In this thesis, we explore and improve on the science of gamma-ray bursts with particular attention to the very-high-energy regime. We begin by discussing Imaging Atmospheric Cherenkov Telescope Arrays (IACTs), which are the primary instruments of observation at very-high-energy gamma rays. We focus on a particular, state-of-the-art IACT array in southern Arizona: Very Energetic Radiation Imaging Telescope Array System (VERITAS). We then discuss the science of gamma-ray bursts and what can be learned from IACT observations. We follow with a couple of technical improvements, allowing one to better search for and characterize gamma-ray bursts with IACTs. The techniques focus on statistical methods for detection of transient sources, as well as angular reconstruction at arbitrary zenith angles of observation. We then use one of our new statistical methods to search for a signal in VERITAS observations of gamma-ray burst locations, with tests designed to search for particular bursts as well as for hints of emission in the entire sample of observations. We conclude that there is no evidence for a signal and follow with a discussion of the particularly interesting non-detection of GRB 150323A. We discuss the implications of this non-detection on the energetics and ambient environment of this burst. We conclude that the VERITAS observations might indicate gamma-ray bursts taking place in the dense wind of Wolf-Rayet stars.

Dans cette thèse, je propose plusieurs modèles et outils numériques afin de mieux comprendre et prédire le comportement et le développement de cultures et dispositifs neuronaux.Les cultures de neurones ont en effet été un outil précieux durant les 20 dernières années : elles ont permis de mieux comprendre la manière dont le cerveau traite les différentes informations qui lui parviennent en donnant aux scientifiques la possibilité de tester les effets de médicaments sur les neurones, ainsi que d'obtenir leurs réponses détaillées à diverses perturbations et stimuli.De plus, de récentes avancées en microfluidiques ont ouvert la voie à la conception de dispositifs neuronaux plus élaborés, rapprochant encore un peu plus la perspective du traitement de signaux complexes via des neurones in vitro.Dans une première partie, je propose un mécanisme pour expliquer les bouffées d'activité épileptiformes présentes dans les cultures, mécanisme que je formule via un modèle théorique concis. J'effectue ensuite une vérification expérimentale des prédictions du modèle sur des cultures et montre que celles-ci sont effectivement compatibles avec le comportement observé in vitro.Dans une seconde partie, je décris plus en détail la description de la dynamique spatio-temporelle du phénomène, notamment le fait que les bursts nucléent en des zones bien précises du réseau neuronal.Comme les prédictions et analyses effectuées dépendent fortement de la structure de ce réseau, je présente ensuite la réalisation d'une plateforme de simulation afin de permettre de modéliser efficacement le développement des réseaux neuronaux. Ce logiciel prend en compte les interactions entre les neurones et leur environnement et constitue la première plateforme à fournir des modèles polyvalents et complets pour décrire l'intégralité du processus de croissance neuronal. Je montre ensuite que ce simulateur est capable de générer des morphologies valides et l'utilise pour proposer des nouvelles topologies de réseaux afin de décrire les cultures de neurones. Je reproduis également des dispositifs neuronaux existants et montre que les activités entretenues par ces structures sont compatibles avec les observations expérimentales. Enfin, je discute plusieurs directions de recherche possibles, pour lesquelles l'utilisation de dispositifs neuronaux spécifiques permettrait de contourner les limitations des cultures neuronales et fournirait ainsi de nouvelles informations sur les processus sous-tendant le développement et la plasticité cérébrale / In this thesis, I provide models and numerical tools to better understand and predict the behavior and development of neuronal cultures and devices.Neuronal cultures have proven invaluable in improving our understanding of how the brain processes information, by enabling researchers to investigate neuronal and network response functions to various perturbations and stimuli.Furthermore, recent progress in microfluidics have opened the gate towards more elaborated neuronal devices, bringing us one step closer to complex signal processing with living in vitro neurons.In a first part, I propose a mechanism to explain the epileptiform bursts of activity present in cultures, mechanism which I formulate as a concise theoretical model. I subsequently test the predictions of this model on cultures and show that they are indeed compatible with the behavior observed in vitro.I further develop this description in the second part of the thesis, where I analyze its spatiotemporal dynamics and the fact that burst nucleate in specific areas in the network.Since predictions and analysis of these nucleation centers strongly depends on the network structure, I develop a simulation platform to enable efficient modeling of the network development. This software takes into account the interactions between the neurons and their environment and is the first platform to provide versatile and complete models to simulate the entire growth process of neurons. I demonstrate that this simulator is able to generate valid neuronal morphologies, then use it to propose new network topologies to describe neuronal cultures, as well as to reproduce existing neuronal devices. I then show that the activities sustained by these structures are compatible with the experimental recordings.Eventually, I discuss several future directions for which the use of neuronal devices would enable to circumvent current limitations of neuronal cultures, thus providing new information on the processes which underlie brain development and plasticity.

