Dissertations / Theses on the topic 'Anisotopy'

L'objectif de la thèse était d'étudier le procédé de Décrépitation à l'Hydrogène (HD) en tant que moyen de recycler les rebus d'aimants frittés Nd-Fe-B en poudres fortement coercitives et anisotropes, pour l'industrie d'aimants liés. Le procédé consiste à appliquer une première hydruration, afin de réduire le matériau massif en poudre, grâce à l'expansion du volume de la maille. Des traitements de désorption de l'hydrogène et de recuit sont ensuite nécessaires pour rétablir les caractéristiques initiales du précurseur (coercivité et anisotropie). Les différentes étapes du procédé HD ont été étudiées à partir d'aimants frittés (NdDy)2(FeCoNbCu)14B utilisés comme précurseurs. Les caractéristiques d'absorption et de désorption de l'hydrogène ont été étudiées par Calorimétrie Différentielles (DSC) et par des mesures de cinétique d'hydruration. Des mesures magnétothermiques ont permis d'analyser l'effet de la présence d'hydrogène résiduel sur les propriétés magnétiques des poudres (NdDy)-(FeCoNbCu)-B. La thèse se focalise sur l'impact des conditions expérimentales appliquées, telles que la température de décrépitation, l'application d'un double cycle de décrépitation, la température de désorption, l'application d'un champ magnétique pendant la désorption de l'hydrogène, la température de recuit, etc. Sur les propriétés magnétiques des poudres (NdDy)-(FeCoNbCu)-B. Parmi ces facteurs, les températures d'absorption et de désorption, et la température de recuit jouent un rôle prépondérant sur les propriétés magnétiques. La double décrépitation améliore la distribution de taille des poudres. La désorption de l'hydrogène sous le champ magnétique réduit le contenu d'hydrogène résiduel des poudres anisotropes, et conduit ainsi à une augmentation de la rémanence (Br). Après l'optimisation des étapes successives du procédé, des poudres anisotropes présentant des propriétés satisfaisantes ont été obtenues : Br = 10. 29 kGs (1. 029 T), Hcj = 14. 3 kOe (1138 kA/m), (BH)Max = 21. 67 MGOe (172. 5 kJ/m3). Les propriétés magnétiques initiales des aimants frittés (NdDy)-(FeCoNbCu)-B ont été restaurées respectivement à 93 %, 46 % et 74 %
The purpose of this thesis was to study the Hydrogen Decrepitation (HD) process as a way to recycle waste scraps of Nd-Fe-B sintered magnets into highly coercitive and anisotropic powders, for the industry of bonded magnets. The process consists in a first hydrogenation, the bulk material being reduced into powder, as a result of the large volume expansion of the lattice. Then Hydrogen Desorption and annealing treatments are requested to restore the initial characteristics of the precursor (coercivity and anisotropy). Starting with sintered (NdDy)2-(FeCoNbCu)14-B magnets as a precursor, the different steps of the HD process have been studied. Differential Scanning Calorimetry (DSC) and Hydrogenation Kinetics measurements were used to investigate the hydrogen absorption and desorption characteristics. Thermal-magnetization measurement was used to investigate the effect of the residual hydrogen content on magnetic properties of the anisotropic (NdDy)-(FeCoNbCu)-B powders. The thesis focuses on the effect of the applied experimental conditions such as hydrogen decrepitation temperature, twice hydrogen decrepitation cycle, hydrogen desorption temperature, magnetic field during hydrogen desorption, annealing temperature etc. . . On magnetic properties of (NdDy)-(FeCoNbCu)-B powders. Among these factors, hydrogen absorption temperature, hydrogen desorption temperature and annealing temperature play important roles on the magnetic properties. Twice hydrogen decrepitation improves the size distribution of the powders. Hydrogen desorption under magnetic field reduces the residual hydrogen content of the anisotropic powders, resulting in raising their remanence (Br). After optimization of the successive steps of the process, anisotropic powders with good properties have been achieved: Br = 10. 29 kGs (1. 029 T), Hcj = 14. 3 kOe (1138 kA/m), (BH)max = 21. 67 MGOe (172. 5 kJ/m3). It corresponds respectively to 93%, 46% and 74% of the magnetic properties of the precursor sintered (NdDy)-(FeCoNbCu)-B permanent magnets

Thesis: Ph. D. in Geotechnical and Geoenvironmental Engineering, Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 313-322).
Permeability anisotropy (the ratio of the horizontal to vertical permeability) is an important parameter used in sedimentary basin models and geotechnical design to model fluid flow, locate hydrocarbon reserves and estimate stress and pressure evolution. The magnitude of the permeability anisotropy for a given mudrock is difficult to measure; further, whether the permeability anisotropy is a constant value or evolves with the basin state is of active debate. This thesis experimentally investigates the development of permeability anisotropy in mechanically compressed mudrocks. A novel measurement method is developed using resedimented cubic specimens. The permeability anisotropy of Resedimented Boston Blue Clay (RBBC) is systematically measured to determine both the magnitude and evolution of the permeability anisotropy. The permeability anisotropy predicted using measurements of the mudrock fabric is compared with the measured permeability anisotropy to understand the relationship between fabric evolution and permeability anisotropy. Finally, resistivity anisotropy is compared with permeability anisotropy to reveal useful field correlations. The results of the RBBC study are contrasted with additional measurements made using mudrocks covering a range of plasticity, clay fraction and mineralogical composition. The permeability anisotropy and the conductivity anisotropy (inverse of the resistivity anisotropy) of uniform RBBC increase from 1.2 to 1.9 as the porosity decreases from 0.49 to 0.36. The permeability decreases by over one order of magnitude and the formation factor triples over this porosity range. Platy particles rotate from ~ 42 to 28 degrees to the horizontal, driving permeability anisotropy development. Further decreasing the porosity of RBBC below porosity 0.36 decreases both the permeability anisotropy and the conductivity anisotropy. Finally, the conductivity anisotropy is shown to equal to the permeability anisotropy within +/-20%. This general behaviour is characteristic of all mudrocks studied. Though small (<2), the permeability anisotropy of uniform mudrocks can significantly increase the permeability anisotropy of larger systems, as shown through layered system models. These models also reveal that the large scale conductivity anisotropy is not equal to the permeability anisotropy, though the relationship identified for uniform mudrocks may still be useful for sites with high measurement resolution.
by Amy Lynn Adams.
Ph. D. in Geotechnical and Geoenvironmental Engineering

