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1
Tackmann, Gunnar [Verfasser]. "Raman interferometry with free-falling and trapped atoms / Gunnar Tackmann." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2013. http://d-nb.info/1049229541/34.
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Chai, Jeng-Da. "Orbital-free density functional theory of atoms, molecules, and solids." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/3125.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Chemical Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Lees, Eitan Jacob. "Suppression of Collective Quantum Jumps of Rydberg Atoms due to Collective Spontaneous Emission from Atoms in Free Space." Miami University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=miami1438276591.
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Persaud, Michael Alan. "Doppler-free two-photon spectroscopy of one electron atoms using pulsed lasers." Thesis, University of Southampton, 1991. https://eprints.soton.ac.uk/361600/.
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In two independent experiments, frequency doubled pulse amplified dye laser light has been used in performing Doppler-free two-photon spectroscopy of the 1S½−2S½ transition in atomic hydrogen and muonium. Absolute values gained for the 1S½−2S½ transition frequencies were 2466 061 416(9) MHz and 2455 528 964(72) MHz for hydrogen and muonium respectively. Values for the ground state Lamb shifts were inferred to be 8171(9) MHz for hydrogen and 8079(73) MHz for muonium. All results were found to be in agreement with current quantum electrodynamic (QED) theory. Assuming QED theory to be accurate, then the hydrogen experiment yielded a new value for the Rydberg constant of 109 737 31.58(4) m−1, which is in agreement with other independent measurements. A separate experiment demonstrated a novel and general technique for efficiently frequency doubling mode-locked laser light, based on second harmonic generation inside an actively stabilised external ring enhancement cavity. When applied to a synchronously pumped mode-locked dye laser, over 100mW average power of tunable light around 243nm was available from the system corresponding to crystal conversion efficiencies in excess of 55%. A simple theoretical model successfully described the performance of this system. FM sideband frequency stabilisation of mode-locked lasers is treated both theoretically and experimentally. For the mode-locked dye laser, a frequency stability to within 500kHz relative to a reference interferometer was routinely possible. The frequency stabilised tunable uv light is ideal for performing Doppler-free coherent multiple pulse spectroscopy and may find application in the synchronous pumping of optical parametric oscillators or in selectively breaking chemical bonds.
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Livesey, John Gregor. "Atom guiding in free-space light beams and photonic crystal fibres." Thesis, St Andrews, 2007. http://hdl.handle.net/10023/356.
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Wickenbrock, A. "Cold atoms in light fields : from free space optical lattices to multimode optical cavities." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1349525/.
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The electromagnetic mode density of the vacuum can be dramatically modified by the presence of an optical resonator. In the strong coupling regime, spontaneous emission in a cavity becomes a reversible process and the intracavity photon number undergoes Rabi oscillations. We load up to 200x10^3 ^133Cs atoms into a nearly confocal lossy cavity and reach the collective strong coupling regime. Normal mode splitting, the hallmark of this regime, is observed and cooperativities up to C_coll = (186±5) are measured. In a second experiment we investigate for the first time the multi-mode character of the coupled cavity-atom system. In a confocal cavity the higher-order transverse cavity modes are degenerate in frequency and accessible to the spontaneous emission of the atomic ensemble. We observe an increase of the coupling constant measured via modal decomposed transmission analysis, which could be attributed to the presence of the higher-order modes. Normal mode splitting proportional to the square root of the atom number was visible for all of the different mode components. Furthermore, we observe a redistribution of the relative weights in the modal transmission composition, which scales with the atom number in the cavity mode. In a second set of experiments, ^87Rb atoms were loaded into a dissipative lin ⊥ lin lattice. By driving the lattice with a biharmonic force, transport can be observed when the systems symmetries are broken: the so called ratchet effect. Research in this area is concerned with the appearance of current reversals. We were able to identify dissipation related symmetry breaking as the underlying cause of an observed current reversal, which occurs as a function of the driving frequency. Furthermore, in a second experiment, we use the ratchet effect as a probe of the optical potential depths. We show that an oscillating force with a frequency far above any other system-inherent timescale, can be used to renormalize the optical potential. The ^87Rb atoms experience an average position dependent force, which becomes controllable over the amplitude of the applied driving.
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Petersen, Ingo [Verfasser]. "Photoelectron Momentum Distributions from Recollision-Free Strong-Field Ionization of Atoms and Molecules / Ingo Petersen." München : Verlag Dr. Hut, 2015. http://d-nb.info/1067708197/34.
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Laine, Patrick L. "Laser flash photolysis studies of halogen atom reactions of atmospheric interest." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42817.
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The Earth's atmosphere is a large photochemical reactor consisting primarily of N2 (~78%) and O2 (~21%) with Ar and water vapor being the next most abundant constituents. All of the remaining gases in the atmosphere are referred to as 'trace gases', and they play a critical role in understanding climate change, urban air quality, ozone production and depletion, and in determining the overall 'health' of the atmosphere. These trace components are present in our atmosphere with mixing ratios, i.e., mole fractions, ranging from sub parts per trillion to several hundred parts per million. One class of trace constituents that play a critical role in atmospheric chemistry are free radicals. Free radicals are highly reactive, often initiating the oxidation of natural and anthropogenic atmospheric species, thereby often controlling the fate and lifetimes of these species. The research comprising this dissertation focuses on laboratory studies of the kinetics and mechanisms of free radical (atomic halogen) reactions that can impact the levels of important trace atmospheric species. In the studies reported herein, laser flash photolysis (LFP) was coupled with time resolved atomic resonance fluorescence (RF) spectroscopic detection of Cl or Br atoms to investigate halogen atom chemistry. The research addresses three groups of reactions: Cl atom reactions with alkyl bromides, Cl and Br-initiated oxidations of small (C2-C6) alkenes, and Cl reactions with CH3SCH3 (DMS, dimethylsulfide) and CH3SeCH3 (DMSe, dimethylselenide).
The alkyl bromide reactions were experimentally unique in that we were able to deduce kinetics of the Cl atom reaction with bromoethane, n-bromopropane, and 1,2-dibromoethane by monitoring the appearance of the Br product by LFP-RF. The Br is formed via elimination that occurs essentially instantaneously following β-H abstraction by the Cl atom. All three of the bromoalkanes investigated are emitted into the atmosphere primarily from anthropogenic sources and all three have been identified by the World Meteorological Organization (WMO) as very short-lived (lifetime less than 6 months) source gases with significant ozone depletion potentials (ODPs). Additionally, the bromoalkanes mentioned above have been of interest as model compounds for larger partially halogenated organics found in the atmosphere, and they have been considered as potential replacement compounds for chlorofluorocarbons (CFCs) that have been banned as a result of the Montreal Protocol. Brominated very short-lived compounds are thought to contribute 20-25% of total stratospheric bromine. Thus, there is considerable interest in understanding the atmospheric chemistry of even the most short-lived organic bromine compounds. Temporal profiles of Br atoms provided important kinetic and mechanistic insight for the reactions over a wide range of temperature and pressure. Temperature-dependent rate coefficients are determined for the alkyl bromides of interest for the first time, and the potential importance of the Cl reaction as an atmospheric degradation pathway for each alkyl bromide is qualitatively assessed.
The studies of halogen atom reactions with alkenes focused on formation of weakly-bound adducts where kinetics of adduct formation and dissociation as well as non-adduct forming channels were evaluated. The elementary steps in the Br initiated oxidation of the alkenes 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-2-butene (tetramethylethylene, TME), and 1,3-butadiene have been investigated. The experimental kinetic database for these reactions is quite sparse. The kinetic results reported herein, suggests that Br reaction with the above olefins is much faster than previously thought. Analysis of the temperature dependence of the "approach to equilibrium" kinetic data in conjunction with electronic structure calculations allows for determination of enthalpy and entropy changes associated with each addition reaction. Where possible, both forward addition and reverse dissociation channels as well as H-abstraction pathways were characterized. The enthalpy change associated with the addition reaction to give the Br−isoprene and Br−1,3-butadiene adducts has been determined for the first time and the bond dissociation enthalpy obtained for the Br−TME adduct is in reasonable agreement with the only other previously reported value. It should be noted that in the case of isoprene and 1,3-butadiene, there are multiple possible adducts that could be formed. In order to help clarify which adducts are more or less likely to be formed, we rely on electronic structure calculations (see Chapter 5) to aid in our overall understanding of the adduct forming channels. Furthermore, for the Br reactions with the three alkenes above, atomic Br kinetics have been monitored directly both in the absence and in the presence of O2 which allowed, for the first time, determination of rate coefficients for the elementary steps in the overall complex mechanism including determination of the Br−olefin + O2 rate coefficient.
Also included in this group of reactions is the chlorine reaction with isoprene. In addition to the well-known fact that isoprene is emitted into the atmosphere from vegetation, a potentially significant marine source of isoprene has received considerable attention. Chlorine has long been thought to exist primarily in marine environments, however, recent findings also suggest a significant Cl production rate in the middle of the continental United States. There are numerous room temperature kinetic studies for the Cl + isoprene reaction in the literature, however, there is only one temperature dependent study reported. Current recommended 298 K rate coefficients for isoprene reactions suggest the Cl reaction is ~ 4x faster than the analogous OH reaction. If indeed this is the case, the Cl reaction could play a non-neglibible role in isoprene oxidation in atmospheric locales where Cl concentrations are relatively high. In addition, the C−Cl bond strength in Cl−C5H8 is obtained from direct measurements of the forward and reversible addition rate coefficients. Our results are compared with the literature data, and the potential importance of Cl-initiated oxidation as an atmospheric sink for isoprene is assessed.
