997,515 research outputs found
Tracking receiver Patent
Design and development of tracking receiver for tracking satellites and receiving radio signal transmissions under adverse noise condition
Method for fiberizing ceramic materials Patent
Process for fiberizing ceramic materials with high fusion temperatures and tensile strengt
Electro-optical device for monitoring wire size
Device recognizes variations in wire size and is being used during computer memory-plane fabrication. Decrease in wire diameter, due to stretching, permits removal of wire from memory-plant mold. Monitoring provides means of detecting imperfect wire and permits fabrication of computer memory plane to be stopped prior to its insertion into mold
Comment on "Quantum Confinement and Optical Gaps in Si Nanocrystals"
We show that the method used by Ogut, Chelikowsky and Louie (Phys. Rev. Lett.
79, 1770 (1997)) to calculate the optical gap of Si nanocrystals omits an
electron-hole polarization energy. When this contribution is taken into
account, the corrected optical gap is in excellent agreement with
semi-empirical pseudopotential calculations.Comment: 3 pages, 1 figur
Collective atomic recoil motion in short-pulse multi-matter-optical wave mixing
An analytical perturbation theory of short-pulse, matter-wave superradiant
scatterings is presented. We show that Bragg resonant enhancement is
incapacitated and both positive and negative order scatterings contribute
equally. We further show that propagation gain is small and scattering events
primarily occur at the end of the condensate where the generated field has
maximum strength, thereby explaining the apparent ``asymmetry" in the scattered
components with respect to the condensate center. In addition, the generated
field travels near the speed of light in a vacuum, resulting in significant
spontaneous emission when the one-photon detuning is not sufficiently large.
Finally, we show that when the excitation rate increases, the generated-field
front-edge-steepening and peak forward-shifting effects are due to depletion of
the ground state matter wave.Comment: This manuscript was submitted for publication in Nov., 200
A head-up display for mid-air drone recovery
During mid-air retrieval of parachute packages, the absence of a natural horizon creates serious difficulties for the pilot of the recovery helicopter. A head-up display (HUD) was tested in an attempt to solve this problem. Both a roll-stabilized HUD and a no-roll (pitch only) HUD were tested. The results show that fewer missed passes occurred with the roll-stabilized HUD when the horizon was obscured. The pilots also reported that the workload was greatly reduced. Roll-stabilization was required to prevent vertigo when flying in the absence of a natural horizon. Any HUD intended for mid-air retrieval should display pitch, roll, sideslip, airspeed, and vertical velocity
Rapid, quantitative determination of bacteria in water
A bioluminescent assay for ATP in water borne bacteria is made by adding nitric acid to a water sample with concentrated bacteria to rupture the bacterial cells. The sample is diluted with sterile, deionized water, then mixed with a luciferase-luciferin mixture and the resulting light output of the bioluminescent reaction is measured and correlated with bacteria present. A standard and a blank also are presented so that the light output can be correlated to bacteria in the sample and system noise can be substracted from the readings. A chemiluminescent assay for iron porphyrins in water borne bacteria is made by adding luminol reagent to a water sample with concentrated bacteria and measuring the resulting light output of the chemiluminescent reaction
The Halo Formation Rate and its link to the Global Star Formation Rate
The star formation history of the universe shows strong evolution with
cosmological epoch. Although we know mergers between galaxies can cause
luminous bursts of star formation, the relative importance of such mergers to
the global star formation rate (SFR) is unknown. We present a simple analytic
formula for the rate at which halos merge to form higher-mass systems, derived
from Press-Schechter theory and confirmed by numerical simulations (for high
halo masses). A comparison of the evolution in halo formation rate with the
observed evolution in the global SFR indicates that the latter is largely
driven by halo mergers at z>1. Recent numerical simulations by Kolatt et al.
(1999) and Knebe & Muller (1999) show how merging systems are strongly biased
tracers of mass fluctuations, thereby explaining the strong clustering observed
for Lyman-break galaxies without any need to assume that Lyman-break galaxies
are associated only with the most massive systems at z~3.Comment: 4 pages, 2 figures. To appear in `The Hy-redshift universe: Galaxy
formation and evolution at high redshift' eds. A.J. Bunker and W.J.M. van
Breuge
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