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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Fluid inclusions in stony meteorites - A cautionary note

Newly discovered fluid inclusions in thin sections of Bjurbole chondrules, shergottite EETA79001, lunar meteorite ALHA81005, and Apollo 16 glasses possess physical properties similar to those of fluid inclusions found in thin sections of five stony meteorites recently described by Warner et al. (1983). The distribution and physical properties of these new fluid inclusions indicate they may be artifacts of thin section preparation; it is suggested that saw coolant was sucked into vacuum vesicles in glasses and minerals through submicroscopic fractures produced during sawing. The similarities between these fluid inclusions and fluid inclusions previously described by Warner et al. (1983) indicate that many of the fluid inclusions reported earlier may be artifacts. Consequently, the origin of any fluid inclusions observed in thin sections of extraterrestrial materials must be interpreted with caution. The most probable true extraterrestrial fluid inclusions are those that have been observed in grains prepared without exposure to liquids of any kind.

Rudnick, R. L.↗
NASA NTRS1986

Comment on the paper 'On the influx of small comets into the earth's upper atmosphere. I - Observations'

The observations of transient decreases or holes in the EUV dayglow reported by Frank et al. (1986) and attributed to an influx of small comets into the earth atmosphere are discussed critically. The techniques used in acquiring and analyzing the observational data are examined, and it is argued that the decreases are probably instrument artifacts. A critique of the geophysical basis of the comet hypothesis is also included. In a reply by Frank et al., the instrument-artifact argument is rejected, in part on the basis of the statistical properties of the holes observed. Additional observational data are presented in graphs and dynamics Explorer 1 images are analyzed in detail.

Chubb, T. A.↗
NASA NTRS1988

Limitations on K-T mass extinction theories based upon the vertebrate record

Theories of extinction are only as good as the patterns of extinction that they purport to explain. Often such patterns are ignored. For the terminal Cretaceous events, different groups of organisms in different environments show different patterns of extinction that to date cannot be explained by a single causal mechanism. Several patterns of extinction (and/or preservational bias) can be observed for the various groups of vertebrates from the uppermost Cretaceous Hell Creek Formation and lower Paleocene Tullock Formation in eastern Montana. The taxonomic level at which the percentage of survivals (or extinctions) is calculated will have an effect upon the perception of faunal turnover. In addition to the better known mammals and better publicized dinosaurs, there are almost 60 additional species of reptiles, birds, amphibians, and fish in the HELL Creek Formation. Simple arithmetic suggests only 33 percent survival of these vertebrates from the Hell Creek Fm. into the Tullock Fm. A more critical examination of the data shows that almost all Hell Creek species not found in the Tullock are represented in one of the following categories; extremely rare forms, elasmobranch fish that underwent rapid speciation taxa that although not known or rare in the Tullock, are found elsewhere. Each of the categories is largely the result of the following biases: taphonomy, ecological differences, taxonomic artifact paleogeography. The two most important factors appear to be the possible taphonomic biases and the taxonomic artifacts. The extinction patterns among the vertebrates do not appear to be attributable to any single cause, catastrophic or otherwise.

Archibald, J. David↗
NASA NTRS1988

AVIRIS data characteristics and their effects on spectral discrimination of rocks exposed in the Drum Mountains, Utah: Results of a preliminary study

Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) data collected over a geologically diverse field site and over a nearby calibration site were analyzed and interpreted in efforts to document radiometric and geometric characteristics of AVIRIS, quantify and correct for detrimental sensor phenomena, and evaluate the utility of AVIRIS data for discriminating rock types and identifying their constituent mineralogy. AVIRIS data acquired for these studies exhibit a variety of detrimental artifacts and have lower signal-to-noise ratios than expected in the longer wavelength bands. Artifacts are both inherent in the image data and introduced during ground processing, but most may be corrected by appropriate processing techniques. Poor signal-to-noise characteristics of this AVIRIS data set limited the usefulness of the data for lithologic discrimination and mineral identification. Various data calibration techniques, based on field-acquired spectral measurements, were applied to the AVIRIS data. Major absorption features of hydroxyl-bearing minerals were resolved in the spectra of the calibrated AVIRIS data, and the presence of hydroxyl-bearing minerals at the corresponding ground locations was confirmed by field data.

Bailey, G. B.↗
NASA NTRS1989

The reduction of wide field/planetary camera images

An overview of the procedures required for reduction of Hubble Space Telescope Wide Field/Planetary Camera images is presented, based on WFPC performance as observed during ground tests. Camera artifacts that must be removed prior to analysis of WFPC images are characterized. WFPC flat-field and dark-current images are also presented. Special emphasis is given to the design of WFPC imaging programs that minimize the effects of camera artifacts on image analysis.

