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Tesi sul tema "Propagation"
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1
Braunstein, Alfredo. "Survey propagation." Doctoral thesis, SISSA, 2004. http://hdl.handle.net/20.500.11767/4250.
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Nechayev, Yuriy Ivanovich. "Investigations into propagation mechanisms for urban radiowave propagation modelling." Thesis, University of Birmingham, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420512.
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Kubicek, Martin. "High dimensional uncertainty propagation for hypersonic flows and entry propagation." Thesis, University of Strathclyde, 2018. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=30780.
Testo completoAbstract (sommario):
To solve complex design problems, engineers cannot avoid to take into account the involved uncertainties. This is important for the analysis and design of hypersonic objects and vehicles, which have to operate in extreme conditions. In this work, two approaches for a high dimensional uncertainty quantification (UQ) are developed. The first approach performs a single-fidelity non-intrusive forward UQ, while the second one performs a multi fidelity UQ, as an extension of the first approach. Both methods are focused on real engineering problems and, therefore, appropriate heuristics are included to achieve an optimal trade-off between accuracy and computational costs. In the first approach, the stochastic domain is decomposed into domains of lower dimensionality, and, then, each domain is handled separately. This is possible due to the application of the HDMR, which is here derived in a new way. This new derivation allowed to deduce important conclusions about the high dimensional modelling, which are used in the prediction scheme. This novel approach for the selection of the higher order interaction effects drastically reduce the required number of samples. In order to have optimally distributed samples for the problem of interest, the adaptive sampling scheme is introduced. Moreover, the multi-surrogate approach is introduced in order to improve the robustness of the method. The single-fidelity approach is tested on a debris re-entry case and the method is validated with respect to the MC simulation method. In the second approach, the multi-fidelity approach has been developed. In order to have the optimal combination of the low fidelity models, the power ratio approach is introduced. To correct the low fidelity model, the classical additive correction, adapted to work within the HDMR approach, is used. The multi-fidelity approach has been tested on the GOCE re-entry case, where the performed tests demonstrate the potentialities of the method.
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Tu, Ronghui. "Generalized Survey Propagation." Thèse, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/19972.
Testo completoAbstract (sommario):
Survey propagation (SP) has recently been discovered as an efficient algorithm in solving classes of hard constraint-satisfaction problems (CSP). Powerful as it is, SP is still a heuristic algorithm, and further understanding its algorithmic nature, improving its effectiveness and extending its applicability are highly desirable.
Prior to the work in this thesis, Maneva et al. introduced a Markov Random Field (MRF) formalism for k-SAT problems, on which SP may be viewed as a special case of the well-known belief propagation (BP) algorithm. This result had sometimes been interpreted to an understanding that “SP is BP” and allows a rigorous extension of SP to a “weighted” version, or a family of algorithms, for k-SAT problems.
SP has also been generalized, in a non-weighted fashion, for solving non-binary CSPs. Such generalization is however presented using statistical physics language and somewhat difficult to access by more general audience.
This thesis generalizes SP both in terms of its applicability to non-binary problems and in terms of introducing “weights” and extending SP to a family of algorithms. Under a generic formulation of CSPs, we first present an understanding of non-weighted SP for arbitrary CSPs in terms of “probabilistic token passing” (PTP).
We then show that this probabilistic interpretation of non-weighted SP makes it naturally generalizable to a weighted version, which we call weighted PTP.
Another main contribution of this thesis is a disproof of the folk belief that “SP is BP”. We show that the fact that SP is a special case of BP for k-SAT problems is rather incidental. For more general CSPs, SP and generalized SP do not reduce from BP. We also established the conditions under which generalized SP may reduce as special cases of BP.
To explore the benefit of generalizing SP to a wide family and for arbitrary, particularly non-binary, problems, we devised a simple weighted PTP based algorithm for solving 3-COL problems. Experimental results, compared against an existing non-weighted SP based algorithm, reveal the potential performance gain that generalized SP may bring.
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Muirhead, Matthew. "Interior wave propagation." Thesis, University of Nottingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289312.
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Mikulica, Tomáš. "Light Propagation Volumes." Master's thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2015. http://www.nusl.cz/ntk/nusl-234902.
Testo completoAbstract (sommario):
This thesis deals with problem of computation of global illumination in real-time. Two methods are described. Namely Reflective Shadow Maps and Light Propagation Volumes. The first of them deals with the problem by using extended Shadow Mapping algorithm. The second one uses scene embedded into a 3D grid together with Spherical harmonics to compute light propagation in the scene. Furthermore this thesis contains results of measurement of the rendering speed of the Light Propagation Volumes algorithm with various settings on several machines. Quality of the resulting output of the algorithm is also evaluated.
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Růžička, Tomáš. "Light Propagation Volumes." Master's thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2016. http://www.nusl.cz/ntk/nusl-255483.
Testo completoAbstract (sommario):
The aim of master thesis is to describe different calculation of global illumination methods including Light Propagation Volumes. All three steps of LPV calculation are widely described: injection, propagation and rendering. It is also proposed several custom extensions improving graphics quality of this method. Two parts of design and implementation are focused on scene description, rendering system, shadow rendering, implementation of LPV method and proposed extensions. As conclusion, measurement and several images of application are presented, followed by comparison in environment with diffenent parameters, thesis summary with evaluation of achieved results and suggestions of further improvements.
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Bertin, Michaël. "Propagation des incertitudes dans un modèle réduit de propagation des infrasons." Thesis, Cachan, Ecole normale supérieure, 2014. http://www.theses.fr/2014DENS0020/document.
