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1
Emi, Keiji. "Microscopic Environmental Studies on Solute-solvent Interaction by Using Pulsed ESR and CW-ESR." Kyoto University, 1998. http://hdl.handle.net/2433/182386.
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Kyoto University (京都大学)0048
新制・課程博士
博士(人間・環境学)
甲第7506号
人博第46号
10||156(吉田南総合図書館)
新制||人||11(附属図書館)
UT51-98-U173
京都大学大学院人間・環境学研究科人間・環境学専攻
(主査)教授 山内 淳, 教授 堀 智孝, 助教授 田村 類
学位規則第4条第1項該当
2
Kirui, Joseph Kiprono. "ESR study of DMTM(TCNQ)₂." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29191.
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The ESR g-value and susceptibility measurements for DMTM(TCNQ)₂ have been studied as a function of angle made by crystal with magnetic field and temperature. The angular dependence of g-value is fitted to g² = α+βcos2θ - γsin2θ for three orthogonal directions of crystal rotation. The principal g-values are close to those expected for TCNQ compounds: g₁ = 2.0034, g₂ = 2.0030, g₃ = 2.0024. The susceptibility as a function of temperature agrees with bulk susceptibility measurements except that the maximum position occurs at about 30 K. The results of Oostra et al. for bulk susceptibility showed a maximum at around 50 K. The phase transition
reported by Visser et al. at 272 K is observed in the ESR data as a 15% decrease in susceptibility. The linewidth is remarkably anisotropic typical of TCNQ salts. The phase transition study is done for two orientations
of the crystal with the magnet field. In one of the orientations the linewidth narrows from 0.15 to 0.11 gauss and in the other it narrows from 0.24 to 0.18 gauss. In the former case there is a growth of a second line due to the twinned stack; transformation twinning takes place at the phase transition. A small level-crossing interaction is inferred from the change in relative intensities of the lines near the crossover.Science, Faculty of
Physics and Astronomy, Department of
Graduate
3
Wilson, Peter John. "Electrochemical ESR of modified electrodes." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47717.
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Maj, Stanislaw Paul. "ESR studies of organo-halide radicals." Thesis, University of Leicester, 1985. http://hdl.handle.net/2381/33795.
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Exposure of a range of dilute solutions of halogenobenzenes in fluoro-trichloromethane to 60Co y-rays at 77 K gave the corresponding cations characterised by their ESR spectra. The approximate spin-densities on the halogens were greater than predicted by comparison with neutral x-bromo radicals and increased from ca, 8% for PhF+ to 23% for PhCl+, 30% for PhBr+ and 46% for PhI+ In accord with the fall in the ionization potential for this series of halogen. For PhBr+, replacement of para hydrogen by Br, OH and SH gave a steady fall in spin-density on Br reflecting increasing n delocallsation onto the para substituent. Evidence for dimer cation formation in concentrated solutions is presented. The major species obtained from benzyl chloride suggested a preferred conformation with the chlorine close to, but not in, the plane of the benzene ring, with a significant barrier for the in-plane site, in contrast with benzyl bromide with strong hyperfine coupling to bromine [Chapters 3, 4 and 9]. Exposure of dilute solutions of Me2C(Br)C(Br)Me2 In CD3OD and MeTHF to 60Co y-rays at 77 K gave the radical Me2CC(Br)Me2. From changes in the e.s.r. spectrum of this radical, it is deduced that the stable structure is asymmetric, but that the rate of migration of bromine between the two equivalent sites becomes fast on the e.s.r. time-scale at ca. 100-1 [Chapter 6]. Evidence is given for the 1,2-intramolecular proton shift in the interconversion of isobutyl to tert-butyl radicals. The parent material was dissolved in a variety of matrices and exposed to 60Co y-rays at 77 K. The reaction was observed using an in-cavity Proportional, Integral and Differential (PID) temperature control system [Chapter 5]. A single crystal of ethyl iodide was grown and irradiated at 77 K with a a 60Co y-ray source. The spectra were orientation dependent but it was not possible to determine the principal g-values and the elements of the hyperfine tensor [Chapter 7]. 1-Bromo adamantane was dissolved in a variety of deuterated matrices and exposed to 60Co y-rays at 77 K. No firm conclusions can be drawn regarding the single proton coupling of ca. 65 G to the bromine. Exposure of dilute solutions of m-dinitrobenzene or s-trinitrobenzene in methyltetrahydrofuran to 60Co y-rays at 77 K gave two species at 77 K. One, favoured at low doses, had features characteristic of mono-anions with the unpaired electron localized on one nitro-group. At high 7-ray doses a second species with triplet state characteristics grew at the expense of the first. The average separation between the two unpaired electrons was estimated to be 5-6 A.
5
Rowland, Ian J. "Halogen 6* radicals : an ESR study." Thesis, University of Leicester, 1988. http://hdl.handle.net/2381/33878.
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The main objective of the study was to characterise, by electron spin resonance (ESR) spectroscopy, novel halogen containing a* radicals. These species are formed by ?-irradiation in a variety of halogen containing systems at liquid nitrogen temperatures. In Chapter One, a brief description of the first halogen a* radical to be identified, the Vx centre in potassium chloride (C12.-), is given in order to illustrate the general magnetic properties of the species. The dependence of these properties on the host matrix is also described. Accepted radiation damage mechanisms are presented with particular reference to dihalogen a* radicals. Some theoretical aspects of the ESR experiment is discussed in Chapter Two which explains briefly some of the phenomena encountered in the study. Sample preparation and analysis are also mentioned. Chapter Three describes the characteristics of the simplest halogen containing a* radical: the hydrogen halide radical anion. Hydrogen fluoride, hydrogen chloride, hydrogen bromide and hydrogen iodide radical anions isolated in a variety of host matrices are reported. The large matrix dependence of their magnetic parameters is explained in terms of intermolecular hydrogen bonding to the halogen. Attention is focused on nitrogen-halogen a* radicals in Chapter Four, where they are shown to be radiolytically formed in ammonium halides, mono, di and trialkylammonium iodides and monoalkylammonium bromides. Alkylamanium chloride radicals could not be identified. Chapter Five primarily explores the effect of the halide counter ion on the solid-state radiolysis of some tetraalkylammonium, trialkylsulphonium and trialkylsulphoxonium cations. During the course of the investigation, sulphur-halogen a* radicals are identified in the trialkylsulphonium salts after annealing. The last chapter investigates the factors which determine the type of species formed following electron capture by carbon halogen bonds. Both adducts and a* radicals are characterised and with particular reference to the specific example of iodoacetamide, consideration is given to the factors influencing their stability.
6
Bakker, M. G. "ESR studies on some naphthalene derivatives." Thesis, University of Canterbury. Chemistry, 1985. http://hdl.handle.net/10092/8639.
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ESR Spectroscopy has been used to study conformational interconversion and addivity relationships in a number of series of naphthalene derivatives. Oscillation of the alkyl rings in 1,2,3,6,7,8-hexahydropyrene ions, and the ions of the related 5, 6 and 7 membered ring compounds has been studied. The temperature dependance of the ESR spectra have been used to assign the coupling constants. The aromatic ring coupling constants in the asymmetric compounds have been assigned on the basis of an additivity relationship.
