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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 1,729 records · Page 96
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Surface Wettability Analysis from Adsorption Energy and Surface Electrical Charge

Surface wettability is determined by the attraction of a liquid phase to a solid surface. It is typically quantified by using contact angle measurements at mineral surfaces in the case of the flotation of mineral particles. Contact angle research to describe wettability has been investigated at different scales by sessile drop measurements, molecular dynamic simulation, and atomic force microscopy. In this study, the density functional theory (DFT) was employed for predicting the surface free energy and contact angles of a well-known hydrophobic phyllosilicate mineral talc and a well-known hydrophilic phyllosilicate mineral muscovite based on the calculated interfacial energy and surface charge. The results revealed that the predicted contact angle at the atomic scale was larger than the experimental value, and identified two interactions: electrostatic interaction and hydrogen bonding, between the hydrophilic muscovite surface and the water layer, while a water-exclusion zone of 3.346 Å was found between the hydrophobic talc surface and the first water layer. This investigation gives a new perspective for wettability determination at the atomic scale.

Geochemistry & Geophysics↗
DOE OSTI2024

Long-Term Dynamics of Atmospheric Sulfur Dioxide in Urban and Rural Regions of China: Urbanization and Policy Impacts

High levels of sulfur dioxide (SO 2 ) due to human activities pose a serious air pollution issue in China, especially in urban agglomerations. However, limited research has investigated the impact of anthropogenic emissions on higher SO 2 concentrations in urban regions compared to rural areas in China. Here, we analyzed the trends in SO 2 concentrations from 1980 to 2021 in China using the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) dataset. SO 2 column concentrations from the Copernicus Atmosphere Monitoring Service (CAMS) and the Ozone Monitoring Instrument (OMI) during the years 2007–2021 were also examined for validation and comparison purposes. Eight representative areas, including four urban regions (Pearl River Delta [PRD], Beijing-Tianjin-Hebei [BTH], Yangtze River Delta [YRD], and Sichuan Basin [SCB]) and four rural regions (Northeast Region [NER], Mongolian Region [MR], West Region [WR], and Tibetan Plateau Region [TR]) were selected for the analysis. Overall, a significant but fluctuating increase in SO 2 concentrations over China was observed during 1980–2021. During 1980–1997 and 2000–2010, there was an increase in SO 2 concentration, while during 1997–2000 and 2010–2021, a decreasing trend was observed. The average increase in SO 2 concentration was approximately 16 times higher in urban regions than in the rural background. We also found that SO 2 dynamics were highly associated with expansion of urban areas, population density, and gross domestic product. Nonetheless, since 2007, SO 2 concentrations have exhibited a downward trend, which is mainly attributed to the air pollution policies implemented by the Chinese government. Our findings highlight the need for further studies on the impact of SO 2 on regional climate change in China.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

A magnetic particle time-of-flight (MagPTOF) diagnostic for measurements of shock and compression-bang time at the NIF [National Ignition Facility]

A magnetic particle time-of-flight (MagPTOF) diagnostic has been designed to measure shock- and compression-bang time using DHe-fusion protons and DD-fusion neutrons, respectively, at the National Ignition Facility (NIF). This capability, in combination with shock-burn weighted areal density measurements, will significantly constrain the modeling of the implosion dynamics. This design is an upgrade to the existing particle time-of-flight (pTOF) diagnostic, which records bang times using DD or DT neutrons with an accuracy better than ±70 ps [H. G. Rinderknecht et al., Rev. Sci. Instrum. 83, 10D902 (2012)]. The inclusion of a deflecting magnet will increase DHe-proton signal-to-background by a factor of 1000, allowing for the first time simultaneous measurements of shock and compression-bang times in DHe-filled surrogate implosions at the NIF.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1972

Density and optical properties of SPARCS plumes

Propellant gases emitted by attitude control systems such as SPARCS (Solar Pointing Aerobee Rocket Control System) and possible interference with experiments aboard the payloads are discussed. The optical properties of seven actual and potential gases emitted by propellant systems (CF4, N2H4, NH3, N2, CO2, Ar, and He) are presented. A compilation of absorption coefficients from 1 Angstrom to 50 microns and a summary of fluorescent spectra and efficiencies are provided. Since Freon-14 (CF4) is of primary importance to SPARCS, an experimental search for the fluorescent spectrum of CF4 was performed by exciting the gas with 920 Angstrom UV photons. The result was compared with an electron impact induced spectrum of CF4, and conclusions drawn about the nature of the radiating species. A detailed study of the CF4 flow fields and plume densities for typical SPARCS controlled payloads was made using gas dynamic codes which included the effects of vehicle shading and condensation. The importance of the optical properties of CF4 plumes was investigated and it is concluded that absorption is negligible but fluoresence may be significant in some cases.

