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1
Grady, Keith J. "Solar flare particle acceleration in collapsing magnetic traps." Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/2839.
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The topic of this thesis is a detailed investigation of different aspects of the particle acceleration mechanisms operating in Collapsing Magnetic Traps (CMTs), which have been suggested as one possible mechanism for particle acceleration during solar flares. The acceleration processes in CMTs are investigated using guiding centre test particle calculations. Results including terms of different orders in the guiding centre approximation are compared to help identify which of the terms are important for the acceleration of particles. For a basic 2D CMT model the effects of different initial conditions (position, kinetic energy and pitch angle) of particles are investigated in detail. The main result is that the particles that gain most energy are those with initial pitch angles close to 90° and start in weak field regions in the centre of the CMT. The dominant acceleration mechanism for these particles is betatron acceleration, but other particles also show signatures of Fermi acceleration. The basic CMT model is then extended by (a) including a magnetic field component in the invariant direction and (b) by making it asymmetric. It is found that the addition of a guide field does not change the characteristics of particle acceleration very much, but for the asymmetric models the associated energy gain is found to be much smaller than in symmetric models, because the particles can no longer remain very close to the trap centre throughout their orbit. The test particle method is then also applied to a CMT model from the literature which contains a magnetic X-line and open and closed field lines and the results are compared with the previous results and the findings in the literature. Finally, the theoretical framework of CMT models is extended to 2.5D models with shear flow and to fully 3D models, allowing the construction of more realistic CMT models in the future.
2
Howdyshell, Marci Lynn. "Micro-magnetic Structures for Biological Applications." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1408718613.
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Eradat, Oskoui Solmaz. "New aspects of particle acceleration in collapsing magnetic traps." Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/11954.
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Collapsing magnetic traps (CMTs) have been suggested as one of the mechanisms that could contribute to particle energisation in solar flares. The basic idea behind CMTs is that charged particles will be trapped on the magnetic field lines below the reconnection region of a flare. This thesis discusses a number of important new aspects in particle energisation processes in CMTs, based on the model by Giuliani et al. (2005). In particular, we extend previous studies of particle acceleration in this CMT model to the relativistic regime and compare our results obtained using relativistic guiding centre theory with results obtained using the non-relativistic guiding centre theory. The similarities and differences found are discussed. We then present a detailed study of the question, what leads to the trapping or escape of particle orbits from CMTs. The answer to this question is investigated by using results from the non-relativistic orbit calculations with guiding centre theory and a number of simple models for particle energy gain in CMTs. We find that there is a critical pitch angle dividing trapped particle orbits from the escaping particle orbits and that this critical pitch angle does not coincide with the initial loss cone angle. Furthermore, we also present a calculation of the time evolution of an anisotropic pressure tensor and of the plasma density under the assumptions that they evolve in line with our kinematic MHD CMT model and that the pressure tensor satisfies the double-adiabatic Chew-Goldburger-Low (CGL) theory. Finally, we make a first step to introduce Coulomb scattering by a Maxwellian background plasma into our guiding centre equations by changing them into a set of stochastic differential equations. We study the influence of a static background plasma onto selected particle orbits by pitch angle scattering and energy losses, and look at its effect on the particle energy and the trapping conditions.
4
Askitopoulos, Alexis. "Polariton condensates in optical traps and strong magnetic fields." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/386219/.
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Semiconductor Microcavities in the strong coupling regime are an ideal test bed for studying light matter interactions at the micro-scale. The eigenstates of these systems, exciton-polaritons, are bosonic hybrid light matter quasi-particles that have been demonstrated to undergo Bose condensation. Owing to their photonic component polaritons are lighter than atoms so their Bose-Einstein condensation (BEC) is attainable at higher temperatures than traditional BEC phase transitions in atomic systems, while the reduced dimensionality of the system has the implication that the BEC phase transition spontaneously occurs only in the presence of a confining potential. In this thesis, the underlying mechanisms of polariton condensation in optically imprinted trapping potential landscapes is examined. Condensation in the ground state of an optical trap, de-localised from the excitation light is demonstrated and investigated and the confined condensate is shown to exhibit well defined quantum mechanical properties. A comparative study of the observed spectral features with a condensate formed with typical non-resonant excitation methods is conducted revealing a significant reduction of the excitation density threshold due to efficient trapping and relaxation of polaritons inside the trap. Decoupling of the optically induced excitonic reservoir results in increased temporal coherence in this system by suppression of the strong interactions with un-condensed particles. Modification of the geometrical properties of the trap results in single excited-state condensation. Contrary to defect and stress induced trapping schemes the condensation process is here driven by polaritons injected into the potential-trap from the trap barriers. This leads to more efficient pumping of the energetically higher modes extending into the trap boundary. We demonstrate how this feature can be exploited to manifest transitions between energetically neighbouring coherent quantum states in the steady state dynamic equilibrium regime and in the transient domain were the intensity tuning of coherent tunnelling modes is also examined. A by-product of the localisation of the condensate inside the photonic trap and the decoupling from the reservoir is the strong susceptibility of this system to small imbalances in the optical pumping of spin states. The population of the two spin states of the condensate can be controlled by small imbalances of the circular components of the excitation. The high density regime in this configuration is then investigated where a linearisation of the polariton dispersion is observed under pulsed excitation. However, a vigorous examination of the transient dynamics in this regime demonstrates the artificial nature of this effect due to transient relaxation and momentum narrowing in the transition from photon lasing to a confined polariton condensate. The confined condensate is an ideal subject for studying strong magnetic field effects on the spin properties of polariton condensates as it emits in a single energy mode for a wide range of excitation powers above threshold compared to the "untrapped" case and doesn’t suffer from de-coherence effects induced from the reservoir that causes line broadening and inhibits the spectral resolution of the spin components. We have performed initial reference strong magnetic field experiments with "unconfined" polariton condensates and present the predicted density dependent collapse of the Zeeman splitting and the modulation of the previously observed paramagnetic screening by the polarisation of the exciting beam. In the final chapter of the thesis we investigate the modulation of the condensation threshold for the non-optically confined case by the application of a magnetic field in the Faraday geometry. The experimental observations are explained by a model based on the suppression of diffusion in the reservoir and the shrinking of the Bohr radius by the application of the magnetic field.
5
Prikockis, Michael Vito. "Physics and Applications of Interacting Magnetic Particles: Effect of Patterned Traps." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1452073910.
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Han, Dian-jiun. "Bose-Einstein condensation of rubidium-87 atoms in a magnetic trap /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Chen, Aaron. "Imprinted Magnetic Traps for Study on Particle Fluctuation, Ordering and Microfluidic Applications." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1364490203.
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Murgia, David. "Microchip ion traps with high magnetic field gradients for microwave quantum logic." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/48045.
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This thesis describes experimental work towards the development of a trapped-ion quantum computer based on microchip ion traps and long-wavelength radiation, using magnetic field gradients. The relationship between experimental parameters and two-qubit gate fidelity is investigated for microchips with two different static magnetic field gradient generation methods. For current-carrying wires and under-chip permanent magnets, optimum ion heights of 110 μm and 200 μm are found respectively. Construction of an experiment capable of demonstrating high-fidelity gates is reported, including innovations for the use of microchip ion traps with permanent magnets. The development of a vacuum system for versatile microchip experiments is described, including new methods for impedance-matched RF delivery, in-vacuum filtering and liquid nitrogen microchip cooling. Protection of both the microchip surface from atomic flux and of ions from the charged imaging viewport are both investigated in detail. A new preparation framework for microchip ion traps before their use in experiments is developed. In order to remove unwanted deposited layers on the microchips, a process of multiple chemical treatments is used. In addition, these characterisation efforts lead to refinement of the microfabrication process for future microchips. The application of large currents to microchips is of fundamental importance to scalable trapped-ion quantum computing using static magnetic field gradients. As part of the characterisation process, currents of ≈ 10A are successfully applied to microfabricated current-carrying wires, demonstrating the viability of these structures for generation of local magnetic fields and gradients in a quantum computing device. The operation of a microchip ion trap experiment with under-chip permanent magnets for a high magnetic field gradient (≈ 140Tm−1) is described. The successful trapping of ytterbium-174 and -171 ions is reported, as well as their use to measure and optimise the ion trap parameters. The thesis concludes with consideration of the expected future results from the ongoing operation of the experiment.
9
Baranov, O. O. "Control of Ion Density Distribution by Use of Magnetic Traps for Plasma Electrons." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35384.
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Method of ion current density control in the vacuum arc deposition setup has been investigated. The
control unit consisted of two electromagnetic coils installed under substrate of 400 mm dia. exposed to the
plasma flux. A planar probe was used to measure the ion current density distribution along the plasma
flux cross-sections at different distances from the plasma duct exit. It was shown that configuration of the
resulting magnetic field generated by the control coils and the guiding and focusing coils of the arc source,
strongly affects the ion current density distribution. Broad range of ion current density from 25 to
340 A/m2 was obtained at dependence on the control coils powering, distance from the plasma duct exit and
the position along the substrate. This method may be suitable for effective controlling of the ion flux extracted
from the plasma sources with guiding magnetic field, over the large substrates.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35384
10
Myers, Jessica Ann, and Jessica Ann Myers. "Hybrid Optical-Magnetic Traps for Studies of 2D Quantum Turbulence in Bose-Einstein Condensates." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/625625.
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Turbulence appears in most natural and man-made flows. However, the analysis of turbulence is particularly difficult. Links between microscopic fluid dynamics and statistical signatures of turbulence appear unobtainable from the postulates of fluid dynamics making turbulence one of the most important unsolved theoretical problems in physics. Two-dimensional quantum turbulence (2DQT), an emerging field of study, involves turbulence in two-dimensional (2D) flows in superfluids, such as Bose-Einstein condensates (BECs). In 2D superfluids, a turbulent state can be characterized by a disordered distribution of numerous vortex cores. The question of how to effectively and efficiently generate turbulent states in superfluids is a fundamental question in the field of quantum turbulence. Therefore, experimental studies of vortex nucleation and the onset of turbulence in a superfluid are important for achieving a deeper understanding of the overall problem of turbulence.