The ESR spectra of a number of methylnaphthalene anions have been recorded and analysed to give the coupling constants. Improved additivity relationships for both the proton and methyl coupling constants have been determined. The temperature dependence of the spectrum of 1,2,3,4-tetramethylnaphthalene has been analysed. In terms of an interconversion between a tight and loose ion pair.
The ESR spectra of a number of methylnaphthalene cations have been generated using AlCl₃/SO₂ and their spectra recorded and analysed. For those methylnaphthalenes which did not have methyl substituents in the 1 and 4 or 1 and 5 positions, a series of compounds with g=2.008 were recorded. Evidence is presented to show that these compounds are methyl derivatives of naphtho [1,8-cd]-1,2 dithiole. An additivity relationship for the proton coupling constants of these compounds has also been found. ESR spectra from the methylperylenes formed in the Scholl Condensation of the methylnaphthalene cations were also observed and analysed
Changes in the ESR spectra of 1,8-dimethylnaphthalene and octamethylnaphthalene were ascribed to the effect of hindered rotation of the methyl groups.
Coupling constants for the ESR spectra of tetracyclopentanaphthalene have been determined.
7
Davidson, Iain G. "ESR studies on γ-irradiated foods." Thesis, University of Aberdeen, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327924.
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Chapter 1 discusses the history, applications and effects (both beneficial and hazardous) of food irradiation and the techniques developed to detect irradiated foods. The basic radiation chemistry of major food components is reviewed. The preparation of 3,5-dimethyl-4-nitrosopyridine-1-oxide (DMNPO) and its dichloro- and dibromo- derivatives is described. Spin trapping of a variety of free radicals by DMNPO showed it to be an efficient trap for carbon-centred radicals but it did not form stable adducts with oxygen-centred radicals at room temperature as had been previously reported. The esr spectra were complicated by couplings arising from the hydrogens and nitrogen of the trap. The dichloro- and dibromo-analogues gave simpler spectra but were much more difficult to isolate. The effects of ionising radiation on spices and the methods used to detect these effects are reviewed. The measurement of free radical concentrations by esr spectroscopy was examined as a dosimetric method of identifying γ-irradiated spices. This proved to be impracticable because of the relatively rapid decay of the radicals and the variation in base-line radical concentrations. The short lived free radicals produced by irradiation were found to arise from the oleoresins. Identification of these radicals was attempted by irradiating the oleoresins and their major components, followed by spin trapping. In some cases, hydrogen abstraction gave the same radicals as those produced by irradiation. Separation of the spin adducts, formed from oleoresin components, by reverse phase HPLC is also described. Irradiation of food is known to cause destruction of vitamins. However, the processes involved are not fully understood. The solid state radiation chemistry of vitamins was investigated by spin trapping and esr spectroscopy. Irradiation of bones produces stable free radicals with characteristic esr spectra. It was shown that measurement of free radical concentrations in irradiated bones by esr spectroscopy could provide a dosimetric technique as the radical concentrations were stable and proportional to the applied dose.
8
Kanschat, Peter. "ESR und spinabhängige Rekombination in mikrokristallinem Silizium." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=962370657.
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Moll, Klaus-Peter. "Mobilität von ESR-Spinsonden nach epikutaner Applikation." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972617426.
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Mamat, Che Rozid. "Director disorder in liquid crystals : ESR investigations." Thesis, University of Southampton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442855.
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Kümmerer, Hans-Jürgen. "Hochfeld-ESR und Doppelresonanz an austauschgekoppelten Spinsystemen." [S.l. : s.n.], 2004. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11513989.
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Moll, Klaus-Peter. "Mobilität von ESR-Spinsonden nach epikutaner Applikation." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2004. http://dx.doi.org/10.18452/15085.
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Im Mittelpunkt der Arbeit stehen Betrachtungen zur Mobilität von epikutan applizierten ESR-Spinsonden, sowie noch weitgehend ungeklärte Fragen zu den Wechselwirkungen zwischen Liposomen und Haut. Dazu gehört vor allem die Frage nach der Integrität von epikutan applizierten Liposomen. Weiterhin wurden die Auswirkungen von Liposomen auf die Flexibilität der intercorneozytären Lipiddoppelmembranen, die Penetration von ESR-Spinsonden unterschiedlicher Hydro-/Lipophilie, sowie die Mobilität von ESR-Spinsonden in der Haut und die Polarität ihrer Mikroumgebung untersucht. Als wichtigste Ergebnisse der Arbeit sind folgende Punkte zu nennen. Liposomen verlieren nach epikutaner Applikation ihre Integrität und bilden auf dem Stratum corneum einen Lipidfilm aus. Dabei nimmt nicht nur der Dispersitätsgrad der Liposomen sondern auch die Flexibilität ihrer Membranen ab. Entgegen der Erwartung führt die epikutane Applikation von liposomalen Zubereitungen nicht zu einer stärkeren Fluidisierung der intercorneozytären Lipiddoppelmembranen als Phosphatpuffer, wohingegen durch Ölsäure eine deutlich stärkere Fluidisierung erreicht wird. Liposomen mit rigiden Membranen führen zu höheren Spinsondenkonzentrationen in der Haut als Liposomen mit fluiden Membranen, und solche aus partialsynthetischen Lipiden führen zu höheren Konzentrationen als Liposomen aus Sojabohnenphospholipiden. Der Vergleich der Penetration von ESR-Spinsonden in die Haut nach epikutaner Applikation von Liposomen mit der Penetration der Spinsonden aus anderen topischen Zubereitungen zeigt, dass eine generelle Aussage zur Penetrationsförderung durch die Anwendung von Liposomen problematisch ist. Es konnte ein Polaritätsprofil der Mikroumgebung von Spinsonden in der Haut erstellt werden, das belegt, dass die Polarität in der Epidermis geringer ist als in der Dermis. Mit zunehmender Inkubationsdauer konnte ein Anstieg der Polartiät in den Hautproben nachgewiesen werden. Die Anwendung eines durch Freed et al. entwickelten Computerprogramms zur Bestimmung von Rotationskorrelationszeiten sich langsam bewegender Moleküle aus Spektren, die mittels spektral-räumlich aufgelöster ESR-Tomografie erhalten wurden, erlaubt die Erstellung von Viskositätsprofilen der oberen Hautschichten in Abhängigkeit von den epikutan applizierten Zubereitungen. Die Bandbreite der ortsabhängig berechneten Rotationskorrelationszeiten von CAT-1 und TEMPOL in der Haut nach epikutaner Applikation der Spinsonden in Liposomen reicht von 5,94 ns bis 1,97 ns. Dies entspricht einer Viskosität der Mikroumgebung von 118 bis 26 mPas.The present thesis was focused on the mobility of epicutaneously applied ESR spinprobes and open questions concerning the interactions between liposomes and skin e.g. the integrity of liposomes after epicutaneous application. Additionally the effect of liposomes on the flexibility of lipid membranes in the stratum corneum, the penetration of ESR spinprobes with different hydrophilic / lipophilic properties as well as the mobility and polarity of the microsurrounding of ESR spinprobes in the skin were investigated. The main results of the investigations are mentioned in the following. There will be a loss of integrity of epicutaneously applied liposomes and a lipid film will be formed on the stratum corneum. At the same time the degree of dispersity and the flexibility of their membranes decreases. Contrary to the expectation the application of liposomal formulations does not lead to a stronger fluidity of the lipid membranes of the stratum corneum than the incubation of the samples with phosphate buffer, whereas the incubation with oleic acid results in a substantial increase of the fluidity. The application of ESR spinprobes in liposomes with rigid membranes leads to higher spinprobe concentrations in the skin than with liposomes having fluid membranes. At the same time the application of liposomes made from semi-synthetic lipids leads to higher concentrations of the spinprobe in the skin, than the application of liposomes made from soybean phospholipids. The penetration of spin probes into the skin out of liposomes compared to other topical preparations shows, that a general statement concerning the penetration enhancing effect of liposomes is difficult. On using the ESR tomography a polarity profile of the skin was obtained, showing that the polarity in the epidermis is lower than in the dermis. With increasing incubation time of the skin samples the polarity increases. The application of a computer program, developed by Freed et al. in order to determine rotational correlation times for slowly tumbling molecules, to spectra, obtained from spectral-spatially resolved ESR tomography, allowed the establishment of viscosity profiles for the upper skin layers in dependency on the applied formulations. The range of the calculated rotational correlation times of CAT-1 and TEMPOL in the skin reaches from 5.94 ns to 1.97 ns. This corresponds to a viscosity of the spinprobes microsurrounding from 118 to 26 mPas.
