Dissertations / Theses: 'Two-mass model'

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Burns, Michael E. "Model-independent mass and spin determination for a sequential decay with a jet and two leptons." [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0024843.

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Mottet, Laetitia. "Simulations of heat and mass transfer within the capillary evaporator of a two-phase loop." Thesis, Toulouse, INPT, 2016. http://www.theses.fr/2016INPT0012/document.

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Le contrôle thermique des composants électroniques embarqués dans les engins spatiaux est souvent assuré par des boucles fluides diphasiques à pompage capillaire (Loop Heat Pipe (LHP) ou Capillary Pumped Loop (CPL)). La présente étude est centrée sur les évaporateurs des LHP. Ils sont composés principalement d’un bâti métallique, d’une mèche poreuse et de cannelures. Le milieu poreux est initialement saturé en liquide. La charge thermique à évacuer est appliquée sur le bâti entraînant la vaporisation du liquide au sein de la mèche. La vapeur est ensuite récoltée au sein des cannelures pour être évacuée. L’étude est effectuée sur une cellule unitaire de l’évaporateur. Dans le but d’étudier les transferts de masse et de chaleur, un modèle de réseau de pores 3D dit mixte a été développé. Les champs de pression et de température sont calculés à partir des équations macroscopiques tandis que la capillarité est gérée à l’aide d’une approche réseau de pore classique. L’un des avantages d’une telle formulation est de pouvoir accéder à la répartition des phases liquide et vapeur au sein de l’espace poral du milieu poreux. Il a ainsi été mis en évidence qu’une zone diphasique (zone où le liquide et la vapeur coexistent) se met en place pour une large gamme de flux lorsque la vapeur apparait dans la structure capillaire. Cette zone diphasique est localisée sous le bâti métallique et est corrélée avec les meilleures performances thermiques de l’évaporateur. Cette observation diffère fortement de l’hypothèse souvent considérée de la présence d’une zone sèche dans cette région. Trois positions différentes de cannelures ont été étudiées. Il a ainsi pu être mis en évidence que la plus large gamme de flux, pour laquelle les performances de l’évaporateur sont les meilleures, est obtenue lorsque les cannelures sont usinées à la surface extérieure de la mèche. Toujours dans le but d’améliorer les performances thermiques de l’évaporateur, une étude paramétrique a été menée pour mettre en évidence les paramètres qui influencent positivement la conductance de l’évaporateur. Finalement, l’étude de l’influence d’une mèche biporeuse/bidispersée, c’est-à-dire d’un milieu poreux caractérisé par deux tailles de pores/liens différentes, a été menée. La distribution des phases liquide et vapeur au sein de la structure capillaire bidispersée est différente de celle d’un milieu mono-poreux du fait des chemins préférentiels créés par les larges pores. Par ailleurs, l’analyse thermique a montré qu’un tel milieu poreux permet de réduire considérablement la température du bâti ainsi que d’augmenter les performances thermiques de l’évaporateur. Un deuxième modèle basé sur une approche continue a été développé. Cette méthode utilise l’algorithme IMPES (IMplicit Pressure Explicit Saturation) et est couplé à la résolution du champ de température avec changement de phase. Ce type de résolution permet d’accéder à un champ de saturation. Les résultats ainsi obtenus sont en bon accord avec ceux prédits par le modèle réseau de pores mixte. Le modèle continu, moins gourmand en temps de calcul, permet d’envisager des simulations sur une plus grande partie de l’évaporateur
The thermal control of electronic devices embedded in spacecraft is often carried out by capillary twophase loop systems (Loop Heat Pipe (LHP) or Capillary Pumped Loop (CPL)). This thesis focuses on the LHP evaporators. They mostly consist of a metallic casing, a porous wick and vapour grooves. The porous medium is initially saturated with liquid. The heat load is applied at the external surface of the casing inducing the vaporisation of the liquid within the wick. The vapour is then evacuated thanks to the vapour grooves. A unit cell of the evaporator is studied and corresponds to our computational domain. A so-called 3D mixed pore network model has been developed in order to study the heat and mass transfers. Pressure and temperature fields are computed from macroscopic equations, while the capillarity is managed using the classical pore network approach. The main advantage of such formulation is to obtain the liquid-vapour phase distribution within the porous medium pore space. The work highlights that a two-phase zone (characterized by the coexistence of the liquid and the vapour) exists for a large range of fluxes when vaporisation takes place within the capillary structure. This twophase zone is located right under the casing and is positively correlated with the best evaporator thermal performances. This result differs from the often made assumption of a dry region under the casing. Three different groove locations are tested. This investigation highlights that evaporator thermal performances are the best over a large range of fluxes for grooves manufactured at the external surface of the wick. In complement, a parametric study is performed to highlight parameters which impact positively the evaporator thermal performances. Finally, a biporous/bidispersed wick, i.e. a wick with a bimodal pore/throat size distribution, is studied. The liquidvapour phase distribution within the capillary structure is different from the one for a monoporous structure due to preferential vapour paths created by the large throats and pores-network. Moreover, the thermal analysis shows that such a porous medium permits to reduce considerably the evaporator wall temperature and to increase the evaporator thermal performances. A second model is developed based on a continuum approach. This method uses the IMPES (IMplicit Pressure Explicit Saturation) algorithm coupled with the heat transfer with phase change. Results are in good agreement with those predicted by the mixed pore network model. The continuum model, requiring less computing time, should allow considering larger sub domains of the evaporator

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Beranek, Sarah [Verfasser], Stefan [Akademischer Betreuer] Schael, and Thomas [Akademischer Betreuer] Hebbeker. "Model independent search for new particles in two-dimensional mass space using events with missing energy, two jets and two leptons with the CMS detector / Sarah Beranek ; Stefan Schael, Thomas Hebbeker." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/116141200X/34.

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Skoglund, Emil. "A NUMERICAL MODEL OF HEAT- AND MASS TRANSFER IN POLYMER ELECTROLYTE FUEL CELLS : A two-dimensional 1+1D approach to solve the steady-state temperature- and mass- distributions." Thesis, Mälardalens högskola, Framtidens energi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-55223.

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Methods of solving the steady state characteristics of a node matrix equation system over a polymer electrolyte fuel cell (PEFC) were evaluated. The most suitable method, referred to as the semi-implicit method, was set up in a MATLAB program. The model covers heat transfer due to thermal diffusion throughout the layers and due to thermal advection+diffusion in the gas channels. Included mass transport processes cover only transport of water vapor and consist of the same diffusion/advection schematics as the heat transfer processes. The mass transport processes are hence Fickian diffusion throughout all the layers and diffusion+advection in the gas channels. Data regarding all the relevant properties of the layer materials were gathered to simulate these heat- and mass transfer processes.Comparing the simulated temperature profiles obtained with the model to the temperature profiles of a previous work’s model, showed that the characteristics and behavior of the temperature profile are realistic. There were however differences between the results, but due to the number of unknown parameters in the previous work’s model it was not possible to draw conclusions regarding the accuracy of the model by comparing the results.Comparing the simulated water concentration profiles of the model and measured values, showed that the model produced concentration characteristics that for the most part alignedwell with the measurement data. The part of the fuel cell where the concentration profile did not match the measured data was the cathode side gas diffusion layer (GDL). This comparison was however performed with the assumption that relative humidity corresponds to liquid water concentration, and that this liquid water concentration is in the same range as the measured data. Because of this assumption it was not possible to determine the accuracy of the model.

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Smith, Austin. "Agreement Level of Running Temporal Measurements, Kinetics, and Force-Time Curves Calculated from Inertial Measurement Units." Digital Commons @ East Tennessee State University, 2021. https://dc.etsu.edu/etd/3861.

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Inertial measurement units (IMUs) and wearable sensors have enabled athlete monitoring and research to become more ecologically valid due to their small size and low cost. IMUs and accelerometers that are placed on the body close to the point of impact and that record at sufficiently high frequencies have demonstrated the highest validity when measuring temporal gait event moments such as ground contact time (GCT) and flight time (FT) as well as peak forces (PF) during upright running. While the use of IMUs has increased in the sport performance and athlete monitoring realm, the potential of the technology’s ability to estimate running force-time curves utilizing the two-mass model (TMM) remains unexplored. The purpose of this study was two-fold. First, was to determine the validity of measuring temporal gait events and peak forces utilizing a commercially available shank-mounted inertial measurement unit. Second, was to determine the validity of force-time curves generated from the TMM utilizing data from shank-mounted inertial measurement units. Ten subjects voluntarily completed submaximal treadmill tests equipped with a force plate while wearing shank-mounted IMUs on each leg. Using the raw data from the IMUs, GCT, FT, total step time (ST), PF, and two-mass model-based force-time (F-t) curves were generated for 25 steps at 8 different speeds. Paired sample T-tests were performed on the gait events and peak force between the IMU and treadmill with both individual step comparison and averages per each speed. 95% confidence intervals were calculated for each timepoint of the force time curves. No statistically significant differences (p > 0.05) and nearly perfect relationships were observed for the step averages for each speed with FT, ST, and PF. Confidence intervals of the corrected mean difference suggest that F-t curves calculated from the TMM may not be valid when assessing the running population as a whole. When performing a sub-group analysis of skilled runners and recreational runners, F-t curves derived from shank-mounted IMUs may be more valid in skilled runners than recreational runners. In skilled runners, the 95% CI for the mean difference contained zero within the first 60% of the GCT duration, whereas the 95% CI recreational runners contained a zero-value in a smaller percentage of the GCT located only in the middle of the GCT at the curve peak height. The results of this study suggest that interchangeability between shank-mounted IMUs and force plates may be very limited when estimating temporal gait events and kinetics. While agreement was low between F-t curves after the peak in skilled runners, use of shank-mounted IMUs to estimate F-t curves may have several benefits still in skilled runners when assessing peak forces and force development from initial contact until peak force.

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Song, Yang. "Unstructured Nodal Discontinuous Galerkin Method for Convection-Diffusion Equations Applied to Neutral Fluids and Plasmas." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/99291.

