• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 138
  • 29
  • 11
  • 10
  • 4
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 238
  • 238
  • 42
  • 35
  • 29
  • 26
  • 25
  • 21
  • 21
  • 21
  • 19
  • 19
  • 19
  • 17
  • 17
  • 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.
141

Vlasov dynamics of 1D models with long-range interactions / Dynamique de Vlasov de modèles 1D en interaction de longue portée

de Buyl, Pierre 05 January 2010 (has links)
Les interactions gravitationnelles et électrostatiques sont deux exemples fondamentaux de systèmes en interaction de longue portée. Les propriétés d'équilibre de modèles simples en interaction de longue portée sont bien comprises et révèlent des comportemens exotiques: capacité spécifique négative et inéquivalence des ensembles statistiques par exemple. La compréhension de l'évolution dynamique dans le cas de systèmes en interaction de longue portée représente encore actuellement un défi théorique. Des modèles simples présentent des propriétés telles que des transitions de phase hors d'équilibre ou des états quasi-stationnaires. Le but de la présente thèse est d'étudier les propriétés dynamiques de systèmes en interaction de longue portée pour des modèles à une dimension. La description cinétique adéquate est donnée par l'équation de Vlasov. Une théorie statistique proposée par D. Lynden-Bell est appropriée pour prédire dans certaines situations l'aboutissement de la dynamique. Un outil de simulation pour l'équation de Vlasov complète cette approche. Une étude détaillée de la transition de phase dans le Laser à Electrons Libres est présentée et la transition est analysée à l'aide de la théorie de Lynden-Bell. Ensuite, la présence d'étirement et de repliement est étudiée dans le modèle Hamiltonian Mean-Field en analogie avec la dynamique des fluides. Enfin, un système de pendules découplés dont les états asymptotiques sont similaires à ceux du modèle Hamiltonian Mean-Field est introduit. Son évolution asymptotique est prédite par la théorie de Lynden-Bell et par une approche exacte. Ce système présente une évolution initiale rapide similaire à la relaxation violente présente dans des modèles plus compliqués. De plus, une transition de phase hors d'équilibre est trouvée si une condition d'auto-consistence est imposée. En résumé, la présente thèse comporte des résultats originaux liés à la présence d'états quasi-stationnaires et de transitions de phase hors d'équilibre dans des modèles unidimensionnels en interaction de longue portée. Les résultats concernant le Laser à Electrons Libres offrent une perspective de réalisation expérimentale des phénomènes décrits dans cette thèse. / Gravitational and electrostatic interactions are fundamental examples of systems with long-range interactions. Equilibrium properties of simple models with long-range interactions are well understood and exhibit exotic behaviors: negative specific heat and inequivalence of statistical ensembles for instance. The understanding of the dynamical evolution in the case of long-range interacting systems still represents a theoretical challenge. Phenomena such as out-of-equilibrium phase transitions or quasi-stationary states have been found even in simple models. The purpose of the present thesis is to investigate the dynamical properties of systems with long-range interactions, specializing on one-dimensional models. The appropriate kinetic description for these systems is the Vlasov equation. A statistical theory devised by D. Lynden-Bell is adequate to predict in some situations the outcome of the dynamics. A complementary numerical simulation tool for the Vlasov equation is developed. A detailed study of the out-of-equilibrium phase transition occuring in the Free-Electron Laser is performed and the transition is analyzed with the help of Lynden-Bell's theory. Then, the presence of stretching and folding in phase space for the Hamiltonian Mean-Field model is studied and quantified from the point of view of fluid dynamics. Finally, a system of uncoupled pendula for which the asymptotic states are similar to the ones of the Hamiltonian Mean-Field model is introduced. Its asymptotic evolution is predicted via both Lynden-Bell's theory and an exact computation. This system displays a fast initial evolution similar to the violent relaxation found for interacting systems. Moreover, an out-of-equilibrium phase transition is found if one imposes a self-consistent condition on the system. In summary, the present thesis discusses original results related to the occurence of quasi-stationary states and out-of-equilibrium phase transitions in 1D models with long-range interaction. The findings regarding the Free-Electron Laser are of importance in the perspective of experimental realizations of the aforementioned phenomena.
142