13
Bersani, Irene <1982>. "H2 production from steam ethanol reforming (ESR)." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3844/1/Bersani_Irene_tesi.pdf.
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Bersani, Irene <1982>. "H2 production from steam ethanol reforming (ESR)." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3844/.
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Trousson, P. M. R. "Computer-based numerical analysis applied to ESR spectroscopy." Thesis, University of Leicester, 1985. http://hdl.handle.net/2381/33959.
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Researches conducted with the help of the electron spin resonance spectroscopy have been very successful so far, in spite of some problems both in resolving power and in sensitivity. In order to overcome these, and to use the technique to its very far limits, we develop here a computer program which process the ESR data post-experimentaly. This work explains how to digitize and record the ESR spectra as well as how this software acts to reveal hyperfine splitting constants, the number of nuclei, and their spins out of complex spectra. This could be done by resolution enhancement (either addition of higher derivatives of the signal or linewidth narrowing by changing the lineshape function) or by CEPSTRAL analysis (modification of the ESR display in order to show out in a clearer may the hyperfine splitting constants). Other aids in the interpratation of spectra are obtained, with the same software, by addition or subtraction of experimental or simulated spectra, by reduction of the noise level and by simulation of spectra correct to second order and including quadrupolar corrections and non-colinear g and A tensors for systems with orthorhombic symmetry. In spite of the fact that the theory presented in the first part might strike one as familiar, we think worthwhile the effort of writting an entirely new computer program, as complete and versatile to use as possible, in order to match the major part of the needs encountered in the analysis of ESR results. Applications of the program have been performed to try to solve some puzzling ESR results. Evidences on the bridged structure of the ?-bromo radical (R2-CC(Br)-R'2) have been found, improvement of the resolution of spectra from spin-trap adduct radicals leads to better fingerprints of these compounds, and simulation of the spectrum from the Acetone radical cation enables us to determine the angle between the molecular bonds.
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Hinds, Chantal Simonette. "ESR studies of radical adsorbed on aluminosilicate catalysis." Thesis, Queen Mary, University of London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243865.
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Day, M. J. "Mechanistic studies using in situ electrochemical-ESR spectroscopy." Thesis, University of Liverpool, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384356.
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Taiwo, Fatai Adetokunbo. "Electron transfer effects in metalloproteins : an ESR study." Thesis, University of Leicester, 1988. http://hdl.handle.net/2381/33944.
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The metal chromophore in metalloproteins is identified as a high affinity site for dry electrons in conformity with previous studies. Relative electron affinities for such centres in a physiologically probable valence hybrid haemoglobin have been determined. A ratio of ca. 2.5 for the electron affinity of oxyhaemog1obin over methaemog1obin is explained in terms of structural differences in the constituent forms. The phenomenon of intersubunit electron transfer in similar systems is considered in terms of haem edge-to-edge minimum separation. The hydrogen peroxide complex of iron haemoproteins is characterised as an oxo compound of iron in the +4 oxidation state (ferryl), by electronic spectroscopy and ESR spectroscopy using low temperature ?-irradiation. Variations in ESR parameters during annealing are explained in terms of structural changes at the haem site. The electron-loss centre in many proteins, consequent upon ?-irradiation, is identified as the polypeptide amide nitrogen. The nitrogen-centred radical first formed may undergo hydrogen transfer reactions to give a terminal carbon-centred radical. ESR features for the nitrogen-centred radical are interpreted in relation to predominant secondary structures in the proteins examined. The catalytic mechanism of xanthine oxidase has been studied by the use of dry electrons as the reducing substrate. The series of intermediates obtained through annealing have ESR parameters identical with those for the enzyme-substrate intermediates obtained by other workers using chemical reducing substrates. A scheme of intramolecular electron transfer is proposed.
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Partridge, Richard Stuart. "ESR studies of radical damage to biological systems." Thesis, University of Leicester, 1992. http://hdl.handle.net/2381/33845.
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Part I; DNA and Higher Order Cell Systems The effects of a range of nitroxides on the radiation damage routes in frozen aqueous DNA have been studied by comparison with nitroxide free systems. The results show that nitroxides affect the yield of both primary and secondary radicals in this system. The differences between the effects of the nitroxides studied are attributed to steric effects. A range of spin-labelled polyanmionium cations (PACs) have been used to probe the motion of PACs when they are complexed with DNA. The results suggest that PACs experience virtually free movement along the DNA backbone. The effects of one of these spin-labelled PACs on irradiated frozen aqueous DNA have been studied. The results show that constraining the nitroxide group to be close to the DNA by attaching it to a PAC increases the effect of the nitroxide on irradiated DNA at low temperatures. At higher temperatures the spin-labelled PAC is less effective and it is proposed that this is due to less efficient diffusion of the spin-labelled PAC. The effects of 7-irradiation on frozen aqueous chicken erythrocyte chromatin and cell nuclei have also been studied in the presence and absence of oxygen. Different yields of both primary and secondary radicals are observed. The results show that the routes of radiation damage in frozen aqueous DNA are affected by the presence of histone proteins and higher order DNA-protein structures. Part II: Radicals Formed by Mechanical Damage to Bone The formation of radicals in compact bone (bovine), demineralized bone protein, and collagen by crushing at 77 K has been studied by comparison to the radicals formed by 7-irradiation. The results show that mechanical damage forms radicals almost exclusively in the organic component of bone. It is proposed that these radicals are formed by homolytic fission of bonds within the collagen matrix.
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Holanda, Junior Lino Martins de 1984. "Ressonância de spin eletrônico (ESR) em compostos intermetálicos." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277002.
