During the design and commissioning of combustion equipment, combustion associated instabilities are commonly encountered. These thermo-acoustic instabilities can cause undesirable noise, vibrations, local thermal and mechanical stresses in the combustor and are prominent in lean combustion. An often used mathematical tool to predict the instability in combustors is the so called network model where the system under study is subdivided in several subsystems and the acoustic state variables are regarded as the input/output of these subsystems. Solving this system of equations gives rise to the complex Eigen-frequencies of the system which tell if the complete system will have an unstable/stable response for specific operating conditions. In such a model it is critical to know what the influence of each subpart is on the acoustic wave propagation to correctly predict the unstable frequencies of the system. The area expansion is a common element found in combustors and the acoustic properties of the area expansion under quiescent conditions are well known, however in the presence of flow, acoustic flow interactions may occur. These interactions change the acoustic properties and are challenging to model and accurate experimental data is needed to validate the modelling. In this study, measurements of the aero-acoustic properties of an area expansion are presented, however the focus is on the experimental techniques and methods used to obtain accurate and precise measurement data in the plane wave frequency regime. The measurement accuracy of the setup used to determine the passive aero-acoustic properties of the area expansion is assessed by measuring a known impedance. Several sources of errors are identified and methods to account for these error sources are given. It is shown that the microphone impedance affects the measurement results and the upper limit of the measurement accuracy for quiescent measurements is governed by this error. The measurement precision of the setup is assessed using a multi-variate analysis and compared with results obtained from a Monte-Carlo simulation. Also the problem to determine the uncertainty of the measured complex pressures receives attention. Using a framework based on the Hilbert-transform, expressions are derived which estimate the uncertainty on the measured complex value from the background signal spectrum. The obtained knowledge is used to determine the scattering matrix of the area expansion. For the quiescent case, the measured results agree within 1.5% of the absolute values and within 1 degree in comparison with the analytical models. In the case with flow, the errors are slightly larger due to the increased flow-noise but a good correspondence with analytical models is found. Also a sudden sound absorption at high flow speeds and low frequencies is observed. / Vid konstruktion och användning av förbränningsutrustning observeras ofta instabiliteter i förbränningsprocessen. Dessa så kallade termo-akustiska instabiliteter kan orsaka buller och vibrationer samt lokala termiska och mekaniska belastningar i förbränningskammaren och de uppstår ofta vid mager förbränningen. Nätverksmodeller används ofta att förutsäga när instabiliteter uppträder och i dessa modeller är hela systemet indelat i olika delsystem och de akustiska ljudfältsstorheterna används som ingående och utgående parametrar. Löser man hela modellen, så får man de komplexa egenfrekvenser som ger information om när systemet är instabilt för vissa operativa förhållanden. I de här modellerna är det kritiskt att veta hur varje delsystem påverkar det akustiska ljudfältet om man vill få korrekta förutsägelser av de frekvenser där systemet kommer att vara instabilt. Ett areasprång är ett element som man ofta hittar i förbrännings-utrustning. Dess akustiska egenskaper är välkända utan strömning, men med strömning kan växelverkan mellan strömning och akustisk tillkomma och påverka de akustiska egenskaperna. Denna inverkan är komplex att modellera och det finns behov av noggranna mätdata för att validera sådana modeller. Denna avhandling presenterar experimentellt bestämda akustiska egenskaper för ett areasprång, men fokus är på förbättringar av de experimentella tekniker och metoder som används för att få precisa och noggranna mätdata för akustiska delelement i planvågsområdet. Den experimentella noggrannheten hos mätuppställningen bedöms genom att mäta upp en bekant impedans. Flera felkällor identifieras och metoder att utvärdera felen presenteras. Dessutom visar det sig att mikrofonimpedansen påverkar mätresultaten och impedansen begränsar mätnoggrannheten i fallet med mätningar utan strömning. Precisionen av mätuppställningen bestäms med hjälp av en multivariat analys