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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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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 C2H+2 and ND3. 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 1Σ and 2Π diatomic species. The rotational cooling is particularly effective for DCl+ and HCl+, 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, C2H+2, which has a 2Π electronic ground state. The (1-0) band of the ν5 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 2Δ5/2-2Π3/2 band together with two 2Σ+– 2Π1/2 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 C2H+2 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 C2H+2 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+ 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+ 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+ 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+ – CaF+ crystal, a linear relationship is obtained. This technique is found to be well mass-resolved, with the signal arising from CaOH+ (57 amu) and CaOD+ (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 C2H+2 and ND3, 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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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+ 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. 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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Oldham, James Martin. "Combination of a cold ion and cold molecular source." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:ef33adcb-609a-4329-b4d8-aca8a1c48661.
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This thesis describes the combination of two sources of cold atomic or molecular species which can be used to study a wide range of ion-molecule reactions. The challenges in forming these species and in determining the fate of reactive events are explored throughout. Reactions occur in a volume within a radio-frequency ion trap, in which ions have previously been cooled to sub-Kelvin temperatures. Ions are laser-cooled, with migration of ions slowed sufficiently to form a quasi-crystalline spheroidal structure, deemed a Coulomb crystal. Fluorescence emitted as a consequence of laser-cooling is detected; the subsequent fluorescence profiles are used to determine the number of ions in the crystal and, in combination with complementary simulations, the temperature of these ions. Motion imparted by trapping fields can be substantial and simulations are required to accurately determine collision energies. A beam of decelerated molecules is aimed at this stationary ion target. An ammonia seeded molecular beam enters a Stark decelerator, based on the original design of Meijer and co-workers. The decelerator uses time-varying electric fields to remove kinetic energy from the molecules, which exit at speeds down to 35 m/s. A fast-opening shutter and focussing elements are subsequently used to maximise the decelerated flux in the reaction volume while minimising undecelerated molecule transmission. Substantial fluxes of decelerated ammonia are obtained with narrow velocity distributions to provide a suitable source of reactant molecules. Combination of these two techniques permits studies of reactions between atomic ions and decelerated molecules that can be entirely state-specific. Changes in the Coulomb crystal fluorescence profile denote changes in the ion identities, the rate of these changes can be used to obtain rate constants. Determination of rate constants is even possible despite the fact that neither reactant nor product ions are directly observed. This work has studied reactions between sympathetically cooled Xe+ ions and guided ND3 and has obtained data consistent with prior studies. Determination of reactive events is complicated if ion identities can change without affecting the fluorescence profile, or if multiple reaction channels are possible. A range of spectroscopic techniques are discussed and considered in regards to determining rate constants and product identities. Pulsed axial excitation of trapped ions can follow rapid changes in average ion weights and subtle changes for small crystals. Time-of-flight mass spectrometry is also demonstrated using the trapping electrodes and is suitable for discrimination of ions formed within the trap.
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Hanna, Thomas Mark. "Dynamics of Feshbach molecule production." Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:676c8932-9c30-4776-a264-67405fe61c0c.
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The variation of a magnetic field in the vicinity of a zero-energy resonance allows highly vibrationally excited molecules (‘Feshbach molecules’) to be produced from an ultracold atomic gas. In this thesis, we study the dynamics of this process. We begin by studying the dissociation of Feshbach molecules, showing that in the limit of a sudden jump the shape of the spectrum of dissociated atoms can act as a probe of the zero-energy resonance. For some resonances, such jumps are within reach of current experiments. We also study the intermediate region between sudden jumps and asymptotically wide, linear ramps. It is shown from a precise derivation how the latter limit leads to a universal spectrum with a shape independent of the implementation of the two-body physics, provided that the near-resonant scattering properties are correctly modelled. We then turn to the dynamics of Feshbach molecule production from thermal and condensed gases. Our microscopic quantum dynamics approach includes the exact twobody evolution as an input to the many-body calculations. We show that in the long-time limit, and the Markov limit for the interactions, the non-Markovian Boltzmann equation (NMBE) we derive for the one-body density matrix reduces to the normal Boltzmann equation. In the limit of short times and small depletion of the atomic gas, the molecule production efficiency can be calculated by thermally averaging the two-body transition probability density. This thermal averaging technique is applied to studies of the formation of Feshbach molecules using a magnetic field modulation that is near-resonant with the molecular bound state energy. The continuum is shown to have a significant effect on both the dynamics and efficiency of this process. We examine the dependence of the molecule production efficiency on the duration, amplitude and frequency of the modulation, as well as the temperature and density of the gas. This method of producing molecules is effective for a wide range of bound state energies, but requires sufficient variation of the two-body energy levels with magnetic field. Lastly, we implement the NMBE for the case of a fast linear ramp across a Feshbach resonance. The solution of this equation is made feasible by including a large part of the required computation in the kernel, which is calculated in advance. The NMBE allows predictions of the molecule production efficiency which go beyond the thermal averaging technique by accounting for the depletion and rethermalisation of the continuum. In the limit of small depletions, the two approaches give the same results. As the depletion increases, the two approaches differ due to many-body effects limiting the maximum possible molecule production efficiency. We have observed this in our simulations by considering higher-density gases. We have therefore shown the suitability and practicability of this beyond mean-field approach for application to further problems in the production of Feshbach molecules from ultracold gases.
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Gingell, Alexander David. "Applications of Coulomb crystals in cold chemistry." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:3b93832d-b9eb-49e1-b4a4-1bb43d7c9c00.
