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1
Alves, Nuno Franco Rodrigues. "Direct simulation Monte Carlo of non-equilbrium rarefied flows." Thesis, Queen Mary, University of London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421089.
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Buxton, Robert Charles. "Direct simulation Monte Carlo modelling of physical vapour deposition." Thesis, University of Leeds, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426851.
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Armour, Jessica D. "On the Gap-Tooth direct simulation Monte Carlo method." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/72863.
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Thesis (S.M.)--Massachusetts Institute of Technology, Computation for Design and Optimization Program, February 2012."February 2012." Cataloged from PDF version of thesis.
Includes bibliographical references (p. [73]-74).
This thesis develops and evaluates Gap-tooth DSMC (GT-DSMC), a direct Monte Carlo simulation procedure for dilute gases combined with the Gap-tooth method of Gear, Li, and Kevrekidis. The latter was proposed as a means of reducing the computational cost of microscopic (e.g. molecular) simulation methods using simulation particles only in small regions of space (teeth) surrounded by (ideally) large gaps. This scheme requires an algorithm for transporting particles between teeth. Such an algorithm can be readily developed and implemented within direct Monte Carlo simulations of dilute gases due to the non-interacting nature of the particle-simulators. The present work develops and evaluates particle treatment at the boundaries associated with diffuse-wall boundary conditions and investigates the drawbacks associated with GT-DSMC implementations which detract from the theoretically large computational benefit associated with this algorithm (the cost reduction is linear in the gap-to-tooth ratio). Particular attention is paid to the additional numerical error introduced by the gap-tooth algorithm as well as the additional statistical uncertainty introduced by the smaller number of particles. We find the numerical error introduced by transporting particles to adjacent teeth to be considerable. Moreover, we find that due to the reduced number of particles in the simulation domain, correlations persist longer, and thus statistical uncertainties are larger than DSMC for the same number of particles per cell. This considerably reduces the computational benefit associated with the GT-DSMC algorithm. We conclude that the GT-DSMC method requires more development, particularly in the area of error and uncertainty reduction, before it can be used as an effective simulation method.
by Jessica D. Armour.
S.M.
4
Rangaraj, Dharanipathy. "Multicomponent aerosol dynamics : exploration of direct simulation Monte Carlo technique /." free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p3144452.
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Wishart, Stuart Jackson. "A Parallel Solution Adaptive Implementation of the Direct Simulation Monte Carlo Method." University of Sydney. School of Aerospace, Mechanical and Mechatronic Engineering, 2005. http://hdl.handle.net/2123/619.
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This thesis deals with the direct simulation Monte Carlo (DSMC) method of analysing gas flows. The DSMC method was initially proposed as a method for predicting rarefied flows where the Navier-Stokes equations are inaccurate. It has now been extended to near continuum flows. The method models gas flows using simulation molecules which represent a large number of real molecules in a probabilistic simulation to solve the Boltzmann equation. Molecules are moved through a simulation of physical space in a realistic manner that is directly coupled to physical time such that unsteady flow characteristics are modelled. Intermolecular collisions and moleculesurface collisions are calculated using probabilistic, phenomenological models. The fundamental assumption of the DSMC method is that the molecular movement and collision phases can be decoupled over time periods that are smaller than the mean collision time. Two obstacles to the wide spread use of the DSMC method as an engineering tool are in the areas of simulation configuration, which is the configuration of the simulation parameters to provide a valid solution, and the time required to obtain a solution. For complex problems, the simulation will need to be run multiple times, with the simulation configuration being modified between runs to provide an accurate solution for the previous run�s results, until the solution converges. This task is time consuming and requires the user to have a good understanding of the DSMC method. Furthermore, the computational resources required by a DSMC simulation increase rapidly as the simulation approaches the continuum regime. Similarly, the computational requirements of three-dimensional problems are generally two orders of magnitude more than two-dimensional problems. These large computational requirements significantly limit the range of problems that can be practically solved on an engineering workstation or desktop computer. The first major contribution of this thesis is in the development of a DSMC implementation that automatically adapts the simulation. Rather than modifying the simulation configuration between solution runs, this thesis presents the formulation of algorithms that allow the simulation configuration to be automatically adapted during a single run. These adaption algorithms adjust the three main parameters that effect the accuracy of a DSMC simulation, namely the solution grid, the time step and the simulation molecule number density. The second major contribution extends the parallelisation of the DSMC method. The implementation developed in this thesis combines the capability to use a cluster of computers to increase the maximum size of problem that can be solved while simultaneously allowing excess computational resources to decrease the total solution time. Results are presented to verify the accuracy of the underlying DSMC implementation, the utility of the solution adaption algorithms and the efficiency of the parallelisation implementation.
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Basik, Beata-Marie. "Direct simulation Monte Carlo model of a couette flow of granular materials." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60433.
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Since life-threatening natural phenomena, such as, snow avalanches and lava flows, and many industrial and agricultural material handling processes may be classified as granular flows, establishing constitutive relationships which model granular flow behaviour is of prime importance. While laboratory experiments attempting to support granular flow theory have been plagued by poor instrumentation, numerical simulations are becoming increasingly helpful in understanding the nature of these flows. The present investigation describes such a simulation developed within the framework of the Direct Simulation Monte Carlo model for rarefied gases presented in Bird (1976) and granular flow kinetic theory according to Lun, et al. (1984). More specifically, the model generates a Couette flow of smooth, inelastic, homogeneous, spherical granular particles. Two different boundary condition models are used to model the flow field's upper and lower boundaries: the Periodic Boundary Condition (PBC) model and the Finite Shear Layer (FSL) model. An essentially uniform shear flow with virtually no slip at the boundaries results from both boundary conditions. Stress and granular temperature results obtained with the PBC and FSL models for the lower range of solids fractions ($ nu < 0.3)$ compare very well with the Lun, et al. (1984) theory. At higher solids fractions, while the total stresses generated with both boundary models are in reasonable agreement with the latter theory and results from other numerical work, higher than expected streaming stresses appear to be compensating for lower than expected collisional stresses; as a result, granular temperature in this range of solids fractions proves to be higher than predicted.
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Parsons, Timothy Langdon. "Object-reuse-oriented design of direct simulation Monte-Carlo software for rarefied gas dynamics." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314287.
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Simmons, Russell. "Direct Simulation Monte Carlo modelling of surface catalytic events in high enthalpy rarefied gas flows." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318865.
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Ahmad, Abdul Ossman. "Advances in an open-source direct simulation Monte Carlo technique for hypersonic rarefied gas flows." Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=26579.
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Hypersonic vehicles that travel through rarefied gas environments are very expensive to design through experimental methods. In the last few decades major work has been carried out in developing numerical methods to capture these types of flows to a certain degree of accuracy. This accuracy is increased using particle based numerical techniques as opposed to continuum computational fluid dynamics. However, one of the modern problems of particle based techniques is the high computational cost associated with it. This thesis presents an enhanced open-source particle based technique to capture high speed rarefied gas flows. This particle based technique is called dsmcFoam and is based on the direct simulation Monte Carlo technique. As a result of the author's work dsmcFoam has become more efficient and accurate. Benchmark studies of the standard dsmcFoam solver will be presented before introducing the main advances. The results of the benchmark investigations are compared with analytical solutions, other DSMC codes and experimental data available in the literature. And excellent agreement is found when good DSMC practice has been followed. The main advances of dsmcFoam discussed are a routine for selecting collision pairs called the transient adaptive sub-cell (TASC) method and a dynamic wall temperature model (DWTM). The DWTM relates the wall temperature to the heat flux. In addition, verification and validation studies are undertaken of the DWTM. Furthermore, the widely used conventional 8 sub-cell method used to select possible collision pairs becomes very cumbersome to employ properly. This is because many mesh refinement stages are required in order to obtain accurate data. Instead of mesh refinement the TASC technique automatically employs more sub-cells, and these sub-cells are based on the number of particles in a cell. Finally, parallel efficiency tests of dsmcFoam are presented in this thesis along with a new domain decomposition technique for parallel processing. This technique splits up the computational domain based on the number of particles, such that each processor has the same number of particles to work with.
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Mirza, Asim [Verfasser]. "Entwicklung eines partikelbasierten Kontinuumsverfahrens zur bidirektionalen Kopplung mit der Direct Simulation Monte Carlo Methode / Asim Mirza." München : Verlag Dr. Hut, 2019. http://d-nb.info/1198542985/34.
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Al-Kouz, Wael G. "Investigation of Supersonic Gas Flows into Nanochannels Using an Unstructured 3D Direct Simulation Monte Carlo Method." Digital WPI, 2009. https://digitalcommons.wpi.edu/etd-dissertations/317.