Lauer, Tod R.↗
NASA NTRS1990

Calibration For On-Machine Inspections

Permanent calibration setup on numerically-controlled machine tool enables fast and reliable calibration of automated probes for inspection of workpieces while still mounted on machine. Setup includes one or more artifacts, dimensions and locations known precisely and stored in memory of computer controlling machine. Before probes used to inspect newly machined part, used to check artifacts. Probe measurements compared with values in memory to determine whether probe readings need adjustment.

Haymaker, Carlton L., Jr.↗
NASA NTRS1990

Knowledge representation to support reasoning based on multiple models

Model Based Reasoning is a powerful tool used to design and analyze systems, which are often composed of numerous interactive, interrelated subsystems. Models of the subsystems are written independently and may be used together while they are still under development. Thus the models are not static. They evolve as information becomes obsolete, as improved artifact descriptions are developed, and as system capabilities change. Researchers are using three methods to support knowledge/data base growth, to track the model evolution, and to handle knowledge from diverse domains. First, the representation methodology is based on having pools, or types, of knowledge from which each model is constructed. In addition information is explicit. This includes the interactions between components, the description of the artifact structure, and the constraints and limitations of the models. The third principle we have followed is the separation of the data and knowledge from the inferencing and equation solving mechanisms. This methodology is used in two distinct knowledge-based systems: one for the design of space systems and another for the synthesis of VLSI circuits. It has facilitated the growth and evolution of our models, made accountability of results explicit, and provided credibility for the user community. These capabilities have been implemented and are being used in actual design projects.

Gillam, April↗
NASA NTRS1990

GSC configuration management plan

The tools and methods used for the configuration management of the artifacts (including software and documentation) associated with the Guidance and Control Software (GCS) project are described. The GCS project is part of a software error studies research program. Three implementations of GCS are being produced in order to study the fundamental characteristics of the software failure process. The Code Management System (CMS) is used to track and retrieve versions of the documentation and software. Application of the CMS for this project is described and the numbering scheme is delineated for the versions of the project artifacts.

Withers, B. Edward↗
NASA NTRS1990

Enroute flight planning: The design of cooperative planning systems

Design concepts and principles to guide in the building of cooperative problem solving systems are being developed and evaluated. In particular, the design of cooperative systems for enroute flight planning is being studied. The investigation involves a three stage process, modeling human performance in existing environments, building cognitive artifacts, and studying the performance of people working in collaboration with these artifacts. The most significant design concepts and principles identified thus far are the principle focus.

Smith, Philip J.↗
NASA NTRS1991

Evaluating some computer enhancement algorithms that improve the visibility of cometary morphology

The observed morphology of cometary comae is determined by ejection circumstances and the interaction of the ejected material with the local environment. Anisotropic emission can provide useful information on such things as orientation of the nucleus, location of active areas on the nucleus, and the formation of ion structure near the nucleus. However, discrete coma features are usually diffuse, of low amplitude, and superimposed on a steep intensity gradient radial to the nucleus. To improve the visibility of these features, a variety of digital enhancement algorithms were employed with varying degrees of success. They usually produce some degree of spatial filtering, and are chosen to optimize visibility of certain detail. Since information in the image is altered, it is important to understand the effects of parameter selection and processing artifacts can have on subsequent interpretation. Using the criteria that the ideal algorithm must enhance low contrast features while not introducing misleading artifacts (or features that cannot be seen in the stretched, unprocessed image), the suitability of various algorithms that aid cometary studies were assessed. The strong and weak points of each are identified in the context of maintaining positional integrity of features at the expense of photometric information.

Larson, S. M.↗
NASA NTRS1990

Digital halftoning methods for selectively partitioning error into achromatic and chromatic channels

A method is described for reducing the visibility of artifacts arising in the display of quantized color images on CRT displays. The method is based on the differential spatial sensitivity of the human visual system to chromatic and achromatic modulations. Because the visual system has the highest spatial and temporal acuity for the luminance component of an image, a technique which will reduce luminance artifacts at the expense of introducing high-frequency chromatic errors is sought. A method based on controlling the correlations between the quantization errors in the individual phosphor images is explored. The luminance component is greatest when the phosphor errors are positively correlated, and is minimized when the phosphor errors are negatively correlated. The greatest effect of the correlation is obtained when the intensity quantization step sizes of the individual phosphors have equal luminances. For the ordered dither algorithm, a version of the method can be implemented by simply inverting the matrix of thresholds for one of the color components.

Mulligan, Jeffrey B.↗
NASA NTRS1992

Software design by reusing architectures

Abstraction fosters reuse by providing a class of artifacts that can be instantiated or customized to produce a set of artifacts meeting different specific requirements. It is proposed that significant leverage can be obtained by abstracting software system designs and the design process. The result of such an abstraction is a generic architecture and a set of knowledge-based, customization tools that can be used to instantiate the generic architecture. An approach for designing software systems based on the above idea are described. The approach is illustrated through an implemented example, and the advantages and limitations of the approach are discussed.

