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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Microscopic Modeling of Intersubband Resonances in InAs/AlSb Quantum Wells

Linear absorption spectra from intersubband resonance in InAs/AlSb quantum wells are analyzed theoretically using the intersubband semiconductor Bloch equation approach. Our model goes beyond the Hartree-Fock approximation and treats particle-particle correlations under the second Born approximation. Electron-electron and -LO phonon scatterings from such a treatment describe intrinsic line broadening to the intersubband resonance. Electron subbands are determined self-consistently with a spurious-state-free 8-band k.p Hamiltonian under the envelope function approximation. To compare with experimental measurements, we also included line broadening due to electron-interface roughness scattering. Excellent agreement was achieved for temperature-dependent absorption spectra in the mid-infrared frequency range, after taking into careful account the interplay of material parameters, nonparabolicity in bandstructure, and many-body effects.

Li, Jian-Zhong↗
NASA NTRS2004

Construction of a Virtual Scanning Electron Microscope (VSEM)

The Imaging Technology Group (ITG) proposed to develop a Virtual SEM (VSEM) application and supporting materials as the first installed instrument in NASA s Virtual Laboratory Project. The instrument was to be a simulator modeled after an existing SEM, and was to mimic that real instrument as closely as possible. Virtual samples would be developed and provided along with the instrument, which would be written in Java.

Fried, Glenn↗
NASA NTRS2004

Microscopic Theory and Simulation of Quantum-Well Intersubband Absorption

We study the linear intersubband absorption spectra of a 15 nm InAs quantum well using the intersubband semiconductor Bloch equations with a three-subband model and a constant dephasing rate. We demonstrate the evolution of intersubband absorption spectral line shape as a function of temperature and electron density. Through a detailed examination of various contributions, such as the phase space filling effects, the Coulomb many-body effects and the non-parabolicity effect, we illuminate the underlying physics that shapes the spectra. Keywords: Intersubband transition, linear absorption, semiconductor heterostructure, InAs quantum well

Li, Jianzhong↗
NASA NTRS2004

Raman Microscopic Characterization of Proton-Irradiated Polycrystalline Diamond Films

The microstructural effects of irradiating polycrystalline diamond films with proton dosages ranging from 10(exp 15) to 10(exp 17) H(+) per square centimeter was examined. Scanning Electron Microscopy and Raman microscopy were used to examine the changes in the diamond crystalline lattice as a function of depth. Results indicate that the diamond lattice is retained, even at maximum irradiation levels.

Newton, R. L.↗
NASA NTRS1992

Scanning electron microscope observations of brine shrimp larvae from space shuttle experiments

Brine shrimp are encysted as gastrula stage embryos, and may remain dehydrated and encysted for years without compromising their viability. This aspect of brine shrimp biology is desirable for studying development of animals during space shuttle flight, as cysts placed aboard a spacecraft may be rehydrated at the convenience of an astronaut, guaranteeing that subsequent brine shrimp development occurs only on orbit and not on the pad during launch delays. Brine shrimp cysts placed in 5 ml syringes were rehydrated with salt water and hatched during a 9 day space shuttle mission. Subsequent larvae developed to the 8th larval stage in the sealed syringes. We studied the morphogenesis of the brine shrimp larvae and found the larvae from the space shuttle experiments similar in rate of growth and extent of development, to larvae grown in sealed syringes on the ground. Extensive differentiation and development of embryos and larvae can occur in a microgravity environment.

short duration↗
NASA NTRS1988

Early quantitative method for measuring germination in non-green spores of Dryopteris paleacea using an epifluorescence-microscope technique

