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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Long-term radiation effects on GaAs solar cell characteristics

This report investigates preliminary design considerations which should be considered for a space experiment involving Gallium Arsenide (GaAs) solar cells. The electron radiation effects on GaAs solar cells were conducted in a laboratory environment, and a statistical analysis of the data is presented. In order to augment the limited laboratory data, a theoretical investigation of the effect of radiation on GaAs solar cells is also developed. The results of this study are empirical prediction equations which can be used to estimate the actual damage of electrical characteristics in a space environment. The experimental and theoretical studies also indicate how GaAs solar cell parameters should be designed in order to withstand the effects of electron radiation damage.

Heinbockel, J. H.↗
NASA NTRS1980

The influence of a voltage ramp on the measurement of I-V characteristics of a solar cell

For efficiency and convenience the voltage applied to a Si solar cell is often fairly rapidly driven from zero to the open circuit value typically at a common rate of 1 V per millisecond. During this time the values of current are determined as a function of the instantaneous voltage thus producing an I-V characteristic. The present paper shows that the customary expressions for the current as a function of cell parameters still remain valid provided that the diffusion length in the expression for the dark current is changed from its steady state value L to the effective diffusion length L1 given by L1 = L(1 + qV/kT.tau) to the -1/2, where V is the ramp rate considered constant and tau is the lifetime of minority carriers. This result is true to a very good approximation provided that low level injection prevails.

Von Roos, O.↗
NASA NTRS1980

Gallium arsenide (GaAs) power conversion concept

A summary design analysis of a GaAs power conversion system for the solar power satellite (SPS) is presented. Eight different satellite configuration options for the solar arrays are compared. Solar cell annealing effects after proton irradiation are considered. Mass estimates for the SPS and the effect of solar cell parameters on SPS array design are discussed.

Nussberger, A. A.↗
NASA NTRS1982

Expected cycle life versus depth of discharge relationships of well behaved single cells and cell strings

The factors that might influence the cycle life vs. depth of discharge relationship are examined. This is done first at the single cell level using a progressively more complex cell life model. This is then extended to multicell battery strings where the stochastic aspects associated with groupings of cells are introduced. These relationships are important when considering the weight, cost, and life of battery packs. The results of this theoretical study are compared with a recent review of actual cell cycling data. The factors examined are the rate of capacity loss, the amount of excess capacity built into the cells, and the penalty in capacity loss resulting from the use of deep depths of discharge. This study suggests that the relationship between cycle life and depth of discharge is not one that can be varied of significantly improved by cell research. The relationship appears to be determined by certain more or less fixed cell parameters. Among multicell strings, the standard deviation, as expected, plays an important role in determining overall battery life.

Thaller, L. H.↗
NASA NTRS1982

Design principles for high efficiency small-grain polysilicon solar cells, with supporting experimental studies

Design principles suggested here aim toward high conversion efficiency (greater than 15 percent) in polysilicon cells. The principles seek to decrease the liabilities of both intragranular and grain-boundary-surface defects. The advantages of a phosphorus atom concentration gradient in a thin (less than 50 microns) base of a p(+)/n(x)/n(+) drift-field solar cell, which produces favorable gradients in chemical potential, minority-carrier mobility and diffusivity, and recombination lifetime (via phosphorus gettering) are suggested. The degrading effects of grain boundaries are reduced by these three gradients and by substituting atoms (P, H, F or Li) for vacancies on the grain-boundary surface. From recent experiments comes support for the benefits of P diffusion down grain boundaries and, for quasi-grain-boundary-free and related structures. New analytic solutions for the n(x)-base include the effect of a power-law dependence between P concentration and lifetime. These provide an upper-bound estimate on the open circuit voltage. Finite-difference numerical solutions of the six Shockley equations furnish complete information about all solar-cell parameters and add insight concerning design.

