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1

Test Frame Simulates Zero Gravity

NASA Technical Reports Server (NTRS)

Counterweighted frame simulates zero gravity in tests of solar-array wing. Net effect close simulation of zero-gravity environment in which wing must function. Frame also facilitates testing and replacement of solar-cell elements and panels.

Chung, D.; Lindberg, D.

1984-01-01

2

NASA Technical Reports Server (NTRS)

An apparatus for mixing liquids under conditions of zero gravity is disclosed. The apparatus is comprised of a closed reservoir for the liquids, with a means for maintaining a positive pressure on the liquids in the reservoir. A valved liquid supply line is connected to the reservoir for supplying the reservoir with the liquids to be mixed in the reservoir. The portion of the reservoir containing the liquids to be mixed is in communication with a pump which alternately causes a portion of the liquids to flow out of the pump and into the reservoir to mix the liquids. The fluids in the reservoir are in communication through a conduit with the pump which alternately causes a portion of the fluids to flow out of the pump and into the sphere. The conduit connecting the pump and sphere may contain a nozzle or other jet-forming structure such as a venturi for further mixing the fluids.

Booth, F. W.; Bruce, R. A. (inventors)

1973-01-01

3

NASA Technical Reports Server (NTRS)

The use of computer graphics to simulate the movement of articulated animals and mechanisms has a number of uses ranging over many fields. Human motion simulation systems can be useful in education, medicine, anatomy, physiology, and dance. In biomechanics, computer displays help to understand and analyze performance. Simulations can be used to help understand the effect of external or internal forces. Similarly, zero-gravity simulation systems should provide a means of designing and exploring the capabilities of hypothetical zero-gravity situations before actually carrying out such actions. The advantage of using a simulation of the motion is that one can experiment with variations of a maneuver before attempting to teach it to an individual. The zero-gravity motion simulation problem can be divided into two broad areas: human movement and behavior in zero-gravity, and simulation of articulated mechanisms.

Badler, N. I.; Fishwick, P.; Taft, N.; Agrawala, M.

1985-01-01

4

NASA Technical Reports Server (NTRS)

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

Edwards, H. W.

1981-01-01

5

Zero-gravity quantity gaging system

NASA Technical Reports Server (NTRS)

The Zero-Gravity Quantity Gaging System program is a technology development effort funded by NASA-LeRC and contracted by NASA-JSC to develop and evaluate zero-gravity quantity gaging system concepts suitable for application to large, on-orbit cryogenic oxygen and hydrogen tankage. The contract effective date was 28 May 1985. During performance of the program, 18 potential quantity gaging approaches were investigated for their merit and suitability for gaging two-phase cryogenic oxygen and hydrogen in zero-gravity conditions. These approaches were subjected to a comprehensive trade study and selection process, which found that the RF modal quantity gaging approach was the most suitable for both liquid oxygen and liquid hydrogen applications. This selection was made with NASA-JSC concurrence.

1989-01-01

6

Grain dynamics in zero gravity

NASA Technical Reports Server (NTRS)

The dynamics of granular materials has proved difficult to model, primarily because of the complications arising from inelastic losses, friction, packing, and the effect of many grains being in contact simultaneously. One interesting limit for which it was recently possible to construct a theory is that where the grain-grain interactions are dominated by binary collisions. The kinetic model of granular systems if similar to the kinetic theory of gases, except that collisional energy losses are always present in the former and must be treated explicitly. Few granular materials on Earth are describable by this limiting model, since gravity tends to collapse the grains into a high-density state where Coulombic friction effects are dominant. The planned Space Station offers an unusual opportunity to test the kinetic grain model and to explore its predictions. Without gravity, the regime of low interparticle velocities, where an elastic description of the collision is still valid, is investigated. This will allow direct interpretation by dynamical computer simulations as well as by kinetic theory.

Werner, B. T.; Haff, P. K.

1987-01-01

7

NASA Astrophysics Data System (ADS)

Experimental results were used to anchor a newly developed three-dimensional, finite-difference hydrodynamics code that was designed to simulate large amplitude slosh in a container moving in a zero-g environment. The results of this anchoring are presented along with a brief description of the SOLA-SLOSH code of Hirt el al. (1983), a description of the experiment, and a description of how the code was used to model pointing errors of a liquid-filled spacecraft during its space maneuvers.

Eastes, T. W.; Chang, Y. M.; Hirt, C. W.; Sicilian, J. M.

8

Zero gravity testing of flexible solar arrays

NASA Technical Reports Server (NTRS)

Zero gravity testing in the KC-135 aircraft of flat fold flexible solar array test specimens sufficiently demonstrated the adequacy of the panel design. The aircraft flight crew provided invaluable assistance and significantly contributed to the design and development of the flexible solar array, and ultimately to the potential success of the solar electric propulsion solar array shuttle flight experiment program.

Chung, D. T.; Young, L. E.

1981-01-01

9

Containing Hair During Cutting In Zero Gravity

NASA Technical Reports Server (NTRS)

Proposed device collects loose hair during barbering and shaving in zero gravity to prevent hair clippings from contaminating cabin of spacecraft. Folds for storage, opens into clear, bubblelike plastic dome surrounding user's head, tray fits around user's throat, and fanlike ring surrounds back of neck. Device fits snugly but comfortably around neck, preventing hair from escaping to outside. Flow of air into hose connected to suction pump removes hair from bubble as cut. Filter at end of hose collects hair.

Haines, Richard F.

1992-01-01

10

Zero-gravity open-type urine receptacle

NASA Technical Reports Server (NTRS)

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

Girala, A. S.

1972-01-01

11

Astronaut Edwin Aldrin during underwater zero-gravity training

NASA Technical Reports Server (NTRS)

Astronaut Edwin Aldrin, pilot for the Gemini 12 space flight, practices egress procedures from mockup of his spacecraft during underwater zero-gravity training. He holds a telescoping hand rail in his left hand which he will use to move from the spacecraft to the Agena Target Docking vehicle (54937); Aldrin prepares to take a 'rest position' during underwater zero-gravity training. His feet are secured to a mockup of the adapter section of the spacecraft by a special foot plate (54938); Aldrin practices work tasks during underwater zero-gravity training. He is placing his feet into special foot plate in adapter section of the spacecraft (54939).

1966-01-01

12

Astronaut Edwin Aldrin during zero gravity ingress and egress training

NASA Technical Reports Server (NTRS)

Astronaut Edwin E. Aldrin Jr., prime crew pilot of the Gemini 12 space flight, undergoes zero gravity ingress and egress training aboard an Air Force KC-135 aircraft. He practices using camera equipment.

1966-01-01

13

Marangoni bubble motion in zero gravity

It is shown experimentally that the Marangoni phenomenon is a primary mechanism for the movement of a gas bubble in a nonisothermal liquid in a low-gravity environment. In such two-phase flow systems, local variations in bubble surface tension are caused by a temperature gradient in the liquid. Shearing stresses thus generated at the bubble surface lead to convection in both

R. L. Thompson; K. J. de Witt

1979-01-01

14

MARANGONI BUBBLE MOTION PHENOMENON IN ZERO GRAVITY

The Marangoni phenomenon is shown to be the primary mechanism for the movement of a gas bubble in a nonisothermal liquid in a low-gravity environment. In such a two-phase system, local variations in surface tension at the bubble surface are caused by a temperature gradient in the liquid. Shearing stresses thus generated at the bubble surface lead to convection in

R. L. THOMPSON; K. J. DeWITT; T. L. LABUS

1980-01-01

15

Liquid motions in containers in zero-gravity

Projected Spacelab experiments on sloshing and oscillations of liquid confined within an enclosure under zero-gravity conditions are discussed. Slight deviations from zero-g termed g-jitter are anticipated as a result of crew movements in the spacecraft, attitude corrections, and unforeseen phenomena. This g-jitter might affect such sensitive transport phenomena as crystal growth. Simulated experiments on earth (using neutral buoyancy tanks, drop

J. P. B. Vreeburg

1977-01-01

16

Passive zero-gravity leg restraint

NASA Technical Reports Server (NTRS)

A passive zero or microgravity leg restraint is described which includes a central support post with a top and a bottom. Extending from the central support post are a calf pad tab, to which calf pad is attached, and a foot pad tab, to which foot tab is attached. Also extending from central support post are knee pads. When the restraint is in use the user's legs are forced between pads by a user imposed scissors action of the legs. The user's body is then supported in a zero or microgravity neutral body posture by the leg restraint. The calf pad has semi-ridig elastic padding material covering structural stiffener. The foot pad has padding material and a structural stiffener. Knee pads have s structural tube stiffener at their core.

Miller, Christopher R. (inventor)

1989-01-01

17

Glass fining experiments in zero gravity

NASA Technical Reports Server (NTRS)

Ground based experiments were conducted to demonstrate that thermal migration actually operated in glass melts. Thermal migration consistent with the theory was found in one experiment on a borax melt, i.e., there was an approximately linear relation between the bubble diameter and bubble velocity for a given temperature and temperature gradient. It also appeared that nearby bubbles were attracted to one another, which could greatly aid fining. Interpretation of these results was not possible because of complications arising from gravity, i.e., floating of the bubbles, circulation currents due to buoyancy-driven natural connection, and flow of the melt out from the cell.

Smith, H. D.

1977-01-01

18

Zero Gravity Cryogenic Vent System Concepts for Upper Stages

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

Alain Ravex; Robin Flachbart; Barney Holt

1999-01-01

19

Astronaut Edwin Aldrin during underwater zero-gravity training

NASA Technical Reports Server (NTRS)

Astronaut Edwin Aldrin, pilot for the Gemini 12 space flight, assumes a rest position during underwater zero-gravity training. The underwater environment creates similar conditions to those found in space. He is secured to the adapter section of the spacecraft by special foot plates.

1966-01-01

20

Solution growth of crystals in zero gravity

NASA Technical Reports Server (NTRS)

A series of experiments will be performed in which triglycine sulfate (TGS) crystals will be grown by a low-temperature solution growth technique in the microgravity environment of the orbital Spacelab. Triglycine sulfate (TGS) crystals will be grown in the Fluid Experiment System (FES) facility on Spacelab 3 by slowly extracting heat at a controlled rate through a seed crystal of TGS suspended on an insulated sting in a saturated solution of TGS. The FES rack assembly designed for SL-3 is shown in Figure I-1, and a detailed view of the test cell layout is presented in Figure I-2. Variations in the liquid density, solution concentration and temperature around the growing crystal will be studied using a variety of techniques, such as schlieren, shadowgraph, and interferometric measurements. Growth in Earth gravity will also be studied by the same optical techniques, and in both cases the resulting crystalline features will be compared and correlated with the growth conditions.

Lai, R. B.

1982-01-01

21

Fluid management system for a zero gravity cryogenic storage system

NASA Technical Reports Server (NTRS)

The fluid management system comprises a mixing/recirculation system including an external recirculation pump for receiving fluid from a zero gravity storage system and returning an output flow of the fluid to the storage system. An internal axial spray injection system is provided for receiving a portion of the output flow from the recirculation pump. The spray injection system thermally de-stratifies liquid and gaseous cryogenic fluid stored in the storage system.

Lak, Tibor I. (Inventor)

1995-01-01

22

Astronaut Edwin Aldrin during underwater zero-gravity training

NASA Technical Reports Server (NTRS)

Astronaut Edwin Aldrin, pilot for the Gemini 12 space flight, practices work tasks in preparation for his extravehicular activity during the Gemini 12 flight. He works with a telescoping hand rail he will use to move from the spacecraft to the Agena Target Docking Vehicle (54934); Aldrin practices extravehicular work task during underwater zero-gravity training. He works on the docking collar of the Agena Target Docking Vehicle mockup using hand holds to secure himself to the vehicle (54935).

1966-01-01

23

Astronaut Edwin Aldrin makes sandwich in zero gravity conditions

NASA Technical Reports Server (NTRS)

Astronaut Edwin E. Aldrin Jr., Apollo 11 lunar module pilot, makes a sandwich in zero gravity conditions in this color reproduction taken from at TV transmission from the Apollo 11 spacecraft during its transearth journey home from the moon. When this picture was made, Apollo 11 was approximately 157,000 nautical miles from earth, traveling at a speed of about 4,300 feet per second.

1969-01-01

24

Development of a compact dilution refrigerator for zero gravity operation

NASA Technical Reports Server (NTRS)

A compact dilution refrigerator design based on internal charcoal adsorption is being tested for operation in zero gravity. This refrigerator is self-contained with no external pumps or gas handling system and provides reliable operation since it has no moving parts. All operations are performed with heaters and are completely computer controlled. The refrigerator is capable of providing many hours of operation at very low temperature before the charcoal pumps must be recycled.

Roach, Pat R.; Helvensteijn, Ben

1990-01-01

25

Crew efficiency on first exposure to zero-gravity

NASA Technical Reports Server (NTRS)

Activation task performance of Skylab crews showed improved efficiency as experience was gained in weightlessness living. During three activation intervals, less than 12 man-hours were lost due to reduced efficiency (including the effects of motion sensitivity) while almost 200 man-hours of productive work were delivered. Work rate improved for tasks in which simulation and training time were extensive and for tasks which allowed zero-gravity operations to be optimized.

Garriott, O. K.; Doerre, G. L.

1977-01-01

26

Oscillations of drops in zero gravity with weak viscous effects

NASA Technical Reports Server (NTRS)

Nonlinear oscillations and other motions of large axially symmetric liquid drops in zero gravity are studied numerically by a boundary-integral method. The effect of small viscosity is included in the computations by retaining first-order viscous terms in the normal stress boundary condition. This is accomplished by making use of a partial solution of the boundary-layer equations which describe the weak vortical surface layer. Small viscosity is found to have a relatively large effect on resonant mode coupling phenomena.

Lundgren, T. S.; Mansour, N. N.

1988-01-01

27

Muscle and the physiology of locomotion. [in zero gravity

NASA Technical Reports Server (NTRS)

NASA's past, current, and planned research on muscle deterioration at zero gravity and development of countermeasures are reviewed; Soviet studies are discussed as well. A definition of muscle mass and strength regulation factors, and improved measurement methods of muscle atrophy are needed. Investigations of tissue growth factors and their receptors, endogenous and exogenous anabolic protein synthesis stimulation, and a potential neurotropic factor are among the projects in progress or planned. At present, vigorous physical exercise during spaceflight is recommended as the most effective countermeasure against skeletal muscle atrophy.

Rambaut, P. C.; Nicogossian, A. E.; Pool, S. L.

1983-01-01

28

Ocular Blood Flow Measured Noninvasively in Zero Gravity

NASA Technical Reports Server (NTRS)

In spaceflight or a reduced-gravity environment, bodily fluids shift to the upper extremities of the body. The pressure inside the eye, or intraocular pressure, changes significantly. A significant number of astronauts report changes in visual acuity during orbital flight. To date this remains of unknown etiology. Could choroidal engorgement be the primary mechanism and a change in the curvature or shape of the cornea or lens be the secondary mechanism for this change in visual acuity? Perfused blood flow in the dense meshwork of capillaries of the choroidal tissue (see the preceding illustration) provides necessary nutrients to the outer layers of the retina (photoreceptors) to keep it healthy and maintain good vision. Unlike the vascular system, the choroid has no baroreceptors to autoregulate fluid shifts, so it can remain engorged, pushing the macula forward and causing a hyperopic (farsighted) shift of the eye. Experiments by researchers at the NASA Glenn Research Center could help answer this question and facilitate planning for long-duration missions. We are investigating the effects of zero gravity on the choroidal blood flow of volunteer subjects. This pilot project plans to determine if choroidal blood flow is autoregulated in a reduced-gravity environment.

Ansari, Rafat R.; Manuel, Francis K.; Geiser, Martial; Moret, Fabrice; Messer, Russell K.; King, James F.; Suh, Kwang I.

2003-01-01

29

Zero-Gravity Vortex Vent and PVT Gaging System

NASA Technical Reports Server (NTRS)

Space Station and satellite reservicing will require the ability to vent gas on orbit from liquid supply or storage tanks and to gage liquid quantity under microgravity conditions. In zero gravity, (zero-g) the vortex vent is capable of venting gas from a tank of liquid containing gas randomly distributed as bubbles. The concept uses a spinning impeller to create centrifugal force inside a vortex tube within a tank. This creates a gas pocket and forces the liquid through a venturi and back into the tank. Gas is then vented from the gas pocket through a liquid detector and then out through an exhaust port. If the liquid detector senses liquid in the vent line, the fluid is directed to the low-pressure port on the venturi and is returned to the tank. The advantages of this system is that it has no rotating seals and is compatible with most corrosive and cryogenic fluids. A prototype was designed and built at the NASA Johnson Space Center and flown on the KC-135 zero-g aircraft. During these test flights, where microgravity conditions are obtained for up to 30 sec, the prototype demonstrated that less than 0.10 percent of the volume of fluid vented was liquid when the tank was half full of liquid. The pressure volume temperature (PVT) gaging system is used in conjunction with the vortex vent to calculate the amount of liquid remaining in a tank under microgravity conditions. The PVT gaging system is used in conjunction with the vortex vent to gage liquid quantity in zero or low gravity. The system consists of a gas compressor, accumulator, and temperature and pressure instrumentation. To measure the liquid in a tank a small amount of gas is vented from the tank to the compressor and compressed into the accumulator. Pressure and temperature in the tank and accumulator are measured before and after the gas transfer occurs. Knowing the total volume of the tank, the volume of the accumulator, the volume of the intermediate lines, and initial and final pressures and temperatures, the mass of the gas leaving the tank is equated to the mass of the gas entering the accumulator. The volume of liquid remaining in the tank is calculated using the ideal gas law.

Downey, M. G.; Trevathan, J. T.

1989-01-01

30

Sediment-transport experiments in zero-gravity

NASA Technical Reports Server (NTRS)

One of the important parameters in the analysis of sediment entrainment and transport is gravitational attraction. The availability of a laboratory in earth orbit would afford an opportunity to conduct experiments in zero and variable gravity environments. Elimination of gravitational attraction as a factor in such experiments would enable other critical parameters (such as particle cohesion and aerodynamic forces) to be evaluated much more accurately. A Carousel Wind Tunnel (CWT) is proposed for use in conducting experiments concerning sediment particle entrainment and transport in a space station. In order to test the concept of this wind tunnel design a one third scale model CWT was constructed and calibrated. Experiments were conducted in the prototype to determine the feasibility of studying various aeolian processes and the results were compared with various numerical analysis. Several types of experiments appear to be feasible utilizing the proposed apparatus.

Iversen, James D.; Greeley, Ronald

1987-01-01

31

Zero Gravity Cryogenic Vent System Concepts for Upper Stages

NASA Technical Reports Server (NTRS)

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 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.

Flachbart, Robin H.; Holt, James B.; Hastings, Leon J.

1999-01-01

32

Zero Gravity Cryogenic Vent System Concepts for Upper Stages

NASA Technical Reports Server (NTRS)

The capability to vent in zero gravity without resettling is a technology need that involves practically all uses of sub-critical cryogenics in space, and 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.

Flachbart, Robin H.; Holt, James B.; Hastings, Leon J.

2001-01-01

33

Precise Determination of the Zero-Gravity Surface Figure of a Mirror without Gravity-Sag Modeling

NASA Technical Reports Server (NTRS)

The zero-gravity surface figure of optics used in spaceborne astronomical instruments must be known to high accuracy, but earthbound metrology is typically corrupted by gravity sag. Generally, inference of the zero-gravity surface figure from a measurement made under normal gravity requires finite-element analysis (FEA), and for accurate results the mount forces must be well characterized. We describe how to infer the zero-gravity surface figure very precisely using the alternative classical technique of averaging pairs of measurements made with the direction of gravity reversed. We show that mount forces as well as gravity must be reversed between the two measurements and discuss how the St. Venant principle determines when a reversed mount force may be considered to be applied at the same place in the two orientations. Our approach requires no finite-element modeling and no detailed knowledge of mount forces other than the fact that they reverse and are applied at the same point in each orientation. If mount schemes are suitably chosen, zero-gravity optical surfaces may be inferred much more simply and more accurately than with FEA.

Bloemhof, Eric E.; Lam, Jonathan C.; Feria, V. Alfonso; Chang, Zensheu

2007-01-01

34

Adiabatic demagnetization refrigerator for use in zero gravity

NASA Technical Reports Server (NTRS)

In this effort, a new design concept for an adiabatic demagnetization refrigerator (ADR) that is capable of operation in zero gravity has been developed. The design uses a vortex precooler to lower the initial temperature of magnetic salt from the initial space superfluid helium dewar of 1.8 K to 1.1 K. This reduces the required maximum magnetic field from 4 Tesla to 2 Tesla. The laboratory prototype vortex precooler reached a minimum temperature of 0.78 K, and had a cooling power of 1 mW at 1.1 K. A study was conducted to determine the dependence of vortex cooler performance on system element configuration. A superfluid filled capillary heat switch was used in the design. The laboratory prototype ADR reached a minimum temperature of 0.107 K, and maintained temperatures below 0.125 K for 90 minutes. Demagnetization was carried out from a maximum field of 2 T. A soft iron shield was developed that reduced the radial central field to 1 gauss at 0.25 meters.

Dingus, Michael L.

1988-01-01

35

Steady State Detached Solidification of Water at Zero Gravity

NASA Technical Reports Server (NTRS)

Steady-state detached solidification of water was calculated using the Moving Meniscus Model. Similar to the experimental observation of many materials in microgravity, detached solidification of water is predicted to occur in a sealed ampoule at zero gravity under proper conditions. For steady detachment, the freezing rate must exceed a critical value, Henry's constant of the dissolved gas must be below a critical value, the temperature of the top of the water must be below a critical value, the contact angle of water on the ampoule wall must exceed a critical value, and the diffusion coefficient must exceed a critical value. Each critical value depends on the physical properties and the other operating conditions. Thus different results are obtained for InSb and water. The critical gas pressure above the melt for water is much smaller than for InSb, the critical freezing rate is larger for water, and the critical contact angle of the melt on the ampoule wall is larger for water. For the gases examined here, the solubilities of Ar, N2 and Ne in water are sufficient for detachment to occur, while the solubility of He is not.

Wang, Yazhen; Regel, Liya L.; Wilcox, William R.

2003-01-01

36

Steady State Detached Solidification of Water at Zero Gravity

NASA Technical Reports Server (NTRS)

Steady-state detached solidification of water was calculated using the Moving Meniscus Model. Similar to the experimental observation of many materials in microgravity, detached solidification of water is predicted to occur in a sealed ampoule at zero gravity under proper conditions. For steady detachment, the freezing rate must exceed a critical value, Henry's constant of the dissolved gas must be below a critical value, the temperature of the top of the water must be below a critical value, the contact angle of water on the ampoule wall must exceed a critical value, and the diffusion coefficient must exceed a critical value. Each critical value depends on the physical properties and the other operating conditions. Thus different results are obtained for InSb and water. The critical gas pressure above the melt for water is much smaller than for InSb, the critical freezing rate is larger for water, and the critical contact angle of the melt on the ampoule wall is larger for water. For the gases examined here, the solubilities of Ar, N2 and Ne in water are sufficient for detachment to occur, while the solubility of He is not.

Wang, Yazhen; Regel, Liya L.; Wilcox, William R.

2001-01-01

37

Thermocapillary simulation of single bubble dynamics in zero gravity

NASA Astrophysics Data System (ADS)

The lack of significant buoyancy effects in zero gravity conditions poses an issue with fluid transfer in a stagnant liquid. In this paper bubble movement in a stagnant liquid is analysed and presented numerically using a computational fluid dynamics (CFD) approach. The governing continuum conservation equations for two phase flow are solved using the commercial software package Ansys-Fluent v.13 and the Volume of Fluid (VOF) method is used to track the liquid/gas interface in 2D and 3D domains. The simulation results are in reasonable agreement with the earlier experimental observations, the VOF algorithm is found to be a valuable tool for studying the phenomena of gas-liquid interaction. The flow is driven via Marangoni influence induced by the temperature difference which in turn drives the bubble from the cold to the hot region. A range of thermal Reynolds (ReT) and Marangoni numbers (MaT) are selected for the numerical simulations, specifically ReT=13-658 and MaT=214-10,721 respectively. The results indicate that the inherent velocity of bubbles decreases with an increase of the Marangoni number, a result that is line with the results of previous space experiments (Kang et al., 2008) [1]. An expression for predicting the scaled velocity of bubble has been derived based on the data obtained in the present numerical study. Some three-dimensional simulations are also performed to compare and examine the results with two-dimensional simulations.

Alhendal, Yousuf; Turan, Ali; Hollingsworth, Peter

2013-07-01

38

A helium-3/helium-4 dilution cryocooler for operation in zero gravity

NASA Technical Reports Server (NTRS)

This research effort covered the development of He-3/He-4 dilution cryocooler cycles for use in zero gravity. The dilution cryocooler is currently the method of choice for producing temperatures below 0.3 Kelvin in the laboratory. However, the current dilution cryocooler depends on gravity for their operation, so some modification is required for zero gravity operation. In this effort, we have demonstrated, by analysis, that the zero gravity dilution cryocooler is feasible. We have developed a cycle that uses He-3 circulation, and an alternate cycle that uses superfluid He-4 circulation. The key elements of both cycles were demonstrated experimentally. The development of a true 'zero-gravity' dilution cryocooler is now possible, and should be undertaken in a follow-on effort.

Hendricks, John B.

1988-01-01

39

Modeling of zero gravity venting: Studies of two-phase heat transfer under reduced gravity

NASA Technical Reports Server (NTRS)

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 filled with initially saturated liquids was previously conducted under zero-gravity conditions and compared with an analytical model which incorporated the effect of interfacial mass transfer on the ullage pressure response during venting. A new model is presented to improve the estimation of the interfacial mass transfer. Duhammel's superposition integral is incorporated to approximate the transient temperature response of the interface, treating the liquid as a semi-infinite solid with conduction heat transfer. Account is also taken of the condensation taking place within the bulk of a saturated vapor as isentropic expansion takes place. Computational results are presented for the venting of R-11 from a given vessel and initial state for five different venting rates over a period of three seconds, and compared to prior NASA experiments. An improvement in the prediction of the final pressure takes place, but is still considerably below the measurements.

Merte, H., Jr.

1986-01-01

40

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

41

Vortex motion phase separator for zero gravity liquid transfer

NASA Technical Reports Server (NTRS)

A vortex motion phase separator is disclosed for transferring a liquid in a zero gravity environment while at the same time separating the liquid from vapors found within either the sender or the receiving tanks. The separator comprises a rigid sender tank having a circular cross-section and rigid receiver tank having a circular cross-section. A plurality of ducts connects the sender tank and the receiver tank. Disposed within the ducts connecting the receiver tank and the sender tank is a pump and a plurality of valves. The pump is powered by an electric motor and is adapted to draw either the liquid or a mixture of the liquid and the vapor from the sender tank. Initially, the mixture drawn from the sender tank is directed through a portion of the ductwork and back into the sender tank at a tangent to the inside surface of the sender tank, thereby creating a swirling vortex of the mixture within the sender tank. As the pumping action increases, the speed of the swirling action within the sender tank increases creating an increase in the centrifugal force operating on the mixture. The effect of the centrifugal force is to cause the heavier liquid to migrate to the inside surface of the sender tank and to separate from the vapor. When this separation reaches a predetermined degree, control means is activated to direct the liquid conveyed by the pump directly into the receiver tank. At the same time, the vapor within the receiver tank is directed from the receiver tank back into the sender tank. This flow continues until substantially all of the liquid is transferred from the sender tank to the receiver tank.

Howard, Frank S. (inventor); Fraser, Wilson M., Jr. (inventor)

1989-01-01

42

Astronaut Edwin Aldrin undergoes zero-gravity egress training aboard KC-135

NASA Technical Reports Server (NTRS)

Astronaut Edwin E. Aldrin Jr., backup crew pilot for the Gemini 9 space flight, undergoes zero-gravity egress training aboard an Air Force KC-135. Extravehicular activity is planned for the Gemini 9 mission.

1966-01-01

43

N zero gravity, aboard the space shuttle Columbia's upcoming flight, Air Force Colonel

N zero gravity, aboard the space shuttle Columbia's upcoming flight, Air Force Colonel Ilan Ramon. By comparing the behavior of the genetically altered cells in space and on earth, Prof. Gazit hopes to discover

Linial, Michal

44

NASA Technical Reports Server (NTRS)

An experimental and analytical study of Thermoacoustic Convection heat transfer in gravity and zero-gravity environments is presented. The experimental apparatus consisted of a cylinder containing air as a fluid. The side wall of the cylinder was insulated while the bottom wall was allowed to remain at the ambient temperature. The enclosed air was rapidly heated by the top surface which consisted of a thin stainless steel foil connected to a battery pack as the power source. Thermocouples were used to measure the transient temperature of the air on the axis of the cylinder. The ouput of the thermocouples was displayed on digital thermometers and the temperature displays were recorded on film using a high-speed movie camera. Temperature measurements were obtained in the zero-gravity environment by dropping the apparatus in the 2-Seconds Zero-Gravity Drop Tower Facilities of NASA Lewis Research Center. In addition, experiments were also performed in the gravity environment and the results are compared in detail with those obtained under zero-gravity conditions.

Parang, Masood

1986-01-01

45

NASA Technical Reports Server (NTRS)

The solidification behavior of gold-silicon alloys containing up to 25 at. % silicon was studied, and a mathematical model of gravity segregation during solidification was developed. A background of knowledge is provided which can be used in the design of zero gravity solidification experiments to be carried out in the 300-ft drop tower, in Aerobee rockets and in future space missions. Such experiments are needed to develop the basic scientific knowledge required for the design of economically viable space manufacturing processes. Some preliminary zero gravity experiments were carried out on a gold-25 at. % silicon alloy using the drop tower facility.

Johnson, A. A.; Anantatmula, R. P.; Horylev, R. J.; Gupta, S. P.; Vatne, R. S.

1975-01-01

46

Assessment of geophysical flows for zero-gravity simulation

NASA Technical Reports Server (NTRS)

The results of research relating to the feasibility of using a low gravity environment to model geophysical flows are presented. Atmospheric and solid earth flows are considered. Possible experiments and their required apparatus are suggested.

Winn, C. B.; Cox, A.; Srivatsangam, R.

1976-01-01

47

The Dirac point electron in zero-gravity Kerr--Newman spacetime

Dirac's wave equation for a point electron in the topologically nontrivial maximal analytically extended electromagnetic Kerr--Newman spacetime is studied in a zero-gravity limit; here, "zero-gravity" means $G\\to 0$, where $G$ is Newton's constant of universal gravitation. The following results are obtained: the formal Dirac Hamiltonian on the static spacelike slices is essentially self-adjoint; the spectrum of the self-adjoint extension is symmetric about zero, featuring a continuum with a gap about zero that, under two smallness conditions, contains a point spectrum. Some of our results extend to a generalization of the zero-$G$ Kerr--Newman spacetime with different electric-monopole-to-magnetic-dipole-moment ratio.

M. K. -H. Kiessling; A. S. Tahvildar-Zadeh

2014-11-11

48

On Calculating the Zero-Gravity Surface Figure of a Mirror

NASA Technical Reports Server (NTRS)

An analysis of the classical method of calculating the zero-gravity surface figure of a mirror from surface-figure measurements in the presence of gravity has led to improved understanding of conditions under which the calculations are valid. In this method, one measures the surface figure in two or more gravity- reversed configurations, then calculates the zero-gravity surface figure as the average of the surface figures determined from these measurements. It is now understood that gravity reversal is not, by itself, sufficient to ensure validity of the calculations: It is also necessary to reverse mounting forces, for which purpose one must ensure that mountingfixture/ mirror contacts are located either at the same places or else sufficiently close to the same places in both gravity-reversed configurations. It is usually not practical to locate the contacts at the same places, raising the question of how close is sufficiently close. The criterion for sufficient closeness is embodied in the St. Venant principle, which, in the present context, translates to a requirement that the distance between corresponding gravity-reversed mounting positions be small in comparison to their distances to the optical surface of the mirror. The necessity of reversing mount forces is apparent in the behavior of the equations familiar from finite element analysis (FEA) that govern deformation of the mirror.

Bloemhof, Eric E.

2010-01-01

49

Extracting Zero-Gravity Surface Figure of a Mirror

NASA Technical Reports Server (NTRS)

The technical innovation involves refinement of the classic optical technique of averaging surface measurements made in different orientations with respect to gravity, so the effects of gravity cancel in the averaged image. Particularly for large, thin mirrors subject to substantial deformation, the further requirement is that mount forces must also cancel when averaged over measurement orientations. The zerogravity surface figure of a mirror in a hexapod mount is obtained by analyzing the summation of mount forces in the frame of the optic as surface metrology is averaged over multiple clockings. This is illustrated with measurements taken from the Space Interferometry Mission (SIM) PT-Ml mirror for both twofold and threefold clocking. The positive results of these measurements and analyses indicate that, from this perspective, a lighter mirror could be used; that is, one might place less reliance on the damping effects of the elliptic partial differential equations that describe the propagation of forces through glass. The advantage over prior art is relaxing the need for an otherwise substantial thickness of glass that might be needed to ensure accurate metrology in the absence of a detailed understanding and analysis of the mount forces. The general insights developed here are new, and provide the basic design principles on which mirror mount geometry may be chosen.

Bloemhof, Eric E.; Lam, Jonathan C.; Feria, Alfonso; Chang, Zensheu

2011-01-01

50

Investigation of crystal growth in zero gravity environment and investigation of metallic whiskers

NASA Technical Reports Server (NTRS)

Theoretical and experimental work reported relates to the effects of near-zero gravity on growths of crystals and metallic whiskers during Skylab and Apollo flight experiments. Studies on growth and characterization of candidate materials for flight experiments cover indium-bismuth compounds, bismuth single crystals, gallium arsenide films and single crystals, and cadmium whiskers.

Davis, J. H.; Lal, R. B.; Walter, H. U.; Castle, J. G., Jr.

1972-01-01

51

NASA Technical Reports Server (NTRS)

The possible utilization of the zero gravity resource for studies in a variety of fluid dynamics and fluid-dynamic related problems was investigated. A group of experiments are discussed and described in detail; these include experiments in the areas of geophysical fluid models, fluid dynamics, mass transfer processes, electrokinetic separation of large particles, and biophysical and physiological areas.

Eisner, M. (editor)

1974-01-01

52

Vacuum/Zero Net-Gravity Application for On-Orbit TPS Tile Repair

NASA Technical Reports Server (NTRS)

The Orbiter Columbia catastrophically failed during reentry February 1, 2003. All space Shuttle flights were suspended, including logistics support for the International Space Station. NASA LaRC s Structures and Materials Competency is performing characterizations of candidate materials for on-orbit repair of orbiter Thermal Protection System (TPS) tiles to support Return-to-Flight activities led by JSC. At least ten materials properties or attributes (adhesion to damage site, thermal protection, char/ash strength, thermal expansion, blistering, flaming, mixing ease, application in vacuum and zero gravity, cure time, shelf or storage life, and short-term outgassing and foaming) of candidate materials are of interest for on-orbit repair. This paper reports application in vacuum and zero net-gravity (for viscous flow repair materials). A description of the test apparatus and preliminary results of several candidate materials are presented. The filling of damage cavities is different for some candidate repair materials in combined vacuum and zero net-gravity than in either vacuum or zero net- gravity alone.

Harvey, Gale A.; Humes, Donald H.; Siochi, Emilie J.

2004-01-01

53

Astronaut Edwin Aldrin undergoes zero-gravity training aboard KC-135

NASA Technical Reports Server (NTRS)

Astronaut Edwin E. Aldrin Jr., lunar module pilot of the Apollo 11 lunar landing mission, undergoes zero-gravity training aboard a U.S. Air Force KC-135 jet aircraft from nearby Patrick Air Force Base, Florida. Aldrin is wearing an Extravehicular Mobility Unit (EMU), the type of equipment which he will wear on the lunar surface.

1969-01-01

54

Vacuum/Zero Net-Gravity Application for On-Orbit TPS Tile Repair

NASA Technical Reports Server (NTRS)

The Orbiter Columbia catastrophically failed during reentry February 1, 2003. All Space Shuttle flights were suspended, including logistics support for the International Space Station. NASA Langley Research Center s (LaRC) Structures and Materials Competency is performing characterizations of candidate materials for on-orbit repair of orbiter Thermal Protection System (TPS) tiles to support Return-to-Flight activities led by Johnson Space Center (JSC). At least ten materials properties or attributes (adhesion to damage site, thermal protection, char/ash strength, thermal expansion, blistering, flaming, mixing ease, application in vacuum and zero gravity, cure time, shelf or storage life, and short-term outgassing and foaming) of candidate materials are of interest for on-orbit repair. This paper reports application in vacuum and zero net-gravity (for viscous flow repair materials). A description of the test apparatus and preliminary results of several candidate materials are presented. The filling of damage cavities is different for some candidate repair materials in combined vacuum and zero net-gravity than in either vacuum or zero net-gravity alone.

Harvey, Gale A.; Humes, Donald H.; Siochi, Emilie J.

2004-01-01

55

Study on processing immiscible materials in zero gravity

NASA Technical Reports Server (NTRS)

An experimental investigation was conducted to evaluate mixing immiscible metal combinations under several process conditions. Under one-gravity, these included thermal processing, thermal plus electromagnetic mixing, and thermal plus acoustic mixing. The same process methods were applied during free fall on the MSFC drop tower facility. The design is included of drop tower apparatus to provide the electromagnetic and acoustic mixing equipment, and a thermal model was prepared to design the specimen and cooling procedure. Materials systems studied were Ca-La, Cd-Ga and Al-Bi; evaluation of the processed samples included the morphology and electronic property measurements. The morphology was developed using optical and scanning electron microscopy and microprobe analyses. Electronic property characterization of the superconducting transition temperatures were made using an impedance change-tuned coil method.

Reger, J. L.; Mendelson, R. A.

1975-01-01

56

Laboratory outreach: student assessment of flow cytometer fluidics in zero gravity.

Due to the the clinical utility of the flow cytometer, the National Aeronautics and Space Administration (NASA) is interested in the design of a space flight-compatible cytometer for use on long-duration space missions. Because fluid behavior is altered dramatically during space flight, it was deemed necessary to validate the principles of hydrodynamic focusing and laminar flow (cytometer fluidics) in a true microgravity environment. An experiment to validate these properties was conducted by 12 students from Sweetwater High School (Sweetwater, TX) participating in the NASA Reduced Gravity Student Flight Opportunity, Class of 2000. This program allows high school students to gain scientific experience by conducting an experiment on the NASA KC-135 zero gravity laboratory aircraft. The KC-135 creates actual zero-gravity conditions in 30-second intervals by flying a highly inclined parabolic flight path. The experiment was designed by their mentor in the program, the Johnson Space Center's flow cytometrist Brian Crucian, PhD, MT(ASCP). The students performed the experiment, with the mentor, onboard the NASA zero-gravity research aircraft in April 2000. PMID:12442765

Crucian, B; Norman, J; Brentz, J; Pietrzyk, R; Sams, C

2000-10-01

57

A study of immiscible liquids, liquid behavior at zero gravity, and dynamic contact lines and angles

NASA Astrophysics Data System (ADS)

The work reported here covers three topics that were investigated as part of preparation for a space based experiment. The intention of the proposed experiment was to study the relationship between container geometry and interface geometry for a free liquid surface at zero gravity.A mathematical theory proposed by Paul Concus and Robert Finn in 1974 and recently developed by Finn yields explicit geometrical criteria for the position of the free surface of a liquid at zero gravity in a cylindrical container of specified cross section. It is possible to find geometrical criteria that promise a particular liquid location. A unified graphical presentation of four geometries is given that can be used directly for the design of containments for liquids at zero gravity. As one application of these design curves, a container was built and tested in a series of 2 second droptower experiments at NASA Lewis Research Center.It was apparent that the space based experiment would require use of sophisticated optical instrumentation that would be most effective if a pair of immiscible liquids were used rather than a single liquid under its vapor. This work identifies 121 transparent immiscible liquid pairs that have properties compatible with optical instrumentation based on laser-induced fluorescence. Physical data such as specific gravity, index of refraction, viscosity, flash point, and toxicity were found in the literature. Compatibility with plexiglas (PMMA), contact angles of the internal meniscus on glass and PMMA, meniscus formation times, and clearing times were measured. A useful noninvasive technique for determining interfacial tensions is explained and used.The contact angle is a critical parameter in the consideration of liquid behavior at zero gravity, therefore, a technique, based on laser light refraction, was developed to objectively measure it. Dynamic contact line experiments were conducted at various velocities, both advancing and receding, using one of the 121 immiscible liquid pairs (nonane/formamide) in contact with glass.

