<p>Crystal structure, morphology and crystallization kinetics of melt-crystallized polypropylene and poly(propylene-stat-ethylene) fractions with 2.7 to 11.0 mol% of ethylene were studied by differential scanning calorimeter, wide- and small-angle X-ray scattering, polarized light microscopy, transmission electron microscopy and infrared spectroscopy. With increasing ethylene content the poly(propylene-stat-ethylene) fractions showed unchanged crystallinity, increased unit cell volume and constant crystal thickness in combination with a shortened helix length. This indicated that a fraction of ethylene defects were incorporated into the crystal structure. During the isothermal crystallization both α- and γ-crystals could be formed. The γ-crystal fraction increased with increasing ethylene content and increasing crystallization temperature. For samples with α- and γ-crystal contents, multimodal melting was observed and a noticeable γ- to α-crystal conversion was observed on slow heating. The spherulitic structure of the copolymers was coarser than that for the homopolymer.</p><p>The crystalline lamellae in copolymers exhibited profound curvature in contrast to the straighter cross-hatched α-crystals typical to the homopolymer. Area dependence of electrical breakdown strength was studied for thin polypropylene homopolymer films. The measurements were performed with an automatic measurement system equipped with a scanning electrode arm. Five different electrodes having areas between 0.045 cm2 and 9.3 cm2 were used and typically 40-80 breakdowns per sample and electrode area were collected. All measurements were performed on dry samples in air at room temperature. The data was analyzed statistically and the Weibull function parameters α and β, the first one related to 63% probability for the sample to break down and the second one to the width of the distribution were fitted to the obtained data. Different features concerning the measurement system and conditions, e.g. criteria for the automatic detection of the breakdowns, effect of electrode edge design, partial discharges, DC ramp speed and humidity were critically analyzed. It was concluded that the obtained α-parameter values were stable and repeatable over several years of time. The β-parameter values, however, varied ± 10-30%, more for the large than the small electrodes, and were also sensitive to the changes both in the sample itself and in the measurement conditions.</p><p>Breakdown strengths of over 50 capacitor grade polypropylene films were analyzed. The obtained α-parameter values were between 450 and 850 V/μm, depending on the film grade and electrode area. In addition to the high breakdown strengths, reflected by the obtained α-values, another, sparse distribution consisting of low breakdown strengths was revealed when the amount of measurement points was high enough. This means that more than one Weibull distribution could be needed to describe the breakdown strength behavior of a polypropylene film. Breakdown values showed decreasing area dependence with decreasing electrode area. Breakdown strengths for larger sample areas were predicted from the small area data by area- and Weibull extrapolation. The area extrapolation led to predicted α-values 50% higher than measured at 4 m² whereas the Weibull extrapolation showed an accuracy of ±15 % when predicted and measured values were compared.</p><p>Breakdown strengths were also extrapolated for film areas similar to those in impregnated power capacitors. It turned out that the power capacitors, tested at the factory, performed much better than predicted by the extrapolation. However, a few weak spots with very low breakdown values were also found. For the poly(ethyelene terephtalate) dielectric, which is not swelled by the impregnation liquid, the large area breakdown strength was predictable. This indicates that for polypropylene film processing and impregnation led, in addition to the improved large area breakdown performance, also to sparse weak spots with low breakdown probabilities. Different Weibull distributions were responsible for the breakdown strengths for the processed and impregnated polypropylene than for the dry film samples.</p>

No description available.

