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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 163 records · Page 9
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NASA NTRS1993

Superfluid turbulence

At low temperatures (below 5 Kelvin), helium is a liquid with a very low kinematic viscosity. It was proposed that wind tunnels could be built using liquid helium as the test fluid. The primary advantages of such wind tunnels would be a combination of large Reynolds numbers and a relatively small apparatus. It is hoped that this combination will allow the study of high Reynolds number flows in an academic setting. There are two basic types of liquid helium wind tunnels that can be built, corresponding to the two phases of liquid helium. The high temperature phase (between approximately 2 to 5 Kelvin) is called helium 1 and is a Navier-Stokes fluid. There are no unanswered scientific questions about the design or operation of a wind tunnel in the helium 1 phase. The low temperature phase (below approximately 2 Kelvin) of liquid helium is called helium 2. This is a quantum fluid, meaning that there are some properties of helium 2 which are directly due to quantum mechanical effects and which are not observed in Navier-Stokes fluids. The quantum effects that are relevant to this paper are: (1) helium 2 is well described as a superposition of two separate fluids called the superfluid and the normal fluid. The normal-fluid component is a Navier-Stokes fluid and the superfluid is an irrotational Euler fluid; and (2) circulation in the superfluid exists only in quantized vortex filaments. All quantized vortex filaments have identical circulations kappa and core size a. The objective of the research at CTR was to develop an understanding of the microscopic processes responsible for the observed Navier-Stokes behavior of helium 2 flows.

Samuels, David C.↗
NASA NTRS1986

Summary Abstract: Vibrations of Ammonia on the Cu (100) Surface

Recently, the TR frequencies for NH3 molecularly adsorbed on Cu(100) have been measured by infrared laser-induced photodesorption using a tunable laser operating in the group frequency range. Additionally, photodesorption, photo-fragmentation, and photoionization has been observed using a CO2 laser in the 10 microns range. In this contribution we report on work in progress where we use quantum chemical methods to analyze the shifts in the NH, frequencies relative to the gas phase upon chemisorption. We also compute the Cu- N stretch vibration, which has been observed experimentally,and the change in the IR intensities associated with chemisorption; this change is insufficient by itself to explain the increased photoionization efficiency observed.

Pettersson, Lars G. M.↗
NASA NTRS1988

The sensitivity of gas-phase models of dense interstellar clouds to changes in dissociative recombination branching ratios

The approach of Bates to the determination of neutral product branching ratios in ion-electron dissociative recombination reactions has been utilized in conjunction with quantum chemical techniques to redetermine branching ratios for a wide variety of important reactions of this class in dense interstellar clouds. The branching ratios have then been used in a pseudo time-dependent model calculation of the gas phase chemistry of a dark cloud resembling TMC-1 and the results compared with an analogous model containing previously used branching ratios. In general, the changes in branching ratios lead to stronger effects on calculated molecular abundances at steady state than at earlier times and often lead to reductions in the calculated abundances of complex molecules. However, at the so-called 'early time' when complex molecule synthesis is most efficient, the abundances of complex molecules are hardly affected by the newly used branching ratios.

Millar, T. J.↗
NASA NTRS1991

Calculations concerning the reaction C + H3(+) - CH(+) + H2

The ion-molecule reaction of C + H3(+) - CH(+) + H2 has not been studied in the laboratory but is thought to be important in the gas phase synthesis of organic molecules in dense interstellar clouds. This reaction was studied theoretically by performing quantum chemical ab initio calculations on the potential surface. It is found that there is no activation barrier to the reaction and that it proceeds smoothly to the first excited electronic state of CH(+). The rate coefficient as a function of temperature can then be estimated using the proper long-range potentials. The rate coefficient at 10 K is calculated to be 2.9 x 10 to the -9th cu cm/sec.

Talbi, D.↗
NASA NTRS1993

Can Bose condensation of alpha particles be observed in heavy ion collisions?

Using a fully self-consistent quantum statistical model, we demonstrate the possibility of Bose condensation of alpha particles with a concomitant phase transition in heavy ion collisions. Suggestions for the experimental observation of the signature of the onset of this phenomenon are made.

Tripathi, Ram K.↗
NASA NTRS1996

Generation of Squeezed Light Using Photorefractive Degenerate Two-Wave Mixing

We present a quantum nonlinear model of two-wave mixing in a lossless photorefractive medium. A set of equations describing the quantum nonlinear coupling for the field operators is obtained. It is found that, to the second power term, the commutation relationship is maintained. The expectation values for the photon number concur with those of the classical electromagnetic theory when the initial intensities of the two beams are strong. We also calculate the quantum fluctuations of the two beams initially in the coherent state. With an appropriate choice of phase, quadrature squeezing or number state squeezing can be produced.

