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Liu, Xiaohua. "Spin Excitations in BCC, FCC, HCP Cobalt and BCC Fe1-xCox Alloys /". The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487932351057225.
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Babu, Bibin. "Connected Me : Hardware for high speed BCC". Thesis, Linköpings universitet, Institutionen för systemteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-79442.
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Body coupled communication (BCC) is a hot topic in personal networking domain. Many works arepublished suggesting different architectures for BCC since its inception in 1995 by Zimmerman. The number ofelectronic gadgets used by a single person increases as time pass by. Its a tedious job to transfer data betweenthen from a user point of view. Many of these gadgets can share their resources and save power and money.The existing wired or wireless networks does not meet the requirements for this network like scalable data rate,security etc. So here comes the novel idea of using human body as communication medium. The aim of thisthesis is to realize a hardware for BCC based on wide band signaling as part of a big project.The human body consists of 70% of water. This property makes the human body a fairly good conductor.By exploiting this basic property makes the BCC possible. A capacitance is formed if we place a metal platenear to the human body with the skin as a dielectric. This capacitance forms the interface between the humanbody and the analog front-end of the BCC transceiver. Any other metal structures near to the human body canattenuate the signal.A first-order communication link is established in software by the human body model and the transceiver inthe loop along with noise and interference. This communication link is used to verify the human body modeland the base band model done as part of the same big project. Based on the results a hardware prototype isimplemented. Measurements are taken in different scenarios using the hardware setup. The trade-off betweendesign parameters are discussed based on the results. At the end, it suggests a road map to take the projectfurther.
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Ellis, M. "The ductile to brittle transition in BCC metals". Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306220.
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Valikova, Irina V., i Andrei V. Nazarov. "Simulation of diffusion under pressure in bcc metals". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194630.
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This work is devoted to simulation of atom configurations in bcc metals near the point defect using the molecular static method. The values of migration and formation volumes are very sensitive to the atomic structure in the vicinity of a defect, which makes it necessary to consider a large number of atoms in the computation cell and to take into account an elastic matrix around the cell. We have developed the new model taking into the consideration these factors. It allows to define “fine structure” of displacement atoms
near the point defect. The atoms of third zone were embedded in an elastic continuum. The displacement of each atom embedded in an elastic continuum was defined as the first and the second terms in solution of elastic equation. In the framework of this model we calculated the formation and migration volumes of defect. Also we take into the consideration that the energy of system (in particular the system with defect) depends on the outer pressure. This dependence gives an addition to the values of migration and formation volumes.
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Valikova, Irina, i Andrei Nazarov. "Simulation of diffusion under pressure in BCC metals". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-195673.
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Soin, Preetma Kaur. "First principles modelling of dislocations in BCC iron". Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/11752.
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This work centers around employing magnetic tight binding to study defects in body centred cubic iron, a material of potentially great importance as a structural component in hydrogen fusion power plants. An existing d-band tight binding model was extended to include charge. The first task was to develop a working scheme for calculating spins and charges self consistently. This was achieved using an extended form of the Harris-Foulkes functional and implemented with a generalisation of the Newton-Raphson minimisation procedure. Having established such a scheme it was tested on bulk structures, point defects and straight dislocations. The motion of dislocations and the opposition to this was also considered though calculation of Peierls barriers.
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Valikova, Irina V., i Andrei V. Nazarov. "Simulation of diffusion under pressure in bcc metals". Diffusion fundamentals 3 (2005) 11, S. 1-15, 2005. https://ul.qucosa.de/id/qucosa%3A14298.
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This work is devoted to simulation of atom configurations in bcc metals near the point defect using the molecular static method. The values of migration and formation volumes are very sensitive to the atomic structure in the vicinity of a defect, which makes it necessary to consider a large number of atoms in the computation cell and to take into account an elastic matrix around the cell. We have developed the new model taking into the consideration these factors. It allows to define “fine structure” of displacement atoms
near the point defect. The atoms of third zone were embedded in an elastic continuum. The displacement of each atom embedded in an elastic continuum was defined as the first and the second terms in solution of elastic equation. In the framework of this model we calculated the formation and migration volumes of defect. Also we take into the consideration that the energy of system (in particular the system with defect) depends on the outer pressure. This dependence gives an addition to the values of migration and formation volumes.
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Valikova, Irina, i Andrei Nazarov. "Simulation of diffusion under pressure in BCC metals". Diffusion fundamentals 2 (2005) 39, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14369.
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Tsai, Joshua Jr-Syan. "Micromechanisms of Near-Yield Deformation in BCC Tantalum". BYU ScholarsArchive, 2021. https://scholarsarchive.byu.edu/etd/8906.
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New materials, optimized for increased strength, ductility, and other desirable properties, have the potential to improve every aspect of modern living. To achieve these optimums, the necessary technological advancements are impeded mainly by the limits of available material models. Innovations in this field rely on research into the nature of material behavior. While a typical model of material behavior in the region near yield involves the initial linear elastic response, followed by yield and isotropic hardening, this fails to explain various important phenomena that manifest in a range of materials, such as pre-yield nonlinearity, anelasticity, yield point phenomena, hardening stagnation, and the Bauschinger effect. These effects have been explained over the past century with the theories of Cottrell atmospheres, the Orowan by-pass mechanism, and back stress. This manuscript compares data from experimental observation in tantalum to these theories to better understand the micromechanisms occurring near yield. Understanding deformation in this region has significant implications in structural and mechanical engineering, as well has having direct applications in the forming of metals. Forty-four dogbone-shaped samples were cut from 99.99% pure tantalum and pulled in load-unload-load and multi-cycle loop tensile tests at room temperature. The specimens were either single crystal, whose orientations were chosen based on desired active slip mode determined by Schmid factors, or bicrystal, based on the orientation of the single grain boundary. Sample behavior was simulated in both crystal plasticity and General Mesoscale finite element models to assist in interpreting results and in suggesting plausible micromechanisms. The experimental results and crystal plasticity simulations suggest alternate explanations to some of the discussed mechanical theories of near-yield deformation. The combined experimental / modeling approach indicates that other slip systems, besides the conventionally assumed {110}, are activated upon yield; particularly the {112} system. The breakaway model traditionally associated with the yield point phenomenon may also be better explained through a different mechanism; back stress development during deformation is shown to result in the observed behavior. Lastly, as is well-known, the Taylor formulation, upon which most crystal plasticity models are based, does not adequately predict yield stress behavior in the presence of grain boundaries; once again, an internal stress mechanism matches much better with the experimental results on single and bicrystals. While not all observations could be fully explained by simply adding internal stress generation to a standard crystal plasticity model, this work anticipates further studies to enable more accurate predictive modeling capabilities and increase understanding of the mechanisms driving the fundamental material properties necessary for future progress.
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Sinclair, Chad. "Co-deformation of a two-phase FCC/BCC material /". *McMaster only, 2001.
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Jennings, G. "Ultra-violet photoelectron spectroscopy of BCC- and FCC- iron". Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306636.
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Svenningsson, Leo. "Fourier transform of BCC andFCC lattices for MRI applications". Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-257148.
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The Cartesian Cubic lattice is known to be sub optimal when consideringband-limited signals but is still used as standard in three-dimensional medical magneticresonance imaging. The optimal sampling lattices are the body-centered cubic latticeand the face-centered cubic lattice. This report discusses the possible use of thesesampling lattices in MRI and presents verification of the non standard Fouriertransform method that is required for MR image creation for these sampling lattices.The results show that the Fourier transform is consistent with analytical models.
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Nazarov, Andrei V., Alexander A. Mikheev, Irina V. Valikova, Aung Moe i Alexander G. Zaluzhnyi. "Kinetic of void growth in fcc and bcc metals". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193483.
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Nazarov, Andrei V., Alexander A. Mikheev, Irina V. Valikova, Aung Moe i Alexander G. Zaluzhnyi. "Kinetic of void growth in fcc and bcc metals". Diffusion fundamentals 6 (2007) 28, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A14203.
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Kazim, Muhammad Irfan. "Variation-Aware System Design Simulation Methodology for Capacitive BCC Transceivers". Doctoral thesis, Linköpings universitet, Elektroniska Kretsar och System, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-122840.