Testo completoAbstract (sommario):
La perturbation d’un système peut donner lieu à de la propagation d’onde. Une façon classique d’appréhender ce phénomène est de rechercher les modes propres de vibration du milieu. Mathématiquement, trouver ces modes consiste à rechercher les valeurs et fonctions propres de l’opérateur de propagation. Cependant, d’un point de vue numérique, l’opération peut s’avérer coûteuse car les matrices peuvent avoir de très grandes tailles. En outre, dans la plupart des applications, des incertitudes sont inévitablement associées à notre modèle. La question se pose alors de savoir s’il faut attribuer d’importantes ressources de calcul pour une simulation dont la précision du résultat n’est pas assurée. Nous proposons dans cette thèse une démarche qui permet à la fois de mieux comprendre l’influence des incertitudes sur la propagation et de réduire considérablement les coûts de calcul pour la propagation des infrasons dans l’atmosphère. L’idée principale est que tous les modes n’ont pas la même importance et souvent, seule une poignée d’entre eux suffit à décrire le phénomène sans perte notable de précision. Ces modes s’avèrent être ceux qui sont les plus sensibles aux perturbations atmosphériques. Plus précisément, l’analyse de sensibilité permet d’identifier les structures de l’atmosphère les plus influentes, les groupes de modes qui leur sont associés et les parties du signal infrasonore qui leur correspondent. Ces groupes de modes peuvent être spécifiquement ciblés dans un calcul de spectre au moyen de techniques de projection sur des sous-espace de Krylov, ce qui implique un gain important en coût de calcul. Cette méthode de réduction de modèle peut être appliquée dans un cadre statistique et l’estimation de l’espérance et de la variance du résultat s’effectue là aussi sans perte notable de précision et avec un coût réduit<br>The perturbation of a system can give rise to wave propagation. A classical approach to understand this phenomenon is to look for natural modes of vibration of the medium. Mathematically, finding these modes requires to seek the eigenvalues and eigenfunctions of the propagation operator. However, from a numerical point of view, the operation can be costly because the matrices can be of very large size. Furthermore, in most applications, uncertainties are inevitably associated with our model. The question then arises as to whether we should allocate significant computational resources for simulation while the accuracy of the result is not guaranteed. We propose in this thesis an approach that allows both a better understanding of the influence of uncertainties on the propagation and a significant decrease of computational costs for infrasound propagation in the atmosphere. The main idea is that all modes do not have the same importance and only a few of them is often sufficient to account for the phenomenon without a significant loss of accuracy. These modes appear to be those which are most sensitive to atmospheric disturbances. Specifically, a sensitivity analysis is used to identify the most influential structures of the atmosphere, the associated groups of modes and their associated parts of the infrasound signal. These groups of modes can be specifically targeted in a spectrum calculation with the projection of the operator onto Krylov subspaces, that allows a significant decrease of the computational cost. This method of model reduction can be applied in a statistical framework as well and estimations of the expectation and the variance of the results are carried out without a significant loss of accuracy and still with a low cost
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Maxwell, Douglas Wayne. "Propagation of Camptotheca acuminata." [College Station, Tex. : Texas A&M University, 2004. http://hdl.handle.net/1969.1/454.
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Izquierdo, Fernández Benjamín. "Electromagnetic propagation in tunnels." Doctoral thesis, Universitat Politècnica de Catalunya, 2011. http://hdl.handle.net/10803/38437.
Testo completoAbstract (sommario):
Introduction of wireless communications systems in railway communications are at the origin of this thesis. Ifercat, the company in charge of the development of Línia 9 of Barcelona Metro, decided that wireless systems were employed in order to increase efficiency and safety. For this reason, characterisation of ISM 5.8GHz band in tunnel environments for broad band wireless train communications becomes necessary. Tunnel environments constitute harsh environments due to humidity, obstacles, power systems, moving trains, curves¿ The Automatic Train Control system requires a 20MHz bandwidth for train-to-ground video transmission in order to get on-board information and surveillance.
Given that Línia 9 was at the early stages of its development at the beginning of the study, a dual-polarised spectral simulator was developed first. Spectral techniques work in both spatial and spatial-frequency domain and are extremely adaptable to changes in the tunnel cross section as the wave front passes down the tunnel. Efficiency of this technique comes from the well-known properties of FFT algorithms. Spectral techniques provide good near-field predictions and can model different antenna configurations easily. On the other hand, boundary conditions present some issues that must be overcome. Long tunnels also represent a problem in terms of required memory space.
The parabolic equation has been used to enhance the performance of spectral techniques far from the source. They complement each other well because parabolic conditions require smooth variations in one direction, thus far from the source, where only field components propagating parallel to the tunnel axis remain, in order to provide accurate results. Application of Leontovich boundary conditions ensures proper solution at the change of media and its low computational cost permits acceleration of predictions.
These two techniques are then combined to verify the measurement campaigns developed at metro tunnels during the thesis. MIMO schemes are used to enhance the system throughput and simulation predictions are compared to measurements with good results. The work presented in this thesis consisted first on implementing both simulators and verifying their correct behaviour with theoretical analytical solutions. Secondly, predictions are compared with measurement campaigns carried out in Barcelona Metro environments. The study focuses on EM attenuation, field distribution, fading characterisation, antenna location and MIMO processing at the frequency band of interest.
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Calle, Juan Carlos. "Indoor propagation simulation software." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2000. http://handle.dtic.mil/100.2/ADA383980.
Testo completoAbstract (sommario):
Thesis (M.S. in Electrical Engineering) Naval Postgraduate School, Sept.ember 2000.<br>Thesis advisors, Lebaric, Jovan ; Adler, Richard. "September 2000." Includes bibliographical references (p. 45-46). Also available online.
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Saeed, Muhammad Azam. "Pulverised biomass flame propagation." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/15264/.
Testo completoAbstract (sommario):
A resource analysis for Pakistan has demonstrated that abundant crop residues offer a viable, and environmental-friendly alternative to currently inadequate, oil-based power generation. Similarly, in many countries there is legislative pressure and incentives to replace coal with biomass, in electricity production. Efficient and safe exploitation of such biofuels requires data on flame propagation rates and explosibility characteristics. Crop residues (bagasse, rice husk, wheat-straw, corn-cob and peanut-shell) and different raw and thermally treated woods were tested using the modified Hartmann tube and the modified 1 m3 explosion vessel. The modified Hartmann tube was operated for varying ignition delays using a digital timer. A hemispherical disperser with drilled pipe was calibrated for the testing of fibrous and coarse size biomass mixtures. Thermogravimetric analysis data from these materials enabled the application of two different models for the determination of volatile release kinetics. Biomass samples were found to have lower activation energies with higher volatile release rates at low temperatures, compared to coals. Despite their higher ash content, pulverised crop-residues showed leaner minimum explosible concentrations (0.2-0.5 equivalence-ratio) than woods (0.3-0.7) - depending on particle size. Biomass samples were more sensitive to explosion than coal, resulting in flame propagation in coarse-size-range fractions (300-500-μm) that was not experienced with coals. Maximum explosion pressures of near 9 barg were measured for the fine size fraction (less than 63-μm) samples, with no less than 7 barg for coarse size fraction (less than 1 mm). Milling of thermally treated biomass samples resulted in higher fines fraction than untreated biomass, for the same sieve size and this was considered as one of the reasons of the higher reactivity (higher flame speed and higher deflagration index of these samples). The detailed data from this work are usable in the design of safe and efficient combustion systems for power generation from crop residues and other biomass fuels.
13
Michaud, Denis 1970. "Neutrino propagation through matter." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=55513.
Testo completoAbstract (sommario):
In this thesis, we examine the evolution of a quantum system through background matter in order to determine the conditions of validity required for a description in terms of an effective Hamiltonian. General scattering rate equations are obtained for coherent diffuse scattering. We find, as expected, that the diffuse scattering rate is small compared to the coherent scattering rate in a medium with low fluctuations allowing an effective Hamiltonian description. However, for a more turbulent background, it is still possible to have more significant contributions to the diffuse scattering which may affect the existing theory of neutrino flavor conversion (MSW effect).
