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Cooper, Catherine J. "Laser cooling and trapping of atoms." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308685.
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Burrows, Kathryn Alice. "Non-adiabatic losses from radio frequency dressed cold atom traps." Thesis, University of Sussex, 2016. http://sro.sussex.ac.uk/id/eprint/61380/.
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Cold atom traps are a promising tool for investigating and manipulating atomic behaviour. Radio frequency (RF) dressed cold atom traps allow high versatility of trapping potentials, which is important for potential applications, particularly in atom interferometry. This thesis investigates non-adiabatic spin flip transitions which can lead to losses of atoms from RF-dressed cold atom traps. We develop two models for the adiabatic potentials associated with RF-dressed traps, for the cases in which gravity does and doesn't have a significant effect. Within these two models we use first order perturbation theory to calculate decay rates for the number of dressed spin flip transitions per unit time. Our obtained decay rates are dependent on the atomic energy. For RF-dressed cold atom traps in which spin flip transitions lead to losses of atoms from the trap, we are able to predict ow non-adiabatic transitions decrease the trapped atom number. We achieve this by modelling the atomic distribution of energies for several different scenarios. The thesis concludes with a comparison to experimental data, including modelling how atomic energies are affected by noise in the currents generating the trapping magnetic fields.
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Morsch, Oliver. "Optical lattices for ultra-cold atoms." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301174.
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Ivanov, Vladyslav Victorovych. "Cold atoms modified radiative properties and evaporative cooling from optical traps /." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2007. http://dare.uva.nl/document/47332.
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Deb, Amita. "Theoretical and experimental studies on ultra-cold atoms in optical traps." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.600174.
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This thesis describes a number of theoretical and experimental studies on the production, manipulation and detection of ultra-cold atoms in arrays of optical traps, i. e. optical lattices for applications such as direct quantum simulation of many-body systems and quantum information processing. A method of deterministically preparing a single atom in each site of an optical lattice is explored and the parameter regime that would be required to implement this protocol in experiments is investigated. A novel method of state-selective spatial transfer of atoms between neighbouring sites of a lattice using an intermediate trap is reported and the experimental parameters worked out. The theory of off-resonant light scattering from atoms in an optical lattice is explored. The possibility of using the far- field intensity distribution and t he frequency spectrum of the light scattered from atoms in an optical lattice for performing thermometry of atoms and for identifying quantum fluctuations in the system are investigated for cases of non-interacting fermions and weakly-interacting bosons. A spatial filtering method for detecting a small number of classical defects in an optical lattice is investigated. Experiments on trapping and manipulating Bose-Einstein condensates (BEC) of 8 1Rb atoms in dynamically configurable t raps created using spatial light modulators are discussed. The construction of a new magnetic trap for trapping and magnetically transporting atoms and the experimental stages subsequently leading to the production of BECs are reported.
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Sand, Karl Jakob. "On the Design and Simulation of Electromagnetic Traps and Guides for Ultra-Cold Matter." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-11733.
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The objective of this thesis is the design and simulation of new electromagnetic traps and guides for ultra-cold matter. The traps and guides are intended for future experiments with small amounts of alkali atoms to study the quantum-mechanical effects of condensation and coupling between trapped drops of cold matter. The main results are with the development and simulation of new wire traps and guides based on the dressing effect realised in strong DC magnetic and RF fields of certain frequencies. Some designs are proposed using only trapping by the DC magnetic field. The principal methodology used in the thesis is to first develop the necessary theory and design formulas to make an initial design, followed by analytical and numerical simulation of the effective trapping potential. This may be followed by optimization of the geometry and the DC driving currents to enhance the trapping performance of the structure. A wire carrying both DC and RF currents is surrounded by a cylindrical minimum potential manifold and can be used as a guide for cold atoms. Bias rings are necessary around the wire to avoid a potential minimum of zero and to move the resulting circular potential minimum up and down along the wire. The minimum potential surfaces around two crossed or two parallel wires touch each other for certain critical values of the DC currents in the two wires. The DC currents must be in opposite directions in two parallel wires. Equations are derived in Chapter 2 for the distance to the circular minimum potential manifold for a single wire, for two crossed wires and for two parallel wires. It is then explained how prospective cold atom transfer between two crossed wires can be achieved by changing the magnitudes of the RF currents in the bias rings around the wires. Electrically controlled atom transfer between two parallel wires does not seem to be practical. A four-wire cell trap made from two crossing pairs of parallel wires has been designed and optimized using a simple Matlab script. It can be used to trap both strong- and weak-field-seeking atoms and may possibly be used to study collision and entanglement between the two types of atoms. With only DC excitation the trap becomes a trap for weak-field-seeking atoms. It then unfortunately has a potential minimum of zero at its centre. A similar 3 x 3 wire dual-well trap has also been designed and optimized in Matlab. It is prospective for the study of entanglement of BEC matter placed in the two wells. A quite low potential barrier in the direction normal to the wireplanes when the two wells are merged could however entail that the trap is inadequate for this purpose or that additional bias fields are necessary. Several multi-wire cell-grids that may find use as part of a quantum register are also described. The cell-grids can be stacked in threedimensions and can trap both strong- and weak-field-seeking atoms. The optimization, also here performed in Matlab, showed weaknesses due to a lack of complexity. A different and better optimization technique is most likely necessary to improve the optimization further. Scaling to micrometre and nanometre size is demonstrated in Chapter 3. When scaling to micrometre size thermally induced spin-flip transitions should be considered. Scaling to nanometre size demands that both thermally induced spin-flips and the effect of the Casimir-Polder force must be taken into account. The effect of the Casimir-Polder force is minimized by the use of carbon nanotubes as conductors. The minimum feasible trapping distance is expected to be no less than 100 nm from the surface of a carbon nanotube. A four micro-wire cell and a 3 x 3 micro-wire structure, both adapted for future realization on a micro-machined substrate, are given as examples of micrometre size structures. Several nanometre size structures are also demonstrated. It is shown that prospective atom transfer between two crossed nanotubes can be done essentially in the same way as for two crossed wires. A four-nanotube cell and several nanotube cell-grids are also exemplified. The depth of the trapping potential is found to be proportional to the RF frequency. If the RF frequency is increased then the DC current level must also increase to maintain the same DC current to angular frequency ratio. The depth of the trap is accordingly also proportional to the DC current level in the conductors. The depth of the trap is thus ultimately limited by the maximum conductor current. A quadrupolar trap similar to the well known Ioffe-Pritchard trap is studied in Chapter 4 with combined DC and RF current excitation of the bias rings. A non-uniform potential minimum is found around the local maximum at the centre of the trap, but this does not prevent the trap from being used to trap weak-field-seeking atoms. The potential maximum at the centre of the quadrupolar trap is more than sufficient for trapping strongfield- seeking atoms. The quadrupolar trap can therefore be used to trap both strong- and weak-field-seeking atoms if the DC bar currents are large enough. Simulations also indicate that the bias rings can be placed relatively closely together to compress clouds of cold atoms into successively smaller traps. As the gap distances become very small the B-field becomes very strong between the bias rings and there is a risk of dielectric breakdown. A metallic cylinder atom guide consisting of a cylinder with a small hole and an external wire is described analytically in Chapter 5 and simulation results from Amperes are compared favourably with the results of calculations in Matlab. It is found that there can only be a B-field zero at the centre of the hole in the cylinder when there is a second field zero further inside the cylinder. The barrier between the two field zeros typically increases in width with increasing cylinder radius and in height with decreasing cylinder radius for a given cylinder current (DC). The smallest cylinder had the highest barrier between the field zeros, but also required the highest DC current in the external wire. Bias rings around the guide must be centred on the hole in the cylinder and the DC ring currents and the spacing between the bias rings must be scaled by the same factor as the ring radius to maintain the same shape and height of the trapping potential along the centre of the hole. The cylinder guide looks promising as a hermetic guide for cold matter. Bias rings are required both to pump atoms along the guide and to remove the zero in the B-field inside the hole.<br>An attachment is added containing 7 animated applications/zip which are described in the thesis
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De, Palatis Michael V. "Production of cold barium monohalide ions." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50251.
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Ion traps are an incredibly versatile tool which have many applications throughout the physical sciences, including such diverse topics as mass spectrometry, precision frequency metrology, tests of fundamental physics, and quantum computing. In this thesis, experiments are presented which involve trapping and measuring properties of Th³⁺. Th³⁺ ions are of unique interest in part because they are a promising platform for studying an unusually low-lying nuclear transition in the 229Th nucleus which could eventually be used as an exceptional optical clock. Here, experiments to measure electronic lifetimes of Th³⁺ are described. A second experimental topic explores the production of sympathetically cooled molecular ions. The study of cold molecular ions has a number of applications, some of which include spectroscopy to aid the study of astrophysical objects, precision tests of quantum electrodynamics predictions, and the study of chemical reactions in the quantum regime. The experiments presented here involve the production of barium monohalide ions, BaX⁺ (X = F, Cl, Br). This type of molecular ion proves to be particularly promising for cooling to the rovibrational ground state. The method used for producing BaX⁺ ions involves reactions between cold, trapped Ba⁺ ions and neutral gas phase reactants at room temperature. The Ba⁺ ion reaction experiments presented in this thesis characterize these reactions for producing Coulomb crystals composed of laser cooled Ba⁺ ions and sympathetically cooled BaX⁺ ions.
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Sanguinetti, Stefano. "ATOMIC PARITY VIOLATION IN HEAVY ALKALIS: Detection by Stimulated Emission for Cesium and Traps for Cold Francium." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2004. http://tel.archives-ouvertes.fr/tel-00006785.
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Le travail présenté porte sur les progrès récents d'expériences de spectroscopie atomique sur césium et francium, visant à des mesures précises de violation de parité (PV) dans ces atomes. Dans le cadre d'une “thèse en cotutelle”, le candidat s'est consacré d'une part aux mesures PV préliminaires (8% de précision) de l'actuelle expérience Cs au LKB à Paris, et d'autre part à la préparation d'un échantillon d'atomes radioactifs de Fr (production et piégeage) aux LNL (INFN) en Italie. Ces deux expériences sont à des stades très différents. Les mesures présentées pour le Cs s'inscrivent en fait dans la lignée d'un travail commencé en 1991, pour la détection de PV par émission stimulée. L'expérience italienne est par contre à ses débuts: pour pouvoir sonder les propriétés du Fr, instable, il faut d'abord produire et rassembler un nombre suffisant d'atomes. La conception de montages PV qui ont démontré leur validité sur le césium constitue une solide base de départ pour le cas du francium.
