Resumo: A compactação do solo tem sido considerada como um dos principais danos ocasionados pelas operações mecanizadas de colheita de madeira, sendo que ocorrem danos diretos ao solo, como a compactação do solo (aumento da densidade do solo), diminuição da aeração e da macroporosidade, presença de camada de impedimento ao crescimento radicular, disponibilidade de água, entre outros. Além dos danos diretos ocorrem os indiretos, que são restrição no crescimento das raízes das plantas, onde ocorrerá a diminuição do crescimento da parte aérea da planta, a susceptibilidade do solo ao processo erosivo, devido a camada compactada, entre outros. A extração de madeira com o trator Skidder é a etapa de colheita na qual se deve ter maior atenção, pois esta máquina provoca grandes danos ao solo, tanto pelo seu peso, quanto pelo arraste de árvores e fustes que realizam sulcos (recalques) no solo. Uma forma de diminuir a compactação do solo é deixar camada de resíduos florestais nos ramais de extração de madeira, com isso haverá a minimização do efeito de compressão do solo pelo trator Skidder com o peso da carga arrastada. O objetivo do presente trabalho foi avaliar o nível de compactação do solo até a 5ª vez que o trator Skidder trafegou no ramal secundário de extração de madeira de Pinus (Pinus elliotti var. elliotti). A avaliação da compactação do solo na testemunha (densificação natural) até a 5ª passada demonstrou que houve compactação até a última vez que o trator Skidder trafegou na área, permitindo constatar que o tráfego de máquinas e fuste nas áreas de colheita promove a compactação do solo. Na interação entre os recalques e o número de passadas houve diferença nos níveis de compactação, sendo que com 5 passadas sobre a mesma área, o recalque do pneu apresentou uma menor compactação (1,34 Mg.m-3) quando comparado com o do fuste... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Soil compaction has been considered one of the major damage caused to the operations of mechanized harvesting, and direct damage occurs to the ground as soil compaction (increased bulk density), reduced aeration and macroporosity, the presence Layer impediment to root growth, water availability, among others. Besides the direct damage occurring indirect damages, which are restricting the growth of plant roots, which occur in the reduction of shoot growth of the plant, susceptibility to soil erosion due to the fact that the presence of the compacted layer, between other damage. To minimize such damage recommend carefully planning machinery traffic on the steps of forest harvesting. With this, the logging with tractor Skidder is the stage at which harvesting should be given more attention, because this machine causes significant damage to land, both by weight and the drag tree trunks and carrying grooves (track) in the soil. One way to reduce soil compaction is to leave layer of forest residues on the extensions of logging, thereby minimizing the effect will be to compress the soil by tractor Skidder with the weight of the load dragged.The aim of this study was to evaluate the level of soil compaction until the 5th time that the tractor Skidder the secondary extension of slash pine logging (Pinus elliottii var. Elliotii). The assessment of soil compaction in control (compression natural) until the 5th month showed that there was compaction until the last time that the tractor Skidder traffic in the area, allowing evidence that the traffic machines and tree trunks collection areas promote soil compaction. In the interaction between the track and the number of passes was no difference in levels of compression, with 5 being passed on to the same site, the track of the tire had a lower density (1.34 Mg.m-3) compared to the tree trunks (1.38 Mg.m-3). At both depths studied... (Complete abstract click electronic access below) / Orientador: Paulo Torres Fenner / Coorientador: Kléber Pereira Lanças / Banca: Ricardo Ralisch / Banca: Maria Helena Moraes / Mestre

Estudos mostram que ocorre uma compactação superficial após alguns anos de utilização do sistema plantio direto (SPD), podendo interferir no desenvolvimento das plantas. A escarificação tem sido utilizada para amenizar os efeitos da compactação sob SPD, porém há evidências de que seus efeitos são de curta duração. O objetivo deste trabalho foi avaliar o comportamento de alguns parâmetros físicos após a escarificação em curto prazo (um ano) nas seguintes profundidades: 0,0-0,10 m; 0,10-0,20 m; 0,20-0,30 m; 0,30-0,40 m. A densidade do solo (Ds) e o grau de compactação (Gc) foram analisados em área de plantio direto por 16 anos (PD), imediatamente após a escarificação (ESC), seis meses (ESC6M) e um ano após a escarificação (ESC12M). Nas camadas superiores a densidade do solo apresentou variação semelhante, com redução significativa em ESC e um aumento expressivo em ESC6M, sendo que a Ds retornou aos valores registrados antes da mobilização em ESC12M. Nos períodos ESC, ESC6M e ESC12M foi observado um aumento da Ds na camada 0,30-0,40 m em comparação com o PD. A escarificação provocou redução do grau de compactação nas camadas 0,0-0,10 m e 0,10-0,20 m, com o Gc retornando aos valores