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Results for “periodic potential”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Preliminary analysis of data from SRI international transient pulse monitor on board P78-2 SCATHA satellite

The satellite charging at high altitudes (SCATHA) program addresses the occurrence of electrostatic discharges causing undesirable effects like deleterious transients in electronic circuits on satellites. The high altitude plasma environment and the effects of the interaction of this environment with the orbiting satellite are studied. The SRI transient pulse monitor (TPM) detects the transient electromagnetic signals induced in selected circuits. As a transient detector the TPM records transient signals, indicates the number of transients observed, and gives peak amplitude of the largest transient during each second's interval. Most of the early data from the TPM contain pulses associated with internal electrical activity and electrostatic charging on the surface of the P78-2 is evidenced. It is found that periods of external discharging do not necessarily coincide with periods in which high potentials are measured on the satellite's surface.

Damron, S. A.↗
NASA NTRS1983

Theory of silicon superlattices - Electronic structure and enhanced mobility

A realistic tight-binding band-structure model of silicon superlattices is formulated and used to study systems of potential applied interest, including periodic layered Si-Si(1-x)Ge(x) heterostructures. The results suggest a possible new mechanism for achieving enhanced transverse carrier mobility in such structures: reduced transverse conductivity effective masses associated with the superlattice band structure. For electrons in 100-line-oriented superlattices, a reduced conductivity mass arises intrinsically from the lower symmetry of the superlattice and its unique effect on the indirect bulk silicon band gap. An order of magnitude estimate of the range of mobility enhancement expected from this mechanism appears to be consistent with preliminary experimental results on Si-Si(1-x)Ge(x) superlattices.

Moriarty, J. A.↗
NASA NTRS1984

The dayside Venus ionosphere. I - Pioneer-Venus retarding potential analyzer experimental observations

The median values of the principal ionospheric quantities of the Venus dayside ionosphere are presented. The values are derived from the quantities measured by the Pioneer-Venus orbiter retarding potential analyzer over a period of two earth years at solar cycle maximum. Quantities reported are total ion density, O(+) density, O2(+) density, sum density (NO(+) + N2(+) + CO(+)), CO2(+) density, ion temperature, electron temperature, and plasma particle pressure. The data are organized to reveal altitude, solar zenith angle, solar longitude, and latitude dependences. The O(+) density exhibits both a solar longitude and a latitude dependence which may be caused by superrotation of the thermosphere and/or ionosphere. Asymmetry between the dawn and dusk terminator regions in the behavior of other quantities is also described.

Miller, K. L.↗
NASA NTRS1987

False lock performance in polarity-type Costas receivers in the presence of periodic data patterns

The authors address the false-lock performance of receivers which use polarity-type Costas loops for the carrier recovery of unbalanced quadrature phase-shift keyed (QPSK), asynchronous QPSK or binary PSK (BPSK) signals in the presence of periodic data patterns. The potential false-lock frequencies are first identified. Expressions for both true-lock and false-lock components are also derived, thereby allowing numerical evaluation of various key parameters for cases of practical interest.

Wang, James June-Ming↗
NASA NTRS1993

The world of NASA microgravity science

It has been said the decades of the 1990's represents a second golden age of science. We are in the midst of one of the most exciting and interesting periods in the history of exploration -- a period which holds the potential for expanding our understanding of scientific phenomena ranging from intricacies of the universe to the subtleties of our own planet. The opportunities to study the effects of microgravity in space seem limitless during the next decade. Using the European Space Agency (ESA) built Spacelab, we will maximize opportunities for development of new microgravity facilities in order to obtain new information and increase our understanding of the effects of gravitational forces on phenomena in biological, chemical and physical systems. NASA intends to move aggressively, but sensibly, to develop additional space research facilities as we built toward the unique Space Station Freedom resources becoming available towards to end of this decade.

Rhome, Robert C.↗
NASA NTRS1994

Mapping ionospheric convection response to IMF B(sub y) negative and B(sub z) positive conditions

We have used the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure to derive electric potential patterns for a period of strong and slowly varying northward Interplanetary Magnetic Field (IMF). Using these patterns we offer some insight into high-latitude convection response to differing IMF conditions between the hours of 0850 and 1720 UT on 14 January 1988. We introduce a newly assimilated data set, Defense Meteorological Satellite Program (DMSP) ion drift measurements, as a means of mapping electric fields in polar regions. Also, for the first time we map both southern and northern hemisphere convection flows. We show that significantly different convection patterns are simultaneously possible in the two polar caps when B(sub z) is positive and that asymmetries in these patterns are influenced by the strength of B(sub y) and B(sub x). When the ratio absolute value of B(sub y)/B(sub z) exceeds unity the polar cap convection increases and changes from sunward to anti-sunward for B(sub z) positive conditions.