14
Robinson, Anthony John. "Dynamic error propagation networks." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303145.
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Dorbec, Paul. "Jeux, graphes et propagation." Habilitation à diriger des recherches, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00975898.
Testo completoAbstract (sommario):
Ce manuscrit d'Habilitation à diriger des recherches décrit mes travaux de recherche récents en théorie des graphes et en théorie des jeux combinatoires. Une première partie est consacrée à l'étude de paramètres de graphes en s'intéressant particulièrement aux contraintes structurelles qui permettent d'améliorer les bornes connues. Dans cette partie, nous traitons notamment la paire-domination, la domination indépendante mais aussi les partitions en cographes et les colorations quasi propres. Une deuxième partie traite de la domination de puissance, une forme itérative de la domination au sujet de laquelle nous proposons un début de synthèse des résultats existants. Enfin, une troisème partie parle de jeux. Nous y traitons d'abord le travail réalisé sur quelques conjectures portant sur un jeu de domino, puis au sujet des jeux en version misère. Nous y parlons enfin du jeu de domination, qui est à l'interface entre le paramètre de graphe et le jeu combinatoire.
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Soliman, Ehab Mohammed. "Delay hierarchy propagation model." Thesis, University of Plymouth, 2005. http://hdl.handle.net/10026.1/2334.
Testo completoAbstract (sommario):
Construction projects are always exposed to delay. Research has shown that most projects encounter delays and this problem is a global one. Previous research related to delays in construction projects have been dedicated to measuring and ranking the direct delays that have occurred. These types of delay are past delays and have already affected many aspects of the project's performance. This type of research is of the reactive type and handles delays after they have happened. The objective of this research is to model the construction project delays that can be used to predict the level of delays that the project could face during its future life. The proposed Delay Hierarchy Propagation Model (DHPM) is the first attempt to model delays in the construction project. This model is an innovative predictive approach to anticipate the future encountered delays before they become real. The model assumes that the direct delay is generated from earlier events or aspects that are found before the direct delay occurs; these events are called the root delay causes. These root delay causes need to be analysed, measured and managed in order to prevent or mitigate the effect of a later direct delay in the project life. The direct delays were analysed by a cause-effect technique to extract a set of root delay causes. The model assumes that the root delay causes will influence the project resources supply rate. The resource shortage then leads to activity delay and, hence possible delay to the whole project. The DHPM consists of two interrelated models: a Resource Shortage Possibility (RSP) model and the Predicting Project Delay model (PPD) model. The RSP model objective is to predict the possibility of resource shortage, whilst the PPD model objectives are to predict the project finish time and to define the critical areas for the project to delay using the output of the RSP model as input. The RSP model was verified through interview questionnaires with a number of selected personnel from the construction industry. The Delphi method was used to enhance the questionnaire results. The RSP model calculations used a combination of fuzzy logic, analytical hierarchy process (AHP) and multi-attribute theory to obtain the model output. A prototype computer program was introduced. The prototype computer program was then tested on a real construction project. The application of the RSP model showed that it is viable. The PPD model used probabilistic networking to predict the finish time of the project. The model introduced two new terms that can be used to define the most critical activities and the possible resource influence to delay. The comparison between PPD and the classical critical path method (CPM), programme evaluation and review technique (PERT) and Monte Carlo simulation revealed that the proposed model provides new information required to enhance delay management by project management staff.
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Bixler, Reid Morris. "Sparse Matrix Belief Propagation." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/83228.
Testo completoAbstract (sommario):
We propose sparse-matrix belief propagation, which executes loopy belief propagation in Markov random fields by replacing indexing over graph neighborhoods with sparse-matrix operations. This abstraction allows for seamless integration with optimized sparse linear algebra libraries, including those that perform matrix and tensor operations on modern hardware such as graphical processing units (GPUs). The sparse-matrix abstraction allows the implementation of belief propagation in a high-level language (e.g., Python) that is also able to leverage the power of GPU parallelization. We demonstrate sparse-matrix belief propagation by implementing it in a modern deep learning framework (PyTorch), measuring the resulting massive improvement in running time, and facilitating future integration into deep learning models.<br>Master of Science
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Berglund, Alexander, Fredrik Herbai, and Jonas Wedén. "Sound Propagation Through Walls." Thesis, Uppsala universitet, Avdelningen för beräkningsvetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-444632.
Testo completoAbstract (sommario):
Infrasound is undetectable by the human ear and excessive exposure may be a substantial health risk. Low frequency sound propagates through walls with minimal attenuation, making it difficult to avoid. This study interprets the results from both analytical calculations and simulations of pressure waves propagating through a wall in one dimension. The wall is thin compared to the wavelength; the model implements properties of three materials commonly used in walls. The results indicate that the geometry of the wall, most importantly the small ratio between wall width and wavelength, is the prime reason for the low levels of attenuation observed in transmitted amplitudes of low frequency sounds, and that damping is negligible for infrasound. Furthermore, a one-dimensional homogeneous wall model gives rise to periodicity in the transmitted amplitude, which is not observed in experiments. Future studies should prioritize the introduction of at least one more dimension to the model, to allow for variable angles of incidence.
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Le, Guilcher Arnaud. "Méthodes de propagation d'interfaces." Thesis, Paris Est, 2014. http://www.theses.fr/2014PEST1030/document.
Testo completoAbstract (sommario):
Ce travail porte sur la résolution de problèmes faisant intervenir des mouvements d'interfaces. Dans les différentes parties de cette thèse, on cherche à déterminer ces mouvements d'interfaces en résolvant des modèles approchés consistant en des équations ou des systèmes d'équations sur des champs. Les problèmes obtenus sont des équations paraboliques et des systèmes hyperboliques. Dans la première partie (chapitre 2), on étudie un modèle simplifié pour la propagation d'une onde de souffle en dynamique des fluides compressibles. Ce modèle peut s'écrire sous la forme d'un système hyperbolique, et on construit un algorithme résolvant numériquement ce système par une méthode de type Fast-Marching. On mène également une étude théorique de ce système pour déterminer des solutions de référence et tester la validité de l'algorithme. Dans la deuxième partie (chapitres 3 à 5), les équations approchées sont de type parabolique, et on cherche à montrer l'existence de solutions de type régime permanent à ces équations. Dans les chapitres 3 et 4, on étudie une équation générique en une dimension associée à des phénomènes de réaction-diffusion. Dans le chapitre 3, on montre l'existence de solutions quasi-planes pour un terme de réaction (terme non-linéaire) assez général, et dans le chapitre 4 on utilise ces résultats pour montrer l'existence d'ondes pulsatoires progressives dans le cas spécifique d'une non-linéarité bistable. Le modèle étudié dans le chapitre 5 est un modèle de champ de phase approchant un modèle de dynamique des dislocations dans un cristal, dans un domaine correspondant physiquement à une source de Frank-Read<br>This work is about the resolution of problems associated with the motion of interfaces. In each part of this thesis, the goal is to determine the motion of interfaces by the use of approached models consisting of equations or systems of equation on fields. The problems we get are parabolic equations and hyperbolic systems. In the first part (Chapter 2), we study a simplified model for the propagation of a shock wave in compressible fluid dynamics. This model can be written as a hyperbolic system, and we construct an algorithm to solve it numerically by a Fast-Marching like method. We also conduct a theoretical study of this system to determine reference solutions and test the algorithm. In the second part (Chapters 3 to 5), the approached models yield parabolic equations, and our goal is to show the existence of permanent regime solutions for these equations. Chapter 3 and 4 are dedicated to the study of a generic one-dimensional equation modelling reaction-diffusion phenomena. In Chapter 3, we show the existence of plane-like solutions for a general reaction term, and in Chapter 4 we use this result to show the existence of pulsating travelling waves in the specific case of a bistable nonlinearity. In Chapter 5, we study a phase-field model approaching a model for the dynamics of dislocations in a crystal, in a domain corresponding to a Frank-Read source
20
Ridgway, Douglas Thacher. "Fluctuation-controlled front propagation /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9820864.