originais um ano após a escarificação. Os maiores valores de Gc foram observados seis meses após a escarificação, porém o solo apresentou grande recuperação visto que em ESC12M o grau de compactação apresentou tendência de retorno aos valores originais em todas as profundidades, possivelmente devido à alta resiliência do solo. Os efeitos da escarificação avaliados pela Ds e Gc apresentaram duração inferior a um ano, sugerindo que neste solo não é necessária esta operação. / Studies show that a surface compaction occurs after some years adoption of no-tillage (NT), which may interfere in plant development. Chiseling has been used to alleviate the effects of soil compaction under NT, but studies show that this operation has short-term effects. The aim of this study was to evaluate the behavior of some physical parameters after chiseling in shortterm (one year) in the following depths: 0.0 to 0.10 m, 0.10-0.20 m, 0.20-0, 30 m, 0.30 to 0.40 m. Soil bulk density (BD) and the degree of compactness (DC) were analyzed in long-term (16 years) no-tillage (NT), chiseling of the long-term no-tillage (CHI), six months (CHI6M) and one year after chiseling (CHI12M). In top layers bulk density showed similar variation, with significant reduction in CHI and a marked increase in CHI6M, returning to the values recorded before mobilization in CHI12M. In periods CHI, CHI6M and CHI12M was an increase in the BD 0.30-0.40 m layer in comparison with NT. Chiseling caused a reduction the degree of compaction in the layers 0.0-0.10 m and 0.10-0.20 m, with DC returning to the original values one year after chiseling. The greatest DC values were observed six months after chiseling, nevertheless the soil showed great recovery whereas in CHI12M the degree of compactness tended to return to the original values in all layers, possibly due the high soil resilience. The duration of chiseling effects measured by BD and DC was less than one year, suggesting in this soil is not necessary this operation.

Estudos mostram que ocorre uma compactação superficial após alguns anos de utilização do sistema plantio direto (SPD), podendo interferir no desenvolvimento das plantas. A escarificação tem sido utilizada para amenizar os efeitos da compactação sob SPD, porém há evidências de que seus efeitos são de curta duração. O objetivo deste trabalho foi avaliar o comportamento de alguns parâmetros físicos após a escarificação em curto prazo (um ano) nas seguintes profundidades: 0,0-0,10 m; 0,10-0,20 m; 0,20-0,30 m; 0,30-0,40 m. A densidade do solo (Ds) e o grau de compactação (Gc) foram analisados em área de plantio direto por 16 anos (PD), imediatamente após a escarificação (ESC), seis meses (ESC6M) e um ano após a escarificação (ESC12M). Nas camadas superiores a densidade do solo apresentou variação semelhante, com redução significativa em ESC e um aumento expressivo em ESC6M, sendo que a Ds retornou aos valores registrados antes da mobilização em ESC12M. Nos períodos ESC, ESC6M e ESC12M foi observado um aumento da Ds na camada 0,30-0,40 m em comparação com o PD. A escarificação provocou redução do grau de compactação nas camadas 0,0-0,10 m e 0,10-0,20 m, com o Gc retornando aos valores originais um ano após a escarificação. Os maiores valores de Gc foram observados seis meses após a escarificação, porém o solo apresentou grande recuperação visto que em ESC12M o grau de compactação apresentou tendência de retorno aos valores originais em todas as profundidades, possivelmente devido à alta resiliência do solo. Os efeitos da escarificação avaliados pela Ds e Gc apresentaram duração inferior a um ano, sugerindo que neste solo não é necessária esta operação. / Studies show that a surface compaction occurs after some years adoption of no-tillage (NT), which may interfere in plant development. Chiseling has been used to alleviate the effects of soil compaction under NT, but studies show that this operation has short-term effects. The aim of this study was to evaluate the behavior of some physical parameters after chiseling in shortterm (one year) in the following depths: 0.0 to 0.10 m, 0.10-0.20 m, 0.20-0, 30 m, 0.30 to 0.40 m. Soil bulk density (BD) and the degree of compactness (DC) were analyzed in long-term (16 years) no-tillage (NT), chiseling of the long-term no-tillage (CHI), six months (CHI6M) and one year after chiseling (CHI12M). In top layers bulk density showed similar variation, with significant reduction in CHI and a marked increase in CHI6M, returning to the values recorded before mobilization in CHI12M. In periods CHI, CHI6M and CHI12M was an increase in the BD 0.30-0.40 m layer in comparison with NT. Chiseling caused a reduction the degree of compaction in the layers 0.0-0.10 m and 0.10-0.20 m, with DC returning to the original values one year after chiseling. The greatest DC values were observed six months after chiseling, nevertheless the soil showed great recovery whereas in CHI12M the degree of compactness tended to return to the original values in all layers, possibly due the high soil resilience. The duration of chiseling effects measured by BD and DC was less than one year, suggesting in this soil is not necessary this operation.

