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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Some O I oscillator strengths and the interstellar abundance of oxygen

Calculated and experimental oscillator strengths for the O I intersystem line at 1356 A and for other O I lines of interest in interstellar absorption-line studies are discussed. Attention is given to experimental f-values for the lines at 1302, 1305, and 1306 A, previous work on the f-values for the lines at 1356 and 1359 A, wave-function expansion, and calculations for permitted as well as intercombination lines. Copernicus observations of several interstellar absorption lines due to O I, C II, P II, and Ni II toward Zeta Oph are reported, equivalent widths are determined, and a curve-of-growth analysis is performed for the O I absorption lines. Oscillator strengths are recommended for the far-UV resonance lines of O I, and it is concluded that the oxygen in the interstellar H I regions toward Zeta Oph is depleted by 45% to 69%.

Zeippen, C. J.↗
NASA NTRS1978

Electric field oscillations measured near an auroral arc

A sounding rocket, launched into the expansive phase of an auroral substorm, measured bursts of electric field oscillations with a typical period of one second and a magnitude exceeding 20 mV/m. The oscillation appear to be due to an MHD wave propagating along the magnetic field. The bursts were observed as the sounding rocket passed over the southern border of an auroral arc. The southern border coincided with an increase in 1-5 keV electron flux and an increase in field-aligned current.

Kintner, P. M.↗
NASA NTRS1978

An observational search for large-scale organization of five-minute oscillations on the sun

The large-scale solar velocity field has been measured over an aperture of radius 0.8 solar radii on 121 days between April and September, 1976. Measurements are made in the line Fe I 5123.730 A, employing a velocity subtraction technique similar to that of Severny et al. (1976). Comparisons of the amplitude and frequency of the five-minute resonant oscillation with the geomagnetic C9 index and magnetic sector boundaries show no evidence of any relationship between the oscillations and coronal holes or sector structure.

Dittmer, P. H.↗
NASA NTRS1978

Sonic-box method employing local Mach number for oscillating wings with thickness

A computer program was developed to account approximately for the effects of finite wing thickness in the transonic potential flow over an oscillating wing of finite span. The program is based on the original sonic-box program for planar wing which was previously extended to include the effects of the swept trailing edge and the thickness of the wing. Account for the nonuniform flow caused by finite thickness is made by application of the local linearization concept. The thickness effect, expressed in terms of the local Mach number, is included in the basic solution to replace the coordinate transformation method used in the earlier work. Calculations were made for a delta wing and a rectangular wing performing plunge and pitch oscillations, and the results were compared with those obtained from other methods. An input quide and a complete listing of the computer code are presented.

Ruo, S. Y.↗
NASA NTRS1978

Wind tunnel tests of a blade subjected to midchord torsional oscillation at high subsonic stall flutter conditions

A mechanical drive system for oscillating blades in a wind tunnel at frequencies up to 767 hertz and amplitudes of + or - 1.2 deg is described. High-speed motion pictures of schlieren images of the flow over a double-circular arc blade oscillating in harmonic motion about the midchord revealed extensive shock patterns at a nominal free stream Mach number of 0.7, a mean angle of attack of 4 deg, and reduced frequency of about 0.7. A phase lag resulting from the slow response of the flow to the motion of the blade increased with increasing reduced frequency. This phase lag, based on the difference between the time the blade attained its maximum angle of attack and the time required for the normal shock to reach its extreme downstream position, was nominally 100 deg at the above conditions.

Boldman, D. R.↗
NASA NTRS1977

Two-dimensional oscillating airfoil test apparatus

A two dimensional oscillating airfoil test apparatus is presented as a method of measuring unsteady aerodynamic forces on an airfoil or rotor blade section. The oscillating airfoil test rig, which is being built for use in an 11 X 11-foot transonic wind tunnel (speed range M = 0.4 - 1.4), will allow determination of unsteady loadings and detailed pressure distributions on representative airfoil sections undergoing simulated pitching and flapping motions. The design details of the motion generating system and supporting structure are presented. This apparatus is now in the construction phase.

