<p>A major fraction of stars will pass through a short period of dramatic events in their final evolutionary stage. Low- to intermediate-mass stars, studied here, are stripped of their outer parts in a slow massive wind. This mass loss reshapes both the star and the surrounding medium. The formation of the wind is a consequence of the non-linear interaction of a number of physical processes. Stellar pulsations and efficient dust formation are examples of such key processes. Time-dependent theoretical models, in combination with observations, are useful tools for understanding these winds.</p><p>The main object of this thesis has been the physical improvement of a theoretical wind model. Here the coupling between the dust and gas in the wind is studied in further detail, allowing drift. The methods that have been developed earlier to describe the micro-physical interaction are overviewed and summarized. Previously dust has often been assumed to move at the same velocity as gas. New time-dependent wind models are presented where grain drift has been treated self-consistently. Specifically, the coupling between dust and gas in the wind has been modeled more realistically, with descriptions of both the modified momentum and energy balances, and drift dependent dust formation. The results of these new ``drift models'' have been compared with the results of non-drift models. </p><p>A general result of the study is that the effects of drift are significant and difficult to predict if a simple analytical theory is used. It has been found that dust in drift models tends to accumulate in certain dense regions, an accumulation that was not possible without drift. Moreover the new models show an increased variability in the wind structure. The use of drift in dust formation tends to markedly increase the produced dust. Some sets of model parameters lead to a wind without including drift, but a corresponding wind does not form when drift is included -- and vice versa. The effects of drift are important and can probably not be ignored in realistic models.</p>

This thesis describes aspects of durability of Swedish softwood in above ground applications. The thesis consists of a summary of nine papers, which all aim to explain the existing variation in above ground microbial durability and moisture sensitivity of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris). The methods used were two field tests, one accelerated durability test, and three water permeability tests. The main conclusions made in the study were that Norway spruce sapwood is more susceptible to discolouring fungi than heartwood. With respect to Scots pine, the only important factor for its natural durability above ground was whether the samples consisted of heartwood or of sapwood. There was also no systematic variation between pine heartwood from different stand origins in above ground conditions. Origin had no influence on durability in practice for neither spruce nor pine. Furthermore, in contradiction with traditional thinking, annual ring width and density had no influence on durability in any of the tests. The material came from two different samplings. The ‘old’ material was sampled in the beginning of the 1980s and consisted of Scots pine and Norway spruce from three different origins: the north, the central area, and the south of Sweden. The material was subjected to different handling conditions and surface and end-grain treatments. The ‘old’ material was used in a large above ground field test, carried out between 1985 and 1994. Unfortunately, the spruce sapwood and heartwood was not separated in this field test. In the field trial with the ‘old’ material, the most important factor for the durability of Norway spruce was the samples’ surface- and end-grain treatment. It was also observed that untreated spruce showed better durability than samples that were painted but without proper end-grain treatment. Samples originating from one of the stands were more sensitive towards air-drying than samples from the other two, which was reflected in a higher average moisture content and mass loss for the untreated samples. With respect to Scots pine, the most important factor was whether the sample consisted of heartwood or of sapwood. The heartwood samples were durable irrespective of their previous treatment. The Scots pine sapwood samples, on the other hand, had a very fluctuating moisture content if they were not surface- and end-painted. This was also reflected in higher mass losses in these samples. Even when properly surface- and end grain treated, the sapwood samples did not perform as well as the heartwood samples. The ‘new’ material consisted of Scots pine taken from six different stands, and Norway spruce from five different stands, all from areas in southern Sweden. The sampling was performed in order to achieve a large variation in wood properties. Thus, logs from areas with different climate and growth conditions were collected. This material was used for laboratory tests, and also for the second field test, which was evaluated after a test period of two years. In the second field test untreated Scots pine and Norway spruce samples from the ‘new’ material were investigated. Effects of origin and different tree diameters were examined. Furthermore, Scots pine was separated to heartwood and sapwood, and Norway spruce to mature and juvenile wood. The Norway spruce samples were sawn with vertical or horizontal annual rings. For the Norway spruce in the second field test, vertical annual rings were shown to be very beneficial for avoiding crack formation, while samples with horizontal annual rings displayed a large number of cracks. Despite this, the larger number of cracks did not result in a higher moisture content or more fungal discoloration. Juvenile wood had a slightly higher average discolouring fungal growth grading than the other spruce samples. For Scots pine, the only factor of importance was whether the samples consisted of heartwood or of sapwood. Annual ring width, density and origin had no significant effect on either fungal growth or moisture uptake. This observation held for both Norway spruce samples and Scots pine samples. An accelerated test was run in order to investigate Norway spruce sapwood and heartwood with respect to their differences in durability towards discolouring fungi and moisture uptake. The Mycologg method was used to accelerate fungal growth during a number of forced moisture cycles. The results showed that sapwood was much more sensitive to discolouring fungi than heartwood. Sapwood also recorded a higher average moisture content than heartwood. The differences that were observed between the types of samples were not due to annual ring width, density or origin. It was observed that Norway spruce sapwood samples and heartwood samples showed differences in liquid water permeability. This observation was made especially evident in a droplet absorption test. Water droplets were absorbed much faster on the sapwood samples in comparison with the heartwood samples. This higher affinity to water suggested that a sapwood surface would reach a higher moisture content than a heartwood surface. This observation provides a major explanation of why the sapwood samples showed poorer durability towards discolouring fungi in the Mycologg trials.

