Дисертації з теми "Metallic channel"
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Görtan, Mehmet Okan [Verfasser], Peter [Akademischer Betreuer] Groche, and Clemens [Akademischer Betreuer] Müller. "Severe plastic deformation of metallic materials by equal channel angular swaging: Theory, experiment and numerical simulation / Mehmet Okan Görtan. Betreuer: Peter Groche ; Clemens Müller." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2014. http://d-nb.info/1110902077/34.
Повний текст джерелаTuran, Cabir. "Investigations on the Effect of Manufacturing on the Contact Resistance Behavior of Metallic Bipolar Plates for Polymer Electrolyte Membrane Fuel Cells." VCU Scholars Compass, 2011. http://scholarscompass.vcu.edu/etd/2629.
Повний текст джерелаSteenberge, Nele van. "Study of structural changes in Zr-based bulk metallic glasses upon annealing and deformation treatments." Doctoral thesis, Universitat Autònoma de Barcelona, 2008. http://hdl.handle.net/10803/3420.
Повний текст джерелаSin embargo, los primeros sistemas amorfos fueron obtenidos por técnicas de solidificación rápida, y requerían velocidades de enfriamiento criticas de hasta 106 K s−1. Por consiguiente, se obtenían cintas finas con un espesor limitado hasta unas decenas de micrómetro. Unos treinta a cuarenta años más tarde, una gama de aleaciones multicomponentes, las cuales requiren velocidades de enfríamiento más lentas, fueron desarrolladas, lo cual significó el nacimiento de los vidrios metálicos macizos. Entre estas aleaciones multicomponentes, las que son a base de Zr han sido protagonistas por su capacidad extraordinaria de formar vidrios. Por el mismo, se hicieron como aleaciones modelo para el estudio de propiedades fúndamentales y comportamientos característicos.
Su límite de fluencia excepcionalmente alto, cerca del límite teórico, les proporciona a los vidrios metálicos macizos un potencial para ser utilizados en aplicaciones estructurales. Desafortunadamente, la deformación plástica a temperatura ambiente occure de una manera muy localizada en bandas de cizalladura. En vez de endurecimiento mécanico, los vidrios metálicos sufren un ablandamiento al deformarlos lo cual impide una deformación plástica estable. Así que, a pesar de su límite de fluencia alto, la ruptura occurirá después de una deformación macroscópica limitada. Este mecanismo de deformación inhomogénea a temperatura ambiente limita la fiabilidad de los vídrios metálicos macizos en aplicaciones estructurales. Lógicamente, la mejora de la plasticidad de estos materiales ha sido ampliamente estudiada durante la última década.
El concepto más explorado para evitar la ruptura catastrófica ha sido probablemente el desarollo de una microestructura heterogenea con una segunda fase. Ésta segunda fase puede tener dimensiones tanto a escala micrómetra como la escala nanométrica y puede ser tanto una fase cristalina como una fase amorfa. Varias rutas han sido probadas para obtener ésta segunda fase en la matriz amorfa: añadir directamente una fase reforzante al material fundido, diseñar una composición adecuada que resulta en un material compuesto al solidificarla o precipitar la segunda fase durante un tratamiento térmico después de colar.
Por tratamientos térmicos por debajo de la temperatura de transición vidria, cambios del orden topológico y químico a corto alcance han sido observado en la literatura. El primer efecto suele deteriorar la plasticidad por relajación de la estructura amorfa. La influencia del cambio de orden químico a corto alcanze se ha estudiado en muy poco detalle. Aparte de los tratamientos térmicos, los tratamientos mecánicos pueden inducir cambios estructurales y microestructurales. El estudio del efecto de estos dos tratamientos forma la parte parte de esta tesis.
Los cambios en el orden topólogico y químico de corto alcance de vídrios metálicos a base de Zr, inducidos por tratamientos térmicos y mecánicos, han sido caracterizados por técnicas de calorimetría, difracción de rayos-X y por microscópia electrónica. Luego, la influencia de estos mismos en el comportamiento mecánico de los vídrios se ha estudiado por tests de compresión y de nanoindentación.
Sin embargo, en la primera parte de ésta tesis, se demuestra que al aplicar la técnica de nanoindentación, se debería tomar en cuenta la existencia de un "size-effect", correlacionado directamente con los cambios estructurales que occuren durante la deformación. Este "size-effect" implica que la dureza y el módulo elástico bajan al aumentar la profundidad de la indentación, similar a lo que se observa normalmente para materiales cristalinos. Durante la deformación, aumenta el volumen libre del vídrio metálico. Este crecimiento del volumen libre influirá en la respuesta del material a la nanoindentación. En particular, se observa un ablandamiento dinámico cuando se aplican cargas elevadas al material. Además, concentraciones más altas de volumen libre en el estado inicial después del colado, ocasionan un ablandamiento mayor y por consecuencia, aumentan el "size-effect".
