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At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Observation of the initiation and progression of damage in compressively loaded composite plates containing a cutout

A series of experiments was carried out to determine the mechanism of failure in compressively loaded laminated plates with a circular cutout. Real time holographic interferometry and photomicrography are used to observe the progression of failure. These observations together with post experiment plate sectioning and deplying for interior damage observation provide useful information for modelling the failure process. It is revealed that the failure is initiated as a localised instability in the zero layers, at the hole surface. With increasing load extensive delamination cracking is observed. The progression of failure is by growth of these delaminations induced by delamination buckling. Upon reaching a critical state, catastrophic failure of the plate is observed. The levels of applied load and the rate at which these events occur depend on the plate stacking sequence.

Waas, A.↗
NASA NTRS1986

MM and subMM molecular line observations of the southwest lobe of L1551: Evidence of a shell structure

Observations have been made of the southwest outflow lobe of L1551 in several millimeter and submillimeter molecular lines. Maps have been made in the J=3-2 and J=2-1 transitions of CO over areas of 7.5 by 2.5 arc minutes and 5 by 5 arc minutes respectively at UKIRT. More detailed maps have also been made in the J=2-1 CO transition over an area of about 6 by 3.5 arc minutes at the NRAO 12m telescope. Additional observations of the J=4-3 transitions of HCN, HCO(+) abd H(13)CO(+) were made at selected positions. The HC(+) J=4-3 transition was detected at several positions along the outflow axis and at the position of IRS 5. Similarly the HCN J=4-3 transition was detected at the position of IRS 5 and also at a position close to HH29. However, the J=4-3 transition of H(13)CO(+) was bit detected at the position of IRS 5 even through it was observed at the position close to HH29 with a peak corrected antenna temperature of 0.23K at a V(LSR) of 1 km s(-1). The detection of the J=4-3 transitions of both HCO(+) and H(13)CO(+) close to the position of HH29 suggest the presence of very dense gas in this region. LVG analysis of the various molecular lines observed give a kinetic temperature between 10 and 15K and a density from 10(5) to 10(6) cm(-3) at the position of IRS 5 at the ambient cloud velocity. At the position close to HH29 LVG analysis of the CO observations gives a density between 10(3) and 10(4) cm(-3) at a kinetic temperature of 25k for a V(LSR) of 0 km s(-1). To the southwest of HH29 there is a large decrease in both the linewidth and intensity of CO emission. This may be due to the interaction between the outflow and a dense clump of gas which gives rise to HH29. The maps of the CO J=3-2 and CO J=2-1 emission integrated in 3.25 km s intervals show the shell structure postulated by Snell and Schloerb (1985).

Rainey, R.↗
NASA NTRS1987

Infrared properties of dust grains derived from IRAS observations

The analysis of several diffuse interstellar clouds observed by the Infrared Astronomy Satellite (IRAS) is presented. The 60/100 micron flux ratios appear to be nearly constant in clouds with up to 1 sup m visual extinction at the center. Observations of a highly regular cloud in Chamaeleon show that the 12/100 micron ratio peaks at an intermediate radial distance and declines towards the center of the cloud. These observations indicate that nonequilibrium emission accounts only for the 12 and 25 micron bands; strong emission observed at the 60 micron band is probably due to equilibrium thermal radiation. The correlation of the 12 micron emission with a red excess observed for a high latitude cloud, L1780, is shown to be consistent with the assumption that both features are due to fluorescence by the same molecular species.

Chlewicki, G.↗
NASA NTRS1986

The hydrogen coma of Comet Halley before perihelion Preliminary observations with Dynamics Explorer 1

The hydrogen coma of Comet Halley has been observed in resonantly scattered solar Lyman-alpha radiation during the period 4-29 January 1986 as the comet approached perihelion. These observations were obtained with the imaging photometer for vacuum-ultraviolet wavelengths on the spacecraft Dynamics Explorer 4. For the initial analysis of observations available in 17 orbits distributed throughout the period, least-squares fits are computed for the observed exponential decrease in brightness with radial distance from the nucleus. Brightness at the nucleus increased from approx. 3 to 17 kR during the observing period. Preliminary analysis yields water production rates of approx. 3.6 x 10 to the 29th power and 1.9 x 10 to the 30th power molecules/sec on 1 and 29 January, respectively.

