J. W. Armstrong

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This paper discusses spacecraft Doppler tracking, the current-generation detector technology used in the low-frequency (∼millihertz) gravitational wave band. In the Doppler method the earth and a distant spacecraft act as free test masses with a ground-based precision Doppler tracking system continuously monitoring the earth-spacecraft relative(More)
Knowledge of the dielectric properties of commodities and insect pests is important in developing thermal treatments for postharvest insect control based on radio frequency (RF) and microwave energy. The dielectric properties of six subtropical and tropical fruits along with four associated insect pests were measured between 1 and 1800 MHz using an(More)
Performance of an Earth-to-deep-space optical telecommunications system is degraded by distortion of the beam as it propagates through the turbulent atmosphere. Conventional approaches to correcting distortions, based on natural or artificial guide stars, have practical difficulties or are not adequate for correction of distortions, which are important for(More)
The performance of an Earth-to-space optical telecommunications system is degraded by distortion (scintillation and tilt) of the beam as it propagates through the turbulent atmosphere. Conventional approaches to correct distortions that are based on natural or artificial guide stars are useful in, for example, astronomical imaging, but have practical(More)
A Laser-lnterferometer Gravitational-Wave Observatory (LIGO) is planned for operation in the United States, with two antennas separated by several thousand kilometers. Each antenna would incorporate laser interferometers with 4 km arm lengths, operating in vacuum. The frequency range covered initially would be from a few tens of Hz to a few kHz, with(More)
Using polarized brightness (pB) measurements made by the High Altitude Observatory (HAO) Mauna Loa Mk III K-coronameter, we investigate the daily changes of path-integrated density at 1.15 R,. During 1996, when simultaneous pB and helioseismology data were available, we find that the correlation of pB (at zero time lag and 207 latitude lag) varies with(More)
We describe preliminary determinations of AlGaAs layer composition using in situ optical reflectance spectroscopy (ORS) data. RHEED oscillations are used to independently determine the composition of the AlGaAs layers. The results are compared with ex situ measurements. Although additional work is needed to refine the uncertainty estimates and reduce(More)
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