Dissertations / Theses: 'Magnus effect'

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CORREA, CARLOS JOSE. "EXPERIMENTAL STUDY OF THE MAGNUS EFFECT." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1985. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33498@1.

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O efeito magnus é verificado experimentalmente em túnel de vento, para escoamentos com números de Reynolds variando de 1,3 x 10 elevado 4 a 4,3 x 10 elevado a 4. Os resultados são avaliados em termos absolutos e adimensionalizados. Levando-se em conta as incertezas provenientes do método de ensaio, são feitas comparações com da dos obtidos por outros pesquisadores. São avaliadas as possibilidades de utilização do efeito em captação de energia eolica, e é também realizado um estudo da influência da forma de Magnus na trajetória de projetis estabilizados giroscopicamente.
The Magnus effect is experimentally studied in a wind tunnel for Reynolds number range from 1,3 x 10 (to) 4 to 4,3 x 10 (to) 4. The results are analysed and compared for both dimensionless and dimensionalized parameters. The uncertainties are estimated and the results compared to those of other investigators. The possibilities of utilization of Magnus effect in wind power generation are analyzed together with its influence in trajectories of spin-stabilized projectiles.

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Jinbo, Maro. "Contribuições ao projeto de sistemas eólicos de efeito magnus com rastreamento da máxima potência." Universidade Federal de Santa Maria, 2016. http://repositorio.ufsm.br/handle/1/12032.

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This work deals with an unconventional wind energy conversion system, in which the wind turbine has rotating cylinders rather than traditional blades. These cylinders can be driven by a brushless DC motor. The turbine operates on the physical principle called Magnus Effect. It presents the mathematical modeling of Magnus turbine and based on this modeling were carried out simulations in PSIM® software. It was implemented and was tested MPPT algorithms type HCC (Hill Climbing Control) for DC brushless motor control for operating the cylinders and hence the power generated by the Magnus turbine. Prototypes of Magnus effect wind system (turbine, generator PMSG, AC / DC converter, DC / DC converter) were built to perform wind tunnel experiments comparing the experimental results with simulated results. We sought to optimize the extraction of wind energy through concepts and innovative solutions in the construction of the turbine, brushless DC servo for rotating cylinders, implementing MPPT algorithms to control the rotation of the cylinder and the static converter. Three turbine concepts are presented and three prototypes were built. Loose cylinders were tested in the wind tunnel and it was measured the lift and drag forces. The "Prototype 3" is 3 m in diameter with two cylinders of 150 mm diameter showed the best experimental results, but still generated mechanical power did not provide an effective net power.
O presente trabalho trata de um sistema eólico não convencional, cuja turbina eólica possui cilindros girantes no lugar das pás tradicionais. Estes cilindros podem ser acionados por um motor brushless CC (sem escovas). O princípio físico de funcionamento desta turbina baseia-se no que se denomina de “Efeito Magnus”. Apresenta-se a modelagem matemática da turbina Magnus e com base nesta modelagem realizam-se simulações no software PSIM®. Programa-se e testa-se algoritmos de rastreamento da máxima potência líquida MPPT (Maximum Power Point Tracking), do tipo HCC (Hill Climbing Control) no controle do motor brushless CC de acionamento dos cilindros e, consequentemente, da potência gerada pela turbina Magnus. Protótipos de sistema eólico de efeito Magnus (turbina, gerador PMSG, conversores CA/CC, CC/CC) foram construídos para realizar experimentos em túnel de vento, possibilitando comparações dos resultados experimentais com os resultados simulados. Busca-se otimizar a extração da energia dos ventos, através de concepções e soluções inovadoras na construção da turbina, servo acionamento CC brushless para os cilindros girantes, implementação de algoritmos MPPT no controle da rotação dos cilindros e do conversor estático. Três concepções da turbina Magnus são apresentadas e três protótipos construídos. Ensaios de cilindros girantes avulsos com variações nos diâmetros e nas espirais sobrepostas são realizados em túnel de vento com colméias e medem-se as forças de sustentação e de arrasto. O “Protótipo 3” de 3 m de diâmetro com dois cilindros lisos de 150 mm de diâmetro apresentou os melhores resultados experimentais, mas ainda a potência mecânica gerada não proporcionou uma potência líquida efetiva.

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Silva, Ricardo Galdino da. "Estudo numérico de movimentação de partículas em escoamentos." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3132/tde-08032007-181139/.

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No trabalho desenvolvido estudaram-se as forças que atuam em uma partícula quando esta se movimenta em escoamentos, com intuito de obter uma metodologia capaz de representar o movimento de uma partícula em um escoamento. A equação do movimento da partícula foi integrada numericamente considerando os termos de massa aparente, arrasto estacionário, arrasto não estacionário (forças de Boussinesq/Basset) e forças de sustentação; efeito Magnus e efeito Saffman. O método dos volumes finitos foi utilizado para simulação do escoamento. Na análise das forças utilizamos tanto experimentos quanto simulações numéricas (FLUENT) para avaliar e aumentar a validade dos modelos apresentados na revisão bibliográfica. O FLUENT foi validado para obtenção do coeficiente de arrasto estacionário e sustentação devido ao efeito Magnus. Palavras-chaves: Efeito Magnus, efeito Saffman, força de Bousinesq/Basset, movimento de partículas e solução numérica.
In the developed work was studied the forces which act on a particle when these is a moving inside of a flow, in order to find out a methodology which is able to represent the particle dynamics on a flow. The equation of particle motion was integrated with a numerical approach taking in account the apparent mass, static drag, dynamic drag (history term; Boussinesq/Basset force) and lift force; Magnus effect and Saffman effect. The finite volume method was used to simulate the flow. In the force analyses we used experimental and numerical simulation (FLUENT) to evaluate and extend the models shown on the review. FLUENT was validated to determine the static drag coefficient and lift coefficient due to Magnus effect.

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Neumüller, Georg. "On Control and stabilisation of floating wind platforms with the help of CFD analysis and the Magnus effect." Thesis, KTH, Numerisk analys, NA, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-213973.

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With new technologies and possibilities arising both in the renewable energy sector as well as in the field of Computational Fluid Dynamics, this thesis describes the simulation of vortex- induced vibrations for floating wind turbine platforms. The aim is to control and stabilize floating wind platforms with the help of CFD and the Magnus effect. The Magnus effect shall hereby be used to reduce the wakes behind the cylinder and thereby not only move the cylinder, but also reduce vibrations. Therefore this thesis consists of three main sets of experiments. The first set simulates vortex-induced vibrations for low Reynolds number flow and compares the results to existing research results. The second set of experiments examines VIV for high or supercritical Reynolds number flow and the last set of experiments adds rotation to the platform, hence studies the impact the Magnus effect has on stabilisation and position controlling. The simulations are conducted on a fully submerged cylinder floating in a virtual test bassin, moored by a two-dimensional spring damper system. The numerical method for solving the incompressible Navier-Stokes equations is the Eulerian cG(1)cG(1), a finite element method (FEM) based on the weak formulation of the former. The spring damper equations are solved using a trapezoidal rule and the coding was based on the Unicorn framework in FEniCS. Calculations were done on a Cray XC40 system at KTH Stockholm. Results showed that the above method in many cases produced results closer to physical results than previous numerical research. It also showed that the Magnus effect can be used even for supercritical Reynolds number flow to stabilise the platforms by reducing wakes behind them. It further shows that this effect is in close relation to the shift of the platform and mostly depends on the natural frequency, the inflow velocity and the rotation speed.
Med hänsyn till de nya teknologier och möjligheter som uppstår både inom området förnybar energi samt strömningsmekaniska beräkningar, beskriver denna avhandling simuleringen av vortexinducerade vibrationer (VIV) för flytande vindturbinplattformar. Syftet är att kontrollera och stabilisera flytande vindturbinplattformar med hjälp av både numerisk strömningssimulering och Magnuseffekten. Magnuseffekten ska användas för att minska virvelströmningar bakom cylindern och därigenom inte bara flytta cylindern, utan också minska vibrationer. Denna avhandling består av tre kategorier av experiment. Den första kategorin simulerar vortexinducerade vibrationer i strömningar med lågt Reynoldstal och jämför resultaten med befintliga forskningsresultat. Den andra kategorin experiment undersöker VIV för strömningar med högt eller superkritiskt Reynoldstal och den sista lägger till rotation till plattformen, dvs den studerar effekterna som Magnuseffekten har på stabilisering och positionskontroll. Simuleringarna utförs på en helt nedsänkt cylinder som flyter i en virtuell testbassäng, förankrat med ett tvådimensionellt fjäderdämpningssystem. Den numeriska metoden som används för att lösa de inkompressibla Navier-Stokesekvationerna är Eulersk cG(1)cG(1), en finit elementmetod (FEM) baserat på den svaga formuleringen av ekvationerna. Fjäderdämparens ekvationer löses med hjälp av trapetsregeln och kodningen är baserad på ramverket Unicorn i FEniCS. Beräkningarna gjordes på ett Cray XC40-system vid KTH Stockholm. Resultaten visade att ovanstående metod i många fall gav resultat närmare de fysiska resultaten än tidigare numerisk forskning. De visade också att Magnuseffekten kan användas för att stabilisera plattformarna genom att minska virvelströmningar bakom dem, detta inkluderar också strömningar med superkritiskt Reynoldstal. Dessutom visar resultaten att den här effekten har en stark koppling till plattformens förskjutning och mestadels beror på den naturliga frekvensen, inflödeshastigheten och rotationshastigheten.

