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1
Meshcheriakov, Dmytro. "Non linear dynamics of magnetic islands in fusion plasmas." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4785.
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Les modes de déchirement sont connus pour détériorer le confinement et limiter les performances dans les machines de fusion. Plusieurs études sur les modes de déchirements ont été menées, en incluant un degré croissant de complexité dans le modèle physique afin de mieux comprendre les observations expérimentales. Une de ces extensions est l'introduction d'une description du plasma comme un fluide à deux espèces, ions et électrons, dont les dynamiques sont fortement différentes. Un autre mécanisme physique connu pour être important est la courbure du champ magnétique non perturbé. Dans cette thèse, nous étudions les questions de la stabilité linéaire et de l'évolution non linéaire des îlots magnétiques, en présence de la courbure des lignes de champ et de la rotation diamagnétique, avec le code MHD non linéaire XTOR-2F, qui inclut le transport anisotrope de chaleur et les effets géométriques. Cette analyse est appliquée à une décharge entièrement non-inductive de Tore Supra. Ce mode d'opération est crucial pour démontrer la possibilité d'un fonctionnement continu sur un réacteur de type tokamak. Dans cette thèse, la possibilité d'une stabilisation complète des modes de déchirement par la rotation diamagnétique, en présence de la courbure toroidale des lignes de champ magnétique, est démontrée. Dans le domaine linéairement stable, le mode est métastable: le niveau de saturation dépend de la taille de l'îlot initial. Dans le domaine non linéaire, la saturation de l'îlot est fortement réduite par la rotation diamagnétique et par le nombre de Lundquist. La question de l'extrapolation des résultats obtenus vers la future generation de machines de fusion est également abordéeTearing modes are known to deteriorate the confinement and limit plasma performance in fusion devices. Various studies of this mode have been performed lately including an increasing level of complexity in the physical description which is required for understanding of experimental observations. One of such extensions is the introduction of diamagnetic rotation into the system. Another physical mechanisms known to be important for tearing mode dynamics is the curvature of unperturbed magnetic field lines and neoclassical physics. In this thesis we investigate the issues of linear stability of the tearing modes in a presence of both curvature and diamagnetic rotation using the non linear full-MHD toroidal code XTOR-2F, which includes anisotropic heat transport, diamagnetic and geometrical effects. This analysis is applied to one of the fully non-inductive discharges on Tore-Supra. Such experiments are crucially important to demonstrate reactor scale steady state operation for the tokamak. In this thesis, the possibility of full linear stabilization of the tearing modes by diamagnetic rotation in the presence of toroidal curvature is shown. In the linearly stable domain, the mode is metastable: saturation level depends on the seed island size. In the non linear regime, the saturation of n=1, m=2 mode is found to be strongly reduced by diamagnetic rotation and by Lundquist number. The question of extrapolation of the obtained results towards future generation of fusion devices is also addressed. In particular, for ITER size machines, the toroidal curvature is expected to be more important due to higher performance factor β
2
Yu, Edmund Po-ning. "Evolution equations for magnetic islands in a reversed field pinch." Access restricted to users with UT Austin EID, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3037030.
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Ayten, Bircan. "Simulation Of The Stabilization Of Magnetic Islands By Ecrh And Eccd." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12611044/index.pdf.
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An almost universal instability in high pressure plasmas is the Neoclassical
Tearing Mode (NTM). NTMs are driven by local perturbations in
the current density and result in magnetic island like deformations of the
magnetic topology. They can be stabilized by compensating the current
perturbations with local electron cyclotron resonance heating (ECRH) or
with non-inductive current drive (ECCD). The modified Rutherford equation
describes the nonlinear evolution of tearing modes as determined by
various contributions to the local current density pertubation. An extensive
investigation of the two terms representing the stabilizing effects from
ECRH and ECCD have been made resulting in accurate description of both
terms. The results of this model can now be compared to the experimental
observations. For this purpose, an extensive data set exists from the past
experiments on tearing mode stabilization by ECRH and ECCD on TEXTOR.
The properly benchmarked model can then be used to predict the
effectiveness of ECRH and ECCD for NTM stabilization on International
Thermonuclear Experimental Reactor (ITER). In addition, a number of
predictions on the effects of ECRH and ECCD on the growth of the NTM
have been made on the basis of crude approximations to the ECRH and
ECCD tems in the modified Rutherford equation. These predictions can
now be checked against the more accurate expressions obtained.
4
Nishimura, Seiya. "Study on multi-scale nonlinear dynamics of magnetic islands in tokamak plasmas." Aix-Marseille 1, 2009. http://www.theses.fr/2009AIX11060.
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Cette thèse est consacrée à la modélisation et à la simulation de la dynamique non linéaire d’un îlot magnétique en présence d’un gradient de pression dans un plasma magnétisé de tokamak. Ce mode nommé ‘’drift tearing’’ est en fait un mode de déchirement couplé à une onde de dérive électronique. Les instabilités de déchirement jouent un rôle important dans la stabilité magnétohydrodynamique des plasmas de fusion thermonucléaire. Il est en effet admis que ces instabilités détermineront la limite en pression dans les plasmas du futur tokamak ITER. Il se trouve que de nombreuses questions restent ouvertes concernant les conditions d'apparition ainsi que la dynamique de ces modes en régime non-linéaire. Un point très important est la vitesse de rotation de l'îlot magnétique qui se développe lors de l'apparition d'une instabilité de déchirement. Cette vitesse de rotation, en particulier son signe, conditionne l'évolution non linéaire de l'îlot. Dans cette thèse, les mécanismes physiques sous-jacents à cette rotation sont explorés. Un résultat important est que le sens de la rotation de l'îlot change en fonction de la viscosité et de la résistivité. Afin de comprendre ce phénomène, un modèle analytique a été développé et a permis de comparer favorablement les prédictions théoriques aux simulations numériques de la dynamique de l'îlot en régime non-linéaire. Ce modèle a aussi permis de démontrer un résultat d'application pratique : l'augmentation de la fréquence de rotation avec le nombre de Prandtl magnétiqueThis thesis is devoted to the modelling and simulation of the nonlinear dynamics of a magnetic island in presence of a pressure gradient in a tokamak plasma. This mode called “drift tearing” is in fact a tearing mode coupled to an electronic drift wave. Tearing instabilities play an important role in the magneto-hydrodynamic stability of thermonuclear fusion plasmas. It is admitted that these instabilities will determine the pressure limit in future plasma tokamak reactors like ITER. There are still many open questions related to the conditions of appearance as well as the nonlinear dynamics of these modes. An important issue is the island rotation which develops during a tearing instability. Indeed, the rotation speed as well as its sign have an important impact on the nonlinear evolution of the magnetic island. In this thesis the physical mechanisms underlying this rotation are explored. An important result is that the rotation direction of the island depends on the viscosity and the resistivity parameters. To understand this phenomenon, a model is developed and validated by numerical simulations. A practical result is derived from this model: the rotation frequency of the magnetic island increases with the magnetic Prandtl number
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Trippl, Michaela. "Islands of Innovation and Internationally Networked Labor Markets. Magnetic Centers for Star Scientists?" Institut für Regional- und Umweltwirtschaft, WU Vienna University of Economics and Business, 2009. http://epub.wu.ac.at/138/1/document.pdf.
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Top researchers and outstanding scientists are an essential source of science-based innovation and regional development. The location pattern and international movements of the scientific elite, are, thus, of fundamental importance. However, despite a growing interest, there is only little empirical evidence about these core issues. Drawing on the results of a world-wide survey of 720 ―star scientists‖ (identified by the number of citations they generated in journals in the ISI databases in the period 1981-2002) this paper seeks to explore the role of islands of innovation in providing employment opportunities for stars. It is shown that US and European islands of innovation and their regional labor markets are at the forefront when it comes to produce (i.e. to educate) and to employ star scientists and to exchange them with other places. Furthermore, the paper provides evidence for the formation of a network among innovative regional labor markets based on international movements of the best and brightest scientific minds. (author´s abstract)Series: SRE - Discussion Papers
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Ciuciulkaite, Agne. "Micromagnetic simulations for the investigation of magnetic vortex array dynamics." Thesis, Uppsala universitet, Materialfysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-280767.
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In this work the dynamics of permalloy circular magnetic islands of 225 nm radius and 10 nm thickness arranged into square lattices was investigated employing micromagnetic simulations.The simulations of the vortex magnetization loops and the ferromagnetic resonance (FMR) spectra were carried out using a free micromagnetics simulation software Mumax3. The obtained data was analyzed using Matlab. The simulations were carried out on a single vortex island as well as on two different lattices. The first lattice is comprised of interacting islands, while the second lattice - of non-interacting islands, separated by 25 nm and by 450 nm edge-to-edge distance, respectively. The magnetization loops were simulated by applying the static magnetic field in-plane of the single island or the lattice. The FMR simulations were carried out by applying the static magnetic field in-plane of the lattice and after the system reached the ground state in that field, the excitation as a sinc pulse was sent out along the out-of-plane direction of the lattice. The analysis of the obtained FMR spectra revealed that the several resonant modes are present for the single vortex island and the lattice, comprised of such islands. However, the physical explanation of the origin of those modes is a subject for further investigations.
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Springer, Felix [Verfasser]. "Probing the energy barrier distribution in arrays of patterned magnetic nano islands / Felix Springer." Konstanz : Bibliothek der Universität Konstanz, 2011. http://d-nb.info/1017326568/34.
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Kumar, Santhosh Tekke Athayil, and santhosh kumar@anu edu au. "Experimental Studies of Magnetic Islands, Configurations and Plasma Confinement in the H-1NF Heliac." The Australian National University. Research School of Physical Sciences and Engineering, 2008. http://thesis.anu.edu.au./public/adt-ANU20080611.171513.