Después, se hizo un estudio sistemático de los cambios de corto y medio alcance, inducido por tratamientos térmicos, en particular por tratamientos a baja temperatura. Aplicando varias técnicas de caracterización, como por ejemplo la calorimetría, difracción de rayos X y microscopía electrónica, cambios importantes de orden quimico han sido observados. Ya durante tratamientos cortos a baja temperatura, se formaban clústers de Cu en una matriz con un contenido de Cu reducido. Más adelante, el estudio se enfocó en la influencia de los cambios microestructurales en las propiedades mecánicas. Aunque los cambios observados eran moderados, su influencia en el comportamiento mecánico, y en particular en la plasticidad en compresión, es enorme cuando los cambios topológicos son todavía moderados (como es el caso durante el tratamiento térmico a baja temperatura). La plasticidad aumenta significativamente, lo que va en contra a la fragilización que suele ocurrir durante los tratamientos térmicos. Durante tratamientos a temperaturas más elevadas, los cambios topológicos empiezan a dominar (disminución del volumen libre) y forman un contrapeso para el efecto positivo de los cambios del orden químico a corto alcance. Posteriormente, se investigó en más detalle la influencia de los cambios de orden químico en la cristalización. Los clústeres de Cu que se forman durante el calentamiento se puede interpretar como fases embrionarias en el proceso de cristalización.
Durante los tratamientos térmicos, se dan tanto cambios de orden topológico como de orden químico, pero tienen un efecto contradictorio en la plasticidad por lo cual puede ser difícil controlarlos. Sin embargo, los cambios beneficiosos de orden químico se pueden obtener por tratamientos mecánicos de deformación severa, por ejemplo por torsión a alta presión (TAP). La deformación no causa una reducción del volumen libre sino la aumenta incluso más. Además, TAP produce una muestra maciza bastante homogenea siempre y cuando el número de revueltas sea menor, lo que es lo contrario de lo que se sabe para materiales cristalinos. Estos materiales suelen requerir más vueltas para evitar una microestructura heterogenea.
Metallic glasses have been the subject of widespread research since the 1950's with significant progress in the understanding in their behavior. As the name suggests, they are amorphous metallic alloys, i.e. with the absence of long-range order. The absence of this long-range order offers them unique physical, chemical and mechanical properties compared to conventional metallic materials.
However, the early amorphous systems were obtained typically by rapid quenching techniques, with critical cooling rates up to 106 K s−1, resulting typically in ribbons or thin foils with a thickness limited to a few tens of micrometer. About thirty to forty years later, a large range of multicomponent alloys was developed which required significant lower critical cooling rates leading to the birth of so-called bulk metallic glass (BMG). Among these multicomponent systems, Zr-based alloys have been key players with outstanding glass forming ability, which has made them to model alloys for the study of fundamental properties and characteristic behaviors.
The exceptionally high yield strength, close to the theoretical limit, and yield strain of these amorphous metallic systems in bulk offer them potential for structural applications. However, plastic deformation at room temperature occurs in a highly localized manner by the formation of a few shear bands. Instead of work hardening, metallic glasses soften upon deformation, which prevents stable plastic elongation. Although BMGs possess a high fracture strength, once yielding has set in, early failure after a small percentage of macroscopic deformation appears. This inhomogeneous deformation mechanism at ambient temperature still limits the reliability of BMGs for structural applications. Logically, the enhancement of ductility of this type of materials has been the subject of many research works in the last decade.
Probably the most explored concept to avoid catastrophic failure has been the development of a heterogeneous microstructure, with a second phase on different length scales, both crystalline and amorphous. Various routes have been tried out to obtain this second phase in the amorphous matrix: physically adding a reinforcing phase to the melt, by direct precipitation from the melt of a properly designed composition or by (partial) nano-crystallization of the glass after casting.
Upon annealing below the glass transition, changes in both topological and chemical short range order have been reported. The former is believed to deteriorate plasticity due to structural relaxation of the amorphous structure.
The effect of changes of the chemical short range order on plasticity has hardly been studied into detail. Besides annealing, deformation has been reported to induce structural and microstructural changes. These (micro-)structural changes, induced by annealing and deformation, form the main topic of the work presented in this thesis.
Topological and chemical changes in the short range order of Zr-based bulk metallic glasses upon annealing and deformation treatments have been characterized by calorimetry, X-ray diffraction and electron microscopy. The influence of these changes on the mechanical behavior of these glasses was investigated through compression tests and nanoindentation tests.
However, in a first part of this thesis, it is shown that one should be aware when applying this technique of the existence of a so-called size-effect, directly linked with the structural changes upon deformation.