The final group of reactions investigated involves reactions of Cl with DMS and DMSe. DMS and DMSe are the most prevalent sulfur and selenium compounds emitted to the atmosphere from the oceans. The oxidation of DMS has been studied extensively due to the interest in the possible role of DMS oxidation in the formation of sulfate aerosols, however, DMSe oxidation processes have hardly been studied at all. And, DMSe oxidation products are likely to be less volatile than the analogous DMS species. Selenium is an essential nutrient for many plants and animals; however, there is a fine line between enough and excess selenium which can be toxic. Most studies suggest that atmospheric deposition is an important source of Se contamination, and it is therefore critical to evaluate the source emissions and fate of Se in the atmosphere. Since the majority of atmospheric Se exists in the form of DMSe, determination of the kinetics and oxidation mechanisms of DMSe will go a long way towards understanding the global biogeochemical cycle of Se.
Both reversible addition and H-abstraction pathways have been characterized, and the first experimental determination of bond strength of the gas-phase DMS−Cl and DMSe−Cl adducts have been obtained.
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Rudek, Benedikt [Verfasser], and Joachim [Akademischer Betreuer] Ullrich. "Multiple Ionization of Heavy Atoms by Intense X-Ray Free-Electron Laser Pulses / Benedikt Rudek ; Betreuer: Joachim Ullrich." Heidelberg : Universitätsbibliothek Heidelberg, 2012. http://d-nb.info/1179784510/34.
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Ortegel, Norbert Verfasser], and Harald [Akademischer Betreuer] [Weinfurter. "State readout of single Rubidium-87 atoms for a loophole-free test of Bell’s inequality / Norbert Ortegel ; Betreuer: Harald Weinfurter." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2016. http://d-nb.info/1119073464/34.
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Beaulieu, Samuel. "Probing femtosecond and attosecond electronic and chiral dynamics : high-order harmonic generation, XUV free induction decay, photoelectron spectroscopy and Coulomb explosion." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0063/document.
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Ce manuscrit de thèse s'articule autour de l'étude de l'interaction entre des impulsions lumineuses ultra brèves et des atomes ainsi que des molécules polyatomiques et chirales en phase gazeuse. En utilisant des techniques développées en physique attoseconde ainsi qu'en femtochimie, notre objectif général est de parvenir à une meilleure compréhension des dynamiques ultrarapides photoinduites dans la matière. Pour ce faire, nous avons développé des sources de lumière à ultra brèves dans le proche infrarouge et l’infrarouge moyen, qui ont été utilisées pour construire une source de rayons X dans la fenêtre de l’eau, basée surla génération d'harmoniques d’ordre élevé (GHOE), ainsi que pour l’étude de nouveaux canaux de GHOE impliquant des états hautement excités (Rydberg). Cette dernière étude a démontré une émission harmonique via l'ionisation depuis des états de Rydberg et la recombinaison radiative sur l'état fondamental, attirant ainsi notre intérêt pour le rôle des états de Rydberg en physique des champs forts. Cela nous a conduit à étudier la décroissance libre de l’induction XUV de paquets d'ondes électroniques comme une nouvelle technique de spectroscopie 2D. De plus, nous avons découvert que l'interaction entre un laser intense et un atome préparé dans une superposition cohérente d'états électroniques peut conduire à la génération de lignes hyper-Raman concomitantes avec la GHOE standard. Ce mécanisme avait été prédit lors des premiers calculs théoriques de GHOE, mais n'avait jamais été démontré expérimentalement. Par la suite, nous nous sommes intéressé à l’étude de systèmes moléculaires, dans lesquelles une excitation électronique induite par la lumière peut déclencher des dynamiques nucléaires. Nous avons étudié la photo isomérisation non-adiabatique de l’acétylène cationique en vinylidène cationique ainsi que le contrôle cohérent de la localisation électronique lors de la photodissociation de H2+. La simplicité de ces systèmes moléculaires a permis la comparaison des résultats expérimentaux avec des calculs théoriques de pointe,révélant l'importance du couplage entre les degrés de liberté nucléaires et électroniques lors de dynamiques moléculaires photoinduites.Un autre pilier majeur de cette thèse est l'étude de l'ionisation de molécules chirales avec des impulsions chirales. On sait depuis les années 70 que l'ionisation d'un ensemble de molécules chirales aléatoirement orientées, en utilisant une impulsion polarisée circulairement, conduit à une forte asymétrie avant-arrière dans le nombre de photoélectrons émis, selon l'axe de propagation de la lumière (DichroismeCirculaire de Photoélectron, DCPE). Avant cette thèse, le DCPE a été largement étudié à l’aide du rayonnement synchrotron (ionisation à un photon) et a récemment été démontré avec des lasers femtoseconde, via des schémas d'ionisation multiphotonique. Dans cette thèse, nous avons montré que le DCPE est un effet universel, c'est-à-dire qu'il émerge dans tous les régimes d'ionisation: l'ionisation àun photon, l'ionisation à multiphonique, l'ionisation au-dessus du seuil ainsi que l’ionisation par effet tunnel. Ensuite, nous avons démontré que la combinaison d’approches standard de femtochimie et du DCPE peuvent être utilisées pour suivre des dynamique de molécules chirales photoexcitées. En utilisant des approches expérimentales similaires, avec des séquences d'impulsions ayant des états de polarisation contre-intuitifs, nous avons démontré un nouvel effet chiroptique, appelé Dichroïsme Circulaire de Photoexcitation (DCPX), qui est décrit par un courant électronique directionnel et chirosensible, lorsque plusieurs niveaux sont peuplés de manière cohérente avec de la lumière chirale. Enfin, nous avons introduit une perspective temporelle à la photoionisation chirale en mesurant l'asymétrie avant arrièredes retards de photoionisation dans les molécules chirales photoionisées par des impulsions lumineuses chiralesThis thesis manuscript is articulated around the investigation of the interaction between ultrashort light pulses and gas-phase atoms, polyatomic and chiral molecules. Using the toolboxes developed in attosecond and strong-field physics as well as in femtochemistry, our general goal is to reach a better understanding of subtle effects underlying ultrafast light-induced dynamics in matter.To do so, we developed cutting-edge near-infrared and mid-infrared few-cycle light sources, which were used to build a water-window soft-X-ray source based on high order harmonic generation (HHG), as well as to study new HHG channels involving highly-excited (Rydberg) states. The latter study revealed a delayed HHG emission from the ionization of Rydberg states and radiative recombination onto the electronicground state, triggering our interest in the role of Rydberg states in strong-field physics. This led us to investigate the laser-induced XUV Free Induced Decay from electronic wave packets as a new background-free 2D spectroscopic technique.More over, we have found out that strong-field interaction with a well prepared coherent superposition of electronic states led to the generation of hyper-Ramanlines concomitant with standard high-order harmonics. These spectral features were predicted in the early-days theoretical calculations of HHG but had never been reported experimentally.After these experiments in rare gas atoms, we moved to molecular targets, in whichlight-induced electronic excitation can trigger nuclear dynamics. Using simple benchmark molecules, we have studied dynamics involving the participation of both nuclear and electronic degrees of freedom: first, we studied the ultrafast non adiabatic photoisomerization of the acetylene cation into vinylidene cation, andsecond, we investigated the coherent control of electron localization during molecular photodissociation of H2+. The simplicity of these molecular targets enabled the comparison of the experimental results with state-of-the-art theoretical calculations,revealing the importance of the coupling between nuclear and electronic degrees of freedom in photoinduced molecular dynamics.The other major pillar of this thesis is the study of ionization of chiral molecules usingchiral light pulses. It has been known since the 70s that the ionization from an ensemble of randomly oriented chiral molecules, using circularly polarized light pulse,leads to a strong forward-backward asymmetry in the number of emitted photoelectrons, along the light propagation axis (Photoelectron Circular Dichroism,PECD). Prior to this thesis, PECD was widely studied at synchrotron facilities (single photonionization) and had recently been demonstrated using table-top lasers in resonant-enhanced multiphoton ionization schemes. In this thesis, we have shownthat PECD is a universal effect, i.e. that it emerges in all ionization regimes, from single photon ionization, to few-photon ionization, to above-threshold ionization, up to the tunneling ionization regime. This bridges the gap between chiral photoionizationand strong-field physics. Next, we have shown how the combination of standard femtochemistry approaches and PECD can be used to follow the dynamics of photoexcited chiral molecules using time-resolved PECD. Using similar experimental approaches, but by using pulse sequences with counter-intuitive polarization states,we have demonstrated a novel electric dipolar chiroptical effect, called Photoexcitation Circular Dichroism (PXCD), which emerges as a directional and chirosensitive electron current when multiple excited bound states of chiral molecules are coherently populated with chiral light. Last, we introduced a time-domain perspective on chiral photoionization by measuring the forward-backward asymmetry of photoionization delays in chiral molecules photoionized by chiral light pulses. Our work thus carried chiral-sensitive studies down to the femtosecond and attosecond ranges
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Rander, Torbjörn. "Photoelectron Spectroscopy on Atoms, Molecules and Clusters : The Geometric and Electronic Structure Studied by Synchrotron Radiation and Lasers." Doctoral thesis, Uppsala University, Department of Physics, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8343.
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Atoms, molecules and clusters all constitute building blocks of macroscopic matter. Therefore, understanding the electronic and geometrical properties of such systems is the key to understanding the properties of solid state objects.
In this thesis, some atomic, molecular and cluster systems (clusters of O2, CH3Br, Ar/O2, Ar/Xe and Ar/Kr; dimers of Na; Na and K atoms) have been investigated using synchrotron radiation, and in the two last instances, laser light. We have performed x-ray photoelectron spectroscopy (XPS) on all of these systems. We have also applied ultraviolet photoelectron spectroscopy (UPS), resonant Auger spectroscopy (RAS) and near-edge x-ray absorption spectroscopy (NEXAFS) to study many of the systems. Calculations using ab initio methods, namely density functional theory (DFT) and Møller-Plesset perturbation theory (MP), were employed for electronic structure calculations. The geometrical structure was studied using a combination of ab initio and molecular dynamics (MD) methods.
