Dissertations / Theses on the topic 'Magnetic characterisation'
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Crawford, Mhairi. "Characterisation of selected magnetic elements." Thesis, University of Glasgow, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410830.
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Bennington-Gray, Suzanne. "Magnetic characterisation of nanostructured magnetic systems using SQUID magnetometry." Thesis, Queen's University Belfast, 2019. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.766289.
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Jordan, Simon Mark. "The MOKE characterisation of magnetic multilayers." Thesis, University of York, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284135.
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Dova, Paraskevi. "Magnetic characterisation of longitudinal thin film media." Thesis, Bangor University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267451.
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Green, L. A. W. "Synthesis and characterisation of FePt magnetic nanoparticles." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1427377/.
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Magnetic nanoparticles (MNPs) are intensively researched due to their high potential in biomedicine, catalysis and high density information storage. FePt NPs are a potential alternative magnetic material to commonly used magnetite NPs for biomedical applications and the synthesis of FePt NPs is an active area of research. The purpose of this thesis has been to develop wet chemical synthetic methods to tune and improve the properties of FePt magnetic nanoparticles. The morphology of magnetic nanoparticles affects the way they interact with each other, and with their surroundings. Changes in shape and composition with varying synthetic conditions can also give clues to the mechanism of formation. Changes in volume, solvent and the nature of the stabiliser have been shown to yield varying morphology in the FePt system. Multicore FePt nanoparticles up to 44 nm in diameter and composed of Pt rich FePt nanocrystals within an iron rich FePt matrix not previously seen in the literature are presented here. Magnetic properties of multicore nanoparticles are size dependent; in dioctyl ether and dibenzyl ether and with decreasing amount of oleic acid, saturation magnetisation and blocking temperature increase with size. The results indicate that coordination of Fe and Pt intermediates with oleic acid and oleylamine respectively hinders deposition of each respective metal in the growth of discrete and multicore nanoparticles. L-glutathione and albumin immediately transferred 20 nm multicore nanoparticles into water and show that large FePt nanoparticles may be stable under physiological conditions following stability tests. The use of an autoclave is shown to increase the Fe content, crystallinity and subsequent magnetic properties of FePt pseudo cube nanoparticles compared to those synthesised under atmospheric pressure. Decreasing amount of oleic acid is also shown to increase the iron content and can lead to elongated FePt nanoparticles under normal pressure. Infra-red studies indicate mono and bi dentate coordination with oleic acid, however shifts of spectra show that the strength of the bi-dentate interactions weaken with increasing oleic acid amount.
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Strømøy, Emilie Kolstø. "Characterisation of the Magnetic Mineralogy, Properties and Magnetic Anomaly Responses of two Garnetiferous Peridotite Bodies in the WGR, Otrøya : Ground Magnetic Surveying, Sampling, Magnetic Characterisation and 2D Modelling." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for geologi og bergteknikk, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-25973.
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Information on magnetisation of earth’s crust comes from the study of magnetic anomalies measured at various elevations using ground, airborne and satellite data, as well as studies of deep-seated rocks exposed at the surface. In the Western Gneiss Region (WGR), western Norway, two well exposed bodies of garnetiferous peridotites lay on the island Otrøya. The WGR is a 25.000 km2 window of Proterozoic Baltica continental crust exposed in the Scandinavian Caledonides, and is one of the largest exposures of deeply subducted rocks on earth. The two bodies exposed on Otrøya contain evidence of the early stability of Archean tectonometamorphic megacrystic mineral assemblages that include high P/T enstatites and majoritic garnet (presently exsolved into Proterozoic and Scandian tectonometamorphic assemblages) (Van Roermund, 2008). The magnetic properties and anomaly responses of these peridotites and their immediate enclosing bedrocks were investigated by sampling orientated blocks, conducting magnetic measurements in field and at lab, as well as conducting a ground magnetic survey. This provides us with information on the magnetic properties of deeply subducted mantle fragments, and adds to the knowledge of what is magnetic in the lower crust and lithospheric mantle.The study of the two peridotite bodies at Otrøya displays several morphologies of magnetite, mostly displaying as discrete forms within seams and cracks, but also as well-defined rims around chromites. The remanent intensity and susceptibility of the rocks are low, however the remanent intensity is somewhat varying. The directions of remanent magnetisation within measured specimens are both negative and positive with positive directions commonly displaying the same direction as the ambient field as well as commonly carrying weaker intensities than the negative. All of the above could be indicative of several stages of magnetite creation, and/or several events of recording of natural remanent magnetisation. The immediate constricting bedrocks displayed substantially higher remanent and induced intensities. Within the measured specimens both intensities were varying with the remanence displaying the largest variance in addition to showing both positive and negative directions. This was reflected in the anomaly map created from the ground magnetic survey due to anomalies, both high and low, displaying within these bedrocks. However, the peridotites correlate with wide anomaly lows. With 2D modelling a magnetic profile over the area was investigated with susceptibility and geometry of the bodies as input parameters. It became evident that the susceptibility contrast of the peridotites and the constricting bedrocks, as well as their geometries, could create anomaly lows as displayed in the anomaly map. However, it could not explain the most negative anomaly responses – an indication on remanence being of importance.
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Moon, James Charles Connor. "Myocardial tissue characterisation using gadolinium cardiovascular magnetic resonance." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429178.
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Thomson, Thomas. "The magnetic characterisation of magneto-optic thin films." Thesis, Bangor University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385760.
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Flynn, David. "The manufacture and characterisation of microscale magnetic components." Thesis, Heriot-Watt University, 2007. http://hdl.handle.net/10399/58.
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Watts, Ian Donald. "Synthesis and characterisation of layered magnetic oxalato-salts." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394502.
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O'Reilly, S. "Magnetic characterisation of thin film NiFe/FeMn multilayers." Thesis, Queen's University Belfast, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.680242.
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Exchange biased thin films form the basis of many high speed electronic devices such as hard disc drives, field sensors and microwave communication devices. It is important to have a detailed understanding of the electromagnetic properties of such thin films in order to determine their suitability for specific applications. As the operating speeds of electronic devices increase the necessary characterisation range expands into' the microwave region i.e. the gigahertz frequency range. One of the most important properties in investigating thin films for potential applications is permeability. The aim of this thesis was to characterise the magnetic properties and permeabilities of exchange biased thin films. Multilayers of the structure [Ni80Fe20 (x nm)/ Fe50Mn50 (y nm)]z were deposited using a sequential sputtering system where x is the thickness of the ferromagnetic layer, y is the thickness of the antiferromagnetic layer and z is the number of times the bilayer is repeated. The hysteresis loops of the multilayers were measured using a vibrating sample magnetometer to investigate their multiple reversal stages. A two port coplanar waveguide permeameter was built to measure the permeability spectrum of the multilayers at various applied magnetic fields. The multilayer hysteresis loops exhibited a stepped structure corresponding to multiple reversals. Each reversal stage was assigned to a particular NiFe layer based on the magnetisation ratios, exchange bias and NiFe layer thickness. NiFe layers of the same thickness with the same relative position within a stack appeared to have the same value of exchange bias. The resonant permeabilities of the multilayers shifted towards higher frequencies as the applied field was increased, in agreement with ferromagnetic resonance theory. This indicated that the resonances originated from the multilayers and were not due to systematic errors or artefacts. Trends within the sample range were observed but further work is needed to confirm these observations.
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Haberle, Veronika. "Automatic Characterisation of Magnetic Indices with Artificial Intelligence." Thesis, Luleå tekniska universitet, Institutionen för system- och rymdteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-79821.
