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Renaud, Marc-André. "Pre-calculated track Monte Carlo dose calculation engine." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121295.
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Modern treatment planning techniques such as inverse planning have increased the demand for rapid dose calculation methods to accommodate the large number of dose distributions required to generate a treatment plan. General-purpose Monte Carlo approaches for dose calculation are known to offer the highest accuracy in dose calculation at the expense of significant computing time. This work adapts a Macro Monte Carlo approach to dose calculation for electrons andprotons for use with a GPU card, using pre-generated tracks from general-purpose Monte Carlo codes. The algorithm was implemented on the CUDA framework for parallel programming on graphics cards. Comparisons of the algorithm inhomogeneous and inhomogeneous geometry with benchmark Monte Carlo codes yielded agreements within 1% in dose regions of at least 50% of Dmax and up to 3% in low dose regions. A Bragg peak positioning error of less than 1 mm was also observed. Additionally, the limited memory available in commercial graphics cards was overcome by subdividing a mother track bank residing on CPU memory into smaller samples of unique tracks. A method to quantify the latent uncertainty in dose values due to the limited size of a pre-generated track bank was developed. It was shown that the latent uncertainty follows a Poisson distribution as a function of the total number of unique tracks in the track bank. The implementation of the algorithm was found to transport particles in sub-second times per million history for every situation simulated, with speed-ups of 500-2600x for electrons over DOSXYZnrc and 2600-11500x for protons over GEANT4 depending on the particle energies and simulation media.<br>Les techniques modernes de planification de traitement, telle que la planification inverse, ont augmenté la demande pour des méthodes rapides de calcul de dose pour accomoder le grand nombre de distributions de dose requises pour générer un plan de traitement. Les approches Monte Carlo d'usage général sont réputées pour offrir la plus haute précision au calcul de dose au détriment d'une demande plus élevée en temps de calcul. Cet oeuvre revisite une approche MonteCarlo macroscopique pour le calcul de dose avec électrons et protons en utilisant des traques pré-calculées à l'aide de codes Monte Carlo d'usage général. L'approche a été mise en oeuvre avec la plate-forme de programmation CUDA pour le programmage parallèle sur cartes graphiques. Des comparaisons de l'algorithme dans des phantômes homogènes et hétérogènes contre des codes Monte Carlo de référence ont démontré un accord de 1% et 1 mm ou mieux. En outre, les problèmes associés à la basse mémoire disponible dans les cartes graphiques commercial ont été surmontés à l'aide de la méthode de banque mère de traques pré-calculés. Une méthode pour quantifier l'incertitude latente dans les valeurs de dose dû au nombre limité de traques uniques dans la banque de traques a été développée. L'incertitude latente calculée suit une distribution de Poisson en fonction du nombre total de traques unique dans la banque de traques. Finalement, l'algorithme transporte tous les particules en moins d'une seconde pour chaque millions d'historiques dans chaque situation simulée. Un facteur d'accélération de 500-2600x pour le transport d'électrons comparé à DOSXYZnrc et 2600-11500x pour les protons comparé à GEANT4 a été observé, dépendamment de l'énergie des particules et de l'environnement dans lequel les particules sont transportées.
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Lee, Li-Chyn 1965. "Comparison of Monte Carlo and analytic critical area calculation." Thesis, The University of Arizona, 1992. http://hdl.handle.net/10150/278175.
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Since the profitability of VLSI industries is related to yield, the IC manufacturer finds it highly desirable to be able to predict the yield by computer-aided methods. A key part in the procedure to obtain yield by computer simulation is to find the critical area of a layout. This thesis is primarily devoted to the calculations of critical area. There are two techniques to find the critical area. In the first technique, an analytic method was used to analyze the circuit geometry in order to find the critical area. In the second technique a Monte Carlo Method is used. A program using this Monte Carlo yield simulation (the main method used in this thesis) has been developed for determining critical area of the metal layer of a 4K random access memory. The analytic method is used in a supporting way. The thesis also proposes an easy method to process the vast amount of layout database. This method reduces the time consumed by Monte Carlo simulation.
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Kawasaki, Kazunori Sturtevant Bradford. "Monte Carlo calculation of the flow of granular materials /." Diss., Pasadena, Calif. : California Institute of Technology, 1986. http://resolver.caltech.edu/CaltechETD:etd-11092007-110816.
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Engdahl, Staffan. "Validation of Ion Therepy Dose Calculation Algorithms by Monte Carlo." Thesis, KTH, Fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-170409.
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Khan, Nadeem. "Dosimetric Calculation of a Thermo Brachytherapy Seed: A Monte Carlo Study." Connect to full text in OhioLINK ETD Center, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=mco1228860927.
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Thesis (M.S.)--University of Toledo, 2008.<br>"In partial fulfillment of the requirements for the degree of Master of Science in Biomedical Sciences." Title from title page of PDF document. Bibliography: p. 153-155.
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Van, der Merwe Carel Johannes. "Calculation aspects of the European Rebalanced Basket Option using Monte Carlo methods." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/5190.
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Thesis (MComm (Statistics and Actuarial Science)--University of Stellenbosch, 2010.<br>ENGLISH ABSTRACT: Life insurance and pension funds offer a wide range of products that are invested in a mix of
assets. These portfolios (II), underlying the products, are rebalanced back to predetermined fixed
proportions on a regular basis. This is done by selling the better performing assets and buying the
worse performing assets. Life insurance or pension fund contracts can offer the client a minimum
payout guarantee on the contract by charging them an extra premium (a). This problem can be
changed to that of the pricing of a put option with underlying . It forms a liability for the insurance
firm, and therefore needs to be managed in terms of risks as well. This can be done by studying the
option’s sensitivities. In this thesis the premium and sensitivities of this put option are calculated,
using different Monte Carlo methods, in order to find the most efficient method.
Using general Monte Carlo methods, a simplistic pricing method is found which is refined by applying
mathematical techniques so that the computational time is reduced significantly. After considering
Antithetic Variables, Control Variates and Latin Hypercube Sampling as variance reduction techniques,
option prices as Control Variates prove to reduce the error of the refined method most
efficiently. This is improved by considering different Quasi-Monte Carlo techniques, namely Halton,
Faure, normal Sobol’ and other randomised Sobol’ sequences. Owen and Faure-Tezuke type
randomised Sobol’ sequences improved the convergence of the estimator the most efficiently. Furthermore,
the best methods between Pathwise Derivatives Estimates and Finite Difference Approximations
for estimating sensitivities of this option are found.
Therefore by using the refined pricing method with option prices as Control Variates together with
Owen and Faure-Tezuke type randomised Sobol’ sequences as a Quasi-Monte Carlo method, more
efficient methods to price this option (compared to simplistic Monte Carlo methods) are obtained.
In addition, more efficient sensitivity estimators are obtained to help manage risks.<br>AFRIKAANSE OPSOMMING: Lewensversekering en pensioenfondse bied die mark ’n wye reeks produkte wat belê word in ’n
mengsel van bates. Hierdie portefeuljes (II), onderliggend aan die produkte, word op ’n gereelde basis
terug herbalanseer volgens voorafbepaalde vaste proporsies. Dit word gedoen deur bates wat beter
opbrengste gehad het te verkoop, en bates met swakker opbrengste aan te koop. Lewensversekeringof
pensioenfondskontrakte kan ’n kliënt ’n verdere minimum uitbetaling aan die einde van die kontrak
waarborg deur ’n ekstra premie (a) op die kontrak te vra. Die probleem kan verander word
na die prysing van ’n verkoopopsie met onderliggende bate . Hierdie vorm deel van die versekeringsmaatskappy
se laste en moet dus ook bestuur word in terme van sy risiko’s. Dit kan gedoen
word deur die opsie se sensitiwiteite te bestudeer. In hierdie tesis word die premie en sensitiwiteite
van die verkoopopsie met behulp van verskillende Monte Carlo metodes bereken, om sodoende die
effektiefste metode te vind.
Deur die gebruik van algemene Monte Carlo metodes word ’n simplistiese prysingsmetode, wat verfyn
is met behulp van wiskundige tegnieke wat die berekeningstyd wesenlik verminder, gevind. Nadat
Antitetiese Veranderlikes, Kontrole Variate en Latynse Hiperkubus Steekproefneming as variansiereduksietegnieke
oorweeg is, word gevind dat die verfynde metode se fout die effektiefste verminder
met behulp van opsiepryse as Kontrole Variate. Dit word verbeter deur verskillende Quasi-Monte
Carlo tegnieke, naamlik Halton, Faure, normale Sobol’ en ander verewekansigde Sobol’ reekse, te
vergelyk. Die Owen en Faure-Tezuke tipe verewekansigde Sobol’ reeks verbeter die konvergensie van
die beramer die effektiefste. Verder is die beste metode tussen Baanafhanklike Afgeleide Beramers
en Eindige Differensie Benaderings om die sensitiwiteit vir die opsie te bepaal, ook gevind.
Deur dus die verfynde prysingsmetode met opsiepryse as Kontrole Variate, saam met Owen en
Faure-Tezuke tipe verewekansigde Sobol’ reekse as ’n Quasi-Monte Carlo metode te gebruik, word
meer effektiewe metodes om die opsie te prys, gevind (in vergelyking met simplistiese Monte Carlo
metodes). Verder is meer effektiewe sensitiwiteitsberamers as voorheen gevind wat gebruik kan word
om risiko’s te help bestuur.
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Fragoso, Margarida. "Application of Monte Carlo techniques for the calculation of accurate brachytherapy dose distributions." Thesis, Institute of Cancer Research (University Of London), 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413609.
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Johns, Dewi. "Radiotherapy dose calculation in oesophageal cancer : comparison of analytical and Monte Carlo methods." Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/105551/.