My PhD dissertation involves the study of vortex nucleation and the onset of turbulence in quasi-2D BECs. First, I discuss experimental apparatus advancements that now enable BECs to be created in a hybrid optical-magnetic trap, an atom trapping configuration conducive to 2DQT experiments. Next, I discuss the design and construction of a quantum vortex microscope and initial vortex detection tests. Finally, I present the first experiments aimed at studying 2DQT carried out in the updated apparatus. Thermal counterflow in superfluid helium, in which the normal and superfluid components flow in opposite directions, is known to create turbulence in the superfluid. However, this phenomenon has not been simulated or studied in dilute-gas BECs as a possible vortex nucleation method. In this dissertation, I present preliminary data from the first experiments aimed at understanding thermal counterflow turbulence in dilute-gas BECs.
11
Thomas, Nicholas, and n/a. "Double-TOP trap for ultracold atoms." University of Otago. Department of Physics, 2005. http://adt.otago.ac.nz./public/adt-NZDU20070321.160859.
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The Double-TOP trap is a new type of magnetic trap for neutral atoms, and is suitable for Bose-Einstein condensates (BECs) and evaporatively cooled atoms. It combines features from two other magnetic traps, the Time-averaged Orbiting Potential (TOP) and Ioffe-Pritchard traps, so that a potential barrier can be raised in an otherwise parabolic potential. The cigar-like cloud of atoms (in the single-well configuration) is divided halfway along its length when the barrier is lifted.
A theoretical model of the trap is presented. The double-well is characterised by the barrier height and well separation, which are weakly coupled. The accessible parameter space is found by considering experimental limits such as noise, yielding well separations from 230 [mu]m up to several millimetres, and barrier heights from 65 pK to 28 [mu]K (where the energies are scaled by Boltzmann�s constant). Potential experiments for Bose-Einstein condensates in this trap are considered.
A Double-TOP trap has been constructed using the 3-coil style of Ioffe-Pritchard trap. Details of the design, construction and current control for these coils are given. Experiments on splitting thermal clouds were carried out, which revealed a tilt in the potential. Two independent BECs were simultaneously created by applying evaporative cooling to a divided thermal cloud.
The Double-TOP trap is used to form a linear collider, allowing direct imaging of the interference between the s and d partial waves. By jumping from a double to single-well trap configuration, two ultra-cold clouds are launched towards a collision at the trap bottom. The available collision energies are centred on a d-wave shape resonance so that interference between the s and d partial waves is pronounced. Absorption imaging allows complete scattering information to be collected, and the images show a striking change in the angular distribution of atoms post-collision. The results are compared to a theoretical model, verifying that the technique is a useful new way to study cold collisions.
12
Stamper-Kurn, Dan M. (Dan Moses) 1971. "Peeking and poking at a new quantum fluid : studies of gaseous Bose-Einstein condensates in magnetic and optical traps." Thesis, Massachusetts Institute of Technology, 2000. https://hdl.handle.net/1721.1/129360.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 2000.Includes bibliographical references (leaves 253-272).
by Dan M. Stamper-Kurn.
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 2000.
13
Lane, Ryan A. "Charged Particle Transport and Confinement Along Null Magnetic Curves and in Various Other Nonuniform Field Configurations for Applications in Antihydrogen Production." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849779/.
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Comparisons between measurements of the ground-state hyperfine structure and gravitational acceleration of hydrogen and antihydrogen could provide a test of fundamental physical theories such as CPT (charge conjugation, parity, time-reversal) and gravitational symmetries. Currently, antihydrogen traps are based on Malmberg-Penning traps. The number of antiprotons in Malmberg-Penning traps with sufficiently low energy to be suitable for trappable antihydrogen production may be reduced by the electrostatic space charge of the positrons and/or collisions among antiprotons. Alternative trap designs may be needed for future antihydrogen experiments. A computational tool is developed to simulate charged particle motion in customizable magnetic fields generated by combinations of current loops and current lines. The tool is used to examine charged particle confinement in two systems consisting of dual, levitated current loops. The loops are coaxial and arranged to produce a magnetic null curve. Conditions leading to confinement in the system are quantified and confinement modes near the null curve and encircling one or both loops are identified. Furthermore, the tool is used to examine and quantify charged particle motion parallel to the null curve in the large radius limit of the dual, levitated current loops. An alternative to new trap designs is to identify the effects of the positron space in existing traps and to find modes of operation where the space charge is beneficial. Techniques are developed to apply the Boltzmann density relation along curved magnetic field lines. Equilibrium electrostatic potential profiles for a positron plasma are computed by solving Poisson's equation using a finite-difference method. Equilibria are computed in a model Penning trap with an axially varying magnetic field. Also, equilibria are computed for a positron plasma in a model of the ALPHA trap. Electric potential wells are found to form self-consistently. The technique is expanded to compute equilibria for a two-species plasma with an antiproton plasma confined by the positron space charge. The two-species equilibria are used to estimate timescales associated with three-body recombination, losses due to collisions between antiprotons, and temperature equilibration. An equilibrium where the three-body recombination rate is the smallest is identified.
14
Hessmo, Björn. "Quantum optics in constrained geometries." Doctoral thesis, Uppsala University, Department of Quantum Chemistry, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1208.
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When light exhibits particle properties, and when matter exhibits wave properties quantum mechanics is needed to describe physical phenomena.
A two-photon source produces nonmaximally entangled photon pairs when the source is small enough to diffract light. It is shown that diffraction degrades the entanglement. Quantum states produced in this way are used to probe the complementarity between path information and interference in Young's double slit experiment.
When two photons have a nonmaximally entangled polarization it is shown that the Pancharatnam phase is dependent on the entanglement in a nontrivial way. This could be used for implementing simple quantum logical circuits.
Magnetic traps are capable of holding cold neutral atoms. It is shown that magnetic traps and guides can be generated by thin wires etched on a surface using standard nanofabrication technology. These atom chips can hold and manipulate atoms located a few microns above the surface with very high accuracy. The potentials are very versatile and allows for highly complex designs, one such design implemented here is a beam splitter for neutral atoms. Interferometry with these confined de Broglie is also considered. These atom chips could be used for implementing quantum logical circuits.
15
Webster, Stephen. "Prospects for Bose-Einstein condensation in caesium : cold collisions and dipole-force trapping." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325563.
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Haigh, Tania J. "Bose-Einstein condensates in coupled co-planar double-ring traps : a thesis presented in partial fulfillment of the requirements for the degree of Masterate of Science in Physics at Massey University, Palmerston North, New Zealand." Massey University, 2008. http://hdl.handle.net/10179/975.
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This thesis presents a theoretical study of Bose-Einstein condensates in a doublering trap. In particular, we determine the ground states of the condensate in the double-ring trap that arise from the interplay of quantum tunnelling and the trap’s rotation. The trap geometry is a concentric ring system, where the inner ring is of smaller radius than the outer ring and both lie in the same two-dimensional plane. Due to the difference in radii between the inner and outer rings, the angular momentum that minimises the kinetic energy of a condensate when confined in the individual rings is different at most frequencies. This preference is in direct competition with the tunnel coupling of the rings which favours the same angular momentum states being occupied in both rings. Our calculations show that at low tunnel coupling ground state solutions exist where the expectation value of angular momentum per atom in each ring differs by approximately an integer multiple. The energy of these solutions is minimised by maintaining a uniform phase difference around most of the ring, and introducing a Josephson vortex between the inner and outer rings. A Josephson vortex is identified by a 2p step in the relative phase between the two rings, and accounts for one quantum of circulation. We discuss similarities and differences between Josephson vortices in cold-atom systems and in superconducting Josephson junctions. Josephson vortices are actuated by a sudden change in the trapping potential. After this change Josephson vortices rotate around the double-ring system at a different frequency to the rotation of the double-ring potential. Numerical studies of the dependence of the velocity on the ground state tunnel coupling and interaction strength are presented. An analytical theory of the Josephson vortex dynamics is also presented which is consistent with our numerical results.
17
Cruz-Cruz, Luis R. "Electronic and magnetic properties of trans-polyacetylene." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/28057.
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Lunney, Matthew David Norwood. "The phase space volume of ion clouds in Paul traps." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39462.
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A new technique is presented for measuring the spatial and momentum distributions of a buffer-gas cooled ion cloud in a Paul trap by extracting it from the trap and fitting the time profile of the extracted ion signal. A thermodynamic model based on the Gibbs distribution has been developed which describes the initial ion cloud phase space volume and fits the measured time distributions of the extracted cloud using only one parameter: temperature. A time-of-flight system has been built to systematically vary the ion extraction conditions and compare predictions of the model to various measurements of the ion cloud time profile. A new numerical method using a multipole expansion was developed to compute the extraction fields. Agreement between the ion simulations and the time-of-flight data is better than 2% of the total flight time.Ion cloud temperatures were measured for seven different trap loadings of potassium ions and four loadings of sodium ions, in both cases down to clouds of about 1000 ions. This is the first time that temperature measurements have been made for such small numbers of buffer-gas cooled ions. The results show that the temperature of the ions above the buffer gas temperature appears to be proportional to the two-thirds power of the number of ions in the cloud.
Dynamic manipulation of the extracted ion cloud phase space volume was also accomplished using a time-varying acceleration voltage to change the ion cloud energy spread in flight.
A concept is also outlined to measure the detailed phase space area of the extracted cloud using the projection-slice theorem of tomographic imaging.
These measurements have applications for the use of ion traps as beam collectors for nuclear physics experiments at isotope separator facilities and possibly for nano-circuit fabrication.
19
Gallet, Yves. "La magnetostratigraphie : aspects fondamentaux et appliques." Paris 7, 1988. http://www.theses.fr/1988PA077056.
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Une eetude magnetostratigraphique de la limite jurassique/cretace au maroc permet de discuter les possibilites de correlation stratigraphique en l'absence d'une biostratigraphie bien etablie. Avec des donnees du forage de cony, on met en evidence des series triasiques et permiennes. Les resultats paleomagnetiques permettent de preciser la derive des poles magnetiques de l'eurasie. On modelise aussi le champ magnetique a l'interieur d'un forage
20
Dieckmann, Kai. "Bose-Einstein condensation with high atom number in a deep magnetic trap." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2001. http://dare.uva.nl/document/58167.
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Thomas, Angharad Mair. "Ultra-cold collisions and evaporative cooling of caesium in a magnetic trap." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403426.
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Jackson, Jarom Silver. "In Situ Magnetic Field Characterization with the Directional Hanle Effect." BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/5982.
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We present a novel method of in situ magnetic field mapping related to the Hanle effect. This method uses the change in spatial radiation pattern of scattered light, which we call a 'directional Hanle effect,' rather than the loss of polarization more commonly associated with the Hanle effect. It is particularly well suited for fields in a magneto-optical trap (MOT), requiring only the addition of a narrow slit and a camera to typical MOT components. The use of this method is demonstrated by measuring the gradient through, and location of, the zero-point of the field in our strontium MOT.