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Capacitive body coupled communication (BCC), frequency range 500 kHz to 15 MHz, is considered an emerging alternate short range wireless technology which can meet the stringent low power consumption (< 1 mW) and low data rate (< 100 kbps) requirements for the next generation of connected devices for applications like internet-of-things (IoT) and wireless sensor network (WSN). But a reliable solution for this mode of communication covering all possible body positions and maximum communication distances around the human body could not be presented so far, despite its inception around 20 years back in 1995. The uncertainties/errors associated with experimental measurement setup create ambiguity about the measured propagation loss or transmission errors. The reason is the usage of either earth grounded lab instruments or the direct coupling of earth ground with transmitter/receiver or the analog front end cut-off frequency limitations in a few MHz region or the balun to provide isolation or the measurements on simplified homogeneous biological phantoms. Another source of ambiguity in the experimental measurements is attributed to the natural variations in human tissue electrophysiological properties from person to person which are also affected by physical factors like age, gender, number of cells at different body locations and humidity. The analytical models presented in the literature are also oversimplified which do not predict the true propagation loss for capacitive BCC channel. An attempt is being made to understand and demonstrate, qualitatively and quantitatively, the physical phenomenon of signal transmission and propagation characteristics e.g., path loss in complex scenarios for capacitive BCC channel by both the experimental observations/measurements and simulation models in this PhD dissertation. An alternate system design simulation methodology has been proposed which estimates the realistic path loss even for longer communication distances > 50 cm for capacitive BCC channel. The proposed simulation methodology allows to vary human tissue dielectric/thickness properties and easily integrates with the circuit simulators as the output is in the form of S-parameters. The advantage is that the capacitive BCC channel characteristics e.g., signal attenuation as a function of different physical factors could be readily simulated at the circuit level to choose appropriate circuit topology and define suitable system specifications. This simulation methodology is based on full-wave electromagnetic analysis and 3D modeling of human body and environment using their conductivity, permittivity, and tangent loss profile to estimate the realistic propagation loss or path loss due to their combined interaction with the electrode coupler for capacitive BCC channel. This methodology estimates the complex path impedance from transmitter to receiver which is important to determine the matching requirements for maximum power transfer. The simulation methodology also contributes towards better understanding of signal propagation through physical channel under the influence of different electrode coupler configurations. The simulation methodology allows to define error bounds for variations in propagation loss due to both numeric uncertainties (boundary conditions, mesh cells) and human body variation uncertainties (dielectric properties, dielectric thicknesses) for varying communication distances and coupler configuration/sizes. Besides proposing the simulation methodology, the digital baseband and passband communication architectures using discrete electronics components have been experimentally demonstrated in the context of IoT application through capacitive BCC channel for data rates between 1 kbps to 100 kbps under isolated earth ground conditions. The experimental results/observations are supported by the simulation results for different scenarios of capacitive BCC channel. The experimental and simulation results help in defining suitable system specifications for monolithic integrated circuit design of analog front end (AFE) blocks for capacitive BCC transmitter/receiver in deep submicron CMOS technologies.The series name Linköping Studies in Science and Technology. Thesis in the printed version is incorrect. The correct name is Linköping Studies in Science and Technology. Dissertations. This is corrected in the electronic version.
In the electronic published version minor errors in the acknowledgements and some typographical mistakes has been corrected.
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Hayward, Erin G. "Atomistic studies of defects in bcc iron: dislocations and gas bubbles". Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44761.
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The structure and interactions of the defects in material on an atomistic scale ulti- mately determine the macroscopic behavior of that material. A fundamental understanding of how defects behave is essential for predicting materials failure; this is especially true in an irradiated environment, where defects are created at higher than average rates. In this work, we present two different atomistic scale computational studies of defects in body centered cubic (bcc) iron. First, the interaction energies between screw dislocations (line defects) and various kinds of point defects will be calculated, using anisotropic linear elastic theory and atomistic simulation, and compared. Second, the energetics and behavior of hydrogen and hydrogen-helium gas bubbles will be investigated.
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Lin, Peter Keng-Yu. "Evolution of grain boundary character distributions in FCC and BCC materials". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ27994.pdf.
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Waterton, Michael. "Characterisation and evolution of the grain boundary network in BCC metals". Thesis, Swansea University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678443.
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Luciani, Giulia. "Strumento per la diagnosi di carcinoma bcc basato su spettroscopia di impedenza". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8586/.
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Il presente lavoro di tesi ha l’obiettivo di sviluppare uno strumento di aiuto alla diagnosi tumorale basato sull’analisi dell’impedenza a diverse frequenze. L’impedenza di un tessuto è intesa come l’opposizione che esso offre nell’essere attraversato da un’eccitazione in corrente o in tensione, pertanto lo strumento prevede l’applicazione di una tensione mediante elettrodi e la conseguente lettura della corrente.
Da un’analisi delle tecniche utilizzate per individuare l’impedenza si è scelta un’eccitazione sinusoidale e si è quindi progettata una catena analogica di acquisizione del segnale. Si è utilizzato un microcontrollore per l’elaborazione dei dati e per inserire sistemi di controllo nel circuito . Sono stati realizzati inoltre elettrodi ad hoc per lo strumento al fine di soddisfare esigenze di dimensioni e di adattamento al progetto circuitale.
Per validare il dispositivo sono state realizzate prove in laboratorio al fine di ricercare l’accuratezza delle misure, inoltre sono previsti dei test sperimentali su pazienti a breve .
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Gilbert, Mark R. "BCC metals in extreme environments : modelling the structure and evolution of defects". Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:d972d28d-5d2d-4392-8cf5-fc5728dc74f6.
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Designing materials for fusion applications is a very challenging problem, requiring detailed understanding of the behaviour of materials under the kinds of extreme conditions expected in a fusion environment. During the lifetime of fusion-reactor components, materials will be subjected to high levels of neutron irradiation, but must still perform effectively at high operating temperatures and under significant loading conditions. Body-centred cubic (bcc) transition metals are some of the most promising candidates for structural materials in fusion because of their relatively high density, which allows for effective neutron-shielding with the minimum volume and mass of material. In this work we perform atomistic simulations on two of the most important of these, Fe and W. In this thesis we describe atomic-scale simulations of defects found in bcc systems. In part I we consider the vacancy and interstitial loop defects that are produced and accumulated as a result of irradiation-induced displacement cascades. We show that vacancy dislocation loops have a critical size below which they are highly unstable relative to planar void defects, and thus offer an explanation as to why they are so rarely seen in TEM observations of irradiated bcc metals. Additionally, we compare the diffusion rates of these vacancy loops to their interstitial counterparts and find that, while interstitial loops are more mobile, the difference in mobility is not as significant as might have been expected. In part II we study screw dislocations, which, as the rate limiting carriers of plastic deformation, are significantly responsible for the strength of materials. We present results from large-scale finite temperature molecular dynamics simulations of screw dislocations under stress and observe the thermally-activated kink-pair formation regime at low stress, which appears to be superseded by a frictional regime at higher stresses. The mobility functions fitted to the results are vital components in simulations of dislocation networks and other large-scale phenomena. Lastly, we develop a multi-string Frenkel-Kontorova model that allows us to study the core structure of screw dislocations. Subtle changes in the form of the interaction laws used in this model demonstrate the difference between the non-degenerate and degenerate core structures. We provide simple criteria to guarantee the correct structure when developing interatomic potentials for bcc metals.
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Valikova, Irina, i Andrei Nazarov. "Simulation of pressure- and temperature dependence of impurity diffusion in BCC metals". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-190167.
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Ramos, Ricardo Jorge Barão. "Barragens em betão compactado com cilindros (BCC) - evolução e utilização em Portugal". Master's thesis, Faculdade de Ciências e Tecnologia, 2011. http://hdl.handle.net/10362/7628.
