The solution of radiation engineering problems on a transputer-based system

Monte Carlo and finite element methods are numerical techniques used for solving complex problems in reactor physics and radiation shielding. In this paper we are concerned with the implementation of existing research-level codes based on these two methods, written originally for serial computers, on an MIMD transputer-based system. Results and performance of the parallelized codes are presented.     

Monte Carlo photon transport on parallel computers

In this paper we consider the implementation of particle tracking Monte Carlo on two different types of parallel computer architectures, namely, (i) the AMT DAP-610 array of processors which is a SIMD machine and (ii) the transputer based Meiko Computing Surface which is a MIMD machine. An analogue, research-level, fixed source, particle transport Monte Carlo code for studying the attenuation and leakage of gamma ray photons in simple, multilayer, shielding configurations, originally written for serial computers, is modified and re-written to run efficiently on these two different types of parallel machine. The philosophy adopted and algorithms developed in transferring the code to the parallel machines are described. Two illustrative problems are solved using realistic cross-section data, involving a 9 MeV source of gamma photons in a lead-void-water sphere and slab. Integral quantities, such as fraction of particles absorbed and escaped, and differential quantities, such as flux distributions and leakage spectra, computed by the parallel codes, are presented in tables and graphs. For equivalent calculations, the CPU times on the DAP and a number of serial computers (e.g. ICL-3900, CRAY XMP/28 in scalar mode, SUN 4, and VAX 11/750) are compared, and the resulting speedup factors quoted. For the Meiko Computing Surface, the performance obtained from running the code when the number of transputers used is varied, is tabulated. Finally, the performance of the two parallel machines is compared.     

Multi-Gbit/s 60 GHz Transceiver Analysis Using FDM Architecture and Six-Port Circuit

This paper presents an analysis and validation by advanced system simulation of compact and low-cost six-port transceivers for future wireless local area networks （WLANs） operating at millimeter-wave frequencies. To obtain realistic simulation results, a six-port model based on the measurement results of a fabricated V-band hybrid coupler, the core component, is used. A frequency-division multiplexing scheme is used by introducing four quadrature phase-shift keying （QPSK） channels in the wireless communication link. The data rate achieved is about 4 Gbit/s. The operating frequency is in the 60-64 GHz unlicensed band. Bit error rate （BER） results are presented, and a comparison is made between single-carrier and multicarrier architectures. The proposed wireless system can be considered an efficient candidate for millimeter-wave communication systems operating at quasi-optical data rates.     

Structural and optical properties of tin oxide branched nanostructures

Branched nanostructures of tin oxide (SnO2) have been synthesized by Vapor-Liquid-Solid (VLS) mechanism using a gold catalyst in the temperature range of 800-850 degrees C under an ambient gas flow of 200 sccm. The microstructural and the optical properties of the as prepared products have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), micro-Raman, and photoluminescence (PL) studies. SnO2 branches with a rutile phase are found to have a preferential orientation along (101). Typical lengths of these branches are found to be approximately 3-5 microm and diameters in the range of 50-100 nm. Selected area electron diffraction (SAED) pattern shows that the SnO2 branches have a tetragonal cross section with [101] crystal direction. A Raman line at 631 cm(-1) (Sn-O bond) is obtained in the micro Raman spectra. Low temperature PL spectrum shows a strong green emission band near 506 nm.     

PtRu Colloid Nanoparticles for CO Oxidation in Microfabricated Reactors

The catalytic activity of PtRu colloid nanoparticles for CO oxidation is investigated in microfabricated reactors. The measured catalytic performance describes a volcano curve as a function of the Pt/Ru ratio. The apparent activation energies for the different alloy catalysts are between 21 and 117 kJ/mol, which agree well with literature. The size distribution of the colloid nanoparticles is determined from STM and TEM, from which an average size of the colloid nanoparticles of 2.2±0.5 nm is determined.     

Hydrothermal Synthesis of Aluminum Terephthalate

A process is described for the synthesis of aluminum terephthalate by autoclaving a suspension of terephthalic acid in an aluminum chloride solution at temperatures from 150 to 390°C and pressures from 2 to 20 MPa. The conditions ensuring the maximum yield of aluminum terephthalate are established. The composition of the reaction product is determined to be Al₂[C₆H₄(COO)₂]₃ ? 2H₂O. The effect of the liner material on the reaction between terephthalic acid and aluminum chloride solutions is analyzed. It is shown that the final product of aluminum terephthalate decomposition during heating in air to 950°C is γ-Al₂O₃.     

Use of an adaptable quality model approach in a production support environment

Many of the early quality models have followed a hierarchical approach; A set of factors that affect quality are defined but there is little scope for expansion. Later models allow collective decisions to be made as to what attributes constitute quality but comparison across projects is difficult as a result.The adaptable quality model overcomes these drawbacks by providing a set of standard quality factors whilst allowing for locally defined factors to be included. The approach enables a consensus to be reached as to what properties constitute quality and how those properties should be measured. This paper details the construction of the model together with results from its use in a production support environment at a major financial institution.     

Joint optimisation of maintenance and production policies considering random demand and variable production rate

This paper deals with a randomly failing manufacturing system M1 which has to satisfy a random demand during a finite horizon given a required service level. To help meet this demand, subcontracting is used through another production system M2. M1 operates with a variable production rate and its failure rate depends on both time and the production rate. In these conditions, as a first step, we establish a preliminary production plan corresponding to a given service level. In a second stage, we integrate the effect of the machine degradation introducing a unitary degradation cost. The optimal production plan is then obtained by minimising the sum of the production, the inventory and the degradation costs. In the final stage, we propose another optimal plan combined with a preventive maintenance policy aiming at reducing the machine degradation while minimising the total cost including the production, inventory and maintenance costs.     

FPA method for optimal production planning under availability/degradation machine and subcontracting constraint

This work treats an industrial problematic of a manufacturing system M₁ subject to random failure and that satisfies a random demand under required service level. To ensure the satisfaction of the demand, it calls up on a second manufacturing system M₂ that is a subcontractor and has a stochastic service level. This paper aims to determine an optimal production plan taking into account the degradation of the manufacturing system following its production rate and its availability. The unavailability of the machine M₁ is due to the non-negligible preventive and corrective maintenance actions duration. To consider a realistic case of the subcontractor, we consider that is not able to respond to the variation of the demand, and then it assumed that the manufacturer can order a minimum fixed quantity. We then derive an optimal production plan taking into account the degradation of the machine and simultaneously minimising: inventory, degradation and production cost. An algorithm based on finite perturbation analysis is proposed to determine the optimal production plan and the sensitivity study of the availability is presented.