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Diatoms as indicators of Holocene climate and environmental change in northern SwedenBigler, Christian January 2001 (has links)
The objective of the thesis was to explore the potential of diatoms (Bacillariophyceae) as indicators of Holocene climate and environmental change in northern Sweden (Abisko region, 68°21'N, 18°49'E). A modern surface-sediment calibration set including 100 lakes was developed and lake-water pH, sedimentary organic content (assessed by loss-on-ignition) and temperature were identified as most powerful environmental variables explaining the variance within the diatom assemblages. Transfer functions based on unimodal species response models (WA-PLS) were developed for lake-water pH and mean July air temperature (July T), yielding coefficients of determination of 0.77 and 0.70, and prediction errors based on leave-one-out cross-validation of 0.19 pH units and 0.96 °C for lake-water pH and July T, respectively. The transfer functions were validated with monitoring data covering two open-water seasons (lake-water pH) and meteorological records covering the 20th century (July T). The good agreement between diatom-based inferences and measured monitoring data confirmed the prediction ability of the developed transfer functions. Analysing a Holocene sediment core from a lake nearby Abisko (Vuoskkujávri), diatoms infer a linearly decreasing July T trend (1.5 °C) since 6,000 cal. BP, which compares well with inferences based on chironomids and pollen from the same sediment core. The lake-water pH inference shows a pattern of moderate natural acidification (c. 0.5 pH units) since the early Holocene, reaching present-day pH values at c. 5,000 cal. BP. By fitting fossil diatom samples to the modern calibration set by means of residual distance assessment within canonical correspondence analysis (CCA), the early Holocene (between 10,600 and 6,000 cal. BP) was identified as a problematic time-period for diatom-based inferences and, consequently, reconstructions during this period are tentative. Pollen-based inferences also show 'poor' fit between 10,600 and 7,500 cal. BP and chironomids probably provide the most reliable July T reconstruction at Vuoskkujávri, with 'poor' fit only during the initial part of the Holocene (between 10,600 and 10,250 cal. BP). Possible factors confounding diatom-based July T inferences were investigated. Using detrended CCA (DCCA), Holocene sediment sequences from five lakes indicate that during the early Holocene, mainly physical factors such as high minerogenic erosion rates, high temperature and low light availability may have regulated diatom assemblages, favouring Fragilaria species. In all five lakes, diatom assemblages developed in a directional manner, but timing and scale of development differed substantially between lakes. The differences are attributed primarily to the geological properties of the lake catchments (with strong effects on lake-water pH), but other factors such as climatic change, vegetation, hydrologic setting and in-lake processes appear to regulate diatom communities in each lake differently. The influence of long-term natural acidification on diatom assemblages progressively declined during the Holocene with corresponding increase of the influence of climatic factors.
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Analysis And Design Of A Cuk Switching RegulatorGunaydin, Zekiye 01 June 2009 (has links) (PDF)
This theses analyzes Cuk converter, that is one of the dc to dc switching converters. For continuous inductor current mode and discontinuous inductor current mode, stedy state operation is analysied. Characteristic parameters are determined. Through State Space Averge Models, Small Signal Models are obtained. Parasitic Resistance effects on steady state and small signal models are determined. Efficency of the switching converter is derived. Open loop transfer functions for continous and discontinuous inductor curret mode are obtained. Parmeters for small signal behaviour is determined and stability is analysied. Parasitic resistance effects on transfer functions is determined. Therotecial analysis are verified with a simulations of designed converter.
