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Shergill, Raminder. "Radicals and radical pairs in chemical and biological systems." Thesis, University of Leicester, 2010. http://hdl.handle.net/2381/11008.
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Magnetic fields of different strengths can be applied to chemical and biological systems to study processes involving radicals or radical pairs. This work uses two such techniques, electron paramagnetic resonance (EPR) spectroscopy (≥ 150 mT) in addition to time resolved EPR spectroscopy and time resolved infrared (TRIR) spectroscopy (≤ 37 mT). The former are used to monitor metalloproteins, and the photochemistry of phosphorus oxides, while TRIR spectroscopy is used to record the magnetic field effects on the reaction kinetics of neutral radical pairs. The thesis begins with an introduction and an overview of the experimental techniques and developments. This is followed by an EPR study of the Fe(III) binding proteins, transferrin and lactoferrin and the effect thereon of catecholamine stress hormones. Catecholamines mediate bacterial growth by sequestering iron from the iron binding proteins. The mechanism of iron capture is unknown, however, the current work reveals Fe(III) binding by the catecholamine and supports subsequent reduction as the most likely route. Since catecholamines are also administered therapeutically, the validity of EPR as a diagnostic technique is examined and iron loss from human serum transferrin is observed. Also within this work, experiments are presented in which TRIR spectroscopy is used to investigate factors that affect the development of magnetic field effects for radical pairs in different solutions. This initially involves studies on acylphosphine oxides. In addition to the reported photoprocesses, alternative chemistry is uncovered, which occurs when bisacylphosphine oxide is in solutions where the solvent is sufficiently nucleophilic. The photochemistry is investigated using time resolved EPR and density functional theory calculations to suggest three possible structures that are responsible for the additional radicals observed. Furthermore, encapsulated organic radical pairs in reverse micelles are studied. These experiments, in combination with dynamic light scattering measurements provide insight into the magnitude of the observed magnetic field effects and the differing kinetics of the radical pair in the reverse micelles.
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Till, Ulrike. "Recombination kinetics of radical pairs." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267949.
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Lewis, Alan. "Spin dynamics in radical pairs." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:45f5b9a7-534d-4b4f-aca7-b87f57eb2840.
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The coherent spin dynamics of radical pairs play a crucial role in their reactions, which consequently cannot be described by a simple kinetic scheme. Instead, simulations of the spin dynamics are required in order to predict the rate and outcome of radical pair reactions, and especially their response to the application of a magnetic field. Unfortunately, the number of spin states of the radical pair increases exponentially with the number of nuclear spins, making deterministic quantum mechanical simulations of realistic radical pairs difficult. To overcome this difficulty, this thesis begins by presenting an efficient stochastic quantum mechanical method capable of describing a radical pair with as many as 20 nuclear spins, which we use to analyse spin-dependent charge recombination rates along molecular wires. This enables us to identify the mechanism of charge recombination of both the singlet and triplet states of the wire by determining their relative contributions to the overall recombination rate. We then derive an approximate semiclassical theory which allows to treat the spin dynamics of much larger radical pairs, since the time required for a semiclassical calculation scales linearly with the number of nuclear spins, rather than exponentially. Using this method, we reproduce the results of the first experiments to show that the outcome of a radical pair reaction may be in uenced by an Earthstrength magnetic field, and calculate the anisotropy in the singlet recombination yield of the radical pair thought to be responsible for avian magnetoreception. We show that our semiclassical theory reduces to the earlier Schulten-Wolynes theory under two additional approximations, and use this simpler theory to reveal that singlet-triplet dephasing plays an important role in the spin dynamics of polaron pairs in the semiconducting polymer layer of organic light emitting diodes. We derive a new expression which relates the magnetic field dependence of the electroluminescence and conductance observed in these materials to the singlet yield of the radical pair recombination reaction, which we confirm produces better agreement with experimental data than the relationships used previously.
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Qureshi, Tariq. "Spin chemistry." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365292.
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Nattrass, Stephen R. "Optically detected magnetic resonance of radical pairs." Thesis, University of Oxford, 1987. http://ora.ox.ac.uk/objects/uuid:cdddfd9c-1ec3-4661-801a-d80dad1a853d.
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Current theories of the effects of static and resonant high frequency magnetic fields on radical pair reaction are presented with a view to establishing how they can form the basis of the high time resolution liquid phase magnetic resonance techniques of MARY and RYDMR. Approximate calculations are performed to reveal RYDMR spectral details for the case of an initial triplet radical pair. The design of unique apparatus to explore the capabilities of the techniques, and routinely collect quantitative data to test theoretical predictions, is described. This includes the development of an ultra-fast waveform scan-digitizing facility which can attain effective sampling rates of up to 20 GHz. The apparatus is employed to provide the first demonstration of recombination exciplex fluorescence from pyrene - dicyanobenzene radical-ion pairs. It is also applied in the dimensional characterization of micellar and microemulsion media prior to their use in enhancing MARY and RYDMR signal intensities from solubilized radical pairs. By means of a laser induced radical fluorescence technique and compartmentalized reaction media, first observations are reported of optically detected RYDMR spectra from neutral radical pairs, the existence of very low field MARY spectral structure and the kinetic effect of a resonant microwave field. The MARY structure is attributed to Heisenberg exchange interaction and shown to be sensitive to microreactor volume.
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Hunter, David A. "Spin-correlated radical pairs in photosynthetic systems, micelles and liquids." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253134.
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Hogben, Hannah J. "Coherent spin dynamics of radical pairs in weak magnetic fields." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:61c4ab7e-406f-4193-949a-b5a70f43e3e1.
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The outcome of chemical reactions proceeding via radical pair (RP) intermediates can be influenced by the magnitude and direction of applied magnetic fields, even for interaction strengths far smaller than the thermal energy. Sensitivity to Earth-strength magnetic fields has been suggested as a biophysical mechanism of animal magnetoreception and this thesis is concerned with simulations of the effects of such weak magnetic fields on RP reaction yields. State-space restriction techniques previously used in the simulation of NMR spectra are here applied to RPs. Methods for improving the efficiency of Liouville-space spin dynamics calculations are presented along with a procedure to form operators directly into a reduced state-space. These are implemented in the spin dynamics software Spinach. Entanglement is shown to be a crucial ingredient for the observation of a low field effect on RP reaction yields in some cases. It is also observed that many chemically plausible initial states possess an inherent directionality which may be a useful source of anisotropy in RP reactions. The nature of the radical species involved in magnetoreception is investigated theoretically. It has been shown that European Robins are disorientated by weak radio-frequency (RF) fields at the frequency corresponding to the Zeeman splitting of a free electron. The potential role of superoxide and dioxygen is investigated and the anisotropic reaction yield in the presence of a RF-field, without a static field, is calculated. Magnetic field effect data for Escherichia coli photolyase and Arabidopsis thaliana cryptochrome 1, both expected to be magnetically sensitive, are satisfactorily modelled only when singlet-triplet dephasing is included. With a view to increasing the reaction yield anisotropy of a RP magnetoreceptor, a brief study of the amplification of the magnetic field experienced by a RP from nearby magnetite particles is presented. Finally in a digression from RPs, Spinach is used to determine the states expected to be immune from relaxation and therefore long-lived in NMR experiments on multi-spin systems.
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Carpenter, Joanna Katharine Hicks. "Magnetic field effects on electron transfer reactions in photosynthetic bacteria." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390466.
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Kleinman, Mark Howard. "The Dynamics of benzylic radical pairs in organized media : binding and mobility." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ34272.pdf.
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Fursman, Catherine E. "Electron spin echo envelope modulation spectroscopy of radical pairs in photosynthetic bacteria." Thesis, University of Oxford, 2000. http://ora.ox.ac.uk/objects/uuid:1ccaf0e5-3a45-4f13-a184-a4f1cf772c9b.
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Electron spin echo envelope modulation (ESEEM) spectroscopy is widely used to study the radical pairs created during the primary steps of photosynthesis. In this thesis the analysis of ESEEM spectra is improved, and some new applications and variations of this experiment suggested. Experimental spectra from species such as P+Q-A, the secondary radical pair formed in the reaction centre of the bacterium Rhodobacter sphaeroides, give information about the exchange and dipolar couplings between the radicals. The model used to analyse the data affects the results; this thesis suggests two improvements. First, the effect of anisotropic hyperfine couplings in the radicals is considered by the addition of a single spin-1/2 nucleus to the model. This approach suggests that previous models neglecting the effect of nuclei may have been slightly in error. Secondly, several model fittings are performed in the time domain. This approach avoids the Fourier transformation to the frequency domain so that experimental dead-time does not corrupt the data. An excellent fit to experimental data is found with a model containing one spin-1/2 nucleus on each radical. The hyperfine coupling parameters resulting from the fit are consistent with independent experimental results. Use is made of the method of Cramér-Rao lower bounds to assess the precision to which experimental parameters are determined from a time domain curve fitting. It is shown that the lower bounds may also be used to determine the optimum sampling strategy for the experiment. An example is given of the novel use of ESEEM to determine the distance between the radicals in the strongly coupled, uncorrelated radical pair Q-AQ-B ESEEM has not yet been used for this purpose, and the simulated spectra produced here indicate that the experiment could be used to evaluate the dipolar coupling and hence the inter-radical distance. This thesis considers the possibility of performing ESEEM at higher frequencies than are usually considered. Calculations show that the increased resolution of the g-tensors allow an experiment performed at the W-band frequency of 95 GHz to make a correlation between the relative orientations of the radicals and the dipolar axis, information which has previously been unavailable from a single experiment.
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Evans, Christopher Riche. "Triplet derived radical pairs in micelles: Decay kinetics and magnetic field effects." Thesis, University of Ottawa (Canada), 1989. http://hdl.handle.net/10393/21399.
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Poudel, Pramod Prasad. "NOVEL AROMATIC ION–PAIRS: SYNERGY BETWEEN ELECTROSTATICS AND Π-FACE AROMATIC INTERACTIONS." UKnowledge, 2012. http://uknowledge.uky.edu/chemistry_etds/4.
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This dissertation focuses on the design and study of charged aromatic molecules where weak π-π interactions synergize with electrostatic interactions to enhance the overall interaction between aromatic moieties. Each chapter investigates some aspect of this hypothetical synergy between electrostatics and π-face aromatic cohesion.
The first chapter unveiled the importance of electrostatics in the intramolecular stacking of flexible aromatic molecular templates 1-2Br and 2a. While our previous studies found dicationic molecular template 1-2Br to have intramolecular π-stacking between electron poor pyridinium and electron rich xylylene moieties, no such stacking interaction was observed in the neutral analog 2a.
