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At least 757 records · Page 42

All sources NASA NTRS DOE OSTI

NASA NTRS2003

Martian Crustal Magnetism: What Have We Learned After Approximately 6 Years of MGS Observations?

The MAG/ER investigation aboard the Mars Global Surveyor (MGS) has established conclusively that an internal, dynamo-generated field does not currently exist at Mars and discovered, unexpectedly, strong magnetization in the crust. An estimate of the upper limit of the current Mars dipole moment derived from the MGS data yields M < ~2 x 10(exp 17) A-m2, which corresponds to a surface equatorial field strength of < 0.5 nT. The intense magnetization of the crust is closely associated with the ancient, heavily cratered high terrain, which lies south of Mars dichotomy boundary. The correlation of magnetization with the old terrain and the role of impacts, which have modified the magnetic properties of the crust, constitute a new and powerful diagnostic tool that is providing a unique view into the early thermal history of the planet, which was almost totally unknown prior to the arrival of MGS. Data from the Lunar Prospector mission complement contemporary analyses and interpretation of crustal magnetism in planetary system bodies that do not currently possess core dynamos. The observation of magnetic lineations over Terra Sirenum (Sirenum Fossae) and Terra Cimmeria, are suggestive of tectonic processes observed at Earth in association with sea-floor spreading and geomagnetic field reversals. If this association is correct, it would indicate the possible existence of plate tectonics and magnetic field reversals in Mars' early history. Alternative models involving fault/graben formation associated with the fracturing of a thin, magnetized crustal layer by tectonic or volcanism-induced stresses, yield equally valid interpretations. To date, no reliable correlation between topography, geology and crustal magnetism has been established and the origin of these remarkable Martian magnetic anomalies remains a mystery.

M H Acuna↗

NASA NTRS1973

Investigation of substrate-mounted thin-film meteoroid sensors for use in large area impact experiments

Two types of sensor designs were investigated: (1)a polysulfone dielectric film with vapor-deposited aluminum and gold sensor plates, bonded to a relatively thick aluminum substrate, and (2) an aluminum oxide (A1203) dielectric layer prepared on an aluminum substrate by anodization, with a layer of vapor-deposited aluminum providing one sensor plate and the substrate serving as the other plate. In the first design, specimens were prepared which indicate the state of the art for application of this type of sensor for elements of a meteoroid detection system having an area as large as 10 sq M. Techniques were investigated for casting large-area polysulfone films on the surface of water and for transferring the films from the water. Methods of preparing sensors by layering of films, the deposition of capacitor plates, and sensor film-to-substrate bonding, as well as techniques for making electrical connections to the capacitor plates, were studied.

Carollo, S. F.↗

NASA NTRS1981

Sputtering and ion plating for aerospace applications

Sputtering and ion plating technologies are reviewed in terms of their potential and present uses in the aerospace industry. Sputtering offers great universality and flexibility in depositing any material or in the synthesis of new ones. The sputter deposition process has two areas of interest: thin film and fabrication technology. Thin film sputtering technology is primarily used for aerospace mechanical components to reduce friction, wear, erosion, corrosion, high temperature oxidation, diffusion and fatigue, and also to sputter-construct temperature and strain sensors for aircraft engines. Sputter fabrication is used in intricate aircraft component manufacturing. Ion plating applications are discussed in terms of the high energy evaporant flux and the high throwing power. Excellent adherence and 3 dimensional coverage are the primary attributes of this technology.

Spalvins, T.↗

NASA NTRS1981

Sputtering and ion plating for aerospace applications

Sputtering and ion plating technologies are reviewed in terms of their potential and present uses in the aerospace industry. Sputtering offers great universality and flexibility in depositing any material or in the synthesis of new ones. The sputter deposition process has two areas of interest: thin film and fabrication technology. Thin film sputtering technology is primarily used for aerospace mechanical components to reduce friction, wear, erosion, corrosion, high temperature oxidation, diffusion and fatigue, and also to sputter-construct temperature and strain sensors for aircraft engines. Sputter fabrication is used in intricate aircraft component manufacturing. Ion plating applications are discussed in terms of the high energy evaporant flux and the high throwing power. Excellent adherence and 3-dimensional coverage are the primary attributes of this technology.