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Rational magnetic flux surfaces in fusion (toroidal plasma confinement) devices can break the magnetic field lines and reconnect
them in the form of magnetic islands. Formation of these magnetic islands can have a serious impact on the plasma confinement properties of the device. Islands can in general degrade the confinement by
mixing up different regions of the plasma. However there has been experimental evidence of confinement improvement by island induced transport barriers, under certain conditions. Even though there are a
large number of theoretical and experimental works on magnetic islands to date, there is clearly a paucity of convincing experimental
understanding on the nature of behaviour of islands in plasma. This thesis reports detailed experimental studies conducted on the H-1NF heliac stellarator, to gain an in-depth understanding of magnetic islands and their influence in plasma confinement.¶
Work reported in this thesis can be mainly divided into three parts: (a) high resolution imaging of vacuum magnetic islands and flux surfaces of H-1NF, (b) accurate computer modeling of H-1NF magnetic
geometry and (c) detailed experiments on magnetic islands in plasma configurations.¶
Electron-beam wire-tomography in the H-1NF has been used for the high resolution mapping of vacuum magnetic flux surfaces and islands. Point-to-point comparison of the mapping results with
computer tracing, in conjunction with an image warping technique, has enabled systematic exploration of magnetic islands and surfaces of interest. A fast mapping technique has been developed, which
significantly reduced the mapping time and made this technique suitable for mapping at higher magnetic fields.¶
Flux surface mapping has been carried out at various magnetic configurations and field strengths. The extreme accuracy of this technique has been exploited to understand the nature of error fields,
by point-by-point matching with computer tracing results. This has helped in developing a best-fit computer model for H-1NF magnetic configurations, which can predict rotational transform correct to
three decimal places. Results from plasma experiments on magnetic configuration studies are best explained by the new model.¶
Experiments with low order magnetic islands in plasma configurations yielded some new results. It has been observed that the low order magnetic islands (m = 2) near the core of the plasma serve as pockets of improved confinement region under favourable conditions. This results in significant profile modifications including enhancement of the radial electric field near the core to a large positive value. The characteristics of islands are found to be
dependent on the plasma collisionality and the island width.¶
Experiments with a magnetic configuration which exhibits no vacuum islands, but the core rotational transform very close to
low order rational value, show a spontaneous transition of the radial electric field near the core to a large positive value (nearly 5
kV/m), with a strong electric field shear (nearly 700 kV/m2) and localised improvement in confinement, during the discharge. Evidence indicates that the transition is driven by the excitation of low order magnetic islands near the axis during the plasma discharge, due to the modification of rotational transform profile by toroidal plasma currents. The situation is similar to the Core Electron-Root Confinement (CERC) observed during high temperature ECH
plasma discharges on other helical devices. This result provides an experimental evidence for the hypothesis that the threshold conditions for observing CERC can be reduced by exciting magnetic islands near
the core of the plasma.
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Kumar, Santhosh Tekke Athayil. "Experimental studies of magnetic islands, configurations and plasma confinement in the H-1 NF heliac /." View thesis entry in Australian Digital Theses Program, 2007. http://thesis.anu.edu.au/public/adt-ANU20080611.171513/index.html.
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Gallen, Sean F. "An investigation of the magnetic fabrics and the paleomagnetism of the Ghost Rocks Formation, Kodiak Islands, Alaska /." Online version, 2008. http://content.wwu.edu/cdm4/item_viewer.php?CISOROOT=/theses&CISOPTR=301&CISOBOX=1&REC=2.
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Alam, Khan. "Growth, Structural, Electronic, and Magnetic Characterization of GaN, CrN, Fe Islands on CrN, and Fe/CrN Bilayer Thin Films." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1478024656083129.
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Monteiro, Luiz Henrique Alves. "Superfícies magnéticas de campos helicoidais toroidais em tokamaks." Universidade de São Paulo, 1990. http://www.teses.usp.br/teses/disponiveis/43/43131/tde-22052014-142315/.
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Propõe-se analisar teoricamente a instabilidade disruptora que ocorre em plasmas confinados em Tokamaks, investigando-se a influencia de campos helicoidais ressonantes em seu equilíbrio. Para isso, considerou-se a superposição do campo magnético do plasma em equilíbrio MHD estático com o campo associado às ressonâncias, levando-se em conta a geometria toroidal do Tokamak. Devido a falta de simetria, as linhas do campo magnético total resultante desta superposição devem formar superfícies magnéticas apenas em algumas regiões do plasma. Usando o método da media, foram obtidas (analiticamente) funções de superfícies aproximadas que contem, em torno das regiões de ressonância do plasma, as linhas deste campo magnético total. Verificou-se que estas superfícies aproximadas têm estruturas de ilhas magnéticas.It is proposed to analyse theoretically the disruptive instability that occurs in confined plasmas in Tokamaks, through investigation of the influence of resonant helical fields on their equilibrium. With this aim, a superposition of the magnetic field of the plasma in static MHD equilibrium with the field associated with the resonances is considered, taking into account the toroidal geometry of the tokamak. Due to the lack of symmetry, the lines of the total magnetic field resulting from this superposition must form magnetic surfaces only around some regions of the plasma. Using the averaging method, functions of approximate magnetic surfaces are obtained (analitically) around the regions of resonances of the plasma (they contain the lines of this total magnetic field). It was verified that these approximate surfaces have structures of magnetic islands.
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Taborda, David Ciro. "Magnetic field modeling for non-axisymmetric tokamak discharges." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-04012017-142757/.
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In this work we study the magnetic field modeling of realistic non-axisymmetric plasma equilibrium configurations and the heat flux patterns on the plasma facing components of tokamak divertor discharges. We start by establishing the relation between generic magnetic configurations and Hamiltonian dynamical systems. We apply the concept of magnetic helicity, used to establish topological bounds for the magnetic field lines in ideal plasmas, and to understand the self-consistency of reconnected magnetic surfaces in non-axisymmetric configurations. After this theoretical discussion, we present some results on magnetohydrodynamic equilibrium and the use of analytical solutions to the Grad-Shafranov equation for describing real tokamak discharges based on the experimental diagnostics and realistic boundary conditions. We also compare the equilibrium reconstruction of a DIII-D discharge obtained with a numerical reconstruction routine, developed as part of this research, and the EFIT code used by several tokamak laboratories around the world. The magnetic topology and plasma profiles obtained with our method are in considerable agreement with the numerical reconstruction performed with the other code. Then, we introduce a simplified description of the generic non-axisymmetric magnetic field created by known sources and implement it numerically for describing the magnetic field due to external coils in tokamak devices. After that, we use this routines to develop a numerical procedure to adjust a suitable set of non-linear parameters of internal filamentary currents, which are intended to model the plasma response based on the magnetic field measurements outside the plasma. Finally, these methods are used to model the magnetic field created by a slowly rotating plasma instability in a real DIII-D discharge. The plasma response modeling is based on the magnetic probe measurements and allow us to calculate the magnetic field in arbitrary locations near the plasma edge. Using this information we determine the non-axisymmetric plasma edge through the magnetic invariant manifolds routine developed during this work. The intersection of the calculated invariant manifold with the tokamak chamber agrees considerably well with the heat flux measurements for the same discharge at the divertor plates, indicating the development of a rotating manifold due to the internal asymmetric plasma currents, giving quantitative support to our simplified description of the magnetic field and the plasma edge definition through the invariant manifolds.Neste trabalho estuda-se a modelagem do campo magnético em configurações realistas de plasmas em equilíbrio não-axissimétrico e o fluxo de calor nos componentes em contato com o plasma em descargas de tokamaks com desviadores poloidais. Começa-se estabelecendo a relação entre configurações magnéticas arbitrárias e sistemas dinâmicos Hamiltonianos. Então aplicamos o conceito de helicidade magnética, que é usado para estabelecer limitações topológicas sobre as linhas de campo magnético em plasmas ideais, assim como para compreender a auto-consistência das superfícies magnéticas reconectadas em configurações não-axissimétricas. Após esta discussão teórica, apresentam-se alguns resultados sobre o equilíbrio magnetohidrodinâmico e o uso de soluções analíticas à equação de Grad-Shafranov para descrever descargas reais em tokamaks, com base em diagnósticos experimentais e condições de contorno realistas. Também realiza-se uma comparação entre a reconstrução do equilíbrio de uma descarga do DIII-D, obtida mediante uma rotina numérica desenvolvida para esta pesquisa, com a obtida mediante o código EFIT, usado amplamente em diversos tokamaks. Após isso, apresenta-se uma descrição simplificada do campo magnético não-axissimétrico, criado por fontes determinadas, e a sua implementação para descrever o campo magnético devido às correntes externas em tokamaks. Então, usam-se estas rotinas para desenvolver um procedimento numérico que ajusta um conjunto adequado de parâmetros não-lineares de correntes filamentares internas, com as quais pretende-se modelar a resposta do plasma com base nas medidas de campo magnético fora do plasma. Finalmente, estes métodos são utilizados para modelar o campo magnético criado por uma instabilidade com rotação lenta numa descarga do DIII-D. Com base nas medidas das sondas magnéticas é possível modelar os campos criados em regiões arbitrárias próximas da borda do plasma. Usando esta informação é possível determinar a borda não-axissimétrica do plasma mediante as invariantes magnéticas calculadas com a utilização de uma rotina desenvolvida durante este trabalho. A intersecção da superfície invariante com a câmara do tokamak coincide satisfatoriamente com as medidas de fluxo de calor nas placas do divertor para a mesma descarga, indicando o desenvolvimento de uma variedade giratória criada pelas correntes de plasma não-axissimétricas, e sustentando quantitativamente a nossa descrição simplificada do campo magnético, assim como a definição da borda do plasma mediante as invariantes magnéticas.
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Silva, Elton Cesar da. "Efeitos da geometria toroidal na atuação de campos helicoidais ressonantes em Tokamaks." Universidade de São Paulo, 2001. http://www.teses.usp.br/teses/disponiveis/43/43131/tde-09102012-151302/.
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Neste trabalho, consideramos os efeitos de um campo magnético ressonante externo sobre o plasma confinado em um tokamak. Este campo magnético pode ser produzido quer por condutores helicoidais ou por um limitador magnético caótico. O principal propósito desse campo magnético ressonante é criar uma região de linhas de força caóticas na borda da coluna de plasma que pode melhorar o confinamento do plasma. O campo magnético de equilíbrio foi obtido resolvendo-se a equação de GRAD-SHAFRANOV em um sistema de coordenadas intrinsecamente toroidal (as coordenadas polares toroidais). Obtivemos o campo magnético, gerado pelos condutores helicoidais, através da solução explícita da equação de LAPLACE no mesmo sistema de coordenadas. A partir desse campo magnético, tomando o termo de mais baixa ordem, obtivemos analiticamente um mapa estroboscópico simplético para um conjunto de anéis limitadores magnéticos caóticos. Calculamos esse mapa estroboscópico simplético usando uma formulação hamiltoniana e adotando a. ação dos limitadores magnéticos caóticos como uma sequência de pulsos do tipo função delta. Com esse mapa estroboscópico simplético, caracterizamos algumas ilhas magnéticas ressonantes e a transição para um regime de caos global através da superposição das mesmas. Usamos esse mapa estroboscópico simplético para estudar o transporte das linhas de força na borda da coluna de plasma. A perda de linhas de força caóticas, que atingem a parede interna do tokamak, segue uma distribuição de POISSON. Calculamos, ainda, o número médio de voltas, ao redor da câmara de vácuo, necessárias para que uma linha de força caótica atinja a parede da câmara.In this work, we have considered the effects of an external resonant magnetic field on the plasma confined in a tokamak. This resonant field can be produced by helical windings or by a chaotic magnetic limiter. The main purpose of this resonant magnetic field is to create a region of chaotic field lines at the edge of the plasma that can improve the confinement of the plasma. The equilibrium tokamak field was obtained by solving the GRAD-SHAFRANOV equation in an intrinsically toroidal coordinate system (the toroidal polar coordinates). We have obtained the magnetic field which has been generated by helical windings through an explicit solution of the LAPCACE equation in the same coordinate system. From this magnetic field, taken in its lowest order, we have analytically obtained a sympletic stroboscopic map for a set of chaotic magnetic limiters. We have calculated this sympletic stroboscopic map by using a Hamiltonian formulation and by supposing the action of the chaotic magnetic limiters as a sequence of delta-function pulses. With this sympletic stroboscopic map we have characterized some resonant magnetic islands and the onset of global chaos through their overlap. We have used this sympletic stroboscopic map in order to study the transport of the field lines at the edge of the plasma. The loss of chaotic field lines that reach the inner wall of the tokamak follows a POISSON distribution. We have also calculated the average number of toroidal turns for a chaotic field line to reach the inner wall of the tokamak.