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In this work a distributed computing system (RTGrid) has been configured and deployed to provide a statistically robust comparison of Monte Carlo (MC) and analytical dose calculations. 52 clinical oesophageal radiotherapy plans were retrospectively re-calculated using the Pencil Beam Enhanced (PBE) and Collapsed Cone Enhanced (CCE) algorithm within the Oncentra v4.3 radiotherapy (RT) Treatment Planning System (TPS). Simulations were performed using the BEAMnrc and DOSXYZnrc codes. The Computing Environment for Radiotherapy Research (CERR) has been used to calculate Dose Volume Histogram (DVH) parameters such as the volume receiving 95% Dose for the Planning Target Volume (PTV) for the PBE, CCE and MC calculated dose distributions. An initial sample of 12 oesophageal radiotherapy treatment plans were simulated using the RTGrid system. The differences in the DVH parameters between the dose calculation methods, and the variance in the 12 cases, were used to calculate the sample size needed. The required sample size was determined to be 37, so a further 40 oesophageal cases were simulated, following the same method. The median difference in the PTV V95% between CCE and MC in the group of 40 cases was found to be 3%. To choose a suitable test for the statistical significance of the difference, the Shapiro-Wilk test was performed, which showed that the differences between the two sets of PTV V95% values did not follow a Gaussian. Therefore the Wilcoxon matched pairs test was indicated, which showed that the null hypothesis (i.e. that the distributions are the same) was rejected with a p-value less than 0.001, so there is very strong evidence for a difference in the two sets of values of PTV V95%. Similar statistical analyses were performed for other DVH parameters, as well as Conformance Indices used to describe the agreement between the 95% dose and the PTV, and estimates of the Tumour Control Probability (TCP). From the results, the use of MC simulations are recommended when non-soft tissue voxels make up > 60% of the PTV.
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Matsuyama, Akinobu. "Study on Monte-Carlo Calculation of Neoclassical Transport Matrix in Nonaxisymmetric Toroidal Plasmas." Kyoto University, 2010. http://hdl.handle.net/2433/120410.
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Heath, Emily C. "Evaluation of the PEREGRINE Monte Carlo dose calculation code for 6 MV photon beams." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=19418.
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The accuracy of conventional dose calculation algorithms employed in external photonbeam treatment planning is limited by their inability to fully model the radiation source andaccount for the electron fluence perturbations which occur in regions of non-uniform density.In this work, we evaluated the dosimetric accuracy of the PEREGRINE Monte Carlo dosecalculation code for 6 MV photons. Dose profiles calculated by PEREGRINE werecompared with measurements in homogeneous and heterogeneous phantoms. A comparisonof dose profiles calculated by PEREGRINE and the EGSnrc Monte Carlo code was alsoperformed. To fully model the Varian Millennium 120 leaf collimator, a new MLCcomponent module was developed for BEAMnrc.Overall, the agreement between PEREGRINE and measurements and EGSnrc is within1% with the exception of the buildup region, where the accuracy of the beam model isaffected by an artificially increased electron subsource weight, and for 30x30 cm2 fieldswhere the beam model does not accurately predict the off-axis fluence. A clinical comparisonof IMRT dose distributions calculated by PEREGRINE and the CORVUS pencil beamalgorithm indicates that the heterogeneity correction implemented in CORVUSunderestimates the dose received by sensitive structures, receiving up to 20% of theprescribed dose, which lie in the vicinity of low density tissues.
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Niklas, Palmqvist. "Volume calculation of the thyroid gland from SPECT images based on Monte Carlo simulations." Thesis, Umeå universitet, Institutionen för fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-147935.
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In this study the volume determination which is a part of the doseplanning for patients with thyrotoxicosis was investigated. The aim was to find an accurate method to determine the active volume with single photon emission tomography (SPECT) which in several studies have shown better results than with the currently used method planar scintigraphy (PS). This was implemented on the Xeleris 3.1 by General Electric (GE) at the University Hospital of Umeå (NUS). The examination time with SPECT is required not to be significantly longer than the examination time with PS. Despite the relatively short examination time, the accuracy of the volume determination should be more accurate. This was analyzed with a true value of the volume, conducted with Monte Carlo simulations of digital anthropomorphic phantoms. It is also important that the developed method is user friendly. The study included ten patients with thyrotoxicosis from which, relative activity uptakes were measured. These uptakes were specified in 22 digital XCAT phantoms which were random sampled with respect to phantom mass. The Monte Carlo program "simulating medical imaging nuclear detectors" (simind) was used to simulate the SPECT-system. The projection images were ordered subset expectation maximization (OSEM) reconstructed and Butterworth filtered. Unfiltered images were used to compare volume calculations with filtered ones. The volume of the thyroid was segmented using threshold values applied to all voxels in the image-sets and the optimization of the thresholds was conducted by numerical calculations. The results in this study shows that the best choice of intensity threshold value is 21.1(24)% of the maximum voxel value for all phantoms. The threshold is valid for OSEM iteration number five and unfiltered image-sets. Butterworth filtered images were less suitable to use than unfiltered images when the thyroid volume was calculated with data from SPECT-simulations of phantoms.
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Palmqvist, Niklas. "Volume calculation of the thyroid gland from SPECT images based on Monte Carlo simulations." Thesis, Umeå universitet, Radiofysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-147941.
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In this study the volume determination which is a part of the doseplanning for patients with thyrotoxicosis was investigated. The aim was to find an accurate method to determine the active volume with single photon emission tomography (SPECT) which in several studies have shown better results than with the currently used method planar scintigraphy (PS). This was implemented on the Xeleris 3.1 by General Electric (GE) at the University Hospital of Umeå (NUS). The examination time with SPECT is required not to be significantly longer than the examination time with PS. Despite the relatively short examination time, the accuracy of the volume determination should be more accurate. This was analyzed with a true value of the volume, conducted with Monte Carlo simulations of digital anthropomorphic phantoms. It is also important that the developed method is user friendly. The study included ten patients with thyrotoxicosis from which, relative activity uptakes were measured. These uptakes were specified in 22 digital XCAT phantoms which were random sampled with respect to phantom mass. The Monte Carlo program "simulating medical imaging nuclear detectors" (simind) was used to simulate the SPECT-system. The projection images were ordered subset expectation maximization (OSEM) reconstructed and Butterworth filtered. Unfiltered images were used to compare volume calculations with filtered ones. The volume of the thyroid was segmented using threshold values applied to all voxels in the image-sets and the optimization of the thresholds was conducted by numerical calculations. The results in this study shows that the best choice of intensity threshold value is 21.1(24)% of the maximum voxel value for all phantoms. The threshold is valid for OSEM iteration number five and unfiltered image-sets. Butterworth filtered images were less suitable to use than unfiltered images when the thyroid volume was calculated with data from SPECT-simulations of phantoms.
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Ishihara, Yoshitomo. "Development of a dose verification system for Vero4DRT using Monte Carlo method." Kyoto University, 2015. http://hdl.handle.net/2433/199186.
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Nielsen, Adam Derek. "Monte Carlo calculation of fluence-to-ambient dose equivalent conversion coefficients for high-energy neutrons." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/16424.
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Lagmago, Kamta Gérard. "Evaluation of Eclipse© Monte Carlo dose calculation for clinical electron beams using heterogeneous phantoms." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40817.
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Accurate dose calculations of photon and electron transport in tissue materials are an important step in the appropriate delivery of cancer radiotherapy. Various commercial treatment planning systems used in radiotherapy provide algorithms for fast dose calculations. It is the responsibility of medical physicists to commission and evaluates these algorithms. In this work, we have evaluated the electron Monte Carlo (MC) algorithm in Eclipse using solid water phantoms with various tissue heterogeneities (water, lung, cortical bone, air) embedded, and using CT data from a real patient. For heterogeneous phantoms, the evaluation is done by comparing dose profiles and percent depth doses (PDDs) calculated on Eclipse with measurements, and with MC simulations using DOSXYZnrc. Measurements of dose profiles and PDDs are taken using EBT Gafchromic films, and we have developed a piece of software in Matlab for extracting dose from EBT Gafchromic films. For the real patient case, we use DOSXYZnrc results as a benchmark against which Eclipse is evaluated. Although Eclipse has been evaluated previously, the originality of the present work lays on the use of digitally reproduced phantom copies on Eclipse and DOSXYZnrc instead of CT scanned phantoms, the use of absolute dose for all comparisons, and the consideration of a real clinical patient. In addition, we have developed a tool for extracting absolute dose profiles and PDDs from EBT Gafchromic films. Our results indicate that, MC results agree in general better with measurements (within 5% or less) than Eclipse MC, whose discrepancies with measurements can be as high as 15% for physical phantoms used and as high as 10% in the case of real patient CT data. Largest discrepancies between measurement (or MC) and Eclipse MC occur at depths near and below tissue heterogeneities with relatively sharp density gradients. The slightly better performance of Eclipse for the real patient case is related to the smoother changes in hetero<br>Les calculs précis de dose déposée dans les tissus par les photons et les électrons constituent une étape préliminaire cruciale dans tout approche de thérapie de cancer par la radiation. Plusieurs entreprises commerciales offrent de nos jours des programmes de planification des thérapies qui incluent des algorithmes de calcul de dose dans les tissus. Il est de la responsabilité du physicien médical de vérifier que ces algorithmes effectuent les calculs de dose avec une précision acceptables selon les standards actuels de radiothérapie. Dans ce mémoire, nous avons effectué une évaluation de l’algorithme Monte Carlo (MC) de calcul de dose (pour les faisceaux d’électrons) du programme de planification en radiothérapie connu sous le nom d’Eclipse. Dans cette évaluation, nous avons utilisé des fantômes solides contenant des tissue de densités diverses (eau, poumon, os, air) ainsi que des images scanner d’un patient réel (humain). Pour les fantômes solides notre évaluation a été faite en comparant les calculs d’Eclipse à des mesures expérimentales utilisant des films EBT Gafchromic d’une part, et d’autre part à des calculs MC plus rigoureux utilisant DOSXYZnrc. Pour le cas d’un patient, nous évaluons Eclipse en le comparant aux résultats MC obtenu via DOSXYZnrc, parce que nous ne pouvons placer un dosimètre à l’intérieur du patient. Nos résultats indiquent que les résultats MC sont plus proches des mesures expérimentales (écarts de l’ordre de 5% ou moins) que ceux d’Eclipse, lesquels ont un écart pouvant atteindre a peu près 15% par rapport aux mesures dans le cas des fantômes et 10% par rapport aux résultats MC pour le cas du patient réel. Les pires imprécisions d’Eclipse MC se retrouvent dans les tissus au voisinage des régions où il y a de fortes hetérogénéités et où les gradients de densités sont importants. En effet, les résultats obtenus par d’Eclipse MC pour le cas d’un patient ré
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Löf, Victor. "The Difference Between a Collapsed Cone Based and a Monte Carlo Based Dose Calculation Algorithm." Thesis, KTH, Fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-169550.