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"This dissertation is devoted to the computational investigation of supersonic gas flows in rectangular nanochannels with scales between 100 nm and 1000 nm, using an unstructured three-dimensional Direct Simulation Monte Carlo (U3DSMC) methodology. This dissertation also contributes to the computational mathematics background of the U3DSMC method with validations and verifications at the micronscale and nanoscale, as well as with the investigation of the statistical fluctuations and errors associated with U3DSMC simulations at the nanoscale. The U3DSMC code is validated by comparisons with previous two dimensional DSMC simulations of flows in micron-scale rectangular channels. The simulation involves the supersonic flow of nitrogen into a microchannel with height of 1.2 m and width of 6 m. The free stream conditions correspond to a pressure of 72,450 Pa, Mach number , Knudsen number and mean free path nm. The U3DSMC centerline temperature, heat flux to the wall, and mean velocity as a function of the transverse direction are in very good agreement with previous 2D results. Statistical fluctuations and errors in U3DSMC have added significance in nanoscale domains because the number of real particles can be very small inside a computational cell. The effect of the number of samples, the number of computational particles in a Delaunay cell, and the Mach number on the fractional errors of density, velocity and temperature are investigated for uniform and pressure-driven nanoscale flows. The uniform nanoflow is implemented by applying a and free stream boundary condition with m-3, K, nm in a domain that requires resolution of a characteristic length scale nm. The pressure-driven flows consider a nanochannel of 500 nm height, 100 nm width and 4 m length. Subsonic boundary conditions are applied with inlet pressure 101,325 Pa and outlet pressure of 10132.5 Pa. The analysis shows that U3DSMC simulations at nanoscales featuring 10-30 particles per Delaunay cell result in statistical errors that are consistent with theoretical estimates. The rarefied flow of nitrogen with speed ratio of 2, 5, and 10, pressure of 10.132 kPa into rectangular nanochannels with height of 100, 500 and 1000 nm is investigated using U3DSMC. The investigation considers rarefaction effects with =0.481, 0.962, 4.81, geometric effects with nanochannel aspect ratios of (L/H) from AR=1, 10, 100 and back-pressure effects with imposed pressures from 0 to 200 kPa. The computational domain features a buffer region upstream of the inlet and the nanochannel walls are assumed to be diffusively reflecting at the free stream temperature of 273 K. The analysis is based on the phase space distributions as well as macroscopic flow variables sampled in cells along the centerline. The phase space distributions show the formation of a disturbance region ahead of the inlet due to slow particles backstreaming through the inlet and the formation of a density enhancement with its maximum inside the nanochannel. The velocity phase-space distributions show a low-speed particle population generated inside the nanochannel due to wall collisions which is superimposed with the free stream high-speed population. The mean velocity decreases, while the number density increases in the buffer region. The translational temperature increases in the buffer region and reaches its maximum near the inlet. For AR=10 and 100 nanochannels the gas reaches near equilibrium with the wall temperature. The heat transfer rate is largest near the inlet region where non-equilibrium effects are dominant. For =0.481, 0.962, 4.81, vacuum back pressure, and AR=1, the nanoflow is supersonic throughout the nanochannel, while for AR=10 and 100, the nanoflow is subsonic at the inlet and becomes sonic at the outlet. For =0.962, AR=1, and imposed back pressure of 120 kPa and 200 kPa, the nanoflow becomes subsonic at the outlet. For =0.962 and AR=10, the outlet pressure nearly matches the imposed back pressure with the nanoflow becoming sonic at 40 kPa and subsonic at 100 kPa. Heat transfer rates at the inlet and mass flow rates at the outlet are in good agreement with those obtained from theoretical free-molecular models. The flows in these nanochannels share qualitative characteristics found in microchannels ad well as continuum compressible flows in channels with friction and heat loss. The rarefied flow of nitrogen with speed ratio of 2, 5, 10, at an atmospheric pressure of 101.32 kPa into rectangular nanochannels with height of 100 and 500 nm is investigated using U3DSMC. The investigation considers rarefaction effects with =0.0962 and 4.81, geometric effects with nanochannel aspect ratios of (L/H) of AR=1 and 10 and vacuum back-pressure. Phase plots and sample-averaged macroscopic parameters are used in the analysis. Under vacuum back pressure the centerline velocity decreases in the buffer region from its free stream value. For 0.481, 0.0962 and AR=1 the Mach number is supersonic at the inlet and remains supersonic throughout the nanochannel. For 0.481, 0.0962 and AR=10, the flow becomes subsonic at the inlet and shows a sharp increase in pressure. The Mach number, subsequently, increases and reaches the sonic point at the outlet. For 0.481, 0.0962 and AR=1 the translational temperature reaches a maximum near the inlet and decreases monotonically up to the outlet. For 0.481, 0.0962 and AR=10, the translational temperature reaches a maximum near the inlet and then decreases to come in near equilibration with the wall temperature of 273 K. "
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Nanson, III Richard A. "Navier/Stokes/Direct Simulation Monte Carlo Modeling of Small Cold Gas Thruster Nozzle and Plume Flows." Digital WPI, 2002. https://digitalcommons.wpi.edu/etd-theses/254.
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This study involves the modeling of small cold-gas (N2) thrusters nozzle and plume flows, their interactions with spacecraft surfaces and the induced pressure environment. These small cold-gas thrusters were used for pitch, yaw and roll control and were mounted on the bottom of the conical Environmental Monitor Payload (EMP) suborbital spacecraft. The pitch and yaw thrusters had 0.906 mm throat diameter and 4.826 mm exit diameter, while the roll thrusters had 1.6 mm throat diameter and 5.882 mm exit diameter. During thruster firing, at altitudes between 670 km and 1200 km, pressure measurements exhibited non-periodic pulses (Gatsonis et al., 1999). The pressure sensor was located inside the EMP and was connected to it's sidewall with a 0.1-m long, 0.022-m diameter tube and the pressure pulses appeared instantaneously with the firings for thrusters without a direct line-of-sight with the sensor entrance. Preliminary analysis showed that the plume of these small EMP thrusters undergoes transition from continuous to rarefied. Therefore, nozzle and plume simulations are performed using a combination of Navier-Stokes and Direct Simulation Monte Carlo codes. This study presents first a validation of the Navier-Stokes code Rampant used for the continuous EMP nozzle and plume simulations. The first Rampant validation example involves a two-dimensional axisymetric freejet expansion and is used to demonstrate the use of Bird's breakdown parameter. Results are compared favorably with those of Bird (1980) obtained through the method of characteristics. The second validation example involves three-dimensional plume simulations of a NASA thruster. This nitrogen nozzle has a throat diameter of 3.18 mm, an exit diameter of 31.8 mm, half-angle of 20 degrees, stagnation temperature of 699 K, stagnation pressure of 6,400 Pa. Simulation results are compared favorably with previous Navier-Stokes and Direct Simulation Monte Carlo numerical work. The third validation example involves three-dimensional simulations of Rothe's (1970) nozzle that has a throat diameter of 2.5 mm, an exit diameter of 20.3 mm, half-angle of 20 degrees, operating at stagnation temperature of 300 K and pressure of 1975 Pa. Numerical results also compared favorably to experimental data. The combined Navier-Stokes/DSMC approach and the EMP simulation results are presented and discussed. The continuous part of the EMP nozzle and plume flow is modeled using the three-dimensional Navier-Stokes Rampant code. The Navier-Stokes domain includes the geometry of the nozzle and the EMP base until transition of the continuous flow established by Bird's breakdown parameter. The rarefied part of the plume flow is modeled using the Direct Simulation Monte Carlo code DAC. Flowfield data obtained inside the breakdown surface from the Navier-Stokes simulation are used as inputs to the DSMC simulations. The DSMC domain includes the input surface and the EMP spacecraft geometry. The combined Navier-Stokes/DSMC simulations show the complex structure of the plume flow as it expands over the EMP surfaces. Plume reflection and backflow are demonstrated. The study also summarizes findings presented by Gatsonis et al. (2000), where the DSMC predictions at the entrance of the pressure sensor are used as inputs to a semi-analytical model to predict the pressure inside the sensor. It is shown that the pressure predictions for the pitch/yaw thrusters are close to the measurements. The plume of a pitch or yaw thruster reaches the pressure sensor after expanding on the EMP base. The pressure predicted for the roll thruster is larger that the measured. This is attributed to the uncertainty in the roll thruster location on the EMP base resulting, in the simulation, in a component of direct flow to the sensor.
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Landon, Colin Donald. "Weighted particle variance reduction of Direct Simulation Monte Carlo for the Bhatnagar-Gross-Krook collision operator." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61882.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 67-69).