Chapter two systematically explored the stacking pattern of electron poor aromatics in the form of oxygen- and / or nitrogen- substituted triangulenium cations, [1(NR)3]+ and [1(O)3(OH)3]+. As indicated in the chemical literature, triazatriangulenium cations [1(NR)3]+ with N- ethyl (and longer alkyl chains) chains were found to pack as face-to-face dimers. This study found the formation of columnar, face-to-face, n-meric association between aromatic cations in the structures with decreased steric interactions of the side chains in the stacking planes ([1(NMe)3]+ and [1(O)3(OH)3]+). Similar iso-structural triangulene based aromatic anions, (2)- and (3)2- didn’t indicate any facial interactions in the solid states.
The possible synergy between unit charge electrostatics and π-face aromatic interactions was explored in aromatic ion pairs 1•2 of triangulene based aromatic cations and aromatic anions. This charge-assisted π-π stacking seems to be the novel way of getting strong π-system interactions where the strongest non-covalent force and the weakest non-covalent force: ionic bonding and π-stacking respectively synergize together. The π-π interaction between ionic aromatics in the solid state was investigated by means of single crystal x-ray diffraction and powder x-ray diffraction (PXRD). The interaction in the solution state was examined by UV-Vis spectroscopy, electrospray ionization mass spectroscopy (ESI-MS) and electrochemical studies. Studies found that optimal synergy was possible only in the ion pairs with no steric interactions of alkyl (or aryl) side chains in the stacking planes (1(O)3•2 & 1(NMe)3•2) and the interaction was found to be comparable with the strongest radical-assisted π-stacking described in the chemical literature.
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Sheppard, Dean. "Cavity-enhanced detection of biologically relevant magnetic field effects." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:69a41655-de81-499d-81fb-e27c3b69280d.
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Magnetoreception is the ability of some animals to use the weak magnetic field of the Earth for navigation over long-distance migrations. It is a well-known phenomenon, but its underlying biophysical mechanisms remain poorly understood. One proposal involves light-induced, magnetically sensitive chemical reactions occurring within cryptochrome proteins, rationalised via the radical pair mechanism (Chapter 1). The absence of evidence in support of this hypothesis is in part due to the lack of sufficiently sensitive techniques to measure magnetic field effects (MFEs) in biological samples. Cavity-enhanced detection, most commonly in the form of cavity ring-down spectroscopy (CRDS) or cavity-enhanced absorption spectroscopy (CEAS), is widely used in the gas phase to provide significant sensitivity gains over traditional single-pass measurements (Chapter 2). However, successful studies in the condensed phase are less prevalent due to the additional background losses inherent to the sample. This thesis reports on the application of broadband (i.e. monitoring > 100nm) variants of CRDS and CEAS to the study of MFEs on the radical recombination reactions of flavin-based systems in solution. The broadband CRDS (BBCRDS) instrument employed in Chapter 4 is able to monitor the spectral changes induced by magnetic fields with submicrosecond time resolution. However, the need to scan both the probe wavelength and time delay to construct time-resolved spectra leads to prohibitively long acquisition times, and hence exposure of sensitive samples to high numbers of photons. The broadband CEAS (BBCEAS) studies reported in Chapter 5 combine the high irradiance and spectral coverage of a supercontinuum radiation (SCR) source with a CCD detector to simultaneously acquire absorption spectra across the visible region (480â700nm). The CW nature of this technique precludes the possibility of following radical pair kinetics in real time. In an effort to combine the respective advantages of these two instruments, which individually have represented powerful advances in capability, a new cavity-enhanced technique is reported for the first time (Chapter 6). The result, optical cavity-enhanced transient absorption spectroscopy (OCTAS), is able to simultaneously monitor spectral evolution and associated MFEs on the microsecond timescale, with comparable sensitivity to the existing techniques. Magnetic responses in animal cryptochrome proteins have successfully been recorded using all three techniques, lending considerable weight to the hypothesis that these molecules are at the heart of the magnetic sense in animals.
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Timmel, Christiane Renate. "Magnetic field effects on radical pair reactions." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267955.
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McKeating, Paul D. "Magnetic field effects on radical pair reactions." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.400216.
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Norman, Stuart A. "Magnetic field effects on radical pair reactions." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437032.
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Fumanal, Quintana Maria. "Radical-Pair Formation in Organic π-Stacked Architectures." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/345173.
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Interest in organic molecule-based materials has extraordinarily grown in both the electronic and data storage industries. Specifically, research in the development of new plastic devices for technological proposes has emerged as they may provide lower manufacturing costs, more versatile synthetic processes and better mechanical properties (i.e. transparency, flexibility) than standard inorganic materials. However, in order to compete with these inorganic-based materials in terms of effectiveness, their conductive, magnetic and switchable characteristics must be improved, such that they can be applied as high-performance molecular conductors, magnets and memory devices. The physical properties of these organic materials not only depend on the nature of its constituent molecules (magnetic, biocompatible) but on how they organize in the solids (polymeric, amorphous, crystalline). Therefore, predicting and achieving a particular final behaviour is challenging and requires investigations on the structure-property relationships as well as on the nature of the chemical species. Over the last years, continuous effort has been done aimed at developing new purely organic-based materials with technologically relevant properties. Since Gomberg's synthesis of the triphenylmethyl neutral radical, a large variety of stable organic radicals have been reported, such as nitroxides, verdazyl-, phenoxyl-, phenalenyl-, dithiazolyl- and triazinyl-based compounds, as well as several functionalized radical ions based on tetracyanoethylene (TCNE), and tetrathiafulvalene (TTF+.) among others. These particular families of organic radicals can be used as versatile templates for the synthesis of new derivatives with improved characteristics by the introduction of different substituents into their basic skeleton. However, further progress in novel materials must be achieved through a rational design of new chemical structures. In this context, the available computational tools can substantially contribute to obtain the necessary knowledge of the factors controlling the final target physical properties, namely conductivity, magnetism and bistability, which are essentially dominated by the electronic structure of these materials. The work presented in this thesis is devoted to study different purely organic derivatives that have been shown to be promising for the development of new functional materials. In particular, the attention has been focused on three different families of organic radicals that present interesting physical properties as a consequence of a Tr-stacked radical-pair formation in the condensed phase, that is: (1) radical ions, (2) phenalenyl- and (3) triazinyl-based compounds. Overall, the present PhD thesis aims at contributing to the field of computational chemistry as well as to the understanding of the electronic properties that govern the Tr-dimerization of these systems, which, ultimately, determine their magnetic and switchable behaviour.En els últims anys, s'ha fet un esforç continu per desenvolupar materials nous purament orgànics amb propietats tecnològicament rellevants. Des de la síntesi de Gomberg del radical neutre trifenilmetil, s'ha reportat una gran varietat de radicals orgànics estables, com ara els nitròxids, verdazils, fenoxils, fenalenils, ditiazolils i compostos basats en triazinil, així com diversos ions radicals funcionalitzats basats en tetracianoetilè (TCNE-•), i tetratiafulvalè (TTF1-.), entre d'altres. Aquestes famílies de radicals orgànics s'utilitzen per a la síntesi de nous derivats amb característiques millorades a partir de la introducció de diferents substituents en el seu esquelet bàsic. No obstant això, els avenços en nous materials s'han d'aconseguir a través d'un disseny racional de les noves estructures químiques. En aquest context, les eines computacionals disponibles poden contribuir substancialment a obtenir els coneixements necessaris sobre els factors que controlen les propietats físiques desitjades, a saber, la conductivitat, el magnetisme i la biestabilitat, dominades fonamentalment per l'estructura electrònica d'aquests materials. El treball presentat en aquesta tesi està dedicat a estudiar diferents derivats purament orgànics que han demostrat ser prometedors per al desenvolupament de nous materials funcionals. En particular, l'atenció s'ha centrat en tres famílies de radicals orgànics que presenten propietats físiques interessants com a conseqüència de la formació de parells de radical Tr, aquests són: (1) els ions radicals, (2) els fenalenils i (3) els compostos basats en triazinil. En global, aquesta tesi doctoral té com a objectiu contribuir al camp de la química computacional, així com a la comprensió de les propietats electròniques que regeixen la dimerització Tr d'aquests sistemes, que, en última instància, determina el seu comportament magnètic i commutable.
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Procopio, Maria <1975>. "Radical pair compass sensor model in avian magnetoreception." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3698/.
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Lau, Jason C. S. "Spin-selective chemical reactions in radical pair magnetoreception." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:695e3b49-c872-4403-8c70-153a3df8430b.
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Many animals on earth need to navigate in their own environments for breeding and foraging. The ability to determine a correct heading and the current location for a migratory bird is critical for its survival. Animals that are sensitive to the Earth’s magnetic field can use it to obtain their direction of travel. In 2000, a paper suggested that radical pair reaction could form the basis for magnetoreception in migratory birds and a flavoprotein, cryptochrome, was proposed as the candidate for the radical pair precursor. Recent in vivo experimental results strongly support the hypothesis that radical pairs formed in the eyes of migratory birds are responsible for their magnetic compass sense. Cryptochrome has also been located in the UV-cones in the retinas of two different species of bird. Radical pairs in living cells are influenced mainly by Zeeman interaction, hyperfine interaction, rotational modulation, etc., and together they influence the recombination reactions of the radical pairs. This thesis considers the possible role of radical pairs in avian magnetoreception, using computer simulations of the quantum mechanical evolution of a radical pair under a variety of conditions. Chapter 1 contains the introductions to spin chemistry, avian magnetoreception, and the mathematical description of the quantum evolution of a radical pair. Chapter 2 describes the four different theoretical models for a general non-diffusion-controlled radical pair reaction and the product yields of a radical pair reaction predicted by these four models are analysed and compared. Chapter 3 introduces a model for avian magnetoreception that integrates photoselection with the radical pair reaction and the model is used to predict the retinal patterns that a bird may be able to use for magnetoreception. The anisotropic singlet product yields of a radical pair comprises the flavin chromophore and the tryptophan of a cryptochrome are also presented in this chapter. A paper based on some parts of this chapter is published [1] in the Journal of The Royal Society Interface. Chapter 4 describes a modified version of an algorithm that is used to calculate the product yields detected in a reaction yield detected magnetic resonance (RYDMR) experiment. The new algorithm is used to analyse the results of two sets of RYDMR experiments in which two radical pair systems, pyrene/1,3-dicyanobenzene and chrysene/1,4-dicyanobenzene, were used. The modulated detection technique used in the RYDMR experiments is also discussed in this chapter.
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Wedge, Christopher J. "Radiofrequency Magnetic Field Effects on Radical Pair Recombination Reactions." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515011.
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Hiscock, Hamish. "Long-lived spin coherence in radical pair compass magnetoreception." Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:98ad538c-b258-4c7f-8467-977bb19372c3.
