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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 NTRS1978

Is gravity a morphological determinant in plants at the cellular level

The present paper deals with the question whether plant development can proceed normally in the weightless state, particularly in the critical stage where single cells produce multicellular units, leading to embryos with the growing regions of shoot and root which, in turn, give rise to all the tissues of the plant body. An experiment that tested whether carrot embryos capable of developing from cultured somatic cells could do so under conditions of weightlessness is described.

Krikorian, A. D.↗
NASA NTRS1979

Impact of cell size on inventory and mapping errors in a cellular geographic information system

The author has identified the following significant results. The effect of grid position was found insignificant for maps but highly significant for isolated mapping units. A modelable relationship between mapping error and cell size was observed for the map segment analyzed. Map data structure was also analyzed with an interboundary distance distribution approach. Map data structure and the impact of cell size on that structure were observed. The existence of a model allowing prediction of mapping error based on map structure was hypothesized and two generations of models were tested under simplifying assumptions.

Wehde, M. E.↗
NASA NTRS1981

Evaluation of the effects of a freeze/thaw environment on cellular glass

Using the evaluation criteria of water vapor permeability and conformability, a protective butylrubber/silicone conformal coating system was selected for use on Foamglas substrates in a freeze/thaw environment. The selection of a specific freeze/thaw cycle which closely models field conditions is discussed. A sampling plan is described which allows independent evaluation of the effects of conformal coatings, cycle number and location within the environmental chamber. The results of visual examination, measurement of density, modulus of rupture and Young's modulus are reported. Based upon statistical evaluation of the experimental results, it is concluded that no degradation in mechanical properties of either coated or uncoated Foamglas occurred within the duration of the test (53 freeze/thaw cycles).

Frickland, P.↗
NASA NTRS1980

The assembly and properties of protobiological structures - The beginnings of cellular peptide synthesis

New data indicate that lysine-rich proteinoids have the ability to catalyze the synthesis of peptide bonds from a variety of amino acids and ATP. This capacity is evident in aqueous solution, in suspension of phase-separated complexes of lysine-rich proteinoid with acidic proteinoids, and in suspension of phase-separated particles composed of lysine-rich proteinoids with polynucleotides. Since the proteinoid complexes can contain other catalytic activities, including ability to catalyze internucleotide bond formation, it is inferred that the first protocells on earth already had a number of biological types of activity.

Fox, S. W.↗
NASA NTRS1981

Phylogenetic sequence of metabolic pathways in Precambrian cellular life

A sequence of major metabolic events is presented as they may have appeared during prokaryote evolution. This is based on (1) the phylogenetic schema derived from sequences of bacterial ferredoxin, 2Fe-2S ferredoxin, 5S ribosomal RNA, and c-type cytochromes; (2) metabolic settings in which these macromolecules are found; and (3) metabolic capabilities of the prokaryotes that carry these molecules.

Barnabas, J.↗
NASA NTRS1983

Freeze/Thaw Properties of Cellular Glass

Without moisture, temperature cycles do no harm. Experiments described in new report indicate inherent material variability greater deterrent to application of material than freeze/thaw effects.

Frickland, P. O.↗
NASA NTRS1983

Fabrication of Structural Cellular Glass

Surface layer quickly heated and compressed. Postcellulation skin densification uses gas burners to head lower surface of material and pinch rollers to compress heated-surface layer. Useful for manufacturing large low cost, parabolic dish solar collectors.

Mitchell, W. D.↗
NASA NTRS1983

Calcium movements and the cellular basis of gravitropism

Evidence that calcium is a significant factor in gravitropism of plants is examined, together with the regulatory mechanism that controls calcium efflux in plant cells. Calcium has been found to accumulate on the upper surface of a plant placed in a horizontal attitude, which is followed by growth to the vertical within a half-hour. It has also been determined that the upper surface of the plant simultaneously experiences a reduced growth rate, compared to the lower surface. The substance calmodulin has been identified as the calcium-binding regulatory protein most influential in the transduction process leading to gravitropism, while chlorpromazine can inhibit its effects. The calcium is transported by ATPase located in the cell membrane. A possibility that the calcium pump is regulated by a feedback mechanism involving the presence of calmodulin is discussed.