Knipp, D. J.↗
NASA NTRS1998

The Mars Gravity Simulation Project

Human beings who make abrupt transitions between one gravitational environment and another undergo severe disruptions of their visual perception and visual- motor coordination, frequently accompanied by "space sickness." Clearly, such immediate effects of exposure to a novel gravitational condition have significant implications for human performance. For example, when astronauts first arrive in Earth orbit their attempts to move about in the spacecraft and to perform their duties are uncoordinated, inaccurate, and inefficient. Other inter-gravitational transitions for which these difficulties can be expected include going from the 0 g of the spacecraft to the. 16 g of the Moon, from 0 g to the .38 g of Mars, and from 0 g back to the 1.0 g of Earth. However, after astronauts have actively interacted with their new gravitational environment for several days, these problems tend to disappear, evidence that some sort of adaptive process has taken place. It would be advantageous, therefore, if there were some way to minimize or perhaps even to eliminate this potentially hazardous adaptive transition period by allowing astronauts to adapt to the altered gravitational conditions before actually entering them. Simultaneous adaptations to both the altered and the normal gravitational environment as a result of repeatedly adapting to one and readapting to the other, a phenomenon known as dual adaptation. The objective of the Mars Gravity Simulator (MGS) Project is to construct a simulation of the visual and bodily effects of altered gravity. This perceptual-motor simulation is created through the use of: 1) differential body pressure to produce simulated hypo-gravity and 2) treadmill-controlled virtual reality to create a corresponding visual effect. It is expected that this combination will produce sensory motor perturbations in the subjects. Both the immediate and adaptive behavioral (postural and ambulatory) responses to these sensory perturbations will be assessed.

Korienek, Gene↗
NASA NTRS2007

Increased Water Storage at Ice-stream Onsets: A Critical Mechanism?

The interdependence of rapid ice flow, surface topography and the spatial distribution of subglacial water are examined by linking existing theories. The motivation is to investigate whether the acceleration of an ice-stream tributary contains a positive feedback that encourages the retention of subglacial water that leads to faster flow. Periodically varying surface and bed topographies are related through a linear ice-flow perturbation theory for various values of mean surface slope, perturbation amplitude and basal sliding speeds. The topographic variations lead to a periodic variation in hydraulic potential that is used to infer the tendency for subglacial water to be retained in local hydraulic potential minima. If water retention leads to enhanced basal sliding, a positive feedback loop is closed that could explain the transition from slower tributary flow to faster-streaming flow and the sustained downstream acceleration along the tributary-ice-stream system. A sensitivity study illustrates that the same range of topographic wavelengths most effectively transmitted from the bed to the surface also strongly influences the behavior of subglacial water. A lubrication index is defined to qualitatively measure the heterogeneity of the subglacial hydrologic system. Application of this index to field data shows that the transition from tributary to ice stream closely agrees with the location where subglacial water may be first stored.

Bindschadler, Robert↗
NASA NTRS2010

Cassini Main Engine Assembly Cover Flight Management and Performance

The Cassini spacecraft has performed its four year Prime Mission at Saturn and is currently in orbit at Saturn performing a two year extended mission. 12Its main engine nozzles are susceptible to impact damage from micrometeoroids and on-orbit dust. The spacecraft has an articulating device known as the Main Engine Assembly (MEA) cover which can close and shield the main engines from these threats. The cover opens to allow for main engine burns that are necessary to maintain the trajectory. Periodically updated analyses of potential on-orbit dust hazard threats have resulted in the need to continue to use the MEA cover beyond its intended use and beyond its design life. This paper provides a detailed Systems-level overview of the flight management of the MEA cover device and its flight performance to date.

Somawardhana, Ruwan P.↗
NASA NTRS2018

Using Reanalysis in Crop Monitoring and Forecasting Systems

Weather observations are essential for crop monitoring and forecasting but they are not always available and in some cases they have limited spatial representativeness. Thus, reanalyses represent an alternative source of information to be explored. In this study, we assess the feasibility of reanalysis-based crop monitoring and forecasting by using the system developed and maintained by the European Commission- Joint Research Centre, its gridded daily meteorological observations, the biased-corrected reanalysis AgMERRA and the ERA-Interim reanalysis. We focus on Europe and on two crops, wheat and maize, in the period 1980-2010 under potential and water-imited conditions. In terms of inter-annual yield correlation at the country scale, the reanalysis-driven systems show a very good performance for both wheat and maize (with correlation values higher than 0.6 in almost all EU28 countries) when compared to the observations-driven system. However, significant yield biases affect both crops. All simulations show similar correlations with respect to the FAO reported yield time series. These findings support the integration of reanalyses in current crop monitoring and forecasting systems and point to the emerging opportunities linked to the coming availability of higher-resolution reanalysis updated at near real time.

