• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 34
  • 12
  • 6
  • 5
  • 4
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 96
  • 16
  • 12
  • 11
  • 10
  • 9
  • 9
  • 9
  • 8
  • 7
  • 6
  • 6
  • 6
  • 6
  • 6
  • 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.
71

Sur la stabilisation de systèmes dynamiques continus non linéaires exploitant les matrices de formes en flèche : application à la synchronisation de systèmes chaotiques / On the stabilization of nonlinear continuous dynamical systems using the arrow forms matrices : application to the synchronization of chaotic systems

Hammami, Sonia 21 December 2009 (has links)
Les travaux effectués, dans le cadre de cette thèse, concernent l’analyse et la synthèse de systèmes dynamiques continus complexes de grande dimension. Pour la classe des systèmes étudiés, est mise en exergue en particulier l’importance du choix de la description des systèmes sur l’étendue des résultats pouvant être obtenus lorsque la méthode d’étude de la stabilité est fixée.L’utilisation des normes vectorielles comme fonction d’agrégation et du critère pratique de Borne et Gentina pour l’étude de la stabilité, associée à la description des systèmes par des matrices caractéristiques de forme en flèche, a permis l’élaboration de nouvelles conditions suffisantes de stabilisabilité de systèmes dynamiques continus non linéaires, monovariables et multivariables, formulées en théorèmes et corollaires.Ces résultats obtenus, pour une classe de processus, pouvant être caractérisés par des matrices instantanées de forme en flèche mince, ont été généralisés au cas des matrices quelconques, pouvant être mises sous forme en flèche mince généralisée ou en flèche épaisse.Les critères élaborés, soit pour l’analyse de la stabilité soit pour la synthèse d’une loi de commande stabilisante, sont ensuite exploités, avec succès, pour la formulation de nouvelles conditions suffisantes de vérification des propriétés de synchronisation, d’anti-synchronisation et de synchronisation hybride de systèmes chaotiques du type maître-esclave, d’un grand intérêt, en particulier, pour garantir une transmission sécurisée / This Thesis deals with the analysis and the synthesis of dynamic large scale continuous systems depending on the choice of the system description.Stability and stabilisability proposed studies are based on the use of vector norms as an aggregation function and of the practical Borne-Gentina criterion, associated to the description of the system by instantaneous characteristic matrix in arrow form.Practical stability conditions, easy to use, are obtained for both dynamic nonlinear continuous single input single output systems and multiple inputs multiple outputs ones, formulated by means of theorems and corollaries. These obtained results for thin arrow form, are generalized to the case of matrices, which can be putted under thin generalized arrow form or thick arrow form. The proposed stability and stabilisability criteria are afterwards, successfully, exploited to formulate new sufficient conditions, guaranteeing the synchronization, the anti-synchronization and the hybrid synchronization properties, for chaotic master-slave systems, having an increasing interest throughout their application in the secure communication field
72

Driver Understanding of the Flashing Yellow Arrow and Dynamic No Turn on Red Sign for Right Turn Applications

Casola, Elizabeth 09 July 2018 (has links)
Since their introduction to the 2009 Edition of the Manual on Uniform Traffic Control Devices, flashing yellow arrows (FYA) have had significant success in communicating the permissive turn message. While widely used for the permissive left turn maneuver, agencies recently have been utilizing flashing yellow arrows for the use with right turn applications as drivers interact with crossing pedestrians. As pedestrian conflicts are a concern during the permissive green phase, there is additional worry for the potential interaction between a pedestrian and vehicle turning right on red. This research explores the existing driver comprehension of permissive right turns during both green and red phases through static evaluation and microsimulation. Proposed traffic devices including the FYA and the Dynamic No Turn on Red sign were evaluated in relation to the existing signal and sign conditions implemented in the field. In comparing the proposed FYA to the existing circular green signal, the survey evaluation determined a statistically significant increase in drivers’ yielding responses when interacting with the FYA as opposed to the circular green. Through application of the VISSIM program, it was determined that right turning speeds with the FYA present were significantly lower than when interacting with solely the circular green. Both the static evaluation and microsimulation determined a strong similarity between the existing circular red and R10-11 sign and the proposed dynamic no turn on red sign which verifies the strong understanding drivers have of the message and the sign itself.
73