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In recent years, the discontinuous Galerkin (DG) method has been successfully applied to solving hyperbolic conservation laws. Due to its compactness, high order accuracy, and versatility, the DG method has been extensively applied to convection-diffusion problems. In this dissertation, a numerical package, texttt{PHORCE}, is introduced to solve a number of convection-diffusion problems in neutral fluids and plasmas. Unstructured grids are used in order to randomize grid errors, which is especially important for complex geometries. texttt{PHORCE} is written in texttt{C++} and fully parallelized using the texttt{MPI} library. Memory optimization has been considered in this work to achieve improved efficiency. DG algorithms for hyperbolic terms are well studied. However, an accurate and efficient diffusion solver still constitutes ongoing research, especially for a nodal representation of the discontinuous Galerkin (NDG) method. An affine reconstructed discontinuous Galerkin (aRDG) algorithm is developed in this work to solve the diffusive operator using an unstructured NDG method. Unlike other reconstructed/recovery algorithms, all computations can be performed on a reference domain, which promotes efficiency in computation and storage. In addition, to the best of the authors' knowledge, this is the first practical guideline that has been proposed for applying the reconstruction algorithm on a nodal discontinuous Galerkin method. TVB type and WENO type limiters are also studied to deal with numerical oscillations in regions with strong physical gradients in state variables. A high-order positivity-preserving limiter is also extended in this work to prevent negative densities and pressure. A new interface tracking method, mass of fluid (MOF), along with its bound limiter has been proposed in this work to compute the mass fractions of different fluids over time. Hydrodynamic models, such as Euler and Navier-Stokes equations, and plasma models, such as ideal-magnetohydrodynamics (MHD) and two-fluid plasma equations, are studied and benchmarked with various applications using this DG framework. Numerical computations of Rayleigh-Taylor instability growth with experimentally relevant parameters are performed using hydrodynamic and MHD models on planar and radially converging domains. Discussions of the suppression mechanisms of Rayleigh-Taylor instabilities due to magnetic fields, viscosity, resistivity, and thermal conductivity are also included. This work was partially supported by the US Department of Energy under grant number DE-SC0016515. The author acknowledges Advanced Research Computing at Virginia Tech for providing computational resources and technical support that have contributed to the results reported within this work. URL: http://www.arc.vt.edu
Doctor of Philosophy
High-energy density (HED) plasma science is an important area in studying astrophysical phenomena as well as laboratory phenomena such as those applicable to inertial confinement fusion (ICF). ICF plasmas undergo radial compression, with an aim of achieving fusion ignition, and are subject to a number of hydrodynamic instabilities that can significantly alter the implosion and prevent sufficient fusion reactions. An understanding of these instabilities and their mitigation mechanisms is important allow for a stable implosion in ICF experiments. This work aims to provide a high order accurate and robust numerical framework that can be used to study these instabilities through simulations. The first half of this work aims to provide a detailed description of the numerical framework, texttt{PHORCE}. texttt{PHORCE} is a high order numerical package that can be used in solving convection-diffusion problems in neutral fluids and plasmas. Outstanding challenges exist in simulating high energy density (HED) hydrodynamics, where very large gradients exist in density, temperature, and transport coefficients (such as viscosity), and numerical instabilities arise from these region if there is no intervention. These instabilities may lead to inaccurate results or cause simulations to fail, especially for high-order numerical methods. Substantial work has been done in texttt{PHORCE} to improve its robustness in dealing with numerical instabilities. This includes the implementation and design of several high-order limiters. An novel algorithm is also proposed in this work to solve the diffusion term accurately and efficiently, which further enriches the physics that texttt{PHORCE} can investigate. The second half of this work involves rigorous benchmarks and experimentally relevant simulations of hydrodynamic instabilities. Both advection and diffusion solvers are well verified through convergence studies. Hydrodynamic and plasma models implemented are also validated against results in existing literature. Rayleigh-Taylor instability growth with experimentally relevant parameters are performed on both planar and radially converging domains. Although this work is motivated by physics in HED hydrodynamics, the emphasis is placed on numerical models that are generally applicable across a wide variety of fields and disciplines.

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Teuber, Katharina [Verfasser], Reinhard [Akademischer Betreuer] Hinkelmann, Reinhard [Gutachter] Hinkelmann, Gunnar [Gutachter] Nützmann, Dirk [Gutachter] Muschalla, and Jann [Gutachter] Strybny. "A three-dimensional two-phase model for flow, transport and mass transfer processes in sewers / Katharina Teuber ; Gutachter: Reinhard Hinkelmann, Gunnar Nützmann, Dirk Muschalla, Jann Strybny ; Betreuer: Reinhard Hinkelmann." Berlin : Technische Universität Berlin, 2020. http://d-nb.info/1204478066/34.

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Zaccarelli, Riccardo. "Mathematical modelling of sound production in birds." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2009. http://dx.doi.org/10.18452/16507.

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In dieser Arbeit wird die Physik der Stimm- und Lautbildung von Vögeln untersucht, wobei zwei verschiedene Zwei-Massen-Modelle des menschlichen Kehlkopfes, sowie die Theorie der Nichtlinearen Dynamik verwendet werden. Die Zwei-Massen-Modelle des menschlichen Kehlkopfes (ein angepasstes Zwei-Massen-Modell und ein Trapez-Modell) wurden dazu an die Größe des Stimmorgans der Vögel (Syrinx) angepasst, um die Druckentstehung, die Steuerung der harmonischen Obertöne und "Register" studieren zu können, die vom Syrinx ohne Kopplung an Quelle und Vokaltrakt erzeugt werden. Unsere Simulationen sind ein erster Schritt in Richtung eines realistischeren Modells der Syrinx. Eine detaillierte Bifurkationsanalyse des Trapezmodells bestätigt, dass die Geometrie und die Ruhelage der Syrinx das harmonische Spektrum drastisch beeinflussen können, und sie gibt Hinweise über mögliche Erzeugungsmechanismen der reichhaltigen harmonischen Spektren während der Einatmung. Des weiteren wird die Bifurkationsanalyse benutzt, um den Beitrag der Muskeln der Syrinx quantitativ zu beschreiben. Dies geschieht in dem Modell mit Hilfe von zeitabhängigen Parametern, welche die Ruhelage der Labia und die Frequenzmodulation steuern.
In this thesis, the physics of birds phonation is discussed using a two-mass models approach and the theory of nonlinear dynamics. Two-mass models of the human larynx (rescaled two-mass model and trapezoidal model) have been adapted to the dimension of the avian syrinx to study pressure onset, control of harmonic overtones and "registers" of the sound radiated by the birds vocal organ (syrinx) in the absence of source-tract coupling. Our simulations are a first step towards more realistic modelling of the syrinx. A detailed bifurcation analysis of the trapezoidal model confirms that the geometry and the rest position of the syrinx can influence the harmonic spectra drastically, suggests possible mechanisms involved in the production of rich-harmonic spectra during inspiration and is used to describe quantitatively the contribution of syringeal muscles. The latter is implemented in the model by means of driving time-dependent parameters controlling the labia rest position and frequency modulation.

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Maestre, Marina Rodrigues. "Análise de modelos lineares mistos com um fator longitudinal quantitativo e um qualitativo ordinal." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/11/11134/tde-06102014-085644/.

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Os experimentos agronômicos que envolvem somente um fator longitudinal são bastante comuns. No entanto, existem casos em que as observações são tomadas considerando dois ou mais desses fatores, como nos casos em que são feitas medidas de uma variável resposta em profundidades diferentes ao longo do tempo, por exemplo. Admite-se que essas observações, tomadas de modo sistemático em cada unidade experimental, sejam correlacionadas e as variâncias nos diferentes níveis do fator longitudinal sejam heterogêneas. Com o uso de modelos mistos, essa correlação entre medidas repetidas e a heterogeneidade de variâncias podem ser modeladas convenientemente. Para que esses modelos sejam ajustados a um conjunto de dados envolvendo presença de dois fatores longitudinais, existe a necessidade de se adaptarem algumas estruturas de variâncias e covariâncias que são comuns em experimentos com somente um fator longitudinal. O objetivo do presente trabalho é utilizar a classe dos modelos lineares mistos para estudar a massa seca de raiz no solo de uma plantação de cana-de-açúcar. O experimento foi casualizado em blocos e as parcelas receberam quatro doses de nitrogênio. Foram feitas medidas repetidas ao longo de dois fatores longitudinais, sendo um qualitativo ordinal (profundidades) e um quantitativo (distâncias da linha de plantio). Por meio dos testes de razão de verossimilhanças, de Wald e utilizando os critérios de informação AIC e BIC, selecionou-se uma estrutura de covariâncias parcimoniosa e outra estrutura para explicar o comportamento médio das respostas. A verificação do ajuste foi feita por meio de gráficos de diagnósticos de resíduos.
Agronomic experiments involving only one longitudinal factor are quite common. However, there are cases that the observations are made by considering two or more of these factors such as where measurements are made in a response variable at different depths along the time, for example. It is admitted that these observations, taken in a systematic way in each experimental unit are correlated and variances are heterogeneous in different levels of longitudinal factor. Using mixed models, this correlation between repeated measures and heterogeneity of variances can be modeled conveniently. To fit these models to data set involving presence of two longitudinal factors, there is need to adapt some variance and covariance structures that are common in experiments with only one longitudinal factor. The objective of this work is to use the class of linear mixed models to study the dry root mass in the soil of a plantation of cane sugar. The experiment was the randomized complete blocks design and parcels received four doses of nitrogen. Repeated measurements were made along two longitudinal factors being one ordinal qualitative (depths) and one quantitative (distances from the row). With the aid of likelihood ratio, Wald tests and using the AIC and BIC information criteria, we selected a parsimonious covariance structure and another structure to explain the average behavior of the responses. Checking the fit was made using diagnostic graphics of residuals.

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Esrael, Daoud. "Dépollution des sols par l'extraction multiphasique : Développement d'un modèle numérique." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0134.