Smedley, Gregory Todd

58

a Study of Immiscible Liquids, Liquid Behavior at Zero Gravity, and Dynamic Contact Lines and Angles

NASA Astrophysics Data System (ADS)

The work reported here covers three topics that were investigated as part of preparation for a space based experiment. The intention of the proposed experiment was to study the relationship between container geometry and interface geometry for a free liquid surface at zero gravity. A mathematical theory proposed by Paul Concus and Robert Finn in 1974 and recently developed by Finn yields explicit geometrical criteria for the position of the free surface of a liquid at zero gravity in a cylindrical container of specified cross section. It is possible to find geometrical criteria that promise a particular liquid location. A unified graphical presentation of four geometries is given that can be used directly for the design of containments for liquids at zero gravity. As one application of these design curves, a container was built and tested in a series of 2 second drop-tower experiments at NASA Lewis Research Center. It was apparent that the space based experiment would require use of sophisticated optical instrumentation that would be most effective if a pair of immiscible liquids were used rather than a single liquid under its vapor. This work identifies 121 transparent immiscible liquid pairs that have properties compatible with optical instrumentation based on laser-induced fluorescence. Physical data such as specific gravity, index of refraction, viscosity, flash point, and toxicity were found in the literature. Compatibility with plexiglas (PMMA), contact angles of the internal meniscus on glass and PMMA, meniscus formation times, and clearing times were measured. A useful non-invasive for determining interfacial tensions is explained and used. The contact angle is a critical parameter in the consideration of liquid behavior at zero gravity, therefore, a technique, based on laser light refraction, was developed to objectively measure it. Dynamic contact line experiments were conducted at various velocities, both advancing and receding, using one of the 121 immiscible liquid pairs (nonane/formamide) in contact with glass.

Smedley, Gregory Todd

1990-01-01

59

A study of immiscible liquids, liquid behavior at zero gravity, and dynamic contact lines and angles

NASA Astrophysics Data System (ADS)

Three topics were investigated as part of preparation for a space based experiment. The intention of the experiment was to study the relationship between container geometry and interface geometry for a free liquid surface at zero gravity. A mathematical theory yields explicit geometrical criteria for the position of the free surface of a liquid at zero gravity in a cylindrical container of specified cross section. It is possible to find geometrical criteria that promise a particular liquid location. A unified graphical presentation of four geometries is given that can be used directly for the design of containments for liquids at zero gravity. As one application of these design curves, a container was built and tested in a series of two second drop-tower experiments. The identification of 121 transparent immiscible liquid pairs that have properties compatible with optical instrumentation based on laser-induced fluorescence is presented. Physical data such as specific gravity, index of refraction, viscosity, flash point, and toxicity were found in the literature. Compatibility with plexiglass (PMMA), contact angles of the internal meniscus on glass and PMMA, meniscus formation times, and clearing times were measured. A useful non-invasive for determining interfacial tensions is explained and used. The contact angle is a critical parameter in the consideration of liquid behavior at zero gravity; therefore, a technique based on laser light refraction was developed to objectively measure it. Dynamic contact line experiments were conducted at various velocities, both advancing and receding, using one of the 121 immiscible liquid pairs (nonane/formamide) in contact with glass.

Smedley, Gregory Todd

60

NASA Technical Reports Server (NTRS)

The work is summarized which was accomplished from January 1974 to October 1974 for the Zero-Gravity Atmospheric Cloud Physics Laboratory. The definition and development of an atmospheric cloud physics laboratory and the selection and delineation of candidate experiments that require the unique environment of zero gravity or near zero gravity are reported. The experiment program and the laboratory concept for a Spacelab payload to perform cloud microphysics research are defined. This multimission laboratory is planned to be available to the entire scientific community to utilize in furthering the basic understanding of cloud microphysical processes and phenomenon, thereby contributing to improved weather prediction and ultimately to provide beneficial weather control and modification.

Greco, R. V.; Eaton, L. R.; Wilkinson, H. C.

1974-01-01

61

Vibrational effects on convection in a square cavity at zero gravity

In this numerical study, we investigate natural convection in a two-dimensional square-section enclosure vibrating sinusoidally parallel to the applied temperature gradient in a zero-gravity field. The full Navier Stokes equations are simplified with the Boussinesq approximation and solved by a finite difference method. Whereas the Prandtl number Pr is fixed to 7.1 (except for some test cases with Pr =

Katsuya Hirata; Tomoaki Sasaki; Hirochika Tanigawa

2001-01-01

62

The Marshall Space Flight Center KC-135 zero gravity test program for FY 1982

NASA Technical Reports Server (NTRS)

During FY-82, researchers and experimenters from Marshall Space Flight Center (MSFC) conducted 11 separate investigations during 26.3 hr of testing aboard the KC-135 zero-gravity aircraft, based at Ellington Air force Base, Texas. Although this represented fewer hours than initially projected, all experiment and test objectives were met or exceeded. This Technical Memorandum compiles all results achieved by MSFC users during FY-82, a year considered to be highly productive.

Shurney, R. E. (editor)

1983-01-01

63

The study of single crystals for space processing and the effect of zero gravity

NASA Technical Reports Server (NTRS)

A study was undertaken to analyze different growth techniques affected by a space environment. Literature on crystal growth from melt, vapor phase and float zone was reviewed and the physical phenomena important for crystal growth in zero-gravity environment was analyzed. Recommendations for potential areas of crystal growth feasible for space missions are presented and a bibliography of articles in the area of crystal growth in general is listed.

Lal, R. B.

1975-01-01

64

NASA Technical Reports Server (NTRS)

The preliminary concept, specifications, and requirements of a reusable zero gravity combustion facility (0-GCF) for use by experimenters aboard the spacelab payload of the space transportation system (STS) orbiter are described. The facility will be amenable to any mission of the STS orbiter in which a spacelab habitable segment and pallet segment are integral and for which orbital mission plans specify induced accelerations of 0.0001 g or less for sufficiently long periods so as not to impact experiment performance.

Dewitt, R. L.

1978-01-01

65

KC-135 zero-gravity two-phase flow pressure drop experiments and modelling

the condensed mercury. High- speed, photographs of nonwemng condensation in constant-diameter glass tubes were used to determine definitions of flow characteristics for normal and zero-gravity conditions. Two types of condensers, a crossflow...-nitrogen-cooled condenser and counterflow-NaK-cooled condenser along were used for different test conditions. For the crossflow-nitrogen-cooled condenser, flow regimes and pressure dmps were studied for nonwetted flow in constant diameter and tapered tubes under normal...

Lambert, Anne

2012-06-07

66

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

67

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

2012-03-01

68

Aerosol deposition along the respiratory tract at zero gravity: a theoretical study

Significant fractions of airborne particles composing inhaled aerosols can deposit along the respiratory tract during breathing. Depending on the environmental condition, some particles that enter the body via the respiratory route can pose health hazards. On earth, three general rate mechanisms are active in this deposition process: (1) inertial impaction; (2) diffusion; and (3) gravity-dependent sedimentation. Space craft, stations, and bases represent unique settings where potentially pathogenic aerosols may be encountered under the unique condition of zero or reduced gravity. The present study was undertaken in order to predict how particle deposition in the human respiratory tract at zero gravity may differ from that on earth. We employed the aerosol deposition model of the Task Group on Lung Dynamics to assess the regional deposition of particles ranging from 0.01 to 10 ..mu..m diameter at two particulate densities, 1 and 4, during simulated tidal breathing and breathing during moderate - heavy exercise. Our results suggest the gas exchange regions of the lungs of space travelers and residents are afforded some protection, relative to their earth-bound counterparts, against the deposition of particles due to the absence of gravity; and approximately 2 to 10 fold reduction in the efficiency of collection of particles > 0.5 ..mu..m in diameter occurred in the pulmonary region during resting conditions and exercise. Deposition along the tracheobronchial tree, however, is not markedly altered in the absence of gravity, indicating airway sites contributing to this structure remain susceptible to insults by inhaled aerosols. 18 references, 2 figures, 2 tables.

Lehnert, B.E.; Smith, D.M.; Holland, L.M.; Tillery, M.I.; Thomas, R.G.

1984-01-01

69

Behavior of the lean methane-air flame at zero-gravity

NASA Technical Reports Server (NTRS)

A special rig was designed and constructed to be compatible with the NASA Lewis Research Center Airborne Research Laboratory to allow the study of the effect of gravity on the behavior of lean limit in a standard 50.4 mm (2 in.) internal diameter tube when the mixtures are ignited at the open end and propagate towards the closed end of the tube. The lean limit at zero gravity was found to be 5.10% methane and the flame was found to extenguish in a manner previously observed for downward propagating flames at one g. It was observed that g-jitter could be maintained at less than + or 0.04 g on most zero g trajectories. All of propagating lean limit flames were found to be sporadically cellularly unstable at zero g. There was no observable correlation between the occurrence of g-jitter and the lean limit, average propagation speed of the flame through the tube or the occurrence of cellular instability.

Noe, K. A.; Strehlow, R. A.

1985-01-01

70

Papilledema has long been associated with elevated intracranial pressure. Classically, tumors, idiopathic intracranial hypertension, and obstructive hydrocephalus have led to an increase in intracranial pressure causing optic nerve head edema and observable optic nerve swelling. Recent reports describe astronauts returning from prolonged space flight on the International Space Station with papilledema (Mader et al., 2011) [1]. Papilledema has not been observed in shorter duration space flight. Other recent work has shown that the difference in intraocular pressure (IOP) and cerebrospinal fluid pressure (CSFp) may be very important in the pathogenesis of diseases of the optic nerve, especially glaucoma (Berdahl and Allingham, 2009; Berdahl, Allingham, et al., 2008; Berdahl et al., 2008; Ren et al., 2009; Ren et al., 2011) [2-6]. The difference in IOP and CSFp across the lamina cribrosa is known as the translaminar pressure difference (TLPD). We hypothesize that in zero gravity, CSF no longer pools in the caudal spinal column as it does in the upright position on earth. Instead, CSF diffuses throughout the subarachnoid space resulting in a moderate but persistently elevated cranial CSF pressure, including the region just posterior to the lamina cribrosa known as the optic nerve subarachnoid space (ONSAS). This small but chronically elevated CSFp could lead to papilledema when CSFp is greater than the IOP. If the TLPD is the cause of optic nerve head edema in astronauts subjected to prolonged zero gravity, raising IOP and/or orbital pressure may treat this condition and protect astronauts in future space travels from the effect of zero gravity on the optic nerve head. Additionally, the same TLPD concept may offer a deeper understanding of the pathogenesis and treatment options of idiopathic intracranial hypertension (IIH), glaucoma and other diseases of the optic nerve head. PMID:22981592

Berdahl, John P; Yu, Dao Yi; Morgan, William H

2012-12-01

71

A Photographic Study of Liquid Hydrogen Under Simulated Zero Gravity Conditions

NASA Technical Reports Server (NTRS)

The transient behavior of liquid hydrogen, under conditions of zero gravity, was studied photographically. The hydrogen was subjected to weightlessness by dropping a Dewar containing this liquid from a height of 9 feet. During the weightless period of approximately 3/4 second, the liquid rose along the walls of the Dewar into the original vapor space. The rise occurred at constant velocity for practically the entire duration of this period. Adhesive forces were concluded to be the primary cause of the liquid rise along the wall.

Brazinsky, Irving; Weiss, Solomon

1962-01-01

72

Zero-Gravity Locomotion Simulators: New Ground-Based Analogs for Microgravity Exercise Simulation

NASA Technical Reports Server (NTRS)

Maintaining health and fitness in crewmembers during space missions is essential for preserving performance for mission-critical tasks. NASA's Exercise Countermeasures Project (ECP) provides space exploration exercise hardware and monitoring requirements that lead to devices that are reliable, meet medical, vehicle, and habitat constraints, and use minimal vehicle and crew resources. ECP will also develop and validate efficient exercise prescriptions that minimize daily time needed for completion of exercise yet maximize performance for mission activities. In meeting these mission goals, NASA Glenn Research Center (Cleveland, OH, USA), in collaboration with the Cleveland Clinic (Cleveland, Ohio, USA), has developed a suite of zero-gravity locomotion simulators and associated technologies to address the need for ground-based test analog capability for simulating in-flight (microgravity) and surface (partial-gravity) exercise to advance the health and safety of astronaut crews and the next generation of space explorers. Various research areas can be explored. These include improving crew comfort during exercise, and understanding joint kinematics and muscle activation pattern differences relative to external loading mechanisms. In addition, exercise protocol and hardware optimization can be investigated, along with characterizing system dynamic response and the physiological demand associated with advanced exercise device concepts and performance of critical mission tasks for Exploration class missions. Three zero-gravity locomotion simulators are currently in use and the research focus for each will be presented. All of the devices are based on a supine subject suspension system, which simulates a reduced gravity environment by completely or partially offloading the weight of the exercising test subject s body. A platform for mounting treadmill is positioned perpendicularly to the test subject. The Cleveland Clinic Zero-g Locomotion Simulator (ZLS) utilizes a pneumatic subject load device to apply a near constant gravity-replacement load to the test subject during exercise, and is currently used in conjunction with the General Clinical Research Center for evaluating exercise protocols using a bedrest analog. The enhanced ZLS (eZLS) at NASA Glenn Research Center features an offloaded treadmill that floats on a thin film of air and interfaces to a force reaction frame via variably-compliant isolators, or vibration isolation system. The isolators can be configured to simulate compliant interfaces to the vehicle, which affects mechanical loading to crewmembers during exercise, and has been used to validate system dynamic models for new countermeasures equipment designs, such as the second International Space Station treadmill slated for use in 2010. In the eZLS, the test subject and exercise device can be pitched at the appropriate angle for partial gravity simulations, such as lunar gravity (1/6th earth gravity). On both the eZLS and the NASA-Johnson Space Center standalone ZLS installed at the University of Texas Medical Branch in Galveston, Texas, USA, the subject's body weight relative to the treadmill is controlled via a linear motor subject load device (LM-SLD). The LM-SLD employs a force-feedback closed-loop control system to provide a relatively constant force to the test subject during locomotion, and is set and verified for subject safety prior to each session. Locomotion data were collected during parabolic flight and on the eZLS. The purpose was to determine the similarities and differences between locomotion in actual and simulated microgravity. Subjects attained greater amounts of hip flexion during walking and running during parabolic flight. During running, subjects had greater hip range of motion. Trunk motion was significantly less on the eZLS than during parabolic flight. Peak impact forces, loading rate, and impulse were greater on the eZLS than during parabolic while walking with a low external load (EL) and rning with a high EL. Activation timing differences existed between locations in all muscles excep

Perusek, Gail P.; DeWitt, John K.; Cavanagh, Peter R.; Grodsinsky, Carlos M.; Gilkey, Kelly M.

2007-01-01

73

NASA Astrophysics Data System (ADS)

A scaled model of the downstream Orion service module propellant tank was constructed to asses the propellant dynamics under reduced and zero-gravity conditions. Flight and ground data from the experiment is currently being used to validate computational models of propel-lant dynamics in Orion-class propellant tanks. The high fidelity model includes the internal structures of the propellant management device (PMD) and the mass-gauging probe. Qualita-tive differences between experimental and CFD data are understood in terms of fluid dynamical scaling of inertial effects in the scaled system. Propellant configurations in zero-gravity were studied at a range of fill-fractions and the settling time for various docking maneuvers was determined. A clear understanding of the fluid dynamics within the tank is necessary to en-sure proper control of the spacecraft's flight and to maintain safe operation of this and future service modules. Understanding slosh dynamics in partially-filled propellant tanks is essential to assessing spacecraft stability.

Kreppel, Samantha

74

NASA Technical Reports Server (NTRS)

The Centaur propellant management and thermal control techniques required for zero gravity coasting were successfully demonstrated during an extended mission following spacecraft separation on the TC-2 flight. As part of the demonstration, two successful engine starts were accomplished. The first engine start followed a one-hour zero gravity coast, and the second engine start followed a three-hour zero gravity coast. All of the Centaur systems performed satisfactorily, the design parameters for zero gravity coasting were verified, and no significant problems were encountered. The flight results showed that the propellant location and behavior, propellant heating, and tank pressure rise rates observed during the zero-gravity coasts were less severe than expected. Consequently, the majority of the propellants remained at the tank bottom, the propellant collection times were very short, and more than 7 hours of coast could have been achieved before a tank venting was required. The tank pressurization prior to the engine starts provided boost pump Net Positive Suction Head values well in excess of the values required. The LO2 tank pressurization was accomplished by a new bubbler method that greatly reduced the helium usage.

Lacovic, R. F.

1975-01-01

75

A Biomechanical Comparison of 1-G and Fully-Loaded Simulated Zero-Gravity Locomotion

NASA Technical Reports Server (NTRS)

Exercise will almost certainly play an integral part in minimizing the bone mineral loss and muscular atrophy that occur during spaceflight. It has been hypothesized that an effective exercise regimen can be developed to elicit loads on the lower extremities and require muscle actions which resemble those encountered on Earth. The Penn State Zero-Gravity Simulator (PSZS) is a device which suspends subjects horizontally from multiple latex cords, with each cord negating the weight of a limb segment. A treadmill mounted on the wall under the PSZS enables subjects to run in simulated 0G. Subjects wear a harness to which a number of springs, which provide a gravity replacement load, are connected. The opposite end of each spring is connected to the side of the treadmill. During exercise, astronauts currently wear a similar harness in which the spring tethering load pulls at both the waist and shoulders. Ground reaction forces, muscular activations, and joint angles of the left leg during overground, treadmill, and fully-loaded zero-gravity simulated (ZLS) locomotion were assessed in order to gain insight into the effectiveness of the exercise regimen used by NASA to prevent the muscular atrophy and bone demineralization which occur in weightlessness. There were three hypotheses to this research. It was hypothesized that there will be no differences in peak ground reaction forces and peak loading rates between overground gait and gait in the full body weight loaded conditions in the ZLS. A second hypothesis was that that there will be no differences in hip, knee, and ankle joint positions between walking or running overground, on a standard treadmill, and in full bodyweight loaded conditions in the ZLS. The third hypothesis was that the muscular activations, as a percentage of maximal voluntary contraction, will be similar between walking or running overground, on a standard treadmill, and in full body-weight loaded conditions in the ZLS.

McCrory, Jean L.

1997-01-01

76

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

2010-04-01

77

Testing of a Spray-Bar Zero Gravity Cryogenic Vent System for Upper Stages

NASA Technical Reports Server (NTRS)

The capability to vent in zero gravity without resettling is a fundamental technology need that involves practically all uses of subcritical 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 then-nal energy from the propellant. In a cooperative effort, Marshall Space Flight Center's (MSFC's) Multipurpose Hydrogen Test Bed (N4HTB) was used to test a unique "spray bar" TVS system developed by Boeing. A schematic of this system is included in Figure 1. The 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. In the mixing mode, the recirculation pump withdraws liquid from the tank and sprays it radially 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 spray bar heat exchanger element, and is vented overboard. The vented vapor cools the circulated bulk fluid, thereby removing thermal energy and reducing tank pressure. Figure 2 is a plot of ullage pressure (P4) and liquid vapor pressure (PSAI) versus time. 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. The primary advantage of the spray bar configuration is that pressure reduction is achieved independent of liquid and vapor location, thereby enhancing the applicability of normal gravity test data to zero gravity conditions. The in-tank components are minimized with the proposed TVS design. Because the recirculation pump is external to the tank, no electrical power penetration of the tank is required for pump or valve operation. This is especially desirable for L02 tanks since the presence of an electrical ignition source in oxygen represents a critical failure mode. Also, since the critical components (pump, motor, valve, orifice) are external to the tank, system checkout and ground servicing/replacement are easier. For zero-g operation, component replacement external to the tank may be a significant benefit. In addition to satisfying the zero g TVS design objectives, the TVS concept tested offers additional benefits to the integrated subcritical cryogenic storage and launch system.

Lak, Tibor; Flachbart, Robin; Nguyen, Han; Martin, James

1999-01-01

78

Pressure drop in fully developed, turbulent, liquid-vapor annular flows in zero gravity

NASA Technical Reports Server (NTRS)

The prediction of frictional pressure drop in fully developed, turbulent, annular liquid-vapor flows in zero gravity using simulation experiments conducted on earth is described. The scheme extends the authors' earlier work on dispersed flows. The simulation experiments used two immiscible liquids of identical density, namely, water and n-butyl benzoate. Because of the lack of rigorous analytical models for turbulent, annular flows, the proposed scheme resorts to existing semiempirical correlations. Results based on two different correlations are presented and compared. Others may be used. It was shown that, for both dispersed and annular flow regimes, the predicted frictional pressure gradients in 0-g are lower than those in 1-g under otherwise identical conditions. The physical basis for this finding is given.

Sridhar, K. R.; Chao, B. T.; Soo, S. L.

1992-01-01

79

Early cardiovascular adaptation to zero gravity simulated by head-down tilt.

The early cardiovascular adaptation to zero gravity, simulated by head-down tilt at 5 degrees, was studied in a series of 10 normal young men. The validity of the model was confirmed by comparing the results with data from Apollo and Skylab flights. Tilt produced a significant central fluid shift with a transient increase in central venous pressure, later followed by an increase in left ventricular size without changes in cardiac output, arterial pressure, or contractile state. The hemodynamic changes were transient with a nearly complete return to the control state within 6 hr. The adaptation included a diuresis and a decrease in blood volume, associated with ADH, renin and aldosterone inhibition. PMID:11541656

Blomqvist, C G; Nixon, J V; Johnson, R L; Mitchell, J H

1980-01-01

80

Human physiological problems in zero gravity - An attempt at understanding through systems analysis

NASA Technical Reports Server (NTRS)

When the experimental situation is that of man exposed to a gravitationless environment for varying periods of time, the possible importance and value of a related modeling effort is readily apparent. One of the main objectives of the Skylab Program, with its missions of 28, 59, and 85 day duration concerned biomedical investigations of various types, and large amounts of relevant experimental data have been gathered and are in the process of being sorted and interpreted. In order to be of eventual usefulness in forming and testing consistent physiological hypotheses concerning the effect of zero gravity on man, a modeling effort was established in 1972 through the General Electric Company, Space Division, Houston, Texas. An account is given of some of the developments completed or in progress as part of this modeling effort. A long-term cardiovascular model and a large model of the systemic circulation are discussed.

White, R. J.; Croston, R. C.

1974-01-01

81

Myosin heavy chain expression in rodent skeletal muscle: effects of exposure to zero gravity

NASA Technical Reports Server (NTRS)

This study ascertained the effects of 9 days of zero gravity on the relative (percentage of total) and calculated absolute (mg/muscle) content of isomyosin expressed in both antigravity and locomotor skeletal muscle of ground control (CON) and flight-exposed (FL) rats. Results showed that although there were no differences in body weight between FL and CON animals, a significant reduction in muscle mass occurred in the vastus intermedius (VI) (P < 0.05) but not in the vastus lateralis (VL) or the tibialis anterior. Both total muscle protein and myofibril protein content were not different between the muscle regions examined in the FL and CON groups. In the VI, there were trends for reductions in the relative content of type I and IIa myosin heavy chains (MHCs) that were offset by increases in the relative content of both type IIb and possibly type IIx MHC protein (P > 0.05). mRNA levels were consistent with this pattern (P < 0.05). The same pattern held true for the red region of the VL as examined at both the protein and mRNA level (P < 0.05). When the atrophy process was examined, there were net reductions in the absolute content of both type I and IIa MHCs that were offset by calculated increases in type IIb MHC in both VI and red VL. Collectively, these findings suggest that there are both absolute and relative changes occurring in MHC expression in the "red" regions of antigravity skeletal muscle during exposure to zero gravity that could affect muscle function.

Haddad, F.; Herrick, R. E.; Adams, G. R.; Baldwin, K. M.

1993-01-01

82

Test Data Analysis of a Spray Bar Zero-Gravity Liquid Hydrogen Vent System for Upper Stages

To support development of a zero-gravity pressure control capability for liquid hydrogen (LH2), a series of thermodynamic venting system (TVS) tests was conducted in 1996 and 1998 using the Marshall Space Flight Center (MSFC) multipurpose hydrogen test bed (MHTB). These tests were performed with ambient heat leaks ≈20 and 50 W for tank fill levels of 90%, 50%, and 25%.

A. Hedayat; J. W. Bailey; L. J. Hastings; R. H. Flachbart

2004-01-01

83

Test Data Analysis of a Spray Bar Zero-Gravity Liquid Hydrogen Vent System for Upper Stages

To support development of a zero-gravity pressure control capability for liquid hydrogen (LH2), a series of thermodynamic venting system (TVS) tests was conducted in 1996 and 1998 using the Marshall Space Flight Center (MSFC) multipurpose hydrogen test bed (MHTB). These tests were performed with ambient heat leaks ~20 and 50 W for tank fill levels of 90%, 50%, and 25%.

A. Hedayat; J. W. Bailey; L. J. Hastings; R. H. Flachbart

2004-01-01

84

An elegant and accurate way to determine the zero-gravity surface figure of an optic from ground-based interferometric metrology is to average the figures found in two or more configurations that are rotated with respect to the direction of gravity, so gravity forces in the frame of the optic cancel in the average. In a recent elucidation of this technique, we emphasized that care must be taken to ensure that mount forces at each attachment point similarly cancel, and we presented some specific mounting schemes that gave accurate zero-gravity surface determinations during fabrication and acceptance testing of the Space Interferometry Mission PT-M1 mirror. Here we show that multiconfiguration averaging techniques work well for the most important special case of a mirror in a flightlike hexapod mount clocked into either two or three symmetrically placed positions. We explicitly compute mount forces (axial forces in the six struts of the hexapod) and show that at any attachment point their average over multiple clocked configurations vanishes in the frame of the optic, ensuring the success of zero-gravity surface figure extraction. PMID:19623238

Bloemhof, Eric E; Lam, Jonathan C; Feria, V Alfonso; Chang, Zensheu

2009-07-20

85

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

86

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

87

Spray Bar Zero-Gravity Vent System for On-Orbit Liquid Hydrogen Storage

NASA Technical Reports Server (NTRS)

During zero-gravity orbital cryogenic propulsion operations, a thermodynamic vent system (TVS) concept is expected to maintain tank pressure control without propellant resettling. In this case, a longitudinal spray bar mixer system, coupled with a Joule-Thompson (J-T) valve and heat exchanger, was evaluated in a series of TVS tests using the 18 cu m multipurpose hydrogen test bed. Tests performed at fill levels of 90, 50, and 25 percent, coupled with heat tank leaks of about 20 and 50 W, successfully demonstrated tank pressure control within a 7-kPa band. Based on limited testing, the presence of helium constrained the energy exchange between the gaseous and liquid hydrogen (LH2) during the mixing cycles. A transient analytical model, formulated to characterize TVS performance, was used to correlate the test data. During self-pressurization cycles following tank lockup, the model predicted faster pressure rise rates than were measured; however, once the system entered the cyclic self-pressurization/mixing/venting operational mode, the modeled and measured data were quite similar. During a special test at the 25-percent fill level, the J-T valve was allowed to remain open and successfully reduced the bulk LH2 saturation pressure from 133 to 70 kPa in 188 min.

Hastings, L. J.; Flachbart, R. H.; Martin, J. J.; Hedayat, A.; Fazah, M.; Lak, T.; Nguyen, H.; Bailey, J. W.

2003-01-01

88

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

When the International Space Station (ISS) is completed and starts its operation, crew members will be stationed for three months or more in orbit aboard the ISS. As they stay longer in the space environment, "habitability" for them will become most important in the design of the interior space. One of the problems about habitability in a zero gravity (0 G) environment is disorientation. Crew members have difficulty in discriminating between "up" and "down" and more serious disorientations may cause space motion sickness. Crew members rely on visual perception to orient themselves because they can't use their sense of equilibrium in a 0 G environment. Although color and the direction of equipment of Space Shuttles or modules has been considered, no systematic study has been conducted on interior space. This study intended to clarify how people acquire visual information and recognize their orientation in a 0 G environment by an experiment in which a subject wears a head-mounted display (HMD) and enters a virtual weightless state represented by computer graphics (CG). Visual information of a room and the degree-of-freedom of motion were varied to examine the influence of the conditions on such a simple task as movement through several connected modules, and the performance and the behavior of each subject were investigated. PMID:12697557

Aoki, H; Yamaguchi, T; Ohno, R

2000-07-01

89

NASA Technical Reports Server (NTRS)

Pathophysiological conditions resulting from prolonged exposure to zero gravity, cabin constraint, altered ambient environment, whether it be noise, vibrations, high temperatures, or combinations of such factors, are studied in laboratory animals and applied to manned space flight. Results and plans for further study are presented. Specific topics covered include: thermoregulation and its role in reflecting stress and adaptation to the gravity free environment and cabin confinement with its altered circadian forcings; renal function and its measurement in electrolyte distribution and blood flow dynamics; gastronintestinal function and an assessment of altered absorptive capacity in the intestinal mucosa; and catecholamine metabolism in terms of distribution and turnover rates in specific tissues.

Musacchia, X. J.

1974-01-01

90

NASA Technical Reports Server (NTRS)

The objectives of this program are: (1) to determine whether the size of red cell aggregates, kinetics and morphology of these aggregates are influenced by near-zero gravity; (2) whether viscosity, especially at low shear rate, is afflicted by near-zero gravity (the latter preventing sedimentation of red cells); (3) whether the actual shape of red cells changes; and (4) whether blood samples obtained from different donors (normal and patients suffering from different disorders) react in the same manner to near-zero gravity.

Dintenfass, L.

1985-01-01

91

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

92

Effects of zero gravity on myofibril content and isomyosin distribution in rodent skeletal muscle

NASA Technical Reports Server (NTRS)

The purpose of this experiment was to investigate the effects of 12.5 days of zero gravity (0 g) exposure (Cosmos 1887 Biosputnik) on the enzymatic properties, protein content, and isomyosin distribution of the myofibril fraction of the slow-twitch vastus intermedius (VI) and the fast-twitch vastus lateralis (VL) muscles of adult male rats. Measurements were obtained on three experimental groups (n = 5 each group) designated as flight group (FG), vivarium control (VC), and synchronous control (SC). Body weight of the FG was significantly lower than that of the two control groups (P less than 0.05). Compared with the two control groups, VI weight was lower by 23% (P less than 0.10), whereas no such pattern was apparent for the VL muscle. Myofibril yields (mg protein/g muscle) in the VI were 35% lower in the FG than in controls (P less than 0.05), whereas no such pattern was apparent for the VL muscle. When myofibril yields were expressed on a muscle basis (mg/g x muscle weight), the loss of myofibril protein was more exaggerated and suggests that myofibril protein degradation is an early event in the muscle atrophy response to 0 g. Analysis of myosin isoforms indicated that slow myosin (Sm) was the primary isoform lost in the calculated degradation of total myosin. No evidence of loss of the fast isomyosins was apparent for either muscle following spaceflight. Myofibril ATPase activity of the VI was increased in the FG compared with controls, which is consistent with the observation of preferential Sm degradation. These data suggest that muscles containing a high percentage of slow-twitch fibers undergo greater degrees of myofibril protein degradation than muscles containing predominantly fast-twitch fibers in response to a relatively short period of 0 g exposure, and the primary target appears to be the Sm molecule.

Baldwin, K. M.; Herrick, R. E.; Ilyina-Kakueva, E.; Oganov, V. S.

1990-01-01

93

Substrate oxidation capacity in rodent skeletal muscle: effects of exposure to zero gravity

NASA Technical Reports Server (NTRS)

A study was conducted, as part of the integrated National Aeronautics and Space Administration Space Life Sciences 1 mission flown in June of 1991, to ascertain the effects of 9 days of exposure to zero gravity on the capacity of rodent skeletal muscle fiber types to oxidize either [14C]pyruvate or [14C]palmitate under state 3 metabolic conditions, i.e., nonlimiting amounts of substrate and cofactors. In addition, activity levels of marker enzymes of the tricarboxylic acid cycle, malate shuttle, and beta-oxidation were measured. Results showed that significant differences in muscle weight occurred in both the predominantly slow vastus intermedius and predominantly fast vastus lateralis of flight vs. control groups (P < 0.05). Total protein content of the muscle samples was similar between groups. Both pyruvate oxidation capacity and the marker oxidative enzymes were not altered in the flight relative to control animals. However, the capacity to oxidize long-chain fatty acids was significantly reduced by 37% in both the high- and low-oxidative regions of the vastus muscle (P < 0.05). Although these findings of a selective reduction in fatty acid oxidation capacity in response to spaceflight are surprising, they are consistent with previous findings showing 1) an increased capacity to take up glucose and upregulate glucose transporter proteins and 2) a marked accumulation of triglycerides in the skeletal muscles of rats subjected to states of unloading. Thus, skeletal muscle of animals exposed to non-weight-bearing environments undergo subcellular transformations that may preferentially bias energy utilization to carbohydrates.

Baldwin, K. M.; Herrick, R. E.; McCue, S. A.

1993-01-01

94

Processing yttrium-barium-copper oxide superconductor zero gravity using a double float zone surface

The effects of processing YBa{sub 2}Cu{sub 3}O{sub x} (Y123) superconductor in the near-zero gravity (0g) environment provided by the NASA KC-135 airplane flying on parabolic trajectories were studied. A new sheet float zone furnace, designed for this study, enabled fast temperature ramps. Up to an 18-gram sample was processed with each parabola. Samples of Y123 were processed as bulk sheets, composites containing Ag and Pd, and films deposited on single crystal Si and MgO substrates. The 0g-processed samples were multi-phase yet retained a localized Y123 stoichiometry where a single ground-based (1g) oxygen anneal at temperatures of 800 C recovered nearly 100-volume percent superconducting Y123. The 1g processed control samples remained multi-phase after the same ground-based anneal with less than 45 volume percent as superconducting Y123. The superconducting transition temperature was 91 K for both 0g and 1g processed samples. A 29 wt.% Ag/Y123 composite had a transition temperature of 93 K. Melt texturing of bulk Y123 in 0g produced aligned grains about a factor of three larger than in analogous 1g samples. Transport critical current densities were at or below 18 A/cm{sup 2}, due to the formation of cracks caused by the rapid heating rates required by the short time at 0g. Y123 deposited on single crystal Si and MgO in 0g was 30 vol.% y123 without an anneal. A weak superconducting transition at 80 K on MgO showed that substrate interactions occurred.

Pettit, D.R.; Peterson, D.E.; Kubat-Martin, K.A.; Petrovic, J.J.; Sheinberg, H.; Coulter, Y.; Day, D.E.

1997-04-01

95

Equilibrium fluid interface behavior under low- and zero-gravity conditions

NASA Astrophysics Data System (ADS)

We describe here some of our recent mathematical work, which forms a basis for the Interface Configuration Experiment scheduled for USML-2. The work relates to the design of apparatus that exploits microgravity conditions for accurate determination of contact angle. The underlying motivation for the procedures rests on a discontinuous dependence of the capillary free surface interface S on the contact angle gamma, in a cylindrical capillary tube whose section (base) omega contains a protruding corner with opening angle 2 alpha. Specifically, in a gravity-free environment, omega can be chosen so that, for all sufficiently large fluid volume, the height of S is uniquely determined as a (single-valued) function mu(x,y) entirely covering the base; the height mu is bounded over omega uniformly in gamma throughout the range absolute value of (gamma -(pion/2)) less than or equal to alpha, while for absolute value of (gamma - (pion/2)) greater than alpha fluid will necessarily move to the corner and uncover the base, rising to infinity (or falling to negative infinity) at the vertex, regardless of volume. We mention here only that procedures based on the phenomenon promise excellent accuracy when gamma is close pion/2 but may be subject to experimental error when gamma is close to zero (orpion), as the 'singular' part of the domain over which the fluid accumulates (or disappears) when a critical angle gamma theta is crossed then becomes very small and may be difficult to observe. We ignore the trivial case gamma is equal to pion/2 (planar free surface), to simplify the discussion.

Concus, Paul; Finn, Robert

1994-08-01

96

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

2004-11-01

97

Understanding the effects of gravity on biological organisms is vital to the success of future space missions. Previous studies in Earth orbit have shown that the common fruitfly (Drosophila melanogaster) walks more quickly and more frequently in microgravity, compared with its motion on Earth. However, flight preparation procedures and forces endured on launch made it difficult to implement on the Earth's surface a control that exposed flies to the same sequence of major physical and environmental changes. To address the uncertainties concerning these behavioural anomalies, we have studied the walking paths of D. melanogaster in a pseudo-weightless environment (0g*) in our Earth-based laboratory. We used a strong magnetic field, produced by a superconducting solenoid, to induce a diamagnetic force on the flies that balanced the force of gravity. Simultaneously, two other groups of flies were exposed to a pseudo-hypergravity environment (2g*) and a normal gravity environment (1g*) within the spatially varying field. The flies had a larger mean speed in 0g* than in 1g*, and smaller in 2g*. The mean square distance travelled by the flies grew more rapidly with time in 0g* than in 1g*, and slower in 2g*. We observed no other clear effects of the magnetic field, up to 16.5 T, on the walks of the flies. We compare the effect of diamagnetically simulated weightlessness with that of weightlessness in an orbiting spacecraft, and identify the cause of the anomalous behaviour as the altered effective gravity. PMID:22219396

Hill, Richard J A; Larkin, Oliver J; Dijkstra, Camelia E; Manzano, Ana I; de Juan, Emilio; Davey, Michael R; Anthony, Paul; Eaves, Laurence; Medina, F Javier; Marco, Roberto; Herranz, Raul

2012-07-01

98

Understanding the effects of gravity on biological organisms is vital to the success of future space missions. Previous studies in Earth orbit have shown that the common fruitfly (Drosophila melanogaster) walks more quickly and more frequently in microgravity, compared with its motion on Earth. However, flight preparation procedures and forces endured on launch made it difficult to implement on the Earth's surface a control that exposed flies to the same sequence of major physical and environmental changes. To address the uncertainties concerning these behavioural anomalies, we have studied the walking paths of D. melanogaster in a pseudo-weightless environment (0g*) in our Earth-based laboratory. We used a strong magnetic field, produced by a superconducting solenoid, to induce a diamagnetic force on the flies that balanced the force of gravity. Simultaneously, two other groups of flies were exposed to a pseudo-hypergravity environment (2g*) and a normal gravity environment (1g*) within the spatially varying field. The flies had a larger mean speed in 0g* than in 1g*, and smaller in 2g*. The mean square distance travelled by the flies grew more rapidly with time in 0g* than in 1g*, and slower in 2g*. We observed no other clear effects of the magnetic field, up to 16.5 T, on the walks of the flies. We compare the effect of diamagnetically simulated weightlessness with that of weightlessness in an orbiting spacecraft, and identify the cause of the anomalous behaviour as the altered effective gravity. PMID:22219396

Hill, Richard J. A.; Larkin, Oliver J.; Dijkstra, Camelia E.; Manzano, Ana I.; de Juan, Emilio; Davey, Michael R.; Anthony, Paul; Eaves, Laurence; Medina, F. Javier; Marco, Roberto; Herranz, Raul

2012-01-01

99

N-Decane-Air Droplet Combustion Experiments in the NASA-Lewis 5 Second Zero-Gravity Facility

NASA Technical Reports Server (NTRS)

The burning of single fuel (n-decane) droplets in a microgravity environment (below 0.00001 of the earth's gravity, achieved in the NASA-Lewis 5-Second Zero-Gravity Facility) was studied, as part of the development of the Droplet Combustion Experiment for eventual operation aboard either the Shuttle middeck or Spacelab. Special attention is given to the combustion equipment used and its operations and performance. Temporal analysis of the local burning rates in these tests showed increasing rates of change in the local burning as droplet combustion progressed. Result point to the need of studying large droplets, with long droplet combustion lifetimes as well as low gas/droplet motion to understand reasons for this unsteadiness.

Haggard, John B.; Brace, Michael H.; Dryer, Frederick L.; Choi, Mun Y.; Williams, Forman A.

