nÃo hà / AÃos elÃtricos de grÃo nÃo orientado sÃo amplamente utilizados na fabricaÃÃo de nÃcleos para motores elÃtricos, sendo o desempenho destes equipamentos afetado pela textura cristalogrÃfica presente nesses materiais. Jà o tamanho de grÃo interfere consideravelmente nas perdas magnÃticas. A textura cristalogrÃfica e o tamanho de grÃo sÃo extremamente influenciados pelo tratamento tÃrmico de recozimento realizado apÃs o processo de laminaÃÃo a frio para obtenÃÃo de tiras metÃlicas desses aÃos. O recozimento promove estados de recristalizaÃÃo na microestrutura do material e esses estados estÃo intimamente relacionados com a textura cristalogrÃfica. O objetivo deste trabalho à avaliar a influÃncia da recristalizaÃÃo no comportamento da textura cristalogrÃfica e das perdas magnÃticas por histerese de um aÃo elÃtrico de grÃo nÃo orientado com 1,28% Si que foi laminado a frio industrialmente com reduÃÃes de 50 e 70%. Amostras do material nas condiÃÃes laminado a frio, parcialmente recristalizadas a 580, 585, 590, 595, 600, 605, 610, 615 e 620ÂC e recozidas a 730ÂC por 12 horas (recozimento em caixa) foram analisadas quanto à microestrutura, textura cristalogrÃfica e perdas magnÃticas por histerese. O material tambÃm foi submetido a tratamentos tÃrmicos para crescimento de grÃo e estes tambÃm foram avaliados com respeito à microestrutura e a textura cristalogrÃfica. Os resultados mostraram o inÃcio da recristalizaÃÃo primÃria nas condiÃÃes parcialmente recristalizadas e os tratamentos tÃrmicos para crescimento de grÃo provocaram a ocorrÃncia de recristalizaÃÃo secundÃria. A textura cristalogrÃfica foi modificada pelas condiÃÃes parcialmente recristalizadas, pelo recozimento em caixa e pela recristalizaÃÃo secundÃria. Quanto Ãs perdas magnÃticas por histerese, o recozimento em caixa promoveu uma diminuiÃÃo destas. / Non-oriented electrical steels are widely used in the manufacture of cores for electric motors being the performance of this equipment affected by the presence of crystallographic texture in these materials. In other hand, the grain size considerably affects the magnetic losses. The crystallographic texture and grain size are greatly influenced by the annealing process performed after cold rolling of these steels. Annealing promotes recrystallization in the microstructure of the material which is closely related with the crystallographic texture. The objective of this study is to evaluate the influence of recrystallization on the evolution of crystallographic texture and hysteresis magnetic losses by in non-oriented grain electrical steel with 1.28% Si that was cold rolled with reductions of 50 and 70% in an industrial plant. Samples of the material in the conditions cold rolled and partially recrystallized at 580, 585, 590, 595, 600, 605, 610, 615 and 620ÂC and annealed at 730ÂC for 12 hours (box annealing) were analyzed in the aspects of microstructure, crystallographic texture and magnetic hysteresis losses. The material was also subjected to heat treatment for grain growth and they were also evaluated with respect to the microstructure and crystallographic texture. The results showed the evolution of primary recrystallization and also the microstructure and texture when the material is subjected to final heat treatment that promotes grain growth and secondary recrystallization. The crystallographic texture has changed in the process of primary recrystallization occurred during box annealing and also in the process of secondary recrystallization after heat treatment simulating the final processing of the material. The evaluation of hysteresis magnetic losses showed that the box annealing promoted a reduction of these.