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This thesis describes the study of a range of ion-molecule reactions at very low collision energies using a newly developed experimental technique which involves the reaction of velocity-selected beams of translationally cold neutral molecules with very low kinetic energy ion ensembles. These studies have been enabled by the construction of a new apparatus for trapping and laser-cooling gas phase atomic ions (40Ca⁺). The laser-cooling process results in the formation of ordered, low kinetic energy, lattice-like ion structures, also known as "Coulomb crystals". The properties of single and multicomponent Coulomb crystals (which may also involve molecular ions), and their manipulation via modulation of the applied fields, are explored experimentally and with the use of molecular dynamics simulations. Variations in the laser-cooling parameters are shown to result in different steady-state populations of the electronic states of 40Ca⁺ involved with the laser cooling cycle, and these are modelled within an appropriate theoretical framework. The imaging of 40Ca⁺ fluorescence as a function of time allows the study of various ion-molecule reactions at collision energies around 300 K, with single ion sensitivity. These reaction studies are extended to low-temperature (collision energies close to 1 K), by combination of the ion trap apparatus with a bent quadrupole guide velocity-selector. Ion-molecule collision energies are shown to be variable over a short range through a change in the quadrupole guide voltage, or the ion trapping parameters; the effect of these modulations on the rate constant is explored for Ca⁺ + CH₃F. Bimolecular rate constants for the reactions of 40Ca⁺ with CH₃F, CH₂F₂ and CH₃Cl have been determined for a range of 40Ca⁺ state populations, allowing resolution of the global rate contributions from the ground and combined excited states. These results are analysed in the context of capture theories and ab initio electronic structure calculations. In each case, suppression of the ground state rate constant is explained by the presence of either a submerged or real barrier on the ground state potential surface. Rates of reaction from the combined excited states are generally found to be in line with capture theories, and in some cases variation is found between the high and low collision energy regimes. Molecular product ions generated in these experiments have been shown to be sympathetically-cooled into the crystal structure, and subsequently identified through resonance-excitation mass spectrometry. Molecular ions were also produced by multiphoton laser ionisation of a thermal background gas of OCS molecules. An ion-molecule reaction involving a molecular ion, that of charge transfer between OCS⁺ and ND₃, has been studied at a collision energy near 1 K for the first time using sympathetically-cooled OCS⁺ and velocity-selected ND₃. These experiments illustrate the generality of the techniques described herein, and should lead to many possibilities for future studies.
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Twyman, Kathryn S. "Electrostatic extraction of buffer-gas-cooled beams for studying ion-molecule chemistry at low temperatures." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:583d8060-5570-401d-a8f8-ef5751cfebbb.
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This thesis describes the design, construction, operation, and characterisation of an experimental apparatus that produces a source of internally cold, slow molecules that can be used for studying ion-molecule reactions at low temperatures. The apparatus combines buffer-gas cooling with a bent quadrupole velocity selector to cool both the translational and rotational degrees of freedom of the molecules. A cold cell (6 K) is filled with a buffer gas, such as helium, that exhibits sufficiently high vapour pressure for cryogenic applications. Hot molecules (150 to 300 K) enter the cell and thermalise with the buffer gas through collisions. Molecules are subsequently loaded into an electrostatic quadrupole guide, which acts as a velocity filter; only translationally cold polar molecules are guided around the bend. Using a buffer-gas-cooled source of molecules for electrostatic velocity selection, rather than a 300 K effusive source, yields a rotationally cold sample, with J ≤ 3. This rotational selectivity will enable the dependence of reaction cross sections on the reactant rotational state to be examined. Mass spectrometry is used to characterise cold molecular beams of ND3 and CH3F, while (2+1) REMPI spectra are recorded for the ammonia isotopologues. The peak velocity of guided ND3 is 75.86(0.70) ms-1 for standard conditions in a 6 K helium buffer gas cell (1.0 sccm ND3 flow rate, 0.6 mbar helium inlet pressure, ± 5 kV voltage). This corresponds to a peak kinetic energy of 6.92(0.13) K. (2+1) REMPI spectroscopy of the B1E''(v2'=5) ← X(1) transition enabled the rotational state distribution of guided ammonia molecules to be established. PGOPHER simulations of the experimental spectra suggest a rotational temperature of 10 K for ND3 molecules (from a 6 K helium buffer gas cell). The extent of translational and rotational cooling can be controlled by varying the molecular and buffer gas densities within the cell, by changing the temperature of the buffer gas cell (we can operate at 6 K or 17 K), or by changing the buffer gas. The translational temperature of guided ND3 is similar in a 6 K helium and 17 K neon buffer gas cell (peak kinetic energies of 6.92(0.13) K and 5.90(0.01) K, respectively) because the heavier neon gas has a slightly lower thermal velocity at 17 K than helium does at 6 K. Despite similar translational temperatures, the rotational temperature of guided ND3 is lower for molecules exiting the 6 K helium cell compared to the 17 K neon buffer gas cell (10 K and 15 K, respectively). The 6 K helium and 17 K neon buffer gas cells provide an excellent opportunity to investigate the effect of rotational cooling on branching ratios and reaction rates in low temperature ion-molecule reactions. The buffer gas cell and velocity guide described in this work will be combined with a linear Paul ion trap, to facilitate the study of cold ion-molecule reactions.
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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.Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Hartl, Hugo M. "Modification of small-molecule organic thin films using energetic beams and plasma." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/129526/9/Hugo%20Hartl%20Thesis.pdf.
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This project investigated directed energy techniques for modifying organic films. These techniques show great promise for creating materials with unique, tailored properties. In this work, ion and electron beams were used to fabricate spatially-defined polymer features in nanometre-scale film of small molecules. An alternative pathway to the direct on-surface fabrication of polymer surface coatings was also investigated and showed that a room temperature, atmospheric pressure plasma can facilitate coupling of small molecules at a catalytic surface. In all cases, it was possible to control the optical properties, chemistry, solubility and hardness of the polymer films by varying the processing parameters.