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Déconfinement de sources acoustiques par utilisation d'une méthode holographique à double informationVigoureux, Dorian 03 July 2012 (has links) (PDF)
L'identification et la caractérisation des sources acoustiques restent encore aujourd'hui deux sujets d'importance pour les industriels qui ont besoin de techniques permettant d'identifier des sources acoustiques ou vibratoires sur des surfaces complexes dans un environnement acoustique non contrôlé. La thèse que nous présentons ici s'inscrit dans ce cadre. Nous y étudions les qualités d'une méthode inverse, appelée iPTF (pour inverse Patch Transfer Functions, pour la résolution de ce problème particulier. Nous consacrerons le premier chapitre de notre étude à la synthèse bibliographique des méthodes les plus pertinentes permettant de résoudre des problèmes similaires. Nous soulignerons également les difficultés de ces méthodes pouvant être liées à leurs applications pratiques ou à leurs fondements théoriques. Dans un second chapitre, nous présenterons la méthode iPTF à partir de sa formulation directe, c'est-à-dire de la source vers le bruit rayonné. Celle-ci est une approche par sous-structuration de domaines permettant l'étude des problèmes vibro-acoustiques en basses et moyennes fréquences. Nous montrerons particulièrement la façon dont l'association des deux formulations directe et indirecte permet de définir une méthode pouvant conduire jusqu'à l'identification des trois champs de vitesses, de pressions et d'intensités sur la surface de l'objet source. Notre troisième chapitre sera consacré à la présentation des premiers résultats d'identification dans un cas d'application numérique simple. Nous effectuerons, dans les chapitres quatre et cinq, une étude des principaux paramètres conditionnant les résultats donnés par la méthode. Le premier de ces deux chapitres présentera la mise en place d'un code de calcul permettant de résoudre rapidement le problème de rayonnement d'une structure simple. La méthode ainsi définie sera utilisée dans le chapitre cinq afin de générer de nombreux champs rayonnés présentant des caractéristiques différentes de façon à étudier la stabilité de la méthode iPTF face à la variation de différents paramètres. Un sixième chapitre présentera une étude approfondie faite sur les ondes évanescentes qui prennent une part non négligeable dans le champ rayonné par les structures. Ces ondes évanescentes, par définition, ne peuvent pas être mesurées au delà du champ proche, ce qui peut être la cause d'une part des défauts d'identification rencontrés lors de l'application de notre méthode. L'étude faite ici aura pour but de déterminer l'importance de ces ondes évanescentes dans le champ rayonné. Nous présenterons enfin, dans un dernier chapitre, les résultats de mesures expérimentales réalisées.
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[en] INTERACTIVE VOLUME VISUALIZATION OF UNSTRUCTURED MESHES USING PROGRAMMABLE GRAPHICS CARDS / [pt] VISUALIZAÇÃO VOLUMÉTRICA INTERATIVA DE MALHAS NÃO-ESTRUTURADAS UTILIZANDO PLACAS GRÁFICAS PROGRAMÁVEISRODRIGO DE SOUZA LIMA ESPINHA 15 June 2005 (has links)
[pt] A visualização volumétrica é uma importante técnica para a
exploração de
dados tridimensionais complexos, como, por exemplo, o
resultado de análises
numéricas usando o método dos elementos finitos. A
aplicação eficiente dessa
técnica a malhas não-estruturadas tem sido uma importante
área de pesquisa nos
últimos anos. Há dois métodos básicos para a visualização
dos dados
volumétricos: extração de superfícies e renderização
direta de volumes. Na
primeira, iso-superfícies de um campo escalar são
extraídas explicitamente. Na
segunda, que é a utilizada neste trabalho, dados escalares
são classificados a partir
de uma função de transferência, que mapeia valores do
campo escalar em cor e
opacidade, para serem visualizados. Com a evolução das
placas gráficas (GPU)
dos computadores pessoais, foram desenvolvidas novas
técnicas para visualização
volumétrica interativa de malhas não-estruturadas. Os
novos algoritmos tiram
proveito da aceleração e da possibilidade de programação
dessas placas, cujo
poder de processamento cresce a um ritmo superior ao dos
processadores
convencionais (CPU). Este trabalho avalia e compara dois
algoritmos para
visualização volumétrica de malhas não-estruturadas,
baseados em GPU: projeção
de células independente do observador e traçado de raios.