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Kalezhi, Josephat. "Modelling data storage in nano-island magnetic materials." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/modelling-data-storage-in-nanoisland-magnetic-materials(9b449925-1a39-4711-8d55-82e6d8ac215c).html.
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Data storage in current hard disk drives is limited by three factors. These are thermal stability of recorded data, the ability to store data, and the ability to read back the stored data. An attempt to alleviate one factor can affect others. This ultimately limits magnetic recording densities that can be achieved using traditional forms of data storage. In order to advance magnetic recording and postpone these inhibiting factors, new approaches are required. One approach is recording on Bit Patterned Media (BPM) where the medium is patterned into nanometer-sized magnetic islands where each stores a binary digit.This thesis presents a statistical model of write errors in BPM composed of single domain islands. The model includes thermal activation in a calculation of write errors without resorting to time consuming micromagnetic simulations of huge populations of islands. The model incorporates distributions of position, magnetic and geometric properties of islands. In order to study the impact of island geometry variations on the recording performance of BPM systems, the magnetometric demagnetising factors for a truncated elliptic cone, a generalised geometry that reasonably describe most proposed island shapes, were derived analytically.The inclusion of thermal activation was enabled by an analytic derivation of the energy barrier for a single domain island. The energy barrier is used in a calculation of transition rates that enable the calculation of error rates. The model has been used to study write-error performance of BPM systems having distributions of position, geometric and magnetic property variations. Results showed that island intrinsic anisotropy and position variations have a larger impact on write-error performance than geometric variations.The model was also used to study thermally activated Adjacent Track Erasure (ATE) for a specific write head. The write head had a rectangular main pole of 13 by 40 nm (cross-track x down-track) with pole trailing shield gap of 5 nm and pole side shield gap of 10 nm. The distance from the pole to the top surface of the medium was 5 nm, the medium was 10 nm thick and there was a 2 nm interlayer between the soft underlayer (SUL) and the medium, making a total SUL to pole spacing of 17 nm. The results showed that ATE would be a major problem and that cross-track head field gradients need to be more tightly controlled than down-track. With the write head used, recording at 1 Tb/in² would be possible on single domain islands.
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Yee, Chin-ming. "Magnetic and gradiometer survey of a site in northeastern Lantau Island Hong Kong." Click to view the E-thesis via HKUTO, 2002. http://sunzi.lib.hku.hk/hkuto/record/B43895025.
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Lamarche, Amy J. "Magnetic structure of Loihi Seamount, an active hotspot volcano in the Hawaiian Island chain." Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969.1/296.
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The use of geophysical techniques to image the interiors of active volcanoes can provide a better understanding of their structure and plumbing. The need for such information is especially critical for undersea volcanoes, whose environment makes them difficult to investigate. Because undersea volcanoes are made up of highly magnetic basaltic rock, it is possible to use variations in the magnetic field to explore the internal structure of such edifices. This study combines magnetic survey data from 12 research cruises to make a magnetic anomaly map of volcanically active Loihi, located in the Hawaiian Island chain. NRM intensities and susceptibility measurements were measured from recovered rock samples and suggest that magnetic properties of Loihi are widely varied (NRM intensities range from 1-157 A/m and susceptibilities from 1.26 x 10-3 to 3.62 x 10-2 S.I.). The average NRM intensity is 26 A/m. The size and strength of magnetic source bodies were determined by using various modeling techniques. A strongly magnetized shield can explain most of the anomaly with a large nonmagnetic zone inside, beneath the summit. Prominent magnetic highs are located along Loihi's north and south rift zone dikes and modeling solutions suggest strongly magnetized source bodies in these areas as well as a thin, magnetic layer atop the nonmagnetic zone. The strong magnetic anomalies found along the volcano's rift zones cannot be readily attributed to recent lava flows at the surface. Instead, the source bodies must continue several kilometers in depth to give reasonable magnetization values and are interpreted as dike intrusions. Nonmagnetic anomalies at the summit and south of the summit suggest the presence of a magma system. The model solution suggests Loihi is an inhomogeneously magnetized seamount with highly magnetic dike intrusions along the rift zones with a nonmagnetic body at its center overlain with a magnetic layer.
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Yee, Chin-ming, and 庾前明. "Magnetic and gradiometer survey of a site in northeastern Lantau Island Hong Kong." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B43895025.
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Boltaev, A. P., I. A. Sherstnev, and F. A. Pudonin. "Multilayered Structures from Periodically Alternating Magnetic Island Layers: Magnetization Processes and Magnetoresistance." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35303.
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The multilayered structures from periodically alternating of island layers of various ferromagnetic are investigated.
This island structures possessed a magnetoresistance of ~1-3 % and can detect of superweak magnetic
fields up to 10-6 Oe at room temperature that allows using them as sensors of magnetic fields. The new
specific vorticose states of magnetization which arises under some conditions in island structures is offered.
Magnetization of these vortical states is distributed on many islands of island structures. It is supposed, what
exactly this vortical magnetization is responsible for appearance of unidirectional magnetic anisotropy too.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35303
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Kikuchi, Y., H. Takahashi, Y. Uesugi, and S. Takamura. "Suppression of Externally Induced Magnetic Island by Plasma Current Oscillation in HYBTOK-II." IEEE, 2003. http://hdl.handle.net/2237/7109.
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Robinson, David. "Evaluation of the performance of the Magnetic Island Solar Suburb - Townsville Solar City." Thesis, Robinson, David (2010) Evaluation of the performance of the Magnetic Island Solar Suburb - Townsville Solar City. Masters by Coursework thesis, Murdoch University, 2010. https://researchrepository.murdoch.edu.au/id/eprint/41508/.
Full textAbstract:
The Townsville: Queensland Solar City is a six year trial of demand-side management and distributed PV generation on Magnetic Island in the Coral Sea off the north Queensland coast. Regional Queensland electricity distributor Ergon Energy is leading the project, to try out alternatives to an imminent and costly upgrade of the network infrastructure supplying the island.
This study examines the effectiveness of the demand-side management measures implemented in the nearly two years since the project commenced. Changes in peak demand and energy consumption on the island are analysed and compared to:
- changes in a control group on the mainland; and
- the targets set for the project
and the impacts on the supply to 7 commercial properties on the island are analysed.
The study found both peak demand and energy consumption were reduced on the island, and at a greater rate than changes in those quantities in the control group, showing that the demand-side measures were having the desired effect. The project target levels of reduced peak load and energy consumption were achieved at the latest measuring points, compared to the predicted business-as-usual case, though growth in peak demand and energy consumption, and achieved reductions, were all less than modelled prior to project commencement. The individual properties analysed showed greater reductions than the island as a whole, pointing to opportunities for greater reductions, and there was evidence of the project inspiring other property owners to initiate their own energy demand management measures.
Once some meter data collection problems are overcome, the code and methods developed for this study, can be applied to a wider range of island properties, to develop a much richer understanding of the impact of individual demand-side measures, both on Magnetic Island, and wherever else they're applied.
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Roberts, Clive Lynton. "Tertiary and Carboniferous magmatism around Lundy Island and the outer Bristol Channel : a geophysical and geochemical perspective." Thesis, Open University, 1997. http://oro.open.ac.uk/54615/.
Full textAbstract:
The British Tertiary Volcanic Province comprises central volcanic complexes with positive gravity and magnetic anomalies, some centres associated with both large volumes of continental flood basalts and regional dyke swarms. The Lundy Island is the southern most expression of Tertiary volcanism and consists of granite intruded by around 200 dykes and associated with positive gravity and magnetic anomalies. The Lundy Dyke Swarm comprises basalt/dolerite and trachyte to rhyolite intrusions within host Tertiary granite (58.7 ± 1.6 Ma) and Devonian sediments. Outcrops of dykes are confined to coastal exposures on Lundy as they are veneered by peat over most of the island. Dykes present paired magnetic anomaly profiles, which allows their trends tobe determined by proton magnetometry. The dykes have a radial disposition superimposed on a ENE-WSW regional trend. Anisotropy of magnetic susceptibility studies indicate that magma for the radial component was emplaced at shallow to moderate inclinations, suggesting a relatively shallow origin near to the western border of Lundy Island. The regional component was emplaced at shallow to sub-horizontalangles, suggesting lateral movement of magma from a possible source 12 km to the northwest. Geochemical signatures indicate that the Lundy Dyke Swarm was transitional between plume-related magmatism and partial melting of the lithospheric mantle, the magma being stored in several small storage bodies at differing depths in the upper continental crust, rather than in one large magma chamber. Basic dykes at Lee Bay (60 ± 0.6 to 63.1 ± 0.7 Ma) pre-date the Lundy Dyke Swarm and were derived from a discrete magma chamber, possibly near to Morte Point. Conversely, other dykes in North Devon (Fremington dyke - 292.4 ± 1.7 Ma; Horse-Shoe Rocks - 339.6 ± 7.4 Ma) are not directly related to Tertiary magmatism, even though the Horse-Shoe Rocks have a Tertiary palaeomagnetic overprint. The Lundy Igneous Complex (comprising granite, dykes and sub-surface basic rocks) is situated close to the intersection of the Variscan Front and the Welsh Caledonides massif where the continental thickness is between 25 and 27 km. Emplacement of magma was assisted by the heavily fractured nature of the host sediments. However, a large positive gravity anomaly to the northwest of Lundy Island does not have a corresponding magnetic anomaly and so is interpreted as the response to relatively dense uplifted basement in the Lundy Horst rather than a large volume of basic rocks. Thus, the Lundy Igneous Complex probably did not produce sub-aerial volcanic activity, as pressure in the magma chamber would not have exceeded the overlying litho static load, despite the fractured nature of the host rocks.
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Zlotnicki, Jacques. "Sur les effets volcanomagnetiques et tectonomagnetiques." Paris 7, 1987. http://www.theses.fr/1987PA077296.
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Etude du champ magnetique terrestre sur les edifices volcaniques ou dans les regions soumises a une activite sismotectonique. Trois themes de recherche sont developpes: l'acquisition des mesures de terrain, les mesures experimentales realisees en laboratoire, et les simulations numeriques. L'etude de terrain porte sur des resultats obtenus sur les volcans de la soufriere de guadeloupe, la montagne pelee de martinique et le piton de la fournaise a la reunion
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Shi, Yuanjing. "Investigation of island geometry variations in bit patterned media storage systems." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/investigation-of-island-geometry-variations-in-bit-patterned-media-storage-systems(b16092b6-7260-4dc5-aa30-7dabb2c7a46f).html.
