Molecular dynamics simulations of the diffusion process in ordered B2 compounds at high temperature were performed using an embedded atom interatomic potential developed to fit NiAl properties. Diffusion in the bulk occurs through a variety of cyclic mechanisms that accomplish the motion of the vacancy through nearest neighbor jumps restoring order to the alloy at the end of the cycle. The traditionally postulated six-jump cycle is only one of the various cycles observed and some of these are quite complex. Diffusion at the grain boundary mainly takes place through sequences of coordinated nearest neighbor jumps yielding to a rearrangement of the grain boundary structure. Two distinct mechanisms resulting in a structural unit migration of the vacancy are also identified. The results are analyzed in terms of the activation and configuration energies calculated using molecular statics simulations. / Master of Science

A resina bulk fill vem ampliando as indicações dos compósitos na qual permite a inserção em incrementos com espessura de até 5mm. A interface adesiva é a principal responsável pela durabilidade de restaurações estéticas. Objetivo: Avaliar a integridade da interface dente/restauração, e a resistência adesiva da dentina após a ciclagem mecânica de dentes restaurados com a resina bulk fill. Materiais e Métodos: Foram selecionados 40 prémolares superiores birradiculares que receberam um preparo MOD com término cervical mesial em esmalte e o término distal em dentina e foram divididos em 2 grupos: 1 incremento de resina e 2 incrementos de resina, e, dois subgrupos: com e sem ciclagem mecânica (n=10). Em seguida, os espécimes foram restaurados, analisados inicialmente em microscopia confocal a laser e posteriormente levados para ciclagem mecânica onde foram realizados 300.000 ciclos na frequência de 1Hz e carga de 80N. Após a ciclagem mecânica, os espécimes foram novamente avaliados em microscopia confocal a laser para avaliação da qualidade da interface, e foi realizado o teste de microtração na dentina das paredes proximais e pulpar dos dentes com ciclagem e sem ciclagem. Posteriormente, foi realizada a análise do padrão de fratura em microscopia confocal a laser. Os valores obtidos na mensuração de gaps foram analisados estatisticamente através da ANOVA seguido de Holm-Sidak; e os valores obtidos na microtração foram analisados estatisticamente através da ANOVA seguido de Tukey. Resultados: Observou-se que o fator incremento promoveu diferença estatística significante tanto em esmalte como em dentina antes e após a ciclagem (p<0,05). A ciclagem promoveu fendas tanto para esmalte como para dentina (p<0,05). Para resistência adesiva não foi observada diferença entre os grupos de 1 e 2 incrementos antes e após a ciclagem (p>0,05), nem na dentina em suas diferentes porções ao comparar os incrementos (p>0,05), mas foi possível observar diferença significante antes e após a ciclagem nas diferentes regiões de dentina (p<0,05). Conclusão: Previamente à ciclagem mecânica, o fator incremento não afetou a interface, a resistência adesiva e os términos cervicais proximais. Posteriormente à ciclagem, a qualidade da interface foi afetada negativamente, o término cervical em dentina apresentou fendas maiores, mas a resistência adesiva se manteve. A ciclagem mecânica influenciou o aumento da quantidade de gaps e trincas e prejudicou a adesão, principalmente na dentina da região distal. / The bulk fill resin extended the composites indications in which it allows the insertion in increments with thickness of up to 5mm. The adhesive interface is the main responsible for the durability of aesthetic restorations. Objective: To evaluate the integrity of the tooth/ restoration interface and dentin adhesive resistance after mechanical cycling of restored teeth with bulk fill resin. Materials and Methods: 40 upper biradicular premolars were selected for the study and received a MOD preparation with mesial cervical terminus in enamel and the distal cervical terminus in dentin and were divided into 2 groups: resin in 1 increment and resin in 2 increments, and 2 subgroups: with and without mechanical cycling (n = 10). Afterwards, the specimens were restored, initially analyzed by confocal laser scanning microscopy and submitted to mechanical cycling with 300,000 cycles, 1Hz frequency and 80N load. After the mechanical cycling, the specimens were evaluated again in confocal laser scanning microscopy to evaluate the interface quality, and microtensile test was performed on the dentin of the proximal walls and pulp of the teeth cycled or not. Later, the analysis of the fracture pattern was performed in confocal laser scanning microscopy. The values obtained in the measurement of gaps were analyzed by ANOVA following test Holm-Sidak and microtensile were analyzed by ANOVA following test Tukey. Results: The increment factor promoted a significant statistically difference for enamel (p <0.05) and dentin (p <0.05) after cycling. The cycling promoted significant cracks for enamel (p <0.05) and dentin (p <0.05). No difference in adhesive resistance was observed between the groups of resin in 1 and 2 increments, before and after cycling. There was no difference in dentin adhesive resistance in the different portions when the increments were compared, but it was possible to observe a significant difference (p <0.05) in the different regions of dentin (p <0.05). Conclusion: Previously to mechanical cycling, the increment factor did not affect the interface, the adhesive resistance and proximal cervical terminus. After the cycling, the interface quality was adversely affected, the cervical terminus in dentin presented higher cracks, but the adhesive resistance remained. Mechanical cycling influenced in the increase of gaps and cracks number and impaired the adhesion, mainly in the dentin of the distal region.

