Dissertations / Theses on the topic 'Flat formation'

In order  to  find  another way to fix peptides      on      surfaces      we      study      the      chemical      and      electro      oxidation       of      a      Silicon      flat      surface      after      silanization.      Traditional      experimental      setup      is      used      to      make      the       oxidations      and      Xray      photoelectron      spectroscope      (XPS)      is      used      to      analyze      the      surfaces.      We      find      that       chemical      oxidation      works      well      but      we      cannot      fix      the      Alanine      molecule      on      the      surface,      unlike      the       electro      oxidation      which      works      for      peptides      fixation.            We      need      to      focus      on      the      electro      oxidation       process,      use      a      more      accurate      method      to      analyze      the      samples      and      probably      used      a      higher      Alanine       concentration.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.
Includes bibliographical references (leaves 85-87).
In the current state of spray forming processes, deposit surfaces formed on a substrate contain porosity. This surface porosity requires secondary operations to be removed. The added expense of these operations prevents the full industrialization of the spray forming process. Thus, a basic understanding of the surface porosity formation is desired. This thesis presents a fundamental analysis of surface porosity formation through modeling and experimentation. Individual splat formation and multiple splat interactions determine surface porosity in uniform droplet spray deposits. A strategy is proposed to minimize surface porosity, first, through control of individual splat formation for a suitable splat geometry, and second, through control of multiple splat interactions. Conditions for a suitable splat geometry are determined by experimentation on the effect of the droplet liquid fraction and the substrate thermal state on the final splat geometry. Pure tin droplets ( 416 [mu]m) are deposited on stainless steel substrates. A droplet liquid fraction of 83% and stainless steel substrate temperature between 150°C and 190°C results in suitable splat geometry. The effect of multiple splat interactions on surface porosity is studied through modeling and experimentation. The model explains the effect of droplet flux and splat solidification on surface porosity. One dimensional heat transfer between splat and substrate is assumed. Experiments are performed with pure tin droplets ( 416 [mu]m and 271 [mu]m) on stainless steel and glass substrates. Results show that slower splat solidification and higher droplet flux reduce surface porosity. A minimum surface porosity of 2.2% is achieved in the uniform droplet spray deposits with tin droplets (416 [mu]m) on a glass substrate.
by Sukyoung Chey.
Ph.D.

Les suies et les hydrocarbures polyaromatiques, qui sont émis à l’échappement des moteurs Diesel, constituent une part importante de la pollution urbaine. Depuis plusieurs années, de nombreuses recherches ont permis de progresser dans le domaine de la cinétique de la combustion des hydrocarbures qui est maintenant relativement bien connue. Il reste néanmoins des zones d’ombre concernant la formation des composés aromatiques (benzène, toluène,…) et des hydrocarbures aromatiques polycycliques (HAP) dont la formation provient d’espèces composées de deux à six atomes de carbone et qui mènent directement ou indirectement à la formation des suies.L’allène, le propyne, le butadiène et le cyclopentène sont des produits intermédiaires importants de la combustion dans les moteurs. Dans ce contexte, ce travail de thèse a permis de mieux comprendre les voies réactionnelles importantes dans la formation du benzène et du toluène. Le chapitre I de ce mémoire présente une revue bibliographique des travaux antérieurs sur l’oxydation du méthane, de l’allène, de propyne, de 1,3-butadiène et du cyclopentène. Le chapitre II présente une description détaillée du montage expérimental utilisé durant cette étude afin d’étudier la structure de la flamme laminaire de prémélange. Les chapitres III, IV et V présentent les résultats expérimentaux obtenus en flamme laminaire de prémélange, ainsi qu’une comparaison avec des simulations effectuées à l’aide de mécanismes réactionnels élaborés durant ce travail de thèse
Soots and polyaromatic hydrocarbons (PAH), which are present in the exhaust gas of diesel engines, represent a large part of the urban pollution. Many efforts have then been focused on reducing the emissions of these compounds. The formation of soot precursors and PAH in combustion involves small unsaturadted hydrocarbons the chemistry of which is still very uncertain. Allene, propyne, 1,3-butadiene and cyclopentene are intermediate products in the combustion in cars engines. This work has led to a better understanding of several important paths in the formation of benzene and toluene. The chapter I of this report presents a bibliographic review of former work on the oxidation of methane, allene, propyne, 1,3-butadiene and cyclopentene. Chapter II gives a detailed description of the experimental set up used during this work to study the structure of the premixed flat laminar flames. Chapters III, IV and V present our experimental results obtained in laminar premixed flat flames and also the comparison with simulations

In my diploma thesis I elaborated a project for realization of the building. Its content is a home for the elderly, which is a three-storey building, where the first floor is designed as an operating section with a doctor's surgery, a medical equipment rental and a dining room with a kitchen. The remaining two above-ground floors are designed as 1 + KK or 1 + 1 flats. Each balcony is designed for each apartment. Further, there are nurses on these floors. The building is designed as brickwork made of brick blocks with additional mineral insulation thermal insulation, the roof structure being solved using pre-prestressed concrete reinforced concrete panels Spiroll. The roof is designed from flat sloping wedges.

