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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 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Crosstalk cancellation on linearly and circularly polarized communications satellite links

The paper discusses the cancellation network approach for reducing crosstalk caused by depolarization on a dual-polarized communications satellite link. If the characteristics of rain depolarization are sufficiently well known, the cancellation network can be designed in a way that reduces system complexity, the most important parameter being the phase of the cross-polarized signal. Relevant theoretical calculations and experimental data are presented. The simplicity of the cancellation system proposed makes it ideal for use with small domestic or private earth terminals.

Overstreet, W. P.↗
NASA NTRS1989

Rigorous analysis of a circular patch antenna excited by a microstrip transmission line

Boundary conditions are enforced on a portion of the microstrip feed line as well as the patch antenna. The integral equation for the unknown currents on the antenna and feed is solved by applying the Galerkin method of moments in the Fourier transform domain. The validity of the solution is tested by comparison of computed results with experimental data. The theoretical treatment proves to be applicable to the most common feeding arrangements, namely, the direct edge-feed and proximity coupling excitation. In the latter case, two-layer substrates having distinct dielectric constants are studied. The purpose of the study is to deduce, for a given overall substrate thickness, the smallest line-ground plane separation for which a match of the radiator to the feed line is still possible. The advantages of such a configuration are discussed.

Davidovitz, Marat↗
NASA NTRS1977

Solid propellant rocket motor internal ballistics performance variation analysis, phase 3

Results of research aimed at improving the predictability of off nominal internal ballistics performance of solid propellant rocket motors (SRMs) including thrust imbalance between two SRMs firing in parallel are reported. The potential effects of nozzle throat erosion on internal ballistic performance were studied and a propellant burning rate low postulated. The propellant burning rate model when coupled with the grain deformation model permits an excellent match between theoretical results and test data for the Titan IIIC, TU455.02, and the first Space Shuttle SRM (DM-1). Analysis of star grain deformation using an experimental model and a finite element model shows the star grain deformation effects for the Space Shuttle to be small in comparison to those of the circular perforated grain. An alternative technique was developed for predicting thrust imbalance without recourse to the Monte Carlo computer program. A scaling relationship used to relate theoretical results to test results may be applied to the alternative technique of predicting thrust imbalance or to the Monte Carlo evaluation. Extended investigation into the effect of strain rate on propellant burning rate leads to the conclusion that the thermoelastic effect is generally negligible for both steadily increasing pressure loads and oscillatory loads.

Sforzini, R. H.↗
NASA NTRS1979

Observations of solar oscillations with periods of 160 minutes

Severny et al. (1976) have reported oscillations of the sun with a period near 160 min. A description is presented of observations made at the Stanford Solar Observatory during the time from 1975 to the present which seem to support the reports by Severny et al. At Stanford the relative velocity between a central circular area of radius 0.5 solar radius on the solar disk and most of the remaining area of the solar disk is measured. A superposed epoch analysis of the observations using a period of 160 min is discussed. An apparent agreement in phase between the obtained observational data and those reported by Severny et al. tends to support the interpretation that solar oscillations are being observed.

Scherrer, P. H.↗
NASA NTRS1984

The Gamma Ray Observatory - A new view of the violent universe

The Gamma Ray Observatory (GRO) has been undertaken by NASA to make the next major thrust in high-energy astrophysics. The GRO will be flown in a circular orbit at an altitude of 400 km with an inclination of 28.5 degrees. The Shuttle will take the GRO to its nominal orbit altitude. The GRO will be removed and will ascend to 400 km using its own propulsion system. The GRO will record and transmit data to the Tracking and Data Relay Satellite, which will then relay the signal to ground. The GRO will consist of four separate instruments that collectively span the photon spectrum from 0.05 to 30,000 MeV, almost six decades in energy. The photon sensitivity over the entire six-decade range will be improved by more than an order of magnitude over the best previously flown instruments. Significant improvements in angular resolution will also be made.

