Relevant bibliographies by topics / Dispersion functions / Dissertations / Theses

Dissertations / Theses on the topic 'Dispersion functions'

To see the other types of publications on this topic, follow the link: Dispersion functions.
Author: Grafiati
Published: 10 December 2022
Last updated: 28 January 2023

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles

Select a source type:

Consult the top 50 dissertations / theses for your research on the topic 'Dispersion functions.'

Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.

You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.

Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.

1

Alves, Claudia Marins. "Stochastic models for the treatment of dispersion in the atmosphere." Laboratório Nacional de Computação Científica, 2006. http://www.lncc.br/tdmc/tde_busca/arquivo.php?codArquivo=135.

Full text
Abstract:
Lagrangian stochastic models are a largely used tool in the study of passive substances dispersion inside the Atmospheric Boundary Layer. Its application is related to the trajectory computation of thousands of particles, that numerically simulate the dispersion of suspense substances in the atmosphere. In this study, the basic concepts related to the Lagrangian stochastic modelling are presented and discussed together with its main characteristics and its computational implementation, to the study of particles dispersion in the atmosphere. In a computational experiment, the obtained results are compared with observational data from the TRACT experiment, that took place in Europe in 1992. The input data needed for the dispersion model are extracted from simulations with the numerical weather forecast model RAMS. Dispersion over Rio de Janeiro region is also tested in a second experiment.
Modelos Lagrangianos estocásticos constituem ferramenta muito utilizada no estudo da dispersão de substâncias passivas na Camada Limite Atmosférica. Sua aplicação consiste em calcular a trajetória de milhares de partículas, que simulam numericamente a dispersão de uma substância em suspensão na atmosfera. Nesta tese, são apresentados e discutidos os conceitos básicos relacionados à Modelagem Lagrangiana Estocástica de Partículas, bem como suas principais características e sua implementação computacional, para o estudo da dispersão de partículas na atmosfera. Numa experimentação computacional, comparam-se os resultados obtidos com dados observacionais provenientes do experimento TRACT, realizado na Europa em 1992. Os dados de entrada necessários ao modelo de dispersão são extraídos de simulações do modelo de previsão numérica do tempo RAMS. A dispersão sobre o Estado do Rio de Janeiro é também testada em um segundo experimento.
APA, Harvard, Vancouver, ISO, and other styles
2

Tjulin, Anders. "Waves in space plasmas : Lower hybrid cavities and simple-pole distribution functions." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3527.

Full text
APA, Harvard, Vancouver, ISO, and other styles
3

Dreiling, Jennifer [Verfasser]. "Crustal structures in southern Madagascar and Sri Lanka in the context of Gondwana’s assembly and break-up : A study based on surface wave dispersion and receiver functions / Jennifer Dreiling." Berlin : Freie Universität Berlin, 2020. http://d-nb.info/121203175X/34.

Full text
APA, Harvard, Vancouver, ISO, and other styles
4

Goncalves, Juliana Bittencourt. "EMPREGO DE UM MODELO DE DISPERSÃO TURBULENTO NO ESTUDO DA UNIVERSALIDADE DA TAXA DE DISSIPAÇÃO DA ENERGIA." Universidade Federal de Santa Maria, 2010. http://repositorio.ufsm.br/handle/1/10254.

Full text
Abstract:
Conselho Nacional de Desenvolvimento Científico e Tecnológico
This study employed different autocorrelation functions and Maclaurin series expansions in the derivation of expressions describing the dissipation rate of turbulent kinetic energy. These expressions have the same functional form, but are described in terms of different numerical coefficients. The values obtained for the numerical coefficients were used in a Lagrangian stochastic dispersion model to simulate the dispersion of contaminants in the Planetary Boundary Layer (PBL). The simulation results were compared with concentration data observed in the Copenhagen experiment. The good performance of the parameterization and analysis through statistical indices showed that the mathematical relationships that describe the turbulent dissipation rate present an uncertainty. The analysis developed in this study indicates that there is no a universal functional form describing the dissipation rate of turbulent energy.
Neste estudo foram empregadas diferentes funções de autocorrelação e expansões em série de Maclaurin na derivação de expressões que descrevem a taxa de dissipação da energia cinética turbulenta. Estas expressões apresentam a mesma forma funcional, porém são descritas em termos de diferentes coeficientes numéricos. Os valores obtidos para os coeficientes numéricos foram empregados em um modelo de dispersão estocástico Lagrangiano para simular a dispersão de contaminantes na Camada Limite Planetária (CLP). Os resultados das simulações foram comparados com dados de concentração do experimento de Copenhagen. O bom desempenho da parametrização e a análise através de índices estatísticos permitiram concluir que as relações matemáticas que descrevem a taxa de dissipação da turbulenta, apresentam uma incerteza. A análise desenvolvida nesse estudo permite concluir que não existe uma forma funcional universal descrevendo a taxa de dissipação de energia turbulenta.
APA, Harvard, Vancouver, ISO, and other styles
5

Gibbons, Luke J. "Nanocomposite Dispersion: Quantifying the Structure-Function Relationship." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/77214.

Full text
Abstract:
The dispersion quality of nanoinclusions within a matrix material is often overlooked when relating the effect of nanoscale structures on functional performance and processing/property relationships for nanocomposite materials. This is due in part to the difficulty in visualizing the nanoinclusion and ambiguity in the description of dispersion. Understanding the relationships between the composition of the nanofiller, matrix chemistry, processing procedures and resulting dispersion is a necessary step to tailor the physical properties. A method is presented that incorporates high-contrast imaging, an emerging scanning electron microscopy technique to visualize conductive nanofillers deep within insulating materials, with various image processing procedures to allow for the quantification and validation of dispersion parameters. This method makes it possible to quantify the dispersion of various single wall carbon nanotube (SWCNT)-polymer composites as a function of processing conditions, composition of SWCNT and polymer matrix chemistry. Furthermore, the methodology is utilized to show that SWCNT dispersion exhibits fractal-like behavior thus allowing for simplified quantitative dispersion analysis. The dispersion analysis methodology will be corroborated through comparison to results from small angle neutron scattering dispersion analysis. Additionally, the material property improvement of SWCNT nanocomposites are linked to the dispersion state of the nanostructure allowing for correlation between dispersion techniques, quantified dispersion of SWCNT at the microscopic scale and the material properties measured at the macroscopic scale.
Ph. D.
APA, Harvard, Vancouver, ISO, and other styles
6

Johnson, Erin R. "A density-functional theory including dispersion interactions." Thesis, Kingston, Ont. : [s.n.], 2007. http://hdl.handle.net/1974/926.

Full text
APA, Harvard, Vancouver, ISO, and other styles
7

Alison, John Michael. "A dielectric study of lossy materials over the frequency range four to eighty-two gigahertz." Thesis, King's College London (University of London), 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263831.

Full text
APA, Harvard, Vancouver, ISO, and other styles
8

Mididoddi, Rajiv. "Investigation on material dispersion as a function of pressure and temperature for sensor design." ScholarWorks@UNO, 2004. http://louisdl.louislibraries.org/u?/NOD,109.

Full text
Abstract:
Thesis (M.S.)--University of New Orleans, 2004.
Title from electronic submission form. "A thesis ... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Electrical Engineering."--Thesis t.p. Vita. Includes bibliographical references.
APA, Harvard, Vancouver, ISO, and other styles
9

Nisa, Khoirin. "On multivariate dispersion analysis." Thesis, Besançon, 2016. http://www.theses.fr/2016BESA2025.

Full text
Abstract:
Cette thèse examine la dispersion multivariée des modelés normales stables Tweedie. Trois estimateurs de fonction variance généralisée sont discutés. Ensuite dans le cadre de la famille exponentielle naturelle deux caractérisations du modèle normal-Poisson, qui est un cas particulier de modèles normales stables Tweedie avec composante discrète, sont indiquées : d'abord par fonction variance et ensuite par fonction variance généralisée. Le dernier fournit la solution à un problème particulier d'équation de Monge-Ampère. Enfin, pour illustrer l'application de la variance généralisée des modèles Tweedie stables normales, des exemples à partir des données réelles sont fournis
This thesis examines the multivariate dispersion of normal stable Tweedie (NST) models. Three generalize variance estimators of some NST models are discussed. Then within the framework of natural exponential family, two characterizations of normal Poisson model, which is a special case of NST models with discrete component, are shown : first by variance function and then by generalized variance function. The latter provides a solution to a particular Monge-Ampere equation problem. Finally, to illustrate the application of generalized variance of normal stable Tweedie models, examples from real data are provided
APA, Harvard, Vancouver, ISO, and other styles
10

Pilemalm, Robert. "Dispersion forces in a four-component density functional theory framework." Thesis, Linköping University, Department of Physics, Chemistry and Biology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-18487.

Full text
Abstract:

The main purpose of this thesis is to implement the Gauss--Legendre quadrature for the dispersion coefficient. This has been done and can be now be made with different number of points. The calculations with this implementation has shown that the relativistic impact on helium, neon, argon and krypton is largest for krypton, that has the highest charge of its nucleus. It was also seen that the polarizability of neon as a function of the imaginary angular frequency decreases monotonically from a static value.

APA, Harvard, Vancouver, ISO, and other styles
11

Valencia, Germán Ayala. "Propriedades físicas de filmes à base de biopolímeros reforçados com laponita." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/74/74132/tde-31072017-094541/.

Full text
Abstract:
Os problemas ambientais provocados pelas embalagens à base de materiais sintéticos não biodegradáveis têm provocado um importante aumento nos estudos sobre filmes à base de biopolímeros. Entretanto, esses filmes têm limitações em suas propriedades, devido, sobretudo à sensibilidade a umidade relativa ambiente. Dentre as alternativas estudadas para melhorar as características desses materiais está o uso de nanopartículas, com destaque para a montmorilonita, que tem problemas de dispersão em água. Outra nanopartícula pouco usada em estudos à base de biopolímeros é a laponita, que é uma nanoargila sintética. Assim, o objetivo geral desta tese foi o desenvolvimento de filmes à base de biopolímeros (colágeno, gelatina e fécula de mandioca), reforçados com uma nanoargila (laponita). Foi estudado o efeito da concentração do biopolímero e da laponita, assim como o método de produção dos filmes (casting e espalhamento mecânico), além da qualidade da dispersão da nanopartícula, sobre as principais propriedades físicas dos filmes nanocompósitos, com especial interesse nas propriedades de superfície. Os filmes foram preparados pela desidratação de soluções formadoras de filmes (SFF), com 2, 4 ou 8 g de biopolímero/100 g SFF; 25 ou 30 g glicerol/100 g de biopolímero; e 0, 1,5; 3; 4,5 e 6 g laponita/100 g de biopolímero. A laponita foi dispersa em água destilada, utilizando-se ultraturrax com velocidade de agitação de 20.000 rpm, por 30 minutos. As partículas de laponita em água tiveram tamanhos menores que 50 nm. Não houve efeito da concentração do biopolímero, nem do método de produção (casting ou espalhamento mecânico) sob as propriedades de topografia superficial e físico-químicas estudadas nos filmes nanocompósitos. As análises de raios X e espectroscopia de infravermelho por transformada de Fourier revelaram que as plaquetas de laponita estiveram esfoliadas e/ou intercaladas nos filmes, e que não houve nenhuma formação de ligação química entre as plaquetas de laponita e os biopolímeros em estudo. A presença de laponita incrementou a irregularidade superficial dos filmes, especialmente naqueles produzidos com colágeno e fécula de mandioca. Outras propriedades dos filmes nanocompósitos, tais como densidade, umidade, cor, opacidade, propriedades térmicas, propriedades mecânicas, solubilidade em água, ângulo de contato à água, isotermas de sorção e permeabilidade ao vapor de água não sofreram alterações com a presença de laponita.
The environmental problems caused by packaging based on non-biodegradable synthetic materials have lead to a significant increase in studies about biopolymer films. However, these films have limited physicochemical properties due mainly to its sensitivity to ambient relative humidity. Among the alternatives studied to improve the physicochemical properties of these materials is the use of nanoparticles, especially the montmorillonite, which has problems of dispersion in water. Another nanoparticle no so much studied in films based on biopolymers is laponite, which is a synthetic nanoparticle. Thus, this these aims to development and characterize films based on biopolymers (collagen, gelatin and cassava starch), with a nanoparticle (laponite). The effects of biopolymer and laponite concentrations were studied, as well as, the film production method (casting and spreading), besides the quality of laponite dispersion and its relationship with the physicochemical properties of the films were investigated, with special interest on the surface properties. The films were produced by the dehydration of filmogenic-forming solutions (FFS), with 2, 4 or 8 g of biopolymer/100 g FFS; 25 or 30 g glycerol/100g of biopolymer; and 0, 1.5, 3, 4.5 and 6 g of laponite/100g of biopolymer. The laponite was dispersed in water using ultraturrax, at 20,000 rpm, for 30 minutes. The laponite particles in water had sizes smaller than 50 nm. There was not effect of biopolymer concentration and film production method (casting or spreading) on the surface and physicochemical properties studied in the nanocomposite films. X-ray analysis and Fourier transform infrared spectroscopy revealed that laponite platelets were exfoliated and/or intercalated in the films, and that there were no formed chemical bonds between laponite platelets and the biopolymers studied. The presence of laponite increased the surface irregularity of the films, especially in those produced with collagen and cassava starch. Other properties in the nanocomposite films, such density, moisture content, color, opacity, thermal properties, mechanical properties, water solubility, water contact angle, sorption isotherms and water vapor permeability were not altered by the presence of laponite.
APA, Harvard, Vancouver, ISO, and other styles
12

Kazemi, Noj. "Circuit analysis of a parallel plate waveguide." Thesis, KTH, Elektroteknisk teori och konstruktion, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-222617.

