The Influence of an Analog-to-Digital Converter on the Probability Characteristics of Gaussian Noise

We analyze the influence of an analog-to-digital converter (ADC) on the statistical characteristics of stationary Gaussian noise with allowance for two main effects. The first effect, caused by the limited magnitude of the signal at the ADC output, is the truncation of tails of the probability distribution function. The second effect is the noise quantization, i.e., transformation of the continuous probability distribution function of input noise to a set of readout probabilities at the ADC output. It seems that these effects were not analyzed in the literature earlier. The efficiency of using ADC, which is the noise standard normalized to the maximum permissible amplitude of the ADC input voltage, is chosen as the parameter characterizing the effect of truncation of the tails of the probability distribution function. In addition, we vary the ADC digit capacity, which determines the noise quantization degree. We propose recommendations on the choice of the digit capacity and the efficiency of using ADC.     

Application of a scanning electron microscope in simulating a beta-emission-induced current

The current induced by emission from a thin ⁶³Ni layer is simulated with allowance for the real spectrum of ejected electrons and their angular distribution in Si and GaN. The calculated results are compared with simulation data obtained for a monoenergetic electron beam perpendicular to the semiconductor detector. For both Si and GaN, the ratio between the currents induced by the SEM beam and β emission from ⁶³Ni is demonstrated to be almost completely independent of the diffusion length, if the electron-beam energy of a scanning electron microscope (SEM) is appropriately selected.     

Rate of generation of nonequilibrium charge carriers by a focused X-ray beam

A model of the interaction between an X-ray beam and a semiconductor sample is proposed for the X-ray-beam induced current method. The spatial distribution of the generation rate of nonequilibrium charge carriers (also called the generation function) is obtained using this model. It is shown that the generation function is proportional to the X-ray probe intensity for a rather broad X-ray beam. The results of calculating contrast profiles of the induced current for the described generation function are compared with those for the generation function proportional to the X-ray probe intensity and also with experimental profiles.     

XBIC using a laboratory X-ray source

Results from using the current method, in which a current is induced by a focused X-ray beam (XBIC = X-ray beam induced current) on a laboratory source are presented. It is shown that by reducing the X-ray probe sizes and improving the resolution, there is a gain in contrast increase for obtained images of grain boundaries in a crystal.     

Comparison theorems for problems of nonlinear anisotropic flow through porous media

Flow law constraints that make it possible to establish comparison theorems (analogs of the theorems of [1, 2]) for nonlinear flows in an anisotropic inhomogeneous medium are formulated. In the theorems obtained the changes in the values of the pressure head and, moreover, the flow rate, filter velocity and pressure head gradients for such perturbations of the problem as the depression of individual surfaces, changes in the given boundary values of the head, etc., are established. The strict monotonicity of the relation between the flow rate and the pressure head difference in a region of the enlarged stream tube type and the possibility of an increase in flow rate with increase in flow resistance are demonstrated. The question of the correspondence between the constraints introduced and certain common models of porous media is discussed. Kazan'. Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 45–51, September–October, 1988.     

Heat‐and mass‐transfer characteristics in a spatial subsonic flow around a blunt body

A study was performed of methods for controlling thermal regimes in a spatial supersonic flow around a blunt body with the simultaneous use of gas injection from the surface of the porous bluntness and heat flow in the shell material. The effect of the nonisothermicity of the shell wall on the heat and masstransfer characteristics in the boundary layer was taken into account by solution of the problem in a conjugate formulation. It is shown that heat conducting materials can be used to advantage to reduce the maximum temperatures in the screen zone.     

Mathematical simulation of two-dimensional problems of diffraction on compositely shaped screens

We propose a mathematical simulation of the two-dimensional problems of diffraction of an Epolarized electromagnetic wave on conducting screens of composite shape and configuration based on the method of virtual sources. Some problems of software development and evaluation of accuracy of computations are considered. Examples of numerical calculations for some characteristic diffraction problems are given.Radiotechnical Institute, Russian Academy of Sciences, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 5, pp. 404–414, May, 1995.     

Self-assembling of Ge quantum dots in the CaF<Subscript>2</Subscript>/Ge/CaF<Subscript>2</Subscript>/Si heteroepitaxial system and the development of tunnel-resonance diode on its basis

A CaF₂/Ge/CaF₂/Si(111) heteroepitaxial structure with Ge quantum dots was grown by molecular-beam epitaxy. A negative differential conductivity and conductivity oscillations caused by resonant hole tunneling were observed at room temperature. The energy spacing between the levels in quantum dots, as determined from the oscillation period, is 40–50 meV depending on the Ge dot size.