Spalvins, T.↗

DOE OSTI2022

Element-specific first order reversal curves measured by magnetic transmission x-ray microscopy

The first-order reversal curve (FORC) method is a macroscopic measurement technique that can be used to extract quantitative and microscopic properties of hysteretic systems. Using magnetic transmission x-ray microscopy (MTXM), local element-specific FORC measurements are performed on a 20 nm thick film of CoTb. The FORCs measured with microscopy reveal a step-by-step domain evolution under the magnetic field cycling protocol and provide a direct visualization of the mechanistic interpretation of FORC diagrams. They are compared with magnetometry FORCs and show good quantitative agreement. Furthermore, the high spatial resolution and element-specific sensitivity of MTXM provide new capabilities to measure FORCs in small regions or specific phases within multicomponent systems, including buried layers in heterostructures. The ability to perform FORCs on very small features is demonstrated with the MTXM-FORC measurement of a rectangular microstructure with vortex-like Landau structures. This work demonstrates the confluence of two uniquely powerful techniques to achieve quantitative insight into nanoscale magnetic behavior.

36 MATERIALS SCIENCE↗

NASA NTRS1982

The reduction, verification and interpretation of MAGSAT magnetic data over Canada

Correlations between the MAGSAT scalar anomaly map produced at the Earth Physics ranch and other geophysical and geological data reveal relationships between high magnetic field and some metamorphic grade shields, as well as between low magnetic field and shield regions of lower metamorphic grade. An intriguing contrast exists between the broad low anomaly field over the Nasen-Gakkel Ridge (a spreading plate margin) and the high anomaly field over Iceland (part of a spreading margin). Both regions have high heat flow, and presumably thin magnetic crust. This indicates that Iceland is quite anomalous in its magnetic character, and possible similarities with the Alpha Ridge are suggested. Interesting correlations exist between MAGSAT anomalies around the North Atlantic, after reconstructing the fit of continents into a prerifting configuration. These correlations suggest that several orogenies in that region have not completely destroyed an ancient magnetization formed in high grade Precambrian rocks.

Coles, R. L.↗

NASA NTRS1982

HOST liner cyclic facilities: Facility description

A quartz lamp box, a quartz lamp annular rig, and a low pressure liner cyclic can rig planned for liner cyclic tests are described. Special test instrumentation includes an IR-TV camera system for measuring liner cold side temperatures, thin film thermocouples for measuring liner hot side temperatures, and laser and high temperature strain gages for obtaining local strain measurements. A plate temperature of 2,000 F was obtained in an initial test of an apparatus with three quartz lamps. Lamp life, however, appeared to be limited for the standard commercial quartz lamps available. The design of vitiated and nonvitiated preheaters required for the quartz lamp annular rig and the cyclic can test rigs is underway.

Schultz, D.↗

NASA NTRS1986

Laser-assisted solar cell metallization processing

The status of the laser-assisted solar cell metallization processing is described. Metallo-organic silver films were spun-on by argon ion laser beam pyrolysis. The metallo-organic decomposition (MOD) film was spun-on an evaporated Ti/Pd film to produce tood adhesion. In a maskless process, the argon ion laser writes the contact pattern. The film is then built up to obtain the required conductivity using conventional silverplating process. The Ti/Pd film in the field is chemically etched using the plated silver film as the mask. The width of the contact pattern is determined by the power of the laser. Widths as thin as 20 microns were obtained using 0.66 W of laser power. Cells fabricated with the 50 micron line widths of 4 ohm-cm floating zone (Fz) silicon-produced efficiencies of 16.6% (no passivation) which were equivalent to the best cells using conventional metallization/lithography and no passivation.

Meier, D. L.↗

NASA NTRS1990

Wave formation on a liquid layer for de-icing airplane wings

Wave formation on a thin liquid layer used for deicing aircraft wings is investigated by studying the stability of airflow over a liquid-coated flat plate at zero angle of incidence. The ratio of the viscosity of the liquid to that of air is very high (over 500,000), and the Reynolds number based on liquid depth and air viscosity is of the order of a few thousand. Under these circumstances the analysis gives two formulas, in closed form, for the growth rate and phase velocity of the waves in terms of the wavenumber and other relevant parameters. The expected wavenumber is that for which the growth rate is the maximum. The instability is one in which the viscosity difference between the two fluids (air and liquid) plays the dominant role, and is of the kind found by Yih (1967).

