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1
Stechow, Adrian von [Verfasser]. "Current sheet dynamics during driven magnetic reconnection / Adrian von Stechow". Greifswald : Universitätsbibliothek Greifswald, 2015. http://d-nb.info/1073164306/34.
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2
Su, Ruitao. "Multi-Field Physics for the Synthesis of Carbon Nanotube Yarn and Sheet". University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439310862.
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Wilson, Fiona. "Equilibrium and stability properties of collisionless current sheet models". Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3548.
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The work in this thesis focuses primarily on equilibrium and stability properties of collisionless current sheet models, in particular of the force-free Harris sheet model. A detailed investigation is carried out into the properties of the distribution function found by Harrison and Neukirch (Physical Review Letters 102, 135003, 2009) for the force-free Harris sheet, which is so far the only known nonlinear force-free Vlasov-Maxwell equilibrium. Exact conditions on the parameters of the distribution function are found, which show when it can be single or multi-peaked in two of the velocity space directions. This is important because it may have implications for the stability of the equilibrium. One major aim of this thesis is to find new force-free equilibrium distribution functions. By using a new method which is different from that of Harrison and Neukirch, it is possible to find a complete family of distribution functions for the force-free Harris sheet, which includes the Harrison and Neukirch distribution function (Physical Review Letters 102, 135003, 2009). Each member of this family has a different dependence on the particle energy, although the dependence on the canonical momenta remains the same. Three detailed analytical examples are presented. Other possibilities for finding further collisionless force-free equilibrium distribution functions have been explored, but were unsuccessful. The first linear stability analysis of the Harrison and Neukirch equilibrium distribution function is then carried out, concentrating on macroscopic instabilities, and considering two-dimensional perturbations only. The analysis is based on the technique of integration over unperturbed orbits. Similarly to the Harris sheet case (Nuovo Cimento, 23:115, 1962), this is only possible by using approximations to the exact orbits, which are unknown. Furthermore, the approximations for the Harris sheet case cannot be used for the force-free Harris sheet, and so new techniques have to be developed in order to make analytical progress. Full analytical expressions for the perturbed current density are derived but, for the sake of simplicity, only the long wavelength limit is investigated. The dependence of the stability on various equilibrium parameters is investigated.
4
Akcaoglu, Fehmi Umit. "Investigating The Effect Of Deformation And Annealing Texture On Magnetic Anisotropy In Low-c Steel Sheets By Magnetic Barkhausen Noise Method". Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615569/index.pdf.
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Deformation and annealing texture in the cold rolled low carbon steels is important for sheet metal forming operations and service performance. The aim of this study is to non-destructively investigate the effect of texture on magnetic anisotropy. Various samples having different textures and residual stress states, due to different % reduction in thickness, annealing and stress relieving treatment, were prepared. Texture maps were obtained by Magnetic Barkhausen noise measurements performed with 100 steps between the ranges of 00-3600 on the surface. Microstructure investigation by optical &scanning electron microscopy
hardness and tension tests were performed
and texture was determined by X-Ray diffraction method. The results were compared, evaluated and discussed to establish relationship between texture and magnetic Barkhausen Noise emission.
5
Matsui, Tatsuki. "Kinetic theory and simulation of collisionless tearing in bifurcated current sheets". Diss., University of Iowa, 2008. http://ir.uiowa.edu/etd/38.
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Souza, Pedro Victor Brondino Duarte de. "Desenvolvimento de um subsistema non-real-time para o gerenciamento de dispositivos periféricos e desenvolvimento de interfaces gráficas". Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-21102016-140615/.
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Ressonância Magnética (RM) é uma técnica bastante versátil, pois é utilizada em muitas áreas de pesquisa, como biologia, física, química, engenharia e medicina. Apesar disso, constitui-se uma desvantagem o alto custo do equipamento e suas restrições físicas para alguns experimentos. Para reduzir essas desvantagens, o grupo de pesquisadores do CIERMag está desenvolvendo um equipamento de RMN multipropósito e, para complementá-lo, este trabalho vem desenvolver um subsistema non-real-time que gerencia os dispositivos periféricos de um experimento. Foi proposta uma rede de dispositivos que é controlada por um Raspberry Pi como elemento central, o qual está conectado ao terminal computadorizado do sistema através de uma rede local (Local Area Network - LAN) via Ethernet e conectado aos dispositivos periféricos via Serial Peripheral Interface (SPI). Com o objetivo de ser possível gerenciar qualquer tipo de dispositivo, foi desenvolvido um conjunto de parâmetros baseado no Transducer Electronic Data Sheet (TEDS), definido no padrão IEEE 1451, de modo que cada dispositivo, normalmente um transdutor, possui seu próprio. Foram elaboradas duas interfaces de software: uma desenvolvida em Python e a outra uma interface web HTML. Ambas as interfaces possuem as mesmas funcionalidades: editor e gerenciador de TEDS, visualização gráfica de medidas dos sensores e interface para os atuadores.Magnetic Resonance (MR) is a very versatile technique, since it is used in many research areas such as biology, physics, chemistry, engineering and medicine. Despite this, the cost of the equipment and its physical restrictions in some experiments constitute a serious drawback. To minimize these problems, the CIERMag research team is developing multipurpose MR equipment and, to complement this equipment, this work develops a non-real-time subsystem that manages the peripheral devices of the experiment. It was proposed a network of devices controlled by a Raspberry Pi as its central element, which is connected to the terminal computer of the system. The protocol adopted for this was Ethernet via Local Area Network (LAN); communication with peripheral transducers was performed with the Serial Peripheral Interface (SPI). With the objective to be able to manage any type of device, we created parameter sets based on Transducer Electronic Data Sheet (TEDS), defined in the IEEE 1451 standard, so each device, normally a transducer, has its own parameter set. We created two software interfaces: one developed with Python and the other is a HTML web interface. Both have the same functionalities: a TEDS editor and manager, a graphical visualization of sensor measurements and also an actuator interface.
7
Kamal, Manish. "A uniform pressure electromagnetic actuator for forming flat sheets". Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1127230699.
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Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xxi, 261 p.; also includes graphics (some col.). Includes bibliographical references (p. 244-254). Available online via OhioLINK's ETD Center
8
Talowski, Catherine. "Contribution à l'amélioration des tôles magnétiques non orientées utilisées en électrotechnique". Grenoble INPG, 1996. http://www.theses.fr/1996INPG0105.
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Actuellement, la principale voie d'amélioration des performances des aciers magnétiques utilisées dans les machines tournantes est l'obtention d'une texture préférentielle type "cubique" {100}<001> ou planaire {100}<0vw>. De plus, pour l'ensemble des tôles magnétiques, le laminage à chaud est une étape incontournable du procédé. Or il a été montré antérieurement que des microstructures de laminé à chaud non recristallisées et fortement déformées hétérogènement coïncidaient avec l'émergence d'une texture finale prononcée et une sensible amélioration des performances magnétiques. Nous avons examiné en laboratoire les possibilités d'obtention de textures {100} par laminage à chaud pour des alliages Fe Si et Fe Si Al d'au moins 0, 1 mm d'épaisseur. L'étude de l'importance des différents recuits et laminage à froid du procédé nous ont permis de préciser la part de divers phénomènes (taux de réduction globale, hétérogénéité du laminage à chaud, teneur en aluminium, microstructure initiale) dans l'accroissement des performances. Enfin, la croissance anormale de germes favorablement orientés a été envisagée pour les alliages Fe Si par l'intermédiaire d'inhibiteur AIN et est une voie de progrès pour le futur. Pour des applications à plus hautes fréquences (supérieure à 50 Hz) l'épaisseur des tôles doit être inférieure à 100 microns pour limiter les courants induits. Partant de travaux anciens, des tôles minces en texture "cubique" ont été obtenues par simple ou double laminage à froid de tôles G. O. Commerciale associés à une croissance anormale contrôlée par différence d'énergie de surface. Nous montrons en particulier l'importance de l'état de recristallisation primaire comme point de départ de la croissance anormale et son influence sur la qualité de la texture finale obtenue sur les performances magnétiques
9
純士, 北尾, i Junji Kitao. "ヒステリシス特性を考慮した有限要素磁界解析の実用化に関する研究". Thesis, https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB13044990/?lang=0, 2017. https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB13044990/?lang=0.
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本論文では，鉄損算出精度向上を目的としたプレイモデルによるヒステリシス特性を考慮した磁界解析の実用化に向けて，ヒステリシスモデルのモデリング精度向上，計算機の記憶容量低減，有限要素磁界解析の計算時間削減に関する手法を提案した．さらに，ヒステリシス特性の考慮の有無が解析結果に与える影響を検討し，提案したヒステリシス特性を考慮した有限要素磁界解析の実用性を明らかにした．In order to achieve the highly accurate analysis of an iron loss for electric machines, this paper proposes finite element magnetic field analyses taking account of the hysteretic property by using the play model. As a consequence, it is verified that the proposed method can accurately estimate an iron loss of a magnetic materials and decrease computational costs. Furthermore, this paper investigates the influence of the hysteretic property in finite element magnetic field analyses to demonstrate its effectiveness.
