise in Gravity Recovery and Climate Experiment (GRACE) observed surface mass variations
Schrama, E.J.O.; Wouters, B.; Lavallée, D.A.
2007-01-01
The Gravity Recovery and Climate Experiment (GRACE) product used for this study consists of 43 monthly potential coefficient sets released by the GRACE science team which are used to generate surface mass thickness grids expressed as equivalent water heights (EQWHs). We optimized both the smoothing
VizieR Online Data Catalog: Surface gravity determination in late-type stars (Morel+, 2012)
Morel, T.; Miglio, A.
2012-06-01
The frequency of maximum oscillation power measured in dwarfs and giants exhibiting solar-like pulsations provides a precise, and potentially accurate, inference of the stellar surface gravity. An extensive comparison for about 40 well-studied pulsating stars with gravities derived using classical methods (ionization balance, pressure-sensitive spectral features or location with respect to evolutionary tracks) supports the validity of this technique and reveals an overall remarkable agreement with mean differences not exceeding 0.05dex (although with a dispersion of up to ~0.2dex). It is argued that interpolation in theoretical isochrones may be the most precise way of estimating the gravity by traditional means in nearby dwarfs. Attention is drawn to the usefulness of seismic targets as benchmarks in the context of large-scale surveys. (1 data file).
Bechert, M.; Scheid, B.
2017-11-01
The draw resonance effect appears in fiber spinning processes if the ratio of take-up to inlet velocity, the so-called draw ratio, exceeds a critical value and manifests itself in steady oscillations of flow velocity and fiber diameter. We study the effect of surface tension on the draw resonance behavior of Newtonian fiber spinning in the presence of inertia and gravity. Utilizing an alternative scaling makes it possible to visualize the results in stability maps of highly practical relevance. The interplay of the destabilizing effect of surface tension and the stabilizing effects of inertia and gravity lead to nonmonotonic stability behavior and local stability maxima with respect to the dimensionless fluidity and the dimensionless inlet velocity. A region of unconditional instability caused by the influence of surface tension is found in addition to the region of unconditional stability caused by inertia, which was described in previous works [M. Bechert, D. W. Schubert, and B. Scheid, Eur. J. Mech B 52, 68 (2015), 10.1016/j.euromechflu.2015.02.005; Phys. Fluids 28, 024109 (2016), 10.1063/1.4941762]. Due to its importance for a particular group of fiber spinning applications, a viscous-gravity-surface-tension regime, i.e., negligible effect of inertia, is analyzed separately. The mechanism underlying the destabilizing effect of surface tension is discussed and established stability criteria are tested for validity in the presence of surface tension.
Surface charges for gravity and electromagnetism in the first order formalism
Frodden, Ernesto; Hidalgo, Diego
2018-02-01
A new derivation of surface charges for 3 + 1 gravity coupled to electromagnetism is obtained. Gravity theory is written in the tetrad-connection variables. The general derivation starts from the Lagrangian, and uses the covariant symplectic formalism in the language of forms. For gauge theories, surface charges disentangle physical from gauge symmetries through the use of Noether identities and the exactness symmetry condition. The surface charges are quasilocal, explicitly coordinate independent, gauge invariant and background independent. For a black hole family solution, the surface charge conservation implies the first law of black hole mechanics. As a check, we show the first law for an electrically charged, rotating black hole with an asymptotically constant curvature (the Kerr–Newman (anti-)de Sitter family). The charges, including the would-be mass term appearing in the first law, are quasilocal. No reference to the asymptotic structure of the spacetime nor the boundary conditions is required and therefore topological terms do not play a rôle. Finally, surface charge formulae for Lovelock gravity coupled to electromagnetism are exhibited, generalizing the one derived in a recent work by Barnich et al Proc. Workshop ‘ About Various Kinds of Interactions’ in honour of Philippe Spindel (4–5 June 2015, Mons, Belgium) C15-06-04 (2016 (arXiv:1611.01777 [gr-qc])). The two different symplectic methods to define surface charges are compared and shown equivalent.
Mass Redistribution in the Core and Time-varying Gravity at the Earth's Surface
Kuang, Wei-Jia; Chao, Benjamin F.; Fang, Ming
2003-01-01
The Earth's liquid outer core is in convection, as suggested by the existence of the geomagnetic field in much of the Earth's history. One consequence of the convection is the redistribution of mass resulting from relative motion among fluid parcels with slightly different densities. This time dependent mass redistribution inside the core produces a small perturbation on the gravity field of the Earth. With our numerical dynamo solutions, we find that the mass redistribution (and the resultant gravity field) symmetric about the equator is much stronger than that anti-symmetric about the equator. In particular, J(sub 2) component is the strongest. In addition, the gravity field variation increases with the Rayleigh number that measures the driving force for the geodynamo in the core. With reasonable scaling from the current dynamo solutions, we could expect that at the surface of the Earth, the J(sub 2) variation from the core is on the order of l0(exp -16)/year relative to the mean (i.e. spherically symmetric) gravity field of the Earth. The possible shielding effect due to core-mantle boundary pressure variation loading is likely much smaller and is therefore negligible. Our results suggest that time-varying gravity field perturbation due to core mass redistribution may be measured with modem space geodetic observations, which will result a new means of detecting dynamical processes in the Earth's deep interior.
(2+1)-dimensional pure gravity for an arbitrary closed initial surface
International Nuclear Information System (INIS)
Hosoya, Akio; Nakao, Ken-ichi.
1989-04-01
The (2+1)-dimensional pure Einstein gravity is studied in the ADM formalism. We completely solve the initial value and the time evolution problems with a closed Riemann surface being an initial surface, choosing the time slicing so that the trace of the extrinsic curvature is independent of spatial coordinates. The possible topology of the two-surface is either a torus or a Riemann surface of genus g≥2. It is shown that the moduli parameters of the torus follow the geodesic curve in the moduli space, while the motion of the moduli is static for the case g≥2. (author)
Prospects for Improving Gravity-Fed Surface Irrigation Systems in Mediterranean European Contexts
Directory of Open Access Journals (Sweden)
Daniele Masseroni
2017-01-01
Full Text Available Traditionally, most irrigation practices in Southern Europe have been based on gravity-fed surface irrigation systems. Currently, these systems remain a relevant typology in the European Union (EU member states of the Mediterranean areas, where it is often the only sustainable method for farmers due to the small size of agricultural holdings, their reduced capacity and readiness to invest and the low ratio between yield profits and irrigation costs. In the last several years, in response to European and national directives, surface irrigation has garnered increasing attention at the political and bureaucratic levels due to frequent criticisms of its postulated low efficiency and high water wastage. However, these systems commonly provide a number of ecosystem services and nature-based solutions that increase the positive externalities in different rural socio-ecological contexts and often have the potential to extend these services and provide solutions that are compatible with economical sustainability. This study aims to discuss the prospects for new practices and for the rehabilitation and modernization of the gravity-fed surface irrigation systems in EU Mediterranean areas to enhance water efficiency, thus gaining both economic advantages and environmental benefits. The difficulties, stimuli for improvements and peculiarities of the irrigation water management of four rural environments located in Italy, Spain and Portugal were analyzed and compared to the current state of the gravity-fed surface irrigation systems with hypothetical future improvements achievable by innovative technologies and practices. In these different case studies, the current gravity-fed surface irrigation systems have an obsolete regulatory structure; water-use efficiency is not a driving criterion for the management of the conveyance and distribution canal network, and farmers are not yet adequately encouraged to adopt more efficient gravity-fed irrigation practices
Quantification of gravity-induced skin strain across the breast surface.
Sanchez, Amy; Mills, Chris; Haake, Steve; Norris, Michelle; Scurr, Joanna
2017-12-01
Quantification of the magnitude of skin strain in different regions of the breast may help to estimate possible gravity-induced damage whilst also being able to inform the selection of incision locations during breast surgery. The aim of this study was to quantify static skin strain over the breast surface and to estimate the risk of skin damage caused by gravitational loading. Fourteen participants had 21 markers applied to their torso and left breast. The non-gravity breast position was estimated as the mid-point of the breast positions in water and soybean oil (higher and lower density than breast respectively). The static gravity-loaded breast position was also measured. Skin strain was calculated as the percentage extension between adjacent breast markers in the gravity and non-gravity loaded conditions. Gravity induced breast deformation caused peak strains ranging from 14 to 75% across participants, with potentially damaging skin strain (>60%) in one participant and skin strains above 30% (skin resistance zone) in a further four participants. These peak strain values all occurred in the longitudinal direction in the upper region of the breast skin. In the latitudinal direction, smaller-breasted participants experienced greater strain on the outer (lateral) breast regions and less strain on the inner (medial) breast regions, a trend which was reversed in the larger breasted participants (above size 34D). To reduce tension on surgical incisions it is suggested that preference should be given to medial latitudinal locations for smaller breasted women and lateral latitudinal locations for larger breasted women. Copyright © 2017 Elsevier Ltd. All rights reserved.
Kusche, J.; Schrama, E.J.O.
2005-01-01
Monitoring hydrological redistributions through their integrated gravitational effect is the primary aim of the Gravity Recovery and Climate Experiment (GRACE) mission. Time?variable gravity data from GRACE can be uniquely inverted to hydrology, since mass transfers located at or near the Earth's
Weiss, P.; Gardette, B.; Chirié, B.; Collina-Girard, J.; Delauze, H. G.
2012-12-01
Extravehicular activity (EVA) of astronauts during space missions is simulated nowadays underwater in neutral buoyancy facilities. Certain aspects of weightlessness can be reproduced underwater by adding buoyancy to a diver-astronaut, therefore exposing the subject to the difficulties of working without gravity. Such tests were done at the COMEX' test pool in Marseilles in the 1980s to train for a French-Russian mission to the MIR station, for the development of the European HERMES shuttle and the COLUMBUS laboratory. However, space agencies are currently studying missions to other destinations than the International Space Station in orbit, such as the return to the Moon, NEO (near-Earth objects) or Mars. All these objects expose different gravities: Moon has one sixth of Earth's gravity, Mars has a third of Earth's gravity and asteroids have virtually no surface gravity; the astronaut "floats" above the ground. The preparation of such missions calls for a new concept in neutral buoyancy training, not on man-made structures, but on natural terrain, underwater, to simulate EVA operations such as sampling, locomotion or even anchoring in low gravity. Underwater sites can be used not only to simulate the reduced gravity that astronauts will experience during their field trips, also human factors like stress are more realistically reproduced in such environment. The Bay of Marseille hosts several underwater sites that can be used to simulate various geologic morphologies, such as sink-holes which can be used to simulate astronaut descends into craters, caves where explorations of lava tubes can be trained or monolithic rock structures that can be used to test anchoring devices (e.g., near Earth objects). Marseilles with its aerospace and maritime/offshore heritage hosts the necessary logistics and expertise that is needed to perform such simulations underwater in a safe manner (training of astronaut-divers in local test pools, research vessels, subsea robots and
A Gravity-Responsive Time-Keeping Protein of the Plant and Animal Cell Surface
Morre, D. James
2003-01-01
The hypothesis under investigation was that a ubiquinol (NADH) oxidase protein of the cell surface with protein disulfide-thiol interchange activity (= NOX protein) is a plant and animal time-keeping ultradian (period of less than 24 h) driver of both cell enlargement and the biological clock that responds to gravity. Despite considerable work in a large number of laboratories spanning several decades, this is, to my knowledge, our work is the first demonstration of a time-keeping biochemical reaction that is both gravity-responsive and growth-related and that has been shown to determine circadian periodicity. As such, the NOX protein may represent both the long-sought biological gravity receptor and the core oscillator of the cellular biological clock. Completed studies have resulted in 12 publications and two issued NASA-owned patents of the clock activity. The gravity response and autoentrainment were characterized in cultured mammalian cells and in two plant systems together with entrainment by light and small molecules (melatonin). The molecular basis of the oscillatory behavior was investigated using spectroscopic methods (Fourier transform infrared and circular dichroism) and high resolution electron microscopy. We have also applied these findings to an understanding of the response to hypergravity. Statistical methods for analysis of time series phenomena were developed (Foster et al., 2003).
Modeling the Salar de Uyuni, Bolivia as an Equipotential Surface of Earth's Gravity Field
Borsa, Adrian; Bills, Bruce
2004-01-01
The salar de Uyuni is a massive dry salt lake that lies at the lowest point of an internal/drainage basin in the Bolivian Altiplano. Its topography is remarkable for its extraordinary flatness over almost a full degree of latitude and longitude. We surveyed a 54 x 45 km region of the salar with kinematic GPS in September, 2002 and found a topographic range of only 80 cm over the entire surveyed area. Furthermore, the survey revealed distinct surface features with several dominant wavelengths and orientations. Some of these appear to be aligned with orographic features that intersect the salar, leading us to conjecture that they are the surface expression of high-density mountains that have been buried by low-density basin sediments. Over the oceans, a similar correspondence between basin bathymetry and surface topography is exploited to map the seafloor using sea-surface satellite altimetry measurements, with the sea surface following geoid undulations due to the underwater mass distribution. On the salar, annual flooding creates a shallow lake whose surface also lies on a equipotential surface shaped by the distribution of underlying mass. The link to the actual salar surface is via the dissolution and redeposition of salt by the lake waters, which appears to push the system to an equilibrium of constant water depth and the coincidence of the shapes of the lake surface and bottom. To test our hypothesis about the origin of the surface features on the salar, we compare our GPS survey elevations with the equipotential surface generated from local gravity measurements in conjunction with gravity and potential values from the EGM96 global geopotential model. 50% of the variance of the GPS elevations can be explained by equipotential surface undulations from the EGM96 model alone, and an additional 40% is explained by the shorter-wavelength equipotential surface derived from local gravity. We examine the unexplained 10% of elevation variance from the standpoint of
International Nuclear Information System (INIS)
Behroozi, F.; Mohazzabi, P.; McCrickard, J.
1995-01-01
The familiar catenary is the shape assumed by a chain or string as it hangs from two points. The mathematical equation of the catenary was first published more than three hundred years ago by Leibnitz and Huygen, among others. Here we consider the shapes assumed by a hanging string in the presence of gravity and surface tension. The surface tension is introduced by suspending the string from a thin horizontal rod while the area bounded by the string and the rod is covered with a soap film. The string then assumes new and wonderful shapes depending on the relative strength of the surface tension and the weight per unit length of the string. When surface tension dominates, the string is pulled inward, assuming a convex shape similar to the Greek letter γ. On the other hand, when gravity is dominant the string is pulled outward and assumes a concave shape best described as a distorted catenary. However, when the gravitational force normal to the string matches the surface tension, the string takes a linear configuration similar to the letter V. Under suitable conditions, the string can be made to assume any of the three configurations by adjusting the separation of its end points. The equations that describe the shape of the string are derived by minimizing the total energy of the system and are presented for the three principal configurations
Impact of dissipation on the energy spectrum of experimental turbulence of gravity surface waves
Campagne, Antoine; Hassaini, Roumaissa; Redor, Ivan; Sommeria, Joël; Valran, Thomas; Viboud, Samuel; Mordant, Nicolas
2018-04-01
We discuss the impact of dissipation on the development of the energy spectrum in wave turbulence of gravity surface waves with emphasis on the effect of surface contamination. We performed experiments in the Coriolis facility, which is a 13-m-diam wave tank. We took care of cleaning surface contamination as well as possible, considering that the surface of water exceeds 100 m2. We observe that for the cleanest condition the frequency energy spectrum shows a power-law decay extending up to the gravity capillary crossover (14 Hz) with a spectral exponent that is increasing with the forcing strength and decaying with surface contamination. Although slightly higher than reported previously in the literature, the exponent for the cleanest water remains significantly below the prediction from the weak turbulence theory. By discussing length and time scales, we show that weak turbulence cannot be expected at frequencies above 3 Hz. We observe with a stereoscopic reconstruction technique that the increase with the forcing strength of energy spectrum beyond 3 Hz is mostly due to the formation and strengthening of bound waves.
Surface state decoherence in loop quantum gravity, a first toy model
International Nuclear Information System (INIS)
Feller, Alexandre; Livine, Etera R
2017-01-01
The quantum-to-classical transition through decoherence is a major facet of the semi-classical analysis of quantum models that are supposed to admit a classical regime, as quantum gravity should be. A particular problem of interest is the decoherence of black hole horizons and holographic screens induced by the bulk-boundary coupling with interior degrees of freedom. Here in this paper we present a first toy-model, in the context of loop quantum gravity, for the dynamics of a surface geometry as an open quantum system. We discuss the resulting decoherence and recoherence and compare the exact density matrix evolution to the commonly used master equation approximation à la Lindblad underlining its merits and limitations. The prospect of this study is to have a clearer understanding of the boundary decoherence of black hole horizons seen by outside observers. (paper)
Barrios, J. M.; Verstraeten, W. W.; Farifteh, J.; Maes, P.; Aerts, J. M.; Coppin, P.
2012-04-01
Lyme borreliosis (LB) is the most common tick-borne disease in Europe and incidence growth has been reported in several European countries during the last decade. LB is caused by the bacterium Borrelia burgdorferi and the main vector of this pathogen in Europe is the tick Ixodes ricinus. LB incidence and spatial spread is greatly dependent on environmental conditions impacting habitat, demography and trophic interactions of ticks and the wide range of organisms ticks parasite. The landscape configuration is also a major determinant of tick habitat conditions and -very important- of the fashion and intensity of human interaction with vegetated areas, i.e. human exposure to the pathogen. Hence, spatial notions as distance and adjacency between urban and vegetated environments are related to human exposure to tick bites and, thus, to risk. This work tested the adequacy of a gravity model setting to model the observed spatio-temporal pattern of LB as a function of location and size of urban and vegetated areas and the seasonal and annual change in the vegetation dynamics as expressed by MODIS NDVI. Opting for this approach implies an analogy with Newton's law of universal gravitation in which the attraction forces between two bodies are directly proportional to the bodies mass and inversely proportional to distance. Similar implementations have proven useful in fields like trade modeling, health care service planning, disease mapping among other. In our implementation, the size of human settlements and vegetated systems and the distance separating these landscape elements are considered the 'bodies'; and the 'attraction' between them is an indicator of exposure to pathogen. A novel element of this implementation is the incorporation of NDVI to account for the seasonal and annual variation in risk. The importance of incorporating this indicator of vegetation activity resides in the fact that alterations of LB incidence pattern observed the last decade have been ascribed
Deville, S.; Champollion, C.; chery, J.; Doerflinger, E.; Le Moigne, N.; Bayer, R.; Vernant, P.
2011-12-01
The assessment of water storage in the unsaturated zone in karstic areas is particularly challenging. Indeed, water flow path and water storage occur in quite heterogeneous ways through small scale porosity, fractures, joints and large voids. Due to this large heterogeneity, it is therefore difficult to estimate the amount of water circulating in the vadose zone by hydrological means. One indirect method consists to measure the gravity variation associated to water storage and withdrawal. Here, we apply a gravimetric method in which the gravity is measured at the surface and at depth on different sites. Then the time variations of the surface to depth (STD) gravity differences are compared for each site. In this study we attempt to evaluate the magnitude of epikarstic water storage variation in various karst settings using a CG5 portable gravimeter. Surface to depth gravity measurements are performed two times a year since 2009 at the surface an inside caves at different depths on three karst aquifers in southern France : 1. A limestone site on the Larzac plateau with a vadose zone thickness of 300m On this site measurements are done on five locations at different depths going from 0 to 50 m; 2. A dolomitic site on the Larzac plateau (Durzon karst aquifer) with a vadose zone thickness of 200m; Measurements are taken at the surface and at 60m depth 3. A limestone site on the Hortus karst aquifer and "Larzac Septentrional karst aquifer") with a vadose zone thickness of only 35m. Measurements are taken at the surface and at 30m depth Therefore, our measurements are used in two ways : First, the STD differences between dry and wet seasons are used to estimate the capacity of differential storage of each aquifer. Surprisingly, the differential storage capacity of all the sites is relatively invariant despite their variable geological of hydrological contexts. Moreover, the STD gravity variations on site 1 show that no water storage variation occurs beneath 10m depth
Near-station terrain corrections for gravity data by a surface-integral technique
Gettings, M.E.
1982-01-01
A new method of computing gravity terrain corrections by use of a digitizer and digital computer can result in substantial savings in the time and manual labor required to perform such corrections by conventional manual ring-chart techniques. The method is typically applied to estimate terrain effects for topography near the station, for example within 3 km of the station, although it has been used successfully to a radius of 15 km to estimate corrections in areas where topographic mapping is poor. Points (about 20) that define topographic maxima, minima, and changes in the slope gradient are picked on the topographic map, within the desired radius of correction about the station. Particular attention must be paid to the area immediately surrounding the station to ensure a good topographic representation. The horizontal and vertical coordinates of these points are entered into the computer, usually by means of a digitizer. The computer then fits a multiquadric surface to the input points to form an analytic representation of the surface. By means of the divergence theorem, the gravity effect of an interior closed solid can be expressed as a surface integral, and the terrain correction is calculated by numerical evaluation of the integral over the surfaces of a cylinder, The vertical sides of which are at the correction radius about the station, the flat bottom surface at the topographic minimum, and the upper surface given by the multiquadric equation. The method has been tested with favorable results against models for which an exact result is available and against manually computed field-station locations in areas of rugged topography. By increasing the number of points defining the topographic surface, any desired degree of accuracy can be obtained. The method is more objective than manual ring-chart techniques because no average compartment elevations need be estimated ?
Second generation diffusion model of interacting gravity waves on the surface of deep fluid
Directory of Open Access Journals (Sweden)
A. Pushkarev
2004-01-01
Full Text Available We propose a second generation phenomenological model for nonlinear interaction of gravity waves on the surface of deep water. This model takes into account the effects of non-locality of the original Hasselmann diffusion equation still preserving important properties of the first generation model: physically consistent scaling, adherence to conservation laws and the existence of Kolmogorov-Zakharov solutions. Numerical comparison of both models with the original Hasselmann equation shows that the second generation models improves the angular distribution in the evolving wave energy spectrum.
Nakamura, T.; Tsuboi, S.
2013-12-01
Recent seismological studies suggested subsurface activities preceding the 2011 Tohoku earthquake; the occurrence of migration of seismicity (Kato et al., 2012) and slow slip events (Ito et al., 2013) in and around the source area one month before the mainshock. In this study, we investigated sea-surface gravity changes observed by the shipboard gravimeter mounted on research vessels before the mainshock. The vessels incidentally passed through the source area along almost the same cruise track twice, four months before and one month before the mainshock. Comparing the sea surface gravity in the former track with that in the latter after Bouguer correction, we find the gravity changes of approximately 7 mGal in coseismic slip areas near the trench axis during the three months. We find these gravity changes even in the crossing areas of the cruise tracks where seafloor topographies have no differences between the tracks. We also find that the topographic differences show positive changes but the gravity changes negative ones in other areas, which is a negative correlation inconsistent with the theoretical relationship between the topographic difference and the gravity change. These mean that the differences of seafloor topographies due to differences between the two cruise tracks are not main causes of the observed gravity changes there. The changes cannot also be explained by drifts of the gravimeter and geostrophic currents. Although we have not had any clear evidences, we speculate that the possible cause may be density increases around the seismogenic zone or uplifts of seafloor in order to explain the changes of this size. We estimate the density increases of 1.0 g/cm**3 in a disk with a radius of 40 km and a width of 200 m or the uplifts of several tens of meters in seafloor areas for the observed gravity changes. Our results indicate that sea-surface gravity observations may be one of valid approaches to monitor the approximate location of a possible great
Borsa, Adrian
2008-01-01
The salar de Uyuni is a massive dry salt lake that lies at the lowest point of an internal drainage basin in the Bolivian Altiplano. A kinematic GPS survey of the salar in September 2002 found a topographic range of only 80 cm over a 54 × 45 km area and subtle surface features that appeared to correlate with mapped gravity. In order to confirm the correlation between topography and gravity/geopotential, we use local gravity measurements and the EGM96 global geopotential model to construct a c...
Tobin, Nicolas; Chamorro, Leonardo P.
2018-03-01
The so-called wake-moment coefficient C˜h and lateral wake deflection of three-dimensional windbreaks are explored in the near and far wake. Wind-tunnel experiments were performed to study the functional dependence of C˜h with windbreak aspect ratio, incidence angle, and the ratio of the windbreak height and surface roughness (h /z0 ). Supported with the data, we also propose basic models for the wake deflection of the windbreak in the near and far fields. The near-wake model is based on momentum conservation considering the drag on the windbreak, whereas the far-wake counterpart is based on existing models for wakes behind surface-mounted obstacles. Results show that C˜h does not change with windbreak aspect ratios of 10 or greater; however, it may be lower for an aspect ratio of 5. C˜h is found to change roughly with the cosine of the incidence angle, and to depend strongly on h /z0 . The data broadly support the proposed wake-deflection models, though better predictions could be made with improved knowledge of the windbreak drag coefficient.
Surface density of spacetime degrees of freedom from equipartition law in theories of gravity
International Nuclear Information System (INIS)
Padmanabhan, T.
2010-01-01
I show that the principle of equipartition, applied to area elements of a surface ∂V which are in equilibrium at the local Davies-Unruh temperature, allows one to determine the surface number density of the microscopic spacetime degrees of freedom in any diffeomorphism invariant theory of gravity. The entropy associated with these degrees of freedom matches with the Wald entropy for the theory. This result also allows one to attribute an entropy density to the spacetime in a natural manner. The field equations of the theory can then be obtained by extremizing this entropy. Moreover, when the microscopic degrees of freedom are in local thermal equilibrium, the spacetime entropy of a bulk region resides on its boundary.
Boddice, Daniel; Metje, Nicole; Tuckwell, George
2017-11-01
Geophysical surveying is widely used for the location of subsurface features. Current technology is limited in terms of its resolution (thus size of features it can detect) and penetration depth and a suitable technique is needed to bridge the gap between shallow near surface investigation using techniques such as EM conductivity mapping and GPR commonly used to map the upper 5 m below ground surface, and large features at greater depths detectable using conventional microgravity (> 5 m below ground surface). This will minimise the risks from unknown features buried in and conditions of the ground during civil engineering work. Quantum technology (QT) gravity sensors potentially offer a step-change in technology for locating features which lie outside of the currently detectable range in terms of size and depth, but that potential is currently unknown as field instruments have not been developed. To overcome this, a novel computer simulation was developed for a large range of different targets of interest. The simulation included realistic noise modelling of instrumental, environmental and location sources of noise which limit the accuracy of current microgravity measurements, in order to assess the potential capability of the new QT instruments in realistic situations and determine some of the likely limitations on their implementation. The results of the simulations for near surface features showed that the new technology is best employed in a gradiometer configuration as opposed to the traditional single sensor gravimeter used by current instruments due to the ability to suppress vibrational environmental noise effects due to common mode rejection between the sensors. A significant improvement in detection capability of 1.5-2 times was observed, putting targets such as mineshafts into the detectability zone which would be a major advantage for subsurface surveying. Thus this research, for the first time, has demonstrated clearly the benefits of QT gravity
The role of surface topography in predicting scattering at grazing incidence from optical surfaces
International Nuclear Information System (INIS)
Rehn, V.; Jones, V.O.; Elson, J.M.; Bennett, J.M.
1980-01-01
Monochromator design and the design of optical experiments at XUV and X-ray wavelengths are frequently limited by scattering from optical components, yet theoretical treatments are few and untested experimentally. This is partly due to the failure of scattering models used in the visible and near UV when the wavelength becomes comparable to, or smaller than, the topographic features on the surface, and partly it is due to the difficulty in measuring the topography on the required size scale. We briefly review the theoretical problems and prospects for accurately predicting both the magnitude and angular distribution of scattering at grazing incidence from optical surfaces. Experimental methods for determining and representing the surface topography are also reviewed, together with their limitations and ranges of applicability. Finally, the first results of our experiments, conducted recently at the Stanford Synchrotron Radiation Laboratory on the angular distribution of scattering by surfaces of known topography are presented and discussed, along with their potential implications for the theory of scattering, and for XUV and X-ray optical components. (orig.)
Hanes, D.M.; Erikson, L.H.
2013-01-01
Ocean surface gravity waves propagating over shallow bathymetry undergo spatial modification of propagation direction and energy density, commonly due to refraction and shoaling. If the bathymetric variations are significant the waves can undergo changes in their direction of propagation (relative to deepwater) greater than 90° over relatively short spatial scales. We refer to this phenomenon as ultra-refraction. Ultra-refracted swell waves can have a powerful influence on coastal areas that otherwise appear to be sheltered from ocean waves. Through a numerical modeling investigation it is shown that San Francisco Bay, one of the earth's largest and most protected natural harbors, is vulnerable to ultra-refracted ocean waves, particularly southwest incident swell. The flux of wave energy into San Francisco Bay results from wave transformation due to the bathymetry and orientation of the large ebb tidal delta, and deep, narrow channel through the Golden Gate. For example, ultra-refracted swell waves play a critical role in the intermittent closure of the entrance to Crissy Field Marsh, a small restored tidal wetland located on the sheltered north-facing coast approximately 1.5 km east of the Golden Gate Bridge.
Unified first law and some general prescription. A redefinition of surface gravity
Energy Technology Data Exchange (ETDEWEB)
Haldar, Sourav; Bhattacharjee, Sudipto; Chakraborty, Subenoy [Jadavpur University, Department of Mathematics, Kolkata, West Bengal (India)
2017-09-15
The paper contains an extensive study of the unified first law (UFL) in the Friedmann-Robertson-Walker spacetime model. By projecting the UFL along the Kodama vector the second Friedmann equation can be obtained. Also studying the UFL on the event horizon it is found that the Clausius relation cannot be obtained from the UFL by projecting it along the tangent to the event horizon as it can be for the trapping horizon. However, it is shown in the present work that Clausius relation can be obtained by projecting the UFL along the Kodama vector on the horizon and the result is found to be true for any horizon. Finally motivated by the Unruh temperature for the Rindler observer, surface gravity is redefined and a Clausius relation is obtained from the UFL by projecting it along a vector analogous to the Kodama vector. (orig.)
Simulation of Solar Radiation Incident on Horizontal and Inclined Surfaces
Directory of Open Access Journals (Sweden)
MA Basunia
2012-12-01
Full Text Available A computer model was developed to simulate the hourly, daily and monthly average of daily solar radiation on horizontal and inclined surfaces. The measured hourly and daily solar radiation was compared with simulated radiation, and favourable agreement was observed for the measured and predicted values on clear days. The measured and simulated monthly averages of total (diffuse and beam daily solar radiation were compared and a reasonable agreement was observed for a number of stations in Japan. The simulation showed that during the rice harvesting season, September to October, there is a daily average of 14.7 MJ/m2 of solar irradiation on a horizontal surface in Matsuyama, Japan. There is a similar amount of solar radiation on a horizontal surface during the major rice harvesting season, November to December, in Bangladesh. This radiation can be effectively utilized for drying rough rice and other farm crops.
Ionization by ion impact at grazing incidence on insulator surface
Martiarena, M L
2003-01-01
We have calculated the energy distribution of electrons produced by ionization of the ionic crystal electrons in grazing fast ion-insulator surface collision. The ionized electrons originate in the 2p F sup - orbital. We observe that the binary peak appears as a double change in the slope of the spectra, in the high energy region. The form of the peak is determined by the initial electron distribution and its position will be affected by the binding energy of the 2p F sup - electron in the crystal. This BEP in insulator surfaces will appear slightly shifted to the low energy side with respect the ion-atom one.
Surface quality inspection of PbWO4 crystals by grazing incidence X-ray diffraction
International Nuclear Information System (INIS)
Mengucci, P.; Di Cristoforo, A.; Lebeau, M.; Majni, G.; Paone, N.; Pietroni, P.; Rinaldi, D.
2005-01-01
High-quality scintillating crystals are required for applications in radiographic systems and high-energy physics detectors to achieve the specified optical properties. In order to study the state of the single crystals surface we propose the use of the grazing incidence X-ray diffraction (GID) technique. This technique allows performing a depth profiling of the sample by changing the incidence angle of the X-ray beam with respect to the sample surface. In this work, two samples of a large PbWO 4 (PWO) single crystal exhibiting different surface roughness values have been studied. Results have shown that GID is a suitable technique for surface quality inspection
Collisions of polyatomic ions with surfaces: incident energy partitioning and chemical reactions
International Nuclear Information System (INIS)
Zabka, J.; Roithova, J.; Dolejsek, Z.; Herman, Z.
2002-01-01
Collision of polyatomic ions with surfaces were investigated in ion-surface scattering experiments to obtain more information on energy partitioning in ion-surface collision and on chemical reactions at surfaces. Mass spectra, translation energy and angular distributions of product ions were measured in dependence on the incident energy and the incident angle of polyatomic projectiles. From these data distributions of energy fractions resulting in internal excitation of the projectile, translation energy of the product ions, and energy absorbed by the surface were determined. The surface investigated were a standard stainless steel surface, covered by hydrocarbons, carbon surfaces at room and elevated temperatures, and several surfaces covered by a self-assembled monolayers (C 12 -hydrocarbon SAM, C 11 -perfluorohydrocarbon SAM, and C 11 hydrocarbon with terminal -COOH group SAM). The main processes observed at collision energies of 10 - 50 eV were: neutralization of the ions at surfaces, inelastic scattering and dissociations of the projectile ions, quasi elastic scattering of the projectile ions, and chemical reactions with the surface material (usually hydrogen-atom transfer reactions). The ion survival factor was estimated to be a few percent for even-electron ions (like protonated ethanol ion, C 2 H 5 O + , CD 5 + ) and about 10 - 10 2 times lower for radical ions (like ethanol and benzene molecular ions, CD 4 + ). In the polyatomic ion -surface energy transfer experiments, the ethanol molecular ion was used as a well-characterized projectile ion. The results with most of the surfaces studied showed in the collision energy range of 13 - 32 eV that most collisions were strongly inelastic with about 6 - 8 % of the incident projectile energy transformed into internal excitation of the projectile (independent of the incident angle) and led partially to its further dissociation in a unimolecular way after the interaction with the surface. The incident energy
Krywonos, Andrey; Harvey, James E; Choi, Narak
2011-06-01
Scattering effects from microtopographic surface roughness are merely nonparaxial diffraction phenomena resulting from random phase variations in the reflected or transmitted wavefront. Rayleigh-Rice, Beckmann-Kirchhoff. or Harvey-Shack surface scatter theories are commonly used to predict surface scatter effects. Smooth-surface and/or paraxial approximations have severely limited the range of applicability of each of the above theoretical treatments. A recent linear systems formulation of nonparaxial scalar diffraction theory applied to surface scatter phenomena resulted first in an empirically modified Beckmann-Kirchhoff surface scatter model, then a generalized Harvey-Shack theory that produces accurate results for rougher surfaces than the Rayleigh-Rice theory and for larger incident and scattered angles than the classical Beckmann-Kirchhoff and the original Harvey-Shack theories. These new developments simplify the analysis and understanding of nonintuitive scattering behavior from rough surfaces illuminated at arbitrary incident angles.
Near-surface gravity actuated pipe (GAP{sup TM}) system for Brazilian deepwater fluid transfer
Energy Technology Data Exchange (ETDEWEB)
Fromage, Lionel; Brown, Paul A. [SBM Offshore (Monaco)
2009-12-19
The recent discovery of new deep water and ultra-deep water oil and gas fields offshore Brazil, including pre-salt reservoirs, has become a focal point for field development Operators and Contractors. The aggressive nature of fluids (sour, high density) in combination with deeper waters implies potential flow assurance issues. These issues challenge riser and pipeline technology to find cost effective solutions for hydrocarbon fluid transfer in field development scenarios involving phased tied-back. The near-surface GAP{sup TM}, system (Gravity Actuated Pipe{sup TM}), which has been in operation for more than two years on the Kikeh field offshore Malaysia in 1325 m of water between a Dry Tree Unit (SPAR) and a turret-moored FPSO, is considered to meet these challenges since such a product is quasi independent of water depth and takes advantage of being near surface to optimize flow assurance. Furthermore the GAP{sup TM} has undergone technical upgrades when compared to the Kikeh project in order to make it suitable for the more hostile met ocean conditions offshore Brazil. This paper presents the design features, the construction and assembly plans in Brazil and the offshore installation of a GAP fluid transfer system for operation in Brazilian deep waters. (author)
Hung, R. J.; Tsao, Y. D.; Leslie, Fred W.; Hong, B. B.
1988-01-01
Time dependent evolutions of the profile of free surface (bubble shapes) for a cylindrical container partially filled with a Newtonian fluid of constant density, rotating about its axis of symmetry, have been studied. Numerical computations of the dynamics of bubble shapes have been carried out with the following situations: (1) linear functions of spin-up and spin-down in low and microgravity environments, (2) linear functions of increasing and decreasing gravity enviroment in high and low rotating cylidner speeds, (3) step functions of spin-up and spin-down in a low gravity environment, and (4) sinusoidal function oscillation of gravity environment in high and low rotating cylinder speeds. The initial condition of bubble profiles was adopted from the steady-state formulations in which the computer algorithms have been developed by Hung and Leslie (1988), and Hung et al. (1988).
International Nuclear Information System (INIS)
Ohya, Kaoru; Kawata, Jun; Mori, Ichiro
1990-01-01
Incidence angle dependences of secondary electron emission from a carbon surface by low energy electron and hydrogen atom are calculated using Monte Carlo simulations on the kinetic emission model. The calculation shows very small increase or rather decrease of the secondary electron yield with oblique incidence. It is explained in terms of not only multiple elastic collisions of incident particles with the carbon atoms but also small penetration depth of the particles comparable with the escape depth of secondary electrons. In addition, the two types of secondary electron emission are distinguished by using the secondary electron yield statistics; one is the emission due to trapped particles in the carbon, and the other is that due to backscattered particles. The high-yield component of the statistics on oblique incidence is more suppressed than those on normal incidence. (author)
VizieR Online Data Catalog: Brown dwarf surface gravities with Keck/NIRSPEC (Martin , 2017)
Martin, E. C.; Mace, G. N.; McLean, I. S.; Logsdon, S. E.; Rice, E. L.; Kirkpatrick, J. D.; Burgasser, A. J.; McGovern, M. R.; Prato, L.
2017-10-01
In this paper, we follow up on prior NIR spectroscopy by our group and use a modified Allers & Liu (A13, 2013ApJ...772...79A) method to determine surface gravities for 228 M, L, and T dwarfs. We present medium-resolution (R~20000) J-band spectra of 85 M dwarfs, 92 L dwarfs, and 51 T dwarfs obtained as part of the Keck NIRSPEC Brown Dwarf Spectroscopic Survey (BDSS). Ninety-seven spectra were published previously in McLean+ (2003ApJ...596..561M), Burgasser+ (2003ApJ...592.1186B), McGovern+ (2004ApJ...600.1020M), Rice+ (2010ApJS..186...63R), Kirkpatrick+ (2010, J/ApJS/190/100), Luhman (2012ARA&A..50...65L), Thompson+ (2013PASP..125..809T), Mace+ (2013, J/ApJS/205/6), Mace+ (2013ApJ...777...36M), and Kirkpatrick+ (2014, J/ApJ/783/122), and the remaining 131 are presented here for the first time. Observation information (spanning 1999 Apr to 2015 Mar) for all of the targets in our sample is listed in Table 1. (4 data files).
Directory of Open Access Journals (Sweden)
J. Y. Jia
2014-11-01
Full Text Available Absolute values of gravity wave momentum flux (GWMF deduced from satellite measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER instrument and the High Resolution Dynamics Limb Sounder (HIRDLS are correlated with sea surface temperature (SST with the aim of identifying those oceanic regions for which convection is a major source of gravity waves (GWs. Our study identifies those latitude bands where high correlation coefficients indicate convective excitation with confidence. This is based on a global ray-tracing simulation, which is used to delineate the source and wind-filtering effects. Convective GWs are identified at the eastern coasts of the continents and over the warm water regions formed by the warm ocean currents, in particular the Gulf Stream and the Kuroshio. Potential contributions of tropical cyclones to the excitation of the GWs are discussed. Convective excitation can be identified well into the mid-mesosphere. In propagating upward, the centers of GWMF formed by convection shift poleward. Some indications of the main forcing regions are even shown for the upper mesosphere/lower thermosphere (MLT.
International Nuclear Information System (INIS)
Munoz-Garcia, Javier; Cuerno, Rodolfo; Castro, Mario
2009-01-01
Continuum models have proved their applicability to describe nanopatterns produced by ion-beam sputtering of amorphous or amorphizable targets at low and medium energies. Here we pursue the recently introduced 'hydrodynamic approach' in the cases of bombardment at normal incidence, or of oblique incidence onto rotating targets, known to lead to self-organized arrangements of nanodots. Our approach stresses the dynamical roles of material (defect) transport at the target surface and of local redeposition. By applying results previously derived for arbitrary angles of incidence, we derive effective evolution equations for these geometries of incidence, which are then numerically studied. Moreover, we show that within our model these equations are identical (albeit with different coefficients) in both cases, provided surface tension is isotropic in the target. We thus account for the common dynamics for both types of incidence conditions, namely formation of dots with short-range order and long-wavelength disorder, and an intermediate coarsening of dot features that improves the local order of the patterns. We provide for the first time approximate analytical predictions for the dependence of stationary dot features (amplitude and wavelength) on phenomenological parameters, that improve upon previous linear estimates. Finally, our theoretical results are discussed in terms of experimental data.
International Nuclear Information System (INIS)
Dreimann, Karsten; Linz, Stefan J.
2010-01-01
Graphical abstract: Deterministic surface pattern (left) and its stochastic counterpart (right) arising in a stochastic damped Kuramoto-Sivashinsky equation that serves as a model equation for ion-beam eroded surfaces and is systematically investigated. - Abstract: Using a recently proposed field equation for the surface evolution of ion-beam eroded semiconductor target materials under normal incidence, we systematically explore the impact of additive stochastic fluctuations that are permanently present during the erosion process. Specifically, we investigate the dependence of the surface roughness, the underlying pattern forming properties and the bifurcation behavior on the strength of the fluctuations.
International Nuclear Information System (INIS)
Lin, Shiang-Jiun; Wu, Cheng-Da; Fang, Te-Hua; Chen, Guan-Hung
2012-01-01
The bombardment process of a Ni cluster onto a Cu (0 0 1) surface is studied using molecular dynamics (MD) simulations based on the tight-binding second-moment approximation (TB-SMA) many-body potential. The effects of incident cluster size, substrate temperature, and incident energy are evaluated in terms of molecular trajectories, kinetic energy, stress, self-diffusion coefficient, and sputtering yield. The simulation results clearly show that the penetration depth and Cu surface damage increase with increasing incident cluster size for a given incident energy per atom. The self-diffusion coefficient and the penetration depth of a cluster significantly increase with increasing substrate temperature. An incident cluster can be scattered into molecules or atoms that become embedded in the surface after incidence. When the incident energy is increased, the number of volcano-like defects and the penetration depth increase. A high sputtering yield can be obtained by increasing the incident energy at high temperature. The sputtering yield significantly increases with cluster size when the incident energy is above 5 eV/atom.
Proper surface channelling of low energy argon ions incident on a nickel (110) crystal
International Nuclear Information System (INIS)
Evdokimov, I.N.; Berg, J.A. van den; Armour, D.G.
1979-01-01
The scattering behaviour of 6 keV argon ions from a nickel (110) surface has been investigated for specular reflection under grazing incidence conditions. The occurrence of an anomalously high energy loss has been confirmed and the transition from chain scattering at large scattering angles to a distinctly different type of scattering at small angles has been investigated. The characteristics of the low angle scattering phenomena, which dominate the observed spectra at scattering angles below about 18 0 , may be explained in terms of a surface hyperchannelling model in which the incident ions are confined to move within the shallow 'potential valleys' between two atomic rows in the surface. The critical angle for occurrence of this phenomena which is distinctly different from surface semichannelling has been evaluated with Lindhard's standard string potential. The experimentally measured critical angles are in good agreement with the calculated ones. (author)
Acoustic-gravity waves generated by atmospheric and near-surface sources
Kunitsyn, Viacheslav E.; Kholodov, Alexander S.; Krysanov, Boris Yu.; Andreeva, Elena S.; Nesterov, Ivan A.; Vorontsov, Artem M.
2013-04-01
Numerical simulation of the acoustic-gravity waves (AGW) generated by long-period oscillations of the Earth's (oceanic) surface, earthquakes, explosions, thermal heating, seiches, and tsunami is carried out. Wavelike disturbances are quite frequent phenomena in the atmosphere and ionosphere. These events can be caused by the impacts from space and atmosphere, by oscillations of the Earth'as surface and other near-surface events. These wavelike phenomena in the atmosphere and ionosphere appear as the alternating areas of enhanced and depleted density (in the atmosphere) or electron concentration (in the ionosphere). In the paper, AGW with typical frequencies of a few hertz - millihertz are analyzed. AGW are often observed after the atmospheric perturbations, during the earthquakes, and some time (a few days to hours) in advance of the earthquakes. Numerical simulation of the generation of AGW by long-period oscillations of the Earth's and oceanic surface, earthquakes, explosions, thermal heating, seiches, and tsunami is carried out. The AGW generated by the near-surface phenomena within a few hertz-millihertz frequency range build up at the mid-atmospheric and ionospheric altitudes, where they assume their typical spatial scales of the order of a few hundred kilometers. Oscillations of the ionospheric plasma within a few hertz-millihertz frequency range generate electromagnetic waves with corresponding frequencies as well as travelling ionospheric irregularities (TIDs). Such structures can be successfully monitored using satellite radio tomography (RT) techniques. For the purposes of RT diagnostics, 150/400 MHz transmissions from low-orbiting navigational satellites flying in polar orbits at the altitudes of about 1000 km as well as 1.2-1.5 GHz signals form high-orbiting (orbital altitudes about 20000 km) navigation systems like GPS/GLONASS are used. The results of experimental studies on generation of wavelike disturbances by particle precipitation are presented
Surface Movement Incidents Reported to the NASA Aviation Safety Reporting System
Connell, Linda J.; Hubener, Simone
1997-01-01
Increasing numbers of aircraft are operating on the surface of airports throughout the world. Airport operations are forecast to grow by more that 50%, by the year 2005. Airport surface movement traffic would therefore be expected to become increasingly congested. Safety of these surface operations will become a focus as airport capacity planning efforts proceed toward the future. Several past events highlight the prevailing risks experienced while moving aircraft during ground operations on runways, taxiways, and other areas at terminal, gates, and ramps. The 1994 St. Louis accident between a taxiing Cessna crossing an active runway and colliding with a landing MD-80 emphasizes the importance of a fail-safe system for airport operations. The following study explores reports of incidents occurring on an airport surface that did not escalate to an accident event. The Aviation Safety Reporting System has collected data on surface movement incidents since 1976. This study sampled the reporting data from June, 1993 through June, 1994. The coding of the data was accomplished in several categories. The categories include location of airport, phase of ground operation, weather /lighting conditions, ground conflicts, flight crew characteristics, human factor considerations, and airport environment. These comparisons and distributions of variables contributing to surface movement incidents can be invaluable to future airport planning, accident prevention efforts, and system-wide improvements.