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Newell, Catherine A. "INELASTIC COLLISIONS IN COLD DIPOLAR GASES." UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_diss/30.
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Inelastic collisions between dipolar molecules, assumed to be trapped in a static electric field at cold (> 10−3K) temperatures, are investigated and compared with elastic collisions. For molecules with a Λ-doublet energy-level structure, a dipole moment arises because of the existence of two nearly degenerate states of opposite parity, and the collision of two such dipoles can be solved entirely analytically in the energy range of interest. Cross sections and rate constants are found to satisfy simple, universal formulas. In contrast, for molecules in a Σ electronic ground state, the static electric field induces a dipole moment in one of three rotational sublevels. Collisions between two rotor dipoles are calculated numerically; the results scale simply with molecule mass, rotational constant, dipole moment, and field strength.
It might be expected that any particles interacting only under the influence of the dipole-dipole interaction would show similar behavior; however, the most important and general result of this research is that at cold temperatures inelastic rate constants and cross sections for dipoles depend strongly upon the internal structure of the molecules. The most prominent difference between the Λ-doublet and rotor molecules is variation of the inelastic cross section with applied field strength. For Λ-doublet dipoles, cross sections decrease with increasing field strength. For rotor dipoles, cross sections increase proportionally with the square of field strength. Furthermore, the rate constants of the two types of molecules depend very differently on the angular orientations of the dipoles in the electric field.
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Zhao, Yongkai. "Cold atoms and molecules." Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2688.
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The ability to cool and trap atoms has revolutionized atomic and ultra-cold physics. Molecular physics is currently undergoing a similar transformation. This thesis aims to research a general cooling method that will be applicable to wide range of molecular and atomic species and other particles. We studied the dynamics of molecules in optical fields, focusing in particular on exploring the molecular self-organisation phenomena in optical cavities to cool molecular ensembles to sub-mK temperatures. Firstly, the general model of cavity cooling from atoms to molecules and the dynamics of a particle in a single cavity mode were discussed. We extended the existing cooling scheme for two-level atoms to an ensemble of multi-level molecules. Then we studied the spatial dynamics of molecules in the new parameter conditions, focusing in particular on exploring the molecular self-organisation phenomena in optical cavities to cool molecular ensembles to sub-mK temperatures. The scheme complements well with our present experimental work on the deceleration and focusing of cold molecules and can extend our present capability to simultaneously cool and trap a large cold molecular ensemble. For simulation of a large ensemble of molecules, we proposed a new statistical model based on the Boltzmann equation beside the traditional discrete model and studied two solution methods. The comparison of the theory and numerical simulations between discrete model and statistical model showed a good agreement, which validated this new model. We then explored the scaling laws with a view to the self-organization and cooling of a large ensemble of species. We studied the cooling of a CN molecular cloud of the density 1013/cm3, with an initial temperature at 10 mK in an optical cavity. We found that more than a third of the molecules are stably trapped by the intracavity field and the final temperature is below 1mK. We discussed the scaling laws in the case when a large ensemble of species is involved. Finally we argue that cavity cooling using a far off-resonant laser source can be a general cooling method that is applicable to any particles and studied the probability and conditions.
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Saleh, H. J. "Laser experiments with cold molecules." Thesis, University of Sussex, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358892.
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Alyabyshev, Sergey. "Dynamics of cold molecules in electromagnetic fields." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/43364.
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The research field of cold and ultracold atoms and molecules is rapidly growing and expanding into different areas of research such as quantum information science and condensed matter physics. The success of this field is due to the possibility of precisely controlling and manipulating atoms and molecules at low temperatures. The progress in this field relies on the development of new methods for controlling collisional dynamics and interactions of particles with electromagnetic fields. This Thesis describes research on modification of the collisional dynamics of ultracold atoms and molecules by external laser and microwave fields as well as new methods
for the detection of weak electromagnetic fields.
First, we study the scattering of atoms and molecules confined in a 2D geometry by optical lattices. In particular we develop a theory for scattering in 2D and derive the equations for the threshold dependence of the collision cross sections. We show that inelastic processes and chemical reactions can be suppressed under strong confinement in one dimension and can be controlled by varying the orientation of the external field with respect to the plane of confinement.
Next, we present a rigorous theory of low-temperature molecular collisions
in the presence of a microwave field. The microwave field can theoretically be
used to trap and control polar molecules. The molecular collisions may lead to trap loss and decoherence. We develop a rigorous quantum theory for molecular scattering in the presence of microwave fields. We study inelastic, spin-changing molecular collisions and Feshbach resonances in the presence of microwave fields. We demonstrate that inelastic collisions accompanied by absorption of microwave photons can be significant.
The detection of weak electromagnetic fields is very important for various applications ranging from fundamental measurements to biomagnetic imaging, and for tests of microwave chips. We present a method for the detection of weak electromagnetic fields in a wide range of frequencies from sub-kHz to THz with ultracold polar molecules. We show that using ultracold molecules one can achieve the sensitivity of two orders of magnitude larger than with a similar method based on ultracold Rb atoms.
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Pikovski, Alexander [Verfasser]. "Cold polar molecules in bilayers / Alexander Pikovski." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2012. http://d-nb.info/1025734750/34.
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Wall, Thomas Edward. "Guiding and decelerating cold, heavy, polar molecules." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.523753.
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Vyskocil, Eric. "Generation of cold pulsed molecular beams." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/7920.