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Touileb, Yazid. "Four-dimensional dose calculation using deformable tetrahedral geometries for hadron therapy." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1179.
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L’estimation de la distribution de dose et d’énergie en présence du mouvement des tissus induit par la respiration, constitue un défi technologique important dans la planification du traitement en hadronthérapie. Notamment pour le cancer pulmonaire, dans lequel de nombreuses difficultés apparaissent comme la variation de densité des tissues, le changement de la forme des organes ainsi que le décalage de la position de la tumeur pendant la respiration. Tous ces paramètres affectent la portée du faisceau d’ions utilisés pendant le traitement, et, par conséquent entraînent une distribution de dose inattendue. L’objectif principal de cette thèse est de proposer une méthode de calcul de dose basée sur les structures tétraédriques, qui permet d’estimer les distributions de dose des organes en mouvement en utilisant les simulations Monte Carlo. Ces distributions de dose sont calculées en utilisant une carte de densité tétraédrique dépendante du temps, décrivant l’anatomie interne du corps humain. De plus, le mouvement interne peut être représenté à l'aide d'une modélisation biomécanique résolue par la méthode des éléments finis (MEF) ou d'une carte de déplacement issue d’un recalage d’images déformable. Contrairement aux méthodes basées sur les structures classiques à base de voxels, la dose déposée s’accumule à l’intérieur de chaque tétraèdre au cours de la déformation, surmontant ainsi le problème du suivi tissulaire puisque le tétraèdre est défini comme une partie d’un tissu dont la composition chimique et la topologie ne changent pas. Dans la première partie de la thèse, nous avons développé une méthode de calcul de dose qui génère une carte de dose 4D en utilisant un modèle tétraédrique spécifique au patient. En outre, nous étudions l’effet du niveau de détail des maillages tétraédriques sur la précision de la distribution de la dose obtenue. Dans la deuxième partie, nous nous concentrons sur l’optimisation de la géométrie tétraédrique pour réduire le temps de simulation, sachant que l’obtention d’une distribution de dose précise peut être coûteux en termes de temps. Pour surmonter ce problème, nous avons proposé une nouvelle approche qui prend en compte la direction du faisceau afin de minimiser l'erreur de l’épaisseur équivalent eau des tétraèdres avant le volume de la tumeur. Cette méthode permet d'obtenir un maillage tétraédrique grossier et, par conséquent, d'améliorer les performances de calcul dans les simulations de Monte Carlo, tout en conservant une distribution de dose précise dans le volume cible<br>The estimation of energy and dose distribution patterns in respiratory-induced organ motion constitutes a significant challenge in hadron therapy treatment planning and dosimetry. Notably for lung cancer in which many difficulties arise, like tissue densities variation and the tumor position shifting during respiration. All these parameters affect the ranges of protons or ions used in treatment when passing through different tissues and can easily result in unexpected dose distribution. The present work consists of calculating the dose distributions of moving organs by means of Monte Carlo simulations and patient-specific modeling tools. The dose distributions are calculated using a time-dependent tetrahedral density map, describing the internal anatomy of the human body. Additionally, the internal motion can be described using either a biomechanical modeling based on Finite Element Analysis (FEA) or deformable image registration displacement map. Unlike methods based on the conventional voxel-based structures, the deposited energy is accumulated inside each tetrahedron during deformation, thus overcoming the problem of tissue tracking since that the tetrahedron is defined as a part of a tissue whose chemical composition and topology do not change. The first part of the Ph.D. project proposes a dose calculation method that generates a 4D dose map using a patient-specific tetrahedral model. Besides, we study the effect of the level of detail of tetrahedral meshes on the accuracy of the resulted dose distribution. In the second part, we focus on the optimization of the tetrahedral geometry to address the problem of time simulation, since obtaining a precise dose distribution can be very time-consuming. To overcome this issue, we've defined a new approach that takes into account the direction of the beam to minimize the error of the water equivalent thickness of the tetrahedrons before the tumor volume. This method allows for a coarsened tetrahedral mesh and as a result, improved computational performance in Monte Carlo simulations while guaranteeing a precise dose distribution in the target volume
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Dang, Hieu-Trung. "Anwendung der Monte-Carlo-Methoden zur Lösung spezieller Probleme des Photonentransports." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2002. http://nbn-resolving.de/urn:nbn:de:swb:14-1021460036109-20379.
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Solutions were developed to solve the special photon transport problems. A respective Monte Carlo code were implemented. The photon transport calculations were made for simulation of light distribution in tissues, for 3D estimation of dosis brachytherapy source, for determination of scattering coincidences in PET and for solving of one special problem for ambient dosimetry. The developed calculation methods are based on a purely statistical approach and can therefore universal applied. The efficiency in respect of precision, numerical effectiveness, as well as memory requirement were optimised and verified by the calculations done. The modification and enhancement can be easy realised thanks to modular, object orientated implementation of the program and enables development of new application fields in physics and medicine<br>Zur Lösung speziellen Probleme des Photonentransports wurden grundlegende Ansätze gewonnen und in einem Transportprogramm umgesetzt. Die Photonen-Transportrechnungen zur Simulation des Lichttransports in trüben Medien, für die dreidimensionale Dosisberechnung für interstitielle Brachytherapiequellen, für die Ermittlung der Streustrahlungsverteilungen in PET-Scannern und für die Lösung eines speziellen Problems der Umgebungsdosimetrie wurden durchgeführt. Die entwickelten Berechnungsmethoden basieren auf einer rein probabilistischen Herangehensweise und lassen sich deshalb universell verwenden. Ihre Leistungsfähigkeit hinsichtlich der Genauigkeit, der numerischen Effektivität sowie des Bedarfs an Rechenresourcen wurde optimiert und konnte durch die durchgeführten Berechnungen bestätigt werden. Durch den modularen, objektorientierten Programmaufbau sind Modifikationen und Erweiterungen relativ einfach durchzuführen. Das ermöglicht eine Erschließung von neuen Anwendungsgebieten in der Physik und Medizin
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Chappell, Isaac Samuel 1972. "Calculation of interface tension and stiffness in a two dimensional Ising Model by Monte Carlo simulation." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/49672.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Physics, 1998.<br>Includes bibliographical references (p. 55).<br>The two dimensional Ising Model is important because it describes various condensed matter systems. At low temperatures, spontaneous symmetry breaking occurs such that two coexisting phases are separated by interfaces. These interfaces can be described as vibrating strings and are characterized by their tension and stiffness. Then the partition function can be calculated as a function of the magnetization with the interface tension and stiffness as parameters. Simulating the two dimensional Ising Model on square lattices of various sizes, the partition function is determined in order to extract the interface tension. The configurations being studied have low probability of actual occurrence and would require a large number of Monte Carlo steps before obtaining a good sampling. By using improved estimators and a trial distribution, fewer steps are needed. Improved estimators decrease the number of steps to achieve a certain level of accuracy. The trial distribution allows increased statistics once the general shape of the probability distribution is calculated from a Monte Carlo simulation. For small lattice sizes, it is easy to run Monte Carlo simulations to generate the trial distribution. At larger lattice sizes, it is necessary to build the trial distribution from a combination of a Monte Carlo simulation and an Ansatz from theory due to lower statistics. The extracted values of the interface tension agree with the analytical solution by Onsager.<br>by Isaac Samuel Chappell, II.<br>S.M.
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Dang, Hieu-Trung. "Anwendung der Monte-Carlo-Methoden zur Lösung spezieller Probleme des Photonentransports." Doctoral thesis, Technische Universität Dresden, 2001. https://tud.qucosa.de/id/qucosa%3A24139.
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Solutions were developed to solve the special photon transport problems. A respective Monte Carlo code were implemented. The photon transport calculations were made for simulation of light distribution in tissues, for 3D estimation of dosis brachytherapy source, for determination of scattering coincidences in PET and for solving of one special problem for ambient dosimetry. The developed calculation methods are based on a purely statistical approach and can therefore universal applied. The efficiency in respect of precision, numerical effectiveness, as well as memory requirement were optimised and verified by the calculations done. The modification and enhancement can be easy realised thanks to modular, object orientated implementation of the program and enables development of new application fields in physics and medicine.<br>Zur Lösung speziellen Probleme des Photonentransports wurden grundlegende Ansätze gewonnen und in einem Transportprogramm umgesetzt. Die Photonen-Transportrechnungen zur Simulation des Lichttransports in trüben Medien, für die dreidimensionale Dosisberechnung für interstitielle Brachytherapiequellen, für die Ermittlung der Streustrahlungsverteilungen in PET-Scannern und für die Lösung eines speziellen Problems der Umgebungsdosimetrie wurden durchgeführt. Die entwickelten Berechnungsmethoden basieren auf einer rein probabilistischen Herangehensweise und lassen sich deshalb universell verwenden. Ihre Leistungsfähigkeit hinsichtlich der Genauigkeit, der numerischen Effektivität sowie des Bedarfs an Rechenresourcen wurde optimiert und konnte durch die durchgeführten Berechnungen bestätigt werden. Durch den modularen, objektorientierten Programmaufbau sind Modifikationen und Erweiterungen relativ einfach durchzuführen. Das ermöglicht eine Erschließung von neuen Anwendungsgebieten in der Physik und Medizin.