som jämförs med en Monte-Carlo analys. Det visar sig att det är lämpligt att använda en multivariat analys för att bestämma noggrannhets-intervaller för de uppmätta spridningskoefficienterna för areasprånget. Problemet att bestämma noggrannhet för det uppmätta komplexa ljud trycket behandlas också. Med hjälp av ett ramverk baserat på Hilbert-transformen, härleds uttryck för uppskattning av noggrannheten i det uppmätta ljud trycket baserat på bakgrundsljudets spektrum. De erhållna kunskaperna används sedan för att bestämma de akustiska egenskaperna för ett areasprång. De uppmäta resultaten är inom 1.5% för absolutvärdet och 1 grad för fasen, jämfört med analytiska modeller i fallet utan strömning. Med strömning är noggrannheten något sämre, beroende på strömningsgenererat brus, men resultaten stämmer fortfarande bra överens med modellen. Dessutom observeras en plötslig ljudsabsorption för högre strömhastigheter och låga frekvenser. / <p>QC 20150522</p>

Because cells are machines, their structure determines their function (health). But their structure also determines cells’ mechanical properties. So if we can understand how cells’ mechanical properties are influenced by specific structures, then we can observe what’s happening inside of cells via mechanical measurements. The Atomic Force Microscope (AFM) has become a standard tool for investigating the mechanical properties of cells. In many experiments, an AFM is used to ‘poke’ adherent cells with nanonewton forces, and the resulting deformation observed via, e.g. Laser Scanning Confocal Microscopy. Results of such experiments are often interpreted in terms of continuum mechanical models which characterize the cell as a linear viscoelastic solid. This “top-down” approach of poking an intact cell —complete with cytoskeleton, organelles etc.— can be problematic when trying to measure the mechanical properties and response of a single cell component. Moreover, how are we to know the sensitivity of the cell’s mechanical properties to partial modification of a single component (e.g. reducing the degree of cross- linking in the actin cortex)? In contrast, the approach taken here —studying the deformation and relaxation of lipid bilayer vesicles— might be called a “bottom-up” approach to cell mechanics. Using Coarse- Grained Molecular Dynamics simulations, we study the deformation and relaxation of bilayer vesicles, when poked with constant force. The relaxation time, equilibrium area expansion, and surface tension of the vesicle membrane are studied over a range of applied forces. Interestingly, the relaxation time exhibits a strong force-dependence. Force-compression curves for our simulated vesicle show a strong similarity to recent experiments where giant unilamellar vesicles were compressed in a manner nearly identical to that of our simulations.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Atualmente, o Brasil se apresenta como um grande produtor agrícola mundial com finalidade alimentícia e bioenergética. Ano a ano recordes de produção são batidos pelo setor agropecuário. Por outro lado, tem-se uma perspectiva de problemas alimentícios e energéticos no mundo, em especial no continente africano onde muitos vivem na miséria e na fome. Neste contexto, esta dissertação de mestrado apresenta uma proposta para a análise da dinâmica espaço-temporal de culturas agrícolas empregando os conceitos e instrumentos da Geomática em busca do desenvolvimento sustentável. Desenvolveu-se uma metodologia para a geração de indicadores da produção agrícola em diferentes níveis da estrutura territorial brasileira que permite a apresentação sintética, por meio de cartogramas e animações digitais, das dinâmicas espacial e espaço-temporal das principais culturas. Para isto foi criada uma base de dados da produção das principais culturas, desenvolvidos indicadores que representem a dinâmica espacial da produção agrícola e desenvolvidas ferramentas de apresentação destes indicadores através da dinâmica espaço-temporal. Finalmente, foram relacionadas as áreas voltadas à produção de alimentos e de expansão agrícola para a bioenergia (etanol e óleo de palma). Pretende-se, através deste trabalho, contribuir na tomada de decisão com ferramentas de visualização da realidade agropecuária brasileira. O trabalho estabelece ligações com os zoneamentos agroecológicos, os instrumentos de segurança alimentar e a pegada ecológica, com a apresentação da produção agrícola das culturas como cana-de-açúcar, milho, soja, palma de óleo e algodão. / At present, Brazil presents itself as a major agricultural producer for food and bio-energy purposes in the entire world. Year-to-year, production records are hit by the agricultural sector. On the other