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Bit-Patterned Media (BPM) has been recognised as one of the candidate technologies to achieve an areal density beyond 1Tb/in2 by fabricating single-domain islands out of continuous magnetic media. Though much attention has been focused on the fabrication of BPM, existing lithography techniques demonstrate difficulties in producing uniform islands over large areas cost effectively; the resulting fabricated islands often vary in position and size. The primary purpose of the research documented in this thesis is to investigate the issue of island geometry variations on the data recovery process from a perpendicular patterned media with head and media configurations optimised to achieve an areal density of 1Tb/in2. In order to achieve the research aim, a read channel model has been implemented as a platform to evaluate the read channel performance numerically. It can be also altered to investigate new read channel designs. The simulated results demonstrate that island geometry variations have a detrimental effect on read channel performance. It has shown that a BPM system can be tolerant to island position variations, but more effort needs to be paid to the effect that island size variations have on the read channel performance. A new read channel design revolving around the design of a modified trellis has been proposed for use in the Viterbi detector in order to combat the effect of island geometry variations. The modified trellis for island position variations results in extra states and branches compared to the standard trellis, while the modified trellis for island size variations results in only extra branches. The novel read channel designs demonstrate an improved read channel performance in the presence of island geometry variations even with increasing amounts of island position and size variations. There are two ways to obtain the read channel performance in terms of the bit-error-rate (BER): a) by running a numerical Monte-Carlo simulation to count the number of bits in error at the output of the read channel model and b) using an analytical approach to calculate the BER by approximating the noise into a known distribution. It is shown that both ways demonstrate very similar results, which indicates as long as the distribution of the noise present in read channel model is predictable, the analytical approach can evaluate the BER performance more efficiently, especially when the BER is low. However, the Monte-Carlo simulation is still useful for understanding of the correlation of the errors. Novel trellis proposed in this work will contribute to the commercial development of BPM in two ways: a) to improve the data recovery process in BPM systems, b) to allow a tolerance of 10% size variations for the existing fabrication techniques.
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Sasco, Romain. "Développement d'un outil chronostratigraphique pour les archives climatiques : datations absolues (K/Ar,⁴⁰Ar/³⁹Ar) et paléomagnétisme appliqués aux laves." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112009/document.
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Développer une échelle de temps à haute résolution temporelle et commune aux différentes archives climatiques est une étape importante afin de quantifier avec précision les rapides variations climatiques passées et pour les placer dans un cadre chronologique unifié facilitant leurs inter-comparaisons et la quantification d’éventuels déphasages entre évènements, marqueurs ou archives climatiques.Le champ magnétique terrestre (CMT) regroupe l’ensemble des caractéristiques désirées pour développer un tel outil chronostratigraphique (expression dipolaire globale à la surface du globe, enregistrement dans diverses archives, variations en intensité indépendantes des variables climatiques). Bien que porteurs d’enregistrements continus, les sédiments ne donnent accès qu’aux variations relatives d’intensité du CMT. De plus, quand leur échelle de temps ne peut plus être placée sur celle des glaces polaires, elle est généralement obtenue par forçage orbital. Les laves, émises sporadiquement, enregistrent l’intensité absolue du CMT et sont datables par méthodes ⁴⁰Ar/³⁹Ar et K-Ar (indépendantes des variables climatiques). Elles fournissent ainsi des couples âge-paléointensité (A-PI) permettant de calibrer les enregistrements sédimentaires et de les transférer sur des échelles de temps et d’intensité absolues. L’échelle de temps ainsi obtenue est par la suite transférable à diverses archives climatiques. Cette étude se focalise sur les derniers 200 ka. Les laves étudiées proviennent des jeunes volcans d’Ardèche et des phases récentes du volcanisme canarien. Les laves ardéchoises ont délivré des résultats de paléointensité non exploitables et des incertitudes trop importantes sur les âges. Aucun couple A-PI pertinent n’a donc été obtenu. Cependant, nos résultats géochronologiques démontrent l’importance de combiner les 2 méthodes de datation K-Ar et ⁴⁰Ar/³⁹Ar pour tester l’exactitude et la signification géologique des âges obtenus. Pour ces laves, porteuses d’indices de contamination crustale et mantellique, nous suggérons que l’excès d’argon est situé dans des sites de rétention basses températures (<600°C). Les âges ⁴⁰Ar/³⁹Ar obtenus, apparemment non affectés par l’excès d’argon, décomposent l’activité volcanique en 3 phases : 1 au Nord (180±30 ka) et 2 au Sud (31±4 ka et 24±8 ka).Les laves canariennes ont produit 14 nouveaux couples A-PI (dont 9 datés conjointement en K-Ar et ⁴⁰Ar/³⁹Ar). Ces données ont été combinées à celles disponibles et triées de manière à ne garder que celles issues de protocoles d’analyses robustes et suffisamment précises. Les 51 données retenues ont été comparées aux courbes sédimentaires disponibles afin d’obtenir de nouvelles contraintes temporelles sur 0-200 ka. Sur 0-80 ka, les données confirment la bonne calibration de GLOPIS-75 initialement basée le minimum d’intensité de l’excursion du Laschamp et sur l’évolution du CMT entre 20 et 10 ka. En particulier, 3 de nos données réparties entre 45 et 60 ka sont cohérentes avec l’évolution du signal magnétique présentée par GLOPIS-75, complétant ainsi le jeu de contraintes sur cet intervalle. De 80 à 140 ka, les données retenues, bien qu’ayant des incertitudes temporelles parfois importantes, sont cohérentes avec les courbes sédimentaires validant ainsi leur niveau moyen de calibration sur cette période. Ces données confirment également la baisse d’intensité lors de l’épisode ancien du Blake à 120 ka, baisse d’intensité bien documentée par PISO-1500 mais très lissée sur SINT-2000. Avant 140 ka, les données sédimentaires et volcaniques disponibles sont trop incohérentes : aucune calibration n’a donc été entreprise sur cette période. Enfin, 2 données produites suggèrent un évènement géomagnétique bref vers 155 ka. Un tel événement n’est pas observé dans les courbes sédimentaires globales et les modèles disponibles vers 155 ka mais quelques études individuelles mentionnent localement un évènement géomagnétique vers 150 ka (Autriche, Russie et Mer de Chine)The understanding of climatic mechanisms and rapid climate changes requires a high-resolution, robust, and precise timescale which allows long-distance and multi-archives correlations.An appropriate tool to construct such a timescale is provided by the Earth magnetic field (EMF). The EMF is independent from climatic variations and its past evolution, global at the surface of the Earth, is recorded by most of the geological/climatic archives. Sedimentary sequences provide continuous records of relative intensities of the EMF on timescales usually based on ice core age models or orbital tuning. Lavas, though discontinuously emitted through time, record the absolute intensity of the EMF during their cooling at the surface of the Earth. Lavas are dated using 2 complementary methods: ⁴⁰Ar/³⁹Ar and K-Ar, both independent from climatic parameters. Lavas have therefore the potential to deliver tie-points (age-paleointensity couples) enabling the time calibration of sedimentary sequences and their transfer onto absolute intensity scale and chronological time scale. This timescale can then be transferred to other climatic archives. The present study focusses on the last 200 ka with lavas sampled from young volcanoes of Ardèche (South Massif Central, France) and recent phases of volcanism in the Canary Islands.Lava flows from Ardèche provided unexploitable paleointensity results and ages with large uncertainties. Therefore, they failed to provide suitable tie-points. However, our geochronological results evidence how crucial the combination of both the K-Ar and 40Ar/39Ar methods is to test the accuracy and geological meaning of the ages. Ardèche lavas have abundant mantellic and crustal xenoliths, potential carriers of excess ⁴⁰Ar*. Our study suggests that the argon excess is located in sites that decrepitate at low temperature (<600°C). Because ⁴⁰Ar/³⁹Ar ages are not affected by excess ⁴⁰Ar*, they provide reliable results. The new age dataset indicates that the volcanic activity of Ardèche can be divided in 3 phases: the oldest one (180±30 ka) took place in the northern part of the studied area and 2 younger phases are expressed in the South (31±4 ka and 24±8 ka).The study of the Canarian lavas produced 14 tie-points (9 out of 14 dated combining K-Ar and ⁴⁰Ar/³⁹Ar results). These data have been added to the available ones for the same time period. The published data have been selected on the basis of robust analytical protocols and accuracy. The 51 data finally selected are compared to available sedimentary stacks. Over the last 80 ka, the volcanic data corroborate the calibration of GLOPIS-75, initially based on volcanic and archeomagnetic data between 10-20 ka and the low intensity observed in the Laschamp excursion. Three newly produced data, dated between 45 and 60 ka, extend the database initially used to older periods and they are also consistent with the initial calibration of GLOPIS-75. Between 80 and 140 ka, though volcanic data have significant uncertainties (in age and/or paleointensity), they are consistent with available sedimentary records and validate their calibration level on the long-term. At a shorter time scale, volcanic data corroborate the intensity low reached during the older phase of the Blake excursion (120 ka) by PISO-1500, whereas this low does not appear in SINT-2000. For ages older than 140 ka, not only the volcanic data are scattered, but also the sedimentary records are different from one another and no conclusions could be drawn. Finally, 2 of our data suggest a brief geomagnetic event around 155 ka. Such an event cannot be seen on available global sedimentary stacks or models, even though some individual studies report a local geomagnetic event around 150 ka (Austria, Russia, and China Sea)
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Beal, Irina. "Event Sedimentology and Hydrodynamic Hindcasting of Storm Surge Deposits: Hurricane Sandy, New Jersey." Master's thesis, Temple University Libraries, 2014. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/281770.
Full textAbstract:
GeologyM.S.
The impact of Hurricane Sandy (October 2012) on the Atlantic Coast of the United States resulted in massive overtopping (aggradation) of coastal barriers, along with localized overwash and breaching. A combination of high-frequency ground-penetrating radar (800 MHz GPR), low-field magnetic susceptibility (MS), and textural and mineralogical analyses was used to reconstruct the sedimentological and hydrodynamic parameters of the storm surge at two New Jersey sites immediately north of hurricane landfall: 1) Mantoloking and 2) Island Beach State Park (IBSP). Mantoloking represents a developed, scour-channelized backdune area with a 30-60 cm thick deposit consisting of 20-23 event horizons. Geophysical images reveal gently landward-dipping reflections. In contrast, IBSP site is a broad (width: 40 m) vegetated dune swale. GPR transects show landward-dipping tangential-oblique reflections as well as a conformable channel cut-and-fill structure (width: 7 m; depth: 1.5 m), producing a 0.7-1.5-m-thick deposit with 24-30 horizons. Within each sand-dominated event horizon, an upward 5-15% increase in mean grain size and 80-100% decrease in MS highlight the importance of hydrodynamic equivalency in lithological segregation within mixed-density fractions. Basal sub-layers enriched in heavy minerals (magnetite, ilmenite, garnet) yield MS of 100-350 μSI, in contrast to <40 μSI in quartz-rich upper sub-layers and pre-storm deposits. Several peaks in MS values correspond to an up to 65% increase in threshold shear stresses associated with individual unidirectional surge flows, with several most-enriched event horizons likely corresponding to waning-stage storm surge peaks recorded by offshore buoys. The sharp contact with the pre-storm surface produces distinct GPR reflections that allow accurate mapping of the thickness and extent of hurricane deposits. Together with potential correlation between lithological anomalies and high amplitude georadar signal return, the approach used in this study has applications to reconstructing event deposits in Quaternary sedimentary records. The new research findings have potential implications for reconstructing surge dynamics of recent hurricane events as well as quantitative hindcasting of hydrodynamic conditions responsible for lithologically diverse intervals in ancient tempestites.