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Ribas, Glauco Salomão Ferreira. "Uma proposta para motivar o aluno a aprender mecância no ensino médio : abordagem com tecnologias de informação e comunicação." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/173055.

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Não porque faltem bons alunos, mas pelo motivo de que aprender Física é importante, por se tratar de uma cultura necessária a qualquer cidadão de uma sociedade e não apenas aos mais vocacionados, trago uma sugestão para que a predisposição em aprender Física dos alunos de ensino médio melhore. Assim este trabalho se ocupa em apresentar recursos e atividades que buscam aproximar a vida do aluno contemporâneo ao ensino de Física, através de uma abordagem com tecnologias de informação e comunicação (TICs). Nosso foco disciplinar é o ensino de Mecânica em um ambiente favorável à aprendizagem significativa e que busca tratar a Física, bem como a Ciência, sob o viés epistemológico de Mario Bunge, isto é, trazendo a modelização subjacente na análise dos fenômenos físicos referentes a esse estudo, além de aplicar essa concepção em atividades computacionais com a planilha eletrônica Calc e os softwares Tracker e Modellus. Também é apresentada a aplicação desta proposta para uma turma de escola pública no horário extracurricular que, além de ressaltar tópicos tradicionalmente importantes sobre Mecânica, inova com atividades experimentais computacionais, tratando a resistência do ar e o efeito Magnus em lançamentos com bolas de basquete e vôlei. Os alunos chegam a perceber que não é a 45º que uma bola deve ser lançada para ir mais longe em situações práticas. Os resultados apresentados foram possíveis por ser exposta ao aluno uma visão da Física menos ingênua e mais próxima da sua realidade com algumas ferramentas essenciais como o software Modellus, determinando um alcance exploratório muito maior, para situações envolvendo esportes como futebol, basquete e vôlei, que a modelização mais idealizada, a qual apenas leva em conta a interação gravitacional dos corpos com a Terra. Ao final deste trabalho, encontra-se o respectivo produto educacional (Apêndice B), contendo toda sequência didática aplicada com algumas melhorias, organizada em guias para o professor e para os alunos.
Not because there are no good students, but for the fact that learning Physics is important, because it is a necessary culture for any citizen of a society and not only for the most educated, I bring a suggestion so that the predisposition to learn Physics of the high school students improve. Thus, this work is focused on presenting resources and activities that seek to bring the contemporary student's life closer to the teaching of Physics, through an approach with information and communication technologies (ICTs). Our disciplinary focus is the teaching of mechanics in an conducive environment to meaningful learning that seeks to treat Physics, as Science, under the epistemological bias of Mario Bunge, namely that, bringing the underlying modeling in the analysis of the physical phenomena related to this study, besides applying this conception in computational activities with the spreadsheet Calc and the softwares Tracker and Modellus. It is also presented the application of this proposal to a public-school class in extracurricular hours that, in addition to highlighting topics traditionally important on Mechanics, innovates with experimental computational activities, dealing with air resistance and Magnus effect in launches with basketball and volleyball. Students can realize that it is not at 45º that a ball should be thrown to go further in practical situations. The results presented were possible because the student was exposed to a less naive view of Physics and closer to his reality with some essential tools such as Modellus software, determining a exploratory reach far greater, for situations involving sports such as soccer, basketball and volleyball, than the most idealized modeling, which only considers the gravitational interaction of bodies with the Earth. At the end of this work, the respective educational product (Appendix B), containing all didactic sequence applied with some improvements, organized in guides for the teacher and for the students.

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Денисов, Станіслав Іванович, Станислав Иванович Денисов, Stanislav Ivanovych Denysov, Тарас Володимирович Лютий, Тарас Владимирович Лютый, Taras Volodymyrovych Liutyi, O. V. Kvasnina, and A. S. Yermolenko. "Minimal Set of Equations for Drift of Ferromagnetic Nanoparticles Induced by Magnetic Fields in Fluids." Thesis, Sumy State University, 2018. http://essuir.sumdu.edu.ua/handle/123456789/67955.

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Recently, it has been established that ferromagnetic nanoparticles subjected to a periodic force and a non-uniformly rotating magnetic field can drift in a viscous fluid due to the Magnus effect. Because the drift phenomenon is of interest for applications such as particle separation, in this work we present a minimal set of equations for describing this phenomenon when a periodic force is induced by a gradient magnetic field.

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Петровський, Михайло Васильович, Михаил Васильевич Петровский, Mykhailo Vasylovych Petrovskyi, Тарас Володимирович Лютий, Тарас Владимирович Лютый, Taras Volodymyrovych Liutyi, and А. С. Єрмоленко. "Метод електромагнітної сепарації феромагнітних наночастинок у суспензіях з урахуванням теплових флуктуацій." Thesis, Сумський державний університет, 2018. http://essuir.sumdu.edu.ua/handle/123456789/67919.

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Спрямований транспорт (дрейф) однодоменних феромагнітних частинок у в’язкій рідині, який можна використати для сепарації частинок за розміром і намагніченістю, виникає внаслідок синхронізованої дії на них змінної сили електричної природи, яка викликає їх коливальний рух, та зовнішнього однорідного магнітного поля, яке породжує змінний момент сил і викликає їх нерівномірне обертання. Фізичною причиною виникнення дрейфового руху є ефект Магнуса, тобто вплив обертання частинки на її траєкторію.

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Rutkauskienė, Rasa. "Levels of magnesium compounds of different solubility in predominant soil types in Lithuania, effects on agricultural plants." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2013~D_20130916_111245-03922.

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In Europe the views on the demand of magnesium by agricultural plants as well as on the need for magnesium fertilization are different. In European countries uses different methods for determining the available magnesium content in soil. Different assessment of soil characteristics in different countries as well as very unequal magnesium fertilization rates for crops have encouraged us to review the methods of determining available magnesium in soil and the effect of magnesium fertilizer on plants. The appropriateness of applying the magnesium determination methods commonly used in different soils in Europe was established and scientifically based as well as their relationship, recalculation algorithms for the values of available magnesium obtained by applying different determination methods were prepared. The effect of the plant available magnesium content in predominant soils of Lithuania determined by different methods and that of magnesium fertilizer on the yield of Italian ryegrass and spring barley were investigated. Summarizing the research developed the most suitable determination of available magnesium in Lithuanian soil and crop fertilization magnesium fertilizer recommendations. Different solubility of magnesium in different soils and magnesium fertilizers on agricultural plants in Lithuania was studied for the first time.
Požiūris į magnio poreikį žemės ūkio augalams, o tuo pačiu tręšimą magnio trąšomis, įvairiose šalyse nėra vienodas. Europos šalyse judrusis magnis dirvožemyje nustatomas labai įvairiais metodais. Skirtingas dirvožemio savybių vertinimas įvairiose šalyse, o taip pat labai nevienodos magnio trąšų normos augalams mus paskatino naujai peržiūrėti judriojo magnio nustatymo metodus dirvožemyje ir magnio trąšų įtaką augalams. Nustatytas ir moksliškai įvertintas dažniausiai Europoje naudojamų judriojo magnio nustatymo metodų taikymo tinkamumas įvairiuose dirvožemiuose, jų tarpusavio priklausomumas, parengti perskaičiavimo algoritmai tarp įvairiais metodais nustatytų judriojo magnio reikšmių. Vyraujančiuose Lietuvos dirvožemiuose ištirta įvairiais metodais nustatyto judriojo magnio kiekio ir magnio trąšų įtaka gausiažiedžių svidrių bei vasarinių miežių derliui ir kokybei. Apibendrinus atliktus tyrimus parengtos tinkamiausių judriojo magnio nustatymo Lietuvos dirvožemiuose metodų ir žemės ūkio augalų tręšimo magnio trąšomis rekomendacijos. Lietuvoje įvairaus tirpumo magnio kiekiai įvairiuose dirvožemiuose ir magnio trąšų įtaka žemės ūkio augalams tirta pirmą kartą.

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Amjad, Asma. "Exchange coupling in molecular magnets: Zero, one and three dimensions." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5755.