Gibson, F. L.↗
NASA NTRS1978

Radiation sensitivity of quartz crystal oscillators experiment for the Long Duration Exposure Facility /LDEF/

A proposed experiment, which has been selected by NASA for inclusion in the Long Duration Exposure Facility (LDEF), is discussed. The objective of the experiment is to obtain information relevant to predicting and improving the radiation sensitivity of quartz oscillators. Specifically, the effect of exposing various grades of quartz oscillators to an orbital environment will be compared with observations obtained using the transmission electron microscope which suggest that the technique may be used to classify quartz-crystals according to their radiation sensitivity.

Venables, J. D.↗
NASA NTRS1979

On the role of the Kelvin wave in the westerly phase of the semiannual zonal wind oscillation

The role of the Kelvin wave, discovered by Hirota (1978), in producing the westerly accelerations of the semiannual zonal wind oscillation in the tropical upper stratosphere is examined quantitatively. It is shown that, for reasonable values of the wave parameters, this Kelvin wave could indeed give rise to the observed accelerations. For the thermal damping rates of Dickinson (1973), the most likely range of phase speeds for a wavenumber 1 disturbance is from 45 to 60 m/sec. For 'photochemically accelerated' damping rates (Blake and Lindzen, 1973), a phase speed in excess of 70 m/sec would be required. The possibility of a significant modulation of the semiannual westerlies by the quasi-biennial oscillation is also suggested.

Dunkerton, T.↗
NASA NTRS1979

Observations of solar oscillations with periods of 160 minutes

Severny et al. (1976) have reported oscillations of the sun with a period near 160 min. A description is presented of observations made at the Stanford Solar Observatory during the time from 1975 to the present which seem to support the reports by Severny et al. At Stanford the relative velocity between a central circular area of radius 0.5 solar radius on the solar disk and most of the remaining area of the solar disk is measured. A superposed epoch analysis of the observations using a period of 160 min is discussed. An apparent agreement in phase between the obtained observational data and those reported by Severny et al. tends to support the interpretation that solar oscillations are being observed.

Scherrer, P. H.↗
NASA NTRS1978

A systems approach to high performance oscillators

The purpose of this paper is to show how systems composed of multiple oscillators and resonators can achieve superior performance compared to a single oscillator. Experimental results are presented for two systems based on quartz crystals which provide state-of-the-art stability over a much wider range of averaging times than has been previously achieved. One system has achieved a factor of five improvement in noise floor compared to all previously reported results.

Stein, S. R.↗
NASA NTRS1979

Changes in the rapid oscillations of AH Herculis during an outburst

High-speed photometric observations of the dwarf nova AH Her were made during the period June 5-12, 1978 at the NASA/University of Arizona 152-cm telescope of the Mount Lemmon Observatory. Observations have shown rapid oscillations beginning after the maximum of an outburst and remaining detectable for five consecutive days. Measurements of the period and amplitude of the oscillations and the intensity of the outburst are presented for each day.

Stiening, R. F.↗
NASA NTRS1979

A possible 2-day oscillation near the tropical stratopause

An examination of daily meteorological rocket data taken during January and February 1977 at Kwajalein, Marshall Islands (9 deg N, 168 deg E) suggests the presence of a large oscillation in the meridional wind with a period near 2 days. Some rocket data taken concurrently at other stations is also presented. The Canal Zone station (9 deg N, 80 deg W) suggests a possible 2-day oscillation, while middle- and high-latitude stations show variability with periods ranging from 2-5 days.

Coy, L.↗
NASA NTRS1979

Investigation of high frequency oscillations in the OV102 elevon actuation subsystems using continuous system modeling program simulation

Two theories emerged as the cause of undesired oscillations at frequencies between 40 and 60 Hz in the Orbiter Vehicle inboard and outboard elevon actuation subsystems during hardware testing. Both the "hardover feedback" and "deadspace" theories were examined using continuous system modeling program simulation. Results did not support the "hardover feedback" theory but showed that deadspace in the torque feedback spring connections to the servospools must be considered to be a possible cause of the oscillations. Further investigation is recommended.

