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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
121

Temporal Patterning and Generation of Neural Diversity in Drosophila Type II Neuroblast Lineages

Bayraktar, Omer 03 October 2013 (has links)
The central nervous system (CNS) has an astonishing diversity of neurons and glia. The diversity of cell types in the CNS has greatly increased throughout evolution and underlies our unique cognitive abilities. The diverse neurons and glia in the CNS are made from a relatively small pool of neural stem cells and progenitors. Understanding the developmental mechanisms that generate diverse cell types from neural progenitors will provide insight into the complexity of the mammalian CNS and guide stem cell based therapies for brain repair. Temporal patterning, during which individual neural progenitors change over time to make different neurons and a glia, is essential for the generation of neural diversity. However, the regulation of temporal patterning is poorly understood. Human outer subventricular zone (OSVZ) neural stem cells and Drosophila type II neural stem cells (called neuroblasts) both generate transit-amplifying intermediate neural progenitors (INPs). INPs undergo additional rounds of cell division to increase the number of neurons and glia generated in neural stem cell lineages. However, it is unknown whether INPs simply expand the numbers of a particular cell type or make diverse neural progeny. In this dissertation, I show that type II neuroblast lineages give rise to extraordinary neural diversity in the Drosophila adult brain and contribute diverse neurons to a major brain structure, the central complex. I find that INPs undergo temporal patterning to expand neural diversity in type II lineages. I show that INPs sequentially generate distinct neural subtypes; that INPs sequentially express Dichaete, Grainyhead, and Eyeless transcription factors; and that these transcription factors are required for the production of distinct neural subtypes. Moreover, I find that parental type II neuroblasts also sequentially express transcription factors and generate different neuronal/glial progeny over time, providing a second temporal identity axis. I conclude that neuroblast and INP temporal patterning axes act combinatorially to specify diverse neural cell types within adult central complex; OSVZ neural stem cells may use similar mechanisms to increase neural diversity in the human brain. This dissertation includes previously published co-authored material.
122

Automatização do traçado dos moldes básicos femininos por meio de software de modelagem paramétrica

Costa, Thays Neves January 2016 (has links)
Esta pesquisa tem por objetivo automatizar a personalização do traçado do processo de construção dos moldes básicos do vestuário feminino, através da utilização de software paramétrico, mais precisamente o Grasshopper. Para a construção do trabalho, foram investigados alguns conceitos que fundamentaram esta pesquisa. São eles: antropometria e seus conceitos aplicados ao vestuário; tabela de medidas e como ela é empregada no desenvolvimento do produto sob medida; a modelagem inserida na sequência do planejamento produtivo do produto de moda; o processo de modelagem do vestuário; os tipos de modelagem: plana e tridimensional; as etapas do processo de construção dos moldes desde os moldes básicos até os moldes de corte. Por fim, uma apresentação dos principais softwares de modelagem do vestuário e os programas escolhidos para a execução desta pesquisa. Fundamentando-se na pesquisa bibliográfica, foram construídos critérios para a seleção e análise do método de traçado dos moldes básicos, com a finalidade de selecionar o melhor método para ser parametrizado. Foram analisados três métodos: SENAC (2004), SENAI (elaborado por Lenir Romero) e Modelagem Industrial Brasileira (Duarte e Saggese, 2010). Para a construção da modelagem da blusa e da saia no Grasshopper, foi selecionado o método do SENAI. Para a construção da manga, o método de Duarte e Saggese foi a melhor alternativa. A partir dos moldes construídos, dois manequins de tamanhos distintos tiveram suas medidas obtidas e por meio delas os moldes foram parametrizados. Para a verificação da aplicabilidade do processo de automatização, foram confeccionados os protótipos dos moldes básicos no tamanho de cada manequim e, posteriormente, um modelo do vestuário estilizado, acompanhando as proporções dos bustos de costura. Assim a dissertação é concluída, verificando a aplicabilidade do processo de automatização dos traçados dos moldes básicos a partir de medidas personalizadas. / This research aims to automate the customization of the layout of the building process of the basic standards of women's clothing, through the use of parametric software, the Grasshopper. For construction were investigated some theoretical issues substantiate this search. They are: anthropometry, applied concepts In clothing; measurement chart; the measurement table and the product tailored; patterning one inserted into the sequence of the production planning product fashion; the clothing patterning process; patterning types: flat and three-dimensional; as steps construction process of the patterns, from the basic pattern to cutting pattern. Finally, a presentation of the main clothing modeling software and the chosen programs to executions of this search. Basing on bibliographic search, were established criterions to selection of the analysis method of the basic patterns, with the goal of selecting the best method to be parameterized. Were examined three methods: SENAC (2004), SENAI (prepared by Lenir Romero) and Brazilian industrial Modeling (Duarte and Saggese, 2010). For Building Modeling blouse and skirt without Grasshopper was selected SENAI method. To construction of sleeve, Duarte and Saggese method was the best alternative. From molds built, two dummies distinguished sizes your had taken measures, and the from these molds. They were parameterized for a validation of the automation process, were made the prototypes grassroots non size each mannequin, and then do uh stylized clothing model, as following the same proportions. This way, this dissertation is competed, validating the automation process of the traces of patterning the basic custom from measurements.
123

