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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 OSTI2022

Structure-Function and Nearest Neighbor Interactions of the Cytochrome b 6 f Complex

Test prediction from our (i) high resolution (2.5 Å) structure of cyanobacterial cytochrome b 6 f complex (Structure, 22, 1008-1015, 2014), and (ii) analysis of quinone/quinol traffic within the b 6 f complex (Biophys. J., 107, 1620-1628, 2014) concerning the rate-limiting step in the linear (non-cyclic) electron transport chain. It was concluded that it arises from access of plastoquinol, the electron/proton donor, to the high potential electron carriers, i. e., the Fe 2 S 2 and cytochrome f proteins. The directed motion of the quinol proceeds via a narrow channel on the lumen or electrochemically positive, p- (lumen) side of the b 6 f complex which was defined by crystal structures of the b 6 f complex with quinol analogue inhibitors (J. Mol. Biol., 370, 39-52, 2007).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Morphological Characterization of UO 2 F 2 and UF 4 Hydrolysis Products

Bulk samples of UO 2 F 2 and UF 4 were aged for 3 weeks under various relative humidity (RH) conditions to examine morphological changes associated with the hydrolysis of the materials. Aged samples were analyzed using scanning electron microscopy (SEM) to examine morphological changes, and Raman spectroscopy was used to correlate these changes with chemical composition. Little to no effect was evident for either material under lower RH conditions (i.e., 16% and 33%–38% RH). Under higher RH conditions (83% and 99%), multiple morphological changes were evident within the UO 2 F 2 samples because of the formation of hydrolysis products and possible interactions at the solid–vapor interface. Only one major morphological change was observed over the aging period—within the UF 4 system at 99% RH. This change can be attributed to the initial formation of anhydrous UO 2 F 2 and, subsequently, its hydrolysis products. After 37 weeks, UO 2 F 2 persisted as a hydrolysis product of UF4; however, no further hydrolysis products were observed. These results suggest that further research into a possible divergence of UF 4 and UO 2 F 2 degradation pathways is warranted.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Nanosecond Breakdown Characteristics of C 4 F 7 N and Various Mixtures at Pressures Above 1 Atmosphere in Comparison with SF 6

This report evaluates the pulsed breakdown performance of C 4 F 7 N under a 6.8 kV/ns voltage excitation. The pulsed dielectric strength of C 4 F 7 N is compared to SF 6 in the same experimental setup, and it is found that C 4 F 7 N concentrations of 50% or greater are required to achieve a dielectric strength greater than or equal to SF 6 . Pure C 4 F 7 N demonstrated higher electric field hold-off for longer time periods and less statistical variance under pulsed conditions when compared to SF 6 . Mixtures of 50%C 4 F 7 N with N 2 or CO 2 as buffer gases showed no appreciable difference in pulsed dielectric strength.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Mechanism of the cadherin–catenin F-actin catch bond interaction

Mechanotransduction at cell–cell adhesions is crucial for the structural integrity, organization, and morphogenesis of epithelia. At cell–cell junctions, ternary E-cadherin/β-catenin/αE-catenin complexes sense and transmit mechanical load by binding to F-actin. The interaction with F-actin, described as a two-state catch bond, is weak in solution but is strengthened by applied force due to force-dependent transitions between weak and strong actin-binding states. Here, we provide direct evidence from optical trapping experiments that the catch bond property principally resides in the αE-catenin actin-binding domain (ABD). Consistent with our previously proposed model, the deletion of the first helix of the five-helix ABD bundle enables stable interactions with F-actin under minimal load that are well described by a single-state slip bond, even when αE-catenin is complexed with β-catenin and E-cadherin. Our data argue for a conserved catch bond mechanism for adhesion proteins with structurally similar ABDs. We also demonstrate that a stably bound ABD strengthens load-dependent binding interactions between a neighboring complex and F-actin, but the presence of the other αE-catenin domains weakens this effect. These results provide mechanistic insight to the cooperative binding of the cadherin–catenin complex to F-actin, which regulate dynamic cytoskeletal linkages in epithelial tissues.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1972

Measured performance of a 1089 K (1500 deg F) heat storage device for sun-shade orbital missions

Tubes designed for a solar heat receiver to serve as an energy source for a Brayton power system were tested for 2002 hours and 1251 sun-shade cycles. The tubes were designed to transfer a constant thermal input to the Brayton system during an orbit. Excess solar energy during a sun period is stored as heat of fusion of lithium fluoride. The niobium - 1% zirconium tubes accommodate the 23 percent volume decrease of LiF during freezing. Test results showed slight, local distortions. The gas discharge temperature varied from 16 K (29 F) below to 28 K (50 F) above the nominal value of 1089 K (1500 F). The tube surface temperatures ranged from 1039 K (1410 F) to 1183 K (1670 F).

