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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
71

Representations for Understanding the Stern-Gerlach Effect

Stenson, Jared R. 08 July 2005 (has links) (PDF)
The traditional explanation of the Stern-Gerlach effect carries with it several very subtle assumptions and approximations. We point out the degree to which this fact has affected the way we practice and interpret modern physics. In order to gain a more complete understanding of the Stern-Gerlach effect beyond the standard approximations and assumptions it typically carries, we introduce the inhomogeneous Stern-Gerlach effect in which the strong uniform field component is removed. This change allows us to easily identify precession as a critical concept. It also provides us with a means by which to study precession and analyze it critically. By applying and comparing several mathematical techniques to this problem we gain insight into the applicability of precession arguments and the role of standard approximations and assumptions in both analytic derivation and interpretation. This approach also allows for a more general discussion regarding the use of representations in physics and teaching.
72

Att vara ett år och gå i förskola

Sundberg-Carlsson, Anna Lena January 2008 (has links)
Syftet med min undersökning är att beskriva samspelssituationer hos en ettåring i en 1-5 årsgrupp i förskolan ur barnets perspektiv och koppla dessa till anknytningsteori och Sterns teoriom självutveckling.Undersökningen har genomförts som en fallstudie där datainsamlingen skett genom observationersom sedan analyserats utifrån de aktuella teorierna.Resultatet visar att ettåringen initierar samspelssignaler som stämmer väl överens med teorin. Av observationerna som gjorts kan man exempelvis dra slutsatsen att barnet behöver merspråklig stimulans och mer lärande samspel. Man kan också se vilka funktioner i den omgivandemiljön som är viktiga. Kunskapen har specialpedagogisk betydelse vid kartläggning avbarn med problematisk utveckling eller funktionsnedsättning samt anpassningen av miljö ocharbetssätt för dessa.Nyckelord: anknytning, ett år, samspel, självutveckling, SternHandledare: Lena LangAnna Lena Sundberg Carlsson Examinator: Elsa Foisack
73

Aluminum Speciation Using Fluorescence Quenching

Smith, Donald Scott 02 May 1994 (has links)
<p> A noninvasive method using fluorescence quenching (FQ) to determine the conditional stability constants (logK') for aluminum with naturally occurring organic ligands has been developed. The method utilizes the Stern-Volmer equation to interpret data from ligand fluorescence suppression by aluminum. The total ligand concentration can also be determined using the measured stability constant and the Ryan-Weber equation. The method has been validated with the model ligand salicylic acid; logK' was found to be 3.5 ± 0.01 vs. 4.0 from the literature. The method was applied to the reference ligand Armadale fulvic acid and chemically realistic values were obtained. In addition, the expected trend of increasing stability constant with decreasing pH was observed. The method was further validated by determining the stability constant for Armadale fulvic acid using an independent technique, PCV colourimetry; the results agreed very well logK' = 4.7 vs. 4.65 for FQ analysis. Application of the method to whole filtered beaver pond water showed an increasing trend in the stability constant as the dissolved organic carbon (DOC) decreased. The Log of the stability constants were 3.15 ± 0.03, 3.26 ± 0.03, and 3.63 ± 0.02 for DOC concentrations 23, 14, and 10 ppm respectively. The method was also applied to size fractionated waters form lake Skjervatjern in Norway and the expected trend of increasing stability constant with increasing molecular weight was observed.</p> / Thesis / Bachelor of Science (BSc)
74

Structure and Dynamics of Molecules at Water/Silica and Water/Carbon Dioxide Interfaces

