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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.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

The influence of stripe width on the threshold current of double-heterojunction lasers

Experimental measurements of the threshold current of oxide-isolated stripe laser as a function of stripe width and p-layer resistivity are presented. A calculation of the influence of carrier outdiffusion has been made, including the effect of current leakage beyond the stripe edges. The calculated threshold increase is in substantial agreement with experiment for stripe widths down to about 10 microns. The data also yield an effective diffusion length of about 7 microns for the lasers studied. Deviations between experimental and calculated thresholds occurring at stripe widths of 4-6 microns are represented by an empirical curve which is compared with previously published calculations of threshold gain.

Ladany, I.↗
NASA NTRS1980

Active notch filter network with variable notch depth, width and frequency

An active notch filter having independently adjustable notch frequency, width, and depth is provided by three equal capacitors connected in series with an operational amplifier (connected in a voltage follower configuration), a potentiometer across the series connected capacitors for notch depth adjustment, and a potentiometer (for notch frequency connected across the center capacitor); with its tap connected to receive a voltage feedback signal from a variable voltage divider comprised of another potentiometer for notch width. Adjusting the voltage dividing potentiometer will independently set the notch width, and adjusting the tap on the potentiometer across the center capacitor will independently adjust the notch frequency of the filter. A second operational amplifier connected in a voltage follower configuration may be used to connect the voltage divider output to the adjustable tap of the potentiometer across the center capacitor.

Black, J. M.↗
NASA NTRS1981

Measurement of the oscillator strengths and autoionization widths of the neutral-aluminum multiplet 3s2 3p2 P0 - 3s 3p2 2P

The hook method is used in conjunction with absorption equivalent width measurements to determine the oscillator strengths and line widths of the Al I multiplet 3s2 3p2 P0 - 3s 3p2 2P at 176 nm. Autoionization is found to be the dominant decay channel for the two levels of the 3p2 2P term, with autoionizing widths of 4.0 and 0.87 x 10 to the 10th/sec for J of 3/2 and 1/2, respectively. The van der Waals scattering cross section for the Al I transition at 176.91 nm by He is determined to be (1.3 + or - 0.3) x 10 to the -14th sq cm at 2400 K, and a solar spectrum calculation centered at 176 nm shows that the Al I features are possible diagnostic probes of (1) solar non-LTE processes, and (2) the temperature minimum and structure of the lower chromosphere.

Lombardi, G. G.↗
NASA NTRS1982

Radial widths, optical depths, and eccentricities of the Uranian rings

Observations of the stellar occultation by the Uranian rings of 15/16 August 1980 are used to estimate radial widths and normal optical depths for segments of rings 6, 5, 4, alpha, beta, eta, gamma, and delta. Synthetic occultation profiles are generated to match the observed light curves. A review of published data confirms the existence of width-radius relations for rings alpha and beta, and indicates that the optical depths of these two rings vary inversely with their radial widths. Masses are obtained for rings alpha and beta, on the assumption that differential precession is prevented by their self-gravity. A quantitative comparison of seven epsilon-ring occultation profiles obtained over a period of 3.4 yr reveals a consistent structure, which may reflect the presence of unresolved gaps and subrings.

Nicholson, P. D.↗
NASA NTRS1982

Effect of orthotropic properties and panel width on the compression strength of graphite-epoxy laminates with holes

An experimental study conducted to evaluate the effect of laminate orthotropic properties and panel width on the compression strength of 48-ply graphite-epoxy laminates with drilled holes is described. The test results are evaluated on the basis of hole size and specimen width and are used in determining parameters necessary for predicting trends using the point stress failure criterion. Good agreement is obtained between experimental and predicted values of failure for panels fabricated from two quasi-isotropic laminates and one orthotropic laminate. The results suggest that panels of different widths having holes that are large in relation to the failure prediction parameter should be included in any test program conducted to develop prediction trends that may be used in design applications.

Rhodes, M. D.↗
NASA NTRS1983

Finite-width currents, magnetic shear, and the current-driven ion-cyclotron instability

Our earlier results that non-local effects due to even a small magnetic shear produce a significant reduction of the growth rate of the ion cyclotron instability driven by a uniform current are now generalized to finite width currents. Externally prescribed as well as self-consistent shears are considered. If the current width Lc exceeds the shear length Ls, the previous results are recovered. Shear becomes less effective with reduction of Lc, and for typical parameters, the growth rate attains its (shearless) local value for Lc/Ls approximately less than 10 to the minus 2. Non-local effects of the finite current width itself come into play if Lc is further reduced to a few ion Larmor radii and can quench the instability. Previously announced in STAR as N83-28996

Bakshi, P.↗
NASA NTRS1985

Pulse-Width-to-Analog-Voltage Converter

Peak output voltage varies linearly with input-pulse duration. Circuit converts pulses of varying widths (as from sound-velocity instrumentation or tachometers) into analog voltages. Peak voltage increases in proportion to pulse width. Voltage used to drive an x-y plotter or storage oscilloscope. Pulse-width-to-voltage converter has peak output voltage that varies with duration of input pulses.