A decrease of hardness and elastic modulus on the maximum penetration depth was found, similar as what is typically observed for crystalline materials. Upon deformation, free volume typically increases. Due to this increase, free volume will influence the response of the material during nanoindentation testing. In particular, a dynamic softening is observed when being plastically deformed at higher loads. Larger free volume concentrations in the as-cast state result in enhanced mechanical softening and, concomitantly, more pronounced indentation size effects.
Afterwards, a systematic study on changes on the short and medium range order upon annealing was performed, in particular at low temperatures. By means of various characterization techniques, like by calorimetry, X-ray diffraction and electron microscopy, important changes in chemical ordering were found, with the formation of Cu-clusters in a more Cu-depleted matrix, already upon low temperature annealing for a short time. In a next step, the study focussed on the influence of this altered microstructures on the mechanical properties. Although the (compositional) changes observed were moderate, their influence on the mechanical behavior, and in particular plasticity under compression, is great, when the topological changes are still moderate (low temperature annealing). Plasticity is enhanced greatly, in large contrast to the generally assumed embrittlement upon annealing. A too large increase in topological short range order (free volume decrease) counterbalances the effect induced by the chemical short range order upon high temperature annealing. Finally, the influence of these changes of chemical short-range order on the crystallization behaviour was studied in more detail. The formation of the Cu-rich clusters upon annealing can thus be understood as a very embryonic phase towards crystallization.
Upon annealing, topological (densification) and chemical ordering occur simultaneously, but these processes have a contradictory effect on plasticity and it might be difficult to control them. Therefore, it is interesting that the beneficial changes in chemical ordering can be achieved also upon high-deformation treatments, e.g. by high-pressure torsion (HPT). Deformation does not lead to the adverse reduction of free volume but even produces some more. HPT itself is able to produce a rather homogeneous bulky sample, in particular for a low amount of revolution - contrary to what is observed in crystalline materials, where more revolutions are necessary to overcome the undesired inhomogeneous microstructure.
Rossi, Paul J. [Verfasser], and Eric Jan [Akademischer Betreuer] Mittemeijer. "Microstructural changes and intermetallic compound formation in metallic bilayers / Paul J. Rossi ; Betreuer: Eric Jan Mittemeijer." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2016. http://d-nb.info/1124841342/34.
Повний текст джерелаKotze, Johannes Paulus. "Thermal energy storage in metallic phase change materials." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/96049.
Повний текст джерелаENGLISH ABSTRACT: Currently the reduction of the levelised cost of electricity (LCOE) is the main goal of concentrating solar power (CSP) research. Central to a cost reduction strategy proposed by the American Department of Energy is the use of advanced power cycles like supercritical steam Rankine cycles to increase the efficiency of the CSP plant. A supercritical steam cycle requires source temperatures in excess of 620°C, which is above the maximum storage temperature of the current two-tank molten nitrate salt storage, which stores thermal energy at 565°C. Metallic phase change materials (PCM) can store thermal energy at higher temperatures, and do not have the drawbacks of salt based PCMs. A thermal energy storage (TES) concept is developed that uses both metallic PCMs and liquid metal heat transfer fluids (HTF). The concept was proposed in two iterations, one where steam is generated directly from the PCM – direct steam generation (DSG), and another where a separate liquid metal/water heat exchanger is used – indirect steam generation, (ISG). Eutectic aluminium-silicon alloy (AlSi12) was selected as the ideal metallic PCM for research, and eutectic sodium-potassium alloy (NaK) as the most suitable heat transfer fluid. Thermal energy storage in PCMs results in moving boundary heat transfer problems, which has design implications. The heat transfer analysis of the heat transfer surfaces is significantly simplified if quasi-steady state heat transfer analysis can be assumed, and this is true if the Stefan condition is met. To validate the simplifying assumptions and to prove the concept, a prototype heat storage unit was built. During testing, it was shown that the simplifying assumptions are valid, and that the prototype worked, validating the concept. Unfortunately unexpected corrosion issues limited the experimental work, but highlighted an important aspect of metallic PCM TES. Liquid aluminium based alloys are highly corrosive to most materials and this is a topic for future investigation. To demonstrate the practicality of the concept and to come to terms with the control strategy of both proposed concepts, a storage unit was designed for a 100 MW power plant with 15 hours of thermal storage. Only AlSi12 was used in the design, limiting the power cycle to a subcritical power block. This demonstrated some practicalities about the concept and shed some light on control issues regarding the DSG concept. A techno-economic evaluation of metallic PCM storage concluded that metallic PCMs can be used in conjunction with liquid metal heat transfer fluids to achieve high temperature storage and it should be economically viable if the corrosion issues of aluminium alloys can be resolved. The use of advanced power cycles, metallic PCM storage and liquid metal heat transfer is only merited if significant reduction in LCOE in the whole plant is achieved and only forms part of the solution. Cascading of multiple PCMs across a range of temperatures is required to minimize entropy generation. Two-tank molten salt storage can also be used in conjunction with cascaded metallic PCM storage to minimize cost, but this also needs further investigation.