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Methods for understanding and generating pulsed beams of translationally cold molecules through electrostatic velocity filtering are reported. Pulsed beams of acetonitrile (CH₃CN) and calcium monofluoride (⁴⁰Ca¹⁹F) in particular are theoretically examined and experimentally obtained. CH₃CN gas molecules are obtained from the vapour pressure above liquid CH₃CN and introduced to the electrostatic guide through a pulsed nozzle. The observed time of flight indicates a longitudinal velocity of 31 m/s and temperature of 2.37 K. ⁴⁰Ca¹⁹F molecules are obtained through laser ablation off a CaF₂ disk and cooled via buffer gas cooling by a cold pulsed Helium beam prior to being introduced into the electrostatic guide. Longitudinal velocities of 4.47 m/s and temperatures of 70.9 mK are obtained. While results for CH₃CN are within theoretical expectations, results for ⁴⁰Ca¹⁹F are not in agreement with theoretical predictions, indicating either a lack of understanding of the process or a limitation in the current experimental design. Nonetheless, the current experimental apparatus may be used, with minor adjustments to perform depletion spectroscopy on these molecules as well as may be used to generate pulsed beams of other molecules such as barium monofluoride (¹³⁸Ba¹⁹F), which may be used in the determination of the electron's electric dipole moment.
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Hudson, Eric R. "Experiments on cold molecules produced via Stark deceleration." Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3219210.
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Friedman, Melissa E. "Pulse shaping for broadband photoassociation of cold molecules." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:18d49cc2-9146-4ff8-b3b3-9e045bff039c.
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The development of the field of the science of ultra-cold matter has opened some exciting possibilities in exploring the quantum-mechanical processes which dominate matter interactions at the sub-microscopic scale. Although methods of cooling atoms are well established, molecular cooling is made difficult by molecules’ additional vibrational and rotational degrees of freedom. It was the goal of the research in this work to approach molecular cooling indirectly, by using broadband shaped-pulse photoassociation for the generation of tightly bound ultracold Rb2 molecules. The experiments towards this goal conducted by our group included a pumpdecay experiment to observe the generation of ground state singlet or triplet molecules. However, attempts to observe an increase in ground state population have been unsuccessful. A pump-probe study of wavepacket dynamics in the 5s+5p electronic state was conducted in order to determine the appropriate timing for the application of an additional pulse to dump population into the ground state. Although the attempt to observe wavepacket oscillations has been unsuccessful, pump-probe studies have yielded the observation of loosely bound excited state molecules as a result of the photoassociation pulse. These results are promising as a first stage in a fully coherent pump-dump approach to stabilisation into the lowest vibrational ground state. This thesis will provide an introduction and overview to the concerns involved in addressing the problem of molecular cooling and generation. Experimental techniques will be discussed including pulsed laser systems, optical parametric amplifi- cation, and the presentation of an original design for pulse shaping with an acoustooptic modulator. The emphasis of these discussions will be on the principles and operating procedures required for the use of these devices as home-built systems. The thesis will conclude with the results of pump-probe experiments utilising the pulse shaper as a spectral cutting device.
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Sarkozy, Laszlo C. "A Source of Translationally Cold Molecular Beams." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1218484224.
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Sarria, Ignacio. "Molecular mechanisms and regulation of cold sensing." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1331842901.
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Cvitaš, Marko Tomislav. "Interactions and collisions of cold molecules : lithium + lithium dimer." Thesis, Durham University, 2004. http://etheses.dur.ac.uk/3667/.
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There is at present great interest in the properties of ultracold molecules. Molecules are created in traps in excited rovibrational states and any vibrational relaxation results in the trap loss. This thesis provides a theoretical study of interactions and collisions in the spin-polarized lithium -b lithium dimer system at ultralow energies. Potential energy surface of the electronic quartet ground state of lithium trimer is generated ab initio using the CCSD(T) method and represented by an IMLS/Shepard fit. Long-range nonadditive interactions are modelled using a symmetric global form with coefficients taken from a fit to the atom-molecule dispersion coefficients. The surface allows barrierless atom-exchange reactions. It has a global minimum of ≈ 4000 cm(^-1) at equilateral geometries with r(_e) = 3.1 Å. The nonadditive interactions are very strong near equilibrium. They increase the well depth by a factor of 4 and reduce the interatomic distance by ≈ 1 Å. Another surface of À symmetry in C(_s) meets the ground state surface at linear geometries at short range. Part of the seam, near D(_ooh) geometries, is in an energetically accessible region for cold collisions. Inside the seam, the lowest À surface correlates with (^4)II rather than (^4)Σ state. Inelastic and reactive collisions are investigated using a quantum mechanical coupled channel method in hyperspherical coordinates. Bosonic and fermionic systems in the spin-stretched states are considered. The inelastic rate coefficients from the rovibrationally excited states of dimer at ultralow collision energies are large, often above 10-(^-10) cm(^3)s(^-1) The elastic cross sections are ≈ 3 orders of magnitude lower at 1 nK. Atom-molecule mixtures, at the densities found in Bose-Einstein condensates of alkali metal atoms that were recently produced, would last only a fraction of a second. Classical Langevin model describes semi-quantitatively the energy dependence of inelastic cross sections above ≈ 50 mK. No systematic differences between the bosonic and fermionic systems were found. Sensitivity of the results on potential was investigated. Reactions in isotopic mixtures of lithium may be exothermic even from the molecular ground state. The reactive rate coefficients are 1 - 2 orders of magnitude smaller than those in systems involving an initially vibrationally excited dimer.
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Bulleid, Nicholas Edward. "Slow, cold beams of polar molecules for precision measurements." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/18078.