Direct Simulation Monte Carlo (DSMC)-the prevalent stochastic particle method for high-speed rarefied gas flows-simulates the Boltzmann equation using distributions of representative particles. Although very efficient in producing samples of the distribution function, the slow convergence associated with statistical sampling makes DSMC simulation of low-signal situations problematic. In this thesis, we present a control-variate-based approach to obtain a variance-reduced DSMC method that dramatically enhances statistical convergence for lowsignal problems. Here we focus on the Bhatnagar-Gross-Krook (BGK) approximation, which as we show, exhibits special stability properties. The BGK collision operator, an approximation common in a variety of fields involving particle mediated transport, drives the system towards a local equilibrium at a prescribed relaxation rate. Variance reduction is achieved by formulating desired (non-equilibrium) simulation results in terms of the difference between a non-equilibrium and a correlated equilibrium simulation. Subtracting the two simulations results in substantial variance reduction, because the two simulations are correlated. Correlation is achieved using likelihood weights which relate the relative probability of occurrence of an equilibrium particle compared to a non-equilibrium particle. The BGK collision operator lends itself naturally to the development of unbiased, stable weight evaluation rules. Our variance-reduced solutions are compared with good agreement to simple analytical solutions, and to solutions obtained using a variance-reduced BGK based particle method that does not resemble DSMC as strongly. A number of algorithmic options are explored and our final simulation method, (VR)2-BGK-DSMC, emerges as a simple and stable version of DSMC that can efficiently resolve arbitrarily low-signal flows.
by Colin Donald Landon.
S.M.
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Nanson, Richard A. "Navier/Stokes/Direct simulation Monte Carlo modeling of small cold gas thruster nozzle and plume flows." Link to electronic thesis, 2002. http://www.wpi.edu/Pubs/ETD/Available/etd-0424102-132343.
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Hammel, Jeffrey Robert. "Development of an unstructured 3-D direct simulation Monte Carlo/particle-in-cell code and the simulation of microthruster flows." Link to electronic thesis, 2002. http://www.wpi.edu/Pubs/ETD/Available/etd-0510102-153614.
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Bergman, Alanah Mary. "Monte Carlo simulation of x-ray dose distributions for direct aperture optimization of intensity modulated treatment fields." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/30720.
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This thesis investigates methods of reducing radiation dose calculation errors as applied to a
specialized x-ray therapy called intensity modulated radiation therapy (IMRT). There are three
major areas of investigation. First, limits of the popular 2D pencil beam kernel (PBK) dose
calculation algorithm are explored. The ability to resolve high dose gradients is partly related
to the shape of the PBK. Improvements to the spatial resolution can be achieved by modifying
the dose kernel shapes already present in the clinical treatment planning system. Optimization
of the PBK shape based on measured-to-calculated test pattern dose comparisons reduces the
impact of some limitations of this algorithm. However, other limitations remain (e.g. assuming
spatial invariance, no modeling of extra-focal radiation, and no modeling of lateral electron
transport). These limitations directed this thesis towards the second major investigation - Monte
Carlo (MC) simulation for IMRT. MC is considered to be the "gold standard" for radiation dose
calculation accuracy. This investigation incorporates MC calculated beamlets of dose deposition
into a direct aperture optimization (DAO) algorithm for IMRT inverse planning (MC-DAO) . The
goal is to show that accurate tissue inhomogeneity information and lateral electronic transport
information, combined with DAO, will improve the quality/accuracy of the patient treatment
plan. MC simulation generates accurate beamlet dose distributions in traditionally difficultto-
calculate regions (e.g. air-tissue interfaces or small (≤ 5 cm² ) x-ray fields). Combining
DAO with MC beamlets reduces the required number of radiation units delivered by the linear
accelerator by ~30-50%. The MC method is criticized for having long simulation times (hours).
This can be addressed with distributed computing methods and data filtering ('denoising').
The third major investigation describes a practical implementation of the 3D Savitzky-Golay
digital filter for MC dose 'denoising'. This thesis concludes that MC-based DAO for IMRT
inverse planning is clinically feasible and offers accurate modeling of particle transport and dose
deposition in difficult environments where lateral electronic dis-equilibrium exists.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Fougere, Nicolas, K. Altwegg, J. J. Berthelier, A. Bieler, D. Bockelée-Morvan, U. Calmonte, F. Capaccioni, et al. "Direct Simulation Monte Carlo modelling of the major species in the coma of comet 67P/Churyumov-Gerasimenko." OXFORD UNIV PRESS, 2016. http://hdl.handle.net/10150/624746.
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We analyse the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) - the Double Focusing Mass Spectrometer data between 2014 August and 2016 February to examine the effect of seasonal variations on the four major species within the coma of 67P/Churyumov-Gerasimenko (H2O, CO2, CO, and O-2), resulting from the tilt in the orientation of the comet's spin axis. Using a numerical data inversion, we derive the non-uniform activity distribution at the surface of the nucleus for these species, suggesting that the activity distribution at the surface of the nucleus has not significantly been changed and that the differences observed in the coma are solely due to the variations in illumination conditions. A three-dimensional Direct Simulation Monte Carlo model is applied where the boundary conditions are computed with a coupling of the surface activity distributions and the local illumination. The model is able to reproduce the evolution of the densities observed by ROSINA including the changes happening at equinox. While O-2 stays correlated with H2O as it was before equinox, CO2 and CO, which had a poor correlation with respect to H2O pre-equinox, also became well correlated with H2O post-equinox. The integration of the densities from the model along the line of sight results in column densities directly comparable to the VIRTIS-H observations. Also, the evolution of the volatiles' production rates is derived from the coma model showing a steepening in the production rate curves after equinox. The model/data comparison suggests that the seasonal effects result in the Northern hemisphere of 67P's nucleus being more processed with a layered structure while the Southern hemisphere constantly exposes new material.
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Somers, William R. "Testing Direct Simulation Monte Carlo Methods Against the Fluid Equations in the Inductively Coupled Plasma Mass Spectrometer." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2621.pdf.
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Mateu, armengol Jan. "Étude numérique des effets du couplage du rayonnement thermique aux jets turbulents libres de vapeur d'eau." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLC052/document.
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Le rayonnement thermique joue un rôle important dans un large éventail d'applications de génie thermique comprenant des écoulements turbulents. La motivation principale de cette thèse est le besoin croissant de précision et fiabilité dans les simulations numériques appliqué à ce domaine.Cette thèse s’intéresse tout particulièrement à la compréhension physique de l’impact du rayonnement thermique sur la dynamique des fluides et le transfert thermique, ainsi que de l’influence des fluctuations turbulentes sur le transfert radiatif dans les écoulements à couche de cisaillement.L'objectif de cette thèse est de fournir des données haute-fidélités de jets libres turbulents couplés au rayonnement thermique afin de développer et de valider des modèles turbulents d’écoulements à couche de cisaillement prenant en compte les interactions de couplage. À cette fin, les jets libres turbulents sont décrits par des simulations numériques directes (DNS) couplées à une méthode de Monte-Carlo réciproque pour résoudre l'équation de transfert radiatif. La dépendance spectrale des propriétés radiatives est prise en compte avec la méthode Correlated-k (ck). L'étude numérique est réalisée avec la plus grande fidélité pour être aussi représentative que possible d'un jet réel dans un milieu participatif. La simulation est optimisée en termes de temps de calcul en tirant parti d'une méthode d'accélération appelée Acoustic Speed Reduction et en injectant de la turbulence artificielle pour améliorer les conditions d'entrée.Deux simulations directes de jets chauffés couplés au rayonnement thermique sont réalisées. D'une part, un jet chauffé avec un rayonnement modéré a été simulé et l’analyse de ses données DNS couplées a permis de dériver une nouvelle loi d’échelle pour la décroissance du profil de température. Cette mise à l'échelle rend compte des effets de la densité modifiée due à un rayonnement modéré. De plus, cela permet de distinguer si le rayonnement thermique modifie ou non la nature des mécanismes de transfert thermique dans la région développée du jet. D'autre part, un jet libre fortement chauffé a été calculé afin de quantifier les effets du rayonnement sur les champs de température et de vitesse moyens ainsi que sur les moments de second ordre.Outre les données DNS couplées, un solver RANS pour les écoulements à densité variable couplé au rayonnement thermique a été développé au cours de cette thèse. L'objectif était de quantifier directement la précision des modèles turbulents existants et d'identifier les paramètres clés pour une modélisation plus poussée des interactions de couplageRadiation plays an important role in a broad range of thermal engineering applications comprising turbulent flows. The growing need for accurate and reliable numerical simulations to support the design stages of such applications is the main motivation of this thesis.Of special interest in this work are the free-shear flows and the fundamental understanding of how radiation can modify their fluid dynamics and heat trans- port as well as how their turbulence fluctuations can alter radiative transfer. The goal of this thesis is to provide high-fidelity data of turbulent free jets coupled with thermal radiation in order to develop and validate free-shear turbulent models accounting for coupling interactions. To this end, turbulent free jets are described by direct numerical simulations (DNS) coupled to a reciprocal Monte- Carlo method to solve the radiative transfer equation. The spectral dependency of the radiative properties is accounted for with an accurate Correlated-k (ck) method. The numerical study is carried out with state-of-the-art fidelity to be as representative as possible of an actual jet in a participating medium. The simulation is optimized in terms of processing time taking advantage of an acceleration method called Acoustic Speed Reduction and by injecting artificial turbulence to enhance inlet boundaries.Two direct simulations of heated jets coupled with thermal radiation are carried out. On the one hand, a heated jet with moderate radiation is simulated. The analysis of its high-fidelity coupled DNS data has allow to derive a new scaling law for the decay of the temperature profile. This scaling accounts for the effects of modified density due to moderate radiation. Moreover, it allows for distinguishing whether thermal radiation modifies the nature of heat transfer mechanisms in the jet developed region or not. On the other hand, a strongly heated free jet is computed in order to quantify the effects of radiation on mean temperature and velocity fields as well as on second order moments.Besides the coupled DNS data, a RANS solver for variable-density flows coupled with thermal radiation has been implemented during the course of this thesis. The goal is to directly quantify the accuracy of the existing turbulent models, and to identify key parameters for further modeling of coupling interactions
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Chamberlin, Ryan Earl. "A three-dimensional direct simulation Monte Carlo methodology on unstructured Delaunay grids with applications to micro and nanoflows." Worcester, Mass. : Worcester Polytechnic Institute, 2007. http://www.wpi.edu/Pubs/ETD/Available/etd-032907-092912/.
