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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Microfocus/Polycapillary-Optic Crystallographic X-Ray System

A system that generates an intense, nearly collimated, nearly monochromatic, small-diameter x-ray beam has been developed for use in macromolecular crystallography. A conventional x-ray system for macromolecular crystallography includes a rotating-anode x-ray source, which is massive (.500 kg), large (approximately 2 by 2 by 1 m), and power-hungry (between 2 and 18 kW). In contrast, the present system generates a beam of the required brightness from a microfocus source, which is small and light enough to be mounted on a laboratory bench, and operates at a power level of only tens of watts. The figure schematically depicts the system as configured for observing x-ray diffraction from a macromolecular crystal. In addition to the microfocus x-ray source, the system includes a polycapillary optic . a monolithic block (typically a bundle of fused glass tubes) that contains thousands of straight or gently curved capillary channels, along which x-rays propagate with multiple reflections. This particular polycapillary optic is configured to act as a collimator; the x-ray beam that emerges from its output face consists of quasi-parallel subbeams with a small angular divergence and a diameter comparable to the size of a crystal to be studied. The gap between the microfocus x-ray source and the input face of the polycapillary optic is chosen consistently with the focal length of the polycapillary optic and the need to maximize the solid angle subtended by the optic in order to maximize the collimated x-ray flux. The spectrum from the source contains a significant component of Cu K (photon energy is 8.08 keV) radiation. The beam is monochromatized (for Cu K ) by a nickel filter 10 m thick. In a test, this system was operated at a power of 40 W (current of 897 A at an accelerating potential of 45 kV), with an anode x-ray spot size of 41+/-2 microns. Also tested, in order to provide a standard for comparison, was a commercial rotating-anode x-ray crystallographic system with a pyrolytic graphite monochromator and a 250-micron pinhole collimator, operating at a power of 3.15 kW (current of 70 mA at an accelerating potential of 45 kV). The flux of collimated Cu K radiation in this system was found to be approximately 16 times that in the rotatinganode system. Data on x-ray diffraction from crystals of tetragonal form of lysozyme (protein) in this system were found to be of high quality and to be reducible by use of standard crystallographic software.

Joy, Marshall↗
NASA NTRS1987

Geometrical analysis of Cys-Cys bridges in proteins and their prediction from incomplete structural information

Analysis of C-alpha atom positions from cysteines involved in disulphide bridges in protein crystals shows that their geometric characteristics are unique with respect to other Cys-Cys, non-bridging pairs. They may be used for predicting disulphide connections in incompletely determined protein structures, such as low resolution crystallography or theoretical folding experiments. The basic unit for analysis and prediction is the 3 x 3 distance matrix for Cx positions of residues (i - 1), Cys(i), (i +1) with (j - 1), Cys(j), (j + 1). In each of its columns, row and diagonal vector--outer distances are larger than the central distance. This analysis is compared with some analytical models.

NASA Discipline Exobiology↗
NASA NTRS1993

Conformational influence of the ribose 2'-hydroxyl group: crystal structures of DNA-RNA chimeric duplexes

We have crystallized three double-helical DNA-RNA chimeric duplexes and determined their structures by X-ray crystallography at resolutions between 2 and 2.25 A. The two self-complementary duplexes [r(G)d(CGTATACGC)]2 and [d(GCGT)r(A)d(TACGC)]2, as well as the Okazaki fragment d(GGGTATACGC).r(GCG)d(TATACCC), were found to adopt A-type conformations. The crystal structures are non-isomorphous, and the crystallographic environments for the three chimeras are different. A number of intramolecular interactions of the ribose 2'-hydroxyl groups contribute to the stabilization of the A-conformation. Hydrogen bonds between 2'-hydroxyls and 5'-oxygens or phosphate oxygens, in addition to the previously observed hydrogen bonds to 1'-oxygens of adjacent riboses and deoxyriboses, are observed in the DNA-RNA chimeric duplexes. The crystalline chimeric duplexes do not show a transition between the DNA A- and B-conformations. CD spectra suggest that the Okazaki fragment assumes an A-conformation in solution as well. In this molecule the three RNA residues may therefore lock the complete decamer in the A-conformation. Crystals of an all-DNA strand with the same sequence as the self-complementary chimeras show a morphology which is different from those of the chimera crystals. Moreover, the oligonucleotide does not match any of the sequence characteristics of DNAs usually adopting the A-conformation in the crystalline state (e.g., octamers with short alternating stretches of purines and pyrimidines). In DNA-RNA chimeric duplexes, it is therefore possible that a single RNA residue can drive the conformational equilibrium toward the A-conformation.

NASA Discipline Number 52-20↗
NASA NTRS1992

Crystal structure of an Okazaki fragment at 2-A resolution

In DNA replication, Okazaki fragments are formed as double-stranded intermediates during synthesis of the lagging strand. They are composed of the growing DNA strand primed by RNA and the template strand. The DNA oligonucleotide d(GGGTATACGC) and the chimeric RNA-DNA oligonucleotide r(GCG)d(TATACCC) were combined to form a synthetic Okazaki fragment and its three-dimensional structure was determined by x-ray crystallography. The fragment adopts an overall A-type conformation with 11 residues per turn. Although the base-pair geometry, particularly in the central TATA part, is distorted, there is no evidence for a transition from the A- to the B-type conformation at the junction between RNA.DNA hybrid and DNA duplex. The RNA trimer may, therefore, lock the complete fragment in an A-type conformation.