Adicionalmente, são
propostas duas adaptações dos algoritmos estudados. Para o
algoritmo de projeção
de células, propõe-se uma estruturação dos dados na GPU
para eliminar o alto
custo de transferência de dados para a placa gráfica. Para
o algoritmo de traçado
de raios, propõe-se fazer a integração da função de
transferência na GPU,
melhorando a qualidade da imagem final obtida e permitindo
a alteração da
função de transferência de maneira interativa. / [en] Volume visualization is an important technique for the
exploration of threedimensional
complex data sets, such as the results of numerical
analysis using the
finite elements method. The efficient application of this
technique to unstructured
meshes has been an important area of research in the past
few years. There are
two basic methods to visualize volumetric data: surface
extraction and direct
volume rendering. In the first, the iso-surfaces of the
scalar field are explicitly
extracted. In the second, which is the one used in this
work, scalar data are
classified by a transfer function, which maps the scalar
values to color and
opacity, to be visualized. With the evolution of personal
computer graphics cards
(GPU), new techniques for volume visualization have been
developed. The new
algorithms take advantage of modern programmable graphics
cards, whose
processing power increases at a faster rate than the one
observed in conventional
processors (CPU). This work evaluates and compares two GPU-
based algorithms
for volume visualization of unstructured meshes: view-
independent cell projection
(VICP) and ray-tracing. In addition, two adaptations of
the studied algorithms are
proposed. For the cell projection algorithm, we propose a
GPU data structure in
order to eliminate the high costs of the CPU to GPU data
transfer. For the raytracing
algorithm, we propose to integrate the transfer function
in the GPU, which
increases the quality of the generated image and allows to
interactively change the
transfer function.
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Contribution à l'analyse des paliers fluides et des joints d'étanchéité utilisés dans lesturbopompes spatiales / Contribution to the analysis of fluid bearings and annular seals used in the aerospace turbopumpsHassini, Mohamed Amine 22 November 2012 (has links)
La conception des turbomachines à haute densité énergétique nécessite de plus en plus la maîtrise d'un plus grand nombre de paramètres fonctionnels. La moindre défaillance d'un composant conduit quasi immédiatement la machine à la rupture. C'est en particulier le cas pour le comportement des composants à films minces.L'appellation "film mince" correspond à tout espace de très faible épaisseur situé entre le rotor et le stator de la turbomachine. Leur but est soit de limiter les fuites de manière à optimiser les performances intrinsèques de la machine, soit alors à supporter et stabiliser le rotor. Ces derniers cas sont plus appelés communément "joints lisses ou annulaires" et "paliers fluides".Lorsqu'un fluide circule dans un espace de très faible épaisseur, typiquement quelques centièmes de millimètres sur une distance très longue, son champ de vitesses, donc de pression, dépend fortement des phénomènes visqueux aux parois dont l'une est mise en rotation et l'autre est immobile. Les efforts fluides sur ces parois peuvent être alors importants et doivent être pris en compte dans le dimensionnement de la machine.La connaissance précise de ces écoulements très complexes est indispensable pour déterminer les efforts statiques et dynamiques appliqués au rotor de manière à pouvoir dimensionner un fonctionnement calme. / The design of high performance aerospace turbo pumps requires more control of an increasing number of functional parameters. Any component failure led almost immediately to a machine failure. This is particularly the case for the behavior of thin film lubricated components.The term "thin film" means any thin space between the rotor and the stator of the engine. Their goal is either to limit leakage to maximize the machine intrinsic performance, or to support and stabilize the rotor. These cases are more commonly called "smooth or annular seals" and "fluid film bearings".When a fluid flows in a space of very small thickness, typically a few hundredths of a millimeter, the velocity field, hence the pressure, are highly dependent on the walls viscous forces. Fluid forces on the walls (which one is rotated and the other is stationary) can then be important and should be taken into account in the design of the machine.The precise knowledge of these complex flows is essential to determine the static and dynamic forces applied to the rotor to ensure a quite functioning of the turbo pump.