A collection of studies are reported that focus on the examination of exchange interactions in complexes containing paramagnetic ions with a large magnetic anisotropy. A number of complementary techniques are used to analyse the complicated systems that arise, including high-field high-frequency electron paramagnetic resonance, inelastic neutron scattering, SQUID magnetometry, and ab initio calculations. The nuclearity of the complexes ranges from dimetallic, to trimetallic, to octametallic. A family of five water- and carboxylate-bridged nickel(II) dimetallics are the focus of a magneto-structural correlation study that succeeds in measuring the magnitude of the exchange interaction despite dominating effects from large zero-field splitting effects. Similar work is reported for four cobalt(II) analogues of these compounds, with the relationship between exchange interactions and geometry also being probed by pressure INS. Charge density studies that combine high resolution X-ray and neutron diffraction studies are reported on cobalt and nickel analogues from the same family of dimetallics, revealing strong evidence for non-direct exchange. A family of four trimetallic triangle complexes containing two nickel(II) ions and one chromium(III) ion bridged by a central fluoride and a total of six carboxylates are reported, and the exchange interactions are elucidated from a global model that accounts for the low-field magnetic, heat capacity, and EPR data. Two new octametallic vanadium(III) wheels—where each pair of adjacent metals are bridged by a fluoride and two carboxylates—are reported along with preliminary results from magnetic measurements and solid state proton NMR spectra, which reveal significant field-dependent effects arising from level crossings at high fields.

Les matériaux supraconducteurs présentent des propriétés physiques et géométriques particulières qui exigent des approches de modélisation spatio-temporelle fines, où les méthodes classiques trouvent rapidement leurs limites en termes de convergence, de précision et de temps de calcul. Ce dernier peut être très conséquent, ce qui est incompatible avec les problèmes de dimensionnement et d’optimisation. Dans ce contexte, ce travail a pour objectif de développer des approches de modélisation multiphysique rapides pour le dimensionnement et l’optimisation des systèmes à base de supraconducteurs. Un intérêt particulier est porté pour les méthodes intégrales. Les verrous scientifiques à lever, qui constituent également l’originalité du travail, résident dans l’intégration des lois de comportement E(J) des supraconducteurs dans les schémas numériques de ce type de méthodes. Dans ce travail on développe un modèle numérique afin d’étudier la distribution de la densité de courant et d’estimer les pertes AC dans les supraconducteurs à haute température (HTS). Le modèle développé est basé sur une formulation intégro-différentielle en termes de potentiel vecteur électrique dans les deux domaines fréquentiel et temporel. Une campagne de test est menée afin de valider et de bien cerner les possibilités offertes et les limites de cette approche pour la modélisation des supraconducteurs
Superconducting materials have particular physical and geometric properties that require spatial-temporal modeling approaches fines, where conventional methods quickly reach their limits in terms of convergence, precision and computational time. The latter can be very consistent, which is incompatible with the design and optimization problems. In this context, this work aims to develop rapid multiphysics modeling approaches for the design and optimization of superconductor-based systems. Particular attention is paid to the integral methods. Scientific obstacles to overcome, which also constitute the originality of the work lies in the integration of behavior laws E (J) of superconducting digital patterns of such methods. A numerical model is developed for a rapid computation of eddy currents in multifilamentary high temperature superconductive (HTS) for the evaluation of AC losses. The developed model is based on an integro-differential formulation in terms of the electric vector potential in the frequency and temporal domains. A test campaign is conducted to validate and clearly identify the possibilities and limitations of this approach for modeling superconductors

As well as being of fundamental interest, understanding plasma turbulence is important for many areas of astrophysics and space physics that remain to be fully understood, such as accretion disk dynamics, the origin of cosmic rays and coronal heating. The anisotropy with respect to the magnetic fi eld is central to understanding plasma turbulence, but this has only recently started to be measured in detail. The solar wind provides a unique opportunity to study this anisotropy due to the range of high precision in situ measurements available. In this thesis, the anisotropy of solar wind turbulence is measured using data from the multi-spacecraft Cluster mission. At all scales measured, the fluctuations are found to be spatially anisotropic: elongated along the direction of the magnetic field. The scaling of the turbulence is also anisotropic, with a steeper spectral index in the direction parallel to the local magnetic fi eld. This is consistent with the fluctuations being in critical balance: having approximately equal linear wave timescales and nonlinear eddy decay timescales. At large scales, the anisotropy of the density and parallel magnetic fi eld fluctuations follows that of the perpendicular Alfvénic turbulence, in agreement with passive scalar theory. One puzzling result, however, is the scaling of the parallel magnetic field at small scales, which does not follow theoretical expectations. For the fi rst time, the technique used to measure the anisotropy of solar wind turbulence is applied to turbulence in reduced magnetohydrodynamic simulations. Again, the anisotropic scaling is seen, which is in agreement with critical balance predictions. It is also shown that when measuring the anisotropy with respect to the global, rather than local magnetic field, the anisotropic scaling cannot always be properly measured, which explains the previous apparently contradictory measurements in the literature.

Thesis: S.M., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 257-260).
Permeability anisotropy (ratio of horizontal to vertical permeability) is an important but uncertain parameter used in characterizing underground formations. While it is a fairly unknown parameter, it is integral for the petroleum industry, where a greater permeability anisotropy understanding can greatly aid in basin modelling, pore pressure prediction, and borehole stability. This research experimentally characterizes the permeability anisotropy of several mudrocks, which are clay-rich sedimentary formations, using re-sedimentation, a process of homogenization of naturally-occurring soils and recreation of the sedimentation environment in a controlled laboratory setting. The permeability anisotropy of resedimented Boston Blue Clay (RBBC), an illitic lean clay (CL), increases from 1.5 to 3 when mechanically compressed from 0.1 to 40 MPa, corresponding to porosities ranging from 0.55 to 0.26. Resedimented Gulf of Mexico - Eugene Island mudrock (RGoM-EI), a smectitic fat clay (CH), exhibits permeability anisotropy increasing from 1 to 5 when compressed to the same stresses, corresponding to porosities ranging from 0.6 to 0.25. Not only does smectitic RGoM-EI mudrock transition to greater anisotropy with compression, but the rate of increase accelerates with compression. These measurements are made using a commercially-available Trautwein® constant rate of strain (CRS) consolidometer with vertical drainage combined with a novel radially-outward draining CRS device. The combination of the vertically and radially draining CRS devices produces permeability anisotropy data quickly, with very little scatter. For RGoM-EI, the effects of horizontal shearing to 29.5% shear strain at 0.14 MPa on permeability anisotropy are negligible. Permeability anisotropy of the homogeneous resedimented mudrocks tested, using a cubic specimen constant head permeameter within a triaxial cell, is directly correlated to their electrical conductivity anisotropy. The permeability anisotropy values measured using this technology, however, are lower than those measured using CRS testing.
by Taylor James Nordquist.
S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2004.
Includes bibliographical references (p. 59-60).
According to the WMAP and earlier COBE observations, the Cosmic Microwave Background (CMB) anisotropy power on large angular scales appears to be significantly lower than predicted by the standard model of cosmology. We propose a scalar field model of the dark energy as a mechanism for suppressing low l multipoles through late-Universe evolution of metric fluctuations and the integrated Sachs-Wolfe (ISW) effect. We find that for a constant dark energy equation of state, theoretical predictions actually give a larger (instead of a desired smaller) value of the quadrupole and other low l multipoles.
by Yukyan Lam.
S.B.

