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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Design and construction of high-sensitivity, infrared bolometers for operation at 300 mK

The design and construction of 300-mK composite bolometers developed for millimeter-wave astronomical observations are described. Graphite fibers are used as the electrical leads for the thermistor to reduce the thermal conductance and heat capacity associated with the leads. A mechanical suspension made of Nylon fibers provides the required thermal conductance. Electrical noise equivalent powers below 1 x 10 exp -16 W/sq rt Hz have been achieved for detectors with thermal time constants of 11 ms. The detectors were installed in a millimeter-wave photometer and used to perform observations of the cosmic microwave background from a balloonborne platform. The flight performance was consistent with the measured laboratory properties.

Alsop, D. C.↗
NASA NTRS1993

Preliminary evaluation of tensile and stress-rupture behavior of W + 24 at. pct Re + 0.4 at. pct HfC wire

Results are presented of an evaluation of tensile properties and stress-rupture bahavior of a small-diameter W24ReHfC (W-24Re-0.4(HfC)) wire, which is considered to be an excellent reinforcing fiber candidate for a variety of metal-matrix composites. The results were compared to data of Petrasek (1972) on W4ReHfC (W-4Re-0.4(HfC)) wire. It was found that the room-temperature (RT) tensile strength of the W24ReHfC wire was about 3250 MPa, higher than that of the W4ReHfC (3160 MPa) and WHfC (2250 MPa) wires. Above 1366 K, the W4ReHfC wire had both a greater tensile strength and the stress rupture strength than the W24ReHfC wire.

Yun, H. M.↗
NASA NTRS1993

On reaction kinetics and atmospheric lifetimes of CF3CFHCF3 and CF3CH2Br

The rate constants for the reaction of the OH radical with CF3CFHCF3 and with CF3CH2Br have been measured as a function of temperature using the discharge flow technique with laser induced fluorescence detection of the OH radicals. The temperature dependent rate coefficients are well described by a simple Arrhenius expression, k(T) = A exp(E/(RT)). For the reaction of OH with CF3CFHCF3 we find A = 3.7 x 10 exp -13 cu cm/molecules/s and E/R = 1615 K; for the reaction of OH with CF3CH2Br we report A = 1.4 x 10 exp -12 cu cm/molecule/s and E/R = 1350 K. These Arrhenius parameters imply rate coefficients at 277 K of 1.09 x 10 exp -15 cu cm/molecule/s for CF3CFHCF3 and 1.06 x 10 exp -14 cu cm/molecule/s for CF3CH2Br. We find atmospheric lifetimes for CF3CFHCH3 and CF3CH2Br of 42 years and 4.1 years, respectively. We also estimate the steady state ozone depletion potential (ODP) of the brominated species relative to CFCl3 as about 0.84 using a semiempirical model.

Nelson, D. D., Jr.↗
NASA NTRS1993

Infrared photodetectors with tailorable response due to resonant plasmon absorption in epitaxial silicide particles embedded in silicon

Tailorable infrared photoresponse in the 1-2 micron range are demonstrated in a device incorporating electrically floating metal silicide particles. Photons absorbed by excitation of the metallic-particle surface plasmon are shown to contribute to the photoresponse. Quantum efficiencies of roughly 0.2 percent are measured at 77 K, with dark currents of less than 2 nA/sq cm at a reverse bias of 1 V and detectivities of 4 x 10 exp 9 - 8 x 10 exp 9 cm sq rt Hz/W are obtained.

Fathauer, R. W.↗
NASA NTRS1991

Wiener-matrix image restoration beyond the sampling passband

A finer-than-sampling-lattice resolution image can be obtained using multiresponse image gathering and Wiener-matrix restoration. The multiresponse image gathering weighs the within-passband and aliased signal components differently, allowing the Wiener-matrix restoration filter to unscramble these signal components and restore spatial frequencies beyond the sampling passband of the photodetector array. A multiresponse images can be reassembled into a single minimum mean square error image with a resolution that is sq rt A times finer than the photodetector-array sampling lattice.