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Dissertação para a obtenção do Grau de Mestre em Engenharia Geológica (Geotecnia) pela Faculdade de Ciências e Tecnologia da Universidade Nova de LisboaA primeira e única barragem de betão compactado com cilindros (BCC) existente em Portugal foi construida em 2005 no Pedrógão. Actualmente encontra-se uma segunda barragem em construção e outras quatro em fase de projecto. Na presente dissertação descreve-se os diferentes tipos de construção de barragens, para além das de betão compactado com cilindros (barragens de aterro e de betão convencional). É também descrita a evolução da utilização do BCC aplicado a este tipo de obras, com especial relevo para a barragem de Pedrógão. São descritos também o método e os ensaios de granulometria, baridade e compactação para a realização de uma mistura de BCC aplicável em barragens, bem como os resultados obtidos. Esta dissertação tem como objectivo principal a realização de uma campanha de ensaios laboratoriais usando uma máquina de corte de diaclases (também conhecida por máquina de Hoek) que, por razões de logística, não foi possivel concretizar. Nos anexos sintetiza-se o trabalho experimental realizado tendo em vista a utilização da referida máquina para ensaios de corte em provetes fabricados com uma mistura de BCC, assim como uma descrição da máquina de Hoek.
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Batista, Hugo Alexandre Antunes. "Análise térmica e estrutural de barragens de BCC - (betão compactado com cilindros)". Master's thesis, Faculdade de Ciências e Tecnologia, 2011. http://hdl.handle.net/10362/7836.
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Dissertação para obtencão do Grau de Mestre
em Engenharia Civil - Perfil EstruturasO Betão compactado com cilindros (BCC) aplicado a barragens é uma técnica empregue inicialmente nos anos 70, mas bastante recente em Portugal. Este tipo de betão tal como o betão convencional sofre uma reacção exotérmica que se caracteriza pela libertação de calor, estando este fenómeno directamente relacionado com o calor de hidratação gerado, bem como da velocidade de colocação de cada camada e temperatura ambiente que se faça sentir no momento dessa colocação. Este fenómeno ocorre desde que é aplicado o betão e podendo perdurar muito após a completa construção da barragem. Neste seguimento são realizadas importantes tarefas em fase de projecto como a análise térmica e consequente análise estrutural para que por um lado se possa optimizar esta construção o máximo possível e por outro prever que a obra será terminada com todos os requisitos de desempenho, segurança e durabilidade. O presente trabalho foca-se na criação de um modelo em 2D utilizando um programa comercial de elementos finitos, o ANSYS, usando assim a sua funcionalidade Birth & Death para recriar a sequência de construção por camadas do betão compactado com cilindros (BCC). Este modelo foi aplicado à Barragem do Pedrogão, a primeira obra de BCC construída em Portugal e para isso foram usadas todas as propriedades do betão que foi empregue na mesma obra. Assim, é possível prever as variações de temperatura sentidas ao longo do tempo na barragem. Este modelo foi verificado quando os seus dados foram comparados às distribuições de temperatura registados na barragem do Pedrogão por meio de termómetros. Além disso é realizada uma análise de tensões podendo-se saber a probabilidade de ocorrência de tracções e compressões no corpo da mesma.
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Valikova, Irina, i Andrei Nazarov. "Simulation of pressure- and temperature dependence of impurity diffusion in BCC metals". Diffusion fundamentals 11 (2009) 53, 2009. https://ul.qucosa.de/id/qucosa%3A14015.
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Hyde, Brian. "Effects of Carbon on Fracture Mechanisms in Nanocrystalline BCC Iron - Atomistic Simulations". Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/27315.
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Atomistic computer simulations were performed using embedded atom method interatomic potentials in α-Fe with impurities and defects. The effects of intergranular carbon on fracture toughness and the mechanisms of fracture were investigated. It was found that as the average grain size changes the dominant energy release mechanism also changes. Because of this the role of the intergranular carbon changes and these mechanisms compete affecting the fracture toughness differently with changing grain size.
Grain boundary accommodation mechanisms are seen to be dominant in the fracture of nanocrystalline α-Fe. To supplement this work we investigate grain boundary sliding using the Σ = 5,(310)[001] symmetrical tilt grain boundary. We observe that in this special boundary sliding is governed by grain boundary dislocation activity with Burgers vectors belonging to the DSC lattice. The sliding process was found to occur through the nucleation and glide of partial grain boundary dislocations, with a secondary grain boundary structure playing an important role in the sliding process. Interstitial impurities and vacancies were introduced in the grain boundary to study their role as nucleation sites for the grain boundary dislocations. While vacancies and H interstitials act as preferred nucleation sites, C interstitials do not.Ph. D.
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Yabuuchi, Kiyohiro. "Mn effect on irradiation hardening behavior and microstructural evolution in BCC Fe". Kyoto University, 2011. http://hdl.handle.net/2433/151904.
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Bhattacharya, Arunodaya. "Ion irradiation effects on high purity bcc Fe and model FeCr alloys". Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112398/document.
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Les alliages binaires FeCr de structure FM (ferrito/martensitique) sont actuellement les candidats les plus prometteurs comme matériaux de structure pour les réacteurs rapides refroidis au sodium et les futurs systèmes de fusion. Cependant, l'impact de Cr sur l'évolution de la microstructure irradié dans ces matériaux n’est pas bien compris. De plus, particulièrement pour les applications de fusion, le scénario de dégâts d'irradiation devrait être compliquée en outre par la présence de grandes quantités d'hélium produit par transmutation nucléaire (~ 10 appm He / dpa). Dans ce contexte, une étude spécifique des effets de l'irradiation ionique (influence du Cr et de l’He sur l’évolution de la microstructure) a été menée à 500 ° C sur une grande variété d’alliages FeCr de haute pureté (à teneur en Cr allant de ~ 3 wt.% À 14 wt.%) ainsi que sur du Fe pur. Les irradiations ont été effectuées à l'aide ions Fe, en mode mono-faisceau et mode dual-beam (irradiation par des ions Fe et co-implantation d'He) afin de pouvoir séparer le dommage ballistique de l’implantation couplée avec de l’He. Trois différentes doses ont été étudiées: dose élevée (157 dpa, avec 17 appm He / dpa), dose intermédiaire (45 dpa, avec 57 appm He / dpa) et in situ à faible dose (0,33 dpa, avec 3030 appm He / dpa). Les expériences ont été effectuées en utilisant l'installation JANNuS triple faisceau du CEA-Saclay et la plateforme in-situ du CSNSM-Orsay. L’évolution microstructurale des échantillons est essentiellement faite par MET, SAT et par EDS en mode STEM. Les principaux résultats sont les suivants : 1) L’étude détaillée de la population des cavités dans du Fe irradié à forte dose a révélé une forte réduction du gonflement du fait de l'ajout d’He. Une réduction drastique de la taille des cavités en dépit d’une densité plus élevée a été observée. Ce comportement a été observé tout au long zone irradié, jusqu’au pic d’endommagement. 2) La microstructure de cavités a également été étudiée dans les alliages FeCr irradiés en double faisceau à forte dose, et les résultats ont été comparés à ceux obtenus dans le Fe pur. L'analyse a été effectuée à une profondeur intermédiaire de 300 à 400 nm sous la surface (pour éviter les effets des interstitiels injectés et les effets de surface), correspondant à 128 dpa, 13 appm He / dpa. L’étude par TEM a montré que l'addition de petites quantités de Cr, aussi basse que 3wt.%, est très efficace pour réduire fortement le gonflement. Une réduction drastique de la taille des cavités a été mise en évidence. Par exemple, la taille moyenne des cavités pour l’alliage Fe3% Cr est de l’ordre de 0,9 nm alors qu’elle est voisine de 6,8 nm pour le Fe pur. De plus, la variation du gonflement en fonction de la teneur en Cr n’est pas monotone et présente un maximum local à environ 9 -. 10wt% Cr. 3) Le couplage des différentes techniques d’analyse, MET classique, STEM/EDS et analyse SAT appliqué à l’étude des alliages FeCr irradiés à faible et moyenne dose révèle la présence de zones enrichies en Cr sur le plan d’habitat des boucles de dislocation. Ce phénomène est relié à un phénomène de ségrégation induite par irradiation (RIS) de Cr au voisinage du coeur des boucles de dislocation. Quand la boucle se développe sous irradiation, les zones de ségrégation ne peuvent probablement pas se redissoudre du fait de la présence d'impuretés telles que le C. Lorsque les boucles sont imagées par MET, ces zones enrichies produisent des franges de contraste au voisinage du plan de la boucle. Une estimation quantitative de cet enrichissement a été déduit par STEM / EDS et l'SAT. La teneur en Cr dans ces domaines se situe entre 23 -. 