Thèses sur le sujet « Physics-guided »

My project focused on the effectiveness of guided inquiry strategies to help students learn physics. Physics is a subject which lends itself to inquiry teaching, where students discover the answers to scientific questions rather than being told the answer. The study involved twelve high school physics students. Student interviews, surveys, and conceptual assessments were used to gauge the effectiveness of this teaching strategy. I collected data and compared two treatment units (inquiry) to a nontreatment unit (traditional). Results were expressed as a percent change in student learning. I also investigated the effect of inquiry teaching on my feelings about teaching, student motivation, and student engagement. The results of my project indicate that students learn effectively through both inquiry and through traditional teaching. Student understanding results did not differ dramatically between comparison units. However, inquiry may be more engaging for students than traditional lecture style teaching. Some students experienced a decrease in motivation while others students experienced an increase in motivation, possibly indicating the existence of multiple intelligences and different learning styles or a lack of experience with the rigors of inquiry. My enjoyment of teaching increased when I taught through guided inquiry. I enjoyed seeing the students discover on their own what I was trying to teach them. I also believe that the inquiry style will better prepare students for standardized tests which emphasize process skills versus content knowledge.

In the area of geothermal energy mapping, scientists have used physics-based models and bottom-hole temperature measurements from oil and gas wells to generate heat flow and temperature-at-depth maps. Given the uncertainties and simplifying assumptions associated with the current state of physics-based models used in this field, this thesis explores an alternate approach for locating geothermally active regions using machine learning methods coupled with physics knowledge of geothermal energy problems, in the emerging field of physics-guided machine learning. There are two primary contributions of this thesis. First, we present a thorough analysis of using state-of-the-art machine learning models to predict a subsurface geothermal parameter, temperature-at-depth, using a rich geo-spatial dataset across the Appalachian Basin. Specifically, we explore a suite of machine learning algorithms such as neural networks (DNN), Ridge regression (R-reg) models, and decision-tree-based models (e.g., XGBoost and Random Forest). We found that XGBoost and Random Forests result in the highest accuracy for subsurface temperature prediction. We also ran our model on a fine spatial grid to provide 2D continuous temperature maps at three different depths using the XGBoost model, which can be used to locate prospective geothermally active regions. Second, we develop a physics-guided machine learning model for predicting subsurface temperatures that not only uses surface temperature, thermal conductivity coefficient, and depth as input parameters, but also the heat-flux parameter that is known to be a potent indicator of temperature-at-depth values according to physics knowledge of geothermal energy problems. Since, there is no independent easy-to-use method for observing heat-flux directly or inferring it from other observed variables. We develop an innovative approach to take into account heat-flux parameters through a physics-guided clustering-regression model. Specifically, the bottom-hole temperature data is initially clustered into multiple groups based on the heat-flux parameter using Gaussian mixture model (GMM). This is followed by training neural network regression models using the data within each constant heat-flux region. Finally, a KNN classifier is trained for cluster membership prediction. Our preliminary results indicate that our proposed approach results in lower errors as the number of clusters increases because the heat-flux parameter is indirectly accounted for in the machine learning model.
Master of Science
Machine learning and artificial intelligence have transformed many research fields and industries. In this thesis, we investigate the applicability of machine learning and data-driven approaches in the field of geothermal energy exploration. Given the uncertainties and simplifying assumptions associated with the current state of physics-based models, we show that machine learning can provide viable alternative solutions for geothermal energy mapping. First, we explore a suite of machine learning algorithms such as neural networks (DNN), Ridge regression (R-reg) models, and decision-tree based models (e.g., XGBoost and Random Forest). We find that XGBoost and Random Forests result in the highest accuracy for subsurface temperature prediction. Accuracy measures show that machine learning models are at par with physics-based models and can even outperform the thermal conductivity model. Second, we incorporate the thermal conductivity theory with machine learning and propose an innovative clustering-regression approach in the emerging area of physics-guided machine learning that results in a smaller error than black-box machine learning methods.

Image-to-image (i2i) translation networks can generate fake images beneficial for many applications in augmented reality, computer graphics, and robotics. However, they require large scale datasets and high contextual understanding to be trained correctly. In this thesis, we propose strategies for solving these problems, improving performances of i2i translation networks by using domain- or physics-related priors. The thesis is divided into two parts. In Part I, we exploit human abstraction capabilities to identify existing relationships in images, thus defining domains that can be leveraged to improve data usage efficiency. We use additional domain-related information to train networks on web-crawled data, hallucinate scenarios unseen during training, and perform few-shot learning. In Part II, we instead rely on physics priors. First, we combine realistic physics-based rendering with generative networks to boost outputs realism and controllability. Then, we exploit naive physical guidance to drive a manifold reorganization, which allowed generating continuous conditions such as timelapses.

In this study, the effect of ‗explicit reflective guided inquiry‘ (ERGI) laboratory practical activities on first-year physics students‘ understanding of nature of science (NOS) and academic performance is investigated. Ninety seven students participated in the study and were systematically assigned to the control group that did recipe-based practical activities and the experimental group that did ERGI laboratory practical activities. Both groups had to answer the same explicit reflective questions on an aspect of NOS at the end of each practical session. Data were collected using the VNOS Form-C questionnaire, focus group interviews, explicit reflective questions, combined practical and theoretical year-end examinations. Using blind scoring, students‘ views were classified as informed, mixed or naïve for each aspect of NOS. The percentage of informed views was larger for the experimental group in each of the seven NOS aspects. Overall, the percentage informed views in the experimental group was larger by a statistically significant margin of 10 percentage points (p = 0.008). The largest differences were observed in the tentative nature of science, the distinction between theory and law, and the role of imagination and creativity. Additionally, males showed more informed NOS understandings than females, while low achieving students were better informed than high achievers, but the differences were not statistically significant. The experimental group did not perform any better than the control group in the practical and theoretical year-end examinations. Therefore, this study demonstrated that ERGI laboratory practical activities activities enhanced first-year physics students‘ understanding of NOS but not their academic performance.
Thesis (PhD)--University of Pretoria, 2017.
Science, Mathematics and Technology Education
PhD
Unrestricted

In this project several tests were performed to evaluate the performance of an On-Board Imager® (OBI) mounted on a clinical linear accelerator. The measurements were divided into three parts; geometric accuracy, image registration and couch shift accuracy, and image quality. A cube phantom containing a radiation opaque marker was used to study the agreement with treatment isocenter for both kV-images and cone-beam CT (CBCT) images. The long term stability was investigated by acquiring frontal and lateral kV images twice a week over a 3 month period. Stability in vertical and longitudinal robotic arm motion as well as the stability of the center-of-rotation was evaluated. Further, the agreement of kV image and CBCT center with MV image center was examined.

A marker seed phantom was used to evaluate and compare the three applications in image registration; 2D/2D, 2D/3D and 3D/3D. Image registration using kV-kV image sets were compared with MV MV and MV-kV image sets. Further, the accuracy in 2D/2D matches with images acquired at non-orthogonal gantry angles was evaluated. The image quality in CBCT images was evaluated using a Catphan® phantom. Hounsfield unit (HU) uniformity and linearity was compared with planning CT. HU accuracy is crucial for dose verification using CBCT data.

The geometric measurements showed good long term stability and accurate position reproducibility after robotic arm motions. A systematic error of about 1 mm in lateral direction of the kV-image center was detected. A small difference between kV and CBCT center was observed and related to a lateral kV detector offset. The vector disagreement between kV- and MV-image centers was  2 mm at some gantry angles. Image registration with the different match applications worked sufficiently. 2D/3D match was seen to correct more accurately than 2D/2D match for large translational and rotational shifts. CBCT images acquired with full-fan mode showed good HU uniformity but half fan images were less uniform. In the soft tissue region the HU agreement with planning CT was reasonable while a larger disagreement was observed at higher densities. This work shows that the OBI is robust and stable in its performance. With regular QC and calibrations the geometric precision of the OBI can be maintained within 1 mm of treatment isocenter.

To improve relatively poor outcomes for locally-advanced lung cancer patients, many current efforts are dedicated to minimizing uncertainties in radiotherapy. This enables the isotoxic delivery of escalated tumor doses, leading to better local tumor control. The current dissertation specifically addresses inter-fractional uncertainties resulting from patient setup variability. An automatic block-matching registration (BMR) algorithm is implemented and evaluated for the purpose of directly localizing advanced-stage lung tumors during image-guided radiation therapy. In this algorithm, small image sub-volumes, termed “blocks”, are automatically identified on the tumor surface in an initial planning computed tomography (CT) image. Each block is independently and automatically registered to daily images acquired immediately prior to each treatment fraction. To improve the accuracy and robustness of BMR, this algorithm incorporates multi-resolution pyramid registration, regularization with a median filter, and a new multiple-candidate-registrations technique. The result of block-matching is a sparse displacement vector field that models local tissue deformations near the tumor surface. The distribution of displacement vectors is aggregated to obtain the final tumor registration, corresponding to the treatment couch shift for patient setup correction. Compared to existing rigid and deformable registration algorithms, the final BMR algorithm significantly improves the overlap between target volumes from the planning CT and registered daily images. Furthermore, BMR results in the smallest treatment margins for the given study population. However, despite these improvements, large residual target localization errors were noted, indicating that purely rigid couch shifts cannot correct for all sources of inter-fractional variability. Further reductions in treatment uncertainties may require the combination of high-quality target localization and adaptive radiotherapy.