Detection of long-range dependence : applications in climatology and hydrology

Rust, Henning January 2007 (has links)
It is desirable to reduce the potential threats that result from the variability of nature, such as droughts or heat waves that lead to food shortage, or the other extreme, floods that lead to severe damage. To prevent such catastrophic events, it is necessary to understand, and to be capable of characterising, nature's variability. Typically one aims to describe the underlying dynamics of geophysical records with differential equations. There are, however, situations where this does not support the objectives, or is not feasible, e.g., when little is known about the system, or it is too complex for the model parameters to be identified. In such situations it is beneficial to regard certain influences as random, and describe them with stochastic processes. In this thesis I focus on such a description with linear stochastic processes of the FARIMA type and concentrate on the detection of long-range dependence. Long-range dependent processes show an algebraic (i.e. slow) decay of the autocorrelation function. Detection of the latter is important with respect to, e.g. trend tests and uncertainty analysis. Aiming to provide a reliable and powerful strategy for the detection of long-range dependence, I suggest a way of addressing the problem which is somewhat different from standard approaches. Commonly used methods are based either on investigating the asymptotic behaviour (e.g., log-periodogram regression), or on finding a suitable potentially long-range dependent model (e.g., FARIMA[p,d,q]) and test the fractional difference parameter d for compatibility with zero. Here, I suggest to rephrase the problem as a model selection task, i.e.comparing the most suitable long-range dependent and the most suitable short-range dependent model. Approaching the task this way requires a) a suitable class of long-range and short-range dependent models along with suitable means for parameter estimation and b) a reliable model selection strategy, capable of discriminating also non-nested models. With the flexible FARIMA model class together with the Whittle estimator the first requirement is fulfilled. Standard model selection strategies, e.g., the likelihood-ratio test, is for a comparison of non-nested models frequently not powerful enough. Thus, I suggest to extend this strategy with a simulation based model selection approach suitable for such a direct comparison. The approach follows the procedure of a statistical test, with the likelihood-ratio as the test statistic. Its distribution is obtained via simulations using the two models under consideration. For two simple models and different parameter values, I investigate the reliability of p-value and power estimates obtained from the simulated distributions. The result turned out to be dependent on the model parameters. However, in many cases the estimates allow an adequate model selection to be established. An important feature of this approach is that it immediately reveals the ability or inability to discriminate between the two models under consideration. Two applications, a trend detection problem in temperature records and an uncertainty analysis for flood return level estimation, accentuate the importance of having reliable methods at hand for the detection of long-range dependence. In the case of trend detection, falsely concluding long-range dependence implies an underestimation of a trend and possibly leads to a delay of measures needed to take in order to counteract the trend. Ignoring long-range dependence, although present, leads to an underestimation of confidence intervals and thus to an unjustified belief in safety, as it is the case for the return level uncertainty analysis. A reliable detection of long-range dependence is thus highly relevant in practical applications. Examples related to extreme value analysis are not limited to hydrological applications. The increased uncertainty of return level estimates is a potentially problem for all records from autocorrelated processes, an interesting examples in this respect is the assessment of the maximum strength of wind gusts, which is important for designing wind turbines. The detection of long-range dependence is also a relevant problem in the exploration of financial market volatility. With rephrasing the detection problem as a model selection task and suggesting refined methods for model comparison, this thesis contributes to the discussion on and development of methods for the detection of long-range dependence. / Die potentiellen Gefahren und Auswirkungen der natürlicher Klimavariabilitäten zu