Sosack, G. S.↗
NASA NTRS1985

Extremely metal-deficient red giants. IV - Equivalent widths for 36 halo giants

Further work on a study of 36 metal-poor field red giants is reported. Chemical abundances previously determined were based on model stellar atmosphere analyses of equivalent widths from photographic image-tube echelle spectrograms obtained with with 4-m reflectors at Kitt Peak and Cerro Tololo. A tabulation of the equivalent-width data (a total of 18, 275 equivalent widths) is presented.

Luck, R. E.↗
NASA NTRS1986

Structure of the Uranian rings. II - Ring orbits and widths

A square-well model was used to calculate the midtimes, widths and optical depths at visible and IR wavelengths of the nine Uranian rings based on 13 occultation measurements from 1977-1983. Many of the measurement campaigns contained data from repeated crossings. An improved kinematical model is developed for the ring system, noting that the gamma and delta rings were confirmed to depart from Keplerian ellipses. Upper limits are calculated for the sizes of shepherd satellites of various potential densities. The ring width determinations demonstrate the existence of significant width perturbations in the rings, which all displayed particle shadowing.

French, R. G.↗
NASA NTRS1986

Terrace width variations in complex lunar craters

The widths of terrace structures in complex craters on the moon are compared to existing theoretical models of their origin. Terrace widths in an individual crater increase monotonically outward toward the crater rim. Similarly, the width W of the terraces lying closest to the rim of a crater of diameter D increases monotonically, obeying a least-squares power-law relation WS (km) = 0.09D exp 0.87 km). A simple model of slumping that ignores inertial forces and assumes a constant bedrock yield strength is in good agreement with the observations.

Pearce, Steven J.↗
NASA NTRS1988

Measurements of air-broadened and nitrogen-broadened half-widths and shifts of ozone lines near 9 microns

Air- and nitrogen-broadened half-widths and line shifts at room temperature for more than 60 individual vibration-rotation transitions in the nu1 fundamental band of (O-16)3 and several transitions in the nu3 band were determined from infrared absorption spectra. These spectra were recorded at 0.005/cm resolution with a Fourier-transform spectrometer. A tunable-diode-laser spectrometer operating in the 1090-1150/cm region was also used to record data on oxygen-, nitrogen-, and air-broadened half-widths for selected individual transitions. The nitrogen- and air-broadened half-widths determined by these two different measurement techniques are consistent to within 4 percent. The results are in good agreement with other published measurements and calculations.

Smith, M. A. H.↗
NASA NTRS1939

Experimental Study of Deformation and of Effective Width in Axially Loaded Sheet-stringer Panels

The deformation of two sheet-stringer panels subjected to end compression under carefully controlled end conditions was measured at a number of points and at a number of loads, most of which were above the load at which the sheet had begun to buckle. The two panels were identical except for the sheet, which was 0.70-inch 24st alclad for specimen 1 and 0.025-inch 24st aluminum alloy for specimen 6. A technique was developed for attaching Tuckerman optical strain gauges to the sheet without disturbing the strain distribution in the sheet by the method of attachment. This technique was used to explore the strain distribution in the sheet at various loads. The twisting and the bending of the stringers was measured by means of pointers attached to the stringers. The shape of the buckles in the sheet of specimen 6 was recorded at two loads by means of plaster casts. The sheet and the stringer loads at failure are compared with the corresponding loads for five similar panels tested at the Navy Model Basin. A detailed comparison is made between the measured deformation of the buckled sheet and the deformation calculated from approximate theories for the deformation in a rectangular sheet with freely supported edges buckling under end compression advanced by Timoshenko, Frankland, and Marguerre. The measured effective width for the specimens is compared with the effective width given by nine different relations for effective width as a function of the edge stress divided by the buckling stress of the sheet. The analysis of the measured stringer deformation is confined to an application of Southwell's method of plotting deformation against deformation over load. It was concluded that the stringer failure in both specimens were due to an instability in which the stringer was simultaneously twisted and bent as a column.

FORMULAS - BUCKLING - KARMAN↗
NASA NTRS1936

The impact on floats or hulls during landing as affected by bottom width

For floats and hulls having V bottoms the impact force does not necessarily increase with increasing width. Therefore, the weight of the float landing gear, side walls, and other parts, and of the fuselage construction need not be increased with increasing bottom width, but the weight of the bottom construction itself, on the other hand, does not increase with increase in bottom width and is largely determined by the type of construction.