In recent years, the development trend of power grids character shows increased demand for using cables of both current overhead and newly constructed lines. In order to preserve reliable operation and to predict the maintenance requirements, it is crucial to regard not only the parameters certified by manufacturers, but also externalities induced by real environment and incorporate these externalities into cable models in simulation software. The diploma thesis deals with determining of characteristic parameters of single core cables in real environment, which are affected by real grounding methods of metal shielding. The emphasis is put on analysis of current cable models in simulation software PSCAD and its evaluation using two-step experiment 1) measurement of shunt parameters in laboratory using electronic bridge model and 2) on field measurement of cable series parameters in real environment.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2014.
Made available in DSpace on 2015-03-18T21:06:14Z (GMT). No. of bitstreams: 1 332922.pdf: 3410507 bytes, checksum: d7467bb6147cb8c861cdab971f3cc6a9 (MD5) Previous issue date: 2014
Para melhor compreender a formação de falhas de solidificação e de porosidade na soldagem híbrida laser - GMAW de chapas de aço com grande espessura, foram feitos ensaios com variação de diâmetro do feixe laser, de potência do feixe laser, de metal de adição, de velocidade de soldagem e com oscilação transversal do feixe laser. Esses ensaios foram realizados utilizando-se uma fonte de laser de disco com 16 kW de potência máxima e duas tochas GMAW em chapas de aço alta resistência e baixa liga que atende ao grau de qualidade X70 da API 5L e depois foram avaliados através de imagens metalográficas e de raios-X. Acredita-se que a geometria do cordão de solda tem grande influência na formação de falhas de solidificação e esse trabalho investigou a relação que há entre uma protuberância no cordão de solda e a falha de solidificação, sugerindo ainda uma forma de medir a severidade dessa protuberância: o ângulo de alargamento da protuberância. Foi verificado também como os parâmetros supracitados influenciam o ângulo de alargamento da protuberância e a formação das falhas de solidificação. Duas novas explicações para a discrepância de resultados encontrados na literatura quanto à formação da falha de solidificação foram propostas. Por fim, analisou-se a porosidade encontrada nos cordões de solda através das imagens metalográficas e de raios-X para determinar as suas principais causas na soldagem híbrida laser - GMA de chapas grossas de aço API 5L X70.

Abstract : To achieve a better understanding of the solidification flaw and porosity formation in hybrid laser - GMA welding of thick steel plates, tests were carried with varying laser beam width, laser beam power, filler metal, welding speed and with transverse beam oscillation. Those tests were carried using a 16 kW maximal power disk laser source and two GMAW torches on high strength low alloy steel plates that complies with the grade X70 from API 5L that were later analyzed through metallographic and X-ray imaging. It is believed that the weld seam geometry has a high influence on the solidification flaw formation and it was investigated in this work the relation between a bulge in the weld seam and the solidification flaw, introducing a new way to measure the severity of the bulge: the bulge widening angle. It was also verified how the aforementioned parameters influence the bulge widening angle and the solidification flaw formation. Two new explanations for the discrepancy found in the literature regarding the formation of the solidification flaws were proposed. Lastly, the porosity found in the weld seams was analyzed through the metallographic and X-ray images to determine its main causes in the hybrid laser - GMA welding of thick API 5L X70 steel plates.

The aim of this diploma thesis is to elaborate the project documentation of a new-built home for the elderly, in the cadastre unit of small town Blížkovice. It is a three-storey building with a basement. On the basement there are cellar berths, garage and technical facilities. On the first floor there is facilities, dining rom, a doctor´s surgery, massage, hairdresser´s and pedicure. On the second and third floor there are common areas and a total of twenty-two residentail units (1+kk – eighteen flats, 2+kk – two flats). The vertical loadbearing structures are made of clay blocks and lost formations. The object is insulated by a contact thermal insulation systém. The horizontal loadbearing structures and staircase are made of reinforced monolithic concrete slab. The roof consists of a flat roof with extensive green and terrace. There are ten parking spaces on the ground.

Bibliography: pages 245-257.
The middle to late Proterozoic Awasib Mountain terrain (AMT) straddles the boundary between the Rehoboth and Gordonia subprovinces in southern Namibia. The AMT is made up of two major crustal components, the older of which is correlated with the Namaqualand Metamorphic Complex (NMC), and the younger with the Sinclair Sequence.