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Aujourd’hui, plus de 65% des sites pollués en France le sont par des COVs (BASOL), considérés comme étant très dangereux et toxiques pour l’homme et l’environnement. Cela nécessite d’utiliser des techniques de traitement pour restaurer les sites et limiter les risques de propagation vers les eaux souterraines. L’extraction multiphasique MPE est une méthode physique de traitement des COVs. Elle a plusieurs avantages : essentiellement économique, le fait de pouvoir être utilisée in-situ et le fait de permettre la remédiation simultanée de deux zones saturée et non saturée du sous-sol. L’objectif de cette thèse est d’étudier cette technique en développant un modèle mathématique qui permet de décrire l’écoulement multiphasiques des différentes phases, le transport et le transfert de masse entre ces phases. Deux sols sableux et un polluant modèles sont choisis et caractérisés. Des dispositifs expérimentaux sont utilisés pour l’étude de l’écoulement diphasique et multiphasique ainsi que l’étude de transfert de masse. Un modèle numérique est développé, il se compose de trois EDPs pour l’écoulement (gazeuse, aqueuse et PLNA) et quatre EDPs pour le transport/transfert de masse pour chaque composé. La validation du modèle MPE est réalisée par la vérification de différentes parties qui le constituent séparément. La partie de l’écoulement diphasique est vérifiée à travers les résultats d’expérience de drainage sur colonne 1D et sur des résultats issus de la littérature d’une cellule type Hele-show 2D. L’importance du choix des conditions aux limites est mise en évidence. La partie de l’écoulement triphasique est vérifiée à travers les résultats d’expériences d’infiltration sur cellule 2D, l’une réalisée au laboratoire et l’autre issue de la littérature. L’étude porte sur l’effet du choix des dimensions d’expériences de laboratoire sur l’extrapolation des résultats à l’échelle du terrain. La partie transport/transfert de polluant est vérifiée à travers des expériences d’extraction sous vide/Venting. Le coefficient de transfert est déterminé avec une meilleure précision que celle des modèles issus de la littérature. Enfin une simulation à l’échelle de terrain est effectuée avec le modèle MPE pour simuler la dépollution d’un site pollué selon un scénario supposé et développé par la MPE. Les limites de la méthode pour la dépollution de la frange capillaire sont mises en évidence
Today, over 65% of polluted sites in France are by VOCs (BASOL), considered to be very dangerous and toxic to humans and the environment. This requires using treatment techniques to restore the sites and limit the risk of spread to groundwater. The multiphase extraction MPE is a physical method of soil VOCs treatment. It has several advantages: essentially economic, being able to be used in site and permitting the simultaneous remediation of both saturated and unsaturated zones. The objective of this thesis is to study this technique by developing a mathematical model to describe the multiphase flow of different phases, transport and mass transfer between these phases. Two sandy soils and a pollutant models are selected and characterized. Experimental devices are used to study the two-phase, multiphase flow and mass transfer. A numerical model is developed; it consists of three PDEs for the flow (gas, water and NAPL) and four PDEs to pollution transport/mass transfer for each compound. MPE Model validation is performed by the verification of different constituent parts separately. The two-phase flow is confirmed by the drainage experiment results of 1D column and of the results of the literature of a 2D Hele-show tank. The importance of the choice of boundary conditions is highlighted. The part of the three-phase flow is verified through the results of infiltration experiments on 2D tank, one conducted in the laboratory and the other of the literature. The study focuses on the effect of the choice of laboratory experiments dimensions on the extrapolation of results across the field. The transport/mass transfer part is verified by SVE/Venting experiments. The transfer coefficient is determined with a precision better than models from the literature. Finally a simulation at the field scale is carried out with the MPE model to simulate the remediation of polluted sites by MPE for a supposed scenario. The limitations of the method for remedying the capillary fringe are highlighted

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Mitra, Biswajit. "Supercritical gas cooling and condensation of refrigerant R410A at near-critical pressures." Diss., Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-06142005-232427/.

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Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2006.
Garimella, Srinivas, Committee Chair ; Ghiaasiaan, S. Mostafa, Committee Member ; Graham, Samuel, Committee Member ; Breedveld, Victor, Committee Member ; Fuller,Tom, Committee Member.

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An, Ni. "Etude numérique de l'interaction sol-atmosphère : application aux remblais en sols traités." Thesis, Paris Est, 2017. http://www.theses.fr/2017PESC1002/document.

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Face au changement climatique global, il est de plus en plus important de prêter attention à la performance thermique-hydro-mécanique des constructions géotechniques sous l'effet des conditions atmosphériques. L'objectif principal de cette étude est d'étudier le comportement hydro-thermique des sols soumis au effets du changement climatique par la modélisation numérique.Un modèle hydro-thermique couplé est tout d'abord développé pour décrire le comportement du sol hydro-thermique. La théorie utilisée pour décrire l'interaction sol-atmosphère est présentée sous forme des bilans de masse et d'énergie. Ensuite, une approche numérique pour analyser le comportement hydro-thermique du sol est proposée en combinant le modèle hydro-thermique couplé avec un modèle d'interaction sol-atmosphère. La validation de cette approche est réalisée par la comparaison entre les résultats numériques obtenus en utilisant le code FreeFem++ et les données des essais de la colonne de séchage qui sont trouvées dans la littérature. Cette approche est d'abord utilisée pour la modélisation numérique des essais à la chambre environnementale, réalisés par Song en 2014. Des résultats de simulation satisfaisants sont obtenus en termes de variations de la température et de la teneur en eau volumétrique du sol. Ensuite, cette approche est appliquée à deux remblais, à Héricourt et à Rouen. Pour le remblai d’Héricourt, une étude numérique a été menée pour une durée de 20 jours. La bonne concordance obtenue entre les résultats de simulation et les mesures montre que l'approche proposée est pertinente pour l'analyse du comportement hydro-thermique du sol dans le cas de remblais bidimensionnels. Elle prouve également que les conditions aux limites et les paramètres du sol adoptés sont appropriés. Dans le cas du remblai de Rouen, deux périodes différentes, 187 jours et 387 jours, sont prises en considération. On vérifie également la bonne performance de l'approche proposée pour estimer le comportement hydro-thermique du remblai sous l'effet du climat. La comparaison entre les calculs et les mesures révèle également l'importance d'adopter correctement les conditions aux limites thermiques et hydrauliques ainsi que les paramètres du sol. De plus, à partir des simulations numériques, plusieurs suggestions sont faites pour collecter des données d'entrée dans l'application de cette approche pour prédire les variations de la température et de la teneur en eau du sol à plus long terme
Facing the global climate change, it is more and more important to pay attention to the thermal-hydro-mechanical performance of geotechnical constructions under the effect of atmospheric conditions. The main objective of this study is to investigate the hydro-thermal behavior of soil subjected to climate change through numerical modelling.A coupled hydro-thermal model is developed for describing the coupled hydro-thermal soil behavior. The soil-atmosphere interaction is studied through the mass and energy balances. Afterwards, a numerical approach to estimate soil hydro-thermal behavior by integrating the coupled hydro-thermal model with a soil-atmosphere interaction model is proposed. The validation of this approach is performed through the comparison between the numerical results using FreeFem++ code and the experimental data available from column drying tests reported in literature. This approach is firstly used for the numerical modelling of the environmental chamber tests carried out by Song in 2014. Satisfactory simulation results are obtained in terms of variations of soil temperature and soil volumetric water content. Afterwards, this approach is further applied to two cases of embankments, in Héricourt and in Rouen respectively. For Héricourt embankment, a numerical investigation was conducted for 20 days, and a good agreement between simulation results and filed measurements is obtained, showing that the proposed approach is suitable for analyzing the soil hydro-thermal behavior in the case of two-dimensional embankments. It proves also that the boundary conditions and the soil parameters adopted are appropriate. In the case of Rouen embankment, two different periods, 187 days and 387 days, are considered. The good performance of the proposed approach in estimating the embankment hydro-thermal behavior under the climate effect is also verified. The comparison between calculations and measurements also reveals the importance of appropriately adopting the thermal and hydraulic boundary conditions as well as the soil parameters. Based on the numerical simulations, several suggestions are made in terms of collection of input data for the application of this approach to predict soil temperature and volumetric water content variations in longer term

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Mathis, Andrew David. "Ribosome Component Turnover Kinetics Describes a Two-Pool Kinetic Model in Dietary Restriction that Suggests RPL10 is Exchanged During Ribosome Lifespan." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/6049.

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The eukaryotic ribosome is a large molecular machine consisting of ~80 ribosomal proteins and 4 rRNAs. The 40S and 60S ribosomal subunits are assembled in the nucleolus by ~200 helper proteins then shipped into the cytoplasm or to the endoplasmic reticulum where protein translation takes place. Eventually ribosomes are removed from the cytoplasm and recycled through ribophagy, however, very is little is known about ribosomal protein exchange after assembly but before ribophagy. Using kinetic turnover measurements of ribosomal proteins and rRNA in vivo we determined ribosomal protein replacement rates are diverse suggesting ribosomal components may be replaced without destruction of the entire ribosome. Measurements from ad libitum fed and dietary restricted mice provide strong evidence that RPL10 exchanges rates are dramatically different between AL and DR while synthesis and degradation do not change. RPL10 turnover can be described using a two-pool kinetic model, which may be applied to many ribosomal proteins.

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Montgomery, Jane Aimée. "A mass spectrometric investigation of two rat models of defective medium chain fatty acid oxidation using deuterium labelled substrates /." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75845.

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Medium chain fatty acid oxidation was investigated in riboflavin deficient and 2-octynoic acid treated rats. Urinary metabolites of deuterium labelled fatty acid substrates were determined using gas chromatography-mass spectrometry. Control and experimental animals both produced labelled dicarboxylic acids. The ratio of chain length of dicarboxylates (C$ sb{ rm n+2}$/C$ sb{ rm c}$) was lowest in riboflavin deficient rats. As mitochondrial $ beta$-oxidation is inhibited, Peroxisomal $ beta$-oxidation appears to increase in response to inhibited mitochondrial oxidation in riboflavin deficiency. Administration of L-carnitine with the labelled substrates to half the rats showed that there were no differences in organic acid excretion between carnitine supplemented and unsupplemented rats. A new method to quantitate individual acylcarnitines in urine using fast atom bombardment-mass spectrometry and deuterium labelled acylcarnitines as internal standards demonstrated that administration of L-carnitine did enhance excretion of free carnitine and short chain acylcarnitines along with some dicarboxylcarnitines in all groups.

