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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

The surroundings of the Milky Way globular cluster NGC 6809

ABSTRACT We study the outer regions of the Milky Way globular cluster NGC 6809 based on Dark Energy Camera observations, which reach nearly 6 mag below the cluster main-sequence (MS) turn-off. In order to unveil its fainter outermost structure, we built stellar density maps using cluster MS stars, once the contamination of field stars was removed from the cluster colour–magnitude diagram. We found that only the resulting stellar density map for the lightest stars exhibits some excesses of stars at opposite sides from the cluster centre that diminish soon thereafter at ∼ 0.32°.Studied globular clusters with apogalactic distances smaller than that of NGC 6809 (5.5 kpc) do not have observed tidal tails. The lack of detection of tidal tails in the studied inner globular cluster sample could be due to the reduced diffusion time of tidal tails by the kinematically chaotic nature of the orbits of these globular clusters, thus shortening the time interval during which the tidal tails can be detected. Further investigations with an enlarged cluster sample are needed to confirm whether chaotic and non-chaotic orbits are responsible for the existence of globular clusters with tidal tails and those with extra-tidal features that are different from tidal tails or without any signatures of extended stellar density profiles.

Piatti, Andrés E.↗
DOE OSTI2021

Long-lived isomeric states and quasiparticle band structures in neutron-rich 162,164 Gd nuclei from β decay

Neutron-rich nuclei 162,164 Eu were produced by bombarding a proton beam on a 238 U target at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory and mass separating the 162,164 Eu products. New level schemes and new γ-ray transitions of the daughters 162,164 Gd were identified from β-decay spectroscopy studies. Additionally, half-lives of the 162,164 Eu were remeasured to clarify the previous ambiguous results. Two quasiparticle band structures were built and compared with neighboring nuclei. The β and γ bands were extended in 162 Gd and a γ band was extended in 164 Gd. Half-lives of the isomeric states at (6 - ) 1449 keV in 162 Gd and (4 - ) 1096 keV in 164 Gd were measured to be 99(3) μs and 0.56(3) μs, respectively. Projected shell model calculations were performed and found to be in good agreement with all of the experimental data.

150 ≤ A ≤ 189↗
DOE OSTI2020

Preserving Manhattan Project historic sites

Beginning in 1943, Project Y – the code name for Los Alamos during World War II – transformed the isolated Pajarito Plateau. The sounds of construction equipment replaced the voices of the Los Alamos Ranch School boys and local homesteaders. Construction crews hurriedly built many structures on mesa tops and in the canyons of Los Alamos. Countless concerns flooded Manhattan Project staff, but designing structures to withstand the test of time was not one of them. The top-secret race to develop an atomic bomb before Nazi Germany was on and everyone felt the pressure. Over the next 75 years, some of the structures slumped into disrepair from exposure to the harsh northern New Mexico environment - concrete cracking and spalling, wood frames rotting. That’s where Los Alamos National Laboratory’s historic preservation team enters the Manhattan Project story.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
DOE OSTI2019

Recognition of Peptidoglycan Fragments by the Transpeptidase PBP4 From Staphylococcus aureus

Peptidoglycan (PG) is an essential component of the cell envelope, maintaining bacterial cell shape and protecting it from bursting due to turgor pressure. The monoderm bacterium Staphylococcus aureus has a highly cross-linked PG, with ~90% of peptide stems participating in DD-cross-links and up to 15 peptide stems connected with each other. These cross-links are formed in transpeptidation reactions catalyzed by penicillin-binding proteins (PBPs) of classes A and B. Most S. aureus strains have three housekeeping PBPs with this function (PBP1, PBP2, and PBP3) but MRSA strains have acquired a third class B PBP, PBP2a, which is encoded by the mecA gene and required for the expression of high-level resistance to β-lactams. Another housekeeping PBP of S. aureus is PBP4, which belongs to the class C PBPs, and hence would be expected to have PG hydrolase (DD-carboxypeptidase or DD-endopeptidase) activity. However, previous works showed that, unexpectedly, PBP4 has transpeptidase activity that significantly contributes to both the high level of cross-linking in the PG of S. aureus and to the low level of β-lactam resistance in the absence of PBP2a. To gain insights into this unusual activity of PBP4, we studied by NMR spectroscopy its interaction in vitro with different substrates, including intact peptidoglycan, synthetic peptide stems, muropeptides, and long glycan chains with uncross-linked peptide stems. PBP4 showed no affinity for the complex, intact peptidoglycan or the smallest isolated peptide stems. Transpeptidase activity of PBP4 was verified with the disaccharide peptide subunits (muropeptides) in vitro, producing cyclic dimer and multimer products; these assays also showed a designed PBP4(S75C) nucleophile mutant to be inactive. Using this inactive but structurally highly similar variant, liquid-state NMR identified two interaction surfaces in close proximity to the central nucleophile position that can accommodate the potential donor and acceptor stems for the transpeptidation reaction. A PBP4:muropeptide model structure was built from these experimental restraints, which provides new mechanistic insights into mecA independent resistance to β-lactams in S. aureus.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