Roux, S. J.↗
NASA NTRS1983

Human cellular immune responsiveness following space flight

Peripheral circulating lymphocytes were separated from astronaut blood samples three times before and two times after the first four US Space Shuttle flights. The ability of the in vitro T lymphocytes to respond to Phytohemagglutinin by blastogenesis was found to be reduced for each crewmember following spaceflight. In addition, the astronauts experienced a postflight increase in neutrophils and a decrease in eosinophils. These postflight changes in leukocytes are shown to increase with subjectively-evaluated increases in the incidence of inflight stress, indicating that stress, and not hypogravity, is likely to be the major effector of these changes.

Taylor, G. R.↗
NASA NTRS1984

Penetrative cellular convection in a stratified atmosphere

In the present investigation of penetrative convection within a simple compressible model, the middle one of the three layers of differing stratification prior to the onset of convection is a convectively unstable polytrope bounded above and below by two stably stratified polytropes. One- and two-mode steady solutions with hexagonal planforms have been studied for Rayleigh numbers up to aobut 1000 times critical, and for a range of Prandtl numbers, horizontal wavenumbers, and stratifications. These indicate that the penetration into the lower stable layer by downward plumes is substantially larger in a stratified medium than in a Boussinesq fluid, and produces an extended region of adiabatic stratification. The strong asymmetry between upward and downward penetration in compressible media has major implications for the mixing of stable regions above and below stellar convection zones.

Massaguer, J. M.↗
NASA NTRS1987

Cellular monotectic model solidification

Succinonitrile (sn) was purified to a superior level using a fractional recrystallization method. The melting point of the best twice recrystallized sn was not raised by following with double distillation. This was tested using differential scanning calorimetry. The peak shape on melting also proved that double distillation after double recrystallization did not improve the quality. Stability and phase diagrams for succinonitrile and glycerol are presented.

Kaukler, William F.↗
NASA NTRS1987

Morphometrics of cellular damage in mice testis receiving X-ray and high-energy particle irradiation

Murine tests were exposed to single, low doses of either X-ray, helium, or argon radiation. Animals were sacrificed seventy-two hours later. Testes were fixed for transmission electron microscopy (TEM) and sectioned at either 60 nm for TEM observation or at 2 micron for counting using routine light microscope methods. Counts of the total population of surviving spermatogonia, including all type A cells, intermediate, and type B cells, were taken from tubule cross sections identified as Stage 6 and Stage 1 according to spermatogonial configuration. The surviving fraction of spermatogonia as compared to control, S/S sub o, was calculated for each dose. For both ions and X-rays, there was a rapid decline in survival at dose levels of .10 to .15 Gy in Stage 6 tubules. This was followed by a more gradual decrease in population. At higher doses, 0.30 Gy for argon and 0.80 Gy for helium and X-rays, the cell survival rates declined rapidly. Pre-leptotene spermatocytes in Stage 1 tubules exhibited a different survival curve indicating the extreme radio-sensitivity of type B spermatogonia. Data verify that the seminiferous tubules are composed of a heterogeneous population of cells with different radio-sensitivities and that these differences are manifested even at very low doses.

Sapp, Walter J.↗
NASA NTRS1987

Cellular automaton supercomputing

Many of the models now used in science and engineering are over a century old. And most of them can be implemented on modern digital computers only with considerable difficulty. Some new basic models are discussed which are much more directly suitable for digital computer simulation. The fundamental principle is that the models considered herein are as suitable as possible for implementation on digital computers. It is then a matter of scientific analysis to determine whether such models can reproduce the behavior seen in physical and other systems. Such analysis was carried out in several cases, and the results are very encouraging.