博士(工学)
Doctor of Philosophy in Engineering
同志社大学
Doshisha University
10
Pera, Thierry. "Lois d'aimantation anisotropes et non linéaires : modélisation et validation expérimentale". Grenoble INPG, 1994. http://www.theses.fr/1994INPG0038.
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Le but de notre étude est de prendre en compte le comportement bidimensionnel non linéaire et anisotrope des tôles magnétiques, utilisées en génie électrique, afin de pouvoir effectuer une modélisation par éléments finis aussi réaliste que possible. Nous avons développé un modèle original de loi de comportement de tôles magnétiques (à grains orientés, à grains non orientés, à texture cubique) fondé sur l'équivalence entre la relation vectorielle B(H) et une représentation magnétique 11. Les données expérimentales nécessaires sont les courbes B(H) suivant la direction de laminage (axe x) et striant la direction travers qui lui est orthogonale (axe y). Le comportement magnétique des tôles est pris en compte par une représentation adéquate des lignes isovaleurs de coénergie dans le plan HxHy. La relation B(H) est ensuite restituée à partir de la densité de coénergie. Une vérification expérimentale du modèle a été effectuée grâce à un cadre en champs tournants. Nous avons implanté le modèle dans un logiciel éléments finis avec une formulation en potentiel scalaire. Des exemples d'application ont été traités (alternateur et transformateur)
11
Bungey, Timothy N. "Topological configurations of coronal magnetic fields and current sheets". Thesis, University of St Andrews, 1996. http://hdl.handle.net/10023/14021.
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The question of topology in the coronal magnetic field is addressed in this thesis. Magnetic reconnection, which plays a major role in many of the fascinating phenomena seen in the solar atmosphere, is likely to occur at the boundaries between different topological regions of the magnetic field. By modelling the coronal field using discrete sources of flux, to represent the concentrations seen at the photospheric surface, we study the varying topological structures present in the field. We generate a criterion for determining the presence of null points above the photospheric surface and establish that any separatrix surfaces present in the field are due to the presence of either null points, or regions where the field tangentially grazes the surface. We follow the evolution of these separatrix surfaces and, in particular, determine the existence of a well-defined separator field line in the absence of coronal null points. Finally, we look locally at the configuration of the magnetic field in the region surrounding a straight current sheet. We derive an analytical expression to describe the topology of both potential and constant-current force-free fields in the neighbourhood of a sheet, and in so doing generalise the previously known expressions.
12
Andriyas, Tushar. "Particle Dynamics and Resistivity Characteristics in Bifurcated Current Sheets". DigitalCommons@USU, 2013. http://digitalcommons.usu.edu/etd/1513.
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Charged particle chaos and its collective effects in different magnetic geometries are investigated in a sequence of various numerical experiments. The fields generated by the particles as a result of interaction with the background electric and magnetic fields is not accounted for in the simulation. An X-line is first used to describe the geometry of the magnetotail prior to magnetic reconnection and a study of the behavior of charged particles is done from a microscopic viewpoint. Another important geometry in the magnetotail prior to substorm onset is Bifurcated Current Sheet. The same analysis is done for this configuration. The existence of at least one positive Lyapunov exponent shows that the motion of the particles is chaotic. By using statistical mechanics, the macroscopic properties of this chaotic motion are studied. Due to particles being charged, an electric field (perpendicular to the magnetic field in weak magnetic field region) accelerates the particles on average. Finite average velocity in the direction of electric field gives rise to an effective resistivity even in a collisionless regime such as solar corona and the magnetotail. Starting from initial velocities that are chosen randomly from a uniform distribution, the evolution of these distributions tends to a Maxwellian by the end of the simulation that is somewhat analogous to collisions in a Lorentz gas model. The effective resistivity due to such collisions is estimated. Ohmic heating is found to occur as a result of such an effective resistivity. Such collisions due to collective particle effects are essentially a different mechanism from classical collision notion. These experiments are done for two types of ions found in the plasma sheet prior to substorm onset, viz., protons and oxygen ions. Observational evidence of oxygen ions in the central plasma sheet, which flow out along open field lines from the ionosphere, were also simulated in the same manner. Oxygen ions have been found to influence the bifurcation of the current sheet and are also important in reconnection and other nonohmic instabilities, such as Kelvin Helmholtz instability, due to their mass. It is found that acceleration in X-line scales with the mass of ion species and the resistivity remains constant for different electric field strengths. In a Bifurcated Current Sheet, the acceleration scales with the square of mass of ion species and the resistivity scales with the electric field. Also, the overall resistivity values found in a Bifurcated Current Sheet are an order of magnitude lower than that found in an X-line.
13
Nozawa, Satoshi. "Three-dimensional magnetohydrodynamic simulation of nonlinear magnetic buoyancy instability of flux sheets with magnetic shear". 京都大学 (Kyoto University), 2006. http://hdl.handle.net/2433/144351.
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Kyoto University (京都大学)0048
新制・論文博士
博士(理学)
乙第11770号
論理博第1464号
新制||理||1442(附属図書館)
23825
UT51-2006-C692
名古屋大学大学院理学研究科宇宙理学第２類
(主査)教授 柴田 一成, 教授 長田 哲也, 助教授 戸谷 友則
学位規則第4条第2項該当
14
Harrison, Michael George. "Equilibrium and dynamics of collisionless current sheets". Thesis, St Andrews, 2009. http://hdl.handle.net/10023/705.
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Ababsa, Mohamed Lamine. "Caractérisation de composants magnétiques et diélectriques pour les machines électriques tournantes très haute température High temperature magnetic characterization using an adapted Epstein frame High temperature characterization of electrical steels using an adapted Epstein frame". Thesis, Artois, 2018. http://www.theses.fr/2018ARTO0205.
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Dans ce travail de thèse, nous avons effectué des mesures de caractérisations magnétiques (cycles d’hystérésis, pertes, H_c…) à très haute température jusqu’à 600 °C, à l’aide d’un dispositif de caractérisation adapté à ces conditions extrêmes qui est un cadre Epstein que nous avons élaboré et réalisé. Sa validation a pu être vérifiée avec un cadre normalisé à température ambiante. Les mesures sont faites sur les deux types de tôles ferromagnétiques les plus utilisées : FeSi GO et NO. Les résultats montrent une réduction avec la température des pertes fer et des différents paramètres qui définissent le cycle d’hystérésis et dévoilent une similarité qui existe entre l’évolution du champ coercitif et les pertes par cycle. Par la suite, nous avons décrit les pertes et le champ coercitif en fonction de la température et la fréquence par des équations empiriques linéaires dans le cas de matériaux saturés et par une extension de l’équation de Bertotti à haute température via une identification de ses paramètres dans le cas des matériaux non saturés. Dans un deuxième temps, nous avons caractérisé l’isolation d’un conducteur destiné à être utilisé à haute température constitué par un fil guipé mica d’origine inorganique, en mesurant la tension des décharges partielles et de claquage. À partir de ces résultats, nous avons montré que l’inhomogénéité de cette isolation le long du conducteur provoque des décharges destructives sans l’apparition de décharge partielle. Ce type de fils est constitué d’une âme en cuivre entourée par une fine couche de nickel, l’influence de cette dernière a été magnétiquement caractérisée au cours de notre travail. L’ensemble de ces études confirment l’importance de la prise en compte des effets de la température élevée et répond aux besoins croissants d’améliorer l’efficacité énergétique dans les différentes utilisations du génie électriqueIn this thesis work, we carried out a magnetic characterization measurements (hysteresis cycles, losses, H_c...) at very high temperatures up to 600 °C, using a characterization device adapted to these extremes conditions which is an Epstein frame that we have developed and implemented. Its validation is verified with a standard frame at ambient temperature. The measurements are performed by two types of ferromagnetic sheets mostly used: FeSi GO and NO. The results show a decrease with temperature in iron losses and different parameters which define the hysteresis cycle, and expose a similarity between the variation of coercive field and the losses per cycle. Subsequently, we described the losses and the coercive field as a function of temperature and frequency. That is done by a linear empirical equations in case of saturated materials and by an extension at high temperature of the Bertotti equation via an identification of its parameters in case of unsaturated materials. In a second phase, by measuring the voltage of partial discharge and of the electrical breakdown we characterized the insulation of a conductor intended to be used at a high temperature covered by mica; this later has an inorganic origin. These results show that the inhomogeneity of this insulation along of the conductor causes destructive discharges without appearance of partial discharges. This kind of wire consists of copper surrounded by a thin nickel layer and this later has been characterized magnetically during our work
16
Bowness, Ruth. "Current sheets in the solar corona : formation, fragmentation and heating". Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2081.