1990-01-01

100

NASA Technical Reports Server (NTRS)

This project aimed to develop a methodology for evaluating performance and acceptability characteristics of the pressurized crew module volume suitability for zero-gravity (g) ingress of a spacecraft and to evaluate the operational acceptability of the NASA crew return vehicle (CRV) for zero-g ingress of astronaut crew, volume for crew tasks, and general crew module and seat layout. No standard or methodology has been established for evaluating volume acceptability in human spaceflight vehicles. Volume affects astronauts'ability to ingress and egress the vehicle, and to maneuver in and perform critical operational tasks inside the vehicle. Much research has been conducted on aircraft ingress, egress, and rescue in order to establish military and civil aircraft standards. However, due to the extremely limited number of human-rated spacecraft, this topic has been un-addressed. The NASA CRV was used for this study. The prototype vehicle can return a 7-member crew from the International Space Station in an emergency. The vehicle's internal arrangement must be designed to facilitate rapid zero-g ingress, zero-g maneuverability, ease of one-g egress and rescue, and ease of operational tasks in multiple acceleration environments. A full-scale crew module mockup was built and outfitted with representative adjustable seats, crew equipment, and a volumetrically equivalent hatch. Human factors testing was conducted in three acceleration environments using ground-based facilities and the KC-135 aircraft. Performance and acceptability measurements were collected. Data analysis was conducted using analysis of variance and nonparametric techniques.

Sanchez, Merri J.

2000-01-01

101

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

2012-09-01

102

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

Halsey

1987-01-01

103

NASA Technical Reports Server (NTRS)

Thermal fining, thermal migration of bubbles under reduced gravity conditions, and data to verify current theoretical models of bubble location and temperatures as a function of time are discussed. A sample, sodium borate glass, was tested during 5 to 6 minutes of zero gravity during rocket flight. The test cell contained a heater strip; thermocouples were in the sample. At present quantitative data are insufficient to confirm results of theoretical calculations.

Wilcox, W. R.; Subramanian, R. S.; Meyyappan, M.; Smith, H. D.; Mattox, D. M.; Partlow, D. P.

1981-01-01

104

NASA Technical Reports Server (NTRS)

The flight responses of common houseflies, velvetbean caterpillar moths, and worker honeybees were observed and filmed for a period of about 25 minutes in a zero-g environment during the third flight of the Space Shuttle Vehicle (flight number STS-3; March 22-30, 1982). Twelve fly puparia, 24 adult moths, 24 moth pupae, and 14 adult bees were loaded into an insect flight box, which was then stowed aboard the Shuttle Orbiter, the night before the STS-3 launch at NASA's Kennedy Space Center (KSC). The main purpose of the experiment was to observe and compare the flight responses of the three species of insects, which have somewhat different flight control mechanisms, under zero-g conditions.

Nelson, T. E.; Peterson, J. R.

1982-01-01

105

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

106

Steady state growth and segregation under zero gravity: InSb

NASA Technical Reports Server (NTRS)

It was established that ideal diffusion controlled steady state conditions, never accomplished on earth, were achieved during the growth of Te-doped InSb crystals in Skylab. Surface tension effects were found to establish non-wetting conditions under which free surface solidification took place in confined geometry. It was further found that, under forced contact conditions, surface tension effects led to the formation of surface ridges (not previously observed on earth) which isolated the growth system from its container. In addition, it was possible for the first time to identify unambiguously: the origin of segregation discontinuities associated with facet growth, the mode of nucleation and propagation or rotational twin boundaries, and the specific effect of mechanical-shock perturbations on segregation. The results obtained prove the advantageous conditions provided by outer space. Thus, fundamental data on solidification thought to be unattainable because of gravity induced interference on earth are now within reach.

Witt, A. F.; Lichtensteiger, M.; Lavine, M. C.; Herman, C. J.

1974-01-01

107

Manual control in space research on perceptual-motor functions under zero gravity conditions (L-10)

NASA Technical Reports Server (NTRS)

Are human abilities to control vehicles and other machines the same in space as those on Earth? The L-10 Manual Control Experiment of the First Materials Processing Tests (FMPT) started from this question. Suppose a pilot has the task to align the head of a space vehicle toward a target. His actions are to look at the target, to determine the vehicle movement, and to operate the manipulator. If the activity of the nervous system were the same as on Earth, the movements, of the eye and hand would become excessive because the muscles do not have to oppose gravity. The timing and amount of movement must be arranged for appropriate actions. The sensation of motion would also be affected by the loss of gravity because the mechanism of the otolith, the major acceleration sensor, depends on gravity. The possible instability of the sensation of direction may cause mistakes in the direction of control of manipulator movement. Thus, the experimental data can be used for designing man-machine systems in space, as well as for investigation of physiological mechanisms. In this experiment, the direction of vehicle heading is expressed by a light spot on an array of light emitting diodes and the manipulator is of a finger stick type. As the light spot moves up and down, the Japanese Payload Specialist, and the subject, must move the manipulator forward and backward to keep the movement of the light spot within the neighborhood of the central point of the display. The position of the light spot is computed in such a manner that when the stick is kept at the neutral position, a motion whose acceleration is proportional to the angle of deflection is added to the movement of the light spot. The Operator Describing Function, which is an expression of human control characteristics, can be calculated from 2 minutes of raw data of the light spot position and stick deflection. The 2 minutes of operation is called a run, and 8 runs with resting periods composes a session. The on-orbit experiment will be conducted on the second, fourth, and seventh days. One session of experiment of each of these days is conducted following the L-4 experiment, which uses the same apparatus. The Payload Specialist, aided by a Mission Specialist, will take our apparatus from a rack container, set up the apparatus, attach electrodes for measurements of eye movement and muscle activity, conduct the L-4 Visual Stability Experiment, conduct one session of the manual control experiment, and then dissemble and stow the apparatus. In addition to the flight experiment, pre-flight and post-flight experiments will be conducted. The data of three sessions on orbit will reflect adaption of physiological systems to microgravity. The data of post-flight experiments, on the other hand, will reflect re-adaptation of physiological systems to the gravity condition on the ground. Control data collected with and without psychological tension will be scheduled just prior to and long before launch.

Tada, Akira

1993-01-01

108

NASA Technical Reports Server (NTRS)

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 with other systems. To facilitate these goals, a rodent suspension model was developed (Overton-Tipton) and a VO2 max testing procedure was perfected. Three methodological developments occurred during this past year deserving of mention. The first was the refinement of the tail suspension model so that (1) the heat dissipation functions of the caudal artery can be better utilized, and (2) the blood flow distribution to the tail would have less external constriction. The second was the development on a one-leg weight bearing model for use in simulated weightlessness studies concerned with change in muscle mass, muscle enzyme activity, and hind limb blood flow. The chemical body composition of 30 rats was determined and used to develop a prediction equation for percent fat using underwater weighing procedures to measure carcass specific gravity and to calculate body density, body fat, and fat free mass.

Tipton, Charles M.

1991-01-01

109

A zero-gravity demonstration of the collision and coalescence of water droplets

NASA Technical Reports Server (NTRS)

The mechanics of the collision and coalescence of liquid droplets is one of the main research areas in the fields of nuclear physics, astrophysics, meteorology and fluid mechanics. The crew members on the Skylab 3 and 4 missions were requested to perform demonstrations of the collision and coalescence of water droplets under the low gravity environment at orbital altitude. In Skylab 4 two water droplets with equal volumes, 30 cu cm each, were used. A dark colored droplet (contaminated with grape drink) moving with a velocity of 3.14 cm/sec collided with a stationary pink colored droplet (contaminated with strawberry drink) and coalescence occurred. Theoretical models are proposed to study the various stages of the collision-coalescence processes. Special considerations are concentrated in the investigation of the bounce-coalescence and coalescence-instability processes. The surface tension of the coalesced droplets was calculated to be 52 dynes/cm in perfect agreement with laboratory measurements made after the flight using a reproduction of the liquids.

Hung, R. J.; Vaughan, O. H.; Smith, R. E.

1974-01-01

110

Test Data Analysis of a Spray Bar Zero-Gravity Liquid Hydrogen Vent System for Upper Stages

NASA Technical Reports Server (NTRS)

To support development of a zero-gravity pressure control capability for liquid hydrogen (LH2), a series of thermodynamic venting system (TVS) tests was conducted in 1996 and 1998 using the Marshall Space Flight Center (MSFC) multipurpose hydrogen test bed (MHTB). These tests were performed with ambient heat leaks =20 and 50 W for tank fill levels of 90%, 50%, and 25%. TVS performance testing revealed that the spray bar was highly effective in providing tank pressure control within a 7-kPa band (131-138 Wa), and complete destratification of the liquid and the ullage was achieved with all test conditions. Seven of the MHTB tests were correlated with the TVS performance analytical model. The tests were selected to encompass the range of tank fill levels, ambient heat leaks, operational modes, and ullage pressurants. The TVS model predicted ullage pressure and temperature and bulk liquid saturation pressure and temperature obtained from the TVS model were compared with the test data. During extended self-pressurization periods, following tank lockup, the model predicted faster pressure rise rates than were measured. However, once the system entered the cyclic mixing/venting operational mode, the modeled and measured data were quite similar.

Hedayat, A.; Bailey, J. W.; Hastings, L. J.; Flachbart, R. H.

2003-01-01

111

NASA Technical Reports Server (NTRS)

The purpose of this experiment was to investigate the effects of 12 days of zero gravity (0G) exposure (Cosmos 1887 Biosputnik) on the enzymatic properties, protein content, and isomyosin distribution of the myofibril fraction of the slow-twitch vastus intermedius (VI) and the fast-twitch vastus lateralis (VL) muscles of adult male rats. Measurements were obtained on three experimental groups (n=5 each group) designated as flight-group (FG), vivarium-control (VC), and synchronous-control (SC). Body weight of the FG was significantly lower than the two control groups (p less than 0.05). Compared to the two control groups, VI weight was lower by 23 percent (p less than 0.10); whereas no such reduction was observed for the VL muscle. Myofibril yields (mg protein/g of muscle) in the VI were 35 percent lower in the FG compared to the controls (p less than 0.05); whereas, no such pattern was apparent for the VL muscle. When myofibril yields were expressed on a muscle basis (mg/g x muscle weight), the loss of myofibril protein was more exaggerated and suggests that myofibril protein degradation is an early event in the muscle atrophy response to 0G. Analysis of myosin isoforms indicated that slow-myosin was the primary isoform lost in the calculated degradation of total myosin. No evidence of loss of the fast isomyosins was apparent for either muscle following space flight. Myofibril ATPase activity of the VI was increased in the FG compared to controls, which is consistent with the observation of preferential slow-myosin degradation. These data suggest that muscles containing a high percent of slow-twitch fibers undergo greater degrees of myofibril protein degradation than do muscles containing predominantly fast-twitch fibers in response to a relatively short period of 0G exposure, and the primary target appears to be the slow-myosin molecule.

Baldwin, K.; Herrick, R.; Oganov, V.

1990-01-01

112

NASA Technical Reports Server (NTRS)

The results obtained show that it is possible to control light-weight robots with flexible links in a manner that produces good response time and does not induce unacceptable link vibrations. However, deflections induced by gravity cause large static position errors with such a control system. For this reason, it is not possible to use this control system for controlling motion in the direction of gravity. The control system does, on the other hand, have potential for use in space. However, in-space experiments will be needed to verify its applicability to robots moving in three dimensions.

Phillips, Warren F.

1989-01-01

113

NASA Technical Reports Server (NTRS)

The gravity induced motions, through the culture media, is calculated of living tissue segments cultured in the NASA rotating zero head space culture vessels. This is then compared with the media perfusion speed which is independent of gravity. The results may be interpreted as a change in the physical environment which will occur by operating the NASA tissue culture systems in actual microgravity (versus unit gravity). The equations governing particle motions which induce flows at the surface of tissues contain g terms. This allows calculation of the fluid flow speed, with respect to a cultured particle, as a function of the external gravitational field strength. The analysis is approached from a flow field perspective. Flow is proportional to the shear exerted on a structure which maintains position within the field. The equations are solved for the deviation of a particle from its original position in a circular streamline as a function of time. The radial deviation is important for defining the operating limits and dimensions of the vessel because of the finite radius at which particles necessarily intercept the wall. This analysis uses a rotating reference frame concept.

Wolf, David A.; Schwarz, Ray P.

1991-01-01

114

NASA Technical Reports Server (NTRS)

The burning rate of single droplets of n-decane in a microgravity environment of the NASA-Lewis 5 Second Zero-Gravity Facility was investigated as a function of time, together with the flame diameter/droplet diameter ratio, for a wide range of test environments other than normal air conditions, using an engineering model of the flight experiment. Oxygen mole fractions were varied from 18 to 50 percent, the total test chamber pressure was varied from 0.5 to 2 atmospheres, and the initial droplet diameter was varied from 0.98 to 2.41 mm. Measurements showed that the average burning rates for n-decane droplets exhibited the same qualitative trends as are found in two current models. Temporal analysis of the local burning rates showed variable rates of change in local burning as the droplet combustion progressed. The causes and implications of these findings are discussed.

Haggard, John B.; Borowski, Brian A.; Dryer, Frederick L.; Choi, Mun Y.; Williams, Forman A.

1991-01-01

115

NASA Technical Reports Server (NTRS)

The design and implementation of a vertical degree of freedom suspension system is described which provides a constant force off-load condition to counter gravity over large displacements. By accommodating motions up to one meter for structures weighing up to 100 pounds, the system is useful for experiments which simulate orbital construction events such as docking, multiple component assembly, or structural deployment. A unique aspect of this device is the combination of a large stroke passive off-load device augmented by electromotive torque actuated force feedback. The active force feedback has the effect of reducing break-away friction by a factor of twenty over the passive system alone. The thesis describes the development of the suspension hardware and the control algorithm. Experiments were performed to verify the suspensions system's effectiveness in providing a gravity off-load and simulating the motion of a structure in orbit. Additionally, a three dimensional system concept is presented as an extension of the one dimensional suspension system which was implemented.

Straube, Timothy Milton

1993-01-01

116

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

117

The Quantum Group Structure of 2D Gravity and Minimal Models II: The Genus-Zero Chiral Bootstrap

The F and B matrices associated with Virasoro null vectors are derived in closed form by making use of the operator-approach suggested by the Liouville theory, where the quantum-group symmetry is explicit. It is found that the entries of the fusing and braiding matrices are not simply equal to quantum-group symbols, but involve additional coupling constants whose derivation is one aim of the present work. Our explicit formulae are new, to our knowledge, in spite of the numerous studies of this problem. The relationship between the quantum-group-invariant (of IRF type) and quantum-group-covariant (of vertex type) chiral operator-algebras is fully clarified, and connected with the transition to the shadow world for quantum-group symbols. The corresponding 3-j-symbol dressing is shown to reduce to the simpler transformation of Babelon and one of the author (J.-L. G.) in a suitable infinite limit defined by analytic continuation. The above two types of operators are found to coincide when applied to states with Liouville momenta going to $\\infty$ in a suitable way. The introduction of quantum-group-covariant operators in the three dimensional picture gives a generalisation of the quantum-group version of discrete three-dimensional gravity that includes tetrahedra associated with 3-j symbols and universal R-matrix elements. Altogether the present work gives the concrete realization of Moore and Seiberg's scheme that describes the chiral operator-algebra of two-dimensional gravity and minimal models.

E. Cremmer; Jean-Loup Gervais; J. -F. Roussel

1993-02-09

118

NASA Technical Reports Server (NTRS)

In an experiment in space it was found that when a cubical frame was slowly withdrawn from a soap solution, the wire frame retained practically a full cube of liquid. Removed from the frame (by shaking), the faces of the cube became progressively more concave, until adjacent faces became tangential. In the present paper a mathematical model describing the shape a liquid takes due to its surface tension while suspended on a wire frame in zero-g is solved by use of Lagrange multipliers. It is shown how the configuration of soap films so bounded is dependent upon the volume of liquid trapped in the films. A special case of the solution is a soap film naturally formed on a cubical wire frame.

Darbro, W.

1978-01-01

119

Zero-gravity Mean Free Surface Curvature of a Confined Liquid in a Radially-Vaned Container

NASA Technical Reports Server (NTRS)

A variety of increasingly intricate container geometries are under consideration for the passive manipulation of liquids aboard spacecraft where the impact of gravity may be neglected. In this study we examine the mean curvature of a liquid volume confined within a radial array of disconnected vanes of infinite extent. This particular geometry possesses a number of desirable characteristics relevant to waste water treatment aboard spacecraft for life support. It is observed that under certain conditions the slender shape of the free surface approaches an asymptote, which can be predicted analytically using new hybrid boundary conditions proposed herein. This contribution represents possibly the final extension of what has been referred to as the method of de Lazzer et al. (1996). The method enables the integration of the Young-Laplace equation over a domain with its boundaries, including the wetted portion of the solid boundaries, symmetry planes, and circular arcs representing free surfaces at the center plane of the liquid body. Asymptotic solutions at several limits are obtained and the analysis is confirmed with numerical computations.

Chen, Yongkang; Callahan, Michael; Weislogel, Mark

2013-01-01

120

NASA Astrophysics Data System (ADS)

Experimental investigations of static liquid fillets formed between small gaps of a cylindrical surface and a flat surface are carried out. The minimum volume of liquid required to form a stable fillet and the maximum liquid content the fillet can hold before becoming unstable are studied. Fillet shapes are captured in photographs obtained by a high speed image system. Experiments were conducted using water, UPA and PF 5060 on two surfaces-stand-blasted titanium and polished copper for different surface inclinations. Experimental data are generalized using appropriate non-dimensional groups. Analytical model are developed to describe the fillet curvature. Fillet curvature data are compared against model predictions and are found to be in close agreement. Bubble point experiments were carried out to measure the capillary pressure difference across the liquid-gas interface in the channels of photo-chemically etched disk stacks. Experiments were conducted using titanium stacks of five different geometrical configurations. Both well wetting liquids (IPA and PF5060) and partially wetting liquid (water) were used during experiments. Test results are found to be in close agreement with analytical predictions. Experiments were carried out to measure the frictional pressure drop across the stack as a function of liquid flow rate using two different liquids (water and IPA) and five stacks of different geometrical configurations. A channel pressure drop model is developed by treating the flow within stack channels as fully developed laminar flow between parallel plates and solving the one-dimensional Navier Stokes equation. An alternate model is developed by treating the flow in channels as flow within porous media. Expressions are developed for effective porosity and permeability for the stacks and the pressure drop is related to these parameters. Pressure drop test results are found to be in close agreement with model predictions. As a specific application of this work, a surface tension propellant management device (PMD) that uses photo-chemically etched disk stacks as capillary elements is examined. These PMDs are used in gas pressurized liquid propellant tanks to supply gas-free propellant to rocket engines in near zero-gravity environment. The experimentally validated models are integrated to perform key analyses for predicting PMD performance in zero gravity.

Purohit, Ghanshyam Purshottamdas

121

NASA Technical Reports Server (NTRS)

It is proposed to use the Shuttle (OFT experiments) or eventually Spacelab to study, in the absence of gravity the low velocity accretion and the bulk properties of icy conglomerates simulating cometary material and their sedimentation and bulk properties in very small acceleration fields. Their behavior when exposed to the direct solar flux is also under consideration.

Delsemme, A. H.

1976-01-01

122

NASA Technical Reports Server (NTRS)

The cardiovascular responses of the Apollo crewmen associated with postflight evaluations indicate varying decrements of orthostatic tolerance. The postflight changes indicate a slightly diminished ability to the cardiovascular system to function effectively against gravity following exposure to weightlessness. The objective of the Skylab LBNP experiments (M092) was to provide information about the magnitude and time course of the cardiovascular changes associated with prolonged periods of exposure to weightlessness. This report details the equipment, signal processing and analysis of the leg volume data obtained from the M092 experiment of the Skylab 3 Mission.

Barnett, R. D.; Gowen, R. J.; Carroll, D. R.

1975-01-01

123

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

124

NASA Technical Reports Server (NTRS)

A two-dimensional numerical model was used to investigate the formation of marine advection fog. The model predicts the evolution of potential temperature, horizontal wind, water vapor content, and liquid water content in a vertical cross section of the atmosphere as determined by vertical turbulent transfer and horizontal advection, as well as radiative cooling and drop sedimentation. The model is designed to simulate the formation, development, or dissipation of advection fog in response to transfer of heat and moisture between the atmosphere and the surface as driven by advection over horizontal discontinuities in the surface temperature. Results from numerical simulations of advection fog formation are discussed with reference to observations of marine fog. A survey of candidate fog or cloud microphysics experiments which might be performed in the low gravity environment of a shuttle-type spacecraft in presented. Recommendations are given for relatively simple experiments which are relevent to fog modification problems.

Rogers, C. W.; Eadie, W. J.; Katz, U.; Kocmond, W. C.

1975-01-01

125

NSDL National Science Digital Library

The definition of the Zero Property of Multiplication will be presented and discussed, along with a review of other vocabulary necessary for this lesson (factors, products, "groups of", Commutative Property). The students will be taken through a guided lesson, showing them and explaining to them the process of multiplying by 0. This will be followed by independent practice for the students, including a peer review of said practice. The lesson will conclude with a whole class review of the Zero Property of Multiplication. At each step along the way, the teacher will be monitoring student progress and decide on a reteaching worksheet, continued independent practice, or an enrichment exercise.

Szewczyk, Joe

2012-06-26

126

It is fundamentally possible to travel with zero energy based on Newton Laws of Motion. According to the first law of motion, a body will continue to travel for infinite distance unless it is acted upon by another force. For a body in motion, the force which stops perpetual motion is friction. However, there are many circumstances that friction is zero, for example in space, where there is vacuum. On earth, gravity makes objects to be in constant contact with each other generating friction but technology exists to separate them in the air using powerful magnetic forces. At low speeds, the friction caused by air is minimal but we can create vacuum even on land for high speed travel. Another condition for travelling is for it to stop at its destination. On land, we can recover the kinetic energy back into electrical energy using brushless permanent magnet generators. These generators can also convert electric energy into kinetic energy in order to provide motion. This article reviews technologies that will allow us to travel with zero energy. It is easier to do it on land but in the air, it is not obvious.

Othman Ahmad; Aroland Kiring; Ali Chekima

2011-09-17

127

NASA Astrophysics Data System (ADS)

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 that has produced 27 Nobel Prizes. It will explore the ongoing interplay between science and technology through historical examples including refrigerators, ice machines, frozen foods, liquid oxygen and nitrogen as well as much colder fluids such as liquid hydrogen and liquid helium. A website has been established to promote the series: www.absolutezerocampaign.org. It contains information on the series, aimed primarily at students at the middle school level. There is a wealth of material here and we hope interested teachers will draw their student’s attention to this website and its substantial contents, which have been carefully vetted for accuracy.

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

2006-12-01

128

Dynamic Simulation for Zero-Gravity Activities

Working and training for space activities is difficult in terrestrial environments. We approach this crucial aspect of space human factors through 3D computer graphics dynamics simulation of crewmembers, their tasks, and physics-based movement modeling. Such virtual crewmembers may be used to design tasks and analyze their physical workload to maximize success and safety without expensive physical mockups or partially realistic

Norman I. Badler; Dimitris N. Metaxas; Gang Huang; Ambarish Goswami; Suejung Huh

129

We review recent progress in massive gravity. We start by showing how different theories of massive gravity emerge from a higher-dimensional theory of general relativity, leading to the Dvali-Gabadadze-Porrati model, cascading gravity and ghost-free massive gravity. We then explore their theoretical and phenomenological consistency, proving the absence of Boulware-Deser ghosts and reviewing the Vainshtein mechanism and the cosmological solutions in these models. Finally we present alternative and related models of massive gravity such as new massive gravity, Lorentz-violating massive gravity and non-local massive gravity.

Claudia de Rham

2014-01-16

130

Structural zeroes and zero-inflated models

Summary In psychosocial and behavioral studies count outcomes recording the frequencies of the occurrence of some health or behavior outcomes (such as the number of unprotected sexual behaviors during a period of time) often contain a preponderance of zeroes because of the presence of ‘structural zeroes’ that occur when some subjects are not at risk for the behavior of interest. Unlike random zeroes (responses that can be greater than zero, but are zero due to sampling variability), structural zeroes are usually very different, both statistically and clinically. False interpretations of results and study findings may result if differences in the two types of zeroes are ignored. However, in practice, the status of the structural zeroes is often not observed and this latent nature complicates the data analysis. In this article, we focus on one model, the zero-inflated Poisson (ZIP) regression model that is commonly used to address zero-inflated data. We first give a brief overview of the issues of structural zeroes and the ZIP model. We then given an illustration of ZIP with data from a study on HIV-risk sexual behaviors among adolescent girls. Sample codes in SAS and Stata are also included to help perform and explain ZIP analyses. PMID:25317011

HE, Hua; TANG, Wan; WANG, Wenjuan; CRITS-CHRISTOPH, Paul

2014-01-01

131

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

132

Atmospheric Science Data Center

article title: Gravity Waves Ripple over Marine Stratocumulus Clouds ... when a pebble is thrown into a still pond, such "gravity waves" sometimes appear when the relatively stable and stratified air masses ... Oct 29, 2003 Images: Gravity Waves location: Indian Ocean thumbnail: ...

2013-04-19

133

In the past, gravity methods have had limited application for monitoring aquifers, primarily due to the poor drift characteristics of relative gravimeters, which made long-term gravity studies of aquifers prohibitively expensive. Recent developments in portable, very accurate, absolute gravity instruments having essentially zero long-term drift have reawakened interest in using gravity methods for hydrologic monitoring. Such instruments have accuracies of

E. Keating; A. H. Cogbill; J. F. Ferguson

2003-01-01

134

NASA Technical Reports Server (NTRS)

Questions of the importance and feasibility of performing experiments on droplet burning at zero gravity in Spacelab were studied. Information on the physics and chemistry of droplet combustion, with attention directed specifically to the chemical kinetics, heat and mass transfer, and fluid mechanics of the phenomena involved, are presented. The work was divided into three phases, the justification, the feasibility, and the conceptual development of a preliminary design. Results from the experiments performed revealed a few new facts concerning droplet burning, notably burning rates in excess of theoretical prediction and a phenomenon of flash extinction, both likely traceable to accumulation of carbon produced by gas-phase pyrolysis in the fuel-rich zone enclosed by the reaction surface. These experiments also showed that they were primarily due to timing difficulties.

Williams, F. A.

1978-01-01

135

NSDL National Science Digital Library

We have heard of calling someone "a total zero" as an insult, but what does "zero" really mean? This thoughtful and informative Website from Dr. Hossein Arsham, Wright Distinguished Research Professor of Statistics and Management Science at the University of Baltimore, discusses the history and philosophy of zero. Items presented include arguments for and against dividing by zero, the ideas of zero as a void and as a number, zero in limits, square roots, and divergent series and floating points. The text is peppered with links to related mathematics, computer science, and history of mathematics sites. The Zero Saga is a good read for mathematicians, college and graduate level students in mathematics, or anyone interested in logic.

Arsham, Hossein.

136

NASA Technical Reports Server (NTRS)

The anomalous gravity field of Venus shows high correlation with surface features revealed by radar. We extract gravity models from the Doppler tracking data from the Pioneer Venus Orbiter (PVO) by means of a two-step process. In the first step, we solve the nonlinear spacecraft state estimation problem using a Kalman filter-smoother. The Kalman filter was evaluated through simulations. This evaluation and some unusual features of the filter are discussed. In the second step, we perform a geophysical inversion using a linear Bayesian estimator. To allow an unbiased comparison between gravity and topography, we use a simulation technique to smooth and distort the radar topographic data so as to yield maps having the same characteristics as our gravity maps. The maps presented cover 2/3 of the surface of Venus and display the strong topography-gravity correlation previously reported. The topography-gravity scatter plots show two distinct trends.

Reasenberg, Robert D.

1993-01-01

137

Cosmological Perturbations in Unimodular Gravity

We study cosmological perturbation theory within the framework of unimodular gravity. We show that the Lagrangian constraint on the determinant of the metric required by unimodular gravity leads to an extra constraint on the gauge freedom of the metric perturbations. Although the main equation of motion for the gravitational potential remains the same, the shift variable, which is gauge artifact in General Relativity, cannot be set to zero in unimodular gravity. This non-vanishing shift variable affects the propagation of photons throughout the cosmological evolution and therefore modifies the Sachs-Wolfe relation between the relativistic gravitational potential and the microwave temperature anisotropies. However, for adiabatic fluctuations the difference between the result in General Relativity and unimodular gravity is suppressed on large angular scales. Thus, no strong constraints on the theory can be derived.

Gao, Caixia; Cai, Yifu; Chen, Pisin

2014-01-01

138

Cosmological perturbations in unimodular gravity

NASA Astrophysics Data System (ADS)

We study cosmological perturbation theory within the framework of unimodular gravity. We show that the Lagrangian constraint on the determinant of the metric required by unimodular gravity leads to an extra constraint on the gauge freedom of the metric perturbations. Although the main equation of motion for the gravitational potential remains the same, the shift variable, which is gauge artifact in General Relativity, cannot be set to zero in unimodular gravity. This non-vanishing shift variable affects the propagation of photons throughout the cosmological evolution and therefore modifies the Sachs-Wolfe relation between the relativistic gravitational potential and the microwave temperature anisotropies. However, for adiabatic fluctuations the difference between the result in General Relativity and unimodular gravity is suppressed on large angular scales. Thus, no strong constraints on the theory can be derived.

Gao, Caixia; Brandenberger, Robert H.; Cai, Yifu; Chen, Pisin

2014-09-01

139

Cosmological Perturbations in Unimodular Gravity

We study cosmological perturbation theory within the framework of unimodular gravity. We show that the Lagrangian constraint on the determinant of the metric required by unimodular gravity leads to an extra constraint on the gauge freedom of the metric perturbations. Although the main equation of motion for the gravitational potential remains the same, the shift variable, which is gauge artifact in General Relativity, cannot be set to zero in unimodular gravity. This non-vanishing shift variable affects the propagation of photons throughout the cosmological evolution and therefore modifies the Sachs-Wolfe relation between the relativistic gravitational potential and the microwave temperature anisotropies. However, for adiabatic fluctuations the difference between the result in General Relativity and unimodular gravity is suppressed on large angular scales. Thus, no strong constraints on the theory can be derived.

Caixia Gao; Robert H. Brandenberger; Yifu Cai; Pisin Chen

2014-05-31

140

NSDL National Science Digital Library

This activity (located on page 3 of the PDF) is a full inquiry investigation into the forces of gravity and air pressure. Groups of learners will construct a simple gravity fountain by making a hole near the bottom of a 2-liter bottle, filling it with water, then as the bottle empties, collecting measurements of the water levels and length of the stream, to make a graph for analysis. Relates to linked video, DragonflyTV GPS: Gravity Fountain.

Twin Cities Public Television, Inc.

2007-01-01

141

NASA Astrophysics Data System (ADS)

Classical two-dimensional Liouville gravity is often considered in conformal gauge which has a residual left and right Virasoro symmetry algebra. We consider an alternate, chiral, gauge which has a residual right Virasoro Kac-Moody algebra, and no left Virasoro algebra. The Kac-Moody zero mode is the left-moving energy. Dirac brackets of the constrained Hamiltonian theory are derived, and the residual symmetries are shown to be generated by integrals of the conserved chiral currents. The central charge and Kac-Moody level are computed. The possible existence of a corresponding quantum theory is discussed.

Compère, Geoffrey; Song, Wei; Strominger, Andrew

2013-05-01

142

Zero separation bounds provide a lower bound on the absolute value of an arithmetic expression, unless the value is zero.\\u000a Such separation bounds are used for verified identification of zero in sign computations with real algebraic numbers, especially\\u000a with number types that record the computation history of a numerical value using expression dags. We summarize results on\\u000a separation bounds and

Stefan Schirra; Otto von Guericke

2009-01-01

143

Zero stiffness tensegrity structures

Tension members with a zero rest length allow the construction of tensegrity structures that are in equilibrium along a continuous path of configurations, and thus exhibit mechanism-like properties; equivalently, they have zero stiffness. The zero-stiffness modes are not internal mechanisms, as they involve first-order changes in member length, but are a direct result of the use of the special tension

M. Schenk; S. D. Guest; J. L. Herder

2007-01-01

144

ERIC Educational Resources Information Center

The concept of zero tolerance dates back to the mid-1990s when New Jersey was creating laws to address nuisance crimes in communities. The main goal of these neighborhood crime policies was to have zero tolerance for petty crime such as graffiti or littering so as to keep more serious crimes from occurring. Next came the war on drugs. In federal…

Moore, Brian N.

2010-01-01

145

Modifications of Einstein's theory of gravity which allow for nonvanishing graviton mass are discussed. The theoretical problems involved are subtle and challenging and call for consideration beyond perturbation theory.

A. Vainshtein

2006-01-01

146

A mechanical gravity brake that prevents hoisted loads within a shaft from free-falling when a loss of hoisting force occurs. A loss of hoist lifting force may occur in a number of situations, for example if a hoist cable were to break, the brakes were to fail on a winch, or the hoist mechanism itself were to fail. Under normal hoisting conditions, the gravity brake of the invention is subject to an upward lifting force from the hoist and a downward pulling force from a suspended load. If the lifting force should suddenly cease, the loss of differential forces on the gravity brake in free-fall is translated to extend a set of brakes against the walls of the shaft to stop the free fall descent of the gravity brake and attached load.

Lujan, Richard E. (Santa Fe, NM)

2001-01-01

147

NASA Astrophysics Data System (ADS)

Mariner 10 traveled to Mercury by using Venus' gravity to bend its course in toward the sun, a correction that would otherwise required vast amounts of rocket fuel. For the first time, an interplanetary spacecraft changed course not with rocket fuel but by using a planet's gravitational field. That maneuver stands, along with the development of the rocket engine, as one of the keys that opened the solar system for exploration. The Pioneer, Voyager, and Galileo missions all used gravity assist, and in fact would not have been possible otherwise. Gravity assist is the most efficient form of space propulsion known. Various aspects of the developmental history of the gravity assist technique and the dispute over who should receive credit for inventing the technique are discussed.

Reichhardt, Tony

1994-03-01

148

NSDL National Science Digital Library

The gravity calculator calculates the gravitational force between two masses. Also included is a visualization of the typical measurement of gravitational force (weight) in different environments (stationary and free fall).

Brendan Cannell, Ronnie Johnson, The Shodor Education Foundation, Inc.

149

Improved Airborne Gravity Results Using New Relative Gravity Sensor Technology

NASA Astrophysics Data System (ADS)

Airborne gravity data has contributed greatly to our knowledge of subsurface geophysics particularly in rugged and otherwise inaccessible areas such as Antarctica. Reliable high quality GPS data has renewed interest in improving the accuracy of airborne gravity systems and recent improvements in the electronic control of the sensor have increased the accuracy and ability of the classic Lacoste and Romberg zero length spring gravity meters to operate in turbulent air conditions. Lacoste and Romberg type gravity meters provide increased sensitivity over other relative gravity meters by utilizing a mass attached to a horizontal beam which is balanced by a ';zero length spring'. This type of dynamic gravity sensor is capable of measuring gravity changes on the order of 0.05 milliGals in laboratory conditions but more commonly 0.7 to 1 milliGal in survey use. The sensor may have errors induced by the electronics used to read the beam position as well as noise induced by unwanted accelerations, commonly turbulence, which moves the beam away from its ideal balance position otherwise known as the reading line. The sensor relies on a measuring screw controlled by a computer which attempts to bring the beam back to the reading line position. The beam is also heavily damped so that it does not react to most unwanted high frequency accelerations. However this heavily damped system is slow to react, particularly in turns where there are very high Eotvos effects. New sensor technology utilizes magnetic damping of the beam coupled with an active feedback system which acts to effectively keep the beam locked at the reading line position. The feedback system operates over the entire range of the system so there is now no requirement for a measuring screw. The feedback system operates at very high speed so that even large turbulent events have minimal impact on data quality and very little, if any, survey line data is lost because of large beam displacement errors. Airborne testing along with results from ground based van testing and laboratory results have shown that the new sensor provides more consistent gravity data, as measured by repeated line surveys, as well as preserving the inherent sensitivity of the Lacoste and Romberg zero length spring design. The sensor also provides reliability during survey operation as there is no mechanical counter screw. Results will be presented which show the advantages of the new sensor system over the current technology in both data quality and survey productivity. Applications include high resolution geoid mapping, crustal structure investigations and resource mapping of minerals, oil and gas.

Brady, N.

2013-12-01

150

Zero-G Condensing Heat Exchanger with Integral Disinfection

NASA Technical Reports Server (NTRS)

The system that operates in a zero gravity environment and has an integral ozone generating capability is disclosed. The system contributes to the control of metabolic water vapors in the air, and also provided disinfection of any resulting condensate within the system, as well as disinfection of the air stream that flows throughout the disclosed system.

Burke, Kenneth A. (Inventor)

2012-01-01

151

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

152

Measurement of the biological center of gravity using an X-ray

NASA Astrophysics Data System (ADS)

It is very important knowledge the center of gravity when observing the behavior of the animals in the low-gravity space. The center of gravity can be measured by using the center of gravity meter. However, the center of gravity meter that measures the use in zero-gravity space. Therefore, we have developed a method for determination of the center of gravity using an X-ray. Absorption of X-rays is related to the mass of the transmission path, so we determined the mass distribution by the X-ray image. It was possible to calculate the center of gravity by analyzing the image. It is not only static data but also to get the dynamic data using the movie. We can analyze the center of gravity changes in the animals in the low-gravity. It may be useful for the analysis of animal behavior to gravity changes.

Kawasaki, Tomomi; Hasegawa, Katsuya

153

Teacher in Space Christa McAuliffe on the KC-135 for zero-G training

NASA Technical Reports Server (NTRS)

Teacher in Space Christa McAuliffe on the KC-135 for zero-G training. McAuliffe, 51-L citizen observer/payload specialist, gets a preview of microgravity during a special flight aboard NASA's KC-135 'zero gravity' aircraft.

1986-01-01

154

Emergent gravity from a mass deformation in warped spacetime

We consider a deformation of five-dimensional warped gravity with bulk and boundary mass terms to quadratic order in the action. We show that massless zero modes occur for special choices of the masses. The tensor zero mode is a smooth deformation of the Randall-Sundrum graviton wave function and can be localized anywhere in the bulk. There is also a vector

Tony Gherghetta; Marco Peloso; Erich Poppitz

2005-01-01

155

ERIC Educational Resources Information Center

This article describes one classroom activity in which the author simulates the Newtonian gravity, and employs the Euclidean Geometry with the use of new technologies (NT). The prerequisites for this activity were some knowledge of the formulae for a particle free fall in Physics and most certainly, a good understanding of the notion of similarity…

Pipinos, Savas

2010-01-01

156

Spherically symmetric spacetimes in massive gravity

We explore spherically symmetric stationary solutions, generated by ``stars'' with regular interiors, in purely massive gravity. We reexamine the claim that the resummation of nonlinear effects can cure, in a domain near the source, the discontinuity exhibited by the linearized theory as the mass m of the graviton tends to zero. First, we find analytical difficulties with this claim, which

Thibault Damour; Ian I. Kogan; Antonios Papazoglou

2003-01-01

157

In topological 1D gravity, the genus zero one-point function combined with the gradient of the action function leads to a spectral curve and its special deformation. After quantization, the partition function is identified as an element in the bosonic Fock space uniquely specified by the Virasoro constraints.

Jian Zhou

2014-12-04

158

Water Immersion Reduced-Gravity Simulation

A water immersion technique for simulating zero- and partial-gravity conditions has been developed and employed to examine several extravehicular task areas in space. The technique allows the pressure-suited subject to move in six degrees of freedom unencumbered by connecting supports and simulates his biomechanical performance in weightless space. The technique is useful in examining the astronaut's capability to execute extravehicular

Otto F. Trout; William J. Bruchey

1969-01-01

159

NASA Astrophysics Data System (ADS)

Many cuts used in practice to solve mixed integer programs are derived from a basis of the linear relaxation. Every such cut is of the form ? T x ? 1, where x ? 0 is the vector of non-basic variables and ? ? 0. For a point bar{x} of the linear relaxation, we call ? T x ? 1 a zero-coefficient cut wrt. bar{x} if ?^T bar{x} = 0, since this implies ? j = 0 when bar{x}_j > 0. We consider the following problem: Given a point bar{x} of the linear relaxation, find a basis, and a zero-coefficient cut wrt. bar{x} derived from this basis, or provide a certificate that shows no such cut exists. We show that this problem can be solved in polynomial time. We also test the performance of zero-coefficient cuts on a number of test problems. For several instances zero-coefficient cuts provide a substantial strengthening of the linear relaxation.

