Effect of an electric field on a floating lipid bilayer: a neutron reflectivity study

We present here a neutron reflectivity study of the influence of an alternative electric field on a supported phospholipid double bilayer. We report for the first time a reproducible increase of the fluctuation amplitude leading to the complete unbinding of the floating bilayer. Results are in good agreement with a semi-quantitative interpretation in terms of negative electrostatic surface tension.Comment: 12 pages, 7 figures, 1 table accepted for publication in European Physical Journal E Replaced with with correct bibliograph

From supported membranes to tethered vesicles: lipid bilayers destabilisation at the main transition

We report results concerning the destabilisation of supported phospholipid bilayers in a well-defined geometry. When heating up supported phospholipid membranes deposited on highly hydrophilic glass slides from room temperature (i.e. with lipids in the gel phase), unbinding was observed around the main gel to fluid transition temperature of the lipids. It lead to the formation of relatively monodisperse vesicles, of which most remained tethered to the supported bilayer. We interpret these observations in terms of a sharp decrease of the bending rigidity modulus $\kappa$ in the transition region, combined with a weak initial adhesion energy. On the basis of scaling arguments, we show that our experimental findings are consistent with this hypothesis.Comment: 11 pages, 3 figure

Compression modulus of macroscopic fiber bundles

We study dense, disordered stacks of elastic macroscopic fibers. These stacks often exhibit non-linear elasticity, due to the coupling between the applied stress and the internal distribution of fiber contacts. We propose a theoretical model for the compression modulus of such systems, and illustrate our method by studying the conical shapes frequently observed at the extremities of ropes and other fiber structures. studying the conical shapes frequently observed at theextremities of ropes and other fiber structures

Neutron reflection study on soluble and insoluble poly[2-(2 '-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene) films

Neutron reflection (NR) has been utilized to study the physical structure of the light-emitting polymer poly[2-(2'-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene) (MEHPPV). Films of soluble MEHPPV (S-MEHPPV) and insoluble MEHPPV (I-MEHPPV) prepared via a chloro precursor polymer were investigated. For S-MEHPPV spin-coated films were found to contain two layers, one of low-density and thickness of approximate to1360 Angstrom with the second layer being thinner, approximate to240 Angstrom, but denser. The thicker layer only covered about 30% of the substrate surface. In contrast, I-MEHPPV formed uniform films across the substrate. We found that during the thermal conversion of the chloro precursor polymer the film thickness was maintained and it was only on cooling that the films contracted. Importantly, the thermal expansion and contraction of I-MEHPPV was reversible. NR showed that thermal annealing of I-MEHPPV had little affect on the films physical structure while for S-MEHPPV only the thinner layer was changed and became more dense. Photoluminescence spectra of S-MEHPPV before and after annealing showed that the densification observed in the neutron reflection measurements was mirrored in the emission properties of the polymer film. (C) 2002 American Institute of Physics

Anti-infectives in Drug Delivery-Overcoming the Gram-Negative Bacterial Cell Envelope.

Infectious diseases are becoming a major menace to the state of health worldwide, with difficulties in effective treatment especially of nosocomial infections caused by Gram-negative bacteria being increasingly reported. Inadequate permeation of anti-infectives into or across the Gram-negative bacterial cell envelope, due to its intrinsic barrier function as well as barrier enhancement mediated by resistance mechanisms, can be identified as one of the major reasons for insufficient therapeutic effects. Several in vitro, in silico, and in cellulo models are currently employed to increase the knowledge of anti-infective transport processes into or across the bacterial cell envelope; however, all such models exhibit drawbacks or have limitations with respect to the information they are able to provide. Thus, new approaches which allow for more comprehensive characterization of anti-infective permeation processes (and as such, would be usable as screening methods in early drug discovery and development) are desperately needed. Furthermore, delivery methods or technologies capable of enhancing anti-infective permeation into or across the bacterial cell envelope are required. In this respect, particle-based carrier systems have already been shown to provide the opportunity to overcome compound-related difficulties and allow for targeted delivery. In addition, formulations combining efflux pump inhibitors or antimicrobial peptides with anti-infectives show promise in the restoration of antibiotic activity in resistant bacterial strains. Despite considerable progress in this field however, the design of carriers to specifically enhance transport across the bacterial envelope or to target difficult-to-treat (e.g., intracellular) infections remains an urgently needed area of improvement. What follows is a summary and evaluation of the state of the art of both bacterial permeation models and advanced anti-infective formulation strategies, together with an outlook for future directions in these fields