本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものである
Kyoto University (京都大学)
0048
新制・論文博士
博士(医学)
乙第10371号
論医博第1709号
新制||医||742(附属図書館)
UT51-2000-F437
(主査)教授 開 祐司, 教授 堤 定美, 教授 岡 正典
学位規則第4条第2項該当

Thesis (Ph.D.); Submitted to the University of California at Berkeley, Berkeley, CA (US); 1 Sep 2003.
Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--55023" Li, Liang-shi. USDOE Director. Office of Science. Office of Basic Energy Sciences (US) 09/01/2003. Report is also available in paper and microfiche from NTIS.

The use of radio frequency (rf) plasma techniques to produce fine structures of precise geometry is widespread in the microelectronics industry. An important factor influencing the functionality of fabricated devices is the wall angle of these structures. In certain applications vertical walls are required - for example to minimise mask degradation and maximise gate densities; in others a sloping sidewall is preferred - to minimise stress in metal coatings when making electrical contact through 'via' holes, for instance. This fine control cannot be achieved on micron and sub-micron scale devices using conventional 'wet' chemical processing techniques and has led to the adoption of so-called 'dry' processing techniques using plasmas. Both vertical and sloping wall profiles can be produced depending upon the plasma conditions. It is apparent, therefore, that a thorough understanding of the processes affecting the etch profile is important. Reactive ion etching (RIE) has been employed to produce micron, and sub-micron size structures in polyimide using an oxygen plasma. Present models of etch directionality all make the initial assumption that the directional component of the etching process can be attributed solely to O2+ ion bombardment of the exposed horizontal surface of the wafer driven by the electric 'sheath' field developed above the electrode. Whether species such as O+ and even multiply charged reactive species such as O++ and O+++ can legitimately be neglected in formulating such a model has yet to be established. That such multiply ionized species exist, however, is highly probable given that plasmas are well known to emit strongly in the ultraviolet. The etching system developed to investigate these problems was equipped with diagnostic techniques including optical emission spectroscopy, mass spectrometry, and a grid energy analyser. The optical emission spectrometer was novel in being capable of measuring emission from the far-ultraviolet emission spectrum of the plasma and was therefore able to detect the high energy ultraviolet light and the singly and multiply ionised species from which this radiation is emitted. Using this technique the role of multiply-ionised species in controlling etch anisotropy was investigated. Results are also presented, obtained from a retarding grid, particle energy analyser built into the surface of the earth electrode, which indicate increased charged particle flux and energy at low pressure providing further information with regard to the process dynamics. The influence of gas pressure and rf excitation frequency on the resultant etch profile have been investigated. Results are presented showing the presence of doubly-ionised atomic oxygen O++ in the plasma. It is shown in this work that O++ also has a role in etch anisotropy at low pressure. This and other more highly charged species need to be considered, therefore, in formulating models of etch anisotropy, etch rate, and etch chemistry and reaction mechanisms. The role of ultraviolet irradiation which is itself of sufficient energy to induce surface reactions must also be considered.

Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1996

I have studied Exchange Bias in epitaxial α-Fe₂O₃ and polycrystalline FeMn and CoMn antiferromagnets coupled to the ferromagnet Permalloy (Ni₈₁Fe₁₉). Despite the nominal magnetocrystalline anisotropy of Permalloy, surface features such as vicinal steps and roughness induced strong uniaxial anisotropy. Exchange coupling with epitaxial α-Fe₂O₃ led to a biaxial anisotropy component in the ferromagnet. Anisotropy axes of the biaxial component remained fixed despite applying magnetic field at elevated temperatures. The magnitude of biaxial anisotropy varied with every temperature cycle, providing implicit evidence of domains in the antiferromagnet. In polycrystalline systems, uniaxial anisotropy of the ferromagnet set-up during growth competes with exchange anisotropy. By setting up an AF/F/AF trilayer, magnetic field cooling allowed control of the net anisotropy. These findings demonstrate that the two crucial factors that impact exchange biased thin films are (1) uniaxial anisotropies in the ferromagnet from surface and growth conditions and (2) exchange coupling with domains in the antiferromagnet. Competing effect of these two factors is the key to understanding any exchange coupled system.

In this dissertation I examine the inner core using two complementary seismic perturbations: seismic body waves and free oscillations of the Earth. I investigate the velocity anisotropy present in the inner core by measuring PKPdf-PKPbc and PKPdf-PKPab differential travel time residuals. A model for an inner core with 3.5% cylindrical anisotropy is consistent with the data. However, the data are better fitted by an inner core which is divided into two ‘hemispheres’, an isotropic eastern hemisphere between 14°E and 151°W and western hemisphere which contains 4.4% anisotropy between 151°W and 14°E. The axis of anisotropy in the inner core is coincident with the Earth’s rotation axis, and an isotropic layer at the top of the western hemisphere of up to 150km in depth is consistent with the data. I find that there is also hemispherical variation in inner core attenuation anisotropy, the western hemisphere displays attenuation anisotropy whilst the eastern hemisphere does not. I examine the possibility of detecting a hemispherical velocity anisotropy structure using free oscillations of the Earth’s normal modes. New theory is derived to allow any existing cylindrical anisotropy model to be confined to only one part of the inner core. When this new theory is used and full coupling between modes is permitted, radial, PKIKP and PKJKP modes all show changes in their frequencies and quality factors. These changes are large enough to be observed in the data, and are dependent on the model of inner core anisotropy which is used. Normal mode data can therefore be used to detect hemispherical structure in inner core anisotropy. I also show that normal mode data can be reconciled with evidence presented by body wave data that the top of the inner core is isotropic.