Andersen, Kent; Weismantel, Robert

160

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

161

ERIC Educational Resources Information Center

The walnut sized brain of the African grey parrot may actually be capable of comprehending abstract mathematical concepts. The bird seems to understand a numerical concept akin to zero--an abstract notion that humans don't typically understand until they are three or four years old. Alex, the 28-year-old parrot who lives in a Brandeis University…

Journal of College Science Teaching, 2005

2005-01-01

162

NSDL National Science Digital Library

This lesson involves students using positive and negative numbers to represent quantities in real-world contexts, explaining the meaning of zero in each situation. Students will understand the positive and negative numbers are used together to describe quantities having opposite values.

Brown, Kathleen

2012-09-16

163

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.

164

A Zero-Gravity Cup for Drinking Beverages in Microgravity

NASA Technical Reports Server (NTRS)

To date, the method for astronauts to drink liquids in microgravity or weightless environments is to suck the liquid from a bag or pouch through a straw. A new beverage cup works in microgravity and allows astronauts to drink liquids from a cup in a manner consistent with that on Earth. The cup is capable of holding beverages with an angled channel running along the wall from the bottom to the lip. In microgravity, a beverage is placed into the cup using the galley dispenser. The angled channel acts as an open passage that contains only two sides where capillary forces move the liquid along the channel until it reaches the top lip where the forces reach an equilibrium and the flow stops. When one sips the liquid at the lip of the channel, the capillary force equilibrium is upset and more liquid flows to the lip from the reservoir at the bottom to re-establish the equilibrium. This sipping process can continue until the total liquid contents of the cup is consumed, leaving only a few residual drops about the same quantity as in a ceramic cup when it is drunk dry on Earth.

Pettit, Donald R.; Weislogel, Mark; Concus, Paul; Finn, Robert

2011-01-01

165

Intravenous fluid flow meter concept for zero gravity environment

NASA Technical Reports Server (NTRS)

Measuring chamber, included in infusion-set tubing, and peristaltic flow meter concept can be incorporated into flow meter that measures fluid flow rates between 100 and 600 cu cm per hour and at the same time maintains sterilization.

Miller, C. G.

1972-01-01

166

Venipuncture and intravenous infusion access during zero-gravity flight

NASA Technical Reports Server (NTRS)

The purpose of this experiment is to establish the difficulty associated with securing an intravenous (IV) catheter in place in microgravity flight and the techniques applicable in training the Crew Medical Officer (CMO) for Space Station Freedom, as well as aiding in the selection of appropriate hardware and supplies for the Health Maintenance Facility (HMF). The objectives are the following: (1) to determine the difficulties associated with venipuncture in a microgravity environment; (2) to evaluate the various methods of securing an IV catheter and attached tubing for infusion with regard to the unique environment; (3) to evaluate the various materials available for securing an intravenous catheter in place; and (4) to evaluate the fluid therapy administration system when functioning in a complete system. The inflight test procedures and other aspects of the KC-135 parabolic flight test to simulate microgravity are presented.

Krupa, Debra T.; Gosbee, John; Billica, Roger; Bechtle, Perry; Creager, Gerald J.; Boyce, Joey B.

1991-01-01

167

Fluid mass sensor for a zero gravity environment

NASA Technical Reports Server (NTRS)

A sensor for measuring the mass of fluids, is described which includes a housing having an inlet and outlet for receiving and dumping the fluid, a rotary impeller within the housing for imparting centrifugal motion to the fluid and a pressure sensitive transducer attached to the housing to sense the rotating fluid pressure. The fluid may be drawn into the housing by entrainment within a gas stream. The resulting mixture is then separated into two phases: gas and liquid. The gas is removed from the housing and the pressure of the liquid, under centrifugal motion, is sensed and correlated with the mass of the fluid.

Fogal, G. L. (inventor)

1976-01-01

168

Dental equipment test during zero-gravity flight

NASA Technical Reports Server (NTRS)

The overall objectives of this program were to establish performance criteria and develop prototype equipment for use in the Health Maintenance Facility (HMF) in meeting the needs of dental emergencies during space missions. The primary efforts during this flight test were to test patient-operator relationships, patent (manikin) restraint and positioning, task lighting systems, use and operation of dental rotary instruments, suction and particle containment system, dental hand instrument delivery and control procedures, and the use of dental treatment materials. The initial efforts during the flight focused on verification of the efficiency of the particle containment system. An absorptive barrier was also tested in lieu of the suction collector. To test the instrument delivery system, teeth in the manikin were prepared with the dental drill to receive restorations, some with temporary filling materials and another with definitive filling material (composite resin). The best particle containment came from the combination use of the laminar-air/suction collector in concert with immediate area suction from a surgical high-volume suction tip. Lighting in the treatment area was provided by a flexible fiberoptic probe. This system is quite effective for small areas, but for general tasks ambient illumination is required. The instrument containment system (elastic cord network) was extremely effective and easy to use. The most serious problem with instrument delivey and actual treatment was lack of time during the microgravity sequences. The restorative materials handled and finished well.

Young, John; Gosbee, John; Billica, Roger

1991-01-01

169

The spinning artificial gravity environment: A design project

NASA Technical Reports Server (NTRS)

The SAGE, or Spinning Artificial Gravity Environment, design was carried out to develop an artificial gravity space station which could be used as a platform for the performance of medical research to determine the benefits of various, fractional gravity levels for astronauts normally subject to zero gravity. Desirable both for its medical research mission and a mission for the study of closed loop life-support and other factors in prolonged space flight, SAGE was designed as a low Earth orbiting, solar powered, manned space station.

Pignataro, Robert; Crymes, Jeff; Marzec, Tom; Seibert, Joe; Walker, Gary

1987-01-01

170

constant amount of material deformation within the zero stiffness mode. A classic example is the Rolamite linear bearing [43]; see Figure 6. A flat blade spring is wrapped around two cylinders; for any displaced configuration of the two rollers... to a change in temperature it will first develop a spherical curvature due to the different thermal expansion coefficients of the two layers, before bifurcating into a cylindrical configuration [28]. As the orientation of the cylindrical axis is ar...

Schenk, Mark; Guest, Simon D.

2013-11-17

171

NASA Technical Reports Server (NTRS)

Flammability limits in a zero gravity environment were defined. Key aspects of a possible spacelab experiment were investigated analytically, experimentally on the bench, and in drop tower facilities. A conceptual design for a spacelab experiment was developed.

Strehlow, R. A.; Reuss, D. L.

1980-01-01

172

NASA Astrophysics Data System (ADS)

One-dimensional topological superconductors are known to host Majorana zero modes at domain walls terminating the topological phase. Their non-Abelian nature allows for processing quantum information by braiding operations that are insensitive to local perturbations, making Majorana zero modes a promising platform for topological quantum computation. Motivated by the ultimate goal of executing quantum-information processing on a finite time scale, we study domain walls moving at a constant velocity. We exploit an effective Lorentz invariance of the Hamiltonian to obtain an exact solution of the associated quasiparticle spectrum and wave functions for arbitrary velocities. Essential features of the solution have a natural interpretation in terms of the familiar relativistic effects of Lorentz contraction and time dilation. We find that the Majorana zero modes remain stable as long as the domain wall moves at subluminal velocities with respect to the effective speed of light of the system. However, the Majorana bound state dissolves into a continuous quasiparticle spectrum after the domain wall propagates at luminal or even superluminal velocities. This relativistic catastrophe implies that there is an upper limit for possible braiding frequencies even in a perfectly clean system with an arbitrarily large topological gap. We also exploit our exact solution to consider domain walls moving past static impurities present in the system.

Karzig, Torsten; Refael, Gil; von Oppen, Felix

2013-10-01

173

Estimation of Systematic Errors in the Canadian Terrestrial Gravity Data From GRACE Gravity Results

NASA Astrophysics Data System (ADS)

Systematic errors in terrestrial gravity data arise from datum errors at the control stations and from elevation and instrumental errors at spot measurements. It is extremely difficult, if at all possible, to estimate and correct these errors through the analysis of the historical records of the gravity projects. The GRACE gravity mission is currently mapping the Earth's gravity field with a homogeneous accuracy better than 1 mGal in gravity, corresponding to a few centimeters in geoid height, for wavelength greater than 300 km. It provides an accurate reference for determining the long-wavelength systematic errors in the terrestrial gravity data. However, the challenge is to remove the short-wavelength components from the terrestrial data in order to eliminate the aliasing errors when estimating systematic errors. In other words, we need an effective low-pass averaging/filtering technique. Several former discussions contribute important insights on characteristics of commonly used methods: Pellinen 1966; Rapp 1977; Gaposchkin 1980; Colombo 1981; Jekeli 1981. In this study, we investigate methods of determining systematic errors in terrestrial gravity through a synthetic gravity field, and apply them to the actual terrestrial gravity data in Canada. EGM96, up to degree and order 360, is used for the synthetic gravity field. First, we test four methods (blockwise, Pellinen's, Gaussian and ideal averaging) to perform low-pass filtering of the EGM96 high frequency gravity field. Second, we derive harmonic gravity models to degree and order 70 from the filtered synthetic field. Third, the new harmonic models are compared to EGM96 (degree and order 70). The best filtering method is expected to give residuals converging towards zero. For the actual gravity field, a harmonic gravity model (degree and order 70) is derived from the filtered Canadian terrestrial gravity data, which are expanded to the entire Earth surface by a GRACE gravity model. This harmonic model is compared to the GRACE gravity model (for the same degree and order) to estimate the systematic errors. Finally, the estimated biases are applied to the terrestrial gravity data for determining a geoid model for Canada, which is validated against GPS/leveling data.

Huang, J.; Véronneau, M.; Mainville, A.

2004-05-01

174

NSDL National Science Digital Library

In this online game, learners attempt to send a rocket ship to various targets. Learners can adjust the angle and thrust of the rocket before it is launched. The game simulates the pull of gravity on the rocket from the Earth and Moon. When learners set up a free account at Kinetic City, they can answer bonus questions at the end of the activity as a quick assessment. As a larger assessment, learners can complete the Smart Attack game after they've completed several activities.

Science, American A.

2009-01-01

175

NSDL National Science Digital Library

On a hot day, some might wish they could get the temperature down a bit. They might not wish it to be as cold as, say absolute zero, but there are many scientists who are interested in doing just that. For those who are curious, absolute zero clocks in at around minus 460 degrees Fahrenheit. This engaging website is meant to serve as a complementary resource to the two-part series that recently aired on NOVA on this engaging topic. Visitors can start by watching a short preview of the program, and then continuing on to look over some of the special interactive features on the site. All told, there are ten different features, including "A Sense of Scale", "How Low Can You Go?", and "Milestones in Cold Research". The "Milestones in Cold Research" is a great place to start, as it's an interactive timeline that chronicles the "netherworld of extraordinarily low temperatures" as investigated by everyone from Galileo to current researchers. Of course, there are also more playful features here, such as "The Ice Trade", which asks users to dispatch ships loaded with natural ice to Florida, Brazil, and India.

176

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

177

Small amplitude forced fluid dynamics from gravity at T=0

NASA Astrophysics Data System (ADS)

The usual derivative expansion of gravity duals of charged fluid dynamics is known to break down in the zero temperature limit. In this case, fluid-gravity duality is not understood precisely. We explore this problem for a zero temperature charged fluid driven by a low frequency, small amplitude and spatially homogeneous external force. In the gravity dual, this corresponds to a time dependent boundary value of the dilaton. We calculate the bulk solution for the dilaton and the leading back reaction to the metric and the gauge fields using the modified low frequency expansion of Faulkner et al. (

Oh, Jae-Hyuk

2011-12-01

178

Soldering Tested in Reduced Gravity

NASA Technical Reports Server (NTRS)

Whether used occasionally for contingency repair or routinely in nominal repair operations, soldering will become increasingly important to the success of future long-duration human space missions. As a result, it will be critical to have a thorough understanding of the service characteristics of solder joints produced in reduced-gravity environments. The National Center for Space Exploration Research (via the Research for Design program), the NASA Glenn Research Center, and the NASA Johnson Space Center are conducting an experimental program to explore the influence of reduced gravity environments on the soldering process. Solder joint characteristics that are being considered include solder fillet geometry, porosity, and microstructural features. Both through-hole (see the drawing and image on the preceding figure) and surface-mounted devices are being investigated. This effort (the low-gravity portion being conducted on NASA s KC-135 research aircraft) uses the soldering hardware currently available on the International Space Station. The experiment involves manual soldering by a contingent of test operators, including both highly skilled technicians and less skilled individuals to provide a skill mix that might be encountered in space mission crews. The experiment uses both flux-cored solder and solid-core solder with an externally applied flux. Other experimental parameters include the type of flux, gravitational level (nominally zero,

Struk, Peter M.; Pettegrew, Richard D.; Watson, J. Kevin; Down, Robert S.; Haylett, Daniel R.

2005-01-01

179

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

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, E-mail: maziashvili@gmail.com [Particle Physics and Cosmology Group, Ilia State University, 3/5 Cholokashvili Ave., Tbilisi 0162, Georgia (United States)

2013-03-01

180

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

Mohsen Alishahiha; Ali Naseh

2010-01-01

181

Critical regimes of internal gravity wave generation

The problem of constructing an asymptotic representation of the solution of the internal gravity wave field exited by a source moving at a velocity close to the maximum group velocity of the individual wave mode is considered. For the critical regimes of individual mode generation the asymptotic representation of the solution obtained is expressed in terms of a zero-order Macdonald function. The results of numerical calculations based on the exact and asymptotic formulas are given.

Vitaly V. Bulatov; Yuriy V. Vladimirov; Vasily A. Vakorin

2005-11-27

182

Observational Bounds on Modified Gravity Models

Modified gravity provides a possible explanation for the currently observed cosmic accelaration. In this paper, we study general classes of modified gravity models. The Einstein-Hilbert action is modified by using general functions of the Ricci and the Gauss-Bonnet scalars, both in the metric and in the Palatini formalisms. We do not use an explicit form for the functions, but a general form with a valid Taylor expansion up to second order about redshift zero in the Riemann-scalars. The coefficients of this expansion are then reconstructed via the cosmic expansion history measured using current cosmological observations. These are the quantities of interest for theoretical considerations relating to ghosts and instabilities. We find that current data provide interesting constraints on the coefficients. The next-generation dark energy surveys should shrink the allowed parameter space for modifed gravity models quite dramatically.

Antonio De Felice; Pia Mukherjee; Yun Wang

2007-06-08

183

Multiphase Flow: The Gravity of the Situation

NASA Technical Reports Server (NTRS)

A brief survey is presented of flow patterns in two-phase, gas-liquid flows at normal and microgravity, the differences between them being explored. It seems that the flow patterns in zero gravity are in general much simpler than those in normal gravity with only three main regimes (namely bubbly, slug and annular flows) being observed. Each of these three regimes is then reviewed, with particular reference to identification of areas of study where investigation of flows at microgravity might not only be interesting in themselves, but also throw light on mechanisms at normal earth gravity. In bubbly flow, the main area of interest seems to be that of bubble coalescence. In slug flow, the extension of simple displacement experiments to the zero gravity case would appear to be a useful option, supplemented by computational fluid dynamics (CFD) studies. For annular flow, the most interesting area appears to be the study of the mechanisms of disturbance waves; it should be possible to extend the region of investigation of the onset and behavior of these waves to much low gas velocities where measurements are clearly much easier.

Hewitt, Geoffrey F.

1996-01-01

184

Analytical Study of Gravity Effects on Laminar Diffusion Flames

NASA Technical Reports Server (NTRS)

A mathematical model is presented for the description of axisymmetric laminar-jet diffusion flames. The analysis includes the effects of inertia, viscosity, diffusion, gravity and combustion. These mechanisms are coupled in a boundary layer type formulation and solutions are obtained by an explicit finite difference technique. A dimensional analysis shows that the maximum flame width radius, velocity and thermodynamic state characterize the flame structure. Comparisons with experimental data showed excellent agreement for normal gravity flames and fair agreement for steady state low Reynolds number zero gravity flames. Kinetics effects and radiation are shown to be the primary mechanisms responsible for this discrepancy. Additional factors are discussed including elipticity and transient effects.

Edelman, R. B.; Fortune, O.; Weilerstein, G.

1972-01-01

185

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

186

Scaling Theorems for Zero Crossings

We characterize some properties of the zero crossings of the Laplacian of signals¿in particular images¿filtered with linear filters, as a function of the scale of the filter (extending recent work by Witkin [16]). We prove that in any dimension the only filter that does not create generic zero crossings as the scale increases is the Gaussian. This result can be

Alan L. Yuille; Tomaso A. Poggio

1986-01-01

187

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

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

188

NASA Technical Reports Server (NTRS)

The behavior of liquids in zero gravity environments is discussed with emphasis on foams, wetting, and wicks. A multipurpose electric furnace (MA-010) for the high temperature processing of metals and salts in zero-g is described. Experiments discussed include: monolectic and synthetic alloys (MA-041); multiple material melting point (MA-150); zero-g processing of metals (MA-070); surface tension induced convection (MA-041); halide eutectic growth; interface markings in crystals (MA-060); crystal growth from the vapor phase (MA-085); and photography of crystal growth (MA-028).

Page, L. W.; From, T. P.

1977-01-01

189

Zero/zero rotorcraft certification issues. Volume 1: Executive summary

NASA Technical Reports Server (NTRS)

This report analyzes the Zero/Zero Rotorcraft Certification Issues from the perspectives of manufacturers, operators, researchers and the FAA. The basic premise behind this analysis is the zero/zero, or at least extremely low visibility, rotorcraft operations are feasible today from both a technological and an operational standpoint. The questions and issues that need to be resolved are: What certification requirements do we need to ensure safety. Can we develop procedures which capitalize on the performance and maneuvering capabilities unique to rotorcraft. Will exptremely low visibility operations be economically feasible. This is Volume 1 of three. It provides an overview of the Certification Issues Forum held in Phoenix, Arizona in August of 1987. It presents a consensus of 48 experts from government, manufacturer, and research communities on 50 specific Certification Issues. The topics of Operational Requirements, Procedures, Airworthiness, and Engineering Capabilities are discussed.

Adams, Richard J.

1988-01-01

190

NASA Technical Reports Server (NTRS)

This chapter discusses potential technologies for achieving artificial gravity in a space vehicle. We begin with a series of definitions and a general description of the rotational dynamics behind the forces ultimately exerted on the human body during centrifugation, such as gravity level, gravity gradient, and Coriolis force. Human factors considerations and comfort limits associated with a rotating environment are then discussed. Finally, engineering options for designing space vehicles with artificial gravity are presented.

Bukley, Angie; Paloski, William; Clement, Gilles

2006-01-01

191

Measurement of absolute gravity acceleration in Firenze

NASA Astrophysics Data System (ADS)

This paper reports the results from the accurate measurement of the acceleration of gravity g taken at two separate premises in the Polo Scientifico of the University of Firenze (Italy). In these laboratories, two separate experiments aiming at measuring the Newtonian constant and testing the Newtonian law at short distances are in progress. Both experiments require an independent knowledge on the local value of g. The only available datum, pertaining to the italian zero-order gravity network, was taken more than 20 years ago at a distance of more than 60 km from the study site. Gravity measurements were conducted using an FG5 absolute gravimeter, and accompanied by seismic recordings for evaluating the noise condition at the site. The absolute accelerations of gravity at the two laboratories are (980 492 160.6 ± 4.0) ?Gal and (980 492 048.3 ± 3.0) ?Gal for the European Laboratory for Non-Linear Spectroscopy (LENS) and Dipartimento di Fisica e Astronomia, respectively. Other than for the two referenced experiments, the data here presented will serve as a benchmark for any future study requiring an accurate knowledge of the absolute value of the acceleration of gravity in the study region.

de Angelis, M.; Greco, F.; Pistorio, A.; Poli, N.; Prevedelli, M.; Saccorotti, G.; Sorrentino, F.; Tino, G. M.

2011-01-01

192

This short report explains the parameters, and their basis, of the D-Zero calorimeter multiplan spread sheet Macintosh Multiplan worksheets have been found to be a valuable asset to the D-Zero design effort. The spread sheet contains parameters (constants) and results that come from the parameters. The full effect of changes in D-Zero calorimeter parameters can be calculated quite easily with Multiplan. When a change in a parameter is made, any results that pertain to that parameter automatically change also. This report will explain how some of the unobvious results were obtained.

Wintercorn, S.J.; /Fermilab

1987-06-15

193

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

194

Canadian low-gravity research using parabolic aircraft

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

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

1992-01-01

195

Zero Waste, Renewable Energy & Environmental

Zero Waste, Renewable Energy & Environmental Stewardship - Connecting loose ends: Thermal RecyclingÂ® Philipp Schmidt-Pathmann, President Waste Recovery Seattle International, LLC. #12;Assisting Agencies #12;Headlines #12;Outline Â· An Environmental Perspective Â· Waste Management Directive in Europe

Columbia University

196

NSDL National Science Digital Library

The EJS Least Action (Gravity/Free) model illustrates the principle of least action for the one dimensional motion of a free particle or a particle subject to a constant gravitational force. The simulation displays height versus time, with the path broken into equally spaced time intervals. The user can set the initial and final heights, as well as the number of time intervals to be used. The user can then adjust the intermediate heights in order to minimize the action along the path, or else allow the computer to implement an algorithm for finding the path of least action. Both the action of the current path and the least action so far observed with the current parameters are displayed. The simulation can also display average values for velocity, change in velocity, acceleration, kinetic energy, potential energy, the Lagrangian function, and total mechanical energy for each segment of the path. This helps to illustrate that the path of least action is also a path of constant acceleration (zero if there is no gravity) and constant total energy. The algorithm minimizes the action by examining three consecutive points on the path. The outer two points are held fixed and basic calculus can be used to determine the value for the middle height that minimizes the action for this segment of the path. This procedure is repeated for each segment of three points on the path, moving left to right. If this entire process is repeated over and over the path will gradually approach the path of global least action. This approach, and the entire EJS Least Action (Gravity/Free) model, was inspired by the Principle of Least Action Interactive page by Edwin Taylor and Slavomir Tuleja.

Timberlake, Todd

2012-09-05

197

Counterterms in Lovelock Gravity

In this paper, we introduce the counterterms that remove the non-logarithmic divergences of the action in third order Lovelock gravity. We do this by defining the cosmological constant in such a way that the asymptotic form of the metric have the same form in Lovelock and Einstein gravities. Thus, we employ the counterterms of Einstein gravity and show that the power law divergences in the action of Lovelock gravity can be removed by suitable choice of coefficients. We find that the dependence of these coefficients on the dimension in Lovelock gravity is the same as in Einstein gravity. We also introduce the finite energy-momentum tensor and employ these counterterms to calculate the finite action and mass of the black hole solutions of third order Lovelock gravity. We calculate the thermodynamic quantities and show that the entropy calculated through the use of Gibbs-Duhem relation is consistent with the obtained entropy by Wald's formula. We, also, find that in contrast to Einstein gravity in which there exists no uncharged extreme black hole, third order Lovelock gravity can have these kind of black holes. Finally investigating the stability of charged black holes of Lovelock gravity in canonical ensemble, we find that the small black holes show a phase transition between very small and small black holes, while the large ones are stable.

M. R. Mehdizadeh; M. H. Dehghani; M. Kord Zangeneh

2015-01-21

198

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

Feasibility of Achieving a Zero-Net-Energy, Zero-Net-Cost Homes 1 fey, 1David Feasibility of Achieving a ZeroNetEnergy, ZeroNetCost Homes 1 #12;2 ACKNOWLEDGEMENTS The material reduction, by requiring design entries to meet "zero net energy" and "zero net cost" criteria

199

Einstein Gravity, Massive Gravity, Multi-Gravity and Nonlinear Realizations

The existence of a ghost free theory of massive gravity begs for an interpretation as a Higgs phase of General Relativity. We revisit the study of massive gravity as a Higgs phase. Absent a compelling microphysical model of spontaneous symmetry breaking in gravity, we approach this problem from the viewpoint of nonlinear realizations. We employ the coset construction to search for the most restrictive symmetry breaking pattern whose low energy theory will both admit the de Rham--Gabadadze--Tolley (dRGT) potentials and nonlinearly realize every symmetry of General Relativity, thereby providing a new perspective from which to build theories of massive gravity. In addition to the known ghost-free terms, we find a novel parity violating interaction which preserves the constraint structure of the theory, but which vanishes on the normal branch of the theory. Finally, the procedure is extended to the cases of bi-gravity and multi-vielbein theories. Analogous parity violating interactions exist here, too, and may be...

Goon, Garrett; Joyce, Austin; Trodden, Mark

2014-01-01

200

Net zero building energy conservation

NASA Astrophysics Data System (ADS)

This research deals with energy studies performed as part of a net-zero energy study for buildings. Measured data of actual energy utilization by a building for a continuous period of 33 months was collected and studied. The peak design day on which the building consumes maximum energy was found. The averages of the energy consumption for the peak month were determined. The DOE EnergyPlus software was used to simulate the energy requirements for the building and also obtain peak energy requirements for the peak month. Alternative energy sources such as ground source heat pump, solar photovoltaic (PV) panels and day-lighting modifications were applied to redesign the energy consumption for the building towards meeting net-zero energy requirements. The present energy use by the building, DOE Energy software simulations for the building as well as the net-zero model for the building were studied. The extents of the contributions of the individual energy harvesting measures were studied. For meeting Net Zero Energy requirement, it was found that the total energy load for the building can be distributed between alternative energy methods as 5.4% to daylighting modifications, 58% to geothermal and 36.6% to solar photovoltaic panels for electricity supply and thermal energy. Thus the directions to proceed towards achieving complete net-zero energy status were identified.

Kadam, Rohit

201

Surface tension and bubble shapes in a partially filled rotating cylinder under low gravity

NASA Technical Reports Server (NTRS)

A computer algorithm is developed to simulate the profile of a free liquid surface for a cylindrical container partially filled with a Newtonian fluid of constant density, rotating about its axis of symmetry. The equilibrium shape of the free surface is governed by a balance of capillary, centrifugal, and gravity forces. The results can be used to determine the profile of a bubble at various rotating speeds under the gravity environments from low gravity, microgravity to zero-gravity. The present paper discusses the further extension of the study of the determination of bubble shape in a higher rotating speed container developed by Hung and Leslie.

Hung, R. J.; Tsao, Y. D.; Leslie, Fred W.; Hong, B. B.

1988-01-01

202

NSDL National Science Digital Library

The D-Zero Experiment is a worldwide collaboration of physics researchers centrally located at the Fermilab National Accelerator Laboratory's Tevratron Collider. The experiment focuses on the fundamental nature of matter, with particular attention paid to "precise studies of interactions of protons and antiprotons at the highest available energies." Researchers will be especially interested in the results section within which they can access summaries of new results, D-Zero results presented at 1999 summer conferences, Run II Fermilab Supersymmetry/ Higgs Workshop documents and summaries, and documents of work conducted by various Physics Groups working in specialized areas. The site also offers a technical section featuring information on experiment upgrades and computing, as well as contact information for experiment collaborators. Note, some areas are restricted to D-Zero collaboration members.

203

Generalized Scale Invariant Gravity

We generalize the scale invariant gravity by allowing a negative kinetic energy term for the classical scalar field. This gives birth to a new scalar-tensor theory of gravity, in which the scalar field is in fact an auxiliary field. For a pure gravity theory without matter, the scale symmetric phase represents an equivalent class of gravity theories, which the Einstein gravity plus a cosmological constant belongs to under a special gauge choice. The one-loop quantum correction of the theory is calculated by using the Vilkovisky-DeWitt's method. We find that the scale symmetry is broken dynamically, and that the Einstein gravity is the ground state of the broken phase. We also briefly discuss the consequent cosmological implications. It is shown that the time-delay experiment restricts the present universe to be very close to the ground state.

Shih-Yuin Lin; Kin-Wang Ng

1997-08-20

204

Shear waves in inhomogeneous, compressible fluids in a gravity field.

While elastic solids support compressional and shear waves, waves in ideal compressible fluids are usually thought of as compressional waves. Here, a class of acoustic-gravity waves is studied in which the dilatation is identically zero, and the pressure and density remain constant in each fluid particle. These shear waves are described by an exact analytic solution of linearized hydrodynamics equations in inhomogeneous, quiescent, inviscid, compressible fluids with piecewise continuous parameters in a uniform gravity field. It is demonstrated that the shear acoustic-gravity waves also can be supported by moving fluids as well as quiescent, viscous fluids with and without thermal conductivity. Excitation of a shear-wave normal mode by a point source and the normal mode distortion in realistic environmental models are considered. The shear acoustic-gravity waves are likely to play a significant role in coupling wave processes in the ocean and atmosphere. PMID:24606251

Godin, Oleg A

2014-03-01

205

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.

206

NASA Astrophysics Data System (ADS)

We point out a misprint in the differential cross section for ?e-->W? reported recently by Ginzburg, Kotkin, Panfil, and Serbo. The corrected expression has a zero in accordance with the general formula derived earlier by Mikaelian. We plot the angular distributions for different values of ?, the anomalousmagnetic-moment parameter of the W. We suggest that the reaction ?e-->W? is an attractive way to measure ? because the distributions are sensitive to it and the zero exists only if ?=+1 as in the standard electroweak theory.

Mikaelian, Karnig O.

1984-09-01

207

Large-distance modification of gravity may be the best mechanism for solving the cosmological constant problem. A simple model of the large-distance modification---four-dimensional (4D) gravity with a hard mass term---is problematic from the theoretical standpoint. Here we discuss a different model, brane-induced gravity, that effectively introduces a soft graviton mass. We study the issues of unitarity, analyticity, and causality in this

G. Gabadadze; M. Shifman

2004-01-01

208

Aspects of multimetric gravity

NASA Astrophysics Data System (ADS)

We present a class of gravity theories containing N >= 2 metric tensors and a corresponding number of standard model copies. In the Newtonian limit gravity is attractive within each standard model copy, but different standard model copies mutually repel each other. We discuss several aspects of these multimetric gravity theories, including cosmology, structure formation, the post-Newtonian limit and gravitational waves. The most interesting feature we find is an accelerating expansion of the universe that naturally becomes small at late times.

Hohmann, M.

2014-09-01

209

Modified entropic gravity revisited

NASA Astrophysics Data System (ADS)

Inspired by Verlinde's idea, some modified versions of entropic gravity have been suggested. Extending them in a unified formalism, herein we derive the generalized gravitational equations accordingly. From gravitational equations, the energy-momentum conservation law and cosmological equations are investigated. The covariant conservation law of energy-momentum tensor severely constrains viable modifications of entropic gravity. A discrepancy arises when two independent methods are applied to the homogeneous isotropic universe, posing a serious challenge to modified models of entropic gravity.

Wang, Tower

2014-09-01

210

NASA Astrophysics Data System (ADS)

It is well known that one could determine the kinematics of gravity by using the Principle of Equivalence and local inertial frames. I describe how the dynamics of gravity can be similarly understood by suitable thought experiments in a local Rindler frame. This approach puts in proper context several unexplained features of gravity and describes the dynamics of spacetime in a broader setting than in Einstein’s theory.

Padmanabhan, T.

2008-10-01

211

NSDL National Science Digital Library

In this activity about center of gravity (page 23 of PDF), learners investigate how the body adjusts to the force of gravity to remain balanced. In part 1, learners use different amounts of weight and meter sticks to explore balance and stability. In part 2, learners will conduct two experiments to explore their own centers of gravity. This guide includes background information, extensions, and data sheets.

Chang, Kimberly; Moreno, Nancy P.; Tharp, Barbara Z.; Institute, National S.

2000-01-01

212

Quantum gravity effects on compact star cores

NASA Astrophysics Data System (ADS)

Using the Tolman-Oppenheimer-Volkoff equation and the equation of state of zero temperature ultra-relativistic Fermi gas based on generalized uncertainty principle (GUP), the quantum gravitational effects on the cores of compact stars are discussed. Our results show that 2m(r)/r varies with r. Quantum gravity plays an important role in the region r˜103r0, where r0˜?0lp, lp is the Planck length and ?0 is a dimensionless parameter accounting for quantum gravity effects. Furthermore, near the center of compact stars, we find that the metric components are g˜r4 and g=[1. All these effects are different from those obtained from classical gravity. These results can be applied to neutron stars or denser ones like quark stars. The observed masses of neutron stars (?2M?) indicate that ?0 can not exceed 1037, not as good as the upper bound ?0<1034 from simple electroweak consideration. This means that incorporating either quantum gravity effects or nuclear interactions, one obtains almost the same mass limits of neutron stars.

Wang, Peng; Yang, Haitang; Zhang, Xiuming

2012-12-01

213

Inflation and reheating in induced gravity

NASA Astrophysics Data System (ADS)

Inflation is studied in the context of induced gravity (IG) ??2R, where R is the Ricci scalar, ? a scalar field and ? a dimensionless constant. We study in detail cosmological perturbations in IG and examine both a Landau-Ginzburg (LG) and a Coleman-Weinberg (CW) potential toy models for small field and large field (chaotic) inflation and find that small field inflationary models in IG are constrained to ??3×10-3 by WMAP 5-yrs data. Finally we describe the regime of coherent oscillations in induced gravity by an analytic approximation, showing how the homogeneous inflaton can decay in its short-scale fluctuations when it oscillates around a non-zero value ?.

Cerioni, A.; Finelli, F.; Tronconi, A.; Venturi, G.

2009-11-01

214

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

215

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

216

Zero Stiffness Tensegrity Structures M. Schenk a

Zero Stiffness Tensegrity Structures M. Schenk a S.D. Guest b, J.L. Herder a aMechanical, Maritime members with a zero rest length allow the construction of tensegrity struc- tures that are in equilibrium interesting observations regarding zero stiffness tensegrity structures. Key words: zero stiffness, tensegrity

Guest, Simon

217

EOS 514: Assignment 8 Low Re flow and viscous gravity currents: Lava lake tectonics and Mantle and mantle plumes. The flows you will analyze are all at low- or zero-Re (i.e., they are "laminar of the dynamics of moving lava lake crusts and the spreading of viscous gravity currents such as lava flows

Jellinek, Mark

218

Effects of gravity and pressure on laminar coflow methaneÂair diffusion flames at pressures from 1 to 60 atmospheres Marc R.J. Charest , Clinton P.T. Groth, Ã?mer L. GÃ¼lder University of Toronto January 2011 Available online 12 February 2011 Keywords: High pressure combustion Zero-gravity combustion

Groth, Clinton P. T.

219

ERIC Educational Resources Information Center

The last ten years have seen an explosion of research in the zero-divisor graphs of commutative rings--by professional mathematicians "and" undergraduates. The objective is to find algebraic information within the geometry of these graphs. This topic is approachable by anyone with one or two semesters of abstract algebra. This article gives the…

Axtell, M.; Stickles, J.

2010-01-01

220

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

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

1985-01-01

221

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

222

Zero Moment Point Manipulability Ellipsoid

In this paper, we propose zero moment point (ZMP) manipulability ellipsoid as an extension to the existing ZMP balance criterion. The ZMP manipulability ellipsoid was developed by combining the ZMP balance criterion, the humanoid robot dynamics and the manipulability of robotic manipulators. The ZMP manipulability ellipsoid represents the ability of a humanoid robot to instantly move the ZMP from its

Nirut Naksuk; C. S. George Lee

2006-01-01

223

Warped brane worlds in critical gravity

NASA Astrophysics Data System (ADS)

We investigate the brane models in arbitrary dimensional critical gravity presented in Lu and Pope (Phys Rev Lett 106:181302, 2011). For the models of the thin branes with codimension one, the Gibbons-Hawking surface term and the junction conditions are derived, with which the analytical solutions for the flat, AdS, and dS branes are obtained at the critical point of the critical gravity. It is found that all these branes are embedded in an AdS spacetime, but, in general, the effective cosmological constant of the AdS spacetime is not equal to the naked one in the critical gravity, which can be positive, zero, and negative. Another interesting result is that the brane tension can also be positive, zero, or negative, depending on the symmetry of the thin brane and the values of the parameters of the theory, which is very different from the case in general relativity. It is shown that the mass hierarchy problem can be solved in the braneworld model in the higher-derivative critical gravity. We also study the thick brane model and find analytical and numerical solutions of the flat, AdS, and dS branes. It is found that some branes will have inner structure when some parameters of the theory are larger than their critical values, which may result in resonant KK modes for some bulk matter fields. The flat branes with positive energy density and AdS branes with negative energy density are embedded in an -dimensional AdS spacetime, while the dS branes with positive energy density are embedded in an -dimensional Minkowski one.

Zhong, Yi; Chen, Feng-Wei; Xie, Qun-Ying; Liu, Yu-Xiao

2014-12-01

224

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

225

Nonstationary Gravity Wave Forcing of the Stratospheric Zonal Mean Wind

NASA Technical Reports Server (NTRS)

The role of gravity wave forcing in the zonal mean circulation of the stratosphere is discussed. Starting from some very simple assumptions about the momentum flux spectrum of nonstationary (non-zero phase speed) waves at forcing levels in the troposphere, a linear model is used to calculate wave propagation through climatological zonal mean winds at solstice seasons. As the wave amplitudes exceed their stable limits, a saturation criterion is imposed to account for nonlinear wave breakdown effects, and the resulting vertical gradient in the wave momentum flux is then used to estimate the mean flow forcing per unit mass. Evidence from global, assimilated data sets are used to constrain these forcing estimates. The results suggest the gravity-wave-driven force is accelerative (has the same sign as the mean wind) throughout most of the stratosphere above 20 km. The sense of the gravity wave forcing in the stratosphere is thus opposite to that in the mesosphere, where gravity wave drag is widely believed to play a principal role in decelerating the mesospheric jets. The forcing estimates are further compared to existing gravity wave parameterizations for the same climatological zonal mean conditions. Substantial disagreement is evident in the stratosphere, and we discuss the reasons for the disagreement. The results suggest limits on typical gravity wave amplitudes near source levels in the troposphere at solstice seasons. The gravity wave forcing in the stratosphere appears to have a substantial effect on lower stratospheric temperatures during southern hemisphere summer and thus may be relevant to climate.

Alexander, M. J.; Rosenlof, K. H.

1996-01-01

226

Holographic Renormalization of New Massive Gravity

We study holographic renormalization for three dimensional new massive gravity (NMG). By studying the general fall off conditions for the metric allowed by the model at infinity, we show that at the critical point where the central charges of the dual 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 fall off may be interpreted as the fact that the dual CFT would be a LCFT.

Mohsen Alishahiha; Ali Naseh

2010-05-10

227

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

228

Nonlinear partially massless from massive gravity?

NASA Astrophysics Data System (ADS)

We show that consistent nonlinear partially massless models cannot be obtained starting from “f-g” massive gravity, with “f” the embedding de Sitter space. The obstruction, which is also the source of f-g acausality, is the very same fifth constraint that removes the notorious sixth ghost excitation. Here, however, it blocks extension of the gauge invariance (appearing for mass to de Sitter cosmological constant tunings) that removed the helicity-zero mode at linear level. Separately, our methods allow us to almost complete the proof that all f-g models are acausal.

Deser, S.; Sandora, M.; Waldron, A.

2013-05-01

229

Particle cloud combustion in reduced gravity

NASA Technical Reports Server (NTRS)

The prinicipal objectives of this microgravity experiment program are to obtain flame propagation rate and flame extinction limit data for several important premixed, quiescent particle cloud combustion systems under near zero-gravity conditions. The data resulting from these experiments are needed for utilization with currently available and tractable flame propagation and extinction theory. These data are also expected to provide standards for the evaluation of fire hazards in particle suspensions in both Earth-based and space-based applications. Both terrestrial and space-based fire safety criteria require the identification of the critical concentrations of particulate fuels and inerts at the flame extinction conditions.

Berlad, A. L.