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This thesis reports on the use of buffer gas cooling to produce slow and intense molecular beams, with the aim of creating a source of molecules that can be used to measure the electron electric dipole moment. A beam of Yb is extracted from a buffer gas cell by entrainment in a flow of helium. The beam is characterised and simulations are performed of the helium flow through the cell to better understand the effect this has on the beam characteristics. The velocity of the beam is found to vary between 65 m/s[superscript -1] and 204 m/s[superscript -1] depending on the helium flow through the cell, in agreement with the predictions of the simulations. The temperature of the beam is 2.4 K and the minimum divergence is 12°. The percentage of Yb that is extracted from the cell is ~10%. Sources which use a pulsed valve to produce a supersonic jet are also characterised at cryogenic temperatures. The addition of a thermalisation cell is found to produce beams that are slower, colder and more intense. The peak beam intensity is 4.5×10[superscript 10] molecules per seradian per pulse, the velocity (206 ± 5) m/s and the translational temperature is (12.3 ± 0.5) K. An electric decelerator is used to decelerate a pulse of YbF molecules from 300 m/s[superscript -1] to 276 m/s[superscript -1] by confining them to a travelling trap. Simulations of the molecules in the decelerator show that its acceptance is greater than those demonstrated previously. A detailed understanding of this deceleration is developed. The Franck-Condon factors for the A[superscript 2]Π[subscript 1/2] (v = 0) − X[superscript 2]Σ[superscript +] (v - 0, 1, 2) transition of YbF are measured. The results show that, using three lasers, the molecule could be laser-cooled.
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Wynar, Roahn Helden. "Ultra-cold molecules in an atomic Bose-Einstein condensate /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004403.
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Drayna, Garrett Korda. "Novel Applications of Buffer-Gas Cooling to Cold Atoms, Diatomic Molecules, and Large Molecules." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:26718757.
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Cold gases of atoms and molecules provide a system for the exploration of a diverse set of physical phenomena. For example, cold gasses of magnetically and electrically polar atoms and molecules are ideal systems for quantum simulation and quantum computation experiments, and cold gasses of large polar molecules allow for novel spectroscopic techniques. Buffer-gas cooling is a robust and widely applicable method for cooling atoms and molecules to temperatures of approximately 1 Kelvin. In this thesis, I present novel applications of buffer-gas cooling to obtaining gases of trapped, ultracold atoms and diatomic molecules, as well as the study of the cooling of large organic molecules. In the first experiment of this thesis, a buffer-gas beam source of atoms is used to directly load a magneto-optical trap. Due to the versatility of the buffer-gas beam source, we obtain trapped, sub-milliKelvin gases of four different lanthanide species using the same experimental apparatus. In the second experiment of this thesis, a buffer-gas beam is used as the initial stage of an experiment to directly laser cool and magneto-optically trap the diatomic molecule CaF. In the third experiment of this thesis, buffer-gas cooling is used to study the cooling of the conformational state of large organic molecules. We directly observe conformational relaxation of gas-phase 1,2-propanediol due to cold collisions with helium gas. Lastly, I present preliminary results on a variety of novel applications of buffer-gas cooling, such as mixture analysis, separation of chiral mixtures, the measurement of parity-violation in chiral molecules, and the cooling and spectroscopy of highly unstable reaction intermediates.Chemical Physics
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Croft, James Francis Edward. "Cold molecular collisions : efficient methods for quantum calculations." Thesis, Durham University, 2012. http://etheses.dur.ac.uk/5903/.
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Multichannel Quantum Defect Theory (MQDT) is shown to be capable of producing quantitatively accurate results for low-energy atom-molecule scattering calculations. With a suitable choice of reference potential and short-range matching distance, it is possible to define a matrix that encapsulates the short-range collision dynamics. Multichannel quantum defect theory can provide an efficient alternative to full coupled-channel calculations for low-energy molecular collisions. However, the efficiency relies on interpolation of the Y matrix that encapsulates the short-range dynamics. It is shown how the phases of the MQDT reference functions may be chosen so as to remove such poles from the vicinity of a reference energy and dramatically increase the range of interpolation. For the test cases of Mg+NH and Li+NH, the resulting optimized Y matrix may be interpolated smoothly over an energy range of several Kelvin and a magnetic field range of over 1000G. Calculations at additional energies and fields can then be performed at a computational cost that is proportional to the number of channels N and not to N cubed. MQDT thus provides a promising method for carrying out low-energy molecular scattering calculations on systems where full exploration of the energy and the field dependence is currently impractical.
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Atherton, Kathryn Mary. "Molecular and physiological analysis of plant cold acclimation." Thesis, University of Newcastle Upon Tyne, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360270.
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Doherty, William Gerard. "Cold atom production via the photo dissociation of small molecules." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:523f87e0-3f19-4382-941c-74b06023b767.
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This thesis describes the development of a relatively novel technique for the gen- eration and subsequent trapping of cold species. Molecules in a pulsed supersonic expansion are photolysed, such that the centre-of-mass velocity vector of one of the fragments is equal in magnitude but opposed in orientation to the lab-frame velocity of the precursor molecule. This technique, known as ‘Photostop’, leaves a fraction of the fragments with a narrow velocity distribution, centered around zero velocity in the lab-frame. They can be shown to have zero velocity by changing the time between photodissociation and ionisation; fragments with a high kinetic energy will leave the ionisation volume prior to interrogation. The underlying velocity distribu- tion is uncovered by using the velocity-map imaging technique, and the temperature of the fragments can be determined. The method was originally optimised for the molecular case. Cold NO has been produced from the dissociation of NO₂ molecules, and a single rotational state has been shown to remain in the ionisation volume 10 μs after dissociation, implying a sample temperature of 1.17 K. Using the optimised experimental conditions de- rived from the velocity cancellation of NO, the atomic case is demonstrated for the dissociation of Br₂ to give zero-velocity Br fragments. The Br atoms are seen for delay times in excess of 100 μs, showing the greater applicability of the method to the atomic case. The temperature of the residual atoms is shown to be in the milliKelvin regime, as determined through detailed Monte Carlo simulation of the motion of the stopped atoms. The possibility of trapping the ultracold Br atoms in a magnetic field is explored, and a quadrupolar trap created between two per- manent bar magnets is demonstrated to confine the atoms spatially, within the ion extraction optics, for delays in excess of 1 ms. The Photostop technique is intended to be a stepping stone on the way to widening the number of chemical species available for study in the ultracold regime. The possibility of improvements to the experiment is considered, in order to increase the efficiency of the experiment such that the number density becomes high enough to be viable as a source of atoms for use in cold chemical reactive studies. The possibility of extending the method so as to be used as a tunable velocity source of atoms is also discussed.