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Savage, Brian Kirk Gurnis Michael. "Regional seismic wavefield propagation /." Diss., Pasadena, Calif. : California Institute of Technology, 2004. http://resolver.caltech.edu/CaltechETD:etd-05262004-100247.
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Price, M. A. "Sound propagation in woodland." Thesis, Open University, 1986. http://oro.open.ac.uk/56924/.
Testo completoAbstract (sommario):
A review of past research into sound propagation in woodland is presented. The attenuation of sound in woodland is small between about 800 and 2000Hz and greater at low and high frequencies. Attenuation measurements made in three contrasting woodlands are presented and compared with theoretical models. Propagation models using simple one- and two-parameter impedance models are used to calculate appropriate ground parameters for the prediction of impedance of the woodland soils. The ground parameters varied on different days in a single stand due to differences in moisture content and compaction. The overall differences between the stands are not significant. The woodland soil has a considerably lower impedance than other outdoor ground surfaces such as grassland or sand. A theoretical model for the attenuation of sound by thermoviscous absorption and scattering within an array of cylinders is assessed by means of a model experiment with wooden rods in an anechoic chamber. An input density 60% lower than the actual density gives a good agreement with measured attenuation. This modified model also predicts the attenuation by the cylinders in the presence of a ground surface. The scattering model is compared with the high frequency attenuation measured in the , woodland, using sampled trunk densities and radius, this underpredicts the observed attenuation, particularly in the stands with a dense branch and foliage structure. Addition of a second. dense, array of non rigid scatterers gives a good agreement with the measured data, thus modelling the scattering and absorbing effects of trunks, branches and leaves, in the high frequencies. Finally, a combined model is presented in which the attenuation caused by ground interference effects. at low frequencies. is added to a prediction of attenuation by the scattering model. across the whole frequency range. This model reproduces the frequency dependence of the attenuation of sound in woodland.
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Becker, Saskia. "The Propagation-Separation Approach." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, 2014. http://dx.doi.org/10.18452/16960.
Testo completoAbstract (sommario):
Lokal parametrische Modelle werden häufig im Kontext der nichtparametrischen Schätzung verwendet. Bei einer punktweisen Schätzung der Zielfunktion können die parametrischen Umgebungen mithilfe von Gewichten beschrieben werden, die entweder von den Designpunkten oder (zusätzlich) von den Beobachtungen abhängen. Der Vergleich von verrauschten Beobachtungen in einzelnen Punkten leidet allerdings unter einem Mangel an Robustheit. Der Propagations-Separations-Ansatz von Polzehl und Spokoiny [2006] verwendet daher einen Multiskalen-Ansatz mit iterativ aktualisierten Gewichten. Wir präsentieren hier eine theoretische Studie und numerische Resultate, die ein besseres Verständnis des Verfahrens ermöglichen. Zu diesem Zweck definieren und untersuchen wir eine neue Strategie für die Wahl des entscheidenden Parameters des Verfahrens, der Adaptationsbandweite. Insbesondere untersuchen wir ihre Variabilität in Abhängigkeit von der unbekannten Zielfunktion. Unsere Resultate rechtfertigen eine Wahl, die unabhängig von den jeweils vorliegenden Beobachtungen ist. Die neue Parameterwahl liefert für stückweise konstante und stückweise beschränkte Funktionen theoretische Beweise der Haupteigenschaften des Algorithmus. Für den Fall eines falsch spezifizierten Modells führen wir eine spezielle Stufenfunktion ein und weisen eine punktweise Fehlerschranke im Vergleich zum Schätzer des Algorithmus nach. Des Weiteren entwickeln wir eine neue Methode zur Entrauschung von diffusionsgewichteten Magnetresonanzdaten. Unser neues Verfahren (ms)POAS basiert auf einer speziellen Beschreibung der Daten, die eine zeitgleiche Glättung bezüglich der gemessenen Positionen und der Richtungen der verwendeten Diffusionsgradienten ermöglicht. Für den kombinierten Messraum schlagen wir zwei Distanzfunktionen vor, deren Eignung wir mithilfe eines differentialgeometrischen Ansatzes nachweisen. Schließlich demonstrieren wir das große Potential von (ms)POAS auf simulierten und experimentellen Daten.<br>In statistics, nonparametric estimation is often based on local parametric modeling. For pointwise estimation of the target function, the parametric neighborhoods can be described by weights that depend on design points or on observations. As it turned out, the comparison of noisy observations at single points suffers from a lack of robustness. The Propagation-Separation Approach by Polzehl and Spokoiny [2006] overcomes this problem by using a multiscale approach with iteratively updated weights. The method has been successfully applied to a large variety of statistical problems. Here, we present a theoretical study and numerical results, which provide a better understanding of this versatile procedure. For this purpose, we introduce and analyse a novel strategy for the choice of the crucial parameter of the algorithm, namely the adaptation bandwidth. In particular, we study its variability with respect to the unknown target function. This justifies a choice independent of the data at hand. For piecewise constant and piecewise bounded functions, this choice enables theoretical proofs of the main heuristic properties of the algorithm. Additionally, we consider the case of a misspecified model. Here, we introduce a specific step function, and we establish a pointwise error bound between this function and the corresponding estimates of the Propagation-Separation Approach. Finally, we develop a method for the denoising of diffusion-weighted magnetic resonance data, which is based on the Propagation-Separation Approach. Our new procedure, called (ms)POAS, relies on a specific description of the data, which enables simultaneous smoothing in the measured positions and with respect to the directions of the applied diffusion-weighting magnetic field gradients. We define and justify two distance functions on the combined measurement space, where we follow a differential geometric approach. We demonstrate the capability of (ms)POAS on simulated and experimental data.