Wolfram, Stephen↗
NASA NTRS1986

Interactions of the interferon system with cellular metabolism

The results of studies concerning the interaction of the interferon (Inf) system with the activities of carcinogens, tumor promoters, and cytochrome P-450 are presented. The results show that the addition of a tumor promoter (TPA or 4-O-methyl-TPA) to a tissue culture enhances virus-induced Inf-gamma production, suggesting a potential value of tumor promoters in the biosynthesis of commercial Inf. On the other hand, the carcinogens were reported to inhibit the induction of Inf-alpha/beta in cultured cells and in intact animals (with no effect on the administered or preformed Inf). The demonstration of a correlation between the carcinogenic potential of a compound and its inhibitive effect on Inf production suggests a possible use of the Inf production assay in the evaluation of the carcinogenicity of chemicals. In addition, it was shown that the induction of Inf-alpha/beta as well as the administration of this Inf depresses the levels of rat liver cytochrome P-450 which is responsible for binding lipophilic drugs, steroids, and carcinogens, thus increasing the toxicity of the respective chemical.

Sonnenfeld, Gerald↗
NASA NTRS1987

Magnetohydrodynamic cellular automata

A generalization of the hexagonal lattice gas model of Frisch, Hasslacher and Pomeau is shown to lead to two-dimensional magnetohydrodynamics. The method relies on the ideal point-wise conservation law for vector potential.

Montgomery, David↗
NASA NTRS1987

Cellular microstructure of chill block melt spun Ni-Mo alloys

Chill block melt spun ribbons of Ni-Mo binary alloys containing 8.0 to 41.8 wt pct Mo have been prepared under carefully controlled processing conditions. The growth velocity has been determined as a function of distance from the quench surface from the observed ribbon thickness dependence on the melt puddle residence time. Primary arm spacings measured at the midribbon thickness locations show a dependence on growth velocity and alloy composition which is expected from dendritic growth models for binary alloys directionally solidified in a positive temperature gradient. Microsegregation across cells and its variation with distance from the quench surface and alloy composition have been examined and compared with theoretical predictions.

Tewari, S. N.↗
NASA NTRS1988

Cellular thermosetting fluoropolymers and process for making them

Thermosetting fluoropolymer foams are made by mixing fluid from thermosetting fluoropolymer components having a substantial fluoride content, placing the mixture in a pressure tight chamber, filling the chamber with a gas, at a relatively low pressure, that is unreactive with the fluoropolymer components, allowing the mixture to gel, removing the gelled fluoropolymer from the chamber and therafter heating the fluoropolymer at a relatively low temperature to simultaneously cure and foam the fluoropolymer. The resulting fluoropolymer product is closed celled with the cells storing the gas employed for foaming. The fluoropolymer resins employed may be any thermosetting fluoropolymer including fluoroepoxies, fluoropolyurethanes and fluoroacrylates.

Lee, Sheng Y.↗
NASA NTRS1988

Effect of surface tension anisotropy on cellular morphologies

A three-dimensional weakly nonlinear analysis for conditions near the onset of instability at the crystal-melt interface was carried out to second order, taking into account the effects of latent heat generation and surface-tension anisotropy of the crystal-melt interface; particular consideration was given to the growth of a cubic crystal in the 001-, 011-, and 111-line directions. Numerical calculations by McFadden et al. (1987), performed for an aluminum-chromium alloy with the assumption of a linear temperature field and an isotropic surface tension, showed that only hexagonal nodes (and not hexagonal cells) occurred near the onset of instability. The results of the present analysis indicate that the nonlinear temperature field (which occurs when thermal conductivities of the crystal and the melt are different and/or the latent heat effects are not negligible) can modify this result and, for certain alloys and processing conditions, can cause the occurrence of hexagonal cells near the onset of instability.

Mcfadden, G. B.↗