Thesis (Ph.D.)--Uniformed Services University of the Health Sciences, 2006 / Typescript (photocopy)

Current state-of-the-art plasma thrusters are limited in power density and thrust density by power losses to plasma-facing walls and electrodes. In the case of Hall effect thrusters, power deposition to the discharge channel walls and anode negatively impact the efficiency of the thruster and limit the attainable power density and thrust density. The current work aims to recreate thruster-relevant wall-interaction physics in a quiescent plasma and investigate them using electrostatic probes, in order to inform the development of the next generation of high-power-density / high-thrust-density propulsion devices. Thruster plasma-wall interactions are complicated by the occurrence of the plasma sheath, a thin boundary layer that forms between a plasma and its bounding wall where electrostatic forces dominate. Sheaths have been recognized since the seminal work of Langmuir in the early 1900’s, and the theory of sheaths has been greatly developed to the present day. The theories are scalable across a wide range of plasma parameters, but due to the difficulty of obtaining experimental measurements of plasma properties in the sheath region, there is little experimental data available to directly support the theoretical development. Sheaths are difficult to measure in situ in thrusters due to the small physical length scale of the sheath (order of micrometers in thruster plasmas) and the harsh plasma environment of the thruster. Any sufficiently small probe will melt, and available optical plasma diagnostics do not have the sensitivity and/or spatial resolution to resolve the sheath region. The goal of the current work is to experimentally characterize plasma sheaths xxvi in a low-density plasma that yields centimeter-thick sheath layers. By generating thick sheaths, spatially-resolved data can obtained using electrostatic probes. The investigation focuses on the effects of electron emission from the wall and several factors that influence it, including wall material, wall temperature, wall surface roughness and topology, as well as the scaling of sheaths from the low-density plasma environment towards thruster conditions. The effects of electron emission and wall material are found to agree with classical fluid and kinetic theory extended from literature. In conditions of very strong emission from the wall, evidence is found for a full transition in sheath polarities rather than a non-monotonic structure. Wall temperature is observed to have no effect on the sheath over boron nitride walls independent of outgassing on initial heat-up, for sub-thermionic temperatures. Wall roughness is observed to postpone the effects of electron emission to higher plasma temperatures, indicating that the rough wall impairs the wall’s overall capacity to emit electrons. Reductions in electron yield are not inconsistent with a diffuse-emission geometric trapping model. Collectively, the experimental data provide an improved grounding for thruster modeling and design.Current state-of-the-art plasma thrusters are limited in power density and thrust density by power losses to plasma-facing walls and electrodes. In the case of Hall effect thrusters, power deposition to the discharge channel walls and anode negatively impact the efficiency of the thruster and limit the attainable power density and thrust density. The current work aims to recreate thruster-relevant wall-interaction physics in a quiescent plasma and investigate them using electrostatic probes, in order to inform the development of the next generation of high-power-density / high-thrust-density propulsion devices. Thruster plasma-wall interactions are complicated by the occurrence of the plasma sheath, a thin boundary layer that forms between a plasma and its bounding wall where electrostatic forces dominate. Sheaths have been recognized since the seminal work of Langmuir in the early 1900’s, and the theory of sheaths has been greatly developed to the present day. The theories are scalable across a wide range of plasma parameters, but due to the difficulty of obtaining experimental measurements of plasma properties in the sheath region, there is little experimental data available to directly support the theoretical development. Sheaths are difficult to measure in situ in thrusters due to the small physical length scale of the sheath (order of micrometers in thruster plasmas) and the harsh plasma environment of the thruster. Any sufficiently small probe will melt, and available optical plasma diagnostics do not have the sensitivity and/or spatial resolution to resolve the sheath region. The goal of the current work is to experimentally characterize plasma sheaths xxvi in a low-density plasma that yields centimeter-thick sheath layers. By generating thick sheaths, spatially-resolved data can obtained using electrostatic probes. The investigation focuses on the effects of electron emission from the wall and several factors that influence it, including wall material, wall temperature, wall surface roughness and topology, as well as the scaling of sheaths from the low-density plasma environment towards thruster conditions. The effects of electron emission and wall material are found to agree with classical fluid and kinetic theory extended from literature. In conditions of very strong emission from the wall, evidence is found for a full transition in sheath polarities rather than a non-monotonic structure. Wall temperature is observed to have no effect on the sheath over boron nitride walls independent of outgassing on initial heat-up, for sub-thermionic temperatures. Wall roughness is observed to postpone the effects of electron emission to higher plasma temperatures, indicating that the rough wall impairs the wall’s overall capacity to emit electrons. Reductions in electron yield are not inconsistent with a diffuse-emission geometric trapping model. Collectively, the experimental data provide an improved grounding for thruster modeling and design.