The Effect of Surface Tension on the Gravity-driven Thin Film Flow of Newtonian and Power-law Fluids
Hu, Bin; Kieweg, Sarah L.
2012-01-01
Gravity-driven thin film flow is of importance in many fields, as well as for the design of polymeric drug delivery vehicles, such as anti-HIV topical microbicides. There have been many prior works on gravity-driven thin films. However, the incorporation of surface tension effect has not been well studied for non-Newtonian fluids. After surface tension effect was incorporated into our 2D (i.e. 1D spreading) power-law model, we found that surface tension effect not only impacted the spreading speed of the microbicide gel, but also had an influence on the shape of the 2D spreading profile. We observed a capillary ridge at the front of the fluid bolus. Previous literature shows that the emergence of a capillary ridge is strongly related to the contact line fingering instability. Fingering instabilities during epithelial coating may change the microbicide gel distribution and therefore impact how well it can protect the epithelium. In this study, we focused on the capillary ridge in 2D flow and performed a series of simulations and showed how the capillary ridge height varies with other parameters, such as surface tension coefficient, inclination angle, initial thickness, and power-law parameters. As shown in our results, we found that capillary ridge height increased with higher surface tension, steeper inclination angle, bigger initial thickness, and more Newtonian fluids. This study provides the initial insights of how to optimize the flow and prevent the appearance of a capillary ridge and fingering instability. PMID:23687391
Above-surface neutralization of multicharged ions incident on a cesiated Au target
International Nuclear Information System (INIS)
Meyer, F.W.; Hughes, I.G.; Overbury, S.H.
1992-01-01
The critical distance above the surface at which conduction band electrons can start to neutralize incident multicharged projectiles by classical overbarrier transitions is inversely proportional to the metal work function. By varying the amount of Cs coverage on a Au single crystal target between O and 1 monolayers, the authors have been able to verify an up to 3.3 eV decrease of the surface work function, corresponding to more than a factor of two decrease relative to that tabulated for clean Au. This change should result in more than doubling the above-surface interaction time. At larger above-surface distances, however, the electron capture most likely occurs into higher principal quantum numbers of the projectile. The subsequent de-excitation cascade by which inner shells of the projectiles are populated may thus require more time. The authors have investigated the overall effect that lowering the work function has on the above-surface component of projectile K-Auger electron emission for grazing incidence N 6+ ions interacting with cesiated Au single crystals. They will present results showing that an enhancement of this component is indeed observed, and that it is strongly dependent on incidence angle
Electron emission induced by resonant coherent ion-surface interaction at grazing incidence
International Nuclear Information System (INIS)
Garcia de Abajo, F.J.; Ponce, V.H.; Echenique, P.M.
1992-01-01
A new spectroscopy based on the resonant coherently induced electron loss to the continuum in ion-surface scattering under grazing incidence is proposed. A series of peaks, corresponding to the energy differences determined by the resonant interaction with the rows of atoms in the surface, is predicted to appear in the energy distribution of electrons emitted from electronic states bound to the probe. Calculations for MeV He + ions scattered at a W(001) surface along the left-angle 100 right-angle direction with a glancing angle of 0--2 mrad show a total yield close to 1
Review of Electrical and Gravity Methods of Near-Surface Exploration for Groundwater
Directory of Open Access Journals (Sweden)
W. O. Raji
2014-12-01
Full Text Available The theory and practice of electrical and gravity methods of geophysics for groundwater exploration was reviewed with illustrations and data examples. With the goal of reducing cases of borehole/water-well failure attributed to the lack of the knowledge of the methods of geophysics for groundwater exploration and development, the paper reviews the basic concepts, field procedures for data acquisition, data processing, and interpretation as applied to the subject matter. Given a case study of groundwater exploration in University of Ilorin Campus, the three important techniques of electrical method of groundwater exploration are explained and illustrated using field data obtained in a previous study. Interpretation of resistivity data shows that an area measuring low resistivity (high conductivity, having thick pile of unconsolidated rock, and underlained by fracture crystalline is a ‘bright spot’ for citing borehole for groundwater abstraction in a basement complex area. Further to this, gravity method of groundwater exploration was discussed with field data from Wokbedilo community in Ethopia. Bouguer and reduced gravity anomaly results were presented as maps and contours to demonstrate how gravity data can be inverted to map groundwater aquifers and subsurface geological structures during groundwater exploration.
Image defects from surface and alignment errors in grazing incidence telescopes
Saha, Timo T.
1989-01-01
The rigid body motions and low frequency surface errors of grazing incidence Wolter telescopes are studied. The analysis is based on surface error descriptors proposed by Paul Glenn. In his analysis, the alignment and surface errors are expressed in terms of Legendre-Fourier polynomials. Individual terms in the expression correspond to rigid body motions (decenter and tilt) and low spatial frequency surface errors of mirrors. With the help of the Legendre-Fourier polynomials and the geometry of grazing incidence telescopes, exact and approximated first order equations are derived in this paper for the components of the ray intercepts at the image plane. These equations are then used to calculate the sensitivities of Wolter type I and II telescopes for the rigid body motions and surface deformations. The rms spot diameters calculated from this theory and OSAC ray tracing code agree very well. This theory also provides a tool to predict how rigid body motions and surface errors of the mirrors compensate each other.
Cox, C.; Au, A.; Klosko, S.; Chao, B.; Smith, David E. (Technical Monitor)
2001-01-01
The upcoming GRACE mission promises to open a window on details of the global mass budget that will have remarkable clarity, but it will not directly answer the question of what the state of the Earth's mass budget is over the critical last quarter of the 20th century. To address that problem we must draw upon existing technologies such as SLR, DORIS, and GPS, and climate modeling runs in order to improve our understanding. Analysis of long-period geopotential changes based on SLR and DORIS tracking has shown that addition of post 1996 satellite tracking data has a significant impact on the recovered zonal rates and long-period tides. Interannual effects such as those causing the post 1996 anomalies must be better characterized before refined estimates of the decadal period changes in the geopotential can be derived from the historical database of satellite tracking. A possible cause of this anomaly is variations in ocean mass distribution, perhaps associated with the recent large El Nino/La Nina. In this study, a low-degree spherical harmonic gravity time series derived from satellite tracking is compared with a TOPEX/POSEIDON-derived sea surface height time series. Corrections for atmospheric mass effects, continental hydrology, snowfall accumulation, and ocean steric model predictions will be considered.
Energy Technology Data Exchange (ETDEWEB)
Gizis, John E. [Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Allers, Katelyn N. [Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837 (United States); Liu, Michael C. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu HI 96822 (United States); Harris, Hugh C. [US Naval Observatory, Flagstaff Station, 10391 West Naval Observatory Road, Flagstaff, AZ 86001 (United States); Faherty, Jacqueline K. [Department of Terrestrial Magnetism, Carnegie Institution of Washington 5241 Broad Branch Road NW, Washington, DC 20015 (United States); Burgasser, Adam J. [Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States); Kirkpatrick, J. Davy [Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States)
2015-02-01
We present spectroscopy, astrometry, and photometry of the brown dwarf WISEP J004701.06+680352.1 (W0047+68), an unusually red field L dwarf at a distance of 12.2 ± 0.4 pc. The three-dimensional space motion identifies it as a member of the AB Dor Moving Group, an identification supported by our classification of W0047+68 as intermediate surface gravity (INT-G) using the Allers and Liu near-infrared classification system. This moving group membership implies near-solar metallicity, age ∼100-125 Myr, M ≈ 0.018 M {sub ☉}, and log g ≈ 4.5; the thick condensate clouds needed to explain the infrared spectrum are, therefore, a result of surface gravity that is lower than that of ordinary field brown dwarfs. From the observed luminosity and evolutionary model radius, we find T {sub eff} ≈ 1300 K, a temperature normally associated with early T dwarfs. Thick clouds are also used to explain the spectral properties of directly imaged giant planets, and we discuss the successes and challenges for such substellar models in matching the observed optical and infrared spectra. W0047+68 shows that cloud thickness is more sensitive to intermediate surface gravity than in most models. We also present a trigonometric parallax of the dusty L6 dwarf 2MASS J21481628+4003593. It lies at 8.060 ± 0.036 parsecs; its astrometry is consistent with the view that it is older and metal-rich.
International Nuclear Information System (INIS)
Kaplan, A. F. H.
2012-01-01
The modulation of the angle-dependent Fresnel absorptivity across wavy molten steel surfaces during laser materials processing, like drilling, cutting, or welding, has been calculated. The absorptivity is strongly altered by the grazing angle of incidence of the laser beam on the processing front. Owing to its specific Brewster-peak characteristics, the 10.64 μm wavelength CO 2 -laser shows an opposite trend with respect to roughness and angle-of-incidence compared to lasers in the wavelength range of 532-1070 nm. Plateaus or rings of Brewster-peak absorptivity can lead to hot spots on a wavy surface, often in close proximity to cold spots caused by shadow domains.
Directory of Open Access Journals (Sweden)
A. M. Abd-Alla
2013-01-01
Full Text Available Estimation is done to investigate the gravitational and rotational parameters effects on surface waves in fibre-reinforced thermoelastic media. The theory of generalized surface waves has been firstly developed and then it has been employed to investigate particular cases of waves, namely, Stoneley waves, Rayleigh waves, and Love waves. The analytical expressions for surface waves velocity and attenuation coefficient are obtained in the physical domain by using the harmonic vibrations and four thermoelastic theories. The wave velocity equations have been obtained in different cases. The numerical results are given for equation of coupled thermoelastic theory (C-T, Lord-Shulman theory (L-S, Green-Lindsay theory (G-L, and the linearized (G-N theory of type II. Comparison was made with the results obtained in the presence and absence of gravity, rotation, and parameters for fibre-reinforced of the material media. The results obtained are displayed by graphs to clear the phenomena physical meaning. The results indicate that the effect of gravity, rotation, relaxation times, and parameters of fibre-reinforced of the material medium is very pronounced.
Yonemoto, Yukihiro; Kunugi, Tomoaki
2014-01-01
The wettability of droplets on a low surface energy solid is evaluated experimentally and theoretically. Water-ethanol binary mixture drops of several volumes are used. In the experiment, the droplet radius, height, and contact angle are measured. Analytical equations are derived that incorporate the effect of gravity for the relationships between the droplet radius and height, radius and contact angle, and radius and liquid surface energy. All the analytical equations display good agreement with the experimental data. It is found that the fundamental wetting behavior of the droplet on the low surface energy solid can be predicted by our model which gives geometrical information of the droplet such as the contact angle, droplet radius, and height from physical values of liquid and solid.
Surface damage through grazing incidence ions investigated by scanning tunneling microscopy
International Nuclear Information System (INIS)
Redinger, Alex
2009-01-01
Surface damage, caused by grazing incidence ions, is investigated with variable temperature scanning tunneling microscopy. The experiments are carried out on a Pt(111) crystal. The kinetic energy of noble gas ions is varied between 1-15 keV and the angle of incidence can be adjusted between θ = 78.5 and θ = 90 measured with respect to the surface normal. The damage patterns of single ion impacts, on flat terraces and at step edges of monoatomic height, are investigated at low surface temperatures. Ions hitting a flat terrace are usually specular reflected. The energy transfer from the ion to the crystal atoms is small and only little damage is produced. In contrast, at ascending step edges, which are illuminated by the ion beam, large angle scattering events occur. Sputtering, adatom and vacancy production is induced. However, a significant fraction of the ions, which hit step edges, enter the crystal and are guided in between two atomic layers parallel to the surface via small angle binary collisions. This steering process is denoted as subsurface channeling. The energy loss per length scale of the channeled particles is low, which results in long ion trajectories (up to 1000A). During the steering process, the ions produce surface damage. Depending on the ion species and the ion energy, adatom and vacancies or surface vacancy trenches of monoatomic width are observed. The surface damage can be used to track the path of the ion. This makes the whole trajectory of single ions with keV energy visible. The number of sputtered atoms per incident ion at ascending step edges, i.e. the step edge sputtering yield, is measured experimentally for different irradiation conditions. For θ = 86 , the sputtering yield is determined from the fluence dependent retraction of pre-existing illuminated step edges. An alternative method for the step edge sputtering yield determination, is the analysis of the concentration of ascending steps and of the removed amount of material as a
Surface damage through grazing incidence ions investigated by scanning tunneling microscopy
Energy Technology Data Exchange (ETDEWEB)
Redinger, Alex
2009-07-10
Surface damage, caused by grazing incidence ions, is investigated with variable temperature scanning tunneling microscopy. The experiments are carried out on a Pt(111) crystal. The kinetic energy of noble gas ions is varied between 1-15 keV and the angle of incidence can be adjusted between {theta} = 78.5 and {theta} = 90 measured with respect to the surface normal. The damage patterns of single ion impacts, on flat terraces and at step edges of monoatomic height, are investigated at low surface temperatures. Ions hitting a flat terrace are usually specular reflected. The energy transfer from the ion to the crystal atoms is small and only little damage is produced. In contrast, at ascending step edges, which are illuminated by the ion beam, large angle scattering events occur. Sputtering, adatom and vacancy production is induced. However, a significant fraction of the ions, which hit step edges, enter the crystal and are guided in between two atomic layers parallel to the surface via small angle binary collisions. This steering process is denoted as subsurface channeling. The energy loss per length scale of the channeled particles is low, which results in long ion trajectories (up to 1000A). During the steering process, the ions produce surface damage. Depending on the ion species and the ion energy, adatom and vacancies or surface vacancy trenches of monoatomic width are observed. The surface damage can be used to track the path of the ion. This makes the whole trajectory of single ions with keV energy visible. The number of sputtered atoms per incident ion at ascending step edges, i.e. the step edge sputtering yield, is measured experimentally for different irradiation conditions. For {theta} = 86 , the sputtering yield is determined from the fluence dependent retraction of pre-existing illuminated step edges. An alternative method for the step edge sputtering yield determination, is the analysis of the concentration of ascending steps and of the removed amount
Oxide surfaces and metal/oxide interfaces studied by grazing incidence X-ray scattering
Renaud, Gilles
Experimental determinations of the atomic structure of insulating oxide surfaces and metal/oxide interfaces are scarce, because surface science techniques are often limited by the insulating character of the substrate. Grazing incidence X-ray scattering (GIXS), which is not subject to charge effects, can provide very precise information on the atomic structure of oxide surfaces: roughness, relaxation and reconstruction. It is also well adapted to analyze the atomic structure, the registry, the misfit relaxation, elastic or plastic, the growth mode and the morphology of metal/oxide interfaces during their growth, performed in situ. GIXS also allows the analysis of thin films and buried interfaces, in a non-destructive way, yielding the epitaxial relationships, and, by variation of the grazing incidence angle, the lattice parameter relaxation along the growth direction. On semi-coherent interfaces, the existence of an ordered network of interfacial misfit dislocations can be demonstrated, its Burger's vector determined, its ordering during in situ annealing cycles followed, and sometimes even its atomic structure can be addressed. Careful analysis during growth allows the modeling of the dislocation nucleation process. This review emphasizes the new information that GIXS can bring to oxide surfaces and metal/oxide interfaces by comparison with other surface science techniques. The principles of X-ray diffraction by surfaces and interfaces are recalled, together with the advantages and properties of grazing angles. The specific experimental requirements are discussed. Recent results are presented on the determination of the atomic structure of relaxed or reconstructed oxide surfaces. A description of results obtained during the in situ growth of metal on oxide surfaces is also given, as well as investigations of thick metal films on oxide surfaces, with lattice parameter misfit relaxed by an array of dislocations. Recent work performed on oxide thin films having
Garland, G D; Wilson, J T
2013-01-01
The Earth's Shape and Gravity focuses on the progress of the use of geophysical methods in investigating the interior of the earth and its shape. The publication first offers information on gravity, geophysics, geodesy, and geology and gravity measurements. Discussions focus on gravity measurements and reductions, potential and equipotential surfaces, absolute and relative measurements, and gravity networks. The text then elaborates on the shape of the sea-level surface and reduction of gravity observations. The text takes a look at gravity anomalies and structures in the earth's crust; interp
International Nuclear Information System (INIS)
Garcia de Abajo, F.J.; Ponce, V.H.; Echenique, P.M.
1994-01-01
The resonant coherent interaction of an ion with an oriented crystal surface, under grazing-incidence conditions with respect to a special direction of the crystal, gives rise to electron loss to the continuum from electronic bound states of the ion. The calculations presented below predict large probabilities for electron emission due to this mechanism. The electrons are emitted with well defined energies, expressed in terms of the condition of resonance. Furthermore, the emission takes place around certain preferential directions, which are determined by both the latter condition and the symmetry of the surface lattice. Our calculations for MeV He + ions scattered at a W(001) surface along the left-angle 100 right-angle direction with glancing angle of 0--2 mrad indicate a yield of emission close to 1. Using heavier projectiles, one obtains smaller yields, but still large enough to be measurable in some cases (e.g., ∼0.9 for 53 MeV B 4+ and an angle of incidence of 1 mrad). Besides, the initial bound state is energy shifted due to the interaction with both the crystal potential and the velocity-dependent image potential. This results in a slight shift of the peaks of emission, which suggests a possible spectroscopy for analyzing the dynamical interaction of electronic bound states with solid surfaces
Zhang, X.; Liang, S.; Wang, G.
2015-12-01
Incident solar radiation (ISR) over the Earth's surface plays an important role in determining the Earth's climate and environment. Generally, can be obtained from direct measurements, remotely sensed data, or reanalysis and general circulation models (GCMs) data. Each type of product has advantages and limitations: the surface direct measurements provide accurate but sparse spatial coverage, whereas other global products may have large uncertainties. Ground measurements have been normally used for validation and occasionally calibration, but transforming their "true values" spatially to improve the satellite products is still a new and challenging topic. In this study, an improved thin-plate smoothing spline approach is presented to locally "calibrate" the Global LAnd Surface Satellite (GLASS) ISR product using the reconstructed ISR data from surface meteorological measurements. The influences of surface elevation on ISR estimation was also considered in the proposed method. The point-based surface reconstructed ISR was used as the response variable, and the GLASS ISR product and the surface elevation data at the corresponding locations as explanatory variables to train the thin plate spline model. We evaluated the performance of the approach using the cross-validation method at both daily and monthly time scales over China. We also evaluated estimated ISR based on the thin-plate spline method using independent ground measurements at 10 sites from the Coordinated Enhanced Observation Network (CEON). These validation results indicated that the thin plate smoothing spline method can be effectively used for calibrating satellite derived ISR products using ground measurements to achieve better accuracy.
Energy Technology Data Exchange (ETDEWEB)
Campante, T. L.; Chaplin, W. J.; Handberg, R.; Miglio, A.; Davies, G. R.; Elsworth, Y. P. [School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Lund, M. N.; Arentoft, T.; Christensen-Dalsgaard, J.; Karoff, C.; Kjeldsen, H.; Lundkvist, M. [Stellar Astrophysics Centre (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Huber, D. [NASA Ames Research Center, MS 244-30, Moffett Field, CA 94035 (United States); Hekker, S. [Astronomical Institute, " Anton Pannekoek," University of Amsterdam, Amsterdam (Netherlands); García, R. A. [Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot (France); IRFU/SAp, Centre de Saclay, F-91191 Gif-sur-Yvette Cedex (France); Corsaro, E. [Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium); Basu, S. [Department of Astronomy, Yale University, New Haven, CT 06520 (United States); Bedding, T. R. [Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney (Australia); Gilliland, R. L. [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802 (United States); Kawaler, S. D., E-mail: campante@bison.ph.bham.ac.uk [Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States); and others
2014-03-10
We present a novel method for estimating lower-limit surface gravities (log g) of Kepler targets whose data do not allow the detection of solar-like oscillations. The method is tested using an ensemble of solar-type stars observed in the context of the Kepler Asteroseismic Science Consortium. We then proceed to estimate lower-limit log g for a cohort of Kepler solar-type planet-candidate host stars with no detected oscillations. Limits on fundamental stellar properties, as provided by this work, are likely to be useful in the characterization of the corresponding candidate planetary systems. Furthermore, an important byproduct of the current work is the confirmation that amplitudes of solar-like oscillations are suppressed in stars with increased levels of surface magnetic activity.
International Nuclear Information System (INIS)
Carter, G.; Nobes, M.J.; Lewis, G.W.; Whitton, J.L.
1982-01-01
The fluence dependence of development of microscopic surface features, particularly etch pits, during 9 keV Ar + ion bombardment of (11,3,1) oriented Cu single crystals has been studied employing quasi-dynamic irradiation and observation techniques in a scanning electron microscope-accelerator system. 9 keV ions are observed not to produce crystallographic pyramids under all irradiation conditions for this surface, a very different result from our earlier studies with higher energy ions. The bombardment does elaborate etch pits however, the habits and growth kinetics of which depend upon both polar and azimuthal angles of ion incidence to the surface. The results are explained in terms of differential erosion of crystal planes modified by the presence of pre-existing and irradiation induces extended defects. (orig.)
Directory of Open Access Journals (Sweden)
Xiaotong Zhang
2016-03-01
Full Text Available Solar radiation incident at the Earth’s surface (Rs is an essential component of the total energy exchange between the atmosphere and the surface. Reanalysis data have been widely used, but a comprehensive validation using surface measurements is still highly needed. In this study, we evaluated the Rs estimates from six current representative global reanalyses (NCEP–NCAR, NCEP-DOE; CFSR; ERA-Interim; MERRA; and JRA-55 using surface measurements from different observation networks [GEBA; BSRN; GC-NET; Buoy; and CMA] (674 sites in total and the Earth’s Radiant Energy System (CERES EBAF product from 2001 to 2009. The global mean biases between the reanalysis Rs and surface measurements at all sites ranged from 11.25 W/m2 to 49.80 W/m2. Comparing with the CERES-EBAF Rs product, all the reanalyses overestimate Rs, except for ERA-Interim, with the biases ranging from −2.98 W/m2 to 21.97 W/m2 over the globe. It was also found that the biases of cloud fraction (CF in the reanalyses caused the overestimation of Rs. After removing the averaged bias of CERES-EBAF, weighted by the area of the latitudinal band, a global annual mean Rs values of 184.6 W/m2, 180.0 W/m2, and 182.9 W/m2 were obtained over land, ocean, and the globe, respectively.
Study of the grazing-incidence X-ray scattering of strongly disturbed fractal surfaces
Energy Technology Data Exchange (ETDEWEB)
Roshchin, B. S., E-mail: ross@crys.ras.ru; Chukhovsky, F. N.; Pavlyuk, M. D.; Opolchentsev, A. M.; Asadchikov, V. E. [Russian Academy of Sciences, Shubnikov Institute of Crystallography, Federal Research Centre “Crystallography and Photonics” (Russian Federation)
2017-03-15
The applicability of different approaches to the description of hard X-ray scattering from rough surfaces is generally limited by a maximum surface roughness height of no more than 1 nm. Meanwhile, this value is several times larger for the surfaces of different materials subjected to treatment, especially in the initial treatment stages. To control the roughness parameters in all stages of surface treatment, a new approach has been developed, which is based on a series expansion of wavefield over the plane eigenstate-function waves describing the small-angle scattering of incident X-rays in terms of plane q-waves propagating through the interface between two media with a random function of relief heights. To determine the amplitudes of reflected and transmitted plane q-waves, a system of two linked integral equations was derived. The solutions to these equations correspond (in zero order) to the well-known Fresnel expressions for a smooth plane interface. Based on these solutions, a statistical fractal model of an isotropic rough interface is built in terms of root-mean-square roughness σ, two-point correlation length l, and fractal surface index h. The model is used to interpret X-ray scattering data for polished surfaces of single-crystal cadmium telluride samples.
Energy Technology Data Exchange (ETDEWEB)
Carbone, D; Metzger, T H [ID01, ESRF, 6 rue Jules Horowitz, F-38043 Grenoble Cedex (France); Biermanns, A; Pietsch, U [Festkoerperphysik, Universitaet Siegen, D-57068 Siegen (Germany); Ziberi, B; Frost, F [Leibniz-Institut fuer Oberflaechenmodifizierung e.V., D-04318 Leipzig (Germany); Plantevin, O [Universite Paris-Sud, Centre de Spectrometrie Nucleaire et de Spectrometrie de Masse, UMR 8609, F-91405 Orsay (France)], E-mail: gcarbone@esrf.fr
2009-06-03
In this review we cover and describe the application of grazing incidence x-ray scattering techniques to study and characterize nanopattern formation on semiconductor surfaces by ion beam erosion under various conditions. It is demonstrated that x-rays under grazing incidence are especially well suited to characterize (sub)surface structures on the nanoscale with high spatial and statistical accuracy. The corresponding theory and data evaluation is described in the distorted wave Born approximation. Both ex situ and in situ studies are presented, performed with the use of a specially designed sputtering chamber which allows us to follow the temporal evolution of the nanostructure formation. Corresponding results show a general stabilization of the ordering wavelength and the extension of the ordering as a function of the ion energy and fluence as predicted by theory. The in situ measurements are especially suited to study the early stages of pattern formation, which in some cases reveal a transition from dot to ripple formation. For the case of medium energy ions crystalline ripples are formed buried under a semi-amorphous thick layer with a ripple structure at the surface being conformal with the crystalline/amorphous interface. Here, the x-ray techniques are especially advantageous since they are non-destructive and bulk-sensitive by their very nature. In addition, the GI x-ray techniques described in this review are a unique tool to study the evolving strain, a topic which remains to be explored both experimentally and theoretically.
Roy, Mousumi; Lewis, Megan; Johnson, Alex; George, Nicolas; Rowe, Charlotte; Guardincerri, Elena
2018-03-01
Imaging shallow subsurface density structure is an important goal in a variety of applications, from hydrogeology to seismic and volcanic hazard assessment. We assess the effectiveness of surface and subsurface gravity measurements in estimating the density structure of a well-characterized rock volume: the mesa (a small, flat-topped plateau) upon which the town of Los Alamos, New Mexico, USA is located. Our gravity measurements were made on the mesa surface above a horizontal tunnel and underground, within the tunnel. We demonstrate that, in the absence of other geophysical data such as seismic data or muon attenuation, subsurface (tunnel) gravity measurements are critical to accurately recovering geologic structure. Without the tunnel data, our resolution is limited to roughly the surface gravity station spacing, but by including the tunnel data we can resolve structure to a depth of 10 times the surface gravity station spacing. Densities were obtained using both forward modeling and a Bayesian inverse modeling approach, incorporating relevant constraints from geologic observations. We find that Bayesian inversion, with geologically relevant prior, is a superior approach to the forward models in terms of both robustness and efficiency and correctly predicts the orientation and elevation of important geologic features.
Coherent reflection from surface gravity water waves during reciprocal acoustic transmissions.
Badiey, Mohsen; Song, Aijun; Smith, Kevin B
2012-10-01
During a recent experiment in Kauai, Hawaii, reciprocal transmissions were conducted between two acoustic transceivers mounted on the seafloor at a depth of 100 m. The passage of moving surface wave crests was shown to generate focused and intense coherent acoustic returns, which had increasing or decreasing delay depending on the direction of propagation relative to the direction of surface wave crests. It is shown that a rough surface two-dimensional parabolic equation model with an evolving sea surface can produce qualitative agreement with data for the dynamic surface returns.
Structured surface reflector design for oblique incidence beam splitter at 610 GHz.
Defrance, F; Casaletti, M; Sarrazin, J; Wiedner, M C; Gibson, H; Gay, G; Lefèvre, R; Delorme, Y
2016-09-05
An iterative alternate projection-based algorithm is developed to design structured surface reflectors to operate as beam splitters at GHz and THz frequencies. To validate the method, a surface profile is determined to achieve a reflector at 610 GHz that generates four equal-intensity beams towards desired directions of ±12.6° with respect to the specular reflection axis. A prototype is fabricated and the beam splitter behavior is experimentally demonstrated. Measurements confirm a good agreement (within 1%) with computer simulations using Feko, validating the method. The beam splitter at 610 GHz has a measured efficiency of 78% under oblique incidence illumination that ensures a similar intensity between the four reflected beams (variation of about 1%).
Ocular surface disease incidence in patients with open-angle glaucoma
Directory of Open Access Journals (Sweden)
Radenković Marija
2016-01-01
Full Text Available Introduction. Ocular surface disease (OSD is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbances, tear film instability with potential damage to the ocular surface, accompanied by increased tear film osmolarity and inflammation of the ocular surface. It is a consequence of disrupted homeostasis of lacrimal functional unit. The main pathogenetic mechanism stems from tear hyperosmolarity and tear film instability. The etiological classification is hyposecretory (Sy-Sjögren and non-Sjögren and evaporative (extrinsic and intrinsic form. Delphi panel classification grades disease stages. Antiglaucoma topical therapy causes exacerbation or occurrence of symptoms of dry eye due to main ingredients or preservatives (benzalkonium chloride - BAK, which are dose- and time-dependent. BAK reduces the stability of the lipid layer of tears, the number of goblet cells, induces apoptosis and inflammatory infiltration. Objective. The aim of this study was the analysis of the OSD incidence in open-angle glaucoma patients caused by topical medicamentous therapy. Methods. Retrospective analysis of examined patients with open-angle glaucoma was used. Results. Increased incidence of moderate and advanced OSD Index degrees in the group of primary open-angle glaucoma (POAG and pseudoexfoliative glaucoma. According to the Delphi Panel Scale the most common grade is IIb (POAG and pseudoexfoliative glaucoma. Evaporative form of OSD prevailed in all treatment groups. High percentage of dry eye in patients with higher concentrations of preservatives applied was noticed. Conclusion. OSD should be timely diagnosed and treated. Dry eye has an impact on surgical outcome and postoperative visual acuity, and in order to improve patient compliance and quality of life, symptoms of dry eye should be addressed and medications with lower concentrations of preservatives should be applied.
Ocular surface disease incidence in patients with open-angle glaucoma.
Radenković, Marija; Stanković-Babić, Gordana; Jovanović, Predrag; Djordjević-Jocić, Jasmina; Trenkić-Božinović, Marija
2016-01-01
Ocular surface disease (OSD) is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbances, tear film instability with potential damage to the ocular surface, accompanied by increased tear film osmolarity and inflammation of the ocular surface. It is a consequence of disrupted homeostasis of lacrimal functional unit. The main pathogenetic mechanism stems from tear hyperosmolarity and tear film instability. The etiological classification is hyposecretory (Sy-Sjögren and non-Sjögren) and evaporative (extrinsic and intrinsic) form. Delphi panel classification grades disease stages. Antiglaucoma topical therapy causes exacerbation or occurrence of symptoms of dry eye due to main ingredients or preservatives (benzalkonium chloride – BAK), which are dose- and time-dependent. BAK reduces the stability of the lipid layer of tears, the number of goblet cells, induces apoptosis and inflammatory infiltration. The aim of this study was the analysis of the OSD incidence in open-angle glaucoma patients caused by topical medicamentous therapy. Retrospective analysis of examined patients with open-angle glaucoma was used. Increased incidence of moderate and advanced OSD Index degrees in the group of primary open-angle glaucoma (POAG) and pseudoexfoliative glaucoma. According to the Delphi Panel Scale the most common grade is IIb (POAG and pseudoexfoliative glaucoma). Evaporative form of OSD prevailed in all treatment groups. High percentage of dry eye in patients with higher concentrations of preservatives applied was noticed. OSD should be timely diagnosed and treated. Dry eye has an impact on surgical outcome and postoperative visual acuity, and in order to improve patient compliance and quality of life, symptoms of dry eye should be addressed and medications with lower concentrations of preservatives should be applied.
Directory of Open Access Journals (Sweden)
Animesh Mukherjee
1991-01-01
Full Text Available Based upon Biot's [1965] theory of initial stresses of hydrostatic nature produced by the effect of gravity, a study is made of surface waves in higher order visco-elastic media under the influence of gravity. The equation for the wave velocity of Stonely waves in the presence of viscous and gravitational effects is obtained. This is followed by particular cases of surface waves including Rayleigh waves and Love waves in the presence of viscous and gravity effects. In all cases the wave-velocity equations are found to be in perfect agreement with the corresponding classical results when the effects of gravity and viscosity are neglected.
International Nuclear Information System (INIS)
Xie Zhi-Kun; Pan Wei-Zhen; Yang Xue-Jun
2013-01-01
Using a new tortoise coordinate transformation, we discuss the quantum nonthermal radiation characteristics near an event horizon by studying the Hamilton-Jacobi equation of a scalar particle in curved space-time, and obtain the event horizon surface gravity and the Hawking temperature on that event horizon. The results show that there is a crossing of particle energy near the event horizon. We derive the maximum overlap of the positive and negative energy levels. It is also found that the Hawking temperature of a black hole depends not only on the time, but also on the angle. There is a problem of dimension in the usual tortoise coordinate, so the present results obtained by using a correct-dimension new tortoise coordinate transformation may be more reasonable
Surface gravity waves and their acoustic signatures, 1-30 Hz, on the mid-Pacific sea floor.
Farrell, W E; Munk, Walter
2013-10-01
In 1999, Duennebier et al. deployed a hydrophone and geophone below the conjugate depth in the abyssal Pacific, midway between Hawaii and California. Real time data were transmitted for 3 yr over an abandoned ATT cable. These data have been analyzed in the frequency band 1 to 30 Hz. Between 1 and 6 Hz, the bottom data are interpreted as acoustic radiation from surface gravity waves, an extension to higher frequencies of a non-linear mechanism proposed by Longuet-Higgins in 1950 to explain microseisms. The inferred surface wave spectrum for wave lengths between 6 m and 17 cm is saturated (wind-independent) and roughly consistent with the traditional Phillips κ(-4) wave number spectrum. Shorter ocean waves have a strong wind dependence and a less steep wave number dependence. Similar features are found in the bottom record between 6 and 30 Hz. But this leads to an enigma: The derived surface spectrum inferred from the Longuet-Higgins mechanism with conventional assumptions for the dispersion relation is associated with mean square slopes that greatly exceed those derived from glitter. Regardless of the generation mechanism, the measured bottom intensities between 10 and 30 Hz are well below minimum noise standards reported in the literature.
Processing yttrium-barium-copper oxide superconductor zero gravity using a double float zone surface
International Nuclear Information System (INIS)
Pettit, D.R.; Peterson, D.E.; Kubat-Martin, K.A.; Petrovic, J.J.; Sheinberg, H.; Coulter, Y.; Day, D.E.
1997-04-01
The effects of processing YBa 2 Cu 3 O x (Y123) superconductor in the near-zero gravity (0g) environment provided by the NASA KC-135 airplane flying on parabolic trajectories were studied. A new sheet float zone furnace, designed for this study, enabled fast temperature ramps. Up to an 18-gram sample was processed with each parabola. Samples of Y123 were processed as bulk sheets, composites containing Ag and Pd, and films deposited on single crystal Si and MgO substrates. The 0g-processed samples were multi-phase yet retained a localized Y123 stoichiometry where a single ground-based (1g) oxygen anneal at temperatures of 800 C recovered nearly 100-volume percent superconducting Y123. The 1g processed control samples remained multi-phase after the same ground-based anneal with less than 45 volume percent as superconducting Y123. The superconducting transition temperature was 91 K for both 0g and 1g processed samples. A 29 wt.% Ag/Y123 composite had a transition temperature of 93 K. Melt texturing of bulk Y123 in 0g produced aligned grains about a factor of three larger than in analogous 1g samples. Transport critical current densities were at or below 18 A/cm 2 , due to the formation of cracks caused by the rapid heating rates required by the short time at 0g. Y123 deposited on single crystal Si and MgO in 0g was 30 vol.% y123 without an anneal. A weak superconducting transition at 80 K on MgO showed that substrate interactions occurred
Molecular dynamics study of the interactions of incident N or Ti atoms with the TiN(001) surface
International Nuclear Information System (INIS)
Xu, Zhenhai; Zeng, Quanren; Yuan, Lin; Qin, Yi; Chen, Mingjun; Shan, Debin
2016-01-01
Graphical abstract: - Highlights: • Interactions of incident N or Ti atoms with TiN(001) surface are studied by CMD. • The impact position of incident N on the surface determines the interaction modes. • Adsorption could occur due to the atomic exchange process. • Resputtering and reflection may simultaneously occur. • The initial sticking coefficient of N on TiN(001) is much smaller than that of Ti. - Abstract: The interaction processes between incident N or Ti atoms and the TiN(001) surface are simulated by classical molecular dynamics based on the second nearest-neighbor modified embedded-atom method potentials. The simulations are carried out for substrate temperatures between 300 and 700 K and kinetic energies of the incident atoms within the range of 0.5–10 eV. When N atoms impact against the surface, adsorption, resputtering and reflection of particles are observed; several unique atomic mechanisms are identified to account for these interactions, in which the adsorption could occur due to the atomic exchange process while the resputtering and reflection may simultaneously occur. The impact position of incident N atoms on the surface plays an important role in determining the interaction modes. Their occurrence probabilities are dependent on the kinetic energy of incident N atoms but independent on the substrate temperature. When Ti atoms are the incident particles, adsorption is the predominant interaction mode between particles and the surface. This results in the much smaller initial sticking coefficient of N atoms on the TiN(001) surface compared with that of Ti atoms. Stoichiometric TiN is promoted by N/Ti flux ratios larger than one.
Zero-gravity Mean Free Surface Curvature of a Confined Liquid in a Radially-Vaned Container
Chen, Yongkang; Callahan, Michael; Weislogel, Mark
2013-01-01
A variety of increasingly intricate container geometries are under consideration for the passive manipulation of liquids aboard spacecraft where the impact of gravity may be neglected. In this study we examine the mean curvature of a liquid volume confined within a radial array of disconnected vanes of infinite extent. This particular geometry possesses a number of desirable characteristics relevant to waste water treatment aboard spacecraft for life support. It is observed that under certain conditions the slender shape of the free surface approaches an asymptote, which can be predicted analytically using new hybrid boundary conditions proposed herein. This contribution represents possibly the final extension of what has been referred to as the method of de Lazzer et al. (1996). The method enables the integration of the Young-Laplace equation over a domain with its boundaries, including the wetted portion of the solid boundaries, symmetry planes, and circular arcs representing free surfaces at the center plane of the liquid body. Asymptotic solutions at several limits are obtained and the analysis is confirmed with numerical computations.
Garel, F.; Kaminski, E.; Tait, S.; Limare, A.
2011-12-01
During an effusive volcanic eruption, the crisis management is mainly based on the prediction of lava flows advance and its velocity. As the spreading of lava flows is mainly controlled by its rheology and the eruptive mass flux, the key question is how to evaluate them during the eruption (rather than afterwards.) A relationship between the heat flux lost by the lava at its surface and the eruption rate is likely to exist, based on the first-order argument that higher eruption rates should correspond to larger power radiated by a lava flow. The semi-empirical formula developed by Harris and co-workers (e.g. Harris et al., Bull. Volc. 2007) is currently used to estimate lava flow rate from satellite surveys yielding the surface temperatures and area of the lava flow field. However, this approach is derived from a static thermal budget of the lava flow and does not explicitly model the time-evolution of the surface thermal signal. Here we propose laboratory experiments and theoretical studies of the cooling of a viscous axisymmetric gravity current fed at constant flux rate. We first consider the isoviscous case, for which the spreading is well-know. The experiments using silicon oil and the theoretical model both reveal the establishment of a steady surface thermal structure after a transient time. The steady state is a balance between surface cooling and heat advection in the flow. The radiated heat flux in the steady regime, a few days for a basaltic lava flow, depends mainly on the effusion rate rather than on the viscosity. In this regime, one thermal survey of the radiated power could provide a consistent estimate of the flow rate if the external cooling conditions (wind) are reasonably well constrained. We continue to investigate the relationship between the thermal radiated heat flux and the effusion rate by using in the experiments fluids with temperature-dependent viscosity (glucose syrup) or undergoing solidification while cooling (PEG wax). We observe a
Incidence of the enterococcal surface protein (esp) gene in human and animal fecal sources
Whitman, R.L.; Przybyla-Kelly, K.; Shively, D.A.; Byappanahalli, M.N.
2007-01-01
The occurrence of the enterococcal surface protein (esp) gene in the opportunistic pathogens Enterococcus faecalis and E. faecium is well-documented in clinical research. Recently, the esp gene has been proposed as a marker of human pollution in environmental waters; however, information on its relative incidence in various human and animal fecal sources is limited. We have determined the occurrence of the esp gene in enterococci from human (n = 64) and animal (n = 233) fecal samples by polymerase chain reaction using two primer sets: one presumably specific for E. faecium (espfm) and the other for both E. faecalis and E. faecium (espfs/fm). We believe that this research is the first to explore the use of espfs/fm for the detection of human waste in natural environmental settings. The incidence in human sources was 93.1% espfm and 100% espfs/fm in raw sewage influent; 30% for both espfm and espfs/fm in septic waste; and 0% espfm and 80% espfs/fm in active pit toilets. The overall occurrence of the gene in animal feces was 7.7% (espfs/fm) and 4.7% (espfm); animal types with positive results included dogs (9/43, all espfm), gulls (10/34, espfs/fm; 2/34, espfm), mice (3/22, all espfs/fm), and songbirds (5/55, all espfs/fm). The esp gene was not detected in cat (0/34), deer (0/4), goose (0/18), or raccoon (0/23) feces. The inconsistent occurrence, especially in septic and pit toilet sewage, suggests a low statistical power of discrimination between animal and human sources, which means a large number of replicates should be collected. Both espfm and espfs/fm were common in raw sewage, but neither one efficiently differentiated between animal and other human sources.
Near-surface current meter array measurements of internal gravity waves
Energy Technology Data Exchange (ETDEWEB)
Jones, H.B.E. [Lawrence Livermore National Lab., CA (United States)
1994-11-15
We have developed various processing algorithms used to estimate the wave forms produced by hydrodynamic Internal Waves. Furthermore, the estimated Internal Waves are used to calculate the Modulation Transfer Function (MTF) which relates the current and strain rate subsurface fields to surface scattering phenomenon imaged by radar. Following a brief discussion of LLNL`s measurement platform (a 10 sensor current meter array) we described the generation of representative current and strain rate space-time images from measured or simulated data. Then, we present how our simulation capability highlighted limitations in estimating strain rate. These limitations spurred the application of beamforming techniques to enhance our estimates, albeit at the expense of collapsing our space-time images to 1-D estimates. Finally, we discuss progress with regard to processing the current meter array data captured during the recent Loch Linnhe field trials.
International Nuclear Information System (INIS)
Christodoulakis, T; Doulis, G; Terzis, Petros A; Melas, E; Grammenos, Th; Papadopoulos, G O; Spanou, A
2010-01-01
The canonical decomposition of all 3+1 geometries admitting two-dimensional space-like surfaces is exhibited as a generalization of a previous work. A proposal, consisting of a specific renormalization Assumption and an accompanying Requirement, which has been put forward in the 2+1 case is now generalized to 3+1 dimensions. This enables the canonical quantization of these geometries through a generalization of Kuchar's quantization scheme in the case of infinite degrees of freedom. The resulting Wheeler-DeWitt equation is based on a renormalized manifold parameterized by three smooth scalar functionals. The entire space of solutions to this equation is analytically given, a fact that is entirely new to the present case. This is made possible through the exploitation of the residual freedom in the choice of the third functional, which is left by the imposition of the Requirement, and is proven to correspond to a general coordinate transformation in the renormalized manifold.
Energy Technology Data Exchange (ETDEWEB)
Maleewong, Montri; Asavanant, Jack [Chulalongkorn University, Department of Mathematics and Advanced Virtual Intelligence Computing Center, Bangkok (Thailand); Grimshaw, Roger [Loughborough University, Department of Mathematical Sciences, Loughborough (United Kingdom)
2005-08-01
We consider steady free surface two-dimensional flow due to a localized applied pressure distribution under the effects of both gravity and surface tension in water of constant depth, and in the presence of a uniform stream. The fluid is assumed to be inviscid and incompressible, and the flow is irrotational. The behavior of the forced nonlinear waves is characterized by three parameters: the Froude number, F, the Bond number, {tau}>1/3, and the magnitude and sign of the pressure forcing parameter {epsilon}. The fully nonlinear wave problem is solved numerically by using a boundary integral method. For small amplitude waves and F<1 but not too close to 1, linear theory gives a good prediction for the numerical solution of the nonlinear problem in the case of bifurcation from the uniform flow. As F approaches 1, the nonlinear terms need to be taken account of. In this case the forced Korteweg-de Vries equation is found to be an appropriate model to describe bifurcations from an unforced solitary wave. In general, it is found that for given values of F<1 and {tau}>1/3, there exists both elevation and depression waves. In some cases, a limiting configuration in the form of a trapped bubble occurs in the depression wave solutions. (orig.)
Vertical incidence of slow Ne{sup 10+} ions on an LiF surface: Suppression of the trampoline effect
Energy Technology Data Exchange (ETDEWEB)
Wirtz, Ludger E-mail: lwirtz@concord.itp.tuwien.ac.at; Lemell, Christoph; Reinhold, Carlos O.; Haegg, Lotten; Burgdoerfer, Joachim
2001-08-01
We present a Monte Carlo simulation of the neutralization of a slow Ne{sup 10+} ion in vertical incidence on an LiF(1 0 0) surface. The rates for resonant electron transfer between surface F{sup -} ions and the projectile are calculated using a classical trajectory Monte Carlo simulation. We investigate the influence of the hole mobility on the neutralization sequence. It is shown that backscattering above the surface due to the local positive charge up of the surface ('trampoline effect') does not take place.
Vertical incidence of slow Ne 10+ ions on an LiF surface: Suppression of the trampoline effect
Wirtz, Ludger; Lemell, Christoph; Reinhold, Carlos O.; Hägg, Lotten; Burgdörfer, Joachim
2001-08-01
We present a Monte Carlo simulation of the neutralization of a slow Ne 10+ ion in vertical incidence on an LiF(1 0 0) surface. The rates for resonant electron transfer between surface F - ions and the projectile are calculated using a classical trajectory Monte Carlo simulation. We investigate the influence of the hole mobility on the neutralization sequence. It is shown that backscattering above the surface due to the local positive charge up of the surface ("trampoline effect") does not take place.
Vertical incidence of slow Ne10+ ions on an LiF surface: Suppression of the trampoline effect
International Nuclear Information System (INIS)
Wirtz, Ludger; Lemell, Christoph; Reinhold, Carlos O.; Haegg, Lotten; Burgdoerfer, Joachim
2001-01-01
We present a Monte Carlo simulation of the neutralization of a slow Ne 10+ ion in vertical incidence on an LiF(1 0 0) surface. The rates for resonant electron transfer between surface F - ions and the projectile are calculated using a classical trajectory Monte Carlo simulation. We investigate the influence of the hole mobility on the neutralization sequence. It is shown that backscattering above the surface due to the local positive charge up of the surface ('trampoline effect') does not take place
McWilliams, J. C.; Lane, E.; Melville, K.; Restrepo, J.; Sullivan, P.