A major fraction of stars will pass through a short period of dramatic events in their final evolutionary stage. Low- to intermediate-mass stars, studied here, are stripped of their outer parts in a slow massive wind. This mass loss reshapes both the star and the surrounding medium. The formation of the wind is a consequence of the non-linear interaction of a number of physical processes. Stellar pulsations and efficient dust formation are examples of such key processes. Time-dependent theoretical models, in combination with observations, are useful tools for understanding these winds. The main object of this thesis has been the physical improvement of a theoretical wind model. Here the coupling between the dust and gas in the wind is studied in further detail, allowing drift. The methods that have been developed earlier to describe the micro-physical interaction are overviewed and summarized. Previously dust has often been assumed to move at the same velocity as gas. New time-dependent wind models are presented where grain drift has been treated self-consistently. Specifically, the coupling between dust and gas in the wind has been modeled more realistically, with descriptions of both the modified momentum and energy balances, and drift dependent dust formation. The results of these new ``drift models'' have been compared with the results of non-drift models. A general result of the study is that the effects of drift are significant and difficult to predict if a simple analytical theory is used. It has been found that dust in drift models tends to accumulate in certain dense regions, an accumulation that was not possible without drift. Moreover the new models show an increased variability in the wind structure. The use of drift in dust formation tends to markedly increase the produced dust. Some sets of model parameters lead to a wind without including drift, but a corresponding wind does not form when drift is included -- and vice versa. The effects of drift are important and can probably not be ignored in realistic models.

Carbon is the basis for life, as we know it, but its origin is still largely unclear. Carbon-rich Asymptotic Giant Branch (AGB) stars (carbon stars) play an important rôle in the cosmic matter cycle and may contribute most of the carbon in the Galaxy. In this thesis it is explored how the dust-driven mass loss of these stars depends on the basic stellar parameters by computing a large grid of wind models. The existence of a critical wind regime and mass-loss thresholds for dust-driven winds are confirmed. Furthermore, a steep dependence of mass loss on carbon excess is found. Exploratory work on the effects of different stellar metallicities and the sizes of dust grains shows that strong dust-driven winds develop also at moderately low metallicities, and that typical sizes of dust grains affect the wind properties near a mass-loss threshold. It is demonstrated that the mass-loss rates obtained with the wind models have dramatic consequences when used in models of carbon-star evolution. A pronounced superwind develops soon after the star becomes carbon rich, and it therefore experiences only a few thermal pulses as a carbon star before the envelope is lost. The number of dredge-up events and the thermal pulses is limited by a self-regulating mechanism: each thermal pulse dredges up carbon, which increases the carbon excess and hence also the mass-loss rate. In turn, this limits the number of thermal pulses. The mass-loss evolution during a thermal pulse (He-shell flash) is considered as an explanation of the observations of so-called detached shells around carbon stars. By combining models of dust-driven winds with a stellar evolution model, and a simple hydrodynamic model of the circumstellar envelope, it is shown that wind properties change character during a He-shell flash such that a thin detached gas shell can form by wind-wind interaction. Finally, it is suggested that carbon stars are responsible for much of the carbon in the interstellar medium, but a scenario where high-mass stars are major carbon producers cannot be excluded. In either case, however, the carbon abundances of the outer Galactic disc are relatively low, and most of the carbon has been released quite recently. Thus, there may neither be enough carbon, nor enough time, for more advanced carbon-based life to emerge in the outer Galaxy. This lends some support to the idea that only the mid-part of the Galactic disc can be a “Galactic habitable zone”, since the inner parts of the Galaxy are plagued by frequent supernova events that are presumably harmful to all forms of life.