Lindholm, F. A.↗
NASA NTRS1986

Lightweight, direct-radiating nickel hydrogen batteries

Two battery module configurations were developed which, in addition to integrating cylindrical nickel hydrogen (NiH2) cells into batteries, provide advances in the means of mounting, monitoring and thermal control of these cells. The main difference between the two modules is the physical arrangement of the cells: vertical versus horizontal. Direct thermal radiation to deep space is accomplished by substituting the battery structure for an exterior spacecraft panel. Unlike most conventional nickel-cadmium (NiCd) and NiH2 batteries, the cells are not tightly packed together; therefore ancillary heat conducting media to outside radiating areas, and spacecraft deck reinforcements for high mass concentration are not necessary. Testing included electrical characterization and a comprehensive regime of environmental exposures. The designs are flexible with respect to quantity and type of cells, orbit altitude and period, power demand profile, and the extent of cell parameter monitoring. This paper compares the characteristics of the two battery modules and summarizes their performance.

Metcalfe, J. R.↗
NASA NTRS1992

Stability limits for bioconvective fractals - Microgravity prospects

Fractal objects are delicate aggregates which show self-similar behavior and vanishing density for increasing length scales. In practice real fractals in nature however possess only a limited region of verifiable self-similarity. As natural fractal objects increase in size, they become easier to disrupt mechanically. Herein the effects of thermal vibrations and gravity are investigated as deforming forces on fractal aggregation. Example calculations are carried out on a biological fractal formed from the surface aggregation of various cells such as alga and bacteria. For typical cell parameters, the predicted diameter of this so-called 'bioconvective' fractal agrees well with the observed limits of about 5 cm. On earth, this size represents an experimental maximum for finding bioconvective fractal objects. To extend this size range of fractals available for statistical study, a reduced gravity environment offers one way to achieve larger fractals. For these enhanced sizes, the present scaling predicts that microgravity can yield up to a 35-fold improvement in extending statistical resolution.

Noever, David A.↗
NASA NTRS1993

High specific energy, high capacity nickel-hydrogen cell design

A 3.5 inch rabbit-ear-terminal nickel-hydrogen cell has been designed and tested to deliver high capacity at a C/1.5 discharge rate. Its specific energy yield of 60.6 wh/kg is believed to be the highest yet achieved in a slurry-process nickel-hydrogen cell, and its 10 C capacity of 113.9 AH the highest capacity yet made at a discharge rate this high in the 3.5 inch diameter size. The cell also demonstrated a pulse capability of 180 amps for 20 seconds. Specific cell parameters, performance, and future test plans are described.

Wheeler, James R.↗
NASA NTRS1993

High specific energy, high capacity nickel-hydrogen cell design

A 3.5 inch rabbit-ear-terminal nickel-hydrogen cell was designed and tested to deliver high capacity at steady discharge rates up to and including a C rate. Its specific energy yield of 60.6 wh/kg is believed to be the highest yet achieved in a slurry-process nickel-hydrogen cell, and its 10 C capacity of 113.9 AH the highest capacity yet of any type in a 3.5 inch diameter size. The cell also demonstrated a pulse capability of 180 amps for 20 seconds. Specific cell parameters and performance are described. Also covered is an episode of capacity fading due to electrode swelling and its successful recovery by means of additional activation procedures.

