Hadron Physics with CLAS12

Hadron spectroscopy has been an essential part of the physics program with the CLAS detector in experimental Hall B at Jefferson Lab. Production of baryon and meson resonances with high energy (polarized) electron and photon beams was studied on a veriety of targets, ranging from hydrogen to lead. Physics topics of interest include: investigation of the spectrum of baryon and meson resonances, transition form-factors, meson-nucleon couplings (mesons in nuclei), and search for exotic and missing states. With the 12 GeV upgrade of the CEBAF machine, hadron spectroscopy in Hall B will be extended to a new domain of higher mass resonances and the range of higher transferred momentum using up to 11 GeV electron beams and the upgraded CLAS12 detector. In this paper a brief description of the CLAS12 detector and the physics program adopted for 12 GeV with emphasis to baryon and meson spectroscopy is presented.Comment: Hadron-09 proceedings, 8 pages, 5 figure

On the Robustness Properties of M-MRAC

The paper presents performance and robustness analysis of the modified reference model MRAC (model reference adaptive control) or M-MRAC in short, which differs from the conventional MRAC systems by feeding back the tracking error to the reference model. The tracking error feedback gain in concert with the adaptation rate provides an additional capability to regulate not only the transient performance of the tracking error, but also the transient performance of the control signal. This differs from the conventional MRAC systems, in which we have only the adaptation rate as a tool to regulate just the transient performance of the tracking error. It is shown that the selection of the feedback gain and the adaptation rate resolves the tradeoff between the robustness and performance in the sense that the increase in the feedback gain improves the behavior of the adaptive control signal, hence improves the systems robustness to time delays (or unmodeled dynamics), while increasing the adaptation rate improves the tracking performance or systems robustness to parametric uncertainties and external disturbances

Flow-induced correlation effects within a linear chain in a polymer melt

A framework for a consistent description of the flow-induced correlation effects within a linear polymer chain in a melt is proposed. The formalism shows how correlations between chain segments in the flow can be incorporated into a hierarchy of distribution functions for tangent vectors. The present model allows one to take into account all the major relaxation mechanisms. Special cases of the derived set of equations are shown to yield existing models and shed some light on the connection between them. Consequences of several assumptions widely used in the literature are analyzed within the developed framework