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Molecular magnets with different dimensionality, whether they are zero-dimensional single-molecule magnets (SMM) or one-dimensional single-chain magnets (SCM) are very interesting, since they allow probing the fundamental aspects bordering quantum and classical physics at the nanoscale level. This dissertation covers experimental studies of two Mn-based exchange-coupled molecule-based magnets and two Co-based single-chain magnets, using both dc Hall-effect magnetometry and electron paramagnet resonance (EPR) techniques. In these multi-dimensional systems, the spin of the molecule exhibits quantum mechanical behavior at low temperature. It is quite interesting to observe the effect of magnetic exchange interactions on the magnetic properties of various complexes; hence they strongly affect the magnetic behavior. In this dissertation, the research is initiated with the study of low-magnetic-nuclearity molecules, starting with a spectroscopic study of a significantly anisotropic Mn(IV) monomer. At low temperature the molecule possesses easy-plane type anisotropy of a remarkable magnitude. Although the molecule is not a single-molecule magnet, the remarkable anisotropy can initiate synthesis of newer and better molecular magnets with Mn(IV) as the main building block. Furthermore, the interplay between the magnetic anisotropy and the inter-ion exchange interactions (J) within the molecule are probed for a dimer and a trimer where the magnetic core is comprised of two and three ions respectively. In the Mn-based case of the dimer, the low coupling between the atoms leads to significant state mixing, thus making it impossible to assign the individual spin states to the dimer or to the respective individual Mn(II) ions. In the case of the trimer, lowering of the symmetry achieved by fine tuning of the inter-ion exchange interactions leads to relieving of frustration in the antiferromagnetic (AF) triangular Mn(III) system, resulting in a well defined ground state and significant zero field splitting. Also a clear hysteretic behavior observed in this system demonstrates its SMM nature at low temperature. Finally, high-field high-frequency magnetic and spectroscopic studies performed on two cobalt-based SCMs reveal that formation of magnetic domains by exchange interactions within the chain are strongly influenced by thermal fluctuations. The chain possesses a uniaxial anisotropy with the quantization axis lying along the length of the chain. Moreover it is shown that modulation of the magnitude of inter- and intra-chain interactions results in a three-dimensional dynamics in one of the samples. Interestingly, detailed dc magnetic studies show a tunable crossover between one- and three-dimensional magnetic dynamics as a function of temperature and/or magnetic field sweep rate. Our voyage through several molecular systems of different dimensionality have allowed us to expand our understanding of the role of exchange interactions on the magnetic behavior in molecular magnetism.
M.A.
Masters
Physics
Sciences
Physics

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Barhoumi, Rabei. "Positioning and addressing single molecule magnets with an STM tip." Thesis, Strasbourg, 2019. https://publication-theses.unistra.fr/restreint/theses_doctorat/2019/BARHOUMI_Rabei_2019_ED182.pdf.

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Les aimants moléculaires de type TbPc2 avec leur anisotropie magnétique élevée associée à des temps de relaxation longs de l’aimantation sont de bons candidats pour le codage et l’enregistrement de l’information. Leur robustesse et leur propension à s’arranger en réseaux se prêtent bien à une étude de leur structure électronique et magnétique par STM/STS à très basse température (4.5 K). Dans ce travail de thèse, il a été possible de mettre en évidence un écrantage Kondo des électrons π et 4f de la molécule de TbPc2 par les électrons du substrat métallique. Les propriétés magnétiques de la molécule dépendent de leur degré d’interaction avec le substrat et des interactions latérales avec les autres molécules. Ainsi le radical π de la molécule est préservé sur Au(111) mais disparait sur Ag(111) sous l’effet d’un transfert de charge entre le substrat et la monocouche moléculaire. Enfin, lorsque la molécule est en interaction forte avec le substrat de Cu(111), un accès direct aux états 4f de l’ion central de Tb est observé par STM comme le montre la détection d’un effet Kondo sur l’ion central de Tb
With their large magnetic anisotropy associated with long relaxation times of the magnetization, TbPc2 molecular magnets are good candidates for encoding and recording data. Their robustness and their propensity to arrange into networks lend themselves well to a study of their electronic and magnetic structure by STM/STS at very low temperature (4.5 K). In this thesis work, it was possible to highlight a Kondo screening of the π and 4f electrons of the TbPc2 molecule by the electrons of the metal substrate. The magnetic properties of the molecule depend on their degree of interaction with the substrate and lateral interactions with other molecules. Thus, the π radical of the molecule is preserved on Au (111) but disappears on Ag (111) under the effect of a charge transfer between the substrate and the molecular monolayer. Finally, when the molecule is in strong interaction with the Cu(111) substrate, a direct access to the 4f states of the central Tb ion by STM is possible as shown by the detection of a Kondo effect on the central Tb ion

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Rodríguez, Cortéz Carlos Alfonso. "Effect of thermal magnons onedge fluctuations innanomagnets." Thesis, Uppsala universitet, Materialfysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-451961.

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Weaver, Andrea Lynn. "The Effect of a Lingual Magnet on Fricative Production: An Acoustic Evaluation of Placement and Adaptation." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd1009.pdf.

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Subedi, Pradeep. "Collective effects in Single Molecule Magnets." Thesis, New York University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3602734.

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Single molecule magnets (SMMs), such as Mn₁₂-acetate, are composed of transition metal ions and consists of identical molecules with large ground-state spin (S = 10) and a strong uniaxial anisotropy (65 K). Below about 3 K, Mn₁₂-acetate exhibits magnetic hysteresis with steps at specific values of longitudinal magnetic field due to resonant quantum tunneling between spin up and down projections along the easy axis. The intermolecular exchange interactions between spins on molecules are quite small and spins are considered to be independent and non-interacting.

However, the molecules do interact with each other both through magnetic dipolar interactions and through the lattice (e.g. phonons). I have investigated collective effects in SMMs due to these intermolecular interactions. In the thesis I will present experiments that explored magnetic ordering due to magnetic dipole interactions in Mn₁₂-acetate and Mn₁₂-acetate-MeOH. I will also present exper- iments on the onset of magnetic de agration in Mn₁₂-acetate due to a thermal instability.

The magnetic ordering studies involved investigating the effect of transverse fields on the susceptibility of single crystals of Mn₁₂-acetate and Mn₁₂-acetate- MeOH. Transverse fields increase quantum spin uctuations that suppress long- range order. However, the suppression of the Curie temperature by transverse fields in Mn₁₂-acetate is far more rapid than predicted by the Transverse-Field Ising Ferromagnetic Model (TFIFM) and instead agrees with the predictions of the Random-Field Ising Ferromagnet Model. It appears that solvent disorder in Mn₁₂-acetate gives rise to a distribution of random-fields that further suppress long-range order. Subsequent studies on Mn₁₂-acetate-MeOH, with the same spin and similar lattice constants but without solvent disorder as Mn₁₂-acetate, agrees with the TFIFM.

The magnetic de agration studies involved studying the instability that leads to the ignition of magnetic deflagration in a thermally driven Mn₁₂-acetate crystal. When spins prepared in a metastable state reverse, Zeeman energy is released that diffuses away. In some circumstances, the heat released cannot be compensated by thermal diffusion, resulting in an instability that gives rise to a front of rapidly reversing spins traveling through the crystal. We observed a sharp crossover from relaxation driven by heat diffusion to a self-sustained reversal front that propagates at a constant subsonic speed.

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Le, Goff Anne. "Figures d'impact : tunnels, vases, spirales et bambous." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2009. http://tel.archives-ouvertes.fr/tel-00489654.

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Nous étudions expérimentalement différentes figures d'impacts de solides sur des liquides. Dans un premier temps, nous lançons à grande vitesse une bille dans un bain. Nous mesurons sa décélération et en déduisons la force exercée par le fluide sur la bille. Nous montrons ainsi qu'une mousse fortement cisaillée se comporte comme un fluide visqueux. Lors de ces impacts violents, de l'air est entraîné dans le bain par le projectile. Il se forme alors au sein du liquide une cavité que nous caractérisons : elle prend la forme d'un tunnel dans la mousse, d'un vase dans une huile visqueuse, et d'une spirale dans l'eau si la bille tourne sur elle-même au moment de l'impact. Nous nous intéressons ensuite à des impacts à plus faible vitesse, en remplaçant le bain par un film liquide : film de savon ou film visqueux étendu sur un plan. Les forces capillaires deviennent alors comparables à l'inertie des projectiles. On montre alors qu'une bille venant frapper un film peut rester piégée dans le liquide. Une mousse, qui contient de nombreux films liquides, peut ainsi freiner puis capturer des solides par capillarité.

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15

Chan, Hung-chiu Kingsley. "Cast keepers for dental magnets : effects of laboratory procedures /." View the Table of Contents & Abstract, 2005. http://sunzi.lib.hku.hk/hkuto/record/B31490335.

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16

Bui, Dinh Tri. "Etude expérimentale des actions hydrodynamiques sur une sphère en translation et rotation dans une gamme de nombres de Reynolds intermédiaires." Vandoeuvre-les-Nancy, INPL, 1992. http://docnum.univ-lorraine.fr/public/INPL_T_1992_BUI_DINH_T.pdf.

