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1

Modeling of Zero Gravity Venting.

National Technical Information Service (NTIS)

The venting of cylindrical containers partially filled with initially saturated liquids was conducted under zero gravity conditions and compared with an analytical model which determined the effect of interfacial mass transfer on the ullage pressure respo...

H. Merte

1984-01-01

2

Zero-Gravity Maneuver Instruments and Instrumentation.

National Technical Information Service (NTIS)

The type ARU-2B/A Attitude Director Indicator (ADI) system was evaluated as a pilot aid in flying a JC-131B aircraft on a ballistic trajectory to produce a zero- or reduced-gravity field. To provide an unburdened display to the pilot, all information nece...

B. C. Dixon

1966-01-01

3

Modeling of Zero Gravity Venting: Studies of Two-Phase Heat Transfer under Reduced Gravity.

National Technical Information Service (NTIS)

The objective is to predict the pressure response of a saturated liquid-vapor system when undergoing a venting or depressurization process in zero gravity at low vent rates. An experimental investigation of the venting of cylindrical containers partially ...

H. Merte

1986-01-01

4

The use of Skylark for near zero gravity experiments

The paper describes the Skylark family of sounding rockets which consists of versatile vehicles for nominally zero gravity experiments giving up to 6.5 min. with a residual acceleration of less than 10 to the -4th g. Two particular motor combinations and their observation times are discussed and the vehicle design features and options are described. The payload consists of experiments

J. B. Hilton

1976-01-01

5

The Zero-Hamiltonian Problem in a Toy Gravity Model

NASA Astrophysics Data System (ADS)

In this work we present new results on the analysis of the zero-Hamiltonian problem in one-dimensional gravity working with generic gauge fixings, As an application of the methods developed by Henneaux et al. and Gitman et al. We obtain systematically the symplectic structures, effective Hamiltonians and reduced phase-space Physics, as an improvement on previous works on the subject.

Delfrate, D. G.; Devecchi, F. P.; França, J. R.; Marchioro, D. F.

2003-03-01

6

Sediment-transport (wind) experiments in zero-gravity

NASA Astrophysics Data System (ADS)

The carousel wind tunnel (CWT) can be a significant tool for the determination of the nature and magnitude of interparticlar forces at threshold of motion. By altering particle and drum surface electrical properties and/or by applying electric potential difference across the inner and outer drums, it should be possible to separate electrostatic effects from other forces of cohesion. Besides particle trajectory and bedform analyses, suggestions for research include particle aggregation in zero and sub-gravity environments, effect of suspension-saltation ratio on soil abrasion, and the effects of shear and shearfree turbulence on particle aggregation as applied to evolution of solar nebula.

Iverson, J.; Gillette, D.; Greeley, R.; Lee, J.; MacKinnon, I.; Marshall, J.; Nickling, W.; Werner, B.; White, B.; Williams, S.

1986-05-01

7

Ball Lightning in Zero Gravity in the Laboratory

NASA Astrophysics Data System (ADS)

We have created balls of orange plasma in atmospheric - pressure air that survive for over 1/2 second without power input. The technique used was to create a pulsed horizontal electric arc in a zero - gravity environment using 6 neon - sign transformers in parallel, each producing 16,000 V at 60 mA. The zero - gravity environment reduces heat losses by reducing thermal convection, creating a larger ball. Previous work (1) suggests that the ball lifetime scales as the square of the ball radius. The balls were photographed after power turnoff with a high - speed 16 mm movie camera. Movies of the balls being formed and decaying will be shown. We suggest that there are several other forms of ball lightning (2). 1.Igor Alexeff et. al. International Conference On Plasma Science, Jeju, Korea, June 2-5, 2003, Conference Record, p 254. 2. Igor Alexeff and Mark Rader, IEEE Transactions on Plasma Science, Vol. 20, No. 6, Dec. 1992, pp.669-671. Igor Alexeff and Mark Rader, Fusion Technology, Vol. 27, May 1995, p. 271.

Alexeff, Igor; Parameswaran, Sriram; Grace, Michael

2004-11-01

8

Design of gravity balancing leg orthosis using non-zero free length springs

For gait retraining of stroke victims, there is a need for rehabilitation devices, which can support the weight of leg during walking. Machines that gravity balances the leg are potentially useful as rehabilitation devices. This paper presents gravity balancing designs for two and three links planar chains using non-zero free length springs. Non-zero free length springs are those springs which

Abhishek Agrawal; Sunil K. Agrawal

2005-01-01

9

Zero Gravity Cryogenic Vent System Concepts for Upper Stages

NASA Astrophysics Data System (ADS)

The capability to vent in zero gravity without resettling is a technology need that involves practically all uses of sub-critical cryogenics in space. Venting without resettling would extend cryogenic orbital transfer vehicle capabilities. However, the lack of definition regarding liquid/ullage orientation coupled with the somewhat random nature of the thermal stratification and resulting pressure rise rates, lead to significant technical challenges. Typically a zero gravity vent concept, termed a thermodynamic vent system (TVS), consists of a tank mixer to destratify the propellant, combined with a Joule-Thomson (J-T) valve to extract thermal energy from the propellant. Marshall Space Flight Center's (MSFC's) Multipurpose Hydrogen Test Bed (MHTB) was used to test both spray bar and axial jet TVS concepts. The axial jet system consists of a recirculation pump heat exchanger unit. The spray bar system consists of a recirculation pump, a parallel flow concentric tube, heat exchanger, and a spray bar positioned close to the longitudinal axis of the tank. The operation of both concepts is similar. In the mixing mode, the recirculation pump withdraws liquid from the tank and sprays it into the tank liquid, ullage, and exposed tank surfaces. When energy extraction is required, a small portion of the recirculated liquid is passed sequentially through the J-T expansion valve, the heat exchanger, and is vented overboard. The vented vapor cools the circulated bulk fluid, thereby removing thermal energy and reducing tank pressure. The pump operates alone, cycling on and off, to destratify the tank liquid and ullage until the liquid vapor pressure reaches the lower set point. At that point, the J-T valve begins to cycle on and off with the pump. Thus, for short duration missions, only the mixer may operate, thus minimizing or even eliminating boil-off losses. TVS performance testing demonstrated that the spray bar was effective in providing tank pressure control within a 6.89 kPa (1psi) band for fill levels of 90%, 50%, and 25%. Complete destratification of the liquid and ullage was achieved at these fill levels. The axial jet was effective in providing tank pressure control within the same pressure control band at the 90% fill level. However, at the 50% level, the system reached a point at which it was unable to extract enough energy to keep up with the heat leak into the tank. Due to a hardware problem, the recirculation pump operated well below the axial jet design flow rate. Therefore, it is likely that the performance of the axial jet would have improved had the pump operated at the proper flow rate. A CFD model is being used to determine if the desired axial jet performance would be achieved if a higher pump flow rate were available. Testing conducted thus far has demonstrated that both TVS concepts can be effective in destratifying a propellant tank, rejecting stored heat energy, and thus, controlling tank pressure.

Ravex, Alain; Flachbart, Robin; Holt, Barney

10

Two-phase computer codes for zero-gravity applications

This paper discusses the problems existing in the development of computer codes which can analyze the thermal-hydraulic behavior of two-phase fluids especially in low gravity nuclear reactors. The important phenomenon affecting fluid flow and heat transfer in reduced gravity is discussed. The applicability of using existing computer codes for space applications is assessed. Recommendations regarding the use of existing earth based fluid flow and heat transfer correlations are made and deficiencies in these correlations are identified.

Krotiuk, W.J.

1986-10-01

11

Comprehensive solution to the cosmological constant, zero-point energy, and quantum gravity problems

NASA Astrophysics Data System (ADS)

We present a solution to the cosmological constant, the zero-point energy, and the quantum gravity problems within a single comprehensive framework. We show that in quantum theories of gravity in which the zero-point energy density of the gravitational field is well-defined, the cosmological constant and zero-point energy problems solve each other by mutual cancellation between the cosmological constant and the matter and gravitational field zero-point energy densities. Because of this cancellation, regulation of the matter field zero-point energy density is not needed, and thus does not cause any trace anomaly to arise. We exhibit our results in two theories of gravity that are well-defined quantum-mechanically. Both of these theories are locally conformal invariant, quantum Einstein gravity in two dimensions and Weyl-tensor-based quantum conformal gravity in four dimensions (a fourth-order derivative quantum theory of the type that Bender and Mannheim have recently shown to be ghost-free and unitary). Central to our approach is the requirement that any and all departures of the geometry from Minkowski are to be brought about by quantum mechanics alone. Consequently, there have to be no fundamental classical fields, and all mass scales have to be generated by dynamical condensates. In such a situation the trace of the matter field energy-momentum tensor is zero, a constraint that obliges its cosmological constant and zero-point contributions to cancel each other identically, no matter how large they might be. In our approach quantization of the gravitational field is caused by its coupling to quantized matter fields, with the gravitational field not needing any independent quantization of its own. With there being no a priori classical curvature, one does not have to make it compatible with quantization.

Mannheim, Philip D.

2011-03-01

12

Transient Boiling Heat Transfer in Saturated Liquid Nitrogen and F113 at Standard and Zero Gravity.

National Technical Information Service (NTIS)

Transient and steady state nucleate boiling in saturated LN2 and F113 at standard and near zero gravity conditions were investigated for the horizontal up, vertical and horizontal down orientations of the heating surface. Two distinct regimes of heat tran...

E. Oker H. Merte

1973-01-01

13

Zero Gravity Aircraft Testing of a Prototype Portable Fire Extinguisher for Use in Spacecraft

NASA Astrophysics Data System (ADS)

For the past five years ADA Technologies has been developing a portable fire extinguisher (PFE) for use in microgravity environments. This technology uses fine water mist (FWM) to effectively and efficiently extinguish fires representative of spacecraft hazards. Recently the FWM PFE was flown on a Zero-G (reduced gravity) aircraft to validate the performance of the technology in a microgravity environment. Test results demonstrated that droplet size distributions generated in the reduced gravity environment were in the same size range as data collected during normal gravity (1-g) discharges from the prototype PFE. Data taken in an obscured test configuration showed that the mist behind the obstacle was more dense in the low-g environment when compared to 1-g discharges. The mist behind the obstacle tended to smaller droplet sizes in both the low-g and 1-g test conditions.

Butz, J.; Carriere, T.; Abbud-Madrid, A.; Easton, J.

2012-01-01

14

Digital holographic microscopy for the cytomorphological imaging of cells under zero gravity

NASA Astrophysics Data System (ADS)

Digital holographic microscopy (DHM) has been gaining interest from cell biology community because of its label free nature and quantitative phase signal output. Besides, fast shutter time, image reconstruction by numerical propagation of the wave fields, and numerical compensation of the aberrations are other intrinsic advantages of this technique that can be explored for harsh imaging conditions. In the frame of this work, a transmission type DHM is developed with a decoupled epifluorescence microscopy mode for cytomorphological monitoring under zero gravity and hyper gravity. With the implemented automatic post processing routines, real time observation of the cell morphology is proven to be feasible under the influence of mechanical disturbances of zero gravity platforms. Post processing of holograms is composed from dynamic numerical compensation of holograms, robust autofocusing and phase image registration. Experiments on live myoblast cells are carried out on two different platforms; random positioning machine (RPM), a ground base microgravity simulation platform, and parabolic flight campaign (PFC), a fixed wing plane flight providing short durations of alternating gravity conditions. Results show clear perinuclear phase increase. During seconds scale microgravity exposure, measurable scale morphological modifications are observed with the accumulated effect of repetitive exposures and short breaks.

Toy, M. Fatih; Richard, Stephane; Kühn, Jonas; Franco-Obregón, Alfredo; Egli, Marcel; Depeursinge, Christian

2012-02-01

15

This paper presents several experimental techniques and concepts in the process of measuring mechanical properties of very soft tissue in an ex vivo tensile test. Gravitational body force on very soft tissue causes pre-compression and results in a non-uniform initial deformation. The global Digital Image Correlation technique is used to measure the full field deformation behavior of liver tissue in uniaxial tension testing. A maximum stretching band is observed in the incremental strain field when a region of tissue passes from compression and enters a state of tension. A new method for estimating the zero strain state is proposed: the zero strain position is close to, but ahead of the position of the maximum stretching band, or in other words, the tangent of a nominal stress-stretch curve reaches minimum at ? ? 1. The approach, to identify zero strain by using maximum incremental strain, can be implemented in other types of image-based soft tissue analysis. The experimental results of ten samples from seven porcine livers are presented and material parameters for the Ogden model fit are obtained. The finite element simulation based on the fitted model confirms the effect of gravity on the deformation of very soft tissue and validates our approach.

Gao, Zhan; Desai, Jaydev P.

2009-01-01

16

This paper presents several experimental techniques and concepts in the process of measuring mechanical properties of very soft tissue in an ex vivo tensile test. Gravitational body force on very soft tissue causes pre-compression and results in a non-uniform initial deformation. The global digital image correlation technique is used to measure the full-field deformation behavior of liver tissue in uniaxial tension testing. A maximum stretching band is observed in the incremental strain field when a region of tissue passes from compression and enters a state of tension. A new method for estimating the zero-strain state is proposed: the zero strain position is close to, but ahead of the position of the maximum stretching band, or in other words, the tangent of a nominal stress-stretch curve reaches minimum at lambda greater or similar 1. The approach, to identify zero strain by using maximum incremental strain, can be implemented in other types of image-based soft tissue analysis. The experimental results of 10 samples from seven porcine livers are presented and material parameters for the Ogden model fit are obtained. The finite element simulation based on the fitted model confirms the effect of gravity on the deformation of very soft tissue and validates our approach. PMID:20015676

Gao, Zhan; Desai, Jaydev P

2009-11-14

17

The long-term and real-time monitoring the cell division and changes of osteoblasts under simulated zero gravity condition were succeed by combing a digital holographic microscopy (DHM) with a superconducting magnet (SM). The SM could generate different magnetic force fields in a cylindrical cavity, where the gravitational force of biological samples could be canceled at a special gravity position by a high magnetic force. Therefore the specimens were levitated and in a simulated zero gravity environment. The DHM was modified to fit with SM by using single mode optical fibers and a vertically-configured jig designed to hold specimens and integrate optical device in the magnet's bore. The results presented the first-phase images of living cells undergoing dynamic divisions and changes under simulated zero gravity environment for a period of 10 hours. The experiments demonstrated that the SM-compatible DHM setup could provide a highly efficient and versatile method for research on the effects of microgravity on biological samples. PMID:22565769

Pan, Feng; Liu, Shuo; Wang, Zhe; Shang, Peng; Xiao, Wen

2012-05-01

18

A study of orientation in a zero gravity environment by means of virtual reality simulation

NASA Astrophysics Data System (ADS)

This study intends to clarify how people acquire visual information and recognize their orientation in a zero gravity environment. An experiment was conducted using virtual reality. In Study 1, each subject was given tasks in which a subject moves through virtual reality from the central room into one of six rooms such as operation room and habitation room. Textures composed by alphabetical letters were stuck on the six surrounding surfaces of the central cubic room. Visual information of the cubic room and the degree-of-freedom of motion were varied, and the subjects' performance was measured. To some extent, the experiment produced a subjective sense of weightlessness. Moreover, we identified different strategies of spatial cognition and behavior under conditions of virtual weightlessness. In Study 2, subjects' orientational skills were tested with pointing and orienting tasks. Subjects followed virtual routes that were constructed of three or four rectangular modules that were connected by the cubical modules. Each subject moved from one end to the other end, and pointed to the start point and reproduced the experienced route using a scale model. The shapes of the routes were changed systematically. Analyses of the results indicate that the ability of special cognition changes with such variables as the number of corners of routes, the geometric number of fields and the number of fields with consideration to the body posture. .

Aoki, Hirofumi; Yamaguchi, Takao; Ohno, Ryuzo

2001-02-01

19

NASA Astrophysics Data System (ADS)

The experiment of dynamic and quantitative phase-contrast imaging of living cells in simulated zero gravity environment were performed by using digital holographic microscopy (DHM) combined with a superconducting magnet (SM). The SM with large gradient high magnetic field was used to simulate zero gravity by levitating biological living samples. The proposed DHM system provided highly efficient and versatile means for dynamically and quantitatively phase-contrast imaging MC3T3-E1 cells. To our knowledge, the phase images of living cells undergoing modifications and division under simulated zero gravity were firstly obtained by using DHM-SM prototype.

Pan, Feng; Liu, Shuo; Wang, Zhe; Shang, Peng; Xiao, Wen

2012-09-01

20

More-effective and -efficient thermal-transport techniques will be needed for heat rejection from equipment on satellites. Circulating two-phase fluid loops were suggested and laboratory tested for possible application in the above areas. In comparison to a single-phase loop, the two-phase system operates at considerably smaller flow rates and maintains a tighter temperature control with higher heat-transfer coefficients. However, the two-phase fluid-flow regimes, pressure gradients, and heat-transfer coefficients must be evaluated for application in the weightless environment of an orbiting satellite. This projecting studies two-phase flow behavior under zero-gravity conditions. The overall objectives of this study were to generate a data base for two-phase pressure drop and the void-quality relationship under simulated zero gravity conditions and to develop analytical models to predict these parameters for bubbly and annular flow. The simulation of zero-gravity two-phase flow was achieved by using two immiscible liquids with equal densities to eliminate the buoyancy component. Although this approach does not eliminate the gravity effects, it provides a representation for void distribution in the absence of gravity. The modeling effort is limited to developing relations for the two-phase friction multiplier and void-quality relation under bubbly and annular-flow conditions. The bubbly flow model is based on the assumption of local homogeneous conditions between the phases but allows for void distribution in the radial direction. Separated-flow conservation equations are used, and single-phase turbulent flow eddy diffusivity relations are employed.

Abdollahian, D.; Grief, R.; Carey, V.P.; Li-Ping, W.

1988-03-01

21

Rat head direction cell responses in zero-gravity parabolic flight.

Astronauts working in zero-gravity (0-G) often experience visual reorientation illusions (VRIs). For example, when floating upside down, they commonly misperceive the spacecraft floor as a ceiling and have a reversed sense of direction. Previous studies have identified a population of neurons in the rat's brain that discharge as a function of the rat's head direction (HD) in a gravitationally horizontal plane and is dependent on an intact vestibular system. Our goal was to characterize HD cell discharge under conditions of acute weightlessness. Seven HD cells in the anterior dorsal thalamus were monitored from rats aboard an aircraft in 0-G parabolic flight. Unrestrained rats locomoted in a clear plexiglas rectangular chamber that had wire mesh covering the floor, ceiling, and one wall. The chamber and surrounding visual environment were relatively up-down symmetrical. Each HD cell was recorded across forty 20-s episodes of 0-G. All HD cells maintained a significant direction-specific discharge when the rat was on the chamber floor during the 0-G and also during the hypergravity pull-out periods. Three of five cells also showed direction-specific responses on the wall in 1-G. In contrast, direction-specific discharge was usually not maintained when the rat locomoted on the vertical wall or ceiling in 0-G. The loss of direction-specific firing was accompanied by an overall increase in background firing. However, while the rat was on the ceiling, some cells showed occasional bursts of firing when the rat's head was oriented in directions that were flipped relative to the long axis of symmetry of the chamber compared with the cell's preferred firing direction on the floor. This finding is consistent with what might be expected if the rat had experienced a VRI. These responses indicate that rats maintain a normal allocentric frame of reference in 0-G and 1-G when on the floor, but may lose their sense of directional heading when placed on a wall or ceiling during acute exposures to 0-G. PMID:15212426

Taube, Jeffrey S; Stackman, Robert W; Calton, Jeffrey L; Oman, Charles M

2004-06-22

22

This paper reports the results of computer modeling of microtubules that end up in the cortical region of a one-cell amphibian embryo, prior to the first cell division. Microtubules are modeled as initially randomly oriented semi-flexible rods, represented by several lines of point-masses interacting with one another like masses on springs with longitudinal and transverse stiffness. They are also considered to be space-filling rods floating in a viscous fluid (cytoplasm) experiencing drag forces and buoyancy from the fluid under a variable gravity field to test gravitational effects. Their randomly distributed interactions with the surrounding spherical container (the cell membrane) have a statistical nonzero average that creates a torque causing a rotational displacement between the cytoplasm and the rigid cortex. The simulation has been done for zero and normal gravity and it validates the observation that cortical rotation occurs in microgravity as well as on Earth. The speed of rotation depends on gravity, but is still substantial in microgravity. PMID:22677068

Nouri, Comron; Tuszynski, Jack A; Wiebe, Mark W; Gordon, Richard

2012-06-05

23

Three dimensional critical wetting experiment in commercial zero-gravity space flight

Without gravity, fluids behave differently and present challenges not observed on Earth. As a result, an understanding of microgravity fluid physics is essential in the development of many space technologies ranging from life support systems on the International Space Station to propellant management devices in spacecraft fuel tanks. Microgravity fluids research has been conducted for decades in drop towers, parabolic

Lauren M Sharp

2011-01-01

24

NASA Astrophysics Data System (ADS)

An experiment is to be automatically carried out on the 1983-1984 Space Shuttle flight as part of the German MAUS program to study the fluid dynamics in tanks under quasi-zero-gravity conditions. The behavior of the fluid will first be described by analytical and numerical procedures, with the results compared to the experiment. The orientation of the fluid under disturbances will be observed, and procedures for calculating fluid motion in the tank as a result of gravity impulses will be developed. The model tank (a cylinder with a diameter of 100 mm) will be filled with a fluid and laterally and dynamically vibrated; the excitation frequency will be varied from 0.1 to 10 Hz and the excitation amplitude from 0 to 40 mm. The eigenfrequency of the oscillating fluid, the mass size of the oscillating fluid, the damping value corresponding to each mode, and the pressure distribution within the tank will be measured. The construction details and requirements of the various experiment components are given together with block diagrams and schematics.

Eckhardt, K.; Ferlic, N.

1981-05-01

25

A zero-gravity thermodynamic vent system for a liquid hydrogen tank

A Thermodynamic Vent System (TVS) to vent a liquid hydrogen tank in low gravity was designed and built by Sundstrand. The TVS was designed and built to a General Dynamic Space Systems Division (GDSSD) specification and was based on earlier laboratory work and design studies done by GDSSD for NASA. The TVS assures that superheated vapor is vented from the tank to control tank pressure with minimum loss of fuel. Major components of the TVS are a swirl flow heat exchanger, an electric motor-driven mixer pump, a fully redundant electronic inverter, and a redundant combined regulator and shutoff valve. The TVS has been extensively tested; the test results compare well with analytical predictions. This paper describes the system and discusses the test results.

Halsey, D.

1987-01-01

26

NASA Astrophysics Data System (ADS)

We introduce a compact and portable photometric system for measurements of the calcium dynamics in cells. The photometer is designed for applications in centrifuges or in zero-gravity environment and thus extremely compact and reliable. It operates with the calcium-sensitive dye Indo-1. The excitation wavelength of 345nm is generated by frequency doubling of a laser diode. Two compact photomultiplier tubes detect the fluorescent emission. The electronics provides the sensitivity of photon counting combined with simultaneous measurement of the temperature, of air pressure, and of gravitational force. Internal data storage during the experiment is possible. A newly developed cell chamber stabilizes the cell temperature to 37.0 percent C +/- 0.1 degree C and includes a perfusion system to supply the cells with medium. The system has a modular set-up providing the possibility to change light source and detectors for investigation of other ions than calcium. Quantitative measurements of the intracellular calcium concentration are based on a comprehensive calibration of our system. First experiments show that the calcium dynamics of osteosarcoma cells stimulated by parathyroid hormone is observable.

Struckmeier, Jens; Tenbosch, Jochen; Klopp, Erk; Born, Matthias; Hofmann, Martin R.; Jones, David W.

2000-04-01

27

Liouville gravity from Einstein gravity

We show that Liouville gravity arises as the limit of pure Einstein gravity in 2+epsilon dimensions as epsilon goes to zero, provided Newton's constant scales with epsilon. Our procedure - spherical reduction, dualization, limit, dualizing back - passes several consistency tests: geometric properties, interactions with matter and the Bekenstein-Hawking entropy are as expected from Einstein gravity.

