SEARCH · Search NASA

Results for “sectionalizing”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7

All sources NASA NTRS DOE OSTI

NASA NTRS2005

Integral cross sections for the direct excitation of the A 3 (sigma) u +, B 3 (pi) g, W 3 (delta) u, B' 3 (sigma) u -, a' 1 (sigma) u -, a 1 (pi) g, w 1 (delta) u, and C 3 (pi) u electronic states in

Integral cross sections for electron impact excitation out of the ground state (X 1(sigma)g +) to the A 3(sigma)u +, B 3(pi)g, W 3(delta)u, B' 3(sigma)u -, a' 1(sigma)u -, a 1(pi)g, w 1(delta)u, and states in N2 are reported at incident energies ranging between 10 and 100 eV. These data have been derived by integrating differential cross sections previously reported by this group. New differential cross section measurements for the a 1(pi)g state at 200 eV are also presented to extend the range of the reported integral cross sections for this state, which is responsible for the emissions of the Lyman-Birge-Hopfield band system (a 1(pi)g (rightwards arrow) X 1(sigma)g +). The present results are compared and critically evaluated against existing cross sec In general, the present cross sections are smaller than previous results at low impact energies from threshold through the excitation function peak regions. These lower cross sections have potentially significant implications on our understanding of UV emissions in the atmospheres of Earth and Titan.

Ultraviolet Imaging Spectograph↗

NASA NTRS1970

The variation of radar cross section with wind

X-band (8910 megahertz) and C-band (4455 megahertz) measurements indicate that two domains exist in the variation of radar cross section with wind at incident angles far from the normal. The first domain for flow windspeeds is characterized by a rapid variation of radar cross section with wind and the second domain at higher windspeeds by an asymptotic approach to an upper limit (saturation). The transaction between the two domains occurs at a windspeed of approximately 10 knots. Recent Joint Ocean Surface Study I observations tend to confirm this observation and offer additional proof of the validity of a composite surface model which relates the radar cross section of the sea to the wave-height spectrum. This confirmation was obtained by comparing the radar cross section measured by the four-frequency radar system with the radar cross section calculated from the ocean wave-height spectrum that had been determined by the optical analysis of photographs taken at the same time. A possible explanation for the wind variation of the radar cross section of the open ocean also was evolved, based on radar measurements in a wave tank under various wind conditions and subsequent comparison with optically determined spectra.

Guinard, N. W.↗

NASA NTRS1973

Multidimensional analysis of fast-spectrum material replacement measurements for systematic estimation of cross section uncertainties

A series of central core and core-reflector interface sample replacement experiments for 16 materials performed in the NASA heavy-metal-reflected, fast spectrum critical assembly (NCA) were analyzed in four and 13 groups using the GAM 2 cross-section set. The individual worths obtained by TDSN and DOT multidimensional transport theory calculations showed significant differences from the experimental results. These were attributed to cross-section uncertainties in the GAM 2 cross sections. Simultaneous analysis of the measured and calculated sample worths permitted separation of the worths into capture and scattering components which systematically provided fast spectrum averaged correction factors to the magnitudes of the GAM 2 absorption and scattering cross sections. Several Los Alamos clean critical assemblies containing Oy, Ta, and Mo as well as one of the NCA compositions were reanalyzed using the corrected cross sections. In all cases the eigenvalues were significantly improved and were recomputed to within 1 percent of the experimental eigenvalue. A comparable procedure may be used for ENDF cross sections when these are available.

Klann, P. G.↗

NASA NTRS1974

NASA patent abstracts bibliography: A continuing bibliography. Section 1: Abstracts (supplement 05)

This bibliography is issued in two sections: Section 1 - Abstracts, and section 2 - Indexes. The abstract section cites 217 patents and applications for patent introduced into the NASA scientific and technical information system during the period of January 1974 through June 1974. Each entry consists of a citation, an abstract, and, in most cases, a key illustration selected from the patent or application for patent. The index section contains entries for 2653 patent and application for patent citations covering the period May 1969 through June 1974. The index section contains five indexes -- subject, inventor, source, number and accession number.

Source record↗

NASA NTRS1975

Effects of forward contour modification on the aerodynamic characteristics of the NACA 641-212 airfoil section

Two different forward contour modifications designed to increase the maximum lift coefficient of the NACA 64 sub 1-212 airfoil section were evaluated experimentally at low speeds. One modification consisted of a slight droop of the leading edge with an increased leading-edge radius; the other modification incorporated increased thickness over the forward 35 percent of the upper surface of the profile. Both modified airfoil sections were found to provide substantially higher maximum lift coefficients than the 64 sub 1-212 section. The drooped leading-edge modification incurred a drag penalty of approximately 10 percent at low and moderate lift coefficients and exhibited a greater nosedown pitching moment than the 64 sub 1-212 profile. The upper surface modification produced about the same drag level as the 64 sub 1-212 section at low and moderate lift coefficients and less nosedown pitching moment than the 64 sub 1-212 profile. Both modified airfoil sections had lower drag coefficients than the 64 sub 1-212 section at high lift coefficients.