Kniffen, D. A.↗
NASA NTRS1993

The spatial distribution of coronae and related features on Venus

Coronae are large quasi-circular geologica features that are common on Venus. They appear to be the surface tectonic and volcanic expressions of mantle diapirs that have impinged on the underside of the venusian lithosphere. We have investigated the spatial distribution of 335 coronae and related features identified in Magellan radar data. It is more clustered than a Poisson distribution, with a statistical certainty of more than 99%. It is dominated by a single large cluster centered near the equator at about 245 deg longitude. The features are preferentially found at elevation and geoid values close to the planetary mean, with a paucity at both the highest and lowest levels of topgraphy and geoid. Some coronae appear aligned in quasi-linear chains. We attribute the clustering of coronae and related features to preferential formation of these features above regions of broad-scale mantle upwelling, and suggest that a major mantle upwelling underlies the one large cluster. We suggest that coronae are rare at the lowest elevations because these may be regions of mantle downwelling. The shortage of coronae at the highest elevations may result both from obscuration by other intense tectonism there and from suppression there of their formation by an unusually thick crust. Corona chains may be produced by enhanced passive mantle uplift below failed or incipient rifts.

Squyres, Steven W.↗
NASA NTRS1959

Determination of Static Strength and Creep Buckling of Unstiffened Circular Cylinders Subjected to Bending at Elevated Temperatures

A method based on a semiempirical procedure is presented for predicting static strength and creep buckling of unstiffened circular cylinders subjected to pure bending at elevated temperatures. The method is applicable to cylinders that are loaded into the inelastic stress range prior to buckling and fail in a local mode. The predicted bending moments associated with static strength and creep buckling are compared with experimental data (taken from NACA RM 57El7) obtained from tests at 500 F on 5052-0 aluminum-alloy cylinders with radius- thickness ratios ranging from 125 to 250.

Mathauser, Eldon E.↗
NASA NTRS2019

A Possible Second Large Subglacial Impact Crater in Northwest Greenland

Following the discovery of the Hiawatha impact crater beneath the northwest margin of the Greenland Ice Sheet, we explored satellite and aerogeophysical data in search of additional such craters. Here we report the discovery of a possible second subglacial impact crater that is 36.5‐km wide and 183 km southeast of the Hiawatha impact crater. Although buried by 2 km of ice, the structure's rim induces a conspicuously circular surface expression, it possesses a central uplift, and it causes a negative gravity anomaly. The existence of two closely spaced and similarly sized complex craters raises the possibility that they formed during related impact events. However, the second structure's morphology is shallower, its overlying ice is conformal and older, and such an event can be explained by chance. We conclude that the identified structure is very likely an impact crater, but it is unlikely to be a twin of the Hiawatha impact crater.

Greenland↗
NASA NTRS2018

Reduced Gravity Airborne Mobility Testbed

Working in conjunction with the NASA Ames research center the goal of this senior design project was to develop a mobile test apparatus to enable wheel-soil interaction in a reduced gravity environment. In addition to collecting accurate wheel-soil interfacing data, a method of maintaining the density of the soil being used during the testing was developed to allow for repeatable testing conditions In order to meet these goals an annular testbed was design and built, providing an alternative to NASA’s linear rover wheel design. The circular design allowed for a smaller footprint and lighter device. The team found it was possible to set the desired slip ratio by rotating the both the annular testbed and wheel at different speeds. The Drawbar Pull force on the wheel was then measured with a torque sensor. Future work to be done includes improving the timing belt system, more robust control system, and more secure testbed base.

