We have advanced the state-of-the-art for nano-fabrication of carbon nanotube (CNT) based field emission devices, and have conducted experimental and theoretical investigations to better understand the reasons for the high reduced brightness achieved. We have demonstrated that once the CNT emitter failure modes are better understood and resolved, such CNT emitters can easily reach reduced brightness on the order of 10⁹ A m⁻² sr⁻¹ V⁻¹ and noise levels of about 1%. These results are about 10% better than the best brightness results from a nanotip emitter archived to date. Our CNT emitters have order of magnitude better reduced brightness than state-of-the-art commercial Schottky emitters. Our analytical models of field emission matched our experimental results well. The CNT emitter was utilized in a modified commercial scanning electron microscope (SEM) and briefly operated to image a sample. We also report a successful emission from a lateral CNT emitter element having a single suspended CNT, where the electron emission is from the CNT sidewall. The lateral CNT emitters have reduced brightness on the order of 10⁸ A m⁻² sr⁻¹ V⁻¹, about 10X less than the vertical CNT emitters we fabricated and analyzed. The characteristics of the lateral field emitter were analyzed for manually fabricated and directly grown CNT emitters. There was no significant difference in performance based on the way the CNT emitter was fabricated. We showed that the fabrication technique for making a single CNT emitter element can be scaled to an array of elements, with potential density of 10⁶-10⁷ CNT emitters per cm². We also report a new localized, site selective technique for editing carbon nanotubes using water vapor and a focused electron beam. We have demonstrated the use of this technique to cut CNTs to length with 10s of nanometers precision and to etch selected areas from CNTs with 10s of nanometers precision. The use of this technique was demonstrated by editing a lateral CNT emitter. We have conducted investigations to demonstrate the effects of higher local water pressure on the CNT etching efficiency. This was achieved by developing a new method of localized gas delivery with a nano-manipulator. / text

The mechanical behavior of a high pressure die cast AM60B Mg alloy is studied. Constant load amplitude fatigue tests were conducted at room, elevated and cold temperatures, with a stress ratio of R=0.1, and frequency of 30 Hz. The objective was to identify the possible effects of temperature on fatigue life cycle. In addition, fatigue crack propagation tests were conducted to ascertain the fatigue response of the alloy and determine its fatigue crack growth rate as a function of the applied stress ratio, experimentally, analytically and computationally, using Walker’s model. The results demonstrated that temperature had a significant influence on the fatigue life, and that the life increased at cold temperature but decreased at elevated temperature as compared to that evaluated at room temperature. In this study, the limit for applicability of LEFM was established for AM60B magnesium alloy. In addition, fatigue crack propagation test results were used to evaluate the coefficients of the Paris model.

Inconel 718 is a high nickel content superalloy possessing high strength at elevated temperatures and resistance to oxidation and corrosion. The non-traditional manufacturing process of wire-electrical discharge machining (EDM) possesses many advantages over traditional machining during the manufacture of Inconel 718 parts. However, certain detrimental effects are also present. The top layer of the machined surface is melted and resolidified to form what is known as the recast layer. This layer demonstrates microstructural differences from the bulk workpiece, resulting in altered material properties. An experimental investigation was conducted to determine the main machining parameters which contribute to recast layer formation in wire-EDM of Inconel 718. It was found that average recast layer thickness increased with energy per spark, peak discharge current, current pulse duration, and open-voltage time and decreased with sparking frequency and table feed rate. Over the range of parameters tested, the recast layer was observed to be between 5 and 10 μm in average thickness, although highly variable in nature. Surface roughness of the cut parts showed an increase with energy per spark. Electron Probe Microanalysis (EPMA) revealed the recast layer to be alloyed with elements from the wire electrode. X-ray diffraction testing showed the residual tensile stresses evident near the cut surface to decrease with energy per spark. Additionally, nano-indentation hardness testing indicated that the recast layer is reduced in hardness and elastic modulus compared to the bulk material. Vibratory tumbling was found to be a moderately effective post-processing tool for recast layer removal when using pre-formed ceramic abrasive media or fine grained aluminum oxide.