Mewes, E↗
NASA NTRS1994

Effect of nonlinear interactions on p-mode frequencies and line widths

We calculate the effect of nonlinear interactions among solar acoustic modes upon the modal frequencies and energy loss rates (or line widths). The frequency shift for a radial p-mode of frequency 3 mHz is found to be about -0.5 microHz. The magnitude of nonlinear frequency shift increases more rapidly with frequency than the inverse mode mass (mode mass is defined as the ratio of energy in the mode to its surface velocity amplitude squared). This frequency shift is primarily due to nonresonant three-mode interactions and is dominated by high l surface gravity waves (f-modes) and p-modes. The line width of a radial p-mode of frequency 3 mHz, due to resonant nonlinear interactions, is about 0.3 microHz. This result is consistent with that of Kumar and Goldreich (1989). We also find, in agreement with these authors, that the most important nonlinear interactions of trapped p-modes involve f-modes and high-frequency p-modes (frequency greater than about 5 mHz) which propagate in the solar photosphere. Thus, using the arguments advanced by Kumar & Goldreich (1989), we conclude that nonlinear couplings cannot saturate the overstable solar p-modes at their small observed amplitudes. Both the nonlinear frequency shifts and line widths, at a fixed frequency, are proportional to the inverse of mode mass which for modes of degree greater than about 100 is approximately l(exp 0.8). Therefore, the frequency of an f-mode of l = 1000, due to nonlinear interactions, is decreased by approximately 0.4%.

Kumar, Pawan↗
NASA NTRS1994

Tests of the Tully-Fisher relation. 1: Scatter in infrared magnitude versus 21 cm width

We examine the precision of the Tully-Fisher relation (TFR) using a sample of galaxies in the Coma region of the sky, and find that it is good to 5% or better in measuring relative distances. Total magnitudes and disk axis ratios are derived from H and I band surface photometry, and Arecibo 21 cm profiles define the rotation speeds of the galaxies. Using 25 galaxies for which the disk inclination and 21 cm width are well defined, we find an rms deviation of 0.10 mag from a linear TFR with dI/d(log W(sub c)) = -5.6. Each galaxy is assumed to be at a distance proportional to its redshift, and an extinction correction of 1.4(1-b/a) mag is applied to the total I magnitude. The measured scatter is less than 0.15 mag using milder extinction laws from the literature. The I band TFR scatter is consistent with measurement error, and the 95% CL limits on the intrinsic scatter are 0-0.10 mag. The rms scatter using H band magnitudes is 0.20 mag (N = 17). The low width galaxies have scatter in H significantly in excess of known measurement error, but the higher width half of the galaxies have scatter consistent with measurement error. The H band TFR slope may be as steep as the I band slope. As the first applications of this tight correlation, we note the following: (1) the data for the particular spirals commonly used to define the TFR distance to the Coma cluster are inconsistent with being at a common distance and are in fact in free Hubble expansion, with an upper limit of 300 km/s on the rms peculiar line-of-sight velocity of these gas-rich spirals; and (2) the gravitational potential in the disks of these galaxies has typical ellipticity less than 5%. The published data for three nearby spiral galaxies with Cepheid distance determinations are inconsistent with our Coma TFR, suggesting that these local calibrators are either ill-measured or peculiar relative to the Coma Supercluster spirals, or that the TFR has a varying form in different locales.

Bernstein, Gary M.↗
NASA NTRS2001

Calculated Half-widths and Line Shifts of Water Vapor Transitions in the 0.7- Micron Region and a Comparison with Published Data

Pressure-broadened half-widths and pressure-induced line shifts for the two most important bands of water vapor in the 0.7-micron region are determined using the complex Robert-Bonamy (CRB) formalism. The calculations are made with nitrogen and oxygen as the perturbing gas from which values for air as the perturbing gas are determined. The intermolecular potential is taken as a sum of electrostatic contributions and Lennard-Jones (6-12) atom-atom, and isotropic induction and dispersion components. The dynamics of the collision process are correct to second order in time. The calculated values are compared with published measurements and agreement is observed for both half-widths and line shifts. The temperature dependence of the half-width, which is necessary for reduction of remotely sensed data, is determined.

Gamache, Robert R.↗
NASA NTRS2007

The Width of a Solar Coronal Mass Ejection and the Source of the Driving Magnetic Explosion

We show that the strength of the magnetic field in the area covered by the flare arcade following a CME-producing ejective solar eruption can be estimated from the final angular width of the CME in the outer corona and the final angular width of the flare arcade. We assume (1) the flux-rope plasmoid ejected from the flare site becomes the interior of the CME plasmoid, (2) in the outer corona (R greater than 2R(sub Sun)) the CME is roughly a spherical plasmoid with legs shaped like a light bulb, and (3) beyond some height in or below the outer corona the CME plasmoid is in lateral pressure balance with the surrounding magnetic field. The strength of the nearly radial magnetic field in the outer corona is estimated from the radial component of the interplanetary magnetic field measured by Ulysses. We apply this model to three well-observed CMEs that exploded from flare regions of extremely different size and magnetic setting. One of these CMEs is an over-and-out CME that exploded from a laterally far offset compact ejective flare. In each event, the estimated source-region field strength is appropriate for the magnetic setting of the flare. This agreement (1) indicates that CMEs are propelled by the magnetic field of the CME plasmoid pushing against the surrounding magnetic field, (2) supports the magnetic-arch-blowout scenario for over-and-out CMEs, and (3) shows that a CME s final angular width in the outer corona can be estimated from the amount of magnetic flux covered by the source-region flare arcade.

Moore, Ronald L.↗