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In this thesis we investigate current sheets in the solar corona. The well known 1D model for the tearing mode instability is presented, before progressing to 2D where we introduce a non-uniform resistivity. The effect this has on growth rates is investigated and we find that the inclusion of the non-uniform term in η cause a decrease in the growth rate of the dominant mode. Analytical approximations and numerical simulations are then used to model current sheet formation by considering two distinct experiments. First, a magnetic field is sheared in two directions, perpendicular to each other. A twisted current layer is formed and we find that as we increase grid resolution, the maximum current increases, the width of the current layer decreases and the total current in the layer is approximately constant. This, together with the residual Lorentz force calculated, suggests that a current sheet is trying to form. The current layer then starts to fragment. By considering the parallel electric field and calculating the perpendicular vorticity, we find evidence of reconnection. The resulting temperatures easily reach the required coronal values. The second set of simulations carried out model an initially straight magnetic field which is stressed by elliptical boundary motions. A highly twisted current layer is formed and analysis of the energetics, current structures, magnetic field and the resulting temperatures is carried out. Results are similar in nature to that of the shearing experiment.
17
Eriksson, Elin. "3D Magnetic Nulls and Regions of Strong Current in the Earth's Magnetosphere". Licentiate thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-292742.
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Plasma, a gas of charged particles exhibiting collective behaviour, can be found everywhere in our vast Universe. The characteristics of plasma in very distant parts of the Universe can be similar to characteristics in our solar system and near-Earth space. We can therefore gain an understanding of what happens in astrophysical plasmas by studying processes occurring in near Earth space, an environment much easier to reach. Large volumes in space are filled with plasma and when different plasmas interact distinct boundaries are often created. Many important physical processes, for example particle acceleration, occur at these boundaries. Thus, it is very important to study and understand such boundaries. In Paper I we study magnetic nulls, regions of vanishing magnetic fields, that form inside boundaries separating plasmas with different magnetic field orientations. For the first time, a statistical study of magnetic nulls in the Earth’s nightside magnetosphere has been done by using simultaneous measurements from all four Cluster spacecraft. We find that magnetic nulls occur both in the magnetopause and the magnetotail. In addition, we introduce a method to determine the reliability of the type identification of the observed nulls. In the manuscript of Paper II we study a different boundary, the shocked solar wind plasma in the magnetosheath, using the new Magnetospheric Multiscale mission. We show that a region of strong current in the form of a current sheet is forming inside the turbulent magnetosheath behind a quasi-parallel shock. The strong current sheet can be related to the jets with extreme dynamic pressure, several times that of the undisturbed solar wind dynamic pressure. The current sheet is also associated with electron acceleration parallel to the background magnetic field. In addition, the current sheet satisfies the Walén relation suggesting that plasmas on both sides of the current region are magnetically connected. We speculate on the formation mechanisms of the current sheet and the physical processes inside and around the current sheet.
18
Spornic, Sorin Aurel. "Automatisation de bancs de caractérisation 2D des tôles magnétiques : influence des formes d'onde sur les mécanismes d'aimantation". Phd thesis, Grenoble INPG, 1998. http://www.theses.fr/1998INPG0154.
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Le travail de notre thèse porte sur le comportement des matériaux magnétiques doux soumis à des variations 2D quelconques du vecteur induction magnétique dans le plan de la tôle. De telles conditions apparaissent par exemple dans les machines électriques tournantes ou les transformateurs triphasés. Les travaux précédents ont été limités à des inductions de formes simples (cercles ou ellipses parcourues à vitesse angulaire constante), qui ne permettent pas de décrire de manière complète le comportement des matériaux. Dans un premier temps nous avons dû élaborer un outil de caractérisation magnétique complète en 2D. Nous avons équipé les deux RSST du LEG d'un système de pilotage informatisé. La précision et la stabilité des mesures ont été nettement améliorées, tout en élargissant l'intervalle des fréquences. Son asservissement numérique a permis l'obtention pour la première fois de formes d'onde 2D complexes de l'induction. Finalement le banc de mesures a été entièrement automatisé. Par la suite cet outil nous a permis l'étude de plusieurs matériaux magnétiques doux, tels que le FeNi, le FeCo et le FeSi NO. - D'abord ces trois matériaux ont été soumis à des inductions circulaires. Nous avons étudié le comportement en fonction du niveau de l'induction et de la fréquence et le comportement réversible, qui permet la mise en évidence de Panisotropie. Le FeNi a permis d'obtenir la courbe complète et atypique des pertes en fonction du niveau d'induction en champ tournant et de valider un modèle de prédiction de celles-ci. Le comportement vectoriel de la loi B(H) dans ce matériau a été également analysé et une tentative de modélisation de l'évolution du champ magnétique a été proposée. - Ensuite nous avons étendu notre étude aux formes d'onde observées dans un moteur asynchrone triphasé. Nous avons testé une méthode de calcul approchée pour les pertes 2D. Finalement, nous avons mis en évidence l'importance de la dérivé temporelle du vecteur induction sur le comportement magnétique et les pertesThe aim of this dissertation is the study of soft magnetic materials under arbitrary vector 2D excitation, turning into the sheet plane. Such conditions appear, for example, inside rotating electric machines or inside three-phase transformers. Previous work has used simplified flux density paths, such as circles or ellipsis covered at constant angular speed, that cannot completely describe the materials'behaviour. The first part of this work was accomplished by the élaboration of a complète 2D magnetic characterisation device. The two RSST of LEG received a computerised driving System (CDS), which clearly improved the measurements accuracy and stability and enlarged the frequency domain. The CDS digital waveform control part allowed for the first time the obtention of complex flux density paths. Finally, the measurement System was completely automated. Thanks to the CDS, the investigation of some soft magnetic materials, such as NiFe, CoFe and NO SiFe, was realised. - First, thèse three materials were characterised under circular flux. The magnetic behaviour was studied with respect to flux and frequency level and also the réversible behaviour, in order to get an anisotropy image. The complète atypical losses évolution could be seen in this manner in the case of NiFe, and a prédiction model was validated. The vector law B(H) was also analysed and a model for the field strength évolution was attempted. - Then this study was enlarged to waveforms observed inside a three-phase induction motor. A2D losses estimation was tested. Finally, the importance of the derivative of the flux density vector with respect to time was highlighted on the magnetic behaviour and the magnetic losses development
19
Cohen, Joel (Joel A. ). "Excitation of forced ion acoustic waves, large plasma sheets, and magnetic field fluctuations over Gakona, Alaska". Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53280.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 47-48).
Two research subjects: (1) excitation of "forced ion acoustic waves", and (2) "simultaneous excitation of plasma density fluctuations and geomagnetic field fluctuations" are reported in my M.S. thesis. The data was acquired in our experiments conducted at Gakona, Alaska from summer 2007 to winter 2008, using DoD/NSF-funded HAARP facilities and our own optical (ASIS) and radio instruments (VLF receiving system of IRIS) aided by GPS satellites as well as AMISR radar at Poker Flat, Alaska. We suggest that "Forced ion acoustic waves" detected by MUIR radar on Oct. 29 during 6:20-6:30 UT arise from keV electron precipitation associated with the occurrence of green aurora. Our work shows, for the first time, that MUIR radar is suitable for probing naturally occurring space plasma processes and not limited to HF heater-induced effects. This would extend the usage of MUIR for the investigation of space weather together with AMISR radar at Poker Flat, to advance our knowledge in space plasma turbulence. The research on "simultaneous excitation of plasma density fluctuations and geomagnetic field fluctuations" is an extension of my B.S. thesis research on thermal filamentation instability, which started in our summer Gakona experiments in 2005. Large plasma sheets (also known as sheet-like filaments) can be excited by HF O-mode and X-mode heater waves via thermal filamentation instability.
(cont.) The dominant nonlinearity is provided by the differential Joule heating acting on electrons, which subsequently gives rise to a cross-field thermal pressure force, to concomitantly generate spatially varying plasma density fluctuations and geomagnetic field fluctuations. It is interesting to find that the fractional density fluctuations are approximately equal to the fractional magnetic field fluctuations. This gives us the theoretical basis to use ground-based magnetometer measurements to infer the density fluctuations in space plasma turbulence. Such a remote sensing technique for probing the space plasma is much more effective and economic than using a beacon satellite.
by Joel Cohen.
S.M.
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Ball, David, Feryal Özel, Dimitrios Psaltis, Chi-Kwan Chan i Lorenzo Sironi. "The Properties of Reconnection Current Sheets in GRMHD Simulations of Radiatively Inefficient Accretion Flows". IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/627036.
