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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Hindlimb suspension diminishes femoral cross-sectional growth in the rat

Growth, functional adaptation, and torsional strength were examined in the femora of 39-day-old male Sprague-Dawley rats subjected to hindlimb suspension for 0, 1, 2, 3, or 4 weeks and were compared with measurements for age-matched control animals. Our goal was to understand the effect of reduced loading on the normal age-related changes in femoral properties during growth. The control animals exhibited growth-related increases in all geometric and torsional properties of the femur. The mean body mass and femoral length of the hindlimb-suspended rats were similar to those of the controls throughout the experiment. Over 4 weeks, the femoral cross-sectional and torsional measurements from the hindlimb-suspended rats demonstrated increases in comparison with the basal values (+33% cross-sectional area, +64% polar moment of inertia, +67% ultimate torque, and +181% torsional rigidity), but the age-matched controls showed significantly greater growth-related increases (+71% cross-sectional area, +136% polar moment of inertia, +127% ultimate torque, and +367% torsional rigidity). The differences in femoral structural strength between the hindlimb-suspended animals and the age-matched controls were attributable to differences in altered cross-sectional geometry.

NASA Discipline Musculoskeletal↗
NASA NTRS1995

Risk cross sections and their application to risk estimation in the galactic cosmic-ray environment

Radiation risk cross sections (i.e. risks per particle fluence) are discussed in the context of estimating the risk of radiation-induced cancer on long-term space flights from the galactic cosmic radiation outside the confines of the earth's magnetic field. Such quantities are useful for handling effects not seen after low-LET radiation. Since appropriate cross-section functions for cancer induction for each particle species are not yet available, the conventional quality factor is used as an approximation to obtain numerical results for risks of excess cancer mortality. Risks are obtained for seven of the most radiosensitive organs as determined by the ICRP [stomach, colon, lung, bone marrow (BFO), bladder, esophagus and breast], beneath 10 g/cm2 aluminum shielding at solar minimum. Spectra are obtained for excess relative risk for each cancer per LET interval by calculating the average fluence-LET spectrum for the organ and converting to risk by multiplying by a factor proportional to R gamma L Q(L) before integrating over L, the unrestricted LET. Here R gamma is the risk coefficient for low-LET radiation (excess relative mortality per Sv) for the particular organ in question. The total risks of excess cancer mortality obtained are 1.3 and 1.1% to female and male crew, respectively, for a 1-year exposure at solar minimum. Uncertainties in these values are estimated to range between factors of 4 and 15 and are dominated by the biological uncertainties in the risk coefficients for low-LET radiation and in the LET (or energy) dependence of the risk cross sections (as approximated by the quality factor). The direct substitution of appropriate risk cross sections will eventually circumvent entirely the need to calculate, measure or use absorbed dose, equivalent dose and quality factor for such a high-energy charged-particle environment.

NASA Discipline Radiation Health↗
NASA NTRS1944

The Wall Interference of a Wind Tunnel of Elliptic Cross Section

The wall interference is obtained for a wind tunnel of elliptic section for the two cases of closed and open working sections. The approximate and exact methods used gave results in practically good agreement. Corresponding to the result given by Glauert for the case of the closed rectangular section, the interference is found to be a minimum for a ratio of minor to major axis of 1:square root of 6 This, however, is true only for the case where the span of the airfoil is small in comparison with the width of the tunnel. For a longer airfoil the favorable ellipse is flatter. In the case of the open working section the circular shape gives the minimum interference.

Tani, Itiro↗
NASA NTRS2005

Chapter 19A – Radar Cross Section

The material in this Section will provide the novice Flight Test Engineer (FTE) with a brief overview of the radar cross section (RCS) concept. Brief details of radar range descriptions, operations, target calibrations, and data reduction are included. It is noted that these range operations concentrate on the "static" test range rather than the much more sophisticated "dynamic" test range. The dynamic test range is what the FTE will probably work with. Radar reflectivity measurement has developed over the last two decades from a relatively simple endeavor involving the measurement of target RCS amplitude statistics to involving wide band, coherent systems that can measure high resolution images of targets as well as, in many cases, the polarization and phasing properties. This rapid growth in RCS technology has occurred because of the increased use of radar in today's commercial and military systems. In general, the goal for commercial systems is to enhance radar reflectivity, whereas the military goal is to reduce radar reflectivity. Also, classification and identification are important for military purposes because in adverse weather radar may be the only system that may be capable of separating enemy targets from friendly ones. This Section will discuss the fundamentals of RCS. Since the flight test techniques associated with RCS measurements are very similar to those of antenna pattern measurements, both will be presented at the same time in Section 19B Antenna Radiation Pattern Measurements.