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Fimbres, Weihs Gustavo Adolfo UNESCO Centre for Membrane Science &amp Technology Faculty of Engineering UNSW. "Numerical simulation studies of mass transfer under steady and unsteady fluid flow in two- and three-dimensional spacer-filled channels." Publisher:University of New South Wales. UNESCO Centre for Membrane Science & Technology, 2008. http://handle.unsw.edu.au/1959.4/41453.

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Hollow fibre and spiral wound membrane (SWM) modules are the most common commercially available membrane modules. The latter dominate especially for RO, NF and UF and are the focus of this study. The main difficulty these types of modules face is concentration polarisation. In SWM modules, the spacer meshes that keep the membrane leaves apart also help reduce the effects of concentration polarisation. The spacer filaments act as flow obstructions, and thus encourage flow destabilisation and increase mass transfer enhancement. One of the detrimental aspects of the use of spacers is an increase of pressure losses in SWM modules. This study analyses the mechanisms that give rise to mass transfer enhancement in narrow spacer-filled channels, and investigates the relationship between flow destabilisation, energy losses and mass transfer. It shows that the regions of high mass transfer on the membrane surface correlate mainly with those regions where the fluid flow is towards the membrane. Based on the insights gained from this analysis, a series of multi-layer spacer designs are proposed and evaluated. In this thesis, a Computational Fluid Dynamics (CFD) model was used to simulate steady and unsteady flows with mass transfer in two- and three-dimensional narrow channels containing spacers. A solute with a Schmidt number of 600 dissolving from the wall and channel Reynolds numbers up to 1683 were considered. A fully-developed concentration profile boundary condition was utilised in order to reduce the computational costs of the simulations. Time averaging and Fourier analysis were performed to gain insight into the dynamics of the different flow regimes encountered, ranging from steady flow to vortex shedding behind the spacer filaments. The relationships between 3D flow effects, vortical flow, pressure drop and mass transfer enhancement were explored. Greater mass transfer enhancement was found for the 3D geometries modelled, when compared with 2D geometries, due to wall shear perpendicular to the bulk flow and streamwise vortices. Form drag was identified as the main component of energy loss for the flow conditions analysed. Implications for the design of improved spacer meshes, such as extra layers of spacer filaments to direct the bulk flow towards the membrane walls, and filament profiles to reduce form drag are discussed.

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Aubras, Farid. "Contribution à l’étude de l’influence des régimes bi-phasiques sur les performances des électrolyseurs de type PEM basse pression : approche numérique, analytique et expérimentale." Thesis, La Réunion, 2018. http://www.theses.fr/2018LARE0011/document.

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Les électrolyseurs à membrane échangeuse de protons basse pression (E-PEMs) apparaissent comme une solution efficace et durable pour la production d’hydrogène. Cette technologie pourrait permettre de pallier l’intermittence des énergies renouvelables (notamment solaire et éolien) en convertissant l’énergie électrique produite en énergie chimique (hydrogène). Durant ces travaux de thèse, trois aspects ont été développés : une approche analytique, une approche numérique, ainsi que approche expérimentale. Ces trois approches ont permis de comprendre l’influence du mélange bi-phasique eau/oxygène à l’anode du système sur les performances électrochimiques des E-PEMS ainsi que déterminer les paramètres opérationnels et intrinsèques qui impactent les performances des E-PEMs. À propos de l'approche expérimentale, des mesures d'impédance électrochimique ainsi que des courbes de polarisation ont été réalisées sur deux différentes cellules d'électrolyseurs de type PEM basse pression (la cellule ITW power de l'Electrochimical innovation Lab (UCL) et la cellule réversible Q-URFC du Laboratoire d'Énergétique, d'Électronique et Procédés (LE2P). À propos de la modélisation numérique, Le modèle expérimentale conjugue une approche multi-échelle macroscopique 2D et mésoscopique 1D. Ce modèle prend en compte le transfert de matière, le transfert de chaleur, les réactions électrochimiques anodique et cathodique et le transfert de charges présents dans le cœur des E-PEMs. D’un point de vue mésoscopique, une attention particulière a été portée sur l’influence des régimes bi-phasiques anodiques (régime de bulles coalescées (BC régime) et régime de bulles non coalescées (NCB régime) sur le transfert de matière à l’anode et sur l’humidification de la membrane. Ces travaux démontrent et confirment l’hypothèse que la transition du NCB régime vers le CB régime augmente le transfert de matière anodique, diminue la résistance ohmique de la membrane et améliore l’efficacité des E-PEMs. À propos de la modèle analytique, l’étude analytique explore une approche adimensionnelle de l'assemblage membrane électrode (AME) en régime stationnaire et isotherme. À l’échelle locale, en 1D, les équations prises en compte sont la conservation du courant dans l’AME, les réactions électrochimiques au sein des couches actives et le transfert de matière à travers la membrane. La résolution a permis d’obtenir des expressions analytiques des surtensions aux électrodes, de la chute ohmique et de la teneur en eau dans la membrane. L’approche adimensionnelle a permis de quantifier analytiquement les sources d’irréversibilités (chute ohmique, surtensions d’activations anodique et cathodique, et de la surtension induite par le bouchonnement des canaux anodiques) respectivement pour les faibles densités de courant, les moyennes densités de courant et les hautes densités de courant. En outre, ce modèle analytique peut être implémenté dans une boucle de contrôle commande. Ces travaux de thèse proposent une contribution à la compréhension du fonctionnement des E-PEMs basse pression en général, et en particulier de l'impact des régimes bi-phasiques sur leurs performances électro-chimiques
Based on proton conduction of polymeric electrolyte membrane (PEM) technology, the water electrolysis (PEMWE) offers an interesting solution for efficiency hydrogen production. During the electrolysis process of water in PEMWE, the anodic side is the place where the water is splitting into oxygen, protons and electrons. The aim of this study is to recognize the link between two-phase flows (anode side) and cell performance under low pressure conditions. We have developed three approaches: the analytical approach and the numerical approach validated by the experimental data. For the numerical model, we have developed a two-dimensional stationary PEMWE model that takes into account electro-chemical reaction, mass transfer (bubbly flow), heat transfer and charges balance through the Membrane Electrodes Assembly (MEA). In order to take into account the changing electrical behavior, our model combines two scales of descriptions: at microscale within anodic active layer and MEA scale. The water management at both scales is strongly linked to the slug flow regime or the bubbly flow regime. Therefore, water content close to active surface areas depends on two-phase flow regimes. Our simulation results demonstrate that the transition from bubble to slug flow in the channel is associated with improvement in mass transport, a reduction of the ohmic resistance and an enhancement of the PEMWE efficiency. Regarding the analytical model, we have developed a one-dimensional stationary isothermal PEMWE model that takes into account electro-chemical reaction, mass transfer and charges balance through the Membrane Electrodes Assembly (MEA). The analytical approach permit to obtain mathematical solution of the activation overpotential, the ohmic losses and the bubbles overpotential respectively for the low current density, the middle current density and the high current density. This approach quantify the total overpotential of the cell, function of the operational and intrinsic numbers. In terms of perspective, the analytical model could be used for the diagnostic of the electrolyzer PEM

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Demircioglu, Filiz. "Application Of Two Receptor Models For The Investigation Of Sites Contaminated With Polychlorinated Biphenyls: Positive Matrix Factorization And Chemical Mass Balance." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612190/index.pdf.

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This study examines the application of two receptor models, namely Positive Matrix Factorization (PMF) and Chemical Mass Balance (CMB), on the investigation of sites contaminated with PCBs. Both models are typically used for apportionment of pollution sources in atmospheric pollution studies, however have gained popularity in the last decade on the investigation of PCBs in soil/sediments. The aim of the study is four-fold
(i) to identify the status of PCB pollution in Lake Eymir area via sampling and analysis of PCBs in collected soil/sediment samples, (ii) to modify the CMB model software in terms of efficiency and user-friendliness (iii) to apply the CMB model to Lake Eymir area PCB data for apportionment of the sources as well as to gather preliminary information regarding degradation of PCBs by considering the history of pollution in the area (iv) to explore the use of PMF for both source apportionment and investigation of fate of PCBs in the environment via use of Monte-Carlo simulated artificial data sets. Total PCB concentrations (Aroclor based) were found to be in the range of below detection limit to 76.3 ng/g dw with a median of. 1.7 ng/g dw for samples collected from the channel between Lake Mogan and Lake Eymir. Application of the CMB model yield contribution of highly chlorinated PCB mixtures (Aroclor 1254 and Aroclor 1260
typically used in transformers) as sources. The modified CMB model software provided user more efficient and user friendly working environment. Two uncertainty equations, developed and existing in literature, were found to be effective for better resolution of sources by the PMF model.

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Shirinda, Obed. "Studying chirality in a ~ 100, 130 and 190 mass regions." Thesis, University of the Western Cape, 2011. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_8742_1319096308.

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Chirality is a nuclear symmetry which is suggested to occur in nuclei when the total angular momentum of the system has an aplanar orientation [Fra97, Fra01]. It can occur for nuclei with triaxial shape, which have valence protons and neutrons with predominantly particle and hole nature. It is expected that the angular momenta of an odd particle and an odd hole (both occupying high-j orbitals) are aligned predominantly along the short and the long axes of the nucleus respectively, whereas the collective rotation occurs predominantly around the intermediate axis of a triaxially deformed nucleus in order to minimize the total energy of the system. Such symmetry is expected to be exhibited by a pair of degenerate DI = 1 rotational bands, i.e. all properties of the partner bands should be identical. The results suggested that spin independence of the energy staggering parameter S(I ) within two-quasiparticle chiral bands (previously suggested a fingerprint of chirality) is found only if the Coriolis interaction can be completely neglected. However, if the configuration is nonrestricted, the Coriolis interaction is often strong enough to create considerable energy staggering. It was also found that staggering in the intra- and inter-band B(M1) reduced transition probabilities (proposed as another fingerprint of chirality) may be a result of effects other than strongly broken chirality. Therefore, the use of the B(M1) staggering as a fingerprint of strongly broken chiral symmetry seems rather risky, in particular if the phase of the staggering is not checked.