Made available in DSpace on 2014-08-20T13:44:50Z (GMT). No. of bitstreams: 1 dissertacao_guilherme_fiss.pdf: 349237 bytes, checksum: 8903edd41c7e4b3cf1dd875b989bdb67 (MD5) Previous issue date: 2011-10-07
The corn (Zea mays L.) is a plant of the Poaceae family, cultivated in many regions around the world. In order to be guaranteed the crop yeld, it is necessary to be produced high-quality seeds. One of the main factors associated with high physiological quality is the time in which the seeds are harvested. Given the above, the present study aims to evaluate the physiological quality of corn seeds, in function of the size and the harvest season. The place used for the seeds collection was a private property located in the municipality of Arroio do Padre-RS, in a commercial maize crop. The variety grown and collected on this site was the BRS 4157 Sol-da-Manhã. The harvesting process occurred in nine different seasons with spaces from three to four days between harvests. After the harvesting process, the seeds were classified into two different formats: flat and round. As for standardizing the experimental units, the spikes were marked at the same level of maturity stage, and, for each harvest, 10 spikes were collected for each repetition. The evaluations were: moisture, verification of the black tip of 100 seeds, germination, accelerated aging, cold test and electrical conductivity. Based on the results, we reached the following conclusions: Corn seeds harvested near the physiological maturity are not different in quality, independent from the size. The best time for the corn harvest is when the seed moisture is between 28 and 33% of moisture. In case of delay in harvest, the round seeds have a lower physiological quality. The loss of seed moisture on the spike in the field is less than 0,6pp.hour-1.
O milho (Zea mays L.) é uma planta da família Poaceae cultivada em diversas regiões do mundo. Para que seja garantida a produtividade da cultura, é necessário que sejam produzidas sementes de alta qualidade. Um dos principais fatores associados à elevada qualidade fisiológica é o ponto em que as sementes são colhidas. Diante do exposto, o presente trabalho teve como objetivo avaliar qualidade fisiológica de sementes de milho em função do formato e da época de colheita. O local utilizado para a coleta de sementes foi em uma propriedade particular localizada no município de Arroio do Padre-RS, em uma lavoura de milho comercial. A variedade cultivada e coletada neste local foi a BRS 4157-Sol-da-Manhã. O processo de colheita ocorreu em nove épocas distintas com intervalos de quatro dias entre as colheitas. Após o processo de colheita as sementes foram classificadas em dois formatos distintos: chato e redondo. Para uniformização das unidades experimentais as espigas foram marcadas no mesmo estádio de maturação, sendo que, em cada colheita, 10 espigas foram coletadas para cada uma das duas repetições. As avaliações realizadas foram: umidade, verificação da ponta negra, germinação, envelhecimento acelerado, teste de frio e condutividade elétrica. Com base nos resultados, chegou-se as seguintes conclusões: Sementes de milho colhidas próximo a maturidade fisiológica não apresentam diferença na qualidade, independente do formato. O melhor ponto para a colheita do milho é quando a umidade das sementes está entre 28 e 33% de umidade. No caso de atraso na colheita, as sementes redondas apresentam menor qualidade fisiológica. A perda de umidade das sementes em espiga no campo é inferior a 0,6pp.hora-1.

Les protoétoiles de masse intermédiaire (IM) (2 ≤ M* ≤ 8 Msun) sont le lien entre les étoiles de faible et haute masse car elles couvrent également un intervalle intermédiaire de luminosités, de densités et de températures [Fuente et al., 2012]. Même si les « IM-YSOs » jouent un rôle important dans l'étude de la formation des étoiles, on a très peu de connaissances sur la formation et l'évolution des premières étapes des protoétoiles de masse intermédiaire. Les études systématiques spectrales sont un outil puissant pour caractériser la composition chimique d'un objet astrophysique, et la seule façon d'obtenir un recensement complet des espèces chimiques. Une étude spectrale fournit également des lignes multiples de la même molécule, donnant la possibilité d'une analyse multifréquences ainsi que d'une modélisation. En outre, grâce aux profils des raies, nous pouvons obtenir des informations sur la cinématique, et identifier les structures au long de la ligne de vue, en tant que sources multiples, des jets ou des cavités, par exemple, [Caux et al., 2011]. Les phénomènes d'éjection (jets, des vents et des « outflows » bipolaires moléculaires), sont une phase inhérente au processus de formation d'étoiles observées dans les YSOs de toutes masses dans des longueurs d'onde millimétriques. Cependant, il n'y a pas d'études systématiques dans l'intervalle de masse intermédiaire comme dans le cas des protoétoiles de faible et haute masse. Compte tenu de l'absence d'une étude systématique de la partie mm/submillimétrique dans le spectre des protoétoiles de masse intermédiaire, au cours de ma thèse, j'ai mené une étude systématique spectrale vers la protoétoile de masse intermédiaire de classe 0 Cep E et de son « outflow » moléculaire
Intermediate-mass (IM) protostars (2 ≤ M∗ ≤8 Msun) are the link between low and the high mass stars as they cover also an intermediate range of luminosities, densities and temperatures [Fuente et al., 2012]. Even though the IM-YSOs are important in the study of star formation, very little is known about the formation and first evolutionary stages of IM protostars. Unbiased spectral surveys are a powerful tool to characterize the chemical composition of an astrophysical object, and the only way to obtain a complete census of the chemical species. A spectral survey provides also multiple lines from the same molecule, giving the possibility of a multi-frequency analysis and modeling. Also, through line profiles, we can obtain kinematic information, and identify structures along the line of sight, as multiple sources, outflows, jets or cavities, e.g. [Caux et al., 2011]. The outflow phenomena (jets, winds and bipolar molecular outflows), are an inherent phase in the process of star formation observed in YSOs of all range of masses at millimeter wavelengths. However, there are not systematic studies in IM range as in the case of of low- and high-mass protostars. Given the lack of a systematic study of the mm/submm spectrum of IM protostars, during my thesis I carried out an unbiased spectral survey towards IM Class 0 Cep E protostar and its molecular outflow