Namkoong, D.↗
NASA NTRS1972

The P prime(f) to N(h) inversion problem in ionospheric soundings

A general review is given of the inversion techniques used to derive the ionospheric electron density N as a function of altitude h from group path P versus frequency f measurements obtained by vertical incidence ionospheric sounders. The paper discusses the medium under investigation, the experimental techniques used to obtain the P(f) data, the theoretical considerations leading to the integral equation relating P(f) to N(h), and the assumptions made in the inversion process. The lamination inversion technique is then presented, with special attention given to mathematical difficulties arising from discontinuities in the P(f) function, infinities in the integrand, and in some cases unknown integration limits. Methods outlined for minimizing the uncertainties due to discontinuities include the use of redundant information - that is the two distinct P(f) functions available for a given N(h) profile - and the use of models based on statistical data. Mathematical procedures are discussed that increase significantly the efficiency and accuracy of the required numerical integrations. The accuracy of the inversion technique is deduced by comparing the resulting N(h) profile with N(h) data obtained by simultaneous but independent observations.

Jackson, J. E.↗
NASA NTRS1985

A theoretical model of artificial spread F echoes

A theoretical model is developed for artificial spread F echoes elicited by irradiating the ionospheric F region with signals from ground-based HF transmitters. Account is taken of the irregularity polarizations, scale length and the magnetic dip angle of the echo. Ray tracing equations are defined for wave propagation in a horizontally stratified ionosphere which has been bathed with HF signals and therefore contains wavelike structures. Irregularities polarized within the meridian plane are found to cause the spread F echoes, while perpendicularly polarized irregularities do not. A magnetic dip angle of 5 deg must be exceeded for the spread F to become strong. The irregularities need scale lengths exceeding 100 m. Modes of operation are identified for inducing the required spread F echoes using ground-based radiotelescopes.

Kuo, S. P.↗
NASA NTRS1986

The importance of diffuse f functions for transition metals

The importance of a diffuse f function for determining the dissociation energy (De) of Cu2 and the 3F-3D energy separation in Ni atom is investigated. It is found that the diffuse f contributes at most 0.05 eV to the De of Cu2 when added to a basis containing tight f functions and a flexibly contracted d basis. The diffuse f function is found to decrease the 3F-3D separation in Ni, but by substantially less than the tight f functions.

Langhoff, S. R.↗
NASA NTRS1986

The generation of kilometer scale irregularities in equatorial spread F

Two rockets launched into spread F during March 1983 show that the intermediate-scale spectrum of density irregularities sometimes exhibits a knee near 1 km scale length. This result confirms previous reports which are reviewed. Two different nonlinear theories of spread F turbulence are studied here and shown to be consistent with the experimental spectra when the knee is observed. Also, the existence or nonexistence of the knee may be effected by two linear mechanisms: the injection of kilometer scale turbulence at the steepened walls of spread F bubbles and the nonlocal role of the compressible E region in the development of spread F. This spectral feature, which seems to be associated with the most turbulent state of equatorial spread F, has not yet been identified in computer simulations.

Labelle, J.↗
NASA NTRS1992

The effects of magnetic storm phases on F-layer irregularities

The effects of magnetic storm phases on F-layer irregularities from auroral to equatorial latitudes in a nearly constant western longitude zone are presented by considering scintillation, spread F, and low-energy (less than 12 eV) electron precipitation data for eight magnetic storms that occurred during the high solar flux period September-November 1981. In the equatorial region, F-layer irregularities can be inhibited during the main phase. In the high latitude region, F-layer irregularities are found to be generated at the auroral latitudes during the main phase. During the recovery phase, when there are conditions of low magnetic activity, low auroral irregularities, and low-energy electron precipitation crossing the subauroral regions, strong F-layer irregularities are found to be generated in the subauroral regions.