1988-01-01

230

Black Hole Remnant from Gravity's Rainbow

In this work, we investigate black hole (BH) physics in the context of gravity rainbow. We investigate this through rainbow functions that have been proposed by Amelino-Camelia, et el. in [arXiv:0806.0339, hep-th/9605211]. This modification will give corrections to both the temperature and the entropy of BH and hence it changes the picture of Hawking radiation greatly when the size of BH approaches the Planck scale. It prevents BH from total evaporation, predicting the existence of BH remnant which may resolve the catastrophic behavior of Hawking radiation as the BH mass approaches zero.

Ahmed Farag Ali

2014-02-21

231

We consider the problem of finding a dual formulation of gravity in the presence of non-trivial matter couplings. In the absence of matter a dual graviton can be introduced only for linearised gravitational interactions. We show that the coupling of linearised gravity to matter poses obstructions to the usual construction and comment on possible resolutions of this difficulty.

Eric A. Bergshoeff; Mees de Roo; Sven F. Kerstan; Axel Kleinschmidt; Fabio Riccioni

2008-03-27

232

Tethered gravity laboratories study

NASA Technical Reports Server (NTRS)

The use is studied of tether systems to improve the lowest possible steady gravity level on the Space Station. Particular emphasis is placed by the microgravity community on the achievement of high quality microgravity conditions. The tether capability is explored for active control of the center of gravity and the analysis of possible tethered configurations.

Lucchetti, F.

1989-01-01

233

NASA Astrophysics Data System (ADS)

1. Gravity triumphant; 2. Stars and their fates; 3. Black holes in our backyard; 4. Galaxies and their nuclei; 5. Quasars and kin; 6. Jets; 7. Blasts from the past; 8. Black holes in hibernation; 9. Cosmic feedback; 10. Checking up on Einstein; 11. Through the horizon; Appendix: Gravity and cosmic dimensions; Index.

Begelman, Mitchell; Rees, Martin

2010-04-01

234

Counterterms in Lovelock Gravity

In this paper, we introduce the counterterms that remove the non-logarithmic divergences of the action in third order Lovelock gravity. We do this by defining the cosmological constant in such a way that the asymptotic form of the metric have the same form in Lovelock and Einstein gravities. Thus, we employ the counterterms of Einstein gravity and show that the power law divergences in the action of Lovelock gravity can be removed by suitable choice of coefficients. We find that the dependence of these coefficients on the dimension in Lovelock gravity is the same as in Einstein gravity. We also introduce the finite energy-momentum tensor and employ these counterterms to calculate the finite action and mass of the black hole solutions of third order Lovelock gravity. We calculate the thermodynamic quantities and show that the entropy calculated through the use of Gibbs-Duhem relation is consistent with the obtained entropy by Wald's formula. We, also, find that in contrast to Einstein gravity in which there ex...

Mehdizadeh, M R; Zangeneh, M Kord

2015-01-01

235

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

236

NASA Astrophysics Data System (ADS)

In this thesis we examine several ways in which we can explore the early universe through gravitationalwaves and the fundamental nature of gravity through cosmology and observations of dynamics within the solar system. Both of these topics have taken center stage, as we are living at a unique time which promises to bring fundamental insights into the nature of gravity with the discovery of new binary pulsar systems, the building of increasingly precise solar system and tabletop experiments and the birth of gravitational-wave observatories to name a few recent and upcoming advances. We rst discuss whether we may be able to directly detect gravitational waves from in ation using future space-based interferometers. We then describe how the direct detection of in ationary gravitational waves will allow us to probe the fundamental physics that operated at the earliest moments of the universe. Next, a new constraint to a general cosmological gravitational wave background is presented using the observations of the cosmic microwave background. Moving away from general relativity, we consider alternative theories of gravity. One reason to consider alternative theories of gravity is the observation that the expansion of the universe is currently accelerating. It is possible that this accelerated expansion is due to a modication of gravity. However, any theory that modies gravity in order to produce accelerated expansion must also conform to the dynamics that we observe within the Solar System. We discuss how the observation of the de ection of light around the Sun places severe limitations on a particular modied gravity theory, known as f(R) gravity. Our discussion of f(R) gravity leads us to ask whether the parameterized post Newtonian parameter, PPN, takes on a universal value. We identify measurements made of strong lensing around early type galaxies in the Sloan Lens ACS (SLACS) survey as a rst step in performing this new test of gravity. Finally, we explore some consequences of Chern-Simons gravity. One of the unique aspects of Chern-Simons gravity is that it introduces parity violation into the gravitational sector. As a consequence, it predicts a different gravitomagnetic eld around the rotating Earth than is predicted in general relativity. We show how recent measurements of this gravitomagnetic eld made by observing the two LAser GEOdynamics Satellites (LAGEOS) and Gravity Probe B satellites constrain Chern-Simons gravity. Finally, we discuss how future observations of binary pulsar systems may allow for a more general exploration of the gravitomagnetic structure around rotating objects.

Smith, Tristan L.

2008-05-01

237

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.

238

NASA Astrophysics Data System (ADS)

Gravity directs the paths of light rays and the growth of structure. Moreover, gravity on cosmological scales does not simply point down: It accelerates the universal expansion by pulling outward, either due to a highly negative pressure dark energy or an extension of general relativity. We have examined methods to test the properties of gravity through cosmological measurements. We have then considered specific possibilities for a sound gravitational theory based on the Galilean shift symmetry. The evolution of the laws of gravity from the early universe to the present acceleration to the future fate - the paths of gravity - carries rich information on this fundamental force of physics, and on the mystery of dark energy.

Linder, E. V.

2014-03-01

239

ZERO WASTE EDUCATOR -VOLUNTEER POSITION DESCRIPTION Position Title: Zero Waste Educator

ZERO WASTE EDUCATOR - VOLUNTEER POSITION DESCRIPTION Position Title: Zero Waste Educator Department: SFU Sustainability Office Position Reports to (Title): Zero Waste Coordinator & Community Zero Waste Educators will assist in the launch of SFU's new Zero Waste initiative on all three SFU

Li, Ze-Nian

240

NET-ZERO CARBON MANUFACTURING AT NET-ZERO COST Dustin Pohlman

1 NET-ZERO CARBON MANUFACTURING AT NET-ZERO COST Dustin Pohlman Industrial Assessment Center energy in manufacturing plants that results in net-zero carbon emissions at net-zero costs. The paper begins by reviewing the economics of net- zero energy buildings and discussing why a different approach

Kissock, Kelly

241

Entropy-zero f-expansions Entropy-zero f-expansions

Ergodic theory and symbolic dynamics 4 Entropy zero #12;Entropy-zero f-expansions Outline The New Math;Entropy-zero f-expansions Some examples Base-r (continued Â 2) Let N(d : w) the number of digits d in wordEntropy-zero f-expansions Entropy-zero f-expansions E. Arthur (Robbie) Robinson The George

Robinson Jr., E. Arthur (Robbie)

242

Complete Classification of 1+1 Gravity Solutions

A classification of the maximally extended solutions for 1+1 gravity models (comprising e.g. generalized dilaton gravity as well as models with non-trivial torsion) is presented. No restrictions are placed on the topology of the arising solutions, and indeed it is found that for generic models solutions on non-compact surfaces of arbitrary genus with an arbitrary non-zero number of holes can be obtained. The moduli space of classical solutions (solutions of the field equations with fixed topology modulo gauge transformations) is parametrized explicitly.

T. Kloesch; T. Strobl

1997-11-25

243

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

244

NASA Technical Reports Server (NTRS)

Zero-Copy Objects System software enables application data to be encapsulated in layers of communication protocol without being copied. Indirect referencing enables application source data, either in memory or in a file, to be encapsulated in place within an unlimited number of protocol headers and/or trailers. Zero-copy objects (ZCOs) are abstract data access representations designed to minimize I/O (input/output) in the encapsulation of application source data within one or more layers of communication protocol structure. They are constructed within the heap space of a Simple Data Recorder (SDR) data store to which all participating layers of the stack must have access. Each ZCO contains general information enabling access to the core source data object (an item of application data), together with (a) a linked list of zero or more specific extents that reference portions of this source data object, and (b) linked lists of protocol header and trailer capsules. The concatenation of the headers (in ascending stack sequence), the source data object extents, and the trailers (in descending stack sequence) constitute the transmitted data object constructed from the ZCO. This scheme enables a source data object to be encapsulated in a succession of protocol layers without ever having to be copied from a buffer at one layer of the protocol stack to an encapsulating buffer at a lower layer of the stack. For large source data objects, the savings in copy time and reduction in memory consumption may be considerable.

Burleigh, Scott C.

2011-01-01

245

Effects of background gravity stimuli on gravity-controlled behavior

NASA Technical Reports Server (NTRS)

Physiological and developmental effects of altered gravity were researched. The stimulus properties of gravity have been found to possess reinforcing and aversive properties. Experimental approaches taken, used animals placed into fields of artificial gravity, in the form of parabolic or spiral centrifuges. Gravity preferences were noted and it was concluded that the psychophysics of gravity and background factors which support these behaviors should be further explored.

Mccoy, D. F.

1976-01-01

246

Stochastic Quantum Gravity, Gravitational Collapse and Grey Holes

Quantum gravity is treated as a stochastic quantization of the spacetime metric of general relativity. It is found that owing to the stochastic fluctuating behavior of the geometry, the singularity in gravitational collapse of a star has a zero probability density of occurring. Moreover, as a star collapses the probability density of a distant observer seeing an infinite red shift at the Schwarzschild radius of the star is zero. Therefore, there is a vanishing probability density of a black hole event horizon forming during gravitational collapse. A grey apparent event horizon forms during the collapse that allows information to escape.

Moffat, J W

2014-01-01

247

Bilateral, Zero-Impedance Static Semiconductor Switch

NASA Technical Reports Server (NTRS)

Static semiconductor switching circuit eliminates the undesirable features of electromechanical relays and conventional semiconductor switching circuits. There is a net zero voltage drop at the terminals and thus a zero impedance for bilateral currents there.

Doughman, C. L.

1968-01-01

248

Propulsion Investigation for Zero and Near-Zero Emissions Aircraft

NASA Technical Reports Server (NTRS)

As world emissions are further scrutinized to identify areas for improvement, aviation s contribution to the problem can no longer be ignored. Previous studies for zero or near-zero emissions aircraft suggest aircraft and propulsion system sizes that would perform propulsion system and subsystems layout and propellant tankage analyses to verify the weight-scaling relationships. These efforts could be used to identify and guide subsequent work on systems and subsystems to achieve viable aircraft system emissions goals. Previous work quickly focused these efforts on propulsion systems for 70- and 100-passenger aircraft. Propulsion systems modeled included hydrogen-fueled gas turbines and fuel cells; some preliminary estimates combined these two systems. Hydrogen gas-turbine engines, with advanced combustor technology, could realize significant reductions in nitrogen emissions. Hydrogen fuel cell propulsion systems were further laid out, and more detailed analysis identified systems needed and weight goals for a viable overall system weight. Results show significant, necessary reductions in overall weight, predominantly on the fuel cell stack, and power management and distribution subsystems to achieve reasonable overall aircraft sizes and weights. Preliminary conceptual analyses for a combination of gas-turbine and fuel cell systems were also performed, and further studies were recommended. Using gas-turbine engines combined with fuel cell systems can reduce the fuel cell propulsion system weight, but at higher fuel usage than using the fuel cell only.

Snyder, Christopher A.; Berton, Jeffrey J.; Brown, Gerald v.; Dolce, James L.; Dravid, Marayan V.; Eichenberg, Dennis J.; Freeh, Joshua E.; Gallo, Christopher A.; Jones, Scott M.; Kundu, Krishna P.; Marek, Cecil J.; Millis, Marc G.; Murthy, Pappu L.; Roach, Timothy M.; Smith, Timothy D.; Stefko, George L.; Sullivan, Roy M.; Tornabene, Robert T.; Geiselhat, Karl A.; Kascak, Albert F.

2009-01-01

249

Modeling Candle Flame Behavior In Variable Gravity

NASA Technical Reports Server (NTRS)

The burning of a candle, as typical non-propagating diffusion flame, has been used by a number of researchers to study the effects of electric fields on flame, spontaneous flame oscillation and flickering phenomena, and flame extinction. In normal gravity, the heat released from combustion creates buoyant convection that draws oxygen into the flame. The strength of the buoyant flow depends on the gravitational level and it is expected that the flame shape, size and candle burning rate will vary with gravity. Experimentally, there exist studies of candle burning in enhanced gravity (i.e. higher than normal earth gravity, g(sub e)), and in microgravity in drop towers and space-based facilities. There are, however, no reported experimental data on candle burning in partial gravity (g < g(sub e)). In a previous numerical model of the candle flame, buoyant forces were neglected. The treatment of momentum equation was simplified using a potential flow approximation. Although the predicted flame characteristics agreed well with the experimental results, the model cannot be extended to cases with buoyant flows. In addition, because of the use of potential flow, no-slip boundary condition is not satisfied on the wick surface. So there is some uncertainty on the accuracy of the predicted flow field. In the present modeling effort, the full Navier-Stokes momentum equations with body force term is included. This enables us to study the effect of gravity on candle flames (with zero gravity as the limiting case). In addition, we consider radiation effects in more detail by solving the radiation transfer equation. In the previous study, flame radiation is treated as a simple loss term in the energy equation. Emphasis of the present model is on the gas-phase processes. Therefore, the detailed heat and mass transfer phenomena inside the porous wick are not treated. Instead, it is assumed that a thin layer of liquid fuel coated the entire wick surface during the burning process. This is the limiting case that the mass transfer process in the wick is much faster than the evaporation process at the wick surface.

Alsairafi, A.; Tien, J. S.; Lee, S. T.; Dietrich, D. L.; Ross, H. D.

2003-01-01

250

Minimal Liouville Gravity correlation numbers from Douglas string equation

We continue the study of $(q,p)$ Minimal Liouville Gravity with the help of Douglas string equation. We generalize the results of \\cite{Moore:1991ir}, \\cite{Belavin:2008kv}, where Lee-Yang series $(2,2s+1)$ was studied, to $(3,3s+p_0)$ Minimal Liouville Gravity, where $p_0=1,2$. We demonstrate that there exist such coordinates $\\tau_{m,n}$ on the space of the perturbed Minimal Liouville Gravity theories, in which the partition function of the theory is determined by the Douglas string equation. The coordinates $\\tau_{m,n}$ are related in a non-linear fashion to the natural coupling constants $\\lambda_{m,n}$ of the perturbations of Minimal Lioville Gravity by the physical operators $O_{m,n}$. We find this relation from the requirement that the correlation numbers in Minimal Liouville Gravity must satisfy the conformal and fusion selection rules. After fixing this relation we compute three- and four-point correlation numbers when they are not zero. The results are in agreement with the direct calculations in Minimal Liouville Gravity available in the literature \\cite{Goulian:1990qr}, \\cite{Zamolodchikov:2005sj}, \\cite{Belavin:2006ex}.

Alexander Belavin; Boris Dubrovin; Baur Mukhametzhanov

2014-09-11

251

Rotating Gravity Gradiometer Study

NASA Technical Reports Server (NTRS)

The application of a Rotating Gravity Gradiometer (RGG) system on board a Lunar Polar Orbiter (LPO) for the measurement of the Lunar gravity field was investigated. A data collection simulation study shows that a gradiometer will give significantly better gravity data than a doppler tracking system for the altitudes under consideration for the LOP, that the present demonstrated sensitivity of the RGG is adequate for measurement of the Lunar gravity gradient field, and that a single RGG instrument will provide almost as much data for geophysical interpretation as an orthogonal three axis RGG system. An engineering study of the RGG sensor/LPO spacecraft interface characteristics shows that the RGG systems under consideration are compatible with the present models of the LPO spacecraft.

Forward, R. L.

1976-01-01

252

Tethered gravity laboratories study

NASA Technical Reports Server (NTRS)

The following subject areas are covered: (1) thermal control issues; (2) attitude control sybsystem; (3) configuration constraints; (4) payload; (5) acceleration requirements on Variable Gravity Laboratory (VGL); and (6) VGL configuration highlights.

Lucchetti, F.

1989-01-01

253

Tethered gravity laboratories study

NASA Technical Reports Server (NTRS)

Variable Gravity Laboratory studies are discussed. The following subject areas are covered: (1) conceptual design and engineering analysis; (2) control strategies (fast crawling maneuvers, main perturbations and their effect upon the acceleration level); and (3) technology requirements.

Lucchetti, F.

1989-01-01

254

Exercise in artificial gravity

Artificial gravity provided by short radius centrifugation is considered a promising countermeasure to the deleterious physiological effects of microgravity during long-duration space flight. We investigated the feasibility ...

Edmonds, Jessica Leigh

2005-01-01

255

Global height datum unification: a new approach in gravity potential space

NASA Astrophysics Data System (ADS)

The problem of “global height datum unification” is solved in the gravity potential space based on: (1) high-resolution local gravity field modeling, (2) geocentric coordinates of the reference benchmark, and (3) a known value of the geoid’s potential. The high-resolution local gravity field model is derived based on a solution of the fixed-free two-boundary-value problem of the Earth’s gravity field using (a) potential difference values (from precise leveling), (b) modulus of the gravity vector (from gravimetry), (c) astronomical longitude and latitude (from geodetic astronomy and/or combination of (GNSS) Global Navigation Satellite System observations with total station measurements), (d) and satellite altimetry. Knowing the height of the reference benchmark in the national height system and its geocentric GNSS coordinates, and using the derived high-resolution local gravity field model, the gravity potential value of the zero point of the height system is computed. The difference between the derived gravity potential value of the zero point of the height system and the geoid’s potential value is computed. This potential difference gives the offset of the zero point of the height system from geoid in the “potential space”, which is transferred into “geometry space” using the transformation formula derived in this paper. The method was applied to the computation of the offset of the zero point of the Iranian height datum from the geoid’s potential value W 0=62636855.8 m2/s2. According to the geometry space computations, the height datum of Iran is 0.09 m below the geoid.

Ardalan, A. A.; Safari, A.

2005-12-01

256

NET-ZERO ENERGY HIGH PERFORMANCE

NET-ZERO ENERGY HIGH PERFORMANCE GREEN BUILDINGSCOLLABORATIVE WORKSHOP AUGUST 6, 2009 SPONSORED. "-- Harvey Perlman, UNL Chancellor #12;Net-Zero Energy, High-Performance Green Buildings | 1 INTRODUCTION EXECUTIVE SUMMARY KEYNOTE SPEAKERS The Path to Net-Zero Energy Buildings Greg Stark, Advanced Commercial

Farritor, Shane

257

40 CFR 180.5 - Zero tolerances.

Code of Federal Regulations, 2010 CFR

...Interpretative Regulations § 180.5 Zero tolerances. A zero tolerance means that no amount...when it is offered for shipment. A zero tolerance for a pesticide chemical...alarming physiological effects upon one or more of the species of the...

2010-07-01

258

Zero Tolerance: Advantages and Disadvantages. Research Brief

ERIC Educational Resources Information Center

What are the positives and negatives of zero tolerance? What should be considered when examining a school's program? Although there are no definitive definitions of zero tolerance, two commonly used ones are as follows: "Zero tolerance means that a school will automatically and severely punish a student for a variety of infractions" (American Bar…

Walker, Karen

2009-01-01

259

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

260

We investigate the new massive conformal gravity which is not invariant under conformal transformations, in comparison to the massive conformal gravity. We find five polarization modes of gravitational waves propagating on the Minkowski spacetimes. The stability of Minkowski spacetimes is guaranteed if the mass squared is not negative and the linearized Ricci tenor is employed to describe a massive spin-2 graviton. However, the small Schwarzschild black hole is unstable against the $s$-mode massive graviton perturbations.

Yun Soo Myung

2014-02-09

261

NASA Technical Reports Server (NTRS)

Work on three different efforts related to gravity data analysis is discussed. The reduction of raw Doppler data from the Apollo 15 subsatellite to produce acceleration profiles as a function of latitude, longitude and altitude; an investigation related to fitting long arcs of Pioneer Venus Orbiter tracking data; and a study of gravity/topography ratios which were found to have a linear trend with longitude are discussed.

Sjogren, William L.

1987-01-01

262

Variational principle and one-point functions in three-dimensional flat space Einstein gravity

NASA Astrophysics Data System (ADS)

We provide a well-defined variational principle for three-dimensional flat space Einstein gravity by adding one-half of the Gibbons-Hawking-York boundary term to the bulk action. We check the zero-point function, recovering consistency with thermodynamics of flat space cosmologies. We then apply our result to calculate the one-point functions in flat space Einstein gravity for the vacuum and all flat space cosmologies. The results are compatible with the ones for the zero-mode charges obtained by canonical analysis.

Detournay, Stephane; Grumiller, Daniel; Schöller, Friedrich; Simón, Joan

2014-04-01

263

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

264

Zero-G experiments in two-phase fluids flow regimes

NASA Technical Reports Server (NTRS)

The two-phase flows studied were liquid and gas mixtures in a straight flow channel of circular cross-section. Boundaries between flow regimes have been defined for normogravity on coordinates of gas quality and total mass velocity; and, when combined with boundary expressions having a Froude number term, an analytical model was derived predicting boundary shifts with changes in gravity level. Experiments with air and water were performed, first in the normogravity environment of a ground laboratory and then in 'zero gravity' aboard a KC-135 aircraft flying parabolic trajectories. Data reduction confirmed regime boundary shifts in the direction predicted, although the magnitude was a little less than predicted. Pressure drop measurements showed significant increases for the low gravity condition.

Heppner, D. B.; King, C. D.; Littles, J. W.

1975-01-01

265

Scalar-tensor gravity theory for dynamical light velocity

A gravity theory is developed with the metric g???=g??+B??????. In the present universe the additional contribution from the scalar field in the metric g??? can generate an acceleration in the expansion of the universe, without negative pressure and with a zero cosmological constant. In this theory, gravitational waves will propagate at a different speed from non-gravitational waves. It is suggested

M. A. Clayton; J. W. Moffat

2000-01-01

266

Pacific Plate gravity lineaments: Diffuse extension or thermal contraction?

We detect strain very close to zero on the Pacific Plate relative to the Nazca Plate for Anomalies C8–C13. Our observations are in the region of the satellite gravity lineaments, 10°–40°S in the central Pacific. Strain was measured by comparing fracture zone spacing on the Pacific and Nazca Plates in an approach similar to that of Goodwillie and Parsons [1992

Kathleen Dallas Gans; Douglas S. Wilson; Ken C. Macdonald

2003-01-01

267

Gravity Before Einstein and Schwinger Before Gravity

NASA Astrophysics Data System (ADS)

Julian Schwinger was a child prodigy, and Albert Einstein distinctly not; Schwinger had something like 73 graduate students, and Einstein very few. But both thought gravity was important. They were not, of course, the first, nor is the disagreement on how one should think about gravity that is being highlighted here the first such dispute. The talk will explore, first, several of the earlier dichotomies: was gravity capable of action at a distance (Newton), or was a transmitting ether required (many others). Did it act on everything or only on solids (an odd idea of the Herschels that fed into their ideas of solar structure and sunspots)? Did gravitational information require time for its transmission? Is the exponent of r precisely 2, or 2 plus a smidgeon (a suggestion by Simon Newcomb among others)? And so forth. Second, I will try to say something about Scwinger's lesser known early work and how it might have prefigured his "source theory," beginning with "On the Interaction of Several Electrons (the unpublished, 1934 "zeroth paper," whose title somewhat reminds one of "On the Dynamics of an Asteroid," through his days at Berkeley with Oppenheimer, Gerjuoy, and others, to his application of ideas from nuclear physics to radar and of radar engineering techniques to problems in nuclear physics. And folks who think good jobs are difficult to come by now might want to contemplate the couple of years Schwinger spent teaching elementary physics at Purdue before moving on to the MIT Rad Lab for war work.

Trimble, Virginia L.

2012-05-01

268

Quantum Gravity in Large Dimensions

Quantum gravity is investigated in the limit of a large number of space-time dimensions, using as an ultraviolet regularization the simplicial lattice path integral formulation. In the weak field limit the appropriate expansion parameter is determined to be $1/d$. For the case of a simplicial lattice dual to a hypercube, the critical point is found at $k_c/\\lambda=1/d$ (with $k=1/8 \\pi G$) separating a weak coupling from a strong coupling phase, and with $2 d^2$ degenerate zero modes at $k_c$. The strong coupling, large $G$, phase is then investigated by analyzing the general structure of the strong coupling expansion in the large $d$ limit. Dominant contributions to the curvature correlation functions are described by large closed random polygonal surfaces, for which excluded volume effects can be neglected at large $d$, and whose geometry we argue can be approximated by unconstrained random surfaces in this limit. In large dimensions the gravitational correlation length is then found to behave as $| \\log (k_c - k) |^{1/2}$, implying for the universal gravitational critical exponent the value $\

Herbert W. Hamber; Ruth M. Williams

2005-11-30

269

New Massive Gravity and AdS{sub 4} Counterterms

We show that the recently proposed Dirac-Born-Infeld extension of new massive gravity emerges naturally as a counterterm in four-dimensional anti-de Sitter space (AdS{sub 4}). The resulting on-shell Euclidean action is independent of the cutoff at zero temperature. We also find that the same choice of counterterm gives the usual area law for the AdS{sub 4} Schwarzschild black hole entropy in a cutoff-independent manner. The parameter values of the resulting counterterm action correspond to a c=0 theory in the context of the duality between AdS{sub 3} gravity and two-dimensional conformal field theory. We rewrite this theory in terms of the gauge field that is used to recast 3D gravity as a Chern-Simons theory.

Jatkar, Dileep P. [Harish-Chandra Research Institute, Chhatnag Road, Jhusi, Allahabad, 211019 (India); Sinha, Aninda [Centre for High Energy Physics, Indian Institute of Science, C. V. Raman Avenue, Bangalore 560012 (India)

2011-04-29

270

New massive gravity and AdS(4) counterterms.

We show that the recently proposed Dirac-Born-Infeld extension of new massive gravity emerges naturally as a counterterm in four-dimensional anti-de Sitter space (AdS(4)). The resulting on-shell Euclidean action is independent of the cutoff at zero temperature. We also find that the same choice of counterterm gives the usual area law for the AdS(4) Schwarzschild black hole entropy in a cutoff-independent manner. The parameter values of the resulting counterterm action correspond to a c=0 theory in the context of the duality between AdS(3) gravity and two-dimensional conformal field theory. We rewrite this theory in terms of the gauge field that is used to recast 3D gravity as a Chern-Simons theory. PMID:21635026

Jatkar, Dileep P; Sinha, Aninda

2011-04-29

271

Asymptotic safety of gravity and the Higgs boson mass

There are indications that gravity is asymptotically safe. The Standard Model (SM) plus gravity could be valid up to arbitrarily high energies. Supposing that this is indeed the case and assuming that there are no intermediate energy scales between the Fermi and Planck scales we address the question of whether the mass of the Higgs boson $m_H$ can be predicted. For a positive gravity induced anomalous dimension $A_\\lambda>0$ the running of the quartic scalar self interaction $\\lambda$ at scales beyond the Planck mass is determined by a fixed point at zero. This results in $m_H=m_{\\rm min}=126$ GeV, with only a few GeV uncertainty. This prediction is independent of the details of the short distance running and holds for a wide class of extensions of the SM as well. For $A_\\lambda 0$ is favored by explicit computations existing in the literature.

Mikhail Shaposhnikov; Christof Wetterich

2010-01-12

272

Approaches to Validation of Models for Low Gravity Fluid Behavior

NASA Technical Reports Server (NTRS)

This paper details the author experiences with the validation of computer models to predict low gravity fluid behavior. It reviews the literature of low gravity fluid behavior as a starting point for developing a baseline set of test cases. It examines authors attempts to validate their models against these cases and the issues they encountered. The main issues seem to be that: Most of the data is described by empirical correlation rather than fundamental relation; Detailed measurements of the flow field have not been made; Free surface shapes are observed but through thick plastic cylinders, and therefore subject to a great deal of optical distortion; and Heat transfer process time constants are on the order of minutes to days but the zero-gravity time available has been only seconds.

Chato, David J.; Marchetta, Jeffery; Hochstein, John I.; Kassemi, Mohammad

2005-01-01

273

[Low Fidelity Simulation of a Zero-Y Robot

NASA Technical Reports Server (NTRS)

The item to be cleared is a low-fidelity software simulation model of a hypothetical freeflying robot designed for use in zero gravity environments. This simulation model works with the HCC simulation system that was developed by Xerox PARC and NASA Ames Research Center. HCC has been previously cleared for distribution. When used with the HCC software, the model computes the location and orientation of the simulated robot over time. Failures (such as a broken motor) can be injected into the simulation to produce simulated behavior corresponding to the failure. Release of this simulation will allow researchers to test their software diagnosis systems by attempting to diagnose the simulated failure from the simulated behavior. This model does not contain any encryption software nor can it perform any control tasks that might be export controlled.

Sweet, Adam

2001-01-01

274

Feasibility of Achieving Net-Zero-Energy Net-Zero-Cost

1 Feasibility of Achieving Net- Zero-Energy Net-Zero-Cost Homes I.S. Walker, Al-Beaini, SSimjanovic,JohnStanley,BretStrogen,IainWalker FeasibilityofAchieving ZeroNetEnergy,Zero NetCostHomes #12;4 ACKNOWLEDGEMENTS

275

Results from the Middeck 0-gravity Dynamics Experiment

NASA Technical Reports Server (NTRS)

The experimental results of the Middick Zero-gravity Dynamics Experiment (MODE) are presented. MODE investigated the dynamics of two key spacecraft components; contained fluids and jointed truss structures. The change in the lateral slosh behavior of contained fluids and the changes in the modal parameters of space structural test articles from one- to zero-gravity were studied. The experimental apparatus used to determine the dynamic characteristics is described. For the MODE fluid experiments, the forced response characteristics of silicone oil and distilled water in cylinder tanks with either a flat or spherical bottom are reported and discussed. A comparison of the measured earth and space results identifies and highlights the effects of gravity on the linear and nonlinear slosh behavior of these fluids. For the MODE structural experiments, an analytic and experimental study is presented. Deployable, erectable, and rotary modules were assembled to form three one- and two-dimensional structures in which variations in bracing wire and rotary joint preload could be introduced. Analysis is compared with ground experimental measurements made on a spring/wire suspension system with a nominal plunge frequency of one Hertz, and with measurements made on the Shuttle middeck. The degree of change in linear modal parameters as well as the change in nonlinear nature of the response is examined. Trends in modal parameters are presented as a function of force amplitude, joint preload, and ambient gravity level.

Van Schoor, M. C.; Crawley, E. F.; Miller, D. W.

1993-01-01

276

Entropy density of spacetime as a relic from quantum gravity

NASA Astrophysics Data System (ADS)

There is a considerable amount of evidence to suggest that the field equations of gravity have the same status as, say, the equations describing an emergent phenomenon like elasticity. In fact, it is possible to derive the field equations from a thermodynamic variational principle in which a set of normalized vector fields are varied rather than the metric. We show that this variational principle can arise as a low-energy [LP=(G ?/c3)1/2?0 ] relic of a plausible nonperturbative effect of quantum gravity, viz. the existence of a zero-point length in the spacetime. Our result is nonperturbative in the following sense: If we modify the geodesic distance in a spacetime by introducing a zero-point length, to incorporate some effects of quantum gravity, and take the limit LP?0 of the Ricci scalar of the modified metric, we end up getting a nontrivial, leading order (LP-independent) term. This term is identical to the expression for entropy density of spacetime used previously in the emergent gravity approach. This reconfirms the idea that the microscopic degrees of freedom of the spacetime, when properly described in the full theory, could lead to an effective description of geometry in terms of a thermodynamic variational principle. This is conceptually similar to the emergence of thermodynamics from the mechanics of, say, molecules. The approach also has important implications for the cosmological constant which are briefly discussed.

Kothawala, Dawood; Padmanabhan, T.

2014-12-01

277

Role of Gravity Waves in Determining Cirrus Cloud Properties

NASA Technical Reports Server (NTRS)

Cirrus clouds are important in the Earth's radiation budget. They typically exhibit variable physical properties within a given cloud system and from system to system. Ambient vertical motion is a key factor in determining the cloud properties in most cases. The obvious exception is convectively generated cirrus (anvils), but even in this case, the subsequent cloud evolution is strongly influenced by the ambient vertical motion field. It is well know that gravity waves are ubiquitous in the atmosphere and occur over a wide range of scales and amplitudes. Moreover, researchers have found that inclusion of statistical account of gravity wave effects can markedly improve the realism of simulations of persisting large-scale cirrus cloud features. Here, we use a 1 -dimensional (z) cirrus cloud model, to systematically examine the effects of gravity waves on cirrus cloud properties. The model includes a detailed representation of cloud microphysical processes (bin microphysics and aerosols) and is run at relatively fine vertical resolution so as to adequately resolve nucleation events, and over an extended time span so as to incorporate the passage of multiple gravity waves. The prescribed gravity waves "propagate" at 15 m s (sup -1), with wavelengths from 5 to 100 km, amplitudes range up to 1 m s (sup -1)'. Despite the fact that the net gravity wave vertical motion forcing is zero, it will be shown that the bulk cloud properties, e.g., vertically-integrated ice water path, can differ quite significantly from simulations without gravity waves and that the effects do depend on the wave characteristics. We conclude that account of gravity wave effects is important if large-scale models are to generate realistic cirrus cloud property climatology (statistics).

OCStarr, David; Singleton, Tamara; Lin, Ruei-Fong

2008-01-01

278

The observable universe could be a 1+3-surface (the "brane") embedded in a 1+3+d-dimensional spacetime (the "bulk"), with standard-model particles and fields trapped on the brane while gravity is free to access the bulk. At least one of the d extra spatial dimensions could be very large relative to the Planck scale, which lowers the fundamental gravity scale, possibly even down to the electroweak (~ TeV) level. This revolutionary picture arises in the framework of recent developments in M theory. The 1+10-dimensional M theory encompasses the known 1+9-dimensional superstring theories, and is widely considered to be a promising potential route to quantum gravity. General relativity cannot describe gravity at high enough energies and must be replaced by a quantum gravity theory, picking up significant corrections as the fundamental energy scale is approached. At low energies, gravity is localized at the brane and general relativity is recovered, but at high energies gravity "leaks" into the bulk, behaving in a truly 1+3+d-dimensional way. This introduces significant changes to gravitational dynamics and perturbations, with interesting testable implications for high-energy astrophysics, black holes and cosmology. Brane-world models offer a phenomenological way to test some of the novel predictions and corrections to general relativity that are implied by M theory. This review discusses the geometry, dynamics and perturbations of simple brane-world models for cosmology and astrophysics, mainly focusing on warped 5-dimensional brane-worlds based on the Randall-Sundrum models.

Roy Maartens

2003-12-10

279

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

280

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

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

281

Zero-order bows in radially inhomogeneous spheres: direct and inverse problems.

Zero-order ray paths are examined in radially inhomogeneous spheres with differentiable refractive index profiles. It is demonstrated that zero-order and sometimes twin zero-order bows can exist when the gradient of refractive index is sufficiently negative. Abel inversion is used to "recover" the refractive index profiles; it is therefore possible in principle to specify the nature and type of bows and determine the refractive index profile that induces them. This may be of interest in the field of rainbow refractometry and optical fiber studies. This ray-theoretic analysis has direct similarities with the phenomenon of "orbiting" and other phenomena in scattering theory and also in seismological, surface gravity wave, and gravitational "lensing" studies. For completeness these topics are briefly discussed in the appendixes; they may also be of pedagogic interest. PMID:22016245

Adam, John A

2011-10-01

282

NASA Technical Reports Server (NTRS)

This report documents the Venus gravity methods and results to date (model MGNP90LSAAP). It is called a handbook in that it contains many useful plots (such as geometry and orbit behavior) that are useful in evaluating the tracking data. We discuss the models that are used in processing the Doppler data and the estimation method for determining the gravity field. With Pioneer Venus Orbiter and Magellan tracking data, the Venus gravity field was determined complete to degree and order 90 with the use of the JPL Cray T3D Supercomputer. The gravity field shows unprecedented high correlation with topography and resolution of features to the 2OOkm resolution. In the procedure for solving the gravity field, other information is gained as well, and, for example, we discuss results for the Venus ephemeris, Love number, pole orientation of Venus, and atmospheric densities. Of significance is the Love number solution which indicates a liquid core for Venus. The ephemeris of Venus is determined to an accuracy of 0.02 mm/s (tens of meters in position), and the rotation period to 243.0194 +/- 0.0002 days.

Konopliv, Alexander S.; Sjogren, William L.

1996-01-01

283

Tethered gravity laboratories study

NASA Technical Reports Server (NTRS)

The scope of the study is to investigate ways of controlling the microgravity environment of the International Space Station by means of a tethered system. Four main study tasks were performed. First, researchers analyzed the utilization of the tether systems to improve the lowest possible steady gravity level on the Space Station and the tether capability to actively control the center of gravity position in order to compensate for activities that would upset the mass distribution of the Station. The purpose of the second task was to evaluate the whole of the experiments performable in a variable gravity environment and the related beneficial residual accelerations, both for pure and applied research in the fields of fluid, materials, and life science, so as to assess the relevance of a variable g-level laboratory. The third task involves the Tethered Variable Gravity Laboratory. The use of the facility that would crawl along a deployed tether and expose experiments to varying intensities of reduced gravity is discussed. Last, a study performed on the Attitude Tether Stabilizer concept is discussed. The stabilization effect of ballast masses tethered to the Space Station was investigated as a means of assisting the attitude control system of the Station.

Lucchetti, F.

1990-01-01

284

NASA Astrophysics Data System (ADS)

This work explores the theoretical and experimental aspects of Lorentz violation in gravity. A set of modified Einstein field equations is derived from the general Lorentz-violating Standard-Model Extension (SME). Some general theoretical implications of these results are discussed. The experimental consequences for weak-field gravitating systems are explored in the Earth- laboratory setting, the solar system, and beyond. The role of spontaneous Lorentz-symmetry breaking is discussed in the context of the pure-gravity sector of the SME. To establish the low-energy effective Einstein field equations, it is necessary to take into account the dynamics of 20 coefficients for Lorentz violation. As an example, the results are compared with bumblebee models, which are general theories of vector fields with spontaneous Lorentz violation. The field equations are evaluated in the post- newtonian limit using a perfect fluid description of matter. The post-newtonian metric of the SME is derived and compared with some standard test models of gravity. The possible signals for Lorentz violation due to gravity-sector coefficients are studied. Several new effects are identified that have experimental implications for current and future tests. Among the unconventional effects are a new type of spin precession for a gyroscope in orbit and a modification to the local gravitational acceleration on the Earth's surface. These and other tests are expected to yield interesting sensitivities to dimensionless gravity- sector coefficients.

Bailey, Quentin G.

2007-08-01

285

Pool film boiling experiments on a wire in low gravity: preliminary results.

This paper reports preliminary results for pool film boiling on a wire immersed in almost saturated FC72 recently obtained during an experimental campaign performed in low gravity on the European Space Agency Zero-G airplane, (reduced gravity level 10(-2)). This is part of a long-term research program on the effect of gravitational and electric forces on boiling. The reported data set refers to experiments performed under the following conditions: (1) Earth gravity without electric field, (2) Earth gravity with electric field, (3) low gravity without electric field, and (4) low gravity with electric field. Although a decrease of gravity causes a heat transfer degradation, the electric field markedly improves heat exchange. This improvement is so effective that, beyond a certain field value, the heat flux is no longer sensitive to gravity. Two main film boiling regimes have been identified, both in normal and in low gravity: one is affected by the electric field and the other is practically insensitive to the field influence. PMID:12446340

Di Marco, P; Grassi, W; Trentavizi, F

2002-10-01

286

A study of two-phase flow in a reduced gravity environment

NASA Technical Reports Server (NTRS)

A test loop was designed and fabricated for observing and measuring pressure drops of two-phase flow in reduced gravity. The portable flow test loop was then tested aboard the NASA-JSC KC135 reduced gravity aircraft. The test loop employed the Sundstrand Two-Phase Thermal Management System (TPTMS) concept which was specially fitted with a clear two-phase return line and condenser cover for flow observation. A two-phase (liquid/vapor) mixture was produced by pumping nearly saturated liquid through an evaporator and adding heat via electric heaters. The quality of the two-phase flow was varied by changing the evaporator heat load. The test loop was operated on the ground before and after the KC135 flight tests to create a one-gravity data base. The ground testing included all the test points run during the reduced gravity testing. Two days of reduced gravity tests aboard the KC135 were performed. During the flight tests, reduced-gravity, one-gravity, and nearly two-gravity accelerations were experienced. Data was taken during the entire flight which provided flow regime and pressure drop data for the three operating conditions. The test results show that two-phase pressure drops and flow regimes can be accurately predicted in zero-gravity.