Wheeler, James R.↗
NASA NTRS1996

Crystallography of the NiHfSi Phase in a NiAl (0.5 Hf) Single-Crystal Alloy

Small additions of Hf to conventionally processed NiAl single crystals result in the precipitation of a high density of cuboidal G-phase along with a newly identified silicide phase. Both of these phases form in the presence of Si which is not an intentional alloying addition but is a contaminant resulting from contact with the ceramic shell molds during directional solidification of the single-crystal ingots. The morphology, crystal structure and Orientation Relationship (OR) of the silicide phase in a NiAl (0.5 at.%Hf) single-crystal alloy have been determined using transmission electron microscopy, electron microdiffraction and energy dispersive X-ray spectroscopy. Qualitative elemental analysis and indexing of the electron microdiffraction patterns from the new phase indicate that it is an orthorhombic NiHfSi phase with unit cell parameters, a = 0.639 nm, b = 0.389 nm and c = 0.72 nm, and space group Pnma. The NiHfSi phase forms as thin rectangular plates on NiAl/111/ planes with an OR that is given by NiHfSi(100))(parallel) NiAl(111) and NiHfSi zone axes(010) (parallel) NiAl zone axes (101). Twelve variants of the NiHfSi phase were observed in the alloy and the number of variants and rectangular morphology of NiHfSi plates are consistent with symmetry requirements. Quenching experiments indicate that nucleation of the NiHfSi phase in NiAI(Hf) alloys is aided by the formation of NiAl group of zone axes (111) vacancy loops that form on the NiAl /111/ planes.

Garg, A.↗
NASA NTRS2000

Over-Expression, Purification and Crystallization of Human Dihydrolipoamide Dehydrogenase

Dehydrolipoamide dehydrogenase (E3; dihydrolipoan-tide:NAD+ oxidoreductase, EC 1.8.1.4) is a common catalytic component found in pyruvate dehydrogenase complex, alpha-ketoglutarate dehydrogenase complex, and branched-chain cc-keto acid dehydrogenase complex. E3 is also a component (referred to as L protein) of the glycine cleavage system in bacterial metabolism (2). Active E3 forms a homodimer with four distinctive subdomain structures (FAD binding, NAD+ binding, central and interface domains) with non-covalently but tightly bound FAD in the holoenzyme. Deduced amino acids from cloned full-length human E3 gene showed a total of 509 amino acids with a leader sequence (N-terminal 35 amino acids) that is excised (mature form) during transportation of expressed E3 into mitochondria membrane. So far, three-dimensional structure of human E3 has not been reported. Our effort to achieve the elucidation of the X-ray crystal structure of human E3 will be presented. Recombinant pPROEX-1 expression vector (from GIBCO BRL Life Technologies) having the human E3 gene without leader sequence was constructed by Polymerase Chain Reaction (PCR) and subsequent ligation, and cloned in E.coli XL1-Blue by transformation. Since pPROEX-1 vector has an internal His-tag (six histidine peptide) located at the upstream region of a multicloning site, one-step affinity purification of E3 using nickelnitriloacetic acid (Ni-NTA) agarose resin, which has a strong affinity to His-tag, was feasible. Also a seven-amino-acid spacer peptide and a recombinant tobacco etch virus protease recognition site (seven amino acids peptide) found between His-tag and first amino acid of expressed E3 facilitated the cleavage of His-tag from E3 after the affinity purification. By IPTG induction, ca. 15 mg of human E3 (mature form) was obtained from 1L LB culture with overnight incubation at 25C. Over 98% of purity of E3 from one-step Ni-NTA agarose affinity purification was confirmed by SDS-PAGE analysis. For crystallization, E3 samples were prepared with and without His-tag. To minimize the aggregation of E3, apo- and holo- forms of E3s were tested, as well as a mutated E3. Dynamic light scattering measurements revealed that the E3 preparations without His-tag and substrate are highly monodispersive with regard to homodimers. Consequent crystallization trials of this E3 preparation led to single crystals of E3 grown by the vapor diffusion method. Crystals were obtained within a few days from solution containing poly (ethylene glycol) monomethyl ether 5000 as a precipitant. Autoindexing and integration of the X-ray diffraction data showed that E3 crystals belong to an orthorhombic system with unit cell parameters a-- 123. 1, b= 165.3 and c=214.3A. Further optimization of protein preparation and crystallization experiments for the structural determination will be discussed.