35% par EDS et 22 % par SAT, ce qui est bien en dessous de la teneur en Cr de la phase α’ riche en CrFeCr binary alloys are a simple representative of the reduced activation ferritic/martensitic (F-M) steels, which are currently the most promising candidates as structural materials for the sodium cooled fast reactors (SFR) and future fusion systems. However, the impact of Cr on the evolution of the irradiated microstructure in these materials is not well understood in these materials. Moreover, particularly for fusion applications, the radiation damage scenario is expected to be complicated further by the presence of large quantities of He produced by the nuclear transmutation (~ 10 appm He/dpa). Within this context, an elaborate ion irradiation study was performed at 500 °C on a wide variety of high purity FeCr alloys (with Cr content ranging from ~ 3 wt.% to 14 wt.%) and a bcc Fe, to probe in detail the influence of Cr and He on the evolution of microstructure. The irradiations were performed using Fe self-ions, in single beam mode and in dual beam mode (damage by Fe ions and co-implantation of He), to separate ballistic damage effect from the impact of simultaneous He injection. Three different dose ranges were studied: high dose (157 dpa, 17 appm He/dpa for the dual beam case), intermediate dose (45 dpa, 57 appm He/dpa for dual beam case) and in-situ low dose (0.33 dpa, 3030 appm He/dpa for the dual beam case). The experiments were performed at the JANNuS triple beam facility and dual beam in situ irradiation facility at CEA-Saclay and CSNSM, Orsay respectively. The microstructure was principally characterized by conventional TEM, APT and EDS in STEM mode. The main results are as follows: 1) A comparison of the cavity microstructure in high dose irradiated Fe revealed strong swelling reduction by the addition of He. It was achieved by a drastic reduction in cavity sizes and an increased number density. This behaviour was observed all along the damage depth, upto the damage peak. 2) Cavity microstrusture was also studied in the dual beam high dose irradiated FeCr alloys, and the results were compared to bcc Fe. The analysis was performed at an intermediate depth 300 – 400 nm below the surface (to avoid injected interstitial effect and surface effects), corresponding to 128 dpa, 13 appm He/dpa. TEM study revealed that the addition of small quantities of Cr, as low as 3wt.%, is highly efficient in strongly reducing void swelling. It was achieved by a drastic reduction of cavity sizes. For instance, average cavity size in Fe3%Cr was 0.9 nm as opposed to 6.8 nm in bcc Fe. Furthermore, the variation of void swelling as a function of Cr content is non-monotonic, with alocal maxima around 9 - 10wt.%Cr. 3) Coupling of conventional TEM, STEM/EDS and APT analysis on low and intermediate dose irradiated FeCr alloys revealed the presence of Cr enriched zones on the habit plane of the dislocation loops. This is expected to be due to radiation induced segregation (RIS) of Cr close to the core of the loops. As the loop grows under irradiation, the segregated areas are probably prevented from re-dissolution by impurity elements such as C. When imaged by TEM using classical diffraction contrast imaging techniques, these enriched zones produce displacement fringe contrast on the loop plane. A quantitative estimate of this enrichment was deduced by STEM/EDSand APT. The Cr content in these areas was between 23 - 35 at.% measured by EDS and 22 ± 2 at.% obtained by APT, whichis well below the Cr content of the Cr-rich α’ phase
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Douat, Benjamin. "Étude de surfaces sous contrainte à l'échelle atomique : application au cas du niobium". Thesis, Poitiers, 2018. http://www.theses.fr/2018POIT2274/document.
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Les mécanismes de déformation plastique des matériaux cubiques à corps centré sont étudiés depuis plus d’un demi-siècle. Il est maintenant bien établi que les dislocations vis contrôlent la plasticité de ces matériaux. Ceci est dû à une structure non-plane du cœur de ces dislocations, qui induit une forte friction de réseau communément appelée ‘pseudo-Peierls’. Le mécanisme supposé est la nucléation thermiquement activée de paires de décrochements. Cette structure de cœur particulière limite également les plans de glissement possibles. Les traces de glissement aux échelles méso et microscopiques apparaissent ‘ondulées’, ce qui a amené à proposer toute une variété de plans de glissement.Dans ce contexte, nous avons analysé à une échelle plus fine, i .e. à l’échelle atomique, les traces de glissement obtenues par déformation en compression de monocristaux de niobium à des températures situées dans le régime de température thermiquement activé: 293 K, 200 K et 90 K. L’analyse par microscopie à effet tunnel sous environnement ultra vide indique qu’à la résolution atomique chaque trace de glissement peut être décomposée en segments associés à des plans de type {112} et {110}. De manière surprenante, il est mis en évidence qu’à 293 K et 200 K du glissement se produit à la fois dans le sens maclage et antimaclage. De plus, toutes les traces de glissement impliquent du glissement sur des plans de type {110}, étayant ainsi la structure de cœur compact prévue par simulations atomistiques ab initio.L’étude in situ de la surface sous contrainte, à T = 293 K et 200 K, a aussi mis en évidence des réorganisations, voire des disparitions, de terrasses atomiques au voisinage de dislocations émergentes. Le calcul des forces d’interaction en élasticité linéaire isotrope montre que les dislocations proches de ces terrasses ne jouent pas de rôle prépondérant sur la position d’équilibre des terrasses. En revanche, celles-ci modifient localement le potentiel chimique de surface, favorisant la diffusion atomique à l’origine des réorganisations de surface constatées expérimentalementThe plastic deformation of body-centred cubic metals is the subject of extensive studies since more than half a century. It is now well established that the screw dislocations control the plasticity of these metallic metals. The reason for this is attributed to a non-planar configuration of the core of these dislocations, which induces a high friction force usually referred to as ‘pseudo-Peierls’. The underlying elementary mechanism is the thermally activated nucleation of kink pairs. While perfect screw dislocations do not have specific glide plane, the non-planar core configuration limits the number of possible slip planes. The slip traces observed at the meso and microscopic scales are wavy, which has leaded to the proposal of several possible slip planes.In this context, we propose an analysis at a finer scale, i.e. the atomic scale, of the slip traces produced by compressive stress on niobium single crystals at three temperatures in the thermally activated temperature regime, namely: 293 K, 200 K and 90 K. The analyses were carried out using a scanning tunnelling microscope under ultra-high vacuum environment. At this scale of observation, the slip traces are made up of crystallographic segments that can be associated with {011} and {112} planes. It is also noticeable that at 200 K and 293 K dislocation glide is observed in both the twinning and the anti-twinning directions. More importantly, all slip traces include segments that belong to {011} planes strongly supporting the latest ab initio atomistic simulations predicting a compact core configuration for screw dislocation.In this study, we also established that, at T = 293 K and 200 K, the sample surface may undergo drastic changes of its vicinal terraces, when they are close to emerging dislocations. The calculation of interaction forces, in the frame of isotropic linear elasticity, indicates that dislocations close to vicinal terraces do not play a major role regarding the stable positions of the vicinal terraces. However, they locally modify the chemical potential of the surface, thus enhancing atomic diffusion which is at the origin of the surface reorganisations experimentally observed
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Schneider, Andreas Simon [Verfasser]. "Mechanical properties of small scale BCC metal structures / vorgelegt von Andreas Simon Schneider". Stuttgart : Max-Planck-Inst. für Metallforschung, 2010. http://d-nb.info/1004952171/34.
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Makarow, Irina. "Correlation of the elastic and plastic anisotropy of rolled FCC and BCC sheet". Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66250.
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Wang, Guofeng Goddard William A. Johnson W. L. "First principles based multiscale modeling of single crystal plasticity application to BCC tantalum /". Diss., Pasadena, Calif. : California Institute of Technology, 2002. http://resolver.caltech.edu/CaltechTHESIS:11132009-112545862.
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Thesis (Ph. D.)--California Institute of Technology, 2010. PQ #3052851.Advisor names found in the Acknowledgements pages of the thesis. Title from home page. Viewed 01/13/2010. Includes bibliographical references.
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Guo, Yaofeng. "Bêta-Bcc et alliages amorphes biocompatibles à base de titane pour les implants". Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI017/document.