Zhang, Hui 16 December 2010 (has links)
No description available.
75

Adjustable Energy Saving Device for Transom Stern Hulls

Salian, Rachit Pravin 10 May 2019 (has links)
The study presents a numerical investigation about the hydrodynamic characteristics of a transom mounted interceptor on the Oliver Hazard Perry class frigate (FFG-7), in order to assess the potential of propulsion power reduction in a wide range of speeds. This study is aimed to design a stern interceptor with optimal efficiency not only at top speed, but also cruising/transfer speeds, by a simple regulation of its variable geometrical characteristics (from a construction and operational standpoint). A high fidelity numerical model is developed in the open source CFD suite OpenFOAM for the prediction of the longitudinal dynamic equilibrium at speed and the total resistance characteristics of the bare hull. The Reynolds Averaged Navier-Stokes Equations are solved using interDyMFoam, a multiphase volume of fluid solver which allows for a dynamic mesh. The numerical model is validated using the results of the experimental model tests conducted on a 1/80th scale model at the United States Naval Academy Hydromechanics Laboratory (NAHL). The validated numerical model is used to predict the hydrodynamic characteristics of the transom mounted interceptor at different interceptor settings and speeds. The results show that the interceptor reduces the amount of resistance, the running trim, and the sinkage of the ship at high speeds. For a speed of 0.392 Froude number (Fr), a drag reduction of 3.76% was observed, as well as a significant reduction in trim. / Master of Science / The drag acting on the hull is an important component that has to be considered during the process of designing the ship. An interceptor is a device that has been developed to improve the performance of hulls by reducing the drag. This research studies the influence of the interceptor on the resistance and motion of the ship across a range of speeds. The geometrical characteristics of the interceptor are varied in order to identify the geometry that would provide optimal performance across the speed range tested. This study is conducted using the Computational Fluid Dynamics (CFD) software OpenFOAM as well as model tests that were conducted on a 1/80th scale model.
76

Undocumented oil leakages : A study about stern tube seals and leakages / Odokumenterade oljeläcklage : En studie om propellerhylstätningar och läckage

Lundberg, Johan January 2021 (has links)
The majority of the vessels in the commercial fleet utilize oil lubricated stern tubes. Unfortunately, this brings about a risk of oil leaking from the stern tube into the marine environment if the stern tube seal would become worn or damaged by foreign materials. Previous studies concluded that, on average, 2.6 litres of oil per day leak out from the stern tube of ships. This essay has investigated the causes that could increase the leakage rate from the stern tube by reviewing literature, interviewing experts, and sending out surveys with questions regarding the subject. The answers that were received painted a clear picture that it is impossible to get a perfect seal on a stern tube. The causes that could influence the leakage rate were design related, such as vibrations, the rotational speed of the propeller shaft, radial and axial movements of the propeller shaft, as well as external causes such as the quality of water and foreign materials, for example, fishing lines and nets. The question whether water lubricated stern tubes were a viable alternative compared to oil lubricated stern tubes was also investigated. The result was that the bearing on a water lubricated stern tube did not have as long lifespan as an oil lubricated bearing. / Majoriteten av fartygen i handelsflottan använder oljesmorda propellerhylsor för att smörja propelleraxeln. Tyvärr medför det en risk att olja kan läcka ut från hylsan om tätningarna skulle bli utslitna eller skadas av främmande föremål. Tidigare forskning har visat att cirka 2,6 liter olja per dag läcker ut genomsnittligen från fartyg i handelsflottan. Denna uppsats har utrett vad som kan påverka läckagemängden från en propellerhylsa genom att utnyttja intervjuer och enkätsvar. Svaren som framkom var att det är mer eller mindre omöjligt att få en perfekt tätning på en propellerhylsa. Saker som kan påverka läckagemängden var designfenomen som vibrationer, axiella- och radiella rörelser och varvtal på propelleraxeln, samt yttre påverkan som vattenkvalité och främmande föremål som fiskelinor och nät. I uppsatsen jämförs även vattensmorda propellerhylsor med fokus på livstid, kostnad och underhåll, med en oljesmord propellerhylsa. En slutsats är att det vattensmorda lagret inte har samma livstid som det oljesmorda.
77