The objective of this study is to examine the emotional regulation strategies used by Walt Disney World on-stage employees as a way to fulfill requirements set forth by the company. Ten Disney on-stage employees were interviewed off-property in Orlando. The emotional regulation framework was divided into several categories: (1) a distinction between deep acting and surface acting, (2) emotional deviance, and (3) emotional exhaustion. "Surface acting" is a strategy by which employees display company-imposed emotions not genuinely felt, whereas "deep acting" occurs when employees do feel the emotions that they are required to express (Hochschild, 1983). Throughout the data reduction process, five key themes surfaced as the most relevant to the initial research questions: (1) Self-Motivated Deep Acting, (2) Organizational Expectations for Surface Acting, (3) "Back-Stage" vs. "Front-Stage" Dichotomy, (4) Benefits of Emotional Training, and (5) Negative Effects of Emotional Regulation. Overall, the researcher found that a key strategy of emotional regulation that Disney employees use frequently is surface acting, although deep acting was found to be more successful. In addition, while emotional exhaustion was a common problem among employees, very few of them will actually engage in emotional deviance in order to avoid the negative consequences of surface acting. Lastly, it was found that highly skilled Walt Disney World employees will have already internalized emotional regulation training and display rules that manage emotional behavior. Therefore, it becomes less essential for the Disney Company to formally monitor its employees' facial expressions and emotional behavior in the future.
ID: 029809526; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.A.)--University of Central Florida, 2011.; Includes bibliographical references (p. 74-85).
M.A.
Masters
Communication
Sciences

Etude des disques d'accretion et de matiere ejectee autour d'etoiles jeunes telles que cep a, w28a2 et g10. 6. Les observations millimetriques a haute resolution font apparaitre des raies qui permettent d'etudier les flots bipolaires des deux premiers objets cites et le disque d'accretion inhomogene en rotation du troisieme. L'observation d'enveloppes froides autour d'objets evolues fait apparaitre une classe d'etoiles peu massives en fin d'evolution, les "pseudo supergeantes f"; une nebuleuse planetaire tres peu evoluee et tres riche en co et la nebuleuse du "lion givre" dont le spectre ir est domine par l'emission de la glace cristalline

L'interférence entre stations de base est considérée comme le principal facteur limitant les performances des réseaux cellulaires. Nous nous intéressons aux différents schémas de coordination multi-point (CoMP) proposés dans la norme LTE-A pour y faire face, en tenant compte de l'aspect dynamique du trafic et de la mobilité des utilisateurs. Les résultats sont obtenus par l'analyse mathématique de modèles markoviens et par des simulations du système. Nous montrons l'importance de l'algorithme d'ordonnancement sur les performances en présence d'utilisateurs mobiles, pour des services de téléchargement de fichier et de streaming vidéo. Nous proposons un nouvel algorithme d'ordonnancement basé sur la dé-priorisation des utilisateurs mobiles se trouvant en bord de cellule, afin d'améliorer l'efficacité globale du système. Nous montrons ensuite qu'il est intéressant d'activer la technique dite Joint Processing uniquement dans un réseau à forte interférence, son activation dans un réseau à faible interférence pouvant conduire à une dégradation des performances. Nous proposons un nouveau mécanisme de coordination où une cellule ne coopère que lorsque sa coopération apporte un gain moyen de débit suffisant pour compenser les pertes de ressources engendrées. Nous considérons enfin la technique de formation de faisceaux coordonnée. Nous montrons notamment que la coordination n'est pas nécessaire lorsque l'on dispose d'un grand nombre d'antennes par station de base, un simple mécanisme d'ordonnancement opportuniste permettant d'obtenir des performances optimales. Pour un nombre limité d’antennes parstation de base, la coordination est nécessaire afin d’éviter l’interférence entre les faisceaux activés, et permet des gains de performance substantiels
Interference is still the main limiting factor in cellular networks. We focus on the different coordinated multi-point schemes (CoMP) proposed in the LTE-A standard to cope with interference, taking into account the dynamic aspect of traffic and users’ mobility. The results are obtained by the analysis of Markov models and system-level simulations. We show the important impact of the scheduling strategy on the network performance in the presence of mobile users considering elastic traffic and video streaming. We propose a new scheduler that deprioritizes mobile users at the cell edge, in order to improve the overall system efficiency. We show that it is interesting to activate Joint Processing technique only in a high-interference network, its activation in a low-interference network may lead to performance degradation. We propose a new coordination mechanism, where a cell cooperates only when its cooperation brings a sufficient mean throughput gain, which compensates the extra resource consumption. Finally, we show that the coordination of beams is not necessary when a large number of antennas is deployed at each base station; a simple opportunistic scheduling strategy provides optimal performance. For a limited number of antennas per base station,coordination is necessary to avoid interference between the activated beams, allowing substantial performance gains