Aim. In this project, theoretical models of dust driven winds of asymptotic giant branch (AGB) stars with effective temperatures within a range of 2400 − 3200 [K] and relative carbon-to-oxygen abundance C/O &gt; 1 are studied. The aim is to understand if and how a detailed description of the grain size in winds of carbon rich AGB stars affects the wind formation and wind driving processes. Method. The computations were performed with a well tested FORTRAN code by calculating a grid of 60 models with different stellar parameters using grain size-dependent opacities. The results were then compared with models where the small particle approximation (SPA) had been used. Conclusions. The results indicate a certain dependency on grain size of the wind properties. The results from the computations of the majority of the models show no significant diferences however, especially not for the mass loss rates. Thus earlier computations performed using the SPA need not necessarily to be rejected.

No description available.

Vernal pools are small, seasonally filling wetlands found throughout forests of north eastern North America. Vernal pools have been proposed as potential 'hot spots' of carbon cycling. A key component of the carbon cycle within vernal pools is the decomposition of leaf litter. I tested the hypothesis that leaf litter decomposition is more rapid within vernal pools than the adjacent upland. Leaf litter mass losses from litterbags incubated in situ within vernal pools and adjacent upland habitat were measured periodically over one year and then again after two years. The experiment was carried out at 24 separate vernal pools, over two replicate years. This is a novel degree of replication in studies of decomposition in temporary wetlands. Factors influencing decomposition, such as duration of flooding, water depth, pH, temperature, and dissolved oxygen were measured. Mass loss was greater within pools than adjacent upland after 6 months, equal after 12 months, and lower within pools than adjacent upland after 24 months. This evidence suggests that vernal pools of Central Ontario are 'hot spots' of decomposition up to 6 months, but not after 12 and 24 months. In the long term, vernal pools may reduce decomposition rates, compared to adjacent uplands.

La perte de masse est introduite dans des modèles évolutifs qui traitent en détail le transport microscopique induit par la diffusion atomique et les accélérations radiatives pour 28 espèces y inclus tous les isotopes de la base de données OPAL. Les propriétés physiques des solutions sont analysées en détail. Lorsque l'amplitude de la vitesse advective causée par la perte de masse est plus grande que la vitesse de triage dirigée vers le centre de l'étoile, le flux local d'un élément est déterminé par des variations du flux qui se déroulent profondément dans l'étoile. Par contre, l'abondance locale dépend aussi des variations locales des accélérations radiatives. Dans ces étoiles, la séparation chimique causée par la diffusion atomique affecte 30% du rayon externe de l'étoile. Les modèles sont aussi comparés à plusieurs observations d'étoiles AmFm, HAeBe et de Population II dans le but de caractériser le rôle que pourrait jouer la perte de masse en tant que processus qui inhibe la diffusion atomique dans les zones stables de ces étoiles. Les anomalies d'abondances observées à la surface de ces étoiles sont reproduites par des modèles évolutifs qui incluent la diffusion atomique et la perte de masse non-séparée. Les taux de perte de masse considérés ne sont contraints que par les abondances en surface puisque leurs amplitudes sont probablement trop petites pour être observées directement. Quant aux étoiles AmFm et HAeBe, les observations d'abondances sont compatibles avec des taux de perte de masse qui sont au maximum 5 fois plus élevés que le taux de perte de masse solaire, alors que les taux requis pour reproduire les observations d'étoiles de Population II sont jusqu'à 50-100 fois plus élevés que le taux solaire. Des taux de perte de masse plus petit que 10^{-14}Msol/an, qui permettent l'apparition d'une zone convective due aux éléments du pic du fer, mènent à des abondances en surface qui ne sont pas compatibles avec les observations. Les abondances en surface d'étoiles AmFm et de Population II sont régies par la séparation chimique qui se déroule profondément dans l'étoile Delta M/M_* allant de -5 à -6, alors que la séparation se produit plus près de la surface Delta M/M_* plus près de -7 dans les étoiles HAeBe. Par rapport aux modèles avec mélange turbulent, la perte de masse mène à une distribution interne des éléments très différente. Le mélange turbulent conduit à des solutions pour lesquelles les abondances sont homogènes depuis la surface jusque profondément dans l'étoile (solution diffusive), alors que la perte de masse permet la séparation chimique dès le bas de la zone convective de surface (solution advective). Ce résultat pourrait peut-être permettre à l'astérosismologie de déterminer l'importance relative de ces deux processus dans l'intérieur de ces étoiles. / Mass loss has been introduced in a stellar evolution code which takes into account all the effects of atomic diffusion and radiative accelerations for the 28 species included in the OPAL opacity database. The physical properties of the solutions are analyzed in detail. When the advective velocity induced by mass loss dominates the inward settling velocity, the local flux for a given element is determined by flux variations which occur deep within the star. However, local abundances are modulated by local variations in radiative accelerations. Atomic diffusion affects the outer 30% of the stellar radius of these stars. The computed models are also compared to observations of AmFm, HAeBe and Population II stars in order to determine to what extent mass loss competes with atomic diffusion in the stable regions of these stars. Mass loss rates are solely constrained via surface abundances, since the mass loss rate amplitudes are likely too small to be observed directly. It is shown that most chemical anomalies observed at the surface of these stars can be reproduced by models with unseparated mass loss. While AmFm and HAeBe abundance determinations are compatible with mass loss rates which are, at most, 5 times larger than the solar mass loss rate, Population II stars require much larger rates (50 to 100 times the solar rate). Mass loss rates smaller than 10^{-14}Msun/yr which lead to an iron peak convection zone are not compatible with surface abundance observations. Surface abundances in AmFm and Population II stars are shown to be the result of chemical separation occurring deep within the star (Delta M/M_* between -5 and -6); however, in HAeBe stars, for which anomalies appear during the pre--main-sequence, the separation occurs nearer the surface (Delta M/M_* = -7). With respect to turbulent mixing, mass loss leads to very different internal abundance distributions. Whereas turbulent mixing homogenizes abundances from the surface down to depths well within the radiative zone (diffusive solution), mass loss allows for chemical stratification up to the bottom of the surface convection zone (advective solution). This could potentially allow for asteroseismic tests which could elucidate the relative importance of both types of processes in these stars. / Cette thèse a été réalisée en cotutelle. Pour la forme, Gérard Jasniewicz était mon codirecteur 'officiel' en France, bien que mon codirecteur était plutôt Olivier Richard qui m'a encadré lorsque j'étais en France.