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Schiavazzi, Daniele. "Redundant Multiresolution Uncertainty Propagation." Doctoral thesis, Università degli studi di Padova, 2013. http://hdl.handle.net/11577/3422585.
Testo completoAbstract (sommario):
Stochastic partial differential equations can be efficiently solved using collocation approaches combined with polynomial expansion in parameter space. Estimators based on these concepts show smaller variance than traditional or stratified Monte Carlo approaches under mild dimensionality. Research efforts in this context are focused on improving the efficiency of these methodologies for high dimensional problems (increasing number of input random variables) or for problems with discontinuous response in parameter space. In the present work, we use Compressive Sampling in order to minimize the number of deterministic computations needed to evaluate expansion coefficients for stochastic responses which are sparse in selected dictionaries of basis. Moreover, multiresolution approximation techniques are extended in the context of non-intrusive uncertainty propagation. Finally, an adaptive Importance Sampling strategy is used where samples are iteratively added to locations containing relevant features of increasingly smaller size. Applications are presented for analytical functions, stochastic differential equations, dynamical systems whose response is discontinuous or characterized by large gradients. Engineering problems involving robust optimization of windmill airfoils and passive damping of structures under uncertainty are also discussed. The last Chapter is devoted to methodologies aiming to restore element conservativeness for numerical and experimental velocity fields.<br>Metodi non intrusivi basati sull’espansione della risposta di un dato sistema nello spazio dei parametri (Chaos expansion methods) consentono di risolvere equazioni differenziali stocastiche con un numero di soluzioni deterministiche minori rispetto ad approcci tradizionali alla Monte Carlo con campionamento classico o stratificato. In tale ambito gli sforzi di ricerca odierni sono volti allo sviluppo di metodologie atte alla riduzione del costo computazionale in problemi caratterizzati da alta dimensionalitá (numero significativo di variabili aleatorie in input) ed al trattamento di problemi con risposta discontinua nello spazio dei parametri. La ricerca condotta si é concentrata sull’utilizzo di recenti tecniche di Compressive Sampling per la minimizzazione del numero di soluzioni deterministiche necessarie alla ricostruzione di risposte dotate di sparsitá secondo un pre-definito dizionario di basi. Inoltre, tecniche di approssimazione multi-risoluzione sono state estese a metodologie non intrusive di propagazione dell’incertezza. Infine, tecniche di Importance Sampling sono state utilizzate per determinare in modo adattativo l’ubicazione di nuovi samples al fine di cogliere le scale maggiormente importanti nelle risposte approssimate. Le metodologie approfondite ed implementate nell’ambito della ricerca svolta sono state applicate ad un insieme di funzioni analitiche, sistemi descritti da equazioni differenziali stocastiche, sistemi dinamici con risposte caratterizzate da elevati gradienti o discontinuitá, problemi ingegneristici con particolare riferimento all’ottimizzazione robusta della performance aerodinamica di profili per pale eoliche e sistemi passivi di smorzamento delle vibrazioni operanti sotto incertezza. Vengono inoltre presentate metodologie atte a ripristinare doti di conservazione di massa in flussi numerici e sperimentali.
25
Leissing, Thomas. "Nonlinear acoustic wave propagation in complex media : application to propagation over urban environments." Phd thesis, Université Paris-Est, 2009. http://tel.archives-ouvertes.fr/tel-00584398.
Testo completoAbstract (sommario):
Dans cette recherche, un modèle de propagation d'ondes de choc sur grandes distances sur un environnement urbain est construit et validé. L'approche consiste à utiliser l'Equation Parabolique Nonlinéaire (NPE) comme base. Ce modèle est ensuite étendu afin de prendre en compte d'autres effets relatifs à la propagation du son en milieu extérieur (surfaces non planes, couches poreuses, etc.). La NPE est résolue en utilisant la méthode des différences finies et donne des résultats en accord avec d'autres méthodes numériques. Ce modèle déterministe est ensuite utilisé comme base pour la construction d'un modèle stochastique de propagation sur environnements urbains. La Théorie de l'Information et le Principe du Maximum d'Entropie permettent la construction d'un modèle probabiliste d'incertitudes intégrant la variabilité du système dans la NPE. Des résultats de référence sont obtenus grâce à une méthode exacte et permettent ainsi de valider les développements théoriques et l'approche utilisée
26
Mahmood, Attiya. "Impact of Antenna Mutual Coupling, Propagation, and Nonreciprocity on Propagation-Based Key Establishment." BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/6831.
Testo completoAbstract (sommario):
Propagation-based key establishment is a physical layer method for generating encryption keys based on two radios observing a reciprocal propagation channel. This work explores the impact of mutual coupling when communicating nodes are equipped with multiple antennas, multipath richness in the propagation environment, and practical limitations caused by the nonreciprocal nature of RF circuits on key establishment. First, network theory is used to formulate a model of a realistic communication system which incorporates transmit sources and receive loads, impedance matching networks, low-noise amplifiers (LNAs), mutually coupled antenna arrays, and a passive eavesdropper. Afterwards, a detailed analysis is performed to quantify the impact of coupling, type of impedance matching network, and proximity of a multi-antenna eavesdropper on key rate metrics. Next, the degradation on key establishment caused by the radiocircuitry non-reciprocal contributions to the propagation channel is analyzed. A calibration technique based on total least square algorithm is used to overcome the non-reciprocity. Results demonstrate that the method is highly effective in removing the impact of non-reciprocal circuit contributions over a range of operational parameters. Lastly, for key establishment, the propagation conditions can cause the available key rate to be significantly different from the secure key rate which takes into account the presence of a passive eavesdropper. To study this in detail, a realistic multiple-input multiple-output (MIMO) propagation environment is modeled for two communicating radios and an eavesdropper. Afterwards different propagation conditions are assumed and results demonstrate that secure key rate converges to available key rate when K-factor is small and the eavesdropper is not located very close (< 2.5 wavelength) to one of the nodes.
27
Leissing, Thomas. "Propagation d'ondes non linéaires en milieu complexe - Application à la propagation en environnement urbain." Phd thesis, Université Paris-Est, 2009. http://tel.archives-ouvertes.fr/tel-00455590.