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Orientador: Pascoal José Giglio PagliusoTese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
Made available in DSpace on 2018-08-24T07:35:54Z (GMT). No. of bitstreams: 1 HolandaJunior_LinoMartinsde_D.pdf: 3936724 bytes, checksum: 5a1e9e5453184dac769d35041c7414d0 (MD5) Previous issue date: 2014
Resumo: Nesta Tese de Doutorado desenvolvemos estudos de Ressonância de Spin Eletrônico (ESR) em compostos intermetálicos, incluindo os férmions pesados ?-YbAlB4, ?-YbAlB4 and ? -YbAlxFe1-xB4, os metais ?-LuAlB4, AlB2 e o isolante Kondo, FeSi. Nossas medidas foram feitas em um espectrômetro modelo ELEXSYS-CW Bruker usando uma cavidade ressonante do tipo TE102 para a faixa de frequência em banda X (?~ 9.4GHz). A técnica de Ressonância de Spin Eletrônico aplicada aos compostos Férmions pesados foi sempre um desafio devido a presença de fortes correlações eletrônicas que tendem a alargar as linhas de ESR. Porem, nos últimos anos essa técnica ganhou renovado interesse após a descoberta do sinal de ESR na rede Kondo YbRh2Si2. Após esse trabalho, ESR voltou a ser considerada uma técnica importante para explorar os elétrons 4f e suas interações microscópicas em compostos de terras raras, uma vez que ela sonda diretamente o íon no sitio da rede. A motivação desse trabalho e, portanto, usar a técnica de ESR para entender a dinâmica dos elétrons 4f pesados em uma rede de Kondo, para os novos compostos férmions pesados ?-YbAlB4, -YbAlB4 and ?-YbAlxFe1-xB4. Neste trabalho buscou-se utilizar a técnica de ESR nesses compostos para alcançar o entendimento microscópio dos critérios que permitem a observação de um sinal de ESR em férmios pesados. Alem do mais, quando o sinal e observado, a sonda de ESR e propícia para acompanhar a evolução dos elétrons 4f em altas temperaturas para quase-partículas pesadas em baixas temperaturas. Nossas observações nos permitiram propor um cenário qualitativo baseado na existência de um modo ressonante acoplado entre ons Kondo e os elétrons de condução. Nos discutimos as características físicas gerais para que compostos férmios pesados sejam candidatos a apresentarem tal sinal de ESR. Ainda neste trabalho, estudamos os compostos intermetálicos ?-LuAlB4, AlB2 e FeSi com propriedades estruturais ou eletrônicas similares as dos compostos ?-YbAlB4, ?-YbAlB4 and ?-YbAlxFe1-xB4 em busca de uma generalizac~ao mais abrangente do cenário proposto neste trabalho
Abstract: In this work, we have performed an Electron Spin Resonance (ESR) study in intermetallic compounds including the heavy fermions ?-YbAlB4, ?-YbAlB4 and ? -YbAlxFe1-xB4, the Fermi liquid metals ?-LuAlB4, AlB2 and the Kondo insulator, FeSi. Our measurements were made on a spectrometer Bruker CW-model ELEXSYS using a resonant cavity TE102 in X Band ( ?~ 9.4GHz). The Electron Spin Resonance technique applied to heavy fermions compounds was little explored due to difficulty in finding ESR signal of Kondo ions due to the large coupling between the resonating spins and conduction electrons. However, in recent years this technique has become focus of great attention especially after the discovery of the ESR signal in a Kondo lattice YbRh2Si2. In this context, ESR was brought to the scene as one of the main techniques to bring insights to this problem since it could probe directly the f electrons of Kondo ions and their interaction with the conduction electrons. The motivation of this work is to use the ESR technique to investigate new heavy fermions compounds and to understand when these systems can present an ESR signal. In these cases ESR can help to understand more deeply how localized f electrons at high-T evolve to itinerant heavy quasi-particles in a low-T metallic state. Our observations for ?-YbAlB4, -YbAlB4 and ?-YbAlxFe1-xB4, allowed us to make some qualitative speculations about this phenomenon and within this scenario, we propose some general characteristics for heavy fermions compounds to become candidates to present ESR signal. In this work we have also measured ?-LuAlB4, AlB2 and the Kondo insulator, FeSi, in an attempt to generalize the ESR results found for ?-YbAlB4, ?-YbAlB4 and ?-YbAlxFe1-xB4 to a more broad family of compounds
Doutorado
Física
Doutor em Ciências
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Lima, José Fernando de. "Simulação computacional de espectros de Ressonância Paramagnética Eletrônica de onda contínua." Universidade de São Paulo, 2001. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-26112008-125439/.
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Neste trabalho foi desenvolvido um programa para simular espectros de ressonância paramagnética eletrônica (RPE) de onda contínua de amostras policristalinas para tensores não coincidentes. O Hamiltoniano de spin utilizado inclui os tensores anisotrópicos g, interação hiperfina, divisão de campo zero e quadrupolar e o termo Zeeman nuclear isotrópico. O programa inclui várias tecnologias novas, tais como: segmentação de campo com teoria de perturbação de autocampo para localizar as posições de campo ressonante, os métodos de distribuição Espiral e Repulsão para determinar o conjunto de orientações e a interpolação bidimensional triangular para reduzir o número de orientações computadas. A conjunção desses algoritmos podem aumentar a velocidade e a precisão das simulações, especialmente na simulação de espectros de sistemas de spin de dimensões grandes. O programa foi testado em algumas situações reais e o resultado obtido pode ser considerado, em alguns casos, equivalente aos programas comerciais e, em outros casos, de qualidade superior.A computer program to simulate continuous wave electron paramagnetic resonance (EPR) powder spectra for noncoincident tensors has been developed. The spin Hamiltonian used includes anisotropic g, hyperfine interaction, zero field splitting and quadrupolar tensors and isotropic nuclear Zeeman term. The program includes a number of new technologies such as: field positions, spiral and repulsion methods for determining a set of orientations and triangular bidimensional interpolation to reduce the number of computed orientations. The conjunction of these algorithms can greatly increase the speed and the accuracy of simulations; especially in simulating powder spectra of spin systems of large dimensions. The program has been tested in some real situations and the obtained result can be considered, in some cases, equivalent to that of commercial software, in other cases, of superior quality.
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Sung, Raymond Chi Wai. "ESR studies of some iron(II) spin crossover complexes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0013/NQ52415.pdf.
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Morris, C. R. "An ESR and ENDOR study of heterocyclic radical cations." Thesis, University College London (University of London), 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.484304.
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Tann, Julie. "ESR studies of liquid phase radiolysis using spin traps." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328546.
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Haywood, R. M. "An ESR investigation of radical-induced damage to proteins." Thesis, University of York, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333719.
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Bartlett, Nick. "An ESR study of gamma-irradiated haemoglobin and DNA." Thesis, University of Leicester, 1985. http://hdl.handle.net/2381/33885.