Hill, D.; Downing, Robert S.

1987-01-01

287

Terrestrial gravity data analysis for interim gravity model improvement

NASA Technical Reports Server (NTRS)

This is the first status report for the Interim Gravity Model research effort that was started on June 30, 1986. The basic theme of this study is to develop appropriate models and adjustment procedures for estimating potential coefficients from terrestrial gravity data. The plan is to use the latest gravity data sets to produce coefficient estimates as well as to provide normal equations to NASA for use in the TOPEX/POSEIDON gravity field modeling program.

1987-01-01

288

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:? Describe the conditions that would lead an object into orbital motion in terms of the effects of gravitational force.? Explain how an object orbits a planet in terms of trajectories and free fall.? 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

289

In the Riemann geometry, the metric's equation of motion for an arbitrary Lagrangian is succinctly expressed in term of the first variation of the action with respect to the Riemann tensor if the Riemann tensor were independent of the metric. Let this variation be called the E-tensor. Noting that the E-tensor and equations of the motion for a general Lovelock gravity have the same differential degree, we define generalized Lovelock gravity as polynomial scalar densities constructed out from the Riemann tensor and its arbitrary covariant derivatives such that they lead to the same differential degree for the E-tensor and the metric's equation of motion. We consider Lagrangian densities which are functional of the metric and the first covariant derivative of the Riemann tensor. We then present the first non-trivial examples of the generalized Lovelock gravity terms.

Qasem Exirifard

2010-06-30

290

Quantum quench across a zero temperature holographic superfluid transition

NASA Astrophysics Data System (ADS)

We study quantum quench in a holographic model of a zero temperature insulator-superfluid transition. The model is a modification of that of arXiv:0911.0962 and involves a self-coupled complex scalar field, Einstein gravity with a negative cosmological constant, and Maxwell field with one of the spatial directions compact. In a suitable regime of parameters, the scalar field can be treated as a probe field whose backreaction to both the metric and the gauge field can be ignored. We show that when the chemical potential of the dual field theory lies between two critical values, the equilibrium background geometry is an AdS soliton with a constant gauge field, while the complex scalar condenses leading to broken symmetry. We then turn on a time dependent source for the order parameter which interpolates between constant values and crosses the order-disorder critical point. In the critical region adiabaticity breaks down, but for a small rate of change of the source v there is a new small- v expansion in fractional powers of v. The resulting critical dynamics is dominated by a zero mode of the bulk field. To lowest order in this small- v expansion, the order parameter satisfies a time dependent Landau-Ginsburg equation which has z = 2, but non-dissipative. These predictions are verified by explicit numerical solutions of the bulk equations of motion.

Basu, Pallab; Das, Diptarka; Das, Sumit R.; Nishioka, Tatsuma

2013-03-01

291

External Resource: Gravity Assist Simulator

NSDL National Science Digital Library

A Messenger Education site to explore gravity assist maneuvers, interaction with gravity, and the idea of a collision, to understand the effects of that interaction. Students explore the simulated encounters of spacecraft and planets to answer the questio

1900-01-01

292

Physiological Considerations of Artificial Gravity

NASA Technical Reports Server (NTRS)

Reasons for the development of artificial gravity environments on spacecraft are outlined. The physiological effects of weightlessness on the human cardiovascular skeletal, and vestibular systems are enumerated. Design options for creating artificial gravity environments are shown.

Cramer, D. B.

1985-01-01

293

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

294

The zero-divisor graphs of semirings

In this paper we study zero-divisor graphs of semirings. We show that all zero-divisor graphs of (possibly noncommutative) semirings are connected and have diameter less than or equal to 3. We characterize all acyclic zero-divisor graphs of semirings and prove that in the case zero-divisor graphs are cyclic, their girths are less than or equal to 4. We also give a description of the zero-divisor graphs over commutative semirings with girth equal to 4 and the ones with girth equal to 3 and only one 3-cycle. Moreover, we characterize all additively cancellative semirings and all rings such that their zero-divisor graph has exactly one 3-cycle.

Dolžan, David

2010-01-01

295

The method of characteristics is a key tool for studying consistency of equations of motion; it allows issues such as predictability, maximal propagation speed, superluminality, unitarity and acausality to be addressed without requiring explicit solutions. We review this method and its application to massive gravity theories to show the limitations of these models' physical viability: Among their problems are loss of unique evolution, superluminal signals, matter coupling inconsistencies and micro-acausality (propagation of signals around local closed timelike/causal curves). We extend previous no-go results to the entire three-parameter range of massive gravity theories. It is also argued that bimetric models suffer a similar fate.

Deser, S; Ong, Y C; Waldron, A

2014-01-01

296

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 resum 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. PMID:21770493

de Rham, Claudia; Gabadadze, Gregory; Tolley, Andrew J

2011-06-10

297

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

298

Consistency of Semiclassical Gravity

We discuss some subtleties which arise in the semiclassical approximation to quantum gravity. We show that integrability conditions prevent the existence of Tomonaga-Schwinger time functions on the space of three-metrics but admit them on superspace. The concept of semiclassical time is carefully examined. We point out that central charges in the matter sector spoil the consistency of the semiclassical approximation unless the full quantum theory of gravity and matter is anomaly-free. We finally discuss consequences of these considerations for quantum field theory in flat spacetime, but with arbitrary foliations.

D. Giulini; C. Kiefer

1994-09-08

299

Loop quantum gravity and observations

Quantum gravity has long been thought to be completely decoupled from experiments or observations. Although it is true that smoking guns are still missing, there are now serious hopes that quantum gravity phenomena might be tested. We review here some possible ways to observe loop quantum gravity effects either in the framework of cosmology or in astroparticle physics.

A. Barrau; J. Grain

2014-10-07

300

Gravity Recovery and Climate Experiment

NSDL National Science Digital Library

The Gravity Recovery and Climate Experiment (GRACE) mission uses twin satellites to make detailed measurements of Earth's gravity field. GRACE materials include a description of the mission, research projects, and personnel. There are also links to news articles, publications, datasets, and software tools for processing gravity data.

301

Mars - Hellas Planitia gravity analysis

Doppler radio tracking data from Viking Orbiter 1 has provided new detailed observations of gravity variations over Hellas Planitia. Line-of-sight Bouguer gravity definitely indicates that isostatic adjustment has occurred. Two theoretical models were tested to obtain fits to the gravity data. Results for a surface deficit model, and a model with a surface deficit and a mass excess at depth

W. L. Sjogren; R. N. Wimberley

1981-01-01

302

Physiological Considerations of Artificial Gravity

NASA Technical Reports Server (NTRS)

Weightlessness produces significant physiological changes. Whether these changes will stabilize or achieve medical significance is not clear. Artificial gravity is the physiological countermeasure, and the tether system represents an attractive approach to artificial gravity. The need for artificial gravity is examined.

Cramer, D. B.

1985-01-01

303

NASA Net Zero Energy Buildings Roadmap

In preparation for the time-phased net zero energy requirement for new federal buildings starting in 2020, set forth in Executive Order 13514, NASA requested that the National Renewable Energy Laboratory (NREL) to develop a roadmap for NASA's compliance. NASA detailed a Statement of Work that requested information on strategic, organizational, and tactical aspects of net zero energy buildings. In response, this document presents a high-level approach to net zero energy planning, design, construction, and operations, based on NREL's first-hand experience procuring net zero energy construction, and based on NREL and other industry research on net zero energy feasibility. The strategic approach to net zero energy starts with an interpretation of the executive order language relating to net zero energy. Specifically, this roadmap defines a net zero energy acquisition process as one that sets an aggressive energy use intensity goal for the building in project planning, meets the reduced demand goal through energy efficiency strategies and technologies, then adds renewable energy in a prioritized manner, using building-associated, emission- free sources first, to offset the annual energy use required at the building; the net zero energy process extends through the life of the building, requiring a balance of energy use and production in each calendar year.

Pless, S.; Scheib, J.; Torcellini, P.; Hendron, B.; Slovensky, M.

2014-10-01

304

Chern--Simons Gravity from 3+1 Dimensional Gravity

In the context of a Poincar\\'e gauge theoretical formulation, pure gravity in 3+1-dimensions is dimensionally reduced to gravity in 2+1-dimensions with or without cosmological constant $\\Lambda$. The dimensional reductions are consistent with the gauge symmetries, mapping ISO(3, 1) gauge transformations into ISO(2,1) ones. One of the reductions leads to Chern-Simons-Witten gravity. The solutions of 2+1-gravity with $\\Lambda\\le 0$ (in particular the black-hole solution recently found by Banados, Teitelboim and Zanelli) and those of 1+1-dimensional Liouville gravity, are thus mapped into 3+1-dimensional vacuum solutions.

G. Grignani; G. Nardelli

1992-11-09

305

Zero Degree Calorimeter for CMS

NASA Astrophysics Data System (ADS)

In 2007 the Large Hadron Collider (LHC) at CERN in Geneva will start to collide protons and lead ions together at extremely high energies. The purpose of the proton-proton running is to study the origin of mass. The purpose of the ion running is to recreate the first few moments of the universe. The Compact Muon Solenoid, or CMS, is one of the experiments at LHC. I am currently working with the Nuclear Physics Team at the University of Kansas on part of CMS, called the Zero Degree Calorimeter (ZDC). I use a simulation toolkit, Geant4, which uses the object-oriented nature of C++ code to allow users to build simulations of particle collisions. Neutrons hit the ZDC and collide with tungsten plates to produce a shower of particles. The ZDC uses tungsten plates to change the neutrons into charged particles, and optical fibers to gather Cerenkov photons that are created. The current goal is to convert as much energy that comes into the ZDC as possible into light energy, and determine the most effective design for the calorimeter. I will present estimates of the ZDC performance for both proton-proton and heavy ion running.

Lehnherr, Megan

2004-10-01

306

Gravity Waves Appearing in a High-Resolution GCM Simulation.

NASA Astrophysics Data System (ADS)

Global characteristics of gravity waves in the lower stratosphere are examined using a GCM with high resolution in both the horizontal (T106, corresponding to about 120 km) and the vertical (600 m). The bottom boundary condition of the model is that of an aquaplanet with perpetual February sea surface temperature. The simulated gravity waves are in good agreement with mesosphere-stratosphere-troposphere (MST) radar observations at a middle latitude on the gravity wave structure and on the frequency spectra as a function of height. The frequency spectra of simulated wind and temperature fluctuations are also examined as a function of latitude. Large values of spectral density are observed at frequencies higher than the inertial frequency (f) in a weak wind region around 20 km, which is consistent with the characteristics of internal gravity waves. An isolated peak is observed near f for horizontal wind spectra at latitudes higher than 10°, while the energy is distributed in a wide range of frequency at lower latitudes where f approaches zero.Further analysis is performed of those fluctuations having periods shorter than 24 h and those having vertical wavelengths smaller than 5 km. These are frequently analyzed as gravity waves using observation data. The distribution of energy and momentum fluxes in the latitude-height section is examined. The result indicates that short-period waves mostly propagate upward and poleward from the equatorial region. The wave energy reaches about 50° lat at the 27-km altitude. A negative (positive) maximum of vertical flux of meridional momentum () is seen above the subtropical jet in the Northern (Southern) Hemisphere for small vertical-scale gravity waves. This is consistent with the preferred equatorward propagation of the wave indicated by a statistical analysis based on MST radar observations. The ratio of potential to kinetic energy maximizes over the equator and decreases poleward. The Eliassen-Palm flux divergence associated with gravity waves is decelerative above the subtropical jet, albeit small.

Sato, Kaoru; Kumakura, Toshiro; Takahashi, Masaaki

1999-04-01

307

It is shown that the Newtonian limit of a stable realization of HD gravity leads to a sharp transition, around 10^{11} proton masses, from the wavelike properties of microscopic particles to the classical behaviour of macroscopic bodies. Besides, due to nonunitarity, a pure state is expected to evolve into a microcanonical ensamble leading to thermal equilibrium even for truly closed systems.

Filippo Maimone; Sergio De Filippo

2002-07-17

308

Quantum Gravity and Turbulence

We apply recent advances in quantum gravity to the problem of turbulence. Adopting the AdS/CFT approach we propose a string theory of turbulence that explains the Kolmogorov scaling in 3+1 dimensions and the Kraichnan and Kolmogorov scalings in 2+1 dimensions. In the gravitational context, turbulence is intimately related to the properties of spacetime, or quantum, foam.

Vishnu Jejjala; Djordje Minic; Y. Jack Ng; Chia-Hsiung Tze

2010-05-18

309

In this article we construct a massive theory of gravity that is invariant under conformal transformations. The massive action of the theory depend on the metric tensor and a scalar field, which are considered as the only field variables. We find the vacuum field equations of the theory and the solution of its Newtonian limit.

F. F. Faria

2013-12-19

310

Acausality of massive gravity.

We show, by analyzing its characteristics, that the ghost-free, 5 degree of freedom, Wess-Zumino massive gravity model admits superluminal shock wave solutions and thus is acausal. Ironically, this pathology arises from the very constraint that removes the (sixth) Boulware-Deser ghost mode. PMID:25166520

Deser, S; Waldron, A

2013-03-15

311

Large-distance modification of gravity may be the mechanism for solving the cosmological constant problem. A simple model of the large-distance modification -- four-dimensional (4D) gravity with the hard mass term-- is problematic from the theoretical standpoint. Here we discuss a different model, the brane-induced gravity, that effectively introduces a soft graviton mass. We study the issues of unitarity, analyticity and causality in this model in more than five dimensions. We show that a consistent prescription for the poles of the Green's function can be specified so that 4D unitarity is preserved. However, in certain instances 4D analyticity cannot be maintained when theory becomes higher dimensional. As a result, one has to sacrifice 4D causality at distances of the order of the present-day Hubble scale. This is a welcome feature for solving the cosmological constant problem, as was recently argued in the literature. We also show that, unlike the 4D massive gravity, the model has no strong-coupling problem at intermediate scales.

G. Gabadadze; M. Shifman

2003-12-24

312

External Resource: Different Gravity

NSDL National Science Digital Library

This article from NASA's Suited for Spacewalking An Activity Guide for Technology Education explains that gravity is an attractive force that all objects have for one another. It doesn't matter whether the object is a planet, a cannon ball, a feather, or

1900-01-01

313

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

Michael Horton

2009-05-30

314

Artificial Gravity Research Plan

NASA Technical Reports Server (NTRS)

This document describes the forward working plan to identify what countermeasure resources are needed for a vehicle with an artificial gravity module (intermittent centrifugation) and what Countermeasure Resources are needed for a rotating transit vehicle (continuous centrifugation) to minimize the effects of microgravity to Mars Exploration crewmembers.

Cromwell, Ronita

2014-01-01

315

Venus - Ishtar gravity anomaly

NASA Technical Reports Server (NTRS)

The gravity anomaly associated with Ishtar Terra on Venus is characterized, comparing line-of-sight acceleration profiles derived by differentiating Pioneer Venus Orbiter Doppler residual profiles with an Airy-compensated topographic model. The results are presented in graphs and maps, confirming the preliminary findings of Phillips et al. (1979). The isostatic compensation depth is found to be 150 + or - 30 km.

Sjogren, W. L.; Bills, B. G.; Mottinger, N. A.

1984-01-01

316

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

317

Spaceborne Gravity Gradiometers

NASA Technical Reports Server (NTRS)

The current status of gravity gradiometers and technology that could be available in the 1990's for the GRAVSAT-B mission are assessed. Problems associated with sensors, testing, spacecraft, and data processing are explored as well as critical steps, schedule, and cost factors in the development plan.

Wells, W. C. (editor)

1984-01-01

318

Gravity actuated thermal motor

The invention discloses a gravity actuated thermal motor which includes a rotor preferably in the form of a ring-shaped annulus which is filled with water. A plurality of collapsible bellows are connected to and extend inwardly from the outer peripheral wall of the annulus into the water-filled chamber. In communication with each of the bellows and extending outwardly from the

Schur

1978-01-01

319

Phenomenological Quantum Gravity

Planck scale physics represents a future challenge, located between particle physics and general relativity. The Planck scale marks a threshold beyond which the old description of spacetime breaks down and conceptually new phenomena must appear. In the last years, increased efforts have been made to examine the phenomenology of quantum gravity, even if the full theory is still unknown.

S. Hossenfelder

2006-11-01

320

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

321

Variable gravity research facility

NASA Technical Reports Server (NTRS)

Spin and despin requirements; sequence of activities required to assemble the Variable Gravity Research Facility (VGRF); power systems technology; life support; thermal control systems; emergencies; communication systems; space station applications; experimental activities; computer modeling and simulation of tether vibration; cost analysis; configuration of the crew compartments; and tether lengths and rotation speeds are discussed.

Allan, Sean; Ancheta, Stan; Beine, Donna; Cink, Brian; Eagon, Mark; Eckstein, Brett; Luhman, Dan; Mccowan, Daniel; Nations, James; Nordtvedt, Todd

1988-01-01

322

NASA Astrophysics Data System (ADS)

In this paper we examine a small but detailed test of the emergent gravity picture with explicit solutions in gravity and gauge theory. We first derive symplectic U(1) gauge fields starting from the Eguchi-Hanson metric in four-dimensional Euclidean gravity. The result precisely reproduces the U(1) gauge fields of the Nekrasov-Schwarz instanton previously derived from the top-down approach. In order to clarify the role of noncommutative spacetime, we take the Braden-Nekrasov U(1) instanton defined in ordinary commutative spacetime and derive a corresponding gravitational metric. We show that the Kähler manifold determined by the Braden-Nekrasov instanton exhibits a spacetime singularity while the Nekrasov-Schwarz instanton gives rise to a regular geometry—the Eguchi-Hanson space. This result implies that the noncommutativity of spacetime plays an important role for the resolution of spacetime singularities in general relativity. We also discuss how the topological invariants associated with noncommutative U(1) instantons are related to those of emergent four-dimensional Riemannian manifolds according to the emergent gravity picture.

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

2013-10-01

323

A unified approach to ZMP and gravity center control in biped dynamic stable walking

Summary form only given. In this paper, to realize dynamic stable walking, a novel control strategy is formulated, which is based on both the centre of gravity (COG) and the zero moment point (ZMP) of the biped supporting leg control. This control algorithm involves the following two stages: 1) trajectory generation of the ZMP for the realization of the arbitrary

K. Sorao; T. Murakami; K. Ohnishi

1997-01-01

324

Gravity recovery using COSMIC GPS data: application of orbital perturbation theory

Â®eld clearly shows the gravity signature due to mass movement in an El Ni~no. Key words: COSMIC Â± GPSGravity recovery using COSMIC GPS data: application of orbital perturbation theory C. Hwang, along-track, and cross- track perturbations, which are more accurate than the commonly used order-zero

Hwang, Cheinway

325

Industrial processes influenced by gravity

NASA Technical Reports Server (NTRS)

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, and biotech industries. Relatively little attention has been given to the role of gravity in such processes. Accordingly, numerous industrial processes and phenomena are identified which involve gravity and/or surface tension forces. Phase separations and mixing are examples that will be significantly different in low gravity conditions. A basis is presented for expanding the scope of the low gravity research program and the potential benefits of such research is indicated.

Ostrach, Simon

1988-01-01

326

Cosmic Expansion in Extended Quasidilaton Massive Gravity

Quasidilaton massive gravity offers a physically well-defined gravitational theory with non-zero graviton mass. We present the full set of dynamical equations governing the expansion history of the universe, valid during radiation domination, matter domination, and a late-time self-accelerating epoch related to the graviton mass. The existence of self-consistent solutions constrains the amplitude of the quasi-dilaton field and the graviton mass, as well as other model parameters. We point out that the effective mass of gravitational waves can be significantly larger than the graviton mass, opening the possibility that a single theory can explain both the late-time acceleration of the cosmic expansion and modifications of structure growth leading to the suppression of large-angle correlations observed in the cosmic microwave background.

Kahniashvili, Tina; Lavrelashvili, George; Agarwal, Nishant; Heisenberg, Lavinia; Kosowsky, Arthur

2014-01-01

327

Black hole remnant from gravity's rainbow

NASA Astrophysics Data System (ADS)

In this work, we investigate black hole (BH) physics in the context of the gravity rainbow. We investigate this through rainbow functions that have been proposed by Amelino-Camelia [Living Rev. Relativity 16, 5 (2013)] and Amelino-Camelia et al. in [Int. J. Mod. Phys. A 12, 607 (1997)]. This modification will give corrections to both the temperature and the entropy of BHs, and hence it changes the picture of Hawking radiation greatly when the size of the BH approaches the Planck scale. It prevents the BH from total evaporation, predicting the existence of a BH remnant, which may resolve the catastrophic behavior of Hawking radiation as the BH mass approaches zero.

Farag Ali, Ahmed

2014-05-01

328

Black-hole thermodynamics in Lovelock gravity

The thermodynamic properties of black holes in Lovelock gravity are examined. In particular, the case of the Einstein Lagrangian plus the four-dimensional Euler density is discussed in detail. In five dimensions, one finds that the specific heat of a black hole becomes positive at small mass, allowing the black hole to achieve stable equilibrium with its environment and giving it an infinite lifetime. This behavior is not universal, however, but it always occurs in 2k+1 dimensions for a Lovelock theory including the 2k-dimensional Euler density. For theories including six-derivative or higher-order interactions, black holes with degenerate zero-temperature horizons are also possible.

Myers, R.C.; Simon, J.Z.

1988-10-15

329

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

330

Gravitational Zero Point Energy induces Physical Observables

We consider the contribution of Zero Point Energy on the induced Cosmological Constant and on the induced Electric\\/Magnetic charge in absence of matter fields. The method is applicable to every spherically symmetric background. Extensions to a generic $f(R) $ theory are also allowed. Only the graviton appears to be fundamental to the determination of Zero Point Energy.

Remo Garattini; Viale Marconi

2010-01-01

331

Computing the Real Zeros of Hypergeometric Functions

Efficient methods for the computation of the real zeros of hypergeometric functions which are solutions of second order ODEs are described. These methods are based on global fixed point iterations which apply to families of functions satisfying first order linear difference differential equations with continuous coefficients. In order to compute the zeros of arbitrary solutions of the hypergeometric equations, we

Amparo Gil; Wolfram Koepf; Javier Segura

2004-01-01

332

Chaotic temperature dependence at zero temperature.

Chaotic temperature dependence at zero temperature. A.C.D. van Enter Center for Theoretical Physics; Abstract We present a class of examples of nearestÂneighbour, boundedÂspin models, in which the lowÂtemperature Gibbs measures do not converge as the temperature is lowered to zero, in any dimension. 1 Introduction

333

Introduction to the concepts of Zero Balancing

This paper presents the theoretical basis for Zero Balancing, a bodywork modality that claims to balance energy and structure within the body. Energy is perceived as anything that is relatively mobile, whilst structure is that which is relatively stable. The relationship between these two is part of everyday life. The practice of Zero Balancing is also discussed. Focussing on the

Pam Geggus

2004-01-01

334

Moving requires handling gravitational and inertial constraints pulling on our body and on the objects that we manipulate. Although previous work emphasized that the brain uses internal models of each type of mechanical load, little is known about their interaction during motor planning and execution. In this report, we examine visually guided reaching movements in the horizontal plane performed by naive participants exposed to changes in gravity during parabolic flight. This approach allowed us to isolate the effect of gravity because the environmental dynamics along the horizontal axis remained unchanged. We show that gravity has a direct effect on movement kinematics, with faster movements observed after transitions from normal gravity to hypergravity (1.8g), followed by significant movement slowing after the transition from hypergravity to zero gravity. We recorded finger forces applied on an object held in precision grip and found that the coupling between grip force and inertial loads displayed a similar effect, with an increase in grip force modulation gain under hypergravity followed by a reduction of modulation gain after entering the zero-gravity environment. We present a computational model to illustrate that these effects are compatible with the hypothesis that participants partially attribute changes in weight to changes in mass and scale incorrectly their motor commands with changes in gravity. These results highlight a rather direct internal mapping between the force generated during stationary holding against gravity and the estimation of inertial loads that limb and hand motor commands must overcome. PMID:24790173

Crevecoeur, F; McIntyre, J; Thonnard, J-L; Lefèvre, P

2014-07-15

335

Hydrodynamic Limit of Mean Zero Condensing Zero Range Processes with Sub-Critical Initial Profiles

NASA Astrophysics Data System (ADS)

Condensing zero range processes are interacting particle systems with zero range interaction exhibiting phase separation at densities above a finite critical density. We prove the hydrodynamic limit of mean zero condensing zero range processes with bounded local jump rate for sub-critical initial profiles, i.e. for initial profiles that are everywhere strictly below the critical density. The proof is based on H.T. Yau's relative entropy method and is made possible by a generalisation of the one block estimate.

Stamatakis, Marios Georgios

2015-01-01

336

Experimental Observation of Lee-Yang Zeros

NASA Astrophysics Data System (ADS)

Lee-Yang zeros are points on the complex plane of physical parameters where the partition function of a system vanishes and hence the free energy diverges. Lee-Yang zeros are ubiquitous in many-body systems and fully characterize their thermodynamics. Notwithstanding their fundamental importance, Lee-Yang zeros have never been observed in experiments, due to the intrinsic difficulty that they would occur only at complex values of physical parameters, which are generally regarded as unphysical. Here we report the first observation of Lee-Yang zeros, by measuring quantum coherence of a probe spin coupled to an Ising-type spin bath. The quantum evolution of the probe spin introduces a complex phase factor and therefore effectively realizes an imaginary magnetic field. From the measured Lee-Yang zeros, we reconstructed the free energy of the spin bath and determined its phase transition temperature. This experiment opens up new opportunities of studying thermodynamics in the complex plane.

Peng, Xinhua; Zhou, Hui; Wei, Bo-Bo; Cui, Jiangyu; Du, Jiangfeng; Liu, Ren-Bao

2015-01-01

337

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

338

Visual analysis of flow boiling at different gravity levels in 4.0 mm tube

NASA Astrophysics Data System (ADS)

The aim of the present paper is to describe the results of flow boiling heat transfer at low gravity and compare them with those obtained at earth gravity, evaluating possible differences. The experimental campaigns at low gravity have been performed during the parabolic flight campaign of October-November 2013. The paper will show the analysis of differences between the heat transfer coefficients and vapour bubble parameters at normal and at zero gravity. The results of 4.0 mm tube are presented and discussed. With respect to terrestrial gravity, heat transfer is systematically lower at microgravity in the range of the experimental conditions. Heat transfer differences for the two gravity conditions are related to the different bubble size in each of them. The size of a bubble in flow boiling is affected by the gravity level, being larger at low gravity, unless inertial forces are largely predominant over buoyancy and other forces acting on the bubble itself when detaching from a heated wall. Vapour bubble parameters (bubble diameter, bubble length, width, and nose velocity) have been measured.

Valencia-Castillo, C. M.; Celata, G. P.; Saraceno, L.; Zummo, G.

2014-11-01

339

Spherically symmetric spacetimes in massive gravity

We explore spherically symmetric stationary solutions, generated by ``stars'' with regular interiors, in purely massive gravity. We reexamine the claim that the resummation of non-linear effects can cure, in a domain near the source, the discontinuity exhibited by the linearized theory as the mass m of the graviton tends to zero. First, we find analytical difficulties with this claim, which appears not to be robust under slight changes in the form of the mass term. Second, by numerically exploring the inward continuation of the class of asymptotically flat solutions, we find that, when m is ``small'', they all end up in a singularity at a finite radius, well outside the source, instead of joining some conjectured ``continuous'' solution near the source. We reopen, however, the possibility of reconciling massive gravity with phenomenology by exhibiting a special class of solutions, with ``spontaneous symmetry breaking'' features, which are close, near the source, to general relativistic solutions and asymptote, for large radii, a de Sitter solution of curvature ~m^2.

Thibault Damour; Ian I. Kogan; Antonios Papazoglou

2002-12-13

340

Nonlinear Properties of Vielbein Massive Gravity

We propose a non-linear extension of the Fierz-Pauli mass for the graviton through a functional of the vielbein and an external Minkowski background. The functional generalizes the notion of the measure, since it reduces to a cosmological constant if the external background is formally sent to zero. Such a term and the explicit external background, emerge dynamically from a bi--gravity theory, having both a massless and a massive graviton in its spectrum, in a specific limit in which the massless mode decouples, while the massive one couples universally to matter. We investigate the massive theory using the Stueckelberg method and providing a 't Hooft-Feynman gauge fixing in which the tensor, vector and scalar Stueckelberg fields decouple. We show that this model has the softest possible ultraviolet behavior which can be expected from any generic (Lorentz invariant) theory of massive gravity, namely that it becomes strong only at the scale Lambda_3 = (m_g^2 M_P)^{1/3}.

Stefan Groot Nibbelink; Marco Peloso; Matthew Sexton

2006-10-15

341

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

342

Locomotion in simulated microgravity: gravity replacement loads

NASA Technical Reports Server (NTRS)

BACKGROUND: When an astronaut walks or runs on a treadmill in microgravity, a subject load device (SLD) is used to return him or her back to the treadmill belt. The gravity replacement load (GRL) in the SLD is transferred, via a harness, to the pelvis and/or the shoulders. This research compared comfort and ground reaction forces during treadmill running in a microgravity locomotion simulator at GRLs of 60%, 80%, and 100% of body weight (BW). Two harness designs (shoulder springs only (SSO) and waist and shoulder springs (WSS)) were used. HYPOTHESES: 1) The 100% BW gravity replacement load conditions would be comfortably tolerated and would result in larger ground reaction forces and loading rates than the lower load conditions, and 2) the WSS harness would be more comfortable than the SSO harness. METHODS: Using the Penn State Zero Gravity Locomotion Simulator (ZLS), 8 subjects ran at 2.0 m x s(-1) (4.5 mph) for 3 min at each GRL setting in each harness. Subjective ratings of harness comfort, ground reaction forces, and GRL data were collected during the final minute of exercise. RESULTS: The 100% BW loading conditions were comfortably tolerated (2.3 on a scale of 0-10), although discomfort increased as the GRL increased. There were no overall differences in perceived comfort between the two harnesses. The loading rates (27.1, 33.8, 39.1 BW x s(-1)) and the magnitudes of the first (1.0, 1.4, 1.6 BW) and second (1.3, 1.7, 1.9 BW) peaks of the ground reaction force increased with increasing levels (60, 80, 100% BW respectively) of GRL. CONCLUSIONS: Subjects were able to tolerate a GRL of 100% BW well. The magnitude of the ground reaction force peaks and the loading rate is directly related to the magnitude of the GRL.

McCrory, Jean L.; Baron, Heidi A.; Balkin, Sandy; Cavanagh, Peter R.

2002-01-01

343

NASA Technical Reports Server (NTRS)

An account is given of the method by which the 'energy gain' accruing to a spacecraft as a result of its 'gravity-assist', parabolic-trajectory flyby of a massive body, such as a planet. The procedure begins with the solution of the two-body portion of the problem, and the results thus obtained are used to calculate changes with respect to the other massive body in the overall scenario, namely the sun. Attention is given to the 'vector diagram' often used to display the gravity-assist effect. The present procedure is noted to be reasonably accurate for flybys in which the plane of the spacecraft's trajectory is approximately the same as that of the planet's orbit around the sun, or the ecliptic plane; this reduces the problem to one in two dimensions.

Cesarone, R. J.

1989-01-01

344

NASA Technical Reports Server (NTRS)

This review of plant gravity sensing examines sensing in organ gravitropism, sensing in single-cell gravitropism, and nongravitropic sensing. Topics related to sensing in organ gravitropism are (1) identification of the gravitropic susceptors, including intracellular asymmetry in equilibrium position and after reorientation, susceptor signal-to-noise ratio, signal integration over threshold stimulation periods, intracellular asymmetry and gravitropic competence, and starch deficiency and gravitropic competence; (2) possible root statocytes and receptors, including identification of presumptive statocytes, cytology, and possible receptors and models of sensing; and (3) negatively gravitropic organs, including identification and distribution of presumptive statocytes and cytology and possible receptors. Topics related to nongravitropic sensing include gravitaxis, reaction wood, gravimorphogenesis, other gravity-influenced organ movements, and cytoplasmic streaming.

Sack, F. D.

1991-01-01

345

Gravity wave initiated convection

NASA Technical Reports Server (NTRS)

The vertical velocity of convection initiated by gravity waves was investigated. In one particular case, the convective motion-initiated and supported by the gravity wave-induced activity (excluding contributions made by other mechanisms) reached its maximum value about one hour before the production of the funnel clouds. In another case, both rawinsonde and geosynchronous satellite imagery were used to study the life cycles of severe convective storms. Cloud modelling with input sounding data and rapid-scan imagery from GOES were used to investigate storm cloud formation, development and dissipation in terms of growth and collapse of cloud tops, as well as, the life cycles of the penetration of overshooting turrets above the tropopause. The results based on these two approaches are presented and discussed.

Hung, R. J.

1990-01-01

346

NASA Astrophysics Data System (ADS)

We present in this paper the design and characterisation of a new sub-system of the VLTI 2nd generation instrument GRAVITY: the Calibration Unit. The Calibration Unit provides all functions to test and calibrate the beam combiner instrument: it creates two artificial stars on four beams, and dispose of four delay lines with an internal metrology. It also includes artificial stars for the tip-tilt and pupil guiding systems, as well as four metrology pick-up diodes, for tests and calibration of the corresponding sub-systems. The calibration unit also hosts the reference targets to align GRAVITY to the VLTI, and the safety shutters to avoid the metrology light to propagate in the VLTI-lab. We present the results of the characterisation and validtion of these differrent sub-units.

Blind, N.; Eisenhauer, F.; Haug, M.; Gillessen, S.; Lippa, Magdalena; Burtscher, L.; Hans, O.; Haussmann, F.; Huber, S.; Janssen, A.; Kellner, S.; Kok, Y.; Ott, T.; Pfuhl, O.; Sturm, E.; Weber, J.; Wieprecht, E.; Amorim, A.; Brandner, W.; Perrin, G.; Perraut, K.; Straubmeier, C.

2014-07-01

347

NASA Astrophysics Data System (ADS)

The Wheeler-DeWitt equation in quantum gravity is timeless in character. In order to discuss quantum to classical transition of the universe, one uses a time prescription in quantum gravity to obtain a time contained description starting from Wheeler-DeWitt equation and WKB ansatz for the WD wavefunction. The approach has some drawbacks. In this work, we obtain the time-contained Schrödinger-Wheeler-DeWitt equation without using the WD equation and the WKB ansatz for the wavefunction. We further show that a Gaussian ansatz for SWD wavefunction is consistent with the Hartle-Hawking or wormhole dominance proposal boundary condition. We thus find an answer to the small scale boundary conditions.

Biswas, S.; Shaw, A.; Modak, B.; Dolgov, A.

348

An inverse dynamic analysis on the influence of upper limb gravity compensation during reaching.

Muscular dystrophies (MDs) are characterized by progressive muscle wasting and weakness. Several studies have been conducted to investigate the influence of arm supports in an attempt to restore arm function. Lowering the load allows the user to employ the residual muscle force for movement as well as for posture stabilization. In this pilot study three conditions were investigated during a reaching task performed by three healthy subjects and three MD subjects: a control condition involving reaching; a similar movement with gravity compensation using braces to support the forearm; an identical reaching movement in simulated zero-gravity. In the control condition the highest values of shoulder moments were present, with a maximum of about 6 Nm for shoulder flexion and abduction. In the gravity compensation and zero gravity conditions the maximum shoulder moments were decreased by more than 70% and instead of increasing during reaching, they remained almost unvaried, fluctuating around an offset value less than 1 Nm. Similarly, the elbow moments in the control condition were the highest with a peak around 3.3 Nm for elbow flexion, while the moments were substantially reduced in the remaining two conditions, fluctuating around offset values between 0 to 0.5 Nm. In conclusion, gravity compensation by lower arm support is effective in healthy subjects and MD subjects and lowers the amount of shoulder and elbow moments by an amount comparable to a zero gravity environment. However the influence of gravity compensation still needs to be investigated on more people with MDs in order to quantify any beneficial effect on this population. PMID:24187187

Essers, J M N Hans; Meijer, Kenneth; Murgia, Alessio; Bergsma, Arjen; Verstegen, Paul

2013-06-01

349

In the context of Lorentz-invariant massive gravity we show that classical solutions around heavy sources are plagued by ghost instabilities. The ghost shows up in the effective field theory at huge distances from the source, much bigger than the Vainshtein radius. Its presence is independent of the choice of the non-linear terms added to the Fierz-Pauli lagrangian. At the Vainshtein

Paolo Creminelli; Alberto Nicolis; Michele Papucci; Enrico Trincherini

2005-01-01

350

Resummation of Massive Gravity

We construct four-dimensional covariant non-linear theories of massive\\u000agravity which are ghost-free in the decoupling limit to all orders. These\\u000atheories resum explicitly all the nonlinear terms of an effective field theory\\u000aof massive gravity. We show that away from the decoupling limit the Hamiltonian\\u000aconstraint is maintained at least up to and including quartic order in\\u000anon-linearities, hence, excluding

Claudia de Rham; Gregory Gabadadze; Andrew J. Tolley

2010-01-01

351

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

352

Gravity, Dimension, Equilibrium, & Thermodynamics

Is it actually possible to interpret gravitation as space's property in a pure classical way. Then, we note that extended self-gravitating system equilibrium depends directly on the number of dimension of the space in which it evolves. Given those precisions, we review the principal thermodynamical knowledge in the context of classical gravity with arbitrary dimension of space. Stability analyses for bounded 3D systems, namely the Antonov instability paradigm, are then rapproched to some amazing properties of globular clusters and galaxies.

Jerome Perez

2006-03-30

353

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

354

Artificial gravity Mars spaceship

NASA Technical Reports Server (NTRS)

Experience gained in the study of artificial gravity for a manned trip to Mars is reviewed, and a snowflake-configured interplanetary vehicle cluster of habitat modules, descent vehicles, and propulsion systems is presented. An evolutionary design is described which permits sequential upgrading from five to nine crew members, an increase of landers from one to as many a three per mission, and an orderly, phased incorporation of advanced technologies as they become available.

Clark, Benton C.

1989-01-01

355

NASA Astrophysics Data System (ADS)

Friedman and Sorkin have observed that the total angular momentum of an asymptotically flat, vacuum, quantum gravitational field in 3+1 dimensions need not be integral. We pursue this idea in the context of asymptotically flat 2+1 gravity, which is an exactly solvable model. We find that, for nontrivial spatial topologies, the quantized pure gravitational field has states of fractional spin. These states are dynamically allowed, in the sense that they solve all the constraints of the theory.

Samuel, Joseph

1993-07-01

356

A bulk viscosity is introduced in the formalism of modified gravity. It is shown that, on the basis of a natural scaling law for the viscosity, a simple solution can be found for quantities such as the Hubble parameter and the energy density. These solutions may incorporate a viscosity-induced Big Rip singularity. By introducing a phase transition in the cosmic fluid, the future singularity can nevertheless in principle be avoided.

Iver Brevik

2012-11-23

357

In view of the enormous difficulties we seem to face in quantizing general relativity, we should perhaps consider the possibility that gravity is a fundamentally classical interaction. Theoretical arguments against such mixed classical-quantum models are strong, but not conclusive, and the question is ultimately one for experiment. I review some work in progress on the possibility of experimental tests, exploiting the nonlinearity of the classical-quantum coupling, that could help settle this question.

S. Carlip

2008-03-24

358

NSDL National Science Digital Library

This fun and simple hands-on astronomy activity lets learners experiment with a bucket, stretchy fabric, marbles, and weights to discover some basics about gravity. Learners will explore how mass curves space, how an object with more mass will curve more space, why things fall to Earth, and why all objects, regardless of their mass, will fall at the same rate into the same massive object. The pdf contains step-by-step instructions, photos, presentation tips, and links to background information.

Pacific, Astronomical S.

