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At least 577 records · Page 32

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NASA NTRS1992

Experimental and theoretical studies of the He(2+)-He system - Differential cross sections for direct, single-, and double-charge-transfer scattering at keV energies

Measurements and calculations of differential cross sections for direct scattering, single-charge transfer, and double-charge transfer in collisions of 1.5-, 2.0-, 6.0-, and 10.0-keV (He-3)2+ with an He-4 target are reported. The measurements cover laboratory scattering angles below 1.5 deg with an angular resolution of about 0.03 deg. A quantum-mechanical molecular-state representation is employed in the calculations; in the case of single-charge transfer a two-state close-coupling calculation is carried out taking into account electron-translation effects. The theoretical calculations agree well with the experimental results for direct scattering and double-charge transfer. The present calculation identifies the origins of oscillatory structures observed in the differential cross sections.

Gao, R. S.↗

NASA NTRS1992

On the implementation and performance of single and double differential detection schemes

A variety of schemes for performing double differential detection of MPSK signals in environments characterized by frequency offset are discussed. Comparisons of their implementation and performance are made with single differential detection systems. The application of the idea of multiple symbol detection in double differential detection schemes is addressed.

Simon, Marvin K.↗

NASA NTRS1992

Anomalous capacitance of quantum well double-barrier diodes

The S-parameters of several different quantum well double barrier diodes have been measured. A technique has been developed for measuring whisker contacted diodes with an HP 8510B automatic network analyzer. Special coaxial mounts using K-connectors were designed to enable measurements up to 20 GHz. The voltage-dependent conductance and capacitance were derived from the measured reflection coefficient of each device. The C/V characteristics were observed to exhibit an anomalous increase at voltages corresponding to the negative differential resistance region (NDR). These are the first reported S-parameter measurements in the negative differential resistance region of quantum well double barrier diodes. A theory is presented that explains, in part, the observed results.

Boric, Olga↗

NASA NTRS1992

Fast plasmoid formation in double arcades

The evolution of two neighboring nonsymmetric arcades with footpoint shearing profiles which can change in time is simulated in order to investigate the quasi-static evolution of a double arcade system. It is found that rapid forced reconnection can take place repeatedly, forming a series of plasmoids. A two-arcade system laterally confined by surrounding fluxes can develop instability with nonsymmetric footpoint shear, but the instability is significantly lower in comparison with the case in which the system is confined by a 'hard box' or periodic boundary conditions. The fast plasmoid formation process due to asymmetry switching is not due to the presence of simulation walls. The behavior of double arcades with asymmetry switching is described using equilibrium bifurcation diagrams with footpoint shear and degree of asymmetry, as two independent control parameters.

Finn, J. M.↗

NASA NTRS1993

Self-Frequency-Doubling Glass-Fiber Laser

Specially prepared germanium and phosphorous-doped glass optical fiber doped with neodymium shown to act as self-frequency-doubling laser. Self-frequency-doubling fiber laser with further refinements, eliminates need for expensive, easily damaged, nonlinear crystals currently used. Enables one to avoid loss and damage mechanisms associated with interfaces of nonlinear crystals as well as to eliminate angle/temperature phase-matching tuning.

Selker, Mark D.↗

NASA NTRS1993

Diode-Pumped, Q-Switched, Frequency-Doubling Laser

Experimental Q-switched, diode-pumped, intracavity-frequency-doubling laser generates pulses of radiation at wavelength of 532 nm from excitation at 810 nm. Principal innovative feature distinguishing laser from others of its type: pulsed operation of laser at pulse-repetition frequencies higher than reported previously. Folded resonator keeps most of second-harmonic radiation away from Q-switcher, laser crystal, and laser diodes. Folding mirror highly reflective at fundamental laser wavelength and highly transmissive at second-harmonic laser wavelength. By virtue of difference of about 0.6 percent between reflectivities in two polarizations at fundamental wavelength, folding mirror favors polarized oscillation at fundamental wavelength. This characteristic desirable for doubling of frequency in some intracavity crystals.