Hicks, R. M.↗

NASA NTRS1977

An experimental estimate of the O/+/-O resonant charge transfer cross section, collision frequency, and energy transfer rate

The resonant-charge-transfer cross section dominates the interaction between neutral and ionized atomic oxygen at temperatures greater than several hundred degrees Kelvin. This cross section is of direct importance to F-region studies of ion diffusion, ion thermal balance, and neutral atmospheric winds and pressure gradients, since it determines collision frequencies and energy and momentum transfer rates. However, the uncertainty in this cross section is roughly 25-40%. Incoherent-scatter measurements allow determination of the product of the atomic oxygen concentration multiplied by the cross section. If present-day atmospheric models are accepted as statistically representative of F-region atomic oxygen concentrations experimental (aeronomical) data presented indicate that the resonant-charge-transfer cross section is about 1.3 times greater than the value presently in general use, though in excellent agreement with the only other available (laboratory) experimental value. This revised cross section has obvious implications for thermospheric studies.

Carlson, H. C.↗

NASA NTRS1978

Model potentials for electron scattering - Converged close coupling calculations for the differential cross section for e/-/N2 at 30-50 eV

A calculation has been made of the elastic scattering and rotational excitation cross sections for e(-)-N2 scattering at 30 and 50 eV using quantum chemical techniques specially designed to be applicable to elastic and inelastic electron scattering by general polyatomic molecules. The angle dependence of the sum of the elastic and rotational excitation differential cross sections is in good agreement with experiment at all scattering angles at both energies, but at 50 eV the difference from experiment exceeds the experimental uncertainty at small scattering angles and near the minimum of the differential cross section. At large scattering angles the rotational excitation cross sections are predicted to exceed the elastic scattering cross sections. The absolute cross sections agree with experiment at some angles but at other angles are as much as 51% (30 eV) or 90% (50 eV) higher; this may be due at least in part to the difficulty of putting the experimental results on an absolute scale.

Onda, K.↗

NASA NTRS1980

Electron impact cross sections for v = 0-1 vibrational excitation in CO at electron energies of 3 to 100 eV

The paper discusses the measurements of normalized, absolute differential cross-sections for electron-impact vibrational transition in CO. Integral and momentum-transfer cross-sections were obtained from these differential results; incident electron energies were in the 3 to 100 eV range, and the scattering angles were 10 to 135 deg. A comparison of these results with measurements made with pure vibrationally elastic cross-sections in N2, and with the data based on a two-potential theory for electron scattering from diatomic molecules showed that the present CO cross-sections are similar to those in N2. This indicates that the long-range effect of the small CO dipole moment is negligible in promoting vibrational excitation; moreover, a significant peak in the integral and momentum-transfer cross-sections is observed at 20 eV. Finally, the low-energy integral cross-sections are compared with a recent set of swarm data for vibrational excitation.

Chutjian, A.↗

NASA NTRS1956

Use of Truncated Flapped Airfoils for Impingement and Icing Tests of Full-Scale Leading-Edge Sections

In an effort to increase the operational range of existing small icing tunnels, the use of truncated airfoil sections has been suggested. With truncated airfoils, large-scale or even full-scale wing-icing-protection systems could be evaluated. Therefore, experimental studies were conducted in the NACA Lewis laboratory icing 'tunnel with an NACA 651-212 airfoil section to determine the effect of truncating the airfoil chord on velocity distribution and impingement characteristics. A 6-foot-chord airfoil was cut successively at the 50- and 30-percent-chord stations to produce the truncated airfoil sections, which were equipped with trailing-edge flaps that were used to alter the flow field about the truncated sections. The study was conducted at geometric angles of attack of 00 and 40, an airspeed of about 156 knots, and volume-median droplet sizes of 11.5 and 18.6 microns. A dye-tracer technique was used in the impingement studies. With the trailing-edge flap on the truncated airfoil deflected so that the local velocity distribution in the impingement region was substantially the same as that for the full-chord airfoil, the local impingement rates and the limits of impingement for the truncated and full-chord airfoils were the same. In general, truncating the airfoils with flaps undeflected resulted in a subs'tantially altered velocity distribution and local impingement rates compared with those of the full-chord airfoil. The use of flapped truncated airfoils may permit impingement and icing studies to be conducted with full-scale leading-edge sections, ranging in size from tip to root sections.

