Pour évaluer l'impact d’un rejet accidentel ou chronique de polluants dans les écosystèmes, il est important d’étudier le dépôt sec des aérosols en milieu rural. Le manque de données expérimentales en milieu rural sur la vitesse de dépôt sec des particules ayant une taille inférieure à 1 μm conduit à des incertitudes au vu des modèles et de leurs différences, qui vont jusqu’à dépasser un ordre de grandeur. Le but de cette étude est de développer une mesure directe de la vitesse de dépôt sec des aérosols (Vd), notamment en utilisant un impacteur à basse pression (Electrical Low Pressure Impactor, ELPI, DEKATI), à travers des mesures expérimentales in situ. L’originalité de la méthode est le calcul des flux de dépôt par corrélation turbulente. Les vitesses de dépôt sec ont été obtenues pour des aérosols atmosphériques de tailles comprises entre 7 nm et 2 μm, sur un terrain plat dans le sud-ouest de la France, sous différentes conditions atmosphériques, ainsi que sur différents couverts (maïs, herbe, sol nu). Vd est analysée en fonction du diamètre des particules et l’impact des conditions micro météorologiques est étudié. / To evaluate the impact of accidental or chronic pollutant releases on ecosystems, we must study the dry deposition of aerosols in rural areas. The lack of experimental data on the dry deposition velocity of particle sizes below 1 μm over rural environments leads to uncertainties regarding models and differences between them, which exceed one order of magnitude. The aim of thisstudy is to develop a method, especially using an Electrical Low Pressure Impactor (Outdoor ELPI, DEKATI) to determine aerosol dry deposition velocities (Vd) over rural areas through experimental measurements. This method is based on eddy covariance flux calculation and spectral analysis correction. Dry deposition velocities were obtained for atmospheric aerosols sizing from 7 nm to2 μm, in the South-West of France on a flat terrain under varied meteorological conditions andvaried substrates (maize, grass and earth). Vd was analysed as a function of the particle diameters, and the impact of micrometeorological parameters was studied.

Efficiency improvement is one of the most important aspects of engineering and especially important in the field of energy production. In the past decades, energy was mostly produced by fossil based technologies involving turbomachines, and the efficiency of these machines nearly quadrupled since the introduction of the first economically viable gas turbines. The progress continues, as there are still areas where improvement can be made. Such area is the High Pressure Turbine stage (HPT), which influences the flow characteristics and losses downstream, which this thesis will examine in more detail. In the open literature it can be found that one of the areas with potential for progress is the external cooling of the nozzle guide vanes (NGV) of the HPT stage. However not many studies go towards supersonic exit velocities even though that is the most common trend followed by the industry these days. The external cooling allows the turbine entry temperature (TET) to go beyond the melting point of the blade material thus increase Carnot efficiency but in the meantime influences the flow characteristics and losses. To understand these influences of the cooling, experiments in an annular sector cascade (ASC) were conducted with exit velocities from Mach 0.95 to 1.2 without and with cooling applied. The findings of the experiments are believed to help the more detailed understanding of the flow behaviour at high exit velocities. When comparing the corresponding runs in the two cases it became obvious that with cooling applied the deviation of the exit flow angle is generally smaller than in the uncooled case. This might be a highly important design feature for designers to work with. From the available data it was concluded that the total pressure distribution across the span is not significantly affected with the introduction of cooling.

