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At least 739 records · Page 41

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NASA NTRS1987

Dynamical factors affecting ozone mixing ratios in the Antarctic lower stratosphere

An account is given of the climatology and interannual variability of dynamical quantities and ozone mixing ratios during the Southern Hemisphere spring for 1979-1984. The seasonal variation in temperature in the lower stratosphere is repeatable; a steep decrease in zonal mean ozone mixing ratios is observed around 60 deg S toward the South Pole in September which, with time, becomes shallower in association with minor warmings and a final warming. Climatological synoptic charts in the lower stratosphere show the circumpolar circulation in the geopotential height field and the prominence of planetary wave 1 in the temperature and ozone fields. When wave activity is strong, there are weaker westeries, higher temperatures, and higher ozone mixing ratios at high latitudes.

Shiotani, Masato↗

NASA NTRS1988

The ratio of microwaves to X-rays in solar flares: The case for the thick target model

The expected ratio of synchrotron microwave radiation to bremsstrahlung X-rays for thick target, thin target, and multithermal solar flare models is calculated. The calculations take into account the variation of the microwave to X-ray ratio with X-ray spectral index. The theoretical results are compared with observed ratios of a sample of 51 solar flares with well known spectral index. From this it is concluded that the nonthermal thick target model with a loop length of and order of 10 to the 9th power cm and a magnetic field of 500 + or - 200 G provides the best fit to the data. The thin target and multithermal models require unreasonably large density or pressure and/or low magnetic field to match the data.

Lu, Edward T.↗

NASA NTRS1988

(1 + 1) resonant enhanced multiphoton ionization via the A2Sigma(+) state of NO - Ionic rotational branching ratios and their intensity dependence

Rotational branching ratios resulting from the (1 + 1) resonant enhanced multiphoton ionization spectroscopy of NO via the 0-0 transition of the A-X band for the four possible branches that can be assigned as R(21.5) are explored using calculation performed in the frozen-core approximation at the Hartree-Fock level. The four different branches, of which three are distinctly different in the perturbative limit, have rather different branching ratios. The mixed R12 + Q22(21.5) branch, which is not intense and has the lowest transition energy, appears to give the best agreement with experimental branching ratio for parallel detection. The agreement is less satisfactory for perpendicular detection. Neither the effect of finite-acceptance angle of the photoelectron detector nor high intensities can explain the discrepancy.

Rudolph, H.↗

NASA NTRS1988

On the aspect ratio of Rayleigh-Benard convection cells

Numerical model calculations of isoviscous bottom-heated convection in a two-dimensional box with aspect ratio twelve are reported. The aim was to determine the preferred aspect ratio of convection cells. Time-dependent runs were started from two widely different initial conditions. At Rayleigh numbers in the range 10 to the 5th to 10 to the 6th about eight cells with a mean aspect ratio of 1.5 formed eventually in each case. Thus neither the preference for approximately square cells nor the stability of very elongated cells could be confirmed. The existence of large-scale convective structures in the earth's mantle must be due to deviations from the simple Rayleigh-Benard model of convection.

Christensen, Ulrich↗

NASA NTRS1988

Mixing ratios of trace gases in the austral polar atmosphere during August and September of 1987

Mixing ratios are presented for a number of long-lived trace gases in the austral polar atmosphere during August and September of 1987. The recent discovery of a 12-year trend of increasing depletion of ozone over the Antarctic Continent in the spring of each year led to numerous theoretical interpretations and several scientific expeditions to the region. The results herein were obtained as part of a major effort involving penetration of the region of ozone depletion by NASA's multi-instrumented aircraft. One of the 14 instruments on the high-altitude ER-2 aircraft collected pressurized air samples between latitudes of 53 degrees and 72 degrees south at pressure altitudes up to 21 km in a series of 12 flights from Punta Arenas, Chile, over the Palmer Peninsula. The sampling system, located in the nose section of ER-2, has an inlet tube in the free airstream, a metal-bellows air pump, and 14 specially treated 1.6 l stainless-steel canisters for containing the pressurized air at 350 kPa. A typical flight profile consisted of a southbound path on the 428 K potential temperature surface, a descent to a pressure altitude of 13.7 km, a climb to the 460 K surface, and return on this surface. Mixing ratios for the trace gases were obtained from gas chromatographic analyses of the pressurized air samples. Of the species measured, the mixing ratios for CH4, CO, N2O, CF2 Cl2, CFCl3, CH3, CCl3, CCl4, and C2F3Cl3 are reported here.