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Goddard, Nicola Jill. "A molecular study of the low temperature inducible barley gene, blt101." Thesis, University of Newcastle Upon Tyne, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384828.
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Reinhed, Peter. "Ions in cold electrostatic storage devices." Doctoral thesis, Stockholm : Department of physics, Stockholm University, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-32659.
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Diss. (sammanfattning) Stockholm : Stockholms universitet, 2010.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Härtill 4 uppsatser.
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Maslau, Siarhei. "Formation of the small molecule metabolism of Escherichia coli." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613391.
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Anderson, Tomas. "Scattering of thermal energy atoms and molecules from cold copper surfaces /." Göteborg : Göteborg university, 2001. http://catalogue.bnf.fr/ark:/12148/cb40192699j.
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Trachy, Marc Lawrence. "Photoassociative ionization in cold rubidium." Diss., Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/695.
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Lee, Byeong-ha. "Gene expression under cold stress in Arabidopsis." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/290038.
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Microarray analysis and mutational approaches were used to investigate regulation of freezing tolerance in plants. Using Arabidopsis, cold-responsive gene expression profiling was performed with Affymetrix GeneChip. Arabidopsis seedlings were cold-treated at 0°C for 0, 3, 6, and 24 hrs. A total of 681 cold-responsive genes were identified. Comparison of the expression profile of cold-responsive genes in the wild type to that of ice1, a mutant defective in cold stress signaling, showed altered transcript levels for many cold-responsive genes in the ice1 mutant even under non-stress conditions, which may explain its altered sensitivity to cold stress. To dissect the regulatory mechanism of cold-responsive gene expression, Arabidopsis plants expressing the luciferase gene driven by stress-responsive promoters were mutated and screened for altered luminescence. fro1 (frostbite 1),fro2 (frostbite 2), and stab1 (stabilized 1) were characterized and the genes responsible for the mutant phenotypes were identified. fro1 showed a lower expression of the stress-responsive RD29A promoter-driven luciferase transgene and endogenous RD29A gene under cold than the wild type. FRO1 encodes a component of complex I in the mitochondrial electron transport chain. These results suggested that cold-inducible gene expression is modulated by the functional status of mitochondria. fro2 was identified from Arabidopsis expressing the CBF3 promoter driven-luciferase transgene, because of its lower luminescence induction under cold. fro2 also showed lower expression of endogenous CBF genes under cold. FRO2 encodes a serine decarboxylase that converts serine to ethanolamine. This result indicated the importance of serine metabolism in CBF gene regulation. stab1 showed higher expression of RD29A promoter-controlled luciferase after stress, but the level of endogenous RD29A transcript was not different from that of the wild type after stress. Nuclear run-on assays suggested that this discrepancy was due to the enhanced stability of the luciferase mRNA. STAB1 encodes a splicing factor similar to the human U5 snRNP-associated 102-kDa protein. stab1 displayed hypersensitivity to cold and altered sensitivity to various stress. These results suggested that STAB1 is required for not only splicing but also the turnover of unstable transcripts and that it has an important role in plant tolerance to abiotic stresses, particularly cold.
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Michaud, Michael R. "Molecular physiology of insect low temperature stress responses." The Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=osu1172184329.
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Lee, Hojoung. "Plant cold acclimation and the characterization of hos1, hos2 and los2 mutants that are sensitive to cold stress." Diss., The University of Arizona, 2002. http://hdl.handle.net/10150/280029.
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The goal of my research was to better understand the mechanism of plant cold acclimation using Arabidopsis thaliana as a model system. Our genetic screening method utilizes a line of transgenic Arabidopsi plants harboring the firefly luciferase reporter gene (LUC) fused to the RD29A promoter (RD29A-LUC), which contains the cold- and osmotic stress-responsive DRE/ CRT element and the ABA-responsive ABRE element (Ishitani et al., 1997). The RD29A-LUC plants were mutagenized with ethylmethane sulfonate and mutants with aberrant luminescence responses were selected from the resulting M2 population by luminescence imaging using a cooled CCD camera (Ishitani et al., 1997). hos2-1 (for high expression of osmotically responsive genes) mutant was isolated based on enhanced expression of RD29A and other stress genes under low temperature treatment (Chapter 2). Enhanced gene expression was observed only in response to cold stress, not to osmotic stress or ABA, in hos2 mutants. Compared with the wild-type plants, the hos2-1 mutant plants are less capable of developing freezing tolerance when treated with low non-freezing temperatures, indicating that HOS2 is a negative regulator of low temperature signal transduction important for plant cold acclimation. Chapter 3 characterized the function of the HOS1 gene that was found to encode a novel protein with a RING (Really Interesting New Gene) finger motif near the amino terminus. The observation that hos1 plants are more sensitive to freezing temperatures even though they have enhanced expression of CBF transcription factors and of their downstream cold responsive genes suggests that controlling the stability of critical proteins in the cell is important in the cellular response to environmental stimuli. In contrast to hos1 and hos2 mutants, the los2 mutant was identified by its reduced expression of the RD29A-LUC transgene under cold treatment but not ABA, salt or PEG treatments (Chapter 4). LOS2 is critical for chilling as well as freezing resistance. The los2 mutation specifically impairs cold regulated expression of the endogenous COR/KIN/RD/LTI genes. The LOS2 gene encodes an enzyme, enolase, which converts 2-phosphoglycerate to phosphoenolpyruvate in the glycolytic pathway. Several lines of the evidence for possible LOS2 function as a transcriptional regulator are presented.
