Dissertations / Theses: 'Magnets – Viscosity'

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Harrison, Simon Andrew. "Characterisation of the mechanisms of magnetisation change in permanent magnet materials through the interpretation of hysteresis measurements." University of Western Australia. School of Physics, 2004. http://theses.library.uwa.edu.au/adt-WU2004.0048.

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The mechanisms by which magnetisation changes occur in magnetic materials may be investigated by a variety of hysteresis measurements. During this study both alternating and rotational hysteresis measurements were used to characterise the mechanisms of magnetisation change in a number of permanent magnet materials. Studies of the time dependence of magnetisation, remanent magnetisations and the dependence of the reversible magnetisation on the irreversible magnetisation were undertaken. These studies revealed that in sintered rare-earth iron magnets the magnetisation change is predominately controlled by domain nucleation, with a lesser contribution from domain wall pinning within the boundary regions of the grains. Similar mechanisms control the magnetisation change in the larger grains of melt-quenched rare-earth iron magnets. In the single domain grains of the melt-quenched materials incoherent rotation mechanisms control the changes of magnetisation. Magnetisation change in MnAlC and sintered AlNiCo was found to be controlled by domain wall pinning within the interior of the grains of the materials. Two devices were constructed for the measurement of rotational hysteresis. The first measures the angular acceleration of a sample set spinning in a magnetic field, from which the rotational hysteresis loss may be determined. The second employs rotating search coils to make direct measurements of the component of magnetisation that contributes to rotational hysteresis loss during the rotation of a sample in a field. Both devices were found to produce data consistent with that in the literature and to be useful for the characterisation of rotational hysteresis in permanent magnet materials. A simple model was used to examine the dependence of rotational hysteresis loss on various material parameters. It was found that the value of the rotational hysteresis integral is dependent on interactions and to a lesser extent distributions in anisotropy. This is contrary to assumptions commonly made in the literature but consistent with published experimental data, which has been reinterpreted. Measurements of rotational hysteresis losses in the materials studied were found to be effected by geometric demagnetisation effects. A method by which such data may be corrected for these effects is proposed. Following correction and consideration of the interactions within the materials, the rotational hysteresis data was found to be consistent with the characterisations performed in linearly alternating fields.

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Patel, Vijay. "Studies of magnetic viscosity in anisotropic materials." Thesis, Keele University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261526.

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Wang, Yingru. "Modeling of polymer melt/nanoparticle composites and magneto-rheological fluids." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1135877847.

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Maurer, Thomas. "Magnetism of anisotropic nano-objects : magnetic and neutron studies of Co1-xNix nanowires." Paris 11, 2009. http://www.theses.fr/2009PA112340.

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Le nanomagnétisme est actuellement un champ d'investigation très actif grâce aux développements de méthodes de synthèse et d'investigation originales. Cette thèse s'attache à sonder le magnétisme de nanofils magnétiques synthétisés par un procédé polyol. Ce procédé présente l'avantage de fournir un large éventail d'objets magnétiques anisotropes présentant une très bonne qualité cristalline. Les nanofils ainsi synthétisés présentent des diamètres variant de 7nm à 20nm, leur conférant un mode de renversement de l'aimantation cohérent. Cette thèse montre que les nanofils ainsi synthétisés ont des coercivités élevées comparées à celles de nanofils synthétisés par d'autres voies. Par ailleurs, les effets de l'oxydation de ces nanofils sur leurs propriétés magnétiques ont été étudiés. Les mesures magnétiques ont révélé une dépendance en température des champs d'échange et coercitif inhabituelle. Cela a permis de mettre en lumière le rôle prépondérant des fluctuations superparamagnétiques des grains antiferromagnétiques d'oxyde de cobalt dans le phénomène d'Exchange Bias. Enfin, cette thèse a aussi pour objectif de développer la technique de Diffusion de Neutrons Polarisés aux Petits Angles pour sonder le magnétisme de nanofils. Jusqu'à présent, cette technique a été surtout réservée à l'étude d'objets magnétiques isotropes. En effet, l'alignement des nanofils est crucial pour extraire des informations quantitatives d'une telle étude. C'est pour cela, qu'outre les nanofils synthétisés par procédé polyol, des nanofils inclus dans des matrices d'alumine poreuse ont aussi été étudiés par cette technique
Magnetism of individual nano-objects is a very active research field thanks to the development of original synthesis routes and investigation tools. This thesis aims at probing the magnetism of nanowires synthesized via a pure chemical route, the polyol process. This process provides a large variety and an excellent crystallinity of the synthesized nanowires. This process allows to tune the diameter of the nanowires from 7nm to 20nm leading to coherent magnetization reversaI in the nanowires. I show how the large shape and magnetocrystalline anisotropies provide large coercivities compared to magnetic nanowires synthesized via other routes. Furthermore, the oxidation of such objects has also been investigated. Magnetic measurements has revealed unsual temperature dependencies of both the coercive and exchange fields, emphasizing the role of the superparamagnetic fluctuations of the CoO antiferromagnetic grains in the Exchange Bias effect. Finally, this thesis also aims at developing Polarized Small Angle Neutron Scattering to probe magnetism in complex nano-objects. Such a technique has been ignored until now to study magnetic anisotropic nano-objects despite being well adapted. The key ingredient to carry through such a study is the perfect alignment of the nanowires. This is why, besides the nanowires synthesized via the polyol process, Polarized Small Angle neutron Scattering measurements have been performed on arrays of magnetic nanowires included in porous alumina membranes

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Senanayake, Tissa. "The influence of Hall currents, plasma viscosity and electron inertia on magnetic reconnection solutions." The University of Waikato, 2007. http://hdl.handle.net/10289/2593.