Testo completoAbstract (sommario):
Dans cette recherche, un modèle de propagation d'ondes de choc sur grandes distances sur un environnement urbain est construit et validé. L'approche consiste à utiliser l'Equation Parabolique Nonlinéaire (NPE) comme base. Ce modèle est ensuite étendu afin de prendre en compte d'autres effets relatifs à la propagation du son en milieu extérieur (surfaces non planes, couches poreuses, etc.). La NPE est résolue en utilisant la méthode des différences finies et donne des résultats en accord avec d'autres méthodes numériques. Ce modèle déterministe est ensuite utilisé comme base pour la construction d'un modèle stochastique de propagation sur environnements urbains. La Théorie de l'Information et le Principe du Maximum d'Entropie permettent la construction d'un modèle probabiliste d'incertitudes intégrant la variabilité du système dans la NPE. Des résultats de référence sont obtenus grâce à une méthode exacte et permettent ainsi de valider les développements théoriques et l'approche utilisée.
28
Dessalermos, Spyridon. "Undersea acoustic propagation channel estimation." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Jun%5FDessalermos.pdf.
Testo completoAbstract (sommario):
Thesis (M.S. in Electrical Engineering and M.S. in Applied Physics)--Naval Postgraduate School, June 2005.<br>Thesis Advisor(s): Joseph Rice, Roberto Cristi. Includes bibliographical references (p. 117-119). Also available online.
29
Zahn, Ralph. "Prion propagation and molecular chaperones." Zürich : Institut für Molekularbiologie und Biophysik, Eidgenössische Technische Hochschule Zürich, 2002. http://e-collection.ethbib.ethz.ch/show?type=habil&nr=4.
Testo completo
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Sander, Tavallaey Shiva. "Wave propagation in sandwich structure." Doctoral thesis, KTH, Vehicle Engineering, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3088.
Testo completo
31
Lagerkvist, Mikael Zayenz. "Techniques for Efficient Constraint Propagation." Licentiate thesis, KTH, Electronic, Computer and Software Systems, ECS, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9511.
Testo completoAbstract (sommario):
<p>This thesis explores three new techniques for increasing the efficiency of constraint propagation: support for incremental propagation, improved representation of constraints, and abstractions to simplify propagation. Support for incremental propagation is added to a propagator centered propagation system by adding a new intermediate layer of abstraction, advisors, that capture the essential aspects of a variable centered system. Advisors are used to give propagators a detailed view of the dynamic changes between propagator runs. Advisors enable the implementation of optimal algorithms for important constraints such as extensional constraints and Boolean linear in-equations, which is not possible in a propagator centered system lacking advisors. Using Multivalued Decision Diagrams (MDD) as the representation for extensional constraints is shown to be useful for several reasons. Classical operations on MDDs can be used to optimize the representation, and thus speeding up the propagation. In particular, the reduction operation is stronger than the use of DFA minimization for the regular constraint. The use of MDDs is contrasted and compared to a recent proposal where tables are compressed. Abstractions for constraint programs try to capture small and essential features of a model. These features may be much cheaper to propagate than the unabstracted program. The potential for abstraction is explored using several examples. These three techniques work on different levels. Support for incremental propagation is essential for the efficient implementation of some constraints, so that the algorithms have the right complexity. On a higher level, the question of representation looks at what a propagator should use for propagation. Finally, the question of abstraction can potentially look at several propagators, to find cases where abstractions might be fruitful. An essential feature of this thesis is a novel model for general placement constraints that uses regular expressions. The model is very versatile and can be used for several different kinds of placement problems. The model applied to the classic pentominoes puzzle will be used through-out the thesis as an example and for experiments.</p><p> </p><br><p>Den här avhandlingen utforskar tre nya tekniker för att öka effektiviteten av villkorspropagering: stöd för inkrementell propagering, val av representation för villkor, samt abstraktion för att förenkla propagering. Ett propageringssystem organiserat efter propagerare utökas med stöd för inkrementell propagering genom att lägga till ett nytt abstraktionslager: rådgivare. Detta lager fångar de essentiella aspekterna hos system organiserade efter variabler. Rådgivare används för att ge propagerare detaljerad information om de dynamiska ändringarna i variabler mellan körningar av propageraren. Utökningen innebär att det går att implementera optimala algoritmer för vissa viktiga villkor såsom tabellvillkor och Boolska linjära olikheter, något som inte är möjligt i ett rent propagator-organiserat system. Användandet av så kallade <em>Multivalued Decision Diagram</em> (MDD) som representation för tabellvillkor visas vara användbart i flera avseenden. Klassiska MDD-operationer kan användas för att optimera representationen, vilket leder till snabbare propagering. Specifikt så är reduktionsoperationen kraftfullare än användandet av DFA-minimering för reguljära villkor. MDD-representationen jämförs också med ett nyligen framlagt förslag för komprimerade tabeller. Abstraktioner för villkorsprogram försöker fånga små men viktiga egenskaper i modeller. Sådana egenskaper kan vara mycket enklare att propagera än den konkreta modellen. Potentialen för abstraktioner undersöks för några exempel. Dessa tre tekniker fungerar på olika nivåer. Stöd för inkrementell propagering är nödvändigt för att kunna implementera vissa villkor effektivt med rätt komplexitet. Valet av representation för villkor är på en högre nivå, då det gäller att se vilka algoritmer som skall användas för ett villkor. Slutligen så måste flera villkor i en modell studeras för att finna rätt typ av abstraktioner. Ett utmärkande drag för den här avhandlingen är en ny modell för generella placeringsvillkor som använder reguljära uttryck. Modellen är mångsidig och kan användas för flera olika typer av placeringsproblem. Modellen specialiserad för pentominopussel används genomgående som exempel för experiment.</p><p> </p><br>Coordinating Constraint Propagation
32
Uddholm, Per. "Numerical Simulation of Flame Propagation." Thesis, Uppsala University, Department of Information Technology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-98325.
Testo completoAbstract (sommario):
<p>The effects of the temperature and length, of the preheat zone, on the deflagration to detonation transition are investigated through numerical simulation. The Navier-Stokes equations, with a reaction term, are solved in one dimension. The time integration is a one-dimensional adaptation of an existing two-dimensional finite volume method code. An iterative scheme, based on an overlap integral, is developed for the determination of the deflagration to detonation transition. The code is tested in a number of cases, where the analytical solution (to the Euler equations) is known. The location of the deflagration to detonation transition is displayed graphically through the preheat zone temperature as a function of the fuel mixture temperature, for fixed exhaust gas temperature and with the preheat zone length as a parameter. The evolution of the deflagration to detonation transition is investigated for an initial state well within the regime where the deflagration to detonation transition occurs. Graphs displaying the temporal evolution of pressure, temperature, reaction rate, and fuel mass fraction are presented. Finally, a method for estimating the flame velocity during the deflagration and detonation phases, as well as the flame acceleration during the intermediate phase, is developed.</p>
33
Karis, Klas, Deborah Merzan, and Jacob Wärnhjelm. "Electron Propagation in Periodic Potentials." Thesis, KTH, Teoretisk fysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103467.
