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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Experimental evaluation of small-scale erectable truss hardware

To aid in the prediction of the dynamic behavior of the space station, a one-tenth scale dynamic test model is to be constructed of commercially available, small scale truss hardware. Tests have been performed to determine the axial stiffness characteristics and failure loads of the truss joint. A parametric study has shown that the stiffness of the joint increases as the attachment bolt torque value is increased. Furthermore, at torque values equal to or higher than 250 in-lbs, hysteresis in the load-deflection curve is essentially eliminated. Also, the joint stiffness remained relatively constant between specimens. The effective stiffness of a joint subassembly tested is 76 percent that of the strut. Tensile and compressive failure occurred in the region of the bonded plug, with lower failure loads corresponding to compressive loadings.

Mcgowan, David M.↗
DOE OSTI2025

Lessons learned from the design and operation of a small-scale cross-flow tidal turbine

In 2023, a first-generation prototype of a small-scale marine current turbine was operated in Sequim Bay, Washington (USA) for 141 days. The system, referred to as the Turbine Lander, was the product of a laboratory-to-field effort to develop a system that enables enhanced ocean sensing or vehicle recharge in remote, energetic settings. The turbine consists of a vertical-axis, cantilevered rotor (1.19 m x 0.85 m) with four foils installed on a gravity foundation. A broader range of constraints including the deployment strategy, site characteristics, and estimated loads, drove the system’s design. This work presents the design, characterization, operation, and post-recovery engineering assessment of the Turbine Lander. Pre-deployment characterization efforts yielded a peak power coefficient of approximately 0.3 for the rotor, although system losses resulted in much lower water-to-wire efficiencies under most operating conditions. The results demonstrate the importance of co-design among key components of the powertrain and control systems to achieve acceptable system efficiency across operating conditions.

Co-design↗
NASA NTRS1977

Results from an exploratory study of airframe noise on a small-scale model of a supersonic transport concept

An exploratory study of airframe noise on a small-scale model of a supersonic transport concept was made. The model was a 0.015 scale version without landing gear of Langley's Advanced Supersonic Technology configuration concept, AST-110. Noise measurements were made at positions corresponding to directly beneath the model and at 30 deg - sideline, for both cruise and the approch flaps configurations, at velocities up to 34 m/s. In general, results showed the cruise noise to be about 3dB above the background flow noise and the approach noise to be about 11 dB above. Overall sound pressure levels and spectral shapes agreed with state of the art predictive techniques.

Preisser, J. S.↗
NASA NTRS1986

A study of large, medium and small scale structures in the topside ionosphere

Alouette and ISIS data were studied for large, medium, and small scale structures in the ionosphere. Correlation was also sought with measurements by other satellites, such as the Atmosphere Explorer C and E and the Dynamic Explorer 2 satellites, of both neutrals and ionization, and with measurements by ground facilities, such as the incoherent scatter radars. Large scale coherent wavelike structures were found from ISIS 2 electron density contours from above the F peak to nearly the satellite altitude. Such structures were also found to correlate with the observation by AE-C below the F peak during a conjunction of the two satellites. Vertical wavefronts found in the upper F region suggest the dominance of diffusion along field lines as well. Also discovered were multiple, evenly spaced field-aligned ducts in the F region that, at low latitudes, extended to the other hemisphere and were in the form of field-aligned sheets in the east-west direction. Low latitude heating events were discovered that could serve as sources for waves in the ionosphere.

Gross, Stanley H.↗
NASA NTRS1988

The small scale structure of the interstellar medium in the Orion association: The flotsam of star formation

The small scale dynamics and structure of the interstellar medium of the Orion OB1b, c association was studied using IUE high dispersion SWP and LWR/LWP spectra. The area surveyed centers on the Belt and encompasses the Orion Cloak. The dynamics and abundances of the ionized and warm neutral gas surrounding the central parts of the association are determined using 35 B stars. Results are compared with the picture of the Orion interstellar medium gained using COPERNICUS, especially for the structure and dynamics of the Orion Cloak.

Sonneborn, G.↗
NASA NTRS2002

A geostatistical analysis of small-scale spatial variability in bacterial abundance and community structure in salt marsh creek bank sediments