Brown, W. A.↗
NASA NTRS1975

Landing impact studies of a 0.3-scale model air cushion landing system for a Navy fighter airplane

An experimental study was conducted in order to determine the landing-impact behavior of a 0.3-scale, dynamically (but not physically) similar model of a high-density Navy fighter equipped with an air cushion landing system. The model was tested over a range of landing contact attitudes at high forward speeds and sink rates on a specialized test fixture at the Langley aircraft landing loads and traction facility. The investigation indicated that vertical acceleration at landing impact was highly dependent on the pitch angle at ground contact, the higher acceleration of approximately 5g occurring near zero body-pitch attitude. A limited number of low-speed taxi tests were made in order to determine model stability characteristics. The model was found to have good pitch-damping characteristics but stability in roll was marginal.

Leland, T. J. W.↗
NASA NTRS1974

NASA objectives for improved solar power plants

The present work describes the principal goals for the main effort of NASA's research and development of solar photovoltaic cells and arrays. These are (1) to reduce array costs from $270/watt to $90/watt (no change in volume) or to $41/watt (high volume production), (2) raise power density from 66 watts/kg to 110 watts/kg, and (3) minimize dynamic interaction problems. The first two goals can be accomplished by increased cell efficiency, reduced cell thickness, the development of a multiple ribbon growth process, and automation of cell production. To minimize dynamic interaction between array and spacecraft, module flexibility will be increased.

Cohn, E. M.↗
NASA NTRS1978

On-board data processing for the IRAS telescope system

Onboard data processing has been developed for the Infrared Astronomical Satellite (IRAS) telescope system to effectively utilize the RF bandwidth and minimize the ground-data processing costs. Use of filtering techniques, data deglitching circuits, and data encoding algorithms are combined with a microprocessor-controlled telescope system to achieve a system dynamic range of 100,000 with a noise equivalent flux density of no less than 10 to the minus 19th W/sq cm. Extraneous data, e.g., noise due to radiation hits, will be removed prior to transmission, thereby optimizing ground-data processing for the highest sensitivity and reliability. Simulation results are presented which demonstrate the advantages gained through the use of onboard data processing and illustrate the possible merging of these techniques with an array for the future evolution of 'smart' sensors.

Lum, H.↗
NASA NTRS1983

A two-dimensional model of the ionosphere of Venus

While most orbits of the Pioneer Venus Orbiter have indicated a substantial nightside ionosphere, this region virtually disappears, existing only as irregular patches of low density plasma, on those orbits during which the solar wind dynamic pressure is large. There observational results are presently interpreted by means of a two-dimensional theoretical model of the Venus ionosphere in which empirical horizontal velocities are adopted. The degree to which the horizontal transport of ions from day to night can maintain the nightside ionosphere is shown to depend on the flow velocities, together with the ionopause height at the terminator. Attention is also given to the role played by electron precipitation in the support of a nightside ionosphere. Indirect evidence is given for an enhanced deuterium/hydrogen ratio on Venus.

Cravens, T. E.↗
NASA NTRS1985

Quasi-neutrality in the polar cusp

Data from the High Altitude Plasma Instrument on Dynamics Explorer have shown a remarkably close correspondence between the densities of suprathermal electrons and positive ions at altitudes between 16,000 and 23,000 km in the polar cusp. It is argued that this quasi-neutrality results from an ambipolar electric field at the magnetopause, which allows the entry of magnetosheath electrons only to the extent required to balance the charge carried by the positive ions.

Burch, J. L.↗
NASA NTRS1986

Short-term variability of nitrogen dioxide in the winter stratosphere

Measurements of limb radiance from the Solar Mesosphere Explorer (SME) satellite are used to infer the NO2 density at the 10- and 16-mbar pressure levels from January 1 to March 31 of 1982. A photochemical-dynamical model is developed using the presently accepted chemistry of the NO(x) family. The dynamical model produces isentropic trajectories which simulate the history of air parcels. From the trajectories the photochemical model calculates NO2 densities, which are compared to those observed by SME. Although the model generally reproduces the spatial and temporal variations rather well, some disagreement was noted for conditions of exceptionally low temperatures. Further analysis indicates that the temperature sensitivity of the N2O5 photolysis cross sections may be overestimated at low temperatures.