AFRIKAANSE OPSOMMING: Tans is die minimering van die gemiddelde leeftydkoste van elektrisiteit (GLVE) die hoofdoel van gekonsentreerde son-energie navorsing. In die kosteverminderingsplan wat voorgestel is deur die Amerikaanse Departement van Energie, word die gebruik van gevorderde kragsiklusse aanbeveel. 'n Superkritiese stoom-siklus vereis bron temperature hoër as 620 °C, wat bo die 565 °C maksimum stoor temperatuur van die huidige twee-tenk gesmelte nitraatsout termiese energiestoor (TES) is. Metaal fase veranderingsmateriale (FVMe) kan termiese energie stoor by hoër temperature, en het nie die nadele van soutgebaseerde FVMe nie. ʼn TES konsep word ontwikkel wat gebruik maak van metaal FVM en vloeibare metaal warmteoordrag vloeistof. Die konsep is voorgestel in twee iterasies; een waar stoom direk gegenereer word uit die FVM (direkte stoomopwekking (DSO)), en 'n ander waar 'n afsonderlike vloeibare metaal/water warmteruiler gebruik word (indirekte stoomopwekking (ISO)). Eutektiese aluminium-silikon allooi (AlSi12) is gekies as die mees geskikte metaal FVM vir navorsingsdoeleindes, en eutektiese natrium – kalium allooi (NaK) as die mees geskikte warmteoordrag vloeistof. Termiese energie stoor in FVMe lei tot bewegende grens warmteoordrag berekeninge, wat ontwerps-implikasies het. Die warmteoordrag ontleding van die warmteruilers word aansienlik vereenvoudig indien kwasi-bestendige toestand warmteoordrag ontledings gebruik kan word en dit is geldig indien daar aan die Stefan toestand voldoen word. Om vereenvoudigende aannames te bevestig en om die konsep te bewys is 'n prototipe warmte stoor eenheid gebou. Gedurende toetse is daar bewys dat die vereenvoudigende aannames geldig is, dat die prototipe werk en dien as ʼn bevestiging van die konsep. Ongelukkig het onverwagte korrosie die eksperimentele werk kortgeknip, maar dit het klem op 'n belangrike aspek van metaal FVM TES geplaas. Vloeibare aluminium allooie is hoogs korrosief en dit is 'n onderwerp vir toekomstige navorsing. Om die praktiese uitvoerbaarheid van die konsep te demonstreer en om die beheerstrategie van beide voorgestelde konsepte te bevestig is 'n stoor-eenheid ontwerp vir 'n 100 MW kragstasie met 15 uur van 'n TES. Slegs AlSi12 is gebruik in die ontwerp, wat die kragsiklus beperk het tot 'n subkritiese stoomsiklus. Dit het praktiese aspekte van die konsep onderteken, en beheerkwessies rakende die DSO konsep in die kollig geplaas. In 'n tegno-ekonomiese analise van metaal FVM TES word die gevolgtrekking gemaak dat metaal FVMe gebruik kan word in samewerking met 'n vloeibare metaal warmteoordrag vloeistof om hoë temperatuur stoor moontlik te maak en dat dit ekonomies lewensvatbaar is indien die korrosie kwessies van aluminium allooi opgelos kan word. Die gebruik van gevorderde kragsiklusse, metaal FVM stoor en vloeibare metaal warmteoordrag word net geregverdig indien beduidende vermindering in GLVE van die hele kragsentrale bereik is, en dit vorm slegs 'n deel van die oplossing. ʼn Kaskade van verskeie FVMe oor 'n reeks van temperature word vereis om entropie generasie te minimeer. Twee-tenk gesmelte soutstoor kan ook gebruik word in samewerking met kaskade metaal FVM stoor om koste te verminder, maar dit moet ook verder ondersoek word.
Bhardwaj, Abhinav. "Metallic Encapsulation for High Temperature (>500 °C) Thermal Energy Storage Applications." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5843.
Повний текст джерелаNechaev, Yury S. "Stimuli and mechanisms of diffusion mass-transport in the processes of structural-phase changes in metallic materials under high-rate deformation: Stimuli and mechanisms of diffusion mass-transport in the processesof structural-phase changes in metallic materials under high-rate deformation." Diffusion fundamentals 2 (2005) 52, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14385.
Повний текст джерелаPedotto, Cristina. "Using IR thermography to determine the heat flux removed by spray cooling a high-temperature metallic surface." Thesis, Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/1044.
Повний текст джерелаNechaev, Yury S. "Stimuli and mechanisms of diffusion mass-transport in the processes of structural-phase changes in metallic materials under high-rate deformation." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-196059.
Повний текст джерелаArvidsson, Sofia, Lena Fransson, and Carin Lundgren. "Communication of Values : A Qualitative Study at Stena Metall." Thesis, Jönköping University, JIBS, EMM (Entrepreneurship, Marketing, Management), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-12368.