In industrial environments, operators are exposed to polluted air which after constant exposure can cause irreversible lethal diseases such as lung cancer. The current air monitoring techniques are carried out sparely in either a single day annually or at few measurement positions for a few days.In this thesis a theory-guided data science (TGDS) model is presented. This hybrid model combines a steady state Computational Fluid Dynamics (CFD) model with a machine learning model. Both the CFD model and the machine learning algorithm was developed in Matlab. The CFD model serves as a basis for the airflow whereas the machine learning model addresses dynamical features in the foundry. Measurements have previously been made at a foundry where five stationary sensors and one mobile robot were used for data acquisition. An Echo State Network was used as a supervised learning technique for airflow predictions at each robot measurement position and Gaussian Processes (GP) were used as a regression technique to form an Echo State Map (ESM). The stationary sensor data were used as input for the echo state network and the difference between the CFD and robot measurements were used as teacher signal which formed a dynamic correction map that was added to the steady state CFD. The proposed model utilizes the high spatio-temporal resolution of the echo state map whilst making use of the physical consistency of the CFD. The initial applications of the novel hybrid model proves that the best qualities of these two models could come together in symbiosis to give enhanced characterizations.The proposed model could have an important role for future characterization of airflow and more research on this and similar topics are encouraged to make sure we properly understand the potential of this novel model.
Industriarbetare utsätts för skadliga luftburna ämnen vilket över tid leder till högre prevalens för lungsjukdomar så som kronisk obstruktiv lungsjukdom, stendammslunga och lungcancer. De nuvarande luftmätningsmetoderna genomförs årligen under korta sessioner och ofta vid få selekterade platser i industrilokalen. I denna masteruppsats presenteras en teorivägledd datavetenskapsmodell (TGDS) som kombinerar en stationär beräkningsströmningsdynamik (CFD) modell med en dynamisk maskininlärningsmodell. Både CFD-modellen och maskininlärningsalgoritmen utvecklades i Matlab. Echo State Network (ESN) användes för att träna maskininlärningsmodellen och Gaussiska Processer (GP) används som regressionsteknik för att kartlägga luftflödet över hela industrilokalen. Att kombinera ESN med GP för att uppskatta luftflöden i stålverk genomfördes första gången 2016 och denna modell benämns Echo State Map (ESM). Nätverket använder data från fem stationära sensorer och tränades på differensen mellan CFD-modellen och mätningar genomfördes med en mobil robot på olika platser i industriområdet. Maskininlärningsmodellen modellerar således de dynamiska effekterna i industrilokalen som den stationära CFD-modellen inte tar hänsyn till. Den presenterade modellen uppvisar lika hög temporal och rumslig upplösning som echo state map medan den också återger fysikalisk konsistens som CFD-modellen. De initiala applikationerna för denna model påvisar att de främsta egenskaperna hos echo state map och CFD används i symbios för att ge förbättrad karakteriseringsförmåga. Den presenterade modellen kan spela en viktig roll för framtida karakterisering av luftflöden i industrilokaler och fler studier är nödvändiga innan full förståelse av denna model uppnås.

This dissertation develops a theoretical framework for guided mode resonance filters (GMRFs) with surface relief gratings based on a physical optics approach. A GMRF is a unique optical device that utilizes the resonance due to the coupling of a diffraction order of a grating with a waveguide mode. This coupling process leads to rapid fluctuations in the reflected and transmitted fields from the GMRF. The reflected output can change from 0% to 100% over extremely small wavelength (or angular) regions with a Lorentzian lineshape. It is shown that the surface relief gratings can be effectively modeled using effective medium theory (EMT). Combining the EMT modeled surface relief grating and thin film theory provides an approximation of the sidelobe levels around a resonance peak and can be used to design a grating that acts as an anti-reflection coating. In addition, EMT can be combined with multilayer waveguide relationships to provide an improved method for determining the wavelength of a resonance. The effect of a finite aperture grating upon the reflected and transmitted output from a GMRF is analyzed. The resonance peak width is found to be inversely proportional to the grating length and the peak efficiency of the GMRF is shown to decrease with reduced grating length. Finally, the design and analysis of a GMRF with a nonlinear waveguide is presented and shown to be capable of providing all-optical switching with low input intensities.

This thesis fills in the gaps in the existing theory of wave phenomena in thick diffraction gratings at extreme angles of scattering, i.e. when the scattered wave propagates parallel or almost parallel to the grating boundaries. A consistent theory of a new type of Bragg scattering of bulk and guided optical modes in thick uniform and non-uniform, dissipative and non-dissipative, slanted periodic gratings has been developed. This type of scattering is called extremely asymmetrical scattering (EAS). One of the main distinctive features of EAS is the strong resonant increase of the scattered wave amplitude compared to the amplitude of the incident wave. Several unique combinations of strong resonances shaping a complex multi-resonant pattern of EAS in different types of gratings have been predicted and investigated theoretically and numerically. This includes the prediction of a new resonant wave effect in non-uniform gratings with varying phase – double-resonant EAS, the discovery of several sharp and strong resonances with respect to scattering angle in gratings with the scattered wave propagating almost parallel to the grating boundaries (grazing-angle scattering (GAS)) for the case of second-order scattering, and the prediction of a new type of eigenmode in gratings with second-order scattering (especially in gratings with large amplitude). In addition, several other important practical problems that may be crucial for the experimental observation and application of EAS and GAS have been solved. These are the determination of the tolerance of EAS to small grating imperfections, e.g., fluctuations of the grating amplitude, prediction of unusually high sensitivity of second-order EAS to small variations of mean structural parameters, determination of the effect of weak dissipation on EAS, etc. Physical reasons for the predicted resonances and effects are explained. In particular, the crucial role of the diffractional divergence for EAS and GAS has been revealed, especially for non-uniform gratings. Methods of analysis involve the approximate and rigorous approaches. The approximate method is based on understanding the role of the diffractional divergence in the geometry of EAS and the two-wave approximation (valid for any types of waves). The rigorous approach is based on the rigorous coupled-wave analysis (RCWA) and, in particular, the known enhanced T-matrix algorithm (by Moharam, et al.) that is numerically stable for narrow and wide gratings with arbitrary amplitude (valid only for bulk electromagnetic waves).

This thesis fills in the gaps in the existing theory of wave phenomena in thick diffraction gratings at extreme angles of scattering, i.e. when the scattered wave propagates parallel or almost parallel to the grating boundaries. A consistent theory of a new type of Bragg scattering of bulk and guided optical modes in thick uniform and non-uniform, dissipative and non-dissipative, slanted periodic gratings has been developed. This type of scattering is called extremely asymmetrical scattering (EAS). One of the main distinctive features of EAS is the strong resonant increase of the scattered wave amplitude compared to the amplitude of the incident wave. Several unique combinations of strong resonances shaping a complex multi-resonant pattern of EAS in different types of gratings have been predicted and investigated theoretically and numerically. This includes the prediction of a new resonant wave effect in non-uniform gratings with varying phase – double-resonant EAS, the discovery of several sharp and strong resonances with respect to scattering angle in gratings with the scattered wave propagating almost parallel to the grating boundaries (grazing-angle scattering (GAS)) for the case of second-order scattering, and the prediction of a new type of eigenmode in gratings with second-order scattering (especially in gratings with large amplitude). In addition, several other important practical problems that may be crucial for the experimental observation and application of EAS and GAS have been solved. These are the determination of the tolerance of EAS to small grating imperfections, e.g., fluctuations of the grating amplitude, prediction of unusually high sensitivity of second-order EAS to small variations of mean structural parameters, determination of the effect of weak dissipation on EAS, etc. Physical reasons for the predicted resonances and effects are explained. In particular, the crucial role of the diffractional divergence for EAS and GAS has been revealed, especially for non-uniform gratings. Methods of analysis involve the approximate and rigorous approaches. The approximate method is based on understanding the role of the diffractional divergence in the geometry of EAS and the two-wave approximation (valid for any types of waves). The rigorous approach is based on the rigorous coupled-wave analysis (RCWA) and, in particular, the known enhanced T-matrix algorithm (by Moharam, et al.) that is numerically stable for narrow and wide gratings with arbitrary amplitude (valid only for bulk electromagnetic waves).

Patient geometry often changes during the course of radiation therapy due to factors such as weight loss, tumor and normal tissue growth or shrinkage, and intra-treatment position variations. It has been shown that these changes can cause the dose delivered to differ from the originally planned dose distribution. Often this will result in the need to create a modified treatment plan, a process known as adaptive radiation therapy. The aim of this thesis is to evaluate the dosimetric effects due to anatomical changes and positioning variations during intensity-modulated radiation therapy through two retrospective studies. MIM Software (Cleveland, OH), a commercially available deformable registration tool, is used for this work. In the first study, the daily dose for four breast cancer patients undergoing a volumetric modulated arc boost treatment to the tumor bed is calculated on pretreatment cone beam computed tomography images. Two treatment isocenters, corresponding to the initial patient set up position, and the shifted position based on pretreatment imaging, are used for dose verification. The results indicate that a planning target volume consisting of the tumor bed and a uniform margin expansion of 1 cm is adequate to account for positioning errors. In the second study, the daily dose is calculated on the pretreatment megavoltage computed tomography images for craniospinal irradiation and head and neck cancer patients undergoing helical tomotherapy. The dose for each treatment fraction is deformed and accumulated to the planning computed tomography image for comparison with the original plan. This study assesses the effects of anatomical changes on treatment delivery. The results indicate a slight decrease in target coverage and no significant increase in dose to critical structures.
Souvent, au cours d'une procédure de radiothérapie, la géométrie du patient change en raison de facteurs tels que la perte de poids, la croissance ou le rétrécissement des tissus tumoral et normal, et les variations de position en cours de traitement. Il a été démontré que ces changements peuvent faire en sorte que la dose de radiation administrée soit différente de la dose initialement planifiée. Souvent, cela se traduit par la nécessité de créer un plan de traitement alternatif, un processus appelé radiothérapie adaptative. L'objectif de cette thèse est d'évaluer les effets dosimétriques causés par des changements anatomiques ainsi que les variations de positionnement au cours de la procédure de radiothérapie avec modulation d'intensité à travers deux études rétrospectives. MIM Software (Cleveland, OH), un outil d'enregistrement non-linéaire disponible sur le marché, est utilisé pour ce travail. Dans la première étude, la dose quotidienne de quatre patients atteints de cancer du sein qui subissent un traitement volumétrique modulée arc-boost dans le lit tumoral est calculée à partir des images prétraitement de tomodensitométrie à faisceau conique. Deux isocentres de traitement, correspondant à la position initiale du patient et à la position ajustée à partir d'imagerie prétraitement, sont utilisés pour la vérification de la dose. Les résultats indiquent que le volume cible prévisionnel comprenant le lit tumoral et une augmentation de la marge uniforme de 1 cm sont suffisants pour tenir compte des erreurs de positionnement. Dans la deuxième étude, la dose quotidienne est calculée sur les images prétraitement de tomodensitométrie à mégavoltage pour l'irradiation craniospinale et aux patients atteints de cancer de la tête et du cou qui obtiennent la tomothérapie hélicoïdale. La dose pour chaque fraction de traitement est déformée et accumulés sur le CT de planification pour être comparée avec le plan original. Cette étude évalue les effets des changements anatomiques sur l'administration du traitement. Les résultats indiquent une légère diminution de la couverture cible et aucune augmentation significative de la dose pour les structures critiques.