No description available.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / The project aimed at numerically modeling the flow and thermal processes occurring in a Volkswagen Citi Golf Chico underhood using computational fluid dynamics (CFD). The motivation for this investigation was to develop and demonstrate the capability of CFD as an automotive analysis tool. This would allow local automobile analysts and designers enhanced analyses of the thermal and flow conditions occurring in this com-pact environment, leading to improved local vehicles. A review of relevant literature indicated that the CFD community in South Africa is small with comparison to the international sector. The application of CFD to analyse automo-biles in South Africa is limited and practised by few. This experience requires develop-ment and refinement, such that South Africa may improve vehicles manufacture in the country. The review also indicated that CFD used in the international communities pro-vides good results, promoting simulation-based engineering. The experimental investigation involved parking a vehicle in the subsonic wind tunnel intake at the Mechanical Engineering Department in Stellenbosch. This tunnel is 3.7 m wide, 4 m long and 2.8 m tall, capable of wind speeds up to 90 m/s. Various equipment including thermocouples, a thermal imager and a hand held hot-wire anemometer pro-vided temperature and velocity measurements within the underhood. A pitot-static probe connected to a pressure transducer measured the wind tunnel velocities. The numerical investigation started with the creation of a three-dimensional geometry of the underhood from measurements taken of the vehicle. This geometry, created with Solid Edge version 14, formed the domain for automatically generating discretised grids using STAR-Design version 3.2. Subsequently, boundary conditions and numerical models were applied to the grids, which included simplified fan and radiator models. The analysis concluded with results obtained from the numerical CFD simulations, per-formed with STAR-CD version 3.24. The validity and accuracy of the numerical solutions was verified and quantified with the numerical results. The evaluation consisted of two test cases (wind tunnel speeds of 0 m/s and 5 m/s), each simulated at three different grid resolutions. Each simulation con-tinued until they fully converged to a single solution. The comparison of the three simu-lations from each case indicated that the results were grid independent. The final in-spection of the results in terms of y+ values and boundary conditions indicated that the models implemented were valid. The comparison of the numerical results for temperatures and fan inlet velocities with the experimentally measured data served as a measure to quantify the applicability of CFD for underhood investigations. The comparison between the two sets of results proved acceptable, with a maximum difference of 10%, indicating that CFD is capable of predicting temperatures and flow fields with reasonable accuracy. The numerical results indicated that while the vehicle travels at higher velocities, the underhood remains well ventilated. The underhood tends to trap the hot air from the radiator and other heat sources when the vehicle remains stationary, causing the air to heat further. This can be addressed by the installation of vents in the side panels near the top of the underhood environment. This should allow the hot air to escape, possibly resulting in a significant reduction of the underhood temperatures. Momentum and energy source terms modelled the effects from the fan and radiator. These models worked well for both cases, but improvement is necessary. Special at-tention should be given to the condition where the radiator fan obstructs the flow through the radiator. A further result of the project was the establishment of a flexible foundation for conduct-ing numerical simulations on automobiles. It allows for the inclusion of additional com-ponents and the implementation of more advanced models for representing effects from various engine components.

Thanks to a range of discovery methods that are sensitive to different regions of parameter space, we now know of over 900 planets in over 700 planetary systems. This large population has allowed exoplanetary scientists to move away from a focus on simple discovery, and towards efforts to study the bigger pictures of planetary system formation and evolution. The interactions between planets and their host stars have proven to be varied in both mechanisms and scope. In particular, tidal interactions seem to affect both the physical and dynamical properties of planetary systems, but characterising the broader implications of this has proven challenging. In this thesis I present work that investigates different aspects of tidal interactions, in order to uncover the scope of their influence of planetary system evolution. I compare two different age calculation methods using a large sample of exoplanet and brown dwarf host stars, and find a tendency for stellar model fitting to supply older age estimates than gyrochronology, the evaluation of a star's age through its rotation (Barnes 2007). Investigating possible sources of this discrepancy suggests that angular momentum exchange through the action of tidal forces might be the cause. I then select two systems from my sample, and investigate the effect of tidal interactions on their planetary orbits and stellar spin using a forward integration scheme. By fitting the resulting evolutionary tracks to the observed eccentricity, semi-major axis and stellar rotation rate, and to the stellar age derived from isochronal fitting, I am able to place constraints on tidal dissipation in these systems. I find that the majority of evolutionary histories consistent with my results imply that the stars have been spun up through tidal interactions as the planets spiral towards their Roche limits. I also consider the influence of tidal interactions on the alignment between planetary orbits and stellar spin, presenting new measurements of the projected spin-orbit alignment angle, λ, for six hot Jupiters. I consider my results in the context of the full ensemble of measurements, and find that they support a previously identified trend in alignment angle with tidal timescale, implying that tidal realignment might be responsible for patterns observed in the λ distribution.

