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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 667 records · Page 37

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NASA NTRS1989

Probabilities for gravitational lensing by point masses in a locally inhomogeneous universe

Probability functions for gravitational lensing by point masses that incorporate Poisson statistics and flux conservation are formulated in the Dyer-Roeder construction. Optical depths to lensing for distant sources are calculated using both the method of Press and Gunn (1973) which counts lenses in an otherwise empty cone, and the method of Ehlers and Schneider (1986) which projects lensing cross sections onto the source sphere. These are then used as parameters of the probability density for lensing in the case of a critical (q0 = 1/2) Friedmann universe. A comparison of the probability functions indicates that the effects of angle-averaging can be well approximated by adjusting the average magnification along a random line of sight so as to conserve flux.

Isaacson, Jeffrey A.↗

NASA NTRS1989

Universal limiter for high order explicit conservative advection schemes

A simple method for construction of nonoscillatory, explicit, conservative advection schemes of arbitrarily high accuracy is described. Four test profiles are considered: an isolated sine-squared wave, a unit step function, a semiellipse, and a narrow Gaussian. A universal limiter guarantees monotonic resolution of the step. Sharpness increases uniformly with the order of the base scheme.

Leonard, B. P.↗

NASA NTRS1988

Hypersonic research at Stanford University

The status of the hypersonic research program at Stanford University is discussed and recent results are highlighted. The main areas of interest in the program are the numerical simulation of radiating, reacting and thermally excited flows, the investigation and numerical solution of hypersonic shock wave physics, the extension of the continuum fluid dynamic equations to the transition regime between continuum and free-molecule flow, and the development of novel numerical algorithms for efficient particulate simulations of flowfields.

Candler, Graham↗

NASA NTRS1989

Investigation of active regions at high resolution by balloon flights of the Solar Optical Universal Polarimeter (SOUP)

SOUP is a versatile, visible-light solar observatory, built for space or balloon flight. It is designed to study magnetic and velocity fields in the solar atmosphere with high spatial resolution and temporal uniformity, which cannot be achieved from the surface of the earth. The SOUP investigation is carried out by the Lockheed Palo Alto Research Laboratory, under contract to NASA's Marshall Space Flight Center. Co-investigators include staff members at a dozen observatories and universities in the U.S. and Europe. The primary objectives of the SOUP experiment are: to measure vector magnetic and velocity fields in the solar atmosphere with much better spatial resolution than can be achieved from the ground; to study the physical processes that store magnetic energy in active regions and the conditions that trigger its release; and to understand how magnetic flux emerges, evolves, combines, and disappears on spatial scales of 400 to 100,000 km. SOUP is designed to study intensity, magnetic, and velocity fields in the photosphere and low chromosphere with 0.5 arcsec resolution, free of atmospheric disturbances. The instrument includes: a 30 cm Cassegrain telescope; an active mirror for image stabilization; broadband film and TV cameras; a birefringent filter, tunable over 5100 to 6600 A with 0.05 A bandpass; a 35 mm film camera and a digital CCD camera behind the filter; and a high-speed digital image processor.

Tarbell, T.↗

NASA NTRS1987

Recent tests at Langley with a University of Tennessee Space Institute (UTSI) skin friction balance

The experience at LaRC with the University of Tennessee Space Institute skin friction balances is summarized. The Karman-Schoenherr flat plate skin friction formulation is included for comparison. It is concluded that the balance is capable of operation in environments as diverse as cryogenic, transonic, high-shear rate of the 0.3 meter Transonic Cryogenic Tunnel, and high-temperature supersonic environment of the Unitary Plan Wind Tunnel. Proposed new research is outlined.

Lawing, Pierce L.↗

NASA NTRS1988

Exploring the living universe: A strategy for space life sciences

The status and goals of NASA's life sciences programs are examined. Ways and mean for attaining these goals are suggested. The report emphasizes that a stronger life sciences program is imperative if the U.S. space policy is to construct a permanently manned space station and achieve its stated goal of expanding the human presence beyond earth orbit into the solar system. The same considerations apply in regard to the other major goal of life sciences: to study the biological processes and life in the universe. A principal recommendation of the report is for NASA to expand its program of ground- and space-based research contributing to resolving questions about physiological deconditioning, radiation exposure, potential psychological difficulties, and life support requirements that may limit stay times for personnel on the Space Station and complicate missions of more extended duration. Other key recommendations call for strengthening programs of biological systems research in: controlled ecological life support systems for humans in space, earth systems central to understanding the effects on the earth's environment of both natural and human activities, and exobiology.