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19

Sousa, Gabriel Oliveira de. "ANÃIS E PONTOS QUÃNTICOS DE FÃSFORO NEGRO INVESTIGADOS POR MODELO CONTÃNUO." Universidade Federal do CearÃ, 2016. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=17789.

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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico
A possibilidade de se obter sistemas bidimensionais a partir de materiais com estrutura cristalina lamelar tem atraÃdo muitas pesquisas nesses materiais, pois as propriedades de poucas camadas diferem bastante dos seus respectivos bulks, o que abre uma gama de possibilidades em aplicaÃÃes tecnolÃgicas. O fÃsforo negro apresenta muitas propriedades interessantes, dentre elas, um gap de energia, que garante a construÃÃo de dispositivos eletrÃnicos (bem diferente do grafeno que Ã um semi metal sem gap). Esse gap pode ser ajustado aumentando o nÃmero de camadas, variando de 0.3 eV para uma monocamada atÃ cerca de 2.0 eV para o bulk, cobrindo um espectro de energia de gap relativamente grande de dispositivos Ãpticos. AlÃm disso, esse material Ã altamente anisotrÃpico em sua estrutura de bandas. Neste trabalho, derivamos a aproximaÃÃo da massa efetiva a partir do modelo tight-binding e usamos o Hamiltoniano aproximado para estudar nanoestruturas de fÃsforo negro. Nesse modelo, o carÃter anisotrÃpico do fÃsforo negro Ã refletido na diferenÃa entre as massas efetivas quando se toma diferentes direÃÃes. Primeiramente, comparamos os resultados numÃrico obtido atravÃs da tÃcnica de diferenÃas finitas com o modelo analÃtico para um ponto quÃntico circular, que devido Ã estrutura de bandas ter um contorno elÃptico, Ã descrito pelas equaÃÃes de Mathieu quando se resolve a equaÃÃo de SchrÃdinger. Os resultados analÃtico e numÃrico mostram boa concordÃncia. Ainda na aproximaÃÃo da massa efetiva, estudamos o efeito de campos externos sobre um anel quÃntico de fÃsforo negro e analisamos o efeito da interaÃÃo entre esses campos e a anisotropia de massa do sistema sobre seus estados eletrÃnicos. Devido Ã anisotropia de massa, esse sistema quando sujeito a um campo magnÃtico, nÃo apresenta oscilaÃÃes Aharonov-Bohm, que podem ser recuperadas aplicando-se um potencial de confinamento elÃptico. Estudamos tambÃm o efeito de um campo elÃtrico nas direÃÃes x e y em um anel quÃntico, e verificamos como a energia Ã alterada pelo campo. Nossos resultados mostram que, como consequÃncia de uma localizaÃÃo da funÃÃo de onda causada pela anisotropia de massa, os nÃveis de energia decrescem quadraticamente (efeito Stark) com o campo aplicado apontando para a direÃÃo armchair, enquanto um decrÃscimo quase linear (efeito Stark linear) aparece para um campo aplicado na direÃÃo zigzag, com uma sÃrie de estados que se cruzam, levando a um comportamento semelhante ao de um poÃo quÃntico duplo sob um campo elÃtrico perpendicular a ele.
The possibility of obtaining two-dimensional systems from layered materials has been attracting a lot of research on these materials, since their few layer properties are very different from their respective bulk ones, which opens up great possibilities in technological applications. Black phosphorus exhibit several interesting properties, among them, a direct energy gap, that enables the possibility of fabricating electronic devices (in contrast e.g. with the gapless semi-metallic graphene), and which can be tuned by the number of layers, varying from 0.3 eV for a bulk up to 2.0 eV for a monolayer, thus covering a relatively large range of the energy spectrum for optical devices. Besides, the fact that this is a very anisotropic material has brought even more attention to it, towards novel ways of exploring this anisotropy in new technologies. In this work, we have derived the effective mass approximation from the tight binding model and used the out coming approximate Hamiltonian to study nanostructures based on monolayer black phosphorus. In this model, the anisotropic features of black phosphorus are reflected in the difference between effective masses in different directions. Firstly, we compare the finite difference methods with the analytical solution for a circular quantum dot, which, due to its elliptical contour of energy bands, is given by Mathieu functions for solving the resulting SchrÃdinger equation. With this comparison, we verify the compatibility between these methods. Within the effective mass approximation, we investigate the effect of external electromagnetic fields on a black phosphorus quantum ring, thus analysing the effect of the interplay between these fields and the system anisotropy on its electronic states. Due to the anisotropy, under an applied magnetic field, this ring does not exhibit Aharonov-Bohm oscillations, which can be recovered by assuming an elliptic ring-like confinement. We also investigate the effect of an external electric field applied in x and y directions in a black phosphorus quantum ring on its energy levels. Our results show that, as a consequence of a wave function localization induced by mass anisotropy, energy levels decay quadratically (Stark effect) with the field if it is applied along the armchair direction, whereas an almost linear Stark effect, along with a series of crossing excited states, is observed for a field applied in the zigzag direction, leading to a behavior that is in close resemblance to a double quantum well under a perpendicular electric field.

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Martin, Ashley N. "The interaction of message content, media sequence, and product involvement: an examination of intended message content sequences across a two-channel strategic IMC effort." Thesis, Kansas State University, 2014. http://hdl.handle.net/2097/18705.

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Master of Science
Department of Journalism and Mass Communications
Curtis Matthews
Integrated marketing communications strategies are being utilized more and more by practitioners who wish to reach their audiences in different ways at different times. However, the omnipresence that results from these multi-channel campaigns presents a new challenge for marketers, as their message and channel sequences may or may not be experienced in the order intended. Past literature has shown that both message order and channel sequence do matter. However, existing literature has not examined intended message sequences where the first channel “teases” the more comprehensive information available in the second channel. Therefore, the aim of this study was to bridge some of the gaps in past research by exploring message content order effects and channel sequence effects across intentional sequences for both high- and low-involvement product categories through the lens of the Elaboration Likelihood Model. A 2 (message content order: tease-to-answer versus answer-to-tease) by 2 (medium sequence: print-to-online versus online-to-print) by 2 (product involvement: high- versus low-involvement) mixed factorial experimental design was conducted to explore how message content order, channel sequence, and product involvement level affected evaluations of brand and message, as well as perceived behavioral intent. The findings indicated that message content order had significant influence over brand and message evaluation, with the tease-to-answer order producing the highest evaluations of brand and message. The findings also indicated that the online-to-print sequence was only effective for increasing behavioral intent under high-involvement conditions. Implications for marketing practitioners and future research are discussed.

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Andari, Nansi. "Observation of a BEH-like boson decaying into two photons with the ATLAS detector at the LHC." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112191/document.

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Dans cette thèse, je présente ma contribution à l'observation d'un nouveau boson au LHC avec le détecteur ATLAS dans le canal de désintégration en deux photons. Ce boson est compatible avec le boson scalaire du Modèle Standard longtemps recherché et a une masse de 126.0 +/-0.4 (stat) +/-0.4 (sys) GeV obtenue en combinant les canaux gamma gamma et ZZ. Les données utilisées sont celles collectées par l'expérience ATLAS durant l'année 2011 avec une énergie de centre de masse de 7 TeV et durant les trois premiers mois du run en 2012 avec une énergie de centre de masse de 8 TeV. La luminosité totale correspondante est de ~10 fb-1. L'excès observé a une significance locale de 4.5 sigma dans le canal gamma gamma et de 5.9 sigma en combinant tous les canaux analysés. De même, diverses contributions aux analyses des données, dans le canal H en gamma gamma, depuis l'année 2009 jusqu'en 2012 sont aussi montrées
In this thesis, I show my contribution to the observation of a new boson at the Large Hadron Collider with the ATLAS detector in the diphoton decay channel. This boson is compatible with the long-searched scalar boson of the Standard Model and has a mass of 126.0+/-0.4+/- 0.4 (sys) GeV obtained when combining the decay channels gamma gamma and ZZ. The data used were collected in the ATLAS experiment during 2011 with a center-of-mass energy of 7 TeV and during the first three months of the 2012 run with a center-of-mass energy of 8 TeV. The total corresponding luminosity is about 10 fb-1. The observed excess has a local significance of 4.5 sigma in the gamma gamma channel and has a significance of 5.9 sigma when combining all the channels used in the analysis. Moreover, diverse contributions to the H into gamma gamma analyses of the data from 2009 to 2012 are also shown

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Schmitt, Romain. "S-nitrosoglutathion et perméabilité intestinale : de la mise en place d’un modèle de chambre de Ussing à l’étude de l’impact de ce donneur de monoxyde d’azote sur la barrière intestinale Involved factors in the maintenance of intestinal barrier homeostasis: a review How to guarantee results from ex vivo studies based on Ussing chamber system for studying intestinal barrier integrity and function Comparison between two derivatization methods of nitrite ion labeled with 15N applied to liquid chromatography-tandem mass spectrometry Influence of S-nitrosoglutathione metabolism on its intestinal permeability Luminal S-nitrosoglutathione effects on intestinal barrier in an ex vivo model of Ussing chamber." Thesis, Université de Lorraine, 2019. http://www.theses.fr/2019LORR0342.