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The complex interactions between the Sun and Earth are referred to as Space Weather. Key parameters include magnetic indices which quantitatively describe geomagnetic activity by determining a baseline that removes the background magnetic field and allows quantification of the remaining activity during geomagnetic events. However, most used indices have a low temporal resolution and rely on a sparse and frozen network of ground magnetic observatories. This thesis introduces a novel way of determining the baseline for future high temporal and spatial resolution magnetic indices. Firstly, the main phenomena and effects of Space Weather are outlined, followed by a review of currently used magnetic indices and their derivation. The computation of a novel baseline introduced in this work relies on basic statistical methods which are applied on magnetic data from a dense and flexible network of ground observatories for the period 1991-2016. The focus is on the investigation of geomagnetic quiet periods for which average annual activity at each observatory is determined. A global latitudinal normalisation function with dependency on solar activity for quiet periods is found. The analysis of the newly derived baseline shows that it provides the temporal, spatial and amplitudinal resolution needed to characterise geomagnetic disturbances adequately. The residual signal has the capability of being used as the basis for further quiet period studies. A first attempt of new indices based on the introduced derivation shows a good agreement with already existing high temporal and spatial resolution magnetic indices. Future indices derived with this baseline lay a favourable fundament for the application of articial intelligence methods.
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Ngo, Duc-The. "Lorentz TEM characterisation of magnetic and physical structure of nanostructure magnetic thin films." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/1841/.
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The work presented in this thesis is an investigation which aims to quantitatively characterise the physical microstructure, magnetic structure and micromagnetic behaviour of nanostructured thin films for magnetic recording and spintronics application. The nanostructures in the present work involve continuous and patterned thin films. Chapters 1, 2, and 3 present the overview backgrounds directly relevant to the work. Chapter 4 focuses on vortex structure in magnetic nanodots. The results confirm that the behaviour of the vortex can be modified by changing the edge geometry of the dots. It is demonstrated a practical method to determine the out-of-plane component of the vortex core with high accuracy and speed. Additionally in-plane curling magnetisation of the vortex is also mapped by reconstructing the electron phase using the transport-of-intensity equation. However this method is susceptible to spurious low spatial frequency and this aspect is explored to show limitations of the method. Chapter 5 deals with the characterisation of magnetic structure in nanoconstrictions intended to trap domain walls (DWs) in the nanoconstrictions. A structure was fabricated with two micron-sized pads as the sources for creation of DWs. A DW can be driven to be pinned at the nanoconstriction resulting in a change of magnetoresistance due to the contribution of the DW to the resistance of the device. The magnetisation configuration around the constriction is studied during the reversal process. It is apparent that that understanding the magnetisation rotation around the constriction and into the pads is the key to the magnetoresistance measurements and the DW resistance is part of this process. Evidences of DW compression at the nanoconstriction were noted. In Chapter 6 the investigation of the physical structure and micromagnetism of CoIr film is described. A hexagonal crystal structure with a [0001] texture normal to the film plane was characterised. Weak anisotropy is observed in the film denoted by a complex reversal on the hard axis due to incoherent rotation of magnetic moments. The film exhibits typical soft magnetic behaviour it merits compared to other soft materials are discussed in light of the results obtained here. Chapter 7 concludes with a discussion of the outcomes of the present thesis. Additionally possible directions for future research in topics discussed in this thesis are proposed.
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Bestmann, Sven. "Physiological characterisation of transcranial magnetic stimulation (TMS) using functional magnetic resonance imaging (fMRI)." Thesis, University College London (University of London), 2004. http://discovery.ucl.ac.uk/1446494/.
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Despite its widespread use, a striking lack of knowledge exists regarding the mechanism of action of transcranial magnetic stimulation (TMS). This thesis describes the physiological characterisation of repetitive TMS (rTMS) to the motor system by means of functional magnetic resonance imaging (fMRI). A detailed analysis of imaging artefacts arising from the simultaneous application of TMS-fMRI was conducted and subsequently, strategies were presented for unperturbed TMS-fMRI. Physiological responses during subthreshold high-frequency rTMS of the primary sensorimotor cortex (Ml/Sl) were visualised within distinct cortical motor regions, comprising PMd, SMA, and contralateral Ml/Sl, while no significant responses were evidenced in the area of stimulation. Repetitive TMS during or before motor behaviour illustrated the context- dependence of rTMS-induced activity changes. The first demonstration of TMS-fMRI at 3 Tesla provided evidence that subthreshold rTMS can activate distinct networks including subcortical motor regions. The subthreshold nature of rTMS was confirmed by simultaneous electromyographic recordings from the target muscle. Stimulation of the dorsal premotor cortex provided evidence that rTMS- evoked local activity changes depend on the input function. The capability of TMS to target distinct networks in the human brain was confirmed. TMS targets a set of cortical and subcortical structures. Local responses may not invariably be elicited, indicating that low levels of synaptic activity, as occurring at low-intensity stimulation, do not necessarily evoke corresponding changes in cortical haemodynamics. It is concluded that combined TMS-fMRI offers a means to assess the mechanism of action of TMS at high spatial and temporal resolution.
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Gallagher, Andrew Patrick. "Theoretical characterisation of magnetic force microscope tip stray fields." Thesis, University of Glasgow, 1999. http://theses.gla.ac.uk/4482/.
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Mateen, Noor E. "Studies in the characterisation of magnetic force microscope probe." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/15745/.
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A magnetically coated tip is a fundamental part of the MFM instrument. These tips’ are bought commercially and/or individually manufactured in various shapes and sizes and with various material coatings and thicknesses. The sheer extent of possible combinations and the lack of a truly standard and reproducible tip is perhaps, one of the major contributing factors that prevent a complete understanding of the instrument and its characteristics and a full comprehension of how the tip interacts with a sample. While the MFM instrument is capable of generating qualitative images, a full metrological characterisation of its magnetic probe is one of the major concerns. In this research project, the practical implications of a diagnostic sample in the form of a simple geometrical wire structure have been demonstrated. With the aid of mathematical modelling, the understanding of the interaction between the tip and the sample is improved. In addition, this research explored the effects of systematic reduction of a tip’s magnetic volume and its resulting images. It highlighted the significance of magnetic volume in image capture and provided a comprehensive quantitative insight in image type, reproducibility and quality. This project thus represents a further step towards the characterisation of MFM probes, which has the potential for ultimately benefitting the nano-magneto-electronic and data storage industry.
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Hole, Christopher. "Pulsed magnetic field characterisation of technological high temperature superconductors." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294363.
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Sado, D. M. "Characterisation of the cardiac interstitium using cardiovascular magnetic resonance." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1420202/.
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In clinical cardiology, different imaging technologies can be used to assess cardiac anatomy, ventricular function and focal myocardial disease. Cardiovascular magnetic resonance (CMR) using late gadolinium enhancement (LGE) is the gold standard non-invasive method for focal myocardial tissue characterisation. However it has limitations, including not allowing quantification of the extracellular volume (ECV) or assessment of diffuse processes. In this thesis, these shortcomings were addressed using novel CMR T1 based methodologies. In early work, the ECV was assessed in health and a variety of cardiac diseases. It was found to be elevated in dilated and hypertrophic cardiomyopathy and aortic stenosis – diseases where diffuse fibrosis is known to occur. There was a more marked ECV elevation in cardiac AL amyloidosis. Further work assessed a potential role for pre contrast T1 in Anderson Fabry disease, finding that it detects disease at an earlier stage than any other imaging marker and is diagnostic of this disease in patients with left ventricular hypertrophy. In patients with iron overload, the T1 was found to strongly correlate with the previous non-invasive gold standard test of CMR T2*. However the T1 appeared to be more sensitive for the detection of earlier disease. Lastly, pilot technical development work evaluated new and faster methods for ECV and T1 assessment and suggested a potential role for this technique in other body organs. The above results were particularly notable in Anderson Fabry disease, iron overload and cardiac amyloidosis. In the case of Anderson Fabry disease and cardiac amyloidosis, sphingolipid and amyloid deposition respectively cannot be measured using current non-invasive clinical techniques. In conclusion, this work has pioneered the use of novel tissue characterisation techniques which have potential roles in earlier diagnosis, pathophysiological insights, prognostication and therapy monitoring in cardiac disease. This will ultimately provide benefit to patients with cardiac disease.