Full text
Abstract:
The aim of this work was to model a four-port waveguide as a simple circuit,by first starting with a two-port then a three-port waveguide. Duethat the work was based on Nathan Marcuvitz book Waveguide handbook,an analytical solution for the circuit parameters was desired. In order toobtain an analytical solution three methods were studied; the Variationalmethod, the Integral equation method and the Static method. Out of thesethree methods the latter was chosen, because its strength of simplifying theboundary conditions. The goal to model a four-port and a three-portedwaveguide was too complicated. This led to that the goal was changed totrying to get a higher accuracy on the existing circuit model for a two-portwaveguide, by solving an extension to the circuit parameter. This was donebecause Marcuvitz only treated the first two modes correctly and it was notclear if the circuit model was stable for the higher orders of Taylor series. Inthe end a circuit model for a waveguide with an iris that treats the first 16modes correctly was solved. By looking at the dispersive properties of thecircuit a comparison with simulation software CST Microwave Studio couldbe done, which resulted in that the circuit model gave good results up to2b/ < 1. It was also showed that the accuracy was about the same as thecircuit model found in Waveguide handbook, but it can be mentioned thatthe accuracy is minimally better for the circuit model that was developed inthis work. Something that was discovered in this work is that the restrictionmentioned in Waveguide handbook for the case when the window is centeredis unreliable, it should be 2b/ < 1. It also appeared that the circuit modelremained stable for higher orders of the Taylor series, in this case up to the16:th order.
M°alet med detta arbete var att modellera en fyr-portars v°agledare somen simpel elektrisk krets, genom att f¨orst b¨orja med en tv°a-portars sedantre-portars -v°agledare. Detta arbete var baserat p°a Nathan Marcuvitz bokWaveguide handbook, d¨arav s¨oktes det en analytisk l¨osning f¨or kretsparametrarna.F¨or att kunna f°a en analytisk l¨osning, studerades tre metoder;Variationsmetoden, Integralsekvationsmetoden samt den Statiskametoden.Av dessa tre metoder valdes den sistn¨amnda, p°a grund av dess styrka medatt f¨orenkla randvillkoren. M°alet att modellera en fyr-portars samt en treportarsv°agledare var alldeles f¨or komplicerat. Detta ledde till att m°alet¨andrades till att f¨ors¨oka f°a en h¨ogre precision p°a den befintliga kretsmodellenf¨or en tv°a portars v°agledare, genom att l¨osa ut flera termer till kretsparametern.Detta gjordes d°a Marcuvitz endast hanterade de tv°a f¨orstamoderna korrekt, samt att det inte framgick ifall kretsmodellen ¨ar stabil f¨orh¨ogre ordningar av Taylor serier. I slut¨andan l¨ostes en kretsmodel f¨or env°agledare med en iris som hanterar de f¨orsta 16 moderna korrekt. Genomatt kolla p°a de dispersiva egenskaperna f¨or kretsen, kunde en j¨amf¨orelse medsimuleringsprogrammet CST Microwave Studio ske, d¨ar slutsatsen blev attkretsmodellen gav goda resultat upp till 2b/ < 1. Det visade ¨aven sig attprecisionen var ungef¨ar densamma som den kretsmodell som°aterfinns i Waveguidehandbook, men det kan n¨amnas att precisionen ¨ar minimalt b¨attref¨or den kretsmodell som togs fram i detta arbete. En sak som uppt¨acktes underdetta arbete var att restriktionen som n¨amns i Waveguide handbook f¨orfallet n¨ar gapet f¨or irisen ¨ar centrerad st¨ammer inte, den b¨or vara 2b/ < 1.Dessutom visade det sig att kretsmodellen fortfarande var stabil f¨or h¨ogreordningar av Taylorserier, i detta fall upp till den 16:e ordningen.
APA, Harvard, Vancouver, ISO, and other styles
13

Dobson, Benjamin Pirnie. "Dispersions of graphene for use as thermal and functional fluids." Thesis, Durham University, 2018. http://etheses.dur.ac.uk/12570/.

Full text
Abstract:
Graphene's combination of properties makes it a material with great potential in a wide range of applications. High thermal conductivity and good tribological properties mean graphene has been proposed as an additive for both lubricants and thermal fluids; being used to form nanofluids with improved properties. However, the use of graphene in these applications requires the significant challenge of dispersing graphene in applied fluids to be overcome. In this work graphene, and its functionalised derivatives were dispersed in both polar and non-polar fluids using a range of techniques, following which the properties of these fluids were analysed. Initially, the dispersibility of reduced graphene oxide (rGO) in water was investigated and a novel method of using N-methyl-2-pyrrolidone (NMP)to act as a dispersant for rGO in polar fluids was developed. Using this method dispersions of rGO in water were produced at over six times the concentration possible by standard dispersion. Working in more applied fluids efforts were made to improve the dispersibility of graphene materials in applied polar fluids such as oils. Stable dispersions of graphene materials in commercial oils were produced through functionalisation of graphene, with a range of reagents, to improve its compatibility with non-polar solvents. These functionalised graphenes were then dispersed in commercial lubricants to form stable dispersions and the tribological properties of these dispersions were tested showing that it was possible for functionalised graphenes to improve the performance of commercial lubricants. To assess the impact of graphene on the thermal properties of applied fluids dispersions of graphene materials were prepared in a commercial coolant. The thermal properties of this nanofluid were then determined and it was shown that the addition of graphene materials can improve the thermal properties of applied fluids.
APA, Harvard, Vancouver, ISO, and other styles
14

Patra, Abhirup. "Surface properties, adsorption, and phase transitions with a dispersion-corrected density functional." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/516784.

Full text
Abstract:
Physics
Ph.D.
Understanding the “incomprehensible” world of materials is the biggest challenge to the materials science community. To access the properties of the materials and to utilize them for positive changes in the world are of great interest. Often scientists use approximate theories to get legitimate answers to the problems. Density functional theory (DFT) has emerged as one of the successful and powerful predictive methods in this regard. The accuracy of DFT relies on the approximate form of the exchange-correlation (EXC) functional. The most complicated form of this functional can be as accurate as more complicated and computationally robust method like Quantum Monte Carlo (QMC), Random Phase Approximation (RPA). Two newest meta-GGAs, SCAN and SCAN+rVV10 are among those functionals. Instantaneous charge fluctuation between any two objects gives rise to the van der Waals (vdW) interactions (often termed as dispersion interactions). It is a purely correlation effect of the interacting electrons and thus non-local in nature. Despite its small magnitude it plays a very important role in many systems such as weakly bound rare-gas dimers, molecular crystals, and molecule-surface interaction. The traditional semi-local functionals can not describe the non-local of vdW interactions; only short- and intermediate-range of the vdW are accounted for in these functionals. In this thesis we investigate the effect of the weak vdW interactions in surface properties, rare-gas dimers and how it can be captured seamlessly within the semi-local density functional approximation. We have used summed-up vdW series within the spherical-shell approximation to develop a new vdW correction to the meta-GGA-MS2 functional. This method has been utilized to calculate binding energy and equilibrium binding distance of different homo- and hetero-dimers and we found that this method systematically improves the MGGA-MS2 results with a very good agreement with the experimental data. The binding energy curves are plotted using this MGGA-MS2, MGGA-MS2-vdW and two other popular vdW-corrected functionals PBE-D2, vdW-DF2. From these plots it is clear that our summed-up vdW series captures the long-range part of the binding energy curve via C6, C8, and, C10 coefficients. The clean metallic surface properties such as surface energy, work functions are important and often play a crucial role in many catalytic reactions. The weak dispersion interactions present between the surfaces has significant effect on these properties. We used LDA, PBE, PBSEsol, SCAN and SCAN+rVV10 to compute the clean metallic surface properties. The SCAN+rVV10 seamlessly captures different ranges of the vdW interactions at the surface and predicts very accurate values of surface energy ( ) , and work function (𝞥) and inter-layer relaxations (𝞭%). Our conclusion is adding non-local vdW correction to a good semi-local density functional such as SCAN is necessary in order to predict the weak attractive vdW forces at the metallic surface. The SCAN+rVV10 has also been employed to study the hydrogen evolution reaction (HER) on 1T-MoS2. We have chosen as a descriptor differential Gibbs free energy (𝚫 GH ) to understand the underlying mechanism of this catalytic reaction. Density functional theory calculations agree with the experimental findings. In the case of layered materials like 1T-MoS2, vdW interactions play an important role in hydrogen binding, that SCAN+rVV10 calculation was able to describe precisely. We have also used SCAN and SCAN+rVV10 functionals to understand bonding of CO on (111) metal surfaces, where many approximations to DFT fail to predict correct adsorption site and adsorption energy. In this case SCAN and SCAN+rVV10 do not show systematic improvements compared to LDA or PBE, rather, both SCAN and SCAN+rVV10 overbind CO more compared to PBE but less compared to the LDA. This overbinding of CO is associated with the incorrect charge transfer from metal to molecule and presumably comes from the density-driven self-interaction error of the functionals. In this thesis we assessed different semi-local functionals to investigate molecule surface systems of 𝞹-conjugated molecules (thiophene, pyridine) adsorbed on Cu(111), Cu(110), Cu(100) surfaces. We find the binding mechanism of these molecules on the metallic surface is mediated by short and intermediate range vdW interactions. Calculated values of binding energies and adsorbed geometries imply that this kind of adsorption falls in the weak chemisorption regime. Structural phase transitions due to applied pressure are very important in materials science. However, pressure induced structural phase transition in early lanthanide elements such as Ce are considered as abnormal first order phase transition. The Ce 𝝰-to-𝝲 isostructural phase transition is one of them. The volume collapse and change of magnetic properties associated with this transition are mediated by the localized f-electron. Semi-local density functionals like LDA, GGA delocalize this f-electron due to the inherent self-interaction error (SIE) of these functionals. We have tested the SCAN functional for this particular problem, and, it was found that the spin-orbit coupling calculations with SCAN not only predicts the correct magnetic ordering of the two phases, but also gives a correct minima for the high-pressure 𝝰-Ce phase and a shoulder for the low-pressure 𝝲-Ce phase.
Temple University--Theses
APA, Harvard, Vancouver, ISO, and other styles
15

Moor, Lilian Piecha. "Proposta de uma nova função de autocorrelação para o estudo do meandro do vento horizontal." Universidade Federal de Santa Maria, 2016. http://repositorio.ufsm.br/handle/1/3935.

Full text
Abstract:
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
In this study is propose a new mathematical expression to describe the observed meandering autocorrelation functions in low-wind speed. The analysis utilizes a large number of the data to show that the new proposed theoretical function reproduces the experimental behavior of the fit curves, well as the negative lobes that characterizing the autocorrelation function for meandering condition. Furthermore, the good agreement of the measured autocorrelation curves with the proposed algebraic autocorrelation function allows to calculate the magnitudes of the meandering period and of the loop parameter. In adition, the parameters founded in this study can be used to simulate the dispersion of contaminant during low wind episodes. The results agree with the values presented and discussed in the literature.
O presente estudo propõe uma nova expressão matemática para descrever as funções de autocorrelação observadas sob condições de meandro do vento horizontal. A análise utiliza um grande número de dados para demonstrar que a função proposta reproduz o comportamento da curva experimental, bem como os lóbulos negativo que caracterizam a função de autocorrelação para a situação de meandro. Além disso, a boa concordância entre as curvas de autocorrelação observadas e a nova função de autocorrelação algébrica, proposta neste trabalho, permitiu realizar o cálculo de grandezas físicas como o parâmetro de oscilação e o período de meandro. Um resultado adicional, foi empregar os valores médios encontrados para os parâmetros do meandro na simulação da dispersão de contaminante durante episódios de vento fraco. Os resultados encontrados estão de acordo com os valores apresentados e discutidos na literatura.
APA, Harvard, Vancouver, ISO, and other styles
16

Carpentier, Florence. "Modélisations de la dispersion du pollen et estimation à partir de marqueurs génétiques." Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20101.

Full text
Abstract:
La dispersion du pollen est une composante majeure des flux de gènes chez les plantes, contribuant à la diversité génétique et à sa structure spatiale. Son étude à l'échelle d'un épisode de reproduction permet de comprendre l'impact des changements actuels (fragmentation, anthropisation....) et de proposer des politiques de conservation. Deux types de méthodes basées sur les marqueurs microsatellites estiment la fonction de dispersion du pollen: (i) les méthodes directes (e.g. mating model) basées sur l'assignation de paternité et nécessitant un échantillonnage exhaustif (position et génotype des individus du site étudié, génotypes de graines échantillonnées sur des mères); (ii) les méthodes indirectes (e.g. TwoGener), nécessitant un échantillonnage réduit (génotypes des graines, génotypes et positions des mères) et résumant les données en indices génétiques. Nous proposons la formalisation statistique de ces deux types de méthodes et montrons qu'elles utilisent des fonctions de dispersion différentes: les méthodes directes estiment une fonction forward potentielle (déplacement du pollen depuis le père), les méthodes indirectes une fonction backward intégrative (de la fécondation jusqu'à l'existence du père). Nous explicitons le lien entre fonctions backward et forward, des hypothèses menant à leur équivalence, et des contraintes affectant les fonctions backward. Nous développons enfin une méthode de calcul bayésien approché qui permet (i) une estimation forward, (ii) avec des intervalles de crédibilité, (iii) à partir d'un jeu de données non exhaustif et d'informations partielles (e.g. positions sans génotype) et (iv) l'utilisation de différents modèles de dispersion
Pollen dispersal is a major component of gene flow in plants. It determines to genetic diversity and spatial genetic structure.Studying it at the scale of a single reproduction event enables to understand the impact of current changes (fragmentation, anthropization ...) and to propose conservation practices.Two types of methods, based on microsatellite markers, estimate pollen dispersal functions : (i) direct methods (e.g. mating model) based on paternity assignment require exhaustif sampling (position and genotype of individuals in the study plot, genotypes of seeds harvested on mothers); (ii) indirect methods (e.g. TwoGener), require a weaker sampling (seeds genotypes, genotypes and positions of their mothers) and summarize data through genetic indices.We propose a statistical formalization of both types of methods and show that they rely on different dispersal functions : the direct methods estimate a potential forward function (pollen transfer from the father), whereas the indirect methods estimate an integrative backward one (from fecondation to father existence). We exhibit the link between forward and backward functions, assumptions leading to their equivalence and constrains affecting the backward functions.Finally, we develop an Approximate Bayesian Computation method, which enable (i) a forward estimation, (ii) with credibility intervals, (iii) from a non exhaustive dataset and partial information (e.g. positions without genotypes) and (iv) the use of different dispersal models
APA, Harvard, Vancouver, ISO, and other styles
17

Hermann, Jan. "Towards unified density-functional model of van der Waals interactions." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/18706.

