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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 595 records · Page 33

Kinetic model of turbulence in an incompressible fluid

A statistical description of turbulence in an incompressible fluid obeying the Navier-Stokes equations is proposed, where pressure is regarded as a potential for the interaction between fluid elements. A scaling procedure divides a fluctuation into three ranks representing the three transport processes of macroscopic evolution, transport property, and relaxation. Closure is obtained by relaxation, and a kinetic equation is obtained for the fluctuation of the macroscopic rank of the distribution function. The solution gives the transfer function and eddy viscosity. When applied to the inertia subrange of the energy spectrum the analysis recovers the Kolmogorov law and its numerical coefficient.

Tchen, C. M.↗

Design and analytical study of a rotor airfoil

An airfoil section for use on helicopter rotor blades was defined and analyzed by means of potential flow/boundary layer interaction and viscous transonic flow methods to meet as closely as possible a set of advanced airfoil design objectives. The design efforts showed that the first priority objectives, including selected low speed pitching moment, maximum lift and drag divergence requirements can be met, though marginally. The maximum lift requirement at M = 0.5 and most of the profile drag objectives cannot be met without some compromise of at least one of the higher order priorities.

Dadone, L. U.↗

Propeller slipstream/wing interaction in the transonic regime

An inviscid model for the interaction between a thin wing and a nearly uniform propeller slipstream is presented. The model allows the perturbation velocities due to the interaction to be potential although the undisturbed slipstream velocity is rotational. A finite difference scheme is used to solve the governing equation. Numerical examples indicate that the slipstream has a strong effect on the aerodynamic properties of the wing section within the slipstream and lesser effects elsewhere. The slipstream swirling motion strongly affects the wing load distribution, however, its effect on the wing's total lift and wave drag is small. The axial velocity increment in the slipstream has a small effect on the wing lift, however, it causes a large increase in wave drag.

Rizk, M. H.↗

Higher-order structure of rRNA

A comparative search for phylogenetically covarying basepair replacements within potential helices has been the only reliable method to determine the correct secondary structure of the 3 rRNAs, 5S, 16S, and 23S. The analysis of 16S from a wide phylogenetic spectrum, that includes various branches of the eubacteria, archaebacteria, eucaryotes, in addition to the mitochondria and chloroplast, is beginning to reveal the constraints on the secondary structures of these rRNAs. Based on the success of this analysis, and the assumption that higher order structure will also be phylogenetically conserved, a comparative search was initiated for positions that show co-variation not involved in secondary structure helices. From a list of potential higher order interactions within 16S rRNA, two higher-order interactions are presented. The first of these interactions involves positions 570 and 866. Based on the extent of phylogenetic covariation between these positions while maintaining Watson-Crick pairing, this higher-order interaction is considered proven. The other interaction involves a minimum of six positions between the 1400 and 1500 regions of the 16S rRNA. Although these patterns of covariation are not as striking as the 570/866 interaction, the fact that they all exist in an anti-parallel fashion and that experimental methods previously implicated these two regions of the molecule in tRNA function suggests that these interactions be given serious consideration.

Gutell, R. R.↗

Attitude and articulation control concepts for the Earth Observing System

A study of pointing requirements and control approaches for the Earth Observing System, EOS, is presented. The proposed instrument set includes several massive instruments with varied articulation requirements, and pointing control requirements in several cases tighter than 0.01 degrees. Approaches to multipayload control and stability are explored, including: (a) the use of interconnected but dynamically isolated payload modules on a large platform, each with independent inertial control, and (b) precision basebody control of smaller platforms, with momentum compensated articulation and on-orbit dynamic balancing of spin-scan instruments. Results from multibody spacecraft models highlight potential payload dynamic interaction problems and suggest the need for dynamic isolation and disturbance rejection control techniques.