Craven, J. D.↗
NASA NTRS1986

Comparative energetics diagnosis of the observed and simulated blockings in the Northern Hemisphere

The blocking phenomena, in particular winter blocking, are stuided using energetic diagnostics. Sequences of blockings during the FGGE winter and summer in observed and simulated circulations, and energy transformations associated with blockings are examined. It is observed that the simulation of the Northern Hemisphere circulation correlates better with the observed circulation during summer than during winter. It is noted that the observed winter blockings are maintained by the supply of kinetic energy to the ultralong waves from the shorter cyclone scales through nonlinear wave-wave interaction; in the simulated winter blocking, the energy converted at the cyclone scale cascades down to the shorter wave range; and the summer blockings are supported by the baroclinic conversion of long waves in both the observed and simulated circulations.

Kung, Ernest C.↗
NASA NTRS1987

Simultaneous observation of Pc 3-4 pulsations in the solar wind and in the earth's magnetosphere

The equatorially orbiting Active Magnetospheric Particle Tracer Explorers CCE and IRM satellites have made numerous observations of Pc 3-4 magnetic field pulsations (10-s to 100-s period) simultaneously at locations upstream of the earth's bow shock and inside the magnetosphere. These observations show solar wind/IMF control of two categories of dayside magnetospheric pulsations. Harmonically structured, azimuthally polarized pulsations are commonly observed from L = 4 to 9 in association with upstream waves. More monochromatic compressional pulsations are clearly evident on occasion, with periods identical to those observed simultaneously in the solar wind. The observations reported here are consistent with a high-latitude (cusp) entry mechanism for wave energy related to harmonically structured pulsations.

Engebretson, M. J.↗
NASA NTRS1987

Catalog of infrared observations. Part 1: Data

The Catalog of Infrared Observations (CIO) is a compilation of infrared astronomical observational data obtained from an extensive literature search of astronomical journals and major astronomical catalogs and surveys. The literature searches are complete for 1965 through 1986 in this Second Edition. The Catalog is published in two parts, with the observational data (roughly 200,000 observations of 20,000 individual sources) listed in Part I, and supporting appendices in Part II. The expanded Second Edition contains a new feature: complete IRAS 4-band data for all CIO sources detected, listed with the main Catalog observations, as well as in complete detail in the Appendix. The appendices include an atlas of infrared source positions, two bibliographies of infrared literature upon which the search was based, and, keyed to the main Catalog listings (organized alphabetically by author and then chronologically), an atlas of infrared spectral ranges, and IRAS data from the CIO sources. The complete CIO database is available to qualified users in printed microfiche and magnetic tape formats.

Gezari, Daniel Y.↗
NASA NTRS1987

Rayleigh lidar observations of gravity wave activity in the stratosphere and lower mesosphere

Forty-two monochromatic gravity wave events were observed in the 25 to 55 km altitude region during 16 nights of Rayleigh lidar measurements at Poker Flat, Alaska and Urbana, Illinois. The measured wave parameters were compared to previous radar and lidar measurements of gravity wave activity. Vertical wavelengths, lambda(z), between 2 and 11.5 km with vertical phase velocities, c(z), between 0.1 and 1 m/s were observed. Measured values of lambda(z) and c(z) were used to infer observed wave periods, T(ob), between 50 and 1000 minutes and horizontal wavelengths, lambda(x), from 25 to 2000 km. Dominant wave activity was found at vertical wavelengths between 2 to 4 km and 7 to 10 km. No seasonal variations were evident in the observed wave parameters. Vertical and horizontal wavelengths showed a clear tendency to increase with T(ob), which is consistent with recent sodium lidar studies of monochromatic wave events near the mesopause. Measured power law relationships between the wave parameters were lambda(z) varies as T(ob) sup 0.96, lambda(x) varies as T(ob) sup 1.8, and c(z) varies as T(ob) sup -0.85. The kinetic energy calculated for the monochromatic wave events varied as k(z) sup -2, k(x) sup -1, and f(ob) sup -1.7. The atmospheric scale heights calculated for each observation date range from 6.5 to 7.6 km with a mean value of 7 km. The increase of rms wind perturbations with altitude indicated an amplitude growth length of 20.9 km. The altitude profile of kinetic energy density decreased with height, suggesting that waves in this altitude region were subject to dissipation or saturation effects.

Miller, M. S.↗
NASA NTRS1988

Cyclic fatigue damage characteristics observed for simple loadings extended to multiaxial life prediction

Fully reversed uniaxial strain controlled fatigue tests were performed on smooth cylindrical specimens made of 304 stainless steel. Fatigue life data and cracking observations for uniaxial tests were compared with life data and cracking behavior observed in fully reversed torsional tests. It was determined that the product of maximum principle strain amplitude and maximum principle stress provided the best correlation of fatigue lives for these two loading conditions. Implementation of this parameter is in agreement with observed physical damage and it accounts for the variation of stress-strain response, which is unique to specific loading conditions. Biaxial fatigue tests were conducted on tubular specimens employing both in-phase and out-of-phase tension torsion cyclic strain paths. Cracking observations indicated that the physical damage which occurred in the biaxial tests was similar to the damage observed in uniaxial and torsional tests. The Smith, Watson, and Topper parameter was then extended to predict the fatigue lives resulting from the more complex loading conditions.