Повний текст джерелаPurpose: The purpose of this thesis is to investigate Stena Metall’s values and how they are communicated within the organization.
Background: In the Fall of 2008, the world was shocked by the worst financial crisis in decades. The crisis had deep effects on the Swedish economy, and many companies suffered heavily. The recycling and environmental service company Stena Metall experienced their first negative result in 30 years, and 900 employees had to leave the company. An action program, including an altered culture was established with the purpose to adapt the operations to the new business environmental conditions. Values, which are a part of the organizational culture, were decided to be an important part of the change. To implement these in the entire organization a well-structured communication process is needed. Within these subjects; values and communication, a qualitative study at Stena Metall has been conducted.
Method: To fulfill the purpose, a qualitative method has been used. Thirteen interviews were conducted to collect data from different levels of the organization. The interviews were designed differently based on the employee’s level of responsibility in the organization. The theoretical framework used when analyzing the empirical material includes earlier research in the areas of culture, with emphasis on values, and communication.
Conclusion: Two set of values have been identified, core values and aspiration values. The findings indicate a gap in the communicational process at Stena Metall. Part of the new information communicated about Stena Metall´s values is lost on its way from the management to the lower levels in the organization. The perception of what the values mean, both core and aspiration values, differs depending on level in the organization.
Javed, Muhammad Tariq. "Mechanisms behind pH changes by plant roots and shoots caused by elevated concentration of toxic elements." Doctoral thesis, Stockholms universitet, Botaniska institutionen, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-64324.
Повний текст джерелаAt the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted. Paper 4: Manuscript.
Millach, Carrobé Laia. "Effect of environmental changes and metal stress on phototrophic microorganisms in extree environments. Development of new methodologies in high-resolution microscopy techniques." Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/457901.
Повний текст джерелаLos efectos del cambio climático inciden directamente en las poblaciones de microorganismos fototróficos de los tapices microbianos, produciendo alteraciones en otros parámetros ambientales como es el incremento de la temperatura, que puede provocar sequías y hasta la desertización de estos ecosistemas, así como otros efectos en la osmolaridad de las células, debido al aumento de la salinidad. Dichos microorganismos son muy abundantes en los tapices microbianos, principalmente las cianobacterias y las microalgas, que además de ser los principales estabilizadores de estos ecosistemas, a veces se encuentran expuestos a diferentes condiciones de estrés. La mayoría de los estudios, que se realizan para valorar los efectos que tienen sobre los microorganismos condiciones ambientales tan variables, utilizan cultivos axénicos que provienen de microorganismos aislados del ambiente natural o bien de colecciones de cultivos; nada más lejos de la realidad, ya que en los ambientes naturales los microorganismos fototróficos establecen asociaciones estables con microorganismos heterotróficos y, a veces, con otros fototróficos. Además, hay pocos estudios que analicen, en estas condiciones y a nivel individual, los efectos de los parámetros ambientales o de la contaminación por metales en estas asociaciones. La falta de metodologías que pueden aplicarse para averiguar estos efectos en un microorganismo en concreto, cuando está asociado con otro de manera selectiva, in vivo, de manera rápida y sin el uso de ningún tipo de tinción, es, por tanto, un reto a la hora de analizar las posibilidades que tienen estos microorganismos frente a cambios tan drásticos. En este trabajo, se ha intentado solucionar dicha problemática mediante la optimización de distintas técnicas que tienen como base el microscopio láser confocal, considerando la característica principal de las cianobacterias y las microalgas, que es la de emitir fluorescencia natural. La clorofila a es el pigmento mayoritario de estos microorganismos y se ha utilizado con anterioridad como bioindicador, especialmente en estudios realizados en metales por otros miembros del grupo. Asimismo, una problemática importante es valorar el papel que juegan estos microorganismos en la resistencia ante cambios repentinos de las condiciones naturales o antropogénicas. En este sentido, también se ha incrementado el interés por las denominadas células durmientes y en el estudio de células viables y no viables. Por este motivo, en este trabajo se ha puesto a punto una nueva metodología que utiliza el microscopio láser confocal y dos láseres específicos y que ha permitido determinar el porcentaje de estas células en muestras expuestas a diferentes condiciones de estrés. Los microscopios electrónicos de rastreo y transmisión, ambos acoplados a un detector de energía dispersiva de rayos X, junto con el microscopio de transmisión de rayos X del sincrotrón ALBA, se han aplicado en muestras expuestas a varios factores de estrés para evaluar los cambios morfológicos en células enteras y en secciones ultrafinas, así como para los estudios de captación de metales extra- e intracelularmente. Los objetivos de este trabajo se han centrado en la aplicación combinada de todas estas metodologías en dos consorcios de microorganismos: Scenedesmus sp. DE2009 y Geitlerinema sp. DE2011. El efecto de la luz y la salinidad (como parámetros ambientales), así como el impacto de metales como plomo, cobre y cromo (como contaminantes), se ha estudiado ampliamente en células individuales de ambos microorganismos. Finalmente, esta tesis está estructurada en distintos capítulos. El Capítulo 3 corresponde con los artículos publicados (uno de ellos en revisión); así pues, los resultados obtenidos de las investigaciones realizadas se exponen en las Secciones 3.1, 3.2 y 3.3 y se discuten globalmente en el Capítulo 4.