[pt] Um espectrômetro de massa por tempo-de-vôo 252Cf-PDMS foi empregado para a realização de três atividades: a) o aperfeiçoamento do espectrômetro com a instalação de novos dispositivos; b) a análise da emissão secundária de agregados iônicos por um alvo de LiF; c) a análise da fragmentação em vôo de íons positivos (LiF)nLi+ metaestáveis. O aperfeiçoamento do espectrômetro consistiu: i) na blindagem elétrica do detector start para aumentar a sua estabilidade; ii) na caracterização de dois pares de placas defletoras já existentes; iii) na instalação de um novo tipo de detector sensível à posição com anodo multi-fios, e iv) no projeto e na instalação de uma lente Einzel para aumentar a transmissão de íons secundários entre a amostra e o detector. A emissão secundária de agregados iônicos por um filme de LiF policristalino, bombardeado por fragmentos de fissão de ~ 60 MeV foi analisada através da técnica tempo-de-vôo (TOF). O detector sensível à posição recém instalado permite o emprego da técnica XY-TOF para analisar distribuições angulares de íons Li e dos agregados (LiF)nLi+. Determinaram-se as distribuições angulares dos agregados com n = 0 a 3, através de medidas simultâneas de suas velocidades axiais e radiais, evento por evento. A vida media de íons metaestáveis (LiF)nLi+* é determinada fazendo uso da configuração do espectrômetro e especialmente do comprimento do tubo de vôo livre. Após serem emitidas, as espécies iônicas metaestáveis monocarregadas são aceleradas por um campo elétrico da ordem de 2 kV/mm, e conduzidas a uma região de campo externo nulo, onde podem se dissociar espontaneamente em um fragmento iônico e outro neutro. Para facilitar a analise dos dados, impede-se a detecção do fragmento iônico através de um filtro eletrostático. Foram analisados os agregados iônicos com n = 1 a 5. Encontrouse que os valores das vidas medias estão na faixa de 30 a 100 ns. Discute-se também a detecção de espécies neutras produzidas por colisão de agregados (LiF)nLi+ com moléculas de gás residual. / [en] A 252Cf-PDMS time-of-flight mass spectrometer was used for the accomplishment of three activities: a) improvement of the spectrometer by introducing new devices; b) analysis of the LiF cluster ion secondary emission; c) analysis of the (LiF)nLi+ metastable íon fragmentation, in flight. The spectrometer improvement consists of: i) the shielding of the start detector to increase its stability, ii) the characterization of two existing deflecting- plate pairs, iii) the installation of a new type of position-sensitive delay line detector for secundary ions, and iv) the project and manufacture of a Einzel lens to increase the transmission of the secondary íons between the sample and the detector. The secondary cluster ion emission of policrystalline LiF, induced by the impact of fission fragments (60 MeV), is analyzed by the time-of-flight technique (TOF). The new position sensitive delay-line detector allows the use of the XY-TOF technique to analyze angular distributions of Li ions and (LiF)nLi+ clusters. Event by event, their axial and radial velocities are measured simultaneously, allowing the angular distributions measurement of clusters with n = 0 to 3. Mean lives of metastable clusters are determined through the measurement of the detection rate dependence on the target bias. After been emitted, the monocharged metatable ions are acelerated by a 2 kV/mm electric field towards a field-free region, where they can spontaneously dissociateinto two fragments, one ion and another neutral. To facilitate the data analysis, it is avoided the detection of ionic fragments by placing an electrostatic filter in front of the detector. Mean lives values of 30 to 100 ns are determined for ionic clusters with n = 1 to 5. The production of neutral species by collision of the (LiF)nLi+ clusters with the gas molecules is also discussed.

Orientador: Carlos Antonio Gamero / Banca: Carlos Eduardo Angeli Furlani / Banca: Maria Hele na Moraes / Resumo: Na operação de semeadura, o estande adequado e a uniformidade de distribuição de sementes são componentes de grande influência na produtividade do milho. Esses fatores podem ser afetados por inúmeras variáveis, sendo a velocidade de operação da semeadora-adubadora uma das mais importantes, além da adequação semente/orifício no disco dosador. A velocidade de deslocamento e a regulagem da semeadora, sendo inadequadas, podem proporcionar baixa população de plantas, acarretando em uma produtividade não desejada. O presente trabalho teve como objetivo analisar o desempenho operacional de uma semeadora-adubadora de precisão, em função de cinco velocidades de deslocamento e dois tipos de martelete, utilizada para a semeadura da cultura do milho em sistema plantio direto. O experimento foi instalado e conduzido em área experimental pertencente à Faculdade de Ciências Agronômicas, UNESP - Botucatu, SP, no período de dezembro de 2007 a maio de 2008. O solo da área experimental foi classificado como Nitossolo Vermelho Distroférrico, textura muito argilosa. O delineamento experimental utilizado foi de blocos ao acaso, com parcelas subdivididas, em esquema fatorial 2x5, sendo dois tipos de marteletes (4 e 5 dentes) e cinco velocidades de deslocamento (3,0; 4,5; 5,0; 7,0 e 9,0 km h-1) com quatro repetições. Assim, o experimento teve 10 tratamentos, totalizando 40 parcelas experimentais. Foram avaliados os dados referentes à porcentagem de cobertura do solo, profundidade do sulco de semeadura, área de solo mobilizado e de deposição de sementes, consumo horário e operacional de combustível, força na barra de tração do trator, velocidade de deslocamento, capacidade de campo efetiva, distribuição longitudinal de sementes, número médio de dias para emergência de plântulas, componentes morfológicos e componentes de produção da planta de milho, danos mecânicos nas... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In the sowing operation, the appropriate stand and the uniformity on the distribution of seeds are mentioned as factors of great influence on the corn yield.. These factors can be affected by several variables, being the planter displacement velocity one of the most important of them, besides the adjustment of seeds in the perforated disc device for seed dosage. The inadequate displacement velocity and adjustment of the planter may provide low population of plants, leading to an undesired yield. The current paper had as its objective to analyze the precision planter's operational and energetically performances according to five different displacement velocities and two types of jumpers used for planting no-tillage corn.The experiment was installed and conducted at the experimental area belonging to the College of Agricultural Science - UNESP located in Botucatu, Sao Paulo state, in the period comprised between December, 2007 and May, 2008. The experimental soil area was classified as Nitossolo Vermelho Distroférrico presenting a deep argillaceous texture. The experimental design consisted of blocks at random with parcels subdivided in factorial scheme 2x5, two types of jumpers (4 and 5 staples) and 5 different displacement velocities (3,0; 4,5; 5,0; 7,0 e 9,0 Km h-1) with four repetitions. Thus, the experiment was composed by 10 treatments, totalizing 40 experimental plots. The evaluated data regarded to the percentage of soil coverage, the sowing line depth, mobilized soil and seed overthrown area, horal and operational fuel consumption, force on the tractor traction bar, displacement velocity, effective field capacity, longitudinal distribution of seeds, average number of days for the emergence of seedlings, morphological and corn production components, mechanical harm on seeds and grain production. The displacement velocity effect was verified on the following variables: horal... (Complete abstract click electronic access below) / Mestre

