Nondestructive ultrasonic measurement of bolt preload using the pulsed-phase locked-loop interferometer

Achieving accurate preload in threaded fasteners is an important and often critical problem which is encountered in nearly all sectors of government and industry. Conventional tensioning methods which rely on torque carry with them the disadvantage of requiring constant friction in the fastener in order to accurately correlate torque to preload. Since most of the applied torque typically overcomes friction rather than tensioning the fastener, small variations in friction can cause large variations in preload. An instrument called a pulsed phase locked loop interferometer, which was recently developed at NASA Langley, has found widespread use for measurement of stress as well as material properties. When used to measure bolt preload, this system detects changes in the fastener length and sound velocity which are independent of friction. The system is therefore capable of accurately establishing the correct change in bolt tension. This high resolution instrument has been used for precision measurement of preload in critical fasteners for numerous applications such as the space shuttle landing gear and helicopter main rotors

Investigation of critical burning of fuel droplets

Fuel droplets were simulated by porous spheres having diameters in the range 0.63 to 1.9 cm and combustion tests were conducted at pressures up to 78 atm in a quiescent cold air environment. Measurements were made of the burning rate and liquid surface temperature during steady combustion. A high pressure flat flame burner apparatus is under development in order to allow testing of high pressure droplet burning in a combustion gas environment. Work was continued on the high pressure strand combustion characteristics of liquid fuels, with the major emphasis on hydrazine. Data was obtained on the burning rate and liquid surface temperatures at pressures in the range 7 to 500 psia. The response of a burning liquid monopropellant to imposed pressure oscillations is being investigated

The investigation of critical pressure burning of fuel droplets Annual report, 1 Jan. - 31 Dec. 1970

Experimental and theoretical results of critical pressure burning of fuel droplet

Giant Fluctuations of Coulomb Drag in a Bilayer System

We have observed reproducible fluctuations of the Coulomb drag, both as a function of magnetic field and electron concentration, which are a manifestation of quantum interference of electrons in the layers. At low temperatures the fluctuations exceed the average drag, giving rise to random changes of the sign of the drag. The fluctuations are found to be much larger than previously expected, and we propose a model which explains their enhancement by considering fluctuations of local electron properties.Comment: 10 pages, 4 figure

Dual-doped thermographic phosphor particles as surrogates for green fluorescent protein-labeled cells in tests of cytometric neurocatheters

We investigated the laser-induced fluorescence of particles of a compound thermographic phosphorLa2O2S:Eu(1%) and Gd2O2S:Eu(1%) to see if they can serve as a surrogate for cells transfected with the green fluorescent protein, in tests of neurocatheters used for intraparenchymal celldelivery. At an excitation wavelength of 337 nm and a concentration of ≈2×106 particles ml−1, the resulting slurries produced fluorescence intensities at 625 nm that were within a factor of 2 of those produced by similar number densities of relevant cells, thus suggesting the utility of this approach

Tuning the electrically evaluated electron Lande g factor in GaAs quantum dots and quantum wells of different well widths

We evaluate the Lande g factor of electrons in quantum dots (QDs) fabricated from GaAs quantum well (QW) structures of different well width. We first determine the Lande electron g factor of the QWs through resistive detection of electron spin resonance and compare it to the enhanced electron g factor determined from analysis of the magneto-transport. Next, we form laterally defined quantum dots using these quantum wells and extract the electron g factor from analysis of the cotunneling and Kondo effect within the quantum dots. We conclude that the Lande electron g factor of the quantum dot is primarily governed by the electron g factor of the quantum well suggesting that well width is an ideal design parameter for g-factor engineering QDs

Simulations of Galactic Cosmic Rays Impacts on the Herschel/PACS Photoconductor Arrays with Geant4 Code

We present results of simulations performed with the Geant4 software code of the effects of Galactic Cosmic Ray impacts on the photoconductor arrays of the PACS instrument. This instrument is part of the ESA-Herschel payload, which will be launched in late 2007 and will operate at the Lagrangian L2 point of the Sun-Earth system. Both the Satellite plus the cryostat (the shield) and the detector act as source of secondary events, affecting the detector performance. Secondary event rates originated within the detector and from the shield are of comparable intensity. The impacts deposit energy on each photoconductor pixel but do not affect the behaviour of nearby pixels. These latter are hit with a probability always lower than 7%. The energy deposited produces a spike which can be hundreds times larger than the noise. We then compare our simulations with proton irradiation tests carried out for one of the detector modules and follow the detector behaviour under 'real' conditions.Comment: paper submitted to Experimental Astronomy in March 200