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Berger, T., J. Konheiser, A. V. Anikeev, V. V. Prikhodko, P. A. Bagryansky, E. Yu Kolesnikov, E. I. Soldatkina, Yu A. Tsidulko, K. Noack, and A. A. Lizunov. "Study of high temperature and high density plasmoids in axially symmetrical magnetic fields." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-27870.
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Within the framework of an Institutional Partnership of the Alexander von Humboldt Foundation, the Budker Institute of Nuclear Physics Novisibirsk (BINP) and Forschungszentrum Dresden-Rossendorf worked together in a joint project devoted to the research at the coupled GDT-SHIP facility of the BINP with the focus on the study of plasma phenomena within the SHIP mirror section. The project began at July 1st, 2005 and ended on August 30th, 2008. It included work packages of significant theoretical, computational and analyzing investigations. The focus of this final report is on the presentation of results achieved whereas the work that was done is described briefly only. Chapter 2 illustrates the GDT-SHIP facility and describes shortly the planned topics of the SHIP plasma research. Chapter 3 explains the main extensions and modifications of the Integrated Transport Code System (ITCS) which were necessary for the calculations of the fast ion and neutral gas particle fields in SHIP, describes briefly the scheme of computations and presents significant results of pre-calculations from which conclusions were drawn regarding the experimental program of SHIP. In chapter 4, the theoretical and computational investigations of self-organizing processes in two-component plasmas of the GDT-SHIP device are explained and the results hitherto achieved are presented. In chapter 5, significant results of several experiments with moderate and with enhanced plasma parameters are presented and compared with computational results obtained with the ITCS. Preparing neutron measurements which are planned for neutron producing experiments with deuterium injection, Monte Carlo neutron transport calculations with the MCNP code were also carried out. The results are presented. Finally, from the results obtained within the joint research project important conclusions are drawn in chapter 6.
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Gao, Lei. "Determination of quantitative nutritional labeling compositional data of lipids by Nuclear Magnetic Resonance (NMR) spectroscopy." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=111577.
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The application of Nuclear Magnetic Resonance (NMR) spectroscopy in the determination of nutrition labeling component data (NLCD) was investigated, with the intent of using this methodology as a primary method to calibrate FTIR instrumentation for NLCD confirmation or screening on a routine basis. Unlike previous NMR studies, this work used three strategies to attain accuracy and reproducibility of NLCD through: (i) appropriate setting of operational parameters for spectral acquisition; (ii) resonance selection by optimizing the signal in proportion to the nuclei population and (iii) integration of resonances by pre-defined fixed chemical shift ranges. Both of 13C NMR spectra and 1H NMR spectra were shown to provide robust and acceptable results on the condition of appropriate acquisition of spectra for quantization purposes and the adoption of standard procedures for spectral processing, integration and calculation purposes. A quantitative approach of NLCD including trans content was determined by the interpretation resonance signals of 13C's and 1H's from methylene groups presented in triglyceride complex of fats and oils. An alternative method based on partial-least-squares (PLS) calibrations was provided as well, the latter proved to be especially useful in dealing with overlapping bands frequently found in 1H spectra. With the diagnostic provided by PLS, the trans and cis signals were shown to be separated in 1H spectra. It is the premise for the trans fat determination based on 1H spectra. Unit conversion from mole to weight % was addressed and a solution was developed based on NMR data per se, without significant assumptions. Validation involving the analysis of three different lipid types (model triacylglycerols, refined and hydrogenated oils) demonstrated that NMR predictions of NLCD were in good agreement with those results either from samples' actual values as well as those obtained using GC and FTIR predictions. Thus with appropriate integration of instrumentation, software and spectral processing accessories, both 13C and 1H NMR can determine NLCD, but with the capability to determine trans, 1H NMR is more practical than 13C NMR due to its much shorter spectral acquisition time. Thus NMR can serve as a primary method for the calibration of FTIR instrumentation, a practical instrumental method for routine NLCD determination and screening.
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Hoogerheide, Shannon Michelle Fogwell. "Trapped positrons for high-precision magnetic moment measurements." Thesis, Harvard University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3566927.
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A single electron in a quantum cyclotron provides the most precise measurement of the electron magnetic moment, given in units of the Bohr magneton by g/2 = 1.001 159 652 180 73 (28) [0.28 ppt]. The most precise determination of the fine structure constant comes from combining this measurement with Standard Model theory, yielding α-1 = 137.035 999 173 (34) [0.25 ppb], limited by the experimental uncertainty of the electron g-value. The most stringent test of CPT symmetry in leptons comes from comparing the electron and positron magnetic moments, limited by the positron uncertainty at 4.2 ppt. A new high-stability apparatus has been built and commissioned for improved measurements of the electron and positron magnetic moments, a greatly improved test of lepton CPT symmetry, and an improved determination of the fine structure constant. These new measurements require robust positron loading from a retractable radioactive source that is small enough to avoid compromising the high-precision environment of our experiment. The design and implementation of such a scheme is a central focus of this work. Robust positron loading at a rate of 1-2 e+/min from a 6.5 μCi 22Na source has been demonstrated.
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Davey, Louise. "Mass selective capture by an RFQ trap of externally injected ions." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60660.
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A system for mass-selective capture of ions by a Paul trap was designed and tested.An Paul trap and associated electronics have been assembled and tested, selectively trapping the ionic clusters C$ sp{+} sb2$ and C$ sp{+} sb3$ from a pulsed laser ion source. The ions were injected at 90 eV, trapped, extracted and detected, several parameters related to these processes were investigated. Simple models of the injection mechanism employed and for evaluating the pseudo-potential well depth of the ion trap are proposed. The overall efficiency of the ion injection system has been evaluated and compared to other methods of ion capture by an RFQ trap from an external source.
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Berger, T., J. Konheiser, A. V. Anikeev, V. V. Prikhodko, P. A. Bagryansky, E. Yu Kolesnikov, E. I. Soldatkina, Yu A. Tsidulko, K. Noack, and A. A. Lizunov. "Study of high temperature and high density plasmoids in axially symmetrical magnetic fields." Forschungszentrum Dresden-Rossendorf, 2009. https://hzdr.qucosa.de/id/qucosa%3A21614.
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Within the framework of an Institutional Partnership of the Alexander von Humboldt Foundation, the Budker Institute of Nuclear Physics Novisibirsk (BINP) and Forschungszentrum Dresden-Rossendorf worked together in a joint project devoted to the research at the coupled GDT-SHIP facility of the BINP with the focus on the study of plasma phenomena within the SHIP mirror section. The project began at July 1st, 2005 and ended on August 30th, 2008. It included work packages of significant theoretical, computational and analyzing investigations. The focus of this final report is on the presentation of results achieved whereas the work that was done is described briefly only. Chapter 2 illustrates the GDT-SHIP facility and describes shortly the planned topics of the SHIP plasma research. Chapter 3 explains the main extensions and modifications of the Integrated Transport Code System (ITCS) which were necessary for the calculations of the fast ion and neutral gas particle fields in SHIP, describes briefly the scheme of computations and presents significant results of pre-calculations from which conclusions were drawn regarding the experimental program of SHIP. In chapter 4, the theoretical and computational investigations of self-organizing processes in two-component plasmas of the GDT-SHIP device are explained and the results hitherto achieved are presented. In chapter 5, significant results of several experiments with moderate and with enhanced plasma parameters are presented and compared with computational results obtained with the ITCS. Preparing neutron measurements which are planned for neutron producing experiments with deuterium injection, Monte Carlo neutron transport calculations with the MCNP code were also carried out. The results are presented. Finally, from the results obtained within the joint research project important conclusions are drawn in chapter 6.
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Collins, Sean Michael 1959. "Electrode material and geometry effects on the electrical properties of particle traps in a parallel plate plasma etch reactor." Thesis, The University of Arizona, 1993. http://hdl.handle.net/10150/278287.
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A newly designed Langmuir probe has been evaluated and was used to map the plasma potential near the powered electrode of a plasma etch chamber in 2 dimensions. Various electrode materials and geometries were used in order to investigate the relationship between electrode design and the presence of localized regions of elevated plasma potential. These regions of elevated plasma potential were known to be responsible for the presence of particle clouds suspended in the plasma during operation. A relationship was established between sharp edges on the powered electrode, insulating materials on the electrode and localized elevation in plasma potential. A thin layer of raised plasma potential has also been discovered at the plasma-sheath boundary. Suggestions for electrode design to reduce the presence of particles suspended in the plasma are made.
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Stacey, John-Patrick. "Stabilization and control in a linear ion trap." Thesis, University of Oxford, 2003. http://ora.ox.ac.uk/objects/uuid:5c019c02-c313-4fb4-92f4-8a342dd5dbf6.
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This thesis describes experimental work towards developing a trapped ion quantum information processor. An existing ion trap apparatus was capable of trapping and laser-cooling single ions or small ion strings of 40 Ca+, and had been used for studies of quantum jumps and natural lifetime measurements in Ca. This thesis describes improvements in this apparatus, which have allowed the stability and the flexibility of experimental control of the ions to be greatly increased. This enabled experiments to read out the spin state of a single trapped ion, and to load ions with isotope selectivity through photoionization. The optical systems were improved by installation of new lasers, optical reference cavities, and a system of acousto-optic modulators for laser intensity switching and frequency control. The photon counting for fluorescence detection was improved, and a new photon time-of-arrival correlation circuit developed. This has permitted rapid and more sensitive detection of micromotion, and hence cancellation of stray fields in the trap. A study of resonant circuits in the low RF, high voltage (10 MHz, 1 kV) regime was carried out with a view to developing a new RF supply for the Paul trap with reduced noise and increased power. A new supply based on a helical resonator was built and used to trap ions. This technique has reduced noise and will permit higher secular frequencies to be attained in the future. A magnetic field B in the ion trap is used to define a quantization axis, and in one series of experiments was required to be of order 100 G to provide a substantial Zeeman splitting. A set of magnetic field coils to control the size and direction of B is described. The design of these posed some problems owing to an unforseen issue with the vacuum chamber. In short, it is magnetizable and acts to first approximation like a magnetic shield. The field coils had to be sufficiently substantial to produce the desired field at the ion even in the presence of this shielding effect, and dark resonance (and other) spectra with Zeeman splitting were obtained to calibrate the field using the ion as a probe. Finally, the thesis describes the successful loading of the ion trap by laser photoionization from a weak atomic beam. This involved two new lasers at 423 nm and 389 nm. Saturated absorption spectroscopy of neutral calcium is first described, then transverse excitation of an atomic beam in our vacuum chamber is used to identify all the main isotopes of calcium and confirm their abundances in our source (a heated sample of natural calcium). Finally, photoionization is used to load the trap. This has three advantages over electron-impact ionization. By avoiding an electron gun, we avoid charging of insulating patches and subsequent electric field drift as they discharge; the flux in the atomic beam and hence calcium (and other) deposits on the electrodes can be greatly reduced; and most importantly, the photoionization is isotope selective. Evidence is presented which suggests that even with an non-enriched source, the rare isotope 43 Ca can be loaded with reasonable efficiency. This isotope is advantageous for quantum information experiments for several reasons, but chiefly because its ground state hyperfine structure can act as a stable qubit.