D. Grumiller; R. Jackiw

2007-01-01

28

Determination of early cardiovascular responses to simulated gravity levels between 0 and 1 G will add knowledge of cardiovascular responses to space flight. Cardiovascular responses to 6 hours in a -5 degrees head-down bedrest model of weightlessness (0 G) were compared to those in head-up tilts of +10 degrees, +20 degrees, and +42 degrees (1/6, 1/3, and 2/3 G, respectively). Six healthy young adult males experienced the four angles on separate days. Impedance cardiography was used to measure thoracic fluid index, cardiac output, stroke volume, and peak flow. Although much intersubject variation occurred, the mean thoracic fluid content at -5 degrees decreased during the first hour and remained decreased; 6-hour values were similar to +10 degrees and +20 degrees. Heart rate decreased the first 2 hours for all angles, then increased, converging at 3-4 hours, and reached control by hour 6. Stroke volume decreased for the first 3 hours at -5 degrees, +10 degrees, +20 degrees; values at all four angles converged at hour 3 and increased in unison thereafter. Cardiac output and peak aortic flow reflected the angle at start of tilt; values at all angles converged by the second hour, decreased through the third hour, and increased thereafter. Pulse pressure decreased for the first 3 hours for angles -5 degrees, +10 degrees, and +20 degrees, converged at the fourth hour, and returned to control. Peak flow at +42 degrees was constant for the first 3 hours and increased thereafter. Blood pressure decreased for the first 2 hours, although the greatest decrease occurred at -5 degrees and +42 degrees; thereafter, values at all angles increased in unison and converged at the fourth hour. Total peripheral resistance increased during the first hour at -5 degrees and +20 degrees and decreased from hour 3 to hours 5-6 at the +42 degrees angle. Cardiovascular values were related to tilt angle for the first 2 hours of tilt, but after hour 3 values at all four angles began to converge, suggesting that cardiovascular homeostatic mechanisms seek a common adapted state regardless of effective gravity level (tilt angle) up to 2/3 G. PMID:2355102

Lathers, C M; Diamandis, P H; Riddle, J M; Mukai, C; Elton, K F; Bungo, M W; Charles, J B

1990-06-01

29

NASA Astrophysics Data System (ADS)

Instability of a thermocapillary flow arising in a rotating thin infinite liquid layer under zero-gravity conditions is investigated. Both boundaries of the layer are assumed to be plane and free and are subject to the tangential thermocapillary Marangoni force. A convective heat transfer at the boundaries is governed by Newton's law and the temperature of the fluid near the boundaries is a linear function of the coordinates. The axis of rotation is perpendicular to a liquid layer. The rotation is slow, which allows us to neglect the centrifugal force. The examined thermocapillary flow is described analytically, being an exact solution of the Navier-Stokes equations. According to the linear theory of stability the obtained neutral curves depict the dependence of the critical Marangoni number on the wave number at different values of the Taylor number for the small Prandtl number (Pr = 0.1). The behavior of the finite-amplitude perturbations beyond the stability threshold is studied numerically.

Shvarts, Konstantin G.

2012-06-01

30

NASA Astrophysics Data System (ADS)

Aims: Here we continue to discuss the principle of the local measurement of dark energy using the normalized Hubble diagram describing the environment of a system of galaxies. Methods: We calculate the present locus of test particles injected a fixed time ago (~the age of the universe), in the standard ? cosmology and for different values of the system parameters (the model includes a central point mass M and a local dark energy density ?loc) and discuss the position of the zero-gravity distance Rv in the Hubble diagram. Results: Our main conclusion are: 1) when the local DE density ?loc is equal to the global DE density ?v, the outflow reaches the global Hubble rate at the distance R2 = (1+zv)Rv, where zv is the global zero-acceleration redshift (?0.7 for the standard model). This is also the radius of the ideal Einstein-Straus vacuole, 2) for a wide range of the local-to-global dark energy ratio ?loc/?v, the local flow reaches the known global rate (the Hubble constant) at a distance R2 ? 1.5 × Rv. Hence, Rv will be between R2/2 and R2, giving upper and lower limits to ?loc/M. For the Local Group, this supports the view that the local density is near the global one.

Teerikorpi, P.; Chernin, A. D.

2010-06-01

31

Space travelling is not possible for human because, by the time, we cross Jupiter, our bones dissolve as there is zero gravity and, by developing a gravity chamber in the space ship itself we will be able to travel in space for generations and explore the universe.

P. Karmakar; Greeninavin

2010-01-01

32

Absolute Zero is a two hour PBS special attempting to bring to the general public some of the advances made in 400 years of thermodynamics. It is based on the book ``Absolute Zero and the Conquest of Cold'' by Tom Shachtman. Absolute Zero will call long-overdue attention to the remarkable strides that have been made in low-temperature physics, a field

Russell J. Donnelly; D. Sheibley; M. Belloni; D. Stamper-Kurn; W. F. Vinen

2006-01-01

33

Estimating the gravity model without gravity using panel data

This article examines the effects of zero trade on the estimation of the gravity model using both simulated and real data with a panel structure, which is different from the more conventional cross-sectional structure. We begin by showing that the usual log-linear estimation method can result in highly deceptive inference when some observations are zero. As an alternative approach, we

Joakim Westerlund; Fredrik Wilhelmsson

2011-01-01

34

Passive and Active Stabilization of Liquid Bridges in Low Gravity

The cylindrical liquid bridge of arbitrary size surrounded by air or vacuum is a fluid configuration that is essentially unique to the zero-gravity environment. An associated technology, which is enhanced in zero gravity, is the float-zone process of crystal growth, which involves a molten liquid bridge between a feed rod and the growing cylindrical crystal. There are several advantages to

David B. Thiessen; Wei Wei; Philip L. Marston

2002-01-01

35

One of the great challenges for 21st century physics is to quantize gravity and generate a theory that will unify gravity\\u000a with the other three fundamental forces of nature. This paper takes the (heretical) point of view that gravity may be an inherently\\u000a classical, i.e., nonquantum, phenomenon and investigates the experimental consequences of such a conjecture. At present there\\u000a is

Stephen Boughn

2009-01-01

36

Zero Tolerance: Safe Schools or Zero Sense?

Zero tolerance polices and an emphasis on school safety have been effective in reducing the incidents of weapons and violence in public schools. Some applications of zero tolerance, however, seem to defy common sense. But, concerns regarding weapons and violence are real. This manuscript argues that well administered zero tolerance policies combined with a comprehensive approach to improve school culture

David L. Stader

2006-01-01

37

Einstein Gravity from Conformal Gravity

We show that that four dimensional conformal gravity plus a simple Neumann boundary condition can be used to get the semiclassical (or tree level) wavefunction of the universe of four dimensional asymptotically de-Sitter or Euclidean anti-de Sitter spacetimes. This simple Neumann boundary condition selects the Einstein solution out of the more numerous solutions of conformal gravity. It thus removes the

Juan Maldacena

2011-01-01

38

NASA Astrophysics Data System (ADS)

We consider spinfoam quantum gravity in the flipped limit, which is the double scaling limit ? ? 0, j ? ? with ?j = const., where ? is the Immirzi parameter, j is the spin and ?j gives the physical area in Planck units. In this regime the amplitude for a 2-complex becomes effectively an integral over Regge-like metrics and seems to enforce Einstein equations in the semiclassical regime. The Immirzi parameter must be considered as dynamical in the sense that it runs to zero when the fine structure of the foam is averaged. In addition to quantum corrections which vanish for ? ? 0, we find new corrections due to the discreteness of geometric spectra.

Magliaro, Elena; Perini, Claudio

2013-02-01

39

A nonmathematical description of the basic ideas behind some recently proposed experiments for testing Einstein's theory of gravitation is given. Mention is made of gravity wave detectors, the possibility of detecting the gamma radiation or radio waves emitted from exploding black holes, the use of a circular cavity waveguide with superconducting walls to detect induced drag caused by a rapidly

P. C. W. Davies

1978-01-01

40

NASA Astrophysics Data System (ADS)

The concept of mass has been central in many areas of physics. Gravitation is not an exception, and it has been one of the long-standing questions whether the graviton, a spin-2 particle that mediates gravity, can have a non-vanishing mass or not. This question is relevant from not only theoretical but also phenomenological viewpoints, since a nonzero graviton mass may lead to late-time acceleration of the universe and thus may be considered as an alternative to dark energy. In 2010, de Rham, Gabadadze and Tolley proposed the first example of a fully nonlinear massive gravity theory and showed that the so called Boulware-Deser ghost, which had been one of the major obstacles against a stable nonlinear theory of massive gravity since 1972, can be removed by construction. Since then, nonlinear massive gravity has been attracting significant interest among physicists and cosmologists. The nonlinear theory of massive gravity provides a theoretical framework in which properties of the remaining five physical degrees of freedom of massive gravity can be studied. As always with any low-energy effective theories, one of the first tasks would be to identify good and bad backgrounds. Depending on the choice of backgrounds, some of the five degrees of freedom may become strongly coupled, may exhibit instantaneous propagation, or may lead to ghost/gradient instabilities. A related subject is to seek interesting solutions such as those relevant for astrophysical objects and those describing self-accelerating cosmology. Those solutions will allow us to study phenomenological and cosmological implications of the theory. Yet another important task would be to seek a possible (partial) UV completion that can be applied beyond the regime of validity of the low-energy effective theory that we currently know of. We invited articles to cover those important subjects in massive gravity. Given the recent rapid developments in the field, however, it must be noted that this focus issue should be best considered as a snapshot. We still hope that the collection of articles provides readers with guidance to the research at the frontier and ideally expedites further progress in the field. Shinji MukohyamaGuest Editor

Mukohyama, Shinji

2013-09-01

41

ERIC Educational Resources Information Center

Questions the effectiveness of the widespread use of zero-tolerance policies enacted by school boards to punish students who violate weapon and drug rules. Suggests that enforcement of zero-tolerance policies has not been equitable. Reviews proposal for alternative to zero tolerance. (PKP)

Henault, Cherry

2001-01-01

42

Do transient gravity waves in a shear flow break?

The propagation of transient gravity waves in a shear flow towards their critical levels is examined using a ray tracing approximation and a higher-degree (quasi-optic) approximation. Because of its transient forcing, the amplitude of transient waves decays to zero in the neighbourhood of the critical region so that it is not clear whether transient gravity waves will reach the convective

M. Pulido; C. Rodas

2008-01-01

43

Absolute Gravity Changes In Alaska

NASA Astrophysics Data System (ADS)

Visco-elastic deformation models such as that of Soldati et al. [1999] predict time varying gravity signals associated with post-seismic deformation following the 1964 Prince William Sound earthquake (Mw=9.2). The rates of change are a function of the upper mantle viscosity. Aseismic creep is also a candidate mechanism for the deformation. The models differ in the spatial distribution of gravity changes; visco-elastic signals span a much larger region. Previous absolute gravity measurements have been made in Fairbanks, Alaska and Palmer, Alaska, during 1990-1991. Estimated uncertainties are in the 3-5 uGal range Visco-elastic gravity changes for Palmer are predicted to range from zero to tens of uGal, depending on the model viscosity and thickness parameters. New absolute gravity measurements at these sites are scheduled for September 2001, with 2 uGal estimated uncertainty. We hope to present initial results of the new measurements, with discussion of their implications for model testing. Different time series and instruments will be merged, and necessary corrections will be discussed

Sasagawa, G. S.

2001-12-01

44

In the present work, the authors construct a theory of cohomological gravity in arbitrary dimensions based upon a local vector supersymmetry algebra. The observables in this theory are polynomial, but generally non-local operators, and have a natural interpretation in terms of a universal bundle for gravity. As such, their correlation functions correspond to cohomology classes on moduli spaces of Riemannian connections. In this uniformization approach, different moduli spaces are obtained by introducing curvature singularities on codimension two submanifolds via a puncture operator. This puncture operator is constructed from a naturally occurring differential form of co-degree two in the theory, and the authors are led to speculate on connections between this continuum quantum field theory, and the discrete Regge calculus. 16 refs.

Birmingham, D. (CERN, Geneva (Switzerland)); Rakowski, M. (Johannes-Gutenberg Universitaet, Mainz (Germany))

1993-07-01

45

The familiar flames from candles and oil lamps are representative examples of wick-stabilized diffusion flames. The shape and burning characteristics of these flames depend strongly on gravity-induced buoyant flows. To obtain a better understanding of the gravity effect, a diffusion flame model has been formulated and numerically solved. In the computation, gravity is treated as a parameter, spanning from zero

AMMAR ALSAIRAFI; SHIH-TUEN LEE; JAMES S. TIEN

2004-01-01

46

Gravity and positional homeostasis of the cell

NASA Astrophysics Data System (ADS)

Normally bilateralization takes place in the presence of the Earth's gravity which produces torque, shear, tension and compression acting upon the naked aggregates of cytoplasm in the zygote which is only stabilized by a weak cytoskeleton. In an initial examination of the effects of these quantities on development, an expression is derived to describe the tendency of torque to rotate the egg and reorganize its constituents. This expression yields the net torque resulting from buoyancy and gravity acting upon a dumbbell shaped cell with heavy and light masses at either end and ``floating'' in a medium. Using crude values for the variables, torques of 2.5 × 10-13 to 8.5 × 10-1 dyne-cm are found to act upon cells ranging from 6.4 ?m to 31 mm (chicken egg). By way of comparison six microtubules can exert a torque of 5 × 10-9 dyne-cm. (1) Gravity imparts torque to cells; (2) torque is reduced to zero as gravity approaches zero; and (3) torque is sensitive to cell size and particulate distribution. Cells must expend energy to maintain positional homeostasis against gravity. Although not previously recognized, Skylab 3 results support this hypothesis: tissue cultures used 58% more glucose on Earth than in space. The implications for developmental biology, physiology, genetics, and evolution are considered. At the cellular and tissue level the concept of ``gravity receptors'' may be unnecessary.

Nace, George W.

47

Virtual waterless manufacturing: zero intake, zero emission.

Innovative application of a systematic approach to reduce freshwater intake and achieve zero emissions could help in reducing the adverse impact of industrial activity on world water resources. Cleantech is a strategic enviro-management technique to reduce the generation of pollutants in a process at source, through minor process modification, material substitution, improved manufacturing practices or low cost treatment. PMID:12731774

Sharma, A

2003-01-01

48

NASA Astrophysics Data System (ADS)

As an exercise in imagining a first encounter with gravity, let's begin with the barest gravitational circumstance. On a planet-sized spherical mass we find rigid poles extending to astronomical distances. At regular intervals along each pole there are Instrument Stations containing a clock, an accelerometer and light senders and receivers. Now imagine a civilization (the RC's) that has evolved in a huge self-sustaining Rotating Cylinder far removed from the sphere or any other astronomical body. The RC's are totally ignorant of gravity but understand well light propagation and the effect of motion on clocks, lengths, etc. Motion is sacred to the RC's because they know they'd die if their cylinder stopped rotating. Their clocks are synchronized so as to reflect the anisotropy of light sent in opposite directions along the cylinder's wall. When they set out to explore the Universe, they come upon the top of one of our tall poles. The RC's inspect the instruments, take data and leave their rocket off except when, in the nick of time, they turn it back on to navigate a soft landing. In their attempt to make sense of their experience, will they prefer a hypothesis resembling General Relativity or a hypothesis more like the one found at GravitationLab.com?

Benish, Richard

2008-05-01

49

The infinite zero structure of completely controllable and observable linear multi-variable systems which give rise to square, non-singular, strictly proper transfer function matrices is investigated via the polynomial matrix approach to the solution of the decoupling problem. In the process various connections between infinite zeros, their degrees and geometric and polynomial matrix ideas are demonstrated. The asymptotic behaviour of closed

ANTONIS I. G. VARDULAKIS

1980-01-01

50

Zeroing in on Supersymmetric Radiation Amplitude Zeros

Radiation amplitude zeros have long been used to test the Standard Model. Here, we consider the supersymmetric radiation amplitude zero in chargino-neutralino associated production, which can be observed at the luminosity upgraded LHC. Such an amplitude zero only occurs if the neutralino has a large wino fraction and hence this observable can be used to determine the neutralino eigenstate content. We find that this observable can be measured by comparing the p{sub T} spectrum of the softest lepton in the trilepton {tilde {chi}}{sub 1}{sup {+-}} {tilde {chi}}{sub 2}{sup 0} decay channel to that of a control process such as {tilde {chi}}{sub 1}{sup +} {tilde {chi}}{sub 1}{sup -} or {tilde {chi}}{sub 2}{sup 0} {tilde {chi}}{sub 2}{sup 0}. We test this technique on a previously generated model sample of the 19 dimensional parameter space of the phenomenological MSSM, and find that it is effective in determining the wino content of the neutralino.

Hewett, JoAnne L.; Ismail, Ahmed; Rizzo, Thomas G.; /SLAC

2012-02-15

51

Graviresponses of osteocytes under altered gravity

NASA Astrophysics Data System (ADS)

Single cell was capable of sensing and responding to alterations of gravity. Osteocytes, as the most abundant cells of the bone tissue playing an important role in the bone mechanotransduction, are very sensitive to mechanical stimuli. However, the effect of altered gravity on osteocytes so far is less known according to the public papers. Further study on this issue will help to verify and develop the theory of how cells perceive and respond to gravity. It also brings new ideas to the study of space bone loss. In our study, Osteocyte-like MLO-Y4 cells were exposed to 30 parabolic flights three times on ZERO-G airbus A300 to investigate the comprehensive effect on osteocytes stimulated by hyper- and hypo-gravity forces. It showed that the cell morphology, as well as cell area and height, was not changed significantly by hyper-gravity and hypo-gravity. However, the cytoskeleton was reorganized. In flight cells, F-actin polymerization was enhanced at the cell periphery and microtubule organizing center disappeared, but no apoptotic feathers were detected. The results of western blot showed that connexin 43 (Cx43) expression was down-regulated, indicating an decrease of gap-junction. In conclusion, hyper- and hypo-gravity stimulation altered the cytoskeleton architecture and suppressed gap-junction of osteocyte-like MLO-Y4 cells.

Di, S. M.; Qian, A. R.; Qu, L. N.; Zhang, W.; Wang, Z.; Ding, C.; Li, Y. H.; Ren, H. G.; Shang, P.

2011-09-01

52

NASA's Artificial Gravity program consists of a team of researchers from Wyle Laboratories, NASA Johnson Space Center, and the University of Texas Medical Branch (UTMB). The short-radius centrifuge (SRC), built by Wyle Laboratories, will be integrated with UTMB's conducted bedrest studies, which mimic the detrimental effects of weightlessness (or microgravity). Bedrest subjects will be spun on the SRC at various accelerations and for various time periods, while being monitored medically. Parameters such as bone loss, muscle atrophy, balance control, and oxygen consumption will then be compared in order to research ways of mitigating the impact on astronauts' physiology. Other potential benefits from these studies extend to population groups on Earth, such as bedridden patients. PMID:15852559

Scott, William B

2005-04-25

53

NASA Astrophysics Data System (ADS)

Nonlinear special relativity (or doubly special relativity) is a simple framework for encoding properties of flat quantum spacetime. In this paper, we show how this formalism may be generalized to incorporate curvature (leading to what might be called 'doubly general relativity'). We first propose a dual to nonlinear realization of relativity in momentum space, and show that for such a dual the spacetime invariant is an energy-dependent metric. This leads to an energy-dependent connection and curvature, and a simple modification to Einstein's equations. We then examine solutions to these equations. We find the counterpart to the cosmological metric, and show how cosmologies based upon our theory of gravity may solve the 'horizon problem'. We discuss the Schwarzschild solution, examining the conditions for which the horizon is energy dependent. Finally, we find the weak field limit.

Magueijo, João; Smolin, Lee

2004-04-01

54

Cardiovascular effects of simulated zero-gravity in humans

NASA Astrophysics Data System (ADS)

Head-down and heat-up tilted bedrest (5 degrees) and head out water immersion (HOWI) for 6 hr were compared. Parameters: Cardiac output (rebreathing method), blood pressure (arm cuff), forearm blood flow (venous occlusion plethysmography), total peripheral (TPR), and forearm vascular (FVR) resistances, Hct, Hb, relativ? plasma volume (PV) changes, and plasma catecholamines (single-isotope assay). During HOWI there was as expected a decrement in TPR, FVR, Mean arterial pressure (MAP, from 100 to 80 mmHg), Hct, and PV, and—as a new finding—catecholamines, which were 30-50% lower compared with both + 5 and - 5 degrees bedrest. During head down tilt, MAP was elevated (to 100-110 mmHg) and catecholamines did not fall, while TPR and FVR slowly decreased over 6 hr. HOWI is a stronger stimulus than - 5 degrees bedrest, probably because HOWI elevates central venous pressure more markedly emptying the peripheral veins, while bedrest permits a distension of veins, which induces an increase in sympathetic nervous activity.

Bonde-Petersen, F.; Suzuki, Y.; Sadámoto, T.; Juel Christensen, N.

55

GAS-611 (Get Away Special 611) Firefly in Zero Gravity.

National Technical Information Service (NTIS)

The Get Away Special 611 (GAS-611) project will carry a small, self-contained biological experiment into a microgravity environment for a period of 120 hours. The payload will be a colony of Lampyridae (fireflies). The ability of this beetle to produce li...

T. Williams

1988-01-01

56

Gravity and Mirror Gravity in Plebanski Formulation

NASA Astrophysics Data System (ADS)

We present several theories of four-dimensional gravity in the Plebanski formulation, in which the tetrads and the connections are the independent dynamical variables. We consider the relation between different versions of gravitational theories: Einsteinian, "topological," "mirror" gravities and gravity with torsion. We assume that our world, in which we live, is described by the self-dual left-handed gravity, and propose that if the Mirror World exists in Nature, then the "mirror gravity" is the right-handed antiself-dual gravity. In this connection, we give a brief review of gravi-weak unification models. In accordance with cosmological measurements, we consider the Universe with broken mirror parity. We also discuss the problems of cosmological constant and communication between visible and mirror worlds. Investigating a special version of the Riemann-Cartan space-time, which has torsion as an additional geometric property, we have shown that in the Plebanski formulation the ordinary and dual "topological" sectors of gravity, as well as the gravity with torsion, are equivalent. Equations of motion are obtained. In this context, we have also discussed a "pure connection gravity" — a diffeomorphism-invariant gauge theory of gravity. Loop Quantum Gravity is also briefly reviewed.

Bennett, D. L.; Laperashvili, L. V.; Nielsen, H. B.; Tureanu, A.

2013-05-01

57

NSDL National Science Digital Library

Elliott Kimmel may have created zeroBio for the students of London, Ontario's Central Secondary School, but high school biology students anywhere would benefit tremendously from a visit to this extensive collection of biology learning resources. In addition to functioning as an online biology textbook, zeroBio offers dissection photos for a number of specimens, multimedia presentations, self-quizzing flashcards for organic chemistry, downloadable worksheets, interactive quizzes, games, puzzles, and more.

2000-01-01

58

Gravity gradient modeling using gravity and DEM

A model of the gravity gradient tensor at aircraft altitude is developed from the combination of ground gravity anomaly data\\u000a and a digital elevation model. The gravity data are processed according to various operational solutions to the boundary-value\\u000a problem (numerical integration of Stokes’ integral, radial-basis splines, and least-squares collocation). The terrain elevation\\u000a data are used to reduce free-air anomalies to

Lizhi Zhu; Christopher Jekeli

2009-01-01

59

Universality of second order transport in Gauss-Bonnet gravity

NASA Astrophysics Data System (ADS)

We compute all the second order transport coefficients of a hydrodynamic theory with a gravity dual which includes a Gauss-Bonnet term. We find that a particular linear combination of the second order transport coefficients, which was found to vanish in generic two derivative gravity theories with matter, remains zero even in the presence of the Gauss-Bonnet term. We contrast this behavior with the shear viscosity to entropy density ratio.

