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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

A note on the performance analysis of static locking in distributed database systems

Even though transaction deadlocks can severely affect the performance of distributed database systems, many current evaluation techniques ignore this aspect. Shyu and Li proposed an evaluation method which takes deadlocks into consideration. However, their technique is limited to exclusive locking. Using this technique, researchers illustrate the impact of deadlocks in the presence of shared locking on distributed database performance.

Kuang, Yinghong↗
NASA NTRS1989

Notes on lunar ilmenite

Opaques (mostly ilmenite) make up 0 to 5 percent of highland rocks, 1 to 11 percent of low-Ti mare basalts, and 10 to 34 percent of high-Ti mare basalts (Carter 1988). Apollos 11 and 17 sampled high-Ti basalts. Apollos 12 and 14 sampled low-Ti basalts. Apollo 15 sampled a complex mixture of mare and highland material. Apollo 16 sampled mainly highland material (Taylor 1975).

Hutson, M. L.↗
NASA NTRS1991

A statistical note on the redundancy of nine standard baroreflex parameters

An accepted method for measuring the responsiveness of the carotid-cardiac baroreflex to arterial pressure changes is to artificially stimulate the baroreceptors in the neck with a pressurized neck chamber. Nine physiological responses to this type of stimulation are quantified and used as indicators of the baroreflex response function. Thirty male humans between the ages of 27 and 46 underwent the carotid-cardiac baroreflex test. The data for the nine response parameters were analyzed by principle component factor analysis. The results indicated that 92.5 percent of the total variance across all nine parameters could be explained in four dimensions. The first two dimensions reflected location points for R-R interval and carotid distending pressure, respectively. The third factor was composed of measures reflecting the gain (responsiveness) of the reflex. The fourth dimension was the ratio of baseline R-R interval to the maximal R-R interval response during simulated hypertension. The data suggest that the analysis of all nine baroreflex parameters is likely to be redundant and researchers should account for these redundancies either in their analyses or conclusions.

Ludwig, David A.↗
NASA NTRS1990

Notes on initial disturbance fields for the transition problem

Initial disturbance fields are categorized and discussed with respect to modes of disturbance and the variants which occur for each test technique. Attention is focused on four fluctuation modes included under the category of stream turbulence: vorticity fluctuations, entropy disturbances or temperature spottiness, noise, and concentration fluctuations. The mechanisms by which particulate matter can affect transition are discussed, along with electrostatic discharges with frequencies in the range from 200 KHz to 30 MHz which is within the critical disturbance-frequency range for many high-speed flows. Acoustic radiation from own vehicle, roughness, and Brownian motion are also covered.

Bushnell, Dennis↗
NASA NTRS1991

A note on the prebiotic synthesis of organic acids in carbonaceous meteorites

Strong similarities between monocarboxylic and hydrocarboxylic acids in the Murchison meteorite suggest corresponding similarities in their origins. However, various lines of evidence apparently implicate quite different precursor compounds in the synthesis of the different acids. These seeming inconsistencies can be resolved by postulating that the apparent precursors also share a related origin. Pervasive D enrichment indicates that this origin was in a presolar molecular cloud. The organic acids themselves were probably synthesized in an aqueous environment on an asteroidal parent body, the hydroxy (and amino) acids by means of the Strecker cyanohydrin reaction.

Kerridge, John F.↗
NASA NTRS1991

Technical notes and correspondence: Stochastic robustness of linear time-invariant control systems

A simple numerical procedure for estimating the stochastic robustness of a linear time-invariant system is described. Monte Carlo evaluations of the system's eigenvalues allows the probability of instability and the related stochastic root locus to be estimated. This analysis approach treats not only Gaussian parameter uncertainties but non-Gaussian cases, including uncertain-but-bounded variation. Confidence intervals for the scalar probability of instability address computational issues inherent in Monte Carlo simulation. Trivial extensions of the procedure admit consideration of alternate discriminants; thus, the probabilities that stipulated degrees of instability will be exceeded or that closed-loop roots will leave desirable regions can also be estimated. Results are particularly amenable to graphical presentation.

Stengel, Robert F.↗
NASA NTRS1992

A note on the very small grains (VSGs) observed at Halley's comet

The most striking feature in the spatial distribution of the smallest dust grains observed at Halley's comet by the VEGA-1 spacecraft is the sharp glitch at a cometocentric distance of about 180,000 km, which approximately corresponds to the cometopause inside which the contaminated solar-wind plasma was rapidly cooled. This glitch is theorized to have been caused by the electrostatic disruption of larger composite grains which rapidly charged up as they traversed the cometopause. The clear asymmetry in the distribution between the inbound and outbound portion of the spacecraft trajectory is also consistent with the dynamical effects of grain charging.

Fomenkova, M. N.↗
NASA NTRS1992

Briefing notes on propulsion stability codes ADMIT, NYQUIST, and SSFREQ

The piping in a liquid rocket can assume complex configurations due to multiple tanks, multiple engines, and structures that piping must go around. The capability to handle some of these complex configurations have been incorporated into the Low Frequency Code (ADMIT), the Nyquist Code (NYQUIST), and the Intermediate Frequency code (SSFREQ). The capability to modify the input on line has been implemented. The configurations allowed include multiple tanks, multiple engines, and the splitting of a pipe into unequal segments going to different (or the same) engines. Straight pipes, bends, inline accumulators, tuned stubs, Helmholtz resonators, parallel resonators, and pumps are the types of piping that may be used. The three codes require the computation of admittance looking toward the tank. Therefore, they all have a number of similar routines for reading in the tank, piping, and engine descriptions. They also have similar routines for computing the admittance looking toward the tank. ADMIT uses only one type of feedline, either a LOX or FUEL line. NYQUIST can use no feedlines, one feedline (either LOX or FUEL), or two feedlines (both LOX and FUEL). SSFREQ requires both feedlines to be present (LOX and FUEL). The common features of the three codes are discussed first, with two sample runs described. Then each of the three codes are discussed along with the sample runs. Several on-line variations are suggested for the second sample run. Input descriptions and the input for the sample runs are given in the appendices.

