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Dissertations / Theses on the topic 'Atomic And Nuclear Physics'
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1
Blundell, S. "The theory of nuclear effects in atomic spectra." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355731.
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James, Jessica. "Nuclear structure effects in atomic parity non-conservation." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259953.
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Vrinceanu, Daniel. "Quantal-classical correspondence in atomic collisions." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/28035.
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O'Connor, Daryl John. "Atomic collisions with surfaces." Thesis, Canberra, ACT : The Australian National University, 1997. http://hdl.handle.net/1885/144473.
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Horsfield, Mark Andrew. "Nuclear Magnetic Resonance in petroleum engineering." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334172.
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Quadrini, Fabio. "Atomic angular momentum polarization in molecular photodissociation." Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670158.
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Xu, Ping. "New methods in nuclear magnetic resonance spectroscopy." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239177.
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Windham, Gordon. "Spin dependence in heavy ion induced nuclear reactions." Thesis, University of Surrey, 1986. http://epubs.surrey.ac.uk/843452/.
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The interest of this work is to explore the spin dependent effects of projectile structure in nuclear heavy ion induced reactions. The projectiles are considered to consist of two clusters which remain inert, the intercluster wavefunctions are obtained by the use of the orthogonality condition model. Excitation to the low lying projectile states is included by the use of coupled channels calculations. The projectile excited states are included by allowing excitation in the inter cluster wavefunctions. Coupling to the excited states is performed by multipole terms arising from a single folding model, which is used consistently throughout the work. The effects of projectile excitation are considered in two areas, elastic and inelastic scattering, and transfer reactions. It is found that the inclusion of the projectile excited states has a very strong effect on the spin dependent elastic observables, in particular the vector analysing powers. In contrast to earlier analysis it is found that projectile excitation plays a dominant role in reproducing the experimentally observed vector analysing powers for the elastic scattering of 6Li from 16O and 28Si at 22.8 MeV. Projectile excitation is also seen to produce strong spin dependent effects in the elastic scattering of Li from 120Sn at 44 MeV and of 19Ffrom 28Si at 60 MeV. The inclusion of projectile excitation via CCBA calculations produces changes in the transfer cross section for the 28Si (19F, 16O)31P(1/2+ ,g.s.) reaction. The observed changes can be understood in terms of the effects of spin dependence in the reaction path. The inclusion of projectile excitation however does not significantly improve the quality of the agreement with experimental data.
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Duce, Suzanne Louise. "Nuclear magnetic resonance imaging and spectroscopy of food." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240194.
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Higgins, Katrina Bernadette. "Positron scattering by atomic hydrogen." Thesis, Queen's University Belfast, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317443.
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Zetie, K. P. "Parity non-conservation in atomic bismuth." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315814.
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Westlén, Daniel. "Why Faster is Better : On Minor Actinide Transmutation in Hard Neutron." Doctoral thesis, KTH, Fysik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4280.
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In this thesis, options for efficient transmutation of transuranium elements are discussed. The focus is on plutonium, americium and curium mainly because of their long-term contribution to the radiotoxicity of spent nuclear fuel. Two innovative helium-cooled core designs are proposed, dedicated to the transmutation of actinides. The performance of the more promising of the two is studied in realistic transient fuel cycle scenarios. During the 1150 day irradiation cycle, a minor actinide consumption of 355 kg/GWth·year is achieved. An analysis of the efficiency of spallation neutron sources in helium-cooled cores is also performed. It is shown that the proton source efficiency, ψ∗, is improved by about 10% when helium is used as coolant, rather than lead-bismuth eutectic. Further, a proposal is made to transmute actinides in the upper part of a BWR core. A net consumption of transuranics is shown possible in the BWR park already when 50% of the BWR fuel is of the proposed evolutionary type. The thesis concludes that efficient transmutation of transuranic elements in dedicated helium-cooled subcritical cores is possible. But, in many instances fuel cycles without dedicated cores may lead to comparable final states. Especially, the evolutionary BWRfuel proposed seems interesting.QC 20100820
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Khan, Umar. "Control of atomic force microscopes." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/372495/.
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Atomic force microscopes or AFMs are instruments which use a mechanical probe to scan a sample and estimate surface topography with nanometer accuracy. The term atomic force originates from the fact that the imaging process relies upon the existence of the inter-atomic interaction force between the mechanical probe and sample surface. These instruments have established themselves as a vital cutting edge tool for investigation of matter at the nanometer scale. Their widespread usage is due not only to their superior resolution but also because they can operate in any medium namely air, liquid and vacuum. Another major advantage is that, unlike their predecessor instruments AFMs do not require their samples to be conductive. This fact alone has enabled in situ imaging of biological samples with unprecedented resolution and without sample alteration. Other instruments like scanning electron microscopes (SEMs) can also view biological samples, however they require the samples to be prepared and dried. While some sample structure may be preserved, AFMs have no such limitation. Despite the fact that AFMs offer all these advantages, the usage of a mechanical probe for image generation causes them to be inherently reliant upon a feedback control loop. This is because the probe motion must be controlled in a suitable manner to avoid letting its motion dynamics distort the sample image. In addition, since the mechanical probe must be sequentially moved over the sample point by point, the imaging times are long and range from a few seconds to in excess of ten minutes. Given that feedback control is an integral part of AFM operation, the end users are forced to manually tune Proportaional-Integral (PI) controllers which are used in most commercial AFMs. Since the vast majority of scientists using AFMs do not necessarily possess a knowledge of feedback control, they do this tuning though a manual trial and error procedure which consumes valuable research time. Although the control systems community has taken considerable interest in AFM control, the methods suggested often require high order controllers and are tested for a specific experimental set up. The primary objective of this research is therefore to develop a novel automated controller synthesis mechanism which has the potential of being used in a diverse range of AFM setups. The method of choice for this research is Multiple Model Adaptive Control (MMAC). The motivation for this decision as well as experimental verification is provided in detail in this thesis. Given the wide commercial usage of PI controllers, the same are used as a starting point for this work. The applicability of the method suggested is however by no means restricted to them, and in the future can be extended to incorporate more sophisticated controllers, for instance robust controllers. The second objective of this research is to investigate two novel methods which have the potential of substantially reducing the AFM imaging time. The first one suggests coarser scan trajectories to save time, and then estimates the sample image using a relatively new signal processing method called Compressive Sensing. The second method suggested uses the AFM's mechanical probe in a novel manner that can also substantially reduce imaging time.
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Peeke, Richard Scot. "Exploring a Novel Approach to Technical Nuclear Forensics Utilizing Atomic Force Microscopy." W&M ScholarWorks, 2014. https://scholarworks.wm.edu/etd/1539626950.
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Belov, Nikolay [Verfasser], and Zoltan [Akademischer Betreuer] Harman. "Nuclear effects in atomic and solid state physics / Nikolay Belov ; Betreuer: Zoltan Harman." Heidelberg : Universitätsbibliothek Heidelberg, 2015. http://d-nb.info/1180396391/34.
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Yan, Haiyang. "Applications of polarized helium-3 filters in neutron scattering." [Bloomington, Ind.] : Indiana University, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3344613.
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Thesis (Ph.D.)--Indiana University, Dept. of Physics, 2008.Title from home page (viewed on Oct 8, 2009). Source: Dissertation Abstracts International, Volume: 70-02, Section: B, page: 1098. Adviser: William Michael Snow.
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Gaunt, Adam P. "Towards micro-imaging with dissolution dynamic nuclear polarisation." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/51219/.