Testo completoAbstract (sommario):
In this bachelor thesis we study the propagation of electrons in crystals. The crystalline structure is modeled as a one dimensional periodic potential primarily composed of delta function potential barriers. We use two different models to describe how a particle behaves in such a periodic structure. The first model is the Kronig Penney model described by S. Gasiorowicz in [ 1]. The second model is described by Olsen and Vignale in the article "The Quantum mechanics of electric conduction in crystals" [ 3]. We show that there exists certain ranges of energy for which electron propagation can occur, namely the allowed energy bands separeted by regions of forbidden energies. In addition, we solve the Schrödinger equation numerically for some simple cases and reproduce some of the results seen from the two mentioned models.
34
Feng, Jiling. "Wave propagation in flexible tubes." Thesis, Brunel University, 2008. http://bura.brunel.ac.uk/handle/2438/5367.
Testo completoAbstract (sommario):
Wave dissipation was previously investigated intensively in the frequency domain, in which the dissipation of waves is described as attenuation of pressure pulse decay with respect to the frequency or harmonics. In this thesis, wave dissipation, including decay of pressure pulse, peak of wave intensity and wave energy, is investigated in the time domain using wave intensity analysis (WIA). Wave intensity analysis benefits to this research in several aspects including: 1) WIA allows for wave dissipation investigated in the time domain; 2) WIA does not make any assumptions about the tube's wall non-linearity and the analysis takes into account the effects of the vessel's wall viscoelastic properties, convective, frictional effects and fluid viscosity; 3) WIA offers a technique (separation) to study wave dissipation in one direction whilst taking into account the effect of reflections from the opposite direction; 4) The physical meaning of wave intensity provides a convenient method to study the dissipation of energy carried by the waves along flexible tubes. In this research, it is found that the degree of dissipation in flexible tube were not only affected by the mechanical properties of the wall property and viscosity of liquid but also by the other factors including initial pressure and pumping speed of piston as well as direction of wave in relation to direction of flow. Also an new technique to separate waves into forward and backward directions only using diameter and velocity might potentially be used to separate the waves in both directions non-invasively based on the non-invasive measurement of diameter (wall movement) available.
35
Yamout, Fadi. "Relevance Feedback Using Weight Propagation." Thesis, University of Sunderland, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485442.
Testo completoAbstract (sommario):
A new relevance feedback technique called Weight Propagation has been developed which provides greater retrieval effectiveness than previously described techniques. Documents judged relevant by the user propagate positive Weights to documents close by in vector similarity space, while documents judged not relevant propagate Negative Weights to such neighbouring documents. Variants of Weight Propagation are also described, namely WPI and WPR (inspired by Ide and Rocchio respectively), and WPY which is the main focus of this thesis, where only the maximum weight propagated to each document is counted. Weight Propagation was further enhanced by introducing a second-order propagation (documents that receive weights themselve!propagate weights to related documents) which increased the precision of the results. WPY is compared against the Rocchio and Ide techniques in the vector model based on the tf.idf weighting scheme, and against the Information-theoretic query expansion technique based on the Kullback-Leibler divergence measure using the DB2 weighting model of the Divergence From Randomness framework. Different RF models were employed such as pseudo relevance feedback in addition to both simulated positive and negative feedback using residual collection technique. The experiments are performed on different test collections such as MED, CISI, Cranfield, LISA, NPL, WTIOG and GOV. Small collections such as MED, CISI, and Cranfield were also tested in the semantic space using Latent Semantic Indexing and the optimal number of dimensions that captures the underlying semantics that exists between the documents is determined for these collections. Retrieval effectiveness is improved since the documents are treated as independent vectors rather than being merged into a single vector as is the case with traditional vector model relevance feedback techniques, or by determining the documents' relevancy based on the lengths of all the documents as with the Kullback-Leibler divergence measure used in traditional probabilistic relevance feedback techniques. In addition, the Weight Propagation technique does not expand terms as in the case with traditional approaches.
36
Wilson, Simon Trevor. "Applications of cyclic belief propagation." Thesis, University of Cambridge, 2000. https://www.repository.cam.ac.uk/handle/1810/251732.
Testo completo
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Qu, Yong. "Breeding and propagation of Meconopsis." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/24899.
Testo completoAbstract (sommario):
Six species of Meconopsis were investigated for self-fertility and cross compatibility in order to incorporate desirable characters from both parents. The six species used were: M. cambrica, M. villosa, M. quintuplinervia, M. betonicifolia, M. horridula, M. aculeata. Chromosome counts were made: M. cambrica, n=14; M. villosa, n=16; M. quintuplinervia, n= c.42; M. betonicifolia, n=40; M. horridula, n=28 and M. aculeata, n=28. Interspecific compatibility was correlated with differences in ploidy level between parents. All crosses made except M. cambrica x quintuplinervia set seeds. M. cambrica, M.
betonicif olia, M. horridula and M. aculeata are self-compatible.
Pollination mechanisms and the likelihood of apogamy were investigated in M. betonicifolia. No apogamy was found and insects are the likely pollinators for this species.
As some of the species do not flower at the same time, pollen staining, pollen germination and storage conditions for the six species were studied. Experimental alteration of flowering periods through controlling temperatures and day-lengths for M. betonicifolia was also carried out. This part of the project shows: (1) pollen stainability (stained by lactophenol cotton blue) for the six species was 85% or more; (2) pollen of all six species except M. quintuplinervia germinated on an agar medium containing sucrose (5 g 1⁻¹) and H₃BO₃ (0.1 mg 1⁻¹); (3) pollen germination percentage decreased with storage time in a desiccator at 4-6°C; and (4) long daylength (16 h) was suitable for growth and flowering of M. betonicifolia. High
temperature (17°C) induced earlier growth and flowering than low temperature (6°C) in M. betonicifolia.
Because of difficulties in vegetative reproduction and seed storage, in vitro establishment of M. betonicifolia was investigated. The unopened capsule sterilization method was used. The seeds in the capsule germinated on Murashige and Skoog medium. Derooted seedlings, hypocotyls and seedling roots from seedlings raised on sterile artificial medium were used as explants for the in vitro establishment. This experiment shows that half strength Murashige and Skoog medium is suitable for in vitro culture of this species. The cytokinin:auxin ratio and growth regulator concentration were found to control morphogenesis of M. betonicifolia in vitro. Derooted seedlings cultured first on nutrient medium containing N⁶-benzyladenine (BA) and kinetin (Kn) differentiated more multiple meristems than those originally cultured on medium containing N⁶-(2-isopentenyl)-adenine (2ip) after being transferred into medium containing 2ip. Multiple meristems were divided and proliferated on medium containing 0.2 mg 1⁻¹ 2,4-dichlorophenoxyacetic acid (2,4-D), 5 mg 1⁻¹ 2ip and 1 mg 1⁻¹ BA. Seedling roots and hypocotyls formed callus on media containing 1, 5 and 10 mg 1⁻¹ 2,4-D.<br>Land and Food Systems, Faculty of<br>Graduate
38
Lu, Chun. "The error propagation in robots." Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5871.