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The ability of night migratory birds to utilise the Earth's magnetic field as a directional cue is thought to arise from a light-activated radical pair reaction in the birds' eye. The field of magnetoreception encompasses a broad range of research areas, from behavioural experiments to theoretical studies. Unfortunately, the computational challenge presented by modelling the multinuclear organic radicals thought to be involved in the sensing mechanism severely hampers the interpretation of experimental results in the framework of the radical pair hypothesis. This thesis presents novel algorithms for more efficient simulation of multinuclear radical pairs as well as a discussion of the insights available from calculations using these new computational tools. I first present improved algorithms for simulating radical pair reactions in a static external magnetic field. With these more efficient algorithms, I am then able to explore in more detail the behaviour of different radical pair systems, and discuss their potential relevance to magnetoreception in Chapter 4. In particular, I examine whether a highly accurate 'compass needle' could arise from a radical pair sensor. One of the most significant behavioural observations in the field of magnetoreception is the finding that exceedingly weak time-dependent magnetic fields can disrupt magnetic orientation in birds. The added complexity of a time-dependent interaction means that simulating the experimental conditions is a considerable challenge. In Chapter 3 I present a calculation method based on a reformulation of Floquet theory which remains the only viable algorithm for modelling multinuclear radical pairs in an oscillatory magnetic field. In Chapter 5 I discuss the effect of these weak time-dependent fields on different candidate radical pairs, and examine the compatibility of the observed behavioural results with the radical pair hypothesis. Finally in Chapter 6 I present a new Information theory-based analytical tool which allows me to assess the accuracy of a radical pair compass without having to make assumptions about the signalling cascade. I consider how a radical pair compass would operate under low light conditions, and how the impact of the limited number of available photons could inform my computational analysis from previous chapters and in future work.
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Rogers, Rachel. "Vectors of Revolution : The British Radical Community in Early Republican Paris, 1792-1794." Phd thesis, Université Toulouse le Mirail - Toulouse II, 2012. http://tel.archives-ouvertes.fr/tel-00797967.
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British radicals established a pro-revolutionary society in Paris in the late months of 1792, at a time when their own government, under William Pitt the Younger, had proscribed all overt support for the French Revolution. The expatriate club was founded at a crossroads in British political and diplomatic culture therefore, and at a vital stage in the course of the French Revolution. Often the victims of judicial pursuit in both Britain and France, the members of the British Club have been deemed "men without countries" by one nineteenth-century commentator. Yet British radical activists in Paris were not simply pawns in a wider diplomatic struggle. In the early French republic, they founded a radical community at White's Hotel, where political agendas intersected with private initiatives. This associational world was part of a broad network of reform stretching across the Channel. It was influenced by a tradition of enquiry and improvement which had developed in Britain during the latter half of the eighteenth century. This tradition led members of the radical community to engage with the Revolution on issues which dominated public debate in France but which also echoed their concern for the overhaul of British political culture. They intervened on the question of the foundation of a new republican constitution at the turn of 1793, providing a range of blueprints which reflected the varied nature of the club's political character. Some also wrote eyewitness observations of the Revolution back to Britain, sketching their impressions for an audience who had, in their view, been misled by a hostile British press.
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Vink, Claire Bridget. "Time resolved infrared studies of weak magnetic field effects on radical pair solutions." Thesis, University of Leicester, 2007. http://hdl.handle.net/2381/30001.
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The thesis describes the development, implementation and application of the first magnetic field time resolved infrared (MFTRIR) spectrometer, capable of studying the kinetics of radical reactions and the effect of weak magnetic fields upon them. The thesis commences with an overview of the theoretical concepts associated with free radicals and their reactions. The idea of the radical pair is presented and the magnetic field susceptibility of this species is discussed in the context of the radical pair mechanism. The construction and development of the MFTRIR spectrometer is then examined, highlighting the important design features and operational principles. The remaining chapters comprise an in depth analysis of the results obtained from the first studies performed using the spectrometer. The radical recombination kinetics and magnetic field dependence are studied for a range of precursor molecules with insights drawn into the structural factures that influence both the magnitude and form of the observed magnetic field effects. Later chapters explore the effects of the radical pair environment by investigating reactions in both isotropic solution and reverse micelle environments. A number of key findings are generated by this work. First is the excellent capability of the new instrument in measuring very small perturbations on radical reactions with weak magnetic fields. Second is the correlation between the size of the observed field effects and the magnetic parameters of the radicals. Third is the ability to remove the effects at very weak magnetic fields (approximately 2mT) without perturbing the effects at higher magnetic fields, through the selective removal of longer lived radical pairs.
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Carrillo, Lozada Alejandro 1983. "Environment-induced anisotropy and the sensitivity of the radical pair mechanism in the avian compass." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277125.
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Orientadores: Marcos Cesar de Oliveira, Silvio Antonio Sachetto VitielloDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: O campo magnético da Terra é essencial na orientação de pássaros migratórios. A explicação mais promissora para esta orientação utiliza o mecanismo de pares ra-dicais (PR) criados em uma reação foto-estimulada, a qual é conjecturada ocorrer em fotorreceptores criptocromo. Esta última conjectura foi particularmente reforçada recentemente pela evidência de sensibilidade magnética do criptocromo humano. Os radicais devem ter uma anisotropia intrínseca, a fim de definir um quadro de referência para esse tipo de bússola. Esta anisotropia, quando introduzida através de interação hiperfinas, impõe imobilidade ao RP formado dentro do olho do pássaro, e implica na preservação do emaranhamento entre os elétrons desemparelhados do PR por tempos longos (de centenas de microssegundos). Consequentemente, os tempos de coerência são também longos, mesmo que o papel do emaranhamento na reação permaneça desconhecido. Mostra-se que esse tipo de anisotropia devido às interações hiperfinas não é necessário para o funcionamento da bússola. Pares radicais isotrópicos, isto é, moléculas que executam um movimento de rotação ou de difusão capaz de remover qualquer anisotropia no Hamiltoniano quando submetidos a um processo de decoerência rápida, são capazes de fornecer a anisotropia necessária para que a bússola funcione. O ambiente no qual o PR está imerso _e responsável pelo referencial da bússola, relaxando a hipótese de imobilidade. Isto expande significativamente a gama de aplicabilidade do mecanismo de PR fornecendo mais elementos para pesquisa experimental, quanto as moléculas candidatas não devem estar fixas na retina. Utilizando esta fonte externa de anisotropia, mostramos que o emara-nhamento não é necessário para o bom funcionamento da bússola dado que estados separáveis podem formar produtos anisotrópicos sob as condições apropriadas. Condições iniciais classicamente correlacionadas para o PR, ou em outras palavras, estados iniciais sem correlação quântica, podem fornecer uma outra fonte da anisotropia necessária para o bom funcionamento da bússola; dado que o estado inicial não _e um estado singleto (ou tripleto) perfeito entre os spins eletrônicos e portanto não _e um estado maximamente emaranhado, esta nova fonte de direção preferencial na criação dos produtos químicos ganha relevância
Abstract: Earth's magnetic field is essential for orientation of migratory birds. The most promising explanation for this orientation employs the photo-stimulated radical pair (RP) mechanism, conjectured to occur in cryptochrome photoreceptors. This last conjecture has been particularly reinforced recently by the evidence of magnetosensivity of human cryptochrome. The radicals must have an intrinsic anisotropy in order to define a reference frame for this kind of compass. This anisotropy, when introduced through hyperfine interactions, imposes immobility of the RP formed within the eye of the bird, and implies that entanglement between the unpaired electrons of the RP is preserved over long times of hundreds of microseconds; therefore the coherence times are longer, even if the role of entanglement in the reaction remains unknown. We show that this kind of anisotropy due to hyperfine interactions is not necessary for the proper functioning of the compass. Isotropic radical pairs, i.e., molecules performing diffusional or rotational motion able to average away any anisotropy in the hamiltonian, when subjected to a fast decoherence process, are able to provide the anisotropy required for the compass to work. The environment in which the RP is immersed is then responsible for the reference frame of the compass, relaxing the immobility assumption. This significantly expands the range of applicability of the RP mechanism providing more elements for experimental search, as the candidate molecules must not be fixed within the retina. Using this external source of anisotropy, we show that entanglement is not necessary for the proper working of the compass, given that separable states can form anisotropic yields under proper conditions. Classically correlated initial conditions for the RP, or in other words, initial states without quantum correlations, can provide another source of the required anisotropy for the proper working of the compass; given that the initial state is not a perfect singlet (or triplet) state between the electronic spins and therefore is not a maximally entangled state, this new source of preferred direction in the creation of the chemical products gains relevance
Mestrado
Física
Mestre em Física
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Robineau, Colin. "La politisation en terrain militant « radical » : ethnographie d’un squat d’activités de l’Est Parisien." Thesis, Paris 2, 2017. http://www.theses.fr/2017PA020055.
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Basée sur une observation participante de deux ans au sein de La Kuizine, un squat d’activités de l’est parisien ouvert par des militants marxistes et/ou anarchistes, la thèse se présente comme une contribution à l’étude du renouveau des entreprises critiques et des pratiques contestataires et apporte une pierre empirique de plus à la connaissance des espaces publics d’aujourd’hui. Accordant une large place au matériau ethnographique, la recherche s’inscrit dans une perspective empruntant à la fois à la tradition interactionniste de la troisième Ecole de Chicago et à la sociologie bourdieusienne afin d’éclairer les mécanismes de domination (re)produits au sein de La Kuizine et les « possibles latéraux » qui y sont expérimentés. En effet, le collectif militant à l’origine de l’initiative avait pour objectif d’en faire un lieu de « solidarité de classe » en y organisant divers ateliers (en particulier des repas à prix libre) à destination des travailleurs et habitants du quartier et en privilégiant l’autogestion comme modus operandi de la décision collective. L’analyse de cet espace – indissociablement physique, social et communicationnel – se situe donc au carrefour de plusieurs disciplines : la science politique, la sociologie, l’anthropologie et les sciences de l’information et de la communication. Ce faisant, la thèse interroge de manière transversale des objets variés : la fabrique sociale de l’engagement radical, le rapport aux champs politique et médiatique d’un micro-espace contestataire, les processus de socialisation politique ainsi que les conditions de possibilité de la critique ordinaire de l’ordre socialThis doctorate thesis is based on a two-year-long participant observation within “La Kuizine”, a social center squat in East Paris that was opened by Marxist and/or Anarchist activists. This piece presents itself as a contribution to the study of the renewal of critical enterprises and protest practices and offers empirical work that can aid in the understanding of public spaces today. A large portion is dedicated to ethnographic material in this thesis – the work here adopts a perspective that borrows both from the interactionist tradition of the third school of Chicago and from the sociology of Pierre Bourdieu in order to reveal the mechanisms of domination (re)produced within “La Kuizine” and the forms of “lateral possible” that are experimented within this space. Indeed, the activist group responsible for founding this squat had as its main goal to make it a space of “class solidarity” by organizing various workshops (including a sliding scale donation daily meal) for workers and inhabitant of the neighborhood. The modus operandi of the space is self-management and collective decision making. The social and communicational analysis of this space is at the crossroads between several fields of research: political science, sociology, anthropology and communication studies. Thus, this doctorate thesis studies various objects in a cross-disciplinary manner: the social construction of radical commitment, the relations to the political and media fields of a micro-protest-space, the processes of political socialization as well as the conditions for the possibility of a critique of the social order
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Dolgorouky, Cristina. "Mesure de la réactivité atmosphérique totale avec les radicaux hydroxyles (OH) : développement et applications en Ile-de-France." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00684758.