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Al-Mohssen, Husain Ali 1977. "Chemical vapor deposition modeling using direct simulation Monte Carlo with non-linear chemistry and level set profile evolution." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/89933.
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Pfeiffer, Marcel [Verfasser]. "Simulation elektromagnetischer Wechselwirkungen in Plasmaströmungen großer Skalengradienten unter Verwendung eines gekoppelten Particle-In-Cell und Direct Simulation Monte Carlo-Verfahrens / Marcel Pfeiffer." München : Verlag Dr. Hut, 2015. http://d-nb.info/1079769005/34.
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Fougere, N., K. Altwegg, J. J. Berthelier, A. Bieler, D. Bockelée-Morvan, U. Calmonte, F. Capaccioni, et al. "Three-dimensional direct simulation Monte-Carlo modeling of the coma of comet 67P/Churyumov-Gerasimenko observed by the VIRTIS and ROSINA instruments on board Rosetta." EDP SCIENCES S A, 2016. http://hdl.handle.net/10150/614711.
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Context. Since its rendezvous with comet 67P/Churyumov-Gerasimenko (67P), the Rosetta spacecraft has provided invaluable information
contributing to our understanding of the cometary environment. On board, the VIRTIS and ROSINA instruments can both
measure gas parameters in the rarefied cometary atmosphere, the so-called coma, and provide complementary results with remote
sensing and in situ measurement techniques, respectively. The data from both ROSINA and VIRTIS instruments suggest that the
source regions of H2O and CO2 are not uniformly distributed over the surface of the nucleus even after accounting for the changing
solar illumination of the irregularly shaped rotating nucleus. The source regions of H2O and CO2 are also relatively different from one
another.
Aims. The use of a combination of a formal numerical data inversion method with a fully kinetic coma model is a way to correlate and
interpret the information provided by these two instruments to fully understand the volatile environment and activity of comet 67P.
Methods. In this work, the nonuniformity of the outgassing activity at the surface of the nucleus is described by spherical harmonics
and constrained by ROSINA-DFMS data. This activity distribution is coupled with the local illumination to describe the inner boundary
conditions of a 3D direct simulation Monte-Carlo (DSMC) approach using the Adaptive Mesh Particle Simulator (AMPS) code
applied to the H2O and CO2 coma of comet 67P.
Results. We obtain activity distribution of H2O and CO2 showing a dominant source of H2O in the Hapi region, while more CO2
is produced in the southern hemisphere. The resulting model outputs are analyzed and compared with VIRTIS-M/-H and ROSINADFMS
measurements, showing much better agreement between model and data than a simpler model assuming a uniform surface
activity. The evolution of the H2O and CO2 production rates with heliocentric distance are derived accurately from the coma model
showing agreement between the observations from the different instruments and ground-based observations.
Conclusions. We derive the activity distributions for H2O and CO2 at the surface of the nucleus described in spherical harmonics,
which we couple to the local solar illumination to constitute the boundary conditions of our coma model. The model presented
reproduces the coma observations made by the ROSINA and VIRTIS instruments on board the Rosetta spacecraft showing our understanding
of the physics of 67P’s coma. This model can be used for further data analyses, such as dust modeling, in a future work.
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Lu, Yongjie. "Application de la methode de simulation directe monte carlo aux ecoulements de transition application a plusieurs techniques de mesure." Paris 6, 1993. http://www.theses.fr/1993PA066158.
Full textAbstract:
La methode de simulation directe monte carlo, adoptant le modele de borgnakke-larsen d'echange d'energie interne-translation et le modele de maxwell d'interaction molecule-paroi, est utilisee dans l'etude des ecoulements de transition rencontres dans les techniques de mesure: sphere tombante, anemometrie a fil chaud et anemometrie laser doppler. Les etudes mettent l'accent sur la force de trainee subie par l'obstacle (sphere et particule spherique) et l'echange de chaleur entre l'ecoulement et l'obstacle (fil cylindrique)
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Masters, Nathan Daniel. "Efficient Numerical Techniques for Multiscale Modeling of Thermally Driven Gas Flows with Application to Thermal Sensing Atomic Force Microscopy." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11574.
Full textAbstract:
The modeling of Micro- and NanoElectroMechanical Systems (MEMS and NEMS) requires new computational techniques that can deal efficiently with geometric complexity and scale dependent effects that may arise. Reduced feature sizes increase the coupling of physical phenomena and noncontinuum behavior, often requiring models based on molecular descriptions and/or first principles. Furthermore, noncontinuum effects are often localized to small regions of (relatively) large systemsprecluding the global application of microscale models due to computational expense. Multiscale modeling couples efficient continuum solvers with detailed microscale models to providing accurate and efficient models of complete systems.
This thesis presents the development of multiscale modeling techniques for nonequilibrium microscale gas phase phenomena, especially thermally driven microflows. Much of this focuses on improving the ability of the Information Preserving DSMC (IP-DSMC) to model thermally driven flows. The IP-DSMC is a recent technique that seeks to accelerate the solution of direct simulation Monte Carlo (DSMC) simulations by preserving and transporting certain macroscopic quantities within each simulation molecules. The primary contribution of this work is the development of the Octant Splitting IP-DSMC (OSIP-DSMC) which recovers previously unavailable information from the preserved quantities and the microscopic velocities. The OSIP-DSMC can efficiently simulate flow fields induced by nonequilibrium systems, including phenomena such as thermal transpiration. The OSIP-DSMC provides an efficient method to explore rarefied gas transport phenomena which may lead to a greater understanding of these phenomena and new concepts for how these may be utilized in practical engineering systems.
Multiscale modeling is demonstrated utilizing the OSIP-DSMC and a 2D BEM solver for the continuum (heat transfer) model coupled with a modified Alternating Schwarz coupling scheme. An interesting application for this modeling technique is Thermal Sensing Atomic Force Microscopy (TSAFM). TSAFM relies on gas phase heat transfer between heated cantilever probes and the scanned surface to determine the scan height, and thus the surface topography. Accurate models of the heat transfer phenomena are required to correctly interpret scan data. This thesis presents results demonstrating the effect of subcontinuum heat transfer on TSAFM operation and explores the mechanical effects of the Knudsen Force on the heated cantilevers.
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Oliveira, Guacira Costa de. "Curto-circuito probabilístico através da simulação de Monte Carlo para sistemas de transmissão em corrente contínua." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/18/18154/tde-15092015-112702/.
Full textAbstract:
A transmissão de energia em corrente contínua, a partir de conversores fonte de tensão, é oportuna ao progresso do sistema elétrico de potência e tem permitido vantajosas aplicações. Muito se dá, devido ao emprego na conexão de sistemas com frequências distintas, além da redução de perdas na transmissão, provida pelas características operacionais destes. VSCs também promovem o controle do fluxo de potência, possibilitando uma efetiva contextualização no âmbito das redes inteligentes. Diante deste cenário, este estudo pretende construir um perfil de corrente através do Cálculo de Curto-Circuito Probabilístico, que emprega a Simulação de Monte Carlo, para prover as informações ao desenvolvimento de projetos de equipamentos, ajustes da proteção e controle de sistemas de transmissão em corrente contínua. A Simulação de Monte Carlo requer muitas iterações, tendo um custo computacional elevado. Se forem executadas em programas comerciais, exige um tempo elevado para leitura dos sinais em arquivos. Devido a isso, um programa de código livre usando linguagem C++, foi desenvolvido para possibilitar acesso aos sinais de interesse ainda em memória, reduzindo desta forma o tempo computacional. Além disso, para melhorar a performance, foram usadas técnicas de processamento paralelo e de computação em nuvem. Desta forma, este estudo contribui com informações indispensáveis ao projeto de equipamentos de proteção dos sistemas de transmissão em corrente contínua de forma a cooperar com o desenvolvimento consistente desta tecnologia.Transmitting electrical power in direct current using a VSC is suitable for the progress of these systems and has remarkable and advantageous applications. This happens in order to connect two systems with distinct frequencies. This type of line is also used in the reduction of losses in transmission over long distances, provided by their operating characteristics. These converters also promote the control of power flow between distinct generation units, making them effective in the context of Smart Grids. Based on this, the purpose of this research is to construct a profile of a current using a Probabilistic Short-Circuit Analysis by Monte Carlo Simulation to provide basic data to the optimum development of design equipment in protection and control. The Monte Carlo Simulation requires many iterations to find an optimal result. An open source program using C++ language was developed to describe all the system models variables in order to decrease the computation time, as it is time consuming to read signals stored on a disk using commercial software. Moreover, in order to lower computation costs, parallel process techniques and cloud computing were used. Therefore, this study contributes to the literature by providing essential information for designing equipment for Direct Current transmission protection systems.