Liz Barrett↗
DOE OSTI2022

Assessments of epistemic uncertainty using Gaussian stochastic weight averaging for fluid-flow regression

Here, we use Gaussian stochastic weight averaging (SWAG) to assess the epistemic uncertainty associated with neural-network-based function approximation relevant to fluid flows. SWAG approximates a posterior Gaussian distribution of each weight, given training data, and a constant learning rate. Having access to this distribution, it is able to create multiple models with various combinations of sampled weights, which can be used to obtain ensemble predictions. The average of such an ensemble can be regarded as the 'mean estimation', whereas its standard deviation can be used to construct 'confidence intervals', which enable us to perform uncertainty quantification (UQ) with regard to the training process of neural networks. We utilize representative neural-network-based function approximation tasks for the following cases: (i) a two-dimensional circular-cylinder wake; (ii) the DayMET dataset (maximum daily temperature in North America); (iii) a three-dimensional square-cylinder wake; and (iv) urban flow, to assess the generalizability of the present idea for a wide range of complex datasets. SWAG-based UQ can be applied regardless of the network architecture, and therefore, we demonstrate the applicability of the method for two types of neural networks: (i) global field reconstruction from sparse sensors by combining convolutional neural network (CNN) and multi-layer perceptron (MLP); and (ii) far-field state estimation from sectional data with two-dimensional CNN. We find that SWAG can obtain physically-interpretable confidence-interval estimates from the perspective of epistemic uncertainty. This capability supports its use for a wide range of problems in science and engineering.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1992

Venus steep-sided domes: Relationships between geological associations and possible petrogenetic models

Venus domes are characterized by steep sides, a circular shape, and a relatively flat summit area. In addition, they are orders of magnitude larger in volume and have a lower height/diameter ratio than terrestrial silicic lava domes. The morphology of the domes is consistent with formation by lava with a high apparent viscosity. Twenty percent of the domes are located in or near tessera (highly deformed highlands), while most other (62 percent) are located in and near coronae (circular deformational features thought to represent local mantle upwelling). These geological associations provide evidence for mechanisms of petrogenesis and several of these models are found to be plausible: remelting of basaltic or evolved crust, differentiation of basaltic melts, and volatile enhancement and eruption of basaltic foams. Hess and Head have shown that the full range of magma compositions existing on the Earth is plausible under various environmental conditions on Venus. Most of the Venera and Vego lander compostional data are consistent with tholeiitic basalt; however, evidence for evolved magmas was provided by Venera 8 data consistent with a quartz monzonite composition. Pieters et al. have examined the color of the Venus surface from Venera lander images and interpret the surface there to be oxidized. Preliminary modeling of dome growth has provided some interpretations of lava rheology. Viscosity values obtained from these models range from 10(exp 14) - 10(exp 17) pa*s, and the yield strength has been calculated to be between 10(exp 4) and 10(exp 6) Pa, consistent with terrestrial silicic rocks. The apparent high viscosity of the dome lavas suggests that the domes have a silicic composition or must augment their viscosity with increased visicularity or crystal content. Sixty-two percent of the Venus domes are associated with coronae, circular features that have been proposed as sites of mantle upwelling, and 20 percent of the domes are located near tessera, relatively high areas of complex deformed terrain. We have investigated several models that are consistent with these geologic associations. The first case involves the differentiation of basalt in a magma reservoir in the crust, perhaps produced by partial melting within a mantle plume. The second case is melting at the base of thickened basaltic crust, and the final case is volatile exsolution and enhancement within a basaltic magma reservoir. The association of domes with tessera might be explained by crustal remelting, while the association with coronae may be consistent with chemical differentiation of a magma reservoir or the exsolution and concentration of volatiles in the reservoir before eruption.

Pavri, B.↗
DOE OSTI2026

Opportunities and challenges in thermochemical conversion of municipal solid waste: A comprehensive review

Recent advancements in thermochemical conversion processes have elucidated new pathways for converting municipal solid waste into valuable resources. This review explores the primary thermochemical conversion methods, including combustion, gasification, pyrolysis, torrefaction, hydrothermal carbonization, and hydrothermal liquefaction, emphasizing their potential roles in waste management and energy recovery. Key challenges including feedstock variability, ash behavior, and scale-up limitations are discussed alongside opportunities for hybrid systems and circular economy integration. A comparative analysis of research publications indicates a significant focus on thermochemical pathways within the broader context of municipal solid waste research, underscoring the growing interest in these technologies. Recent advancements in each thermochemical process, alongside their operational, technical, and economic challenges, are discussed. Comparative data reveal that torrefaction enhances the hydrophobicity and grindability of municipal solid waste components, though its energy densification benefits are more modest than those observed in biomass. Hydrothermal carbonization and liquefaction are highlighted for their ability to process high-moisture and heterogeneous waste streams. The review also synthesizes recent findings on reactor configurations, emissions control, and synergistic effects in co-processing municipal solid waste fractions. The findings underscore the importance of developing standardized protocols for municipal solid waste characterization and the need for innovative hybrid systems to improve efficiency.