2004-12-01
Oceanic surface gravity waves are approximately irrotational, weakly nonlinear, and conservative, and they have a much shorter time scale than oceanic currents and longer waves (e.g., infragravity waves) --- except where the primary surface waves break. This provides a framework for an asymptotic theory, based on separation of time (and space) scales, of wave-averaged effects associated with the conservative primary wave dynamics combined with a stochastic representation of the momentum transfer and induced mixing associated with non-conservative wave breaking. Such a theory requires only modest information about the primary wave field from measurements or operational model forecasts and thus avoids the enormous burden of calculating the waves on their intrinsically small space and time scales. For the conservative effects, the result is a vortex force associated with the primary wave's Stokes drift; a wave-averaged Bernoulli head and sea-level set-up; and an incremental material advection by the Stokes drift. This can be compared to the "radiation stress" formalism of Longuet-Higgins, Stewart, and Hasselmann; it is shown to be a preferable representation since the radiation stress is trivial at its apparent leading order. For the non-conservative breaking effects, a population of stochastic impulses is added to the current and infragravity momentum equations with distribution functions taken from measurements. In offshore wind-wave equilibria, these impulses replace the conventional surface wind stress and cause significant differences in the surface boundary layer currents and entrainment rate, particularly when acting in combination with the conservative vortex force. In the surf zone, where breaking associated with shoaling removes nearly all of the primary wave momentum and energy, the stochastic forcing plays an analogous role as the widely used nearshore radiation stress parameterizations. This talk describes the theoretical framework and presents some
The equivalent incidence angle for porous absorbers backed by a hard surface
DEFF Research Database (Denmark)
Jeong, Cheol-Ho; Brunskog, Jonas
2013-01-01
experiment using a free-field absorption measurement technique with a source at the equivalent angle. This study investigates the equivalent angle for locally and extendedly reacting porous media mainly by a numerical approach: Numerical minimizations of a cost function that is the difference between...... coefficients by free-field techniques, a broad incidence angle range can be suggested: 20 hi65 for extended reaction and hi65 for locally reacting porous absorbers, if an average difference of 0.05 is allowed.......An equivalent incidence angle is defined as the incidence angle at which the oblique incidence absorption coefficient best approximates the random incidence absorption coefficient. Once the equivalent angle is known, the random incidence absorption coefficient can be estimated by a single...
International Nuclear Information System (INIS)
Hughes, I.G.; Zeijlmans van Emmichoven, P.A.; Havener, C.C.; Overbury, S.H.; Robinson, M.T.; Zehner, D.M.; Meyer, F.W.
1992-01-01
Characteristic variations in the total electron yield γ as a function of crystal azimuthal orientation are reported for slow N 2+ , N 5+ and N 6+ ions incident on a Au(011) single crystal, together with measurements of γ as a function of incident ion velocity. Kinetic electron emission is shown to arise predominantly in close collisions between incident ions and target atoms, and potential electron emission is found to be essentially constant within our present velocity range. The incident ion charge state is shown to play no role in kinetic electron emission. Extremely fast neutralization times of the order of 10 - 15 secs are needed to explain the observations
Evanescent wave scattering at off-axis incidence on multiple cylinders located near a surface
International Nuclear Information System (INIS)
Lee, Siu-Chun
2015-01-01
The scattering characteristics of an infinite cylinder are strongly influenced by the incidence angle relative to its axis. If the incident wave propagates in the plane normal to the axis of the cylinder, the polarization of the scattered wave remains unchanged and the scattered wave propagates in the same plan as the incident wave. At off-axis incidence such that the incident direction makes an oblique angle with the cylinder axis, the scattered wave is depolarized, and its spatial distribution becomes three-dimensional. This paper presents the scattering solution for oblique incidence on multiple parallel cylinders located near a planar interface by an evanescent wave that is generated by total internal reflection of the source wave propagating in the higher refractive index substrate. Hertz potentials are utilized to formulate the interaction of inhomogeneous waves with the cylinders, scattering at the substrate interface, and near field scattering between the cylinders. Analytic formulas are derived for the electromagnetic fields and Poynting vector of scattered radiation in the near-field and their asymptotic forms in the far-field. Numerical examples are shown to illustrate scattering of evanescent wave by multiple cylinders at off-axis incidence. - Highlights: • Developed an exact solution for off-axis incidence on multiple cylinders. • Included depolarization, near-field scattering, and Fresnel effect in theory. • Derived analytic formulas for scattered radiation in the far field. • Illustrated evanescent scattering at off-axis incidence by numerical data
den Boer, J. W.; Coutinho, R. A.; Yzerman, E. P. F.; van der Sande, M. A. B.
2008-01-01
STUDY OBJECTIVES: Given an observed geographical variation in Legionnaires' disease incidence in The Netherlands, the aim of the study was to test the hypothesis that the type of drinking water production was an independent determinant of the incidence of Legionnaires' disease. DESIGN: For the
de Rham, Claudia
2014-01-01
We review recent progress in massive gravity. We start by showing how different theories of massive gravity emerge from a higher-dimensional theory of general relativity, leading to the Dvali–Gabadadze–Porrati model (DGP), cascading gravity, and ghost-free massive gravity. We then explore their theoretical and phenomenological consistency, proving the absence of Boulware–Deser ghosts and reviewing the Vainshtein mechanism and the cosmological solutions in these models. Finally, we present alt...
Directory of Open Access Journals (Sweden)
B V Murlimanju
2012-01-01
Full Text Available Context: It was suggested that the accessory neurovascular foramina of the mandible might be of significance in relation to the effectiveness of local anesthesia following the routine inferior alveolar nerve block. Aims: To investigate the incidence of neurovascular foramina over the lingual surface of the mandible in South Indian population. Settings and Design: The study was conducted at the department of anatomy. Materials and Methods: The study included 67 human adult dry mandibles, the exact ages and sexes of which were not known. The location and number of neurovascular foramina were topographically analyzed. Statistical Analysis Used: Descriptive statistics. Results: The foramina were observed in 64 mandibles (95.5% and were often multiple in most of the cases. They were located between the two medial incisors in 8 mandibles (1.9%, between the medial and lateral incisor in 34 mandibles (50.7%; 25-bilateral; 7-right; 2-left, between the lateral incisor and canine in 7 mandibles (10.4%; 2-bilateral; 3-right; 2-left, between the canine and first premolar in 6 cases (8.9%; 3 on each side. Foramina were also present around the genial tubercle in 56 mandibles (83.6%. Among them, 52 mandibles showed a single foramen just above the genial tubercle, 34 mandibles had foramina below the tubercles, 13 mandibles had foramina on the right side of genial tubercle and 17 were having on the left side. Conclusion: Since the anatomical details of these foramina are important to various fields of dentistry and oncology, the present investigation was undertaken. The clinical significance and implications are emphasized.
Zhang, Chuanchao; Liao, Wei; Zhang, Lijuan; Jiang, Xiaolong; Chen, Jing; Wang, Haijun; Luan, Xiaoyu; Yuan, Xiaodong
2018-06-01
A simple and convenient means to self-organize large-area uniform periodic microstructures on fused silica by using multiple raster scans of microsecond CO2 laser pulses with beam spot overlapping at normal incidence is presented, which is based on laser-induced periodic surface structures (LIPSS) attributed to the interference between surface phonon polaritons and incident CO2 laser. The evolution of fused silica surface morphologies with increasing raster scans indicates that the period of microstructures changed from 10.6 μm to 9 μm and the profiles of microstructures changed from a sinusoidal curve to a half-sinusoidal shape. Numerical simulation results suggest that the formation of the half-sinusoidal profile is due to the exponential relationship between evaporation rate and surface temperature inducing by the intensive interference between surface phonon polaritons and incident laser. The fabricated uniform periodic microstructures show excellent structural color effect in both forward-diffraction and back-diffraction.
International Nuclear Information System (INIS)
Moh, Jeong Hah; Cho, Y. I.
2014-01-01
This paper presents the theoretical analysis of a flow driven by surface tension and gravity in an inclined circular tube. A governing equation is developed for describing the displacement of a non-Newtonian fluid(Power-law model) that continuously flows into a circular tube owing to surface tension, which represents a second-order, nonlinear, non-homogeneous, and ordinary differential form. It was found that quantitatively, the theoretical predictions of the governing equation were in excellent agreement with the solutions of the equation for horizontal tubes and the past experimental data. In addition, the predictions compared very well with the results of the force balance equation for steady
Polar gravity fields from GOCE and airborne gravity
DEFF Research Database (Denmark)
Forsberg, René; Olesen, Arne Vestergaard; Yidiz, Hasan
2011-01-01
Airborne gravity, together with high-quality surface data and ocean satellite altimetric gravity, may supplement GOCE to make consistent, accurate high resolution global gravity field models. In the polar regions, the special challenge of the GOCE polar gap make the error characteristics...... of combination models especially sensitive to the correct merging of satellite and surface data. We outline comparisons of GOCE to recent airborne gravity surveys in both the Arctic and the Antarctic. The comparison is done to new 8-month GOCE solutions, as well as to a collocation prediction from GOCE gradients...... in Antarctica. It is shown how the enhanced gravity field solutions improve the determination of ocean dynamic topography in both the Arctic and in across the Drake Passage. For the interior of Antarctica, major airborne gravity programs are currently being carried out, and there is an urgent need...
Ion-enhanced gas-surface chemistry: The influence of the mass of the incident ion
International Nuclear Information System (INIS)
Gerlach-Meyer, U.; Coburn, J.W.; Kay, E.
1981-01-01
There are many examples of situations in which a gas-surface reaction rate is increased when the surface is simultaneously subjected to energetic particle bombardment. There are several possible mechanisms which could be involved in this radiation-enhanced gas-surface chemistry. In this study, the reaction rate of silicon, as determined from the etch yield, is measured during irradiation of the Si surface with 1 keV He + , Ne + , and Ar + ions while the surface is simultaneously subjected to fluxes of XeF 2 or Cl 2 molecules. Etch yields as high as 25 Si atoms/ion are observed for XeF 2 and Ar + on Si. A discussion is presented of the extent to which the results clarify the mechanisms responsible for ion-enhanced gas-surface chemistry. (orig.)
Mashhoon, Bahram
2017-01-01
Relativity theory is based on a postulate of locality, which means that the past history of the observer is not directly taken into account. This book argues that the past history should be taken into account. In this way, nonlocality---in the sense of history dependence---is introduced into relativity theory. The deep connection between inertia and gravitation suggests that gravity could be nonlocal, and in nonlocal gravity the fading gravitational memory of past events must then be taken into account. Along this line of thought, a classical nonlocal generalization of Einstein's theory of gravitation has recently been developed. A significant consequence of this theory is that the nonlocal aspect of gravity appears to simulate dark matter. According to nonlocal gravity theory, what astronomers attribute to dark matter should instead be due to the nonlocality of gravitation. Nonlocality dominates on the scale of galaxies and beyond. Memory fades with time; therefore, the nonlocal aspect of gravity becomes wea...
Highly charged ions impinging on a stepped metal surface under grazing incidence
Robin, A; Niemann, D; Stolterfoht, N; Heiland, W
We report on energy loss measurements and charge state distributions for 60 keV N6+ and 75 keV N5+ ions scattered off a Pt(110)(1x2) single crystal surface. In particular, the influence of surface steps on the energy loss and the outgoing charge states is discussed. The scattering angle and the
International Nuclear Information System (INIS)
Tsuji, Kouichi; Hirokawa, Kichinosuke; Sasaki, Atsushi.
1994-01-01
We had previously shown that takeoff-angle-dependent X-ray fluorescence (TAD-XRF) at glancing incidence is a useful method for the characterization of thin films. Here we report the effect of surface roughness of the substrate on TAD-XRF of an ultrathin film at a glancing incidence. An optically flat glass, scratched glasses and plano-convex lenses were used as substrates. A large-range contour such as warp and a roughness of microscopic scale affect the TAD-XRF profile. Therefore, to characterize the ultrathin film by the TAD-XRF method, the material whose roughness is being investigated should be used as the substrate in TAD-XRF measurement. (author)
Massive gravity from bimetric gravity
International Nuclear Information System (INIS)
Baccetti, Valentina; Martín-Moruno, Prado; Visser, Matt
2013-01-01
We discuss the subtle relationship between massive gravity and bimetric gravity, focusing particularly on the manner in which massive gravity may be viewed as a suitable limit of bimetric gravity. The limiting procedure is more delicate than currently appreciated. Specifically, this limiting procedure should not unnecessarily constrain the background metric, which must be externally specified by the theory of massive gravity itself. The fact that in bimetric theories one always has two sets of metric equations of motion continues to have an effect even in the massive gravity limit, leading to additional constraints besides the one set of equations of motion naively expected. Thus, since solutions of bimetric gravity in the limit of vanishing kinetic term are also solutions of massive gravity, but the contrary statement is not necessarily true, there is no complete continuity in the parameter space of the theory. In particular, we study the massive cosmological solutions which are continuous in the parameter space, showing that many interesting cosmologies belong to this class. (paper)
Solar flux incident on an orbiting surface after reflection from a planet
Modest, M. F.
1980-01-01
Algorithms describing the solar radiation impinging on an infinitesimal surface after reflection from a gray and diffuse planet are derived. The following conditions apply: only radiation from the sunny half of the planet is taken into account; the radiation must fall on the top of the orbiting surface, and radiation must come from that part of the planet that can be seen from the orbiting body. A simple approximate formula is presented which displays excellent accuracy for all significant situations, with an error which is always less than 5% of the maximum possible reflected flux. Attention is also given to solar albedo flux on a surface directly facing the planet, the influence of solar position on albedo flux, and to solar albedo flux as a function of the surface-planet tilt angle.
Structured surface reflector design for oblique incidence beam splitter at 610 GHz
Defrance , Fabien; Casaletti , Massimiliano; Sarrazin , Julien; Wiedner , Martina; Gibson , Hugh; Gay , Gregory; Lefevre , Roland; Delorme , Yan
2016-01-01
International audience; An iterative alternate projection-based algorithm is developed to design structured surface reflectors to operate as beam splitters at GHz and THz frequencies. To validate the method, a surface profile is determined to achieve a reflector at 610 GHz that generates four equal-intensity beams towards desired directions of ±12.6° with respect to the specular reflection axis. A prototype is fabricated and the beam splitter behavior is experimentally demonstrated. Measureme...
DEFF Research Database (Denmark)
Jentzsch, G.; Knudsen, Per; Ramatschi, M.
2000-01-01
Air-borne and satellite based altimetry are used to monitor the Greenland ice-cap. Since these measurements are related to fiducial sites at the coast, the robustness of the height differences depends on the stability of these reference points. To benefit from the accuracy of these methods...... observations. Near the coast ocean tidal loading causes additional vertical deformations in the order of 1 to 10 cm Therefore, tidal gravity measurements were carried out at four fiducial sites around Greenland in order to provide corrections for the kinematic part of the coordinates of these sites. Starting...
Mars - Hellas Planitia gravity analysis
Sjogren, W. L.; Wimberley, R. N.
1981-01-01
Doppler radio tracking data from Viking Orbiter 1 has provided new detailed observations of gravity variations over Hellas Planitia. Line-of-sight Bouguer gravity definitely indicates that isostatic adjustment has occurred. Two theoretical models were tested to obtain fits to the gravity data. Results for a surface deficit model, and a model with a surface deficit and a mass excess at depth are displayed. The mass-at-depth model produced very marked improvement in the data fit as compared to the surface deficit model. The optimum depth for the mass excess is 130 km.
Energy Technology Data Exchange (ETDEWEB)
Hulbert, S.L.; Sharma, S.
1987-01-01
At present, grazing incidence mirrors are used almost exclusively as the first optical element in VUV and soft x-ray synchrotron radiation beamlines. The performance of these mirrors is determined by thermal and mechanical stress-induced figure errors as well as by figure errors remaining from the grinding and polishing process. With the advent of VUV and soft x-ray undulators and wigglers has come a new set of thermal stress problems related to both the magnitude and the spatial distribution of power from these devices. In many cases the power load on the entrance slits and gratings in these beamlines is no longer negligible. The dependence of thermally-induced front-end mirror figure errors on various storage ring and insertion device parameters (especially those at the National Synchrotron Light Source) and the effects of these figure errors on two classes of soft x-ray beamlines are presented.
Differential Deposition for Surface Figure Corrections in Grazing Incidence X-Ray Optics
Ramsey, Brian D.; Kilaru, Kiranmayee; Atkins, Carolyn; Gubarev, Mikhail V.; Broadway, David M.
2015-01-01
Differential deposition corrects the low- and mid- spatial-frequency deviations in the axial figure of Wolter-type grazing incidence X-ray optics. Figure deviations is one of the major contributors to the achievable angular resolution. Minimizing figure errors can significantly improve the imaging quality of X-ray optics. Material of varying thickness is selectively deposited, using DC magnetron sputtering, along the length of optic to minimize figure deviations. Custom vacuum chambers are built that can incorporate full-shell and segmented Xray optics. Metrology data of preliminary corrections on a single meridian of full-shell x-ray optics show an improvement of mid-spatial frequencies from 6.7 to 1.8 arc secs HPD. Efforts are in progress to correct a full-shell and segmented optics and to verify angular-resolution improvement with X-ray testing.
Proteins on surfaces investigated by microbeam grazing incidence small angle X-ray scattering
Energy Technology Data Exchange (ETDEWEB)
Gebhardt, Ronald; Riekel, Christian; Burghammer, Manfred [European Synchrotron Radiation Facility, B.P. 220, F-38043 Grenoble Cedex (France); Vendrely, Charlotte [Universite de Cergy-Pontoise, ERRMECE, F-95000, Cergy-Pontoise (France); Mueller-Buschbaum, Peter [TU Muenchen, Physik Department E13, Muenchen (Germany)
2009-07-01
Grazing incidence small angle scattering with a 1 micron x-ray beam ({mu}GISAXS) is applied to study structural ordering of casein micelles and fibroin in solution cast films. {mu}GISAXS scans provide the possibility to locate highly ordered areas and to investigate variation in the molecular packing. In the case of the casein micelles, ordered film structures have been generated by decreasing their natural size dispersion. While dynamic light scattering was used to characterize the different size fractions in solution, {mu}GISAXS and roughness are measured on the resulting casein films. GISAXS-Patterns are analyzed by simulations providing the dimension and nearest neighbor distances of casein micelles. In the case of fibroin, ordering of nano-fibers formed during the drying process is investigated. The experimental data are analyzed by simulations and compared to SEM, AFM and Raman scattering experiments.
International Nuclear Information System (INIS)
Hurkmans, A.; Overbosch, E.G.; Olander, D.R.; Los, J.
1976-01-01
The trapping probability of potassium atoms on a polycrystalline tungsten surface has been measured as a function of the angle of incidence and as a function of the energy of the incoming atoms. Below an energy of 1 eV the trapping was complete; above 20 eV only reflection occurred. The trapping probability increased with increasing angle of incidence. The measurements are compared with a simple model of the fraction of atoms initially trapped. The model, a one-dimensional cube model including a Boltzmann distribution of the velocities of oscillating surface atoms, partially explains the data. The trapping probability as a function of incoming energy is well described for normal incidence, justifying the inclusion of thermal motion of the surface atoms in the model. The angular dependence can be explained in a qualitative way, although there is a substantial discrepancy for large angles of incidence, showing the presence of surface structure. (Auth.)
International Nuclear Information System (INIS)
Dragila, R.; Vukovic, S.
1988-01-01
The properties of surfave waves that are associated with a boundary between a rare plasma and a dense magnetoactive plasma and that propagate along a dc magnetic field are investigated. It is shown that the presence of the magnetic field introduces symmetry in terms of the polarization of the incident electromagnetic wave that excites the surface waves. A surface wave excited by an incident p-polarized (s-polarized) electromagnetic wave leaks in the form of an s-polarized (p-polarized) electromagnetic wave. The rate of rotation of polarization is independent of the polarization of the incident wave. Because a surface wave can leak in the form of an s-polarized electromagnetic wave, it can also be pumped by such a wave, and conditions were found for excitation of a surface wave by an s-polarized incident electromagnetic wave
Lujan, Richard E.
2001-01-01
A mechanical gravity brake that prevents hoisted loads within a shaft from free-falling when a loss of hoisting force occurs. A loss of hoist lifting force may occur in a number of situations, for example if a hoist cable were to break, the brakes were to fail on a winch, or the hoist mechanism itself were to fail. Under normal hoisting conditions, the gravity brake of the invention is subject to an upward lifting force from the hoist and a downward pulling force from a suspended load. If the lifting force should suddenly cease, the loss of differential forces on the gravity brake in free-fall is translated to extend a set of brakes against the walls of the shaft to stop the free fall descent of the gravity brake and attached load.
Directory of Open Access Journals (Sweden)
Barceló Carlos
2005-12-01
Full Text Available Analogue models of (and for gravity have a long and distinguished history dating back to the earliest years of general relativity. In this review article we will discuss the history, aims, results, and future prospects for the various analogue models. We start the discussion by presenting a particularly simple example of an analogue model, before exploring the rich history and complex tapestry of models discussed in the literature. The last decade in particular has seen a remarkable and sustained development of analogue gravity ideas, leading to some hundreds of published articles, a workshop, two books, and this review article. Future prospects for the analogue gravity programme also look promising, both on the experimental front (where technology is rapidly advancing and on the theoretical front (where variants of analogue models can be used as a springboard for radical attacks on the problem of quantum gravity.
Zooplankton incidence in abnormally high sea surface temperature in the Eastern Arabian Sea
Digital Repository Service at National Institute of Oceanography (India)
Goswami, S.C.
Zooplankton in an abnormally high sea surface temperature (33.1 to 33.8 degrees C) and alternate bands of slick formation were studied in the Eastern Arabian Sea during 26 and 29 April 1981. The phenomenon which may be due to intense diurnal heating...
Surface Collisions of Small Cluster Ions at Incident Energies 10-102 eV
Czech Academy of Sciences Publication Activity Database
Herman, Zdeněk
2004-01-01
Roč. 233, - (2004), s. 361-371 ISSN 1387-3806 R&D Projects: GA MŠk ME 561 Grant - others:XE(CZ) EURATOM-IPP.CR Institutional research plan: CEZ:AV0Z4040901 Keywords : surface collisions * cluster ions * unimolecular dissociation Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.235, year: 2004
Alvarez, Enrique
2004-01-01
Gravitons should have momentum just as photons do; and since graviton momentum would cause compression rather than elongation of spacetime outside of matter; it does not appear that gravitons are compatible with Swartzchild's spacetime curvature. Also, since energy is proportional to mass, and mass is proportional to gravity; the energy of matter is proportional to gravity. The energy of matter could thus contract space within matter; and because of the inter-connectedness of space, cause the...
Wang, K.; Gu, N.; Zhang, H.; Zhou, G.
2017-12-01
The Tanlu fault is a major fault located in the eastern China, which stretches 2400 km long from Tancheng in the north to Lujiang in the south. It is generally believed that the Tanlu fault zone was formed in Proterozoic era and underwent a series of complicated processes since then. To understand the upper crustal structure around the southern segment of the Tanlu fault zone, in 2017 we deployed 53 short period seismic stations around the fault zone to the southeast of Hefei, capital city of Anhui province. The temporary array continuously recorded the data for about one month from 17 March to 26 April 2017. The seismic array spans an area of about 30km x 30Km with an average station spacing of about 5-6km. The vertical component data were used for extracting Rayleigh wave phase and group velocity dispersion data for the period of 0.2 to 5 seconds. To improve imaging the upper crustal structure of the fault zone, we jointly inverted the surface wave dispersion data and the gravity data because they have complementary strengths. To combine surface wave dispersion data and gravity observations into a single inversion framework, we used an empirical relationship between seismic velocity and density of Maceira and Ammon (2009). By finding the optimal relative weighting between two data types, we are able to find a shear wave velocity (Vs) model that fits both data types. The joint inversion can resolve the upper crustal fault zone structure down to about 7 km in depth. The Vs model shows that in this region the Tanlu fault is associated with high velocity anomalies, corresponding well to the Feidong complex seen on the surface. This indicates that the Tanlu fault zone may provide a channel for the intrusion of hot materials.
Energy Technology Data Exchange (ETDEWEB)
Grannell, R.B.; Whitcomb, J.H.; Aronstam, P.S.; Clover, R.C.
1981-06-01
Recommendations for carrying out surveys which achieve 15, 10 and 5 microgal precisions are presented. Achieving the smaller standard deviations will require more field effort and will be more costly. For a 60 station survey, at commercial rates in 1981, typical costs are estimated to be $20,000, $26,000 and $35,000 respectively, for data collection, reduction and interpretation. These figures exclude instrument purchase or rental. Twenty geothermal areas in the western United States which might be suitable for precise repetitive gravity monitoring were evaluated. The evaluation criteria included capability for subsidence on a geological basis, estimated electrical production, environmental impact, and anticipation of production in the near future. It is felt that the most promising areas in order of priority are: (1) the Salton Sea field, California; (2) Valles Caldera, New Mexico; (3) The Geysers-Clear Lake; and (4) Westmorland, California; (5) Roosevelt Hot Springs, Utah; and (6) Heber; (7) Brawley; and (8) Long Valley, California.
DEFF Research Database (Denmark)
Jentzsch, G.; Knudsen, Per; Ramatschi, M.
2000-01-01
Air-borne and satellite based altimetry are used to monitor the Greenland ice-cap. Since these measurements are related to fiducial sites at the coast, the robustness of the height differences depends on the stability of these reference points. To benefit from the accuracy of these methods...... on the centimeter level, station corrections regarding the Earth tides and the ocean tidal loading have to be applied. Models for global corrections esp. for the body tides are available and sufficient, but local corrections regarding the effect of the adjacent shelf area still have to be inferred from additional...... observations. Near the coast ocean tidal loading causes additional vertical deformations in the order of 1 to 10 cm Therefore, tidal gravity measurements were carried out at four fiducial sites around Greenland in order to provide corrections for the kinematic part of the coordinates of these sites. Starting...
International Nuclear Information System (INIS)
Wouters, P.A.A.F.; Emmichoven, P.A.Z. van; Niehaus, A.
1989-01-01
The experimental setup used to measure electron spectra at well defined detection angles for grazing incidence doubly charged ion-surface collisions at keV-energies is described. Electron spectra are reported for the rare gas ions colliding with a Cu(110)-surface. The spectra are analyzed in terms of various spontaneous ionization processes using a newly developed model. It is found that double capture followed by atomic auto-ionization on the incoming trajectory and Auger-capture processes in which the first and second hole in the doubly charged projectiles are successively filled are the main processes contributing to the electron spectra. From a comparison of model calculations with measured spectra it is concluded that the metal electrons cannot adapt adiabatically to the sudden changes of the charge state of the projectile in front of the surface. A parameter characterizing the partly diabatic behavior is determined. The variation of spectra upon adsorption of a monolayer of oxygen on the surface is reported and discussed. (author)
Tracy, Cameron L.; Chen, Chien-Hung; Park, Sulgiye; Davisson, M. Lee; Ewing, Rodney C.
2018-04-01
Nuclear forensics involves determination of the origin and history of interdicted nuclear materials based on the detection of signatures associated with their production and trafficking. The surface oxidation undergone by UO2 when exposed to air is a potential signature of its atmospheric exposure during handling and transport. To assess the sensitivity of this oxidation to atmospheric parameters, surface sensitive grazing-incidence x-ray diffraction (GIXRD) measurements were performed on UO2 samples exposed to air of varying relative humidity (34%, 56%, and 95% RH) and temperature (room temperature, 50 °C, and 100 °C). Near-surface unit cell contraction was observed following exposure, indicating oxidation of the surface and accompanying reduction of the uranium cation ionic radii. The extent of unit cell contraction provides a measure of the extent of oxidation, allowing for comparison of the effects of various exposure conditions. No clear influence of relative humidity on the extent of oxidation was observed, with samples exhibiting similar degrees of unit cell contraction at all relative humidities investigated. In contrast, the thickness of the oxidized layers increased substantially with increasing temperature, such that differences on the order of 10 °C yielded readily observable crystallographic signatures of the exposure conditions.
International Nuclear Information System (INIS)
Kawata, Jun; Ohya, Kaoru.
1994-01-01
A Monte Carlo simulation of the secondary electron emission from beryllium is combined with a model of bowl structure for surface roughness, for analyzing the difference between the electron emissions for normal and oblique incidences. At normal incidence, with increasing the roughness parameter H/W, the primary energy E pm at which the maximum electron yield occurs becomes higher, and at more than the E pm , the decrease in the yield is slower; where H and W are the depth and width of the bowl structure, respectively. The dispersion of incident angle to the microscopic surface causes a small increase in the yield at oblique incidence, whereas the blocking of primary electrons from bombarding the bottom of the structure causes an opposite trend. The strong anisotropy in the polar angular distribution with respect to the azimuthal angle is calculated at oblique incidence. (author)
Arruda, Claúdia; Artico, Gabriela; Freitas, Roseli; Filho, Antônio; Migliari, Dante
2016-08-01
Predisposing factors in chronic hyperplastic candidosis (CHC) have been poorly recognized. This study aimed at assessing the prevalence of Candida spp. in areas of the oral mucosa showing greater prevalent rate of CHC, such as the retrocomissural area, the lateral borders of the tongue, and the hard-palate mucosa in four groups of individuals presenting predisposing factors as follows: Smoking habits (group I); patients with low salivary flow rate (SFR) (hyposalivation - group II); patients with loss of vertical dimension of occlusion (LVDO -group III); and control subjects (group IV). A total of 44 individuals (age 4090 years, mean: 55.8 years) were divided into four groups: Group I (11 smokers); group II (10 hyposalivation patients); group III (10 LVDO patients); and group IV (control, 13 healthy subjects). All individuals were tested for Candida-pseudohyphae form by direct examination and for Candida spp. culture growth in samples obtained from the retrocomissural, tongue's lateral border, and hard-soft palatal mucosa. Direct examination showed a statistically significant prevalence rate for pseudohyphae (p < 0.05) on the retrocomissural and on tongue's lateral borders of individuals with LVDO. A statistically significant (p < 0.05) culture growth for Candida spp. was found on the retrocomissural areas of those with hyposalivation and with LVDO, and on the palate mucosa and on the tongue's lateral borders in the smokers and in the individuals with LVDO when compared with those of the control group. While direct examination is effective for detecting pseudohyphae, LVDO and tobacco smoking seem to be factors of relevance to the development of CHC. Since CHC has been linked to a high rate of malignant transformation, this study analyzes some clinical (and exogenous) factors that may contribute to the development of CHC and addresses some preventive measures to reduce its incidence.
Directory of Open Access Journals (Sweden)
Carlos Barceló
2011-05-01
Full Text Available Analogue gravity is a research programme which investigates analogues of general relativistic gravitational fields within other physical systems, typically but not exclusively condensed matter systems, with the aim of gaining new insights into their corresponding problems. Analogue models of (and for gravity have a long and distinguished history dating back to the earliest years of general relativity. In this review article we will discuss the history, aims, results, and future prospects for the various analogue models. We start the discussion by presenting a particularly simple example of an analogue model, before exploring the rich history and complex tapestry of models discussed in the literature. The last decade in particular has seen a remarkable and sustained development of analogue gravity ideas, leading to some hundreds of published articles, a workshop, two books, and this review article. Future prospects for the analogue gravity programme also look promising, both on the experimental front (where technology is rapidly advancing and on the theoretical front (where variants of analogue models can be used as a springboard for radical attacks on the problem of quantum gravity.
International Nuclear Information System (INIS)
Giribet, G E
2005-01-01
Claus Kiefer presents his book, Quantum Gravity, with his hope that '[the] book will convince readers of [the] outstanding problem [of unification and quantum gravity] and encourage them to work on its solution'. With this aim, the author presents a clear exposition of the fundamental concepts of gravity and the steps towards the understanding of its quantum aspects. The main part of the text is dedicated to the analysis of standard topics in the formulation of general relativity. An analysis of the Hamiltonian formulation of general relativity and the canonical quantization of gravity is performed in detail. Chapters four, five and eight provide a pedagogical introduction to the basic concepts of gravitational physics. In particular, aspects such as the quantization of constrained systems, the role played by the quadratic constraint, the ADM decomposition, the Wheeler-de Witt equation and the problem of time are treated in an expert and concise way. Moreover, other specific topics, such as the minisuperspace approach and the feasibility of defining extrinsic times for certain models, are discussed as well. The ninth chapter of the book is dedicated to the quantum gravitational aspects of string theory. Here, a minimalistic but clear introduction to string theory is presented, and this is actually done with emphasis on gravity. It is worth mentioning that no hard (nor explicit) computations are presented, even though the exposition covers the main features of the topic. For instance, black hole statistical physics (within the framework of string theory) is developed in a pedagogical and concise way by means of heuristical arguments. As the author asserts in the epilogue, the hope of the book is to give 'some impressions from progress' made in the study of quantum gravity since its beginning, i.e., since the end of 1920s. In my opinion, Kiefer's book does actually achieve this goal and gives an extensive review of the subject. (book review)
Luznik, L.; Lust, E.; Flack, K. A.
2014-12-01
There are few studies describing the interaction between marine current turbines and an overlying surface gravity wave field. In this work we present an experimental study on the effects of surface gravity waves of different wavelengths on the wave phase averaged performance characteristics of a marine current turbine model. Measurements are performed with a 1/25 scale (diameter D=0.8m) two bladed horizontal axis turbine towed in the large (116m long) towing tank at the U.S. Naval Academy equipped with a dual-flap, servo-controlled wave maker. Three regular waves with wavelengths of 15.8, 8.8 and 3.9m with wave heights adjusted such that all waveforms have the same energy input per unit width are produced by the wave maker and model turbine is towed into the waves at constant carriage speed of 1.68 m/s. This representing the case of waves travelling in the same direction as the mean current. Thrust and torque developed by the model turbine are measured using a dynamometer mounted in line with the turbine shaft. Shaft rotation speed and blade position are measured using in in-house designed shaft position indexing system. The tip speed ratio (TSR) is adjusted using a hysteresis brake which is attached to the output shaft. Free surface elevation and wave parameters are measured with two optical wave height sensors, one located in the turbine rotor plane and other one diameter upstream of the rotor. All instruments are synchronized in time and data is sampled at a rate of 700 Hz. All measured quantities are conditionally sampled as a function of the measured surface elevation and transformed to wave phase space using the Hilbert Transform. Phenomena observed in earlier experiments with the same turbine such as phase lag in the torque signal and an increase in thrust due to Stokes drift are examined and presented with the present data as well as spectral analysis of the torque and thrust data.
Pipinos, Savas
2010-01-01
This article describes one classroom activity in which the author simulates the Newtonian gravity, and employs the Euclidean Geometry with the use of new technologies (NT). The prerequisites for this activity were some knowledge of the formulae for a particle free fall in Physics and most certainly, a good understanding of the notion of similarity…
F.C. Gruau; J.T. Tromp (John)
1999-01-01
textabstractWe consider the problem of establishing gravity in cellular automata. In particular, when cellular automata states can be partitioned into empty, particle, and wall types, with the latter enclosing rectangular areas, we desire rules that will make the particles fall down and pile up on
Wahr, John; Smeed, David; Leuliette, Eric; Swenson, Sean
2014-05-01
Seasonal variability of sea surface height and mass within the Red Sea, occurs mostly through the exchange of heat with the atmosphere and wind-driven inflow and outflow of water through the strait of Bab el Mandab that opens into the Gulf of Aden to the south. The seasonal effects of precipitation and evaporation, of water exchange through the Suez Canal to the north, and of runoff from the adjacent land, are all small. The flow through the Bab el Mandab involves a net mass transfer into the Red Sea during the winter and a net transfer out during the summer. But that flow has a multi-layer pattern, so that in the summer there is actually an influx of cool water at intermediate (~100 m) depths. Thus, summer water in the southern Red Sea is warmer near the surface due to higher air temperatures, but cooler at intermediate depths (especially in the far south). Summer water in the northern Red Sea experiences warming by air-sea exchange only. The temperature profile affects the water density, which impacts the sea surface height but has no effect on vertically integrated mass. Here, we study this seasonal cycle by combining GRACE time-variable mass estimates, altimeter (Jason-1, Jason-2, and Envisat) measurements of sea surface height, and steric sea surface height contributions derived from depth-dependent, climatological values of temperature and salinity obtained from the World Ocean Atlas. We find good consistency, particularly in the northern Red Sea, between these three data types. Among the general characteristics of our results are: (1) the mass contributions to seasonal SSHT variations are much larger than the steric contributions; (2) the mass signal is largest in winter, consistent with winds pushing water into the Red Sea through the Strait of Bab el Mandab in winter, and out during the summer; and (3) the steric signal is largest in summer, consistent with summer sea surface warming.
Venus gravity - Analysis of Beta Regio
Esposito, P. B.; Sjogren, W. L.; Mottinger, N. A.; Bills, B. G.; Abbott, E.
1982-01-01
Radio tracking data acquired over Beta Regio were analyzed to obtain a surface mass distribution from which a detailed vertical gravity field was derived. In addition, a corresponding vertical gravity field was evaluated solely from the topography of the Beta region. A comparison of these two maps confirms the strong correlation between gravity and topography which was previously seen in line-of-sight gravity maps. It also demonstrates that the observed gravity is a significant fraction of that predicted from the topography alone. The effective depth of complete isostatic compensation for the Beta region is estimated to be 330 km, which is somewhat deeper than that found for other areas of Venus.
International Nuclear Information System (INIS)
Isham, C.
1989-01-01
Gravitational effects are seen as arising from a curvature in spacetime. This must be reconciled with gravity's apparently passive role in quantum theory to achieve a satisfactory quantum theory of gravity. The development of grand unified theories has spurred the search, with forces being of equal strength at a unification energy of 10 15 - 10 18 GeV, with the ''Plank length'', Lp ≅ 10 -35 m. Fundamental principles of general relativity and quantum mechanics are outlined. Gravitons are shown to have spin-0, as mediators of gravitation force in the classical sense or spin-2 which are related to the quantisation of general relativity. Applying the ideas of supersymmetry to gravitation implies partners for the graviton, especially the massless spin 3/2 fermion called a gravitino. The concept of supersymmetric strings is introduced and discussed. (U.K.)
International Nuclear Information System (INIS)
Markov, M.A.; West, P.C.
1984-01-01
This book discusses the state of the art of quantum gravity, quantum effects in cosmology, quantum black-hole physics, recent developments in supergravity, and quantum gauge theories. Topics considered include the problems of general relativity, pregeometry, complete cosmological theories, quantum fluctuations in cosmology and galaxy formation, a new inflationary universe scenario, grand unified phase transitions and the early Universe, the generalized second law of thermodynamics, vacuum polarization near black holes, the relativity of vacuum, black hole evaporations and their cosmological consequences, currents in supersymmetric theories, the Kaluza-Klein theories, gauge algebra and quantization, and twistor theory. This volume constitutes the proceedings of the Second Seminar on Quantum Gravity held in Moscow in 1981
Thuillet, F.; Maurel, C.; Michel, P.; Biele, Jens; Ballouz, Ronald; Richardson, D. C.
2017-01-01
The asteroid sample return mission, Hayabusa2 JAXA) was launched on December 3rd, 2014. It will reach the C-type near-Earth asteroid (162173) Ryugu in 2018 and bring back samples from its surface to Earth in 2020. Hayabusa2 will release the European (DLR/CNES) lander MASCOT (Mobile Asteroid SCOuT) on the asteroid surface to perform in-situ measurements [1]. Ryugu’s surface is expected to be composed of a gran- ular layer (regolith), whose physical properties are currently unknown. MASCOT’s...
Is nonrelativistic gravity possible?
International Nuclear Information System (INIS)
Kocharyan, A. A.
2009-01-01
We study nonrelativistic gravity using the Hamiltonian formalism. For the dynamics of general relativity (relativistic gravity) the formalism is well known and called the Arnowitt-Deser-Misner (ADM) formalism. We show that if the lapse function is constrained correctly, then nonrelativistic gravity is described by a consistent Hamiltonian system. Surprisingly, nonrelativistic gravity can have solutions identical to relativistic gravity ones. In particular, (anti-)de Sitter black holes of Einstein gravity and IR limit of Horava gravity are locally identical.
International Nuclear Information System (INIS)
Tsuji, Kouichi; Wagatsuma, Kazuaki; Yamada, Takashi; Utaka, Tadashi
1997-01-01
We have studied X-ray fluorescence analysis under glancing incidence and glancing take-off conditions. Recently, we have developed a third apparatus for detecting glancing-incidence and take-off X-ray fluorescence, which makes it possible to measure the incident-angle dependence, the take-off-angle dependence. X-ray reflectivity, and X-ray diffraction. Primarily, we have measured the take-off angular dependence of X-ray fluorescence using this apparatus. Glancing take-off X-ray fluorescence has some advantages in comparison with glancing-incidence X-ray fluorescence. The surface density and the absolute angles were determined by analysing the take-off angle dependence of the fluorescent X-rays emitted from identical atoms with the aid of the reciprocity theorem. (Author)
Chu, Huaqiang; Dong, Bingzhi; Zhang, Yalei; Zhou, Xuefei
2012-01-01
A bio-diatomite dynamic membrane (BDDM) reactor for surface water treatment under a water head of 30, 40, 50, 60 and 70 cm, respectively, was investigated, which was very effective for pollutants removal. The water head exerted strong influences on filtration flux of BDDM during the precoating process, as well as on the formation of BDDM and turbidity variations. A high filtration flux (approximately 200-300 L/m2 h) could be achieved in the long filtration times of BDDM with a stable effluent turbidity of approximately 0.11-0.25 NTU. The BDDM could remove particles larger than 25 μm completely. The adopted sintered diatomite mainly consisted of macro pores, which were beneficial for improving the filtration flux of BDDM. During the backwash stage, the BDDM could be removed completely by the air backwash.
Energy Technology Data Exchange (ETDEWEB)
Luis, F. J. de; Perez-Garcia, M.; Barbero, F. J.; Batlles, F. J.
2004-07-01
This work gathers and it exposes a set of educational contents extracted from the general bibliography and from the own experience in Engineering studies and courses on the application of a vector representation to the description of the apparent movement of the sun, the shading evaluation and the incidence of radiation on surfaces. (Author)
International Nuclear Information System (INIS)
Schupp, P.
2007-01-01
Heuristic arguments suggest that the classical picture of smooth commutative spacetime should be replaced by some kind of quantum / noncommutative geometry at length scales and energies where quantum as well as gravitational effects are important. Motivated by this idea much research has been devoted to the study of quantum field theory on noncommutative spacetimes. More recently the focus has started to shift back to gravity in this context. We give an introductory overview to the formulation of general relativity in a noncommutative spacetime background and discuss the possibility of exact solutions. (author)
Favrie, N.; Gavrilyuk, S.
2017-07-01
A new numerical method for solving the Serre-Green-Naghdi (SGN) equations describing dispersive waves on shallow water is proposed. From the mathematical point of view, the SGN equations are the Euler-Lagrange equations for a ‘master’ lagrangian submitted to a differential constraint which is the mass conservation law. One major numerical challenge in solving the SGN equations is the resolution of an elliptic problem at each time instant. This is the most time-consuming part of the numerical method. The idea is to replace the ‘master’ lagrangian by a one-parameter family of ‘augmented’ lagrangians, depending on a greater number of variables, for which the corresponding Euler-Lagrange equations are hyperbolic. In such an approach, the ‘master’ lagrangian is recovered by the augmented lagrangian in some limit (for example, when the corresponding parameter is large). The choice of such a family of augmented lagrangians is proposed and discussed. The corresponding hyperbolic system is numerically solved by a Godunov type method. Numerical solutions are compared with exact solutions to the SGN equations. It appears that the computational time in solving the hyperbolic system is much lower than in the case where the elliptic operator is inverted. The new method is applied, in particular, to the study of ‘Favre waves’ representing non-stationary undular bores produced after reflection of the fluid flow with a free surface at an immobile wall.
International Nuclear Information System (INIS)
Brown, R.E.; Camp, J.B.; Darling, T.W.
1990-01-01
An experiment is being developed to measure the acceleration of the antiproton in the gravitational field of the earth. Antiprotons of a few MeV from the LEAR facility at CERN will be slowed, captured, cooled to a temperature of about 10 K, and subsequently launched a few at a time into a drift tube where the effect of gravity on their motion will be determined by a time-of-flight method. Development of the experiment is proceeding at Los Alamos using normal matter. The fabrication of a drift tube that will produce a region of space in which gravity is the dominant force on moving ions is of major difficulty. This involves a study of methods of minimizing the electric fields produced by spatially varying work functions on conducting surfaces. Progress in a number of areas is described, with stress on the drift-tube development
High-resolution gravity model of Venus
Reasenberg, R. D.; Goldberg, Z. M.
1992-01-01
The anomalous gravity field of Venus shows high correlation with surface features revealed by radar. We extract gravity models from the Doppler tracking data from the Pioneer Venus Orbiter by means of a two-step process. In the first step, we solve the nonlinear spacecraft state estimation problem using a Kalman filter-smoother. The Kalman filter has been evaluated through simulations. This evaluation and some unusual features of the filter are discussed. In the second step, we perform a geophysical inversion using a linear Bayesian estimator. To allow an unbiased comparison between gravity and topography, we use a simulation technique to smooth and distort the radar topographic data so as to yield maps having the same characteristics as our gravity maps. The maps presented cover 2/3 of the surface of Venus and display the strong topography-gravity correlation previously reported. The topography-gravity scatter plots show two distinct trends.
International Nuclear Information System (INIS)
Hooft, G.
2012-01-01
The dynamical degree of freedom for the gravitational force is the metric tensor, having 10 locally independent degrees of freedom (of which 4 can be used to fix the coordinate choice). In conformal gravity, we split this field into an overall scalar factor and a nine-component remainder. All unrenormalizable infinities are in this remainder, while the scalar component can be handled like any other scalar field such as the Higgs field. In this formalism, conformal symmetry is spontaneously broken. An imperative demand on any healthy quantum gravity theory is that black holes should be described as quantum systems with micro-states as dictated by the Hawking-Bekenstein theory. This requires conformal symmetry that may be broken spontaneously but not explicitly, and this means that all conformal anomalies must cancel out. Cancellation of conformal anomalies yields constraints on the matter sector as described by some universal field theory. Thus black hole physics may eventually be of help in the construction of unified field theories. (author)
National Oceanic and Atmospheric Administration, Department of Commerce — This data base (14,559 records) was received in January 1986. Principal gravity parameters include elevation and observed gravity. The observed gravity values are...
National Oceanic and Atmospheric Administration, Department of Commerce — The NGS Absolute Gravity data (78 stations) was received in July 1993. Principal gravity parameters include Gravity Value, Uncertainty, and Vertical Gradient. The...
AllahTavakoli, Y.; Safari, A.; Ardalan, A.; Bahroudi, A.
