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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 NTRS2000

Software Fault Tolerance: A Tutorial

Because of our present inability to produce error-free software, software fault tolerance is and will continue to be an important consideration in software systems. The root cause of software design errors is the complexity of the systems. Compounding the problems in building correct software is the difficulty in assessing the correctness of software for highly complex systems. After a brief overview of the software development processes, we note how hard-to-detect design faults are likely to be introduced during development and how software faults tend to be state-dependent and activated by particular input sequences. Although component reliability is an important quality measure for system level analysis, software reliability is hard to characterize and the use of post-verification reliability estimates remains a controversial issue. For some applications software safety is more important than reliability, and fault tolerance techniques used in those applications are aimed at preventing catastrophes. Single version software fault tolerance techniques discussed include system structuring and closure, atomic actions, inline fault detection, exception handling, and others. Multiversion techniques are based on the assumption that software built differently should fail differently and thus, if one of the redundant versions fails, it is expected that at least one of the other versions will provide an acceptable output. Recovery blocks, N-version programming, and other multiversion techniques are reviewed.

Torres-Pomales, Wilfredo↗
NASA NTRS2001

A Planet Detection Tutorial and Simulator

Detection of extra-solar planets has been a very popular topic with the general public for years. Considerable media coverage of recent detections (currently at about 50) has only heightened the interest in the topic. School children are particularly interested in learning about recent astronomical discoveries. Scientists have the knowledge and responsibility to present this information in both an understandable and interesting format. Most classrooms and homes are now connected to the internet, which can be utilized to provide more than a traditional 'flat' presentation. An interactive software package on planet detection has been developed. The major topics include: "1996 - The Break Through Year In Planet Detection"; "What Determines If A Planet Is Habitable?"; "How Can We Find Other Planets (Search Methods)"; "All About the Kepler Mission: How To Find Terrestrial Planets"; and "A Planet Detection Simulator". Using the simulator, the student records simulated observations and then analyzes and interprets the data within the program. One can determine the orbit and planet size, the planet's temperature and surface gravity, and finally determine if the planet is habitable. Originally developed for the Macintosh, a web based browser version is being developed.

Knoch, David↗
NASA NTRS2004

Renormalization Group Tutorial

Complex physical systems sometimes have statistical behavior characterized by power- law dependence on the parameters of the system and spatial variability with no particular characteristic scale as the parameters approach critical values. The renormalization group (RG) approach was developed in the fields of statistical mechanics and quantum field theory to derive quantitative predictions of such behavior in cases where conventional methods of analysis fail. Techniques based on these ideas have since been extended to treat problems in many different fields, and in particular, the behavior of turbulent fluids. This lecture will describe a relatively simple but nontrivial example of the RG approach applied to the diffusion of photons out of a stellar medium when the photons have wavelengths near that of an emission line of atoms in the medium.

Bell, Thomas L.↗
NASA NTRS2004

Tutorial on Solar Energetic-Particle Events

Particles from the Sun at energies above approx. 1 MeV/nucleon have been studied in space for over 35 years. There have been major advances in instrumentation for studying elemental and isotopic composition, kinetic energy, charge states, time intensity histories, and anisotropies of energetic particles. There have also been extensive improvements in the observations of solar phenomena, including radio bursts, Coronal Mass Ejections (CMEs), and solar photons from soft X-ray to gamma-ray energies. Despite these advances, there is a lack of agreement as to the acceleration processes responsible for the particles seen in space shortly after the solar event. In particular, the relative importance of solar flares and CME-driven shocks is disputed for events of moderate to larger size. The reasons for this will be reviewed, and the prospects for resolving this issue will be evaluated.

vonRosenvinge, Tycho T.↗
NASA NTRS2003

Information Power Grid (IPG) Tutorial 2003

For NASA and the general community today Grid middleware: a) provides tools to access/use data sources (databases, instruments, ...); b) provides tools to access computing (unique and generic); c) Is an enabler of large scale collaboration. Dynamically responding to needs is a key selling point of a grid. Independent resources can be joined as appropriate to solve a problem. Provide tools to enable the building of a frameworks for application. Provide value added service to the NASA user base for utilizing resources on the grid in new and more efficient ways. Provides tools for development of Frameworks.

Meyers, George↗
NASA NTRS2003

Rad hard technology tutorial

Explore the source record for details and available documents.

radiation-hard radiation-tolerant microelectronics↗
NASA NTRS1994

Tutorial on Solid State Recording Technology

The selection of the appropriate technology for various applications is dependent on many considerations which relate to performance and cost.

electronic technologies magnetic technologies opti↗
NASA NTRS1993

(presentation) Precision Mechanisms for Space Interferometers: A Tutorial

To maximize salability, spaceborne interferometer designs must minimize actuator cost while maximizing science quality and quantity. Interferometer designers must have the knowledge to design a system with the simplist, most reliable, and least expensive actuators possible.

actuators interferometry cost design↗