A new β and N-substituted pyrrole, N-trimethylsilylethoxymethyl-3-methyl-4-pyrrole carboxylate ethyl ester (MPCE-SEM) is synthesised and copolymerised electrochemically with unsubstituted pyrrole to gives free-standing films for conductivity measurements. The electrochemical polymerisation of MPCE-SEM gives only soluble dimers and oligomers rather than polymers because the steric constraints stabilise the oligomeric cation radical of MPCE-SEM. The thiophene monomers containing mesogenic group at the 3-position via an alkyl chain are synthesised and polymerised chemically to give insoluble, infusible polymers and do not exhibit liquid crystalline behaviour. The conductivities of pressed-pellets of the polymer powders are lower than 10^-5S/cm. The electrochemical polymerisation of the thiophene monomers containing mesogenic group of 4-methoxyazbenzen-4'-yloxy or 4-butylazobenzen-4'-yloxy in dichloromethane solution gives a low yield of polymers, which is accompanied by the formation of soluble dimers and oligomers as well as degradation of the resulting polymer and the mesogenic group. Poly{N -11-[(4-cyanobiphenyl-4'-yloxy) undecyl] pyrrole} obtained from chemical polymerisation of the corresponding monomer shows high molecule weight, is soluble in common solvents and fusible showing smectic A liquid crystalline behaviour. This polymer in the melt (175^oC) has a conductivity of 6.6 x 10^-15 S/cm. X-ray photoelectron spectrometry analysis on the melt processed film gives an estimated doping level of an anion every 6-7 monomer units. Electrochemical oxidation of the N-substituted pyrrole monomers gives the electroactive conjugated free-standing polymer films. The conductivities of the free standing polymer films are lower than 10^-4 S/cm. A conducting copolymer containing a side chain liquid crystalline group, poly{N-8-[(4-cyanobiphenyl-4'-yloxy)octyl]-2,5-di(2-thienyl) pyrrole} can be obtained electrochemically from the corresponding monomer. The polymer is slightly soluble in chloroform giving a dark green solution but is not liquid crystalline.

Currently, the world population is aging. People over 75 is one of the fastest growing age groups. This is the group most affected by Alzheimer's disease. Reliable early diagnosis and tracking methods are essential to assist therapy and prevention. This research aims to study anisotropy texture in tomographic brain scans to diagnose and quantify the severity of Alzheimer's disease. A full methodology to study computer tomography, magnetic resonance imaging and multispectral magnetic resonance imaging is presented in this thesis. Before applying any texture method to the tomographic brain images, a segmentation technique has to be used to extract the different regions of interest. We propose the use of connected filters and iterative region merging to perform the segmentation. Gradient vector histogram is applied to study the texture anisotropy of computer tomography scans. Computer tomography scans present evidence of texture changes in demented subjects compare to normal subjects. The overlap between these groups is considerable, so anisotropy texture using computer tomography does not seem to add more useful information to the diagnosis of Alzheimer's disease than other clinical criteria. Another method to study texture anisotropy is grey-level dependance histogram, which is based in a 3D generalisation for arbitrary orientation of the 2D co-occurrence matrices. This texture technique is applied to magnetic resonance imaging scans, where features extracted from the grey matter component have a strong correlation with the mini mental state examination1 scores. Finally, Multispectral Grey-Level Dependence Histogram (MGLDH), Absolute Difference Histogram (ADH) and spatial correlations are texture techniques designed to study multispectral images. These techniques are applied to multispectral magnetic resonance images. We evaluate the performance of the different multispectral texture methods, and compare them with single channel texture methods.

The study of magnetic anisotropy in molecular systems permeates the physical sciences and finds application in areas as diverse as biomedical imaging and quantum information processing. The ability to understand and subsequently to design improved agents requires a detailed knowledge of their fundamental operation. This work outlines the background theory of the electronic structure of magnetic molecules and provides examples, for elements across the Periodic Table, of how it may be employed to aid in the understanding of magnetically anisotropic molecules. The magnetic anisotropies of a series of dimetallic NiII2 complexes and a RuIII2MnII triangle are determined through multi-frequency Electron Paramagnetic Resonance (EPR) spectroscopy and ab initio calculations. The magnetic anisotropy of the former is found to be on the same order of magnitude as the isotropic exchange interactions, while that of the latter is found to be caused by large antisymmetric exchange interactions involving the RuIII ions. An intuitive electrostatic strategy for the prediction of the magnetic anisotropy of DyIII complexes is presented, allowing facile determination of magnetic anisotropy for low symmetry molecules. Through the presentation of the first near-linear pseudo-two-coordinate 4f-block complex, a new family of DyIII complexes with unprecedented Single Molecule Magnet (SMM) properties is proposed. Design criteria for such species are elucidated and show that in general any two-coordinate complex of DyIII is an attractive synthetic target. The exchange interaction between two DyIII ions is directly measured with multi-frequency EPR spectroscopy, explaining the quenching of the slow magnetic relaxation in the pure species compared to the SMM properties of the diluted form. The interpretation of this complex system was achieved with supporting ab initio calculations.

Thesis (M.S.) -- University of Maryland, College Park, 2003.
Thesis research directed by: Dept. of Materials Science and Nuclear Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

The interpretation of geophysical field measurements of seismic anisotropy is presently limited by our knowledge of the controls of the elastic anisotropy of sedimentary rocks in the subsurface. Traditionally, laboratory ultrasonic velocity measurements have been used to provide important information on bulk aggregate seismic anisotropy, however, they do not allow the discrimination of the contribution from the various microstructural parameters (e. g., crystallographic lattice preferred orientation (LPO), preferentially aligned porosity, aligned fractures and the non-random spatial distribution of mineral phases). In this study the results from scanning electron microscope-electron backscattered diffraction (SENI-EBSD), quantitative X-ray diffraction (QXRD), image analysis, ultrasonic velocity measurements, palaeomagnetism, anisotropic magnetic susceptibility, and numerical modelling are combined to elucidate the controls of the elastic anisotropy of siliciclastic sedimentary rocks from an oil reservoir. SEM-EBSD was used to measure both the overall and individual constituent mineral phase LPO (Maddock et al. 2004). As phyllosilicates are both very fine-grained, with a high aspect-ratio and low crystallinity, their LPO contribution was established via a combination of image analysis and numerical modelling (Bingham approximation). These analytical and predictive methods for determining phyllosilicate fabric intensity produced consistent results. For the first time, the azimuthally preferred orientation of elongate grains within sedimentary rocks was determined using anisotropic magnetic susceptibility of ferrous minerals and were compared to those predictions obtained using EBSD. The strength of the fabric-texture (J), as determined by EBSD, is proportional to the maximum compressional and shear-wave anisotropy, as calculated from the Christoffel equation, by taking a Hill average of the bulk aggregate elastic constants. The quartz and feldspar velocity maxima aligned in a constructive fashion throughout most of the samples. It is possible that the preferred alignment of crystals detected by EBSD reflects the palaeoflow direction. The predicted symmetries of velocity anisotropy ranged from orthorhombic in the phyllosilicate-free, well-sorted, mature sandstones to strong vertical transverse isotropy in the unfractured phyllosilicate-rich mudstones. Vertical transverse isotropy is predicted to be oriented, such that, the plane of azimuthal isotropy is aligned parallel to bedding i. e., parallel to the horizontally aligned clays and micas. Similarly, orthorhombic symmetry is predicted to be oriented, such that, one plane of symmetry is aligned approximately parallel to bedding whilst the other symmetry plane is aligned parallel to the single most dominant fracture set. The results from this study provide the input needed for a general mathematical model for the reservoir allowing the prediction of seismic anisotropy for any rock in the reservoir given accurate modal proportions. The resulting model is an advance on the empirical correlations that are usually used to determine how seismic velocities are affected by factors such as clay content and porosity. In particular, the bulk aggregate elastic stiffness tensor obtained during this study can be integrated with high-pressure ultrasonic measurements to enable the prediction of the additional contribution from grain-scale effects such as shape-preferred orientations, and grain boundary compliances (Hall et al. 2007). The results from this study have also provided the basic data to allow field seismic data to be inverted to obtain estimates of in situ fracture density and orientation (Kendall et al. 2006). In summary, analysis of a suite of siliciclastic hydrocarbon reservoir rocks has shown that the LPO of constitutive minerals can offer information about the nature of a reservoir. The results suggest that seismic anisotropy is not only indicative of lithology but can also be an indicator of reservoir quality and palaeoflow direction.