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Sahelgozin, Maral [Verfasser]. "Design and construction of a transportable quantum gravimeter and realization of an atom-chip magnetic trap / Maral Sahelgozin." Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2019. http://d-nb.info/1190283417/34.
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Henn, Emanuel Alves de Lima. "Variação da temperatura cinética em átomos aprisionados bombeados por campos externos." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-06062007-183559/.
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Neste trabalho apresentamos o estudo da variação da temperatura cinética de átomos aprisionados magneticamente bombeados por campos eletromagnéticos externos. Aprisionamos átomos de Sódio em uma armadilha magnética de quadrupolo e submetemos esses átomos a um campo magnético externo oscilante. Medimos a temperatura e o número dos átomos remanescentes na armadilha a partir de imagens de tempo de vôo. O processo de medida consiste em desligar a armadilha, deixando a nuvem atômica expandir balisticamente e então fazer uma imagem da fluorescência desses átomos gerada por um pulso de luz próximo da ressonância atômica. Do tamanho da nuvem e do número de fótons capturados podemos obter a temperatura e o número de átomos da amostra. Observamos um significativo resfriamento para algumas freqüências de oscilação do campo externo e posterior aquecimento para freqüências um pouco maiores. Observamos ainda simultaneamente ao resfriamento uma grande perda de átomos da armadilha. Por fim, apresentamos algumas simulações numéricas que reproduzem o fenômeno observado, bem como um modelo que explica os experimentos baseado em excitação seletiva dos átomos confinados pelo campo magnético externo.In this work we present a study of the shift of the kinetic temperature of magnetically trapped atoms, excited by external electromagnetic fields. We trapped Sodium atoms in a quadrupole magnetic trap and applied an oscilating magnetic field to these atoms. We mesured the temperature and the number of the remaining atoms from time of flight images. The measure is done turning off the trap, leaving the cloud of atoms in a ballistic expansion and making an image of the fluorescence of these atoms after the shot of a near ressonant light. From the size of the cloud and the number of photons captured we can measure the temperature and number of atoms in the sample. We observed cooling of the atoms for some frequencies of the external field and heating for frequencies a bit larger. We observed that a high number of atoms were lost from the trap simultaneously with the cooling. Finally, we present numerical simulations that reproduce the observed phenomena and a model that explains the experiments\' results based on selective excitation of the trapped atoms by the external field.
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Dobson, Laura Elizabeth. "Cardiovascular magnetic resonance imaging in severe aortic stenosis : impact of surgical and trans-catheter aortic valve replacement on reverse remodelling and fibrosis." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/12944/.
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Introduction: Aortic stenosis (AS) is the commonest valvular lesion in the developed world and is associated with adverse cardiac remodelling. With its excellent accuracy and reproducibility, cardiovascular magnetic resonance (CMR) imaging is an ideal tool to assess cardiac remodelling and reverse remodelling following surgical aortic valve replacement (SAVR) and transcatheter aortic valve implantation (TAVI). The aims of this thesis were: 1) to evaluate gender differences in AS and following aortic valve replacement, 2) to evaluate the incidence of post-procedural myocardial infarction following SAVR and TAVI, 3) to describe the immediate effect of TAVI on reverse remodelling and 4) to assess the impact of TAVI-induced left bundle branch block (LBBB) . Methods: Between January 2009 and April 2015, patients with severe AS undergoing either TAVI or SAVR were prospectively recruited. Patients underwent comprehensive 1.5T CMR evaluation pre-procedure, prior to hospital discharge and 6m post-procedure. Results: 1) Women with severe AS have a lower indexed left ventricular (LV) mass than men (65.3± 18.4 vs. 81.5±21.3g/m2, p < 0.001). 6m following valve replacement, LV mass regression is similar between genders (men 21.7±10.1 vs. women 18.4±11.0%, p=0.121). 2) Myocardial infarction (MI) is more frequent following SAVR than TAVI (n=10 (26%) vs. n=3 (5%), p=0.004). 3) Over 10% of LV mass regression occurs prior to hospital discharge following TAVI and is more pronounced in the absence of myocardial fibrosis (p=0.005). 4) TAVI-induced LBBB is associated with a reduced LVEF 6m following TAVI compared with those with a narrow QRS (-2.1±6.9 vs. +4.6±7.8%, p=0.002). Conclusions: TAVI and SAVR are associated with favourable cardiac reverse remodelling which does not differ according to gender and begins prior to hospital discharge. SAVR is associated with a higher incidence of post-procedural MI than TAVI. TAVI-induced LBBB should be avoided where possible due to its unfavourable effects on cardiac reverse remodelling.
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Rosenau, Felix. "HOPE - un piège magnétique pour neutron ultra-froid dédié à la mesure du temps de vie du neutron : conception et premières données expérimentales." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY036/document.
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Le temps de vie du neutron libre joue un rôle important dans la physique des particules comme dans des modèles cosmologiques. Notre connaissance de la valeur précise du temps de vie du neutron est limitée par les incertitudes systématiques des deux méthodes expérimentales couramment utilisées, les méthodes dites de "faisceau" et de "bouteille matérielle". En outre une déviation systématique des valeurs de temps de vie obtenues par les deux méthodes s'est manifestée au cours des dernières décennies.Le projet HOPE fait parti d'une nouvelle génération d'expériences qui cherchent à mesurer le temps de vie du neutron en stockant des neutrons ultra-froids (UCN) dans un potentiel magnéto-gravitationnel. HOPE génère les champs magnétiques nécessaires par une combinaison d'aimants permanents puissants de terre rare, qui produisent des champs magnétiques maximaux d'environ 1.3 T, et un système de bobines supraconductrices. Dans cette thèse je donnerai une description détaillée de l'appareil, des effets systématiques possibles et comment nous envisageons d'étudier et de maîtriser ces effets. Ensuite les résultats d'un premier temps de faisceau, effectué à la source PF2, vont être présentés et discutés. Les résultats sont encourageants puisque nous avons atteint des constants de temps de stockages maximaux de 881(46) s, ce qui indique des pertes d'UCN très faibles pendant la phase du stockageThe lifetime of the free neutron plays an important role in fundamental particle physics as well as cosmological models. Our knowledge of the precise value of the neutron lifetime is limited by the systematical inaccuracies of the two commonly used experimental approaches, the so called “beam” and “material bottle” methods. Moreover a systematic deviation of the lifetime-values extracted from both methods has become manifest over the past decades.The HOPE project is part of a new generation of experiments that aims to determine the neutron lifetime by storing ultra cold neutrons (UCN) in a combined magneto-gravitational potential. HOPE generates the necessary gradient magnet fields by a combination of highly potent rare-earth permanent magnets with a maximum B-field strength of about 1.3 T and a set of superconducting coils. In this thesis I give a detailed description of the apparatus, possible systematical effects and how we are planning to investigate and cope with those effects. Subsequently the results from a first beamtime at the PF2 source will be presented and discussed. The results are encouraging as we reached a maximum storage-time constants of 881(46) s, indicating a very small UCN loss rate during storage
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Laidler, Christopher I. "Application of microwave sidebands from an optically injected diode laser to atomic physics and the construction of a magnetic trap for neutral atoms." Thesis, Swansea University, 2013. https://cronfa.swan.ac.uk/Record/cronfa42839.
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Magalhães, Kilvia Mayre Farias. "Obtenção da degenerescência quântica em sódio aprisionado." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-24012008-083710/.
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Usando a técnica de resfriamento evaporativo para átomos comprimidos numa armadilha magnética tipo QUIC, implementamos experimentos para observar Condensação de Bose-Einstein de átomos de sódio. Nessa armadilha magnética temos átomos advindos de uma armadilha magneto-óptica, a qual é carregada por um feixe desacelerado como etapa de pré-resfriamento. Nossas medidas foram baseadas em imagens de absorção fora de ressonância de um feixe de prova pela amostra atômica. Essas imagens foram feitas in situ, ou seja, na presença do campo da armadilha magnética, pelo fato do número de átomos ser baixo e a técnica de tempo de vôo não ser adequada a essa situação. Baseado no perfil de densidade e na temperatura medidos, calculamos a densidade de pico no espaço de fase D, a qual é seguida nas várias etapas de evaporação. Nossos resultados mostram que para uma freqüência final de evaporação de 1,65 MHz nós superamos o valor esperado para D (2,612) alcançar o ponto crítico, no centro da amostra, para obter a condensação. Devido ao baixo número de átomos restantes no potencial, a interação não produz efeitos consideráveis e dessa forma um modelo de gás ideal permite justificar essa observação.Using a system composed of a QUIC trap loaded from a slowed atomic beam, we have performed experiments to observe the Bose-Einstein Condensation of Na atoms. In order to obtain the atomic distribution in the trap, we use an in situ out of resonance absorption image of a probe beam to determine the temperature and the density, which are use to calculate the phase space D. We have followed D as a function of the final evaporation frequency. The results show that at 1.65 MHz we crossed the critical value for D which corresponds to the point to start Bose-Condensation of the sample. Due to the low number of atoms remaining in the trap at the critical point, the interaction produce minor effects and therefore an ideal gas model explains well the observations.
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Wiesel, Marco [Verfasser], Gerhard [Akademischer Betreuer] Birkl, and Wolfgang [Akademischer Betreuer] Quint. "Preparation and Investigation of Highly Charged Ions in a Penning Trap for the Determination of Atomic Magnetic Moments / Marco Wiesel ; Gerhard Birkl, Wolfgang Quint." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://d-nb.info/1136078711/34.