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Hoepfner, Patrick J. "A Monte Carlo calculation of virtual source size and energy spread for a liquid metal ion source /." Full text open access at:, 1985. http://content.ohsu.edu/u?/etd,77.
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Miller, Dean Allan. "Monte Carlo dosimetry and activation calculation for a proposed fusion device : MCNP analysis of aAlcator C-MOD." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/15123.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1985.<br>MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.<br>Bibliography: leaf 109.<br>by Dean Allan Miller.<br>M.S.
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FONSECA, GABRIEL P. "Monte Carlo modeling of the patient and treatment delivery complexities for high dose rate brachytherapy." reponame:Repositório Institucional do IPEN, 2015. http://repositorio.ipen.br:8080/xmlui/handle/123456789/25298.
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Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-12-10T16:54:22Z
No. of bitstreams: 0<br>Made available in DSpace on 2015-12-10T16:54:22Z (GMT). No. of bitstreams: 0<br>Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)<br>Tese (Doutorado em Tecnologia Nuclear)<br>IPEN/T<br>Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP<br>FAPESP:11/01913-4
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zhang, zichang. "Systemic Investigation of Ga2O3 from Material to Device." OpenSIUC, 2020. https://opensiuc.lib.siu.edu/dissertations/1865.
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Ga2O3, which is a novel and ultra-wide band gap oxide semiconductor material, has attracted more and more attention due to its chemical and thermal stability and various potential applications to devices. This dissertation focuses on systemic investigation of β-Ga2O3 and ε- Ga2O3 from fundamental material properties, device modeling and verification of circuit performance. ab initio calculation was employed to do theoretical investigation of material properties. Based on Generalized Gradient Approximations (GGA), we calculate the band structure, effective mass of electron, density of states and phonon band structure. However, calculated band gap is only 2.36 eV and 2.16 eV, which is much lower than experimental measured value. In order to overcome the underestimation, the GGA+U method was carried out for both materials. band gap as 4.8 eV and 5.0 eV are finally identified, which have a good agreement with experimental results. Device simulation is done with Monte Carlo (MC) method and Drift-Diffusion method. Firstly, we used traditional ensemble MC to calculate the mobility of bulk material. We found conventional phonon scattering model cannot capture electron-phonon interaction (EPI) very well due to complex phonon structure of β-Ga2O3. Therefore, a refined MC method was proposed. By including multi-phonon scattering model, the refined MC works very well with multi-phonon modes EPI. The calculated mobility of bulk material is 118 cm2/(V•s), which is close to measured 120 cm2/(V•s). Using obtained mobility, the performance of depletion-mode β-Ga2O3 MOSFET was simulated in Silvaco TCAD.
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Hong, Qian. "Monte Carlo calculation and analysis of neutron and gamma fields at spallation neutron sources for simulating cosmic radiation." Thesis, University of Central Lancashire, 2015. http://clok.uclan.ac.uk/16647/.
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The research of the neutron induced Single Event Effect (SEE) at aircraft altitudes or at ground level are very important since the neutron radiation is able to cause serious errors or damages on electronic components and system. TheWeapons Neutron Research (WNR) facility at Los Alamos Neutron Science Center (LANSCE), and ANITA (Atmospheric-like Neutrons from thIck TArget) facility at The Svedberg Laboratory (TSL) both provide spallation neutron source for radiation testing of electronic components. A local beam monitoring system was successfully developed by S. Platt and L. Zhang in the University of Central Lancashire for measuring neutron dosimetry during accelerated SEE testing of electronic devices with using silicon photodiode. However, such silicon photodiode is sensitive to gamma-ray as well. For above reasons, characterization of neutron and gamma fields at spallation neutron sources used for accelerated SEE testing has become the purpose of this work. Monte Carlo calculation of radiation fields at spallation neutron source was used to characterize neutron and gamma energy spectra for accelerated single event effect testing. Geant4 (GEometry ANd Tracking version 4) toolkit, using Monte Carlo method, was used to simulate a preliminary model of spallation neutron source at LANSCE (ICE House, WNR) and TSL (ANITA) for understanding physical mechanisms of neutron and gamma interactions with matter. At first, two preliminary spallation neutron sources on basis of WNR (ICE House) and ANITA facilities were modeled with using two intra-nuclear cascade models (bertini, binary) provided by Geant4 reference physics lists. The result of neutron spectrum with binary INC model agrees well with LANSCE measurement data and independent calculation results in each case. In this computation, gamma dose rates at WNR and ANITA were calculated, and gamma dose rate from the simulation is consistent with the ANITA measurement results. The results of photon energy spectra with using Geant4 toolkit presents a continuum between 0.1MeV and 10MeV, and the annihilation peak at 0.5MeV. However, calculation results of neutron spectrum at ANITA facility with using binary INC model match ANITA measurements less well in absolute neutron yield above 20MeV, which is likely due to the missing geometry components in preliminary spallation neutron source simulation. A more complex model of ANITA facility was constructed with adding bending magnet, shielding components, detector system, and collimator, which makes modelling as realistically as possible. The discrepancy in absolute neutron yield between simulation results and measurements data has improved at Standard User Position (SUP) of ANITA facility, in contrast with the preliminary modelling of ANITA neutron source. At the same time, a new position referred as Close User Position (CUP) was investigated in order to compare with ANITA measurement informed by Monte Carlo N-Particle eXtended (MCNPX) simulation results. The neutron spatial distribution, radius effect for neutrons, neutron beam profiles, and time of flight spectra were calculated at the SUP and CUP positions for different collimator apertures of 3 cm, 10.2 cm, and 30 cm, respectively. A comparison of simulated neutron beam profiles folded with 238U (n, f) cross-section with ANITA measurements at the SUP and CUP-TOF positions was used for validating improved ANITA neutron source modelling. The neutron beam profiles in the horizontal direction were predicted with using Geant4, which filled the gap of geometrical limitation at ANITA facility for accelerated single event effect testing. It is the first time to predict gamma dose rate at the SUP and CUP positions for 3 cm, 10.2 cm, and 30 cm collimators with using Geant4 modelling of ANITA neutron source. In addition, the gamma dose rate at the SUP position is consistent with ANITA measurement data. Finally, the gamma yield, photon spatial distribution, dose rate against energy are considered for gamma field at the SUP and CUP positions, which have contributed to understand and analyse gamma interactions with matter.
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Wang, Yu. "Ab initio calculation of H interactions with defects in fcc metals : crack tip dislocations and vacancies." Thesis, Toulouse, INPT, 2014. http://www.theses.fr/2014INPT0125/document.
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Dans de nombreuses applications technologiques des alliages métalliques structurés, la fragilisation par l'hydrogène (HE) est une préoccupation majeure car elle peut pénétrer dans la plupart des métaux, dégrader leurs propriétés et conduire à des défaillances prématurées. Malgré de nombreux efforts durant ces dernières décennies, au cours desquelles de nombreux mécanismes microscopiques ont été proposées, une compréhension claire des mécanismes de fragilisation H n'a pas encore été atteint. Depuis qu'il processus se produisent sur une échelle atomique, les mécanismes exacts conduisant à HE ne sont pas facilement identifiés expérimentalement. Une amélioration possible serait d'utiliser des simulations à l'échelle atomique pour essayer de capturer les détails des processus de déformation et de rupture au niveau atomique, permettant l'enquête du mécanisme microscopique pertinente. Dans un tel contexte, l'objectif de ce travail de thèse est de comprendre et de quantifier les interactions H avec des défauts comme postes vacants, les luxations et les fissures dans les métaux cfc par la modélisation multi-échelle. L'étude est organisé en quatre parties principales. Dans la première partie, nous avons utilisé des premiers calculs principe (basée sur la théorie fonctionnelle de la densité) pour décrire H interaction avec une vacance de Nickel. Plus précisément, les énergies de ségrégation de plusieurs atomes d'hydrogène en un seul et di-postes vacants ont été calculés. Deux énergies caractéristiques qui ont été trouvés à clarifier les pics expérimentaux observés chez Spectra désorption thermique dans la littérature. Les concentrations de groupes H-inoccupation équilibre a ensuite été évalué, dans des conditions pertinentes à SE et de corrosion sous contrainte (CSC) des alliages à base de Ni (industrie nucléaire), par des simulations de Monte Carlo et un modèle thermodynamique développé à partir de nos données DFT. Dans la deuxième partie, nous avons quantifié l'effet de piégeage de postes vacants sur H diffusion dans Nickel. Avec DFT barrières de saut calculé, liés à H piégeage et dépiégeage dans les postes vacants, nous avons utilisé accéléré Kinetic Monte Carlo (KMC) simulations pour évaluer le coefficient H de diffusion en fonction de la concentration de vacance et de la température. Dans la troisième partie, nous avons étudié la diffusion des grappes H-vacance de Ni, basée sur la combinaison de DFT et une méthode statistique. Calculs DFT de barrières de saut d'inoccupation ont été effectuées pour les clusters contenant de un à six H à l'intérieur du poste vacant. Avec ces barrières calculés et les concentrations calculées précédentes de grappes H-inoccupation, un modèle simple stochastique similaire à la procédure KMC a été développé pour estimer le coefficient de diffusion de grappes H-inoccupation en fonction de la concentration et de la température M. Dans la dernière partie, nous avons étudié l'interaction de l'hydrogène avec une pointe de fissure émoussée en aluminium par EAM combinée (potentiel interatomique semi-empirique) et calculs DFT. Méthode atome