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Dos, Santos Morgane. "Modélisation de la topologie des dépôts d’énergie créés par un rayonnement ionisant à l’échelle nanométrique dans les noyaux cellulaires et relation avec les événements précoces radio-induits." Thesis, Bordeaux 1, 2013. http://www.theses.fr/2013BOR14865/document.
Full textAbstract:
Les rayonnements ionisants sont connus pour induire des dommages critiques au sein de la matière biologique et spécialement au sein de l’ADN. Parmi ces dommages, les cassures doubles brins de l’ADN (DSB) sont considérées comme les principales responsables des effets létaux des rayonnements. Comprendre et prédire comment ces cassures sont créées et réparées dans les noyaux cellulaires demeure un défi dans la recherche en radiobiologie. Ce travail s’inscrit dans ce contexte, dans la modélisation des cassures double brin de l’ADN (DSB) à partir des dépôts d’énergie créés par l’irradiation au niveau intracellulaire. Le détail topologique au niveau nanométrique des dépôts d’énergie nécessaire à ce travail est obtenu par modélisation Monte Carlo à l’aide du code Geant4 et, en particulier son extension Geant4-DNA pour des processus à très faible énergie. Les dommages étudiés étant ceux localisés dans l’ADN, le premier objectif de ce travail a été de réaliser une géométrie détaillée de celui-ci afin de l’implémenter dans les calculs Monte Carlo. Deux types de noyaux cellulaires, représentant un fibroblaste et un endothélium, ont été décrits afin d’évaluer l’influence de la densité d’ADN dans les résultats sur la topologie des dépôts pouvant donner lieux à des cassures de la molécule. Cette géométrie nous permet d’effectuer une première sélection des dépôts d’énergie pouvant contribuer aux cassures car situées sur la chaîne sucre-phosphate. Ces dépôts sont ensuite analysés à l’aide d’un algorithme de clustérisation de manière à les regrouper sous forme d’agrégats afin d’étudier leur localisation et complexité. Néanmoins, dans cette étude, seule les interactions physiques entre les rayonnements ionisants et la cible sont modélisées, il n’est donc pas possible d’obtenir un nombre absolu de cassures de brins car cette modélisation n’inclue pas l’étape de création et de transport des radicaux libres pouvant donner lieu à des dommages indirects. Ainsi, le but de ce travail était d’évaluer la dépendance relative des dommages radio-induits directs avec la densité d’ADN, la qualité du rayonnement, la morphologie du noyau ou encore la condensation de la chromatine. Les différentes modélisations réalisées ont permis de quantifier l’influence de ces différents paramètres dans le nombre et la complexité des dommages directs induits dans l’ADN, pouvant ensuite contribuer aux effets tardifs sur le devenir cellulaireIonizing radiations are known to induce critical damages on biological matter and especially on DNA. Among these damages, DNA double strand breaks (DSB) are considered as key precursor of lethal effects of ionizing radiations. Understand and predict how DNA double and simple strand breaks are created by ionising radiation and repaired in cell nucleus is nowadays a major challenge in radiobiology research. This work presents the results on the simulation of the DNA double strand breaks produced from the energy deposited by the irradiation at the intracellular level. At the nanometric scale, the only method to accurately simulate the topological details of energy deposited on the biological matter is the use of Monte Carlo codes. In this work, we used the Geant4 Monte Carlo code and, in particular, the low energy electromagnetic package extensions, referred as Geant4-DNA processes.In order to evaluate DNA radio-induced damages, the first objective of this work consisted in implementing a detailed geometry of the DNA on the Monte Carlo simulations. Two types of cell nuclei, representing a fibroblast and an endothelium, were described in order to evaluate the influence of the DNA density on the topology of the energy deposits contributing to strand breaks. Indeed, the implemented geometry allows the selection of energy transfer points that can lead to strand breaks because they are located on the backbone. Then, these energy transfer points were analysed with a clustering algorithm in order to reveal groups of aggregates and to study their location and complexity.In this work, only the physical interactions of ionizing radiations are simulated. Thus, it is not possible to achieve an absolute number of strand breaks as the creation and transportation of radical species which could lead to indirect DNA damages is not included. Nevertheless, the aim of this work was to evaluate the relative dependence of direct DNA damages with the DNA density, radiation quality, cell nuclei morphology or also chromatin condensation. The results presented in this work have allowed the quantification of the influence of these different parameters in the number and complexity of directs DNA damages which can then contribute to the late effects on cell fate
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Zachreson, Matthew R. "Comparing Theory and Experiment for Analyte Transport in the First Vacuum Stage of the Inductively Coupled Plasma Mass Spectrometer." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3538.
Full textAbstract:
The Direct Simulation Monte Carlo algorithm as coded in FENIX is used to model the transport of trace ions in the first vacuum stage of the inductively coupled plasma mass spectrometer. Haibin Ma of the Farnsworth group at Brigham Young University measured two radial trace density profiles: one 0.7 mm upstream of the sampling cone and the other 10 mm downstream. We compare simulation results from FENIX with the experimental results. We find that gas dynamic convection and diffusion are unable to account for the experimentally-measured profile changes from upstream to downstream. Including discharge quenching and ambipolar electric fields, however, makes it possible to account for the way the profiles change.
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Ameur, Djilali. "Modélisation analytique et simulation numérique par la méthode de Monte-Carlo d'un écoulement de gaz dans des micro-canaux." Paris 6, 2008. http://www.theses.fr/2008PA066102.
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L’objectif de la thèse est de modéliser l’écoulement d’un gaz (azote) dans des micro-filtres. La région du filtrage est une membrane qui contient des orifices, en fait des micro-canaux, dont le diamètre est de quelques micromètres. Au voisinage de chaque orifice, l’écoulement du gaz supposé normal à la membrane, est en régime de raréfaction dit de ‘transition’, intermédiaire entre le régime continu relevant des équations de Navier-Stokes et le régime moléculaire libre où les molécules du gaz évoluent sans interactions entre elles. Deux approches sont utilisées pour analyser l’écoulement dans un micro-canal. La première, théorique, est basée sur une analyse adimensionnelle des équations de Navier-Stokes avec des conditions de glissement à la paroi. La seconde, numérique, est statistique et est basée sur une simulation de Monte Carlo (DSMC). Une étude paramétrique sur différentes géométries de micro-canaux est faite dans le cas d’un écoulement isotherme. Le comportement d’écoulement gazeux à travers un micro-canal est ensuite étudié en appliquant un gradient de température entre son entrée et sa sortie. Cette analyse permet de mettre en évidence le phénomène de transpiration thermique. En s’appuyant sur les résultats numériques, un modèle analytique est proposé. L’effet du coefficient d’accommodation à la paroi sur l’écoulement est aussi étudié. En fin, les effets de compressibilité sont étudiés dans un micro-canal, puis les relations liant le débit et les gradients de pression. Une simulation numérique d’écoulement au travers d’une série de micro-canaux est aussi présentée
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Cherradi, el Fadili Ibrahim. "Simulation numérique directe d'écoulements gazeux par la méthode de Monte-Carlo : application à l'étude de mélanges gazeux entre le régime continu et le régime moléculaire libre." Paris 11, 1987. http://www.theses.fr/1987PA112401.
Full textAbstract:
L'objet de cette thèse est de mettre au point un code de simulation qui permet d'étudier des écoulements de gaz raréfiés en régime de raréfaction dit de "transition", intermédiaire entre le régime continu (relevant de la mécanique des milieux continus) et le régime moléculaire libre (relevant d’une approche mathématique relativement simple). La méthode de simulation numérique utilisée est la méthode directe de Monte Carlo. Elle consiste à suivre par le calcul des milliers de "molécules simulées " ; chacune d'elles étant représentative d'un nombre beaucoup plus grand de "molécules réelles". Le gaz simulé peut être: un mélange de différents types de molécules (monoatomiques, diatomiques ou polyatomiques) en différentes proportions. La modélisation du processus de collisions intermoléculaires représente le "noyau" de la simulation : elle est basée sur les trois points essentiels suivants : - le respect de la fréquence de collision se faisant par l'utilisation de la méthode du compteur de temps de collision. - le traitement des collision avec l'hypothèse des "molécules-sphères rigides" de section fixe ou bien variable avec la vitesse relative des molécules collisionnelles. - le modèle des échanges entre énergie de translation et énergie interne des paires collisionnelles de molécules. Le bon fonctionnement et l'efficacité de l'outil numérique ainsi obtenu sont illustrés par l'étude de l'écoulement de Couette plan. En effet, les résultats des simulations ont été comparés d'une manière satisfaisante aux résultats théoriques aussi bien dans le cas d'un gaz pur que dans le cas d'un mélange. En s'éloignant progressivement du régime continu vers le régime moléculaire libre, le comportement du coefficient de viscosité a été étudié pour un gaz unique et pour un mélange. Enfin pour un mélange binaire proche du régime continu, la variation du coefficient de viscosité en fonction de la concentration relative des gaz est étudiée.