reduzieren ist ein wünschenswertes Ziel. Solche Gefahren sind etwa Dürren und Hitzewellen, die zu Wasserknappheit führen oder, das andere Extrem, Überflutungen, die einen erheblichen Schaden an der Infrastruktur nach sich ziehen können. Um solche katastrophalen Ereignisse zu vermeiden, ist es notwendig die Dynamik der Natur zu verstehen und beschreiben zu können. Typischerweise wird versucht die Dynamik geophysikalischer Datenreihen mit Differentialgleichungssystemen zu beschreiben. Es gibt allerdings Situationen in denen dieses Vorgehen nicht zielführend oder technisch nicht möglich ist. Dieses sind Situationen in denen wenig Wissen über das System vorliegt oder es zu komplex ist um die Modellparameter zu identifizieren. Hier ist es sinnvoll einige Einflüsse als zufällig zu betrachten und mit Hilfe stochastischer Prozesse zu modellieren. In dieser Arbeit wird eine solche Beschreibung mit linearen stochastischen Prozessen der FARIMA-Klasse angestrebt. Besonderer Fokus liegt auf der Detektion von langreichweitigen Korrelationen. Langreichweitig korrelierte Prozesse sind solche mit einer algebraisch, d.h. langsam, abfallenden Autokorrelationsfunktion. Eine verläßliche Erkennung dieser Prozesse ist relevant für Trenddetektion und Unsicherheitsanalysen. Um eine verläßliche Strategie für die Detektion langreichweitig korrelierter Prozesse zur Verfügung zu stellen, wird in der Arbeit ein anderer als der Standardweg vorgeschlagen. Gewöhnlich werden Methoden eingesetzt, die das asymptotische Verhalten untersuchen, z.B. Regression im Periodogramm. Oder aber es wird versucht ein passendes potentiell langreichweitig korreliertes Modell zu finden, z.B. aus der FARIMA Klasse, und den geschätzten fraktionalen Differenzierungsparameter d auf Verträglichkeit mit dem trivialen Wert Null zu testen. In der Arbeit wird vorgeschlagen das Problem der Detektion langreichweitiger Korrelationen als Modellselektionsproblem umzuformulieren, d.h. das beste kurzreichweitig und das beste langreichweitig korrelierte Modell zu vergleichen. Diese Herangehensweise erfordert a) eine geeignete Klasse von lang- und kurzreichweitig korrelierten Prozessen und b) eine verläßliche Modellselektionsstrategie, auch für nichtgenestete Modelle. Mit der flexiblen FARIMA-Klasse und dem Whittleschen Ansatz zur Parameterschätzung ist die erste Voraussetzung erfüllt. Hingegen sind standard Ansätze zur Modellselektion, wie z.B. der Likelihood-Ratio-Test, für nichtgenestete Modelle oft nicht trennscharf genug. Es wird daher vorgeschlagen diese Strategie mit einem simulationsbasierten Ansatz zu ergänzen, der insbesondere für die direkte Diskriminierung nichtgenesteter Modelle geeignet ist. Der Ansatz folgt einem statistischen Test mit dem Quotienten der Likelihood als Teststatistik. Ihre Verteilung wird über Simulationen mit den beiden zu unterscheidenden Modellen ermittelt. Für zwei einfache Modelle und verschiedene Parameterwerte wird die Verläßlichkeit der Schätzungen für p-Wert und Power untersucht. Das Ergebnis hängt von den Modellparametern ab. Es konnte jedoch in vielen Fällen eine adäquate Modellselektion etabliert werden. Ein wichtige Eigenschaft dieser Strategie ist, dass unmittelbar offengelegt wird, wie gut sich die betrachteten Modelle unterscheiden lassen. Zwei Anwendungen, die Trenddetektion in Temperaturzeitreihen und die Unsicherheitsanalyse für Bemessungshochwasser, betonen den Bedarf an verläßlichen Methoden für die Detektion langreichweitiger Korrelationen. Im Falle der Trenddetektion führt ein fälschlicherweise gezogener Schluß auf langreichweitige Korrelationen zu einer Unterschätzung eines Trends, was wiederum zu einer möglicherweise verzögerten Einleitung von Maßnahmen führt, die diesem entgegenwirken sollen. Im Fall von Abflußzeitreihen führt die Nichtbeachtung von vorliegenden langreichweitigen Korrelationen zu einer Unterschätzung der Unsicherheit von Bemessungsgrößen. Eine verläßliche Detektion von langreichweitig Korrelierten Prozesse ist somit von hoher Bedeutung in der praktischen Zeitreihenanalyse. Beispiele mit Bezug zu extremem Ereignissen beschränken sich nicht nur auf die Hochwasseranalyse. Eine erhöhte Unsicherheit in der Bestimmung von extremen Ereignissen ist ein potentielles Problem von allen autokorrelierten Prozessen. Ein weiteres interessantes Beispiel ist hier die Abschätzung von maximalen Windstärken in Böen, welche bei der Konstruktion von Windrädern eine Rolle spielt. Mit der Umformulierung des Detektionsproblems als Modellselektionsfrage und mit der Bereitstellung geeigneter Modellselektionsstrategie trägt diese Arbeit zur Diskussion und Entwicklung von Methoden im Bereich der Detektion von langreichweitigen Korrelationen bei.
143