2015-12-01
The current research provides a method for tracking near-surface mass-density anomalies via using only land-based gravity data, which is based on a special version of Poisson's Partial Differential Equation (PDE) of the gravitational field at Earth's surface. The research demonstrates how the Poisson's PDE can provide us with a capability to extract the near-surface mass-density anomalies from land-based gravity data. Herein, this version of the Poisson's PDE is mathematically introduced to the Earth's surface and then it is used to develop the new method for approximating the mass-density via derivatives of the Earth's gravitational field (i.e. via the gradient tensor). Herein, the author believes that the PDE can give us new knowledge about the behavior of the Earth's gravitational field at the Earth's surface which can be so useful for developing new methods of Earth's mass-density determination. In a case study, the proposed method is applied to a set of gravity stations located in the south of Iran. The results were numerically validated via certain knowledge about the geological structures in the area of the case study. Also, the method was compared with two standard methods of mass-density determination. All the numerical experiments show that the proposed approach is well-suited for tracking near-surface mass-density anomalies via using only the gravity data. Finally, the approach is also applied to some petroleum exploration studies of salt diapirs in the south of Iran.
Park, G.; Gao, X.; Sorooshian, S.
2005-12-01
The atmospheric model is sensitive to the land surface interactions and its coupling with Land surface Models (LSMs) leads to a better ability to forecast weather under extreme climate conditions, such as droughts and floods (Atlas et al. 1993; Beljaars et al. 1996). However, it is still questionable how accurately the surface exchanges can be simulated using LSMs, since terrestrial properties and processes have high variability and heterogeneity. Examinations with long-term and multi-site surface observations including both remotely sensed and ground observations are highly needed to make an objective evaluation on the effectiveness and uncertainty of LSMs at different circumstances. Among several atmospheric forcing required for the offline simulation of LSMs, incident surface solar radiation is one of the most significant components, since it plays a major role in total incoming energy into the land surface. The North American Land Data Assimilation System (NLDAS) and North American Regional Reanalysis (NARR) are two important data sources providing high-resolution surface solar radiation data for the use of research communities. In this study, these data are evaluated against field observations (AmeriFlux) to identify their advantages, deficiencies and sources of errors. The NLDAS incident solar radiation shows a pretty good agreement in monthly mean prior to the summer of 2001, while it overestimates after the summer of 2001 and its bias is pretty close to the EDAS. Two main error sources are identified: 1) GOES solar radiation was not used in the NLDAS for several months in 2001 and 2003, and 2) GOES incident solar radiation when available, was positively biased in year 2002. The known snow detection problem is sometimes identified in the NLDAS, since it is inherited from GOES incident solar radiation. The NARR consistently overestimates incident surface solar radiation, which might produce erroneous outputs if used in the LSMs. Further attention is given to
Newtonian gravity in loop quantum gravity
Smolin, Lee
2010-01-01
We apply a recent argument of Verlinde to loop quantum gravity, to conclude that Newton's law of gravity emerges in an appropriate limit and setting. This is possible because the relationship between area and entropy is realized in loop quantum gravity when boundaries are imposed on a quantum spacetime.
Holographic entanglement entropy in Lovelock gravities
de Boer, J.; Kulaxizi, M.; Parnachev, A.
2011-01-01
We study entanglement entropies of simply connected surfaces in field theories dual to Lovelock gravities. We consider Gauss-Bonnet and cubic Lovelock gravities in detail. In the conformal case the logarithmic terms in the entanglement entropy are governed by the conformal anomalies of the CFT; we
Huang, N. E.; Long, S. R.; Bliven, L. F.; Tung, C.-C.
1984-01-01
On the basis of the mapping method developed by Huang et al. (1983), an analytic expression for the non-Gaussian joint probability density function of slope and elevation for nonlinear gravity waves is derived. Various conditional and marginal density functions are also obtained through the joint density function. The analytic results are compared with a series of carefully controlled laboratory observations, and good agreement is noted. Furthermore, the laboratory wind wave field observations indicate that the capillary or capillary-gravity waves may not be the dominant components in determining the total roughness of the wave field. Thus, the analytic results, though derived specifically for the gravity waves, may have more general applications.
Generation of H-, H2(v double-prime), and H atoms by H2+ and H3+ ions incident upon barium surfaces
International Nuclear Information System (INIS)
Hiskes, J.R.; Karo, A.M.
1989-01-01
The generation of vibrationally excited molecules by electron excitation collisions and the subsequent generation of negative ions by dissociative attachment to these molecules has become a standard model for volume source operation. These processes have been supplemented recently by the demonstration of atom-surface recombination to form vibrationally excited molecules, and enhanced negative ion formation by protons incident upon barium electrodes. In this paper we consider the additional processes of molecular vibrational excitation generated by recombination of molecular ions on the electrode surfaces, and negative ion formation by vibrationally excited molecules rebounding from low work-function electrodes. 10 refs., 4 figs
Byrne, Michael
1999-01-01
Einstein said that gravity is an acceleration like any other acceleration. But gravity causes relativistic effects at non-relativistic speeds; so gravity could have relativistic origins. And since the strong force is thought to cause most of mass, and mass is proportional to gravity; the strong force is therefore also proportional to gravity. The strong force could thus cause relativistic increases of mass through the creation of virtual gluons; along with a comparable contraction of space ar...
International Nuclear Information System (INIS)
Ginsparg, P.
1991-01-01
These are introductory lectures for a general audience that give an overview of the subject of matrix models and their application to random surfaces, 2d gravity, and string theory. They are intentionally 1.5 years out of date
Failures in sand in reduced gravity environments
Marshall, Jason P.; Hurley, Ryan C.; Arthur, Dan; Vlahinic, Ivan; Senatore, Carmine; Iagnemma, Karl; Trease, Brian; Andrade, José E.
2018-04-01
The strength of granular materials, specifically sand is important for understanding physical phenomena on other celestial bodies. However, relatively few experiments have been conducted to determine the dependence of strength properties on gravity. In this work, we experimentally investigated relative values of strength (the peak friction angle, the residual friction angle, the angle of repose, and the peak dilatancy angle) in Earth, Martian, Lunar, and near-zero gravity. The various angles were captured in a classical passive Earth pressure experiment conducted on board a reduced gravity flight and analyzed using digital image correlation. The data showed essentially no dependence of the peak friction angle on gravity, a decrease in the residual friction angle between Martian and Lunar gravity, no dependence of the angle of repose on gravity, and an increase in the dilation angle between Martian and Lunar gravity. Additionally, multiple flow surfaces were seen in near-zero gravity. These results highlight the importance of understanding strength and deformation mechanisms of granular materials at different levels of gravity.
Chiral gravity, log gravity, and extremal CFT
International Nuclear Information System (INIS)
Maloney, Alexander; Song Wei; Strominger, Andrew
2010-01-01
We show that the linearization of all exact solutions of classical chiral gravity around the AdS 3 vacuum have positive energy. Nonchiral and negative-energy solutions of the linearized equations are infrared divergent at second order, and so are removed from the spectrum. In other words, chirality is confined and the equations of motion have linearization instabilities. We prove that the only stationary, axially symmetric solutions of chiral gravity are BTZ black holes, which have positive energy. It is further shown that classical log gravity--the theory with logarithmically relaxed boundary conditions--has finite asymptotic symmetry generators but is not chiral and hence may be dual at the quantum level to a logarithmic conformal field theories (CFT). Moreover we show that log gravity contains chiral gravity within it as a decoupled charge superselection sector. We formally evaluate the Euclidean sum over geometries of chiral gravity and show that it gives precisely the holomorphic extremal CFT partition function. The modular invariance and integrality of the expansion coefficients of this partition function are consistent with the existence of an exact quantum theory of chiral gravity. We argue that the problem of quantizing chiral gravity is the holographic dual of the problem of constructing an extremal CFT, while quantizing log gravity is dual to the problem of constructing a logarithmic extremal CFT.
Mikš, Antonín; Novák, Pavel
2017-09-01
The paper is focused on the problem of determination of the point of incidence of a light ray for the case of reflection or refraction at the spherical optical surface, assuming that two fixed points in space that the sought light ray should go through are given. The requirement is that one of these points lies on the incident ray and the other point on the reflected/refracted ray. Although at first glance it seems to be a simple problem, it will be shown that it has no simple analytical solution. The basic idea of the solution is given, and it is shown that the problem leads to a nonlinear equation in one variable. The roots of the resulting nonlinear equation can be found by numerical methods of mathematical optimization. The proposed methods were implemented in MATLAB, and the proper function of these algorithms was verified on several examples.
Energy Technology Data Exchange (ETDEWEB)
Yoshimoto, K. (Japan Sewage Works Agency, Tokyo (Japan)); Mori, T. (Shimane Univ., Shimane (Japan). Faculty of Agriculture)
1992-09-10
A part of sulfide dissolved in the sewage is oxidized by oxygen dissolved in the sewage from the gas phase inside by the re-aeration. In addition, a part of type of the dissolvable sulfides is diffused in the gas phase as a hydrogen sulfide gas by the turbulence and so on in the sewage. When hydrogen sulfide diffused in the gas phase is oxidized to sulfuric acid by the sulfur oxidation bacteria, the corrosion and deterioration of concrete by that sulfuric acid are concerned even in the gravity sewer pipe as same as in the sewer pipe downstream from the discharge opening of the pressurized transport pipe for a long distance. When the gravity sewer pipe is planned and designed, it is required for establishing the necessary countermeasure at the places where the generation of sulfide is predicted, by estimating the sulfide concentration in the sewage accurately. In this report, making the slime adhered on the gravity sewer pipe wall and the slime grown in the laboratory as the objects, some knowledges on the sulfide flux from the anaerobic slime were obtained by measuring the sulfide flux and so forth. 16 refs., 4 figs., 3 tabs.
International Nuclear Information System (INIS)
Schoutens, K.; van Nieuwenhuizen, P.; State Univ. of New York, Stony Brook, NY
1991-11-01
We briefly review some results in the theory of quantum W 3 gravity in the chiral gauge. We compare them with similar results in the analogous but simpler cases of d = 2 induced gauge theories and d = 2 induced gravity
... medlineplus.gov/ency/article/003587.htm Urine specific gravity test To use the sharing features on this page, please enable JavaScript. Urine specific gravity is a laboratory test that shows the concentration ...
Cadiz, California Gravity Data
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (32 records) were gathered by Mr. Seth I. Gutman for AridTech Inc., Denver, Colorado using a Worden Prospector gravity meter. This data base...
National Oceanic and Atmospheric Administration, Department of Commerce — The Central Andes gravity data (6,151 records) were compiled by Professor Gotze and the MIGRA Group. This data base was received in April, 1997. Principal gravity...
National Oceanic and Atmospheric Administration, Department of Commerce — The Decade of North American Geology (DNAG) gravity grid values, spaced at 6 km, were used to produce the Gravity Anomaly Map of North America (1987; scale...
International Nuclear Information System (INIS)
Pinheiro, R.
1979-01-01
The properties and production of gravitational radiation are described. The prospects for their detection are considered including the Weber apparatus and gravity-wave telescopes. Possibilities of gravity-wave astronomy are noted
Northern Oklahoma Gravity Data
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (710 records) were compiled by Professor Ahern. This data base was received in June 1992. Principal gravity parameters include latitude,...
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (24,284 records) were compiled by the U. S. Geological Survey. This data base was received on February 23, 1993. Principal gravity...
International Nuclear Information System (INIS)
Vega, H.J. de
1990-01-01
One of the main challenges in theoretical physics today is the unification of all interactions including gravity. At present, string theories appear as the most promising candidates to achieve such a unification. However, gravity has not completely been incorporated in string theory, many technical and conceptual problems remain and a full quantum theory of gravity is still non-existent. Our aim is to properly understand strings in the context of quantum gravity. Attempts towards this are reviewed. (author)
International Nuclear Information System (INIS)
La, H.
1992-01-01
A new geometric formulation of Liouville gravity based on the area preserving diffeo-morphism is given and a possible alternative to reinterpret Liouville gravity is suggested, namely, a scalar field coupled to two-dimensional gravity with a curvature constraint
Bergshoeff, E.; Pope, C.N.; Stelle, K.S.
1990-01-01
We discuss the notion of higher-spin covariance in w∞ gravity. We show how a recently proposed covariant w∞ gravity action can be obtained from non-chiral w∞ gravity by making field redefinitions that introduce new gauge-field components with corresponding new gauge transformations.
Induced quantum conformal gravity
International Nuclear Information System (INIS)
Novozhilov, Y.V.; Vassilevich, D.V.
1988-11-01
Quantum gravity is considered as induced by matter degrees of freedom and related to the symmetry breakdown in the low energy region of a non-Abelian gauge theory of fundamental fields. An effective action for quantum conformal gravity is derived where both the gravitational constant and conformal kinetic term are positive. Relation with induced classical gravity is established. (author). 15 refs
Amelino-Camelia, Giovanni
2003-01-01
Comment: 9 pages, LaTex. These notes were prepared while working on an invited contribution to the November 2003 issue of Physics World, which focused on quantum gravity. They intend to give a non-technical introduction (accessible to readers from outside quantum gravity) to "Quantum Gravity Phenomenology"
MacKeown, P. K.
1984-01-01
Clarifies two concepts of gravity--those of a fictitious force and those of how space and time may have geometry. Reviews the position of Newton's theory of gravity in the context of special relativity and considers why gravity (as distinct from electromagnetics) lends itself to Einstein's revolutionary interpretation. (JN)
Gravity study of the Middle Aterno Valley
di Nezza, Maria; di Filippo, Michele; Cesi, Claudio; Ferri, Fernando
2010-05-01
A gravity study was carried out to identify the geological and structural features of the Middle Aterno Valley, and intramontane depression in the central Appennines, which was targeted to assess the seismic hazard of the city of L'Aquila and surrounding areas, after the Abruzzo 2009 earthquake. Gravity anomalies have been used for the construction of a 3D model of the area, and gravity data for the construction of Bouguer and residual anomaly maps. These data, together with geological surface data allowed for the understanding of the Plio-quaternary tectonic setting of the basins. The study area has been differentiated into different domains with respect to structural and morphological features of different styles of faults. Geology and gravity data show that the local amplification phenomena are due to the fact that the historical center of L'Aquila was built on a coarse breccias (debris-flow deposits with decameter scale limestone blocks) overlying sandy and clayey lacustrine sediments. As these sediments have a low density, gravity prospecting very easily identifies them. Residual anomalies, showing a relative gravity low corresponding to the historical center of L'Aquila, and surrounding areas, indicated that these sediments are up to 250 m-thick. Gravity prospecting also revealed the uprooting of the reliefs which outcrop in the area of Coppito. These reliefs, practically outcrop in the middle of the basin. Here, the gravity anomalies are negative and not positive as would be expected from outcropping geological bedrock.
International Nuclear Information System (INIS)
Dvali, Gia; Kolanovic, Marko; Nitti, Francesco; Gabadadze, Gregory
2002-01-01
We propose a framework in which the quantum gravity scale can be as low as 10 -3 eV. The key assumption is that the standard model ultraviolet cutoff is much higher than the quantum gravity scale. This ensures that we observe conventional weak gravity. We construct an explicit brane-world model in which the brane-localized standard model is coupled to strong 5D gravity of infinite-volume flat extra space. Because of the high ultraviolet scale, the standard model fields generate a large graviton kinetic term on the brane. This kinetic term 'shields' the standard model from the strong bulk gravity. As a result, an observer on the brane sees weak 4D gravity up to astronomically large distances beyond which gravity becomes five dimensional. Modeling quantum gravity above its scale by the closed string spectrum we show that the shielding phenomenon protects the standard model from an apparent phenomenological catastrophe due to the exponentially large number of light string states. The collider experiments, astrophysics, cosmology and gravity measurements independently point to the same lower bound on the quantum gravity scale, 10 -3 eV. For this value the model has experimental signatures both for colliders and for submillimeter gravity measurements. Black holes reveal certain interesting properties in this framework
Thermodynamics and phases in quantum gravity
International Nuclear Information System (INIS)
Husain, Viqar; Mann, R B
2009-01-01
We give an approach for studying quantum gravity effects on black hole thermodynamics. This combines a quantum framework for gravitational collapse with quasi-local definitions of energy and surface gravity. Our arguments suggest that (i) the specific heat of a black hole becomes positive after a phase transition near the Planck scale,(ii) its entropy acquires a logarithmic correction and (iii) the mass loss rate is modified such that Hawking radiation stops near the Planck scale. These results are due essentially to a realization of fundamental discreteness in quantum gravity, and are in this sense potentially theory independent.
International Nuclear Information System (INIS)
Lessor, D.L.; Duke, C.B.; Lippel, P.H.; Brandes, G.R.; Canter, K.F.; Horsky, T.N.
1990-10-01
Intensities of positrons specularly diffracted from Cu(111) were measured at the Brandeis positron beam facility and analyzed in the energy range 8eV i = 4eV. At lower energies strong energy dependences occur associated both with multiple elastic scattering phenomena within atomic layers of Cu parallel to the surface and with the thresholds of inelastic channels (e.g., plasmon creation). Use of the free electron calculation of V i shows that energy dependence of inelastic processes is necessary to obtain a satisfactory description of the absolute magnitude of the diffracted intensities below E = 50eV. Detailed comparison of the calculated and observed diffraction intensities reveals the necessity of incorporating surface loss processes explicitly into the model in order to achieve a quantitative description of the measured intensities for E 40 degree. 30 refs., 5 figs., 1 tab
Tribology Experiment in Zero Gravity
Pan, C. H. T.; Gause, R. L.; Whitaker, A. F.; Finckenor, M. M.
2015-01-01
A tribology experiment in zero gravity was performed during the orbital flight of Spacelab 1 to study the motion of liquid lubricants over solid surfaces. The absence of a significant gravitational force facilitates observation of such motions as controlled by interfacial and capillary forces. Two experimental configurations were used. One deals with the liquid on one solid surface, and the other with the liquid between a pair of closed spaced surfaces. Time sequence photographs of fluid motion on a solid surface yielded spreading rate data of several fluid-surface combinations. In general, a slow spreading process as governed by the tertiary junction can be distinguished from a more rapid process which is driven by surface tension controlled internal fluid pressure. Photographs were also taken through the transparent bushings of several experimental journal bearings. Morphology of incomplete fluid films and its fluctuation with time suggest the presence or absence of unsteady phenomena of the bearing-rotor system in various arrangements.
Einstein gravity emerging from quantum weyl gravity
International Nuclear Information System (INIS)
Zee, A.
1983-01-01
We advocate a conformal invariant world described by the sum of the Weyl, Dirac, and Yang-Mills action. Quantum fluctuations bring back Einstein gravity so that the long-distance phenomenology is as observed. Formulas for the induced Newton's constant and Eddington's constant are derived in quantized Weyl gravity. We show that the analogue of the trace anomaly for the Weyl action is structurally similar to that for the Yang-Mills action
Danailov, D; O'Connor, D J
2002-01-01
Recent experiments and our molecular-dynamics simulations indicate that the main signal of the angular scattering spectra of glancing incidence scattering are not affected by the thermal motion of surface atoms and can be explained by our row-model with averaged cylindrical potentials. At the ICACS-18 Conference [Nucl. Instr. and Meth. B 164-165 (2000) 583] we reported good agreement between experimental and calculated multimodal azimuthal angular scattering spectra for the glancing scattering of 10 and 15 keV [Nucl. Instr. and Meth. B 180 (2001) 265, Appl. Surf. Sci. 171 (2001) 113] He sup 0 beam along the [1 0 0] direction on the Fe(1 0 0) face. Our simulations also predicted that in contrast to the 2D angular scattering distribution, the 1D azimuthal angular distribution of scattered particles is very sensitive to the interaction potential used. Here, we report more detailed calculations incorporating the influence of terraces and surface steps on surface channeling, which show a reduction of the angular s...
International Nuclear Information System (INIS)
Brown, J.D.
1988-01-01
This book addresses the subject of gravity theories in two and three spacetime dimensions. The prevailing philosophy is that lower dimensional models of gravity provide a useful arena for developing new ideas and insights, which are applicable to four dimensional gravity. The first chapter consists of a comprehensive introduction to both two and three dimensional gravity, including a discussion of their basic structures. In the second chapter, the asymptotic structure of three dimensional Einstein gravity with a negative cosmological constant is analyzed. The third chapter contains a treatment of the effects of matter sources in classical two dimensional gravity. The fourth chapter gives a complete analysis of particle pair creation by electric and gravitational fields in two dimensions, and the resulting effect on the cosmological constant
Gravity interpretation via EULDPH
International Nuclear Information System (INIS)
Ebrahimzadeh Ardestani, V.
2003-01-01
Euler's homogeneity equation for determining the coordinates of the source body especially to estimate the depth (EULDPH) is discussed at this paper. This method is applied to synthetic and high-resolution real data such as gradiometric or microgravity data. Low-quality gravity data especially in the areas with a complex geology structure has rarely been used. The Bouguer gravity anomalies are computed from absolute gravity data after the required corrections. Bouguer anomaly is transferred to residual gravity anomaly. The gravity gradients are estimated from residual anomaly values. Bouguer anomaly is the gravity gradients, using EULDPH. The coordinates of the perturbing body will be determined. Two field examples one in the east of Tehran (Mard Abad) where we would like to determine the location of the anomaly (hydrocarbon) and another in the south-east of Iran close to the border with Afghanistan (Nosrat Abad) where we are exploring chromite are presented
International Nuclear Information System (INIS)
Tannous, Jose Trancoso
2001-01-01
This is a morphological analysis study through SEM of the differences of the laser tissue interaction as a function of the laser beam irradiation angle, under different parameters of energy. Fourteen freshly extracted molars stored in a 0,9% sodium chloride solution were divided in seven pairs and were irradiated with 100, 200, 300, 400, 500, 600 and 700 mJ per pulse, respectively. Each sample received three enamel irradiations and three cement irradiations, either in the punctual or in the contact mode, one near to the other, with respectively 30, 45 and 90 inclinations degrees of dental surface-laser-beam incidence. Four Er:YAG pulses (2,94 μm, 7-20 Hz, 0,1-1 J energy/pulse - Opus 20 - Opus Dent) with water cooling system (0,4 ml/s) were applied. After the laser irradiation the specimens were analysed through scanning electron microscope (SEM). The results were analysed by SEM micrographs showing a great difference on the laser tissue interaction characteristics as a function of the irradiation angle of the laser beam. All the observations led to conclude that, considering the laser parameters used, the incidence angle variation is a very important parameter regarding the desired morphological effects. This represents an extremely relevant detail on the technical description of the Er:YAG laser irradiation protocols on dental tissues. (author)
International Nuclear Information System (INIS)
Mielke, Eckehard W.
2006-01-01
Anomalies in Yang-Mills type gauge theories of gravity are reviewed. Particular attention is paid to the relation between the Dirac spin, the axial current j5 and the non-covariant gauge spin C. Using diagrammatic techniques, we show that only generalizations of the U(1)- Pontrjagin four-form F and F = dC arise in the chiral anomaly, even when coupled to gravity. Implications for Ashtekar's canonical approach to quantum gravity are discussed
Energy Technology Data Exchange (ETDEWEB)
Rousseau, P
2006-09-15
This thesis reports two studies about the interaction with insulating surfaces of keV ions or atoms under grazing incidence. The first part presents a study of charge exchange processes occurring during the interaction of singly charged ions with the surface of NaCl. In particular, by measuring the scattered charge fraction and the energy loss in coincidence with electron emission, the neutralization mechanism is determined for S{sup +}, C{sup +}, Xe{sup +}, H{sup +}, O{sup +}, Kr{sup +}, N{sup +}, Ar{sup +}, F{sup +}, Ne{sup +} and He{sup +}. These results show the importance of the double electron capture as neutralization process for ions having too much potential energy for resonant capture and not enough for Auger neutralization. We have also studied the ionisation of the projectile and of the surface, and the different Auger-like neutralization processes resulting in electron emission, population of conduction band or excited state. For oxygen scattering, we have measured an higher electron yield in coincidence with scattered negative ion than with scattered atom suggesting the transient formation above the surface of the oxygen doubly negative ion. The second study deals with the fast atom diffraction, a new phenomenon observed for the first time during this work. Due to the large parallel velocity, the surface appears as a corrugated wall where rows interfere. Similarly to the Thermal Atom Scattering the diffraction pattern corresponds to the surface potential and is sensitive to vibrations. We have study the H-NaCl and He-LiF atom-surface potentials in the 20 meV - 1 eV range. This new method offers interesting perspectives for surface characterisation. (author)
International Nuclear Information System (INIS)
Burkhard, N.R.
1979-01-01
The gravity inversion code applies stabilized linear inverse theory to determine the topography of a subsurface density anomaly from Bouguer gravity data. The gravity inversion program consists of four source codes: SEARCH, TREND, INVERT, and AVERAGE. TREND and INVERT are used iteratively to converge on a solution. SEARCH forms the input gravity data files for Nevada Test Site data. AVERAGE performs a covariance analysis on the solution. This document describes the necessary input files and the proper operation of the code. 2 figures, 2 tables
Classical Weyl transverse gravity
Energy Technology Data Exchange (ETDEWEB)
Oda, Ichiro [University of the Ryukyus, Department of Physics, Faculty of Science, Nishihara, Okinawa (Japan)
2017-05-15
We study various classical aspects of the Weyl transverse (WTDiff) gravity in a general space-time dimension. First of all, we clarify a classical equivalence among three kinds of gravitational theories, those are, the conformally invariant scalar tensor gravity, Einstein's general relativity and the WTDiff gravity via the gauge-fixing procedure. Secondly, we show that in the WTDiff gravity the cosmological constant is a mere integration constant as in unimodular gravity, but it does not receive any radiative corrections unlike the unimodular gravity. A key point in this proof is to construct a covariantly conserved energy-momentum tensor, which is achieved on the basis of this equivalence relation. Thirdly, we demonstrate that the Noether current for the Weyl transformation is identically vanishing, thereby implying that the Weyl symmetry existing in both the conformally invariant scalar tensor gravity and the WTDiff gravity is a ''fake'' symmetry. We find it possible to extend this proof to all matter fields, i.e. the Weyl-invariant scalar, vector and spinor fields. Fourthly, it is explicitly shown that in the WTDiff gravity the Schwarzschild black hole metric and a charged black hole one are classical solutions to the equations of motion only when they are expressed in the Cartesian coordinate system. Finally, we consider the Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmology and provide some exact solutions. (orig.)
Takagi, Kentaro; Nair, Selvakumar V.; Watanabe, Ryosuke; Seto, Keisuke; Kobayashi, Takayoshi; Tokunaga, Eiji
2017-12-01
Surface plasmon polariton (SPP) resonance spectra for noble metals (Au, Ag, and Cu) were comprehensively studied in the Kretschmann attenuated total reflection (ATR) geometry, in the wavelength (λ) range from 300 to 1000 nm with the angle of incidence (θ) ranging from 45 to 60° and the film thickness (d) ranging from 41 to 76 nm. The experimental plasmon resonance spectra were reproduced by a calculation that included the broadening effects as follows: (1) the imaginary part of the bulk dielectric constant, (2) the thickness-dependent radiative coupling of the SPP at the metal-air interface to the prism, (3) the lack of conservation of the wavevector parallel to the interface kx(k||) caused by the surface roughness, (4) scanning λ at a fixed θ (changing both energy and kx at the same time) over the SPP dispersion relation. For Au and Ag, the experimental results were in good agreement with the calculated results using the bulk dielectric constants, showing no film thickness dependence of the plasmon resonance energy. A method to extract the true width of the plasmon resonance from raw ATR spectra is proposed and the results are rigorously compared with those expected from the bulk dielectric function given in the literature. For Au and Ag, the width increases with energy, in agreement with that expected from the relaxation of bulk free electrons including the electron-electron interaction, but there is clear evidence of extra broadening, which is more significant for thinner films, possibly due to relaxation pathways intrinsic to plasmons near the interface. For Cu, the visibility of the plasmon resonance critically depends on the evaporation conditions, and low pressures and fast deposition rates are required. Otherwise, scattering from the surface roughness causes considerable broadening of the plasmon resonance, resulting in an apparently fixed resonance energy without clear incident angle dependence. For Cu, the observed plasmon dispersion agrees well with
Venus spherical harmonic gravity model to degree and order 60
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.
Andreu, Vicente; Pascual, Juan Antonio; Gimeno, Eugenia; Picó, Yolanda
2013-04-01
Heavy metals have been during decades a result of the human fingerprint on the ecosystems, mainly in waters, soils or vegetation, being considered as a major s threat also on human health. However, the increasing in human population shows other aspect, such as the so called "emerging contaminants". They constitute an increasing group of compounds that includes, among others, personal care products, drugs of abuse and pharmaceuticals. These contaminants have become, in recent years, of great concern for researchers and, even, for the population. Among these substances, the presence of pharmaceuticals in the ecosystems compartments has becoming an increasing problem for environmental sustainability, and also for human health, with consequences very scarcely known. They reach the nature from waste waters treatment plants, industrial waste effluents, uncontrolled landfills, etc. affecting particularly the fauna in its different levels. Some pharmaceuticals have shown toxicity not only to bacteria, algae and invertebrates but also to fish, mollusks, etc. This work is focused on the study of the presence of 17 relevant pharmaceuticals and 7 heavy metals (Cd, Co, Cr, Cu, Ni, Pb and Zn) in surface waters of the irrigation channels and the lagoon of the Pego-Oliva Marsh Natural Park (Valencian Community, Spain), which is characterized by a long history of human pressures, such as marsh transformation for agricultural uses, urbanization, etc. In this area, 34 sampling zones were selected, covering the main land uses. The interactions and possible relationships between both groups of contaminants were studied, together with the influences of the source of water samples, land uses and their spatial distribution. All water samples appeared contaminated with at least with two compounds. Ibuprofen and codeine were the compounds more frequently detected in concentrations between detection limit and a maximum of 59 ng/L and 63 ng/L respectively. Regarding the studied metals, Zn
Meyers, Michael C
2017-03-01
Numerous injuries have been attributed to playing on artificial turf. More recently, newer generations of artificial turf have been developed to duplicate the playing characteristics of natural grass. Although artificial turf has been deemed safer than natural grass in some studies, few long-term studies have been conducted comparing match-related collegiate soccer injuries between the 2 playing surfaces. Collegiate male soccer athletes do not experience any difference in the incidence, mechanisms, or severity of match-related injuries between FieldTurf and natural grass. Cohort study; Level of evidence, 2. Male soccer athletes from 11 universities were evaluated over 6 seasons. Demographic features and predictors included player position, cleat design, player weight, turf age, and environmental factors. Outcomes of interest included injury incidence, injury category, time loss, injury mechanism and situation, type of injury, injury grade and anatomic location, injury severity, head and lower extremity trauma, and elective medical procedures. All match-related injuries were evaluated by the attending head athletic trainer and team physicians on site and subsequently in the physician's office when further follow-up and treatment were deemed necessary. In sum, 765 collegiate games were evaluated for match-related soccer injuries sustained on FieldTurf or natural grass during 6 seasons. Overall, 380 team games (49.7%) were played on FieldTurf versus 385 team games (50.3%) played on natural grass. A total of 722 injuries were documented, with 268 (37.1%) occurring on FieldTurf and 454 (62.9%) on natural grass. Multivariate analysis per 10 team games indicated a significant playing surface effect: F 2,720 = 7.260, P = .001. A significantly lower total injury incidence rate (IIR) of 7.1 (95% CI, 6.6-7.5) versus 11.8 (95% CI, 11.3-12.2; P < .0001) and lower rate of substantial injuries, 0.7 (95% CI, 0.5-1.0) versus 1.9 (95% CI, 1.5-2.3; P < .03), were documented on Field
Low-Gravity Centrifuge Facilities for Asteroid Lander and Material Processing and Manufacturing
Asphaug, E.; Thangavelautham, J.; Schwartz, S.
2018-02-01
We are developing space centrifuge research facilities for attaining low-gravity to micro-gravity geological environmental conditions representative of the environment on the surfaces of asteroids and comets.
Interior Alaska Bouguer Gravity Anomaly
National Oceanic and Atmospheric Administration, Department of Commerce — A 1 kilometer Complete Bouguer Anomaly gravity grid of interior Alaska. Only those grid cells within 10 kilometers of a gravity data point have gravity values....
Consistency of orthodox gravity
Energy Technology Data Exchange (ETDEWEB)
Bellucci, S. [INFN, Frascati (Italy). Laboratori Nazionali di Frascati; Shiekh, A. [International Centre for Theoretical Physics, Trieste (Italy)
1997-01-01
A recent proposal for quantizing gravity is investigated for self consistency. The existence of a fixed-point all-order solution is found, corresponding to a consistent quantum gravity. A criterion to unify couplings is suggested, by invoking an application of their argument to more complex systems.
Generalized pure Lovelock gravity
Concha, Patrick; Rodríguez, Evelyn
2017-11-01
We present a generalization of the n-dimensional (pure) Lovelock Gravity theory based on an enlarged Lorentz symmetry. In particular, we propose an alternative way to introduce a cosmological term. Interestingly, we show that the usual pure Lovelock gravity is recovered in a matter-free configuration. The five and six-dimensional cases are explicitly studied.
Generalized pure Lovelock gravity
Directory of Open Access Journals (Sweden)
Patrick Concha
2017-11-01
Full Text Available We present a generalization of the n-dimensional (pure Lovelock Gravity theory based on an enlarged Lorentz symmetry. In particular, we propose an alternative way to introduce a cosmological term. Interestingly, we show that the usual pure Lovelock gravity is recovered in a matter-free configuration. The five and six-dimensional cases are explicitly studied.
Drongelen AW van; Roszek B; Hilbers-Modderman ESM; Kallewaard M; Wassenaar C; LGM
2002-01-01
This RIVM study was performed to gain insight into wheelchair-related incidents with powered and manual wheelchairs reported to the USA FDA, the British MDA and the Dutch Center for Quality and Usability Research of Technical Aids (KBOH). The data in the databases do not indicate that incidents with
Venus: radar determination of gravity potential.
Shapiro, I I; Pettengill, G H; Sherman, G N; Rogers, A E; Ingalls, R P
1973-02-02
We describe a method for the determination of the gravity potential of Venus from multiple-frequency radar measurements. The method is based on the strong frequency dependence of the absorption of radio waves in Venus' atmosphere. Comparison of the differing radar reflection intensities at several frequencies yields the height of the surface relative to a reference pressure contour; combination with measurements of round-trip echo delays allows the pressure, and hence the gravity potential contour, to be mapped relative to the mean planet radius. Since calibration data from other frequencies are unavailable, the absorption-sensitive Haystack Observatory data have been analyzed under the assumption of uniform surface reflectivity to yield a gravity equipotential contour for the equatorial region and a tentative upper bound of 6 x 10(-4) on the fractional difference of Venus' principal equatorial moments of inertia. The minima in the equipotential contours appear to be associated with topographic minima.
International Nuclear Information System (INIS)
Jevicki, A.; Ninomiya, M.
1985-01-01
We are concerned with applications of the simplicial discretization method (Regge calculus) to two-dimensional quantum gravity with emphasis on the physically relevant string model. Beginning with the discretization of gravity and matter we exhibit a discrete version of the conformal trace anomaly. Proceeding to the string problem we show how the direct approach of (finite difference) discretization based on Nambu action corresponds to unsatisfactory treatment of gravitational degrees. Based on the Regge approach we then propose a discretization corresponding to the Polyakov string. In this context we are led to a natural geometric version of the associated Liouville model and two-dimensional gravity. (orig.)
CERN. Geneva
2007-01-01
Of the four fundamental forces, gravity has been studied the longest, yet gravitational physics is one of the most rapidly developing areas of science today. This talk will give a broad brush survey of the past achievements and future prospects of general relativistic gravitational physics. Gravity is a two frontier science being important on both the very largest and smallest length scales considered in contemporary physics. Recent advances and future prospects will be surveyed in precision tests of general relativity, gravitational waves, black holes, cosmology and quantum gravity. The aim will be an overview of a subject that is becoming increasingly integrated with experiment and other branches of physics.
Directory of Open Access Journals (Sweden)
J. Ambjørn
1995-07-01
Full Text Available The 2-point function is the natural object in quantum gravity for extracting critical behavior: The exponential falloff of the 2-point function with geodesic distance determines the fractal dimension dH of space-time. The integral of the 2-point function determines the entropy exponent γ, i.e. the fractal structure related to baby universes, while the short distance behavior of the 2-point function connects γ and dH by a quantum gravity version of Fisher's scaling relation. We verify this behavior in the case of 2d gravity by explicit calculation.
Ehrenfest's principle in quantum gravity
International Nuclear Information System (INIS)
Greensite, J.
1991-01-01
The Ehrenfest principle d t = is proposed as (part of) a definition of the time variable in canonical quantum gravity. This principle selects a time direction in superspace, and provides a conserved, positive definite probability measure. An exact solution of the Ehrenfest condition is obtained, which leads to constant-time surfaces in superspace generated by the operator d/dτ=ΛθxΛ, where Λ is the gradient operator in superspace, and θ is the phase of the Wheeler-DeWitt wavefunction Φ; the constant-time surfaces are determined by this solution up to a choice of initial t=0 surface. This result holds throughout superspace, including classically forbidden regions and in the neighborhood of caustics; it also leads to ordinary quantum field theory and classical gravity in regions of superspace where the phase satisfies vertical stroked t θvertical stroke>>vertical stroked t ln(Φ * Φ)vertical stroke and (d t θ) 2 >>vertical stroked t 2 θvertical stroke. (orig.)
Directory of Open Access Journals (Sweden)
S. G. Pugacheva
2015-01-01
Full Text Available The source of gravity anomalies of the Moon are large mascons with a high mass concentration at a depth of volcanic plains and lunar Maria. New data on the gravitational field of the Moon were obtained from two Grail spacecrafts. The article presents the data of physical and mechanical properties of the surface soil layer of the lunar Maria and gives an assessment of the chemical composition of the soil. There have been calculated heterogeneity parameters of the surface macro-relief of the lunar Maria: albedo, soil density, average grain diameter of the particles forming the surface layer and the volume fraction occupied by particles. It can be assumed that mascons include rich KREEP rocks with a high content of thorium and iron oxide. Formation of mascons is connected with intensive development of basaltic volcanism on the Moon in the early periods of its existence.
Global gravity field from recent satellites (DTU15) - Arctic improvements
DEFF Research Database (Denmark)
Andersen, O. B.; Knudsen, P.; Kenyon, S.
2017-01-01
Global marine gravity field modelling using satellite altimetry is currently undergoing huge improvement with the completion of the Jason-1 end-of-life geodetic mission, but particularly with the continuing Cryosat-2 mission. These new satellites provide three times as many geodetic mission...... altimetric sea surface height observations as ever before. The impact of these new geodetic mission data is a dramatic improvement of particularly the shorter wavelength of the gravity field (10-20 km) which is now being mapped at significantly higher accuracy. The quality of the altimetric gravity field...... is in many places surpassing the quality of gravity fields derived using non-commercial marine gravity observations. Cryosat-2 provides for the first time altimetry throughout the Arctic Ocean up to 88°N. Here, the huge improvement in marine gravity mapping is shown through comparison with high quality...
Energy Technology Data Exchange (ETDEWEB)
De Marco, Roland [Nanochemistry Research Institute, Department of Applied Chemistry, Curtin University of Technology, GPO Box U 1987, Perth, WA 6845 (Australia)]. E-mail: r.demarco@exchange.curtin.edu.au; Jiang, Z.-T. [Nanochemistry Research Institute, Department of Applied Chemistry, Curtin University of Technology, GPO Box U 1987, Perth, WA 6845 (Australia); Martizano, Jay [Nanochemistry Research Institute, Department of Applied Chemistry, Curtin University of Technology, GPO Box U 1987, Perth, WA 6845 (Australia); Lowe, Alex [Nanochemistry Research Institute, Department of Applied Chemistry, Curtin University of Technology, GPO Box U 1987, Perth, WA 6845 (Australia); Pejcic, Bobby [Nanochemistry Research Institute, Department of Applied Chemistry, Curtin University of Technology, GPO Box U 1987, Perth, WA 6845 (Australia); Riessen, Arie van [Materials Research Group, Department of Applied Physics, Curtin University of Technology, GPO Box U 1987, Perth, WA 6845 (Australia)
2006-08-15
A marriage of electrochemical impedance spectroscopy (EIS) and in situ synchrotron radiation grazing incidence X-ray diffraction (SR-GIXRD) has provided a powerful new technique for the elucidation of the mechanistic chemistry of electrochemical systems. In this study, EIS/SR-GIXRD has been used to investigate the influence of metal ion buffer calibration ligands, along with natural organic ligands in seawater, on the behaviour of the iron chalcogenide glass ion-selective electrode (ISE). The SR-GIXRD data demonstrated that citrate - a previously reported poor iron calibration ligand for the analysis of seawater - induced an instantaneous and total dissolution of crystalline GeSe and Sb{sub 2}Se{sub 3} in the modified surface layer (MSL) of the ISE, while natural organic ligands in seawater and a mixture of ligands in a mimetic seawater ligand system protected the MSL's crystalline inclusions of GeSe and Sb{sub 2}Se{sub 3} from oxidative attack. Expectedly, the EIS data showed that citrate induced a loss in the medium frequency time constant for the MSL of the ISE, while seawater's natural organic ligands and the mimetic ligand system preserved the medium frequency EIS response characteristics of the ISE's MSL. The new EIS/SR-GIXRD technique has provided insights into the suitability of iron calibration ligands for the analysis of iron in seawater.
Terrestrial Sagnac delay constraining modified gravity models
Karimov, R. Kh.; Izmailov, R. N.; Potapov, A. A.; Nandi, K. K.
2018-04-01
Modified gravity theories include f(R)-gravity models that are usually constrained by the cosmological evolutionary scenario. However, it has been recently shown that they can also be constrained by the signatures of accretion disk around constant Ricci curvature Kerr-f(R0) stellar sized black holes. Our aim here is to use another experimental fact, viz., the terrestrial Sagnac delay to constrain the parameters of specific f(R)-gravity prescriptions. We shall assume that a Kerr-f(R0) solution asymptotically describes Earth's weak gravity near its surface. In this spacetime, we shall study oppositely directed light beams from source/observer moving on non-geodesic and geodesic circular trajectories and calculate the time gap, when the beams re-unite. We obtain the exact time gap called Sagnac delay in both cases and expand it to show how the flat space value is corrected by the Ricci curvature, the mass and the spin of the gravitating source. Under the assumption that the magnitude of corrections are of the order of residual uncertainties in the delay measurement, we derive the allowed intervals for Ricci curvature. We conclude that the terrestrial Sagnac delay can be used to constrain the parameters of specific f(R) prescriptions. Despite using the weak field gravity near Earth's surface, it turns out that the model parameter ranges still remain the same as those obtained from the strong field accretion disk phenomenon.
Discussion of entanglement entropy in quantum gravity
International Nuclear Information System (INIS)
Ma, Chen-Te
2018-01-01
We study entanglement entropy in gravity theory with quantum effects. A simplest model is a two dimensional Einstein gravity theory. We use an n-sheet manifold to obtain an area term of entanglement entropy by summing over all background fields. Based on AdS/CFT correspondence, strongly coupled conformal field theory is expected to describe perturbative quantum gravity theory. An ultraviolet complete quantum gravity theory should not depend on a choice of an entangling surface. To analysis the problem explicitly, we analyze two dimensional conformal field theory. We find that a coefficient of a universal term of entanglement entropy is independent of a choice of an entangling surface in two dimensional conformal field theory for one interval to show a tentative evidence. Finally, we discuss that translational invariance in a quantum system at zero temperature, size goes to infinity and no mass scales, except for cut-off, possibly be a necessary condition in quantum gravity theory by ruing out a volume law of entanglement entropy. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (71 records) were gathered by various governmental organizations (and academia) using a variety of methods. This data base was received in...
Bergshoeff, Eric A.; Hohm, Olaf; Townsend, Paul K.
2012-01-01
We present a brief review of New Massive Gravity, which is a unitary theory of massive gravitons in three dimensions obtained by considering a particular combination of the Einstein-Hilbert and curvature squared terms.
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (65,164 records) were gathered by various governmental organizations (and academia) using a variety of methods. The data base was received...
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (55,907 records) were gathered by various governmental organizations (and academia) using a variety of methods. This data base was received...
International Nuclear Information System (INIS)
Hertog, Thomas; Hollands, Stefan
2005-01-01
We study the stability of designer gravity theories, in which one considers gravity coupled to a tachyonic scalar with anti-de Sitter (AdS) boundary conditions defined by a smooth function W. We construct Hamiltonian generators of the asymptotic symmetries using the covariant phase space method of Wald et al and find that they differ from the spinor charges except when W = 0. The positivity of the spinor charge is used to establish a lower bound on the conserved energy of any solution that satisfies boundary conditions for which W has a global minimum. A large class of designer gravity theories therefore have a stable ground state, which the AdS/CFT correspondence indicates should be the lowest energy soliton. We make progress towards proving this by showing that minimum energy solutions are static. The generalization of our results to designer gravity theories in higher dimensions involving several tachyonic scalars is discussed
Carroll versus Galilei gravity
Energy Technology Data Exchange (ETDEWEB)
Bergshoeff, Eric [Centre for Theoretical Physics, University of Groningen,Nijenborgh 4, 9747 AG Groningen (Netherlands); Gomis, Joaquim [Departament de Física Cuàntica i Astrofísica and Institut de Ciències del Cosmos,Universitat de Barcelona,Martí i Franquès 1, E-08028 Barcelona (Spain); Rollier, Blaise [Centre for Theoretical Physics, University of Groningen,Nijenborgh 4, 9747 AG Groningen (Netherlands); Rosseel, Jan [Faculty of Physics, University of Vienna,Boltzmanngasse 5, A-1090 Vienna (Austria); Veldhuis, Tonnis ter [Centre for Theoretical Physics, University of Groningen,Nijenborgh 4, 9747 AG Groningen (Netherlands)
2017-03-30
We consider two distinct limits of General Relativity that in contrast to the standard non-relativistic limit can be taken at the level of the Einstein-Hilbert action instead of the equations of motion. One is a non-relativistic limit and leads to a so-called Galilei gravity theory, the other is an ultra-relativistic limit yielding a so-called Carroll gravity theory. We present both gravity theories in a first-order formalism and show that in both cases the equations of motion (i) lead to constraints on the geometry and (ii) are not sufficient to solve for all of the components of the connection fields in terms of the other fields. Using a second-order formalism we show that these independent components serve as Lagrange multipliers for the geometric constraints we found earlier. We point out a few noteworthy differences between Carroll and Galilei gravity and give some examples of matter couplings.
International Nuclear Information System (INIS)
Williams, Ruth M
2006-01-01
A review is given of a number of approaches to discrete quantum gravity, with a restriction to those likely to be relevant in four dimensions. This paper is dedicated to Rafael Sorkin on the occasion of his sixtieth birthday
The holographic bound in the scalar-tensor and f(R) gravities
International Nuclear Information System (INIS)
Firouzjaee, J.T.
2013-01-01
The holographic bound has been extended to the different theory of gravities such as scalar-tensor gravity and f(R) gravity according to the Noether charge definition of the entropy for a black hole surface. We have introduced some popular examples of the flat FRW cosmology in order to investigate holographic bound in scalar-tensor and f(R) gravity. Using the holographic bound, we put an additional constraint on scalar-tensor gravity and the f(R) gravity parameters. We also discuss the transformation from Jordan frame to Einstein frame. (orig.)
Streaming gravity mode instability
International Nuclear Information System (INIS)
Wang Shui.