Vedder, James F.↗

NASA NTRS1988

Fatigue crack closure behavior at high stress ratios

Fatigue crack delay behavior at high stress ratio caused by single peak overloads was investigated in two thicknesses of 7475-T731 aluminum alloy. Closure measurements indicated no closure occurred before or throughout the overload plastic zones following the overload. This was further substantiated by comparing the specimen compliance following the overload with the compliance of a low R ratio test when the crack was fully open. Scanning electron microscope studies revealed that crack tunneling and possibly reinitiation of the crack occurred, most likely a result of crack-tip blunting. The number of delay cycles was greater for the thinner mixed mode stress state specimen than for the thicker plane strain stress state specimen, which is similar to low R ratio test results and may be due to a larger plastic zone for the mixed mode cased.

Turner, C. Christopher↗

NASA NTRS1989

The D/H ratio for Jupiter

Observations of Jupiter's spectrum near the R5(0) HD line at 6063.88 A are reported. A feature with an equivalent width of 0.065 + or - 0.021 mA is coincident with the expected line. This feature is compared with HD profiles computed for inhomogeneous scattering models for Jupiter to yield a range for the Jovian D/H ratio of 1.0-2.9 x 10 to the -5th. This D/H ratio is in the lower range of previously reported D/H values for Jupiter and corresponds to an essentially solar D/H ratio for Jupiter. The detection of HD features in the presence of probable blends with spectral features of minor atmospheric hydrocarbon molecules is discussed. Such blends may make unambiguous identification of HD features difficult.

Smith, Wm. Hayden↗

NASA NTRS1989

Molecular hydrogen line ratios in four regions of shock-excited gas

Five emission lines of molecular hydrogen, with wavelengths in the ranges of 2.10-2.25 and 3.80-3.85 microns, have been observed in four objects of different type in which the line emission is believed to be excited by shocks. The relative intensities of the lines 1 - 0 S(1):1 - 0 S(O):2 - 1 S(1) are approximately 10.5:2.5:1.0 in all four objects. The 0 - 0 S(13):1 - 0 O(7) line ratio, however, varies from 1.05 in OMC-1 to about 2.3 in the Herbig-Haro object HH 7. The excitation temperature derived from the S(13) and O(7) lines is higher than that derived from the 1 - 0 and 2 - 1 S(1) lines in all four objects, so the shocked gas in these objects cannot be characterized by a single temperature. The constancy of the (1-0)/(2-1) S(1) line ratio between sources suggests that the post-shock gas is 'thermalized' in each source. The S(13)/O(7) ratio is particularly sensitive to the density and temperature conditions in the gas.

Burton, M. G.↗

NASA NTRS1989

The ratio of microwaves to X-rays in solar flares - The case for the thick-target model

Lu, Edward T.↗

NASA NTRS1989

The infrared-to-radio ratio within NGC 5236 (M83) and NGC 6946

A detailed comparison of the distribution of 60-micron IR and 20-cm radio continuum emission within NGC 5236 (M83) and NGC 6946 is presented. In the disks of both galaxies, a slow decrease of the 60-micron-to-20-cm ratio with increasing radius is observed. Values of this ratio within the central regions are enhanced by roughly a factor of 3 with respect to the outer disks, whereas the corresponding enhancement in radio surface brightness is at least a factor of 20. The 100-micron-to-20-cm ratio shows a similar but shallower gradient. To account for these observations, it is suggested that spiral galaxies are characterized by an IR disk with a shorter scale length than that of the radio continuum disk, the latter being smeared as a result of cosmic-ray propagation.

Bicay, M. D.↗

NASA NTRS1989

Anomalously high intercombination line ratios in symbiotic stars - Extreme Bowen pumping?

International Ultraviolet Explorer observations of the ratio of the O III intercombination lines near 1660 A are assembled, showing that the observed ratios in symbiotic stars are significantly higher than the theoretically predicted optically thin limit of 2.5. The presence of an enhancing physical process is thereby indicated. It is suggested that Bowen pumping of the lower level of the 1666.2 A line in an 'external saturation' limit, coupled with appreciable optical depth, could logically explain the high ratios. Some tentative evidence for this is presented and the relevance of far-infrared observations of the O III 51.8 and 88.3 micron lines in symbiotic sources is emphasized.

Kastner, S. O.↗

NASA NTRS1989

The effect of density variations on elemental abundance ratios in gaseous nebulae

Using numerical analysis it is demonstrated that when there are changes in gas density within a nebulae various empirical methods for determining the electron density can give different results. Eleven different species are considered which have line pair ratios that are well-known electron density (Ne) diagnostic tools. In the presence of varying density, there is a progression in inferred values of Ne from N+ (122/204 microns) at the lowest to C(2+) (1906/1909 A) at the highest. For many of the 11 species there is a fixed order in the inferred density, while for others the order can change somewhat for different mixes of densities. When there are nonconstant density conditions, it is shown that systematic biases may occur in the empirical determination of chemical abundance ratios. Tabular material is presented that delineates the maximum bias that can occur in the determination of a particular abundance ratio in a two-component model.