Experiments were done to investigate the role of vortex formation in the drag force generation of low aspect ratio, normal flat plates starting from rest. This very simplified case is a first, fundamental step toward understanding the more complicated flow of hovering flight, which relies primarily on drag for propulsion. The relative importance of the plate's free end, or tip, with varying aspect ratio was also studied.

Identifying the relationship among aspect ratio, vortex formation, and drag force can provide insight into the wing aspect ratios and kinematics found nature, with the eventual goal of designing man-made flapping wing micro air vehicles.

The experiments were carried out using flat plate models in a towing tank at a moderate Reynolds number of 3000. Two aspect ratios, 6 and 2, were considered, the latter in order to have a highly tip-dominated case. A force balance measured the time-varying drag, and multiple, perpendicular sections of the flow velocity were measured quantitatively using digital particle image velocimetry. Vorticity fields were calculated from the velocity data, and features in the drag force for different aspect ratios were related to the vortex dynamics. Finally, since the flow is highly three-dimensional, dye flow visualization was done to characterize its structure and to augment the two-dimensional digital particle image velocimetry data.

博士
淡江大學
化學工程與材料工程學系博士班
98
In this research we focus on investigations of the formation of porous polymeric flat-sheet and hollow fiber membranes by phase separation methods. First, flat-sheet pourse membrames are prepared by non-solvent induced phase separation (NIPS), thermal induced phase separation (TIPS), and cold-solvent induced phase separation (CIPS) methods. The mechanisms for membrane formation by varios methods are discussed. Next, formation of microporous PVDF membranes by precipitation of casting dopes made from different solvents (DMF, TEP and DMSO) in different alcohol baths (methanol, 1-propanol, isopropanol, 1-butanol and 1-octanol) are reported. The effects of solvents’ polarities and alcohols’ carbon number, on the crystal types of the formed PVDF membranes are discussed. In addition, template-leaching method is used to prepare microporous poly(VDF-co-HFP) membranes. A composite film consists of poly(VDF-co-HFP) and poly(VDF-co- TFE-co-HFP) is prepared by common solution blending-drying method. Then, the terpolymer is leached out in an acetone aqueous solution to yield a microporous membrane. By controlling the terpolymer content in the blend and the leaching condition, membranes with different porous structures and porosity are obtained. These hydrophobic flat membranes are applied to membrane distillation. Finally, pourse polymeric hollow fiber membrames are prepared by NIPS spinning process with special consideration on the effects of inner and outer non-solvent.

Thesis (M.S.)--University of Wisconsin--Madison, 1985.
Typescript. Eight maps on folded leaves in pocket. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 119-123).

碩士
國立交通大學
工學院碩士在職專班精密與自動化工程組
98
Due to application needs, the trend of notebook development is toward lighter and slimmer. Backlight units in a TFT-LCD provide a suitable lighting mechanism. The light-guide plate - a component in the backlight unit is necessary to change formation from wedge type to flat type. However, the area and thickness of a flat type Light-guide plate are greatly different in dimension, and therefore require different injection conditions than other injection workpieces. Not only is a high speed injection machine needed, but the quality and stability of flat type LGP must be controlled. Therefore, reference on existing theory of operation is necessary, and other issues of high speed injection must be considered. The purpose of this study is to study warp of LGP under different process factor. This is achieved using the Taguchi Methods /Design of Experiments approach. Each experimental condition in this study uses different process factors and high speed injection machine with optical PMMA material. The main influencing factor and best condition for robust character & accuracy can be determined by measuring the amount of warp after RA test. Further, the operation window of the main factor can be built up. The results of this study show that the main factors affecting the robust character of S/N are the fill-in speed and packing pressure. The main factors affecting accuracy are the fill-in speed and mold temperature. A high fill-in speed produces a high shear rate (shear thinning), reduced viscosity, and a more uniform pressure and temperature inside the mold. These factors reduce the residual stress on a flat-type LGP, and hence, produce less warp. Setting the packing pressure too high will produce uneven contraction, which results in warp. In terms of accuracy, mold temperature is always affected be cooling behavior, if the workpiece cools down unevenly, there will be uneven contraction, which will result in warp.