Building High-performing Web Rendering of Large Data Sets

Burwall, William January 2023 (has links)
Interactive visualization is an essential tool for data analysis. Cloud-based data analysis software must handle growing data sets without relying on powerful end-user hardware. This thesis explores and tests various methods to speed up primarily time series plots of large data sets on the web for the biotechnology research company Sartorius. To increase rendering speed, I focused on two main approaches: downsampling and hardware acceleration. To find which sampling algorithms suit Sartorius's needs, I implemented multiple alternatives and compared them quantitatively and qualitatively. The results show that downsampling increases or eliminates data set size limits and that test users favored algorithms maintaining local outliers. With hardware acceleration that substantially increased the amount of simultaneously rendered points for more detailed representations, these methods pave the way for efficient visualization of large data sets on the web.
74

Microbiological and molecular biological analysis of oil contaminated marine sediments : 30 years after the spill

AlRoumi, Dina K. January 2003 (has links)
No description available.
75

Perforated Hollow Core Waveguides for Alkali Vapor-cells and Slow Light Devices

Giraud Carrier, Matthieu C 01 February 2016 (has links) (PDF)
The focus of this work is the integration of alkali vapor atomic vapor cells into common silicon wafer microfabrication processes. Such integrated platforms enable the study of quantum coherence effects such as electromagnetically induced transparency, which can in turn be used to demonstrate slow light. Slow and stopped light devices have applications in the optical communications and quantum computing fields. This project uses hollow core anti-resonant reflecting optical waveguides (ARROWs) to build such slow light devices. An explanation of light-matter interactions and the physics of slow light is first provided, as well as a detailed overview of the fabrication process. Following the discovery of a vapor transport issue, a custom capillary-based testing platform is developed to quantify the effect of confinement, temperature, and wall coatings on rubidium transport. A mathematical model is derived from the experimental results and predicts long transport times. A new design methodology is presented that addresses the transport problem by increasing the number of rubidium entry points. This design also improves chip durability and decreases environmental susceptibility through the use of a single copper reservoir and buried channel waveguides (BCWs). New chips are successfully fabricated, loaded, and monitored for rubidium spectra. Absorption is observed in several chips and absorption peaks depths in excess of 10% are reported. The chip lifetime remains comparable to previous designs. This new design can be expanded to a multi-core platform suitable for slow and stopped light experimentation.
76

Tailoring the Spectral Transmission of Optofluidic Waveguides

Phillips, Brian S. 09 August 2011 (has links) (PDF)
Optofluidics is a relatively new and exciting field that includes the integration of optical waveguides into microfluidic platforms. The purpose of this field of study is to miniaturize previously developed optical systems used for biological and chemical analysis with the end goal of placing bench-top optics into microscopic packages. Mundane optical alignment and sample manipulation procedures would then be intrinsic to the platform and allow measurements to be completed quickly and with reduced human interaction. Biosensors based on AntiResonant Reflecting Optical Waveguides (ARROWs) consist of hollow-core waveguides used for fluid sample manipulation and analysis, as well as solid-core waveguides used in interfacing external components located at the chip edges. Hollow-core ARROWs are particularly useful for their ability to provide specifically tailored analyte volumes that are easily configurable depending upon the target experiment. Adaptations of standard planar microfabrication methods allow for complex integrated ARROW designs. Integrated spectral filtering with high rejection can be implemented on-chip, removing the need for additional off-chip components and increasing device sensitivity. Additional techniques to increase device sensitivity and utility, such as hybrid ARROW platforms and optical manipulation of samples, are also explored.
77

ARROW-Based On-Chip Alkali Vapor-Cell Development

Hulbert, John Frederick 22 May 2013 (has links) (PDF)
The author presents the successful development of an on-chip, monolithic, integrated rubidium vapor-cell. These vapor-cells integrate ridge waveguide techniques with hollow-core waveguiding technology known as Anti-Resonant Reflecting Optical Waveguides (ARROWs). These devices are manufactured on-site in BYU's Integrated Microelectronic Laboratory (IML) using common silicon wafer microfabrication techniques. The ARROW platform fabrication is outlined, but the bulk of the dissertation focuses on novel packaging techniques that allow for the successful introduction and sealing of rubidium vapor into these micro-sized vapor-cells. The unique geometries and materials utilized in the ARROW platform render common vapor-cell sealing techniques unusable. The development of three generations of successful vapor-cells is chronicled. The sealing techniques represented in these three generations of vapor-cells include high-temperature epoxy seals, cold-weld copper crimping, variable pressure vacuum capabilities, indium solder seals, and electroplated passivation coatings. The performance of these seals are quantified using accelerated lifetime tests combined with optical spectroscopy. Finally, the successful probing of the rubidium absorption spectrum, electromagnetically induced transparency, and slow light on the ARROW-based vapor-cell platform is reported.
78