Full text
Abstract:
Van der Waals-Wechselwirkungen (vdW) sind allgegenwärtig und spielen eine zentrale Rolle in einer großen Anzahl biologischer und moderner synthetischer Materialien. Die am weitesten verbreitete theoretische Methode zur Berechnung von Materialeigenschaften, die Dichtefunktionaltheorie (DFT) in semilokaler Näherung, vernachlässigt diese Wechselwirkungen jedoch größtenteils, was zur Entwicklung vieler verschiedener vdW-Modelle führte. Die hier vorgestellte Arbeit ebnet den Weg hin zu einem vereinheitlichten vdW-Modell welches die besten Elemente der unterschiedlichen Klassen von vdW-Modellen vereint. Zu diesem Zweck haben wir einen vereinheitlichten theoretischen Rahmen geschaffen, der auf dem Reichweite-separierten Adiabatischer-Zusammenhang-Fluktuations-Dissipations-Theorem aufbaut und die meisten existierenden vdW-Modelle umfasst. Wir analysieren die MBD-korrelierte Wellenfunktion am prototypischen Beispiel von π–π-Wechselwirkungen in supramolekularen Komplexen und stellen fest, dass diese Wechselwirkungen größtenteils durch delokalisierte kollektive Ladungsfluktuationen entstehen. Um zu dem langreichweitigen vdW-Modell ein ausgewogenes kurzreichweitiges Dichtefunktional zu identifizieren, präsentieren wir eine umfassende Untersuchung zum Zusammenspiel der kurz- und langreichweitigen Energiebeiträge in acht semilokalen Funktionalen und drei vdW-Modellen für eine große Spanne von Systemen. Die Bindungsenergieprofile vieler der DFT+vdW-Kombinationen unterscheiden sich sowohl quantitativ als auch qualitativ stark voneinander. Schließlich untersuchen wir die Performance des Vydrov–Van Voorhis-Polarisierbarkeitsfunktionals über das Periodensystem der Elemente hinweg und identifizieren eine systematische Unterschätzung der Polarisierbarkeiten und vdW-C₆-Koeffizienten für s- und d-Block-Elemente. Als Lösung entwickeln wir eine orbitalabhängige Verallgemeinerung des Funktionals.
The ubiquitous long-range van der Waals interactions play a central role in nearly all biological and modern synthetic materials. Yet the most widely used theoretical method for calculating material properties, the density functional theory (DFT) in semilocal approximation, largely neglects these interactions, which motivated the development of many different vdW models. The work in this thesis paves way towards a unified vdW model that combines best elements from the different classes of the vdW models. To this end, we developed a unified theoretical framework based on the range-separated adiabatic-connection fluctuation--dissipation theorem that encompasses most existing vdW models. We analyze the MBD correlated wave function on the prototypical case of π–π interactions in supramolecular complexes and find that these interactions are largely driven by delocalized collective charge fluctuations. To identify a balanced short-range density functional to accompany the long-range vdW model, we present a comprehensive study of the interplay between the short-range and long-range energy contributions in eight semilocal functionals and three vdW models on a wide range of systems. The binding-energy profiles of many of the DFT+vdW combinations differ both quantitatively and qualitatively, and some of the qualitative differences are independent of the choice of the vdW model. Finally, we investigate the performance of the Vydrov—Van Voorhis polarizability functional across the periodic table, identify systematic underestimation of the polarizabilities and vdW C₆ coefficients for s- and d-block elements, and develop an orbital-dependent generalization of this functional to resolve the issue.
APA, Harvard, Vancouver, ISO, and other styles
18

Gunasinghe, Rosi Najeela. "Structural and electronic properties of boron nano structures: A dispersion-corrected density functional study." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2012. http://digitalcommons.auctr.edu/dissertations/341.

Full text
Abstract:
We have revisited the general constructing schemes for a large family of stable hollowboron fullerenes with 80 + 8n (n = 0,2,3,...) atoms. In contrast to the hollow pentagon boron fullerenes with 12 hollow pentagons, the stable boron fullerenes constitute 12 filled pentagons and 12 additional hollow hexagons, which are more stable than the empty pentagon boron fullerenes including the “magic” B80 buckyball. Based on results from first-principles density-functional calculations, an empirical rule for filled pentagons is proposed along with a revised electron counting scheme to account for the improved stability and the associated electronic bonding feature. We have also studied the relative stability of various boron fullerene structures and structural and electronic properties of B80 bucky ball and boron nanotubes via dispersion-corrected density-functional calculations. Our results reveal that the energy order of fullerenes strongly depends on the exchange-correlation functional employed in the calculation and the vibrational stability for the icosahedral B80 with the inclusion of dispersion corrections, in contrast to the instability to a tetrahedral B80 with puckered capping atoms from preceding density functional theory calculations. Similarly, the dispersion-corrected density-functional calculations yield non-puckered boron nanotube conformations and an associated metallic state for zigzag tubes. A systematic study elucidates the importance of incorporating dispersion forces to account for the intricate interplay of two and three centered bonding in boron nanostructures.
APA, Harvard, Vancouver, ISO, and other styles
19

Edwards, Angela Celeste. "Probing the Hydrogen Bonding Interaction at the Gas-Surface Interface using Dispersion Corrected Density Functional Theory." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/71784.

Full text
Abstract:
he interactions of the chemical warfare agent sulfur mustard with amorphous silica were investigated using electronic structure calculations. In this thesis, the binding energies of sulfur mustard and mimic species used in the laboratory were calculated using density functional theory and fully ab initio calculations. The wB97XD and B97D functionals, which include functions to account for long-range dispersion interactions, were compared to experimental trends. The hydroxylated amorphous silica surface was approximated using a gas-phase silanol molecule and clusters containing a single hydroxyl moiety. Recent temperature programmed desorption experiments performed in UHV concluded that sulfur mustard and its less toxic mimics undergo molecular adsorption to amorphous silica. Hydrogen bonding can occur between surface silanol groups and either the sulfur or chlorine atom of the adsorbates, and the calculations indicate that the binding energies for the two hydrogen bond acceptors are similar. The adsorption of sulfur mustard and its mimics on silica also exhibits the presence of significant van der Waals interactions between alkyl of the adsorbates and the surface. These interactions, in combination with the formation of a hydrogen bond between a surface silanol group and the Cl or S atoms of the adsorbates, provide remarkably large binding energies.
Master of Science
APA, Harvard, Vancouver, ISO, and other styles
20

Kim, Jeong-Han. "Optical display of the Airy function and transient wave propagation in a dispersive medium." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-02132009-172038/.

Full text
APA, Harvard, Vancouver, ISO, and other styles
21

Othman, Rahimah. "Production of functional pharmaceutical nano/micro-particles by solvent displacement method using advanced micro-engineered dispersion devices." Thesis, Loughborough University, 2016. https://dspace.lboro.ac.uk/2134/22905.

Full text
Abstract:
The rapid advancement of drug delivery systems (DDS) has raised the possibility of using functional engineered nano/micro-particles as drug carriers for the administration of active pharmaceutical ingredients (APIs) to the affected area. The major goals in designing these functional particles are to control the particle size, the surface properties and the pharmacologically active agents release in order to achieve the site-specification of the drug at the therapeutically optimal rate and dose regimen. Two different equipment (i.e. glass capillary microfluidic device and micro-engineered membrane dispersion cell) were utilised in this study for the formation of functional nano/micro-particles by antisolvent precipitation method. This method is based on micromixing/direct precipitation of two miscible liquids, which appear as a straightforward method, rapid and easy to perform, does not require high stirring rates, sonication, elevated temperatures, surfactants and Class 1 solvents can be avoided. Theoretical selection of a good solvent and physicochemical interaction between solvent-water-polymer with the aid of Bagley s two-dimensional graph were successfully elucidated the nature of anti-solvent precipitation method for the formation of desired properties of functional pharmaceutical nano/micro-engineered particles. For the glass capillary microfluidic experiment, the organic phase (a mixture of polymer and tetrahydrofuran/acetone) was injected through the inner glass capillary with a tapered cross section culminated in a narrow orifice. The size of nanoparticles was precisely controlled by controlling phase flow rates, orifice size and flow configuration (two- phase co-flow or counter-current flow focusing). The locations at which the nanoparticles would form were determined by using the solubility criteria of the polymer and the concentration profiles found by numerical modelling. This valuable results appeared as the first computational and experimental study dealing with the formation of polylactide (PLA) and poly(ε-caprolactone) (PCL) nanoparticles by nanoprecipitation in a co-flow glass capillary device. The optimum formulations and parameters interactions involved in the preparation of paracetamol encapsulated nanoparticles (PCM-PCL NPs) using a co-flow microfluidic device was successfully simulated using a 25-full factorial design for five different parameters (i.e. PCL concentration, orifice size, flow rate ratios, surfactant concentration and paracetamol amount) with encapsulation efficiency and drug loading percentage as the responses. PCM-loaded composite NPs composed of a biodegradable poly(D,L-lactide) (PLA) polymer matrix filled with organically modified montmorillonite (MMT) nanoparticles were also successfully formulated by antisolvent nanoprecipitation in a microfluidic co-flow glass capillary device. The incorporation of MMT in the polymer matrix improved the drug encapsulation efficiency and drug loading, and extended the rate of drug release in simulated intestinal fluid (pH 7.4). The encapsulation of MMT and PCM in the NPs were well verified using transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), x-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). PCL drug-carrier nanoparticles were also produced by rapid membrane micromixing combined with nanoprecipitation in a stirred cell employing novel membrane dispersion. The size of the NPs was precisely controlled by changing the aqueous-to-organic volumetric ratio, stirring rate, transmembrane flux, the polymer content in the organic phase, membrane type and pore morphologies. The particle size decreased by increasing the stirring rate and the aqueous-to-organic volumetric ratio, and by decreasing the polymer concentration in the aqueous phase and the transmembrane flux. The existence of the shear stress peak within a transitional radius and a rapid decline of the shear stress away from the membrane surface were revealed by numerical modelling. Further investigation on the PCL nanoparticles loaded immunosuppressive rapamycin (RAPA) drug were successfully synthesised by anti-solvent nanoprecipitation method using stainless steel (SS) ringed micro-engineered membrane. Less than 10 μm size of monohydrate piroxicam (PRX) micro-crystals also was successfully formed with the application of anti-solvent precipitation method combined with membrane dispersion cell that has been utilised in the formation of functional engineered nanoparticles. This study is believed to be a new insight into the development of integrated membrane crystallisation system.
APA, Harvard, Vancouver, ISO, and other styles
22

Forsythe, Martin Blood Zwirner. "Advances in Ab Initio Modeling of the Many-Body Effects of Dispersion Interactions in Functional Organic Materials." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:26718708.

Full text
Abstract:
Accurate treatment of the long-range electron correlation energy, including dispersion interactions, is essential for describing the structure, dynamics, and function of a wide variety of systems. Among the most accurate models for including dispersion into density functional theory (DFT) is the range-separated many-body dispersion (MBD) method [A. Ambrosetti et al., J. Chem. Phys. 2014, 140, 18A508], in which the long-range correlation energy is computed from a model system of coupled quantum harmonic oscillators. In this work, we seek to extend the applicability of the MBD model by developing the analytical gradients necessary to compute MBD corrections to ionic forces, unit-cell stresses, phonon modes, and self-consistent updates to the Kohn-Sham potential. We include all implicit coordinate dependencies arising from charge density partitioning, as we find that neglecting these terms leads to unacceptably large relative errors in the MBD forces. Such errors would impact the predictive nature of ab initio molecular dynamics simulations employing MBD. We develop a new efficient implementation of the MBD correlation energy and forces within the Quantum ESPRESSO software package and rigorously test its numerical stability and convergence properties for condensed phase simulations. Additionally, we re-parameterize the MBD model for use with a wide variety of generalized gradient approximation exchange-correlation functionals. We demonstrate the efficiency and accuracy of these MBD gradient corrections for optimizations of isolated dispersively bound molecular systems, as well as representative condensed phase systems including adsorbed hydrocarbons, layered materials, and hydrogen-bonded crystals. Where highly accurate reference geometries are available, we find the DFT+MBD method significantly improves the predicted structures of these systems and consistently outperforms popular pairwise-additive DFT-D dispersion corrections. Though significant work remains in the benchmarking and testing of these contributions to the MBD model, we are optimistic that these methodological developments will enable many exciting discoveries of beyond-pairwise dispersive effects in organic materials.
Physics
APA, Harvard, Vancouver, ISO, and other styles
23

Lucena, Rodrigo Ferreira de. "Avaliações e testes dos métodos MASW e ReMi por meio do tratamento de dados empíricos e sintéticos em um programa de processamento e inversão desenvolvido em MATLAB e sua implicação em um problema geológico na Bacia de Taubaté." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/44/44138/tde-17062016-135652/.