Shaverin, Evgeny; Yarom, Amos

2013-04-01

60

Flight test results from a strapdown airborne gravity system

. In June 1995, a flight test was carried out over the Rocky Mountains to assess the accuracy of airborne gravity for geoid\\u000a determination. The gravity system consisted of a strapdown inertial navigation system (INS), two GPS receivers with zero baseline\\u000a on the airplane and multiple GPS master stations on the ground, and a data logging system. To the best

M. Wei; K. P. Schwarz

1998-01-01

61

The history of the development of nuclear weapons starting with the detonation of the A-bombs on Japan is reviewed. An overview of nuclear weapon effects is presented. The effects of electromagnetic pulse (EMP), initial nuclear radiation, thermal radiation and blast are discussed with reference to how people outside can survive when ground zero is only a few miles away. 8

Haaland

1984-01-01

62

On my way to Ground Zero in an almost empty train. Each stop takes me farther downtown, farther toward the site. I think of myself as Marlowe, Conrad's protagonist in Heart of Darkness, traveling in a steamboat down a river into a jungle, toward a primal nightmare. When Marlowe finds Kurtz, he discovers more than he bargained for. I too

DEVIN SULLIVAN

63

ERIC Educational Resources Information Center

|An excerpt from the opening piece in "Everything That Rises: A Book of Convergences" by Lawrence Weschler is presented where the author is talking with Joel Meyerowitz, the only photographer granted unimpeded access to the clean-up operations at ground zero after the terrorist attacks of September 11, 2001. The two discuss the parallels between…

Chronicle of Higher Education, 2006

2006-01-01

64

An old concept known as ZBM (zero ballistic missiles) now challenges analysts and policymakers to think a new about a radical transformation of the strategic environment. Until recently, the notion of eliminating all ballistic missiles designed for deep strikes beyond an immediate battlefield seemed favorful. However, the drastic shift in the geopolitical terrain and the rising apprehension about the spread

Frye

2009-01-01

65

ERIC Educational Resources Information Center

|Describes the robots used to aid in rescue and recovery at Ground Zero after the September 11, 2001 attack on the World Trade Center. The robots were developed as a result of national Science Foundation Quick Response Research Awards. Describes several awards that were made following the attack. (JOW)|

Techniques: Connecting Education and Careers, 2002

2002-01-01

66

NSDL National Science Digital Library

The purpose of this assessment probe is to elicit students' ideas about gravity. The probe is designed to determine whether students recognize that gravity is a universal force that exists everywhere in space, regardless of whether air is present.

Eberle, Francis; Keeley, Page

2005-01-01

67

Minimum length, extra dimensions, modified gravity and black hole remnants

NASA Astrophysics Data System (ADS)

We construct a Hilbert space representation of minimum-length deformed uncertainty relation in presence of extra dimensions. Following this construction, we study corrections to the gravitational potential (back reaction on gravity) with the use of correspondingly modified propagator in presence of two (spatial) extra dimensions. Interestingly enough, for r?0 the gravitational force approaches zero and the horizon for modified Schwarzschild-Tangherlini space-time disappears when the mass approaches quantum-gravity energy scale. This result points out to the existence of zero-temperature black hole remnants in ADD brane-world model.

Maziashvili, Michael

2013-03-01

68

Gravity modulator and gravity-modulation reception

US Patent & Trademark Office Database

An arrangement of gravity modulator and gravity-modulation receiver where photons or electromagnetic radiation is modulated electronically or mechanically to reach either a solid, liquid or mixed target possibly through or followed by a surrounding medium to produce gravity modulation in the target to effect gravity signaling which is received by a gravity-modulation receiver in or not in physical contact with the target. In the receiver, one or more piezo-electric transducer/s or quartz crystal/s receive the gravity modulation amplified for further signal processing. When not in physical contact with the target, the piezo-electric transducer/s is/are loaded with a resonator mass of natural resonant frequency either equal to, half, one third or one fifth of the frequency of the gravity modulator, the quartz crystal/s is/are gravity biased with a high-density metal piece along one direction of the oscillation mode of the crystal/s with natural resonant frequency similar to the resonator mass.

2013-08-27

69

ERIC Educational Resources Information Center

|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)|

MacKeown, P. K.

1984-01-01

70

Thermodynamics of black holes in gravity's rainbow formalisms

NASA Astrophysics Data System (ADS)

Several results in the context of quantum gravity and related frameworks suggest the plausibility of modifications to the uncertainty principle and to the energy-momentum dispersion relation of special relativity. One of these frameworks is provided by gravity's rainbow. We analyze the consequences that such modifications may have for black hole thermodynamics from the perspective of two different gravity's rainbow formalisms. In this scenario, we show that the temperature of the black hole may vanish in the limit of zero mass under feasible conditions.

Galán, Pablo; Mena Marugán, Guillermo A.

2007-05-01

71

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

National Technical Information Service (NTIS)

Most people take the constant presence of gravitys pull for granted. However, the Earth's gravitational strength actually varies from location to location. This variation occurs because mass, which influences an object's gravitational pull, is not evenly ...

F. Lemoine D. Smith D. Rowlands M. Zuber G. Neumann D. Chinn D. Pavlis

2000-01-01

72

Gravity Monitoring of Canal Infiltration: Results from Dutch Flats, Nebraska

NASA Astrophysics Data System (ADS)

Gravity monitoring provides a cost-effective means of monitoring subsurface mass changes of engineering interest. In July to October 2003, we conducted a gravity monitoring study of canal infiltration in the Dutch Flats irrigated farming area of western Nebraska, USA. An unlined east-west canal on the north edge of the monitoring network leaks southward into the existing shallow aquifer. Due to irrigation requirements, infiltration from the canal started in early spring, before the first measurement campaign, and continued until August. Sixteen gravity stations were co-located on monitoring wells near the canal, with an additional two far-field reference stations. Absolute gravity measurements by the National Geodetic Survey on the reference stations in July and September show no significant change at either station. Relative to the July baseline, the August campaign shows gravity increases of ~20 ?Gal at the northern-most stations, with smaller changes at other stations. September and October surveys show gravity increases of ~20 ?Gal more southward, and gravity values decreasing to near zero at the canal. Gravity changes are limited to [-54,+30] ?Gal during the experiment, suggesting water loss from the shallow aquifer as the dominant process during the gravity monitoring experiment.

Gettings, P.; Chapman, D. S.; Kress, W.

2009-12-01

73

We investigate the possibility of disposing of interaction between Prover and Verifier in a zeroknowledgeproof if they share beforehand a short random string.Without any assumption, we prove that non-interactive zero-knowledge proofs exist for some numbertheoretic languages for which no efficient algorithm is known.If deciding quadratic residuosity (modulo composite integers whose factorization is not known) iscomputationally hard, we show that the

Manuel Blum; Alfredo De Santis; Silvio Micali; Giuseppe Persiano

1991-01-01

74

Windows in the U.S. consume 30 percent of building heating and cooling energy, representing an annual impact of 4.1 quadrillion BTU (quads) of primary energy. Windows have an even larger impact on peak energy demand and on occupant comfort. An additional 1 quad of lighting energy could be saved if buildings employed effective daylighting strategies. The ENERGY STAR{reg_sign} program has made standard windows significantly more efficient. However, even if all windows in the stock were replaced with today's efficient products, window energy consumption would still be approximately 2 quads. However, windows can be ''net energy gainers'' or ''zero-energy'' products. Highly insulating products in heating applications can admit more useful solar gain than the conductive energy lost through them. Dynamic glazings can modulate solar gains to minimize cooling energy needs and, in commercial buildings, allow daylighting to offset lighting requirements. The needed solutions vary with building type and climate. Developing this next generation of zero-energy windows will provide products for both existing buildings undergoing window replacements and products which are expected to be contributors to zero-energy buildings. This paper defines the requirements for zero-energy windows. The technical potentials in terms of national energy savings and the research and development (R&D) status of the following technologies are presented: (1) Highly insulating systems with U-factors of 0.1 Btu/hr-ft{sup 2}-F; (2) Dynamic windows: glazings that modulate transmittance (i.e., change from clear to tinted and/or reflective) in response to climate conditions; and (3) Integrated facades for commercial buildings to control/ redirect daylight. Market transformation policies to promote these technologies as they emerge into the marketplace are then described.

Arasteh, Dariush; Selkowitz, Steve; Apte, Josh; LaFrance, Marc

2006-05-17

75

Copper proteins play key roles in biological processes such as electron transfer and dioxygen activation; the active site of each of these proteins is classified as either type 1, 2, or 3, depending on its optical and electron paramagnetic resonance properties. We have built a new type of site that we call “type zero copper” by incorporating leucine, isoleucine, or phenylalanine in place of methionine at position 121 in C112D Pseudomonas aeruginosa azurin. X-ray crystallographic analysis shows that these sites adopt distorted tetrahedral geometries, with an unusually short Cu-O(G45 carbonyl) bond (2.35–2.55 Å). Relatively weak absorption near 800 nm and narrow parallel hyperfine splittings in EPR spectra are the spectroscopic signatures of type zero copper. Copper K-edge x-ray absorption spectra suggest elevated Cu(II) 4p character in the d-electron ground state. Cyclic voltammetric experiments demonstrate that the electron transfer reactivities of type zero azurins are enhanced relative to that of the corresponding type 2 (C112D) protein.

Lancaster, Kyle M.; DeBeer George, Serena; Yokoyama, Keiko; Richards, John H.; Gray, Harry B.

2009-01-01

76

NUT-charged black holes in Gauss-Bonnet gravity

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

Dehghani, M.H. [Physics Department and Biruni Observatory, College of Sciences, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of); Department of Physics, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L 3G1 (Canada); Perimeter Institute for Theoretical Physics, 35 Caroline Street North, Waterloo, Ontario (Canada); Mann, R.B. [Department of Physics, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L 3G1 (Canada); Perimeter Institute for Theoretical Physics, 35 Caroline Street North, Waterloo, Ontario (Canada)

2005-12-15

77

Superconducting gravity gradiometer for sensitive gravity measurements. I. Theory

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

H. A. Chan; H. J. Paik

1987-01-01

78

Zero Tolerance Policies. Research Brief

ERIC Educational Resources Information Center

|Much of this brief comes from the ERIC Digest on Zero Tolerance Policies (ERIC #: ED451579). State legislatures and school boards are adopting a growing number of zero-tolerance polices toward weapons, guns, and violence. Zero-tolerance polices are rules intended to address specific school-safety issues. Despite the controversies that it has…

Muir, Mike

2004-01-01

79

ZERO TOLERANCE, NAMING AND SHAMING

Zero tolerance and public shaming are increasingly advocated for both crimes of the powerless and crimes of the powerful. In this essay we argue against zero tolerance with respect to both kinds of crime. However, we defend naming and shaming with respect to crimes of the powerful. Part I of the paper begins from the assumption that both zero tolerance

John Braithwaite; Peter Drahos

80

Zero Tolerance Policies. Research Brief

ERIC Educational Resources Information Center

Much of this brief comes from the ERIC Digest on Zero Tolerance Policies (ERIC #: ED451579). State legislatures and school boards are adopting a growing number of zero-tolerance polices toward weapons, guns, and violence. Zero-tolerance polices are rules intended to address specific school-safety issues. Despite the controversies that it has…

Muir, Mike

2004-01-01

81

A Demonstration of Einstein's Equivalence of Gravity and Acceleration

ERIC Educational Resources Information Center

|In 1907, Einstein described a "Gedankenexperiment" in which he showed that free fall in a gravitational field is indistinguishable from a body at rest in an elevator accelerated upwards in zero gravity. This paper describes an apparatus, which is simple to make and simple to operate, that acts as an observable footnote to Einstein's example. It…

Newburgh, Ronald

2008-01-01

82

Asymptotic Safety in quantum gravity

NASA Astrophysics Data System (ADS)

Asymptotic Safety (sometimes also referred to as nonperturbative renormalizability) is a concept in quantum field theory which aims at finding a consistent and predictive quantum theory of the gravitational field. Its key ingredient is a nontrivial fixed point of the theory's renormalization group flow which controls the behavior of the coupling constants in the ultraviolet (UV) regime and renders physical quantities safe from divergences. Although originally proposed by Steven Weinberg to find a theory of quantum gravity the idea of a nontrivial fixed point providing a possible UV completion can be applied also to other field theories, in particular to perturbatively nonrenormalizable ones. The essence of Asymptotic Safety is the observation that nontrivial renormalization group fixed points can be used to generalize the procedure of perturbative renormalization. In an asymptotically safe theory the couplings do not need to be small or tend to zero in the high energy limit but rather tend to finite values: they approach a nontrivial UV fixed point. The running of the coupling constants, i.e. their scale dependence described by the renormalization group (RG), is thus special in its UV limit in the sense that all their dimensionless combinations remain finite. This suffices to avoid unphysical divergences, e.g. in scattering amplitudes. The requirement of a UV fixed point restricts the form of the bare action and the values of the bare coupling constants, which become predictions of the Asymptotic Safety program rather than inputs. As for gravity, the standard procedure of perturbative renormalization fails since Newton's constant, the relevant expansion parameter, has negative mass dimension rendering general relativity perturbatively nonrenormalizable. This has driven the search for nonperturbative frameworks describing quantum gravity, including Asymptotic Safety which -- in contrast to other approaches -- is characterized by its use of quantum field theory methods, without depending on perturbative techniques, however.

Nink, Andreas; Reuter, Martin; Saueressig, Frank

2013-06-01

83

NASA Astrophysics Data System (ADS)

Unimodular gravity is classically equivalent to standard Einstein gravity, but differs when it comes to the quantum theory: the conformal factor is non-dynamical, and the gauge symmetry consists of transverse diffeomorphisms only. Furthermore, the cosmological constant is not renormalized. Thus the quantum theory is distinct from a quantization of standard Einstein gravity. Here we show that within a truncation of the full renormalization group flow of unimodular quantum gravity, there is a non-trivial ultraviolet (UV)-attractive fixed point, yielding a UV completion for unimodular gravity. We discuss important differences to the standard asymptotic-safety scenario for gravity, and provide further evidence for this scenario by investigating a new form of the gauge-fixing and ghost sector. Communicated by P R L V Moniz

Eichhorn, Astrid

2013-06-01

84

Canonical gravity with fermions

NASA Astrophysics Data System (ADS)

Canonical gravity in real Ashtekar-Barbero variables is generalized to allow for fermionic matter. The resulting torsion changes several expressions in Holst’s original vacuum analysis, which are summarized here. This in turn requires adaptations to the known loop quantization of gravity coupled to fermions, which is discussed on the basis of the classical analysis. As a result, parity invariance is not manifestly realized in loop quantum gravity.

Bojowald, Martin; Das, Rupam

2008-09-01

85

Anisotropic stress and stability in modified gravity models

The existence of anisotropic stress of a purely geometrical origin seems to be a characteristic of higher order gravity models, and has been suggested as a probe to test these models observationally, for example, in weak lensing experiments. In this paper, we seek to find a class of higher order gravity models of f(R,G) type that would give us a zero anisotropic stress and study the consequences for the viability of the actual model. For the special case of a de Sitter background, we identify a subclass of models with the desired property. We also find a direct link between anisotropic stress and the stability of the model as well as the presence of extra degrees of freedom, which seems to be a general feature of higher order gravity models. Particularly, setting the anisotropic stress equal to zero for a de Sitter background leads to a singularity that makes it impossible to reach the de Sitter evolution.

Saltas, Ippocratis D. [Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH (United Kingdom); Kunz, Martin [Departement de Physique Theorique, Universite de Geneve, 1211 Geneva 4 (Switzerland)

2011-03-15

86

Zero Temperature Hope Calculations

The primary purpose of the HOPE code is to calculate opacities over a wide temperature and density range. It can also produce equation of state (EOS) data. Since the experimental data at the high temperature region are scarce, comparisons of predictions with the ample zero temperature data provide a valuable physics check of the code. In this report we show a selected few examples across the periodic table. Below we give a brief general information about the physics of the HOPE code. The HOPE code is an ''average atom'' (AA) Dirac-Slater self-consistent code. The AA label in the case of finite temperature means that the one-electron levels are populated according to the Fermi statistics, at zero temperature it means that the ''aufbau'' principle works, i.e. no a priory electronic configuration is set, although it can be done. As such, it is a one-particle model (any Hartree-Fock model is a one particle model). The code is an ''ion-sphere'' model, meaning that the atom under investigation is neutral within the ion-sphere radius. Furthermore, the boundary conditions for the bound states are also set at the ion-sphere radius, which distinguishes the code from the INFERNO, OPAL and STA codes. Once the self-consistent AA state is obtained, the code proceeds to generate many-electron configurations and proceeds to calculate photoabsorption in the ''detailed configuration accounting'' (DCA) scheme. However, this last feature is meaningless at zero temperature. There is one important feature in the HOPE code which should be noted; any self-consistent model is self-consistent in the space of the occupied orbitals. The unoccupied orbitals, where electrons are lifted via photoexcitation, are unphysical. The rigorous way to deal with that problem is to carry out complete self-consistent calculations both in the initial and final states connecting photoexcitations, an enormous computational task. The Amaldi correction is an attempt to address this problem by distorting the outer part of the self-consistent potential in such a way that in the final state after photoexcitation or photoionization the newly occupied orbital sees the hole left in the initial state. This is very important to account for the large number of Rydberg states in the case of low densities. In the next Section we show calculated photoabsorptions compared with experimental data in figures with some rudimentary explanations.

Rozsnyai, B F

2002-07-26

87

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

Most people take the constant presence of gravitys pull for granted. However, the Earth's gravitational strength actually varies from location to location. This variation occurs because mass, which influences an object's gravitational pull, is not evenly distributed within the planet. Changes in topography, such as glacial movement, an earthquake, or a rise in the ocean level, can subtly affect the

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

2000-01-01

88

ZERO SUPPRESSION FOR RECORDERS

A zero-suppression circuit for self-balancing recorder instruments is presented. The essential elements of the circuit include a converter-amplifier having two inputs, one for a reference voltage and the other for the signal voltage under analysis, and a servomotor with two control windings, one coupled to the a-c output of the converter-amplifier and the other receiving a reference input. Each input circuit to the converter-amplifier has a variable potentiometer and the sliders of the potentiometer are ganged together for movement by the servoinotor. The particular noveity of the circuit resides in the selection of resistance values for the potentiometer and a resistor in series with the potentiometer of the signal circuit to ensure the full value of signal voltage variation is impressed on a recorder mechanism driven by servomotor.

Fort, W.G.S.

1958-12-30

89

We study the N{sub f}-flavor Gross-Neveu model in 2+1 dimensions with a baryon chemical potential {mu}, using both analytical and numerical methods. In particular, we study the self-consistent Boltzmann equation in the Fermi liquid framework using the quasiparticle interaction calculated to O(1/N{sub f}), and find solutions for zero sound propagation for almost all {mu}>{mu}{sub c}, the critical chemical potential for chiral symmetry restoration. Next we present results of a numerical lattice simulation, examining temporal correlation functions of mesons defined using a point-split interpolating operator, and finding evidence for phononlike behavior characterized by a linear dispersion relation in the long wavelength limit. We argue that our results provide the first evidence for a collective excitation in a lattice simulation.

Hands, Simon [Department of Physics, University of Wales Swansea, Singleton Park, Swansea SA2 8PP (United Kingdom); Strouthos, Costas G. [Department of Physics, Duke University, Durham, North Carolina 27708 (United States); Division of Science and Engineering, Frederick Institute of Technology, Nicosia 1303 (Cyprus)

2004-09-01

90

Two phase fluid flow in reduced gravity environments

NASA Astrophysics Data System (ADS)

Analytical and experimental methods and the results of testing heat pipe models operational in conditions of reduced gravity are presented. Two monogroove heat pipe test articles were constructed with glass windows and filmed in zero gravity using high speed cameras aboard the NASA KC-135 zero-g aircraft. The tests confirmed the modeling predictions, namely, that the heat pipes prime in a very short time after entrance into zero-g and that the time necessary for priming to occur can be predicted. The tests also confirmed the monogroove blockage phenomenon predicted by the model. It is proposed that the blockage can be eliminated by increasing the width of the monogroove slit at a number of points along the length of the pipe.

Peterson, G. P.

91

NASA Astrophysics Data System (ADS)

Cultures of human lymphocytes exposed in microgravity to the mitogen concanavalin A showed less than 3 percent of the activation of ground controls. This result supports the hypothesis, based on simulations at low g and experiments at high g, that microgravity depresses whereas high gravity enhances cell proliferation rates. The effects of gravity are particularly strong in cells undergoing differentiation.

Cogoli, A.; Tschopp, A.; Fuchs-Bislin, P.

1984-07-01

92

Superconducting tensor gravity gradiometer

NASA Astrophysics Data System (ADS)

A sensitive gravity gradiometer can provide much needed gravity data of the earth and improve the accuracy of inertial navigation. A complete determination of all five independent components of the gravity gradient tensor is possible in principle by rotating a single in-line component gradiometer. In order to avoid dynamically induced noise sources arising from rotation, a hard-mounted assembly of component gradiometers may nevertheless be advantageous in an ultra-sensitive device. Superconductivity and other properties of materials at low temperatures can be used to obtain a sensitive, low-drift, gravity gradiometer. By differencing the outputs of accelerometer pairs using superconducting circuits, it is possible to construct a non-rotating tensor gravity gradiometer. Additional superconducting circuits can be provided to determine the linear and angular acceleration vectors. A three-axis in-line gravity gradiometer (a “vector” gradiometer) is being developed for satellite geodesy. A two-dimensional spring concept for a three-axis cross component gradiometer is discussed. The superconducting tensor gravity gradiometer constitutes a complete package of inertial navigation instruments with angular and linear acceleration readouts as well as gravity signals. Accuracy of inertial navigation could be improved by use of such a gradiometeraided inertial navigator.

Paik, H. J.

1981-12-01

93

Demonstrating Reduced Gravity.

National Technical Information Service (NTIS)

A miniature drop tower, Reduced-Gravity Demonstrator is developed to illustrate the effects of gravity on a variety of phenomena including the way fluids flow, flames burn, and mechanical systems (such as pendulum) behave. A schematic and description of t...

H. Pearlman D. Stocker D. Gotti D. Urban H. Ross T. Sours

1996-01-01

94

Demonstrating Reduced Gravity.

ERIC Educational Resources Information Center

|Describes the construction of the Reduced-Gravity Demonstrator, which can be used to illustrate the effects of gravity on a variety of phenomena, including the way fluids flow, flames burn, and mechanical systems behave. Presents experiments, appropriate for classroom use, to demonstrate how the behavior of common physical systems change when…

Pearlman, Howard; And Others

1996-01-01

95

National Technical Information Service (NTIS)

The report describes the progress made towards the design and fabrication of a cryogenic gravity meter intended to have a sensitivity of about 25 millimicrogal. The cryogenic gravity meter consists of two parts--a suspension unit and a detection module. T...

V. S. Tuman

1970-01-01

96

National Technical Information Service (NTIS)

The report describes the progress made towards the design and fabrication of a cryogenic gravity meter intended to have a sensitivity of about 25 millimicrogal. The cryogenic gravity meter consists of two parts--a suspension unit and a detection module. T...

A. Waleh V. S. Tuman

1972-01-01

97

Gravity, Entropy, and Thermodynamics

The intrinsic motions of light, time, and gravity are primordial forms of entropy, causing: 1) the creation, expansion, and cooling of space; 2) the creation, expansion, and aging of history; 3) the creation and expansion of historic spacetime, respectively. The charges of matter are the symmetry debts of light (Noether's Theorem). Gravity pays the entropy-interest on matter's symmetry debt by

John A. Gowan

98

Natural vibration characteristics of gravity structures

NASA Astrophysics Data System (ADS)

A forced vibration procedure is presented to estimate fundamental and higher frequencies of vibrations and associated mode shapes of gravity structures. The gravity structures considered are retaining walls and gravity dams. The validity of the proposed procedure is tested on three test problems of varying complexity for which the natural vibration frequencies and mode shapes either have known analytical solutions or have been determined via numerical means/field tests by others. Also included are the results of natural vibration frequencies and associated mode shapes for a spillway control structure located near the abutment end of an embankment dam obtained using the proposed procedure. For all problems considered, fundamental frequency and mode shape results using the proposed procedure are compared with the results obtained using an alternative procedure in which static deflections due to the structure's own weight are used as the starting point for free vibrations by setting the gravity vector to zero. All results compare well. The merits of the proposed procedure are discussed. Published in 2006 by John Wiley & Sons, Ltd.

