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Souza, Pedro Victor Brondino Duarte de. "Desenvolvimento de um subsistema non-real-time para o gerenciamento de dispositivos periféricos e desenvolvimento de interfaces gráficas." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-21102016-140615/.
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Ressonância Magnética (RM) é uma técnica bastante versátil, pois é utilizada em muitas áreas de pesquisa, como biologia, física, química, engenharia e medicina. Apesar disso, constitui-se uma desvantagem o alto custo do equipamento e suas restrições físicas para alguns experimentos. Para reduzir essas desvantagens, o grupo de pesquisadores do CIERMag está desenvolvendo um equipamento de RMN multipropósito e, para complementá-lo, este trabalho vem desenvolver um subsistema non-real-time que gerencia os dispositivos periféricos de um experimento. Foi proposta uma rede de dispositivos que é controlada por um Raspberry Pi como elemento central, o qual está conectado ao terminal computadorizado do sistema através de uma rede local (Local Area Network - LAN) via Ethernet e conectado aos dispositivos periféricos via Serial Peripheral Interface (SPI). Com o objetivo de ser possível gerenciar qualquer tipo de dispositivo, foi desenvolvido um conjunto de parâmetros baseado no Transducer Electronic Data Sheet (TEDS), definido no padrão IEEE 1451, de modo que cada dispositivo, normalmente um transdutor, possui seu próprio. Foram elaboradas duas interfaces de software: uma desenvolvida em Python e a outra uma interface web HTML. Ambas as interfaces possuem as mesmas funcionalidades: editor e gerenciador de TEDS, visualização gráfica de medidas dos sensores e interface para os atuadores.Magnetic Resonance (MR) is a very versatile technique, since it is used in many research areas such as biology, physics, chemistry, engineering and medicine. Despite this, the cost of the equipment and its physical restrictions in some experiments constitute a serious drawback. To minimize these problems, the CIERMag research team is developing multipurpose MR equipment and, to complement this equipment, this work develops a non-real-time subsystem that manages the peripheral devices of the experiment. It was proposed a network of devices controlled by a Raspberry Pi as its central element, which is connected to the terminal computer of the system. The protocol adopted for this was Ethernet via Local Area Network (LAN); communication with peripheral transducers was performed with the Serial Peripheral Interface (SPI). With the objective to be able to manage any type of device, we created parameter sets based on Transducer Electronic Data Sheet (TEDS), defined in the IEEE 1451 standard, so each device, normally a transducer, has its own parameter set. We created two software interfaces: one developed with Python and the other is a HTML web interface. Both have the same functionalities: a TEDS editor and manager, a graphical visualization of sensor measurements and also an actuator interface.
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Murakami, Nayara Saty. "Processamento e caracterização do gel Magic-f com raios-x, espectroscopia por RMN e EPR e espectrofotometria UV/Vis." Universidade Tecnológica Federal do Paraná, 2017. http://repositorio.utfpr.edu.br/jspui/handle/1/2642.
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Este trabalho teve como objetivo realizar o processamento do gel polimérico MAGICf, irradiá-lo e caracterizá-lo com quatro métodos de leitura, uma vez que a dosimetria com gel polimérico é uma área promissora no âmbito de controle de qualidade dos tratamentos radioterápicos, pois permite a avaliação de dose tridimensionalmente. Os métodos para caracterização do gel MAGIC-f foram: Tomografia Computadorizada (TC), espectroscopia de Ressonância Magnética Nuclear (RMN), Ressonância Paramagnética Eletrônica (EPR) e espectrofotometria UV/Vis. Para a caracterização por esse último método, foi feita uma nova formulação do gel MAGIC-f adicionando fluoresceína. Os resultados da caracterização desse gel dosimétrico com tomografia computadorizada e EPR não foram satisfatórios, porém com a espectroscopia de RMN obteve-se bons resultados, assim como com a espectrofotometria UV/Vis. A nova formulação do gel para a caracterização com espectrofotometria mostrou-se ser um método inovador e bastante promissor para essa área.This work aimed to perform the processing of the MAGIC-f polymeric gel, to irradiate it and to characterize it with four methods of reading, since the dosimetry with polymeric gel is a promising area within the scope of quality control of the radiotherapeutic treatments, because it allows dose evaluation three-dimensional. The methods for characterization of the MAGIC-f gel were: Computed Tomography (CT), Nuclear Resonance Magnetic (NMR) and Electron Paramagnetic Resonance (EPR) spectroscopy, and UV/Vis spectrophotometry. For characterization with this last method, a new MAGIC-f gel formulation was made adding fluorescein. The results of the characterization of this dosimetric gel with computed tomography and EPR were not satisfactory, but with NMR spectroscopy satisfactory results were obtained as well as UV / Vis spectrophotometry. The new gel formulation for characterization with UV / Vis spectrophotometry has proved to be an innovative and very promising method for this area.
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Allsopp, Richard Antony. "Electron spin resonance studies of magnetic defects in solids." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253301.
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Fong, Kin Chung. "High Sensitivity Electron Spin Resonance by Magnetic Resonance Force Microscopy at Low Temperature." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1228338129.
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Elbahrawy, Mohammed. "High field electron magnetic resonance in complex correlated spin systems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-39380.
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In this thesis we used ESR to investigate magnetic properties of low D vandium and copper oxides in which small quantum spins are arranged in 1D chains and 2D layers. The thesis covers five different low dimensional spin systems. They turned out to be experimental reliazation of some of the most intersiting theoritical models in the field of quantum magnetism.
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Bingham, Stephen John. "Magnetic circular dichroism and electron paramagnetic resonance of transition ions." Thesis, University of East Anglia, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357179.
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Hunter, David M. "Studies of electron transfer in plastocyanins by nuclear magnetic resonance." Thesis, University of Newcastle Upon Tyne, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270171.
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Crook, Nigel Paul. "The application of quantitative environmental magnetic measurements to sedimentary systems." Thesis, Manchester Metropolitan University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248812.
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Caldwell, Joshua D. "Investigation of electron-nuclear spin interactions in two-dimensional electron systems via magnetoresistively detected magnetic resonance." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0008397.
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Oprea, Corneliu I. "Density Functional Response Theory with Applications to Electron and Nuclear Magnetic Resonance." Doctoral thesis, Stockholm, : Bioteknologi, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4367.
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Latham, C. D. "Conduction electron interactions in sodium and potassium studied by magnetic resonance techniques." Thesis, University of Exeter, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380738.
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Conduction electron interactions in sodium and potassium studied by magnetic resonance techniques Christopher D. Latham Department of Physics, Stocker Road, University of Exeter, EX4 4QL, UK. Abstract Pure sodium consists of a mixture of body centred cubic (BCC) and hexagonal close packed (HCP) crystals at low temperatures and these two phases exhibit subtly di?erent many body e?ects despite their almost identical conduction electron densities. This thesis represents a ?rst attempt to unravel the di?erences in the values of the many body parameters which characterize the description of the two phases in terms of the Fermi liquid theory. Fresh theoretical estimates of several many body parameters are presented and shortcomings in earlier theoretical work are highlighted. It has been found that the cause of these e?ects can be attributed to the di?erent and anisotropic phonon spectra in the two crystal phases. This has little e?ect on the lowest order many body parameters; the cyclotron e?ective masss, m * c, the paramagnetic susceptibility, ?p and the Landau-Silin Fermi liquid theory spin coe?cient, B0; but the second spin coe?cient B1 is very di?erent in the two crystal phases; it also seems likely that it is highly anisotropic. This di?erence leads to the observation of splittings in the microwave transmission spin wave spectra and di?erent spin wave coalescence angles for the two phases. Experimental results of measurements on sodium are presented. The conduction electron spin resonance (CESR), observed by the 35 GHz microwave transmission spectometer at Exeter, is split into two distinct lines which can be identi?ed with the two crystal phases present. A continuum region between the lines indicates that there is some averaging of electron spins among crystal grains or there may be some sodium present in an intermediate, faulted crystal phase in the samples. These observations con?rm the earlier work of Myler (1982), who used re?ection methods, and demonstrate with exceptional clarity, the presence of the two crystal phases. Analysis of the microwave transmission spectra, in various ?eld orientations, of spin waves, Gantmakher-Kaner oscillations, and cyclotron wave signals shows no observable di?er¬ences between the two phases of the quantities m * c, ?p and B0. The estimated values, con?rmed by spin wave measurements, of B1 are -0.01 ± 0.01 in BCC sodium and -0.05 ± 0.01 in HCP sodium at 5 K. The strong possibility of anisotropy in B1 may result in ambiguity in the values obtained from spin wave measurements depending on the details of the methods used to solve for the various quantities. For the ?rst time the microwave frequency size e?ect (MFSE) has been properly identi?ed and measured for potassium metal. This is the microwave frequency version of the radio frequency size e?ect but with the additional complication that the time of ?ight of the conduction electrons across the sample is comparable with the period of the microwaves. The electron orbits are identi?ed as being the symmetrical “type II” orbits, in the terminology of size e?ect studies. Unusually high quality spectra obtained during the early test work on the 35 GHz spectrometer enabled this study to be made. August 1987
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Stefan, Anca Irina. "Modeling and design of resonators for electron paramagnetic resonance imaging and ultra high field magnetic resonance imaging." Columbus, Ohio : Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1133293403.
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Zhou, Haosheng. "Theory of the magnetic resonance spectrum of spin-polarized hydrogen gas." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26678.
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The Green's function method is applied to investigate the magnetic spin resonance spectra of three-dimensional and two-dimensional spin-polarized quantum gases.
The Hartree-Fock approximation is employed to calculate the one-particle Green's function of the atoms, then this one-particle Green's function is used for the calculation of the vertex part of the Green's function. Such a combination yields a self-consistent result. The absorption spectra are obtained from the calculation of the susceptibility in terms of the two-particle Green's function (bubble diagram). Some general expressions for the dispersion relation, for the effective mass of a spin wave, and for the dipolar frequency shift are given in the calculation.
In order to estimate the shift of the electron-spin-resonance (ESR) frequency, the effective dipole-dipole interactions among the hydrogen atoms are included in the calculation. These effective interactions are deduced from the ladder approximation, and hence are characterized by the scattering amplitude. The scattering amplitude is calculated numerically. The result shows that the theoretical value of the shift is smaller than the experimentally observed value by about 35%.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Suwuntanasarn, Nakorn Physical Environmental & Mathematical Sciences Australian Defence Force Academy UNSW. "Magnetic resonance studies of issues critical to solid state quantum computer." Awarded by:University of New South Wales - Australian Defence Force Academy, 2008. http://handle.unsw.edu.au/1959.4/40263.