Tectonic and geological processes on Earth often result in structural anisotropy of the subsurface, which can be imaged by various geophysical methods. In order to achieve appropriate and realistic Earth models for interpretation, inversion algorithms have to allow for an anisotropic subsurface. Within the framework of this thesis, I analyzed a magnetotelluric (MT) data set taken from the Cape Fold Belt in South Africa. This data set exhibited strong indications for crustal anisotropy, e.g. MT phases out of the expected quadrant, which are beyond of fitting and interpreting with standard isotropic inversion algorithms. To overcome this obstacle, I have developed a two-dimensional inversion method for reconstructing anisotropic electrical conductivity distributions. The MT inverse problem represents in general a non-linear and ill-posed minimization problem with many degrees of freedom: In isotropic case, we have to assign an electrical conductivity value to each cell of a large grid to assimilate the Earth's subsurface, e.g. a grid with 100 x 50 cells results in 5000 unknown model parameters in an isotropic case; in contrast, we have the sixfold in an anisotropic scenario where the single value of electrical conductivity becomes a symmetric, real-valued tensor while the number of the data remains unchanged. In order to successfully invert for anisotropic conductivities and to overcome the non-uniqueness of the solution of the inverse problem it is necessary to use appropriate constraints on the class of allowed models. This becomes even more important as MT data is not equally sensitive to all anisotropic parameters. In this thesis, I have developed an algorithm through which the solution of the anisotropic inversion problem is calculated by minimization of a global penalty functional consisting of three entries: the data misfit, the model roughness constraint and the anisotropy constraint. For comparison, in an isotropic approach only the first two entries are minimized. The newly defined anisotropy term is measured by the sum of the square difference of the principal conductivity values of the model. The basic idea of this constraint is straightforward. If an isotropic model is already adequate to explain the data, there is no need to introduce electrical anisotropy at all. In order to ensure successful inversion, appropriate trade-off parameters, also known as regularization parameters, have to be chosen for the different model constraints. Synthetic tests show that using fixed trade-off parameters usually causes the inversion to end up by either a smooth model with large RMS error or a rough model with small RMS error. Using of a relaxation approach on the regularization parameters after each successful inversion iteration will result in smoother inversion model and a better convergence. This approach seems to be a sophisticated way for the selection of trade-off parameters. In general, the proposed inversion method is adequate for resolving the principal conductivities defined in horizontal plane. Once none of the principal directions of the anisotropic structure is coincided with the predefined strike direction, only the corresponding effective conductivities, which is the projection of the principal conductivities onto the model coordinate axes direction, can be resolved and the information about the rotation angles is lost. In the end the MT data from the Cape Fold Belt in South Africa has been analyzed. The MT data exhibits an area (> 10 km) where MT phases over 90 degrees occur. This part of data cannot be modeled by standard isotropic modeling procedures and hence can not be properly interpreted. The proposed inversion method, however, could not reproduce the anomalous large phases as desired because of losing the information about rotation angles. MT phases outside the first quadrant are usually obtained by different anisotropic anomalies with oblique anisotropy strike. In order to achieve this challenge, the algorithm needs further developments. However, forward modeling studies with the MT data have shown that surface highly conductive heterogeneity in combination with a mid-crustal electrically anisotropic zone are required to fit the data. According to known geological and tectonic information the mid-crustal zone is interpreted as a deep aquifer related to the fractured Table Mountain Group rocks in the Cape Fold Belt.
Tektonische und geologische Prozesse verursachen häufig eine strukturelle Anisotropie des Untergrundes, welche von verschiedenen geophysikalischen Methoden beobachtet werden kann. Zur Erstellung und Interpretation geeigneter, realistischer Modelle der Erde sind Inversionsalgorithmen notwendig, die einen anisotropen Untergrund einbeziehen können. Für die vorliegende Arbeit habe ich einen magnetotellurischen (MT) Datensatz vom Cape Fold Gürtel in Südafrika untersucht. Diese Daten weisen auf eine ausgeprägte Anisotropie der Kruste hin, da z.B. die MT Phasen außerhalb des erwarteten Quadranten liegen und nicht durch standardisierte isotrope Inversionsalgorithmen angepasst und ausgewertet werden können. Um dieses Problem zu beheben, habe ich eine zweidimensionale Inversionsmethode entwickelt, welche eine anisotrope elektrische Leitfähigkeitsverteilungen in den Modellen zulässt. Die MT Inversion ist im allgemeinen ein nichtlineares, schlecht gestelltes Minimierungsproblem mit einer hohen Anzahl an Freiheitsgraden. Im isotropen Fall wird jeder Gitterzelle eines Modells ein elektrischer Leitfähigkeitswert zugewiesen um den Erduntergrund nachzubilden. Ein Modell mit beispielsweise 100 x 50 Zellen besitzt 5000 unbekannte Modellparameter. Im Gegensatz dazu haben wir im anisotropen Fall die sechsfache Anzahl, da hier aus dem einfachen Zahlenwert der elektrischen Leitfähigkeit ein symmetrischer, reellwertiger Tensor wird, wobei die Anzahl der Daten gleich bleibt. Für die erfolgreiche Inversion von anisotropen Leitfähigkeiten und um die Nicht-Eindeutigkeit der Lösung des inversen Problems zu überwinden, ist eine geeignete Einschränkung der möglichen Modelle absolut notwendig. Dies wird umso wichtiger, da die Sensitivität von MT Daten nicht für alle Anisotropieparameter gleich ist. In der vorliegenden Arbeit habe ich einen Algorithmus entwickelt, welcher die Lösung des anisotropen Inversionsproblems unter Minimierung einer globalen Straffunktion berechnet. Diese besteht aus drei Teilen: der Datenanpassung, den Zusatzbedingungen an die Glätte des Modells und die Anisotropie. Im Gegensatz dazu werden beim isotropen Fall nur die ersten zwei Parameter minimiert. Der neu definierte Anisotropieterm wird mit Hilfe der Summe der quadratischen Abweichung der Hauptleitfähigkeitswerte des Modells gemessen. Die grundlegende Idee dieser Zusatzbedingung ist einfach. Falls ein isotropes Modell die Daten ausreichend gut anpassen kann, wird keine elektrische Anisotropie zusätzlich in das Modell eingefügt. Um eine erfolgreiche Inversion zu garantieren müssen geeignete Regularisierungsparameter für die verschiedenen Nebenbedingungen an das Modell gewählt werden. Tests mit synthetischen Modellen zeigen, dass bei festgesetzten Regularisierungsparametern die Inversion meistens entweder in einem glatten Modell mit hohem RMS Fehler oder einem groben Modell mit kleinem RMS Fehler endet. Die Anwendung einer Relaxationsbedingung auf die Regularisierung nach jedem Iterationsschritt resultiert in glatteren Inversionsmodellen und einer höheren Konvergenz und scheint ein ausgereifter Weg zur Wahl der Parameter zu sein. Die vorgestellte Inversionsmethode ist im allgemeinen in der Lage die Hauptleitfähigkeiten in der horizontalen Ebene zu finden. Wenn keine der Hauptrichtungen der Anisotropiestruktur mit der vorgegebenen Streichrichtung übereinstimmt, können nur die dazugehörigen effektiven Leitfähigkeiten, welche die Projektion der Hauptleitfähigkeiten auf die Koordinatenachsen des Modells darstellen, aufgelöst werden. Allerdings gehen die Informationen über die Rotationswinkel verloren. Am Ende meiner Arbeit werden die MT Daten des Cape Fold Gürtels in Südafrika analysiert. Die MT Daten zeigen in einem Abschnitt des Messprofils (> 10 km) Phasen über 90 Grad. Dieser Teil der Daten kann nicht mit herkömmlichen isotropen Modellierungsverfahren angepasst und daher mit diesen auch nicht vollständig ausgewertet werden. Die vorgestellte Inversionsmethode konnte die außergewöhnlich hohen Phasenwerte nicht wie gewünscht im Inversionsergebnis erreichen, was mit dem erwähnten Informationsverlust der Rotationswinkel begründet werden kann. MT Phasen außerhalb des ersten Quadranten können für gewöhnlich bei Anomalien mit geneigter Streichrichtung der Anisotropie gemessen werden. Um diese auch in den Inversionsergebnissen zu erreichen ist eine Weiterentwicklung des Algorithmus notwendig. Vorwärtsmodellierungen des MT Datensatzes haben allerdings gezeigt, dass eine hohe Leitfähigkeitsheterogenität an der Oberfläche in Kombination mit einer Zone elektrischer Anisotropie in der mittleren Kruste notwendig sind um die Daten anzupassen. Aufgrund geologischer und tektonischer Informationen kann diese Zone in der mittleren Kruste als tiefer Aquifer interpretiert werden, der im Zusammenhang mit den zerrütteten Gesteinen der Table Mountain Group des Cape Fold Gürtels steht.