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Nuclear magnetic resonance (NMR) of small samples and nuclei with a low gyromagnetic ratio is intrinsically insensitive due to the received signal dependence on Boltzmann's statistics. This insensitivity can be partially overcome through the application of hyper polarisation techniques such as Dissolution Dynamic Nuclear Polarisation (D-DNP). It is hoped that the hyper polarised 13C signal received from labelled small molecules could facilitate imaging of metabolic and transporter processes in biological systems. In order to realise this, appropriate molecules and experimental hardware must be used. A detailed description of the experimental set-up used for carrying out DDNP is given and the system is characterised. the advantageous use of a dual iso-centre magnet system is elucidated with optimisation of acquisition of fast relaxing molecules. such a system allows for interrogation of processes with short relaxation times, not possible with traditional, stand-alone polarisers. To acquire the maximum amount of hyper-polarised 13C signal in an imaging experiment, parallel acquisition techniques have been implemented and the hardware designed with such goals in mind. Multiple coils have been used to allow accelerated image acquisition. As such this work has validated the SENSE algorithm for artefact free, image reconstruction on the micro-scale. These techniques require an array of coils which add to the complexity of the design of the probehead. Decoupling methods and array coil construction must be considered the methods used to ensure well isolated coils, such as geometric decoupling, are presented. The novel fabrication and implementation of micro-coils for imaging and spectroscopy of nL scale samples is presented this will help facilitate the acquisition of images showing metabolic processes in active transport in cells. By placing the coils close to the sample it is possible to gain sensitivity relative to the mass of the sample in question. To achieve signal detection on the order of nL a novel, exible micro-coil array has been fabricated and the results of NMR experiments carried out on both protons and 13C are shown. This is the final stage before integrating the coils with the D-DNP system. The acquisition of 13C signal with the micro-coils displays optimal electronic characteristics when compared with other detectors presented in the literature. The final goal of the work is to produce a system that is capable of micro imaging in small biological samples such as the Xenopus Oocyte with a view to monitoring metabolic processes and transportation without the need for the use of the large fluorescing proteins (GFP's) that have been used in previous work (1). The need for GFP's attached to metabolites results in the measured data being non-physical as the fluorescing protein is often much larger than the molecule being transported. It is hoped that the use of hyperpolarised small molecules (such as pyruvic acid) may be able to remove this need for GFP's in the study of metabolite transportation.
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Williams, James Francis. "The submitted works of J.F. Williams for the Degree of Doctor of Science : subtitled "Experimental studies in atomic collisions"." Thesis, Canberra, ACT : The Australian National University, 2017. http://hdl.handle.net/1885/139006.
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Cronin, Alexander D. "New techniques for measuring atomic parity violation /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/9766.
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Magrakvelidze, Maia. "Nuclear dynamics and ionization of diatomic molecules in intense laser fields." Thesis, Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/2283.
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McGeorge-Henderson, Ben P. "Novel acquisition strategies for dissolution dynamic nuclear polarisation." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/43266/.
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Dynamic Nuclear Polarisation (DNP) produced molecules with spin polarisation levels that are up to three orders of magnitude larger than their thermal equilibrium values. Most DNP mechanisms work at temperatures of 2 K and lower, meaning that the sample is stored in the solid-state. Combining DNP with a rapid temper- ature jump to room temperature allows liquid-state NMR analysis with a signal that is ve orders of magnitude higher than observed with thermal polarisation. However, the information obtained during a dissolution experiment is limited by the intrinsic liquid-state longitudinal relaxation of the spins of interest. is thesis looks to increase the information acquired in a number of ways. First, by devel- oping a new dissolution system for the dual iso-centre magnet it was possible to reproducibly perform enhanced NMR acquisition 600 ms following sample disso- lution. is has allowed the observation of hyperpolarised 13C spins with T1 times as low as 200 ms. Complimentary information can be obtained following sample dissolution by observing multiple spin species simultaneously. 13C and 15N spins are both polarised by microwave irradiation of the same frequency, so both can be analysed during a single dissolution DNP experiment. A novel probe has been used that contains six individual 13C microcoils. ese coils are separated in space and operate independently. is probe, in conjunction with dissolution DNP, can be used for observing dynamic molecular information on the time scale of 200 ms, however with further development this time scale should drop to less than 100 ms while maintaining a required minimum spectral resolution. Initial tests have been performed with both thermally polarised and hyperpolarised samples.
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Sun, Jianhua. "Studies of Molecular Dynamics of Fmoc-Alanine-d3 through Solid State Deuteron Nuclear Magnetic Resonance." W&M ScholarWorks, 2013. https://scholarworks.wm.edu/etd/1539626936.
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Kelleher, Aidan Michael. "A measurement of the neutron electric form factor at very large momentum transfer using polarized electrons scattering from a polarized helium-3 target." W&M ScholarWorks, 2010. https://scholarworks.wm.edu/etd/1539623565.
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Knowledge of the electric and magnetic elastic form factors of the nucleon is essential for an understanding of nucleon structure. of the form factors, the electric form factor of the neutron has been measured over the smallest range in Q2 and with the lowest precision. Jefferson Lab experiment 02-013 used a novel new polarized 3He target to nearly double the range of momentum transfer in which the neutron form factor has been studied and to measure it with much higher precision. Polarized electrons were scattered off this target, and both the scattered electron and neutron were detected. GEn was measured to be 0.0242 +/- 0.0020(stat) +/- 0.0061(sys) and 0.0247 +/- 0.0029(stat) +/- 0.0031(sys) at Q2 = 1.7 and 2.5 GeV2, respectively.
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Tracy, James L. Jr. "A binding energy study of the Atomic Mass Evaluation 2012 and an updated beta-decay study of neutron-rich 74Cu." Thesis, Mississippi State University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10243335.
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A study of ground state binding energy values listed in the Atomic Mass Evaluation 2012 (AME2012) using an interpretive approach, as opposed to the exploratory methods of previous models, is presented. This model is based on a postulate requiring all protons to pair with available neutrons to form bound alpha clusters as the ground state for an N = Z core upon which excess neutrons are added. For each core, the trend of the binding energy as a function of excess neutrons in the isotopic chain can be fit with a three-term quadratic function. The quadratic parameter reveals a smooth decaying exponential function. By re-envisioning the determination of mass excess, the constant-term fit parameters, representing N = Z nuclei, reveal a near-symmetry around Z = 50. The linear fit parameters exhibit trends which are linear functions of core size. A neutron drip-line prediction is compared against current models. By considering the possibility of an alpha-cluster core, a new ground-state structure grouping scheme is presented; nucleon-nucleon pairing is shown to have a greater role in level filling. This model, referred to as the Alpha-Deuteron-Neutron Model, yields promising first results when considering root-mean-square variances from the AME2012.
The beta-decay of the neutron-rich isotope 74Cu has been studied using three high-purity Germanium clover detectors at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. A high-resolution mass separator greatly improved the purity of the 74Cu beam by removing isobaric contaminants, thus allowing decay through its isobar chain to the stable 74Ge at the center of the LeRIBSS detector array without any decay chain member dominating. Using coincidence gating techniques, 121 gamma-rays associated with 74Cu were isolated from the collective singles spectrum. Eighty-seven of these were placed in an expanded level scheme, and updated beta-feeding level intensities and log( ft) values are presented based on multiple newly-placed excited states up to 6.8 MeV. The progression of simulated Total Absorption gamma-ray Spectroscopy (TAGS) based on known levels and beta feeding values from previous measurements to this evaluation are presented and demonstrate the need for a TAGS measurement of this isotope to gain a more complete understanding of its decay scheme.