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The spins of phosphorus doped in silicon are potential candidates for a quantum computing device, with models based on the use of nuclear and/or electron spins suggested. For a quantum computing device, several essential criteria must be demonstrated before any physical implementation, and these include qubit control gates, long decoherence time and scalability. Scalability and compatibility with existing fabrication technologies are strong points in favour of a silicon based system. For spin based schemes, silicon has the potential to provide a host with zero nuclear spin (isotopically purifed 28Si) and also the phosphorus donor provides both nuclear and electron half integer spins (ideal case). In this work, a magnetic resonance method (electron spin resonance) was utilised to investigate these critical issues (controllable quantum gates and decoherence time) for the electron spins of phosphorus donors in silicon. Electron spin resonance (ESR) studies of an ensemble of phosphorus electron spins in silicon were conducted via both continuous wave and pulsed methods. For pulsed ESR operations, two low temperature (4 K and millikelvin) X-band pulsed ESR systems were built. They were designed especially to suit Si:P decoherence time measurements. The design, modelling, construction and evaluation of the probe heads are described. With the aid of computer simulations, the performance of the probe heads was optimised and a rectangular loop gap resonator was found to be the most suitable for wafer type samples. The resonant frequency, quality factor, and coupling coeffcient were calculated via simulation and are in reasonable agreement with experimental results. This demonstrates the effectiveness of such simulations as a tool for optimising the probe head performance. A millikelvin pulsed ESR system was set up through the combination of a dilution refrigerator, superconducting magnet and the in-house construction of a pulsed ESR spectrometer. This novel system allows pulsed ESR experiments on an ensemble system to be realised down to the millikelvin temperature range, hence providing conditions considered most favourable for quantum computing studies. The use of light in combination with the pulsed ESR systems was also explored in an endeavour to overcome the problem of very long spin-lattice relaxation time, T1, allowing the decoherence time to be measured more effciently. With these novel low temperature pulsed ESR units, two-pulse electron spin echo experiments were conducted on phosphorus donors in silicon (both natural silicon (natSi) and 28Si) with the phosphorus concentration in the range of 1015- 1016 P/cm3 and to lower temperatures than previously investigated. Decoherence times measured for both natSi:P and 28Si:P (with similar donor concentrations) were longer than previously reported. Discussions on several effective ways to obtain even longer Si:P decoherence times including variations to sample configurations and experimental conditions are presented. In addition to the pulsed ESR studies, the Si:P controllable quantum gate functions, A gate and J gate, were examined by the continuous wave technique via Stark shift and exchange interaction experiments respectively. Stark shift experiments on bulk samples were carried out to investigate possible manipulation of the spins by the applied electric field. Continuous wave ESR was also used to examine low energy ion implanted Si:P devices, both by single (P+) and dimer (P+2 ) implanted donors. The outcomes from these studies provide materials information useful in formulating a strategy toward the Si:P device fabrication via the top down approach.
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Cruickshank, Paul Alexander Sawchuk. "Instrumental aspects of high-field force-detected electron spin resonance." Thesis, University of St Andrews, 2003. http://hdl.handle.net/10023/7114.
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Magnetic resonance force microscopy (MRFM) is a new measurement technique combining scanning probe microscopy (SPM) and MR spectroscopy, offering the potential of high resolution chemical specific imaging. MRFM is based on the principle of force detection of magnetic resonance (FDMR) in which the magnetisation of a sample in a magnetic field is coupled to an atomic force microscopy cantilever via a field gradient. Magnetic resonance is used to modulate the sample magnetisation at the cantilever resonant frequency and the resulting oscillating force on the cantilever leads to oscillations which may be detected optically. The high sensitivity of force detection offers the potential for single electron spin sensitivity. This thesis describes instrumental aspects of ESR based FDMR experiments and presents the first results at high fields (3.3T). High fields are advantageous for sensitivity and spectral resolution. However, they pose significant technical challenges. FDMR measurements on the organic conductor (fluoranthene)2PF6 were carried out in experiments based around an existing quasi-optical high field ESR spectrometer. Further measurements on (FA)2PF6 and DPPH are presented together with progress towards the construction of a high field MRFM system, based on a commercial SPM instrument. Experiments were performed with both magnet-on-cantilever and sample-on-cantilever configurations with the former the favoured method for potential imaging applications. Signal detection uses a novel fibre-optic interferometer. Cantilever magnets of low conductivity ferrite appear to be more promising for high Q measurements than the metallic magnets favoured by most other groups. Experiment sensitivities are estimated at around 4.4 x 10⁸ polarised electron spins, comparable to conventional commercial ESR spectrometers. Experimental consistency was difficult, especially regarding the positioning of probe and sample, an area in which refinement is essential for repeatable and sensitive experiments. The potential for imaging is attractive and the prospect of single spin detection is discussed.
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Noble, Christopher John 1967. "Applications of magnetic resonance in materials science and solid state physics." Monash University, Dept. of Physics, 2001. http://arrow.monash.edu.au/hdl/1959.1/9064.
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McDonald, Darren. "A gyrokinetic analysis of electron plasma waves at resonance in magnetic field gradients." Thesis, University of St Andrews, 1995. http://hdl.handle.net/10023/13975.
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To produce nuclear fusion in a Tokamak reactor requires the heating of a plasma to a temperature of the order of 10 keV. Electron cyclotron resonant heating (ECRH), in which the plasma is heated by radio waves in resonance with the Larmor frequency of the plasma's electrons, is one scheme under consideration for achieving this. A description of such a heating scheme requires a theory to explain the propagation and absorption of high frequency waves in a plasma in the presence of a magnetic field gradient. A WKB analysis can describe some of the processes involved but a complete explanation requires the use of full wave equations. In this thesis we shall develop a technique for deriving such equations which will be shown to be simpler and more general than calculations performed by earlier workers. The technique relies on including the effect of the magnetic gradient across the Larmor orbit of the electrons in the resonance condition of the wave, the so called Gyrokinetic correction, which has been ignored in calculations by previous workers. Once derived, the equations are solved numerically and the results applied to a number of experiments currently being performed on Tokamak fusion. In addition, we shall also look at the energy loss processes of runaway electrons, which have been shown experimentally to be shorter than would be expected.
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Peterschmitt, Simon. "Development of a Stable and Efficient Electron Cyclotron Resonance Thruster with Magnetic Nozzle." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX053.
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Les propulseurs plasmas sont le sujet d’un intérêt grandissant pour équiper de petits satellites. Des miniaturisations de technologies matures ont été proposées ainsi que des concepts innovants, tels le propulseur à résonance cyclotron électronique muni d’une tuyère magnétique (ECRT). Ce propulseur pourrait réaliser une rupture technologique car il est sans grilles, sans neutraliseur et n’a besoin que d’un seul générateur. Le présent travail consiste à développer un ECRT accompagné du dispositif expérimental nécessaire, capable de démontrer avec précision une grande efficacité durant un fonctionnement prolongé en régime permanent. Les précédentes études sur l’ECRT étaient limitées par un manque de précision sur des mesures clés, en raison du dispositif et des technologies nécessaires à l’étude de ce propulseur. La procédure et le dispositif expérimentaux sont donc largement améliorés pour augmenter la précision des mesures. Toutefois, des spécificités dues à la tuyère magnétique compliquent l’interprétation des mesures de densité de courant d’ion. Notre analyse s’appuie donc principalement sur des mesures de poussées obtenues avec une balance. Par ailleurs, nous montrons que les performances du propulseur augmentent significativement quand on diminue la pression dans le caisson de test jusqu’à 10-7 mbar Xénon. En outre, d’éventuels effets de caisson sont explorés en testant le propulseur à l’ONERA (Palaiseau, France) et à JLU (Giessen, Allemagne). En prenant en considération ces difficultés expérimentales, nous étudions l’efficacité du propulseur en fonction de la géométrie de l’injection de gaz neutre, de la topologie du champ magnétique, et des conditions aux limites de la tuyère magnétique. De plus, nous abordons la question de l’érosion du propulseur, de deux manières : premièrement par une modification des matériaux et deuxièmement par une modification de la structure de couplage (coaxiale, ou guide d’onde circulaire). Le couplage de type guide d’onde produit des ions à des énergies trop faibles pour les exigences de la propulsion spatiale ; en revanche, une structure de couplage coaxiale usinée en graphite semble diminuer substantiellement l’érosion sans compromettre l’efficacité. Ces résultats permettent de concevoir et de tester un propulseur ~ 30 W et un propulseur ~ 200 W dont les performances sont répétables dans le temps. L’efficacité et la durée de vie sont considérablement augmentées : une première campagne de test indique une efficacité allant jusqu’à ~ 50% et une durée de vie estimée de un à quelques milliers d’heures. Pour éclairer les résultats expérimentaux, nous proposons une nouvelle démarche de modélisation, fondée sur l’étude des trajectoires des électrons et sur une approche du chauffage électronique au moyen d’une équation de Fokker-Planck. Cette démarche débouche sur le calcul de la fonction de distribution en énergie des électrons dans le propulseur ; celle-ci détermine le courant d’ions extrait et l’énergie des ionsPlasma thrusters are the subject of growing interest as a means for small satellite propulsion. Miniaturizations of mature technologies as well as innovative concepts have been proposed such as the electron-cyclotron resonance thruster with magnetic nozzle (ECRT). This thruster appears as a potentially disruptive technology because it is gridless, neutralizerless, and only requires one power supply. This work consists in the development of an ECRT with magnetic nozzle and its accompanying experimental test bench, able to accurately demonstrate high thruster efficiency during prolonged steady state operation. Previous studies on the ECRT were limited by a significant lack of accuracy on key measurements, due to the specific setup and technology needed for this thruster. The experimental procedure and the setup are thus heavily upgraded to improve the accuracy of experimental data. However, peculiarities of the magnetic nozzle complicate the interpretation of the ion current density measurements, thus our analysis of performance is mainly based on thrust balance measurements. Besides, thruster performance is shown to significantly increase when decreasing vacuum tank pressure down to 10-7 mbar Xenon, and facility effects are investigated by testing the thruster both at ONERA (France) and at JLU (Germany). Well aware of these experimental difficulties, we study the efficiency of the thruster as a function of neutral gas injection, magnetic field topology, and boundary conditions of the magnetic nozzle. In addition, we address erosion issues in two ways: first by a change of materials, and second by a change of coupling structure (coaxial, or circular waveguide). Waveguide coupling yields insufficient ion energies for space propulsion requirements but manufacturing the coaxial coupling structure with graphite appears to substantially mitigate erosion. These results enable to design and test a ~ 30 W and a ~ 200 W thruster consistently yielding state-of-the-art efficiencies as compared to other thruster types while having sufficient estimated lifetime. In order to shed light on the experimental outcomes, a new modelling approach is developed based on the study of electron trajectories and a Fokker-Planck heating model calculating the formation of the electron energy distribution function in the thruster
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Orwick, Marcella Christine. "Biophysical and magnetic resonance studies of membrane proteins." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:e7974f5f-a5ab-4867-aa5f-feff99716c0f.