Powell, W. W., Sr.↗
NASA NTRS1980

Transonic unsteady airloads on an energy efficient transport wing with oscillating control surfaces

An aspect ratio 10.8 supercritical wing with oscillating control surfaces is described. The wing is instrumental with 252 static orifices and 164 in situ dynamic pressure transducers for studying the effects of control surface deflection on steady and unsteady pressures at transonic speeds. Results from initial wind tunnel tests conducted in the Langley Transonic Dynamics Tunnel are discussed. Unsteady pressure results are presented for two trailing edge control surfaces oscillating separately at the design Mach number of 0.78. Some experimental results are compared with analytical results obtained by using linear lifting surface theory.

Sandford, M. C.↗
NASA NTRS1980

Development and performance of a laser heterodyne spectrometer using tunable semiconductor lasers as local oscillators

A diode laser based IR heterodyne spectrometer for laboratory and field use was developed for high efficiency operation between 7.5 and 8.5 microns. The local oscillator is a PbSSe tunable diode laser kept continuously at operating temperatures of 12-60 K using a closed cycle cooler. The laser output frequency is controlled and stabilized using a high precision diode current supply, constant temperature controller, and a shock isolator mounted between the refrigerator cold tip and the diode mount. Single laser modes are selected by a grating placed in the local oscillator beam. The system employs reflecting optics throughout to minimize losses from internal reflection and absorption, and to eliminate chromatic effects. Spectral analysis of the diode laser output between 0 and 1 GHz reveals excess noise at many diode current settings, which limits the infrared spectral regions over which useful heterodyne operation can be achieved. System performance has been studied by making heterodyne measurements of etalon fringes and several Freon 13 (CF3Cl) absorption lines against a laboratory blackbody source. Preliminary field tests have also been performed using the Sun as a source.

Glenar, D.↗
NASA NTRS1980

Microwave tunable laser source: A stable, precision tunable heterodyne local oscillator

The development and capabilities of a tunable laser source utilizing a wideband electro-optic modulator and a CO2 laser are described. The precision tunability and high stability of the device are demonstrated with examples of laboratory spectroscopy. Heterodyne measurements are also presented to demonstrate the performance of the laser source as a heterodyne local oscillator. With the use of five CO2 isotope lasers and the 8 to 18 GHz sideband offset tunability of the modulator, calculations indicate that 50 percent spectral coverage in the 9 to 12 micron region is achievable. The wavelength accuracy and stability of this laser source is limited by the CO2 laser and is more than adequate for the measurement of narrow Doppler-broadened line profiles. The room-temperature operating capability and the programmability of the microwave tunable laser source are attractive features for its in-the-field implementation. Although heterodyne measurements indicated some S/N degradation when using the device as a local oscillator, there does not appear to be any fundamental limitation to the heterodyne efficiency of this laser source. Through the use of a lower noise-figure traveling wave tube amplifier and optical matching of the output beam with the photomixer, a substantial increase in the heterodyne S/N is expected.

Sachse, G. W.↗
NASA NTRS1980

Sub mm laser local oscillators: Design criteria and results

Diagnostic results are given of the spectral features and the power conversion efficiency of submillimeter (SMM) laser local oscillators. Several criteria are obtained for the design of frequency stable and efficient smm lasers for local oscillator applications. Finally, a design is described and results on the power output and power and frequency stability are given. The mode pattern is very close to a Gaussian profile so that efficient coupling to a quasioptical mixer is possible. The laser provides sufficient output power at a large number of lines to drive the mixer into the low conversion loss regime. Radiometric integration times of several minutes with a spectral resolution of 1 MHz will be possible. With present state-of-the-art Schottky mixers and low noise preamplifiers a radiometric temperature resolution of a few K can be expected over a spectral range from 500to 900 GHz.

Koepf, G. A.↗
NASA NTRS1979

Effect of rotational excitation on the band oscillator strength of OH

In the study described, a single-frequency tunable CW dye laser was used to obtain accurate absorption measurements of the band oscillator strength for various rotational-electronic lines in some transitions of OH. The band oscillator strength is shown to decrease linearly with the energy of rotational excitation. This decrease is attributed exclusively to the lengthening of the internuclear distance due to rotation.

Wang, C. C.↗