High speed BiCMOS current mode differential track-and-hold circuit

A new principle for a high speed BiCMOS differential track-and-hold circuit based on current mode processing is presented, and simulation results are given. The main characteristics are an acquisition time of 5.5 ns for 8 bit precision and a small-signal bandwidth of 1 GHz     

The thermoelastic behaviour of semicrystalline and of glassy poly(ether-ether-ketone)

A thermoelastic evaluation, based on simultaneous measurements of the mechanical work and of the concomitant heat of deformation by a stretching micro calorimeter, was performed on semicrystalline and glassy PEEK. The objective of this study was to utilize the sensitive technique to detect differences that would account for observed effects of micro structure on mechanical performance. A clear difference was detected beyond a 0.6% strain, where the behaviour of glassy PEEK began to exhibit inelastic features such as yielding and plastic deformation. This difference between the glassy and the semicrystalline polymers was considered the reason for the superior mechanical fatigue and fracture properties produced by the latter micro structure.     

Post-deposition treatment effects on hydroxyapatite vacuum plasma spray coatings

The purpose of this work is to evaluate the effects of post-deposition heat treatments on high and low crystallinity hydroxyapatite coatings on Ti6Al4V alloy. HA layers were produced by the vacuum plasma spray (VPS) technique, and the desired degrees of crystallinity were obtained by changing the deposition parameters. An analysis of the mechanical properties of the coatings and their adhesion to the substrate has been done by shear strength test. X-ray diffraction analysis was used to detect the structure and the chemical components in which HA dissociates during the deposition process and heat treatments. The data obtained indicates that heat treatments can increase the crystallinity of HA, but they also introduce a mechanical degradation of the coatings. After heat treatments, it was also observed that a large amount of tetracalcium phosphate was formed.     

Differential calorimeter for studying composites

The novel design of the DK-600/K differential thermal-flux calorimeter, with a cell volume of 6.5 cm³, is intended for the study of materials in the temperature range 300–900 K. The sensitivity of the calorimeter is 22 μV/mW at 300 K and 8 μV/mW at 900 K; the reaction threshold is 80 μW in the temperature scanning mode and 7 μW in the isothermal mode. Comparison of some characteristics of the DK-600/K with analogs from a number of foreign firms shows that it is competitive. Translated from Izmeritel'naya Tekhnika, No. 3, pp. 41–43, March, 1994.     

FOCUS-type fuel assembly for PWRs

In recent years the development efforts for Siemens PWR fuel assemblies were mainly concentrated on reducing the fuel cycle costs and increasing the operational reliability of the fuel assemblies.The first objective was aimed at increasing the average discharge burnup to > 50 MWd/kgU and increasing the critical heat flux. The high envisaged burnup required to develop a corrosion resistant cladding tube outside the Zry-4 range. The decision was made to use a Duplex cladding tube consisting of a corrosion optimized outer layer on a Zry-4 base material. A ZrSnFeCr alloy with reduced tin content was chosen for the outer layer. The critical heat flux could be increased by introducing mixing vanes on the spacer grids within the active length.To reach the second objective, reliable avoidance of spacer grid damage during core loading and unloading and reduction of fuel rod defects by debris fretting, the spacer grid corners were improved and a debris separation grid was developed.These design improvements were introduced into the new FOCUS-type fuel assembly. The name FOCUS stands for “Fuel assembly with Optimized Cladding and Upgraded Structure”.     

Measurement of interfacial area concentration in subcooled liquid-vapour flow

In two-fluid modelling, accurate prediction of the interfacial transport of mass, momentum and energy is required. Experiments were carried out to obtain a database for the development of interfacial transport models, or correlations, for subcooled water-steam flow in vertical conduits. The experimental data of interest included the interfacial area concentration, interfacial condensation heat transfer and bubble relative velocity. This paper focuses on the interfacial area concentration. The interfacial area concentration was obtained by measuring the distributions of bubble volume and surface area as well as the area-averaged void fraction at various axial locations in subcooled water-steam condensing vertical upward flow under low flow rate and low pressure conditions. The bubble size and surface area were determined using high-speed photography and digital image processing techniques. The area-averaged void fraction was measured by a single-beam gamma densitometer. The results were compared with existing correlations, which were developed on the basis of data obtained for air-water adiabatic flows. Poor agreement between the present data and the existing correlations was obtained. Accordingly, new correlations suitable for subcooled liquid-vapour bubbly flow are proposed.     

Synthesis and characterization of tungsten disulphide films grown by pulsed-laser deposition

The synthesis and characterization of tungsten disulphide (WS₂) films grown on 440C stainless steel substrates using the 248 nm line from a KrF excimer laser are reported. Film properties could be adjusted by controlling substrate temperature and by laser or thermal anneals. X-ray photoelectron spectroscopy, glancing angle XRD, Raman spectroscopy and high-resolution scanning electron microscopy were used to evaluate film chemistry, crystallinity and morphology. Films grown at room temperature were amorphous, near stoichiometric, and had a multiplicity of chemical states. Local order and bonding were improved most dramatically through post-deposition laser anneals. Crystallite size could be increased by raising the substrate temperature during deposition and, to a lesser degree, by post-deposition thermal anneals. Local disorder was observed within the larger crystallites compared to those that were laser annealed. Crystallinity was induced in amorphous films by mechanical rubbing at room temperature under conditions where frictional heating was negligible. The degree of control over film properties provided by PLD demonstrates its value for growing/designing tribological coatings.     

A forward-looking system for planning and monitoring metrological support to an organization

The ARM-Uchet computerized system is considered, which is intended for accounting, planning, and monitoring for metrological support to an organization and has been implemented on an IBM PC AT. Schemes are given for the basic modes of operation and for the software suites, as well as the database structure.Translated from Izmeritel'naya Tekhnika, No. 7, pp. 70–71, July, 1994.     

Effective single-band Hamiltonian for electron-phonon coupling in cuprate superconductors

We derive an effective single-band Hubbard type Hamiltonian for CuO₂ planes. The Hamiltonian includes both electron-electron repulsion and electron-phonon coupling to oxygen vibrational modes. We start with first-principles density functional theory parameters and then map onto a single-band model. Unlike previous mappings to a single-band Hamiltonian, ours explicitly preserves the Fermi surface shape and matrix elements of the many-band Hamiltonian. We consider both in-plane oxygen breathing modes as well as out-of-plane tilting modes. The latter modes have a quadratic electron-phonon coupling, and are also highly anharmonic in La₂CuO₄ based superconductors. The coupling to breathing modes is too small to account for highT _c, while the coupling to quadratic modes is much stronger even though they would be neglected in a standard Migdal-Eliashberg approach to superconductivity.     

Integrated scheduling of flexible manufacturing systems employingautomated guided vehicles

Centralized and distributed automated guided vehicle system (AGVS) models for materials handling, and the model for part processing are integrated into a single coherent model. This formulation can be used to collectively schedule and control the entire flexible manufacturing system (FMS) as opposed to the traditional separate scheduling of part processing and material handling. The two AGVS models are based on Petri nets and can be directly used in the scheduling method that uses Petri nets for formulation and heuristic search for solution. This method employs a global search to seek the optimal operation of an entire FMS. Scheduling examples are presented and the method compares favorably with the results simulated using heuristic dispatch rules