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Dunning, Alexander. "Coherent atomic manipulation and cooling using composite optical pulse sequences." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/364735/.
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The laser cooling of atoms to ultracold temperatures has propelled many groundbreaking advances in fundamental research and precision measurement, through such applications as quantum simulators and interferometric sensors. Laser cooling remains, however, highly species-selective, and techniques for its application to molecules are still in their infancy. This thesis broadly concerns the development of laser cooling schemes, based on sequences of coherent optical pulses, which can in principle be applied to a wide range of species. We describe a cooling scheme, in which a velocity-selective impulse analogous to that in Doppler cooling is generated by a light-pulse Ramsey interferometer, and present a proof-of-concept demonstration of the scheme using ultracold rubidium-85 atoms as a test-bed. We realise an interferometer for the atoms, as they are in free-fall after release from a magneto-optical trap, by inducing stimulated Raman transitions between their ground hyperfine states. We provide a comprehensive characterisation of these Raman light-pulse interferometer optics, where particular attention is paid to light shift effects. Raman pulses, and indeed coherent operations in any quantum control system, unavoidably suffer from systematic errors in the control field intensity and frequency, and these lead to reductions in pulse fidelity and readout contrast. In parallel to the work on interferometric cooling in this thesis, we report our preliminary investigations into composite pulses, whereby `naive' single pulses are replaced by sequences of rotations with tailored durations and phases, for improving pulse fidelity in the presence of inhomogeneities. We find that composite pulses can indeed be highly effective in our cold atom system, and propose that their application in such devices as interferometric sensors is a promising prospect.
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Beck, William A. "Semiclassical, Monte Carlo model of atomic collisions : stopping and capture of heavy charged particles and exotic atom formation /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/9796.
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Wisniewski, Daniel. "Simulations of Dynamic Nuclear Polarization pathways in large spin ensembles." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/39045/.
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Dynamic Nuclear Polarization (DNP) is a method for signal enhancement in NMR, with numerous applications ranging from medicine to spectroscopy. Despite the success of applications of DNP, the understanding of the underlying theory is still limited. Much of the work on the theory of DNP has been carried out on small spin systems; this is a restriction due to the exponential growth of the Liouville space in quantum simulations. In the work described in this thesis, a methodology is presented by which this exponential scaling can be circumvented. This is done by mathematically projecting the DNP dynamics at resonance onto the Zeeman subspace of the density operator. This has successfully been carried out for the solid effect, cross effect and recently for the Overhauser effect in the solid state (see appendix A.4). The results are incoherent state-dependent dynamics, resembling classical behaviour. Such form of effective dynamics allows the use of kinetic Monte Carlo algorithms to simulate polarization dynamics of very large spin systems; orders of magnitude larger than has previously been possible. We verify the accuracy of the mathematical treatment of SE-DNP and CE-DNP, and illustrate the insight large spin-system simulations provide into the mechanism of DNP. For SE-DNP the mechanism of polarization to the bulk of spin systems is determined to be spin diffusion, and we carried out studies into the efficiency and performance of radicals, with an outlook on radical design. We also show that the Zeeman projection can be applied to heteronuclear spin systems if the nuclear species are close in frequency, and we present a formalism for simulating C-13 nuclear spin systems based on a linear rate approach, enabling simulations of thousands of spins in a matter of minutes. A study into the scaling of the kinetic Monte Carlo algorithm error, and the simulation run time, with respect to an increasing number of spins is also presented. For CE-DNP the error analysis led to establishing a parameter regime in which the effective dynamics are accurate. We show that spin diffusion is the mechanism of transfer of polarization to bulk nuclei. We also show how the effective rates for CE-DNP can be used to understand the efficiency of bi-radicals, point to optimisation possibilities, and hold a potential to aid in bi-radical design. We finally show large scale simulations for CE-DNP bi-radical systems with improved parameters; leading to very rapid build-up of nuclear polarization.
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Pérez, Linde Angel Joaquin. "Application of cross polarisation techniques to dynamic nuclear polarisation dissolution experiments." Thesis, University of Nottingham, 2010. http://eprints.nottingham.ac.uk/11417/.
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Dynamic Nuclear Polarisation (DNP) was suggested for the first time by Albert Overhauser in early 1950s. In DNP experiments the polarisation from electrons can be transferred to nuclei by irradiation of the electron resonance line. There are several possible mechanisms for polarisation transfer that involve DNP in solid state depending on the width of the electron line in respect to the nuclear Larmor frequency. In this thesis, the efficiency of TEMPO radical (2,2,6,6 tetramethilpiperidine, 1 oxyl) for DNP is demonstrated in combination with nuclear polarisation transfer techniques for dissolution experiments. New cryo-probes were developed for DNP and cross polarisation (CP) for operation temperatures as low as 1.5 K. Two of them were designed for dissolution experiments. Some published sequences of nuclear polarisation transfer were tested at low temperatures and compared. Novel sequences were implemented for efficient CP in organic samples doped with TEMPO to allow for a consecutive dissolution experiment. The combination of DNP with new CP sequences at low temperatures, achieved at least twice the 13C polarisation obtained with DNP and in a substantially shorter time (between 5 to 10 minutes) in samples doped with TEMPO. The polarisation levels obtained in samples of [13C-1] labelled Na acetate in a few minutes was comparable to the polarisation obtained with trityl radicals in a few hours. In addition, another strategy was investigated by using brute force polarisation as a mechanism for achieving large levels of nuclear spin order. The problem presented by this method is the long relaxation time required to obtain the thermal equilibrium polarisation. By doping with lanthanides samples of [13C-1] labelled Na acetate in 1:1 glycerol-water, it was possible to obtain thermal equilibrium for a 13C spin system in less than one hour.
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Møller, Morten. "Optimizing the structure of scanning probes for atomic manipulation." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/44916/.
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Scanning probe microscopy (SPM) allows us to directly measure the interactions between a probe and a sample at the atomic scale. Techniques such as non-contact atomic force microscopy (NC-AFM), allows us to to characterize the forces present on a surface, resolve the atomic structure of molecules or examine their chemical properties, while scanning tunneling microscopy (STM) allows their electronic properties to be characterized. As the interactions take place at the atomic scale, the atomistic state of the probe apex plays a crucial role. In AFM, it is the atomic scale forces between the outermost atoms of the probe and surface that are dominant, while for STM the density of states (DOS) that contribute to tunneling are crucial. Therefore, understanding and controlling the tip termination is crucial to derive meaningful interpretations from experimental data. In this thesis, the role of the tip termination is examined for various surfaces and situations. We find that determining the "right" tip state depends critically on the experiment and several general strategies for shaping the tip apex into a preferred state are therefore outlined. H:Si(100) surfaces were used as a substrate for lithographic patterning using STM. We have successfully implemented an automated extraction routine for performing large scale patterning with high fidelity and single atom specificity. Our ultimate goal is to combine the extraction routine with SPM image recognition software to allow analysis and manipulation of atomic scale features without human intervention. To perform manipulations reliably, the tip influence on "what we see" (tip imaging states), or specifically on what the recognition software can identify, needs to be considered. We find, counter-intuitively, that atomic scale manipulation with the highest fidelity occurs when silicon dimers are observed as rows as opposed to when atomic resolution imaging occurs. The tip state influence on measuring surface diffusion of PTCDA on Ag(110) surfaces, was also investigated. We find that the adsorption kinetics of diffusing molecules can only be detected for specific tip imaging states. To allow examination with no-human intervention, the tip state needs to be carefully considered, and a combination of analytical and spectroscopic tools needs to be implemented in conjunction with the experiment. Additionally, characterization of the tip apex was investigated at the tunnel junction between a STM tip and a metal surface using field emission measurements. Our results suggest that field emission measurements performed at the tunnel junction are sensitive to changes in the nanoscopic/mesoscopic tip apex structure, thus opening up the possibility of automating the process of characterization the tip apex.