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Les implants de corps humain biocompatibles à base de Ti de faible module de Young et sans élèments toxiques sont développés dans deux régimes de matériaux, les alliags cristallins à base de Ti-Nb(-Sn) et les alliages amorphes à base de Ti -Fe -Si. Une série d'alliages à base de Ti-Nb(-Sn) a été synthétisée par une aspiration coulée par la moule de cuivre et soumis à différents traitements thermiques (refroidissement du four ou trempe à l'eau). La microstructure, les propriétés thermiques et mécaniques des échantillons traités telles que la coulée et la chaleur ont été étudiées. On montre que l'addition de Sn augmente la stabilité de la phase β. Les modules de Young de ces alliages ont été également mesurés avec des mesures par ultrasons. Les alliages Ti74Nb26 trempés à l'eau avaient le plus faible module de Young. L'addition de Sn a peu d'impact sur le module de Young des alliages Ti-Nb. Les alliages amorphes à base de Ti- Fe-Si ont été synthétisés par filage à l'état fondu. La capacité de formation des verres, les propriétés thermiques et les propriétés de corrosion des alliages à base de Ti- Fe-Si ont été étudiées. La composition vitreuse a été conçue en fonction de la règle de l'eutectique profond. On a constaté que la région la plus proche du point eutectique ternaire(Ti65Fe30Si5) est une région quasi-cristalline icosaédrique, tandis que le côté plus raide (Si côté riche) de ce point eutectique ternaire est la région de formation de verre. L'effet de L'addition élémentaire mineur (Ge, Pd, Zr) sur la capacité de formation de verre des alliages à base de Ti- Fe-Si a été également étudié. L'observation in situ d'amorphisation des alliages vitreux Ti40Zr10Cu34Pd14Sn2 en faisceau synchrotron a été effectuée. L'alliage a été vitrifié avec succès dans un appareil à sustentation aérodynamiqueThe Ti-based biocompatible human body implants of low Young's modulus and without toxic elements are developed in two regime of materials, crystalline Ti-Nb(-Sn) based alloys and amorphous Ti-Fe-Si based alloys. A series of Ti-Nb(-Sn) alloys were synthesized by copper mould suction casting and subjected to different heat treatments (furnace cooling or water quenching). The microstructure, thermal and mechanical properties of the as-cast and heat treated samples were investigated. It is shown that the addition of Sn increases the stability of the β phase. The Young's moduli of these alloys were also measured by ultrasonic measurements. Water-quenched Ti74Nb26 alloy was found to exhibits the lowest Young's modulus. Sn addition has little impact on the Young's moduli of the TiNb alloys. The Ti-Fe-Si based amorphous alloys were synthesized by melt spinning. The glass forming ability, thermal properties and corrosion properties of Ti-Fe-Si based alloys were investigated. The glassy compositions were designed according to the deep eutectic rule. It was found that the region near ternary eutectic point (Ti65Fe30Si5) is an icosahedral quasicrystal forming region, whereas the steeper side (Si rich side) of this ternary eutectic point is the glass forming region. Effect of minor elemental addition (Ge, Pd, Zr) on glass forming ability of the Ti-Fe-Si based alloys was also studied. The in situ observation of amorphization of Ti40Zr10Cu34Pd14Sn2 glassy alloy in synchrotron beam was conducted. The alloy was successfully vitrified in an aerodynamic levitation apparatus
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Vasconcelos, Jean Rubens. "EstimaÃÃo da eficiÃncia tÃcnica dos Cursos de PÃs-GraduaÃÃo Stricto Sensu da Universidade Federal do CearÃ: triÃnio 2010 â 2012". Universidade Federal do CearÃ, 2013. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=11380.
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nÃo hÃEste trabalho analisarà a eficiÃncia tÃcnica dos cursos de mestrado acadÃmico e de doutorado ofertados pela Universidade Federal do Cearà durante os anos de 2010, 2011 e 2012, tendo como base de dados os indicadores adotados pela CAPES para a consolidaÃÃo de sua avaliaÃÃo periÃdica dos cursos de pÃs-graduaÃÃo prescrita em lei. Como ferramenta de decisÃo, optou-se pelo uso da tÃcnica matemÃtica da AnÃlise EnvoltÃria de Dados â DEA, com orientaÃÃo ao produto e sob a perspectiva dos mÃtodos CCR e BCC, onde cada curso ou programa de pÃs-graduaÃÃo foi considerado uma DMU. No comparativo das inferÃncias apresentadas pelos dois modelos, pode-se observar uma tendÃncia de queda na eficiÃncia dos cursos ao longo do perÃodo investigado, apesar da alavancagem na quantidade de insumos durante esse mesmo tempo, evidenciando, pois, algumas desproporÃÃes entre as variÃveis, sobretudo no que concerne Ãs especificidades acadÃmicas inerentes a cada DMU, somadas ainda à ausÃncia de oferta para os cursos de doutorado em alguns programas.
This research will analyze the technical efficiency on academic master and doctorate courses offered by the Cearà Federal University in the years of 2010, 2011 and 2012, having as data base the indicators adopted by CAPES for the consolidation of its periodic evaluation prescribed by laws on post-graduate courses. As decision making tool, was chosen the mathematic technique of Data Envelopment Analysis â DEA, output oriented and under the perspectives of CCR and BBC models where every post-graduate program / course was considered a DMU. Comparing the inferences presented by both models, it could be observed a decreasing tendency of efficiency on courses throughout the investigation period, despite the input growth during this very same period, evidencing therefore, some discrepancies between the variants, mainly concerning academic specifications related to each DMU, also adding the lack of provision for doctoral courses in some study programs.
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Escobedo, Juan Pablo. "Measurement of shear strength and texture evolution in BCC materials subjected to high pressures". Online access for everyone, 2007. http://www.dissertations.wsu.edu/Dissertations/Fall2007/j_escobedo_120507.pdf.
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Gomes, De Aguiar Veiga Roberto. "Computational insights into the strain aging phenomenon in bcc iron at the atomic scale". Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00708423.
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Static strain aging is an important concept in metalurgy that refers to the hardening of a material that has undergone plastic deformation and then is aged for a certain period of time. A theory proposed in the late 1940s by Cottrell and Bilby explains this phenomenon as being caused by the pinning of dislocations by impurities (e.g., carbon atoms in solid solution) that migrate to the vicinity of the line defect. In the course of this PhD work, the atomistic mechanism behind the static strain aging phenomenon in bcc iron has been studied by means of computer simulations. Given the fact that diffusion in the solid state proceeds slowly, thus preventing the use of molecular dynamics at low temperatures (when the effect of the dislocation stress field on carbon diffusion is more pronounced), we have preferentially employed a method coupling molecular statics with atomistic kinetic Monte Carlo. Three major points have been addressed by this thesis: (i) the effect of the stress field of an edge or screw dislocation on a carbon atom diffusing nearby; (ii) the diffusion of a carbon atom in the tight channel found in the dislocation core (pipe diffusion); and (iii) the equilibrium carbon distribution in a Cottrell atmosphere. The main effect of the dislocation stress field outside the dislocation core consists of biasing carbon diffusion, such that some transitions become more likely than others. This effect is expected to drive the early stages of Cottrell atmosphere formation, when the mutual interaction between carbon atoms is negligible. Right in the dislocation core, as expected, carbon was seen to diffuse faster than in the bulk. Carbon concentration in the neighborhood of an edge or a screw dislocation was modeled by an approach based in statistical physics using the binding energies calculated by molecular statics, revealing a good agreement with experimental data obtained by atom probe techniques.
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Kashinath, Abishek. "Helium behavior at fcc-bcc semicoherent interfaces: trapping, clustering, nucleation, and growth of cavities". Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/88276.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 153-171).
He implanted into metals precipitates into nanoscale bubbles that grow into voids, degrading the properties of engineering alloys in nuclear energy applications. In this thesis, multi-scale modeling techniques and neutron reflectometry measurements are used to study the He trapping, clustering and growth of clusters at fcc-bcc interfaces. Choosing Cu-Nb as a model fcc-bcc interface, a predictive Cu-Nb-He interatomic potential is constructed using density functional theory. These calculations show that two-body radial forces are sucient to describe interactions of He with fcc Cu and bcc Nb. Atomistic simulations reveal that He is initially trapped in the form of stable, sub-nanometer platelet-shaped clusters and not bubbles at the Cu-Nb interface. This behavior occurs due to the spatial heterogeneity of interface energy: He wets high energy, heliophilic regions while avoiding low energy, heliophobic ones. Using these insights, the maximum He concentration that can be stored without forming bubbles at any interface in terms of its location-dependent energy distribution may be predicted. The modeling predictions are validated by neutron reflectometry measurements, which show that interfacial He bubbles form only above a critical He concentration and provide evidence for the presence of stable He platelets below a critical He concentration. This work paves the way for the design of composite structural materials with increased resistance to He-induced degradation by tailoring the types of interfaces they contain.
by Abishek Kashinath.