Rahman, Zia-Ur↗
NASA NTRS1991

Cryogenic monocrystalline silicon Fabry-Perot cavity for the stabilization of laser frequency

A 1.6 kg silicon monocrystal was used to make a Fabry-Perot optical cavity operated at cryogenic temperatures. High-resolution thermal expansion measurements were made as the silicon cooled to 4.2 K, in order to characterize the cavity as a length reference standard. A helium-neon laser was then locked to a transmission resonance at liquid-helium temperatures, and the laser frequency tracked the cavity resonance with error fluctuations at the level of 10 Hz/sq rt Hz in the bandwidth dc to 1 Hz. Implications of the combined set of data, thermal expansion plus frequency-tracking fluctuations, for using such a system as a frequency standard are discussed.

Richard, J.-P.↗
NASA NTRS1991

Multiresponse imaging system design for improved resolution

Multiresponse imaging is a process that acquires A images, each with a different optical response, and reassembles them into a single image with an improved resolution that can approach 1/sq rt A times the photodetector-array sampling lattice. Our goals are to optimize the performance of this process in terms of the resolution and fidelity of the restored image and to assess the amount of information required to do so. The theoretical approach is based on the extension of both image restoration and rate-distortion theories from their traditional realm of signal processing to image processing which includes image gathering and display.

Alter-Gartenberg, Rachel↗
NASA NTRS1991

Transportation technology: Earth-to-orbit propulsion

The topics presented are covered in viewgraph form and include the following: (1) sensor autodiagnosis and autocalibration; (2) autodiagnostic and autocalibration program; (3) plume diagnostics; (4) plume diagnostics program; (5) failure modeling; (6) mass data storage and retrieval; (7) fiber optic instrumentation bus; (8) model based diagnostics; (9) safety monitoring system (SMS); (10) control and real time diagnostics; (11) current intelligent controls program; (12) augumented intelligent controls program; (13) current real time diagnostics program; (14) augumented RT diagnostics program; and (15) control and diagnostic system hardware.

Gorland, S.↗
NASA NTRS1942

Tensile and pack compressive tests of some sheets of aluminum alloy, 1025 carbon steel, and chromium-nickel steel

Tensile and compressive stress-strain curves, stress-deviation curves, and secant modulus-stress curves are given for longitudinal and transverse specimens of 17S-T, 24S-T, and 24S-RT aluminum-alloy sheet in thicknesses from 0.032 to 0.081 inch, 1025 carbon steel sheet in thicknesses of 0.054 and 0.120 inch, and chromium-nickel steel sheet in thicknesses form 0.020 to 0.0275 inch. Significant differences were found between the tensile and the compressive stress-strain curves, and also the corresponding corollary curves; similarly, differences were found between the curves for the longitudinal and transverse directions. These differences are of particular importance in considering the compressive strength of aircraft structures made of thin sheet. They are explored further for the case of compression by giving tangent modulus-stress curves in longitudinal and transverse compression and dimensionless curves of the ratio of tangent modulus to Young's modulus and of the ratio of reduced modulus for a rectangular section to Young's modulus, both plotted against the ratio of stress to secant yield strength.

Atchison, C S↗
NASA NTRS1943

Bearing Strengths of Some Wrought-aluminum Alloys

Although a number of investigations of the bearing strength of aluminum alloys have been made, the problem remains one of considerable interest to the aircraft industry. For this reason it has seemed advisable to make additional tests of the commonly used aircraft alloys in an effort to establish a better basis for the selection of allowable bearing values. Current design practice does not recognize the effect of edge distance upon bearing strengths, and for this reason edge distance was one of the principal variables considered in this investigation. The increasing emphasis being placed upon permanent set limitations makes it essential that more information on bearing yield phenomena be obtained. The object of this investigation was to determine bearing yield and ultimate strengths of the following aluminum alloy products: 17S-T, 24S-T, Alclad 24S-T, 24S-RT, 52S-0, 52S-1/2H, 52S-H, 53S-T, and 61S-T extrusions. Ratios of these bearing properties to tensile properties were also determined.