Full text
Abstract:
Os métodos de ondas superficiais com ênfase nas ondas Rayleigh foram utilizados como o núcleo desse trabalho de Doutorado. Inicialmente, as ondas Rayleigh foram modeladas permitindo o estudo de sensibilidade de suas curvas de dispersão sob diferentes configurações de parâmetros físicos representando diversos modelos de camadas, em que pôde ser observado parâmetros com maior e menor sensibilidade e também alguns efeitos provocados por baixas razões de Poisson. Além disso, na fase de inversão dos dados a modelagem das ondas Rayleigh foi utilizada para a construção da função objeto, que agregada ao método de mínimos quadrados, a partir do método de Levenberg-Marquardt, permitiu a implementação de um algoritmo de busca local responsável pela inversão de dados das ondas superficiais. Por se tratar de um procedimento de busca local, o algoritmo de inversão foi complementado por uma etapa de pré-inversão com a geração de um modelo inicial para que o procedimento de inversão fosse mais rápido e eficiente. Visando uma eficiência ainda maior do procedimento de inversão, principalmente em modelos de camadas com inversão de velocidades, foi implementado um algoritmo de pós-inversão baseado em um procedimento de tentativa e erro minimizando os valores relativos da raiz quadrada do erro quadrático médio (REQMr) da inversão dos dados. Mais de 50 modelos de camadas foram utilizados para testar a modelagem, a pré-inversão, inversão e pós-inversão dos dados permitindo o ajuste preciso de parâmetros matemáticos e físicos presentes nos diversos scripts implementados em Matlab. Antes de inverter os dados adquiridos em campo, os mesmos precisaram ser tratados na etapa de processamento de dados, cujo objetivo principal é a extração da curva de dispersão originada devido às ondas superficiais. Para isso, foram implementadas, também em Matlab, três metodologias de processamento com abordagens matemáticas distintas. Essas metodologias foram testadas e avaliadas com dados sintéticos e reais em que foi possível constatar as virtudes e deficiências de cada metodologia estudada, bem como as limitações provocadas pela discretização dos dados de campo. Por último, as etapas de processamento, pré-inversão, inversão e pós-inversão dos dados foram unificadas para formar um programa de tratamento de dados de ondas superficiais (Rayleigh). Ele foi utilizado em dados reais originados pelo estudo de um problema geológico na Bacia de Taubaté em que foi possível mapear os contatos geológicos ao longo dos pontos de aquisição sísmica e compará-los a um modelo inicial existente baseado em observações geomorfológicas da área de estudos, mapa geológico da região e informações geológicas globais e locais dos movimentos tectônicos na região. As informações geofísicas associadas às geológicas permitiram a geração de um perfil analítico da região de estudos com duas interpretações geológicas confirmando a suspeita de neotectônica na região em que os contatos geológicos entre os depósitos Terciários e Quaternários foram identificados e se encaixaram no modelo inicial de hemi-graben com mergulho para Sudeste.
The surface wave methods to Rayleigh waves were used as the center of this Doctoral work. Initially, the Rayleigh waves were modeled, what enabled the study of the sensitivity of dispersion curves about different sets of physical parameters representing several layer models, wherein it could be observed parameters with higher and lower sensitivity and also some effects caused by low Poisson ratios. Moreover, in the data inversion step the Rayleigh modeling was used for the construction of the object function, that aggregate to the least-squares method, by Levenberg-Marquardt, allowed the implementation of a local search algorithm responsible for data inversion of the surface waves. By reason of being a local search procedure, the data inversion algorithm was complemented with a pre-inversion step wherein an initial model was generated so that the inversion procedure was faster and efficient. Seeking a more efficiency of the inversion procedure, mainly to layer models with velocities inversion, it was implemented a post-inversion algorithm based in a trial and error procedure minimizing the values of the relative Root Mean Squared Error (rRMSE) of the data inversion. More than 50 layer models were used to test the data modeling, pre-inversion, inversion and post-inversion allowing the precise fit of the mathematical and physical parameters present in the several scripts implemented in Matlab. Before to invert the field-acquired data, they need to be treated in the data processing step, whose main aim is the extraction of the dispersion curve caused due the surface waves. For this, three processing methodologies with different mathematical approaches were implemented, also in Matlab. These methodologies were tested and evaluated with synthetic and real data and it was possible to find their strengths and weaknesses, as well as the limitations caused by discretization of the field data. Lastly, the data processing, pre-inversion, inversion and post-inversion steps were unified to form a complete data treatment program of surface waves (Rayleigh). It was used to real data originated by study of a geological problem in the Bacia de Taubaté wherein it was possible to map the geologic contacts along of the seismic acquisition points. The results were compared to an existing initial model based in geomorphological observations of the study area, geological map and global and local geologic information of the tectonic movements in the region. The geophysical The surface wave methods to Rayleigh waves were used as the center of this Doctoral work. Initially, the Rayleigh waves were modeled, what enabled the study of the sensitivity of dispersion curves about different sets of physical parameters representing several layer models, wherein it could be observed parameters with higher and lower sensitivity and also some effects caused by low Poisson ratios. Moreover, in the data inversion step the Rayleigh modeling was used for the construction of the object function, that aggregate to the least-squares method, by Levenberg-Marquardt, allowed the implementation of a local search algorithm responsible for data inversion of the surface waves. By reason of being a local search procedure, the data inversion algorithm was complemented with a pre-inversion step wherein an initial model was generated so that the inversion procedure was faster and efficient. Seeking a more efficiency of the inversion procedure, mainly to layer models with velocities inversion, it was implemented a post-inversion algorithm based in a trial and error procedure minimizing the values of the relative Root Mean Squared Error (rRMSE) of the data inversion. More than 50 layer models were used to test the data modeling, pre-inversion, inversion and post-inversion allowing the precise fit of the mathematical and physical parameters present in the several scripts implemented in Matlab. Before to invert the field-acquired data, they need to be treated in the data processing step, whose main aim is the extraction of the dispersion curve caused due the surface waves. For this, three processing methodologies with different mathematical approaches were implemented, also in Matlab. These methodologies were tested and evaluated with synthetic and real data and it was possible to find their strengths and weaknesses, as well as the limitations caused by discretization of the field data. Lastly, the data processing, pre-inversion, inversion and post-inversion steps were unified to form a complete data treatment program of surface waves (Rayleigh). It was used to real data originated by study of a geological problem in the Bacia de Taubaté wherein it was possible to map the geologic contacts along of the seismic acquisition points. The results were compared to an existing initial model based in geomorphological observations of the study area, geological map and global and local geologic information of the tectonic movements in the region. The geophysical information associated with geological information allowed the generation of an analytical profile of the study region with two geological interpretation confirming the suspect of neotectonic movements in the region wherein the geological contacts between the quaternary and tertiary deposits were identified and they agreed with the initial model of a hemi-graben with dip to Southeast.
APA, Harvard, Vancouver, ISO, and other styles
24

Barbosa, Itamar Magno. "Estudo das dispersões metrológicas em redes neurais artificiais do tipo Multilayer Perceptrons através da aplicação em curvas de calibração." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/3/3142/tde-12082010-113757/.

Full text
Abstract:
Este trabalho é um estudo das dispersões metrológicas em aproximações de funções tidas como não conhecidas ou não totalmente conhecidas. A metodologia alternativa para esse fim são as redes neurais artificiais do tipo Multilayer Perceptrons (MLP), aqui utilizadas como aproximadoras de funções. As funções aproximadas são curvas de calibração decorrentes de indicações de instrumentos ou sistemas de medição numa calibração. Essas curvas levam consigo propriedades metrológicas e possuem, neste trabalho, papel de ponte entre os elementos considerados da teoria metrológica e os elementos considerados da teoria da Inteligência Computacional: as Multilayer Perceptrons (MLPs). Uma balança externa de medição de esforços aerodinâmicos e uma Língua Eletrônica (LE), aplicada na medição da concentração de cátions, foram os meios de aplicação dos conceitos dessa metodologia alternativa. As proposições desta tese visam implementar melhorias na exatidão do ajuste das curvas de calibração por meio da consideração dos seguintes fatores: grandezas de influências, incertezas nos Valores Objetivos (VOs), tendência de medição de erros sistemáticos ocultos ou não solvidos e indicadores de desempenho metrológicos. A indicação da qualidade na medição ou a indicação da competência metrológica de um laboratório de calibração é estabelecida pelos valores das incertezas, e a curva de calibração é o ponto de partida para os cálculos desses valores. Visto que o estabelecimento dessa curva é uma das dificuldades para o cálculo das incertezas e a própria curva é uma fonte de incerteza, sua aproximação requer uma a cuidadosa e meticulosa metodologia, daí a importância estratégica deste trabalho. As dispersões metrológicas possuem conotação de incertezas nas medições e elas são a base para a determinação de seu valor numérico; assim, os indicadores de desempenho podem representar essas dispersões e a recíproca também é verdadeira: a incerteza padrão pode ser um dos indicadores de desempenho. Sintetizando, nesta tese é mostrado de que forma a teoria da inteligência computacional adentra na teoria da metrologia e vice versa, nas esferas dos elementos aqui considerados.
The present study investigates metrological dispersions in fitting partially or totally unknown functions. An alternative method is the application of a multilayer perceptron neural network used here to fit functions. The fitting functions are calibration curves from calibration indications of measurement systems or instruments. These curves hold metrological properties and establish a link between elements of Metrological theory and elements of Computing Intelligence theory: the Multilayer Perceptrons. An external balance of aerodynamic forces and moments and an electronic tongue applied in the measurement of cation concentrations were the measurement systems used to apply the concepts of this alternative methodology. This thesis proposes improvements in the accuracy of fitting calibration curves considering the following factors: influence quantities, uncertainties about target values, tendency of hidden or not solved systematic errors and metrological performance functions. The measurement quality indicator or the laboratory metrological competence indicator is established by uncertainty values and the calibration curve is the starting point for the calculation of these values. The establishment of this curve is one of the difficulties in assessing uncertainties and the curve itself is an uncertainty source. Therefore, a careful and meticulous methodology is necessary in curve approximation, which explains the strategic importance of this work. Metrological dispersions have connotation of uncertainty in measurements and are the basis for calculating their numerical values, the performance functions can represent metrological dispersions and the opposite is also true: the standard uncertainty can be a performance function. Making a synthesis, this thesis demonstrates how computing intelligence theory takes into account the metrological theory and vice versa, in the elements of these theories that were discussed in the present study.
APA, Harvard, Vancouver, ISO, and other styles
25

Campos, Vanessa Ellen Wendt [UNESP]. "O efeito da fragmentação na diversidade específica e funcional de primatas no Brasil." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/141536.

Full text
Abstract:
Submitted by VANESSA ELLEN WENDT CAMPOS null (vanessaellen@hotmail.com) on 2016-07-14T18:11:05Z No. of bitstreams: 1 Vanessa_Completo.pdf: 3530663 bytes, checksum: fa3beebf319fc93620723a321d5c7529 (MD5)
Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-07-18T20:26:08Z (GMT) No. of bitstreams: 1 campos_vew_me_rcla.pdf: 3530663 bytes, checksum: fa3beebf319fc93620723a321d5c7529 (MD5)
Made available in DSpace on 2016-07-18T20:26:08Z (GMT). No. of bitstreams: 1 campos_vew_me_rcla.pdf: 3530663 bytes, checksum: fa3beebf319fc93620723a321d5c7529 (MD5) Previous issue date: 2016-03-30
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
As florestas tropicais representam um dos biomas mais ameaçados pelas ações antrópicas no mundo. Os primatas representam 40% da biomassa de vertebrados frugívoros nas florestas tropicais, mas mais da metade das espécies estão ameaçadas de extinção. Tendo em vista a importância dos primatas no funcionamento dos ecossistemas devido a sua função de dispersores de sementes, é de extrema relevância entender como a fragmentação das florestas tropicais afetam as comunidades de primatas e suas funções. Portanto, nossos objetivos são: 1) analisar a relação entre diversidade funcional e filogenética de primatas e como esses índices são influenciados pela riqueza; 2) determinar o efeito da fragmentação das florestas tropicais na riqueza específica e funcional dos primatas; 3) determinar quais características funcionais são perdidas com a fragmentação, na Amazônia e na Mata Atlântica brasileira. Para isso, montamos bancos de dados de ocorrência dos primatas e de suas características funcionais ligadas à dispersão de sementes para gerar os índices de diversidade funcional (FD), regularidade funcional (FEve) e divergência funcional (FDiv) e relacioná-los com métricas da paisagem: área do fragmento, isolamento médio entre os fragmentos, distância em relação à zona urbana, distância à floresta contínua, conectividade funcional e porcentagem de cobertura vegetal no entorno do fragmento. A diversidade funcional dos primatas é fortemente correlacionada com a diversidade filogenética (R2= 0.94 e p<0.001). A redução da área dos fragmentos e da conectividade funcional, assim como o aumento do isolamento médio entre os remanescentes florestais diminuem a diversidade (FD), a regularidade (FEve) e a divergência funcional (FDiv) dos primatas. As espécies de primatas de grande porte que possuem grandes áreas de vida e que dispersam grandes sementes são as espécies mais prejudicadas pela fragmentação. Nosso trabalho permitiu ressaltar que além da perda de riqueza específica de primatas, a fragmentação nas florestas tropicais também afeta o serviço de dispersão de sementes, o que, consequentemente, pode alterar a estrutura das comunidades vegetais.
Tropical forests are the most threatened biome by human activities worldwide. Primates represent almost 40% of the frugivore vertebrate biomass in tropical forests and more than half of their species are threatened by extinction. Given the importance of primates as seed dispersers for the ecosystem functioning, it is extremely important to understand how the fragmentation of tropical forests affects primate communities and the functions they provide. Therefore, this project aims at: 1) analyzing the relationship between primate functional and phylogenetic diversities and how those indices are influenced by species richness; 2) determining the influence of forest fragmentation on primate species richness and functional diversity; 3) determining which functional traits are lost with habitat fragmentation, in Amazonian and Atlantic Forests of Brazil. To do this, we built a database of primates’ occurrence and their functional traits related to seed dispersal to compute indices of functional diversity (FD), functional evenness (Feve) and functional divergence (FDiv). Then, we related these indices to landscape metrics: patch size, average isolation between patches, distance to the nearest urban area, distance to the nearest continuous forest, functional connectivity and percentage of forest cover surrounding the fragment. Functional diversity is strongly correlated with phylogenetic diversity (R2= 0.94 e p<0.001). The decrease of fragment areas and functional connectivity, and the increase of average isolation between forest remnants, reduce primate functional diversity (FD), regularity (FEve) and divergence (FDiv). Large primates with large home ranges that disperse large seeds are the most affected by fragmentation. Our results enable highlighting that beyond the loss of primate species richness, the fragmentation of tropical forests also affect seed dispersal service, which consequently may alter the structure of plant communities.
FAPESP: 2014/14739-0
CNPq: 830816/1999-2
APA, Harvard, Vancouver, ISO, and other styles
26

Kerber, Torsten. "Dispersionskorrekturen von DFT für Festkörperprobleme." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16634.