[Some symbols cannot be rendered in the following metadata – please see the PDF file for an accurate version of the Abstract] ¶ Recombination within the bulk and at the surfaces of crystalline silicon has been investigated in this thesis. Special attention has been paid to the surface passivation achievable with plasma enhanced chemical vapour deposited (PECVD) silicon nitride (SiN) films due to their potential for widespread use in silicon solar cells. The passivation obtained with thermally grown silicon oxide (SiO2) layers has also been extensively investigated for comparison. ¶ Injection-level dependent lifetime measurements have been used throughout this thesis to quantify the different recombination rates in silicon. New techniques for interpreting the effective lifetime in terms of device characteristics have been introduced, based on the physical concept of a net photogeneration rate. The converse relationships for determining the effective lifetime from measurements of the open-circuit voltage (Voc) under arbitrary illumination have also been introduced, thus establishing the equivalency of the photoconductance and voltage techniques, both quasi-static and transient, by allowing similar possibilities for all of them. ¶ The rate of intrinsic recombination in silicon is of fundamental importance. It has been investigated as a function of injection level for both n-type and p-type silicon, for dopant densities up to ~5x1016cm-3. Record high effective lifetimes, up to 32ms for high resistivity silicon, have been measured. Importantly, the wafers where commercially sourced and had undergone significant high temperature processing. A new, general parameterisation has been proposed for the rate of band-to-band Auger recombination in crystalline silicon, which accurately fits the experimental lifetime data for arbitrary injection level and arbitrary dopant density. The limiting efficiency of crystalline silicon solar cells has been re-evaluated using this new parameterisation, with the effects of photon recycling included. ¶ Surface recombination processes in silicon solar cells are becoming progressively more important as industry drives towards thinner substrates and higher cell efficiencies. The surface recombination properties of well-passivating SiN films on p-type and n-type silicon have been comprehensively studied, with Seff values as low as 1cm/s being unambiguously determined. The well-passivating SiN films optimised in this thesis are unique in that they are stoichiometric in composition, rather than being silicon rich, a property which is attributed to the use of dilute silane as a process gas. A simple physical model, based on recombination at the Si/SiN interface being determined by a high fixed charge density within the SiN film (even under illumination), has been proposed to explain the injection-level dependent Seff for a variety of differently doped wafers. The passivation obtained with the optimised SiN films has been compared to that obtained with high temperature thermal oxides (FGA and alnealed) and the limits imposed by surface recombination on the efficiency of SiN passivated solar cells investigated. It is shown that the optimised SiN films show little absorption of UV photons from the solar spectrum and can be easily patterned by photolithography and wet chemical etching. ¶ The recombination properties of n+ and p+ emitters passivated with optimised SiN films and thermal SiO2 have been extensively studied over a large range of emitter sheet resistances. Both planar and random pyramid textured surfaces were studied for n+ emitters, where the optimised SiN films were again found to be stoichiometric in composition. The optimised SiN films provided good passivation of the heavily doped n+-Si/SiN interface, with the surface recombination velocity increasing from 1400cm/s to 25000cm/s as the surface concentration of electrically active phosphorus atoms increased from 7.5x1018cm-3 to 1.8x1020cm-3. The optimised SiN films also provided reasonable passivation of industrial n+ emitters formed in a belt-line furnace. It was found that the surface recombination properties of SiN passivated p+ emitters was poor and was worst for sheet resistances of ~150./ . The hypothesis that recombination at the Si/SiN interface is determined by a high fixed charge density within the SiN films was extended to explain this dependence on sheet resistance. The efficiency potential of SiN passivated n+p cells has been investigated, with a sheet resistance of 80-100./ and a base resistivity of 1-2.cm found to be optimal. Open-circuit voltages of 670-680mV and efficiencies up to ~20% and ~23% appear possible for SiN passivated planar and textured cells respectively. The recombination properties measured for emitters passivated with SiO2, both n+ and p+, were consistent with other studies and found to be superior to those obtained with SiN passivation. ¶ Stoichiometric SiN films were used to passivate the front and rear surfaces of various solar cell structures. Simplified PERC cells fabricated on 0.3.cm p-type silicon, with either a planar or random pyramid textured front surface, produced high Voc’s of 665-670mV and conversion efficiencies up to 19.7%, which are amongst the highest obtained for SiN passivated solar cells. Bifacial solar cells fabricated on planar, high resistivity n-type substrates (20.cm) demonstrated Voc’s up to 675mV, the highest ever reported for an all-SiN passivated cell, and excellent