Minimax matrix correction of inconsistent systems of linear algebraic equations with block matrices of coefficients

The problem of correction of matrices (extended matrices) of inconsistent systems of linear algebraic equations with block structure and with the cost function of minimax type is considered. These problems are reduced to a constrained optimization problem, which, in turn, is reduced to a series of linear programming problems. All problems of matrix correction are illustrated by numerical examples.     

Study of the charge collection efficiency of CdZnTe radiation detectors

The charge collection efficiency of CdZnTe radiation detectors with two different configurations: aSchottky diode detector and aresistive detector are compared. The average charge collection efficiencies for three different directions of irradiation (negative electrode, positive electrode and perpendicular to the electric field) are calculated. The mobility-lifetime product of the CdZnTe substrates is evaluated from the dependence of the measured spectra upon detector bias voltage. The measurement of the average charge collection efficiency is based on monitoring the shift of the peak channel with bias voltage in an experimental setup which is well calibrated. Two types of radiation are used:gamma photons from several radioactive sources andalpha particles from an²⁴¹Am source. The models for the evaluation of mobility-lifetime product from the measured data for the two types of detector configurations as well as for the two types of radiation sources, are compared and discussed. The CdZnTe (Zn = 10%) substrates under study are obtained commercially and are grown by the high pressure Bridgeman method. The mobility-lifetime products and specific resistivity of the two types of detectors are evaluated and compared. A lower resistivity material has a narrower depletion region and behaves like a thinner detector thus exhibiting better collection efficiencies. Therefore, medium resistivity material which is completely inadequate for resistive detectors can still yield high performance Schottky detectors. The preferred direction of irradiation, i.e. from the negative electrode, is possible only in the case of n-type material which is reverse biased by negative voltages applied to the Schottky gate. The mobility-lifetime products that are derived on both the resistive detector (with specific resistivity of ≈1.10¹⁰ ω.cm) and the Schottky diode (with specific resistivity of ≈1.10⁶ Ω.cm) are μ_nτ_n ≈-4.10⁻⁴ cm²V⁻¹ and μ_pτ_p≅ 8.10⁻⁵ cm²V⁻¹.     

Resonance Excitation of Photoluminescence in an Aqueous Uranyl Chloride Solution

We have measured photoluminescence spectra of an aqueous uranyl chloride solution under excitation by various light sources: semiconductor light-emitting diodes and cw laser. The excitation wavelength lay within a resonance absorption band of uranyl chloride, which ensured photoluminescence detection at exposure times of 10^–3 s using an extremely small volume of the substance (10^–9 cm³). The photoluminescence spectra were measured using a small minispectrometer, which allowed us to analyze the spectra in the range 200–1000 nm.     

Emission of opal photonic crystals under pulsed laser excitation

Infiltration of opal with nonlinear optical materials is shown to markedly raise its emission intensity in the visible range under pulsed laser excitation. Evidence is presented for three-photon parametric scattering in both uninfiltrated and infiltrated globular photonic crystals, with excitation of “slow” photons in the visible range. Our results indicate that synthetic opal crystals can be used as photon traps for studying the emission spectra of organic and inorganic materials infiltrated in opal pores.     

Dispersion of optical and acoustic phonons in diamond and germanium crystals

The dispersion laws of the optical and acoustic branches in diamond-like crystals have been derived using idealized models of crystal lattices. Two types of analytical expressions have been proposed, whose parameters can be derived from inelastic neutron scattering experiments and the properties of acoustic waves. The calculation results are in satisfactory agreement with experimental data for the crystallographic directions [100], [110], and [111]. The group velocities of optical and acoustic phonons have been determined, and expressions for the effective mass of optical phonons have been derived.     

Annealing effect on reflectivity spectra of opal photonic crystals

We analyze broadband visible reflectivity spectra of opal photonic crystals annealed in an argon atmosphere and air. Scanning electron microscopic examination has shown that the crystals consist of close-packed spheres with a mean diameter in the range 200–290 nm. Incorporation of even small amounts of carbon (?0.5 wt %) increases the density of the opal matrix. The presence of carbon shifts the Bragg reflection peak of the opal and increases its intensity.     

Optical properties of three-dimensional magnetic opal photonic crystals

We have studied the optical properties of opal photonic crystals infiltrated with the M_0.35Zn_0.65Fe₂O₄ (M = Ni, Co) ferrites. The crystals consisted of amorphous SiO₂ nanospheres. The visible reflectivity spectra of the crystals were used to determine parameters of their photonic band gap and their refractive index.     

Singularities of radiation-flux absorption in a cylindrical cavity

The distribution of radiation absorbed by the inner surface of a cylindrical cavity is found by the Monte Carlo method for a different nature of the reflection and different ratios between the input beam and cavity diameters.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 2, pp. 304–308, August, 1985.