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Kim, Soo Y. "Cold single atoms for cavity QED experiments." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26581.
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Thesis (Ph.D)--Physics, Georgia Institute of Technology, 2009.<br>Committee Chair: Chapman, Michael; Committee Member: Citrin, David; Committee Member: Kennedy, T. A. Brian; Committee Member: Kuzmich, Alexander; Committee Member: Raman, Chandra. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Halkyard, Paul Lee. "Dynamics in cold atomic gases : resonant behaviour of the quantum delta-kicked accelerator and Bose-Einstein condensates in ring traps." Thesis, Durham University, 2010. http://etheses.dur.ac.uk/529/.
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In this thesis, the dynamics of cold, trapped atomic gases are investigated, and the prospects for exploiting their nonlinear dynamics for inertial sensing are discussed. In the first part, the resonant and antiresonant dynamics of the atom-optical quantum delta-kicked accelerator with an initial symmetric momentum distribution are considered. The system is modelled as an ideal, non-interacting atomic gas, with a temperature-dependence governed by the width of the initial momentum distribution. The existence of resonant and antiresonant behaviour is established, and analytic expressions describing the dynamics of momentum moments of the time-evolved momentum distribution are derived. In particular, the momentum moment dynamics in both the resonant and antiresonant regimes depend strongly on the width of the initial momentum distribution. The resonant dynamics of all even-ordered momentum moments are shown to exhibit a power-law growth with an exponent given by the order of the moment in the zero-temperature regime, whereas for a broad, thermal initial momentum distribution the exponent is reduced by one. The cross-over in the intermediate regime is also examined, and a characteristic time is determined up to which the system exhibits dynamics associated with the zero-temperature regime. A similar analysis is made for the temperature-dependence of the antiresonant dynamics. This general behaviour is demonstrated explicitly by considering a Maxwell-Boltzmann and uniform momentum distribution, allowing exact expressions describing the dynamics of the second- and fourth-order momentum moments, and momentum cumulants, to be obtained. The relevance of these results to the potential of using this system in accurate determinations of the local gravitational acceleration is discussed. In the second part, the dynamics of one- and two-component Bose-Einstein Condensates prepared in a counter-rotating superposition of flows in a quasi-1D toroidal trap are studied. Particular attention is paid to the dynamical stability of the initial state in the presence of atom-atom interactions, included via a mean-field description within the Gross-Pitaevskii equation. A broad regime of dynamical stability using a two-component BEC is identified, in which a typical implementation using Rb-87 is predicted to lie. A proof-of-principle Sagnac atom-interferometer using a two-component Rb-87 BEC is then presented, and the accumulation of the Sagnac phase is shown to be possible via relative population measurement or, alternatively, through the continuous monitoring the precession of atomic density fringes. In contrast to conventional Sagnac interferometers, the accumulation of the Sagnac phase is independent of the enclosed area of the interferometer. The prospects of using this system for high-precision determinations of rotation is discussed.
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Bruce, Graham D. "Alternative techniques for the production and manipulation of ultracold atoms." Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/2617.
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This Thesis contains details of the construction and characterisation of a compact apparatus for the cooling of ultracold atoms to quantum degeneracy, and their manipulation in flexible holographic optical traps. We have designed and built two iterations of this apparatus. The first version consists of a stainless steel single-cell vacuum chamber, in which we confine ⁸⁷Rb and ⁶Li or ⁷Li in a Magneto-Optical Trap. We characterise the alternative methods of pulsed atomic dispenser and Light Induced Atomic Desorption (LIAD) to rapidly vary the background pressure in the vacuum chamber with the view to enabling efficient evaporative cooling in the single chamber, loading MOTs of up to 10⁸ atoms using pulsed dispensers. The LIAD is found to be ineffective in loading large MOTs in this setup, while the pulsed dispensers method gradually increases the background pressure in the chamber over time. Based on the results of this first iteration, we designed and built a second single-chamber apparatus for cooling of ⁸⁷Rb to quantum degeneracy. The LIAD technique was used to successfully load MOTs containing 8x10⁷ atoms in this single pyrex cell with a rapidly-varying background pressure. The lifetime of an atomic cloud loaded from the MOT into a magnetic trap increased by a factor of 6 when LIAD was used. The holographic optical traps for cold atoms are generated using a Spatial Light Modulator, and we present our novel method for improving the quality of holographic light patterns to the point where they are suitable for trapping ultracold atoms using a feedback algorithm. As demonstrations of this new capability, we show power-law optical traps which provide an efficient, reversible route to Bose-Einstein Condensation and a dynamic ring trap for the investigation of superfluidity in cold atoms.
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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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Clements, Ethan Robert. "CHARACTERIZATION OF OPTICAL LATTICES USING PUMP-PROBESPECTROSCOPY AND FLUORESCENCE IMAGING." Miami University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=miami1470323164.
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Walker, Graeme. "Trans-spectral transfer of orbital angular momentum and creation of an ultra high density cold atom trap." Thesis, University of Glasgow, 2013. http://theses.gla.ac.uk/4498/.
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In recent years there has been great interest in the applications of the interaction of the phase and intensity of laser light in atomic vapours. The generation of light beams with arbitrary phase and intensity patterns can now be easily achieved by using Spatial Light Modulators (SLMs). The transformation of quantized units of phase information to atomic vapours has implications in the fields of quantum optics for the realisation of sources of entangled photons, optical switching, and quantum information storage. Spatially shaped beams with non-trivial intensity geometries have found use in single atom quantum well traps and for the enhancement of density of standard Magneto Optical Traps. The work in this thesis is focussed around two main pro jects, involving the interaction of holographically shaped light beams with cold trapped atoms and with a hot atomic vapour respectively. An enhancement to the previously investigated technique of a SPontaneous force Optical Trap SPOT of 87 Rb is presented here which aims to solve various issues which naturally arise from compressing cold atoms in a Magneto Optical Trap (MOT) such as unavoidable heating during the compression. High density/high atom number traps are highly sought after in many experiments for more efficient transfer of atoms to Bose Einstein Condensates and for improved quantum storage capabilities in cold atom traps. The highest density achieved in our SPOT was 2.5 × 10^12 atoms cm−3 for 2 × 10^8 atoms at a temperature of approximately 100µK. This represents almost 2 orders of magnitude increase in density from the standard MOT setup with no adverse heating of the trap while maintaining 75% of the atoms. In the second part of this work hot atomic vapours are utilized for the efficient transfer of orbital angular momentum information from near infra-red pump fields, driving from 5S_1/2 to 5D_5/2 on a two-photon transition, to a cascade from 5D_5/2 to 6P_3/2 to 5S_1/2 generating 5230nm light and a coherent blue, 420nm, beam respecitively. This generation is performed using four wave mixing in 85 Rb. We observe the complete conversion of all input quantum information, the Orbital Angular Momentum (OAM) from the pump fields to the blue. In addition we show the additional phase coherence effects of this experiment through the use of simple superpositions of Laguerre-Gaussian (LG) modes showing that the process is indeed quantum in nature. A theoretical basis for the transfer of all OAM information to only the 420nm beam is also discussed here.
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Simoneau-Roy, Maxime. "Le riborégulateur thiB d'Escherichia coli : une régulation en trans?" Mémoire, Université de Sherbrooke, 2014. http://hdl.handle.net/11143/5377.
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La régulation de l’expression génétique est essentielle afin qu’un organisme puisse s’adapter aux changements environnementaux. Chez les bactéries, la régulation peut s’effectuer à plusieurs étapes de l’expression des gènes (transcription, stabilité de l’ARN, traduction, maturation et dégradation des protéines) et par des mécanismes impliquant différents types de molécules (ADN, ARN, protéines, métabolites ou ions inorganiques). Traditionnellement, les protéines se situaient au centre de ces mécanismes de régulation. On sait maintenant que certains ARN, dont les riborégulateurs, ont également un grand rôle à jouer dans ce processus. Un riborégulateur est un élément génétique retrouvé dans une région non-codante de certains ARN messagers (ARNm), qui peut lier directement un ligand spécifique afin de réguler l’expression de son transcrit. Chez Escherichia coli (E. coli), trois riborégulateurs lient la thiamine pyrophosphate (TPP). Un d’entre eux, le riborégulateur thiB, n’a toujours pas été étudié. On croit qu’il contrôlerait, au niveau de l’initiation de la traduction, l’expression de l’opéron thiBPQ encodant un transporteur ABC de la thiamine. De plus, un petit ARN nommé SroA a précédemment été identifié grâce à des techniques de séquençage d’ARN. SroA correspond à l’aptamère du riborégulateur thiB, mais aucun rôle ne lui a été attribué à ce jour.
Le présent mémoire porte sur la caractérisation du riborégulateur thiB d’E. coli. Dans un premier temps, nous avons démontré que le riborégulateur est fonctionnel. Le mécanisme permettant la régulation génétique en cis est cependant plus complexe que seulement la régulation prédite au niveau traductionnel. Dans un second temps, nous avons utilisé deux approches différentes à l’échelle transcriptomique afin de vérifier si SroA régule l’expression de certains ARNm en trans. Plusieurs cibles potentielles découlent de cette étude. Une caractérisation préliminaire de certaines d’entre elles est présentée ici et devra être poursuivie par des travaux subséquents. Les résultats présentés ici suggèrent que le riborégulateur thiB régulerait l’expression de l’opéron thiBPQ (en cis) et d’autres gènes en trans.
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Dinkelaker, Aline. "Smooth inductively coupled ring trap for cold atom optics." Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=19200.
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The main topic in this thesis is the proof-of-principle experiment for an inductively coupled magnetic ring trap for applications in atom interferometry and quantum gas investigations. Atom interferometry utilises the wave nature of atoms for precision measurements of gravitational and inertial effects and to test fundamental physics. Due to their symmetry, their periodic boundary conditions and their large enclosed areas, ring traps provide attractive geometries for atom interferometry. By tightening the trap and reducing the trap radius, toroidal traps also have excellent conditions to study super uid properties in degenerate gases. The trapping potential for the inductively coupled magnetic ring trap is formed by the superposition of an external AC eld and a local AC eld, created by the induced current in a copper ring. These fields cancel in a ring and create a time-averaged trapping potential. By inducing the current in the conductor and using AC over DC elds several problems of existing trapping mechanisms are addressed. We create a smooth, scalable trapping potential for cold atoms. We load the inductively coupled ring trap with ~ 10p6s laser cooled p87sRb atoms. The atoms can be observed evolving around the ring in the horizontal plane, until the ring is completely filllled. We record vacuum limited lifetimes of ~ 1:3s after initial Majorana losses. With an added o set eld we also gain exibility in the trap geometry regarding the radius (~5 mm) and the trap width (~0:5 mm). In a subsequent experiment, the setup and the ring trap parameters are changed to allow for the creation of p87sRb Bose-Einstein condensate and for the implementation of atom interferometry in the ring trap. A vertical, smaller ring trap with a radius of ~ 1:8 mm is created. Laser cooled atoms are loaded either at the top or at the bottom of the ring.