embarqué (EAM) simulations potentiels ont été réalisées pour évaluer l'effet de H sur la dislocation émission d'une pointe de fissure émoussée en mode mixte chargement. Ce phénomène peut être comprise par le changement induit H de l'empilement instable faute de l'énergie (γus) dans le modèle de Rice. Par conséquent, DFT et EAM calculs de γus ont été effectuées, y compris les effets de H et des charges en mode mixte. Il est montré que l'effet de la charge perpendiculaire au plan de glissement est très forte, contrairement à l'effet de la surface sous-H, ce qui est négligeable<br>In many technological applications of structured metallic alloys, hydrogen embrittlement (HE) is a major concern as it can penetrate in most metals, degrade their properties and lead to premature failures. Despite numerous efforts in the past decades during which many microscopic mechanisms were proposed, a clear understanding of H embrittlement mechanisms has not been achieved yet. Since HE processes occur on an atomic-scale, the exact mechanisms leading to HE are not easily identified experimentally. One possible improvement would be to use atomic-scale simulations to try to capture details of deformation and fracture processes at the atomic level, enabling the investigation of relevant microscopic mechanism. In such context, the goal of this PhD work is to understand and quantify H interactions with defects like vacancies, dislocations and cracks in fcc metals through multi-scale modeling. The study is organized in four main parts. In the first part, we employed first principle calculations (based on density functional theory) to describe H interaction with a vacancy in Nickel. More specifically, the segregation energies of multiple H atoms in a single and di-vacancies were computed. Two characteristic energies were found which clarify the experimental peaks observed in Thermal Desorption Spectra in the literature. The equilibrium concentrations of H-vacancy clusters was then evaluated, under conditions relevant to HE and stress corrosion cracking (SCC) of Ni based alloys (nuclear industry),by Monte Carlo simulations and a thermodynamic model developed from our DFT data. In the second part, we quantified the trapping effect of vacancies on H diffusion in Nickel. With DFT computed jump barriers, related to H trapping and detrapping in vacancies, we employed accelerated Kinetic Monte Carlo (KMC) simulations to evaluate the H diffusion coefficient as a function of vacancy concentration and temperature. In the third part, we studied the diffusion of H-vacancy clusters in Ni, based on the combination of DFT and a statistical method. DFT calculations of vacancy jump barriers were performed for clusters containing from one to six H inside the vacancy. With these computed barriers and previous calculated concentrations of H-vacancy clusters, a simple stochastic model similar to the KMC procedure was developed to estimate the diffusion coefficient of H-vacancy clusters as a function of H concentration and temperature. In the last part, we studied the interaction of hydrogen with a blunted crack tip in Aluminum by combined EAM (semi-empirical interatomic potential) and DFT calculations. Embedded atom method (EAM) potential simulations were performed to evaluate the H effect on dislocation emission from a blunted crack tip under mixed mode loading. This phenomenon can be understood by the H induced change of the unstable stacking fault energy (γus ) in Rice’s model. Therefore, DFT and EAM calculations of γus were performed including the effects of H and of the mixed mode loads. It is shown that the effect of the load perpendicular to the glide plane is very strong, contrary to the effect of sub-surface H, which is negligible
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MORAIS, GUSTAVO JARDIM DE. "ANALYSIS OF EXTREME VALUES THEORY AND MONTE CARLO SIMULATION FOR THE CALCULATION OF VALUE-AT-RISK IN STOCK PORTFOLIOS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2011. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=34443@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO<br>COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR<br>PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO<br>Após as recentes crises financeiras que se abateram sobre os mercados financeiros de todo o mundo, com mais propriedade a de 2008/2009, mas ainda a crise no Leste Europeu em Julho/2007, a moratória Russa em Outubro/1998, e, no âmbito nacional, a mudança no regime cambial brasileiro, em Janeiro/1999, as instituições financeiras incorreram em grandes perdas em cada um desses eventos e uma das principais questões levantadas acerca dos modelos financeiros diziam respeito ao gerenciamento de risco. Os diversos métodos de cálculo do Value-atrisk, bem como as simulações e cenários traçados por analistas não puderam prever sua magnitude nem tampouco evitar que a crise se agravasse. Em função disso, proponho-me à questão de estudar os sistemas de gerenciamento de risco financeiro, na medida em que este pode e deve ser aprimorado, sob pena de catástrofes financeiras ainda maiores. Embora seu conteúdo se mostre tão vasto na literatura, as metodologias para cálculo de valor em risco não são exatas e livres de falhas. Nesse contexto, coloca-se necessário o desenvolvimento e aprimoramento de ferramentas de gestão de risco que sejam capazes de auxiliar na melhor alocação dos recursos disponíveis, avaliando o nível de risco à que um investimento está exposto e sua compatibilidade com seu retorno esperado.<br>After recent financial crisis that have hit financial markets all around the world, with more property on 2008/2009 periods, the Eastern Europe crisis in 2007, the Russian moratorium on October/1998, and with Brazilian national exchange rate regime change on January/1999, financial institutions have incurred
in large losses on each of these events and one of the main question raised about the financial models related to risk management. The Value-at-Risk management and its many forms to calculate it, as well as the simulations and scenarios predicted by analysts could not predict its magnitude or prevent crisis worsened. As a result, I intent to study the question of financial systems management, in order to improve the existing methods, under the threat that even bigger financial disasters are shall overcome. Although it s content is vast on scientific literature, the Value-at-Risk calculate is not exact and free of flaws. In this context, there is need for the development and improvement of risk management tools that are able to assist in a better asset equities allocation of resources, equalizing the risk level of an investment and it s return.
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Matsugi, Kiyotomo. "Evaluation of 4D dose to a moving target with Monte Carlo dose calculation in stereotactic body radiotherapy for lung cancer." Kyoto University, 2013. http://hdl.handle.net/2433/174802.
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Tarchalski, Mikolaj. "Nuclear heating measurements in the Maria reactor and implementation of neutron and photon calculation scheme." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4101.
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Les travaux réalisés durant cette thèse rentrent dans cette problématique. Ils concernent d’une part le développement d’un schéma de calculs et d’évaluation des échauffements nucléaires générés dans le réacteur MARIA en utilisant les codes français de transport neutronique TRIPOLI-4 © et APOLLO-2. Les travaux dans ce volet ont concerné principalement les calculs des échauffements photoniques induits par les rayonnements gammas essentiellement. D’autre part des travaux expérimentaux ont été conduits durant cette thèse. Ils ont concerné la mesure des échauffements nucléaires dans des emplacements spécifiques du réacteur MARIA. Cela a permis une première validation des schémas de calcul adoptés. Des comparaisons C/E ont été effectuées. Elles sont présentées et discutées dans cette thèse. Cela a permis d’émettre des recommandations quant aux techniques de mesure des échauffements nucléaires dans le réacteur MARIA et les moyens de modélisation qui peuvent être associés. Les comparaisons calculs-expérience font l’objet du cinquième. Les écarts relevés entre les résultats des modélisations et les mesures des échauffements nucléaires pour différentes configurations de mesures (au moyen de GT et de calorimètre mono cellule KAROLINA) permettent de dégager grâce à ces premiers travaux de thèse des recommandations pertinentes pour les travaux futurs<br>This thesis work presents a calculation scheme which enables evaluation of heat generation from nuclear reactions in the MARIA nuclear reactor by use French computational codes TRIPOLI-4 © (TRIPOLI-4 is a registered trademark of CEA) and Apollo-2. Particular attention was devoted to the heat induced by gamma radiation. The thesis also presents measurements of nuclear heating in selected locations inside MARIA MTR reactor. This allows reaching first steps of validation and qualification of computer calculations. Research and analysis presented in the thesis allow one to compare the results obtained by using proposed calculation scheme with the experimental measurement methods. Finally, further works and perspectives were proposed on the development of the calculations and experimental measurements of nuclear heating in nuclear reactors.Qualifying the calculations was possible by performing especially dedicated 7-day core measurement campaigns. Nuclear heating measurements were performed with gamma thermometers and specially designed KAROLINA calorimeter. All measurement devices used were mounted in a dedicated probe, designed and built for this purpose, which allowed for the adjustment of instruments position inside the MARIA core. The main scientific hypothesis of this work is that currently available Monte Carlo simulations of neutron and gamma transport can be used to correct and accurate calculations of prompt nuclear heating in nuclear reactor, whereas delayed component of nuclear heating can be determined experimentally. For this purpose new calculation scheme and improvements in nuclear heating measurements were implemented
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CINTRA, FELIPE B. de. "Avaliacao da metodologia de calculo de dose em microdosimetria com fontes de eletrons com o uso do codigo MCNP5." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9619.
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Made available in DSpace on 2014-10-09T12:28:44Z (GMT). No. of bitstreams: 0<br>Made available in DSpace on 2014-10-09T13:57:15Z (GMT). No. of bitstreams: 0<br>Dissertacao (Mestrado)<br>IPEN/D<br>Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Jabbari, Najafabadi Keivan. "Development of a fast Monte Carlo code for dose calculation in a treatment planning and feasibility study of high contrast portal imaging." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=32605.