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Le monoxyde d’azote (NO) est connu pour ses nombreuses actions afin de maintenir l’homéostasie de la barrière intestinale, régulant la sécrétion de mucus, le stress oxydant, le système immunitaire… Le S-nitrosoglutathion (GSNO), donneur de NO naturellement produit par l’organisme, a montré une action bénéfique sur le renforcement de la barrière intestinale. L’enjeu est aujourd’hui de comprendre les mécanismes inhérents à cette observation. Pour ce faire une étude en Chambre de Ussing a été menée. Une fois le modèle d’étude validé par le suivi de marqueurs de perméabilité, les études histologiques et d’expression des protéines de jonctions cellulaires, le métabolisme du GSNO administré dans la lumière de l’intestin ont été explorés. Également, l’effet du GSNO sur la perméabilité de la barrière intestinale a été étudié. Les résultats permettent aujourd’hui d’envisager le GSNO comme une piste thérapeutique intéressante et prometteuse aux multiples applications possibles : intestinales, cardiovasculaires ou encore cérébrales
Nitric oxide is known for its many actions to maintain intestinal barrier homeostasis, regulating mucus secretion, oxidative stress, immune system… S-nitrosoglutathione (GSNO), a nitric oxide donor naturally produced by the organism, has shown a beneficial effect on the intestinal barrier reinforcement. Nowadays, challenge is to understand the mechanisms inherent to this observation. For that, a Ussing chamber study was performed. After the model validation, by following permeability markers, histological studies, and cell junction proteins expression study, the GSNO metabolism administered in the intestinal lumen was explored. Also, GSNO effect on the intestinal barrier permeability was evaluated. Results allow today to consider GSNO as an interesting and promising drug candidate, in the context of intestinal, cardiovascular or cerebral pathologies

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Lochon, Hippolyte. "Modélisation et simulation d'écoulements transitoires eau-vapeur en approche bifluide." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4726/document.

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Cette thèse traite de la modélisation et de la simulation des écoulements diphasiques transitoires eau-vapeur. Dans de nombreuses installations industrielles, des écoulements monophasiques d'eau liquide sont susceptibles de devenir diphasiques lors de certaines situations transitoires. La modélisation de ces écoulements peut s'avérer délicate car deux phénomènes physiques interagissant fortement entre eux, le changement de phase et la propagation d'ondes de pression, sont alors à prendre en compte. Une approche bifluide statistique, ne supposant aucun équilibre entre les phases, est utilisée afin de modéliser de tels écoulements. Les modèles obtenus sont de type convection-source et s'apparentent au modèle de Baer-Nunziato. Différentes lois de fermeture pour ces modèles sont comparées sur des cas expérimentaux de transitoires eau-vapeur tels que les coups de bélier et la dépressurisation d'une tuyauterie d'eau liquide suite à une rupture.La simulation numérique des différents modèles est effectuée grâce à une méthode à pas fractionnaires. Un nouveau schéma de convection, robuste et efficace, capable de gérer toute equation d'état est utilisé dans la première étape de cette méthode. La seconde étape est dédiée au traitement des termes sources et requiert différents schémas implicites. Une grande attention est accordée à la vérification de tous les schémas numériques utilisés grâce à des études de convergence. Une nouvelle modélisation du transfert de masse est également proposée, sur la base de travaux dédiés à la brusque dépressurisation d'eau liquide en approche homogène. La validation du modèle est effectuée grâce de nombreuses comparaisons calcul-expérience
This thesis deals with the modelling and the computation of steam-water two-phase flows. Liquid water flows are involved in many industrial facilities and a second phase may appear in some transients situations. Thus, pressure wave propagation and mass transfer are physical phenomena that need to be properly included in the modelling of such two-phase flows. A statistical two-fluid approach is used, leading to models similar to the Baer-Nunziato one. They include both convective and source terms without any assumption on the equilibrium between phases. Different closure laws for such models are compared on steam-water transient experiments including water-hammers and fast depressurization of liquid water. The computation of the different models is based on a fractional step method. A new convective scheme, able to deal with any Equation Of State, is used in the first step of the method. When compared with other schemes, it appears to be accurate, efficient and very robust. The second step of the method is dedicated to the treatment of source terms and requires several implicit schemes. Particular attention is paid to the verification of every scheme involved in the method. Convergence studies are carried out on test-cases with analytical solutions to that purpose. Based on existing work on fast depressurization of liquid water in an homogeneous approach, a new formulation of the mass transfer is proposed. Many comparisons between computational and experimental results are detailled in order to validate the models

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Ghalehchian, Javad Saien. "Evaluation of liquid-liquid extraction column performance for two chemical systems : a study for application of drop breakage, hydrodynamic and mass transfer models in a computer program to simulate the steady state behaviour of a rotating disc contactor for liquid-liquid extraction." Thesis, University of Bradford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.578243.

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Jakel, Roland. "Berechnung von Schockspektren und praktische Anwendung der dynamischen Stoßanalyse in Creo Elements / Pro Mechanica." Universitätsbibliothek Chemnitz, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-68407.

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Der Vortrag stellt Idee und Grundlagen der Berechnung von Schockantwortspektren dar. Er zeigt, wie man exemplarisch für einen Halbsinusstoß das Schockantwortspektrum in der PTC FEM-Software Creo Elements / Pro Mechanica berechnen kann. Die Schockantworten eines Ein- und Zweimassenschwingers werden sowohl zeitaufgelöst als auch über die dynamische Stoßanalyse berechnet. Die modalen Superpositionsmethoden "Absolute Summe" und "SRSS" (Square Root of the Sum of the Squares - geometrischer Mittelwert) werden vorgestellt. Als reales Beispiel werden Schockanalysen für verschiedene Halbsinusimpulse mit einem Wärmebildgerät der Firma Carl Zeiss Optronics GmbH durchgeführt und mit einer zeitaufgelösten Analyse verglichen. Abschließend wird auf die Erzeugung von Antwortspektren für die Substrukturauslegung eingegangen
The presentation explains idea and fundamentals of shock response spectra analysis. With help of the PTC FEM-software Creo Elements / Pro Mechanica the shock response spectra (SRS) for an exemplary half sine shock is calculated. The shock response of a one-mass and a two-mass oscillator are analyzed per dynamic time as well as per dynamic shock analysis. The modal superposition methods "absolute sum" and "SRSS" (Square Root of the Sum of the Squares) are explained. The method is applied for different half sine shocks on a realistic example: A thermal imaging system of the company Carl Zeiss Optronics GmbH. Finally, the creation of response spectra for global-local analysis is explained

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Chen, Bo-Hao, and 陳柏豪. "Two-Mass Vehicle Model for Extracting Bridge Frequencies and Spectral Analysis." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/2z6625.

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碩士
國立交通大學
土木工程系所
106
To assess or monitor the health of bridges, the most important parameter is the bridge frequency. Traditionally, the direct approach is the main way to measure bridge frequencies, which relies the installation of several sensors on a bridge and calculates bridge frequencies by measuring dynamic responses obtained at sensor locations. Since the direct approach wastes time and manpower, the indirect approach was proposed and developed over the past twenty years. Through the theory of vehicle-bridge interaction (VBI), the bridge responses can be obtained from the dynamic responses of the test vehicle. In the model of VBI, the entire test vehicle is simulated as a single mass conventionally. However, the unsprung mass of the test vehicle is the actual component in direct contact with the ground. As such, a two-mass vehicle model is proposed to truly reflect the dynamic behavior of the bridge in this study. In the numerical analysis, for the bridge pavement subject to roughness condition, the effects of unsprung mass on the identification of bridge frequencies is investigated, which serves as a reference in designing the test vehicle in the future. Concerning the spectral analysis, both FFT(fast Fourier transform) and HHT(Hilbert-Huang transform) are applied to process the spectrum signals. The difference between the two methods and the feasibility of the methods are discussed. Furthermore, the signals are processed by averaging to reduce the effect of road surface roughness and enhance the identification of bridge frequencies.

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Cao, Cheng-Yi, and 曹成翊. "Wheel Size Embedded Two-Mass Vehicle Model for Scanning Bridge Frequencies." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/fwf52m.

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碩士
國立交通大學
土木工程系所
107
In order to supervise and maintain the health condition of bridges, the bridge frequency can be one of the important indicators among related parameters. Generally, if a bridge suffers any damage, the partial or overall stiffness of the bridge will be affected, thus making bridge frequencies shifted. The traditionally direct approach is the main method to measure bridge frequencies, which relies on the installation of several sensors along the bridge and the calculation of bridge frequencies by gauging the dynamic responses from sensors. As the direct approach is time-consuming and laborious, the indirect approach has been developed in recent years. In the theory of vehicle-bridge interaction (VBI), the bridge frequencies can be captured from the dynamic responses of the test vehicle. The original vehicle model was assumed to be a point mass. As it is unrealistic to reflect the vehicle responses, the wheel size embedded two-mass vehicle model is proposed in this study. The effects of the wheel size and other related parameters on the identification of bridge frequencies are investigated. From the results of numerical simulation, it is found that as the wheel size increases, the relative error of the bridge frequency identification decreases; as the unsprung mass increases, the identification of bridge frequency becomes clear.

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Hsiao, Chih-hsien, and 蕭志賢. "Development of Simulation Model to Analysis Two Stage Airbag Mass Flow Rate." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/98958980913834936256.

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碩士
國立中正大學
機械工程所
94
The purpose of this research is to develop a finite element model of HYBIRDⅢ, the advantage of this model is not only suitable accu-racy on dynamic response, but also can save the time of computation. The dummy model then combine with vehicle model to simulate sled test using nonlinear FEM code LS-DYNA, and apply it to design two-stage airbag mass flow rate. At first this research focus on model the key deformable compo-nents of dummy, and validate with dummy calibration tests. The mainly modified parts are head and neck, both compare by real Head-Drop-Test and Neck-Bending-Test. The validated dummy model then combine with vehicle model to simulate sled test and compared the acceleration data record from dummy head sensor. 50% male rigid dummy model build in LS-DYNA has also used to do similar simula-tion and compared the results with deformable dummy. After that two type of the mass flow rate has been used to simulate sled test with 50% male dummy and 95% female rigid body dummy. The simulated results reveal that the mass flow rate suitable foe male dummy could cause larger impart force to the female dummy that might induce seri-ous injury. Therefore, two-stage airbag with intelligent control must be applied to protect different types of occupants.