Temple University--Theses
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Beal, Irina. "Beal_Calculations.xls." Master's thesis, Temple University Libraries, 2014. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/281771.
Full textAbstract:
GeologyM.S.
The impact of Hurricane Sandy (October 2012) on the Atlantic Coast of the United States resulted in massive overtopping (aggradation) of coastal barriers, along with localized overwash and breaching. A combination of high-frequency ground-penetrating radar (800 MHz GPR), low-field magnetic susceptibility (MS), and textural and mineralogical analyses was used to reconstruct the sedimentological and hydrodynamic parameters of the storm surge at two New Jersey sites immediately north of hurricane landfall: 1) Mantoloking and 2) Island Beach State Park (IBSP). Mantoloking represents a developed, scour-channelized backdune area with a 30-60 cm thick deposit consisting of 20-23 event horizons. Geophysical images reveal gently landward-dipping reflections. In contrast, IBSP site is a broad (width: 40 m) vegetated dune swale. GPR transects show landward-dipping tangential-oblique reflections as well as a conformable channel cut-and-fill structure (width: 7 m; depth: 1.5 m), producing a 0.7-1.5-m-thick deposit with 24-30 horizons. Within each sand-dominated event horizon, an upward 5-15% increase in mean grain size and 80-100% decrease in MS highlight the importance of hydrodynamic equivalency in lithological segregation within mixed-density fractions. Basal sub-layers enriched in heavy minerals (magnetite, ilmenite, garnet) yield MS of 100-350 μSI, in contrast to <40 μSI in quartz-rich upper sub-layers and pre-storm deposits. Several peaks in MS values correspond to an up to 65% increase in threshold shear stresses associated with individual unidirectional surge flows, with several most-enriched event horizons likely corresponding to waning-stage storm surge peaks recorded by offshore buoys. The sharp contact with the pre-storm surface produces distinct GPR reflections that allow accurate mapping of the thickness and extent of hurricane deposits. Together with potential correlation between lithological anomalies and high amplitude georadar signal return, the approach used in this study has applications to reconstructing event deposits in Quaternary sedimentary records. The new research findings have potential implications for reconstructing surge dynamics of recent hurricane events as well as quantitative hindcasting of hydrodynamic conditions responsible for lithologically diverse intervals in ancient tempestites.
Temple University--Theses
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Beal, Irina. "Beal_CAMSIZERdata.xlsx." Master's thesis, Temple University Libraries, 2014. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/281772.
Full textAbstract:
GeologyM.S.
The impact of Hurricane Sandy (October 2012) on the Atlantic Coast of the United States resulted in massive overtopping (aggradation) of coastal barriers, along with localized overwash and breaching. A combination of high-frequency ground-penetrating radar (800 MHz GPR), low-field magnetic susceptibility (MS), and textural and mineralogical analyses was used to reconstruct the sedimentological and hydrodynamic parameters of the storm surge at two New Jersey sites immediately north of hurricane landfall: 1) Mantoloking and 2) Island Beach State Park (IBSP). Mantoloking represents a developed, scour-channelized backdune area with a 30-60 cm thick deposit consisting of 20-23 event horizons. Geophysical images reveal gently landward-dipping reflections. In contrast, IBSP site is a broad (width: 40 m) vegetated dune swale. GPR transects show landward-dipping tangential-oblique reflections as well as a conformable channel cut-and-fill structure (width: 7 m; depth: 1.5 m), producing a 0.7-1.5-m-thick deposit with 24-30 horizons. Within each sand-dominated event horizon, an upward 5-15% increase in mean grain size and 80-100% decrease in MS highlight the importance of hydrodynamic equivalency in lithological segregation within mixed-density fractions. Basal sub-layers enriched in heavy minerals (magnetite, ilmenite, garnet) yield MS of 100-350 μSI, in contrast to <40 μSI in quartz-rich upper sub-layers and pre-storm deposits. Several peaks in MS values correspond to an up to 65% increase in threshold shear stresses associated with individual unidirectional surge flows, with several most-enriched event horizons likely corresponding to waning-stage storm surge peaks recorded by offshore buoys. The sharp contact with the pre-storm surface produces distinct GPR reflections that allow accurate mapping of the thickness and extent of hurricane deposits. Together with potential correlation between lithological anomalies and high amplitude georadar signal return, the approach used in this study has applications to reconstructing event deposits in Quaternary sedimentary records. The new research findings have potential implications for reconstructing surge dynamics of recent hurricane events as well as quantitative hindcasting of hydrodynamic conditions responsible for lithologically diverse intervals in ancient tempestites.
Temple University--Theses
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Hilscher, Paul Peter. "Study of multi-scale interaction and dissipation based on gyro-kinetic model in fusion plasmas." Kyoto University, 2013. http://hdl.handle.net/2433/180447.
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Février, Olivier. "Modélisation globale du contrôle des îlots magnétiques dans les tokamaks." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4070/document.
Full textAbstract:
Dans les plasmas de tokamak peuvent se développer des instabilités MHD (Magneto-Hydro-Dynamiques) se manifestant sous la forme d’îlots magnétiques qui réduisent le confinement. Ces îlots peuvent être contrôlés par la génération localisée de courant dans le plasma. Dans cette thèse, nous nous intéressons à la modélisation des îlots magnétiques et de leur contrôle en utilisant une description fluide (MHD) du plasma, à l’aide du code XTOR. Nous détaillons l'inclusion d'une source de courant au sein du modèle MHD, ce qui nécessite l'ajout d'une équation supplémentaire pour modéliser la propagation de la densité de courant le long des lignes de champ magnétique. Cette implémentation est ensuite vérifiée sur la base de modèles analytiques, nous permettant de retrouver l'influence de paramètres tels que la largeur du dépôt ou son désalignement. Nous avons mis en évidence des effets non-décrits par les modèles asymptotiques, liés à la nature de la localisation spatiale de la source de courant. Nous nous sommes ensuite intéressés aux stratégies de contrôle envisageable pour la suppression des îlots. Nous avons ajouté au sein du code XTOR un système de contrôle qui ajuste le dépôt de courant selon les stratégies choisies. Des simulations MHD non-linéaires des différents schémas de contrôle ont été effectuées, et les différentes stratégies comparées, permettant de préciser pour chacune une gamme d’intérêtMagneto-Hydro-Dynamic (MHD) instabilities are susceptible to develop within a tokamak plasma. These instabilities manifest themselves as magnetic islands which reduce the plasma confinement. The islands can however be controlled by driving current inside them. In this thesis, we consider the modeling of the magnetic islands and their control using first principle approaches, which rely on a global MHD description of the plasma. We have detailed the inclusion a RF-driven current like source term in an MHD code, which requires special care to be given to the modeling of the current density evolution. The implementation has been benchmarked against the asymptotic models, allowing us to retrieve the influence of parameters such as deposition width or misalignment with respect to the island width and position. Beyond these aspects, we have evidenced new effects, linked to the 3D nature of the current deposition. We have observed a flip instability in which an island, reduced by the ECCD, brutally inverse its phase so that its X-Point faces the current deposition, allowing the mode the grow further. We then moved on to the topic of the best suitable control strategies for the control of the island. We have implemented in XTOR a control system that mimics the experimental ones and adapt the current deposition in function of a preset strategy. Nonlinear MHD simulations have been carried out using different control schemes, allowing us to quantify the gain to expect from each of these methods depending on the characteristics of the current deposition
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Mills, Carol. "“The Pilot’s Wife” and Hosting Tourism on Magnetic Island: A Memoir and Autoethnographic Enquiry of Place, Self and Narrative within Structures of Authority and Power." Thesis, Curtin University, 2018. http://hdl.handle.net/20.500.11937/76666.
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This thesis (exegesis and creative work, a memoir) draws on my experience of establishing a floatplane business with my husband Paul on Magnetic Island within the Great Barrier Reef Marine Park. It describes events prior to and including an Administrative Appeals Tribunal hearing in 2007 on the legality of the floatplane operations within the Marine Park. The study provides new information about the composition of tourism communities in Australia, causes of conflicts and resolution processes.
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Poye, Alexandre. "Dynamique des ilots magnétiques en présence de feuille de courant et en milieu turbulent." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4793/document.
Full textAbstract:
La stabilité des plasmas de fusion est un enjeu crucial dans le cadre du développement de nouvelles sources d'énergie. L'interaction entre le plasma et le champ magnétique peut en effet amener à la destruction du confinement : c'est une disruption. Le sujet de cette thèse porte sur les îlots magnétiques, une des causes des disruptions. Ces îlots magnétiques sont observés expérimentalement et analytiquement. Les théories peuvent prévoir la croissance d'un îlot magnétique et sa taille, mais les restrictions sur le domaine de validité de la théorie sont fortes et elles dé-corrèlent largement les domaines de validité théoriques et expérimentaux. Dans une première partie, nous montrons que, génériquement, les méthodes de contrôle dynamiques d'évolution des îlots magnétiques, basées notamment sur une relation entre la taille de l'îlot et la perturbation de flux magnétique à la résonance, devraient prendre en compte la modification du flux magnétique moyenné le long de la ligne de champ. Nous donnons aussi des limites quand au cadre de notre assertion (coalescence des îlots, effondrement du point X, ...). la seconde partie de la thèse aborde un nouvel effet dû au courant de part et d'autre de l'îlot magnétique. Il change la dynamique de l'îlot et la perception que l'on en a. Jusqu'à présent la dynamique de l'îlot était étudiée principalement au travers de mécanisme actifs au niveau de la résonance. Nous démontrons que la présence de courant aux abords de l'îlot peuvent jouer un rôle très important sur sa croissance et sur sa taille finale. La troisième partie détaille comment la turbulence aux abords d'un îlot magnétique peut affecter sa croissanceThe fusion plasma stability is a critical point for the developpement of newenergy source. The interaction between the plasma and the magnetic field can drive to the confinement descrution : it is a disruption. The topic of this thesis is the magnetic island, one of disruption causes. Those magnetic islands are observed theoretically and numerically. The theory can predict the growth and the final size of magnetic islands, but restrictions of its validity range are strong and they decorrelate the experimental and theoritical validity domain. In the first part, we show that the dynamic method of magnetic island control, based on the link between the island size and the perturbed magnetic flux at the resonance, should take in account the modification of the magnetic flux averaged along the field line. We show aswell the limitation of our assertion (magnetic island coalescence, X point collapse ...). The second part of the thesis address a new effet du to the current on sides of the magnetic island. This effect changes the magnetic island dynamics and the perception we got on it. Until now, the magnetic island dynamics have been studied through active mechanisms at the resonance. We show that the presence of current on sides can play an important role on the growth and saturation of the magnetic island. The last part of thesis details how the turbulence on the outskirts of a magnetic island can affect the island growth. We show that a turbulence generate by an interchange instability can penetrate into a stable zone concerning tearing mode and induce by a 3D mechanisme the growth of an magnetic island
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Mannoubi, Soumaya. "Caractérisation de MamK et Mamk-like les "actins-like" responsables de l'alignement des magnétosomes chez Magnetsirillum magneticum AMB-1." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4004.