1989-05-01
In this paper, we study the stability of a current sheet with a sheared flow in a gravitational field which is perpendicular to the magnetic field and plasma flow. This mixing mode caused by a combined role of the sheared flow and gravity is named the streaming gravity mode instability. The conditions of this mode instability are discussed for an ideal four-layer model in the incompressible limit. (author). 5 refs
International Nuclear Information System (INIS)
Accioly, A.J.
1987-01-01
A possible classical route conducting towards a general relativity theory with higher-derivatives starting, in a sense, from first principles, is analysed. A completely causal vacuum solution with the symmetries of the Goedel universe is obtained in the framework of this higher-derivative gravity. This very peculiar and rare result is the first known vcuum solution of the fourth-order gravity theory that is not a solution of the corresponding Einstein's equations.(Author) [pt
Nelson, George
2004-01-01
Gravity is the name given to the phenomenon that any two masses, like you and the Earth, attract each other. One pulls on the Earth and the Earth pulls on one the same amount. And one does not have to be touching. Gravity acts over vast distances, like the 150 million kilometers (93 million miles) between the Earth and the Sun or the billions of…
Automated borehole gravity meter system
International Nuclear Information System (INIS)
Lautzenhiser, Th.V.; Wirtz, J.D.
1984-01-01
An automated borehole gravity meter system for measuring gravity within a wellbore. The gravity meter includes leveling devices for leveling the borehole gravity meter, displacement devices for applying forces to a gravity sensing device within the gravity meter to bring the gravity sensing device to a predetermined or null position. Electronic sensing and control devices are provided for (i) activating the displacement devices, (ii) sensing the forces applied to the gravity sensing device, (iii) electronically converting the values of the forces into a representation of the gravity at the location in the wellbore, and (iv) outputting such representation. The system further includes electronic control devices with the capability of correcting the representation of gravity for tidal effects, as well as, calculating and outputting the formation bulk density and/or porosity
Seasonal gravity change at Yellowstone caldera
Poland, M. P.; de Zeeuw-van Dalfsen, E.
2017-12-01
The driving forces behind Yellowstone's dynamic deformation, vigorous hydrothermal system, and abundant seismicity are usually ascribed to "magmatic fluids," which could refer to magma, water, volatiles, or some combination. Deformation data alone cannot distinguish the relative importance of these fluids. Gravity measurements, however, provide an indication of mass change over time and, when combined with surface displacements, can constrain the density of subsurface fluids. Unfortunately, several decades of gravity surveys at Yellowstone have yielded ambiguous results. We suspect that the difficulty in interpreting Yellowstone gravity data is due to seasonal variations in environmental conditions—especially surface and ground water. Yellowstone gravity surveys are usually carried out at the same time of year (generally late summer) to minimize the impact of seasonality. Nevertheless, surface and subsurface water levels are not likely to be constant from year to year, given annual differences in precipitation. To assess the overall magnitude of seasonal gravity changes, we conducted gravity surveys of benchmarks in and around Yellowstone caldera in May, July, August, and October 2017. Our goal was to characterize seasonal variations due to snow melt/accumulation, changes in river and lake levels, changes in groundwater levels, and changes in hydrothermal activity. We also hope to identify sites that show little variation in gravity over the course of the 2017 surveys, as these locations may be less prone to seasonal changes and more likely to detect small variations due to magmatic processes. Preliminary examination of data collected in May and July 2017 emphasizes the importance of site location relative to sources of water. For example, a site on the banks of the Yellowstone River showed a gravity increase of several hundred microgals associated with a 50 cm increase in the river level. A high-altitude site far from rivers and lakes, in contrast, showed a
Gravity Before Einstein and Schwinger Before Gravity
Trimble, Virginia L.
2012-05-01
Julian Schwinger was a child prodigy, and Albert Einstein distinctly not; Schwinger had something like 73 graduate students, and Einstein very few. But both thought gravity was important. They were not, of course, the first, nor is the disagreement on how one should think about gravity that is being highlighted here the first such dispute. The talk will explore, first, several of the earlier dichotomies: was gravity capable of action at a distance (Newton), or was a transmitting ether required (many others). Did it act on everything or only on solids (an odd idea of the Herschels that fed into their ideas of solar structure and sunspots)? Did gravitational information require time for its transmission? Is the exponent of r precisely 2, or 2 plus a smidgeon (a suggestion by Simon Newcomb among others)? And so forth. Second, I will try to say something about Scwinger's lesser known early work and how it might have prefigured his "source theory," beginning with "On the Interaction of Several Electrons (the unpublished, 1934 "zeroth paper," whose title somewhat reminds one of "On the Dynamics of an Asteroid," through his days at Berkeley with Oppenheimer, Gerjuoy, and others, to his application of ideas from nuclear physics to radar and of radar engineering techniques to problems in nuclear physics. And folks who think good jobs are difficult to come by now might want to contemplate the couple of years Schwinger spent teaching elementary physics at Purdue before moving on to the MIT Rad Lab for war work.
International Nuclear Information System (INIS)
Capozziello, Salvatore; De Laurentis, Mariafelicia
2011-01-01
Extended Theories of Gravity can be considered as a new paradigm to cure shortcomings of General Relativity at infrared and ultraviolet scales. They are an approach that, by preserving the undoubtedly positive results of Einstein’s theory, is aimed to address conceptual and experimental problems recently emerged in astrophysics, cosmology and High Energy Physics. In particular, the goal is to encompass, in a self-consistent scheme, problems like inflation, dark energy, dark matter, large scale structure and, first of all, to give at least an effective description of Quantum Gravity. We review the basic principles that any gravitational theory has to follow. The geometrical interpretation is discussed in a broad perspective in order to highlight the basic assumptions of General Relativity and its possible extensions in the general framework of gauge theories. Principles of such modifications are presented, focusing on specific classes of theories like f(R)-gravity and scalar–tensor gravity in the metric and Palatini approaches. The special role of torsion is also discussed. The conceptual features of these theories are fully explored and attention is paid to the issues of dynamical and conformal equivalence between them considering also the initial value problem. A number of viability criteria are presented considering the post-Newtonian and the post-Minkowskian limits. In particular, we discuss the problems of neutrino oscillations and gravitational waves in extended gravity. Finally, future perspectives of extended gravity are considered with possibility to go beyond a trial and error approach.
van Velzen, F.J.J.; Ofec, R.; Schulten, E.A.J.M.; ten Bruggenkate, C.M.
2015-01-01
Purpose This prospective cohort study evaluates the 10-year survival and incidence of peri-implant disease at implant and patient level of sandblasted, large grid, and acid-etched titanium dental implants (Straumann, soft tissue level, SLA surface) in fully and partially edentulous patients.
Mars geodesy, rotation and gravity
International Nuclear Information System (INIS)
Rosenblatt, Pascal; Dehant, Veronique
2010-01-01
This review provides explanations of how geodesy, rotation and gravity can be addressed using radioscience data of an orbiter around a planet or of the lander on its surface. The planet Mars is the center of the discussion. The information one can get from orbitography and radioscience in general concerns the global static gravitational field, the time variation of the gravitational field induced by mass exchange between the atmosphere and the ice caps, the time variation of the gravitational field induced by the tides, the secular changes in the spacecraft's orbit induced by the little moons of Mars named Phobos and Deimos, the gravity induced by particular targets, the Martian ephemerides, and Mars' rotation and orientation. The paper addresses as well the determination of the geophysical parameters of Mars and, in particular, the state of Mars' core and its size, which is important for understanding the planet's evolution. Indeed, the state and dimension of the core determined from the moment of inertia and nutation depend in turn on the percentage of light elements in the core as well as on the core temperature, which is related to heat transport in the mantle. For example, the radius of the core has implications for possible mantle convection scenarios and, in particular, for the presence of a perovskite phase transition at the bottom of the mantle. This is also important for our understanding of the large volcanic province Tharsis on the surface of Mars. (invited reviews)
Gravity model improvement using GEOS-3 (GEM 9 and 10)
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.
Martin-Espanol, Alba; Zammit-Mangion, Andrew; Clarke, Peter J.; Flament, Thomas; Helm, Veit; King, Matt A.; Luthcke, Scott B.; Petrie, Elizabeth; Remy, Frederique; Schon, Nana;
2016-01-01
We present spatiotemporal mass balance trends for the Antarctic Ice Sheet from a statistical inversion of satellite altimetry, gravimetry, and elastic-corrected GPS data for the period 2003-2013. Our method simultaneously determines annual trends in ice dynamics, surface mass balance anomalies, and a time-invariant solution for glacio-isostatic adjustment while remaining largely independent of forward models. We establish that over the period 2003-2013, Antarctica has been losing mass at a rateof -84 +/- 22 Gt per yr, with a sustained negative mean trend of dynamic imbalance of -111 +/- 13 Gt per yr. West Antarctica is the largest contributor with -112 +/- 10 Gt per yr, mainly triggered by high thinning rates of glaciers draining into the Amundsen Sea Embayment. The Antarctic Peninsula has experienced a dramatic increase in mass loss in the last decade, with a mean rate of -28 +/- 7 Gt per yr and significantly higher values for the most recent years following the destabilization of the Southern Antarctic Peninsula around 2010. The total mass loss is partly compensated by a significant mass gain of 56 +/- 18 Gt per yr in East Antarctica due to a positive trend of surface mass balance anomalies.
Arctic Ocean gravity, geoid and sea-ice freeboard heights from ICESat and GRACE
DEFF Research Database (Denmark)
Forsberg, René; Skourup, Henriette
2005-01-01
Gravity Project in combination with GRACE gravity field models to derive an improved Arctic geoid model. This model is then used to convert ICESat measurements to sea-ice freeboard heights with a coarse lowest-level surface method. The derived freeboard heights show a good qualitative agreement...... all major tectonic features of the Arctic Ocean, and has an accuracy of 6 mGal compared to recent airborne gravity data, illustrating the usefulness of ICESat data for gravity field determination....
International Nuclear Information System (INIS)
Francois, P.
1996-01-01
We undertook a study programme at the end of 1991. To start with, we performed some exploratory studies aimed at learning some preliminary lessons on this type of analysis: Assessment of the interest of probabilistic incident analysis; possibility of using PSA scenarios; skills and resources required. At the same time, EPN created a working group whose assignment was to define a new approach for analysis of incidents on NPPs. This working group gave thought to both aspects of Operating Feedback that EPN wished to improve: Analysis of significant incidents; analysis of potential consequences. We took part in the work of this group, and for the second aspects, we proposed a method based on an adaptation of the event-tree method in order to establish a link between existing PSA models and actual incidents. Since PSA provides an exhaustive database of accident scenarios applicable to the two most common types of units in France, they are obviously of interest for this sort of analysis. With this method we performed some incident analyses, and at the same time explores some methods employed abroad, particularly ASP (Accident Sequence Precursor, a method used by the NRC). Early in 1994 EDF began a systematic analysis programme. The first, transient phase will set up methods and an organizational structure. 7 figs
Energy Technology Data Exchange (ETDEWEB)
Francois, P
1997-12-31
We undertook a study programme at the end of 1991. To start with, we performed some exploratory studies aimed at learning some preliminary lessons on this type of analysis: Assessment of the interest of probabilistic incident analysis; possibility of using PSA scenarios; skills and resources required. At the same time, EPN created a working group whose assignment was to define a new approach for analysis of incidents on NPPs. This working group gave thought to both aspects of Operating Feedback that EPN wished to improve: Analysis of significant incidents; analysis of potential consequences. We took part in the work of this group, and for the second aspects, we proposed a method based on an adaptation of the event-tree method in order to establish a link between existing PSA models and actual incidents. Since PSA provides an exhaustive database of accident scenarios applicable to the two most common types of units in France, they are obviously of interest for this sort of analysis. With this method we performed some incident analyses, and at the same time explores some methods employed abroad, particularly ASP (Accident Sequence Precursor, a method used by the NRC). Early in 1994 EDF began a systematic analysis programme. The first, transient phase will set up methods and an organizational structure. 7 figs.
Thermosyphon Flooding Limits in Reduced Gravity Environments
Gibson, Marc A.; Jaworske, Donald A.; Sanzi, James L.; Ljubanovic, Damir
2012-01-01
Fission Power Systems have long been recognized as potential multi-kilowatt power solutions for lunar, Martian, and extended planetary surface missions. Current heat rejection technology associated with fission surface power systems has focused on titanium water thermosyphons embedded in carbon composite radiator panels. The thermosyphons, or wickless heat pipes, are used as a redundant and efficient way to spread the waste heat from the power conversion unit(s) over the radiator surface area where it can be rejected to space. It is well known that thermosyphon performance is reliant on gravitational forces to keep the evaporator wetted with the working fluid. One of the performance limits that can be encountered, if not understood, is the phenomenon of condenser flooding, otherwise known as evaporator dry out. This occurs when the gravity forces acting on the condensed fluid cannot overcome the shear forces created by the vapor escaping the evaporator throat. When this occurs, the heat transfer process is stalled and may not re-stabilize to effective levels without corrective control actions. The flooding limit in earth's gravity environment is well understood as experimentation is readily accessible, but when the environment and gravity change relative to other planetary bodies, experimentation becomes difficult. An innovative experiment was designed and flown on a parabolic flight campaign to achieve the Reduced Gravity Environments (RGE) needed to obtain empirical data for analysis. The test data is compared to current correlation models for validation and accuracy.
Gravity and Heater Size Effects on Pool Boiling Heat Transfer
Kim, Jungho; Raj, Rishi
2014-01-01
The current work is based on observations of boiling heat transfer over a continuous range of gravity levels between 0g to 1.8g and varying heater sizes with a fluorinert as the test liquid (FC-72/n-perfluorohexane). Variable gravity pool boiling heat transfer measurements over a wide range of gravity levels were made during parabolic flight campaigns as well as onboard the International Space Station. For large heaters and-or higher gravity conditions, buoyancy dominated boiling and heat transfer results were heater size independent. The power law coefficient for gravity in the heat transfer equation was found to be a function of wall temperature under these conditions. Under low gravity conditions and-or for smaller heaters, surface tension forces dominated and heat transfer results were heater size dependent. A pool boiling regime map differentiating buoyancy and surface tension dominated regimes was developed along with a unified framework that allowed for scaling of pool boiling over a wide range of gravity levels and heater sizes. The scaling laws developed in this study are expected to allow performance quantification of phase change based technologies under variable gravity environments eventually leading to their implementation in space based applications.
Roecker, S.; Ebinger, C.; Tiberi, C.; Mulibo, G.; Ferdinand-Wambura, R.; Mtelela, K.; Kianji, G.; Muzuka, A.; Gautier, S.; Albaric, J.; Peyrat, S.
2017-08-01
The Eastern Rift System (ERS) of northern Tanzania and southern Kenya, where a cratonic lithosphere is in the early stages of rifting, offers an ideal venue for investigating the roles of magma and other fluids in such an environment. To illuminate these roles, we jointly invert arrival times of locally recorded P and S body waves, phase delays of ambient noise generated Rayleigh waves and Bouguer anomalies from gravity observations to generate a 3-D image of P and S wave speeds in the upper 25 km of the crust. While joint inversion of gravity and arrival times requires a relationship between density and wave speeds, the improvement in resolution obtained by the combination of these disparate data sets serves to further constrain models, and reduce uncertainties. The most significant features in the 3-D model are (1) P and S wave speeds that are 10-15 per cent lower beneath the rift zone than in the surrounding regions, (2) a relatively high wave speed tabular feature located along the western edge of the Natron and Manyara rifts, and (3) low (∼1.71) values of Vp/Vs throughout the upper crust, with the lowest ratios along the boundaries of the rift zones. The low P and S wave speeds at mid-crustal levels beneath the rift valley are an expected consequence of active volcanism, and the tabular, high-wave speed feature is interpreted to be an uplifted footwall at the western edge of the rift. Given the high levels of CO2 outgassing observed at the surface along border fault zones, and the sensitivity of Vp/Vs to pore-fluid compressibility, we infer that the low Vp/Vs values in and around the rift zone are caused by the volcanic plumbing in the upper crust being suffused by a gaseous CO2 froth on top of a deeper, crystalline mush. The repository for molten rock is likely located in the lower crust and upper mantle, where the Vp/Vs ratios are significantly higher.
Directory of Open Access Journals (Sweden)
Cahill R. T.
2015-10-01
Full Text Available A new quantum gravity experiment is reported with the data confirming the generali- sation of the Schrödinger equation to include the interaction of the wave function with dynamical space. Dynamical space turbulence, via this interaction process, raises and lowers the energy of the electron wave function, which is detected by observing conse- quent variations in the electron quantum barrier tunnelling rate in reverse-biased Zener diodes. This process has previously been reported and enabled the measurement of the speed of the dynamical space flow, which is consistent with numerous other detection experiments. The interaction process is dependent on the angle between the dynamical space flow velocity and the direction of the electron flow in the diode, and this depen- dence is experimentally demonstrated. This interaction process explains gravity as an emergent quantum process, so unifying quantum phenomena and gravity. Gravitational waves are easily detected.
Ortín, Tomás
2015-01-01
Self-contained and comprehensive, this definitive new edition of Gravity and Strings is a unique resource for graduate students and researchers in theoretical physics. From basic differential geometry through to the construction and study of black-hole and black-brane solutions in quantum gravity - via all the intermediate stages - this book provides a complete overview of the intersection of gravity, supergravity, and superstrings. Now fully revised, this second edition covers an extensive array of topics, including new material on non-linear electric-magnetic duality, the electric-tensor formalism, matter-coupled supergravity, supersymmetric solutions, the geometries of scalar manifolds appearing in 4- and 5-dimensional supergravities, and much more. Covering reviews of important solutions and numerous solution-generating techniques, and accompanied by an exhaustive index and bibliography, this is an exceptional reference work.
International Nuclear Information System (INIS)
Goetz, G.
1988-01-01
It is shown that the plane-wave solutions for the equations governing the motion of a self-gravitating isothermal fluid in Newtonian hydrodynamics are generated by a sine-Gordon equation which is solvable by an 'inverse scattering' transformation. A transformation procedure is outlined by means of which one can construct solutions of the gravity system out of a pair of solutions of the sine-Gordon equation, which are interrelated via an auto-Baecklund transformation. In general the solutions to the gravity system are obtained in a parametric representation in terms of characteristic coordinates. All solutions of the gravity system generated by the one-and two-soliton solutions of the sine-Gordon equation can be constructed explicitly. These might provide models for the evolution of flat structures as they are predicted to arise in the process of galaxy formation. (author)
International Nuclear Information System (INIS)
Rumpf, H.
1987-01-01
We begin with a naive application of the Parisi-Wu scheme to linearized gravity. This will lead into trouble as one peculiarity of the full theory, the indefiniteness of the Euclidean action, shows up already at this level. After discussing some proposals to overcome this problem, Minkowski space stochastic quantization will be introduced. This will still not result in an acceptable quantum theory of linearized gravity, as the Feynman propagator turns out to be non-causal. This defect will be remedied only after a careful analysis of general covariance in stochastic quantization has been performed. The analysis requires the notion of a metric on the manifold of metrics, and a natural candidate for this is singled out. With this a consistent stochastic quantization of Einstein gravity becomes possible. It is even possible, at least perturbatively, to return to the Euclidean regime. 25 refs. (Author)
Linder, Eric V.
2018-03-01
A subclass of the Horndeski modified gravity theory we call No Slip Gravity has particularly interesting properties: 1) a speed of gravitational wave propagation equal to the speed of light, 2) equality between the effective gravitational coupling strengths to matter and light, Gmatter and Glight, hence no slip between the metric potentials, yet difference from Newton's constant, and 3) suppressed growth to give better agreement with galaxy clustering observations. We explore the characteristics and implications of this theory, and project observational constraints. We also give a simple expression for the ratio of the gravitational wave standard siren distance to the photon standard candle distance, in this theory and others, and enable a direct comparison of modified gravity in structure growth and in gravitational waves, an important crosscheck.
Gerhardt, Claus
2018-01-01
A unified quantum theory incorporating the four fundamental forces of nature is one of the major open problems in physics. The Standard Model combines electro-magnetism, the strong force and the weak force, but ignores gravity. The quantization of gravity is therefore a necessary first step to achieve a unified quantum theory. In this monograph a canonical quantization of gravity has been achieved by quantizing a geometric evolution equation resulting in a gravitational wave equation in a globally hyperbolic spacetime. Applying the technique of separation of variables we obtain eigenvalue problems for temporal and spatial self-adjoint operators where the temporal operator has a pure point spectrum with eigenvalues $\\lambda_i$ and related eigenfunctions, while, for the spatial operator, it is possible to find corresponding eigendistributions for each of the eigenvalues $\\lambda_i$, if the Cauchy hypersurface is asymptotically Euclidean or if the quantized spacetime is a black hole with a negative cosmological ...
Airborne Gravity: NGS' Gravity Data for EN08 (2013)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for New York, Vermont, New Hampshire, Massachusettes, Maine, and Canada collected in 2013 over 1 survey. This data set is part of the Gravity...
Airborne Gravity: NGS' Gravity Data for TS01 (2014)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Puerto Rico and the Virgin Islands collected in 2009 over 1 survey. This data set is part of the Gravity for the Re-definition of the...
Airborne Gravity: NGS' Gravity Data for AN08 (2016)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2016 over one survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum...
Airborne Gravity: NGS' Gravity Data for CN02 (2013 & 2014)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Nebraska collected in 2013 & 2014 over 3 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical...
Airborne Gravity: NGS' Gravity Data for EN01 (2011)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for New York, Canada, and Lake Ontario collected in 2011 over 1 survey. This data set is part of the Gravity for the Re-definition of the...
Airborne Gravity: NGS' Gravity Data for AN03 (2010)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 and 2012 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical Datum...
Airborne Gravity: NGS' Gravity Data for EN06 (2016)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Maine, Canada, and the Atlantic Ocean collected in 2012 over 2 surveys. This data set is part of the Gravity for the Re-definition of the...
Airborne Gravity: NGS' Gravity Data for ES01 (2013)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Florida, the Bahamas, and the Atlantic Ocean collected in 2013 over 1 survey. This data set is part of the Gravity for the Re-definition of...
Zhou, Xiao; Yang, Gongliu; Wang, Jing; Wen, Zeyang
2018-05-14
In recent decades, gravity compensation has become an important way to reduce the position error of an inertial navigation system (INS), especially for a high-precision INS, because of the extensive application of high precision inertial sensors (accelerometers and gyros). This paper first deducts the INS's solution error considering gravity disturbance and simulates the results. Meanwhile, this paper proposes a combined gravity compensation method using a simplified gravity model and gravity database. This new combined method consists of two steps all together. Step 1 subtracts the normal gravity using a simplified gravity model. Step 2 first obtains the gravity disturbance on the trajectory of the carrier with the help of ELM training based on the measured gravity data (provided by Institute of Geodesy and Geophysics; Chinese Academy of sciences), and then compensates it into the error equations of the INS, considering the gravity disturbance, to further improve the navigation accuracy. The effectiveness and feasibility of this new gravity compensation method for the INS are verified through vehicle tests in two different regions; one is in flat terrain with mild gravity variation and the other is in complex terrain with fierce gravity variation. During 2 h vehicle tests, the positioning accuracy of two tests can improve by 20% and 38% respectively, after the gravity is compensated by the proposed method.
Miniaturised Gravity Sensors for Remote Gravity Surveys.
Middlemiss, R. P.; Bramsiepe, S. G.; Hough, J.; Paul, D. J.; Rowan, S.; Samarelli, A.; Hammond, G.
2016-12-01
Gravimetry lets us see the world from a completely different perspective. The ability to measure tiny variations in gravitational acceleration (g), allows one to see not just the Earth's gravitational pull, but the influence of smaller objects. The more accurate the gravimeter, the smaller the objects one can see. Gravimetry has applications in many different fields: from tracking magma moving under volcanoes before eruptions; to locating hidden tunnels. The top commercial gravimeters weigh tens of kg and cost at least $100,000, limiting the situations in which they can be used. By contrast, smart phones use a MEMS (microelectromechanical system) accelerometer that can measure the orientation of the device. These are not nearly sensitive or stable enough to be used for the gravimetry but they are cheap, light-weight and mass-producible. At Glasgow University we have developed a MEMS device with both the stability and sensitivity for useful gravimetric measurements. This was demonstrated by a measurement of the Earth tides - the first time this has been achieved with a MEMS sensor. A gravimeter of this size opens up the possiblility for new gravity imaging modalities. Thousands of gravimeters could be networked over a survey site, storing data on an SD card or communicating wirelessly to a remote location. These devices could also be small enough to be carried by a UAVs: airborne gravity surveys could be carried out at low altitude by mulitple UAVs, or UAVs could be used to deliver ground based gravimeters to remote or inaccessible locations.
International Nuclear Information System (INIS)
Romney, B.; Barrau, A.; Vidotto, F.; Le Meur, H.; Noui, K.
2011-01-01
The loop quantum gravity is the only theory that proposes a quantum description of space-time and therefore of gravitation. This theory predicts that space is not infinitely divisible but that is has a granular structure at the Planck scale (10 -35 m). Another feature of loop quantum gravity is that it gets rid of the Big-Bang singularity: our expanding universe may come from the bouncing of a previous contracting universe, in this theory the Big-Bang is replaced with a big bounce. The loop quantum theory predicts also the huge number of quantum states that accounts for the entropy of large black holes. (A.C.)
Terrestrial gravity data analysis for interim gravity model improvement
1987-01-01
This is the first status report for the Interim Gravity Model research effort that was started on June 30, 1986. The basic theme of this study is to develop appropriate models and adjustment procedures for estimating potential coefficients from terrestrial gravity data. The plan is to use the latest gravity data sets to produce coefficient estimates as well as to provide normal equations to NASA for use in the TOPEX/POSEIDON gravity field modeling program.
Three-dimensional gravity investigation of the Hanford reservation
International Nuclear Information System (INIS)
Richard, B.H.; Deju, R.A.
1977-07-01
Models of the basalt surface buried under the Hanford reservation are constructed from gravity data. The method uses a modified third order polynomial surface to remove the regional effects and a gravity-geologic method to remove the water table effects. When these influences are subtracted from previous data, the anomaly remaining directly reflects the irregularity of the underlying basalt surface. The Umtanum Anticline and the Cold Creek Syncline are delineated beneath the overlying surficial deposits. Along the crest of the Umtanum Anticline, a number of gravity lows are evident. These may identify locations of breaching by an ancestral river. In addition, the data are examined to determine optimum gravity data spacing for modeling. Optimum results were obtained using a station separation of one per four square miles. Less will delineate only the major underlying structures. It is also very important to have all data points distributed in a regularly spaced grid
Gravity Data for South America
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (152,624 records) were compiled by the University of Texas at Dallas. This data base was received in June 1992. Principal gravity parameters...
Interior Alaska Gravity Station Data
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data total 9416 records. This data base was received in March 1997. Principal gravity parameters include Free-air Anomalies which have been...
Gravity Station Data for Spain
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data total 28493 records. This data base was received in April 1997. Principal gravity parameters include Free-air Anomalies which have been...
Gravity Station Data for Portugal
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data total 3064 records. This data base was received in April 1997. Principal gravity parameters include Free-air Anomalies which have been...
Ultrasonic hydrometer. [Specific gravity of electrolyte
Swoboda, C.A.
1982-03-09
The disclosed ultrasonic hydrometer determines the specific gravity (density) of the electrolyte of a wet battery, such as a lead-acid battery. The hydrometer utilizes a transducer that when excited emits an ultrasonic impulse that traverses through the electrolyte back and forth between spaced sonic surfaces. The transducer detects the returning impulse, and means measures the time t between the initial and returning impulses. Considering the distance d between the spaced sonic surfaces and the measured time t, the sonic velocity V is calculated with the equation V = 2d/t. The hydrometer also utilizes a thermocouple to measure the electrolyte temperature. A hydrometer database correlates three variable parameters including sonic velocity in and temperature and specific gravity of the electrolyte, for temperature values between 0 and 40/sup 0/C and for specific gravity values between 1.05 and 1.30. Upon knowing two parameters (the calculated sonic velocity and the measured temperature), the third parameter (specific gravity) can be uniquely found in the database. The hydrometer utilizes a microprocessor for data storage and manipulation.
International Nuclear Information System (INIS)
Faria, F. F.
2014-01-01
We construct a massive theory of gravity that is invariant under conformal transformations. The massive action of the theory depends on the metric tensor and a scalar field, which are considered the only field variables. We find the vacuum field equations of the theory and analyze its weak-field approximation and Newtonian limit.
DEFF Research Database (Denmark)
Skielboe, Andreas
Gravity governs the evolution of the universe on the largest scales, and powers some of the most extreme objects at the centers of galaxies. Determining the masses and kinematics of galaxy clusters provides essential constraints on the large-scale structure of the universe, and act as direct probes...
Newburgh, Ronald
2010-01-01
It's both surprising and rewarding when an old, standard problem reveals a subtlety that expands its pedagogic value. I realized recently that the role of gravity in the range equation for a projectile is not so simple as first appears. This realization may be completely obvious to others but was quite new to me.
Discrete Lorentzian quantum gravity
Loll, R.
2000-01-01
Just as for non-abelian gauge theories at strong coupling, discrete lattice methods are a natural tool in the study of non-perturbative quantum gravity. They have to reflect the fact that the geometric degrees of freedom are dynamical, and that therefore also the lattice theory must be formulated
International Nuclear Information System (INIS)
Pullin, J.
2015-01-01
Loop quantum gravity is one of the approaches that are being studied to apply the rules of quantum mechanics to the gravitational field described by the theory of General Relativity . We present an introductory summary of the main ideas and recent results. (Author)
International Nuclear Information System (INIS)
Meszaros, A.
1984-05-01
In case the graviton has a very small non-zero mass, the existence of six additional massive gravitons with very big masses leads to a finite quantum gravity. There is an acausal behaviour on the scales that is determined by the masses of additional gravitons. (author)
Venus - Ishtar gravity anomaly
Sjogren, W. L.; Bills, B. G.; Mottinger, N. A.
1984-01-01
The gravity anomaly associated with Ishtar Terra on Venus is characterized, comparing line-of-sight acceleration profiles derived by differentiating Pioneer Venus Orbiter Doppler residual profiles with an Airy-compensated topographic model. The results are presented in graphs and maps, confirming the preliminary findings of Phillips et al. (1979). The isostatic compensation depth is found to be 150 + or - 30 km.
International Nuclear Information System (INIS)
Aros, Rodrigo; Contreras, Mauricio
2006-01-01
In this work the Poincare-Chern-Simons and anti-de Sitter-Chern-Simons gravities are studied. For both, a solution that can be cast as a black hole with manifest torsion is found. Those solutions resemble Schwarzschild and Schwarzschild-AdS solutions, respectively
International Nuclear Information System (INIS)
Williams, J.W.
1992-01-01
After a brief introduction to Regge calculus, some examples of its application is quantum gravity are described in this paper. In particular, the earliest such application, by Ponzano and Regge, is discussed in some detail and it is shown how this leads naturally to current work on invariants of three-manifolds
Directory of Open Access Journals (Sweden)
Rovelli Carlo
1998-01-01
Full Text Available The problem of finding the quantum theory of the gravitational field, and thus understanding what is quantum spacetime, is still open. One of the most active of the current approaches is loop quantum gravity. Loop quantum gravity is a mathematically well-defined, non-perturbative and background independent quantization of general relativity, with its conventional matter couplings. Research in loop quantum gravity today forms a vast area, ranging from mathematical foundations to physical applications. Among the most significant results obtained are: (i The computation of the physical spectra of geometrical quantities such as area and volume, which yields quantitative predictions on Planck-scale physics. (ii A derivation of the Bekenstein-Hawking black hole entropy formula. (iii An intriguing physical picture of the microstructure of quantum physical space, characterized by a polymer-like Planck scale discreteness. This discreteness emerges naturally from the quantum theory and provides a mathematically well-defined realization of Wheeler's intuition of a spacetime ``foam''. Long standing open problems within the approach (lack of a scalar product, over-completeness of the loop basis, implementation of reality conditions have been fully solved. The weak part of the approach is the treatment of the dynamics: at present there exist several proposals, which are intensely debated. Here, I provide a general overview of ideas, techniques, results and open problems of this candidate theory of quantum gravity, and a guide to the relevant literature.
Quantum Gravity Effects in Cosmology
Directory of Open Access Journals (Sweden)
Gu Je-An
2018-01-01
Full Text Available Within the geometrodynamic approach to quantum cosmology, we studied the quantum gravity effects in cosmology. The Gibbons-Hawking temperature is corrected by quantum gravity due to spacetime fluctuations and the power spectrum as well as any probe field will experience the effective temperature, a quantum gravity effect.
Even-dimensional topological gravity from Chern-Simons gravity
International Nuclear Information System (INIS)
Merino, N.; Perez, A.; Salgado, P.
2009-01-01
It is shown that the topological action for gravity in 2n-dimensions can be obtained from the (2n+1)-dimensional Chern-Simons gravity genuinely invariant under the Poincare group. The 2n-dimensional topological gravity is described by the dynamics of the boundary of a (2n+1)-dimensional Chern-Simons gravity theory with suitable boundary conditions. The field φ a , which is necessary to construct this type of topological gravity in even dimensions, is identified with the coset field associated with the non-linear realizations of the Poincare group ISO(d-1,1).
Directory of Open Access Journals (Sweden)
A. V. Vikulin
2014-01-01
Full Text Available Gravity phenomena related to the Earth movements in the Solar System and through the Galaxy are reviewed. Such movements are manifested by geological processes on the Earth and correlate with geophysical fields of the Earth. It is concluded that geodynamic processes and the gravity phenomena (including those of cosmic nature are related. The state of the geomedium composed of blocks is determined by stresses with force moment and by slow rotational waves that are considered as a new type of movements [Vikulin, 2008, 2010]. It is shown that the geomedium has typical rheid properties [Carey, 1954], specifically an ability to flow while being in the solid state [Leonov, 2008]. Within the framework of the rotational model with a symmetric stress tensor, which is developed by the authors [Vikulin, Ivanchin, 1998; Vikulin et al., 2012a, 2013], such movement of the geomedium may explain the energy-saturated state of the geomedium and a possibility of its movements in the form of vortex geological structures [Lee, 1928]. The article discusses the gravity wave detection method based on the concept of interactions between gravity waves and crustal blocks [Braginsky et al., 1985]. It is concluded that gravity waves can be recorded by the proposed technique that detects slow rotational waves. It is shown that geo-gravitational movements can be described by both the concept of potential with account of gravitational energy of bodies [Kondratyev, 2003] and the nonlinear physical acoustics [Gurbatov et al., 2008]. Based on the combined description of geophysical and gravitational wave movements, the authors suggest a hypothesis about the nature of spin, i.e. own moment as a demonstration of the space-time ‘vortex’ properties.
Power laws for gravity and topography of Solar System bodies
Ermakov, A.; Park, R. S.; Bills, B. G.
2017-12-01
When a spacecraft visits a planetary body, it is useful to be able to predict its gravitational and topographic properties. This knowledge is important for determining the level of perturbations in spacecraft's motion as well as for planning the observation campaign. It has been known for the Earth that the power spectrum of gravity follows a power law, also known as the Kaula rule (Kaula, 1963; Rapp, 1989). A similar rule was derived for topography (Vening-Meinesz, 1951). The goal of this paper is to generalize the power law that can characterize the gravity and topography power spectra for bodies across a wide range of size. We have analyzed shape power spectra of the bodies that have either global shape and gravity field measured. These bodies span across five orders of magnitude in their radii and surface gravities and include terrestrial planets, icy moons and minor bodies. We have found that despite having different internal structure, composition and mechanical properties, the topography power spectrum of these bodies' shapes can be modeled with a similar power law rescaled by the surface gravity. Having empirically found a power law for topography, we can map it to a gravity power law. Special care should be taken for low-degree harmonic coefficients due to potential isostatic compensation. For minor bodies, uniform density can be assumed. The gravity coefficients are a linear function of the shape coefficients for close-to-spherical bodoes. In this case, the power law for gravity will be steeper than the power law of topography due to the factor (2n+1) in the gravity expansion (e.g. Eq. 10 in Wieczorek & Phillips, 1998). Higher powers of topography must be retained for irregularly shaped bodies, which breaks the linearity. Therefore, we propose the following procedure to derive an a priori constraint for gravity. First, a surface gravity needs to be determined assuming typical density for the relevant class of bodies. Second, the scaling coefficient of the
Normal gravity field in relativistic geodesy
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
Metastable gravity on classical defects
International Nuclear Information System (INIS)
Ringeval, Christophe; Rombouts, Jan-Willem
2005-01-01
We discuss the realization of metastable gravity on classical defects in infinite-volume extra dimensions. In dilatonic Einstein gravity, it is found that the existence of metastable gravity on the defect core requires violation of the dominant energy condition for codimension N c =2 defects. This is illustrated with a detailed analysis of a six-dimensional hyperstring minimally coupled to dilaton gravity. We present the general conditions under which a codimension N c >2 defect admits metastable modes, and find that they differ from lower codimensional models in that, under certain conditions, they do not require violation of energy conditions to support quasilocalized gravity
Assessing GOCE Gravity Models using Altimetry and In-situ Ocean Current Observation
DEFF Research Database (Denmark)
Knudsen, Per; Andersen, Ole Baltazar; Honecker, Johanna
gravity models provided by the GOCE mission have enhanced the resolution and sharpened the boundaries of those features and the associated geostrophic surface currents reveal improvements for all of the ocean's current systems. In this study, a series of 23 newer gravity models including observations from...... as quantified quality measures associated with the 23 GOCE gravity models.......The Gravity and steady state Ocean Circulation Explorer (GOCE) satellite mission measures Earth's gravity field with an unprecedented accuracy at short spatial scales. Previous results have demonstrated a significant advance in our ability to determine the ocean's general circulation. The improved...
Quantum gravity from noncommutative spacetime
International Nuclear Information System (INIS)
Lee, Jungjai; Yang, Hyunseok
2014-01-01
We review a novel and authentic way to quantize gravity. This novel approach is based on the fact that Einstein gravity can be formulated in terms of a symplectic geometry rather than a Riemannian geometry in the context of emergent gravity. An essential step for emergent gravity is to realize the equivalence principle, the most important property in the theory of gravity (general relativity), from U(1) gauge theory on a symplectic or Poisson manifold. Through the realization of the equivalence principle, which is an intrinsic property in symplectic geometry known as the Darboux theorem or the Moser lemma, one can understand how diffeomorphism symmetry arises from noncommutative U(1) gauge theory; thus, gravity can emerge from the noncommutative electromagnetism, which is also an interacting theory. As a consequence, a background-independent quantum gravity in which the prior existence of any spacetime structure is not a priori assumed but is defined by using the fundamental ingredients in quantum gravity theory can be formulated. This scheme for quantum gravity can be used to resolve many notorious problems in theoretical physics, such as the cosmological constant problem, to understand the nature of dark energy, and to explain why gravity is so weak compared to other forces. In particular, it leads to a remarkable picture of what matter is. A matter field, such as leptons and quarks, simply arises as a stable localized geometry, which is a topological object in the defining algebra (noncommutative *-algebra) of quantum gravity.
Quantum gravity from noncommutative spacetime
Energy Technology Data Exchange (ETDEWEB)
Lee, Jungjai [Daejin University, Pocheon (Korea, Republic of); Yang, Hyunseok [Korea Institute for Advanced Study, Seoul (Korea, Republic of)
2014-12-15
We review a novel and authentic way to quantize gravity. This novel approach is based on the fact that Einstein gravity can be formulated in terms of a symplectic geometry rather than a Riemannian geometry in the context of emergent gravity. An essential step for emergent gravity is to realize the equivalence principle, the most important property in the theory of gravity (general relativity), from U(1) gauge theory on a symplectic or Poisson manifold. Through the realization of the equivalence principle, which is an intrinsic property in symplectic geometry known as the Darboux theorem or the Moser lemma, one can understand how diffeomorphism symmetry arises from noncommutative U(1) gauge theory; thus, gravity can emerge from the noncommutative electromagnetism, which is also an interacting theory. As a consequence, a background-independent quantum gravity in which the prior existence of any spacetime structure is not a priori assumed but is defined by using the fundamental ingredients in quantum gravity theory can be formulated. This scheme for quantum gravity can be used to resolve many notorious problems in theoretical physics, such as the cosmological constant problem, to understand the nature of dark energy, and to explain why gravity is so weak compared to other forces. In particular, it leads to a remarkable picture of what matter is. A matter field, such as leptons and quarks, simply arises as a stable localized geometry, which is a topological object in the defining algebra (noncommutative *-algebra) of quantum gravity.
DEFF Research Database (Denmark)
Forsberg, René; Sideris, M.G.; Shum, C.K.
2005-01-01
The gravity field of the earth is a natural element of the Global Geodetic Observing System (GGOS). Gravity field quantities are like spatial geodetic observations of potential very high accuracy, with measurements, currently at part-per-billion (ppb) accuracy, but gravity field quantities are also...... unique as they can be globally represented by harmonic functions (long-wavelength geopotential model primarily from satellite gravity field missions), or based on point sampling (airborne and in situ absolute and superconducting gravimetry). From a GGOS global perspective, one of the main challenges...... is to ensure the consistency of the global and regional geopotential and geoid models, and the temporal changes of the gravity field at large spatial scales. The International Gravity Field Service, an umbrella "level-2" IAG service (incorporating the International Gravity Bureau, International Geoid Service...
Getting the Swing of Surface Gravity
Thomas, Brian C.; Quick, Matthew
2012-01-01
Sports are a popular and effective way to illustrate physics principles. Baseball in particular presents a number of opportunities to motivate student interest and teach concepts. Several articles have appeared in this journal on this topic, illustrating a wide variety of areas of physics. In addition, several websites and an entire book are…
International Nuclear Information System (INIS)
Nelson, J.E.; Regge, T.
1991-01-01
We analysed the algebra of observables for the simple case of a genus 1 initial data surface Σ 2 for 2+1 De Sitter gravity. Here we extend the analysis to higher genus. We construct for genus 2 the group of automorphisms H of the homotopy group π 1 induced by the mapping class group. The group H induces a group D of canonical transformations on the algebra of observables which is related to the braid group for 6 threads. (orig.)
New variables for classical and quantum gravity
Ashtekar, Abhay
1986-01-01
A Hamiltonian formulation of general relativity based on certain spinorial variables is introduced. These variables simplify the constraints of general relativity considerably and enable one to imbed the constraint surface in the phase space of Einstein's theory into that of Yang-Mills theory. The imbedding suggests new ways of attacking a number of problems in both classical and quantum gravity. Some illustrative applications are discussed.
Directory of Open Access Journals (Sweden)
HUANG Motao
2016-11-01
Full Text Available Centred on the support requirement of flying track control for a long range spacecraft, a detail research is made on the computation of external disturbing gravity field, the survey accuracy of gravity anomaly on the earth' surface and the program of surveying line layout for marine gravity survey. Firstly, the solution expression of navigation error for a long range spacecraft is analyzed and modified, and the influence of the earth's gravity field on flying track of spacecraft is evaluated. Then with a given limited quota of biased error of spacecraft drop point, the accuracy requirement for calculating the external disturbing gravity field is discussed and researched. Secondly, the data truncation error and the propagated data error are studied and estimated, and the quotas of survey resolution and computation accuracy for gravity anomaly on the earth' surface are determined. Finally, based on the above quotas, a corresponding program of surveying line layout for marine gravity survey is proposed. A numerical test has been made to prove the reasonableness and validity of the suggested program.
CERN. Geneva
2017-01-01
Extensions of Einstein’s theory of General Relativity are under investigation as a potential explanation of the accelerating expansion rate of the universe. I’ll present a cosmologist’s overview of attempts to test these ideas in an efficient and unbiased manner. I’ll start by introducing the bestiary of alternative gravity theories that have been put forwards. This proliferation of models motivates us to develop model-independent, agnostic tools for comparing the theory space to cosmological data. I’ll introduce the effective field theory for cosmological perturbations, a framework designed to unify modified gravity theories in terms of a manageable set of parameters. Having outlined the formalism, I’ll talk about the current constraints on this framework, and the improvements expected from the next generation of large galaxy clustering, weak lensing and intensity mapping experiments.
The relativistic gravity train
Seel, Max
2018-05-01
The gravity train that takes 42.2 min from any point A to any other point B that is connected by a straight-line tunnel through Earth has captured the imagination more than most other applications in calculus or introductory physics courses. Brachystochron and, most recently, nonlinear density solutions have been discussed. Here relativistic corrections are presented. It is discussed how the corrections affect the time to fall through Earth, the Sun, a white dwarf, a neutron star, and—the ultimate limit—the difference in time measured by a moving, a stationary and the fiducial observer at infinity if the density of the sphere approaches the density of a black hole. The relativistic gravity train can serve as a problem with approximate and exact analytic solutions and as numerical exercise in any introductory course on relativity.
Gomberoff, Andres
2006-01-01
The 2002 Pan-American Advanced Studies Institute School on Quantum Gravity was held at the Centro de Estudios Cientificos (CECS),Valdivia, Chile, January 4-14, 2002. The school featured lectures by ten speakers, and was attended by nearly 70 students from over 14 countries. A primary goal was to foster interaction and communication between participants from different cultures, both in the layman’s sense of the term and in terms of approaches to quantum gravity. We hope that the links formed by students and the school will persist throughout their professional lives, continuing to promote interaction and the essential exchange of ideas that drives research forward. This volume contains improved and updated versions of the lectures given at the School. It has been prepared both as a reminder for the participants, and so that these pedagogical introductions can be made available to others who were unable to attend. We expect them to serve students of all ages well.
Energy Technology Data Exchange (ETDEWEB)
Lamon, Raphael
2010-06-29
Quantum gravity is an attempt to unify general relativity with quantum mechanics which are the two highly successful fundamental theories of theoretical physics. The main difficulty in this unification arises from the fact that, while general relativity describes gravity as a macroscopic geometrical theory, quantum mechanics explains microscopic phenomena. As a further complication, not only do both theories describe different scales but also their philosophical ramifications and the mathematics used to describe them differ in a dramatic way. Consequently, one possible starting point of an attempt at a unification is quantum mechanics, i.e. particle physics, and try to incorporate gravitation. This pathway has been chosen by particle physicists which led to string theory. On the other hand, loop quantum gravity (LQG) chooses the other possibility, i.e. it takes the geometrical aspects of gravity seriously and quantizes geometry. The first part of this thesis deals with a generalization of loop quantum cosmology (LQC) to toroidal topologies. LQC is a quantization of homogenous solutions of Einstein's field equations using tools from LQG. First the general concepts of closed topologies is introduced with special emphasis on Thurston's theorem and its consequences. It is shown that new degrees of freedom called Teichmueller parameters come into play and their dynamics can be described by a Hamiltonian. Several numerical solutions for a toroidal universe are presented and discussed. Following the guidelines of LQG this dynamics are rewritten using the Ashtekar variables and numerical solutions are shown. However, in order to find a suitable Hilbert space a canonical transformation must be performed. On the other hand this transformation makes the quantization of geometrical quantities less tractable such that two different ways are presented. It is shown that in both cases the spectrum of such geometrical operators depends on the initial value problem
Energy Technology Data Exchange (ETDEWEB)
Chatzistavrakidis, Athanasios [Van Swinderen Institute for Particle Physics and Gravity, University of Groningen,Nijenborgh 4, 9747 AG Groningen (Netherlands); Khoo, Fech Scen [Department of Physics and Earth Sciences, Jacobs University Bremen,Campus Ring 1, 28759 Bremen (Germany); Roest, Diederik [Van Swinderen Institute for Particle Physics and Gravity, University of Groningen,Nijenborgh 4, 9747 AG Groningen (Netherlands); Schupp, Peter [Department of Physics and Earth Sciences, Jacobs University Bremen,Campus Ring 1, 28759 Bremen (Germany)
2017-03-13
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.