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Martin, P. J. P. "Electrical, magnetic and optical characterisation of donor-acceptor systems." Thesis, Cranfield University, 1991. http://dspace.lib.cranfield.ac.uk/handle/1826/10404.
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Three novel donor-acceptor systems have been characterised through their spectroscopic properties, magnetic susceptibility, conductivity and second harmonic generation. The magnetic properties of (H2DPE)xx+(DPE)^ x(TCNQ)gX and (H2DPA)xx+(DPA) 1 x(TCNQ)gX' where DPE = 1,2-di(4-pyridyl)ethylene, DPA = 1,2-di(4-pyridyl)ethane, TCNQ = tetracyanoquinodimethane and H2 signifies proton diquaternisation, have been found to depend upon the stoichiometry: For x > \ the magnetic susceptibility decreases with increasing x whereas for x ~ \ it is anomolously large, being ferromagnetically enhanced above the Curie Law value. A possible model involving spin dilution is proposed and its predictions are compared with the experimental results. Langmuir-Blodgett (LB) films of the long-chained analogues of the materials, (C^g)2DPE (TCNQ) 2 and (Cig^DPE^TCNQ)^" where (C16) 2 = bis(hexadecyl) were deposited and characterised. The conductivities of the LB films of the mixed valence system were found to be ~ 1000 times greater than those of the system lacking TCNQ^ molecules. Multiple layer LB films of trans-4-[4- (dimethylamino)styryl]-1- octadecylpyridinium iodide and trans-4-[4-(dimethylamino)styryl]-1- octadecylquinolinium iodide interleaved with 4,4'-dioctadecyl-3,5,3',5' -tetramethyldipyrrylmethene hydrobromide were deposited. The materials form an interlocking bilayer structure which renders their LB films exceptionally well-organised. The films’ second harmonic generation was investigated and one film was found to give the largest second harmonic signal yet seen from an LB structure.
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Crisan, Alina Daniela. "Synthesis and characterisation of nanostructured magnetic FePt-based alloys." Le Mans, 2009. http://cyberdoc.univ-lemans.fr/theses/2009/2009LEMA1002.pdf.
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Ce travail de thèse est une contribution à l'étude et au développement d'aimants permanents de type spring magnet. Ces matériaux sont constitués de grains magnétiques durs dispersés dans une matrice magnétique douce. Le couplage des grains magnétiques durs à travers la matrice douce permet d'augmenter significativement la coercivité et l'aimantation rémanente et par conséquent la valeur du produit (BH)max, facteur de qualité ou de mérite des aimants permanents. L'objectif de ce travail est de réaliser ce type d'aimant permanent à partir d'alliages nano cristallisés à base de FePt. Pour cela, la méthode de trempe ultra-rapide sur roue a été utilisée pour produire un précurseur métastable à base de FePtNbB, suivi d'un traitement de dévitrification partielle permettant d'obtenir des grains nano cristallisées de phase dure, de symétrie quadratique à face centrée (phase L10) avec une forte anisotropie uniaxiale (7MJ/m3), disperses dans une matrice résiduelle magnétiquement douce de composition Fe(PtNb). Les mesures par calorimétrie différentielle et diffraction in situ du rayonnement synchrotron en température et sous pression ont permis d'optimiser les paramètres de cristallisation. Les propriétés structurales des échantillons ont été étudiées par diffraction de rayons X, microscopie électronique à transmission, analyse dispersive en énergie X et spectrométrie Mössbauer du 57 Fe alors que les caractéristiques magnétiques ont été mesurées avec des magnétomètres SQUID et VSM. Les performances obtenues à 300K montrent que ces échantillons sont de bons candidats comme aimants permanents: coercivité de 850kA/m, champs rémanent de 0. 7T et facteur de mérite (BH)max de 69kJ/m3The present work is a contribution to the study and development of a new class of permanent magnets based on the exchange spring effect. These materials are made of hard magnetic grains dispersed in a soft magnetic matrix. The coupling of hard magnetic grains through the soft matrix allows a significant improvement of the coercivity and remanence, and by consequence, an improved maximum energy product may be obtained in these alloys. The aim of this work is to synthesize this type of magnetic material starting with nanocrystalline FePt-based alloys. The rapid solidification by melt spinning method has been used to cast metastable precursor alloys with composition FePtNbB. After annealing, a microstructure made of hard magnetic nanograins of face-centred-tetragonal symmetry (L10 phase) with high uniaxial magnetic anisotropy (7 MJ/m3), dispersed in a residual soft magnetic phase with composition FePt(NbB) has been obtained. The differential scanning calorimetry studies as well as in situ X-ray diffraction of synchrotron radiation in temperature and applied pressure have allowed the optimization of parameters of crystallization of the metastable precursor. The structural parameters of the samples were investigated using X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy and 57Fe Mössbauer spectrometry while the magnetic parameters were determined using VSM and SQUID magnetometry. The performances obtained at 300K, coercivity 850kA/m, remanence 0. 7 T and (BH)max 69 kJ/m3 show that these alloys are good candidates as permanent magnets
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Cohen, Neil Stephen. "Preparation and characterisation of magnetoresistive materials." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300558.
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Beydoun, Donia Chemical Engineering & Industrial Chemistry UNSW. "Development of a novel magnetic photocatalyst : preparation, characterisation and implication for organic degradation in aqueous systems." Awarded by:University of New South Wales. Chemical Engineering and Industrial Chemistry, 2000. http://handle.unsw.edu.au/1959.4/20451.
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Magnetic photocatalysts were synthesised by coating a magnetic core with a layer of photoactive titanium dioxide. This magnetic photocatalyst is for use in slurry-type reactors in which the catalyst can be easily recovered by the application of an external magnetic field. The first attempt at producing this magnetic photocatalyst involved the direct deposition of titanium dioxide onto the surface of magnetic iron oxide particles. The photoactivity of these Fe3O4/TiO2 was lower than that of single-phase TiO2 and was found to decrease with an increase in the heat treatment. These observations were explained in terms of an unfavourable heterojunction between the titanium dioxide and the iron oxide core. Fe ion diffusion from the iron oxide core into the titanium dioxide matrix upon heat treatment, leading to a highly doped TiO2 lattice, was also contributing to the observed low activities of these samples. These Fe3O4/TiO2 particles were found to be unstable, with photodissolution of the iron oxide phase being encountered. This photodissolution was dependent on the heat treatment applied, the greater the extent of the heat treatment, the lower the incidence of photodissolution. This was explained in terms of the stability of the iron oxide phases present, as well as the lower photoactivity of the titanium dioxide matrix. In fact, the observed photodissolution was found to be induced-photodissolution. That is, the photogenerated electrons in the titanium dioxide phase were being injected into the lower lying conduction band of the iron oxide core, leading to its reduction and then dissolution. Thus, the approach of directly depositing TiO2 onto the surface of a magnetic iron oxide core proved ineffective in producing a stable magnetic photocatalyst. The introduction of an intermediate passive SiO2 layer between the titanium dioxide phase and the iron oxide phase inhibited the direct electrical contact and hence prevented the photodissolution of the iron oxide phase. Improvements in the photoactivity were seen to be due to the inhibition of both the electronic and chemical interactions between the iron oxide and titanium dioxide phases. Preliminary optimisation experiments revealed that a thin SiO2 layer is sufficient for inhibiting the photodissolution. The thickness of the TiO2 coating was found not to have a significant effect on the photocatalytic performance of the coated particles. Finally, heat treating for 20 minutes at 450??C was sufficient for converting the titanium dioxide into a photoactive phase, longer heating times had no beneficial effect on the photoactivity.
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Wilson, Stephen Ronald. "The characterisation of colloids and macromolecules by linear magnetic birefringence." Thesis, London South Bank University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245149.
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Thomas, Andy. "Preparation and characterisation of magnetic single and double barrier junctions." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=970062214.
