The minimum weight design of circular sandwich plates

Résumé Dans ce mémoire nous étudions le problème statique du choix des dimensions suivant: Comment doit varier l'épaisseur de point en point dans les plaques circulaires fléchies du type sandwich, pourque leur poids soit minimum, mais sans qu'il existe du fluage illimité? Comme hypothèse de base, nous avons pris la condition de plasticité devon Mises et la règle de fluage associée. Les plaques sont simplement posées ou encastrées le long de leur contour et portent une charge répartie symétriquement par rapport à l'axe. Les résultats obtenus sont comparés à ceux du problème analogue, où l'on utilise la condition de plasticité deTresca. Nous avons présenté finalement quelques résultats numériques.     

Shock-induced arrhythmogenesis in the myocardium

The focus of this article is the investigation of the electrical behavior of the normal myocardium following the delivery of high-strength defibrillation shocks. To achieve its goal, the study employs a complex three-dimensional defibrillation model of a slice of the canine heart characterized with realistic geometry and fiber architecture. Defibrillation shocks of various strengths and electrode configurations are delivered to the model preparation in which a sustained ventricular tachycardia is induced. Instead of analyzing the post-shock electrical events as progressions of transmembrane potential maps, the study examines the evolution of the postshock phase singularities (PSs) which represent the organizing centers of reentry. The simulation results demonstrate that the shock induces numerous PSs the majority of which vanish before the reentrant wavefronts associated with them complete half of a single rotation. Failed shocks are characterized with one or more PSs that survive the initial period of PS annihilation to establish a new postshock arrhythmia. The increase in shock strength results in an overall decrease of the number of PSs that survive over 200 ms after the end of the shock; however, the exact behavior of the PSs is strongly dependent on the shock electrode configuration. (c) 2002 American Institute of Physics.     

On the indentation of an inhomogeneous plastic solid

Summary The problem considered here is that of the indentation of a semi infinite, inhomogeneous rigid-plastic solid by a smooth, flat ended punch under conditions of plane strain. It is assumed that the yield stress of the solid k(x, y) has the form k ⁰+k(x, y) where k ⁰ is a constant and is small. A perturbation method of solution developed by Spencer [1] is used, and general results are obtained for arbitrary values of k(x, y). Some particular cases are then considered.     

Comparison of one- and two-dimensional detectors on simulated and spin-stand readback waveforms

Shingled writing (SW) and two-dimensional magnetic recording (TDMR) are two complementary candidate technologies proposed to extend the life of magnetic recording. SW enables the writing of narrow tracks with a wider writer by shingling the tracks; each track partially overlaps the preceding track leaving only a fraction of that track on the medium. TDMR is the companion technology to SW that enables reading of narrower tracks with a wider reader. In this work we compare the performances of 1D and 2D detectors in the shingled writing environment, using both comprehensive channel models and spin-stand readback.     

Etch frustration in congruent lithium niobate single crystals induced by femtosecond ultraviolet laser irradiation

Modification of the chemical etching behaviour of undoped congruent z-cut lithium niobate single crystals is achieved by pre-illumination of the –z face of the crystal with sub-ps ultraviolet laser radiation at 248 nm, at energy fluences below the threshold for ablation. A systematic study of the effect of the energy fluence and total exposure on the etch frustration is presented. Received: 23 July 2001 / Accepted: 28 September 2001 / Published online: 20 December 2001     

Cobalt‐mediated catalytic chain‐transfer polymerization (CCTP) in water and water/alcohol solution

This article describes the use of cobalt‐mediated catalytic chain transfer in aqueous solution under fed conditions for the preparation of macromonomers of acidic, hydroxy, and zwitterionic functional monomers. Use of a batch reaction leads to hydrolysis of catalyst, a mixture of mechanisms and poor control of the reaction. A feed process is described that adds catalyst as a solution in monomer over the course of the reaction. The feed process is applied to a range of monomers of methacrylic acid ( 2 ), 2‐aminoethyl methacrylate hydrochloride ( 3 ), 2‐hydroxyethyl methacrylate ( 4 ), 2‐methacryloxyethyl phosphoryl choline ( 5 ), glycerol monomethyl methacrylate ( 6 ), and 3‐O‐methacryloyl‐1,2:5,6‐di‐O‐isopropylidene‐D ‐glucofuranose ( 7 ). Use of the feed process for water‐soluble monomers in conjunction with 1 as a catalytic chain‐transfer agent gives high‐conversion, > 90%, water‐soluble macromonomers. The number‐average molecular mass (M_n was determined by integration of the ¹H NMR spectrum comparing the vinylic end group with the remainder of the backbone. Pseudo‐Mayo plots were constructed by measuring the M_n at high conversion as a function of [monomer]/[catalyst] to give observed chain‐transfer constants of 1120, 958, and 1058 for 4, 6, and 2, respectively. All products were obtained as relatively high‐solid, homogeneous, low‐viscosity aqueous solutions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2378–2384, 2001     

Current state-of-the-art of pulsed laser deposition of optical waveguide structures: Existing capabilities and future trends

Pulsed laser deposition (PLD) has now reached a stage of maturity where the growth of thin films is routine. All that is required is a pulsed ultra-violet (UV) wavelength laser, a vacuum chamber, a target, and a substrate placed in near proximity to the plasma plume. Whether the film that you grow is the film that you need, and whether the thickness, uniformity, optical quality, stoichiometry, degree of crystallinity, orientation and much more is what is desired is another question entirely. PLD is both a science and an art and there are many tricks-of-the-trade that need to be considered to ensure that materials grown are the materials wanted. This paper discusses the practicalities of PLD systems, target geometries, heating regimes for successful epitaxial growth of crystalline films, the problem of particulates, laser sources to use, and in the context of our most recent PLD system, the number of independent lasers and targets used. We show that the use of multiple targets permits a combinatorial approach, whereby stoichiometry can be adjusted to grow designer materials, and in particular multilayer systems, ideally suited for active optical waveguides, a truly demanding end application where optical quality and in-plane losses must be reduced to an absolute minimum.     

Ultraviolet laser-induced sub-micron periodic domain formation in congruent undoped lithium niobate crystals

We report the formation of ordered sub-micron periodic surface domains on the –z face of congruent undoped lithium niobate single crystals induced by pulsed ultraviolet laser illumination of the sample faces under specific irradiation conditions. We demonstrate the utility of this simple light-induced technique for achieving periodic domain inversion and investigate the nature and spatial structure of these nano-domains by scanning force microscopy. We also demonstrate subsequent re-inversion of a small region of these light-induced nano-domains using scanning force microscopy.     

Holographic recording mechanisms of gratings in indium oxide films using 325 nm helium–cadmium laser irradiation

UV (325 nm) holographic recording of gratings in indium oxide films fabricated by reactive pulsed laser deposition has been investigated as a function of growth temperature, oxygen pressure and angle of incidence of the plasma plume on the substrate. The influence of the ambient environment (air or vacuum) and the film temperature during recording has also been studied. Large steady state refractive index changes up to 6×10^-3 were observed in layers grown at an oblique angle of 75°. About 77% of the magnitude of these changes residues after thermal annealing and is attributed to UV-induced permanent structural rearrangements. In contrast, refractive index changes in films grown at normal incidence were smaller in magnitude and completely reversible. Received: 30 July 2001 / Accepted: 20 November 2001 / Published online: 23 January 2002