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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Stochastic Spatio-Temporal Uncertainty in GIS-Based Water Quality Modeling of the Land Water Interface

Salah, Ahmad Mohamad 27 February 2009 (has links)
Integrated water resources management has been used for decades in various formats. The limited resources and the ever growing population keep imposing pressure on decision makers to better-, and reliably, manage the available waters. On the other hand, the continuous development in computing and modeling power has helped modelers and decision makers considerably. To use these models, assumptions have to be made to fill in the gaps of missing data and to approximate the current conditions. The type and amount of information available can also be used to help select the best model from the currently available models. Advances in data collection have not kept up to the pace of advances in model development and the need for more and reliable input parameter values. Hence, uncertainty in model input parameters also needs to be quantified and addressed. This research effort develops a spatially-based modeling framework to model watersheds from both water quantity and quality standpoints. In this research, Gridded Surface Sub-Surface Hydrologic Analysis (GSSHA) and CE-QUAL-W2 models are linked within the Watershed Modeling System (WMS); a GIS interface for hydrologic and hydraulic models, to better handle both models pre and post processing. In addition, stochastic analysis routines are developed and used to examine and address the uncertainty inherent in the modeling process of the interface between land and water in the designated watershed. The linkage routines are developed in WMS using C++. The two models are linked spatially and temporally with the general direction of data flow from GSSHA to CE-QUAL-W2. Pre-processing of the CE-QUAL-W2 model is performed first. Then stochastic parameters and their associated distributions are defined for stochastic analysis in GSSHA before a batch run is performed. GSSHA output is then aggregated by CE-QUAL-W2 segments to generate multiple CE-QUAL-W2 runs. WMS then reads the stochastic CE-QUAL-W2 runs upon successful completion for data analysis. Modelers need to generate a WMS Gage for each location where they want to examine the stochastic output. A Gage is defined by a segment and a layer in the CE-QUAl-W2 model. Once defined, modelers are able to view a computed credible interval with lower, upper bounds in addition to the mean time series of a pre-selected constituent. Decision makers can utilize this output to better manage watersheds by understanding and incorporating the spatio-temporal uncertainty for the land-water interface.
22

Approche physico-statistique de la désagrégation des précipitations satellite dans les Tropiques / A physical-statistical approach for disaggregating satellite precipitation in the tropics