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On étudie expérimentalement, par une méthode de trajectographie stroboscopique, les actions exercées par un fluide visqueux incompressible sur une sphère en mouvement de translation et rotation simultanées. Le domaine exploré est celui des nombres de Reynolds compris approximativement entre 10 et 100, qui sont ceux que l'on rencontre fréquemment dans le calcul de trajectoires de particules solides en suspension dans un fluide. Les résultats, qui portent essentiellement sur le coefficient de portance, sont tout à fait originaux et contribuent aux connaissances existantes en les complétant par un apport dans une gamme de nombres de Reynolds jusqu'a présent inexplorée. Une corrélation empirique pour le coefficient de portance est finalement proposée

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17

Gonzalez, Gabriel. "Electron transport in single molecule magnet transistors and optical [lambda] transitions in the ¹⁵N-V⁻ center in diamond." Orlando, Fla. : University of Central Florida, 2009. http://purl.fcla.edu/fcla/etd/CFE0002740.

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18

Lincoln, Derek M. "The electronic structure and field effects of an organic-based room temperature magnetic semiconductor." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1193833038.

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19

Lipfert, Tobias. "Ordering effects in quantum optics." Thesis, Lille 1, 2019. http://www.theses.fr/2019LIL1R007/document.

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En optique quantique, la nature quantique de la lumière se manifeste dans des effets d’ordonnement d’opérateurs, inexistants en optique classique. Cette thèse est consacrée à une étude détaillée de ce type d’effets d’ordonnement dus à la dynamique des systèmes physiques. Nous considérons deux systèmes en particulier, 1) la conversion paramétrique descendante dans un milieu χ (2), et 2) un ion dans un piège de Paul entraı̂né par un champ classique; décrit par un modèle de Jaynes-Cummings non linéaire. Les effets d’ordonnement dans ces systèmes dynamiques sont étudiés via le développement et l’approximation de Magnus. Dans le scénario de conversion paramétrique descendante, nous considérons deux cas, (i) une pompe monochromatique (où une solution exacte de la dynamique est connue) et (ii) une pompe spectralement large. Pour la pompe monochromatique, nous écrivons explicitement la décomposition de Bloch-Messiah et obtenons les modes propres et les paramètres de compression. Nous comparons ces résultats exacts avec les approximations de Magnus en incluant certains ou aucun effets d’ordonnement. Nous effectuons une analyse similaire pour la pompe spectralement large lorsque la décomposition de Bloch-Messiah ne peut être évaluée que numériquement. Pour le modèle dynamique de Jaynes-Cummings non linéaire, nous analysons, à nouveau, les effets d’ordonnement via des approximations de Magnus et obtenons la solution exacte, qui n’avait pas été publiée dans la littérature auparavant. Enfin, nous évaluons pour la première fois les limites supérieures exactes (qui dépassent les limites suffisantes) de la convergence du développement de Magnus pour les deux modèles dynamiques à solutions exactes
In quantum optics, the quantum nature of light manifests itself in operator ordering effects, nonexistent in classical optics. This thesis is devoted to a detailed study of such ordering effects that are due to the dynamics of physical systems. We consider two systems in particular, 1) parametric down-conversion in a χ(2) medium, and 2) an ion in a Paul trap driven by a classical field; described by a nonlinear Jaynes-Cummings model. Ordering effects in these dynamical systems are studied via the Magnus expansion and approximation. In the parametric down-conversion scenario we consider two cases, (i) a monochromatic pump (where an exact solution of the dynamics is known), and (ii) a spectrally broad pump. For the monochromatic pump, we write explicitly the Bloch-Messiah decomposition and obtain the squeezing eigenmodes and parameters. We compare these exact results with the Magnus approximations that contain some or no ordering effects. We perform similar analysis for the spectrally broad pump, where the Bloch-Messiah decomposition can only be evaluated numerically. For the dynamics in the nonlinear Jaynes-Cummings model we again analyze ordering effects via Magnus approximations and obtain the exact solution, which has not been published in the literature before. Lastly, we evaluate the exact upper bounds (which exceed sufficient bounds) of convergence of the Magnus expansion for the two models with exact solutions, for the first time

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20

Ohm, Thorsten. "Effet tunnel quantique de l'aimantation dans un aimant moleculaire, Fe8." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10187.

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Nous avons étudié les retournements d'aimantation par effet tunnel quantique dans des aimants moléculaires. Nos expériences montrent clairement l'effet tunnel quantique dans l'aimant moléculaire Fe8. Ce système se compose d'un ensemble d'aimants nanoscopiques identiques et orientes parallèlement. Chacune des molécules porte un spin s = 10. Les mesures de relaxation sont faites en utilisant des magnétomètres à squid aux performances uniques. Ces magnétomètres permettent des mesures de haute sensibilité en champ fort, jusqu'a 8 tesla, et aux très basses températures (>50 mK). A haute température le système Fe8 se comporte comme un système superparamagnetique qui relaxe par activation thermique au-dessus d'une barrière de 24 K. Au-dessous de 0,4 K la relaxation est indépendante de la température ce qui est le signe d'un effet tunnel quantique du spin moléculaire à travers la barrière. Le temps de relaxation varie fortement avec le champ externe et montre des effets résonants. Dans le régime quantique la courbe de relaxation est non-exponentielle et bien décrite par une exponentielle étirée. Le début de la courbe de relaxation suit une loi en racine carrée du temps. Nous montrons que le champ dipolaire entre les molécules a une forte influence sur la relaxation mais le champ dipolaire n'agit pas comme une force : il permet ou empêche l'effet tunnel quantique dans une molécule. Nous présentons un modelé phénoménologique simple qui explique pourquoi la courbe de relaxation ressemble à une exponentielle étirée. Dans ce modèle nous supposons que chaque molécule a une résonance très étroite et que la distribution du champ local évolue pendant la relaxation. De plus, nous présentons un calcul numérique sur l'évolution de la distribution du champ local. Un calcul de Monte-Carlo avec des distributions réalistes montre lui aussi l'existence de corrélations inhabituelles en accord qualitatif avec nos observations.

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DAMENTO, MICHAEL ANTHONY. "DETECTION OF MAGNETIZATION REVERSAL IN A NEODYMIUM-IRON-BORON MAGNET USING A HALL-EFFECT MICROPROBE." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183945.

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Magnetization processes in a sintered Nd-Fe-B permanent magnet (NEOMAX-35) were examined on a small scale using a Hall-effect microprobe with an active area 75 μm on a side. Probes were made by evaporating bismuth through a stencil mask onto glass slides. Experiments were performed by placing a probe onto the polished pole face of a Nd-Fe-B magnet and inserting the probe-magnet assembly into an electromagnet. Barkhausen steps, indicating rapid domain wall motion, were observed (superimposed upon the blank probe signal) in the demagnetization of a fully magnetized magnet. Magnetization traces for a thermally demagnetized Nd-Fe-B magnet did not exhibit measurable Barkhausen steps until a field of approximately 1.2 T was applied. The following observations were made for two thermally demagnetized samples which were cycled through minor hysteresis loops (maximum applied field of approximately 2 T): (1) virgin magnetization traces did not contain measurable Barkhausen steps, however all other forward and reverse magnetization traces did; (2) the initial reverse magnetization trace exhibited more and larger Barkhausen steps than subsequent traces; and (3) some Barkhausen steps were repeatable, that is, occurring at approximately the same field on each subsequent forward or reverse trace. Hall voltage signals were on the order of millivolts for probe currents of 10 mA.

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22

陳鴻釗 and Hung-chiu Kingsley Chan. "Cast keepers for dental magnets: effects of laboratory procedures." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B45007706.

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23

BharrathSingh, Kathy. "Prototypes and the perceptual magnet effect in the perception of vowels." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ57602.pdf.

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24

Parois, Pascal. "The effect of pressure on clusters, chains and single-molecule magnets." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/1789/.

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This research deals with the investigation of the correlation between the structures of molecules and their magnetic properties as a function of pressure. To do so, different kinds of molecules have been chosen from single-molecules magnets, chains to small molecules. The variety of molecules is necessary to find the best candidates for high pressure X-ray crystallography and high pressure magnetic measurements. Bonds lengths and angles have been successfully altered by using high pressure without the complicating issues of chemical modifications. These structural changes produced a significant effect on the magnetic properties. A tilting of the Jahn-Teller axis in [Mn12O12(O2CCH2tBu)16(H2O)4].MeNO2.CH2Cl2 has been observed both structurally and magnetically. Modification of π–π interactions from edge to edge interaction to offset π–π stacking in [Gd(PhCOO)3(DMF)]n or a conversion from a CH–π interaction to a π–π interaction in [N(PhCH2)(CH2CH3)3]2[Fe2OCl6] are also reported.

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25

Bharrathisingh, Kathy 1966 Carleton University Dissertation Psychology. "Prototypes and the perceptual magnet effect in the perception of vowels." Ottawa.:, 2000.

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26

Guerra, Gabriel Andrés Fonseca. "Study of the longitudinal spin Seebeck effect in hybrid structures with yttrium iron garnet and various metallic materials." Universidade Federal de Pernambuco, 2014. https://repositorio.ufpe.br/handle/123456789/12719.

