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Three-dimensional simulations of the ozone layer and atmospheric dynamics of earth-like habitable planets
Full text linkThis thesis investigates how the atmospheric circulation and ozone distribution of a planet with the size, the mass, the continental distribution and topography, the oceans, and the atmospheric composition and circulation of the present day Earth (Earth-like planet) is altered by local and global radiative forcing changes using three-dimensional simulations. These simulations are generated using the coupled 3D chemistry-climate model CESM1(WACCM), which incorporates the entire atmosphere up to an altitude of 140 km, as well as parametrizations for the full atmospheric chemistry, photochemistry, cloud microphysics and small-scale gravity wave flux. These features allow for a realistic simulation of the composition and dynamics of the Earth's atmosphere.
The investigation is composed of three studies. In the first study, the effects in the lower tropospheric dynamics generated by a local radiative forcing change on the present day Earth are investigated. The forcing change is implemented by changing the local soil colour and therefore the local albedo. In order to isolate the generated perturbation from the background waves, a small-scale perturbation analysis is performed for the first 5 days of the simulation. The soil colour change generates an upwards propagating convective perturbation, which induces a radially propagating circular wave at an altitude of 2 km. This wave has a mean wave velocity of (v) = 200 ± 50 m/s, a mean horizontal wavelength (λ) = 3000 ± 500 km and a mean wave period (p) = 4 ± 1 h. In addition to this wave, a secondary wave is also generated over the tropical Amazon convection zone when the primary wave collides with it. The secondary wave has a mean wave velocity (v) = 220± 40 m/s, a mean horizontal wavelength (λ) = 2600 ± 600 km and a mean wave period (p) = 3 ± 1 h.
The second study expands the scope of the first study by investigating how a global radiative forcing change affects the atmospheric circulation and ozone distribution of an Earth-like planet orbiting a Sun-like star. In this study, the forcing change is implemented by tidally locking the planet. The simulations reveal that, when the full photochemistry and atmospheric dynamics are included, the planet's middle atmosphere adjusts to the new conditions within a relatively short time (roughly 80 days from the start of the simulation) and its atmospheric circulation and ozone distribution are altered.
The Brewer-Dobson circulation is replaced by a day side upwelling and a night side downwelling. The total ozone content of the tidally locked planet is reduced by
19.3% compared to the Earth due to radiation and transport changes. Specifically, the total ozone content mean is reduced by 23.21% on the day side and by 15.52% on the night side. The middle stratospheric ozone accumulates on the day side of the planet resulting in a day-night variation of 40%. In comparison, the Earth's daynight variation is only 2%. The lower stratospheric ozone is mainly influenced by the altered circulation and is characterised by enhanced night side zone and depleted day side regions. The planet's mesospheric ozone is similar to the Earth's mesospheric ozone distribution, with decreased ozone on the day side and enhanced ozone on the night side. For a distant observer, the planet's total ozone content will vary up to 23% during its revolution around its parent star.
Finally, the third study is an extension of the second study. It investigates, in more detail, the 3D atmospheric circulation of a tidally locked planet. An intercomparison with the fast rotating Earth is performed and the effects of the sea surface temperature (SST) on the middle atmosphere of the tidally locked planet are simulated and analysed. For this study, two extreme SSTs are used: a present day Earth SST and a tidally locked aquaplanet SST. The simulation shows that the SST has a limited influence on the middle atmosphere. The warmer present day Earth SST generated, on average, a lower tropospheric heating of 3.7 K, an upper tropospheric cooling of 4 K, a lower stratospheric heating of 3.8 K, a lower mesospheric cooling of 1.13 K and an upper mesospheric heating of 4.3 K. The lower stratospheric heating is possibly generated by the increased infrared radiation flux from the warmer present day Earth SST surface, as the lower stratospheric ozone will absorb the increased infrared radiation at 9.6 μm. The SST change has no significant influence on the primary ozone layer, while the warmer SST leads to a strong increase of the secondary ozone layer. The tropospheric and stratospheric results are in agreement with past studies of the influence of SST variability on the Earth's troposphere and stratosphere. The lower mesospheric cooling is consistent with increased mesospheric wave-breaking due to the warmer present day Earth SST. Both simulations are characterised by an upwelling on the day side and downwelling on the night side, while the stratospheric and mesospheric circulation is only weakly influenced by the underlying SST. Generally, the reduced Coriolis force of the tidally locked planet leads to enhanced meridional mixing and consequently to a relatively isothermal temperature distribution of the middle atmosphere. The occurrence of large-scale vortices and variable jet streams depends, to some extent, on the SST distribution