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LaForge, Aaron Christopher. "Three-body dynamics in single ionization of atomic hydrogen by 75 keV proton impact." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2010. http://scholarsmine.mst.edu/thesis/pdf/Laforge_09007dcc80798b26.pdf.
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Thesis (Ph. D.)--Missouri University of Science and Technology, 2010.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 21, 2010) Includes bibliographical references (p. 82-87).
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Mieszczynski, Cyprian. "Atomic scale structural modifications in irradiated nuclear fuels." Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01057120.
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This thesis work reports in depth analyses of measured µ-XRD and µ-XAS data from standard UO2, chromia (Cr2O3) doped UO2 and MOX fuels, and interpretation of the results considering the role of chromium as a dopant as well as several fission product elements. The lattice parameters of UO2 in fresh and irradiated samples and elastic strain energy densities in the irradiated UO2 samples have been measured and quantified. The µ-XRD patterns have further allowed the evaluation of the crystalline domain size and sub-grain formation at different locations of the irradiated fuel pellets. Attempts have been made to determine lattice parameter and next neighbor atomic environment in chromia-precipitates found in fresh chromia-doped fuel pellets. The local structure around Cr in as-fabricated chromia-doped UO2 matrix and the influence of irradiation on the state of chromium in irradiated fuel matrix have been addressed. Finally, for a comparative understanding of fission gases behavior and irradiation induced re-solution phenomenon in standard and chromia-doped UO2, the last part of the present work tries to clarify the fission gas Kr atomic environment in these irradiated fuels. The work performed on Kr, by micro-beam XAS, comprises the determination of Kr next neighbor distances, an estimation of gas atom densities in the aggregates, and apparent internal pressures in the gas bubbles.
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Swanson, Donald Raymond. "Properties of ³He films on Nuclepore and a path integral theory of atomic scattering at the surface of liquid ?He /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu148732358362224.
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Goulding, Philip. "The use of electric potential sensors in nuclear magnetic resonance and particle detection applications." Thesis, University of Sussex, 2015. http://sro.sussex.ac.uk/id/eprint/57919/.
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The work in this thesis extends the applications of the Electric Potential Sensor (EPS) designed by the Sensor Research Technology Centre. Combined is work undertaken in two areas related by their application in security systems: low-field nuclear magnetic resonance with electric-field acquisition, and particle detection for alpha, beta and neutron radiation. In both these areas the EPS is used as to acquire signals. The first half of the thesis consists of the work undertaken to design a low-field Nuclear Magnetic Resonance spectrometer to detect drugs and explosives. In doing so, the use of the electric field detection technique - patented by Sussex University - is extended to low-field NMR work. The eventual negative results in this field lead first to the design of a simpler proton magnetometer apparatus, a design which would confirm the use of the EPS at low frequencies, and eventually to a change in direction of the research: particle detection. Detailed in this first section are a theoretical explanation of NMR in chapter 2, and a chapter covering the design and testing of the equipment in chapter 3. The particle detection part of the thesis covers modifications made to the EPS in order to detect particles and experiments conducted to confirm their operation. As in the NMR section, the work is split into a theory chapter which underpins the work, providing context for the experiments chapter. Chapter 5 covers the detection of alpha, beta and neutron radiation and the use of feedback to control the RC time constant of the front end of the sensor. The work in this thesis concludes negative results in the NMR area, but proves the EPS particle detector as a viable, cost effective alternative to conventional detectors.
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Boulet, Antoine. "Density functional theory for Fermi systems with large s-wave scattering length : application to atomic and nuclear physics." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS212/document.
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Dans ce travail de thèse, des théories de type fonctionnelle de la densité sont développées pour des systèmes en interaction forte possédant une longueur de diffusion en onde s, notée as, anormalement grande. Les gaz atomiques ou la matière neutronique sont des exemples physiques de tels systèmes. La théorie des perturbations à N-corps est tout d'abord utilisée pour décrire les systèmes de fermions dilués. Cette approche conduit par exemple à la fonctionnelle de Lee-Yang qui est valide dans une plage de densité très restreinte lorsque la longueur de diffusion en onde s devient grande. Pour étendre le domaine de validité de l’approche perturbative, des techniques de resommation associées à l’approximation dite en échelle sont utilisée. Cette approche conduit à des expressions compactes pour l'énergie et/ou la self-énergie on-shell dans des systèmes infinis pouvant être appliquées à des systèmes plus ou moins denses. Cela conduit également à une énergie finie du gaz atomique à la limite unitaire, i.e. lorsque |askF|→+∞. Les fonctionnelles ainsi déduites restent assez complexes et manquent en général de pouvoir prédictif. Pour simplifier ces fonctionnelles, des approximations appelées respectivement approximations de “l’espace des phases” ou de “l'espace des phases partiel” sont proposées pour l'énergie ou la self-énergie. Ces approximations simplifient non seulement la forme des fonctionnelles, mais améliorent également leur pouvoir prédictif tout en reproduisant correctement la limite de basse densité. Guidé par les techniques de resommation non-perturbatives développées dans cette thèse, plusieurs nouvelles fonctionnelles sont proposées ainsi que leurs extensions permettant d’inclure des effets de portée effective. Ces fonctionnelles non empiriques, qui ne contiennent aucun paramètre libre, sont testées par rapport aux propriétés des systèmes d'atomes froids et/ou de la matière neutronique. Ces fonctionnelles reproduisent très bien les propriétés obtenues dans les calculs ab-initio ou observées expérimentalement dans les systèmes d'atomes froids. L'équation d'état de la matière neutronique est également reproduite jusqu'à ρ = 0.01 fm⁻³. La réponse statique de la matière neutronique, récemment calculée dans des théories ab-initio, est également mieux reproduite par rapport aux fonctionnelles empiriques utilisées généralement en physique nucléaire. Cette étude a aussi mis en évidence la nécessité de mieux comprendre les propriétés des quasi-particules telle que la masse effective. Pour progresser sur ce point, en partant des expressions resommées de la self-énergie et de l’approximation de l’espace des phases partiel, des expressions compactes du potentiel chimique et de la masse effective ont été obtenues ; ces expressions étant compatibles avec les fonctionnelles proposées dans la première partie de cette thèse. Ces expressions devraient élargir considérablement le domaine de validité des fonctionnelles non-empiriques par rapport aux théories perturbatives. Enfin, il est montré que les développements de ce travail sont également utiles pour réconcilier les paramètres généralement utilisés dans les fonctionnelles empiriques de la physique nucléaire avec les propriétés de l’interaction nucléaire forteIn the present work, a density functional theory (DFT) is developed for systems interacting through an anomalously large s-wave scattering length as. Examples of such systems are atomic gas or neutron matter. The Many-Body Perturbation Theory (MBPT) is first discussed to describe dilute Fermi systems. This approach leads to the well-known Lee-Yang functional valid in a very narrow range of density when the s-wave scattering length is large. To extend the domain of validity of the perturbative approach, resummation techniques with the ladder approximation is used. This leads to compact expressions for both the energy and/or the on-shell self-energy in infinite spin-degenerated systems that can be applied from diluted to dense systems. It also leads to finite energy in atomic gas at the unitary limit, i.e. when |askF|→+∞. The deduced functionals remain rather complex and lacks of predictive power in general. To simplify the functional, approximations called phase-space or partial phase-space approximations respectively for the energy or for the self-energy, are proposed. These approximations not only simplify the form of the functionals, but also improve their predictive power at various density while properly reproducing the low density limit. Guided by the non-perturbative resummation technique developed in this thesis, several novel functionals are proposed as well as extensions of them to include effective range effects. These non-empirical functionals, that essentially contain no free parameters, are tested against cold atom and/or neutron matter properties. A very good reproduction of ab initio and experimental observations in cold atom is obtained. The equation of state obtained for neutron matter is also reproduced up to ρ = 0.01 fm⁻³. The static response of neutron matter, recently obtained from ab initio theory, is also better reproduced compared to standardly used empirical nuclear DFT. This study has also pointed out the necessity to better understand quasi-particle properties like the effective mass. To further progress, starting from resummed expressions of the self-energy together with partial phase-space approximation, compact expressions of the chemical potential and effective masses are obtained that are eventually compatible with the DFTs proposed in the first part of this thesis. These expressions are anticipated to significantly extend the domain of validity compared to the perturbative approach. We finally show that the developments made in this work are also useful to reconcile the parameters generally used in the empirical nuclear DFT with the properties of the strong nuclear interaction
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Peng, Sheng. "Ultraviolet sources for advanced applications in the vacuum UV and near UV." W&M ScholarWorks, 2004. https://scholarworks.wm.edu/etd/1539623467.
