Production and properties of micro‐porous glas bubble zinc and aluminium composites

Micro‐porous syntactic foams were produced by means of integration of glass bubbles into aluminium and zinc matrices. Preforms of glass bubbles were pressure infiltrated with the alloys AlSi9Cu9 ans ZnAl4Cu using squeeze casting. The preforms were sintered thermically without the use of bonding agents. Using the combination of different sintering steps syntactic foams with locally different densities could be produced. The mechanical properties of the foams were tested indicating a high compression strength of the foams and a very good compression energy absorption. Furthermore, corrosion behaviour and behaviour at higher temperatures were investigated.     

Study of the degree of III conditioning of the phase space of pencil-beam radiotherapy using singular value decomposition

Dose distribution optimization algorithms are necessary in pencil-beam radiotherapy to exploit efficiently the multiple parameters of this powerful irradiation technique. We propose as an optimization technique singular value decomposition (SVD) analysis, which allows the measurement of ill conditioning of the stereotactic radiotherapy inverse problem and yields optimal weights for conformal treatment. Our approach to dose distribution optimization is to recover estimates of the minibeams weights from well-defined previsional dose matrices to study the influence of the different parameters on the stereotactic radiotherapy inverse procedure. The adjustment of the different parameters of the stereotactic irradiation to the “SVD optimizer” procedure is realized taking into account the ratio of the quality reconstruction to the calculation time. It will permit a more efficient use of the SVD optimizer in clinical applications with real three-dimensional lesions. We show the efficiency of the SVD optimizer in analyzing and predicting ill conditioning in stereotactic radiotherapy and in recognizing the topography of the different beams to create an optimal vector containing the beam weights (reconstructed weighting vector).     

A mechanical model for the deformational behavior of the polymeric membranes operating in pressure-driven processes

A mechanical model consisting of three elements (elastic, viscoelastic, and plastic) is proposed to describe the deformational behavior of a polymeric membrane operating in a pressure-driven process. The changes in the membrane thickness are proposed to be calculated from the experimentally obtained flux data. The advantages of a mechanical model over the conventional method of hysteresis area measurement as the mechanical stability of the polymeric membranes are discussed. © 1992 John Wiley & Sons, Inc.     

The design of experiments when there are errors in all the variables

The Error-in-Variables Model (EVM) applies to a large class of problems in parameter estimation in which there is error in all the variables. This property makes it of more general applicability than the widely used technique of ordinary Least Squares. While there is a voluminous literature on EVM there is nothing on a general method for designing experiments when EVM applies. In this paper we present an extension of the concept of D-optimality to provide such a general method. It is illustrated by applying it to the estimation of copolymer reactivity ratios and to fitting an ellipse.     

Numerical simulation of ion-exchange in glass for integratedoptical components

A numerical model based on the finite-element method for solving the nonlinear diffusion equation of ion-exchange in glasses is presented. The model is applied to the calculation of the concentration profile for a Ag⁺-Na⁺ ion-exchanged channel waveguide. The calculated concentration profile is in good agreement with a measured refractive-index profile of a waveguide fabricated with the same parameters as used in the calculations     

Silver Electrodeposition from Photographic Processing Solutions

This paper describes the parameters that are important in the industrial practice of silver removal from photographic fixers. The experiments were performed under potentiostatic control using synthetic solutions. The current efficiency was analysed as a function of the cathodic potential taking into account the deposit quality. A cathodic potential of ?0.5 V against a saturated calomel electrode is recommended. The conditions to prevent the darkening of the electrodeposit were investigated. The determination of silver concentration in the solution was made by direct potentiometry. The results obtained with synthetic fixers were corroborated by making the silver deposition from commercial fixers in an electrochemical reactor with rotating cylinder electrode intercalated in an electrolytic flow circuit in order to simulate practical conditions.     

Designer's casebook-bridge-controlled duty-cycle oscillator withgrounded capacitor

A circuit that uses the parallel connection of a Schmitt-trigger-type multivibrator and a voltage-controlled current source is proposed. The circuit was developed for use with integrated silicon sensors. The operation of the circuit is described