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L’imagerie proton est étudiée comme alternative à la tomodensitométrie X pour la planification de traitement en hadronthérapie. En obtenant directement les pouvoirs d’arrêt relatifs des tissus, l’incertitude sur le parcours des particules pourrait être réduite. Un scanner à protons est constitué d’un calorimètre ou d’un détecteur de parcours afin d’obtenir l’information sur l’énergie déposée par chaque proton dans l’objet imagé et de deux ensembles de trajectographes enregistrant la position et direction de chaque particule en amont et en aval de l’objet. Ce travail concerne l’étude des données d’un scanner à protons et l’utilisation possible de toutes les informations enregistrées. Une étude de reconstruction d’image a permis de montrer que les informations sur le taux de transmission et sur la déviation de chaque particule peuvent être utilisées pour produire des images aux propriétés visuelles intéressantes pour le diagnostic. La preuve de concept de la possibilité d’une imagerie quantitative utilisant ces informations est présentée. Ces résultats sont une première étape vers l’imagerie proton utilisant toutes les données enregistrées. / Proton computed tomography is being studied as an alternative to X-ray CT imaging for charged particle therapy treatment planning. By directly mapping the relative stopping power of the tissues, the uncertainty on the range of the particles could be reduced. A proton scanner consists in a calorimeter or range-meter to obtain the information on the energy lost by each proton in the object, as well as two sets of tracking planes to record the position and direction of each particle upstream and downstream from the object. This work concerns the study of the outputs of a proton scanner and the possible use of all the recorded information. A reconstruction study made it possible to show that the information on the transmission rate and on the scattering of each particle can be used to produce images with visual properties that could be of interest for diagnostics. The proof of concept of the possibility of quantitative imaging using this information is also put forward. These results are the first step towards a clinical use of proton imaging with all the recorded data.

After the historic chess match between Deep Blue and Garry Kasparov, many researchers considered the game of chess solved and moved on to the more complex game of soccer. Artificial intelligence research has shifted focus to creating artificial players capable of mimicking the task of playing soccer. A new training algorithm is presented in this thesis for training teams of players from zero knowledge, evaluated on a simplified version of the game of soccer. The new algorithm makes use of the charged particle swarm optimiser as a neural network trainer in a coevolutionary training environment. To counter the lack of domain information a new relative fitness measure based on the FIFA league-ranking system was developed. The function provides a granular relative performance measure for competitive training. Gameplay strategies that resulted from the trained players are evaluated. It was found that the algorithm successfully trains teams of agents to play in a cooperative manner. Techniques developed in this study may also be widely applied to various other artificial intelligence fields. / Dissertation (MSc)--University of Pretoria, 2013. / Computer Science / unrestricted