Full text
Abstract:
In der vorliegenden Arbeit wird die Korrektur weitreichender Dispersionswechselwirkungen fuer Dichtefunktionaltheorie fuer Rechnungen unter Anwendung periodischer Randbedingungen erweitert. Am Beispiel des Graphit wird der Einfluss der Dispersionskorrektur auf Strukturparameter und Energien gezeigt. Die berechneten Werte fuer Schichtabstand und Wechselwirkungsenergie stimmen sehr gut mit experimentell bestimmten Daten ueberein. Anhand von Clusterstudien wird gezeigt, dass die Dispersionskorrektur nur sehr langsam mit der Systemgroesse konvergiert. Die genaue Beschreibung der Dispersionswechselwirkungen zwischen Graphitschichten mit der PBE+D-Methode ist nur bei Anwendung periodischer Randbedingungen oder durch eingebettete Clustermodelle moeglich. Der Vergleich der PBE+D- mit der genauen, aber sehr aufwendigen [MP2:PBE + delta-CCSD(T)]-Methode zeigt, dass die strukturellen Unterschiede zwischen beiden Methoden gering sind. Die berechneten Reaktionsenergien unterscheiden sich hingegen deutlich. Die neu entwickelte, effiziente [PBE+D + delta-MP2 + delta-CCSD(T)]-Methode ergaenzt die PBE+D-Energie um zwei Korrekturterme. Der erste Term, die delta-MP2-Korrektur, behebt die Ueberstabilisierung polarer Strukturen (PBE) mit einer MP2-Rechnung am Basissatzlimit. Der zweite Term ueberprueft die delta-MP2-Korrektur durch eine CCSD(T)-Rechnung fuer einen kleinen Cluster. Die [PBE+D + delta-MP2 + delta-CCSD(T)]-Methode wird fuer die Reaktion von C4H8-Kohlenwasserstoffen mit H-Ferrierit angewendet. In der Zeolithpore wurden pi-Komplexe, Butylkationen und Oberflaechenalkoxide als Intermediate identifiziert. Die Isomerisierung von Butenen in der H-Ferrierit-Pore wird mit der Umlagerung linearer Butylkationen in der Gasphase verglichen. Der geschwindigkeitsbestimmende Schritt ist in beiden Faellen die Bildung des tert-Butylkations aus einem methylverbrueckten Butylkation. Die CCSD(T)-Methode ist zur Bestimmung genauer Energieprofile erforderlich.
In this work, the long-range dispersion correction for density functional theory is extended to periodic boundary conditions. The influence of the dispersion correction on energy and structural parameters is shown for graphite. The calculated values of the interlayer distance and the interaction energy are in good agreement with experimental ones. By a series of cluster calculations it is shown, that the dispersion correction converges very slowly with respect to the system size. The accurate description of the dispersion interaction between graphite layers requires the usage of PBE+D method applying periodic boundary conditions or embedded cluster models. For structural parameters, the PBE+D methods compares well with the accurate but computationally very demanding [MP2:PBE+CCSD(T)] method. However, the calculated reaction energies differ remarkably. The newly developed, efficient [PBE+D + MP2 + CCSD(T)] method extends the PBE+D energy by two correction terms. The first one, the MP2 correction, rectifies the over stabilization of polar structures (PBE) by a MP2 calculation at the basis set limit. The second term verifies the MP2 correction by a CCSD(T) calculation for a small cluster model. The [PBE+D + MP2 + CCSD(T)] method is applied for the reaction of C4H8 hydro carbons witr the zeolite Ferrierite. Within the pore of a zeolite, pi complexes, butyl cations and surface alkoxides are identified as minima on the potential energy surface. The isomerization of butenes is compared to the rearrangement of linear butyl cations in the gas phase. In both cases, the rate determining step is the formation of the tertial butyl cation from a methyl bridged cation. The CCSD(T) method is for the determination of accurate energy profiles required.
APA, Harvard, Vancouver, ISO, and other styles
27

Grossman, Esther Florence. "Comparing B3LYP and its dispersion-corrected form to B97-D3 for studying adsorption and vibrational spectra in nitrogen reduction." Ohio University Honors Tutorial College / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors155628790845.

Full text
APA, Harvard, Vancouver, ISO, and other styles
28

Bovo, Alex Augusto de Abreu. "Diversidade e riqueza funcional de assembleias de aves na Mata Atlântica." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/11/11150/tde-19042016-111324/.

Full text
Abstract:
A composição das assembleias de aves sofre mudanças de acordo com alterações na paisagem em que ocorrem. A transição de florestas para outros usos do solo pode modificar também o conjunto de funções e, consequentemente, impactar os processos ecológicos desempenhados pelas aves. Desse modo, a presente dissertação teve como objetivos principais: 1) identificar características da estrutura da paisagem que apresentem relação com a diversidade e riqueza funcional de assembleias de aves; e 2) identificar alterações morfológicas na assembleia de aves consumidoras de frutos e discutir seus possíveis impactos no processo de dispersão de sementes. Para isso, um levantamento bibliográfico foi realizado resultando em um banco de dados com 48 assembleias de fragmentos florestais da Mata Atlântica oriundas de 33 estudos. Para cada fragmento foi utilizado um buffer de 2000 m de raio para criar uma paisagem focal, o uso do solo foi classificado em \'floresta\' ou \'não-floresta\', e métricas foram calculadas. As assembleias de aves foram caracterizadas a partir de índices de composição de diversidade e riqueza funcional, usando diversas características morfológicas e de habitat. Regressões lineares e modelos mistos foram usadas para investigar a relação entre características da estrutura da paisagem e i) diversidade e riqueza funcional de aves florestais (obj. 1) e ii) riqueza de espécies, diversidade funcional e características morfológicas para aves consumidoras de frutos (obj. 2). Os resultados mostraram que a área do fragmento, juntamente com área nuclear foram as características mais importantes em relação à manutenção das funções na assembleia de aves florestais, demonstrando a importância de grandes áreas florestais. Para as alterações morfológicas, a diminuição na quantidade de cobertura florestal foi relacionada à diminuição de valores de massa corpórea, índice de asa e largura de bico. A redução desses valores pode implicar na dispersão de sementes menores, na redução de dispersão de espécies com sementes grandes e na redução da área abrangida pela chuva de sementes.
Bird assemblages composition suffer alteration according to landscape changes. The substitution of forest by others land uses can affect the group of functions, and consequently, the ecological process played by birds. This dissertation had two main goals: 1) to identify landscape metrics which has relation with functional diversity and richness of bird assemblages; and 2) to identify morphological changes in fruit-eater bird assemblage and discuss the potentials impacts on the seed dispersal process. To reach this, a database was created using literature data, with 48 bird assemblages of Atlantic Forest remnants from 33 studies. From the most central point of each fragment, was created a focal landscape of 2000 meters buffer, the land use was classified in \'forest\' or \'non-forest\' and metrics was calculated. The index of bird assemblages used were composition and functional diversity and richness, calculated using morphological and habitat traits. Linear regression and mixed models were used to investigate relationships between landscape metrics and i) functional diversity and richness of forest birds (obj. 1) and ii) functional diversity, species richness and morphological traits of fruit-eater birds (obj. 2). The results showed that fragment area and core area were the most important traits to preserve the functions in bird assemblage, demonstrating the importance of big blocks of forest. To morphological changes, the decreasing on forest over was related to decreases on values of: body mass, hand-wing index and bill width. The reduction of these values can promote the dispersal of smaller seeds, reduction on dispersal of plants with big seed and decreases of area cover by seed rain.
APA, Harvard, Vancouver, ISO, and other styles
29

Vilamiu, Raphael Gustavo d'Almeida. "Generalização da decomposição por EMD para grafos e sua aplicação à dispersão geográfica da dengue." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/306715.

Full text
Abstract:
Orientador: Wilson Castro Ferreira Junior
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matemática, Estatística e Computação Científica
Made available in DSpace on 2018-08-16T08:15:58Z (GMT). No. of bitstreams: 1 Vilamiu_RaphaelGustavod'Almeida_D.pdf: 17502226 bytes, checksum: af859cc18d3a4c5a74c324d3e6c0865a (MD5) Previous issue date: 2010
Resumo: Nesta tese, desenvolvemos uma técnica para gerar grafos à partir de conjuntos de séries temporais considerando a correlação entre estas e uma extensão do Método de Decomposição Empírica (EMD) para grafos (GEMD). Tal trabalho se justifica pelo fato de que uma grande gama de sinais formados por conjuntos de séries temporais não possuem uma localização bem definida em nenhum espaço n-dimensional. Desta forma, as relações entre as séries temporais só são satisfatoriamente representadas com o uso de grafos. Contudo, o desenvolvimento do GEMD é dependente do uso de algum método de interpolação em grafos. Tais métodos são escassos e não produzem propriedades satisfatórias para o uso no GEMD. Para esta finalidade, estendemos a interpolação por Funções de Base Radial (RBF) em Grafos (GRBF), onde a norma euclidiana no cálculo da matriz de interpolação por RBF é substituída pela norma induzida pelo grafo. Testes numéricos sugerem que a extensão possui boas propriedades de convergência e uma técnica é desenvolvida para garantir a existência e unicidade da solução. Finalmente, aplicamos o GEMD em um conjunto de dados de incidência de Dengue Hemorrágica na Tailândia. Os modos intrínsecos encontrados desta forma não apresentam nenhuma onda viajante emanando de nenhuma das províncias, contrastando com o resultado utilizando o EMD original [5]. Além disso, os períodos médios dos modos intrínsecos de [5] são claramente distintos dos encontrados pela decomposição por GEMD
Abstract: In this thesis, we developed a technique to generate a graph from a set of temporal series, which are then decomposed trough an extension of the Empirical Mode Decomposition (EMD) on Graphs (GEMD) created by us. This procedure is justified by the fact that a huge amount of signals cannot be properly localized on an n-dimensional space which can only be properly represented by a graph. The development of the GEMD is dependent on some graph interpolation method. Such methods are scarce in the literature and do not have the necessary properties to accomplish the GEMD decomposition. For this goal, we extend the Radial Basis Functions (RBF) interpolation to graphs (GRBF), where the euclidean norm used in the calculation of the RBF interpolation matrix is substituted by a graph induced norm. Numerical tests suggests that GRBF have good convergence properties and we present a technique which guarantees the existence and uniqueness of the solution. We finally apply the GEMD decomposition to a data set of Dengue Hemorrhagic Fever incidence in Thailand. The intrinsic modes found in this way do not show any traveling wave emanating from any of the provinces, contrasting with the results found using the original EMD [5]. Moreover, the mean period for the intrinsic modes in [5] are clearly diverse of those found by GEMD decomposition
Doutorado
Doutor em Matemática Aplicada
APA, Harvard, Vancouver, ISO, and other styles
30

Yang, Qianqian. "Novel analytical and numerical methods for solving fractional dynamical systems." Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/35750/1/Qianqian_Yang_Thesis.pdf.

Full text
Abstract:
During the past three decades, the subject of fractional calculus (that is, calculus of integrals and derivatives of arbitrary order) has gained considerable popularity and importance, mainly due to its demonstrated applications in numerous diverse and widespread fields in science and engineering. For example, fractional calculus has been successfully applied to problems in system biology, physics, chemistry and biochemistry, hydrology, medicine, and finance. In many cases these new fractional-order models are more adequate than the previously used integer-order models, because fractional derivatives and integrals enable the description of the memory and hereditary properties inherent in various materials and processes that are governed by anomalous diffusion. Hence, there is a growing need to find the solution behaviour of these fractional differential equations. However, the analytic solutions of most fractional differential equations generally cannot be obtained. As a consequence, approximate and numerical techniques are playing an important role in identifying the solution behaviour of such fractional equations and exploring their applications. The main objective of this thesis is to develop new effective numerical methods and supporting analysis, based on the finite difference and finite element methods, for solving time, space and time-space fractional dynamical systems involving fractional derivatives in one and two spatial dimensions. A series of five published papers and one manuscript in preparation will be presented on the solution of the space fractional diffusion equation, space fractional advectiondispersion equation, time and space fractional diffusion equation, time and space fractional Fokker-Planck equation with a linear or non-linear source term, and fractional cable equation involving two time fractional derivatives, respectively. One important contribution of this thesis is the demonstration of how to choose different approximation techniques for different fractional derivatives. Special attention has been paid to the Riesz space fractional derivative, due to its important application in the field of groundwater flow, system biology and finance. We present three numerical methods to approximate the Riesz space fractional derivative, namely the L1/ L2-approximation method, the standard/shifted Gr¨unwald method, and the matrix transform method (MTM). The first two methods are based on the finite difference method, while the MTM allows discretisation in space using either the finite difference or finite element methods. Furthermore, we prove the equivalence of the Riesz fractional derivative and the fractional Laplacian operator under homogeneous Dirichlet boundary conditions – a result that had not previously been established. This result justifies the aforementioned use of the MTM to approximate the Riesz fractional derivative. After spatial discretisation, the time-space fractional partial differential equation is transformed into a system of fractional-in-time differential equations. We then investigate numerical methods to handle time fractional derivatives, be they Caputo type or Riemann-Liouville type. This leads to new methods utilising either finite difference strategies or the Laplace transform method for advancing the solution in time. The stability and convergence of our proposed numerical methods are also investigated. Numerical experiments are carried out in support of our theoretical analysis. We also emphasise that the numerical methods we develop are applicable for many other types of fractional partial differential equations.
APA, Harvard, Vancouver, ISO, and other styles
31

Kooshapur, Sheema [Verfasser], Michael [Akademischer Betreuer] [Gutachter] Manhart, and Insa [Gutachter] Neuweiler. "Modelling dispersion on the pore scale based on the velocity distribution function / Sheema Kooshapur ; Gutachter: Insa Neuweiler, Michael Manhart ; Betreuer: Michael Manhart." München : Universitätsbibliothek der TU München, 2016. http://d-nb.info/1118722388/34.

Full text
APA, Harvard, Vancouver, ISO, and other styles
32

Raoult, Cécile. "Modélisation numérique non-linéaire et dispersive des vagues en zone côtière." Thesis, Paris Est, 2016. http://www.theses.fr/2016PESC1150/document.