Results on the dissociation behavior of CH3Br and O2 molecules in clusters are presented. The dissociation of the Na2 molecule has been characterized and the molecular field splitting of the Na 2p level in the dimer has been measured. The molecular field splitting of the CH3Br 3d level has been measured and the structure of CH3Br clusters has been determined to be similar to the structure of the bulk solid. The diffusion behavior of O2, Kr and Xe on large Ar clusters, as a function of doping rate, has been investigated. The shake-down process has been observed from excited states of Na and K. Laser excited Na atoms have been shown to be magnetically aligned. The shake-down process was used to characterize the origin of various final states that can be observed in the spectrum of ground-state K.
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Bradshaw, N. "Atom and free radical reactive scattering." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375081.
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Machado, Jorge Felizardo Dias Cunha. "High precision tests of QED : measurement of the alpha-particle and helion rms charge radius and the transition energies in highly-charged ions." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS016/document.
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Ce travail vise à contribuer à l’amélioration de notre connaissance de l’électrodynamique quantique des états liés, par des mesures de haute précision dans des états exotiques de la matière. Bien que notre connaissance de l’électrodynamique quantique des états liés et du problème relativiste à plusieurs corps aient fait des progrès importants ces dernières années, il reste des questions fondamentales dont la résolution nécessite d’augmenter le nombre et la précision des tests expérimentaux. La première partie de ce travail a été réalisée dans le cadre de l’expérience récente sur les ions muoniques d’hélium (μ4He+ et μ3He+) conduite par la collaboration CREMA. Cette expérience vise à fournir de nouvelles valeurs précises pour les rayons de charge moyens des noyaux des isotopes stables de l’hélium. Ces valeurs sont extraites de la mesure du déplacement de Lamb, c’est-à-dire, de la mesure de la différence d’énergie entre les États 2S − 2P. Une mesure des énergies de transition d’une précision d’au moins 50 ppm, permet de déterminer les rayons de charge des noyaux des isotopes d’hélium avec une incertitude de 0,03%, dix fois plus précise que les résultats précédents obtenus à partir de la diffusion d’électrons. La deuxième partie de ce travail a été de réaliser des mesures de haute précision de transitions de rayons X dans des ions fortement chargés, à l’aide d’un spectromètre à double cristal plan. Ces ions étaient produits dans le plasma d’une source d’ions de type ECRIS (electron-cyclotron resonance ion source). Le spectromètre utilisé est non seulement capable de fournir des mesures de haute précision, mais aussi des mesures sans référence à des énergies de transition théorique ou expérimentales. Quatre énergies de transition de n = 2 → n = 1 ont été mesurées pour des ions d’argon de trois états de charge différents, héliumoïde, lithiumoïde et berylliumoïde, avec une précision meilleure que 3 ppm. La largeur naturelle de chaque raie a également été obtenue expérimentalement. Les résultats trouvés sont en excellent accord avec les calculs théoriques les plus récentsThis work aims to provide insight on Bound-State Quantum-Electrodynamics (BSQED) by experimental fundamentals high-precision tests in exotic states of matter. Although BSQED and the relativistic many-body problem have been undergoing important progress, there are still some issues that require the increase of the number and accuracy of experimental fundamental tests. The first part of this work was done within the framework of the recent experiment in muonic helium ions (μ4He+ and μ3He+) by the CREMA collaboration. This experiment, aims to provide new accurate values for the root-mean-square (rms) charge radii of the helium isotopes nuclei that are extracted from the measurement of the Lamb Shift, i.e., the measurement of the energy difference between the 2S − 2P states. With the goal of measuring the transition energies with an accuracy of at least 50 ppm, the rms charge radii of the helium isotopes will be determined with an uncertainty of 0.03%, a factor of ten more precise than previous results obtained from electron scattering. The second part of this work aims the high-precision measurement of x-ray transitions in Highly-Charged Ions (HCI) using a Double-Crystal Spectrometer (DCS). These ions were produced in the plasma of an Electron-Cyclotron Resonance Ion Source (ECRIS). This kind of spectrometer is able not only to provide high-precision measurements but also reference-free measurements, without reference to any theoretical or experimental energy. Four transitions energies from n = 2 → n = 1 have been measured in an argon plasma in three different charge states, He-, Be- and Li-like, with an accuracy of better than 3 ppm. Besides the energies, the natural width of each transition has also been experimentally obtained. The obtained results are in excellent agreement with the most recent theoretical calculations
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Ren, Wendong. "Photoinduced Atom Transfer Radical Polymerization." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1619122320374689.
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Wang, Aileen Ruiling Zhu Shiping. "Diffusion-controlled atom transfer radical polymerization." *McMaster only, 2005.
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Ding, Shijie. "Atom transfer radical polymerization." Laramie, Wyo. : University of Wyoming, 2006. http://proquest.umi.com/pqdweb?did=1225138911&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Lush, Rachel K. "Hydrogen atom abstraction pathways to functionalised free radicals." Thesis, University of Oxford, 2001. http://ora.ox.ac.uk/objects/uuid:84e82ee6-f8b4-4f11-a3d2-30af12f4e0b3.
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Radical translocation chemistry has classically been employed for the generation of carboncentred radicals as a means of remotely functionalising nominally unreactive sites. Previous work within the group had investigated vinyl radicals to effect translocation and had identified a need for a more reactive abstracting radical. In this regard, the high energy of alkoxyl radicals would facilitate rapid 1,5-hydrogen abstraction as opposed to simple reduction. This thesis describes the use of alkoxyl radicals, generated from N-alkoxyphthalimides, to abstract a hydrogen atom selectively from the α-position of a lactam ring. Alkoxyl radicals generated from precursors designed to lead to intramolecular trapping of the translocated radical were prone to β-scission in preference to 1,5-hydrogen atom abstraction. This is attributed to a combination of developing π-overlap in the transition state and stabilisation of the resulting radical both by nitrogen and the attached alkyl substituents. Incorporation of an alkenyl trap onto the lactam ring led to successful 1,5-hydrogen atom abstraction and stereoselective cyclisation, although β-scission remained the dominant pathway. Translocation initiated by nitrogen-centred radicals was investigated and it was found that 1,5-hydrogen abstraction occurred in preference to β-scission; intramolecular trapping of the translocated radical proved impossible either because the precursors were unstable to the reaction conditions or because increased steric bulk impeded hydrogen abstraction by the less reactive aminyl radical. Preparation of bicyclic pyrrolidinones via successive 5-endo-5-exo-trig cyclisations was investigated; the precursors were found to undergo direct reduction in preference to cyclisation. Alkyl or aryl groups attached to the a-acylamino carbon may lead to preferential 5-endo cyclisation by stabilisation of the developing radical in the transition state.
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Shen, Youqing. "Atom transfer radical polymerization and its continuous processes /." *McMaster only, 2001.
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Faoro, Riccardo. "Few-body interactions in cold Rydberg atoms." Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS180/document.
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L’objectif de cette thèse est l’étude des différents aspects de l’interaction à quelques corps entre des atomes de Rydberg froids. Cette thèse a été réalisée dans le cadre d’une cotutelle entre l’Université Paris-Saclay et l’Université de Pise en travaillant sur deux différents montages expérimentaux sur des atomes de Rydberg froids : respectivement sur le Cs au Laboratoire Aimé Cotton et sur le Rb au département de Physique de l’Université de Pise. Au Laboratoire Aimé Cotton nous avons démontré l’existence des nouvelles interactions à quelques corps dans un gas gelé d’atomes de Rydberg. Ces nouvelles résonances sont la généralisation des résonances de Förster bien connues dans le domaine des atomes de Rydberg. Ces résonances agissent sur les degrés de liberté interne des atomes de Rydberg et ont l’effet d’un transfert résonant d’énergie et de population comme dans le cas des FRET (Fluorescence Resonance Energy Transfer). Comme dans le cas de la résonance de Förster à deux corps, les résonances FRET à trois corps sont accordées à la résonance avec un champ électrique externe et peuvent être observées pour différents nombres quantique principaux. Les effets à trois corps sont observés en absence de tout effet à deux corps et sont qualifiés de Borroméens. La présence d’un champ externe peut générer d’autres résonances entre atomes de Rydberg qui sont interdites en absence de champ électrique. Ces résonances, qu’on peut qualifier des résonances quasi-interdites, sont dues à un couplage dipole-dipole de type Förster. Nous avons identifié toutes ces résonances liées au couplage entre les niveaux de multiplicité de n différents.Dans le montage expérimental à Pise on a étudié les effets mécaniques liés à la répulsion van der Waals entre atomes de Rydberg. Nous avons étudié l’expansion due à l’interaction van der Waals dans une chaîne 1D des atomes de Rydberg de Rb qui ont étés excités avec une excitation laser hors résonance. La comparaison entre les différents désaccords de l’excitation laser démontre le rôle central joué par l’interaction van der WaalsThe aim of this thesis is to investigate different aspects of few-body interactions in cold Rydberg atoms. It has been realized in a co-tutelle program between the University of Paris-Saclay and the University of Pisa working on two different experimental set ups: one at Laboratoire Aimé Cotton on cold Cs Rydberg atoms and a second at Physics Department of Pisa on cold Rb Rydberg atoms. In Laboratoire Aimé Cotton we demonstrated the existence of new few-body interactions we observed in a frozen Rydberg gas of Cs atoms. These new resonances are a generalization of already known two-body Förster resonances. They act on the internal degrees of freedom of the Rydberg atoms leading to a resonant energy transfer analogous to the one in FRET (Fluorescence Resonance Energy Transfer). In analogy with Förster resonance, three-body FRETs are tuned with an external electric field and can be observed for different principal quantum number. The three-body interaction appeared in the absence of any two-body ones and for this reasons it has a Borromean character. The presence of this external electric field leads to additional resonances between Rydberg atoms supposedly forbidden. These resonances, we call quasi-forbidden Förster resonances, are due to dipole-dipole interaction as in the case of Förster resonance. We investigated these resonances finding a large number close to the allowed two-body and three-body FRET. A precise study was necessary in order to identify and discriminate these resonances from the allowed ones.In the experiment in Pisa we instead focus our attention on the mechanical effect of van der Waals repulsion between Rydberg atoms. We studied the spatial expansion due to a van der Waals interaction in a 1D chain of Rb Rydberg atoms excited with an off-resonant laser excitation. The comparison of the spatial expansion for different detuning of the laser excitation reveals the central role of the van der Waals interaction whose strength is equal to the detuning of the laser excitation
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Erbing, Axel. "In pursuit of next generation photovoltaics : An electronic structure study of lead-free perovskite solar cells." Licentiate thesis, Stockholms universitet, Fysikum, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-181608.