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Abstract This thesis examines magnetic reconnection in the solar corona. Magnetic reconnection is the only mechanism which allows the magnetic topology of magnetized plasmas to be changed. Many of the dynamic processes in the Sun's atmosphere are believed to be driven by magnetic reconnection and studying the behaviour of such phenomena is a key step to understanding the reconnection mechanism. In Chapters 1 to 3, we discuss the physical and mathematical framework on which current magnetohydrodynamic reconnection models are based. The aim of the thesis is to investigate theoretical models of magnetic reconnection using variety of analytic and numerical techniques within the theoretical frame work of magnetohydrodynamics (MHD). In Chapter 4 we use a line-tied X-point collapse model for compressible plasmas to investigate the role of viscosity on the energy release mechanism. This model also provides the basis for the investigation of Chapter 5 which explores the impact of Hall currents in the transient X-point energy dissipation. Chapter 6 is concerned with how reconnection is modified in the presence of generalized Ohm's law which includes both Hall current and electron inertia contributions. In contrast to the closed X-point collapse geometry adopted for compressible plasmas previously, we find it more convenient to explore this problem using an open incompressible geometry in which plasma is continually entering and exiting the reconnection region. Specially, we find the scaling of the Hall-MHD system size analytically, rather than numerically as in the X-point problem of Chapter 5. Chapter 7 summarizes the results of investigations in Chapters 4, 5 and 6.

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Critelli, Renato Anselmo Júdica. "Strongly coupled non-Abelian plasmas in a magnetic field." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-18072016-183858/.

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In this dissertation we use the gauge/gravity duality approach to study the dynamics of strongly coupled non-Abelian plasmas. Ultimately, we want to understand the properties of the quark-gluon plasma (QGP), whose scientifc interest by the scientific community escalated exponentially after its discovery in the 2000\'s through the collision of ultrarelativistic heavy ions. One can enrich the dynamics of the QGP by adding an external field, such as the baryon chemical potential (needed to study the QCD phase diagram), or a magnetic field. In this dissertation, we choose to investigate the magnetic effects. Indeed, there are compelling evidences that strong magnetic fields of the order $eB\\sim 10 m_\\pi^2$ are created in the early stages of ultrarelativistic heavy ion collisions. The chosen observable to scan possible effects of the magnetic field on the QGP was the viscosity, due to the famous result $\\eta/s=1/4\\pi$ obtained via holography. In a first approach we use a caricature of the QGP, the $\\mathcal=4$ super Yang-Mills plasma to calculate the deviations of the viscosity as we add a magnetic field. We must emphasize, though, that a magnetized plasma has a priori seven viscosity coefficients (five shears and two bulks). In addition, we also study in this same model the anisotropic heavy quark-antiquark potential in the presence of a magnetic field. In the end, we propose a phenomenological holographic QCD-like model, which is built upon the lattice QCD data, to study the thermodynamics and the viscosity of the QGP with an external strong magnetic field.
Nesta dissertação utilizamos uma abordagem via dualidade gauge/gravity para estudar a dinâmica de plasmas não-Abelianos fortemente interagentes. Nosso objetivo último visa aplicações para o plasma de quarks e glúons (QGP), cujo interesse científico cresceu exponencialmente depois de sua descoberta em meados dos anos 2000 ao colidir-se íons ultrarelativísticos. Podemos enriquecer a dinâmica do QGP ao adicionarmos campos externos, como o potencial químico (para exploração do diagrama de fases hadrônico), ou um campo magnético. Nesta dissertação, tomamos como norte a exploração dos efeitos magnéticos. De fato, acredita-se que campos magnéticos da ordem de $eB\\sim 10 m_\\pi^2$ sejam criados nos estágios iniciais do QGP. O observável escolhido para sondar possíveis efeitos do campo magnético no QGP foi a viscosidade, em partes pelo famoso resultado $\\eta/s=1/4\\pi$ obtido holograficamente. Utilizamos num primeiro momento uma caricatura da QCD, a $\\mathcal=4$ super Yang-Mills para calcular o que muda na viscosidade com o advento do campo magnético. Devemos salientar, contudo, que um plasma altamente magnetizado possui a priori sete coeficientes de viscosidade (cinco de cisalhamento e duas volumétricas). Também exploramos, nesse mesmo modelo, o potencial de um par pesado de quark-antiquark na presença de um campo magnético. Por fim, propomos um modelo holográfico fenomenológico mais semelhante a QCD, sendo ele ``calibrado\'\' pelos dados da QCD na rede, para estudar a termodinâmica e a viscosidade do QGP imerso num forte campo magnético.