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Lower Vocal Tract Morphologic Adjustments Are Relevant for Voice Timbre in SingingMainka, Alexander, Poznyakovskiy, Anton, Platzek, Ivan, Fleischer, Mario, Sundberg, Johan, Mürbe, Dirk 08 June 2016 (has links)
The vocal tract shape is crucial to voice production. Its lower part seems particularly relevant for voice timbre. This study analyzes the detailed morphology of parts of the epilaryngeal tube and the hypopharynx for the sustained German vowels /a/, /e/, /i/, /o/, and /u/ by thirteen male singer subjects who were at the beginning of their academic singing studies. Analysis was based on two different phonatory conditions: a natural, speech-like phonation and a singing phonation, like in classical singing. 3D models of the vocal tract were derived from magnetic resonance imaging and compared with long-term average spectrum analysis of audio recordings from the same subjects. Comparison of singing to the speech-like phonation, which served as reference, showed significant adjustments of the lower vocal tract: an average lowering of the larynx by 8 mm and an increase of the hypopharyngeal cross-sectional area (+ 21.9%) and volume (+ 16.8%). Changes in the analyzed epilaryngeal portion of the vocal tract were not significant. Consequently, lower larynx-to-hypopharynx area and volume ratios were found in singing compared to the speech-like phonation. All evaluated measures of the lower vocal tract varied significantly with vowel quality. Acoustically, an increase of high frequency energy in singing correlated with a wider hypopharyngeal area. The findings offer an explanation how classical male singers might succeed in producing a voice timbre with increased high frequency energy, creating a singer‘s formant cluster.
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Paleoekologická rekonstrukce prostředí Komořanského jezera v pozdním glaciálu na základě analýzy rozsivek / Palaeoecological reconstruction of Komořany Lake in Late Glacial based on diatom analysisPoštulková, Anna January 2016 (has links)
Diatom analysis of basal part of profile PK-1-L contributes to multi-proxy research of former Lake Komořany. At this part of profile radiocarbon dating (dates sediments into Late Glacial and Early Holocene) and LOI (loss on ignition) had been conducted before, of which results have been utilized to more accurate interpretation of diatom analysis conclusions. Apart from diatom valves, presence of stomatocysts of Chrysophyceae has been observed. Having separated diatom valves from 32 sediment samples in intervals 0,4-0,6 cm, permanent preparates have been created. Concentration of valves in a gramme of dry sediment and relative abundance of diatom taxons in each sample have been investigated using light microscopy. In a half of samples subdominants and rare taxons have been observed separately to eliminate the interference from dominant taxons. Cluster analysis based on relative abundances of diatom taxons have been calculated and on its results have been subsequently determined three diatom accumulation zones (DAZ). Moreover trophic and saprobic indices have been calculated and levels of pH, conductivity and concentration of total phosphorus (TP) have been estimated by transfer functions. Even before beginning of Holocene the major shift in composition of diatom communities have happened, to the...