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Malgré de récentes avancées, les traitements par radiothérapie (RT) demeurent insatisfaisants : la tolérance des tissus sains aux rayonnements limite la délivrance de fortes doses (potentiellement curatives) à la tumeur. Pour remédier à ce problème, de nouvelles approches basées sur des modes de dépôt de dose innovants sont aujourd’hui à l’étude. Parmi ces approches, la technique synchrotron “Minibeam Radiation Therapy” (MBRT) a démontré sa capacité à élever la résistance des tissus sains aux rayonnements, ainsi qu’à induire un important retard de croissance tumorale. La MBRT combine des faisceaux submillimétriques à un fractionnement spatial de la dose. Dans ce contexte, l’alliance de la balistique plus avantageuse des particules chargées (et leur sélectivité biologique) à la préservation des tissus sains observée en MBRT permettrait de préserver d’avantage les tissus sains. Cette stratégie innovante a été explorée durant ce travail de thèse. Deux voies ont notamment été étudiées: la MBRT par faisceaux de protons (pMBRT), et d’ions très lourds. Premièrement, la preuve de concept expérimentale de la pMBRT a été réalisée dans un centre clinique (Institut Curie, Centre de Protonthérapie d’Orsay). De plus, l'évaluation de potentielles optimisations de la pMBRT, à la fois en terme de configuration d’irradiation et de génération des minifaisceaux, a été menée dans une étude Monte Carlo (MC). Dans la seconde partie de ce travail, un nouvel usage potentiel des ions très lourds (néon et plus lourds) en radiothérapie a été évalué dans une étude MC. Les combiner à un fractionnement spatial permettrait de tirer profit de leur efficacité dans le traitement de tumeurs radiorésistantes (hypoxiques), un des principaux défis de la RT, tout en minimisant leurs effets secondaires. Les résultats obtenus au terme de ce travail sont favorables à une exploration approfondie de ces deux approches innovantes. Les données dosimétriques compilées dans ce manuscrit serviront à guider prochaines les expérimentations biologiques. / Despite recent breakthroughs, radiotherapy (RT) treatments remain unsatisfactory : the tolerance of normal tissues to radiations still limits the possibility of delivering high (potentially curative) doses in the tumour. To overcome these difficulties, new RT approaches using distinct dose delivery methods are being explored. Among them, the synchrotron minibeam radiation therapy (MBRT) technique has been shown to lead to a remarkable normal tissue resistance to very high doses, and a significant tumour growth delay. MBRT allies sub-millimetric beams to a spatial fractionation of the dose. The combination of the more selective energy deposition of charged particles (and their biological selectivity) to the well-established normal tissue sparing of MBRT could lead to a further gain in normal tissue sparing. This innovative strategy was explored in this Ph.D. thesis. In particular, two new avenues were studied: proton MBRT (pMBRT) and very heavy ion MBRT. First, the experimental proof of concept of pMBRT was performed at a clinical facility (Institut Curie, Orsay, France). In addition, pMBRT setup and minibeam generation were optimised by means of Monte Carlo (MC) simulations. In the second part of this work, a potential renewed use of very heavy ions (neon and heavier) for therapy was evaluated in a MC study. Combining such ions to a spatial fractionation could allow profiting from their high efficiency in the treatment of hypoxic radioresistant tumours, one of the main challenges in RT, while reducing at maximum their side effects. The promising results obtained in this thesis support further explorations of these two novel avenues. The dosimetry knowledge acquired will serve to guide the biological experiments.

Sandstorms are frequently accompanied by intense electric fields and lightning. In a very narrow region close to the ground, sand particles undergo a charge exchange during which larger-sized sand grains become positively charged and smaller-sized sand grains become negatively charged and then all particles become suspended by the turbulent fluid motion. Although the association of intense electric fields with sandstorms has long been observed, the mechanism that causes these intense electric fields has not yet been described. Here, we hypothesize that differently sized sand particles are differentially transported by turbulence in the flow, resulting in a large-scale charge separation and a consequential large-scale electric field. To confirm our hypothesis, we combined a large-eddy simulation framework comprising a turbulent atmospheric boundary layer and movement of sand particles with an electrostatic Gauss law to investigate the physics of the electric fields in sandstorms. We varied the strength of the sandstorm from weak to strong as parametrized by the number density of the entrained sand particles. Our simulations reproduced observational measurements of both mean and root mean squared fluctuation values of the electric field. Our results allowed us to propose a law in which the electric field scales to two-thirds of the power of the concentration of the sand particles in weak-to-medium strength sandstorms. The underlying approach to simulate the solid particle-laden flow is Eulerian-Eulerian in which the particles are characterized by statistical descriptors. To explore the essential physics of the electric field generation in a sandstorm, we model the high-Reynolds-number atmospheric boundary-layer (ABL) using two different canonical turbulent flows: one model is that of a turbulent boundary-layer (TBL), and the second one is that of a turbulent half-channel flow. For the particle phase, the direct quadrature method of moments (DQMOM) is chosen in which the abscissas and weights of the quadrature method are tracked directly. The utilization of this framework is proposed to examine the transport of sand in sandstorms. Furthermore, the physical mechanisms necessary for production and sustenance of large-scale electric fields in sandstorms is investigated.