Turbulent being(s) : proliferating curses and shamanic practice in post-Soviet Kyzyl, Tuva

Stelmaszyk, Malgorzata January 2018 (has links)
This thesis is about curses. It shows how the mechanics of cursing are intrinsically linked to shamanic practice in the ethnographic context of social, economic and political shifts in post-Soviet Kyzyl, the capital of the Autonomous Republic of Tuva. Moving beyond discourses that understand 'economics' as narrowly pertaining to wealth, power and the circulation of goods, the thesis explores curses as distinct social mechanisms within an 'occult economy' that constitutes a wider sociocosmic politics emergent from human and non-human interactions. Along these lines, while presenting Tuvan shamanism as central to cursing phenomena, the thesis explores the distinctiveness and efficacy of shamanic practice as a form of artistry embedded in instrument-derived (shamanic drum) and human (the shaman's voice) sound production. Thus, it challenges the 'classical' readings of shamanism which emphasise trance and mediumship usually seen as involving significant changes in the 'physical' and 'psychic' states of the shamans. Contextualizing cursing in the practice of Tuvan shamanism, the thesis illuminates the significance of sound creation among Tuvans in order to introduce the notion of 'turbulence' as integral not only to shamanic sound production, but also to immediate experiences of cursing and the overall patterning of the cosmos. More than that, bringing sounds and turbulence together in the context of shamanic rituals, it shows how sounds are imbued with a potency of their own rather than simply constituting a sonorous aspect of shamanic words. Along these lines, it contributes to a better understanding of im/materiality and the logic of representation. Lastly, exploring the multiplication of curses in the post-Soviet context, the thesis also offers an interpretative framework which unveils how occult phenomena can become efficacious analytical tools, allowing us to grasp the mosaic-like characteristics of the sociocultural contexts in which they are embedded. In this way, the thesis attempts to emancipate 'occultism' from the rigid dichotomies of tradition and modernity, and challenge those anthropological approaches to post-colonial transformations which emphasise cultural revivalism and ethnic identity, remaining caught in the usual dynamics of 'the old' and 'the new' - dynamics we need to leave behind.
124

Microfabrication with Smooth, Thin CNT/Polymer Composite Sheets

Boyer, Nathan Edward 01 June 2016 (has links)
Carbon nanotube (CNT)/polymer composite sheets can be extremely high strength and lightweight, which makes them attractive for fabrication of mechanical structures. This thesis demonstrates a method whereby smooth, thin CNT/polymer composite sheets can be fabricated and patterned on the microscale using a process of photolithography and plasma etching. CNT/polymer composites were made from CNTs grown using chemical vapor deposition using supported catalyst growth and floating catalyst growth. The composite sheets had a roughness of approximately 30nm and were about 61¼m or 261¼m depending on whether they were made from supported catalyst grown or floating catalyst grown CNTs. The composites were patterned using an oxygen plasma as the etchant and a hard mask of silicon nitride.
125