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A fast and accurate treatment planning system is essential for radiation therapy and Monte Carlo (MC) techniques produce the most accurate results for dose calculation in treatment planning. In this work, we developed a fast Monte Carlo code based on pre-calculated data (PMC, Pre-calculated Monte Carlo) for applications in radiation therapy treatment planning. The PMC code takes advantage of large available memory in current computer hardware for extensive generation of pre-calculated data. Primary tracks of electrons are generated in the middle of homogeneous materials (water, air, bone, lung) and with energies between 0.2 and 18 MeV using the EGSnrc code. Secondary electrons are not transported but their position, energy, charge and direction are saved and used as a primary particle. Based on medium type and incident electron energy, a track is selected from the pre-calculated set. The performance of the method is tested in various homogeneous and heterogeneous configurations and the results were generally within 2% compared to EGSnrc but with a 40-60 times speed improvement. Pre-calculated Monte Carlo codes are accurate, fast and physics-independent and therefore applicable to different radiation types including heavy-charged particles. In another project, we worked on Monte Carlo feasibility study to use orthogonal bremsstrahlung beams for imaging in radiation therapy. The basic characteristics of orthogonal bremsstrahlung beams are studied and the feasibility of improved contrast imaging in linear accelerator with such a beam is evaluated. In the context of this work orthogonal bremsstrahlung beams represent the component of the bremsstrahlung distribution perpend<br>Un plan de traitement rapide et précis est essentiel en radiothérapie et les techniques par Monte-Carlo produisent les résultats les plus précis pour le calcul de dose. Dans la présente recherche, nous avons développé un script de Monte-Carlo rapide basé sur des données pré-calculée (PMC, Monte Carlo pré-calculé) pour des applications en radiothérapie. Le code informatique PMC prend l'avantage d'une grande quantité de mémoire actuellement installée de nos jours sur les ordinateurs afin de générer des données pré-calculées. Les traces primaires des électrons sont générées au centre de matériaux homogènes (eau, air, os, poumons) avec des énergies entre 0.2 et 18 MeV en utilisant le code EGSnrc. Les électrons secondaires ne sont pas transportés, mais leurs positions, énergies, charges et directions sont sauvegardées et utilisées comme particules primaires. D'après le type de matériel et d'énergie de l'électron, le tracé est sélectionné et utilisé comme particule primaire. La performance de cette méthode est testée dans plusieurs types de configurations homogènes et non- homogènes. Les résultats, lorsque comparés à ceux de EGSnrc, sont à l'intérieur d'une marge de 2% tandis que la rapidité de calcul est de 40 à 60 fois supérieure. Les codes informatiques pré calculés de Monte-Carlo sont précis, rapide et indépendant de la physique et par conséquent applicables à plusieurs type de faisceaux tels que les particules à haute charge. Dans un autre projet, nous avons étudié la capacité du code Monte-Carlo à utiliser des faisceaux orthogonaux de bremsstrahlung dans le cadre d'imagerie en radiothérapie. Les caracté
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Speiser, Michael Paul. "Development and validation of a virtual Monte Carlo radiotherapy source model and characterization of the influence of heterogeneities on dose calculation accuracy." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1680033161&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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De, Pietri Marco. "Development of a Human Unstructured Mesh Model Based on CT Scans for Dose Calculation in Medical Radiotherapy." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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Questo lavoro di tesi analizza l’opportunità di applicare dei metodi Monte Carlo nei campi della Radioterapia Superficiale e Ortovoltaica. Inizialmente i protocolli di cura attualmente esistenti sono stati studiati. Una revisione della letteratura è stata condotta sulle tipologie ed evoluzione dei fantocci umani computazionali. I passaggi pratici per la realizzazione di due tipi di fantocci basati su paziente, partendo da immagini TAC, sono stati descritti. Questi due tipi, modelli voxel e modelli a mesh non strutturate, sono stati studiati e comparati attraverso simulazioni. Dalla collaborazione con il reparto di Fisica Medica dell’Arcispedale S. Maria Nuova di Reggio Emilia, un modello di un tubo a Raggi X è stato modellato e validato con misure sperimentali. Questa sorgente è stata utilizzata su fantocci di teste attraverso simulazioni con MCNP6. In particolare è stata valutata la distribuzione spaziale della dose, dentro al modello, a tensioni crescenti all’interno del tubo. Il confronto dei risultati delle simulazioni ha permesso di valutare le interazioni dei fotoni all’interno del modello e le dosi al Planning Target Volume (PTV) e Organ At Risk (OAR) a tensioni della sorgente crescenti. Queste applicazioni hanno dimostrato che un prototipo di Sistema di Piano di Trattamento (TPS) è facilmente implementabile e può fornire preziose informazioni aggiuntive su questi tipi di radioterapia. Sebbene i protocolli esistenti siano in uso da molti anni, con innegabili tassi di cura elevati, è opinione dell’autore che l’integrazione di un TPS basato su Monte Carlo possa fornire potenziali benefici a questi tipi di radioterapia. In particolare, potrebbe fornire informazioni aggiuntive sulla scelta dei parametri di trattamento, portando a migliori risultati nella terapia e qualità di vita del paziente oncologico.
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Raabe, Wolfgang Verfasser], and Rüdiger [Akademischer Betreuer] [Kiesel. "Calculation of Monte-Carlo Sensitivities for a portfolio of time coupled options and application to conventional power plants / Wolfgang Raabe. Betreuer: Rüdiger Kiesel." Duisburg, 2015. http://d-nb.info/107743927X/34.
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Raabe, Wolfgang [Verfasser], and Rüdiger [Akademischer Betreuer] Kiesel. "Calculation of Monte-Carlo Sensitivities for a portfolio of time coupled options and application to conventional power plants / Wolfgang Raabe. Betreuer: Rüdiger Kiesel." Duisburg, 2015. http://d-nb.info/107743927X/34.
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COELHO, PAULO R. P. "Padrao experimental em espectrometria de neutrons rapidos utilizando neutrons da reacao DT e avaliacao de metodos de calculo de blindagem." reponame:Repositório Institucional do IPEN, 1993. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10330.
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Escobar-Corral, Nuria Verfasser], Achim [Akademischer Betreuer] [Stahl, and Michael J. [Akademischer Betreuer] Eble. "Validation of a time dependent Monte Carlo dose calculation for radiotherapy using a new moving phantom / Nuria Escobar-Corral ; Achim Stahl, Michael J. Eble." Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/1130402959/34.
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Escobar-Corral, Nuria [Verfasser], Achim [Akademischer Betreuer] Stahl, and Michael J. [Akademischer Betreuer] Eble. "Validation of a time dependent Monte Carlo dose calculation for radiotherapy using a new moving phantom / Nuria Escobar-Corral ; Achim Stahl, Michael J. Eble." Aachen : Universitätsbibliothek der RWTH Aachen, 2016. http://d-nb.info/1130402959/34.
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Ravaux, Simon. "Qualification du calcul de l'échauffement photonique dans les réacteurs nucléaires." Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00961188.
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Ce travail de thèse répond à un besoin de qualification des outils permettant decalculer les échauffements photoniques dans les réacteurs nucléaires. En effet, laproblématique des échauffements g dans les matériaux de structure a pris de l'importanceces dernières années, notamment pour la sûreté des réacteurs de 3ème génération danslesquels un réflecteur lourd en acier est introduit.Les photons présents dans le coeur sont tous directement ou indirectement issus desinteractions des neutrons avec la matière. Ils sont créés au moment de l'interaction ou endifféré par l'intermédiaire de noyaux créés au moment de l'interaction. Par conséquent, lepremier axe de travail a été d'effectuer une analyse critique des données de productionphotonique dans les bibliothèques de données nucléaires standards. La découverted'omissions dans la bibliothèque JEFF-3.1.1 nous a amené à proposer une méthode deproduction de nouvelles évaluations contenant de nouveaux spectres d'émission de photong. Ces nouvelles évaluations ont ensuite été proposées et en partie acceptées pour lanouvelle version de la bibliothèque JEFF.Il existe deux codes de transport de particules développés au CEA : TRIPOLI4 etAPOLLO2. Le deuxième axe de travail a été de qualifier ces deux codes. Pour cela, nousavons interprété les mesures d'échauffement g effectuées dans le cadre du programmeexpérimental PERLE. Des détecteurs thermoluminescents (TLD) ont été introduits dans unréflecteur lourd en acier entourant un réseau de crayons combustibles. Nous avons dûproposer un schéma de calcul spécifique aux deux codes afin de calculer la réponse desTLD.Les comparaisons calcul-mesure ont montré que TRIPOLI4 permettait decorrectement estimer l'échauffement dans le réflecteur relativement à l'échauffement dans lazone fissile. En effet, les écarts calcul-mesure sont inférieurs à l'incertitude expérimentale à1s. Pour le calcul APOLLO2, nous avons tout d'abord commencé par une phase devalidation par rapport à TRIPOLI4 afin d'estimer les biais liés aux approximations imposéespar le traitement déterministe du transport des particules. Après cette phase de validation,nous avons pu montrer qu'APOLLO2, comme TRIPOLI4, permettait d'estimer correctementl'échauffement dans le réflecteur avec des écarts calcul-mesure comparables à l'incertitudeexpérimentale.
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Kimstrand, Peter. "Beam Modelling for Treatment Planning of Scanned Proton Beams." Doctoral thesis, Uppsala University, Oncology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8640.
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<p>Scanned proton beams offer the possibility to take full advantage of the dose deposition properties of proton beams, i.e. the limited range and sharp peak at the end of the range, the Bragg peak. By actively scanning the proton beam, laterally by scanning magnets and longitudinally by shifting the energy, the position of the Bragg peak can be controlled in all three dimensions, thereby enabling high dose delivery to the target volume only. A typical scanned proton beam line consists of a pair of scanning magnets to perform the lateral beam scanning and possibly a range shifter and a multi-leaf collimator (MLC). Part of this thesis deals with the development of control, supervision and verification methods for the scanned proton beam line at the The Svedberg laboratory in Uppsala, Sweden. </p><p>Radiotherapy is preceded by treatment planning, where one of the main objectives is predicting the dose to the patient. The dose is calculated by a dose calculation engine and the accuracy of the results is of course dependent on the accuracy and sophistication of the transport and interaction models of the dose engine itself. But, for the dose distribution calculation to have any bearing on the reality, it needs to be started with relevant input in accordance with the beam that is emitted from the treatment machine. This input is provided by the beam model. As such, the beam model is the link between the reality (the treatment machine) and the treatment planning system. The beam model contains methods to characterise the treatment machine and provides the dose calculation with the reconstructed beam phase space, in some convenient representation. In order for a beam model to be applicable in a treatment planning system, its methods have to be general. </p><p>In this thesis, a beam model for a scanned proton beam is developed. The beam model contains models and descriptions of the beam modifying elements of a scanned proton beam line. Based on a well-defined set of generally applicable characterisation measurements, ten beam model parameters are extracted, describing the basic properties of the beam, i.e. the energy spectrum, the radial and the angular distributions and the nominal direction. Optional beam modifying elements such as a range shifter and an MLC are modelled by dedicated Monte Carlo calculation algorithms. The algorithm that describes the MLC contains a parameterisation of collimator scatter, in which the rather complex phase space of collimator scattered protons has been parameterised by a set of analytical functions. </p><p>Dose calculations based on the phase space reconstructed by the beam model are in good agreement with experimental data. This holds both for the dose distribution of the elementary pencil beam, reflecting the modelling of the basic properties of the scanned beam, as well as for complete calculations of collimated scanned fields.</p>
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Narabayashi, Masaru. "Dosimetric evaluation of the impacts of different heterogeneity correction algorithms on target doses in stereotactic body radiation therapy for lung tumors." Kyoto University, 2015. http://hdl.handle.net/2433/198933.