Hemmati, Hamid↗

NASA NTRS1993

Double-V block fingers with cruciform recess

In a robot having a gripper including a pair of fingers and a drive motor for driving the fingers toward and away from one another while the fingers remain parallel to each other, the fingers consist of finger pads, which interface with a handle on an object to be grasped, and a shank, which attaches the fingers to the robot gripper. The double-V finger has two orthogonal V-grooves forming in the center of the finger pads and recessed cruciform. The double-V finger is used with a handle on the object to be grasped which is the negative of the finger pads. The handle face consists of V-shaped pads capped with a rectangular cruciform. As the gripper is brought into place near the handle, the finger pads are lined up facing the handle pads. When the finger pad and the handle pad are in proper alignment, the rectangular ridges on the handle fall inside the rectangular grooves on the finger, and the grip is complete.

Voellmer, George M.↗

NASA NTRS1992

Double dipole antenna SIS receivers at 100 and 400 GHz

Antenna patterns were measured between 95 and 120 GHz for a double dipole antenna / ellipsoidal lens combination. The structure produces a non-astigmatic beam with low side lobe levels over that whole band. A heterodyne SIS receiver based on this concept gave a best noise temperature of 145 K DSB at 98 GHz. Measurements were also made with a 400 GHz heterodyne SIS receiver, using a double dipole antenna in conjunction with a hyperhemispherical lens. The best noise temperature was 220 K DSB at 402 GHz. On-chip stubs were used to tune out the SIS junction capacitance.

Skalare, A.↗

NASA NTRS1992

Double-slot antennas on extended hemispherical dielectric lenses

An investigation of the coupling efficiencies to a gaussian-beam of a double-slot antenna on a hyperhemispherical lens is presented. It is shown that both lenses couple equally well to an appropriate gaussian beam (about 80 percent). The radiation patterns of both lenses with a double-slot antenna are computed using the ray-tracing method. The experimental radiation patterns are presented and show close agreement to the theoretically computed patterns.

Filipovic, Daniel F.↗

NASA NTRS1992

Solution of the Schroedinger equation for a double minimum potential

We apply Richardson's extrapolation to zero mesh size to calculate the dissociation energies and wavefunctions of a double minimum potential curve for the E,F1Sigma(+)g state of H2. We demonstrate that a double minimum potential presents no difficulties and that this extrapolation method is to be preferred over a quadratic extrapolation or the use of a basis expansion.

Goorvitch, D.↗

NASA NTRS1992

Resistivity due to weak double layers - A model for auroral arc thickness

We have calculated the resistivity due to a sequence of fluctuating weak double layers aligned parallel to the ambient magnetic field line. The average response of an electron drifting through a 1D randomly oriented array of WDLs is studied using a test particle approach. The average is taken over the randomly fluctuating values of the electric field associated with the double layers. Based on our calculations, we estimate that a 350 eV electron energy the thickness of the visual auroral arc is about 2.5 km and that of the auroral fine structure as about 250 m when mapped down to the ionosphere. The significance of our calculations is discussed in the context of magnetosphere-ionosphere coupling.

Prakash, Manju↗

NASA NTRS1992

The Objective Double Crystal Spectrometer

The solar corona, supernova remnants, the hot diffuse interstellar gas in the Galaxy, galactic halos, and the hot intracluster gas in rich clusters of galaxies, are examples of extended astrophysical plasmas which emit line-rich spectra in the X-ray spectral range from 1.5 to 25 A. These phenomena represent a significant fraction of the baryonic matter in the universe. The study of the composition, structure and dynamics of these astrophysical plasmas requires observations with both high spectral and spatial resolution simultaneously. The Objective Double Crystal Spectrometer, coupled with a grazing incidence X-ray telescope, represents a stigmatic instrument which is highly efficient for the study of such sources. We describe the configuration and performance (spatial resolution, spectral resolution and efficiency) of the Objective Double Crystal spectrometer.

Walker, Arthur B. C., Jr.↗

NASA NTRS1931

The effectiveness of a double-stem injection valve in controlling combustion in a compression-ignition engine

An investigation was made to determine to what extent the rates of combustion in a compression-ignition engine can be controlled by varying the rates of fuel injection. The tests showed that the double-stem valve operated satisfactorily under all normal injection conditions; the rate of injection has a definite effect on the rate of combustion; the engine performance with the double-stem valve was inferior to that obtained with a single-stem valve; and the control of injection rates permitted by an injection valve of two stages of discharge is not sufficient to effect the desired rates of combustion.