The 'high-pressure' atmospheric (TIG) arc plasma is studied by means of a multi-Langmuir probe system. In order to determine the appropriate regime of operation, definitions of the plasma parameters for the description of the argon arc are considered and evaluations are presented. A description of the probe basic techniques is followed by an in-depth discussion of the different regimes of probe operation. The emphasis is put on atmospheric and flowing (arc) regimes. Probe sheath theories are compared and “Nonidealities” like cooling due to plasma-probe motion and probe emission mechanisms are then described. The extensive literature review reveals that the existing probe theories are inappropriate for a use in the TIG arc, because of ‘high’ pressure (atmospheric), broad range of ionization across the arc, flowing conditions, and ultimately, to the uncertainty about onset of Local Thermodynamical Equilibrium. The Langmuir probe system is built to operate in floating and biased conditions. The present work represents the first extensive investigation of electrostatic probes in arcs where the experimental difficulties and the primary observed quantities are presented in great detail. Analysis methodologies are introduced and experimental results are presented towards a unified picture of the resulting arc structure by comparison with data from emission spectroscopy. Results from different measurements are presented and comparison is made with data on TIG arcs present in literature. Probe obtained temperatures are lower than the values obtained from emission spectroscopy and this ‘cooling’ is attributed to electron-ion recombination. However, it is believed that probes can access temperatures regions not attainable by emission spectroscopy. Only axial electric potential and electric field are obtained because of the equipotential-probe requirement. Estimations of the sheath voltage and extension are obtained and a qualitative picture of the ion and electron current densities within the arc is given.

Por meio deste estudo objetivou-se avaliar a viabilidade de um novo acesso artroscópico para o recesso palmar da articulação interfalângica distal em eqüinos pela bainha sinovial comum aos tendões flexores digitais, com as finalidades de proporcionar segurança e eficiência durante a artrocentese, permitir visualização efetiva das estruturas anatômicas, além de criar condições para manipulação de instrumentos artroscópicos. Foram utilizadas 20 peças anatômicas, correspondentes aos membros torácicos de 10 eqüinos. Os conjuntos de um a cinco formaram o Grupo I, cujo o acesso cirúrgico foi medial, e os conjuntos seis a 10 formaram o Grupo II, onde o acesso cirúrgico foi lateral. Posteriormente, avaliou-se o procedimento em animais de experimentação com a aplicação da técnica artroscópica proposta em seis articulações interfalângicas distais dos membros torácicos de três eqüinos (GIII), sem enfermidade previamente diagnosticada através de exames físicos e radiográficos. Os procedimentos no Grupo III foram efetuados sob anestesia geral, em decúbito lateral, e todos animais foram observados durante seis semanas. Neste período, além da avaliação dos parâmetros físicos, foram efetuados controles radiográficos contrastados, visando a avaliar a recuperação e o tempo necessário para oclusão da membrana divisória entre a bainha digital e o interior da articulação interfalângica distal. A técnica proposta alcançou os objetivos propostos, oferecendo nova alternativa para o acesso ao recesso palmar da articulação interfalângica distal nos eqüinos / This study was carried out in order to evaluate the viability of a new arthroscopic approach of the palmar recess of the the interphalangeal joint in horses through the synovial sheath that involves the digital flexor tendon. The purposes of the study were to provide safety and efficiency during arthrocentesis, to allow effective visualization of the anatomical structures and provide means for the manipulation of arthroscopic instruments. Initially, 20 anatomic parts corresponding to the forelimbs of 10 horses were used. Sets numbers 1 through 5 formed Group I in wich a medial surgical approach was performed. Sets numbers 6 through 10 formed Group II, in which there was a lateral surgical approach. Later, the procedure in experimental animals was analyzed. This analysis was done using the proposed arthroscopic technique in 6 distal interphalangeal joints of the forelimbs of three horses (GIII). There was no previously disease diagnosed through physical and radiographic exams. The procedures in Group III were done under put general anesthesia in the lateral recumbence position and all the animals were under observation during six weeks. In the post-operative period a physical and contrasted radiographic exams were done to evaluate the recovery as well as the necessary healing time of the membrane between the digital sheath and distal interphalangeal joint. The technique responded positively to its objectives offering a new alternative to the approach of the palmar recess in the distal interphalangical joint in horses

