369 research outputs found
Picosecond Pulse Radiolysis Study of Primary Reactions in Solutions
No full textAprès la découverte des rayonnements ionisants et leurs effets chimiques, il était important d’étudier et de comprendre les mécanismes de formations des radicaux libres et des produits moléculaires caractérisés par leurs courtes durées de vie. Ceci a encouragé les groupes de recherches à développer leurs outils pour qu’ils puissent réaliser ces études. De nos jours la radiolyse impulsionnelle se manifeste comme un outil fondamental permettant de sonder les effets chimiques ainsi que les mécanismes réactionnels dans le milieu étudié.Le laboratoire de Chimie Physique d’Orsay « LCP » est un laboratoire interdisciplinaire abritant la plateforme « ELYSE » qui est un centre de cinétiques rapides. Grâce au laser femtoseconde et à l’accélérateur d’électrons picoseconde, nous avons eu la possibilité, dans le domaine de la radiolyse, de remonter en temps, en étudiant les effets chimiques dans un milieu réactionnel, jusqu’à ~ 5 ps.Nous nous sommes intéressés par les réactions primaires induites par les rayonnements ionisants en solution et ELYSE représentait l’outil principal pour ces études. Les résultats obtenus concernent :- La détermination directe du rendement radiolytique du radical hydroxyle « HO• » en fonction du temps à l’échelle de la picoseconde ;- Etude de l’effet direct du rayonnement ionisant sur les solutions aqueuses concentrées ainsi que la vérification de la réaction de transfert d’électron ultrarapide entre le soluté et le trou positif « H2O•+ » issu lors de la radiolyse de l’eau ;- Etude à température ambiante de la réaction de transfert d’électron entre un électron solvaté (donneur d’électron) et un soluté organique (accepteur d’électron) en milieu visqueux ;- Etude à température ambiante de la solvatation de l’électron dans l’éthylène glycol et dans le propan-2-ol.Following the discovery of ionizing radiations and their chemical effects, it was important to study and comprehend the formation mechanisms of short lived free radicals and molecular products. In order to perform such studies, researchers and research groups worked on developing tools allowing both formation and detection of those species at short time scales. Nowadays, pulse radiolysis imposed itself as a fundamental and efficient tool allowing scientists to probe chemical effects as well as reaction mechanisms in studied media.The laboratoire de Chimie Physique d’Orsay “LCP” is an interdisciplinary laboratory hosting the platform of fast kinetics known as “ELYSE”. Due to its femtosecond laser and its picosecond electron accelerator, we have the possibility to study chemical effects of ionizing radiations interaction with media at ultrashort times up to ~5 ps.Knowing that we are interested in primary reactions induced in aqueous media by ionizing radiations, ELYSE represents the essential tool in performing our studies. The obtained results concern:- First direct determination of hydroxyl radical “HO•” radiolytic yield as function of time at picosecond time scale ;- Direct effect of ionizing radiation in highly concentrated aqueous solutions as well as investigation of the ultrafast electron transfer reaction between solute molecules and positive holes “H2O•+” formed upon water radiolysis ;- Study at room temperature of electron transfer reaction between solvated electron (electron donor) and organic solutes (electron acceptors) en viscous medium ;- Study at room temperature of electron’s solvation dynamics in ethylene glycol and 2-propanol
Etudes de radiolyse pulsée picoseconde et stationnaire des solutions aqueuses concentrées
No full textLe mécanisme de radiolyse de l’eau est bien établi. Sous l’effet des rayonnements ionisants, les produits de la radiolyse de l’eau pure sont les radicaux et les produits moléculaires tels que les électrons solvatés, les atomes hydrogènes, les radicaux hydroxyles, le peroxyde d’hydrogène et les ions hydroniums. Lorsque les solutions concentrées sont irradiées, le résultat de la radiolyse change à cause de la fraction d’énergie absorbée par le soluté, cette fraction est négligeable dans le cas des solutions diluées. Les produits de la radiolyse du solvant peuvent réagir avec les molécules du solvant engendrant des changements dans leurs rendements radiolytiques ainsi qu’un changement dans le mécanisme de radiolyse du solvant. L’effet du rayonnement ionisant sur les solutions concentrées est appelé l’effet direct du rayonnement ionisant. La compréhension de cet effet est fondamentale dans plusieurs domaines tels que l’énergie nucléaire, la radiothérapie et la radiobiologie.L’objectif de ce travail est de comprendre le mécanisme de radiolyse des solutions concentrées ainsi que de quantifier l’effet direct du rayonnement ionisant en étudiant des solutions concentrées d’halogénures tels que les bromures de sodium et les chlorures de sodium, de même