Jones, David J.↗
NASA NTRS1988

The spectroscopic observation of the CH radical in its a4Sigma(-) state

The first spectroscopic observation of CH in the a 4Sigma(0-) state are reported. The molecule was generated in a discharge-flow system in the reaction betweeen fluorine atoms and methane or between oxygen atoms and acetylene at a total pressure of about 1 Torr. Several resonances associated with the N = 1 - 0 transitions of 4Sigma(-) CH were observed at three separate laser wavelengths, while those for the N = 2 - 1 transition were observed at two wavelengths. Each observed Zeeman component consists of a well-split doublet arising from proton hyperfine structure. The reasons for assigning the observations to CH in its a 4Sigma(-) state are discussed.

Nelis, Thomas↗
NASA NTRS1988

A study of field-aligned currents observed at high and low altitudes in the nightside magnetosphere

Field-aligned current structures on auroral field lines observed at low and high altitudes using DE 1 and ISEE 2 magnetometer, and particle data observed when the spacecraft are in magnetic conjunction in the near-midnight magnetosphere, are investigated. To minimize latitudinal ambiguity, the plasma-sheet boundary layer observed with ISEE 2 and the discrete aurora at the poleward edge of the auroral oval with DE 1 are studied. The overall current observed at highest latitudes is flowing into the ionosphere, and is likely to be carried by ionospheric electrons flowing upward. There are, however, smaller-scale current structures within this region. The sense and magnitude of the field-aligned currents agree at the two sites. The ISEE 2 data suggests that the high-latitude downward current corresponds to the high-latitude boundary of the plasma-sheet boundary layer, and may be associated with the ion beams observed there.

Elphic, R. C.↗
NASA NTRS1988

Exosat and IUE observations of SW UMa during superoutburst

IUE and Exosat observations obtained during the March 1986 superoutburst of the SU UMa type dwarf nova SW UMa are presented. The observations show the presence of a hot, extensive, optically thick disk. The UV fluxes show an increase of 1000 over the quiescent values, implying a large increase in mass accretion rate. The Exosat obserations show an increase in the soft X-ray count rate by a factor of 44 over quiescence, while the medium-energy flux remains undetected. The most surprising result is that the softness ratio in superoutburst is similar to the quiescent value of 0.3. No variation at the orbital or spin periods or at the superhump period are evident in the superoutburst X-ray data. A transient variation is observed at 5.1 minutes similar to that observed in the optical a few days after the X-ray observations.

Szkody, Paula↗
NASA NTRS1987

Substorm-associated lower hybrid waves in the plasma sheet observed by ISEE 1

Observations of the electric field at frequencies from 2-128 Hz, using the burst mode of the spherical double probe on ISEE 1, have been examined for a time period previously identified as containing the traversal of a near-earth neutral line past the satellite. Intense waves (3 to over 30 mV/m) at approximately half the lower hybrid frequency were observed throughout the plasma sheet from the neutral sheet to the boundary, but only during the period of the large dc electric field and E x B velocity associated with the substorm neutral line. The wave number deduced from linear fits of the data was comparable to the inverse electron gyroradius. These results are consistent with the lower-hybrid drift instability. Although peaks between the ion and electron plasma frequency were sometimes observed simultaneously, the integrated power below 100 Hz was usually at least one to two orders of magnitude greater than that above 100 Hz. Although theoretical work has suggested that the instability would be suppressed at the neutral sheet, the largest waves observed occurred right at the neutral sheet when the southward component of the magnetic field was 6 gamma. The observed waves could provide an anomalous resistivity of about (3-1000) x 10 to the -7th S (compared to the classical value of 1 x 10 to the -18th S).