Made available in DSpace on 2014-06-11T19:27:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-03-12Bitstream added on 2014-06-13T19:56:10Z : No. of bitstreams: 1 berlingieri_ma_me_jabo.pdf: 1229129 bytes, checksum: 914f852c063ecbfa177b5697c287aeef (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Nesta pesquisa foram investigados aspectos anatômicos e biométricos da face flexora dos dígitos de 20 novilhas mestiças da raça Nelore, com idades entre 24 e 36 meses, criadas em sistema extensivo. O material foi proveniente de matadouro sob Fiscalização do Serviço de Inspeção Oficial e mantido sob congelamento a -18°C até o momento da dissecação. Após tricotomia e limpeza das regiões distais ao metacarpo e metatarso, as faces palmar e plantar dos dígitos foram dissecadas in natura e as estruturas anatômicas identificadas e medidas com auxílio de paquímetro universal. As mensurações foram feitas em milímetros (mm) e incluíram o comprimento, a largura e a espessura das estruturas anatômicas digitais. A técnica de dissecação in natura foi considerada útil para a execução deste estudo e as estruturas identificadas e mensuradas incluíram os ligamentos acessórios distais dos paradígitos, ligamentos anulares palmares e plantares, bainha digital tendínea, ligamentos anulares proximais e distais, ligamentos interdigitais distais, tendões flexores digitais superficiais e profundos e a manica flexoria. Os dados biométricos obtidos indicam diferenças (p≤0,05) entre membros, antímeros e dígitos, especialmente nas estruturas anatômicas localizadas distalmente. Devido à escassez de estudos biométricos sobre o assunto, os achados deste trabalho podem servir como valores de referência para a faixa etária de novilhas avaliadas e contribuir em pesquisas morfológicas futuras / In the present work anatomic and biometric studies of the distal aspect in the flexor aspect of digits were carried out for 20 cross-breed heifer of Nelore breed aging around 24-36 months raised in an extensive regiment. The materials came from shamble under the Official Fiscalization of Inspect Service and were kept under freezing at -18°C until dissection. After the clipper and cleaning the distal areas, from metacarpus to metatarsus, the structures were dissected and measured by using a universal caliper rule (mm) on length (proximal-distal), widht (abaxial-axial) and thickness (dorso-palmar or dorso-plantar). The dissected structures included the paradigits distal accessories ligaments, palmar and plantar annular ligaments and tendon digital sheath, proximal and distal annular ligaments, interdigital distal ligament, superficial digital flexor tendon and deep digital flexor tendon and manica flexoria. The measured data indicate differences (p≤0,05) among the limb, right, left and respective digits mainly in the more distal analyzed structures. Due to scarcity of biometric studies about this topic, the data found in this work might be useful as a reference for the analyzed group, as well in the anatomic detailed structures which are essential to understanding many of the pathological process of locomotor apparatus in cattle

A síndrome Kranz é um conjunto de características anatômicas, ultra-estruturais e bioquímicas que culminam na realização da fotossíntese C4. Tal síndrome apresenta grande diversidade dentre as Angiospermas, tornando-se conveniente seu estudo em todos os níveis acima citados para a completa caracterização da mesma. No presente trabalho foi investigada a síndrome Kranz de Gomphrena arborescens e G. scapigera (Amaranthaceae) com ênfase na origem ontogenética da bainha Kranz, na descrição ultra-estrutural e na confirmação bioquímica sobre o tipo de fotossíntese C4. O desenvolvimento foliar dessas espécies indica que a bainha Kranz é originada da camada mais interna do mesofilo, a endoderme foliar. Uma discussão sobre os termos presentes na literatura para a descrição dessa bainha, todos eles focados em sua função na fotossíntese C4, demonstra a importância de se utilizar termos que informem a origem ontogenética dessa bainha, como endoderme e periciclo. Na