Non-NASA Center↗
NASA NTRS2005

Structural and energetic consequences of mutations in a solvated hydrophobic cavity

The structural and energetic consequences of modifications to the hydrophobic cavity of interleukin 1-beta (IL-1beta) are described. Previous reports demonstrated that the entirely hydrophobic cavity of IL-1beta contains positionally disordered water. To gain a better understanding of the nature of this cavity and the water therein, a number of mutant proteins were constructed by site-directed mutagenesis, designed to result in altered hydrophobicity of the cavity. These mutations involve the replacement of specific phenylalanine residues, which circumscribe the cavity, with tyrosine, tryptophan, leucine and isoleucine. Using differential scanning calorimetry to determine the relative stabilities of the wild-type and mutant proteins, we found all of the mutants to be destabilizing. X-ray crystallography was used to identify the structural consequences of the mutations. No clear correlation between the hydrophobicities of the specific side-chains introduced and the resulting stabilities was found.

Solvents/chemistry↗
NASA NTRS1965

Rotating filters permit wide range of optical pyrometry

Gear-driven dual filter disks of graduated density vary linearly with respect to rotation, allowing a wide range of photographic pyrometry. this technique is applicable in metallurgy, glass, plastics and refractory research, and crystallography.

Exton, R. J.↗
NASA NTRS1973

High voltage electron microscopy of lunar samples

Lunar pyroxenes from Apollo 11, 12, 14, and 15 were investigated. The iron-rich and magnesium-rich pyroxene specimens were crushed to a grain size of ca. 50 microns and studied by a combination of X-ray and electron diffraction, electron microscopy, 57 Fe Mossbauer spectroscopy and X-ray crystallography techniques. Highly ordered, uniform electron-dense bands, corresponding to exsolution lamellae, with average widths of ca. 230A to 1000A dependent on the source specimen were observed. These were?qr separated by wider, less-dense interband spacings with average widths of ca. 330A to 3100A. In heating experiments, splitting of the dense bands into finer structures, leading finally to obliteration of the exsolution lamellae was recorded. The extensive exsolution is evidence for significantly slower cooling rates, or possibly annealing, at temperatures in the subsolidus range, adding evidence that annealing of rock from the surface of the moon took place at ca. 600 C. Correlation of the band structure with magnetic ordering at low temperatures and iron clustering within the bands was studied.

Fernandez-Moran, H.↗
NASA NTRS1974

Interfaces in directionally solidified eutectics

Consideration of the interface between the phases in directionally solidified eutectic structures with respect to its morphology, crystallography, stability, and overall response to internal and external stress fields. Yielding behavior in such eutectic structures is shown to be controlled by several possible mechanisms. Two that can be related to the interface in directionally-solidified eutectic alloys are: (1) the interaction of slip dislocations with interface dislocations of the semicoherent boundaries, and (2) restrictions of allowable deformation mechanisms in two contiguous phases due to orientation effects. Evidence found thus far for elastic-plastic eutectic composites indicates that interfaces are capable of diverting fatigue cracks parallel to the loading axis.

Hertzberg, R. W.↗
NASA NTRS1974

A lunar rock of deep crustal origin - Sample 76535

Review of the mineral chemistry, crystallography, mosaic assemblages, and oriented inclusions of lunar rock sample 76535, and discussion of its depth of formation. Its texture, chemistry, and phase relationships are shown to indicate that it formed deep within the lunar crust. It is the first crystalline lunar rock found to date to contain evidence of a high pressure mineral assemblage formed under static conditions.

Gooley, R.↗
NASA NTRS1977

Large-area soft X-ray imaging system

System consists of large-area focusing collector and position sensitive proportional counter. Device can be used to study plasmas, with X-ray imaging in biological sciences, and crystallography.

Gorenstein, P.↗
NASA NTRS1977

Image improvement and three-dimensional reconstruction using holographic image processing

Holographic computing principles make possible image improvement and synthesis in many cases of current scientific and engineering interest. Examples are given for the improvement of resolution in electron microscopy and 3-D reconstruction in electron microscopy and X-ray crystallography, following an analysis of optical versus digital computing in such applications.

Stroke, G. W.↗
NASA NTRS1977

Evaluation of low cost/high temperature fiber and blanket insulation

Twelve fiber materials comprising water-felted fiber cakes and blanket insulation were subjected to furnace exposures at 1000, 1200, 1400, and 1600 C for up to 500 hours to establish the time-temperature limits below which these insulation materials can withstand repeated thermal cycles without detrimental shrinkage, thermal conductivity increase, or physical changes. Test samples were inspected periodically during the exposure cycles and weight loss and dimensional shrinkage were measured. Density, fiber crystallography, and thermal conductivity were measured after exposure and properties were compared with those of unexposed controls.

Strauss, E. L.↗
NASA NTRS1979

Pyroxenes in Serra de Mage - Cooling history in comparison with Moama and Moore County

Thin sections and single grains of pyroxenes from the Serra de Mage feldspar cumulate eucrites were studied by X-ray crystallography, electron microprobe and optical techniques. It was concluded that the pyroxene crystallized as pigeonite. On cooling augite was exsolved along (001) and inverted to hypersthene, with exsolution of (100) augite from hypersthene during continued slow cooling. The estimated original bulk composition of the pigeonite pyroxene is Wo10En51Fs39. The compositional data, textural relations, and existence of P2 sub 1 ca hypersthene suggest very low cooling (about 0.0004 deg C/year) below 800 deg. The Serra de Mage augite lamellae were found to be as thick or thicker than those of Moore County and Moama meteorites.

Harlow, G. E.↗