Science, technologie, et théories économiques de la croissance des années 50 à aujourd’hui / Science, Technology and Economic Growth Theories in the Post-War Era

Ballandonne, Matthieu 21 November 2014 (has links)
Cette thèse a pour objectif d’étudier la façon dont les économistes ont théorisé la relation entre science, technologie et croissance économique des années cinquante à aujourd’hui. Nous identifions deux approches des liens entre science, technologie et croissance : une approche « néoclassique » et une approche « évolutionniste ». L’approche « néoclassique » considère les progrès scientifiques et technologiques comme exogènes aux processus économiques et analyse les processus de croissance comme étant soumis à des rendements constants. L’approche « évolutionniste » défend quant à elle une représentation interactionniste des liens entre science et technologie, considère les progrès technologiques et scientifiques comme étant endogènes aux processus économiques et analyse les processus de croissance comme étant soumis à des rendements croissants. Nous analysons l’émergence de ces deux approches dans les années cinquante et soixante et expliquons leur opposition avec une domination de l’approche « néoclassique » jusque dans les années quatre-vingt (Partie 1). Nous montrons ensuite que l’approche « évolutionniste » devient dominante à partir des années quatre-vingt (Partie 2). / The aim of this thesis is to examine the way economists theorized the links between science, technology, and economic growth in the post-war era. We identify two approaches of the links between science, technology, and economic growth : a “neoclassical” approach and an “evolutionary” approach. The “neoclassical” approach considers scientific and technological progress as exogenous to economic processes and makes the hypothesis of constant returns to scale. The “evolutionary” approach defends an interactive representation of the links between science and technology, considers scientific and technological progress as endogenous to economic processes, and makes the hypothesis of increasing returns to scale. We study the development of the two approaches in the fifties and sixties, and explain their opposition and the dominance of the “neoclassical” approach up to the eighties (Part 1). We then show that the “evolutionary” approach has been the most influential since the eighties (Part 2).
79

Topics in finite graph Ramsey theory

Borgersen, Robert David 18 January 2008 (has links)
For a positive integer $r$ and graphs $F$, $G$, and $H$, the graph Ramsey arrow notation $F \longrightarrow (G)^H_r$ means that for every $r$-colouring of the subgraphs of $F$ isomorphic to $H$, there exists a subgraph $G'$ of $F$ isomorphic to $G$ such that all the subgraphs of $G'$ isomorphic to $H$ are coloured the same. Graph Ramsey theory is the study of the graph Ramsey arrow and related arrow notations for other kinds of ``graphs" (\emph{e.g.}, ordered graphs, or hypergraphs). This thesis surveys finite graph Ramsey theory, that is, when all structures are finite. One aspect surveyed here is determining for which $G$, $H$, and $r$, there exists an $F$ such that $F \longrightarrow (G)^H_r$. The existence of such an $F$ is guaranteed when $H$ is complete, whether ``subgraph" means weak or induced, and existence results are also surveyed when $H$ is non-complete. When such an $F$ exists, other aspects are surveyed, such as determining the order of the smallest such $F$, finding such an $F$ in some restricted family of graphs, and describing the set of minimal such $F$'s. / February 2008
80

An Empirical Comparison Of Interest Rate Models For Pricing Zero Coupon Bond Options

Senturk, Huseyin 01 August 2008 (has links) (PDF)
The aim of this study is to compare the performance of the four interest rate models (Vasicek Model, Cox Ingersoll Ross Model, Ho Lee Model and Black Der- man Toy Model) that are commonly used in pricing zero coupon bond options. In this study, 1{5 years US Treasury Bond daily data between the dates June 1, 1976 and December 31, 2007 are used. By using the four interest rate models, estimated option prices are compared with the real observed prices for the begin- ing work days of each months of the years 2004 and 2005. The models are then evaluated according to the sum of squared errors. Option prices are found by constructing interest rate trees for the binomial models based on Ho Lee Model and Black Derman Toy Model and by estimating the parameters for the Vasicek and the Cox Ingersoll Ross Models.

Page generated in 0.0345 seconds