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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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The objective is to provide a low cost, simple experiment for either demonstration purposes or as a laboratory experiment that will teach the student the importance of the thermal-mechanical history of a metallic alloy in determining that material's mechanical behavior. Hairpins are subjected to various treatments. The experimental equipment and procedures are discussed.
While it is now well established that copper-oxide-based power, or virtually any other ceramic superconductor powder, can be consolidated and encapsulated within a metal matrix by explosive consolidation, the erratic superconductivity following fabrication has posed a major problem for bulk applications. The nature of this behavior was found to arise from microstructural damage created in the shock wave front, and the residual degradation in superconductivity was demonstrated to be directly related to the peak shock pressure. The explosively fabricated or shock loaded YBa2Cu3Ox examples exhibit drastically altered rho (or R) - T curves. The deterioration in superconductivity is even more noticeable in the measurement of ac magnetic susceptibility and flux exclusion or shielding fraction which is also reduced in proportion to increasing peak shock pressure. The high frequency surface resistance (in the GHz range) is also correspondingly compromised in explosively fabricated, bulk metal-matrix composites based on YBa2Cu3O7. Transmission electron microscopy (including lattice imaging techniques) is being applied in an effort to elucidate the fundamental (microstructural) nature of the shock-induced degradation of superconductivity and normal state conductivity. One focus of TEM observations has assumed that oxygen displaced from b-chains rather than oxygen-vacancy disorder in the basal plane of oxygen deficient YBa2Cu3Ox may be a prime mechanism. Shock-wave displaced oxygen may also be locked into new positions or interstitial clusters or chemically bound to displaced metal (possibly copper) atoms to form precipitates, or such displacements may cause the equivalent of local lattice cell changes as a result of stoichiometric changes. While the shock-induced suppression of T(sub c) is not desirable in the explosive fabrication of bulk metal-matrix superconductors, it may be turned into an advantage if the atomic-scale distortion can be understood and controlled as local flux pinning sites.
The present systematic reanalysis of a substantial portion of extant photometric data on the Saturn E Ring has calibrated every observation on the basis of a common 3D model. A simple power-law model is found to describe the ring's normal optical depth profile with orbital radius; this trend is departed from, however, near the density peak, where there emerges a 30-percent localized decrease in thickness. No power-law size distribution is found to be compatible with available photometry. The peculiar size distribution points to a ring origin in a process that was not collisional or disruptive.
An analysis is conducted of spatially resolved Voyager 2 Photopolarimeter Subsystem (PPS) observations at 2650 and 7500 A. The continuum absorber that is tropospherically abundant, if confined to the region below the methane haze layer, indicates an optical depth for that layer no greater than 0.8; models in which this optical depth is as large as 3.0 yield too much limb darkening, in the case where the continuum absorber is mixed with both the methane haze and deeper clouds. Tropospheric aerosols are noted to have phase functions with shallow backward lobes.
We have investigated the electrical and metallurgical behavior of the Ni-InP contact system. Specific contact resistivity (Rc) values in the low 10 exp -7 Omega-sq cm range are achieved with Ni-only contacts on n-InP by sintering at 400 C for several minutes. The postsinter contact metallization consists of three layers, arranged in the sequence: InP/Ni3P/Ni2P/In. Extended sintering (40 min) at 400 C brings about a rise in Rc to the 10 exp -4 Omega-sq cm range. After extended sintering, the contact metallization is found to consist of only two layers, arranged in the sequence: InP/Ni2P/In. Based on the correlation between low Rc and the presence of Ni3P at the metal-InP interface, it is suggested that the presence of Ni3P is the cause of the low Rc values. We show that the sintering schedule used to achieve low values of Rc is accompanied by substantial metal-InP interdiffusion that results in severe device degradation.