Environmental occurrence and behaviour of the flame retardant decabromodiphenyl ethane

Ricklund, Niklas January 2010 (has links)
The environmental occurrence and behaviour of the brominated flame retardant (BFR) decabromodiphenyl ethane (dbdpe) has only been studied to a limited extent. It is structurally similar to decabromodiphenyl ether (decaBDE), which makes it conceivable that dbdpe may also become an environmental contaminant of concern. A method for environmental analysis and comparative assessments of dbdpe and decaBDE was developed. Both BFRs were studied in: a mass balance of the Henriksdal WWTP in Stockholm (Paper I); an international survey of sewage sludge (Paper II); sediment along a transect from Henriksdal WWTP to the outer archipelago of Stockholm and from isolated Swedish lakes (Paper III); and a benthic food web from the Scheldt estuary (Paper IV). Dbdpe was found in sludge from every country surveyed, indicating that it may be a worldwide concern. The WWTP mass balance showed that virtually all of the BFRs were transferred from wastewater to sludge. A small fraction was emitted via the effluent, confirming emissions to the aquatic environment. In the marine sediment, the BFR levels close to the WWTP outfall were high. They decreased along the transect to low levels in the outer archipelago. The study of lake sediment showed a widespread presence of dbdpe in the Swedish environment and provided evidence that it originates from long range atmospheric transport. In the food web, dbdpe did bioaccumulate to a small extent which was similar to decaBDE. The transfer of the BFRs from sediment to benthic invertebrates was low, while transfer from prey to predator was higher. Biodilution was observed rather than biomagnification. This work suggests that the persistence, the susceptibility to long range atmospheric transport, and the potential for bioaccumulation are similar for dbdpe and the regulated decaBDE that it is replacing. Thus, there is a risk that a problematic environmental pollutant is being replaced with a chemical that is equally problematic. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Manuscript.
144

Robotsystem 15:s påverkan på den svenska ytstridstaktiken / The impact of RBS 15 on Swedish naval tactics