Guilloteau, Clément 07 November 2016 (has links)
Les précipitations sont un phénomène dont la variabilité s'étend sur une très large gamme d'échelles : de l'échelle millimétrique de la goutte d'eau (échelle microphysique) à l'échelle des circulations atmosphériques globales (échelle synoptique). Il n'existe pas de système unique capable de fournir des observations des précipitations couvrant toutes ces échelles. Les observations satellite sont celles qui actuellement résolvent le plus efficacement les grandes échelles spatiales et temporelles : de la méso-échelle à l'échelle synoptique. Dans cette thèse, nous explorons en zone tropicale les capacités des satellites à résoudre les échelles spatiales de l'ordre de 100km, jusqu'aux échelles kilométriques ; et les échelles temporelles comprises entre 24 heures et 15 minutes (afin de résoudre le cycle diurne). L'approche retenue est physico-statistique. Si les grandes échelles peuvent être résolues par des approches déterministes combinant les mesures de multiples instruments spatiaux, plusieurs facteurs limitent la pertinence des approches déterministes à fine échelle : - Les limites instrumentales en terme de résolution spatiale. - Le nombre d'instruments en orbite qui limite la fréquence d'échantillonnage des mesures. - La nature dynamique de la variabilité fine échelle. En particulier, aux fines échelles, c'est la difficulté à parfaitement localiser les structures précipitantes qui entraine les erreurs d'estimation les plus importantes. L'approche physico-statistique est ici synonyme de déterministe (pour les grandes échelles) et probabiliste (pour les fines échelles). Le premier objectif de cette thèse est de déterminer précisément la limite des échelles qui peuvent être résolues de façon déterministe. L'approche physico-statistique de l'estimation des intensités de précipitation est implémentée dans cette thèse à partir d'une méthode multicapteur déterministe pré-existante : l'algorithme TAPEER, développé dans le cadre de la mission Megha-Tropiques, qui fournit une estimation du cumul pluviométrique journalier à une résolution de 1°. C'est la génération d'ensembles désagrégés par une méthode stochastique multi-échelle qui a été retenue ici. Les ensembles sont contraints par une information fine échelle : un masque de détection des aires précipitantes dérivé des images infrarouge metosat-SG à une résolution de 3km (et avec une image toutes les 15 minutes). La génération d'ensemble permet de caractériser l'incertitude sur l'estimation à travers la dispersion des réalisations de l'ensemble. Chaque réalisation de l'ensemble est générée de façon à reproduire le plus fidèlement possible les propriétés statistiques (distribution de fréquence des intensités, autocorrélation spatiale et temporelle) des véritables champs de précipitation. Ces champs et cette technique ont un apport pour les applications hydrologiques, par exemple pour améliorer le ruissellement lié aux précipitations intenses dans les modèles. Considérer plusieurs réalisations permet de plus d'étudier la propagation des incertitudes à travers un modèle. / Rainfall variability involves a wide range of scales: from the millimeter-scale associated with microphysics to the synoptic scale of the global atmospheric circulation. No existing observation system is able to cover all these scales by itself. Satellite-based observation systems are currently the most efficient systems to resolve the large spatial and temporal scales: from mesoscale meteorology to the synoptic scale. This thesis is dedicated to the exploration of satellites ability to resolve spatial scales from 100km to 2km and temporal scales from 24h to 15 min (in order to resolve the diurnal cycle). The chosen approach is both physical and statistical (or deterministic and probabilistic). The idea is that the deterministic approach can resolve the large scales, but several factors limit its relevance when dealing with fine scales: -The limited resolution of the instruments. -The number of orbiting instruments that limits temporal sampling. -The dynamic nature of fine scale variability. At fines scales, most of the errors in rainfall estimation from satellite comes from not perfectly localizing the precipitating cells. The first objective of this thesis is to identify precisely the lowest limit in scale where the deterministic approach is appropriate. The implementation of the physical-statistical approach relies on an existing multisensor estimate of daily precipitation at a 1° resolution: the TAPEER algorithm developed as part of the Megha-Tropiques mission. The chosen method is a hybrid physical disaggregation and stochastic downscaling via a multiscale representation. The result is an ensemble of high-resolution probable realizations of the rain intensity field. The ensemble is constrained by a high resolution rain detection mask derived from meteosat-SG infrared images at 3km resolution (one image every 15 minutes). The uncertainty associated with the final estimation is handled through the ensemble dispersion. Every realization is generated so that its statistical properties (frequency distribution of the intensities, autocorrelation function) mimic those of the true rain field. The generated fields and the proposed technique contribute to hydrological applications for instance by improving the runoff associated to high precipitation rates in models. Using several realizations is a way to study uncertainty propagation through a model.
23

A Discussion of different teaching strategies adopted during a Statistics tutorial

Pavlika, Vasos 31 May 2012 (has links) (PDF)
In this discusses four different approaches used during a statistics tutorial of a group of first year undergraduates studying computer science related degrees at the University of Westminster UK. The four approaches were each implemented in an attempt to keep the students interested in the statistics topics delivered. It was found that “Chalk and Talk” (i.e. board work) was not the best form of imparting knowledge to the students of the group as determined by student analysing feedback forms and generally observing student behaviour and listening to student comments over a number of years delivering statistics topics. The duration of each tutorial was two hours. The teaching strategies adopted were: a) A class quiz. b) Group explanation of material to members of the individual’s group. c) Group explanation of material to members of the entire class. d) Students teaching at the front of the class. Each of the methods will now be discussed with the relative merits and defects included for a comparison. It was found that each method worked better at the end of each module when the students were more familiar with the topics introduced on the module.
24

A Discussion of different teaching strategies adopted during a Statistics tutorial

Pavlika, Vasos 31 May 2012 (has links)
In this discusses four different approaches used during a statistics tutorial of a group of first year undergraduates studying computer science related degrees at the University of Westminster UK. The four approaches were each implemented in an attempt to keep the students interested in the statistics topics delivered. It was found that “Chalk and Talk” (i.e. board work) was not the best form of imparting knowledge to the students of the group as determined by student analysing feedback forms and generally observing student behaviour and listening to student comments over a number of years delivering statistics topics. The duration of each tutorial was two hours. The teaching strategies adopted were: a) A class quiz. b) Group explanation of material to members of the individual’s group. c) Group explanation of material to members of the entire class. d) Students teaching at the front of the class. Each of the methods will now be discussed with the relative merits and defects included for a comparison. It was found that each method worked better at the end of each module when the students were more familiar with the topics introduced on the module.
25

Hydrodynamic synchronization in cilia carpets and its robustness to noise and perturbations

