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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Resonance compression of an acoustic beam in a crystal

The resonance excitation of an intense acoustic beam in a crystal is described for a special geometry of pump-wave reflection from the crystal surface. The resonance appears in the vicinity of the total internal reflection angle under the condition that the wave field in a compressed reflected beam propagating almost parallel to the surface is close to the volume eigenmode satisfying the free boundary condition. Criteria for the existence of such modes are considered in detail. Conversion conditions are analyzed under which a “parasitic” reflected wave of the same branch as the incident wave is absent and entire energy from the incident wave falls within a narrow intense acoustic beam of another branch. It is shown that, when the surface is chosen parallel to the crystal symmetry plane, the conversion criterion is reduced to the sole condition on the elastic moduli of the medium. Analysis is performed by analytic and numerical methods for skew cuts of monoclinic, rhombic, trigonal, and hexagonal crystals, when the boundary is the symmetry plane, while the sagittal plane has no symmetry. A number of crystals are found in which resonance excitation is very close to conversion.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

High-pressure behavior of cuprospinel CuFe 2 O 4 : Influence of the Jahn-Teller effect on the spinel structure

The Jahn-Teller-effect at Cu 2+ in cuprospinel CuFe 2 O 4 was investigated using high-pressure, single crystal synchrotron x-ray diffraction (XRD) techniques at beamline BL10A at the Photon Factory, KEK, Japan. Six data sets were collected in the pressure range from ambient to 5.9 GPa at room temperature. Structural refinements based on the data were performed at 0.0, 1.8, 2.7, and 4.6 GPa. The unit cell volume of cuprospinel decreases continuously from 590.8 (6) Å 3 to 579.5 (8) Å 3 up to 3.8 GPa. Leastsquares fitting to a third-order Birch-Murnaghan equation of state yields zero-pressure volume V 0 = 590.7 (1) Å 3 and bulk modulus K 0 = 188.1 (4.4) GPa with K’ fixed at 4.0. The crystal chemical composition determined by electron-probe analysis and x-ray site-occupancy refinement is represented as [Cu 0.526 Fe 0.474 ] [6] [Cu 0.074 Fe 1.926 ]O 4 . Most of the Cu 2+ are preferentially distributed onto the tetrahedral (T) site of the spinel structure. At 4.6 GPa, a cubic-tetragonal phase transition is indicated by a splitting of the a axis of the cubic structure into a smaller a axis and a longer c axis, with unit cell parameters a = 5.882 (1) Å and c = 8.337 (1) Å. The tetragonal crystal structure with space group I4 1 /amd was refined to R1 = 0.0182 and wR2 = 0.0134 using observed 35 x-ray reflections. At the T site, the tetrahedral O-T-O bond angles along the c-axis direction of the unit cell decreases slightly from 109.47 ° to 108.7 (4) °, which generates a stretched tetrahedral geometry along the c-axis. The cubic-totetragonal transition induced by the Jahn-Teller effect at Cu 2+ is attributable to the angular distortion at the tetrahedral site. At the octahedral (M) site, on the other hand, the two M-O bonds parallel to the caxis are shortened with respect to the four M-O bonds parallel to the ab-plane, which are lengthened as a result of the phase transition, leading to a compressed octahedral geometry along the c-axis. With the competing distortions between the stretched tetrahedron and the compressed octahedron along the c-axis, the a unit cell parameter is shortened with respect to the c unit cell parameter, giving a c/a ratio slightly greater than unity as referred to cubic lattice (c/a = 1.002). The c/a value increases to 1.007 with pressure, suggesting a further evolution of the stretched tetrahedron and the compressed octahedron. The variation of c/a ratio of the cuprospinel is similar to that observed in the tetragonally distorted cuprospinel with Cu 2+ fully occupying the octahedral site of the structure.

