Ion temperature gradient turbulence in helical and axisymmetric RFP plasmas

Turbulence induced by the ion temperature gradient (ITG) is investigated in the helical and axisymmetric plasma states of a reversed field pinch device by means of gyrokinetic calculations. The two magnetic configurations are systematically compared, both linearly and nonlinearly, in order to evaluate the impact of the geometry on the instability and its ensuing transport, as well as on the production of zonal flows. Despite its enhanced confinement, the high-current helical state demonstrates a lower ITG stability threshold compared to the axisymmetric state, and ITG turbulence is expected to become an important contributor to the total heat transport.Comment: 8 pages, to appear in Phys. Plasma

Microtearing Modes in Reversed Field Pinch Plasmas

In the reversed field pinch RFX-mod strong electron temperature gradients develop when the Single-Helical-Axis regime is achieved. Gyrokinetic calculations show that in the region of the strong temperature gradients microtearing instabilities are the dominant turbulent mechanism acting on the ion Larmor radius scale. The quasi-linear evaluation of the electron thermal conductivity is in good agreement with the experimental estimates.Comment: To appear in Physical Review Letter

Microturbulence studies in RFX-mod

Present-days Reversed Field Pinches (RFPs) are characterized by quasi-laminar magnetic configurations in their core, whose boundaries feature sharp internal transport barriers, in analogy with tokamaks and stellarators. The abatement of magnetic chaos leads to the reduction of associated particle and heat transport along wandering field lines. At the same time, the growth of steep temperature gradients may trigger drift microinstabilities. In this work we summarize the work recently done in the RFP RFX-mod in order to assess the existence and the impact upon transport of such electrostatic and electromagnetic microinstabilities as Ion Temperature Gradient (ITG), Trapped Electron Modes (TEM) and microtearing modes.Comment: Work presented at the 2010 Varenna workshop "Theory of Fusion Plasmas". To appear in Journal of Physics Conference Serie

On the mutual effect of ion temperature gradient instabilities and impurity peaking in the reversed field pinch

The presence of impurities is considered in gyrokinetic calculations of ion temperature gradient (ITG) instabilities and turbulence in the reversed field pinch device RFX-mod. This device usually exhibits hollow Carbon/Oxygen profiles, peaked in the outer core region. We describe the role of the impurities in ITG mode destabilization, and analyze whether ITG turbulence is compatible with their experimental gradients.Comment: 19 pages, 9 figures, accepted for publication in Plasma Phys. Control. Fusio

Psicofarmacología cosmética y subjetividad: experiencias de uso de psicofármacos estimulantes como mejoradores cognitivos en Montevideo

La expansión del uso de psicofármacos en las últimas décadas ha incluido diferentes modalidades de consumo, no siempre conectadas a una patología; es en ese marco que emerge el concepto de psicofarmacología cosmética, definida como el uso de un psicofármaco para que una persona que no está enferma se sienta mejor de lo que está. Un ejemplo de uso cosmético es el consumo de psicofármacos estimulantes como mejoradores cognitivos, es decir, desconectado de sus indicaciones oficiales (el tratamiento del TDAH y la narcolepsia) con el objetivo de mejorar capacidades cognitivas como la atención y la memoria. La literatura describe una asociación entre el uso de esos fármacos y la búsqueda de performance en el estudio y en el trabajo, invitando a indagar acerca de sus relaciones con formas actuales de experiencia y subjetividad. De esa forma, esta tesis se propuso a abordar el uso de psicofármacos estimulantes como mejoradores cognitivos en adultos en Montevideo. Para ello, se realizaron entrevistas en profundidad a 15 adultos residentes en Montevideo que han utilizado psicofármacos estimulantes, como medio de explorar motivos, circuitos y redes de circulación, percepción de riesgo y beneficio, modos de uso y relaciones entre los psicofármacos estimulantes y otras sustancias, así como las relaciones entabladas entre estimulantes, estilo de vida y cultura y las lógicas y significaciones asociadas al consumo. Si bien algunos entrevistados asociaron el consumo de psicofármacos estimulantes a un diagnóstico de TDAH, se observó asimismo la persistencia de características en común con relatos en los que no hubo una indicación médica, permitiendo indagar acerca de la controvertida frontera entre tratamiento y mejoramiento. Con el trabajo realizado, se busca contribuir al ámbito de la psicología clínica con el mapeo, aunque contingente e incompleto, de líneas por las cuales los sujetos se desplazan en la actualidad, ampliando la escucha a problemáticas contemporáneas. A la vez, se espera aportar elementos para pensar nuestra praxis y apuntar a la construcción de prácticas éticas en un escenario en constante cambio.The expansion of psychopharmaceutical use in recent decades has encompassed various forms of consumption, not always connected to pathology. It is within this context that the concept of cosmetic psychopharmacology emerges, defined as the use of a psychopharmaceutical by a non-ill individual to enhance their well-being. An example of cosmetic use is the consumption of stimulant psychopharmaceuticals as cognitive enhancers, detached from their official indications (the treatment of ADHD and narcolepsy), with the aim of improving cognitive abilities such as attention and memory. The literature describes an association between the use of these drugs and the pursuit of performance in studying and working, prompting investigation into their relationships with current forms of experience and subjectivity. Thus, this thesis aims to address the use of stimulant psychopharmaceuticals as cognitive enhancers in adults in Montevideo. To achieve this, in-depth interviews were conducted with 15 adult residents of Montevideo who have used stimulant psychopharmaceuticals, as a means to explore motives, circuits and networks of circulation, risk and benefit perception, modes of use, and the relationships between stimulant psychopharmaceuticals and other substances, as well as the connections between stimulants, lifestyle, culture, and the logics and meanings associated with consumption. While some interviewees associated the use of stimulant psychopharmaceuticals with a diagnosis of ADHD, common characteristics were also observed in accounts where there was no medical indication, allowing for an inquiry into the controversial boundary between treatment and enhancement. Through this work, the aim is to contribute to the field of clinical psychology by mapping, albeit contingently and incompletely, the paths along which individuals navigate in the present, expanding the understanding of contemporary issues. Additionally, it is expected to provide insights for reflecting on our praxis and aiming towards the construction of ethical practices in an ever-changing landscape.Agencia Nacional de Investigación e Innovación (ANII

Geometrical Features Underlying the Perception of Colinearity

The magnitude of the Poggendorff bias in perceived collinearity was measured with a 2AFC task and roving pedestal, and was found to be in the region of 6–8 deg, within the range of previous estimates. Further measurements dissected the bias into several components: (1) The small (∼1 deg) repulsion of the orientation of the pointer from the parallel, probably localized in the part of the line near the intersection (2) A small (1 deg) bias in the orientation of virtual lines crossing the gap between two parallels, towards the orientation of the parallels, or equivalently (4) An orthogonal bias in actively constructing a virtual line across the gap. We conclude that orientation repulsion by itself is an inadequate explanation of the Poggendorff effect, and that a full explanation must take account of the way in which observers construct virtual lines in visual space in order to carry out elementary geometrical tasks such as extrapolation