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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Estimate of true incomplete exchanges using fluorescence in situ hybridization with telomere probes

PURPOSE: To study the frequency of true incomplete exchanges in radiation-induced chromosome aberrations. MATERIALS AND METHODS: Human lymphocytes were exposed to 2 Gy and 5 Gy of gamma-rays. Chromosome aberrations were studied using the fluorescence in situ hybridization (FISH) technique with whole chromosome-specific probes, together with human telomere probes. Chromosomes 2 and 4 were chosen in the present study. RESULTS: The percentage of incomplete exchanges was 27% when telomere signals were not considered. After excluding false incomplete exchanges identified by the telomere signals, the percentage of incomplete exchanges decreased to 11%. Since telomere signals appear on about 82% of the telomeres, the percentage of true incomplete exchanges should be even lower and was estimated to be 3%. This percentage was similar for chromosomes 2 and 4 and for doses of both 2 Gy and 5 Gy. CONCLUSIONS: The percentage of true incomplete exchanges is significantly lower in gamma-irradiated human lymphocytes than the frequencies reported in the literature.

NASA Discipline Radiation Health↗
NASA NTRS1999

Estimate of the frequency of true incomplete exchanges in human lymphocytes exposed to 1 GeV/u Fe ions in vitro

PURPOSE: To study the frequency of true incomplete exchanges induced by high-LET radiation. MATERIALS AND METHODS: Human lymphocytes were exposed to 1 GeV/u Fe ions (LET = 140 keV/microm). Chromosome aberrations were analysed by a fluorescence in situ hybridization using a combination of whole-chromosome-specific probes and human telomere probes. Chromosomes 1, 3 and 4 were investigated. RESULTS: The percentage of incomplete exchanges was between 23 and 29% if telomere signals were not considered. The percentage decreased to approximately 10% after ruling out false incomplete exchanges containing telomere signals. The final estimation of true incomplete exchanges was <10%. CONCLUSION: Within a degree of uncertainty, the percentage of true incomplete exchanges in 1 GeV/u Fe ion-irradiated human lymphocytes was similar to that induced by gamma rays.

NASA Center JSC↗
NASA NTRS1992

Numerical evaluation of the incomplete airy functions and their application to high frequency scattering and diffraction

The incomplete Airy integrals serve as canonical functions for the uniform ray optical solutions to several high frequency scattering and diffraction problems that involve a class of integrals characterized by two stationary points that are arbitrarily close to one another or to an integration endpoint. Integrals of such analytical properties describe transition region phenomena associated with composite shadow boundaries. An efficient and accurate method for computing the incomplete Airy functions would make the solutions to such problems useful for engineering purposes. Here, a convergent series solution form for the incomplete Airy functions is derived. Asymptotic expansions involving several terms were also developed and serve as large argument approximations. The combination of the series solution form with the asymptotic formulae provides for an efficient and accurate computation of the incomplete Airy functions. Validation of accuracy is accomplished using direct numerical integration data.

Constantinides, E. D.↗
NASA NTRS1993

Efficient and accurate computation of the incomplete Airy functions

The incomplete Airy integrals serve as canonical functions for the uniform ray optical solutions to several high-frequency scattering and diffraction problems that involve a class of integrals characterized by two stationary points that are arbitrarily close to one another or to an integration endpoint. Integrals with such analytical properties describe transition region phenomena associated with composite shadow boundaries. An efficient and accurate method for computing the incomplete Airy functions would make the solutions to such problems useful for engineering purposes. In this paper a convergent series solution for the incomplete Airy functions is derived. Asymptotic expansions involving several terms are also developed and serve as large argument approximations. The combination of the series solution with the asymptotic formulae provides for an efficient and accurate computation of the incomplete Airy functions. Validation of accuracy is accomplished using direct numerical integration data.

Constantinides, E. D.↗
NASA NTRS2003

Truly incomplete and complex exchanges in prematurely condensed chromosomes of human fibroblasts exposed in vitro to energetic heavy ions