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The recent development of perovskite-based solar cells have shown a remarkably fast increase in power conversion efficiency making them a promising low-cost alternative to conventional cells. The most successful class of materials however, the lead-halide perovskites, are held back due to toxicity and stability issues significantly limiting their use. Because of this, the investigation of new, lead-free, light-absorber materials as a replacement is an important step towards improved solar cells. The focus of this licentiate thesis is the study of bismuth-based materials and their photovoltaic properties through electronic structure calculations. Specifically, the cubic-phase AgBi2I7 under gradual substitution of either bromine or antimony is investigated using density functional theory under periodic boundary conditions. This enables calculations of the system's energy levels and band structure. Furthermore, the energy variance of the employed model of the system is sampled with respect to its level of ion disorder to obtain a better understanding of the distribution of ions within the crystal. The materials are found to have good optical properties but comparatively low efficiencies. The introduced substitutions allow fine-tuning of the system's band gap and is shown to increase the overall performance of the solar cells. In addition, spin-orbit coupling effects are demonstrated to be important when treating these bismuth-based systems. The crystal structure is found to have a significant preference for separating its silver ions and cation vacancies.
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Degenhardt, Carsten. "Freie und gespeicherte Calcium-Atome für ein optisches Frequenznormal." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972556060.
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Zhou, Wenqiao. "AQUEOUS METAL-FREE ATOM TRANSFER RADICAL POLYMERIZATION USING RESORUFIN AS PHOTOREDOX CATALYST." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1627036614505481.
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Baumgartner, Florian. "Measuring the acceleration of free fall with an atom chip BEC interferometer." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/6873.
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We show that a Bose-Einstein condensate (BEC) interferometer on an atom chip is capable of making an absolute force measurement. We demonstrate this by making an absolute measurement of the gravitational acceleration g. We implement two interferometer arms by splitting a BEC into two symmetric wells using radio-frequency (rf) adiabatic potentials. The independent control of the rf currents running through the chip surface allows us to change the polarisation of the rf field and hence the orientation of the double well potential. Tilting of the system with respect to the horizontal introduces an energy difference Δ V and the relative phase between the BECs starts to evolve. After moving the atoms back to their initial position and overlapping the clouds in free fall we measure the resulting phase from the interference pattern. In order to derive a number for g from experimental results a detailed analysis and understanding of the interferometer scheme is essential. For this type of interferometer we have identified two main limitations to the accuracy of the measurement: a systematic error due to rf field gradients, and a statistical error due to phase spreading from atom-atom interactions. Taking all errors into account we expect a value for g to within 16%. The statistical uncertainty of the measurement is 5%. We have a strategy for reducing all systematic errors to less than 1%. In order to reduce the rate of phase spreading we want to squeeze the relative number of atoms between the wells in future experiments.
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Boutalib, Abderrahim. "Etude théorique de la surface de potentiel du système HO::(2) + H. : Influence de la corrélation électronique." Pau, 1986. http://www.theses.fr/1986PAUU3009.
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Calcul des géométries du points de sille et des barrières d'activation pour les réactions d'abstraction (HO::(2) + H->H::(2) + O::(2)) et d'approche concertée (HO::(2) + H->H::(2)O + O) pour la méthode SDCI à l'ordre d'une base DZ dans la région de valence, augmentée par des orbitales de polarisation de type D sur chaque atome O. Evaluation des paramètres cinétiques dans le cadre de la théorie de l'état de transition : énergies d'activation et constantes de vitesse. Faible probabilité du mécanisme de réaction concertée
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Verma, Abhinav. "Development and application of a free energy force field for all atom protein folding." Karlsruhe : Forschungszentrum Karlsruhe, 2007. http://d-nb.info/987646559/34.
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Kafle, Rudra Prasad. "Theoretical Study of Bose-Einstein Condensate-Based Atom Michelson Interferometers." Digital WPI, 2012. https://digitalcommons.wpi.edu/etd-dissertations/184.
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Atom interferometers and gyroscopes are highly sensitive atom-optical devices which are capable to measure inertial, gravitational, electric, and magnetic fields and to sense rotations. Theoretically, the signal-to-noise ratio of atomic gyroscopes is about a hundred billion times more than that of their optical counterparts for the same particle flux and the enclosed area. Ultra cold atoms from a Bose-Einstein condensate (BEC) can easily be controlled and coherently manipulated on small chips by laser pulses. Atom-optical devices will therefore play a significant role in fundamental research, precision measurements, and navigation systems. In BEC-based atom interferometers, a BEC in a trap is split by using laser pulses, the split clouds are allowed to evolve, they are reflected, and then recombined by laser pulses to observe interference. The split clouds accumulate spatial phase because of the trap and the nonlinearity caused by atom-atom interactions. A velocity mismatch due to reflection laser pulses also introduces a phase gradient across each cloud. These factors contribute to spatial relative phase between the clouds at recombination, causing the loss of contrast of the interference fringes. The main objective of this dissertation is to study the dynamics of a split condensate in atom Michelson interferometers, investigate the effect of trap frequencies, nonlinearity, and the velocity mismatch on the contrast, and to obtain the best theoretical limit of performance in terms of the experimental parameters: trap frequencies, number of atoms, and the velocity imparted to the clouds by the splitting laser pulses.
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Gherardi, David Mark. "Studies of particle and atom manipulation using free space light beams and photonic crystal fibres." Thesis, St Andrews, 2009. http://hdl.handle.net/10023/703.
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Machado, Jorge Felizardo Dias Cunha. "High precision tests of QED Measurement of the alpha-particle and helion rms charge radius and the transition energies in highly-charged ions." Doctoral thesis, Sorbonne université, 2018. http://hdl.handle.net/10362/33710.
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Ce travail vise à contribuer à l’amélioration de notre connaissance de l’électrodynamique quantique des états liés, par des mesures de haute précision dans des états exotiques de la matière. Bien que notre connaissance de l’électrodynamique quantique des états liés et du problème relativiste à plusieurs corps aient fait des progrès importants ces dernières années, il reste des questions fondamentales dont la résolution nécessite d’augmenter le nombre et la précision des tests expérimentaux. La première partie de ce travail a été réalisée dans le cadre de l’expérience récente sur les ions muoniques d’hélium (μ4He+ et μ3He+) conduite par la collaboration CREMA. Cette expérience vise à fournir de nouvelles valeurs précises pour les rayons de charge moyens des noyaux des isotopes stables de l’hélium. Ces valeurs sont extraites de la mesure du déplacement de Lamb, c’est-à-dire, de la mesure de la différence d’énergie entre les États 2S − 2P. Une mesure des énergies de transition d’une précision d’au moins 50 ppm, permet de déterminer les rayons de charge des noyaux des isotopes d’hélium avec une incertitude de 0,03%, dix fois plus précise que les résultats précédents obtenus à partir de la diffusion d’électrons. La deuxième partie de ce travail a été de réaliser des mesures de haute précision de transitions de rayons X dans des ions fortement chargés, à l’aide d’un spectromètre à double cristal plan. Ces ions étaient produits dans le plasma d’une source d’ions de type ECRIS (electron-cyclotron resonance ion source). Le spectromètre utilisé est non seulement capable de fournir des mesures de haute précision, mais aussi des mesures sans référence à des énergies de transition théorique ou expérimentales. Quatre énergies de transition de n = 2 → n = 1 ont été mesurées pour des ions d’argon de trois états de charge différents, héliumoïde, lithiumoïde et berylliumoïde, avec une précision meilleure que 3 ppm. La largeur naturelle de chaque raie a également été obtenue expérimentalement. Les résultats trouvés sont en excellent accord avec les calculs théoriques les plus récentsThis work aims to provide insight on Bound-State Quantum-Electrodynamics (BSQED) by experimental fundamentals high-precision tests in exotic states of matter. Although BSQED and the relativistic many-body problem have been undergoing important progress, there are still some issues that require the increase of the number and accuracy of experimental fundamental tests. The first part of this work was done within the framework of the recent experiment in muonic helium ions (μ4He+ and μ3He+) by the CREMA collaboration. This experiment, aims to provide new accurate values for the root-mean-square (rms) charge radii of the helium isotopes nuclei that are extracted from the measurement of the Lamb Shift, i.e., the measurement of the energy difference between the 2S − 2P states. With the goal of measuring the transition energies with an accuracy of at least 50 ppm, the rms charge radii of the helium isotopes will be determined with an uncertainty of 0.03%, a factor of ten more precise than previous results obtained from electron scattering. The second part of this work aims the high-precision measurement of x-ray transitions in Highly-Charged Ions (HCI) using a Double-Crystal Spectrometer (DCS). These ions were produced in the plasma of an Electron-Cyclotron Resonance Ion Source (ECRIS). This kind of spectrometer is able not only to provide high-precision measurements but also reference-free measurements, without reference to any theoretical or experimental energy. Four transitions energies from n = 2 → n = 1 have been measured in an argon plasma in three different charge states, He-, Be- and Li-like, with an accuracy of better than 3 ppm. Besides the energies, the natural width of each transition has also been experimentally obtained. The obtained results are in excellent agreement with the most recent theoretical calculations
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Zivic, Nicolas. "Synthèse de naphtalimides et dicétopyrrolopyrroles originaux pour les photopolymérisations radicalaire et cationique dans des conditions d'irradiation douces." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0056/document.