Transverse anisotropy is an important phenomenon of practical and scientific interest. Although the presence of ray tissue explains the high radial modulus in many hardwoods, experimental data in the literature shows that this is not the case for pine. It is possible that anisotropy in softwoods may be explained by the cellular structure and associated deformation mechanisms.

An experimental approach was developed by which local radial modulus in spruce was determined at sub-annual ring scale. Digital speckle photography (DSP) was used, and the density distribution was carefully characterized using x-ray densitometry and the SilviScan apparatus. A unique set of data was generated for radial modulus versus a wide range of densities. This was possible since earlywood density shows large density variations in spruce. Qualitative comparison was made between data and predictions from stretching and bending honeycomb models. The hypothesis for presence of cell wall stretching was supported by data.

A model for wood was therefore developed where both cell wall bending and stretching are included. The purpose was a model for predictions of softwood moduli over a wide range of densities. The relative importance of the deformation mechanisms was investigated in a parametric study. A two-phase model was developed and radial and tangential moduli were predicted. Comparison with experimental data showed good agreement considering the nature of the model (density is the only input parameter). Agreement is much better than for a regular honeycomb model. According to the model, cell wall bending dominates at both low and high densities during tangential loading. In radial loading, cell wall stretching dominates at higher densities.

Spin-orbit coupling (SOC) reduces the spatial symmetry of ferromagnetic solids. That is, the physical properties of ferromagnetic materials are anisotropic, depending on the magnetization direction. In this thesis, by means of numerical calculations with full-relativistic density functional theory, we studied two kinds of physical properties: surface magnetic anisotropy energy (MAE) and anisotropic thermoelectric power due to Lifshitz transitions. After a short introduction to the full-relativistic density functional theory in Chapter 2, the MAE of ferromagnetic thin films is studied in Chapter 3. For such systems, separation of different contributions, such as bulk magnetocrystalline anisotropy (MCA) energy, shape anisotropy energy, and surface/interface anisotropy energy, is crucial to gain better understanding of experiments. By fitting our calculating results for thick slabs to a phenomenological model, reliable surface MAE could be obtained. Following this idea, we have studied the MAE of Co slabs with different geometries, focusing on the effects of orbital polarization correction (OPC). We found that the surface anisotropy is mainly determined by the geometry. While OPC gives better results of orbital moments, it overestimates the MAE. In the second part of Chapter3, the effects of electric fields on the MAE of L10 ferromagnetic thin films are studied. Using a simple model to simulate the electric field, our calculations are in good agreement with previous experimental results. We predicted that for CoPt, even larger effects exist. Moreover, we found that it is the amount of screening charge that determines the magnetoelectric coupling effects. This gives us some clue about how to achieve electric field control of magnetization direction. In Chapter 4, Lifshitz transitions in L10 FePt caused by a canted magnetic field are studied. We found several Lifshitz transitions in ordered FePt with tiny features in DOS. Using a two-band model, it is demonstrated that at such transitions, the singular behaviour of kinetic properties is due to the interband scattering, and the singularity itself is proportional to the derivative of the singular DOS. For FePt, such singularity will be smeared into anomaly by chemical disorder. Using CPA, we studied the effects of energy level broadening for the critical bands in FePt. We found that for experimentally available FePt thin films, Lifshitz transitions would induce up to a 3% increase of thermopower as the magnetization is rotated from the easy axis to the hard axis
Spin-Bahn-Kopplung reduziert die Symmetrie ferromagnetischer Festkörper. Das bedeutet, dass die physikalischen Eigenschaften ferromagnetischer Stoffe anisotrop bezüglich der Magnetisierungsrichtung sind. In dieser Dissertation werden mittels numerischer voll-relativistischer Dichtefunktional-Rechnungen zwei Arten physikalischer Eigenschaften untersucht: magnetische Oberflächen-Anisotropieenergie (MAE) und anisotrope Thermokraft durch Lifshitz-Übergänge. Nach einer kurzen Einführung in die relativistische Dichtefunktional-Theorie in Kapitel 2 wird in Kapitel 3 die MAE ferromagnetischer dünner Filme untersucht. In diesen Systemen ist es für ein Verständnis experimenteller Ergebnisse wichtig, verschiedene Beiträge zu separieren: Volumenanteil der magnetokristallinen Anisotropie (MCA), Formanistropie und Oberflächen bzw. Grenzflächenanisotropie. Durch Anpassen berechneter Daten für dicke Schichten an ein phänomenologisches Modell konnten verlässliche Oberflächen Anisotropien erhalten werden. In dieser Weise wurde die MAE von Co- Schichten mit unterschiedlichen Geometrien untersucht, wobei der Einfluss von Orbitalpolarisations-Korrekturen (OPC) im Vordergrund stand. Es wurde gefunden, dass die Oberflächenanisotropie hauptsächlich von der Geometrie bestimmt wird. Während OPC bessere Ergebnisse für die Orbitalmomente liefert, wird die MAE überschätzt. Im zweiten Teil von Kapitel 3 wird der Einfluss elektrischer Felder auf die MAE von dünnen ferromagnetischen Filmen mit L10-Struktur untersucht. Unter Verwendung eines einfachen Modells zur Simulation des elektrischen Feldes liefern die Rechnungen gute Übereinstimmung mit vorliegenden experimentellen Ergebnissen. Es wird vorhergesagt, dass für CoPt ein noch größerer Effekt existiert. Weiterhin wurde gefunden, dass die magnetoelektrische Kopplung von der Größe der Abschirmladung bestimmt wird. Dies ist eine