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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Emission measures, electron densities, and nonthermal velocities from optically thin UV lines near a quiet solar limb

Calibrated intensities and line widths are presented for 45 optically thin chromospheric and transition-zone UV lines observed in a quiet area near the solar limb. The observations were made over the wavelength range from 1175 to 1915 A with the slit spectrograph on the Skylab Apollo Telescope Mount. Three nonthermal-velocity components are derived from the transition-zone line widths: a main component of 23 km/s and two high-velocity components of 45 and 75 km/s, respectively, which contribute 5% to 10% of the averaged intensity. Absolute intensities are determined as a function of height, emission measures are obtained as functions of height as well as temperature, and electron densities are estimated from density-sensitive line ratios. The densities estimated from different sets of lines are found not to agree with each other, but the values obtained from the Si III multiplet between 1297 and 1301 A are considered to be the most reliable. An atmospheric model with inhomogeneous structures extending high above the solar surface is suggested.

Moe, O. K.↗
NASA NTRS1977

A photon-counting multichannel spectrometer

A multichannel detector system is described in which the positions of individual photon events in a high-gain image intensifier are decoded in the output of a video detector. The high-gain intensifier consists of a pair of three-stage electrostatic image-tube assemblies each containing three fiber-optically-coupled tubes potted in a rugged package with an internal high-voltage supply. Operation of the electrooptical system is discussed along with the pulse-detection process and the operation of the spectrograph in which the image-tube assembly is mounted. It is noted that the spectrometer detects 1.0 count/sec per A for an object of magnitude 13.0 at the peak of its response in the visual band when no light is lost on the slit, that a 10% coincidence correction is reached at an overall count rate of 860 per sec, and that the response follows an exponential law up to count rates of about 4000 per sec. The measured spectrum of the Seyfert galaxy NGC 5548 is provided as an example of the raw data produced by the instrument on a 1.5 meter telescope.

Shectman, S. A.↗
NASA NTRS1976

Active image restoration with a flexible mirror

The 30 by 5 cm aperture telescope described uses six moveable mirrors to compensate for phase distortions induced by the atmosphere. A feedback system is used to adjust the mirrors in real time to maximize the intensity of light passing through a narrow slit in the image plane. Using the telescope, diffraction-limited images of objects were obtained, using both laser and white light, through 250 meters of turbulent atmosphere.

Buffington, A.↗
NASA NTRS1977

Chromospheric limb spectra from Skylab - 2000 to 3200 A

Chromospheric limb spectra of a quiet-sun region between 2000 and 3200 A recorded by the normal-incidence spectrograph on Skylab are discussed. The spectral resolution is 0.12 A, and the projected slit area on the sun is 2 by 60 arcsec. A list of lines with wavelengths, identifications, and absolute intensities is given for the spectrum recorded at +4 arcsec outside the white-light limb. The intensity behavior outside the limb is shown for lines of the ions C II, Si II, Cr II, Mn II, Fe II, Fe III, Co II, and Ni II. The widths of the intersystem lines of Si II and C II increase monotonically with height above the limb. The full width at half-maximum of the Si II lines increases from 0.034 A at the limb to 0.27 A at +12 arcsec above the limb. The widths of the C II lines increase from 0.17 A at +2 arcsec to 0.31 A at +12 arcsec.

Doschek, G. A.↗
NASA NTRS1977

Correction of atmospheric distortion with an image-sharpening telescope

A 30 x 5 cm aperture telescope employing six movable mirrors to compensate for atmospherically induced phase distortion is built and tested. A feedback system adjusts the mirrors in real time to maximize the intensity of light passing through a narrow slit in the image plane. Essentially diffraction-limited performance is achieved when imaging both laser and white-light objects through 250 m of turbulent atmosphere. The behavior of the telescope is accurately predicted by computer simulations. The system has yet to achieve its full potential, but has already operated successfully for objects as dim as 5th magnitude.

Buffington, A.↗
NASA NTRS1977

Spatially resolved excitation temperature measurements in a hypersonic flow using the hook method

Following an analysis of the hook equations for variation of refractivity along a spectrograph slit a series of experiments is reported, in which CO2 was used as the test gas, and the flow variations were spatially resolved. The hooked spectra were used to measure the ground state number densities of the impurity atom of CrI present in the flow. The excitation temperature of the CrI 1-eV level was obtained from the separation of the hooks of the CrI 425.4-nm transition resonance line and simultaneously the 434.4-nm CrI eV lower level line, from the shock to the body of the hypersonic shock tunnel flow. This excitation temperature is compared with theoretical calculations of the CO2 gas temperature. Some further applications of the hook type methods to gas diagnostics are discussed.