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Bacteriorhodopsin (bR) is a 7TM membrane protein expressed in Halobacterium salinarum. Due to its stability and high expression levels, bR serves as a model for other 7TM membrane proteins. Neurotensin receptor 1 (NTS1) is a member of pharmacologically relevant G protein-coupled receptor superfamily, and is the high affinity receptor for neurotensin, a 13mer peptide that can be found in the brain, gut, and central nervous system. NTS1 is a target for Parkinson’s, Schizophrenia, and drug addiction. This thesis aims to develop pulsed magnetic resonance techniques and sample preparation forms for high resolution structural studies on 7TM proteins. In this thesis, pulsed dipolar distance electron paramagnetic resonance (EPR) methods for the study of proteins in their native membrane are established. bR is spin-labeled, and a wellresolved distance distribution is measured in excellent agreement with other structural data. Preliminary distance data for a photoexcited state of bR suggests quaternary rearrangements in the native membrane that are agreement with published AFM results. A fitting method is developed to enable measurements of systems with rapid signal decay, a common feature in reconstituted systems studied by pulsed EPR methods. A physical chemical characterization of nanosized-bilayer discs termed Lipodisqs®, and the successful incorporation of bR is presented. Lipodisqs® are formed from DMPC and a polymer that is able to solubilize DMPC vesicles into discrete particles. Lipodisqs® possess a broad phase transition with increased lipid ordering compared to a DMPC dispersion. The SMA polymer interacts with the lipid tails, but does not perturb the headgroup. BR is incorporated in the monomeric form, and EPR dynamic and distance measurements confirm that Lipodisqs® preserve the native structure of bR, whilst detergent solubilisation increases the overall mobility compared to bR in its native membrane, suggesting that Lipodisqs® serve as an excellent medium for EPR studies on 7TM membrane proteins. A cysteine-depleted mutant of active, ligand binding NTS1 is constructed. Cysteines are reintroduced at positions that may be able to monitor agonist and inverse-agonist induced conformational and dynamic changes. A spin-labeling protocol is developed, and preliminary EPR measurements are discussed. Dynamic nuclear polarization (DNP) results are presented with uniformly-13C-labelled bR in the PM, resulting in a DNP enhancement of 16 using the biradical nitroxide polarizing agent, TOTAPOL. DNP-enhanced solid state NMR (ssNMR) is typically carried out at cryogenic temperatures, resulting in poor spectral resolution compared to ambient temperatures. Two different forms of samples are prepared that could potentially lead to better-resolved DNP spectra. BR is reverse labelled by adding natural abundance amino acids to isotopically labelled growth medium, resulting in the partial depletion of resonance signals that may obscure and crowd the NMR spectra. A crystalline sample of bR is prepared using the LCP method for crystallization, which is to date the most successful method for the crystallization of GPCRs. In summary, the first pulsed dipolar measurements of a protein in its native membrane are shown, Lipodisqs® are characterized and found to be a suitable medium for structural and functional studies of 7 TM membrane proteins, the first preliminary EPR studies on a ligand binding GPCR are presented, and novel sample preparation techniques are developed for the nitroxide-based DNP enhancement of ssNMR data. This thesis opens up several avenues for future research into 7TM membrane proteins.
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Reppart, William J. "Magnetic and crystallographic investigations of selected single crystal systems /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487262513407635.
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Richert, Sabine. "Electron paramagnetic resonance studies and magnetic field effects on porphyrin nanostructures and triad systems." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:9575a056-1a68-4f26-a970-4ad8d0d17c4f.
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The studies presented in this thesis deal with the investigation of inter- and intramolecular interactions in porphyrin nanostructures and molecular triad systems using a variety of different electron paramagnetic resonance (EPR) based techniques as well as optical spectroscopy. Dipolar and exchange couplings were investigated in a range of linear and cyclic copper-containing porphyrin nanostructures by continuous wave (cw) and pulse EPR. The magnitude of the exchange interaction, J, and trends in this property could be determined by numerical simulations of the cw EPR spectra or pulse dipolar evolution data. Using double electron-electron resonance (DEER), through-bond exchange coupling in a bis-copper six-porphyrin nanoring could directly be measured over a distance of ~4 nm. By comparison of the results with those obtained for a singly connected but otherwise identical system, the J-coupling in this ring structure containing two identical, parallel paths was further shown to be the result of constructive quantum interference. In a ten-membered porphyrin nanoring containing two copper and eight zinc centres, the interaction between the central metals of the porphyrins and axial nitrogen ligands of different molecular templates was investigated by cw EPR, electron nuclear double resonance (ENDOR) and DEER. The weak coupling between copper and axial nitrogen ligands could be detected and it was found that the difference in binding affinity between copper and zinc to axial nitrogen ligands influences the structure of the formed complexes and preferred location of the copper centres. We were able to show that the template design allows control over the complex geometry on a molecular level. Triplet state delocalisation was investigated in a series of ladder complexes, formed between linear zinc porphyrin oligomers and bidentate nitrogen ligands, by transient cw EPR and pulse ENDOR techniques. It was found that even though the porphyrin units are held in an approximately co-planar arrangement within the ladder complex, which should favour long-range electronic communication, complete delocalisation is restricted to two porphyrin units at low temperatures and no delocalisation across the bridging ligand was observed. In a different project on symmetric and asymmetric zinc porphyrin oligomers with varying side and end groups, the influence of electronic symmetry on triplet state delocalisation was determined to be the major factor governing and limiting the extent of triplet state delocalisation in linear porphyrin oligomers. Triplet states of zinc porphyrins with different side groups have also been investigated in liquid crystal solvents by EPR. The alignment of the porphyrins is observed to depend strongly on the side groups of the porphyrin core. The orientation and conformations of the porphyrins could be obtained by simulation of the transient cw EPR spectra and order parameters were determined. The influence of small (< 10 G) magnetic fields on the recombination kinetics of spin-correlated radical pairs formed upon photo-excitation of molecular triad systems was studied by transient absorption techniques. Molecular triads serve as model compounds for the study of anisotropic magnetic field effects, which could previously only be detected at comparatively high fields of >30 G. Here it is shown for the first time that hyperfine-driven magnetic field effect anisotropy is observable at magnetic fields comparable to that of the Earth (~0.5 G), underlining the feasibility of a chemical compass for avian magnetoreception.
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Eveson, Robert W. "Geminate free radical processes and magnetic field effects." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325978.
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Morley, Gavin W. "Designing a quantum computer based on pulsed electron spin resonance." Thesis, University of Oxford, 2005. http://ora.ox.ac.uk/objects/uuid:adc7aa2a-8981-4602-88a2-27e5ae362b05.
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Electron spin resonance (ESR) experiments are used to assess the possibilities for processing quantum information in the electronic and nuclear spins of endohedral fullerenes. It is shown that ¹⁵N@C₆₀ can be used for universal two-qubit quantum computing. The first step in this scheme is to initialize the nuclear and electron spins that each store one qubit. This was achieved with a magnetic field of 8.6 T at 3 K, by applying resonant RF and microwave radiation. This dynamic nuclear polarization technique made it possible to show that the nuclear T₁ time of ¹⁵N@C₆₀ is on the order of twelve hours at 4.2 K. The electronic T₂ is the limiting decoherence time for the system. At 3.7 K, this can be extended to 215 μs by using amorphous sulphur as the solvent. Pulse sequences are described that could perform all single-qubit gates to the two qubits independently, as well as CNOT gates. After these manipulations, the value of the qubits should be measured. Two techniques are demonstrated for this, by measuring the nuclear spin. Sc@C₈₂ could also be useful for quantum computation. By comparing ESR measurements with density functional theory calculations, it is shown how the orientation of a Sc@C₈₂ molecule in an applied magnetic field affects the molecule's Zeeman and hyperfine coupling. Hence the g- and A-tensors are written in the coordinate frame of the molecule. Pulsed ESR measurements show that the decoherence time at 20 K is 13 μs, which is 20 times longer than had been previously reported. Carbon nanotubes have been filled with endohedral fullerenes, forming 1D arrays that could lead to a scalable quantum computer. N@C₀₆ and Sc@C₈₂ have been used for this filling in various concentrations. ESR measurements of these samples are consistent with simulations of the dipolar coupling.
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Kamenskyi, Dmytro. "Electron spin resonance studies of frustrated quantum spin systems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-108777.
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Since the last few decades frustrated spin systems have attracted much interest. These studies are motivated by the rich variety of their unusual magnetic properties and potential applications. In this thesis, excitation spectra of the weakly coupled dimer system Ba3Cr2O8, the spin-1/2 chain material with distorted diamond structure Cu3(CO3)2(OH)2 (natural mineral azurite), and the quasi-twodimensional antiferromagnet with triangle spin structure Cs2CuBr4 have been studied by means of high-field electron spin resonance. Two pairs of gapped modes corresponding to transitions from a spin-singlet ground state to the first excited triplet state with zero-field energy gaps, of 19.1 and 27 K were observed in Ba3Cr2O8.
The observation of ground-state excitations clearly indicates the presence of a non-secular term allowing these transitions. Our findings are of crucial importance for the interpretation of the field-induced transitions in this material (with critical fields Hc1 = 12.5 T and Hc2 = 23.6 T) in terms of the magnon Bose-Einstein condensation. The natural mineral azurite, Cu3(CO3)2(OH)2, has been studied in magnetic fields up to 50 T, revealing several modes not observed previously. Based on the obtained data, all three critical fields were identified.
A substantial zero-field energy gap, Δ = 9.6 K, has been observed in Cs2CuBr4 above the ordering temperature. It is argued that contrary to the case for the isostructural Cs2CuCl4, the size of the gap can not be explained solely by the uniform Dzyaloshinskii-Moriya interaction, but it is rather the result of the geometrical frustration stabilizing the spin-disordered state in Cs2CuBr4 in the close vicinity of the quantum phase transition between a spiral magnetically ordered state and a 2D quantum spin liquid.