The effects of climate change directly affect the populations of phototrophic microorganisms in microbial mats, causing alterations in other environmental parameters such as the increase in temperature. This in turn causes drought and sometimes the desertification of these ecosystems, as well as affecting the osmolarity of cells due to the increase in salinity. The microorganisms referred to are highly abundant in microbial mats; principally, they are cyanobacteria and microalgae, which, apart from being the main stabilisers of these ecosystems, are exposed to distinct stress conditions at the same time. Most studies carried out to assess the impact on microorganisms of such variable environmental conditions use axenic cultures that come from microorganisms isolated from the natural environment or else from culture collections. Nothing could be further from reality, since—in natural environments—phototrophic microorganisms establish stable associations with heterotrophic bacteria and, at times, with other phototrophs. In addition, very few studies analyse (in these conditions and at individual level) the effects of environmental parameters or of metal pollution in these associations. The lack of methodologies that can be applied to ascertain these effects in a specific microorganism, when this is selectively associated with another, in vivo, swiftly and without using any type of staining, is therefore a challenge in analysing the possibilities of these microorganisms when facing such drastic changes. In the current work, an attempt has been made to solve this problem by means of the optimisation of distinct techniques, based on confocal laser microscopy and centring on the main characteristic of cyanobacteria and microalgae, which is the emission of natural fluorescence. Chlorophyll a is the majority pigment in these microorganisms and has previously been used as a bioindicator, in studies carried out with metals by other members of the group. Determining the role played by these microorganisms in the resistance to sudden changes in natural or anthropogenic conditions is a further, and important, issue. In addition, in this respect, the interest in dormant cells and in the study of viable and non-viable cells has increased. For this reason, a new methodology has been developed in this work; using a confocal laser microscope and two specific lasers, this has allowed us to ascertain the percentage of these cells in samples exposed to distinct stress conditions. The electronic scanning and transmission microscopes, both coupled to an X-ray dispersive energy detector, jointly with the X-ray transmission microscope from the ALBA synchrotron, have been used in samples prepared to evaluate morphological changes due to stress factors both in complete cells and in ultrafine sections, as well as in studies of extra- and intracellular metal extraction. The objectives of this work centre on the combined application of all these methodologies on two consortia of microorganisms: Scenedesmus sp. DE2009 and Geitlerinema sp. DE2011. The effect of light and salinity (as environmental parameters), in addition to the impact of lead, copper and chromium (as pollutants) was studied extensively in individual cells for both microorganisms. Finally, this thesis is organised into distinct chapters. The Chapter 3 correspond to the articles that have already been published (one of them currently under review); thus, the results obtained from the research carried out are therefore presented in Sections 3.1, 3.2 and 3.3 and are discussed globally in Chapter 4.
Biscéré, Tom. "Effets des métaux et des changements climatiques sur les coraux." Electronic Thesis or Diss., Sorbonne université, 2018. http://www.theses.fr/2018SORUS382.
Повний текст джерелаCoral reefs have largely degraded in recent decades under the influence of human activities. Among those disturbances, the increase in metal concentrations affects many reefs worldwide (e.g. Australian Great Barrier Reef, Costa Rica, Red Sea, New Caledonia). Furthermore, reefs have now to face climate change, and more particularly temperature increase and ocean acidification. In this context, the aims of my thesis were to (1) determine the effects of the main metals present in lateritic sediments (iron, manganese, nickel and cobalt) on coral physiology using concentrations representative of those measured along the New Caledonian coastline, and to (2) define their potential roles in this context of climate change. My results showed that metals affect coral metabolism in different ways. While at ambient temperature, a nickel or manganese enrichment stimulates host metabolism and symbiont photosynthesis, conversely a cobalt enrichment inhibits calcification and becomes even toxic for the host and symbionts, from 1 μg L-1. Despite its importance in photosynthetic processes, an iron enrichment induces a decrease in Symbiodinium densities and an inhibition of calcification rates. Under thermal stress, manganese enhances coral tolerance to temperature increase, likely by stimulating their antioxidant defenses, while nickel worsens its effects by decreasing even more their growth. These works represent an important step towards a better understanding of coral responses to metal enrichment and would explain, to some extent, species susceptibility to climate change
Grünker, Ronny, Irena Senkovska, Ralf Biedermann, Nicole Klein, Martin R. Lohe, Philipp Müller, and Stefan Kaskel. "A highly porous flexible Metal–Organic Framework with corundum topology." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-138599.