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Le radical hydroxyle (OH) représente le plus important oxydant dans la troposphère et le puits de la plus grande partie des composés à l'état de trace de l'atmosphère. Si les sources des radicaux hydroxyles sont aujourd'hui relativement bien connues, le terme 'puits' des OH, connu sous le terme de réactivité atmosphérique totale avec les radicaux OH (ou réactivité OH) (s-1), reste encore difficile à quantifier. En raison de la complexité des instruments nécessaires, peu de mesures de OH et de réactivité sont actuellement disponibles et la nouvelle méthode proposée par Sinha et al., (2008) représente une alternative prometteuse pour la quantification de la réactivité atmosphérique totale avec les radicaux hydroxyles. Cette méthode est appelée Méthode Comparative de Réactivité (CRM) et est basée sur la mesure rapide d'une molécule normalement absente de l'atmosphère (ici pyrrole, C4H5N) et qui réagit à un taux connu avec les radicaux hydroxyles produits artificiellement dans une petite cellule de réaction en verre. La comparaison des concentrations de pyrrole obtenues en présence/absence d'air ambiant, dans un champ de radicaux constant, permet de quantifier la réactivité de l'air ambiant. Cette thèse a eu pour objectif principal le développement et l'optimisation de cette méthode pour la mesure de réactivité en zone urbaine, fortement riche en monoxyde d'azote (NO), composé identifié comme produisant des artefacts de la mesure. De même, il fallait proposer une méthodologie pour intégrer toutes les corrections, inhérentes à la méthode, à appliquer aux valeurs brutes de réactivité. Une fois la méthode mise au point, le deuxième objectif de ces travaux était la caractérisation de la réactivité atmosphérique totale avec les radicaux OH à Paris, une des rares mégacités existantes en Europe et où aucune mesure de réactivité n'avait été rapportée auparavant. L'étude réalisée pendant la campagne d'hiver 2010 du projet européen MEGAPOLI a permis de caractériser le niveau de réactivité à Paris pendant deux régimes de masses d'air différentes, océanique / continental. Ainsi il a été possible de distinguer un niveau de réactivité purement local de Paris et Ile de France (impacté par le caractère " trafic " de cette ville européenne et étant comparable aux niveaux enregistrés à New York et Tokyo), et un niveau fort, importé, caractéristique d'un transport longue distance. De même, l'étude a révélé que pendant l'import continental, de forts pourcentages ont été enregistrés de réactivité manquante, définie comme la différence entre la valeur mesurée et une valeur théorique, calculée à partir des composés réagissant avec OH et mesurés pendant la campagne. La nature des espèces non-mesurées et contribuant à cette réactivité a été déterminée comme oxydée, issue des processus de " processing " des masses d'air sur le trajet long distance. Ce travail apporte dans un premier temps des informations uniques sur la méthode CRM pour la mesure de la réactivité OH (fonctionnement, traitement des données) et contribue par la suite à la caractérisation des niveaux de réactivité dans la région parisienne.
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Wang, Yifei. "Magnetic field effects in exciplex- and exciton-based organic light emitting diodes and radical-doped devices." Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/6010.
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Organic semiconductors (OSCs) have already been shown to have great potential to play an important role in the future of clean energy generation (organic solar cells) and provide energy efficient lighting (organic light-emitting diodes, OLED). Prior research has found that the light-emission efficiency of OLED is severely limited by the magnetic state (technically the spin-configuration) of the light-emission process. In this thesis, we work on the processes using external magnetic fields that can overcome these magnetic limitations. A major focus of this research is to enhance the performance of OLED, while at the same time to unravel the scientific mechanisms by which magnetic fields act on OSCs devices.
Thermally activated delayed fluorescence (TADF) is a next-generation OLED emission technology which enables nearly 100% light-emission efficiency without using heavy precious metals. TADF characteristics depend on the probability of reverse intersystem crossing (RISC) from the triplet excited states (T1) to singlet excited states (S1). The conversion (T1 to S1) process depends strongly on spin dynamics, thus we predict a dramatic magnetic field effects (MFEs) in such TADF OLED devices. In subsequent experiments we observed that changes in TADF devices due to various forms of electrical stress can lead to enormous increases in magnetic field effects (MFEs) on the current (> 1400%) and electroluminescence (> 4000%). Our work provides a flexible and inexpensive pathway towards magnetic functionality and field sensitivity in current organic devices. Such OLED pave the way for novel magnetic sensitive OSCs devices with integrated optical, electronic and magnetic characteristics.
Organic magnetoresistance (OMAR) has been observed to alter the current and efficiency of OLED without any ferromagnetic components. Here we utilizes slight alterations to the device properties, the addition of a radical-doped functional layer, in which the spin-relaxing effects of localized nuclear spins and electronic spins interfere, to address the assumption about the importance of the hyperfine interaction and to attempt to differentiate between the different models for OMAR. A feature where the magnitude of OMAR exhibits a plateau over a wide range of doping fraction was observed at all temperatures investigated. This phenomenon is well explained by a theory in which a single dopant spin strongly interacts, by exchange, with one of the bottleneck sites. A similar can be used to explain the efficiency increases observed in organic solar cells for certain doping fractions.
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Handsel, Jennifer. "Anisotropy and spin relaxation in the condensed phase." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:8a268360-4e6c-4a18-96e2-f60a57b5b5df.
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Chapter 1 introduces the concept of spin, how spins interact, and how the spin state in a radical pair can affect the outcome of a chemical reaction between the unpaired electrons. The computational methodology for simulating such radical pairs is also discussed. Chapter 2 discusses anisotropy in the singlet recombination yield of a radical pair in a carotenoid-porphyrin-fullerene triad, containing many hyperfine couplings. The singlet yield was calculated as a function of the direction of an applied magnetic field, using symmetry in the molecule to reduce the size of the problem. The symmetry reduction was partially successful, however it was not possible to include all the hyperfine couplings in the molecule. Chapter 3 introduces a radical pair located on a flavin ligand and a tryptophan residue in the protein cryptochrome, and discusses the spin-relaxation mechanism of singlet-triplet dephasing. Magnetic field effect curves, describing the formation of a secondary radical pair as a function of applied magnetic field, were found to be broader in longer-lived radical pairs, due to dephasing caused by spin-selective recombination to the singlet ground state. Additional singlet-triplet dephasing may occur due to hopping of one of the unpaired electrons, between a zone of strong exchange interaction and a zone of negligible exchange interaction, although this is an incomplete description of the spin-relaxation. Chapter 4 discusses the effect of rotational tumbling on spin-relaxation in the flavin-tryptophan radical pair in cryptochrome. Simulations indicated that the resulting modulation of anisotropic hyperfine couplings contributed modestly to spinrelaxation during transient absorption measurements, but was insufficient to explain the lack of an experimental low-field effect, or to explain the width of the experimental magnetic field effect curves as a function of magnetic field strength. Chapter 5 discusses magnetic field effects on the mutual annihilation of a pair of triplet excitons in tetracene and anthracene crystals. The experimental singlet recombination yield was found, for the first time, to be modulated as a function of the direction of a applied magnetic field as weak as 2 mT. Simulations indicated that this anisotropy arose due to the zero field splitting of the electronic state in each triplet exciton. The direction of the external magnetic field altered the singlet component of the eigenstates of the Hamiltonian, and therefore altered the timeaverage of the singlet probability of a triplet exciton pair. This is different to the already established mechanism under a strong magnetic field, where the anisotropy arises from level crossings of eigenstates.
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Painter, Michael Scott. "Characterizing the Role of Magnetic Cues Underlying Spatial Behavior." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/74049.
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In the 50+ years since the discovery of magnetic compass orientation by migratory songbirds, evidence for the use of magnetic cues has been obtained for a range of taxonomic groups, including several classes of vertebrate and invertebrate taxa. Surprisingly, however, the biophysical mechanisms and biological substrate that underlie magnetic sensing are still not fully understood. Moreover, while use of magnetic cues for compass orientation is intuitive, the functional significance of other forms of behavioral responses mediated by magnetic cues, such as spontaneous magnetic alignment, is less clear. The following research was carried out to investigate the mechanisms underlying magnetic orientation in vertebrates and invertebrates. This involved the modification of existing experimental systems to characterize responses to magnetic cues in laboratory animals (flies, mice) and the development of novel techniques for studying the role of magnetic cues in the spatial behavior of free-living animals (red foxes). Chapter II examines magnetic orientation in wild-type Drosophila melanogaster larvae. We show that three strains of larvae reared under non-directional ultraviolet (UV) light exhibit quadramodal spontaneous orientation along the anti-cardinal compass directions (i.e. northeast, southeast, southwest, northwest) when tested in a radially symmetrical environment under UV light. Double-blind experiments cancelling the horizontal component of the magnetic field confirmed that the response is dependent on magnetic cues rather non-magnetic features of the test environment. Furthermore, we argue that the larval quadramodal pattern of response is consistent with properties of magnetic compass orientation observed in previous studies of adult Drosophila and laboratory mice, both of which have been proposed to be mediated by a light-dependent magnetic compass mechanism. Chapter III explores the use of novel biologging techniques to collect behavioral and spatial data from free-roaming mammals. Specifically, a previous observational study of free- roaming red foxes found a 4-fold increase in the success of predatory 'mousing' attacks when foxes were facing ~north-northeast, consistent with magnetic alignment responses reported for a range of terrestrial animals. The authors propose that the magnetic field may be used to increase accuracy of mousing attacks. Using tri-axial accelerometer and magnetometer bio-loggers fitted to semi-domesticated red foxes, we created ']magnetic ethograms' from behavioral and magnetic machine learning algorithms 'trained'] to identify three discrete behaviors (i.e. foraging, trotting, and mousing-like jumps) from raw accelerometer signatures and to classify the magnetic headings of mousing-like jumps into 45° sectors from raw magnetometer data. The classifier's ability to accurately identify behaviors from a separate fox not used to train the algorithm suggests that these techniques can be used in future experiments to obtain reliable magnetic ethograms for free-roaming foxes. We also developed the first radio-frequency emitting collar that broadcasts in the low MHz frequency range shown to disrupt magnetic compass responses in a host of animals. The radio-frequency collars coupled with biologgers will provide a powerful tool to characterize magnetic alignment responses in predatory red foxes and can be adapted for use in studies of magnetic alignment and magnetic compass orientation in other free-roaming mammals. Chapter 3 discusses findings from a magnetic nest building assay involving male labratory mice. Mice trained to position nests in one of four directions relative to the magnetic field exhibited both learned magnetic compass responses and fixed magnetic nest positioning orientation consistent with northeast-southwest spontaneous magnetic alignment behavior previously reported for wild mice and bank voles. This is the first mammalian assay in which both learned magnetic compass orientation and spontaneous magnetic alignment were exhibited in the same species, and suggests that the use of magnetic cues in rodents may be more flexible that previously realized.Ph. D.