A Semi-Algebraic Two Level Solver

We develop a simple semi-algebraic 2-level solver built on traditional multigrid ideas. It is designed to be easily incorporated into existing simulation software. It exhibits good convergence for many classes of challenging problems including discontinuous diffusion, convection- diffusion, and Helmholtz equations. It has built-in structure that makes it simple to generalize in several interesting directions.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1972

Solid state image sensing arrays

The fabrication of a photodiode transistor image sensor array in silicon, and tests on individual elements of the array are described along with design for a scanning system for an image sensor array. The spectral response of p-n junctions was used as a technique for studying the optical-absorption edge in silicon. Heterojunction structures of Sb2S3- Si were fabricated and a system for measuring C-V curves on MOS structures was built.

Sadasiv, G.↗
NASA NTRS1972

Fatigue and fracture basic research at the Langley Research Center.

This paper gives some examples of projects underway. The projects are grouped according to the primary parameter being studied: loads, configuration, environment, or material. Significant topics include the effect of truncated loads, the effect of proof-tests, interference fasteners, accelerated and real-time tests for supersonic aircraft materials, crack-growth rates in built-up structures, and a model method by which material can be selected for a particular set of operating conditions.

Davidson, J. R.↗
NASA NTRS1972

Materials - Fiber composites.

Fiber composite materials, their properties, their state of technical advancement, and the plans underway to further the development and application of these materials for efficient flight structures are reviewed. It is considered that the costs of composite materials will drop sharply as the volume and manufacturing expertise is increased. The tailorability of structural elements and unique applications requiring high stiffness seem to be particularly attractive features. A good measure of the state of the technology is the sophistication of the structures being built and flown. Several examples are cited.

Brooks, G. W.↗
NASA NTRS1976

Resizing procedure for optimum design of structures under combined mechanical and thermal loading

An algorithm is reported for resizing structures subjected to combined thermal and mechanical loading. The algorithm is applicable to uniaxial stress elements (rods) and membrane biaxial stress members. Thermal Fully Stressed Design (TFSD) is based on the basic difference between mechanical and thermal stresses in their response to resizing. The TFSD technique is found to converge in fewer iterations than ordinary fully stressed design for problems where thermal stresses are comparable to the mechanical stresses. The improved convergence is demonstrated by example with a study of a simplified wing structure, built-up with rods and membranes and subjected to a combination of mechanical loads and a three dimensional temperature distribution.

Adelman, H. M.↗
NASA NTRS1977

Acoustical properties of materials and muffler configurations for the 80 by 120 foot wind tunnel

Techniques for measuring the impedance of the muffler configurations and of porous plates with grazing flow were investigated and changes in the configuration parameters to enhance acoustic performance are explored. The feasibility of a pulse reflection technique for measuring the impedance of built-up structures in situ was demonstrated. A second technique involving the use of an open-end impedance tube with grazing flow was used to obtain detailed design data for the perforated plate configuration. Acoustic benefits associated with configuration changes such as curving the baffles, spacing and staggering baffle partitions, and techniques for alleviating baffle self-generated noise are described.

Scharton, T. D.↗
NASA NTRS1984

The effect of direct and reflected radiation on the temperatures of space structures

As an orbiting structure passes from the bright side to the dark side of the earth, substantial differences in surface heating may take place due to direct sunlight and albedo. Most structures are built of convex curved elements to spread out the reflected energy. A change in the shortwave absorptivity and emissivity maintains the temperature of electronic components within a narrow range. Temperature extremes may also be reduced by the use of thermal capacity of the system or by shielding the surface from direct sunlight. For an instrument deployed from a Shuttle, a temperature must be established for it in the cargo bay before deployment. The effect of obstructed views by surfaces such as the Shuttle arm complicates solar flux computations because of the object's mobility. For typical orbits, the earth's albedo and the direct long wavelength radiation may be as much as 30 percent of the direct solar flux. Irradiation due to direct and reflected solar, long wave radiation and reflected radiation from earth, and from Shuttle surfaces is largely dependent on the specular reflection from the radiators as the Shuttle rolls and its surfaces block the sun. Through a judicious choice of surface properties, thermal capacitance and orbit attitude programming, the temperature response of a system can be controlled.