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Muckley, Eric S. "Constructing a magneto-optical trap for cold atom trapping /." Click here to view, 2009. http://digitalcommons.calpoly.edu/physsp/2.
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Thesis (B.S.)--California Polytechnic State University, 2009.<br>Project advisor: Katharina Gillen. Title from PDF title page; viewed on Jan. 14, 2010. Includes bibliographical references. Also available on microfiche.
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Van, Dongen Janelle. "Simultaneous cooling and trapping of 6Li and 85/87Rb." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/351.
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This thesis provides a summary of the laser system constructed in the Quantum Degenerate Gases Laboratory for laser cooling and trapping of 85/87Rband 6Li as well as of experiments that have been pursued in our lab to date. The first chapter provides an overview of the experimental focus of the QDG lab. The second and third chapters provide the fundamental theory behind laser cooling and trapping. The fourth chapter provides details of the laser system. The fifth chapter describes an experiment performed on the subject of dual-injection, performed in collaboration with Dr. James Booth of the British Columbia Institute of Technology (BCIT) involving the dual-injection of a single slave amplifier. The last chapter describes the progress made on the experimental setup needed for the study of Feshbach resonances between 85/87Rb and 6Li and the photoassociative formation of molecules.
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Pollum, Laura L. "Digital ion trap mass spectrometry for cold ion-molecule chemistry." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:18c6451d-d247-4384-9257-f8864e038343.
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A promising new approach for studying cold ion-molecule chemical reactions is the combination of laser- or sympathetically-cooled trapped ions and slow-moving molecules from a cold molecule source, such as a quadrupole velocity selector or a Stark decelerator. Previous reaction studies using trapped atomic ions and slow molecules from a quadrupole velocity selector were able to reach average collision energies as low as 1 K. However, the guided molecules had an approximately room temperature rotational energy distribution, so the reactions studied were not truly cold. Thus, a new molecular source for producing translationally and rotationally cold molecules utilizing buffer gas cooling and quadrupole velocity selection was constructed by K. Twyman and characterized for use in cold reaction studies. This new source of cold molecules is referred to as the buffer gas guide. A new ion trap has been designed and built for use with the existing buffer gas guide. The new ion trap apparatus is compact and mechanically compatible with this new guide. It uses a linear Paul ion trap with cylindrical electrodes to trap ions. Two optical axes (one axial and one radial) enable efficient cooling of small ion crystals. A field-free time-of-flight tube and ion detection assembly are also incorporated into the apparatus. A new technique for determining the mass and quantity of trapped ions has also been developed, termed digital ion trap mass spectrometry. The new technique uses a digital RF waveform to trap ions before ejecting the ions radially from the trap using an ejection pulse applied to the trap electrodes. The ions are then detected after free flight along a time-of-flight tube. This technique was characterized by ejecting crystals of various sizes and compositions: Ca<sup>+</sup> only, Ca<sup>+</sup>/CaF<sup> +</sup>, Ca<sup>+</sup>/CaOH<sup> +</sup>/CaOD<sup>+</sup>, and Ca<sup>+</sup>/NH<sup> +</sup><sub style='position: relative; left: -.6em;'>3</sub> /NH<sup> +</sup><sub style='position: relative; left: -.6em;'>4</sub> /H<sub>3</sub>O<sup>+</sup>. A linear relationship between the number of ions ejected (determined by comparing experimental and simulated crystal images) and the integral of the time-of-flight peak was observed for Ca<sup>+</sup> and Ca<sup>+</sup>/CaF<sup> +</sup>. All mass peaks were resolved. Simulations of the trapped ions and their trajectories through the time-of-flight tube were also performed, and excellent agreement between the simulated and experimental mass resolution was observed. Progress towards combining the buffer gas guide with the previously independent ion trap is also presented. It is anticipated that the combined buffer gas guide ion trap apparatus will enable the study of ion-molecule reactions at low temperatures with translationally and rotationally cold molecules. It is anticipated that the new digital ion trap mass spectrometry technique will simplify the study of reactions when multiple product ions whose masses are separated by only 1 AMU are formed. A new ion trap has been designed and built for use with the existing buffer gas guide. The new ion trap apparatus is compact and mechanically compatible with this new guide. It uses a linear Paul ion trap with cylindrical electrodes to trap ions. Two optical axes (one axial and one radial) enable efficient cooling of small ion crystals. A field-free time-of-flight tube and ion detection assembly are also incorporated into the apparatus. A new technique for determining the mass and quantity of trapped ions has also been developed, termed digital ion trap mass spectrometry. The new technique uses a digital RF waveform to trap ions before ejecting the ions radially from the trap using an ejection pulse applied to the trap electrodes. The ions are then detected after free flight along a time-of-flight tube. This technique was characterized by ejecting crystals of various sizes and compositions: Ca+ only, Ca+/CaF+, Ca+/CaOH+/CaOD+, and Ca+/NH+3/NH+4/H3O+. A linear relationship between the number of ions ejected (determined by comparing experimental and simulated crystal images) and the integral of the time-of-flight peak was observed for Ca+ and Ca+/CaF+. All mass peaks were resolved. Simulations of the trapped ions and their trajectories through the time-of-flight tube were also performed, and excellent agreement between the simulated and experimental mass resolution was observed. Progress towards combining the buffer gas guide with the previously independent ion trap is also presented. It is anticipated that the combined buffer gas guide ion trap apparatus will enable the study of ion-molecule reactions at low temperatures with translationally and rotationally cold molecules. It is anticipated that the new digital ion trap mass spectrometry technique will simplify the study of reactions when multiple product ions whose masses are separated by only 1 AMU are formed.
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Steer, Edward. "Development and characterisation of a cold molecule source and ion trap for studying cold ion-molecule chemistry." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:13c3a622-ba78-4a53-902c-666ec461f708.
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A novel apparatus, combining buffer-gas cooling, electrostatic velocity selection and ion trapping, has been constructed and characterised. This apparatus is designed to investigate cold ion-molecule chemistry in the laboratory, at a variable translational and internal (rotational) temperature. This improves on previous experiments with translationally cold but rotationally hot molecule sources. The ability to vary the rotational temperature of cold molecules will allow for the experimental investigation of post-Langevin capture theories.
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Sarshar, Zahra. "Hydrocarbon trap adsorbents for reducing cold-start emissions of automotive exhaust." Thesis, Université Laval, 2008. http://www.theses.ulaval.ca/2008/25807/25807.pdf.
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Shields, Brendan John. "Loading a planar RF Paul Trap from a cold Yb⁺ source." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36117.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.<br>Includes bibliographical references (p. 61-63).<br>In this thesis, we demonstrate a functioning planar radio frequency, three-rod Paul Trap, loaded with Yb+ ions that have been photoionized from a source of neutral atoms, which were cooled in a magneto-optical trap. Planar ion traps have only recently been successfully loaded[1], and never from a cold ion source. Additionally, ionizing directly from a MOT allows for isotope selection.<br>by Brendan John Shields.<br>S.B.
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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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Sheridan, Kevin Thomas. "Experimental techniques for cold chemistry and molecular spectroscopy in an ion trap." Thesis, University of Sussex, 2013. http://sro.sussex.ac.uk/id/eprint/47145/.
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A range of experimental techniques for application in reaction studies between ionic and neutral atoms/molecules and high resolution spectroscopy experiments with sympathetically cooled molecular ions are presented. A novel ion trap loading scheme using the photo-ionisation of atoms generated by the pulsed laser ablation of a solid calcium target has been characterised. We have identified the range of ablation laser fluences that must be used in order to produce a flux of neutral calcium atoms, which is a prerequisite for isotope selective ion trap loading. Calcium ions are trapped and laser cooled in a linear radio-frequency ion trap. We have developed a spectroscopy scheme that allows the entire fluorescence spectrum of trapped ions to be rapidly collected with high precision while maintaining a low ion temperature and good ion localisation throughout interrogation. The scheme has been demonstrated by measuring the saturation intensity of the calcium ion 4S1/2→4P1/2 transition. We have developed a novel scheme to measure the secular motion of trapped ions and demonstrated the application of the technique to ion-neutral collision reaction experiments. Employing pulsed excitation and Doppler velocimetry, we have measured the centre-of-mass mode frequency of single ions as well as large ion crystals with a frequency precision better than 2x10-3 within an interrogation time on the order of seconds. This method has been used to measure the mass of ions and observe charge exchange collisions between trapped calcium isotopes. In particular, we have measured the 44Ca++40Ca!40Ca++44Ca reaction cross section and demonstrated the single-event resolution of the technique. Finally, we have developed a novel all-optical broadband scheme for exciting, amplifying and measuring the secular motion of ions in the trap. Oscillation induced by optical excitation has been coherently amplified to control and measure the ion's secular motion. Requiring only a single interrogation laser, the ion's oscillation amplitude can be precisely controlled. The application of this technique to non-destructive spectroscopy of trapped molecular ions is discussed.
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Ladouceur, Keith. "Experimental advances toward a compact dual-species laser cooling apparatus." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/2508.
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This thesis describes the advances made towards a dual-species magneto-optical trap (MOT) of Li and Rb for use in photoassociation spectroscopy, Feshbach resonance studies, and, as long-term aspirations, the formation of ultracold heteronuclear polar molecules. The initial discussion will focus on a brief theoretical overview of laser cooling and trapping and the production of ultracold molecules from a cold atom source. Subsequently, details of the experimental system, including those pertaining to the required laser light, the vacuum chamber, and the computer control system will be presented. Finally, preliminary optimization and characterization measurements showing the performance of a single species Li MOT are introduced. These measurements demonstrated the loading of over 8 x 107 Li atoms directly into a MOT without the need for a Zeeman slower.
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Pynn, Ralph M. "The Newfoundland and Labrador cod trap fishery : the basis for a future cod grow out industry /." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ42432.pdf.