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This dissertation documents a systematic study consisting of experimental investigations and theoretical analyses of intense ultraviolet sources in VUV and near-UV. Some engineering issues regarding two prototypes of electrodeless lamps using rf and microwave are discussed.;Various excimers that produce intense UV light are investigated, including: (1) A benchmark Xe2 excimer which has been proven to be very efficient in our novel rf capacitively coupled discharge lamp; (2) A rarely studied excimer, KrI, which suffers from predissociation and was reported to be very weak or invisible by most of other studies; (3) XeI excimer whose emission dominates around 253 nm and is promising as a mercury-free lamp for antibacterial applications. In the above studies, discharge temperatures are estimated from the emission band width. An elaborate kinetic model is developed for KrI to account for the KrI* and I2* intensities as a function of pressure. It was found that Kr2* plays the rule for energy transfer instead of Kr* in the pressure of interest. The electromagnetic wave interaction with charge particles is studied in our 2D and 3D EM-PIC simulations for both the rf and microwave lamps. Important plasma parameters, such as the electron density and temperature are obtained for various pressures. The electron energy distribution function that is important to account for excimer excitation is obtained.;We also performed a high-level ab initio calculation in Gaussian to produce the ground state potential curve for KrI, which agrees with previous scattering experiments and is necessary for predicting spectral emissions. as a systematic study to account for the KrI emission spectra at high pressure, we use a semiclassical model to account for emissions between a bound excited state and an unbound ground state. An explicit expression is obtained to represent the observed spectral intensity. Important molecular constants are obtained for KrI and compared with previous results.
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Changizi, Sara A. "Pairing correlation in atomic nuclei under extreme conditions." Doctoral thesis, KTH, Skolan för teknikvetenskap (SCI), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-217522.
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The pairing correlation has long been recognized as the dominant many-body correlation beyond the nuclear mean field. Pairing plays an essential role in many nuclear phenomena including the occurrence of a systematic odd-even staggering (OES) of the nuclear binding energy. Pairing interaction plays, in particular, a significant role in the stability of weakly bound nuclei. Therefore it has been one of the most critical topics in nuclear physics because of the weakly bound structure of all newly discovered nuclei. Beyond the line of stability, pairing interaction is not a residual interaction anymore. Its strength can be of the same order of magnitude as the mean field. In this thesis we have focused on the pairing interaction in atomic nuclei under extreme conditions to investigate the structure of loosely bound nuclei near the dripline; to probe and globally assess different outcomes of various zero-range pairing interactions and their effect on the loosely bound low angular momentum states. How much can density-dependence in zero-range pairing interaction nuclei affect the line of stability? Calculations predict that pure density-dependent pairing interaction so-called surface interaction enhances the collectivity and gives stronger neutron pairing gap in nuclei far from stability, while, the density dependence pairing interaction does not affect the gap for bound nuclei as much. The odd-even staggering of nuclear binding energies has been investigated to estimate the empirical pairing gap. A 3-point formula Δ(3)C (1/2[B(N,Z)+B(N −2,Z)−2B(N −1,Z)]) is advocated in this thesis, which we believe it is more suitable to measure the magnitude of pairing gap in even-even nuclei. The strength of Δ(3)C can be a good indicator of the two-particle spatial correlation. One-quasiparticle energies and binding energy for those odd nuclei, which can be approximated by spherical symmetry, are calculated to obtain binding energy odd-even staggering (OES) in all known semi-magic even-even nuclei. The pairing strength is fitted globally to all available data on the OES of semi-magic nuclei with Z ≥ 8. The difference between different zero-range density-dependent pairing interactions reduces with this global fitted parameter. The difference between the mean pairing gap and the OES gets larger as we get closer to the dripline. At the end of the thesis, a simple model has been developed which shows that when the mean-field becomes shallower the odd-even staggering of charge radii is reduced.This thesis covers results that are not included in the three published papers and some complementary works on the subject.Parkopplingen i atomkärnan anses vara den dominerande mångkropparskorrelationen efter kärnmedelfältet. Parkoppling i atomkärnan spelar en viktig roll i många kärnfenomen,inklusive förekomsten av en systematisk udda-jämn förskjutning (OES) av bindningsenergin.Hos svagt bundna atomkärnor däremot spelar parkopplingen en signifikant roll för stabiliteten. Det gäller alla de nyupptäckta neutronrika atomkärnor som karakteriseras aven svag bindningsenergi där således parkopplingen blir ett kritiskt fenomen. När vi lämnar stabilitetslinjen och närmar oss linjen av spontan neutronsönderfall är parkopplingeninte längre obetydlig, utan tvärtom spelar en viktig roll för stabiliteten hos atomkärnan.Dess styrka kan vara av samma storleksordning som medelfältet. I denna avhandling har vi fokuserat på parkopplingen i atomkärnor under extrema villkor i syfte att undersöka strukturen hos löst bundna atomkärnor nära linjen för neutronsönderfall; att utforska och globalt bedöma resultaten av olika parkopplingar baserad på en deltakraft (räckvidd noll) och deras effekt på löst bundna tillstånd med lågt rörelsemängdsmoment. Hur mycket kan ett täthetsberoende i parkopplingen påverka stabilitetslinjen? Beräkningarna förutsäger att ren densitetsberoende växelverkan för parkoppling, så kallad ytväxelverkan, ökar kollektiviteten i atomkärnan och ger ett större pargap för neutroner i kärnor långt ifrån stabilitetslinjen,medan densitetsberoende parkoppling påverkar inte gapet för bundna kärnor i samma omfattning.Udda-jämn-spridning av bindningsenergier har undersökts för att hitta storleken på parkopplingens gap. En 3-punktsformel Δ(3)C (1/2[B(N,Z)+B(N −2,Z)−2B(N −1,Z)]) förespråkas i denna avhandling, som vi anser vara mera lämplig för att mäta storleken på pargapet i jämn-jämna kärnor. Storleken på Δ(3)C kan vara en bra indikator på rumskorrelationen mellan två nukleoner. En-kvasipartikelenergi för de udda kärnorna, som kan approximeras med sfärisk symmetri, beräknas för att erhålla udda-jämn spridning (OES) med avseende på bindningsenergin för alla kända semi-magiska jämn-jämna kärnor. Parkopplingsstyrkan är globalt anpassat med all tillgänglig data på OES vad gäller semi-magiska kärnor med Z ≥ 8. Skillnaden mellan olika täthetsberoende parkopplingar med vår växelverkan minskar med dessa globalt anpassade parametrar. Skillnaden mellan det teoretiska genomsnittliga parkopplingsgapet och OES blir större när vi kommer närmare tröskeln för atomkärnans stabilitet. I slutet av avhandlingen har en schematisk modell utvecklats som, genom attgöra medelfältet grundare, reducerar de udda-jämnt spridda laddningsradierna. Avhandlingen innehåller dessutom resultat som inte ingår i de tre publicerade artiklarna samt några kompletterande arbeten om ämnet.