qu’une étude préliminaire sur les solutions concentrées d’acide nitrique.Tout d’abord, en effectuant la radiolyse stationnaire des solutions concentrées de bromures de sodium, nous avons quantifié le rendement radiolytique de formation de Br3- qui est l’unique produit stable de ces solutions sous rayonnements sous différentes conditions expérimentales.Ensuite, en effectuant la radiolyse pulsée picoseconde sur l’installation ELYSE des solutions aqueuses de NaCl, NaBr et HNO3, nous avons montré l’ionisation direct du soluté après le passage du faisceau d’electron. Selon les cinétiques obtenues, nous avons montré que la formation Br2•-, Cl2•-, NO3• prend place durant l’impulsion picoseconde d’électron d’électron. La radiolyse pulsée picoseconde nous a permis donc de conclure qu’il existe deux voies pour la formation de Br2•- et Cl2•-. La première voie résulte de l’ionisation directe du soluté. La deuxième résulte du changement dans le mécanisme de radiolyse de l’eau dû à la forte concentration des ions halogénures autour des molécules d’eau ionisées. Nos résultats montrent que la formation du radical hydroxyle HO• dans les solutions concentrées est marginale puisque la molécules d’eau ionisée, le trou H2O+ , réagit très rapidement avec les ions halogénures.The mechanism of water radiolysis is well established. As a result of the action of ionizing radiation on pure water, radicals and molecular products such as solvated electrons, hydrogen atoms, hydroxyl radicals, hydrogen peroxide and hydronium ions are formed. When highly concentrated solutions are irradiated, the outcome of irradiation is changed due to the important fraction of energy being absorbed by the solute which in the case of diluted solutions is skipped. Products of solvent radiolysis may react with the molecules of the solute leading to the change in their yields and moreover, may cause changes in the mechanism of solvent radiolysis. The action of ionizing radiation on highly concentrated solutions is named direct action of radiation. The understanding of direct effect of ionizing radiation is very important in several aspects, for example in nuclear energy, or radiotherapy or radiobiology. The aim of this work was to understand the mechanism and quantify the direct action of ionizing radiation in model systems such as highly concentrated sodium bromide and sodium chloride solutions. Firstly, by performing gamma radiolysis of highly concentrated solution of sodium bromide we quantify the yield of direct ionization of bromide ions for different experimental conditions.Secondly, by carrying out picosecond pulse radiolysis of aqueous solutions of NaCl, NaBr, and HNO3, we showed the direct ionization of the solute after the passage of electron beam. On the base of recorded kinetics, we showed that the formation of Br2•-, Cl2•-, NO3• takes place during the electron pulse. Picosecond pulse radiolysis allowed us to conclude that two ways of formation of Br2•- and Cl2•- exist. The first results from the direct ionization of the solute. The second results from the change in the mechanism of water radiolysis due to the high concentration of halide ions around the molecules of ionized water. Our results show that the formation of HO• radical in highly concentrated solutions is marginal and only stem from the dissociation of excited water, since the molecules of ionized water react with halide ions instead of hydronium ions leading to the formation of HO• hydroxyl radical
Bibliometric Review of Mehran University of Engineering & Technology Research Journal: 2011-2018
No full textAim: The aim of this study is to evaluate the bibliometric indicators of articles published in Mehran University of Engineering & Technology Research Journal (MUETRJ) during the period of 2011-18.
Methodology: The data of publications published in MUETAJ was downloaded from website of e-journal and analyzed various bibliometric attributes during July 2017 to 15th January 2018. The pattern of authorship, gender-wise distribution of first author, page-length of articles and institutional affiliation of the first author of publications were calculated and analyzed. Microsoft Office Excel spreadsheet was prepared for data analysis.
Results: Total 582 articles published in 32 issues of 8 volumes during the projected period with average of 18.1% articles per issue and 72.75 articles per year. Total 1777 authors contributed with an average of 3 authors per article in MUETRJ. A gender-wise distribution showed that number of male authors were much higher (n=1551; 87.2%) as compare to females authors (n=226; 12.7%). A majority of articles were written by multi-authored (n=570; 97.3%) as opposite to single author (n=12; 2%). Most the articles (n=140; 24%) have 10 pages length followed by 8 pages length (n=136; 23.7%). It was observed that Mehran University of Engineering & Technology presented itself as major contributor with 258 articles (44.3%).