Orientador: Kleber Roberto Pirota / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-19T11:29:30Z (GMT). No. of bitstreams: 1 CostaArzuza_LuisCarlos_M.pdf: 3383467 bytes, checksum: 8fac04d42ba77c741416d15d643d402a (MD5) Previous issue date: 2011 / Resumo: Este trabalho visa estudar o comportamento histerético, observado a baixos campos magnéticos, do fenômeno da magnetoimpedância gigante (GMI) em fitas amorfas a base de CoFeSiB com anisotropia magnética transversal. O fenômeno da GMI consiste na variação da impedância elétrica (aproximadamente do 100%) de uma amostra magnética mole quando submetida à aplicação de campo magnético DC externo. Apesar da importância da presença de histerese na GMI, tanto do ponto de vista básico quanto do tecnológico, existem poucos estudos na literatura que visam à explicação da origem desse efeito. Desde o ponto de vista fundamental, o completo entendimento do fenômeno poderia revelar importantes aspectos envolvidos com o processo de magnetização nos materiais considerados. De um ponto de vista prático, a presença da histerese na GMI tanto pode ser desfavorável, quando pensamos na fabricação de sensores, quanto favorável, se levamos em consideração a sua possível aplicação em sistemas de memória magnética. Por outro lado, o método denominado curva de inversão da primeira ordem (first-order reversal curve, FORC, em inglês) mostra-se uma poderosa ferramenta para o estudo e compreensão de fenômenos histeréticos, principalmente da histerese magnética presente em curvas de magnetização de materiais ferromagnéticos. Tal método, fundamentado no modelo clássico de Preisach, dá importantes informações através de medidas de ciclos de histerese secundarias da curva principal. Neste trabalho utilizamos a técnica FORC para estudar o fenômeno da histerese na GMI. Utilizamos fitas amorfas de composição (CoxFe1-x)70Si12B18, com x = 0,040 e 0,045 como sistema de estudo devido a suas propriedades magnéticas moles. Tais fitas possuem 22 µm de espessura, 0,8 mm de largura e constante de anisotropia de 139 J/m3 e 145 J/m3 respetivamente. As medidas de GMI foram realizadas com um analisador de rede vetorial (vector network analizer, VNA, em inglês). Tal equipamento, combinado a um sistema de bobina e fonte de corrente, permitiu-nos fazer medidas de impedância em função da frequência (entre 10 MHz e 1 GHz) e do campo magnético aplicado (até 100 Oe). Consideramos como principal resultado deste trabalho o desenvolvimento de um método eficiente para testar e aprimorar modelos teóricos sobre a origem de tal histerese. Os resultados obtidos do comportamento histeretico no volume e na superficie, foram interpretados levando-se em conta uma estrutura magnética estática volumétrica não uniforme e ao amortecimento das paredes de domínio / Abstract: We studied the hysteretic behavior, observed at low magnetic fields, of the giant magnetoimpedance (GMI) phenomenon in CoFeSiB amorphous ribbons with transversal magnetic anisotropy. The GMI phenomenon consists in the electrical impedance variation (around 100 %) of a soft magnetic sample in the presence of an external DC magnetic field.Despite the importance of hysteresis presence in GMI from technological and basic points of view, it exists only few studies about the description of this effect. From the fundamental outlook, the complete understanding of the phenomenon could reveal important aspects involved in the magnetization process of the concerned materials. For practical applications, the hysteretic GMI can be unfavorable (for example for sensor development) or favorable (for example for magnetic storage memories). On the other side, first-order reversal curve (FORC) method is a powerful tool for the study and understanding of hysteretic phenomena, mainly for the hysteresis present in the magnetization curves of ferromagnetic materials. This method, based on the classical Preisach model, allows to extract important information through minor hysteresis loops inside the major one. In this work, we used the FORC technique to study the GMI hysteretic phenomenon. We investigated amorphous ribbons of (CoxFe1-x)70Si12B18 composition, where x = 0.040 and 0.045. Those ribbons were 2 µm thick and 0.8 mm wide. The GMI measurements were performed with a vector network analyzer (VNA). This equipment, coupled with a system of coil and power supply, allowed impedance measurements versus frequency (between 10 MHz and 1 GHz) and applied magnetic field (until 100 Oe). We consider that the main achievement of this work is the development of an efficient method allowing to test and improve theoretical models about the hysteresis origin. The obtained results were interpreted taking into account a non homogeneous static magnetic structure along the ribbon volume with domain walls damping / Mestrado / Física / Mestre em Física

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第16400号 / 工博第3481号 / 新制||工||1526(附属図書館) / 29031 / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 引原 隆士, 教授 田畑 修, 准教授 山田 啓文 / 学位規則第4条第1項該当