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Reichhart, Lea. "ZEPLIN-III direct dark matter search : final results and measurements in support of next generation instruments." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7914.
Full textAbstract:
Astrophysical observations give convincing evidence for a vast non-baryonic component, the so-called dark matter, accounting for over 20% of the overall content of our Universe. Direct dark matter search experiments explore the possibility of interactions of these dark matter particles with ordinary baryonic matter via elastic scattering resulting in single nuclear recoils. The ZEPLIN-III detector operated on the basis of a dualphase (liquid/gas) xenon target, recording events in two separate response channels { scintillation and ionisation. These allow discrimination between electron recoils (from background radiation) and the signal expected from Weakly Interacting Massive Particle (WIMP) elastic scatters. Following a productive first exposure, the detector was upgraded with a new array of ultra-low background photomultiplier tubes, reducing the electron recoil background by over an order of magnitude. A second major upgrade to the detector was the incorporation of a tonne-scale active veto detector system, surrounding the WIMP target. Calibration and science data taken in coincidence with ZEPLIN-III showed rejection of up to 30% of the dominant electron recoil background and over 60% of neutron induced nuclear recoils. Data taking for the second science run finished in May 2011 with a total accrued raw fiducial exposure of 1,344 kg days. With this extensive data set, from over 300 days of run time, a limit on the spin-independent WIMP-nucleon cross-section of 4.8 10-8 pb near 50 GeV/c2 WIMP mass with 90% confidence was set. This result combined with the first science run of ZEPLIN-III excludes the scalar cross-section above 3.9 10-8 pb. Studying the background data taken by the veto detector allowed a calculation of the neutron yield induced by high energy cosmic-ray muons in lead of (5.8 0.2) 10-3 neutrons/muon/(g/cm2) for a mean muon energy of 260 GeV. Measurements of this kind are of great importance for large scale direct dark matter search experiments and future rare event searches in general. Finally, this work includes a comprehensive measurement of the energy dependent quenching factor for low energy nuclear recoils in a plastic scintillator, such as from the ZEPLIN-III veto detector, increasing accuracy for future simulation packages featuring large scale plastic scintillator detector systems.
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Cherradi, el Fadili Ibrahim. "Simulation numérique directe d'écoulements gazeux par la méthode de Monte-Carlo application à l'étude de mélanges gazeux entre le régime continu et le régime moléculaire libre /." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376039268.
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Strid, Carl-Fabian. "MAC-E-Filter characterization for PTOLEMY : a relic neutrino direct detection experiment." Thesis, Luleå tekniska universitet, Rymdteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-75678.
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The cosmic neutrino background (CNB) can be composed of both active and hypothetical sterileneutrinos. At approximately one second after big bang, neutrinos decoupled from radiationand matter at a temperature of approximately one MeV. Neutrinos played an important role inthe origin and evolution of our universe and have been indirectly verified by cosmological dataon the BBN (Big Bang nucleosynthesis) of the Big Bang.It was Steven Weinberg in 1962 that first theorized on the direct detection of relic neutrinos.The signal of the relic neutrino capture on a tritium target can be observed by studying theendpoint of the electrons kinetic energy that are above the endpoint energy of the beta decayspectrum. The PTOLEMY project aims to archive direct detection of the relic neutrinobackground with a large tritium target of 100 gram, MAC-E-Filter, RF-tracking, Time of flighttracking and a cryogenic calorimetry.In this thesis the MAC-E-Filter have been simulated in two filter configurations. In the firstconfiguration, the electron were simulated five times in the filter. Two in the opposite sideof the detector, one in the middle, and two at the detector. In the second configuration theelectrons was simulated in the entrance solenoid at a fixed position of y = -0.19634954 m fromthe center of the filter and in random positions. Both multiple electrons and single electronswere simulated in the second configuration.In the single electron configuration the electron had a starting position of y = -0.19634954 mfrom the center of the filter, and an initial kinetic energy of 18.6 KeV. The first filter configurationsuccessfully accomplished to simulate the electron track, as the electron was reflectedback and forth between the entry and detector solenoid. The electric and magnetic field profilediered at the entry and detector solenoid. The second filter configuration successfully showedthat the electron will reach the end solenoid, when the filter length was 0.5 m. When the filterlength was increased to 0.7 m, then the electron was reflected in the middle of the filter. Thesimulation showed that the electron energy dropped below 1 eV from 18.6 KeV as the electronpropagated through the filter. The magnetic and electric fields decreased exponentially in thedirection of the detector solenoid. The Simulation of multiple electrons showed mixed resultsand would need more modifications in order to come to a final conclusion.
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Bernardo, Félix Ferreira. "Impacto do heaping em modelos para dados de duração." Master's thesis, Instituto Superior de Economia e Gestão, 2007. http://hdl.handle.net/10400.5/1007.
Full textAbstract:
Mestrado em Econometria Aplicada e PrevisãoDados de duração são muitas vezes obtidos recorrendo a questionários em que os sujeitos sao inquiridos sobre aspectos do seu passado. Dados retrospectivos podem conter vários tipos de imprecisões uma delas é o aparecimento de frequências anormalmente elevadas para certas durações. Na literatura este tipo de anormalidade é conhecido por heaping . Alguns trabalhos anteriores demonstraram que até heaping simétrico pode conduzir a inconsistência dos estimadores de máxima verosimilhanca. No trabalho que se segue aprofundamos, recorrendo à simulação de Monte Carlo, as consequências do heaping na estimação dos parametros de um modelo Weibull para dados de duração completos e censurados à direita. Comparamos ainda as consequências, para a estimação por máxima verosimilhanca, de diferentes percentagens de heaping e diferentes dimensões de censura.
Duration data are, many times, acquired by questionnaires where the subjects are inquired about some aspects of its past. Retrospective data may contain some form of response error where the most notorious are the appearance of abnormally high frequencies for certain durations. In the literature this type of abnormality is known as heaping. Some previous works have shown that even symmetrical heaping can lead to inconsistency of maximum likelihood estimators. In the work that follows we use Monte Carlo simulation to study the consequences of heaping in the estimation of the parameters of a Weibull model with completed and right censored duration data. We evaluate also the consequences, for maximum likelihood estimation, of different percentages of heaping and different dimensions of censoring.
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Zachreson, Matthew R. "Comparing Theory and Experiment for Analyte Transport in the First Vacuum Stage of the Inductively Coupled Plasma Mass Spectrometer." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5610.
Full textAbstract:
The inductively coupled plasma mass spectrometer (ICP-MS) has been used in laboratories for many years. The majority of the improvements to the instrument have been done empirically through trial and error. A few fluid models have been made, which have given a general description of the flow through the mass spectrometer interface. However, due to long mean free path effects and other factors, it is very difficult to simulate the flow details well enough to predict how changing the interface design will change the formation of the ion beam. Towards this end, Spencer et al. developed FENIX, a direct simulation Monte Carlo algorithm capable of modeling this transitional flow through the mass spectrometer interface, the transitional flow from disorganized plasma to focused ion beam. Their previous work describes how FENIX simulates the neutral ion flow. While understanding the argon flow is essential to understanding the ICP-MS, the true goal is to improve its analyte detection capabilities. In this work, we develop a model for adding analyte to FENIX and compare it to previously collected experimental data. We also calculate how much ambipolar fields, plasma sheaths, and electron-ion recombination affect the ion beam formation. We find that behind the sampling interface there is no evidence of turbulent mixing. The behavior of the analyte seems to be described simply by convection and diffusion. Also, ambipolar field effects are small and do not significantly affect ion beam formation between the sampler and skimmer cones. We also find that the plasma sheath that forms around the sampling cone does not significantly affect the analyte flow downstream from the skimmer. However, it does thermally insulate the electrons from the sampling cone, which reduces ion-electron recombination. We also develop a model for electron-ion recombination. By comparing it to experimental data, we find that significant amounts of electron-ion recombination occurs just downstream from the sampling interface.
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Rocheman, Simon. "Validation expérimentale des outils de simulation des réactions nucléaires induites par les neutrons et les protons dans le silicium : irradiation d'une diode silicium et d'une caméra CCD." Montpellier 2, 2008. http://www.theses.fr/2008MON20241.