Abstract - Which abilities are the students training in the subject of physics? The purpose of this study was to examine teachers' plans, LPPs (Local Educational Planning) to see which abilities are trained and how. I have created a content analysis of the teachers' plans, LPPs and how the teachers practice the abilities of the students in the subject of physics. I analysed two LPPs in the grade 5 and two LPPs in the grade 6. The LPPs are from two different schools and two teachers' one in each grade. My first purpose was to examine which abilities, prescribed in Lgr 11 students are training and if the abilities create a common thread between grade 5 and grade 6 in the subject of physics. My second purpose was to examine what kind of teaching the students are training the abilities which can be found in Lgr 11. The study addresses three different kinds of teaching which are more open, more guided or in a combined way of teaching. My study answered the following questions: Which abilities in Lgr 11 are the students training in the subject of physics in grade 5 and 6? What kind of teaching are the students training the abilities in Lgr 11? The study was based on a content analysis of the LPPs and the theory I used to analyse was The Big 5. I also used interview by email with the teachers who gave me the LPPs. Based on the results and the analysis of the study, I came to the conclusion that all four LPPs in the two different schools were practicing the abilities prescribed in Lgr 11 and that they used The Big 5 to clarify the abilities that the topic addresses. All four LPPs have a common thread between grade 5 and 6 where some abilities are recorded again others are excluded and supplemented with new ones. Based on the results and the analysis, I came to the conclusion that both teachers teach the skills prescribed in Lgr 11 in the subject of physics in an open way of teaching, i.e. when students are active participants in the teaching. Combined teaching was used several times when the students e.g. had to try out for a given topic. Guided teaching was used only once in all four LPPs e.g. when the teachers prepare a list of concepts.

La modélisation des phénomènes dynamiques en géophysique repose sur une compréhension de la physique sous-jacente, décrite sous la forme d'EDP, et sur leur résolution par des modèles numériques. Le nombre croissant d'observations de systèmes physiques, l'essor récent de l'apprentissage profond et l'énorme puissance de calcul requise par les solveurs numériques, qui entrave la résolution des modèles existants, suggèrent que l'avenir des modèles physiques pourrait être orienté données. Mais pour cela, l'apprentissage profond doit relever plusieurs défis, tels que l'interprétabilité et la cohérence physique des modèles, qui sont encore largement sous-estimés par la communauté de l'apprentissage profond. Dans cette thèse, nous étudions la prédiction de la température de surface de la mer (SST) à l'aide de modèles hybrides, combinant un modèle physique et un modèle orienté données (un réseau de neurones). Assurer la plausibilité physique des modèles hybrides nécessite de bien poser leur apprentissage : sinon, la grande versatilité des réseaux neuronaux peut conduire la partie orientée données à contourner le modèle physique. Notre étude est divisée en deux parties : une étude théorique sur les modèles hybrides et une confrontation pratique de notre modèle à des simulations de données réelles. Tout d'abord, nous proposons un nouveau cadre générique d'apprentissage bien posé basé sur l'optimisation d'une borne supérieure de l'erreur de prédiction. Deuxièmement, nous étudions des observations océaniques réelles de la SST et des champs de vitesse du courant Gulf Stream dans l'Atlantique Nord (à partir du modèle NATL60). Cette application met en évidence les défis posés par la confrontation de l'apprentissage automatique de phénomènes physiques à la complexité de la physique du monde réel
The modeling of dynamical phenomena in geophysics and climate is based on a deep understanding of the underlying physics, described in the form of PDEs, and on their resolution by numerical models. The ever-increasing number of observations of physical systems, the recent rise of deep learning and the huge computational power required by numerical solvers, which hinders the resolution of existing models, suggest that the future of physical models could be data-driven. But for this prognosis to come true, deep learning must tackle several challenges, such as the interpretability and physical consistency of deep models, still largely under-addressed by the deep learning community.In this thesis, we address both challenges: we study the prediction of sea surface temperature (SST) using hybrid models combining a data-driven and a physical model. Ensuring the physical plausibility of hybrid models necessitates well-posing their learning: otherwise, the high versatility of neural networks may lead the data-driven part to bypass the physical part.Our study is divided into two parts: a theoretical study on hybrid models, and a practical confrontation of our model on simulations of real data. First, we propose a new generic well- posed learning framework based on the optimization of an upper-bound of a prediction error. Second, we study real-like ocean observations of SST and velocity fields from the Gulf Stream current in the North Atlantic (from the NATL60 model). This application highlights the challenges raised by confronting physics aware learning to the complexity of real-world physics. It also raises issues such as model generalization, which we discuss as a possible perspective

Biological effects and prostate motion were studied for prostate cancer patients treated with external beam radiotherapy. The prostate motion was determined using an ultrasound-based patient positioning system (BAT: B-mode Acquisition and Targeting) just after conventional patient setup. The changes in planned biological effects due to prostate motion were calculated for the prostate target organ and for the rectum and bladder normal tissues using TCP (tumor control probability) and NTCP (normal tissue complication probability) calculations, respectively. The prostate TCP calculations were carried out for both prostate PTV and GTV structures, whereas the rectum and bladder wall structures were used for the NTCP calculations.

The insertion of Modern and Contemporary Physics (FMC) in High School (IN) supported by researchers from the School of Sciences and Physical Education is linked to a concern with the initial training and continuing education. In this paper, we present results of research through an undergraduate Supplementary Discipline (DCG), the initial training of teachers, aiming at achieving the contents of FMC Health and cross-cutting theme in the planning of teaching undergraduates in physics. The implementation of this discipline occurred in the 2nd half of 2011, the degree course in Physics UFSM. To produce this DCG was made a research on the topic Radioactivity and Nuclear Energy (EN / Rad) in major journals and conferences in the area of Science Education and Physical Education in the period 2005 to 2010. The results of this investigation, which have focused on the proposed training for the classroom, pointed a small number of implementations. We also carried out an analysis of the curriculum, the graduate courses in Physics at the federal universities of RS, especially UFSM, regarding the relationship of the disciplines of the grid that addressed the conceptual and procedural contents on the subject EN / Rad. In the analysis of documents were used content analysis procedures. The results of this analysis, from the perspective of National Curricular Guidelines (DCN) for courses in Physics, presented a temporal mismatch between these disciplines with differing emphasis. In this sense, the DCG has come to contribute to the Initial Training for the elaboration of didactic plans, relating the theme EN / Rad and Health, along activities for discussion and didactic plans, results pointing to the levels of coordination between these two themes. The main result was presented in planning the sequence and importance given to the Health theme in these relationships, demonstrating that the Health theme is used as an illustration, usually at the end of the planning, configuring itself as a weak link.
A inserção da Física Moderna e Contemporânea (FMC) no Ensino Médio (EM) defendida por pesquisadores das áreas de Ensino de Ciências e de Ensino de Física está vinculada a uma preocupação com a formação inicial e continuada de professores. Neste trabalho, apresentam-se resultados de pesquisa, através de uma Disciplina Complementar de Graduação (DCG), na formação inicial de professores, visando à articulação dos conteúdos de FMC e o tema transversal Saúde nos planejamentos didáticos dos licenciandos em Física. A implementação desta disciplina ocorreu no 2º semestre de 2011, no curso de licenciatura em Física da UFSM. Para a elaboração desta DCG foi realizada uma investigação sobre o tema Energia Nuclear e Radioatividade (EN/Rad) nos principais periódicos e eventos da área de Ensino de Ciências e Ensino de Física, no período de 2005 a 2010. Os resultados desta investigação, que tiveram como foco as propostas de ensino para a sala de aula, apontaram um número reduzido de implementações. Também foi realizada uma análise das grades curriculares, dos cursos de licenciatura em Física das universidades federais do RS, em especial da UFSM, quanto à relação das disciplinas da grade que contemplassem os conteúdos conceituais e procedimentais sobre o tema EN/Rad. Na análise dos documentos foram utilizados os procedimentos de análise de conteúdo. Os resultados desta análise, sob a ótica das Diretrizes Curriculares Nacionais (DCN) para os cursos de Física, apresentaram uma incompatibilidade temporal entre estas disciplinas de diferentes ênfases. Neste sentido, a DCG veio a contribuir na Formação Inicial para a elaboração de planejamentos didáticos, relacionando o tema EN/Rad e a Saúde, ao longo de atividades de discussão e de planejamentos didáticos, apontando como resultados os níveis de articulação entre estes dois temas. O principal resultado apresentado nos planejamentos foi a sequência e a relevância dada ao tema Saúde nestas relações, demonstrando que o tema Saúde é utilizado como uma ilustração, geralmente, ao final dos planejamentos, configurando-se como uma articulação frágil.

In radiation therapy an uncertainty in the delivered dose always exists because anatomic changes are unpredictable and patient specific. Image guided radiation therapy (IGRT) relies on imaging in the treatment room to monitor the tumour and surrounding tissue to ensure their prescribed position in the radiation beam. The goal of this thesis was to determine the dosimetric impact on the misaligned radiation therapy target for three cancer sites due to common setup errors; organ motion, tumour tissue deformation, changes in body habitus, and treatment planning errors. For this purpose, a novel 3D ultrasound system (Restitu, Resonant Medical, Inc.) was used to acquire a reference image of the target in the computed tomography simulation room at the time of treatment planning, to acquire daily images in the treatment room at the time of treatment delivery, and to compare the daily images to the reference image. The measured differences in position and volume between daily and reference geometries were incorporated into Monte Carlo (MC) dose calculations. The EGSnrc (National Research Council, Canada) family of codes was used to model Varian linear accelerators and patient specific beam parameters, as well as to estimate the dose to the target and organs at risk under several different scenarios. After validating the necessity of MC dose calculations in the pelvic region, the impact of interfraction prostate motion, and subsequent patient realignment under the treatment beams, on the delivered dose was investigated. For 32 patients it is demonstrated that using 3D conformal radiation therapy techniques and a 7 mm margin, the prescribed dose to the prostate, rectum, and bladder is recovered within 0.5% of that planned when patient setup is corrected for prostate motion, despite the beams interacting with a new external surface and internal tissue boundaries. In collaboration with the manufacturer, the ultrasound system was adapted from transabdominal imaging to n
Des incertitudes dans la dose délivrée aux patients existent toujours car les changements anatomiques sont imprévisibles et spécifiques à chaque patient. La radiothérapie guidée par l'image (IGRT) dépend de l'imagerie en ligne afin de suivre la tumeur et les tissus sains adjacents, et s'assure que leur positions, par rapport au faisceau de radiation, est telle que planifiés. L'objectif de cette thèse a été de déterminer l'impact dosimétrique du désalignement de la cible par rapport au faisceau de radiation du aux erreurs d'installation, aux mouvement des organes, à la déformation de la tumeur, aux changements de l'habitus du corps et aux erreurs dans la planification du traitement. À cette fin, un nouveau système ultrason 3D (Restitu, Resonant Medical, Inc.) a été utilisé pour acquérir des images référence de la cible dans la salle de simulation tomodensitométrique au moment de la planification du traitement, et ensuite pour acquérir des images quotidiennes de la cible au moment du traitement. Les images quotidiennes ont été comparées à l'image de référence et les différences de position et volume ont été incorporées dans des calculs de dose Monte Carlo. La famille de logiciels EGSNRC (National Research Council, Canada) a été utilisée pour modéliser des accélérateurs linéaires Varian et des paramètres spécifiques à chaque patient ainsi que pour estimer la dose à la cible et aux organes à risque. Premièrement, les calculs de dose Monte Carlo, longs mais précis, ont été validés pour la région homogène du pelvis. Ensuite, l'influence du mouvement de la prostate inter fractions et du réalignement du patient sur la distribution de dose délivrée a été investiguée. Pour 32 patients nous avons démontré que l'utilisation des techniques conformes 3D combinée à une marge de 7 mm autour de la cible se traduit par une différence de moins de 0.5% entre la dose délivrée et la dose planifiée pour la prostate,$