Yih, Chia-Shun↗

NASA NTRS1995

Analysis of LDEF experiment AO187-2 chemical and isotopic measurements of micrometeoroids by secondary ion mass spectrometry

#Experiment AO187-2, that was flown on board the Long Duration Exposure Facility(LDEF), was designed to measure the chemical and isotopic compositions of interplanetary dust impinging on the spacecraft from outer space. Information on the nature and composition of orbital debris was also anticipated. The spacecraft maintained a constant orientation with respect to its velocity vector thereby defining leading and trailing edges that faced respectively into and away from the direction of motion. Arrays of individual capture cells each 80.8 sq cm in size and totaling 237 in number were exposed on both the leading and trailing edges of LDEF. Each cell consisted of a pure Ge target surface slightly separated from a thin (2.5 micrometers) metallized plastic 'entrance foil.' The basic concept was that incoming projectiles would penetrate the foil, strike the Ge target plate at high velocity producing a vapor-liquid cloud that would re-deposit material on the underside of the plastic foil. This material would then be analyzed using the sensitive surface analysis technique of Secondary Ion Mass Spectrometry (SIMS). In practice, most of the plastic entrance foils failed during the extended period of orbital exposure probably due to a combination of UV embrittlement, large densities of impact events and (for the leading edge) the effects of atomic oxygen erosion in orbit. However the foils failed gradually and most remained in place on the capture cells for a significant fraction of the duration of the flight . Because most of the impactors were small (less than 10 micrometers) they were heated and dispersed in traversing the entrance foils producing clouds of molten droplets and vapor that produced easily identifiable 'extended impacts' on the Ge target plates. Fortunately, it proved possible to make ion probe measurements of projectile compositions from material deposited on the Ge in the extended impact structures.

Zinner, Ernst↗

NASA NTRS1989

A transition detection study at Mach 1.5, 2.0, and 2.5 using a micro-thin hot-film system

A boundary-layer transition detection study was conducted in the NASA Langley unitary plan wind tunnel with an array of microthin hot films on a flat plate at Mach numbers 1.5, 2.0, and 2.5 and Reynolds numbers (1.0-4.5) x 10 to the 6th/ft. Transition locations were obtained online from the variation of normalized rms voltages from an array of hot-film sensors for both natural transition and a grit-induced wedge of turbulence. The effects of Mach number and Reynolds number on the location and length of the transition region for the two types of transition are presented from the online data. Also shown are the unit Reynolds number effects on transition Reynolds number, voltage-versus-time traces, spectra, and the data-acquisition system.

Johnson, Charles B.↗

NASA NTRS1987

A higher-order theory for geometrically nonlinear analysis of composite laminates

A third-order shear deformation theory of laminated composite plates and shells is developed, the Navier solutions are derived, and its finite element models are developed. The theory allows parabolic description of the transverse shear stresses, and therefore the shear correction factors of the usual shear deformation theory are not required in the present theory. The theory also accounts for the von Karman nonlinear strains. Closed-form solutions of the theory for rectangular cross-ply and angle-ply plates and cross-ply shells are developed. The finite element model is based on independent approximations of the displacements and bending moments (i.e., mixed finite element model), and therefore, only C sup o -approximation is required. The finite element model is used to analyze cross-ply and angle-ply laminated plates and shells for bending and natural vibration. Many of the numerical results presented here should serve as references for future investigations. Three major conclusions resulted from the research: First, for thick laminates, shear deformation theories predict deflections, stresses and vibration frequencies significantly different from those predicted by classical theories. Second, even for thin laminates, shear deformation effects are significant in dynamic and geometrically nonlinear analyses. Third, the present third-order theory is more accurate compared to the classical and firt-order theories in predicting static and dynamic response of laminated plates and shells made of high-modulus composite materials.

Reddy, J. N.↗

NASA NTRS1970

Improved heat shield/radiator

Thermally conductive metal shield is put in direct thermal contact with the mounting plate for the radiation detectors. External surfaces of the shield are insulated by an insulation blanket. The internal faces are covered with a thin layer of quartz with a metallic thermally conductive coating on the hidden faces.