A method is described to determine germination by blue-light excited red fluorescence in the positively photoblastic spores of Dryopteris paleacea Sw. This fluorescence is due to chlorophyll as evidenced from 1) a fluorescence-emission spectrum in vivo, where a bright fluorescence around 675 nm is obtained only in red light (R)-irradiated spores and 2) in vitro measurements with acetone extracts prepared from homogenized spores. Significant amounts of chlorophyll can be found only in R-treated spores; this chlorophyll exhibits an emission band around 668 nm, when irradiated with 430 nm light at 21 degrees C. Compared to other criteria for germination, such as swelling of the cell, coat splitting, greening, and rhizoid formation, which require longer periods after induction for their expression, chlorophyll fluorescence can be used to quantify germination after two days. This result is confirmed by fluence-response curves for R-induced spore germination; the same relationship between applied R and germination is obtained by the evaluation with the epifluorescence method 2 days after the light treatment as compared with the evaluation with bright-field microscopy 5 days after the inducing R. Using this technique we show for the first time that Ca2+ contributes to the signal-transduction chain in phytochrome-mediated chlorophyll synthesis in spores of Dryopteris paleacea.

NASA Discipline Plant Biology↗
NASA NTRS1998

Production of otoconia in the endolymphatic sac in the Japanese red-bellied newt, Cynops pyrrhogaster: light and transmission electron microscopic study

The formation of otoconia in the endolymphatic sac (ES) of the larval newt, Cynops pyrrhogaster, has been studied by light and transmission electron microscopy. Some of the epithelial cells of the ES contain an abundance of swollen vesicles, Golgi complexes, rough endoplasmic reticula and ribosomes at the late larval stages 50 and 51, approximately 26-30 days after eggs are laid. Five days later, at stage 52, crystals are present in the vacuoles between the epithelial cells. Serial sections indicate that these vacuoles actually form small canals which lie in the wall and join the lumen of the ES. Reconstruction of the ES shows that several canals are contained in the ES wall. At stage 56, about 72 days after eggs are laid, a large number of otoconia are present in the ES lumen, while the otoconia disappear from the canals. It appears that the otoconia are first produced in the canals and then released to the lumen. Some epithelial cells of the ES are thought to expel the organic and inorganic material to the canals to form the otoconia in situ. The process of formation of the otoconia in the ES is discussed.

Non-NASA Center↗
NASA NTRS1992

FT-IR microscopic mappings of early mineralization in chick limb bud mesenchymal cell cultures

Chick limb bud mesenchymal cells differentiate into chondrocytes and form a cartilaginous matrix in culture. In this study, the mineral formed in different areas within cultures supplemented with 4 mM inorganic phosphate, or 2.5, 5.0, and 10 mM beta-glycerophosphate (beta GP), was characterized by Fourier-transform infrared (FT-IR) microscopy. The relative mineral-to-matrix ratios, and distribution of crystal sizes at specific locations throughout the matrix were measured from day 14 to day 30. The only mineral phase detected was a poorly crystalline apatite. Cultures receiving 4 mM inorganic phosphate had smaller crystals which were less randomly distributed around the cartilage nodules than those in the beta GP-treated cultures. beta GP-induced mineral consisted of larger, more perfect apatite crystals. In cultures receiving 5 or 10 mM beta GP, the relative mineral-to-matrix ratios (calculated from the integrated intensities of the phosphate and amide I bands, respectively) were higher than in the cultures with 4 mM inorganic phosphate or in the in vivo calcified chick cartilage.

NASA Discipline Musculoskeletal↗
NASA NTRS1990

Histomorphometric and electron microscopic analyses of tibial epiphyseal plates from Cosmos 1887 rats

Previous studies have shown that the changes seen in the bones of growing rats exposed to microgravity are due in part to changes that occur in the growth plate during spaceflight. In this study, growth plates of rats flown aboard Cosmos 1887 (12.5-day flight plus 53.5-h recovery at 1 g) were analyzed using light and electron microscopy and computerized planimetry. The proliferative zone of flight animals was found to be significantly (P less than or equal to 0.01) larger than that of controls, while the reserve and hypertrophic/calcification zones were significantly reduced. Flight animals also had more cells per column in the proliferative zone than did controls and less in the hypertrophic/calcification region. The total number of cells, however, was significantly greater in flight animals. No difference was found in perimeter or in shape factor, but area was significantly less in flight animals. Electron microscopy showed that collagen fibrils in flight animals were wider than in controls. Since the time required for a cell to cycle through the growth plate is 2-3 days at 1 g, the results reported here represent both the effects of exposure to microgravity and the initial stages of recovery from that exposure.

