Automatic partitioning of unstructured meshes for the parallel solution of problems in computational mechanics

Most of the recently proposed computational methods for solving partial differential equations on multiprocessor architectures stem from the 'divide and conquer' paradigm and involve some form of domain decomposition. For those methods which also require grids of points or patches of elements, it is often necessary to explicitly partition the underlying mesh, especially when working with local memory parallel processors. In this paper, a family of cost-effective algorithms for the automatic partitioning of arbitrary two- and three-dimensional finite element and finite difference meshes is presented and discussed in view of a domain decomposed solution procedure and parallel processing. The influence of the algorithmic aspects of a solution method (implicit/explicit computations), and the architectural specifics of a multiprocessor (SIMD/MIMD, startup/transmission time), on the design of a mesh partitioning algorithm are discussed. The impact of the partitioning strategy on load balancing, operation count, operator conditioning, rate of convergence and processor mapping is also addressed. Finally, the proposed mesh decomposition algorithms are demonstrated with realistic examples of finite element, finite volume, and finite difference meshes associated with the parallel solution of solid and fluid mechanics problems on the iPSC/2 and iPSC/860 multiprocessors.     

Two-dimensional elastoplasticity: Approximation by mixed finite elements

Two-dimensional elastoplastic problems are used to assess the performance of a family of mixed finite elements in the non-linear regime. In particular, four-node bilinear quadrilateral elements that exhibit high accuracy in coarse meshes are used to simulate plane stress, plane strain, axisymmetric and (shear-deformable) plate bending problems. The excellent performance of these elements is demonstrated with a number of discriminating examples selected from the literature. In addition, agreement is observed in the limit load predicted by the axisymmetric solid and plate bending elements.     

Electronic passivation of silicon surfaces by halogens

We report the electronic passivation of a silicon surface by iodine termination. The resulting surface recombination velocity on Si(100) is less than 1 cm/s which is better than that obtained in concentrated hydrofluoric acid (HF). We have produced a surface recombination velocity of 20 cm/s using bromine. We present a simple model for these phenomena of a surface coverage of Si-X where X is a monovalently bonded halogen atom. The effectiveness of the passivation by halogens is shown to be limited by the oxidation of halogens by dissolved oxygen in solution. We demonstrate the use of halogen:methanol solutions as an alternative to HF for the control of silicon surface chemistry.     

The possibility of new high-transmission,high finesse,Perot-Fabry interferometers for far ir spectroscopy

Finesse as high as 260 and peak transmission close to 98% at frequencies around 30 cm^?1 are predicted at 10 K by coating the Perot-Fabry (PF) mirrors with a suitable thickness of High Tc (HTC) superconductor YBaCuO. In fact, Finesse will be limited by the lack of parallelism and the lack of perfect flatness of the mirrors to values around 100. These predictions are based upon phenomenological models for both the YBaCuO coating and the MgO support, i.e. from direct transmission measurements of MgO and YBaCuO in the Far IR, which had to be fitted by the models.     

Dynamique des lasers à fibre dopée à I’erbium

The dynamics of the erbium doped fiber laser is analysed both experimentally and theoretically. This laser operates spontaneously in self-pulsing, in sinusoidal or in CW regime. Experiments have allowed to determine the control parameters : the cavity losses, the pumping rate and the ion pairs concentration. An antiphase dynamics is observed when the laser operates simultaneously at 1.55 µn and 1.536 µm. The self-pulsing behavior is attributed to a fast energy transfer which occurs between two neighboring ions (pair induced quenching). A simple model considering the active medium as a mixture of isolated ions and ions pairs is developped and leads to a good qualitative agreement with the experimental results.     

Implementation and Application of a New Elastoplastic Model Based on a Multiaxial Criterion to Assess the Stress State near Underground Openings

The inelastic MSDPu (for Mises-Schleicher and Drucker-Prager unified) criterion has been developed over the last decade, and has been applied to simple problems for a wide range of geomaterials. This paper presents the approach taken to introduce this multiaxial criterion into a commercially available finite difference code using an elastoplastic framework. The paper begins with a brief review of the MSDPu formulation. Then, the main components of the elastoplastic model and the implementation procedure are described. The ensuing model, called MSDPu-EP (for MSDPu elastoplasticity model), is then validated against some existing and recently developed analytical solutions for the stress state around a circular opening. The newly developed model is further applied to evaluate the stress state near underground openings, using the geometry of a tunnel and of vertical backfilled stopes. A brief discussion follows.     

The psychology of thinking before the cognitive revolution: Otto Selz on problems, schemas, and creativity.

Otto Selz has been hailed as one of the most important precursors of the cognitive revolution, yet surprisingly few studies of his work exist. He is often mentioned in the context of the Würzburg School of the psychology of thinking and sometimes in the context of Gestalt psychology. In this paper, it is argued that Selz’s emphasis on the role of problems and schemas in the direction of thought processes and creativity sets him apart from the program of the Würzburg School. On the other hand, by developing a theory of thinking that is exclusively at the intentional level, Selz also differs from psychologists that take physics as a model for psychology, such as the Gestalt psychology of Wolfgang K?hler. Special emphasis is given in this paper to Selz’s use of the concept of problem or task and the concept of the schema. It is further argued that the concept of the schema is the result of Selz’s adaptation of the theory of relations as developed by the philosopher Meinong. The paper begins with a sketch of Selz’s life that ended so tragically. (PsycINFO Database Record (c) 2010 APA, all rights reserved)