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Arango, Yulieth Cristina. "Electron spin resonance (ESR) spectroscopy of low-dimensional spin systems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-69811.
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The research in low-dimensional (low-D) quantum spin systems has become an arduous challenge for the condensed matter physics community during the last years. In systems with low dimensional magnetic interactions the exchange coupling is restricted to dimensions lower than the full three-D exhibited by the bulk real material. The remarkable interest in this field is fueled by a continuous stream of striking discoveries like superconductivity, quantum liquid and spin gap states, chiral phases, etc, derived from the strong effect of quantum fluctuations on the macroscopic properties of the system and the competition between electronic and magnetic degrees of freedom. The main goal of the current studies is to reach a broad understanding of the mechanisms that participate in the formation of those novel ground states as well as the characteristic dependence with respect to relevant physical parameters. In this thesis we present the results of an Electron Spin Resonance (ESR)-based study on different quasi-1D spin systems, exemplifying the realization of 1D-magnetic spin-chains typically containing transition metal oxides such as Cu2+ or V4+.
The local sensitivity of the ESR technique has been considered useful in exploring magnetic excitation energies, dominant mechanisms of exchange interactions, spin fluctuations and the dimensionality of the electron spin system, among others. Aside from ESR other experimental results, e.g., magnetization and nuclear magnetic resonance besides some theoretical approaches were especially helpful in achieving a proper understanding and modeling of those low-D spin systems.
This thesis is organized into two parts: The first three chapters are devoted to the basic knowledge of the subject. The first chapter is about magnetic exchange interactions between spin moments and the effect of the crystal field potential and the external magnetic field. The second chapter is a short introduction on exchange interactions in a 1D-spin chain, and the third chapter is devoted to ESR basics and the elucidation of dynamic magnetic properties from the absorption spectrum parameters.
The second part deals with the experimental results. In the fourth chapter we start with the magnetization results from the zero-dimensional endohedral fullerene Dy3N@C80. This system is seemingly ESR “silent” at the frequency of X-band experiments. The fifth chapter shows an unexpected temperature dependence of the anisotropy in the homometallic ferrimagnet Na2Cu5Si4O14 containing alternating dimer-trimer units in the zig-zag Cu-O chains. In the sixth chapter different magnetic species in the layer structure of vanadium oxide nanotubes (VOx-NT) have been identified, confirming earlier magnetization measurements. Moreover the superparamagnetic-like nature of the Li-doped VOx-NT samples was found to justify its ferromagnetic character at particular Li concentration on the room temperature scale. In the seventh chapter the Li2ZrCuO4 system is presented as a unique model to study the influence of additional interactions on frustrated magnetism. The eighth chapter highlights the magnetic properties of the pyrocompound Cu2As2O7. The results suggest significant spin fluctuations below TN.
The thesis closes with the summary and the list of references.
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Freytag, Nicolas. "The electron spin polarization in the lowest Landau level : a study by nuclear magnetic resonance." Université Joseph Fourier (Grenoble), 2001. http://www.theses.fr/2001GRE10125.
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Drew, Daniel L. Jr. "Investigating the Structure and Dynamic Properties of Bacteriophage S21 Pinholin Using Solid-State Nuclear Magnetic Resonance and Electron Paramagnetic Resonance Spectroscopy." Miami University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=miami1610187893016095.
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Almeida, António José Sousa de. "Magnetic resonance studies of spin systems in semiconductor nanocrystals." Doctoral thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/18636.
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Doutoramento em FísicaEsta tese apresenta um estudo experimental de sistemas de spins fornecidos por dopantes electrónicos e por defeitos capturadores de carga em nanocristais (NCs) semiconductores, por meio de técnicas de ressonância magnética. Aqui, investigámos problemas que têm efeitos limitadores de performance nas propriedades de NCs semiconductores para o seu uso em aplicações tecnológicas. Nomeadamente, estudámos a dopagem electrónica de NCs semiconductores. A dopagem é crítica para controlar o comportamento de semiconductores, que de outra forma seriam isoladores. Investigámos também defeitos capturadores de carga, que podem ter um impacto negativo na conductividade de NCs semiconductores ao capturar portadores de carga em estados electrónicos deslocalizados de NCs. Para além disso, abordámos a origem da anisotropia magnética em NCs de materiais diamagnéticos. Nesta tese, reportamos investigações usando medidas de ressonância paramagnética electrónica (RPE) quantitativa, dizendo respeito à eficiência de dopagem electrónica de Si NCs com átomos de P e à sua dependência com o ambiente envolvendo os NCs. Das medidas de RPE quantitativas, estimamos eficiências de dopagem nos NCs que são consistentes com a incorporação da maioria dos dopantes P como dadores substitucionais nos NCs. Observamos também que a eficiência de dopagem dos NCs varia em várias ordens de grandeza dependendo do ambiente envolvendo os NCs, devido a uma forte compensação dos dadores por moléculas absorbidas na superfície dos NCs. Usando espectroscopia RPE dependente da temperatura, mostramos também que a energia de ionização dos dopantes P em Si NCs aumenta relativamente ao seu correspondente cristal macroscópico devido a confinamento. Usamos espectroscopia RPE dependente da temperatura para estudar a interacção entre múltiplos dopantes incorporados num único Si NC e o seu impacto na estrutura electrónica destes NCs. Monitorizámos experimentalmente a interacção de troca em pares de dadores P (dímeros de dadores) em Si NCs através de um desvio da ressonância magnética do seu estado tripleto em relação ao paramagnetismo de Curie. Mostrámos que a interacção de troca entre dadores próximos entre si pode ser bem descrita pela teoria de massa efectiva, permitindo o cálculo de muitas configurações de dopantes e permitindo a consideração de efeitos estatísticos cruciais em conjuntos de nanocristais. Descobrimos que dímeros de dadores induzem estados discretos num NC, e que a sua separação energética difere em até três ordens de grandeza para dímeros colocados aleatoriamente num conjunto de NCs devido a uma enorme dependência da energia de troca na configuração do dímero. Investigámos também sistemas de spins induzidos por defeitos capturadores de carga e como estes defeitos podem afectar a dopagem de NCs. Identificamos a presença de dois estados de carga de um defeito em NCs de CdSe usando espectroscopia RPE combinada com a afinação electrónica de NCs através de dopagem com Ag induzida quimicamente. A partir de de RPE foto-induzido, mostramos que estes defeitos têm um papel central na fixação do nível de Fermi em conjuntos de NCs. Através da análise da dependência do sinal de RPE dos defeitos com a concentração de dopantes de Ag, mostramos também que os defeitos actuam como capturadores efectivos de electrões nos NCs. Do RPE dependente da temperatura, estimamos um limite inferior para a energia de ionização dos defeitos estudados. Com base nas características do espectro RPE dos defeitos observados, propomos que está associado a lacunas de Se com o estado paramagnético sendo o estado positivo do defeito. Para além disso, mostramos que as interacções magnéticas entre spins associados a defeitos nos NCs podem induzir efeitos de anisotropia magnética em conjuntos de NCs que não são esperados acontecer no cristal macroscópico correspondente. Usando espectroscopia de ressonância ferromagnética (RFM) com dependência angular, medimos a anisotropia magnética em conjuntos de aleatórios de NCs de CdSe através da gravação do espectro de ressonância magnética para várias orientações do campo magnético externo. As dependências angulares do campo ressonante são diferente para conjuntos aparentemente similares de NCs de CdSe. Mostramos que a forma e amplitude da variação angular do RFM pode ser bem descrita po um modelo simples que toma em consideração as interacções dipolo-dipolo entre dipolos localizados na superfície dos NCs. Os dipolos na superfície podem originar de ligações pendentes em sítios da superfície que não estão passivados por ligantes. Dos nossos cálculos, descobrimos que para diferentes conjuntos aleatórios de NCs a força da anisotropia magnética induzida por interacções dipolo-dipolo pode tomar valores abrangendo quatro ordens de grandeza, dependendo do arranjo específico dos NCs no conjunto e da distribuição específica dos dipolos na superfície de cada NC. Esta enorme variabilidade pode justificar a disparidade de anisotropias magnéticas observada nas nossas experiências.
This thesis presents an experimental study of systems of spins provided by electronic dopants and by charge trapping defects in semiconductor NCs, by means of magnetic resonance spectroscopy techniques. Here, we have investigated issues that have performance-limiting effects on the properties of semiconductor NCs for their use in technological applications. Namely, we have studied the electronic doping of semiconductor NCs. Doping is critical to control the behavior of semiconductors, which would otherwise be electrically insulating. We have further investigated charge trapping defects in semiconductor NCs, which can have a negative impact on the conductivity of semiconductor NCs by capturing charge carriers from delocalized electronic states of the NCs. Moreover, we addressed the origin of magnetic anisotropy in NCs of diamagnetic materials. In this thesis, we report investigations using quantitative electron paramagnetic resonance (EPR) measurements concerning the efficiency of electronic doping of Si NCs with P atoms and its dependence on the environment surrounding the NCs. From quantitative EPR measurements, we estimate doping efficiencies in the NCs that are consistent with the incorporation of most P dopants as substitutional donors in the NCs. We further observe that the doping efficiency of the NCs varies by several orders of magnitude depending on the NCs surrounding environment due to a strong compensation of donors by molecules adsorbed to the NCs surface. Using temperature-dependent EPR spectroscopy, we further show that the ionization energy of P dopants in Si NCs increases with respect to their bulk counterpart due to confinement. We use temperature-dependent EPR spectroscopy to study the interaction between multiple P dopants incorporated in a single Si NC and its impact on the electronic structure of these NCs. We experimentally probe the exchange interaction in pairs of P donors (donor dimers) in Si NCs via a deviation of their triplet-state magnetic resonance from Curie paramagnetism. We showed that the exchange coupling of closely spaced donors can be well described by effective mass theory, enabling the calculation of many dopant configurations and allowing the consideration of statistical effects crucial in NC ensembles. We find that donor dimers induce discrete states in a NC, and that their energy splitting differs by up to three orders of magnitude for randomly placed dimers in a NC ensemble due to an enormous dependence of the exchange energy on the dimer configuration. We also investigate systems of spins induced by charge trapping defects and how these defects can affect the doping of NCs. We identify the presence of two charge states of a defect in CdSe NCs using EPR spectroscopy, combined with electronic tuning of NCs via chemically induced Ag doping. From light-induced EPR, we show that these defects have a central role on Fermi level pinning of NC ensembles. By analyzing the dependence of the EPR signal of the defects on the concentration of Ag dopants, we further demonstrate that the defects act as effective electron traps in the NCs. From temperaturedependent EPR, we estimate a lower limit for the ionization energy of the studied defects. Based on the characteristics of the EPR spectrum of the observed defect, we propose that it is associated to Se vacancies with the paramagnetic state being the positively charged state of the defect. Moreover, we show that magnetic interactions between spins associated to defects in NCs can induce magnetic anisotropy effects in NCs ensembles that are not expected to occur in their bulk counterpart. Using angulardependent ferromagnetic resonance (FMR) spectroscopy, we measure the magnetic anisotropy in different random ensembles of CdSe NCs by recording magnetic resonance spectra for various orientations of the external magnetic field. The observed angular dependencies of resonant field are different for apparently similar CdSe NC ensembles. We show that the shape and amplitude of the FMR angular variation can be well described by a simple model that considers magnetic dipole-dipole interactions between dipoles located at the NCs surface. The surface dipoles may originate from dangling bonds on surface sites that are not passivated by ligands. From our calculations, we find that for different random ensembles of NCs the strength of the magnetic anisotropy induced by dipole-dipole interactions may take values spanning four orders of magnitude, depending on the specific arrangement of the NCs in the ensemble and the specific distribution of the surface dipoles in each NC. This huge variability may justify the disparity of magnetic anisotropies observed in our experiments.
