Byla provedena měření turbulentní Rayleighovy-Bénardovy konvekce v kryogenním heliu v rozsahu Rayleighových čísel 1e8

MIMO systems are mainly used in application for wireless communication. Their principle is to use a large number of antennas for transmition and the reception of a signal. The core of these systems is to use space-time coding and either block or trellis space-time code. In the future, it is assumed enormous enlargement MIMO systems in many applications

Nowdays, optical fibers are one of important parts of computer networks, especially for their ability to transfer information for long distance. This thesis doesn´t utilize optical fibers as carriers, but as sources of information, specifically as sensors intended to detect physical effects acting on the optical fiber, which is usually used for telecommunication purposes. Linear and nonlinear properties of the fiber are used to gain information about acting effects on the optical fiber.

Les particules de suie, issues de la combustion incomplète, peuvent, en fonction des conditions de combustion, contenir une part plus ou moins importante de composés organiques (OC/TC). Par ailleurs, dès lors que ces nanoparticules sont émises dans l'atmosphère, des composés organiques volatiles peuvent s'adsorber, formant une gangue autour de ces agrégats fractals. L'impact de cette composition initiale ou de ce « vieillissement atmosphérique » sur les propriétés morphologiques et radiatives de ces particules n'est pas bien connu. Ceci a un impact sur les modèles radiatifs climatiques mais aussi sur l'interprétation des signaux délivrés par les différents diagnostics optiques pouvant être utilisés pour la métrologie des aérosols. En particulier, ce travail vise à juger de la pertinence de l'usage de diagnostics optiques pour caractériser les particules de suie en conditions atmosphériques. Afin d'étudier l'impact des composés organiques initialement présents dans la particule ou adsorbés en post-combustion sur leurs propriétés radiatives, nous avons étudié en laboratoire des suies produites par une flamme de diffusion (miniCAST) pour différentes richesses globales et avons ajouté un revêtement organique d'acide. Dans le but de générer en laboratoire une couche d'acide oléique sur des particules de référence, un dispositif de « coating » a été mis en œuvre et qualifié. Les particules ainsi générées et recouvertes ou non, ont été caractérisées en masse (mesures TEOM), en taille (mesures SMPS) et morphologiquement (densité effective). L'épaisseur de coating ainsi que la restructuration morphologique causée par l'ajout d'une gangue de matière organique ont ainsi été quantifiées. Les propriétés radiatives, ont été mesurées par extinction spectrale (Turbidimétrie) et diffusion (diffusion angulaire et spectrale). Un effort particulier a été mené pour que des mesures expérimentales puissent valider des résultats de calculs numériques préexistants. Par ailleurs, ces différentes techniques de mesures (optiques et non optique) ont conduit à la généralisation de la théorie Rayleigh Debye Gans for Fractal Aggregates (RDG-FA) à des particules de type agrégats fractals polydispersés recouverts d'un revêtement organique (RDG-CFA). Ceci permettant d'appréhender de façon phénoménologique l'impact du coating sur les propriétés radiatives et d'entrevoir une implantation plus aisée dans les codes de simulation climatique ou pour l'interprétation des mesures optiques dans l'atmosphère. Enfin, une attention particulière a été portée sur la technique d'incandescence induite par laser (LII) afin d'étudier la faisabilité de l'application de cette technique aux particules organiques ou ayant interagi avec les composés atmosphériques au cours de leur vieillissement. / Soot particles resulting from incomplete combustion may contain a more or less important part of organic compounds (OC / TC), depending on the combustion conditions. Moreover, once these nanoparticles are emitted into the atmosphere, volatile organic compounds can adsorb, forming a coating around these fractal aggregates. The impact of the initial composition or the atmospheric aging on the morphological and radiative properties of these particles is not well known. This has an impact on the radiative climate models but also on the interpretation of the signais delivered by the different optical diagnostics that can be used for aerosol metrology. In particular, this work aims to evaluate the relevance of the use of optical diagnostics to characterize soot particles in atmospheric conditions. In order to study the impact of organic compounds initially present in the particle or adsorbed in post-combustion on their radiative properties, we have studied soot produced by a diffusion flame (miniCAST) for different global richnesses and added an organic acid coating. In order to produce an oleic acid layer on reference particles, a coating device has been implemented and qualified. Particles thus generated, coated or not, were characterized in mass (TEOM measurements), in size (SMPS measurements) and morphologically (effective density). The coating thickness as well as the morphological restructuring caused by the addition of an organic coating was thus quantified. The radiative properties were measured by spectrally resolved light extinction and scattering (angular and spectrally resolved). A special effort was made to allow experimental measurements to validate pre-existing numerical results. Moreover, these different measurement techniques (optical and non-optical) have led to the generalization of the Rayleigh Debye Gans for Fractal Aggregates (RDG-FA) theory to particles of the polydispersed fractal aggregate type coated with an organic layer (RDG-CFA). This allows to understand phenomenologically the impact of a coating on the radiative properties and to permit an easier implementation in climate simulation codes or for the interpretation of optical measurements in the atmosphere. Finally, special attention was paid to the laser induced incandescence technique (LII), to study the applicability of this technique to organic particles or having interacted with atmospheric compounds during their aging processes.