Robert W Borek↗
NASA NTRS2006

Effects of Nuclear Cross Sections at Different Energies on the Radiation Hazard from Galactic Cosmic Rays

The radiation hazard for astronauts from galactic cosmic rays is a major obstacle in long duration human space explorations. Space radiation transport codes have been developed to calculate radiation environment on missions to the Moon, Mars or beyond. We have studied how uncertainties in fragmentation cross sections at different energies affect the accuracy of predictions from such radiation transport. We find that, in deep space, cross sections between 0.3 and 0.85 GeV/u usually have the largest effect on dose-equivalent behind shielding in solar minimum GCR environments, and cross sections between 0.85 and 1.2 GeV/u have the largest effect in solar maximum GCR environments. At the International Space Station, cross sections at higher energies have the largest effect due to the geomagnetic cutoff.

Lin, Z. W.↗
NASA NTRS2006

Electron Impact Excitation Cross Section Measurement for n=3 to n=2 Line Emission in Fe(17+) to Fe(23+)

We have measured the electron impact excitation cross sections for the strong iron L-shell 3 --> 2 lines of Fe XVIII to Fe XXIV at the EBIT-I electron beam ion trap using a crystal spectrometer and NASA-Goddard Space Flight Centers 6 x 6 pixel array microcalorimeter. The cross sections were determined by direct normalization to the well established cross section of radiative electron capture through a sophisticated model analysis which results in the excitation cross section for the strong Fe L-shell lines at multiple electron energies. This measurement is part of a laboratory X-ray astrophysics program utilizing the Livermore electron beam ion traps EBIT-I and EBIT-II.

Chen, H.↗
NASA NTRS2007

Novel Thin Film Sensor Technology for Turbine Engine Hot Section Components

Degradation and damage that develops over time in hot section components can lead to catastrophic failure of the turbine section of aircraft engines. A range of thin film sensor technology has been demonstrated enabling on-component measurement of multiple parameters either individually or in sensor arrays including temperature, strain, heat flux, and flow. Conductive ceramics are beginning to be investigated as new materials for use as thin film sensors in the hot section, leveraging expertise in thin films and high temperature materials. The current challenges are to develop new sensor and insulation materials capable of withstanding the extreme hot section environment, and to develop techniques for applying sensors onto complex high temperature structures for aging studies of hot propulsion materials. The technology research and development ongoing at NASA Glenn Research Center for applications to future aircraft, launch vehicles, space vehicles, and ground systems is outlined.

Wrbanek, John D.↗
NASA NTRS1999

Spanwise transition section for blended wing-body aircraft

A blended wing-body aircraft includes a central body, a wing, and a transition section which interconnects the body and the wing on each side of the aircraft. The two transition sections are identical, and each has a variable chord length and thickness which varies in proportion to the chord length. This enables the transition section to connect the thin wing to the thicker body. Each transition section has a negative sweep angle.

Hawley, Arthur V.↗
NASA NTRS2010

UV Absorption Cross Sections of Nitrous Oxide (N2O) and Carbon Tetrachloride (CCl4) Between 210 and 350 K and the Atmospheric Implications

Absorption cross sections of nitrous oxide (N2O) and carbon tetrachloride (CCl4) are reported at five atomic UV lines (184.95, 202.548, 206.200, 213.857, and 228.8 nm) at 27 temperatures in the range 210-350 K. In addition, UV absorption spectra of CCl4 are reported between 200-235 nm as a function of temperature (225-350 K). The results from this work are critically compared with results from earlier studies. For N2O, the present results are in good agreement with the current JPL recommendation enabling a reduction in the estimated uncertainty in the N2O atmospheric photolysis rate. For CCl4, the present cross section results are systematically greater than the current recommendation at the reduced temperatures most relevant to stratospheric photolysis. The new cross sections result in a 5-7% increase in the modeled CCl4 photolysis loss, and a slight decrease in the stratospheric lifetime, from 51 to 50 years, for present day conditions. The corresponding changes in modeled inorganic chlorine and ozone in the stratosphere are quite small. A CCl4 cross section parameterization for use in 37 atmospheric model calculations is presented.