Chugh, Ashok K.

2007-04-01

99

A possibility to solve the problems with quantizing gravity

NASA Astrophysics Data System (ADS)

It is generally believed that quantum gravity is necessary to resolve the known tensions between general relativity and the quantum field theories of the standard model. Since perturbatively quantized gravity is non-renormalizable, the problem how to unify all interactions in a common framework has been open since the 1930s. Here, I propose a possibility to circumvent the known problems with quantizing gravity, as well as the known problems with leaving it unquantized: By changing the prescription for second quantization, a perturbative quantization of gravity is sufficient as an effective theory because matter becomes classical before the perturbative expansion breaks down. This is achieved by considering the vanishing commutator between a field and its conjugated momentum as a symmetry that is broken at low temperatures, and by this generates the quantum phase that we currently live in, while at high temperatures Planck's constant goes to zero.

Hossenfelder, Sabine

2013-10-01

100

On wormhole throats in f ( R) gravity theory

NASA Astrophysics Data System (ADS)

We study the existence and properties of wormhole throats in modified f ( R) gravity theory. Specifically, we concentrate on the cases where the lapse is not necessarily constant, and hence are not limited to the zero tidal force scenarios. In the class of theories whose actions are generated by Lagrangians of the form f ( R) = ? ? n R n we find parameters which allow for the existence of energy condition respecting throats, which do not exist in Einstein gravity. We also consider the effect of the modified action on the anisotropy of the models, and find that modified gravity can minimize the amount of anisotropy required to support the existence of a throat. In both these respects, the sector containing theories with positive n is more promising than the negative n sector in comparison to Einstein gravity alone, with large n being most favorable.

DeBenedictis, Andrew; Horvat, Dubravko

2012-11-01

101

NSDL National Science Digital Library

This broadcast reports on Gravity Probe B, a satellite designed to test the frame dragging prediction of Einstein's theory of general relativity, where a spinning object such as the Earth will push spacetime in front of it. Gravity Probe B uses gyroscopes which will shift direction while orbiting the Earth (if general relativity is correct). The broadcast contains comments from a scientist who has worked on the Gravity Probe B mission for over 44 years. There is a brief explanation of the difference between the behavior of gravity in Newtonian physics and general relativity. The broadcast also discusses why it took so long to build the satellite (a dozen technologies had to be invented first), the cost involved, and whether the plug would be pulled on the mission; however, Gravity Probe B was finally launched on April 20, 2004. The broadcast is 30 minutes in length.

102

This video from NASA's Dawn mission shows that the gravity field of Vesta closely matches the surface topography of the giant asteroid Vesta. The video shows shaded topography from Dawn's framing camera on the left, with troughs and craters visible, and color-contoured data from Dawn's gravity experiment on the right. Red shows the areas with a higher than average gravity field and blue-purple shows the areas where the field is weaker on average. The highest topography, on the rim of the Rheasilvia basin deep in the southern hemisphere, shows a particularly strong gravity field. The topography model is derived from framing camera images from Dawn's high-altitude mapping orbit (420 miles or 680 kilometers above the surface), and the gravity data come from the low-altitude mapping orbit (130 miles or 210 kilometers above the surface). Vesta takes approximately 5.34 hours to make a rotation.

Anthony Greicius

2012-04-24

103

Disappearing cosmological constant in f( R) gravity

NASA Astrophysics Data System (ADS)

For higher-derivative f( R) gravity, where R is the Ricci scalar, a class of models is proposed, which produce viable cosmology different from the ACDM at recent times and satisfy cosmological, Solar System, and laboratory tests. These models have both flat and de Sitter spacetimes as particular solutions in the absence of matter. Thus, a cosmological constant is zero in a flat spacetime, but appears effectively in a curved one for sufficiently large R. A “smoking gun” for these models would be a small discrepancy in the values of the slope of the primordial perturbation power spectrum determined from galaxy surveys and CMB fluctuations. On the other hand, a new problem for dark energy models based on f( R) gravity is pointed out, which is connected with the possible overproduction of new massive scalar particles (scalarons) arising in this theory in the very early Universe.

Starobinsky, A. A.

2007-10-01

104

Unified theory of nonlinear electrodynamics and gravity

We describe a class of unified theories of electromagnetism and gravity. The Lagrangian is of the BF type, with a potential for the B field, the gauge group is U(2) (complexified). Given a choice of the potential function the theory is a deformation of (complex) general relativity and electromagnetism, and describes just two propagating polarizations of the graviton and two of the photon. When gravity is switched off the theory becomes the usual nonlinear electrodynamics with a general structure function. The Einstein-Maxwell theory can be recovered by sending some of the parameters of the defining potential to zero, but for any generic choice of the potential the theory is indistinguishable from Einstein-Maxwell at low energies. A real theory is obtained by imposing suitable reality conditions. We also study the spherically-symmetric solution and show how the usual Reissner-Nordstrom solution is recovered.

Torres-Gomez, Alexander; Krasnov, Kirill; Scarinci, Carlos [School of Mathematical Sciences, University of Nottingham, Nottingham, NG7 2RD (United Kingdom)

2011-01-15

105

Absolute Zero: Science Educator's Guide

NSDL National Science Digital Library

This guide provides recommendations for curricular modules on low temperature physics. Designed for teachers and informal educators of middle school students. this guide complements the Absolute Zero Community Education Outreach Guide. Suggestions on leading discussions, increasing student participation, and the use of inquiry are included. This material is related to a two-part public broadcasting special, Absolute Zero, produced by Meridian Productions and Windfall Films. Absolute Zero is underwritten by the National Science Foundation and the Alfred P. Sloan Foundation and is based largely on Tom Shachtmanâs acclaimed book, Absolute Zero and the Conquest of Cold.

2008-09-18

106

NASA Astrophysics Data System (ADS)

This proposal obtains the photometric zero points in 53 of the 62 UVIS/WFC3 filters: the 18 broad-band filters, 8 medium-band filters, 16 narrow-band filters, and 11 of the 20 quad filters {those being used in cycle 17}. The observations will be primary obtained by observing the hot DA white dwarf standards GD153 and G191-B2B. A redder secondary standard, P330E, will be observed in a subset of the filters to provide color corrections. Repeat observations in 16 of the most widely used cycle 17 filters will be obtained once per month for the first three months, and then once every second month for the duration of cycle 17, alternating and depending on target availability. These observations will enable monitoring of the stability of the photometric system. Photometric transformation equations will be calculated by comparing the photometry of stars in two globular clusters, 47 Tuc and NGC 2419, to previous measurements with other telescopes/instruments.;

Kalirai, Jasonjot

2008-07-01

107

Gravity-induced cellular and molecular processes in plants studied under altered gravity conditions

NASA Astrophysics Data System (ADS)

With the ability to sense gravity plants possess a powerful tool to adapt to a great variety of environmental conditions and to respond to environmental changes in a most beneficial way. Gravity is the only constant factor that provides organisms with reliable information for their orientation since billions of years. Any deviation of the genetically determined set-point angle of the plants organs from the vector of gravity is sensed by specialized cells, the statocytes of roots and shoots in higher plants. Dense particles, so-called statoliths, sediment in the direction of gravity and activate membrane-bound gravireceptors. A physiological signalling-cascade is initiated that eventually results in the gravitropic curvature response, namely, the readjust-ment of the growth direction. Experiments under microgravity conditions have significantly contributed to our understanding of plant gravity-sensing and gravitropic reorientation. For a gravity-sensing lower plant cell type, the rhizoid of the green alga Chara, and for statocytes of higher plant roots, it was shown that the interactions between statoliths and the actomyosin system consisting of the actin cytoskeleton and motor proteins (myosins) are the basis for highly efficient gravity-sensing processes. In Chara rhizoids, the actomyosin represents a guid-ing system that directs sedimenting statoliths to a specific graviperception site. Parabolic flight experiments aboard the airbus A300 Zero-G have provided evidence that lower and higher plant cells use principally the same statolith-mediated gravireceptor-activation mechanism. Graviper-ception is not dependent on mechanical pressure mediated through the weight of the sedimented statoliths, but on direct interactions between the statoliths's surface and yet unknown gravire-ceptor molecules. In contrast to Chara rhizoids, in the gravity-sensing cells of higher plants, the actin cytoskeleton is not essentially involved in the early phases of gravity sensing. Dis-rupting the actomyosin system did not impair the sedimentation of statoliths and did not prevent the activation of gravireceptors. However, experiments in microgravity and inhibitor experiments have demonstrated that the actomyosin system optimizes the statolith-receptor interactions by keeping the sedimented statoliths in motion causing a consistent activation of different gravireceptor molecules. Thereby, a triggered gravitropic signal is created which is the basis for a highly sensitive control and readjustment mechanism. In addition, the results of recent parabolic flight studies on the effects of altered gravity conditions on the gene expres-sion pattern of Arabidopsis seedlings support these findings and provide new insight into the molecular basis of the plants response to different acceleration conditions. The work was financially supported by DLR on behalf of Bundesministerium für Wirtschaft und Technologie (50WB0815).

Vagt, Nicole; Braun, Markus

108

Holographic renormalization of new massive gravity

We study holographic renormalization for three-dimensional new massive gravity. By studying the general falloff conditions for the metric allowed by the model at infinity, we show that at the critical point where the central charges of the dual conformal field theory (CFT) are zero, it contains a leading logarithmic behavior. In the context of AdS/CFT correspondence it can be identified as a source for an irrelevant operator in the dual CFT. The presence of the logarithmic falloff may be interpreted as the fact that the dual CFT would be a logarithmic conformal field theory.

Alishahiha, Mohsen [School of Physics, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of); Naseh, Ali [School of Physics, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531, Tehran (Iran, Islamic Republic of); Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran (Iran, Islamic Republic of)

2010-11-15

109

Spin foam models of Riemannian quantum gravity

NASA Astrophysics Data System (ADS)

Using numerical calculations, we compare three versions of the Barrett-Crane model of four-dimensional Riemannian quantum gravity. In the version with face and edge amplitudes as described by De Pietri, Freidel, Krasnov and Rovelli, we show the partition function diverges very rapidly for many triangulated 4-manifolds. In the version with modified face and edge amplitudes given by Perez and Rovelli, we show the partition function converges so rapidly that the sum is dominated by spin foams where all the spins labelling faces are zero except for small, widely separated islands of higher spin. We also describe a new version which appears to have a convergent partition function without drastic spin-zero dominance. Finally, after a general discussion of how to extract physics from spin foam models, we discuss the implications of convergence or divergence of the partition function for other aspects of a spin foam model.

Baez, John C.; Christensen, J. Daniel; Halford, Thomas R.; Tsang, David C.

2002-09-01

110

A zero-home locator includes a fixed phototransistor switch and a moveable actuator including two symmetrical, opposed wedges, each wedge defining a point at which switching occurs. The zero-home location is the average of the positions of the points defined by the wedges.

Stone, W.J.

1983-10-31

111

Zero knowledge proofs of identity

In this paper we extend the notion of zero knowledge proofs of membership (which reveal one bit of information) to zero knowledge proofs of knowledge (which reveal no information whatsoever). After formally defining this notion, we show its relevance to identification schemes, in which parties prove their identity by demonstrating their knowledge rather than by proving the validity of assertions.

U. Fiege; Amos Fiat; Adi Shamir

1987-01-01

112

Gravity measurements over Burdwood Bank

Gravity measurements in the South Atlantic Ocean over Burdwood Bank show a large negative gravity anomaly extending along its northern edge. An interpretation of the gravity data has been made based on the seismic refraction measurements of Ludwig et al. (1968) and shows that the negative gravity anomaly can be largely attributed to a basin containing low density sediments about

F. J. Davey

1972-01-01

113

National Technical Information Service (NTIS)

Newton's and Einstein's descriptions of gravity are compared and contrasted with the examples of a terrestrial projectile and the black hole. The role of black holes is described in astrophysical contexts.

J. V. Narlikar

1986-01-01

114

National Technical Information Service (NTIS)

The project describes the feasibility of using artificial gravity simulators, such as have been used in research training in the National Space Program, to stimulate functional independence in patients with neuromuscular disabilities. It was hypothesized ...

C. Vallbona M. Partridge J. Canzoneri G. Midgley E. Pevny

1970-01-01

115

ERIC Educational Resources Information Center

|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…

Nelson, George

2004-01-01

116

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 vacuum solution of the fourth-order gravity theory that

A. J. Accioly

1987-01-01

117

Marine gravity image available

NASA Astrophysics Data System (ADS)

The image below shows the gravity field from 30-72°S computed from Geosat geodetic mission (GM) and exact repeat mission (ERM) data. A color shaded-relief image of these gravity anomalies is available from NOAA in poster form (report MGG-8, [Marks et al., 1993] and also as a digital gridded data set on CD-ROM. To order, contact the National Geophysical Data Center, E/GC3, 325 Broadway, Boulder, CO 80303.

118

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 ? F = dC arise in the chiral anomaly, even when coupled to gravity. Implications

Eckehard W. Mielke; Eckehard W

2006-01-01

119

NASA Astrophysics Data System (ADS)

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.

Capozziello, Salvatore; de Laurentis, Mariafelicia

2011-12-01

120

Seesaw modification of gravity

NASA Astrophysics Data System (ADS)

We discuss a model in which the fundamental scale of gravity is restricted to 10-3 eV. An observable modification of gravity occurs simultaneously at the Hubble distance and at around 0.1 mm. These predictions can be tested both by the table-top experiments and by cosmological measurements. The model is formulated as a brane-world theory embedded in a space with two or more infinite-volume extra dimensions. Gravity on the brane reproduces the four-dimensional laws at observable distances but turns to the high-dimensional behavior at larger scales. To determine the crossover distance we smooth out the singularities in the Green’s functions by taking into account softening of the graviton propagator due to the high-dimensional operators that are suppressed by the fundamental scale. We find that irrespective of the precise nature of microscopic gravity the ultraviolet and infrared scales of gravity modification are rigidly correlated. This fixes the fundamental scale of gravity at 10-3 eV. The result persists for nonzero thickness branes.

Dvali, Gia; Gabadadze, Gregory; Hou, Xin-Rui; Sefusatti, Emiliano

2003-02-01

121

NASA Astrophysics Data System (ADS)

The strongest of six experiments showing without ambiguity that gravity is faster than the speed of light (c) sets a lower limit to the propagation speed of gravitational force of 20 billion c. Such speeds are allowed and are causal in Lorentzian relativity. Meanwhile, changes in gravitational potential account for the relativistic effects of gravitation such as light-bending, and they propagate at speed c. This dichotomy of speeds strongly favors the Le Sage model for the physical interpretation of relativistic gravitation over the now-dubious geometric interpretation. In the former, space is filled with a flux of ultra-fast, ultra-small “gravitons”. Then the apple falls from the tree, not because of a force originating within the Earth, but because Earth blocks part of an otherwise isotropic flux striking the apple. These concepts are now extensively developed in the references below. ** “Possible new properties of gravity”, Astrophys.&SpaceSci. 244:249-261 (1996) ** “The speed of gravity What the experiments say”, Phys.Lett.A 250:1-11 (1998) ** “Reply to comments on ‘The speed of gravity’”, Phys.Lett.A 262:261-263 (1999) ** “Experimental Repeal of the Speed Limit Found.Phys. 32:1031-1068 (2002) ** Pushing Gravity, M. Edwards, ed., Apeiron Press, Montreal, 93-122 ** Meta Research “Gravity” CD, http://metaresearch.org/ (available at meeting)

Van Flandern, Tom

2006-12-01

122

Eliminating clutter by coordinate zeroing

NASA Astrophysics Data System (ADS)

Shallow water doppler sonar is limited by clutter that masks the presence of slow targets. Clutter arises from scattering from irregularities in the bottom or from fish schools. If the source and receiver are fixed in a bi-static sonar configuration, then the bottom scatterers (and sometimes the fish) have only a zero doppler component. Clutter arises from the doppler leakage resulting from sonar signals that are inherently short in time and therefore cannot resolve bottom reverberation in frequency. Here long continuous pulse compressions signals are considered (m-sequences). Ambiguity diagrams are compared with simple CW pulse and PCM pulses. The unique correlation properties of M-sequences lead to a signal sampling method that resolves sonar returns in complete ortho-normal (CON) data sets. Zero doppler returns are identified as either direct arrivals or reverberation returns and then their particular coordinate can be set zero (coordinate zeroing) without affecting other data points. In this way, the zero-doppler bottom reverberation and all doppler leakage is eliminated. As an example, the return from a slow doppler target is imbedded in a very large number of reverberation returns that have higher signal level. As the zero doppler contributions are removed by coordinate zeroing the target becomes detectable.

Deferrari, Harry; Rodgers, Andrew

2005-04-01

123

A new zero voltage and zero current power switching technique

NASA Astrophysics Data System (ADS)

An outline is presented of work done by the authors on a novel converter topology where the power switching occurs at both zero current and zero voltage, giving it some major advantage over the present state of the art. A description is given of the application of this topology to both high- and low-output-voltage converters. Design details and test results are given, together with a full analysis of the operation of the converters.

Weinberg, A. H.; Ghislanzoni, L.

124

National Technical Information Service (NTIS)

The purpose of the paper was to design an automatic flight control system capable of simulating zero-, Moon-, or Mars-gravity environments (=0.005g) in the 'zero-g', KC-135. The problem analysis consists of a mathematical investigation of the simulation o...

R. W. Kennedy

1964-01-01

125

Zero Order Diffraction Display Systems.

National Technical Information Service (NTIS)

This program examined the relative attributes of ZOD (Zero Order Diffraction) microimages FIH (Focused Image Holograms), and Standard Ektachrome (EK) material for application to high brightness displays. Specific comparison of brightness, resolution, cont...

B. R. Clay B. E. Hendrickson

1978-01-01

126

Acquirement of pure gravity orbit using precise formation flying technology

NASA Astrophysics Data System (ADS)

Pure gravity orbit is an orbit removed non-gravity disturbances, which can give a more precise relation between gravity and orbit, and can be used to navigation satellite, earth gravity felid measurement, gravity wave detection and other fundamental physical test mission. In this paper, the author propose a system concept of a new pure gravity orbit acquirement method named inner formation flying system, which treats the PM and the outer satellite as a pair of formation flying satellites. The inner formation flying system consists of an outer satellite and an inner satellite. The outer satellite is a small satellite with a cavity in the center. The inner satellite is a PM flying in the housing of the outer satellite's cavity. So the inner satellite is shielded from non-gravitational forces of atmosphere drag and radiation pressure and flies along a purely gravitational path. From the view of formation flying, the outer satellite can be treated as a formation satellite with zero or small distance to the inner reference satellite. So the analysis of mechanic and dynamics of inner formation is made at first. Then a control architecture including feed forward and feedback strategies is presented and the controller is designed. The simulation is carried out in a high precision formation flying simulation environment at last to validate the inner formation flying methods.

Zhaokui, Wang; Yulin, Zhang

2013-01-01

127

Experimental concept for examination of biological effects of magnetic field concealed by gravity

NASA Astrophysics Data System (ADS)

Space is not only a place to study biological effects of gravity, but also provides unique opportunities to examine other environmental factors, where the biological actions are masked by gravity on the ground. Even the earth's magnetic field is steadily acting on living systems, and is known to influence many biological processes. A systematic survey and assessment of its action are difficult to conduct in the presence of dominant factors, such as gravity. Investigation of responses of biological systems against the combined environment of zero-gravity and zero-magnetic field might establish the baseline for the analysis of biological effects of magnetic factors. We propose, in this paper, an experimental concept in this context, together with a practical approach of the experiments, both in orbit and on the ground, with a thin magnetic shielding film. Plant epicotyl growth was taken as an exemplar index to evaluate technical and scientific feasibility of the proposed system concept.

Yamashita, M.; Tomita-Yokotani, K.; Hashimoto, H.; Takai, M.; Tsushima, M.; Nakamura, T.

2004-01-01

128

NASA Astrophysics Data System (ADS)

The thesis is devoted to a number of fundamental issues at the intersection of particle physics and cosmology. In particular, we invent one of the first models of the brane inflationary scenario in string theory, the so-called D-brane inflation. In this picture, the role of the inflation field is played by the brane-anti-brane separation. Branes are slowly attracted toward each other. During this slow motion, the potential energy of their tension causes the four-dimensional space to inflate. Inflation ends by the brane collision and annihilation, which reheats the Universe. Thus, in our picture inflation acquires a novel geometric meaning as seen from high-dimensional string theory. Another subject investigated in the thesis is the large distance modification of gravity, which is motivated by the observed mysterious accelerated expansion of the Universe. We study different aspects of the two possible approaches leading to modified gravity. One is Dvali-Gabadadze-Porrati (DGP) model, in which gravity gets modified at large distances because of the presence of extra dimensions. We study some cosmological and gravitational aspects of this theory. We also discuss an alternative picture in which gravity is modified directly in four dimensions due to the addition of some lower dimensional curvature invariants to the Einstein's action. We show that such local modifications of gravity are not viable, as they always propagate additional degrees of freedom that are excluded either by experiments or by the consistency requirements of the theory.

Solganik, Sviatoslav

129

A Lifshitz black hole in four dimensional R2 gravity

NASA Astrophysics Data System (ADS)

We consider a higher derivative gravity theory in four dimensions with a negative cosmological constant and show that vacuum solutions of both Lifshitz type and Schrödinger type with arbitrary dynamical exponent z exist in this system. Then we find an analytic black hole solution which asymptotes to the vacuum Lifshitz solution with z = 3/2 at a specific value of the coupling constant. We analyze the thermodynamic behavior of this black hole and find that the black hole has zero entropy while non-zero temperature, which is very similar to the case of BTZ black holes in new massive gravity at a specific coupling. In addition, we find that the three dimensional Lifshitz black hole recently found by E. Ayon-Beato et al. has a negative entropy and mass when the Newton constant is taken to be positive.

Cai, Rong-Gen; Liu, Yan; Sun, Ya-Wen

2009-10-01

130

NASA Astrophysics Data System (ADS)

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-soliton 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.

Goetz, Guenter

1988-05-01

131

NASA Astrophysics Data System (ADS)

Einstein-Strauss Hermitian gravity was recently formulated as a gauge theory where the tangent group is taken to be the pseudo-unitary group instead of the orthogonal group. A Higgs mechanism for massive gravity was also formulated. We generalize this construction to obtain massive Hermitian gravity with the use of a complex Higgs multiplet. We show that both the graviton and antisymmetric tensor acquire the same mass. At the linearized level, the theory is ghost free around Minkowski background and describes a massive graviton with five degrees of freedom and an antisymmetric field with three degrees of of freedom. We determine the strong coupling scales for these degrees of freedom and argue that the potential nonlinear ghosts, if they exist, have to decouple from the gravitational degrees of freedom in strong coupling regime.

Chamseddine, Ali H.; Mukhanov, Viatcheslav

2012-08-01

132

Clifford tetrads, null zig zags, and quantum gravity

. Quantum gravity has been so elusive because we have tried to approach it by two paths which can never meet: standard quantum\\u000a field theory and general relativity. These contradict each other, not only in superdense regimes, but also in the vacuum,\\u000a where the divergent zero-point energy would roll up space to a point. The solution is to build in a

Marcus S. Cohen

2003-01-01

133

New energy definition for higher-curvature gravities

NASA Astrophysics Data System (ADS)

We propose a novel but natural definition of conserved quantities for gravity models of quadratic and higher order in curvature. Based on the spatial asymptotics of curvature rather than of metric, it avoids the more egregious problems—such as zero-energy “theorems” and failure in flat backgrounds—in this fourth-derivative realm. In D>4, the present expression indeed correctly discriminates between second-derivative Gauss-Bonnet and generic, fourth-derivative actions.