The existence of multiple hydrodynamic states (MHS) in trickle bed operation has been proved by hysteresis observed in flow loops, as well as variation between different prewetting modes. The most common theory presented as explanation for the existence of MHS, is the film vs. rivulet concept. Based on this concept, it was suspected that in-situ upsets might promote the formations of films, thereby providing a method through which the hydrodynamic states of the Dry and Levec modes can be manipulated to perform like the Kan Liquid and Super modes. Large performance enhancements can be obtained by altering the prewetting procedure, even for systems with a low surface tension. For the water system, the gas liquid mass transfer coefficient of the Kan Liquid and Super modes could be as much as 6 times greater than that of the Dry mode. For the low surface tension system, the gas liquid mass transfer of the Kan Liquid and Super modes could be up to 8 times greater than that of the Dry mode. Through a thorough investigation of various types of transient upsets and manipulation strategies, it was confirmed that prewetting is indeed the only way by which drastic variation in hydrodynamic states may be obtained. None of the investigated upsets (hysteresis, periodic operation or surface tension doping) resulted in changes in the liquid morphology that could compare to the significant variation that was observed by varying the prewetting mode. Two methods were identified by which the hydrodynamic gaps between the less uniform (Dry and Levec) modes and the more uniform modes (Kan Liquid and Super) could be bridged. The first is to reduce the Levec draining time, while the second method may be seen as an in-situ type of Kan Liquid prewetting. This type of prewetting was obtained during doping with a low surface tension liquid, at a flow rate associated with the high interaction regime for the low surface tension system. Though the hysteresis cycles did not drastically alter the predominant flow type, interesting trends were observed, some of which raised doubt about the application of the films vs. rivulet concept. One mode in particular displayed behaviour which contributed to this doubt, namely the Kan Gas mode; • Gas liquid mass transfer on this mode decreased with an increase in liquid flow rate • Relatively low pressure drops on this mode corresponded to relatively high liquid holdup • It was the only mode that exhibited no hysteresis with gas flow variation, on any of the hydrodynamic parameters The various trends and variations observed with the different types of upsets, leads to the conclusion that the concept of films vs. rivulets simply does not provide adequate explanation of the observed results. In general, two flow types may be distinguished. That which is caused by an initial increase in liquid flow rate as opposed to that which is caused by an initial increase in gas flow rate An investigation to determine the behaviour of each of the investigated parameters near the transition boundaries on all the modes, as well as a repetition of this study with non-intrusive visual techniques is recommended. / Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2008. / Chemical Engineering / unrestricted

Trickle flow is encountered in a variety of process engineering applications where gas and liquid flow through a packed bed of stationary solid. Owing to the complexities of three interacting phases, a fundamentally exhaustive description of trickle flow hydrodynamics has not been achieved. A complicating factor in describing the hydrodynamics is the fact that the hydrodynamic state is dependent not only on the present operating conditions but also on their entire history, including fluid flow rate changes and pre-wetting procedures. This phenomenon is termed hydrodynamic multiplicity and is the subject of this work. Hydrodynamic multiplicity greatly complicates both the experimental investigation into the behaviour of a trickle flow column and the theoretical modelling of the observed behaviour. Broadly speaking, this study addresses hydrodynamic multiplicity on three levels. First, a conceptual framework is proposed that can be used to study hydrodynamic multiplicity with limited resources. It is based on the absolute limiting values that the hydrodynamic parameters can adopt for a certain set of conditions, and encompasses both flow rate hysteresis loops and pre-wetting procedures. There are 5 such hydrodynamic modes. When the existing literature is critically evaluated in light of this framework, it is established that the reported experimental studies have not addressed all the issues. Previous modelling attempts are also shown to be unable to qualitative explain all the existing data. Moreover, authors have suggested different (and often contradictory) physical mechanisms responsible for hydrodynamic multiplicity. Secondly, an experimental investigation intended to supplement the existing literature and illustrate the utility of the proposed framework is launched. This includes bed-scale measurements of liquid holdup, pressure drop and gas-liquid mass transfer for a variety of conditions including different flow rates, pressures, particle shapes, particle porosity and surface tension. The second part of the experimental effort uses radiography and tomography in new ways to visualise the temporal and spatial characteristics of the different hydrodynamic modes. The tomographic investigation incorporates advanced image processing techniques in order to culminate in a pore-level evaluation of the hydrodynamic modes that reveals additional features of hydrodynamic multiplicity. Thirdly, the experimental insights are condensed into a set of characteristic trends that highlight the features of hydrodynamic multiplicity. A pore-level capillary mechanism is then introduced to qualitatively explain the observed behaviour. The mechanism shows how the differences in advancing and receding contact angles and the characteristics of the packed structure (or pore geometries) are ultimately responsible for the observed hydrodynamic multiplicity behaviour. Lastly, the effect of hydrodynamic multiplicity on trickle bed reactor performance is discussed. It is established experimentally that depending on the reaction conditions, different modes yield optimal performance. The idea of optimizing the performance by manipulating the hydrodynamic state is introduced. In totality, this work advances the understanding of trickle flow hydrodynamics in general and hydrodynamic multiplicity in particular. / Thesis (PhD (Chemical Engineering))--University of Pretoria, 2008. / Chemical Engineering / unrestricted

