Configuration of a genetic algorithm used to optimise fibre steering in composite laminates

In a previous study, a genetic algorithm (GA) was applied to define the optimum orientation of fibres in a unidirectional laminate in which the fibre orientations were allowed to vary continuously across the domain. The results were positive, but computation time was excessively long. The present study was undertaken to address this issue. The elements used by the GA (encoded representation, fitness criterion, operators affecting the population) were examined and optimised to reduce computation time. It was found that the use of a strain-based fitness criterion was better than use of a stress-based criterion, regardless of whether the load was above or below the elastic limit. A good balance of elitism and mixing was necessary in the GA parameters to obtain the fastest convergence. Automatic imaging of the GA output was achieved using the SAMCEF software package.     

Overall mass transfer in the swirling flow induced by a tangential inlet between coaxial cones

An electrochemical method is used to measure mass transfer coefficients between an electrolytic solution and the inner core of a system formed by stationary coaxial cones of the same apex angle. A swirling decaying flow is induced by means of a tangential inlet at the system base. The average mass transfer coefficients are measured at three axial positions from the tangential inlet for both laminar and turbulent flow regimes. Pressure drops between the inlet and the outlet of the experimental device are also investigated. Flow visualization revealed the existence of axially fixed toroidal vortices. The overall mass transfer coefficients along the conical gap are found to be greater than those measured in annular swirling decaying flow for the same values of the annular gap thickness, of the tangential inlet diameter and of the Reynolds number based on the mean axial velocity at the bottom of the conical gap. The enhancement in mass transfer, up to 50% compared with that measured in a cylindrical arrangement, is not counter-balanced by an increase in pressure drop, which remains of the same order of magnitude as that measured in a classical annular configuration.     

Study of mixing in an axisymmetric coflowing liquid jet by coupling L.D.A. to an electrochemical method

Local and simultaneous velocity and concentration fluctuations were analysed in an axisymmetric jet of an aqueous electrolyte solution moving in a codirectional water stream. The determination of the convection velocity of the turbulent eddies as well as correlation between axial velocity and concentration fluctuations was made possible by coupling L.D.A. to an electrochemical technique. The influence of the ratio of the coflowing stream velocity to the jet exit velocity was investigated. The mean velocity and concentration profiles, the turbulence intensity, the integral length scales relative to axial velocity and concentration were also determined.     

Determination of heterogeneities in a scraped surface heat exchanger using electrochemical sensors

An experimental investigation of a scaled-down model of an industrial exchanger, using an electrochemical technique, was undertaken in order to show the presence of hydrodynamic heterogeneities at low axial Reynolds number. Heterogeneities were revealed in the bowls with respect to the generalised Taylor number as the result of the perturbations added to the flow by blade rotation at both ends of the exchanger. Shear heterogeneities associated to flow visualisations were correlated to temperature heterogeneities observed in the bowls. Shear fluctuations were revealed in the scraped part describing two distinctive zones at low rotation speed caused by varying viscosity in the flow field. A complex spiral flow was observed by flow visualisation characterising a mass transfer evolution comprised between these two distinctive zones at low Taylor number.     

Testing for decreasing heterogeneity in a new time-varying frailty model

Frailty models adjust for between-cluster variability in survival data by including a cluster-specific random factor, the frailty term, in the Cox model. The frailty term is assumed to be constant over time. This assumption is questionable in some particular settings, e.g., in cancer clinical trials on chronic myeloid leukaemia. We therefore relax the time-constant heterogeneity assumption and consider frailty models with a time-varying frailty term. Instead of working with hazard models, we rather model the log cumulative hazard function, making use of the mixed model framework, and introduce a time-varying random effect at that level. Simulations demonstrate that the proposed method has acceptable size and power to detect time-dependent clustering. The method is applied to data from a large-scale multicentre clinical trial in patients with chronic myeloid leukaemia.     

Modeling and experimental validation of sharpening mechanism based on thermal oxidation for fabrication of ultra-sharp silicon nanotips

This paper aims at modeling the thermal oxidation of silicon pillars leading to the formation of very sharp silicon tips. The model is used to determine optimum process parameters with respect to the initial shape of the silicon pillars and the geometry of the desired tip. The modeling concept is to extend a previous approach, which predicts the oxidation mechanism of silicon cylinders versus their initial radius. The silicon pillar geometry is approximated by a superposition of silicon cylindrical structures featuring a local curvature radius. Experimental validation has been performed for several initial silicon pillar shapes, at 1000/spl deg/C and 1100/spl deg/C under dry oxidation conditions, leading to formation of very sharp silicon tips. The numerical predictions are shown to agree well with these experimental data. The motivation of this study aims at designing and fabricating a nanoelectromechanical filter device. Its vibrating part consists of a silicon nanotip, covered with a thin gold layer, the geometrical features of which affect the center frequency of the nanofilter device.     

Scheduling divisible loads on star and tree networks: results and open problems

Many applications in scientific and engineering domains are structured as large numbers of independent tasks with low granularity. These applications are thus amenable to straightforward parallelization, typically in master-worker fashion, provided that efficient scheduling strategies are available. Such applications have been called divisible-loads because a scheduler may divide the computation among worker processes arbitrarily, both in terms of number of tasks and of task sizes. Divisible load scheduling has been an active area of research for the last 15 years. A vast literature offers results and scheduling algorithms for various models of the underlying distributed computing platform. Broad surveys are available that report on, accomplishments in the field. By contrast, We propose a unified theoretical perspective that synthesizes previously published results, several novel results, and open questions, in a view to foster hover divisible load scheduling research. Specifically, we discuss both one-round and multiround algorithms, and we restrict our scope to the popular star and tree network topologies, which we study with both linear and affine cost models for communication and computation.     

Complete Suspension of Microcapsules in Baffled and Unbaffled Stirred Tanks

The study of rotational speed for complete suspension have been carried out by varying different parameters: density ratio, stirrer diameter, clearance of stirrer, solid particle diameter, and particle concentration. The equations of correlation available in the literature were tested in order to obtain the one giving the best prediction of experimental values. The proposed correlation enables the determination of the minimal rotational speed for complete suspension of microcapsules in a pilot reactor with a good accuracy. The results will be used for the scale up of a microencapsulation process from laboratory to the pilot stirred vessel, for which it is considered that the extrapolation factor is the minimal rotational speed for complete suspension.     

Noniterative stable transmission/reflection method for low-lossmaterial complex permittivity determination

This paper describes a new noniterative transmission/reflection method applicable to permittivity measurements using arbitrary sample lengths in wide-band frequencies. This method is based on a simplified version of the well-known Nicolson-Ross-Weir (NRW) method. For low-loss materials, this method is stable over the whole frequency range: no divergence is observed at frequencies corresponding to integer multiples of one half wavelength in the sample. The accuracy on the dielectric permittivity is similar to that obtained with a more recently proposed iterative technique. A general equation for complex permittivity determination including the Stuchly, NRW, and new noniterative methods, is also proposed