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La photopolymérisation joue un rôle prééminent dans l'industrie comme en témoigne son nombre d'applications croissant dans des domaines classiques tels que les revêtements, les encres et les adhésifs mais aussi dans des domaines de haute technologie comme l’optoélectronique, l’imagerie laser, la stéréolithographie et la nanotechnologie. En effet, la photopolymérisation présente de nombreux avantages. C’est un processus rapide. Elle peut être réalisée à température ambiante et/ou sans solvant, permettant ainsi de limiter la formation de COV. Enfin, la photopolymérisation permet de réticuler dans des zones spatialement bien définies puisqu’elle se fait uniquement dans les zones exposées au rayonnement lumineux. Depuis 2011, le système photoamorçant fait l’objet d’intenses recherches pour développer des systèmes capables d’amorcer des réactions de polymérisation dans des conditions d’irradiation douces de manière à limiter les risques de toxicité et les coûts relatifs à l’utilisation de sources UV. Néanmoins, les systèmes reportés sont caractérisés par des réactivités modérées et peuvent difficilement rivaliser avec les systèmes UV actuels. Dans ce contexte, nous avons synthétisé une large librairie de molécules photosensibles construites à partir de chromophores naphtalimides ou dicétopyrrolopyrroles et capables d’amorcer une réaction de polymérisation dans des conditions d’irradiation douces. La fonctionnalisation ad hoc des chromophores et les propriétés photochimiques qui en découlent ont été exploitées pour développer des systèmes photoamorçants très performants capables d’absorber la lumière dans le domaine du proche UV ou du visible, émise par les LEDsPhotoinitiated polymerization has gained significant importance in industry as illustrated by the large number of applications of this technique in conventional areas such as coatings, inks, and adhesives but also high-tech domains, like optoelectronics, laser imaging, stereolithography, and nanotechnology. Indeed, photopolymerization presents several advantages such as decreasing the time of reaction, the possibility to be performed at room temperature or without solvents limiting the formation of volatile organic compounds. Moreover, the possibility to irradiate with high precision specific zones allows the spatial-control of the polymerization. Since 2011, photoinitiating systems able to initiate polymerization under soft light irradiation sources have been the subject of intense efforts to minimize the risks and the cost related to UV irradiation. However, even if some results are promising, the reported systems still present moderate reactivity and can hardly compete with actual UV systems. In this context, we have synthesized a large library of photosensitive molecules based on naphthalimide and dicetopyrrolopyrrole derivatives are able to initiate the polymerization under soft irradiation sources. The ad hoc functionalization of the chromophore and the consequent tuning of the photochemical properties have been used to develop highly efficient photoinitiating systems able to absorb into the near UV and visible spectra emitted by LED
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Verma, Abhinav [Verfasser]. "Development and application of a free energy force field for all atom protein folding / Abhinav Verma." Karlsruhe : Forschungszentrum Karlsruhe, 2007. http://d-nb.info/987646559/34.
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Sebetci, Ali. "The Structure, Energetics And Melting Behavior Of Free Platinum Clusters." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/1209980/index.pdf.
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The Voter and Chen version of an embedded-atom model, derived by fitting to experimental data of both the diatomic molecule and bulk platinum simultaneously, has been applied to study the locally stable structures, energetics, growth patterns and melting behavior of free platinum clusters in the size range of N=2-56 and N=75. Using the constant-energy molecular dynamics simulations, thermal and conjugate-gradient minimization techniques, the global minima and the other locally stable structures have been distinguished from those stationary structures that correspond to saddle points of the potential energy surface. The number of isomers and the probabilities of sampling different basins of attractions of the clusters from 2 to 22 atoms are obtained. The energy spectra of these clusters have been analyzed. The correlations between the total energy of the 75-atom cluster and the isomer number and the energy-spectrum-width of the isomers are investigated. The number of isomers of 75-atom cluster as a function of the total energy is presented, and the isomer probability distribution is discussed. The melting behavior of Pt_N clusters in the size range of N=12-14, 54-56, and N=75 has been studied. An atom-resolved analysis method including physical quantities such as the root-mean-square bond-length fluctuations and the coordination numbers for indivudual atoms as the functions of the temperature has been presented. Comparisons have been made with the results of previous calculations using electronic structure and empirical potential methods. The results show that the global minima have structures based on either octahedral, decahedral or icosahedral packing.
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Adash, Uma. "Synthetic and kinetic investigations into living free-radical polymerisation used in the preparation of polymer therapeutics." Thesis, University of Canterbury. Chemistry, 2006. http://hdl.handle.net/10092/1282.
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The aim of this work was to successfully prepare polymers of N-(2-hydroxypropyl)methacrylamide, (PHPMA) using controlled/"living" free-radical polymerisation technique. For this purpose, atom transfer radical polymerisation (ATRP) and reversible addition-fragmentation (chain) transfer (RAFT) polymerisation were used in preparation of a number of base polymers with the intention of quantitatively converting them into PHPMA. Both methods were applied under varying polymerisation conditions, and the kinetics of the systems investigated. Various rate constants were measured, while computer modelling of the experimental data allowed estimation of other kinetic parameters of interest. Investigations into solvent and ligand effects on the kinetics of ATRP of the activated ester methacryloyloxy succinimide (MAOS) and one of the archetypal methacrylate monomers, methyl methacrylate (MMA) were carried out. The method of RAFT was also employed in polymerisation of MAOS and a number of other monomers in the hope of finding the best synthetic precursor of PHPMA. Polymers of methacryloyl chloride (MAC) and p-nitrophenyl methacrylate (NPMA) were prepared, as well as the polymers of HPMA itself and N-isopropyl methacrylamide. Polymerisation of MMA by RAFT was also attempted in view of adding to current knowledge on the monomer's behaviour and the kinetic characteristics of its RAFT polymerisation. Preparation of PHPMA from PMAOS, PMAC and PNPMA was attempted. Successful preparation of PHPMA from the polymer of the acid chloride was achieved under mild reaction conditions, while displacement of N-hydroxysuccinimide groups of PMAOS resulted in unexpected modification of the polymer under the conditions used. Conversion of PNPMA into PHPMA was not achieved. At this stage these results suggest inadequacy of both PMAOS and PNPMA as reactive polymeric precursors.
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Ohl, de Mello Daniel [Verfasser], Gerhard [Akademischer Betreuer] Birkl, and Thomas [Akademischer Betreuer] Walther. "Rydberg interactions in a defect-free array of single-atom quantum systems / Daniel Ohl de Mello ; Gerhard Birkl, Thomas Walther." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2020. http://d-nb.info/1207075485/34.
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Velte, Ulrich [Verfasser]. "Orbit simulations and optical phase locking techniques for an atom interferometric test of the universality of free fall / Ulrich Velte." Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2018. http://d-nb.info/1171466757/34.
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Nicolaï, Adrien. "Conformational dynamics and free-energy landscape of human and E.coli Hsp70 chaperones from all-atom and coarse-grained numerical simulations." Thesis, Dijon, 2012. http://www.theses.fr/2012DIJOS060.
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Les protéines de choc thermique Hsp70 [70 kDa Heat Shock Protein] sont considérées comme des chaperons moléculaires très importants qui assistent au repliement des protéines naissantes ainsi qu’au repliement des protéines dénaturées en condition de stress dans le milieu intracellulaire. Les protéines Hsp70 sont présentes chez tous les organismes, tels que l’humain, la bactérie ou encore la levure et ont pour propriété d’avoir une séquence d’acides aminés hautement conservée entre les différentes espèces. [...] Ainsi la connaissance à l’échelle atomique des structures de la protéine hHsp70 dans ses conformations ouverte et fermée est un prérequis essentiel pour comprendre les interactions entre les deux domaines NBD et SBD de la protéine et pour élucider les mécanismes de communication inter-domaine. Cependant, il n’existe pas de structure expérimentale complète de la protéine hHsp70. Dans cette thèse, nous présentons les structures « tout-atome » des conformations ouverte et fermée de la protéine hHsp70, qui ont été modélisées par homologie à partir de la structure par diffraction des rayons X [DRX] de la protéine Hsp110 de la levure Sacharomyces cerevisae [dans la conformation ouverte] et à partir de la structure résolue par Résonance Magnétique Nucléaire [RMN] de la protéine Hsp70 de la bactérie E. coli [dans la conformation fermée]. Ces deux modèles structuraux de la protéine humaine Hsp70, dans les états ouvert et fermé, ont ensuite été relaxés par dynamique moléculaire non biaisée à la température de 300K en utilisant un solvant explicite sur une échelle de temps respectivement de 2.7 et 0.5 μs. L’hétérogénéité conformationelle de la protéine hHsp70 observée dans les simulations de dynamique moléculaire a été comparée à celle extraite d’expériences de resonance par transfert d’énergie entre fluorophores [FRET pour Förster resonance energy transfer] et de diffraction aux petits angles [SAXS pour Small Angle X-ray Scattering] effectuées sur des protéines homologues à hHsp70. [...] Une fois les structures 3D « tout-atome » résolues, la transition entre la conformation ouverte et la conformation fermée [et vice-versa] des protéines Hsp70 a été étudiée en utilisant deux techniques de simulations numériques : une analyse des modes normaux [Normal Mode Analysis où NMA] de la protéine Hsp70 dans chacune de ces deux conformations et une nouvelle méthode développée au cours de cette thèse, basée sur le concept de paysage d’énergie libre [Free-Energy Landscape où FEL]. [...] Cette étude a également permis d’identifier les sous-domaines et résidus clés qui apparaissent comme jouant un rôle important dans la dynamique conformationelle de la protéine Hsp70 dans l’approximation harmonique. Pour comprendre comment la fixation du nucléotide dans le domaine NBD peut engendrer un changement important de conformation de la protéine Hsp70, nous avons réalisé des simulations de dynamique moléculaire