Direct volume rendering techniques for scalar fields make use of transfer functions to map optical properties to the field; the field can subsequently be visualized through the drawing of isosurfaces in the volume spanned by the field. The utility of this approach is limited in the case of nested or clustered structures with the same isovalue and further does not easily allow for quantitative measurements of the visualized data. This report explores the use of topological structures (contour trees and Morse-Smale complexes) as an augmentation of traditional direct volume rendering and describes a fully functional implementation in the visualization software Inviwo. The implementation is evaluated through analysis of valency charge density fields in cubic MgO2 and FeO2. It is demonstrated that both contour trees and Morse-Smale complexes provide information and segmentation of initial volume data that allows for selective transfer function application (based on the segmentation), on-demand information on critical points and an overview of the scalar field through a topological representation embedded in the visualized volume. Analysis of the provided charge density fields show that contour trees generate physically irrelevant artefacts and thus are ill-suited for analysing highly symmetric data. On the other hand, the Morse-Smale complex approach is used to extract information of the bond strength of O-O contacts in MgO2 and FeO2 consistent with previous findings, as well as information on electronic charge configuration consistent with previous findings on MgO2. In the case of FeO2, the electronic configuration results are not consistent. This is speculated to be due to a combination of factors, most notably the lack of periodic boundary conditions in the implementation and the more complicated structure of FeO2.   In light of the partially accurate data analysis, as well as the added functionality and utility provided to visualization software, this approach to topology-guided visualization is considered promising and worthy of further study and/or development.

Integrated optics-based approaches to beam steering, beam shaping, beam collimation, and quasi-phasematched (QPM) second harmonic generation (SHG) of light offer significant advantages over conventional approaches based on bulk optics. The research in this dissertation addresses the analysis and design of optical guided-wave devices for both efficient quasi-phasematched second harmonic generation in diffused channel waveguides, as well as Bragg deflection of beams in planar waveguides. It is known that the normalized SHG efficiency depends on the linear properties of the waveguide through the overlap of the modal fields at the fundamental and second harmonic wavelengths. To analyze the linear modal properties, a fast and accurate modeling tool, based on an improved, semi-vector, Fourier method of analysis, is presented. The tool incorporates the Wentzel-Kramers-Brillouin (WKB) and effective index methods to accurately determine the computational parameters required for the numerical calculation in the Fourier method so that automatic variation of the waveguide parameters is permitted. Using the modeling tool, the dependence of the SHG process on the waveguide parameters is investigated in detail, leading to waveguide designs with improved mode confinement, and consequently higher SHG efficiency. The phasematching characteristics of these improved designs are also calculated, and it is found that non-critical phasematching, or phasematching with wide tolerances to variations in the waveguide parameters, is possible in certain cases. The analysis of the waveguide-SHG process also indicates that efficiency can be improved by utilizing thin films on the waveguide surface to ensure that the peaks of the fundamental and second harmonic modes are coincident. This contributes to higher SHG efficiency through improved mode overlap as well, but it is demonstrated that this approach is clearly distinct from and independent of the mode-confinement approach. The analysis of planar overlays is based on recursion relations for the phase shift upon reflection at interfaces. The significance of this approach is demonstrated through the "matching" of the diffused waveguide to an independently-designed, multilayer overlay for the purposes of obtaining specific modal characteristics in the "integrated" structure. On a different note but incorporating similar approaches for analysis and design, beam shaping, steering, and collimation in planar waveguides, using Bragg gratings with finite area and non-uniform depth variation, are also discussed.

The daily uncertainty concerning tumor localization is one of the major problems during the course of radiation therapy. Image guided-radiation therapy (IGRT) can be used to improve the localization and adjustment of the planning target volume. The aim of this work was to evaluate both the IGRT technique used for prostate cancer patients at the department of the Karolinska University Hospital and an alternative on-line adaptive radiation therapy (ART) method with an On-Board Imager (OBI).

In the first part of the thesis 2D and 3D image registration with an OBI were compared. Ten prostate cancer patients were involved in the analyses. Two different statistical tests were used to determine significant systematic deviations between the two methods. The second part concerns daily dose verifications and dose plan reoptimization of one intensity modulated radiation therapy (IMRT) prostate cancer patient treated with IGRT. The study was based on cone-beam computed tomography (CBCT) images acquired at 6 different treatment fractions. The risk of developing late rectal and bladder toxicity was quantified using normal tissue complication probability (NTCP) calculations. Additional measurements on an Alderson phantom were performed to verify the accuracy of using the CBCT images for dose calculations.

A statistically significant difference between the 2D-2D and the 3D-3D match applications could be observed in lateral and longitudinal direction. However, the effect differed among the patients. The phantom measurements showed small dose deviations between the CT and CBCT image, with a mean dose increase to the prostate and seminal vesicles (SV) of 2.5 %. The daily dose to the prostate and SV of the IMRT patient showed to be satisfactory. The daily dose to the rectum did not exceed the prescribed rectal dose except at one treatment fraction and the highest risk of developing late rectal toxicity was about 10.4 %. Large daily bladder dose variations were observed and at two treatment fractions the bladder dose restrictions were exceeded. With a reoptimization process of the dose plan, the dose to the bladder could be reduced while conserving the dose to the target.

This work shows that for these specific patient cases appropriate doses to the prostate and SV can be delivered with IGRT. However, introducing a suitable ART method could lead to a reduction of inter-fractional rectal and bladder dose variations.

Two ultrasound systems were studied to investigate the effects of positional and volumetric prostate variations on dosimetry over the course of external radiation therapy. A 2D system, currently used at the Montreal General Hospital for patient repositioning, was compared to a 3D system invented recently. Prostate variations were quantified from ultrasound images acquired daily during a 2003 clinical study. A method was devised to introduce ultrasound information in a Monte Carlo Treatment Planning System previously developed at McGill. Patient repositioning was evaluated for both systems using dose-volume histograms of Voxel Monte Carlo dose calculation. Repositioning with the 3D system, neglecting volume changes, was found to bring the target dose to within 1 % of the planned dose, rather than the 12 % of the clinical 2D system. However, when considering the varying 3D volumes, the dose could only be corrected to within 7 %. These results indicate that the 3D system provides not only a more accurate assessment of prostate displacements, but also volumetric information that significantly affects the dosimetry.

Recently a periodic surface model was developed to assist geometric construction in computer-aided nano-design. This implicit surface model helps create super-porous nano structures parametrically and support crystal packing. In this thesis, a new approach for pathway search in phase transition simulation of crystal structures is proposed. The approach relies on the interpolation of periodic loci surface models. Respective periodic plane models are reconstructed from the positions of individual atoms at the initial and final states, and surface correspondence is found using a Simulated Annealing-like algorithm. With geometric constraints imposed based on physical and chemical properties of crystals, two surface interpolation methods are used to approximate the intermediate atom positions on the transition pathway in the full search of the minimum energy path. This hybrid approach integrates geometry information in configuration space and physics information to allow for efficient transition pathway search. The methods are demonstrated by examples of FeTi, VO2, and FePt. Additionally, two new particle swarm optimization (PSO) algorithms are developed and applied to crystal structure relaxation of the initial and final states. The PSO algorithms are integrated into the Quantum-Espresso open-source software package and tested against the default Broyden-Fletcher-Goldfarb-Shanno relaxation method.

Many studies have shown that the computed tomography dose index (CTDI100) which is considered to be the main dose descriptor for CT dosimetry fails to provide a realistic reflection of the dose involved in cone beam CT (CBCT) scans. The main reason for this failure is that CTDI100 measurements are performed within standard head and body phantoms made of polymethyl methacrylate (PMMA) that are only 150 cm long, which is less than or similar to beam widths used for CBCT scans. Therefore, much of the scatter that would contribute to the dose received by a patient is not recorded. Several practical approaches have been proposed to overcome drawbacks of the CTDI100. The aim of this project was to investigate the various dose indices based on the approaches proposed. The dose indices studied were: (1) CTDIIEC proposed by the International Electrotechnical Commission (IEC) and based on measuring CTDI100 using a reference beam and the application of a correction factor based on free-in-air CTDI measurements, (2) f(0,150) the cumulative dose measured with a small ionization chamber within the standard PMMA phantoms, (3) f100 (150) the cumulative dose measured in the standard PMMA phantoms with a 100 mm pencil ionization chamber, (4) f(0,∞) proposed by the American Association of Physicists in Medicine (AAPM) TG - 111 and similar to f(0,150), but measured in infinitely long phantoms made of PMMA, polyethylene, and water, (5) f100 (∞) similar to f100 (150), but measured in infinitely long phantoms. The project also aimed to facilitate the use of indices defined in long phantoms through the generation of correction factors that could be applied to measurements in standard phantoms. This project was based on the use of the Monte Carlo (MC) technique. MC EGSnrc-based user codes namely BEAMnrc and DOSXYZnrc were used to simulate the On-Board-Imager (OBI) imaging system mounted on a Varian TrueBeam linear accelerator. The MC model was benchmarked against experimental measurements and good agreement shown. PMMA, polyethylene, and water head and body phantoms of various lengths and diameters were simulated including a new polyethylene phantom named ICRU/AAPM phantom made by the International Commission on Radiation Units and Measurements (ICRU) and AAPM. A wide range of beam widths with different beam qualities were employed. Four scanning protocols using two acquisition modes (full and half), employed in routine clinical practice, were utilized. In addition, organ doses resulting from three CBCT scans (head, thorax, and pelvis) were evaluated in terms of absorbed dose to organs and tissues using MC simulations on the International Commission on Radiological Protection (ICRP) 110 adult male and female reference computational phantoms. The suitability of the dose indices for CBCT dosimetry was investigated by taking three factors into consideration: (1) the efficiency of the approach as a dose descriptor to report CTDI∞, which is close to the dose received by body tissues near to the middle of a CBCT scan of a patient, (2) the simplicity of the application of the approach in the clinical environment in terms of availability of the measuring instruments, simplicity of the technique, and the number of the scans required to accomplish a quality assurance (QA) assessment, i.e. the QA time, and (3) the ability of the approach in providing an evaluation of organ doses resulting from CBCT scans. To facilitate the use of long phantoms, the relationship between f(0,150) and f100 (150) measurements obtained within the standard PMMA phantoms and those for f(0,∞) obtained within longer phantoms of different compositions were studied. Considering the three factors for the dose indices investigated, all the dose indices were found to be comparable, but each index has advantages and disadvantages. Overall, f(0,150) was considered to be the most suitable with f100 (150) providing an alternative for wider beams. Therefore, the dose indices f(0,150) followed by f100 (150) are recommended for practical CBCT dosimetry. In addition, a function called Gx(W)100 was proposed for evaluating the cumulative dose in long phantoms, and correction factors were also provided to avoid the use of long phantoms. The Gx(W)100 function did not vary significantly with tube potential, but the tube potential did influence the correction factors. The use of the Gx(W)100 function is recommended for estimation of f(0,∞) values from f100 (150) measurements taken in the standard PMMA phantoms.