International Nuclear Information System (INIS)
Lamon, Raphael
2010-01-01
Quantum gravity is an attempt to unify general relativity with quantum mechanics which are the two highly successful fundamental theories of theoretical physics. The main difficulty in this unification arises from the fact that, while general relativity describes gravity as a macroscopic geometrical theory, quantum mechanics explains microscopic phenomena. As a further complication, not only do both theories describe different scales but also their philosophical ramifications and the mathematics used to describe them differ in a dramatic way. Consequently, one possible starting point of an attempt at a unification is quantum mechanics, i.e. particle physics, and try to incorporate gravitation. This pathway has been chosen by particle physicists which led to string theory. On the other hand, loop quantum gravity (LQG) chooses the other possibility, i.e. it takes the geometrical aspects of gravity seriously and quantizes geometry. The first part of this thesis deals with a generalization of loop quantum cosmology (LQC) to toroidal topologies. LQC is a quantization of homogenous solutions of Einstein's field equations using tools from LQG. First the general concepts of closed topologies is introduced with special emphasis on Thurston's theorem and its consequences. It is shown that new degrees of freedom called Teichmueller parameters come into play and their dynamics can be described by a Hamiltonian. Several numerical solutions for a toroidal universe are presented and discussed. Following the guidelines of LQG this dynamics are rewritten using the Ashtekar variables and numerical solutions are shown. However, in order to find a suitable Hilbert space a canonical transformation must be performed. On the other hand this transformation makes the quantization of geometrical quantities less tractable such that two different ways are presented. It is shown that in both cases the spectrum of such geometrical operators depends on the initial value problem. Furthermore, we
International Nuclear Information System (INIS)
Hartle, J.B.
1985-01-01
Simplicial approximation and the ideas associated with the Regge calculus provide a concrete way of implementing a sum over histories formulation of quantum gravity. A simplicial geometry is made up of flat simplices joined together in a prescribed way together with an assignment of lengths to their edges. A sum over simplicial geometries is a sum over the different ways the simplices can be joined together with an integral over their edge lengths. The construction of the simplicial Euclidean action for this approach to quantum general relativity is illustrated. The recovery of the diffeomorphism group in the continuum limit is discussed. Some possible classes of simplicial complexes with which to define a sum over topologies are described. In two dimensional quantum gravity it is argued that a reasonable class is the class of pseudomanifolds
Systems and Methods for Gravity-Independent Gripping and Drilling
Parness, Aaron (Inventor); Frost, Matthew A. (Inventor); Thatte, Nitish (Inventor); King, Jonathan P. (Inventor)
2016-01-01
Systems and methods for gravity independent gripping and drilling are described. The gripping device can also comprise a drill or sampling devices for drilling and/or sampling in microgravity environments, or on vertical or inverted surfaces in environments where gravity is present. A robotic system can be connected with the gripping and drilling devices via an ankle interface adapted to distribute the forces realized from the robotic system.
International Nuclear Information System (INIS)
Konopleva, N.P.
1996-01-01
The problems of application of nonperturbative quantization methods in the theories of the gauge fields and gravity are discussed. Unification of interactions is considered in the framework of the geometrical gauge fields theory. Vacuum conception in the unified theory of interactions and instantons role in the vacuum structure are analyzed. The role of vacuum solutions of Einstein equations in definition of the gauge field vacuum is demonstrated
Gravity, Time, and Lagrangians
Huggins, Elisha
2010-01-01
Feynman mentioned to us that he understood a topic in physics if he could explain it to a college freshman, a high school student, or a dinner guest. Here we will discuss two topics that took us a while to get to that level. One is the relationship between gravity and time. The other is the minus sign that appears in the Lagrangian. (Why would one…
Spontaneously generated gravity
International Nuclear Information System (INIS)
Zee, A.
1981-01-01
We show, following a recent suggestion of Adler, that gravity may arise as a consequence of dynamical symmetry breaking in a scale- and gauge-invariant world. Our calculation is not tied to any specific scheme of dynamical symmetry breaking. A representation for Newton's coupling constant in terms of flat-space quantities is derived. The sign of Newton's coupling constant appears to depend on infrared details of the symmetry-breaking mechanism
Rovelli, Carlo
2008-01-01
The problem of describing the quantum behavior of gravity, and thus understanding quantum spacetime , is still open. Loop quantum gravity is a well-developed approach to this problem. It is a mathematically well-defined background-independent quantization of general relativity, with its conventional matter couplings. Today research in loop quantum gravity forms a vast area, ranging from mathematical foundations to physical applications. Among the most significant results obtained so far are: (i) The computation of the spectra of geometrical quantities such as area and volume, which yield tentative quantitative predictions for Planck-scale physics. (ii) A physical picture of the microstructure of quantum spacetime, characterized by Planck-scale discreteness. Discreteness emerges as a standard quantum effect from the discrete spectra, and provides a mathematical realization of Wheeler's "spacetime foam" intuition. (iii) Control of spacetime singularities, such as those in the interior of black holes and the cosmological one. This, in particular, has opened up the possibility of a theoretical investigation into the very early universe and the spacetime regions beyond the Big Bang. (iv) A derivation of the Bekenstein-Hawking black-hole entropy. (v) Low-energy calculations, yielding n -point functions well defined in a background-independent context. The theory is at the roots of, or strictly related to, a number of formalisms that have been developed for describing background-independent quantum field theory, such as spin foams, group field theory, causal spin networks, and others. I give here a general overview of ideas, techniques, results and open problems of this candidate theory of quantum gravity, and a guide to the relevant literature.
Directory of Open Access Journals (Sweden)
Rovelli Carlo
2008-07-01
Full Text Available The problem of describing the quantum behavior of gravity, and thus understanding quantum spacetime, is still open. Loop quantum gravity is a well-developed approach to this problem. It is a mathematically well-defined background-independent quantization of general relativity, with its conventional matter couplings. Today research in loop quantum gravity forms a vast area, ranging from mathematical foundations to physical applications. Among the most significant results obtained so far are: (i The computation of the spectra of geometrical quantities such as area and volume, which yield tentative quantitative predictions for Planck-scale physics. (ii A physical picture of the microstructure of quantum spacetime, characterized by Planck-scale discreteness. Discreteness emerges as a standard quantum effect from the discrete spectra, and provides a mathematical realization of Wheeler’s “spacetime foam” intuition. (iii Control of spacetime singularities, such as those in the interior of black holes and the cosmological one. This, in particular, has opened up the possibility of a theoretical investigation into the very early universe and the spacetime regions beyond the Big Bang. (iv A derivation of the Bekenstein–Hawking black-hole entropy. (v Low-energy calculations, yielding n-point functions well defined in a background-independent context. The theory is at the roots of, or strictly related to, a number of formalisms that have been developed for describing background-independent quantum field theory, such as spin foams, group field theory, causal spin networks, and others. I give here a general overview of ideas, techniques, results and open problems of this candidate theory of quantum gravity, and a guide to the relevant literature.
Semiclassical unimodular gravity
International Nuclear Information System (INIS)
Fiol, Bartomeu; Garriga, Jaume
2010-01-01
Classically, unimodular gravity is known to be equivalent to General Relativity (GR), except for the fact that the effective cosmological constant Λ has the status of an integration constant. Here, we explore various formulations of unimodular gravity beyond the classical limit. We first consider the non-generally covariant action formulation in which the determinant of the metric is held fixed to unity. We argue that the corresponding quantum theory is also equivalent to General Relativity for localized perturbative processes which take place in generic backgrounds of infinite volume (such as asymptotically flat spacetimes). Next, using the same action, we calculate semiclassical non-perturbative quantities, which we expect will be dominated by Euclidean instanton solutions. We derive the entropy/area ratio for cosmological and black hole horizons, finding agreement with GR for solutions in backgrounds of infinite volume, but disagreement for backgrounds with finite volume. In deriving the above results, the path integral is taken over histories with fixed 4-volume. We point out that the results are different if we allow the 4-volume of the different histories to vary over a continuum range. In this ''generalized'' version of unimodular gravity, one recovers the full set of Einstein's equations in the classical limit, including the trace, so Λ is no longer an integration constant. Finally, we consider the generally covariant theory due to Henneaux and Teitelboim, which is classically equivalent to unimodular gravity. In this case, the standard semiclassical GR results are recovered provided that the boundary term in the Euclidean action is chosen appropriately
MODIFIED GRAVITY SPINS UP GALACTIC HALOS
Energy Technology Data Exchange (ETDEWEB)
Lee, Jounghun [Astronomy Program, Department of Physics and Astronomy, FPRD, Seoul National University, Seoul 151-747 (Korea, Republic of); Zhao, Gong-Bo [National Astronomy Observatories, Chinese Academy of Science, Beijing 100012 (China); Li, Baojiu [Institute of Computational Cosmology, Department of Physics, Durham University, Durham DH1 3LE (United Kingdom); Koyama, Kazuya, E-mail: jounghun@astro.snu.ac.kr [Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, PO1 3FX (United Kingdom)
2013-01-20
We investigate the effect of modified gravity on the specific angular momentum of galactic halos by analyzing the halo catalogs at z = 0 from high-resolution N-body simulations for a f(R) gravity model that meets the solar-system constraint. It is shown that the galactic halos in the f(R) gravity model tend to acquire significantly higher specific angular momentum than those in the standard {Lambda}CDM model. The largest difference in the specific angular momentum distribution between these two models occurs for the case of isolated galactic halos with mass less than 10{sup 11} h {sup -1} M {sub Sun }, which are likely least shielded by the chameleon screening mechanism. As the specific angular momentum of galactic halos is rather insensitive to other cosmological parameters, it can in principle be an independent discriminator of modified gravity. We speculate a possibility of using the relative abundance of low surface brightness galaxies (LSBGs) as a test of general relativity given that the formation of the LSBGs occurs in fast spinning dark halos.
Granular Superconductors and Gravity
Noever, David; Koczor, Ron
1999-01-01
As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with a relatively high percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 104 was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field and exposed without levitation to low-field strength AC magnetic fields. Changes in observed gravity signals were measured to be less than 2 parts in 108 of the normal gravitational acceleration. Given the high sensitivity of the test, future work will examine variants on the basic magnetic behavior of granular superconductors, with particular focus on quantifying their proposed importance to gravity.
Sjogren, W. L.; Ananda, M.; Williams, B. G.; Birkeland, P. W.; Esposito, P. S.; Wimberly, R. N.; Ritke, S. J.
1981-01-01
Results of Pioneer Venus Orbiter observations concerning the gravity field of Venus are presented. The gravitational data was obtained from reductions of Doppler radio tracking data for the Orbiter, which is in a highly eccentric orbit with periapsis altitude varying from 145 to 180 km and nearly fixed periapsis latitude of 15 deg N. The global gravity field was obtained through the simultaneous estimation of the orbit state parameters and gravity coefficients from long-period variations in orbital element rates. The global field has been described with sixth degree and order spherical harmonic coefficients, which are capable of resolving the three major topographical features on Venus. Local anomalies have been mapped using line-of-sight accelerations derived from the Doppler residuals between 40 deg N and 10 deg S latitude at approximately 300 km spatial resolution. Gravitational data is observed to correspond to topographical data obtained by radar altimeter, with most of the gravitational anomalies about 20-30 milligals. Simulations evaluating the isostatic states of two topographic features indicate that at least partial isostasy prevails, with the possibility of complete compensation.
Minkel, Donald Howe
Effects of gravity on buckle folding are studied using a Newtonian fluid finite element model of a single layer embedded between two thicker less viscous layers. The methods allow arbitrary density jumps, surface tension coefficients, resistance to slip at the interfaces, and tracking of fold growth to a large amplitudes. When density increases downward in two equal jumps, a layer buckles less and thickens more than with uniform density. When density increases upward in two equal jumps, it buckles more and thickens less. A low density layer with periodic thickness variations buckles more, sometimes explosively. Thickness variations form, even if not present initially. These effects are greater with; smaller viscosities, larger density jump, larger length scale, and slower shortening rate. They also depend on wavelength and amplitude, and these dependencies are described in detail. The model is applied to the explosive growth of the salt anticlines of the Paradox Basin, Colorado and Utah. There, shale (higher density) overlies salt (lower density). Methods for simulating realistic earth surface erosion and deposition conditions are introduced. Growth rates increase both with ease of slip at the salt-shale interface, and when earth surface relief stays low due to erosion and deposition. Model anticlines grow explosively, attaining growth rates and amplitudes close to those of the field examples. Fastest growing wavelengths are the same as seen in the field. It is concluded that a combination of partial-slip at the salt-shale interface, with reasonable earth surface conditions, promotes sufficiently fast buckling of the salt-shale interface due to density inversion alone. Neither basement faulting, nor tectonic shortening is required to account for the observed structures. Of fundamental importance is the strong tendency of gravity to promote buckling in low density layers with thickness variations. These develop, even if not present initially.
Gravity signatures of terrane accretion
Franco, Heather; Abbott, Dallas
1999-01-01
In modern collisional environments, accreted terranes are bracketed by forearc gravity lows, a gravitational feature which results from the abandonment of the original trench and the initiation of a new trench seaward of the accreted terrane. The size and shape of the gravity low depends on the type of accreted feature and the strength of the formerly subducting plate. Along the Central American trench, the accretion of Gorgona Island caused a seaward trench jump of 48 to 66 km. The relict trench axes show up as gravity lows behind the trench with minimum values of -78 mgal (N of Gorgona) and -49 mgal (S of Gorgona) respectively. These forearc gravity lows have little or no topographic expression. The active trench immediately seaward of these forearc gravity lows has minimum gravity values of -59 mgal (N of Gorgona) and -58 mgal (S of Gorgona), respectively. In the north, the active trench has a less pronounced gravity low than the sediment covered forearc. In the Mariana arc, two Cretaceous seamounts have been accreted to the Eocene arc. The northern seamount is most likely a large block, the southern seamount may be a thrust slice. These more recent accretion events have produced modest forearc topographic and gravity lows in comparison with the topographic and gravity lows within the active trench. However, the minimum values of the Mariana forearc gravity lows are modest only by comparison to the Mariana Trench (-216 mgal); their absolute values are more negative than at Gorgona Island (-145 to -146 mgal). We speculate that the forearc gravity lows and seaward trench jumps near Gorgona Island were produced by the accretion of a hotspot island from a strong plate. The Mariana gravity lows and seaward trench jumps (or thrust slices) were the result of breaking a relatively weak plate close to the seamount edifice. These gravity lows resulting from accretion events should be preserved in older accreted terranes.
DEFF Research Database (Denmark)
Jain, Maulik; Andersen, Ole Baltazar; Dall, Jørgen
2013-01-01
The project deals with sea surface height and gravity field determination in open ocean using Cryosat-2 LRM data. A three parameter model is being used to find the retracking offset for sea surface height determination. The estimates from the three parameter model are further improved upon by using...... a two parameter model. The sea surface heights thus obtained are used to develop sea surface height anomalies which are further processed to give gravity fields. Retracker performance evaluation is done using sea surface height anomaly and gravity field anomaly....
DEFF Research Database (Denmark)
Hwang, C.W.; Hsiao, Y.S.; Shih, H.C.
2007-01-01
[ 1] An airborne gravity survey was conducted over Taiwan using a LaCoste and Romberg (LCR) System II air-sea gravimeter with gravity and global positioning system (GPS) data sampled at 1 Hz. The aircraft trajectories were determined using a GPS network kinematic adjustment relative to eight GPS ...... using airborne and surface gravity data and the other using surface data only, and the former yields a better agreement with the GPS-derived geoidal heights. Bouguer anomalies derived from airborne gravity by a rigorous numerical integration reveal important tectonic features....
Lightning incidents in Mongolia
Directory of Open Access Journals (Sweden)
Myagmar Doljinsuren
2015-11-01
Full Text Available This is one of the first studies that has been conducted in Mongolia on the distribution of lightning incidents. The study covers a 10-year period from 2004 to 2013. The country records a human death rate of 15.4 deaths per 10 million people per year, which is much higher than that of many countries with similar isokeraunic level. The reason may be the low-grown vegetation observed in most rural areas of Mongolia, a surface topography, typical to steppe climate. We suggest modifications to Gomes–Kadir equation for such countries, as it predicts a much lower annual death rate for Mongolia. The lightning incidents spread over the period from May to August with the peak of the number of incidents occurring in July. The worst lightning affected region in the country is the central part. Compared with impacts of other convective disasters such as squalls, thunderstorms and hail, lightning stands as the second highest in the number of incidents, human deaths and animal deaths. Economic losses due to lightning is only about 1% of the total losses due to the four extreme weather phenomena. However, unless precautionary measures are not promoted among the public, this figure of losses may significantly increase with time as the country is undergoing rapid industrialization at present.
Mars - Crustal structure inferred from Bouguer gravity anomalies.
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.
Spectral analysis of the gravity and topography of Mars
Bills, Bruce G.; Frey, Herbert V.; Kiefer, Walter S.; Nerem, R. Steven; Zuber, Maria T.
1993-01-01
New spherical harmonic models of the gravity and topography of Mars place important constraints on the structure and dynamics of the interior. The gravity and topography models are significantly phase coherent for harmonic degrees n less than 30 (wavelengths greater than 700 km). Loss of coherence below that wavelength is presumably due to inadequacies of the models, rather than a change in behavior of the planet. The gravity/topography admittance reveals two very different spectral domains: for n greater than 4, a simple Airy compensation model, with mean depth of 100 km, faithfully represents the observed pattern; for degrees 2 and 3, the effective compensation depths are 1400 and 550 km, respectively, strongly arguing for dynamic compensation at those wavelengths. The gravity model has been derived from a reanalysis of the tracking data for Mariner 9 and the Viking Orbiters, The topography model was derived by harmonic analysis of the USGS digital elevation model of Mars. Before comparing gravity and topography for internal structure inferences, we must ensure that both are consistently referenced to a hydrostatic datum. For the gravity, this involves removal of hydrostatic components of the even degree zonal coefficients. For the topography, it involves adding the degree 4 equipotential reference surface, to get spherically referenced values, and then subtracting the full degree 50 equipotential. Variance spectra and phase coherence of orthometric heights and gravity anomalies are addressed.
Cosmological tests of modified gravity.
Koyama, Kazuya
2016-04-01
We review recent progress in the construction of modified gravity models as alternatives to dark energy as well as the development of cosmological tests of gravity. Einstein's theory of general relativity (GR) has been tested accurately within the local universe i.e. the Solar System, but this leaves the possibility open that it is not a good description of gravity at the largest scales in the Universe. This being said, the standard model of cosmology assumes GR on all scales. In 1998, astronomers made the surprising discovery that the expansion of the Universe is accelerating, not slowing down. This late-time acceleration of the Universe has become the most challenging problem in theoretical physics. Within the framework of GR, the acceleration would originate from an unknown dark energy. Alternatively, it could be that there is no dark energy and GR itself is in error on cosmological scales. In this review, we first give an overview of recent developments in modified gravity theories including f(R) gravity, braneworld gravity, Horndeski theory and massive/bigravity theory. We then focus on common properties these models share, such as screening mechanisms they use to evade the stringent Solar System tests. Once armed with a theoretical knowledge of modified gravity models, we move on to discuss how we can test modifications of gravity on cosmological scales. We present tests of gravity using linear cosmological perturbations and review the latest constraints on deviations from the standard [Formula: see text]CDM model. Since screening mechanisms leave distinct signatures in the non-linear structure formation, we also review novel astrophysical tests of gravity using clusters, dwarf galaxies and stars. The last decade has seen a number of new constraints placed on gravity from astrophysical to cosmological scales. Thanks to on-going and future surveys, cosmological tests of gravity will enjoy another, possibly even more, exciting ten years.
Norsk, P.; Shelhamer, M.
2016-01-01
This panel will present NASA's plans for ongoing and future research to define the requirements for Artificial Gravity (AG) as a countermeasure against the negative health effects of long-duration weightlessness. AG could mitigate the gravity-sensitive effects of spaceflight across a host of physiological systems. Bringing gravity to space could mitigate the sensorimotor and neuro-vestibular disturbances induced by G-transitions upon reaching a planetary body, and the cardiovascular deconditioning and musculoskeletal weakness induced by weightlessness. Of particular interest for AG during deep-space missions is mitigation of the Visual Impairment Intracranial Pressure (VIIP) syndrome that the majority of astronauts exhibit in space to varying degrees, and which presumably is associated with weightlessness-induced fluid shift from lower to upper body segments. AG could be very effective for reversing the fluid shift and thus help prevent VIIP. The first presentation by Dr. Charles will summarize some of the ground-based and (very little) space-based research that has been conducted on AG by the various space programs. Dr. Paloski will address the use of AG during deep-space exploration-class missions and describe the different AG scenarios such as intra-vehicular, part-of-vehicle, or whole-vehicle centrifugations. Dr. Clement will discuss currently planned NASA research as well as how to coordinate future activities among NASA's international partners. Dr. Barr will describe some possible future plans for using space- and ground-based partial-G analogs to define the relationship between physiological responses and G levels between 0 and 1. Finally, Dr. Stenger will summarize how the human cardiovascular system could benefit from intermittent short-radius centrifugations during long-duration missions.
Directory of Open Access Journals (Sweden)
Shan Gao
2011-04-01
Full Text Available The remarkable connections between gravity and thermodynamics seem to imply that gravity is not fundamental but emergent, and in particular, as Verlinde suggested, gravity is probably an entropic force. In this paper, we will argue that the idea of gravity as an entropic force is debatable. It is shown that there is no convincing analogy between gravity and entropic force in Verlinde’s example. Neither holographic screen nor test particle satisfies all requirements for the existence of entropic force in a thermodynamics system. Furthermore, we show that the entropy increase of the screen is not caused by its statistical tendency to increase entropy as required by the existence of entropic force, but in fact caused by gravity. Therefore, Verlinde’s argument for the entropic origin of gravity is problematic. In addition, we argue that the existence of a minimum size of spacetime, together with the Heisenberg uncertainty principle in quantum theory, may imply the fundamental existence of gravity as a geometric property of spacetime. This may provide a further support for the conclusion that gravity is not an entropic force.
Active Response Gravity Offload System
Valle, Paul; Dungan, Larry; Cunningham, Thomas; Lieberman, Asher; Poncia, Dina
2011-01-01
The Active Response Gravity Offload System (ARGOS) provides the ability to simulate with one system the gravity effect of planets, moons, comets, asteroids, and microgravity, where the gravity is less than Earth fs gravity. The system works by providing a constant force offload through an overhead hoist system and horizontal motion through a rail and trolley system. The facility covers a 20 by 40-ft (approximately equals 6.1 by 12.2m) horizontal area with 15 ft (approximately equals4.6 m) of lifting vertical range.
Teleparallel equivalent of Lovelock gravity
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.
International Nuclear Information System (INIS)
Joret, H.
1990-06-01
Solid surfaces of organic and inorganic materials have been bombarded by fast heavy ions (several MeV). It is shown that the charge state of the projectile has a strong influence on the atomic and molecular ion desorption yield. Experimental studies proved that molecular ions can be emitted intact from deep layers underneath the surface (volume emission) with the existence of a crater emission. On the other hand light ions like H(+), H(+)-2, H(+)-3 are emitted from the surface of the solid in a time around 10 -16 second. The H(+) depends on the incident charge state g-i. When using slow ions (keV) the same dependence was observed for the first time and compared to the fast ion results. The equilibrum charge state of fast ions passing through solids was measured. The influence of the angle of incidence was investigated. Langmuir-Blodgett films of fatty acid were used. A geometrical model is developed for the 50 angstroms layer [fr
DEFF Research Database (Denmark)
Jiang, Q.D.; Smilgies, D.M.; Feidenhans'l, R.
1996-01-01
The surface morphology and in-plane epitaxy of thin films of SmBa(2)Cu3O(7-delta) (Sm-BCO) grown on SrTiO3 (001) substrates with various thicknesses have been investigated by scanning tunneling microscopy (STM) and grazing incidence x-ray diffraction (GIXRD). As revealed by GIXRD, SmBCO films as ...... films above h(c2), introduction of screw dislocations leads to spiral growth.......The surface morphology and in-plane epitaxy of thin films of SmBa(2)Cu3O(7-delta) (Sm-BCO) grown on SrTiO3 (001) substrates with various thicknesses have been investigated by scanning tunneling microscopy (STM) and grazing incidence x-ray diffraction (GIXRD). As revealed by GIXRD, SmBCO films...... substrate. Three different types of surface morphology were observed by STM with increasing film thickness h: a) 2D growth for hh(c2). With GIXRD, a density modulation is observed in the films with a thickness below h(c2). For thicker...
International Nuclear Information System (INIS)
Aldama, Mariana Espinosa
2015-01-01
The gravity apple tree is a genealogical tree of the gravitation theories developed during the past century. The graphic representation is full of information such as guides in heuristic principles, names of main proponents, dates and references for original articles (See under Supplementary Data for the graphic representation). This visual presentation and its particular classification allows a quick synthetic view for a plurality of theories, many of them well validated in the Solar System domain. Its diachronic structure organizes information in a shape of a tree following similarities through a formal concept analysis. It can be used for educational purposes or as a tool for philosophical discussion. (paper)
Lanczos-Lovelock gravity from a thermodynamic perspective
International Nuclear Information System (INIS)
Chakraborty, Sumanta
2015-01-01
The deep connection between gravitational dynamics and horizon thermodynamics leads to several intriguing features both in general relativity and in Lanczos-Lovelock theories of gravity. Recently in http://arxiv.org/abs/1312.3253 several additional results strengthening the above connection have been established within the framework of general relativity. In this work we provide a generalization of the above setup to Lanczos-Lovelock gravity as well. To our expectation it turns out that most of the results obtained in the context of general relativity generalize to Lanczos-Lovelock gravity in a straightforward but non-trivial manner. First, we provide an alternative and more general derivation of the connection between Noether charge for a specific time evolution vector field and gravitational heat density of the boundary surface. This will lead to holographic equipartition for static spacetimes in Lanczos-Lovelock gravity as well. Taking a cue from this, we have introduced naturally defined four-momentum current associated with gravity and matter energy momentum tensor for both Lanczos-Lovelock Lagrangian and its quadratic part. Then, we consider the concepts of Noether charge for null boundaries in Lanczos-Lovelock gravity by providing a direct generalization of previous results derived in the context of general relativity. Another very interesting feature for gravity is that gravitational field equations for arbitrary static and spherically symmetric spacetimes with horizon can be written as a thermodynamic identity in the near horizon limit. This result holds in both general relativity and in Lanczos-Lovelock gravity as well. In a previous work [http://arxiv.org/abs/1505.05297] we have shown that, for an arbitrary spacetime, the gravitational field equations near any null surface generically leads to a thermodynamic identity. In this work, we have also generalized this result to Lanczos-Lovelock gravity by showing that gravitational field equations for Lanczos
Airborne Gravity: NGS' Gravity Data for AN05 (2011)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2011 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for AN06 (2011)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2011 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for CS08 (2015)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for CS08 collected in 2006 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for AS02 (2010)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for ES02 (2013)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Florida and the Gulf of Mexico collected in 2013 over 1 survey. This data set is part of the Gravity for the Re-definition of the American...
Airborne Gravity: NGS' Gravity Data for AN04 (2010)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for CS05 (2014)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Texas collected in 2014 over 2 surveys. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for CS07 (2014 & 2016)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Texas collected in 2014 & 2016 over 3 surveys,TX14-2, TX16-1 and TX16-2. This data set is part of the Gravity for the Re-definition of...
Airborne Gravity: NGS' Gravity Data for AS01 (2008)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2008 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for CS04 (2009)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Texas collected in 2009 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Airborne Gravity: NGS' Gravity Data for AN02 (2010)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Alaska collected in 2010 over 1 survey. This data set is part of the Gravity for the Re-definition of the American Vertical Datum (GRAV-D)...
Lovelock gravities from Born–Infeld gravity theory
Directory of Open Access Journals (Sweden)
P.K. Concha
2017-02-01
Full Text Available We present a Born–Infeld gravity theory based on generalizations of Maxwell symmetries denoted as Cm. We analyze different configuration limits allowing to recover diverse Lovelock gravity actions in six dimensions. Further, the generalization to higher even dimensions is also considered.
Lovelock gravities from Born-Infeld gravity theory
Concha, P. K.; Merino, N.; Rodríguez, E. K.
2017-02-01
We present a Born-Infeld gravity theory based on generalizations of Maxwell symmetries denoted as Cm. We analyze different configuration limits allowing to recover diverse Lovelock gravity actions in six dimensions. Further, the generalization to higher even dimensions is also considered.
Crustal movements and gravity; Movimientos de la corteza y gravedad
Energy Technology Data Exchange (ETDEWEB)
Rodriguez Pujol, E.
2011-07-01
Gravity time variation inter seismic rates differ globally, regionally and locally if they are measured in active regions or in stable regions. In the long run, gravity in the surface of the earth changes with time mainly due to the slow vertical movements of the earth crust, tectonic faults and especially, in regions close to the plate boundaries. In non-active regions gravity change rates are about 0-0.4 microGal/year (0-1.2mm/year) while unveiling in active regions rates about 1-4 microGal/year (2-12 mm/year). Absolute gravity measurements can give us valuable information about interseismic vertical displacements of the earth crust. (Author) 54 refs.
Experimental Observation of Negative Effective Gravity in Water Waves
Hu, Xinhua; Yang, Jiong; Zi, Jian; Chan, C. T.; Ho, Kai-Ming
2013-01-01
The gravity of Earth is responsible for the formation of water waves and usually difficult to change. Although negative effective gravity was recently predicted theoretically in water waves, it has not yet been observed in experiments and remains a mathematical curiosity which is difficult to understand. Here we experimentally demonstrate that close to the resonant frequency of purposely-designed resonating units, negative effective gravity can occur for water waves passing through an array of resonators composing of bottom-mounted split tubes, resulting in the prohibition of water wave propagation. It is found that when negative gravity occurs, the averaged displacement of water surface in a unit cell of the array has a phase difference of π to that along the boundary of the unit cell, consistent with theoretical predictions. Our results provide a mechanism to block water waves and may find applications in wave energy conversion and coastal protection. PMID:23715132
Pressure Profiles in a Loop Heat Pipe under Gravity Influence
Ku, Jentung
2015-01-01
During the operation of a loop heat pipe (LHP), the viscous flow induces pressure drops in various elements of the loop. The total pressure drop is equal to the sum of pressure drops in vapor grooves, vapor line, condenser, liquid line and primary wick, and is sustained by menisci at liquid and vapor interfaces on the outer surface of the primary wick in the evaporator. The menisci will curve naturally so that the resulting capillary pressure matches the total pressure drop. In ground testing, an additional gravitational pressure head may be present and must be included in the total pressure drop when LHP components are placed in a non-planar configuration. Under gravity-neutral and anti-gravity conditions, the fluid circulation in the LHP is driven solely by the capillary force. With gravity assist, however, the flow circulation can be driven by the combination of capillary and gravitational forces, or by the gravitational force alone. For a gravity-assist LHP at a given elevation between the horizontal condenser and evaporator, there exists a threshold heat load below which the LHP operation is gravity driven and above which the LHP operation is capillary force and gravity co-driven. The gravitational pressure head can have profound effects on the LHP operation, and such effects depend on the elevation, evaporator heat load, and condenser sink temperature. This paper presents a theoretical study on LHP operations under gravity-neutral, anti-gravity, and gravity-assist modes using pressure diagrams to help understand the underlying physical processes. Effects of the condenser configuration on the gravitational pressure head and LHP operation are also discussed.
Contravariant gravity on Poisson manifolds and Einstein gravity
International Nuclear Information System (INIS)
Kaneko, Yukio; Watamura, Satoshi; Muraki, Hisayoshi
2017-01-01
A relation between gravity on Poisson manifolds proposed in Asakawa et al (2015 Fortschr. Phys . 63 683–704) and Einstein gravity is investigated. The compatibility of the Poisson and Riemann structures defines a unique connection, the contravariant Levi-Civita connection, and leads to the idea of the contravariant gravity. The Einstein–Hilbert-type action yields an equation of motion which is written in terms of the analog of the Einstein tensor, and it includes couplings between the metric and the Poisson tensor. The study of the Weyl transformation reveals properties of those interactions. It is argued that this theory can have an equivalent description as a system of Einstein gravity coupled to matter. As an example, it is shown that the contravariant gravity on a two-dimensional Poisson manifold can be described by a real scalar field coupled to the metric in a specific manner. (paper)
Alvarez-Gaume, Luis; Kounnas, Costas; Lust, Dieter; Riotto, Antonio
2016-01-01
We discuss quadratic gravity where terms quadratic in the curvature tensor are included in the action. After reviewing the corresponding field equations, we analyze in detail the physical propagating modes in some specific backgrounds. First we confirm that the pure $R^2$ theory is indeed ghost free. Then we point out that for flat backgrounds the pure $R^2$ theory propagates only a scalar massless mode and no spin-two tensor mode. However, the latter emerges either by expanding the theory around curved backgrounds like de Sitter or anti-de Sitter, or by changing the long-distance dynamics by introducing the standard Einstein term. In both cases, the theory is modified in the infrared and a propagating graviton is recovered. Hence we recognize a subtle interplay between the UV and IR properties of higher order gravity. We also calculate the corresponding Newton's law for general quadratic curvature theories. Finally, we discuss how quadratic actions may be obtained from a fundamental theory like string- or M-...
International Nuclear Information System (INIS)
Jones, K.R.W.
1995-01-01
We develop a nonlinear quantum theory of Newtonian gravity consistent with an objective interpretation of the wavefunction. Inspired by the ideas of Schroedinger, and Bell, we seek a dimensional reduction procedure to map complex wavefunctions in configuration space onto a family of observable fields in space-time. Consideration of quasi-classical conservation laws selects the reduced one-body quantities as the basis for an explicit quasi-classical coarse-graining. These we interpret as describing the objective reality of the laboratory. Thereafter, we examine what may stand in the role of the usual Copenhagen observer to localise this quantity against macroscopic dispersion. Only a tiny change is needed, via a generically attractive self-potential. A nonlinear treatment of gravitational self-energy is thus advanced. This term sets a scale for all wavepackets. The Newtonian cosmology is thus closed, without need of an external observer. Finally, the concept of quantisation is re-interpreted as a nonlinear eigenvalue problem. To illustrate, we exhibit an elementary family of gravitationally self-bound solitary waves. Contrasting this theory with its canonically quantised analogue, we find that the given interpretation is empirically distinguishable, in principle. This result encourages deeper study of nonlinear field theories as a testable alternative to canonically quantised gravity. (author). 46 refs., 5 figs
International Nuclear Information System (INIS)
Goldman, T.; Hughes, R.J.; Nieto, M.M.
1988-01-01
No one has ever dropped a single particle of antimatter. Yet physicists assume that it would fall to the ground just like ordinary matter. Their arguments are based on two well established ideas: the equivalence principle of gravitation and the quantum-mechanical symmetry between matter and antimatter. Today this line of reasoning is being undermined by the possibility that the first of these ideas, the principle of equivalence, may not be true. Indeed all modern attempts to include gravity with the other forces of nature in a consistent, unified quantum theory predict the existence of new gravitational-strength forces, that among other things, will violate the principle. Such effects have been seen already in recent experiments. Hence, an experiment to measure the gravitational acceleration of antimatter could be of great importance to the understanding of quantum gravity. An international team has been formed to measure the graviational acceleration of antiprotons. Such an experiment would provide an unambiquous test, if new gravitational interactions do exist. 10 figs
Shoberg, Thomas G.; Stoddard, Paul R.
2013-01-01
The ability to augment local gravity surveys with additional gravity stations from easily accessible national databases can greatly increase the areal coverage and spatial resolution of a survey. It is, however, necessary to integrate such data seamlessly with the local survey. One challenge to overcome in integrating data from national databases is that these data are typically of unknown quality. This study presents a procedure for the evaluation and seamless integration of gravity data of unknown quality from a national database with data from a local Global Positioning System (GPS)-based survey. The starting components include the latitude, longitude, elevation and observed gravity at each station location. Interpolated surfaces of the complete Bouguer anomaly are used as a means of quality control and comparison. The result is an integrated dataset of varying quality with many stations having GPS accuracy and other reliable stations of unknown origin, yielding a wider coverage and greater spatial resolution than either survey alone.
Is there a quantum theory of gravity
International Nuclear Information System (INIS)
Strominger, A.
1984-01-01
The paper concerns attempts to construct a unitary, renormalizable quantum field theory of gravity. Renormalizability and unitarity in quantum gravity; the 1/N expansion; 1/D expansions; and quantum gravity and particle physics; are all discussed. (U.K.)
Quantum Gravity in Two Dimensions
DEFF Research Database (Denmark)
Ipsen, Asger Cronberg
The topic of this thesis is quantum gravity in 1 + 1 dimensions. We will focus on two formalisms, namely Causal Dynamical Triangulations (CDT) and Dy- namical Triangulations (DT). Both theories regularize the gravity path integral as a sum over triangulations. The difference lies in the class...
Topological strings from Liouville gravity
International Nuclear Information System (INIS)
Ishibashi, N.; Li, M.
1991-01-01
We study constrained SU(2) WZW models, which realize a class of two-dimensional conformal field theories. We show that they give rise to topological gravity coupled to the topological minimal models when they are coupled to Liouville gravity. (orig.)
Newton-Cartan gravity revisited
Andringa, Roel
2016-01-01
In this research Newton's old theory of gravity is rederived using an algebraic approach known as the gauging procedure. The resulting theory is Newton's theory in the mathematical language of Einstein's General Relativity theory, in which gravity is spacetime curvature. The gauging procedure sheds
Fixed points of quantum gravity
Litim, D F
2003-01-01
Euclidean quantum gravity is studied with renormalisation group methods. Analytical results for a non-trivial ultraviolet fixed point are found for arbitrary dimensions and gauge fixing parameter in the Einstein-Hilbert truncation. Implications for quantum gravity in four dimensions are discussed.
Neutron Stars : Magnetism vs Gravity
Indian Academy of Sciences (India)
however, in the magnetosphere, electromagnetic forces dominate over gravity : Fgr = mg ~ 10-18 Newton ; Fem = e V B ~ 10-5 Newton; (for a single electron of mass m and charge e ) ; Hence, the electromagnetic force is 1013 times stronger than gravity !!
Measuring wood specific gravity, correctly
G. Bruce Williamson; Michael C. Wiemann
2010-01-01
The specific gravity (SG) of wood is a measure of the amount of structural material a tree species allocates to support and strength. In recent years, wood specific gravity, traditionally a foresterâs variable, has become the domain of ecologists exploring the universality of plant functional traits and conservationists estimating global carbon stocks. While these...
Magnetic Fields Versus Gravity
Hensley, Kerry
2018-04-01
Deep within giant molecular clouds, hidden by dense gas and dust, stars form. Unprecedented data from the Atacama Large Millimeter/submillimeter Array (ALMA) reveal the intricate magnetic structureswoven throughout one of the most massive star-forming regions in the Milky Way.How Stars Are BornThe Horsehead Nebulasdense column of gas and dust is opaque to visible light, but this infrared image reveals the young stars hidden in the dust. [NASA/ESA/Hubble Heritage Team]Simple theory dictates that when a dense clump of molecular gas becomes massive enough that its self-gravity overwhelms the thermal pressure of the cloud, the gas collapses and forms a star. In reality, however, star formation is more complicated than a simple give and take between gravity and pressure. Thedusty molecular gas in stellar nurseries is permeated with magnetic fields, which are thought to impede the inward pull of gravity and slow the rate of star formation.How can we learn about the magnetic fields of distant objects? One way is by measuring dust polarization. An elongated dust grain will tend to align itself with its short axis parallel to the direction of the magnetic field. This systematic alignment of the dust grains along the magnetic field lines polarizes the dust grains emission perpendicular to the local magnetic field. This allows us to infer the direction of the magnetic field from the direction of polarization.Magnetic field orientations for protostars e2 and e8 derived from Submillimeter Array observations (panels a through c) and ALMA observations (panels d and e). Click to enlarge. [Adapted from Koch et al. 2018]Tracing Magnetic FieldsPatrick Koch (Academia Sinica, Taiwan) and collaborators used high-sensitivity ALMA observations of dust polarization to learn more about the magnetic field morphology of Milky Way star-forming region W51. W51 is one of the largest star-forming regions in our galaxy, home to high-mass protostars e2, e8, and North.The ALMA observations reveal
Impact Of GOCE On The Nordic Gravity Field Modelling
DEFF Research Database (Denmark)
Yidiz, Hasan; Forsberg, René; Tscherning, C. C.
2011-01-01
GOCE level-2 Tzz and Txx gravity gradients at satellite altitude are used in combination as input data to predict surface free air gravity anomalies over the Nordic region using Least Square Collocation. We test the performance of using covariance functions created separately from Tzz gradients a...... Surface model, both the NKG-2004 quasi-geoid model of the Nordic and Baltic Area and the one obtained using second generation GOCE spherical harmonic coefficients based on time-wise method can successfully reproduce the higher level of the Baltic Sea relative to the Atlantic Ocean....
Gravity Scaling of a Power Reactor Water Shield
International Nuclear Information System (INIS)
Reid, Robert S.; Pearson, J. Boise
2008-01-01
Water based reactor shielding is being considered as an affordable option for potential use on initial lunar surface reactor power systems. Heat dissipation in the shield from nuclear sources must be rejected by an auxillary thermal hydraulic cooling system. The mechanism for transferring heat through the shield is natural convection between the core surface and an array of thermosyphon radiator elements. Natural convection in a 100 kWt lunar surface reactor shield design has been previously evaluated at lower power levels (Pearson, 2006). The current baseline assumes that 5.5 kW are dissipated in the water shield, the preponderance on the core surface, but with some volumetric heating in the naturally circulating water as well. This power is rejected by a radiator located above the shield with a surface temperature of 370 K. A similarity analysis on a water-based reactor shield is presented examining the effect of gravity on free convection between a radiation shield inner vessel and a radiation shield outer vessel boundaries. Two approaches established similarity: 1) direct scaling of Rayleigh number equates gravity-surface heat flux products, 2) temperature difference between the wall and thermal boundary layer held constant on Earth and the Moon. Nussult number for natural convection (laminar and turbulent) is assumed of form Nu = CRa n . These combined results estimate similarity conditions under Earth and Lunar gravities. The influence of reduced gravity on the performance of thermosyphon heat pipes is also examined
International Nuclear Information System (INIS)
Ban, G.
1992-04-01
In this thesis divided in 2 parts, the author first presents the operating of MiniMafios 16/18 GHz ECR ion sources and methods of extracted multicharged ion identification and then, studies the highly charged ion interactions with a metallic surface and the formation of 'hollow atoms'. 556 figs., 17 tabs
International Nuclear Information System (INIS)
QEB, Inc. has completed a two-dimensional coherence analysis of gravity and magnetic data from the Casper, Wyoming NTMS quadrangle. Magnetic data from an airborne survey were reduced to produce a Residual Magnetic map, and gravity data obtained from several sources were reduced to produce a Complete Bouguer Gravity map. Both sets of data were upward continued to a plane one kilometer above the surface; and then, to make the magnetic and gravity data comparable, the magnetic data were transformed to pseudo-gravity data by the application of Poisson's relationship for rocks that are both dense and magnetic relative to the surrounding rocks. A pseudo-gravity map was then produced and an analysis made of the two-dimensional coherence between the upward continued Bouguer gravity and the pseudo-gravity data. Based on the results of the coherence analysis, digital filters were designed to either pass or reject wavelength bands with high coherence
Superconducting gravity gradiometer for sensitive gravity measurements. I. Theory
International Nuclear Information System (INIS)
Chan, H.A.; Paik, H.J.
1987-01-01
Because of the equivalence principle, a global measurement is necessary to distinguish gravity from acceleration of the reference frame. A gravity gradiometer is therefore an essential instrument needed for precision tests of gravity laws and for applications in gravity survey and inertial navigation. Superconductivity and SQUID (superconducting quantum interference device) technology can be used to obtain a gravity gradiometer with very high sensitivity and stability. A superconducting gravity gradiometer has been developed for a null test of the gravitational inverse-square law and space-borne geodesy. Here we present a complete theoretical model of this instrument. Starting from dynamical equations for the device, we derive transfer functions, a common mode rejection characteristic, and an error model of the superconducting instrument. Since a gradiometer must detect a very weak differential gravity signal in the midst of large platform accelerations and other environmental disturbances, the scale factor and common mode rejection stability of the instrument are extremely important in addition to its immunity to temperature and electromagnetic fluctuations. We show how flux quantization, the Meissner effect, and properties of liquid helium can be utilized to meet these challenges
Energy Technology Data Exchange (ETDEWEB)
Maxfield, Travis; Sethi, Savdeep [Enrico Fermi Institute, University of Chicago,Chicago, IL 60637 (United States)
2017-02-22
We study the dynamics of gravitational lumps. By a lump, we mean a metric configuration that asymptotes to a flat space-time. Such lumps emerge in string theory as strong coupling descriptions of D-branes. We provide a physical argument that the broken global symmetries of such a background, generated by certain large diffeomorphisms, constrain the dynamics of localized modes. These modes include the translation zero modes and any localized tensor modes. The constraints we find are gravitational analogues of those found in brane physics. For the example of a Taub-NUT metric in eleven-dimensional supergravity, we argue that a critical value for the electric field arises from standard gravity without higher derivative interactions.
International Nuclear Information System (INIS)
Francaviglia, M.
1990-01-01
Although general relativity is a well-established discipline the theory deserves efforts aimed at producing alternative or more general frameworks for investigating the classical properties of gravity. These are either devoted to producing alternative viewpoints or interpretations of standard general relativity, or at constructing, discussing and proposing experimental tests for alternative descriptions of the dynamics of the gravitational field and its interaction (or unification) with external matter fields. Classical alternative theories of gravitation can roughly classified as follows; theories based on a still 4-dimensional picture, under the assumption that the dynamics of the gravitational field is more complicated than Einstein's and theories based on higher-dimensional pictures. This leads to supergravity and strings which are not included here. Theories based on higher-dimensional pictures on the assumption that space-time is replaced by a higher-dimensional manifold. Papers on these classifications are reviewed. (author)
Is quantum gravity unpredictable
International Nuclear Information System (INIS)
Gross, D.J.