Bell, C. E.↗

High speed turboprop aeroacoustic study (single rotation). Volume 1: Model development

A frequency-domain noncompact-source theory for the steady loading and volume-displacement (thickness) noise of high speed propellers has been developed and programmed. Both near field and far field effects have been considered. The code utilizes blade surface pressure distributions obtained from three-dimensional nonlinear aerodynamic flow field analysis programs as input for evaluating the steady loading noise. Simplified mathematical models of the velocity fields induced at the propeller disk by nearby wing and fuselage surfaces and by angle-of-attack operation have been developed to provide estimates of the unsteady loading imposed on the propeller by these potential field type interactions. These unsteady blade loadings have been coupled to a chordwise compact propeller unsteady loading noise model to provide predictions of unsteady loading noise caused by these installation effects. Finally, an analysis to estimate the corrections to be applied to the free-field noise predictions in order to arrive at the measurable fuselage sound pressure levels has been formulated and programmed. This analysis considers the effects of fuselage surface reflection and diffraction together with surface boundary layer refraction. The steady loading and thickness model and the unsteady loading model have been verified using NASA-supplied data for the SR-2 and SR-3 model propfans. In addition, the steady loading and thickness model has been compared with data from the SR-6 model propfan. These theoretical models have been employed in the evaluation of the SR-7 powered Gulfstream aircraft in terms of noise characteristics at representative takeoff, cruise, and approach operating conditions. In all cases, agreement between theory and experiment is encouraging.

Whitfield, C. E.↗

The behavior of outgassed materials in thermal vacuums

Scientists at the NASA White Sands Test Facility (WSTF) are investigating the relationship between outgassing and condensation for aerospace materials in space-like environments. The WSTF throughput test method was validated by previous testing at WSTF using palmitic acid. Data from these tests were compared with data from other preliminary tests by using adipic and behenic acids. The comparison indicates that surface forces between outgassed molecules and the condensing surfaces cause the condensation flux to be different from the incident flux. These forces can also cause the evaporative flux to be different from the expected value. These discrepancies are discussed in terms of both potential and dynamic interactions of outgassed molecules with surfaces. Although these surface forces are noticeable, their overall effect on the test is minimal.

Mahone, William↗

Issues in CSI analysis for large scale systems

Future spacecraft such as the International Space Station result in flexible models with hundreds, or perhaps thousands of modes in a frequency range where the potential for control/structure interaction exists. This provides the analyst with a formidable model reduction problem at both the component and the system level. Approaches to normal modes as a structural representation, applicability of alternate structural representations and algorithms for selecting important modal degrees of freedom at both the component and the system level are discussed. Practical implementation of these techniques on a large scale model of the Space Station are presented.

Blelloch, Paul↗

Dynamics of phase separation of binary fluids

The results of molecular-dynamics studies of surface-tension-dominated spinodal decomposition of initially well-mixed binary fluids in the absence and presence of gravity are presented. The growth exponent for the domain size and the decay exponent of the potential energy of interaction between the two species with time are found to be 0.6 +/- 0.1, inconsistent with scaling arguments based on dimensional analysis.

Ma, Wen-Jong↗

Advanced electromagnetic methods for aerospace vehicles

During this period the research program addressed the following three topics: (1) composite materials; (2) precipitation static (P-Static); and (3) antenna technology. On the topic of Composite Materials our main efforts were directed toward making measurements on several new samples of composite materials made available to ASU by Stanford Research Institute (SRI) through the efforts of Mr. Frank Casler of AVRADA. These samples can be classified into three distinct materials with each material having its own distinct electrical properties. In addition, attempts were made to make predictions of the effects on antenna patterns by composite materials. This will take a greater emphasis in the next reporting period. In Precipitation Static (P-Static), the main effort was devoted toward developing a Voltage Finite-Difference Time-Domain computer code to account for the voltage variation on a conducting body as the primary source of corona discharge, instead of the electric field. Due to complexities stemming from the interactions between the potentials, the fields, and current sources, the decision was made to begin with a simple two-dimensional problem without the corona discharge and check our programs in a series of simple models, culminating in the full corona discharge problem. This report deals with the first stage of such development. During this reporting period, the main effort in Antenna Technology was toward the design, fabrication, and testing of a cavity-backed slot antenna using ferrite material. Using the ferrite material available to us during this period, the resonances of this antenna were around 5 and 8 GHz. Attempts will be made to model such an antenna and to lower its resonance down into the VHF and UHF bands.

Balanis, Constantine A.↗

Large area mapping of soil moisture using the ESTAR passive microwave radiometer

Investigations designed to study land surface hydrologic-atmospheric interactions, showing the potential of L band passive microwave radiometry for measuring surface soil moisture over large areas, are discussed. Satisfying the data needs of these investigations requires the ability to map large areas rapidly. With aircraft systems this means a need for more beam positions over a wider swath on each flightline. For satellite systems the essential problem is resolution. Both of these needs are currently being addressed through the development and verification of Electronically Scanned Thinned Array Radiometer (ESTAR) technology. The ESTAR L band radiometer was evaluated for soil moisture mapping applications in two studies. The first was conducted over the semiarid rangeland Walnut Gulch watershed located in south eastern Arizona (U.S.). The second was performed in the subhumid Little Washita watershed in south west Oklahoma (U.S.). Both tests showed that the ESTAR is capable of providing soil moisture with the same level of accuracy as existing systems.