I present the construction of a low-velocity intense source (LVIS) of laser-cooled neutral strontium using permanent ring magnets. The LVIS consists of a magneto-optical trap from which cold strontium is extracted in a well-collimated beam. I also present the development and implementation of a full suite of low-noise, high-bandwidth laser control electronics including a microcontroller unit. This microcontroller remotely controls and monitors the current driver, temperature controller, and PID lock circuit for each diode laser simultaneously. The current driver output is accurate to within 2 micro-amps and repeatable to with a few nano-amps. The noise spectral density of the current driver hits a floor of 10^(-10) amps per root Hz at ~50 Hz and has a modulation bandwidth of ~50 MHz. The PID lock-circuit includes a scan-balancing option that we have used to scan an AR coated laser diode ~30 GHz mode-hop free. I describe the construction of an 80 mW frequency doubled 461 nm laser system using PPKTP for cooling and trapping neutral strontium in the LVIS. The LVIS, the electronics systems, and the 461 nm laser system represent major milestones on the way to producing a matter-wave interferometer using Sr-87 ions. The interferometer is based on an optical Raman transition between the hyperfine ground states of the Sr-87 ion. The ions will be produced by exciting the strontium LVIS beam to an auto-ionizing state in the continuum. In the interferometer two half-pi pulses of light and one pi pulse will be delivered to the ions to split and recombine their wave functions. I present calculations of the predicted sensitivity and a discussion of the possible applications. I present a method for locking a 407.8 nm laser to the 5s doublet S J=1/2 to 5p doublet P J=3/2 strontium ion transition in a neutral vapor. I present calculations for the necessary vacuum levels for the experiment and describe the preparation and assembly of the vacuum apparatus. The major vacuum system consists of two connected elastomer sealed chambers: one at 10^(-7) Torr and the other at 10^(-10) Torr separated by a region of low conductance. I present a Sr vapor cell constructed from standard CF fittings that allows the strontium to be heated to ~730 C, which can also be run as a thermal beam. I present a method for protecting the viewports on small-form alkali-earth vapor cells using lead or indium foil during the evaporation of oxide layers. Finally, I report on the current status of the experiment as well as detail future work on the apparatus.

No description available.

Proton radiotherapy is a cancer treatment which has the potential to offer greater cure rates and/or fewer serious side effects than conventional radiotherapy. Its availability in the UK is currently limited to a single low-energy fixed beamline for the treatment of ocular tumours, but a number of facilities designed to treat deep-seated tumours are in development. This thesis focusses on the quantitative use of x-ray computed tomography (CT) images in planning proton radiotherapy treatments. It arrives at several recommendations that can be used to inform clinical protocols for the acquisition of planning scans, and their subsequent use in treatment planning systems. The primary tool developed is a software CT scanner, which simulates images of an anthropomorphic virtual phantom, informed by measurements taken on a clinical scanner. The software is used to investigate the accuracy of the stoichiometric method for calibrating CT image pixel values to proton stopping power, with particular attention paid to the impact of beam hardening and photon starvation artefacts. The strength of the method adopted is in allowing comparison between CT-estimated and exactly-calculated proton stopping powers derived from the same physical data (specified in the phantom), leading to results that are difficult to obtain otherwise. A number of variations of the stoichiometric method are examined, identifying the best-performing calibration phantom and CT tube voltage (kVp). Improvements in accuracy are observed when using a second-pass beam hardening correction algorithm. Also presented is a method for identifying the proton paths where stopping power uncertainties are likely to be greatest. Estimates of the proton range uncertainties caused by CT artefacts and calibration errors are obtained for a range of realistic clinical scenarios. The current practice of including planning margins equivalent to 3.5% of the range is found to ensure coverage in all but the very worst of cases. Results herein suggest margins could be reduced to <2% if the best-performing protocol is followed; however, an analysis specific to the CT scanner and treatment site in question should be carried out before such a change is made in the clinic.

No description available.