Bhansali, Sanjay↗
NASA NTRS1994

Engineering design knowledge recycling in near-real-time

It is hypothesized that the capture and reuse of machine readable design records is cost beneficial. This informal engineering notebook design knowledge can be used to model the artifact and the design process. Design rationale is, in part, preserved and available for examination. Redesign cycle time is significantly reduced (Baya et al, 1992). These factors contribute to making it less costly to capture and reuse knowledge than to recreate comparable knowledge (current practice). To test the hypothesis, we have focused on validation of the concept and tools in two 'real design' projects this past year: (1) a short (8 month) turnaround project for NASA life science bioreactor researchers was done by a team of three mechanical engineering graduate students at Stanford University (in a class, ME210abc 'Mechatronic Systems Design and Methodology' taught by one of the authors, Leifer); and (2) a long range (8 to 20 year) international consortium project for NASA's Space Science program (STEP: satellite test of the equivalence principle). Design knowledge capture was supported this year by assigning the use of a Team-Design PowerBook. Design records were cataloged in near-real time. These records were used to qualitatively model the artifact design as it evolved. Dedal, an 'intelligent librarian' developed at NASA-ARC, was used to navigate and retrieve captured knowledge for reuse.

Leifer, Larry↗
NASA NTRS1994

An efficient system for reliably transmitting image and video data over low bit rate noisy channels

This research project is intended to develop an efficient system for reliably transmitting image and video data over low bit rate noisy channels. The basic ideas behind the proposed approach are the following: employ statistical-based image modeling to facilitate pre- and post-processing and error detection, use spare redundancy that the source compression did not remove to add robustness, and implement coded modulation to improve bandwidth efficiency and noise rejection. Over the last six months, progress has been made on various aspects of the project. Through our studies of the integrated system, a list-based iterative Trellis decoder has been developed. The decoder accepts feedback from a post-processor which can detect channel errors in the reconstructed image. The error detection is based on the Huber Markov random field image model for the compressed image. The compression scheme used here is that of JPEG (Joint Photographic Experts Group). Experiments were performed and the results are quite encouraging. The principal ideas here are extendable to other compression techniques. In addition, research was also performed on unequal error protection channel coding, subband vector quantization as a means of source coding, and post processing for reducing coding artifacts. Our studies on unequal error protection (UEP) coding for image transmission focused on examining the properties of the UEP capabilities of convolutional codes. The investigation of subband vector quantization employed a wavelet transform with special emphasis on exploiting interband redundancy. The outcome of this investigation included the development of three algorithms for subband vector quantization. The reduction of transform coding artifacts was studied with the aid of a non-Gaussian Markov random field model. This results in improved image decompression. These studies are summarized and the technical papers included in the appendices.

Costello, Daniel J., Jr.↗
NASA NTRS1995

Property-Based Software Engineering Measurement

Little theory exists in the field of software system measurement. Concepts such as complexity, coupling, cohesion or even size are very often subject to interpretation and appear to have inconsistent definitions in the literature. As a consequence, there is little guidance provided to the analyst attempting to define proper measures for specific problems. Many controversies in the literature are simply misunderstandings and stem from the fact that some people talk about different measurement concepts under the same label (complexity is the most common case). There is a need to define unambiguously the most important measurement concepts used in the measurement of software products. One way of doing so is to define precisely what mathematical properties characterize these concepts regardless of the specific software artifacts to which these concepts are applied. Such a mathematical framework could generate a consensus in the software engineering community and provide a means for better communication among researchers, better guidelines for analysis, and better evaluation methods for commercial static analyzers for practitioners. In this paper, we propose a mathematical framework which is generic, because it is not specific to any particular software artifact, and rigorous, because it is based on precise mathematical concepts. This framework defines several important measurement concepts (size, length, complexity, cohesion, coupling). It is not intended to be complete or fully objective; other frameworks could have been proposed and different choices could have been made. However, we believe that the formalism and properties we introduce are convenient and intuitive. In addition, we have reviewed the literature on this subject and compared it with our work. This framework contributes constructively to a firmer theoretical ground of software measurement.