The biological, technical and computational aspects of this project collectively focused on using electron tomography (ET) for the high-resolution (10-20 nm) 3D reconstruction of entire insulin-secreting beta cells within islets of Langerhans isolated from mouse pancreata. Islets were cultured overnight to represent either steady-state (non-stimulated) or elevated glucose (stimulated) conditions, prior to fast-freezing, freeze-substitution, plastic embedment and cutting into 250-400 nm thick sections for tomographic imaging using intermediate voltage electron microscopy (EM). 3D images (tomograms) of each section were used to evaluate the performance of the new technical and computational approaches developed, and make biological comparisons of intercellular structure-function. Analysis focused on key compartments/organelles of the insulin-secretory pathway - Golgi apparatus, mitochondria, insulin secretory granules and multi-granular bodies. To allow the application of ET to entire mammalian cells, several technical limitations were addressed. Since segmenting (delimiting compartments of interest) tomograms manually, represented the major ërate-limiting stepí of ET, an interactive approach for 3D segmentation using novel interpolation algorithms (crude smooth, pointwise smooth and spherical interpolation) to iteratively predict the shape of 3D surfaces between user-drawn contours was developed. The performance of these tools in segmenting a range of compartment types was examined, and found to significantly enhance the speed and accuracy of manual segmentation. To better compensate for the physical collapse of plastic sections in the EM, a novel method was developed for estimating section collapse by analyzing approximately spherical organelles. Using this method on mature insulin granules in high-resolution datasets, coupled with measurements from the whole cell reconstructions, section collapse was found to be substantially less (~25%) than the value (40%) previously used to re-scale 3D models. Other new approaches developed to further improve the accuracy and quality of tomograms, included interactive tools for fiducial tracking, and the use of larger gold particles, a ëreduced second axisí to account for the missing wedge problem, and deformation grids to account for anisotropic deformation. As well as affording more efficient and precise mapping of cell ultrastructure in 3D for subsequent quantitative analysis, these developments provided new insights for future automated (hybrid) segmentation pipelines and new computational approaches for improving quality and isotropic accuracy of volumetric image data. The Interpolator and DrawingTools for segmentation, AnalysisTools for estimating section collapse and BeadHelper for tracking fiducial particles, written as plug-ins for the IMOD software package distributed by the University of Colorado, are now being used by the wider ET community with significant positive feedback. Using the novel approaches developed, four insulin-secreting beta cells - two from the periphery of an islet frozen 1 hr after stimulation with 11 mM glucose, and two from the periphery of another islet under steady-state 5.6 mM glucose conditions - were reconstructed in their entirety in 3D. Quantitative data on the key compartments/organelles provided new information regarding global changes in cellular organization, and enabled robust comparisons of each pair of functionally equivalent cells at unprecedented spatial resolution. Relative differences in the number, dimensions, architecture and distribution of organelles per cubic micron of cellular volume (including mitochondrial branching) reflected differences in the cellsí individual capacity/readiness to respond to secretagogue stimulation. In the two stimulated cells this was reflected by inverse relationships between the number/size of mature granules versus immature granules, the number/size of mitochondria, and the volume of the trans-Golgi network relative to the entire Golgi ribbon. Complementary stereological analysis of whole islets indicated which cells were the most representative under stimulated versus non-stimulated conditions, and revealed a marked natural heterogeneity between cells both within and between individual islets. Overall, this project led to significant improvements in efficiency and accuracy for segmenting cellular compartments/organelles, and in image quality and accuracy for tomogram computation and reconstruction through use of the newly developed techniques. The improved 3D reconstruction and analysis of pancreatic beta cells in toto in native tissue provided a powerful approach for quantitatively mapping the organelles involved in insulin synthesis/secretion at unprecedented detail, and afforded a level of insight into the complex 3D organization of mammalian cells not previously achieved by any other analytical technique or imaging method.