At the neuronal synapse, neurotransmitter-filled synaptic vesicles (SVs) fuse with the presynaptic plasma membrane during activity. Following exocytosis, SVs must be retrieved for neurotransmission to be maintained. Several modes of SV recycling have been identified. During mild neuronal activity, clathrin-mediated endocytosis has been regarded as the dominant SV retrieval mode, however the recently identified ultrafast endocytosis mode may also be important in this condition. During elevated activity, activity-dependent bulk endocytosis (ADBE) is the dominant SV retrieval pathway. In ADBE, large invaginations are formed from the plasma membrane, which then undergo scission to create bulk endosomes. In a second distinct step, SVs bud from these endosomes and specifically repopulate the reserve SV pool. However, since its first identification, only few molecules have been shown to participate in ADBE. The aim of this PhD was to identify novel molecules and elucidate the molecular mechanism of ADBE. To achieve this, two independent biochemical approaches were designed to purify and enrich bulk endosomes from primary neuronal cultures. In the first approach, bulk endosomes and SVs were labelled with a dye, FM1-43, using a strong stimulus. Cells were broken mechanically and the post nuclear supernatant, that contains all intracellular organelles, was collected. The supernatant was then subjected to subcellular fractionation using discontinuous Nycodenz gradients. This stimulated sample was always processed in parallel with a basal sample, where no neuronal stimulus was applied, in order to visualise activity dependent FM loading. After different fractionation protocols were applied, bulk endosomes were efficiently separated from SVs, as revealed by tracking fluorescence in different fractions. The fractionation results were further validated by electron microscopy, where bulk endosomes and SVs were labelled with horseradish peroxidase and purified using the established protocol. Immunoblotting against selected SV cargo proteins from stimulated bulk endosome and SV samples, indicated the specific and preferential localisation of VAMP4 on bulk endosomes, in contrast to other SV cargo. The molecular identity of bulk endosomes was also approached by submitting the bulk endosome fractions to semi-quantitative mass spectrometry. This analysis revealed many different proteins that were identified in bulk endosome samples and quantification approaches further indicated proteins that can be localised on bulk endosomes and have a potential role in ADBE. A second magnetic isolation approach was designed, to purify bulk endosomes using a completely different methodology. In this case, bulk endosomes were specifically labelled with iron nanoparticles, which are preferentially taken up by bulk endosomes since they are larger than SVs. The cells were broken as before and post nuclear supernatant was acquired. In this case, the supernatant was submitted to magnetic isolation that separated iron beads labelled structures from all other intracellular organelles. An extensive immunoblotting analysis of magnetic bulk endosomes validated that VAMP4 and syndapin I, two essential ADBE proteins, were enriched in these purified samples. These magnetic bulk endosomes were also analysed using semi-quantitative MS and revealed many proteins with a potential role in ADBE. Significant overlap between the two independent methods was observed, further validating these approaches. Combining these two methods with bioinformatics tools allowed the identification of the molecular signature of ADBE as well as novel key candidates for this process. Specific molecules were investigated for their role in ADBE and SV recycling using a variety of different real-time fluorescent imaging assays. A major focus was on rab small GTPases. High molecular weight dextran uptake was used to specifically study the role of these proteins in ADBE, as it preferentially reports uptake via larger bulk endosomes. A pH sensitive chimeric protein, synaptophysin-pHluorin, was used to investigate the role of these proteins in CME. Additional imaging assays were used to answer emerging questions regarding the function and localisation of these targets in the presynapse. Using these approaches, rab11A and rab35 were found to promote ADBE and accelerate clathrin-mediated endocytosis. This effect was specific to high intensity stimulation, while SV exocytosis was not affected. Further research on the role of both novel and established ADBE molecules will provide key future insights into the mechanism of both bulk endosome generation/scission and subsequent SV reformation. A very promising group is rab proteins and now evidence for their implication in SV recycling is presented here. Identification and characterisation of new targets will allow to investigate the role of ADBE in neurotransmission in both physiology and pathophysiology.