Non-NASA Center↗
NASA NTRS2003

Near-infrared detection of potential evidence for microscopic organisms on Europa

The possibility of an ocean within the icy shell of Jupiter's moon Europa has established that world as a primary candidate in the search for extraterrestrial life within our Solar System. This paper evaluates the potential to detect evidence for microbial life by comparing laboratory studies of terrestrial microorganisms with measurements from the Galileo Near Infrared Imaging Spectrometer (NIMS). If the interior of Europa at one time harbored life, some evidence may remain in the surface materials. Examination of laboratory spectra of terrestrial extremophiles measured at cryogenic temperatures reveals distorted, asymmetric nearinfrared absorption features due to water of hydration. The band centers, widths, and shapes of these features closely match those observed in the Europa spectra. These features are strongest in reddish-brown, disrupted terrains such as linea and chaos regions. Narrow spectral features due to amide bonds in the microbe proteins provide a means of constraining the abundances of such materials using the NIMS data. The NIMS data of disrupted terrains exhibit distorted, asymmetric near-infrared absorption features consistent with the presence of water ice, sulfuric acid octahydrate, hydrated salts, and possibly as much as 0.2 mg cm(-3) of carbonaceous material that could be of biological origin. However, inherent noise in the observations and limitations of spectral sampling must be taken into account when discussing these findings.

Extraterrestrial Environment↗
NASA NTRS2002

Scanning Electron Microscope Mapping System Developed for Detecting Surface Defects in Fatigue Specimens

An automated two-degree-of-freedom specimen positioning stage has been developed at the NASA Glenn Research Center to map and monitor defects in fatigue specimens. This system expedites the examination of the entire gauge section of fatigue specimens so that defects can be found using scanning electron microscopy (SEM). Translation and rotation stages are driven by microprocessor-based controllers that are, in turn, interfaced to a computer running custom-designed software. This system is currently being used to find and record the location of ceramic inclusions in powder metallurgy materials. The mapped inclusions are periodically examined during interrupted fatigue experiments. The number of cycles to initiate cracks from these inclusions and the rate of growth of initiated cracks can then be quantified. This information is necessary to quantify the effect of this type of defect on the durability of powder metallurgy materials. This system was developed with support of the Ultra Safe program.

Bonacuse, Peter J.↗
NASA NTRS2002

Light Microscopy Module: On-Orbit Microscope Planned for the Fluids Integrated Rack on the International Space Station

The Light Microscopy Module (LMM) is planned as a remotely controllable, automated, on-orbit facility, allowing flexible scheduling and control of physical science and biological science experiments within the Fluids Integrated Rack (FIR) on the International Space Station. Initially four fluid physics experiments in the FIR will use the LMM the Constrained Vapor Bubble, the Physics of Hard Spheres Experiment-2, Physics of Colloids in Space-2, and Low Volume Fraction Entropically Driven Colloidal Assembly. The first experiment will investigate heat conductance in microgravity as a function of liquid volume and heat flow rate to determine, in detail, the transport process characteristics in a curved liquid film. The other three experiments will investigate various complementary aspects of the nucleation, growth, structure, and properties of colloidal crystals in microgravity and the effects of micromanipulation upon their properties.

Motil, Susan M.↗
NASA NTRS2006

Novel Confocal Microscopic and Flow Cytometric Based Assays to Visualize and Detect the (Beta)2-Adrenergic Receptor in Human Lymphocyte and Mononuclear Cell Populations

The data show that immunophenotyping of leukocyte populations with (beta)2AR is possible with the commercially available Ab, although the FC assay is limited to the IST as a result of the Ab binding site to the intracellular C-terminus of the 2AR. The FC assay has applications for measuring alterations in total (beta)2AR in human leukocyte populations as changes in fluorescence. In addition, CM confirms that both surface and intracellular compartments stain positively for the (beta)2AR and can be used for qualitative assays that screen for changes in receptor compartmentalization and localization.

Salicru, A. N.↗