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During February/March 1994, a series of aircraft-based aerosol measurements were carried out in the Pacific Basin troposphere using a differential absorption lidar system deployed by NASA Langley, and optical spectrometer probes and a wire-impactor system operated by NASA Ames. A modified Klett inversion algorithm was applied to extract altitude profiles of aerosol backscattering from the IR lidar signal. The algorithm that we have designed for this purpose utilizes the in situ aerosol measurements to normalize the lidar profile at the aircraft altitude and to supply the lidar ratio as a function of height. The lidar-derived aerosol backscattering coefficients were then compared to the backscattering coefficients calculated from the in situ measurements. During several local aircraft descents, we found good agreement between the remote lidar and in situ results for the absolute value of the aerosol backscattering coefficient and its altitude variation only when we allowed for several layers with different aerosol refractive indices. The agreement validates our lidar calibration method and provides an indication of the variation in aerosol refractive index as a function of altitude. Two of the three case studies performed in this paper reveal layers of anthropogenic aerosols transported long distances into the Pacific Basin troposphere. A third case implies the existence of a layer of dustlike aerosol particles in the lower troposphere, most likely of Asian origin.
We have identified a set of 23 Halo CMEs through July 2002 and 21 Partial Halo CMEs from the LASCO Halo CME Mail Archive for which Ultraviolet Coronagraph Spectrometer (UVCS) spectra exist. For each event we have collected basic information such as the event speed, whether or not UVCS caught the bright front, lines detected, Doppler shift and associated flare class. We have also obtained excellent observations of some of the spectacular events in November 2003, and we have made theoretical calculations pertaining to CME expansion at the heights observed by UVCS. We first analyzed the halo CMEs on 21 April and 24 August 2002 and the partial halo on 23 July 2002, because the X-class flares associated with these CMEs were extensively observed by RHESSI and other instruments as part of the MAX MILLENIUM campaign. These very fast CMEs showed extremely violent disruption of the pre-CME streamers, little or no cool prominence material, and the unusual (for UVCS heights) hot emission line [Fe XVIII]. Results, including a discussion of the current sheet interpretation for the [Fe XVIII] emission, are published in Raymond et al. and presented at the Fall 2002 AGU meeting and the solar physics summer school in L'Aquila, Italy. We are currently preparing two papers on the Dec. 28, 2000 partial halo event. This event was chosen to take advantage of the SEP event measured by WIND and ACE, and because a Type II radio burst coincides with the time that broad, blue-shifted O VI emission appeared in the UVCS spectra. One paper deals with a new density and velocity diagnostic for very fast CMEs; pumping of O VI lambda 1032 by Ly beta and pumping of O VI lambda 1038 by O VI lambda 1032. The other discusses physics of the shock wave and association with the SEP event. In the coming year we plan to expand the list of Halo and Partial Halo events observed by UVCS through the end of 2003. We will look at those events as a class to search for correlation between UV spectral characteristics and other CME and flare parameters. We will also choose several events for more detailed study, probably including the November 2003 events. We expect to support extended visits to CfA by S. Mancuso and A. Ciaravella. In the past year the grant covered some salary support for members of the SAO UVCS team and a 1 month visit to CfA by Angela Ciaravella, along with trips to meetings by J. Lin and J. Raymond and page charges for two papers.
density was performed over a range of temperatures below the glass transition temperature. The physical characterization, elastic properties and notched tensile strength all as a function of molecular weight and test temperature were determined. For the uncrosslinked SI material, it was shown that notched tensile strength is a strong function of both temperature and molecular weight, whereas stiffness is only a strong function of temperature. For the crosslinked PETI-SI material, it was shown that the effect of crosslinking significantly enhances the mechanical performance of the low molecular weight material; comparable to that exhibited by the high molecular weight material.
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We have identified a set of 23 Halo CMEs and 21 Partial Halo CMEs from the LASCO Halo CME Archive for which UVCS spectra exist through July 2002. For each event we have collected basic information such as the event speed, whether or not UVCS caught the bright front, lines detected, Doppler shift and associated flare class. We are currently analyzing the subset for which UVCS caught the CME front. We also obtained excellent observations of some of the spectacular events in November 2003, and we have made theoretical calculations pertaining to CME expansion at the heights observed by UVCS. In one event we were able to analyze the properties of the current sheet in detail.