Full text
Abstract:
Au cours de cette thèse, un modèle potentiel résolvant les équations d’Euler-Zakharov a été développé dans le but de simuler la propagation de vagues et d’états de mer irréguliers et multi-directionnels, du large jusqu’à la côte, sur des bathymétries variables. L’objectif est de représenter les effets non-linéaires et dispersifs le plus précisément possible pour des domainescôtiers bidimensionnels (dans le plan horizontal) de l’ordre de quelques kilomètres.La version 1DH initiale du modèle, résolvant le problème aux limites de Laplace à l’aide de schémas aux différences finies d’ordre élevé dans la direction horizontale combinés à une approche spectrale sur la verticale, a été améliorée et validée. L’implémentation de conditions aux limites de type Dirichlet et Neumann pour générer des vagues dans le domaine a été étudiée en détail. Dans la pratique, une zone de relaxation a été utilisée en complément deces conditions pour améliorer la stabilité du modèle.L’expression analytique de la relation de dispersion a été établie dans le cas d’un fond plat. Son analyse a montré que la représentation des effets dispersifs s’améliorait significativement avec l’augmentation de la résolution sur la direction verticale (i.e. avec le degré maximal de la basede polynômes de Tchebyshev utilisée pour projeter le potentiel des vitesses sur la verticale).Une étude de convergence menée pour des ondes solitaires modérément à fortement non-linéaires a confirmé la convergence exponentielle avec la résolution verticale grâce à l’approche spectrale, ainsi que les convergences algébriques en temps et en espace sur l’horizontale avec des ordres d’environ 4 (ou plus) en accord avec les schémas numériques utilisés.La comparaison des résultats du modèle à plusieurs jeux de données expérimentales a démontré les capacités du modèle à représenter les effets non-linéaires induits par les variations de bathymétrie, notamment les transferts d’énergie entre les composantes harmoniques, ainsi que la représentation précise des propriétés dispersives. Une formulation visco-potentielle a également été implémentée afin de prendre en compte les effets visqueux induits par la dissipation interne et le frottement sur le fond. Cette formulation a été validée dans le cas d’une faible viscosité avec un fond plat ou présentant une faible pente.Dans le but de représenter des champs de vagues 2DH, le modèle a été étendu en utilisant une discrétisation non-structurée (par nuage de points) du plan horizontal. Les dérivées horizontales ont été estimées à l’aide de la méthode RBF-FD (Radial Basis Function-Finite Difference), en conservant l’approche spectrale sur la verticale. Une étude numérique de sensibilité a été menée afin d’évaluer la robustesse de la méthode RBF-FD, en comparant différents types de RBFs, avec ou sans paramètre de forme et l’ajout éventuel d’un polynôme. La version 2DH du modèle a été utilisée pour simuler deux expériences en bassin, validant ainsi l’approche choisie et démontrant son applicabilité pour simuler la propagation 3D des vagues faisant intervenir des effets non-linéaires. Dans le but de réduire le temps de calcul et de pouvoir appliquer le code à des simulations sur de grands domaines, le code a été modifié pour utiliser le solveur linéaire direct en mode parallèle
In this work, a potential flow model based on the Euler-Zakharov equations was developed with the objective of simulating the propagation of irregular and multidirectional sea states from deep water conditions to the coast over variable bathymetry. A highly accurate representation of nonlinear and dispersive effects for bidimensional (2DH) nearshore and coastal domains on the order of kilometers is targeted.The preexisting 1DH version of the model, resolving the Laplace Boundary Value problem using a combination of high-order finite difference schemes in the horizontal direction and a spectral approach in the vertical direction, was improved and validated. The generation of incident waves through the implementation of specific Dirichlet and Neumann boundary conditions was studied in detail. In practice, these conditions were used in combination witha relaxation zone to improve the stability of the model.The linear dispersion relation of the model was derived analytically for the flat bottom case. Its analysis showed that the accuracy of the representation of dispersive effects improves significantly by increasing the vertical resolution (i.e. the maximum degree of the Chebyshev polynomial basis used to project the potential in the vertical). A convergence study conducted for moderate to highly nonlinear solitary waves confirmed the exponential convergence in the vertical dimension owing to the spectral approach, and the algebraic convergence in time and in space (horizontal dimension) with orders of about 4 (or higher) in agreement with the numerical schemes used.The capability of the model to represent nonlinear effects induced by variable bathymetry, such as the transfer of energy between harmonic components, as well as the accurate representation of dispersive properties, were demonstrated with comparisons to several experimental data sets. A visco-potential flow formulation was also implemented to take into account viscous effects induced by bulk viscosity and bottom friction. This formulation was validated inthe limit of small viscosity for mild slope bathymetries.To represent 2DH wave fields in complex nearshore domains, the model was extended using an unstructured discretization (scattered nodes) in the horizontal plane. The horizontal derivatives were estimated using the RBF-FD (Radial Basis Function - Finite Difference) method, while the spectral approach in the vertical remained unchanged. A series of sensitivity tests were conducted to evaluate numerically the robustness of the RBF-FD method, including a comparison of a variety of RBFs with or without shape factors and augmented polynomials. The 2DH version of the model was used to simulate two wave basin experiments, validating the approach and demonstrating the applicability of this method for 3D wave propagation, including nonlinear effects. As an initial attempt to improve the computational efficiency ofthe model for running simulations of large spatial domains, the code was adapted to use a parallelized direct linear solver
APA, Harvard, Vancouver, ISO, and other styles
33

Morais, Douglas Souza Figueiredo. "Estudo da crosta no sudoeste do cráton amazônico utilizando técnicas sismológicas /." Rio Claro, 2018. http://hdl.handle.net/11449/182036.

Full text
Abstract:
Orientador: João Carlos Dourado
Resumo: Técnicas sismológicas como Função do Receptor, Análise de Dispersão de Ondas de Superfície, Correlação de ruídos sísmicos e razão espectral H/V são cada vez mais estudadas e utilizadas para o conhecimento geológico da crosta. Sendo possível determinar a composição crustal média e os principais contatos obtidos por fortes contrastes de impedância tais como limite crosta superior e inferior, assim como, limite crosta inferior e manto superior (descontinuidade de Moho). O conhecimento da velocidade de percurso das ondas de um sismo registrados através de uma estação sismográfica fornecem informações, como: o tempo de percurso, relação Vp/Vs e outros. A região de Pontes e Lacerda/MT está localizada no Sudoeste do Cráton Amazônico e o levantamento dos dados se deram em fases distintas com implantação de sismômetros alinhados em direção perpendicular (NE-SW) às principais estruturas da Faixa Móvel Aguapeí (NNW-SSE). Além da coleta de dados dessas estações temporárias foram compilados dados de sismos para a estação fixa PTLB, esta estação faz parte das estações sismológicas coordenadas pela UNB (Universidade Nacional de Brasília) e pela USP (Universidade de São Paulo). A espessura média encontrada na crosta para a região variou pouco para as diferentes técnicas abordadas, sendo que, para a técnica de Função do Receptor (estação fixa PTLB) foi obtido valor de aproximadamente 44 Km de espessura e, para as estações temporárias (S01 ao S10) valor médio de 42 km. Já a seção sísmica gerad... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Seismic techniques such as receiver function, surface wave dispersion, seismic noise correlation and H / V spectral ratio are increasingly studied and used for geological knowledge of the crust. It is possible to determine the average crustal composition and the main contacts obtained by strong impedance contrasts as upper and lower crust boundary, as well as, lower crust limit and upper mantle (Moho discontinuity). The knowledge of the speed of travel of the waves of an earthquake recorded through a seismographic station provides information, such as: the travel time, Vp / Vs ratio and others. The region of Pontes e Lacerda / MT is located in the Southwest of the Amazonian craton and the data were taken in different phases with the implantation of seismometers aligned in a perpendicular direction (NE-SW direction) to the main structures of the Faixa Móvel Aguapeí (direction NNW- SSE). In addition to collecting data from these temporary stations, earthquake data were collected for the PTLB fixed station. The average thickness found in the crust for the region did not vary much for the different techniques, and for the Receiver Function (PTLB fixed station), a value of approximately 44 Km of thickness was obtained and for the temporary stations (S01 to S10) average value of 42 km. The seismic section generated by the correlation of the signals for all short-time temporary stations brought the signals coherence in 4s, 5s and later coherence ranging from 9.5 to 11 seconds. This ... (Complete abstract click electronic access below)
Doutor
APA, Harvard, Vancouver, ISO, and other styles
34

Favre-Bac, Lisa. "Rôle de corridor écologique des fossés pour la dispersion des espèces végétales dans les paysages agricoles." Thesis, Rennes 1, 2015. http://www.theses.fr/2015REN1S053/document.

Full text
Abstract:
La mise en place de réseaux écologiques est considérée comme l'un des moyens de pallier aux effets néfastes de la fragmentation sur la biodiversité. Dans les paysages agricoles, les éléments linéaires non cultivés peuvent constituer de larges réseaux, et jouer un rôle d'habitat-refuge et/ou de corridor de dispersion pour les espèces végétales. L'objectif de cette thèse est de comprendre quel rôle un réseau dense de fossés de drainage peut jouer dans le maintien et la dispersion d'espèces végétales dans un paysage agricole intensif du nord de la France. Nous avons également cherché à savoir dans quelle mesure les caractéristiques du paysage, la connectivité du réseau et les traits d'histoire de vie des espèces végétales impactent la dispersion des propagules au sein du réseau de fossés. Nos résultats montrent que les fossés jouent bien un rôle de corridor écologique pour les espèces végétales. En ciblant plus précisément les espèces hydrochores, nous avons démontré qu'elles dépendaient essentiellement de la composition et de la connectivité du réseau de fossés et des éléments immédiatement adjacents aux berges. Le réseau détermine également la structuration des flux de gènes chez deux espèces végétales de berges de fossés. Enfin, nos résultats montrent que la réponse des espèces à un gradient de connectivité du réseau dépend d'une combinaison de traits de dispersion, et qu'une diminution de cette connectivité entraîne une convergence fonctionnelle de ces traits à l'échelle de la métacommunauté. L'ensemble de ces résultats permet de mieux comprendre le rôle de corridor des fossés pour les espèces végétales, afin de permettre leur intégration au sein des projets de continuités écologiques dans les paysages agricoles
The establishment of ecological networks is considered as one of the solutions to mitigate the negative effects of fragmentation on biodiversity. In agricultural landscapes, non-crop linear elements may form large networks, and constitute refuge habitats and/or dispersal corridors for plant species. The objective of this study is to understand which role may a dense drainage ditch network play for the maintenance and dispersal of plant species in an intensive agricultural landscape located in northern France. In addition, we also investigated the impact of landscape characteristics, network connectivity and plant species life-history traits on propagule dispersal within the ditch network. Our results indicate that ditches are indeed ecological corridors for plant species. By focusing more specifically on hydrochorous species, we demonstrated that they essentially depend on ditch network composition and connectivity and on elements immediately adjacent to the banks. The network also drives patterns of gene flow for two ditch bank plant species. Finally, our results also indicate that species’ response to ditch network connectivity depends on a combination of dispersal traits, and that connectivity reduction leads to functional convergence of those traits at the metacommunity scale. Together, these results provide a better understanding of the corridor role of ditches for plant species, in order to include these features into ecological network planning in agricultural landscapes
APA, Harvard, Vancouver, ISO, and other styles
35

Greim, Dominik [Verfasser], and Jürgen [Akademischer Betreuer] Senker. "Disorder in solids probed by NMR chemical shielding using semi empirical dispersion corrected density functional theory / Dominik Greim ; Betreuer: Jürgen Senker." Bayreuth : Universität Bayreuth, 2020. http://d-nb.info/1223023354/34.

Full text
APA, Harvard, Vancouver, ISO, and other styles
36

Emin, Azad [Verfasser]. "Dispersive mixing of oil in plasticized starch by extrusion processing to design functional foods / Azad Emin." München : Verlag Dr. Hut, 2013. http://d-nb.info/1042307571/34.

Full text
APA, Harvard, Vancouver, ISO, and other styles
37

Emin, M. Azad [Verfasser]. "Dispersive mixing of oil in plasticized starch by extrusion processing to design functional foods / Azad Emin." München : Verlag Dr. Hut, 2013. http://d-nb.info/1042307571/34.

Full text
APA, Harvard, Vancouver, ISO, and other styles
38

Silva, Danylo Alves da. "Implementação de uma correção de dispersão empírica aos métodos semiempíricos RM1 (Recife Model 1) e PM6 (Parametric method 6)." Pós-Graduação em Química, 2017. https://ri.ufs.br/handle/riufs/6653.

Full text
Abstract:
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
In the present study, the implementation and parameterization of the dispersion correction functions, denominated DM1 and DM2, was carried out to the quantum semiempirical methods RM1 and PM6, in the program Mopac2007. The aim of this study is to improve the description of weak interactions by the methods above mentioned with the addition of na energy correction. The DM1 methodology contains 7 parameters while the DM2 model presents 13 parameters for the correction function. Unlike previous work, the correction was used to adjust not only the energy, but also the geometric parameters. The parameterization was performed using a training set composed by 10 structures from S22 database and 24 structures from S66 database. The results show that RM1-DM1 and RM1- DM2 improved the total response function when compared to RM1, the RM1- DM1 is better at describing the geometries of the complexes on the other hand, the RM1-DM2 is more efficient in reproducing the dispersion energy. The PM6- DM1 and PM6-DM2 methods, for the test set, had a smaller response function than PM7 and PM6 and their extensions with correction of dispersion forces. The best response function for PM6-DM1 and PM6-DM2 is related to the description of the geometries of the complexes, with the dispersion energy being slightly higher than that obtained by the PM6-DH2 method. The semiempirical methods discussed here, together with the theory of density functional, with the most popular B3LYP functional, were used to calculate the geometry of cyclodextrin/guest complexes. The results obtained, with semiempirical methods, showed that AM1, PM3, PM6-DM1 and PM6-DM2 presented the lowest values of RMSD and variability for a set of 43 cyclodextrins. The DFT methodology was used to calculate the geometry of a set of 9 cyclodextrins/guest complexes, the result was compared to semiempirical methods. The best DFT result was obtained with the 6-31G base, it is similar to obtained by the RM1 method. For this set, the methods AM1, PM6-DM1 and PM6-DM2 presented the best results in the description of the geometries.
No presente estudo foi realizada a implementação e parametrização das funções de correção de dispersão, denominadas DM1 e DM2, aos métodos semiempíricos quânticos RM1 e PM6, no programa Mopac2007. O estudo tem o como finalidade melhorar a descrição de interações fracas pelos métodos supracitados com a adição de uma correção de energia. A metodologia DM1 contém 7 parâmetros enquanto, o modelo DM2 apresenta 13 parâmetros para a função de correção. Diferente de trabalhos anteriores a correção foi usada para ajustar, não somente, a energia, mas também parâmetros geométricos. A parametrização foi executada usando um conjunto treinamento que usa 10 estruturas do banco de dados S22 e 24 estruturas do banco de dados S66. Os parâmetros obtidos através do conjunto treinamento foram aplicados ao conjunto teste, o qual é formado pelas 54 estruturas que não fizeram parte do conjunto treinamento. Os resultados mostram que RM1-DM1 e RM1-DM2 melhoraram a função resposta total quando comparado ao RM1, sendo o RM1-DM1 melhor em descrever as geometrias dos complexos e RM1-DM2 mais eficiente em reproduzir a energia de dispersão. Os métodos PM6-DM1 e PM6-DM2 para o conjunto teste apresentaram uma função resposta menor do que o PM7 e PM6 e suas extensões com correção das forças de dispersão. A melhor função resposta para PM6-DM1 e PM6-DM2 está relacionada a descrição das geometrias dos complexos, sendo a energia de dispersão um pouco maior do que a obtida pelo método PM6-DH2. Os métodos semiempíricos, aqui abordados, junto com a teoria do funcional da densidade, com o funcional mais popular B3LYP, foram usados para calcular a geometria de complexos ciclodextrina/convidado. Os resultados obtidos com os métodos semiempíricos mostraram que os métodos AM1, PM3, PM6-DM1 e PM6-DM2 apresentam os menores valores de RMSD e variabilidade para um conjunto de 43 ciclodextrinas. A metodologia DFT foi usada para calcular a geometria para um conjunto de 9 complexos ciclodextrinas/convidado, o resultado foi comparado aos métodos semiempíricos. O melhor resultado DFT foi obtido com a base 6-31G, esse é semelhante ao obtido pelo método RM1. Para esse conjunto os métodos AM1, PM6-DM1 e PM6-DM2 apresentaram os melhores resultados na descrição das geometrias.
São Cristóvão, SE
APA, Harvard, Vancouver, ISO, and other styles
39

Hutridurga, Ramaiah Harsha. "HOMOGÉNÉISATION ET DISPERSION POUR DES ÉCOULEMENTS COMPLEXES EN MILIEU POREUX ET APPLICATIONS." Phd thesis, Ecole Polytechnique X, 2013. http://pastel.archives-ouvertes.fr/pastel-00866253.