Zawodny, J. M.↗
NASA NTRS1986

Ocean surface pressure fields from satellite-sensed winds

The University of Washington's planetary boundary layer model is inverted to use remotely sensed satellite scatterometer-derived surface winds as input to calculate maritime surface pressure fields. The analysis of three different synoptic storm situations is performed using the model and is then compared to conventional National Weather Service analyses. Agreement is good. Isolation of the PBL secondary flow, stratification and thermal wind effects in the model revealed that each may be significant under certain conditions. However, the model shows sensitivity to the thermodynamic features only in a general sense and even a neutral stratification solution gives a good approximation. The high density of the scatterometer data produces mesoscale (hundreds of kilometers) dynamic details, which cannot be confirmed by conventional data at this stage.

Brown, Robert A.↗
NASA NTRS1991

GaAs Schottky barrier varactor diodes for submillimeter wavelength power generation

The development of GaAs Schottky barrier diodes for frequencies well into the submillimeter wavelength range is discussed. These devices have the highest cutoff frequencies yet obtained for varactor diodes and have produced sufficient output power to drive Schottky mixers at frequencies as high as 640 GHz. The fundamental design tradeoff between cutoff frequency and capacitance modulation is explored. As the doping density is increased and the anode diameter is reduced, the dynamic cutoff frequency increases, reaching a maximum of roughly 5 THz. It is concluded that the maximum output frequency from harmonic multipliers based on standard GaAs varactor diodes will be about 1 THz.

Crowe, T. W.↗
NASA NTRS1991

Transport of energy by disturbances in arbitrary steady flows

An exact equation governing the transport of energy associated with disturbances in an arbitrary steady flow is derived. The result is a generalization of the familiar concept of acoustic energy and is suggested by a perturbation expansion of the general energy equation of fluid mechanics. A disturbance energy density and flux are defined and identified as exact fluid dynamic quantities whose leading-order regular perturbation representations reduce in various special cases to previously known results. The exact equation on disturbance energy is applied to a simple example of nonlinear wave propagation as an illustration of its general utility in situations where a linear description of the disturbance is inadequate.

Myers, M. K.↗
NASA NTRS1994

Predicting Flow-Induced Vibrations In A Convoluted Hose

Composite model constructed from two less accurate models. Predicts approximately frequencies and modes of vibrations induced by flows of various fluids in convoluted hose. Based partly on spring-and-lumped-mass representation of dynamics involving springiness and mass of convolution of hose and density of fluid in hose.

Harvey, Stuart A.↗
NASA NTRS1995

Investigation of the basic physics of high efficiency semiconductor hot carrier solar cell

The main purpose of this research program is to investigate potential semiconductor materials and their multi-band-gap MQW (multiple quantum wells) structures for high efficiency solar cells for aerospace and commercial applications. The absorption and PL (photoluminescence) spectra, the carrier dynamics, and band structures have been investigated for semiconductors of InP, GaP, GaInP, and InGaAsP/InP MQW structures, and for semiconductors of GaAs and AlGaAs by previous measurements. The barrier potential design criteria for achieving maximum energy conversion efficiency, and the resonant tunneling time as a function of barrier width in high efficiency MQW solar cell structures have also been investigated in the first two years. Based on previous carrier dynamics measurements and the time-dependent short circuit current density calculations, an InAs/InGaAs - InGaAs/GaAs - GaAs/AlGaAs MQW solar cell structure with 15 bandgaps has been designed. The absorption and PL spectra in InGaAsP/InP bulk and MQW structures were measured at room temperature and 77 K with different pump wavelength and intensity, to search for resonant states that may affect the solar cell activities. Time-resolved IR absorption for InGaAsP/InP bulk and MQW structures has been measured by femtosecond visible-pump and IR-probe absorption spectroscopy. This, with the absorption and PL measurements, will be helpful to understand the basic physics and device performance in multi-bandgap InAs/InGaAs - InGaAs/InP - InP/InGaP MQW solar cells. In particular, the lifetime of the photoexcited hot electrons is an important parameter for the device operation of InGaAsP/InP MQW solar cells working in the resonant tunneling conditions. Lastly, time evolution of the hot electron relaxation in GaAs has been measured in the temperature range of 4 K through 288 K using femtosecond pump-IR-probe absorption technique. The temperature dependence of the hot electron relaxation time in the X valley has been measured.

Alfano, R. R.↗