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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

On the design of prioritized multiplexing systems

Systems in which many data sources are multiplexed over a single communication channel are considered. Data from all the sources are generated in fixed-length packets, and are stored in a common buffer with finite capacity. Packets overflowed or removed from the buffer prior to transmission are lost. The system performance measure is the set of packet loss probabilities associated with the sources. Queueing disciplines vary depending on the stringency of prioritization and the utilization of system resources. The set of all possible performances is characterized as the set of all queueing disciplines is spanned. Whether a given performance is possible can be deduced. Strategies that achieve the minimum overall loss probability are identified. The extreme disciplines are specified, and their performances are calculable by means of a given algorithm.

Clare, L. P.↗
NASA NTRS1983

High temperature deformation of hot-pressed polycrystalline orthoenstatite

Artificial hot pressed polycrystalline samples were prepared from purified powder of Bamble, Norway, orthoenstatite, (Mg0.86Fe0.14)SiO3. The uniaxial creep behavior of the polycrystalline orthoenstatite was studied over stress ranges of 10-180 MPa and temperatures of 1500-1700 K (0.82-0.93 T sub m) under two different oxygen fugacities, namely equilibrium (Mo-MoO2 buffer) and a reducing (graphite heating element) atmosphere, respectively. An intergranular glassy phase of different compositions with a cavitational creep deformation were observed. In the Mo-MoO2 buffer atmosphere with PO2 approx. 10 to the minus 11 power - 10 to the minus 13 power atmospheres, the results of an analytical electron microscopy analysis indicate that the glassy phases are richer in Ca and Al due to the residual impurities after hot pressing. In the reducing atmosphere with an oxygen fugacity of PO2 approx. 10 to the minus 3 power - 10 to the minus 25 power atmospheres, the results of analytical electron microscopy analysis indicate that the glassy phase is almost pure silica with the presence of free iron precipitate on grain facets and at triple junctions due to the reduction of bulk materials.

Dehghan-Banadaki, A.↗
NASA NTRS1984

Development of a new class of chemical and biological ultrasensors: Ribonuclease contamination and control

In order to define ribonuclease contamination, an assay for ribonuclease having picogram level sensitivity was established. In this assay, polycytidylic acid is digested by ribonuclease leading to smaller fragments of poly C that remain soluble after treatment of the sample with perchloric acid and lanthanum acetate. An absorbance measurement at 260 nm of the supernatant from the centrifuged sample measures the ribonuclease. A standard curve is shown. Using this assay procedure, ribonuclease contamination was found to be significant in routine laboratory proteins, in particular, bovine serum albumin, lysozyme, catalase, and cytochrome C. This was confirmed by demonstrating a considerable reduction in this activity in the presence of phosphate buffer since phosphate inhibits ribonuclease. Ribonuclease contamination was not significantly encountered in routine laboratory glassware, plasticware, column surfaces, chromatographic particles, and buffer reagents, including airborne contamination. Some contamination could be introduced by fingerprints, however.

Source record↗
NASA NTRS1984

Maser and secondary clock in telecommunications networks

Telecommunication networks of time division switches, interconnected by digital transmission are being put into place. At each switch, each incoming bit stream is brought into its own buffer. Then the clock in the switch reads each buffer to re-establish phase. Care must be taken to keep frequency differences between various clocks from becoming too large. Based on empirically defined data transmission requirements, one major network has determined that fractional frequency inequality between switches should be no worse than 1.7 X 10 to the minus 9 power. A network needs near frequency equality between its own switches, and also between its switches and other networks with which it interfaces. As a practical matter, the best way to achieve needed frequency equality is for each network to have master clock with an accuracy which is at least as good as 1 X 10 to the minus 10 power. The relationship between the master and the secondary clock is discussed. The questions of master clock accuracy and precision and the free-running capability of the secondary clocks are examined.