QC 20171114
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Devience, Stephen J. "Nuclear Magnetic Resonance with Spin Singlet States and Nitrogen Vacancy Centers in Diamond." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11628.
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Nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) are techniques widely utilized by many scientific fields, but their applications are often limited by short spin relaxation times and low sensitivity. This thesis explores two novel forms of NMR addressing these issues: nuclear spin singlet states for extending spin polarization lifetime and nitrogen-vacancy centers for sensing small samples.Chemistry and Chemical Biology
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Breeds, Edward. "Novel hardware for temperature-jump DNP." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/52518/.
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Although NMR is a versatile technique, the low values associated with nuclear spin polarization provide inherently weak signals. A novel system to perform temperature-jump dynamic nuclear polarization (DNP) has been designed and developed at the University of Nottingham, with the aim to enhance this signal and improve the sensitivity of the NMR experiment. This system utilizes a bespoke helium flow cryostat, located within the bore of a superconducting magnet, to achieve temperatures down to 1.75 K for high levels of polarization to build up on an electron spin population. This high level of polarization can then be transferred to a nuclear species of interest using microwave irradiation, while remaining at low temperature, allowing the weak signals associated with NMR to become enhanced. Following ample nuclear polarization build-up, a powerful mid-IR laser is used to rapidly bring the sample to 300 K, ensuring the spectra benefit from the line narrowing associated with liquid-state NMR. An Er:YAG laser with a wavelength of 2.94 μm has been chosen for this as it couples energy directly into the vibrational modes of hydroxyl groups present within the sample. The rapid heating mechanism underpins the success of this experiment twofold. Firstly, performing the temperature-jump in a shorter time period preserves a greater signal enhancement. This needs to be done carefully as too much heating will obliterate the sample, destroying the signal. Secondly, a temperature-jump without dilution of the sample, as occurs in dissolution DNP, allows sample recycling to take place. This opens the technique up for otherwise unavailable applications, such as multidimensional correlation spectroscopy with repetitive excitations. Development of the cryo-system, heating mechanism and NMR probe, alongside preliminary experiments and calculations, suggest that this technique should greatly improve the sensitivity of the liquid state NMR experiment.
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Fernandes, Carolina C. "Multinuclear magnetic resonance spectroscopy in the human brain at ultra high-field." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/46607/.
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In this thesis, new acquisition and analysis methods are described for multinuclear magnetic resonance spectroscopy (MRS) for the quantification of brain metabolites at ultra high magnetic field strengths (7T). An analytical model was derived for the optimisation of the stimulated echo acquisition mode (STEAM) sequence timing parameters for lactate detection. The effects of the chemical shift displacement artefact on the J-modulated signal for a weakly-coupled spin system were considered in the three applied directions of field gradients and the product operator formalism was used to obtain expressions for the signal modulation in each compartment of the excited volume. The validity of this model was demonstrated experimentally in a phantom and acquisitions with optimised parameters were performed on a healthy volunteer. The spectra acquired with an echo time (TE) of 144 ms and with an optimised mixing time and TE of 288 ms showed easily detectable lactate peaks in the normal human brain. Additionally, the acquisition with the longer TE resulted in a spectrum with less lipid/macromolecular (MM) contamination. The simulations demonstrated that the proposed analytical model is suitable for correctly predicting the resulting lactate signal. With the optimised parameters, it was possible to use a simple sequence with sufficient signal-to-noise ratio (SNR) to reliably distinguish lactate from overlapping resonances in a healthy brain at ultra high-field. Estimation of metabolic changes during neuronal activation represents a challenge for in vivo MRS, especially for metabolites with low concentration and signal overlap, such as lactate. This thesis also includes work focused on the reliable quantification of lactate during a paradigm with 15 minutes of visual stimulation. The lipid and MM signals were significantly reduced by using a long TE (144 ms) sequence and the remaining MM signals in the vicinity of the lactate peak were individually fitted with simulated Lorentzian peaks, to ensure a good fit of the inverted lactate doublet. Statistically significant changes in lactate (~10%) and glutamate (~3%) levels during stimulation were detected in the visual cortex and agree with previous measurements. Furthermore, the use of a prolonged stimulation period unveiled a distinctive metabolic response pattern, which can provide further insight into brain activation mechanisms. 13C MRS combined with the infusion of labelled substrates is able to provide unique information on the relationship between neuroenergetics and brain function. However, the lack of sensitivity associated with the general complexity of 13C experiments has hampered its widespread use for research into human brain disease. In this study, a new methodology for acquisition and analysis of 13C signal is presented for the study of neuroenergetics and neurotransmission in a deep brain structure - anterior cingulate cortex - that is thought to play a major role in the processing of sensory information and can be impaired in patients with schizophrenia. In vitro testing was performed to evaluate the performance of the implemented sequence for signal localisation and polarisation transfer, both proving adequate for the intended purpose. In vivo data were acquired in four subjects, one diagnosed with early schizophrenia, with a protocol which involved 60 minutes of infusion of [1-13C]glucose. Turnover curves for the labelled products were generated from the dynamic 13C spectra with a temporal resolution of 10 minutes and were in agreement with the ones obtained from rodent experiments. Therefore, the feasibility of 13C experiments for the study of psychosis was here demonstrated, taking advantage of the increase in SNR at ultra high-field for determination of metabolic fluxes.
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Coupier, B. "Studies towards the understanding of the effects of ionizing radiations at the molecular scales (20 to 150 keV H+/H + He Collisions; Dissociative Electron Attachment to Water)." Phd thesis, Université Claude Bernard - Lyon I, 2005. http://tel.archives-ouvertes.fr/tel-00012069.