Jackson, T. J.↗

The Effect of Surface Induced Flows on Bubble and Particle Aggregation

Almost 20 years have elapsed since a phenomenon called "radial specific coalescence" was identified. During studies of electrolytic oxygen evolution from the back side of a vertically oriented, transparent tin oxide electrode in alkaline electrolyte, one of the authors (Sides) observed that large "collector" bubbles appeared to attract smaller bubbles. The bubbles moved parallel to the surface of the electrode, while the electric field was normal to the electrode surface. The phenomenon was reported but not explained. More recently self ordering of latex particles was observed during electrophoretic deposition at low DC voltages likewise on a transparent tin oxide electrode. As in the bubble work, the field was normal to the electrode while the particles moved parallel to it. Fluid convection caused by surface induced flows (SIF) can explain these two apparently different experimental observations: the aggregation of particles on an electrode during electrophoretic deposition, and a radial bubble coalescence pattern on an electrode during electrolytic gas evolution. An externally imposed driving force (the gradient of electrical potential or temperature), interacting with the surface of particles or bubbles very near a planar conducting surface, drives the convection of fluid that causes particles and bubbles to approach each other on the electrode.

Guelcher, Scott A.↗

Advanced Keyboard

Using chordic technology, a data entry operator can finger key combinations for text or graphics input. Because only one hand is needed, a disabled person may use it. Strain and fatigue are less than when using a conventional keyboard; input is faster, and the system can be learned in about an hour. Infogrip, Inc. developed chordic input technology with Stennis Space Center (SSC). (NASA is interested in potentially faster human/computer interaction on spacecraft as well as a low cost tactile/visual training system for the handicapped.) The company is now marketing the BAT as an improved system for both disabled and non-disabled computer operators.

Source record↗

Do vestibular otolith organs participate in human orthostatic blood pressure control?

We hypothesized that vestibular otolith organ stimulation contributes to human orthostatic responses. Twelve subjects underwent three 60 degrees upright tilts: (1) with the neck flexed from 0 degrees to 30 degrees relative to the body during 60 degrees tilt, such that the head moved from horizontal to 90 degrees above horizontal (0 to 1 Gz otolith stimulation); (2) with the head and body aligned, such that they tilted together to 60 degrees (0 to 0.87 Gz otolith stimulation); and (3) with the neck flexed 30 degrees relative to the body during supine conditions, and the neck then extended to -30 degrees during 60 degrees body tilting, such that the head remained at 30 degrees above horizontal throughout body tilting (constant 0.5 Gz otolith stimulation). All three tilt procedures increased thoracic impedance, sympathetic nerve activity (N = 8 of 12), arterial pressure, and heart rate relative to supine conditions (all P < 0.04). Within the first 20 s of tilt, arterial pressure increased most obviously in the 0 to 1 Gz otolith condition. Thoracic impedance tended to increase more in otolith-constant conditions, but no dependent variable differed significantly between tilt conditions, and no significant time x tilt interactions emerged. Otolith inputs may contribute to early transient adjustments to orthostasis. However, lack of significant main effects of tilt condition and time x tilt interactions suggests that potential otolith effects on the variables we studied are relatively subtle and ephemeral, or that other mechanisms compensate for a lack of change in otolith input with orthostasis.

Non-NASA Center↗

Red light regulation of ethylene biosynthesis and gravitropism in etiolated pea stems