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The first half of this thesis is concerned with studying the mechanism of autoxidation of haemoglobin and myoglobin. The paramagnetic Y-irradiated forms were used in this ESR study as the native protein is diamagnetic. On irradiation of haemoglobin distinct radical centres are seen representing the ? and ? subunits formed by electron addition to the FeO2 unit. The radical yields are found to be both pH and solvent dependent. A similar centre is formed on irradiation of myoglobin which is pH but not solvent dependent. Warming these centres above 77 K results in conversion into new centres with g-values approaching those of low-spin Fe(III). This conversion is interpreted mechanistically in terms of proton transfer from the distal histidine to the (FeO2) unit [assuming that the (FeO2)- unit is hydrogen-bonded to the distal histidine]. Further anneal results in the loss of signal in the g = 2 region and the growth of the high-spin Fe(III) signal at g = 6 as a result of loss of HO2-. To substantiate this theory experiments were done using haemoglobin Glycera which has a distal leucine instead of histidine (i.e. there are no hydrogen bonding sites available) . The primary centre formed in this case has a g-value which is close to that of superoxide. This indicates that the centres formed in haemoglobin and myoglobin have more spin-density on iron which would result if the centres were hydrogen bonded. The second half of the thesis concerns the mechanism of Y-irradiation damage in DNA. In irradiated frozen samples of DNA two ESR signals are found at 77 K. One has been shown to be the guanine cation, the other the thymine anion. Annealing these samples, in the absence of oxygen, results in the protonation of the anion and loss of the cation. Further anneal results in loss of signal altogether. As y-irradiation produces strand breaks in DNA it is surprising that no sugar radicals are detected. By incorporation of different additives I found that this mechanism of radical interconversion can be altered. Addition of electron scavengers such as CuCl2 prevented the formation of the thymine radicals without affecting the guanine cation yield. Addition of I had the reverse effect reducing the formation of guanine cations. However, addition of soft heavy metal compounds such as HgCl2 and cis Pt (NH3)2Cl2 resulted in the formation of a new radical which has identical parameters with radicals previously found in the sugar moiety of dCMP and in the thymine base moiety of dTMP.
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Aliabadi, Azar. "ESR and Magnetization Studies of Transition Metal Molecular Compounds." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-195440.
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Molecule-based magnets (molecular magnets) have attracted much interest in recent decades both from an experimental and from a theoretical point of view, not only because of their interesting physical effects, but also because of their potential applications: e.g., molecular spintronics, quantum computing, high density information storage, and nanomedicine. Molecular magnets are at the very bottom of the possible size of nanomagnets. On reducing the size of objects down to the nanoscale, the coexistence of classical properties and quantum properties in these systems may be observed. In additional, molecular magnets exist with structural variability and permit selective substitution of the ligands in order to alter their magnetic properties. Therefore, these characteristics make such molecules suitable candidates for studying molecular magnetism. They can be used as model systems for a detailed understanding of interplay between structural and magnetic properties of them in order to optimize desired magnetic properties.
This thesis considers the investigation of magnetic properties of several new transition metal molecular compounds via different experimental techniques (continuous wave electron spin resonance (CW ESR), pulse ESR, high-field/high-frequency ESR (HF-ESR) and static magnetization techniques).
The first studied compounds were mono- and trinuclear Cu(II)-(oxamato, oxamidato)/bis(oxamidato) type compounds. First, all components of the g-tensor and the tensors of onsite ACu and transferred AN HF interactions of mononuclear Cu(II)- bis(oxamidato) compounds have been determined from CW ESR measurements at 10 GHz and at room temperature and pulse ELDOR detected NMR measurements at 35 GHz and at 20 K. The spin density distributions of the mononuclear compounds have been calculated from the experimentally obtained HF tensors. The magnetic exchange constants J of their corresponding trinuclear compounds were determined from susceptibility measurements versus temperature. Our discussion of the spin density distribution of the mononuclear compounds together with the results of the magnetic characterization of their corresponding trinuclear compounds show that the spin population of the mononuclear compounds is in interplay with the J values of their corresponding trinuclear compounds.
The second studied compounds were polynuclear Cu(II)-(bis)oxamato compounds with ferrocene and ferrocenium ligands. The magnetic properties of these compounds were studied by susceptibility measurements versus temperature to determine J values. In addition, the ESR technique is used to investigate the magnetic properties of the studied compounds because they contain two different magnetic ions and because only the ESR technique can selectively excite different electron spin species. These studies together with geometries of the ferrocenium ligands determined by crystallographic studies indicate that the magnetic interaction between a central Cu(II) and a Fe(III) ions changed from the antiferromagnetic coupling to the ferromagnetic coupling when a stronger distortion of the axial symmetry in the feroccenium cation exists. Therefore, the degree of the distortion of the feroccenium cation is a control parameter for the sign of the interaction between the central Cu(II) ion and the Fe(III) spins of the studied compounds.
The last two studied molecular magnets were a binuclear Ni(II) compound (Ni(II)-dimer) and a cube-like tetranuclear compound with a [Fe4O4]-cube core (Fe4-cube). HF-ESR measurements enabled us to determine the g-factor, the sign, and the absolute value of the magnetic anisotropy parameters. Using this information together with static magnetization measurements, the J value and the magnetic ground state of the studied compounds have been determined. In Ni(II)-dimer, two Ni(II) ions, each having a spin S = 1, are coupled antiferromagnetically that leads to a ground state with total spin Stot = 0. An easy plane magnetic anisotropy with a preferable direction for each Ni(II) ion is found. For Fe4-cube, a ground state with total spin Stot = 8 has been determined. The analysis of the frequency dependence and temperature dependence of HF-ESR lines reveals an easy axis magnetic anisotropy (Dcube = -22 GHz (-1 K)) corresponding to an energy barrier of U = 64 K for the thermal relaxation of the magnetization. These results indicate that Fe4-cube is favorable to show single molecular magnet (SMM) behavior.
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Vecchi, Ilaria <1980>. "Studi ESR di sistemi complessi basati su cristalli liquidi." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/452/1/Vecchi_Scienze_Chimiche_XIXCICLO_ESAME2007.pdf.
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Vecchi, Ilaria <1980>. "Studi ESR di sistemi complessi basati su cristalli liquidi." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/452/.
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Wild, Mark Thomas. "Electron spin resonance dating of some volcanic rocks." Thesis, Lancaster University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387646.
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Li, Xiying. "FEW ELECTRON PARAMAGNETIC RESONANCES DETECTION TECHNIQUES ON THE RUBY SURFACE." Case Western Reserve University School of Graduate Studies / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=case1121296112.
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Burlon, Oliver. "Expression und Aufreinigung von Cx43-Halbkanälen für ESR-spektroskopische Untersuchungen." [S.l.] : [s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=964424657.
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Essen, Univ., Diss., 2001.Computerdatei im Fernzugriff. Buch-Ausg. u.d.T.: Burlon, Oliver: Expression und Aufreinigung von Connexinen für ESR-spektroskopische Untersuchungen / vorgelegt von Oliver Burlon.
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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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Podnieks, Emma Cameron. "Theory of Single Spin Detection Using an ESR-STM Technique." Thesis, University of Bristol, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486143.
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Cutting, Graham Russell. "An ESR study of the radicals occluded during emulsion polymerisations." Thesis, Lancaster University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360617.
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Davies, Carol Lesley. "An ESR and Endor study of radicals produced by antioxidants." Thesis, Cardiff University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428672.
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Youn, Jin Young. "Polymorphisms of FSHR, ESR and CYP19A1 and ovarian stimulation outcome." Thesis, Boston University, 2012. https://hdl.handle.net/2144/31627.