Smith, J. W.↗

NASA NTRS1989

A numerical study of the contrarotating vortex pair associated with a jet in a crossflow

An implicit two-factor partially flux split solver for the thin-layer Navier-Stokes equations is used to solve the aerodynamic/propulsive interaction between a subsonic jet exhausting perpendicularly through a flat plat plate into a crossflow. The algorithm is applied to flows with a range of jet to crossflow velocity ratios between 4 and 8. The computed velocity field is analyzed and comparisons are made with experimentally determined properties of the contrarotating vortex pair.

Roth, Karlin R.↗

NASA NTRS1988

The flight test of a grazing incidence relay optics telescope for solar X-ray astronomy utilizing a thinned, back-illuminated CCD detector

The new AS&E Ultrahigh Resolution Soft X-ray Solar Research Rocket Payload has been successfully flown twice on Black Brant IX Sounding Rockets from White Sands Missile Range. These flights, conducted on 15 August 1987 and 11 December 1987, provided the first test of the new payload which consists of 3.8X magnifying hyperboloid-hyperboloid grazing incidence relay optic used in conjunction with an existing Wolter-I primary mirror. An RCA SID 500 series CCD detector was utilized in a thinned, back-illuminated configuration for recording the images. The 5.4 m effective focal length of the compound optics system resulted in a plate scale of 1 arc second per pixel which is comparable to the inherent resolution of the primary mirror. These flights represent the first use in X-ray astronomy of either of these two new technologies. These observations are presented with comparison to laboratory measurements and theoretical expectations of the instrument performance.

Moses, J. Daniel↗

NASA NTRS1993

Is there uniformitarian or catastrophic tectonics on Venus?

The distribution and modification of craters on Venus favors a near global, volcanic resurfacing event about 500 Myrs ago. Such an event indicates that the tectonic evolution of Venus was catastrophic rather than uniformitarian. The creation of a global, single-plate lithosphere on Venus about 500 Myrs ago can explain a variety of tectonic features on Venus that are not consistent with the thin lithosphere required by a uniformitarian hypothesis. A lithosphere on Venus that has thickened for 500 Myrs has a present thickness of about 300 km whereas steady-state heat loss from Venus requires a mean lithospheric thickness near 40 km. A thick lithosphere on Venus can support the high plateaus (elevations of 3-4 km) and mountain belts (up to 9 km) using the same isostatic compensation concepts applicable to the earth. If a thick lithosphere is thinned by a mantle plume, elevation is caused by thermal isostasy. The elevation due to the thinning of a 300 km thick lithosphere is about 3 km. Thus the domal elevation of Beta Regio can be explained by the same mechanism responsible for the elevation of the Hawaiian Swell. While the broad highland plateaus on Venus may be associated with thermal isostasy, the mountain belts in Ishtar Terra clearly cannot be. The high topography of Freyja Montes is almost certainly associated with underthrusting and the likely compensation mechanism is Airy isostasy associated with a thickened crust. With a density contrast delta, of 500 kg m(exp -3) an elevation of 9 km requires a crustal thickening of about 70 km. With a thick lithosphere there is no difficulty in supporting such a thick crust.

Turcotte, Donald L.↗

NASA NTRS1999

Non-Linear Finite Element Modeling of THUNDER Piezoelectric Actuators

A NASTRAN non-linear finite element model has been developed for predicting the dome heights of THUNDER (THin Layer UNimorph Ferroelectric DrivER) piezoelectric actuators. To analytically validate the finite element model, a comparison was made with a non-linear plate solution using Von Karmen's approximation. A 500 volt input was used to examine the actuator deformation. The NASTRAN finite element model was also compared with experimental results. Four groups of specimens were fabricated and tested. Four different input voltages, which included 120, 160, 200, and 240 Vp-p with a 0 volts offset, were used for this comparison.

Taleghani, Barmac K.↗

NASA NTRS1945

Column and Plate Compressive Strengths of Aircraft Structural Materials: Extruded 24S-T Aluminum Alloy

Column and plate compressive strengths of extruded 24S-T aluminum alloy were determined both within and beyond the elastic range from tests of thin-strip columns and local-instability tests of H-, Z-,and channel-section columns. These tests are part of an extensive research investigation to provide data on the' structural strength of various aircraft materials. The results are presented in the form of curves and charts that are suitable for use in the design and analysis of aircraft structures.

Heimerl, George J.↗