Deser, S.; Tekin, Bayram

2007-04-01

134

Planar diagrams, two-dimensional lattice gravity and surface models

NASA Astrophysics Data System (ADS)

Some discrete lattice models for quantum two-dimensional euclidean gravity are shown to be equivalent to zero-dimensional planar field theories. Explicit expressions are given for partition functions. A universal continuum limit exists for open surfaces, but not for closed ones, and is argued to describe a space with negative average curvature. Extensions to those models to higher dimensions and to surface models are briefly discussed. Chercheur CNRS.

David, F.

135

Canadian low-gravity research using parabolic aircraft

NASA Astrophysics Data System (ADS)

An active experimental program being implemented by Canada in microgravity, which relies heavily on the use of parabolic aircraft, is discussed. The advantages of zero-gravity aircraft include low cost and quick turnaround. These aircraft have demonstrated their value for prototyping experimental hardware developments planned for flight at other facilities, such as sounding rockets and Shuttle-based carriers which are supported by the Canadian Space Agency.

Campbell, Glen S.; Vezina, L.; Aitken, J. F.

1992-12-01

136

NASA Astrophysics Data System (ADS)

Gravity is one of the most inexplicable forces of nature, controlling everything, from the expansion of the Universe to the ebb and flow of ocean tides. The search for the laws of motion and gravitation began more than two thousand years ago, a quest that Prabhakar Gondhalekar recounts in The Grip of Gravity. Beginning with Aristotle and concluding with Planck, Gondhalekar outlines a 'genealogy' of gravity and lucidly explains how previous explanations have shaped the most recent development in the field, string theory. In this work, physicist and astronomer Gondhalekar describes experiments, both planned and proposed, and clearly explains natural phenomena like ocean tides, seasons, ice ages, the formation of planets, stars, and exotic objects like black holes and neutron stars, which are all controlled by gravity. Including anecdotes and thumb-nail sketches of the personalities involved, The Grip of Gravity provides an introduction to the foundation of modern physics and shows how the current developments in string theory may lead to a new and radical interpretation of gravity. Prabhakar Gondhalekar is an Honorary Fellow in the Department of Physics and Astronomy, University College, London. Until his retirement in 1998, he was the head of the Space Astronomy Group at the Rutherford Appleton Laboratory, where he had been a researcher for 18 years. His research has included a number of topics in galactic and extragalactic astronomy, with his major work focusing on the interstellar medium and active galactic nuclei. Gondhalekar has been awarded Royal Society, Leverhulme Trust, and NATO Research Fellowships to do research in universities in the United States and Israel.

Gondhalekar, Prabhakar

2001-09-01

137

NASA Astrophysics Data System (ADS)

Given a uniformly dense sphere with a hole through its center, gravity is supposed to cause an object dropped into the hole to oscillate between the extremities. This is a prediction of both Newton's and Einstein's theories of gravity. Though every physicist knows what is supposed to happen, nobody has ever seen it happen. Failure to back up the predicted oscillation with empirical evidence is not due to insurmountable technical obstacles; a laboratory experiment to test it is quite feasible. According to the ideals of science, we should not be satis ed with analogies or extrapolations suggesting that the prediction is correct. We should, if possible, get the answer directly from Nature.

Benish, R.

2011-06-01

138

Resummation of Massive Gravity

We construct four-dimensional covariant nonlinear theories of massive gravity which are ghost-free in the decoupling limit to all orders. These theories resume explicitly all the nonlinear terms of an effective field theory of massive gravity. We show that away from the decoupling limit the Hamiltonian constraint is maintained at least up to and including quartic order in nonlinearities, hence excluding the possibility of the Boulware-Deser ghost up to this order. We also show that the same remains true to all orders in a similar toy model.

Rham, Claudia de [Department de Physique Theorique, Universite de Geneve, 24 Quai E. Ansermet, CH-1211 Geneve (Switzerland); Gabadadze, Gregory [Center for Cosmology and Particle Physics, Department of Physics, New York University, New York 10003 (United States); Tolley, Andrew J. [Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106 (United States)

2011-06-10

139

NASA Astrophysics Data System (ADS)

We investigate a simple generalization of the metric exponential f(R) gravity theory that is cosmologically viable and compatible with solar system tests of gravity. We show that, as compared to other viable f(R) theories, its steep dependence on the Ricci scalar R facilitates agreement with structure constraints, opening the possibility of f(R) models with an equation-of-state parameter that could be differentiated from a cosmological constant (wde=-1) with future surveys at both background and perturbative levels.

O'Dwyer, Márcio; Jorás, Sérgio E.; Waga, Ioav

2013-09-01

140

Orbital Gravity Gradiometry Beyond GOCE: Instrument Concept

NASA Astrophysics Data System (ADS)

With the recent maturation of 4-K space cryocooler technology, a multi-year gravity mapping mission based on an advanced superconducting gravity gradiometer (SGG) can now be planned. The original SGG fully developed in the 1990’s had mechanically suspended test masses, which limited the intrinsic sensitivity to 1 mE/?Hz. In zero-g, mechanically free test masses can be magnetically levitated around a common central tube, which improves the sensitivity and axis alignment by two orders of magnitude beyond the earlier device. Using multiple pairs of such magnetically levitated test masses with a baseline of 20 cm, one can construct a three-axis or tensor gradiometer of 0.01 mE/?Hz sensitivity over a frequency band of 0.5 mHz to 0.1 Hz. With the instrument's acceleration rejection capability of one part in 10^9, drag-free and attitude control requirements for the spacecraft will be within the capability of current technology. Such a mission represents a factor of 300 improvement in gradient sensitivity over GOCE with a wider bandwidth. Time-varying gravity signals will be resolved with harmonic degrees up to ~100, extending the resolution of GRACE by a factor of 2. The multiple-axis measurement of the gradiometer will give a better east-west resolution of gravity over satellite-to-satellite tracking. In this paper, we will discuss the design and expected performance of the SGG. We will also report the test results of the new magnetic levitation scheme by a current on a single tube.

Moody, M. V.; Paik, H.; Venkateswara, K. Y.; Shirron, P. J.; Dipirro, M. J.; Canavan, E. R.; Han, S.; Ditmar, P.; Klees, R.; Jekeli, C.; Shum, C.

2010-12-01

141

Transient Gravity Wave Critical Layer.

National Technical Information Service (NTIS)

Numerical simulations of gravity wave, critical layer interactions are presented, which confirm theoretical predictions of critical layer behavior and explain important features of gravity wave observations in the atmosphere, including momentum deposition...

T. J. Dunkerton

1984-01-01

142

Gravity Referenced Elevation Encoder Development.

National Technical Information Service (NTIS)

Recent progress in the development of a gravity-sensor-based instrument for determining the elevation angle of DSN antennas is described. The benefits of such a system include the capability to locate the Gravity Referenced Elevation Encoder (GREE) direct...

R. E. Goddard

1993-01-01

143

Prediction of flammability limit of an unconfined premixed gas in the absence of gravity

The existence of flammability limits in an unconfined gas mixture is investigated in the absence of gravity forces. Results of numerical calculations are presented for lean methane-air mixtures. For an adiabatic system, no flammability limit is found. However, when the heat loss due to radiative band emission from carbon dioxide and water in the burned gas region is included, a lean flammability limit is predicted. The predicted burning velocity does not approach zero at this limit, but has a finite minimum value. Comparison of the calculated flammability limit and minimum burning velocity with experiments at zero gravity shows reasonable agreement.

Sibulkin, M.; Frendi, A. (Div. of Engineering, Brown Univ., Providence, RI (US))

1990-12-01

144

? Abstract Gravity-driven bubbly flows are a specific class of flows, where all action is provided by gravity. An industrial example,is formed,by the so-called bubble column: a vertical cylinder filled with liquid through,which,bubbles,flow that are introduced at the bottom of the cylinder. On the bubble scale, gravity gives rise to buoyancy of individual bubbles. On larger scales, gravity acts on

Robert F. Mudde

2005-01-01

145

NASA Astrophysics Data System (ADS)

Preface; 1. Why things move; 2. From the falling apple to Apollo II; 3. How strong is gravity?; 4. Fusion reactors in space; 5. Living in curved spacetime; 6. Ocean tides and gravity waves; 7. The strange world of black holes; 8. Cosmic energy machines; 9. The Big Bang; 10. The Universe: from simplicity to complexity; 11. Gravity and the creation of matter; 12. The many faces of gravity.

Vishnu Narlikar, Jayant

1996-10-01

146

Gravity in the Weightless Economy

This paper studies the international mobility of technology through the lens of multinational firms. We show that gravity applies to the activity of multinational firms, and the strength of gravity is greatest in technologically-complex, research and development intensive industries. To explain gravity in the weightless economy, we develop a model in which a multinational's production can be fragmented into intermediates

Wolfgang Keller; Stephen R Yeaple

2009-01-01

147

ZERI: Zero Emissions Research Initiative

NSDL National Science Digital Library

Sponsored by the Zero Emissions Research Foundation based in Geneva, Switzerland, ZERI seeks to support industry's transformation to zero emission operations. ZERI advocates either full use of inputs in an industry's own final product or conversion of the inputs for use by other industries or processes. At the site, the user can get information about the fourth Annual World ZERI Congress, read research articles and reports, or learn about ZERI's Worldwide Projects. The site also provides access to other ZERI sites in Brazil, Mexico, Namibia, Japan, and Germany.

148

Assuming the existence of a Multidirectional Homogeneous and Constant Shower of Elementary Particles (MHCSEP) traveling at light speed in space, several basic laws of physics are derived mainly by geometrical considerations. When placing two bodies in space, obstruction of the MHCSEP creates an attractive force among them that coincides, for two bodies, with Newton's law of gravity, generating a mechanical

Jonny Heiss

2000-01-01

149

Baryogenesis by Quantum Gravity

A novel mechanism of baryogenesis is proposed on the basis of the phase transition from the conformal invariant spacetime to the Einstein spacetime in quantum gravity. Strong-coupling gravitational excitations with dynamical mass about 1017 GeV are generated at the transition. They eventually decay into ordinary matters. We show that the low energy effective interactions between the gravitational potential describing the

Ken-Ji Hamada; Azusa Minamizaki; Akio Sugamoto

2008-01-01

150

Gravity in five-dimensional braneworld backgrounds often exhibits problematic features, including kinetic ghosts, strong coupling, and the vDVZ discontinuity. These problems are an obstacle to producing and analyzing braneworld models with interesting and potentially observable modifications of 4d gravity. We examine these problems in a general AdS{sub 5}/AdS{sub 4} setup with two branes and localized curvature from arbitrary brane kinetic terms. We use the interval approach and an explicit ''straight'' gauge-fixing. We compute the complete quadratic gauge-fixed effective 4d action, as well as the leading cubic order corrections. We compute the exact Green's function for gravity as seen on the brane. In the full parameter space, we exhibit the regions which avoid kinetic ghosts and tachyons. We give a general formula for the strong coupling scale, i.e. the energy scale at which the linearized treatment of gravity breaks down, for relevant regions of the parameter space. We show how the vDVZ discontinuity can be naturally but nontrivially avoided by ultralight graviton modes. We present a direct comparison of warping versus localized curvature in terms of their effects on graviton mode couplings. We exhibit the first example of DGP-like crossover behavior in a general warped setup.

Bao, Ruoyu; /Chicago U., EFI /Chicago U.; Carena, Marcela; /Fermilab; Lykken, Joseph; /Chicago U., EFI /Chicago U. /Fermilab; Park, Minjoon; /Chicago U., EFI /Chicago U.; Santiago, Jose; /Fermilab

2005-11-01

151

Doppler radio tracking of the Pioneer Venus orbiter has provided gravity measures over a significant portion of Venus. Feature resolution is approximately 300-1000 km within an area extending from 10 deg S to 40 deg N latitude and from 70 deg W to 130 deg E longitude (approximately equal to 200 deg). Many anomalies were detected, and there is considerable

W. L. Sjogren; R. J. Phillips; P. W. Birkeland; R. N. Wimberly

1980-01-01

152

The quantum fermions plus gravity system (QGD) is studied using the loop representation. A Hamiltonian is constructed that governs the evolution in the physical time given by a (``clock'') scalar field. The Hamiltonian, defined via a regularization, is finite, background independent, and diffeomorphism invariant; it acts on intersections and end points of open curves. The dynamics is thus coded into

Hugo A. Morales-Técotl; Carlo Rovelli

1994-01-01

153

Starting from the definition of entropy used in statistical mechanics we show that it is proportional to the gravity action. For a stationary black hole this entropy is expressed as S=E/2T, where T is the Hawking temperature and E is shown to be the Komar energy. This relation is also compatible with the generalized Smarr formula for mass.

Banerjee, Rabin; Majhi, Bibhas Ranjan [S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata-700098 (India)

2010-06-15

154

Gravity in five-dimensional braneworld backgrounds often exhibits problematic features, including kinetic ghosts, strong coupling, and the van Dam-Veltman-Zakharov (vDVZ) discontinuity. These problems are an obstacle to producing and analyzing braneworld models with interesting and potentially observable modifications of 4d gravity. We examine these problems in a general AdS{sub 5}/AdS{sub 4} setup with two branes and localized curvature from arbitrary brane kinetic terms. We use the interval approach and an explicit straight gauge-fixing. We compute the complete quadratic gauge-fixed effective 4d action, as well as the leading cubic order corrections. We compute the exact Green's function for gravity as seen on the brane. In the full parameter space, we exhibit the regions which avoid kinetic ghosts and tachyons. We give a general formula for the strong coupling scale, i.e., the energy scale at which the linearized treatment of gravity breaks down, for relevant regions of the parameter space. We show how the vDVZ discontinuity can be naturally but nontrivially avoided by ultralight graviton modes. We present a direct comparison of warping versus localized curvature in terms of their effects on graviton mode couplings. We exhibit the first example of Dvali-Gabadadze-Porrati (DGP)-like crossover behavior in a general warped setup.

Bao Ruoyu; Park, Minjoon [Enrico Fermi Institute and Department of Physics, University of Chicago, 5640 South Ellis Ave., Chicago, Illinois 60637 (United States); Carena, Marcela; Santiago, Jose [Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, Illinois 60510 (United States); Lykken, Joseph [Enrico Fermi Institute and Department of Physics, University of Chicago, 5640 South Ellis Ave., Chicago, Illinois 60637 (United States); Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, Illinois 60510 (United States)

2006-03-15

155

NASA Astrophysics Data System (ADS)

Starting from the definition of entropy used in statistical mechanics we show that it is proportional to the gravity action. For a stationary black hole this entropy is expressed as S=E/2T, where T is the Hawking temperature and E is shown to be the Komar energy. This relation is also compatible with the generalized Smarr formula for mass.

Banerjee, Rabin; Majhi, Bibhas Ranjan

2010-06-01

156

ERIC Educational Resources Information Center

|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.|

Newburgh, Ronald

2010-01-01

157

National Technical Information Service (NTIS)

The report describes a cryogenic gravity meter which has a theoretical sensitivity of about 25 millimicrogal. The instrument consists of two parts--a suspension unit and a detection module. There are nine other units of power supplies, amplifiers, and oth...

A. Waleh V. S. Tuman

1971-01-01

158

ERIC Educational Resources Information Center

|Proposes an error gravity/distribution factor to give a mathematically consistent evaluation method to error analysis. Such an approach assumes that "seriousness" of error is related to frequency of output and not to notions of degree of communicative difficulty. Distribution of error type is also taken into account. (PJM)|

Palmer, David

1980-01-01

159

An experiment measuring the gravitational acceleration of antimatter would be of great importance to the understanding of quantum gravity. If the equivalence principle of gravitation, which holds that two objects fall with the same gravitational acceleration irrespective of mass or material composition, is found to be violated by accurate measurements of the gravitational acceleration of antimatter, substantial implications would follow

Terry Goldman; Richard J. Hughes; Michael Martin Nieto

1988-01-01

160

NSDL National Science Digital Library

This lab is between a Level 2 and Level 3 inquiry activity in that it should be assigned after students understand acceleration but before they learn about the acceleration gravity. Because there are many sources of error when using a pendulum, students c

Horton, Michael

2009-05-30

161

Stepping Back from Zero Tolerance

ERIC Educational Resources Information Center

|Schools' use of zero tolerance policies has been increasing since the 1980s as part of a societal movement to crack down on drug abuse and violence among youth. But far from making schools safer, this harsh, inflexible approach to discipline has been eroding the culture of schools and creating devastating consequences for children, writes…

Browne-Dianis, Judith

2011-01-01

162

We consider the notion of dimension in four categories: the category of (unbounded) separable metric spaces and (metrically proper) Lipschitz maps, and the category of (unbounded) separable metric spaces and (metrically proper) uniform maps. A unified treatment is given to the large scale dimension and the small scale dimension. We show that in all categories a space has dimension zero

N. Brodskiy; J. Dydak; J. Higes; A. Mitra

2007-01-01

163

Zero order diffraction display systems

This program examined the relative attributes of ZOD (Zero Order Diffraction) microimages FIH (Focused Image Holograms) holograms, and Standard Ektachrome (EK) material for application to high brightness displays. Specific comparison of brightness, resolution, contrast, and colorimetry were made using a breadboard viewing screen system allowing simultaneous side-by-side projection of the three media. Typical subject matter included aerial maps, resolution, and

B. R. Clay; B. E. Hendrickson

1978-01-01

164

Questioning Zero and Negative Numbers

ERIC Educational Resources Information Center

After experiencing a Developing Mathematical Ideas (DMI) class on the construction of algebraic concepts surrounding zero and negative numbers, the author conducted an interview with a first grader to determine the youngster's existing level of understanding about these topics. Uncovering young students' existing understanding can provide focus…

Wilcox, Virginia B.

2008-01-01

165

A versatile zero ripple topology

NASA Astrophysics Data System (ADS)

A lightweight and efficient converter topology is described that presents zero ripple current on both input and output terminals simultaneously. The static and dynamic analyses are performed by using state representation with the current-injected method. A hardware application suitable for a Space Station battery conditioner is presented as a validation of the theoretical model.

Capel, A.; Spruyt, H.; Weinberg, A.; O'Sullivan, D.; Crausaz, A.

166

OBSERVED POLARIZATION OF BROWN DWARFS SUGGESTS LOW SURFACE GRAVITY

Light scattering by atmospheric dust particles is responsible for the polarization observed in some L dwarfs. Whether this polarization arises from an inhomogeneous distribution of dust across the disk or an oblate shape induced by rotation remains unclear. Here, we argue that the latter case is plausible and, for many L dwarfs, the more likely one. Furthermore, evolutionary models of mature field L dwarfs predict surface gravities ranging from about 200 to 2500 m s{sup -2} (corresponding to masses of {approx}15-70 M {sub Jupiter}). Yet comparison of observed spectra to available synthetic spectra often does not permit more precise determination of the surface gravity of individual field L dwarfs, leading to important uncertainties in their properties. Since rotationally induced non-sphericity, which gives rise to non-zero disk-integrated polarization, is more pronounced at lower gravities, polarization is a promising low gravity indicator. Here, we combine a rigorous multiple scattering analysis with a self-consistent cloudy atmospheric model and observationally inferred rotational velocities and find that the observed optical polarization can be explained if the surface gravity of the polarized objects is about 300 m s{sup -2} or less, potentially providing a new method for constraining L dwarf masses.

Sengupta, Sujan [Indian Institute of Astrophysics, Koramangala 2nd Block, Bangalore 560 034 (India); Marley, Mark S., E-mail: sujan@iiap.res.i, E-mail: Mark.S.Marley@NASA.go [NASA Ames Research Center, MS-245-3, Moffett Field, CA 94035 (United States)

2010-10-20

167

Entropy and temperature of black holes in a gravity's rainbow

NASA Astrophysics Data System (ADS)

The linear relation between the entropy and area of a black hole can be derived from the Heisenberg principle, the energy-momentum dispersion relation of special relativity, and general considerations about black holes. There exist results in quantum gravity and related contexts suggesting the modification of the usual dispersion relation and uncertainty principle. One of these contexts is the gravity’s rainbow formalism. We analyze the consequences of such a modification for black hole thermodynamics from the perspective of two distinct rainbow realizations built from doubly special relativity. One is the proposal of Magueijo and Smolin and the other is based on a canonical implementation of doubly special relativity put forward recently by the authors. In these scenarios, we obtain modified expressions for the entropy and temperature of black holes. We show that, for a family of doubly special relativity theories satisfying certain properties, the temperature can vanish in the limit of zero black hole mass. For the Magueijo and Smolin proposal, this is only possible for some restricted class of models with bounded energy and unbounded momentum. With the proposal of a canonical implementation, on the other hand, the temperature may vanish for more general theories; in particular, the momentum may also be bounded, with bounded or unbounded energy. This opens new possibilities for the outcome of black hole evaporation in the framework of a gravity’s rainbow.

Galán, Pablo; Mena Marugán, Guillermo A.

2006-08-01

168

The influence of simulated low-gravity environments on growth, development and metabolism of plants.

Low-gravity environments may be simulated through appropriate horizontal clinostat rotation. This simulation is accomplished through a biological nullification of the directional component of gravitational force. Measuring biologically effective gravity force by organ response, it is readily demonstrated that biologically active gravitational force may be treated as a two-dimensional vector. Though the magnitude dimension of this vector remains virtually constant anywhere on earth, the biologically effective direction dimension may be quantitatively altered by clinostat rotation, provided appropriate angular velocities and angles of inclination of clinostat axes are employed. Using oat seedlings, a rotation rate of 2 rpm, and a horizontal axis clinostat, a 'zero g' environment may be simulated. This simulated 'zero g' condition is attested by the inability of plants to perceive unidirectional gravitational force of sufficient magnitude to elicit directional growth. Under such conditions, plants will grow in the direction imparted by the initial orientation of the plants in the system. Geotropic curvature responses to subsequent geostimulation are, however, greater in seedlings grown under these conditions, nullifying the direction dimension of gravitational force, than in seedlings grown with rotation but with normal unidirectional gravity loads. Root growth under simulated 'zero' gravity conditions is likewise enhanced as compared to plants grown with rotation but normal unidirectional gravity. These differences in magnitude of growth and response to subsequent geostimulation are inexplicable on bases of modified auxin economy or production. Respiration rates are, however, materially enhanced by the simulated 'zero g' environments. This enhancement of respiration, as well as growth, quantitatively diminishes as the unidirectional gravity load is increased. These results imply that the primary effect of low-gravity environments is likely that of modifying the magnitude of respiratory metabolism. Such a modification is partly or wholly explicable on a basis of a modified distribution pattern of metabolically active particulate cell inclusions. PMID:11973847

Dedolph, R R

1967-01-01

169

NSDL National Science Digital Library

This site has students understanding that: 1) Without air resistance, all objects would fall at the same acceleration, regardless of mass. 2) Gravity is the force that causes objects to fall. 3) Air resistance, a type of friction, works against gravity to decrease the acceleration of a falling object. Included in this two day lesson plan are the objectives, needed materials, procedures, adaptations for older students, discussion questions, a rubric for assessment, extension activities, suggested reading, links to other sites, vocabulary, and academic standards. Students can click on a vocabulary word to hear its pronunciation and a sentence using the word. Teachers can link to Teaching Tools to create custom worksheets, puzzles, and quizzes. A printable version can be downloaded. Teachers can purchase the video, The Invisible Force, and download comprehension questions and answers.

Discoveryschool.com; Cahill, Mary

2007-12-12

170

NASA Astrophysics Data System (ADS)

Many concepts of chaotic action in astrodynamics can be appreciated through simulations with home computers and software. Many astrodynamical cases are illustrated. Although chaos theory is now applied to spaceflight trajectories, this presentation employs only inert bodies with no onboard impulse, e.g., from rockets or outgassing. Other nongravitational effects are also ignored, such as atmosphere drag, solar pressure, and radiation. The ability to simulate gravity behavior, even if not completely rigorous, on small mass-market computers allows a fuller understanding of the new approach to astrodynamics by home astronomers, scientists outside orbital mechanics, and students in middle and high school. The simulations can also help a lay audience visualize gravity behavior during press conferences, briefings, and public lectures. No review, evaluation, critique of the programs shown in this presentation is intended. The results from these simulations are not valid for - and must not be used for - making earth-colliding predictions.