L'exérèse des tumeurs cancéreuses est une procédure courante pour le traitement de nombreux cancers. L'enjeu est de réaliser une excision la plus complète possible pour éviter les récidives tout en épargnant le plus possible les tissus sains bordant la tumeur. La détection de positons est une modalité d'imagerie particulièrement adaptée au repérage de résidus tumoraux lors de l'éxerèse car sa forte sélectivité spatiale permet de s'affranchir du bruit provenant de la fixation non spécifique du radiotraceur dans les tissus situés en profondeur, offrant ainsi une meilleur sensibilité et un meilleur rapport signal sur bruit que la détection de photons gamma. L'utilisation pour le contrôle d'exérèse impose cependant une contrainte forte sur les dimensions du détecteur qui doit être manipulable facilement par le chirurgien et pouvoir être inséré dans des plaies opératoires potentiellement étroites. Une nouvelle génération de photodétecteurs appelés photomultiplicateurs silicium (SiPM) est particulièrement adaptée à cette application car ceux-ci allient la compacité et la robustesse des technologies silicium avec d'excellentes performances de détection. Mon travail de thèse porte sur le développement et la caractérisation de nouvelles sondes positon basées sur ces photodétecteurs. Dans un premier temps, un travail de caractérisation des SiPMs a été réalisé pour évaluer leurs performances pour la détection de positons. Deux prototypes de prototypes de détecteurs aux rôles complémentaires ont ensuite été réalisé: le premier est un imageur, basé sur l'assemblage de deux scintillateurs avec une ou deux matrices de SiPMs, qui permet de réaliser rapidement l'image de la distribution de traceur sur une large surface de tissus. Le second détecteur est une sonde de comptage, constituée de fibres scintillantes couplées à des SiPMs individuels via des fibres claires et capable d'être couplée à l'outil d'exérèse. Elle permet de guider l'outil du chirurgien vers les tissus repérés préalablement avec l'imageur. La caractérisation de l'imageur a montré sa capacité à détecter des résidus tumoraux de petite taille (15mg) avec une résolution submillimétrique. La sonde de comptage présente quant à elle, une efficacité de détection de 80%.

Purpose: The aim of this thesis is to study the European (ESTRO/EAU/EORTC) and American (ABS) guidelines how to report the permanent seed implant and the most significant dosimetric parameters. It will also report on the permanent seed implant at Södersjukhuset, Karolinska University Hospital according to the guidelines. A large number of studies on pre- and post-implant dosimetry on permanent seed implants have recently been published but none is considered a standard. This makes it difficult, if not impossible, to compare data from different centres. The differences in reporting will also be discussed in this thesis. Another part of the study is to investigate how the morbidity correlates with the dose. The results in this report will give an overview of the experience at Södersjukhuset.

Matherials and Methods: This study includes 198 patients who received implants between 2004-2007 with I-125 seeds under transperineal ultrasound at Södersjukhuset (to a prescribed dose of 145 Gy). The dose-planning system VariSeed 7.1 was used with an online connection to the ultrasound system with real-time verification. Dose constraints for the planning system are V(100)>99%, V(150)>60%, V(200)>25%, UrD(10)<130% and UrD(30)<125%. Outer and inner wall of rectum was outlined for 55 patients as recommended by ESTRO/EAU/EORTC and doses to rectum were also computed.

Results: The median value for dosimetric parameters at Södersjukhuset, Karolinska University Hospital are for the prostate; D(90)=174Gy (153-194Gy), V(100)= 99% (93-100%), V(150)= 57% (40-74%), for the urethra; UrD(30) = 130% (112-147%), UrD(10) = 124% (107-142%) and for the rectum; RD2cc= 98Gy (73-128Gy), RD0.1cc=164Gy (119-240Gy), RV(100)=0.3cc (0.0-1.3cc), RV(150)=0.0cc (0.0-0.2cc). These values correspond to recommended data, except for the V(150) value. Regarding the clinically observed results, 3 patients had a relapse in their cancer, 2 patients had mild proctitis and 15 patients had urinary problems.

Discussion and Conclusions: The significant dosimetric parameters for reporting according to ESTRO/EAU/EORTC and ABS for prostate are D90[Gy], V(100)[%] and V(150)[%], for urethra are D(30) and D(10), and for rectum RD2cc and RD0.1cc. These parameters consider as a minimum to use and they further recommend secondary parameters to report. Other authors have also recommended to report RV(100) and RV(150) for rectum. This study did not show any relationship between UrD(10), UrD(30) and urinary morbidity. According to the recommendations every patient should undergo a CT-based evaluation. Further investigations are needed on whether a post-implant CT-study is necessary for real-time implantation, as there is not enough published data on this aspect.

This thesis explores the five-space experimental implementation and monolithic adaptation of the Equality subsystem from a parallel relational database optical machine called the Multi-Wavelength Optical Content-Addressable Parallel Processor (MW-OCAPP). MW-OCAPP uses a novel polarization- and wavelength-encoding scheme to achieve an input/output-limited experimental peak bit comparison rate of 96,000/sec. Recognizing the severe diffraction-limit penalty for using a free-space optical processor with relatively long path lengths, a system based on guided-wave optics called the Equivalency Processing Parallel Photonic Integrated Circuit (EP3IC) was developed. Although algorithmically identical to MW-OCAPP's equality operation, EP3IC's peak bit comparison rate for a similarly configured machine is over six orders of magnitude faster. It achieves this substantial performance advantage by making use of integrated high-speed detectors and electro-optic modulators. This integrated circuit solution provides relatively low-power operation, fast switching speed, a compact system footprint, vibration tolerance, and a design that is highly manufacturable.

Les moteurs thermoacoustiques sont des oscillateurs autonomes constitués d'un résonateur acoustique partiellement occupé par un matériau poreux (stack) soumis à un important gradient de température grâce à un apport de chaleur externe. Lorsque le gradient de température imposé le long du stack devient supérieur à un certain gradient critique, appelé seuil de déclenchement, l'interaction fluide-parois se traduit par l'amplification d'une onde acoustique auto-entretenue de fort niveau sur le mode le plus instable du résonateur. L'objet des travaux présentés dans ce mémoire est double. D'une part, il est de proposer un formalisme pour la description du fonctionnement de moteurs thermoacoustiques facilement généralisable à l'ensemble de ces systèmes, qu'ils soient à ondes stationnaires ou à ondes progressives. D'autre part, il est de proposer une approche expérimentale pour la caractérisation du noyau thermoacoustique (incluant le stack et la portion de guide inhomogène en température), qui permette de décrire le comportement de systèmes thermoacoustiques sans formuler d'hypothèses sur la forme du champ de température ou la géométrie du stack.Une modélisation analytique des conditions marginales de stabilité et du taux d'amplification de l'onde est tout d'abord proposée, basée sur l'écriture des matrices de transfert des différents éléments qui constituent le moteur. Ces matrices de transfert associées aux conditions aux limites du système étudié conduisent à une équation caractéristique dont la forme dépend de la géométrie de moteur considérée. La solution de cette équation est une pulsation acoustique complexe dont la partie imaginaire correspond au coefficient d'amplification thermoacoustique.La mesure de la matrice de transfert du noyau thermoacoustique constitue la partie expérimentale des travaux exposés. Elle est réalisée pour différentes conditions de chauffage au moyen d'une méthode à quatre microphones. Dans un premier temps, les résultats expérimentaux sont introduits dans le modèle développé précedemment pour prédire le seuil de déclenchement de divers moteurs thermoacoustiques équipés de ce noyau. Les résultats obtenus grâce à cette méthode sont très proches des observations expérimentales, validant ainsi le banc de mesure et le modèle décrivant les conditions de stabilité. Dans un second temps, les données expérimentales sont utilisées pour affiner un modèle analytique décrivant les mécanismes couplés de propagation acoustique et de transport de la chaleur dans le noyau thermoacoustique : ceci permet notamment d'ajuster les valeurs de paramètres acoustiques et thermiques au moyen d'une méthode inverse.Au-delà du seuil de déclenchement, l'amplification et la saturation de l'onde résultent pour une bonne part du transport de chaleur thermoacoustique et de la convection forcée liée à la génération d'un écoulement redressé (vent acoustique), ces deux mécanismes étant généralement responsables d'une dynamique d'évolution complexe de l'amplitude de pression acoustique au cours du régime transitoire. La dernière partie de ces travaux est consacrée à l'introduction de ces deux effets dans le modèle décrit ci-avant, donnant ainsi accès à la description du régime transitoire de l'onde. Une modélisation simplifiée des transports de chaleur associés au vent acoustique de Rayleigh est notamment proposée, qui permet de montrer que cet effet joue vraisemblablement un rôle important dans la dynamique des régimes transitoires observés expérimentalement dans un générateur thermoacoustique quart d'onde.

La sensibilité des méthodes acoustiques non-linéaires à la présence ainsi qu'à l'évolution des microendommagements a été prouvée dans différents travaux sur une large gamme de matériaux. Parmi les méthodes appliquées figure la résonance non-linéaire dont la sensibilité à l'endommagement est prouvée pour un seul mode de vibration à travers la décroissance de la fréquence de résonance ƒ et celle facteur de qualité Q en fonction de la déformation dynamique. Ainsi, les paramètres non-linéaires hystérétiques (NLH) ƒ et Q ne sont connus que dans une gamme fréquentielle réduite. Le présent travail de thèse propose l'utilisation d'une approche originale permettant de suivre la dispersion des paramètres ƒ et Q à travers la génération d'ondes guidées dans des plaques en composites à matrices polymère et métallique. De plus, l'approche en ondes guidées a également permis de définir un nouveau paramètre NLH V liée au mode de Lamb A0. L'un des résultats originaux de ce travail est que le rapport V/ƒ s'avère constant (~ 2) quelle que soit la fréquence considérée et ce pour les deux types de composites. Ce résultat prometteur montre pour la première fois qu'il est possible de généraliser le comportement NLH dans les structures en plaques moyennant le formalisme de Lamb. Finalement, le travail de thèse s'est également intéressé à la définition d'un nouveau paramètre NLH large bande, noté ∆S, afin de suivre la sensibilité du spectre de vibration à l'endommagement. Les mesures ont montré que ∆S pouvait se distinguer de par une réponse pouvant être nonlinéaire dès les premiers niveaux d'excitation ou à partir d'un niveau seuil. Ce résultat très prometteur montre à quel point il est important d'élargir le domaine fréquentiel pour une détection précoce de l'endommagement et ce même à des niveaux d'excitation où l'on croyait le matériau se comporter de façon linéaire.