Lu, Yajun↗
NASA NTRS1982

Evolution of perturbations in an inflationary universe

The evolution of inhomogeneous density perturbations in a model of the very early universe that is dominated for a time by a constant energy density of a false quantum-mechanical vacuum is analyzed. During this period, the universe inflates exponentially and supercools exponentially, until a phase transition back to the true vacuum reheats the matter and radiation. Focus is on the physically measurable, coordinate-independent modes of inhomogeneous perturbations of this model and it is found that all modes either are constant or are exponentially damped during the inflationary era.

Frieman, J. A.↗
NASA NTRS1990

Photovoltaic characteristics of n(+)pp(+) InP solar cells grown by OMVPE

The photovoltaic characteristics of n(+)/p/p(+) homojunction InP solar cells fabricated by organometallic vapor-phase epitaxy (OMVPE) are described. The cells are characterized by I-V, C-V and quantum efficiency measurements, and simulations are used to obtain various device and material parameters. The I-V characteristics show a high recombination rate in the depletion region; this is shown to be independent of the impurity used. It is shown that cadmium is easier to use as an acceptor for the p base and p(+) buffer and is therefore beneficial. The high quantum efficiency of 98 percent at long wavelengths measured in these cells indicates a very good collection efficiency in the base. The short-wavelength quantum efficiency is poor, indicating a high surface recombination.

Tyagi, S.↗
NASA NTRS1978

Infrared spectra of molecules and materials of astrophysical interest

The Raman spectra of gaseous, liquid and solid, and infrared spectra of gaseous and solid isopropylamine-d sub 0 and -d sub 2 was investigated between 4000 and 50 cm superscript -1. Differences between the spectrum of the solid phase and that of the fluid phases were interpreted in terms of an equilibrium between low energy s-trans and high energy gauche conformers, and a complete vibrational assignment was proposed for the s-trans conformer. The far infrared spectra of the gaseous compounds contained bands due to the asymmetric amino and coupled methyl torsions; the assignment of these bands was aided by observation of a number of two quantum transitions for each vibrational mode. The asymmetric potential functions were calculated, which resulted in values for the enthalpy differences between conformers in the gaseous phase of 446 and 523 callmole for the sub 0 -d and -d sub 2 compounds, respectively. The methyl torsional potential function of isopropylamine-d sub 0 was calculated which led to a value for the barrier height to internal rotation of the methyl rotors of 4.23 + or - 0.06 kcal/mole. Values for the ideal gas thermodynamic functions were calculated over a range of temperatures.

Durig, J. R.↗
NASA NTRS1992

Photon number squeezed states in semiconductor lasers

Electromagnetic fields, with the noise on one quadrature component reduced to below the quantum mechanical zero-point fluctuation level and the noise on the other quadrature component enhanced to above it, are currently of great interest in quantum optics because of their potential applications to various precision measurements. Such squeezed states of light are usually produced by imposing nonlinear unitary evolution on coherent (or vacuum) states. On the other hand, squeezed states with reduced photon number noise and enhanced phase noise are generated directly by a constant current-driven semiconductor laser. This is the simplest scheme for the generation of nonclassical light, and so far it has yielded the largest quantum noise reduction. The mutual coupling between a lasing junction and an external electrical circuit provides opportunities for exploring the macroscopic and microscopic quantum effects in open systems.