Full textAbstract:
Les bactéries magnétotactiques (MTB) ont la capacité de s'orienter dans un champ magnétique grâce à un organite procaryote constitué d'un nanocristal magnétique biominéralisé et entouré d'une membrane biologique : le magnétosome. La synthèse de cet organite est un processus complexe contrôlé génétiquement par une série de gènes spécifiques aux MTB (les gènes mam) qui sont regroupés sur le chromosome bactérien. Chez la souche modèle Magnetospirillum magneticum AMB-1 cet ensemble de gènes forme un îlot génomique (MAI) auquel s'ajoute un second groupe distinct de 7 gènes homologues aux gènes mam (gènes mam-like) récemment identifié dont le rôle physiologique est très peu caractérisé. Parmi les produits des gènes mam, MamK est impliqué dans l'alignement des magnétosomes. Cette « actin-like » prokaryote qui forme des filaments selon un processus ATP-dépendant a été caractérisée ces dernières années. Dans le MIS de AMB-1, un gène homologue mamK-like a été identifié. Ainsi différentes approches pluridisciplinaires ont été mises en place pour comprendre le rôle de MamK et MamK-like. L'expression des gènes du MIS a été quantifiée. Les souches dépourvues des gènes mamK et mamK-like ainsi que le double mutant ont été obtenues puis phénotypées par différentes techniques d'imagerie. Les interactions entre les deux protéines ont été également testées. Enfin, les deux protéines ont été et leurs propriétés biochimiques caractérisées. L'ensemble de ces données nous permet de proposer un modèle selon lequel MamK et MamK-like participeraient tous deux à l'alignement des magnétosomes bactériens, vraisemblablement par la formation de filaments hybridesMagnetotactic bacteria (MTB) have the ability to orient in a magnetic field through a prokaryotic organelle composed of a magnetic nanocrystal surrounded by a biological membrane: the magnetosome. The synthesis of this organelle is a genetically complex process controlled by a series of specific genes (mam genes) grouped together on the bacterial chromosome. In the strain model Magnetospirillum magneticum AMB-1 this set of genes form a genomic island (MAI) and a second distinct group of seven genes homologous to mam genes (mam-like genes) recently identified. The physiological role of this islet magnetosome (MIS) is very little characterized to date.Among the products of mam genes, MamK is involved in the alignment of the magnetosomes. This « actin-like » which forms prokaryote filaments according an ATP - dependent process has been characterized in recent years. In the MIS of AMB-1, a homologous gene mamK-like was identified. And various multidisciplinary approaches have been developed to understand the role of MamK and MamK-like. The MIS gene expression was quantified. The strains lacking genes of mamK, mamK-like and the obtained of double mutant were then phenotyped by different imaging techniques. The interactions between the two proteins were also tested. Finally, the two proteins were overexpressed and their biochemical properties characterized. All of these data allows us to propose a model whereby MamK and MamK-like participate in both the alignment of bacterial magnetosomes, presumably by the formation of hybrid filaments
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Perinotto, Hélène. "Dynamique de mise en place des avalanches de débris sur les flancs aériens des volcans insulaires : le cas de La Réunion." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0414/document.
Full textAbstract:
Les avalanches de débris, qui résultent du démantèlement des flancs des édifices volcaniques et montagneux, sont des écoulements granulaires rapides et dangereux dont le monteur est la gravité et qui présentent des distances de transport extrêmement importantes. La dynamique de leur mise en place et leurs mécanismes de transport permettant cette très grande mobilité sont des phénomènes qui demeurent encore mal compris. De nombreux modèles existent pour expliquer la grande mobilité des avalanches de débris et incluent des processus basés sur la lubrification ou la fluidification de la masse granulaire mais également sur le phénomène de désintégration dynamique des éléments. Cependant la grande majorité des modèles proposés souffre du manque d’observations de terrain et de quantification de l’évolution des matériaux au cours de leur transport au sein de la masse granulaire. Afin d’identifier les principaux mécanismes de transport des avalanches de débris, nous proposons dans ce travail une étude de terrain détaillée de dépôts d’avalanches de débris volcaniques qui résultent du démantèlement d’un volcan bouclier océanique, le Piton des Neiges (île de La Réunion, océan Indien). L’approche est couplée à un examen morphométrique (dimension fractale et circularité), exoscopique et granulométrique des particules présentes dans les dépôts. Elle est complétée par l’examen de la fabrique des dépôts basée sur l’anisotropie de la susceptibilité magnétique (ASM). Les données obtenues nous permettent de mettre en évidence une évolution de la dynamique de transport et de mise en place des dépôts d’avalanches de débris depuis les zones sources jusqu’aux domaines de dépôt distaux. On montre également que la désintégration dynamique et le gonflement dispersif qui l’accompagne opèrent tout au long du transport et à toutes les échelles au-dessus d’une limite inférieure de broyage à 500 μm. En dessous de cette limite, la réduction granulométrique résulte uniquement de processus d’attrition par friction entre les particules. La grande mobilité des avalanches de débris pourrait ainsi être expliquée par l’effet combiné de la libération d’énergie élastique par la désintégration dynamique des particules > 500μm et par une réduction de la friction interne à la matrice liée aux interactions dispersives des particules fines (< 500 μm). L’ensemble des données permettent également de préciser les directions de transport et l’ampleur des avalanches de débris liées aux déstabilisations du massif du Piton des NeigesDebris avalanches, resulting from flank collapses that shape volcanic and mountainous edifices are rapidand dangerous gravity-driven granular flows that travel long run out distances. The dynamic and the transport mechanisms behind this high mobility remain poorly understood. The numerous models proposed to explain this high mobility include processes based on lubrication or fluidisation of the granular mass of the flow body, but also the dynamic disintegration of the transported particles. To date,all these proposed mechanisms lack observational support and quantification of the state of the particles of the granular mass during the transport. To identify the main transport mechanisms, we propose here detailed field studies of volcanic debris avalanches deposits resulting of flank-collapse events on an oceanic shield volcano, the Piton des Neiges (La Réunion Island, Indian Ocean). This study has been combined with morphometric (fractal dimension and circularity), exoscopic and grain-size analyses. Moreover, the fabric of the deposits has been investigated by with the characteristics of the anisotropy of the magnetic susceptibility (ASM). From these data we highlight a proximal to distal evolution of the debris avalanches transport and emplacement dynamics. We demonstrate that syn-transport dynamic disintegration continuously operates with the distance from the source down to a grinding limit of 500μm. Below this limit, the particle size reduction exclusively results from the attrition of the particles by frictional interactions. Thus, the exceptional mobility of debris avalanches may be explained by thecombined effect of elastic energy release during the dynamic disintegration of the larger clasts (> 500μm) and frictional reduction within the matrix due to the dispersive interactions between the finer particles (< 500 μm). All these data also allow to specify the transport direction and the approximate size of the debris avalanches related to the Piton des Neiges destabilisations
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Siccinio, Mattia [Verfasser]. "Kinetic investigation of magnetic islands in tokamaks / Mattia Siccinio." 2010. http://d-nb.info/1004277571/34.
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Yu, Edmund Po-ning 1972. "Evolution equations for magnetic islands in a reversed field pinch." 2001. http://hdl.handle.net/2152/10894.
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Chen, Shou-Yuan, and 陳士元. "The magnetic properties of Fe/Ag submicrometer pyramidal islands on Si(100)." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/97448163949383341774.
Full textAbstract:
碩士國立臺灣科技大學
機械工程系
91
In this study, we deposited Ag buffer layer with various thickness on an RCA-cleaned Si(100) substrate in a molecular-beam epitaxial system. Small pyramidal Ag islands with a (100) truncated top and four (111) sidewalls were successfully formed on Si(100) substrates. We systematically studied the magnetic properties of Fe films grown on the buffer of Ag layers at 100℃. The magnetic behavior of Fe films is strongly dependent on the thickness, morphology, and surface roughness of the Ag buffer layers. The Ag film, in order to reduce the total surface free energy, forms isolated three-dimensional square islands with a (100) truncated top and four (111) sidewalls on the Si(100) substrate. The average height, grain size and surface roughness of these Ag islands were tuned by varying the deposition thickness of the Ag film. From RHEED observation, we found that Ag(100) plane matched with Si(100) plane. The orientation relationship between Ag and Si is Ag(100)[011] // Si(100)[011]. The coercivity of the Fe films increased as the roughness of the Ag buffer layer increased. The in-plane easy axis of the Fe film was rotated 45° while the thickness of the Ag buffer layer reaches 100 Å and the Ag rough surface provides a source of domain wall pinning. The Fe film that deposited on the sidewalls of the pyramidal islands played an important role on the magnetic properties of the parallel and perpendicular of the directions and initial magnetization reversal.
38
Hölzl, Matthias [Verfasser]. "Diffusive heat transport across magnetic islands and stochastic layers in tokamaks / Matthias Hölzl." 2010. http://d-nb.info/1000443388/34.
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Van, Vuuren Gary Wayne. "The influence of rotating and locked magnetic islands on edge transport in Tokoloshe tokamak." Thesis, 1993. http://hdl.handle.net/10413/6469.