Reanalysis↗
NASA NTRSDate not supplied

Evaluation of Iodine and Silver as Biocides for Potable Water in Human Missions beyond Low Earth Orbit

Chemical biocides play an important role in potable water storage and distribution systems. They provide protection against microbial growth that can negatively impact efficient water transport and crew health. Molecular iodine and ionic silver have been used on the International Space Station for decades. Future orbiting and surface habitats will have potable water systems that will require reliable potable water storage and challenging transport schemes during daily operations with potentially lengthy and repeated periods of non-use. Based on a review of literature, experimental data, and flight data this paper categorizes the advantages and disadvantages of the two heritage biocides on ISS: iodine and silver. The history of biocide practices on ISS is compared to requirements of future human missions beyond low Earth Orbit. The upstream water quality supply and downstream water uses are defined with respect to the two biocides. The methods of injection and removal of the two biocides are compared for a range of downstream water uses including drinking water, hygiene water, technical water, oxygen generation water, and extravehicular activity water. The paper provides mission planners with a technical and engineering assessment of the two biocides and identifies gaps in knowledge and on-orbit experiences.

Dean Muirhead↗
NASA NTRS1979

ATS-5 and ATS-6 potentials during eclipse

The ATS 5 and ATS 6 data for spacecraft charging during eclipse conditions is analyzed. The ATS 5 and ATS 6 charged to voltages greater than 100 volts for about 55 percent of the eclipse periods examined. The mean spacecraft potential during eclipse was 2 keV for ATS 5, and the highest potential measured was 10 kilovolts. For ATS 6, the mean potential during eclipse was 4 keV, the highest potential measured 20 keV. The average measured spacecraft potentials for both ATS 5 and 6 depend approximately linearly upon Kp. This relationship is due mainly to the dependence of electron current density on Kp near midnight. Spacecraft potentials at geosynchronous orbit may, to a rough approximation, thus be inferred from ground-based measurements of Kp, the planetary 3-hour index.

Rubin, A. G.↗
DOE OSTI2020

A Climatology and Extreme Value Analysis of Large Hail in China

In this paper, hail size records are analyzed at 2254 stations in China and a hail size climatology is developed based on gridded hail observations for the period 1960–2015. It is found that the annual percentiles of hail size records changed sharply and national-wide after 1980, therefore two periods, 1960–79 and 1980–2015, are studied. There are some similarities between the two periods in terms of the characteristics of hail size such as the spatial distribution patterns of mean annual maximum hail size and occurrence week of annual maximum hail size. The 1980–2015 period had higher observation density than the 1960–79 period, but showed smaller mean annual maximum hail size, especially in northern China. In the majority of grid boxes, the annual maximum hail size experienced a decreasing trend during the 1980–2015 period. A Gumbel extreme value model is fitted to each grid box to estimate the return periods of maximum hail size. The scale and location parameter of the fitted Gumbel distributions are higher in eastern China than in western China, thereby reflecting a greater likelihood of large hail in eastern China. In southern China, the maximum hail size exceeds 127 mm for a 10-yr return period, whereas in northern China maximum hail size exceeds this threshold for a 50-yr return period. Furthermore, the Gumbel model is found to potentially underestimate the maximum hail size for certain return periods, but provides a more informed picture of the spatial distribution of extreme hail size and the regional differences.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1995

Visualization of the electrostatic potential distribution in both polar ionospheres using multiple satellite measurements

During the time from December 1991 through March 1992, there were four operational DMSP satellites in polar orbit. All four satellites carried the Special Sensor-Ions, Electrons, Scintillation (SSIES) plasma package which included an ion drift meter. Data from the drift meter, combined with the magnetic field data, allowed the calculation of the electrostatic potential in the ionosphere along the satellite's path. Simultaneous polar coverage by four satellites was unprecedented, providing researchers with almost continuous monitoring of the potential distribution in both hemispheres for the four month period. Combining the magnitude and location of the potential data from each of the four satellites in order to examine the varying potential distribution pattern in both hemispheres presented a major challenge in data visualization. The problem was solved by developing a three-dimensional presentation of the data where the potentials are color coded and represented by the vertical dimension. This paper presents examples from a computer animation of several days of data demonstrating evolution of the size and shape of the potential distribution, along with how these changes correspond to variations in other geophysical parameters, such as the IMF orientation and the K(sub p) index.