碩士
淡江大學
教育科技學系
89
The purpose of the study is to design and develop a web-based prototype courseware on optical refraction by ISD model. The Guided Discovery Learning Theory is the main instructional strategy used in the study. It is expected to increase student’s ability about thinking and understanding of nature phenomenon. The foundation of instructional strategy in the study is to use different kinds of scientific representation to help students realize the meaning of refraction equation. Through the example that reveals misconception, students are guided to understand the relation between optical refraction and image formation. We not only try to make students realize the reason about what causes optical refraction, but also expect them to explain the reason of nature phenomenon such as mirage and rainbow with previously learn concepts. The development of the online learning material was based on ISD model, including analysis, design, development and evaluation, and formative evaluation. The process helps control every step of development to make sure the system is not out of our original design. Finally, this research offers personal conclusions and recommendations about developing online learning material for future related research.

碩士
國立彰化師範大學
科學教育研究所
106
This study aimed to use action research to carry out guided inquiry instruction in one 10 grader physics class in Malaysia, and explored the difficulties encountered in the implementation of inquiry teaching and the strategies for improvement by means of action research. In addition, researcher wanted to report the changes of students' motivation to physics, the learning of physics concept and understanding of students' view of scientific inquiry. One-year inquiry teaching were implemented in a class with 8 students, which was conducted in three stages. Preparation stage: The stage of pre-research in inquiry teaching (observation period, second stage: the first and second stages of teaching in the development period, the third stage: the stage of data analysis and writing of papers. Data collection included classroom video and sound recording, teachers' diary, SMTSL, scientific inquiry viewpoint questionnaire (VASI) and physics concept map before and after the test, as well as interview and worksheets. Finding indicated that the three problems faced in the action research are: The study object is not suitable for group cooperative learning, simulation experiment cannot arouse students' interest; and inquiry learning is closed only in the initial stage of inquiry teaching. Solutions were: to replace the open questions in the worksheets so that the students can freely play to answer, and to increase the hands-on experimental activities and each student has one’s duty to take to facilitate the cooperative learning. After the study, students' motivation in scientific learning show that their self-efficacy, value of scientific learning, performance goal, achievement goal and learning environment stimulation increased significantly. Students’ view of scientific inquiry increased significantly in the constructs of“There is no single set or sequence of steps followed in all investigations”」、“Inquiry procedures are guided by the question asked”and “Research conclusions must be consistent with the data collected”.Finally students’ concept mapping measurement increased significantly after the inquiry-based instruction.

A tenet of modern radiotherapy (RT) is to identify the treatment target accurately, following which the high-dose treatment volume may be expanded into the surrounding tissues in order to create the clinical and planning target volumes. Respiratory motion can induce errors in target volume delineation and dose delivery in radiation therapy for thoracic and abdominal cancers. Historically, radiotherapy treatment planning in the thoracic and abdominal regions has used 2D or 3D images acquired under uncoached free-breathing conditions, irrespective of whether the target tumor is moving or not. Once the gross target volume has been delineated, standard margins are commonly added in order to account for motion. However, the generic margins do not usually take the target motion trajectory into consideration. That may lead to under- or over-estimate motion with subsequent risk of missing the target during treatment or irradiating excessive normal tissue. That introduces systematic errors into treatment planning and delivery. In clinical practice, four-dimensional (4D) imaging has been popular in For RT motion management. It provides temporal information about tumor and organ at risk motion, and it permits patient-specific treatment planning. The most common contemporary imaging technique for identifying tumor motion is 4D computed tomography (4D-CT). However, CT has poor soft tissue contrast and it induce ionizing radiation hazard. In the last decade, 4D magnetic resonance imaging (4D-MRI) has become an emerging tool to image respiratory motion, especially in the abdomen, because of the superior soft-tissue contrast. Recently, several 4D-MRI techniques have been proposed, including prospective and retrospective approaches. Nevertheless, 4D-MRI techniques are faced with several challenges: 1) suboptimal and inconsistent tumor contrast with large inter-patient variation; 2) relatively low temporal-spatial resolution; 3) it lacks a reliable respiratory surrogate. In this research work, novel 4D-MRI techniques applying MRI weightings that was not used in existing 4D-MRI techniques, including T2/T1-weighted, T2-weighted and Diffusion-weighted MRI were investigated. A result-driven phase retrospective sorting method was proposed, and it was applied to image space as well as k-space of MR imaging. Novel image-based respiratory surrogates were developed, improved and evaluated.

Dissertation

Modern image guided radiation therapy involves the use of an isocentrically mounted imaging system to take radiographs of a patient's position before the start of each treatment. Image guidance helps to minimize errors associated with a patients setup, but the radiation dose received by patients from imaging must be managed to ensure no additional risks. The Varian On-Board Imager (OBI) (Varian Medical Systems, Inc., Palo Alto, CA) does not have an automatic exposure control system and therefore requires exposure factors to be manually selected. Without patient specific exposure factors, images may become saturated and require multiple unnecessary exposures. A software based automatic exposure control system has been developed to predict optimal, patient specific exposure factors. The OBI system was modelled in terms of the x-ray tube output and detector response in order to calculate the level of detector saturation for any exposure situation. Digitally reconstructed radiographs are produced via ray-tracing through the patients' volumetric datasets that are acquired for treatment planning. The ray-trace determines the attenuation of the patient and subsequent x-ray spectra incident on the imaging detector. The resulting spectra are used in the detector response model to determine the exposure levels required to minimize detector saturation. Images calculated for various phantoms showed good agreement with the images that were acquired on the OBI. Overall, regions of detector saturation were accurately predicted and the detector response for non-saturated regions in images of an anthropomorphic phantom were calculated to generally be within 5 to 10 % of the measured values. Calculations were performed on patient data and found similar results as the phantom images, with the calculated images being able to determine detector saturation with close agreement to images that were acquired during treatment. Overall, it was shown that the system model and calculation method could potentially be used to predict patients' exposure factors before their treatment begins, thus preventing the need for multiple exposures.
Graduate
0760
0574
0756

Structural Health Monitoring (SHM) systems for future structures and vehicles would involve a process of damage identification and prediction of certain quantities of interest that concerns the function and safety. This process provides SHM systems the ability to not only save cost but also enhance the service life, safety and reliability of the structures and vehicles. Integrated SHM system (ISHM) is an advancement of SHM system that has additional capability of predicting the component life/failure. ISHM system development involves detailed understanding of diagnostic waves, hardware components, signal processing paradigms and intelligent use of algorithms. Diagnostic waves like the guided waves are the elastic waves that propagate in a direction defined by the material boundaries. These waves have the capability of traveling large distance probing the entire thickness in plates/shells. Thus, they are widely used by SHM systems in monitoring the plate structures. Piezoelectric transducers are often employed in the interrogation using guided waves. Most SHM systems employing guided waves are designed for specific structures. Current paradigms of SHM systems are unable to enable the transition from simple or ideal structures to realistic and complicated structures. This is due to the challenges at the fundamental level involving transducer, wave propagation and phenomena of guided wave scattering with damages to evaluate the possible solutions through mathematical modeling and signal analysis capability required by ISHM systems. This thesis aims to develop understanding of these problems at a fundamental level. Complex system level understanding is still needed which is left out as open problem. A primary requirement in designing SHM system is the proper understanding of wave characteristics such as number of modes, wavelength and dispersiveness. Although three-dimensional elasticity solution and simplified theories are available to understand them, their applicability in SHM problem requires a much more detailed look. Effort toward this direction has led to the development of simpler models. However, mathematical models are not available for understanding the wave characteristics in complex structures involving stiffeners and adhesive joints. This problem is addressed in this thesis. There is a fair amount of understanding developed regarding transducer characteristics. This is accomplished by analytical and finite element models of transducers in the past. However, simplified transducer model that are computationally fast to suit SHM system requirements needs to be developed. The development of such model is presented in this thesis. Apart from modeling the transducers and wave scattering due to damage, signal correlation and calibration are needed for practical implementation in SHM. Characterization studies reported in published literature are limited to quasi-static and low frequencies applications. However, SHM of aerospace structures employ guided waves typically in the frequency range of 100-500 kHz. Methods to characterize the transducers at this frequency range needs to be developed, which is addressed in this thesis. Another major requirement of SHM system is the design and development of sensor-actuator network and appropriate algorithm. Techniques developed earlier involving transducer arrays in this regard have limitation due to complexity of geometry and signal interpretation that needs to be addressed. The network with suitable algorithm should ideally monitor large area including the critical areas of failure with minimum number of transducers. ISHM systems further require some capability to estimate the useful life of the damaged structure in order to take suitable decisions. Efficient techniques to achieve these are not developed. Overall, there is a need to improve highly interdisciplinary areas involving mathematical modeling, transducer design, fabrication and characterization, damage detection and monitoring strategies. In this thesis, various novel techniques to combine mathematical model with experimental signals to enhance the damage detection capability are presented. In this thesis, developments in the three main aspects of SHM systems are focused upon. They are (1) development of mathematical models of sensors/actuators, wave propagation and scattering due to damage (2) characterization and calibration of transducers and (3) development of technique to monitor wide variety of damages within the scope of ultrasonic guided wave based SHM. The thesis comprises of ten chapters. First chapter is devoted to the background and motivation for the problem addressed in this thesis. In second chapter, brief overview of available mathematical models and conventional damage monitoring strategy is presented. The significant contributions reported in the subsequent chapters in this thesis are outlined below In chapter 3, a reduced-order model of guided wave propagation in thick structures with reduced-order approximation of higher-order elasto-dynamic field is formulated. The surface normal and shear tractions of the thick structure are satisfied in a closed form. The time-frequency Fourier spectral finite element is developed and is validated using detailed and computationally intensive finite element simulations. Natural frequencies obtained from the developed spectral finite element and the detailed finite element simulations are compared. Transient response due to broad frequency band and narrow frequency band excitations given in the form of surface tractions are validated by comparing with the detailed finite element simulations. Using the developed spectral finite element, wave scattering from a free edge and a notch are simulated and validated by comparing with the detailed finite element simulations. In chapter 4, two-dimensional plane wave and flexural wave scattering models for more complicated features such as stiffener with delamination and stiffener with bolt failures in a stiffened panel are derived using ultrasonic ray tracing based approach combined with wave-field representation. Dispersion relations are reformulated for the base plate where it is bolted with the stiffener. Surface conditions due to contact stiffness and contact damping are modeled by introducing springs and dampers. Scattering coefficients for the bonded and bolted stiffeners are derived. The scattering coefficients are evaluated for various different frequencies. Results are compared for different stiffener parameters. In chapter 5, a simplified analytical model of a piezoelectric actuator with uniform electrodes is modeled. The problem is to determine the launched guided wave characteristics in the structure. The analytical model is derived considering two-dimensional elasticity based approach and Airy’s stress function. The actuator model is used to specify the displacement boundary conditions in the detailed finite element model. The radiated wave patterns in a plate due to actuation from transducers of different shapes are obtained and validated with experiments. Phased array actuators are modeled in the detailed finite element model using the displacements estimated from the actuator model. The radiated wave pattern from the detailed finite element simulations are validated with experiments. Chapter 6 is devoted to the design and characterization of transducers for ultrasonic guided wave applications. The characterization techniques involve the estimation of voltage response for the induced strain by the guided wave at various different frequencies. First, a novel removable bonding technique and a calibration technique are demonstrated and related advantages are discussed. Performance of the piezoelectric thin film under quasi-static, dynamic and transient impact loadings are analyzed first. Next, a guided wave technique is developed to characterize piezoelectric thin film sensors and actuators at ultrasonic frequencies. The transducers with inter digital electrodes are characterized for frequency tuning and directional sensitivity. This characterization study enables in the selection of optimal frequency bands for interrogation. Further, the characterization of transducers with thermal degradation is presented. In chapter 7, a novel guided wave technique to calibrate the thin film sensors for ultrasonic applications is presented. Calibration procedure involves the estimation of the piezoelectric coefficient at ultrasonic range of frequencies. Calibration is done by the measurement of voltage generated across thin films when guided waves are induced on them. With the proposed technique, piezoelectric coefficient can be estimated accurately at any frequency of the propagating wave. Similarly, the measurement of piezoelectric coefficient of thin films with inter digital electrodes is presented. The estimation of piezoelectric coefficient at various different directions using laser Doppler vibrometer is presented. Lastly, the degradation of piezoelectric coefficient is studied for increasing thermal fatigue. In chapter 8, toward SHM methodology development, a guided wave based technique to detect and monitor cracks in a structure is presented. To establish the methodology, a detailed study is carried out on the effect of crack and specimen size on the guided wave propagation characteristics. Using the wave characteristics, an analytical way of modeling Lamb wave propagation in the specimen with plastic zone is proposed. The feasibility to determine plastic zone and fatigue crack propagation with integrated piezoelectric transducers is demonstrated experimentally and the results are verified analytically. A method is further established to detect damage at initial stage and crack-tip plastic zone size along with crack length for a given stress amplitude or vice-versa. An approach to estimate fatigue life from the transducer signals is also proposed. In chapter 9, a compact circular array of sensor-actuator network and an algorithm is presented to monitor large plate structures. A method based on the wavelet transforms of transducer signals is established to localize and estimate the severity of damages. Experiments are conducted to demonstrate the capability of the circular array based method in the localization and quantification of various types of damages like debonding of stiffeners, failure of bolted joints, corrosion and hole-enlargement. A damage index is then computed from wavelet time-frequency map that indicates the severity of damage. Chapter 10 ends with the concluding remarks on the work done with simultaneous discussion on the future scope. The work reported in this thesis is interdisciplinary in nature and it aims to combine the modeling and simulation techniques with realistic data in SHM to impart higher confidence levels in the prediction of damages and its prognosis. The work also aims in incorporating various mathematical models of wave propagation and ray tracing based algorithm to optimize the detection scheme employed in SHM. The future direction based on this study could be aimed at developing intelligent SHM systems with high confidence levels so that statistical machine learning would be possible to deal with complex real-world SHM problems.