Hong, Y. S.↗
NASA NTRS2000

Crystallization and Initial X-Ray Diffraction Analysis of Human Pyruvate Dehydrogenase

Human pyruvate dehydrogenase (E1) is a component enzyme of the pyruvate dehydrogenase complex. The enzyme catalyzes the decarboxylation of pyruvate followed by a reductive acetylation of lipoyl groups of the dihydrolipoamide acetyltransferase component of the pyruvate dehydrogenase complex. El is an alpha(sub 2)Beta(sub 2) tetrameric assembly of an approximate molecular mass of 154 kDa. The crystals of this recombinant enzyme have been grown from polyethylene glycol 3350 using vapor diffusion method at 295K. The crystals are characterized as orthorhombic, space group P2(sub 1)2(sub 1)2(sub 1), with cell parameters of a = 64.2, b = 126.9 and c = 190.2 A. Crystals diffracted to a minimum d-spacing of 2.5 A. The asymmetric unit contains one alpha(sub 2)Beta(sub 2) tetrameric El assembly, and self-rotation function analysis showed a pseudo-twofold symmetry relating the two monomers.

Ciszak, Ewa↗
NASA NTRS2002

Crystallization and Preliminary X-ray analysis of Human Recombinant Acid beta-glucocerebrosidase, a treatment for Gaucher's Disease

Acid beta-glucocerebrosidase (N-acylsphingosyl - O - beta-D - glucoside:glucohydrolase) is a lysosomal glycoprotein that catalyzes the hydrolysis of the glycolipid glucocerebroside to glucose and ceramide. Inadequate levels of this enzyme underly the pathophysiology of Gaucher's disease. Cerezyme(R) (Genzyme Corporation, Cambridge, MA) is a partially deglycosylated form of recombinant human acid beta-glucocerebrosidase that is commercially available for the treatment of Gaucher patients. Although acid beta-glucocerebrosidase belongs to a large family of glycosidases, relatively little is known regarding its structural biology. We report the crystallization and the initial diffraction analysis of Cerezyme(R). The crystals are C-centered orthorhombic, with unit-cell parameters of a = 285.0 A, b = 110.2 A, and c = 91.7 A. A 99.9 A complete data set has been collected to 2.75 A with an R(sub sym) of 8.8 %.

Roeber, Dana F.↗
NASA NTRS2002

Crystallization and Preliminary X-ray Analysis of Der f 2, a Potent Allergen Derived from the House Dust Mite

Although a number of allergens have been identified and isolated, the underlying molecular basis for the potent immune response is poorly understood. House dust mites (Dermatophugoides sp.) are particularly ubiquitous contributors to atopy in developed countries. The rhinitis, dermatitis, and asthma associated with allergic reactions to these arthropods are often caused by relatively small (125-129 amino acids) mite proteins of unclear biological function. Der f 2, a major allergen from the mite Dermatophagoides farinae, has been recombinantly expressed and characterized. The Der f 2 protein has been crystallized in our laboratory and a native data set collected at a synchrotron source. The crystals belong to the orthorhombic space group I422 with unit cell parameters of a = 95.2 Angstroms, b = 95.2 Angstroms, and c = 103.3 Angstroms. An essentially complete (97.2%) data set has been collected to 2.4 Angstroms. Attempts to solve the crystal structure of Der f 2 by molecular replacement using the available NMR coordinates for either Der f 2 or Der p 2 (the homologous protein from D. pterovssinus) failed to reveal a creditable solution.