We examine the Rayleigh–Bénard convection as modelled by the Boussinesq equation. Our aim is at deriving bounds for the heat enhancement factor in the vertical direction, the Nusselt number, which reproduce physical scalings. In the first part of the dissertation, we examine the the simpler model when the acceleration of the fluid is neglected (Pr=∞) and prove the non-optimality of the temperature background field method by showing a lower bound for the Nusselt number associated to it. In the second part we consider the full model (Pr<∞) and we prove a new upper bound which improve the existing ones (for large Pr numbers) and catches a transition at Pr~Ra^(1/3).

The master's thesis consists of two parts. The first part contains the azimuth -- slowness analysis for period 3s<=T<=6s, which was conducted by the FK analysis for 10 stations of the WEBNET network. In the second part there is the surface wave group velocity measurement for every station pair of 10 WEBNET stations. The interstation group velocity was obtained by the cross--correlation of microseismic noise records. Local group velocities are connected with the instantaneous period data. The Love wave group velocities are visualised by the 2D tomography calculation. The thesis also contains the additional Love waves dispersion analysis for just one station pair. Powered by TCPDF (www.tcpdf.org)

The recent worldwide economic crisis, climate change and global warming have emphasized that the need for low carbon emissions while also ensuring the economic feasibility. In this paper, wind power potential of ETD in KTH was investigated. The technical and economical feasibility of tower mounted small scale standalone wind turbine installation is conducted. The potential of wind power production was statistically analysed. The average wind speed data of four-season interval of one year period (2011) which its measurement was taken on the roof top of the ETDB, and this was adopted and analysed in order to find out the potential of wind power generation. The Rayleigh distribution probability was applied to calculate the wind speed distribution at KTH, by doing so the annual wind power potential at the area and annual energy production of the chosen wind turbine was estimated, after the selection of a proper wind turbine have been made upon the site conditions. Therefore, the study result shows that installation of the wind turbine at 24 meters hub height for this particular area will have a better performance of annual energy production, capacity factor, carbon savings and better economical value than the current turbine installed at 17 meters height at the ETD. The economic evaluation shows that the turbine can save an electricity bill of US$3661.05 per year and cover 1.84% of the electricity consumption of the ETD by reducing its respective CO2 emission from the electricity use at the department. Moreover, the payback period of the turbine installation with the inclusion of the green certificate is approximately 14 years which is more feasible if it is considered for small wind turbines too, which is already in practice for renewables including wind power in Sweden.

