| 1. |
- Vaz da Cruz, Vinicius
(author)
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Quantum Nuclear Dynamics in Resonant X-ray Scattering of Gas-Phase and Liquid Systems
- 2018
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Doctoral thesis (other academic/artistic)abstract
- This thesis focuses on the role of the nuclear degrees of freedom in X-ray induced molecular processes. An important part of it is devoted to establishing theoretical principles to model and interpret high-resolution resonant X-ray scattering experiments in gases and liquids. Our investigations address the resonant inelastic x-ray scattering (RIXS) of H2O(g), H2O(l) and CH3OH(g) and Auger emission induced by hard X-rays in CO(g). The simulations for gas-phase systems are based on a multi-mode wave packet formalism and on potential energy surfaces computed with multi-configurational approaches.For liquid systems, we propose a classical/quantum formalism for simulating RIXS based on a combination of ab initio molecular dynamics, density functional theory calculations and quantum nuclear wave packet propagation. The developed model is able to reproduce the experimental observation of shortening of the vibrational progression in H2O(l).We show that electronically-elastic RIXS has an intrinsic capability to map the potential energy surface and to carry out vibrational analysis of the electronic ground state in free molecules as well as liquids. For gas-phase water, we see that the landscape of different core-excited states cause the nuclear wave packet to be localized along specific directions thus allowing to reconstruct one-dimensional potential energy curves. For liquid water, we propose a model for deriving, from experiment, confidence intervals for the molecular potential energy curves along the OH bonds, which are determined by the local arrangement of the hydrogen bond network.We also investigate the role of ultra-fast rotations induced by photoionization by hard X-rays. In this case, the ejection of a fast photoelectron results in an ultra-fast rotational motion of the molecule, which combined with the anisotropy of the Auger process causes the spectral profile to be split due to a dynamical Doppler effect.
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| 2. |
- Bergersen, Henrik, 1978-
(author)
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Free Neutral Clusters and Liquids Studied by Electron Spectroscopy and Lineshape Modeling
- 2008
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Doctoral thesis (other academic/artistic)abstract
- The electronic and geometrical structure of free neutral clusters and liquids have been studied using synchrotron-radiation based photoelectron and Auger electron spectroscopy in combination with lineshape modeling. A novel experimental setup has been developed for studies of liquids, based on the liquid microjet technique. Theoretical lineshapes have been computed using both classical (molecular dynamics) and quantum mechanical (mainly density functional theory) methods.Clusters are finite ensembles of atoms or molecules, ranging in size from a few to several thousand atoms. Apart from being fundamentally interesting, clusters are also promising as building blocks for nano-technology. In this thesis results are presented for rare-gas and molecular clusters, ranging from weakly van-deer-Waals bonded to hydrogen bonded. It is shown that the combination of core-level photoelectron spectroscopy (XPS) and lineshape modeling can be used to estimate the sizes of clusters. A model for treating the effect of inter-molecular nuclear relaxation upon ionization is proposed. The structure of single-component molecular clusters are investigated by molecular dynamics simulations, validated against XPS data. Finally, the radial structure of a two-component molecular cluster is investigated by XPS.Liquids have been studied for centuries, but still many questions remain regarding the microscopic properties. With the recent development of the liquid microjet technique, new insight into the atomic structure can be obtained. In this thesis we study aqueous solutions using photoelectron and Auger electron spectroscopy (AES). We investigate the structure of surface active molecules by XPS, study the Auger decay after core-level ionization in aqueous potassium chloride (KCl), and follow the changes in molecular structure of glycine as a function of pH.
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| 3. |
- Deglaire, Paul, 1978-
(author)
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Analytical Aerodynamic Simulation Tools for Vertical Axis Wind Turbines
- 2010
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Doctoral thesis (other academic/artistic)abstract
- Wind power is a renewable energy source that is today the fastest growing solution to reduce CO2 emissions in the electric energy mix. Upwind horizontal axis wind turbine with three blades has been the preferred technical choice for more than two decades. This horizontal axis concept is today widely leading the market. The current PhD thesis will cover an alternative type of wind turbine with straight blades and rotating along the vertical axis. A brief overview of the main differences between the horizontal and vertical axis concept has been made. However the main focus of this thesis is the aerodynamics of the wind turbine blades. Making aerodynamically efficient turbines starts with efficient blades. Making efficient blades requires a good understanding of the physical phenomena and effective simulations tools to model them. The specific aerodynamics for straight bladed vertical axis turbine flow are reviewed together with the standard aerodynamic simulations tools that have been used in the past by blade and rotor designer. A reasonably fast (regarding computer power) and accurate (regarding comparison with experimental results) simulation method was still lacking in the field prior to the current work. This thesis aims at designing such a method. Analytical methods can be used to model complex flow if the geometry is simple. Therefore, a conformal mapping method is derived to transform any set of section into a set of standard circles. Then analytical procedures are generalized to simulate moving multibody sections in the complex vertical flows and forces experienced by the blades. Finally the fast semi analytical aerodynamic algorithm boosted by fast multipole methods to handle high number of vortices is coupled with a simple structural model of the rotor to investigate potential aeroelastic instabilities. Together with these advanced simulation tools, a standard double multiple streamtube model has been developed and used to design several straight bladed rotor ranging from 2 kW to 20 kW.
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