99 - GENERAL AND MISCELLANEOUS↗
DOE OSTI2020

Two-Dimensional van der Waals Nanoplatelets with Robust Ferromagnetism

We have synthesized unique colloidal nanoplatelets of the two-dimensional (2D) van der Waals ferromagnet CrI3 and have characterized these nanoplatelets structurally, magnetically, and by magnetic circular dichroism spectroscopy. The CrI3 nanoplatelets have lateral dimensions of ~25 nm and thicknesses of only ~4 nm, corresponding to just a few CrI3 monolayers. Magnetic and magneto-optical measurements demonstrate robust 2D ferromagnetic ordering with Curie temperatures similar to bulk CrI3, despite their small size. These data also show magnetization steps akin to those observed in micron-sized few-layer 2D sheets associated with concerted spin-reversal of individual CrI3 layers within few-layer van der Waals stacks. Similar data have also been obtained for CrBr3 and anion-alloyed Cr(I1–xBrx)3 nanoplatelets. These results represent the first example of lateral nanostructures of 2D van der Waals ferromagnets of any composition. The demonstration of robust ferromagnetism at nanometer lateral dimensions opens new doors for miniaturization in spintronics devices based on van der Waals ferromagnets.

De Siena, Michael C.↗
DOE OSTI2026

Delving into the depths of NGC 3783 with XRISM

Using XRISM/Resolve 439 ks time-averaged spectra of the well-known Seyfert-1.5 active galactic nucleus (AGN) in NGC 3783, we investigated the nature of the Fe Kα emission line at 6.4 keV, the strongest and most common X-ray line observed in AGNs. Even the narrow component of the line is resolved with evident Fe Kα 1 (6.404 keV) and Kα 2 (6.391 keV) contributions with a 2:1 flux ratio, fully consistent with a neutral gas with negligible bulk velocity. The narrow and intermediate-width components have a full width at half maximum of 350 ± 50 km/s and 3510 ± 470 km/s, respectively, suggesting that they arise in the outer disk/torus and/or broad line region. We detect a 10% excess flux around 4–7 keV that is not described well by a symmetric Gaussian line but is consistent with a relativistically broadened emission line. In this study we took the simplest approach, modelling the asymmetric line as a single emission line (assuming neutral, He-like, or H-like iron) convolved with a relativistic disk line model. As expected, the inferred inclination angle (i) is highly sensitive to the assumed ionisation state and ranges between 17 and 44°. This model also constrains the black hole spin via the extent of the red wing: the required gravitational redshift in the fitted disk-line profile disfavours a non-spinning (Schwarzschild) black hole. The derived inner radius is close to the radius of the innermost stable circular orbit (rISCO) and is strongly correlated with the black hole spin. To better constrain the spin, we fixed the inner radius to r ISCO and derived a lower limit on the spin of a ≥ 0.29 at the 3σ confidence level. A Compton shoulder is detected in our data as well as a 2–3σ detection of the Cr Kα and Ni Kα lines.