O objetivo da presente pesquisa consiste em identificar feições macro e micromorfológicas (em escala de campo e do microscópio óptico, respectivamente) e evidências analíticas (parâmetros físicos e químicos) que indiquem possíveis mecanismos de translocações, perdas e acumulações de matéria no interior da cobertura pedológica, possivelmente responsáveis pela modificação do modelado em um transecto localizado na região de São Pedro (SP). O transecto estudado, denominado Espraiado, subdivide-se em 5 segmentos: segmento superior, segmento médio e segmentos inferiores a, b e c. O segmento superior apresenta baixas declividades e presença do Neossolo Quarzarênico, solo espesso e arenoso caracterizado pela sequência vertical de horizontes A, AE, E com bandas e C-1. O segmento médio apresenta declividades comparativamente médias e presença dos Argissolos Amarelo e Acinzentado, caracterizados pela espessura menor que a do Neossolo Quartzarênico e pela sequência de horizontes A, AE, E com bandas, Bt, C-2 e C-3. Os segmentos inferiores possuem as maiores declividades e solos com a maior presença de argila e a menor espessura do transecto: Cambissolo Háplico, com sequência de horizontes A, ABi, Bi, C-2 e C-3; e Neossolo Litólico, com sequência de horizontes A, C-2 e C-3. As feições identificadas, principalmente macro e micromorfológicas, indicam a ocorrência de processos químicos e mecânicos no interior da cobertura pedológica, desencadeados principalmente pela circulação da água no interior dos solos e responsáveis pela redistribuição e/ou remoção de material em todo o transecto. No Neossolo Quartzarênico, onde há provavelmente maior infiltração de água e dominância do fluxo interno vertical, foi encontrada maior presença das seguintes feições: bandas e interbandas, interpretadas como evidências de-iluviação de plasma; golfos nas partículas de quartzo, interpretados como evidências de dissolução de sílica; e feições relacionadas ao fenômeno de plasma infusion, o qual provoca a desintegração das partículas de areia em partículas menores. Nos Argissolos (Amarelo e Acinzentado) e no Cambissolo Háplico, onde há menor infiltração de água e provavelmente maior presença de fluxo interno lateral, estas feições aparecem em menor quantidade, mas dominam outras, tais como: bandas e interbandas, provavelmente associadas à perda de de plasma do horizonte subjacente; oríficos e concavidades superficiais provavelmente associados ao processo de piping, mosqueamentos que indicam processos de hidromorfia e, portanto, maior mobilidade do ferro reduzido, e feições relacionadas à mobilização de plasma e esqueleto nos macroporos. As únicas feições encontradas que indicam a deposição ou precipitação de elementos no sistema foram as bandas do Neossolo Quartzarênico (as quais indicam simultaneamente perda de matéria), e as denominadas “superfícies duplas" das partículas de quartzo. Desta forma, parece que a cobertura pedológica do transecto Espraiado caracteriza-se principalmente pela perda generalizada de matéria, provavelmente associada a uma perda de volume dos solos e a um rebaixamento do modelado local, assim como descrito em outras áreas tropicais. Assim, os resultados apresentados estão em desacordo com a idéia de oposição entre os processos pedogenéticos e morfogenéticos, comumente presente na visão tradicional das relações solo-relevo, uma vez que os processos deduzidos são possivelmente responsáveis não apenas por mudanças de características morfológicas da cobertura pedológica, mas também por mudanças no modelado. Além disto, a presença destes processos na área estudada parece estar de acordo com os princípios da teoria de etchplanação. / The objective of this research is to identify macro and micromorphological features (field and and optical microscopic scale, respectively) and analitycal evidences (physical and chemical parameters), indicative of translocations, losses and acumulations mechanisms inside the soils, that probably leads to changes in the form of a transect, localized in São Pedro region, São Paulo State, Brazil. The studied transect, called Espraiado, is divided into five segments: superior segment, medium segment and a, b and c inferior segments. The superior segment presents low slope angles and presence of quartz sand, that is a deep soil characterized of the vertical sequence of A, AE, E (with bands) and C-1 horizons. The medium segment has moderate slope angles and the presence of podzolic soils, that are shallower than quartz sand soil and follow vertical sequence of horizons: A, AE, E (with bands), Bt, C-2 and C-3. The inferior segments have the highest slope angles and soils with the highest clay content and the lowest thickness of the transect: cambic soil, that has vertical sequence of A, ABi, Bi, C-2 and C-3 horizons; or A, C-2 and C-3 horizons. The identified macro and micromorphological features suggest the occurrence of chemical and mechanical processes inside the pedological cover, mainly triggered for water circulation in soils. These processes are probably responsible for material translocation and/or remotion in the whole transect. In quartz sand soil, where there are probably high water infiltration rates and dominant internal vertical flux, there are the great amounts of the follow features: bands/interband, interpreted as plasma e-illuviation evidences, embayed quartz particles, interpreted as silica dissolution evidences, and plasma infusion, a phenomenon that leads to the desintegration of sand-sized particles and the formation of silt-sized particles. In podzolic and cambic soils ,where there are probably lower water infiltration rates soils and dominant internal lateral flux, there are fewer of these features and dominance of others, like bands/interbands probably related to plasma losses; holes and concavities probably related to piping processes, motlles suggesting hydromorfic processes that induce the mobility of reduced Fe, and features associated to plasma and skeleton mobility in macropores. Only two features suggest deposition or precipitation of elements in the soil system: bands, mainly in quartz sand soil, and the “double surfaces" of the quartz particles. It seems that pedological cover of the Espraiado transect is mainly characterized by general losses that lead to soil volume loss and landsurface lowering, as described in other tropical areas. Therefore, the presented results disagree with the opposition idea of pedogenetic and morphogenetic processes, presented in traditional views of soil-landforms relationships, since the deduced processes in this research are probably responsible for both soil and landform changes. Furthermore, the presence of the identified chemical processes in Espraiado transect appear to conform to concepts of etchplanation.