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Guégan, Frédéric. "Joint experimental and theoretical approaches in coordination chemistry : from the trans effects to Single Molecule Magnets." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1267/document.
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Dans ce travail, nous nous sommes principalement intéressé à la description et à la rationalisation de certaines propriétés des complexes de coordination, par des approches mixtes expérience/théorie. La première de ces études, purement théorique, revisite les propriétés de coordination des ligands par des méthodes de type DFT conceptuelle. Dans un premier temps, les ligands seuls sont étudiés, puis les résultats de cette première approche sont utilisés pour caractériser et rationaliser les effets trans dans les complexes octaédriques. La deuxième étude ci-présentée concerne la synthèse et la caractérisation de complexes polynucléaires de Cu(II) et de ligands de type base de Schiff dérivés d'acides aminés. Dans un premier temps, la réactivité de ces complexes en solution est rationalisée par des mesures spectroscopiques et des calculs de type DFT. Puis, les propriétés magnétiques de deux complexes trinucléaires sont présentées et analysées grâce au support de calculs ab initio de haut niveau. Enfin, dans la troisième étude nous nous intéressons à des complexes mononucléaires d'ion lanthanides présentant une dynamique lente de l'aimantation à basse température. Des mesures magnétiques, mais aussi de luminescence et de diffraction de neutrons polarisés, combinées à des calculs de type SA-CASSCF/RASSI-SO permettent de rationaliser les propriétés magnétiques ainsi observéesIn this work, we focused on the description and rationalisation of certain properties of coordination complexes through the use of joint experiment/theory approaches. The first study is purely theoretical, and revisits the coordination properties of ligands using conceptual DFT methods. In a first time, ligands alone are studied, and the results of this study are then employed to characterise and rationaliser the trans effects in octahedral complexes. The second study deals with the syntheses and characterisation of polynuclear Cu(II) complexes deriving from amino-acid based Schiff base-like ligands. In a first time, the reactivity of these complexes in solution is rationalised through the use of spectroscopies and DFT calculations. Then, the magnetic properties of two trinuclear complexes are presented and analysed thanks to high level ab initio calculations. Finally, in the third study we focus on mononuclear lanthanide-based complexes presenting a slow dynamics of magnetisation at low temperature. Magnetic measurements, as well as luminescence and polarised neutron diffraction experiments, combined to SA-CASSCF/RASSI-SO calculation allow the rationalisation of the observed magnetic properties
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Naik, Devang S. "Bose-Einstein Condensation: Building the Testbeds to Study Superfluidity." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-09072006-141453/.
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Thesis (Ph. D.)--Physics, Georgia Institute of Technology, 2007.Davidovic, Dragomir, Committee Member ; Kennedy, T.A. Brian, Committee Member ; Chapman, Mike, Committee Member ; Raman, Chandra, Committee Chair ; Bunz, Uwe, Committee Member.
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Bera, Manabendra Nath. "Zeeman Deceleration of Supersonic Beam trapping of Paramagnetic Atoms in a Traveling Magnetic Wave." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00599318.
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Le développement de différentes techniques pour contrôler les degrés de liberté internes et externes des molécules et pour produire (ultra-) froide, piège des moléculaire ensembles ouvrir des voies différentes à la physique et la chimie dans le régime de basse température. Il s'agit notamment de nombreux territoires en physique comme, phases quantiques de la matière, traitement de l'information quantique, les froides collisions moléculaires, les chimies froides et aussi de divers tests de haute précision pour la physique fondamentale. Cette thèse décrit diverses expériences de guidage et de décélération des faisceaux supersoniques d'atomes paramagnétiques à l'aide de champs magnétique inhomogène dépendent du temps. Ces champs magnétiques inhomogènes ont été utilisés pour exercer une force sur les atomes ou les molécules paramagnétiques, qui résultent de l'effet Zeeman. Le principe du ralentisseur Zeeman nouvellement développé est de produire un déplacement tridimensionnel du piège magnétique, à la vitesse initiale du faisceau. Le contrôle de la dépendance temporelle du champ magnétique nous permet de contrôler la vitesse du piège magnétique co-mobile, procurant ainsi une décélération d'une classe de vitesse du faisceau supersonique. Le piège magnétique co- mobile est déduit à partir d'une onde magnétique mobile, offrant un minimum de distorsion du piège lors de sa propagation. Les propriétés transverses du piège sont réglables grâce à un champ magnétique transversal quadrupolaire, qui peut être ajusté indépendamment des propriétés de vitesses et l'accélération du piège. Une grande part du travail de thèse a été consacrée à la conception, la réalisation et la construction du montage expérimental, consistant en un jet supersonique et en un dispositif complexe de bobines pour réaliser l'onde magnétique progressive, formant un piège magnétique mobile. Le jet froid pulsé d'atomes métastables est produit par expansion supersonique à travers une valve refroidie à l'azote liquide, excités dans l'état métastable par une décharge électrique. Nous avons guidé le jet d'argon au travers d'un tube capillaire le guidage et la décélération ont été démontrés. Le piège magnétique mobile est formé par la combinaison d'un champ magnétique quadrupolaire et d'un champ magnétique axial modulé spécialement. Le champ quadrupolaire est continu et un gradient de champ est dirigé seulement dans la direction transverse du jet. Le circuit plan produit une onde magnétique sinusoïdale avec un gradient de champ dans la direction axiale. Avec l'électronique fabriquée au laboratoire, ou peut produire une onde magnétique progressive d'amplitude 0.69T (avec un courant AC de 300A) et de fréquence 40 kHz. On obtient ainsi une onde qui se déplace à une vitesse de 464m/s. Plusieurs expériences de principe ont été réalisées en utilisant le jet froid pulsé d'argon métastable. Nous avons étudié les propriétés de guidage du quadrupole pour divers courants et pour différents atomes (hélium et argon) et comparé les résultats aux prédictions théoriques de simulations numériques. Le jet d'argon métastable a été guidé en 3D à des vitesses variées (464m/s, 400m/s, 392m/s) avec un décélérateur de 28cm de long. La température observée du paquet guidé est de 100mK. L'expérience de décélération a été réalisée avec le jet d'argon métastable depuis la vitesse de 400m/s jusqu'à 370m/s et depuis la vitesse de 392m/s jusqu'à 365m/s. Les résultats expérimentaux sont comparés avec les simulations numériques.
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Leung, Kent [Verfasser], Peter [Akademischer Betreuer] Fierlinger, and PETER [Akademischer Betreuer] BOENI. "Development of a new superfluid helium ultra-cold neutron source and a new magnetic trap for neutron lifetime measurements / Kent Leung. Gutachter: Peter Fierlinger ; Peter Böni. Betreuer: Peter Fierlinger." München : Universitätsbibliothek der TU München, 2013. http://d-nb.info/1031511776/34.
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Lindenfels, David-Friedrich von [Verfasser], and Wolfgang [Akademischer Betreuer] Quint. "Experimental Studies of Highly Charged Ions in a Penning Trap for the Measurement of Electron Magnetic Moments by Double-Resonance Spectroscopy / David-Friedrich Freiherr von Lindenfels ; Betreuer: Wolfgang Quint." Heidelberg : Universitätsbibliothek Heidelberg, 2015. http://d-nb.info/1180502809/34.
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Leung, Kent Kwan Ho [Verfasser], Peter [Akademischer Betreuer] Fierlinger, and PETER [Akademischer Betreuer] BOENI. "Development of a new superfluid helium ultra-cold neutron source and a new magnetic trap for neutron lifetime measurements / Kent Leung. Gutachter: Peter Fierlinger ; Peter Böni. Betreuer: Peter Fierlinger." München : Universitätsbibliothek der TU München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:91-diss-20130213-1119646-0-0.
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Corrêa, Thiago Reginaldo. "Implicações do uso de campos magnéticos oscilantes em um mot de rubídio." Universidade do Estado de Santa Catarina, 2012. http://tede.udesc.br/handle/handle/1969.
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This work presents a study about infuences that a quadripolar magnetic field periodically time dependent, can promote in a magneto-optical trap (MOT). The intention reflects the interest in finding an oscillating field configuration that enables the capture and provide benefits if compared to the typical process of trapping. In many papers that will be cited here, a MOT uses a magnetic field that promotes a linear steady magnetic field gradient from the center of the trap. Applying experimental results involving magnetic field oscillations, which will be quoted in detail throughout this text, came the initiative to mathematically model the problem and seek a form of oscillation that may result in a more efficient trapping. Numerical results in a one-dimensional model suggests that the number of atoms is strongly aflected by fuctuations, but we have not found, for the modulations suggests in this work, an oscillation model that could provide an increase of the trap atoms. It was noted that the oscillation frequency of the atom is subjected, aflect the amplitude of the oscillations in the number of trapped atoms.
Neste trabalho apresentamos um estudo sobre as influências que um campo quadripolar magnético, periodicamente dependente do tempo, pode promover em uma armadilha magnético-óptica (Magneto Optical Trap - MOT). O objetivo deste trabalho reflete o interesse em encontrar uma configuração de campo oscilante que possibilite o aprisionamento e forneça vantagens em relação ao processo típico de armadilhamento. Em muitos dos trabalhos que serão citados aqui, um MOT utiliza um campo magnético quadripolar estacionário que promove um gradiente de campo magnético linear à partir do centro da armadilha. Usando resultados experimentais envolvendo oscilações no campo magnético, que serão citados mais detalhadamente no decorrer deste texto, surgiu a iniciativa de modelar o problema matematicamente e buscar uma forma de oscilação que possa resultar em um aprisionamento mais eficiente. Resultados numéricos concebidos em um modelo unidimensional sugerem que o número de átomos é fortemente afetado pelas oscilações, mas não foi possível encontrar, para as modulações sugeridas neste trabalho, uma modulação que pudesse fornecer aumento expressivo no número de átomos armadilhados. Foi possível constatar que a freqüência da oscilação a que o átomo é submetido, afetará a amplitude das oscilações no número de átomos armadilhados.
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Alcantara, Katianne Fernandes de. "Simulação de resfriamento a laser em armadilha magnética e construção de laser de cavidade estentida." Universidade do Estado de Santa Catarina, 2010. http://tede.udesc.br/handle/handle/2002.