1984-01-01
An investigation of Hawking's proposal that the inclusion of topologically non-trivial manifolds in the functional integral of quantum gravity leads to the loss of quantum coherence is carried out. We discuss some of the problems associated with Hawking's Dollar-matrix theory, including the breakdown of the connection between symmetry principles and conservation laws. It is proposed to use Kaluza-Klein theories to study this issue, since these theories contain well-defined euclidean instantons. These can be used to perform explicit semiclassical calculations of the effects of space-time foam. A general method is presented for constructing Kaluza-Klein instantons based on solutions of ordinary Yang-Mills theory. It is argued that none of these will lead to a breakdown of quantum mechanics. The physical effects of space-time foam are discussed in some detail using explicit instantons of a four-dimensional Kaluza-Klein theory. (orig.)
International Nuclear Information System (INIS)
Gregory, Ruth
2007-01-01
The study of braneworlds has been an area of intense activity over the past decade, with thousands of papers being written, and many important technical advances being made. This book focuses on a particular aspect of braneworlds, namely perturbative gravity in one specific model: the Randall-Sundrum model. The book starts with an overview of the Randall-Sundrum model, discussing anti-de Sitter (AdS) space and the Israel equations in some detail. It then moves on to discuss cosmological branes, focusing on branes with constant curvature. The book then turns to brane gravity, i.e. what do we, as brane observers, perceive the gravitational interaction to be on the brane as derived from the actual five-dimensional gravitational physics? After a derivation of the general brane equations from the Israel equations, the remainder of the book deals with perturbative gravity. This part of the book is extremely detailed, with calculations given explicitly. Overall, the book is quite pedagogical in style, with the aim being to explain in detail the topics it chooses to cover. While it is not unusual to have books written on current and extremely popular research areas, it is unusual to have calculations written so explicitly. This is both a strength and a weakness of this book. It is a strength because the calculations are presented in a detail that students learning the topic will definitely appreciate; however, the narrow focus of the book also means that it lacks perspective and fails to present the broader context. In choosing to focus on one particular aspect of Randall-Sundrum branes, the book has not managed to communicate why a large number of theorists have worked so intensively on this model. In its early stages, the explicit detail of the Randall-Sundrum model would be extremely useful for a student starting out in this research area. In addition, the calculational detail later in the computation of the graviton propagator on the brane would also be welcome not
International Nuclear Information System (INIS)
Henneaux, Marc; Teitelboim, Claudio
2005-01-01
We show that duality transformations of linearized gravity in four dimensions, i.e., rotations of the linearized Riemann tensor and its dual into each other, can be extended to the dynamical fields of the theory so as to be symmetries of the action and not just symmetries of the equations of motion. Our approach relies on the introduction of two superpotentials, one for the spatial components of the spin-2 field and the other for their canonically conjugate momenta. These superpotentials are two-index, symmetric tensors. They can be taken to be the basic dynamical fields and appear locally in the action. They are simply rotated into each other under duality. In terms of the superpotentials, the canonical generator of duality rotations is found to have a Chern-Simons-like structure, as in the Maxwell case
Stochastic quantization and gravity
International Nuclear Information System (INIS)
Rumpf, H.
1984-01-01
We give a preliminary account of the application of stochastic quantization to the gravitational field. We start in Section I from Nelson's formulation of quantum mechanics as Newtonian stochastic mechanics and only then introduce the Parisi-Wu stochastic quantization scheme on which all the later discussion will be based. In Section II we present a generalization of the scheme that is applicable to fields in physical (i.e. Lorentzian) space-time and treat the free linearized gravitational field in this manner. The most remarkable result of this is the noncausal propagation of conformal gravitons. Moreover the concept of stochastic gauge-fixing is introduced and a complete discussion of all the covariant gauges is given. A special symmetry relating two classes of covariant gauges is exhibited. Finally Section III contains some preliminary remarks on full nonlinear gravity. In particular we argue that in contrast to gauge fields the stochastic gravitational field cannot be transformed to a Gaussian process. (Author)
International Nuclear Information System (INIS)
Maity, Debaprasad
2015-01-01
In this work we propose a mechanism of natural preheating of our universe induced by the inflation field dependent effective mass term for the gravitational wave. For any single field inflationary model, the inflation must go through the oscillatory phase after the end of inflation. As has recently been shown, if the gravitational fluctuation has inflation dependent mass term, there will be a resonant amplification of the amplitude of the gravitational wave during the oscillatory phase of inflation though parametric resonance. Because of this large enhancement of the amplitude of the gravitational wave, we show that universe can be naturally pre-heated through a minimally coupled matter field with gravity. Therefore, during the pre-heating phase, there is no need to introduce any arbitrary coupling between the matter field and the inflation. (author)
Teleparallel Gravity An Introduction
Aldrovandi, Ruben
2013-01-01
Teleparallel Gravity (TG) is an alternative theory for gravitation, which is equivalent to General Relativity (GR). However, it is conceptually different. For example in GR geometry replaces the concept of force, and the trajectories are determined by geodesics. TG attributes gravitation to torsion, which accounts for gravitation by acting as a force. TG has already solved some old problems of gravitation (like the energy-momentum density of the gravitational field). The interest in TG has grown in the last few years. The book here proposed will be the first one dedicated exclusively to TG, and will include the foundations of the theory, as well as applications to specific problems to illustrate how the theory works.
Frè, Pietro Giuseppe
2013-01-01
‘Gravity, a Geometrical Course’ presents general relativity (GR) in a systematic and exhaustive way, covering three aspects that are homogenized into a single texture: i) the mathematical, geometrical foundations, exposed in a self consistent contemporary formalism, ii) the main physical, astrophysical and cosmological applications, updated to the issues of contemporary research and observations, with glimpses on supergravity and superstring theory, iii) the historical development of scientific ideas underlying both the birth of general relativity and its subsequent evolution. The book is divided in two volumes. Volume One is dedicated to the development of the theory and basic physical applications. It guides the reader from the foundation of special relativity to Einstein field equations, illustrating some basic applications in astrophysics. A detailed account of the historical and conceptual development of the theory is combined with the presentation of its mathematical foundations. Differe...
Mannheim, Philip D
2005-01-01
This timely and valuable book provides a detailed pedagogical introduction and treatment of the brane-localized gravity program of Randall and Sundrum, in which gravitational signals are able to localize around our four-dimensional world in the event that it is a brane embedded in an infinitely-sized, higher dimensional anti-de Sitter bulk space. A completely self-contained development of the material needed for brane-world studies is provided for both students and workers in the field, with a significant amount of the material being previously unpublished. Particular attention is given to issues not ordinarily treated in the brane-world literature, such as the completeness of tensor gravitational fluctuation modes, the causality of brane-world propagators, and the status of the massless graviton fluctuation mode in brane worlds in which it is not normalizable.
International Nuclear Information System (INIS)
Pope, C.N.
1980-02-01
The material contained in this thesis is concerned with the functional integral approach to the quantum theory of gravity. It seems to be necessary to work with metrics of positive definite signature (Euclidean metrics) and then analytically continue the result back to the Lorentzian regime. The dominant contributions to the functional integral come from metrics which are stationary points of the action, i.e. classical solutions of the Euclideanized Einstein equations. These are known as Gravitational Instantons. Boundary conditions have to be placed upon the metrics included in the functional integral, and these are determined by the physical problem being considered. Three types of boundary condition have arisen in this context, corresponding to (i) zero temperature physics, and the calculation of particle scattering amplitudes, (ii) finite temperature effects, such as black hole radiance, and (iii) the study of the structure of the gravitational vacuum on Planck length scales. Instantons in the first category are asymptotically flat in all four directions, those in the second are asymptotically flat in three directions and periodic in the fourth, and those which arise in studying the gravitational vacuum are compact without boundaries. Much of the thesis is concerned with considering these various kinds of instanton, and particularly with the effects of their non-trivial topology. One way in which this can be investigated is by means of the various topological index theorems, and these are applied to a variety of situations. Self-dual metrics seem to have particular significance in quantum gravity, and they are discussed in detail. Finally, some recent work on the calculation of the propagation of particles in the gravitational vacuum is described. (author)
Burrage, Clare; Sakstein, Jeremy
2018-03-01
Theories of modified gravity, where light scalars with non-trivial self-interactions and non-minimal couplings to matter—chameleon and symmetron theories—dynamically suppress deviations from general relativity in the solar system. On other scales, the environmental nature of the screening means that such scalars may be relevant. The highly-nonlinear nature of screening mechanisms means that they evade classical fifth-force searches, and there has been an intense effort towards designing new and novel tests to probe them, both in the laboratory and using astrophysical objects, and by reinterpreting existing datasets. The results of these searches are often presented using different parametrizations, which can make it difficult to compare constraints coming from different probes. The purpose of this review is to summarize the present state-of-the-art searches for screened scalars coupled to matter, and to translate the current bounds into a single parametrization to survey the state of the models. Presently, commonly studied chameleon models are well-constrained but less commonly studied models have large regions of parameter space that are still viable. Symmetron models are constrained well by astrophysical and laboratory tests, but there is a desert separating the two scales where the model is unconstrained. The coupling of chameleons to photons is tightly constrained but the symmetron coupling has yet to be explored. We also summarize the current bounds on f( R) models that exhibit the chameleon mechanism (Hu and Sawicki models). The simplest of these are well constrained by astrophysical probes, but there are currently few reported bounds for theories with higher powers of R. The review ends by discussing the future prospects for constraining screened modified gravity models further using upcoming and planned experiments.
2000-01-01
The space vehicle Gravity Probe B (GP-B) is the relativity experiment developed at Stanford University to test two extraordinary predictions of Albert Einstein's general theory of relativity. The experiment will measure, very precisely, the expected tiny changes in the direction of the spin axes of four gyroscopes contained in an Earth-orbiting satellite at a 400-mile altitude. So free are the gyroscopes from disturbance that they will provide an almost perfect space-time reference system. They will measure how space and time are very slightly warped by the presence of the Earth, and, more profoundly, how the Earth's rotation very slightly drags space-time around with it. These effects, though small for the Earth, have far-reaching implications for the nature of matter and the structure of the Universe. GP-B is among the most thoroughly researched programs ever undertaken by NASA. This is the story of a scientific quest in which physicists and engineers have collaborated closely over many years. Inspired by their quest, they have invented a whole range of technologies that are already enlivening other branches of science and engineering. In this photograph, engineer Gary Reynolds is inspecting the inside of the probe neck during probe thermal repairs. GP-B is scheduled for launch in April 2004 and managed for NASA by the Marshall Space Flight Center. Development of the GP-B is the responsibility of Stanford University along with major subcontractor Lockheed Martin Corporation. (Image credit to Russ Leese, Gravity Probe B, Stanford University)
Measuring antimatter gravity with muonium
Directory of Open Access Journals (Sweden)
Kaplan Daniel M.
2015-01-01
Full Text Available The gravitational acceleration of antimatter, ḡ, has never been directly measured and could bear importantly on our understanding of gravity, the possible existence of a fifth force, and the nature and early history of the universe. Only two avenues for such a measurement appear to be feasible: antihydrogen and muonium. The muonium measurement requires a novel, monoenergetic, low-velocity, horizontal muonium beam directed at an atom interferometer. The precision three-grating interferometer can be produced in silicon nitride or ultrananocrystalline diamond using state-of-the-art nanofabrication. The required precision alignment and calibration at the picometer level also appear to be feasible. With 100 nm grating pitch, a 10% measurement of ḡ can be made using some months of surface-muon beam time, and a 1% or better measurement with a correspondingly larger exposure. This could constitute the first gravitational measurement of leptonic matter, of 2nd-generation matter and, possibly, the first measurement of the gravitational acceleration of antimatter.
Gravity-matter entanglement in Regge quantum gravity
International Nuclear Information System (INIS)
Paunković, Nikola; Vojinović, Marko
2016-01-01
We argue that Hartle-Hawking states in the Regge quantum gravity model generically contain non-trivial entanglement between gravity and matter fields. Generic impossibility to talk about “matter in a point of space” is in line with the idea of an emergent spacetime, and as such could be taken as a possible candidate for a criterion for a plausible theory of quantum gravity. Finally, this new entanglement could be seen as an additional “effective interaction”, which could possibly bring corrections to the weak equivalence principle. (paper)
Artificial gravity - The evolution of variable gravity research
Fuller, Charles A.; Sulzman, Frank M.; Keefe, J. Richard
1987-01-01
The development of a space life science research program based on the use of rotational facilities is described. In-flight and ground centrifuges can be used as artificial gravity environments to study the following: nongravitational biological factors; the effects of 0, 1, and hyper G on man; counter measures for deconditioning astronauts in weightlessness; and the development of suitable artificial gravity for long-term residence in space. The use of inertial fields as a substitute for gravity, and the relations between the radius of the centrifuge and rotation rate and specimen height and rotation radius are examined. An example of a centrifuge study involving squirrel monkeys is presented.
Lorentz invariance violation in modified gravity
International Nuclear Information System (INIS)
Brax, Philippe
2012-01-01
We consider an environmentally dependent violation of Lorentz invariance in scalar-tensor models of modified gravity where General Relativity is retrieved locally thanks to a screening mechanism. We find that fermions have a modified dispersion relation and would go faster than light in an anisotropic and space-dependent way along the scalar field lines of force. Phenomenologically, these models are tightly restricted by the amount of Cerenkov radiation emitted by the superluminal particles, a constraint which is only satisfied by chameleons. Measuring the speed of neutrinos emitted radially from the surface of the earth and observed on the other side of the earth would probe the scalar field profile of modified gravity models in dense environments. We argue that the test of the equivalence principle provided by the Lunar ranging experiment implies that a deviation from the speed of light, for natural values of the coupling scale between the scalar field and fermions, would be below detectable levels, unless gravity is modified by camouflaged chameleons where the field normalisation is environmentally dependent.
Lorentz invariance violation in modified gravity
Energy Technology Data Exchange (ETDEWEB)
Brax, Philippe, E-mail: philippe.brax@cea.fr [Institut de Physique Theorique, CEA, IPhT, CNRS, URA 2306, F-91191Gif/Yvette Cedex (France)
2012-06-06
We consider an environmentally dependent violation of Lorentz invariance in scalar-tensor models of modified gravity where General Relativity is retrieved locally thanks to a screening mechanism. We find that fermions have a modified dispersion relation and would go faster than light in an anisotropic and space-dependent way along the scalar field lines of force. Phenomenologically, these models are tightly restricted by the amount of Cerenkov radiation emitted by the superluminal particles, a constraint which is only satisfied by chameleons. Measuring the speed of neutrinos emitted radially from the surface of the earth and observed on the other side of the earth would probe the scalar field profile of modified gravity models in dense environments. We argue that the test of the equivalence principle provided by the Lunar ranging experiment implies that a deviation from the speed of light, for natural values of the coupling scale between the scalar field and fermions, would be below detectable levels, unless gravity is modified by camouflaged chameleons where the field normalisation is environmentally dependent.
REXUS 16 Low Gravity Experiment
Manoliu, L.; Ciuca, I.; Lupu, E. S.; Ciobanu, I.; Cherciu, C.; Soare, C.; Murensan, C.; Dragomir, D.; Chitu, C.; Nachila, C.
2015-09-01
The REXUS/BEXUS is a programme realized under a bilateral agency agreement between the German Aerospace Centre (DLR) and the Swedish National Space Board (SNSB) (Source: www.rexusbexus.net) . Within this programme, the experiment proposed by LOW Gravity was given the opportunity to fly on board of REXUS 16 from Kiruna, Sweden, in May 2014. Since space settlements are within our reach and material processing in reduced gravity is a key requirement, we aim to improve this field by investigating the melting and welding processes taking place in milligravity on board of a sounding rocket. Our main objective is to analyze the surface deformation and physical properties of titanium and acid core solder alloys welded/melted under miligravity conditions with a 25W LASER diode. The main components of our experiment are the metal samples, the LASER diode and the control electronics. The metal samples are placed in front of an optical system and are shifted during approximately 120 seconds of milligravity. The optical system is connected via an optic fiber to the LASER diode. The electronics consists of two custom-made boards: the mainboard which is connected to the REXUS interface and controls the LASER diode and the sample shifting and the logboard which has an SD card to log all experiment data (sample position, experiment acceleration and rotation rate, pressure and temperature, battery voltage and LASER diode status). During the flight, due to unexpected vibration levels, the fiber optics was damaged at T+70 and the experiment could not fulfill its main objective. A GoPro camera mounted inside the experiment box recorded the experiment operation. Valuable information regarding temperature and battery voltage was also sent remotely to our Ground Station. This data enabled us to perform a thorough failure analysis. Parallel readings of these parameters taken by other experiments and by the REXUS Service Module corroborate our data and increase the accuracy of our analysis
Recent advancements in conformal gravity
International Nuclear Information System (INIS)
O’Brien, James G.; Chaykov, Spasen S.; Moss, Robert J.; Dentico, Jeremy; Stulge, Modestas; Stefanski, Brian
2017-01-01
In recent years, due to the lack of direct observed evidence of cold dark matter, coupled with the shrinking parameter space to search for new dark matter particles, there has been increased interest in Alternative Gravitational theories. This paper, addresses three recent advances in conformal gravity, a fourth order renormalizable metric theory of gravitation originally formulated by Weyl, and later advanced by Mannheim and Kazanas. The first section of the paper applies conformal gravity to the rotation curves of the LITTLE THINGS survey, extending the total number of rotation curves successfully fit by conformal gravity to well over 200 individual data sets without the need for additional dark matter. Further, in this rotation curve study, we show how MOND and conformal gravity compare for each galaxy in the sample. Second, we look at the original Zwicky problem of applying the virial theorem to the Coma cluster in order to get an estimate for the cluster mass. However, instead of using the standard Newtonian potential, here we use the weak field approximation of conformal gravity. We show that in the conformal case we can get a much smaller mass estimate and thus there is no apparent need to include dark matter. We then show that this calculation is in agreement with the observational data from other well studied clusters. Last, we explore the calculation of the deflection of starlight through conformal gravity, as a first step towards applying conformal gravity to gravitaitonal lensing. (paper)
Stochastic Gravity: Theory and Applications
Directory of Open Access Journals (Sweden)
Hu Bei Lok
2008-05-01
Full Text Available Whereas semiclassical gravity is based on the semiclassical Einstein equation with sources given by the expectation value of the stress-energy tensor of quantum fields, stochastic semiclassical gravity is based on the Einstein–Langevin equation, which has, in addition, sources due to the noise kernel. The noise kernel is the vacuum expectation value of the (operator-valued stress-energy bitensor, which describes the fluctuations of quantum-matter fields in curved spacetimes. A new improved criterion for the validity of semiclassical gravity may also be formulated from the viewpoint of this theory. In the first part of this review we describe the fundamentals of this new theory via two approaches: the axiomatic and the functional. The axiomatic approach is useful to see the structure of the theory from the framework of semiclassical gravity, showing the link from the mean value of the stress-energy tensor to the correlation functions. The functional approach uses the Feynman–Vernon influence functional and the Schwinger–Keldysh closed-time-path effective action methods. In the second part, we describe three applications of stochastic gravity. First, we consider metric perturbations in a Minkowski spacetime, compute the two-point correlation functions of these perturbations and prove that Minkowski spacetime is a stable solution of semiclassical gravity. Second, we discuss structure formation from the stochastic-gravity viewpoint, which can go beyond the standard treatment by incorporating the full quantum effect of the inflaton fluctuations. Third, using the Einstein–Langevin equation, we discuss the backreaction of Hawking radiation and the behavior of metric fluctuations for both the quasi-equilibrium condition of a black-hole in a box and the fully nonequilibrium condition of an evaporating black hole spacetime. Finally, we briefly discuss the theoretical structure of stochastic gravity in relation to quantum gravity and point out
Effects of gravity level on bubble formation and rise in low-viscosity liquids
Suñol, Francesc; González-Cinca, Ricard
2015-05-01
We present an experimental analysis of the effects of gravity level on the formation and rise dynamics of bubbles. Experiments were carried out with millimeter-diameter bubbles in the hypergravity environment provided by the large-diameter centrifuge of the European Space Agency. Bubble detachment from a nozzle is determined by buoyancy and surface tension forces regardless of the gravity level. Immediately after detachment, bubble trajectory is deviated by the Coriolis force. Subsequent bubble rise is dominated by inertial forces and follows a zig-zag trajectory with amplitude and frequency dependent on the gravity level. Vorticity production is enhanced as gravity increases, which destabilizes the flow and therefore the bubble path.
Airborne Gravity: NGS' Gravity Data for ES03 (2013)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Maryland, Pennsylvania, New Jersey, West Virginia, Virginia, Delaware, and the Atlantic Ocean collected in 2013 over 1 survey. This data...
Airborne Gravity: NGS' Gravity Data for EN10 (2013)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for New York, Pennsylvania, New Jersey, Connecticut and the Atlantic Ocean collected in 2013 over 1 survey. This data set is part of the...
Airborne Gravity: NGS' Gravity Data for EN09 (2016)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data for Massachusetts, Connecticut, Rhode Island, New Hampshire, New York, and the Atlantic Ocean collected in 2012 over 1 survey. This data set is...
Singularity resolution in quantum gravity
International Nuclear Information System (INIS)
Husain, Viqar; Winkler, Oliver
2004-01-01
We examine the singularity resolution issue in quantum gravity by studying a new quantization of standard Friedmann-Robertson-Walker geometrodynamics. The quantization procedure is inspired by the loop quantum gravity program, and is based on an alternative to the Schroedinger representation normally used in metric variable quantum cosmology. We show that in this representation for quantum geometrodynamics there exists a densely defined inverse scale factor operator, and that the Hamiltonian constraint acts as a difference operator on the basis states. We find that the cosmological singularity is avoided in the quantum dynamics. We discuss these results with a view to identifying the criteria that constitute 'singularity resolution' in quantum gravity
Natural inflation and quantum gravity.
de la Fuente, Anton; Saraswat, Prashant; Sundrum, Raman
2015-04-17
Cosmic inflation provides an attractive framework for understanding the early Universe and the cosmic microwave background. It can readily involve energies close to the scale at which quantum gravity effects become important. General considerations of black hole quantum mechanics suggest nontrivial constraints on any effective field theory model of inflation that emerges as a low-energy limit of quantum gravity, in particular, the constraint of the weak gravity conjecture. We show that higher-dimensional gauge and gravitational dynamics can elegantly satisfy these constraints and lead to a viable, theoretically controlled and predictive class of natural inflation models.
International Nuclear Information System (INIS)
Goradia, S.G.
2006-01-01
Why is gravity weak? Gravity is plagued with this and many other questions. After decades of exhausting work we do not have a clear answer. In view of this fact it will be shown in the following pages that there are reasons for thinking that gravity is just a composite force consisting of the long-range manifestations of short range nuclear forces that are too tiny to be measured at illuminated or long ranges by particle colliders. This is consistent with Einstein's proposal in 1919
Cutoff for extensions of massive gravity and bi-gravity
International Nuclear Information System (INIS)
Matas, Andrew
2016-01-01
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. (paper)
International Nuclear Information System (INIS)
Ne'eman, Y.
1998-01-01
The relatively simple Fibre-Bundle geometry of a Yang-Mills gauge theory - mainly the clear distinction between base and fibre - made it possible, between 1953 and 1971, to construct a fully quantized version and prove that theory's renormalizability; moreover, nonperturbative (topological) solutions were subsequently found in both the fully symmetric and the spontaneously broken modes (instantons, monopoles). Though originally constructed as a model formalism, it became in 1974 the mathematical mold holding the entire Standard Model (i.e. QCD and the Electroweak theory). On the other hand, between 1974 and 1984, Einstein's theory was shown to be perturbatively nonrenormalizable. Since 1974, the search for Quantum Gravity has therefore provided the main motivation for the construction of Gauge Theories of Gravity. Earlier, however, in 1958-76 several such attempts were initiated, for aesthetic or heuristic reasons, to provide a better understanding of the algebraic structure of GR. A third motivation has come from the interest in Unification, making it necessary to bring GR into a form compatible with an enlargement of the Standard Model. Models can be classified according to the relevant structure group in the fibre. Within the Poincare group, this has been either the R 4 translations, or the Lorentz group SL(2, C) - or the entire Poincare SL(2, C) x R 4 . Enlarging the group has involved the use of the Conformal SU(2, 2), the special Affine SA(4, R) = SL(4, R) x R 4 or Affine A(4, R) groups. Supergroups have included supersymmetry, i.e. the graded-Poincare group (n =1...8 m its extensions) or the superconformal SU(2, 2/n). These supergravity theories have exploited the lessons of the aesthetic-heuristic models - Einstein-Cartan etc. - and also achieved the Unification target. Although perturbative renormalizability has been achieved in some models, whether they satisfy unitarity is not known. The nonperturbative Ashtekar program has exploited the understanding of
An improved model for the Earth's gravity field
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.
Renormalization and asymptotic freedom in quantum gravity
International Nuclear Information System (INIS)
Tomboulis, E.T.
1984-01-01
The article reviews some recent attempts to construct satisfactory theories of quantum gravity within the framework of local, continuum field theory. Quantum gravity; the renormalization group and its fixed points; fixed points and dimensional continuation in gravity; and quantum gravity at d=4-the 1/N expansion-asymptotic freedom; are all discussed. (U.K.)
Paschalis, Eleftherios P; Gamsjaeger, Sonja; Dempster, David; Jorgetti, Vanda; Borba, Victoria; Boguszewski, Cesar L; Klaushofer, Klaus; Moreira, Carolina A
2017-01-01
Chronic obstructive pulmonary disease (COPD) is associated with low areal bone mineral density (aBMD) by dual-energy X-ray absorptiometry (DXA) and altered microstructure by bone histomorphometry and micro-computed tomography. Nevertheless, not all COPD patients sustain fragility fractures. In the present study, we used Raman microspectroscopic analysis to determine bone compositional properties at actively forming trabecular surfaces (based on double fluorescent labels) in iliac crest biopsies from 19 postmenopausal COPD patients (aged 62.1 ± 7.3 years). Additionally, we analyzed trabecular geometrical centers, representing tissue much older than the forming surfaces. Eight of the patients had sustained fragility fractures, and 13 had received treatment with inhaled glucocorticoids. None of the patients had taken oral glucocorticoids. The monitored parameters were mineral/matrix ratio (MM), nanoporosity, and relative glycosaminoglycan (GAG), lipid, and pyridinoline contents (PYD). There were no significant differences between the glucocorticoid-treated patients and those who did not receive any. On the other hand, COPD patients sustaining fragility fractures had significantly lower nanoporosity and higher MM and PYD values compared with COPD patients without fragility fractures. To the best of our knowledge, this is the first study to discriminate between fracture and non-fracture COPD patients based on differences in the material properties of bone matrix. Given that these bone material compositional differences are evident close to the cement line (a major bone interface), they may contribute to the inferior bone toughness and coupled with the lower lumbar spine bone mineral density values result in the fragility fractures prevalent in these patients. © 2016 American Society for Bone and Mineral Research. © 2016 American Society for Bone and Mineral Research.
Quantum gravity and quantum cosmology
Papantonopoulos, Lefteris; Siopsis, George; Tsamis, Nikos
2013-01-01
Quantum gravity has developed into a fast-growing subject in physics and it is expected that probing the high-energy and high-curvature regimes of gravitating systems will shed some light on how to eventually achieve an ultraviolet complete quantum theory of gravity. Such a theory would provide the much needed information about fundamental problems of classical gravity, such as the initial big-bang singularity, the cosmological constant problem, Planck scale physics and the early-time inflationary evolution of our Universe. While in the first part of this book concepts of quantum gravity are introduced and approached from different angles, the second part discusses these theories in connection with cosmological models and observations, thereby exploring which types of signatures of modern and mathematically rigorous frameworks can be detected by experiments. The third and final part briefly reviews the observational status of dark matter and dark energy, and introduces alternative cosmological models. ...
Topological gravity with minimal matter
International Nuclear Information System (INIS)
Li Keke
1991-01-01
Topological minimal matter, obtained by twisting the minimal N = 2 supeconformal field theory, is coupled to two-dimensional topological gravity. The free field formulation of the coupled system allows explicit representations of BRST charge, physical operators and their correlation functions. The contact terms of the physical operators may be evaluated by extending the argument used in a recent solution of topological gravity without matter. The consistency of the contact terms in correlation functions implies recursion relations which coincide with the Virasoro constraints derived from the multi-matrix models. Topological gravity with minimal matter thus provides the field theoretic description for the multi-matrix models of two-dimensional quantum gravity. (orig.)
Alternative Hamiltonian representation for gravity
Energy Technology Data Exchange (ETDEWEB)
Rosas-RodrIguez, R [Instituto de Fisica, Universidad Autonoma de Puebla, Apdo. Postal J-48, 72570, Puebla, Pue. (Mexico)
2007-11-15
By using a Hamiltonian formalism for fields wider than the canonical one, we write the Einstein vacuum field equations in terms of alternative variables. This variables emerge from the Ashtekar's formalism for gravity.
Alternative Hamiltonian representation for gravity
International Nuclear Information System (INIS)
Rosas-RodrIguez, R
2007-01-01
By using a Hamiltonian formalism for fields wider than the canonical one, we write the Einstein vacuum field equations in terms of alternative variables. This variables emerge from the Ashtekar's formalism for gravity
Random manifolds and quantum gravity
International Nuclear Information System (INIS)
Krzywicki, A.
2000-01-01
The non-perturbative, lattice field theory approach towards the quantization of Euclidean gravity is reviewed. Included is a tentative summary of the most significant results and a presentation of the current state of art
Gravity Data For Colombia 1997
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (9,050 records), were observed and processed by the Instituto Geografico Agustin Codazzi(IGAC), in Colombia from 1958 to 1996. This data...
Interior Alaska Bouguer Gravity Anomaly
National Oceanic and Atmospheric Administration, Department of Commerce — A 1 kilometer Complete Bouguer Anomaly gravity grid of interior Alaska. All grid cells within the rectangular data area (from 61 to 66 degrees North latitude and...
Unifying Einstein and Palatini gravities
International Nuclear Information System (INIS)
Amendola, Luca; Enqvist, Kari; Koivisto, Tomi
2011-01-01
We consider a novel class of f(R) gravity theories where the connection is related to the conformally scaled metric g μν =C(R)g μν with a scaling that depends on the scalar curvature R only. We call them C theories and show that the Einstein and Palatini gravities can be obtained as special limits. In addition, C theories include completely new physically distinct gravity theories even when f(R)=R. With nonlinear f(R), C theories interpolate and extrapolate the Einstein and Palatini cases and may avoid some of their conceptual and observational problems. We further show that C theories have a scalar-tensor formulation, which in some special cases reduces to simple Brans-Dicke-type gravity. If matter fields couple to the connection, the conservation laws in C theories are modified. The stability of perturbations about flat space is determined by a simple condition on the Lagrangian.
Defying gravity using Jenga™ blocks
Tan, Yin-Soo; Yap, Kueh-Chin
2007-11-01
This paper describes how Jenga™ blocks can be used to demonstrate the physics of an overhanging tower that appears to defy gravity. We also propose ideas for how this demonstration can be adapted for the A-level physics curriculum.
Badler, N. I.; Fishwick, P.; Taft, N.; Agrawala, M.
1985-01-01
The use of computer graphics to simulate the movement of articulated animals and mechanisms has a number of uses ranging over many fields. Human motion simulation systems can be useful in education, medicine, anatomy, physiology, and dance. In biomechanics, computer displays help to understand and analyze performance. Simulations can be used to help understand the effect of external or internal forces. Similarly, zero-gravity simulation systems should provide a means of designing and exploring the capabilities of hypothetical zero-gravity situations before actually carrying out such actions. The advantage of using a simulation of the motion is that one can experiment with variations of a maneuver before attempting to teach it to an individual. The zero-gravity motion simulation problem can be divided into two broad areas: human movement and behavior in zero-gravity, and simulation of articulated mechanisms.
Distinguishing modified gravity models
International Nuclear Information System (INIS)
Brax, Philippe; Davis, Anne-Christine
2015-01-01
Modified gravity models with screening in local environments appear in three different guises: chameleon, K-mouflage and Vainshtein mechanisms. We propose to look for differences between these classes of models by considering cosmological observations at low redshift. In particular, we analyse the redshift dependence of the fine structure constant and the proton to electron mass ratio in each of these scenarios. When the absorption lines belong to unscreened regions of space such as dwarf galaxies, a time variation would be present for chameleons. For both K-mouflage and Vainshtein mechanisms, the cosmological time variation of the scalar field is not suppressed in both unscreened and screened environments, therefore enhancing the variation of constants and their detection prospect. We also consider the time variation of the redshift of distant objects using their spectrocopic velocities. We find that models of the K-mouflage and Vainshtein types have very different spectroscopic velocities as a function of redshift and that their differences with the Λ-CDM template should be within reach of the future ELT-HIRES observations
International Nuclear Information System (INIS)
Deser, S.
1987-01-01
We obtain the Einstein action plus quadratic curvature corrections generated by closed bosonic, heterotic and supersymmetric strings by matching the four-graviton amplitude (to first order in the slope parameter and fourth power of momenta) with an effective local gravitational action. The resulting corrections are first shown to be of the Gauss-Bonnet form. It is then noted that, by the very nature of the slope expansion, the field-redefinition theorem applies. Consequently, only the curvature-squared term is determined, while squares of its contractions are explicitly seen not to contribute. This latter property has a generalization to all orders which implies that the effective gravitational action is unavoidably ghost-free. The properties of solutions to these corrected theories are then examined. First neglecting dilatons, we find the explicit 'Schwarzschild' metrics. Both asymptotically flat and de Sitter solutions are present. The latter are however shown to be unstable. The former have horizons and singularities which are respectively smaller and less violent than in Einstein gravity; the correct sign of the slope parameter also ensures absence of naked singularities. When dilatons are included, the cosmological vacua are gratifyingly excluded. (orig.)
2004-01-01
In this photo, the Gravity Probe B (GP-B) space vehicle is being encapsulated atop the Delta II launch vehicle. The GP-B is the relativity experiment developed at Stanford University to test two extraordinary predictions of Albert Einstein's general theory of relativity. The experiment will measure, very precisely, the expected tiny changes in the direction of the spin axes of four gyroscopes contained in an Earth-orbiting satellite at a 400-mile altitude. So free are the gyroscopes from disturbance that they will provide an almost perfect space-time reference system. They will measure how space and time are very slightly warped by the presence of the Earth, and, more profoundly, how the Earth's rotation very slightly drags space-time around with it. These effects, though small for the Earth, have far-reaching implications for the nature of matter and the structure of the Universe. GP-B is among the most thoroughly researched programs ever undertaken by NASA. This is the story of a scientific quest in which physicists and engineers have collaborated closely over many years. Inspired by their quest, they have invented a whole range of technologies that are already enlivening other branches of science and engineering. Launched April 20, 2004 , the GP-B program was managed for NASA by the Marshall Space Flight Center. Development of the GP-B is the responsibility of Stanford University along with major subcontractor Lockheed Martin Corporation. (Image credit to Russ Underwood, Lockheed Martin Corporation).
Dubovsky, S L
2004-01-01
We systematically study the most general Lorentz-violating graviton mass invariant under three-dimensional Eucledian group using the explicitly covariant language. We find that at general values of mass parameters the massive graviton has six propagating degrees of freedom, and some of them are ghosts or lead to rapid classical instabilities. However, there is a number of different regions in the mass parameter space where massive gravity can be described by a consistent low-energy effective theory with cutoff $\\sim\\sqrt{mM_{Pl}}$ free of rapid instabilities and vDVZ discontinuity. Each of these regions is characterized by certain fine-tuning relations between mass parameters, generalizing the Fierz--Pauli condition. In some cases the required fine-tunings are consequences of the existence of the subgroups of the diffeomorphism group that are left unbroken by the graviton mass. We found two new cases, when the resulting theories have a property of UV insensitivity, i.e. remain well behaved after inclusion of ...
Distinguishing modified gravity models
Energy Technology Data Exchange (ETDEWEB)
Brax, Philippe [Institut de Physique Théorique, Université Paris-Saclay, CEA, CNRS, F-91191 Gif/Yvette Cedex (France); Davis, Anne-Christine, E-mail: philippe.brax@cea.fr, E-mail: A.C.Davis@damtp.cam.ac.uk [DAMTP, Centre for Mathematical Sciences, University of Cambridge, Cambridge, CB3 0WA (United Kingdom)
2015-10-01
Modified gravity models with screening in local environments appear in three different guises: chameleon, K-mouflage and Vainshtein mechanisms. We propose to look for differences between these classes of models by considering cosmological observations at low redshift. In particular, we analyse the redshift dependence of the fine structure constant and the proton to electron mass ratio in each of these scenarios. When the absorption lines belong to unscreened regions of space such as dwarf galaxies, a time variation would be present for chameleons. For both K-mouflage and Vainshtein mechanisms, the cosmological time variation of the scalar field is not suppressed in both unscreened and screened environments, therefore enhancing the variation of constants and their detection prospect. We also consider the time variation of the redshift of distant objects using their spectrocopic velocities. We find that models of the K-mouflage and Vainshtein types have very different spectroscopic velocities as a function of redshift and that their differences with the Λ-CDM template should be within reach of the future ELT-HIRES observations.
Nonperturbative quantum gravity
International Nuclear Information System (INIS)
Ambjørn, J.; Görlich, A.; Jurkiewicz, J.; Loll, R.
2012-01-01
Asymptotic safety describes a scenario in which general relativity can be quantized as a conventional field theory, despite being nonrenormalizable when expanding it around a fixed background geometry. It is formulated in the framework of the Wilsonian renormalization group and relies crucially on the existence of an ultraviolet fixed point, for which evidence has been found using renormalization group equations in the continuum. “Causal Dynamical Triangulations” (CDT) is a concrete research program to obtain a nonperturbative quantum field theory of gravity via a lattice regularization, and represented as a sum over spacetime histories. In the Wilsonian spirit one can use this formulation to try to locate fixed points of the lattice theory and thereby provide independent, nonperturbative evidence for the existence of a UV fixed point. We describe the formalism of CDT, its phase diagram, possible fixed points and the “quantum geometries” which emerge in the different phases. We also argue that the formalism may be able to describe a more general class of Hořava–Lifshitz gravitational models.
Directory of Open Access Journals (Sweden)
Bernard S. Kay
2015-12-01
Full Text Available We give a review, in the style of an essay, of the author’s 1998 matter-gravity entanglement hypothesis which, unlike the standard approach to entropy based on coarse-graining, offers a definition for the entropy of a closed system as a real and objective quantity. We explain how this approach offers an explanation for the Second Law of Thermodynamics in general and a non-paradoxical understanding of information loss during black hole formation and evaporation in particular. It also involves a radically different from usual description of black hole equilibrium states in which the total state of a black hole in a box together with its atmosphere is a pure state—entangled in just such a way that the reduced state of the black hole and of its atmosphere are each separately approximately thermal. We also briefly recall some recent work of the author which involves a reworking of the string-theory understanding of black hole entropy consistent with this alternative description of black hole equilibrium states and point out that this is free from some unsatisfactory features of the usual string theory understanding. We also recall the author’s recent arguments based on this alternative description which suggest that the Anti de Sitter space (AdS/conformal field theory (CFT correspondence is a bijection between the boundary CFT and just the matter degrees of freedom of the bulk theory.
Multi-Beam Surface Lidar for Lunar and Planetary Mapping
Bufton, Jack L.; Garvin, James B.
1998-01-01
Surface lidar techniques are now being demonstrated in low Earth orbit with a single beam of pulsed laser radiation at 1064 nm that profiles the vertical structure of Earth surface landforms along the nadir track of a spacecraft. In addition, a profiling laser altimeter, called MOLA, is operating in elliptical Martian orbit and returning surface topography data. These instruments form the basis for suggesting an improved lidar instrument that employs multiple beams for extension of sensor capabilities toward the goal of true, 3-dimensional mapping of the Moon or other similar planetary surfaces. In general the lidar waveform acquired with digitization of a laser echo can be used for laser distance measurement (i.e. range-to-the-surface) by time-of-flight measurement and for surface slope and shape measurements by examining the detailed lidar waveform. This is particularly effective when the intended target is the lunar surface or another planetary body free of any atmosphere. The width of the distorted return pulse is a first order measure of the surface incidence angle, a combination of surface slope and laser beam pointing. Assuming an independent and absolute (with respect to inertial space) measurement of laser beam pointing on the spacecraft, it is possible to derive a surface slope with-respect-to the mean planetary surface or its equipotential gravity surface. Higher-order laser pulse distortions can be interpreted in terms of the vertical relief of the surface or reflectivity variations within the area of the laser beam footprint on the surface.
PPN-limit of Fourth Order Gravity inspired by Scalar-Tensor Gravity
Capozziello, S.; Troisi, A.
2005-01-01
Based on the {\\it dynamical} equivalence between higher order gravity and scalar-tensor gravity the PPN-limit of fourth order gravity is discussed. We exploit this analogy developing a fourth order gravity version of the Eddington PPN-parameters. As a result, Solar System experiments can be reconciled with higher order gravity, if physical constraints descending from experiments are fulfilled.
Effect of the Earth's inner structure on the gravity in definitions of height systems
Tenzer, Robert; Foroughi, Ismael; Pitoňák, Martin; Šprlák, Michal
2017-04-01
In context of the vertical datum unification, the geoid-to-quasi-geoid separation has been of significant interest in recent years, because most of existing local vertical datums are realized in the system of either normal or orthometric heights. Nevertheless, the normal-orthometric heights are still used in many other countries where the normal gravity values along leveling lines were adopted instead of the observed gravity. Whereas the conversion between the orthometric and normal heights is defined by means of the mean gravity disturbances (i.e. differences between the mean values of the actual and normal gravity) along the plumbline within the topography, differences between the normal and normal-orthometric heights can be described by means of the surface gravity disturbances. Since the normal gravity field does not reflect the topographic masses and actual mass density distribution inside the Earth, the definition of gravity represents a principal aspect for a realization of particular vertical datum. To address this issue in this study, we investigate effects of the Earth's inner density structure on the surface and mean gravity disturbances, and discuss their impact on the vertical datum realization. These two gravity field quantities are computed globally with a spectral resolution complete to a spherical harmonic degree 2160 using the global gravity, terrain, ice-thickness, inland bathymetry and crustal structure models. Our results reveal that both, the surface and mean gravity disturbances mostly comprise the gravitational signal of topography and masses distributed below the geoid surface. Moreover, in polar areas, a significant contribution comes from large glaciers. In contrast, the contributions of anomalous density distribution within the topography attributed to major lakes, sediments and bedrock density variations are much less pronounced. We also demonstrate that the mean gravity disturbances within the topography are significantly modified
Radion and holographic brane gravity
International Nuclear Information System (INIS)
Kanno, Sugumi; Soda, Jiro
2002-01-01
The low energy effective theory for the Randall-Sundrum two-brane system is investigated with an emphasis on the role of the nonlinear radion in the brane world. The equations of motion in the bulk are solved using a low energy expansion method. This allows us, through the junction conditions, to deduce the effective equations of motion for gravity on the brane. It is shown that the gravity on the brane world is described by a quasi-scalar-tensor theory with a specific coupling function ω(Ψ)=3Ψ/2(1-Ψ) on the positive tension brane and ω(Φ)=-3Φ/2(1+Φ) on the negative tension brane, where Ψ and Φ are nonlinear realizations of the radion on the positive and negative tension branes, respectively. In contrast with the usual scalar-tensor gravity, the quasi-scalar-tensor gravity couples with two kinds of matter; namely, the matter on both positive and negative tension branes, with different effective gravitational coupling constants. In particular, the radion disguised as the scalar fields Ψ and Φ couples with the sum of the traces of the energy-momentum tensor on both branes. In the course of the derivation, it is revealed that the radion plays an essential role in converting the nonlocal Einstein gravity with generalized dark radiation to local quasi-scalar-tensor gravity. For completeness, we also derive the effective action for our theory by substituting the bulk solution into the original action. It is also shown that quasi-scalar-tensor gravity works as a hologram at low energy in the sense that the bulk geometry can be reconstructed from the solution of quasi-scalar-tensor gravity
Curved backgrounds in emergent gravity
Chaurasia, Shikha; Erlich, Joshua; Zhou, Yiyu
2018-06-01
Field theories that are generally covariant but nongravitational at tree level typically give rise to an emergent gravitational interaction whose strength depends on a physical regulator. We consider emergent gravity models in which scalar fields assume the role of clock and rulers, addressing the problem of time in quantum gravity. We discuss the possibility of nontrivial dynamics for clock and ruler fields, and describe some of the consequences of those dynamics for the emergent gravitational theory.
Minimal Length, Measurability and Gravity
Directory of Open Access Journals (Sweden)
Alexander Shalyt-Margolin
2016-03-01
Full Text Available The present work is a continuation of the previous papers written by the author on the subject. In terms of the measurability (or measurable quantities notion introduced in a minimal length theory, first the consideration is given to a quantum theory in the momentum representation. The same terms are used to consider the Markov gravity model that here illustrates the general approach to studies of gravity in terms of measurable quantities.
Scattering of internal gravity waves
Leaman Nye, Abigail
2011-01-01
Internal gravity waves play a fundamental role in the dynamics of stably stratified regions of the atmosphere and ocean. In addition to the radiation of momentum and energy remote from generation sites, internal waves drive vertical transport of heat and mass through the ocean by wave breaking and the mixing subsequently produced. Identifying regions where internal gravity waves contribute to ocean mixing and quantifying this mixing are therefore important for accurate climate ...
Absolute gravity measurements in California
Zumberge, M. A.; Sasagawa, G.; Kappus, M.
1986-08-01
An absolute gravity meter that determines the local gravitational acceleration by timing a freely falling mass with a laser interferometer has been constructed. The instrument has made measurements at 11 sites in California, four in Nevada, and one in France. The uncertainty in the results is typically 10 microgal. Repeated measurements have been made at several of the sites; only one shows a substantial change in gravity.
Dark Matter in Quantum Gravity
Calmet, Xavier; Latosh, Boris
2018-01-01
We show that quantum gravity, whatever its ultra-violet completion might be, could account for dark matter. Indeed, besides the massless gravitational field recently observed in the form of gravitational waves, the spectrum of quantum gravity contains two massive fields respectively of spin 2 and spin 0. If these fields are long-lived, they could easily account for dark matter. In that case, dark matter would be very light and only gravitationally coupled to the standard model particles.
International Nuclear Information System (INIS)
Au, G.
1995-03-01
One of the greatest challenges facing theoretical physics lies in reconciling Einstein's classical theory of gravity - general relativity -with quantum field theory. Although both theories have been experimentally supported in their respective regimes, they are as compatible as a square peg and a round hole. This article summarises the current status of the superstring approach to the problem, the status of the Ashtekar program, and problem of time in quantum gravity
Gravity as Quantum Entanglement Force
Lee, Jae-Weon; Kim, Hyeong-Chan; Lee, Jungjai
2010-01-01
We conjecture that the total quantum entanglement of matter and vacuum in the universe tends to increase with time, like entropy, and that an effective force is associated with this tendency. We also suggest that gravity and dark energy are types of quantum entanglement forces, similar to Verlinde's entropic force, and give holographic dark energy with an equation of state comparable to current observational data. This connection between quantum entanglement and gravity could give some new in...