Structural Health Monitoring (SHM) systems for future structures and vehicles would involve a process of damage identification and prediction of certain quantities of interest that concerns the function and safety. This process provides SHM systems the ability to not only save cost but also enhance the service life, safety and reliability of the structures and vehicles. Integrated SHM system (ISHM) is an advancement of SHM system that has additional capability of predicting the component life/failure. ISHM system development involves detailed understanding of diagnostic waves, hardware components, signal processing paradigms and intelligent use of algorithms. Diagnostic waves like the guided waves are the elastic waves that propagate in a direction defined by the material boundaries. These waves have the capability of traveling large distance probing the entire thickness in plates/shells. Thus, they are widely used by SHM systems in monitoring the plate structures. Piezoelectric transducers are often employed in the interrogation using guided waves. Most SHM systems employing guided waves are designed for specific structures. Current paradigms of SHM systems are unable to enable the transition from simple or ideal structures to realistic and complicated structures. This is due to the challenges at the fundamental level involving transducer, wave propagation and phenomena of guided wave scattering with damages to evaluate the possible solutions through mathematical modeling and signal analysis capability required by ISHM systems. This thesis aims to develop understanding of these problems at a fundamental level. Complex system level understanding is still needed which is left out as open problem. A primary requirement in designing SHM system is the proper understanding of wave characteristics such as number of modes, wavelength and dispersiveness. Although three-dimensional elasticity solution and simplified theories are available to understand them, their applicability in SHM problem requires a much more detailed look. Effort toward this direction has led to the development of simpler models. However, mathematical models are not available for understanding the wave characteristics in complex structures involving stiffeners and adhesive joints. This problem is addressed in this thesis. There is a fair amount of understanding developed regarding transducer characteristics. This is accomplished by analytical and finite element models of transducers in the past. However, simplified transducer model that are computationally fast to suit SHM system requirements needs to be developed. The development of such model is presented in this thesis. Apart from modeling the transducers and wave scattering due to damage, signal correlation and calibration are needed for practical implementation in SHM. Characterization studies reported in published literature are limited to quasi-static and low frequencies applications. However, SHM of aerospace structures employ guided waves typically in the frequency range of 100-500 kHz. Methods to characterize the transducers at this frequency range needs to be developed, which is addressed in this thesis. Another major requirement of SHM system is the design and development of sensor-actuator network and appropriate algorithm. Techniques developed earlier involving transducer arrays in this regard have limitation due to complexity of geometry and signal interpretation that needs to be addressed. The network with suitable algorithm should ideally monitor large area including the critical areas of failure with minimum number of transducers. ISHM systems further require some capability to estimate the useful life of the damaged structure in order to take suitable decisions. Efficient techniques to achieve these are not developed. Overall, there is a need to improve highly interdisciplinary areas involving mathematical modeling, transducer design, fabrication and characterization, damage detection and monitoring strategies. In this thesis, various novel techniques to combine mathematical model with experimental signals to enhance the damage detection capability are presented. In this thesis, developments in the three main aspects of SHM systems are focused upon. They are (1) development of mathematical models of sensors/actuators, wave propagation and scattering due to damage (2) characterization and calibration of transducers and (3) development of technique to monitor wide variety of damages within the scope of ultrasonic guided wave based SHM. The thesis comprises of ten chapters. First chapter is devoted to the background and motivation for the problem addressed in this thesis. In second chapter, brief overview of available mathematical models and conventional damage monitoring strategy is presented. The significant contributions reported in the subsequent chapters in this thesis are outlined below In chapter 3, a reduced-order model of guided wave propagation in thick structures with reduced-order approximation of higher-order elasto-dynamic field is formulated. The surface normal and shear tractions of the thick structure are satisfied in a closed form. The time-frequency Fourier spectral finite element is developed and is validated using detailed and computationally intensive finite element simulations. Natural frequencies obtained from the developed spectral finite element and the detailed finite element simulations are compared. Transient response due to broad frequency band and narrow frequency band excitations given in the form of surface tractions are validated by comparing with the detailed finite element simulations. Using the developed spectral finite element, wave scattering from a free edge and a notch are simulated and validated by comparing with the detailed finite element simulations. In chapter 4, two-dimensional plane wave and flexural wave scattering models for more complicated features such as stiffener with delamination and stiffener with bolt failures in a stiffened panel are derived using ultrasonic ray tracing based approach combined with wave-field representation. Dispersion relations are reformulated for the base plate where it is bolted with the stiffener. Surface conditions due to contact stiffness and contact damping are modeled by introducing springs and dampers. Scattering coefficients for the bonded and bolted stiffeners are derived. The scattering coefficients are evaluated for various different frequencies. Results are compared for different stiffener parameters. In chapter 5, a simplified analytical model of a piezoelectric actuator with uniform electrodes is modeled. The problem is to determine the launched guided wave characteristics in the structure. The analytical model is derived considering two-dimensional elasticity based approach and Airy’s stress function. The actuator model is used to specify the displacement boundary conditions in the detailed finite element model. The radiated wave patterns in a plate due to actuation from transducers of different shapes are obtained and validated with experiments. Phased array actuators are modeled in the detailed finite element model using the displacements estimated from the actuator model. The radiated wave pattern from the detailed finite element simulations are validated with experiments. Chapter 6 is devoted to the design and characterization of transducers for ultrasonic guided wave applications. The characterization techniques involve the estimation of voltage response for the induced strain by the guided wave at various different frequencies. First, a novel removable bonding technique and a calibration technique are demonstrated and related advantages are discussed. Performance of the piezoelectric thin film under quasi-static, dynamic and transient impact loadings are analyzed first. Next, a guided wave technique is developed to characterize piezoelectric thin film sensors and actuators at ultrasonic frequencies. The transducers with inter digital electrodes are characterized for frequency tuning and directional sensitivity. This characterization study enables in the selection of optimal frequency bands for interrogation. Further, the characterization of transducers with thermal degradation is presented. In chapter 7, a novel guided wave technique to calibrate the thin film sensors for ultrasonic applications is presented. Calibration procedure involves the estimation of the piezoelectric coefficient at ultrasonic range of frequencies. Calibration is done by the measurement of voltage generated across thin films when guided waves are induced on them. With the proposed technique, piezoelectric coefficient can be estimated accurately at any frequency of the propagating wave. Similarly, the measurement of piezoelectric coefficient of thin films with inter digital electrodes is presented. The estimation of piezoelectric coefficient at various different directions using laser Doppler vibrometer is presented. Lastly, the degradation of piezoelectric coefficient is studied for increasing thermal fatigue. In chapter 8, toward SHM methodology development, a guided wave based technique to detect and monitor cracks in a structure is presented. To establish the methodology, a detailed study is carried out on the effect of crack and specimen size on the guided wave propagation characteristics. Using the wave characteristics, an analytical way of modeling Lamb wave propagation in the specimen with plastic zone is proposed. The feasibility to determine plastic zone and fatigue crack propagation with integrated piezoelectric transducers is demonstrated experimentally and the results are verified analytically. A method is further established to detect damage at initial stage and crack-tip plastic zone size along with crack length for a given stress amplitude or vice-versa. An approach to estimate fatigue life from the transducer signals is also proposed. In chapter 9, a compact circular array of sensor-actuator network and an algorithm is presented to monitor large plate structures. A method based on the wavelet transforms of transducer signals is established to localize and estimate the severity of damages. Experiments are conducted to demonstrate the capability of the circular array based method in the localization and quantification of various types of damages like debonding of stiffeners, failure of bolted joints, corrosion and hole-enlargement. A damage index is then computed from wavelet time-frequency map that indicates the severity of damage. Chapter 10 ends with the concluding remarks on the work done with simultaneous discussion on the future scope. The work reported in this thesis is interdisciplinary in nature and it aims to combine the modeling and simulation techniques with realistic data in SHM to impart higher confidence levels in the prediction of damages and its prognosis. The work also aims in incorporating various mathematical models of wave propagation and ray tracing based algorithm to optimize the detection scheme employed in SHM. The future direction based on this study could be aimed at developing intelligent SHM systems with high confidence levels so that statistical machine learning would be possible to deal with complex real-world SHM problems.