Повний текст джерелаDieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich
Grünker, Ronny, Irena Senkovska, Ralf Biedermann, Nicole Klein, Martin R. Lohe, Philipp Müller, and Stefan Kaskel. "A highly porous flexible Metal–Organic Framework with corundum topology." Royal Society of Chemistry, 2011. https://tud.qucosa.de/id/qucosa%3A27762.
Повний текст джерелаDieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
Bragaglia, Valeria. "Epitaxial Growth and Ultrafast Dynamics of GeSbTe Alloys and GeTe/Sb2Te3 Superlattices." Doctoral thesis, Humboldt-Universität zu Berlin, 2017. http://dx.doi.org/10.18452/18406.
Повний текст джерелаThe growth by molecular beam epitaxy of Ge-Sb-Te (GST) alloys resulting in quasi-single-crystalline films with ordered configuration of intrinsic vacancies is demonstrated. It is shown how a structural characterization based on transmission electron microscopy, X-ray diffraction and density functional theory, allowed to unequivocally assess the vacancy ordering in GST samples, which was so far only predicted. The understanding of the ordering process enabled the realization of a fine tuning of the ordering degree itself, which is linked to composition and crystalline phase. A phase diagram with the different growth windows for GST is obtained. High degree of vacancy ordering in GST is also obtained through annealing and via femtosecond-pulsed laser crystallization of amorphous material deposited on a crystalline substrate, which acts as a template for the crystallization. This finding is remarkable as it demonstrates that it is possible to create a crystalline GST with ordered vacancies by using different fabrication procedures. Growth and structural characterization of GeTe/Sb2Te3 superlattices is also obtained. Their structure resembles that of ordered GST, with exception of the Sb and Ge layers stacking sequence. The possibility to tune the degree of vacancy ordering in GST has been combined with a study of its transport properties. Employing global characterization methods such as XRD, Raman and Far-Infrared spectroscopy, the phase and ordering degree of the GST was assessed, and unequivocally demonstrated that vacancy ordering in GST drives the metal-insulator transition (MIT). In particular, first it is shown that by comparing electrical measurements to XRD, the transition from insulating to metallic behavior is obtained as soon as vacancies start to order. This phenomenon occurs within the cubic phase, when GST evolves from disordered to ordered. In the second part of the chapter, a combination of Far-Infrared and Raman spectroscopy is employed to investigate vibrational modes and the carrier behavior in amorphous and crystalline phases, enabling to extract activation energies for the electron conduction for both cubic and trigonal GST phases. Most important, a MIT is clearly identified to occur at the onset of the transition between the disordered and the ordered cubic phase, consistently with the electrical study. Finally, pump/probe schemes based on optical-pump/X-ray absorption and Terahertz (THz) spectroscopy-probes have been employed to access ultrafast dynamics necessary for the understanding of switching mechanisms. The sensitivity of THz-probe to conductivity in both GST and GeTe/Sb2Te3 superlattices showed that the non-thermal nature of switching in superlattices is related to interface effects, and can be triggered by employing up to one order less laser fluences if compared to GST. Such result agrees with literature, in which a crystal to crystal switching of superlattice based memory cells is expected to be more efficient than GST melting, therefore enabling ultra-low energy consumption.
Chen, Yu-Shuai, and 陳友帥. "Impact of Metallic Furniture on UWB Channel Statistical Characteristics." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/35843169324683821413.
Повний текст джерела淡江大學
電機工程學系碩士班
94
Radio wave is easily effected by obstacles in indoor environments. The obstacles are walls, ceilings, furniture in indoor environment. These obstacles will cause multiple reflection and diffraction of the radio waves and the phenomenon is called as multi-path effect. Due to this multi-path effect, the intersymbol inference (ISI) which increases the bit error rate and outage probability of the communication system occurred. As a result, the quality of communication becomes worse. The bit error rate (BER) performance for ultra-wide band (UWB) indoor communication with impact of metallic furniture is investigated. The impulse responses of different indoor environments for any transmitter and receiver location are computed by shooting and bouncing ray/image and inverse Fourier transform techniques. By using the impulse responses of these multipath channels, the BER performance for binary pulse amplitude modulation (BPAM) impulse radio UWB communication system are calculated. Numerical results have shown that the multi-path effect by the metallic cabinets is an important factor for BER performance. Also the outage probability for the UWB multi-path environment with metallic cabinets is more serious (about 18%) than with wooden cabinets. Finally, it is worth noting that in these cases the present work provides not only comparative information but also quantitative information on the performance reduction.
Görtan, Mehmet Okan. "Severe plastic deformation of metallic materials by equal channel angular swaging: Theory, experiment and numerical simulation." Phd thesis, 2014. https://tuprints.ulb.tu-darmstadt.de/4077/1/Dissertation_MehmetOkanG%C3%B6rtan.pdf.