tout-atome non biaisée [sur une échelle de temps de 2 μs] de la protéine Hsp70 de la bactérie E. coli [appelée E. coli DnaK], dans trois conditions de nucléotides différentes [liée à l’ATP, liée à l’ADP et sans nucléotide]. [...] Finalement, en combinant l’analyse des modes normaux et du paysage d’énergie libre de la protéine Hsp70, nous avons pu établir une liste de résidus et de structures locales impliqués dans la dynamique conformationelle et dans les mécanismes de communication de la protéine hHsp70. La plupart de ces résidus ont été identifiés expérimentalement comme jouant un rôle crucial dans la communication entre les domaines NBD et le domaine SBD de protéines Hsp70 homologues. Notre étude nous a également permis d’identifier de nouveaux résidus clés. Ces nouveaux résidus pourraient être testés expérimentalement par mutagénèse et leurs positions pourraient être de nouvelles cibles pour la fixation d’inhibiteurs de fonctions biologiques de Hsp70, notamment dans le cas de tumeurs cancéreusesThe 70 kDa heat shock proteins [Hsp70s] are key molecular chaperones which assist in the correct folding of nascent proteins and refolding of proteins under stress conditions in the intracellular environment. Hsp70s are present in all organisms and are highly conserved between the different species. [...] The conformational dynamics between the two conformations is governed by the ATP binding, ATP hydrolysis and by nucleotide exchange through an allosteric mechanism which is not fully understood.Knowledge of the conformations of hHsp70 at the atomic level is central to understand the interactions between its NBD and SBD. However, no complete structure of hHsp70 is known. In the present thesis, we report two conformations of hHsp70, constructed by homology modeling from the yeast Saccharomyces cerevisiae co-chaperone protein Hsp110 [openconformation] and from the bacteria Escherichia coli Hsp70 [closed conformation]. The open and closed conformations of hHsp70 built by homology were relaxed by using unbiased all-atom molecular dynamics [MD] simulations at 300 K in explicit solvent on a timescale of 2.7 and 0.5 μs, respectively. The conformational heterogeneity of hHsp70 observed in MD simulations was comparedwith those extracted from single-molecule Forster resonance energy transfer [FRET]experiments and to small-angle X-ray scattering [SAXS] data of Hsp70 homologs. [...] In the present thesis, the transitions between the open and closed conformation of Hsp70s were studied by using two different computational methods: the Normal Mode Analysis [NMA] and a new method developed in the present thesis based on the Free-Energy Landscape [FEL] concept.[...] These collective modes provide a mechanistic representation of the communication between the NBD and the SBD and allow us to identify subdomains and residues that appear to have a critical role in the conformational dynamics of Hsp70s in the harmonicapproximation. Second, in order to understand how the nucleotide binding in the NBD of Hsp70 induces a conformational change of the whole protein, we performed unbiased all-atom MD simulations [2 μs] of E. coli Hsp70 [named E. Coli DnaK], in three different nucleotide-binding states [ATPbound,ADP-bound and nucleotide free]. [...] Finally, by combining the NMA and the FEL analysis, we established a list of the local structures and of the residues relevant for the conformational dynamics and for the interdomain communication in hHsp70. Most of these residues could be related to previous experimental evidences of their role in the interdomain communication between the NBD and SBD domains of Hsp70 homologs but other were never identified before. All the relevant residues found in MD could be tested experimentally by mutational analysis and could be crucial locations to dock small peptides and for the design of inhibitors for the cancer therapy
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Holmlund, Dick, and Patrik Mikaelsson. "Hur gammal kan en atom bli? : En beskrivning av naturvetenskapliga frågor och deras innehåll skickade till två populärvetenskapliga tidskrifter." Thesis, Linköpings universitet, Institutionen för beteendevetenskap och lärande, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-69083.
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Utvecklingen under de senaste decennierna visar att färre elever intresserar sig för naturvetenskapliga studier och många har svårt att se meningen med innehållet. Det finns en omfattande forskning som visar att det inte är naturvetenskapen i sig som eleverna avfärdar utan att det mer handlar om hur innehållet hanteras i skolan. Utanför skolan verkar många ta del av viktiga diskussioner kopplade till naturvetenskap och ställer bland annat frågor till olika medier där forskare bemöter och svarar på allmänhetens intresse. Detta spontana intresse undersöks i detta arbete med hjälp av innehållsanalys. Urvalet är hämtat från två populärvetenskapliga tidskrifter med omfattning av 1492 antal frågor. Frågorna är beskriva med huvud- och underkategorier och skildrar hur allmänhetens spontana intresse ser ut utifrån nordiska förhållanden. Resultaten visar att allmänheten har stort intresse för naturvetenskap. Biologi dominerar med stora intressen för zoologi och människan. Fysik är den näst populära kategorin där astronomi är den klart dominerande underkategorin. Kemi får minst antal frågor. Resultaten visar stor likhet med internationella studier och diskuteras i relation till dessa samt utifrån implikationer för lärares arbete med att möta elever i skolan.
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Dieudonne, Lucile. "Synthesis, characterisation and cytotoxicity evaluation of novel polymeric carriers for polymer therapeutics : from free radical polymerisation to atom transfer radical polymerisation." Thesis, Cardiff University, 2008. http://orca.cf.ac.uk/55722/.
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Polymer therapeutics include water-soluble polymers designed as carriers for drugs, proteins or DNA. Over the last two decades, they have found increasing clinical use against cancer and other diseases. A growing number is in clinical trials or on the market. However, the polymers used so far have limitations including heterogeneity in structure, molecular weight, polydispersity, drug carrying capacity, lack of control of architecture and biodegradability of polymer backbone. Therefore, the aim of this study was to synthesise and characterise a library of linear/star homo/copolymers with potential for further development as second-generation polymer therapeutics. Atom Transfer Radical Polymerisation (ATRP) and (chain transfer agent - CTA) Free Radical Polymerisation (FRP) techniques were used to synthesise water-soluble amine-based acrylamide and methacrylate homo/copolymers. Nuclear magnetic resonance, gel permeation chromatography, infrared and titration were used for characterisation. In vitro cytotoxicity studies of the polymers towards a murine melanoma cell line were performed using a cell viability evaluating colorimetric assay. Molecular weights (from 3,000 to 550,000 g.mol --1) were successfully adjusted by varying either the initiator or CTA to monomer ratios. Semitelechelic homo/copolymers with either carboxylic acid or hydroxyl termini were obtained using mercapto-based CTA. Either stable or degradable star-shaped poly(dimethylaminoethyl methacrylate) were obtained by copper-mediated ATRP using previously synthesised multifunctional initiators (4, 5 or 8 initiating moieties). A linear increase of predictable molecular weight with monomer conversion and narrow polydispersity (1.3) were observed. Amongst other molecular parameters systematically tested, the amount of cationic residues had the most striking effect on the cell viability. To conclude, conditions were optimised for the synthesis of a library of water- soluble amine-based homo/copolymers with different molecular weight, composition, charge density and architecture using several polymerisation techniques. Preliminary evaluation of polymer cytotoxicity associated to molecular parameters is vital for intelligently designing future, novel, and biocompatible polymeric carriers.
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Adamov, Minja Gemisic. "Measurements of local electric fields by doppler-free laser spectroscopy of hydrogen resonance lines." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2007. http://dx.doi.org/10.18452/15576.
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In dieser Arbeit wurde eine einfache laserspektroskopische Messmethode für lokale elektrische Feldstärken im Hinblick auf ihre Messmöglichkeiten und -grenzen untersucht. Als empfindliche optische Feldsensoren dienen dabei Wasserstoffatome, für die die Stark-Aufspaltung der Spektrallinien im elektrischen Feld wohl bekannt und exakt berechenbar ist. Die experimentellen Untersuchungen wurden an einer Niederdruck-Gaszelle durchgeführt, in der ein elektrisch geheizter Wolframdraht für thermische Dissoziation von Wasserstoffmolekülen sorgte. Die Wasserstoffatome wurden durch zwei gegenläufige Laserstrahlen Doppler-frei angeregt. Die Durchstimmung der schmalbandigen Laserstrahlung über den Wellenlängenbereich der Zwei-Photonen-Resonanz lieferte direkt das vom elektrischen Feld hervorgerufene Stark-Spektrum des angeregten Zustands. Weil die Methode im Gegensatz zu ähnlichen, erheblich aufwendigeren Verfahren nur die niedrigsten Wasserstoff-Energieniveaus benutzt, die mit Zwei-Photonen-Anregung direkt aus dem Grundzustand erreichbar sind, kommt sie mit einem einzigen Laser aus. Für das erste angeregte Niveau mit n = 2 wird Strahlung bei 243 nm benötigt, das nächsthöhere Niveau mit n = 3 erfordert 205 nm. Für n = 2 wurden Untersuchungen an Wasserstoff und Deuterium durchgeführt und Stark-Spektren mittels optogalvanischer Detektion gemessen. Schwerpunkt der Arbeit waren aber die Messungen an Wasserstoff für n = 3, bei denen zusätzlich Balmer-alpha-Fluoreszenz im Sichtbaren zur Detektion eingesetzt werden konnte. Bei elektrischen Feldern bis 200 V/cm wurden Stark-Spektren für drei verschiedene Polarisationszustände der Laserstrahlung aufgenommen. Als Ergebnis konnte jeweils ein Paar isolierter Stark-Komponenten in den Spektren identifiziert werden, dessen gut messbarer Frequenzabstand durch Vergleich mit theoretischen Werten die Bestimmung der elektrischen Feldstärke ermöglicht.A method for electric field measurements that observes the Stark spectra of the low excited levels n = 2 and n = 3 of atomic hydrogen has been explored in this work. As advantage these levels can be excited Doppler-free from the ground state by a single laser and the highly resolved Stark spectra are easy to understand and to be calculated. Good sensitivity of electric field measurements is achieved with specially designed solid state laser systems, which provide tuneable pulsed UV radiation with a high pulse peak-power and a narrow bandwidth needed for Doppler-free two-photon excitation. Using hydrogen and deuterium the Stark spectra of the n = 2 level are detected as optogalvanic signal. For three different cases of laser polarization the n = 3 spectra of hydrogen are measured simultaneously with optogalvanic and laser induced Balmer alpha fluorescence detection. Electric fields down to 200 V/cm can be determined from the Stark spectra of n = 2 level, while the spectra of n = 3 level enable measurements of electric fields as small as 50 V/cm in each of the three cases of laser polarization.