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Braga, Helena Carolina. "O operador de Wigner aplicado a colisões de mudança de estrutura fina entre átomos alcalinos no regime frio." Universidade de São Paulo, 2002. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-09042008-091650/.
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Neste trabalho abordamos os processos de perdas colisionais por mudança de estrutura fina e por escape radiativo. Estes processos são importantes por serem os principais fatores limitantes da densidade e da permanência de átomos confinados em armadilhas magneto-ópticas. A utilização do formalismo de Wigner nos possibilitou tratar a dinâmica dos graus de liberdade internos do sistema de forma puramente quântica, enquanto tratamos os graus de liberdade translacionais de maneira semiclássica. Com este formalismo deduzimos equações inéditas para uma colisão unidimensional e desenvolvemos um algoritmo, também inédito, para a resolução numérica de tais equações.<br>In this work we study the collision loss processes caused by fine-structure change and radiative escape. These processes are important because they limit the density and the confinement time of atoms in magneto-optical traps. The use of the Wigner-function formalism allows us to treat the internal degrees of freedom purely quantum mechanically, while treating the dynamics of the external degrees of freedom quasi-classically. This dissertation employs this formalism to derive for the first time, quasi-classical equations describing one-dimensional cold collisions, including dissipation due to spontaneous emission, and an algorithm, also for the first time, to solve numerically the mentioned set of coupled equations.
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Stoller, Gerlind. "Charakterisierung des Triggerfaktors - einer ribosomenassoziierten Peptidyl-Prolyl-cis-trans-Isomerase aus Escherichia coli." [S.l. : s.n.], 1998. http://deposit.ddb.de/cgi-bin/dokserv?idn=960869263.
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Hu, Zhen Kimble H. Jeff Kimble H. Jeff. "Quantum optics with cold atoms--nonlinear spectroscopy and road toward single-atom trap /." Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-10112007-092812.
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Binet, Emmanuelle. "Contrôle qualité des protéines er régulation par protéolyse et trans-traduction." Paris 11, 2001. http://www.theses.fr/2001PA112297.
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Dans tout le règne du vivant, la protéolyse intervient non seulement dans l'élimination des protéines défectueuses, mais aussi dans la régulation de nombreux processus essentiels à la cellule. Différentes stratégies existent pour permettre aux protéases de reconnaître spécifiquement leurs cibles. L'une d'entre elles est de marquer les polypeptides à éliminer avec des signaux spécifiques reconnus par les protéases. Chez les procaryotes, il existe un système, dit SsrA, qui permet de cibler des polypeptides issus d'une traduction défectueuse vers la protéolyse. Par un mécanisme d'action particulier, la trans-traduction, ce système marque les protéines co-traductionnellement avec un peptide étiquette, SsrA, reconnu spécifiquement par certaines protéases. L'acteur principal de la trans-traduction est un petit ARN stable, l'ARNtm, de nature et de fonction originales. Il est en effet composé de deux domaines fonctionnels qui lui confèrent à la fois une activité d'ARNt et une activité d'ARNm. Nous nous sommes intéressés à l'analyse des signaux induisant l'intervention du système SsrA chez Escherichia coli. Nous avons purifié et identifié des cibles endogènes du système. L'étude de ces cibles nous a permis de démontrer que le processus de trans-traduction est induit lorsqu'un ribosome est stoppé au niveau d'une séquence de terminaison de traduction inefficace. De telles séquences sont connues pour provoquer des événements de recodage, dont la trans-lecture. La trans-traduction permettrait d'éviter la synthèse de protéines anormales, potentiellement délétères, issues d'une déficience du processus de fin de traduction. Nous avons aussi recherché par mutagenèse des facteurs intervenant dans la dégradation des protéines marquées par l'étiquette SsrA. Nous avons montré que la protéase dépendante de l'énergie ClpXP est probablement le seul composant majeur impliqué dans la dégradation des protéines cytoplasmiques trans-traduites qui peut être complètement inactivé<br>Proteolysis is universally involved in degrading abnormal proteins and in regulating numerous processes including some that are essential for cells. Various strategies allow proteases to specifically identify their targets. One of these consists of tagging polypeptide targets with specific signals which are recognized by the proteases. Prokaryotes use the SsrA system that targets for proteolysis polypeptides that are synthesized after a misfunction of the translation process. Through a particular mechanism called trans-translation, this system tags proteins co-translationnally with a peptide, SsrA, recognized by specific proteases. The main character of trans-translation is a small and stable RNA named tmRNA. It is composed of two functional domains responsible for tRNA and mRNA activity. We focused on the signals involved in the recognition of SsrA's targets. We purified and identified endogenous targets of the system. Studying them, we could demonstrate that the trans-translation process is induced when ribosome's stop on top of a sequence that inefficiently signals the end of translation. This type of sequence provokes recoding events such as readthroughs. Trans-translation could prevent synthesis of potentially toxic abnormal proteins produced through an aberrant ending of translation. We also looked for proteins involved in degrading the polypeptides tagged by SsrA. Of the major component involved in degrading cytoplasmic trans-translated proteins, we have shown that the energy-dependent protease ClpXP is probably the only one that can be fully inactivated
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Prakash, Satya. "De novo engineering of trans-activating riboswitches in E. coli." Thesis, University of Warwick, 2018. http://wrap.warwick.ac.uk/114021/.
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RNA molecules play a major role in cellular processes such as replication, transcription, and translation. As a result, RNA-based engineering methods have emerged as important tools in biotechnology. However, the structure and function of RNA depends on global interactions, which often prevents the use of a modular design strategy, particularly with allosteric conformations. Using RNA secondary structure prediction tools, computational methods can successfully design RNA switches that work in E. coli. The overarching aim of my research is to develop synthetic RNA switches that could be used for regulation and sensing of molecules in living cells. We have engineered RNA based synthetic signal transduction cascade consisting of a single RNA molecule (regazyme, an RNA chimera of an aptazyme with a riboregulator) that upon sensing a ligand (theophylline) self cleaves and releases a riboregulating small RNA. This small RNA binds to a cis-repressed mRNA allowing translation of a reporter protein. This system can be adapted to be induced by other ligands and can be used as a biosensor. I have also integrated a riboregulated RNA switch into the E. coli genome to study its behaviour at single-cell level. This reduces the transcriptional and translational noise in data collection to inform more accurate computational design of RNA regulatory units. We used computational design to engineer higher-order RNA-triggered riboregulators organized as a hierarchical toehold activation cascade. This has been studied in a single cell as well as in a population of E. coli cells. These RNA riboregulators can be used for construction of new, complex and portable synthetic gene circuits. In addition, I have engineered sense and antisense riboregulators consisting of the small RNA reverse complement of a known riboregulator. This riboregulator can transcribe two small RNAs from the same DNA template depending on the direction of transcription. These two small RNAs independently trans-activate translation of their cognate target genes and both RNAs also silence each other by antisense interaction. We have also engineered an RNA-based tunable antiterminator, a TNA-derived adaptor that acts as a signal converter in a genetic circuit, converting a translation signal to a transcription signal (unpublished). I have engineered a minimum alphabet riboregulator that has only three nucleotides (GCU) that currently validating (unpublished). In order to explore the use of directed evolution for the engineering of RNA switches, I am developing an evolution-based system for generation and selection of new biomolecules. These evolved new biomolecules could be used in future medical applications such as molecular sensing. I have been using T7 and P2 bacteriophages as the basis for this evolutionary system. I have engineered the genome of the T7 phage with (regazyme, Riboswitch and riboregulators) using homologous recombination with marker-based selection. These engineered phages can be used to evolve new biomolecules such as other regazymes, riboswitches and riboregulators.
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Deb, Nabanita. "Towards cold state-selected ion-molecule reactions." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:1a3899d3-7476-49ac-8f4b-3c0e7a7e8680.
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In recent years there has been much progress in the field of cold and ultracold molecular physics and a variety of experimental techniques for producing cold matter now exist. In particular, the generation of trapped molecular ions at mK temperatures has been achieved by sympathetic-cooling with laser-cooled atomic ions. By implementing schemes to selectively prepare and control the internal quantum state of molecular ions, and developing detection techniques, it will be increasingly possible to study cold state-selected chemical collisions in an ion-trap. Most molecular species produced in a selected rovibrational state have a lifetime of a few seconds, before the population is redistributed across numerous rovibrational states by interaction with the ambient blackbody radiation (BBR). Consequently, the investigation of state-selected reaction dynamics at low temperatures in experiments where long time scales (minutes to hours) are required, is hindered. This thesis looks into developing strategies that maintain state selection in molecular ions, allowing one to observe state-selected reactions in cold environments, in particular the state-selected reaction between C<sub>2</sub>H<sup>+</sup><sub>2</sub> and ND<sub>3</sub>. Examining reactive ion molecule collisions under cold conditions provides insight into fundamental reaction dynamics, which are thermally averaged out at higher temperatures. A theoretical model is used to investigate laser-driven, blackbody-mediated, rotational cooling schemes for several <sup>1</sup>Σ and <sup>2</sup>Π diatomic species. The rotational cooling is particularly effective for DCl<sup>+</sup> and HCl<sup>+</sup>, for which 92% and >99% (respectively) of the population can be driven into the rovibrational ground state. For the other systems a broadband optical pumping source is found to enhance the population that can be accumulated in the rovibrational ground state by up to 29% more than that achieved when exciting a single transition. The influence of the rotational constant, dipole moments and electronic state of the diatomics on the achievable rotational cooling is also studied. This approach is extended to consider the BBR interaction and rotational cooling of a linear polyatomic ion, C<sub>2</sub>H<sup>+</sup><sub>2</sub>, which has a <sup>2</sup>Π electronic ground state. The (1-0) band of the ν<sub>5</sub> cis-bending mode is infrared active and strongly overlaps the 300 K blackbody spectrum. Hence the lifetimes of state-selected rotational levels are found to be short compared to the typical timescale of ion trapping experiments. Laser cooling schemes are proposed that could be experimentally viable, which involves simultaneous pumping of a set of closely spaced Q-branch transitions on the <sup>2</sup>Δ<sub>5/2</sub>-<sup>2</sup>Π<sub>3/2</sub> band together with two <sup>2</sup>Σ<sup>+</sup>– <sup>2</sup>Π<sub>1/2</sub> lines. It is shown that this should lead to >70% of total population in the lowest rotational level at 300 K and over 99% at 77 K. In order to identify states of the acetylene ion that could be trapped sufficiently long enough for state-selected reactions in the ion trap with decelerated ND3, the theoretical work has been complemented by experimental investigations into the production of C<sub>2</sub>H<sup>+</sup><sub>2</sub> in selected states, and ion trapping of the same using sinusoidal and digital trapping voltages. Appropriate (2+1) REMPI (Resonance Enhanced Multiphoton Ionization) schemes are used to produce C<sub>2</sub>H<sup>+</sup><sub>2</sub> in different quantum states, with (1+1) Resonance Enhanced Multiphoton Dissociation (REMPD) employed to detect the ion thus produced. The concept of digital ion trapping for ejection onto MCPs is introduced. A comprehensive comparison between sinusoidal and digital trapping fields has been performed with respect to trap depth and stability regions. Programs have been developed to calculate the stability regions for different ions under varying experimental conditions. The trap depth has been derived for both digital and sinusoidal trapping fields. It is observed that as τ increases, the trap depth of a digital trap increases. For τ = 0.293, the trap depth and stability diagram for both sinusoidal and digital trapping fields would be equivalent. The trap depth at which the sinusoidal trap operates experimentally in our research group is ~1.36 eV. In contrast, the experimental parameters at which the digital trap operates generates a trap depth of 1.21 eV. Ca<sup>+</sup> Coulomb crystals have been formed, stably trapped and stored for extended periods of time in both sinusoidally and digitally time-varying trapping fields. The sympathetic cooling of a diverse range of ions into Ca<sup>+</sup> Coulomb crystals is demonstrated, again using both sinusoidal and digital trapping fields. Mass spectrometric detection of ionic reaction products using a novel ejection scheme has been developed, where ejection is achieved by switching off the trapping voltage and converting the quadrupole trap into an extractor-repeller pair by providing the ion trap electrodes with appropriate ejection pulses. This technique is developed using a digital trapping voltage rather than the sinusoidal trapping voltage, as ejection with sinusoidal trapping voltages is not clean (resonance circuitry used in the electronics induces ringing after switching off the trapping voltage). Coulomb crystals, both pure Ca<sup>+</sup> and multi-component crystals, are ejected from the ion trap and the TOF trace obtained is recorded on an oscilloscope. When the integrated, base-line subtracted TOF peak is plotted against the number of ions in a Ca+ crystal and sympathetically-cooled Ca<sup>+</sup> – CaF<sup>+</sup> crystal, a linear relationship is obtained. This technique is found to be well mass-resolved, with the signal arising from CaOH<sup>+</sup> (57 amu) and CaOD<sup>+</sup> (58 amu) resolvable on the TOF trace. This technique would enable one to monitor a reaction in a Coulomb crystal where the reactant and product species are both either lighter or heavier than calcium, such as the reaction between C<sub>2</sub>H<sup>+</sup><sub>2</sub> and ND<sub>3</sub>, something which has not been previously possible. It is, also, potentially a very important technique for reactions with many product channels.