Solovev, Anton 28 January 2022 (has links)
Motile cilia are hair-like cell appendages that actively bend themselves, thus driving the surrounding fluid in motion. For many microorganisms, such as unicellular Paramecium, cilia are essential for their motility. Higher animals, including mammals, utilize cilia for transporting fluids. For example, in humans, large collections of cilia, called cilia carpets, remove mucus and pathogens from the airways. Cilia constitute an example of biological oscillators that can spontaneously synchronize their beat in the form of metachronal waves, i.e., traveling waves of cilia phase. These waves may arise purely by hydrodynamic interactions between the cilia and supposedly enhance fluid transport. Our goal is to theoretically understand how the properties of individual cilia, e.g., cilia beat pattern, determine the emergent behavior, e.g., the direction of the metachronal wave. Additionally, we address the robustness of hydrodynamically-induced synchronization with respect to intrinsic active fluctuations of the cilia beat and disorder of intrinsic cilia frequencies. Both of these effects are not yet well understood. In this thesis, we studied metachronal synchronization in cilia carpets using a theoretical physicist’s toolbox. First, we proposed a novel multi-scale modeling framework Lagrangian Mechanics of Active Systems (LAMAS) to describe fluid-structure interactions for active elastic structures, such as cilia. We quantified hydrodynamic interactions between cilia using detailed hydrodynamic simulations with a realistic cilia beat pattern. In the dynamical simulations for N = 2 cilia, we found that cilia would synchronize either in-phase or anti-phase, depending on their relative positions. For a lattice of N ≫ 1 cilia, we found the emergence of metachronal waves, many of which are locally stable. Nevertheless, just a single wave has a predominantly large basin of attraction, i.e., it is likely to be selected from a random initial condition. In the presence of noise, synchronization abruptly breaks up beyond a characteristic noise strength. Likewise, for cilia with non-identical intrinsic frequencies, synchronization is lost beyond a characteristic level of frequency disorder. In large cilia carpets, noise excites long-wavelength perturbations, whose relaxation times are proportional to the square of the system length. Thus, in large systems, we predict locally synchronized domains, instead of the global synchronization.
26

Risikomaße

Huschens, Stefan 30 March 2017 (has links) (PDF)
Das vorliegende Skript ist aus einer Lehrveranstaltung hervorgegangen, die von mir mehrere Jahre an der Fakultät Wirtschaftswissenschaften der TU Dresden gehalten wurde. Diese Lehrveranstaltung hatte erst die Bezeichnung "Monetäre Risikomaße" und später "Risikomaße". Mehrere frühere Fassungen dieses Skripts, das häufig überarbeitet und erweitert wurde, trugen den Namen Monetäre Risikomaße (Auflagen 1 bis 7). Die einzelnen Kapitel enthalten in der Regel die drei abschließenden Abschnitte "Übungsaufgaben", "Beweise" und "Ergänzung und Vertiefung" mit Material zum jeweiligen Kapitel, das nicht in der Vorlesung vorgetragen wurde.
27

Stokastisk modellering & hantering av maskinhaveri : En fallstudie på Gunnebo Industries / Stochastic modelling of machine failure & maintenance management : A case study conducted at Gunnebo Industries

Jönsson, Alexander, Åberg, Andreas January 2020 (has links)
Studien är utförd för att identifiera faktorer som påverkar materialflödet negativt i en tillverkningsindustri. På fallföretaget Gunnebo Industries observerades ett specifikt problemområde med fluktuationer som grundar sig i smidesmaskiners driftsäkerhet. Dessa skapar påföljder som försvårar materialhanteringen. Rapporten illustrerar sedan hur stokastisk modellering av maskinfel kan användas som ett indikationsverktyg. Resultatet påvisar en weibullfördelning för samtliga smidesmaskiner. Modellen kan användas för att finna potentiella förbättringsområden eller till och med för att utveckla implementerbara förbättringar. Den reflekterar över nuvarandetillstånd, likt värdeflödesanalys, men med fokus på maskiners pålitlighet. Dessutom diskuteras diverse faktorer som influerar modellen samt hur den i sin tur kan användas vid vidare forskning och analys. / The thesis is conducted on the basis of identifying negatively influencing factors on the flow of material within a manufacturing environment. At Gunnebo Industries the case study revealed a specific problem with fluctuations caused by machine reliability. The report illustrates how stochastic modelling of machine failure can be utilized as a tool of indication. The model can be used to uncover potential refinements regarding production and maintenance. It reflects on current state, complemented by what is attainable. Similarly to value stream mapping, but by emphasizing machine reliability. Furthermore, a discussion is formed regarding various interesting factors influencing the model, and how it in turn can be used in further research and analysis.
28

Étude de la macro-dispersion de particules inertes dans des milieux poreux 3D fortement hétérogènes / Study of the macro-dispersion of inert particles in highly heterogeneous 3D porous media