Risley, A.↗
NASA NTRS1985

Water loss from Venus: Implications for the Earth's early atmosphere

The atmosphere of Venus outgassed rapidly as a result of planetary heating during accretion, resulting in massive water loss. The processes affecting atmospheric chemistry following accretion have consisted largely of hydrogen escape and internal re-equilibrium. The initial bulk composition of Venus and Earth are assumed to have been roughly similar. Chemical speciation on Venus was controlled by the temperature and oxygen buffering capacity of the surface magma. It is also assumed that the surfaces of planetary bodies of the inner solar system were partly or wholly molten during accretion with a temperature estimated at 1273 to 1573 K. To investigate the range of reasonable initial atmospheric compositions on Venus, limits have to be set for the proportion of total hydrogen and the buffered fugacity of oxygen. Using the C/H ratio of 0.033 set for Earth, virtually all of the water generated during outgassing must later have been lost in order to bring the current CO2/H2O ratio for Venus up to its observed value of 10 sup 4 to 10 sup 5. The proportion of H2O decreases in model atmospheres with successfully higher C/H values, ultimately approaching the depleted values currently observed on Venus. Increasing C/H also results in a rapid increase in CO/H2O and provides an efficient mechanism for water loss by the reaction CO+H2O = CO2 + H2. This reaction, plus water loss mechanisms involving crustal iron, could have removed a very large volume of water from the Venusian atmosphere, even at a low C/H value.

Richardson, S. M.↗
NASA NTRS1985

Advanced seals for Liquid Oxygen (LOX) turbopumps

Reliability, life and vehicle pay load can be enhanced by improved seals on space vehicle propulsion systems. Development of two types of fluid-film seals for application to advanced LOX turbomachines are summarized. The first is a floating ring, helium buffered seal whose function is to exclude intrusion of liquid oxygen (LOX) into the turbine drive. The other is a spiral groove, LOX, face-type configuration designed to break down pressure and minimize leakage of LOX. The Rayleigh-step, floating ring gas seals require low clearances to minimize leakage and stiff films to assure tracking excursions of the rotor and to overcome Coulomb friction between the rings and housings. The design and test results of these buffer seals are described. Results indicate significant performance improvement over seals used on contemporary engines. The possibilities of reducing helium storage requirements and thus increasing payload appear promising. A unique configuration of spiral groove LOX seal was required to avoid detrimental vaporization in the flow path. It was found that fluid turbulence and inertia influence groove geometry and in particular groove depth must be much greater than spiral groove seals using conventional fluids.

Shapiro, W.↗
NASA NTRS1987

Synthetic aperture radar signal processing on the MPP

Satellite-borne Synthetic Aperture Radars (SAR) sense areas of several thousand square kilometers in seconds and transmit phase history signal data several tens of megabits per second. The Shuttle Imaging Radar-B (SIR-B) has a variable swath of 20 to 50 km and acquired data over 100 kms along track in about 13 seconds. With the simplification of separability of the reference function, the processing still requires considerable resources; high speed I/O, large memory and fast computation. Processing systems with regular hardware take hours to process one Seasat image and about one hour for a SIR-B image. Bringing this processing time closer to acquisition times requires an end-to-end system solution. For the purpose of demonstration, software was implemented on the present Massively Parallel Processor (MPP) configuration for processing Seasat and SIR-B data. The software takes advantage of the high processing speed offered by the MPP, the large Staging Buffer, and the high speed I/O between the MPP array unit and the Staging Buffer. It was found that with unoptimized Parallel Pascal code, the processing time on the MPP for a 4096 x 4096 sample subset of signal data ranges between 18 and 30.2 seconds depending on options.

Ramapriyan, H. K.↗
NASA NTRS1986

The distribution of chromium among orthopyroxene, spinel and silicate liquid at atmospheric pressure

The Cr distributions for a synthetic silicate melt equilibrated with bronzitic orthopyroxene and chromite spinel between 1334 and 1151 C over a range of oxygen fugacities between the nickel-nickel oxide and iron-wuestite buffers are studied. The occurrence, chemical composition, and structure of the orthopyroxene-silicate melt and the spinel-silicate melt are described. It is observed that the Cr content between bronzite and the melt increases with falling temperature along a given oxygen buffer and decreases with falling oxygen fugacity at a given temperature; however, the Cr content of the melt in equilibrium with spinel decreases with falling temperature and increases with lower oxygen fugacity.