Conclusion: The participation of 96 national and international institutes related to engineering and technological sciences in publishing research papers shows their confidence in MUETRJ
Water radiolysis in extreme conditions of temperature and LET. Scavenging of HO• by Br- ions
No full textL’objectif de cette thèse est de contribuer à la compréhension du mécanisme d’oxydation de Br- dans lequel le radical HO• intervient. Le rendement du radical HO• étant alors intimement lié au rendement d’oxydation de Br-, c’est sur lui que l'influence de différents paramètres physicochimiques a été étudiée : température, TEL, débit de dose, pH, nature du gaz saturant. Les solutions ont été irradiées avec 4 types de rayonnement : rayons X de 13 à 18 keV, électrons de 7 et 10 MeV, faisceaux d’ions C6+ de 975 MeV et He2+ de 70 MeV. Le développement d’un autoclave optique avec circulation de solution compatible avec le rayonnement de TEL élevé a permis de réaliser les premières expériences à TEL élevé constant et à température élevée. Cette cellule s’est avérée être aussi compatible avec les expériences pompe-sonde picoseconde réalisées avec l’accélérateur ELYSE.Le rendement de capture du radical hydroxyle a donc été estimé à TEL élevé mais aussi à haute température. Une meilleure compréhension du mécanisme d’oxydation de Br- en est issue, notamment en milieu acide et en comparant les résultats cinétiques avec les simulations Monte Carlo pour les temps inférieurs à la µs, et Chemsimul pour les produits stables (formation de Br2•- et de Br3-).The purpose of this thesis is to contribute to the understanding of the oxidation mechanism of Br- in which the HO• radical is involved. The HO• radiolytic yield is strongly connected with the oxidation yield of Br-, and therefore we have studied the influence of different physical and chemical parameters on this global yield: temperature, LET, dose rate, pH, saturation gas. The solutions have been irradiated with 4 types of ionizing rays: X- rays (from 13 to 18 keV), electrons (from 7 to 10 MeV), C6+-ions beam of 975 MeV and He2+-ions beam of 70 MeV.The development of an optical autoclave with solution flow, compatible with high LET ionizing rays has allowed us conduct the first experiments at constant high LET and high temperature. This cell has turned out to be compatible with the picosecond pump-probe experiments performed with the ELYSE accelerator.The HO• scavenging yield has been, therefore, estimated at both high LET and high temperature. A better understanding of the Br- oxidation mechanism has been achieved, in acid medium, in particular, by comparing the kinetics results with Monte Carlo Simulations for time scales inferior to the microsecond and with Chemsimul for the stable products (Br2•- and Br3- formations)
Pathogen simulation using soil and water tool (SWAT) model and bacteroides source tracking technique
No full textThe Upper Salem River Watershed (USRW), located in southern New Jersey, is listed as impaired for pathogens by The New Jersey Department of Environmental Protection (NJDEP) (NJDEP 2011). A 2003 Total Maximum Daily Load (TMDL) for the watershed recommended the use of pathogen source tracking to identify pathogen sources and develop a quantitative model to simulate pathogen pollution in the watershed (NJDEP 2003). This research comprises three parts: a) Fecal coliform and E. coli simulation using the Soil and Water Assessment Tool (SWAT) model in the USRW; this is the first study to conduct sensitivity analysis, calibration and validation of the SWAT model for two widely used pathogen indicators for multiple sampling stations in one watershed. The results of the sensitivity analysis indicate that pathogen input is the most sensitive parameter in the simulation of both indicators. Fecal coliform and E. coli simulation at five of six sampling stations generally showed good calibration and validation based on Nash-Sutcliffe efficiency values (0.04 to 0.71). b) Investigation of temperature effects on the persistence of bovine-Bacteroides; the primary goal of this part of the research was to identify the decay rate of bovine- Bacteroides in stream water at 4°C, 20°C and 30°C. The decay constant of bovine-Bacteroides was calculated between 0.01 h-1 in the mesocosm incubated at 4°C to 0.05 h-1 in the mesocosm at 30°C. Comparison of this study with other similar studies indicates that as temperature increased, a greater discrepancy in compared constant values was observed. c) Pathogen source tracking was done using a multiple linear regression analysis in the USRW. The primary goals of this research phase were to use a bovine-Bactreroides source tracking technique to investigate if bovine feces are a contributing pathogen source to the river system and to identify the spatial distribution of bovine pathogen discharge to the USRW. The results of the simulated model showed agreement with the potential bovine distribution sources (i.e., animal feeding facilities). A probability of occurrence map of bovine derived pathogens was also developed to spatially identify which sub-watersheds have greater likelihood of pathogen contributions from bovine sources.Ph. D.Includes bibliographical referencesby Mehran Niaz
Prosthetic rehabilitation of a mandibular root amputated molar using single crown
No full textIn teeth with furcation involvement, root amputation is one of the treatment choices. A challenge which a dentist may encounter with is the prosthetic treatment of such teeth when their adjacent teeth are intact. According to the current goal of operative dentistry based on conservative treatment, it would be desirable to do in a manner resulting in minimal damage to the adjacent sound teeth. In the following case report, a step-by-step conservative treatment sequences of a mandibular molar with distal root amputation which not involving surrounding teeth is described. During 18 months follow-up, the results were satisfactory
Proprietes thermodynamiques d'agregats metalliques a faible nombre d'atomes en phase condensee : catalyse de transfert d'electron simulation du developpement photographique
No full textSIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
ASO Author Reflections: Transdiaphragmatic Approach for Simultaneous Resection of Colorectal Liver and Lung Metastases
No full textSimultaneous resection of colorectal cancer, liver and lung metastase
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