This dissertation describes a proof-of-principle experiment demonstrating a technique for stable isotope enrichment called Magnetically Activated and Guided Isotope Separation (MAGIS) (1). Over the past century a large number of enriched isotopes have become available, thanks largely to electromagnetic separators called calutrons that were developed during World War II. These isotopes have found applications across an array of fields including medicine, basic science, and energy. Due to substantial maintenance and operating costs, the United States decommissioned the last of its calutrons in 1998, leading to demand for alternative methods of isotope separation. Our experiment suggests the promise for MAGIS as a viable alternative for replenishing stockpiles previously provided by calutrons. Our apparatus combines optical pumping with a scalable magnetic field gradient to enrich lithium-7 (Li-7) by suppressing lithium-6 (Li-6) throughput in a lithium atomic beam. We first evaporate lithium metal in a crucible in order to generate thermal, high flux beam. We then perform optical pumping on Li-6 atoms, magnetically polarizing a substantial fraction of Li-6 atoms into the entirely high-field seeking 2²S₁/₂, F = 1/2 ground state. The resultant beam then samples a magnetic field gradient produced by a 1.5 m long array of rare-earth permanent magnets bent over its length by 20 mrad. This geometry prevents high-field seeking lithium atoms from reaching the plane beyond the magnets, while efficiently deflecting low-field seeking atoms. We measured Li-6 suppression – using independent techniques – along the plane after the magnets beyond a factor of 200, corresponding to Li-7 enrichment to better than 99.95%. As apparatus-specific hindrances appeared to limit this suppression, we believe that we should achieve better enrichment on a commercial apparatus. We also measured both the absolute flux beyond the single, 1.5 in tall magnet array and the efficiency for guiding feedstock material to the collection plane. Given the planar configuration for the field gradient, the flux that we measured should scale linearly with both magnet height and the number of arrays surrounding the source. Our measurements therefore indicate that – at source temperatures that we actually investigated – a commercial apparatus fitting within a volume of just several cubic meters should yield hundreds of grams of enriched (to beyond 99.95%) Li-7 per year. In addition, we observed a competitive ratio between collected material and feedstock with greater than 20% of lithium incident upon the magnet array reaching beyond the magnets. Benchmarking our work against the calutron, we demonstrated comparable enrichment in a manner that should scale to the production of similar quantities. In contrast, however, MAGIS should require vastly less energy input. While calutrons required massive currents for maintaining a static magnetic field over a substantial area, the only non-shared energy expense for MAGIS is the cost for running the low power lasers for optical pumping. Via additional analysis, we have supplemented this proof-of-principle experiment with schemes for applying MAGIS to over half of the stable isotopes in the periodic table. Due to the success of this demonstration and the broad applicability of the principles, we believe that MAGIS will play an important role in the future of stable isotope enrichment.
text

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.
Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7382. Adviser: Henrique Reis. Includes bibliographical references (leaves 314-326) Available on microfilm from Pro Quest Information and Learning.

Le but principal de ce projet est de préparer l’implantation clinique du système Clarity qui utilise une sonde ultrasonore pour visualiser l’anatomie interne du patient. Ce système est utilisé pour les cas de prostate et nécessite d’être adapté pour les cas de poumon. L’utilité de ce système est de suivre un substitut afin d’inférer la position d’une tumeur pulmonaire. L’hypothèse de cette étude est qu’un substitut interne serait mieux corrélé avec une tumeur pulmonaire que le seraient des marqueurs externes. Les sous-objectifs sont : 1) aborder l’adaptation du montage pour faire des acquisitions sur des patients ; 2) explorer la performance des algorithmes de détection de mouvements ainsi que des métriques de qualité d’image sur des images US et ciné IRM; 3) démontrer que la corrélation entre un substitut interne et une structure pulmonaire est plus grande que celle avec un substitut externe. Pour les acquisitions d’images US, la sonde est placée sur les volontaires et fixée à la table de traitement à l’aide d’un bras mécanique. Il a été démontré qu’une pression insuffisante peut causer une perte de signal dû à la forme curviligne de la sonde. La diminution de la moyenne des intensités de l’image et de l’écart-type confirme une perte de signal lors d’amplitudes respiratoires élevées justifiée par une perte de contact entre la sonde et la peau malgré la fixation de la sonde. Entre les algorithmes de corrélation croisée normalisée (NCC), d’erreur moyenne quadratique (RMS) et de flux optique, la méthode NCC semble la plus robuste pour suivre le substitut interne (structure dans le foie) dans les images IRM pour 5/9 volontaires sains ( = 0, 050). Cette méthode est utilisé présentement pour les cas de prostate. Le flux optique s’est montré plus efficace pour des cas spécifiques ce qui démontre l’intérêt d’adapter l’algorithme pour les cas de poumons. Enfin, il a été démontré sur les images IRM qu’un substitut interne au niveau du foie est plus efficace pour la majorité des volontaires (8/9) en comparaison avec un marqueur sur la peau placé dans la région abdominale. Le marqueur abdominal possède une meilleure corrélation qu’un marqueur thoracique (9/9) illustrant l’importance du positionnement d’un marqueur externe pour le suivi d’une tumeur pulmonaire.
The main objective of this thesis is to prepare the clinical implementation of the Clarity ultrasound system for indirect lung tumours tracking using a surrogate. It is currently used for motion management during prostate treatments and requires adaptation. Our hypothesis is that an internal marker would have a better correlation with the tumour’s position than an external surrogate. The sub-objectives are : 1) test different setups for the image acquisition on patients ; 2) explore the algorithms’ performance for motion detection as well as the image quality metrics on US and dynamic MRI images ; 3) evaluate the correlation between surrogates and a lung structure to determine which performs best. The ultrasound probe is fixed on the treatment couch for the acquisition on healthy volunteers using a mechanical arm. Low pressure on the patient’s skin results in a loss of signal due to the curvilinear shape of the probe. We observed a loss of contact between the probe and the volunteers’ skin due to ample movements causing a deterioration of the image quality. We tested three different motion detection algorithms on dynamic MRI images : normalized cross-correlation (NCC), root mean square error (RMS) and optical flow. The NCC algorithm is the most robust out of the three for 5/9 volunteers for the internal surrogate tracking ( < 0.050). In specific cases, the optical flow method performed better indicating an interest in developping a new algorithm for indirect lung tracking. Finally, the correlation between the surrogates and a lung structure were calculated using the MRI images. The internal surrogate inside the liver was proven more efficient for indirect lung tumour tracking for 8/9 volunteers. External markers give a greater prediction error. It has also been shown that the positioning of the external marker on the patient’s skin impacts the correlation. The abdominal marker is better than the thoracic one for all the volunteers.

The majority of bacteria are organized in surface-associated communities, the so called biofilms. Crucial processes that drive the formation of such biofilms are the motility of bacteria on a substrate, enabling cells to reach each others vicinity, and attractive cell-cell-interactions, driving the formation of microcolonies. These colonies, aggregates consisting of thousands of cells, are the precursors of biofilms. In this thesis we investigate the role of cell appendages, called type IV pili, in the substrate motion of bacteria and the formation of bacterial microcolonies. Therefore, we study the bacterial dynamics with the help of experiments and theoretical models. We introduce a novel simulation tool in the tradition of Brownian dynamics simulations. In this computational model, that was developed alongside experimental observations, we study how explicit pili dynamics, pili-substrate and pili–pili interactions drive the cell dynamics. First, we apply our model to investigate how individual cells move on a substrate due to cycles of protrusion and retraction of type IV pili. We show that the characteristic features, in particular persistent motion, can solely originate from collective interactions of pili. Next, we perform experiments to study the coalescence of bacterial microcolonies. With the help of experiments and our computational model, we identify a spatially-dependent gradient of motility of cells within the colony as the origin of a separation of time scale, a feature which is in disagreement with the coalescence dynamics of fluid droplets. Additionally, we show that altering the force generation of pili can cause demixing of cells within bacterial aggregates. Finally, we combine our knowledge of the substrate motion of cells and of the pili-mediated interactions of colonies to identify the main processes (aggregation, fragmentation and cell divisions) that drive assembly of colonies. Starting from experiments, we develop a mathematical model and observe excellent qualitative and quantitative agreement to experimental data of the density of colonies of different sizes. In summary, hand in hand with experiments, we develop theoretical frameworks to unravel the role of type IV pili in bacterial surface motility, microcolony dynamics and colony formation.:1. Introduction 2. Computational model of bacterial motility and mechanics 3. Motility of single bacteria on a substrate 4. Coalescence and internal dynamics of bacterial microcolonies 5. Demixing of bacterial microcolonies 6. Self-assembly of microcolonies 7. Summary and Outlook A. Details of the Simulation model B. Experimental protocols C. Geometric estimation of the parameters of the stochastic model D. Solutions for simplified models of pili-mediated cell motion E. Image analysis of experimental data F. Simulations and data analysis G. The mean squared relative distance (MSRD)

Image guided radiation therapy (IGRT) is a new type of radiotherapy used to deliver lethal doses of radiation to mobile tumors, while preventing surrounding healthy structures from receiving high doses of radiation. It relies on image guidance to track the tumor and ensure its prescribed position in the radiation beam. The main goal of this work was to determine if a new three-dimensional ultrasound (3D US) image guidance device, called the Restitu System, could safely replace (or be used interchangeably with) an existing method involving x-ray images of implanted fiducial markers (FMs) for prostate IGRT. Using comparison statistics called 95 % limits of agreement (LOA), it was found that the new 3D US system did not produce measurements that agreed sufficiently closely to those made using the FM technique, and therefore, could not safely replace FMs for prostate IGRT. Ultrasound image quality and user variability were determined to have a significant impact on the agreement between the two methods. It was further shown that using the Restitu System offered no significant clinical advantages over a conventional patient re-positioning technique.