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Jiang, Ji. "Modélisation quantique des agrégats d'hélium dopés." Phd thesis, Université Paris-Est, 2013. http://tel.archives-ouvertes.fr/tel-00861164.
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La photo-dissociation d'une molécule comme CH3I dans l'agrégat d'hélium présente un grand intérêt pour comprendre la recombinaison et la solvatation des photo-fragments après la dissociation dans un liquide quantique. Après la recombinaison certaines structures de D@Hen(D= Ar^+, I^q, q= -1, 0, +1, +2) montrent les stabilités particulières avec les nombres magiques bien définis. Notre but ultime est d'étudier théoriquement la dynamique de la photo-dissociation de CH3I dans les agrégats d'hélium et de comparer avec les résultats expérimentaux disponibles dans la littérature. Notre recherche préliminaire est motivée par les données disponibles sur les espèces de couche ouverte comme D@Hen (D= Ar^+, Mg^+) et commence par un test sur notre modèle potentiel analytique pour les systèmes D@Hen à plusieurs corps. Notre modèle inclut les énergies électrostatique classique et quantique de dispersion,et également les énergies de charge/dipôle induit et de dipôle induit/dipôle induit dans le cas où le dopant D est ionique. La représentation analytique de l'interaction D-He est obtenue en fittant les fonctions ayant une forme asymptotique physiquement correcte aux résultats de calculs ab initio corrélés de haut niveau pour la molécule D-He. La matrice "Diatomices-in-Molecules" (DIM) de notre modèle potentiel à plusieurs corps est construite pour les situations avec l'anisotropie électronique et le couplage spin-orbite (SOC) pour l'atome lourd D est inclus dans la base de couplage du type s-l pour l'atome D. Les structures et les énergies de cohésion de systèmes D@Hen sont étudiées en fonction de la taille du système n par la méthode MonteCarlo quantique de diffusion (DMC).De nouvelles sous-routines pour évaluer le potentiel D-He ont été programmées pour le programme DMC existant et une fonction d'essai améliorée a été appliquée dans le calcul DMC
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Botas, Sanmartín Pablo [Verfasser], and Joao [Akademischer Betreuer] Seco. "Adaptive proton radiation therapy via fast Monte Carlo dose calculation to correct for inter- and intra-fraction motion and geometry changes / Pablo Botas Sanmartin ; Betreuer: Joao Seco." Heidelberg : Universitätsbibliothek Heidelberg, 2019. http://d-nb.info/1179782143/34.
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Rohde, Ulrich [Projektleiter], and Carsten Beckert. "Entwicklung eines 3D Neutronentransportcodes auf der Basis der Ray-Tracing-Methode und Untersuchungen zur Aufbereitung effektiver Gruppenquerschnitte für heterogene LWR-Zellen." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-28540.
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Standardmäßig erfolgt die Datenaufbereitung der Neutronenwirkungsquerschnitte für Reaktorkernrechnungen mit 2D-Zellcodes. Ziel dieser Arbeit war es, einen 3D-Zellcode zu entwickeln, mit diesem Code 3D-Effekte zu untersuchen und die Notwendigkeit einer 3D-Datenaufbereitung der Neutronenwirkungsquerschnitte zu bewerten. Zur Berechnung des Neutronentransports wurde die Methode der Erststoßwahrscheinlichkeiten, die mit der Ray-Tracing-Methode berechnet werden, gewählt. Die mathematischen Algorithmen wurden in den 2D/3D-Zellcode TransRay umgesetzt. Für den Geometrieteil des Programms wurde das Geometriemodul eines Monte-Carlo-Codes genutzt. Das Ray-Tracing wurde auf Grund der hohen Rechenzeiten parallelisiert. Das Programm TransRay wurde an 2D-Testaufgaben verifiziert. Für einen Druckwasser-Referenzreaktor wurden folgende 3D-Probleme untersucht: Ein teilweise eingetauchter Regelstab und Void (bzw. Moderator mit geringerer Dichte) um einen Brennstab als Modell einer Dampfblase. Alle Probleme wurden zum Vergleich auch mit den Programmen HELIOS (2D) und MCNP (3D) nachgerechnet. Die Abhängigkeit des Multiplikationsfaktors und der gemittelten Zweigruppenquerschnitte von der Eintauchtiefe des Regelstabes bzw. von der Höhe der Dampfblase wurden untersucht. Die 3D berechneten Zweigruppenquerschnitte wurden mit drei üblichen Näherungen verglichen: linearer Interpolation, Interpolation mit Flusswichtung und Homogenisierung. Am 3D-Problem des Regelstabes zeigte sich, dass die Interpolation mit Flusswichtung eine gute Näherung ist. Demnach ist hier eine 3D-Datenaufbereitung nicht notwendig. Beim Testfall des einzelnen Brennstabs, der von Void (bzw. Moderator geringerer Dichte) umgeben ist, erwiesen sich die drei Näherungen für die Zweigruppenquerschnitte als unzureichend. Demnach ist eine 3D-Datenaufbereitung notwendig. Die einzelne Brennstabzelle mit Void kann als der Grenzfall eines Reaktors angesehen werden, in dem sich eine Phasengrenzfläche herausgebildet hat.
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Rohde, Ulrich [Projektleiter], and Carsten Beckert. "Entwicklung eines 3D Neutronentransportcodes auf der Basis der Ray-Tracing-Methode und Untersuchungen zur Aufbereitung effektiver Gruppenquerschnitte für heterogene LWR-Zellen." Forschungszentrum Rossendorf, 2006. https://hzdr.qucosa.de/id/qucosa%3A21681.
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Standardmäßig erfolgt die Datenaufbereitung der Neutronenwirkungsquerschnitte für Reaktorkernrechnungen mit 2D-Zellcodes. Ziel dieser Arbeit war es, einen 3D-Zellcode zu entwickeln, mit diesem Code 3D-Effekte zu untersuchen und die Notwendigkeit einer 3D-Datenaufbereitung der Neutronenwirkungsquerschnitte zu bewerten. Zur Berechnung des Neutronentransports wurde die Methode der Erststoßwahrscheinlichkeiten, die mit der Ray-Tracing-Methode berechnet werden, gewählt. Die mathematischen Algorithmen wurden in den 2D/3D-Zellcode TransRay umgesetzt. Für den Geometrieteil des Programms wurde das Geometriemodul eines Monte-Carlo-Codes genutzt. Das Ray-Tracing wurde auf Grund der hohen Rechenzeiten parallelisiert. Das Programm TransRay wurde an 2D-Testaufgaben verifiziert. Für einen Druckwasser-Referenzreaktor wurden folgende 3D-Probleme untersucht: Ein teilweise eingetauchter Regelstab und Void (bzw. Moderator mit geringerer Dichte) um einen Brennstab als Modell einer Dampfblase. Alle Probleme wurden zum Vergleich auch mit den Programmen HELIOS (2D) und MCNP (3D) nachgerechnet. Die Abhängigkeit des Multiplikationsfaktors und der gemittelten Zweigruppenquerschnitte von der Eintauchtiefe des Regelstabes bzw. von der Höhe der Dampfblase wurden untersucht. Die 3D berechneten Zweigruppenquerschnitte wurden mit drei üblichen Näherungen verglichen: linearer Interpolation, Interpolation mit Flusswichtung und Homogenisierung. Am 3D-Problem des Regelstabes zeigte sich, dass die Interpolation mit Flusswichtung eine gute Näherung ist. Demnach ist hier eine 3D-Datenaufbereitung nicht notwendig. Beim Testfall des einzelnen Brennstabs, der von Void (bzw. Moderator geringerer Dichte) umgeben ist, erwiesen sich die drei Näherungen für die Zweigruppenquerschnitte als unzureichend. Demnach ist eine 3D-Datenaufbereitung notwendig. Die einzelne Brennstabzelle mit Void kann als der Grenzfall eines Reaktors angesehen werden, in dem sich eine Phasengrenzfläche herausgebildet hat.
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Skwarcan-Bidakowski, Alexander. "Nuclear reactor core model for the advancednuclear fuel cycle simulator FANCSEE. Advanceduse of Monte Carlo methods in nuclear reactorcalculations." Thesis, Institutionen för Reaktorfysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-324260.
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A detailed reactor core modeling of the LOVIISA-2 PWR and FORSMARK-3BWR was performed in the Serpent 2 Continuous Energy Monte-Carlocode.Both models of the reactors were completed but the approximations ofthe atomic densities of nuclides present in the core differedsignificantly.In the LOVIISA-2 PWR, the predicted atomic density for the nuclidesapproximated by Chebyshev Rational Approximation method (CRAM)coincided with the corrected atomic density simulated by the Serpent2 program. In the case of FORSMARK-3 BWR, the atomic density fromCRAM poorly approximated the data returned by the simulation inSerpent 2. Due to boiling of the moderator in the core of FORSMARK-3,the model seemed to encounter problems of fission density, whichyielded unusable results.The results based on the models of the reactor cores are significantto the FANCSEE Nuclear fuel cycle simulator, which will be used as adataset for the nuclear fuel cycle burnup in the reactors.<br>FANCSEE
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Malusek, Alexandr. "Calculation of scatter in cone beam CT : Steps towards a virtual tomograph." Doctoral thesis, Linköping : Department of Medical and Health Sciences, Linköping University, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11275.