Les matériaux actifs sont des matériaux qui réagissent quand on leur applique un champ extérieur comme la température, la lumière, un champ magnétique ou un champ électrique. Ces champs changent les propriétés du matériau comme la longueur, la susceptibilité magnétique ou la permittivité électrique. Ces changements peuvent être utilisé pour faire du travail. Quelques exemples sont les matériaux piézoélectriques, qui changent de longueur quand on applique un champ électrique, les alliages à mémoire de forme qui changent leur longueur sous l’action de la température. Un matériau plus récent qu’on appelle les alliages mémoire de forme magnétique se de forme sous l’action d’un champ magnétique. Dans cette thèse, on utilise ce matériau pour Confectionner un actionneur. Pour ce faire, on utilise la thermodynamique des procédés irréversibles pour modéliser le matériau. La thermodynamique s’avère très versatile pour ce type de matériau car il permet de quantifier l’ échange et la transformation d’ énergie dans le matériau. Aussi, étant donné que le matériau se comporte d’une façon non-linéaire et hystérique, le cadre énergétique nous permets justement de prendre en compte ces non- linearités. Cette thèse utilise l’approche énergétique notamment les Hamiltonien à ports pour modéliser un actionneur à base d’alliage à mémoire de forme. Cette méthode nous permets aussi de concevoir des lois de commande pour contrôler le matériau. / Active materials are a class of material which react to an external stimulus such as temperature,photons, magnetic field or electric field. These stimuli cause some properties of the material tochange usually their length. Some examples are piezoelectric material which change their lengthunder the action of an electric field, Shape Memory alloys which alter their shape on applicationof heat, and more recently Magnetic Shape Memory Alloys (MSMA) which undergo a deformationon application of a magnetic field. Harnessing this property of MSMAs, we hereby present anactuator using this novel material. We extensively make use of an energy framework, namely thethermodynamics of irreversible processes to model the material. This framework has been provento be very versatile in modelling energy exchange and transformation as it occurs in the materialand also to incorporate hysteresis which arises naturally in such materials. Another advantage of thismethod is its ability to give us constitutive laws based on simple assumptions. Furthermore, usingan energy framework allows us to apply some energy based control. Port Hamiltonian Control is onesuch method and it is not limited only to linear models. This latter characteristic has proven veryuseful since MSMAs are very non-linear in nature.

The substantial increase in the unemployment rate after the crisis in the year 2008, its persistence and slow gradual decreasing in European countries is the reason that makes us think about if the theory of hysteresis is applicable to European labour markets. The main objective of this work is to verify the hypothesis of hysteresis in labour markets at regional level in Greece and Spain. The unit root tests were used on the time series of unemployment rate between 2001-2015 for Greek regions and 2002-2016 for the Spanish regions. The result is that the theory of hysteresis in unemployment is applicable on all the regions in both countries. When the data series of employment are used, the results are different. In Greece only Crete and in Spain regions Andalusia, Balearic Islands, Canary Islands, Kastilie la Mancha, Catalonia, Valencia, Murcia and Ceuta exhibit the hysteresis in employment. There are also differences between rates of men and women in Spanish regions. When unemployment rates are considered, only three region have different results. But when employments rates are used most of women's time series can't be described as non-stationary in contrast of those of the men's.