2008-01-01

359

Massive Gravity from Higher Derivative Gravity with Boundary Conditions

With an appropriate choice of parameters, a higher derivative theory of gravity can describe a normal massive sector and a ghost massless sector. We show that, when defined on an asymptotically de Sitter spacetime with Dirichlet boundary conditions, such a higher derivative gravity can provide a framework for a unitary theory of massive gravity in four spacetime dimensions. The resulting theory is free not only of higher derivative ghosts but also of the Boulware-Deser mode.

Minjoon Park; Lorenzo Sorbo

2012-10-29

360

Gravity field information from Gravity Probe-B

NASA Technical Reports Server (NTRS)

The Gravity Probe-B Mission will carry the Stanford Gyroscope relativity experiment into orbit in the mid 1990's, as well as a Global Positioning System (GPS) receiver whose tracking data will be used to study the earth gravity field. Estimates of the likely quality of a gravity field model to be derived from the GPS data are presented, and the significance of this experiment to geodesy and geophysics are discussed.

Smith, D. E.; Lerch, F. J.; Colombo, O. L.; Everitt, C. W. F.

1989-01-01

361

We consider gravity in three dimensions with an arbitrary number of curvature corrections. We show that such corrections are always functions of only three independent curvature invariants. Demanding the existence of a holographic c-theorem we show how to fix the coefficients in the action for an arbitrarily high order, recovering the new massive gravity lagrangian at quadratic order. We calculate the central charge $c$ and show that using Cardy's formula it matches the entropy of black hole solutions, which we construct. We also consider fluctuations about an AdS background, and find that it is possible to obtain two derivative equations by imposing a single constraint, thereby lifting the pathologic massive modes of new massive gravity. If we do not impose this, there is a set of ghosty massive modes propagating in the bulk. However, at $c=0$ these become massless and it is expected that these theories encode the dynamics of the spin two sector of strongly coupled logarithmic CFT's.

Miguel F. Paulos

2010-05-10

362

Minimal Massive Gravity (MMG) is an extension of three-dimensional Topologically Massive Gravity that, when formulated about Anti-de Sitter space, accomplishes to solve the tension between bulk and boundary unitarity that other models in three dimensions suffer from. We study this theory at the chiral point, i.e. at the point of the parameter space where one of the central charges of the dual conformal field theory vanishes. We investigate the non-linear regime of the theory, meaning that we study exact solutions to the MMG field equations that are not Einstein manifolds. We exhibit a large class of solutions of this type, which behave asymptotically in different manners. In particular, we find analytic solutions that represent two-parameter deformations of extremal Banados-Teitelboim-Zanelli (BTZ) black holes. These geometries behave asymptotically as solutions of the so-called Log Gravity, and, despite the weakened falling-off close to the boundary, they have finite mass and finite angular momentum, which w...

Giribet, Gaston

2014-01-01

363

NASA Astrophysics Data System (ADS)

Minimal massive gravity (MMG) is an extension of three-dimensional topologically massive gravity that, when formulated about anti-de Sitter space, accomplishes solving the tension between bulk and boundary unitarity that other models in three dimensions suffer from. We study this theory at the chiral point, i.e. at the point of the parameter space where one of the central charges of the dual conformal field theory vanishes. We investigate the nonlinear regime of the theory, meaning that we study exact solutions to the MMG field equations that are not Einstein manifolds. We exhibit a large class of solutions of this type, which behave asymptotically in different manners. In particular, we find analytic solutions that represent two-parameter deformations of extremal Bañados-Teitelboim-Zanelli black holes. These geometries behave asymptotically as solutions of the so-called log gravity, and, despite the weakened falling off close to the boundary, they have finite mass and finite angular momentum, which we compute. We also find time-dependent deformations of Bañados-Teitelboim-Zanelli that obey Brown-Henneaux asymptotic boundary conditions. The existence of such solutions shows that the Birkhoff theorem does not hold in MMG at the chiral point. Other peculiar features of the theory at the chiral point, such as the degeneracy it exhibits in the decoupling limit, are discussed.

Giribet, Gaston; Vásquez, Yerko

2015-01-01

364

Quantum gravity and renormalization

NASA Astrophysics Data System (ADS)

The properties of quantum gravity are reviewed from the point of view of renormalization. Various attempts to overcome the problem of non-renormalizability are presented, and the reasons why most of them fail for quantum gravity are discussed. Interesting possibilities come from relaxing the locality assumption, which also can inspire the investigation of a largely unexplored sector of quantum field theory. Another possibility is to work with infinitely many independent couplings, and search for physical quantities that only depend on a finite subset of them. In this spirit, it is useful to organize the classical action of quantum gravity, determined by renormalization, in a convenient way. Taking advantage of perturbative local field redefinitions, we write the action as the sum of the Hilbert term, the cosmological term, a peculiar scalar that is important only in higher dimensions, plus invariants constructed with at least three Weyl tensors. We show that the FRLW configurations, and many other locally conformally flat metrics, are exact solutions of the field equations in arbitrary dimensions d>3. If the metric is expanded around such configurations the quadratic part of the action is free of higher-time derivatives. Other well-known metrics, such as those of black holes, are instead affected in nontrivial ways by the classical corrections of quantum origin.

Anselmi, Damiano

2015-01-01

365

Granular Superconductors and Gravity

NASA Technical Reports Server (NTRS)

As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with a relatively high percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 104 was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field and exposed without levitation to low-field strength AC magnetic fields. Changes in observed gravity signals were measured to be less than 2 parts in 108 of the normal gravitational acceleration. Given the high sensitivity of the test, future work will examine variants on the basic magnetic behavior of granular superconductors, with particular focus on quantifying their proposed importance to gravity.

Noever, David; Koczor, Ron

1999-01-01

366

Dynamics of Superfluid Helium in Low-Gravity

NASA Technical Reports Server (NTRS)

This report summarizes the work performed under a contract entitled 'Dynamics of Superfluid Helium in Low Gravity'. This project performed verification tests, over a wide range of accelerations of two Computational Fluid Dynamics (CFD) codes of which one incorporates the two-fluid model of superfluid helium (SFHe). Helium was first liquefied in 1908 and not until the 1930s were the properties of helium below 2.2 K observed sufficiently to realize that it did not obey the ordinary physical laws of physics as applied to ordinary liquids. The term superfluidity became associated with these unique observations. The low temperature of SFHe and it's temperature unifonrmity have made it a significant cryogenic coolant for use in space applications in astronomical observations with infrared sensors and in low temperature physics. Superfluid helium has been used in instruments such as the Shuttle Infrared Astronomy Telescope (IRT), the Infrared Astronomy Satellite (IRAS), the Cosmic Background Observatory (COBE), and the Infrared Satellite Observatory (ISO). It is also used in the Space Infrared Telescope (SIRTF), Relativity Mission Satellite formally called Gravity Probe-B (GP-B), and the Test of the Equivalence Principle (STEP) presently under development. For GP-B and STEP, the use of SFHE is used to cool Superconducting Quantum Interference Detectors (SQUIDS) among other parts of the instruments. The Superfluid Helium On-Orbit Transfer (SHOOT) experiment flown in the Shuttle studied the behavior of SFHE. This experiment attempted to get low-gravity slosh data, however, the main emphasis was to study the low-gravity transfer of SFHE from tank to tank. These instruments carried tanks of SFHE of a few hundred liters to 2500 liters. The capability of modeling the behavior of SFHE is important to spacecraft control engineers who must design systems that can overcome disturbances created by the movement of the fluid. In addition instruments such as GP-B and STEP are very sensitive to quasi-steady changes in the mass distribution of the liquid. The CFD codes were used to model the fluid's dynamic motion. Tests in one-g were performed with the main emphasis on being able to compute the actual damping of the fluid. A series of flights on the NASA Lewis reduced gravity DC-9 aircraft were performed with the Jet Propulsion Laboratory (JPL) Low Temperature Flight Facility and a superfluid Test Cell. The data at approximately 0.04g, lg and 2g were used to determine if correct fundamental frequencies can be predicted based on the acceleration field. Tests in zero gravity were performed to evaluate zero gravity motion.

Frank, David J.

1997-01-01

367

Geometric scalar theory of gravity

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.; Goulart, E.; Salim, J.M.; Toniato, J.D. [Instituto de Cosmologia Relatividade Astrofisica ICRA - CBPF Rua Dr. Xavier Sigaud 150 - 22290-180 Rio de Janeiro - Brazil (Brazil); Moschella, U., E-mail: novello@cbpf.br, E-mail: eduhsb@cbpf.br, E-mail: Ugo.Moschella@uninsubria.it, E-mail: egoulart@cbpf.br, E-mail: jsalim@cbpf.br, E-mail: toniato@cbpf.br [Università degli Studi dell'Insubria - Dipartamento di Fisica e Matematica Via Valleggio 11 - 22100 Como - Italy (Italy)

2013-06-01

368

Insight into Impact Crater Crustal Structure using Gravity Data

NASA Astrophysics Data System (ADS)

Impact cratering is one of the most important geologic process occurring on planetary surfaces. On Earth, craters are rare; there are only ~175 identified impact structures. Understanding the detailed structural geology and impact mechanics requires understanding how the crust has responded to the impact. Mapping the surface geology provides information in two dimensions that can be extrapolated for short distances into the third dimension (depth). Geophysical techniques and drilling are required to understand details of the third dimension. Gravity studies are a powerful technique to understand the structure at depth, particularly as it can be done quickly and cheaply. Gravity measurements essentially map the density distribution of the crust with near-surface density contrasts producing the largest short-wavelength anomalies. The central uplift of an impact structure is one of the most deformed parts wherein material is uplifted from relatively deep levels, folded and faulted. Gravity studies allow the dimensions of the uplift to be determined (e.g., diameter, height). The bulk density of the central peak provides constraints on bulk shock effects (compression or dilation). The gravity signature of a central peak, compared with the adjacent crater floor and the exterior provides insight into the nature of deeper deformation under the central peak. For example, the amount of uplift within the central peak may decrease with depth until a point is reached at which the deformation is zero. Alternatively, the deformation, as well deformation on the bounding faults, may sole into a decollement at depth; deformation will end abruptly at a particularly structural level. The boundary between a sedimentary section and crystalline basement or a major strength-contrast in a sediments may act as a decollement. Depending upon which scenario occurs, the central uplift gravity anomaly will differ. The Chesapeake Bay structure (85 km) serves as an example of how gravity can be used to define details of a central uplift. CBIS has an 8 mGal central positive anomaly and a surrounding 10 mGal negative (defining the 35 km inner basin); the block-faulted outer margin does not display an anomaly. The central high is caused by high-density crystalline basement brought up in the central peak; the annular low is caused by low-density breccias. The overall horizontal and vertical dimensions, as well as the original recognition, of the central uplift were made using gravity data. The margins of the structure do not exhibit gravity anomalies as the bounding faults simply displace blocks of the sedimentary section against each other and there are no resulting density contrasts. The bounding faults also do not exhibit a gravity anomaly as they do not significantly displace the basement, hence no density anomalies are created.

Plescia, J. B.

2011-12-01

369

Renormalizability of Topologically Massive Gravity

We consider renormalizability of topologically massive gravity in three space-time dimensions. With a usual parametrization of the metric tensor, we establish the statement that topologically massive gravity is in fact renormalizable. In this proof, we make use of not only a recently found, new infrared regularization method of scalar mode but also a covariant ultraviolet regulator with a specific combination of higher derivative terms which is motivated by the new massive gravity in three dimensions.

Ichiro Oda

2009-05-11

370

Entropic Gravity in Rindler Space

We show that Rindler horizons are entropic screens and gravity is an entropic force in Rindler space by deriving the Verlinde entropy formula from the focusing of light due to a mass close to the horizon. Consequently, gravity is also entropic in the near horizon regions of Schwarzschild and de Sitter space-times. In different limits, the entropic nature of gravity in Rindler space leads to the Bekenstein entropy bound and the uncertainty principle.

Edi Halyo

2011-04-13

371

Scattering of internal gravity waves

Scattering of Internal Gravity Waves Abigail Leaman Nye Selwyn College A dissertation submitted to the University of Cambridge for the degree of Doctor of Philosophy April 2009 Summary Internal gravity waves play a fundamental role in the dynamics... subsequently produced. Identifying regions where internal gravity waves contribute to ocean mixing and quantifying this mixing are therefore important for accurate climate and weather predictions. Field studies report significantly enhanced measurements...

Leaman Nye, Abigail

2011-04-19

372

On zero energy states in graphene

We obtain zero energy states in graphene for a number of potentials and discuss the relation of the decoupled Schr\\"odinger-like equations for the the spinor components with non relativistic $\\cal{PT}$ symmetric quantum mechanics.

C. -L. Ho; P. Roy

2014-05-27

373

ZERO SITE MANUAL ZACKENBERG ECOLOGICAL RESEARCH OPERATIONS

ZERO SITE MANUAL ZACKENBERG ECOLOGICAL RESEARCH OPERATIONS Zackenberg secretariat Department The Zackenberg Ecological Research Operations (at the Department of Bioscience, Aarhus University) appreciates ecosystem research in the high Arctic. According to the framework programme of Zackenberg Ecological

374

Planar Multicontact Locomotion Using Hybrid Zero Dynamics

is presented which leverages the concept of zero dynamics, allowing for a low dimensional representation of the full order dynamics. Within the optimization, constraints are constructed based on the interaction be- tween the robot and the walking surface...

Lack, Jordan Thomas

2013-11-26

375

Zero-Valent Metal Emulsion for Reductive Dehalogenation of DNAPLs

NASA Technical Reports Server (NTRS)

A zero-valent metal emulsion is used to dehalogenate solvents, such as pooled dense non-aqueous phase liquids (DNAPLs), including trichloroethylene (TCE). The zero-valent metal emulsion contains zero-valent metal particles, a surfactant, oil and water, The preferred zero-valent metal particles are nanoscale and microscale zero-valent iron particles.

Reinhart, Debra R. (Inventor); Clausen, Christian (Inventor); Gelger, Cherie L. (Inventor); Quinn, Jacqueline (Inventor); Brooks, Kathleen (Inventor)

2006-01-01

376

Zero-Valent Metal Emulsion for Reductive Dehalogenation of DNAPLS

NASA Technical Reports Server (NTRS)

A zero-valent metal emulsion is used to dehalogenate solvents, such as pooled dense non-aqueous phase liquids (DNAPLs), including trichloroethylene (TCE). The zero-valent metal emulsion contains zero-valent metal particles, a surfactant, oil and water. The preferred zero-valent metal particles are nanoscale and microscale zero-valent iron particles

Reinhart, Debra R. (Inventor); Clausen, Christian (Inventor); Geiger, Cherie L. (Inventor); Quinn, Jacqueline (Inventor); Brooks, Kathleen (Inventor)

2003-01-01

377

Active Response Gravity Offload System

NASA Technical Reports Server (NTRS)

The Active Response Gravity Offload System (ARGOS) provides the ability to simulate with one system the gravity effect of planets, moons, comets, asteroids, and microgravity, where the gravity is less than Earth fs gravity. The system works by providing a constant force offload through an overhead hoist system and horizontal motion through a rail and trolley system. The facility covers a 20 by 40-ft (approximately equals 6.1 by 12.2m) horizontal area with 15 ft (approximately equals4.6 m) of lifting vertical range.

Valle, Paul; Dungan, Larry; Cunningham, Thomas; Lieberman, Asher; Poncia, Dina

2011-01-01

378

Conformal Tensors via Lovelock Gravity

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.

David Kastor

2013-06-24

379

Conformal Tensors via Lovelock Gravity

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

2013-01-01

380

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

381

On the robustness of entanglement in analogue gravity systems

NASA Astrophysics Data System (ADS)

We investigate the possibility of generating quantum-correlated quasi-particles utilizing analogue gravity systems. The quantumness of these correlations is a key aspect of analogue gravity effects and their presence allows for a clear separation between classical and quantum analogue gravity effects. However, experiments in analogue systems, such as Bose-Einstein condensates (BECs) and shallow water waves, are always conducted at non-ideal conditions, in particular, one is dealing with dispersive media at non-zero temperatures. We analyse the influence of the initial temperature on the entanglement generation in analogue gravity phenomena. We lay out all the necessary steps to calculate the entanglement generated between quasi-particle modes and we analytically derive an upper bound on the maximal temperature at which given modes can still be entangled. We further investigate a mechanism to enhance the quantum correlations. As a particular example, we analyse the robustness of the entanglement creation against thermal noise in a sudden quench of an ideally homogeneous BEC, taking into account the super-sonic dispersion relations.

Bruschi, D. E.; Friis, N.; Fuentes, I.; Weinfurtner, S.

2013-11-01

382

Humans use internal models to estimate gravity and linear acceleration.

Because sensory systems often provide ambiguous information, neural processes must exist to resolve these ambiguities. It is likely that similar neural processes are used by different sensory systems. For example, many tasks require neural processing to distinguish linear acceleration from gravity, but Einstein's equivalence principle states that all linear accelerometers must measure both linear acceleration and gravity. Here we investigate whether the brain uses internal models, defined as neural systems that mimic physical principles, to help estimate linear acceleration and gravity. Internal models may be used in motor contro, sensorimotor integration and sensory processing, but direct experimental evidence for such models is limited. To determine how humans process ambiguous gravity and linear acceleration cues, subjects were tilted after being rotated at a constant velocity about an Earth-vertical axis. We show that the eye movements evoked by this post-rotational tilt include a response component that compensates for the estimated linear acceleration even when no actual linear acceleration occurs. These measured responses are consistent with our internal model predictions that the nervous system can develop a non-zero estimate of linear acceleration even when no true linear acceleration is present. PMID:10217143

Merfeld, D M; Zupan, L; Peterka, R J

1999-04-15

383

The lunar environment as a fractional-gravity biological laboratory

NASA Astrophysics Data System (ADS)

A quarter of a century ago men stepped upon the lunar surface and established the possibility of human expansion beyond Earth. When humans return to the moon to occupy it with greater permanency, an applied lunar biological laboratory would provide a means of conducting experiments on the long-term effects of fractional gravity in animals and plants and provide necessary data to enhance the health, safety and well-being of lunar workers and inhabitants. In-depth studies can go beyond zero-g observations, on-orbit centrifuge studies, and ground-based research providing important insight into continuous 1/6- g effects on biological systems. Studies concentrating on development, gravity sensing, and adaptation/readaptation would provide preliminary data on whether long-term fractional gravity is detrimental or compromising to fundamental biological function. Food production research in 1/6- g would provide important information for on site application to improve the yield and quality of food (animal and plant) produced in the unique lunar environment. The purpose of this paper is to discuss some examples of the major gravitational biology areas that could be studied on the moon and applied to lunar population needs utilizing lunar biological facilities and continuous fractional gravity.

Garshnek, V.

384

International Space University variable gravity research facility design

NASA Astrophysics Data System (ADS)

A manned mission to Mars will require long travel times between Earth and Mars. However, exposure to long-duration zero gravity is known to be harmful to the human body. Some of the harmful effects are loss of heart and lung capacity, inability to stand upright, muscular weakness, and loss of bone calcium. A variable gravity research facility (VGRF) that will be placed in low Earth orbit (LEO) was designed by students of the International Space University 1989 Summer Session held in Strasbourg, France, to provide a testbed for conducting experiments in the life and physical sciences in preparation for a mission to Mars. This design exercise was unique because it addressed all aspects concerning a large space project. This report describes the VGRF design that was developed by international participants specializing in the following areas: the politics of international cooperation; engineering, architecture; in-space physiological, materials, and life science experimentation; data communications; and business and management.

Bailey, Sheila G.; Chiaramonte, Francis P.; Davidian, Kenneth J.

1994-03-01

385

The International Space University's variable gravity research facility design

NASA Astrophysics Data System (ADS)

A manned mission to Mars will require long travel times between Earth and Mars. However, exposure to long-duration zero gravity is known to be harmful to the human body. Some of the harmful effects are loss of heart and lung capacity, inability to stand upright, muscular weakness and loss of bone calcium. A variable gravity research facility (VGRF) that would be placed in low Earth orbit (LEO) was designed by students of the International Space University 1989 Summer Session held in Strasbourg, France, to provide a testbed for conducting experiments in the life and physical sciences in preparation for a mission to Mars. This design exercise was unique because it addressed all aspects concerning a large space project. The VGRF design was described which was developed by international participants specializing in the following areas: the politics of international cooperation, engineering, architecture, in-space physiology, material and life science experimentation, data communications, business, and management.

Bailey, Sheila G.; Chiaramonte, Francis P.; Davidian, Kenneth J.

1991-09-01

386

Cosmological perturbations in massive gravity and the Higuchi bound

In de Sitter spacetime there exists an absolute minimum for the mass of a spin-2 field set by the Higuchi bound m{sup 2} ? 2H{sup 2}. We generalize this bound to arbitrary spatially flat FRW geometries in the context of the recently proposed ghost-free models of Massive Gravity with an FRW reference metric, by performing a Hamiltonian analysis for cosmological perturbations. We find that the bound generically indicates that spatially flat FRW solutions in FRW massive gravity, which exhibit a Vainshtein mechanism in the background as required by consistency with observations, imply that the helicity zero mode is a ghost. In contradistinction to previous works, the tension between the Higuchi bound and the Vainshtein mechanism is equally strong regardless of the equation of state for matter.

Fasiello, Matteo; Tolley, Andrew J., E-mail: matte@case.edu, E-mail: andrew.j.tolley@case.edu [Department of Physics, Case Western Reserve University, 10900 Euclid Ave, Cleveland, OH 44106 (United States)

2012-11-01

387

Logarithmic AdS Waves and Zwei-Dreibein Gravity

We show that the parameter space of Zwei-Dreibein Gravity (ZDG) in AdS3 exhibits critical points, where massive graviton modes coincide with pure gauge modes and new `logarithmic' modes appear, similar to what happens in New Massive Gravity. The existence of critical points is shown both at the linearized level, as well as by finding AdS wave solutions of the full non-linear theory, that behave as logarithmic modes towards the AdS boundary. In order to find these solutions explicitly, we give a reformulation of ZDG in terms of a single Dreibein, that involves an infinite number of derivatives. At the critical points, ZDG can be conjectured to be dual to a logarithmic conformal field theory with zero central charges, characterized by new anomalies whose conjectured values are calculated.

Eric A. Bergshoeff; Andrés F. Goya; Wout Merbis; Jan Rosseel

2014-01-21

388

Utilization of Low Gravity Environment for Measuring Liquid Viscosity

NASA Technical Reports Server (NTRS)

The method of drop coalescence is used for determining the viscosity of highly viscous undercooled liquids. Low gravity environment is necessary in order to allow for examining large volumes affording much higher accuracy for the viscosity calculations than possible for smaller volumes available under 1 - g conditions. The drop coalescence method is preferred over the drop oscillation technique since the latter method can only be applied for liquids with vanishingly small viscosities. The technique developed relies on both the highly accurate solution of the Navier-Stokes equations as well as on data from experiments conducted in near zero gravity environment. Results are presented for method validation experiments recently performed on board the NASA/KC-135 aircraft. While the numerical solution was produced using the Boundary Element Method. In these tests the viscosity of a highly viscous liquid, glycerine at room temperature, was determined using the liquid coalescence method. The results from these experiments will be discussed.

Antar, Basil N.; Ethridge, Edwin

1998-01-01

389

Crustal structure beneath the southern Appalachians: nonuniqueness of gravity modeling

Gravity models computed for a profile across the long-wavelength paired negative-positive Bouguer anomalies of the southern Appalachian Mountains show that the large negative anomaly can be explained by a crustal root zone, whereas the steep gradient and positive anomaly east of the root may be explained equally well by three different geometries: a suture zone, a mantle upwarp, or a shallow body. Seismic data support the existence of a mountain root but are inadequate to resolve differences among the three possible geometries for the positive anomaly. The presence of outcropping mafic and ultramafic rocks in the southern Appalachians and the inferred tectonic history of the Appalachian orogen are most consistent with the suture-zone model. Crust similar to continental crust probably exists beneath the Coastal Plain and inner continental shelf where the gravity anomalies return to near-zero values.

Hutchinson, Deborah R.; Grow, John A.; Klitgord, Kim D.

1983-01-01

390

The daily mean zero-flux plane during soil-controlled evaporation: A Green's function approach

NASA Astrophysics Data System (ADS)

solution is presented of the linearized Richards equation with inclusion of gravity and with appropriate boundary conditions describing the combined soil-controlled surface evaporation and the downward infiltration, following the application of a given amount of precipitation or irrigation. This solution is shown to agree with available field measurements, namely the evolution with time of the zero-flux plane depth and of the rate of soil-controlled evaporation from the bare soil surface. The problem is solved by means of the Green's function method; the result is general enough to be also applicable to flow problems in linear soils with boundary conditions substantially different from the ones considered herein.

Brutsaert, Wilfried

2014-12-01

391

Massive Gravity: A Lorentz-Symmetric Aether

This is a heuristic introduction to massive gravity based on an analogy with perfect fluids. I will argue that massive gravity can be thought of as Einstein gravity in the presence of a medium with unusual properties.

Mirbabayi, Mehrdad

2014-01-01

392

Zero cosmological constant and nonzero dark energy from the holographic principle

NASA Astrophysics Data System (ADS)

The first law of thermodynamics and the holographic principle applied to an arbitrary large cosmic causal horizon are shown to naturally demand a zero cosmological constant and a non-zero dynamical dark energy in the form of the holographic dark energy. A semiclassical analysis shows that the holographic dark energy has a parameter d = 1 and an equation of state comparable to current observational data if the entropy of the horizon saturates the Bekenstein-Hawking bound. This result indicates that quantum field theory should be modified on a large scale to explain the dark energy. The relations among the dark energy, the quantum vacuum energy and the entropic gravity are also discussed.

Lee, Jae-Weon

2013-09-01

393

Topological charged black holes in generalized Ho?ava-Lifshitz gravity

NASA Astrophysics Data System (ADS)

As a candidate of quantum gravity in ultrahigh energy, the (3 +1 )-dimensional Ho?ava-Lifshitz (HL) gravity with critical exponent z ?1 indicates anisotropy between time and space at short distance. In the paper, we investigate the most general z =d Ho?ava-Lifshitz gravity in arbitrary spatial dimension d , with a generic dynamical Ricci flow parameter ? and a detailed balance violation parameter ? . In arbitrary dimensional generalized HLd +1 gravity with z ?d at long distance, we study the topological neutral black hole solutions with general ? in z =d HLd +1 , as well as the topological charged black holes with ? =1 in z =d HLd +1 . The HL gravity in the Lagrangian formulation is adopted, while in the Hamiltonian formulation, it reduces to Dirac-De Witt's canonical gravity with ? =1 . In particular, the topological charged black holes in z =5 HL6 , z =4 HL5 , z =3 ,4 HL4 , and z =2 HL3 with ? =1 are solved. Their asymptotical behaviors near the infinite boundary and near the horizon are explored, respectively. We also study the behavior of the topological black holes in the (d +1 )-dimensional HL gravity with U (1 ) gauge field in the zero temperature limit and finite temperature limit, respectively. Thermodynamics of the topological charged black holes with ? =1 , including temperature, entropy, heat capacity, and free energy are evaluated.

Li, Tian-Jun; Qi, Yong-Hui; Wu, Yue-Liang; Zhang, Yun-Long

2014-12-01

394

Gravity Estimation from a Simulated GRACE Mission: Short vs. Long Arcs

NASA Technical Reports Server (NTRS)

We present simulations of gravity estimation from a GRACE-like satellite mission: low-low intersatellite tracking with a precision of order 1 micron s(exp -1) yielding gravity fields of degree and order 120. We employ a unique parameterization of the intersatellite baseline vector which allows the gravity estimation to be performed (relatively) independently of the GPS (global positioning system) tracking data once sufficiently accurate orbits are obtained. This considerably simplifies data processing during the gravity estimation. During that process only certain components of the baseline parameterization need be adjusted; other components are uncorrelated with gravity and may be adopted unchanged from the initial GPS orbits. The technique is also amenable to very short arcs of data. We present comparisons of gravity estimation from 30 days of observations with arcs of length 15 minutes vs. arcs of one day. Our 'truth' field is the EGM96 (Earth Gravitational Model) model; our prior field is a degree-70 clone of EGM96, perturbed from it by amounts comparable to the standard errors of EGM96 (and identically zero for degrees 71-120). For a high inclination orbit, the short-arc analysis recovers low order gravity coefficients remarkably well, although higher order terms, especially sectorial terms, are understandably less accurate. The simulations suggest that either long or short arcs of GRACE data are likely to improve parts of the geopotential spectrum by several orders of magnitude. This is especially so for low order coefficients, which are markedly improved for all degrees through 120.

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

2001-01-01

395

NASA Technical Reports Server (NTRS)

Derivation of first and second partials of the gravitational potential is given in both normalized and unnormalized form. Two different recursion formulas are considered. Derivation of a general gravity gradient torque algorithm which uses the second partial of the gravitational potential is given. Derivation of the geomagnetic field vector is given in a form that closely mimics the gravitational algorithm. Ada code for all algorithms that precomputes all possible data is given. Test cases comparing the new algorithms with previous data are given, as well as speed comparisons showing the relative efficiencies of the new algorithms.

Gottlieb, Robert G.

1993-01-01

396

NASA Astrophysics Data System (ADS)

The differences between the Jordan frame and the Einstein frame in Brans-Dicke theory have been widely discussed in the literature. However, there is no consensus on this subject. In this dissertation, this issue is first attacked by working on the cosmological consequences. Then the equivalence theorem in quantum field theory is used to argue the differences between the two frames. The recent holographic principle is applied to the Brans- Dicke theory to get the corresponding holographic bounds in the two frames. The most recent developments in cosmology: the quintessence model and the brane Universe, are also briefly discussed. Other alternative theories of gravity are briefly mentioned in this dissertation.

Gong, Yungui

2001-09-01

397

New Massive Gravity Holography

We investigate the holographic renormalization group flows and the classical phase transitions that occur in two dimensional QFT model dual to the New Massive 3D Gravity coupled to scalar matter. Specific matter self-interactions generated by quadratic superpotential are considered. The off-critical $AdS_3/CFT_2$ correspondence determines the exact form of the $ QFT_2$ 's $\\beta$ -function and the singular part of the reduced free energy. The corresponding scaling laws and critical exponents characterizing the RG fixed points as well as the values of the mass gaps in the massive phases are obtained.

U. Camara dS; C. P. Constantinidis; G. M. Sotkov

2010-09-14

398

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

399

The Symmetric Teleparallel Gravity

We study symmetric teleparallel (STP) gravity model, in which only spacetime non-metricity is nonzero. First we obtain STP equivalent Einstein-Hilbert Lagrangian and give an approach for a generic solution in terms of only metric tensor. Then we obtain a spherically symmetric static solution to the Einstein's equation in STP space-time and discuss the singularities. Finally, we study a model given by a Lagrangian 4-form quadratic in non-metricity. Thus, we seek Schwarzschild-type solutions because of its observational success and obtain some sets of solutions. Finally, we discuss physical relevance of the solutions.

M. Adak

2006-11-14

400

Gravity and Granular Materials

NASA Technical Reports Server (NTRS)

We describe experiments that probe a number of different types of granular flow where either gravity is effectively eliminated or it is modulated in time. These experiments include the shaking of granular materials both vertically and horizontally, and the shearing of a 2D granular material. For the shaken system, we identify interesting dynamical phenomena and relate them to standard simple friction models. An interesting application of this set of experiments is to the mixing of dissimilar materials. For the sheared system we identify a new kind of dynamical phase transition.

Behringer, R. P.; Hovell, Daniel; Kondic, Lou; Tennakoon, Sarath; Veje, Christian

1999-01-01

401

It is shown that, under a conformal transformation with reference to the Higgs field, the Higgs boson can be completely decoupled from electroweak interactions with no apparent change in known properties of leptons, quarks and vector bosons. Higgs boson becomes part of a scalar-tensor gravity which can be relevant for Dark Energy. It interacts with matter sector via higher-dimensional terms (e.g. neutrino Majorana mass), and via the fields (of new physics) whose masses are not generated by the Higgs mechanism. Dark Matter and two-Higgs-doublet model are the simplest examples.

Durmus A. Demir

2011-12-11

402

Gravity from Quantum Information

It is suggested that the Einstein equation can be derived from Landauer's principle applied to an information erasing process at a local Rindler horizon and Jacobson's idea linking the Einstein equation with thermodynamics. When matter crosses the horizon, the information of the matter disappears and the horizon entanglement entropy increases to compensate the entropy reduction. The Einstein equation describes an information-energy relation during this process, which implies that entropic gravity is related to the quantum entanglement of the vacuum and has a quantum information theoretic origin.

Jae-Weon Lee; Hyeong-Chan Kim; Jungjai Lee

2010-01-29

403

The study of anisotropies in the Cosmic Microwave Background radiation is progressing at a phenomenal rate, both experimentally and theoretically. These anisotropies can teach us an enormous amount about the way that fluctuations were generated and the way they subsequently evolved into the clustered galaxies which are observed today. In particular, on sub-degree scales the rich structure in the anisotropy spectrum is the consequence of gravity-driven acoustic oscillations occurring before the matter in the universe became neutral. The frozen-in phases of these sound waves imprint a dependence on many cosmological parameters, that we may be on the verge of extracting.

Douglas Scott; Martin White

1995-05-22

404

The detection of a stochastic background of long-wavelength gravitational waves (tensors) in the cosmic microwave background (CMB) anisotropy would be an invaluable probe of the high energy physics of the early universe. Unfortunately a combination of factors now makes such a detection seem unlikely: the vast majority of the CMB signal appears to come from density perturbations (scalars) - detailed fits to current observations indicate a tensor-to-scalar quadrupole ratio of T/S gravity wave signal down to T/S \\sim 10% and optimistic assumptions about polarization of the CMB only lower this another order of magnitude.

J. P. Zibin; Douglas Scott; Martin White

1999-04-18

405

Probing Quantum Gravity Through Exactly Soluble Midi-Superspaces I

It is well-known that the Einstein-Rosen solutions to the 3+1 dimensional vacuum Einstein's equations are in one to one correspondence with solutions of 2+1 dimensional general relativity coupled to axi-symmetric, zero rest mass scalar fields. We first re-examine the quanization of this midi-superspace paying special attention to the asymptotically flat boundary conditions and to certain functional analytic subtleties associated with regularization. We then use the resulting quantum theory to analyze several conceptual and technical issues of quantum gravity.

A. Ashtekar; M. Pierri

1996-06-28

406

Conceptualization and design of a variable-gravity research facility

NASA Technical Reports Server (NTRS)

The goal is to provide facilities for the study of the effects of variable-gravity levels in reducing the physiological stresses upon the humans of long-term stay time in zero-g. The designs studied include: twin-tethered two module system with a central despun module with docking port and winch gear; and rigid arm tube facility using shuttle external tanks. Topics examined included: despun central capsule configuration, docking clearances, EVA requirements, crew selection, crew scheduling, food supply and preparation, waste handling, leisure use, biomedical issues, and psycho-social issues.

1987-01-01

407

Modified Gravity (MOG) Black Holes and their Observable Shadows

The shadows cast by non-rotating and rotating modified gravity (MOG) black holes are determined by the two parameters mass $M$ and angular momentum $J=Ma$. The sizes of the shadows cast by the spherically symmetric static Schwarzschild-MOG and Kerr-MOG rotating black holes increase significantly as the free parameter $\\alpha$ is increased from zero. The Event Horizon Telescope (EHT) shadow image measurements can determine whether Einstein's general relativity is correct or whether it should be modified in the presence of strong gravitational fields.

Moffat, J W

2015-01-01

408

NASA Technical Reports Server (NTRS)

The recent advances in the psychological aspects of space station design are discussed, including the impact of the increase in awareness of both the public in general as well as space environmental experts of the importance of psychological factors when designing space stations and training astronauts.

Ludwig, E.

1984-01-01

409

Evaluation of AAFE apparatus to measure residual and transient convection in zero-gravity

NASA Technical Reports Server (NTRS)

An evaluation apparatus which photographs convective and diffusive flows in crystal growth experiments is presented. Results in the following catagories are reported: (1) Human factors; (2) Electrical and mechanical; (3) Optical performance; and (4) Thermal performance.

Ruff, R. C.; Facemire, B. R.; Witherow, W. K.

1978-01-01

410

Radiation and zero-gravity effects on human leukocytes and Neurospora crassa

NASA Technical Reports Server (NTRS)

The two parts of this experiment have resulted in proof that neither orbital space flight nor any of the stresses connected with it produced significant, unpredicted genetic damage, at least insofar as chromosomal-aberration production is a valid measure of this general type of effect. Furthermore, the Gemini 11 results lead to the conclusion that no synergistic effect exists between radiation and factors that are associated with space flight. No significant difference was found between dose-effect curves for survival or mutation induction of the inflight and ground-based samples irradiated on filters. Thus, like the blood experiment, this part of the experiment failed to result in data that were appropriate for confirmation of the apparent synergism that was observed in the Gemini 3 blood experiment. Also, the Nuerospora crassa experiment provided conclusive data that there is no difference in the genetic effects of irradiation during space flight and the genetic effects obtained in ground-based experiments. Both the Gemini 11 blood experiment and the Neurospora crassa experiment thus have failed to result in data confirmatory of the apparent synergism observed on the Gemini 3 mission.

Bender, M. A.; Deserres, F. J.; Gooch, P. C.; Miller, I. R.; Smith, D. B.; Kondo, S.

1971-01-01

411

Growth of single crystals by vapor transport in zero-gravity environment, ground-based experiments

NASA Technical Reports Server (NTRS)

Mass and heat transfer phenomena associated with the growth of single crystals by chemical vapor transport reactions were investigated. In this technique, a gaseous transport agent reacts with the solid source material to form exclusively gaseous products. The gas phase species migrate from the source to the condensation zone of the closed reaction ampoule where the reverse reaction occurs with formation of single crystals. The necessary concentration gradient is achieved by means of a temperature gradient.

Wiedemeier, H.

1978-01-01

412

Design, fabrication and acceptance testing of a zero gravity whole body shower, volume 1

NASA Technical Reports Server (NTRS)

The effort to design whole body shower for the space station prototype is reported. Clothes and dish washer/dryer concepts were formulated with consideration given to integrating such a system with the overall shower design. Water recycling methods to effect vehicle weight savings were investigated and it was concluded that reusing wash and/or rinse water resulted in weight savings which were not sufficient to outweigh the added degree of hardware complexity. The formulation of preliminary and final designs for the shower are described. A detailed comparison of the air drag vs. vacuum pickup method was prepared that indicated the air drag concept results in more severe space station weight penalties; therefore, the preliminary system design was based on utilizing the vacuum pickup method. Tests were performed to determine the optimum methods of storing, heating and sterilizing the cleansing agent utilized in the shower; it was concluded that individual packages of pre-sterilized cleansing agent should be used. Integration features with the space station prototype system were defined and incorporated into the shower design as necessary.

1973-01-01

413

NASA Technical Reports Server (NTRS)

The development of a laboratory prototype water quality monitoring system for use in the evaluation of candidate water recovery systems and for study of techniques for measuring potability parameters is reported. Sensing techniques for monitoring of the most desirable parameters are reviewed in terms of their sensitivities and complexities, and their recommendations for sensing techniques are presented. Rationale for selection of those parameters to be monitored (pH, specific conductivity, Cr(+6), I2, total carbon, and bacteria) in a next generation water monitor is presented along with an estimate of flight system specifications. A master water monitor development schedule is included.

Misselhorn, J. E.; Witz, S.; Hartung, W. H.

1973-01-01

414

NASA Technical Reports Server (NTRS)

Electrophoretic mobilities (EPM) of peripheral lymphocytes were studied from normal subjects, chronic hemodialysis patients and kidney transplant recipients. A technique to separate B lymphocytes and null cells from non-T lymphocyte preparation was developed. The experiments were designed to determine which subpopulation of the non-T lymphocytes is primarily affected and shows a decreased EPM in chronic hemodialysis patients and kidney transplant recipients.

Rubin, A. L.; Stenzel, K. H.; Cheigh, J. S.; Seaman, G. V. F.; Novogrodsky, A.