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Ce travail s'inscrit dans le cadre d'études récentes pour la compréhension à l'échelle moléculaire des effets des rayonnements ionisants sur les systèmes biologiques, mises en oeuvre par le groupe IPM de l'IPNL en collaboration avec l'Institut für Ionenphysik de l'Université d'Innsbruck. Il est composé de deux parties. La première présente un nouvel ensemble de mesures des sections efficaces d'ionisation de l'hélium par impact de protons ou d'atomes d'hydrogène dans la gamme d'énergie d'intérêt pour la radiobiologie (20 à 150keV). Il s'agit de systèmes modèles d'intérêt pour la compréhension des phénomènes de base, et les collisions H + He ont fait l'objet, jusqu'à présent, de peu d'études utilisant les techniques de coïncidences. En outre, cette étude avec l'hélium a été faite dans l'intention de réaliser un test général de fonctionnement de l'appareillage avant d'aller vers des systèmes plus complexes. Des études similaires ont été ensuite réalisées en remplaçant la cible d'hélium par l'eau ou par des molécules d'intérêt biologique (Uracil, Thymine ...). La seconde partie de la thèse traite d'un autre type de radiations ionisantes que l'on peut voir comme une des conséquences secondaires des radiations étudiées dans la première partie. Des électrons de faible énergie (1 à 16eV) sont émis lors du bombardement de la matière par des protons ou des atomes d'hydrogène rapides; ces électrons ayant à leur tour des effets ionisants sur l'environnement. Une étude de l'attachement dissociatif des électrons sur l'eau a été entreprise à l'université d'Innsbruck, motivée par l'existence d'importants désaccords entre les précédentes études sur le même sujet. Le problème de la discrimination des ions à grande énergie cinétique dans le monochromateur trochoïdal utilisé pour cette étude a fait l'objet d'une attention particulière.
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Kaya, Dilan. "Quantal Effects On Growth Of Instabilities In Nuclear Matter." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/2/1116037/index.pdf.
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The quantal Boltzmann&ndashLangevin equation is used to obtain a dispersion relation for the growth rates of instabilities in infinite nuclear matter. The dispersion relation is solved numerically for three different potentials. The quantal results are compared with the semi-classical solutions. It is seen that with the inclusion of the quantal effects the growth rates of the fastest growing modes in the system are reduced and these modes have the tendency to occur at longer wavelengths for all the potentials considered. Furthermore, the boundaries of the spinodal region is determined by the phase diagrams using the same three potentials and it is observed that the expanding nuclear matter undergoes liquid-gas phase transition at reduced temperatures when the quantum effects are included.
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Lo, Monaco L. "Nucleon transfer in heavy ion reactions." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371555.
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Ferreras, Jorge. "One-dimensional Bose gases on an atom chip." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/53074/.
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Ultracold atomic gases have proven to be an excellent tool for research in quantum systems. A Bose gas can be trapped on an atom chip using very well defined and tunable spatially-dependent potentials. The proximity of the atoms to the chip permits the use of low currents allowing for highly accurate temporal changes. Excellent experimental apparatus is needed to achieve Bose-Einstein condensation with a sufficient atom number to study low-dimensional physics. The setup described in this document utilises a set of current-carrying structures on top of which an atom chip sits. For improved atom loading rate, a two-dimensional loading stage was added, extending the lifetime of the magnetic trap. From this loading stage to the atom chip, Bose-Einstein condensation of 105 Rubidium-87 atoms was achieved in less than 30 s, allowing for a large rate of experimental cycles. The high spatial and temporal tunability of this setup results in the ability to split the atomic cloud and quench the trapping potential geometry. Maximising the ratio between trapping frequencies for different spatial directions leads to the system presenting features of a one-dimensional gas. Manipulating the coherence dynamics of a one-dimensional Bose-Einstein condensate creates fluctuations in the phase properties of the wavefunction. These fluctuations are observed as atom density perturbations after releasing the trapping potentials, and are a tool for temperature measurements. When the cloud of atoms is positioned at a few tens of micrometres from the surface of the atom chip, corrugations in the microstructures of the chip affect the trapping potentials at very low temperatures 1 μK. This effect is simulated and quantified in the thesis, with the aim of improving future setups. Additionally, the effect is explored for microscopy purposes. The behaviour of a Bose-Einstein condensate, especially the expansion rate, has long been studied. In this thesis, the Gross-Pitaevskii Equation is introduced, finding its numerical solutions to the two-dimensional and three-dimensional forms, using the Split-Step Fourier Method. The results show very good agreement with the experimental results, as well as with other well- established theories of condensates. The creation of such a toolbox opens up the opportunity to further investigate the coherence dynamics of low-dimensional systems.
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Argenti, Luca. "The B-spline K-matrix Method in Atomic Physics." Doctoral thesis, Scuola Normale Superiore, 2009. http://hdl.handle.net/11384/85858.
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In the course of this thesis the B-spline K-matrix method, a theoretical technique
capable of reproducing the single ionization continuum of atoms, was developed.
Two systems were addressed in particular: helium and boron, as representatives
of two- and three-active-electron atoms.
Some of the findings presented here resulted in original cont
ributions to the scientific literature. Total and partial photoionization cros
s sections and asymmetry parameters of the fundamental helium state were examined up
to the sixth ionization threshold, yielding the first
ab initio reproduction of the first intruder state
effects below N=4 threshold, the first reproduction of dipole
asymmetry parameters below N=6 threshold and of nondipole anisotropy param
eter γ below N=2 threshold.
Most of the material presented here relies on the multiple ba
sis implementation of the B-spline K-matrix method which allows the reprod
uction of almost arbitrarily excited metastable satellites below a prescri
bed threshold. The new technique, when used to investigate helium triplet states,
yielded the most accurate and extensive existing characterization of triplet me
tastable states up to the fifth ionization threshold. Within more than 1700 natural and unnatural S, P and D doubly excited states, eleven intruder states were discov
ered, entirely unknown before.
At least two experimental groups, at ELETTRA in Trieste and at BESSY II in Berlin, are recently tackling the problem of measuring the m
etastable 2^3S helium photoionization cross section. We therefore undertook a parallel theoretical investigation of the photoionization process of both the fundame
ntal and the excited ^3S helium states. The latter prelude to the future investigati
on of the radiative decay of doubly excited states and already revealed interesting p
eculiar features.
To this purpose, we devised an extension of the K-matrix method to treat the
atom-radiation interaction non perturbatively.
A general three electron package has been developed and appl
ied to study boron resonances. Specific formulas were derived to obtain arbitrary tensorial one-particle and scalar two-particle matrix elements between three electron states on non-orthogonal basis as required for an efficient exploitation of B-splines.
A detailed study of the B-spline effective completeness led to a general result
which assure that B-spline based methods are well conditioned for a large class of
knot grids.
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Howe, D. "High spin spectroscopy of the nucleus sup(152)Dy." Thesis, University of Liverpool, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372696.
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Mirijanian, James Julian. "Techniques to Characterize Vapor Cell Performance for a Nuclear-Magnetic-Resonance Gyroscope." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/724.
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Research was performed to improve the procedures for testing performance parameters of vapor cells for a nuclear-magnetic-resonance gyroscope. In addition to summarizing the theoretical infrastructure of the technology, this research resulted in the development and successful implementation of new techniques to characterize gyro cell performance.
One of the most important parameters to measure for gyro performance is the longitudinal spin lifetime of polarized xenon atoms in the vapor cell. The newly implemented technique for measuring these lifetimes matches results from the industry standard method to within 3.5% error while reducing the average testing time by 76% and increasing data resolution by 54%. The vapor cell test methods were appended with new software to expedite the analysis of test data and to investigate more subtle details of the results; one of the two isotopes of xenon in the cells tends to exhibit troublesome second-order effects during these tests due to electric-quadrupole coupling, but now the added analysis capabilities can accurately extract relevant results from such data with no extra effort. Some extraneous lifetime measurement techniques were explored with less substantial results, but they provided useful insight into the complex workings of the gyro cell test system.