Carlon, Nabilah Rontu↗
NASA NTRS2010

Economical Fabrication of Thick-Section Ceramic Matrix Composites

A method was developed for producing thick-section [>2 in. (approx.5 cm)], continuous fiber-reinforced ceramic matrix composites (CMCs). Ultramet-modified fiber interface coating and melt infiltration processing, developed previously for thin-section components, were used for the fabrication of CMCs that were an order of magnitude greater in thickness [up to 2.5 in. (approx.6.4 cm)]. Melt processing first involves infiltration of a fiber preform with the desired interface coating, and then with carbon to partially densify the preform. A molten refractory metal is then infiltrated and reacts with the excess carbon to form the carbide matrix without damaging the fiber reinforcement. Infiltration occurs from the inside out as the molten metal fills virtually all the available void space. Densification to <5 vol% porosity is a one-step process requiring no intermediate machining steps. The melt infiltration method requires no external pressure. This prevents over-infiltration of the outer surface plies, which can lead to excessive residual porosity in the center of the part. However, processing of thick-section components required modification of the conventional process conditions, and the means by which the large amount of molten metal is introduced into the fiber preform. Modification of the low-temperature, ultraviolet-enhanced chemical vapor deposition process used to apply interface coatings to the fiber preform was also required to accommodate the high preform thickness. The thick-section CMC processing developed in this work proved to be invaluable for component development, fabrication, and testing in two complementary efforts. In a project for the Army, involving SiC/SiC blisk development, nominally 0.8 in. thick x 8 in. diameter (approx. 2 cm thick x 20 cm diameter) components were successfully infiltrated. Blisk hubs were machined using diamond-embedded cutting tools and successfully spin-tested. Good ply uniformity and extremely low residual porosity (<2 percent) were achieved, the latter being far lower than that achieved with SiC matrix composites fabricated via CVI or PIP. The pyrolytic carbon/zirconium nitride interface coating optimized in this work for use on carbon fibers was incorporated in the SiC/SiC composites and yielded a >41 ksi (approx. 283 MPa) flexural strength.

Babcock, Jason↗
NASA NTRS2010

The Effect of New Ozone Cross Sections Applied to SBUV and TOMS Retrievals

The ozone cross sections as measured by Bass and Paur have been used for processing of SBUV and TOMS data since 1986. While these cross sections were a big improvement over those previously available, there were known minor problems with accuracy for wavelengths longward of 330 nm and with the temperature dependance. Today's requirements to separate stratospheric ozone from tropospheric ozone and for the derivation of minor species such as BrO and N02 place stringent new requirements on the accuracy needed. The ozone cross section measurements of Brion, Daumont, and Malicet (BDM) are being considered for use in UV-based ozone retrievals. They have much better resolution, an extended wavelength range, and a more consistent temperature dependance. Tests show that BDM retrievals exhibit lower retrieval residuals in the satellite data; i.e., they explain our measured atmospheric radiances more accurately. Total column ozone retrieved by the TOMS instruments is about 1.5% higher than before. Ozone profiles retrieved from SBUV using the new cross sections are lower in the upper stratosphere and higher in the lower stratosphere and troposphere.

McPeters, Richard D.↗
NASA NTRS2017

Carbonaceous Chondrite Thin Section Preparation

Carbonaceous chondrite meteorites have long posed a challenge for thin section makers. The variability in sample hardness among the different types, and sometimes within individual sections, creates the need for an adaptable approach at each step of the thin section making process. This poster will share some of the procedural adjustments that have proven to be successful at the NASA JSC Meteorite Thin Section Laboratory. These adjustments are modifications of preparation methods that have been in use for decades and therefore do not require investment in new technology or materials.