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Eichel, Rüdiger-Albert. "New concepts in two-dimensional pulse electron paramagnetic resonance spectroscopy : resolution enhancement by magnetic field modulation /." Zürich : [s.n.], 2001. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=14394.
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Pinheiro, Teresa J. T. "The interaction of cytochrome c with anionic phospholipid bilayers : a nuclear and electron magnetic resonance study." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333368.
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Karube, Kosuke. "Ferromagnetic critical behavior and critical universality in itinerant-electron metamagnet UCoAl." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199086.
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Forino, Paola Caterina. "Nuclear magnetic resonance study of the electron doped Dirac-Mott Insulator double perovskite Ba2Na(1-x)CaxOsO6." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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Osmium-based materials exhibit unconventional magnetism due to the interplay between spin orbit coupling and strong electronic correlations.
In this thesis we investigate for the first time the effect of charge doping on the Dirac Mott insulator double perovskites Ba2Na(1-x)CaxOsO6 by using Nuclear Magnetic Resonance technique. We study in details the evolution of the magnetic phase diagram as a function of doping and applied magnetic field.
The system rapidly evolves from a canted to a collinear antiferromagnetic ground state with a monotonic increase of the magnetic transition temperature. Furthermore, the system remains insulating in the whole range of doping, despite the injection of extra electrons. This indicates that the Dirac-Mott insulating state of this material is unusually robust.
In particular, the results show an unexpected thermally activated charge dynamics which suggests the presence of polarons dominating the high temperature excitations of this Dirac-Mott insulator.
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Vähäkangas, J. (Jarkko). "Extended and finite graphenes:computational studies of magnetic resonance and magneto-optic properties." Doctoral thesis, University of Oulu, 2016. http://urn.fi/urn:isbn:9789526208619.
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Abstract
In this thesis, the magnetic resonance and magneto-optical rotation parameters are studied in single-layer carbon systems of two different dimensionalities. Based on electronic structure calculations, the spectral parameters are predicted for both extended (2D) and finite, molecular (0D) systems consisting of pure sp²-hybridised pristine graphene (G), as well as hydrogenated and fluorinated, sp³-hybridised graphene derivatives, graphane (HG) and fluorographene (FG), respectively.
Nuclear magnetic resonance (NMR) parameters are calculated for G, HG and FG systems at their large-system limit. For their 0D counterparts, graphene flakes, qualitative spectral trends are predicted as functions of their size and perimeter type. The last group of studied carbon systems consists of 2D graphenes containing spin-1/2 paramagnetic defects. Electron spin resonance (ESR) parameters and paramagnetic NMR shieldings are predicted for four different paramagnetic systems, including the vacancy-defected graphane and fluorographene, as well as graphene with hydrogen and fluorine adatoms. The magneto-optic properties of G and HG flakes are studied in terms of Faraday optical rotation and nuclear spin optical rotation parameters, to investigate the effects of their finite size and also the different level of hydrogenation.
All the different investigated parameters displayed characteristic sensitivity to the electronic and atomic structure of the studied graphenes. The parameters obtained provide an insight into the physics of these 0D and 2D carbon materials, and encourage experimental verification.
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Russ, Jennifer Lynn. "Studies of Solution Paramagnetic-Substrate Nuclear and Electron Intermolecular Interactions." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/27050.
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Advanced nuclear and electron magnetic resonance techniques (i.e. nuclear magnetic resonance (NMR), dynamic nuclear polarization (DNP), and magnetic resonance imaging (MRI)) were used to study the attitude and dynamics of TEMPO (2,2,6,6-tetramethylpiperidinyloxy)-substrate systems and the relaxivity properties of water-soluble trimetallic nitride template functionalized endohedral metallofullerenes (TNT-fMF). The attitude and average distance of interaction for each TEMPO-substrate system was determined from comparing density functional theory (DFT) calculation results with experimental hyperfine coupling constants leading to an improved understanding of solution dynamics. The short-lived solvent-solute interactions of the TEMPO-substrate molecules, such as transient complex formation, are governed by weak hydrogen-bonding interactions. The collisions in solution were explained by determining the favored orientations of the two molecules interacting using calculated relative energy minima and reproducibility of the experimental results by the calculated coupling constants.
Water-soluble TNT-fMFs are studied as candidates for the next generation MRI contrast agents as diagnostic agents and also as possible therapeutic agents to kill cancer cells and decrease tumors. The TNT-fMFs are being studied as part of a multi-modal platform dependent upon which metal atoms are encapsulated inside: Gd â MRI contrast agent (diagnostic), Lu and Ho â radio labeled for use as a therapeutic agent, Tb â fluorescence, and Lu â x-ray contrast. The current commercial MRI contrast agent, OmniscanTM, contains one gadolinium atom; however, the metal is complexed to, not encapsulated in, the molecule. TNT-fMFs fully encapsulate three metal atoms to ensure the patient does not run the risk of metal poisoning. The r1 and r2 relaxivities of TNT-fMFs containing either Gd, Lu, Ho, or Sc metals were measured at 0.35T. The data for the Gd containing TNT-fMFs indicated the metallofullerene has significantly higher relaxivities than OmniscanTM, and can be the next generation MRI contrast agent. The Ho containing species has a high r2/r1 ratio compared to the other samples showing it is a potential T2 agent, and has therapeutic capabilities.Ph. D.
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Cabañas, Francisco Xavier. "A study of level crossing effects in TCNQ salts." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28632.
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ESR results for DEM(TCNQ)₂ and for MEM(TCNQ)₂ are presented as examples of TCNQ salts with and without level crossing effects. In the case of DEM(TCNQ)₂ we are performing ESR on a system with two types of spins. The latter are due to the two kinds of stacks of the acceptor TCNQ molecules in DEM(TCNQ)₂. The level crossing occurs when the g value of these two kinds of electrons are the same. This is compared to the case of MEM(TCNQ)₂ where there is only one kind of TCNQ stack and consequently no level crossing effect. It is found that g values and susceptibilities of the ESR spectra for DEM(TCNQ)₂ can be fitted very well to an interaction between the stacks of the form J ∑i,j,Si,Sj; with J > 0. This
gives an antiferromagnetic coupling between every spin on one type of stack with every spin on the other type of stack. This type of interaction is also in qualitative agreement with the published results for HMM(TCNQ)₂. The experimental results in DEM(TCNQ)₂ and MEM(TCNQ)₂ also show that there are small but significant differences in the g tensors when the temperature or the crystalline environment are changed, and consequently the g tensor in these compounds does not depend only on the orientation of TCNQ molecule in the magnetic field as previously assumed. These differences in g are typically less than 2 x 10⁻⁴.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Hong, Sungkun. "Nanoscale Magnetic Imaging with a Single Nitrogen-Vacancy Center in Diamond." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10671.
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Magnetic imaging has been playing central roles not only in fundamental sciences but also in engineering and industry. Their numerous applications can be found in various areas, ranging from chemical analysis and biomedical imaging to magnetic data storage technology. An outstanding problem is to develope new magnetic imaging techniques with improved spatial resolutions down to nanoscale, while maintaining their magnetic sensitivities. For instance, if detecting individual electron or nuclear spins with nanomter spatial resolution is possible, it would allow for direct imaging of chemical structures of complex molecules, which then could bring termendous impacts on biological sciences. While realization of such nanoscale magnetic imaging still remains challenging, nitrogen-vacancy (NV) defects in diamond have recently considered as promising magnetic field sensors, as their electron spins show exceptionally long coherence even at room temperature. This thesis presents experimental progress in realizing a nanoscale magnetic imaging apparatus with a single nitrogen-vacancy (NV) color center diamond. We first fabricated diamond nanopillar devices hosting single NV centers at their ends, and incorporated them to a custom-built atomic force microscope (AFM). Our devices showed unprecedented combination of magnetic field sensitivity and spatial resolution for scanning NV systems. We then used these devices to magnetically image a single isolated electronic spin with nanometer resolution, for the first time under ambient condition. We also extended our study to improve and generalize the application of the scanning NV magnetometer we developed. We first introduced magnetic field gradients from a strongly magnetized tip, and demonstrated that the spatial resolution can be further improved by spectrally distinguishing identical spins at different locations. In addition, we developed a method to synchronize the periodic motion of an AFM tip and pulsed microwave sequences controlling an NV spin. This scheme enabled employment of 'AC magnetic field sensing scheme' in imaging samples with static and spatially varying magnetizations.Engineering and Applied Sciences
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Coelho, Felipe Bessa. "Controlador para bobinas de shimming via HTTP." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-25112016-143505/.