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Bellini, Eleonora. "Characterisation of magnetic nanostructures for spintronic applications by electron microscopy." Thesis, University of Glasgow, 2011. http://theses.gla.ac.uk/3011/.
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The work presented in this PhD thesis concerns the characterisation of the physical structure, composition and domain structure of advanced magnetic materials by electron microscopy within the FP6 European Research Training Network "Spinswitch". In particular the investigations concerned MgO/CoFeB/MgO multilayers to be employed in magnetic sensors (this work was done in collaboration with INESC-MN Lisbon-Portugal); Ni80Fe20/Cu electrodeposited nanowires to be employed as spin transfer torque devices (this work was done in collaboration with NIRDTP Iasi-Romania and University of Salamanca); multilayers with perpendicular anisotropy which represent potential candidates to be employed in the next generation of MRAMs (this work was done in collaboration with Spintec-CEA-Grenoble). Chapter 1 will provide an overview of the physics behind the topics treated during this work and a description of the general motivations of the research carried out. Chapter 2 will provide an overview of all the experimental techniques employed for the fabrication and characterisation of the samples investigated for this research. Chapter 3 aims to present an investigation using conventional transmission electron microscopy (CTEM) and Lorentz microscopy (LTEM) to characterise respectively the physical microstructure and the domain structure of the CoFeB free layer, embedded in a multilayer composed by SiN/MgO(50)/CoFeB(t)/MgO(15), with t from 30 Å down to 14 Å. We carried out first the investigation of the physical structure performed by selected area diffraction and bright field imaging of planar samples and physically the plan view sections show the structure of the films appears similar. The magnetization reversal behaviour observed during Lorentz TEM experiments are found to vary considerably with the CoFeB thickness, with both domain wall formation and magnetisation rotation seen. In the thicker film the behaviour was characteristic of a typical soft magnetic material with uniaxial anisotropy. However the magnetic reversal of the thinner film was more complex. A particular characteristic of the 14 Å CoFeB layer is the variation of domain wall angle seen when varying the orientation of the applied field This wall asymmetry suggests the presence of a unidirectional anisotropic energy term. To assist in the interpretation of these experimental results a modified Stoner–Wohlfarth model has been constructed and calculations have been carried out by using a MATLAB code. The purpose of the project presented in Chapter 4 was the advanced characterisation of multilayered electrodeposited NiFe/Cu nanowires grown in alumina and polycarbonate templates. In particular the objective was the characterisation of the structure and local chemistry of the nanowires by TEM and the classification of nanowire switching deduced by Lorentz microscopy experiments, which are challenging for this specific material system. In order to perform TEM studies on single nanowires, they should be extracted from their template. The chemical etching used to remove the nanowires from the template in addition to issues related to the deposition of Cu, led to nanowires with edge and compositional irregularities, detrimental for their magnetic properties. Indeed, we were not able to classify the nanowire switching and investigate domain walls forming during the reversal process, but we could only observe a change in the magnetising state. A lot of the work described in this chapter deals with the difficulties associated with imaging these challenging nanowires. Issues were discovered that may have resulted from deposition and/or etching for TEM preparation, therefore we do rely heavily on simulations and calculations. The research presented in Chapter 5 will describe the investigation of the reorientation process of the easy axis for two different multilayer systems magnetised out of plane, and the evolution of their domain structure for increasing temperature, and trying to understand the role of the insertion of a Co/Pt/Ni/Pt multilayer from a microscopic point of view. The two multilayers represent the free layer of a perpendicular MTJ (pMTJ) and this study represents a state of development of materials for pMTJs. Experiments were performed by MOKE magnetometry in polar configuration and Lorentz Microscopy in Fresnel mode. Materials were prepared in Spintec-CEA, Grenoble (France) where the MOKE experiments were also carried out, and Lorentz Microscopy experiments were performed in Glasgow. For the first multilayer (with Co/Pt/Ni/Pt) we found that for lower temperatures (25°C - 220°C) the specimen appears to have a strong perpendicular anisotropy. We observed a small scale random domain structure that we can ascribe to perpendicularly magnetised domains. For higher temperatures (220°C - 300°C) we found a behaviour typical of a soft magnetic material magnetised in plane with low anisotropy and high susceptibility. For the second multilayer (without Co/Pt/Ni/Pt), for instrumental reasons, we were not able to investigation of the magnetic behaviour of the specimen for temperatures above 110°C. The magnetisation is out of plane for all the temperatures investigated. The sample develops a different domain structure when the sample is heated below 100°C or above 100°C. In the first case isotropic serpentine domain structure is visible, with a large periodicity, whereas in the second case, an anisotropic stripe domain structure is visible with a small periodicity.
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Al-Saadi, Ali. "Preparation and characterisation of encapsulation magnetic metal iron oxide nanoparticles." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:57bdcf38-9d45-48ab-a971-a2d60e2e4391.
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One of the most challenging goals in nanoparticle research is to develop successful protocols for the large-scale, simple and possibly low-cost preparation of morphologically pure nanoparticles with enhanced properties. The work presented in this thesis was focused on the synthesis, characterisation and testing of magnetic nanoparticles and their potential applications. There are a number of magnetic nano-materials prepared for specific applications such as metal oxide nanoparticles encapsulated with various porous materials including Fe₃O₄/Fe₂O₃ coated with soft bio-organic materials such as glycol chitosan and bovine serum albumin and hard materials such as silica (SiO₂) and zinc sulphide (ZnS). The preparation of these materials was achieved principally by bottom-up methods with different approaches including micro-emulsion, precipitation, electrostatic and thermolysis processes. The thesis also presents the uses of various analytical techniques for characterising different types of nano-materials including Attenuated Total Reflection Fourier Transformer Infrared Vibrational Spectroscopy (ATR-FTIR), Ultraviolet Visible- Near Infrared (UV-Vis-NIR) Spectroscopy, Zeta Potentiometric Surface Charge Analysis, Superconducting Quantum Interference Device (SQUID) and Vibration Sample Magnetometry (VSM) for magnetic analysis and powder X-Ray Diffraction (XRD) for crystallographic pattern analysis. There are many applications of magnetic nanoparticles, including nano-carriers for biological and catalytic reagents. The magnetic nanoparticles can facilitate separation in order to isolate the carriers from solution mixtures as compared to many inefficient and expensive classic methods, which include dialysis membrane, electrophoresis, ultracentrifugation, precipitation and column separation methods. There are six key chapters in this thesis: the first chapter introduces the up-to-date literature regarding magnetic nano-materials. The uses of magnetic nano-materials in drug binding and for protein separation are discussed in the second and third chapters. The fourth chapter presents the use of magnetic nanoparticle in conjunction with a photo-catalytic porous overlayer for the photo-catalytic reduction of organic molecules. The fifth chapter describes different analytical techniques used for the characterisation of nanoparticles and the underlying principles and the experimental details are also given. The sixth chapter summarises the results and provides an overview of the work in a wider context of future applications of magnetic nanoparticles.
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Robinson, Ian. "Synthesis, characterisation and functionalisation of magnetic nanoparticles for biomedical applications." Thesis, University of Liverpool, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.533928.
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Lu, Le Trong. "Water-dispersible magnetic nanoparticles for biomedical applications : synthesis and characterisation." Thesis, University of Liverpool, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.569653.
