63,738 research outputs found

    Concept for controlled transverse emittance transfer within a linac ion beam

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    For injection of beams into circular machines with different horizontal and vertical emittance acceptance, the injection efficiency can be increased if these beams are flat, i.e. if they feature unequal transverse emittances. Generation of flat electron beams is well known and has been demonstrated already in beam experiments. It was proposed also for ion beams that were generated in an Electron Cyclotron-Resonance (ECR) source. We introduce an extension of the method to beams that underwent charge state stripping without requiring their generation inside an ECR source. Results from multi-particle simulations are presented to demonstrate the validity of the method.Comment: 23 pages (preprint style), 14 Figures, submitted to PRST-A

    One-particle reducible contribution to the one-loop scalar propagator in a constant field

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    Recently, Gies and Karbstein showed that the two-loop Euler-Heisenberg Lagrangian receives a finite one-particle reducible contribution in addition to the well-known one-particle irreducible one. Here, we demonstrate that a similar contribution exists for the propagator in a constant field already at the one-loop level, and we calculate this contribution for the scalar QED case. We also present an independent derivation of the Gies-Karbstein result using the worldline formalism, treating the scalar and spinor QED cases in a unified manner.Comment: 13 pages, 4 figures. Minor corrections mad

    A Participatory Research Project Exploring Young People’s Views of an Employability Course Designed for those with Special Educational Needs

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    This participatory action research project explored young people’s (YP) experience of a Supported Internship Programmeme (SIP) at a Further Education College (FE). Methods: Four co-researchers aged 18-25 who were currently attending an SIP at a FE college in an inner London borough took part (via video conferencing). The co-researchers chose to take part in interviews and create presentations of photos they took in college in order to share their views. Interview questions generated with co-researchers influenced the primary research question: What do YP want their teachers to know about their experience on a SIP during a pandemic? The researcher used inductive thematic analysis to generate themes which were discussed with co-researchers. Findings were shared with the co-researchers’ classmates and teachers. Co-researchers provided feedback on the project. Findings: coresearchers’ experiences of the SIP met the psychological needs of competence, autonomy and relatedness and also supported resilience. Lockdown periods limited co-researchers’ opportunities to meet their psychological needs. Implications: Public health policy around the Covid-19 pandemic may have had a disproportionally negative impact on this group. However, insights into the strengths of the SIP and ideas generated by the coresearchers may guide to ongoing support for YP with SEND. This research examined what supports YP with SEND to share their views on what is important to them in their educational experience. It was found use of photo-voice and individual interviews were successful methods. However, more time for co-researchers to develop their own initiatives and projects would be beneficial. Co-researchers were able to provide critical, insightful reflections not only on their own experience but the wider impact of public policy. Key words: Special Educational Needs and disabilities, SEN, SEND, employability course, supported internship programme, young people, participatory research, participatory action research, Pandemic, Corona-Virus, Lockdown, Further education, Preparing for adulthood, photo-voice

    Mixed symmetry tensors in the worldline formalism

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    We consider the first quantised approach to quantum field theory coupled to a non-Abelian gauge field. Representing the colour degrees of freedom with a single family of auxiliary variables the matter field transforms in a reducible representation of the gauge group which - by adding a suitable Chern-Simons term to the particle action - can be projected onto a chosen fully (anti-)symmetric representation. By considering F families of auxiliary variables, we describe how to extend the model to arbitrary tensor products of F reducible representations, which realises a U(F) "flavour" symmetry on the worldline particle model. Gauging this symmetry allows the introduction of constraints on the Hilbert space of the colour fields which can be used to project onto an arbitrary irreducible representation, specified by a certain Young Tableau. In particular the occupation numbers of the wavefunction - i.e. the lengths of the columns (rows) of the Young Tableau - are fixed through the introduction of Chern-Simons terms. We verify this projection by calculating the number of colour degrees of freedom associated to the matter field. We suggest that, using the worldline approach to quantum field theory, this mechanism will allow the calculation of one-loop scattering amplitudes with the virtual particle in an arbitrary representation of the gauge group.Comment: 1+32 page

    Uncovering the Hidden Conflicts in Securities Class Action Litigation: Lessons from the State Street Case

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    Courts, Congress, and commentators have long worried that stockholder plaintiffs in securities and M&A litigation and their counsel may pursue suits that benefit themselves rather than absent stockholders or the corporations in which they invest. Following congressional reforms that encouraged the appointment of institutional stockholders as lead plaintiffs in securities actions, significant academic commentary has focused on the problem of “pay to play”—the possibility that class action law firms encourage litigation by making donations to politicians with influence over institutional stockholders, particularly public sector pension funds. A recent federal securities class action in the District of Massachusetts, however, suggests that the networks of influence between class plaintiffs and their counsel are much more complex and difficult to detect. After appointing a special master to look into fee issues, the court discovered that a large class action firm had paid over $4 million in “bare referral” fees to an attorney who did little work on the case but had recommended the larger firm to a public sector pension fund “after considerable favors, political activity, money spent and time dedicated in Arkansas.” This is only one of the less-visible ways that class counsel may route benefits to class plaintiffs. Current class action processes do not routinely identify these potential conflicts of interest. Instead, they tend to surface when nonlitigants bring them to public attention. Because neither the lead plaintiff nor the defendants have a strong incentive to voluntarily address these conflicts, we propose revisions to the class certification process that would require class plaintiffs to disclose more information regarding their relationships with class counsel. We also propose that courts routinely appoint special masters or class guardians as part of the settlement approval process to ensure that class plaintiffs’ statements are subject to discovery and adversarial review

    Comment on "Effect of growth interruptions on the light emission and indium clustering of InGaN/GaN multiple quantum wells" [Appl. Phys. Lett. 79, 2594 (2001)]

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    This entry is a comment on "Effect of growth interruptions on the light emission and indium clustering
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