vonGlahn, Uwe H.↗

NASA NTRS1982

Electron impact cross sections for the 2,2P state excitation of lithium

Electron impact excitation of the 2p 2P state of Li was studied at 10, 20, 60, 100, 150 and 200 eV. Relative differential cross sections in the angular range 3-120 deg were measured and then normalized to the absolute scale by using the optical f value. Integral and momentum transfer cross sections were obtained by extrapolating the differential cross sections to 0 deg and to 180 deg. The question of normalizing electron-metal-atom collision cross sections in general was examined and the method of normalization to optical f values in particular was investigated in detail. It has been concluded that the extrapolation of the apparent generalized oscillator strength (obtained from the measured differential cross sections) to the zero momentum transfer limit with an expression using even powers of the momentum transfer and normalization of the limit to the optical f value yields reliable absolute cross sections.

Vuskovic, L.↗

NASA NTRS1984

Wind tunnel wall interference in closed, ventilated and adaptive test sections

A wall interference correction method for closed rectangular test sections was developed which uses measured wall pressures. Measurements with circular discs for blockage and a rectangular wing as a lift generator in a square closed test section validate this method. These measurements are intended to be a basis of comparison for measurements in the same tunnel using ventilated (in these case, slotted) walls. Using the vortex lattice method and homogeneous boundary conditions, calculations were performed which show sufficiently high pressure levels at the walls for correction purposes in test sections with porous walls. In Gottingen, an adaptive test section (which is a deformable rubber tube of 800 mm diameter) was built and a computer program was developed which is able to find the necessary wall adaptation for interference-free measurements in a single step. To check the program prior to the first run, the vortex lattice method was used to calculate wall pressure distributions in the nonadapted test section as input data for the one-step method. Comparison of the pressure distribution in the adapted test section with free-flight data shows nearly perfect agreement. An extension of the computer program can be made to evaluate the remaining interference corrections.

Holst, H.↗

NASA NTRS1986

Determination of band oscillator strengths of atmospheric molecules from high resolution vacuum ultraviolet cross section measurements

An account is given of progress in work on (1) the determination of band oscillator strengths of the Schumann-Runge absorption bands of (16)O2 and (18)O2 from cross section measurements conducted at 79 K; (2) the determination of the absolute absorption cross section of the Schumann-Runge bands of (16)O(18)O from optical depth measurements performed on mixtures of (16)O2, (18)O2 and (16)O(18)O at 79K; and (3) the influence of Schumann-Runge linewing contributions on the determination of the Herzberg continuum absorption cross section of (16)O2 in the wavelength region 194 to 204 nm. The experimental investigations are effected at high resolution with a 6.65 m scanning spectrometer which is, by virtue of its small instrumental width (EWHM = 0.0013 nm), uniquely suitable for cross section measurements of molecular bands with discrete rotational structure. Absolute cross sections, which are independent of the instrumental function and from which band oscillator strengths are directly determined, are measured for the absorption bands that are most predissociated. Such measurements are needed for (1) accurate calculations of the stratospheric production of atomic oxygen and heavy ozone formed following the photopredissociation of (18)O(16)O by solar radiation penetrating between the absorption lines of (16)O2; (2) elucidation of the mechanism of predissociation of the upper state of the Schumann-Runge bands; and (3) determination of the true shape of the Herzberg continuum cross section.

Parkinson, W. H.↗

NASA NTRS1988

Impact and extinction signatures in complete Cretaceous-Tertiary (K-T) boundary sections

The Zumaya, Caravaca and Agost sections in Spain, the El Kef section in Tunisia and the Negev (Nahal Avdat) sections in Israel are among the most continuous, expanded and complete K-T boundary sections. The distribution patterns of the planktic faunas were quantitatively analyzed in closely spaced samples across the K-T boundary in these sections, in conjuction with the geochemistry, stable isotopes, mineralogy and magnetostratigraphy. Three hundred foraminiferal specimens were randomly selected and determined. Reliable estimates for the foraminiferal productivity changes across the K-T boundary and for the 1 to 2 Ma interval preceding the K-T boundary were made from the numbers of individuals/gram of sediment corrected for the sedimentation rates (calculated from magnetic reversals and lithology). No gradual or stepwise extinction is seen below the K-T boundary nor any productivity decrease. Stable isotope analyses show a warming just after deposition of the ejecta layer, not cooling as predicted by nuclear winter scenarios, although the duration of such cooling may be too short to be observed even in these complete sections. Low REE values and cpx spherules with quench textures idential to quench-textures in diagenetically altered spherules, strongly indicate an oceanic site of (one of) the impactor(s).