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Ulloa, Iván de Jesús Davis. "The –Ing construction in the language pair English/Spanish: radiality and subjectification." Universidade Federal de Juiz de Fora (UFJF), 2018. https://repositorio.ufjf.br/jspui/handle/ufjf/6684.
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O objetivo do presente trabalho é identificar, descrever e analisar a construção –ING no par linguístico inglês/espanhol. A construção exibe uma série de usos na língua inglesa e ensiná-la ou traduzi-la para usuários de outras línguas impõe alguns desafios. No caso de falantes de língua espanhola como público alvo, a maioria tende a interpretar a construção como sendo verbal, no aspecto progressivo, o que representa apenas uma função da construção. No tocante ao referencial teórico, a pesquisa é baseada no trabalho de Langacker (1987, 1990, 1991, 2006, 2008) com o intuito de investigar o uso da construção. A Teoria dos Protótipos (ROSCH, 1973), as Categorias Radiais (BRUGMAN, 1981; LAKOFF, 1987), e a Gramática das Construções (FILLMORE & KAY, 1999; GOLDBERG, 1995, 2006), além da abordagem semântica sobre a construção –ING (WIERZBICKA, 1988), serão essenciais para a descrição da construção sob uma perspectiva conceptual. Com relação à metodologia, assume-se uma abordagem tanto quantitativa quanto qualitativa dos dados (COOK, T.D. & REICHARDT, C.S., 1979; RICHARDSON, R. J.,1985; CRESWELL, J., 2010), compilados a partir de um corpus bilíngue paralelo no par linguístico Inglês/Espanhol, de 1199 ocorrências da construção –ING. A hipótese central do estudo é que a construção, em sua função verbal progressiva, é mais central ou prototípica (ROSCH, 1973) em relação à sua rede construcional, envolvendo outras funções, quais sejam, nominal, adjetival e adverbial. Essas funções, por sua vez, assumem posições mais periféricas e se relacionam com a função verbal por meio de relações de extensão metafórica (GOLDBERG, 1995, 2006). Argumenta-se, então, que essas relações estabelecem um continuum entre as funções, variando de um nível mais concreto, mais ancorado no contexto de fala a um nível mais abstrato, mais subjetificado (LANGACKER, 1990). Por meio de uma análise baseada em corpus (BERBER SARDINHA, 2002, 2004) argumenta-se, por fim, que existe uma organização radial (BRUGMAN, 1981; LAKOFF, 1987) para a construção –ING, que passa de um domínio mais concreto, mais situado ou “ancorado” no evento de fala e se torna, assim, mais objetificado (como “processo”) a um domínio mais abstrato, menos situado, menos ancorado no evento de fala e, portanto, mais subjetificado (como “coisa”) (LANGACKER, 2008).
The aim of this dissertation is to identify, describe and analyze the –ING construction from the English language. The –ING construction has a number of uses in the English language and either teaching or translating it to speakers of other languages poses some challenges. In the case of having Spanish speakers as audience, most of them tend to interpret the construction as a verbal one, in the progressive aspect, which is only one function of the construction. As for the theoretical framework, we chiefly based our research on Langacker’s work (1987, 1990, 1991, 2008) in order to account for this construction. We also rely on Prototype Theory (ROSCH, 1973), Radial Categories (BRUGMAN, 1981; LAKOFF, 1987), and Construction Grammar (FILLMORE & KAY, 1999; GOLDBERG, 1995, 2006), apart from a semantic approach to the –ING construction (WIERZBICKA, 1988), which will be essential for describing the –ING construction from a conceptual perspective. In regard to methodology we take both a quantitative and qualitative approach to data (COOK, T.D. & REICHARDT, C.S., 1979; RICHARDSON, R.J., 1985; CRESWELL, J., 2010) compiled from an English/Spanish parallel corpus of 1199 verbal –ING occurrences. Our main hypothesis is that the –ING construction, in its verbal function, is more central or prototypical (ROSCH, 1973) in respect to its conceptual network and its other functions, namely nominal, adjectival and adverbial. These functions, in turn, exhibit a more peripheral role and are linked to the verbal function through metaphorical extension relationships (GOLDBERG, 1995, 2006). These relationships, we argue, establish a continuum between these functions, going from the most or more grounded level up to the most abstract, subjectified level. By performing a corpus-based analysis of the data (BERBER-SARDINHA, 2002, 2004) we finally argue that there is a radial organization (BRUGMAN, 1981; LAKOFF, 1987) for the –ING construction, which goes from a more concrete level, being this more situated or “grounded” (LANGACKER, 1987, 1990, 1991, 2008) and thus more objectified (as a “here and now process”), until it gets to a more abstract level, therefore, less situated and more subjectified (taken as a “thing”) (LANGACKER, 2008).
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Vidal, Marie-Hélène. "Influence d'un champ magnétique sur les recombinaisons géminées : étude de systèmes, anthraquinone-donneurs d'hydrogène." Paris 11, 1987. http://www.theses.fr/1987PA112265.
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Cette étude porte sur l'influence d'un champ magnétique sur l'orientation de réactions chimiques passant par l'intermédiaire d'une paire de radicaux libres à spins corrélés (radicaux en "cage"). Dans la première partie, nous avons exposé la théorie dite de la "paire de radicaux" permettant d'interpréter l'évolution de tels systèmes : les mécanismes de passage singulet-triplet et les différentes interactions à l'intérieur des paires ainsi que le traitement quantique de résolution du système. La technique utilisée pour cette étude est la photolyse laser nanoseconde (absorption) qui est décrite dans la deuxième partie. Dans la troisième partie, nous présentons les résultats expérimentaux obtenus sur les systèmes Anthraquinone (AQ) - Donneurs d'hydrogène :-nous montrons qu'il n'y a pas d'effet de champ sur de tels systèmes en solution homogène même à viscosité élevée, et donnons les spectres d'absorption des différents intermédiaires de réaction. -Par contre, nous mettons en évidence un effet de champ important lorsqu’AQ est confinée dans des micelles de SDS (HS), celles-ci jouant le rôle de donneur d'hydrogène. Nous obtenons le spectre d'absorption du radical semi-quinone AQH· en "cage" et proposons un mécanisme pour sa disparition vers les espèces AQH-S et AQH2. -L'addition du 9,10 Dihydroanthracene (DH2) à l'intérieur de la micelle, près de AQ permet, par la création de paires (AQH· DH·) peu mobiles d'augmenter l'effet de champ. -Des paires de radicaux immobilisées par une matrice protéique ont également été étudiées dans des centres réactionnels de bactéries photosynthétiques : dans ce cas, le champ de demi-effet est déplacé vers les champs faibles par rapport aux systèmes précédentsThis study is devoted to magnetic field effects on chemical reactions which involve a radical pair with correlated spins (radicals in a "cage"). In the first part, the radical pair theory is described: mechanisms of singlet-triplet mixing, the different interactions inside the pair and a quantum mechanical treatment of the radical pair. The details of the experimental method (nanosecond laser flash photolysis) are reported in the second part. In the third part are shown experimental results obtained on Anthraquinone (AQ) - Hydrogen donors systems:There is no magnetic field effect in homogeneous solution even at a high viscosity. The absotption spectra of the different reaction intermediates are obtained. However a magnetic field effect is put forward when AQ is introduced in SDS micelles which are hydrogen donors. The absorption spectrum of the AQH· semi-quinone radical in "cage" is shown and a mechanism is proposed for its disappearance to generate the AQH-S and AQH2 species. The addition of 9, 10 Dihydroanthracene (DH2) inside the micelle near AQ induces an increase of the magnetic field effect by creation of (AQH· DH·) pairs which diffuse slowly. Fixed radical pairs in a protein matrix were studied in reaction centers of photosynthetic bacteria: in that case, the half-effect field is shifted to low fields when compared to the precedingly described systems
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Pooam, Marootpong. "The biological effects of applied magnetic fields on cryptochrome and response." Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS062.
Full textAbstract:
Cryptochromes (cry) sont des flavoprotéines absorbant la lumière bleue conservées qui ont été liées à perception de stimuli électromagnétiques dans de nombreux organismes. Nous avons principalement étudié le mécanisme d'interaction entre les champs magnétiques (MF) et cry dans le cadre de la théorie des paires de radicaux. Nous avons étudié la réponse d'Arabidopsis cry-1 in vivo à MF. Les activités biologiques du cry ont été renforcées par MF. Les effets des MF ont pu être observés même si MF était donné exclusivement pendant les intervalles d'obscurité entre expositions à la lumière. Cette découverte a indiqué que l'étape de réaction magnétiquement sensible dans photocycle du cry doit se produire pendant la réoxydation des flavines. De plus, nous avons également utilisé la fréquence (RF) stimulée par cry-Arabidopsis comme outils de diagnostic pour confirmer l'hypothèse de la paire de radicaux. Dans l'étude, nous avons trouvé un effet perturbateur des RF sur l'activité du cryptochrome. Notre découverte pourrait confirmer l'apparition du mécanisme de la paire de radicaux et l'implication du cry pour la magnétoréception. De plus, nous avons également montré un effet perturbateur de la condition MF statique de bas niveau (LLF) où les champs magnétiques externes étaient presque éliminés. Le résultat de cette condition était cohérent avec l'effet de l'exposition aux RF. En outre, nous avons également signalé que LLF pourrait augmenter l'expression de certains gènes induits par le PEMF dans dans les les cellules humaines. Cette découverte pourrait fournir des preuves à l'appui de l'effet des champs électriques magnétiques et non induits sur la physiologie humaineCryptochromes are highly conserved blue-light-absorbing flavoproteins that have been linked to the perception of electromagnetic stimuli in numerous organisms. We mainly studied the mechanism for the interaction between magnetic fields and cryptochromes in the context of the radical-pair theory. We investigated the response of Arabidopsis cryptochrome-1 in vivo to a static magnetic field. The biological activities of cryptochrome were enhanced by the magnetic field. Interestingly, the effects of the magnetic fields could be observed even the magnetic field was given exclusively during dark intervals between light exposures. This finding indicated that the magnetically sensitive reaction step in the cryptochrome photocycle must occur during flavin reoxidation. Moreover, we also used frequency (RF) stimulated to Arabidopsis cryptochrome as the diagnostic tools to confirm the radical-pair hypothesis. In the study, we found a disruptive effect of RF on the activity of cryptochrome. Our findings could confirm the occurrence of the radical-pair mechanism and the involvement of cryptochrome for magnetoreception. Additionally, we also showed a disruptive effect of the low-level static magnetic field (LLF) condition where the external magnetic fields were almost eliminated. The result of this condition was consistent with the effect of RF exposure. Furthermore, we also reported that LLF could increase the expression of some PEMF-induced genes in human cells. This finding could provide the evidence to support the effect of magnetic, not induced electric fields in human physiology
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Harman, David Grant, and harmandg@hotmail com. "Mechanisms of the Intriguing Rearrangements of Activated Organic Species." The Australian National University. Faculty of Science, 2003. http://thesis.anu.edu.au./public/adt-ANU20031210.143110.