Modélisation des couches minces électriques dans les bio-microsystèmes

De Vroey, Laurent 13 February 2008 (has links)
L'utilisation de systèmes électromécaniques microstructurés pour analyser et manipuler des solutions biologiques ou des cellules vivantes (bio-MEMS) a pris un essor considérable ces dernières années. Dans ce genre de dispositifs, l'utilisation de champs électriques est fréquente, que ce soit pour percer les membranes des cellules et effectuer une transfection de gènes par exemple (électroporation), pour les déplacer ((di )électrophorèse) ou agir sur le milieu dans lequel elles baignent (électro-hydrodynamique). La modélisation des phénomènes induits par ces champs électriques dans les solutions aqueuses est un problème multi-physique et multi-échelle. Au déplacement des électrons s'ajoute en effet la migration des ions présents dans la solution. Ceux-ci se concentrent en particulier aux abords des électrodes formant des couches minces dont les paramètres évoluent de façon encore mal connue en fonction notamment des conditions d'alimentation. La thèse se concentre sur les applications électro-hydrodynamiques dans lesquelles une solution saline est mise en mouvement par des forces électriques agissant sur ses ions, concentrés dans des couches de charges minces, au voisinage des électrodes. Sont d'abord présentés les résultats expérimentaux et des modèles simples du problème électromécanique dans le cas de structures 2D à électrodes coplanaires. Devant l’importance des écarts entre les résultats théoriques et expérimentaux, des modèles plus complets sont alors proposés et évalués. Malgré les améliorations fournies par ces modèles, des écarts importants subsistent entre théorie et expérimentation, et une étude totalement découplée des aspects électriques et mécaniques est alors réalisée sur une structure 1D. Cette étude permet de mieux cerner les dépendances de certains paramètres physiques vis-à-vis des conditions d’alimentation avec une comparaison systématique des résultats expérimentaux et des résultats de modèles circuits linéaires et non linéaires, au travers d’une approche fréquentielle par diagrammes de Bode et d’une approche temporelle par figures de Lissajous. Il a ainsi pu être mis en évidence l’importance pratique potentielle de certains phénomènes rarement pris en compte dans des modèles globaux : saturation des couches minces, permittivité non constante, effets de bords,… Des applications pratiques ont pu être dégagées et testées expérimentalement, dans le domaine des micro-mélangeurs. Outre ces développements, une brève étude est décrite, portant sur la modélisation des cellules et de leurs membranes extrêmement fines en regard des autres dimensions caractéristiques du système, dans la perspective par exemple d'applications en électroporation. Une autre étude est faite portant sur l’utilisation potentielle de méthodes numériques dites « sans maillage » pour ce type d’applications, l’accent étant mis sur la résolution du problème de Poisson dans des systèmes 2D. / Analysis and manipulation of biological solutions or cells in micro-electromechanical systems has considerably improved during last years. In such systems, it is common to use electric fields, in order e.g. to increase cells membrane porosity, which is known as electroporation, and thus allow for gene transfection. Electric fields can also generate the motion of cells in a solution by (di-)electrophoresis effects or induce the movement of the solution itself, through electro-hydrodynamic effects. Finding theoretical models for those phenomena requires a multi-physic and multi-scale approach. The ions present in the saline solution react mechanically to the electrical excitation of the system. They migrate to the regions close to the electrodes, in very thin layers whose parameters vary in non-obvious ways, depending namely on the power supply conditions. The text focuses on electro-hydrodynamic applications in which a flow is generated by electric forces acting on the ions present in the solution, mostly in thin charge layers near the electrodes. Experimental results and simple existing models are first presented for 2D coplanar electrodes systems. Regarding the important differences between models and experimentation, more complete models are then proposed and tested. In spite of the improvements of those new models, some important differences remain, so that a fully decoupled approach of electrical and mechanical aspects is needed, which is pursued on a 1D structure. This new study allows for a better understanding of the dependences of some physical parameters with regard to supply conditions, with a systematic comparison of experimental results and non-linear circuit models results. A frequency approach with Bode diagrams is used, as well as a time approach with Lissajous figures. It has been shown that some phenomena are of practical and fundamental importance, which are not always taken into account in more general and global models : saturation phenomena, non constant physical parameters, border effects,… Practical applications have been deduced and tested experimentally, in the case of micro-mixing. A brief study is also mentioned, concerning the modeling of cells with extremely thin membranes compared to the other characteristic dimensions of the system, in the perspective e.g. of electroporation applications. Another short study is performed about the potential use of « meshless » numerical methods for the solving of this kind of applications, focusing more specifically on the solving of a Poisson problem in 2D.
78

Figurações da homossexualidade e da homoafetividade em King & King e Orações para Bobby / Figurations of homosexuality and homoaffection in King & King and Prayers for Bobby