Small-scale variations in bacterial abundance and community structure were examined in salt marsh sediments from Virginia's eastern shore. Samples were collected at 5 cm intervals (horizontally) along a 50 cm elevation gradient, over a 215 cm horizontal transect. For each sample, bacterial abundance was determined using acridine orange direct counts and community structure was analyzed using randomly amplified polymorphic DNA fingerprinting of whole-community DNA extracts. A geostatistical analysis was used to determine the degree of spatial autocorrelation among the samples, for each variable and each direction (horizontal and vertical). The proportion of variance in bacterial abundance that could be accounted for by the spatial model was quite high (vertical: 60%, horizontal: 73%); significant autocorrelation was found among samples separated by 25 cm in the vertical direction and up to 115 cm horizontally. In contrast, most of the variability in community structure was not accounted for by simply considering the spatial separation of samples (vertical: 11%, horizontal: 22%), and must reflect variability from other parameters (e.g., variation at other spatial scales, experimental error, or environmental heterogeneity). Microbial community patch size based upon overall similarity in community structure varied between 17 cm (vertical) and 35 cm (horizontal). Overall, variability due to horizontal position (distance from the creek bank) was much smaller than that due to vertical position (elevation) for both community properties assayed. This suggests that processes more correlated with elevation (e.g., drainage and redox potential) vary at a smaller scale (therefore producing smaller patch sizes) than processes controlled by distance from the creek bank. c2002 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

Non-NASA Center↗
DOE OSTI2025

Pursuing small-scale measures of penetration resistance in Ti-5553 alloy

This work was originally proposed to illustrate the performance of a particular set of differently processed Ti-5553 plates under dynamic threats. It became clear that the larger question, at present, is whether the small-scale shaped charge design of an RP-4 detonator can be employed to efficiently explore the dynamic penetration resistance of representative test articles. The initial penetration testing that employed three variants of thermomechanical processing of Ti-5553 plates appeared to demonstrate that there was a noticeable difference in their performance. The remaining pertinent question was regarding the variation in the shaped charge performance and how it compares to the variation from the three titanium plate tests. Based on the limited testing presented here the RP-4 shaped charge detonator appears to have an average depth of penetration in 6061 aluminum of 90mm with a 1.5CD stand off.

shaped charge penetration↗
DOE OSTI2022

Toward Accurate Modeling of Galaxy Clustering on Small Scales: Constraining the Galaxy-halo Connection with Optimal Statistics

Applying halo models to analyze the small-scale clustering of galaxies is a proven method for characterizing the connection between galaxies and their host halos. Such works are often plagued by systematic errors or limited to clustering statistics that can be predicted analytically. In this work, we employ a numerical mock-based modeling procedure to examine the clustering of Sloan Digital Sky Survey DR7 galaxies. We apply a standard halo occupation distribution (HOD) model to dark matter only simulations with a ΛCDM cosmology. To constrain the theoreStical models, we utilize a combination of galaxy number density and selected scales of the projected correlation function, redshift-space correlation function, group multiplicity function, average group velocity dispersion, mark correlation function, and counts-in-cells statistics. We design an algorithm to choose an optimal combination of measurements that yields tight and accurate constraints on our model parameters. Compared to previous work using fewer clustering statistics, we find a significant improvement in the constraints on all parameters of our halo model for two different luminosity-threshold galaxy samples. Most interestingly, we obtain unprecedented high-precision constraints on the scatter in the relationship between galaxy luminosity and halo mass. However, our best-fit model results in significant tension (>4σ) for both samples, indicating the need to add second-order features to the standard HOD model. To guarantee the robustness of these results, we perform an extensive analysis of the systematic and statistical errors in our modeling procedure, including a first of its kind study of the sensitivity of our constraints to changes in the halo mass function due to baryonic physics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

A Strong Gravitational Lens Is Worth a Thousand Dark Matter Halos: Inference on Small-scale Structure Using Sequential Methods

Strong gravitational lenses are a singular probe of the Universe’s small-scale structure—they are sensitive to the gravitational effects of low-mass (<10 10 M ⊙ ) halos even without a luminous counterpart. Recent strong-lensing analyses of dark matter structure rely on simulation-based inference (SBI). Modern SBI methods, which leverage neural networks as density estimators, have shown promise in extracting the halo-population signal. However, it is unclear whether the constraints from these models are limited by the methodology or the data. In this study, we introduce an accelerator-optimized simulation pipeline that can generate lens images with realistic subhalo populations in milliseconds. Leveraging this simulator, we identify the main limitation of our fiducial SBI analysis: training set size. We then adopt a sequential neural posterior estimation (SNPE) approach, allowing us to refine the training distribution to align with the observed data. Using only one-fifth as many mock Hubble Space Telescope images, SNPE matches the constraints on the low-mass halo population produced by our best nonsequential model. Our experiments suggest that an over 3 order-of-magnitude increase in training set size and GPU hours would be required to achieve an equivalent result without sequential methods. While the full potential of the existing lens sample remains to be explored, the notable improvement in constraining power enabled by our sequential approach highlights that current constraints are limited primarily by methodology and not the data itself. Moreover, our results emphasize the need to treat training set generation and model optimization as interconnected stages of any cosmological analysis using SBI.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Parameters of small scale ionization inhomogeneities in the F region of the ionosphere

The results of the parameters of small-scale ionization inhomogeneities study of the ionosphere's F-region for October-November 1965 and January-February 1966 are presented. It is shown that the most probable values of the inhomogeneity parameters are as follows: degree of anisotropy 1.4-2; vertical dimension 200-400 m; horizontal dimensions along major and minor axes 400-1000 and 200-600 m, respectively; rate of chaotic motions 30-60 m/sec; lifetime 6-9 sec.