wichtige Einsicht, um die Magnetisierungsrichtung durch ein elektrisches Feld kontrollieren zu können. In Kapitel 4 werden Lifshitz-Übergänge untersucht, die ein gekantetes Magnetfeld hervorruft. Es wurden mehrere Lifshitz-Übergänge in geordnetem FePt gefunden, welche kleine Anomalien in der Zustandsdichte hervorrufen. Mit Hilfe eines Zweiband-Modells wird gezeigt, dass an solchen Übergängen das singuläre Verhalten kinetischer Eigenschaften durch Interband- Streuung verursacht wird und dass die Singularität proportional zur Ableitung der singulären Zustandsdichte ist. In FePt wird durch chemische Unordnung diese Singularität zu einer Anomalie verschmiert. Der Einfluss einer Verbreiterung der Energieniveaus der kritischen Bänder in FePt wurde mittels CPA untersucht. Es wurde gefunden, dass in experimentell verfügbaren dünnen FePt-Filmen Lifshitz-Übergänge bis zu 3% Erhöhung der Thermokraft erzeugen, wenn die Magnetisierung von der leichten in die harte Richtung gedreht wird

After nearly 15 years of research effort, High Temperature Superconductors (HTS) are finding a wide range of practical applications. A clear understanding of the factors controlling the current carrying capacity of these materials is a prerequisite to their successful technological development. The critical current density (Jc) in HTS is directly dependent on the structure and pinning of the Flux Line Lattice (FLL) in these materials. This thesis presents an investigation of the Jc anisotropy in HTS. The use of thin films grown on off c-axis (vicinal) substrates allowed the effect of current directions outside the cuprate planes to be studied. With this experimental geometry Berghuis, et al. (Phys. Rev. Lett. 79,12, pg. 2332) observed a striking flux channelling effect in vicinal YBa2Cu3O7-δ (YBCO) films. By confirming, and extending, this observation, it is demonstrated that this is an intrinsic effect. The results obtained, appear to fit well with the predictions of a field angle dependent cross-over from a three dimensional rectilinear FLL to a kinked lattice of strings and pancakes. The pinning force density for movement of strings inside the cuprate planes is considerably less than that on vortex pancake elements. When the FLL is entirely string-like this reduced pinning leads to the observed channelling minima. It is observed that anti-phase boundaries enhance the Jc in vicinal YBCO films by strongly pinning vortex strings. The effect on the FLL structure cross-over of increasing anisotropy has been elucidated using de-oxygenated vicinal YBCO films. Intriguingly, the counter intuitive prediction that the range of applied field angle for which the kinked lattice is fully developed reduces with increasing anisotropy, appears to be confirmed. Although vortex channelling cannot be observed in c-axis YBCO films, the pinning force density for vortex string channelling has been extracted by observing string dragging. By studying the effect of rotating the applied field at a constant angle to the cuprate planes, it is possible to observe the cross-over into the string pancake regime in c-axis films. In the 3D region, the observed behaviour is well explained by the anisotropic Ginzburg-Landau model. Measurements were also made on thin films of the much more anisotropic Bi 2Sr2CaCu2O8+x material, grown on vicinal substrates. The absence of any flux channelling effect and clear adherence to the expected Kes-Law behaviour in the observed Jc characteristics does not provide evidence for the existence of the predicted 'crossing lattice' in Bi 2Sr2CaCu2O8+x.

Symmetry in photonic crystals is reflected in the structure of their photonic bands and symmetry breaking can result in the development of complete photonic band gaps, leading to enhanced optical properties. This can be difficult for self-assembled nanostructures, due to their restriction by fundamental principles to preferential geometries, but can be achieved through the application of external stimuli. In order to explore such an approach, elastomeric, nanoengineered, polymer photonic crystal structures have been fabricated on a large scale, through a method of shear induced self-assembly of 200nm monodisperse, polymer spheres with a core-shell structure. Determination of the assembly geometry through light diffraction experiments reveals a highly symmetric structure of close-packed, core-shell particles, with its orientation governed by the directionality imposed by the fabrication procedure. In these tuneable photonic crystals, application of external strain at directions of different crystallographic symmetry, accompanied by synchronised optomechanical measurements, reveals strong anisotropic optomechanical properties. It is shown that mechanical properties are primarily dominated by the viscoelastic nature of the shell material, while the strain-induced symmetry breaking reveals previously forbidden resonant peaks. Experiments involving uniaxial extension at principal and non-principal directions verify the underlying symmetry of the crystal lattice and consistently reproduce the anisotropic optical properties, providing information regarding the dual microstructure that controls the optomechanical response of these systems. Simulations based on a model of close-packed hard spheres predict the appearance of secondary resonances and suggest a structural transition from an fcc to a lower symmetry monoclinic crystal lattice. A more elaborate micromechanical model does not verify this transition but predicts the strain dependence of dominant spectroscopic peaks. Experiments involving different crosslinking densities reveal individual contributions from the elements comprising the material's dual microstructure. The inherently low refractive index contrast featured by these polymeric systems forbids the development of full photonic band gaps but symmetry based principles can be applicable to other structures with similar topological restrictions. Results provide a possible route for fabrication of active deformable nanostructures and aid our understanding of self-assembly in these complex systems, leading to optimised large-scale fabrication.

