Two-dimensional phase unwrapping using a minimum spanning treealgorithm

Phase unwrapping refers to the determination of phase from modulo 2pi data, some of which may not be reliable. In 2D, this is equivalent to confining the support of the phase function to one or more arbitrarily shaped regions. A phase unwrapping algorithm is presented which works for 2D data known only within a set of nonconnected regions with possibly nonconvex boundaries. The algorithm includes the following steps: segmentation to identify connectivity, phase unwrapping within each segment using a Taylor series expansion, phase unwrapping between disconnected segments along an optimum path, and filling of phase information voids. The optimum path for intersegment unwrapping is determined by a minimum spanning tree algorithm. Although the algorithm is applicable to any 2D data, the main application addressed is magnetic resonance imaging (MRI) where phase maps are useful.     

Properties of nitrogen-implanted SOI substrates

Properties of nitrogen-implanted silicon-on-insulator (SOI) substrates prepared by implanting different doses of 200 keV nitrogen into 50-70 Ω-cm, p-type silicon substrates at a temperature of 500°C were studied. The distribution of nitrogen was studied using Auger electron spectroscopy. The electrical properties of the active overlayer were studied using Hall-effect measurements and capacitance-voltage depth profile analysis. The insulating integrity of the buried nitride was studied by directly measuring the leakage current from top to bottom through the substrate. Additionally, electric field strength and surface roughness measurements were performed. Nitrogen concentrations in the buried layer increased from below to above the stoichiometric value for Si₃N₄ for increasing dose in the range studied. Nitrogen-related n-type doping is observed in all samples examined, and the magnitude of the doping increased with the increasing implant dose. Insulating buried nitride layers are formed only in samples implanted with very high doses     

Particular cases of resonant tunneling in multibarrier quantum structures

An investigation was made of the resonance conditions in systems of one-dimensional potential barriers of a general kind. The types of systems are identified and the conditions determined which are necessary for observing a broad resonance in which the first three derivatives of the energy transmission coefficient are equal to zero. The conditions are found for observing an isolated resonance with complete transparency on a background of resonances with incomplete transparency.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 49–53, August, 1993.     

Offset dual-disk dielectric resonator antenna of very highpermittivity

An aperture-coupled offset dual-disk dielectric resonator antenna of very high permittivity is investigated experimentally. It is found that the new configuration offers an impedance bandwidth 4.6 times wider than that of the single element. The voltage standing wave ratio, radiation patterns, and antenna gain of the configuration are studied     

Relationship between the chemical structure and pharmacological action of cardiac glycosides of the strophanthidin series

The possibility has been shown of finding and creating highly effective cardiotonic drugs for pediatric practice on the basis of cardenolides obtained by the chemical transformation of natural cardiac glycosides.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 581–585, July–August, 1995. Original article submitted November 21, 1994.     

Design and simulation of waveguide electrooptic beam deflectors

Numerical simulation based on the scalar beam propagation method, was used to investigate the performance of waveguide electrooptic beam deflectors. The deflectors under investigation consist of a stack of electrooptically controlled prisms in a waveguide. The results were compared to earlier simplified analysis. It was found that for given overall device dimensions, the number of interfaces between prisms in a prism-type electrooptic deflector has significant influence on the device performance when it is small. To avoid wavefront distortion, unwanted reflection from the interfaces, and asymmetry in the deflection angles caused by small number of interfaces, one should use more than about ten interfaces in a typical deflector. Additional insights of device operation and design issues are discussed     

New theoretical concept of thin electromagnetic wave absorber usingresonant and scattering effect of dielectric and magnetic materials

Thin electromagnetic absorber such as less than 2~3 mm will be required for wireless LAN for domestic and business use together with millimeter wave broadcasting in the future. To make a thin construction, many resonators with lossy material were used. This paper present theoretical results that are useful for absorber designs     

High-speed tandem of MQW modulators for coded pulse generation with 14-dB fiber-to-fiber gain

We report on a tandem of electroabsorption modulators integrated with an amplifier by the identical active layer (IAL) approach. A 14 dB fiber-to-fiber is obtained by the use of constant As-P ratio MQW active layer and operation at 10 Gb/s is demonstrated. A record modulator saturation power of 35 mW is also reported.     

A Current-Mode, Dual Slope, Integrated Capacitance-to-Pulse Duration Converter

A capacitance-to-pulse duration converter, specifically designed for interfacing capacitive sensors, is presented. The operating principle is a double slope approach implemented using transconductor-based Miller integrators. The main strengths of the proposed circuit are: 1) intrinsically small sensitivity to temperature; 2) simplicity of trimming offset and gain to correct the sensor parameter spread; and 3) fast wake-up time. The circuit nonidealities are analyzed in order to identify the elements responsible for the residual temperature sensitivity and jitter on the pulse duration. The effectiveness of the method is demonstrated by measurements performed on a prototype, designed and fabricated using the 0.35 mum, 3.3 V Bipolar-CMOS-DMOS process BCD6 of STMicroelectronics.     

Analysis of the formation of structures and chaotic dynamics in a nonrelativistic electron beam with a virtual cathode in the presence of a decelerating field

A nonrelativistic electron beam with a virtual cathode situated in the diode gap with a decelerating field is experimentally and theoretically studied. A 1D model of the electron beam in the presence of a decelerating field is constructed. Nonlinear nonstationary processes in this system are investigated by means of numerical analysis of the model. The processes are described and interpreted with regard to formation and interaction of structures in the electron flow. The theoretical results are qualitatively confirmed by the experimental data showing that the system under study can be considered as a promising controlled source of chaotic oscillations in the microwave range.