Full text
Abstract:
Ce travail est une contribution pour mieux comprendre le transport de solutés dans un milieu poreux. Ce phénomène se rencontre dans de nombreux domaines: transport de contaminants dans les eaux souterraines, séquestration du CO2, stockage souterrain des déchets nucléaires, simulations de réservoirs pétroliers. On obtient la dispersion effective de Taylor en tenant compte de la convection, de la diffusion, de la géométrie du milieu poreux et des réactions chimiques. Le but de la théorie d'homogénéisation est, à partir d'équations microscopiques, de dériver un modèle effectif à l'échelle macroscopique. Ici, on applique la méthode de convergence à deux échelles avec dérive pour arriver au comportement effectif. Dans un premier temps, on considère les réactions de type adsorption à la surface des pores. À l'échelle microscopique, le phénomène de transport est modélisé par des équations couplées de type advection-diffusion, une pour la concentration dans le fluide et l'autre pour la concentration à la surface de milieu poreux. Le couplage est fait par les isothermes d'adsorption. Le système microscopique avec des coefficients fortement oscillants est étudié dans un régime de forte convection i.e., dans un régime de grand nombre de Péclet. La présence de forte convection dans le modèle microscopique se traduit par l'apparition d'une large dérive dans les profils de concentrations. On considère à la fois l'isotherme linéaire et l'isotherme non linéaire et les résultats ainsi obtenus sont comparés. Dans la deuxième partie, on généralise nos résultats concernant le transport réactif d'un seul soluté à ceux de plusieurs solutés dans un cadre linéaire. Dans ce cas, les paramètres effectifs sont obtenus en utilisant le principe de Factorisation et la convergence à deux échelles avec dérive. On étudie numériquement le comportement des paramètres effectifs par rapport au nombre de Péclet et au nombre de Damköhler. On utilise Freefem++ pour effectuer des tests numériques en dimension deux.
APA, Harvard, Vancouver, ISO, and other styles
40

Choi, Yeonsik. "Novel functional polymeric nanomaterials for energy harvesting applications." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/282877.

Full text
Abstract:
Polymer-based piezoelectric and triboelectric generators form the basis of well-known energy harvesting methods that are capable of transforming ambient vibrational energy into electrical energy via electrical polarization changes in a material and contact electrification, respectively. However, the low energy conversion efficiency and limited thermal stability of polymeric materials hinder practical application. While nanostructured polymers and polymer-based nanocomposites have been widely studied to overcome these limitations, the performance improvement has not been satisfactory due to limitations pertaining to long-standing problems associated with polymeric materials; such as low crystallinity of nanostructured polymers, and in the case of nanocomposites, poor dispersion and distribution of nanoparticles in the polymer matrix. In this thesis, novel functional polymeric nanomaterials, for stable and physically robust energy harvesting applications, are proposed by developing advanced nanofabrication methods. The focus is on ferroelectric polymeric nanomaterials, as this class of materials is particularly well-suited for both piezoelectric and triboelectric energy harvesting. The thesis is broadly divided into two parts. The first part focuses on Nylon-11 nanowires grown by a template-wetting method. Nylon-11 was chosen due to its reasonably good ferroelectric properties and high thermal stability, relative to more commonly studied ferroelectric polymers such as polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)). However, limitations in thin-film fabrication of Nylon-11 have led to poor control over crystallinity, and thus investigation of this material for practical applications had been mostly discontinued, and its energy harvesting potential never fully realised. The work in this thesis shows that these problems can be overcome by adopting nanoporous template-wetting as a versatile tool to grow Nylon-11 nanowires with controlled crystallinity. Since the template-grown Nylon-11 nanowires exhibit a polarisation without any additional electrical poling process by exploiting the nanoconfinement effect, they have been directly incorporated into nano-piezoelectric generators, exhibiting high temperature stability and excellent fatigue performance. To further enhance the energy harvesting capability of Nylon-11 nanowires, a gas -flow assisted nano-template (GANT) infiltration method has been developed, whereby rapid crystallisation induced by gas-flow leads to the formation of the ferroelectric δʹ-phase. The well-defined crystallisation conditions resulting from the GANT method not only lead to self-polarization but also increases average crystallinity from 29 % to 38 %. δʹ-phase Nylon-11 nanowires introduced into a prototype triboelectric generator are shown to give rise to a six-fold increase in output power density as observed relative to the δʹ-phase film-based device. Interestingly, based on the accumulated understanding of the template-wetting method, Nylon-11, and energy harvesting devices, it was found that thermodynamically stable α-phase Nylon-11 nanowires are most suitable for triboelectric energy generators, but not piezoelectric generators. Notably, definitive dipole alignment of α-phase nanowires is shown to have been achieved for the first time via a novel thermally assisted nano-template infiltration (TANI) method, resulting in exceptionally strong and thermally stable spontaneous polarization, as confirmed by molecular structure simulations. The output power density of a triboelectric generator based on α-phase nanowires is shown to be enhanced by 328 % compared to a δʹ-phase nanowire-based device under the same mechanical excitation. The second part of the thesis presents recent progress on polymer-based multi-layered nanocomposites for energy harvesting applications. To solve the existing issues related to poor dispersion and distribution of nanoparticles in the polymer matrix, a dual aerosol-jet printing method has been developed and applied. As a result, outstanding dispersion and distribution. Furthermore, this method allows precise control of the various physical properties of interest, including the dielectric permittivity. The resulting nanocomposite contributes to an overall enhancement of the device capacitance, which also leads to high-performance triboelectric generators. This thesis therefore presents advances in novel functional polymeric nanomaterials for energy harvesting applications, with improved performance and thermal stability. It further offers insight regarding the long-standing issues in the field of Nylon-11, template-wetting, and polymer-based nanocomposites.
APA, Harvard, Vancouver, ISO, and other styles
41

Veit, Max David. "Designing a machine learning potential for molecular simulation of liquid alkanes." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/290295.

Full text
Abstract:
Molecular simulation is applied to understanding the behaviour of alkane liquids with the eventual goal of being able to predict the viscosity of an arbitrary alkane mixture from first principles. Such prediction would have numerous scientific and industrial applications, as alkanes are the largest component of fuels, lubricants, and waxes; furthermore, they form the backbones of a myriad of organic compounds. This dissertation details the creation of a potential, a model for how the atoms and molecules in the simulation interact, based on a systematic approximation of the quantum mechanical potential energy surface using machine learning. This approximation has the advantage of producing forces and energies of nearly quantum mechanical accuracy at a tiny fraction of the usual cost. It enables accurate simulation of the large systems and long timescales required for accurate prediction of properties such as the density and viscosity. The approach is developed and tested on methane, the simplest alkane, and investigations are made into potentials for longer, more complex alkanes. The results show that the approach is promising and should be pursued further to create an accurate machine learning potential for the alkanes. It could even be extended to more complex molecular liquids in the future.
APA, Harvard, Vancouver, ISO, and other styles
42

Gunasinghe, Rosi. "Electronic and Magnetic Properties of Carbon-based and Boron-based Nano Materials." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2017. http://digitalcommons.auctr.edu/cauetds/64.

Full text
Abstract:
The structural and electronic properties of covalently and non-covalently functionalized graphene are investigated by means of first-principles density-functional-theory. The electronic characteristics of non-covalently functionalized graphene by a planar covalent organic framework (COF) are investigated. The aromatic central molecule of the COF acts as an electron donor while the linker of the COF acts as an electron acceptor. The concerted interaction of donor acceptor promotes the formation of planar COF networks on graphene. The distinctive electronic properties of covalently functionalized fluorinated epitaxial graphene are attributed to the polar covalent C–F bond. The partial ionic character of the C–F bond results in the hyperconjugation of C–F σ-bonds with an sp2 network of graphene. The implications of resonant-orbital-induced doping for the electronic and magnetic properties of fluorinated epitaxial graphene are discussed. Isolation of single-walled carbon nanotubes (SWNTs) with specific chirality and diameters is critical. Water-soluble poly [(m- phenyleneethynylene)- alt- (p- phenyleneethynylene)], 3, is found to exhibit high selectivity in dispersing SWNT (6,5). The polymer’s ability to sort out SWNT (6,5) appears to be related to the carbon–carbon triple bond, whose free rotation allows a unique assembly. We have also demonstrated the important role of dispersion forces on the structural and electronic stability of parallel displaced and Y-shaped benzene dimer conformations. Long-range dispersive forces play a significant role in determining the relative stability of benzene dimer. The effective dispersion of SWNT depends on the helical pitch length associated with the conformations of linkages as well as π-π stacking configurations. We have revisited the constructing schemes for a large family of stable hollow boron fullerenes with 80 + 8n (n = 0,2,3,...) atoms. In contrast to the hollow pentagon boron fullerenes the stable structures constitute 12 filled pentagons and 12 additional hollow hexagons. Based on results from density-functional calculations, an empirical rule for filled pentagons is proposed along with a revised electron counting scheme. We have also studied the relative stability of various boron fullerene structures and structural and electronic properties of B80 bucky ball and boron nanotubes. Our results reveal that the energy order of fullerenes strongly depends on the exchange-correlation functional employed in the calculation. A systematic study elucidates the importance of incorporating dispersion forces to account for the intricate interplay of two and three centered bonding in boron nanostructures.
APA, Harvard, Vancouver, ISO, and other styles
43

Shukla, Ushma. "Dispersion épizoochore des graines par les ongulés sauvages dans des paysages changeants : le cerf élaphe comme étude de cas." Thesis, Orléans, 2020. http://www.theses.fr/2020ORLE3060.

Full text
Abstract:
L'épizoochorie définit la dispersion des plantes véhiculées sur le corps des animaux. Elle concerne herbacées et graminées, arbres et arbustes étant dispersés par endozoochorie et vecteurs abiotiques. Filtre biotique sélectif, elle façonne les communautés végétales locales à partir du pool régional d'espèces. Les populations abondantes d’ongulés sauvages et leurs longs déplacements créent ainsi de fréquents "liens mobiles" entre patchs d'habitat. J’ai ainsi étudié le rôle de ces animaux, notamment du cerf élaphe, comme vecteurs de dispersion épizoochore dans la structuration des communautés végétales locales en tenant compte des traits des plantes favorisant la dispersion. Puis, j’ai évalué comment structure et composition du paysage affectaient les déplacements individuels du cerf, les distances de dispersion et le site de dépôt des graines. Finalement, j’ai comparé différents modes de dispersion à l’échelle du vecteur individuel. Pour répondre à ces questions, j'ai combiné données empiriques de terrain et approches de modélisation écologique. J'ai constaté que la zoochorie constitue un signal faible, par rapport aux facteurs abiotiques, dans la structuration des communautés végétales, mais les traits facilitant la dispersion sont de bons prédicteurs. J'ai montré l'importance de tenir compte du domaine vital individuel pour ne pas surestimer les distances de dispersion. En outre, j'ai démontré qu’il fallait considérer la charge totale en graines véhiculées car elle révèle la complémentarité des modes de dispersion. Pour finir, j'alerte sur le rôle sous-estimé des ongulés sauvages et domestiques dans la propagation des plantes exotiques, réelle menace pour la biodiversité
Epizoochory is one mode of plant dispersal, where seeds are conveyed externally on animals. It mostly concerns forbs and graminoids, shrubs and trees relying more on endozoochory or abiotic vectors. Epizoochory is considered a strong biotic filter that shapes local plant assemblages from the regional pool of species. Abundant populations of large-bodied ungulates and their home range movements provide frequent ‘mobile links’ among habitat patches. For my thesis, I was interested in assessing the role of wild ungulates, especially red deer, in epizoochorous seed dispersal. I addressed 1) the role of ungulates in structuring local plant communities with respect to dispersal-related plant traits, 2) the effect of landscape composition on movement decisions made by individual red deer on subsequent seed dispersal kernels, and 3) the complementarity of ungulate-mediated dispersal modes and their overall influence on local plant communities. I used a combination of empirical field data and ecological modeling to address these questions. I found that zoochory presents a weak signal in structuring plant communities compared to other abiotic factors, but that dispersal-enabling traits were good predictors. I demonstrated the importance of accounting for home ranging behavior in range-resident ungulates in the seed dispersal kernel, which prevents from over-estimating dispersal distances. Moreover, I underlined how considering the total seed load dispersed by individual red deer is crucial and reveals the complementarity of dispersal modes in the total dispersal kernel. Finally, I highlighted the underrated role of ungulates in spreading invasives as a real threat to biodiversity
APA, Harvard, Vancouver, ISO, and other styles
44

Casas, Grasiela. "Padrões de diversidade de aves e rede de interação mutualística ave-planta em mosaico floresta-campo." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/141942.