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AHMAD, ALI. "Study of impulsive magnetic reconnection due to resistive tearing mode with the effect of viscosity and dynamic flow in fusion plasmas." Kyoto University, 2015. http://hdl.handle.net/2433/199415.

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Tawhid-Al-Islam, Kazi M. "Electromagnetic Effect on the Rheology of Liquid Suspension." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/513297.

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Physics
Ph.D.
Innovative methods to control the viscosity and turbulence in the flow of liquid suspension can be engineered by way of incorporating the concepts of electric and magnetic field into the rheology of complex fluids. Rheology of liquid Chocolate is a very crucial factor in determining the cost of manufacturing process as well as formulating varieties of end consumer products, for example, containing less fat. We have invented a method to lower the viscosity of liquid chocolate flow with the application of electric field. In the lab, we have found that viscosity of chocolate samples is reduced by 40~50% with our method. Thus, fat content in those samples can be reduced by 10% or more. Therefore, we expect to see much healthier and tastier chocolate product in the market once this technology gets implemented in commercial manufacturing. High viscosity and turbulence in blood flow greatly increase the risk of cardiac diseases. Hence, discovering new method to address turbulence suppression and viscosity reduction is critically important. In our study, we have found that in the in-vitro experiment, if blood is subjected to flow through a channel placed inside a strong magnetic field, its viscosity reduces by 10~20%. Based on these findings, a Megneto-Rheology (MR) therapeutic device has been developed to examine the effect on the blood pressure in human subjects. Preliminary clinical trials show that application of this MR therapy reduces blood pressure by 10% or more. In this thesis, above mentioned inventions for the flow of Blood and liquid Chocolate will be thoroughly discussed.
Temple University--Theses

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Tawhid-Al-Islam, Kazi M. "blood_flow with Mag_field." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/526135.

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Physics
Ph.D.
Innovative methods to control the viscosity and turbulence in the flow of liquid suspension can be engineered by way of incorporating the concepts of electric and magnetic field into the rheology of complex fluids. Rheology of liquid Chocolate is a very crucial factor in determining the cost of manufacturing process as well as formulating varieties of end consumer products, for example, containing less fat. We have invented a method to lower the viscosity of liquid chocolate flow with the application of electric field. In the lab, we have found that viscosity of chocolate samples is reduced by 40~50% with our method. Thus, fat content in those samples can be reduced by 10% or more. Therefore, we expect to see much healthier and tastier chocolate product in the market once this technology gets implemented in commercial manufacturing. High viscosity and turbulence in blood flow greatly increase the risk of cardiac diseases. Hence, discovering new method to address turbulence suppression
Temple University--Theses

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Tawhid-Al-Islam, Kazi M. "blood_flow without Mag_field." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/526136.

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Physics
Ph.D.
Innovative methods to control the viscosity and turbulence in the flow of liquid suspension can be engineered by way of incorporating the concepts of electric and magnetic field into the rheology of complex fluids. Rheology of liquid Chocolate is a very crucial factor in determining the cost of manufacturing process as well as formulating varieties of end consumer products, for example, containing less fat. We have invented a method to lower the viscosity of liquid chocolate flow with the application of electric field. In the lab, we have found that viscosity of chocolate samples is reduced by 40~50% with our method. Thus, fat content in those samples can be reduced by 10% or more. Therefore, we expect to see much healthier and tastier chocolate product in the market once this technology gets implemented in commercial manufacturing. High viscosity and turbulence in blood flow greatly increase the risk of cardiac diseases. Hence, discovering new method to address turbulence suppression

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Küppersbusch, Carolin Sarah [Verfasser], and Achim [Akademischer Betreuer] Rosch. "Magnetic oscillations in two-dimensional Dirac systems and Shear viscosity and spin diffusion in a two-dimensional Fermi gas / Carolin Sarah Küppersbusch. Gutachter: Achim Rosch." Köln : Universitäts- und Stadtbibliothek Köln, 2015. http://d-nb.info/1079321616/34.

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Wolff, Marc. "Mathematical and numerical analysis of the resistive magnetohydrodynamics system with self-generated magnetic field terms." Strasbourg, 2011. http://www.theses.fr/2011STRA6101.

