Radar interferometer measurements of space debris using the Evpatoria RT-70 transmitter

The ability of the Evpatoria RT-70 radar complex to perform research on space debris was investigated in four trial experiments during 2001-2003. The echo-signals of 25 objects at geostationary, highly elliptical and medium-altitude orbits were recorded on magnetic tapes at radio telescopes in Russia, Italy, China and Poland. The multi-antenna system configuration gives potential to supplement the classic radar data with precise angular observations using the technique of Very Long Baseline Interferometry. The first stage of such processing was fulfilled by the correlator in N. Novgorod, Russia. The cross-correlation of transmitted and received signals was obtained for the 11 objects on the Evpatoria-Bear Lakes, Evpatoria-Urumqi and Evpatoria-Noto baselines. This activity also promoted developing the optical observations of geostationary objects, conducted for the improvement of the radar target ephemerides. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

Nondestructive measurements of stoichiometry in undoped semi-insulating gallium arsenide by x-ray bond method

The influences of microdefects and dislocations on the lattice parameters of undoped semi-insulating GaAs single crystals were analyzed, and a novel nondestructive method for measuring stoichiometry in undoped semi-insulating GaAs was established in this letter. The comparison of this method with coulometric titration indicates that the method of nondestructive measurements is indeed convenient and reliable. (C) 1996 American Institute of Physics.

Defects in GaSb studied by coincidence Doppler broadening measurements

Undoped, Zn-doped and Te-doped GaSb with different concentrations were investigated by positron lifetime spectroscopy (PAS) and the Doppler broadening technique. Detection sensitivity of the latter technique was improved by using a second Ge-detector for the coincident detection of the second annihilation photon. PAS measurement indicated that there were vacancies in these samples. By combining the Doppler broadening measurements, the native acceptor defects in GaSb were identified to be predominantly Ga vacancy (V-Ga) related defects.

Photoluminescence measurements on erbium-doped silicon

Erbium-implanted silicones were treated by lamp-heating rapid thermal annealing (RTA). Two types of erbium-related photoluminescence spectra appear under different anneal temperatures. 750 degrees C annealing optimizes the luminescence intensity, which does not change with anneal time. Exciton-mediated energy transfer model in erbium-doped silicon was presented. The emission intensity is related to optical active erbium concentration, lifetime of excited Er3+ ion and spontaneous emission time. The thermal quenching of the erbium luminescence in Si is caused by thermal ionization of erbium-bound exciton complex and nonradiative energy backtransfer processes, which correspond to the activation energy of 6.6 meV and 47.4 meV respectively.

Evaluation of the Uncertainties Caused by the Forward Scattering in Turbidity Measurement of the Coagulation Rate

The forward scattering light (FSL) received by the detector can cause uncertainties in turbidity measurement of the coagulation rate of colloidal dispersion, and this effect becomes more significant for large particles. In this study, the effect of FSL is investigated on the basis of calculations using the T-matrix method, an exact technique for the computation of nonspherical scattering. The theoretical formulation and relevant numerical implementation for predicting the contribution of FSL in the turbidity measurement is presented. To quantitatively estimate the degree of the influence of FSL, an influence ratio comparing the contribution of FSL to the pure transmitted light in the turbidity measurement is introduced. The influence ratios evaluated under various parametric conditions and the relevant analyses provide a guideline for properly choosing particle size, measuring wavelength to minimize the effect of FSL in turbidity measurement of coagulation rate.