bifaciality factors. Planar PERC cells fabricated on gettered 0.2.cm multicrystalline silicon have also demonstrated very high Voc’s of 655-659mV and conversion efficiencies up to 17.3% using a single layer anti-reflection coating. Short-wavelength internal quantum efficiency measurements confirmed the excellent passivation achieved with the optimised stoichiometric SiN films on n+ emitters, while long-wavelength measurements show that there is a loss of short-circuit current at the rear surface of SiN passivated p-type cells. The latter loss is attributed to parasitic shunting, which arises from an inversion layer at the rear surface due to the high fixed charge (positive) density in the SiN layers. It has been demonstrated that that a simple way to reduce the impact of the parasitic shunt is to etch away some of the silicon from the rear contact dots. An alternative is to have locally diffused p+ regions under the rear contacts, and a novel method to form a rear structure consisting of a local Al-BSF with SiN passivation elsewhere, without using photolithography, has been demonstrated.

The phenomenon called soil aggregate coalescence occurs at contact-points between aggregates and causes soil strength to increase to values that can inhibit plant root exploration and thus potential yield. During natural wetting and drying, soil aggregates appear to ‘weld’ together with little or no increase in dry bulk density. The precise reasons for this phenomenon are not understood, but it has been found to occur even in soils comprised entirely of water stable aggregates. Soil aggregate coalescence has not been widely observed and reported in soil science and yet may pose a significant risk for crops preventing them from achieving their genetic and environmental yield potentials. This project used soil penetrometer resistance and an indirect tensile-strength test to measure the early stages of aggregate coalescence and to evaluate their effects on the early growth of tomato plants. The early stages of aggregate coalescence were thought to be affected by a number of factors including: the matric suction of water during application and subsequent drainage, the overburden pressure on moist soil in the root zone, the initial size of soil aggregates prior to wetting, and the degree of sodicity of the soil aggregates. Seven mainexperiments were conducted to evaluate these factors. The matric suction during wetting of a seedbed affects the degree of aggregate slaking that occurs, and the strength of the wetted aggregates. The matric suction during draining affects the magnitude of ‘effective stresses’ that operate to retain soil structural integrity as the soil drains and dries out. An experiment was conducted to evaluate the influence of matric suction (within a range of suctions experienced in the field) on aggregate coalescence using soils of two different textures. Sieved aggregates (0.5 to 2 mm diameter) from a coarse-textured and two fine-textured (swelling) soils were packed into cylindrical rings (4.77 cm i.d., 5 cm high) and subjected to different suctions on wetting (near-saturation, and 1 kPa), and on draining (10 kPa on sintered-glass funnels, and 100 kPa on ceramic pressure plates). After one-week of drainage, penetrometer resistance was measured as a function of depth to approximately 45 mm (penetrometer had a recessedshaft, cone diameter = 2 mm, advanced at a rate of 0.3 mm/min). Tensile strength of other core-samples was measured after air-drying using an indirect “Brazilian” crushing test. For the coarse-textured soil, penetrometer resistance was significantly greater for samples wet to near-saturation, despite there being no significant increase in dry bulk density; this was not the case for the finer-textured soils, and it was difficult to distinguish the effects of variable bulk density upon drying from those of the imposed wetting treatments. In both coarse- and fine-textured soils, the tensile strength was significantly greater for samples wet to near-saturation. Thus wetting- and draining-suctions were both found to influence the degree of soil aggregate coalescence as measured by penetrometer resistance and tensile strength. Aggregate coalescence in irrigated crops is known to develop as the growing season progresses. It was therefore thought to be linked to the repeated occurrence of matric suctions that enhance the phenomenon during cycles of wetting and draining. An experiment was conducted to determine the extent of aggregate coalescence in a coarsetextured and two fine-textured (swelling clay) soils during 8 successive cycles of wetting and draining. Sieved aggregates (0.5 to 2 mm diameter) from each soil were packed into cylindrical rings (4.77 cm i.d., 5 cm high) and wetted to near saturation for 24 h. They were then drained on ceramic pressure plates to a suction of 100 kPa for one week, after which penetrometer resistance and tensile strength were measured as described above. The degree of expression of aggregate coalescence depended on soil type. For the coarse-textured soil, repeated wetting and draining significantly increased bulk density, penetrometer resistance and tensile strength. For the fine-textured soil, penetrometer resistance and bulk density did not vary significantly with repeated wetting and draining; on the contrary, there was evidence in these swelling clay soils to suggest bulk density and penetrometer resistance decreased. However, there was a progressive increase in