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Non-ideal magnetohydrodynamic (MHD) effects may play a significant role in determining the dynamics, thermal properties, and observational signatures of radiatively inefficient accretion flows onto black holes. In particular, particle acceleration during magnetic reconnection events may influence black hole spectra and flaring properties. We use representative general relativistic magnetohydrodynamic (GRMHD) simulations of black hole accretion flows to identify and explore the structures and properties of current sheets as potential sites of magnetic reconnection. In the case of standard and normal evolution (SANE) disks, we find that in the reconnection sites, the plasma beta ranges from 0.1 to 1000, the magnetization ranges from 10(-4) to 1, and the guide fields are weak compared with the reconnecting fields. In magnetically arrested (MAD) disks, we find typical values for plasma beta from 10(-2) to 10(3), magnetizations from 10(-3) to 10, and typically stronger guide fields, with strengths comparable to or greater than the reconnecting fields. These are critical parameters that govern the electron energy distribution resulting from magnetic reconnection and can be used in the context of plasma simulations to provide microphysics inputs to global simulations. We also find that ample magnetic energy is available in the reconnection regions to power the fluence of bright X-ray flares observed from the black hole in the center of the Milky Way.
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Hudson, Frederick Michael Lewis. "NMR characterization guides the design of beta hairpins and sheets while providing insights into folding cooperativity and dynamics /". Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/8639.
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Jerems, Frank. "The magnetic and magnetoelastic properies of meld-spun MbFe2 based alloys and their temperature dependencies". Thesis, University of Hull, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.484232.
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Cester, Christophe. "Étude des pertes magnétiques supplémentaires dans les machines asynchrones alimentées par onduleur à modulation de largeur d'impulsion". Grenoble INPG, 1996. http://www.theses.fr/1996INPG0068.
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La banalisation de l'emploi d'onduleras à Modulation de Largeur d'Impulsion pour l'alimentation des machines asynchrones rend indispensable l'étude des pertes magnétiques supplémentaires qu'ils engendrent. L'influence des paramètres principaux de la MLI, fréquence de hachage et paramètre de modulation est étudiée, grâce à un banc de mesure de type cadre Epstein spécialement adapté. L'emploi d'un moteur instrumenté de 4 kW permet d'observer les formes d'ondes réellement présentes dans les différentes parties du circuit magnétique et de montrer que la déformation du signal MLI entraîne une forte augmentation des pertes magnétiques. Le calcul des pertes totales du moteur à partir des formes d'ondes révèle qu'il existe un écart important avec les pertes fer mesurées par la méthode standardisée, car celle-ci ne permet pas une décomposition détaillée des pertes. Une méthode plus précise est donc proposée. Cependant, l'amélioration du calcul des pertes fer passe aussi par une meilleure prise en compte de la géométrie et des phénomènes locaux, que seule une simulation par éléments finis permet d'approcher. Une méthode originale d'estimation des pertes basée sur une caractérisation préalable du matériau dans un large domaine d'inductions et de fréquences est donc présentée. Cette méthode permet de retrouver les cycles d'hystérésis dynamiques dans des conditions d'excitation quelconques. Elle a été associée au logiciel de calcul par éléments finis FLUX2D et appliquée avec succès au calcul des pertes magnétiques dans le stator et le rotor d'une machine asynchrone
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Krings, Andreas. "Iron Losses in Electrical Machines - Influence of Material Properties, Manufacturing Processes, and Inverter Operation". Doctoral thesis, KTH, Elektrisk energiomvandling, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145243.
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As the major electricity consumer, electrical machines play a key role for global energy savings. Machine manufacturers put considerable efforts into the development of more efficient electrical machines for loss reduction and higher power density achievements. A consolidated knowledge of the occurring losses in electrical machines is a basic requirement for efficiency improvements. This thesis deals with iron losses in electrical machines. The major focus is on the influences of the stator core magnetic material due to the machine manufacturing process, temperature influences, and the impact of inverter operation. The first part of the thesis gives an overview of typical losses in electrical machines, with focus put on iron losses. Typical models for predicting iron losses in magnetic materials are presented in a comprehensive literature study. A broad comparison of magnetic materials and the introduction of a new material selection tool conclude this part. Next to the typically used silicon-iron lamination alloys for electrical machines, this thesis investigates also cobalt-iron and nickel-iron lamination sheets. These materials have superior magnetic properties in terms of saturation magnetization and hysteresis losses compared to silicon-iron alloys. The second and major part of the thesis introduces the developed measurement system of this project and presents experimental iron loss investigations. Influences due to machine manufacturing changes are studied, including punching, stacking and welding effects. Furthermore, the effect of pulse-width modulation schemes on the iron losses and machine performance is examined experimentally and with finite-element method simulations. For nickel-iron lamination sheets, a special focus is put on the temperature dependency, since the magnetic characteristics and iron losses change considerably with increasing temperature. Furthermore, thermal stress-relief processes (annealing) are examined for cobalt-iron and nickel-iron alloys by magnetic measurements and microscopic analysis. A thermal method for local iron loss measurements is presented in the last part of the thesis, together with experimental validation on an outer-rotor permanent magnet synchronous machine.QC 20140516
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Mozetic, Halston José. "Micro estampagem e recozimento conjugado com campo induzido : efeitos no desempenho eletromagnético para chapas elétricas de grão não orientado". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/109171.
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O trabalho aborda o desenvolvimento e implantação de um processo de recozimento conjugado com campo magnético induzido. Para este trabalho foi escolhido como material o FeSi, ABNT NM71-2000/ 35F 420M com GNO (Grão-Não-Orientado) devido ao baixo custo de obtenção das peças e também por ser um material de fácil aquisição no mercado. O processo tem como benefício minimizar as perdas magnéticas produzidas pelo corte convencional na borda das chapas elétricas. Para realizar o processo o sistema é composto de um forno, enrolamento de indução e fonte de alimentação. Os parâmetros utilizados no tratamento térmico situam-se na faixa de temperatura de aquecimento até 910ºC e uma indução magnética mínima na faixa de 80 até aproximadamente 1,5 T. Para melhorar as propriedades magnéticas de forma contundente na região deformada buscou-se através do recozimento conjugado com campo induzido um alinhamento dos domínios, ou seja, uma ordenação dos “spins” que juntamente com a elevação de temperatura tenderam a ter um mesmo sentido, facilitando de maneira significativa à passagem do fluxo magnético, propriedade importante para o desempenho dos núcleos das máquinas elétricas. Para avaliar o desempenho do processo, chapas do mesmo material foram cortadas por eletroerosão a fio, onde o perfil do corte permitiu um fluxo magnético uniforme e constante. O efeito do processo de recozimento com indução de campo magnético foi medido conforme determina a norma, ou seja, utilizando o “Quadro de Epstein” para chapas elétricas. Os resultados foram correlacionados com os dados obtidos a partir do uso do ferro-silício, ABNT NM71-2000/35F 420M, com as mesmas condições de uso e testes de laboratório. Do ponto de vista científico, uma das contribuições deste trabalho, está na influência da indução de campo magnético durante o tratamento térmico das amostras, pois é possível verificar um ganho nas propriedades magnéticas apresentadas. Este trabalho permite afirmar que é possível desenvolver e melhorar as propriedades magnéticas em ferro silício com alto desempenho e também sugerir que outras aplicações, onde seja necessário aumento do desempenho magnético, este processo possa ser aplicado.This work presents and discusses the development and application of an annealing process together with the induced magnetic field. For this study development, the chosen material is the iron silicon, ABNT NM71-2000/ 35F 420M, due to the low trading costs and eases of purchase on the market. The process has the benefit of minimizing magnetic losses produced by conventional cutting the edge of the hot plates. To carry out the process system consists of a furnace, induction coil and power supply. The parameters used in the heat treatment are in the range of heating temperature to 910 ° C and a minimum magnetic induction in the range of about 80 to 1.5 T. The challenge of this work was in the fact that structure changes in the silicon iron, allied to inclusions of non-magnetizable materials, modify for worse the performance of magnetic cores. To obtain a structure that the magnetic field could permeate, the silicon iron alloys were selected to eliminate, at most, the presence of non-magnetizable materials, and only then consider a heat treatment process with magnetic induction to make the material suitable for use in cores of electrical machines. To improve the magnetic properties, an alignment of dipoles of the material, through induced magnetic field during annealing was intended. Annealing with induced magnetic field was carried out, observing the performance of the initial magnetic permeability of the samples, and subsequently measured with field saturation equipment. The results were correlated with the obtained data from the use of the FeSi, ABNT NM71-2000/35F 420M, with the same conditions of use and laboratory tests. From the scientific point of view, one of the contributions of this work is the influence of induced magnetic field during the heat treatment of the samples, since it was possible to verify a significant gain in the magnetic properties of the cores electrical machines during the performance tests. As a result of this work, the possibility of using annealing with magnetic induction was presented as a way to increase the permeability of a material with high carbon content, in this particular case, the silicon iron. This work suggests that it is possible to develop and improve the magnetic properties of iron and silicon with high performance also suggest that other applications where necessary increase in magnetic performance, this process can be applied.
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Zoufalý, Marek. "Snížení zapínacího proudu transformátoru". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2016. http://www.nusl.cz/ntk/nusl-220367.
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In this thesis is described the function and design of the transformer designed on ferromagnetic core, composed of transformer sheets. It is explained a transient inrush current of the transformer. In this work is inserted voltage and current waveforms, designed printed circuit board, serving to reduce the inrush current.
