Impedance boundary method of moments with extended boundaryconditions

An improved impedance boundary method of moments is proposed to accurately and efficiently determine the propagation characteristics of multilayer planar optical waveguides whose refractive index profiles contain large step index changes or a graded-index region combined with step index changes. Extended impedance boundary conditions are used in the impedance boundary method of moments to replace regions in the waveguide structure which have refractive index discontinuities. Two methods for determining the extended boundary conditions include the standard transfer matrix method and a procedure utilizing a cascaded transmission line representation with successive calculation of input impedances. Simulation results show significantly improved convergence rates in the determination of propagation constants     

An improved single sensor parity space algorithm for sequential probability ratio test

In our paper we propose a modification of the single sensor parity algorithm in order to make the statistical properties of the generated residual determinable in advance. The algorithm is tested via computer simulated ramp failure at the temperature readings of the pressurizer.     

Highly efficient ceramic catalytic blocks with a honeycomb structure

Compositions and technologies are suggested for preparing highly efficient catalyst blocks with a honeycomb structure to be used for reducing nitrogen oxides with ammonia in flue gases from thermal power plants. The blocks have high structural strength and catalytic activity.     

Noninvasive real-time multipoint temperature control for ultrasoundphased array treatments

A method for noninvasively estimating spatiotemporal temperature changes in samples using diagnostic ultrasound, and using these as inputs to a multipoint ultrasound phased array temperature controller, is presented in this paper. This method is based on a linear relationship between the apparent tissue echo pattern displacements and temperature, as seen along A-lines acquired with diagnostic ultrasound when the sample is heated by external heating fields. The proportionality constant between echo displacement and temperature is determined by the local change in speed of sound due to temperature and the linear coefficient of thermal expansion of the material. Accurate estimation of the displacements and proportionality constant yields accurate calibrated high-resolution (1 mm spatial, sub-°C) noninvasive sample temperature estimates. These are used as inputs to a multipoint temperature controller, capable of controlling ultrasound phased array treatments in real-time. Phantom and in vitro results show that the noninvasively estimated temperature values can effectively be used to control ultrasound hyperthermia treatments, almost replacing invasive thermocouple measurements. The mathematical background and assumptions of the noninvasive temperature estimator and the controller are presented in this paper, together with experimental results showing estimator and controller performance and limitations. To the best of our knowledge, this paper presents the first demonstration of real-time treatment control based entirely on noninvasive temperature estimates     

Hierarchical production control for a flow shop with dynamic setup changes and random machine breakdowns

In this paper, we study a manufacturing system consisting of two machines separated by two intermediate buffers, and capable of producing two different products. Each product requires a constant processing time on each of the machines. Each machine requires a constant non-negligible setup change time from one product to the other. The demand rate for each product is considered to be piecewise constant. Each machine undergoes failure and repair. The time-to-failure and time-to-repair are exponentially distributed random variables. The setup change and processing operations are resumable. We model our system as a continuous time, continuous flow process. An optimal control problem is formulated for the system to minimize the total expected discounted cost over an infinite horizon. To determine the optimal control policy structure, a discrete version of the problem is solved numerically using a dynamic programming formulation with a piecewise linear penalty function. A real-time control algorithm is then developed with the objective of maintaining low work-in-process inventory and keeping the production close to the demand. The algorithm uses a hierarchical control structure to generate the loading times for each product on each machine in real time and to respond to random disruptions in the system. The system is simulated using this algorithm to study its performance. The performance of the algorithm is also compared to alternative policies.     

Chemical characterization of in vivo aged zinc phosphate dental cements

The chemical composition of zinc phosphate dental cements aged in vivo was studied. Twenty-seven samples aged 2 to 43 years were investigated using X-ray diffraction, infrared spectroscopy, ³¹P nuclear magnetic resonance spectroscopy, thermogravimetric analysis and differential scanning calorimetry. Evidence for the presence of zinc oxide, amorphous zinc phosphate, water of hydration and crystalline zinc phosphate tetrahydrate was found. The latter was identified as hopeite; it was present in 92% of the cements studied. No correlation with time concerning either the chemical structure of the components or their relative amounts was found. Zinc phosphate dental cements show very good chemical stability on long-term use.     

Modified refraction-interference method for calculating the geometric and optical parameters of optical waveguides

We describe a ray method for analysis of the geometric and optical characteristics of two-layer fiber optical waveguides. We have analyzed the effect of the polarization of the illuminating beam on the overall pattern of the intensity distribution. We consider the characteristic types of rays for a single-layer and two-layer fiber optical waveguide. We have obtained definitive dependences of the beam intensity for each ray individually. We have developed a program for calculation of the scattering pattern in fiber optical waveguides illuminated by a broad beam. Translated from Izmeritel'naya Tekhnika, No. 3, pp. 39–42, March, 1996.     

The Bi-Rb (bismuth-rubidium) system

This work was supported by ASM International. Literature searched through 1988. Dr. Pelton is the Alloy Phase Diagram Program Co-Category Editor for binary alkali alloys.