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Passagem, Henry Fernandes. "Fotoassociação de curto alcance em átomos de rubídio." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-11032016-111138/.
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Neste trabalho, estudamos a fotoassociação de átomos de rubídio no regime de curto alcance. Realizamos espectroscopia por perda de átomos em uma armadilha magneto-óptica de 85Rb usando um laser de fibra de alta potência, o qual possuia largura de linha da ordem de 1MHz e 50W de potência no intervalo de 1060nm a 1070nm. Dois níveis vibracionais do potencial excitado 0u+ foram observados (v=137 e v=138). Além disso, medimos o tempo de vida de uma armadilha óptica de dipolo cruzada. Como esperado, o tempo de vida é menor quando o laser está sintonizado na ressonância. Um modelo teórico prevê a distribuição dessas moléculas nos níveis vibracionais do estado eletrônico fundamental após o processo de fotoassociação. Os resultados, nos sugerem perspectivas para a produção de moléculas de Rb2 no estado vibracional fundamental.<br>In this work, we studied short-range photoassociation of rubidium atoms. We realize trap-loss spectroscopy in a magneto-optical trap of 85Rb using high power fiber laser, which had around 1MHz linewidth and 50W power at 1060nm to 1070nm interval. Two vibrational levels of the 0u+ excited potential were observed (v=137 e v=138). Besides that, we measured the lifetime of a crossed optical dipole trapped. As expected, the lifetime is shorter when the laser is tuned on resonance. A theoretical model predicts the molecular distribution in the vibrational levels of electronic ground state. The results suggest us perspectives to produce Rb2 molecules in the ground vibrational state.
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Menegatti, Carlos Renato. "Armadilha de dipolo para átomos e moléculas." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-29082011-104357/.
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Neste trabalho apresentamos a construção de um novo sistema experimental para aprisionamento de átomos e moléculas. Trata-se de uma armadilha de dipolo cruzada totalmente óptica, formada por um laser de fibra com 40 W de potência com comprimento de onda em 1064 nm. Nesse sistema foi demonstrado o aprisionamento de átomos Rb e K e moléculas Rb2. Realizamos dois experimentos distintos neste se novo sistema: No primeiro, estudamos a evolução temporal de amostras dos isótopos 85Rb e 87Rb na armadilha de dipolo cruzada. Pudemos medir pela primeira vez o processo de mudança de estrutura hiperfina em átomos sem a presença de luz ressonante, e observamos a fotoassociação dos átomos pelo laser da armadilha de dipolo. E no segundo, desenvolvemos uma técnica que permite o estudo rápido e direto do decaimento no número de moléculas de Rb2 na armadilha. Com essa técnica, observamos também o comportamento dessas moléculas na presença de átomos preparados em um determinado estado hiperfino do estado fundamental. Estes resultados juntamente com um desenvolvimento teórico, nos sugerem novas perspectivas rumo a produção de um sistema que possa produzir e aprisionar moléculas KRb no estado fundamental 1Σ+ (v = 0).<br>In this work, we present the construction of a new experimental system for trapping atoms and molecules. It is an all optical crossed dipole trap, formed by a fiber laser with 40 W of power at 1064 nm. In this system, we have trapped K and Rb atoms as well as Rb2 molecules. We have carried out two experiments in this new system. In the first, we studied the temporal evolution of atomic samples of different isotopes, 85Rb and 87Rb, in the crossed trap dipole. We were able to measure for the first time the hyperfine-changing collisions of atoms in the absence of resonant light, and we have observed photoassociation of atoms by the dipole trap laser beam. In the other experiment, we have developed a technique that allows us to study the trapped molecule population decay in the trap. It was also observed the molecule population decay in the presence of atoms prepared in a given hyperfine state of the ground state. These results together with a theoretical development may suggest us new perspectives towards the production of a system that can produce and trap KRb molecules in the ground state 1Σ+ (v = 0).
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Marangoni, Bruno Spolon. "Colisões heteronucleares em uma armadilha de dipolo." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-24042013-111126/.
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Neste trabalho, apresentamos uma montagem experimental capaz de aprisionar átomos de K e Rb simultaneamente em uma armadilha óptica de dipolo cruzada. Contudo, para atingir este feito foi necessário, durante o desenvolvimento do projeto, estudar cada espécie atômica de forma isolada. Assim, desenvolvemos uma técnica inédita para carregar uma armadilha de dipolo diretamente de uma armadilha magneto-óptica de 39K, constatando a importância da estrutura hiperfina do estado 4P3/2 no processo de carregamento. Também observamos e explicamos o processo de fotoassociação de Rb devido ao laser em 1071 nm, inclusive a diferença isotópica entre 85Rb e 87Rb. Na sequência, realizamos o carregamento duplo com K e Rb na armadilha e observamos a fotoassociação de KRb. Um modelo teórico simples prevê a distribuição dos níveis vibracionais obtidos. O mesmo modelo abre caminho para um possível bombeamento óptico para a produção e acúmulo de moléculas de KRb no estado X1Σ+ (v = 0).<br>In this paper, we present an experimental setup to simultaneously trap atoms of K and Rb in a crossed optical dipole trap. This accomplishment required the individual study of each atomic species during the project development. This allowed the development of a new technique for loading a dipole trap directly from a magneto-optical trap of 39K, providing evidence of the importance of the hyperfine structure of the state 4P3/2 in the loading process. We also observe and explain the photoassociation process of Rb2 due to the dipole trap laser at 1071 nm, including an isotopic difference between 85Rb and 87Rb. In the sequence, we performed dual species loading of K and Rb and observed the photoassociation process of KRb. A simple theoretical model predicts the final distribution of vibrational levels obtained. The same model provides a potential path to optically pump the molecules and accumulate them in the molecular ground state X1Σ+ (v = 0) for KRb.
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Kas, Milaim. "Cold chemistry of molecular anions: a theoretical investigation in the context of hybrid trap experiments." Doctoral thesis, Universite Libre de Bruxelles, 2018. https://dipot.ulb.ac.be/dspace/bitstream/2013/279061/4/main.pdf.
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Hybrid trap experiments are set-ups that allow to study the interaction between ions and atoms in cold controlled environment. In such context, molecular anions present specific theoretical and experimental interests and challenges. In this work, we have used extensive \textit{ab initio} methods to investigate several collisional anionic systems: (1) M + OH$^{-}$ (where M are alkali or alkaline earth atoms), (2) Rb and H + OH(H$_{2}$O)$_{n}^{-}$ (with $n=0,1,2,3,4$) and (3) Rb and Li + C$_{2}^{-}$. Several molecular properties such as vertical detachment energies or electroaffinities, optimized structures, harmonic frequencies, potential energy curves or surfaces, etc have been calculated using high level quantum chemistry approaches. The results have been used to make predictions on the related reactivity in low energy regime. We emphasis on electronic detachment processes by carefully analysing the difference between the neutral and anionic potential energy surface. The Rb + OH$^{-}$ system is currently under experimental investigation. Therefore, a detailed study of its reactivity is carried out in the present work. We have analysed the different reactive channels arising from both collision involving the ground state and first electronic excited state of Rb. Using our calculated potentials and a capture model based dynamics, we have extracted cross sections and rate constants. Comparison with other alkali and earth alkaline atoms are made. Hydrated hydroxide cluster anions are planned by the experimental group as upcoming studied systems. We present here our preliminary results on the possible outcome when considering collisions with Rb and we discuss their implications for hybrid trap experiments. We make comparison with H as a colliding partner and consider our results in the context of astrochemistry. Finally we propose the C$_{2}^{-}$ molecular anion as an alternative to OH$^{-}$. Its interaction and reactivity with Rb and Li are investigated and the results are used to motivate our suggestion. Furthermore, for the Rb+OH$^{-}$ and Rb+C$_{2}^{-}$ system, we have also investigated the effect of a non-thermal collision energy distribution on the rate constants. At last, in light of the discussions related to each topic, general conclusions on the use of molecular anions in hybrid trap experiments are drawn.<br>Doctorat en Sciences<br>info:eu-repo/semantics/nonPublished
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Souther, Nathan Jon. "Light Shift Measurements of Cold Rubidium Atoms using Raman Pump-Probe Spectroscopy." Miami University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=miami1250622906.