New criteria were established to define the signal to noise ratio on a consistent basis from cell to cell across various parameters such as cell volume, temperature, and vapor pressure. A technique for measuring gas pressures inside the sealed cells helped link cell performance to cell development processes. This led to informed decisions on filling and sealing methods that consistently yielded cells with better performance in the last few months of this work. When this research began, cells with xenon lifetimes over ten seconds were rare in our lab; by the end, anything under 30 seconds was a disappointment. Not only did the test procedures improve, but so did the parameters being tested, and quite significantly at that. At the same time, many new avenues for continued progress have been opened; the work presented here, while instrumental, is only the beginning.
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Buck, Duncan. "Type IIb Kähler moduli : inflationary phenomenology." Thesis, University of Nottingham, 2010. http://eprints.nottingham.ac.uk/11088/.
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The inflationary paradigm of standard big bang cosmology provides a mechanism to generate primordial curvature perturbations and explain the large scale homogeneity and isotropy of the observable universe. This is achieved through requiring a period of accelerated expansion during the early universe and requires a deep understanding of particle physics for its correct formulation. With the emergence of string theory as a potential description of a fundamental laws of nature provides a the natural framework in which we can construct realistic models of inflation seems plausible. A common feature of string theories is the requirement of extra dimensions and, in the absence of a complete formulation of the theory, it is necessary to dimensionally reduce the theories to give a 4d effective theory. String compactifications provide a promising approach through which this can be done. However compactifications lead to the generation of a large number of massless scalar fields (moduli) which would mediate unobserved 'fifth forces'. Methods of stabilising these fields give rise to exponentially flat potentials which provide the means of obtaining inflation quite naturally. In the introductory chapters a review of Type IIb flux compactifications gives methods to stabilise the complex structure moduli and dilaton through the use of fluxes. In order to stabilise the Kähler moduli additional non perturbative corrections to the superpotential are required. We introduce the well know class of meta stable de Sitter string vacua obtained when such corrections are included. An additional class vacua at large volume are discussed, these are found when leading order perturbative corrections to the Kähler potential are also considered. The large volume vacua are then shown to give rise to a model of inflaton using a Kähler modulus as an inflaton field. We show that there exists a large class of inflationary solutions corresponding to a constant volume V of the compactification manifold. In a second chapter on this inflationary model the existence of a basin of attraction for inflation with a constant volume is described. We also find a larger class of inflationary solutions when we evolve the axionic components of the Kähler moduli and the phenomenological aspects are discussed. We finally review the standard slow roll analysis and discuss its use in multiple field inflationary models. We introduce two multiple field extensions to the standard single field slow roll approach. We proceed with an investigation into the suitability of the multiple field slow roll approaches in predicting the slow roll footprint of Supergravity models of inflation. This is achieved through comparing the results with single field results and numerical simulation data when more complex models are considered.
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Frantsuzov, Ilya. "An NMR relaxometry study of heteronuclear effects upon proton transfer in hydrogen bonds." Thesis, University of Nottingham, 2010. http://eprints.nottingham.ac.uk/11334/.
Full textAbstract:
The inherent quantum-mechanical nature of the proton transfer process in hydrogen bonds has been investigated through its effects on the nuclear spin-lattice relaxation rate. The fast magnetic field-cycling techniques employed allowed a direct measure of the rate characterising this dynamic process, which is closely related to the potential energy environment experienced by the mobile proton. Various heteronuclear effects from magnetic and non-magnetic nuclei outside the hydrogen bond were characterised. The contribution to proton tunnelling from the displacement of heavy atoms in the molecule is an important consideration within a complete description of the process. This interdependence was accurately measured for the carboxyl-group oxygen atoms in benzoic acid dimers through the isotope effect. Careful comparison of ¹⁶O and ¹⁸O-enriched benzoic acid relaxation allowed this relationship to be measured from the difference in low-temperature tunnelling rates. Fluctuating dipolar interactions caused by proton transfer motion couples the Zeeman states of different nuclear species. The cross-relaxation occurring through this natural coupling was explored as a function of field in 2,4,6-trifluorobenzoic acid and ¹³C-enriched pure benzoic acid. Characterising the strength of this interaction endeavoured to broaden the comprehension of heteronuclear coupling and served as confirmation of the model used. Beyond the carboxylic acid dimer, this investigation also showed dynamic disorder in intermolecular short, strong hydrogen bonds of pyridine-3,5-dicarboxylic acid. This proton transfer mechanism was found to be strongly dependent on the molecular vibrational modes creating a pathway between two potential minima. A finite change in entropy between the proton sites ensured that greatest proton mobility occurred at intermediate temperature, between relatively stable configurations at the extremes of temperature. A study of different sources of molecular dynamics within one compound showed the efficiency of field-cycling NMR at separating their contributions to relaxation. Dynamic rates from the proton transfer and methyl group rotation in 4-methylbenzoic acid were reliably extracted to the extent of identifying separate contributions from a small percentage of molecules around impurity centres.
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Omotani, John. "I've got the world on a brane." Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/12345/.
Full textAbstract:
This thesis treats several topics in the study of extra-dimensional models of the world, concerning Heterotic M-Theory and the dynamics of branes. We describe a reduction to five dimensions, over a Calabi-Yau manifold, of an improved version of Heterotic M-Theory, which is valid to all orders in the gravitational coupling. This provides a starting point for considering the consequences of the improved theory for the very fruitful phenomenology of the original. We investigate the singularities formed by the collision of gravitating branes in scalar field theory. By considering the asymptotic structure of the spacetime, the properties of the horizons formed and the growth of the curvature we argue that the singularity is not a black brane, as one might have expected, but rather a big crunch. Finally, we construct a restricted class of multi-galileon theories as braneworld models with codimension greater than one, developing in the process some of the formalism needed for the general construction.
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Mullinger, Karen Julia. "Simultaneous EEG and fMRI at high fields." Thesis, University of Nottingham, 2008. http://eprints.nottingham.ac.uk/14142/.
Full textAbstract:
The work described in this thesis involves an investigation of the implementation and application of simultaneous EEG and fMRI. The two techniques arc complementary, with EEG providing excellent temporal resolution and fMRI having good spatial resolution. Combined EEG/fMRI thus forms a powerful tool for neuroscience studies. In initial work, methods for improving the removal of the gradient and pulse artefacts, which are induced in EEG traces recorded during concurrent MRI, have been developed. Subsequently, the effects of the EEG hardware on MR images were investigated. This involved acquiring a series of scans to identify the sources of B0- and B1 inhomogeneities and the extent to which these affect EPI data. The adverse effects on data quality of combining EEG and fMRI increase with field strength. Consequently, EEG-fMRI at 7T is particularly challenging, although a number of advantages make its implementation desirable. Safety tests were performed which showed the presence of the EEG system caused a negligible increase in RF heating effects during scanning at 7T. After elimination of a number of noise sources, the first simultaneous EEG-fMRI experiments at 7T using commercially available equipment were performed. Concurrent EEG/fMRI at 3T was then used to investigate the correlation between the BOLD (blood oxygenation level dependent) response measured during visual stimulation and both the preceding alpha power and the strength of the driven, electrical response. In considering the correlation of the range of variation of the alpha power and BOLD response, a trend emerged which allowed tentative conclusions to be drawn. Variation of the BOLD and driven response with the frequency of visual stimulation relative to a subject's individual alpha frequency (IAF) was also investigated. A significant increase in the driven response, accompanied by a decrease in the BOLD response was observed in visual cortex when it was driven at the IAF.