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Nicolas, Adrien. "Optical quantum memories with cold atomic ensembles : a free space implementation for multimode storage, or a nanofiber-based one for high collection efficiency." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066494/document.
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Nous étudions expérimentalement deux mémoires quantiques pour la lumière utilisant la transparence électromagnétiquement induite (EIT) dans des nuages froids de césium.Nous expliquons la pertinence des mémoires quantiques pour le développement de réseaux quantiques à longue distance, et décrivons la théorie de l’EIT en soulignant les paramètres essentiels pour l’implémentation de mémoires quantiques.Notre premier cas d’étude est un piège magnéto-optique en espace libre. Notre principal résultat est la démonstration du caractère multimode de ce système pour le stockage quantique de la lumière. Pour cela, nous utilisons des faisceaux de Laguerre-Gauss (LG), porteurs de moment angulaire orbital (OAM). Dans une première étape, nous avons montré que l’état de moment orbital d’impulsions lumineuses en régime de photons uniques est préservé lors du stockage dans la mémoire. Ensuite, nous avons implémenté un bit quantique comme une superposition de modes LG ayant des hélicités opposées. Nous avons développé un système original pour mesurer ces bits quantiques qui nous a permis de caractériser l’action de la mémoire. Nous avons ainsi pu montrer que le stockage quantique de ces bits quantiques.Le second système, également un nuage d’atomes froids, a la particularité que les atomes sont piégés optiquement autour d’un nano-guide d’onde. Ce design innovant permet une plus grande interaction entre lumière et matière, et facilite l’interfaçage des photons dans et hors de la mémoire. Nous décrivons la construction de ce dispositif et les premiers pas vers son utilisation en tant que mémoire quantiqueWe present an experimental study of two optical quantum memory systems based on electromagnetically induced transparency (EIT) in cold cesium atoms.We explain the relevance of quantum memories for the development of large-scale quantum networks, we give a comprehensive theory of the EIT phenomenon and underline the role of relevant parameters regarding the implementation of quantum memories.The first system under study is prepared in a free-space magneto-optical trap. The main result of this thesis is the demonstration of the spatial multimode capability of this system at the quantum level. For this, we used Laguerre-Gaussian (LG) light beams, i.e. beams possessing a non-zero value of orbital angular momentum (OAM). In a first step, we showed that the orbital angular momentum of stored light pulses is preserved by the memory, deep in the single photon regime. In a second step, we encoded information in the orbital angular momentum state of a weak light pulse and defined a qubit using two LG beams of opposite helicities. We developed an original setup for the measurement of this OAM qubit and used it to characterize the action of the memory during the storage of such a light pulse. Our results show that the memory performs the quantum storage of such a qubit.The second system under study, also a cloud of cold atoms, has the specificity that the atoms are trapped optically in the vicinity of a nano-waveguide. This innovative design ensures a higher light-matter interaction and facilitates the interfacing of photons into and out of the memory. We describe the building of this setup and the first steps towards quantum memory implementations
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Buch, Mundó Ignasi 1984. "Investigation of protein-ligand interactions using high-throughput all-atom molecular dynamics simulations." Doctoral thesis, Universitat Pompeu Fabra, 2012. http://hdl.handle.net/10803/101407.
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Investigation of protein-ligand interactions has been a long-standing application for molecular dynamics (MD) simulations given its importance to drug design. However, relevant timescales for biomolecular motions are orders of magnitude longer than the commonly accessed simulation times. Adequate sampling of biomolecular phase-space has therefore been a major challenge in computational modeling that has limited its applicability. The primary objective for this thesis has been the brute-force simulation of costly protein-ligand binding modeling experiments on a large computing infrastructure. We have built and developed GPUGRID: a peta-scale distributed computing infrastructure for high-throughput MD simulations. We have used GPUGRID for the calculation of protein-ligand binding free energies as well as for the reconstruction of binding processes through unguided ligand binding simulations. The promising results presented herein, may have set the grounds for future applications of high-throughput MD simulations to drug discovery programs.
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Xavier, Jean Frederick Brito. "O uso de metadados para a preservação digital no Arquivo da Marinha: a implementação do Software ICA-AToM." Insitituto Brasileiro de Informação em Ciência e Tecnologia, 2014. http://ridi.ibict.br/handle/123456789/838.
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JEAN FREDERICK BRITO XAVIER.pdf: 1785438 bytes, checksum: f17977271213d535cec1a6521da9380b (MD5)Made available in DSpace on 2016-06-23T17:19:42Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) JEAN FREDERICK BRITO XAVIER.pdf: 1785438 bytes, checksum: f17977271213d535cec1a6521da9380b (MD5) Previous issue date: 2014-09-28
O presente trabalho investiga a aplicação do software livre ICA-AToM em um dos maiores Arquivos brasileiros: o Arquivo da Marinha. Este software foi arquitetado para funcionar na internet e é baseado em normas arquivísticas internacionais, como a Norma Internacional de Registro de Autoridade Arquivística para Entidades Coletivas, Pessoas e Famílias ISAAR (CPF), a Norma Geral Internacional de Descrição Arquivística - ISAD(G) e a Norma Internacional para Descrição de Instituições com Acervo Arquivístico ISDIAH. Apesar de ter sido criado com base em normas indicadas pelo Conselho Internacional de Arquivos – CIA, esse trabalho questiona até que ponto o ICA-AToM atende ao processo de descrição documental do Arquivo da Marinha. Para medir a eficiência deste sofware, no que diz respeito a garantir o acesso da documentação do Arquivo da Marinha, é realizada, nas análises, uma comparação dos metadados utilizados na versão do ICA-AToM instalada no Arquivo da Marinha com os metadados estabelecidos pela Norma Brasileira Arquivística de Descrição – NOBRADE e pelo Modelo de Requisitos para Sistemas Informatizados de Gestão Arquivística de Documentos e-ARQ Brasil. Buscou-se entender cada um dos metadados especificados nestas normas e relacioná-los com as possíveis vantagens de uso dos mesmos. O resultado obtido nestas comparações foi a constatação de um conjunto de metadados e sugestões para que o Arquivo da Marinha possa otimizar o uso deste software e da sua descrição arquivística, que é fundamental na tarefa de garantir o acesso e a preservação do seu acervo.
The present work investigates the aplication of the free software Ica atom in one of the biggest brazilian archives: the Marine Archive. This software was created to work in the internet and based in archivistic international rules, like the international rule of register of archivistic authority to group entities, people and families ISAAR (CPF), the international rule of archivistic description ISAD(G) and the International standard for describing institutions with archival holdings-ISDIAH. Despite of being created based on rules indicated by the international Council of Archives - CIA, this work questions until what point the ICA-AToM answers to the process of documental description of the Marine Archive. To mesure the eficiency of this software, in order to garantee the access to the documents of the Marine Archive, a comparison of the metadatas used in the version of ICA-AToM, situated in the Marine Archive with the metadatas stablished by the brazilian archivistic rule of description (NOBRADE), is done in the analysis and by the “modelo de requisitos para sistemas informatizados de gestão arquivistica de documentos” - e-ARQ Brasil. There was an attempt to understand each one of the metadatas especyfied in these rules and relate them to the possible advantages of their use. The result of these comparisons was the realization of a group of metadatas and sugestions for that Marine Archive can optimize the use of this software and of its archivistic description, which is fundamental in the ensuring task the access and preservation of its collection.
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Bakioglu, Levent. "Polymerization And Characterization Of Poly(ethyl Methacrylate)." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/1081363/index.pdf.
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In this study, ethyl methacrylate was polymerized by free radical polymerization at 600C, 700C, 800C at open atmosphereatom transfer radical polymerization, (ATRP), at 800C in vacuum and in gamma irradiation in vacuum. The polymer obtained was white, hard material. The kinetic curves for free radical polymerization and ATRP by gamma radiation were S-type. However, the curve for polymerization by gamma irradiation raises more smoothly. For ATRP by thermal initiation gives a lineer change of conversion with time. It was observed that the molecular weight can be controlled and low molecular weight polymer could be obtained by ATRP method. The characterization of polymers were made by FTIR, DSC, 1H and 13C NMR techniques.
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Hetti, Mimi. "Synthesis and Characterization of Polymeric Magnetic Nanocomposites for Damage-Free Structural Health Monitoring of High Performance Composites." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-211082.
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The poly(glycidyl methacrylate)-modified magnetite nanoparticles, Fe3O4-PGMA NPs, were investigated and applied in nondestructive flaw detection of polymeric materials in this research. The Fe3O4 endowed magnetic property to the materials for flaw detection while the PGMA promoted colloidal stability and prevented particle aggregation. The magnetite nanoparticles (Fe3O4 NPs) were successfully synthesized by coprecipitation and then surface-modified with PGMA to form PGMA-modified Fe3O4 NPs by both grafting-from and grafting-to approaches. For the grafting-from approach, the Fe3O4 NPs were surface-functionalized with α-bromo isobutyryl bromide (BIBB) to form BIB-modified Fe3O4 NPs (Fe3O4-BIB NPs) with covalent linkage. The resultant Fe3O4-BIB NPs were used as surface-initiators to grow PGMA by surface-initiated atom transfer radical polymerization (SI-ATRP). For the grafting-to approach, the Fe3O4 NP were surface-functionalized with (3-mercaptopropyl)triethoxysilane (MCTES) to form MCTES-modified Fe3O4 NPs (Fe3O4-MCTES NPs). The PGMA with Br-end group was pre-synthesized by ATRP and then was grafted to the surface of the Fe3O4-MCTES NPs by coupling reaction.