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Ce travail est consacré à la construction de méthodes numériques permettant la simulation de processus d'implosion de coquilles en fusion par confinement inertiel (FCI) avec prise en compte des termes de champ magnétique auto-généré. Dans ce document, on commence par décrire le modèle de magnétohydrodynamique résistive à deux températures considéré ainsi que les relations de fermeture utilisées. Le système d'équations ainsi obtenu est alors divisé en sous-systèmes selon la nature de l'opérateur mathématique sous-jacent pour lesquels l'on propose ensuite des schémas numériques adaptés. On insiste notamment sur le développement de schémas volumes finis pour l'opérateur hyperbolique, ce dernier correspondant aux équations d'Euler ou de la magnétohydrodynamique idéale selon que l'on tienne compte ou non des termes de champ magnétique. Plus précisement, on propose une nouvelle classe de schémas d'ordre élevé à directions alternées construits dans le formalisme Lagrange + projection sur grille cartésienne qui présentent l'originalité d'être particulièrement bien adaptés aux calculateurs modernes grâce, entre autres, au traitement par directions alternées et à l'utilisation de techniques de viscosité artificielle. Cette propriété est illustrée par des mesures de performance séquentielle et d'efficacité parallèle. On combine ensuite les schémas hyperboliques développés avec des méthodes de type volumes finis permettant le traitement semi-implicite des termes de conduction thermique et résistive et une prise en compte explicite des termes de champ magnétique auto-générés. Afin d'étudier les caractéristiques et les effets des champs magnétiques auto-générés, on présente enfin un cas test de capsule FCI simulée à partir du début de la phase de décélération
This work is devoted to the construction of numerical methods that allow the accurate simulation of inertial confinement fusion (ICF) implosion processes by taking self-generated magnetic field terms into account. In the sequel, we first derive a two-temperature resistive magnetohydrodynamics model and describe the considered closure relations. The resulting system of equations is then split in several subsystems according to the nature of the underlying mathematical operator. Adequate numerical methods are then proposed for each of these subsystems. Particular attention is paid to the development of finite volume schemes for the hyperbolic operator which actually is the hydrodynamics or ideal magnetohydrodynamics system depending on whether magnetic fields are considered or not. More precisely, a new class of high-order accurate dimensionally split schemes for structured meshes is proposed using the Lagrange-remap formalism. One of these schemes' most innovative features is that they have been designed in order to take advantage of modern massively parallel computer architectures. This property can for example be illustrated by the dimensionally split approach or the use of artificial viscosity techniques and is practically highlighted by sequential performance and parallel efficiency figures. Hyperbolic schemes are then combined with finite volume methods for dealing with the thermal and resistive conduction operators and taking magnetic field generation into account. In order to study the characteristics and effects of self-generated magnetic field terms, simulation results are finally proposed with the complete two-temperature resistive magnetohydrodynamics model on a test problem that represents the state of an ICF capsule at the beginning of the deceleration phase

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Fridström, Richard. "Resonant magnetic perturbation effect on the tearing mode dynamics : Novel measurements and modeling of magnetic fluctuation induced momentum transport in the reversed-field pinch." Doctoral thesis, KTH, Fusionsplasmafysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-218052.

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The tearing mode (TM) is a resistive instability that can arise in magnetically confined plasmas. The TM can be driven unstable by the gradient of the plasma current. When the mode grows it destroys the magnetic field symmetry and reconnects the magnetic field in the form of a so-called magnetic island. The TMs are inherent to a type of device called the reversed-field pinch (RFP), which is a device for toroidal magnetic confinement of fusion plasmas. In the RFP, TMs arise at several resonant surfaces, i.e. where the field lines and the perturbation have the same pitch angle. These surfaces are closely spaced in the RFP and the neighboring TM islands can overlap. Due to the island overlap, the magnetic field lines become tangled resulting in a stochastic magnetic field, i.e. the field lines fill a volume instead of lying on toroidal surfaces. Consequently, a stochastic field results in an anomalously fast transport in the radial direction. Stochastic fields can also arise in other plasmas, for example, the tokamak edge when a resonant magnetic perturbation (RMP) is applied by external coils. This stochastization is intentional to mitigate the edge-localized modes. The RMPs are also used for control of other instabilities. Due to the finite number of RMP coils, however, the RMP fields can contain sidebands that decelerate and lock the TMs via electromagnetic torques. The locking causes an increased plasma-wall interaction. And in the tokamak, the TM locking can cause a plasma disruption which is disastrous for future high-energy devices like the ITER. In this thesis, the TM locking was studied in two RFPs (EXTRAP T2R and Madison Symmetric Torus) by applying RMPs. The experiments were compared with modern mode-locking theory. To determine the viscosity in different magnetic configurations where the field is stochastic, we perturbed the momentum via an RMP and an insertable biased electrode. In the TM locking experiments, we found qualitative agreement with the mode-locking theory. In the model, the kinematic viscosity was chosen to match the experimental locking instant. The model then predicts the braking curve, the short timescale dynamics, and the mode unlocking. To unlock a mode, the RMP amplitude had to decrease by a factor ten from the locking amplitude. These results show that mode-locking theory, including the relevant electromagnetic torques and the viscous plasma response, can explain the experimental features. The model required viscosity agreed with another independent estimation of the viscosity. This showed that the RMP technique can be utilized for estimations of the viscosity. In the momentum perturbation experiments, it was found that the viscosity increased 100-fold when the magnetic fluctuation amplitude increased 10-fold. Thus, the experimental viscosity exhibits the same scaling as predicted by transport in a stochastic magnetic field. The magnitude of the viscosity agreed with a model that assumes that transport occurs at the sound speed -- the first detailed test of this model. The result can, for example, lead to a clearer comparison between experiment and visco-resistive magnetohydrodynamics (MHD) modeling of plasmas with a stochastic magnetic field. These comparisons had been complicated due to the large uncertainty in the experimental viscosity. Now, the viscosity can be better constrained, improving the predictive capability of fusion science.

QC 20171122

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AHMAD, ALI. "核融合プラズマにおける粘性と動的流れの影響を受けた抵抗性ティアリングモードによる突発的磁気リコネクションに関する研究." Kyoto University, 2015. http://hdl.handle.net/2433/199546.