Full textAbstract:
The β-acyloxyalkyl radical rearrangement has been known since 1967 but its
mechanism is still not fully understood, despite considerable investigation. Since the
migration of a β-trifluoroacetoxy group generally proceeds more rapidly and with more varied regiochemistry than its less electronegative counterparts, this reaction was studied
in the hope of understanding more about the subtleties of the mechanism of the β- acyloxyalkyl radical rearrangement. The mechanism of the catalysed rearrangement of Nalkoxy-
2(1H)-pyridinethiones was also explored because preliminary studies indicated that the transition state (TS) for this process was isoelectronic with TSs postulated for the β-acyloxyalkyl radical and other novel rearrangements.
¶
A kinetic study of the rearrangement of the 2-methyl-2-trifluoroacetoxy-1-heptyl
radical in solvents of different polarity was undertaken using a radical clock method. Arrhenius equations for the rearrangement in each solvent were: hexane, log10[kr (s-1)] =
11.8±0.3 – (48.9±0.7)/ θ; benzene, log10[kr (s-1)] = 12.0±0.2 – (43.7±0.8)/ θ; and
propionitrile, log10[kr (s-1)] = 11.9±0.2 – (42.0±0.3)/ θ. Rate constants at 75˚C were:
hexane, kr = 2.9 × 104; benzene, kr = 2.8 × 105; and propionitrile, kr = 4.0 × 105 s-1.
The equilibrium constant for the reversible rearrangement at 80°C in benzene was 15.1
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Gauger, E. M. "Applications of quantum coherence in condensed matter nanostructures." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:fb792980-bfc4-4771-b5d5-b9ecc7d40cd8.
Full textAbstract:
This thesis is concerned with studying the fascinating quantum properties of real-world nanostructures embedded in a noisy condensed matter environment. The interaction with light is used for controlling and manipulating the quantum state of the systems considered here. In some instances, laser pulses also provide a way of actively probing and controlling environmental interactions. The first two research chapters assess two different ways of performing all-optical spin qubit gates in self-assembled quantum dots. The principal conclusion is that an `adiabatic' control technique holds the promise of achieving a high fidelity when all primary sources of decoherence are taken into account. In the next chapter, it is shown that an optically driven quantum dot exciton interacting with the phonons of the surrounding lattice acts as a heat pump. Further, a model is developed which predicts the temperature-dependent damping of Rabi oscillations caused by bulk phonons, finding an excellent agreement with experimental data. A different system is studied in the following chapter: two electron spin qubits with no direct interaction, yet both exchange-coupled to an optically active mediator spin. The results of this study show that these general assumptions are sufficient for generating controlled electron spin entanglement over a wide range of parameters, even in the presence of noise. Finally, the Radical Pair model of the avian compass is investigated in the light of recent experimental results, leading to the surprising prediction that the electron spin coherence time in this molecular system seems to approach the millisecond timescale.
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Liu, Guoquan. "Functionalization of endohedral fullerenes and their application in quantum information processing." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:ef834d92-f198-4651-8316-19a95b348113.
Full textAbstract:
Quantum information processing (QIP), which inherently utilizes quantum mechanical phenomena to perform information processing, may outperform its classical counterpart at certain tasks. As one of the physical implementations of QIP, the electron-spin based architecture has recently attracted great interests. Endohedral fullerenes with unpaired electrons, such as N@C60, are promising candidates to embody the qubits because of their long spin decoherence time. This thesis addresses several fundamental aspects of the strategy of engineering the N@C60 molecules for applications in QIP. Chemical functionalization of N@C60 is investigated and several different derivatives of N@C60 are synthesized. These N@C60 derivatives exhibit different stability when they are exposed to ambient light in a degassed solution. The cyclopropane derivative of N@C60 shows comparable stability to pristine N@C60, whereas the pyrrolidine derivatives demonstrate much lower stability. To elucidate the effect of the functional groups on the stability, an escape mechanism of the encapsulated nitrogen atom is proposed based on DFT calculations. The escape of nitrogen is facilitated by a 6-membered ring formed in the decomposition of the pyrrolidine derivatives of N@C60. In contrast, the 4-membered ring formed in the cyclopropane derivative of N@C60 prohibits such an escape through the addends. Two N@C60-porphyrin dyads are synthesized. The dyad with free base porphyrin exhibits typical zero-field splitting (ZFS) features due to functionalization in the solid-state electron spin resonance (ESR) spectrum. However, the nitrogen ESR signal in the second dyad of N@C60 and copper porphyrin is completely suppressed at a wide range of sample concentrations. The dipolar coupling between the copper spin and the nitrogen spins is calculated to be 27.0 MHz. To prove the presence of the encapsulated nitrogen atom in the second dyad, demetallation of the copper porphyrin moiety is carried out. The recovery of approximately 82% of the signal intensity confirms that the dipolar coupling suppresses the ESR signal of N@C60. To prepare ordered structure of N@C60, the nematic matrix MBBA is employed to align the pyrrolidine derivatives of N@C60. Orientations of these derivatives are investigated through simulation of their ESR spectra. The derivatives with a –CH3 or phenyl group derived straightforward from the N-substituent of the pyrrolidine ring are preferentially oriented based on their powder-like ESR spectra in the MBBA matrix. An angle of about is also found between the directors of fullerene derivatives and MBBA. In contrast, the derivatives with a –CH₂ group inserted between the phenyl group and the pyrrolidine ring are nearly randomly distributed in MBBA. These results illustrate the applicability of liquid crystal as a matrix to align N@C60 derivatives for QIP applications.
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Landler, Lukas. "Spontaneous directional preferences in taxonomically and ecologically distinct organisms: examining cues and underlying mechanisms." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/73328.
Full textAbstract:
The focus of this research was the spontaneous magnetic alignment responses of animals. We show that snapping turtles (Chelydra serpentina) and crayfish (Cambarus sciotensis) spontaneously align their body axes relative to the magnetic field. In snapping turtles, this response is sensitive to low-level radio frequency fields, consistent with a mechanism involving a light-dependent radical pair mechanism. Findings from the turtle experiments also suggest that the Earth's magnetic field plays an important role in encoding spatial information in novel surroundings, and may help to organize multiple locales into a 'mental map' of familiar space. Given the importance of magnetic input in many aspects of spatial behavior, another important finding was that magnetic alignment of yearling turtles was disrupted by high levels of maternally transferred mercury, an industrial waste product found at high levels in some fresh water ecosystems. In crayfish, we investigated the effects of ectosymbionts (Annelida: Branchiobdellida) on magnetic alignment responses. Interestingly, the response of crayfish to magnetic cues parallels the complex symbiotic interaction between crayfish and their ectosymbiotic worms, which changes from mutualistic to parasitic with increasing worm density. Our working hypothesis was that these changes in spatial behavior may increase or decrease contact to other crayfish, and therefore increase or decrease transmission rates. Next, to address the ontogeny of the SMA, we attempted to replicate an earlier study showing a possible magnetic alignment response in chicken embryos. Although chicken embryos did show non-random alignment, we were not able to find a magnetic effect. Alignment is also an important feature of animal constructions and is very likely to have fitness consequences, which we explored in woodpecker cavity alignments in a meta-analysis of available global data. The latitudinal and continental pattern in 23 species of woodpeckers suggests that an alignment response can have the proximate function to regulate microclimate in the cavity and therefore, presumably, optimize incubation temperatures and increase hatching success. Overall, the presented findings show how experimental and observational studies of spontaneous alignment behavior can provide insight into the ecology and sensory biology of a wide range of animals.Ph. D.
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Li, Jing. "Applications of optical-cavity-based spectroscopic techniques in the condensed phase." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:d6a0c476-e67f-4390-a63a-e3cb9e60bf2c.
Full textAbstract:
Cavity ring-down spectroscopy (CRDS) and cavity enhanced absorption spectroscopy (CEAS) are two well-established absorption spectroscopic techniques originally developed for gas-phase samples. Condensed-phase applications of these techniques still remain rare, complicated as they are by additional background losses induced by condensed-phase samples as well as the intracavity components in which the sample is constrained. This thesis is concerned with the development and application of optical-cavity-based techniques in the condensed phase. Polarization-dependent evanescent wave CRDS (EW-CRDS) has been used to study the molecular orientation at the solid/air and solid/liquid interfaces. An increase in average orientation angle with respect to the surface normal has been observed for both methylene blue and coumarin molecules as a function of coverage at the fused silica/air interface. An orientation-angle-dependent photobleaching of pyridin molecules at the fused silica/methanol interface have also been observed. EW-CRDS has also been used to monitor slow in situ photobleaching of thin dye films deposited on the prism surface. The photobleaching dynamics is interpreted as a combination of first- and second-order processes. A significant fraction of this thesis has been devoted to studying magnetic field effects (MFEs) on the kinetics of the radical pair (RP) reactions in solution, in an effort to understand the ability of animals to sense the geomagnetic field. Two novel optical-cavity-based techniques – broadband CEAS (BBCEAS) and CRDS have been developed for this purpose. BBCEAS uses a supercontinuum (SC) source as the cavity light source and a CCD camera as photodetector, enabling simultaneous acquisition of absorption spectrum across the whole visible region (400 – 800 nm). In CRDS, a tunable optical parametric oscillator has been used as the cavity light source. Combined with the switching of external magnetic field (SEMF) method, this technique allows the decay kinetics of the geminate RPs to be monitored, with nanosecond resolution. Both BBCEAS and CRDS provide sensitivity superior to single-pass transient absorption (TA), a technique traditionally used in the MFE studies. A series of photochemical systems have been studied by BBCEAS and CRDS, respectively, among which, the MFEs of drosophila melanogaster cryptochrome has been observed. Importantly, this is the first time an MFE has been observed in an animal cryptochrome, and provides key supporting evidence for the cryptochrome hypothesis of magnetoreception in animals. Besides the optical-cavity-based techniques, a novel fluorescence detection method of MFEs has also been demonstrated. This technique proved ultrahigh sensitivity when applicable.
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Ahadi, Mostafa. "Contribution à l'étude théorique de la relaxation de spin dans les systèmes bidimensionnels en présence d'un potentiel intermoléculaire." Paris 6, 1986. http://www.theses.fr/1986PA066156.