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Laser cooling in high magnetic fields, presents a series of difficulties due to inhomogeneous broadening of the frequency due to Zeeman Effect. In the first part of this work we investigate the laser cooling of Li by a Monte Carlo simulation, the 2S(1/2)-> 2P(3/2) transition at 670.96 nm in a magnetic trap under the characteristics of trap operating at the LASER laboratory of the Institute of Physics, UFRJ. In the second part, we built a diode laser with extended Littrow cavity emitting in 972 nm using the configuration of extended cavity Littrow. The purpose of this laser is, after a double frequency doubling, to use it to study the hydrogen atom in the transition 1S -> 2S at 243 nm.
O resfriamento a laser em altos campos magnéticos, apresenta uma série de dificuldades devido ao alargamento inomogêneo da transição causado pelo efeito Zeeman. Na primeira parte desse trabalho investigamos o resfriamento a laser de Lítio através de uma simulação de Monte Carlo, na transição 2S1/2 -> 2P3/2 em 670.96 nm, em uma armadilha magnética com as características da armadilha em funcionamento no laboratório LASER do instituto de Física da UFRJ. Na segunda parte, foi construído um laser de diodo em cavidade estendida emitindo em 972 nm utilizando a configuração de Cavidade Estendida de Littrow. O propósito desse laser e após um duplo dobramento de freqüência, utilizá-lo para estudo do átomo de Hidrogênio na transição 1S -> 2S em 243 nm.
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Gutiérrez, Gimeno Manuel. "Análisis de nuevas estrategias cardioprotectoras destinadas a modular el remodelado ventricular tras infarto agudo de miocardio: estudio preclínico y seguimiento mediante técnicas de imagen no invasiva de alta resolución." Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/669462.
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Introducción: la cardiopatía isquémica es una de las principales causas de morbimortalidad en todo el mundo. En las últimas décadas se ha logrado disminuir considerablemente la mortalidad de los pacientes con infarto agudo de miocardio, a costa de un aumento de los casos de insuficiencia cardíaca crónica. En consecuencia, es necesario idear nuevos enfoques terapéuticos para prevenir el remodelado cardíaco y la aparición de insuficiencia cardíaca. El área total de necrosis se debe a la combinación de la lesión isquémica y el daño por reperfusión (desencadenado por la restauración repentina del flujo sanguíneo en el territorio infartado). Éste último juega un papel clave en el desarrollo del remodelado cardíaco e insuficiencia cardíaca. Los bloqueadores del receptor P2Y12 son un grupo de agentes antiplaquetarios de uso habitual en el infarto agudo de miocardio, en el que existen diferentes subtipos con diferentes perfiles farmacocinéticos y farmacodinámicos (ej. el agente tradicional clopidogrel frente al de nueva generación ticagrelor). Se cree que ticagrelor tiene efectos sobre el metabolismo de la adenosina, una molécula con efectos cardioprotectores. En esta tesis queremos demostrar que ticagrelor ejerce un efecto cardioprotector sobre el corazón infartado mayor que el ejercido por clopidogrel y que este efecto es independiente de su efecto antiplaquetario.
Material y métodos: se diseñó un modelo animal (porcino) de infarto agudo de miocardio compuesto por dos estudios con un mismo diseño. Los animales fueron aleatorizados a grupos de igual tamaño que recibieron diferentes intervenciones (placebo, clopidogrel y ticagrelor). Después de la dosis de carga inicial se indujo un infarto en todos los animales y, en los días posteriores, fueron llevados a una instalación de resonancia magnética (RM) donde se estudiaron parámetros cardiacos funcionales y estructurales (motilidad global y segmentaria, edema, obstrucción microvascular y necrosis). Finalmente, los animales fueron sacrificados para para realizar análisis histológicos y moleculares en los que se evaluó la expresión y activación de moléculas relacionadas con la formación de edema y supervivencia celular (ej. acuaporina-4, AMPK). Mientras que el primer estudio se centró en los efectos durante las primeras 24 horas post infarto, el segundo estaba destinado a la evaluación de los efectos crónicos (3d y 42d después del infarto).
Resultados: El uso de cualquier agente antiplaquetario reduce el daño miocárdico en comparación con placebo (menos edema y necrosis miocárdica, mejores parámetros funcionales en RM) pero ticagrelor lo hace en mayor medida que clopidogrel. La reducción observada, tanto del edema como de la necrosis, es estadísticamente significativa y concuerda con los resultados de los análisis moleculares. La expresión de acuaporina 4 se reduce y la expresión y activación de AMPK aumenta en animales tratados con ticagrelor. Acuaporina 4 es un canal transportador que facilita la entrada de agua en la célula en condiciones de estrés. Por otro lado, AMPK actúa disminuyendo el edema extracelular y promoviendo la supervivencia celular. Ticagrelor también muestra un impacto positivo sobre los parámetros funcionales en las fases aguda y crónica después del infarto. Tanto la fracción de eyección del ventrículo izquierdo como la motilidad regional se ven menos afectadas en los animales tratados con ticagrelor a día 3 y día 42. Es importante remarcar que todos los beneficios descritos con ticagrelor se anulan al añadir un antagonista del receptor de adenosina. Este hecho muestra que los efectos cardioprotectores de ticagrelor están mediados por adenosina.
Conclusión: En esta tesis demostramos que ticagrelor, un inhibidor de nueva generación del receptor P2Y12, presenta efectos cardioprotectores adicionales en comparación con clopidogrel y que estos efectos están mediados por adenosina. El impacto positivo se observa en las fases aguda y crónica después del infarto de miocardio y está presente tanto en parámetros estructurales como funcionales.Introduction: ischemic heart disease is one of the leading causes of morbidity and mortality worldwide. A sharp decline in the mortality rate of patients suffering from acute myocardial infarction has been achieved, at the cost of rising cases of chronic heart failure. In consequence, it is necessary to devise new therapeutic approaches to prevent cardiac remodeling and the ensuing heart failure. In this regard, cardioprotection appears as a foreseeable mainstay. We now know the total necrotic area derives from a combination of the ischemic injury and an added damage produced by the sudden restoration of blood flow in the obstructed coronary artery’s territory, the reperfusion injury. Reperfusion injury plays a key role in the development of cardiac remodeling and chronic heart failure. P2Y12 blockers are a group of antiplatelet agents that are standard care in the setting of acute myocardial infarction. However, within the group there are different subtypes with different pharmacokinetic and pharmacodynamic profiles (e.g., the standard of care clopidogrel and the new generation P2Y12 receptor blocker ticagrelor). Ticagrelor is believed to have effects on adenosine metabolism, molecule with cardioprotective implications. In this thesis we mean to prove that ticagrelor exerts a higher cardioprotective impact as compared to clopidogrel on the infarcted heart, independently of their antiplatelet effect. Material and methods: we designed an animal (swine) myocardial infarction model composed by two studies with a common layout. Animals were randomly allocated to equally sized groups receiving different interventions (placebo, clopidogrel and ticagrelor). An infarction was induced in all animals after the initial loading dose and, in the following days, they were brought to a magnetic resonance (MR) facility where functional and structural cardiac parameters were studied. Global and segmental motility as well as cardiac oedema, microvascular obstruction and late necrosis were assessed. Finally, the animals were sacrificed and their heart sliced to perform histologic and molecular analysis that assessed the expression and activation of molecules related to oedema formation and cell survival (i.e. aquaporin-4, AMPK molecules). Whereas the first study was centred in the effects in the first 24h after myocardial infarction, the second study was intended for evaluation of the chronic effects (3d and 42d after MI). Results: The use of any antiplatelet agent reduces myocardial damage as compared to placebo (less myocardial oedema and necrosis, better functional parameters in MR). However, ticagrelor does so to a greater extent than clopidogrel. The observed reduction is statistically significant in both oedema and necrosis and concurs with the results of molecular analyses. The expression of acuaporine-4 is reduced and the expression and activation of AMPK increased in animals treated with ticagrelor. Acuaporine-4 is a channel transporter that eases the entrance of water in the cell under stress conditions. On the other hand, AMPK acts by diminishing extracellular oedema and promoting cell survival. Ticagrelor also shows a positive impact on functional parameters in both, acute and chronic phases after myocardial infarction. Left ventricle ejection fraction as well as regional wall motion are less impaired in animals treated with ticagrelor than clopidogrel at day 3 and day 42. Remarkably, all the positive effects described with ticagrelor are reversed when an adenosine receptor blocker is added. This fact shows the cardioprotective potential of ticagrelor is mediated by adenosine. Conclusion: In this thesis we demonstrate ticagrelor, a new generation of P2Y12 inhibitor, shows additional cardioprotective effects as compared to clopidogrel and that these effects are mediated by adenosine. The positive impact is observed in the acute and chronic phases after myocardial infarction and is present in both, structural and functional parameters.
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Meerkin, Jarrod D. "Musculo-skeletal adaptation and altered loading environments: An amputee model." Thesis, Queensland University of Technology, 2000. https://eprints.qut.edu.au/36750/1/36750_Digitised%20Thesis.pdf.
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Amputation of the lower limb may result in musculo-skeletal changes similar to those that occur following space flight, immobilisation and prolonged bed rest. The similarities desist when one considers the invasive nature of amputation surgery and the impact that partial loss of a limb has on the loading characteristics of the affected leg. The aim of this study was to determine the musculo-skeletal changes that occur following trans-femoral and trans-tibial amputation, and to compare differences in the musculo-skeletal characteristics of these groups, which may occur as a function of the modified loading environment. Unique to this investigation was the study of a new trans-femoral amputee, which was incorporated to investigate the time course of any changes in muscle and bone atrophy and decreases in muscle strength in the early post-operative period. This study was also designed to provide a comparison with longer-term amputees and examine relationships between muscle morphology and strength and identified changes in gait behaviour by reference to normal gait patterns.
Eight unilateral trans-femoral and 8 trans-tibial amputees (mean age 35.2yrs. ± 9.8 and 35.3yrs. ± 8.9 respectively) were subjects in the study. There were 7 males and 1 female in each of the amputee groups. A control group of similar number was used, with subjects matched on age, weight, height and gender. In the first phase of the investigation dual energy x-ray absorptiometry and magnetic resonance imaging was used to measure bone mineral density (B:MD) of the lumbar spine (L2-IA) and femoral neck (FN) and to calculate the volume and cross-sectional area (CSA) of selected muscles. Strength evaluation was assessed by measurement of maximal isometric hip torque using a Kin-Com dynamometer.
Gait analyses were undertaken to determine differences in the angular kinematics of the residual and sound limb together with an electromyographic (EMG) assessment of the onset and offset of the activity of 4 hip muscles of the residual and sound thigh, which was synchronised with the kinematic measures. Differences in ground reaction force (GRF) between the residual and sound limb of each group were also examined.