análise ultra-estrutural, foram identificados possíveis fatores que interferem na fotossíntese de ambas as espécies, como o espessamento e a composição da parede da bainha Kranz, o posicionamento centrípeto dos cloroplastos e a presença de retículo periférico nos mesmos. Embora a análise bioquímica tenha resultado em informações ainda não conclusivas, o dimorfismo dos cloroplastos sugere a realização da fotossíntese C4 do tipo NADP-ME. O presente trabalho, de uma forma geral, contribui ao conhecimento da síndrome Kranz dentre as Amaranthaceae s.s., um grupo em que a ultra-estrutura e a bioquímica ainda são pouco conhecidas, e ressalta a importância dos estudos anatômicos, principalmente com enfoque ontogenético, para o melhor conhecimento da diversidade da síndrome Kranz dentre as Angiospermas. / The Kranz syndrome is a set of anatomical, ultrastructural and biochemical features that culminate in the C4 photosynthesis. This syndrome has a huge diversity among Angiosperms, so it became suitable to survey all the levels above cited for its complete characterization. In the present work the Kranz syndrome of Gomphrena arborescens and G. scapigera (Amaranthaceae) is studied, with emphasis on the ontogenetic origin of the Kranz sheath, on the ultrastructural description, and on the biochemical confirmation about the C4 photosynthesis kind. The foliar development of these species shows that the Kranz sheath is originated from the inner layer of the mesophyll, the foliar endodermis. A discussion about the literature terms used to describe the Kranz sheath, all of them referring to the function of this layer in C4 photosynthesis, demonstrates the importance of using terms that inform the ontogenetic origin of this layer, such as endodermis and perycicle. The ultrastructural analysis identified possible factors that interfere on the C4 photosynthesis of both species, such as wall thickening and composition of Kranz sheath cells, the centripetal position of chloroplasts and the peripheral reticulum in chloroplasts. Although biochemical analysis has resulted in no conclusive information, the chloroplast dimorphism suggests the NADP-ME C4 photosynthesis. This work, in a general way, contributes to the knowledge of the Kranz syndrome among Amaranthaceae s.s., a group that has the ultrastructure and the biochemistry of C4 photosynthesis poorly known. It also draws attention to the importance of anatomical surveys concerning the ontogenetic origin of Kranz sheath for a better understanding on the diversity of Kranz syndrome among Angiosperms.

<div>The proliferation of single-use plastics in the foodware and packaging sector has stimulated interest in sustainable material substitutes that can be processed efficiently and which possess sufficient structural integrity. Herein, we study the structure, mechanical response and diffusion properties of leaf-sheath from a representative palm species—<i>Areca catechu</i>—widely cultivated in the Indian sub-continent and Southeast Asia. The study of this material system, and the specific attributes, are motivated by the use of this material in foodware applications. Foodware such as plates and bowls can be produced from the areca sheath, directly, in a single step, by stretch forming analogous to sheet metals. The material is eco-friendly, biodegrading in ~100 days. Formability and water diffusion are two key attributes of relevance for foodware, since the former attribute determines the shape change capability of the material and range of producible shapes; and the latter, foodware product (structural) integrity and life.<br></div><div><br></div><div>We characterize the morphology (external structure) and anatomy (internal structure) of the sheath using imaging techniques and composition analysis. The sheath is shown to resemble a composite material, with structural characteristics intermediate between those of the palm leaf and stem. By measuring the mechanical response of the sheath to various types of 1D and 2D loading (e.g., uniaxial tension and compression, biaxial stretching, rolling), and hydration conditions, we show that the sheath material has high stretch-formability, especially when hydrated. This formability is similar to that of the most ductile sheet metals. The formability is shown to be further enhanced by addition of small quantities of NaOH (~5%) during hydration. Local deformation measurements in biaxial stretching, based on analysis of distortion of grid-markers inscribed onto sheath samples, have enabled characterization of strain-field anisotropy and mode of failure in the sheath. By consolidating the mechanical test results, we present a forming limit diagram for the leaf-sheath.