Pazmino, John

2007-02-01

171

NASA Astrophysics Data System (ADS)

The paper summarizes the fundamental gravity field constants for Mars and a brief historical review of early determinations and current-day accurate estimates. These include the planetary gravitational constant, global figure, dynamical oblateness, mean density, and rotational period. Topographic results from data acquired from the 1967 opposition to the most recent, 1988, opposition are presented. Both global and selected local topographic variations and features are discussed. The inertia tensor and the nonhydrostatic component of Mars are examined in detail. The dimensionless moment of inertia about the rotational axis is 0.4 for a body of uniform density and 0.37621 if Mars were in hydrostatic equilibrium. By comparing models of both gravity and topography, inferences are made about the degree and depth of compensation in the interior and stresses in the lithosphere.

Esposito, P. B.; Banerdt, W. B.; Lindal, G. F.; Sjogren, W. L.; Slade, M. A.; Bills, B. G.; Smith, D. E.; Balmino, G.

172

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.

Brown, R.E.; Camp, J.B.; Darling, T.W.

1990-01-01

173

NASA Astrophysics Data System (ADS)

We find a new class of theories of massive gravity with five propagating degrees of freedom where only rotations are preserved. Our results are based on a nonperturbative and background-independent Hamiltonian analysis. In these theories the weak field approximation is well behaved and the static gravitational potential is typically screened à la Yukawa at large distances, while at short distances no van Dam-Veltman-Zakharov discontinuity is found and there is no need to rely on nonlinear effects to pass the solar system tests. The effective field theory analysis shows that the ultraviolet cutoff is (mMPl)1/2?1/?m, the highest possible. Thus, these theories can be studied in the weak-field regime at all the phenomenologically interesting scales and are candidates for a calculable large-distance modified gravity.

Comelli, D.; Nesti, F.; Pilo, L.

2013-06-01

174

NASA Astrophysics Data System (ADS)

Emergent gravity is aimed at constructing a Riemannian geometry from U(1) gauge fields on a noncommutative spacetime. But this construction can be inverted to find corresponding U(1) gauge fields on a (generalized) Poisson manifold given a Riemannian metric ( M, g). We examine this bottom-up approach with the LeBrun metric which is the most general scalar-flat Kähler metric with a U(1) isometry and contains the GibbonsHawking metric, the real heaven as well as the multi-blown up Burns metric which is a scalar-flat Kähler metric on {{C}^2} with n points blown up. The bottom-up approach clarifies some important issues in emergent gravity.

Lee, Sunggeun; Roychowdhury, Raju; Yang, Hyun Seok

2012-09-01

175

Cambridge Cosmology: Quantum Gravity

NSDL National Science Digital Library

This section of Cambridge Cosmology explains the concepts of quantum gravity and quantum cosmology, and how they are useful in understanding space and the space-time continuum. This includes the M-theory, formerly known as the string theory, and the Holographic Principle, in order to explain phenomena such as black holes and the first one-hundredth of a second of the Big Bang.

Hertog, Thomas; Herdeiro, Carlos; Chamblin, H.; Ashbourn, J.; Reall, Harvey

176

I review the problem of dark energy focussing on cosmological constant as the candidate and discuss what it tells us regarding\\u000a the nature of gravity. Section 1 briefly overviews the currently popular “concordance cosmology” and summarizes the evidence\\u000a for dark energy. It also provides the observational and theoretical arguments in favour of the cosmological constant as a\\u000a candidate and emphasizes

T. Padmanabhan

2008-01-01

177

Gravity, Time, and Lagrangians

ERIC Educational Resources Information Center

|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…

Huggins, Elisha

2010-01-01

178

Preliminary results of the test of the Newtonian Law of Gravitation conducted by Ander et al., in a borehole in the Greenland ice-cap were reported at this meeting. In this paper we consider the interpretations of these results in terms of a non-Newtonian component of gravity, and compare them with the results of other geophysical inverse-square law tests. 8 refs.

Hughes, R.J.; Goldman, T.; Nieto, M.M.

1988-01-01

179

NSDL National Science Digital Library

Students take a series of gravity measurements to estimate the height of the walkway near the top of the atrium in Howe-Russell. Students turn in a copy of the data sheet plus 1) an explanation of how they converted dial measurements to mgals; 2) plot of instrument drift/Earth tides correction; 3) estimate of elevation of the walkway using a Free-Air Correction; and 4) a brief (paragraph or two) discussion of potential errors in the survey.

180

Noncommutative Symmetries and Gravity

NASA Astrophysics Data System (ADS)

Spacetime geometry is twisted (deformed) into noncommutative spacetime geometry, where functions and tensors are now star-multiplied. Consistently, spacetime diffeomorhisms are twisted into noncommutative diffeomorphisms. Their deformed Lie algebra structure and that of infinitesimal Poincaré transformations is defined and explicitly constructed. This allows to construct a noncommutative theory of gravity. This article is based on common work with Christian Blohmann, Marija Dimitrijevig, Frank Meyer, Peter Schupp and Julius Wess.

Aschieri, Paolo

2006-11-01

181

Full gravity gradient tensors from vertical gravity by cosine transform

NASA Astrophysics Data System (ADS)

We present a method to calculate the full gravity gradient tensors from pre-existing vertical gravity data using the cosine transform technique and discuss the calculated tensor accuracy when the gravity anomalies are contaminated by noise. Gravity gradient tensors computation on 2D infinite horizontal cylinder and 3D "Y" type dyke models show that the results computed with the DCT technique are more accurate than the FFT technique regardless if the gravity anomalies are contaminated by noise or not. The DCT precision has increased 2 to 3 times from the standard deviation. In application, the gravity gradient tensors of the Hulin basin calculated by DCT and FFT show that the two results are consistent with each other. However, the DCT results are smoother than results computed with FFT. This shows that the proposed method is less affected by noise and can better reflect the fault distribution.

Jiang, Fu-Yu; Huang, Yan; Yan, Ke

2012-06-01

182

On Black Hole Stability in Critical Gravities

NASA Astrophysics Data System (ADS)

We consider extended cosmological gravities with Ricci tensor and scalar squared terms in diverse dimensions. These theories admit solutions of Einstein metrics, including the Schwarzschild-Tangherlini AdS black holes, whose mass and entropy vanish at the critical point. We perform linearized analysis around the black holes and show that in general the spectrum consists of the usual spin-2 massless and ghost massive modes. We demonstrate that there is no exponentially-growing tachyon mode in the black holes. At the critical point, the massless spin-2 modes have zero energy whilst the massive spin-2 modes are replaced by the log modes. There always exist certain linear combination of massless and log modes that has negative energy. Thus the stability of the black holes requires that the log modes to be truncated out by the boundary condition.

Liu, Haishan; Lü, H.; Luo, Mingxing

183

NSDL National Science Digital Library

This Science Object is the third of three Science Objects in the Gravity and Orbits SciPack. It provides an understanding of how gravitational forces influence the motion of an object in orbit. When a force acts toward a single center, an object's forward motion and its motion toward that center can combine to create a curved path around the center. Gravity governs the motion of all objects in the solar system. The Sun's gravitational pull holds the Earth and other planets in their orbits, just as the planets' gravitational pull keeps their moons in orbit around them. Learning Outcomes:ï¿½ Describe the conditions that would lead an object into orbital motion in terms of the effects of gravitational force.ï¿½ Explain how an object orbits a planet in terms of trajectories and free fall.ï¿½ Identify gravity as the force that keeps the planets in their orbits around the Sun and the moons in their orbits around the planets.

National Science Teachers Association (NSTA)

2006-11-01

184

Alternative Theories of Gravity

NASA Astrophysics Data System (ADS)

This work investigates alternative theories of gravity, the solutions to their field equations and the constraints that can be imposed upon them from observation and experiment. Specifically, we consider the cosmologies and spherically symmetric solutions that can be expected to result from scalar-tensor and fourth-order theories of gravity. We find exact cosmological solutions of various different kinds; isotropic and anisotropic, homogeneous and inhomogeneous. These solutions are used to investigate the behaviour of the Universes at both late and early times, to investigate the effects of corrections to general relativity on approach to an initial singularity and to look for effects which may be observable in the present day Universe. We use physical processes, such as the primordial nucleosynthesis of the light elements, to impose constraints upon any deviations from the standard model. Furthermore, we investigate the vacuum spherically symmetric solutions of these theories. This environment is of particular interest for considerations of the local effects of gravity, where the most accurate experiments and observations of gravitational phenomena can be performed. Exact solutions are obtained for this situation and their stability analysed. It is found that a variety of new behaviour is obtainable in these theories that was not previously possible in the standard model. This new behaviour allows us an extended framework in which to consider gravitational physics, and its cosmological consequences.

Clifton, T.

2006-10-01

185

“Zero tolerance” has become the international “buzz word” of the secondary building administrator. As school violence has increased so have the legislative and regulatory policy-making mandates calling for increased disciplinary consequences for inappropriate student behavior. Ethical problem-solving and decision-making have taken a back seat to reactive discipline by school officials. Media publicity has forced proactive principals to become reactive impulsive

Kevin Gorman; Patrick Pauken

2003-01-01

186

Disposable remote zero headspace extractor

The remote zero headspace extractor uses a sampling container inside a stainless steel vessel to perform toxicity characteristics leaching procedure to analyze volatile organic compounds. The system uses an in line filter for ease of replacement. This eliminates cleaning and disassembly of the extractor. All connections are made with quick connect fittings which can be easily replaced. After use, the bag can be removed and disposed of, and a new sampling container is inserted for the next extraction.

Hand, Julie J. (Idaho Falls, ID); Roberts, Mark P. (Arco, ID)

2006-03-21

187

Examination of Biological Effects of Magnetic Field Concealed by Gravity

NASA Astrophysics Data System (ADS)

Response of biological systems against combined environment of zero-gravity and zero-magnetic field should be examined as the baseline to investigate biological effects of magnetic field that might be concealed by gravity. Space offers unique opportunities to conduct such study because long term microgravity is available for the scientific use. However, magnetic environment has been neither well controlled nor documented both in space and ground based experiments. Biological specimen is exposed to the various magnetic field of Earth during the revolutions in orbit. The profile of magnetic field varying in time depends on the orbital parameters and attitude of the space platform. Furthermore, the onboard 1 G control group is subjected to centrifugation spinning where magnetic field varies differently from the microgravity experiment group. It can not be accepted as the 1 G control in terms of magnetic environment. We propose experiment set up to shield exotic magnetic field experienced in orbiting space experiment platform. Thin film of amorphous metal or alloys has shielding capability, and is feasible to implement for space experimentation. In order to simulate zero-gravity and zero-magnetic field on ground, we developed a 3D- clinostat that equips a magnetic shielding layer for specimen. In order to evaluate effects of normal magnetic field of Earth, steady magnetic field is induced at the site of specimen inside the shield layer either in orbit or on 3D-clinostat. To fill the matrix of experimental design, 1 G control under the magnetic shielded condition, and 1 G control that is exposed to the normal field should be taken. Degree of magnetic shielding magnitude required for plant studies and other issues were examined by the preliminary experiments using a 3D-clinostat for the studies of etiolated seedlings.

Yamashita, M.; Tomita-Yokotani, K.; Hashimoto, H.; Nakamura, T.

188

Modified dispersion relations lead to a finite zero point gravitational energy

We compute the zero point energy in a spherically symmetric background distorted at high energy as predicted by Gravity's Rainbow. In this context we setup a Sturm-Liouville problem with the cosmological constant considered as the associated eigenvalue. The eigenvalue equation is a reformulation of the Wheeler-DeWitt equation. With the help of a canonical decomposition, we find that the relevant contribution

Remo Garattini; Gianluca Mandanici

2011-01-01

189

Methods are described and demonstrated for detecting the coherent evolution of nuclear spin observables in zero magnetic field with the full sensitivity of high field NMR. The principle motivation is to provide a means of obtaining solid state spectra of the magnetic dipole and electric quadrupole interactions of disordered systems without the line broadening associated with random orientation with respect to the applied magnetic field. Comparison is made to previous frequency domain and high field methods. A general density operator formalism is given for the experiments where the evolution period is initiated by a sudden switching to zero field and is terminated by a sudden restoration of the field. Analytical expressions for the signals are given for a variety of simple dipolar and quadrupolar systems and numerical simulations are reported for up to six coupled spin-1/2 nuclei. Experimental results are reported or reviewed for /sup 1/H, /sup 2/D, /sup 7/Li, /sup 13/C, and /sup 27/Al nuclei in a variety of polycrystalline materials. The effects of molecular motion and bodily sample rotation are described. Various extensions of the method are discussed, including demagnetized initial conditions and correlation by two-dimensional Fourier transformation of zero field spectra with themselves or with high field spectra.

Zax, D.B.; Bielecki, A.; Zilm, K.W.; Pines, A.; Weitekamp, D.P.

1985-11-15

190

The perception of gravity by a plant.

Ever since geotropism was first studied in plants, attempts have been made to create model systems which might simulate the perception by a plant of a gravitational change. The most resilient of these models, the so-called statolith theory, has now enjoyed a run of over 75 years and demonstrates its viability by reappearing in many different forms. It has shown its value by anticipating the now well understood graviperception mechanism in the Chara rhizoid and this will be described. However, it is unlikely that many features of this relatively simple system can be translated to the higher plant. We now know precisely, at least in many primary roots, the distribution and approximate numbers of the cells that perceive gravity. There is no reason to assume that an identical system operates in shoots, since it is now clear that the fundamental hormonal bases of these two systems are different. We also know much about the ultrastructure of many geoperceptive cells, but apart from speculative models a satisfactory explanation of this very rapid and flexible system eludes us. A possible model system is proposed and ways of testing it in zero gravity are suggested. PMID:11536552

Juniper, B E

1977-12-30

191

Linearized Torsion Waves in a Tensor-Tensor Theory of Gravity

We investigate a linearized tensor-tensor theory of gravity with torsion and a perturbed torsion wave solution is discovered in background Minkowski spacetime with zero torsion. Furthermore, gauge transformations of any perturbed tensor field are derived in general background non-Riemannian geometries. By calculating autoparallel deviations, both longitudinal and transverse polarizations of the torsion wave are discovered.

Chih-Hung Wang

2007-01-01

192

Some consequences of gravity-wave critical layers in the upper atmosphere

Atmospheric gravity waves exhibit singular properties at levels where the ambient wind Doppler-shifts their frequency to zero. Some possible consequences are indicated, including the production of turbulence, its termination in the region of the turbopause, the production of kinked wind profiles, and the apparent transport by the wind of ionization irregularities induced by the waves.

C. O. Hines

1968-01-01

193

NASA Astrophysics Data System (ADS)

How accurately do we need to measure seasonal variations in Mars gravity, in order to significantly contribute to an understanding of the seasonal climate cycle? It has long been understood that seasonal cycles of volatile mass transport on Mars, mainly involving CO2 exchange between the atmosphere and the polar caps, will change the gravitational field by measurable amounts. In recent years, the gravitational field models, which are obtained from measured Doppler shifts in the tracking data for Mars-orbiting satellites, have become accurate enough that they can resolve some seasonal variations. However, the present models only resolve seasonal cycles for two parameters, nominally J2 and J3, which are zonal components of degree 2 and 3, respectively. In fact, what is actually observed is an unresolved linear combination of even degree zonals, in the guise of J2, and a similar combination of odd degree zonals for J3. Mars climate models are currently constrained mainly by the surface atmospheric pressure measurements made at the two Viking Lander sites. Wood and Paige (1992) showed that the observed seasonal pressure cycles at these two locations can be very well simulated by a simple one-dimensional surface thermal balance model, when its 6 free parameters (separate values for albedo and emissivity for each polar cap, and a soil thermal inertia for each hemisphere ) are properly chosen. However, it also emerged that the preferred values for albedo and emissivity are quite different from those obtained via optical remote sensing. It thus appears that the 1-D climate model yields aliased estimates of these parameters. It seems clear that, if we had sufficiently accurate gravity measurements, it would be equivalent to having a global grid of effective Viking Lander pressure measurements, with the number of grid points related to the spatial resolution of the gravity measurements. For example, if the seasonal variations were seen in a full Nth degree and order gravity model, that would comprise M = (N+1)2 -4 separate time series (M = 437 for N = 20), and would dramatically decrease the aliasing of thermal parameters in the climate models. To partially address this question, we have used the MarsWRF GCM to compute an annual cycle of surface and atmospheric mass values, on a 5x5 degree surface grid, at 10 day time steps, and then converted the resulting mass distributions into equivalent gravitational potential spherical harmonic coefficients. We can then compare the corresponding signal amplitude spectrum to the estimated gravitational model error amplitude spectrum, for various future mission measurement scenarios. From these simulations, it appears that resolving the seasonal cycle in a full N = 20 gravity model with 30 day time steps, will require substantial improvements beyond the current generation of Mars gravity models. The job of finding solutions to the associated technical problems is still in an early phase. However, it appears that adaptations to Mars of Earth-orbiting gravity missions, such as GRACE or GOCE, should suffice.

Bills, B. G.; Mischna, M. A.

2011-12-01

194

Algebraic quantum gravity (AQG): I. Conceptual setup

NASA Astrophysics Data System (ADS)

We introduce a new top down approach to canonical quantum gravity, called algebraic quantum gravity (AQG). The quantum kinematics of AQG is determined by an abstract *-algebra generated by a countable set of elementary operators labelled by an algebraic graph. The quantum dynamics of AQG is governed by a single master constraint operator. While AQG is inspired by loop quantum gravity (LQG), it differs drastically from it because in AQG there is fundamentally no topology or differential structure. A natural Hilbert space representation acquires the structure of an infinite tensor product (ITP) whose separable strong equivalence class Hilbert subspaces (sectors) are left invariant by the quantum dynamics. The missing information about the topology and differential structure of the spacetime manifold as well as about the background metric to be approximated is supplied by coherent states. Given such data, the corresponding coherent state defines a sector in the ITP which can be identified with a usual QFT on the given manifold and background. Thus, AQG contains QFT on all curved spacetimes at once, possibly has something to say about topology change and provides the contact with the familiar low energy physics. In particular, in two companion papers we develop semiclassical perturbation theory for AQG and LQG and thereby show that the theory admits a semiclassical limit whose infinitesimal gauge symmetry agrees with that of general relativity. In AQG everything is computable with sufficient precision and no UV divergences arise due to the background independence of the fundamental combinatorial structure. Hence, in contrast to lattice gauge theory on a background metric, no continuum limit has to be taken. There simply is no lattice regulator that must be sent to zero.

Giesel, K.; Thiemann, T.

2007-05-01

195

Horava gravity: Symmetries and Generalized Particle Dynamics

NASA Astrophysics Data System (ADS)

In the search for a theory of Quantum Gravity a new proposal was recently made by P. Horava. The main feature of this new proposed theory is that it is power-counting renormalizable by construction, and could prove to be truly renormalizable, although more work is needed in this direction. The renormalizability of the theory is a central issue. Indeed, General Relativity does not have this property, implying that to construct its quantum version we need to "complete" the theory in the UV. Horava suggested a possible way to provide a UV completion of GR by giving up full spacetime reparametrization symmetry, which is one of the fundamental assumptions of GR, and adding appropriate higher order terms in the action. In this Thesis we review Horava's theory and analyze some of the issues related to the breaking of the spacetime structure. Specifically, we derive the general static spherically symmetric solutions for Horava's theory with a nonvanishing radial "shift" field gtr. Such "hedgehog" configurations are not considered in GR, since gtr can be mapped to zero with an appropriate reparametrization, but they are physically distinct solutions in Horava gravity where the reparametrization is not allowed by the reduced symmetry. These new solutions exhibit specific properties from the particle dynamics point of view and possess an extra gauge symmetry. We also study the deformed kinematics of point particles allowed by the reduced reparametrization symmetry. The main result is that particles can have generalized dispersion relations that include higher even powers of the momentum. We analyze the implications of this and provide some examples that may be converted into possible experimental tests for the deviations of this new theory of gravity from standard GR.

Capasso, Dario

196

Geometric scalar theory of gravity

NASA Astrophysics Data System (ADS)

We present a geometric scalar theory of gravity. Our proposal will be described using the ``background field method" introduced by Gupta, Feynman, Deser and others as a field theory formulation of general relativity. We analyze previous criticisms against scalar gravity and show how the present proposal avoids these difficulties. This concerns not only the theoretical complaints but also those related to observations. In particular, we show that the widespread belief of the conjecture that the source of scalar gravity must be the trace of the energy-momentum tensor — which is one of the main difficulties to couple gravity with electromagnetic phenomenon in previous models — does not apply to our geometric scalar theory. From the very beginning this is not a special relativistic scalar gravity. The adjective ``geometric" pinpoints its similarity with general relativity: this is a metric theory of gravity. Some consequences of this new scalar theory are explored.

Novello, M.; Bittencourt, E.; Moschella, U.; Goulart, E.; Salim, J. M.; Toniato, J. D.

2013-06-01

197

Gravity in the Weightless Economy

We show that gravity applies to the activity of multinational …rms, and the strength of gravity is greatest in technologically-complex, research and development intensive industries. To explain gravity in the weightless economy, we develop a model in which a multinational's production can be fragmented into intermediates that vary in the codi…ability of their technology. Poorly codi…ed technology requires face-to-face communication

Wolfgang Keller; Stephen R. Yeaple

2010-01-01

198

Cascading gravity is ghost free

We perform a full perturbative stability analysis of the 6D cascading gravity model in the presence of 3-brane tension. We demonstrate that for sufficiently large tension on the (flat) 3-brane, there are no ghosts at the perturbative level, consistent with results that had previously only been obtained in a specific 5D decoupling limit. These results establish the cascading gravity framework as a consistent infrared modification of gravity.

Rham, Claudia de [Departement de Physique Theorique, Universite de Geneve, 24 Quai E. Ansermet, CH-1211 Geneve (Switzerland); Khoury, Justin [Center for Particle Cosmology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6395 (United States); Tolley, Andrew J. [Perimeter Institute for Theoretical Physics, 31 Caroline St. N., Waterloo, ON, N2L 2Y5 (Canada)

2010-06-15

199

We study Einstein gravity in dimensions D{>=}4 modified by curvature squared at critical point where the theory contains only massless gravitons. We show that at the critical point a new mode appears leading to a logarithmic gravity in the theory. The corresponding logarithmic solution may provide a gravity description of logarithmic conformal field theories (CFT) in higher dimensions. We note also that for special values of the parameters of the theory, the model admits solutions with nonrelativistic isometries.

Alishahiha, Mohsen; Fareghbal, Reza [School of physics, Institute for Research in Fundamental Sciences (IPM), P. O. Box 19395-5531, Tehran (Iran, Islamic Republic of)

2011-04-15

200

Artificial Gravity for Space Travel

This study presents magnetic concepts for artificial gravity and artificial balance on space travel. The magnetic pseudo gravity system could be constructed on any size manned spacecraft, low-gravity planet and moon. Qualitative analysis of the magnetic methods via soft ferrite, Fe oxide nano-particles and ferrofluids is elucidated. The magnetic method could ensure that weight-bearing bones of space travelers are continually

Shun-Wen Cheng

2007-01-01

201

Conformal tensors via Lovelock gravity

NASA Astrophysics Data System (ADS)

Constructs from conformal geometry are important in low dimensional gravity models, while in higher dimensions the higher curvature interactions of Lovelock gravity are similarly prominent. Considering conformal invariance in the context of Lovelock gravity leads to natural, higher curvature generalizations of the Weyl, Schouten, Cotton and Bach tensors, with properties that straightforwardly extend those of their familiar counterparts. As a first application, we introduce a new set of conformally invariant gravity theories in D = 4k dimensions, based on the squares of the higher curvature Weyl tensors.

Kastor, David

2013-10-01

202

Reconstruction of Multidimensional Signals from Zero Crossings.