1720 MHz OH masers have been detected towards a number of supernova remnants (SNRs) at the shock interface where the SNR slams into the interstellar medium. Models indicate that these masers are shock excited and can only be produced under tight constraints of the physical conditions. In particular, the masers can only form behind a C-type shock. Jets from newlyformed stars plow into the surrounding gas, creating nebulous regions known as Herbig Haro (HH) objects. Signatures of C-type shocks have been found in many HH objects. If conditions behind the shock fronts of HH objects are able to support 1720 MHz OH masers they would be a usefull diagnostic tool for star formation. A survey toward HH objects detected a number of 1720 MHz OH lines in emission, but future observations with arrays are required to confirm the presence of masers. / Physics / M.Sc. (Astronomy)

Orientador: Claudio Bianor Sverzut / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola / Made available in DSpace on 2018-08-13T10:50:42Z (GMT). No. of bitstreams: 1 Teixeira_RicardoRodrigues.pdf: 2062039 bytes, checksum: a4971055a27800f110bd3f6cbcdef9ae (MD5) Previous issue date: 2009 / Resumo: A cultura do tomateiro tem grande importância econômica e alimentar no país. A partir do momento da colheita ocorrem perdas cumulativas de qualidade em decorrência de fatores agroclimáticos como alta temperatura e variações constantes na umidade relativa do ar, além dos fatores relacionados ao manuseio pós-colheita, como danos mecânicos, local de manuseio e equipamentos inadequados para sanitização, classificação e embalagem, treinamento de colhedores e beneficiadores, além do armazenamento e transporte precários. Através de estudos das diversas tarefas que são necessárias a partir do momento da colheita dos tomates, foram analisados os processos para gerar subsídios para utilização de uma unidade móvel de beneficiamento de tomates de mesa com intuito de diminuir a perda pós-colheita, tendo como conseqüência um menor tempo de exposição do produto a condições adversas, mantendo a qualidade dos mesmos e consequentemente, aumentado sua vida de prateleira. A unidade móvel pode ser utilizada não somente para diminuição das perdas e manutenção da qualidade, mas também para melhorar o ambiente de trabalho, proporcionando uma infra-estrutura de apoio aos trabalhadores no campo. / Abstract: The tomato crop has economic and alimentary importance in Brazil. Since the harvesting the losses begins and goes cumulatively decreasing the quality of the product because, at first place, of the climate factors such as temperature, air humidity variation and at second, after harvested, because of the handling done during process from the field to the market, which means: selection, warehousing, cleaning, package, transportation and selling.. By studding the tasks necessary after the tomato harvesting, many information were analyzed given subsidies to use an itinerant unity to do the handling process of in nature tomato in order to avoid post harvest losses and, in consequence, letting the product less exposed to adverse conditions that occurs in the post harvest, kipping the quality and increasing the shelf life. In addition, the itinerant unity gives better work conditions as support for the field work too. / Universidade Estadual de Campi / Tecnologia Pós-Colheita / Doutor em Engenharia Agrícola