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A Ressonância Magnética (RM) é uma técnica extremamente promissora para diversas áreas do conhecimento, desde seu uso conhecido em medicina até aplicações na indústria a fim de melhorar a eficiência de diversos processos. Este projeto trata do desenvolvimento de uma das partes do Espectrômetro Digital de RM desenvolvido pelo Centro de Imagens e Espectroscopia in vivo por Ressonância Magnética (CIERMag), o controlador de bobinas de shimming. O ajuste de shimming oferece melhorias significativas no resultado de experimentos e é parte integral de qualquer sistema de RM tanto por imagens como por espectroscopia. Foi idealizado um equipamento para estabelecer as correntes adequadas em bobinas de shimming que pode ser acessado tanto local como remotamente, permitindo a integração com outros subsistemas do Espectrômetro Digital. O equipamento consiste de hardware específico para estabelecer e analisar as correntes estabelecidas em bobinas de shimming e também de software adequado. Este projeto estabelece as diretrizes de funcionamento do controlador de bobinas de shimming e como ele interage com outros equipamentos.Magnetic Resonance is an extremely promising technique to many areas of knowledge, from its use in medicine to industrial applications where it can improve the efficiency of different processes. This project describes the development of one element of the Digital Spectrometer being developed by CIERMag: the shimming coil controller. Shimming adjustments in magnetic resonance improves experiments results significantly and is an integral part of any magnetic resonance system, from imaging to spectroscopy. A system as developed to establish the proper currents in shimming coils that can be accessed both locally and remotely, easing the integration with other subsystems of the Digital Spectrometer. The controller consists of both custom built hardware and software to establish and analyze the currents in shimming coils. This project also establishes the controller requirements and how it interacts with other systems.
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Weiss, Leah Rachel. "Spin-sensitive probes of triplet excitons in organic semiconductors." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/286356.
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Spin interactions play a key role in the function of molecular materials from naturally occurring biological complexes to synthetic materials for light-harvesting and light-emission. This thesis investigates the spin interactions of spin-1 triplet excitons formed by singlet fission. Singlet fission produces two triplet excitons from one light-induced singlet state and holds promise to enable solar energy generation beyond traditional efficiency limits. As the lifetime of triplet pairs depends sensitively on their spin degree of freedom, in this thesis we deploy spin-sensitive techniques to understand the interactions and evolution of triplet pairs. After introducing the relevant theoretical and experimental background underlying singlet fission and the role of spin, we describe the first observation of strongly exchange coupled, high-spin triplet-pair states ($S=2$) in a solid-state organic semiconductor and show that the singlet fission process allows for the formation of long-lived, strongly coupled spin-two states. We then describe the development and use of photoluminescence-detected avoided level-crossings in applied magnetic fields to quantify the strength of exchange coupling and identify specific optical signatures of exchange-coupled triplet pairs. Using high magnetic fields ($\leq\mbox{60 T}$) we isolate and measure the exchange coupling and optical signatures of multiple distinct triplet pairs in the same material. Finally, we probe the mechanisms of formation and decay of spin polarization from triplet pair states using pulsed spin resonance. The measured dynamics are consistent with polarization driven by fluctuations in exchange coupling between pairs and spin-orbit mediated decay of triplet excitons to the ground state. The combined measurements of the spin parameters and polarization dynamics of triplet pairs from ns to ms timescales provides a quantitative picture of the spin states generated by singlet fission.
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Domiciano, Joao Baptista. "Contribuição da interação spin-spin no espectro de ressonância paramagnética eletrônica de ions Ni2+ diluídos em cristais de fluorborato de zinco hexahidratado." Universidade de São Paulo, 1985. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-27022014-145619/.
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Espectros de Ressonância Paramagnética Eletrônica de Ni POT. 2+ diluídos em monocristais de Zn(FB IND 4)IND 2 6 H IND 2O foram registrados na banda X, entre 77 e 300 K. Os cristais foram crescidos nas concentrações de Ni POT 2+ de 0,5; 0,8; 1,5, 3,9. 5; 15; 33; 53; 75 78; 85; 88; 92; 98 e 100%. Desenvolvemos um método de medi da de concentração de Ni POT 2+, por espectrofotometria, para a determinação da concentração real, pois verificamos que nos cristais a proporção de Ni POT 2 + é sempre maior que na solução utilizada para o crescimento . Do espectro, obtivemos a largura da 2ª linha do níquel, H IND z2 e verificamos que na região de temperaturas altas a largura de linha, para todas as concentrações, obedece à lei H IND ms = a + bT POT 2. O primeiro termo varia com a concentração, por representar a contribuição da interação spin-spin e o termo bT POT 2, que é a contribuição da relaxação spin- rede, mantém-se praticamente constante com a concentração, como era de se esperar. As análises dos espectros indicaram que eles resultam da superposição de várias linhas e, para compreendermos as estruturas do espectro aplicamos , pela primeira vez , um modelo teórico que denominamos Modelo de Pares. Tal aplicação nos permitiu redeterminar, tanto os parâmetros da Hamiltoniana de Spin, D e g, quanto as larguras de linha das linhas componentes. Com a largura de linha das linhas componentes desta estrutura, pudemos obter os parâmetros de interação spin- spin, a. A aplicação do Modelo de Pares indica que a contribuição da interação spin- spin é de natureza basicamente dipolar. A análise geral dos dados experimentais mostra que os resultados experimentais obtidos concordam com os modelos teóricos existentes.Electron Paramagnetic Resonance (EPR) spectra of Ni 2+ diluted in single crystals of Zn(BF4) 26H2O were obtained in the X- band between 77 and 300 K. Samples were grown with Ni2+ concentrations of 0.5; 0.8; 1,5; 3.9 ; 5; 15; 33; 53; 75; 78; 85; 88; 92; 98 and 100%. These values were determined by an optical absorption method developped for the present work . Analysis of the maximum slope line width of the second line (Hz2) has been shown that it obeys the H = a + bT2 law. The a parameter which is associated with the spin-spin interaction changes with concentration while the coefficient of the quadratic term bT which represents the spin-latice relaxation contribution remains, pratically, the same for all the specimens. Careful analysis of thermal and concentration variations of the spectra indicated that they are formed by superposition of several lines. The structure of these lines was studied applying, for the first time, a theoretical model considering interacting pairs of magnetic ions. This model enabled us to determine the D and g spin Hamiltonian parameters, and the individual line whidth which gave the nature of the spin- spin interact i on basically of dipolar origin. Finally we concluded that our experimental results agree with available theoretical models.
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McKay, Johannes Erik. "Methodologies and application development of high field PELDOR for spin labelled proteins." Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/8820.
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The function of a biological molecule is linked to its underlying structure, and determination of that structure can lead to significant insights into its function and how this is performed. There already exist a number of important tools in structural biology, however, the pulsed electron paramagnetic resonance (EPR) technique called pulsed electron-electron double resonance (PELDOR) is the only one capable of accurately measuring isolated distances between attached spin-labels over the range of ~2 to 10 nm, a range which is usually impossible to measure directly with other techniques such as nuclear magnetic resonance (NMR) and X-ray crystallography. This can provide constraints for refinement of structures determined from NMR and X-ray crystallography, or insights into protein docking and protein mechanics. With recent developments in EPR spectrometer instrumentation and spin-labelling it has become possible to conduct PELDOR experiments in the high field EPR regime ( > 3 Tesla) where measurement sensitivity is increased. These experiments can reveal relative orientations of nitroxide spin-labels in complement to their separation, however, analysis and interpretation of these results has been difficult to perform routinely. This thesis presents a characterisation of the high field spectrometer HiPER showing that it is well suited when optimised for making PELDOR experiments. To perform analysis of PELDOR signals from this spectrometer custom signal simulation code has been written. Two case studies are presented. The first relates to the use of the Rx spin label with the PELDOR experiment to derive orientation information from the spin labelled protein Vps75. The recently developed spin label Rx is proposed to attach more rigidly to underlying structure, offering potentially increased accuracy in determination of structure constraints and additional information about relative orientations of different structural features. An orientation selective PELDOR study is presented which compares molecular dynamics (MD) simulations of spin labels attached to sites on the α-helix of the protein Vps75. This has shown great potential for utilising the Rx spin label in a repeatable way on α-helix residue sites for determination of structural constraints. The second case relates to orientation selective PELDOR measurements of spin labelled oligomeric membrane protein structures. High field PELDOR offers great potential in increasing measurement sensitivity and accuracy of structural constraints in oligomeric proteins. A methodology of signal analysis for this class of protein is presented along with measurements of the membrane channel protein MscS. Difficulties of PELDOR measurement on these labelled proteins are discussed and observed relaxation of the spin echo, relevant to pulsed EPR experiments, are investigated and possible mechanisms are presented.
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Worthoff, Wieland Alexander [Verfasser]. "Dynamics of Electron and Nuclear Spin Interaction in Laser Assisted Nuclear Magnetic Resonance Spectroscopy of Gallium Arsenide Nanostructures / Wieland Alexander Worthoff." Aachen : Shaker, 2011. http://d-nb.info/1070150576/34.
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Vidoto, Edson Luiz Géa. "Projeto e construção de um equipamento de imagens por ressonância magnética para uso em rotina clínica e em pesquisa." Universidade de São Paulo, 2001. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-13092007-164543/.
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Neste trabalho medidas de condutividade alternada e de corrente versus tensão foram realizadas em dispositivos emissores de luz baseados em poli(2-metoxi-5-(2\'-etil-hexiloxi)-1,4-fenileno vinileno)-MEH-PPV com óxido de zinco (ZnO) como eletrodo transparente e injetor de buracos e alumínio (Al) como eletrodo metálico e injetor de elétrons. MEH-PPV é um derivado do PPV que emite no vermelho. O ZnO tem função trabalho similar à do ITO, mas é menos agressivo ao polímero, menos caro e mais fácil de ser processado. A curva I vs. V retificada mostrou que a corrente direta depende da temperatura. As componentes real e imaginária da condutividade (ac) apresentam comportamento típico de alguns materiais desordenados: a componente imaginária aumenta como função da freqüência e a componente real mostrou-se independente da freqüência para baixas freqüências e varia como uma lei de potência no domínio de freqüências mais altas O modelo de energias livres aleatórias-RFEB e uma resistência em série para o fenômeno de interface foram desenvolvidos e ajustados para os resultados ac. Com base neste ajuste teórico-experimental, obtemos importantes parâmetros do dispositivo, bem como informações quantitativas sobre o fenômeno de transporte no MEH-PPV.In this work current vs. voltage (I vs. V) and alternating conductivity (ac) measurements were carried out in poly[(2-methoxy- 5-hexyloxy)-pphenylenevinilene] ? MEH-PPV light-emitting diodes having zinc oxide (ZnO) as transparent anode and Al as metallic cathode. MEH-PPV is a PPV derivative, which emits in the red spectral region; ZnO has a work function similar to that of ITO, but it is less aggressive to the polymer, less expensive and easily processed. The retificated I vs. V curves shows that the direct current depends on the temperature. Moreover, the real and imaginary components of alternating conductivity (ac) present typical behavior of somewhat disordered material: the imaginary component grows as a function of the frequency and the real component was observed to be frequency independent for lower frequencies, and follows a power-law above a certain frequency. The Random Energy Free Barrier model approaches and a resistance in series for the interface phenomenon were developed and adjusted for the ac results. From this experimental-theoretical fitting we obtained important parameters of the devices as well as, quantitative informations about the MEH-PPV transport phenomenon.