National Technical Information Service (NTIS)

We present theoretical and experimental results showing that it is possible to reconstruct a broad class of multidimensional signals from only zero crossing information. The importance of zero crossing locations in determining the nature of both one- and ...

S. R. Curtis A. V. Oppenheim

1986-01-01

203

Massive gravity acausality redux

NASA Astrophysics Data System (ADS)

Massive gravity (mGR) is a 5(=2s+1) degree of freedom, finite range extension of GR. However, amongst other problems, it is plagued by superluminal propagation, first uncovered via a second order shock analysis. First order mGR shock structures have also been studied, but the existence of superluminal propagation in that context was left open. We present here a concordance of these methods, by an explicit (first order) characteristic matrix computation, which confirms mGR's superluminal propagation as well as acausality.

Deser, S.; Izumi, K.; Ong, Y. C.; Waldron, A.

2013-10-01

204

NASA Astrophysics Data System (ADS)

Doppler radio tracking of the Pioneer Venus orbiter has provided gravity measures over a significant portion of Venus. Feature resolution is approximately 300-1000 km within an area extending from 10 deg S to 40 deg N latitude and from 70 deg W to 130 deg E longitude (approximately equal to 200 deg). Many anomalies were detected, and there is considerable correlation with radar altimetry topography (Pettengill et al., 1980). The amplitudes of the anomalies are relatively mild and similar to those on earth at this resolution. Calculations for isostatic adjustment reveal that significant compensation has occurred.

Sjogren, W. L.; Phillips, R. J.; Birkeland, P. W.; Wimberly, R. N.

1980-12-01

205

NASA Astrophysics Data System (ADS)

We present a new application of Boundary String Field Theory: calculating the induced-gravity action on a D-brane. Using a simple quadratic tachyon potential to model a D-brane fluctuating in the flat target space we derive the effective action in terms of the extrinsic curvature to all orders in alpha'. We identify both the Born-Infeld structure as well as the Einstein-Hilbert term at order alpha'. This corroborates the conjectured existence of the latter term in the brane-world scenarios. The higher order terms in Ricci scalar and extrinsic curvature suggest a pattern which calls for an explanation.

Cheung, Yeuk-Kwan E.; Laidlaw, Mark; Savvidy, Konstantin

2004-12-01

206

The physical modes of a recently proposed D-dimensional 'critical gravity', linearized about its anti-de Sitter vacuum, are investigated. All 'log mode' solutions, which we categorize as 'spin-2' or 'Proca', arise as limits of the massive spin-2 modes of the noncritical theory. The linearized Einstein tensor of a spin-2 log mode is itself a 'nongauge' solution of the linearized Einstein equations whereas the linearized Einstein tensor of a Proca mode takes the form of a linearized general coordinate transformation. Our results suggest the existence of a holographically dual logarithmic conformal field theory.

Bergshoeff, Eric A.; Rosseel, Jan [Centre for Theoretical Physics, University of Groningen, Nijenborgh 4, 9747 AG Groningen (Netherlands); Hohm, Olaf [Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Townsend, Paul K. [Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge, CB3 0WA (United Kingdom)

2011-05-15

207

Bootstrapping gravity solutions

NASA Astrophysics Data System (ADS)

We construct an algorithm to determine all stationary axi-symmetric solutions of 3-dimensional Einstein gravity with a minimally coupled self-interacting scalar field. We holographically renormalize the theory and evaluate then the on-shell action as well as the stress tensor and scalar one-point functions. We study thermodynamics, derive two universal formulas for the entropy and prove that global AdS provides a lower bound for the mass of certain solitons. Several examples are given in detail, including the first instance of locally asymptotically flat hairy black holes and novel asymptotically AdS solutions with non-Brown-Henneaux behavior.

Aparício, João; Grumiller, Daniel; Lopez, Esperanza; Papadimitriou, Ioannis; Stricker, Stefan

2013-05-01

208

Critical Exponents in Zero Dimensions

NASA Astrophysics Data System (ADS)

In the vicinity of the onset of an instability, we investigate the effect of colored multiplicative noise on the scaling of the moments of the unstable mode amplitude. We introduce a family of zero dimensional models for which we can calculate the exact value of the critical exponents ? m for all the moments. The results are obtained through asymptotic expansions that use the distance to onset as a small parameter. The examined family displays a variety of behaviors of the critical exponents that includes anomalous exponents: exponents that differ from the deterministic (mean-field) prediction, and multiscaling: non-linear dependence of the exponents on the order of the moment.

Alexakis, A.; Pétrélis, F.

2012-11-01

209

NASA Astrophysics Data System (ADS)

It is shown in the first part of this paper that a combined model comprising ordinary and quintessential matter can support a traversable wormhole in Einstein-Maxwell gravity. Since the solution allows zero tidal forces, the wormhole is suitable for a humanoid traveler. The second part of the paper shows that the electric field can be eliminated (Einstein gravity), but only by tolerating enormous tidal forces. Such a wormhole would still be capable of transmitting signals.

Kuhfittig, Peter K. F.

210

Transmission Zeros of Flexible Spinning Spacecraft

This paper shows that the transmission zeros of flexible spinning spacecraft exhibit properties entirely analogous to those of undamped, non-spinning flexible space structures. Thus, the extensive results concerning the zeros in the undamped case (relationships to the poles; sensitivites; computation) apply without change to the zeros of spinning flexible spacecraft.

Trevor Williams

1991-01-01

211

Zero Tolerance in Tennessee Schools: An Update.

ERIC Educational Resources Information Center

As required by Tennessee law, this report examines the state's zero-tolerance disciplinary data collected by the Tennessee Department of Education for school years 1999-00, 2000-01, and 2001-02. The first section displays statewide zero-tolerance statistics. The second section focuses on the zero-tolerance statistics of Tennessee's five major…

Potts, Kim; Njie, Bintou; Detch, Ethel R.; Walton, Jason

212

Modified gravity and cosmology

NASA Astrophysics Data System (ADS)

In this review we present a thoroughly comprehensive survey of recent work on modified theories of gravity and their cosmological consequences. Amongst other things, we cover General Relativity, scalar-tensor, Einstein-æther, and Bimetric theories, as well as TeVeS, f(R), general higher-order theories, Ho?ava-Lifschitz gravity, Galileons, Ghost Condensates, and models of extra dimensions including Kaluza-Klein, Randall-Sundrum, DGP, and higher co-dimension braneworlds. We also review attempts to construct a Parameterised Post-Friedmannian formalism, that can be used to constrain deviations from General Relativity in cosmology, and that is suitable for comparison with data on the largest scales. These subjects have been intensively studied over the past decade, largely motivated by rapid progress in the field of observational cosmology that now allows, for the first time, precision tests of fundamental physics on the scale of the observable Universe. The purpose of this review is to provide a reference tool for researchers and students in cosmology and gravitational physics, as well as a self-contained, comprehensive and up-to-date introduction to the subject as a whole.

Clifton, Timothy; Ferreira, Pedro G.; Padilla, Antonio; Skordis, Constantinos

2012-03-01

213

General relativity (GR) is a phenomenologically successful theory that rests on firm foundations, but has not been tested on cosmological scales. The deep mystery of dark energy (and possibly even the requirement of cold dark matter (CDM)) has increased the need for testing modifications to GR, as the inference of such otherwise undetected fluids depends crucially on the theory of gravity. Here, I discuss a general scheme for constructing consistent and covariant modifications to the Einstein equations. This framework is such that there is a clear connection between the modification and the underlying field content that produces it. I argue that this is mandatory for distinguishing modifications of gravity from conventional fluids. I give a non-trivial example, a simple metric-based modification of the fluctuation equations for which the background is exact ?CDM, but differs from it in the perturbations. I show how this can be generalized and solved in terms of two arbitrary functions. Finally, I discuss future prospects and directions of research. PMID:22084286

Skordis, Constantinos

2011-12-28

214

NASA Astrophysics Data System (ADS)

We study collinear and soft singularities in perturbative quantum gravity by constructing an effective field theory similar to soft-collinear effective theory for QCD (SCET). We find that the soft sector exhibits factorization properties similar to those of SCET. The collinear sector is, however, quite different. While the leading-power collinear effective Lagrangian is trivial, the presence of the metric field h ++ with negative scaling dimension allows for collinear divergences in loop diagrams with couplings to non-collinear sources. We provide a compact proof of the well-known fact that there are no collinear singularities in perturbative quantum gravity by demonstrating the decoupling of h ++ from the sources. We briefly discuss the connection of our approach to recent work by Akhoury et al. (Phys. Rev. D84 (2011) 104040) as well as to the Weinberg's original paper (Phys. Rev. 140 (1965) B516), where the cancellation of the collinear singularities was demonstrated for the first time in the eikonal approximation.

Beneke, Martin; Kirilin, Grisha

2012-09-01

215

After reviewing some aspects of gravity in two dimensions, I show that non-trivial embeddings of sl(2) in a semi-simple (super) Lie algebra give rise to a very large class of extensions of 2D gravity. The induced action is constructed as a gauged WZW model and an exact expression for the effective action is given.

Sevrin, A.

1993-06-01

216

Reduced Gravity Zblan Optical Fiber.

National Technical Information Service (NTIS)

Two optical fiber pullers have been designed for pulling ZBLAN optical fiber in reduced gravity. One fiber puller was designed, built and flown on board NASA's KC135 reduced gravity aircraft. A second fiber puller has been designed for use on board the In...

D. S. Tucker G. L. Workman G. A. Smith

2000-01-01

217

We define various Born-Infeld gravity theories in 3+1 dimensions which reduce to Horava's model at the quadratic level in small curvature expansion. In their exact forms, our actions provide z{yields}{infinity} extensions of Horava's gravity, but when small curvature expansion is used, they reproduce finite z models, including some half-integer ones.

Guellue, Ibrahim; Sisman, Tahsin Cagri; Tekin, Bayram [Department of Physics, Middle East Technical University, 06531, Ankara (Turkey)

2010-05-15

218

Nonperturbative model of Liouville gravity

We formulate nonperturbative 2D gravity in the framework of Liouville theory. In particular, we express the specific heat Z of pure gravity in terms of an expansion of integrals on moduli spaces of punctured Riemann spheres. We recognize the relevant divisors on moduli spaces and write the integrands in terms of the Liouville action. We evaluate the integrals (rational intersections)

Marco Matone; G. Galilei

1997-01-01

219

Antimatter Gravity and Antihydrogen Production

Certain modern theories of gravity predict that antimatter will fall differently than matter in the Earth's gravitational field. However, no experimental tests of gravity on antimatter exist and all conclusions drawn from experiments on matter depend, at some level, on a specific model. We have proposed a direct measurement that would compare the gravitational acceleration of antiprotons to that of

Michael H. Holzscheiter; T. Goldman; Michael Martin Nieto

1995-01-01

220

Gravity referenced elevation encoder development

Recent progress in the development of a gravity-sensor-based instrument for determining the elevation angle of DSN antennas is described. The benefits of such a system include the capability to locate the Gravity Referenced Elevation Encoder (GREE) directly on the primary reflector (thus bypassing structural flexure and deformation error sources), anticipated lower maintenance costs compared to the present gimbal encoders, direct

R. E. Goddard

1993-01-01

221

Liquid distributions in unsaturated porous media under different gravitational accelerations and corresponding macroscopic gaseous diffusion coefficients were investigated to enhance understanding of plant growth conditions in microgravity. We used a single-component, multiphase lattice Boltzmann code to simulate liquid configurations in two-dimensional porous media at varying water contents for different gravity conditions and measured gas diffusion through the media using a multicomponent lattice Boltzmann code. The relative diffusion coefficients (D rel) for simulations with and without gravity as functions of air-filled porosity were in good agreement with measured data and established models. We found significant differences in liquid configuration in porous media, leading to reductions in D rel of up to 25% under zero gravity. The study highlights potential applications of the lattice Boltzmann method for rapid and cost-effective evaluation of alternative plant growth media designs under variable gravity. PMID:16173154

Chau, Jessica Furrer; Or, Dani; Sukop, Michael C

2005-08-01

222

Inhalation of particles generated as a result of thermal degradation from fire or smoke, as may occur on spacecraft, is of major health concern to space-faring countries. Knowledge of lung airflow and particle transport under different gravity environments is required to addresses this concern by providing information on particle deposition. Gravity affects deposition of particles in the lung in two ways. First, the airflow distribution among airways is changed in different gravity environments. Second, particle losses by sedimentation are enhanced with increasing gravity. In this study, a model of airflow distribution in the lung that accounts for the influence of gravity was used for a mathematical description of particle deposition in the human lung to calculate lobar, regional, and local deposition of particles in different gravity environments. The lung geometry used in the mathematical model contained five lobes that allowed the assessment of lobar ventilation distribution and variation of particle deposition. At zero gravity, it was predicted that all lobes of the lung expanded and contracted uniformly, independent of body position. Increased gravity in the upright position increased the expansion of the upper lobes and decreased expansion of the lower lobes. Despite a slight increase in predicted deposition of ultrafine particles in the upper lobes with decreasing gravity, deposition of ultrafine particles was generally predicted to be unaffected by gravity. Increased gravity increased predicted deposition of fine and coarse particles in the tracheobronchial region, but that led to a reduction or even elimination of deposition in the alveolar region for coarse particles. The results from this study show that existing mathematical models of particle deposition at 1 G can be extended to different gravity environments by simply correcting for a gravity constant. Controlled studies in astronauts on future space missions are needed to validate these predictions. PMID:16603478

Asgharian, Bahman; Price, Owen; Oberdörster, Gunter

2006-06-01

223

Geologic interpretation of gravity anomalies

This Russian textbook provides a sufficiently complete and systematic illumination of physico-geologic and mathematical aspect of complex problem of interpretation of gravity anomalies. The rational methods of localization of anomalies are examined in detail. All methods of interpreting gravity anomalies are described which have found successful application in practice. Also given are ideas of some new methods of the interpretation of gravity anomalies, the prospects for further development and industrial testing. Numerous practical examples to interpretation are given. Partial Contents: Bases of gravitational field theory; Physico-geologic bases of gravitational prospecting; Principles of geologic interpretation of gravity anomalies; Conversions and calculations of anomalies; Interpretation of gravity anomalies for bodies of correct geometric form and for bodies of arbitrary form; Geologic interpretation of the results of regional gravitational photographing; Searches and prospecting of oil- and gas-bearing structures and of deposits of ore and nonmetalliferous useful minerals.

Andreyev, B.A.; Klushin, I.G.

1990-04-19

224

Fate of the phantom dark energy universe in semiclassical gravity

NASA Astrophysics Data System (ADS)

The fate of the phantom dark energy universe in semiclassical gravity is investigated. Quantum corrections coming from massless fields conformally coupled with gravity are considered, to see if they can lead to avoidance of the big rip singularity, which shows up in a flat Friedmann-Robertson-Walker universe, filled with phantom dark energy and modeled by an equation of state of the form p=?? with ?<-1. The dynamics of the model are discussed for all values of the two parameters, named ?>0 and ?<0, which come from quantum corrections. It is concluded that, when -1<(?)/(3?)<0, almost all solutions develop future singularities (the corresponding scale factor and energy density go down to zero in finite time). However, when -1>(?)/(3?), almost all solutions describe a universe bouncing infinitely many times (an oscillating universe).

Haro, Jaume; Amoros, Jaume; Elizalde, Emilio

2011-06-01

225

In this paper, we explicitly prove the presymplectic forms of the Palatini and Ashtekar gravity to be zero along gauge orbits of the Lorentz and diffeomorphism groups, which ensures the diffeomorphism invariance of these theories.

Yan Luo; Ming-Xue Shao; Zhong-Yuan Zhu

1998-01-01

226

Superconducting gravity gradiometer for sensitive gravity measurements. I. Theory

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.

Chan, H.A.; Paik, H.J.

1987-06-15

227

Superconducting gravity gradiometer for sensitive gravity measurements. I. Theory

NASA Astrophysics Data System (ADS)

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.

Chan, H. A.; Paik, H. J.

1987-06-01

228

Gravity quantized: Loop quantum gravity with a scalar field

...''but we do not have quantum gravity.'' This phrase is often used when analysis of a physical problem enters the regime in which quantum gravity effects should be taken into account. In fact, there are several models of the gravitational field coupled to (scalar) fields for which the quantization procedure can be completed using loop quantum gravity techniques. The model we present in this paper consists of the gravitational field coupled to a scalar field. The result has similar structure to the loop quantum cosmology models, except that it involves all the local degrees of freedom of the gravitational field because no symmetry reduction has been performed at the classical level.

Domagala, Marcin; Kaminski, Wojciech [Instytut Fizyki Teoretycznej, Uniwersytet Warszawski, ul. Hoza 69, 00-681 Warszawa (Warsaw), Polska (Poland) (Poland); Giesel, Kristina [Excellence Cluster Universe, Technische Universitaet Muenchen, Boltzmannstrasse 2, 85748 Garching (Germany); Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803 (United States); Lewandowski, Jerzy [Instytut Fizyki Teoretycznej, Uniwersytet Warszawski, ul. Hoza 69, 00-681 Warszawa (Warsaw), Polska (Poland) (Poland); Institute for Gravitation and the Cosmos, Physics Department, Penn State, University Park, Pennsylvania 16802 (United States)

2010-11-15

229

The system pumping speed was calculated by taking the reciprocal of the sum of the reciprocal pump speed and the reciprocal line conductances. The conductances of the pipe were calculated from the following formulas taken from the Varian vacuum manual. This report updates the original to reflect the pumping curves and basic vacuum system characteristics for the purchased components and installed piping of the D-Zero vacuum system. The system consists of two Edward's E2M275 two stage mechanical pumps, a Leybold-Heraeus WSU2000 Blower and three Varian 4' diffusion pumps (one for each cryostat). Individual pump and system pumping speed curves and a diagram of the system is included.

Wintercorn, S.J.; /Fermilab

1986-04-07

230

Landau Levels and Riemann Zeros

NASA Astrophysics Data System (ADS)

The number N(E) of complex zeros of the Riemann zeta function with positive imaginary part less than E is the sum of a “smooth” function Nmacr (E) and a “fluctuation.” Berry and Keating have shown that the asymptotic expansion of Nmacr (E) counts states of positive energy less than E in a “regularized” semiclassical model with classical Hamiltonian H=xp. For a different regularization, Connes has shown that it counts states “missing” from a continuum. Here we show how the “absorption spectrum” model of Connes emerges as the lowest Landau level limit of a specific quantum-mechanical model for a charged particle on a planar surface in an electric potential and uniform magnetic field. We suggest a role for the higher Landau levels in the fluctuation part of N(E).

Sierra, Germán; Townsend, Paul K.

2008-09-01

231

NASA Astrophysics Data System (ADS)

We describe how a certain simple modification of general relativity, in which the local cosmological constant is allowed to depend on the space-time curvature, predicts the existence of halos of modified gravity surrounding spherically symmetric objects. We show that the gravitational mass of an object weighed together with its halo can be much larger than its gravitational mass as seen from inside the halo. This effect could provide an alternative explanation of the dark-matter phenomenon in galaxies. In this case, the local cosmological constant in the solar system must be some six orders of magnitude larger than its cosmic value obtained in the supernova type Ia experiments. This is well within the current experimental bounds, but may be directly observable in future high-precision experiments.

Krasnov, Kirill; Shtanov, Yuri

232

We propose a phantom crossing Dvali-Gabadadze-Porrati (DGP) model. In our model, the effective equation of state of the DGP gravity crosses the phantom divide line. We demonstrate crossing of the phantom divide does not occur within the framework of the original DGP model or the DGP model developed by Dvali and Turner. By extending their model, we construct a model that realizes crossing of the phantom divide. DGP models can account for late-time acceleration of the universe without dark energy. Phantom Crossing DGP model is more compatible with recent observational data from Type Ia Supernovae (SNIa), Cosmic Microwave Background (CMB) anisotropies, and Baryon Acoustic Oscillations (BAO) than the original DGP model or the DGP model developed by Dvali and Turner.

Hirano, Koichi [Department of Physics, Ichinoseki National College of Technology, Ichinoseki 021-8511 (Japan); Komiya, Zen [Department of Physics, Tokyo University of Science, Tokyo 162-8601 (Japan)

2010-08-12

233

Topological parameters in gravity

NASA Astrophysics Data System (ADS)

We present the Hamiltonian analysis of the theory of gravity based on a Lagrangian density containing the Hilbert-Palatini term along with three topological densities, Nieh-Yan, Pontryagin and Euler. The addition of these topological terms modifies the symplectic structure nontrivially. The resulting canonical theory develops a dependence on three parameters which are coefficients of these terms. In the time gauge, we obtain a real SU(2) gauge theoretic description with a set of seven first-class constraints corresponding to three SU(2) rotations, three spatial diffeomorphisms and one to evolution in a timelike direction. The inverse of the coefficient of the Nieh-Yan term, identified as the Barbero-Immirzi parameter, acts as the coupling constant of the gauge theory.

Kaul, Romesh K.; Sengupta, Sandipan

2012-01-01

234

NASA Astrophysics Data System (ADS)

This thesis summarizes research projects that I have been involved in during my graduate studies at Vanderbilt University. My research spanned different areas of theoretical high energy physics with gravity as a common denominator. I explore both fundamental and phenomenological aspects of: (i) mathematical physics where I have studied relations between partition functions of certain class of conformal field theories and Fischer-Griess Monster group; (ii) cosmology, where I performed a numerical study of a horizon size modes of scalar field; (iii) a black hole physics project involving possible extensions of the non-hair theorem in a presence of exotic types of scalar field; and (iv) a study of phenomenological space-time foam models and their relation to Planck scale physics.

Jankiewicz, Marcin

235

NASA Astrophysics Data System (ADS)

In this paper we elaborate on the idea of an emergent spacetime which arises due to the dynamical breaking of diffeomorphism invariance in the early universe. In preparation for an explicit symmetry breaking scenario, we consider nonlinear realizations of the group of analytical diffeomorphisms which provide a unified description of spacetime structures. We find that gravitational fields, such as the affine connection, metric, and coordinates, can all be interpreted as Goldstone fields of the diffeomorphism group. We then construct a Higgs mechanism for gravity in which an affine spacetime evolves into a Riemannian one by the condensation of a metric. The symmetry breaking potential is identical to that of hybrid inflation but with the noninflaton scalar extended to a symmetric second-rank tensor. This tensor is required for the realization of the metric as a Higgs field. We finally comment on the role of Goldstone coordinates as a dynamical fluid of reference.

Kirsch, Ingo

2005-07-01

236

Discrete Quantum Gravity in the Regge Calculus Formalism

We discuss an approach to the discrete quantum gravity in the Regge calculus formalism that was developed in a number of our papers. The Regge calculus is general relativity for a subclass of general Riemannian manifolds called piecewise flat manifolds. The Regge calculus deals with a discrete set of variables, triangulation lengths, and contains continuous general relativity as a special limiting case where the lengths tend to zero. In our approach, the quantum length expectations are nonzero and of the order of the Plank scale, 10{sup -33} cm, implying a discrete spacetime structure on these scales.

Khatsymovsky, V.M. [Budker Institute of Nuclear Physics, Siberian Division, Russian Academy of Sciences, pr. Akademika Lavrent'eva 11, Novosibirsk, 630090 (Russian Federation)

2005-09-01

237

Quantization of Linearized Gravity in Cosmological Vacuum Spacetimes

NASA Astrophysics Data System (ADS)

Linearized Einstein gravity (with possibly non-zero cosmological constant) is quantized in the framework of algebraic quantum field theory by analogy with Dimock's treatment of electromagnetism [Rev. Math. Phys.4 (1992) 223-233]. To achieve this, the classical theory is developed in a full, rigorous and systematic fashion, with particular attention given to the circumstances under which the symplectic product is weakly non-degenerate and to the related question of whether the space of solutions is separated by the classical observables on which the quantum theory is modeled.

Fewster, Christopher J.; Hunt, David S.

2013-03-01

238

Model selection for modified gravity.