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Gaussian Process Methods for Estimating Radio Channel CharacteristicsOttosson, Anton, Karlstrand, Viktor January 2020 (has links)
Gaussian processes (GPs) as a Bayesian regression method have been around for some time. Since proven advant-ageous for sparse and noisy data, we explore the potential of Gaussian process regression (GPR) as a tool for estimating radiochannel characteristics. Specifically, we consider the estimation of a time-varying continuous transfer function from discrete samples. We introduce the basic theory of GPR, and employ both GPR and its deep-learning counterpart deep Gaussian process regression (DGPR)for estimation. We find that both perform well, even with few samples. Additionally, we relate the channel coherence bandwidth to a GPR hyperparameter called length-scale. The results show a tendency towards proportionality, suggesting that our approach offers an alternative way to approximate the coherence band-width. / Gaussiska processer (Gaussian processes, GPs) har länge använts för Bayesiansk regression. Då de visat sig fördelaktiga för gles och brusig data utforskar vi möjligheterna för GP-regression (Gaussian process regression, GPR) som ett verktyg för att estimera egenskaper hos radiokanaler.I synnerhet betraktas skattning av en tidsvarierande överföringsfunktion utifrån diskreta samplingar. Vi presenterar den grundläggande teorin kring GPR, och använder både GPR och dess djupinlärningsmotsvarighet DGPR (deep Gaussian process regression) för skattning. Båda ger goda resultat, även när samplingarna är få. Utöver detta så relaterar vi koherensbandbredden hos en radiokanal till en hyperparameter i GPR-modellen. Resultaten visar på en tendens till proportionalitet, vilket antyder att vår metod kan användas som ett alternativt sätt att approximera koherensbandbredden. / Kandidatexjobb i elektroteknik 2020, KTH, Stockholm
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Déconfinement de sources acoustiques par utilisation d'une méthode holographique à double information / Acoustical sources deconfining using a holographic method based on twin informationsVigoureux, Dorian 03 July 2012 (has links)
L’identification et la caractérisation des sources acoustiques restent encore aujourd’hui deux sujets d’importance pour les industriels qui ont besoin de techniques permettant d’identifier des sources acoustiques ou vibratoires sur des surfaces complexes dans un environnement acoustique non contrôlé. La thèse que nous présentons ici s'inscrit dans ce cadre. Nous y étudions les qualités d'une méthode inverse, appelée iPTF (pour inverse Patch Transfer Functions, pour la résolution de ce problème particulier. Nous consacrerons le premier chapitre de notre étude à la synthèse bibliographique des méthodes les plus pertinentes permettant de résoudre des problèmes similaires. Nous soulignerons également les difficultés de ces méthodes pouvant être liées à leurs applications pratiques ou à leurs fondements théoriques. Dans un second chapitre, nous présenterons la méthode iPTF à partir de sa formulation directe, c'est-à-dire de la source vers le bruit rayonné. Celle-ci est une approche par sous-structuration de domaines permettant l’étude des problèmes vibro-acoustiques en basses et moyennes fréquences. Nous montrerons particulièrement la façon dont l'association des deux formulations directe et indirecte permet de définir une méthode pouvant conduire jusqu'à l'identification des trois champs de vitesses, de pressions et d'intensités sur la surface de l'objet source. Notre troisième chapitre sera consacré à la présentation des premiers résultats d'identification dans un cas d'application numérique simple. Nous effectuerons, dans les chapitres quatre et cinq, une étude des principaux paramètres conditionnant les résultats donnés par la méthode. Le premier de ces deux chapitres présentera la mise en place d'un code de calcul permettant de résoudre rapidement le problème de rayonnement d'une structure simple. La méthode ainsi définie sera utilisée dans le chapitre cinq afin de générer de nombreux champs rayonnés présentant des caractéristiques différentes de façon à étudier la stabilité de la méthode iPTF face à la variation de différents paramètres. Un sixième chapitre présentera une étude approfondie faite sur les ondes évanescentes qui prennent une part non négligeable dans le champ rayonné par les structures. Ces ondes évanescentes, par définition, ne peuvent pas être mesurées au delà du champ proche, ce qui peut être la cause d'une part des défauts d'identification rencontrés lors de l'application de notre méthode. L'étude faite ici aura pour but de déterminer l'importance de ces ondes évanescentes dans le champ rayonné. Nous présenterons enfin, dans un dernier chapitre, les résultats de mesures expérimentales réalisées. / Nowadays, both identification and characterization of acoustical sources remain two important topics in industry as such method are often required to localize acoustical or vibrational