58 GEOSCIENCES↗
DOE OSTI2020

An Analytical Model for the Tension-Shear Coupling of Woven Fabrics with Different Weave Patterns under Large Shear Deformation

It is essential to accurately describe the large shear behavior of woven fabrics in the composite preforming process. An analytical model is proposed to describe the shear behavior of fabrics with different weave patterns, in which tension-shear coupling is considered. The coupling is involved in two parts, the friction between overlapped yarns and the in-plane transverse compression between two parallel yarns. By introducing the concept of inflection points of a yarn, the model is applicable for fabrics with different weave patterns. The analytical model is validated by biaxial tension-shear experiments. A parametric study is conducted to investigate the effects of external load, yarn geometry, and weave structure on the large shear behavior of fabrics. The developed model can reveal the physical mechanism of tension-shear coupling of woven fabrics. Moreover, the model has a high computational efficiency due to its explicit expressions, thus benefiting the material design process.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Electrofracturing of Shale at Elevated Pressure

Electrofracturing deeply buried shale formations could be used to increase reservoir permeability and improve reservoir production without requiring large volumes of freshwater. This paper describes a novel experimental system and initial test results to electrofracture shale under high confining pressures. Core-scale laboratory testing was performed on twelve rock samples recovered from a shale gas reservoir. Each sample was subjected to confining pressures of 20.7 MPa (3000 psi) or 58.6 MPa (8000 psi), representative of overburden pressures at depth. Samples were then subjected to application of high voltage until specimen fracture. The experiments produced deformed samples with multiple fracture types, both parallel and oblique to bedding planes. Electrofracturing increased permeabilities by up to nine orders of magnitude for extended time periods. Rock fracture and throughgoing fractures were demonstrated. Computed tomography images revealed the creation of fractures and tube/tunnel flow channels, which resisted closure under hydrostatic pressures up to 58.6 MPa. The breakdown energy and permeability changes in the sample were independent of applied confining pressure. The cumulative energy input required for fracture depended on applied confining pressure and sample length. The energy required to fracture samples up to 9 cm in length is generally more than 0.5 kJ/cm, but no greater than 1 kJ/cm. Our results show that electrofracture of shales under confining pressure is possible and could be a possible water-free mechanism for reservoir stimulation.

04 OIL SHALES AND TAR SANDS↗
DOE OSTI2023

Vaterite Optical Petrography in Lake Sturgeon Otoliths

Vaterite occurring in fish otoliths exhibits plumose and spherulitic habits, the latter being like those grown from aqueous solutions. Vaterite spherulites are known to have sheaf-like texture and can be up to 100 μm in size. In thin section, the spherulites typically show uniaxial positive interference figures between cross-polarizers using a polarizing light microscope but without conoscopic or Bertrand lenses because the spherulites mimic the effect of these lenses. Plumose vaterite can show both uniaxial (+) and biaxial (+) interference figures with a small 2V, which suggests that crystal structural models for vaterite should have the plane of the carbonate group parallel to the optic axis or acute bisectrix. Finally, vaterite spherulites grown from aqueous solution exhibit similar structure and growth habits.

58 GEOSCIENCES↗
DOE OSTI2016

SURFACE DENSITY EFFECTS IN QUENCHING: CAUSE OR EFFECT?

There are very strong observed correlations between the specific star formation rates (sSFRs) of galaxies and their mean surface mass densities, Σ, as well as other aspects of their internal structure. These strong correlations have often been taken to argue that the internal structure of a galaxy must play a major physical role, directly or indirectly, in the control of star formation. In this paper we show by means of a very simple toy model that these correlations can arise naturally without any such physical role once the observed evolution of the size–mass relation for star-forming galaxies is taken into account. In particular, the model reproduces the sharp threshold in Σ between galaxies that are star-forming and those that are quenched and the evolution of this threshold with redshift. Similarly, it produces iso-quenched-fraction contours in the f {sub Q}( m , R {sub e}) plane that are almost exactly parallel to lines of constant Σ for centrals and shallower for satellites. It does so without any dependence on quenching on size or Σ and without invoking any differences between centrals and satellites, beyond the different mass dependences of their quenching laws. The toy model also reproduces several other observations, including the sSFR gradients within galaxies and the appearance of inside-out build-up of passive galaxies. Finally, it is shown that curvature in the main-sequence sSFR–mass relation can produce curvature in the apparent B / T ratios with mass. Our analysis therefore suggests that many of the strong correlations that are observed between galaxy structure and sSFR may well be a consequence of things unrelated to quenching and should not be taken as evidence of the physical processes that drive quenching.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Determination of Burgers vectors in close-packed metals using g.b = 2 contrast.