Both bare and modified Fe3O4 NPs exhibited superparamagnetism and the existence of iron oxide in the form of Fe3O4 was confirmed. The particle size of individual Fe3O4 NPs was about 8 – 24 nm but they aggregated to form clusters. The PGMA-modified NPs formed stable dispersion in chloroform and had larger cluster sizes than the unmodified ones because of the PGMA polymer layer. However, the uniformity of the NP clusters could be improved with PGMA surface grafting. The PGMA surface layer of the grafting-from (Fe3O4-gf-PGMA) NPs was thin and dense while that of the grafting-to (Fe3O4-gt-PGMA) NPs was thick and loose. The hydrodynamic diameters (Zave) of Fe3O4-gf-PGMA NP clusters could be controlled between 176 to 643 nm, dependent on the PGMA contents and reaction conditions. During SI-ATRP, side reactions happened and caused NP aggregation as well as increase of size of NP clusters. However, the aggregation has been minimized through optimization of reaction conditions. Oppositely, Zave values of Fe3O4-gt-PGMA NPs had little variation of about 120 – 190 nm. And the PGMA content of the Fe3O4-gt-PGMA NPs was limited to 12.5% because of the spatial hindrance during grafting process.
The saturation magnetization (Ms) of the unmodified Fe3O4 NPs was about 77 emu/g, while those of the grafting-from and grafting-to Fe3O4-PGMA NPs were 50 – 66 emu/g and 63 – 70 emu/g, respectively. For Fe3O4-PGMA NPs with similar Fe3O4 contents, the grafting-to NPs had slightly higher Ms than the grafting-from counterparts. In addition, the Ms of both kinds of the Fe3O4-PGMA NPs with higher Fe3O4 content (> 87%) were also higher than that of the fluidMAG-Amine, the commercially available amine-modified MNPs. Besides, both kinds of Fe3O4-PGMA NPs also had much higher Fe3O4 contents and Ms values than most of the reported PGMA-modified MNPs.
The magnetic epoxy nanocomposites (MENCs) were prepared by blending the modified Fe3O4 NPs into bisphenol A diglycidyl ether (BADGE)-based epoxy system and the distributions of both kinds of the PGMA-modified NPs were much better than that of the oleic acid-modified Fe3O4 NPs. Similar to the NPs, the MENCs also exhibited superparamagnetism. By cross-section TEM observation, the grafting-to Fe3O4-PGMA NPs formed more homogeneous distributions with smaller cluster size than the grafting-from counterparts and gave higher Ms of the MENCs. Nondestructive flaw detection of surface and sub-surface defects could be successfully achieved by brightness contrast of images given through eddy current testing (ET) method, which is firstly reported. The mechanical properties of the materials were influenced very slightly when 2.5% or lower Fe3O4-gt-PGMA NPs were present while the presence of the Fe3O4-gf-PGMA NPs (1 – 2.5 %) gave mild improvement of the storage modulus and increase of the glass-rubber transition temperature(Tg) of the MENCs. Furthermore, the Fe3O4-PGMA NPs could be evenly coated onto the functionalized ultra-high molecular weight poly(ethylene) (UHMWPE) textiles. The Fe3O4-gt-PGMA NPs were coated on the textile in order to prepare NP-coated textile-reinforced composite. Preliminary result of ET measurement showed that the Fe3O4-gt-PGMA NPs coated on the textiles could visualize the structure of the textile hidden inside and their relative depth. Accordingly, the incorporation of MNPs to polymers opens a new pathway of damage-free structural health monitoring of polymeric materials.
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Eliah, Dawod Ibrahim. "Structural integrity of highly ionized peptides." Thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-387886.
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In order to understand the behaviour and function of proteins, their three dimensional structure needs to be known. Determination of macro-molecules’ structures is done using X-ray diffraction or electron microscopy, where the resulting diffraction pattern is used for molecular reconstruction. These methods are however limited by radiation damage.The aim of this work is to study radiation damage of peptides in proteins using computer simulations. Increased understanding of the atomic and molecular dynamics can contribute to an improvement of the method ofimaging biological molecules. To be able to describe the processes that take place as accurately as possible, the problem must treated quantum mechanically.Thus, the simulations are performed with molecular dynamics based on first principles. In order to capture the dynamics of the excited states of the molecule when exposed to X-rays, time-dependent density functional theory with delta self-consistent field is used. These simulations are compared to ground state simulations. The results of the thesis conclude that the excited and ground state simulations result in differences in the dynamics, which are most pronounced for lager molecules.
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Rost, Ulrike. "Organisation and Recognition of Artificial Transmembrane Peptides." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2016. http://hdl.handle.net/11858/00-1735-0000-002B-7CA6-D.
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Nilson, Katharina. "Phthalocyanines on Surfaces : Monolayers, Films and Alkali Modified Structures." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8209.
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Chou, Chi-Hui, and 周繼暉. "Subcycle Dynamics of Photon Emission Spectra of Rare Gases Atoms Excited by Attosecond Pulses and Driven by Near-Infrared Laser Field:Self-Interaction-Free Time-Dependent Density-Functional-Theory Approach." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/14198550818925137426.
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碩士國立臺灣大學
應用物理所
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We present an ab initio method to study the sub-cycle dynamics of hydrogen, helium and neon atoms in near-infrared(NIR) laser fields subject to excitation by a single extreme ultraviolet attosecond pulse(SAP). We extended the self-interaction-free time-dependent density functional theory(TD-KLI-SIC) to describe multi-electron system and solve the time-dependent Kohn-Sham equations by time-dependent generalized pseudospectral(TDGPS) method. We calculated the photon emission spectra and population of several excited states as the function of the time delay between the NIR pulse and SAP. The phenomena can be explain by two-photon absorption.
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Ohl, de Mello Daniel. "Rydberg interactions in a defect-free array of single-atom quantum systems." Phd thesis, 2020. https://tuprints.ulb.tu-darmstadt.de/11504/1/Dissertation_Final_Ohl_de_Mello.pdf.
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Neutral atoms trapped and manipulated by laser light provide experimentally well accessible quantum systems allowing for a high degree of control over external and internal degrees of freedom. Arrays of dipole traps in which the atoms are confined individually in a configurable geometry constitute a versatile platform for quantum simulation and information applications.
By exciting these atoms into Rydberg states, interactions of variable strength and range can be introduced into the system, allowing for the implementation of entangling gate operations or spin Hamiltonians. A crucial requirement for these schemes to function in a reliable way is the
ability to create defect-free arrays of single atoms. This is generally a challenge in these types of systems, as common atom loading schemes are limited to roughly 50% probability of filling each site.
In this work, a technique for the rearrangement of atoms within a scalable architecture based on micro-optical lens arrays was developed and implemented, resulting in the creation of uniformly filled regions containing more than 100 atoms, which represent the largest defect-free structures
realized so far in systems of this kind. This was accomplished by filling the empty traps in a pre-defined pattern with an atom one by one using an optical tweezer. Thus, structures with up to 5 x 5 atoms could be rendered defect-free in more than 99% of attempts. Although the success
rate drops below unity for larger clusters, a value of 3.1% for a 100-atom structure is still viable for experiments working with post-selection methods. The filling fraction of even the largest examined structures was observed to be higher than 88%, surpassing common loading schemes by a significant margin. The measurements presented in this thesis build on a region of the array containing 361 sites, being limited by available laser power. In contrast, the addressable range of the optical tweezer includes more than 1500 sites and microlens arrays with up to a million lenses are commercially available.
By implementing coherent Rydberg excitation of this assembled atom array, significant progress toward a universal quantum computer or flexible quantum simulator has been made. Using a two-photon excitation scheme, coherent dynamics between the ground and Rydberg state could be observed simultaneously in a 5 x 5 region of the array, with two-photon Rabi frequencies on the order of Omega = 2Pi x 500kHz measured for a Rydberg laser beam waist of w_0,B = 18.7(10) µm. The choice of an appropriate Rydberg state and interatomic spacing led to the presence of strong nearest-neighbor interactions and allowed for the demonstration of the Rydberg blockade effect by observing a collective enhancement of the Rabi frequency consistent with the expected scaling ~ sqrt(N) as well as the suppression of multiple excitations. This mechanism represents the fundamental constituent of a two-qubit gate operation.
The architecture introduced in this work offers a scalability unique among quantum simulation platforms and the presented results underpin its potential to propel the atom-optical approach for quantum information processing beyond the threshold of quantum supremacy. Different approaches for scaling up the system have been explored, indicating that defect-free structures of more than 1000 atoms are within range with feasible experimental improvements. Through a detailed analysis of the factors limiting the coherence of the observed dynamics, strategies for
future experimental improvements have been developed. Among these, increasing the coupling strength to the Rydberg state into the megahertz regime by increasing laser power and implementing single-site addressing represents the most straight-forward and promising approach.
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Goban, Akihisa. "Strong Atom-Light Interactions Along Nanostructures: Transition from Free-space to Nanophotonic Interfaces." Thesis, 2015. https://thesis.library.caltech.edu/8872/1/AGoban_thesis.pdf.
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An exciting frontier in quantum information science is the integration of otherwise "simple" quantum elements into complex quantum networks. The laboratory realization of even small quantum networks enables the exploration of physical systems that have not heretofore existed in the natural world. Within this context, there is active research to achieve nanoscale quantum optical circuits, for which atoms are trapped near nano-scopic dielectric structures and "wired" together by photons propagating through the circuit elements. Single atoms and atomic ensembles endow quantum functionality for otherwise linear optical circuits and thereby enable the capability of building quantum networks component by component. Toward these goals, we have experimentally investigated three different systems, from conventional to rather exotic systems : free-space atomic ensembles, optical nano fibers, and photonics crystal waveguides. First, we demonstrate measurement-induced quadripartite entanglement among four quantum memories. Next, following the landmark realization of a nanofiber trap, we demonstrate the implementation of a state-insensitive, compensated nanofiber trap. Finally, we reach more exotic systems based on photonics crystal devices. Beyond conventional topologies of resonators and waveguides, new opportunities emerge from the powerful capabilities of dispersion and modal engineering in photonic crystal waveguides. We have implemented an integrated optical circuit with a photonics crystal waveguide capable of both trapping and interfacing atoms with guided photons, and have observed the collective effect, superradiance, mediated by the guided photons. These advances provide an important capability for engineered light-matter interactions, enabling explorations of novel quantum transport and quantum many-body phenomena.