sources on complex surfaces in an acoustical environment that may not be well-known. The PhD Thesis we present hereby is set in this purpose. We will study the ability of an inverse method, named iPTF (standing for inverse Patch Transfert Functions) used to solve this particular problem. In our first chapter we will present a bibliographical study of the different methods dealing with the resolution of similar problems. We will particularly underline the difficulties encountered with these methods, either regarding their practical application or their theoretical bases. The presentation of the iPTF method will be made in the second chapter. This presentation will be organized starting from the direct formulation, that is from the source to the radiated sound. This direct method is a sub-domai decomposition based approach, allowing the study of vibro-acoustical problems in low and mid frequencies. We will especially explain how the association of both direct and reverse formulation enables to identify the pressure, velocity and intensity fields on the source. The third chapter will concerne the presentation of the first identification results in a simple numerical application. In the fourth and fifth chapters, the main parameters conditioning the results given by our method will be studied. The first of these two chapters will introduce a calculation routine used to compute quickly the radiation field of a simple structure. This routine will then be used in our fifth chapter in order to build numerous fields having different characteristics. Using all these fields will let us know the stability of our method regarding different parameters. A sixth chapter will present a precise study of evanescent waves that constitute a non-neglectful part of the radiated field. According to their definition, those evanescent waves cannot be taken into account beyond the near-field, and this may be the reason of some difficulties while applying our method. The objective of the study herein presented is to determine the importance of those evanescent waves in the radiated field. We eventually present, in a last chapter, the results of experimental measures conducted during the preparation of this PhD Thesis.
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[en] PLC CHANNEL MODELLING / [pt] MODELAGEM DO CANAL PLCRODRIGO SILVA MELLO 11 July 2005 (has links)
[pt] O crescente interesse na utilização das redes de
distribuição de energia
elétrica como uma alternativa para o fornecimento de
serviços de
telecomunicações, tem motivado a pesquisa e o
desenvolvimento de sistemas
capazes de superar as características hostis deste
ambiente como canal de
comunicação. Com esta finalidade, este trabalho procura
estimar o
comportamento da rede PLC através da modelagem da função
de transferência do
canal, para a faixa de freqüência de 300 kHz a 30 MHz,
por
meio de um conjunto
de parâmetros, os quais podem ser deduzidos da medição
da
resposta em
freqüência. Dois modelos são apresentados para descrever
a
resposta em
freqüência complexa de típicos canais power line,
cobrindo
todos os efeitos que os
caracterizam, tais como o efeito de propagação por
multipercursos causado pelas
inúmeras reflexões nas junções da rede e o
desvanecimento
seletivo em
freqüência. Os experimentos revelam que estes modelos
apresentam todas as
características principais da rede PLC podendo
representar
ferramentas úteis e
efetivas na prática, oferecendo a possibilidade de
realizar pesquisas para
diferentes topologias de rede, a fim de estudar seu
impacto no sistema de
comunicação pela rede de energia elétrica. Além disso,
propõem-se modelos de
ajuste da função de transferência do canal a dados
empíricos pelo método dos
mínimos quadrados. / [en] The crescent interest on the utilization of the low
voltage power distribution
grid as an alternative to provide services of
telecommunication has motivated the
systems development able to surpass the hostile
characteristics of this
environment as a communication channel. Therefore, this
work seek to estimate
the behavior of PLC network (Power Line Communication)
through the modelling
of the channel transfer function, to the range of 300 kHz
to 30 MHz, by means of
a set of parameters, which can be derived from the measure
of the frequency
response. Two models are presented to describe the complex
frequency response
of power line channels, covering all effects that define
them, for example, the
multipaths propagation generated by uncountable
reflections on the network
connections and selective fading in the frequency. The
results of experiments
show that these models present the most important
characteristics of PLC
network, representing useful and effective tools in the
practice, offering the
possibility to do researches to different network
topologies, in order to study the
impact of these effects on the PLC system. Moreover,
they`re proposed channel
transfer function adjustment models through empiric data
and the least square
method.
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