Balan, N.↗
NASA NTRS1996

Ground-Recorded Sonic Boom Signatures of F-18 Aircraft in Formation Flight

Two F-18 aircraft were flown, one above the other, in two formations, in order for the shock systems of the two aircraft to merge and propagate to the ground. The first formation had the canopy of the lower F-18 in the tail shock of the upper F-18 (called tail-canopy). The second formation had the canopy of the lower F- 18 in the inlet shock of the upper F-18 (called inlet-canopy). The flight conditions were Mach 1.22 and an altitude of 23,500 ft . An array of five sonic boom recorders was used on the ground to record the sonic boom signatures. This paper describes the flight test technique and the ground level sonic boom signatures. The tail-canopy formation resulted in two, separated, N-wave signatures. Such signatures probably resulted from aircraft positioning error. The inlet-canopy formation yielded a single modified signature; two recorders measured an approximate flattop signature. Loudness calculations indicated that the single inlet-canopy signatures were quieter than the two, separated tail-canopy signatures. Significant loudness occurs after a sonic boom signature. Such loudness probably comes from the aircraft engines.

Bahm, Catherine M.↗
NASA NTRS1997

Radiation Near 2f(sub p) and Intensified Emissions Near f(sub p) in the Dayside and Nightside Auroral Region and Polar Cap

This paper reports the discovery in the DE 1 data of propagating radiation near 2f(sub p) (the H component) and relatively intense electromagnetic waves near f(sub p) with fields typically less than or approximately equal to 1 mV/m (the PF or plasma frequency component) on both the dayside and the nightside of Earth. These emissions are observed at auroral and polar cap latitudes for radial distances ranging from 2.5 to 4.5 R(sub E). The H component is unique in that no other 2f(sub p) emissions are known to be generated where the electron gyrofrequency f(sub g) exceeds 2f(sub p). Since existing theories for 2f(sub p) radiation assume f(sub g)/f(sub p) less than 1, new theories will be required to explain the H component. The PF waves near f(sub p) are electromagnetic, but with large ratios E/cB approximately 20. On the basis of cold plasma theory, the wave frequencies and the ratios E/cB, the PF component plausibly consists of zeta-mode and/or whistler mode waves near f(sub p), presumably driven by an electron instability. The H emissions have modest bandwidths of approximately 50% at frequencies ranging from 5 to 20 kHz. Grounds for interpreting the H component as emissions generated near 2f(sub p) are provided by the very good frequency tracking of the PF and H components and typical frequency ratios near 2.0. Strong evidence exists that part of the H component is propagating, electromagnetic radiation, based on propagation effects and spin modulation patterns. However, no magnetic signals have yet been detected for the H component, so that it could be partly electrostatic. Cold plasma theory and the observed wave characteristics favor interpreting the H component as composed of omicron mode and/or zeta mode signals. Combining the DE 1 observations with rocket observations, it is predicted that the much more intense Langmuir-like fields observed in the low altitude auroral zones should also generate observable 2f(sub p) radiation. This prediction should be testable using Polar and future rocket flights. Directions for future research are also described.

Cairns, Iver H.↗
NASA NTRS2000

Fin Buffeting Features of an Early F-22 Model

Fin buffeting is an aeroelastic phenomenon encountered by high performance aircraft, especially those with twin vertical tails that must operate at high angles of attack. This buffeting is a concern from fatigue and inspection points of view. To date, the buffet (unsteady pressures) and buffeting (structural response) characteristics of the F-15 and F/A-18 fins have been studied extensively using flow visualization, flow velocity measurements, pressure transducers, and response gages. By means of windtunnel and flight tests of the F-15 and F/A-18, this phenomenon is well studied to the point that buffet loads can be estimated and fatigue life can he increased by structural enhancements to these airframes. However, prior to the present research, data was not available outside the F-22 program regarding fin buffeting on the F-22 configuration. During a test in the Langley Transonic Dynamics Tunnel, flow visualization and unsteady fin surface pressures were recorded for a 13.3%-scale F-22 model at high angles of attack for the purpose of comparing with results available for similar aircraft configurations. Details of this test and fin buffeting are presented herein.

Moses, Robert W.↗
NASA NTRS2000

Results From F-18B Stability and Control Parameter Estimation Flight Tests at High Dynamic Pressures

A maximum-likelihood output-error parameter estimation technique has been used to obtain stability and control derivatives for the NASA F-18B Systems Research Aircraft. This work has been performed to support flight testing of the active aeroelastic wing (AAW) F-18A project. The goal of this research is to obtain baseline F-18 stability and control derivatives that will form the foundation of the aerodynamic model for the AAW aircraft configuration. Flight data have been obtained at Mach numbers between 0.85 and 1.30 and at dynamic pressures ranging between 600 and 1500 lbf/sq ft. At each test condition, longitudinal and lateral-directional doublets have been performed using an automated onboard excitation system. The doublet maneuver consists of a series of single-surface inputs so that individual control-surface motions cannot be correlated with other control-surface motions. Flight test results have shown that several stability and control derivatives are significantly different than prescribed by the F-18B aerodynamic model. This report defines the parameter estimation technique used, presents stability and control derivative results, compares the results with predictions based on the current F-18B aerodynamic model, and shows improvements to the nonlinear simulation using updated derivatives from this research.