Full textAbstract:
L'environnement spatial est un environnement radiatif principalement composé de protons. En plus de représenter un danger pour l'électronique, ces particules sont à l'origine de neutrons secondaires dans l'atmosphère. Lorsqu'elles traversent la matière, ces protons et ces neutrons peuvent provoquer des réactions nucléaires et ainsi créer des particules ionisantes. Par ce biais, les réactions nucléaires induites avec le silicium des composants électroniques peuvent provoquer des dysfonctionnements. Ces erreurs posent de réels problèmes dans les applications avioniques et spatiales. Des outils de simulation de réactions nucléaires ont été développés pour prévoir l'occurrence de ces erreurs. Des bases de données décrivant les réactions nucléaires neutron – silicium et proton – silicium entre 1 MeV et 200 MeV ont été générées à partir d'un code de calcul. L'objectif de ce travail de thèse est de valider ces bases de données. Dans un premier temps, des données expérimentales publiques de physique nucléaire nous ont permis de vérifier certains aspects des bases de données. Dans un second temps, nous avons irradié deux détecteurs à base de silicium (une diode et un capteur de caméra CCD) et confronté les simulations de ces expériences à l'aide des bases de données aux résultats expérimentauxThe spatial environment is a radiative environment mostly composed of protons. These particles are not only a danger for electronic component but they also leads to secondary neutrons in the atmosphere. When these protons and neutrons go through matter, they can induce nuclear reaction and then create ionizing particles. By this mean, nuclear reactions induced with silicon in electronic component can cause malfunctions. These mistakes are a real issue for applications in planes or space. Some nuclear reaction simulation tools have been developed to predict the error rate. For neutron - silicon and proton - silicon reactions between 1 and 200 MeV, databases have been generated by a nuclear physic code. The aim of this work of thesis is to validate the databases. In a first step, nuclear physic public experimental data have been used to verify some aspects of the databases. In addition, we irradiated two silicon based sensors (a diode and a CCD camera) and we confronted the simulation of these experiment using databases to experimental results
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Turgut, Ozhan Hulusi. "Effects Of Extrapolation Boundary Conditions On Subsonic Mems Flows Over A Flat Plate." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12606962/index.pdf.
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In this research, subsonic rarefied flows over a flat-plate at constant pressure are investigated using the direct simulation Monte Carlo (DSMC) technique. An infinitely thin plate (either finite or semi-infinite) with zero angle of attack is considered. Flows with a Mach number of 0.102 and 0.4 and a Reynolds number varying between 0.063 and 246 are considered covering most of the transitional regime between the free-molecule and the continuum limits. A two-dimensional DSMC code of G.A. Bird is used to simulate these flows, and the code is modified to examine the effects of various inflow and outflow boundary conditions. It is observed that simulations of the subsonic rarefied flows are sensitive to the applied boundary conditions. Several extrapolation techniques are considered for the evaluation of the flow properties at the inflow and outflow boundaries. Among various alternatives, four techniques are considered in which the solutions are found to be relatively less sensitive. In addition to the commonly used extrapolation techniques, in which the flow properties are taken from the neighboring boundary cells of the domain, a newly developed extrapolation scheme, based on tracking streamlines, is applied to the outflow boundaries, and the best results are obtained using the new extrapolation technique together with the Neumann boundary conditions. With the new technique, the flow is not distorted even when the computational domain is small. Simulations are performed for various freestream conditions and computational domain configurations, and excellent agreement is obtained with the available experimental data.
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Pakalidou, Nikoletta. "Self-assembly of two-dimensional convex and nonconvex colloidal platelets." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/selfassembly-of-twodimensional-convex-and-nonconvex-colloidal-platelets(072e9fad-3e34-4803-b3df-6aed3ce756c7).html.
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One of the most promising routes to create advanced materials is self-assembly. Self-assembly refers to the self-organisation of building blocks to form ordered structures. As the properties of the self-assembled materials will inherit the properties of the basic building blocks, it is then possible to engineer the properties of the materials by tailoring the properties of the building blocks. In order to create mesoscale materials, the self-assembly of molecular building blocks of different sizes and interactions is important. Mesoscopic materials can be obtained by using larger building blocks such as nano and colloidal particles. Colloidal particles are particularly attractive as building blocks because it is possible to design interparticle interactions by controlling both the chemistry of the particles' surface and the properties of the solvent in which the particles are immersed. The self-assembly of spherical colloidal particles has been widely reported in the literature. However, advances in experimental techniques to produce particles with different shapes and sizes have opened new opportunities to create more complex structures that cannot be formed using spherical particles. Indeed, the particles' shape and effective interactions between them dictate the spatial arrangement and micro-structure of the system, which can be engineered to produce functional materials for a wide range of applications. The driving forces determining the self-assembly of colloidal particles can be modified by the use of external influences such as geometrical confinement and electromagnetic forces. Geometrical confinement, for example, has been used to design quasi two-dimensional materials such as multi-layered structures of spheres, dimers, rods, spherical caps, and monolayers of platelets with various geometries and symmetries. In this dissertation, we present three computer simulations studies using Monte Carlo and Molecular Dynamics simulations determining the self-assembly of monolayer colloidal platelets with different shapes confined in two dimensions. These particles have been selected due to recent experiments in colloidal particles with similar shapes. All the particles' models are represented by planar polygons, and three different effects affecting their self-assembly have been analysed: (a) the curvature of the particles' vertices; (b) the curvature of the particles' edges; and finally (c) the addition of functional groups on the particles' surface. These studies aim to demonstrate that the subtle changes on the particle's shape can be used to engineer complex patterns for the fabrication of advanced materials. Monte Carlo simulations are performed to study the self-assembly of colloidal platelets with rounded corners with 4, 5, and 6-fold symmetries. Square platelets provide a rich phase behaviour that ranges between disorder-order and order-order phase transitions. Suprisingly, the disk-like shape of pentagons and hexagons prevents the total crystallisation of these systems, even at a high pressure state. A hysteresis gap is observed by the analysis of compression and expansion runs for the case of square platelets and the thermodynamic method known as direct coexistence method is used to be accurately determined the point of the order-order transition. Further, unexpected results are obtained by performing Molecular Dynamics simulations in systems with platelets with 3, 4, 5, and 6-fold symmetries when all the sides of each polygon are curved. Macroscopic chiral symmetry breaking is observed for platelets with 4 and 6-fold symmetries, and for the first time a rule is promoted to explain when these chiral structures can be formed driven only by packing effects. This unique rule is verified also for platelets with the same curved sides as previously when functional chains tethered to either vertices or sides. Indeed, square platelets with curved sides confined in two dimensions can form chiral structures at medium densities when flexible chains tethered to either vertices or sides. Triangular platelets with curved sides can form chiral structures only when the chains are tethered to the corners, since the chains experience an one-hand rotation to sterically protect one side. When the chains are symmetrically tethered to the sides, local chiral symmetry breaking is observed as both left-hand and right-hand sides on each vertex are sterically protected allowing the same probability for rotation either in clockwise or anticlockwise direction.
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Janzon, Krister. "Monte Carlo Path Simulation and the Multilevel Monte Carlo Method." Thesis, Umeå universitet, Institutionen för fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-151975.
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A standard problem in the field of computational finance is that of pricing derivative securities. This is often accomplished by estimating an expected value of a functional of a stochastic process, defined by a stochastic differential equation (SDE). In such a setting the random sampling algorithm Monte Carlo (MC) is useful, where paths of the process are sampled. However, MC in its standard form (SMC) is inherently slow. Additionally, if the analytical solution to the underlying SDE is not available, a numerical approximation of the process is necessary, adding another layer of computational complexity to the SMC algorithm. Thus, the computational cost of achieving a certain level of accuracy of the estimation using SMC may be relatively high. In this thesis we introduce and review the theory of the SMC method, with and without the need of numerical approximation for path simulation. Two numerical methods for path approximation are introduced: the Euler–Maruyama method and Milstein's method. Moreover, we also introduce and review the theory of a relatively new (2008) MC method – the multilevel Monte Carlo (MLMC) method – which is only applicable when paths are approximated. This method boldly claims that it can – under certain conditions – eradicate the additional complexity stemming from the approximation of paths. With this in mind, we wish to see whether this claim holds when pricing a European call option, where the underlying stock process is modelled by geometric Brownian motion. We also want to compare the performance of MLMC in this scenario to that of SMC, with and without path approximation. Two numerical experiments are performed. The first to determine the optimal implementation of MLMC, a static or adaptive approach. The second to illustrate the difference in performance of adaptive MLMC and SMC – depending on the used numerical method and whether the analytical solution is available. The results show that SMC is inferior to adaptive MLMC if numerical approximation of paths is needed, and that adaptive MLMC seems to meet the complexity of SMC with an analytical solution. However, while the complexity of adaptive MLMC is impressive, it cannot quite compensate for the additional cost of approximating paths, ending up roughly ten times slower than SMC with an analytical solution.