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Plíšek, Oldřich. "Analýza ztrát v železe malého asynchronního motoru". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2018. http://www.nusl.cz/ntk/nusl-376984.
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The aim of this master´s thesis is to analyze core losses of a small induction motor. Analyzed values are obtained from laboratory measurements, software analysis and 2D finite element method simulation. The theoretical part of this thesis consists of two parts. The analysis of the higher spatial harmonics presents in the induction motor and the analysis of core losses of the motor. Practical part consists of laboratory measurements according to ČSN. Measured values are used to calculate individual losses. The next part consists of creating a model for software analysis (Maxwell RMxprt). The generated model is converted into a 2D simulation environment (Maxwell 2D), where it is adapted to obtain values from the examined parts (rotor and stator teeth and rotor cage). Results of simulations at different loads are compared and analyzed from the point of view of higher harmonics.
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Boughanmi, Walid. "Eco-conception des motorisations électriques : Application à la machine asynchrone". Thesis, Artois, 2012. http://www.theses.fr/2012ARTO0207/document.
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Environ 300 millions de moteurs électriques, de puissance moyenne comprise entre 0,75 kW et 300 kW, sont utilisés dans l’industrie, l’infrastructure et les grands bâtiments. En plus, 30 millions sont renouvelés chaque année. En France, l’énergie électrique consommée par ces moteurs représente environ deux-tiers l’énergie électrique consommée dans l’industrie. Une amélioration, même faible, des performances environnementales de chaque unité apporte donc des gains environnementaux conséquents. La démarche d’éco-conception d’une machine électrique permet d’introduire, contrairement aux autres démarches classiques, les aspects environnementaux lors de la conception de la machine en tenant compte de toutes les phases du cycle de vie, depuis l’extraction des matières premières nécessaires à la fabrication des pièces de la machine jusqu’à son démantèlement et son recyclage. Cette démarche permet de concevoir une machine électrique avec un meilleur écobilan global. Dans ce travail, un outil performant destiné à l’Analyse du Cycle de Vie (ACV), prenant en compte plusieurs critères d’impacts afin d’éviter le transfert de pollution d’un critère à l’autre, a été utilisé pour améliorer significativement les performances éco-énergétiques des moteurs électriques. Un premier prototype de moteur « vert » réalisé avec de nouveaux concepts a été fabriqué et comparé à une machine de référence. Sa réalisation a été dictée par le souci de réduire au maximum son empreinte environnementale en utilisant des matériaux plus respectueux de l’environnement, mais aussi en augmentant son efficacité énergétique. Le prototype est ainsi fabriqué à base de tôle à grains orientés, de fil émaillé UV sans solvant, de plastique d’origine végétale et de roulements éco-énergétiques. Ce moteur prototype possède une haute éco-efficacité énergétique puisque son rendement est augmenté de l’ordre de trois points par rapport au moteur standard, sans augmenter sa masse, de plus il comporte un système d’isolation qui n’utilise pas de solvant et des plastiques biosourcésApproximately 300 million of electric motors, with average power range from 0.75 kW to 300 kW, are used in industry, infrastructure and large buildings. In addition, 30 millions are renewed each year. In France, the electrical power consumed by these motors is about two-third of the electrical energy consumed in the industry. Thus, an improvement, even small, of the environmental performance of each motor would provide substantial environmental benefits. Contrary to the conventional approaches, the eco-design of an electrical machine can introduce environmental aspects during the design of the machine, taking into account all phases of the life cycle from the extraction of raw materials to the decommissioning and the recycling. This approach has been applied in this study to design an electrical motor, which has a better global energetic eco-balance. Therefore, a Life Cycle Analysis (LCA) tool is used; it takes into account several impact criteria to avoid pollution transfers from one criterion to another. A first "Green" prototype motor made with a high energetic eco-efficiency was fabricated and tested. The study was dictated by the need to minimize its global environmental impact by using materials more environmentally friendly, but also in order to increase its energy efficiency. The prototype is made with a grain oriented steel sheets, an enameled wire polymerized by UV and without solvents, some plastic based on biopolymers and with eco-energetic bearings. The eco-designed motor has a high energetic eco-efficiency; its performance is increased by about 3 % compared to the standard motor and without increasing its mass
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Halfar, Tomáš. "Zlepšení energetických parametrů asynchronních strojů malého výkonu". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2013. http://www.nusl.cz/ntk/nusl-219929.
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The master’s thesis Improvement power parameter of small induction motors deals with issues of lowering the losses of small induction motors. The first part introduces with design and principles of operation of induction motors. Also introduces to theoretical problematic of losses, their lowering and measuring. In the practical part there are results of the measuring the losses in the induction motor ATAS Elektromotory Náchod a.s. T22VT512 (71-0512). There are proposed methods of increasing the efficiency of induction motor due to measuring and their verification in the Maxwell software. The last part is dedicated to measuring the losses of prototype motor from ATAS and comparison of results with previous motor.
30
Berlin, Alexander. "Magnetic Pulse Welding of Mg Sheet". Thesis, 2011. http://hdl.handle.net/10012/6210.
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Because of its low density and high strength, magnesium (Mg) and its alloys are being sought after in the automotive industry for structural applications. Although many road-going cars today contain cast Mg parts, in the fabrication of chassis structural members the wrought alloys are required. One of the challenges of fabrication with wrought Mg is welding and joining the formed sheets. Because of the commonly observed difficulties in fusion welding of Mg such as hot cracking and severe Heat Affected Zone (HAZ), this work aimed to establish the feasibility of the solid-state process Magnetic Pulse Welding in producing lap welds of Mg sheet.
Mg AZ31 alloy sheets have been lap-welded with Magnetic Pulse Welding (MPW), an Impact Welding technique, using H-shaped symmetric coils connected to a Pulsar MPW-25 capacitor bank. MPW uses the interaction between two opposing magnetic fields to create a high speed oblique collision between the metal surfaces. The oblique impact sweeps away the contaminated surface layers and forces intimate contact between clean materials to produce a solid-state weld. Various combinations of similar and dissimilar metals can be welded using MPW. Other advantages of MPW are high speed, high strength, and the possibility of being mounted on a robotic arm. The present research focuses on the feasibility and mechanical performance of an MPW weld of 0.6 mm AZ31 Mg alloy sheets made in a lap joint configuration.
Tensile shear tests were carried out on the joints produced. Load bearing capacity showed linear increase with capacitor bank discharge energy up to a certain value above which a parabolic increase was seen. Strength was estimated to be at least as high as base metal strength by measuring the fracture surface area of selected samples. The fracture surface of samples welded at higher discharge energy showed two regions. In the beginning of the bond a platelet-featured fracture brittle in appearance and a ductile, micro-voiding fracture in the latter part.
The joint cross section morphology consisted of a flattened area that had two symmetric bond zones 1 mm wide each separated by an unbonded centre zone ~3mm wide. Reasons for the morphology were presented as a sequence of events based on the transient nature of the oblique collision angle.
The interface microstructure was studied by optical and electron microscopy. Examination of the bonds has revealed sound and defect free interfaces. No microcracking, porosity, resolidification, or secondary phase formation was observed. Metallographic examination of the unbonded centre zone revealed anisotropic deformation and a lack of cleaning from the interface. This zone is formed as a result of normal impact in the initial stage of collision. The bond zone interface of the joint was characterized by a smooth interface consisting of refined grains. In samples welded at higher energy interfacial waves developed in the latter half of the bond zone. Transmission electron microscopy (TEM) of the bond zone revealed a continuous interface having an 8-25 μm thick interlayer that coincided with the waves and had a dislocation cell structure and distinct boundaries with adjacent material. Equiaxed 300 nm dynamic recrystallized (DRX) grains were found adjacent to the interlayer as well as other slightly larger elongated grains. The interlayer is thought to be formed in plasticized state at elevated temperature through severe shear strain heating. The interlayer corresponds to a ductile fracture surface and, along with the interfacial waves, is responsible for the joint’s high strength.
31
Fu, Wei-Tsung, i 傅瑋宗. "Extended solutions for Harris Sheet magnetic field with Kappa velocity distribution". Thesis, 2005. http://ndltd.ncl.edu.tw/handle/20363578369673096049.
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Yu, Shih-hong, i 余世鴻. "Preparation and Electromagnetic Characterization of Magnetic Sheet Absorbers for High-Frequencies". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/19718879193204029510.