Roeber, Dana↗
NASA NTRS2003

Curve Fitting Solar Cell Degradation Due to Hard Particle Radiation

This paper investigates the suitability of the equation for accurately defining solar cell parameter degradation as a function of hard particle radiation. Y = Y/sub o/ + C/sub 1/ * Log(1 + /spl phi///spl phi//sub x/) + C/sub 2/ * Log(1 + /spl phi///spl phi//sub y/) The paper also provides methods for determining the constants in the equation and compares results from this equation to those obtained by the more traditionally used. Y = /spl Sigma/(a/sub i/ * [In(/spl phi/)]/sup i/)

Edward M. Gaddy↗
NASA NTRS2003

Mineralogical and chemical characterization of iron-, manganese-, and copper-containing synthetic hydroxyapatites

The National Aeronautics and Space Administration's (NASA) Advanced Life Support (ALS) Program is evaluating the use of Fe-, Mn-, and Cu-containing synthetic hydroxyapatite (SHA) as a slow release fertilizer for crops that might be grown on the International Space Station or at Lunar and Martian outposts. Separate Fe-, Mn-, and Cu-containing SHA materials along with a transition-metal free SHA (pure-SHA) were synthesized using a precipitation method. Chemical and mineralogical analyses determined if and how Fe, Mn, and Cu were incorporated into the SHA structure. X-ray diffraction (XRD), Rietveld refinement, and transmission electron microscopy (TEM) confirmed that SHA materials with the apatite structure were produced. Chemical analyses indicated that the metal containing SHA materials were deficient in Ca relative to pure-SHA. The shift in the infrared PO4-mu 3 vibrations, smaller unit cell parameters, smaller particle size, and greater structural strain for Fe-, Mn-, and Cu-containing SHA compared with pure-SHA suggested that Fe, Mn, and Cu were incorporated into SHA structure. Rietveld analyses revealed that Fe, Mn, and Cu substituted into the Ca2 site of SHA. An Fe-rich phase was detected by TEM analyses and backscattered electron microscopy in the Fe-containing SHA material with the greatest Fe content. The substitution of metals into SHA suggests that metal-SHA materials are potential slow-release sources of micronutrients for plant uptake in addition to Ca and P.

NASA Center JSC↗
NASA NTRS2003

Stereology techniques in radiation biology

Clinicians involved in conventional radiation therapy are very concerned about the dose-response relationships of normal tissues. Before proceeding to new clinical protocols, radiation biologists involved with conformal proton therapy believe it is necessary to quantify the dose response and tolerance of the organs and tissues that will be irradiated. An important focus is on the vasculature. This presentation reviews the methodology and format of using confocal microscopy and stereological methods to quantify tissue parameters, cell number, tissue volume and surface area, and vessel length using the microvasculature as a model tissue. Stereological methods and their concepts are illustrated using an ongoing study of the dose response of the microvessels in proton-irradiated hemibrain. Methods for estimating the volume of the brain and the brain cortex, the total number of endothelial cells in cortical microvessels, the length of cortical microvessels, and the total surface area of cortical microvessel walls are presented step by step in a way understandable for readers with little mathematical background. It is shown that stereological techniques, based on a sound theoretical basis, are powerful and reliable and have been used successfully.

Non-NASA Center↗
NASA NTRS2003

Crystallization and preliminary X-ray analysis of Der f 2, a potent allergen derived from the house dust mite (Dermatophagoides farinae)

Although a number of allergens have been identified and isolated, the underlying molecular basis for the potent immune response is poorly understood. House dust mites (Dermatophagoides sp.) are ubiquitous contributors to atopy in developed countries. The rhinitis, dermatitis and asthma associated with allergic reactions to these arthropods are frequently caused by relatively small (125-129 amino acids) mite proteins of unknown biological function. Der f 2, a major allergen from the mite D. farinae, has been recombinantly expressed, characterized and crystallized. The crystals belong to the tetragonal space group I4(1)22, with unit-cell parameters a = b = 95.2, c = 103.3 A. An essentially complete (97.2%) data set has been collected to 2.4 A at a synchrotron source. Attempts to solve the crystal structure of Der f 2 by molecular replacement using the NMR coordinates for either Der f 2 or Der p 2 (the homologous protein from D. pteronyssinus) failed, but preliminary searches using the crystalline Der p 2 atomic coordinates appear to be promising.

Pyroglyphidae/chemistry/immunology↗