Sandeman, R. J.↗
NASA NTRS1974

Raman spectra of gaseous and solid N2F4

The Raman spectrum of gaseous N2F4 at a pressure of 760 Torr was recorded with a spectral slit width of 3 kaysers. Ten of the expected eleven fundamentals of the symmetric motions of both the gauche and trans isomers give rise to strongly polarized Raman lines. These new data require a reassignment of some of the fundamentals for both the C2 and C2h conformers. The Raman of the solid at 18 K was also recorded. Both conformers were found in the solid even after annealing the sample for 9 hr at a temperature of 101.6 K and 3 hr at a temperature of 106.8 K. Bands attributable to the gauche isomer became more intense relative to those for the trans isomer after several hours of annealing.

Durig, J. R.↗
NASA NTRS1977

Optical spectrum of HDE 245770 /A0535 + 26/

Narrow-band spectrophotometric observations of HDE 245770 with the multichannel spectrometer and slit spectra obtained with the SIT digital spectrograph at the Cassegrain focus of the 5-m Hale telescope indicate that this star is of spectral type B0 with emission at H-alpha, H-beta, and probably 5876 A of He I. There is some evidence that it is of luminosity class III. The reddening is estimated in various ways and corresponds to a B-V color excess of 0.80. If the star is really a giant, its distance is approximately 1.8 kpc. No variations larger than 1% at the reported 104-x X-ray pulse period are evident in the data in visual magnitude, color, or H-alpha emission intensity. This is not surprising, since the optical star is much more luminous than the X-ray object, and the heating effect of the X-ray source (which is assumed to be one component of a binary) on the B0 star's atmosphere can produce at most a few percent modulation in visual light.

Wade, R. A.↗
NASA NTRS1977

Emission measures and structure of the transition region of a sunspot from emission lines in the far ultraviolet

Absolute intensities of emission lines in the wavelength range from 1200 A to 1817 A from the large sunspot in McMath region 12510 near the disk center are presented. The intensities are averaged across the umbra and penumbra of the sunspot. The observations were made with the NRL slit spectrograph on Skylab. Emission measures are derived from the measured intensities. Assuming a balance between the divergence of the conductive energy flux and the radiative energy losses, a self-consistent model of the lower transition region in the sunspot is constructed. The model gives a constant pressure of about 0.19 dyn/sq cm and a conductive flux which decreases approximately one order of magnitude between 200,000 and 40,000 K. The temperature gradient is relatively constant, increasing slowly with decreasing temperature

Cheng, C.-C.↗
NASA NTRS1977

A search for a turbulent-free region in the solar transition zone

A search for a turbulence-free transition-zone region was conducted. The data used were spectra recorded by a slit spectrograph on Skylab. It was found that the nonthermal turbulent motions are smallest in certain active regions and quiescent prominences. The spectra of one such region, a quiescent prominence, are discussed. The nonthermal turbulence in the region is between about 2 and 7 km/s. Therefore, the widths of lines emitted by transition-zone ions are determined primarily by the ion temperature. To within the experimental error, temperatures derived from the line widths are equal to the temperatures of maximum emitting efficiency obtained using the ionization equilibrium calculations of Jordan (1969).

Feldman, U.↗
NASA NTRS1977

Acoustics-turbulence interaction

An investigation of the instability frequency was undertaken. Measurements revealed that the hot wire probe induces and sustains stable upstream oscillation of the free shear layer. The characteristics of the free shear layer tone are found to be different from the slit jet wedge edgetone phenomenon. The shear tone induced by a plane wedge in a plane free shear layer was then examined in order to further document the phenomenon. The eigenvalues and eigenfunctions of the tone fundamental show agreement with the spatial stability theory. A comprehensive summary of the results is also included.

Hussain, A. K. M. F.↗
NASA NTRS1977

Selected developments in laser wire stripping

The operation of mechanical and thermal strippers and the early development of laser wire strippers are reviewed. NASA sponsored development of laser wire stripping for space shuttle includes bench-type strippers as well as an advanced portable hand-held stripper which incorporates a miniaturized carbon dioxide laser and a rotating optics unit with a gas-jet assist and debris exhaust. Drives and controls girdle the wire and slit the remaining slug without manual assistance. This unit can strip wire sizes 26 through 12 gage. A larger-capacity hand-held unit for wire sizes through 1/0 gage was built using a neodynium-doped yttrium aluminum garnet (Nd:YAG) laser. The hand-held units have a flexible umbilical cable to an accompanying cart that carries the power supply, gas supply, cooling unit, and the controls.