Reexamination of dislocation images giving double contrast in the electron microscope for g.b = 2 as a possible means for Burgers vector determinations. In fcc foils which have been cut parallel to an active slip plane, the g.b = 2 criterion provides a quick positive Burgers vector analysis which can be carried out during observation. The method is also applicable to basal dislocations in hcp. A comparison between calculated two-beam profiles and experimental images in aluminum is discussed, and several commonly observed characteristics of g.b = 2 contrast are described.

Kestenbach, H.-J.↗
NASA NTRS1973

BUCLASP 2: A computer program for instability analysis of biaxially loaded composite stiffened panels and other structures

The use of the computer program BUCLASP2 is described. The program is intended for linear instability analyses of structures such as unidirectionally stiffened panels. Any structure that has a constant cross section in one direction, that may be idealized as an assemblage of beam elements and laminated flat and curved plant strip elements can be analyzed. The loadings considered are combinations of axial compressive loads and in-plane transverse loads. The two parallel ends of the panel must be simply supported and arbitrary elastic boundary conditions may be imposed along any one or both external longitudinal side. This manual consists of instructions for use of the program with sample problems, including input and output information. The theoretical basis of BUCLASP2 and correlations of calculated results with known solutions, are presented.

Tripp, L. L.↗
NASA NTRS1974

SEASAT study documentation

The proposed spacecraft consists of a bus module, containing all subsystems required for support of the sensors, and a payload module containing all of the sensor equipment. The two modules are bolted together to form the spacecraft, and electrical interfaces are accomplished via mated connectors at the interface plane. This approach permits independent parallel assembly and test operations on each module up until mating for final spacecraft integration and test operations. Proposed program schedules recognize the need to refine sensor/spacecraft interfaces prior to proceeding with procurement, reflect the lead times estimated by suppliers for delivery of equipment, reflect a comprehensive test program, and provide flexibility for unanticipated problems. The spacecraft systems are described in detail along with aerospace ground equipment, ground handling equipment, the launch vehicle, imaging radar incorporation, and systems tests.

Source record↗
NASA NTRS1977

A forward-scatter polarimeter for chemical analysis

Photopolarimeter measures two states of orthogonal polarization parallel and perpendicular to scattering plane, defined by directions of incident and scattering light, to determine effective gaseous depolarization factor. Instrument can be used for environmental, spectroscopic, and meteorological analysis.

Fymat, A. L.↗
NASA NTRS1979

The Minimum Induced Drag of Aerofoils

Equations are derived to demonstrate which distribution of lifting elements result in a minimum amount of aerodynamic drag. The lifting elements were arranged (1) in one line, (2) parallel lying in a transverse plane, and (3) in any direction in a transverse plane. It was shown that the distribution of lift which causes the least drag is reduced to the solution of the problem for systems of airfoils which are situated in a plane perpendicular to the direction of flight.

Munk, M. M.↗
NASA NTRS1980

A note on sound radiation into a uniformly flowing fluid

Sound radiation generated by mechanical or vibratory source arrangements and, in some instances of planar or piston types, encompasses all magnitudes of the wavelength or frequency as well as disposition of the observation site. The comparative increase in average total radiated power from infinitesimally small or point sources of periodic strength, on passing from rest to steady rectilinear motion, depends only on Mach number in the noncompact case; and a formally analogous rise in output is linked, to the presence of a steady parallel flow past a rigid plane wall in which a compact circular piston executes normal oscillations. The perspective of effects connected with such a background is flow is widened by regard for an elongated or strip piston, which prototype permits a straightforward and general analysis.

Levine, H.↗
NASA NTRS1981

Surface waves on Saturn's magnetopause

Voyager 1 magnetometer data have shown that small-amplitude surface waves occurred on Saturn's dayside magnetopause, causing multiple inbound crossings of this boundary. These waves were travelling approximately parallel to Saturn's equatorial plane along the magnetopause ('tailward'), suggesting that they were driven by the rotation of Saturn's magnetosphere. Hydromagnetic waves (possibly slow mode) were observed in the adjacent magnetosheath.