Astronomy and AstroPhysics↗
DOE OSTI2024

High-Resolution Frequency-Domain Spectroscopic and Modeling Studies of Photosystem I (PSI), PSI Mutants and PSI Supercomplexes

Photosystem I (PSI) is one of the two main pigment–protein complexes where the primary steps of oxygenic photosynthesis take place. This review describes low-temperature frequency-domain experiments (absorption, emission, circular dichroism, resonant and non-resonant hole-burned spectra) and modeling efforts reported for PSI in recent years. In particular, we focus on the spectral hole-burning studies, which are not as common in photosynthesis research as the time-domain spectroscopies. Experimental and modeling data obtained for trimeric cyanobacterial Photosystem I (PSI 3 ), PSI 3 mutants, and PSI 3 –IsiA 18 supercomplexes are analyzed to provide a more comprehensive understanding of their excitonic structure and excitation energy transfer (EET) processes. Detailed information on the excitonic structure of photosynthetic complexes is essential to determine the structure–function relationship. We will focus on the so-called “red antenna states” of cyanobacterial PSI, as these states play an important role in photochemical processes and EET pathways. The high-resolution data and modeling studies presented here provide additional information on the energetics of the lowest energy states and their chlorophyll (Chl) compositions, as well as the EET pathways and how they are altered by mutations. We present evidence that the low-energy traps observed in PSI are excitonically coupled states with significant charge-transfer (CT) character. The analysis presented for various optical spectra of PSI 3 and PSI 3 -IsiA 18 supercomplexes allowed us to make inferences about EET from the IsiA 18 ring to the PSI 3 core and demonstrate that the number of entry points varies between sample preparations studied by different groups. In our most recent samples, there most likely are three entry points for EET from the IsiA 18 ring per the PSI core monomer, with two of these entry points likely being located next to each other. Therefore, there are nine entry points from the IsiA 18 ring to the PSI 3 trimer. We anticipate that the data discussed below will stimulate further research in this area, providing even more insight into the structure-based models of these important cyanobacterial photosystems.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1979

The global distribution of long-term total ozone variations during the period 1957-1975

Total ozone observations in the international network have been used as a basis for the analysis of the mean monthly ozone distribution over the globe for the period 1957-1975. It has been found that during the period 1961-1970 the total ozone amount increased in the Northern Hemisphere by about 12 percent and that this increase seems to be significant at all latitudes. Although the data were sparse for the Southern Hemisphere, there did not appear to be any significant ozone changes during the 10 year period. Relatively large geographic variations were found in the ozone trends and it is suggested that these variations are related to large scale changes in the atmospheric circular pattern.

London, J.↗
NASA NTRS1982

Verification of LANDSAT imagery for morphametric and topological studies of drainage basins in a section of the western plateau of Sao Paulo State: Tiete-Aguapei watershed

The potential of using LANDSAT MSS imagery for morphometric and topological studies of drainage basins was verified. Using Tiete and Aguapei watershed (Western Plateau) as the test site because of its homogeneous landscape. Morphometric variables collected for ten drainage basins include: circularity index; river density; drainage density; topographic texture; areal and index length; basin parameter; and main river length 1st order and 2nd order channel length. The topographical variables determined were: order; magnitude; bifuraction ratio; weighted bifuraction ratio; number of segments; number of linking; trajectory length; and topological diameter. Data were collected on topographical maps at the scale of 1:250,000 and 1:59,000 and on LANDSAT imagery at the scale of 1:250,000. The results which were summarized on tables for further analysis, show that LANDSAT imagery can supply the lack of topographic charts for drainage studies.

Parada, N. D. J.↗
NASA NTRS1984

Supersonic separated flow past a cylindrical obstacle on a flat plate

An experimental investigation of three-dimensional boundary-layer separation on a flat plate ahead of a circular cylinder at Mach 2.36 was made. Emphasis was given to the laminar flow regime and to the flow region upstream of the cylinder. The heights and diameters of the cylinders used in the study were larger than the undisturbed boundary-layer thickness at the cylinder location. Data were obtained by oil flow visualization, Schlieren observations, static pressure measurements, and laser anemometry. Oil flow visualization revealed three separation lines on the flat plate ahead of the cylinder. A postulated flowfield structure, which was suggested by this skin-friction pattern, could not be confirmed by the velocity measurements. Velocity measurements indicated an unsteady flow structure.

Ozcan, O.↗