I detta arbete har elektrokemisk impedansspektroskopi använts för att producera reproducerbara impedansdata för katodmaterialet NMC811. Data som skulle kunna användas som basen för parametrisering och konstruktionen av en fysik-baserad modell. Dessutom har effekten av laddningstillstånd, temperatur, och historian av cellen på impedansen undersökts. Baserat på resultaten av preliminära test så har experiment konstruerats i vilka katodens impedans i en NMC811//Grafit cell har undersökts vid olika temperaturer och laddningstillstånd, både efter laddning och urladdning av cellen. Reproducerbara resultat kunde erhållas och det visades hur laddningstillstånd och temperatur har en stor påverkan på impedansen. Tyvärr så kunde inget sägas om hystereseffekten på grund av dålig stabilitet i lågfrekvensområdet av impedansmätningarna. / In this work, electrochemical impedance spectroscopy has been used to try and produce reproducible impedance data for the cathode material NMC811. Data that could serve as the basis of parameter extraction for the construction of a physics-based model. Furthermore, the effect of state of charge, temperature, and history of the cell on the impedance has been analysed. Based on the results of preliminary tests, an experimental cycle was constructed in which the cathode impedance of a NMC811//Graphite cell was measured at varying temperatures and state of charge, both following charge and discharge of the cell. Reproducible results were achieved, and it was shown how the state of charge and temperature of the cell had a major effect on the measured impedance. Unfortunately, no conclusions could be made about the history effect on impedance due to poor stability in the low frequency regions of the impedance measurements.

This work deals with simple fluxmeter which is able, together with other device, to show hysteresis loop. Hysteresis loop is a graphic expression of dependence of magnetic induction on intensity of magnetic field. Oscilloscope is used to display the hysteresis loop. This device is fully sufficient for the display. The measured objects are solenoids from various kinds of materials with the same shape. The main aim of this work is the design, realization and description of the fluxmeter. The fluxmeter consists of several partial blocks. The first one, on which this work is focused, is signal generator which is able to generace different kinds of signal. The generated signal comes on primary winding of solenoid where a magnetic field on a given intensity rises. An amplifier is used to obtain the sufficient intensity. Next thing this work is focused on is the design of the integrator which is necessary for the correct function of the fluxmeter. As suggested, there is shown the block diagram of linking of individual parts. There are described the measured results at the end of this work.

Contact angle behavior controls the spreading, sticking, or movement of fluid droplets on top of solid substrates, and the immiscible displacement of mixed fluids in porous media. Therefore, it influences applications such as oil recovery, CO2 geological storage, water transport in unsaturated soils, and DNAPL soil remediation techniques. The attraction forces and geometrical-molecular arrangement at the atomic scale define the strength of the interfacial tension that changes in response to changes in temperature, pressure, or the fluid composition within the system. Contact line behavior such as contact line pinning or depinning, microscale roughness, and changes in interfacial tensions influence advancing and receding contact angles. This study consists of a comprehensive database of published advancing and receding contact angles to understand the underlying mechanisms of contact line pinning and depinning and the implications of these phenomena on advancing and receding contact angles. Calcite experiments that investigate advancing and receding contact angle measurements as a function of ionic concentration complement the published literature. Critical results include: an advancing contact angle trend with calcite as a function of ionic concentration, a point of minimum contact angle hysteresis when brine concentrations are close to 0.1 M, and that contact angle behavior depends on cation type and the calcite surface anisotropy. Contact line pinning prevents flow and increases contact angle hysteresis. An analysis of the database suggests that the wide range of contact angle hysteresis of calcite and quartz with water results both from hydrogen bonds and microscale roughness at the surface which leads to pinned contact lines. The Jamin effect reduces significantly in calcite when the resultant injection brines have an ionic concentration close to 0.1 M. Thus, the pressure difference required to displace a non-wetting fluid for a wetting fluid reduces, and leads to enhanced recovery of trapped oil, gas or DNAPL.