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Submitted by Daniella Sodre (daniella.sodre@ufpe.br) on 2015-04-08T12:40:55Z No. of bitstreams: 2 DISSERTAÇÃO Gabriel Fonseca.pdf: 3837074 bytes, checksum: e2c9b20882785e374170658d648ee389 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5)
Made available in DSpace on 2015-04-08T12:40:55Z (GMT). No. of bitstreams: 2 DISSERTAÇÃO Gabriel Fonseca.pdf: 3837074 bytes, checksum: e2c9b20882785e374170658d648ee389 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2014-03-10
Conselho Nacional de Desenvolvimento Científi co e Tecnol ógico; Coordenação de Aperfeiçoamento de Pessoal de Ní vel Superior; Financiadora de Estudos e Projetos; Fundação de Amparo a Ciência e Tecnologia do Estado de Pernambuco.
In this master thesis we study experimentally the longitudinal spin Seebeck effect (LSSE) in bilayers made of a ferromagnetic insulator (FMI) and a metallic layer (M). We also present a theoretical model based on the spin current density ⃗ Js carried by a non-equilibrium magnon distribution, generated by a thermal gradient ∇T across the thickness of the FMI. When ⃗ Js reach the FMI/M interface it is pumped towards the M layer due to conservation of the angular momentum, so, the M layer is essential for the LSSE existence. Here the FMI consists of a Yttrium Iron Garnet (YIG) lm, grown over a Gadolinium Gallium Garnet (GGG) substrate. Different metallic materials were used as the M layer i.e. Pt and Ta that have normal behavior and Py that is a ferromagnetic metal (FMM). The experimental procedure consists of systematic measurements of the electric voltage VISHE, produced by ⃗ Js through the Inverse Spin Hall Effect (ISHE) in the normal metal or (FMM) layer. In YIG/Pt measurements were done in the temperature range from 20 to 300 K. The experimental data are tted to the proposed model for the LSSE and good agreement is obtained. The results shows that the Py and Ta can be used to detect the LSSE with the ISHE. The results of this master thesis have strong interest in the area of spin caloritronics helping to the development of the eld and to raise possibilities of new spintronic devices. ----- Nesta diserta ção e estudado experimentalmente o Efeito Seebeck de Spin Longi- tudinal (LSSE), em bicamadas formadas por um isolante ferromagn etico (FMI) e um lme metalico (M). Tamb em foi desenvolvido um modelo te orico baseado na den- sidade de corrente de spin ⃗ Js que existe quando uma distribui c~ao de m agnons fora do equil brio e gerada por um gradiente t ermico ∇T aplicado na sec ção transversal do FMI. Quando ⃗ Js chega na interface FMI/M e bombeada para a camada M satis- fazendo a conserva ção do momentum angular, assim que a camada NM e essencial para ter um LSSE. Como camada FMI foi utilizada a granada de trio e ferro (YIG) crescida num substrato de (GGG). Diferentes materiais metalicos foram utilizados como camada M, sendo Pt e Ta paramagn eticos e o Py ferromagnetico. O proced- imento experimental consiste na medi c~ao sistem atica da voltagem el etrica VISHE, que e produzida por ⃗ Js por meio do efeito Hall de spin inverso (ISHE) que ocorre na camada M. As medidas em YIG/Pt foram feitas numa faixa ampla de temperatura de 20 a 300 K. Os dados experimentais são fi tados com a teoria proposta para o LSSE encontrando-se boa concordância. Nossos resultados mostram que o Py e o Ta s~ao bons candidatos para detec ção do LSSE. Esta disserta ção e de grande interesse na area da caloritrônica de spin, ajudando no desenvolvimento deste campo e na concep ção de novos dispositivos tecnol ogicos baseados na spintrônica.

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27

Prescimone, Alessandro. "Effect of high-pressure on molecular magnetism." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/4619.

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The effect of pressure on a number of magnetically interesting compounds such as single-molecule magnets and dimeric copper and manganese molecules has been investigated to probe the validity of ambient magneto-structural correlations. The first chapter is an introduction to the equipment and methodologies that have been adopted to carry out the experimental high-pressure work. The second chapter reports the first combined high-pressure single crystal X-ray diffraction and high pressure magnetism study of four single-molecule magnets (SMMs). At 1.5 GPa the structures [Mn6O2(Et-sao)6(O2CPh(Me)2)2(EtOH)6] (1) – an SMM with a record effective anisotropy barrier of ~86 K – and [Mn6O2(Etsao) 6(O2C-naphth)2(EtOH)4(H2O)2] (2) both undergo significant structural distortions of their metallic skeletons which has a direct effect upon the observed magnetic response. Up to 1.5 GPa pressure the effect is to flatten the Mn-N-O-Mn torsion angles weakening the magnetic exchange between the metal centres. In both compounds one pairwise interaction switches from ferro- to antiferromagnetic, with the Jahn-Teller (JT) axes compressing (on average) and re-aligning differently with respect to the plane of the three metal centres. High pressure dc χMT plots display a gradual decrease in the low temperature peak value and slope, simulations showing a decrease in |J| with increasing pressure with a second antiferromagnetic J value required to simulate the data. The “ground states” change from S = 12 to S = 11 for 1 and to S = 10 for 2. Magnetisation data for both 1 and 2 suggest a small decrease in |D|, while out-of-phase (χM //) ac data show a large decrease in the effective energy barrier for magnetisation reversal. The third SMM is the complex [Mn3(Hcht)2(bpy)4](ClO4)3·Et2O·2MeCN (3·Et2O·2MeCN) that at 0.16 GPa loses all associated solvent in the crystal lattice, becoming 3. At higher pressures structural distortions occur changing the distances between the metal centres and the bridging oxygen atoms making |J| between the manganese ions weaker. No significant variations are observed in the JT axis of the only MnIII present in the structure. Highpressure dc χMT plots display a gradual decrease in the low temperature peak value and slope. Simulations show a decrease in J with increasing pressure although the ground state is preserved. Magnetisation data do not show any change in |D|. The fourth SMM, [(tacn)6Fe8O2(OH)12](ClO4)3.9Br4.1⋅6H2O, (4) is the largest inorganic compound ever studied at high-pressure. Up to 2.0 GPa the conformation of the complex remains largely unaffected, with the counter ions and water molecules moving around to accommodate a compression of the unit cell volume. High pressure magnetic susceptibility data collected up to 0.93 GPa confirm minimal changes in the intra-molecular exchange interactions. The third chapter focuses on three hydroxo-bridged CuII dimers: [Cu2(OH)2(H2O)2(tmen)2](ClO4)2 (5), [Cu2(OH)2(tben)2](ClO4)2 (6) and [Cu2(OH)2(bpy)2](BF4)2 (7) have been structurally determined up to 2.5, 0.9 and 4.7 GPa, respectively. 6 and 7 have never been reported before. Pressure imposes important distortions in the structures of all three complexes, particularly on the bond distances and angles between the metal centres and the bridging hydroxo groups. 5 undergoes a phase transition between 1.2 and 2.5 GPa caused by the loss of a coordinated water molecule. This leads to a loss of symmetry and dramatic changes in the molecular structure of the complex. The structural changes are manifested in different magnetic behaviours of the complexes as seen in dc susceptibility measurements up to ~0.9 GPa: J becomes less antiferromagnetic in 5 and 6 and more ferromagnetic in 7. The fourth chapter shows the compression of two oxo-bridged MnII/MnIII mixed valence dimers: [Mn2O2(bpy)4](ClO4)3⋅3CH3CN, (8) has been squeezed up to 2.0 GPa whilst [Mn2O2(bpy)4](PF6)3⋅2CH3CN⋅1H2O, (9) could be measured crystallographically up to 4.55 GPa. 9 has never been reported before, while 8 has been reported in a different crystallographic space group. The application of pressure imposes significant alterations in the structures of both complexes. In particular, in 8 the Mn-Mn separation is reduced by the contraction of some of the Mn-O bond distances, 9 shows essentially analogous behaviour: the Mn-Mn distance and nearly all the Mn-N bonds shrink significantly. The magnetic behaviour of the complexes has been measured up to 0.87 GPa for 8 and 0.84 GPa for 9, but neither display any significant differences with respect to their ambient data.

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28

Danielsson, Oskar. "Wave Energy Conversion : Linear Synchronous Permanent Magnet Generator." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7194.

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29

Xue, Shaoshen. "Investigation of iron losses in permanent magnet machines accounting for temperature effect." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/19064/.

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30

Samin, Adib J. Jr. "An analysis of neutron radiation effects on NdFeB permanent magnets." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1405899609.

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31

Maurand, Romain. "SQUID à nanotube de carbone : jonction Josephson à boîte quantique, jonction-Ä, effet Kondo et détection magnétique d'une molécule aimant." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00593729.