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Thesis (M.A.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
Ovarian stimulation is frequently used in many assisted reproductive technologies (ART) procedures to increase the number of dominant follicles. However, achieving the optimal response to ovarian stimulation without complications can be difficult. In our study, we predict that future ovarian stimulation procedures will be more individually catered to each patient. A study that established a predictor model for ovarian stimulation showed that genetic single nucleotide polymorphisms (SNP) are good predictive factors (Fauser et al., 2007). Thus the objective of this study was to determine if there was any association between the various parameters that measure the success of ovarian stimulation and FSHR, CYP19, ESRJ and ESR2 singe nucleotide polymorphisms (SNP). A total of two hundred and four women undergoing either in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) were genotyped to study the distribution of the different SNPs. Complete clinical information was available for a range of forty nine to seventy three women to study any association between genotype and basal FSH level (day 3), basal 17 -beta estradiol level, number of follicles, number of eggs and the level of 17-beta estradiol during hCG administration. The association was studied using the one way ANOVA test and linear regression model. There was a significant correlation between the CYP 19Al rs10046 genotypes and FSH level (p=0.004), number of follicles (p=0.03) and level of 17-beta estradiol during hCG administration (p=0.04). Also, FSHR rs2268263 genotype was significantly linked to FSH level between the G-allele group (A/G and G/G) and the homozygote A group (p=0.04). Taken all together, these results suggest that several genes-especially CYP 19AJ and FSHR rs2269263- play a significant role in determining the success of ovarian stimulation.
2031-01-01
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Iwamoto, Wellington Akira 1979. "Ressonância de spin eletrônico (ESR) em sistemas de dimensões reduzidas." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278522.
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Orientador: Pascoal José Giglio PagliusoTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-08-18T12:30:25Z (GMT). No. of bitstreams: 1 Iwamoto_WellingtonAkira_D.pdf: 11664469 bytes, checksum: 8790fc8d822330998a201e2b73fea42c (MD5) Previous issue date: 2011
Resumo: Sistemas de dimensões reduzidas possuem muitas aplicações tecnológicas. Há uma corrida para o desenvolvimento de dispositivos cada vez menores assim como para alcançar o controle e manipulação de dispositivos na escala nanométrica. Isto requer estudos sistemáticos de propriedades físicas em sistemas de tamanhos reduzidos. O foco deste trabalho é o estudo de Ressonância de Spin Eletrônico (ESR) em sistemas de dimensões reduzidas. Os materiais escolhidos para esse estudo foram filmes finos de GaAs, GaN dopados com Mn (GaMnAs e GaMnN), filmes finos amorfos de silício dopados com terras-raras a-Si:RE (RE = Y, Gd, Er e Lu) e nanopartículas (NPs) dopadas com impurezas magnéticas de terras-raras e metal de transição em matrizes metálicas Ag:R (R = Er, Yb e Mn) e em isolantes NaYF4:Gd. A finalidade desse estudo é explorar as propriedades magnéticas microscópicas destes sistemas. Os resultados das medidas em filmes de GaMnAs e GaMnN indicaram ausência de ferromagnetismo de longo alcance. Os experimentos de ESR mostraram ausência da relação entre largura de linha (?H) de ESR e a concentração de íons de Mn2+, mas foi observado que ?H aumenta conforme o nível de cristalinidade das amostras aumenta. Além disso, há um aumento de ?H em baixas temperaturas para os filmes com maior nível de cristalinidade, sugerindo uma correlação magnética de curto alcance entre os íons magnéticos se estabelecendo nessas amostras. Resultados similares foram encontrados para os filmes de GaMnN, exceto na medida de magnetização em função do campo magnético para GaMnN, a qual podemos observar ¿loops¿ ferromagnéticos abaixo de T ? 50 K ao contrário dos filmes de GaMnAs que não observamos nenhum ¿loop¿ ferromagnético em T = 2 K. Para outro grupo de filmes de a-Si:RE, foi estudado o efeito de redução na densidade de estados ligações pendentes (D0) nos filmes Si dopados com diferentes espécies de terras-raras (RE¿s) em função das diferentes concentrações. De acordo com nossos resultados, a dopagem com RE reduz a intensidade do sinal de ESR dos estados D0 com uma dependência exponencial das concentrações de RE¿s. As NPs de Ag:R e de NaYF4:Gd foram preparadas pelo método químico. Nós observamos uma forma de linha de ESR tipicamente Lorentziana consistente com os estados fundamentais dos íons de Er3+, Yb3+ e Mn2+ em simetria cúbica. O fator g encontrado para esses íons nas NPs é muito próximo ao observado em sistemas isolantes cúbicos, ao contrário do encontrado em metais, onde é observado um deslocamento de g. Além disso, não foi possível observar a relaxação Korringa para as linhas de ESR de Er3+, Yb3+ e Mn2+ no sistema de NPs que é observada, tipicamente, em metais. Logo, esses resultados nos levam a acreditar que a interação de troca (Jfs) entre os momentos localizados dos íons magnéticos (ML) e os elétrons de condução (c-e) está ausente no sistema de NPs de Ag:R, indicando que a natureza desta interação deveria ser reexaminada na escala nanométrica. Para as NPs de NaYF4:Gd, o controle do tamanho da partícula foi adquirido segundo a quantidade de rps = precursor/surfactantes. Não foi observada nenhuma evidência de cluster de Gd e observamos o espectro de ESR com as mesmas características já observadas no sistema bulk : três linhas de ressonância, sendo essas linhas com origens bem controvérsias, das quais não sabemos se é de origem de um campo cristalino de combinações de simetria cúbica com tetragonal ou mesmo rômbica ou mesmo de sítios de Gd3+ com simetrias mais baixas
Abstract: Reduced dimensions systems present many potencial technological applications. There is great interest in the development of small scale devices as well as in the control and manipulation at the nanoscale and in study of finite size on physical properties. The main goal of this work is the study of Electron Spin Resonance (ESR) in systems of reduced dimensions. The materials chosen for this study were thin films of GaAs, GaN doped with Mn (GaMnAs and GaMnN), amorphous silicon thin films doped with rare-earth a-Si:RE (RE = Y, Gd, Er and Lu) and nanoparticles (NPs) doped with magnetic impurities such as of rare earth and transition metal doped Ag:R (R = Er, Yb and Mn) and insulating NaYF4:Gd. The purpose of this study is to explore the microscopic magnetic properties of these systems. The results of the measurements in GaMnAs and GaMnN films indicated absence of long range ferromagnetism. the ESR results reveal no relationship between ESR linewidth (?H) and the Mn2+ concentration in this films. Instead, a broadening of the ESR ?H was found as a function of the increasing in the crystallinity level of the films. Furthermore, for the films with higher level of crystallinity, a significant broadening of the ESR ?H is observed as the temperature is decreased, suggesting the development of short-range magnetic correlations between the Mn2+ ions. Similar results were found for films GaMnN, except in the magnetization versus magnetic field experiments for GaMnN, which we could observe ferromagnetic loops in T < 50 K, in constract of GaMnAs films where no ferromagnetic loop in T = 2 K was found for all measured films. For the other group of films, a-Si, we studied the suppresion effects in the density of dangling bonds species D0 states as function concentration for different Rare-Earth (RE¿s) species. According to our data, the RE-doping reduces the ESR signal intensity of the D0 states with an exponential dependence on the Re¿s concentrations. Ag:R and NaYF4:Gd NPs were prepared by chemical method. We observed a typical Lorentzian line-shape ESR lines for all studied dopants (R = Er, Yb e Mn). The gfactor found for Er3+, Yb3+ e Mn2+ in the nanoparticles is very close to g-value found in ground-states of these ions in insulating cubic systems, in contrast that what was found in metals, where it is observed a g-shift for the metallic system. Furthermore, it was not possible to observe the Korringa relaxation for the ESR lines of Er3+, Yb3+ e Mn2+ in the NPs system typically observed in metals. Therefore, the results suggest that the exchange interaction (Jfs) between localized magnetic moments (ML) and conduction electrons (c-e) is absent in Ag:R NPs, indicating that the nature of this interaction needs to be reexamined at the nanoscale range. For NaYF4:Gd NPs, the particle control size was obtained by the amount of rps = precursor/surfactant. There was no evidence of Gd clusters in our results and we found the same characteristics observed in the bulk system: three resonance lines, with the controversies origins. It is still unknown the source of crystalline field of cubic symmetry with tetragonal combinations or orthorhombic or even Gd3+ sites with lower symmetries
Doutorado
Física da Matéria Condensada
Doutor em Ciências
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Strange, R. W. "A spin-label ESR study of drug binding to DNA." Thesis, Keele University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356546.