Emery, A. F.↗
NASA NTRS1986

Design sensitivity analysis using EAL. Part 2: Shape design parameters

A numerical implementation of shape design sensitivity analysis of built-up structures is presented, using the versatility and convenience of an existing finite element structural analysis code and its data base management system. This report is a continuation of a previous report on conventional design parameters. The finite element code used in the implementation presented is the Engineering Analysis Language (EAL), which is based on a hybrid analysis method. It has been shown that shape design sensitivity computations can be carried out using the database management system of EAL, without writing a separate program and a separate data base. The material derivative concept of continuum mechanics and an adjoint variable method of design sensitivity analysis are used to derive shape design sensitivity information of structural performances. A domain method of shape design sensitivity analysis and a design component method are used. Displacement and stress functionals are considered as performance criteria.

Dopker, B.↗
NASA NTRS1987

Sizing and shape design sensitivity analysis using a hybrid finite element code

The practical (software) implementation of the theoretical FEM-based design sensitivity analysis method of Haug et al. (1986) is described and demonstrated. The fundamental principles of the method are reviewed; the problems involved in applying it to the Engineering Analysis Language (EAL) hybrid FEM code (Whetstone, 1983) are discussed; the formulations for beams, plate bending, and built-up structures are given in detail; programming aspects are considered; and numerical results for sample problems are presented in extensive tables. It is shown that the use of a data-base management system with an FEM such as EAL makes it possible to obtain accurate sizing and shape design sensitivity information using only one program with one data base.

Dopker, Bernhard↗
NASA NTRS1989

Design of a thrust stand for high power electric propulsion devices

A thrust stand for use with high power electric propulsion devices has been designed and tested. The thrust stand was specifically tailored to the needs of a 0.1 to 0.25 MW magnetoplasmadynamic (MPD) thruster program currently in progress at the NASA Lewis Research Center. The thrust stand structure was built as an inverted pendulum arrangement, supported at the base by water-cooled electrical power flexures. Thrust stand tares due to thruster discharge current were demonstrated to be negligible. Tares due to an applied field magnet current, after considerable effort, were reduced to less than 3.0 percent of measured thrust. These tares, however, could be determined independently and subtracted from the indicated thrust measurement. The paper gives a detailed description of the thrust stand design and operation with a 0.1 MW class MPD device. Other thrust stand tares due to vibration and thermal effects are discussed, along with issues of accuracy and repeatability.

Haag, Thomas W.↗
NASA NTRS1989

Design of a thrust stand for high power electric propulsion devices

A thrust stand for use with high power electric propulsion devices was designed and tested. The thrust stand was specifically tailored to the needs of a 100 to 250 kW magnetoplasmadynamic (MPD) thruster program currently in progress at the NASA Lewis Research Center. The thrust stand structure was built as an inverted pendulum arrangement, supported at the base by water-cooled electrical power flexures. Thrust stand tares due to thruster discharge current were demonstrated to be negligible. Tares due to an applied field magnet current, after considerable effort, were reduced to less than 3.0 percent of measured thrust. These tares, however, could be determined independently and subtracted from the indicated thrust measurement. A detailed description is given for the thrust stand design and operation with a 100 kW class MPD device. Other thrust stand tares due to vibration and thermal effects are discussed, along with issues of accuracy and repeatability.

Haag, Thomas W.↗
NASA NTRS1990

The status of cesium beam frequency standards

There has been a lot of progress in cesium beam frequency standards in the last few years some of which will be reported here. Optical pumping is being pursued actively in a number of laboratories. Optically slowed and cooled beams have been demonstrated as well as traps for cold neutral atoms. The microwave cavity performance with regard to local phase shift at the beam holes was improved by use of carefully designed and built ring structures for the cavity ends. Work is being done on improvements in electronics with some emphasis on use of digital circuitry and microprocessors. The frequency pulling due to microwave Delta M = +/- 1 transitions (Ramsey pulling) was analyzed and shown to be important. Status of cesium beam frequency standards in some of the laboratories as well as some of the commercial work is discussed. Optical pumping and detection are discussed.

Cutler, Leonard S.↗