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Magnetic nanoparticles have attracted a great attention due to their diverse potential applications in biology and technology and a substantial number of synthetic methods have been developed to produce these materials. Chemical synthesis approaches have been a particular focus of the field, because of their ability to tune the size, shape and composition, as well as surface of the nanoparticles. To produce magnetic nanoparticles for biomedical applications, one of the primary requirements is to make nanoparticles that are dispersible and stable in aqueous medium under physiological conditions. The focus of this thesis has been the development of methods to synthesise magnetic nanoparticles of different compositions and shape that are dispersible and stable in water. Monodisperse water-dispersible magnetic Co nanoparticles were fabricated using a facile reduction method in water in the presence of hydrophilic polymers. The size and shape of the nanoparticles were both tunable by varying the conditions of synthesis. The size of the spherical nanoparticles would be tuned between 2-7.5 nm by changing the concentration of the polymer. The synthesis approach could also be used to produce nanorods of 15 x 36 nm. The spherical nanoparticles were superparamagnetic at room temperature and were stable in water and in electrolyte solutions of up to 0.23 mM NaCI. The preliminary use of the Co nanoparticles as a MRI contrast enhancer was tested and provided evidence that these materials have considerable potential in this application. Using a similar method, water-dispersible and colloidal stable CoPt nanoparticles were prepared. The effect of structure, functional group and combinations of stabilising ligands on the morphology of the nanoparticles was investigated. It was found that multiple-thiol functional groups play a critical role in the formation of hollow nanoparticles. The size of hollow nanoparticles could be tuned in the range of7-54 nm by changing the concentration and molecular weight of the ligands. The hollow nanoparticles were water-dispersible and superparamagnetic at room temperature. They were stable in wide range of pH from I to 12.5 and at electrolyte concentrations as high as 2 M NaCI. An experiment on tracking stem cells labelled with the CoPt hollow nanoparticles indicated that MRl can effectively detect low numbers of labelled cells due to the enhanced contrast provided by the nanoparticles. CoPt hollow nanoparticles may, thus, have potential applications in MRI. CoFe and cobalt ferrite nanoparticles were synthesised by thermal decomposition in organic solvent to take advantage of the superior control over monodispersity and morphology of the nanoparticles afforded by solvent based syntheses. In the case of CoFe nanoparticles, a layer of Pt was also deposited on the nanoparticles to make core/shell structures. Varying reaction conditions, such as reaction time, had an insignificant effect on monodispersity, size and shape of Co Fe nanoparticles. However, these parameters had a substantial impact on the cobalt ferrite nanoparticles. Cobalt ferrite nanoparticles with sizes in a broad range from 4 nm to over 30 nm and diverse shapes including spherical, cubic and star-like, were synthesised by changing surfactant concentration and reaction time. Ligand exchange using hydrophilic silane and/or polymer ligands were demonstrated to be efficacious on CoFe, CoFelPt and cobalt ferrite nanoparticles. After ligand exchange, the nanoparticles were reasonably stable in water. The work presented in this thesis demonstrates that chemical synthesis is an efficient route to the production of magnetic nanoparticles of diverse composition and shape and so magnetic properties. Moreover, these materials were found to be stable in aqueous solutions. However, it is clear that the application of such magnetic nanoparticles in biology and medicine will require substantial further effort in the development of ligand shells able to withstand the rigours of the biological environment. Given the success of chemical synthesis demonstrated in this thesis, the development of ligand shell systems is now a major challenge of the field.
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He, Taigang. "Magnetic resonance imaging relaxometry for myocardial tissue characterisation in thalassemia." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.521112.
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Challoner, Robin. "Applications of multinuclear magnetic resonance to the characterisation of zeolites." Thesis, Durham University, 1989. http://etheses.dur.ac.uk/6427/.
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The following research is primarily concerned with the characterisation of the novel, unidimensional, zeolite theta-1 by solid-state multinuclear magnetic resonance spectroscopy. Some study has also been made of the zeolites ZSM-5 and NaY. The high-silica form of as-synthesised theta-1 is studied by high-resolution (^13)C and (^29)Si MASNMR. The (^13)C spectra are interpreted as showing the presence of both neutral and protonated diethylamine template molecules. These observations are discussed in terms of the possible presence of acid sites and their spatial distribution. The (^29)Si NMR results are consistent with the template molecules occupying the 10-T channels only. The (^29)Si spin-lattice relaxation mechanism is investigated under a variety of conditions. Changes in the (^29)Si NMR spectra on calcinations indicate the possibility of a minor framework rearrangement.Theta-1 synthesised using a diethanolamine template is also investigated. The template distribution is examined, and evidence for structural modification by the presence of the template is presented. The nature of the non-framework aluminium species produced on hydrothermal dealumination and the broad linewidths observed for such species in (^27) A1 NMR are also investigated. The signal response to the application of a single pulse of finite duration to a system of I=(^3)/2 nuclei is used to illustrate the differences between selective and non-selective excitation of the central transition, and the requirements for quantitivity. A series of model compounds is investigated by quadrupole nutation NMR, and more complex zeolite systems containing quadrupolar nuclei are investigated by a variety of techniques.
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Ibrahim, Rafat Mohamed. "Growth and characterisation of some magnetic oxides for spintronic applications." Thesis, University of Sheffield, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425578.
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Chen, Shu. "FePt magnetic nanoparticles : syntheses, functionalisation and characterisation for biomedical applications." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2151.
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Iron platinum (FePt) has attracted growing interest because of its high Curie temperature, magneto-crystalline anisotropy and chemical stability. Nanoparticles (NPs) made of this alloy are promising candidates for a wide range of biomedical applications including magnetic separation, magnetic targeted drug delivery, hyperthermia for cancer therapy and also as magnetic resonance imaging (MRI) contrast agents. This thesis presents the synthesis, functionalization and characterization of FePt NPs along with a toxicity study and an investigation into their application as MRI contrast agents. Regarding their synthesis, different approaches have been explored including the co-reduction of Fe and Pt precursors in an aqueous media, the thermal decomposition in a conventional high-boiling solvent such as benzyl ether, and in low-melting organic salts (ionic liquids). The data revealed an inhomogeneous composition distribution of Fe and Pt between particles obtained in aqueous media, due to the iron salts hydrolysis, and a mismatch in the co-reduction kinetic of the two metal precursors. While the iron content in the NPs could be increased by using more hydrolytically stable iron precursors or stronger reducing agents, there are remaining limiting parameters which prevent further Fe content increase in NPs. In contrast, by excluding the water from the reaction system and using a Fe²⁻ iron precursor, homogenous 1:1 Fe to Pt ratio NPs can be obtained through a modified thermal decomposition pathway in benzyl ether. Based on the study of synthesis in this conventional chemical, the potential of ionic liquids (ILs) to be used as novel solvents for FePt NPs synthesis was further explored. It was then demonstrated that ionic liquids (ILs) can not only be used as a solvent for synthesis of FePt NPs, but also can provide an exciting alternative pathway to direct synthesis fct-FePt NPs. In the context of the bioapplication of FePt NPs, a family of FePt NPs was specifically designed to enhance their MRI contrast agents properties. In contrast with previous reports, this thesis demonstrates that FePt NPs can be made non-toxic and provides the first data on their cellular uptake mechanisms. A six times increase in the FePt based T₂ contrast properties compared to clinical iron oxide NPs is reported. The relationship between the MRI contrast properties and the NPs architecture is explored and rationalised as the basis for the design of NPs as enhanced MRI contrast agents. Finally, the first observations of cellular and in vivo MR imaging with FePt NPs is also reported. This study opens the way for several applications of FePt NPs such as regenerative medicine and stem cell therapy, thus providing a bio-platform to develop novel diagnostic and therapeutic agents.
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Hiscox, Lucy Victoria. "Early characterisation of neurodegeneration with high-resolution magnetic resonance elastography." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31198.