hand, there is a perspective for severe problems in food and energy supply in the world, especially in Africa, where many people live in poverty and hunger. In this context, this masters dissertation presents a proposal for the analysis of the spatio-temporal dynamics of the agricultural production using the concepts and tools of Geomatics in pursuit of sustainable development. It was developed a methodology for the generation of agricultural production indicators at different levels of Brazilian territorial structure which allows the synthetic presentation, through cartograms and digital animations, of the spatial and spatio-temporal dynamics of the main crops. For this, a database of the production of main crops was created, indicators that represent the spatial dynamics of agricultural production and presentation tools for these indicators through the space-temporal dynamics were developed. Finally, the areas with focus in the food production and agricultural expansion for bio-energy (ethanol and palm oil) production were related. It is intended, through this work, to contribute to the decision making with visualization tools of the reality of Brazilian agriculture. Links were developed with agro-ecological zoning, with the instruments of food security and with the ecological footprint, with the presentation of the agricultural production of crops such as sugar cane, corn, soybeans, palm oil and cotton.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Atualmente, o Brasil se apresenta como um grande produtor agrícola mundial com finalidade alimentícia e bioenergética. Ano a ano recordes de produção são batidos pelo setor agropecuário. Por outro lado, tem-se uma perspectiva de problemas alimentícios e energéticos no mundo, em especial no continente africano onde muitos vivem na miséria e na fome. Neste contexto, esta dissertação de mestrado apresenta uma proposta para a análise da dinâmica espaço-temporal de culturas agrícolas empregando os conceitos e instrumentos da Geomática em busca do desenvolvimento sustentável. Desenvolveu-se uma metodologia para a geração de indicadores da produção agrícola em diferentes níveis da estrutura territorial brasileira que permite a apresentação sintética, por meio de cartogramas e animações digitais, das dinâmicas espacial e espaço-temporal das principais culturas. Para isto foi criada uma base de dados da produção das principais culturas, desenvolvidos indicadores que representem a dinâmica espacial da produção agrícola e desenvolvidas ferramentas de apresentação destes indicadores através da dinâmica espaço-temporal. Finalmente, foram relacionadas as áreas voltadas à produção de alimentos e de expansão agrícola para a bioenergia (etanol e óleo de palma). Pretende-se, através deste trabalho, contribuir na tomada de decisão com ferramentas de visualização da realidade agropecuária brasileira. O trabalho estabelece ligações com os zoneamentos agroecológicos, os instrumentos de segurança alimentar e a pegada ecológica, com a apresentação da produção agrícola das culturas como cana-de-açúcar, milho, soja, palma de óleo e algodão. / At present, Brazil presents itself as a major agricultural producer for food and bio-energy purposes in the entire world. Year-to-year, production records are hit by the agricultural sector. On the other hand, there is a perspective for severe problems in food and energy supply in the world, especially in Africa, where many people live in poverty and hunger. In this context, this masters dissertation presents a proposal for the analysis of the spatio-temporal dynamics of the agricultural production using the concepts and tools of Geomatics in pursuit of sustainable development. It was developed a methodology for the generation of agricultural production indicators at different levels of Brazilian territorial structure which allows the synthetic presentation, through cartograms and digital animations, of the spatial and spatio-temporal dynamics of the main crops. For this, a database of the production of main crops was created, indicators that represent the spatial dynamics of agricultural production and presentation tools for these indicators through the space-temporal dynamics were developed. Finally, the areas with focus in the food production and agricultural expansion for bio-energy (ethanol and palm oil) production were related. It is intended, through this work, to contribute to the decision making with visualization tools of the reality of Brazilian agriculture. Links were developed with agro-ecological zoning, with the instruments of food security and with the ecological footprint, with the presentation of the agricultural production of crops such as sugar cane, corn, soybeans, palm oil and cotton.