In cellular communication systems, the estimation of Doppler spread has a wide range of applications such as handoff, channel assignment scheme, adaptivetransmission, power control, etc. A great quantity of Doppler spread estimation algorithms have been proposed in the literature. But there has been few investigations which gives a comprehensive comparison of these algorithms. Therefore, it is of great signicance to compare and evaluate the performance of the existing algorithms in the same simulation framework. In this report, the uplink of WCDMA is considered. Four different types of Doppler spread estimation algorithms are evaluated and compared in a link level baseband simulator. The performance and the ability to implement are considered as the metrics for evaluation. Both Rayleigh and Rician fading channel model are applied, and the effect of speed, signal to noise ratio, Rician factor and the angle of arrived line of sight component are also tested. Moreover, the computational complexity is analysed to evaluate the practical value for implementation. / Estimatering av en mobils hastighet i form av Dopplerspridning har ett brett spektrum av tillmpningar i cellulra kommunikationssystem ssom fr yttningen avmobiler mellan celler, kanaltilldelningsschema, adaptiv sndning, eektstyrning,etc. En stor mngd algoritmer fr estimering av Dopplerspriding har frslagitsi litteraturen, men det r ovanligt med heltckande jmfrelser mellan med dessaalgoritmer. Drfr r det av stor betydelse att jmfra och utvrdera resultaten avbentliga algoritmer inom ramen fr samma simuleringsvertyg.I denna rapport anvnds upplnken fr WCDMA fr utvrdering av fyra olikatyper av algoritmer fr estimering av Dopplerspridning. Metriker fr utvrderingenr prestanda och implementeringsvnlighet. Bde Rayleigh och Rician fdningskanalmodeller har utvrderas, samt eekten av mobilens hastighet, signaltill brus frhllande, Rician faktor och infallsvinkel i ppet flt scenario. Dessutomhar den berkningsmssiga komplexiteten analyseras fr att utvrdera den praktiskaanvndbarheten i riktiga system.

<div>This research has been studied a laser-induced spark in flowing gases. The relationship between the minimum ignition energy (MIE), the turbulence intensity, and the flame kernel propagation speed is considered. Plasma emission, produced by the laser-induced spark, and flame kernel generation by the plasma are investigated. The energy balance equation between an ignition energy and energy losses by heat transfer is studied at laminar flows and turbulent flows. Hydrogen and air mixtures were used in a premixed jet burner for ignition experiments. Particle image velocimetry (PIV) examined the velocity and the turbulence intensity under the turbulent flows. The flame kernel development was visualized using Schlieren imaging and infrared images (IR camera). Flame kernel temperatures were measured through Rayleigh scattering and infrared images (IR camera). Plasma evaluations were captured through an intensified CCD camera (ICCD camera). Minimum ignition energies were measured at the laminar flows and the turbulent flows. The MIE decreases with an increase in the turbulence intensity which changed by ignition locations and perforated plates at the constant bulk velocity. Improved mixing rates due to the ignition locations or the geometry of the perforated plates decrease the MIE at the constant bulk velocity. The turbulence intensity increases wrinkles in the flame kernel surface, thus the contact between the flame kernel and reactants increases due to the wrinkles. Therefore, the flame kernel propagation speed increases as the turbulence intensity is higher since the increased reaction by the wrinkles and the contact. Thus, the MIE decreases as the turbulence intensity increases at the constant ignition condition, including bulk velocities and ignition heights, since the high turbulence intensity increases the flame kernel propagation speed. Laser energy differences affect the plasma expansions by the laser absorption. Laser-supported radiation (LSR) wave speeds were measured and calculated using energy balance equations. Velocity does not affect the flame kernel temperature distribution during the early reaction steps because the plasma generates a flame kernel and determines the flame kernel temperature distribution. The MIE increases with increasing the bulk velocity. The energy losses considering convection, conduction, and radiation were calculated using the flame kernel radius, the flame kernel temperature, mixture properties, and the flame speed. The energy balance equation in the ignition of flowing gases is newly written at the laminar flows and the turbulent flows.</div>

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