Τα νανοϋλικά, τα υλικά δηλαδή που οι διαστάσεις τους είναι στην νανοκλίμακα, έχουν διαφορετικές ιδιότητες από τα αντίστοιχα υλικά σε μεγαλύτερη κλίμακα. Για αυτό το λόγο, τα νανοϋλικά παρουσιάζουν ιδιαίτερο ενδιαφέρον για περαιτέρω μελέτη και έρευνα. Σε αυτά τα υλικά ανήκει και το οξείδιο του ψευδαργύρου (ZnO). Το οξείδιο του ψευδαργύρου είναι ένας σύνθετος ημιαγωγός τύπου II-IV με άμεσο ενεργειακό χάσμα (Eg=3.37 eV) σε θερμοκρασία δωματίου και με μεγάλη ενέργεια σύνδεσης εξιτονίου (60 meV). Σκοπός της παρούσας διπλωματικής εργασίας είναι η σύνθεση, ο χαρακτηρισμός και η μελέτη ιδιοτήτων νανοσύνθετων υλικών οξειδίου του ψευδαργύρου. Προς αυτόν τον σκοπό, θα παρασκευάσουμε νανοδομές ZnO, με τη μέθοδο του ατμού-υγρού-στερεού (VLS), σε τριζωνικό φούρνο. Στην πορεία της εργασίας, στο πρώτο κεφάλαιο θα δοθούν οι ορισμοί της νανοτεχνολογίας και των νανουλικών. Στο δεύτερο κεφάλαιο, θα αναλυθεί η δομή και οι ιδιότητες του οξειδίου του ψευδαργύρου (ZnO), βάσει των κυρίων μεθόδων ανάπτυξης των νανοδομών του ZnO. Στο τρίτο κεφάλαιο, θα γίνει ανάλυση των μεθόδων χαρακτηρισμού των νανοδομών του ZnO,που θα ακολουθήσουμε στην παρούσα εργασία. Στο επόμενο κεφάλαιο (4ο), θα παρουσιαστεί η μέθοδος παρασκευής των νανοδομών του ZnO και στο αμέσως επόμενο, παρουσιάζονται τα αποτελέσματα του χαρακτηρισμού των νανοδομών ZnO, με τις μεθόδους PL, SEM και XRD. Στο τελευταίο κεφάλαιο αναφέρονται τα συμπεράσματα που προέκυψαν από την παρούσα διπλωματική εργασία. / Nanomaterials, materials on the scale of a few nanometers, have different properties in comparison with larger-scale materials. For this reason, nanomaterials are of particular interest for further study and research. Zinc Oxide (ZnO) belongs to these materials. ZnO is a complex II-VI semiconductor with a direct band-gap energy (Eg = 3.37 eV) at room temperature and a large exciton binding energy (60 meV). The aim of the present diploma thesis, is the preparation, the characterization and the study of the properties of ZnO nanoparticles. In order to accomplish that, we are going to produce nanostructures of ZnO, using the Vapor-Solid-Solid method, in a three-zone furnace. In the first chapter, we give the definitions of nanomaterials and various methods of producing them. In the chapter that follows, we are analyzing the properties of ZnO, the main methods of producing nanostructures of ZnO as well as the ways of exploiting these specific nanostructures. Thereafter, in chapter three, the three methods of characterizing the samples with the nanostructures, are analyzed. In the next chapter, the experimental procedure is presented, whereas on the fifth chapter the results are presented, using the methods of SEM, PL and XRD. In the final chapter we make about conclusion about this diploma thesis

Made available in DSpace on 2014-06-11T19:28:57Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-07-08Bitstream added on 2014-06-13T19:58:20Z : No. of bitstreams: 1 silva_lh_me_sjc.pdf: 2510222 bytes, checksum: 9b0884b924775ed48bb9667a27133675 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O objetivo deste estudo foi desenvolver um novo formato de pilar protético estético em zircônia (3Y-TZP) visando suprimir a utilização do parafuso trespassante utilizado no formato convencional de pilares protéticos em zircônia. Inicialmente foi feita a caracterização do material utilizado na técnica de colagem de barbotina (slip casting) através da confecção de uma barra que teve suas propriedades mecânicas, módulo de elasticidade (E) e coeficiente de Poisson (), grau de contração e dimensão de suas partículas após sinterização avaliados pelos métodos de frequências naturais de vibração e microscopia eletrônica de varredura (MEV), respectivamente. Previamente à confecção do pilar protótipo, este teve seu comportamento mecânico avaliado e comparado a um pilar de 3YTZP convencional com parafuso trespassante pela análise por elementos finitos (FEA) durante sua instalação em implante e recebendo carga oblíqua simulando força de mastigação (210,5 N). O protótipo foi confeccionado pela técnica de colagem de barbotina em um molde de gesso obtido a partir de uma duplicata ampliada em cera. A densidade final foi avaliada pelo método de Archimedes em água. Obteve-se o módulo de elasticidade de 187,97 ± 4,84 GPa e coeficiente de Poisson de 0,19 ± 0,04 para