Full textAbstract:
The turbulence and fluctuation induced transport in the edge plasma of the Tokoloshe tokamak was studied using a Langmuir probe array. In this thesis three separate experiments are presented, each of which examines a particular aspect of the edge plasma. In the first experiment measurements of edge plasma parameters are presented. These include standard parameters (such as Ne, Op , Te, etc.) as well as features such as the velocity shear, T(t) during periods of both high and low Mirnov activity, Te/Te and Q. These are compared with results from other machines as well as predictions of several turbulence theories. It was found that many of the results are very similar to those obtained on other machines and that, since the operating parameter space on Tokoloshe is well within the parameter space described by drift wave theories, resistivity-driven gradient driven turbulence theories do not describe the edge turbulence. In the second experiment external windings are used to produce fields which can slow and lock magnetic islands in the toroidally rotating plasma. Edge parameters are again presented and these results compared with those from the so-called 'reference' plasmas, i.e. ones in which no locking occurred. During locking some parameters are dramatically altered, e.g.Te/Te Standard transport theory ignores the effect of Te/Te since they are usually small in reference discharges. During the locked phase, however, certain measurements used to deduce T and Q are greatly affected by increases in Te/Te. As a result, certain assumptions regarding these measurements are no longer valid. Comparison of results for different island positions (produced by different coils) indicates that the assumption of poloidal and toroidal symmetry of edge conditions is invalid. The third experiment investigates the high frequency (~60 kHz), low amplitude, magnetic oscillation which characterises the locked phase and which exhibits some small degree of correlation with the fluctuations observed on (e.g.) Of'. Since over 80% of the spectral power of Te/Te lies below 70 kHz and since Of /Te depends strongly on Te/Te , it is suggested that the magnetic mode and these large variations in Te, may be due to a similar physical process.Thesis (Ph.D.)-University of Natal, 1993.
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Kumar, Santhosh Tekke Athayil. "Experimental Studies of Magnetic Islands, Configurations and Plasma Confinement in the H-1NF Heliac." Phd thesis, 2007. http://hdl.handle.net/1885/49287.
Full textAbstract:
Rational magnetic flux surfaces in fusion (toroidal plasma confinement) devices can break the magnetic field lines and reconnect them in the form of magnetic islands. Formation of these magnetic islands can have a serious impact on the plasma confinement properties of the device. Islands can in general degrade the confinement by mixing up different regions of the plasma. However there has been experimental evidence of confinement improvement by island induced transport barriers, under certain conditions. Even though there are a large number of theoretical and experimental works on magnetic islands to date, there is clearly a paucity of convincing experimental understanding on the nature of behaviour of islands in plasma. This thesis reports detailed experimental studies conducted on the H-1NF heliac stellarator, to gain an in-depth understanding of magnetic islands and their influence in plasma confinement. ¶ ...
41
Lloyd, Sally Stevens. "Simulating magnetic islands of the H-1NF heliac using the MHD equilibrium code HINT." Phd thesis, 2003. http://hdl.handle.net/1885/146369.
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Chin, An-Li, and 秦安立. "Investigation of magnetic islands on Si(111)-5×2/Au Surface with Scanning Tunneling Microscopy." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/40323786130594547151.
Full textAbstract:
碩士國立中正大學
物理系
91
We make the Si (111)-5×2/Au by depositing Au 0.5 ML as the substrate. Then the substrate is deposited Co at room temperature and annealed for 5 min. We investigate the self-assembly of magnetic islands are on Si (111)-5×2/Au, and the feature of the clusters are as follow.The density of the islands is as a liner function with cobalt coverage, and the islands size increase with temperature. Now we observe that the shape of the cluster is hexagon when we anneal at 600°C and 700°C. Espe. When temperature of the substrate is 500°C, the surface is mixed by domed and hexagonal islands which is formed phase transition.
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"Effects of Resonant Magnetic Perturbations on the STOR-M Tokamak Discharges." Thesis, 2014. http://hdl.handle.net/10388/ETD-2014-04-1539.
Full textAbstract:
Studies of resonant magnetic perturbations (RMP) have been an active topic in the tokamak research. The RMP technique involves the use of magnetic perturbations generated by external coils installed on a tokamak device. The resonant interaction between the plasma and RMP has favorable effects on magnetohydrodynamic (MHD) stability and other plasma parameters in tokamaks. The RMP experiments are carried out in the Saskatchewan Torus-Modified (STOR-M) tokamak using (l = 2, n = 1) helical coils carrying a static current pulse. The effect of RMP on the (m = 2, n = 1) magnetic islands is examined during ohmic discharges with high MHD activities. The amplitude and frequency of (2, 1) Mirnov fluctuations are significantly reduced after application of RMP. A phase of improved plasma confinement, characterized by a reduction in the H_alpha emission level and an increase in the soft x-ray (SXR) emission, is induced after application of RMP. It is also observed using the ion Doppler spectroscopy (IDS) that RMP can strongly affect the plasma
rotation in STOR-M. It is found that during the RMP pulse, the toroidal velocity of C_III impurities (located at the plasma edge) increases in the co-current direction. However, the toroidal velocities of O_V and C_VI impurities (located near the plasma core) change direction from counter-current to co-current. The reduction of the toroidal flow velocity is accompanied by a reduction of the MHD frequency. It is also found that radial profiles of ion saturation current and floating potential in the edge region can be modified by RMP. An increase in the pedestal plasma density and a more negative electric field are observed at the plasma edge region during the RMP pulse. An internal probe array is assembled and installed in STOR-M to study the RMP penetration and the plasma response to RMP.
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Cahyna, Pavel. "Difuze částic z tokamaku vlivem stochastizace magnetických siločar." Doctoral thesis, 2010. http://www.nusl.cz/ntk/nusl-296117.
Full textAbstract:
The thesis summarizes the current state of research of thermonuclear fusion with magnetic confinement and decribes the possible role of stochastization of magnetic field lines and magnetic perturbations in solving some of the problems that are encountered on the road to the exploitation of fusion. It presents a theoretical introduction to deterministic chaos and explains the connection of this theory to magnetic perturbations in tokamak. The results are presented mainly in the form of publications in journals and conference proceedings. Among them are: the comparison of chaotic diffusion of particles and field lines, where significant differences were found; the application of chaotic diffusion of particles to the problem of runaway electrons originating in disruptions, where our simulations contributed to explaining the experimental results from the JET tokamak; the calculation of spectra of perturbations for the COMPASS tokamak, done as a preparation for the upcoming experiments; and modelling of screening of perturbations by plasma, where the observations of divertor footprints show as a promising method to detect the screening.
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Tuen, Li Huey. "Stability of a two-volume MRxMHD model in slab geometry." Master's thesis, 2017. http://hdl.handle.net/1885/131789.
Full textAbstract:
Ideal MHD models are known to be inadequate to describe various
physical attributes of a toroidal field with non-continuous
symmetry, such as magnetic islands and stochastic regions.
Motivated by this omission, a new variational principle MRXMHD
was developed; rather than include an infinity of magnetic flux
surfaces, MRxMHD has a
finite number of flux surfaces, and thus
supports partial plasma relaxation. The model comprises of
relaxed plasma regions which are separated by nested ideal MHD
interfaces (flux surfaces), and can be encased in a perfectly
conducting wall. In each region the pressure is constant, but can
jump across interfaces. The
field and
field pitch, or
rotational transform, can also jump across the interfaces. Unlike
ideal MHD, MRxMHD plasmas can support toroidally non-axisymmetric
confined magnetic fields, magnetic islands and stochastic
regions.
In toroidally non-axisymmetric plasma, the existence of
interfaces in MRxMHD is contingent on the irrationality of the
rotational transform of flux surfaces. That is, the KAM theorem
shows that invariant tori (flux surfaces) continue to exist for
sufficiently small perturbations to an integrable system (which
describes flux surfaces), provided that the rotational transform
is sufficiently irrational. Building upon the MRxMHD stability
model, we study the effects of irrationality of the rotational
transform at interfaces in MRxMHD on plasma stability. We present
an MRxMHD equilibrium model to investigate the effects of
magnetic field pitch within the plasma and across the
aforementioned flux surfaces within a chosen geometry. In this
model, it is found that the 2D system stability conditions are
dependent on the interface and resonant surface magnetic field
pitch at minimised energy states, and the stability of a system
as a function of magnetic
field pitch destabilises at particular values of magnetic
field pitch. We benchmark the treatment of a
two-volume system, along with the calculations for background and
perturbed magnetic fields to existing cylindrical
working.
An expression is formulated for the stability eigenvalues by
creating a model for the slab geometry system. The eigenvalues
for system stability at a minimum energy state are found to
depend upon the rationality of the magnetic field pitch at
resonant surfaces. Various system parameter scans are conducted
to determine their affect upon system stability and their
implications. While tearing instabilities exist at low order
rational resonances, investigating the instability of high-order
rationals requires study of pressure-driven instabilities.
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Lin, Ger-Pin, and 林哲平. "Study of magnetic properties and microstructures of FePt island films." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/01227935614145379058.
Full textAbstract:
博士臺灣大學
材料科學與工程學研究所
98
The development of recording media of continuous films is restricted by super-paramagnetic limit. Patterned media has been suggested as a potential solution for this physical limit. In this study, we describe a simple and cheap method to fabricate large-area patterned media. The grain size of the magnetic films must be reduced to improve the signal-to-noise ratio. The exchange coupling effect between magnetic grains should be minimized in order to decrease transition noise. This discontinuous nano-size island magnetic film was suggested to reduce the exchange coupling effect between magnetic islands and increased the recording density. In order to increase the recording density, the size of magnetic islands must be reduced by modifying the experiment condition. FePt films (15 nm) were fabricated with (Fe/Pt)n multilayer on amorphous glass substrates then post-annealed at 700 ℃ for 30 mins to obtain better perpendicular magnetic anisotropy and ordering degree. The chemical composition of FePt films is Fe59Pt41. The magnetic easy axis [001] of L10 FePt phase in the FePt films was perpendicular to the film plane. This nano-size island-shape FePt film with perpendicular magnetic anisotropy may be a good candidate for ultra-high density recording media. The X-ray diffraction patterns of the annealed FePt films with heat treatment on amorphous glass substrates shown that the fct-FePt(001) peak and fct-FePt(002) peak appeared in 5-nm FePt film. However, the intensity of the fct-FePt(001) peak and fct-FePt(002) peak were weaker as the thickness of FePt film increasing to 30 nm, but the intensity of the fct-FePt (111) peak enhanced. As the thickness of FePt films was increased, the easy axis orientation of FePt films would turn from perpendicular to parallel to the film plane. However, the ordering degree of the FePt film would increase with FePt film thickness. The particle size of 1-nm thick FePt film on glass that annealed at 700 ℃ for 10 minutes distributed between 2.5 to 5 nm, and the density of islands is 1.37×1013 islands/inch2. A discontinuous and well-separated nano-size island magnetic film can reduce the exchange coupling of the media and increase the recording density. The driving force of FePt island formation was the surface energy difference between the substrate and FePt alloy. The nucleation site number of FePt islands increased with the surface energy difference between the substrate and FePt alloy. Therefore, the density of islands of 1-nm thick FePt film annealed at 700 ℃ for 10 minutes on carbon film (1.44×1013 islands/inch2) was slightly larger than that of 1-nm thick FePt film annealed at 700 ℃ for 10 minutes on glass. But, the fcc-FePt phase still existed in the 1-nm thick FePt film which annealed at 700 ℃ for 10 minutes on carbon film. Due to the thick Ag under-layer, the grain growth and island cluster occurred easily in the FePt (1 nm~7.5 nm)/Ag (100 nm) bi-layer films, and the size distribution of metallic islands would be very broad. However, the Ag under layer could improve the ordering of FePt film. The lattice mismatch between Ag under layer and FePt film would provide additional strain energy and promote the occurrence of the fct-FePt (111) preferred orientation. The orientation of magnetic easy axis of FePt (1 nm~7.5 nm) films with Ag (100 nm) under-layer would turn from perpendicular to parallel to the film plane. Due to the Ag atom has larger diffusion coefficient during annealing process, the metallic islands had better roundness in FePt (1 nm)/Ag (1 nm ~3 nm) bi-layer films. Investigation of the microstructures and magnetic properties of the ordered FePt films revealed that the 1 nm-FePt film annealed at 700 ℃ for 10 minutes had perpendicular magnetic anisotropy and formed well-separated FePt nano-size islands. It is suitable for ultra-high density magnetic recording media. But, the out-of-plane coercivity of the well-separated FePt nano-size islands was about 20 kOe, and it was too large for recording head to reverse its moments. In order to reduce the writing field of FePt nano-island film, we introduced Fe capping layer (0.5~5 nm) on the FePt nano-island films. The exchange coupling effect between Fe capping layer and FePt nano-island would decrease the writing field of the island films.