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Borodi, Gheorghe. "On the combination of a low energy hydrogen atom beam with a cold multipole ion trap." Doctoral thesis, Universitätsbibliothek Chemnitz, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200900932.
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Der erste Teil der Aktivitäten dieser Arbeit bestand in der Entwicklung einer modernen Ionenspeicher Apparatur zur Untersuchung chemischer Prozesse mit atomarem Wasserstoff. Die Integration eines differentiell gepumpten Radikalenstrahls in eine vorhandene temperaturvariable 22-Pol Speicherapparatur erforderte größere Änderungen an dieser. Da astrophysikalische Fragestellungen im Vordergrund standen, führt die Einleitung zunächst in das Gebiet der Astrophysik und -chemie ein. Die Grundlagen der Ionenspeicherung in temperaturvariablen Hf-Speichern sind ausführlich in der Literatur dokumentiert. Daher ist die Beschreibung der Apparatur (Kapitel 2) relativ kurz gehalten. Viel Mühe wurde in die Entwicklung einer intensiven und stabilen Quelle für Wasserstoffatome aufgewandt, deren kinetische Energie variiert werden kann. Das Kapitel 3 beschreibt dieses Modul in vielen Details, wobei der Einsatz von magnetischen Hexapolen zum Führen der Atome und die chemische Behandlung der Oberflächen zur Reduzierung der H-H Rekombination einen wesentlichen Platz einnimmt. Durch die außergewöhnliche Empfindlichkeit der Speichertechnik kann das neue Instrument zur Untersuchung von vielen Reaktionen eingesetzt werden, die von astrochemischer und fundamentaler Bedeutung sind. Die Ergebnisse dieser Arbeit sind im Kapitel 4 zusammengestellt, einige Reprints und Entwürfe von Publikationen findet man im Anhang. Die Reaktionen von CO2+ mit Wasserstoffatomen und -molekülen erwiesen sich als sehr geeignet, um in situ H and H2 Dichten über den gesamten Temperaturbereich der Apparatur zu bestimmen (10 K - 300 K). Zum ersten mal wurden Reaktionen von H- and D-Atomen mit den Kohlenwasserstoffionen CH+, CH2+, and CH4+ bei Temperaturen des interstellaren Raums untersucht. Ein sehr interessantes, noch nicht ganz verstandenes Stoßsystem ist die Wechselwirkung von protoniertem Methan mit H-Atomen. Im Ausblick der Arbeit werden einige Ideen aufgezeigt, wie man das Instrument verbessern kann, und es werden einige Reaktionen erwähnt, die man als nächste untersuchen könnte. Diese Dissertation ist einen Beitrag zum Projekt 5 der Forschergruppe Laboratory Astrophysics: Structure, Dynamics and Properties of Molecules and Grains in Space, die von der DFG im Zeitraum von 2000 bis 2006 unterstützt wurde<br>The first part of the activities of this thesis was to develop a sophisticated ion storage apparatus dedicated to study chemical processes with atomic hydrogen. The integration of a differentially pumped radical beam source into an existing temperature variable 22-pole trapping machine has required major modifications. Since astrophysical questions have been in the center of our interest, the introduction first gives a short overview of astrophysics and -chemistry. The basics of ion trapping in temperature variable rf traps is well-documented in the literature; therefore, the description of the basic instrument (Chapter 2) is kept rather short. Much effort has been put into the development of an intense and stable source for hydrogen atoms the kinetic energy of which can be changed. Chapter 3 describes this module in detail with emphasis on the integration of magnetic hexapoles for guiding the atoms and special treatments of the surfaces for reducing H-H recombination. Due to the unique sensitivity of the rf ion trapping technique, this instrument allows one to study a variety of reactions of astrochemical and fundamental interest. The results of this work are summarized in Chapter 4, some reprints and drafts are reproduced in the appendix. Reactions of CO2+ with hydrogen atoms and molecules have been established as calibration standard for in situ determination of H and H2 densities over the full temperature range of the apparatus (10 K - 300 K). For the first time, reactions of H- and D-atoms with the ionic hydrocarbons CH+, CH2+, and CH4+ have been studied at temperatures of interstellar space. A very interesting, not yet fully understood collision system is the interaction of protonated methane with H. The outlook presents some ideas, how to improve the new instrument and a few reaction systems are mentioned which may be studied next. This thesis is a contribution to the project 5 of the research unit Laboratory Astrophysics: Structure, Dynamics and Properties of Molecules and Grains in Space which has been supported by the DFG from 2000 to 2006
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Collier, Justine. "Déblocage de ribosomes et étiquetages de polypeptides par trans-traduction chez Escherichia coli." Paris 11, 2004. http://www.theses.fr/2004PA112047.
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L’ARNtm et SmpB permettent la libération des ribosomes lorsque la traduction est défectueuse. Les polypeptides dont la biosynthèse est bloquée sont en même temps étiquetés, ce qui induit leur élimination par des protéases. Ce mécanisme est nommé trans-traduction. SmpB et l’ARNtm sont ubiquitaires chez les eubactéries. Nous montrons que les SmpB de plusieurs espèces bactériennes peuvent étiqueter des polypeptides avec l’ARNtm d’E. Coli in vivo, ce qui illustre la conservation fonctionnelle du système de trans-traduction. Nous montrons aussi que la trans-traduction n’est pas affectée in vivo à des concentrations sublétales aminoglycosides néomycine B ou paromomycine. Elle améliore même la survie d’E. Coli en présence de ces antibiotiques et d’érythromycine, probablement en limitant l’accumulation de polypeptides anormaux et la séquestration des ribosomes. Par ailleurs, le gène codant pour l’ARNtm a été génétiquement modifié pour identifier des polypeptides préférentiellement étiquetés in vivo chez E. Coli. Nous montrons que des protéines complètes peuvent être étiquetées par l’ARNtm, si la terminaison de la traduction de leur messager est défectueuse. Enfin, nous montrons que le messager secM est trans-traduit, car il est clivé à un site de blocage traductionnel précédemment caractérisé. Nous proposons qu’il existe une activité endoribonucléasique encore inconnue, qui serait associée au ribosome et activée en réponse à un blocage traductionnel. Elle agirait en concertation avec la trans-traduction. Elle pourrait intervenir dans certaines voies de régulation cellulaire ou limiter certains évènements de recodage<br>TmRNA and SmpB can rescue ribosomes stalled on a messenger during translation. Nascent polypeptides are tagged, which induces their degradation by proteases. This mechanism is called trans-translation. First, we show that SmpB from multiple bacterial species can tag polypeptides in vivo, together with E. Coli tmRNA. This result illustrates the remarquable functionnal conservation of the trans-translation mechanism. Second, we show that trans-translation is not affected in vivo by sublethal concentrations of the aminoglycosides neomycin B and paromomycin. Moreover, trans-translation conferes a growth advantage in the presence of these antibiotics and erythromycin, probably by limiting accumulation of abnormal polypeptides and stalled ribosomes. Third, the gene encoding tmRNA was genetically modified, in order to identify polypeptides that are preferentially tagged in vivo by trans-translation in E. Coli. We show that complete proteins can also be tagged by tmRNA, if translation termination of their messengers is poorly efficient. Finally, we show that secM messenger is trans-translated, because it is cleaved at a site of ribosome pausing during translation elongation. We propose that their is an endonucleolytic activity associated with the ribosome, which is induced in response to ribosome stalling. In cooperation with trans-translation, it could participate in some regulation pathways or could limit some recoding events during translation
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Truppe, Stefan. "New physics with cold molecules : precise microwave spectroscopy of CH and the development of a microwave trap." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/18997.
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Cold polar molecules provide unique opportunities to test fundamental physics and chemistry. Their permanent electric dipole moments and rich internal structure arising from their vibrational and rotational motion, makes them sensitive probes for new physics. These features also make them ideal for studying ultracold chemistry, for simulating the behaviour of strongly interacting many-body quantum systems, and for quantum information science. This thesis describes a number of advances in cold molecule physics. The optimum method for producing an intense, pulsed, supersonic beam of cold CH molecules is investigated, resulting in a beam with 3.5x10^9 ground state CH molecules per steradian per shot. The beam has a translational temperature of 400 mK and a velocity that is tuneable between 400 and 1800 m/s. The lowest-lying Λ-doublet transitions of ground state CH, at 3.3 GHz and 0.7 GHz, are exceptionally sensitive to variations in the fine-structure constant α and the electron-to-proton mass ratio μ. Many modern theories predict that these constants may depend on time, position, or local matter density. Using a novel spectroscopic method, the frequencies of these microwave transitions are measured with accuracy down to 3 Hz. By comparing to radio-astronomical observations, the hypothesis that fundamental constants may differ between the high and low density environments of the Earth and the interstellar medium of the Milky Way is tested. These measurements find no variation and set upper limits of |Δα/α| < 2.1x10^-7 and |Δμ/μ| < 4.3x10^-7. The frequency of the lowest millimetre-wave transition of CH, near 533 GHz, is also measured with an accuracy of 0.6 kHz. The development of a novel type of trap for ground state polar molecules is presented. Trapping polar molecules is a necessary condition to cool them to ultracold temperatures of 1 μK and below. The trap uses a high intensity microwave field in a Fabry-Pérot resonator. Experimental and theoretical investigations are presented that explore the modes of the cavity, how to obtain the highest possible quality factor, and how to optimally couple the microwave power into the cavity. Finally, a cold supersonic beam of BH molecules is developed. This molecule appears to be particularly well-suited to direct laser cooling due to its favourable rotational structure and Franck-Condon factors. The laser cooling concept is described, and a first spectroscopic investigation of the relevant molecular structure is presented.
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Pereira, Andrea Antunes. "Estudo de colisões inelásticas heteronucleares no sistema rubídio(Rb)/césio(Cs) em regimes de baixas temperaturas." Universidade de São Paulo, 1999. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-09092008-123340/.