Full textAbstract:
Présentation d'un formalisme très général de la relaxation de spin par suite de la diffusion relative des molécules dans un fluide 2d, au moyen d'une équation de Smoluchowski qui tient compte du potentiel intermoléculaire et qui est résolue par la technique des différences finies. Déduction des expressions des fonctions de corrélation, des densités spectrales et des vitesses de relaxation de spin associés à un mécanisme de relaxation dipolaire, dû à une diffusion moléculaire sur des supports bidimensionnels. Application à l'étude de la géométrie des phases lamellaires.
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Guix, Ràfols Francesc Xavier. "Study of the pathophysiological role of nitric oxide on the amyloid-induced toxicity attending to the biochemical modifications and cellular damages." Doctoral thesis, Universitat Pompeu Fabra, 2009. http://hdl.handle.net/10803/7162.
Full textAbstract:
Aquesta tesi demostra que el peroxinitrit produït com a conseqüència del pèptid beta-amiloide (A) contribueix l'augment de la relació A42/A40 que ocorre a la malaltia d'Alzheimer. L'A42 contribueix a l'aparició de la malaltia degut a la seva major toxicitat (quan es compara amb l'A40) que resulta d'una gran estabilitat i capacitat agregativa. A més el peroxinitrit incrementa la toxicitat d'aquest degut a què potencia la seva agregació en forma d'oligomers altament tòxics. De fet els oligomers formats de nitro-A42 presenten una major toxicitat que aquells formats de A42 . En conjunt aquest resultats senyalen l'important paper que l'A42 té en la malaltia d'Alzheimer.Per altra banda, des de la identificació dels agregats d'A i la subseqüent formació dels cabdells neurofibrilars (NFT) com a els dos trets distintius de la malaltia, un gran esforç s'ha dedicat a establir els mecanismes moleculars que uneixen ambdós processos. Aquesta tesi demostra que el peroxinitrit format a partir de l'agregació de d'Ai la conseqüent nitrotirosinació de proteïnes, potencia l'agregació de la proteïna tau en forma de fibres. D'aquesta forma, la nitrotirosinació de la proteïna triosafosfat isomerasa (TPI) podria ser el vincle entre la toxicitat derivada del agregats d'Ai la patologia derivada de la proteïna tau. Per tant, la nitrotirosinació de la TPI podria explicar la progressió temporal que ocorre als cervells de pacients amb la malaltia d'Alzheimer des de la toxicitat induïda per l'Ai l'aparició dels NFT. Els resultats presentats en aquesta tesi podrien obrir nous aspectes en la recerca de la malaltia d'Alzheimer així com en altres malalties que cursin amb estrès oxidatiu i plegament erroni de proteïnes.
This thesis demonstrates that amyloid ß-peptide (Aß)-induced peroxynitrite contributes to the switch of the Aβ42/Aβ40 ratio that occurs in Alzheimer's disease (AD). Since Aβ42 is more toxic due to its higher aggregation and stability, it contributes to the trigger of the disease. In addition the aggregation of Aβ42 in form of the highly toxic oligomers is incremented by the presence of peroxynitrite. Moreover, these nitro-Aß42 oligomers are more toxic than those non-nitrated. All these results support the important role of peroxynitrite in AD etiology.
Furthermore, since the identification of Aß accumulation and the subsequent formation of neurofibrillary tangles (NFT) as the two defining pathological hallmarks of AD, a fair amount of research on AD has been driven by the need to find the molecular mechanism linking Aß and NFT. This thesis shows the Aß-induced peroxynitrite, and the consequent nitrotyrosination of proteins, promotes tau fibrillization. Thus triosephosphate isomerase (TPI) nitrotyrosination could be the link between Aß-induced toxicity and tau pathology. Therefore, TPI nitrotyrosination may explain the temporal progression from Aß toxicity to NFT formation in AD brain. The work presented in this thesis could open a novel angle in the research of the pathophysiology of AD and could also have an impact to the research in other neurodegenerative diseases involving oxidative stress and protein misfolding.
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Liu, Kuo-Tung, and 劉國棟. "EPR study of some radical, radical pairs, crystal structure and structure phase transition." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/48801286222124598918.
Full textAbstract:
碩士國立師範大學
物理研究所
82
The thesis includes the following four researches: 1.Two chemically inequivallent [N(CH3)3]+ radical species produced via r-irradiation were detected by EPR in TrMCC crystal. This indicates a twofold, static disorder of the TrM ions. 2.The hexagonal P63/m to monoclinic P21/m structural phase transition in TMCC has been investigated by EPR. The result indicates the presence of merohedral twinning below the phase transition. 3.Two chemically inequivallent V4+ ions were detected by EPR in vanadium-doped KTiOPO4 crystal. The results allow one to identify the occupation sites of the doped V4+ ions and to conclude that the doped V4+ ions form VO2+ ions. 4.Irradiation of (NH4)2S2O8 single crystal with uv light produces two kinds of radical pairs, pairs I and pairs II. Radical pairs I is stable at room temperature, and can be identified to be SO5- pairs. Radical pairs II can be produced by uv-irradiation and detected by EPR only at low temperatures and identified to be SO4- pairs.
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秦婉甄. "The Effectiveness of the Rating of Similarity Degree and Creative Radical laborate Mnemonics in Distinguishing the Chinese Character Pairs of Similar Patterns." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/49762051440185871281.
Full textAbstract:
碩士國立臺灣師範大學
創造力發展碩士班
102
This thesis includes two studies. The participants in the first study were 80 ethnic Chinese whose native language is not Chinese. They were tested on various exercises with 60 character pairs of similar pattern to evaluate the rating of the similarity degree. The data was analyzed by descriptive statistics and the two-way ANOVA. The objects of the second study were 23 Chinese-as-the-second-language (CSL) learners. To discover how the creative radical elaborate mnemonics affecting the differentiation of similar characters during the process of target language learning, the data was examined by methods of descriptive statistics and the t-TEST. In the first study, it reveals obvious differences when the participants were tested on similarity evaluation with a series of characters of similar forms. The second study reflects the participants' progress was vivid when they apply the creative radical-sophisticated learning strategies to the test on distinguishing word meanings. However, the application of the strategy shows little influence on the rating of the similarity degree among participants. This thesis displays that various creative radical elaborate mnemonics are helpful in learning character pairs of similar patterns, including the sinogram-based theory, the key-images, the Chinese radicals and Chinese-stem deriving instructional method, and the elaborated instructional method. Moreover, the rating of the similarity degree is useful to reflect how well a learner can distinguish characters of similar patterns.
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Chen, Yu-Jen, and 陳俞臻. "(1) Temperature and Matrix Effects Dependence on the Triplet Radical Pairs Generated from Photolysis of N-Tosylpyrrole Derivatives, (2) Photochemistry of Heteroaromatic Fused ??-1,2,3-Triazoline Derivatives, (3) Application of Tetrazole Modified Calix[4]a." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/54411936287525538177.
Full textAbstract:
博士國立交通大學
應用化學研究所
98
In part 1, the photolysis (230-325 nm) of N-tosyl pyrrole 37, 2-phenyl-N-tosyl pyrrole 72, 2,5-diphenyl-N-tosyl pyrrole 73, and N-(2-naphthyl)-sulfonyl pyrrole 75 in a 2-methyltetrahydrofuran glassy matrix at 4 K gives electron paramagnetic resonance (EPR) spectra with triplet characteristics; the zero-field-splitting (zfs) parameters D' for the corresponding radical pairs (RPs) 93, 94, 95, and 96 are 0.0239, 0.0190, 0.0174, and 0.0241 cm-1, respectively. Irradiation of 37 at RT allows the isolation of two rearranged products 38 and 39 and a polymeric material, which is consistent with cleavage of the N-S bond followed by recombination of RP 93. Triplet RPs 97, 98 obtained from the photolysis of N-tosylpyrrolosultine 24 and N-tosylpyrroloadduct 58, are stable at 77 K for at least 10 h. It is note worthy that the zfs parameters of triplet RPs 93-98 as well as their temperature and matrix dependencies are strikingly similar to those reported for triplet 3,4-dimethylene-N-tosylpyrrole biradicals 18, which possess same core structure. Furthermore, the X-ray crystallography also success proved the existence of RRs 95. In part 2, the phenyl and quinoxaline fused ??-1,2,3-triazolines 186a and 186c were synthesized in good yields using Knoevenagel condensation and intramolecular 1,3-dipolar cycloaddition as two of the key reactions. Photolysis (254 nm light) of ??-1,2,3-triazolines 186a or 186c in acetonitrile led to the homolytic cleavage of nitrogen that generated diethyl diazomalonate 189, highly reactive intermediates aziridines 188a,c, and isoindoles B. The latter two species subsequently underwent rearrangement to give the nitrogen extrusion product 187a,c, and polymers. Furthermore, the reactive intermediates were trapped by dienophiles to give the corresponding cycloadducts. Subsequent rearrangement of the N-bridged cycloadducts gave N-substituted pyrrolo[3,4-b]quinoxaline 192c and 195c in 6% and 9% yields, respectively. Irradiation of 186a with fumaronitrile led to the isolation of cycloadduct 196a with retention of stereochemistry. Thermal reaction of 186c gave more nitrogen extruded product 187c than the photolysis did, which implied that zwitterionic intermediate might be involved in the former. In part 3, calix[4]arenes 264a (R = OMe) and 264b (R = NO2) with 5,17-bis-p-substituted-phenylazo and 25,27-bis-oxymethyltetrazole groups were synthesized using the 1,3-dipolar cycloaddition of oxyacetonitrile azocalix[4]arenes 263a and 263b activated with trimethylsilyl azide, respectively. UV-vis screening of calix[4]arenes 264a and 264b with 14 metal ions showed that 264a (with p-methoxyphenylazo substituent) was a highly chromogenic sensor to Ca2+, while 364b (with p-nitrophenylazo substituent) showed color changes toward Ca2+, Ba2+, and Pb2+. Job plot experiments revealed a 1:1 binding stoichiometry for each of the complexes. The association constants for 264a•Ca2+, 264b•Ca2+, 264b•Ba2+, and 264b•Pb2+ were determined by Benesi-Hildebrand plots to be 9.1 ?e 104, 3.1 ?e 105, 1.1 ?e 105, and 1.6 ?e 105 M-1, respectively. Based on 1H NMR titration results, Ca2+ was bound to the two partially deprotonated hydroxyl azophenol groups and one of the two tetrazole groups of 264a and 264b.
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Huan-YuKU and 古煥宇. "Quantum Steering in Radical-pair Model." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/62218923283755717405.