Lepping, R. P.↗
NASA NTRS1982

Stellar populations in the edge-on spiral galaxy NGC 4565. I - Surface brightness and color distributions

Results are presented for photographic and photoelectric photometry of the edge-on Sb galaxy NGC 4565. Major-axis, minor-axis, and perpendicular surface brightness profiles are determined, along with color gradients parallel and perpendicular to the plane of the galaxy. It is found that the galaxy's light can be deconvolved naturally into five components: (1) a starlike nucleus located at the center of the bulge and the edge of the dust lane; (2) a thin disk containing the gas and dust, the young OB stars, and the spiral arms; (3) a thick disk that may be a locally isothermal sheet of old Population I metal-rich stars; (4) a bulge that merges smoothly into the thick disk at a radial distance of about 2.9 kpc; and (5) a corona whose light dominates the perpendicular profiles from about 2.9 to at least 8.2 kpc above the galactic plane.

Jensen, E. B.↗
NASA NTRS1986

Passive Element Shapes Antenna Radiation Pattern

Parasitic waveguide element suppresses ground-reflected multipath radiation. Small section of waveguide placed in front of phased-array antenna operating at 850 MHz modifies radiation field by reducing power density parallel to and below ground plane without significantly affecting primary radiation at angles greater than 20 degrees above horizontal. Acts as parasitic radiator that shifts phase of portion of wavefront by approximately 180 degrees, causing partial cancellation in ground plane, thereby reducing radiation intensity in that direction by about 10 dB. Produces corresponding reduction in multipath radiation scattered from ground. Waveguide technique also used to decouple two nearby antennas.

Bonebright, M. E.↗
NASA NTRS1985

Hgi2 Sub 2 Crystal Growth for Nuclear Detectors

The objectives of this program are to obtain a benchmark quality sample grown at low-g conditions and to study vapor growth phenomena under space conditions. Ground-based crystals show a defect structure which impairs their performance as nuclear radiation detectors. These defects may be caused by the gravitational force acting on the crystal in its weakended state at the elevated growth temperature and by irregular convection patterns in the vapor during growth. Mechanical strength measurements have been performed (uniaxial compression tests) which show that the crystals exhibit slip parallel to the c-planes at stresses as low as 1/2 psi. Preliminary calculations using a simple linearized model indicate the oscillating instabilities in the convection part of the vapor transport system are unlikely, even at 1-g, provided that the utmost care is taken in the preparation of the crystal growth source material.

Schnepple, W. F.↗
NASA NTRS1986

New insights into typical Archaean structures in greenstone terranes of western Ontario

Ongoing detailed field work in selected granitoid complexes of the western Wabigoon and Wawa Subprovinces, southern Canadian Shield, has led to several new conclusions: (1) Prominent gneiss domes are composed of prestrained tonalite-granodiorite and represent dense hoods of magmatic granitoid diapirs; (2) the deformation history of the prestrained gneiss remains to be unraveled; (3) the gneiss lacked a thick cover of mafic metavolcanics or other dense rocks at the time of magmatic diaprisim; (4) the synclinoral structure of large greenstone belts is older than the late gneiss domes and may have been initiated by volcano-tectonic processes; (5) small greenstone masses within the gneiss are complexly deformed, together with the gneiss; and, (6) no compelling evidence has been found of ductile early thrusting in the gneiss terranes. Zones of greenstone enclaves occur in hornblende-rich contaminated tonalite and are apt to be deformed magmatic septa. Elsewhere, the tonalite gneiss is biotite-rich and hornblende-poor. These conclusions rest on several new pieces of structural evidence; (1) oval plutons of syenite-diorite have magmatic strain fabrics and sharp contacts that are parallel to an axial-plane foliation in the surrounding refolded gneiss; (2) gneiss domes are lithologically composite and contain large sheath-like structures which are deformed early plutons, distorted earlier gneiss domes, or early ductile nappes produced by folding of planar plutonic septa, and (3) the predomal attitudes of gneissosity varied from point to point.

Schwerdtner, W. M.↗