Повний текст джерелаKashanianfard, Mani. "Electromagnetic Wave Transmission through Sub-wavelength Channels and Bends Using Metallic Wires." Thesis, 2009. http://hdl.handle.net/10012/4654.
Повний текст джерелаChen, Ting-Huei, and 陳亭卉. "The studies of flow channels on the metallic bipolar plate for the performance of PEMFC." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/75147569408052095672.
Повний текст джерела國立勤益科技大學
機械工程系
98
Nowadays, ultra fine channels and ribs cannot be formed on the commonly used graphite bipolar plates owing to low strength and brittleness of the graphite material. Therefore, this study used the stainless steel plate, SUS316L, with 1mm thick stainless, as the material of the bipolar plates, and these metallic bipolar plates are with reaction area of 20mm×20mm, height and depth of 0.8mm and ribs widths of 0.2mm, 0.4mm and 0.6mm respectively (open area rate of 85.36%, 70.24%, 58.19%,respectively). These formed metallic bipolar plates were assembled with MEA and subsequent cell performance experiments were performed to discussed the affections between the dimensions of the ribs and the channels and the performance of the proton exchange membrane fuel cell (PEMFC). The experimental results show that the metallic bipolar plate with ribs width of 0.4 mm has the optimum cell performance. The current density of the fuel cell with the metallic bipolar plate with rib width of 0.4 mm was 34.21% higher than the current density of the fuel cell with the metallic bipolar plate with rib width of 0.6mm while the voltage was 0.499V. Although, the metallic bipolar plate with 0.2mm rib width comprising the largest reaction area between fuel and MEA, the excessive open area rate reduced the effective electron transmitting, and increased internal resistance. Therefore, the performance of the metallic bipolar plate with 0.2 mm rib width is lower than the one with 0.4 mm rib width. On the other hand, the flow rate of the gas also affects the performance of the cells. When the flow rate of the gas was set at 60cc/min, better cell performances were found in all of the three cells with different rib and channel dimensions of the metallic bipolar plates. There were no significant performance differences between these three fuel cells when the flow rate of the gas was increased to 80cc/min because sufficient fuel was supplied for reaction when the flow rate was at 60cc/min. When the flow rate of the gas was set at 40cc/min, concentration polarization occurred in the fuel cells with bipolar plates with 0.6 and 0.4 mm ribs width owing to the short channel length with insufficient fuel flow. Better performance was found in the fuel cell with bipolar plate with 0.2mm rib width because of the longer length of the channel and the sufficient time for reaction.
Wang, Shung-ping, and 王祥賓. "Finite Element Analysis on Forming and Efficiency of Micro-Channels of Metallic Bipolar Plate for Fuel Cell." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/50866379950579641527.
Повний текст джерела國立臺灣科技大學
機械工程系
101
Bipolar plate is an important component of the fuel cell. Because there is no suitable fabrication process for mass-production of bipolar plate, the cost of portable fuel cell is still too high now a days. In this study, the rubber pad forming process was used to fabricate the micro-channels on metallic bipolar plate and the effect on process parameters of the rubber pad forming were analyzed. Polyurethane rubbers were used for the rubber pads, and SUS316L stainless steel sheets with a thickness of 0.1mm were tested in the experiment. Firstly, finite element analysis (FE, Ansys CFX software) was used to analyze the efficiency of fuel cell by geometric factor of channels numerically, in order to figure out the influence of velocity and pressure on channel depth, channel width, rib width. Secondly, finite element analysis (FE, Abaqus / Standard software) was also used to analyze the rubber pad forming process numerically. Finally, the experimental and numerical results showed a good agreement in this study. Furthermore, an optimization design of micro-channels for fuel cell was developed under rubber pad forming process.
Soltani, Fatemeh. "Growth of metallic nanowires by chemical etching and the use of microfluidics channels to produce quantum point contacts." Thesis, 2010. http://hdl.handle.net/1828/2387.
Повний текст джерелаZhang, Yong, Irene Mei Ling Lee, Hao Tan, Qin Jing, and Yi Li. "Effect of Microstructure Changes on Mechanical Properties of La₆₆Al₁₄(Cu, Ni)₂₀ Amorphous and Crystalline Alloys." 2003. http://hdl.handle.net/1721.1/3824.
Повний текст джерелаSingapore-MIT Alliance (SMA)
Müller, Georg Alexander. "Ion-beam induced changes of magnetic and structural properties in thin Fe films." Doctoral thesis, 2004. http://hdl.handle.net/11858/00-1735-0000-0006-B4EE-3.
Повний текст джерелаSevastopolev, Ruslan. "Effect of conformal cooling in Additive Manufactured inserts on properties of high pressure die cast aluminum component." Thesis, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-50949.
Повний текст джерела