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This thesis contributes to recent interest within medical imaging regarding the development and clinical application of magnetic resonance elastography (MRE) to the human brain. MRE is a non-invasive phase-contrast MRI technique for measurement of brain mechanical properties in vivo, shown to reflect the composition and organisation of the complex tissue microstructure. MRE is a promising imaging biomarker for the early characterisation of neurodegeneration due to its exquisite sensitivity to variation among healthy and pathological tissue. Neurodegenerative diseases are debilitating conditions of the human nervous system for which there is currently no cure. Novel biomarkers are required to improve early detection, differential diagnosis and monitoring of disease progression, and could also ultimately improve our understanding of the pathophysiological mechanisms underlying degenerative processes. This thesis begins with a theoretical background of brain MRE and a description of the experimental considerations. A systematic review of the literature is then performed to summarise brain MRE quantitative measurements in healthy participants and to determine the success of MRE to characterise neurological disorders. This review further identified the most promising acquisition and analysis methods within the field. As such, subsequent visits to three brain MRE research centres, within the USA and Germany, enabled the acquisition of exemplar phantom and brain data to assist in discussions to refine an experimental protocol for installation at the Edinburgh Imaging Facility, QMRI (EIF-QMRI). Through collaborations with world-leading brain MRE centres, two high-resolution - yet fundamentally different - MRE pipelines were installed at the EIF-QMRI. Several optimisations were implemented to improve MRE image quality, while the clinical utility of MRE was enhanced by the novel development of a Graphical User Interface (GUI) for the optimised and automatic MRE-toanatomical coregistration and generation of MRE derived output measures. The first experimental study was performed in 6 young and 6 older healthy adults to compare the results from the two MRE pipelines to investigate test-retest agreement of the whole brain and a brain structure of interest: the hippocampal formation. The MRE protocol shown to possess superior reproducibility was subsequently applied in a second experimental study of 12 young and 12 older cognitively healthy adults. Results include finding that the MRE imaging procedure is very well tolerated across the recruited population. Novel findings include significantly softer brains in older adults both across the global cerebrum and in the majority of subcortical grey matter structures including the pallidum, putamen, caudate, and thalamus. Changes in tissue stiffness likely reflect an alteration to the strength in the composition of the tissue network. All MRE effects persist after correcting for brain structure volume suggesting changes in volume alone were not reflective of the detected MRE age differences. Interestingly, no age-related differences to tissue stiffness were found for the amygdala or hippocampus. As for brain viscosity, no group differences were detected for either the brain globally or subcortical structures, suggesting a preservation of the organisation of the tissue network in older age. The third experiment performed in this thesis finds a direct structure-function relationship in older adults between hippocampal viscosity and episodic memory as measured with verbal-paired recall. The source of this association was located to the left hippocampus, thus complementing previous literature suggesting unilateral hippocampal specialisation. Additionally, a more significant relationship was found between left hippocampal viscosity and memory after a new procedure was developed to remove voxels containing cerebrospinal fluid from the MRE analysis. Collectively, these results support the transition of brain MRE into a clinically useful neuroimaging modality that could, in particular, be used in the early characterisation of memory specific disorders such as amnestic Mild Cognitive Impairment and Alzheimer's disease.
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Cross, Graham Hugh. "Electrical and magnetic characterisation of a series of TCNQ salts." Thesis, Sheffield Hallam University, 1985. http://shura.shu.ac.uk/19516/.
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The electrical and magnetic properties of a series of 12 isostructural TCNQ salts of bis-pyridinium cations are reported and these properties are related to the structural characteristics. The role of the cation lattice in stabilising a regular TCNQ stack in these salts is discussed. For comparison with this series, the electrical and magnetic properties of two TCNQ salts of bis-pyridinium cations with ordered structures and two salts of dialkyldiphenylphosphonium cations are reported. Within the isostructural series of salts, the stoichiometry takes values of between 1:3 and 1:5, and the cation length determines the stoichiometry. In all these salts, the hydrated cation lattice is disordered and the TCNQs stack in regular columns. The room temperature conductivities, measured along the stacking axis, are in the range 0.05 to 500 S/cm with the highest conductivities observed in dehydrated salts having the approximate stoichiometry, 1:4.5. The 1:5 salts possess the lowest conductivity of the series and in these salts the cation lattice is partially ordered. The 1:3 and 1:4 salts are small band gap semi-conductors whereas the conductivity of the 1:5 salts is not simply activated within the experimental range of temperatures. In these salts the conductivity obeys the empirical power law: [mathematical equation]. The temperature dependence of the magnetic susceptibility of all but the 1:3 salts of the isostructural series is characteristic of a system of partially localised triplet excitons. The magnitude of the singlet-triplet exchange energy exhibits a stoichiometric dependence and is lower in the 1:5 salts where the spin concentration is lower. The magnetic susceptibility of the 1:3 salts varies with temperature according to the Curie-Weiss law. The apparent low spin concentration supports the evidence found for alloy formation in these salts where the cation lattice is partially occupied by neutral or monoquaternised base.
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Bromwich, Thomas Joseph. "The development and characterisation of magnetic nanodots for information storage applications." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426380.
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Zamani, Sahar. "Magnetic resonance imaging characterisation of water transport in cement-based materials." Thesis, University of Surrey, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.606806.
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This work addresses a better understanding of water dynamics in cement paste and mortar materials. Permeability to water and water transport diffusion are measured using magnetic resonance profiling. Water self diffusion in one and two dimensions is measured using nuclear magnetic resonance pulsed field gradient diffusometry. With regard to water permeability of cement paste and mortars, three topics are addressed. The permeability is measured as a function of relative humidity for cement pastes of different sizes and as a function of sand size for mortars. The relative liquid water and water vapour permeability are calculated using a modified version of a model suggested by Barogbel-Bouny et aI.. The intrinsic permeability values for cement pastes are similar to those measured by beam bending methods by Vichit-Vadakan and Scberer The values found for mortars are similar to those measured by Baroghel-Bouny et at. The time dependence of the equilibration of the water concentration profile is also measured. With regard to water transport diffusion, mortars with different sand sizes are studied during water ingress/egress cycles. It is shown that ingress of water into dried mortars slows dramatically after some time most likely due to pore blocking by particulate fines carried with the water. Two indicative transport diffusion coefficients are obtained corresponding to the water diffusion before and after the blockage is encountered. With regard to diffusometry, the water self-diffusion coefficient was measured in a cement paste and found to decrease rapidly in the early stages of hydration. The capillary pore size distribution is measured from an analysis of restricted diffusion data in a mature sample. No evidence of capillary pore anisotropy is found
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Deakin, Tom. "Characterisation of Advanced Materials for use as Future Magnetic Recording Media." Thesis, University of York, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503314.
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Bright, Molly Gallogly. "Novel methods for characterisation of cerebrovascular reactivity using magnetic resonance imaging." Thesis, University of Oxford, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540125.
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Stephens, Deborah Ann. "Structural and magnetic characterisation of some mixed metal oxides and oxyhalides." Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/1512/.
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This thesis investigates the structural and physical effects of changing the ratio of Mn:Ga in the anion deficient perovskite, YSr\(_3\)Mn\(_{4-x}\)GaxO\(_{10.5}\). YSr\(_3\)Mn\(_{4-x}\)GaxO\(_{10.5}\) crystallises in the tetragonal space group I4/mmm, with lattice parameters a~7.64 Å and c~15.66 Å. Magnetic characterisation indicates that the material is antiferromagnetic overall, with ferromagnetic ordering in the [001] direction of the unit cell. Earlier work on the structural analogue, Y\(_{1.07}\)Sr\(_{2.93}\)Mn\(_{2.67}\)Ga\(_{1.33}\)O\(_{10.5}\), identified a magnetic peak in the neutron diffraction pattern that could not be fitted following refinement of NPD data. This work concluded that the extra peak was due to a small MnO impurity. The effects of oxidation and fluorination on the structural and physical properties of YSr\(_3\)Mn\(_{4-x}\)Ga\(_x\)O\(_{10.5}\) with various Mn:Ga ratios are investigated. The physical and structural effects of substituting Mn\(^{3+}\) or Co\(^{3+}\) for Fe\(^{3+}\) in the perovskite related material, Pb\(_4\)Fe\(_3\)O\(_8\)Cl, have been investigated using XRPD, NPD and magnetic susceptibility measurements. An earlier characterisation of Pb\(_8\)WO\(_{10}\)Cl\(_2\) suggested a deficit on all atom sites within the unit cell. This work suggests a different structure with an intact cation and main oxygen sub-lattice. The site of an additional oxygen was established linked to tungsten. Pb\(_8\)WO\(_{10}\)Cl\(_2\) crystallises in space group I4/mmm, with a = 3.9846(2) and c = 22.690(2) Å.