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Carmichael, Sarah J. "Signalling molecule production by Escherichia coli and Campylobacter jejuni." Thesis, University of Central Lancashire, 2006. http://clok.uclan.ac.uk/7647/.
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Quorum sensing (QS) is a density-dependent gene regulation signalling mechanism utilized by bacteria to enable the simultaneous expression of bacterial phenotypes in a given population. Several QS mechanisms and different classes of signalling molecules, including acyl-homoserine lactones (AHLs), have now been identified in numerous bacterial species. AHL production by clinical and laboratory isolates of Escherichia coli and Campylobacter jejuni has been investigated in this study. Laboratory, blood and urine E.coli isolates were analysed via three reporter strain bioassays for putative AHL production. The initial results indicated that the E.coli blood isolates produced a compound(s) capable of activating one of the bioassays. Subsequent analysis by thin layer chromatography and mass spectroscopy suggested that this active compound may have been a cyclic dipeptide, although the apparent inability to isolate subsequent samples of this active compound has prevented confirmation of this finding. All of the C. jejuni isolates tested induced activity in the Agrobacterium liquid culture bioassay, in a growth-dependant manner, indicating the possible presence of an exogenous AHL. Comparative analysis of the genome sequenced C. jejuni strain, NCTC 11 168-GS and its clinical counterpart, C. jejuni NCTC 11168-0, has indicated that these variants respond differently to changes in the levels of dissolved oxygen and toxic oxygen derivatives and as a consequence produce different levels of the active compound. FIPLC separation and HPLC-mass spectroscopy has indicated that this active compound may be N-hexadecanoylhomoserine lactone, providing preliminary evidence of a previously unidentified AHL-mediated QS mechanism within the Epsilon Prozeobacteria class.
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Lösekann, Tina. "Molecular characterization of methanotrophic and chemoautotrophic communities at cold seeps." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980287979.
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Syeda, Fahima. "Molecular and physiological basis for cold-induced angiogenesis in fishes." Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/3221/.
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Angiogenesis- growth of capillaries from a pre-existing network- can be induced in cold-acclimated fishes, where torpor onset and increased oxygen availability, suggests that the primary stimulus for angiogenesis is not metabolic. It was hypothesised that cold-induced angiogenesis was due to increased blood viscosity, therefore endothelial mechanotransduction of high shear stress, and that warm-induced capillary rarefaction was due to reduced shear stress. The reversal of elevated shear stress by vasoconstriction using the nitric oxide synthase inhibitor, L-NNA, and cyclooxygenase inhibitor, indomethacin had different effects. L-NNA administration hinted towards capillary regression at low temperatures but there was a trend towards increased capillarity at intermediate and high temperatures, whereas indomethacin had no effect. Neither warm acclimation nor vasodilatation using the α-adrenoceptor antagonist, prazosin, had an effect on capillarity. Investigation of the effects of NO on heart rate at high temperature showed NO may reduce heart rate at high temperature. However, this does not explain the trend towards an increase in capillarity with L-NNA at high temperature. Evidence is presented for the absence of eNOS in fishes suggesting either nNOS-derived NO or prostanoids are responsible for vascular tone. Microarray analyses were used to identify signalling pathways that would explain the discrepancies, but proved inadequate to reveal significant endothelial responses to cold acclimation.
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Sokhoyan, Ruzan. "Formation of molecules in ultra-cold atomic gazes via quasi-resonant fields." Phd thesis, Université de Bourgogne, 2010. http://tel.archives-ouvertes.fr/tel-00689121.
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We study the nonlinear mean-field dynamics of diatomic molecule formation at coherent photo- and magneto-association of ultracold atoms focusing on the case when the system is initially in the all-atomic state. We show that in the limit of strongly nonlinear interaction between an ultra-cold atomic-molecular system and a quasi-resonant electromagnetic field, the molecule formation process, depending on the characteristics of the associating field, may evolve according two different scenarios, namely, weak- and strong-oscillatory regimes. In the first case the number of molecules increases without pronounced oscillations of atom-molecule populations, while in the second case high-amplitude Rabi-type oscillations arise. Assuming an arbitrary external field configuration, we construct analytical solutions to describe the system's temporal dynamics in the both interaction regimes. Further, we investigate the influence of inter-particle elastic scattering on the dynamics of coherent molecule formation subject to an external field configuration of the resonance-crossing Landau-Zener model. We derive an approximate solution which for the first time describes the whole temporal dynamics of the molecule formation in this general case.
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Austen, L. A. "Production of p-wave Feshbach molecules from an ultra-cold Fermi gas." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1338129/.
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This thesis studies the dynamics of Feshbach molecule production from a gas of ultracold spin polarised Fermi atoms. A magnetic field is used to vary the strength of the interaction between the atoms exploring the limits of weakly paired atoms and tightly bound diatomic molecules. A mean field approximation is used to study the thermodynamics and dynamics of the system. The two-body interaction is modelled using a separable potential that reproduces the near threshold behaviour of the system close to a Feshbach resonance. For atoms in the same internal state interactions occur in the p-wave, such that they have one quanta of relative orbital angular momentum (ℓ = 1). The presence of a magnetic field fixes a quantisation axis for this angular momentum, leading to a splitting of the resonance feature into three components. It is shown that in certain cases these components may be treated separately on both a two-body and thermodynamic level. Consequently the many-body dynamics are also treated as if these components are distinct. In order to study molecule production the gas is prepared in a state similar to the Bardeen-Cooper-Schrieffer (BCS) state in a superconductor. A linear sweep of the magnetic field through a Feshbach resonance is used to convert the weakly paired atoms into tightly bound molecules. The variation of the molecule production efficiency is studied as the initial temperature, density initial magnetic field and final magnetic field are varied. Also studied is the variation of molecule production as a function of the rate at which the magnetic field is varied. It is shown that high densities are needed to explore a range of initial magnetic fields and sweep rates.