Cattell, C. A.↗
NASA NTRS1988

Observations of vertical velocities in the tropical upper troposphere and lower stratosphere using the Arecibo 430-MHz radar

The first clear-air observations of vertical velocities in the tropical upper troposphere and lower stratosphere (8-22 km) using the Arecibo 430-MHz radar are presented. Oscillations in the vertical velocity near the Brunt-Vaisala period are observed in the lower stratosphere during the 12-hour observation period. Frequency power spectra from the vertical velocity time series show a slope between -0.5 and -1.0. Vertical wave number spectra computed from the height profiles of vertical velocities have slopes between -1.0 and -1.5. These observed slopes do not agree well with the slopes of +1/3 and -2.5 for frequency and vertical wave number spectra, respectively, predicted by a universal gravity-wave spectrum model. The spectral power of wave number spectra of a radial beam directed 15 deg off-zenith is enhanced by an order of magnitude over the spectral power levels of the vertical beam. This enhancement suggests that other geophysical processes besides gravity waves are present in the horizontal flow. The steepening of the wave number spectrum of the off-vertical beam in the lower stratosphere to near -2.0 is attributed to a quasi-inertial period wave, which was present in the horizontal flow during the observation period.

Cornish, C. R.↗
NASA NTRS1988

Some 5-13 micrometer airborne observations of Comet Wilson 1986l: Preliminary results

Comet Wilson was observed from the Kuiper Airborne Observatory approximately 23.6 and 25.7 Apr. 1987, UT (approx. 3 to 5 days after perihelion) using the NASA-Ames Faint Object Grating Spectrometer. Spectrophotometric data were observed with a 21 inch aperture between 5 and 13 micrometer and with a spectral resolution of 50 to 100. Spectra of the inner coma and nucleus reveal a fairly smooth continuum with little evidence of silicate emission. The 5 to 8 micrometer color temperature of the comet was 300 + or - 15 K, approx. 15 percent higher than the equilibrium blackbody temperature. All three spectra of the nucleus show a new emission feature at approx. 12.25 micrometer approx. two channels (.22 micrometer) wide. Visual and photographic observations made during the time of these observations showed a broad faint, possible two component tail. No outburst activity was observed.

Lynch, David K.↗
NASA NTRS1988

Observations of stratospheric temperature changes coincident with the recent Antarctic ozone depletions

A high degree of correlation between the recent decline in Antarctic total ozone and cooling of the stratosphere during Austral spring has been noted in several recent studies (e.g., Sekiguchi, 1986; Angel, 1986). This study analyzes the observed temperature trends in detail, focusing on the spatial and temporal aspects of the observed cooling. Ozone losses and stratospheric cooling can be correlated for several reasons: (1) ozone losses (from an unspecified cause) will directly reduce temperatures due to decreased solar ultraviolet absorption (Shine, 1986), and/or (2) changes in both ozone and temperature structure due to modification of stratospheric circulation patterns (Mahlman and Fels, 1986). In order to scrutinize various ozone depletion scenarios, detailed information on the observed temperature changes is necessary; the goal is to provide such data. The data used are National Meteorological Center (NMC) Climate Analysis Center (CAC) derived temperatures, covering 1000 to 1 mb (0 to 48 km), for the period 1979 to 1987. Discussions on data origin and quality (assessed by extensive comparisons with radiosonde observations), along with other details of these observations, can be found in Newman and Randel (1988).

Randel, William J.↗
NASA NTRS1988

Astrometric observations of comets and asteroids and subsequent orbital investigations

The 155-cm reflector was used for observations of comets and minor planets on 28 nights during April-October. Twenty-two of the observations refer to comets, 62 to numbered minor planets (numbered, that is, by the end of the semester: only nine of them refer to minor planets already numbered at the time of the last report), and the remainer to unnumbered minor planets. Observations were made of four new comets discovered during the semester and a fifth discovered in January. Observations of Wilson (19861), P/Tempel 2 and two other returning short-period comets are also continuing. Among the odd numbered minor planets observed were the earth-approaching objects (1685) Toro and (1980) Tezcatlipoca. The Earth approacher 1980 PA was numbered (3908).

Mccroskey, Richard E.↗
NASA NTRS1988

Solar coronal and magnetic field observations near the time of the 1988 March 18 solar eclipse

Observations made during the interval March 1-31, 1988, are presented which were designed to provide a synoptic context in which data from the March 18, 1988, total solar eclipse can be interpreted. Daily observations made with the Mark III K-coronameter and the H-alpha prominence monitor at the Mauna Loa Solar Observatory, along with photographic records of the Sun in H-alpha from the flare patrol at Mees Solar Observatory on Haleakala, Maui, are included. Observations of the longitudinal component of the photospheric magnetic field made at Mees Solar Observatory were also gathered around the period of the eclipse. Together with the white-light image of the corona at the eclipse, these coronal and magnetic field observations assembled into synoptic maps for this epoch, are presented. On the basis of these observations, an interpretation of the global density distribution of the corona at the time of the eclipse is constructed.

Sime, D. G.↗