Santos, Itamar Onório dos 21 September 2016 (has links)
O presente trabalho estuda as figurações da homossexualidade e da homoafetividade no livro King & King, de Linda de Haan e Stern Nijland, e no filme Orações para Bobby, de Russel Mulcahy. Dialogamos com as duas e apontamos para as suas diferenças e complementaridades. Nossa análise está centrada nas relações de poder e afetividade presentes em seus processos discursivos. Nossa pesquisa fundamenta-se, primordialmente, em dois fecundos teóricos da modernidade, Michel Foucault e Judith Butler, e visa a compreender o exercício disciplinador na construção e manutenção das ordens regulatórias da homossexualidade e da homoafetividade. / The present work studies the figurations of homosexuality and homoaffection in the book King & King, by Linda de Haan and Stern Nijland, and in the film Prayers for Bobby, by Russel Mulcahy. We dialogue with both and point to their differences and complementarities. Our analysis is centered on the relations of power and affectivity presented in their discursive processes. Our research is based primarily on two fecund scholars of modernity, Michel Foucault and Judith Butler, and aims to understand the disciplinary exercise in the construction and maintenance of the regulatory orders of homosexuality and homoaffection.
79

Figurações da homossexualidade e da homoafetividade em King & King e Orações para Bobby / Figurations of homosexuality and homoaffection in King & King and Prayers for Bobby

Itamar Onório dos Santos 21 September 2016 (has links)
O presente trabalho estuda as figurações da homossexualidade e da homoafetividade no livro King & King, de Linda de Haan e Stern Nijland, e no filme Orações para Bobby, de Russel Mulcahy. Dialogamos com as duas e apontamos para as suas diferenças e complementaridades. Nossa análise está centrada nas relações de poder e afetividade presentes em seus processos discursivos. Nossa pesquisa fundamenta-se, primordialmente, em dois fecundos teóricos da modernidade, Michel Foucault e Judith Butler, e visa a compreender o exercício disciplinador na construção e manutenção das ordens regulatórias da homossexualidade e da homoafetividade. / The present work studies the figurations of homosexuality and homoaffection in the book King & King, by Linda de Haan and Stern Nijland, and in the film Prayers for Bobby, by Russel Mulcahy. We dialogue with both and point to their differences and complementarities. Our analysis is centered on the relations of power and affectivity presented in their discursive processes. Our research is based primarily on two fecund scholars of modernity, Michel Foucault and Judith Butler, and aims to understand the disciplinary exercise in the construction and maintenance of the regulatory orders of homosexuality and homoaffection.
80

[pt] ESTUDO DO COMPORTAMENTO DOS QUANTUM DOTS EM MEIO AQUOSO E APLICAÇÃO DESTES NANOMATERIAIS COMO SONDA PARA DETERMINAÇÃO DE RUTINA E QUERCETINA / [en] STUDY OF QUANTUM DOTS IN AQUEOUS MEDIUM AND THEIR APPLICATION AS PROBES FOR THE DETERMINATION OF RUTIN AND QUERCETIN