1977-01-01

415

Separation of lymphocytes by electrophoresis under terrestrial conditions and at zero gravity

NASA Technical Reports Server (NTRS)

Electrophoretic mobility (EPM) of human peripheral lymphocytes were examined with the following objectives: To determine differences in EPM of lymphocytes under immuno-stimulated and immuno-suppressed states. To define the conditions necessary for the separation of lymphocyte sub-populations in normal and pathological conditions; To investigate immunological active, charged chemical groups on lymphocyte surfaces; and to investigate pathophysiological mechanisms of immune responsiveness, as reflected by alterations in EPM. To evaluate the potential of lymphocyte electrophoresis as: (1) a means of monitoring the immune status of kidney transplant recipients, (2) in predicting the outcome of kidney transplants, and (3) as a method for separation of lymphocyte sub-populations, the EPM was studied for unfractionated human peripheral lymphocytes and of populations enriched with T and "B" cells from normal adults, hemodialysis patients and kidney transplant recipients.

Rubin, A. L.

1977-01-01

416

On a zero-gravity limit of the Kerr--Newman spacetimes and their electromagnetic fields

We discuss the limit of vanishing $G$ (Newton's constant of universal gravitation) of the maximal analytically extended Kerr--Newman electrovacuum spacetimes {represented in Boyer--Lindquist coordinates}. We investigate the topologically nontrivial spacetime emerging in this limit and show that it consists of two copies of flat Minkowski spacetime glued at a timelike solid cylinder. As $G\\to 0$, the electromagnetic fields of the Kerr-Newman spacetimes converge to nontrivial solutions of Maxwell's equations on this background spacetime. We show how to obtain these fields by solving Maxwell's equations with singular sources supported only on a circle in a spacelike slice of the spacetime. These sources do not suffer from any of the pathologies that plague the alternate sources found in previous attempts to interpret the Kerr--Newman fields on the topologically simple Minkowski spacetime. We characterize the singular behavior of these sources and prove that the Kerr-Newman electrostatic potential and magnetic stream function are the unique solutions of the Maxwell equations among all functions that have the same blow-up behavior at the ring singularity.

A. Shadi Tahvildar-Zadeh

2014-10-01

417

Mobile work station concept for assembly of large space structures (zero gravity simulation tests)

NASA Technical Reports Server (NTRS)

The concept presented is intended to enhance astronaut assembly of truss structure that is either too large or complex to fold for efficient Shuttle delivery to orbit. The potential of augmented astronaut assembly is illustrated by applying the result of the tests to a barebones assembly of a truss structure. If this structure were assembled from the same nestable struts that were used in the Mobile Work Station assembly tests, the spacecraft would be 55 meters in diameter and consist of about 500 struts. The struts could be packaged in less than 1/2% of the Shuttle cargo bay volume and would take up approximately 3% of the mass lift capability. They could be assembled in approximately four hours. This assembly concept for erectable structures is not only feasible, but could be used to significant economic advantage by permitting the superior packaging feature of erectable structures to be exploited and thereby reduce expensive Shuttle delivery flights.

Heard, W. L., Jr.; Bush, H. G.; Wallsom, R. E.; Jensen, J. K.

1982-01-01

418

NASA Technical Reports Server (NTRS)

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 virals, pharmaceutical and immunological agents by means of electrophoresis, as the Apollo 16 flight demonstrated that a mixed population of latex spheres (.2 and .8 microns) could be successfully separated by electrophoresis in space and without sedimentation with minimal convection. This prompted NASA scientists to look into the possibility of carrying out types of biochemical experiments that would utilize space for medical purposes.

1974-01-01

419

Instability of ocular torsion in zero gravity - Possible implications for space motion sickness

NASA Technical Reports Server (NTRS)

It is proposed that study of the eye torsion reflex and its behavior under novel gravitational states may possibly provide the basis for a long-sought test to predict space motion sickness (SMS). Measures of eye torsion such as ocular counterrolling and spontaneous eye torsion, were examined during hypo- and hypergravity in parabolic flight on the NASA KC-135 aircraft. Ten subjects, including two astronauts, one who had experienced SMS and one who had not, were ranked according to scores of torsional inability at 0 G and divided into two equal groups of high and low susceptibility to SMS. At 1.8 G the groups were significantly different in both the instability measure and the measure of torsional ability. No differences were detected in eye torsion in either 0 G or 1.8 G and none of the tests were significantly different in 1 G. Results suggest that tests of eye torsion on the KC-135 might differentiate those who would experience SMS from those who would not, although it is noted that this is not yet proven.

Diamond, Shirley G.; Markham, Charles H.; Money, Ken E.

1990-01-01

420

Options for transpiration water removal in a crop growth system under zero gravity conditions

NASA Technical Reports Server (NTRS)

The operation of a microgravity crop-growth system is a critical feature of NASA's Closed Ecological Life Support System (CELSS) development program. Transpiration-evolved water must be removed from the air that is recirculated in such a system, perhaps supplying potable water in the process. The present consideration of candidate systems for CELSS water removal gives attention to energy considerations and to a mechanical, inertial-operation water-separation system that was chosen due to the depth of current understanding of its operation.

Blackwell, C. C.; Kliss, M.; Yendler, B.; Borchers, B.; Yendler, Boris S.; Nguyen, Thoi K.; Waleh, Ahmad

1991-01-01

421

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

422

Proposal for the design of a zero gravity tool storage device

NASA Technical Reports Server (NTRS)

Astronauts frequently use a variety of hand tools during space missions, especially on repair missions. A toolbox is needed to allow storage and retrieval of tools with minimal difficulties. The toolbox must contain tools during launch, landing, and on-orbit operations. The toolbox will be used in the Shuttle Bay and therefore must withstand the hazardous space environment. The three main functions of the toolbox in space are: to protect the tools from the space environment and from damaging one another, to allow for quick, one-handed access to the tools; and to minimize the heat transfer between the astronaut's hand and the tools. This proposal explores the primary design issues associated with the design of the toolbox. Included are the customer and design specifications, global and refined function structures, possible solution principles, concept variants, and finally design recommendations.

Stuckwisch, Sue; Carrion, Carlos A.; Phillips, Lee; Laughlin, Julia; Francois, Jason

1994-01-01

423

Application and use of spinal immobilization devices in zero-gravity flight

NASA Technical Reports Server (NTRS)

A KC-135 parabolic flight was performed for the purpose of evaluation of spinal immobilization techniques in microgravity. The flight followed the standard 40 parabola profile with four NASA/KRUG experimenters involved. One performed as coordinator/recorder, one as test subject, and two as the Crew Medical Officers (CMO). The flight was to evaluate the application of spinal immobilization devices and techniques in microgravity as are performed during initial stabilization or patient transport scenarios. The sequence of detail for examination of the following objectives included: attempted cervical spine immobilization with all free floating, the patient restrained to the floor, various hand positioning techniques; c-collar placement; Kendrick Extrication Device (KED) application with various restraints for patient and CMO; patient immobilization and transport using the KED; patient transported on KED and spine board. Observations for each task are included. Major conclusions and issues are also included.

Krupa, Debra T.; Gosbee, John; Billica, Roger; Boyce, Joey B.

1991-01-01

424

Manual control in space--research on perceptual-motor functions under zero gravity condition.

Microgravity effects on human factor were studied through a series of manual control experiments conducted in the First Material Processing Test. The Japanese Payload Specialist operated a finger stick for 130 seconds to maintain a light spot movement around the center of a vertical LED array display. The stick angle is doubly integrated to make the controlled element motion. The light spot position indicates the difference between the motion and pseudo-random wave patterns which drives the man-machine tracking system. 24 runs were conducted in each of 2 months before launch, immediately pre-flight, and post-flight experiments. During the flight experiments, the PS felt pain in fast eye movement. He was obliged to fix his line of sight at the center of display and to watch the displayed error movement using peripheral view. He also felt difficulty in supporting his body against reaction force of his hand movement. During a few days after landing, disturbance was observed in the PS's posture. The operator describing function analysis revealed the disappearance of the "regression" phenomenon and increment of the effective time delay. As the result, the flight describing function showed better fit to the simplified model of lead with pure time delay. PMID:12101353

Tada, A; Suematsu, S; Okabe, M

2001-10-01

425

Free-surface phenomena under low- and zero-gravity conditions

NASA Technical Reports Server (NTRS)

An apparatus to measure contact angle was constructed to exploit the proposed internal-corner criterion. If 2 alfa is the internal angle between two intersecting vertical planes and gamma is the contact angle, a meniscus at the corner rises to a finite height if alfa + gamma pi/2 and to an infinite height if alfa + gamma pi/2. The apparatus operates by decreasing the angle alfa from pi/2 until the meniscus height changes abruptly. A number of liquids are tested on glass and plexiglas.

Coles, D.

1985-01-01

426

KC-135 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 microgravity, two-phase flow pressure drop experiments. The data are those of a recent experiment (Hill and Best 1990) funded by the U.S. Air Force and conducted by Foster-Miller in conjunction with Texas A M University. A boiling and condensing experiment was built in which R-12 was used as the working fluid. A Foster-Miller two phase pump was used to circulate a freon mixture and allow separate measurements of the vapor and liquid flow streams. The experimental package was flown five times aboard the NASA KC-135 aircraft which simulates 0- g'' conditions by its parabolic flight trajectory. Test conditions included stratified and annual flow regimes in 1- g'' which became bubbly, slug or annular flow regimes in 0- g''.

Lambert, A.; Reinarts, T.R.; Best, F.R. (Nuclear Engineering Dept., Texas A M University, College Station, Texas (USA)); Hill, W.S. (Foster-Miller Inc., 350 Second Ave., Waltham, Massachusetts (USA))

1991-01-10

427

Equilibrium Fluid Interface Behavior Under Low- and Zero-Gravity Conditions. 2

NASA Technical Reports Server (NTRS)

The mathematical basis for the forthcoming Angular Liquid Bridge investigation on board Mir is described. Our mathematical work is based on the classical Young-Laplace-Gauss formulation for an equilibrium free surface of liquid partly filling a container or otherwise in contact with solid support surfaces. The anticipated liquid behavior used in the apparatus design is also illustrated.

Concus, Paul; Finn, Robert

1996-01-01

428

Cooperative control of two arms in the transport of an inertial load in zero gravity

NASA Technical Reports Server (NTRS)

In designing a robot control system for dual arm configurations, the control engineer is faced with two challenges: to derive the equations of motion for a given situation, and to meet certain desired control requirements (for instance, minimum energy). The former may involve closed kinematic chains, such as the case when the two arms are grasping a common object. The latter usually involves nonlinear optimization. These issues are considered in the context of transporting an inertial load using two planar three-link arms. A generalized 'reduction transformation' is applied to the dynamics to remove the singularity in the system equations. A suboptimal minimum energy method is presented to reduce a difficult 12-state, six-control nonlinear optimization to two independent, nonconflicting suboptimizations. A simulation example is provided to illustrate the degree of energy reduction possible using the optimal arm torque distribution that was developed.

Carignan, Craig R.; Akin, David L.

1988-01-01

429

Preliminary design for a Zero Gravity Test Facility (ZGTF). Volume 1: Technical

NASA Technical Reports Server (NTRS)

The functional requirements and best conceptual design of a test facility that simulates weightless operating conditions for a high gain antenna systems (HGAS), that will broadcast to the Tracking Data Relay Satellites were defined. The typical HGAS defined is mounted on a low Earth orbiting satellite, and consists of an antenna with a double gimbal pointing system mounted on a 13 foot long mast. Typically, the gimbals are driven by pulse modulated dc motors or stepper motors. These drivers produce torques on the mast, with jitter that excites the satellite and may cause disturbances to sensitive experiments. The dynamic properties of the antenna support structure (mast), including flexible mode characteristics were defined. The torque profile induced on the spacecraft by motion of the high gain antenna was estimated. Gain and phase margins of the servo control loop of the gimbal drive electronics was also verified.

Germain, A.

1981-01-01

430

Renormalizability of Topologically Massive Gravity

We consider renormalizability of topologically massive gravity in three space-time dimensions. With a usual parametrization of the metric tensor, we establish the statement that topologically massive gravity is in fact renormalizable. In this proof, we make use of not only a recently found, new infrared regularization method of scalar mode but also a covariant ultraviolet regulator with a specific combination

Ichiro Oda

2009-01-01

431

Gravity research at Cottrell observatory

The Cottrell gravity research observatory and work in progress are described. Equipment in place and equipment to be installed, the cryogenic gravity meter (CGM), concrete pads to support the vertical seismometer, CGM, and guest experiments, techniques of data analysis, and improvements needed in the CGM are discussed. Harmonic earth eigenvibrations with multipole moments are examined and their compatibility with a

V. S. Tuman; J. D. Anderson; E. L. Lau

1977-01-01

432

Canonical Analysis of Unimodular Gravity

This short note is devoted to the Hamiltonian analysis of the Unimodular Gravity.We treat the unimodular gravity as General Relativity action with the unimodular constraint imposed with the help of Lagrange multiplier. We perform the canonical analysis of the resulting theory and determine its constraint structure.

J. Kluson

2014-09-29

433

A USGS hydrologist prepares equipment to conduct a gravity survey to evaluate small variations in the earth's gravity field. The USGS Office of Groundwater Branch of Geophysics develops and tests new tools and field methods to support USGS analysis of groundwater flow systems....

434

Specific Gravity of Lapis Lazuli

IN the course of some work on lapis lazuli, we were astonished to find how wide was the discrepancy between the specific gravities of our specimens and the values accorded to this rock by all the standard textbooks. Of more than five hundred representative specimens examined, we found that 95 per cent had specific gravities falling within the range 2.75-2.90,

B. W. Anderson; C. J. Payne

1934-01-01

435

Three Least-Squares Minimization Approaches to Interpret Gravity Data Due to Dipping Faults

NASA Astrophysics Data System (ADS)

We have developed three different least-squares minimization approaches to determine, successively, the depth, dip angle, and amplitude coefficient related to the thickness and density contrast of a buried dipping fault from first moving average residual gravity anomalies. By defining the zero-anomaly distance and the anomaly value at the origin of the moving average residual profile, the problem of depth determination is transformed into a constrained nonlinear gravity inversion. After estimating the depth of the fault, the dip angle is estimated by solving a nonlinear inverse problem. Finally, after estimating the depth and dip angle, the amplitude coefficient is determined using a linear equation. This method can be applied to residuals as well as to measured gravity data because it uses the moving average residual gravity anomalies to estimate the model parameters of the faulted structure. The proposed method was tested on noise-corrupted synthetic and real gravity data. In the case of the synthetic data, good results are obtained when errors are given in the zero-anomaly distance and the anomaly value at the origin, and even when the origin is determined approximately. In the case of practical data (Bouguer anomaly over Gazal fault, south Aswan, Egypt), the fault parameters obtained are in good agreement with the actual ones and with those given in the published literature.

Abdelrahman, E. M.; Essa, K. S.

2015-02-01

436

Three Least-Squares Minimization Approaches to Interpret Gravity Data Due to Dipping Faults

NASA Astrophysics Data System (ADS)

We have developed three different least-squares minimization approaches to determine, successively, the depth, dip angle, and amplitude coefficient related to the thickness and density contrast of a buried dipping fault from first moving average residual gravity anomalies. By defining the zero-anomaly distance and the anomaly value at the origin of the moving average residual profile, the problem of depth determination is transformed into a constrained nonlinear gravity inversion. After estimating the depth of the fault, the dip angle is estimated by solving a nonlinear inverse problem. Finally, after estimating the depth and dip angle, the amplitude coefficient is determined using a linear equation. This method can be applied to residuals as well as to measured gravity data because it uses the moving average residual gravity anomalies to estimate the model parameters of the faulted structure. The proposed method was tested on noise-corrupted synthetic and real gravity data. In the case of the synthetic data, good results are obtained when errors are given in the zero-anomaly distance and the anomaly value at the origin, and even when the origin is determined approximately. In the case of practical data (Bouguer anomaly over Gazal fault, south Aswan, Egypt), the fault parameters obtained are in good agreement with the actual ones and with those given in the published literature.

Abdelrahman, E. M.; Essa, K. S.

2014-06-01

437

Progress in the Determination of the Earth's Gravity Field

NASA Technical Reports Server (NTRS)

Topics addressed include: global gravity model development; methods for approximation of the gravity field; gravity field measuring techniques; global gravity field applications and requirements in geophysics and oceanography; and future gravity missions.

Rapp, Richard H. (editor)

1989-01-01

438

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

439

NASA Astrophysics Data System (ADS)

For variable gravity models the strength of gravity, as measured by Newton's "constant" or the Planck mass, depends on the value of a scalar field, the cosmon. We discuss two simple four-parameter models with a quadratic or constant cosmon potential. They are compatible with all presently available cosmological observations, including inflation. The inflaton and the scalar field of quintessence are the same cosmon field. Dark energy constitutes a small, almost constant fraction of the energy density during the radiation- and matter-dominated epochs (early dark energy). In the present epoch we witness a transition to a new dark energy-dominated epoch. Our models are free of a big bang singularity. The stability of solutions generates an arrow of time. Our picture of the Universe is unusual, with a shrinking or static scale factor, while the masses of particles increase and the size of atoms shrinks. The evolution of the Universe can be very slow for all cosmological epochs including inflation, with typical time scale 1010 yr, and in sharp contrast to the usual big bang picture. The map to the equivalent Einstein frame with constant particle masses and expanding scale factor can be singular at the big bang.

Wetterich, C.

2014-01-01

440

Lunar gravity - A harmonic analysis

NASA Technical Reports Server (NTRS)

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 be strong localized negative anomalies located in broad regions of positive gravity which correspond closely to the highlands. The rms pressure levels calculated from equivalent-surface height variations show that the moon and earth support nearly equal pressures, whereas Mars is appreciably stronger. The moon appears to support larger loads than earth owing to its weaker central gravity field and perhaps a colder upper lithosphere. Significant differences between the low-degree gravity and topography spectra indicate that the longer-wavelength topographic features are isostatically compensated.

Ferrari, A. J.

1977-01-01

441

We present numerical simulations of penetrative convection and gravity wave excitation in the Sun. Gravity waves are self-consistently generated by a convective zone overlying a radiative interior. We produce power spectra for gravity waves in the radiative region as well as estimates for the energy flux of gravity waves below the convection zone. We calculate a peak energy flux in waves below the convection zone to be three orders of magnitude smaller than previous estimates for m=1. The simulations show that the linear dispersion relation is a good approximation only deep below the convective-radiative boundary. Both low frequency propagating gravity waves as well as higher frequency standing modes are generated; although we find that convection does not continually drive the standing g-mode frequencies.

Tamara M. Rogers; Gary A. Glatzmaier

2005-08-25

442

Lovelock gravity from entropic force

In this paper, we first generalize the formulation of entropic gravity to (n+1)-dimensional spacetime. Then, we propose an entropic origin for Gauss-Bonnet gravity and more general Lovelock gravity in arbitrary dimensions. As a result, we are able to derive Newton's law of gravitation as well as the corresponding Friedmann equations in these gravity theories. This procedure naturally leads to a derivation of the higher dimensional gravitational coupling constant of Friedmann/Einstein equation which is in complete agreement with the results obtained by comparing the weak field limit of Einstein equation with Poisson equation in higher dimensions. Our study shows that the approach presented here is powerful enough to derive the gravitational field equations in any gravity theory. PACS: 04.20.Cv, 04.50.-h, 04.70.Dy.

A. Sheykhi; H. Moradpour; N. Riazi

2012-10-03

443

Quench cooling under reduced gravity

NASA Astrophysics Data System (ADS)

We report quench cooling experiments performed with liquid O2 under different levels of gravity, simulated with magnetic gravity compensation. A copper disk is quenched from 300 to 90 K. It is found that the cooling time in microgravity is very long in comparison with any other gravity level. This phenomenon is explained by the insulating effect of the gas surrounding the disk. A weak gas pressurization (which results in subcooling of the liquid with respect to the saturation temperature) is shown to drastically improve the heat exchange, thus reducing the cooling time (about 20 times). The effect of subcooling on the heat transfer is analyzed at different gravity levels. It is shown that this type of experiment cannot be used for the analysis of the critical heat flux of the boiling crisis. The film boiling heat transfer and the minimum heat flux of boiling are analyzed as functions of gravity and subcooling.

Chatain, D.; Mariette, C.; Nikolayev, V. S.; Beysens, D.

2013-07-01

444

Superconductivity, superfluidity and zero-point oscillations

Currently it is thought that in order to explain the phenomenon of superconductivity is necessary to understand the mechanism of formation of electron pairs. However, the paired electrons cannot form a superconducting condensate. They perform disorderly zero-point oscillations and there are no attractive forces in their ensemble. To create a unified ensemble of particles, the pairs must order their zero-point fluctuations so that an attraction between the particles appears. For this reason, the ordering of zero-point oscillations in the electron gas is the cause of superconductivity and the parameters characterizing this order determine the properties of superconductors. The model of condensation of zero-point oscillations creates the possibility to obtain estimates for the critical parameters of elementary superconductors, which are also in the satisfactory agreement with measured data. On the another hand, the phenomenon of superfluidity in He-4 and He-3 can be similarly explained due to the ordering of zero-point fluctuations. Thus it is established that the both related phenomena are based on the same physical mechanism.

B. V. Vasiliev

2010-09-13

445

ZERO EMISSION POWER GENERATION TECHNOLOGY DEVELOPMENT

Clean Energy Systems (CES) was previously funded by DOE's ''Vision 21'' program. This program provided a proof-of-concept demonstration that CES' novel gas generator (combustor) enabled production of electrical power from fossil fuels without pollution. CES has used current DOE funding for additional design study exercises which established the utility of the CES-cycle for retrofitting existing power plants for zero-emission operations and for incorporation in zero-emission, ''green field'' power plant concepts. DOE funding also helped define the suitability of existing steam turbine designs for use in the CES-cycle and explored the use of aero-derivative turbines for advanced power plant designs. This work is of interest to the California Energy Commission (CEC) and the Norwegian Ministry of Petroleum & Energy. California's air quality districts have significant non-attainment areas in which CES technology can help. CEC is currently funding a CES-cycle technology demonstration near Bakersfield, CA. The Norwegian government is supporting conceptual studies for a proposed 40 MW zero-emission power plant in Stavager, Norway which would use the CES-cycle. The latter project is called Zero-Emission Norwegian Gas (ZENG). In summary, current engineering studies: (1) supported engineering design of plant subsystems applicable for use with CES-cycle zero-emission power plants, and (2) documented the suitability and availability of steam turbines for use in CES-cycle power plants, with particular relevance to the Norwegian ZENG Project.

Ronald Bischoff; Stephen Doyle

2005-01-20

446

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

447

Correlation of gravity anomalies and geology in the San Antonio region, Texas

together form a graben, overlie the in- terior and frontal zones of the Ouachita belt in the area. Initial movements along the faults probably occurred in late Jurassic time (Murray, 1961, p. 176, GFl&lgpu&1. FEATLBIFB Ol GRAVITY ANQNAI, Y NAP Th... with the residual grav- ity anomalies. In the analysis, the assumed regional gravity anomaly was used as the zero line for the com- puted anomaly. The 0. 2 g/cm density contrast between 3 granite and schist corresponds to that assumed by Barnes and others (1954...

Gordon, Patrick Thomas

2012-06-07

448

Absolute Zero: Community Education Outreach Guide

NSDL National Science Digital Library

This guide provides curricular resources for study of the history and science of the quest for ever colder temperature. Designed for teachers and informal educators of middle school students. this guide offers hands-on demonstrations, questions to encourage student participation, suggestions for class activities, and ways to encourage students to continue studying the science. Topics include low-temperature physics and the impact of technologies such as air conditioning, refrigeration and liquefied gases. 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

449

From net energy to zero energy buildings: Defining life cycle zero energy buildings (LC-ZEB)

There are various definitions of ‘zero energy’ and ‘net-zero’ energy building. In most cases, the definitions refer only to the energy that is used in the operation of the building, ignoring the aspects of energy use related to the construction and delivery of the building and its components. On the other hand the concept of ‘net energy’ as used in

Patxi Hernandez; Paul Kenny

2010-01-01

450

Dechlorination of pentachlorophenol by zero valent iron and modified zero valent irons

The disappearance of pentachlorophenol (PCP) from aqueous solutions in contact with zero valent metals (ZVMs) may be due to dechlorination reactions or sorption to ZVM-related surfaces. Previously reported results on PCP and zero valent iron measured only PCP loss from aqueous solutions and attributed this loss to reaction. In this study, the total amount of unreacted PCP, both that in

Young-Hun Kim; Elizabeth R. Carraway

2000-01-01

451

Main Street Zero Energy Buildings: The Zero Energy Method in Concept and Practice: Preprint

Ongoing work at the National Renewable Energy Laboratory indicates that net-zero energy building (NZEB) status is both achievable and repeatable today. This paper presents a definition framework for classifying NZEBs and a real-life example that demonstrates how a large-scale office building can cost-effectively achieve net-zero energy.

Torcellini, P.; Pless, S.; Lobato, C.; Hootman, T.

2010-07-01

452

Internal dynamics of IGBT under zero-voltage and zero-current switching conditions

Soft switching involves turning the semiconductor device on or off with minimal switching stress. Zero voltage switching (ZVS) and zero current switching (ZCS) are the two most popular variants of soft switching schemes. The turn-off performance of insulated gate bipolar transistors (IGBT's) under ZVS and ZCS environments is critically evaluated in this paper. It is shown that the turn-off mechanism

Malay Trivedi; Krishna Shenai

1999-01-01

453

The Effect of Gravity on the Combustion of Bulk Metals

NASA Technical Reports Server (NTRS)

In recent years, metal combustion studies at the University of Colorado have focused on the effects of gravity (g) on the ignition and burning behavior of bulk metals. The impetus behind this effort is the understanding of the ignition conditions and flammability properties of structural metals found in oxygen (O2) systems for space applications. Since spacecraft are subjected to higher-than-1g loads during launch and reentry and to a zero-gravity environment while in orbit, the study of ignition and combustion of bulk metals at different gravitational accelerations is of great practical concern. From the scientific standpoint, studies conducted under low gravity conditions provide simplified boundary conditions, since buoyancy is removed, and make possible the identification of fundamental ignition and combustion mechanisms. This investigation is intended to provide experimental verification of the influence of natural convection on the burning behavior of metals. In addition, the study offers the first findings of the influence of gravity on ignition of bulk metals and on the combustion mechanism and structure of metal-oxygen, vapor-phase diffusion flames in a buoyancy-free environment. Titanium (Ti) and magnesium (Mg) metals were chosen because of their importance as elements of structural materials and their simple chemical composition-pure metals instead of multicomponent alloys to simplify chemical and spectroscopic analyses. In addition, these elements present the two different combustion modes observed in metals: heterogeneous or surface burning (for Ti) and homogeneous or gas-phase reaction (for Mg). Finally, Mg, Ti, and their oxides exhibit a wide range of thermophysical and chemical properties. Metal surface temperature profiles, critical and ignition temperatures, propagation rates, burning times, and spectroscopic measurements are obtained under normal and reduced gravity. Visual evidence of all phenomena is provided by high-speed photography.

Branch, Melvyn C.; Abbud-Madrid, Angel; Daily, John W.

1997-01-01

454

Log amplifier with pole-zero compensation

A logarithmic amplifier circuit provides pole-zero compensation for improved stability and response time over 6-8 decades of input signal frequency. The amplifer circuit includes a first operational amplifier with a first feedback loop which includes a second, inverting operational amplifier in a second feedstock loop. The compensated output signal is provided by the second operational amplifier with the log elements, i.e., resistors, and the compensating capacitors in each of the feedback loops having equal values so that each break point is offset by a compensating break point or zero.

Brookshier, W.

1985-02-08

455

The zero-magnetization Heusler ferrimagnet

NASA Astrophysics Data System (ADS)

An unusual zero-moment half-metallic state has been predicted in stoichiometric Heusler compounds with 24 valence electrons, where, unlike an antiferromagnet, the two sublattices are chemically or crystallographically inequivalent. We have examined the following candidate materials: Cr2FeGe, Cr2CoGa, Fe2VGa, and Mn3Ga with various annealing and milling treatments. The Fe2VGa compound is identified as a weak itinerant ferromagnet, but both cubic Mn3Ga and perfectly ordered Cr2CoGa are potential zero-magnetization ferrimagnets.

Hakimi, M.; Venkatesan, M.; Rode, K.; Ackland, K.; Coey, J. M. D.

2013-05-01

456

Log amplifier with pole-zero compensation

A logarithmic amplifier circuit provides pole-zero compensation for improved stability and response time over 6-8 decades of input signal frequency. The amplifier circuit includes a first operational amplifier with a first feedback loop which includes a second, inverting operational amplifier in a second feedback loop. The compensated output signal is provided by the second operational amplifier with the log elements, i.e., resistors, and the compensating capacitors in each of the feedback loops having equal values so that each break point or pole is offset by a compensating break point or zero.

Brookshier, William (Downers Grove, IL)

1987-01-01

457

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

458

Lovelock gravity from entropic force

NASA Astrophysics Data System (ADS)

In this paper, we first generalize the formulation of entropic gravity to (n+1)-dimensional spacetime and derive Newton's law of gravity and Friedmann equation in arbitrary dimensions. Then, we extend the discussion to higher order gravity theories and propose an entropic origin for Gauss-Bonnet gravity and more general Lovelock gravity in arbitrary dimensions. As a result, we are able to derive Newton's law of gravitation as well as the corresponding Friedmann equations in these gravity theories. This procedure naturally leads to a derivation of the higher dimensional gravitational coupling constant of Friedmann/Einstein equation which is in complete agreement with the results obtained by comparing the weak field limit of Einstein equation with Poisson equation in higher dimensions. Our strategy is to start from first principles and assuming the entropy associated with the apparent horizon given by the expression previously known via black hole thermodynamics, but replacing the horizon radius r_+ with the apparent horizon radius R. Our study shows that the approach presented here is powerful enough to derive the gravitational field equations in any gravity theory and further supports the viability of Verlinde's proposal.

Sheykhi, A.; Moradpour, H.; Riazi, N.

2013-05-01

459

Supersymmetrizing Massive Gravity

When four scalar fields with global Lorentz symmetry are coupled to gravity and take a vacuum expectation value breaking diffeomorphism invariance spontaneously, the graviton becomes massive. This model is supersymmetrized by considering four N=1 chiral superfields with global Lorentz symmetry. When the scalar components of the chiral multiplets z^A acquire a vacuum expectation value, both diffeomorphism invariance and local supersymmetry are broken spontaneously. The global Lorentz index A becomes identified with the space-time Lorentz index making the scalar fields z^A vectors and the chiral spinors psi^A spin-3/2 Rarita-Schwinger fields. The global supersymmetry is promoted to a local one using the rules of tensor calculus of coupling the N=1 supergravity Lagrangian to the four chiral multiplets. We show that the spectrum of the model in the broken phase consists of a massive spin-2 field, two massive spin-3/2 fields with different mass and a massive vector.

Ola Malaeb

2013-03-14

460

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 [Jefferson Laboratory of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States)

2005-07-15

461

NASA Astrophysics Data System (ADS)

General concept of non-minimal field theory is discussed and a catalog of models describing the curvature coupling of gravity field with scalar, electromagnetic, vector and gauge fields is presented. Non-minimal extensions of the Einstein-Maxwell, Einstein-Yang-Mills and Einstein-Yang-Mills-Higgs theories are considered in detail. New exact solutions of the self-consistent non-minimally extended field equations, which describe non-minimal Wu-Yang monopole, non-minimal Wu-Yang wormhole, non-minimal Dirac monopole, non-minimal electrically charged objects, are presented. Physical phenomena induced by the curvature coupling are discussed, the main attention is focused on the problem of alternative explanation of the accelerated expansion of the universe and on an effective cosmological constant formation due to the non-minimal coupling.

Boyarsky, Alexey; Ruchayskiy, Oleg; Dvali, Gia

462

Thermodynamics of black holes in massive gravity

NASA Astrophysics Data System (ADS)

We present a class of charged black hole solutions in an (n +2 )-dimensional massive gravity with a negative cosmological constant, and study the thermodynamics and phase structure of the black hole solutions in both the grand canonical and canonical ensembles. The black hole horizon can have a positive, zero, or negative constant curvature characterized by the constant k . By using the Hamiltonian approach, we obtain conserved charges of the solutions and find that the black hole entropy still obeys the area formula and the gravitational field equation at the black hole horizon can be cast into a form similar to the first law of black hole thermodynamics. In the grand canonical ensemble, we find that the thermodynamics and phase structure depend on the combination k -?2/4 +c2m2 in the four-dimensional case, where ? is the chemical potential and c2m2 is the coefficient of the second term in the potential associated with the graviton mass. When it is positive, the Hawking-Page phase transition can happen; when as it is negative, the black hole is always thermodynamically stable with a positive capacity. In the canonical ensemble, the combination turns out to be k +c2m2 in the four-dimensional case. When it is positive, a first-order phase transition can happen between small and large black holes if the charge is less than its critical value. In the higher-dimensional [(n +2 )?5 ] case, even when the charge is absent, the small/large black hole phase transition can also appear, and the coefficients for the third (c3m2) and/or fourth (c4m2) terms in the potential associated with the graviton mass in massive gravity can play the same role as that of the charge in the four-dimensional case.

Cai, Rong-Gen; Hu, Ya-Peng; Pan, Qi-Yuan; Zhang, Yun-Long

2015-01-01

463

The Gravity Probe B Flight Dewar

NASA Technical Reports Server (NTRS)

Gravity Probe B (GP-B) is the relativity experiment developed at Stanford University to test two extraordinary predictions of Albert Einstein's general theory of relativity. This photograph is of the Gravity Probe B flight dewar, a metal container made like a vacuum bottle that is used especially for storing liquefied gases, that will maintain the experiment at a temperature just above absolute zero, staying cold for two years. The experiment will measure, very precisely, the expected tiny changes in the direction of the spin axes of four gyroscopes contained in an Earth-orbiting satellite at 400-mile altitude. So free are the gyroscopes from disturbance that they will provide an almost perfect space-time reference system. They will measure how space and time are very slightly warped by the presence of the Earth, and, more profoundly, how the Earth's rotation very slightly drags space-time around with it. These effects, though small for the Earth, have far-reaching implications for the nature of matter and the structure of the Universe. GP-B is among the most thoroughly researched programs ever undertaken by NASA. This is the story of a scientific quest in which physicists and engineers have collaborated closely over many years. Inspired by their quest, they have invented a whole range of technologies -- technologies that are already enlivening other branches of science and engineering. Launched in 2004 and managed for NASA by the Marshall Space Flight Center, development of the GP-B is the responsibility of Stanford University, with major subcontractor Lockheed Martin Corporation. (Photo Credit: Lockheed Martin Corporation/R. Underwood)

2001-01-01

464

We systematically study the most general Lorentz-violating graviton mass invariant under three-dimensional Eucledian group using the explicitly covariant language. We find that at general values of mass parameters the massive graviton has six propagating degrees of freedom, and some of them are ghosts or lead to rapid classical instabilities. However, there is a number of different regions in the mass parameter space where massive gravity can be described by a consistent low-energy effective theory with cutoff $\\sim\\sqrt{mM_{Pl}}$ free of rapid instabilities and vDVZ discontinuity. Each of these regions is characterized by certain fine-tuning relations between mass parameters, generalizing the Fierz--Pauli condition. In some cases the required fine-tunings are consequences of the existence of the subgroups of the diffeomorphism group that are left unbroken by the graviton mass. We found two new cases, when the resulting theories have a property of UV insensitivity, i.e. remain well behaved after inclusion of arbitrary higher dimension operators without assuming any fine-tunings among the coefficients of these operators, besides those enforced by the symmetries. These theories can be thought of as generalizations of the ghost condensate model with a smaller residual symmetry group. We briefly discuss what kind of cosmology can one expect in massive gravity and argue that the allowed values of the graviton mass may be quite large, affecting growth of primordial perturbations, structure formation and, perhaps, enhancing the backreaction of inhomogeneities on the expansion rate of the Universe.

S. L. Dubovsky

2004-09-13

465

NASA Technical Reports Server (NTRS)

The space vehicle Gravity Probe B (GP-B) is the relativity experiment developed at Stanford University to test two extraordinary predictions of Albert Einstein's general theory of relativity. The experiment will measure, very precisely, the expected tiny changes in the direction of the spin axes of four gyroscopes contained in an Earth-orbiting satellite at a 400-mile altitude. So free are the gyroscopes from disturbance that they will provide an almost perfect space-time reference system. They will measure how space and time are very slightly warped by the presence of the Earth, and, more profoundly, how the Earth's rotation very slightly drags space-time around with it. These effects, though small for the Earth, have far-reaching implications for the nature of matter and the structure of the Universe. GP-B is among the most thoroughly researched programs ever undertaken by NASA. This is the story of a scientific quest in which physicists and engineers have collaborated closely over many years. Inspired by their quest, they have invented a whole range of technologies that are already enlivening other branches of science and engineering. In this photograph, engineer Gary Reynolds is inspecting the inside of the probe neck during probe thermal repairs. GP-B is scheduled for launch in April 2004 and managed for NASA by the Marshall Space Flight Center. Development of the GP-B is the responsibility of Stanford University along with major subcontractor Lockheed Martin Corporation. (Image credit to Russ Leese, Gravity Probe B, Stanford University)

2000-01-01

466

Internal Gravity Waves Bruce R. Sutherland

Internal Gravity Waves Bruce R. Sutherland 4-183 CCIS, Dept. Physics University of Alberta Edmonton is periodic in both space and time, it is referred to as an internal gravity wave. Internal gravity waves" and "internal waves". (The dynamics of internal waves are broadly discussed in the textbook "Internal Gravity

Sutherland, Bruce

467

Constraining Modified Gravity with Euclid

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

Matteo Martinelli; Erminia Calabrese; Francesco De Bernardis; Alessandro Melchiorri; Luca Pagano; Roberto Scaramella

2010-10-27

468

String theory, gravity and experiment

The aim of these lectures is to give an introduction to several topics which lie at the intersection of string theory, gravity theory and gravity phenomenology. One successively reviews: (i) the "membrane" approach to the dissipative dynamics of classical black holes, (ii) the current experimental tests of gravity, and their theoretical interpretation, (iii) some aspects of the string-inspired phenomenology of the gravitational sector, and (iv) some possibilities for observing string-related signals in cosmology (including a discussion of gravitational wave signals from cosmic superstrings).

Thibault Damour; Marc Lilley

2008-02-28

469

Mars - Hellas Planitia gravity analysis

NASA Astrophysics Data System (ADS)

Doppler radio tracking data from Viking Orbiter 1 has provided new detailed observations of gravity variations over Hellas Planitia. Line-of-sight Bouguer gravity definitely indicates that isostatic adjustment has occurred. Two theoretical models were tested to obtain fits to the gravity data. Results for a surface deficit model, and a model with a surface deficit and a mass excess at depth are displayed. The mass-at-depth model produced very marked improvement in the data fit as compared to the surface deficit model. The optimum depth for the mass excess is 130 km.

Sjogren, W. L.; Wimberley, R. N.

1981-02-01

470

Mars - Hellas Planitia gravity analysis

NASA Technical Reports Server (NTRS)

Doppler radio tracking data from Viking Orbiter 1 has provided new detailed observations of gravity variations over Hellas Planitia. Line-of-sight Bouguer gravity definitely indicates that isostatic adjustment has occurred. Two theoretical models were tested to obtain fits to the gravity data. Results for a surface deficit model, and a model with a surface deficit and a mass excess at depth are displayed. The mass-at-depth model produced very marked improvement in the data fit as compared to the surface deficit model. The optimum depth for the mass excess is 130 km.

Sjogren, W. L.; Wimberley, R. N.

1981-01-01

471

Ocean gravity and geoid determination

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

472

Zero-Safe Nets: Modeling Transactions via Transition Synchronization

Zero-Safe Nets: Modeling Transactions via Transition Synchronization Roberto Bruni and Ugo of the same zero-safe net. Zero-safe nets (ZS nets) have been introduced in [BM97] to provide a basic called stable places), ZS nets include a set of zero places. These are idealized resources that remain in

Bruni, Roberto

473

Net Zero Ft. Carson: making a greener Army base

The US Army Net Zero program seeks to reduce the energy, water, and waste footprint of bases. Seventeen pilot bases aim to achieve 100% renewable energy, zero depletion of water resources, and/or zero waste to landfill by 2020. Some bases are pursuing Net Zero in a single secto...

474

Gravity's Rainbow: a bridge towards Horava-Lifshitz gravity

We investigate the connection between Gravity's Rainbow and Horava-Lifshitz gravity, since both theorie