Moore, R L↗
NASA NTRS1943

A Subpress for Compressive Tests

A subpress for compressive tests is described. The subpress was designed primarily for use in developing and investigating methods for testing thin sheet metal in compression. Provision was made for testing fixed-end and flat-end specimens with or without various types of lateral support against buckling. Compressive stress-strain data for a sheet of 0.032-inch 24S-RT aluminum alloy were obtained with the subpress by the pack method and by the single-thickness method. The data showed small scatter and the stress-strain curves obtained by the two methods were in close agreement.

Aitchison, C S↗
NASA NTRS1924

A Constant Pressure Bomb

This report describes a new optical method of unusual simplicity and of good accuracy suitable to study the kinetics of gaseous reactions. The device is the complement of the spherical bomb of constant volume, and extends the applicability of the relationship, pv=rt for gaseous equilibrium conditions, to the use of both factors p and v. The method substitutes for the mechanical complications of a manometer placed at some distance from the seat of reaction the possibility of allowing the radiant effects of reaction to record themselves directly upon a sensitive film. It is possible the device may be of use in the study of the photoelectric effects of radiation. The method makes possible a greater precision in the measurement of normal flame velocities than was previously possible. An approximate analysis shows that the increase of pressure and density ahead of the flame is negligible until the velocity of the flame approaches that of sound.

Stevens, F W↗
NASA NTRS1993

Inelastic deformation mechanisms in SCS-6/Ti 15-3 MMC lamina under compression

An investigation was undertaken to study the inelastic deformation mechanisms in (0)(sub 8) and (90)(sub 8) Ti 15-3/SCS-6 lamina subjected to pure compression. Monotonic tests were conducted at room temperature (RT), 538 C and 650 C. Results indicate that mechanical response and deformation characteristics were different in monotonic tension and compression loading whereas some of those differences could be attributed to residual stress effects. There were other differences because of changes in damage and failure modes. The inelastic deformation in the (0)(sub 8) lamina under compression was controlled primarily by matrix plasticity, although some evidence of fiber-matrix debonding was observed. Failure of the specimen in compression was due to fiber buckling in a macroscopic shear zone (the failure plane). The inelastic deformation mechanisms under compression in (90)(sub 8) lamina were controlled by radial fiber fracture, matrix plasticity, and fiber-matrix debonding. The radial fiber fracture was a new damage mode observed for MMC's. Constitutive response was predicted for both the (0)(sub 8) and (90)(sub 8) laminae, using AGLPLY, METCAN, and Battelle's Unit Cell FEA model. Results from the analyses were encouraging.

Newaz, Golam M.↗
NASA NTRS1994

The electrocortical correlates of fluctuating states of attention during vigilance tasks

This study investigated the electrocortical correlates of attention. Sixteen subjects (seven females, nine males) engaged in a forty-minute target detection vigilance task. Task-irrelevant probe tones were presented every 2-4 seconds. While performing the vigilance task, the subjects were asked to press a button if they were daydreaming (i.e. having a task unrelated thought or TUT). Continuous electroencephalograms (EEG's) and event-related potentials (ERP's) were recorded from the subjects during the entire task. The continuous EEG data were analyzed for differences in absolute power throughout the task as well as before and after the subjects indicated that they were daydreaming (TUT response). ERP's elicited by task-irrelevant probe tones were analyzed in the same manner. The results indicated performance decrements as reflected by increased RT to correct detections, and decreased number of hits. Further, as the task progressed, the number of reports of daydreaming increased. The analysis of the EEG data indicated a significant difference in the absolute power of the different frequency bands across periods. The greatest difference was observed at the posterior parietal electrode sites. In addition, when the EEG data was converted into band ratios (beta/alpha and beta/alpha+theta), the pre-TUT conditions were found to be significantly different than the post-TUT conditions in the posterior sites. The ERP components (N1, N2, and P2) were not significantly different before and after a TUT response or across periods. However, the ERP's across periods exhibited amplitudes that were similar to those found in previous studies of vigilance and ERP's.