Hairston, Marc R.↗
NASA NTRSDate not supplied

An Orbital Photogeologic Map of the Jezero Crater Rim: Diverse Targets for Mars 2020 Future Exploration.

The Perseverance rover on the Mars 2020 mission is currently collecting samples in Jezero crater for potential future return to Earth by the Mars Sample Return (MSR) mission. Jezero is a 45 km diameter mid- to late-Noachian-aged crater selected for its diverse geology and potential for preserving evidence of ancient life. The rover is approaching the crater rim, an area of interest for its potential to preserve diverse lithologies representative of a large period of geologic history. It has significant astrobiological potential, as it may preserve evidence of uplifted deep crust and ancient hydrothermal environments. Impact megabreccia in the crater rim may be exhumed pre-Noachian crust from the Isidis impact, which would likely be the oldest materials ever investigated by a rover on Mars. Additionally, the rim hosts outcrops of the regionally extensive and potentially volcanic olivine/carbonate unit and mafic capping unit, which could have implications for the evolution of Mars volcanism. Regional maps have delineated the lithologies present in and around Jezero as a whole. The largest scale that the crater rim geology has been mapped is 1:5000.

M C Deahn↗
NASA NTRS2007

Deep Dielectric Charging of Spacecraft Polymers by Energetic Protons

The majority of research in the field of spacecraft charging concentrates on electron charging effects with little discussion of charging by protons. For spacecraft orbiting in the traditional LEO and GEO environments this emphasis on electrons is appropriate since energetic electrons are the dominant species in those orbits. But for spacecraft in orbits within the inner radiation belts or for interplanetary and lunar space probes, proton charging (center dot) effects may also be of concern. To examine bulk spacecraft charging effects in these environments several typical highly insulating spacecraft polymers were exposed to energetic protons (center dot) with energies from 1 Me V to lO Me V to simulate protons from the solar wind and from solar energetic proton events. Results indicate that effects in proton charged dielectrics are distinctly different than those observed due to electron charging. In most cases, the positive surface potential continued to increase for periods on the order of minutes to a day, followed by long time scale decay at rates similar to those observed for electron charging. All samples charged to positive potentials with substantially lower magnitudes than for equivalent electron doses. Possible explanations for the different behavior of the measured surface potentials from proton irradiation are discussed; these are related to the evolving internal charge distribution from energy dependent electron and proton transport, electron emission, charge migration due to dark current and radiation induced conductivity, and electron capture by embedded protons.

radiation induced conductivity↗
DOE OSTI2026

Energy Storage and the Law of Averages: How Storage Can Make Electricity More Affordable

The electric grid is planned, built, and operated to satisfy peak demand. But because peak demand only occurs for a few hours per year, customers end up paying full price for grid infrastructure that is only used for a small fraction of the year—an increasingly expensive proposition as peak demand continues to grow and more infrastructure is required to meet it. The emergence of cost-competitive energy storage technologies in recent years, however, offers the potential for a grid that is planned, built, and operated based on average demand. By strategically siting and operating energy storage throughout the electric grid, excess generation in low-demand periods can be captured and stored near customers, which then reduces the amount of electricity that needs to be generated and moved through the transmission and distribution systems during high-demand periods. This paper describes these potential benefits, supported by real-world examples of energy storage projects that have created cost savings, which points to the potential for profound and far-reaching reductions in the cost of electricity if energy storage technologies are deployed at scale throughout the electric grid. These examples will be of use to system planners and operators, utility regulators, decision makers, and stakeholders in those processes as they look for opportunities to reduce the cost of electricity in their respective systems and jurisdictions.

25 ENERGY STORAGE↗
NASA NTRS1984

Microwave bistatic reflectivity dependence on the moisture content and matric potential of bare soil

Results are presented of an experimental program to determine the functional dependence of the microwave reflectivity of nonvegetated soil surfaces upon volumetric soil moisture and matric potential. A combination evaporation-drainage field experiment was conducted on a bare Captina slit loam with reflectivity, soil moisture content, and matric potential monitored for extended time periods. Results show that for a restricted pressure range (approximately -0.05 to -0.75 bar) there is excellent linear correlation between the log of bistatic reflectivity and both volumetric moisture content and matric potential. Layering effects due to steep moisture content (and matric potential) gradients in the profile are demonstrated to have two distinct and significant effects on the reflectivity response. At near saturation of rough surfaces a very thin dry surface layer appears to modify the effective roughness. This leads to a saturation of reflectivity at high moisture contents. As the surface proceeds to dry further, deeper layers produce coherent interference patterns in the reflectivity response, particularly at the higher frequencies.

Waite, W. P.↗