Spanogle, J A↗

NASA NTRS1957

Wind-tunnel Investigation of External-flow Jet-augmented Double Slotted Flaps on a Rectangular Wing at an Angle of Attack of 0 Degree to High Momentum Coefficients

A wind-tunnel investigation has been made to determine the characteristics of external-flow jet-augmented double slotted flaps which appear suitable for application to airplanes with pod-mounted engines. The investigation included tests of the rectangular wing with an aspect ratio of 6 over a momentum-coefficient range from 0 to 28. Lift coefficients larger than the jet reaction in the lift direction were obtained with the external-flow jet-augmented double slotted flaps.

HIGH-LIFT DEVICES - COMPLETE WINGS↗

NASA NTRS1941

Wind-tunnel investigation of NACA 23012, 23021, and 23030 airfoils equipped with 40-percent-chord double slotted flaps

Report presents the results of an investigation conducted in the NACA 7 by 10-foot win tunnel to determine the effect of the deflection of main and auxiliary slotted flaps on the aerodynamic section characteristics of large-chord NACA 23012, 23021, 23030 airfoils equipped with 40-percent-chord double slotted flaps. The complete aerodynamic section characteristics and envelope polar curves are given for each airfoil-flap combination. The effect of airfoil thickness is shown, and comparisons are made of single slotted flaps with double slotted flaps on each of the airfoils.

Harris, Thomas A↗

NASA NTRS1994

Double-Square-Loop Triband Frequency-Selective Microwave Reflector

Double-square-loop antenna elements arrayed on dielectric panel. Dichroic microwave reflector consisting of planar square array of double-square-loop copper elements on thin sheet of Kapton (or equivalent) polyimide supported by Kevlar (or equivalent) aromatic polyamid honeycomb sandwich panel. Array and panel designed to reflect most of incident electromagnetic radiation of frequencies between 7.2 and 8.4 GHz (in X band) and to transmit most of that at 2.3 GHz (in S Band) and 13.8 GHz {in K(sub u) band}.

Wu, Te-Kao↗

NASA NTRS1993

Qualification test of the Ross Double Planetary Mixer

This test report describes the qualification test of the Ross Double Planetary Mixer used to mix room temperature vulcanized (RTV) silicone (Dow Corning 90-006-2) for the redesigned solid rocket motor (RSRM) nozzle joints. Testing was completed 18 June 1993 in the M-113A Nozzle Fabrication Facility at Thiokol Corporation, Space Operations, Brigham City, Utah. The Ross mixer provides better mixing and better control on temperature and humidity, resulting in better quality RTV and a longer usable pot life. The test began on 3 May 1993 and was stopped due to operator error during the tensile strength and elongation testing. Specimens were ruined without gathering any useful data. A 'no test' was declared, the problem was remedied, and the test was re-run with MSFC approval. The test was run and all pass/fail criteria were met, most with a considerable margin. The Ross Double Planetary Mixer met all certification objectives and is recommended for immediate use for mixing RTV silicone for RSRM nozzle joints.

Lueders, Kurt F.↗

NASA NTRS1995

A study of the vortex flow over 76/40-deg double-delta wing

A low-speed wind-tunnel study of the flow about a 76/40-deg double-delta wing is described for angles of attack ranging from -10 to 25 deg and Reynolds numbers ranging from 0.5 to 1.5 Million. The study was conducted to provide data for the purpose of understanding the vortical flow behavior and for validating Computational Fluid Dynamics methods. Flow visualization tests have provided insight into the effect of the angle of attack and Reynolds number of the vortex-dominated flow both on and off of the surface of the double-delta wing. Upper surface pressure recordings from pressure orifices and Pressure Sensitive Paint have provided data on the pressures induced by the vortices. Flowfield surveys were carried out at an angle of attack of 10 deg by using a thin 5-hole probe. Numerical solutions of the compressible thin-layer Navier-Stokes equations were conducted and compared to the experimental data.

Verhaagen, N. G.↗