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Cao, Zhan John. "One and Two-Dimensional Mass Spring Computational Model for Phononic Band Gap Analysis." Thesis, 2009. http://hdl.handle.net/10012/4662.

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Computation model is presented for mass spring systems of one and two dimensional phononic band gap crystals and micro-electro-mechanical systems. The computation model is veri ed with existing work, and phononic band gap microelectro- mechanical systems are analyzed. Phononic band gap in the scienti c and industrial community is discussed. The motivation and the recent popular methods are discussed. The computation models are highlighted with their pros and cons and adequate computational applications. The one dimensional mass spring model is developed and the simulator operation is validated through comparison with the published simulation data in the original paper by J.S. Jensen et al.. Additionally, the one dimensional mass spring simulator is validated for a micro-electro-mechanical system band structure. The two dimensional mass spring model is developed, as well, the simulator operation is validated through comparison with the published simulation data in the original paper by J.S. Jensen et al.. The two-dimensional simulator is utilized to analyze solid square-shaped, hollow square-shaped, solid diamond-shaped, and hollow diamond-shaped inclusion micro-electro-mechanical band gap structures. The solid inclusion-based micro-electro-mechanical band gap results are compared with hollow inclusion-based micro-electro-mechanical structures.

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Liang, Jyh-Feng, and 梁志鋒. "A Study On the Comparison Of Two Receptor Models:Chemical Mass Balance Model and Positive Matrix Factorization Model." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/94883354832951295833.

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碩士
中興大學
環境工程學系所
94
Two receptor models, Chemical Mass Balance (CMB) and Positive Matrix Factorization (PMF), are applied to estimate the source contributions of TaChia area in this study. There are thirty three samples of PM2.5 and PM2.5~10 , respectively. And four samples are impacted by Asian Dust Storm. This research will analysis the source contribution of Asian Dust Storm by receptor model. CMB model is written by Matlab program language. Condition Index and π matrix are used to identify the collinearity of source profiles by CMB model. Their advantages are that collinearity of source profiles are defined definitely and source profiles can be chosen flexible. PMF model is used the EPA PMF 1.1 version developed by USEPA. The results of two models are compared. Vehicle emissions, vegetative burning, ammonium sulfate, ammonium nitrate, crustal materials, incinerator, oil-fired boiled are analyzed to the source contributions of PM2.5 by two receptor models. Vehicle emissions are the major source contributions of PM2.5, and it was estimated about 57 % and 35 % of PM2.5 by CMB model and PMF model. The second to fourth source contributions are vegetative burning, ammonium sulfate, ammonium nitrate, and they accounts for 44.3 % and 48.4 % of total source contributions to CMB model and PMF model, respectively. Six sources include vehicle emissions, crustal materials, marine spray, ammonium nitrate, incinerator, vegetative burning are resolved to the source contribution of PM2.5~10 by two receptor models. The results show that vehicle emission and crustal materials are primary and secondary source contributions of PM2.5~10. They accounts for 74 % and 61 % of total source contributions to PM2.5~10 according to the results obtained from CMB model and PMF model, respectively. Vehicle emissions estimated by CMB model are still 52 % of total source contribution higher than 35 % estimated by PMF model. The contribution of Asian dust storm is only resolved by CMB model, and it accounts for 3.4 % of total source contributions. Instead, PMF model can’t resolve the contribution of Asian dust storm. In conclusion, the major sources identified by the two receptor models are the same. The reason why high differences of contributions to vehicle emissions may be the source profile collected from the foreign area and it is not proper for the characteristics of vehicle emissions for TaChia area. Incinerator and crustal materials are low percentages of total contributions and their regression coefficient(r2) are low of the results between CMB model and PMF model. The reasons may be due to the incompleteness of profiles and a lack of local-specific profiles. In addition, a lack of samples to Asian dust storm, PMF model can’t resolve the source contribution of Asian dust storm.

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Wang, Fu-Ming, and 王富民. "A Study On The Comparison Of Different Collinearity In Source Profiles By Two Models: Chemical Mass Balance Model and Positive Matrix Factorization Model." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/40923560255277401158.

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OVEISY, ALI. "A Two-Dimensional Horizontal Wave Propagation and Mud Mass Transport Model on Muddy Coastal Regions." Thesis, 2009. http://hdl.handle.net/1974/2000.

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It is well known that surface water waves interact with fluid mud on the sea bed. Wave mud interaction results in high wave energy dissipation and mud mass transport. This kind of wave energy dissipation, which generally is much more significant than wave dissipation due to bottom friction, should be considered in the simulation of wave evolution and transformation in muddy coastal environments. In this research, a two-dimensional horizontal wave propagation and morphodynamic model for muddy coasts was developed. The model can be applied on a general three dimensional bathymetry of a soft muddy coast to calculate wave damping, fluid mud transport and resulting bathymetry change under wave action. In addition to the effect of wave-mud interaction on wave propagation, the dissipation due to wave-mud interaction was also implemented in SWAN (a third generation numerical model for Simulating WAves Nearshore) using a multilayered wave mud interaction model. These two models combined can be used for generation and propagation of waves in muddy coastal areas. The nonlinear constitutive equations of the visco-elastic-plastic model are adopted for the rheological behavior of fluid mud in this research. The results of the numerical model are compared against a series of wave-basin experiments, wave flume experiments and field observations. Comparisons between the simulated results with the both field and laboratory data reveal the capability of the proposed model to predict the wave transformation and mud mass transport.
Thesis (Ph.D, Civil Engineering) -- Queen's University, 2009-07-24 11:18:18.622

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Jeng, Pei-Lin, and 鄭培琳. "Research on the Mass Transfer Mechanism of Solutes in Homogeneous Phase with a Two-Dimensional Diffusion Model." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/19660369592699547703.

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碩士
國立中興大學
化學工程學系所
94
Cytoplasm serves not only as the reactor of the biochemical processes in the cell, but also the important medium for the housekeeping, which is critical in maintaining the homeostasis within the cell. Examples include synthesis of proteins and transport of mRNA from nucleus via cytoplasm to rough ER to complete translation. Cytoplasm is thought to be composed of cytosol in aqueous phase, a variety of protein, cytoskeleton filaments, and cytoplasmic matrix, which in turn comprises organic/inorganic molecules and enzymes. It requires nutrients, metabolism and intracellular communication all functioning properly to keep the interior and exterior of a living cell at desired conditions. Thus it is apparent that the cytoplasmic transport plays an extremely important role in the regulation of the physiological conditions inside and outside the cell. Cytoplasmic transport is categorized into active and passive transport. Dynein, as a molecular motor, carrying biomolecules and moving along cytoskeleton is exemplified as active transport. Whereas passive transport essentially arises from the concentration gradient across the cytosol. In this study, fluorescent microinjection into mouse oocytes and M2 medium is employed to study the diffusion processes, in addition, a two-dimensional mathematical model quantifies the experimental results. Coupled results from experiments and model enable the determination of the diffusion coefficients of various medium, as well as the time length required to achieve steady states. The model simulates molecular diffusion to reasonable degree and flourishes the succeeding research on intracellular communication including both active and passive transport.

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吳政緯. "The Design and Model Analysis of the Dynamic Balance Mass for the Crankshaft of a Two–cylinder Reciprocating Air Compressor." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/37479110826794951081.

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碩士
國立彰化師範大學
機電工程學系
99
Improving the vibration problem is the main goal of this study by finding the optimal crankshaft counterweight of the two-cylinder reciprocating compressor. Therefore this research mainly aims for designing the appropriate crankshaft counterweight with effective way to reduce the vibration of the two-cylinder commercial reciprocating compressor. First, we will establish an analytical computation and procedure for calculating counterweight of the crank based on the dimension of air compressor and drive specifications. Second, design issue is created for a new crankshaft that fit the air compressor with vibration and noise suppression requirements. Finite element software of ANSYS is used to do the simulation for the modal analysis of the crankshaft. A new crankshaft counterweight is proposed effectively to increase the first mode of the natural frequency for the crankshaft of the compressor.

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ANH, LE DINH, and 黎定安. "A study on the two-dimensional flow and mass transfer model for the cathode of a proton exchange membrane fuel cell." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/99647822940208799247.

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碩士
大葉大學
機械工程研究所碩士班
93
A two-dimensional, transient mathematical model for the mass transfer of reactant gas in the cathode gas channel of a PEMFC is developed. This model accounts concurrently for gas flow and multi-component species (oxygen, water vapor and nitrogen) transport in the gas channel at specified cell current densities. The governing equations along with the boundary and initial conditions are solved numerically by using finite-difference methods. The numerical results show that the oxygen and water vapor concentrations in the gas channel are strong functions of stoichiometry. However, at a fixed stoichiometry, the current density has only slight influence on the concentration variations. The fully-developed Sherwood number for oxygen mass transfer in the gas channel is found to be 6.0, which agrees well with the Sherwood number estimated from the correlation between mass and heat transfer. Furthermore, two-dimensional models by using for gas diffusion layer and catalyst layer are coupled with gas channel model in order to build the cell performance. An analysis can be made of the effects due to some design and operating parameters such as flow rate, inlet pressure, oxygen mole fraction to bring out physical meanings influencing on the cell and consequently obtain a fuel cell with high performance.

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Dhaliwal, Saminder K. "Search for Neutral Minimally Supersymmetric Standard Model Higgs Decaying to Two Hadronic Taus with the ATLAS Detector in pp collisions at 7 TeV Center of Mass Energy." Thesis, 2013. http://hdl.handle.net/1807/35175.

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This thesis presents the first search for a neutral Minimal Supersymmetric Standard Model Higgs boson decaying to a pair of hadronic taus in proton-proton collisions with a center-of-mass energy of √s = 7 TeV. Results are presented for an integrated lumi- nosity of 1.056 fb−1 using data from the ATLAS detector at the Large Hadron Collider. After signal selection, 245 events are observed. The number of events is consistent the background estimate of 256 ± 26. An exclusion limit for the Higgs boson production is derived as a function of (cross-section)×(branching ratio). This limit is presented as a function of two parameters: mA and tanβ in the mmax scenario. A point in the (mA, h tanβ) phase space is excluded if the signal hypothesis is rejected at the 95% confidence level.