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La manipulation de la matière au niveau nanométrique a ouvert depuis une quinzaine d'années de nouveaux champs fondamentaux et applicatifs pour les scientifiques et les industriels. Dans ce nouveau paradigme, la nanoélectronique quantique se propose de fonder une nouvelle électronique basée sur les phénomènes quantiques de la matière et plus particulièrement sur la nature quantique des électrons. Ce projet de thèse s'articule autour d'un système électronique quantique hybride supraconducteur/nanotube de carbone (CNT) dénommé nano-SQUID. Ce dispositif présente une boucle supraconductrice contenant deux jonctions CNT en parallèle. Il couple de façon unique les propriétés d'un interféromètre supraconducteur SQUID avec celles de jonctions Josephson à boîte quantique moléculaire. A travers des expériences de transport réalisées, à des températures de quelques dizaines de milli-Kelvins, dans un cryostat à dilution inversé, nous avons étudié les interactions électroniques entre une boîte quantique nanotube et des électrodes supraconductrices. Nous nous sommes particulièrement focalisés sur l'influence de l'état de spin du nanotube sur le courant supraconducteur, qui peut, dans certaines conditions, conduire à la réalisation d'un jonction-. Par un contrôle électrostatique des paramètres microscopiques du dispositif nous avons ainsi pu définir un diagramme de phase expérimental des transitions 0- d'une jonction Josephson à boîte quantique. La dernière partie de cette thèse a porté sur l'utilisation du nano-SQUID comme magnétomètre. En effet, en couplant un aimant moléculaire au CNT composant le SQUID, il a été montré théoriquement qu'il est possible de détecter le retournement d'aimantation d'un spin unique. Nous avons ainsi couplé au nano-SQUID l'aimant moléculaire Double Decker Holmium et réalisé les premières mesures de détections magnétiques aux résultats prometteurs.

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32

Zhao, Zhidong. "Modeling Shape Effects in Nano Magnetic Materials With Web Based Micromagnetics." ScholarWorks@UNO, 2005. http://scholarworks.uno.edu/td/157.

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This research work focuses on the geometry and shape effects on submicron magnetic material. A web based micromagnetics program is written to model the hysteresis loop of nano magnetic samples with arbitrary geometry shapes and multiple magnetic materials. Three material samples have been modeled with this program along with nano magnets with a variety of geometric shapes. Shape anisotropy has been introduced to a permalloy ring by adding a cross-tie structure with various widths. The in-plane hysteresis loop and reversal behavior have no notable difference in direction parallel to the cross-tie, but greatly changed in perpendicular and diagonal directions. The switching field distribution is significantly reduced. The two distinct "onion" bit states of the modified ring elements are stabilized in the hysteresis in the diagonal direction. The changes in the modified rings make them better candidates for Magnetic Random Access Memory elements. Two Pac-Man elements, PM I and PM II, geometrically modified from disc and half disc respectively, are modeled. The PM I element undergoes a magnetic reversal through a two-stage mechanism that involves nucleation in the left and right middle areas followed by vortex core formation and vortex core motion in the lower middle area. The reversal process of the PM II element lacks the vortex core formation and motion stage. The switching field of the PM I and PM II elements are the same but the switching field distribution of the PM II elements is much narrower than that of the PM I element. Only the PM II element meets MRAM application requirements. The thickness dependence of the magnetic properties of a core-shell structure has been studied. The nano particles have a cobalt core and a permalloy shell. The nano spheres are the same size but with various shell thickness. Simulations reveal a multi-stage reversal process without the formation of a Bloch wall for thin-shell structure and smooth reversal process with the formation and motion of a Bloch wall for thick-shell structure. Gradual transition of the hysteresis loop patterns has been observed.

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33

Yu, Riqing. "Metal uptake, assimilation and stoichiometric effects in daphnia magna /." View Abstract or Full-Text, 2002. http://library.ust.hk/cgi/db/thesis.pl?BIOL%202002%20YUR.

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34

Shepherd, Marie Norfleet. "The Effects of a Middle School Magnet Program on Eighth Grade Student Performance." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30498.

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Magnet schools were developed in the early 1970s when a large number of urban school districts began seeking alternatives to court-ordered desegregation mandates (Levine and Steel, 1994). Since that time, numerous studies have been conducted on the effectiveness of magnet schools in providing a racially balanced learning environment as well as increasing academic achievement. The purpose of the causal-comparative study was to determine if the math and science magnet program at a middle school affected achievement, attendance, and parent perceptions. This study conducted three different analyses. A chi square analysis of the student population was conducted to determine racial balanced on attendance data from the school years 1993-94 through 1996-97, and if the racial balance of the magnet program mirrored that of the district. Three-way ANCOVA analyses, with a 2x2x2 factorial design were performed on attendance and the five components of the 1997 Stanford Achievement Test Form 9-TA results for the eighth grade population at the targeted middle school enrolled during the 1996-97 school year. Complete data for 177 eighth grade students was utilized. Attendance and achievement served as the dependent variables. The independent variables tested were group membership (magnet, non-magnet), gender (male, female), and race/ethnicity (black, white). Socio-economic status (SES) and Literacy Passport Test (LPT) scores served as the covariates in the study. A survey of school effectiveness was sent to a random sample of parents. A t-test was performed to determine if there was a statistically significant difference between the perceptions of parents of magnet students and parents of student not enrolled in the program on school effectiveness. The racial balance of the magnet program did not mirror that of the district. There was more of an equally distributed number of blacks and whites in the magnet program. Within the district, approximately 68% of the student enrollment was black, the white enrollment was approximately 31%. Magnet students achieved statistically significantly higher scores on each of the five components of the Stanford Achievement Test Form 9-TA than non-magnet students. Gender and race/ethnicity differences were statistically significant in science achievement in that male and white students achieved higher scores than female and black students. There was a statistically significant difference in attendance between magnet students and non-magnet students. Magnet students attended school more than non-magnet students. There was no significant difference in perceptions of parents of magnet and non-magnet students. Both groups felt that the school was very good. Implications for future avenues of research were also suggested.
Ed. D.

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Xu, Yan 1963 Jan 31. "Effect of quench rate on the coercivity of Nd-Fe-B permanent magnets." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=55669.

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Cheng, Yihong, Kai Chen, and Shufeng Zhang. "Giant magneto-spin-Seebeck effect and magnon transfer torques in insulating spin valves." AMER INST PHYSICS, 2018. http://hdl.handle.net/10150/627032.

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We theoretically study magnon transport in an insulating spin valve (ISV) made of an antiferromagnetic insulator sandwiched between two ferromagnetic insulator (FI) layers. In the conventional metal-based spin valve, the electron spins propagate between two metallic ferromagnetic layers, giving rise to giant magnetoresistance and spin transfer torque. Here, the incoherent magnons in the ISV serve as angular momentum carriers and are responsible for the angular momentum transport between two FI layers across the antiferromagnetic spacer. We predict two transport phenomena in the presence of the temperature gradient: a giant magneto-spin-Seebeck effect in which the output voltage signal is controlled by the relative orientation of the two FI layers and magnon transfer torque that can be used for switching the magnetization of the FI layers with a temperature gradient of the order of 0.1 Kelvin per nanometer. Published by AIP Publishing.

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37

Trijau, Marie. "Approche moléculaire et mécaniste de la réponse transgénérationnelle lors d'une irradiation gamma chronique chez le cladocère Daphnia magna." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0467/document.

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Afin de protéger durablement les écosystèmes face aux rejets planifiés ou accidentels de radionucléides dans l’environnement, il est essentiel d’évaluer l’impact de l’exposition des organismes aux radiations ionisantes sur le long terme, à l’échelle de plusieurs générations. Dans ce contexte, ce travail de doctorat vise à améliorer la caractérisation des processus moléculaires et la prédiction des effets transgénérationnels lors d’une exposition aux radiations gamma. Une approche expérimentale concerne l’étude des modifications épigénétiques radio-induites, c’est-à-dire des modifications des mécanismes régulant l’activité des gènes sans modification de la séquence d’ADN elle-même et de leur transmission au fil des générations. Cette étude a permis de mettre en évidence que certaines modifications de la méthylation de l’ADN, l’un des mécanismes épigénétiques les plus étudiés, peuvent être transmises par la lignée germinale aux les générations non-exposées (génération F3) suite à une exposition parentale (génération F0) externe aux radiations gamma (6,5 µGy.h-1 et 41,3 mGy.h-1) pendant 25 jours. Dans une seconde approche, un modèle mécaniste DEBtox (Budget Energétique Dynamique appliqué à la toxicologie) est modifié pour permettre l’analyse des effets des radiations gamma sur la croissance et la reproduction de D. magna à l’échelle de plusieurs générations. Pour ce faire, on utilise des compartiments de dommage, dont le niveau peut être hérité d’une génération à la suivante. Le modèle est ajusté aux données avec des méthodes d’inférence bayésienne afin d’estimer les paramètres tout en tenant compte des incertitudes qui leur sont associées
In order to durably protect ecosystems facing planned or accidental releases of radionuclides, the long-term impact of organism exposure to ionizing radiation must be studied on a multigenerational scale. The aim of this PhD is to improve the characterization of molecular processes and the prediction of transgenerational effects during a gamma irradiation. First, an experimental approach investigated on radio-induced modifications of epigenetic processes, i.e. changes in mechanisms that regulate gene expression without changing DNA sequence itself and on the transmission of these modifications to subsequent generations. Significant changes in DNA methylation, a well-studied epigenetic mechanism, detected in generation F3 clearly showed that epigenetic modifications could be transmitted to unexposed generations, in response to the exposure of a parental generation (F0) to external gamma radiation (6.5 µGy.h-1 et 41.3 mGy.h-1) for 25 days. Second, a mechanistic modelling approach used a modified version of the DEBtox model (Dynamic Energy Budget model applied to toxicology) in order to analyze effects of gamma radiation on D. magna growth and reproduction over several generations. To that end, damage compartments, with damage levels that were transmitted from one generation to the next, were included. The model was fitted to data using Bayesian inference methods, in order to estimate the parameters while considering their associated uncertainty

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38

Bingham, Nicholas Steven. "Magnetism in Complex Oxides Probed by Magnetocaloric Effect and Transverse Susceptibility." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4440.