23 December 2021 (has links)
[pt] As nanopartículas semicondutoras (pontos quânticos ou QDs), na forma de dispersões coloidais aquosas, foram usadas como sondas para determinação indireta de flavonóides. As características especiais desses materiais, decorrente do efeito de confinamento quântico alcançado nas estruturas cujas dimensões são da ordem de poucos nm de diâmetro, resultam em propriedades fotofisicas únicas que podem ser alteradas pelo ajuste do tamanho e/ou na modificação da superfície destes nanocristais. Uma vez que os flavonóides não fluorescem naturalmente, nanopartículas de CdS modificadas com ácido 2-mercaptopropiônico (sonda dos QDs de 2MPA-CdS) e de CdTe modificadas com ácido 3-mercaptopropiônico (sonda dos QDs de 3MPA-CdTe) foram sintetizadas em fase aquosa coloidal e usadas para a determinação indireta de rutina (RUT) e de quercetina (QUE) por meio de medição de decréscimo da fotoluminescência das sondas. A utilização dos QDs como sensores na quantificação destes compostos permitiu a realização de medições fotoluminescentes rápidas e simples, sem a necessidade do uso de complexos procedimentos de derivatização química, usulamente indicados para estes casos. Verificou-se, através do modelo de Stern-Volmer, que o sinal fotoluminescente dos QDs de 2MPA-CdS é atenuado pela presença de RUT, e esta supressão de sinal foi proporcional à concentração de analito na dispersões coloidas (faixa de resposta linear entre 0,5 e 4,0 x 10-5 mol L-1), com limite de detecção (LD) de 1,2 x 10-6 mol L-1. Observou-se também que a supressão de sinal fotoluminescente foi uma combinação da contribuição do efeito filtro (devido à absorção de parcial de radiação pelo analito no comprimento de onda de excitação) e de supressão estática (proveniente da ligação e troca de energia entre analito e QDs). A abordagem foi usada na determinação seletiva de RUT em formulação farmacêutica e em amostras simuladas contendo RUT e QUE ou em saliva fortificada com RUT, nesses dois últimos casos foi associando um método a uma separação prévia de componentes por cromatografia de camada fina. A seletividade em relação a outros flavonóides também foi avaliada. A sonda de 3MPA-CdTe QDs foi usada para a determinação de QUE tanto na dispersão original quanto na dispersão organizada por surfactente (brometo de cetiltrimetilamônio ou CTAB). A QUE foi quantificada em meio não organizado e o método aplicado na análise de suplemento contendo QUE e ácido ascórbico e na análise de extratos de cebolas roxa e amarela. A técnica de cromatografia de camada fina foi utilizada com o intuito de separar a QUE de interferentes presentes na cebola. O modelo de Stern-Volmer foi utilizado para estabelecer uma relação linear entre a fotoluminescência medida na dispersão dos QDs e a quantidade de QUE adicioanda na dispersão. A curva analítica cobriu a faixa de concentrações de QUE entre 0,5 a 6,0 x 10-5 mol L-1 com LD de 0,5 x 10-5 mol L-1. Estudos realizados indicaram que a natureza do quenching formado é estático. Finalmente, um estudo sistemático da interação entre diversos flavonóides e o QDs de 3MPA-CdTe foi estudado de modo a se estabelecer a função do surfactante CTAB no processo de interação entre sonda e supressor. Verificou-se maior estabilidade de sinal da sonda neste meio, e interaçōes analito-QDs distintas daquelas obtidas na ausência do surfactante. / [en] The semiconductor nanoparticles (quantum dots or QDs), in the form of aqueous colloidal dispersions, were used as probes for the indirect determination of flavonoids. The special characteristics of these materials, due to the quantum confinement effect achieved in structures whose dimensions are of the order of a few nm, in diameter, result in unique photophysical properties that can be changed by adjusting the size and/or by surface modification of these nanocrystals. Since flavonoids do not present natural fluorescence, CdS nanoparticles modified with 2-mercaptopropionic acid (2MPA-CdS QDs probe) and CdTe modified with 3-mercaptopropionic acid (3MPA-CdTe QDs probe) have been synthesized in colloidal aqueous phase and used for indirect determination of rutin (RUT) and quercetin (QUE) by measuring the photoluminescence decreasing from the probes. The use of QDs as probes for the quantification of these compounds has allowed the quick and simple photoluminescence measurements without the need for complex chemical derivatization procedures, usually indicated in these cases. It was found, through the Stern-Volmer model, that the photoluminescence of the 2MPA-CdS QDs is attenuated by the presence of RUT, and such a signal suppression was proportional to the concentration of analyte in colloidal dispersion (linear response range between 0,5 to 4.0 x 10-5 mol L-1), with limit of detection (LOD) of 1.2 x 10-6 mol L-1. It was also observed that photoluminescence suppression was a combination of the contribution of inner filter effect (due to partial radiation absorption by the analyte at the wavelength of excitation) and static supression (from the binding and energy exchange between analyte and QDs). The method was used to the selective determination of RUT in pharmaceutical formulation and in simulated samples containing QUE/RUT and/or saliva fortified with RUT. For these former two samples, thin layer chromatography was used to establish prior separation of components. The selectivity towards other flavonoids was also evaluated. The 3MPA-CdTe QDs probe was used to determine QUE in original dispersion and in dispersion containing surfactant (cetyltrimethylammonium bromide or CTAB). QUE was quantified in a non-organized environment (without surfactant) and the method was applied for the analysis in supplement containing QUE and ascorbic acid and for the analysis of purple and yellow onions. Thin layer chromatography was used in order to separate interfering present in onions. The Stern-Volmer model was used to establish a linear relationship between the photoluminescence measurement of the QDs dispersion and the amount of QUE added into the dispersion. The analytical curve covered the range of concentrations between 0.5 to 6.0 x 10-5 mol L-1 of QUE with LD 0.5 x 10-5 mol L-1. Studies indicate that the nature of formed quenching is static. Finally, a systematic study of the interaction between various flavonoids and CdTe-3MPA QDs was studied in order to establish the CTAB surfactant function in the interaction between probe and quencher. It was observed more signal stability of the probe in this medium, and interactions distinct analyte-QDs from those obtained in the absence of surfactant.

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