930 research outputs found

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    Hyperpolarized xenon-129 production and applications

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    Hyperpolarized 3He and 129Xe were initially developed and used in the nuclear physics community. Lately they are primarily used in Medical Resonance Imaging (MRI). Although first MRI polarized gas images were acquired using 129Xe, the research community has focused mostly on 3He, due to the well-known polarizing methods and higher polarization numbers achieved. The main purpose of this thesis is to present a novel design of a large-scale SEOP polarizer for producing large quantities of highly polarized 129Xe. High Rb-Xe spin-exchange rates through long-lived van de Waals molecules at low total pressure, implemented in a novel counterflow polarizer design, resulted in xenon polarization as high as 50% for 1.2 liters/hour, with a maximum of 64% for 0.3 l/h. We characterized and improved the polarization process by finding the optimum operating parameters of the polarizer. Two new methods to efficiently use high-power diode lasers are described: a new optical arrangement for a better beam shaping of fiber coupled lasers and the first external-cavity spectrum narrowing of a stack of laser diode arrays. A new accumulation technique for the hyperpolarized xenon was developed and full recovery of polarization after a freeze-thaw cycle was demonstrated for the first time. Two approaches for xenon delivery, frozen and gas states, were developed. Hyperpolarized xenon transportation to Brigham and Women\u27s Hospital was successfully accomplished for collaborative research. First MRI images using hyperpolarized xenon acquired at BWH are presented. Final chapter is focused on describing a low field human MRI scanner using hyperpolarized 3He. We built a human scale imager with open access for orientational studies of the lung functionality. Horizontal and vertical human lung images were acquired as a first stage of this project

    Is Romanian mothers\u27 employment status during a child\u27s first year of life correlated with school-age children\u27s behavior problems?

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    Although research studies are more likely now than in the past to include children and families of varied racial and ethnic backgrounds, no attempts have been made to examine the relationship between early maternal employment among Romanian mothers and their children\u27s behavioral problems. Therefore, based on a sample drawn from a Romanian population, this thesis investigates whether maternal employment during the first year of the child\u27s life is related to Romanian school-age children\u27s behavioral problems, considering control variables like period of maternal employment, employment type, child care type, family income; child\u27s age, maternal educational level, and family type. Findings illustrate that there is no statistically significant relationship between early maternal employment and children\u27s later behavioral problems. It can be inferred that Romania\u27s generous maternity leave policy has beneficial effects on children\u27s behavioral problems, therefore, the effects found by studies conducted on American populations are not found in Romanian populations

    Les auteurs dramatiques anglais contemporains à l’épreuve des pratiques collaboratives

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    Bien que la figure de l’auteur demeure investie d’une forte autorité dans le théâtre anglais contemporain, qui accorde traditionnellement une place de choix aux nouvelles écritures dramatiques, elle se trouve ébranlée depuis le début du xxie siècle par un accroissement notable des pratiques collaboratives. Fondé sur une analyse des discours des dramaturges sur leur rôle (tel qu’il leur échoit mais aussi tel qu’ils le revendiquent), l’article examine comment ces évolutions influent sur le statut des auteurs au sein du monde du théâtre anglais, ou plus précisément sur le système de reconnaissance et de valorisation dans lequel ils s’inscrivent et dont ils contribuent à refaçonner les contours par leurs prises de position. Il s’intéresse notamment au développement d’une posture collaborative, particulièrement manifeste dans la volonté, exprimée par un nombre croissant d’auteurs, sinon de se démettre de leur autorité, du moins de la partager davantage, non seulement avec leurs collaborateurs artistiques, mais également avec les spectateurs.Although the figure of the author remains retains significant authority in contemporary English theatre, which traditionally accords a place of choice to new dramatic writing, it has been undermined since the early 21st century by a notable increase in collaborative practices. Founded on an analysis of playwrights’ discourses regarding their role (as it falls to them, but also as they lay claim to it), this article examines how these evolutions affect the status of authors within the English theatre world or, more precisely, the recognition and valorization system they belong to and whose outlines they help reshape through their positions. It focuses, notably, on the development of a collaborative stance that is particularly evident in the will expressed by a growing number of authors not to relinquish their authority, but to share it a bit more, at least, with both their artistic collaborators and the spectators
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