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Armadilhamento duplo de átomos neutros constitui um dos avanços mais recentes no estudo de colisões frias. Obtivemos experimentalmente as taxas de perda devido a interação de espécies alcalinas mistas (Cs/Rb). Utilizamos uma armadilha magneto-óptica mista operando com feixes de alta intensidade permitindo o resfriamento e confinamento das amostras com sucesso. Esse trabalho apresenta-se de forma relevante pois corresponde a primeira etapa para o estudo do processo de formação de moléculas frias heteronucleares. Uma comparação entre duas técnicas de monitoramento dos processos de carga de átomos foi realizada. Os resultados tanto qualitativamente como quantitativamente foram satisfatórios. Determinamos as taxas de perda, de interesse e analisamos essas taxas considerando a proporção entre as massas dos átomos envolvidos e enfocando o efeito causado pela diferença de massa entre eles concluindo assim o objetivo principal dessa dissertação.<br>Double trapping of neutral atoms is one of the most recent advances in the study of collisions cold. Experimentally obtained the rates of loss due to the interaction of species alkaline mixed (Cs / Rb). We use a magneto-optical trap mixed operating with beams of high intensity allowing the cooling and containment of the samples successfully. This work is so important because it represents the first step to study the process of formation of molecules heteronucleares cold. A comparison between two techniques of monitoring procedures for cargo of atoms was performed. The results both qualitatively and quantitatively were satisfactory. And the rates of loss of interest and analyze the rates considering the ratio between the masses of atoms involved and focusing on the effect caused by the difference of mass between them thus completing the main objective of this dissertation.
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Dong, Jiaxin. "Impact of dynamin II domains on the function of dynamin II in vesicle formation at the trans Golgi network." [S.l.] : [s.n.], 2001. http://www.diss.fu-berlin.de/2001/72/index.html.
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Lytle, Christian, and Christian Lytle. "Spectroscopy of Neutral Mercury in a Magneto-Optical Trap Based on a Novel Ytterbium Fiber-Amplified Cooling Laser Source." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/621471.
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In this dissertation I present experimental results obtained on the mercury optical clock project in the research group of Jason Jones at the University of Arizona. The project began in 2008 with the purpose of investigating the feasibility of neutral mercury as an optical clock species. The first series of investigations involved building the essential apparatus and scanning the doppler-broadened 6¹S₀ - 6³P₀ clock transition in ¹⁹⁹Hg. Here I present significant modifications to the cooling and trapping laser, improvements to the spectroscopy laser linewidth, and attempts to measure the 2-photon transition in ¹⁹⁹Hg. After previously demonstrating spectroscopy of the mercury clock transition using an optically-pumped semiconductor laser for the cooling and trapping source (OPSL), we replaced the OPSL with a a fiber-amplified ECLD system. We custom built a fiber amplifier to provide gain at 1015 nm, demonstrating the system can yield up to 5 W of signal power with excellent suppression of the ASE power. We find that the ASE is well suppressed by using a two-stage configuration and short sections of gain fiber. The linewidth of our original spectroscopy laser was over 10 kHz, which is unsuitable to resolve of sub-Doppler features. To enhance the performance of our spectroscopy system, we integrated faster feedback bandwidth using AOMs, and incorporated derivative gain into the system. This resulted in a feedback bandwidth for our spectroscopy laser of over 200 kHz. With this system, we demonstrate anactively stabilized linewidth of 525 Hz for our spectroscopy system. Using the upgraded cooling and spectroscopy laser systems, we demonstrate spectroscopy of the clock system and confirm temperature measurements derived from the transition linewidth. We also describe attempts to detect the recoil shift and 2-photon transition in neutral mercury.
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SARKISSIAN, MARC. "Resultats fonctionnels des anastomoses colo-anales : a propos de 125 resections abdomino-trans-sphincteriennes pour cancer du rectum." Toulouse 3, 1990. http://www.theses.fr/1990TOU31523.
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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.<br>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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Milori, Debora Marcondes Bastos Pereira. "Caracterização de uma armadilha magneto-optica para átomos de sódio em célula de vapor." Universidade de São Paulo, 1994. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-30042009-090336/.
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Dentro as técnicas de controle do movimento atômico utilizando pressão de radiação, aprisionamento tem merecido maior destaque por produzir amostras de átomos mais frios (temperaturas da ordem de μK), com altas densidades e confinadas em pequenas regiões do espaço. Devido a essas motivações, tem sido grande o esforço para desenvolver e caracterizar estas armadilhas atômicas. Uma das mais eficientes armadilhas de átomos neutros construídas até agora é a armadilha magneto-óptica. O átomo uma vez capturado por este tipo de armadilha passa por um intenso processo de desaceleração via efeito Doppler e acaba por ficar confinado no poço de potencial gerado pela interação com o campo magnético. O número e a densidade de átomos aprisionados, o tamanho da nuvem e o processo de carga possuem forte dependência com os parâmetros da armadilha, tais como: Este trabalho trata da caracterização de uma armadilha deste tipo para átomos de sódio através de um estudo sistemático para descobrir as condições de sua melhor performance. Paralelamente a este estudo, desenvolvemos modelos teóricos para entender em detalhe os processos de produção dessas nuvens de átomos aprisionados e as forças envolvidas neste tipo de material que é esse gás super resfriado.<br>Among the various atomic motion control techniques using radiation pressure magneto-optic trapping has been looked at with great enthusiasm because it produces samples of cold atoms (temperatures about μK), with high densities and confined in small regions of space. Due to these motivations the efforts for developing and characterizing these atoms traps has been high. Once the atom is captured by the magneto-optic trap, it goes through an intense process of desacceleration via Doppler Effect and ends up confined in the potential well genered by the interaction with the magnetically Field. The number and the density of the trapped atoms, the size of the cloud and the loading process are strongly related to trap parameters, such as: magnetic Field gradient, laser beam intensity and background vapor temperature. This work deals with the characterization of a trap of this kind for sodium atoms through a systematic study, in order to discover the conditions for a better performance. At the same time theoretical models are developed in order to understand in depth the atomic forces involved in the production of a new kind of material which is this highly refrigerated gas.
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Salas, Andres David Rodriguez. "Geração de uma armadilha magneto-óptica de estrôncio 88." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-05112012-155605/.
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Neste trabalho é apresentada a construção da montagem de um sistema experimental para resfriar átomos de estrôncio. A construção do sistema está focada no estudo do espalhamento coletivo em nuvens atômicas frias e ultrafrias por meio da teoria de Mie. O estrôncio é um elemento que conta com dois estágios de resfriamento, o primeiro utilizando a transição forte entre estados singletos ¹S₀-¹P ₁ de Γ = (2 π)32 MHz, e o segundo com uma transição fraca entre estados singleto e tripleto ¹S₀-³P₁ de Γ = (2 π)7,5 MHz. O objetivo deste trabalho é a construção do sistema para resfriar átomos de estrôncio utilizando a primeira transição. A construção do sistema se apresenta em várias partes, primeiro a construção do um forno como fonte de vapor de estrôncio, onde o estrôncio metálico é aquecido até uma temperatura T = 600°C. O forno conta com um sistema de microtubos encarregados de colimar o feixe atômico, estes microtubos tem um diâmetro interno D ≈ 180µm e um comprimento de 8mm. Depois da implementação do forno e do sistema de microtubos foi medido o perfil de velocidades transversais e a divergência do feixe atômico que sai do forno. A largura tem um valor wr = (2π)108 MHze a divergência do feixe de α ≈4,12. A segunda parte do sistema conta com a construção do desacelerador Zeeman, responsável por desacelerar os átomos do feixe atômico utilizando um feixe laser contrapropagante de λ=461 nm, circularmente polarizado e com uma dessintonização utilizada, após a caracterização do sistema, de Δ=(-2π)580MHz. Os átomos sentiram os efeitos da força de pressão radiativa dentro de um tubo de comprimento de 0,28m. Para compensar o efeito Doppler causado pelo movimento dos átomos foi utilizado um arranjo de bobinas em configuração spin flip para gerar o campo. A terceira e principal parte do sistema foi a construção da armadilha magnetoóptica (AMO). Onde os átomos que saem do desacelerador Zeeman são confinados e resfriados pela combinação de seis feixes contrapropagantes, dos quais três são retrorefletidos utilizando a transição Γ=(2π)32MHz. A dessintonia dos feixes após da caracterização do sistema foi de Δ=(-2π)39MHz. Depois da construção do sistema foi feita a primeira caracterição da armadilha magneto-óptica de átomos de estrôncio 88 em nosso grupo, onde obtivemos a temperatura dos átomos na armadilha para o eixo vertical da expansão foi de Tv=4.7mK e para o eixo horizontal de TH=4mK. Também foi medido o tempo de carga dos átomos na armadilha tcarga=0.15s como bombeamento óptico de estado ³P₂-³D₂. O tempo de vida foi de 0.3s e 0.03s com e sem bombeamento óptico, respectivamente.<br>This work presents the construction of the assembly of an experimental system for cooling strontium atoms. The construction of the system is focused on the collective scattering in atomic cold cloud and ultra cold using the Mie theory. The strontium is an element that permits two stage of cooling, the first using the strong transition between singlet states ¹S₀-¹P₁ of Γ=(2π) 32 MHz, and a second stages is the weak transition between singlet and triplet states ¹S₀-³P₁ de Γ=(2π) 7.5MHz. The objective of this work is building the system for cooling strontium atoms using the first transition. The construction of the system is presented in several parts. First is described the construction of oven as vapor source strontium, where the strontium metal is heated to Temperature Range T = 600°C. The oven has a microtubule system responsible for collimating the atomic beam, these microtubules has an internal diameter of D ≈ 180µm and a length of 8mm. After implementation of the oven system and the microtubes were measured transverse velocity profile and the divergence of the atomic beam that leaves the oven, the width value was f wr=(2π)108MHzand beam divergence value was α ≈ 4,12. The second part of the system relies on the construction of the Zeeman slower responsible for decelerating the atoms of the atomic beam using a laser beam antipropagating of λ = 461 nm nm with a circularly polarized , the detuning used after of the characterization of the system was Δ = (2π)580 MHz. Atoms felt the effects of pressure force radiative within a tube length of 0.28m to compensate the Doppler shift due to motion a of atoms used an arrangement of coils in configuration \"spin flip\" to generate the magnetic field to compensate this effect. The third and main part of the system was the construction of magneto-optical trap (MOT), the atoms coming out of the Zeeman decelerator are confined and cooled by a combination of six counterpropagating beams, three of which are retro reflected using the transition Γ = (2π)32MHz, the detuning of the beam after the characterization of the system was Δ = (-2π) 39 MHz and the opposite polarization for each pair of beam in the same direction. After the construction of the system was made the first magneto-optical trap of strontium atoms 88, the temperature of the trap was atoms to the vertical he expansion was Tv = 4.7mK and the horizontal axis TH = 4 mK 4, also was measured loading time of the atoms in the trap tcharge = 0.15s as optical pumping state ³P₂- ³D₂. The lifetime with and without optical pumping was tlife = 0.3s and tlife = 0.03s respectively.