Gravity as a thermodynamic phenomenon
Moustos, Dimitris
2017-01-01
The analogy between the laws of black hole mechanics and the laws of thermodynamics led Bekenstein and Hawking to argue that black holes should be considered as real thermodynamic systems that are characterised by entropy and temperature. Black hole thermodynamics indicates a deeper connection between thermodynamics and gravity. We review and examine in detail the arguments that suggest an interpretation of gravity itself as a thermodynamic theory.
Energy Technology Data Exchange (ETDEWEB)
Au, G
1995-03-01
One of the greatest challenges facing theoretical physics lies in reconciling Einstein`s classical theory of gravity - general relativity -with quantum field theory. Although both theories have been experimentally supported in their respective regimes, they are as compatible as a square peg and a round hole. This article summarises the current status of the superstring approach to the problem, the status of the Ashtekar program, and problem of time in quantum gravity.
Gravity a very short introduction
Clifton, Timothy
2017-01-01
Gravity is one of the four fundamental interactions that exist in nature. It also has the distinction of being the oldest, weakest, and most difficult force to quantize. Understanding gravity is not only essential for understanding the motion of objects on Earth, but also the motion of all celestial objects, and even the expansion of the Universe itself. It was the study of gravity that led Einstein to his profound realizations about the nature of space and time. Gravity is not only universal, it is also essential for understanding the behavior of the Universe, and all astrophysical bodies within it. In this Very Short Introduction Timothy Clifton looks at the development of our understanding of gravity since the early observations of Kepler and Newtonian theory. He discusses Einstein's theory of gravity, which now supplants Newton's, showing how it allows us to understand why the frequency of light changes as it passes through a gravitational field, why GPS satellites need their clocks corrected as they orbi...
Interplay between topology, gauge fields and gravity
Corichi Rodriguez Gil, Alejandro
In this thesis we consider several physical systems that illustrate an interesting interplay between quantum theory, connections and knot theory. It can be divided into two parts. In the first one, we consider the quantization of the free Maxwell field. We show that there is an important role played by knot theory, and in particular the Gauss linking number, in the quantum theory. This manifestation is twofold. The first occurs at the level of the algebra of observables given by fluxes of electric and magnetic field across surfaces. The commutator of the operators, and thus the basic uncertainty relations, are given in terms of the linking number of the loops that bound the surfaces. Next, we consider the quantization of the Maxwell field based on self-dual connections in the loop representation. We show that the measure which determines the quantum inner product can be expressed in terms of the self linking number of thickened loops. Therefore, the linking number manifests itself at two key points of the theory: the Heisenberg uncertainty principle and the inner product. In the second part, we bring gravity into play. First we consider quantum test particles on certain stationary space-times. We demonstrate that a geometric phase exists for those space-times and focus on the example of a rotating cosmic string. The geometric phase can be explicitly computed, providing a fully relativistic gravitational Aharonov-Bohm effect. Finally, we consider 3-dimensional gravity with non-vanishing cosmological constant in the connection dynamics formulation. We restrict our attention to Lorentzian gravity with positive cosmological constant and Euclidean signature with negative cosmological constant. A complex transformation is performed in phase space that makes the constraints simple. The reduced phase space is characterized as the moduli space of flat complex connections. We construct the quantization of the theory when the initial hyper-surface is a torus. Two important
Nucleate Boiling Heat Transfer Studied Under Reduced-Gravity Conditions
Chao, David F.; Hasan, Mohammad M.
2000-01-01
Boiling is known to be a very efficient mode of heat transfer, and as such, it is employed in component cooling and in various energy-conversion systems. In space, boiling heat transfer may be used in thermal management, fluid handling and control, power systems, and on-orbit storage and supply systems for cryogenic propellants and life-support fluids. Recent interest in the exploration of Mars and other planets and in the concept of in situ resource utilization on the Martian and Lunar surfaces highlights the need to understand how gravity levels varying from the Earth's gravity to microgravity (1g = or > g/g(sub e) = or > 10(exp -6)g) affect boiling heat transfer. Because of the complex nature of the boiling process, no generalized prediction or procedure has been developed to describe the boiling heat transfer coefficient, particularly at reduced gravity levels. Recently, Professor Vijay K. Dhir of the University of California at Los Angeles proposed a novel building-block approach to investigate the boiling phenomena in low-gravity to microgravity environments. This approach experimentally investigates the complete process of bubble inception, growth, and departure for single bubbles formed at a well-defined and controllable nucleation site. Principal investigator Professor Vijay K. Dhir, with support from researchers from the NASA Glenn Research Center at Lewis Field, is performing a series of pool boiling experiments in the low-gravity environments of the KC 135 microgravity aircraft s parabolic flight to investigate the inception, growth, departure, and merger of bubbles from single- and multiple-nucleation sites as a function of the wall superheat and the liquid subcooling. Silicon wafers with single and multiple cavities of known characteristics are being used as test surfaces. Water and PF5060 (an inert liquid) were chosen as test liquids so that the role of surface wettability and the magnitude of the effect of interfacial tension on boiling in reduced
2000-01-01
In this photo, the Gravity Probe B (GP-B) space vehicle is being assembled at the Sunnyvale, California location of the Lockheed Martin Corporation. The GP-B is the relativity experiment developed at Stanford University to test two extraordinary predictions of Albert Einstein's general theory of relativity. The experiment will measure, very precisely, the expected tiny changes in the direction of the spin axes of four gyroscopes contained in an Earth-orbiting satellite at a 400-mile altitude. So free are the gyroscopes from disturbance that they will provide an almost perfect space-time reference system. They will measure how space and time are very slightly warped by the presence of the Earth, and, more profoundly, how the Earth's rotation very slightly drags space-time around with it. These effects, though small for the Earth, have far-reaching implications for the nature of matter and the structure of the Universe. GP-B is among the most thoroughly researched programs ever undertaken by NASA. This is the story of a scientific quest in which physicists and engineers have collaborated closely over many years. Inspired by their quest, they have invented a whole range of technologies that are already enlivening other branches of science and engineering. Launched April 20, 2004 , the GP-B program was managed for NASA by the Marshall Space Flight Center. Development of the GP-B is the responsibility of Stanford University along with major subcontractor Lockheed Martin Corporation. (Image credit to Russ Underwood, Lockheed Martin Corporation).
Relativistic theory of gravity
International Nuclear Information System (INIS)
Logunov, A.A.; Mestvirishvili, M.A.
1985-01-01
This work presents an unambiguous construction of the relativistic theory of gravity (RTG) in the framework of relativity and the geometrization principle. The gauge principle has been formulated, and the Lagrangian density of the gravitational field has thus been constructed. This theory explains the totality of the available experimental data on the solar system and predicts the existence of gravitational waves of the Faraday-Maxwell type. According to the RTG, the Universe is infinite and ''flat'', hence it follows that its matter density should be equal to its critical density. Therefore, an appreciable ''hidden mass'' exceeding the presently observed mass of the matter almost 40-fold should exist in the Universe in some form of the matter or other. In accordance with the RTG, a massive body having a finite density ceases to contract under gravitational forces within a finite interval of proper time. From the viewpoint of an external reference frame, the brightness of the body decreases exponentially (it is getting darker), but nothing extraordinary happens in this case because its density always remains finite and, for example, for a body with the mass of about 10 8 M 0 it is equal to 2 g/cm 3 . That is why it follows from the RTG that there could be no object whatsoever (black holes) in which gravitational collapse of matter develops to an infinite density. As has been shown, the presence of a cosmological term necessarily requires the introduction of a term with an explicit dependence on the Minkowski metrics. For the long-range gravitational forces the cosmological constant vanishes
Geometric scalar theory of gravity beyond spherical symmetry
Moschella, U.; Novello, M.
2017-04-01
We construct several exact solutions for a recently proposed geometric scalar theory of gravity. We focus on a class of axisymmetric geometries and a big-bang-like geometry and discuss their Lorentzian character. The axisymmetric solutions are parametrized by an integer angular momentum l . The l =0 (spherical) case gives rise to the Schwarzschild geometry. The other solutions have naked singular surfaces. While not a priori obvious, all the solutions that we present here are globally Lorentzian. The Lorentzian signature appears to be a robust property of the disformal geometries solving the vacuum geometric scalar theory of gravity equations.
Superconducting gravity gradiometer for sensitive gravity measurements. II. Experiment
International Nuclear Information System (INIS)
Chan, H.A.; Moody, M.V.; Paik, H.J.
1987-01-01
A sensitive superconducting gravity gradiometer has been constructed and tested. Coupling to gravity signals is obtained by having two superconducting proof masses modulate magnetic fields produced by persistent currents. The induced electrical currents are differenced by a passive superconducting circuit coupled to a superconducting quantum interference device. The experimental behavior of this device has been shown to follow the theoretical model closely in both signal transfer and noise characteristics. While its intrinsic noise level is shown to be 0.07 E Hz/sup -1/2/ (1 Eequivalent10/sup -9/ sec/sup -2/), the actual performance of the gravity gradiometer on a passive platform has been limited to 0.3--0.7 E Hz/sup -1/2/ due to its coupling to the environmental noise. The detailed structure of this excess noise is understood in terms of an analytical error model of the instrument. The calibration of the gradiometer has been obtained by two independent methods: by applying a linear acceleration and a gravity signal in two different operational modes of the instrument. This device has been successfully operated as a detector in a new null experiment for the gravitational inverse-square law. In this paper we report the design, fabrication, and detailed test results of the superconducting gravity gradiometer. We also present additional theoretical analyses which predict the specific dynamic behavior of the gradiometer and of the test
Exactly solvable models of 2D-quantum gravity on the lattice. Course 5
International Nuclear Information System (INIS)
Kazakov, V.A.
1990-01-01
It is shown that statistical mechanical models defined on randomly triangulated surfaces can be solved exactly and that thereby the results on 2-D quantum gravity can be confirmed. (author). 32 refs.; 4 figs.; 2 tabs
Dark Matter Explanation from Quasi-Metric Gravity
Østvang, Dag
2010-01-01
The gravitational field of an isolated, axisymmetric flat disk of spinning dust is calculated approximately in the weak-field limit of quasi-metric gravity. Boundary conditions single out the exponential disk as a "preferred" physical surface density profile. Besides, collective properties of the disk, in the form of an extra "induced associated" surface density playing the role of "dark matter", also emerge. Taken as an idealized model of spiral galaxy thin disks, it is shown that including ...
Gravity enhanced acoustic levitation method and apparatus
Barmatz, M. B.; Allen, J. L.; Granett, D. (Inventor)
1985-01-01
An acoustic levitation system is provided for acoustically levitating an object by applying a single frequency from a transducer into a resonant chamber surrounding the object. The chamber includes a stabilizer location along its height, where the side walls of the chamber are angled so they converge in an upward direction. When an acoustic standing wave pattern is applied between the top and bottom of the chamber, a levitation surface within the stabilizer does not lie on a horizontal plane, but instead is curved with a lowermost portion near the vertical axis of the chamber. As a result, an acoustically levitated object is urged by gravity towards the lowermost location on the levitation surface, so the object is kept away from the side walls of the chamber.
(2+1)-dimensional quantum gravity
International Nuclear Information System (INIS)
Hosoya, Akio; Nakao, Ken-ichi.
1989-05-01
The (2+1)-dimensional pure Einstein gravity is studied in the canonical ADM formalism, assuming that the spatial surface is closed and compact. Owing to the constraints, the dynamical variables are reduced to the moduli parameters of the 2-surface. Upon quantization, the system becomes a quantum mechanics of moduli parameters in a curved space endowed with the Weil-Petersson metric. In the case of torus in particular, the superspace, on which the wave function of universe is defined, turns out to be the fundamental region is the moduli space. The solution of the Wheeler-DeWitt equation is explicitly given as the Maass form which is perfectly regular in the superspace. (author)
Çavşak, Hasan; Elmas, Ali
2014-01-01
In this study, various calculations comparisons are made to achieve the best results in gravity computation. In the three dimensional (3D) gravity study, mass surfaces are defined by dividing the triangle surfaces. The more triangle surface is taken, the more precise definition of mass are made. Triangular pyramids are taken into consideration as the 3D master model. This model is formed between each triangle surface and calculation point. This method can describe complex shaped formation per...
How to turn gravity waves into Alfven waves and other such tricks
International Nuclear Information System (INIS)
Newington, Marie E; Cally, Paul S
2011-01-01
Recent observations of travelling gravity waves at the base of the chromosphere suggest an interplay between gravity wave propagation and magnetic field. Our aims are: to explain the observation that gravity wave flux is suppressed in magnetic regions; to understand why we see travelling waves instead of standing waves; and to see if gravity waves can undergo mode conversion and couple to Alfven waves in regions where the plasma beta is of order unity. We model gravity waves in a VAL C atmosphere, subject to a uniform magnetic field of various orientations, considering both adiabatic and radiatively damped propagation. Results indicate that in the presence of a magnetic field, the gravity wave can propagate as a travelling wave, with the magnetic field orientation playing a crucial role in determining the wave character. For the majority of magnetic field orientations, the gravity wave is reflected at low heights as a slow magneto-acoustic wave, explaining the observation of reduced flux in magnetic regions. In a highly inclined magnetic field, the gravity wave undergoes mode conversion to either field guided acoustic waves or Alfven waves. The primary effect of incorporating radiative damping is a reduction in acoustic and magnetic fluxes measured at the top of the integration region. By demonstrating the mode conversion of gravity waves to Alfven waves, this work identifies a possible pathway for energy transport from the solar surface to the upper atmosphere.
Approaches to Validation of Models for Low Gravity Fluid Behavior
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.
Mass Tracking with a MEMS-based Gravity Sensor
Pike, W. T.; Mukherjee, A.; Warren, T.; Charalambous, C.; Calcutt, S. B.; Standley, I.
2017-12-01
We achieve the first demonstration of the dynamic location of a moving mass using a MEMS sensor to detect gravity. The sensor is based on a microseismometer developed for planetary geophysics. In an updated version of the original Cavendish experiment the noise floor of the sensor, at 0.25 µgal/rtHz, allows the determination of the dynamic gravitational field from the motion of the mass of an oscillating pendulum. Using the determined noise floor we show that this performance should be sufficient for practical subsurface gravity surveying, in particular detection of 50-cm diameter pipes up to 10 m below the surface. Beyond this specific application, this sensor with a mass of less than 250 g per axis represents a new technology that opens up the possibility of drone deloyments for gravity mapping.
Guo, Zhikui; Chen, Chao; Tao, Chunhui
2016-04-01
Since 2007, there are four China Da yang cruises (CDCs), which have been carried out to investigate polymetallic sulfides in the southwest Indian ridge (SWIR) and have acquired both gravity data and bathymetry data on the corresponding survey lines(Tao et al., 2014). Sandwell et al. (2014) published a new global marine gravity model including the free air gravity data and its first order vertical gradient (Vzz). Gravity data and its gradient can be used to extract unknown density structure information(e.g. crust thickness) under surface of the earth, but they contain all the mass effect under the observation point. Therefore, how to get accurate gravity and its gradient effect of the existing density structure (e.g. terrain) has been a key issue. Using the bathymetry data or ETOPO1 (http://www.ngdc.noaa.gov/mgg/global/global.html) model at a full resolution to calculate the terrain effect could spend too much computation time. We expect to develop an effective method that takes less time but can still yield the desired accuracy. In this study, a constant-density polyhedral model is used to calculate the gravity field and its vertical gradient, which is based on the work of Tsoulis (2012). According to gravity field attenuation with distance and variance of bathymetry, we present an adaptive mesh refinement and coarsening strategies to merge both global topography data and multi-beam bathymetry data. The local coarsening or size of mesh depends on user-defined accuracy and terrain variation (Davis et al., 2011). To depict terrain better, triangular surface element and rectangular surface element are used in fine and coarse mesh respectively. This strategy can also be applied to spherical coordinate in large region and global scale. Finally, we applied this method to calculate Bouguer gravity anomaly (BGA), mantle Bouguer anomaly(MBA) and their vertical gradient in SWIR. Further, we compared the result with previous results in the literature. Both synthetic model
International Nuclear Information System (INIS)
Snyder, D.B.; Carr, W.J.
1982-01-01
Exploration for a high-level-nuclear-waste-repository site in the Yucca Mountain area, Nevada, resulted in the addition of 423 new gravity stations during the past 2 years to the 934 existing stations to form the data base of this study. About 100 surface-rock samples, three borehole gamma-gamma logs, and one borehole gravity study provide excellent density control. A linear increase in density of 0.26 g/cm 3 per km is indicated in the tuff sequences makes the density contrast across the basal contact of the tuff the only strong source of gravity fluctuations. Isostatic and 2.0g/cm 3 Bouguer corrections were applied to the observed gravity values to remove deep-crust-related regional gradients and topographic effects, respectively. The resulting residual-gravity plot shows significant gravity anomalies that correlate closely with the structures inferred from drill-hole and surface geologic studies. Gravity highs over the three Paleozoic rock outcrops within the study area - Bare Mountain, the Calico Hills, and the Striped Hills - served as reference points for the gravity models. At least 3000 m of tuff fills a large steep-sided depression in the prevolcanic rocks beneath Yucca Mountain and Crater Flat. The gravity low and thick tuff section probably lie within a large collapse area comprising the Crater Flat-Timber Mountain-Silent Canyon caldera complexes. Gravity lows in Crater Flat itself are thought to coincide with the source areas of the Prow Pass Member, the Bullfrog Member, and the unnamed member of the Crater Flat Tuff. Southward extension of the broad gravity low associated with Crater Flat into the Amargosa Desert is evidence for sector graben-type collapse segments related to the Timber Mountain caldera and superimposed on the other structures within Crater Flat. 13 figures, 4 tables
Light fermions in quantum gravity
International Nuclear Information System (INIS)
Eichhorn, Astrid; Gies, Holger
2011-01-01
We study the impact of quantum gravity, formulated as a quantum field theory of the metric, on chiral symmetry in a fermionic matter sector. Specifically we address the question of whether metric fluctuations can induce chiral symmetry breaking and bound state formation. Our results based on the functional renormalization group indicate that chiral symmetry is left intact even at strong gravitational coupling. In particular, we found that asymptotically safe quantum gravity where the gravitational couplings approach a non-Gaußian fixed point generically admits universes with light fermions. Our results thus further support quantum gravity theories built on fluctuations of the metric field such as the asymptotic-safety scenario. A study of chiral symmetry breaking through gravitational quantum effects may also serve as a significant benchmark test for other quantum gravity scenarios, since a completely broken chiral symmetry at the Planck scale would not be in accordance with the observation of light fermions in our universe. We demonstrate that this elementary observation already imposes constraints on a generic UV completion of gravity. (paper)
Quantum gravity as Escher's dragon
International Nuclear Information System (INIS)
Smilga, A.V.
2003-01-01
The main obstacle in attempts to construct a consistent quantum gravity is the absence of independent flat time. This can in principle be cured by going out to higher dimensions. The modern paradigm assumes that the fundamental theory of everything is some form of string theory living in space of more than four dimensions. We advocate another possibility that the fundamental theory is a form of D = 4 higher derivative gravity. This class of theories has a nice feature of renormalizability, so that perturbative calculations are feasible. There are also finite N = 4 supersymmetric conformal supergravity theories. This possibility is particularly attractive. Einstein's gravity is obtained in a natural way as an effective low-energy theory. The N= 1 supersymmetric version of the theory has a natural higher dimensional interpretation due to V.I. Ogievetsky and E.S. Sokatchev, which involves embedding our curved Minkowski spacetime manifold into flat eight-dimensional space. Assuming that a variant of the finite N = 4 theory also admits a similar interpretation, this may eventually allow one to construct consistent quantum theory of gravity. We argue, however, that, even though future gravity theory will probably use higher dimensions as construction scaffolds, its physical content and meaning should refer to four dimensions, where an observer lives
The Juno Gravity Science Instrument
Asmar, Sami W.; Bolton, Scott J.; Buccino, Dustin R.; Cornish, Timothy P.; Folkner, William M.; Formaro, Roberto; Iess, Luciano; Jongeling, Andre P.; Lewis, Dorothy K.; Mittskus, Anthony P.; Mukai, Ryan; Simone, Lorenzo
2017-11-01
The Juno mission's primary science objectives include the investigation of Jupiter interior structure via the determination of its gravitational field. Juno will provide more accurate determination of Jupiter's gravity harmonics that will provide new constraints on interior structure models. Juno will also measure the gravitational response from tides raised on Jupiter by Galilean satellites. This is accomplished by utilizing Gravity Science instrumentation to support measurements of the Doppler shift of the Juno radio signal by NASA's Deep Space Network at two radio frequencies. The Doppler data measure the changes in the spacecraft velocity in the direction to Earth caused by the Jupiter gravity field. Doppler measurements at X-band (˜ 8 GHz) are supported by the spacecraft telecommunications subsystem for command and telemetry and are used for spacecraft navigation as well as Gravity Science. The spacecraft also includes a Ka-band (˜ 32 GHz) translator and amplifier specifically for the Gravity Science investigation contributed by the Italian Space Agency. The use of two radio frequencies allows for improved accuracy by removal of noise due to charged particles along the radio signal path.
Self Completeness of Einstein Gravity
Dvali, Gia
2010-01-01
We argue, that in Einsteinian gravity the Planck length is the shortest length of nature, and any attempt of resolving trans-Planckian physics bounces back to macroscopic distances due to black hole formation. In Einstein gravity trans-Planckian propagating quantum degrees of freedom cannot exist, instead they are equivalent to the classical black holes that are fully described by lighter infra-red degrees of freedom and give exponentially-soft contribution into the virtual processes. Based on this property we argue that pure-Einstein (super)gravity and its high-dimensional generalizations are self-complete in deep-UV, but not in standard Wilsonian sense. We suggest that certain strong-coupling limit of string theory is built-in in pure Einstein gravity, whereas the role of weakly-coupled string theory limit is to consistently couple gravity to other particle species, with their number being set by the inverse string coupling. We also discuss some speculative ideas generalizing the notion of non-Wilsonian sel...
Scale-invariant gravity: geometrodynamics
International Nuclear Information System (INIS)
Anderson, Edward; Barbour, Julian; Foster, Brendan; Murchadha, Niall O
2003-01-01
We present a scale-invariant theory, conformal gravity, which closely resembles the geometrodynamical formulation of general relativity (GR). While previous attempts to create scale-invariant theories of gravity have been based on Weyl's idea of a compensating field, our direct approach dispenses with this and is built by extension of the method of best matching w.r.t. scaling developed in the parallel particle dynamics paper by one of the authors. In spatially compact GR, there is an infinity of degrees of freedom that describe the shape of 3-space which interact with a single volume degree of freedom. In conformal gravity, the shape degrees of freedom remain, but the volume is no longer a dynamical variable. Further theories and formulations related to GR and conformal gravity are presented. Conformal gravity is successfully coupled to scalars and the gauge fields of nature. It should describe the solar system observations as well as GR does, but its cosmology and quantization will be completely different
Gravity gradient preprocessing at the GOCE HPF
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.
Generalized uncertainty principle, quantum gravity and Horava-Lifshitz gravity
International Nuclear Information System (INIS)
Myung, Yun Soo
2009-01-01
We investigate a close connection between generalized uncertainty principle (GUP) and deformed Horava-Lifshitz (HL) gravity. The GUP commutation relations correspond to the UV-quantum theory, while the canonical commutation relations represent the IR-quantum theory. Inspired by this UV/IR quantum mechanics, we obtain the GUP-corrected graviton propagator by introducing UV-momentum p i =p 0i (1+βp 0 2 ) and compare this with tensor propagators in the HL gravity. Two are the same up to p 0 4 -order.
Dilaton gravity, Poisson sigma models and loop quantum gravity
International Nuclear Information System (INIS)
Bojowald, Martin; Reyes, Juan D
2009-01-01
Spherically symmetric gravity in Ashtekar variables coupled to Yang-Mills theory in two dimensions and its relation to dilaton gravity and Poisson sigma models are discussed. After introducing its loop quantization, quantum corrections for inverse triad components are shown to provide a consistent deformation without anomalies. The relation to Poisson sigma models provides a covariant action principle of the quantum-corrected theory with effective couplings. Results are also used to provide loop quantizations of spherically symmetric models in arbitrary D spacetime dimensions.
Dualities and emergent gravity: Gauge/gravity duality
de Haro, Sebastian
2017-08-01
In this paper I develop a framework for relating dualities and emergence: two notions that are close to each other but also exclude one another. I adopt the conception of duality as 'isomorphism', from the physics literature, cashing it out in terms of three conditions. These three conditions prompt two conceptually different ways in which a duality can be modified to make room for emergence; and I argue that this exhausts the possibilities for combining dualities and emergence (via coarse-graining). I apply this framework to gauge/gravity dualities, considering in detail three examples: AdS/CFT, Verlinde's scheme, and black holes. My main point about gauge/gravity dualities is that the theories involved, qua theories of gravity, must be background-independent. I distinguish two senses of background-independence: (i) minimalistic and (ii) extended. I argue that the former is sufficiently strong to allow for a consistent theory of quantum gravity; and that AdS/CFT is background-independent on this account; while Verlinde's scheme best fits the extended sense of background-independence. I argue that this extended sense should be applied with some caution: on pain of throwing the baby (general relativity) out with the bath-water (extended background-independence). Nevertheless, it is an interesting and potentially fruitful heuristic principle for quantum gravity theory construction. It suggests some directions for possible generalisations of gauge/gravity dualities. The interpretation of dualities is discussed; and the so-called 'internal' vs. 'external' viewpoints are articulated in terms of: (i) epistemic and metaphysical commitments; (ii) parts vs. wholes. I then analyse the emergence of gravity in gauge/gravity dualities in terms of the two available conceptualisations of emergence; and I show how emergence in AdS/CFT and in Verlinde's scenario differ from each other. Finally, I give a novel derivation of the Bekenstein-Hawking black hole entropy formula based on
Equation of state in the presence of gravity
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.
Partial gravity - Human impacts on facility design
Capps, Stephen; Moore, Nathan
1990-01-01
Partial gravity affects the body differently than earth gravity and microgravity environments. The main difference from earth gravity is human locomotion; while the main dfference from microgravity is the specific updown orientation and reach envelopes which increase volume requirements. Much data are available on earth gravity and microgravity design; however, very little information is available on human reactions to reduced gravity levels in IVA situations (without pressure suits). Therefore, if humans commit to permanent lunar habitation, much research should be conducted in the area of partial gravity effects on habitat design.
Nucleate pool boiling: High gravity to reduced gravity; liquid metals to cryogens
Merte, Herman, Jr.
1988-01-01
Requirements for the proper functioning of equipment and personnel in reduced gravity associated with space platforms and future space station modules introduce unique problems in temperature control; power generation; energy dissipation; the storage, transfer, control and conditioning of fluids; and liquid-vapor separation. The phase change of boiling is significant in all of these. Although both pool and flow boiling would be involved, research results to date include only pool boiling because buoyancy effects are maximized for this case. The effective application of forced convection boiling heat transfer in the microgravity of space will require a well grounded and cogent understanding of the mechanisms involved. Experimental results are presented for pool boiling from a single geometrical configuration, a flat surface, covering a wide range of body forces from a/g = 20 to 1 to a/g = 0 to -1 for a cryogenic liquid, and from a/g = 20 to 1 for water and a liquid metal. Similarities in behavior are noted for these three fluids at the higher gravity levels, and may reasonably be expected to continue at reduced gravity levels.
Dynamics of flexural gravity waves: from sea ice to Hawking radiation and analogue gravity.
Das, S; Sahoo, T; Meylan, M H
2018-01-01
The propagation of flexural gravity waves, routinely used to model wave interaction with sea ice, is studied, including the effect of compression and current. A number of significant and surprising properties are shown to exist. The occurrence of blocking above a critical value of compression is illustrated. This is analogous to propagation of surface gravity waves in the presence of opposing current and light wave propagation in the curved space-time near a black hole, therefore providing a novel system for studying analogue gravity. Between the blocking and buckling limit of the compressive force, the dispersion relation possesses three positive real roots, contrary to an earlier observation of having a single positive real root. Negative energy waves, in which the phase and group velocity point in opposite directions, are also shown to exist. In the presence of an opposing current and certain critical ranges of compressive force, the second blocking point shifts from the positive to the negative branch of the dispersion relation. Such a shift is known as the Hawking effect from the analogous behaviour in the theory of relativity which leads to Hawking radiation. The theory we develop is illustrated with simulations of linear waves in the time domain.
Testing chameleon gravity with the Coma cluster
International Nuclear Information System (INIS)
Terukina, Ayumu; Yamamoto, Kazuhiro; Lombriser, Lucas; Bacon, David; Koyama, Kazuya; Nichol, Robert C.
2014-01-01
We propose a novel method to test the gravitational interactions in the outskirts of galaxy clusters. When gravity is modified, this is typically accompanied by the introduction of an additional scalar degree of freedom, which mediates an attractive fifth force. The presence of an extra gravitational coupling, however, is tightly constrained by local measurements. In chameleon modifications of gravity, local tests can be evaded by employing a screening mechanism that suppresses the fifth force in dense environments. While the chameleon field may be screened in the interior of the cluster, its outer region can still be affected by the extra force, introducing a deviation between the hydrostatic and lensing mass of the cluster. Thus, the chameleon modification can be tested by combining the gas and lensing measurements of the cluster. We demonstrate the operability of our method with the Coma cluster, for which both a lensing measurement and gas observations from the X-ray surface brightness, the X-ray temperature, and the Sunyaev-Zel'dovich effect are available. Using the joint observational data set, we perform a Markov chain Monte Carlo analysis of the parameter space describing the different profiles in both the Newtonian and chameleon scenarios. We report competitive constraints on the chameleon field amplitude and its coupling strength to matter. In the case of f(R) gravity, corresponding to a specific choice of the coupling, we find an upper bound on the background field amplitude of |f R0 | < 6 × 10 −5 , which is currently the tightest constraint on cosmological scales
Testing chameleon gravity with the Coma cluster
Energy Technology Data Exchange (ETDEWEB)
Terukina, Ayumu; Yamamoto, Kazuhiro [Department of Physical Science, Hiroshima University, Higashi-Hiroshima, Kagamiyama 1-3-1, 739-8526 (Japan); Lombriser, Lucas; Bacon, David; Koyama, Kazuya; Nichol, Robert C., E-mail: telkina@theo.phys.sci.hiroshima-u.ac.jp, E-mail: lucas.lombriser@port.ac.uk, E-mail: kazuhiro@hiroshima-u.ac.jp, E-mail: david.bacon@port.ac.uk, E-mail: kazuya.koyama@port.ac.uk, E-mail: bob.nichol@port.ac.uk [Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Portsmouth, PO1 3FX (United Kingdom)
2014-04-01
We propose a novel method to test the gravitational interactions in the outskirts of galaxy clusters. When gravity is modified, this is typically accompanied by the introduction of an additional scalar degree of freedom, which mediates an attractive fifth force. The presence of an extra gravitational coupling, however, is tightly constrained by local measurements. In chameleon modifications of gravity, local tests can be evaded by employing a screening mechanism that suppresses the fifth force in dense environments. While the chameleon field may be screened in the interior of the cluster, its outer region can still be affected by the extra force, introducing a deviation between the hydrostatic and lensing mass of the cluster. Thus, the chameleon modification can be tested by combining the gas and lensing measurements of the cluster. We demonstrate the operability of our method with the Coma cluster, for which both a lensing measurement and gas observations from the X-ray surface brightness, the X-ray temperature, and the Sunyaev-Zel'dovich effect are available. Using the joint observational data set, we perform a Markov chain Monte Carlo analysis of the parameter space describing the different profiles in both the Newtonian and chameleon scenarios. We report competitive constraints on the chameleon field amplitude and its coupling strength to matter. In the case of f(R) gravity, corresponding to a specific choice of the coupling, we find an upper bound on the background field amplitude of |f{sub R0}| < 6 × 10{sup −5}, which is currently the tightest constraint on cosmological scales.
Enhanced Gravity Tractor Technique for Planetary Defense
Mazanek, Daniel D.; Reeves, David M.; Hopkins, Joshua B.; Wade, Darren W.; Tantardini, Marco; Shen, Haijun
2015-01-01
Given sufficient warning time, Earth-impacting asteroids and comets can be deflected with a variety of different "slow push/pull" techniques. The gravity tractor is one technique that uses the gravitational attraction of a rendezvous spacecraft to the impactor and a low-thrust, high-efficiency propulsion system to provide a gradual velocity change and alter its trajectory. An innovation to this technique, known as the Enhanced Gravity Tractor (EGT), uses mass collected in-situ to augment the mass of the spacecraft, thereby greatly increasing the gravitational force between the objects. The collected material can be a single boulder, multiple boulders, regolith or a combination of different sources. The collected mass would likely range from tens to hundreds of metric tons depending on the size of the impactor and warning time available. Depending on the propulsion system's capability and the mass collected, the EGT approach can reduce the deflection times by a factor of 10 to 50 or more, thus reducing the deflection times of several decades to years or less and overcoming the main criticism of the traditional gravity tractor approach. Additionally, multiple spacecraft can orbit the target in formation to provide the necessary velocity change and further reduce the time needed by the EGT technique to divert hazardous asteroids and comets. The robotic segment of NASA's Asteroid Redirect Mission (ARM) will collect a multi-ton boulder from the surface of a large Near-Earth Asteroid (NEA) and will provide the first ever demonstration of the EGT technique and validate one method of collecting in-situ mass on an asteroid of hazardous size.
Energy Technology Data Exchange (ETDEWEB)
Herrmann, Enrico [Walter Burke Institute for Theoretical Physics, California Institute of Technology,Pasadena, CA 91125 (United States); Trnka, Jaroslav [Center for Quantum Mathematics and Physics (QMAP),Department of Physics, University of California,Davis, CA 95616 (United States)
2016-11-22
We study on-shell diagrams for gravity theories with any number of supersymmetries and find a compact Grassmannian formula in terms of edge variables of the graphs. Unlike in gauge theory where the analogous form involves only dlog-factors, in gravity there is a non-trivial numerator as well as higher degree poles in the edge variables. Based on the structure of the Grassmannian formula for N=8 supergravity we conjecture that gravity loop amplitudes also possess similar properties. In particular, we find that there are only logarithmic singularities on cuts with finite loop momentum and that poles at infinity are present, in complete agreement with the conjecture presented in http://dx.doi.org/10.1007/JHEP06(2015)202.
Universality of quantum gravity corrections.
Das, Saurya; Vagenas, Elias C
2008-11-28
We show that the existence of a minimum measurable length and the related generalized uncertainty principle (GUP), predicted by theories of quantum gravity, influence all quantum Hamiltonians. Thus, they predict quantum gravity corrections to various quantum phenomena. We compute such corrections to the Lamb shift, the Landau levels, and the tunneling current in a scanning tunneling microscope. We show that these corrections can be interpreted in two ways: (a) either that they are exceedingly small, beyond the reach of current experiments, or (b) that they predict upper bounds on the quantum gravity parameter in the GUP, compatible with experiments at the electroweak scale. Thus, more accurate measurements in the future should either be able to test these predictions, or further tighten the above bounds and predict an intermediate length scale between the electroweak and the Planck scale.
Experimental tests of relativistic gravity
International Nuclear Information System (INIS)
Damour, Thibault
2000-01-01
The confrontation between Einstein's gravitation theory and experimental results, notably binary pulsar data, is summarized and its significance discussed. Experiment and theory agree at the 10 -3 level or better. All the basic structures of Einstein's theory (coupling of gravity matter; propagation and self-interaction of the gravitational field, including in strong field conditions) have been verified. However, the theoretical possibility that scalar couplings be naturally driven toward zero by the cosmological expansion suggests that the present agreement between Einstein's theory and experiment might be compatible with the existence of a long-range scalar contribution to gravity (such as the dilation field, or a moduli field, of string theory). This provides a new theoretical paradigm, and new motivations for improving the experimental tests of gravity
Rheological measurements in reduced gravity
Bakhtiyarov, Sayavur I.; Overfelt, Ruel A.
1999-01-01
Rheology of fluidized beds and settling suspensions were studied experimentally in a series of reduced gravity parabolic flights aboard NASA's KC-135 aircraft. Silica sands of two different size distributions were fluidized by air. The slurries were made using silica sand and Glycerol solution. The experimental set up incorporated instrumentation to measure the air flow rate, the pressure drop and the apparent viscosity of the fluidized sand and sand suspensions at a wide range of the shear rates. The fluidization chamber and container had transparent walls to allow visualization of the structure changes involved in fluidization and in Couette flow in reduced gravity. Experiments were performed over a broad range of gravitational accelerations including microgravity and double gravity conditions. The results of the flight and ground experiments reveal significant differences in overall void fraction and hence in the apparent viscosity of fluidized sand and sand suspensions under microgravity as compared to one-g conditions.
Studies in gravity and supergravity
International Nuclear Information System (INIS)
Castellani, L.
1981-01-01
The canonical treatment for theories with local gauge invariances is reviewed and an algorithm for the construction of all the gauge generators is found. This algorithm is then applied to Yang-Mills theories and to (metric) gravity. The first part of the work is concluded with a complete treatment of hamiltonian first order tetrad gravity. In the second part, the geometrical aspects of (super)gravity theories are concentrated on. After an interlude with path integrals in curved space (equivalence is shown with canonical quantization), N = 2 supergravity in superspace, and conformal supergravity in the group manifold scenario are studied. A progress report is added, regarding a study on higher divergences in quantum field theory
Gravity with Intermediate Goods Trade
Directory of Open Access Journals (Sweden)
Sujin Jang
2017-12-01
Full Text Available This paper derives the gravity equation with intermediate goods trade. We extend a standard monopolistic competition model to incorporate intermediate goods trade, and show that the gravity equation with intermediates trade is identical to the one without it except in that gross output should be used as the output measure instead of value added. We also show that the output elasticity of trade is significantly underestimated when value added is used as the output measure. This implies that with the conventional gravity equation, the contribution of output growth can be substantially underestimated and the role of trade costs reduction can be exaggerated in explaining trade expansion, as we demonstrate for the case of Korea's trade growth between 1995 and 2007.
Lorentzian wormholes in Lovelock gravity
International Nuclear Information System (INIS)
Dehghani, M. H.; Dayyani, Z.
2009-01-01
In this paper, we introduce the n-dimensional Lorentzian wormhole solutions of third order Lovelock gravity. In contrast to Einstein gravity and as in the case of Gauss-Bonnet gravity, we find that the wormhole throat radius r 0 has a lower limit that depends on the Lovelock coefficients, the dimensionality of the spacetime, and the shape function. We study the conditions of having normal matter near the throat, and find that the matter near the throat can be normal for the region r 0 ≤r≤r max , where r max depends on the Lovelock coefficients and the shape function. We also find that the third order Lovelock term with negative coupling constant enlarges the radius of the region of normal matter, and conclude that the higher order Lovelock terms with negative coupling constants enlarge the region of normal matter near the throat.
Observational tests of modified gravity
International Nuclear Information System (INIS)
Jain, Bhuvnesh; Zhang Pengjie
2008-01-01
Modifications of general relativity provide an alternative explanation to dark energy for the observed acceleration of the Universe. Modified gravity theories have richer observational consequences for large-scale structures than conventional dark energy models, in that different observables are not described by a single growth factor even in the linear regime. We examine the relationships between perturbations in the metric potentials, density and velocity fields, and discuss strategies for measuring them using gravitational lensing, galaxy cluster abundances, galaxy clustering/dynamics, and the integrated Sachs-Wolfe effect. We show how a broad class of gravity theories can be tested by combining these probes. A robust way to interpret observations is by constraining two key functions: the ratio of the two metric potentials, and the ratio of the gravitational 'constant' in the Poisson equation to Newton's constant. We also discuss quasilinear effects that carry signatures of gravity, such as through induced three-point correlations. Clustering of dark energy can mimic features of modified gravity theories and thus confuse the search for distinct signatures of such theories. It can produce pressure perturbations and anisotropic stresses, which break the equality between the two metric potentials even in general relativity. With these two extra degrees of freedom, can a clustered dark energy model mimic modified gravity models in all observational tests? We show with specific examples that observational constraints on both the metric potentials and density perturbations can in principle distinguish modifications of gravity from dark energy models. We compare our result with other recent studies that have slightly different assumptions (and apparently contradictory conclusions).
The optimal shape of an object for generating maximum gravity field at a given point in space
Wang, Xiao-Wei; Su, Yue
2014-01-01
How can we design the shape of an object, in the framework of Newtonian gravity, in order to generate maximum gravity at a given point in space? In this work we present a study on this interesting problem. We obtain compact solutions for all dimensional cases. The results are commonly characterized by a simple "physical" feature that any mass element unit on the object surface generates the same gravity strength at the considered point, in the direction along the rotational symmetry axis.
Acoustic-gravity nonlinear structures
Directory of Open Access Journals (Sweden)
D. Jovanović
2002-01-01
Full Text Available A catalogue of nonlinear vortex structures associated with acoustic-gravity perturbations in the Earth's atmosphere is presented. Besides the previously known Kelvin-Stewart cat's eyes, dipolar and tripolar structures, new solutions having the form of a row of counter-rotating vortices, and several weakly two-dimensional vortex chains are given. The existence conditions for these nonlinear structures are discussed with respect to the presence of inhomogeneities of the shear flows. The mode-coupling mechanism for the nonlinear generation of shear flows in the presence of linearly unstable acoustic-gravity waves, possibly also leading to intermittency and chaos, is presented.
Wenjie Tian, David; Booth, Ivan
2016-02-01
According to Lovelock’s theorem, the Hilbert-Einstein and the Lovelock actions are indistinguishable from their field equations. However, they have different scalar-tensor counterparts, which correspond to the Brans-Dicke and the Lovelock-Brans-Dicke (LBD) gravities, respectively. In this paper the LBD model of alternative gravity with the Lagrangian density {{L}}{LBD}=\\frac{1}{16π }≤ft[φ ≤ft(R+\\frac{a}{\\sqrt{-g}}{}*{RR}+b{ G }\\right)-\\frac{{ω }{{L}}}{φ }{{{\
Airborne Gravity: NGS' Gravity Data for MS02 (2016)
National Oceanic and Atmospheric Administration, Department of Commerce — Airborne gravity data over southern Arizona and New Mexico overlapping into Mexico collected in 2016 over 2 surveys, AZ16-1 and AZ16-2. This data set is part of the...
Einstein's Gravity and Dark Energy/Matter
Sarfatti, J
2003-01-01
Should Einstein's general relativity be quantized in the usual way even though it is not renormalizable the way the spin 1/2 lepto-quark - spin 1 gauge force boson local field theories are? Condensed matter theorists using P.W. Anderson's "More is different" approach, consistent with Andrei Sakharov's idea of "metric elasticity" with gravity emergent out of quantum electrodynamic zero point vacuum fluctuations, is the approach I take in this paper. The QED vacuum in globally-flat Minkowski space-time is unstable due to exchange of virtual photons between virtual electrons and positron "holes" near the -mc2 Fermi surface well inside the 2mc2 energy gap. This results in a non-perturbative emergence of both Einstein's gravity and a unified dark energy/dark matter w = -1 exotic vacuum zero point fluctuation field controlled by the local macro-quantum vacuum coherent field. The latter is a Bose-Einstein condensate of virtual off-mass-shell bound electron-positron pairs. The dark matter exotic vacuum phase with pos...
Modeling of the Earth's gravity field using the New Global Earth Model (NEWGEM)
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 Data for California and Southern Nevada
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity data (88,514 records) were compiled largely from a state-wide regional gravity study program organized by the California Division of Mines and Geology in...
Gravity Data for Indiana (300 records compiled)
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity data (300 records) were compiled by Purdue University. This data base was received in February 1993. Principal gravity parameters include Free-air...
Gravity Data for the Greater Portland Area
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (1,522 records) were compiled by the Portland State University. This data base was received in August 1990. Principal gravity parameters...
Steps towards a quantum theory of gravity
International Nuclear Information System (INIS)
Unruh, W.G.
1984-01-01
The paper concerns simple experiments in quantum gravity. 'Schroedinger's Cat' experiment to test semiclassical quantum gravity, and the gravitational single slit experiment to demonstrate the wave-particle duality for photons, are both described and discussed. (U.K.)
Idaho Batholith Study Area Gravity Data
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (32,152 records) were compiled by the U. S. Geological Survey. This data base was received on February 23, 1993. Principal gravity...
Nevada Isostatic Residual Gravity Over Basement
National Oceanic and Atmospheric Administration, Department of Commerce — This study of gravity data from Nevada is part of a statewide analysis of mineral resources. The main objective of the gravity study were: 1) to infer the structure...
SEG US Bouguer Gravity Anomaly Grid
National Oceanic and Atmospheric Administration, Department of Commerce — The SEG gravity data are the product of the ad hoc Gravity Anomaly Map (GAM) Committee, sponsored by the Society of Exploration Geophysicists (SEG) and the U.S....
Wisconsin Gravity Data for the Rhinelader Area
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (195 records) were compiled by Barbara Eckstein. This data base was received in January 1987. Principal gravity parameters include Free-Air...
Gravity Data For The State of Ohio
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (6,591 records) were compiled by the U. S. Geological Survey. This data base was received on February 23, 1993. Principal gravity parameters...
Wisconsin Gravity Data for the Marshfield Area
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (8388 records) were compiled by Professor Ervin. This data base was received in April 1993. Principal gravity parameters include Free-Air...
Energy Technology Data Exchange (ETDEWEB)
Bejarano, Cecilia; Guzman, Maria Jose [Instituto de Astronomia y Fisica del Espacio (IAFE, CONICET-UBA), Buenos Aires (Argentina); Ferraro, Rafael [Instituto de Astronomia y Fisica del Espacio (IAFE, CONICET-UBA), Buenos Aires (Argentina); Universidad de Buenos Aires, Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Buenos Aires (Argentina)
2015-02-01
Null tetrads are shown to be a valuable tool in teleparallel theories of modified gravity. We use them to prove that Kerr geometry remains a solution for a wide family of f(T) theories of gravity. (orig.)
Wisconsin Gravity Data for the Prentice Area
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (898 records) were compiled by Professor Ervin. This data base was received in January 1987. Principal gravity parameters include Free-Air...
Gravity Data for the State of Nevada
National Oceanic and Atmospheric Administration, Department of Commerce — Gravity data for the entire state of Nevada and adjacent parts of California, Utah, and Arizona are presented. About 80,000 gravity stations were compiled primarily...
Gravity Data For The State of Utah
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (41,960 records) were compiled by the U. S. Geological Survey. This data base was received on February 23, 1993. Principal gravity...
Wisconsin Gravity Data for the Sawyers Area
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (3814 records) were compiled by Professor Ervin. This data base was received in April 1993. Principal gravity parameters include Free-Air...
Gravity Data for portions of Ohio
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (1,037 records) were compiled by Doctor Stierman. This data base was received in June 1992. Principal gravity parameters include Free-Air...
Maine Offshore Free-air Anomaly Gravity
National Oceanic and Atmospheric Administration, Department of Commerce — The gravity station data (5,363 records) were compiled by the U. S. Geological Survey. This data base was received on February 23, 1993. Principal gravity parameters...