Crystal structure, morphology and crystallization kinetics of melt-crystallized polypropylene and poly(propylene-stat-ethylene) fractions with 2.7 to 11.0 mol% of ethylene were studied by differential scanning calorimeter, wide- and small-angle X-ray scattering, polarized light microscopy, transmission electron microscopy and infrared spectroscopy. With increasing ethylene content the poly(propylene-stat-ethylene) fractions showed unchanged crystallinity, increased unit cell volume and constant crystal thickness in combination with a shortened helix length. This indicated that a fraction of ethylene defects were incorporated into the crystal structure. During the isothermal crystallization both α- and γ-crystals could be formed. The γ-crystal fraction increased with increasing ethylene content and increasing crystallization temperature. For samples with α- and γ-crystal contents, multimodal melting was observed and a noticeable γ- to α-crystal conversion was observed on slow heating. The spherulitic structure of the copolymers was coarser than that for the homopolymer. The crystalline lamellae in copolymers exhibited profound curvature in contrast to the straighter cross-hatched α-crystals typical to the homopolymer. Area dependence of electrical breakdown strength was studied for thin polypropylene homopolymer films. The measurements were performed with an automatic measurement system equipped with a scanning electrode arm. Five different electrodes having areas between 0.045 cm2 and 9.3 cm2 were used and typically 40-80 breakdowns per sample and electrode area were collected. All measurements were performed on dry samples in air at room temperature. The data was analyzed statistically and the Weibull function parameters α and β, the first one related to 63% probability for the sample to break down and the second one to the width of the distribution were fitted to the obtained data. Different features concerning the measurement system and conditions, e.g. criteria for the automatic detection of the breakdowns, effect of electrode edge design, partial discharges, DC ramp speed and humidity were critically analyzed. It was concluded that the obtained α-parameter values were stable and repeatable over several years of time. The β-parameter values, however, varied ± 10-30%, more for the large than the small electrodes, and were also sensitive to the changes both in the sample itself and in the measurement conditions. Breakdown strengths of over 50 capacitor grade polypropylene films were analyzed. The obtained α-parameter values were between 450 and 850 V/μm, depending on the film grade and electrode area. In addition to the high breakdown strengths, reflected by the obtained α-values, another, sparse distribution consisting of low breakdown strengths was revealed when the amount of measurement points was high enough. This means that more than one Weibull distribution could be needed to describe the breakdown strength behavior of a polypropylene film. Breakdown values showed decreasing area dependence with decreasing electrode area. Breakdown strengths for larger sample areas were predicted from the small area data by area- and Weibull extrapolation. The area extrapolation led to predicted α-values 50% higher than measured at 4 m2 whereas the Weibull extrapolation showed an accuracy of ±15 % when predicted and measured values were compared. Breakdown strengths were also extrapolated for film areas similar to those in impregnated power capacitors. It turned out that the power capacitors, tested at the factory, performed much better than predicted by the extrapolation. However, a few weak spots with very low breakdown values were also found. For the poly(ethyelene terephtalate) dielectric, which is not swelled by the impregnation liquid, the large area breakdown strength was predictable. This indicates that for polypropylene film processing and impregnation led, in addition to the improved large area breakdown performance, also to sparse weak spots with low breakdown probabilities. Different Weibull distributions were responsible for the breakdown strengths for the processed and impregnated polypropylene than for the dry film samples. / QC 20101027