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碩士逢甲大學
航太與系統工程所
100
Absorbing sheets are fabricated by mixing magnetic powders with polyurethane for the purpose of electromagnetic wave absorption and shielding. The sheets possess characteristics such as flexibility, light-weighted and thin-thickness which are superior to traditional ferrite-tiles and metal shielding sheets. In this study, Mn-Zn ferrite particles, two types of high-permeability powders and Fe-Si-Cr particles are respectively mixed with aqueous-based polyurethane resin to fabricate microwave absorbing composites in different weight ratios. The scattering parameters S11 and S21 of the toroidal samples in a coaxial airline with a network analyzer are measured in the frequency range of 2 ~ 18 GHz. The maximum absorption and shielding effectiveness of composite absorbers are -8.52 dB(at 16 GHz), 10 dB (at 11 GHz) for the high-permeability E series and -7.51 dB(at 10 GHz), 10 dB (at 8.56 GHz) for the high-permeability powder C02 series, and -8.01 dB (at 5.2 GHz), 10 dB (at 6 GHz) for the Fe-Si-Cr absorbing sheets.
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Zharkova, Valentina V., i Mykola Gordovskyy. "Particle Acceleration Asymmetry in a Reconnecting Nonneutral Current Sheet". 2009. http://hdl.handle.net/10454/3753.
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NoThe acceleration of electrons and protons caused by a super-Dreicer electric field directed along the longitudinal component By of the magnetic field is investigated. The three-component magnetic field in a nonneutral current sheet occurring at the top of the reconnecting flaring loops on the charged particle trajectories and energies is considered. Particle trajectories in the reconnecting current sheet (RCS) and their energy spectra at the point of ejection from the RCS are simulated from the motion equation for different sheet thicknesses. A super-Dreicer electric field of the current sheet is found to accelerate particles to coherent energy spectra in a range of 10-100 keV for electrons and 100-400 keV for protons with energy slightly increasing with the sheet thickness. A longitudinal By component was found to define the gyration directions of particles with opposite charges toward the RCS midplane, i.e., the trajectory symmetry. For the ratio By/Bz < 10-6 the trajectories are fully symmetric, which results in particle ejection from an RCS as neutral beams. For the ratio By/Bz > 10-2 the trajectories completely lose their symmetry toward the RCS midplane, leading to the separation of particles with opposite charges into the opposite halves from an RCS midplane and the following ejection into different legs of the reconnecting loops. For the intermediate values of By/Bz the trajectories are partially symmetric toward the midplane, leading to electrons prevailing in one leg and protons in the other.
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蔡秉霖. "Influence of capping layer on magneto-optical kerr effect in magnetic sheet-film systems". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/06008240754030579930.
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碩士國立彰化師範大學
光電科技研究所
96
The objective of my thesis is mainly to investigate influence of capping layer on magneto-optical Kerr effect in magnetic sheet-film systems. To prevent the unwanted oxidation of the magnetic layer, we overlay the capping layer on the optically magnetic layer. With a capping layer, the magnetic character of the magnetic layer didn’t change and the capping layer increase intensity of the kerr rotation. We change three materials of capping layer. The three materials are SiNX, MgO, and Ta. With change the material of the capping layer, we also change the depth of every capping layer. Otherwise, we change the different incident angle. When the incident angle is sixty, the intensity of the kerr rotation present the best result. We first discuss the the capping later of SiNX and MgO which both are insulated material. With the depth of capping layer from 0nm to 60 nm, the capping layer increase the intensity of kerr rotation by the thin-film system. With the depth of capping layer from 60nm to 100 nm, the capping layer decrease the intensity of kerr rotation by the thin-film system by the bulk material system. Secondly, the capping layerof Ta is metal material, the capping layer decrease the intensity of kerr rotation by the thin-film system by the skin effect.
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Muñoz, Sepúlveda Patricio A. "Fully kinetic PiC simulations of current sheet instabilities for the Solar corona". Doctoral thesis, 2015. http://hdl.handle.net/11858/00-1735-0000-0023-964F-4.
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Hsupeng, Boryau, i 徐彭伯堯. "Formation of discontinuities and expansion waves in the outflow region of magnetic reconnection in an asymmetric current sheet". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/93992301969362824267.
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碩士國立中央大學
太空科學研究所
103
The current sheets observed in the solar wind, magnetopause, and nightside plasma sheet can be asymmetric, in which the plasma densities and/or magnetic field magnitudes on the two sides of the current sheet are not equal. A hybrid code is used to simulate the 1-D Riemann problem for the generation and evolution of MHD discontinuities and expansion waves in the outflow region of magnetic reconnection in an asymmetric current sheet. In a symmetric current sheet, four types of compound structures are found: (a) RD-SS compound structure: slow shock (SS) is attached to the downstream of rotational discontinuity (RD), (b) SS-RD: SS is followed by an adjacent RD, (c) SS-RD-SS: RD is trapped inside SS, and (d) switch-off slow shock (SSS). In the asymmetric current sheet, the rotational angle of magnetic field across an RD on the side with a higher plasma density is usually larger than that with a lower plasma density. In the asymmetric cases, only a pure RD, a single SS, or a pair of separated RD and SS may appear on one side of the current sheet. When the asymmetry is further increased, RD may become absent in the low density side. For a highly asymmetric current sheet, a slow expansion wave (SE) is formed behind the rotational discontinuity (RD) on the side with a very high plasma density, as expected from Levy et al. [1964].
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Yang, Nai-Ju, i 楊乃如. "Flow and heat transfer of viscoelastic fluids saturated in porous media over a stretching sheet subject to a uniform transverse magnetic field". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/01131595551092144809.
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碩士國立暨南國際大學
土木工程學系
94
The study for flow and heat transfer in a steady laminar boundary layer flow is presented analytically for an incompressible viscoelastic fluid saturated in a porous medium subject to a transverse uniform magnetic field past a semi-infinite stretching sheet with a quadratic distribution of surface temperature and quadratic distribution of surface heat flux, respectively. Applying the boundary layer theory proposed by Prandtl in 1904, we simplify the momentum and energy equations to a set of ordinary differential equations using a similarity transform. The energy equation we considered includes the viscous dissipation, internal heat generation or absorption, work due to deformation, Joule heating and radiation. The exact solutions for temperature are given in tems of the Kummer`s functions as well as Gamma functions. The surface temperature gradient for the prescribed surface temperature (PST) and surface temperature for the prescribed heat flux (PHF) for various parameters are drawn and tabulated. The appropriate physical interpretations about thermal characteristic are proposed in this thesis, and the asymptotic solutions for temperature functions with two heating conditions when modified Prandtl number is very large are also given.
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Raath, Jan Louis. "A comparative study of cosmic ray modulation models / Jan Louis Raath". Thesis, 2015. http://hdl.handle.net/10394/15516.
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Until recently, numerical modulation models for the solar modulation of cosmic rays have
been based primarily on finite difference approaches; however, models based on the solution
of an appropriate set of stochastic differential equations have become increasingly
popular. This study utilises such a spatially three-dimensional and time-stationary model,
based on that of Strauss et al. (2011b). The remarkable numerical stability and powerful
illustrative capabilities of this model are utilised extensively and in a distinctly comparative
fashion to enable new insights into the processes of modulation. The model is
refined to provide for both the Smith-Bieber (Smith and Bieber, 1991) and Jokipii-Kota
(Jokipii and Kota, 1989) modifcations to the Parker heliospheric magnetic field (Parker,
1958) and the implications for modulation are investigated. During this investigation
it is conclusively illustrated that the Parker field is most conducive to drift dominated
modulation, while the Jokipii-Kota and Smith-Bieber modifcations are seen to induce
successively larger contributions from diffusive processes. A further refinement to the
model is the incorporation of a different profile for the heliospheric current sheet. This
profile is defined by its latitudinal extent given by Kota and Jokipii (1983), as opposed
to the profile given by Jokipii and Thomas (1981). An extensive investigation into current
sheet related matters is launched, illustrating the difference between these current
sheet geometries, the associated drift velocity fields and the effect on modulation. At
high levels of solar activity, such that the current sheet enters deep enough into the polar
regions, the profile of Kota and Jokipii (1983) is found to significantly reduce the effective
inward (outward) drifts of positively (negatively) charged particles during A > 0 polarity
cycles. The analogous effect is true for A < 0 polarity cycles and the overall effect is of
such an extent that the A > 0 and A < 0 solutions are found to coincide at the highest
levels of solar activity to form a closed loop. This is a result that has never before been
achieved without having to scale down the drift coefficient to zero at solar maximum,
as was done by e.g. Ndiitwani et al. (2005). Furthermore, it is found that the drift
velocity fields associated with these two current sheet profiles lead to significant differences
in modulation even at such low levels of solar activity where no difference in the
geometries of these profiles are yet in evidence. The model is finally applied to reproduce
four observed galactic proton spectra, selected from PAMELA measurements (Adriani
et al., 2013) during the atypical solar minimum of 2006 to 2009; a new proton local interstellar
spectrum was employed. The results are found to be in accordance with that
found by other authors and in particular Vos (2011), i.e. the diffusion was required to
consistently increase from 2006 to 2009 and, in addition, the rigidity dependence below ~
3 GV was required to change over this time so that the spectra became increasingly softer.MSc (Space Physics), North-West University, Potchefstroom Campus, 2015
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Sonti, Rajesh. "Conformational Analysis of Designed and Natural Peptides : Studies of Aromatic/Aromatic and Aromatic/Proline Interactions by NMR". Thesis, 2013. http://etd.iisc.ac.in/handle/2005/3335.