Confluent human fibroblast cells (AG1522) were irradiated with gamma rays, 490 MeV/nucleon silicon ions, or iron ions at either 200 or 500 MeV/nucleon. The cells were allowed to repair at 37 degrees C for 24 h after exposure, and a chemically induced premature chromosome condensation (PCC) technique was used to condense chromosomes in the G2 phase of the cell cycle. Incomplete and complex exchanges were analyzed in the irradiated samples. To verify that chromosomal breaks were truly unrejoined, chromosome aberrations were analyzed using a combination of whole-chromosome specific probes and probes specific for the telomere region of the chromosome. Results showed that the frequency of unrejoined chromosome breaks was higher after irradiation with the heavy ions of high LET, and consequently the ratio of incomplete to complete exchanges increased steadily with LET up to 440 keV/microm, the highest LET included in the present study. For samples exposed to 200 MeV/nucleon iron ions, chromosome aberrations were analyzed using the multicolor FISH (mFISH) technique, which allows identification of both complex and truly incomplete exchanges. Results of the mFISH study showed that 0.7 and 3 Gy iron ions produced similar ratios of complex to simple exchanges and incomplete to complete exchanges; these ratios were higher than those obtained after exposure to 6 Gy gamma rays. After 0.7 Gy of iron ions, most complex aberrations were found to involve three or four chromosomes, which is a likely indication of the maximum number of chromosome domains traversed by a single iron-ion track.

NASA Discipline Radiation Health↗
NASA NTRS2003

Truly Incomplete and Complex Chromosomal Exchanges in Human Fibroblast Cells Exposed In Situ to Energetic Heavy Ions

Confluent human fibroblast cells (AG 1522) were irradiated with gamma rays, 490 MeV/nucleon Si, or with Fe ions at either 200 or 500 MeV/nucleon. The cells were allowed to repair at 37 C for 24 hours after exposure, and a chemically induced premature chromosome condensation (PCC) technique was used to condense chromosomes in the G2 phase of the cell cycle. Incomplete and complex exchanges were analyzed in the irradiated samples. In order to verify that chromosomal breaks were truly unrejoined, chromosome aberrations were analyzed using a combination of whole chromosome specific probes and probes specific for the telomere region of the chromosome. Results showed that the frequency of unrejoined chromosome breaks was higher after high-LET radiation, and consequently, the ratio of incomplete to complete exchanges increased steadily with LET up to 440 keV/micron, the highest LET value in the present study. For samples exposed to 200 MeV/nucleon Fe ions, chromosome aberrations were analyzed using the multicolor FISH (mFISH) technique that allow identification of both complex and truly incomplete exchanges. Results of the mFISH study showed that 0.7 and 3 Gy dose of the Fe ions produced similar ratios of complex to simple exchanges and incomplete to complete exchanges, values for which were higher than those obtained after a 6 Gy gamma exposure. After 0.7 Gy of Fe ions, most complex aberrations were found to involve three or four chromosomes, which is a likely indication of the maximum number of chromosome domains traversed by a single Fe ion track.

Wu, Honglu↗
NASA NTRS1978

Estimation from incomplete multinomial data

The vector of multinomial cell probabilities was estimated from incomplete data, incomplete in that it contains partially classified observations. Each such partially classified observation was observed to fall in one of two or more selected categories but was not classified further into a single category. The data were assumed to be incomplete at random. The estimation criterion was minimization of risk for quadratic loss. The estimators were the classical maximum likelihood estimate, the Bayesian posterior mode, and the posterior mean. An approximation was developed for the posterior mean. The Dirichlet, the conjugate prior for the multinomial distribution, was assumed for the prior distribution.

Credeur, K. R.↗
NASA NTRS1992

Incomplete fuzzy data processing systems using artificial neural network

In this paper, the implementation of a fuzzy data processing system using an artificial neural network (ANN) is discussed. The binary representation of fuzzy data is assumed, where the universe of discourse is decartelized into n equal intervals. The value of a membership function is represented by a binary number. It is proposed that incomplete fuzzy data processing be performed in two stages. The first stage performs the 'retrieval' of incomplete fuzzy data, and the second stage performs the desired operation on the retrieval data. The method of incomplete fuzzy data retrieval is proposed based on the linear approximation of missing values of the membership function. The ANN implementation of the proposed system is presented. The system was computationally verified and showed a relatively small total error.

Patyra, Marek J.↗
NASA NTRS1971

The analysis of incomplete data.

In this paper, we attempt to provide a simple taxonomy for incomplete-data problems and at the same time develop unified methods of analysis. The emphasis is on techniques which are natural extensions of the complete-data analysis and which will handle rather general classes of incomplete-data problems as opposed to custom-made techniques for special problems. The principle of estimation is either maximum likelihood or is at least based on maximum likelihood.

Hartley, H. O.↗
NASA NTRS1977

The incomplete inverse and its applications to the linear least squares problem

A modified matrix product is explained, and it is shown that this product defiles a group whose inverse is called the incomplete inverse. It was proven that the incomplete inverse of an augmented normal matrix includes all the quantities associated with the least squares solution. An answer is provided to the problem that occurs when the data residuals are too large and when insufficient data to justify augmenting the model are available.