Full text
Abstract:
Estudos clássicos com diversidade taxonômica, apesar de serem essenciais, não consideram as diferenças funcionais entre as espécies de uma comunidade. A abordagem considerando atributos funcionais e diversidade funcional vem preenchendo esta lacuna. A compreensão da estrutura e dinâmica de interações mutualísticas também é um elemento essencial em estudos de biodiversidade, permitindo a investigação de mecanismos ecológicos e evolutivos. Porém, a maioria dos estudos com redes de interação disponíveis na bibliografia são pequenas em número de espécies e interações, e é possível que estes dados não tenham sido suficientemente amostrados. Além disto, estudos têm mostrado que muitas métricas utilizadas em análises de rede de interação são sensíveis ao esforço amostral e ao tamanho da rede. Os objetivos desta tese foram: 1) investigar a diversidade taxonômica (DT) e funcional (DF) de aves e os padrões de organização de espécies de aves em comunidades refletindo convergência de atributos (TCAP: Trait Convergence Assembly Patterns) ao longo de transições entre floresta e campo; 2) analisar a estrutura de redes de dispersão de sementes de plantas por aves, utilizando as métricas de rede aninhamento, modularidade, conectância e distribuição do grau; 3) desenvolver um método estatístico visando avaliar suficiência amostral para métricas de redes de interação usando o método bootstrap de reamostragem com reposição. A composição de espécies de aves diferiu entre os ambientes, indicando uma substituição de espécies ao longo da transição floresta-borda-campo. DT diferiu significativamente somente entre floresta e borda de floresta, enquanto que ambas diferiram significativamente do campo em relação à DF. DT e DF podem indicar diferentes processos de organização de comunidades ao longo de mosaicos floresta-campo. A correlação significativa entre TCAP e o gradiente floresta-campo indica que provavelmente mecanismos de nicho atuam na organização da comunidade de aves, associados a mudanças na estrutura do habitat ao longo da transição floresta-borda-campo agindo como filtros ecológicos. Redes de dispersão de sementes de plantas por aves aparentemente apresentam um processo comum de organização, independentemente das diferenças na intensidade de amostragem e continentes onde as 19 redes utilizadas foram amostradas. Usando reamostragem bootstrap, encontramos que suficiência amostral pode ser alcançada com diferentes tamanhos amostrais (número de eventos de interação) para o mesmo conjunto de dados, dependendo da métrica de rede utilizada.
Classic studies on taxonomic diversity, though essential, do not consider the functional differences between species in a community. Studies using functional traits and functional diversity are filling this gap. Understanding the structure and dynamics of mutualistic interactions is also essential for biodiversity studies and allows the investigation of ecological and evolutionary mechanisms. However, most networks published are small in the number of species and interactions, and they are likely to be under-sampled. In addition, studies have demonstrated that many network metrics are sensitive to both sampling effort and network size. The aims of this thesis were: 1) to investigate bird taxonomic diversity (TD), functional diversity (FD), and patterns of trait convergence (TCAP: Trait Convergence Assembly Patterns) across forest-grassland transitions; 2) to analyse the structure of seed-dispersal networks between plants and birds using the metrics of nestedness, modularity, connectance and degree distribution; 3) to develop a statistical framework to assess sampling sufficiency for some of the most widely used metrics in network ecology, based on methods of bootstrap resampling. Bird species composition indicated species turnover between forest, forest edge and grassland. Regarding TD, only forest and edges differed. FD was significantly different between grassland and forest, and between grassland and edges. TD and FD responded differently to environmental change from forest to grassland, since they may capture different processes of community assembly along such transitions. Trait-convergence assembly patterns indicated niche mechanisms underlying assembly of bird communities, linked to changes in habitat structure across forest-edge-grassland transitions acting as ecological filters. Seed dispersal mutualistic networks apparently show a common assembly process regardless differences in sampling methodology or continents where the 19 networks were sampled. Using bootstrap resampling we found that sampling sufficiency can be reached at different sample sizes (number of interaction events) for the same dataset, depending on the metric of interest.
APA, Harvard, Vancouver, ISO, and other styles
45

Sauer, Elmar [Verfasser], and Joachim [Akademischer Betreuer] Groß. "A new dispersion contribution based on the PCP-SAFT equation of state in the framework of classical density functional theory / Elmar Sauer ; Betreuer: Joachim Groß." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2019. http://d-nb.info/1195798415/34.

Full text
APA, Harvard, Vancouver, ISO, and other styles
46

Alves, Claudia Marins. "Modelos estocásticos para tratamento da dispersão de material particulado na atmosfera." Laboratório Nacional de Computação Científica, 2006. https://tede.lncc.br/handle/tede/62.

Full text
Abstract:
Made available in DSpace on 2015-03-04T18:50:49Z (GMT). No. of bitstreams: 1 tese.pdf: 5590910 bytes, checksum: a89ccd96ade2b696f0e5b9163dc31bf5 (MD5) Previous issue date: 2006-11-13
Lagrangian stochastic models are a largely used tool in the study of passive substances dispersion inside the Atmospheric Boundary Layer. Its application is related to the trajectory computation of thousands of particles, that numerically simulate the dispersion of suspense substances in the atmosphere. In this study, the basic concepts related to the Lagrangian stochastic modelling are presented and discussed together with its main characteristics and its computational implementation, to the study of particles dispersion in the atmosphere. In a computational experiment, the obtained results are compared with observational data from the TRACT experiment, that took place in Europe in 1992. The input data needed for the dispersion model are extracted from simulations with the numerical weather forecast model RAMS. Dispersion over Rio de Janeiro region is also tested in a second experiment.
Modelos Lagrangianos estocásticos constituem ferramenta muito utilizada no estudo da dispersão de substâncias passivas na Camada Limite Atmosférica. Sua aplicação consiste em calcular a trajetória de milhares de partículas, que simulam numericamente a dispersão de uma substância em suspensão na atmosfera. Nesta tese, são apresentados e discutidos os conceitos básicos relacionados à Modelagem Lagrangiana Estocástica de Partículas, bem como suas principais características e sua implementação computacional, para o estudo da dispersão de partículas na atmosfera. Numa experimentação computacional, comparam-se os resultados obtidos com dados observacionais provenientes do experimento TRACT, realizado na Europa em 1992. Os dados de entrada necessários ao modelo de dispersão são extraídos de simulações do modelo de previsão numérica do tempo RAMS. A dispersão sobre o Estado do Rio de Janeiro é também testada em um segundo experimento.
APA, Harvard, Vancouver, ISO, and other styles
47

Crabot, Julie. "Continuité écologique, fragmentation et dynamique spatio-temporelle des communautés en rivières intermittentes." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1319.

Full text
Abstract:
L’écologie vise à comprendre comment les espèces et les individus sont distribués dans l’espace et dans le temps. De nombreux progrès ont récemment été réalisés dans l’analyse spatiale des communautés mais les mécanismes ont souvent été considérés comme à l’équilibre. Cela pourrait affecter la compréhension du rôle de processus déterministes (comme l’influence de facteurs environnementaux locaux) et stochastiques (comme une variation aléatoire du taux de mortalité) dans le maintien des écosystèmes, et d’autant plus pour les milieux dynamiques régulièrement soumis à des changements drastiques des conditions environnementales. Mon objectif dans cette thèse était ainsi d’améliorer la connaissance de la structure spatiale et temporelle des communautés en milieu dynamique en s’appuyant sur le cas de rivières intermittentes, sujettes à des cessation d’écoulement et/ou des assèchements. Le Chapitre 3 a contribué à l’amélioration d’un outil largement utilisé dans les analyses spatiales de communautés. En effet, les tests de Mantel, visant à mesurer la corrélation entre deux matrices de distance et tester sa significativité, sont un outil courant dans l’étude des métacommunautés pour mesurer la contribution du filtre environnemental et de la dispersion. Nous avons montré que la Moran Spectral Randomization permettait de corriger la surestimation de la corrélation entre deux matrices de distance présentant une autocorrélation spatiale. Nos résultats suggèrent que les analyses de communautés fondées sur ces tests ont pu surestimer la part accordée au filtre environnemental dans la structuration des communautés et que notre méthode permettra à de futures analyses de s’affranchir de ce biais. Les tests de Mantel étant utilisé dans d’autres domaines tels que la génétique, l’amélioration que nous proposons pourrait avoir des implications plus larges que le cadre de l’écologie des communautés. Dans le Chapitre 4, j’ai montré que la distribution spatiale et temporelle des assecs pouvait influencer la dynamique des communautés en rivière intermittente. L’influence de la localisation d’une perturbation, définie ici comme un changement extrême des conditions environnementales, sur la structure de communautés avec une dispersion contrainte dans une direction de l’espace avait été testée avec des simulations et sur des mésocosmes mais cela n’avait encore jamais été testé sur des données in situ. Les bassins versants avec des assèchements en amont présentaient des communautés plus dissimilaires entre elles que les communautés de bassins versants avec des assèchements en aval. Les assèchements en amont du réseau ont pu freiner la recolonisation par les organismes aquatiques, conduisant à moins d’homogénéisation des communautés. La fréquence et la durée des assecs avaient également une influence sur la dynamique temporelle des communautés, menant globalement à une plus grande variabilité dans le temps des taxons et des traits biologiques observés à un site, cette relation dépendant par ailleurs de la configuration spatiale d’assèchement. En comparant des rivières françaises exposées à des assèchements depuis des siècles et des rivières tchèques exposées à des assèchements depuis moins d’une décennie et dont l’intermittence est due à des perturbations anthropiques, j’ai montré des différences de réponse des communautés aquatiques à l’intermittence (Chapitre 5). Considérer la diversité bêta spatiale et temporelle a permis de mettre en évidence la plus forte variabilité de composition taxonomique qu’induisent les assèchements sur les communautés des rivières tchèques. De plus, une forte sensibilité des taxons résilients à l’augmentation de l’intermittence ayant été mise en évidence dans le Chapitre 5 pour les rivières qui ne sont pas naturellement intermittentes, l’augmentation de la durée et la longueur des assèchements attendue avec le changement climatique pourraient menacer le rétablissement des communautés après un assec dans ces rivières
Ecology aims at understanding how species and individuals are distributed in space and time. Progress has been recently made in spatial analyses of communities but structuring mechanisms are often considered as static or stable over time. This could affect the understanding of the role of deterministic (such as the influence of local environmental factors) and stochastic processes (such as random fluctuations of mortality rates) in maintaining ecosystems, especially for dynamic ecosystems regularly exposed to drastic changes of environmental conditions. My objective in this thesis was to improve knowledge on spatial and temporal structures of communities in dynamic ecosystems, based on the study of intermittent rivers, experiencing interruption of flow and/ or loss of surface water. The Chapter 3 contributed to improve a statistical tool routinely used in spatial analyses of community. Mantel tests, measuring the correlation between two distance matrices and its significance, are frequently used to study to which extent environmental filtering and dispersal structure metacommunities. We showed that Moran Spectral Randomization allowed us to correct the overestimation of the correlation between distance matrices when they presented spatial autocorrelation. Our results suggest that community analyses based on those tests may have overestimated the structuring role of environmental filtering and that our method will allow future analyses to avoid this bias. In addition, Mantel tests being used in other domains such as genetics, the improvement suggested here will have larger outcomes than community ecology. In Chapter 4, I showed that spatial and temporal distributions of drying event influenced community dynamics in intermittent rivers. The influence of the spatial pattern of disturbances, defined here as an extreme change of environmental conditions, had been previously tested with simulations and mesocosms but not in situ. Upstream-drying river basins harboured more dissimilar communities compared to downstream-drying basins. Upstream drying events may restrain recolonization for aquatic dispersers and lead to a lesser homogenisation of communities. Frequency and duration of drying events also influenced the temporal dynamics of communities and generally led to a higher temporal variability of taxonomic and functional compositions; this relationship was, however, dependent on the spatial drying pattern. By comparing French rivers that have been exposed to drying for centuries and Czech rivers recently exposed to flow intermittence caused by anthropic disturbances, I showed that aquatic communities responded differently to intermittence (Chapter 5). Measuring spatial and temporal beta diversity highlighted the higher variability of communities induced by drying in Czech rivers from both taxonomic and functional perspectives. In addition, a higher sensitivity of resilient taxa to increasing flow intermittence was found in Chapter 5 for non-natural intermittent rivers and this suggests that the increase of drying duration and drying length induced by climate change might jeopardize the recovery of community of these ecosystems after drying in near future
APA, Harvard, Vancouver, ISO, and other styles
48

Emin, M. Azad [Verfasser], and H. P. [Akademischer Betreuer] Schuchmann. "Dispersive mixing of oil in plasticized starch by extrusion processing to design functional foods / M. Azad Emin. Betreuer: H. P. Schuchmann." Karlsruhe : KIT-Bibliothek, 2013. http://d-nb.info/1044349573/34.

Full text
APA, Harvard, Vancouver, ISO, and other styles
49

Válková, Hana. "Modelování v perfusním MR zobrazování." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2014. http://www.nusl.cz/ntk/nusl-220837.

Full text
Abstract:
This thesis deals with the magnetic resonance perfusion data analysis especially DCEMRI. In its introduction the thesis describes the problem of DCE-MRI data aquisition, the necessity of appropriate contrast agent and basic principles of perfusion analysis. The dynamic behavior of contrast agent vascular distribution can be described by arterial input function (AIF). The shape of the curves close to the area of interest is affected by dispersion which is called vascular transport function (VTF) due to the distribution of the contrast agent to the region of interest. Finally the tissue residual function describes system behavior of tissue. The practical part of the diploma thesis is aimed at implementation of model curves AIF, VTF and TRF. Furthermore, a simulation program was created for easy manipulation with introduced models moreover the program is used to perform an estimation of perfusion parameters based on nonblind deconvolution. The method is validated on synthetic data and illustrated on clinical data of the renal cell carcinoma patient.
APA, Harvard, Vancouver, ISO, and other styles
50

Tuma, Christian. "A QM/QM hybrid method for MP2/Plane-Wave-DFT studies of extended systems." Doctoral thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=983810583.

Full text
APA, Harvard, Vancouver, ISO, and other styles
You might also be interested in the bibliographies on the topic 'Dispersion functions' for other source types:
Journal articles Books
We offer discounts on all premium plans for authors whose works are included in thematic literature selections. Contact us to get a unique promo code!

To the bibliography