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Miglioli, Isabella <1982>. "Sistemi liquido cristallini complessi: simulazioni al calcolatore e studi ESR." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2010. http://amsdottorato.unibo.it/2656/1/Miglioli_Isabella_tesi.pdf.
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The aim of this PhD thesis was to study at a microscopic level different liquid crystal (LC) systems, in
order to determine their physical properties, resorting to two distinct methodologies, one involving computer
simulations, and the other spectroscopic techniques, in particular electron spin resonance (ESR) spectroscopy.
By means of the computer simulation approach we tried to demonstrate this tool effectiveness for calculating anisotropic static properties of a LC material, as well as for predicting its behaviour and features. This
required the development and adoption of suitable molecular models based on a convenient intermolecular
potentials reflecting the essential molecular features of the investigated system.
In particular, concerning the simulation approach, we have set up models for discotic liquid crystal dimers and
we have studied, by means of Monte Carlo simulations, their phase behaviour and self-assembling properties,
with respect to the simple monomer case. Each discotic dimer is described by two oblate GayBerne ellipsoids
connected by a flexible spacer, modelled by a harmonic "spring" of three different lengths. In particular we
investigated the effects of dimerization on the transition temperatures, as well as on the characteristics of
molecular aggregation displayed and the relative orientational order.
Moving to the experimental results, among the many experimental techniques that are typically employed
to evaluate LC system distinctive features, ESR has proved to be a powerful tool in microscopic scale
investigation of the properties, structure, order and dynamics of these materials. We have taken advantage
of the high sensitivity of the ESR spin probe technique to investigate increasingly complex LC systems
ranging from devices constituted by a polymer matrix in which LC molecules are confined in shape of nano-
droplets, as well as biaxial liquid crystalline elastomers, and dimers whose monomeric units or lateral groups
are constituted by rod-like mesogens (11BCB).
Reflection-mode holographic-polymer dispersed liquid crystals (H-PDLCs) are devices in which LCs are
confined into nanosized (50-300 nm) droplets, arranged in layers which alternate with polymer layers, forming
a diffraction grating. We have determined the configuration of the LC local director and we have derived
a model of the nanodroplet organization inside the layers. Resorting also to additional information on the
nanodroplet size and shape distribution provided by SEM images of the H-PDLC cross-section, the observed
director configuration has been modeled as a bidimensional distribution of elongated nanodroplets whose
long axis is, on the average, parallel to the layers and whose internal director configuration is a uniaxial quasi-
monodomain aligned along the nanodroplet long axis. The results suggest that the molecular organization is
dictated mainly by the confinement, explaining, at least in part, the need for switching voltages significantly
higher and the observed faster turn-off times in H-PDLCs compared to standard PDLC devices.
Liquid crystal elastomers consist in cross-linked polymers, in which mesogens represent the monomers
constituting the main chain or the laterally attached side groups. They bring together three important aspects: orientational order in amorphous soft materials, responsive molecular shape and quenched topological constraints.
In biaxial nematic liquid crystalline elastomers (BLCEs), two orthogonal directions, rather than the one of
normal uniaxial nematic, can be controlled, greatly enhancing their potential value for applications as novel
actuators. Two versions of a side-chain BLCEs were characterized: side-on and end-on. Many tests have
been carried out on both types of LCE, the main features detected being the lack of a significant dynamical
behaviour, together with a strong permanent alignment along the principal director, and the confirmation of
the transition temperatures already determined by DSC measurements. The end-on sample demonstrates a
less hindered rotation of the side group mesogenic units and a greater freedom of alignment to the magnetic
field, as already shown by previous NMR studies. Biaxial nematic ESR static spectra were also obtained
on the basis of Molecular Dynamics generated biaxial configurations, to be compared to the experimentally
determined ones, as a mean to establish a possible relation between biaxiality and the spectral features.
This provides a concrete example of the advantages of combining the computer simulation and spectroscopic
approaches.
Finally, the dimer α,ω-bis(4'-cyanobiphenyl-4-yl)undecane (11BCB), synthesized in the "quest" for the
biaxial nematic phase has been analysed. Its importance lies in the dimer significance as building blocks
in the development of new materials to be employed in innovative technological applications, such as faster
switching displays, resorting to the easier aligning ability of the secondary director in biaxial phases. A
preliminary series of tests were performed revealing the population of mesogenic molecules as divided into
two groups: one of elongated straightened conformers sharing a common director, and one of bent molecules,
which display no order, being equally distributed in the three dimensions. Employing this model, the
calculated values show a consistent trend, confirming at the same time the transition temperatures indicated
by the DSC measurements, together with rotational diffusion tensor values that follow closely those of the
constituting monomer 5CB.
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Miglioli, Isabella <1982>. "Sistemi liquido cristallini complessi: simulazioni al calcolatore e studi ESR." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2010. http://amsdottorato.unibo.it/2656/.
Full textAbstract:
The aim of this PhD thesis was to study at a microscopic level different liquid crystal (LC) systems, in
order to determine their physical properties, resorting to two distinct methodologies, one involving computer
simulations, and the other spectroscopic techniques, in particular electron spin resonance (ESR) spectroscopy.
By means of the computer simulation approach we tried to demonstrate this tool effectiveness for calculating anisotropic static properties of a LC material, as well as for predicting its behaviour and features. This
required the development and adoption of suitable molecular models based on a convenient intermolecular
potentials reflecting the essential molecular features of the investigated system.
