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Regular Lattice (regular + lattice)

Distribution by Scientific Domains
Physics and Astronomy40%

Selected Abstracts

How good are the Electrodes we use in PEFC?

FUEL CELLS, Issue 3 2004
M. Eikerling
Abstract Basically, companies and laboratories implement production methods for their electrodes on the basis of experience, technical capabilities and commercial preferences. But how does one know whether they have ended up with the best possible electrode for the components used? What should be the (i) optimal thickness of the catalyst layer? (ii) relative amounts of electronically conducting component (catalyst, with support , if used), electrolyte and pores? (iii) "particle size distributions" in these mesophases? We may be pleased with our MEAs, but could we make them better? The details of excellently working MEA structures are typically not a subject of open discussion, also hardly anyone in the fuel cell business would like to admit that their electrodes could have been made much better. Therefore, we only rarely find (far from systematic) experimental reports on this most important issue. The message of this paper is to illustrate how strongly the MEA morphology could affect the performance and to pave the way for the development of the theory. Full analysis should address the performance at different current densities, which is possible and is partially shown in this paper, but vital trends can be demonstrated on the linear polarization resistance, the signature of electrode performance. The latter is expressed through the minimum number of key parameters characterizing the processes taking place in the MEA. Model expressions of the percolation theory can then be used to approximate the dependence on these parameters. The effects revealed are dramatic. Of course, the corresponding curves will not be reproduced literally in experiments, since these illustrations use crude expressions inspired by the theory of percolation on a regular lattice, whereas the actual mesoscopic architecture of MEA is much more complicated. However, they give us a flavour of reserves that might be released by smart MEA design. [source]

Reduction of sidelobe levels in interrupted phased array antennas by means of a genetic algorithm,

INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 2 2007
David A. Tonn
Abstract Interruptions in the regular lattice of a phased array antenna can lead to elevated sidelobe levels in the resulting antenna pattern. A method for reducing the sidelobe level in such an array is presented, based on the use of a genetic algorithm that modifies the element weights in the array. Results are presented for both scanned and unscanned arrays. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007. [source]

Linearly polarized all-fiber laser using a short section of highly polarizing microstructured fiber

LASER PHYSICS LETTERS, Issue 2 2008
M. Delgado-Pinar
Abstract A linearly polarized all-fiber erbium laser is presented in this work. The polarization selective element consists on a piece of a single-mode, polarizing microstructured fiber, which is placed within the laser cavity. The microstructured fiber shows a regular lattice of air-holes, in which four holes next to the core were enlarged. This fiber shows a polarization dependent loss of 16 dB/m around 1550 nm. The laser cavity presents different losses for each polarization and, as a consequence, a highly polarized emission is obtained. The polarization ratio of the emitted power was in excess of 20 dB. (© 2007 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

Asymptotics for the voltage potential in a periodic network with localized defects

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 10 2008
Eric Bonnetier
Abstract We compare the potential uh of a 2D regular lattice of conductors of size h, to the potential uh,d of a defective lattice, where some conductive links have different conductivities. We show that to first order in h, each defect contributes to the difference uh,d,uh as a product of three terms: A polarization matrix, the gradient of the potential u of the limiting continuous medium obtained as h,,,0, and the gradient of Green's function of the limiting medium. Establishing the asymptotics of uh,d,uh involves uniform W1,, estimates on the potentials uh. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Auxetic lattice of multipods

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2009
Peter V. Pikhitsa
Abstract Auxetics are novel counterintuitive materials that grow thicker perpendicularly to the applied force when stretched and therefore are described by a negative Poisson's ratio. We show that a regular lattice of individual multipods properly assembled in three dimensions has the ultimate negative Poisson's ratio ,1: the lattice expands or contracts uniformly in all directions. Our ball-and-stick working model verifies the mathematical construction. Application of the model to real materials is discussed. Our result is important for understanding the ways to create entangled materials with interesting mechanical properties. [source]