o material. O grau de contração de sinterização foi de 58 vol% e o tamanho do grão foi de 0,705 ± 0,424 μm. Na análise por FEA verificou-se concentrações de tensões na região inicial da rosca para ambos os pilares, e durante o carregamento foram observadas tensões de tração no lado em que incidiu a carga, com presença de tensões de compressão no lado oposto. Ainda, observou-se durante o carregamento do pilar protético convencional concentração de tensão na região do pescoço do parafuso trespassante. A densidade final obtida para o pilar protótipo em 3Y-TZP foi de 95,68% em... / The purpose of this study was to develop a new esthetic zirconia (3YYTZP) implant abutment shape to suppress the use of the fixing screw commonly used by the conventional zirconia abutments. A material characterization, Young’s modulus (E), Poisson’s rate (), shrinkage and particles dimensions after sintering was performed for a bar shape specimen obtained by slip casting evaluated by the natural torsional and flexural vibration frequencies and scanning electron microscope (SEM), respectively. Previously to the prototype abutment confection, its mechanical behavior was evaluated and compared to a conventional zirconia abutment with a fixing screw by finite element analisys (FEA) simulating the abutment installation and oblique loading (210.5 N). The prototype was confectioned by the slip casting technique using a gypsum mould obtained from a wax expanded replica. The abutment had its density measured by Archimedes’ method. Through the natural vibration frequencies a Young’s modulus of 187.97 ± 4.84 GPa and a Poisson’s rate of 0.19 ± 0.04 were obtained for the material. The shrinkage was 58 vol% and the grain size was 0,705 ± 0,424 μm . The FEA showed stress concentration at the first thread pitch for both abutments, and tensile stress concentration were observed at the side that received the oblique load with compressive stress at the opposite side. Whereas, for the conventional abutment model a stress concentration was observed at the screw’s stem. The final density for the zirconia prototype abutment was 95.68% from the theoretical density (6.12 g.cm-3). The zirconia abutment obtained by slip casting presented satisfactory physical properties. The suppressing of the fixing screw could provide better performance to the abutment due to the lack of stress concentration in the screw when an oblique load is applied, when evaluated by FEA

Made available in DSpace on 2015-03-26T13:30:42Z (GMT). No. of bitstreams: 1 texto completo.pdf: 851127 bytes, checksum: ecfdf02c9cd43f58963fe56b126f4b98 (MD5) Previous issue date: 2012-07-19 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / The eusocial stingless bee Melipona quadrifasciata anthidioides belongs to the Meliponini, a tribe that comprises important pollinators of tropical and subtropical plants. Within a typical eusocial colony there are drones and females that include different casts, i.e. workers and queen(s). In this species, the caste differentiation can be influenced by the Juvenile Hormone (JH). When JH is topically applied in last instar male larvae, they originate individuals with queen s phenotype in which the male-like reproductive system persists. Take into account that different individuals play different roles in the colony, it is reasonable to assume that they can be distinguished by their sensorial organs. Sensilla are basic integumental unit that are important for the insect thermo, mechanical, higro, CO2 and chemical perceptions. In addition, these sensory structures may be distinguished by their morphologies and functions. The objective of this study was to compare the antennal sensilla of individuals of different sexes and castes, including queen-like males of M. quadrifasciata anthidioides, showing for the first time details of their antennal topographies. Images of antenna dorsal surfaces were taken with the scanning electron microscope. Different types of antennal sensilla can be classified as follows: trichoid (ST, subtypes I to VII), placoid, basiconic, coeloconic and ampullacea. The the ST I and placoid sensilla were the most abundant sensillum types found in all individuals, even more in males. On the other hand, basiconic sensilla were only found in females, i.e. in workers and queens. The ST II is the third most