It is believed that the interfacial structure can significantly affect the magnetic properties of magnetic multilayer thin films. X-ray scattering techniques provide a powerful method with which to study the bulk and interface morphology in these systems, and are therefore crucial in developing an understanding of the dominant factors influencing the magnitude of the perpendicular magnetic anisotropy (PMA).The inter-relation between magnetic and structural properties of a series of magnetic multilayer thin films is investigated. Magnetometry measurements on a series of Fe/Au multilayers showed that some samples exhibited in-plane magnetization. X-ray data and simulations showed that the interface roughness was high in these samples. However, the formation and propagation of uncorrelated roughness followed a systematic trend for surface growth. On the other hand, x-ray data and simulations for a single 100-bilayer sample showed that the interfaces are much better defined with significantly lower roughness. This was the only sample to show perpendicular anisotropy supposing the suggestion that the absence of PMA in all other samples is associated with high interface roughness. Magnetometry measurements of the PMA in Co/Pt multilayers show an increase in effective anisotropy at about 15 bilayers. X-ray data showed that the roughness of the interfaces was correlated in all samples and that the interfaces were sharp with no detectable interdiffusion. No systematic trend in roughness or crystallographic texture is detected with increasing bilayer repeat X-ray measurements on four series of Co/Pd multilayers show interface roughness independent of bilayer repeat number. For Co/Pt, the in-plane correlation length was independent of bilayer number while for Co/Pd and Fe/Au it increased. A saturation of the in-plane correlation length for the Au/Fe system where island growth of the Au occurs was observed. The out-of-plane correlation length increased with bilayer repeat for Co/Pt and Co/Pd. The interfaces in samples with higher PMA had a fractal parameter close to unity.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 83-96).
Optical anisotropy measurement is essential for material characterization and biological imaging. Many optical anisotropy imaging techniques have been developed, such as fluorescence polarization microscopy(FPM), liquid crystal based polarization microscopy (LC Polscope), polarization state optical coherence tomography (ps OCT), and polarization Raman spectroscopy. Quantitative phase microscopy (QPM) is another important modality of optical imaging. By implementing interferometry, we can quantitatively map the complex field distribution of the sample with high imaging speed and high throughput. Furthermore, we can use QPM system to reconstruct the three-dimensional structure of the sample by solving inverse scattering problem. My major work is developing high speed, high sensitivity quantitative polarization imaging system. Firstly, I proposed a polarization microscope system for directly imaging sample's retardance distribution by inserting two quarter wave plates between the two crossed linear polarizers in conventional polarization microscopy, before and after the sample. This imaging concept is validated with experimental data of wave plates and liquid crystal retarders. Secondly, I proposed quantitative polarization interference microscopy (QPIM) through designing a compact polarization-resolved interference microscopy system that captures interferograms bearing sample's linear birefringence information. To extract the retardance and the orientation angle maps from a single-shot measurement, we have further developed a mathematical model for QPIM. Our QPIM system has been validated by measuring a calibrated quarterwave plate, whose fast-axis orientation angle and retardance were determined with great accuracies. We have demonstrated this application by capturing transient retardance changes in a custom-designed parallel-aligned nematic liquid crystal-based device. Finally, I proposed an imaging concept for three-dimensionally reconstruct the polarization distribution for the sample by solving anisotropic Helmholtz equation. All of these three novel imaging techniques have the potential to be applied to the study of sickle cell disease polymerization dynamics, acrosome process of crab sperms, label-free visualization of neuron action potential and semiconductor inspection in the future.
by Baoliang Ge.
S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2005.
Page 230 blank.
Includes bibliographical references (p. 181-190).
Real-time polymerase chain reaction (PCR) is the gold-standard for quantitation in both mutation and gene expression analyses. Already this technique has found valuable clinical application in disease diagnosis and progression evaluation. As the number of known gene-disease correlations continues to rise, there will be increased demand for higher throughput and decreased cost for these analyses. Present real-time PCR measurement is based upon the fluorescent intensity of either intercalating dyes or oligonucleotide probes. Intercalating dye methods suffer from a lack of binding specificity, while probe methods are expensive and require increased assay optimization. In this thesis, a new method is presented for monitoring real-time PCR that utilizes the fluorescent anisotropy (FA) of labeled primers. FA, when measured at constant temperature, is indicative of the molecular mass to which the fluorophore is attached. Specificity is improved with the FA method over the use of intercalating dyes since the selective binding of primers is required for signal change. Assay complexity and cost are reduced compared to fluorogenic probe methods since the probes are eliminated. The design of a prototype instrument, which successfully implements this new method, is presented. Instrument and assay performance are compared to intercalating dye assays run in commercially available instrumentation. Theoretical limits on performance are also presented and compared to experimental results. Excellent repeatability and linearity are observed with respect to these benchmarks. This new method, having both high specificity and low optimization complexity, is expected to be particularly applicable to the demanding robustness requirements of nano-scale PCR.
by Bryan Lee Crane.
Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995.
Includes bibliographical references (p. 171-180).
by James B. Gaherty.
Ph.D.

It has now become comparatively common in shear-wave exploration to use the measurements of the polarization direction of the leading shear-wave and the travel-time delay between this and the slow split shear-wave, to give a direct indication of the orientation and strength of anisotropy. It is important to investigate and develop suitable techniques to extract these parameters from seismic data. To investigate the anisotropic properties of shear-wave propagating in anisotropic medium, I first develop a vector convolutional model for a shear-wave propagating through an anisotropic medium in Chapter 2. Based on this unified model, four algebraic processing techniques have been developed to estimate the shear-wave polarisation and time-delay for near-offset VSPs. The techniques include both cumulative and interval techniques for either dual/multi or single sources data. These techniques are algebraic exact solutions, faster than any possible numerical equivalent, and robust to noise. Uncertainties in the ground coupling of shear sources, alignment of the source polarization, the transfer function between the geophone and the formation, and the orientation of the receiver tool in the borehole, may be amongst the principal causes of inaccuracy when estimating shear-wave splitting from multicomponent near-offset VSP data. In Chapter 3, investigations using synthetic seismograms computed for a zero-offset VSP in an anisotropic half-space, address the frequency independent part of this problem to determine how much uncertainty can be tolerated for simple amplitude and orientation variations in the source and geophone components, while still maintaining a shear-wave polarization estimated for the faster split shear-wave accurate to within 5°.

The magnetic properties of the (FexNi1-x)2B family of materials are explored using DFT calculations utilizing the FPLO and SPR-KKR code packages. It is found that a uniaxial magnetocrystalline anisotropy exists at around x = 0.8 with a magnetocrystalline anisotropy energy at around 0.3 MJ/m^3. A calculation of the lattice constant for these materials were attempted but failed due to the emergence of local minima and the calculations of magnetic properties were instead done using lattice parameters interpolated between known experimental values.