Smit, J.↗

NASA NTRS1990

Calibration of the 13- by 13-inch adaptive wall test section for the Langley 0.3-meter transonic cryogenic tunnel

A 13 by 13 inch adaptive wall test section was installed in the 0.3 Meter Transonic Cryogenic Tunnel circuit. This new test section is configured for 2-D airfoil testing. It has four solid walls. The top and bottom walls are flexible and movable whereas the sidewalls are rigid and fixed. The wall adaptation strategy employed requires the test section wall shapes associated with uniform test section Mach number distributions. Calibration tests with the test section empty were conducted with the top and bottom walls linearly diverged to approach a uniform Mach number distribution. Pressure distributions were measured in the contraction cone, the test section, and the high speed diffuser at Mach numbers from 0.20 to 0.95 and Reynolds numbers from 10 to 100 x 10 (exp 6)/per foot.

Mineck, Raymond E.↗

NASA NTRS1992

High resolution absorption cross sections in the transmission window region of the Schumann-Runge bands and Herzberg continuum of O2

Results are presented on measurements, conducted in the wavelength region 180-195 nm, and at different pressures of oxygen (between 2.5-760 torr) in order to separate the pressure-dependent absorption from the main cross sections, of the absorption cross sections of the Schumann-Runge bands in the window region between the rotational lines of S-R bands of O2. The present cross sections supersede the earlier published cross sections (Yoshino et al., 1983). The combined cross sections are presented graphically; they are available at wavenumber intervals of about 0.1/cm from the National Space Science Data Center. The Herzberg continuum cross sections are derived after subtracting calculated contributions from the Schumann-Runge bands. These are significantly smaller than any previous measurements.

Yoshino, K.↗

NASA NTRS1993

Total electron scattering and electronic state excitations cross sections for O2, CO, and CH4

Available electron collision cross section data concerning total and elastic scattering, vibrational excitation, and ionization for O2, CO, and CH4 have been critically reviewed, and a set of cross sections for modeling of planetary atmospheric behavior is recommended. Utilizing these recommended cross sections, we derived total electronic state excitation cross sections and upper limits for dissociation cross sections, which in the case of CH4 should very closely equal the actual dissociation cross section.

Kanik, I.↗

NASA NTRS1993

Carbon analyses of IDP's sectioned in sulfur and supported on beryllium films

Carbon is the only major element in interplanetary dust whose abundance, distribution and chemical state are not well understood. Information about carbon could clarify the relationship between the various classes of IDP's, conventional meteorites, and sources (e.g., comets vs. asteroids). To date, the most reliable estimates of C abundance in Interplanetary Dust Particles (IDP's) have been obtained by analyzing particles on thick-flat Be substrates using thin-window energy-dispersive spectroscopy in the SEM. These estimates of C abundance are valid only if C is homogeneously distributed, because detected C x-rays originate from the outer 0.1 micrometers of the particle. An alternative and potentially more accurate method of measuring C abundances is to analyze multiple thin sections (each less than 0.1 less than 0.1 micrometers thick) of IDP's. These efforts however, have been stymied because of a lack of a suitable non-carbonaceous embedding medium and the availability of C-free conductive substrates. We have embedded and thin-sectioned IDP's in glassy sulfur, and transferred the thin sections to Be support films approximately 25 nm thick. The sections were then analyzed in a 200 KeV analytical TEM. S sublimes rapidly under vacuum in the TEM, leaving non-embedded sections supported on Be. Apart from quantitative C (and O) analyses, S sectioning dramatically expands the range of analytical measurements that can be performed on a single IDP.

Bradley, J. P.↗

NASA NTRS2000

Parameterized Cross Sections for Pion Production in Proton-Proton Collisions

An accurate knowledge of cross sections for pion production in proton-proton collisions finds wide application in particle physics, astrophysics, cosmic ray physics, and space radiation problems, especially in situations where an incident proton is transported through some medium and knowledge of the output particle spectrum is required when given the input spectrum. In these cases, accurate parameterizations of the cross sections are desired. In this paper much of the experimental data are reviewed and compared with a wide variety of different cross section parameterizations. Therefore, parameterizations of neutral and charged pion cross sections are provided that give a very accurate description of the experimental data. Lorentz invariant differential cross sections, spectral distributions, and total cross section parameterizations are presented.

Blattnig, Steve R.↗