Testo completoAbstract (sommario):
The accuracy of a robot manipulator has been receiving scrutinity since the widespread acceptance of robot manipulators. The relationship between two consecutive joint coordinate frames of a robot manipulator can be completely defined by five link parameters; one is the joint variable and the other four are the geometric parameters. The basis for the open-loop manipulator control is often the relationship between the Cartesian coordinates of the end-effector and the joint coordinates; therefore, the accuracy of the Cartesian position and orientation of the end-effector with regard to the real world depends on the errors of the five link parameters for each link. For design optimization and robot calibration, it is very important to develop a model for quantitative characterization and evaluation of the positioning and orientational errors of the end-effector. A static error propagation model is developed in order to describe the relationships between the six Cartesian errors and the five independent kinematic errors for each link. In this thesis, a general method for evaluating the end-effector errors produced by a mix of arbitrarily distributed errors is presented. Based on this method, any different combinations of biased and mixed error distributions can be dealt with directly to give a quantative error propagation analysis. Numerical results are presented for one, two and three degrees-of-freedom robot manipulators. Comparison of the results of the proposed model with other published model are presented and analyzed.
39
Bourbon, Claire. "Propagation de la 2-birationalité." Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14279/document.
Testo completoAbstract (sommario):
L’objet de cette thèse est l’étude de la propagation de la 2-birationalité pour les 2-extensions de corps de nombres. Le problème étudié se présente comme suit : étant donnés un corps 2-rationnel totalement réel K, une extension quadratique totalement imaginaire L de K, et une 2-extension totalement réelle de K de K, à quelles conditions la 2-birationalité du compositum L = KL se lit-elle sur L ? La thèse se structure en trois parties : l’étude du cas absolument quadratique d’abord, le cas relativement quadratique ensuite ; le cas général enfin. Le résultat principal de la thèse résout complètement le problème posé en toute généralité. En fin de thèse, diverses illustrations numériques sont proposées à l’aide du PARI, ainsi qu’une étude des tours d’extensions 2-birationnelles<br>This thesis deals with the propagation of 2-birationality for 2-extensions of numbers fields. More precisely, le t K be a 2-rational totally real number field, L a CM quadratic extension of K, and let K be a totally real 2-extension of K. Under which conditions can one read the 2-birationaltiy of the compositum L = LK from L ? This work is divided into three parts : we first study the absolute quadratic case, then the relatively quadratic case, then finally the general case. The thesis’s main result solves the whole problem. We also illustrate the result with various numeric examples, obtained with PARI and a focus at the end on 2-birational extensions’ towers
40
Sander, Tavallaey Shiva. "Wave propagation in sandwich structures /." Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3088.
Testo completo
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Mandehgar, Mahboubeh. "THz propagation in the Atmosphere." Thesis, Linnéuniversitetet, Institutionen för fysik och elektroteknik (IFE), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-25561.
Testo completo
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Meurer, Thomas. "Wave propagation in hysteretic media." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/19090.
Testo completo
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Kamalarasa, Sanmugarasa. "Buckle propagation in submarine pipelines." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328779.
Testo completo
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Joia, Ivo Alexander. "Electromagnetic propagation through controlled turbulence." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319988.
Testo completo
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Hodgkins, Andrew D. "Crack propagation in nuclear graphite." Thesis, University of Manchester, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488486.
Testo completo
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McBurnie, Sarah E. "Sound propagation through bubbly liquids." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531980.
Testo completo
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McKelvie, Marion Lindsay. "Ultrasonic propagation in cancellous bone." Thesis, University of Hull, 1988. http://hydra.hull.ac.uk/resources/hull:8397.
Testo completoAbstract (sommario):
The thesis covers two main areas of work. The first is detailed experimental work and the second is the evaluation of existing ultrasonic theories in attempt to apply them to the propagation in cancellous bone. The work is related to a new technique which uses ultrasonic attenuation to measure and predict osteoporosis, especially in the elderly population. The ultrasonic attenuation, the longitudinal ultrasonic velocity, the scattering effect and the attenuation as a function of frequency were measured on a range of cancellous bone samples, from healthy to severely osteoporotic, and also a few cortical samples. The cancellous bone was human os calces and vertebrae. The relationships between the ultrasonic propagation and the structural parameters and density of the bone were investigated, and were considered both for whole bones and separate purely cancellous samples. Image analysis of photomicrographs taken under low magnification was carried out to find the architectural parameters of the bone structure. The ultrasonic measurements were also compared with quantitative computed tomography assessment and compressive strength testing. Many theories which are currently used to evaluate ultrasonic propagation in a porous material are reviewed, and three particular ones are developed in detail and applied to models of cancellous bone. The self consistent theory (SCT), Biot's theory and the multiple scattering theory based on the work of Waterman and Truell were all assessed for their limits with repect to this particular application, and each had its own deficiencies. The Blot theory, however, proved the most successful at predicting the experimental attenuation results observed, but still only in a limited way.
48
McBride, Hugh Joseph. "Wave propagation in elastic solids." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/24107.
Testo completo
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Zhao, Xin. "Wave Propagation under Ice Covers." Thesis, Clarkson University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3667183.
Testo completoAbstract (sommario):
<p> The operational ocean wave model needs a sea ice component to simulate the global ocean waves. Current ocean wave models treat ice covered regions crudely. The purpose of this thesis is to provide a unified continuum model for the wave ice interaction. Sea ice is constantly subject to environmental forcing. As a result, its physical appearance and mechanical properties vary dynamically. There are three existing classic wave ice interaction models: viscous layer, mass loading, and thin elastic plate models. Viscous layer models may be used to simulate grease ice, mass loading model is probably suitable for pancake ice, and thin elastic plate model may be used to describe a continuous ice sheet floating in water. This situation means that for different kind of sea ice we need different wave ice interaction models. Recently, a proposed viscoelastic wave ice interaction model synthesized the three classic models into one model. Under suitable limiting conditions this model converges to the three previous models. Based on this new development, the present study expands the viscoelastic model for wave propagation through two connected ice covered ocean regions. By doing so, the complete theoretical framework for evaluating wave propagation through various ice covers may be implemented in the operational ocean wave models. In this thesis, we introduce a three-layer viscoelastic model to include the eddy viscosity in turbulent boundary layer under the ice cover into previous viscoelastic model and the methods to calculate wave reflection and transmission. We also use recent results of a laboratory study to determine the viscoelstic model parameters with an inverse method. The thesis concludes with a numerical procedure for implementing the viscoelastic dispersion relation into the ocean wave model and some ideas of model parameterization. </p>
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Ambrizzi, Tercio. "Rossby wave propagation and teleconnections." Thesis, University of Reading, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335893.
Testo completo