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Lin, Xichen. "Monte Carlo Simulation and Integration." Scholarship @ Claremont, 2018. https://scholarship.claremont.edu/cmc_theses/2009.
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In this paper, we introduce the Tootsie Pop Algorithm and explore its use in different contexts. It can be used to estimate more general problems where a measure is defined, or in the context of statistics application, integration involving high dimensions. The Tootsie Pop Algorithm was introduced by Huber and Schott[2] The general process of Tootsie Pop Algorithm, just like what its name suggests, is a process of peeling down the outer shell, which is the larger enclosing set, to the center, which is the smaller enclosed. We obtain the average number of peels, which gives us an understanding of the ratio between the size of the shell and the size of the center. Each peel is generated by a random draw within the outer shell: if the drawn point is located in the center, we are done, else we update the outer shell such that the drawn point is right on its edge.
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Lee, Ming Ripman, and 李明. "Monte Carlo simulation for confined electrolytes." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31240513.
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Swetnam, Adam D. "Monte Carlo simulation of lattice polymers." Thesis, University of Warwick, 2011. http://wrap.warwick.ac.uk/49196/.
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The phase behaviour of lattice polymers and peptides, under various conditions, is investigated using Monte Carlo simulation. Wang-Landau sampling is used so that, in principle, phase diagrams can be determined from a single simulation. It is demonstrated that the pseudophase diagram for polymer molecules, in several environments, can be plotted when sampling only from the internal degrees of freedom, by determining an appropriate density of states. Several improvements to the simulation methods used are detailed. A new prescription for setting the modification factor in the Wang-Landau algorithm is described, tested and found, for homopolymers, to result in near optimum convergence throughout the simulation. Different methods of selecting moves from the pull move set are detailed, and their relative efficiencies determined. Finally, it is shown that results for a polymer in a slit with one attractive surface can be determined by sampling only from the internal degrees of freedom of a lattice polymer. Adsorption of lattice polymers and peptides is investigated by determining pseudophase diagrams for individual molecules. The phase diagram for a homopolymer molecule, near a surface with a pattern of interaction, is determined, with a pseudophase identified where the polymer is commensurate with the pattern. For an example lattice peptide, the existence of the new pseudophase is found to depend on whether both hydrophobic and polar beads are attracted to the surface. The phase diagram for a ring polymer under applied force, with variable solvent quality, is determined for the first time. The effect, on the phase diagram, of topological knots in the ring polymer is investigated. In addition to eliminating pseudophases where the polymer is flattened into a single layer, it is found that non-trivial knots result in additional pseudophases for tensile force.
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Lee, Ming Ripman. "Monte Carlo simulation for confined electrolytes /." Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B22055009.
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Guillemin, Perrine. "Recherche de la haute conversion en cycle thorium dans les réacteurs CANDU et REP : Développement des méthodes de simulation associées et étude de scénarios symbiotiques." Grenoble INPG, 2009. http://www.theses.fr/2009INPG0176.
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Ce travail explore la compétitivité des réacteurs actuels (CANDU et REP) en cycle thorium afin de pallier au problème d'utilisation des ressources naturelles en uranium et aux problèmes de disponibilité et de coût des réacteurs de quatrième génération dans le cadre d'un nucléaire durable. Ce travail s'est focalisé sur l'analyse neutronique de deux types de gestion du combustible thorium : la production d'233U à partir de combustible Th/Pu et la conversion d'233U dans ces réacteurs. En particulier, la régénération en CANDU Th/U multirecyclé a été établie. En amont de ces études, les outils et les données utilisés ont fait l'objet d'une validation par une comparaison entre codes (stochastique et déterministe). Des scénarios symbiotiques, combinant réacteurs et combustibles uranium et thorium, ont été évalués et comparés. Ce travail a abouti à la quantification des gains sur la consommation des ressources, avec des modifications technologiques mineures des réacteurs. Des modifications plus poussées pour obtenir la régénération en REP ont été proposées et étudiées à titre préliminaireIn the frame of a sustainable nuclear energy, this study assesses Thorium-fueled CANDU and PWR competitiveness to reduce access difficulties to cheap uranium resources and Gen. IV cost and availability problems. It focuses on neutronic analysis of two thorium fuel management options : 233U production from Th/Pu fuels and 233U conversion in these reactors. In particular, breeding in multirecycled Th/U CANDU has been established. Before this work, simulation methods and nuclear data have been validated by cross-checking two different types of codes (probabilistic and deterministic). Symbiotic scenarios, with various reactor and fuel combinations have been evaluated and compared. Resources savings have been quantified through core slight modifications. Deeper modifications towards breeding in PWR have been proposed and preliminarily studied
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Bryskhe, Henrik. "Optimization of Monte Carlo simulations." Thesis, Uppsala University, Department of Information Technology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-121843.
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This thesis considers several different techniques for optimizing Monte Carlo simulations. The Monte Carlo system used is Penelope but most of the techniques are applicable to other systems. The two mayor techniques are the usage of the graphics card to do geometry calculations, and raytracing. Using graphics card provides a very efficient way to do fast ray and triangle intersections. Raytracing provides an approximation of Monte Carlo simulation but is much faster to perform. A program was also written in order to have a platform for Monte Carlo simulations where the different techniques were implemented and tested. The program also provides an overview of the simulation setup, were the user can easily verify that everything has been setup correctly. The thesis also covers an attempt to rewrite Penelope from FORTAN to C. The new version is significantly faster and can be used on more systems. A distribution package was also added to the new Penelope version. Since Monte Carlo simulations are easily distributed, running this type of simulations on ten computers yields ten times the speedup. Combining the different techniques in the platform provides an easy to use and at the same time efficient way of performing Monte Carlo simulations.
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Voegele, Simon. "Shortfall-Minimierung Theorie und Monte Carlo Simulation /." St. Gallen, 2007. http://www.biblio.unisg.ch/org/biblio/edoc.nsf/wwwDisplayIdentifier/02922300001/$FILE/02922300001.pdf.
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Jud, Andreas. "Monte-Carlo-Simulation einer Überstruktur auf Lipidmembranen." [S.l. : s.n.], 1998. http://www.diss.fu-berlin.de/1998/18/index.html.
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Yangthaisong, Anucha. "Monte Carlo simulation of silicon-germanium transistors." Thesis, Durham University, 2002. http://etheses.dur.ac.uk/4025/.
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Self-consistent Monte Carlo simulation studies of n-channel Si/SiGe modulation doped field effect transistors (MODFETs) and silicon-on-insulator lateral bipolar junction transistors (SOI- LBJTs) are reported in this thesis. As a preliminary to the device studies Monte Carlo simulations of electron transport in bulk Si strained as if grown on Si(_0.77)Ge(_0.23) and Si(_0.55)Ge(_0.45) substrates have been carried out at 300 K, for field strengths varied from 10(^4) to 2 x 10(^7) Vm(^-1). The calculations indicate an enhancement of the average electron drift velocity when Si is tensilely strained in the growth plane. The enhancement of electron velocity is more marked at low and intermediate electric fields, while at very high fields the velocity saturates at about the same value as unstrained Si. In addition the ensemble Monte Carlo method has been used to study the transient response to a stepped electric field of electrons in strained and unstrained Si. The calculations suggest that significant velocity overshoots occurs in strained material. Simulations of n-channel Si/Si(_1=z)Ge(_z) MODFETs with Ge fractions of 0.23, 0.25, and 0.45 have been performed. Five depletion mode devices with x = 0.23 and 0.25 were studied. The simulations provide information on the microscopic details of carrier behaviour, including carrier velocity, kinetic energy and carrier density, as a function of position in the device. Detailed time-dependent voltage signal analysis has been carried out to test device response and derive the frequency bandwidth. The simulations predict a current gain cut-off frequency of 60 ± 10 GHz for a device with a gate length of 0.07 /nm and a channel length of 0.25 um. Similar studies of depletion and enhancement mode n-channel Si/Sio.55Geo.45 MODFETs with a gate length of 0.18 /im have been carried out. Cut-off frequencies of 60 ±10 GHz and 90± 10 GHz are predicted for the depletion and enhancement mode devices respectively. A Monte Carlo model has also been devised and used to simulate steady state and transient electron and hole transport in SOI-LBJTs. Four devices have been studied and the effects of junction depth and silicon layer thickness have been investigated. The advantage of the silicon-on-insulator technology SOI device is apparent in terms of higher collector current, current gain, and cut-off frequency obtained in comparison with an all-silicon structure. The simulations suggest that the common-emitter current gain of the most promising SOI-LBJT structure considered could have a cut-off frequency approaching 35 ± 5 GHz.
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Mee, Richard A. W. "Monte Carlo simulation of step growth polymerization." Thesis, Queen's University Belfast, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318843.
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Sharma, Anupam. "Numerical simulations of blast-impact problems using the direct simulation Monte Carlo." 2004. http://etda.libraries.psu.edu/theses/approved/WithheldIndex/ETD-721/index.html.
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