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Martin-Smith, Keith Michael. "The role of epifaunal crustaceans on Sargassum spp. at Magnetic Island, Great Barrier Reef, Australia." Thesis, 1994. https://researchonline.jcu.edu.au/24116/1/01front.pdf.
Full textAbstract:
Generalisations about the community ecology of invertebrates associated with plant surfaces have been developed largely from studies on terrestrial insect-plant systems and by limited studies on temperate marine macroalgal systems. This study was designed to quantify the seasonal variation in populations of a tropical macroalga and its associated epifauna, to investigate the causal factors producing the phenological patterns and to relate these findings to the general area of plant-arthropod relationships. The system investigated was four sympatric species of the brown alga Sargassum and their mobile epifauna, living at Magnetic Island, Queensland, Australia (19°10'S, 146°50'E).
Over two annual cycles all species of Sargassum showed pronounced seasonality in size and reproduction but not in density; three of four species grew annual laterals from perennial axes in spring, reached maximum size in summer, reproduced and subsequently senesced, while the fourth species showed the opposite phenology. Epiphytic algae on the surface of Sargassum were primarily absent during the spring and summer periods of Sargassum growth but attained high abundance during the winter on the residual portions. Epifauna was diverse and abundant on all species of Sargassum, being dominated numerically by gammarid amphipods, sphaeromatid isopods, tanaids, errant polychaetes and gastropods. There were few significant differences between abundance of epifauna on different species of Sargassum and few or no representatives of the reef cryptofauna: this suggested that the epifauna was a distinct algal-associated community. All epifaunal taxa also showed distinct, repeated seasonal changes in abundance. Gammarid amphipods, sphaeromatid isopods, tanaids and polychaetes — together with many of the less abundant taxa — had abundance maxima in winter and minima in summer. Conversely, only one dominant taxon, gastropods, and two less abundant taxa had summer maxima and winter minima. At finer temporal scales, epifaunal abundance was consistent over a time scale of hours and days, and moderately variable over a scale of weeks. There were few significant day-night variations in abundance of epifauna.
Manipulative experiments were run to test hypotheses about factors influencing the abundance of epifauna. Recolonisation experiments showed that the populations of epifauna were extremely dynamic in space and time, equilibrial communities being re-established on defaunated plants in approximately two weeks. The influence of predation by fishes was examined with an eight-week exclusion experiment: no effect of predation was detected although cage artifacts may have obscured abundance changes of small magnitude. The influence of habitat complexity and heterogeneity was examined using artificial plants with and without epiphytic algae: a very significant positive correlation was found between the abundance of epiphytic algae and the abundance of many taxa of epifauna. Analysis of the results at the community level revealed that communities became increasingly similar over the eight weeks of the experiment, as epiphytes accumulated on the originally epiphyte-free artificial plants. It is suggested, therefore, that the seasonal patterns of abundance of epifauna, both at the community and taxon level, are driven primarily by fluctuations in the abundance of epiphytic algae.
A detailed study of the sphaeromatid isopods was conducted to determine whether the above results and hypotheses were applicable at the species level, as opposed to the family or community level. Resolution of the seasonal pattern of abundance for the sphaeromatid family revealed that each of three common genera had distinct, unimodal phenologies: Cerceis and Cymodoce showed autumn maxima while Neonaesa had a winter maximum. Size-frequency distributions of all genera suggested that reproduction occurred continuously over extended periods of time and that adults emigrated from Sargassum upon reaching a certain size. For these isopods the Sargassum and epiphytes acted as a nursery habitat for juveniles, providing habitable space and a potential food source. A series of laboratory and field experiments with artificial substrata revealed that various aspects of habitat structure (size and colour) and habitat architecture (number, size and arrangement of habitable spaces) were important determinants of colonisation by Cymodoce. It is suggested that the observed patterns of abundance for sphaeromatid isopods on Sargassum were produced by the selective colonisation of epiphytes by juveniles in response to a complex set of habitat criteria.
Although complicated at a local scale, broad scale patterns in the Sargassum-epifauna system are similar to those in temperate macroalgal-epifauna interactions. Sargassum and its associated epifauna, in common with these other systems, appears to be a 'passive' system, wherein associations are facultative and unspecialised. This contrasts strongly with 'active' terrestrial systems where plants and arthropods commonly have highly specialised, often obligate relationships. Thus, paradigms developed from terrestrial systems about the role of factors such as habitat structure or secondary compounds will need to be revised before they can be applied to marine plant-arthropod interactions.
48
Hu, Wenbao. "A model study of the electromagnetic response of a channel, an island and a seamount in the South China Sea." Thesis, 1986. http://hdl.handle.net/1828/5723.
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Harrington, Jane Therese. "'Being here': heritage, belonging and place making: a study of community and identity formation at Avebury (England), Magnetic Island (Australia) and Ayutthaya (Thailand)." Thesis, 2004. https://researchonline.jcu.edu.au/71/1/01front.pdf.
Full textAbstract:
This thesis looks at the way cultural heritage can be more broadly considered to include
intangible aspects of our lives. Such intangible heritage encompasses the general values
and worldviews of a community and enshrines a community’s character and identity.
Through meanings, associations, values and ways of life, people individually and
collectively create a meaningful relationship with place. Place and community are
mutually constituted through social action and practice and the attribution of meaning in a
process of ‘place making’ and of reasserting belonging.
It is recognised that communities are fluid categories that can be ‘re-sited’ in relation to
new questions or different places and times. Both individual and community identity are a
form of production, and consist as a process that is never complete. That is, identity is not
only a matter of ‘being’ but also a process of ‘becoming’. By addressing case studies in
three World Heritage listed locations – Magnetic Island (Australia), Avebury (England)
and Ayutthaya (Thailand) – the thesis considers the dissonance between heritage as
defined and practised through hegemonic instruments and discourses (including
international organisations, bureaucratic structures and the Academy), and heritage as
conceived by contemporary communities as being the aspects of their lived existence that
they desire to retain for future generations.
Through discussion of emplaced communities and a series of case studies, consideration
is given to the hegemonic dominance of sanctioned determinations of heritage that
attribute significance and in the process can mute local values and narratives. The thesis
challenges the ongoing emphasis on tangible aspects of heritage and reviews the
natural/cultural heritage dichotomy, demonstrating that attachments to nature are
predicated on experiences, practices and engagements with the environment that are
grounded in social and cultural processes. I further explore the way in which the voicing
of opinions in a struggle over place can be regulated by prevailing scientific discourses
and discursive fields, placing a reliance on arguments about conservation that are
ancillary to more specific but less articulatable concerns to do with place and identity.
Finally, I illustrate the significance of the lived traditions, rituals, ceremonies, skills and
practices of the contemporary communities to a holistic understanding of heritage at both
the local and broader levels.
I conclude that it is by understanding what it is that communities find important, and how
such attachments and values are formed, transmitted and retained to create a ‘sense of
place’, that community participation in heritage can be meaningfully achieved.
Community assertions of the aspects of their lives that can be considered important to
pass on to their children are not enshrined in the monuments, structures and archaeology
that heritage professionals are more likely to identify, but in the sense of belonging that
arises through the mutual construction of community and place, reinforced through social
practices, memories and local narratives.
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Harrington, Jane Therese. "Being here : : heritage, belonging and place making : a study of community and identity formation at Avebury (England), Magnetic Island (Australia) and Ayutthaya (Thailand) /." 2004. http://eprints.jcu.edu.au/71/1/01front.pdf.
Full textAbstract:
This thesis looks at the way cultural heritage can be more broadly considered to include
intangible aspects of our lives. Such intangible heritage encompasses the general values
and worldviews of a community and enshrines a community’s character and identity.
Through meanings, associations, values and ways of life, people individually and
collectively create a meaningful relationship with place. Place and community are
mutually constituted through social action and practice and the attribution of meaning in a
process of ‘place making’ and of reasserting belonging.
It is recognised that communities are fluid categories that can be ‘re-sited’ in relation to
new questions or different places and times. Both individual and community identity are a
form of production, and consist as a process that is never complete. That is, identity is not
only a matter of ‘being’ but also a process of ‘becoming’. By addressing case studies in
three World Heritage listed locations – Magnetic Island (Australia), Avebury (England)
and Ayutthaya (Thailand) – the thesis considers the dissonance between heritage as
defined and practised through hegemonic instruments and discourses (including
international organisations, bureaucratic structures and the Academy), and heritage as
conceived by contemporary communities as being the aspects of their lived existence that
they desire to retain for future generations.
Through discussion of emplaced communities and a series of case studies, consideration
is given to the hegemonic dominance of sanctioned determinations of heritage that
attribute significance and in the process can mute local values and narratives. The thesis
challenges the ongoing emphasis on tangible aspects of heritage and reviews the
natural/cultural heritage dichotomy, demonstrating that attachments to nature are
predicated on experiences, practices and engagements with the environment that are
grounded in social and cultural processes. I further explore the way in which the voicing
of opinions in a struggle over place can be regulated by prevailing scientific discourses
and discursive fields, placing a reliance on arguments about conservation that are
ancillary to more specific but less articulatable concerns to do with place and identity.
Finally, I illustrate the significance of the lived traditions, rituals, ceremonies, skills and
practices of the contemporary communities to a holistic understanding of heritage at both
the local and broader levels.
I conclude that it is by understanding what it is that communities find important, and how
such attachments and values are formed, transmitted and retained to create a ‘sense of
place’, that community participation in heritage can be meaningfully achieved.
Community assertions of the aspects of their lives that can be considered important to
pass on to their children are not enshrined in the monuments, structures and archaeology
that heritage professionals are more likely to identify, but in the sense of belonging that
arises through the mutual construction of community and place, reinforced through social
practices, memories and local narratives.