Armstrong, W. C.↗
NASA NTRS1992

Working Notes from the 1992 AAAI Workshop on Automating Software Design. Theme: Domain Specific Software Design

The goal of this workshop is to identify different architectural approaches to building domain-specific software design systems and to explore issues unique to domain-specific (vs. general-purpose) software design. Some general issues that cut across the particular software design domain include: (1) knowledge representation, acquisition, and maintenance; (2) specialized software design techniques; and (3) user interaction and user interface.

Keller, Richard M.↗
NASA NTRS1992

Working Notes from the 1992 AAAI Spring Symposium on Practical Approaches to Scheduling and Planning

The symposium presented issues involved in the development of scheduling systems that can deal with resource and time limitations. To qualify, a system must be implemented and tested to some degree on non-trivial problems (ideally, on real-world problems). However, a system need not be fully deployed to qualify. Systems that schedule actions in terms of metric time constraints typically represent and reason about an external numeric clock or calendar and can be contrasted with those systems that represent time purely symbolically. The following topics are discussed: integrating planning and scheduling; integrating symbolic goals and numerical utilities; managing uncertainty; incremental rescheduling; managing limited computation time; anytime scheduling and planning algorithms, systems; dependency analysis and schedule reuse; management of schedule and plan execution; and incorporation of discrete event techniques.

Drummond, Mark↗
NASA NTRS1992

NLS cycle 1 and NLS 2 base heating technical notes. Appendix 3: Preliminary cycle 1 NLS base heating environments. Cycle 1 NLS base heating environments. NLS 2 650K STME base heating environments

A preliminary analysis of National Launch System ascent plume induced base heating environments has been completed to support the Induced Environments Panel's objective to assist in maturing the NLS vehicle (1.5 stage and heavy launch lift vehicle) design. Environments during ascent have been determined from this analysis for a few selected locations on the engine nozzles and base heat shield for both vehicles. The environments reflect early summer 1991 configurations and performance data and conservative methodology. A more complete and thorough analysis is under way to update these environments for the cycle 1 review in January 1992.

Bender, Robert L.↗
NASA NTRS1993

A note on the computation of antenna-blocking shadows

A simple and readily applied method is provided to compute the shadow on the main reflector of a Cassegrain antenna, when cast by the subreflector and the subreflector supports. The method entails some convenient minor approximations that will produce results similar to results obtained with a lengthier, mainframe computer program.

Levy, R.↗
NASA NTRS1992

A note on dust grain charging in space plasmas

Central to the study of dust-plasma interactions in the solar system is the electrostatic charging of dust grains. While previous calculations have generally assumed that the distributions of electrons and ions in the plasma are Maxwellian, most space plasmas are observed to have non-Maxwellian tails and can often be fit by a generalized Lorentzian (kappa) distribution. Here we use such a distribution to reevaluate the grain potential, under the condition that the dominant currents to the grain are due to electron and ion collection, as is the case in certain regions of space. The magnitude of the grain potential is found to be larger than that in a Maxwellian plasma as long as the electrons are described by a kappa distribution: this enhancement increased with ion mass and decreasing electron kappa. The modification of the grain potential in generalized Lorentzian plasmas has implications for both the physics (e.g., grain growth and disruption) and the dynamics of dust in space plasmas. These are also briefly discussed.

Rosenberg, M.↗
NASA NTRS1992

Technical note - Plasma-sprayed ceramic thermal barrier coatings for smooth intermetallic alloys

A new approach for plasma spray deposition of ceramic thermal barrier coatings directly to smooth substrates is described. Ceramic thermal barrier coatings were directly applied to substrates that had been coated with low-pressure plasma sprayed NiCrAlY bond coats and then centerless ground to simulate a smooth oxidation-resistant substrate. As the high-temperature oxidation behavior of NiAl+Zr is superior to that of MCrALY alloy, the bond coat is not required for oxidation resistance.

Miller, R. A.↗
NASA NTRS1992

A note on the effects of viscosity on the stability of a trailing-line vortex

The linear stability of the Batchelor (1964) vortex is examined with emphasis on new viscous modes recently found numerically by Khorrami (1991). Unlike the previously reported inviscid modes of instability, these modes are destabilized by viscosity and exhibit small growth rates at large Reynolds numbers. The analysis presented here uses a combination of asymptotic and numerical techniques. The results confirm the existence of the additional modes of instability due to viscosity.

Duck, Peter W.↗
NASA NTRS1993

Comment on 'A note on the possible connection between the El Chichon eruption and ocean production in the northwest Arabian Sea during 1982' by A. E. Strong

Strong argues that the El Chichon aerosol cloud resulted in relaxed southwest monsoon circulation and the dramatically reduced seasonal phytoplankton bloom documented in the northwestern Arabian Sea during summer and fall of 1982. It is argued here that Strong's ideas suggest a clear demonstration of an atmosphere-ocean interaction with implications for the ocean's biological CO2 pump. Strong's paper highlights the fundamentally different effects of volcanic aerosols on satellite infrared and visible band observations of the ocean.

Brock, John C.↗
NASA NTRS1993

A note on decentralized integral controllability

A concept of decentralized integral controllability (DIC) defined on a given gain space Phi is clarified and related to the original definition given by Morari and Zafirou (1989). This leads to a simple proof of the existence of DIC on Phi from which existence conditions for DIC can be routinely deduced in the sense of Morari and Zafirou.

Nwokah, O. D. I.↗