O objetivo da presente pesquisa consiste em identificar feições macro e micromorfológicas (em escala de campo e do microscópio óptico, respectivamente) e evidências analíticas (parâmetros físicos e químicos) que indiquem possíveis mecanismos de translocações, perdas e acumulações de matéria no interior da cobertura pedológica, possivelmente responsáveis pela modificação do modelado em um transecto localizado na região de São Pedro (SP). O transecto estudado, denominado Espraiado, subdivide-se em 5 segmentos: segmento superior, segmento médio e segmentos inferiores a, b e c. O segmento superior apresenta baixas declividades e presença do Neossolo Quarzarênico, solo espesso e arenoso caracterizado pela sequência vertical de horizontes A, AE, E com bandas e C-1. O segmento médio apresenta declividades comparativamente médias e presença dos Argissolos Amarelo e Acinzentado, caracterizados pela espessura menor que a do Neossolo Quartzarênico e pela sequência de horizontes A, AE, E com bandas, Bt, C-2 e C-3. Os segmentos inferiores possuem as maiores declividades e solos com a maior presença de argila e a menor espessura do transecto: Cambissolo Háplico, com sequência de horizontes A, ABi, Bi, C-2 e C-3; e Neossolo Litólico, com sequência de horizontes A, C-2 e C-3. As feições identificadas, principalmente macro e micromorfológicas, indicam a ocorrência de processos químicos e mecânicos no interior da cobertura pedológica, desencadeados principalmente pela circulação da água no interior dos solos e responsáveis pela redistribuição e/ou remoção de material em todo o transecto. No Neossolo Quartzarênico, onde há provavelmente maior infiltração de água e dominância do fluxo interno vertical, foi encontrada maior presença das seguintes feições: bandas e interbandas, interpretadas como evidências de-iluviação de plasma; golfos nas partículas de quartzo, interpretados como evidências de dissolução de sílica; e feições relacionadas ao fenômeno de plasma infusion, o qual provoca a desintegração das partículas de areia em partículas menores. Nos Argissolos (Amarelo e Acinzentado) e no Cambissolo Háplico, onde há menor infiltração de água e provavelmente maior presença de fluxo interno lateral, estas feições aparecem em menor quantidade, mas dominam outras, tais como: bandas e interbandas, provavelmente associadas à perda de de plasma do horizonte subjacente; oríficos e concavidades superficiais provavelmente associados ao processo de piping, mosqueamentos que indicam processos de hidromorfia e, portanto, maior mobilidade do ferro reduzido, e feições relacionadas à mobilização de plasma e esqueleto nos macroporos. As únicas feições encontradas que indicam a deposição ou precipitação de elementos no sistema foram as bandas do Neossolo Quartzarênico (as quais indicam simultaneamente perda de matéria), e as denominadas “superfícies duplas” das partículas de quartzo. Desta forma, parece que a cobertura pedológica do transecto Espraiado caracteriza-se principalmente pela perda generalizada de matéria, provavelmente associada a uma perda de volume dos solos e a um rebaixamento do modelado local, assim como descrito em outras áreas tropicais. Assim, os resultados apresentados estão em desacordo com a idéia de oposição entre os processos pedogenéticos e morfogenéticos, comumente presente na visão tradicional das relações solo-relevo, uma vez que os processos deduzidos são possivelmente responsáveis não apenas por mudanças de características morfológicas da cobertura pedológica, mas também por mudanças no modelado. Além disto, a presença destes processos na área estudada parece estar de acordo com os princípios da teoria de etchplanação. / The objective of this research is to identify macro and micromorphological features (field and and optical microscopic scale, respectively) and analitycal evidences (physical and chemical parameters), indicative of translocations, losses and acumulations mechanisms inside the soils, that probably leads to changes in the form of a transect, localized in São Pedro region, São Paulo State, Brazil. The studied transect, called Espraiado, is divided into five segments: superior segment, medium segment and a, b and c inferior segments. The superior segment presents low slope angles and presence of quartz sand, that is a deep soil characterized of the vertical sequence of A, AE, E (with bands) and C-1 horizons. The medium segment has moderate slope angles and the presence of podzolic soils, that are shallower than quartz sand soil and follow vertical sequence of horizons: A, AE, E (with bands), Bt, C-2 and C-3. The inferior segments have the highest slope angles and soils with the highest clay content and the lowest thickness of the transect: cambic soil, that has vertical sequence of A, ABi, Bi, C-2 and C-3 horizons; or A, C-2 and C-3 horizons. The identified macro and micromorphological features suggest the occurrence of chemical and mechanical processes inside the pedological cover, mainly triggered for water circulation in soils. These processes are probably responsible for material translocation and/or remotion in the whole transect. In quartz sand soil, where there are probably high water infiltration rates and dominant internal vertical flux, there are the great amounts of the follow features: bands/interband, interpreted as plasma e-illuviation evidences, embayed quartz particles, interpreted as silica dissolution evidences, and plasma infusion, a phenomenon that leads to the desintegration of sand-sized particles and the formation of silt-sized particles. In podzolic and cambic soils ,where there are probably lower water infiltration rates soils and dominant internal lateral flux, there are fewer of these features and dominance of others, like bands/interbands probably related to plasma losses; holes and concavities probably related to piping processes, motlles suggesting hydromorfic processes that induce the mobility of reduced Fe, and features associated to plasma and skeleton mobility in macropores. Only two features suggest deposition or precipitation of elements in the soil system: bands, mainly in quartz sand soil, and the “double surfaces” of the quartz particles. It seems that pedological cover of the Espraiado transect is mainly characterized by general losses that lead to soil volume loss and landsurface lowering, as described in other tropical areas. Therefore, the presented results disagree with the opposition idea of pedogenetic and morphogenetic processes, presented in traditional views of soil-landforms relationships, since the deduced processes in this research are probably responsible for both soil and landform changes. Furthermore, the presence of the identified chemical processes in Espraiado transect appear to conform to concepts of etchplanation.