Source record↗

NASA NTRS1989

Materials properties numerical database system established and operational at CINDAS/Purdue University

A computerized comprehensive numerical database system on the mechanical, thermophysical, electronic, electrical, magnetic, optical, and other properties of various types of technologically important materials such as metals, alloys, composites, dielectrics, polymers, and ceramics has been established and operational at the Center for Information and Numerical Data Analysis and Synthesis (CINDAS) of Purdue University. This is an on-line, interactive, menu-driven, user-friendly database system. Users can easily search, retrieve, and manipulate the data from the database system without learning special query language, special commands, standardized names of materials, properties, variables, etc. It enables both the direct mode of search/retrieval of data for specified materials, properties, independent variables, etc., and the inverted mode of search/retrieval of candidate materials that meet a set of specified requirements (which is the computer-aided materials selection). It enables also tabular and graphical displays and on-line data manipulations such as units conversion, variables transformation, statistical analysis, etc., of the retrieved data. The development, content, accessibility, etc., of the database system are presented and discussed.

Ho, C. Y.↗

NASA NTRS1990

Investigation of air transportation technology at Princeton University, 1988-1989

The Air Transportation Technology Program at Princeton University, a program emphasizing graduate and undergraduate student research, proceeded along several avenues during the past year. A study of optimal trajectories for penetration of microbursts when encounter is unavoidable was conducted. The emphasis of current wind shear research is on developing an expert system for wind shear avoidance. A knowledge-based reconfigurable flight control system that is implemented with the Pascal programming language using parallel microprocessors was developed. This expert system could be considered a prototype for a failure-tolerant control system that can be constructed using existing hardware. Development of a real-time cockpit simulator continued during the year. The simulator provides a single-person crew station with both conventional and advanced control devices; it currently is programmed to simulate the Navion single-engine general aviation airplane. Alternatives for the air traffic control system giving particular attention to the institutional structure of the FAA are analyzed. A simple numerical procedure for estimating the stochastic robustness of control systems is being investigated. The revitalization of the general aviation industry is also discussed.

Stengel, Robert F.↗

NASA NTRS1990

CSMA/RN: A universal protocol for gigabit networks

Networks must provide intelligent access for nodes to share the communications resources. In the range of 100 Mbps to 1 Gbps, the demand access class of protocols were studied extensively. Many use some form of slot or reservation system and many the concept of attempt and defer to determine the presence or absence of incoming information. The random access class of protocols like shared channel systems (Ethernet), also use the concept of attempt and defer in the form of carrier sensing to alleviate the damaging effects of collisions. In CSMA/CD, the sensing of interference is on a global basis. All systems discussed above have one aspect in common, they examine activity on the network either locally or globally and react in an attempt and whatever mechanism. Of the attempt + mechanisms discussed, one is obviously missing; that is attempt and truncate. Attempt and truncate was studied in a ring configuration called the Carrier Sensed Multiple Access Ring Network (CSMA/RN). The system features of CSMA/RN are described including a discussion of the node operations for inserting and removing messages and for handling integrated traffic. The performance and operational features based on analytical and simulation studies which indicate that CSMA/RN is a useful and adaptable protocol over a wide range of network conditions are discussed. Finally, the research and development activities necessary to demonstrate and realize the potential of CSMA/RN as a universal, gigabit network protocol is outlined.

Foudriat, E. C.↗

NASA NTRS1990

The International Space University

The International Space University (ISU) was founded on the premise that any major space program in the future would require international cooperation as a necessary first step toward its successful completion. ISU is devoted to being a leading center for educating future authorities in the world space industry. ISU's background, goals, current form, and future plans are described. The results and benefits of the type of education and experience gained from ISU include technical reports describing the design projects undertaken by the students, an exposure to the many different disciplines which are a part of a large space project, an awareness of the existing activities from around the world in the space community, and an international professional network which spans all aspects of space activities and covers the globe.

