Image enhancement in diffraction orders during acoustooptical interaction

Enhancement of an optical image in different diffraction orders in the course of acoustooptical interaction is performed theoretically and experimentally. It is shown that, varying the diffraction parameters in the process of detuning from the strict Bragg synchronism, image enhancement can be obtained in either the zero or the first order.     

The influence of transition metals – Fe,Co, Cu on transformation of organic matters from Domanic rocks in hydrothermal catalytic system

Character of conversion of organic matter from Domanic rocks of Pervomaiskoye field (Tatarstan) of Semiluki horizon of upper Devonian deposits in the hydrothermal-catalytic system at temperature of 300?°C in carbon dioxide medium was studied with the application of complex of oil-soluble precursors of catalysts containing Fe, Co, and Cu. In presence of catalysts complex, content of organic extract increases, in which content of hydrocarbon fractions, saturated and aromatic hydrocarbons, increases 1.5 times, while resins content decreases by two times. As result of kerogen destruction in products of experiments, the content of asphaltenes and carbonaceous substances such as carbenes and carboides increase.     

Approach to 3-d ultrasound high resolution imaging for mechanically moving large-aperture transducer based upon Fourier transform

A new three-dimensional (3-D) acoustic image formation technique is proposed that is based on the transmission of wide bandwidth pulse signals and the application of the 3-D fast Fourier transform. A solution to the Helmholtz wave equation has been obtained using the Born approximation. The solution contains analytical expressions for the spatial spectra of the transmit and receive radiation patterns for transducers of various geometries with lenses of fixed focal distances. It has been shown that the proposed algorithms allow for radiation patterns with constant widths at depths both behind and in front of the focal point, starting practically from the plane of the transducer. The theoretical and experimental investigations and computer simulation for both spherical and rectangular transducer shapes have been performed. The results were used to estimate the beamwidths and the side lobe levels. A variant of the linear array has been studied for a cylindrical lens of a fixed focal distance moving in a lateral direction. It has been shown that, in this case, a high resolution (of the order of a few wavelengths) can be achieved along all three Cartesian coordinates at a very high scanning velocity. The influence of the moving scatterers' velocity in inhomogeneous medium on the spatial radiation pattern characteristics has been estimated.     

Off-axis measurements of atmospheric trace gases by use of an airborne ultraviolet-visible spectrometer

An airborne UV-visible spectrometer, the Gas Analyzer Spectrometer Correlating Optical Differences, airborne version (GASCOD/A4pi) was successfully operated during the Airborne Polar Experiment, Geophysica Aircraft in Antarctica airborne campaign from Ushuaia (54 degrees 49' S, 68 degrees 18' W), Argentina in southern spring 1999. The instrument measured scattered solar radiation through three optical windows with a narrow field of view (FOV), one from the zenith, two from the horizontal, as well as actinic fluxes through 2pi FOV radiometric heads. Only a few airborne measurements of scattered solar radiation at different angles from the zenith are available in the literature. With our configuration we attempted to obtain the average line-of-sight concentrations of detectable trace gases. The retrieval method, based on differential optical absorption spectroscopy, is described and results for ozone are shown and compared with measurements from an in situ instrument as the first method of validation.     

A note to output feedback adaptive control for uncertain system with static nonlinearity

The problem of control design for a system represented as linear stationary and static nonlinear parts is considered. It is assumed that the linear part is unknown and strictly minimum phase. The nonlinear part is known inaccurately, it is irreducible to an input of the linear block, and generally does not satisfy sector restrictions. An adaptive regulator ensuring asymptotic stability is synthesized. The output of a control system, but not its derivatives, is used as a measured variable.     

Reconstruction and electron states of a Ga2Se3-GaAs heterointerface

It is established by electron microscopy and electron diffraction analysis that the formation of Ga₂Se₃(110) layers on GaAs(100) and (111) surfaces during heat treatment of the latter in selenium vapor is accompanied by the formation of transition regions with crystallographic orientations [310] and , respectively. It follows from an investigation of the spectrum of surface electron states in the resulting heterostructures that a reduction in the density of surface electron states is achieved only after selenium vapor treatment in a narrow interval of treatment durations (from 5 min to 30 min under the conditions established in the present study). All the results are discussed on the basis of concepts involving reconstruction of the gallium arsenide surface during chalcogen treatment. Fiz. Tekh. Poluprovodn. 33, 712–715 (June 1999)