abundant type of sensilla found in M. quadrifasciata anthidioides and the ST III and IV occurred only in the first flagellomere, being the first one bigger in females in comparison to males and the second one capable of separating the castes according to their types and length, though their numbers are not different. Moreover, the ST V and VI and the ampullacea types occurred only at the antenna s tip, with ST V being lower in number and smaller. ST VI is also larger in queens, separating them from other individuals, and greater in females. On the other hand, the other sensillae were seen along all antennas surface. The chaetic sensillum had apical pore and this pore was only found in females. Despite queen-like males had queen s phenotype, according to the Morisita similarity index, they resembled more the males, especially 2n ones, regarding the antenna phenotype and the composition of their sensilla. Generally speaking, irrespective of gender and cast, individuals of the stingless bee M. quadrifasciata anthidioides have similar sensillum types. However, they differed significantly in respect to the sensilla number and length and these differences were discussed here according to the gender and cast of this species. / A abelha sem ferrão Melipona quadrifasciata anthidioides é conhecida popularmente como mandaçaia e pertence à tribo Meliponini que inclui importantes insetos eusociais polinizadores de espécies de plantas tropicais e subtropicais. Em um ninho típico de abelhas sociais há indivíduos de diferentes sexos e castas. Esses são compostos pelos zangões e pelas castas femininas que incluem as operárias e a(s) rainha(s). Entretanto, quando o hormônio juvenil (HJ) é aplicado topicamente em larvas de machos, eles desenvolvem fenótipo da rainha. Entretanto, esses rainhóides ainda retêm o sistema reprodutivo masculino. Considerando que os indivíduos de diferentes castas e sexos desempenham papéis diferentes no ninho, podemos afirmar que os seus órgãos sensoriais como, por exemplo, as sensilas antenais também o sejam. Essas estruturas sensoriais podem ser diferenciadas tanto pela sua morfologia quanto pela função que desempenham como, por exemplo, a quimio- e mecanorrecepção. O objetivo deste trabalho foi estudar comparativamente as sensilas antenais de indivíduos de diferentes sexos e castas, incluindo os machos 2n e rainhóides, de M. quadrifasciata anthidioides, através de imagens da superfície dorsal das antenas, que foram feitas ao microscópio eletrônico de varredura. As diferentes sensilas antenais foram identificadas como sendo: sensilas tricóides (ST, dos subtipos I ao VI), placóides, basicônicas, céticas, celocônicas e ampuláceas. As sensilas basicônicas possuem um poro apical e são exclusivas das fêmeas (rainhas e operárias). As ST I e as placóides são as mais abundantes em todos os indivíduos, sendo encontradas em maior quantidade nos machos. Já as sensilas basicônicas possuem um poro apical e são exclusivas das fêmeas (rainhas e operárias). As ST II são o terceiro tipo de sensilas mais abundante em M. quadrifasciata anthidioides e as ST III e IV ocorrem apenas no primeiro flagelômero, sendo o primeiro tipo de sensila maior nas fêmeas que nos machos e o segundo tipo capaz de separar as castas femininas quanto ao seu comprimento, mas não diferem à quantidade. Por outro lado, as ST V e VI e ampuláceas ocorrem apenas na extremidade do último flagelômero antenal, com ST V sendo menor nos machos de M. quadrifasciata anthidioides tanto em quantidade quanto em comprimento, mas sendo úteis ainda para a distinção das castas femininas. As ST VI são mais compridas nas rainhas, separando-as dos demais indivíduos, e maiores nas fêmeas. Apesar dos rainhóides se assemelharem às rainhas quanto à morfologia externa, uma análise utilizando o índice de similaridade de Morisita mostrou que eles se assemelham mais aos machos, principalmente os 2n, quanto às suas antenas e a composição das sensilas, colocando-os em um grupo separado das fêmeas. Embora de maneira geral os mesmos tipos de sensilas tenham sido encontrados nas diferentes classes de indivíduos de M. quadrifasciata anthidioides, diferenças significativas foram observadas no número e no comprimento dos morfotipos das mesmas. Essas diferenças foram discutidas de acordo com a função do sexo e das castas dessa espécie.