Morduch, G. E.↗
NASA NTRS1978

Incomplete nested dissection for solving n by n grid problems

Nested dissection orderings are known to be very effective for solving sparse positive definite linear systems which arise from n by n grid problems. In this paper we consider incomplete nested dissection, an ordering which corresponds to the premature termination of nested dissection. Analyses of the arithmetic and storage requirements for incomplete nested dissection are given and the ordering is shown to be competitive with nested dissection with regard to arithmetic operations and superior to that ordering in storage requirements.

George, A.↗
NASA NTRS1980

Estimation of incomplete multinomial data

Program estimates cell probabilities for data observed to fall in one of two or more categories when exact category cannot be determined. Data are assumed to be randomly incomplete. Estimation minimizes risk of quadratic loss. Program should be useful in projects where multinomial data is analyzed, but where observations are sometimes incomplete. Program is in FORTRAN IV and Assembler for batch execution on CYBER 173.

Credeur, K. R.↗
NASA NTRS1988

On the efficient calculation of the incomplete Airy function with application to edge diffraction

When the geometrical theory of diffraction (GTD) and its extensions are used to calculate fields across transition regions or in focal areas, various special functions are necessary to create uniform representations. One such transition function is the incomplete Airy function, which is applicable when two reflection points are arbitrarily close to each other and the endpoint of the domain considered. An efficient calculation of the incomplete Airy function is presented and shown to equal known asymptotic expansions when its argument is away from the critical point. By using these expansions, uniform field expressions are found which are consistent with the GTD and maintain its computational efficiency.

Cwik, Tom↗
NASA NTRS1992

The effect of geometry and incomplete sampling on peculiar velocity in superclusters

Two simple geometries, including observational effects such as orientation and incomplete sampling have been examined to determine the relative contributions of geometry and peculiar velocity to the elongation in the redshift direction seen in studies of superclusters. It is found that a loop with a redshift cutoff produces an elongation in the redshift direction in the range of 250-1000 km/s. Since Bahcall (1987) found approximately 2000 km/s in peculiar velocity, it is concluded that up to 50 percent of the observed peculiar velocity could be due to incomplete sampling of a loop geometry.

Henriksen, Mark J.↗
NASA NTRS1993

Survey incompleteness and the evolution of the QSO luminosity function

We concentrate on a type of QSO survey which depends on selecting QSO candidates based on combinations of colors. Since QSO's have emission lines and power-law continua, they are expected to yield broadband colors unlike those of stellar photospheres. Previously, the fraction of QSO's expected to be hiding (unselected) within the locus of stellar (U-J, J-F) colors was estimated at about 15 percent. We have now verified that the KK88 survey is at least 11 percent incomplete, but have determined that it may be as much as 34 percent incomplete. The 'missing' QSO's are expected to be predominantly at z less than or = 2.2. We have studied the proper motion and variability properties of all stellar objects with J less than or = 22.5 or F less than or = 21.5 in the SA 57 field which has previously been surveyed with a multicolor QSO search by KK88.

Majewski, Steven R.↗
NASA NTRS1940

Investigations on the Incompletely Developed Plane Diagonal-Tension Field

This report presents the results of an investigation on the incompletely developed diagonal-tension field. Actual diagonal-tension beams work in an intermediate stage between pure shear and pure diagonal tension; the theory developed by wagner for diagonal tension is not directly applicable. The first part of the paper reviews the most essential items of the theory of pure diagonal tension as well as previous attempts to formulate a theory of incomplete diagonal tension. The second part of the paper describes strain measurement made by the N. A. C. A. to obtain the necessary coefficients for the proposed theory. The third part of the paper discusses the stress analysis of diagonal-tension beams by means of the proposed theory.

Kuhn, Paul↗
NASA NTRS1940

Stresses in single-spar wing constructions with incompletely built-up ribs

It is shown that the force distribution resulting from incomplete ribs in single spar wing structures may be determined with the aid of the shear field method by a statistically indeterminate computation. A numerical computation is given of the force distribution of a wing structure whose two neighboring incomplete ribs with web missing in half the section are torsionally loaded.

Reinitzhuber, F↗
NASA NTRS1997

Graph Embedding Techniques for Bounding Condition Numbers of Incomplete Factor Preconditioning

We extend graph embedding techniques for bounding the spectral condition number of preconditioned systems involving symmetric, irreducibly diagonally dominant M-matrices to systems where the preconditioner is not diagonally dominant. In particular, this allows us to bound the spectral condition number when the preconditioner is based on an incomplete factorization. We provide a review of previous techniques, describe our extension, and give examples both of a bound for a model problem, and of ways in which our techniques give intuitive way of looking at incomplete factor preconditioners.

Guattery, Stephen↗