Yamamoto, Yoshihisa↗
NASA NTRS2007

NASA Tech Briefs, May 2007

Topics include: Noise-Canceling Helmet Audio System; Program Analyzes Spacecraft/Ground Radio Links; Two-Way Communication Using RFID Equipment and Techniques; Six-Message Electromechanical Display System; Scanning Terahertz Heterodyne Imaging Systems; Master Clock and Time-Signal-Distribution System; Synchronous Phase-Resolving Flash Range Imaging; Integrated Radial Probe Transition From MMIC to Waveguide; Bar-Code System for a Microbiological Laboratory; MMIC Amplifier Produces Gain of 10 dB at 235 GHz; Mapping Nearby Terrain in 3D by Use of a Grid of Laser Spots; Digital Beam Deflectors Based Partly on Liquid Crystals; Narrow-Band WGM Optical Filters With Tunable FSRs; Better Finite-Element Analysis of Composite Shell Structures; Computing Spacecraft-Pointing Vectors for Limb Tracking; Enhanced Master Controller Unit Tester; Rover Graphical Simulator; Increasing Durability of Flame-Sprayed Strain Gauges; Multifunctional, High-Temperature Nanocomposites; Multilayer Impregnated Fibrous Thermal Insulation Tiles; Radiation-Shielding Polymer/Soil Composites; Film/Adhesive Processing Module for Fiber-Placement Processing of Composites; Fabrication of Submillimeter Axisymmetric Optical Components; Electrochemical Disposal of Hydrazines in Water; Statistical Model of Evaporating Multicomponent Fuel Drops; Resistively Heated SiC Nozzle for Generating Molecular Beams; Compact Packaging of Photonic Millimeter-Wave Receiver; Diffractive Combiner of Single-Mode Pump Laser-Diode Beams; Wide-Band, High-Quantum-Efficiency Photodetector; A Robustly Stabilizing Model Predictive Control Algorithm; Modeling Evaporation of Drops of Different Kerosenes; Development of Vapor-Phase Catalytic Ammonia Removal System; Several Developments in Space Tethers; Design Concept for a Nuclear Reactor-Powered Mars Rover; Formation-Initialization Algorithm for N Spacecraft; and DNSs of Multicomponent Gaseous and Drop-Laden Mixing Layers Achieving Transition to Turbulence.

Source record↗
NASA NTRS1988

String-driven inflation

It is argued that, in fundamental string theories, as one traces the universe back in time a point is reached when the expansion rate is so fast that the rate of string creation due to quantum effects balances the dilution of the string density due to the expansion. One is therefore led into a phase of constant string density and an exponentially expanding universe. Fundamental strings therefore seem to lead naturally to inflation.

Turok, Neil↗
NASA NTRS1988

Cosmic strings

Cosmic strings are linear topological defects which are predicted by some grand unified theories to form during a spontaneous symmetry breaking phase transition in the early universe. They are the basis for the only theories of galaxy formation aside from quantum fluctuations from inflation based on fundamental physics. In contrast to inflation, they can also be observed directly through gravitational lensing and their characterisitc microwave background anisotropy. It was recently discovered that details of cosmic string evolution are very differnt from the so-called standard model that was assumed in most of the string-induced galaxy formation calculations. Therefore, the details of galaxy formation in the cosmic string models are currently very uncertain.

Bennett, David P.↗
NASA NTRS1990

Multi-Pinned-Phase Charge-Coupled Device

Multi-pinned-phase (MPP) technology allows charge-coupled device (CCD) to operate totally inverted during both integration and readout while maintaining other performance characteristics. MPP-CCD made with positive doping implants defining barrier phases. When all phases biased together into inversion, dark current reduced, and potential of charge-collecting wells is difference between potentials of barrier and collection phases. Advantages include complete elimination of residual image effects during integration and readout, low pixel nonuniformity, and increase in quantum efficiency in near infrared because higher operating temperatures used. More tolerant to ionizing radiation environments.

Janesick, James R.↗
NASA NTRS2014

Advanced Propulsion Physics Lab: Eagleworks Investigations

Eagleworks Laboratory is an advanced propulsions physics laboratory with two primary investigations currently underway. The first is a Quantum Vacuum Plasma Thruster (QVPT or Q-thrusters), an advanced electric propulsion technology in the development and demonstration phase. The second investigation is in Warp Field Interferometry (WFI). This is an investigation of Dr. Harold "Sonny" White's theoretical physics models for warp field equations using optical experiments in the Electro Optical laboratory (EOL) at Johnson Space Center. These investigations are pursuing technology necessary to enable human exploration of the solar system and beyond.

Scogin, Tyler↗
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 NTRS1991

High-Power AlGaAs Quantum-Well Lasers On Si Substrates

AlxGa1-xAs lasers of graded-index-of-refraction, separate-confinement-heterostructure, single-quantum-well type fabricated on silicon substrates by migration-enhanced molecular-beam epitaxy followed by metalorganic vapor-phase epitaxy. They are intermediate products of continuing effort to develop low-threshold-current, high-efficiency lasers for parallel optical interconnections between large-scale optoelectronic integrated circuits.

Kim, Jae-Hoon↗
NASA NTRS1992

Growth of III-V films by control of MBE growth front stoichiometry

For the growth of strain-layer materials and high quality single and multiple quantum wells, the instantaneous control of growth front stoichiometry is critical. The process of the invention adjusts the offset or phase of molecular beam epitaxy (MBE) control shutters to program the instantaneous arrival or flux rate of In and As4 reactants to grow InAs. The interrupted growth of first In, then As4, is also a key feature.

Grunthaner, Frank J.↗