Söderqvist, Henrik January 2011 (has links)
Sveriges ytstridskrafter hade länge en förmåga att hävda sig mot fiendens stridskrafter ute till havs på 1950- och 60-talen. Nedrustningsprogrammet av försvaret på 1960-talet innebar att teknikutvecklingen bromsade upp och flottans större fartyg kryssare, fregatter och jagare skulle bytas ut till en lätt flotta med små snabba enheter. Detta resulterade i att flottans taktik anpassades till ett tillbakadraget uppträdande längs med kustbandet och inom skärgården. Svenska officerare bevittnade på när Sovjetunionen rustade upp och utvecklade nya vapen och fartyg med robotar av högsta kvalité i Östersjöområdet. Detta hot medförde att officerarna i flottan ville satsa på ett långräckviddigt vapen för att bli mer jämbördig mot fiendens styrka ute till havs. Resultatet blev en svenskutvecklad sjömålsrobot, Robotsystem 15 (RBS 15), som infördes i marinen i början av 1980-talet. RBS 15:s höga kvalité och förmåga medförde en satsning på utvecklingen av flera tekniska kringutrustningar som behövdes för att fulländat utföra en sjörobotstrid. Studiens syfte är att studera RBS 15:s införande i den svenska flottan och vilken påverkan detta hade på taktiken. Fallet RBS 15 prövas utifrån hypoteser grundade från teorier om hur tekniken påverkar taktiken. Tekniken påvisas påverka taktiken via de hypoteser som bestyrks i studien. Slutsatser från studien är att RBS 15 påverkade taktiken genom att den: möjliggjorde ett offensivt handlande, initierade utvecklingen av nya tekniska resurser och var den avgörande faktorn för att den marina organisationen medvetet ville utveckla ytstridstaktiken. Den nya förmågan innebar en markant skillnad i det svenska taktiska uppträdandet. Flottans ytstridskrafter tillämpade ett mer framskjutet uppträdande och kunde bestrida fiendens kontroll till sjöss. / During the 1950’s and 1960’sSweden’s surface warships had an ability to match enemy forces at sea. The disarmament of the Swedish Defense in the 1960’s implied a retardation of technique development and major warships like cruisers, frigates and destroyers were planned to be changed to a lighter fleet consisting of small, fast units. The result of this change was that the Navy tactics were adjusted to a retired behavior. Swedish officers witnessed the rearmament of the Soviet Union that developed new weapons and vessels with high class long-range anti-ship missiles in theBaltic Searegion. The consequence of this threat was that the naval officers wanted to develop a long-range weapon to equal enemy forces at sea. The result was a Swedish innovation of an anti-ship missile system (RBS 15) which was introduced in the Swedish Navy in the beginning of the 1980’s. RBS 15’s high quality and ability also implied a development of several peripheral technical equipments that were necessary for perfection in naval missile combat. The aim of the current study is to clarify whether or not the introduction of RBS 15 into the Swedish Navy was affecting tactics. The case RBS 15 is tested by hypotheses outgoing from theories how technologies affect tactics. It is demonstrated that the technologies affect tactics from the hypotheses that are confirmed in the study. Conclusions from the study are that the RBS 15 affected tactics since it: Facilitated to take offensive action, initiated development of new technical resources and was the crucial factor implementing that the naval organization decided to develop the tactics for the new Swedish surface warships. This new capability implicated a marked difference in the Swedish tactical behavior at sea. Naval warships were applying a more offensive tactic and had the ability to fight the enemy’s control of the sea.
145

Microfabrication of Plasmonic Biosensors in CYTOP Integrating a Thin SiO2 Diffusion and Etch-barrier Layer

Hanif, Raza 18 April 2011 (has links)
A novel process for the fabrication of Long Range Surface Plasmon Polariton (LRSPP) waveguide based biosensors is presented herein. The structure of the biosensor is comprised of Au stripe waveguide devices embedded in thick CYTOP claddings with a SiO2 solvent diffusion barrier and etch-stop layer. The SiO2 layer is introduced to improve the end quality of Au waveguide structures, which previously deformed during the deposit of the upper cladding process and to limit the over-etching of CYTOP to create micro-fluidic channels. The E-beam evaporation method is adapted to deposit a thin SiO2 on the bottom cladding of CYTOP. A new micro-fluidic design pattern is introduced. Micro-fluidic channels were created on selective Au waveguides through O2 plasma etching. The presented data and figures are refractive index measurements of different materials, thickness measurements, microscope images, and AFM images. Optical power cutback measurements were performed on fully CYTOP-cladded symmetric LRSPP waveguides. The end-fire coupling method was used to excite LRSPP modes with cleaved polarization maintaining (PM) fibre. The measured mode power attenuation (MPA) was 6.7 dB/mm after using index-matched liquid at input and output fibre-waveguide interfaces. The results were compared with the theoretical calculations and simulations. Poor coupling efficiency and scattering due to the SiO2 are suspected for off-target measurements.
146