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Lau, Siu Ha. "Molecular epidemiology of pathogenic escherichia coli." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517731.
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Varnasseri-Ghandali, Mehrvash. "Properties of a novel molecular ultra-cold laser produced Rydberg plasma." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.525929.
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Leckie, Gregor Wheelwright. "Molecular studies on a human common cold virus, human rhinovirus nine." Thesis, University of Leicester, 1987. http://hdl.handle.net/2381/35391.
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The molecular cloning of the common cold virus, rhinovirus 9, was achieved using the hybrid (RNA:CDNA) cloning protocol first described by Wood and Lee (1976). Two experiments were required to clone the complete genome; the first was primed by poly dT17 while the second was primed by an oligonucleotide which annealed to a sequence in the P2 region of the genome. Plasmids containing cDNA representative of the rhinovirus 9 genome were identified by in situ hybridisation. Such plasmids were characterised by the restriction endonuclease mapping of their cDNA inserts. This analysis indicated that plasmids containing cDNA derived from the entire 7.1 Kb genome of rhinovirus 9 had been obtained. The cloned rhinovirus 9 cDNAs were sub-cloned into M13 sequencing vectors (Messing et al., 1977) either as restriction endonuclease fragments or as randomly sheared, end-repaired fragments. The nucleotide sequence of these derived sub-clones was determined by the chain termination protocol of Sanger and colleagues (1977). The subsequent analysis and interpretation of the complete nucleotide sequence of rhinovirus 9, and its derived amino acid sequence, was carried out using the computer programs of Staden (1980) and Devereux (1984).
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Bumby, James. "Progress towards a source of cold, slow molecules for tests of fundamental physics." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/44971.
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This thesis reports on two beam sources of ytterbium fluoride (YbF), and assesses their viability for use in precision measurements of the electron electric dipole moment. The first source is a single-stage cryogenic buffer-gas source optimised for high extraction efficiency and low forward velocity. The thermalisation of the YbF rotational and translational temperatures with the buffer gas were measured through laser-induced fluorescence spectroscopy of molecules within the beam. The velocity distributions and fluxes of beams produced by this source were measured for buffer gas flow rates between 10 and 40 SCCM. We found that the mean beam velocities were between 190 and 210 m/s, and characteristic molecular fluxes were of the order 2*10^9 /sr/pulse. The second source is a two-stage cryogenic buffer-gas source, where the first stage is supposed to produce a high flux and the second stage is meant to slow the beam to low velocity. We found optimal behaviour running at lower pressures than the single-stage source, and measured YbF beams with a peak velocity of 70 m/s. Although not fully optimised, the source shows clear evidence of deceleration in the second stage, and drastically outperforms even the best measured fluxes from the single-stage source in terms of molecules with velocities below 100 m/s. The characteristic flux from this second source is of the order 7*10^7 /sr/pulse. As part of our parametrisation procedure, we developed a novel experimental technique to measure velocity distributions in the limit of low signal-to-noise ratios. We optically bleached population from a target hyperfine level of certain Doppler classes within the molecular beam. By integrating over all bleached molecules, we measured the number of YbF molecules with a given velocity. This technique was experimentally implemented, and was found to be in good agreement with results obtained using more traditional measurement schemes.
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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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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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White, Andrew John. "Molecular analysis of low temperature and stress responsive barley gene family, blt4." Thesis, University of Newcastle Upon Tyne, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283675.
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Devkota, Batsal. "Structural studies of ribonucleoprotein complexes using molecular modeling." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/22713.
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Thesis (Ph. D.)--Biology, Georgia Institute of Technology, 2008.Committee Chair: Harvey, Stephen C; Committee Member: Hud, Nicholas V; Committee Member: McCarty, Nael A; Committee Member: Wartell, Roger M.
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Jalajakumari, Meachery Bhaskaran. "Molecular organization and functional analysis of the CFA/II CS3 region of Enterotoxigenic Escherichia coli /." Title page, abstract and contents only, 1992. http://web4.library.adelaide.edu.au/theses/09PH/09phj26.pdf.
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Surey, Sarina. "Understanding the molecular mechanisms of spinal cord cavitation after spinal cord injury." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5721/.
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Spinal cord injury (SCI) is a neurodegenerative disease with research centered on axon regeneration and preservation to cure paralysis. Mice and rats are widely studied and experienced models used to imitate SCI due to differences in vascular disruption, blood vessel loss and cavitation at SCI epicenters. This study investigates sub-acute SCI responses, documenting angiogenic/inflammatory factors and matrix deposition in both species. Although cavitation was absent in mice, the lesion site in rats was larger at 8 and 15 days post lesion (dpl). Absence of cavitation in mice correlated with increased levels of pro-angiogenic/wound healing factors within the wound compared to rats at 8 dpl, coinciding with microarray analysis along with increased axonal sparing at T7 and T9 spinal segments. Despite similar deficits in thermal sensitivity 2 hours after injury, by 7 days the responses were comparable to controls in both species. Furthermore, inducing inflammation directly after injury using zymosan resulted in inflammatory-induced angiogenic responses between both species at 8 dpl, contributing to tissue damage and micro-cavities in the CNS. In conclusion angiogenic responses in mice attenuates wound cavitation, reducing secondary axon damage and thus induces axon sprouting/regeneration. These results suggest potential therapeutic utility of manipulating angiogenic/inflammatory responses after human SCI.