Drobzhev, V. I.↗
NASA NTRS1990

A mathematical model of the structure and evolution of small-scale discrete auroral arcs

A three-dimensional fluid model for the structure and evolution of small-scale discrete auroral arcs originating from Alfven waves is developed and used to study the nonlinear macroscopic plasma dynamics of these auroral arcs. The results of simulations show that stationary auroral arcs can be unstable to a collisionless tearing mode which may be responsible for the observed transverse structuring in the form of folds and curls. At late times, the plasma becomes turbulent having transverse electric field power spectra that tend toward a universal k exp -5/3 spectral form.

Seyler, Charles E.↗
NASA NTRS1990

Small-scale structure in the diffuse interstellar medium

The initial results of a study to probe the small-scale structure in the diffuse interstellar medium (ISM) through IUE and optical observations of interstellar absorption lines toward both components of resolvable binary stars is reported. The binaries (Kappa CrA, 57 Aql, 59 And, HR 1609/10, 19 Lyn, and Theta Ser) observed with IUE have projected linear separations ranging from 5700 to 700 Au. Except for Kappa CrA, the strengths of the interstellar absorption lines toward both components of these binaries agree to within 10 percent. In the case of Kappa CrA, the optically thin interstellar Mg I and Mn II lines are about 50 percent stronger toward Kappa-2 CrA than Kappa-1 CrA. Higher resolution observations of interstellar Ca II show that this difference is concentrated in the main interstellar component at V(LSR) = 9 + or - 2 km/s. Interestingly, this velocity corresponds to an intervening cloud that may be associated with the prominent Loop I shell in the local ISM. Given the separation (23 arcsec) and distance (120 pc) of Kappa CrA, the line strength variations indicate that this cloud has structure on scales of 2800 AU or less.

Meyer, David M.↗
NASA NTRS1984

4 X 7 M Modeling Program. The Use of Small-Scale Modeling in Defining Flow Improvements for the Langley 4 X 7-Meter Tunnel

The use of small scale modeling in defining flow improvements for the Langley 4 x 7 meter wind tunnel is presented. Topics covered in viewgraph format include: description of the 4 x 7 meter wind tunnel, description of the 1/24 scale model, wind tunnel circuit flow characteristics, open test section turbulence characteristics, and conclusions.

Applin, Zachery T.↗
NASA NTRS1980

Radar measurement of heterogeneous small-scale surface texture on Mars Chryse

Radar measurements from Chryse Planitia in 1978 confirm earlier estimates of 4-5 deg rms slope (on meter scales) over 45-50 deg W longitude. The new measurements also confirm a skewing of the measured spectra. This has now been interpreted as a combined result of large-scale surface tilt and a side effect of the decrease in small-scale roughness as the subradar point moves from the basin floor toward the west.

Simpson, R. A.↗
NASA NTRS1977

Small scale turbulence in the Crab Nebula: Evidence of lower hybrid parametric instabilities driven by the pulsar wave

Strong small scale turbulence is observed in the Crab Nebula from the temporal pulse broadening data. It is shown that the strong 30 Hz pulsar wave can parametrically excite instabilities near the lower hybrid frequency in the thermal plasma of the Crab Nebula with a characteristic wavelength of the order of the scale size a of the turbulence observed. These instabilities provided a coupling mechanism between the pulsar wave and the Nebula plasma.

Lee, L. C.↗
NASA NTRS1992

Theory of small-scale density and electric field fluctuations in the nightside Venus ionosphere

Recently, it has been reported that small-scale (lambda about 0.1-2 km) density irregularities occur during 100-Hz electric field bursts in the nightside ionosphere of Venus. This paper provides a detailed analysis of the lower-hybrid-drift instability as a mechanism to generate the observed irregularities. A fully electromagnetic theory is developed that is relevant to the finite beta plasma in Venus's ionosphere and includes collisional effects (e.g., electron-ion, electron-neutral, and ion-neutral collisions). The key features of the analysis that favor this instability are the following: (1) it is a flute mode and propagates orthogonal to the ambient magnetic field; (2) it is a relatively short wavelength mode and the Doppler-shifted frequency can be greater than about 100 Hz; (3) it can produce both electric field and density fluctuations, as well as magnetic field fluctuations in a finite beta plasma; and (4) it is most unstable in low-beta plasmas so that it is likely to occur in the low-density, high-magnetic-field ionospheric holes. These features are consistent with observational results.

Huba, J. D.↗