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Huang, Ke Colin. "ELECTRORHEOLOGY FOR ENERGY PRODUCTION AND CONSERVATION." Diss., Temple University Libraries, 2010. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/64954.

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Physics
Ph.D.
Recently, based on the physics of viscosity, we developed a new technology, which utilizes electric or magnetic fields to change the rheology of complex fluids to reduce the viscosity, while keeping the temperature unchanged. The method is universal and applicable to all complex fluids with suspended particles of nano-meter, sub-micrometer, or micrometer size. Completely different from the traditional viscosity reduction method, raising the temperature, this technology is energy-efficient, as it only requires small amount of energy to aggregate the suspended particles. In this thesis, we will first discuss this new technology in detail, both in theory and practice. Then, we will report applications of our technology to energy science research. Presently, 80% of all energy sources are liquid fuels. The viscosity of liquid fuels plays an important role in energy production and energy conservation. With an electric field, we can reduce the viscosity of asphalt-based crude oil. This is important and useful for heavy crude oil and off-shore crude oil production and transportation. Especially, since there is no practical way to raise the temperature of crude oil inside the deepwater pipelines, our technology may play a key role in future off-shore crude oil production. Electrorehology can also be used to reduce the viscosity of refinery fuels, such as diesel fuel and gasoline. When we apply this technology to fuel injection, the fuel droplets in the fuel atomization become smaller, leading to faster combustion in the engine chambers. As the fuel efficiency of internal combustion engines depends on the combustion speed and timing, the fast combustion produces much higher fuel efficiency. Therefore, adding our technology on existing engines improves the engine efficiency significantly. A theoretical model for the engine combustion, which explains how fast combustion improves the engine efficiency, is also presented in the thesis.
Temple University--Theses

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Majumdar, Madhabi. "Elastic Constants, Viscosities and Fluctuation Modes of Certain Bent-Core Nematic Liquid Crystals Studied by Dynamic Light Scattering and Magnetic Field Induced Orientational Distortion." Kent State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=kent1321991835.

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Finco, Cécile. "Étude de l’impact simultané des propriétés électriques, diélectriques et magnétiques du sous-sol sur la mesure géophysique par méthode électromagnétique inductive dans le domaine temporel (TDEM)." Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS103.

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La méthode géophysique électromagnétique inductive dans le domaine temporel (TDEM) est employée dans des domaines tels que l’hydrologie ou l’exploration minière et permet l’établissement de modèles de résistivité électrique du sous-sol. L’application de cette méthode avec des dispositifs d’acquisition réduits, avec des boucles de quelques mètres de côté, rend la mesure plus sensible aux autres paramètres électromagnétiques : la permittivité diélectrique et la viscosité magnétique. L’objet du travail de recherche présenté ici est de réaliser des sondages TDEM avec des dispositifs d’acquisition réduits et d’en extraire non seulement un modèle de résistivité électrique du sous-sol, mais aussi de permittivité diélectrique et de viscosité magnétique. L’acquisition d’un sondage TDEM avec des dispositifs à petites boucles implique également une sensibilité à la réponse du système sur lui-même, plus importante. Des simulations de cette réponse ont été menées afin de pouvoir l’estimer le plus précisément possible et la prendre en compte lors du traitement des données. Une géométrie d’acquisition des mesures est ensuite proposée pour rendre l’interprétation multi-paramètres de la mesure plus accessible. Les effets des propriétés électromagnétiques se superposent sur la mesure en configuration centrale. L’utilisation de géométries avec une sensibilité plus faible à la permittivité diélectrique et la viscosité magnétique permettra de séparer les contributions des différents paramètres. Ces développements méthodologiques ont enfin été testés lors d’acquisitions sur le site test de Garchy (Nièvre)
The geophysical electromagnetic inductive method in the time domain (TDEM) is used in fields such as hydrology or in mining exploration. It allows the establishment of electrical resistivity models of the subsurface. Using this methods with reduced acquisition loops with a width of only a few meters, makes the measurement more sensitive to additional parameters : the dielectric permittivity and the magnetic permeability. The present research work aims to acquire a small-loop TDEM sounding and to extract not only an electical resistivity model but also an estimation of the dielctric permittivity and of the magnetic viscosity. The acquisition of a small-loop TDEM sounding implies a increased sensitivity to the response from the acquisition system itself, in part because of the reduced distance between the transmission and reception loops. Simulations aiming to reproduce this system response have been carried out to be able to take it into account during the data processing step. A specific acquisition geometry is then proposed to ease the multi-parameter interpretation of the TDEM data. The effects from the electric, dielectric and magnetic properties of the ground are overlapping on the measurements in the central configuration. Using different geometry with lower sensivities to dielectric permittivity and magnetic viscosity should make the contribution of each parameter easier to isolate. These methological developments were then tested with field measurement on the test site of Garchy (Nièvre, France)

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Hafid, Hamid. "Influence des paramètres morphologiques des granulats sur le comportement rhéologique des bétons frais : étude sur systèmes modèles." Thesis, Paris Est, 2012. http://www.theses.fr/2012PEST1026/document.