An exploratory case study design and a mixed-methods approach was used to discover the impact of the Activity Bursts in the Classroom (ABC) Fitness Program on students in special education classroom settings, elementary and middle school. Both classrooms were comprised of students with the primary disability of emotional disturbance. Special education intervention teachers’ perceptions of their students engagement and behavior were collected before and during the implementation of the ABC for Fitness Program intervention. Special education intervention teachers completed the Teacher Assessment of Student Engagement, participated in an ABC for Fitness training session, a question and answer session, completed daily written behavior incident logs, a mid-point check-in, and a semi-structured interview. There were four themes found throughout the research. Intervention teachers perceptions’ of student engagement increased as the students enjoyed the ABC for Fitness Program activities. The classroom environment was improved through improving the student to teacher relationship, the ABC for Fitness Program intervention required adaptations for student success to the timing (e.g. length and number of times the exercises and cool down were implemented) ), structure, and the additional of visual cue cards (e.g. Fit Deck cards). The special education intervention teachers faced specific challenges unique to their setting such as structure and focus. Results indicated three main findings: 1) Special education intervention teachers’ perceptions of student engagement during the intervention improved; 2) Special education teachers needed to be able to adapt program to suit their students’ specific needs; and, 3) The ABC for Fitness Program was beneficial to participating special education intervention teachers’ classrooms environment in promoting positive interactions between students and staff.

Thesis (Ph. D.)--University of Chicago, Dept. of Physics, June 1997. / Includes bibliographical references. Also available on the Internet.

No description available.

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains xiii, 82 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 65-66).

Gamma-ray Bursts (GRBs) are powerful explosions that emit most of their energy, as their name suggests, in gamma-rays of typical energies of about 1 MeV. This emission lasts for about two minutes or less and it is called the prompt emission. The isotropic energy radiated in GRBs is equivalent to the energy that the Sun will radiate in its entire lifetime. After decades of studying this cosmological phenomenon, we have come to learn that it involves a collimated and relativistic jet. Also, we know that they radiate energy in the X-ray, optical and radio bands for days, weeks and years, respectively, which is called the afterglow. Recently, NASA's Fermi Satellite was launched and, in addition to MeV photons, it detected GeV photons from these astrophysical sources. We show that these GeV photons are produced when the GRB jet interacts with the medium that surrounds it: the external forward shock model. We arrive at this conclusion not only by studying the GeV emission, but also by studying the afterglow observations (Chapter 2). We corroborate this model by studying the electron acceleration in the external forward shock model and find that electrons can radiate at the maximum observed energy of ~ 10 GeV (Chapter 3). We also provide an extensive analysis of the most recent afterglow observations of GRB 090902B within the same framework of an external forward shock origin. We find that the data for this burst requires a small deviation from the traditionally used power-law electron energy distribution, however, our previous results remain unchanged (Chapter 4). To conclude, we use the end of the prompt emission phase, which exhibits a steep X-ray temporal decay, to constrain the behavior of the central engine responsible for launching the relativistic jet (Chapter 5). / text

The radiative mechanism responsible for the prompt gamma-ray burst (GRB) emission remains elusive. For the last decade, optically thin synchrotron emission from shocks internal to the GRB jet appeared to be the most plausible explanation. However, the synchrotron interpretation is incompatible with a significant fraction of GRB observations, highlighting the need for new ideas. In this thesis, it is shown that the narrow, dominating component of the prompt emission from the bright GRB090902B is initially consistent only with emission released at the optically thick jet photosphere. However, this emission component then broadens in time into a more typical GRB spectrum, which calls for an explanation. In this thesis, a previously unconsidered way of broadening the spectrum of photospheric emission, based on considerations of the lateral jet structure, is presented and explored. Expressions for the spectral features, as well as polarization properties, of the photospheric emission observed from structured, relativistic jets are derived analytically under simplifying assumptions on the radiative transfer close to the photosphere. The full, polarized radiative transfer is solved through Monte Carlo simulations, using a code which has been constructed for this unique purpose. It is shown that the typical observed GRB spectrum can be obtained from the photosphere, without the need for additional, commonly assumed, physical processes (e.g. energy dissipation, particle acceleration, or additional radiative processes). Furthermore, contrary to common expectations, it is found that the observed photospheric emission can be highly linearly polarized (up to $\sim 40 \, \%$). In particular, it is shown that a shift of $\pi/2$ of the angle of polarization is the only shift allowed by the proposed model, consistent with the only measurement preformed to date. A number of ways to test the theory is proposed, mainly involving simultaneous spectral and polarization measurements. The simplest measurement, which tests not only the proposed theory but also common assumptions on the jet structure, involves only two consecutive measurements of the angle of polarization during the prompt emission. / <p>QC 20131204</p>

Thesis (Ph. D.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (p. 162-187). Also available via the World Wide Web.

Thesis (M. Phil.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.