AC “back to back” switching device in industrial application

In industrial applications, among several varieties of semiconductor devices available, a silicon-controlled rectifier (SCR) is often used in managing and protecting various systems with different applications. Hence, it is of the utmost importance to design a control system which can operate over a range of electrical loads without any modifications in its hardware and/or software. This paper analyzes and investigates in detail the power circuit effects on conduction delay and SCR functioning. Moreover, two different commonly used driving systems for SCR application have been introduced, discussed, and evaluated. Concerning driving systems, here, three aspects have paramount importance and are consequently taken into consideration, namely the driver system losses, the conduction delay, and in particular, some power quality indices. The conduction delay is a parameter of great importance, as being able to control and reduce it to the minimum allowed by the application can bring significant practical advantages (both in terms of application and economic terms, as better summarized in the article). Theoretical analysis has been performed, followed and verified by simulation studies and, for some cases, laboratory experimental test results are presented which provide credibility to the study.©2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license http://creativecommons.org/licenses/by/4.0/fi=vertaisarvioitu|en=peerReviewed

Chemical Sensors (Modelling the Photophysics of Cation Detection by Organic Dyes)

La présence croissante de diverses substances dans notre environnement, conséquencedes activités anthropiques de ces dernières décennies, a entraîné un besoingrandissant et urgent de nouveaux matériaux et dispositifs dans la quête de senseurschimiques efficaces et fiables. D'énormes progrès technologiques ont permis de mettreà disposition toute une gamme d'outils techniques pour leur développement, enprenant en compte les exigences à respecter en terme de sélectivité ou de rapidité deréponse, entre autres. Dans ce contexte, les méthodes de chimie quantique permettentune compréhension fondamentale des processus en jeu dans la détection des espèceschimiques, et par extension, l'élaboration de manière rationnelle de nouveauxmatériaux sensibles. Certaines molécules organiques pouvant être largementfonctionnalisées, elles constituent un point de départ idéal en raison des importantesmodulations possibles de leurs propriétés par des modifications structuralesappropriées.Cette étude vise à développer de manière rationnelle des chromoionophores pour lacomplexation de cations par une approche combinant méthodes de chimiecomputationnelles et caractérisation par spectroscopie optique. Deux pointsprincipaux ont été traités à l'aide de la Théorie de la Fonctionnelle de la Densité(DFT) et son extension dépendante du temps (TD-DFT): d'une part les relationsstructure moléculaire-propriétés optiques de chromophores, d'autre part le phénomènede complexation. En particulier, la détection de l'ion Zn2+, démontrée de manièrethéorique et expérimentale, est finalement réalisée après intégration du senseurmoléculaire dans un dispositif à fibre optique.The increasing presence of various substances in our environment has brought abouta growing need for rapid emergence of new materials and devices in the quest forefficient and reliable chemical sensors. Massive technological progress have madeavailable an extensive range of technical tools to serve their development, accountingfor the requirements to be fulfilled (selectivity, quick response..). In this context,quantum chemistry methods provide a fundamental understanding of the processes atstake in the detection of chemical species and allow for rational design of sensingmaterials. Certain organic molecules can be extensively functionalised and thusconstitute an evident starting point owing to the tunability of their propertiesprovided by appropriate choice of structural modifications. The versatility of somechromophores associated to the selectivity offered by receptor units constitute theresearch playground for the development of ever better chemosensors.The present research aims at the rational development of chromoionophores for thecomplexation of cations, combining computational chemistry methods with basicspectroscopic characterisation. Using Density Functional Theory (DFT) and its timedependentextension (TD-DFT), two main aspects were treated, namely therelationship between molecular structure and optical properties of organicchromophores featuring valuable characteristics, and the complexation phenomenon.Photophysics of Zn2+ ion detection were more specifically studied, and recognitionwas demonstrated with both quantum-chemical calculations and experiments,accounting for the future integration of the chemical sensor in an optical fibre device.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Electrochemical synthesis of new electroactive polymers from dithienylene-vinylene derivatives

peer reviewedHighly conjugated thiophene derivatives, based on thienylene-vinylene and thieneylene-vinylene-phenylene units, have been synthesized in order to examine: (i) the effect of such regular conjugated monomer structures on the polymerization; (ii) the optical and electrochemical properties of the corresponding conjugated polymers. The all-trans monomers have been prepared by a Wittig reaction and the polymers have then been synthesized electrochemically. The polymers are electrochromic and can be reversibly doped both oxidatively and reductively. Their electrochemical behavior and optical properties have been analysed on the basis of quantum-chemical calculations

Stereoselective ROP of rac- and meso-lactides using achiral TBD as catalyst

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) polymerizes rac-lactide (rac-LA) to form highly isotactic polylactide (PLA) with a Pm = 0.88, while meso-LA yields heterotactic PLA (Pm ~ 0.8) at −75 °C. The stereocontrol of the cryogenic-based ring-opening polymerization comes from a perfect imbrication of both chiral LA and the propagating chiral end-group interacting with the achiral TBD catalyst