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Les granulats naturels alluvionnaires sont utilisés actuellement à hauteur de 70 à 80% en volume dans la composition d'un béton et représentent désormais une ressource non renouvelable dont l'accessibilité diminue. Les formulations actuelles de béton visent à augmenter la part de granulats de roche massive concassés. Ces matériaux, de par leur histoire de fabrication, n'ont pas du tout la même morphologie. La substitution des granulats roulés par des granulats concassés affecte considérablement la mise en œuvre du matériau. Dans un premier temps, nous étudions spécifiquement l'influence de la morphologie des granulats sur les propriétés d'empilement des grains. Nous montrons que, le facteur d'aspect des grains affecte fortement la compacité dense et lâche aléatoire. À l'inverse, pour des grains de facteur d'aspect identique, l'impact de la convexité sur la mesure de la compacité dense est faible. Nous étendons, dans un deuxième temps, notre étude au comportement rhéologique de nos systèmes composés d'émulsion inverse et de sables monodisperses. Pour cela, nous construisons des courbes d'écoulement à l'échelle locale grâce à un imageur à résonance magnétique. Nous montrons que cette méthode est, de nos jours, la plus précise pour des mesures de viscosités, car elle prend en compte la migration et la localisation du matériau durant l'écoulement. Nous montrons également que le facteur d'aspect contrôle tout d'un point de vue rhéologique dans le régime où il n'y a pas de réseau percolé de contacts entre grains
Natural alluvial aggregates compose up to 70 at 80% of the volume of today's concrete and now represent for a non-renewable resource whose accessibility is reduced. Actually, concrete mix designs tend to increase the share of aggregate crushed rock mass. These materials have a very different morphology because of their manufacturing process. The substitution of rolled aggregates by crushed aggregates affects the concrete workability. At first, we study specifically the influence of the morphology of the aggregates on the packing properties. We show that the aspect ratio strongly affects the dense and random loose packing. However, for particles of the same aspect ratio, the impact of the convexity of the measure of dense packing is low. In a second step, we go further in our study by measuring the rheological behavior of our systems composed of inverse emulsion and monodisperse sands. To that purpose, we construct flow curves at the local scale thanks to a magnetic resonance imager. We show that this method is, nowadays, the most accurate for viscosity measurements because it takes into account the migration and location of the material during flow. We also show that the aspect ratio control everything of a rheological point of view in the regime where there is no percolated network of contacts between particles

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Loppinet, Benoit. "Etude de la structure de solutions d'ionomères en solvants polaires par diffusion aux petits angles." Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10208.

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Ce travail presente l'etude, principalement par diffusion aux petits angles (dpa) de neutrons et de rayons-x, de solutions d'ionomeres. Les differentes analyses de l'intensite dpa (variation de contraste, analyse du comportement asymptotique, positions du pic d'interferences), appliquees aux solutions d'ionomeres perfluores (ipf), menent a la conclusion de la presence de particules colloidales de symetrie cylindrique. Cette geometrie est obtenue pour des solutions de trois ipf dans des solvants varies couvrant une gamme importante de constante dielectrique. La valeur du rayon depend de l'ipf et du solvant. En particulier les solutions dans l'eau se trouvent avoir les particules aux rayons les plus importants. Les etudes complementaires de solutions d'ipf par viscosimetrie font apparaitre des comportements dependant fortement du solvant (presence ou non d'effet polyelectrolyte suivant le solvant). Quelques mesures rmn mettent en evidence le comportement atypique des solutions aqueuses. L'etude par dpa de solutions aqueuses d'autres ionomeres, copolymeres d'ethylene et d'acide methacrylique, met la encore en evidence l'existence de particules colloidales, de geometrie ellipsoidale, dont la taille depend du taux de neutralisation

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20

Yen, You-Hsuan, and 顏佑軒. "Experimental study on the viscosity of magnetic nanofluids." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/fqj256.

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碩士
國立臺灣大學
應用力學研究所
107
Viscosity of magnetic nanofluid with Fe3O4 particles was studied experimentally using a modified Brookfield viscometer (based on circular Couette flow), with its cylindrical test section enclosed by an electric coil for generating the magnetic field through the application of an applied current. The test section together with the coil were immersed in a circulating water tank for removing the heat due to Joule heating, such that the test fluid was kept at a constant temperature during the experiment. Both the modified viscometer and the cooling system were developed by the previous investigators, and here we performed detailed tests of stable magnetic nanofluid fluids, for demonstrating that the magnetic nanofluids can potentially be served as a smart fluid. Fe3O4 particles were synthesized using the classical co-precipitation method, and their sizes were measured as around 9.7 nm using X-ray diffraction. The particles were then coated with oleic acid for providing repulsive steric force against van der Waals force, avoiding the coagulation of particles in liquid. The coated particles are then dispersed into base fluid for the synthesis of magnetic nanofluids. Two base fluids, vacuum pump oil (VPO) and transformer oil (TO), were used. The viscosities of Fe3O4-VPO nanofluid and Fe3O4-TO nanofluid were measured for different temperature (16oC – 30oC), different volume fraction (0% – 4%), different magnetic field strength (0 – 100 Gauss, measured at the top of the test section), and different times after the fluids were synthesized (aging effect). We found: (1) The viscosity of the nanofluid decreases, but the ratio of the viscosity of the nanofluid to that of the base fluid increases slightly, as the temperature increases. (2) The viscosity of the nanofluid increases with the magnetic field strength and volume fraction. (3) Through a repeated periodic excitation of applied magnetic field (field is on for 5 minutes and then off for 5 minutes within a cycle), it was found that the viscosity of magnetic nanofluid could be tuned “instantaneously” as desired by the magnetic field. In particular, viscosity was enhanced when the magnetic field was on, and recovered when the field was off; and the enhancement was proportional to the field strength. (4) The nanofluids in this study are shear thinning nanofluids under the action of magnetic field. (5) The aging effect is minor for Fe3O4-VPO nanofluid, but is substantial for Fe3O4-TO nanofluid. Thus the Fe3O4-VPO nanofluid is more appropriate for application.