Laser-Induced Recoverable Surface Patterning on Ni50Ti50 Shape Memory Alloys

Ilhom, Saidjafarzoda 01 July 2018 (has links)
Shape memory alloys (SMAs) are a unique class of smart materials exhibiting extraordinary properties with a wide range of applications in engineering, biomedical, and aerospace technologies. In this study, an advanced, efficient, low-cost, and highly scalable laser-assisted imprinting method with low environmental impact to create thermally controllable surface patterns is reported. Two different imprinting methods were carried out mainly on Ni50Ti50 (at. %) SMAs by using a nanosecond pulsed Nd:YAG laser operating at 1064 nm wavelength and 10 Hz frequency. First, laser pulses at selected fluences were directly focused on the NiTi surface, which generated pressure pulses of up to a few gigapascal (GPa), and thus created micro-indents. Second, a suitable transparent overlay serving as a confining medium, a sacrificial layer, and a mesh grid was placed on the NiTi sample, whereafter the laser was focused through the confinement medium, ablating the sacrificial layer to create plasma and pressure, and thus pushing and transferring the grid pattern onto the sample. Scanning electron microscope (SEM) and laser profiler images show that surface patterns with tailorable sizes and high fidelity could be obtained. The depth of the patterns was shown to increase and later level off with the increase in laser power and irradiation time. Upon heating, the depth profile of the imprinted SMA surfaces changed where the maximum depth recovery ratio of 30 % was observed. Recovery ratio decreased and saturated at about 15 % when the number of pulses were increased. A numerical simulation of the laser irradiation process was performed showing that considerably high pressure and temperature could be generated depending on the laser fluence. The stress wave closely followed the rise time of the laser pulse to its peak value and followed by the rapid attenuation and dispersion of the stress through the sample.
126

Micro-bending and patterning via high energy pulse laser peening

Pence, Chelsey Nicole 01 May 2014 (has links)
High energy pulse laser peening (HEPLP) is a manufacturing process, in which a strong shock wave is produced and induces high pressures on the surface of the target material. Generally, this process is used to improve material properties such as the hardness and fatigue life. First a 2D multi-physics model for the process was investigated, which simulates the pressure induced on the surface of the target material. The model can be coupled with commercial finite element software, such as ABAQUS, to more accurately simulate the HEPLP process to find stresses and deformations on the surface. Next two novel applications using the HEPLP process were investigated. The first, laser shock bending is a sheet metal micro-forming process using HEPLP to accurately bend, shape, precision align, or repair micro-components with bending angles less than 10°. Negative bending angle (away from laser beam) can be achieved with the high-energy pulsed laser, in addition to the conventional positive laser bending mechanism. In this thesis, various experimental and numerical studies on aluminum sheets were conducted to investigate the different deformation mechanisms, positive and negative. The experiments were conducted with the sheet thickness varying from 0.25 to 1.75 mm and laser pulse energy of 0.2 to 0.5 J. A critical thickness threshold of 0.7-0.88 mm was found that the transition of positive negative bending mechanism occurs. A statistic regression analysis was also developed to determine the bending angle as a function of laser process parameters for positive bending cases. The second application studied used HEPLP to imprint complex two-dimensional (2D) patterns dental implant material of cpTi. Pure titanium (commercial pure cpTi) is an ideal dental implant material, without the leeching of toxic alloy elements. Evidence has shown that unsmooth implant surface topologies may contribute to the osteoblast differentiation in human mesenchymal pre-osteoblastic cells, which is helpful to avoid long-term peri-abutment inflammation issues for the dental implant therapy with transcutaneous devices. Studies have been conducted on the grit blasted, acid etched, or uni-directional grooved Ti surface, however, for these existing approaches the surface quality is difficult to control or may even damage the implant. The strong shock wave generated by HEPLP is used to press a stainless steel grid, used as a stamp, on Ti foils to imprint a 2D pattern. In this study, the multiple grid patterns and grid sizes were applied to test for cell-attachment improvements. Then, the cell culture tests were conducted with the patterned surface to investigate the contribution of these 2D patterns, with the control tests of the other existing implant surface topography forming approaches. The micro-patterns proved successful in increasing the cell-attachment, increasing the number of cells attaching to the material and also contributing to the cell-growth within the grooved areas.
127

New micropatterning techniques for the spatial addressable immobilization of proteins