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Krupskaya, Yulia. "Magnetic Properties of Molecular and Nanoscale Magnets." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-73289.
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The idea of miniaturizing devices down to the nanoscale where quantum ffeffects become relevant demands a detailed understanding of the interplay between classical and quantum properties. Therefore, characterization of newly produced nanoscale materials is a very important part of the research in this fifield. Studying structural and magnetic properties of nano- and molecular magnets and the interplay between these properties reveals new interesting effects and suggests ways to control and optimize the respective material. The main task of this thesis is investigating the magnetic properties of molecular magnetic clusters and magnetic nanoparticles recently synthesized by several collaborating groups. This thesis contains two main parts focusing on each of these two topics.
In the first part the fundamental studies on novel metal-organic molecular complexes is presented. Several newly synthesized magnetic complexes were investigated by means of different experimental techniques, in particular, by electron spin resonance spectroscopy. Chapter 1 in this part provides the theoretical background which is necessary for the interpretation of the effects observed in single molecular magnetic clusters. Chapter 2 introduces the experimental techniques applied in the studies. Chapter 3 contains the experimental results and their discussion. Firstly, the magnetic properties of two Ni-based complexes are presented. The complexes possess different ligand structures and arrangements of the Ni-ions in the metal cores. This difffference dramatically affffects the magnetic properties of the molecules such as the ground state and the magnetic anisotropy. Secondly, a detailed study of the Mn2Ni3 single molecular magnet is described. The complex has a bistable magnetic ground state with a high spin value of S = 7 and shows slow relaxation and quantum tunnelling of the magnetization. The third section concentrates on a Mn(III)-based single chain magnet showing ferromagnetic ordering of the Mn-spins and a strong magnetic anisotropy which leads to a hysteretic behavior of the magnetization. The last section describes a detailed study of the static and dynamic magnetic properties of three Mn-dimer molecular complexes by means of static magnetization, continuous wave and pulse electron spin resonance measurements. The results indicate a systematic dependence of the magnetic properties on the nearest ligands surrounding of the Mn ions.
The second part of the thesis addresses magnetic properties of nano-scaled magnets such as carbon nanotubes fifilled with magnetic materials and carbon-coated magnetic nanoparticles. These studies are eventually aiming at the possible application of these particles as agents for magnetic hyperthermia. In this respect, their behavior in static and alternating magnetic fifields is investigated and discussed. Moreover, two possible hyperthermia applications of the studied magnetic nanoparticles are presented, which are the combination of a hyperthermia agents with an anticancer drug and the possibility to spatially localize the hyperthermia effffect by applying specially designed static magnetic fifields.
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Seleznyova, Kira. "Magnetic properties and magnetic resonances of single crystals based on iron borate : Experimental studies and modelling." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0398/document.
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La thèse porte sur la synthèse et l'étude des propriétés magnétiques de borates de fer-gallium,FexGa1-xBO3 avec 0 supérieur ou égal à x supérieur ou égal à 1. Ces matériaux sont prometteurs pour les applications; en plus, grâce à la présence, en fonction de x, de différents types d’ordre magnétique, ils sont bien adaptés au traitement de nombreux problèmes du magnétisme des solides.Le borate de fer, FeBO3 est un antiferromagnétique possédant un plan de facile aimantation et un faible ferromagnétisme. Les caractéristiques du borate de fer sont radicalement modifiées par substitution isomorphe fer – gallium diamagnétique.Nous avons mis au point une route de synthèse de monocristaux FexGa1-xBO3 de haute qualité. Comme principales techniques expérimentales, nous avons choisi les résonances magnétiques électronique (RME) et nucléaire (RMN). Selon le contenu du fer, nous avons observé:(i) la résonance antiferromagnétique, (ii) la résonance de clusters magnétiques et (iii) la résonance paramagnétique électronique (RPE). Les différents états magnétiques ont été identifiés et leurs caractéristiques – la température de Néel, le champ de Dzyaloshinskii-Moriya; les paramètres de l’hamiltonien de spin de Fe3+, etc.– ont été déterminées. La coordinence et la symétrie de sites de 11B et 71Ga ont été précisées par RMN à rotation sous l’angle « magique » (MAS). Moyennant la simulation des spectres de RPE et de MAS RMN, à l’aide de codes mis au point ad hoc, les distributions de paramètres dues au désordre local ont été déterminées. L’analyse théorique, tenant compte de contributions du champ cristallin et de l’interaction dipôle-dipôle, permet d’expliquer l’anisotropie magnétocristalline de volume et de surfaceThe thesis is concerned with synthesis and studying magnetic properties of iron-galliumborates, FexGa1-xBO3 with [0 supérieur ou égal à x supérieur ou égal à 1]. These materials are promising candidates for applications;besides, occurrence of different types of magnetic ordering, depending on x, makes them suitablefor treating a number of fundamental problems in solid state magnetism.Iron borate, FeBO3 is a two-sublattice easy-plane antiferromagnet with weakferromagnetism. Physical characteristics of iron borate are radically modified by isomorphoussubstitution of a part of iron by diamagnetic gallium.We have started with developing a synthesis route for growing high-quality FexGa1-xBO3single crystals. As main experimental techniques, we have chosen Electron and Nuclear MagneticResonances (EMR, NMR). Depending on iron contents and temperature, we have observed:(i) Antiferromagnetic, (ii) Cluster Magnetic and (iii) Electron Paramagnetic Resonance (EPR).Different magnetic states have been identified and their characteristics: Néel temperature,Dzyaloshinskii-Moriya field; spin Hamiltonian parameters of isolated Fe3+ ion, etc., have beendetermined. Coordination and site symmetry of 11B and 71Ga nuclei have been specified by meansof Magic Angle Spininng (MAS) NMR. Carrying out computer simulations of EPR and MASNMR spectra with laboratory-developed codes, the parameter distributions caused by localdisorder have been determined. Theoretical analysis taking into account crystal field and dipoledipolecontributions allow interpreting volume and surface magnetocrystalline anisotropy of thecrystals
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POSSANI, RAFAEL G. "Re-engenharia do software SCMS para uma linguagem orientada a objetos (JAVA) para uso em construções de phantoms segmentados." reponame:Repositório Institucional do IPEN, 2012. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9933.
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Made available in DSpace on 2014-10-09T12:32:58Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:06:11Z (GMT). No. of bitstreams: 0
Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Bell, Stacey. "Site-directed spin-labelling of proteins for EPR spectroscopy : application to protein complexes and development of new methods for cysteine rich proteins." Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/8237.
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The work described in this thesis is an experimental study into the application of Electron Paramagnetic Resonance (EPR) Spectroscopy for the study of biological systems. Using a variety of methods of site-directed spin-labelling (SDSL), this thesis aims to explore long range structure in an assortment of recombinant and native proteins, and complexes thereof. The work described in this thesis covers all aspects of the work, from experimental design, molecular biology and cloning, protein expression and purification, as well as functional characterisation, and finally EPR distance measurements, data analysis and interpretation. Challenges and pitfalls will also be addressed. Chapters 1 and 2 introduce EPR spectroscopy, and its application in the study of long range structure in biological systems. The experimental techniques employed throughout this thesis are also introduced. Chapter 3 details an investigation into the complement C3b:factor H complex. This chapter addresses the challenges associated with the SDSL of cysteine rich proteins. Utilising hidden cysteine residues in native proteins for spin-labelling purposes will also be addressed. Chapter 4 looks at the interactions of the human myosin regulatory light chain (RLC) with cardiac myosin binding protein C (cMyBP-C). Optimisation of expression and purification protocols will be the focus, as well as addressing issues with protein solubility and spin labelling efficiencies. Chapter 5 explores the development of new methods of SDSL, for the specific labelling of cysteine rich proteins. The ability of Escherichia coli to read through the amber stop codon will be exploited for the incorporation of unnatural amino acids for labelling purposes, and novel spin labels, specific for labelling cysteine pairs tested in several model systems. Furthermore, native paramagnetic centres in recombinant proteins will be explored as potential labelling sites.
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Nemat-Nasser, Syrus C. "A high-pressure apparatus with in situ electron spin resonance probe for the characterization of phase transitions in magnetic materials and superconductors /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p9956444.
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Faraj, Achraf Al. "Biodistribution and biological impact of nanoparticles using multimodality imaging techniques : (Magnetic resonance imaging)." Phd thesis, Université Claude Bernard - Lyon I, 2009. http://tel.archives-ouvertes.fr/tel-00696221.
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As novel engineered nanoparticles such as single-walled carbon nanotubes (SWCNT) are extensively used in nanotechnology due to their superior properties, it becomes critical to fully understand their biodistribution and effect when accidently inhaled. There fore, development of animaging technique which allow longitudinal in vivo follow-up of SWCNT effect based on their intrinsic properties is highly desirable. Non invasive free-breathing hyperpolarized 3He lung MRI protocol was developed complementary to proton systemic MR protocol to allow monitoring SWCNT based on their intrinsic iron impurities after intrapulmonary exposition. Combined toproton lung MRI and ex vivo optical and electron microscopy at different time points, this protocol represents a powerful multimodality imaging techniques which allows a full characterization of the biodistribution and biological impacts of iron containing SWCNT. SWCNT was found to produce granulomatous and inflammatory reactions in a time and dose dependent manner with their bio persistenc eafter intrapulmonary exposition.From biological impact evaluations after intrapulmonary exposition towards biomedical applications, SWCNT hold promise for applications in nanomedicine field with their distinct architecture and their novel physicochemical properties. The biodistribution and pharmacological profile of various well-dispersed pristine and functionalized SWCNT were assessed in blood and target tissues after their intra venous administration by longitudinal in vivo susceptibility weighted MRI and their potential effect on liver metabolism by ex vivo HRMAS 1H NMR. No presence ofacute toxicological effect (variation in liver metabolism) was observed confirmed by the absence of clustering in NMR spectra using Principal Component Analysis (specific biomarkers of toxicity).
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Khazen, Khashayar. "Ferromagnetic resonance investigation of GaMnAs nanometric layers." Paris 6, 2008. https://tel.archives-ouvertes.fr/tel-00329331v2.