Cunningham, Stephen G.↗
NASA NTRS1995

Critical point of the solar wind by radio sounding data

Results of the close-to-Sun plasmas sounding at the transonic region of the solar wind, where the sub-to supersonic flow transition proceeds (at 10 to 40 solar radii from the Sun), are presented. Natural sources of two types were used, water vapour maser sources at 1.35 cm and guasars at 2.9 m wavelength. scattering observations cover the period of 1986 to 1993, Russian Academy of Sciences telescopes RT-22 and DCR-1000 were used, IPS index and scattering angle being the immediate results of observations. Extensive studies of the scintillation index and scattering angle radial profiles reveal a remarkable structural detail, 'transonic region forrunner'-narrow region of diminished scattering close to the internal border of the extended transonic region with its characteristic enhanced scattering. Comparisons of the scattering and plasma velocity profiles let it possible to determine the critical point positions by the comparatively simple scattering observations. This new possibility widely improves the process of the basic data accumulation in the fundamental problem of the solar wind acceleration mechanism.

Lotova, N. A.↗
NASA NTRS1995

Radio maps of the solar wind transonic region

Extensive radio astronomical exploration of near-solar plasmas was carried out in 1987-1993 at radial distances nowadays inaccessible for direct spacecraft experiments. Radio wave sounding experiments were carried out using two types of natural sources-water vapor masers at 1.35 cm and quasars at 2.9 m wavelength. Russian Academy of Sciences radio telescopes RT-22 and DCR-1000 were used. The results of daily observations formed the radial dependence of the radio wave scattering from whence structural peculiarities of the solar wind flow were derived. Simultaneous observations of several sources makes it possible to realize radio maps visualizing the plasma flow stream structure. The 1987 to 1993 maps allow to analyse the transonic region structural changes in relation to the 11-year cycle phase.

Lotova, N. A.↗
NASA NTRS1996

A Velocity Distribution Model for Steady State Heat Transfer

Consider a box that is filled with an ideal gas and that is aligned along Cartesian coordinates (x, y, z) having until length in the 'y' direction and unspecified length in the 'x' and 'z' directions. Heat is applied uniformly over the 'hot' end of the box (y = 1) and is removed uniformly over the 'cold' end (y = O) at a constant rate such that the ends of the box are maintained at temperatures T(sub 0) at y = O and T(sub 1) at y = 1. Let U, V, and W denote the respective velocity components of a molecule inside the box selected at some random time and at some location (x, y, z). If T(sub 0) = T(sub 1), then U, Y, and W are mutually independent and Gaussian, each with mean zero and variance RT(sub 0), where R is the gas constant. When T(sub 0) does not equal T(sub 1) the velocity components are not independent and are not Gaussian. Our objective is to characterize the joint distribution of the velocity components U, Y, and W as a function of y, and, in particular, to characterize the distribution of V given y. It is hoped that this research will lead to an increased physical understanding of the nature of turbulence.

Hall, Eric B.↗
NASA NTRS1997

Adhesive Properties of Cured Phenylethynyl containing Imides

As part of a program to develop structural adhesives for high performance aerospace applications, several phenylethynyl containing oligomer blends of Larc(TM) MPEI and a reactive plasticizer designated LaRC LV-1 21 were prepared and evaluated. The fully imidized blends exhibited minimum melt viscosity as low as 1000 poise at 371 C. Ti/Ti lap shear specimens fabricated at 316 C under 15 psi gave RT strength of approx. 4300 psi and no change in strength was observed at 177 C. The chemistry and properties of this new MPEI as well as some blends of MPEI with LV-121 are presented and compared to the linear version, LARC(TM)-PETI-5.

Chang, Alice C.↗