Microfabrication of Plasmonic Biosensors in CYTOP Integrating a Thin SiO2 Diffusion and Etch-barrier Layer

Hanif, Raza 18 April 2011 (has links)
A novel process for the fabrication of Long Range Surface Plasmon Polariton (LRSPP) waveguide based biosensors is presented herein. The structure of the biosensor is comprised of Au stripe waveguide devices embedded in thick CYTOP claddings with a SiO2 solvent diffusion barrier and etch-stop layer. The SiO2 layer is introduced to improve the end quality of Au waveguide structures, which previously deformed during the deposit of the upper cladding process and to limit the over-etching of CYTOP to create micro-fluidic channels. The E-beam evaporation method is adapted to deposit a thin SiO2 on the bottom cladding of CYTOP. A new micro-fluidic design pattern is introduced. Micro-fluidic channels were created on selective Au waveguides through O2 plasma etching. The presented data and figures are refractive index measurements of different materials, thickness measurements, microscope images, and AFM images. Optical power cutback measurements were performed on fully CYTOP-cladded symmetric LRSPP waveguides. The end-fire coupling method was used to excite LRSPP modes with cleaved polarization maintaining (PM) fibre. The measured mode power attenuation (MPA) was 6.7 dB/mm after using index-matched liquid at input and output fibre-waveguide interfaces. The results were compared with the theoretical calculations and simulations. Poor coupling efficiency and scattering due to the SiO2 are suspected for off-target measurements.
147

A Methodology for Capability-Based Technology Evaluation for Systems-of-Systems

Biltgen, Patrick Thomas 26 March 2007 (has links)
Post-Cold War military conflicts have highlighted the need for a flexible, agile joint force responsive to emerging crises around the globe. The 2005 Joint Capabilities Integration and Development System (JCIDS) acquisition policy document mandates a shift away from stove-piped threat-based acquisition to a capability-based model focused on the multiple ways and means of achieving an effect. This shift requires a greater emphasis on scenarios, tactics, and operational concepts during the conceptual phase of design and structured processes for technology evaluation to support this transition are lacking. In this work, a methodology for quantitative technology evaluation for systems-of-systems is defined. Physics-based models of an aircraft system are exercised within a hierarchical, object-oriented constructive simulation to quantify technology potential in the context of a relevant scenario. A major technical challenge to this approach is the lack of resources to support real-time human-in-the-loop tactical decision making and technology analysis. An approach that uses intelligent agents to create a "Meta-General" capable of forecasting strategic and tactical decisions based on technology inputs is used. To demonstrate the synergy between new technologies and tactics, surrogate models are utilized to provide intelligence to individual agents within the framework and develop a set of tactics that appropriately exploit new technologies. To address the long run-times associated with constructive military simulations, neural network surrogate models are implemented around the forecasting environment to enable rapid trade studies. Probabilistic techniques are used to quantify uncertainty and richly populate the design space with technology-infused alternatives. Since a large amount of data is produced in the analysis of systems-of-systems, dynamic, interactive visualization techniques are used to enable "what-if" games on assumptions, systems, technologies, tactics, and evolving threats. The methodology developed in this dissertation is applied to a notional Long Range Strike air vehicle and system architecture in the context of quantitative technology evaluation for the United States Air Force.
148

Spring to Summer Transitions of Ozone and Its Precursors over North America and Photochemistry over Antarctica

Choi, Yunsoo 28 June 2007 (has links)
The horizontal and vertical distributions of ozone and its precursors over North America during spring and summer are frequently determined by several factors: cloud convection, lightning NOx production, mixing depth, and long-range transport. The critical factors that contribute to the spatial distribution of air pollutants are studied using the Regional chEmical trAnsport Model (REAM) with diverse satellite measurements as well as in-situ surface and aircraft measurements. Surface and aircraft measurements show a large amount of reactive nitrogen tracers over the Antarctic plateau during summer. These enhanced measurements are investigated, and their photochemical impact is accessed by 1-D CTM and REAM.
149