Very little work has been done in the Yb-Sb-Te system of compounds. Exploratory synthesis of various compounds in the system has been performed in the search for new thermoelectric materials. The compounds in the system were examined due to the fact that the system is known to act as a concentrated Kondo system, a heavy fermion. Heavy fermions are known to possess high densities of state which are useful in thermoelectric applications. TWO compounds in the system, YbSb2Te4 and YbSb4Te7, have been successfully synthesized in bulk by two methods: low temperature mechanical alloying and high temperature direct synthesis. The Hall mobility, Seebeck coefficient, electrical resistivity, and thermal conductivity were measured on both the unannealed and annealed compounds up to 550 C to determine the dimensionless thermoelectric figure of merit, ZT. The results indicate that both compounds make promising candidates for use in thermoelectric devices.
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La0.7Ca0.3MnO3 (a = 3.86 angstroms) epitaxial thin films have been grown on SrTiO3 (a = 3.905 angstroms), LaAlO3 (a = 3.79 angstroms), and YAlO3 (a/square root of 2 = 3.66 angstroms, b/square root of 2 = 3.77 angstroms) substrates. The films were analyzed with x-ray diffraction, x-ray photoemission spectroscopy, dc and ac resistivity, and dc magnetization.
The results of the NACA tests to determine the tensile strength of some structural sheet materials heated to failure at temperature rates from 0.2 deg. F to 100 deg F per second under constant load conditions are reviewed . Yield and rupture stresses obtained under rapid-heating conditions are compared with the results of conventional elevated-temperature tensile tests. The relation between rapid-heating tests, short-time creep tests, and conventional creep tests is discussed . The application of a phenomenological theory for calculating rapid-heating curves is shown. Methods are given for predicting yield and rupture stresses and temperatures from master curves and temperature-rate parameters
Prompted by the detection of stratospheric cloud layers by Cassini's Composite Infrared Spectrometer (CIRS; see Anderson, C.M., Samuelson, R.E. [2011]. Icarus 212, 762-778), we have re-examined the observations made by the Descent Imager/Spectral Radiometer (DISR) in the atmosphere of Titan together with two constraints from measurements made outside the atmosphere. No evidence of thin layers (<1 km) in the DISR image data sets is seen beyond the three previously reported layers at 21 km, 11 km, and 7 km by Karkoschka and Tomasko (Karkoschka, E., Tomasko, M.G. [2009]. Icarus 199, 442-448). On the other hand, there is evidence of a thicker layer centered at about 55 km. A rise in radiance gradients in the Downward-Looking Visible Spectrometer (DLVS) data below 55 km indicates an increase in the volume extinction coefficient near this altitude. To fit the geometric albedo measured from outside the atmosphere the decrease in the single scattering albedo of Titan's aerosols at high altitudes, noted in earlier studies of DISR data, must continue to much higher altitudes. The altitude of Titan's limb as a function of wavelength requires that the scale height of the aerosols decrease with altitude from the 65 km value seen in the DISR observations below 140 km to the 45 km value at higher altitudes. We compared the variation of radiance with nadir angle observed in the DISR images to improve our aerosol model. Our new aerosol model fits the altitude and wavelength variations of the observations at small and intermediate nadir angles but not for large nadir angles, indicating an effect that is not reproduced by our radiative transfer model. The volume extinction profiles are modeled by continuous functions except near the enhancement level near 55 km altitude. The wavelength dependence of the extinction optical depth is similar to earlier results at wavelengths from 500 to 700 nm, but is smaller at shorter wavelengths and larger toward longer wavelengths. A Hapke-like model is used for the ground reflectivity, and the variation of the Hapke single scattering albedo with wavelength is given. Fits to the visible spectrometers looking upward and downward are achieved except in the methane bands longward of 720 nm. This is possibly due to uncertainties in extrapolation of laboratory measurements from 1 km-am paths to much longer paths at lower pressures. It could also be due to changes in the single scattering phase functions at low altitudes, which strongly affect the path length through methane that the photons travel. We demonstrate the effects on the model fits by varying each model parameter individually in order to illustrate the sensitivity of our determination of each model parameter.