Dartois, Arthur 14 December 2016 (has links)
Les milieux poreux font partie des formations géologiques assez répandue dans la nature et son sujet d'études intensives. L'engouement de ce sujet vient des multiples secteurs d'applications de ces recherches et leur importance dans notre société. Que ce soit de la part des sociétés pétrolières qui souhaitent optimiser leurs moyens de productions, les agences de contrôles environnementaux qui veulent prévenir la contamination de nappe phréatique et la fuite de déchets nucléaires ou encore des industriels avec des problèmes de drainages et de réhabilitation de mines, tous ces acteurs dépendent des recherches faites dans ce domaine. Cependant, un des principaux problèmes de ce sujet est l'inaccessibilité des milieux que nous voulons étudier. Pour palier à cela de nombreuses équipes se sont tournées vers la simulation numérique. Cette thèse s'inscrit dans ce cadre et utilise le module PARADIS du logiciel d'hydrogéologie H2olab pour modéliser le transport de particules dans des milieux poreux fortement hétérogènes. Grâce aux données obtenues et à des comparaisons avec la littérature nous montrerons l'effet du passage au 3D sur la topologie de l'écoulement et les répercussions sur le transport de particules ainsi que l'effet de la diffusion moléculaire sur les coefficients de macro-dispersion. Enfin nous proposerons deux lois de transport reliant macrodispersion, variance du champ de perméabilité et diffusion moléculaire. / Heterogeneous porous media have been intensively studied these last fifty years. The popularity of this subject come from the multiple areas where these researches can be applied and their importance to our society. Whether from the oil companies that want to optimize their methods of production, environmental control agencies who want to prevent contamination of ground water and leakage of nuclear waste or industrial with drainage issues and mine rehabilitation, all these actors depend on research done in this area. However, one of the main problems of this subject is the accessibility of these porous media which are often several hundred meters underground. To overcome this, many teams have turned to computer simulation. This thesis is among them and uses the PARADIS module from the hydrogeology software H2olab to model particle transport in highly heterogeneous porous media. Thanks to the data obtained and comparisons with the literature, we show the impact of switching from a 2D to a 3D porous media on the ow topology and the repercussions on the particle transport. Furthermore, we also investigated the effect of molecular diffusion coefficients on macro-dispersion. Finally, we will propose two empirical functions linking macro-dispersion variance of the permeability field and molecular diffusion.
29

Netradiční výrazové prostředky a techniky. Matematické principy v komparaci netradičního výtvarného a hudebního díla / Unconventional Means of expression and techniques. Mathematical principles in comparing unconventional visual and musical art

Effenbergerová, Klára January 2011 (has links)
Univerzita Karlova v Praze / Pedagogická fakulta / Katedra výtvarné výchovy // Charles University in Prague / Faculty of Education / The Department of Fine Art Education Netradiční výrazové prostředky a techniky Matematické principy v komparaci netradičního výtvarného a hudebního díla UnconventionalMeansofexpressionandtechniques Mathematical principles in comparing unconventional visual and musical art Klára Effenbergerová Výtvarná výchova - pedagogika Prezenční studium, 5. ročník Datum dokončení: květen 2011 Vedoucí práce: Doc. PhDr. Jaroslav Bláha, Ph.D. Abstract The thesis deals with a comparative analysis of a project called Poéme électronique in the Philips Pavilion (1958), while an emphasis is put on its mathematical background and broader interdisciplinal contexts. Particular attention is devoted to grand oldman Iannis Xenakis. The thesis tries to interpret the phenomenon of Electronic poetry, which we understand as an effort to design a multimedia "Gesamtkunstwerk". This brings the necessitate of the multi-specialized synthetic approach in searching of a relationship between the kinds of arts, and the analysis of interactions of individual project components.
30

Risikomaße

Huschens, Stefan 30 March 2017 (has links)
Das vorliegende Skript ist aus einer Lehrveranstaltung hervorgegangen, die von mir mehrere Jahre an der Fakultät Wirtschaftswissenschaften der TU Dresden gehalten wurde. Diese Lehrveranstaltung hatte erst die Bezeichnung "Monetäre Risikomaße" und später "Risikomaße". Mehrere frühere Fassungen dieses Skripts, das häufig überarbeitet und erweitert wurde, trugen den Namen Monetäre Risikomaße (Auflagen 1 bis 7). Die einzelnen Kapitel enthalten in der Regel die drei abschließenden Abschnitte "Übungsaufgaben", "Beweise" und "Ergänzung und Vertiefung" mit Material zum jeweiligen Kapitel, das nicht in der Vorlesung vorgetragen wurde.

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