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Letuka, Pheletso. "Cardiovascular magnetic resonance characterisation of the phenotype of resistant uncontrolled hypertension." Master's thesis, Faculty of Health Sciences, 2019. https://hdl.handle.net/11427/31763.
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Background: Resistant hypertension (RH) is defined as blood pressure (BP) that remains elevated (>140/90mmHg) despite being treated with an antihypertensive regimen of 3 or more medications from different classes, including a long-acting calcium channel blocker, an angiotensin converting enzyme inhibitor or angiotension receptor blocker and a diuretic. The prevalence of RH in South Africa is currently unknown, however, clinical reports suggest that it is not rare. Patients with RH are significantly predisposed to cardiovascular (CV) diseases compared to patients with controlled BP. Consequences of RH include left ventricular hypertrophy, heart failure, ischaemic heart disease, chronic kidney disease leading to end-stage renal disease, stroke, vascular dementia, CV death and peripheral arterial disease. A proportion of patients with RH who never achieve BP control despite maximal medical treatment, represent a potentially novel and distinctive phenotype which is different from RH patients whose BP canbe controlled. Recognising and categorising such patients becomes the initial and crucial step in stratifying phenotypes and defining mechanisms of treatment resistance. Objectives: The aim of this study was to identify patients with resistant uncontrolled hypertension (RUH) and compare phenotypes in these patients to resistant controlled hypertensives (RCH). Methods: We enrolled 50 patients from the Groote Schuur Hospital Hypertension Clinic: a teriary referral hospital for RH. Patients on 4 or more antihypertensive medication including a diuretic, with BP< 140/90mmHg were considered RCH, and those with BP ≥ 140/90 considered RUH. Assessments included clinical examination, electrocardiography, echocardiography, applanation tonometry, serum biomarkers and cardiovascular magnetic resonance (CMR - which included biventricular volumes and function, myocardial strain, tissue characteristics and late gadolinium enhancement - LGE). Results: Thirty were diagnosed with RUH and twenty with RCH. Patients with RUH were more likely to have a longer duration since diagnosis of hypertension (10.5±10.7 vs. 3.6±3.4, p=0.02) and more likely to be on treatment that included an ACE-inhibitor (90% vs. 58%, p=0.01). As expected, patients with RUH had significantly higher systolic BP (155.6±21.6 vs. 137.8±16.5 mmHg, p< 0.001), diastolic BP (88.4±14.5 vs. 77.5±13.6 mmHg, p= 0.03), mean arterial BP (115.4±17.2 vs 101±15.3 mmHg, p= 0.004) and pulse pressure (67.3±14.2 vs. 60.1±12.4 mmHg, p=0.001). Further, RUH patients had significantly lower large artery elasticity (12.5±4 vs 14.7±3.8ml/mmHgx100, p=0.08) and lower small artery elasticity (4.1±2.1 vs. 6.9±3.6ml/mmHgx100, p< 0.001). RUH patients also had a higher systemic vascular resistance (1754±418.4 vs. 1363±371.5dyneXsecXcm-5, p=0.002). On CMR, RUH patients had lower right ventricular (RV) end-systolic and end-diastolic volumes (p=0.02), as well as higher indexed left ventricular mass (LVMI) (61.6±17.6 vs 52.9±13.9 g/m2 , p= 0.06). There were no differences in native T1, extracellular volume quantification and LGE volume fraction between RUH and RCH patients. Conclusions: Patients with RUH have a greater involvement and more severe CV phenotype, that is likely to result in increased CV morbidity and mortality, including greater target end organ damage as a result of vascular adaptations and concentric remodeling.
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Feuersenger, Jürgen. "Synthesis and characterisation of 3d-4f-complexes and their magnetic properties." Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14195/document.
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Ce travail de thèse décrit (i) la synthèse de complexes hétérométalliques d’ions 3d et 4f à partir de précuseurs de Mn, Fe et Co, de sels de lanthanides et de ligands organiques et (ii) l'étude de leurs structures et propriétés. 41 complexes polynucléaires ont été synthétisés dans le cadre de ce travail. Les structures moléculaires de tous les composés ont été déterminées par diffraction des rayons X. Les propriétés magnétiques de 22 complexes ont été étudiées, dont quatre montrent une relaxation lente de leur aimantation considérée comme la signature d’un comportement de molécule-aimant. L'activité catalytique du complexe {Mn4Dy6Li2} calciné a aussi été étudiée et s'est avérée efficace pour l'oxydation du monoxyde de carbone. L'étude systématique de complexes isostructuraux de lanthanides a montré que l'incorporation d’ions 4f peut introduire de l’anisotropie magnétique et que l’ion DyIII est généralement le meilleur candidat pour le ciblage de molécules-aimants hétérométalliques 3d- 4fThis dissertation describes the syntheses of 3d-4f-metal complexes starting from preformed compounds of Mn, Fe and Co, lanthanide salts and organic ligands and also the investigation of their structures and properties. 41 new polynuclear heterometallic metal complexes were synthesised in the course of this work with different interesting properties. The structures of all obtained compounds have been confirmed using X-ray diffraction. The magnetic properties of 22 complexes were studied, of which four show frequency dependent out-of-phase signals as expected for SMMs. The catalytic activity of calcinated {Mn4Dy6Li2} was investigated and proved effective for the oxidation of CO. It was established, that the use of precursors leads to new families of compounds. Moreover the study of isostructural compounds across the lanthanide series showed 1) that the incorporation of 4f ions introduces magnetic anisotropy and 2) DyIII is usually the best candidate for targeting 3d-4f-SMMs
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McDiarmid, Adam Kenneth. "Tissue characterisation in acquired heart disease with cardiovascular magnetic resonance imaging." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/10420/.
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Objectives: To apply and refine conventional and developing cardiac magnetic resonance (CMR) imaging tissue characterisation techniques, with the aim of applying them to better understand cardiac remodelling in health, disease and as an outcome surrogate in clinical trials. Background: Cardiac structure, function and perfusion are routinely assessed with a range of imaging modalities in both research and clinical practice. Cardiac magnetic resonance (CMR) imaging is emerging as the gold standard tool for many of these assessments. The use of gadolinium containing contrast agents in CMR protocols allows the detection of myocardial scar and focal fibrosis and provides important prognostic information. The developing field of T1 mapping allows measurement of the extracellular volume, a surrogate for fibrosis that offers further insights into diffuse myocardial change not previously possible. Methods: CMR tissue characterisation techniques were applied in sequential studies of: ischaemic cardiomyopathy, health, athletic cardiac adaptation and in a randomised controlled study examining the effects of spironolactone in heart failure with preserved ejection fraction. Results & Conclusions: Late gadolinium enhancement (LGE) imaging is of limited application in predicting functional recovery of dysfunctional segments in ischaemic cardiomyopathy (Chapter 3). Modified Look-Locker Inversion recovery (MOLLI) T1 and extracellular mapping techniques can be applied reproducibly in health and following either bolus or split dose gadolinium administration (Chapters 4 & 5). T1 mapping provides important insights into athletic cardiac remodelling that may allow its application in distinguishing between athletic and myopathic change (Chapter 6). Individuals with heart failure with preserved ejection fraction (HF-PEF) have diffuse myocardial fibrosis as measured with T1 mapping. Early results of a randomised controlled study suggest that the beneficial effects of spironolactone in HF-PEF may in part be due to regression of diffuse myocardial fibrosis (Chapter 7).
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Tayler, Alexander B. "Experimental characterisation of bubbly flow using MRI." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/241036.