tensile strength as cycles of wetting and draining progressed. The expansive nature of the fine-textured soil appears to have masked the development of aggregate coalescence as measured by penetrometer resistance, but its expression was very clear in measurements of tensile strength despite the reduction in bulk density with successive wetting and draining. Field observations have indicated that aggregate coalescence is first expressed at the bottom of the seedbed and that it develops progressively upward to the soil surface during the growing season. This suggests that overburden pressures may enhance the onset of the phenomenon by increasing the degree of inter-aggregate contact. Soils containing large quantities of particulate organic matter were known to resist the onset of aggregate coalescence to some extent. An experiment was conducted to evaluate the effects of soil organic matter and overburden pressures, by placing brass cylinders of various weights (equivalent to static load pressures of 0, 0.49, 1.47 and 2.47 kPa) on the top of dry soil aggregates (0.5 – 2 mm diameter) having widely different soil organic carbon contents placed in steel rings 5 cm high and 5 cm i.d. With the weights in place, the aggregates were wetted to near-saturation for 24 h and then drained on ceramic pressure plates to a suction of 100 kPa for one week. Bulk density, penetrometer resistance and tensile strength were measured when the samples were removed from the pressure plates and they all increased significantly with increasing overburden pressure in the soil with low organic matter content, but not in the soil with high organic matter content. The amount of tillage used to prepare seedbeds influences the size distribution of soil aggregates produced – that is, more tillage produces finer seedbeds. The size distribution of soil aggregates affects the number of inter-aggregate contact points and this was thought to influence the degree of aggregate coalescence that develops in a seedbed. Previous work has shown that soil organic matter reduces aggregate coalescence and so an experiment was conducted to evaluate the effects of aggregate size and organic matter on the phenomenon. For soils with high and low organic matter contents, aggregate size fractions of < 0.5, 0.5 – 2, 2 – 4, and < 4 mm were packed into soil cores (as above) and wetted to near-saturation then drained to 100 kPa suction as described above. Penetrometer resistance and tensile strength were measured and found to increase directly with the amount of fine material present in the soil cores – being greater in the < 0.5 mm and < 4 mm fractions, and being less in the 0.5 – 2 mm and 2 – 4 mm fractions. In all cases, penetrometer resistance and tensile strength were lower in the samples containing more organic matter. The rate at which soil aggregates are wetted in a seedbed affects the degree of slaking and densification that occurs, and the extent to which aggregates are wetted influences the overall strength of a seedbed. Both wetting rate and the extent of wetting were believed to influence the onset of aggregate coalescence and were thought to be affected by soil organic matter and irrigation technique. An experiment was therefore designed to separate these effects so that improvements to management could be evaluated for their greatest efficacy – that is, to determine whether management should focus on improving irrigation technique or increasing soil organic matter content, or both. The rate of wetting was controlled by spraying (or not spraying) soil aggregates (0.5 – 2 mm diameter) with polyvinyl alcohol (PVA). Samples of coarse- and fine-textured soils were packed into steel rings (as above) and subjected to different application rates of water (1, 10 and 100 mm/h) using a dripper system controlled by a peristaltic pump. Samples were brought to either a near-saturated state or to a suction of 10 kPa for 24 h, and then drained on a pressure plate at a suction of 100 kPa for one week. Measurements of penetrometer resistance and tensile strength were then made as described above. As expected, penetrometer resistance was lower in samples treated with PVA before wetting (slower wetting rates) and in samples held at a greater suction (10 kPa) after initial wetting (greater inter-aggregate strength). The effects were more pronounced in the coarse-textured soil. In both coarse- and fine-textured soils, tensile strengths increased with increasing wetting rate (greatest for 100 mm/h) and extent of wetting (greater when held at near-saturated conditions). The rate of wetting was found to be somewhat more important for promoting aggregate coalescence than the extent of wetting. Because aggregate coalescence often occurs with little or no increase in bulk density, an explanation for the increase in penetrometer resistance and tensile strength is unlikely to be explained by a large increase in the number of inter-aggregate contacts. An increase in the strength of existing points of inter-aggregate contact was therefore considered in this work. For inter-aggregate bond strengths to increase, it was hypothesized that small increases in the amount of mechanically (or spontaneously) dispersed clay particles, and subsequent deposition at inter-aggregate contact points could increase aggregate coalescence as measured by penetrometer resistance and tensile strength. An experiment was devised to manipulate the amount of spontaneously dispersed clay in coarse- and