Frequency domain analysis of acoustic wave propagation in heterogeneous media considering iterative coupling procedures between the method of fundamental solutions and Kansa's method

Acoustic wave propagation in heterogeneous media is a topic of significant interest in many areas of science and engineering, including aeroacoustics and sound propagation in oceans. In the present work, numerical frequency domain models based on the joint use of the method of fundamental solutions and of the radial basis function collocation method (also known as Kansa's method) are discussed. In this context, the method of fundamental solutions is used to model the homogeneous part of the propagation domain, while Kansa's method is employed to model the presence of heterogeneities. The coupling between the two parts of the propagation domain is performed iteratively, allowing independent spatial discretization between the different subdomains of the model (i.e. matching collocation points at common surfaces are not necessary). Additionally, an optimised algorithm, based on the use of a varying relaxation parameter, is employed to speed up and/or to ensure the convergence of the iterative coupling process. At the end of the paper, numerical results illustrate the applicability and potentialities of the proposed formulations. Copyright © 2011 John Wiley & Sons, Ltd.     

Study of the measurement of the transverse emittances of a beam by the three gradients method: Application to the case of a focusing by solenoid

Within the framework of the ALTO project (Linear Accelerator near the Orsay Tandem), IPN Orsay will use NEPAL facility of LAL as the ALTO injector. In order to calculate the beam optics of the linear accelerator, it is necessary to find out the electrons beam emittance at the exit of the buncher station.

According to previous studies there are several methods for measuring this emittance: direct methods like the Pepper Pot technique, and indirect ones namely the three distances method and the three gradients technique. Moreover, the latter requires a variable optic element (i.e. quadrupole, solenoid…). Generally, the solenoid is used to focus the beam when the later has a symmetry axe of revolution compared to the direction of propagation and it has the same emittance in the two horizontal and vertical planes. In the case of ALTO injector, we did not have the certainty if the beam presented such symmetry. The effects of coupling introduced by the action of the solenoid were thus to be planned to determine the emittance starting from the transverse profiles measurement. This is why we developed a general method of calculation which takes into account the coupling when the horizontal and vertical emittances are different. The first part of this study is dedicated to its presentation. The second part is dedicated to the presentation of emittance measurement results obtained by using this method.     

Numerical study of natural convection in a cavity of high aspect ratio by using the lattice Boltzmann method

A comprehensive numerical study has been conducted to investigate two‐dimensional, steady heat transfer of natural convection in a divided enclosure of high aspect ratio. The vertical walls of the enclosure are maintained at different temperatures, while the horizontal walls are adiabatics. A numerical hybrid scheme with lattice Boltzmann for fluid velocity and finite difference for the temperature is adopted. Parametric studies of the effects of aspect ratio, number and length of partitions attached to the cold wall of the enclosure on heat transfer and fluid flow have been performed. Copyright © 2007 John Wiley & Sons, Ltd.     

Electron doping into the surface of SrTiO3 single crystal by using a field effect transistor structure having a polyvinyl alcohol gate insulator layer

We fabricated an n-channel accumulation-type field-effect transistor (FET) on a SrTiO₃ single crystal having a polyvinyl alcohol (PVA) layer and a Na⁺-doped PVA layer as a gate insulator. Both devices show an n-type FET performance having a response time of 10 - 100 second order. This slow response is due to the gradual formation of an electric double layer by solvated Na⁺ ions moving through the water absorbed in the PVA layer towards the surface of SrTiO₃ by applying a gate voltage (V_G), which is manifested by the fact that Na⁺-doping into the PVA layer dramatically reduces the driving voltages and the response time. In these devices, metallic or semiconducting behaviors are observed if the applied V_G is large enough to form a conducting channel during cooling of the devices. These results indicate that electrons are certainly doped into the surface of SrTiO₃ by applying V_G in both devices.     

Modeling and monitoring the nonlinear profile of heat treatment process data by using an approach based on a hyperbolic tangent function

In this article, a new approach is proposed which uses the hyperbolic tangent function to model and monitor vacuum heat treatment process data. The proposed hyperbolic tangent function approach is compared to the smoothing spline approach. The latter serves as the benchmark when the vacuum heat treatment profile is investigated. The vector of the obtained parameter estimates is monitored by using Hotelling's method for the hyperbolic tangent function approach, and the metrics method used for the smoothing spline approach. For the purposes of verification, data from a real aluminum alloy heat treatment process is used to illustrate the proposed approach. In Phase I, the modified hyperbolic tangent function and the smoothing spline are first utilized to fit the process data. The proposed approach provides a better fitting result than the smoothing spline approach. In Phase II, the proposed approach produces a much better out-of-control average run length (ARL) performance than the smoothing spline approach when the heat treatment profile shows process abnormalities.