Dando continuidade a uma pesquisa estética iniciada em 1991, este projeto de pesquisa em arte propõe a realização da série FORMIGAS, e o texto desta dissertação trata das relações entre a ética e a estética que essa obra estabelece ao longo dos quatro anos de duração do seu processo instaurador. No decorrer desse período, uma primeira versão dessa mesma série, composta por uma seqüência de nove eletrongrafias de caras de formigas de várias espécies, gerou um impasse ético que a presente versão, composta por uma seqüência de quinze eletrongrafias de caras de formigas do gênero acromyrmex, propõe discutir e contornar. / The current paper is a research project in art that discusses the relation between the ethics and the aesthetics brought about by the making of the ANT series. It is part of an aesthetic investigation initiated in 1991 and the series instauration process has taken four years. A first version of the series was composed by a sequence of nine electrongraphs of ant faces of several species, and the second version is composed by fifteen electrongraphs of ant faces of the genus acromyrmex. The first version raised an ethical dilemma which the second one and this paper are meant to discuss and resolve.

L’objectif de ce travail est d’obtenir un modèle 3D d’un objet à partir d’une série d’images prisesavec un Microscope Electronique à Balayage (MEB). Pour cela, nous utilisons la technique dereconstruction 3D qui est une application bien connue du domaine de vision par ordinateur.Cependant, en raison des spécificités de la formation d’images dans le MEB et dans la microscopieen général, les techniques existantes ne peuvent pas être appliquées aux images MEB. Lesprincipales raisons à cela sont la projection parallèle et les problèmes d’étalonnage de MEB entant que caméra. Ainsi, dans ce travail, nous avons développé un nouvel algorithme permettant deréaliser une reconstruction 3D dans le MEB tout en prenant en compte ces difficultés. De plus,comme la reconstruction est obtenue par auto-étalonnage de la caméra, l’utilisation des mires n’estplus requise. La sortie finale des techniques présentées est un nuage de points dense, pouvant donccontenir des millions de points, correspondant à la surface de l’objet. / The goal of this work is to obtain a 3D model of an object from its multiple views acquired withScanning Electron Microscope (SEM). For this, the technique of 3D reconstruction is used which isa well known application of computer vision. However, due to the specificities of image formation inSEM, and in microscale in general, the existing techniques are not applicable to the SEM images. Themain reasons for that are the parallel projection and the problems of SEM calibration as a camera.As a result, in this work we developed a new algorithm allowing to achieve 3D reconstruction in SEMwhile taking into account these issues. Moreover, as the reconstruction is obtained through cameraautocalibration, there is no need in calibration object. The final output of the presented techniques isa dense point cloud corresponding to the surface of the object that may contain millions of points.

Dando continuidade a uma pesquisa estética iniciada em 1991, este projeto de pesquisa em arte propõe a realização da série FORMIGAS, e o texto desta dissertação trata das relações entre a ética e a estética que essa obra estabelece ao longo dos quatro anos de duração do seu processo instaurador. No decorrer desse período, uma primeira versão dessa mesma série, composta por uma seqüência de nove eletrongrafias de caras de formigas de várias espécies, gerou um impasse ético que a presente versão, composta por uma seqüência de quinze eletrongrafias de caras de formigas do gênero acromyrmex, propõe discutir e contornar. / The current paper is a research project in art that discusses the relation between the ethics and the aesthetics brought about by the making of the ANT series. It is part of an aesthetic investigation initiated in 1991 and the series instauration process has taken four years. A first version of the series was composed by a sequence of nine electrongraphs of ant faces of several species, and the second version is composed by fifteen electrongraphs of ant faces of the genus acromyrmex. The first version raised an ethical dilemma which the second one and this paper are meant to discuss and resolve.