fine-textured soils of high and low organic matter content. The degree of sodicity of each soil was manipulated by varying the exchangeable sodium percentage (ESP) of soil aggregates (0.5 – 2mm) above and below a nominal threshold value of 6. Dry aggregates were then packed into steel rings (as above) and subjected to wetting near saturation, then draining to a suction of 100 kPa for one week as described above. Measurements were then taken of penetrometer resistance and tensile strength, both of which were affected by ESP in different ways. In the coarse-textured soil, sodicity enhanced aggregate slaking and dispersion, which increased bulk density. While penetrometer resistance also increased, its effect on aggregate coalescence could not be separated from a simple effect of increased bulk density. Similarly, the effect of sodicity on aggregate coalescence in the fine-textured soil was confounded by the higher water contents produced by greater swelling, which produced lower-than-expected penetrometer resistance. Measurements of tensile strength were conducted on air-dry samples, and so the confounding effects of bulk density and water content were eliminated and it was found that tensile strength increased with sodicity in both coarse- and fine-textured soils. The presence of dispersed clay was therefore implicated in the development of aggregate coalescence in this work. Finally, a preliminary evaluation of how the early stages of aggregate coalescence might affect plant growth was attempted using tomatoes (Gross lisse) as a test plant. Seeds were planted in aggregates (0.5 – 4 mm) of a coarse- or fine-textured soil packed in steel rings. These were wetted at a rate of 1 mm/h to either near-saturation (for maximum coalescence) or to a suction of 10 kPa (for minimum coalescence) and held under these conditions for 24 h. All samples were then transferred to a ceramic pressure plate for drainage to 100 kPa suction for one week. Samples were then placed in a growth-cabinet held at 20C with controlled exposure to 14 h light/day. Germination of the seeds, plant height, and number and length of roots were observed. Germination of the seeds held at near-saturation in both coarse- and fine-textured soils was delayed by 24 h compared with seeds held at 10 kPa suction. Neither the number nor the length of tomato roots differed significantly between the different treatments and soils. In the coarse-textured soil, however, the total root length over a period of 14 days was somewhat greater in the uncoalesced samples than in the coalesced samples, but this difference was not statistically significant. These results suggest that aside from delaying germination, aggregate coalescence may not have a large effect on early growth of tomato plants. However, this is not to say that detrimental effects may not be manifest at later stages of plant growth, and this certainly needs to be evaluated, particularly because aggregate coalescence increase with repeated cycles of wetting and draining. In conclusion, the primary findings of the work undertaken in this thesis were: • Rapid wetting of soil aggregates to near-saturation enhanced the onset of soil aggregate coalescence as measured by (in some cases) penetrometer resistance at a soil water suction of 100 kPa, and (in most cases) tensile strength of soil cores in the air-dry state. The rate of wetting appeared to be more important in bringing on aggregate coalescence than how wet the soil eventually became during wetting. This means reducing the rate at which irrigation water is applied to soils may reduce the onset of aggregate coalescence more effectively than controlling the total amount of water applied – though both are important. The literature reports that aggregate coalescence occurs in the field over periods of up to several months, involving multiple wetting and draining cycles, but the work here demonstrated that this can occur over much shorter time periods depending on conditions imposed. • Aggregate coalescence occurred in coarse-textured soils regardless of whether the bulk density increased during wetting and draining. In finer-textured soils, the response to wetting conditions varied and was complicated by changes in bulk density and water content due to swelling. • Small overburden pressures enhanced the onset of aggregate coalescence, but these effects were diminished in the presence of high soil organic matter contents. • Finer aggregate size distributions (which are often produced in the field by excessive tillage during seedbed preparation) invariably led to greater aggregate coalescence than coarser aggregate size distributions. The effects of aggregate size were mitigated to some extent by higher contents of soil organic matter. • Sodicity enhanced aggregate coalescence as measured by tensile strength, but when penetrometer resistance was measured in the moist state, the effects were masked to some extent by higher water contents generated by swelling and dispersion. This work suggests that tensile strength (in the air dry state) may be a more effective measure of aggregate coalescence than penetrometer resistance. • Early plant response to aggregate coalescence was not large, but the response may become magnified during later stages of growth. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1297583 / Thesis (Ph.D.) -- School of Earth and Environmental Sciences, 2007