In this article, we review model selection predictions for modified gravity scenarios as an explanation for the observed acceleration of the expansion history of the Universe. We present analytical procedures for calculating expected Bayesian evidence values in two cases: (i) that modified gravity is a simple parametrized extension of general relativity (GR; two nested models), such that a Bayes' factor can be calculated, and (ii) that we have a class of non-nested models where a rank-ordering of evidence values is required. We show that, in the case of a minimal modified gravity parametrization, we can expect large area photometric and spectroscopic surveys, using three-dimensional cosmic shear and baryonic acoustic oscillations, to 'decisively' distinguish modified gravity models over GR (or vice versa), with odds of ?1:100. It is apparent that the potential discovery space for modified gravity models is large, even in a simple extension to gravity models, where Newton's constant G is allowed to vary as a function of time and length scale. On the time and length scales where dark energy dominates, it is only through large-scale cosmological experiments that we can hope to understand the nature of gravity. PMID:22084296

Kitching, T D; Simpson, F; Heavens, A F; Taylor, A N

2011-12-28

239

Revisiting Noether gauge symmetry for F( R) theory of gravity

NASA Astrophysics Data System (ADS)

Noether gauge symmetry for F( R) theory of gravity has been explored recently. The fallacy is that, even after setting gauge to vanish, the form of F( R)? R n (where n?1 is arbitrary) obtained in the process, has been claimed to be an outcome of gauge Noether symmetry. On the contrary, earlier works proved that any nonlinear form other than F(R) ? R^{3/2} is obscure. Here, we show that, setting gauge term zero, Noether equations are satisfied only for n=2, which again does not satisfy the field equations. Thus, as noticed earlier, the only form that Noether symmetry admits is F(R) ? R^{3/2}. Noether symmetry with non-zero gauge has also been studied explicitly here, to show that it does not produce anything new.

Sk, Nayem; Sanyal, Abhik Kumar

2012-12-01

240

Tethered Variable Gravity Laboratory Study: Low Gravity Process Identification Report.

National Technical Information Service (NTIS)

Experiments are described performable in the variable gravity environment, and the related compatible/beneficial residual accelerations, both for pure and applied research in the fields of Fluid Mechanics (static and dynamic), Materials Sciences (Crystal ...

M. Briccarello

1989-01-01

241

Screening mechanisms in modified gravity

NASA Astrophysics Data System (ADS)

The ubiquitous role of light scalar fields in modified gravity models necessitates the introduction of screening mechanisms whereby gravitation in the solar system can be described by the General Theory of Relativity to an extremely precise level. On larger scales, the laws of gravity can be modified with various phenomelogical consequences. We review the status of the three main mechanisms when a single scalar field modifies gravity. We emphasize the qualitative and quantitative differences between the models subject to the chameleon and the Damour–Polyakov mechanisms on the one hand, and the Vainshtein mechanism on the other hand.

Brax, Philippe

2013-11-01

242

Gravity gradient preprocessing at the GOCE HPF

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

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

2009-01-01

243

Parametrized post-Newtonian limit of fourth order gravity inspired by scalar-tensor gravity

Based on the dynamical equivalence between higher order gravity and scalar-tensor gravity the parametrized post-Newtonian (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.

Capozziello, S. [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II', INFN, Sez. di Napoli, Compl. Univ. di Monte S.Angelo, Edificio G, Via Cinthia, I-80126, Naples (Italy); Troisi, A. [Dipartimento di Fisica 'E.R. Caianiello', Universita di Salerno, INFN, Sez. di Napoli, Gruppo Collegato di Salerno, Via S. Allende, I-84081, Baronissi, SA (Italy)

2005-08-15

244

Zero Tolerance: One Size for All

Zero-tolerance policies have proliferated throughout American school districts in the past ten years. This case is focused on a special needs student who unintentionally violates the district’s zero-tolerance policy for weapons at school. Designed to proffer students an opportunity to discuss the development of policy, legal and instructional implications of zero-tolerance as well as workable solutions to a complicated problem,

Martha Livingston; Darlene Bruner

2001-01-01

245

Zero sound in dipolar Fermi gases

We study the propagation of sound in a homogeneous dipolar gas at zero temperature, which is known as zero sound. We find that undamped zero sound propagation is possible only in a range of solid angles around the direction of polarization of the dipoles. Above a critical dipole moment, we find an unstable mode, by which the gas collapses locally perpendicular to the dipoles' direction.

Ronen, Shai [JILA and Department of Physics, University of Colorado, Boulder, Colorado 80301 (United States); Institute for Theoretical Physics, University of Innsbruck, and Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck (Austria); Bohn, John L. [JILA and Department of Physics, University of Colorado, Boulder, Colorado 80301 (United States)

2010-03-15

246

Unifying Einstein and Palatini gravities

We consider a novel class of f(R) gravity theories where the connection is related to the conformally scaled metric g{sub {mu}{nu}=}C(R)g{sub {mu}{nu}} 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.

Amendola, Luca; Enqvist, Kari; Koivisto, Tomi [Institut fuer Theoretische Physik, University of Heidelberg, Philosophenweg 16, 69120 Heidelberg (Germany); Physics Department, University of Helsinki, and Helsinki Institute of Physics, FIN-00014 University of Helsinki (Finland); Institute for Theoretical Physics and Spinoza Institute, Leuvenlaan 4, 3584 CE Utrecht (Netherlands)

2011-02-15

247

Unifying Einstein and Palatini gravities

NASA Astrophysics Data System (ADS)

We consider a novel class of f(R) gravity theories where the connection is related to the conformally scaled metric g^??=C(R)g?? 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.

Amendola, Luca; Enqvist, Kari; Koivisto, Tomi

2011-02-01

248

Critical Gravity in Four Dimensions

We study four-dimensional gravity theories that are rendered renormalizable by the inclusion of curvature-squared terms to the usual Einstein action with a cosmological constant. By choosing the parameters appropriately, the massive scalar mode can be eliminated and the massive spin-2 mode can become massless. This ''critical'' theory may be viewed as a four-dimensional analogue of chiral topologically massive gravity, or of critical 'new massive gravity' with a cosmological constant, in three dimensions. We find that the on-shell energy for the remaining massless gravitons vanishes. There are also logarithmic spin-2 modes, which have positive energy. The mass and entropy of standard Schwarzschild-type black holes vanish. The critical theory might provide a consistent toy model for quantum gravity in four dimensions.

Lue, H. [China Economics and Management Academy, Central University of Finance and Economics, Beijing 100081 (China); Institute for Advanced Study, Shenzhen University, Nanhai Avenue 3688, Shenzhen 518060 (China); Pope, C. N. [George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A and M University, College Station, Texas 77843 (United States); DAMTP, Centre for Mathematical Sciences, Cambridge University, Wilberforce Road, Cambridge CB3 OWA (United Kingdom)

2011-05-06

249

Industrial Processes Influenced by Gravity.

National Technical Information Service (NTIS)

In considering new directions for low gravity research with particular regard to broadening the number and types of industrial involvements, it is noted that transport phenomena play a vital role in diverse processes in the chemical, pharmaceutical, food,...

S. Ostrach

1988-01-01

250

Gravity and the Expanding Universe

NSDL National Science Digital Library

This video segment, adapted from NOVA, traces the evolving history of theories about gravity and a force that may oppose it, along with our understanding of the impact of both of these forces on our expanding universe.

Foundation, Wgbh E.

2005-12-17

251

[The biomechanic criterium of adequacy of the modelled and natural force of gravity].

A proposed criterion of the adequacy of modeled (short radius centrifugation) and natural force of gravity (direct problem) helped to the statement and resolution of a reverse simulation problem in calculation of the SRC rotation speed as a function of subject's height with the zero difference in the adequacy criterion The model is fulfiled as a doctor's interface for computational experiments. It was shown that SRC should be rotated at 2 g to reproduce the natural force of gravity for medium-height human subjects (180 cm). PMID:15909850

Akulov, V A

252

NASA Astrophysics Data System (ADS)

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 Poincaré group, this has been either the R4 translations, or the Lorentz group SL(2,C) --- or the entire Poincaré SL(2,C)× R4. Enlarging the group has involved the use of the Conformal SU(2,2), the special Affine overline SA(4,R)=overline SL(4,R)× R4 or Affine overline A(4,R) groups. Supergroups have included supersymmetry, i.e. the graded-Poincaré group (n=1. . . 8 in 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 instantons and self-dual solutions in QCD, in the complexification and in the selection of new variables. Note that supergravity involves Lie Derivatives as supertranlations, and several models have treated local spacetime translations similarly. The reduction of the larger groups, down to Poincaré, has involved spontaneous fibration and spontaneous symmetry breakdown. In this context, noncommutative geometry may allow for further geometrization.

Ne'Eman, Y.

1998-04-01

253

Absolute Gravity Changes In Alaska

Visco-elastic deformation models such as that of Soldati et al. [1999] predict time varying gravity signals associated with post-seismic deformation following the 1964 Prince William Sound earthquake (Mw=9.2). The rates of change are a function of the upper mantle viscosity. Aseismic creep is also a candidate mechanism for the deformation. The models differ in the spatial distribution of gravity changes;

G. S. Sasagawa

2001-01-01

254

High Spin Topologically Massive Gravity

NASA Astrophysics Data System (ADS)

We study the high spin fields coupled to topologically massive gravity in AdS3, paying special attention to the nature of the theory at the critical point. We propose an action incorporating the high spin AdS3 gravity and the topological Chern-Simons term for high spin fields. We discuss the fluctuation spectrum around the AdS3 vacuum and find that besides the usual massless modes there are local massive modes.

Chen, Bin

2012-12-01

255

Lunar gravity - A harmonic analysis

A sixteenth-degree and sixteenth-order spherical harmonic lunar gravity field has been derived from the long-term Keplerian variations in the orbits of the Apollo subsatellites and Lunar Orbiter 5. This model resolves the major mascon gravity anomalies of the lunar near side and is in very good agreement with line-of-sight acceleration results. The far-side map shows the major ringed basins to

A. J. Ferrari

1977-01-01

256

Consistent extension of Horava gravity.

We propose a natural extension of Horava's model for quantum gravity, which is free from the notorious pathologies of the original proposal. The new model endows the scalar graviton mode with a regular quadratic action and remains power-counting renormalizable. At low energies, it reduces to a Lorentz-violating scalar-tensor gravity theory. The deviations with respect to general relativity can be made weak by an appropriate choice of parameters. PMID:20482165

Blas, D; Pujolàs, O; Sibiryakov, S

2010-05-07

257

NASA Astrophysics Data System (ADS)

We present a new constraint on the biased galaxy formation picture. Gravitational instability theory predicts that the two-point mass density correlation function, ?(r), has an inflection point at the separation r=r0, corresponding to the boundary between the linear and nonlinear regime of clustering, ?~=1. We show how this feature can be used to constrain the biasing parameter b2??g(r)/?(r) on scales r~=r0, where ?g is the galaxy-galaxy correlation function, which is allowed to differ from ?. We apply our method to real data: the ?g(r), estimated from the Automatic Plate Measuring (APM) galaxy survey. Our results suggest that the APM galaxies trace the mass at separations r>~5 h-1 Mpc, where h is the Hubble constant in units of 100 km s-1 Mpc-1. The present results agree with earlier studies, based on comparing higher order correlations in the APM with weakly nonlinear perturbation theory. Both approaches constrain the b factor to be within 20% of unity. If the existence of the feature that we identified in the APM ?g(r)-the inflection point near ?g=1-is confirmed by more accurate surveys, we may have discovered gravity's smoking gun: the long-awaited ``shoulder'' in ?, predicted by Gott and Rees 25 years ago.

Gaztañaga, Enrique; Juszkiewicz, Roman

2001-09-01

258

Magnetic-Field Modulation of Gravity: Martian, Lunar, and Time-Varying Gravity

Magnetic micro-gravity is used to simulate on Earth gravity conditions that occur on the moon, Mars or in interstellar space.\\u000a The possibilities offered by this magnetic method are theoretically studied so as to develop ground-based devices enabling\\u000a one to simulate various gravity conditions. The results of this theoretical study focus on perfect gravity compensation (micro-gravity),\\u000a partial gravity compensation (lunar or

Clément Lorin; Alain Mailfert; Denis Chatain

2011-01-01

259

NASA has been studying human adaptation to low-gravity (zero-g) environments for several years, beginning with the first manned space flight in 1961. As both flight and scientific opportunities have steadily increased, NASA has advanced in the development of sophisticated human experiments. Difficulties encountered include the ability to preserve samples for extended duration flights and the development of flight certifiable biomedical

Catherine D. Kramer; Elizabeth M. Kalla

1997-01-01

260

METHODOLOGICAL NOTES: Similarity in problems related to zero-gravity hydromechanics

NASA Astrophysics Data System (ADS)

On introduction of gravitational acceleration into the calculation of length and velocity scales, a set of dimensionless parameters appears in the mathematical model which enable the behaviour of convection and heat and mass transfer under changing gravitational conditions to be predicted. By directly simulating the equations of motion and heat transfer, the effectiveness of the proposed formulation of conservation laws in treating such phenomena in liquids is demonstrated for both isothermal and non-isothermal cases and under both terrestrial and space conditions.

Volkov, P. K.

1998-12-01

261

National Technical Information Service (NTIS)

The primary purpose of this research is to study the physiological mechanisms associated with the exercise performance of rats subjected to conditions of simulated weightlessness. A secondary purpose is to study related physiological changes associated wi...

C. M. Tipton

1991-01-01

262

The Complete Book of Spaceflight: From Apollo 1 to Zero Gravity

A commanding encyclopedia of the history and principles of spaceflight-from earliest conceptions to faster-than-light galaxy-hopping Here is the first truly comprehensive guide to space exploration and propulsion, from the first musings of the Greeks to current scientific speculation about interstellar travel using \\

David Darling

2002-01-01

263

Preparation of Alloys with Specific Physical Properties under Zero Gravity Conditions.

National Technical Information Service (NTIS)

Based on a study of the literature, possibilities offered by Spacelab for preparation of new or the improvement of conventional materials with specific physical properties were studied. For hard magnetic materials, the lack of thermal convection in space ...

H. Ahlborn H. Richter

1979-01-01

264

Experimental and Analytical Study of Two-Phase Flow in Zero Gravity.

National Technical Information Service (NTIS)

More effective and efficient thermal transport techniques will be needed for heat rejection from equipment on satellites. Circulating two-phase fluid loops have been suggested and laboratory tested for possible application in the above areas. In compariso...

D. Abdollahian R. Grief V. P. Carey W. Li-Ping

1988-01-01

265

KC135 zero-gravity two phase flow pressure drop: Experiments and modeling

Two-phase flow, thermal management systems are currently being considered as an alternative to conventional, single phase systems for future space missions because of their potential to reduce overall system mass, size, and pumping power requirements. Knowledge of flow regime transitions, heat transfer characteristics, and pressure drop correlations is necessary to design and develop two-phase systems. This work is concerned with

Anne Lambert; Thomas R. Reinarts; Frederick R. Best; Wayne S. Hill

1991-01-01

266

The Complete Book of Spaceflight: From Apollo 1 to Zero Gravity

NASA Astrophysics Data System (ADS)

A commanding encyclopedia of the history and principles of spaceflight-from earliest conceptions to faster-than-light galaxy-hopping Here is the first truly comprehensive guide to space exploration and propulsion, from the first musings of the Greeks to current scientific speculation about interstellar travel using "warp drives" and wormholes. Space buffs will delight in its in-depth coverage of all key manned and unmanned missions and space vehicles-past, present, and projected-and its clear explanations of the technologies involved. Over the course of more than 2,000 extensively cross-referenced entries, astronomer David Darling also provides fascinating insights into the cultural development of spaceflight. In vivid accounts of the major characters and historical events involved, he provides fascinating tales of early innovators, the cross-pollination that has long existed between science fiction and science fact, and the sometimes obscure links between geopolitics, warfare, and advances in rocketry.

Darling, David

2002-11-01

267

National Technical Information Service (NTIS)

The feasibility of extracting, isolating, purifying, separating, or preparing medical and biological products of high socio-economic value in space was studied. In particular, the study was designed to concentrate on the isolation or purification of viral...

1974-01-01

268

Principal Facts for Gravity Stations in Sulphur Springs Valley, Arizona.

National Technical Information Service (NTIS)

Observed gravity values, station locations, terrain corrections, and Bouguer gravity data are provided in tabular form for approximately 410 gravity observations in Sulphur Springs Valley, Arizona. (Author)

D. L. Peterson

1972-01-01

269

Analysis of zero-adjusted count data

In this paper a zero adjusted discrete model is developed. Such a situation arises when the proportion of zeros in the data is higher (lower) than that predicted by the original model. The effect of such an adjustment is studied. The failure rates and the survival functions of the adjusted and the non-adjusted models are compared. The relative error incurred

Pushpa L. Gupta; Ramesh C. Gupta; Ram C. Tripathi

1996-01-01

270

Henri Fayol and Zero Tolerance Policies

Zero tolerance policies have been increasingly popular in both education and business. Henri Fayol was the one of the earliest and influential thinkers in modern management theory. He defined management as a body of knowledge and defined his 14 administrative principles. It is an interesting exercise to apply Fayol’s teachings to the theory of zero tolerance and attempt to determine

Lee SCHIMMOELLER

2012-01-01

271

Sparse Channel Estimation with Zero Tap Detection

Algorithms for the estimation of a channel whose impulse response is characterized by a large number of zero tap coecients are developed and compared. Exploiting the sparsity of the channel, the estimation problem is transformed into an equivalent on-o keying (OOK) detection problem, whose solution gives an indication on the position of the zero taps. The proposed schemes are compared

Cecilia Carbonelli; Satish Vedantam; Urbashi Mitra

2007-01-01

272

ZERO DYNAMICS OF UNDERACTUATED PLANAR BIPED WALKERS

The zero dynamics of a hybrid model of bipedal walking are introduced and studied for a class of N-link, planar robots with one degree of underactuation and outputs that depend only on the conflguration variables. Asymptotically stable solutions of the zero dynamics correspond to asymptotically stabilizable orbits of the full hybrid model of the walker. The Poincare map of the

E. R. Westervelt; J. W. Grizzle; D. E. Koditschek

2002-01-01

273

Zeros of expansions in orthogonal polynomials

The theory of bi-orthogonal polynomials is exploited to investigate the location of zeros of truncated expansions in orthogonal polynomials. It turns out that, subject to additional conditions, these zeros can be confined to certain real intervals. Two general techniques are being used: the first depends on a theorem that links strict sign consistency of a generating function to loci of

A. Iserles; E. B. Saff

1989-01-01

274

Student Dress Codes Using Zero Tolerance?

ERIC Educational Resources Information Center

In this article, the author focuses on the issue involving zero tolerance in the Texas district whether the dress code policy is reasonable. In a small Texas school district, over 700 students were suspended in a single month for violating a zero-tolerance dress code policy. This suspension, which attracted national attention and threats of…

Essex, Nathan L.

2004-01-01

275

Controllability, zeros, and filtrations for singular systems

The global zero module of a matrix pencil measures controllability and uncontrollability of an associated singular linear system. If the global zero module vanishes, then the polynomial filtration on the Wedderburn-Forney space of the pencil kernel corresponds to the global controllability filtration of the system. This correspondence gives a new structural interpretation of a matrix pencil's Kronecker indices

Cheryl B. Schrader; Bostwick F. Wyman; Steven J. Giust

1995-01-01

276

Determining Absolute Zero Using a Tuning Fork

ERIC Educational Resources Information Center

The Celsius and Kelvin temperature scales, we tell our students, are related. We explain that a change in temperature of 1 degree C corresponds to a change of 1 Kelvin and that atoms and molecules have zero kinetic energy at zero Kelvin, -273 degrees C. In this paper, we will show how students can derive the relationship between the Celsius and…

Goldader, Jeffrey D.

2008-01-01

277

Zero-Knowledge Proofs of Identity

In this paper we extend the notion of interactive proofs of assertions to interactive proofs of knowledge. This leads to the definition of unrestricted input zero-knowledge proofs of knowledge in which the prover demonstrates possession of knowledge without revealing any computational information whatsoever (not even the one bit revealed in zero-knowledge proofs of assertions). We show the relevance of these

Uriel Feige; Amos Fiat; Adi Shamir

1988-01-01

278

On pole-zero modeling of speech

Three different types of pole-zero modeling have been investigated. The main concept lying in these methods is to fit a high order pole predictor to the speech spectrum, and then to decompose the resulting predictor into a pole predictor and a zero predictor. To obtain the predictor parameters by Padé approximation, either Trench algorithm or Berlekamp-Massey algorithm can be used

Kil Song; Chong Un

1980-01-01

279

Dynamic zero compression for cache energy reduction

Dynamic Zero Compressionreduces the energy required for cache accesses by only writing and reading a single bit for every zero-valued byte. This energy-conscious com- pression is invisible to software and is handled with ad- ditional circuitry embedded inside the cache RAM arrays and the CPU. The additional circuitry imposes a cache area overhead of 9% and a read latency overhead

Luis Villa; Michael Zhang; Krste Asanovi?

2000-01-01

280

Holographic conductivity of zero temperature superconductors

NASA Astrophysics Data System (ADS)

Using the recently found by G. Horowitz and M. Roberts (arXiv:0908.3677) numerical model of the ground state of holographic superconductors (at zero temperature), we calculate the conductivity for such models. The universal relation connecting conductivity with the reflection coefficient was used for finding the conductivity by the WKB approach. The dependence of the conductivity on the frequency and charge density is discussed. Numerical calculations confirm the general arguments of (arXiv:0908.3677) in favor of non-zero conductivity even at zero temperature. In addition to the Horowitz-Roberts solution we have found (probably infinite) set of extra solutions which are normalizable and reach the same correct RN-AdS asymptotic at spatial infinity. These extra solutions (which correspond to larger values of the grand canonical potential) lead to effective potentials that also vanish at the horizon and thus correspond to a non-zero conductivity at zero temperature.

Konoplya, R. A.; Zhidenko, A.

2010-03-01

281

Gravity darkening in binary stars

NASA Astrophysics Data System (ADS)

Context. Interpretation of light curves of many types of binary stars requires the inclusion of the (cor)relation between surface brightness and local effective gravity. Until recently, this correlation has always been modeled by a power law relating the flux or the effective temperature and the effective gravity, namely Teff ? geff? . Aims: We look for a simple model that can describe the variations of the flux at the surface of stars belonging to a binary system. Methods: This model assumes that the energy flux is a divergence-free vector anti-parallel to the effective gravity. The effective gravity is computed from the Roche model. Results: After explaining in a simple manner the old result of Lucy (1967, Z. Astrophys., 65, 89), which says that ? ~ 0.08 for solar type stars, we first argue that one-dimensional models should no longer be used to evaluate gravity darkening laws. We compute the correlation between log Teff and log geff using a new approach that is valid for synchronous, weakly magnetized, weakly irradiated binaries. We show that this correlation is approximately linear, validating the use of a power law relation between effective temperature and effective gravity as a first approximation. We further show that the exponent ? of this power law is a slowly varying function, which we tabulate, of the mass ratio of the binary star and the Roche lobe filling factor of the stars of the system. The exponent ? remains mostly in the interval [0.20,0.25] if extreme mass ratios are eliminated. Conclusions: For binary stars that are synchronous, weakly magnetized and weakly irradiated, the gravity darkening exponent is well constrained and may be removed from the free parameters of the models.

Espinosa Lara, F.; Rieutord, M.

2012-11-01

282

Feasibility of Achieving a Zero-Net-Energy, Zero-Net-Cost Homes

A green building competition, to be known as the Energy Free Home Challenge (EFHC), is scheduled to be opened to teams around the world in 2010. This competition will encourage both design innovation and cost reduction, by requiring design entries to meet 'zero net energy' and 'zero net cost' criteria. For the purposes of this competition, a 'zero net energy'

S. Al-Beaini; S. Borgeson; B. Coffery; D. Gregory; K. Konis; C. Scown; J. Simjanovic; B. Strogen; I. Walker

2009-01-01

283

Inferring the depth of the zonal jets on Jupiter and Saturn from odd gravity harmonics

NASA Astrophysics Data System (ADS)