博士
元智大學
化學工程與材料科學學系
95
One-step synthesis of platinum nanoparticles and nanostructured thin film by spray pyrolysis in low-pressure flat flame was performed here. The particle formation mechanisms were also examined. The effects of fuel/oxidant ratio, chamber pressure, precursor concentration, operation time and flame temperature on particle or thin film characteristics were investigated. The flame-derived particles and thin film were characterized for size and morphology by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The crystal phase and grain size were analyzed by X-ray diffraction (XRD). The X-ray absorption spectroscopy (XAS) was used to investigate the oxidation state, the local atomic structure, average local coordination number, and to identify neighboring atoms of the particle samples. The TEM and HRTEM results suggest that the flame-derived particles are submicrometer spherical hollow particles with nanocrystalline crusts. Increasing the operation time resulted in slightly increased nanocrystals size, due probably to the extended radiative heating of the deposited particles by the flame. The XAS results suggested a Pt-Pt bonding from the first shell data of the as-derived particles. The oscillation by XANES at high energy side of the absorption edge for flame-derived particles is very similar to that of Pt foil, indicating a metallic state of the as-derived particles, except those prepared with the lowest flame temperature, 1078K. The unusual nano-thin films derived are composed of metallic platinum nanoparticles of face-center-cubic crystal structure when flame temperature is 1378K and above, even with an oxygen-enriched flame. The volume-averaged crystallite size increased strongly with flame temperature and precursor concentration, but slightly with operation time. The XRD patterns of the flame-derived thin film samples were identified to match those of f.c.c. platinmu in all cases except those obtained at 1078K. The chamber pressure does not have a direct impact on crystallite size but affects the flame temperature significantly, which in turn affects the crystallite size of the particles thus prepared. The formation mechanisms were proposed for both the hollow spheres and thin films. Micro-explosion of the nanocrystalline hollow spheres was suspected to have resulted in the unusual nano-thin films by the combined technique.

It is well known that above a critical field strength sufficiently large to overcome damping by capillary forces, the free surface of a perfectly conducting liquid will spontaneously deform into one or more sharp protrusions known as conic cusps. Such cusps undergo tip sharpening while rapidly accelerating toward regions of highest electric field strength, eventually giving rise to beams of ions and/or charged droplets . These charged beams form the basis for liquid metal ion sources (LMIS) commonly used in focused ion beam systems, scanning ion microscopy, micromilling, ion mass spectrometry, implantation, and lithography. During the past few decades, there has been growing interest in optimizing the formation, growth, and stability of conic cusps in liquid metals for a new class of efficient and highly miniaturizable satellite micropropulsion devices consisting of microarrays of externally wetted solid needles coated with a film of liquid metal propellant. The thrust levels generated by such microarrays is suitable for propulsion of small satellites and precision pointing maneuvers for larger satellites.

This thesis addresses the formation, growth, and instability of conic cusp formations in perfectly conducting, electrified viscous liquids on flat and curved surfaces. We use finite element simulations based on the arbitrary Lagrangian-Eulerian (ALE) method for coupling the vacuum and liquid domains across the accelerating interface. The simulations in Chapters 2–4 describe the evolution of liquid flow subject to electric field distributions generated by opposing flat parallel and solid electrodes. In particular, we examine in Chapter 2 the growth of a small liquid protuberance on an otherwise flat viscous liquid layer of perfectly conducting fluid subject to an initial uniform electric field. Previous studies in the literature have established that tip sharpening proceeds via a self-similar process in two distinct limits: the Stokes regime at Re = 0 and the inviscid regime Re → ∞. These simulations, conducted at fixed capillary number Ca and for 0.1 ≤ Re ≤ 50,000, which span the viscous to inviscid regimes, demonstrate that the conic tip always undergoes self-similar growth irrespective of Reynolds number. Field self-enhancement due to conic cusp tip sharpening is shown to generate divergent power law growth in finite time (so-called blowup behavior) of the interfacial and volumetric forces acting at the advancing tip. The computed blow up exponents at the tip surface associated with the various terms in the Navier-Stokes equation and interface normal stress condition reveal the different forces at play as Re increases. Rescaling of the tip shape by the capillary stress exponent yields excellent collapse onto a universal conic tip shape with interior half-angle dependent on the magnitude of the Maxwell stress. The simulations clearly show that the interior cone angle adopts values both above and below the Taylor cone angle value of 49.3°. Additional details of the modeled flow dispel prevailing misconceptions that dynamic cones resemble conventional Taylor cones or that viscous stresses at finite Re can be neglected. In Chapter 3, we demonstrate how the rapid acceleration of the curved liquid interface also generates a thin surface boundary layer with very high local strain rate in the vicinity of the conic tip. The value of the surface vorticity along the moving interface is shown to be in excellent agreement with theoretical predictions. More importantly, the results in Chapters 2 and 3 demonstrate that the velocity streamlines are always at an oblique angle to the moving interface, contrary to commonly held belief that the streamlines always lie tangent to the moving boundary. In Chapter 4, we extend the simulations to include variation of the capillary number and find that for sufficiently high Re and Ca, the advancing interface develops significant oscillations. Fourier analysis of these interface oscillations indicates that the extracted instability wavelength characteristic of flows at smaller values of Re tends to exceed the simplified theoretical prediction based on inviscid flow. By contrast, the extracted instability wavelength for the largest values of Re examined tends to fall below the inviscid prediction.