The properties of composite materials in which spherical inclusions are embedded in a matrix of some kind, have been studied for many decades and many analytical models have been developed which measure these properties. There has been a steady progression in the complexity of models over the years, providing greater insight into the nature of these materials and improving the accuracy in the measurement of their properties. Some of the properties with which this thesis is concerned are, the elastic, thermal and electrical properties of such composites. The size of the spherical inclusion which acts as the reinforcing phase, has a major effect on the overall properties of composite materials. Once an inclusion is embedded into a matrix, a third region of different properties between the inclusion and matrix is known to develop which is called the interphase. It is well known in the composite community that the smaller the inclusion is, the larger the interphase region which develops around it. Therefore, with the introduction of nanoparticles as the preferred reinforcing phase for some composites, the interphase has a major effect on its properties. It is the aim of this thesis to consider the role of the interphase on the properties of composites by modeling it as an inhomogeneous region. There is much scientific evidence to support the fact that the interphase has an inhomogeneous nature and many papers throughout the thesis are cited which highlight this. By modeling the inhomogeneous properties by arbitrary mathematical functions, results are obtained for the various properties in terms of these general functions. Some specific profiles for the inhomogeneous region are considered for each property in order to demonstrate and test the models against some established results.

<p>In this thesis the conductivity of strained materials has been investigated using density functional theory and a semiclassical transport theory based on the Boltzmann equation.</p><p>In transition metals trends are reproduced without adjustable parameters. The introduction of one temperature dependent cross section allowed the reproduction of resistivity trends between 10 and 1000K.</p><p>The effect of strain on transition metals in bcc and fcc structure was studied deforming the unit cell along the tetragonal deformation path. The anisotropy of the conductivity varied on wide range of the c/a-ratio. The orbitals at the Fermi level determined the principal behavior. Pairs of elements with permutated number of electrons and holes in the 4d band showed similar behavior. The concept of the tetragonal deformation was also applied on semiconductors.</p><p>The deformation of Vanadium in X/V superlattices (X=Cr,~Fe,~Mo) due to Hydrogen loading depends on the properties of X. It was found that counteracting effects due to the presence of Hydrogen influence the conductivity.</p><p>It is shown that a small magnetic moment of the V host reduces the hydrogen solubility. Depending on the magnitude of the tetragonal distortion of V, the hydrogen dissolution becomes favored for larger moments.</p><p>Finally, extra charge filling of the bandstructure of Cr and Mo decreases the Fermi velocity and increases the density of states at the Fermi energy.</p>

L'aéroacoustique est une filière de l'acoustique qui étudie la génération de bruit par un mouvement fluidique turbulent ou par les forces aérodynamiques qui interagissent avec les surfaces. Ce secteur en pleine croissance a attiré des intérêts récents en raison de l'évolution de la transportation aérienne, terrestre et spatiale. Alors que les tests sur un objet réel sont possibles, leur implantation est généralement compliquée et les résultats sont facilement corrompus par le bruit ambiant. Par conséquent, les tests plus strictement contrôlés au laboratoire utilisant les modèles de dimensions réduites sont préférables. Toutefois, lorsque les dimensions sont réduites par un facteur de M, l'amplitude et la bande passante des ondes acoustiques correspondantes se multiplient respectivement par 10logM en décibels et par M. Les microphones avec une bande passante de plusieurs centaines de kHz et une plage dynamique couvrant de 40Pa à 4 kPa sont ainsi nécessaires pour les mesures aéroacoustiques. Les microphones MEMS ont été étudiés depuis plus de vingt ans, et plus récemment, l'industrie des semiconducteurs se concentre de plus en plus sur ce domaine. Par rapport à tous les autres principes de fonctionnement, grâce à la miniaturisation, les microphones de type piézorésistif peuvent atteindre une bande passante plus élevée et ils sont ainsi bien adaptés pour les mesures aéroacoustiques. Dans cette thèse, deux microphones MEMS de type piézorésistif à base de silicium polycristallin (poly-Si) latéralement cristallisé par l'induction métallique (MILC) sont conçus et fabriqués en utilisant respectivement les techniques de microfabrication de surface et de volume. Ces microphones sont calibrés à l'aide d'une source d'onde de choc (N-wave) générée par une étincelle électrique. Pour l'échantillon fabriqué par le micro-usinage de surface, la sensibilité statique mesurée est de 0.4 μV/V/Pa, la sensibilité dynamique est de 0.033 μV/V/Pa et la plage fréquentielle commence à 100 kHz avec une fréquence du premier mode de résonance à 400 kHz. Pour l'échantillon fabriqué par le micro-usinage de volume, la sensibilité statique mesurée est de 0.28 μV/V/Pa, la sensibilité dynamique est de 0.33 μV/V/Pa et la plage fréquentielle commence à 6 kHz avec une fréquence du premier mode de résonance à 715 kHz.