In particular, concerning the simulation approach, we have set up models for discotic liquid crystal dimers and
we have studied, by means of Monte Carlo simulations, their phase behaviour and self-assembling properties,
with respect to the simple monomer case. Each discotic dimer is described by two oblate GayBerne ellipsoids
connected by a flexible spacer, modelled by a harmonic "spring" of three different lengths. In particular we
investigated the effects of dimerization on the transition temperatures, as well as on the characteristics of
molecular aggregation displayed and the relative orientational order.
Moving to the experimental results, among the many experimental techniques that are typically employed
to evaluate LC system distinctive features, ESR has proved to be a powerful tool in microscopic scale
investigation of the properties, structure, order and dynamics of these materials. We have taken advantage
of the high sensitivity of the ESR spin probe technique to investigate increasingly complex LC systems
ranging from devices constituted by a polymer matrix in which LC molecules are confined in shape of nano-
droplets, as well as biaxial liquid crystalline elastomers, and dimers whose monomeric units or lateral groups
are constituted by rod-like mesogens (11BCB).
Reflection-mode holographic-polymer dispersed liquid crystals (H-PDLCs) are devices in which LCs are
confined into nanosized (50-300 nm) droplets, arranged in layers which alternate with polymer layers, forming
a diffraction grating. We have determined the configuration of the LC local director and we have derived
a model of the nanodroplet organization inside the layers. Resorting also to additional information on the
nanodroplet size and shape distribution provided by SEM images of the H-PDLC cross-section, the observed
director configuration has been modeled as a bidimensional distribution of elongated nanodroplets whose
long axis is, on the average, parallel to the layers and whose internal director configuration is a uniaxial quasi-
monodomain aligned along the nanodroplet long axis. The results suggest that the molecular organization is
dictated mainly by the confinement, explaining, at least in part, the need for switching voltages significantly
higher and the observed faster turn-off times in H-PDLCs compared to standard PDLC devices.
Liquid crystal elastomers consist in cross-linked polymers, in which mesogens represent the monomers
constituting the main chain or the laterally attached side groups. They bring together three important aspects: orientational order in amorphous soft materials, responsive molecular shape and quenched topological constraints.
In biaxial nematic liquid crystalline elastomers (BLCEs), two orthogonal directions, rather than the one of
normal uniaxial nematic, can be controlled, greatly enhancing their potential value for applications as novel
actuators. Two versions of a side-chain BLCEs were characterized: side-on and end-on. Many tests have
been carried out on both types of LCE, the main features detected being the lack of a significant dynamical
behaviour, together with a strong permanent alignment along the principal director, and the confirmation of
the transition temperatures already determined by DSC measurements. The end-on sample demonstrates a
less hindered rotation of the side group mesogenic units and a greater freedom of alignment to the magnetic
field, as already shown by previous NMR studies. Biaxial nematic ESR static spectra were also obtained
on the basis of Molecular Dynamics generated biaxial configurations, to be compared to the experimentally
determined ones, as a mean to establish a possible relation between biaxiality and the spectral features.
This provides a concrete example of the advantages of combining the computer simulation and spectroscopic
approaches.
Finally, the dimer α,ω-bis(4'-cyanobiphenyl-4-yl)undecane (11BCB), synthesized in the "quest" for the
biaxial nematic phase has been analysed. Its importance lies in the dimer significance as building blocks
in the development of new materials to be employed in innovative technological applications, such as faster
switching displays, resorting to the easier aligning ability of the secondary director in biaxial phases. A
preliminary series of tests were performed revealing the population of mesogenic molecules as divided into
two groups: one of elongated straightened conformers sharing a common director, and one of bent molecules,
which display no order, being equally distributed in the three dimensions. Employing this model, the
calculated values show a consistent trend, confirming at the same time the transition temperatures indicated
by the DSC measurements, together with rotational diffusion tensor values that follow closely those of the
constituting monomer 5CB.
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Safarzynska, Karolina. "Socio-economic Determinants of Demand for Private Tutoring." Oxford University Press, 2011. http://dx.doi.org/10.1093/esr/jcr045.
Full textAbstract:
This study examines socio-economic factors underlying the demand for private tutoring. The analysis utilizes two samples of students from lower- and upper-level secondary schools in Poland based on the PISA 2006 data set. Special attention is paid to channels through which private tutoring may endure socio-economic inequalities, especially in the context of the gender gap in education outcomes. We find that parents' decisions concerning private education are sensitive to student gender, which may raise concerns for policymakers committed to provide equal opportunities and outcomes in education. At the level of gymnasium (lower-level secondary school), female students are more likely to enrol in private tutoring in mathematics than male students. The evidence indicates the opposite with respect to private tutoring in Polish and preparatory courses for the gymnasium final examination. The grade from the final exam does not affect the probability of graduating from gymnasium, but it is used by upper secondary schools for the admission purpose. In upper secondary schools, we find that male students are less likely to participate in private education services than female students. This may be indicative of an increase in power of students in household's decision-making as they graduate from gymnasium. (author's abstract)
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Kheir, Maria El. "An ESR and ENDOR study of silicon and carbon centred radicals." Thesis, Cardiff University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276847.
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Bernhardt, Dietrich [Verfasser]. "Dielektronische Rekombination lithium- und berylliumartiger Xenonionen am Schwerionenspeicherring ESR / Dietrich Bernhardt." Gießen : Universitätsbibliothek, 2012. http://d-nb.info/106417356X/34.
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Martins, George Balster. "Teoria de ESR de momentos magnéticos diluídos e localizados em sólidos." [s.n.], 1994. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277824.
Full textAbstract:
Orientador: Gaston Eduardo BarberisTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-07-20T06:31:40Z (GMT). No. of bitstreams: 1 Martins_GeorgeBalster_D.pdf: 1918598 bytes, checksum: f220566a71da56c956fe10da13327a07 (MD5) Previous issue date: 1994
Resumo: Não informado
Abstract: Not informed.
Doutorado
Física
Doutor em Ciências
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Bonello, Jean-François. "La famille multigénique Esr : expression et fonction dans l'albumen de maïs." Lyon, École normale supérieure (sciences), 2000. http://www.theses.fr/2000ENSL0162.
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Rhodes, C. J. "Structural studies of organic and organosilicon free radicals by ESR spectroscopy." Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370439.
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Karlsson, Alexander. "Statistical Study on Langmuir Turbulence Radar Signatures Observed by the ESR." Thesis, KTH, Rymd- och plasmafysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-175783.
Full textAbstract:
In this thesis data taken by the EISCAT Svalbard Radar during the International PolarYear have been analyzed. The radar data have been searched for anomalous radarechoes. These radar echoes appear in an altitude range between 200 and 300 km, showa strong enhancement of the backscattered power and are limited in altitude to tensof kilometers. These anomalous radar echoes also show a distinct zero Doppler shiftedpeak in the ion line spectrum. The power prole of the data have been visually inspectedto identify the anomalies. The data have then been analyzed using a Matlab programcalled GUISDAP in order to get basic plasma parameters. It has been found that thereis a high occurrence of these anomalies during particle precipitation and at a certainE-region electron density peak more than 40 % of the data contains these anomalies.
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Whittaker, David Thomas Edward. "Dimanganese decacarbonyl : a new reagent for radical organic synthesis." Thesis, University of York, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341094.
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Le, Masurier Peter John. "Magnetic resonance studies of dimer liquid crystals." Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243072.
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