Bulk metallic glasses (BMGs) have displayed impressive mechanical properties, but the use and dimensions of material have been limited due to critical cooling rate requirements and low ductility. The application of severe plastic deformation by equal channel angular extrusion (ECAE) for consolidation of bulk amorphous metals (BAM) and amorphous metal matrix composites (AMMC) is investigated in this dissertation. The objectives of this research are a) to better understand processing parameters which promote bonding between particles and b) to determine by what mechanisms the plasticity is enhanced in bulk amorphous metal matrix composites consolidated by ECAE. To accomplish the objectives BAM and AMMCs were produced via ECAE consolidation of Vitreloy 106a (Zr58.5Nb2.8Cu15.6Ni12.8Al10.3-wt%), ARLloy #1 (Hf71.3Cu16.2Ni7.6Ti2.2Al2.6 -wt%), and both of these amorphous alloys blended with crystalline phases of W, Cu and Ni. Novel instrumented extrusions and a host of postprocessing material characterizations were used to evaluate processing conditions and material properties. The results show that ECAE consolidation at temperatures within the supercooled liquid region gives near fully dense (>99%) and well bonded millimeter scale BAM and AMMCs. The mechanical properties of the ECAE processed BMG are comparable to cast material: σf = 1640 MPa, εf = 2.3%, E = 80 GPa for consolidated Vitreloy 106a as compared to σf = 1800 MPa, εf = 2.5%, E = 85 GPa for cast Vitreloy 106, and σf = 1660 MPa, εf = 2.0%, E = 97 GPa for ARLloy #1 as compared to σf = 2150 MPa, εf < 2.5%, E = 102 GPa for Hf52Cu17.9Ni14.6Ti5Al10. The mechanical properties of AMMCs are substandard compared to those obtained from melt-infiltrated composites due to non-ideal particle bonding conditions such as surface oxides and crystalline phase morphology and chemistry. It is demonstrated that the addition of a dispersed crystalline phase to an amorphous matrix by ECAE powder consolidation increases the plasticity of the amorphous matrix by providing locations for generation and/or arrest of adiabatic shear bands. The ability of ECAE to consolidated BAM and AMMCs with improved plasticity opens the possibility of overcoming the size and plasticity limitations of the monolithic bulk metallic glasses.

Renewable forms of energy are becoming increasingly important as the world quickly depletes its current energy reserves, and rapidly increases the concentration of pollutants in our environment. Solar technology based on organic semiconductors provides a promising candidate to fulfill a portion of our future energy needs in an environmentally sustainable manner. Organic semiconductors are a collection of pi-conjugated small molecules and polymers which can be implemented in photovoltaic cells that are potentially quite low cost. Currently, however, their commercial applications are limited due to a relatively low efficiency in converting sunlight into usable power. The fundamental physics of such devices must be clarified if these materials are to compete with traditional inorganic solar cells. In this dissertation, two emerging experimental tools are implemented in investigations of the internal electric fields present within operating organic photovoltaic cells. The first set of investigations utilizes the vibrational Stark effect to quantify the electric fields which often form at the interfaces between two organic semiconducting materials. Such interfaces are at the heart of the photocurrent generation process in these devices and any electric fields formed crucially alter device performance. We quantitatively determine the interfacial field present in blends of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) and show that this field depends strongly on annealing conditions. Finally we discuss a correlation between this interfacial electric field, crystalinity and device performance. The second set of investigations take advantage of electric field induced second harmonic generation microscopy to examine the electric potential across active organic solar cells. We again investigate blends of PCBM and P3HT as well as poly(4,4-dioctyldithieno(3,2-b:2',3'-d)silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl) (PSBTBT) and PCBM. In the former we find that the potential drop across the device shifts dramatically over time under illumination, while in the latter we find a nearly linear drop which remains constant through device operation. We then extend our examinations of PSBTBT:PCBM with EFISH by quantifying the extent of space charge accumulation throughout such devices. / text

Modeling of airflow resistance in grain bulk requires knowledge of the tortuosity and velocity of the air flow through the grain bulk. In this study, experiments were carried out to determine these characteristics of airflow paths by analyzing digital images of smoke-visualized airflow paths inside a grain bulk obtained with a high speed camera. Colored smoke with approximately the same density as air was introduced into the test box for the visualization of the airflow through the grain bulk. Soybeans with a moisture content of 8.82% on wet basis were used in this study. The high quality videos obtained by recoding the fast movement of the smoke through the grain bulk was first separated into frames using a commercial software, VirtualDub (CRIM, Montreal, Québec, Canada), and the 512× 384 pixel RGB image files (frames) extracted from the recorded videos and read into ImageJ an image processing Java-based software developed by the United State National institute of Health, to track the movement of the smoke in the images, frame by frame to determine lengths, tortuosities of the different flow paths, as well as their velocities.