Barnes, S. J.↗
NASA NTRS1986

Kinetics of OH + CO reaction under atmospheric conditions

A pulsed laser photolysis-pulsed laser-induced fluorescence technique is used to directly measure the temperature, pressure, and H2O concentration dependence on k1 in air. K1 is found to increase linearly with increasing pressure at pressures of not greater than 1 atm, and the pressure dependence of k1 at 299 K is the same in N2 buffer gas as in O2 buffer gas. The rate constant in the low-pressure limit and the slope of the k1 versus pressure dependence are shown to be the same at 262 K as at 299 K. The present results significantly reduce the current atmospheric model uncertainties in the temperature dependence under atmospheric conditions, in the third body efficiency of O2, and in the effect of water vapor on k1.

Hynes, A. J.↗
NASA NTRS1986

The adsorption and reaction of adenine nucleotides on montmorillonite

The binding of AMP to Zn(2+)-montmorillonite is investigated in the presence of salts and Good's zwitterion buffers, PIPES and MES. The initial concentrations of nucleotide and the percent adsorbtion are used to calculate the adsorption isotherms, and the Langmuir adsorption equation is used for the analysis of data. The adsorption coefficient was found to be three times greater in the presence of 0.2 M PIPES than in its absence. In addition, basal spacings measured by X-ray diffraction were increased by the buffer. These results are interpreted in terms of a model in which the adsorption of AMP is mediated by a Zn(2+) complex of PIPES in different orientations in the interlamellar region of the montmorillonite. Mixed ligand complexes of this type are reminiscent of the complexes observed between metal ions and biological molecules in living systems.

Ferris, James P.↗
NASA NTRS1987

Performance boundaries for prioritized multiplexing systems

Systems in which many data sources are multiplexed over a single communication channel are considered. Data from all the sources are generated in fixed-length packets and are stored in a common buffer with finite capacity. Packets that overflowed or were removed from the buffer prior to transmission are lost. The system performance measure is the set of packet loss probabilities associated with the sources. Queueing disciplines vary depending on the stringency of prioritization and the utilization of the system resources. The set of all possible performances is characterized as the set of all queueing disciplines is spanned. Whether a given performance is possible can be deduced. Strategies that achieve the minimum overall loss probability are identified. The extreme disciplines are specified, and their performances are calculable by means of a given algorithm.

Clare, Loren P.↗
NASA NTRS1988

Merging Digital Data With A Video Signal

Data displayed on television image of experiment. Video images of experiment sent with digital data on experiment to remote station. Digital data raw and unformatted or in form of characters. For minimal power consumption, interface circuit built of CMOS and HMOS integrated-circuit chips. Buffer/decoder circuit enables experiment computer to communicate with board without excessive loading of computer bus by board. Memory multiplexer/memory array implements buffer-swapping scheme as one buffer is read, other filled with new data.

Collins, Thomas J., III↗
NASA NTRS1987

Continuous flow electrophoresis system experiments on shuttle flights STS-6 and STS-7

A space continuous flow electrophoresis system (CFES) was developed that would incorporate specific modifications to laboratory instruments to take advantage of weightlessness. The specific objectives were to use a model sample material at a high concentration to evaluate the continuous flow electrophoresis process in the CFES instrument and compare its separation resolution and sample throughput with related devices on Earth and to expand the basic knowledge of the limitations imposed by fluid flows and particle concentration effects on the electrophoresis process by careful design and evaluation of the space experiment. Hemoglobin and polysaccharide were selected as primary samples. The results from space show a large band spread of the high concentration of the single species of hemoglobin that was due to the mismatch of electrical conductivity between the sample and the buffer. On STS-7 the major objective was to evaluate the influence of the electrical properties of the sample constituents on the resolution of the CFES. As expected, the polystyrene latex microspheres dispersed in a solution with 3 times the electrical conductivity of the curtain buffer separated with a larger band spread than in the 2nd experiment.