Filipponi, Luisa, n/a January 2006 (has links)
Bio-microdevices are miniaturised devices based on biologically derived components (e.g., DNA, proteins, and cells) combined or integrated with microfabricated substrates. These devices are of interest for numerous applications, ranging from drug discovery, to environmental monitoring, to tissue engineering. Before a bio-microdevice can be fully developed, specific fabrication issues need to be addressed. One of the most important is the spatial immobilization of selected biomolecules in specific micro-areas of the device. Among the biomolecules of interest, the controlled immobilization of proteins to surfaces is particularly challenging due to the complexity of these macromolecules and their tendency to lose bioactivity during the immobilization step. The present Thesis reports on three novel micropatterning techniques for the spatial immobilization of proteins with bioactivity retention and improved read-out of the resulting micropatterns. The technologies developed are based on three different micropatterning approaches, namely 1) direct-writing UV laser microablation (proLAB), 2) a novel microcontact printing method (�CPTA) and 3) a replica molding method combined with bead selfassembly (BeadMicroArray). The first two technologies, proLAB and �CPTA, are an implementation of existing techniques (laser ablation and �CP, respectively), whereas the third, i.e., the BeadMicroArray, is a totally new technique and type of patterning platform. 'ProLAB' is a technology that uses a micro-dissection tool equipped with a UV laser (the LaserScissors�) for ablating a substrate made of a layer of ablatable material, gold, deposited over a thin polymer layer. The latter layer is transparent to the laser but favours protein adsorption. In the present work microchannels were chosen as the structure of interest with the aim of arranging them in 'bar-codes', so to create an 'information-addressable' microarray. This platform was fabricated and its application to specific antigen binding demonstrated. The second technique that was developed is a microstamping method which exploits the instability of a high-aspect ratio rubber stamp fabricated via soft-lithography. The technique is denominated microcontact printing trapping air (�CPTA) since the collapsing of a rubber stamp made of an array of micro-pillars over a plane glass surface resulted in the formation of a large air gap around the entire array. The method can be successfully employed for printing micro-arrays of proteins, maintaining biological activity. The technique was compared with robotic spotting and found that microarrays obtained with the �CPTA method were more homogeneous and had a higher signal-tonoise ratio. The third technique developed, the BeadMicroArray, introduces a totally new platform for the spatial addressable immobilization of proteins. It combines replica molding with microbead self-assembling, resulting in a platform where diagnostic beads are entrapped at the tip of micropillars arranged in a microarray format. The fabrication of the BeadMicroArray involves depositing functional microbeads in an array of V-shaped wells using spin coating. The deposition is totally random, and conditions were optimised to fill about half the array during spin coating. After replica molding, the resulting polymer mold contains pyramid-shaped posts with beads entrapped at the very tip of the post. Thanks to the fabrication mode involved, every BeadMicroArray fabricated contains a unique geometric code, therefore assigning a specific code to each microarray. In the present work it was demonstrated that the functionality of the beads after replica molding remains intact, and that proteins can be selectively immobilized on the beads, for instance via biorecognition. The platform showed a remarkable level of selectively which, together with an efficient blocking towards protein non-specific adsorption, lead to a read-out characterized by a very good signal-to-noise. Also, after recognition, a code was clearly visible, therefore showing the encoding capacity of this unique microarray.
128

Electrochromism and over-oxidation in conjugated polymers: Improved color switching and a novel patterning approach

Tehrani, Payman January 2006 (has links)
<p>During the last 30 years a new research and technology field of organic electronic materials has grown thanks to a groundbreaking discovery made during the late 70’s. This new field is today a worldwide research effort focusing on exploring this new class of materials that also enable many new areas of electronics applications. In the organic electronics research field conducting organic molecules and polymers are synthesized and used in devices. The reason behind the success of conducting polymers is the flexibility to develop materials with new functionalities via clever chemical design and the possibility to use low-cost production techniques to manufacture devices.</p><p>This thesis reviews and describes different aspects of the organic electronics, here focusing on electrochromic displays; device improvements, the study of degradation and also patterning technology for rational manufacturing processing. The color contrast in electrochromic displays based on conjugated polymers was increased with approximately a factor of two by adding an extra electrochromic polymer. It was found that electrochemical over-oxidation (ECO) limits the flexibility in choosing desired electrochromic materials. ECO is one of the main degradation mechanisms in electrochromic displays. ECO is an efficient and fast process to permanently reduce the electronic conductivity in polythiophenes. From this, a novel patterning process was developed, in which the films of polythiophenes can be patterned through local and controlled deactivation of the conductivity. The ECO has been combined with different patterning tools to enable the use of existing printing tools for manufacturing. In combination with screen-printing, low-cost and high volume roll-to-roll patterning was demonstrated, while together with photolithography, patterning down to 2 µm can be achieved. Systematic studies have shown that conductivity contrasts beyond 107 can be achieved, which is enough for various simple electronic systems. To generate better understanding of the ECO phenomena the effect of pH on the over-oxidation characteristics was studied. The results suggest that a part of the mechanism for over-oxidation depends on the OH– concentration of the electrolyte used.</p>
129