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Cette thèse est dédiée à l’étude des propriétés magnétiques des couches nanométriques de GaMnAs par Résonance ferromagnétique (RFM). Trois séries des échantillons sont étudiées afin d' élucider l’influence des contraintes, la concentration des trous et la concentration de manganèse, sur les propriétés magnétiques de GaMnAs. Dans la première série, les échantillons de Ga1-xMnxAs avec x=0. 07 déposés sur les substrats de GaAs (en compression) et GaInAs (en extension) sont étudiés. Les résultats des mesures de l’aimantation, la résistivité et l’effet de Hall sont présentés. Les axes faciles de l’aimantation et le type d’anisotropie sont déterminés par mesures RFM. Les variations angulaires des spectres RFM sont étudiées en détails et le facteur g, la température de Curie et les constantes d’anisotropie sont déterminées en fonction de la température. La résonance des ondes de spin sont également observées et interprétées. Les observations sont comparées aux modèles phénoménologiques proposés et le spin stiffness et l’intégrale d’échange entre les ions de manganèse sont déduits. La deuxième étude concerne une série des échantillons de GaMnAs avec même niveau de dopage de Mn de 7% concentration atomique dont les concentrations de trous étaient variées via la passivation par l’hydrogène. Les concentrations des trous sont déduites des mesures d’effet Hall sous la condition de forts champs appliqués et à très basses températures. Les concentrations de trous mesurés correspondent aux différents régimes de conductivités ; de régime isolant aux régimes bande d’impureté et métallique. Les échantillons sont caractérisés par magnétométrie SQUID et les mesures de résistivité. L’aimantation en fonction de la concentration de trous est comparée aux prédictions du modèle RKKY. Les mesures de ERDA sont appliquées à la fin de déterminer la concentration de hydrogène dans l’échantillon ferromagnétique avec la concentration de trous la plus faible dans la série. La structure des domaines de cet échantillon est étudiée par microscopie magnéto-optique d’effet Kerr. Les spectres RFM sont analysés en détail et la concentration de trous correspondant à la formation de l’ordre ferromagnétique est estimée à 1019cm-3. Les facteurs g dépendent de la concentration de trous et la température. La relation entre les facteurs g et les polarisations de trous des échantillons calculées théoriquement est présentée. L’étude d’anisotropie des échantillons est fournie la détermination des constantes d’anisotropie magnétocrystallines en fonction de la concentration de trous et la température. Leurs variations sont comparées aux modèles théoriques. Les surfaces d’énergie sont déduites des constantes d’anisotropie magnétocrystallines mesurées, sont calculées en fonction de l’aimantation et les orientations et les grandeurs du champ appliqué. L’influence d’augmentation du niveau de dopage, de 7% à 21% concentration atomique est étudiée dans la troisième série des échantillons. Contrairement des prédictions théoriques, la température de Curie n’est pas augmentée en dessous de 180K. Les paramètres de RFM sont comparés à ceux des échantillon standard de GaMnAs avec 7% concentration atomique de Mn. La raison est attribuée au haut niveau de la compensation magnétique. Les mesures sont également comparées aux prédictions théoriques basées sur les approximations de champ moyen. La relaxation de l’aimantation est étudiée en fonction des contraintes, la concentration de trous et Mn aussi bien que la température. Les constantes de damping, sont trouvées d’être anisotropes. Cette anisotropie, dépend fortement aux procès dont contribution est la dominante pour une configuration particulaire du systèmeThis thesis is dedicated to the study of the magnetic properties of GaMnAs nanometric layers by the ferromagnetic resonance (FMR) technique. Three series of samples have been studied to investigate independently the influence of the strain, the hole concentration and the Mn concentration on the magnetic properties of GaMnAs. In the first series, the Ga1-xMnxAs samples with x=0. 07, grown on GaAs (compressive strain) and GaInAs (tensile strain) substrates are studied. The results of magnetization, resistivity and Hall effect measurements are presented. From the FMR measurements the easy axes of magnetization and the type of magnetic anisotropy are determined. The angular variations of the FMR spectra are studied in detail and the g-factor, Curie temperature and the magnetocrystalline anisotropy constants are determined as function of temperature. Spin wave resonance were equally observed and interpreted. The observations are compared to the proposed phenomenological models and the spin stiffness and the exchange integral between the Mn ions are deducedThe second study concerns a series of GaMnAs samples with the same Mn doping level of 7% atomic concentration in which the hole concentrations was varied via a hydrogen passivation technique. The hole concentrations are deduced from Hall effect measurements in high fields and low temperatures. The measured hole concentrations correspond to different conductivity regimes from insulating to impurity band and metallic regimes. The samples are characterized by SQUID magnetometry and resistivity measurements. The magnetization as a function of hole concentration is compared to the predictions of the RKKY model. ERDA measurements are performed to determine the concentration of hydrogen in the ferromagnetic sample with the lowest hole concentration. The domain structure of this samples is investigated by magneto-optical Kerr effect microscopy. The FMR spectra are analyzed in details and the hole concentration corresponding to the onset of ferromagnetism is estimated to 1019cm-3. The g-factors depend on the hole concentration and temperature. The relation between the g-factors and the theoretically calculated hole polarization of the samples is presented. The anisotropy studies of the samples have provided the investigation of the magnetocrystalline anisotropy constants as a function of the hole concentration and the temperature. Their variations are compared to the theoretical models. The energy surfaces deduced from the measured magnetocrytalline anisotropy constants are calculated as a function of magnetization and applied field orientations and magnitudes. The influence of increasing the doping level from 7% to 21% atomic concentration is studied in the third series of samples. Contrary to the theoretical predictions, the critical temperature is not increased above 180K. The FMR parameters are compared to those of standard GaMnAs sample doped with 7%atomic concentration of Mn. The reason for no further increase in TC is attributed to high level of magnetic compensation. The measurements are also compared to the theoretical predictions based on the mean field approximations. The relaxation of the magnetization is studied as a function of strain, hole concentration, Mn concentration as well as temperature. The damping constants were found to be anisotropic. This anisotropy however depends strongly on the process whose contribution is dominant for a specific configuration of the system
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Effenberger, Fernando Bacci. "Nanomateriais magnéticos para aplicações em terapia e imagem." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/46/46136/tde-10092012-111655/.
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Em virtude da grande atenção que os nanomateriais magnéticos recebem atualmente, cientistas de diversas áreas (química, física, engenharia e medicina) vêm estudando as propriedades e as aplicações de nanopartículas magnéticas, gerando uma grande demanda por materiais de alta qualidade. As propriedades dos nanomateriais magnéticos são fortemente dependentes de suas propriedades intrínsecas (p. ex., composição, cristalinidade, tamanho e forma) e das interações entre as partículas, portanto sofrendo grande influencia do método de síntese aplicado. Várias técnicas para produção de nanomateriais magnéticos são conhecidas, porém muitas delas geram materiais com baixa qualidade no que diz respeito a tamanho médio e faixa de distribuição de tamanhos nas amostras. O presente trabalho teve por objetivo estudar a síntese de nanopartículas de magnetita (Fe3O4) por decomposição térmica do acetilacetonato de ferro (III), um método já conhecido e que se destaca pela alta qualidade de amostras (elevado controle no tamanho, estreita distribuição de tamanhos e forma bem definida), porém de alto custo. Estudamos a influência dos aditivos normalmente empregados no meio reacional no controle da morfologia, tamanho e polidispesão das amostras preparadas e sugerimos outros reagentes (monoóis, dióis e polióis) em busca de novas condições de síntese de nanopartículas magnéticas com morfologia e tamanho controlados. Do ponto de vista prático, reduzimos o custo de produção de nanomateriais magnéticos de alta qualidade pela utilização de aditivos mais baratos e de fácil obtenção no mercado. Os diferentes aditivos propostos modificaram as propriedades magnéticas ligadas às interações dipolares entre as partículas magnéticas. A influência dos aditivos foi testada em crescimentos sucessivos usando partículas de magnetita já formadas como sementes. O perfil de crescimento se mostrou diferente em função dos reagentes empregados e as amostras tiveram suas interações hiperfinas medidas para avaliar a relação entre o tamanho e aumento da cristalinidade das partículas formadas. O revestimento das partículas de magnetita com ouro foi estudado buscando aumentar a biocompatibilidade e proteger os núcleos magnéticos, porém as estruturas core-shell obtidas não apresentaram comportamento superparamagnético. Os estudos das interações hiperfinas mostraram perda da cristalinidade após o revestimento com ouro. As partículas de magnetita foram aplicadas para produzir calor através de hipertermia magnética, sendo que a interação entre as partículas se mostrou fundamental para o aumento do calor gerado. Outra aplicação biomédica testada foi o uso das partículas de magnetita como contraste para imagem por ressonância magnética nuclear. Nossas amostras mostraram desempenho semelhante às partículas disponíveis no mercado a alto custoMagnetic nanomaterials have received a great deal of attention from scientists of various research fields (chemistry, physics, engineering and medicine) that have been studying the properties and applications of magnetic nanoparticles, generating a great demand for high quality materials. The magnetic properties of nanomaterials are strongly dependent on their intrinsic properties (eg., composition, crystallinity, size and shape) and the interactions between particles, therefore are influenced by the method of synthesis applied. Various techniques for the production of nanomarerials are known, but many of them produce poor quality materials, regarding to the average size, broad size distribution range and variable shape. The present work aimed to study the synthesis of magnetite nanoparticles (Fe3O4) by thermal decomposition of iron (III) acetylacetonate, a method already known for delivering high quality samples (high control on the size and narrow size distribution ), but at high cost. We studied the influence of additives normally used in the reaction medium to control the morphology, size and polydispersion and suggested other reagents (monols, diols and polyols) in the search for new conditions to synthesize magnetic nanoparticles with controlled size and morphology. From a practical viewpoint, we have reduced cost of producing high-quality magnetic nanoparticles using cheaper additives available on the market. The different additives used in the synthetic protocol modified the magnetic properties which are related to dipolar interactions between magnetic particles. The influence of additives was tested in successive growth using magnetite particles previously formed as seeds. The growth profile showed to be different depending on the additives used and the samples had their hyperfine interactions measured to estimate the relationship between the size increasing and the crystallinity of the particles formed. The coating of the magnetite particles with gold was studied in order to increase the biocompatibility and to protect the magnetic core. In this case, the core-shell structure lost the superparamagnetic behavior. Studies of hyperfine interactions showed the loss of crystallinity after coating the nanoparticles with gold. The synthesized particles were used to produce heat by magnetic hyperthermia, where the interaction between the particles proved to be crucial to increase the generated heat. Another biomedical application tested was the use of magnetite particles as contrast agent for magnetic resonance imaging. Our samples showed similar performance to the commercially available particles at high cost.