Environmental conditions affect the formation of apoplastic barriers (endodermis and exodermis) in roots. This was shown on many species in many research papers. The exodermal layer is more variable in response to stress conditions than endodermal layer. Cadmium toxicity, as many other stresses, induces faster development of apoplastic barriers. Most of research papers published so far, however characterized only the response of main root to this type of stress factor. Lateral roots, an important part of the root system absorptive surface, are neglected and there is not much information about their response to cadmium stress. The pattern of apoplastic barriers development was therefore analysed in main and also in lateral roots of various size and position on maternal root axis. We found significant differences in response to cadmium stress among these different root types. Then we summed up the differences between these types of roots. Short lateral roots were generally more responsive to cadmium stress, cadmium affected root branching as well as differentiation of apoplastic barriers in lateral roots. These results help us to better understand the response of complex roots system to environmental conditions. In the second part of this work, the role of CASP genes in exodermal development was...

Plants are able to cope with changing environmental conditions or withstand its adverse effects due to their plastic development. One way to adapt to fluctuating amounts of nutrients and water in the environment or the presence of toxic substances is to regulate the movement of substances between the plant and the environment. Beside other, this regulation is also possible at the level of the root system, by the formation of apoplastic barriers endodermis and exodermis. Some species posses endodermis only, in others exodermis in hypodrermal layers of the root can be found. These barriers differentiate in three stages and prevent free movement of coumpounds though apoplast. The transport to the symplast is the key point of regulating the uptake of substances into the plant and the endodermis is the fundamental structure. The presence of exodermis, however, affects the apoplast permeability of the surface root layers and can therefore influence the involvement of the primary cortex cells in the uptake of substances from the environment. In this work the impact of phosphate deficiency on the formation of apoplastic barriers was studied focusing on exodermis and the effect of its differentiation on the occurrence of membrane transporters and involvement of primary cortex cells in the uptake of...

No description available.

The objective of this dissertation is to demonstrate the use of in situ TEM mechanical testing to find mechanical properties of as received, self-ion, and proton irradiated Fe-9%Cr ODS. The desire to work at small scale in the characterization of irradiated materials to reduce costs and improve throughput, require the development of novel methods to assess mechanical properties in volume-limited irradiation damage layers. Yet at these micrometer or nanometer scales, the mechanical properties can begin to be impacted by size effects. In this work micropillar compression, cantilever bending, lamellae indentation, and clamped beam fracture testing is conducted on ion-irradiated Fe-9%Cr ODS to find yield stress, elastic modulus, flow stress, and fracture toughness. Micropillars in compression allow us to define a minimum sample dimension, which approaches the obstacle spacing of the material, at which size effects are observed. This relationship between sample dimension and obstacle spacing defined through micropillar compression is extended to a new testing geometry, cantilever bending, and material property, flow stress. Lessons learned during the cantilever bending informed the clamped beam design for conducting fracture testing on a ductile engineering alloy at micrometer scales. Finally, lamellae indentation was conducted to link qualitative observations of the microstructure under load with literature strength of obstacle values. By combining an understanding of the microstructure of irradiated Fe-9%Cr ODS and the in situ TEM technique, one can find the bulk-like mechanical properties of ion irradiated Fe-9%Cr ODS.

No description available.