Full textAbstract:
碩士國立成功大學
物理學系
103
It is known that some species use the geomagnetic fi eld of Earth for orientation and navigation. The chemical compass of the radical-pair model may explain the behaviour of a bird's navigation. Some papers have already suggested that the sensitivity on the singlet-product yield is the key quantify for the navigation . Since the radical-pair model is based on quantum mechanics, it is suggested that long-lived quantum coherence and entanglement may play a role in navi- gation. However, the entanglement is shown to be independent of the direction between the geomagnetic eld and the radical pair. In this thesis, we use the quantum steering, which is from the consideration of the local hidden state, to investigate the radical-pair model. Steering is a quantum correlation between Bell's inequality and entanglement. We show that the temporal steerable weight depends on the direction of the geomagnetic eld. It may help us to understand the quantum correlation in the radical-pair model.
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Chen, Jun-Ru, and 陳俊儒. "Magnetic effect on radical pair coupling dependent enzyme - Lysine 5,6-aminomutase." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/zm6fu9.
Full textAbstract:
碩士國立東華大學
物理學系
106
With the development of Quantum mechanics, we have different cognize in chemical reaction. When a system has more than one radical, alteration of the coupled spin-state population by an external magnetic field may lead to changes in the chemical reaction rate through spin-selective chemistry. Migratory birds in the evolution of nature, magnetic field is beneficial to migratory birds navigation through the radical-pair mechanism. We show the reaction of lysine 5,6-aminomutase (5,6-LAM) is magnetic field dependent. The enzyme catalytic efficiency decreased 16% at 7600 gauss. It compares with simulated Q-band EPR spectrum of a transient CoII 4-thialysyl• RP intermediate in 5,6-LAM, the isotropy exchange interaction (2J) = 8000 gauss. This means that magnetic effect is Singlet (ΣS = 0)-Triplet (ΣS = 1) Energy Level Crossing at 7600gauss, application of an external magnetic field in the range of 6500 to 8500 gauss triggers intersystem crossing to the singlet {cob(II)alamin-substrate} radical-pair state. Lysine 5,6-Aminomutase (5,6-LAM) is an B12(Adenosylcobalamin; AdoCbl) and B6(Pyridoxal phosphate; PLP) dependent enzyme. The radical mechanism provides by 4-thia-L-lysine inhibitors indirectly. The catalytic from homolysis Co-C bond on AdoCbl, formatting the 5'-deoxyadenosyl radical (Ado•) and Cob(II)alamin. Ado• abstracts a C5(H) from the substrate, formatting substrate radical, product will product after free radical ripple effect. Magnetic effect of 5,6-LAM, show the reaction of nature substrate proceeds via radical pair intermediates. The energy gap is 8000gauss, Hyperfine structure interaction and Spin Rephasing mechanism are severely restricted. The magnetic field effect caused by J-resonance is clearly shown in the high magnetic field position, and added a new evidence for the magnetic field effect of enzymes.
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Chen, Yu-Jen, and 陳俞臻. "The Synthesis and Photochemistry of Radical Pair Precursors: N-Benzenesulfonyl Substituted Pyrroles, Imidazole and Indole." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/3287f4.
Full textAbstract:
碩士國立交通大學
應用化學系
90
A series of 39, 47, 52 and 53 in 2-methyltetrahydrofuran glass matrices at 77 K were irradiated with 230-325 nm (NiSO4-filtered, UV light), which gave triplet EPR spectra, and the zero-field splitting (zfs) parameters D' values are 0.0228, 0.0225, 0.0190 and 0.0176 cm-1, respectively. At 4 K, the D' values of 51 and 47 are 0.0239 and 0.0237 cm-1, respectively. The radical pairs derived from 51 (12-44 K) and 47 (8-52 K) both showed linear Curie plots, thereby indicating either the ground state are triplets or that singlet and triplet states are degenerate (≦30 cal/mole difference). An addition product of Ts and MNP was observed when 51 was photolyzed in the presence of spin trapping agent. N-benzenesulfonyl substituted hetercyclic molecules 85 and 88 also gave triplet EPR spectra, which are consistent with triplet radical pairs. Results indicate that nitro-sulfur bonds were easily cleaved by 230-325 nm photolysis, and the results are supported by ab initio calculations. Therefore, the reported D' value (0.0226 cm-1) of a biradical by Professor Berson in the photolysis of N-tosyl pyrrole diazene 18 (J. A. Berson, J. Am. Chem. Soc. 1997, 119, 1416.) may not be a triplet biradical and could be a triplet radical pair instead.
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Yi-KuiChen and 陳怡魁. "Studying tautomeric reactions of radical compounds of adenine thymine base pair by Nature Bond Orbital analysis." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/02252977472290178984.
Full textAbstract:
碩士國立成功大學
化學系碩博士班
98
The tautomerism, which takes place in DNA base pairing, might lead to confusing genetic coding. In the charged DNA pairing radicals, either radical cations or anions, the rates of tautomerism processes would increase and, consequently, changes of genetic codes become noteworthy. The proton transferring mechanism reported for the adenine thymine base pair have been subjected to quantum mechanic studies in order to lay the foundation for future studies in DNA pairing. Through molecular calculations at density function level [DFT/6-31G(d)], the initiator, transition state(s), intermediate and final products involved in two-step proton migration mechanism have been studied. From the result of electronic distribution and spin, we assumed a proton or hydrogen atom was transferred. Furthermore, we performed analysis of the natural bond orbital to obtain information about this reaction by E2 value and electronic structure. We found out that the oxygen of thymine transformed from ketone form to enol form in transforming from A-T base pair to a radical anion.
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Gourlay, Matthew D., John Kendrick, and Frank J. J. Leusen. "Predicting the Spontaneous Chiral Resolution by Crystallization of a Pair of Flexible Nitroxide Radicals." 2008. http://hdl.handle.net/10454/4621.
Full textAbstract:
NoThe separation of racemates into pure enantiomers through crystallization is an important industrial process. This study provides further validation of a novel, predictive approach for spontaneous resolution in which crystal structure prediction simulations are used to explore the relative stabilities of racemic solids versus enantiopure solids. 2-(4-Hydroxyphenyl)-2,5,5-trimethylpyrrolidine-1-oxy (compound 1) has previously been shown to be a racemic conglomerate, while a similar compound, 2-(3-hydroxyphenyl)-2,5,5-trimethylpyrrolidine-1-oxy (compound 2), was not. A conformational search using the Dreiding force field revealed 10 conformational minima for compound 1, and 20 for compound 2. Atomic charges were calculated using unrestricted DFT B3LYP 6-311G** optimized structures, and a crystal structure prediction was performed using the Dreiding force field, considering all low-energy gas-phase conformations and all relevant space groups. Analysis of the predicted crystal structures suggests that compound 1 is a racemic conglomerate, but compound 2 is not. This is in agreement with the experimental evidence.
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YEH, SHU-WEN, and 葉淑文. "Sequence effects on the proton-transfer reaction of the guanine-cytosine base pair radical anion and cation." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/36783145464605377950.
Full textAbstract:
博士國立中山大學
化學系研究所
100
The formation of base pair radical anions and cations is closely related to many fascinating research fields in biology and chemistry such as genetic mutation, radiation-induced DNA damage and dynamics of charge transfer in DNA. However, the relevant knowledge so far mainly comes from studies on isolated base pair radical anions and cations, and their behavior in the DNA environment is less understood. In this study, we focus on how the nucleobase sequence affects the properties of the guanine–cytosine (G:C) base pair radical anion and cation. The energetic barrier and reaction energy for the proton transfer along the N1(G)–H‧‧‧N3(C) hydrogen bond and the stability of (G:C)‧ (i.e., electron affinity and ionization potential of G:C) embedded in different sequences of base-pair trimer were evaluated using density functional theory and two-layer ONIOM method. The computational results demonstrated that the presence of neighboring base pairs has an important influence on the behavior of (G:C)‧ in the gas phase. The excess electron and positive hole were found to be localized on the embedded G:C and the charge leakage to neighboring base pairs was very minor in all of the investigated sequences. Accordingly, the sequence behavior of the proton transfer reaction and the stability of (G:C)‧ is chiefly governed by electrostatic interactions with adjacent base pairs. However, the effect of base stacking, due to its electrostatic nature, is severely screened upon hydration, and thus, the sequence dependence of the properties of (G:C)‧ in aqueous environment becomes relatively weak and less than that observed in the gas phase. The effect of geometry relaxation associated with neighboring base pairs as well as the possibility of proton transfer along the N2(G)–H‧‧‧O2(C) channel have also been investigated. The implications of the present findings to the electron transport and radiation damage of DNA are discussed.
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Sáenz, de Viguera Erkiaga Luis. "Dena Ongi Dabil! ¡Todo Va Dabuten! Tensión y Heterogeneidad de La Cultura Radical Vasca en el límite del Estado Democrático (1978- ...)." Diss., 2007. http://hdl.handle.net/10161/390.
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Lin, Yi-Feng, and 林義峰. "Part Ⅰ Synthesis and Photochemistry of a series of radical pair precursors contain 1-toluene sulphonyl benzimidazoles and their derivatives Part Ⅱ Synthesis of (4,4´-dicarboxylate-2,2´-bipyridyl) ruthenium complexes applied in the solar cell." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/45209660368849627531.
Full textAbstract:
碩士國立交通大學
應用化學系所
93
The major part of this thesis is about the syntheses and EPR studies of a series of radical pair precursors (55, 56 and 57) which contain 1-toluene sulphonyl benzimidazoles as the key components. The photolysis (230-325 nm) of 55 at 77 K in a MTHF matrix gave EPR signals characteristic of a randomly oriented triplet radical pair and its zero-field splitting parameters are determined to be |D/hc| = 0.0144 cm-1 and |E/hc| = 0.0020 cm-1, respectively. Furthermore, the photolysis of 55 in the presence of MNP in CDCl3 at room temperature gave not only the Photo-Fries rearrangement products 72 and 73, but also the radical trapping product, Ts-MNP. The results support that 55 is a good precursor for radical pair under photochemical conditions, and the overall photochemical quantum yield for radical pair formation is determined to be 0.24 �b 0.07. The photolysis of 56, a precursor for two triplet radical pairs linked by a meta-xylene unit, gave EPR signals which are consistent with a triplet species rather than a quintet species and the D´ value of 85 and 86 is smaller than 84 taken at 77 K. Finally, the photolysis of 57 at 77 K in MTHF glassy matrix did not show EPR signals of the predicted three triplet states plus a quartet state. Compound 57 was found to be inert under low temperature glassy matrixes which was confirmed by a low temperature UV/vis study at the same matrixes (carried out by Dr. Itoh in Japan). In part Ⅱ, the preparation of dye sensitized TiO2 solar cells was carried out. Cis-di(thiocynato)bis(2,2´-bipyridyl-4,4´-dicarboxylate) ruthenium (Ⅱ), the N3 dye, which has the record high quantum efficiency (10-12%) for light to energy transfer was out first target compound. A similar analogue, 92, was also synthesized. Further work is needed before we can find a substitute for the N3 dye in Dye Sensitized Solar Cells.