<br></div><div><br></div><div>The structural integrity and life of foodware products produced from the leaf-sheath are directly determined by diffusion of liquids (e.g., water, oils) through the sheath wall thickness. Water and oils are important constituents of semi-solid and solid foods. Diffusion of water is also important for designing the hydration cycle to enhance formability. The diffusion of water through the sheath material process is studied using mass gain measurements and<i> in situ</i> imaging of water transport.<br></div><div><br></div><div>We determine the diffusion coefficient for water, which is critical for estimating product life. The diffusion coefficient for the matrix is shown to be one order of magnitude greater than for the fiber. We vary salt concentration in the water by controlled additions of NaCl and note a non-monotonic dependence of the diffusion on concentration. By subjecting the leaf-sheath to a short-time (~ 3 minutes) thermal treatment (~ 80⁰C), a hydrophobic wax layer can be made to secrete onto the leaf surface. This wax coating is found to significantly reduce the water diffusion, enabling the sheath foodware life to be increased. <br></div><div><br></div><div>Lastly, we argue, that since the leaf-sheath is a “waste product” of the palm, it has negligible embodied energy (4 to 5 orders of magnitude smaller) compared to paper and plastics based foodware.<br></div><div><br></div><div>We discuss the implications of the results for single-step forming of high-aspect ratio products and structures from the palm sheath, methods to reduce diffusion of liquids and improve foodware product life, and some directions for future research into mechanical behavior of plant leaf materials from a forming perspective.<br></div>

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No description available.

Induktiefgekoppelde-plasmareaktore (IGP’s) het toepassings in verskeie industrieë, insluitend die voorbereiding van metaalpoeiers vir laagvervaardiging. Die skermgas (ook skutgas gnoem) speel ’n belangrike rol in die termiese afskerming van die reaktorwand in ’n IGP. Die energie wat verloor word deur die wand van die reaktor kan verminder word deur die hittesone weg van die wand af te beweeg. Hierdie verplasing van die hittesone word bereik deur ’n skermgas te gebruik wat moeiliker ioniseer as die plasmagas. Die ioniseringsgraad van waterstof is laer as dié van argon weens die hoër elektriese geleidingsvermoë van argon by soortgelyke temperature. Waterstof word dus in klein hoeveelhede in die skutgas gebruik met argon as die hoof bestandeel en hoofplasmagas. Die waterstof voorkom dus plasmavorming naby die wand. Die skutgas het ook ’n heelwat hoër vloeisnelheid en verminder sodoende die beskikbare tyd vir hitte-oordrag na die wand. Die besondere hoë temperature wat in ’n IGP bereik word, belemmer egter die meting van eenvoudige lesings soos vloeisnelheid en temperatuur. Rekenaarmodelle voorsien ons van die geleentheid om die fisiese en chemiese eienskappe van ’n plasma te ondersoek asook die nodige gereedskap om die gedrag van die plasma te analiseer sonder eksperimentele lesings. Daar is verskeie numeriese modelle van IGP-sisteme in die literatuur alhoewel nie een van dié modelle die effek van die skutgassamestelling in ag neem nie. Die hoeveelheid waterstof in die skutgas kan groot newe-effekte hê op die plasmagas a.g.v. die hoër ionisasiepotensiaal van waterstof. ’n Oormaat waterstof in die skutgas is ook ’n verkwisting van voermateriaal. Albei die faktore het ’n invloed op die ekonomiese uitvoerbaarheid van die plasmaproses. Hierdie navorsing het beoog om die optimale skutgassamestelling te vind vir die reaktor wat by Necsa gebruik word vir sferoïedisering. Die werk is uitgevoer met die kommersiële eindige-elementsagtewarepakket COMSOL Multiphysics R. Hierdie rekenaarmodel dui daarop dat die wand beskerm kan word van plasmavorming met ’n waterstof/argon skutgas wat sodoende ook die energieverliese deur die wand verminder. Waterstof verbeter die skutgas se hitte-oordragvermoë, maar verskuif die hittesone weg van die wand af. As gevolg van hierdie twee kompeterende meganismes bestaan daar ’n optimale bedrywingspunt by 3 vol% H2 in die skutgas. Die model is bevestig deur die energiebalans van die model te vergelyk met eksperimentele resultate. / Dissertation (MEng)--University of Pretoria, 2020. / Advanced Metals Initiative Suid Afrikaanse Akademie vir Wetenskap en Kuns / Chemical Engineering / MEng / Unrestricted