Ph. D.
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Srivastava, Ashish Kumar. "Orientation, Microstructure and Pile-Up Effects on Nanoindentation Measurements of FCC and BCC Metals". Thesis, University of North Texas, 2008. https://digital.library.unt.edu/ark:/67531/metadc6050/.
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This study deals with crystal orientation effect along with the effects of microstructure on the pile-ups which affect the nanoindentation measurements. Two metal classes, face centered cubic (FCC) and body centered cubic (BCC, are dealt with in the present study. The objective of this study was to find out the degree of inaccuracy induced in nanoindentation measurements by the inherent pile-ups and sink-ins. Also, it was the intention to find out how the formation of pile-ups is dependant upon the crystal structure and orientation of the plane of indentation. Nanoindentation, Nanovision, scanning electron microscopy, electron dispersive spectroscopy and electron backscattered diffraction techniques were used to determine the sample composition and crystal orientation. Surface topographical features like indentation pile-ups and sink-ins were measured and the effect of crystal orientation on them was studied. The results show that pile-up formation is not a random phenomenon, but is quite characteristic of the material. It depends on the type of stress imposed by a specific indenter, the depth of penetration, the microstructure and orientation of the plane of indentation. Pile-ups are formed along specific directions on a plane and this formation as well as the pile-up height and the contact radii with the indenter is dependant on the aforesaid parameters. These pile-ups affect the mechanical properties like elastic modulus and hardness measurements which are pivotal variables for specific applications in micro and nano scale devices.
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Srivastava, Ashish Kumar Mirshams Reza. "Orientation, microstructure and pile-up effects on nanoindentation measurements of FCC and BCC metals". [Denton, Tex.] : University of North Texas, 2008. http://digital.library.unt.edu/permalink/meta-dc-6050.
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Aguiar, Veiga Roberto Gomes de. "Computational insights into the strain aging phenomenon in bcc iron at the atomic scale". Thesis, Lyon, INSA, 2011. http://www.theses.fr/2011ISAL0084/document.
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Le vieillissement statique est un concept important dans la métallurgie qui se réfère à un durcissement de la matière ayant subi une déformation plastique et est ensuite vieilli pendant une certaine période de temps. La théorie proposée dans les années 1940 par Cottrell et Bilby explique ce phénomène comme étant causé par l'épinglage des dislocations par les impuretés (par exemple, les atomes de carbone en solution solide) qui migrent au voisinage du défaut de ligne. Au cours de ce travail de thèse, le mécanisme atomistique responsable du phénomène du vieillissement statique dans le fer alpha a été étudié par des simulations numériques. Etant donné que la diffusion à l'état solide se déroule lentement, l'utilisation de la dynamique moléculaire à basse température (lorsque l'effet du champ de contraintes sur la dislocation de diffusion du carbone est plus prononcé) a été évitée, et nous avons utilisé préférentiellement le couplage de la statique moléculaire avec le Monte-Carlo cinétique atomistique. Trois points principaux ont été abordés dans cette thèse: (i) l'effet du champ de contraintes d'une dislocation coin ou vis sur un atome de carbone qui diffuse à proximité, (ii) la diffusion de l'atome de carbone dans le cour de la dislocation («pipe diffusion»), et (iii) la distribution d'équilibre des atomes de carbone dans une atmosphère de Cottrell. Le principal effet du champ de contrainte de la dislocation à l'extérieur du coeur est de biaiser la diffusion de l'impurité, de sorte que certains sauts (transitions) deviennent plus probables que d'autres. Cet effet va conduire aux premiers stades de la formation de l'atmosphère de Cottrell, lorsque l'interaction mutuelle entre atomes de carbone est négligeable. Au cœur de la dislocation, comme prévu, nos résultats indiquent que le carbone diffuse plus vite que dans le volume. La concentration de carbone dans le voisinage d'une dislocation coin ou vis a été modélisée par une approche de physique statistique en utilisant les énergies de liaison calculées par la statique moléculaire. Cette approche est en bon accord avec les données expérimentalesStatic strain aging is an important concept in metalurgy that refers to the hardening of a material that has undergone plastic deformation and then is aged for a certain period of time. A theory proposed in the late 1940s by Cottrell and Bilby explains this phenomenon as being caused by the pinning of dislocations by impurities (e.g., carbon atoms in solid solution) that migrate to the vicinity of the line defect. In the course of this PhD work, the atomistic mechanism behind the static strain aging phenomenon in bcc iron has been studied by means of computer simulations. Given the fact that diffusion in the solid state proceeds slowly, thus preventing the use of molecular dynamics at low temperatures (when the effect of the dislocation stress field on carbon diffusion is more pronounced), we have preferentially employed a method coupling molecular statics with atomistic kinetic Monte Carlo. Three major points have been addressed by this thesis: (i) the effect of the stress field of an edge or screw dislocation on a carbon atom diffusing nearby; (ii) the diffusion of a carbon atom in the tight channel found in the dislocation core (pipe diffusion); and (iii) the equilibrium carbon distribution in a Cottrell atmosphere. The main effect of the dislocation stress field outside the dislocation core consists of biasing carbon diffusion, such that some transitions become more likely than others. This effect is expected to drive the early stages of Cottrell atmosphere formation, when the mutual interaction between carbon atoms is negligible. Right in the dislocation core, as expected, carbon was seen to diffuse faster than in the bulk. Carbon concentration in the neighborhood of an edge or a screw dislocation was modeled by an approach based in statistical physics using the binding energies calculated by molecular statics, revealing a good agreement with experimental data obtained by atom probe techniques
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Schold, Linnér Elisabeth. "Image processing on optimal volume sampling lattices : Thinking outside the box". Doctoral thesis, Uppsala universitet, Avdelningen för visuell information och interaktion, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-265340.
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This thesis summarizes a series of studies of how image quality is affected by the choice of sampling pattern in 3D. Our comparison includes the Cartesian cubic (CC) lattice, the body-centered cubic (BCC) lattice, and the face-centered cubic (FCC) lattice. Our studies of the lattice Brillouin zones of lattices of equal density show that, while the CC lattice is suitable for functions with elongated spectra, the FCC lattice offers the least variation in resolution with respect to direction. The BCC lattice, however, offers the highest global cutoff frequency. The difference in behavior between the BCC and FCC lattices is negligible for a natural spectrum. We also present a study of pre-aliasing errors on anisotropic versions of the CC, BCC, and FCC sampling lattices, revealing that the optimal choice of sampling lattice is highly dependent on lattice orientation and anisotropy. We suggest a new reference function for studies of aliasing errors on alternative sampling lattices. This function has a spherical spectrum, and a frequency content proportional to the distance from the origin, facilitating studies of pre-aliasing in spatial domain. The accuracy of anti-aliased Euclidean distance transform is improved by application of more sofisticated methods for computing the sub-spel precision term. We find that both accuracy and precision are higher on the BCC and FCC lattices than on the CC lattice. We compare the performance of several intensity-weighted distance transforms on MRI data, and find that the derived segmentation result, with respect to relative error in segmented volume, depends neither on the sampling lattice, nor on the sampling density. Lastly, we present LatticeLibrary, a open source C++ library for processing of sampled data, supporting a number of common image processing methods for CC, BCC, and FCC lattices. We also introduce BccFccRaycaster, a tool for visualizing data sampled on CC, BCC, and FCC lattices. We believe that the work summarized in this thesis provide both the motivation and the tools for continuing research on application of the BCC and FCC lattices in image processing and analysis.
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Varillas, Javier. "A molecular dynamics study of nanocontact plasticity and dislocation avalanches in FCC and BCC crystals". Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/667172.