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Magnetic oxides exhibit rich complexity in their fundamental physical properties determined by the intricate interplay between structural, electronic and magnetic degrees of freedom. The common themes that are often present in these systems are the phase coexistence, strong magnetostructural coupling, and possible spin frustration induced by lattice geometry. While a complete understanding of the ground state magnetic properties and cooperative phenomena in this class of compounds is key to manipulating their functionality for applications, it remains among the most challenging problems facing condensed-matter physics today. To address these outstanding issues, it is essential to employ experimental methods that allow for detailed investigations of the temperature and magnetic field response of the different phases. In this PhD dissertation, I will demonstrate the relatively unconventional experimental methods of magnetocaloric effect (MCE) and radio-frequency transverse susceptibility (TS) as powerful probes of multiple magnetic transitions, glassy phenomena, and ground state magnetic properties in a large class of complex magnetic oxides, including La0.7Ca0.3-xSrxMnO3 (x = 0, 0.05, 0.1, 0.2 and 0.25), Pr0.5Sr0.5MnO3, Pr1-xSrxCoO3 (x = 0.3, 0.35, 0.4 and 0.5), La5/8−xPrxCa3/8MnO3 (x = 0.275 and 0.375), and Ca3Co2O6. First, the influences of strain and grain boundaries, via chemical substitution and reduced dimensionality, were studied via MCE in La0.7Ca0.3-xSrxMnO3. Polycrystalline, single crystalline, and thin-film La0.7Ca0.3-xSrxMnO3 samples show a paramagnetic to ferromagnetic transition at a wide variety of temperatures as well as an observed change in the fundamental nature of the transition (i.e. first-order magnetic transition to second order magnetic transition) that is dependent on the chemical concentration and dimensionality. Systematic TS and MCE experiments on Pr0.5Sr0.5MnO3 and Pr0.5Sr0.5CoO3 have uncovered the different nature of low-temperature magnetic phases and demonstrate the importance of coupled structural/magnetocrystalline anisotropy in these half-doped perovskite systems. These findings point to the existence of a distinct class of phenomena in transition-metal oxide materials due to the unique interplay between structure and magnetic anisotropy, and provide evidence for the interplay of spin and orbital order as the origin of intrinsic phase separation in manganites. While Pr0.5Sr0.5MnO3 provides important insights into the influence of first- and second-order transitions on the MCE and refrigerant capacity (RC) in a single material, giving a good guidance on the development of magnetocaloric materials for active magnetic refrigeration, Pr1-xSrxCoO3 provides an excellent system for determining the structural entropy change and its contribution to the MCE in magnetocaloric materials. We have demonstrated that the structural entropy contributes significantly to the total entropy change and the structurally coupled magnetocrystalline anisotropy plays a crucial role in tailoring the magnetocaloric properties for active magnetic refrigeration technology. In the case of La5/8−xPrxCa3/8MnO3, whose bulk form is comprised of micron-sized regions of ferromagnetic (FM), paramagnetic (PM), and charge-ordered (CO) phases, TS and MCE experiments have evidenced the dominance of low-temperature FM and high-temperature CO phases. The "dynamic" strain liquid state is strongly dependent on magnetic field, while the "frozen" strain-glass state is almost magnetic field independent. The sharp changes in the magnetization, electrical resistivity, and magnetic entropy just below the Curie temperature occur via the growth of FM domains already present in the material, even in zero magnetic field. The subtle balance of coexisting phases and kinetic arrest are also probed by MCE and TS experiments, leading to a new and more comprehensive magnetic phase diagram. A geometrically frustrated spin chain compound Ca3Co2O6 provides an interesting case study for understanding the cooperative phenomena of low-dimensional magnetism and topological magnetic frustration in a single material. Our MCE studies have yielded new insights into the nature of switching between multi-states and competing interactions within spin chains and between them, leading to a more comprehensive magnetic phase diagram.

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39

Sorbom, Brandon Nils. "The effect of irradiation temperature on REBCO Jc degradation and implications for fusion magnets." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/120392.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 143-154).
Recent advances in high temperature superconductors (HTS) have opened up a new parameter space for the design of tokamak fusion pilot plants. While previously the maximum on-axis field in a superconducting tokamak was limited to ~6 T, HTS allows tokamaks to be designed with much higher on-axis fields, leading to smaller reactor designs. For these designs, it is critical to determine the lifetime of modern HTS technology in an environment relevant to compact, high-field fusion reactors as well as develop strategies to mitigate this damage. While some studies have been undertaken to assess the lifetime of coated conductors in a fast neutron environment, facilities do not exist to perform cryogenic neutron irradiations at the present. In addition, reactor studies are costly and activate the samples, requiring long cooldown times and specialized analysis facilities to handle radioactive material. In order to complement reactor irradiation studies of HTS and determine whether elevated temperature irradiation has an effect on Jc degradation, REBCO coated conductors were irradiated with a 1.2 MeV proton beam at 80 K, 323 K, and 423 K. Proton irradiation at cryogenic temperatures was found to substantially reduce the amount of Jc degradation in the REBCO samples irradiated to high fluences, a result of great importance to superconducting REBCO magnets in fusion applications where the radiation will occur at T < 80 K. An analysis of temperature, field, and angle dependencies of Jc was performed to investigate the microstructural mechanisms behind the Jc degradation at different temperatures. The key mechanism driving the differences in Jc degradation was found to be radiation-enhanced diffusion at higher temperatures, leading to grain boundary widening between superconducting crystals which in turn blocked supercurrent transport through the conductor. Molecular dynamics simulations suggest that the same mechanism (enhanced diffusion to grain boundaries) also applies to neutron irradiations. This motivates a re-evaluation of previous REBCO neutron irradiation studies at temperatures between 323 K and 383 K, specifically with regards to predictions about REBCO lifetimes in a fusion environment. The work in this thesis suggests that at cryogenic temperatures, the Jc degradation observed in these studies could be substantially less than previously reported.
by Brandon Nils Sorbom
Ph. D.

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40

Parisot, Florian. "Étude mécaniste des effets transgénérationnels des radiations ionisantes alpha et gamma chez Daphnia magna." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4104/document.

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Les activités anthropiques liées à l'industrie nucléaire contribuent à des rejets continus de radionucléides dans les écosystèmes terrestres et aquatiques. Les travaux réalisés au cours de ce doctorat visent à apporter de nouvelles connaissances relatives aux effets des radiations ionisantes au cours d’une exposition multigénérationnelle de l’invertébré aquatique, Daphnia magna. Une irradiation gamma externe à des débits de doses pertinents du point de vue environnemental a été réalisée sur D. magna pendant trois générations successives. Les résultats mettent en évidence une accumulation et une transmission d’altérations de l’ADN au fil des générations, en parallèle d’une augmentation de la sensibilité des daphnies. Les données d’irradiation gamma et celles d’une étude antérieure de contamination alpha ont été analysées à l’aide du modèle mathématique DEBtox. Le modèle montre que les deux types de rayonnements agissent différemment sur les daphnies au cours des générations. Ce projet de recherche indique clairement qu’à l’avenir il est important d’étudier et de comprendre les effets transgénérationnels des radiations ionisantes à faibles doses
Anthropogenic activities related to the nuclear industry contribute to continuous discharges of radionuclides into terrestrial and aquatic ecosystems. The aim of this PhD was to bring new knowledge on the effects of ionizing radiation during a multigenerational expose of the aquatic invertebrate, Daphnia magna. An external gamma radiation at environmentally relevant dose rates was performed on D. magna over three successive generations. Results show an accumulation and a transmission of DNA alterations over generations, in parallel of an increase in sensitivity of organisms. Gamma radiation data and those of a previous study of alpha contamination were analyzed using the mathematical model DEBtox. The model shows that the two types of radiation act differently on daphnia over generations. This research clearly indicates the importance of further studying and understanding transgenerational effects induced by low doses radiation in the future

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41

Wu, Lijian. "Analytical modelling of electromagnetic performance and parasitic effects of permanent magnet machines." Thesis, University of Sheffield, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.647997.