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21

Chang, Ming-Hsuan, and 張銘軒. "Effect of magnetic field on the viscosity of nanofluids." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/72314836250890157451.

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碩士
國立臺灣大學
應用力學研究所
104
Nanofluid is a liquid (called base fluid) suspended uniformly and stably with nano particles. The thermal conductivity and viscosity of nanofluid could be substantially greater than that of the base fluid, because of the particle agglomeration according to the literature. Thus, it would be beneficial for the application if we could control the particle agglomeration via an external means, such as an applied magnetic or electric field, outside the fluidic system. Fe3O4-Engine oil nanofluid was prepared using the two-step method, together with the modification of an existing viscometer (Brookfield, DV2T model) for the experiment in the present study. Metal wire is coilled around the cylindrical test tube of the viscometer, so that we can generate a magnetic field along the axis of the tube via an applied electric field, for accessing the effect of magnetic field on the viscosity of nanofluids. According to the present experiments, we found: (1) the viscosity of nanofluid increases with volume fraction but decrease with temperature. However, the temperature ratio between the nanofluid and base fluid remains unchanged as the temperature varies. (2) The viscosity of nanofluid increases as the strength of the magnetic field increases. (3) The viscosity can recover to the original state when the applied magnetic field is cutoff for relative low applied magnetic field, but cannot for relative high magnetic field because of the temperature rise associated with Joule heating. (4) Two results may occur for a long-term application of a magnetic field: the viscosity decreases because of the increase of the temperature, and increases because of the particle agglomeration. The degree of precipitation increases as the magnetic field increases, and the magnetic effect on viscosity is more feasible at lower temperature. It is hoped that the present study is helpful for understand the physics, and for a boarder application of nanofluids.

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22

Liu, Yu-En, and 劉宇恩. "Study of the viscosity of magnetic nanofluids via slit viscometer." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/jpqcnp.

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碩士
國立臺灣大學
應用力學研究所
107
The viscosity of magnetic nanofluid was studied experimentally using Fe3O4-VPO (vacuum pump oil) nanofluid in a slit viscometer. Magnetic nanocrystals of Fe3O4 were prepared by the co-precipitation method, whose size was measured as about 8 nm using the X-ray diffraction (XRD). The nano Fe3O4 particles were then coated with oleic acid, and dispersed in base fluid, for forming the nanofluid. The coated oleic acid was em-ployed for providing the steric force to counterbalance the van der Waals force between particles, ensuring the stability of nanofluid. Two base fluids, kerosene and vacuum pump oil, were used for synthesizing nanofluids. The sizes of particles in diluted Fe3O4-kerosene nanofluids were measured as 8300 nm, with an average at 27 nm, using the dynamic light scattering (DLS) technique. By comparing the DLS measurement with the XRD measurement, it is suggested that the particles in nanofluid for application is in general in agglomerated state. The slit viscometer was fabricated in this study by molding a polydimethylsiloxane (PDMS) channel on a glass substrate, with the pressure drop of the flow along the rec-tangular channel measured using a built-in manometer, for assessing the fluid viscosity. The magnetic field was applied to the flow by sandwiching the channel with two perma-nent magnetic plates, placed perpendicular or parallel to the vorticity of the flow, for stud-ying the effect of field orientation. The field strength can be adjusted by changing the dis-tance between the magnetic plates, and the volume flow rate can be adjusted through the setting of the volume flow rate of the syringe pump driving the flow. The main differences between the present device and those in the literature are that here the channel of the vis-cometers is smaller and the magnetic field is applied using permanent magnet plates, such that less test fluid is required and cooling can be avoided, respectively. The measurement using the present device was validated through the measurement using a modified Brookfield viscometer with the magnetic field generated by an electric coil surrounding the test section. Measurements of Fe3O4-VPO nanofluids of different volume fractions (1.2% and 3%) under different shear rates (1.25 – 2.5 s-1), magnetic field strength (0 – 160 gauss) and magnetic field direction were performed. We found: (1) Viscosity can be enhanced sub-stantially through the application of a moderate magnetic field, for example, 50% and 300% increases were measured for a nanofluid of volume fraction 3% under 1.25 s-1 at 160 Gauss, when the field was applied parallel and perpendicular to the vorticity of the flow, respectively. (2) Shearing thinning of the viscosity of magnetic nanofluid is substan-tial, for example, the viscosity enhancement in (1) was reduced from 300% to 130% if the shear rate was increased from 1.25 s-1 to 2.5 s-1 when the field is applied perpendicular to the vorticity. (3) Aging effect is minor when the magnetic field is less than 100 Gauss, but shows moderate changes at a higher field strength. For example, twice of the viscosity increase was observed for a nanofluid of 1.2% volume fraction at 160 Gauss under 1.25 s-1.