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This study aims to investigate the underlying mechanisms which govern the development of dense defect networks in nanoscale crystal plasticity, either under contact and uniaxial loading conditions, with emphasis on the onset of intermittent avalanche phenomena. The investigation is based on a comprehensive set of massive molecular dynamics (MD) simulations performed with embedded-atom method potentials in face-centered cubic (FCC) and body-centered cubic (BCC) crystals.
The first part of the thesis concerns the combined role of elasticity and plasticity in nanocontact loadings, where attention is given to the mechanisms leading to the formation of a permanent nanoimprint as well as to the onset of material pile-up at the contact vicinity. It is found that the topographical arrangement of the slip traces emitted at the surface into specific deformation patterns is a distinctive feature of the underlying dislocation glide and twinning processes occurring in FCC and BCC crystals as a function of temperature and surface orientation. A mechanistic analysis is made on the influence of the defect nucleation events in conjunction with the development of entangled defect networks upon the material hardness and its evolution towards a plateau level with increasing indenter-tip penetration. Complementary MD simulations of the uniaxial stress-strain curve of the plastically deformed region are carried out with the purpose of establishing a direct correlation between nanoscale material responses attaining under uniaxial and contact loading conditions. The results of this comparison illustrate on the key role played by defect nucleation processes on the formation of permanent nanoimprints, which differs from the conventional view in that in micro and macroscopic scales imprint formation is essentially governed by the evolutionary character of a preexisting (entangled) defect network: the greater the dislocation density, the larger the measured hardness. In overall, this work provides a fundamental insight into the understanding of why BCC surfaces are harder than FCC surfaces at the nanoscale.
A statistical physics background is devised to investigate the influence of the dislocation mechanisms on the onset of avalanche events that are inherent to crystal plasticity. The analysis is predicated upon the notion in that the size distribution of such avalanches follows power-law scaling. To investigate the avalanche size distributions in cubic crystals, a group of novel MD simulations are performed where the computational cells containing a periodic arrangement of a preexisting dislocation network are subjected to uniaxial straining under displacement control at different strain rates and temperatures. Under sufficiently slow driving, the dislocation networks evolve through the emission of dislocation avalanches which do not overlap in time. This illustrates that the mobilized entangled dislocation arrangements exhibit quiescent periods during each plastic (dissipative) event, enabling comparison with experimental results which are also performed under strict displacement controlled conditions. The results illustrate on the attainment of a transitional slip size separating two power-law avalanche regimes as a function of the fundamental dislocation glide processes at the crossroads of self-organized and tuned criticality models. Detailed analyses of the MD simulations furnish specific mechanisms characterizing dislocation avalanche emission and propagation in FCC and BCC metals throughout a wide temperature range, which is central in supporting the onset of the aforementioned two power-law regimes.En este estudio se investigan los mecanismos fundamentales para el desarrollo de las densas redes de defectos que se producen durante la deformación plástica de metales mediante ensayos uniaxiales y de indentación en escalas nanométricas. Estos procesos de deformación plástica se caracterizan por la producción de eventos intermitentes o avalanchas de dislocaciones. La investigación se basa en un extenso grupo de simulaciones de dinámica molecular en las que se emplean potenciales interatómicos del tipo embedded-atom method en cristales cúbicos centrados en las caras (CCC) y cúbicos centrados en el cuerpo (CC). La primera parte de esta tesis discute el papel combinado de la elasticidad y plasticidad en los nanocontactos. Se presta una especial atención a los mecanismos que llevan a la formación de nanohuellas plásticas así como al desarrollo de apilamiento de material alrededor del nanocontacto. Se encuentra que los arreglos topográficos de trazas de deslizamiento (emitidas a la superficie) muestran patrones específicos de deformación, los cuales son a su vez un rasgo distintivo de los mecanismos de deslizamiento de dislocaciones y procesos de nanomaclado que ocurren en los materiales CCC y CC en función de la temperatura y la orientación de la superficie. Se presenta un estudio mecanístico sobre la influencia de los eventos de nucleación de defectos, que llevan al desarrollo de una compleja red de defectos, sobre la nanodureza y su convergencia hacia un valor relativamente constante a medida que el indentador penetra en la superficie La modelización del comportamiento uniaxial de la zona deformada debajo de las nanoindentaciones permite la correlación entre ambos tipos de ensayos. Los resultados de esta comparación ilustran el importante papel que juegan los procesos de nucleación de dislocaciones sobre la formación de nanohuellas plásticas, lo que difiere (en términos mecanísticos) del comportamiento plástico convencional encontrado en escales micro y macroscópicas, donde el carácter evolutivo de una red de defectos preexistente gobierna la formación de huella, cumpliéndose así que cuanto mayor es la densidad de defectos, mayores son también las macro y microdurezas. En general, este trabajo aporta un trasfondo fundamental para comprender la razón por la que las superficies CC son más duras que las CCC en la nano escala. En la última parte de esta investigación se utilizan modelos de física estadística para investigar la influencia de los mecanismos de propagación de dislocaciones sobre la emisión de avalanchas plásticas. El análisis se basa en la noción de que la distribución del tamaño de las avalanchas sigue una ley potencial universal. Para investigar esta distribución en cristales cúbicos, se realizan un grupo de simulaciones novedosas donde las celdas computaciones, que contienen arreglos periódicos de las redes de dislocaciones, son sometidas a cargas uniaxiales a diferentes temperaturas y velocidades de deformación. A velocidades de deformación suficientemente lentas, las redes de dislocaciones evolucionan a través de la emisión de avalanchas que no se sobreponen en el tiempo, lo que ilustra que la movilización de las redes ocurre de tal manera que se garantiza una alternancia entre periodos de inactividad y cada evento plástico. La comparación entre resultados experimentales y computacionales lleva a encontrar la existencia de una magnitud de deslizamiento crítico que separa a dos regímenes de avalanchas cuya distribución de tamaños obedece leyes potenciales. Este resultado demuestra que los procesos de avalanchas son claramente dependientes de los mecanismos de deslizamiento e interacción de dislocaciones presentes en el material; aspecto que describe la transición entre el modelo de criticalidad gobernada por la tensión y el de criticalidad auto-organizada. Las simulaciones muestran los mecanismos específicos que caracterizan la emisión y propagación de avalanchas en metales CC y CCC en un amplio rango de temperatura, lo que es de gran importancia para justificar la utilización de estos modelos de criticalidad.
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Kowalewski, Maciej Matthew Zbigniew. "Engineering and investigation of the interlayer exchange coupling in bcc Fe/Cu/Fe(001) structures". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0020/NQ37722.pdf.
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Tarleton, Edmund. "Dislocation-dynamics modelling of crack-tip plastic zones and brittle-ductile transitions in BCC metals". Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526123.
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Patra, Anirban. "Modeling the mechanical behavior and deformed microstructure of irradiated BCC materials using continuum crystal plasticity". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50366.
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The mechanical behavior of structural materials used in nuclear applications is significantly degraded as a result of irradiation, typically characterized by an increase in yield stress, localization of inelastic deformation along narrow dislocation channels, and considerably reduced strains to failure. Further, creep rates are accelerated under irradiation. These changes in mechanical properties can be traced back to the irradiated microstructure which shows the formation of a large number of material defects, e.g., point defect clusters, dislocation loops, and complex dislocation networks. Interaction of dislocations with the irradiation-induced defects governs the mechanical behavior of irradiated metals. However, the mechanical properties are seldom systematically correlated to the underlying irradiated microstructure. Further, the current state of modeling of deformation behavior is mostly phenomenological and typically does not incorporate the effects of microstructure or defect densities.
The present research develops a continuum constitutive crystal plasticity framework to model the mechanical behavior and deformed microstructure of bcc ferritic/martensitic steels exposed to irradiation. Physically-based constitutive models for various plasticity-induced dislocation migration processes such as climb and cross-slip are developed. We have also developed models for the interaction of dislocations with the irradiation-induced defects. A rate theory based approach is used to model the evolution of point defects generated due to irradiation, and coupled to the mechanical behavior. A void nucleation and growth based damage framework is also developed to model failure initiation in these irradiated materials. The framework is used to simulate the following major features of inelastic deformation in bcc ferritic/martensitic steels: irradiation hardening, flow localization due to dislocation channel formation, failure initiation at the interfaces of these dislocation channels and grain boundaries, irradiation creep deformation, and temperature-dependent non-Schmid yield behavior. Model results are compared to available experimental data.