In this thesis the conductivity of strained materials has been investigated using density functional theory and a semiclassical transport theory based on the Boltzmann equation. In transition metals trends are reproduced without adjustable parameters. The introduction of one temperature dependent cross section allowed the reproduction of resistivity trends between 10 and 1000K. The effect of strain on transition metals in bcc and fcc structure was studied deforming the unit cell along the tetragonal deformation path. The anisotropy of the conductivity varied on wide range of the c/a-ratio. The orbitals at the Fermi level determined the principal behavior. Pairs of elements with permutated number of electrons and holes in the 4d band showed similar behavior. The concept of the tetragonal deformation was also applied on semiconductors. The deformation of Vanadium in X/V superlattices (X=Cr,~Fe,~Mo) due to Hydrogen loading depends on the properties of X. It was found that counteracting effects due to the presence of Hydrogen influence the conductivity. It is shown that a small magnetic moment of the V host reduces the hydrogen solubility. Depending on the magnitude of the tetragonal distortion of V, the hydrogen dissolution becomes favored for larger moments. Finally, extra charge filling of the bandstructure of Cr and Mo decreases the Fermi velocity and increases the density of states at the Fermi energy.

The bulk modulus of pure hydraulic oil and its dependency on pressure and temperature has been studied extensively over the past years. A comprehensive review of some of the more common definitions of fluid bulk modulus is conducted and comments on some of the confusion over definitions and different methods of measuring the fluid bulk modulus are presented in this thesis. In practice, it is known that there is always some form of air present in hydraulic systems which substantially decreases the oil bulk modulus. The term effective bulk modulus is used to account for the effect of air and/or the compliance of transmission lines. A summary from the literature of the effective bulk modulus models for a mixture of hydraulic oil and air is presented. Based on the reviews, these models are divided into two groups: “compression only” models and “compression and dissolve” models. A comparison of various “compression only” models, where only the volumetric compression of air is considered, shows that the models do not match each other at the same operating conditions. The reason for this difference is explained and after applying some modifications to the models, a theoretical model of the “compression only” model is suggested. The “compression and dissolve” models, obtained from the literature review, include the effects of the volumetric compression of air and the volumetric reduction of air due to the dissolving of air into the oil. It is found that the existing “compression and dissolve” models have a discontinuity at some critical pressure and as a result do not match the experimental results very well. The reason for the discontinuity is discussed and a new “compression and dissolve” model is proposed by introducing some new parameters to the theoretical model. A new critical pressure (PC) definition is presented based on the saturation limit of oil. In the new definition, the air stops dissolving into the oil after this critical pressure is reached and any remaining air will be only compressed afterwards. An experimental procedure is successfully designed and fabricated to verify the new proposed models and to reproduce the operating conditions that underlie the model assumptions. The pressure range is 0 to 6.9 MPa and the temperature is kept constant at °C. Air is added to the oil in different forms and the amount of air varies from about 1 to 5%. Experiments are conducted in three different phases: baseline (without adding air to the oil), lumped air (air added as a pocket of air to the top of the oil column) and distributed air (air is distributed in the oil in the form of small air bubbles). The effect of different forms and amounts of air and various volume change rates are investigated experimentally and it is shown that the value of PC is strongly affected by the volume change rate, the form, and the amount of air. It is also shown that the new model can represent the experimental data with great accuracy. The new proposed “compression and dissolve” model can be considered as a general model of the effective bulk modulus of a mixture of oil and air where it is applicable to any form of a mixture of hydraulic oil and air. However, it is required to identify model parameters using experimental measurements. A method of identifying the model parameters is introduced and the modeling errors are evaluated. An attempt is also made to verify independently the value of some of the parameters. The new proposed model can be used in analyzing pressure variations and improving the accuracy of the simulations in low pressure hydraulic systems. The new method of modeling the air dissolving into the oil can be also used to improve the modeling of cavitation phenomena in hydraulic systems.