In Chapter 5, we explore the effect of substrate curvature on the flow and stability of electrified films by examining the behavior of a thin viscous film of perfectly conducting liquid on two types of curved surfaces. These shapes, which include a solid conical needle with a spherical cap tip and a solid parabolic needle, are intended to mimic substrates used in some externally wetted microemitter arrays in LMIS systems. For the simulations in Chapter 5, the needle is situated below a counter electrode perforated with a circular aperture. The films are shown to develop both on-axis and off-axis cusp-like protrusions depending on the parameter range examined. In particular, the formation of off-axis protrusions are directly traced to substrate shapes which manifest an abrupt change in curvature, as present in a solid conical needle with a spherical cap tip. The simulations reported here are anticipated to help optimize fabrication of externally wetted needle shapes for use in a variety of LMIS systems.

Τα παραγόμενα πρωτογενή ηλεκτρόνια εντός του φωτοαγώγιμου υλικού ενός μαστογραφικού ανιχνευτή ενεργού μήτρας άμεσης μετατροπής κατά την ακτινοβόληση, αποτελούν το πρωτογενές σήμα το οποίο προχωρώντας σχηματίζει το τελικό σήμα (εικόνα). Έτσι, η ποιότητα της μαστογραφικής εικόνας εξαρτάται άμεσα από τα χαρακτηριστικά των πρωτογενών ηλεκτρονίων. Ερευνώνται οι διαδικασίες σχηματισμού του πρωτογενούς σήματος και τα χαρακτηριστικά των πρωτογενών ηλεκτρονίων σε κατάλληλα φωτοαγώγιμα υλικά, όπως τα a-Se, a-As2Se3, GaSe, GaAs, Ge, CdTe, CdZnTe, Cd0.8Zn0.2Te, ZnTe, PbO, TlBr, PbI2 και HgI2, με την ανάπτυξη μοντέλου προσομοίωσης με τεχνικές Monte Carlo της παραγωγής των πρωτογενών ηλεκτρονίων για διάφορα φάσματα ακτίνων Χ στο μαστογραφικό εύρος ενεργειών. Το μοντέλο προσομοιώνει την αλληλεπίδραση φωτονίων-ύλης και την ατομική αποδιέγερση. Επιπρόσθετα, ειδικότερα για το a-Se, πραγματοποιείται μία προκαταρτική μελέτη της συσχέτισης των χαρακτηριστικών αρχικού και τελικού σήματος, με επίλυση των εξισώσεων του Νεύτωνα για την ολίσθηση των πρωτογενών ηλεκτρονίων στο κενό υπό την επίδραση ενός απλού ηλεκτρικού πεδίου. Για το ίδιο υλικό, αναπτύσσεται αφενός μεν αλγόριθμος υπολογισμού της κατανομής του ηλεκτρικού δυναμικού εντός του ανιχνευτή με χρήση υπάρχουσας αναλυτικής λύσης αφετέρου δε ένα πρωταρχικό μοντέλο Monte Carlo για τις ηλεκτρονιακές αλληλεπιδράσεις. Τα σημαντικότερα ευρήματα είναι: (i) το ποσοστό των πρωτογενών ηλεκτρονίων που εκπέμπονται εμπρόσθια είναι περίπου 60 % με την πιθανότερη πολική γωνία εκπομπής μεταξύ 50ο και 70ο, (ii) τα ηλεκτρόνια εκπέμπονται σε δύο λοβούς γύρω από τις αζιμουθιακές γωνίες φ=0 και π, (iii) περίπου το 80 % των πρωτογενών ηλεκτρονίων παράγεται στο σημείο πρόσπτωσης των ακτίνων Χ ενώ η πλειονότητά τους παράγεται εντός των πρώτων 300 μm από την επιφάνεια του ανιχνευτή, (iv) οι χωρικές κατανομές των ηλεκτρονίων στα a-Se, a-As2Se3, GaSe, GaAs, Ge, PbO και TlBr είναι σχεδόν ανεξάρτητες του μαστογραφικού φάσματος ενώ στα υπόλοιπα υλικά παρουσιάζουν φασματική εξάρτηση, (v) για το πρακτικό μαστογραφικό εύρος (15-40 keV) και στο πρωταρχικό στάδιο της δημιουργίας του σήματος τα a-Se, a-As2Se3 και Ge έχουν την ελάχιστη αζιμουθιακή ομοιομορφία κατά την εκπομπή των ηλεκτρονίων ενώ τα CdZnTe, Cd0.8Zn0.2Te και CdTe τη μέγιστη, το a-Se παρουσιάζει την καλύτερη ενδογενή χωρική διακριτική ικανότητα αλλά το μικρότερο παραγόμενο αριθμό ηλεκτρονίων, το PbO παρουσιάζει το ελάχιστο χώρο παραγωγής πρωτογενών ηλεκτρονίων (ακτίνας R=200 μm, βάθους Dmax=320 μm), ενώ το CdTe το μέγιστο (R=500 μm, Dmax=660 μm), (vi) τέλος, υπάρχουν σημαντικές ενδείξεις ότι τα PbI2 και HgI2 αποτελούν τις καλύτερες επιλογές φωτοαγώγιμου υλικού.
The x-ray induced primary electrons inside the photoconductor of direct conversion digital flat panel mammographic detectors, comprise the primary signal which propagates in the material and forms the final signal (image). Consequently, the quality of the mammographic image strongly depends on the characteristics of primary electrons. An investigation is made concerning the primary signal formation and the characteristics of primary electrons inside a-Se, a-As2Se3, GaSe, GaAs, Ge, CdTe, CdZnTe, Cd0.8Zn0.2Te, ZnTe, PbO, TlBr, PbI2 and HgI2, which are suitable photoconductors for direct detectors. A Monte Carlo model has been developed that simulates the primary electron production inside the materials mentioned for various x-ray spectra in the mammographic energy range. The model simulates the photon interactions and the atomic deexcitations. Furthermore, particularly for a-Se, a preliminary study is made concerning the correlation between the characteristics of primary and final signal, solving Newton’s equations of electron drifting in vacuum under the influence of a simple electric field. For the same material, an algorithm that calculates the electric potential distribution inside the detector from an existing analytical solution has been developed as well as a primitive Monte Carlo model for electron interactions. The most important findings are: (i) the percentage of primary electrons being forwards ejected is approximately 60 % with the most probable polar angles ranging from 50o to 70o, (ii) the electrons prefer to be emitted at two lobes around azimuthal angles φ=0 and π, (iii) approximately 80% of primary electrons are produced at the point of x-ray incidence whereas their majority is produced within the first 300 μm from detector’s surface, (iv) the electron spatial distributions for a-Se, a-As2Se3, GaSe, GaAs, Ge, PbO and TlBr are almost spectral independent while for the rest of materials there is a spectral dependence, (v) at the practical mammographic energies (15-40 keV) and at the primitive stage of signal formation a-Se, a-As2Se3 and Ge have the minimum azimuthal uniformity in electron emission whereas CdZnTe, Cd0.8Zn0.2Te and CdTe the maximum one, a-Se has the best inherent spatial resolution but the minimum number of primary electrons, PbO has the minimum bulk space in which electrons can be produced (radius R=200 μm, depth Dmax=320 μm) whereas CdTe has the maximum one (R=500 μm, Dmax=660 μm), (vi) finally, there is strong evidence indicating that PbI2 and HgI2 could be the best choices for this kind of applications.