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23

Senanayake, Tissa. "The influence of Hall currents, plasma viscosity and electron inertia on magetic reconnection solutions." 2007. http://adt.waikato.ac.nz/public/adt-uow20070613.141123/index.html.

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24

Chou, Shih-Kai, and 周士凱. "Experimental study of the effect of magnetic field on the viscosity of Fe3O4-nanofluids." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/9j3h6t.

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碩士
國立臺灣大學
應用力學研究所
106
Nanofluid is a liquid suspended uniformly and stably with nanoparticles. Its application in heat transfer enhancement was studied extensively for the past two decades, and the focus has been shifted recently to other applications. Both the thermal conductivity and viscosity of nanofluid can be increased significantly because of the particle agglomeration. The work of this thesis is to study experimentally the effect of an applied magnetic field on the viscosity of nanofluid, and investigate the possibility of manipulation of viscosity via the magnetic field. The nanofluids in this study were synthesized using two-step method, with Fe3O4 nano particles dispersed in two viscous base liquids, engine oil (EO) and vacuum pump oil (VPO), without using surfactants. The magnetic field was applied electrically through a coil around the cylindrical test chamber of a commercial Searle viscometer. However, it was found that Joule heating is significant for such a device even for a moderate magnetic field around 100 Gauss. The decrease of viscosity associated with the Joule heating is of the same order as the increase of viscosity associated with the magnetic field. A cooling system was thus designed and fabricated successfully in this study for removing the heat, so that the sole effect of magnetic field on viscosity can be studied. The findings for magnetic nanofluids in this study are as follows. (1) Fe3O4-EO nanofluid is more stable than Fe3O4-VPO nanofluid because of the higher viscosity of engine oil. (2) The viscosity of nanofluid increases with volume fraction of the suspended particles and temperature of the fluid in the absence of magnetic field. (3) The viscosity of nanofluid can be doubled by adding a small amount of nano particles (1 % volume fraction) at a moderate applied magnetic field (100 Gauss). (4) The viscosity of nanofluid responses sharply to the applied magnetic field. It can be increased by applying a magnetic field, and recovers after the field has been shut down, suggesting that the viscosity of nanofluid can be controlled effectively via the magnetic field. (5) The agglomeration of particles, and thus the settling, can be enhanced by the applied magnetic field. (6) The shear thinning effect associated with non-Newtonian behavior for the present nanofluids is more obvious because of the applied magnetic field.

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25

Eser, Bekir Engin. "Spectroscopic and Kinetic Investigation of the Catalytic Mechanism of Tyrosine Hydroxylase." 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-12-7355.

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Tyrosine Hydroxylase (TyrH) is a pterin-dependent mononuclear non-heme iron oxygenase. TyrH catalyzes the hydroxylation reaction of tyrosine to dihydroxyphenylalanine (DOPA). This reaction is the first and the rate-limiting step in the biosynthesis of the catecholamine neurotransmitters. The active site iron in TyrH is coordinated by the common facial triad motif, 2-His-1-Glu. A combination of kinetic and spectroscopic techniques was applied in order to obtain insight into the catalytic mechanism of this physiologically important enzyme. Analysis of the TyrH reaction by rapid freeze-quench Mossbauer spectroscopy allowed the first direct characterization of an Fe(IV) intermediate in a mononuclear nonheme enzyme catalyzing aromatic hydroxylation. Further rapid kinetic studies established the kinetic competency of this intermediate to be the long-postulated hydroxylating species, Fe(IV)O. Spectroscopic investigations of wild-type (WT) and mutant TyrH complexes using magnetic circular dichroism (MCD) and X-ray absorption spectroscopy (XAS) showed that the active site iron is 6-coordinate in the resting form of the enzyme and that binding of either tyrosine or 6MPH4 alone does not change the coordination. However, when both tyrosine and 6MPH4 are bound, the active site becomes 5-coordinate, creating an open site for reaction with O2. Investigation of the kinetics of oxygen reactivity of TyrH complexes in the absence and presence of tyrosine and/or 6MPH4 indicated that there is a significant enhancement in reactivity in the 5-coordinate complex in comparison to the 6-coordinate form. Similar investigations with E332A TyrH showed that Glu332 residue plays a role in directing the protonation of the bridged complex that forms prior to the formation of Fe(IV)O. Rapid chemical quench analyses of DOPA formation showed a burst of product formation, suggesting a slow product release step. Steady-state viscosity experiments established a diffusional step as being significantly rate-limiting. Further studies with stopped-flow spectroscopy indicated that the rate of TyrH reaction is determined by a combination of a number of physical and chemical steps. Investigation of the NO complexes of TyrH by means of optical absorption, electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) techniques revealed the relative positions of the substrate and cofactor with respect to NO, an O2 mimic, and provided further insight into how the active site is tuned for catalytic reactivity upon substrate and cofactor binding.

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