Analytic investigation of the process of formation of a spatially inhomogeneous structural state in a steel plate subjected to rapid cooling

We analyze the process of formation of a spatially inhomogeneous phase composition of several types of steel in cooling with convective heat exchange with the environment. The principles of the classical theory of heat conduction and the theory of interpolational models of structural state formation in rapidly cooled steels are used for numerical prediction. On this basis, we develop a technique for the analysis of phase composition. It is shown that the percentage of the martensitic constituent in steels increases as the external heat removal becomes more intense; at the same time, the tendency to complete hardening in steel is intensified. These observations are in a good agreement with experiment.Pidstrygach Institute of Applied Problems in Mechanics and Mathematics, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 6, pp. 101–104, November–December, 1993.     

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     

Synthesis of silicon carbide whiskers using the vapour-liquid-solid mechanism in a silicon-rich droplet

SiC whiskers can be produced from 1350–1500 °C by carbothermal reduction of the silica in a fixed bed percolated by a hydrogen flow. At 1450 °C and above, the addition of iron to the silica-carbon mixture leads to the formation of submicrometre whiskers in the bed, ending with a silicon-rich droplet. The iron has evaporated and condensed at a lower temperature, a few centimetres downstream from the bed, allowing the formation of silicon carbide whiskers ending with an iron droplet according to the vapour-liquid-solid (VLS) mechanism. Submicrometre whiskers are also obtained without iron over a broader range of temperatures. Silicon carbide whisker production in a fixed bed is then possible using a (VLS) mechanism in a silicon-rich droplet and may be controlled without the addition of transition metals, thus improving the purity.Supported by Pechiney Electrometallurgie and the European Communities, Brite project RIIB.A267C.     

The Influence of Water-soluble Polymers and pH on Hydroxypropyl-β-Cyclodextrin Complexation of Drugs

The effect of water-soluble polymers and ionization of the drug molecules on the cyclodextrin, mainly 2-hydroxypropyl-β-cyclodextrin (HPβCD), solubilization of drugs was investigated. HPβCD has significant solubilizing effect on acetazolamide, prazepam, and sulfamethoxazole in aqueous solutions. All three polymers tested-i.e., hydroxypropyl methylcellulose (HPMC), polyvinylpyrrolidone (PVP), and carboxymethylcellulose-increase the solubilizing effect of HPβCD. The polymers increase the solubilization by increasing the apparent stability constant (K_c of the drug-HPβCD complex. Thus, addition of 0.10% (w/v) HPMC to the aqueous complexation medium results in a 56% increase in K, for the acetazolamide-HPβCD complex and a 200% increase in K_c for the prazepam-HPβCD complex. Addition of 0.25% (w/v) PVP to the complexation medium results in a 138% increase in K for the sulfamethoxazole-HPβCD complex. The HPβCD solubilization of the drugs can also be improved by ionization of the drug molecule through pH adjustments. However, larger improvements of the HPβCD solubilization are obtained when both methods are used simultaneously compared to when either method is used separately.     

The molecular mechanisms of actin-based intracellular motility by Listeria monocytogenes

A rapid, sensitive method was developed for the quantification of the R- and S-enantiomers of ketoprofen and their acyl glucuronide conjugates in the plasma and dialysate of hemodialysis-dependent anephric patients. Unconjugated R- and S-ketoprofen plasma concentrations were determined directly by liquid chromatography using a S,S-Whelk-O1 chiral stationary phase. R- and S-Ketoprofen glucuronide for use as standard were resolved using a C18 reversed-phase HPLC column with a mobile phase containing the ion-pair reagent tetrabutylammonium hydrogen sulfate. Plasma glucuronides, however, could not be directly quantified due to matrix interference. Therefore, the glucuronides were isolated using reversed-phase HPLC and quantified after alkaline hydrolysis using the S,S-Whelk-O1 chiral stationary phase column.     

Improvement of the anticorrosive properties of galvanic metallic coatings

We analyze various possibilities for improving the anticorrosive properties of metallic coatings, including alloying, modification of the base (prior to coating), the choice of the optimum (for producing anticorrosive structures) conditions of electrolysis, the use of multilayer coatings (sandwich-type structures), and modification of coatings by depositing passive layers by high-energy treatment (laser, electron-beam, plasmachemical, etc.).Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 5, pp. 81–87, September – October, 1994.     

Computer optimization of transducer transfer functions usingconstraints on bandwidth, ripple, and loss

Transducers, having one piezoelectric layer near its half-wave resonance and N quarter-wave layers, are designed using computer optimization to adjust the thicknesses and impedances of the various layers so as to fit the resulting transfer function to a target function. An augmented Mason model is used to evaluate the transducer. Optimization of fit is by a steepest descent algorithm. Essentially error-free fits are achieved for target functions that match the underlying dynamics. By applying classical filter theory to a lumped-element transducer model, the transducers dynamics are identified as all-pole filters, which are characterized by polynomials of order N to N+1. The design methodology is tested by designing a series of low-loss transducers that explore fractional bandwidths from 45 to 116%. From these studies there appears to be constraints on the minimum Q of the poles, and other properties. Typical power transfer efficiencies of -1 dB are achieved by impedance scale matching. Using a second-order Fano bound, it is shown that the matching layers function as an optimal compensation network for low-loss flat bandpass transducers. Finally, by the inclusion of loss, lower Q poles are demonstrated with a Bessel transducer     

Effect of rotation on the structure of a convecting mushy layer

Summary Nonlinear natural convection in a mushy layer during solidification of a binary alloy is investigated under a high gravity environment where the rotation axis is inclined to the high gravity vector. Asymptotic and scaling analyses are applied to convective flow within the mushy layer and in vertical chimneys. The main result is that, for some particular moderate rotation range, vertical velocity in the chimneys decreases rapidly with increasing rotation rate and appears to have opposite signs across some rotation dependent vertical level.