Snyder, Robert S.↗
NASA NTRS1987

A modular BLSS simulation model

A bioregenerative life support system (BLSS) for extraterrestrial use will be faced with coordination problems more acute than those in any ecosystem found on Earth. A related problem in BLSS design is providing an interface between the various life support processors, one that will allow for their coordination while still allowing for system expansion. A modular model is presented of a BLSS that interfaces system processors only with the material storage reservoirs, allowing those reservoirs to act as the principal buffers in the system and thus minimizing difficulties with processor coordination. The modular nature of the model allows independent development of the detailed submodels that exist within the model framework. Using this model, BLSS dynamics were investigated under normal conditions and under various failure modes. Partial and complete failures of various components, such as the waste processors or the plants themselves, drive transient responses in the model system, allowing the examination of the effectiveness of the system reservoirs as buffers. The results from simulations help to determine control strategies and BLSS design requirements. An evolved version could be used as an interactive control aid in a future BLSS.

Rummel, John D.↗
NASA NTRS1985

Seal Technology for Liquid Oxygen (LOX) Turbopumps

Two types of advanced seals for liquid oxygen (LOX) turbopumps were investigated. One was a spiral-groove face seal whose function is to seal high-pressure LOX at the impeller end of the turbopump. The other was a floating-ring, Rayleigh-step, helium buffered seal used to prevent LOX ingress to the turbine side of the unit. For each seal type, two sizes were investigated (50 and 20 mm). A turbine-driven test rig was designed and manufactured, and a test program was completed on the 50 mm floating-ring, Rayleigh-step, helium buffered seal. Significant results were: vaporization in the flow path could cause failure by overheating; therefore, the spiral-groove pumping portion of the seal that provides the fluid film must circulate fluid without disruption if vaporization occurs in the sealing dam. This is successfully accomplished by a pressure-balanced spiral-groove concept that is described. The spiral-groove configuration is affected by turbulence in the fluid film and pressure drops due to fluid inertia at sudden contractions. The net results of these effects are deep grooves, large operating films, and high power loss when compared against seals operating with laminar films. Turbulence and inertia are induced by the high-density and low-viscosity characteristics of LOX. The program clearly pointed out the need to consider system environmental factors such as thermal and centrifugal distortions and rotor vibrations in the seal design.

Shapiro, Wilbur↗
NASA NTRS1987

AVIRIS onboard data handling and control

The timing and flow of detector and ancillary data for the Airborne Visible/Infrared imaging spectrometer (AVIRIS) are controlled within the instrument by its digital electronics assembly. In addition to providing detector and signal chain timing, the digital electronics receives, formats, and rate-buffers digitized science data; collects and formats ancillary (calibration and engineering) data; and merges both into a single tape record. Overall AVIRIS data handling is effected by a combination of dedicated digital electronics to control instrument timing, image data flow, and data rate buffering and a microcomputer programmed to handle real-time control of instrument mechanisms and the coordinated preparation of ancillary data.

Steinkraus, Ronald E.↗
NASA NTRS1986

Mathematical models of continuous flow electrophoresis: Electrophoresis technology

Two aspects of continuous flow electrophoresis were studied: (1) the structure of the flow field in continuous flow devices; and (2) the electrokinetic properties of suspended particles relevant to electrophoretic separations. Mathematical models were developed to describe flow structure and stability, with particular emphasis on effects due to buoyancy. To describe the fractionation of an arbitrary particulate sample by continuous flow electrophoresis, a general mathematical model was constructed. In this model, chamber dimensions, field strength, buffer composition, and other design variables can be altered at will to study their effects on resolution and throughput. All these mathematical models were implemented on a digital computer and the codes are available for general use. Experimental and theoretical work with particulate samples probed how particle mobility is related to buffer composition. It was found that ions on the surface of small particles are mobile, contrary to the widely accepted view. This influences particle mobility and suspension conductivity. A novel technique was used to measure the mobility of particles in concentrated suspensions.

Saville, Dudley A.↗
NASA NTRS1989

Solar-powered alkali metal vapor lasers

The emission spectrum of the A(1 Sigma u +) - X(1 Sigma g +) band of Na2 has been recorded following excitation by monochromatic radiation in the region of X-A and X-B absorption. The spectral profile has been investigated as a function of excitation wavelength, sodium vapor temperature and buffer gas pressure. Additionally, gain measurements were made for the satellite of the A-X band as a function of the sodium vapor temperature and buffer gas pressure.

Blount, Charles E.↗