During gravitropism, the accumulation of auxin in the lower side of the stem causes increased growth and the subsequent curvature, while the gaseous hormone ethylene plays a modulating role in regulating the kinetics of growth asymmetries. Light also contributes to the control of gravitropic curvature, potentially through its interaction with ethylene biosynthesis. In this study, red-light pulse treatment of etiolated pea epicotyls was evaluated for its effect on ethylene biosynthesis during gravitropic curvature. Ethylene biosynthesis analysis included measurements of ethylene; the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC); malonyl-conjugated ACC (MACC); and expression levels of pea ACC oxidase (Ps-ACO1) and ACC synthase (Ps-ACS1, Ps-ACS2) genes by reverse transcriptase-polymerase chain reaction analysis. Red-pulsed seedlings were given a 6 min pulse of 11 micromoles m-2 s-1 red-light 15 h prior to horizontal reorientation for consistency with the timeline of red-light inhibition of ethylene production. Red-pulse treatment significantly reduced ethylene production and MACC levels in epicotyl tissue. However, there was no effect of red-pulse treatment on ACC level, or expression of ACS or ACO genes. During gravitropic curvature, ethylene production increased from 60 to 120 min after horizontal placement in both control and red-pulsed epicotyls. In red-pulsed tissues, ACC levels increased by 120 min after horizontal reorientation, accompanied by decreased MACC levels in the lower portion of the epicotyl. Overall, our results demonstrate that ethylene production in etiolated epicotyls increases after the initiation of curvature. This ethylene increase may inhibit cell growth in the lower portion of the epicotyl and contribute to tip straightening and reduced overall curvature observed after the initial 60 min of curvature in etiolated pea epicotyls.

Non-NASA Center↗

Cloud Optical Depth Retrievals from Solar Background "signal" of Micropulse Lidars

Pulsed lidars are commonly used to retrieve vertical distributions of cloud and aerosol layers. It is widely believed that lidar cloud retrievals (other than cloud base altitude) are limited to optically thin clouds. Here we demonstrate that lidars can retrieve optical depths of thick clouds using solar background light as a signal, rather than (as now) merely a noise to be subtracted. Validations against other instruments show that retrieved cloud optical depths agree within 10-15% for overcast stratus and broken clouds. In fact, for broken cloud situations one can retrieve not only the aerosol properties in clear-sky periods using lidar signals, but also the optical depth of thick clouds in cloudy periods using solar background signals. This indicates that, in general, it may be possible to retrieve both aerosol and cloud properties using a single lidar. Thus, lidar observations have great untapped potential to study interactions between clouds and aerosols.

Chiu, J. Christine↗

Anomalous Thrust Production from an RF Test Device Measured on a Low-Thrust Torsion Pendulum

This paper describes the eight-day August 2013 test campaign designed to investigate and demonstrate viability of using classical magnetoplasmadynamics to obtain a propulsive momentum transfer via the quantum vacuum virtual plasma. This paper will not address the physics of the quantum vacuum plasma thruster, but instead will describe the test integration, test operations, and the results obtained from the test campaign. Approximately 30-50 micro-Newtons of thrust were recorded from an electric propulsion test article consisting primarily of a radio frequency (RF) resonant cavity excited at approximately 935 megahertz. Testing was performed on a low-thrust torsion pendulum that is capable of detecting force at a single-digit micronewton level, within a stainless steel vacuum chamber with the door closed but at ambient atmospheric pressure. Several different test configurations were used, including two different test articles as well as a reversal of the test article orientation. In addition, the test article was replaced by an RF load to verify that the force was not being generated by effects not associated with the test article. The two test articles were designed by Cannae LLC of Doylestown, Pennsylvania. The torsion pendulum was designed, built, and operated by Eagleworks Laboratories at the NASA Johnson Space Center of Houston, Texas. Approximately six days of test integration were required, followed by two days of test operations, during which, technical issues were discovered and resolved. Integration of the two test articles and their supporting equipment was performed in an iterative fashion between the test bench and the vacuum chamber. In other words, the test article was tested on the bench, then moved to the chamber, then moved back as needed to resolve issues. Manual frequency control was required throughout the test. Thrust was observed on both test articles, even though one of the test articles was designed with the expectation that it would not produce thrust. Specifically, one test article contained internal physical modifications that were designed to produce thrust, while the other did not (with the latter being referred to as the "null" test article). Test data gathered includes torsion pendulum displacement measurements which are used to calculate generated force, still imagery in the visible spectrum to document the physical configuration, still imagery in the infrared spectrum to characterize the thermal environment, and video imagery. Post-test data includes static and animated graphics produced during RF resonant cavity characterization using the COMSOL Multiphysics® software application. Excerpts from all of the above are included and discussed in this paper. Lessons learned from test integration and operations include identification of the need to replace manual control of the resonant cavity target frequency with an automated frequency control capability. Future test plans include the development of an automatic frequency control circuit. Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma. Future test plans include independent verification and validation at other test facilities.

Brady, David↗