Source record↗
NASA NTRS1977

High resolution 10 mu spectrometry at different planetary latitudes. A practical Hadamard transform spectrometer for astronomical application

Infrared observations at different latitudes were studied in order to obtain spectra in the 10 micrometers region to understand differences in chemical composition or physical structure of the optical features. In order to receive such spectra of a rotating planet, simultaneous observations at different latitudes were made. A Hadamard transform spectrometer with 15 entrance slits was used to obtain 15 simultaneous spectra, at a resolution of 0.01 micrometers. The spectral band covered contained 255 spectral elements.

Tai, M. H.↗
NASA NTRS1978

Silicon crystals: Process for manufacturing wafer-like silicon crystals with a columnar structure

Wafer-like crystals suitable for making solar cells are formed by pouring molten Si containing suitable dopants into a mold of the desired shape and allowing it to solidify in a temperature gradient, whereby the large surface of the melt in contact with the mold is kept at less than 200 D and the free surface is kept at a temperature of 200-1000 D higher, but below the melting point of Si. The mold can also be made in the form of a slit, whereby the 2 sides of the mold are kept at different temperatures. A mold was milled in the surface of a cylindrical graphite block 200 mm in diameter. The granite block was induction heated and the bottom of the mold was cooled by means of a water-cooled Cu plate, so that the surface of the mold in contact with one of the largest surfaces of the melt was held at approximately 800 D. The free surface of the melt was subjected to thermal radiation from a graphite plate located 2 mm from the surface and heated to 1500 D. The Si crystal formed after slow cooling to room temperature had a columnar structure and was cut with a diamond saw into wafers approximately 500 mm thick. Solar cells prepared from these wafers had efficiencies of 10 to 11%.

Authier, B.↗
NASA NTRS1977

The rotation of Uranus

The rotation rate of Uranus is investigated by measuring the tilts of reflected Fraunhofer lines observed through a slit spectrograph. The data obtained are corrected for the effect of astronomical seeing, and the data-reduction procedures are outlined in detail. Observations are discussed which indicate that the planet's pole of rotation is parallel to the pole of its satellites' orbits and that Uranus may not rotate as a solid body. A rotational period of 15.57 + or - 0.80 hr is derived for northern midlatitudes on Uranus by adopting a planetary diameter of 51,800 + or - 600 km. Possible sources of small systematic errors are briefly considered.

Brown, R. A.↗
NASA NTRS1977

Numerical determination of the fundamental eigenvalue for the Laplace operator on a spherical domain

Methods for obtaining approximate solutions for the fundamental eigenvalue of the Laplace-Beltrami operator (i.e., the membrane eignevalue problem for the vibration equation) on the unit spherical surface are developed. Two types of spherical surface domains are considered: the interior of a spherical triangle, and the exterior of a great circle arc extending for less than pi radians (a spherical surface with a slit). In both cases, zero boundary conditions are imposed. In order to solve the resulting second-order elliptic partial differential equations in two independent variables, a finite difference approximation is employed. The fundamental eigenvalue is approximated by iteration utilizing the power method and point successive overrelaxation. Some numerical results are given and compared, in certain special cases, with analytical solutions to the eigenvalue problem. The significance of the numerical eigenvalue results is discussed in terms of the singularities in the solution of three-dimensional boundary-value problems near a polyhedral corner of the domain.

Walden, H.↗
NASA NTRS1978

A uniqueness proof for a transonic flow problem

The uniqueness of the first-order lifting-line correction to the two-dimensional transonic small disturbance potential for the flow past a lifting, three-dimensional, large-aspect-ratio wing is proved. The correction is the solution of a linear equation of mixed type in the plane slit along the positive x-axis. The boundary data consist of Neumann data, continuity restrictions, the Kutta condition, and the form of the asymptotic behavior at infinity. The zeroth-order flow is assumed to be shock-free, and hence the correction is shock-free.

Cook, L. P.↗
NASA NTRS1977

Evaluation of flawed composite structure under static and cyclic loading

This paper presents the results of a program investigating the effects of initial defects on the fatigue and fracture response of composite laminates. The structural laminates investigated were a typical angle-ply laminate, a polar/hoop-wound pressure vessel laminate, and a typical engine fan blade laminate. Defects investigated were full- and half-penetration circular holes, full- and half-penetration slits, and countersink holes. Results are presented showing the effects of the defect size and type on the static fracture strength, fatigue performance, and residual static strength. The results of inspection procedures are shown, describing the effect of cyclic and static loadings on damage propagation in composite laminates. The data in this study were used to define proof test levels as a qualification procedure in composite structure subjected to cyclic loading.

Porter, T. R.↗