This thesis presents a study of the inner plasma disk of Saturn. The results are derived from measurements by the instruments on board the Cassini spacecraft, mainly the Cassini Langmuir probe (LP), which has been in orbit around Saturn since 2004. One of the great discoveries of the Cassini spacecraft is that the Saturnian moon Enceladus, located at 3.95 Saturn radii (1 RS = 60,268 km), constantly expels water vapor and condensed water from ridges and troughs located in its south polar region. Impact ionization and photoionization of the water molecules, and subsequent transport, creates a plasma disk around the orbit of Enceladus. The plasma disk ion components are mainly hydrogen ions H+ and water group ions W+ (O+, OH+, H2O+, and H3O+). The Cassini LP is used to measure the properties of the plasma. A new method to derive ion density and ion velocity from Langmuir probe measurements has been developed. The estimated LP statistics are used to derive the extension of the plasma disk, which show plasma densities above ~20 cm-3 in between 2.7 and 8.8 RS. The densities also show a very variable plasma disk, varying with one order of magnitude at the inner part of the disk. We show that the density variation could partly be explained by a dayside/nightside asymmetry in both equatorial ion densities and azimuthal ion velocities. The asymmetry is suggested to be due to the particle orbits being shifted towards the Sun that in turn would cause the whole plasma disk to be shifted. We also investigate the ion loss processes of the inner plasma disk and conclude that loss by transport dominates loss by recombination in the entire region. However, loss by recombination is still important in the region closest to Enceladus (~±0.5 RS) where it differs with only a factor of two from ion transport loss.

No description available.

ν Octantis is a spectroscopic binary with a semi-major axis and period of 2.55 AU and 2.9 years, respectively. Ramm et al. (2009) discovered a 52 ms^(-1) radial-velocity (RV) perturbation with a period of 417 days in this system. All evidence, both photometric and spectroscopic, suggests the perturbation is the result of a 2.5 MJ planet orbiting the primary star. However, when assuming a “normal” prograde coplanar orbit, celestial mechanics predicts this orbit is unstable, contradicting the observed stability. Simulations by Eberle and Cuntz (2010) showed a retrograde orbit for the planet to be stable for at least 10^7 years. In this thesis, we performed a 10^8 -yr simulation of the retrograde orbit, and found it remained stable. Simulations over a range of planetary semi-major axes, eccentricities, and primary/secondary masses showed that stable retrograde orbits are not possible past a semi-major axis of 1.315 +/- 0.092 AU . Therefore, planetary retrograde orbits are most likely inherently more stable than prograde orbits owing to the absence of stability at known mean-motion resonances. Eccentricity simulations showed that the period of the planet's dominant eccentricity variation is related to the planet's semi-major axis by a second order exponential. However, retrograde orbits tend to have longer eccentricity periods than prograde orbits at the same semi-major axis. There is also evidence that this eccentricity period is connected to the orbital stability. By fitting a keplerian to both Ramm et al. (2009) and current radial velocities, the period of the ν Octantis binary was determined to be 1050.04 +/- 0.02 days with an eccentricity of 0.2359 +/- 0.001 . The planetary orbital solution for just the data reduced in this thesis gave a period of 416.9 +/- 2.1 days and an eccentricity of 0.099 +/- 0.015 , with an RMS scatter of 9.6 ms^(-1). Therefore, the orbital elements are within 1σ of the Ramm et al. (2009) elements. Assuming a retrograde coplanar orbit about the primary star then the planet has a mass of M_pl = 2.3 M_J and a semi-major axis of a_pl = 1.21 +/- 0.09 AU.