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This thesis describes the first application of ultra-fast magnetic resonance imaging (MRI) towards the characterisation of bubbly flow systems. The principle goal of this study is to provide a hydrodynamic characterisation of a model bubble column using drift-flux analysis by supplying experimental closure for those parameters which are considered difficult to measure by conventional means. The system studied consisted of a 31 mm diameter semi-batch bubble column, with 16.68 mM dysprosium chloride solution as the continuous phase. This dopant served the dual purpose of stabilising the system at higher voidages, and enabling the use of ultra-fast MRI by rendering the magnetic susceptibilities of the two phases equivalent. Spiral imaging was selected as the optimal MRI scan protocol for application to bubbly flow on the basis of its high temporal resolution, and robustness to fluid flow and shear. A velocimetric variant of this technique was developed, and demonstrated in application to unsteady, single-phase pipe flow up to a Reynolds number of 12,000. By employing a compressed sensing reconstruction, images were acquired at a rate of 188 fps. Images were then acquired of bubbly flow for the entire range of voidages for which bubbly flow was possible (up to 40.8%). Measurements of bubble size distribution and interfacial area were extracted from these data. Single component velocity fields were also acquired for the entire range of voidages examined. The terminal velocity of single bubbles in the present system was explored in detail with the goal of validating a bubble rise model for use in drift-flux analysis. In order to provide closure to the most sophisticated bubble rise models, a new experimental methodology for quantifying the 3D shape of rising single bubbles was described. When closed using shape information produced using this technique, the theory predicted bubble terminal velocities within 9% error for all bubble sizes examined. Drift-flux analysis was then used to provide a hydrodynamic model for the present system. Good predictions were produced for the voidage at all examined superficial gas velocities (within 5% error), however the transition of the system to slug flow was dramatically overpredicted. This is due to the stabilising influence of the paramagnetic dopant, and reflects that while drift-flux analysis is suitable for predicting liquid holdup in electrolyte stabilised systems, it does not provide an accurate representation of hydrodynamic stability. Finally, velocity encoded spiral imaging was applied to study the dynamics of single bubble wakes. Both freely rising bubbles and bubbles held static in a contraction were examined. Unstable transverse plane vortices were evident in the wake of the static bubble, which were seen to be coupled with both the path deviations and wake shedding of the bubble. These measurements demonstrate the great usefulness for spiral imaging in the study of transient multiphase flow phenomena.
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Arnold, John Andrew Carey. "Development of a computerised system for objective carotid plaque characterisation." Thesis, King's College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325181.
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Brown, William James. "Observations and characterisation of rapid variations in the Earth's internal magnetic field." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/10392/.
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The internal magnetic field of Earth is generated by dynamo processes in the fluid outer core, variations in flow resulting in the constantly changing form of the magnetic field. The rapid dynamics of the core are largely unknown; the mantle and crust filter and mask small-scale spatial and temporal features and field sources external to the Earth contaminate the limited observations. Geomagnetic jerks represent the most rapid observed variations of the internal field, on the scale of months, and are poorly understood. Jerks are sharp changes between periods of an otherwise linear rate of change of the field. The main aims of this thesis are: to systematically catalogue observations of jerks, focussing on 1957–2008, and to quantify their characteristics; to assess how representative observations of jerks are through synthetic field modelling; and to evaluate what the results of these analyses inform us about the nature of the source of jerks in the core. I identify jerks in observations via a two-step method, removing contaminating external signal before identifying possible times at which a simple jerk model produces a good fit to data. I quantify the properties of the model and fit, providing uncertainty estimates, all with minimal prior information on the occurrences of jerks. Jerks are found to be frequent, regional and not globally contemporaneous. Jerks are identified every year but with relative abundance in 1968–71, 1973–74, 1977–79, 1983–85, 1989–93, 1995–98 and 2002–03. The amplitudes of jerks in Europe are seen to vary periodically, suggesting a regular generation mechanism. Limited observations preclude a global assessment of this. I create stochastic synthetic field models to assess the significance of observations and to infer compatible jerk characteristics. These models reinforce the view that jerks occur in localised patches at the Earth's surface without a consistent temporal or spatial distribution. Spherical harmonic (SH) analysis of the synthetic and observed jerks suggests that despite the localised nature of jerk signals, they can be represented by a potential field with most power below SH degree 4. A lag time of 6 months between variations in Earth's rotation and geomagnetic jerks suggests that sufficiently electrically conductive material must be present in the lower ~130 km of the mantle. At the core-mantle boundary, the power spectrum of the SH jerk models and the demonstrated ability to model jerks with a stochastic process, indicates a chaotic, turbulent core-surface flow regime is a likely generation mechanism.
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Spence, Daniel. "Design, synthesis and characterisation of enzyme-activated magnetic resonance imaging contrast agents." Thesis, University of Nottingham, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517867.
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Chong, K. K. R. "The characterisation of nanostructured magnetic materials using image spectroscopy and electron tomography." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597636.
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In this dissertation, two advanced TEM techniques, image spectroscopy and electron tomography, are applied to the quantitative structural and chemical characterisation of nanostructured magnetic materials, in both two and three dimensions (3D), at nanometre spatial resolution. In image spectroscopy, chemical information is obtained by acquiring extended energy-selected series of images, which are interpreted using a combination of computer processing and traditional electron energy-loss spectroscopy (EELS) analysis. In tomography, 3D microstructural and chemical information is obtained by acquiring ultra-high tilt series of high-angle-annular dark field (HAADF) or energy-filtered TEM (EFTEM) images, and subsequently applying tomographic reconstruction and visualisation algorithms to the data. The techniques are applied to the characterisation of materials that include closely-spaced FeNi nanoparticles coated in oxide shells, lithographically patterned Ni pillars, platinum nanoparticles, chromium carbides in stainless steel, titanomagnetite and an ALH meteorite sample. Biological samples include magnetotactic crystals and bacteria cells, greigite-containing bacterial cells and amyloid plaque cores. The chemical data from image spectroscopy and morphological data from electron tomography are cross-correlated. Furthermore, experimental tomographic data are compared with tomographic reconstructions of image simulations.
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Barton, Sarah Jane. "Proton magnetic resonance methods for characterisation of tumours for diagnosis and grading." Thesis, St George's, University of London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272205.
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France, Derek Edward. "The mineral magnetic characterisation of goethite and haematite in soils and sediments." Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263900.
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Bulluck, H. "Tissue characterisation by cardiovascular magnetic resonance in ST-segment elevation myocardial infarction." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/1539982/.
Full textAbstract:
Acute ST-segment elevation myocardial infarction (STEMI) and its associated co-morbidities are among the leading causes of death and disability worldwide. We used multi-parametric mapping by cardiovascular magnetic resonance (CMR) to provide insights into the pathological processes underlying the ischaemic insult and LV remodelling. In Chapter 4 we showed that T1 mapping could quantify the AAR as well as T2 mapping. Secondly, the presence of a hypo-intense core on T1 or T2 maps performed equally well to detect intramyocardial haemorrhage (IMH). Lastly, we showed that post-contrast T1 maps could accurately delineate acute MI size. In chapter 5, we found that 6 standard deviations (SD) was the most accurate semi-automatic method both for acute and chronic MI size quantification using paired CMR scans. However, all 4 of the promising semi-automated techniques assessed (5-SD, 6SD, full width half maximum and Otsu) were equally precise. In chapter 6, we showed that the majority of patients with IMH had residual iron at follow-up and the latter was associated with adverse LV remodelling. Adverse LV remodelling itself was associated with delayed resolution of oedema in the MI zone. The remote extracellular volume fraction (ECV) was higher in the STEMI patients within the first week, when compared to controls, but only remained elevated in those patients who developed adverse LV remodelling. In Chapter 7, we obtained the minimal detectable changes for percentage change in LV end-diastolic volume (%ΔLVEDV – 12%) and %Δ in LV end-systolic volume (%ΔLVESV – 13%) in paired acute and follow-up STEMI patients. Combining %ΔLVEDV and %ΔLVESV revealed 4 patterns of LV remodelling. In conclusion, T1, T2 and T2* CMR mapping complement each other, and provide valuable insights into the pathophysiology of STEMI and adverse LV remodelling. These parameters could be used to risk-stratify, assess response to treatment and for prognostication in reperfused STEMI patients.