Harrington, R.↗
NASA NTRS2019

N2 and H2 Broadened Isobutane Infrared Absorption Cross Sections and Butane Upper Limits on Titan

High resolution infrared absorption cross sections of isobutane, (CH3)3CH, were measured in the 1050-1900 cm-1spectral range by Fourier transform spectroscopy. Four sample temperatures (210, 234, 265 and 296 K) were used with three pressures (10, 30 and 100 Torr) of N2and H2broadening gas. Spectra of pure isobutane samples were also recorded. These cross sections are useful for the interpretation of infrared spectra of the Giant Planets and Titan. The isobutane cross sections give an upper limit of 3.91e-8for its fractional abundance on Titan based on CIRS/Cassini infrared spectra. Using n-butane, CH3(CH2)2CH3, cross sections from the literature, we obtain an upper limit of 5.13e-7for its abundance on Titan. The combined upper limit for both isomers of butane, C4H10, on Titan of 5.52e-7is consistent with the lower limit of recent model predictions

Dan Hewett↗
NASA NTRSDate not supplied

Bistable Deployable Composite Booms With Parabolic Cross-Sections

This paper investigates how stable equilibrium states in the extended and coiled configurations can be predicted in thin-shelled composite booms with parabolic cross-sections. These conic shapes potentially offer greater stiffness properties when compared to circular cross-sections, which is critical for improving the load bearing performance of deployed booms. Inducing bistability through the choice of composite shell layups in parabolic booms would allow for controllable self-deployment due to a less energetic coiled state when compared to monostable booms. An inextensional analytical model is used to predict the stable coiled diameters of tape spring and Collapsible Tubular Mast (CTM) booms with parabolic cross-sections. The parabolic section is discretized into circular segments using biarc spline interpolation, which allows them to be integrated into the strain energy minimization procedure used to obtain the equilibrium states. When the parabolic booms are parametrically compared against circular booms with identical layups, flattened height, and mass, the former are found to generally have better stiffness performance while being less efficient in stowed volume as evidenced by larger coiled diameters. Analytical coiled diameters and their strain energy are verified with finite element simulations for optimal parabolic tape spring and CTM booms.

Andrew J. Lee↗
NASA NTRS1971

A numerical method of calculating the boundary-induced interference in slotted or perforated wind tunnels of rectangular cross section

A numerical method is presented for calculating the boundary-induced interference at subsonic speeds. The wind tunnel slot width or wall porosity can vary throughout the test section. The interference can be computed at any point in the test section. The model can be any configuration and can be located anywhere in the test section. Several examples are given, and comparison is made with other methods where available.

Keller, J. D.↗
NASA NTRS1972

Upper-Limit Charge Exchange Cross Sections for Mercury(+) on Molybdenum and Cesium(+) on Aluminum

Upper-limit charge exchange cross sections are calculated for Hg(+) on Mo and Cs(+) on Al. The cross sections are calculated from the polarization interaction at low ion energies (1 to 500 eV) and by assuming favorable curve crossings with a hard-core reaction radius at higher energies (500 eV to 10 keV). The cross sections for Hg(+) on Mo becomes greater than corresponding Hg Hg(+) resonance values at ion energies below 2 eV, whereas the Cs(+) Al values remain considerably lower than the Cs(+)Cs resonance value at all ion energies. It is also shown that charge exchange of slow Hg(+) with Mo may be important for spacecraft with electron bombardment thrusters.

Dugan, J. V., Jr.↗
NASA NTRS1972

Calculation of linearized supersonic flow over slender cones of arbitrary cross section

Supersonic linearized conical-flow theory is used to determine the flow over slender pointed cones having horizontal and vertical planes of symmetry. The geometry of the cone cross sections and surface velocities are expanded in Fourier series. The symmetry condition permits the uncoupling of lifting and nonlifting solutions. The present method reduces to Ward's theory for flow over a cone of elliptic cross section. Results are also presented for other shapes. Results by this method diverge for cross-sectional shapes where the maximum thickness is large compared with the minimum thickness. However, even for these slender-body shapes, lower order solutions are good approximations to the complete solution.

Mascitti, V. R.↗
NASA NTRS1972

Measurement of relative cross sections for simultaneous ionization and excitation of the helium 4 2s and 4 2p states

The relative cross sections for simultaneous ionization and excitation of helium by 200-eV electrons into the 4 2s and 4 2p states were measured via a fast delayed coincidence technique. Results show good agreement with the relative cross sections for single electron excitation of helium and hydrogen. An application of the results of the measurement to the development of ultraviolet intensity standard is suggested. This technique involves the use of known branching ratios, a visible light flux reference, and the measured relative cross sections.

Sutton, J. F.↗