Moving‐least‐squares‐particle hydrodynamics—I. Consistency and stability

The Smooth‐Particle‐Hydrodynamics (SPH) method is derived in a novel manner by means of a Galerkin approximation applied to the Lagrangian equations of continuum mechanics as in the finite‐element method. This derivation is modified to replace the SPH interpolant with the Moving‐Least‐Squares (MLS) interpolant of Lancaster and Saulkaskas, and define a new particle volume which ensures thermodynamic compatibility. A variable‐rank modification of the MLS interpolants which retains their desirable summation properties is introduced to remove the singularities that occur when divergent flow reduces the number of neighbours of a particle to less than the minimum required. A surprise benefit of the Galerkin SPH derivation is a theoretical justification of a common ad hoc technique for variable‐h SPH. The new MLSPH method is conservative if an anti‐symmetric quadrature rule for the stiffness matrix elements can be supplied. In this paper, a simple one‐point collocation rule is used to retain similarity with SPH, leading to a non‐conservative method. Several examples document how MLSPH renders dramatic improvements due to the linear consistency of its gradients on three canonical difficulties of the SPH method: spurious boundary effects, erroneous rates of strain and rotation and tension instability. Two of these examples are non‐linear Lagrangian patch tests with analytic solutions with which MLSPH agrees almost exactly. The examples also show that MLSPH is not absolutely stable if the problems are run to very long times. A linear stability analysis explains both why it is more stable than SPH and not yet absolutely stable and an argument is made that for realistic dynamic problems MLSPH is stable enough. The notion of coherent particles, for which the numerical stability is identical to the physical stability, is introduced. The new method is easily retrofitted into a generic SPH code and some observations on performance are made. Copyright © 1999 John Wiley & Sons, Ltd.     

Fuel Cells: Structure‐Morphology‐Property Relationships of Non‐Perfluorinated Proton‐Conducting Membranes (Adv. Mater. 42/2010)

A fundamental understanding of structure‐morphology‐property relationships of proton exchange membranes (PEMs) is crucial in order to improve the cost, performance, and durability of PEM fuel cells (PEMFCs). In this context, there has been an explosion over the past five years in the volume of research carried out in the area of non‐perfluorinated, proton‐conducting polymer membranes, with a particular emphasis on exploiting phase behavior associated with block and graft copolymers. This progress report highlights a selection of interesting studies in the area that have appeared since 2005, which illustrate the effects of factors such as acid and water contents and morphology upon proton conduction. It concludes with an outlook on future directions.     

EUV‐Lithographie für zukünftige IC‐Chips. EUV‐Lithography for Future IC‐Technology

In the past the overwhelming success of the semiconductor industry was based on the realisation of ever smaller structures on chips in ever shorter periods. This allowed to increase the computational speed of the processors and the amount of data that can be stored in a memory chip. This reduction of the critical dimension was mastered within optical lithography by transition to smaller wavelengths. Those lithography technologies that are currently in the development or test phase, based on 193 nm or as well 157 nm laser sources, will not achieve dimensions around 50 nm. A fundamental change of technology is thus emerging. The currently favored basis for dimensions of 50 nm and below is EUV lithography, based on an optical technology with an exposure wavelength of 13,4 nm. This substantial reduction of the wavelength also implies a radical change of the methodology used up to now.     

Vakuum‐Drehdurchführungen mit Magnetflüssigkeitsdichtungen. Magnetic‐liquid‐sealed vacuum rotary feedthrough

Most vacuum manufacturing processes require some type of motion to take place within the chamber. A magnetic liquid sealed feedthrough is a device that transmits rotary motion into a vacuum chamber with minimal torque requirements and minimal contamination level. The are widely employed in high and ultra‐high vacuum conditions, such as: semiconductor fabrication industry, coating equipment, high power X‐ray generators, robotics applications and the others. In the paper is given principle of operation of a magnetic liquid seal and various standard and special designs of vacuum rotary feedthroughs, sealed with magnetic liquid are described.