Moes, Timothy R.↗
NASA NTRS2003

Anharmonic Vibrational Spectroscopy of the F-(H20)n, complexes, n=1,2

We report anharmonic vibrational spectra (fundamentals, first overtones) for the F-(H(sub 2)O) and F-(H(sub 2)O)2 clusters computed at the MP2 and CCSD(T) levels of theory with basis sets of triple zeta quality. Anharmonic corrections were estimated via the correlation-corrected vibrational self-consistent field (CC-VSCF) method. The CC-VSCF anharmonic spectra obtained on the potential energy surfaces evaluated at the CCSD(T) level of theory are the first ones reported at a correlated level beyond MP2. We have found that the average basis set effect (TZP vs. aug-cc-pVTZ) is on the order of 30-40 cm(exp -1), whereas the effects of different levels of electron correlation [MP2 vs. CCSD(T)] are smaller, 20-30 cm(exp -1). However, the basis set effect is much larger in the case of the H-bonded O-H stretch of the F-(H(sub 2)O) cluster amounting to 100 cm(exp -1) for the fundamentals and 200 cm (exp -1) for the first overtones. Our calculations are in agreement with the limited available set of experimental data for the F-(H(sub 2)O) and F-(H(sub 2)O)2 systems and provide additional information that can guide further experimental studies.

Chaban, Galina M.↗
NASA NTRS2003

Independent Review of the Failure Modes of F-1 Engine and Propellants System

The F-1 is the powerful engine, that hurdled the Saturn V launch vehicle from the Earth to the moon on July 16,1969. The force that lifted the rocket overcoming the gravitational force during the first stage of the flight was provided by a cluster of five F-1 rocket engines, each of them developing over 1.5 million pounds of thrust (MSFC-MAN-507). The F-1 Rocket engine used RP-1 (Rocket Propellant-1, commercially known as Kerosene), as fuel with lox (liquid Oxygen) as oxidizer. NASA terminated Saturn V activity and has focused on Space Shuttle since 1972. The interest in rocket system has been revived to meet the National Launch System (NLS) program and a directive from the President to return to the Moon and exploration of the space including Mars. The new program Space Launch Initiative (SLI) is directed to drastically reduce the cost of flight for payloads, and adopt a reusable launch vehicle (RLV). To achieve this goal it is essential to have the ability of lifting huge payloads into low earth orbit. Probably requiring powerful boosters as strap-ons to a core vehicle, as was done for the Saturn launch vehicle. The logic in favor of adopting Saturn system, a proven technology, to meet the SLI challenge is very strong. The F-1 engine was the largest and most powerful liquid rocket engine ever built, and had exceptional performance. This study reviews the failure modes of the F-1 engine and propellant system.

Ray, Paul↗
NASA NTRS2004

Flight Test Results for the F-16XL With a Digital Flight Control System

In the early 1980s, two F-16 airplanes were modified to extend the fuselage length and incorporate a large area delta wing planform. These two airplanes, designated the F-16XL, were designed by the General Dynamics Corporation (now Lockheed Martin Tactical Aircraft Systems) (Fort Worth, Texas) and were prototypes for a derivative fighter evaluation program conducted by the United States Air Force. Although the concept was never put into production, the F-16XL prototypes provided a unique planform for testing concepts in support of future high-speed supersonic transport aircraft. To extend the capabilities of this testbed vehicle the F-16XL ship 1 aircraft was upgraded with a digital flight control system. The added flexibility of a digital flight control system increases the versatility of this airplane as a testbed for aerodynamic research and investigation of advanced technologies. This report presents the handling qualities flight test results covering the envelope expansion of the F-16XL with the digital flight control system.

Stachowiak, Susan J.↗
NASA NTRS2004

F-OWL: An Inference Engine for Semantic Web

Understanding and using the data and knowledge encoded in semantic web documents requires an inference engine. F-OWL is an inference engine for the semantic web language OWL language based on F-logic, an approach to defining frame-based systems in logic. F-OWL is implemented using XSB and Flora-2 and takes full advantage of their features. We describe how F-OWL computes ontology entailment and compare it with other description logic based approaches. We also describe TAGA, a trading agent environment that we have used as a test bed for F-OWL and to explore how multiagent systems can use semantic web concepts and technology.

Zou, Youyong↗