Davidian, Kenneth J.↗

NASA NTRS1989

The making of the mechanical universe

The Mechanical Universe project required the production of over 550 different animated scenes, totaling about 7 and 1/2 hours of screen time. The project required the use of a wide range of techniques and motivated the development of several different software packages. A documentation is presented of many aspects of the project, encompassing artistic design issues, scientific simulations, software engineering, and video engineering.

Blinn, James↗

NASA NTRS1989

Large-scale structure formation and cosmic microwave anisotropy in a cold plus hot dark matter universe

Several particle physics models suggest the simultaneous existence of both cold and hot forms of dark matter particles. Assuming a Harrison-Zel'dovich spectrum of primordial density fluctuations and Omega = 1, the formation of structure in a universe dominated by a combination of cold dark matter and massive neutrinos is explored. It is found that the presence of the hot dark matter component can cause enough power on large scales to explain some recent observations, while there is still sufficient power on small scales to allow galactic structure formation. Spatial anisotropies in the microwave background radiation are computed and found to be compatible with observational limits.

Schaefer, Robert K.↗

NASA NTRS1989

Phase transitions as the origin of large scale structure in the universe

A review of the formation of large scale structure through gravitational growth of primordial perturbations is given. This is followed by a discussion of how symmetry breaking phase transitions in the early universe might have produced the required perturbations, in particular through the formation and evolution of a network of cosmic strings.

Turok, Neil↗

NASA NTRS1988

Redshift surveys and the description of clustering in the universe

Results from recent redshift surveys at the Harvard-Smithsonian Center for Astrophysics are reviewed. Consideration is given to the spectroscopy of nearby galaxies, the distribution of nearby galaxies, clusters of galaxies, voids, filaments, bubbles, large scale flows, and the distribution of rich Abell clusters. Emphasis is given to the way in which redshift surveys can be used to study large scale structure and clustering in the universe.

Huchra, John P.↗

NASA NTRS1990

The International Space University

Davidian, Kenneth J.↗

NASA NTRS1989

A model for the distribution of dark matter, galaxies, and the intergalactic medium in a cold dark matter-dominated universe

The spatial distribution of the cold-dark-matter (CDM) and baryonic components of CDM-dominated cosmological models are characterized, summarizing the results of recent theoretical investigations. The evolution and distribution of matter in an Einstein-de Sitter universe on length scales small enough so that the Newtonian approximation is valid is followed chronologically, assuming (1) that the galaxies, CDM, and the intergalactic medium (IGM) are coupled by gravity, (2) that galaxies form by taking mass and momentum from the IGM, and (3) that the IGM responds to the energy input from the galaxies. The results of the numerical computations are presented in extensive graphs and discussed in detail.

Ryu, Dongsu↗

NASA NTRS1990

Self-similar perturbations of a Friedmann universe

The present analysis of spherically symmetric self-similar solutions to the Einstein equations gives attention to those solutions that are asymptotically k = 0 Friedmann at large z values, and possess finite but perturbed density at the origin. Such solutions represent nonlinear density fluctuations which grow at the same rate as the universe's particle horizon. The overdense solutions span only a narrow range of parameters, and resemble static isothermal gas spheres just within the sonic point; the underdense solutions may have arbitrarily low density at the origin while exhibiting a unique relationship between amplitude and scale. Their relevance to large-scale void formation is considered.

Carr, Bernard J.↗

NASA NTRS1990

Universal Lambert and Kepler algorithms for autonomous rendezvous

This paper describes Lambert and Kepler algorithms designed to be the core of an autonomous rendezvous guidance system for an onboard computer. Applications include robotic and piloted missions to the moon and planets. Flight software must be compact, fast, and totally reliable. Although high accuracy is not essential for flight, in double precision these algorithms are accurate to at least 14 places almost everywhere. Both are universal; they apply to elliptic, parabolic, hyperbolic, and even rectilinear trajectories. The algorithms are improvements to those published by Battin (1987).

Klumpp, Allan R.↗