Ion backflow studies with a triple-GEM stack with increasing hole pitch

Gas Electron Multipliers have undergone a very consistent development since their invention in 1997. Their production procedures have been tuned in such a way that nowadays it is possible to produce foils with areas of the order of the square meter that can operate at a reasonable gain, uniform over large areas and with a good stability in what concerns electrical discharges. For the third run of LHC, they will be included in the CMS and ALICE experiments after significant upgrades of the detectors, confirming that these structures are suitable for very large experiments. In the special case of Time Projection Chambers, the ion backflow and the energy resolution are sensitive issues that must be addressed and the GEM has shown to be able to deal with both of them. In this work, a stack of three GEMs with different pitches has been studied as a possible future approach for ion-backflow suppression to be used in TPCs and other detection concepts. With this approach, an ion backflow of 1 % with an energy resolution of 12 % at 5.9 keV has been achieved with the detector operating in an Ar/CO2 (90/10) mixture at a gain of ~ 2000.Comment: 15 pages, 11 figure

Verses, subverses and subversions in contemporary postcolonial poetry : the arts of resistance in the works of Linton Kwesi Johnson and Lesego Rampolokeng

Includes bibliographical references (leaves 136-141).This dissertation seeks to analyse insubordination and resistance manifested in postcolonial and post-apartheid poetry as ways of subverting dominant Western discourses. More specifically, I focus my analysis on textual strategies of resistance in the poetry of Linton Kwesi Johnson and Lesego Rampolokeng. The syncretistic quality in the oeuvres of both poets is related to diaspora, hybridity and crealisation as forms of writ[h]ing against (neo)colonially-based hegemonic discourses. Postcolonial critiques at large will frame this analysis of strategies of domination and resistance, but some discussions from the domain of history, sociology and cultural studies may also enter the debate. In this regard there is a great variety of theories and arguments dealing with the contradictions and incongruities in the question of power relations interconnecting domination and resistance. This study is arranged in three pivotal debates. There is firstly an in-depth discussion of underpinning theories that deal with strategies of domination and resistance in the postcolonial domain This is a threefold task carried out by scrutinising (a) the origins of colonial discourse and its binarist tendencies, (b) the pitfalls of anticolonialist resistance based on dualistic opposites, and (c) the hybrid and insubordinate nature of resistance as an efficient alternative to transcend such binaries. Afterwards I seek to investigate how strategies of diasporic resistance and cultural hybridism employed in the poetry of Linton Kwesi Johnson can contribute to moving away from the limitations of dichotomies and also subvert hegemonic power. And finally, I look at crealisation, mockery and insubordination as strategies of resistance in the postapartheid poetry of Lesego Rampolokeng. Besides that, this project is concerned with the increasing importance of academic studies on postcolonial literatures. The present research aims therefore to analyse postcolonial and post-apartheid poems as strategic techniques to decentre dominant Western rhetoric that tries to naturalise inequalities and injustices in the relations between power holders and the powerless in both local and global contexts

Direct measurement of finite-time disentanglement induced by a reservoir

We propose a method for directly probing the dynamics of disentanglement of an initial two-qubit entangled state, under the action of a reservoir. We show that it is possible to detect disentanglement, for experimentally realizable examples of decaying systems, through the measurement of a single observable, which is invariant throughout the decay. The systems under consideration may lead to either finite-time or asymptotic disentanglement. A general prescription for measuring this observable, which yields an operational meaning to entanglement measures, is proposed, and exemplified for cavity quantum electrodynamics and trapped ions.Comment: 4 pages, 2 figure

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Descrição do sistema: 1. Desenvolvimento, 2. Requisitos, 3. Objetivo, 4. Acesso, 5. Operacionalização.bitstream/item/63862/1/DT72.pd

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