Effects on the polarization due to Fast Steering Mirrors

En los instrumentos polarimétricos de imagen es necesario introducir un sistema de estabilización de imagen para la adecuada adquisición de las medidas. Esto se realiza mediante un sistema de control en lazo cerrado en el que un espejo, denominado Fast Steering Mirror (FSM), realiza los movimientos de rotación adecuados para estabilizar la imagen mediante actuadores piezoeléctricos que cambian su inclinación (tip-tilt). Es bien conocido que el estado de polarización de un haz cambia, en general, al ser reflejado por un espejo y este cambio viene determinado por el tipo de recubrimientos (i.e.: metálicos, dieléctricos...) y el ángulo de incidencia. Todo ello viene caracterizado por la matriz de Mueller del espejo y es parte de la calibración del instrumento. Sin embargo, el espejo de estabilización cambia su ángulo con el tiempo por lo que producirá efectos de polarización residual sistemática y despolarización. Tradicionalmente se ha asumido que estos efectos son despreciables y no se han tenido en consideración, sin ninguna evaluación en detalle. Esta problemática es extensible a cualquier instrumento polarimétrico que disponga de sistemas de apuntamiento de este tipo. En este trabajo se desarrollan los modelos matemáticos necesarios y se analizan diversos casos prácticos, para poder alcanzar las máximas prestaciones polarimétricas de estos instrumentos. En particular, se ha estudiado el caso del instrumento SO/PHI (Polarimetric and Helioseismic Imager on Solar Orbiter) a bordo de la misión Solar Orbiter de la Agencia Espacial Europea y NASA, así como el caso de instrumentos para la distribución de claves cuántica (QKD, Quantum Key Distribution) que disponen de sistemas FSM similares. De los resultados obtenidos se deduce que los FSM producen cambios en los estados de polarización y despolarización del haz incidente en los instrumentos polarimétricos y, por tanto, deben tenerse en cuenta. La magnitud de estos efectos depende de forma crítica en el ángulo de incidencia nominal, el rango de movimiento de los FSM durante la operación y los tiempos de integración de los detectores del instrumento. Aunque habitualmente, de forma no cuantitativa, se han elegido los parámetros de diseño adecuados en los casos de los sistemas estudiados, los modelos desarrollados en este trabajo permiten definir los requisitos de los FSM durante su diseño para evitar estos efectos indeseados durante el funcionamiento de los instrumentos.In polarimetric imaging instruments it is necessary to introduce an image stabilization system for the proper acquisition of measurements. This is achieved through a closed-loop control system in which a mirror, called Fast Steering Mirror (FSM), performs the appropriate rotational movements to stabilize the image using piezoelectric actuators that change its tilt (tip-tilt ). It is well known that the polarization state of a beam changes, in general, when it is reflected by a mirror and this change is determined by the type of coatings (i.e.: metallic, dielectric...) and the angle of incidence. All of this is characterized by the mirror’s Mueller matrix and is part of the instrument’s calibration. However, the stabilizing mirror changes its angle over time so it will produce systematic residual polarization and depolarization effects. These effects have traditionally been assumed to be negligible and have not been taken into consideration, without any detailed evaluation. This problem is also applicable to any polarimetric instrument that has pointing systems of this type. In this work, the necessary mathematical models are developed and various practical cases are analyzed, in order to achieve the maximum polarimetric performance of these instruments. In particular, the case of the SO/PHI (Polarimetric and Helioseismic Imager on Solar Orbiter) instrument on board the Solar Orbiter mission of the European Space Agency and NASA has been studied, as well as the case of instruments for the distribution of quantum keys ( QKD, Quantum Key Distribution) which have similar FSM systems. On the basis of the obtained results, it is clear that in polarimetric instruments in which FSMs are used the polarization and depolarization state of the incident beam changes, therefore these variations must be taken into account. The magnitude of these effects critically depends on the nominal angle of incidence, the range of motion of the FSMs during operation, and the integration times of the instrument’s detectors. Although usually, in a non-quantitative way, the appropriate design parameters have been chosen in the cases of the studied systems, the models developed in this work allow defining the requirements of the FSM during their design to avoid these undesired effects during the operation of the systems. instruments. instrumentos.Máster Universitario en Ingeniería Electrónic

Towards the Situated Engagement Evaluation Model (SEEM) : making the invisible visible

This thesis explores the multifaceted concept of engagement within online learning environments. Key research aims are to suggest approaches and an extendable model for evaluating, monitoring and developing understanding of online learner engagement. The overall intention is to offer educators insight, practical guidance and tools for supporting timely intervention in fostering learner engagement. This thesis reviews the major theoretical perspectives on learning and highlights the role of student engagement in relation to the research literature. It discusses the limitations of the methods applied in current research and attempts to address this problem by crossing the disciplinary boundaries to draw together a range of perspectives and methodologies. A review of the literature provides a foundation for a learner engagement evaluation model that employs a variety of evaluation methods and accommodates the possible diversity of learning experiences. The proposed ‘Situated Engagement Evaluation Model’ (SEEM) is positioned to reflect the wide theoretical perspective of social learning. It constitutes a comprehensive system of intertwined components (Learning Content; Pedagogical Design Elements; Learning Profiles; and Dialogue and Communication) that learners may interact with, and integrates dynamically changing preferences and predispositions (e.g. cultural, emotional, cognitive) potentially informative in engagement studies. Prior to (and independently of) the development of SEEM, four empirical studies were conducted and reported here. These explored patterns of online engagement with respect to learning content, learning profiles, patterns of communication and elements of pedagogical design. Studies were then revisited to evaluate the usefulness of SEEM for monitoring and evaluating student engagement, and to discuss its potential for guiding intervention to improve learning experiences. The practical relevance for integrated and automated implementation of SEEM in online learning is considered further

Integrating social software into course design and tracking student engagement : early results and research perspectives

The uptake of social software is becoming more widespread in many sectors of education and organizational development. However, there is little empirical research on the impacts of adopting these technologies, and so it is difficult to determine appropriate pedagogic models and whether or not the desired learning outcomes are being realized. This paper reports early findings of an ongoing pilot study which is based on the concept of collaborative learning and supported by means of social software. It describes the educational philosophy behind the study and the teaching techniques used. The application of various features of social software, including blogs, file management and personalization, are discussed, as well as the different techniques for facilitating and measuring the level of student engagement with social software. The results indicate that student engagement with social software can be shaped by course design and activities that integrate educational technology into the course structure