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OLIVEIRA, TIAGO B. de. "Estudo dos parâmetros dosimétricos de sementes de Iodo-125 desenvolvidas pelo IPEN-CNEN/SP utilizadas em braquiterapia por simulação computacional pelo método de Monte Carlo." reponame:Repositório Institucional do IPEN, 2016. http://repositorio.ipen.br:8080/xmlui/handle/123456789/26392.
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Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-06-22T14:06:41Z
No. of bitstreams: 0<br>Made available in DSpace on 2016-06-22T14:06:41Z (GMT). No. of bitstreams: 0<br>Dissertação (Mestrado em Tecnologia Nuclear)<br>IPEN/D<br>Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Nygren, Nelly. "Optimization of the Gamma Knife Treatment Room Design." Thesis, KTH, Fysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-300904.
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Radiation shielding is a central part of the design of treatment rooms for radiation therapy systems. The dose levels that medical staff and members of the public can be exposed to outside the treatment rooms are regulated by authorities and influence the required wall thicknesses and possible locations for the systems. Several standard methods exist for performing shielding calculations, but they are not well adapted to the stereotactic radiosurgery system Leksell Gamma Knife because of its self-shielding properties. The built-in shielding makes the leakage radiation anisotropic and generally have lower energy than the primary radiation from the Gamma Knife's cobalt sources. Oversimplifications made in the standard shielding calculation methods regarding the field can lead to excessively thick shielding and limit the number of suitable locations for the system. In this thesis project, a simulation-based dose calculation algorithm was developed, that uses Monte Carlo-generated data in two steps. The algorithm uses a phase space to accurately describe the radiation field around the Gamma Knife. Information about individual photons in the field is then combined with a generated library of data describing the resulting dose outside a wall depending on the wall thickness and the photon energy. The dose calculation algorithm is fast enough to be integrated into optimization processes, in which the algorithm is used iteratively while varying room design parameters. Demonstrated in this report is a case with a room of fixed size, in which the Gamma Knife's position and the walls' thicknesses are varied, with the aim to find the room design resulting in the minimum wall thicknesses needed to achieve acceptable dose levels outside. The results in this thesis indicate that the dose calculation algorithm performs well and could likely be used in more complex optimizations with more design variables and more advanced design goals.<br>Strålsäkerhet är en viktig aspekt vid uppförandet av behandlingsrum för strål-terapisystem. Strålningsnivåerna som sjukvårdspersonal och allmänheten kan exponeras för utanför behandlingsrummet regleras av myndigheter och påverkar vilken väggtjocklek som behövs och vilka platser som är lämpliga att placera systemen på. Flertalet metoder för strålskyddsberäkning existerar, men de är inte väl anpassade till det stereotaktiska radiokirurgiska systemet Leksell Gamma Knife, eftersom det har ett inbyggt strålskydd. Det inbyggda strålskyddet gör att strålfältet runt Gamma Knife är anisotropt och generellt har lägre energi än primärstrålningen från systemets koboltkällor. Förenklingar som görs rörande strålfältet i flera existerande metoder för strålskyddsberäkning kan leda till att överdrivet tjocka strålskydd används eller begränsa antalet lämpliga platser att placera systemet på. I detta projekt utvecklades en dosberäkningsalgoritm, som i två steg använder data genererad genom Monte Carlo-simuleringar. Algoritmen använder ett fasrum för att detaljerat beskriva strålfältet runt Gamma Knife. Information om enskilda fotoner i fältet används sen i kombination med ett genererat bibliotek av data som beskriver det dosbidrag som en foton bidrar med utanför behandlingsrummet, baserat på fotonens energi och väggarnas tjocklek. Dosberäkningsalgoritmen är snabb nog att integreras i optimeringsprocesser där den används iterativt samtidigt som rumsdesignparametrar varieras. I denna rapport demonstreras ett fall med ett rum av bestämd storlek, där positionen av Gamma Knife i rummet och väggarnas tjocklekar varieras. Optimeringens syfte i exemplet är att hitta den rumsdesign som med de minsta väggtjocklekarna resulterar i acceptabla strålningsnivåer utanför rummet. Resultaten tyder på att dosberäkningsalgoritmen sannolikt kan användas i mer komplexa optimeringar med fler designvariabler och mer avancerade designmål.
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Cai, Li. "Condensation et homogénéisation des sections efficaces pour les codes de transport déterministes par la méthode de Monte Carlo : Application aux réacteurs à neutrons rapides de GEN IV." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112280/document.
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Dans le cadre des études de neutronique menées pour réacteurs de GEN-IV, les nouveaux outils de calcul des cœurs de réacteur sont implémentés dans l’ensemble du code APOLLO3® pour la partie déterministe. Ces méthodes de calculs s’appuient sur des données nucléaires discrétisée en énergie (appelées multi-groupes et généralement produites par des codes déterministes eux aussi) et doivent être validées et qualifiées par rapport à des calculs basés sur la méthode de référence Monte-Carlo. L’objectif de cette thèse est de mettre au point une technique alternative de production des propriétés nucléaires multi-groupes par un code de Monte-Carlo (TRIPOLI-4®). Dans un premier temps, après avoir réalisé des tests sur les fonctionnalités existantes de l’homogénéisation et de la condensation avec des précisions meilleures accessibles aujourd’hui, des incohérences sont mises en évidence. De nouveaux estimateurs de paramètres multi-groupes ont été développés et validés pour le code TRIPOLI-4®à l’aide de ce code lui-même, puisqu’il dispose de la possibilité d’utiliser ses propres productions de données multi-groupes dans un calcul de cœur. Ensuite, la prise en compte de l’anisotropie de la diffusion nécessaire pour un bon traitement de l’anisotropie introduite par des fuites des neutrons a été étudiée. Une technique de correction de la diagonale de la matrice de la section efficace de transfert par diffusion à l’ordre P1 (nommée technique IGSC et basée sur une évaluation du courant des neutrons par une technique introduite par Todorova) est développée. Une amélioration de la technique IGSC dans la situation où les propriétés matérielles du réacteur changent drastiquement en espace est apportée. La solution est basée sur l’utilisation d’un nouveau courant qui est projeté sur l’axe X et plus représentatif dans la nouvelle situation que celui utilisant les approximations de Todorova, mais valable seulement en géométrie 1D. A la fin, un modèle de fuite B1 homogène est implémenté dans le code TRIPOLI-4® afin de produire des sections efficaces multi-groupes avec un spectre critique calculé avec l’approximation du mode fondamental. Ce modèle de fuite est analysé et validé rigoureusement en comparant avec les autres codes : Serpent et ECCO ; ainsi qu’avec un cas analytique.L’ensemble de ces développements dans TRIPOLI-4® permet de produire des sections efficaces multi-groupes qui peuvent être utilisées dans le code de calcul de cœur SNATCH de la plateforme PARIS. Ce dernier utilise la théorie du transport qui est indispensable pour la nouvelle filière à neutrons rapides. Les principales conclusions sont : -Le code de réseau en Monte-Carlo est une voie intéressante (surtout pour éviter les difficultés de l’autoprotection, de l’anisotropie limitée à un certain ordre du développement en polynômes de Legendre, du traitement des géométries exactes 3D), pour valider les codes déterministes comme ECCO ou APOLLO3® ou pour produire des données pour les codes déterministes ou Monte-Carlo multi-groupes.-Les résultats obtenus pour le moment avec les données produites par TRIPOLI-4® sont comparables mais n’ont pas encore vraiment montré d’avantage par rapport à ceux obtenus avec des données issues de codes déterministes tel qu’ECCO<br>In the framework of the Generation IV reactors neutronic research, new core calculation tools are implemented in the code system APOLLO3® for the deterministic part. These calculation methods are based on the discretization concept of nuclear energy data (named multi-group and are generally produced by deterministic codes) and should be validated and qualified with respect to some Monte-Carlo reference calculations. This thesis aims to develop an alternative technique of producing multi-group nuclear properties by a Monte-Carlo code (TRIPOLI-4®).At first, after having tested the existing homogenization and condensation functionalities with better precision obtained nowadays, some inconsistencies are revealed. Several new multi-group parameters estimators are developed and validated for TRIPOLI-4® code with the aid of itself, since it has the possibility to use the multi-group constants in a core calculation.Secondly, the scattering anisotropy effect which is necessary for handling neutron leakage case is studied. A correction technique concerning the diagonal line of the first order moment of the scattering matrix is proposed. This is named the IGSC technique and is based on the usage of an approximate current which is introduced by Todorova. An improvement of this IGSC technique is then presented for the geometries which hold an important heterogeneity property. This improvement uses a more accurate current quantity which is the projection on the abscissa X. The later current can represent the real situation better but is limited to 1D geometries.Finally, a B1 leakage model is implemented in the TRIPOLI-4® code for generating multi-group cross sections with a fundamental mode based critical spectrum. This leakage model is analyzed and validated rigorously by the comparison with other codes: Serpent and ECCO, as well as an analytical case.The whole development work introduced in TRIPLI-4® code allows producing multi-group constants which can then be used in the core calculation solver SNATCH in the PARIS code platform. The latter uses the transport theory which is indispensable for the new generation fast reactors analysis. The principal conclusions are as follows:-The Monte-Carlo assembly calculation code is an interesting way (in the sense of avoiding the difficulties in the self-shielding calculation, the limited order development of anisotropy parameters, the exact 3D geometries) to validate the deterministic codes like ECCO or APOLLO3® and to produce the multi-group constants for deterministic or Monte-Carlo multi-group calculation codes. -The results obtained for the moment with the multi-group constants calculated by TRIPOLI-4 code are comparable with those produced from ECCO, but did not show remarkable advantages