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42

Kieffer, Christophe. "Conception optimale d’un système de refroidissement magnétocalorique à actionneur intégré : Application à la climatisation automobile." Thesis, Besançon, 2012. http://www.theses.fr/2012BESA2035/document.

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La technologie de la réfrigération magnétique présentée dans ce manuscrit constitue une alternative prometteuse à la technologie de production de froid. Le travail effectué a porté tout d’abord sur une étude de la production de froid magnétique et un état de l’art de cette technologie émergente. Nous nous sommes fixés pour objectif de dimensionner et réaliser un réfrigérateur magnétique qui se présente sous la forme d’un actionneur intégré. Le dimensionnement a été réalisé par le biais d’un modèle à éléments finis. Il s’agit d’un dispositif présentant deux entrefers, dont un suffisamment large pour pouvoir accueillir un régénérateur magnétocalorique au sein duquel la valeur de l’induction est la plus élevée possible tout en offrant un profil d’induction de forme trapézoïdale. La réalisation du démonstrateur sur la base des étudeseffectuées par éléments finis constitue la première étape vers la réalisation d’un réfrigérateur magnétique intégré pouvant être logé dans une automobile. Pour finir, et afin d’améliorer encore les performances de notre dispositif, une optimisation de l’inducteur électromagnétique a été effectuée par le biais d’un modèle à éléments finis couplé à un algorithme d’optimisation
The magnetic refrigeration technology is a promising alternative technology to the production of cold. The work carried out focuses on the technology of magnetic refrigeration, a state of the art of this emerging technology has also been done. A magnetocaloric regenerator is placed in the air gap of the motor. It is necessary to design a motor with an air gap wide enough and where the induction will be as high as possible in order to insert the magnetocaloric regenerator. The regenerator is a hollow cylinder whose dimensions are adapted to the air gap of the synchronous machine. It is intended to contain the magnetocaloric material. The design of the electric motor is made in order to obtain a maximal variation of induction ΔB in the air gap and a temperature difference ΔT as large as possible, improving the magnetocaloric performance of the prototype. The profile of induction should also be as close as possible to a rectangular signal. The realization of the demonstrator based on the finite element studies is the first step towards the realization of integrated magnetic refrigerator which can be housed in an automobile. Finally, and in order to improve the performance of our device, an optimization of the electromagnetic inductor was carried out with a finite element model coupled to an optimizationalgorithm

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43

Coulson, I. M. "The effect of temperature on the properties of permanent magnet alloys of the NdFeBCo system." Thesis, University of Sunderland, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380706.

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44

Meier, Lori T. "The Effect of School Culture on Science Education at an Ideologically Innovative Elementary Magnet School." Digital Commons @ East Tennessee State University, 2010. https://dc.etsu.edu/etsu-works/5915.

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This ethnographic case study investigated how school culture influenced teachers curriculum design and science instruction at an elementary magnet school with an espoused innovative ideology. Data was analyzed using a theoretical framework that emphasizes five interdependent school culture indicators. Findings suggest that the schools culture hinders the effective teaching of science. Despite high levels of perceived efficacy from teachers and administrators, as well as generous lab space and materials to teach science, it was infrequently taught. Given a wide berth to plan their individual curriculums that aligned with distinct magnet philosophies, teachers regularly relied on innovative-looking science explorations as a substitute or inherently accepted the science amnesty provided by the curriculum and organization of the school.

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45

Wayman, Matthew C. "The Transfer of Volatiles Within Interacting Magmas and its Effect on the Magma Mingling Process." Kent State University Honors College / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ksuhonors1312924338.

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46

Mccaskey, Alexander Joseph. "Effects of Electron-Vibron Coupling in Single-Molecule Magnet Transport Junctions Using a Hybrid Density Functional Theory and Model Hamiltonian Approach." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/48026.

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Recent experiments have shown that junctions consisting of individual single-molecule magnets (SMMs) bridged between two electrodes can be fabricated in three-terminal devices, and that the characteristic magnetic anisotropy of the SMMs can be affected by electrons tunneling through the molecule. Vibrational modes of the SMM can couple to electronic charge and spin degrees of freedom, and this coupling also influences the magnetic and transport properties of the SMM. The effect of electron-vibron coupling on transport has been extensively studied in small molecules, but not yet for junctions of SMMs. The goals of this thesis will be two-fold: to present a novel approach for studying the effects of this electron-vibron coupling on transport through SMMs that utilizes both density functional theory calculations and model Hamiltonian construction and analysis, and to present a software framework based on this hybrid approach for the simulation of transport across user-defined SMMs. The results of these simulations will indicate a characteristic suppression of the current at low energies that is strongly dependent on the overall electron-vibron coupling strength and number of molecular vibrational modes considered.
Master of Science

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47

Bourgeois, Jacob. "Modeling effects of adding a flux channel to a planar magnet-coil actuator." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32875.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.
Includes bibliographical references (p. 38).
Planar magnet-coil actuators are used in many different MEMS devices. This report describes one way to improve the actuator range per current input of planar coil actuators. This is accomplished by adding a flux channel around and beneath the actuator's magnet. The Lorentz force is created by putting a current carrying planar coil over a magnet in an actuator assembly. The Lorentz force depends on the current vector and the magnetic field vector. In this thesis the Lorentz force is altered by changing the direction and concentration of the magnetic field. Magnetic fields may be modeled as flux lines traveling from the north face of the magnet to the south face along the least resistant path. Iron is a magnetic material with 4000 times the magnetic permeability of air, so when iron is placed in a magnetic field, the majority of the magnetic flux will travel from North to South through the iron. This "channel" alters the way the magnetic field would normally travel given the bare magnet. The magnetic flux that travels through the channel depends in part upon the channel geometry. The result of varying the width of this channel is modeled and tested in this work. The physical principle was examined in simulations by varying channel width and then extracting the corresponding actuator output. A relationship was fit to the simulated results.
(cont.) The actuator output augmentation was maximized at a critical width and remained steady thereafter. Beyond the critical width, the addition of the flux channel was able to produce more than 45% increase in the actuator force. Experimental results showed less than a 5% difference from the simulated results.
by Jacob Bourgeois.
S.B.

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48

Constantino, Carlos. "The effect of sewage effluent on trace metal speciation : implications for the biotic ligand model approach." Thesis, Brunel University, 2013. http://bura.brunel.ac.uk/handle/2438/7442.

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This research examined the suitability of the biotic ligand model (BLM) approach for assessing environmental risk in surface waters consisting substantially of treated sewage effluent, and the implications of its use within a compliance-based regulatory framework aimed at controlling discharges of metals into the aquatic environment. The results from a series of Daphnia magna acute copper toxicity assays conducted in an undiluted sewage effluent medium demonstrated that BLMs could predict an acute copper toxicity endpoint with suitable accuracy. This finding contributes further support for the use of BLMs for assessing risk and compliance, even in effluent impacted waters. Additional studies, however, also demonstrated that effluent derived organic matter contained a greater concentration of metal complexing ligands per milligram of dissolved organic carbon than organic matter derived from natural sources. This indicates that effluent derived organic matter offers greater protection against the potentially adverse effects from metals than the protection offered by organic matter derived from natural sources. These studies also demonstrated that improvements in the accuracy of BLM forecasts were achievable by taking these differences into account which, from a regulatory perspective, is also desirable since this enhances the environmental relevance of compliance criteria. These findings therefore justify that consideration for the influence of site-specific metal complexation characteristics should included as part of the regulatory framework within which BLMs will be applied. The implication of the BLM approach for Severn Trent Water Limited is that, as currently proposed, the approach will require a reduction in the concentration of copper in the effluent discharges for a small number of wastewater treatment works (9), whereas for zinc, concentration reductions may be required for numerous treatment works (126).

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Romero, Javier. "Electronic transport and correlations in single magnetic molecule devices." Doctoral diss., University of Central Florida, 2014. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6348.

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In this dissertation, we study the most important microscopic aspects that grant molecules such as Single Molecule Magnets (SMMs) their preferential spin direction. We do so by proposing and solving a model that includes correlations between electrons occupying atomic orbitals. In addition, we study the relation between the non-equilibrium electronic transport signatures in a SMM model weakly coupled to a three-terminal single electron transistor device, and the interference features of the SMM model in the presence of a magnetic field. Finally, we investigate the equilibrium transport features in a giant-spin model of a SMM in the Kondo regime. We study how the magnetic field modulation of the energy in a highly anisotropic molecule can affect the conductance of the molecule in the Kondo regime.
Ph.D.
Doctorate
Physics
Sciences
Physics

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50

Watzman, Sarah June. "Thermal Energy Conversion Utilizing Magnetization Dynamics and Two-Carrier Effects." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1523621461827864.

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Dissertations / Theses on the topic 'Magnus effect'

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