A diversity of animals move on and bury within dry and wet granular media, such as dry desert sand or rainforest soils. Little is known about the biomechanics and neural control strategies used to move within these complex terrains. Burial and subsurface locomotion provides a particularly interesting behavior in which to study principles of interaction because the entire body becomes surrounded by the granular environment. In this dissertation, we used three model organisms to elucidate control principles of movement within granular substrates: the sand-specialist sandfish lizard which dives into dry sand using limb-ground interactions, and swims subsurface using body undulations; the long-slender shovel-nosed snake which undulates subsurface in dry sand with low slip; and the ocellated skink, a desert generalist which buries into both wet and dry substrates. Using muscle activation measurements we discovered that the sandfish targeted optimal kinematics which maximized forward speed and minimized the mechanical cost of transport. The simplicity of the sandfish body and kinematics coupled with a fluid-like model of the granular media revealed the fundamental mechanism responsible for neuromechanical phase lags, a general timing phenomenon between muscle activation and curvature along the body that has been observed in all undulatory animals that move in a variety of environments. Kinematic experiments revealed that the snake moved subsurface using a similar locomotion strategy as the sandfish, but its long body and low skin friction enabled higher performance (lower slip). The ocellated skink used a different locomotor pattern than observed in the sandfish and snake but that was sufficient for burial into both wet and dry media. Furthermore, the ocellated skink could only reach shallow burial depths in wet compared to dry granular media. We attribute this difference to the higher resistance forces in wet media and hypothesize that the burial efficacy is force-limited. These studies reveal basic locomotor principles of burial and subsurface movement in granular media and demonstrate the impact of environmental interaction in locomotor behavior.

Modeling of airflow resistance in grain bulk requires knowledge of the tortuosity and velocity of the air flow through the grain bulk. In this study, experiments were carried out to determine these characteristics of airflow paths by analyzing digital images of smoke-visualized airflow paths inside a grain bulk obtained with a high speed camera. Colored smoke with approximately the same density as air was introduced into the test box for the visualization of the airflow through the grain bulk. Soybeans with a moisture content of 8.82% on wet basis were used in this study. The high quality videos obtained by recoding the fast movement of the smoke through the grain bulk was first separated into frames using a commercial software, VirtualDub (CRIM, Montreal, Québec, Canada), and the 512× 384 pixel RGB image files (frames) extracted from the recorded videos and read into ImageJ an image processing Java-based software developed by the United State National institute of Health, to track the movement of the smoke in the images, frame by frame to determine lengths, tortuosities of the different flow paths, as well as their velocities.

Zur richtigen Auslegung von fördertechnischen Anlagen in verschiedenen Industriezweigen, insbesondere in Häfen, ist es notwendig, die Arbeitsparameter der Schüttgutfördermaschinen zu kennen. Da die komplexe Bewegung des Materials im Senkrechtschneckenförderer (SSF) eine analytische Auslegung des Fördersystems verhindert, werden hier (semi-)empirische Modelle verwendet. Für eine umfassende Analyse der Transportvorgänge in SSF wurde am Institut für Aufbereitungsmaschinen der TU Freiberg im Rahmen der vorliegenden Arbeit ein Versuchsstand mit einem industriellen SSF konzipiert und gebaut, an dem der Transport von sieben Arten von Schüttgütern mit einer Schneckendrehzahl von 50 bis 320 1/min untersucht wurden. Anhand einer Literaturrecherche wurde ebenso der Einfluss des Aufgabeorts auf die Arbeitsparameter überprüft. Die erhaltenen Ergebnisse wurden statistisch ausgewertet und mit Hilfe derer eine semi-empirische Formel zur Auslegung anderer SSF entwickelt. Darüber hinaus wurden diverse Phänomene beim Transport unterschiedlicher Schüttgüter beobachtetet und in der vorliegenden Arbeit analysiert.

Thesis (Ph.D.)--University of Wollongong, 2009. / Typescript. Includes bibliographical references: leaf 308-322.