Briand, Lionel↗
NASA NTRS1997

Property-Based Software Engineering Measurement

Little theory exists in the field of software system measurement. Concepts such as complexity, coupling, cohesion or even size are very often subject to interpretation and appear to have inconsistent definitions in the literature. As a consequence, there is little guidance provided to the analyst attempting to define proper measures for specific problems. Many controversies in the literature are simply misunderstandings and stem from the fact that some people talk about different measurement concepts under the same label (complexity is the most common case). There is a need to define unambiguously the most important measurement concepts used in the measurement of software products. One way of doing so is to define precisely what mathematical properties characterize these concepts, regardless of the specific software artifacts to which these concepts are applied. Such a mathematical framework could generate a consensus in the software engineering community and provide a means for better communication among researchers, better guidelines for analysts, and better evaluation methods for commercial static analyzers for practitioners. In this paper, we propose a mathematical framework which is generic, because it is not specific to any particular software artifact and rigorous, because it is based on precise mathematical concepts. We use this framework to propose definitions of several important measurement concepts (size, length, complexity, cohesion, coupling). It does not intend to be complete or fully objective; other frameworks could have been proposed and different choices could have been made. However, we believe that the formalisms and properties we introduce are convenient and intuitive. This framework contributes constructively to a firmer theoretical ground of software measurement.

Briand, Lionel C.↗
NASA NTRS1999

Analyses of Transistor Punchthrough Failures

The failure of two transistors in the Altitude Switch Assembly for the Solid Rocket Booster followed by two additional failures a year later presented a challenge to failure analysts. These devices had successfully worked for many years on numerous missions. There was no history of failures with this type of device. Extensive checks of the test procedures gave no indication for a source of the cause. The devices were manufactured more than twenty years ago and failure information on this lot date code was not readily available. External visual exam, radiography, PEID, and leak testing were performed with nominal results Electrical testing indicated nearly identical base-emitter and base-collector characteristics (both forward and reverse) with a low resistance short emitter to collector. These characteristics are indicative of a classic failure mechanism called punchthrough. In failure analysis punchthrough refers to an condition where a relatively low voltage pulse causes the device to conduct very hard producing localized areas of thermal runaway or "hot spots". At one or more of these hot spots, the excessive currents melt the silicon. Heavily doped emitter material diffuses through the base region to the collector forming a diffusion pipe shorting the emitter to base to collector. Upon cooling, an alloy junction forms between the pipe and the base region. Generally, the hot spot (punch-through site) is under the bond and no surface artifact is visible. The devices were delidded and the internal structures were examined microscopically. The gold emitter lead was melted on one device, but others had anomalies in the metallization around the in-tact emitter bonds. The SEM examination confirmed some anomalies to be cosmetic defects while other anomalies were artifacts of the punchthrough site. Subsequent to these analyses, the contractor determined that some irregular testing procedures occurred at the time of the failures heretofore unreported. These testing irregularities involved the use of a breakout box and were the likely cause of the failures. There was no evidence to suggest a generic failure mechanism was responsible for the failure of these transistors.

Nicolas, David P.↗
NASA NTRS1997

An Approach to Building a Traceability Tool for Software Development

It is difficult in a large, complex computer program to ensure that it meets the specified requirements. As the program evolves over time, a11 program constraints originally elicited during the requirements phase must be maintained. In addition, during the life cycle of the program, requirements typically change and the program must consistently reflect those changes. Imagine the following scenario. Company X wants to develop a system to automate its assembly line. With such a large system, there are many different stakeholders, e.g., managers, experts such as industrial and mechanical engineers, and end-users. Requirements would be elicited from all of the stake holders involved in the system with each stakeholder contributing their point of view to the requirements. For example, some of the requirements provided by an industrial engineer may concern the movement of parts through the assembly line. A point of view provided by the electrical engineer may be reflected in constraints concerning maximum power usage. End-users may be concerned with comfort and safety issues, whereas managers are concerned with the efficiency of the operation. With so many points of view affecting the requirements, it is difficult to manage them, communicate information to relevant stakeholders. and it is likely that conflicts in the requirements will arise. In the coding process, the implementors will make additional assumptions and interpretations on the design and the requirements of the system. During any stage of development, stakeholders may request that a requirement be added or changed. In such a dynamic environment, it is difficult to guarantee that the system will preserve the current set of requirements. Tracing, the mapping between objects in the artifacts of the system being developed, addresses this issue. Artifacts encompass documents such as the system definition, interview transcripts, memoranda, the software requirements specification, user's manuals, the functional specifications, design reports, and system code. Tracing helps 1) validate system features against, the requirement specification, 2) identify error sources and, most importantly, 3) manage change. With so many people involved in the development of the system, it becomes necessary to identify the reasons behind the design requirements or the implementation decisions. This paper is concerned with an approach that maps documents to constraints that capture properties of and relationships between the objects being modeled by the program. Section 2 provides the reader with a background on traceability tools. Section 3 gives a brief description of the context monitoring system on which the approach suggested in this paper is based. Section 4 presents an overview of our approach to providing traceability. The last section presents our future direction of research.

Delgado, Nelly↗