A single case study involving a 19-year-old motor accident victim who sustained a traumatic trans-femoral amputation of his right leg was conducted to determine the structural and functional changes over a 9-month period. Structural and functional evaluations were repeated every 3 months, beginning at 4 months post amputation, using similar methodologies and procedures described for the longer-term amputees.
In the longer-term amputees the volume and CSA of the residual musculature of the trans-femoral group was significantly lower by comparison with the sound limb and no difference was found between the residual and sound musculature of the trans-tibial group. Mean torque of the residual hip was lower than that of the sound hip of the trans-femoral and trans-tibial group but the difference was not significant. Bone mineral density of the residual FN was significantly lower than that of the sound FN of the trans-femoral group but there was no difference in the trans-tibial group. No differences were found between the two experimental groups and controls at the L2-1A site. Muscle volume was significantly correlated with BMD of the L2- 1A vertebrae in the residual and sound limb of the trans-tibial group.
Trans-femoral and trans-tibial amputees had a significantly slower walking velocity than that of the control group. Cadence of the trans-femoral group was significantly lower than both trans-tibial and the control groups. Stride length was not significantly different between the trans-femoral and control group but was significantly lower in the trans-tibial group. Significant differences were found between the trans-femoral and control group in the range of ankle and knee motion of the sound limb and between the sound and residual ankle, knee and hip joints of the trans-femoral and trans-tibial group. Mean GRF was lower in the residual limb compared to the sound limb for both groups, although the differences were not significant. The activity of rectus femoris, biceps femoris and adductor longus in the sound limb of the trans-femoral group were generally active for a longer duration compared to the controls and the duration of activity of these same muscles differed between the residual and sound limb musculature of the trans-tibial group.
In the case study subject, BMD in the residual FN was 38.4 per cent lower than the sound FN at 4 months, decreasing to 42.1 per cent at the end of the 9-month evaluation. At this time point bone loss of the case study subject was greater than the average difference between the residual and sound limb of the longer-term amputees suggesting some recovery of bone mass may be possible. Rectus femoris and biceps femoris showed greater atrophy than the intact muscles, psoas major, adductor longus and the gluteals. At 7-months post amputation, hip torque of the residual limb in all planes of movement was lower by comparison with the sound limb.
There was considerable intra-group variability in the data, which reflected the heterogeneity of the groups with respect to surgical fixation procedures, types of prosthesis used and their different physical activity levels. It was shown that longerterm trans-femoral amputees experienced considerable muscle and bone atrophy of their residual limb, which was greater than that experienced by the trans-tibial group.
Although loading was not measured directly the difference between the two groups of amputees perhaps reflected their altered loading environment. Isometric hip torque was not different between the residual and sound limb of the trans-femoral and trans-tibial group, an unexpected result in the trans-femoral group considering the muscle atrophy present. The morphological changes combined with the prosthetic components were likely responsible for differences in amputee gait function. In the more recent amputee, muscle and bone atrophy was most rapid in the first 4 months but the volume and CSA of rectus femoris and biceps femoris continued to decrease up to 13 months post amputation. Isometric torque of the hip flexors and extensors decreased between 7 and 10 months and stabilised by 13 months post amputation while there was no change in the torque of the hip abductors and adductors from the initial measure. The potential for recovery of BMD, muscle size and muscle strength must be considered and may be applied to the design of more effective prostheses and rehabilitation strategies aimed at improving functional outcomes.
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Rodríguez, Palomares José Fernando. "Cambios dinámicos del tamaño del infarto y la obstrucción de la microcirculación tras administración de constraste mediante cardio-resonancia magnética y su valor pronóstico en el remodelado ventricular izquierdo." Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/382827.
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Antecedentes del tema: En el contexto de un infarto agudo de miocardio (IAM), diversos autores han postulado que el realce tardío de gadolinio (RTG) no sólo reflejaría la necrosis miocárdica sino que también el área en riesgo. Sin embargo, no existe información sobre el tiempo óptimo tras la administración de contraste que permitiría la diferenciación de dichas áreas. Además, se conoce que el tamaño de la necrosis miocárdica presenta un papel importante en el remodelado ventricular izquierdo en pacientes con infarto agudo de miocardio con elevación del segmento ST (SCACEST). La necrosis miocárdica determinada mediante cardio-resonancia magnética (CRM) disminuye en el tiempo secundaria a un proceso de cicatrización miocárdica, aunque, se desconoce la cantidad, velocidad y duración de dicho proceso de cicatrización miocárdica.
El objetivo de nuestro estudio fue determinar en pacientes post-IAM si el tiempo tras la administración de contraste influía en el tamaño del RTG así como el tiempo que predice mejor el tamaño del infarto y la recuperación funcional en el seguimiento.
Métodos: Los pacientes fueron evaluados mediante CRM (n=60 pacientes) en la primera semana post-IAM, a los 3 meses y a los 12 meses tras la revascularización percutánea. Las secuencias de inversión-recuperación en disparo único (ss-IR) fueron adquiridas a diferentes intervalos temporales tras la administración de contraste y comparadas con las secuencias de inversión-recuperación segmentadas (seg-IR). El tiempo de inversión fue ajustado de forma adecuada, y, posteriormente, las imágenes fueron randomizadas y analizadas de forma ciega a fin de describir los volúmenes de realce tardío a diferentes intervalos temporales.
Resultados: En el contexto de un IAM reciente, el volumen de RTG decrece en los siguientes minutos tras la administración de contraste con un volumen máximo 3 minutos post-contraste y un mínimo a los 25 minutos tras la administración del bolus (p= 0.005); sin embargo, el volumen del RTG permanece constante en el tiempo en pacientes en fase crónica del IAM (p=0.886). Además, también se observó un cambio en el índice de transmuralidad post-contraste. Un infarto transmural (>75%) a los 25 minutos de la administración de contraste predice de forma más precisa la ausencia de la mejoría de la contractilidad segmentaria, un mayor incremento de los volúmenes ventriculares izquierdos y una mayor reducción de la fracción de eyección en el seguimiento en comparación con la transmuralidad estudiada a los 10 minutos (post-contraste).
La masa media infartada en el primer estudio (necrosis aguda), en la fase crónica precoz (cicatrización precoz) y tardía (cicatrización tardía) fue de 25 ± 17 g, 17 ± 12 g, and 15 ± 11 g, respectivamente. Los pacientes fueron divididos en tertiles, basados en el tamaño de la necrosis, mostrando los infartos de mayor tamaño una mayor reducción absoluta del tamaño de la necrosis. Hubo una reducción de 8 gr ó 32% en el tamaño del infarto entre la fase aguda y la fase crónica precoz (p<0.01) y una reducción de 2 gramos adicionales (12%) entre la fase crónica precoz y la tardía (p<0.01).
Conclusiones: En nuestro estudio se observa una reducción del volumen de RTG en los minutos inmediatos a la administración de contraste. Dicha reducción ocurre en la fase aguda post-IAM y no en la fase crónica. Además, la transmuralidad establecida 25 minutos tras la administración de contraste fue la que mejor predijo el tamaño de la necrosis y la recuperación funcional en el seguimiento. Además, se observó que la cicatrización de la necrosis miocárdica es un proceso continuo tras la reperfusión miocárdica con una reducción mayor en los primeros meses post-IAM. La naturaleza dinámica de la cicatrización miocárdica durante el primer año post-IAM indica que las decisiones basadas en el tamaño del infarto y las intervenciones que valoran la reducción del tamaño de la necrosis, deben tener en cuenta el momento temporal en que son cuantificadas.Background: In acute myocardial infarction (MI), late Gadolinium enhancement (LGE) has been proposed to include the infarcted myocardium and area at risk. However, little information is available on the optimal timing after contrast injection to differentiate these 2 areas. Also, the role of infarct size on left ventricular (LV) remodeling in heart failure after an acute ST-segment elevation myocardial infarction (STEMI) is well recognized. Infarct size, as determined by cardiovascular magnetic resonance (CMR), decreases over time following a healing process. The amount, rate, and duration of infarct healing are unknown. Our aim was to determine in acute and chronic MI whether imaging time after contrast injection influences the LGE size that better predicts infarct size and functional recovery. Methods: Subjects were evaluated by cardiovascular magnetic resonance (CMR) the first week (n = 60), 3 months and 12 months after a percutaneously revascularized STEMI. Inversion-recovery single-shot (ss-IR) imaging was acquired at multiple time points following contrast administration and compared to segmented inversion-recovery (seg-IR) sequences. Inversion time was properly adjusted and images were blinded, randomized and measured for LGE volumes. Results: In acute MI, LGE volume decreased over several minutes (p = 0.005) with the greatest volume occurring at 3 minutes and the smallest at 25 minutes post-contrast injection; however, LGE volume remained constant over time in chronic MI (p = 0.886). Depending on the imaging time, in acute phase, a change in the transmurality index was also observed. A transmural infarction (>75%) at 25 minutes better predicted the absence of improvement in the wall motion score index (WMSI), a higher increase in left ventricular volumes and a lower ejection fraction compared to 10 minutes. Mean infarct sizes at baseline (acute necrosis), early follow-up (early scar), and late follow-up (late scar) were 25 ± 17 g, 17 ± 12 g, and 15 ± 11 g, respectively. Patients were stratified in tertiles, based on infarct size, with the largest infarcts having the greatest absolute decrease in mass at early and late scar. The percent reduction of infarct mass was independent of initial infarct size. There was an 8 g or 32% decrease in infarct mass between acute necrosis and early scar (p < 0.01) with a 2 g or 12% additional decrease in infarct mass between early and late scar (p < 0.01). Conclusions: A change was observed in LGE volume in the minutes following contrast administration in acute but not in chronic MI. Infarct transmurality 25 minutes post-contrast injection better predicted infarct size and functional recovery at follow-up. Also, we observed that infarct healing is a continuous process after reperfusion for STEMI, with greatest reduction in infarct size in the first few months. The dynamic nature of infarct healing through the first year after STEMI indicates that decisions based on infarct size, and interventions to reduce infarct size, must take into consideration the time frame of measurement.
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Lewoczko-Adamczyk, Wojciech. "Bose-Einstein condensation in microgravity." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2009. http://dx.doi.org/10.18452/15970.