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Dinesh, M. "Design Of Two-Axis Displacement-Amplifying Compliant Mechanisms Using Topology Optimization." Thesis, 2008. http://hdl.handle.net/2005/751.

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This thesis deals with the design of two-axis displacement-amplifying compliant mechanisms (DaCMs) using topology optimization. The two-axis compliant mechanisms considered here are XY positioners and two-axis inertial sensors. A building block approach, with several single-axis DaCMs as building blocks, is used to conceive designs of compliant platforms that provide two orthogonal and independent movement of a common platform. Spring-mass-lever (SML) models of these designs are developed to simplify the analysis and design of the complicated arrangements of building blocks. The XY positioners designed in this work have perfectly de-coupled motion without compromising on the frequency; the best design of the stage has a displacement amplification of five resulting in the enhanced range of 4.2 % of the mechanism size–a significant improvement from the 1.67 %, the maximum range of the designs reported so far. Nearly 100% improvement is observed in the sensitivity of the two-axis accelerometer as compared with an existing design that occupied the same area. Multiple prototypes of XY positioners were fabricated on polypropylene sheets using CNC machining; and on spring steel and aluminium using wire-cut electro discharge machining. Mask layouts for two-layer two-axis accelerometers are designed for micro-fabrication using reactive ion etching and wafer bonding.

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Ramodibe, Mohau Armatto. "From communication to communigation: a conceptual model to strengthen South Africa’s government communication system – the case of Mpumalanga Province." Thesis, 2017. http://hdl.handle.net/10500/25706.

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Text in English
This study adopted a quantitative approach in order to produce numbers in relation to the diffusion of the new media. A descriptive quantitative survey was conducted – with sampling done in multi-stage probability – which comprised clustering, simple random, systematic, stratified sampling techniques, convenience and census sampling. A sample size of 379 respondents was selected, comprising 347 citizen-respondents and 32 government communicators (heads of communication). Data was collected utilising two (2) standardised questionnaires – one tailor-made for the citizens and the other for government communicators. Informed by the Diffusion of Innovations theory, this study has established that new media channels have difussed extensively within communities in the Province of Mpumalanga. This has provided a strong motivation to recommend that the communication policy of the South African government be amended, to include new media channels, like social media, as official government communication channels.
Communication Science
D. Litt. et Phil. (Communication)

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(8115878), Matthew T. Moore. "Numerical Simulation of a Continuous Caster." Thesis, 2019.

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Heat transfer and solidification models were developed for use in a numerical model of a continuous caster to provide a means of predicting how the developing shell would react under variable operating conditions. Measurement data of the operating conditions leading up to a breakout occurrence were provided by an industrial collaborator and were used to define the model boundary conditions. Steady-state and transient simulations were conducted, using boundary conditions defined from time-averaged measurement data. The predicted shell profiles demonstrated good agreement with thickness measurements of a breakout shell segment – recovered from the quarter-width location. Further examination of the results with measurement data suggests pseudo-steady assumption may be inadequate for modeling shell and flow field transition period following sudden changes in casting speed. An adaptive mesh refinement procedure was established to increase refinement in areas of predicted shell growth and to remove excess refinement from regions containing only liquid. A control algorithm was developed and employed to automate the refinement procedure in a proof-of-concept simulation. The use of adaptive mesh refinement was found to decrease the total simulation time by approximately 11% from the control simulation – using a static mesh.

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(11171943), Srivathsan Sudhakar. "Boiling in Capillary-Fed Porous Evaporators Subject to High Heat Fluxes." Thesis, 2021.

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Thermal management in next generation power electronic devices, radar applications and semiconductor packaging architectures is becoming increasingly challenging due to the need to reject localized high heat fluxes as well as large total powers. Air cooling has been considered as a simple and reliable method for thermal management compared to architectures that incorporate liquid cooling. However, air-cooled heat sinks typically require effective heat spreading to provide the requisite level of area enhancement to dissipate high heat fluxes. Compared to solid metallic heat spreaders, advanced heat sinks that incorporate two-phase heat transfer devices such as vapor chambers can significantly enhance the power dissipation capabilities in such configurations. Vapor chambers are devices that utilize evaporation/boiling processes within a sealed cavity to achieve efficient heat spreading. In high-heat-flux applications, boiling can occur within the internal wick structure of the vapor chamber at the location of the heat input (i.e., the evaporator). The maximum dryout heat flux and thermal resistance of the device is dictated by the resulting two-phase flow and heat transfer in the porous evaporator due to boiling. While various works in the literature have introduced new evaporator wick designs to improve the dryout heat flux during boiling, the enhancement is limited to small, millimeter scale hotspots or at a very high thermal resistance. In additixon, the effective design of such evaporator systems requires mechanistic models that can accurately predict the dryout limit and thermal performance.

This thesis first explores the usage of a novel ‘two-layer’ evaporator wick for passive high heat flux dissipation over large heater areas at a low thermal resistance. Moreover, a new mechanistic (first principles based) model framework is introduced for dryout limit and thermal performance prediction during boiling in capillary fed evaporators, by considering the resulting simultaneous flow of two phases (liquid and vapor) within the microscale porous media.

The novel two-layer wick concept uses a thick ‘cap’ layer of porous material to feed liquid to a thin ‘base’ layer through an array of vertical liquid-feeding ‘posts’. Vapor ‘vents’ in the cap layer allow for vapor formed during the boiling process (which is constrained to the base layer) to escape out of the wick. This two-layer structure decouples the functions of liquid resupply and capillary-fed boiling heat transfer, making the design realize high heat flux dissipation greater than 500 W/cm2 over large heat input areas of ~1 cm2. A reduced-order model is first developed to demonstrate the performance of a vapor chamber incorporating such a two-layer evaporator wick design. The model comprises simplified hydraulic and thermal resistance networks for predicting the capillary-limited maximum heat flux and the overall thermal resistance, respectively. The reduced-order model is validated against a higher fidelity numerical model and then used to analyze the performance of the vapor chamber with varying two-layer wick geometric feature sizes. The fabrication of the proposed two-layer wick is then presented. The thermal performance of the fabricated wicks is characterized using a boiling test facility that utilizes high speed visualization to identify the characteristic regimes of boiling operation in the wicks. The performance is also benchmarked to conventional single-layer wicks.

It is observed that single-layer wicks exhibit an unfavorable boiling regime where the center of the heater area dries out locally, leading to a high value of thermal resistance. The two-layer wicks avoid local dryout due to the distributed feeding provided by the posts and enhance the dryout heat flux significantly compared to single-layer wicks. A two-layer design that consists of a 10 × 10 array of liquid feeding posts provided a 400% improvement in the dryout heat flux. Following a parametric analysis of the effect of particle size, two-layer wicks composed of 180 – 212 µm particles and a 15 × 15 array of liquid feeding posts yielded a maximum heat flux dissipation of 485 W/cm2 over a 1 cm2 heat input area while also maintaining a low thermal resistance of only ~0.052 K/W. The effect of vapor venting and liquid-feeding areas is also experimentally studied. By understanding these effects, a parametrically optimized design is fabricated and shown to demonstrate an extremely high dryout limit of 512 W/cm2. We identify that the unique area-scalability of the two-layer wick design allows it to achieve an unprecedented combination of high total power and low-thermal-resistance heat dissipation over larger areas than was previously possible in the literature.

The results from the characterization of two-layer wicks revealed that the overall performance of the design was limited by the boiling process in the thin base wick layer. A fundamental model-based understanding of the resulting two-phase flow and heat transfer process in such thin capillary-fed porous media was still lacking. This lack of a mechanistic model precluded the accurate prediction of dryout heat flux and thermal performance of the two-layer wick. Moreover, such an understanding is needed for the optimal design of advanced hybrid evaporator wicks that leverage capillary-fed boiling. Despite the existence of various experimental works, there are currently no mechanistic approaches that model this behavior. To fill this unmet need, this thesis presents a new semi-empirical model for prediction of dryout and thermal resistance of capillary-fed evaporator systems. Thermal conduction across the solid and volumetric evaporation within the pores are solved to obtain the temperature distribution in the porous structure. Capillary-driven lateral liquid flow from the outer periphery of the evaporator to its center, with vapor flow across the thickness, is considered to obtain the local liquid and vapor pressures. Experiments are conducted on sintered copper particle evaporators of different particle sizes and heater areas to collect data for model calibration. To demonstrate the wider applicability of the model for other types of porous evaporators, the model is further calibrated against a variety of dryout limit and thermal resistance data collected from the literature. The model is shown to predict the experimentally observed trends in the dryout limit with mean particle/pore size, heater size, and evaporator thicknesses. This physics–based modeling approach is then implemented into a vapor chamber model to predict the thermal performance limits of air-cooled heat sinks with embedded vapor chambers. The governing energy and momentum equations of a low-cost analytical vapor chamber modeling approach is coupled with the evaporator model to capture the effect of boiling in the evaporator wick. An example case study illustrating the usage of the model is demonstrated and compared to a purely evaporation-based modeling approach, for quantifying the differences in dryout limit prediction, signifying the need to account for boiling in the evaporator wick.

The understanding gained from this thesis can be utilized for the prediction of dryout and thermal performance during boiling in capillary limited evaporator systems. The work also suggests the usage of a universal relative permeability correlation for the two-phase flow configuration studied herein for capillary-fed boiling, based on a wide calibration to experimental data. The modeling framework can also be readily leveraged to find novel and unexplored designs of advanced evaporator wicks. From an application standpoint, the new vapor chamber model developed here can be used for the improved estimation of performance limits specifically when high heat fluxes are encountered by the device. This will enable better and informed design of air-cooled heat sink architectures with embedded vapor chambers for high performance applications.

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Dissertations / Theses on the topic 'Two-mass model'

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