ミナミ タイヘイヨウ ヒカク チタイ ジョウヤク ケイセイ カテイ ニ オケル オーストタリア ノ カクグンシュク ガイコウ セイサク

Alternate bilayer structures of N,N'-bis(2,5-di-tert-butylphenyl)-3,4,9,10- perylene dicarboximide (PDI), freebase phthalocyanines (Pc), and double-linked free-base phthalocyanine-fullerene dyad (Pc-C 60) were prepared by the Langmuir-Schäfer method and studied using a range of optical spectroscopy methods including femtosecond pump-probe and up-conversion. An efficient quenching of the PDI fluorescence by Pc and Pc-C 60 dyad was observed in both steady-state and time-resolved fluorescence measurements. The quenching takes place in less than a few picoseconds, and is due to energy transfer from perylene dicarboximide to phthalocyanine chromophore in PDI|Pc and PDI|Pc-C 60 films. In the PDI|Pc-C 60 bilayer structure the energy transfer is followed by a charge separation in the Pc-C 60 layer, yielding a long-lived (a few microseconds) intermolecular charge separated state similar to that reported recently for Pc-C 60 Langmuir-Blodgett films (Lehtivuori, H.; et al. J. Phys. Chem. C 2008, 112, 9896-9902)

High voltage RESURF LDMOS for smart power integrated circuits

An in-depth comprehension of the electrical behaviour of a RESURF LDMOS is given. Avalanche breakdowns are evaluated leading to simple design rules based on analytical formulations for a first order analysis, and on bidimensional numerical simulations for a second order analysis. A 2D numerical simulator is used to study the influence of some critical parameters on the breakdown voltage and the on behavior. Such parameters include the epitaxy doping and thickness, the channel-drain distance, the channel junction depth. On state investigation is conducted to evaluate the on-resistance and the current flow of the device and to study the improvement which can be expected from technics such as surface doping or SIPOS deposition. With such design rules the RESURF LDMOS is a good applicant for power switches in smart power IC. To illustrate and validate these design rules medium voltage diodes (350-550 volts) are processed and tested.Une étude détaillée du comportement électrique des transistors LDMOS de type RESURF est donnée. Le claquage par avalanche est évalué à la fois par des règles analytiques simples, pour une approche de premier ordre, et par une analyse numérique bidimensionnelle pour une compréhension plus fine. Un logiciel de simulation numérique travaillant en 2 dimensions, BIDIM2, est utilisé pour évaluer l'influence de certains paramètres critiques (épaisseur et concentration d'epitaxie, distance canal-drain, profondeur de jonction de canal) sur la tension de claquage et la résistance à l'état passant. L'étude à l'état passant du transistor permet de déterminer sa résistance passante ainsi que la répartition du courant pour prévoir les améliorations qui peuvent être apportées par des techniques telles que le surdopage localisé en surface ou l'utilisation de couches semi-résistives (telle que le SIPOS). On extrait ainsi un certain nombre de règles de conception pour les transistors LDMOS RESURF qui confirment que ce composant est aisément utilisable dans les circuits intégrés haute tension. Pour valider ces règles des diodes RESURF de moyenne tension (350-550 V) sont réalisées et testées

Evaluation des performances du transistor MOS de puissance sur carbure de silicium. Compromis résistance passante, tenue en tension et vitesse de commutation

The DC trade-off " ON resistance versus voltage capability " is determined for the SiC multicellular Power MOSFET transistor. First, this limit is analytically calculated for the bulk material. Then, the influence of the size of the MOSFET cell is considered. Under dynamic condition, the switching behaviour is simulated and analysed. We confirm that the DC performances of the SiC device are better than those of Si structures. From a dynamic point of view, a degradation can or not occur depending upon the voltage capability of the considered device. The degradation is due to the drain-gate Miller capacitance increase with the drain doping value.On détermine le compromis statique " résistance passante — tenue en tension " des transistors MOS de puissance multicellulaires sur carbure de silicium. Cette limite est d'abord calculée analytiquement pour le matériau volumique. L'influence de la taille des cellules du transistor MOS est ensuite prise en compte. Au niveau dynamique, la commutation résistive est également simulée. On confirme que les performances statiques de composants SiC sont potentiellement meilleures que celles de leurs homologues Si. D'un point de vue dynamique, on montre que selon la tenue en tension considérée, une dégradation du temps de commutation peut ou non apparaître. Celle-ci est expliquée par l'accroissement de la capacité drain-grille corrélative à l'augmentation de dopage