碩士
國立東華大學
材料科學與工程學系
99
In this study, we have successfully prepared the dual phase TiO2 nanopowder as visible-light photocatalyst using flat-flame chemical vapor condensation method. First, we found that the type of buffer gas has significant effect on the phase transformation. Due to higher specific heat of nitrogen than that of argon, nitrogen is more capable of maintaining particles at high temperature, and to promote the rutile formation. We also realized that the dual phase formation by partial phase transformation from anatase to rutile is critical in the enhancement of photocatalytic reaction. Second, the increase of gap distance increases the heating time and collision time for the particles, thus increases the rutile content of the particles. Third, we managed to proceed our experiment by fixing the acetylene flow rate at either 600 sccm or 800 sccm, while vary the acetylene/oxygen flow ratio for 1:3, 1:4, 1:5, and 1:6, for the flame. We found that at low temperature and oxygen-deficient condition, the rutile formation is at the expense of visible-light photonic center, while at high temperature and oxygen-rich condition, the rutile formation does not interfere with its visible-light absorption. At high temperature and oxygen-rich condition, the rutile formation is promoted by thermal energy, and does not necessarily need the nucleation agent, such as visible-light photonic center. From the TEM observation, this powder consists of majorly fine anatase particles and some scattered large rutile particles. The nanopowder produced under this condition has the highest visible-light absorption capability as well as methylene blue photocatalytic decomposition reactivity. Finally, we concluded that the defect level in anatase formed by carbon doping and related effect is responsible for the visible-light absorption, and the dual phase is responsible for the reduction of the electron-hole recombination. With both carbon doping and dual-phase formation, the visible-light photocatalytic ability of our powder is greatly enhanced.

This report explores Club Cubano Inter-Americano’s history in order to show how it helped situate Cuban immigrants within the Anglo and Latino communities in New York City in the early 20th century, and it examines the ways in which immigrants balanced their island heritage with community building in the United States. The different parts of the report focus on the organization’s foundation, leadership, activities, events, and treatment of race. A historiography of similar social groups provides a necessary background of the overall structure and goals of Cuban mutual-aid societies. Although the question of race was never officially present in Club-related rhetoric, a number of similarities link its makeup and functions to an existing tradition of Afro-Cuban mutual-aid societies on the island and abroad. The analysis of the New York Club Cubano Inter-Americano provides a glimpse into a part of the Cuban migration in the United States that simply does not fit with the rest.
text