Pełny tekst źródłaStreszczenie:
This thesis describes NMR studies which probe weak interactions between amino acid side chains in folded peptide structures. Aromatic/aromatic interactions between facing phenylalanine residues have been probed in antiparallel β-sheets, while aromatic/proline interactions have been examined using cyclic peptide disulfides that occur in the venom of marine cone snails. Novel intramolecular hydrogen bonded structures in hybrid peptides containing backbone homologated residues, specifically γ-amino acids, are also described.
Chapter 1 provides a brief background to the principles involved in the design of antiparallel β-sheet structures and an introduction to previous studies on aromatic/aromatic and aromatic/proline interactions in influencing peptide conformations. A summary of the NMR methods used is also presented. Chapter 2 discusses the structural characterisation of a designed 14 residue, three stranded β-sheet peptide, Boc-LFVDP-PLFVADP-PLFV-OMe (LFV14). The results described in this Chapter support the presence of multiple conformational states about the χ1 (Cα-Cβ) torsional degree of freedom for the interacting aromatic pairs in solution. Chapter 3 presents the structural characterisation of a designed 19 residue three stranded hybrid β-sheet peptide, Boc-LVβFVDPGLβFVVLDPGLVLβFVV-OMe (BBH19). β-amino acid residues (β-phenylalanine, βPhe) were incorporated at facing positions on antiparallel β-sheets. The BBH19 structure provides an example of interaction between the N and C-terminal strands in a three stranded structure with an α/β hybrid backbone. Chapter 4 focuses on studies of the conformations of the contryphan In936 (GCVDLYPWC*) from Conus inscriptus and the related peptide Lo959 (GCPDWDPWC*) from Conus loroissi. Both peptides possess a macrocyclic 23 membered ring, with multiple accessible conformational states. Chapter 5 describes conformational analysis of a novel 20 membered cyclic peptide disulfide, CIWPWC (Vi804), from Conus virgo. NMR structures were calculated for Vi804 and an analog peptide, CIDWPWC, DW3-Vi804. Chapter 6 explores the solution conformation of hybrid sequences containing α and γ residues. Oligopeptides of the type (αγ)n and (αγγ)n have been studied in solution by NMR methods. Chapter 7 provides a summary of the results described in this thesis and highlights the major conclusions.
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Xing, Xiaoyan. "Criterion for interchange instability in the plasma sheet". Thesis, 2008. http://hdl.handle.net/1911/22255.
Pełny tekst źródłaStreszczenie:
Interchange instability is an important dynamic mechanism in plasma physics and has been advanced as an explanation of a variety of phenomena in the magnetospheric physics. This work derives a new instability criterion for interchange motion in a plasma that connects to a finite-conductivity wall. The new criterion is for a arbitrary magnetic <beta> (ratio between thermal pressure and magnetic pressure averaged within flux tube) system, which contains background shear flow, whereas most classical criteria did not consider all of these conditions. Thus this new result is more appropriate to be applied in a real plasma system like the Earth's plasma sheet, which exhibits a wide range of <beta> values and background shear flow. Based on magnetosphere-ionosphere coupling theory and ideal MHD adiabatic theory in the inner plasma sheet, a theoretical model was constructed in the ionosphere region. A finite boundary layer was set up between two regions of uniform-content flux tubes, and a perturbation on the boundary layer was investigated. Both analytical and numerical approaches are used to study the stability of the plasma configuration. The flux tubes are interchange unstable when the angle between the gradient of flux tube volume, defined as V = dsB , and the gradient of adiabatic specific entropy PV 5/3 is larger than arccos<b> 1lnPV5/3 1ln V/ 21+5<b>/6 . Combining this new criterion with the statistical calculation of the plasma sheet characteristics by using the Tsyganenko magnetic field model (the 1996 version) and the Tsyganenko-Mukai plasma model, it is found that, in the Earth's inner plasma sheet, the angle between the two gradients is typically of the order of 15°, which indicates that the statistical-average Earth's plasma sheet is interchange stable. This result is applicable to the study of interchange instability and plasma transport in the global-MHD and other large-scale magnetosphere simulations, and provides a theoretical base for the study of analogous dynamic processes in the magnetospheres of other planets like Jupiter.
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Sonti, Rajesh. "Conformational Analysis of Designed and Natural Peptides : Studies of Aromatic/Aromatic and Aromatic/Proline Interactions by NMR". Thesis, 2013. http://etd.iisc.ernet.in/2005/3335.
Pełny tekst źródłaStreszczenie:
This thesis describes NMR studies which probe weak interactions between amino acid side chains in folded peptide structures. Aromatic/aromatic interactions between facing phenylalanine residues have been probed in antiparallel β-sheets, while aromatic/proline interactions have been examined using cyclic peptide disulfides that occur in the venom of marine cone snails. Novel intramolecular hydrogen bonded structures in hybrid peptides containing backbone homologated residues, specifically γ-amino acids, are also described.
Chapter 1 provides a brief background to the principles involved in the design of antiparallel β-sheet structures and an introduction to previous studies on aromatic/aromatic and aromatic/proline interactions in influencing peptide conformations. A summary of the NMR methods used is also presented. Chapter 2 discusses the structural characterisation of a designed 14 residue, three stranded β-sheet peptide, Boc-LFVDP-PLFVADP-PLFV-OMe (LFV14). The results described in this Chapter support the presence of multiple conformational states about the χ1 (Cα-Cβ) torsional degree of freedom for the interacting aromatic pairs in solution. Chapter 3 presents the structural characterisation of a designed 19 residue three stranded hybrid β-sheet peptide, Boc-LVβFVDPGLβFVVLDPGLVLβFVV-OMe (BBH19). β-amino acid residues (β-phenylalanine, βPhe) were incorporated at facing positions on antiparallel β-sheets. The BBH19 structure provides an example of interaction between the N and C-terminal strands in a three stranded structure with an α/β hybrid backbone. Chapter 4 focuses on studies of the conformations of the contryphan In936 (GCVDLYPWC*) from Conus inscriptus and the related peptide Lo959 (GCPDWDPWC*) from Conus loroissi. Both peptides possess a macrocyclic 23 membered ring, with multiple accessible conformational states. Chapter 5 describes conformational analysis of a novel 20 membered cyclic peptide disulfide, CIWPWC (Vi804), from Conus virgo. NMR structures were calculated for Vi804 and an analog peptide, CIDWPWC, DW3-Vi804. Chapter 6 explores the solution conformation of hybrid sequences containing α and γ residues. Oligopeptides of the type (αγ)n and (αγγ)n have been studied in solution by NMR methods. Chapter 7 provides a summary of the results described in this thesis and highlights the major conclusions.
42
KUNCLOVÁ, Kateřina. "Ověření pozičního chování u savců". Master's thesis, 2017. http://www.nusl.cz/ntk/nusl-320564.
Pełny tekst źródłaStreszczenie:
This thesis was focused on determining the orientation of the body of domestic sheep while grazing or resting. Attention was also paid to the assessment of environmental conditions that may affect the position of animal behaviour. Data were collected through the direct observation compared to the previous studies, which have been based on satellite images from Google Earth. In this experiment, only selected designated individuals were evaluated. The direct observation detected the individual preferences of animals, not only the direction but also the location. The evaluating of photos of the animals found out, according to the time of day,north and west facing position of the body. The more significant directional preference was documented in resting individuals.
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鬼頭, 哲太郎, i Tetsutaro Kito. "iPS cell sheets created by a novel magnetite tissue engineering method for reparative angiogenesis". Thesis, 2013. http://hdl.handle.net/2237/18436.
Pełny tekst źródła
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Kumar, Rajeev. "Synthesis and development of multifunctional carbonaceous nanostructures for magnetic, optical and catalytic applications". Thesis, 2019. https://etd.iisc.ac.in/handle/2005/4951.
Pełny tekst źródłaStreszczenie:
Owing to the ease of functionalization, low synthesis-cost and polymorphism,
carbonaceous nanostructures such as carbon globules, nanotubes (CNTs) and graphene sheets
emerged technologically as one of the most important class of multifunctional materials. In this
thesis a wide variety of carbon based nanostructures were synthesized by the simple pyrolysis
method, characterized and their applicabilities are demonstrated. Among the synthesized
materials, metallic particles embedded amorphous carbon globules, CNTs of different
morphologies such as spiralling tendrils, cup and box type bamboos, hollow and filled onions
etc. are the exotic ones. We also demonstrated a way to synthesize nanoscale particles of various
metallic alloys, which can be useful for any structural design in powder metallurgy. These
carbon coated metallic particles, which protect themselves against any environmental corrosion,
are otherwise, difficult to synthesize by any other conventional method. The structure,
morphology, size distribution of the dispersed metallic particles in carbon nanostructures were
investigated and correlated with their optical, magnetic, electronic and chemical properties.