Early development of the olfactory placode and early rostrocaudal patterning of the caudal neural tube

Maier, Esther January 2009 (has links)
The development of the nervous system is a complex process. Cell divisions, cell differentiation and signalling interactions must be tightly regulated. To comprehend the mature nervous system, we have to understand its assembly during development. Two main questions were addressed in this thesis: (1) how is the caudal part of the central nervous system specified and (2) how is the early development of the olfactory placode regulated? By using tissue and whole embryo assays in the chick, we identified signalling molecules involved in these processes and propose possible mechanisms for their function. The central nervous system is regionalized along its rostrocaudal axis during development. However, the mechanisms by which cells in the caudal part of the neuraxis acquire rostrocaudal regional identity have been unresolved. We provide evidence that at gastrula stages cells in the caudal neural plate are specified as cells of caudal spinal cord character in response to Wnt and FGF signals and that cells of rostral spinal cord and caudal hindbrain character only emerge later at neurulation stages in response to retinoic acid signalling acting on previously caudalized cells. In the hindbrain and spinal cord distinct motor neuron subtypes differentiate at precise rostrocaudal positions from progenitor cells. We provide evidence that cells in the caudal neural plate have acquired sufficient positional information to differentiate into motor neurons of the correct rostrocaudal subtype. The olfactory placode gives rise to all the structures of the peripheral olfactory system, which, in the chick consists of the olfactory nerve, the sensory epithelium, where the olfactory sensory neurons (OSN) are located and the respiratory epithelium, that produces the mucus. Several studies have addressed the role of signalling cues in the specification of OSNs but much less is known about the regulation of sensory versus respiratory patterning and the events controlling early neurogenesis in the developing olfactory placode. We show that by stage 14 the olfactory placode is specified to give rise to both cells of sensory and respiratory epithelial character. Moreover, cells of respiratory epithelial character require BMP signalling, whereas cells of sensory epithelial character require FGF signalling. We suggest a mechanism in which FGF and BMP signals act in an opposing manner to regulate olfactory versus respiratory epithelial cell fate decision. BMP signalling has also been implicated in the regulation of neurogenesis in the sensory epithelium, and we show that BMP signals are required for the generation of OSNs, because in the absence of BMP signalling cells in the sensory epithelium do not mature. Independently, we also analyzed the role of Notch signalling during early olfactory development both in vitro and in vivo and provide evidence that active Notch signalling is required to prevent cells in the olfactory placode from premature differentiation.
130

Fonctionnalisation de surface et intégration de colloïdes par assemblage dirigé

Delapierre, François-Damien 08 October 2012 (has links) (PDF)
Nous présentons des procédés de fonctionnalisation de surface par assemblage dirigé de colloïdes en suspension. La motivation de ce projet est de montrer que des techniques simples fondées sur des phénomènes de démouillage de suspensions colloïdales permettent de diriger le dépôt de particules sur des surfaces structurées, de façon déterministe avec une résolution micrométrique. L'objectif de ces travaux est de développer une technique de structuration simple, polyvalente et utilisable en routine. Deux verrous technologiques majeurs ont été levés : d'une part l'optimisation des paramètres d'assemblage a permis d'étendre considérablement les vitesses d'assemblage et d'autre part, l'optimisation des structures de capture à rendu possible le multiplexage des dépôts et la création de réseaux imbriqués de particules de types différents. Ce processus a été appliqué avec succès à des particules magnétiques. Ces particules fixées à la surface peuvent servir de points d'ancrage pour des colonnes magnétiques. Plusieurs exemples d'applications telles que la capture de cellules au sein de liquides biologiques, la fabrication de micro-flagelles artificielles, ou de micro-capteurs de force ont été développées. Ces techniques ont également été adaptées pour l'assemblage de cellules, de levures et de bactéries sur des surfaces. Cela a conduit au développement de substrats de capture et de mise en culture permettant la création de réseaux constitués de plusieurs types de cellules précisément localisées.

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