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Fritsch, Amilson Rogelso. "Montagem e caracterização de uma armadilha magneto-óptica de rubídio." Universidade do Estado de Santa Catarina, 2011. http://tede.udesc.br/handle/handle/2008.
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Previous issue date: 2011-07-20<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>In this work we present the building and characterization of a Magneto-Optical Trap (from now on named MOT) for Rubidium atoms. We perform experiments for studying the e¤ect of a broadband light over trapped atoms. In order to carry out this study we used a incandescent lamp which is broad in the wavelength spectrum. We observed in a MOT, with a number of 109 trapped atoms, that the broadband light increases the emitted .uorescence by the cloud of atoms. This could indicate an e¤ective enlargement in the trap e¢ciency. However, we cannot distinguish, based on our experiments, if this di¤erence is due to an increasing in the number of the trapped atoms or if it is just scattered light caused by the increasing in the intensity of the incident light over the
cloud. Thus, we did an analysis in the answer of the laser beam versus the variation in the intensity of lasers used for trapping. In a second step, we perform this study but with a lower number of trapped atoms, 108 atoms, and we verify that the heating of the lamps implies in the increasing of the loss of atoms in the trap, diminishing the number of trapped atoms. Hence, this lead us to make a study on the collisions dynamics that are in the trap, in order to understand the in.uence of the temperature on the trap e¢ciency. We observe that a small uniform increasing in the chamber temperature would lead to a great loss in the trap , but the increasing in the temperature caused by the lamps is a local increasing and generates a degassing of the chamber, increasing the quantity of the background vapour.<br>Neste trabalho apresentamos a construção e caracterização de uma armadilha magneto-óptica, a qual utilizamos para aprisionamento de átomos de Rb. Após a construção da armadilha e sua caracterização, fizemos experimentos para estudar os efeitos da luz de banda larga sobre os átomos aprisionados. Para esse estudo, utilizamos lâmpadas incandescentes que possuem um espectro largo de comprimentos de onda. Verificamos que em uma armadilha com 109 átomos aprisionados, a luz de banda larga aumenta a fluorescência emitida pela nuvem de átomos, tendo fortes indícios que isto representa efetivamente um aumento na eficiência da armadilha. No entanto, com os experimentos que fizemos, não podemos distinguir se essa diferença é referente a um aumento de átomos aprisionados ou apenas espalhamento de luz causado pelo aumento da intensidade de luz incidida sobre a nuvem. Fizemos então uma comparação da resposta dos átomos, frente a variações na intensidade dos feixes de laser utilizados para o aprisionamento. Por motivos que serão discutidos neste trabalho, refizemos esse estudo com um número menor de átomos aprisionados, 108 átomos, e verificamos que o aquecimento das lâmpadas reflete no aumento das perdas na armadilha, diminuindo então o número de átomos aprisionados. Isto nos levou a fazer um estudo sobre a dinâmica das colisões presentes na armadilha, para entendermos a influência da temperatura na eficiência da armadilha. Verificamos que um pequeno aumento uniforme na temperatura da câmara levaria a grandes perdas na armadilha, mas o aumento da temperatura causado pelas lâmpadas é um aumento local, e gera um processo de desgaseificação da câmara, aumentando a quantidade de átomos, "diferentes de Rb", presentes no vapor de fundo.
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Garcia, Ferrer Irene. "Structural and functional studies on Escherichia coli alpha-2-macroglobulin: a snap- trap peptidase inhibitor." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/346636.
Full textAbstract:
The balance between proteolytic and antiproteolytic activity is crucial in many biological processes such as nutrition, immune defence, virulence and tissue remodelling. Therefore, it is controlled by several mechanisms, among which by peptidic peptidase inhibitors that are encoded in the genomes of many organisms, representing up to 1% of genes in metazoa but being scarce and sketchy in bacteria. However, among bacterial peptidase inhibitors, some proteins with homology to the highly abundant metazoan a2-macroglobulins (a2Ms) have been described, which may have been acquired by bacteria from metazoa by horizontal gene transfer. Although a 2Ms have been extensively characterised in metazoa, where they play important roles in innate immunity, the biological role, mechanism of action and molecular structure of bacterial a2Ms (ba2Ms) remained largely unknown.
In this thesis, the characterisation of the Escherichia coli a2M, ECAM, was undertaken in order to elucidate its role in the bacterial cell. The results unveiled a novel mechanism of peptidase inhibition, called the snap-trap mechanism, that is probably shared by other monomeric a2Ms, both from bacteria and metazoa. In this, attacking endopeptidases cleave the native inhibitor in an accessible bait region, thus causing a major conformational rearrangement and producing induced species that covalently traps peptidases through a highly reactive thioester bond. The rearrangement, involving most of the 13 domains of ECAM, but also key structural elements of the mechanism, were described by producing the first atomic models of ECAM in both conformations, by using X-ray crystallography and cryo-electron microscopy. Through a covalent trap, ECAM prevents peptidases from cleaving large substrates, such as components of the bacterial cell wall, thus protecting E. coli cells against potentially damaging proteolytic activity. Therefore, it seems that ECAM participates in defence mechanisms in bacteria that thrive in the presence of peptidases, for which this thesis provides the first experimental evidence by in vivo functional assays.
In summary, through a multifaceted approach that combined structural, biochemical and functional characterisation, this thesis yielded a mechanistic model for ECAM, significantly enriching our understanding of ba2Ms and providing new insights into bacterial defence mechanisms.<br>La regulació de l'activitat proteolítica és crucial per al bon funcionament dels organismes, ja que afecta processos biològics com la nutrició, la defensa immunològica, la virulència de determinats microorganismes o la remodelació de teixits. Per això, en el genoma de pràcticament tots els éssers vius s'hi troben gens que codifiquen per inhibidors de peptidases que permeten el control dels enzims proteolítcs mitjançant la reducció de la seva activitat. Els inhibidors de peptidases són molt abundants en el genoma dels animals, on poden arribar a representar fins a un 1% dels gens, però la seva presència en bacteris és limitada. Malgrat això, alguns bacteris necessiten sobreviure en ambients rics en peptidases, com per exemple l'intestí humà, i per tant els inhibidors de peptidases son importants mecanismes de defensa en aquests microorganismes.
Entre els inhibidors de peptidases codificats en els genomes bacterians, se n'han trobat que presenten homologia amb les a2 -macroglobulines (a2Ms) de metazoa, proteïnes altament abundants que participen, entre altres, en la immunitat innata dels animals. Tot i que s'ha postulat que les a2Ms bacterianes provenen de la transferència gènica horitzontal de gens de metazoa, la funció biològica, el mecanisme d'acció i l'estructura molecular d'aquestes proteïnes s'ha mantingut desconeguda.
En aquesta tesi s'ha caracteritzat la a2M bacteriana de Escherichia coli, anomenada ECAM, per tal de definir la seva funció en la cèl•lula bacteriana. Els resultats obtinguts han permès descriure un nou mecanisme d'inhibició de peptidases, el qual s'ha anomenat mecanisme "snap-trap". En aquest, les peptidases que aconsegueixen accedir al periplasma de E. coli tallen la forma nativa d'ECAM en una regió anomenada esquer (bait region). Això causa un canvi conformacional i produeix la forma activada de la proteïna, la qual pot unir covalentment la peptidasa a través d'un enllaç tioèster molt reactiu. Aquest canvi conformacional i els elements estructurals implicats en el mecanisme d'acció d'ECAM s'han pogut descriure mitjançant l'obtenció de models atòmics de la proteïna en les dues conformacions, tant per cristal•lografia de raigs X com per criomicroscòpia electrònica. Un cop atrapades, les peptidases romanen inhibides i no poden tallar substrats d' alts pesos mol•leculars com podrien ser els components proteics de la paret bacteriana, explicant així la funció protectora que ECAM exerceix en la cèl•lula bacteriana i que ha sigut demostrada experimentalment per primer cop en aquesta tesi.
En resum, a través de la combinació d'estudis estructurals, bioquímics i funcionals, s'ha obtingut un model del mecanisme d'acció d'ECAM a la cèl•lula bacteriana. Així, es contribueix a enriquir el coneixement sobre les a2Ms bacterianes i s'aporta informació sobre els mecanismes de defensa que presenten determinats bacteris.
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Silva, Ilde Guedes da. "Estruturas espaciais de átomos de Na em armadilha magneto-óptica." Universidade de São Paulo, 1994. http://www.teses.usp.br/teses/disponiveis/54/54131/tde-21022014-101849/.
Full textAbstract:
Neste trabalho demonstramos o confinamento de átomos de sódio usando a armadilha magneto-óptica, onde os átomos foram capturados diretamente a partir da distribuição inicial do vapor atômico a uma temperatura ambiente, contido em uma célula fechada. Observamos além da nuvem de átomos aprisionados, estruturas circulares em forma de anek, que surgem devido ao desalinhamento introduzido nos feixes de aprisionamento. Estudamos o comportamento do raio do anel em função de vários parâmetros utilizados na armadilha magneto-óptica como por exemplo: gradiente de campo magnético, intensidade do laser, dessintonia e desalinhamento. Os experimentos foram realizados no regime de baixa densidade (N<10s) onde o raio do anel é independente do número de átomos aprisionados. Assim, os resultados obtidos podem ser explicados utilizando um modelo simples que leva em conta a força de vórtice dependente da coordenada radial (ou macroscópica) e as forças usuais presentes na armadilha magneto-óptica<br>In this work we demonstrate the confinement of neutral sodium atoms using the magneto-optical trap, where the atoms were captured directly from the low velocity tail of the room-temperature atomic vapor contained in the closed vacuum cell. We observed besides the cloud shaped, circular structures like a ring of trapped atoms that apeears when we introduce a misalignment among the trapping beams. We studied the behavior of ring radius with respect to several trapping parameters as: magnetic-field gradient, laser intensity, detuning, and misalignment. The experiments were performed in the low density regime (N<10s), so the ring radius is independent of the number of trapped atoms. Hence, the results obtained can be explained using a simple model that takes into account a radial coordinate dependent (or macroscopic) vortex force and the usual magneto-optical trap forces