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Ultra-kalte atomare Gase werden in zahlreichen Laboren weltweit untersucht und finden unter anderem Anwendung in Atomuhren und in Atominterferometer. Die Einsatzgebiete erstrecken sich von der Geodäsie über die Metrologie bis hin zu wichtigen Fragestellungen der Fundamentalphysik, wie z.B. Tests des Äquivalenzprinzips. Doch die beispiellose Messgenauigkeit ist durch die irdische Gravitation eingeschränkt. Zum einen verzerrt die Schwerkraft das Fallenpotential und macht damit die Reduktion der atomaren Energie unter einem bestimmten Limit unmöglich. Zum anderen werden die aus einer Falle frei gelassenen Teilchen durch die Erdanziehung beschleunigt und so ist deren Beobachtungszeit begrenzt. Im Rahmen dieser Arbeit werden die Ergebnisse des Projektes QUANTUS (Quantengase Unter Schwerelosigkeit) dargestellt. Auf dem Weg zur Implementierung eines Quantengasexperimentes im Weltraum wurde innerhalb einer deutschlandweiten Zusammenarbeit eine kompakte, portable und mechanisch stabile Apparatur zur Erzeugung und Untersuchung eines Bose-Einstein-Kondensats (BEC) unter Schwerelosigkeit im Fallturm Bremen entwickelt. Sowohl die Abbremsbeschleunigung von bis zu 50 g als auch das begrenzte Volumen der Fallkapsel stellen hohe Ansprüche an die mechanische Stabilität und die Miniaturisierung von optischen und elektronischen Komponenten. Der Aufbau besteht aus einer im ultra-hoch Vakuum geschlossenen magnetischen Mikrofalle (Atomchip) und einem kompakten auf DFB-Dioden basierenden Lasersystem. Mit diesem Aufbau ließ sich das erste BEC unter Schwerelosigkeit realisieren und nach 1 Sekunde freier Expansion zu beobachten. Weder die schwache Krümmung des Fallenpotentials noch die lange Beobachtungszeit würden in einem erdgebundenen Experiment realisierbar. Die erfolgreiche Umsetzung des Projektes eröffnet ein innovatives Forschungsgebiet - degenerierte Quantengase bei ultratiefen Temperaturen im pK-Bereich, mit großen freien Evolutions- und Beobachtungszeiten von mehreren Sekunden.Recently, cooling, trapping and manipulation of neutral atoms and ions has become an especially active field of quantum physics. The main motivation for the cooling is to reduce motional effects in high precision measurements including spectroscopy, atomic clocks and matter interferometry. The spectrum of applications of these quantum devices cover a broad area from geodesy, through metrology up to addressing the fundamental questions in physics, as for instance testing the Einstein’s equivalence principle. However, the unprecedented precision of the quantum sensors is limited in terrestial laboratories. Freezing atomic motion can be nowadays put to the limit at which gravity becomes a major perturbation in a system. Gravity can significantly affect and disturb the trapping potential. This limits the use of ultra-shallow traps for low energetic particles. Moreover, free particles are accelerated by gravitational force, which substantially limits the observation time. Targeting the long-term goal of studying cold quantum gases on a space platform, we currently focus on the implementation of a Bose-Einstein condensate (BEC) experiment under microgravity conditions at the drop tower in Bremen. Special challenges in the construction of the experimental setup are posed by a low volume of the drop capsule as well as critical decelerations up to 50g during recapture at the bottom of the tower. All mechanical and electronic components were thus been designed with stringent demands on miniaturization and mechanical stability. This work reports on the observation of a BEC released from an ultra-shallow magnetic potential and freely expanding for one second. Both, the low trapping frequency and long expansion time are not achievable in any earthbound laboratory. This unprecedented time of free evolution leads to new possibilities for the study of BEC-coherence. It can also be applied to enhance the sensitivity of inertial quantum sensors based on ultra-cold matter waves.
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Tan, Yi Lei. "Structural and Biophysical Characterisation of Denatured States and Reversible Unfolding of Sensory Rhodopsin II." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/289718.
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Our understanding of the folding of membrane proteins lags behind that of soluble proteins due to the challenges posed by the exposure of hydrophobic regions during in vitro chemical denaturation and refolding experiments. While different folding models are accepted for soluble proteins, only the two-stage model and the long-range interactions model have been proposed so far for helical membrane proteins. To address our knowledge gap on how different membrane proteins traverse their folding landscapes, Chapter 2 investigates the structural features of SDS-denatured states and the kinetics for reversible unfolding of sensory rhodopsin II (pSRII), a retinal-binding photophobic receptor from Natronomonas pharaonis. pSRII is difficult to denature, and only SDS can dislodge the retinal chromophore without rapid aggregation. Even in 30% SDS (0.998 $\mathit{\Chi}_{SDS}$), pSRII retains the equivalent of six out of seven transmembrane helices, while the retinal binding pocket is disrupted, with transmembrane residues becoming more solvent-exposed. Folding of pSRII from an SDS-denatured state harbouring a covalently-bound retinal chromophore shows deviations from an apparent two-state behaviour. SDS denaturation to form the sensory opsin apo-protein is reversible. This chapter establishes pSRII as a new model protein which is suitable for membrane protein folding studies and has a unique folding mechanism that differs from those of bacteriorhodopsin and bovine rhodopsin. In Chapter 3, SDS-denatured pSRII, acid-denatured pSRII and sensory opsin obtained by hydroxylamine-mediated bleaching of pSRII were characterised by solution state NMR. 1D $^1$H and $^{19}$F NMR were first used to characterise global changes in backbone amide protons and tryptophan side-chains. Residue-specific changes in backbone amide chemical shifts and peak intensities in 2D [$^1$H,$^{15}$N]-correlation spectra were analysed. While only small changes in the chemical environment of backbone amides were detected, changes in backbone amide dynamics were identified as an important feature of SDS- and acid-denatured pSRII and sensory opsin. $^{15}$N relaxation experiments were performed to study the backbone amide dynamics of SDS-denatured pSRII, reflecting motions on different timescales, including fast fluctuations of NH bond vectors on the ps-ns timescale and the lack of exchange contributions on the µs timescale. These studies shed insight on differences in the unfolding pathways under different denaturing conditions and the crucial role of the retinal chromophore in governing the structural integrity and dynamics of the pSRII helical bundle. Hydrogen bonds play fundamental roles in stabilising protein secondary and tertiary structure, and regulating protein function. Successful detection of hydrogen bonds in denatured states and during protein folding would contribute towards our understanding on the unfolding and folding pathways of the protein. Previous studies have demonstrated residue-specific detection of stable and transient hydrogen bonds in small globular proteins by measuring $^1{\it J}_{NH}$ scalar coupling constants using NMR. In Chapter 4, different methods for measuring $^1{\it J}_{NH}$ scalar coupling were explored using RalA, a small GTPase with a mixed alpha/beta fold, as proof-of-concept. Detection of hydrogen bonds was then attempted with OmpX, a beta-barrel membrane protein, both in its folded state in DPC micelles and in the urea-denatured state. While $^1{\it J}_{NH}$ measurement holds promise for studying hydrogen bond formation, further optimisation of NMR experiments and utilisation of perdeuterated samples are required to improve the precision of such measurements in large detergent-membrane protein complexes. Naturally occurring split inteins can mediate spontaneous trans-splicing both in vivo and in vitro. Previous studies have demonstrated successful assembly of proteorhodopsin from two separate fragments consisting of helices A-B and helices C-G via a splicing site in the BC loop. To complement the in vitro unfolding/folding studies, pSRII assembly in vivo was attempted by introducing a splicing site in the loop region of the beta-hairpin constituting the BC loop of pSRII. The expression conditions for the N- and C-terminal pSRII-intein segments were optimised, and the two segments co-expressed. However, the native chromophore was not observed. Further optimisation is required for successful in vivo trans-splicing of pSRII and application of this approach towards understanding the roles of helices and loops in the folding of pSRII.
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Brahimi, Sonia. "Caractérisation géophysique (méthodes potentielles, imagerie sismique) de structures géologiques : des terranes panafricains de la chaine trans-saharienne, aux vallées-tunnel et incisions glaciaires de la Mer du Nord et d'Algérie." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAH005.
Full textAbstract:
L’analyse des données magnétiques et gravimétriques de la partie nord de la ceinture trans-saharienne a permis de proposer une carte de compartimentalisation géophysique et rhéologique des structures crustales et de visualiser les terranes du bouclier Touareg sur plus de 1000 km au nord, sous les bassins sédimentaires sahariens et plusieurs aspects ont pu être discutés. Un pseudo réseau de quatre générations successives de paléovallées et incisions a été mis en évidence dans la succession glaciaire de l’Ordovicien supérieur au NE du bassin d’Illizi sur la base des données sismiques de haute résolution. Pour chaque incision, la géométrie ainsi que les faciès sismiques de leur remplissage ont été déterminés. Un parallélisme entre la distribution de certaines paléovallées et l'orientation des anomalies magnétiques a été observé, mais aucune relation stratigraphique entre ces structures n'a été identifiée sur les sections sismiques. Un réseau complexe de vallées tunnel glaciaires du Pléistocène en mer du Nord a été identifié sur la base de données aéromagnétiques à haute résolution. Une analyse magnétique détaillée a été réalisée en combinant plusieurs méthodes magnétiques. A la fin, des modèles magnétiques synthétiques 2D ont été calculés pour les incisions ordoviciennes, appliqué pour le cas du bassin d’Illizi. Les résultats obtenus montrent que leur détection magnétique est possible, si toutes fois un levé magnétique à haute résolution serait disponibleThe magnetic and gravimetric data analysis of the northern part of the trans-saharan belt allowed to propose a geophysical and rheological compartmentalization map of its crustal structures and to visualize the Tuareg shield terranes over 1000 km to the north, under the saharan sedimentary basins and several aspects have been discussed. A pseudo network of four successive generations of paleovalleys and incisions has been identified on the upper Ordovician glacial succession in the north-eastern part of the Illizi basin on the basis of high-resolution seismic data. For each incision, the geometry and seismic facies of their filling have been determined. Parallelism between the distribution of some paleovalleys and magnetic anomaly orientations has been observed, but no stratigraphic relationship between them has been identified on seismic sections. A complex network of Pleistocene glacial tunnel valleys in the North Sea has been identified on the basis of high-resolution aeromagnetic data. A detailed magnetic analysis was performed by combining several magnetic methods. Finally, 2D synthetic magnetic models were calculated for Ordovician incisions, applied in the case of the Illizi basin. The results obtained show that their magnetic detection is possible, if a high-resolution magnetic survey would still be available