This framework represents the state-of-the-art in constitutive modeling of the deformation behavior of irradiated materials.
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Goel, Archak. "Design of Functionally Graded BCC Type Lattice Structures Using B-spline Surfaces for Additive Manufacturing". University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1552398559313737.
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Bodewits, Karin. "Biosynthesis pathway & transport of endotoxin : promising antibacterial drug targets in the Burkholderia cepacia complex (BCC)". Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5791.
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Burkholderia cepacia complex (Bcc) species are opportunistic pathogens in patients with cystic fibrosis (CF), which are able to cause lethal infections. The Bcc are inherently resistant to most classes of antibiotics, which makes successful treatment problematic. Lipid A (also known as endotoxin), the hydrophobic anchor of lipopolysaccaride (LPS), is the bio-active component of LPS. One of several unique characteristics of the lipid A of the Bcc, is the permanent attachment of 4-amino-4-deoxy-L-arabinose (L-Ara4N) to the lipid A molecule. Also, the genes involved in L-Ara4N biosynthesis are necessary for viability in B. cenocepacia. Here we present research on lipid A biosynthesis, modi cation, and transport in the Bcc and highlight promising antimicrobial targets. The synthetic antibiotic CHIR-090 is an inhibitor of LpxC, an enzyme involved in the lipid A biosynthetic pathway. I investigated the activity of CHIR-090 against the Bcc and found that sensitivity to this antibiotic was both species- and strain-specific. CHIR-090 displayed MICs between 0.1 and 12.5 μg/ml against a panel of B. multivorans, the most prevalent Burkholderia species in CF. The species- and strain-specific sensitivity towards CHIR-090 was further explored and a strong correlation was found between the presence of a unique open reading frame, named LpxC2, in resistant species. To address the problem of multiple drug-resistance of the Bcc, we investigated the activity of the pyridoxal 50-phosphate (PLP)-dependent enzyme inhibitor cycloserine (CS) against the Bcc. CS is used as a second line of defense against M. tuberculosis. The activity of the D-enantiomer of CS (DCS) against the Bcc was tested and displayed MICs between 2 and 128 μg/ml and acted bactericidal towards the Bcc. Additionally, DCS inhibition of recombinant ArnB from B. cenocepacia J2315, a PLP-dependent enzyme necessary for viability in the Bcc, was studied. ArnB was inhibited reversibly by DCS. ArnB was further explored as a promising drug-target in the Bcc, but only CS has been identified as an inhibitor so far. In this thesis it was attempted to find the reason why is L-Ara4N modification of lipid A necessary for viability in B. cenocepacia. Therefore, two proteins were characterised, which are involved in lipid A transport: LptA, the periplasmic lipid A binding protein, and LptB, the cytoplasmic ATP-ase. LptA was found to be able to bind both modified and unmodified lipid A in vitro and therefore is not L-Ara4N specific. Furthermore, LptA could bind deep-rough-, rough-, and smooth- LPS, similar to that described for Escherichia coli LptA. The kinetic parameters of LptB were determined in vitro (kcat = 5.71 min-1 and KM = 0.88 mM), and were comparable to E. coli LptB. The ATP-ase activity of LptB was not influenced by the presence of any forms of LPS (modified or non-modified). Therefore, we concluded that both B. cenocepacia J2315 LptA and LptB are not L-Ara4N specific.
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Thompson, Gregory B. "Predicting Polymorphic Phase Stability in Multilayered Thin Films". The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1046469309.
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Andersson, Isak, i Melki Karlsson. "Body Coupled Communication: Ändring av prototypkort". Thesis, Linköpings universitet, Elektroniksystem, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-112864.
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Kommunikation genom att använda människokroppen som överföringsmedium, med kapacitiv koppling mellan hud och sensor, har varit ett pågående forskningsområde för PAN (Personal Area Network) sedan Thomas Guthrie Zimmerman introducerade tekniken 1995. Anledningen till detta är att undersöka fördelar och användningsområden för en kommunikationsmetod som ej sänder ut RF-signaler och därmed minska risken för obehörig avlyssning. Denna rapport beskriver ett examensarbete som undersöker möjligheten till eliminering av USB- till UART-konverterare på Microchip BodyCom genom mjukvaru-USB-stack och kombinera denna med Body Coupled Communication funktionalitet i en gemensam mikrokontroller. Vidare studeras om programkoden i Body Coupled Communication sändare kan modifieras för att utöka funktionaliteten. Det var givet i förutsättningarna att mikrokontroller från Microchip skulle användas, vidare var lågt pris respektive låg strömförbrukning viktigt, särskilt för sändaren. Metoden för att uppnå detta har varit användning av Microchip BodyCom development kit tillsammans med Microchip USB low pin count development kit och Microchip USB firmwareframework. Resultatet blev att USB- till UART-omvandlare kunde integreras med Microchip BodyCom genom att använda mjukvaru-USB-stack och en modifierad programkod för BodyCom i en gemensam mikrokontroller. Endast fantasin sätter gränsen för vad Body Coupled Communication kan användas till. Det skulle t.ex. vara möjligt att utbyta elektroniska visitkort genom en handskakning eller öppna en låst dörr endast genom att ta i handtaget.Communication using the human body as a transmission medium, the capacitive coupling between the skin and sensor, has been an active research area for PAN (Personal Area Network) since Thomas Guthrie Zimmerman introduced the technique in 1995. The reason for this is to examine the benefits and uses of a communication method that does not emit RF signals and thus reduce the risk of unauthorized interception. This report describes a thesis that examines the possibility of elimination of USB to UART converter on Microchip BodyCom through software USB-stack and combine this with Body Coupled Communication functionality in a single microcontroller. Furthermore, studies on if the application code in Body Coupled Communication transmitters can be modified to extend functionality. It was given in the conditions that microcontrollers from Microchip should be used, furthermore, low price and low power consumption were important, especially for the transmitter. The method for achieving this has been the use of Microchip BodyCom development kit with USB Microchip low pin count development kit and Microchip USB firmware framework. The result was that the USB- to UART-converter could be integrated with Microchip BodyCom, using software USB-stack and a modified program code for BodyCom in a single microcontroller. Only your imagination sets the limits for Body Coupled Communication can be used for. For example, it would be possible to exchange electronic business cards by a handshake or open a locked door only by using the handle.
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Zermatten, Pierre-Jean. "Étude du transport tunnel dépendant du spin dans des jonctions tunnels magnétiques épitaxiées Fe/MgO/Fe bcc". Phd thesis, Université Joseph Fourier (Grenoble), 2008. http://tel.archives-ouvertes.fr/tel-00345079.
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La prédiction et l'observation de très forts taux de magnétorésistance tunnel (TMR) dans des jonctions tunnel magnétiques à base de MgO a ouvert de nouvelles perspectives d'applications dans le domaine de l'électronique de spin. Ces forts taux de TMR ne peuvent s'expliquer qu'en prenant en compte la structure cristalline des électrodes et le filtrage de la barrière tunnel dépendant des symétries. Un dispositif original de mesures de transport sous champ magnétique d'objets de taille nanométrique a été développé au cours de cette thèse. Il associe une électronique d'acquisition rapide et un Microscope à Force Atomique (AFM) muni d'une pointe métallique. Ce dispositif très versatile permet de contacter électriquement et d'étudier de différents types de nano-objets sans étapes compliquées de nanofabrication.
Ce dispositif a été utilisé pour étudier l'influence des interfaces sur le transport dans des jonctions tunnel Fe/MgO/Fe (100) cristallines obtenues par épitaxie. Deux états résonants d'interface (IRS) ont été observés pour la première fois dans ce système à 0.2eV et 1.1eV au dessus du niveau de Fermi pour les électrons minoritaires. Ces IRS modifient fortement le transport tunnel et le dominent autour de 1V avec une inversion de la TMR dynamique. Une étude en fonction de l'épaisseur de MgO a permis de trouver la symétrie dominant le transport de ces IRS.
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Rashetnikava, Alena, Alexander Germanov, Irina Valikova i Andrei Nazarov. "Molecular dynamics simulation of atomic structure in the vicinity of point defects in FCC and BCC metals". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-190156.
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