We have demonstrated multifunctionality of our synthesized carbonaceous materials. Our
investigation highlights the non-linear absorption of laser beams in metallic nanoparticles
embedded carbon materials, making them potential candidates for optical limiters. Furthermore,
the dispersion of nano-sized metallic particles inside amorphous carbon matrix proves to be
microwave absorption enhancers, enabling their use as electromagnetic interference (EMI)
shields. In addition, the catalytic activity of most of our samples is excellent, but can be further
improved by controlling the amount of defects via nitrogen doping. The catalytic performance
for reduction of 4-nitrophenol by some selective samples exceeds many of the catalysts reported
earlier. The performance of some of our samples in electronic devices such as in infrared photodetectors
is exceptional. The use of the samples for magnetorheological applications for energy storage
and many other applications cannot be undermined. Hence, our work demonstrates that
our synthesized samples are versatile and truly multifunctional
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O'Connell, Adam Brett. "Development of an acute excitotoxic model of Huntington's disease in sheep". Thesis, 2020. http://hdl.handle.net/2440/127292.
Pełny tekst źródłaStreszczenie:
Huntington’s disease (HD) is an autosomal dominant neurodegenerative disorder. The earliest and most severe neuropathological change in HD occurs within the striatum. Exogenous excitotoxic lesioning of the rodent and non-human primate (NHP) striatum is used to model HD. Apart from NHPs, no other excitotoxic large animal model of HD has been established. Sheep have the potential to be an important species for modelling neurodegenerative disease, primarily because of neuroanatomical similarities between the sheep and human brain. This thesis describes the development of an excitotoxic sheep model of HD using the excitotoxin, quinolinic acid (QA). QA is an N-methyl-D-aspartate (NMDA) glutamate receptor agonist that produces pathological changes within the striatum that resemble those seen in HD. Sixteen castrated-male, 18 month old, Merino-Border Leicester cross sheep underwent two surgical procedures, four weeks apart, to infuse 75 μl of 180 mM QA (experimental group) or 75 μl of saline (control group) into the left (first surgery) and then the right (second surgery) caudate nucleus of the striatum. Longitudinal magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS) and diffusion tensor imaging (DTI) of the brains of the sheep was performed on a 3-Tesla scanner pre-surgically, one week after the first surgery, five weeks after the first surgery and sixteen weeks after the first surgery to investigate the neuropathological changes that occur in vivo after QA lesioning of the sheep striatum. The phenotypic consequences of lesioning the sheep striatum with QA were investigated using a veterinary neurological examination, dopamine agonist induced rotation and a two-choice discrimination task. The author / investigator was blind to the treatment group. MRI revealed QA-lesion hyperintensity and dilation of the lateral ventricles, consistent with atrophy of the caudate nucleus. MRS and DTI revealed a significant decrease in the neuronal marker N-acetylaspartate (NAA), and in fractional anisotropy (FA) in the acutely-lesioned (one week after surgery) striatae of the QA-lesioned sheep, followed by recovery in NAA and a significant increase in FA in the chronic (five to sixteen weeks) QA-lesioned striatae. NAA and FA changes are consistent with neuronal loss and structural disruption in the acute lesion, followed by recovery of reversibly impaired neurons, structural reorganisation and gliosis in the chronic lesion. Heterogeneous neuronal loss and damage and gliosis were visible on histological analysis of the QA-lesioned sheep striatae, supporting the in vivo MRS and DTI detected changes. Neurological examination of the sheep revealed evidence of laterality and mild hind limb motor paresis in seven out of eight of the QA-lesioned sheep, however the examination was not informative of lesion characteristics. A directional bias was evident in the QA-lesioned sheep during rotation studies. However, the direction and magnitude of bias in individual sheep at any one timepoint varied markedly, making identification of QA-lesioned individuals difficult. There was no difference between the QA-lesioned and saline-treated sheep in performance of the acquisition and reversal phases of the two-choice discrimination task. The behavioural studies described in this thesis were not suitable for comprehensive identification and characterisation of QA lesions in the striatum of sheep. This is the first description of the development of an acute excitotoxic sheep model of HD. The experiments demonstrate that longitudinal analysis of the neuropathological changes in the QA-lesioned sheep striatum is possible using advanced magnetic resonance modalities performed on a clinically relevant 3-Tesla scanner and that neuropathological changes are consistent with HD-like pathology in other species. Furthermore, phenotypic investigation of the QA-lesioned sheep is possible, however more refined methods than those described need to be utilised. The excitotoxic sheep model of HD is clinically relevant HD model with potential for use in disease mechanism and therapy investigations.Thesis (Ph.D.) -- University of Adelaide, Adelaide Medical School, 2020
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Viana, José Pedro Cruz da Rocha. "Estudo e caracterização mecânica por via experimental de modelos de subestruturas eletromecânicas aplicadas ao fabrico de transformadores de grande potência". Master's thesis, 2015. http://hdl.handle.net/1822/40207.
Pełny tekst źródłaStreszczenie:
Dissertação de mestrado integrado em Engenharia MecânicaDurante o projeto de um transformador de potência é importante que se faça a prevenção da ocorrência de falhas que podem colocar o equipamento fora de serviço, e assim, gerar elevados prejuízos económicos, entre outros. De acordo com os vários registos na área das falhas dos transformadores de potência, aquela que apresenta uma maior taxa de ocorrência e que, por sinal, é a que coloca mais transformadores fora de serviço, é a falha por curto-circuito. O trabalho aqui desenvolvido relaciona-se com continuo desenvolvimento do projeto dos transformadores de potência tendo em vista a sua otimização, de forma a que o transformador mais recente resista mais e melhor do que o seu imediato antecessor. A Efacec Energia S.A. é um fabricante deste tipo de equipamentos tendo proporcionado e encorajado o estudo aqui desenvolvido. O conjunto de chapa magnética da culaça aliado às respetivas travessas são os elementos do circuito magnético dos transformadores de potência que terão de suportar os esforços de curto-circuito para garantir a integridade física do circuito magnético. O trabalho aqui desenvolvido encontra-se relacionado com a determinação dos esforços e dos deslocamentos que as chapas magnéticas da culaça e a travessa do circuito magnético têm de resistir. O conhecimento e a determinação destes valores em situação de curto-circuito permitirá influenciar o projeto estrutural dos transformadores de potência. No âmbito do trabalho desta Dissertação de Mestrado, foram executados vários ensaios experimentais a um protótipo do circuito magnético de um transformador de tipo Core. As chapas magnéticas, neste tipo de transformador, encontram-se sujeitas a uma força de aperto, que se converte em pressão, derivada do binário aplicado aos pernos da travessa. Assim, quando em situação de curtocircuito, devido ao aperto dos pernos a movimentação da culaça do circuito magnético e da travessa é limitada, mas não impossível. A travessa, para além de garantir um aperto teoricamente uniforme nas chapas magnéticas da culaça também serve para fazer o levantamento do circuito magnético durante o processo de montagem do transformador. Foram igualmente realizados testes aos binários de aperto dos pernos, por forma a validar os cálculos teóricos das forças de compressão teóricas. Os resultados obtidos permitiram ganhar conhecimentos numa área desconhecida para a Efacec, o que pode no futuro influenciar positivamente o projeto e o desenvolvimento dos novos transformadores.
During the design of a power transformer it is important to make the prevention of failures that can put the equipment out of service, and thus generate high economic losses, among others. According to several records registered in the area of the faults in power transformers, the one that has a higher occurrence rate is the failure by short-circuit and, in consequence, is the one that puts more transformers out of service. The work developed here relates to the continuous development of the design of power transformers with a view to their optimization, so that the latest transformer resist more and better than its immediate predecessor. The company Efacec Energia SA is a manufacturer of this type of equipment that has provided and encouraged the study developed here. The magnetic sheets of the yoke combined with the transformer frame are the elements of the magnetic circuit of the power transformers that will bear the short-circuit efforts to ensure the physical integrity of the magnetic circuit. The work developed here is related to determining the efforts and displacements that the magnetic sheets of the yoke and the frame of the magnetic circuit must resist. The knowledge and determination of these values in a short-circuit situation will influence the structural design of power transformers. In the work of this Thesis, were executed several experimental tests on a prototype of the magnetic circuit of a Core type transformer. In this type of power transformer, the magnetic sheets are subjected to a clamping force, which becomes pressure, derived from the torque applied to the pins of the transformer frame. Thus, when in a short-circuit situation, due to tightening of the bolts, the displacement of the magnetic circuit and of the frame is limited, but not impossible. The frame, as well as ensure a theoretically uniform tightening of magnetic sheets of the yoke, also serves to lift the magnetic circuit during the assembly process transformer They were also executed tests about the torque applied to the bolts in a way to validate the theoretical calculations of the compressive forces. The results achieved, allowed Efacec to gain knowledge in an unknown area, which can positively influence the future design and development of new transformers.