Rubin, R. H.↗

NASA NTRS1989

The (C-13)/(C-12) ratio in cosmic ray sources

Published measurement data on the production C-13 during interstellar propagation of cosmic rays (Webber et al., 1987; Guzik et al., 1985) are combined with observational data to determine the relative abundance of C-13 in the cosmic-ray source. The theoretical basis and implementation of the calculations are described in detail, and the results are presented in graphs. (C-13)/(C-12) is estimated as 0.003 + or - 0.005, consistent with the solar ratio (0.011), not consistent with the local abundance ratio (0.023), and in agreement with the source ratio predicted by Prantzos et al. (1985) using the isotopic abundances of WR-star ejecta.

Webber, W. R.↗

NASA NTRS1990

Limits on the antiproton/proton ratio in the cosmic radiation from 100 MeV to 1580 MeV

A search for antiprotons (p-bars) in the cosmic radiation with energies below 1580 MeV at the top of the atmosphere was performed using the PBAR balloon-borne magnetic spectrometer. No antiprotons were observed in 124,000 proton events. For the energy interval 100-640 MeV, an upper limit is reported to the p-bar/p ratio of 2.8 x 10 to the -5th at the top of the atmosphere, after correcting for instrumental efficiencies and contributions from secondary particles. No antiproton was observed in the energy interval 640-1580 MeV, which yields an upper limit to the p-bar/p ratio of 6.1 x 10. By combining both data sets, the limits on the p-bar/p ratio can be improved to 2.0 x 10 to the -5th. The detector performance and instrumental efficiencies of the individual detector components are discussed. A detail Monte Carlo calculation was used to evaluate the instrumental efficiency for both antiprotons and protons as a function of momentum.

Salamon, M. H.↗

NASA NTRS1990

Measurements of the nitric acid to NO(x) ratio in the troposphere

Nitric acid concentrations, measured by both teflon/nylon filter packs (FP) and the tungstic oxide denuder (DEN), are compared with the average NO(x) concentrations from LIF and chemiluminescent methods. The HNO3/NO(x) ratio based on FPs ranged from 0.8 to 10.4, with a mean of 3.4. The DEN nitric acid concentrations produced ratios ranging from less than 0.3 to 9.8, with a mean of 2.6. Average marine ratios were larger than those from continental regions, in part due to continental anthropogenic sources of NO(x).

Huebert, B. J.↗

NASA NTRS1990

Solar coronal Ar/Fe and Ne/Mg abundance ratios derived from ultraviolet forbidden line spectra

An Ar/Fe abundance ratio of 0.031 + or - 35 percent and an upper limit of 0.4 to the Ne/Mg abundance ratio are determined for solar coronal active regions using solar spectra. Forbidden lines occur at 1324.45 A for Mg V, 1349.38 A for Fe XII, 1375.98 A for Ca XV, and 1392.12 A for Ar XI. The unobserved Ne V line is predicted to fall at 1574.68 A. These abundance ratios are consistent with lower abundances of Ne and Ar in the corona relative to low first ionization potential elements.

Doschek, G. A.↗

NASA NTRS1990

Self-induced roll oscillations of low-aspect-ratio rectangular wings

Experimental investigation of small aspect ratio rectangular wings mounted on a free-to-roll sting balance indicated that self-induced roll oscillations are possible when the aspect ratio of such wings is less than 0.5. The oscillations are probably driven by the periodic changes in the location and strength of the side edge vortices, as it has been shown for the 'wing rock' motion of delta wings, where similar changes in the leading edge vortex strength and position cause the roll oscillations. During the roll oscillation cycle the roll angle, normal force, and the side force were recorded and presented for three wings with aspect ratios of 0.25, 0.35, and 0.47. This data indicates that the lift loss during roll oscillations of rectangular wings is less than what was measured for similar delta wings. Also, the flow field of such slender rectangular wings at high angles of attack is more complicated due to the additional leading edge vortex, when compared with the flow field over slender delta wings.

Levin, Daniel↗

NASA NTRS1991

Effect of lift-to-drag ratio upon pilot rating for a preliminary version of the HL-20 lifting body

A man-in-the-loop simulation study of the handling qualities of the HL-20 lifting body vehicle has been performed in a fixed-base simulation cockpit. The study was aimed at identifying opportunities to improve the original design of the vehicle from a handling qualities and landing performance perspective. A subsonic aerodynamic model of the HL-20 was used as a baseline, and visual approaches and landings were made at various vehicle lift-to-drag (L/D) ratios. It is concluded that there is a high degree of correlation between maximum L/D ratio and pilot rating. Using the pilot ratings Level 1, flying qualities were found to be possible for configurations with a maximum L/D ratio of 3.8 or higher.

Jackson, E. B.↗