Chemical Composition Of Atmospheric Particles In The Aegean Region

Munzur, Basak 01 February 2008 (has links) (PDF)
Daily aerosol samples were collected at the &Ccedil / andarli which is located on Aegean coast of Turkey. A rural site was selected to monitor atmospheric pollution by long range transport. Sampling was performed in both summer and winter seasons, and in total 151 samples were obtained. Concentrations of elements in the samples were measured in order to identify sources and possible source locations of pollutants. Measured concentrations of trace elements at the &Ccedil / andarli station were compared with those measured at various sites around the world and, also in Turkey. As a result of comparison, level of pollution at the Aegean Region was found to be lower than the Mediterranean Region and Black Sea Region. Air flow climatology at &Ccedil / andarli was investigated in order to determine potential source regions for pollutants. Frequency of air flows from Russia and Western Europe are higher suggesting that emissions from these industrial regions affect the chemical composition of particulate matter. Besides these, it was concluded that contributions from Central and Eastern European countries are significantly high because of frequent air mass transport. Concentrations of elements measured at &Ccedil / andarli station were found to show short and seasonal variations. Such variations in concentrations are explained by variations in the source strengths and transport patterns. Positive matrix factorization (PMF) was applied to determine sources of elements and contribution of sources to each element. This analysis revealed 5 sources, two local anthropogenic emissions factor, one soil factor, one sea salt factor and one long range transport factor. Distribution of Potential Source Contribution Function (PSCF) values showed that main sources of SO42- are observed in Bulgaria, Romania, Poland, Ukraine and central part of Aegean region.
150

Nonlinear and wavelength-tunable plasmonic metasurfaces and devices

Lee, Jongwon 15 January 2015 (has links)
Wavelength-tunable optical response from solid-state optoelectronic devices is a desired feature for a variety of applications such as spectroscopy, laser emission tuning, and telecommunications. Nonlinear optical response, on the other hand, has an important role in modern photonic functionalities, including efficient frequency conversions, all-optical signal processing, and ultrafast switching. This study presents the development of optical devices with wavelength tunable or nonlinear optical functionality based on plasmonic effects. For the first part of this study, widely wavelength tunable optical bandpass filters based on the unique properties of long-range surface plasmon polaritons (LR SPP) are presented. Planar metal stripe waveguides surrounded by two different cladding layers that have dissimilar refractive index dispersions were used to develop a wide wavelength tuning. The concept was demonstrated using a set of index-matching fluids and over 200nm of wavelength tuning was achieved with only 0.004 of index variation. For practical application of the proposed concept, a thermo-optic polymer was used to develop a widely tunable thermo-optic bandpass filter and over 220 nm of wavelength tuning was achieved with only 8 ºC of temperature variation. Another novel approach to produce a widely wavelength tunable optical response for free-space optical applications involves integrating plasmonic metasurfaces with quantum-electronic engineered semiconductor layers for giant electro-optic effect, which is proposed and experimentally demonstrated in the second part of this study. Coupling of surface plasmon modes formed by plasmonic nanoresonators with Stark tunable intersubband transitions in multi-quantum well structures induced by applying bias voltages through the semiconductor layer was used to develop tunable spectral responses in the mid-infrared range. Experimentally, over 310 nm of spectral peak tuning around 7 μm of wavelength with 10 ns response time was achieved. As the final part of this study, highly nonlinear metasurfaces based on coupling of electromagnetically engineered plasmonic nanoresonators with quantum-engineered intersubband nonlinearities are proposed and experimentally demonstrated. In the proof-of-concept demonstration, an effective nonlinear susceptibility over 50 nm/V was measured and, after further optimization, over 480 nm/V was measured for second harmonic generation under normal incidence. The proposed concept shows that it is possible to engineer virtually any element of the nonlinear susceptibility tensor of the nonlinear metasurface. / text

Page generated in 0.0628 seconds