Investigation of robotics-assisted tilt table technology for cardiopulmonary exercise testing in stroke patients
Full text linkDue to the lack of exercise testing devices that can be employed in stroke patients with severe disability, the aim of this PhD research was to investigate the clinical feasibility of using a robotics-assisted tilt table (RATT) as a method for cardiopulmonary exercise testing (CPET) and exercise training in stroke patients. For this purpose, the RATT was augmented with force sensors, a visual feedback system and a work rate calculation algorithm. As the RATT had not been used previously for CPET, the first phase of this project focused on a feasibility study in 11 healthy able-bodied subjects. The results demonstrated substantial cardiopulmonary responses, no complications were found, and the method was deemed feasible. The second phase was to analyse validity and test-retest reliability of the primary CPET parameters obtained from the RATT in 18 healthy able-bodied subjects and to compare the outcomes to those obtained from standard exercise testing devices (a cycle ergometer and a treadmill). The results demonstrated that peak oxygen uptake (V'O2peak) and oxygen uptake at the submaximal exercise thresholds on the RATT were ̴20% lower than for the cycle ergometer and ̴30% lower than on the treadmill. A very high correlation was found between the RATT vs the cycle ergometer V'O2peak and the RATT vs the treadmill V'O2peak. Test-retest reliability of CPET parameters obtained from the RATT were similarly high to those for standard exercise testing devices. These findings suggested that the RATT is a valid and reliable device for CPET and that it has potential to be used in severely impaired patients. Thus, the third phase was to investigate using the RATT for CPET and exercise training in 8 severely disabled stroke patients. The method was technically implementable, well tolerated by the patients, and substantial cardiopulmonary responses were observed. Additionally, all patients could exercise at the recommended training intensity for 10 min bouts. Finally, an investigation of test-retest reliability and four-week changes in cardiopulmonary fitness was carried out in 17 stroke patients with various degrees of disability. Good to excellent test-retest reliability and repeatability were found for the main CPET variables. There was no significant difference in most CPET parameters over four weeks. In conclusion, based on the demonstrated validity, reliability and repeatability, the RATT was found to be a feasible and appropriate alternative exercise testing and training device for patients who have limitations for use of standard devices
Bildungserfolg trotz Migrationshintergrund: Ressourcen von bildungserfolgreichen jungen Erwachsenen mit Migrationshintergrund in der Schweiz
Full text linkDie vorliegende Arbeit beschäftigt sich mit den familiären, schulischen, sozialen und individuellen Ressourcen, die aus Sicht von bildungserfolgreichen Migrantinnen und Migranten zum Erreichen der Hochschul- bzw. Fachhochschulreife beigetragen haben. Auf dem Hintergrund der Schulleistungsforschung, psychologischer Modelle zur Erklärung von Bildungsentscheidungen und dem Resilienzkonzept wurden 41 Personen im Rahmen von leitfadengestützten problemzentrierten Interviews zu ihrer Bildungsbiografie befragt. Die Datenanalyse der transkribierten Interviews erfolgte im Rahmen einer inhaltlich strukturierenden qualitativen Inhaltsanalyse. Unter Einbezug von soziodemografischen Merkmalen der Stichprobe (Geschlecht, HISEI, ISCED, Migrationsstatus und besuchter Schultyp) wurden die qualitativen Ergebnisse weitergehenden Analysen zugeführt. Für den Bereich der Familie stellen sich die Orientierung an der Akkulturationsstrategie Integration, hohe Bildungsaspirationen der Eltern gekoppelt mit ausgeprägten schulischen Unterstützungsleistungen sowie vorhandene familiäre Vorbilder wie ältere Geschwister als zentrale Ressourcen für den Bildungserfolg der Befragten heraus. Im Bereich der schulischen Ressourcen schildern die Befragten gut durchmischte Klassen, ein positives Klassenklima sowie ein vertrauensvolles Verhältnis zu den Lehrpersonen als förderlich für ihre erfolgreiche Bildungsbiografie. Eine aktive Freizeitgestaltung im Sinne der Mitgliedschaft in Vereinen und dem Kontakt mit der einheimischen Bevölkerung sowie Kontakte mit anderen Personen mit Migrationshintergrund werden im Bereich der sozialen Ressourcen herausgestrichen. Hinsichtlich individueller Ressourcen verfügen die befragten Personen über gute Deutschkenntnisse, lernen primär aus Interesse an der Sache und weisen ein positives akademisches Selbstkonzept auf. Insgesamt wird die Familie als einflussreichste Ressource und Einflussfaktor für den Verlauf der eigenen Bildungsbiografie betrachtet
Exploring the pathogen-commensal continuum: Cell wall auxotrophic bacteria in gnotobiotic mice
Full text linkThe intestinal tract of all known vertebrate animals is colonized with a high density of bacteria, forming host-specific communities. These communities are usually composed of a broad range of different species that have co-evolved with the host, to form very close and beneficial. In this thesis we developed a new tool for the study of host-microbiota interactions, based on the use of a proliferation controlled commensal E. coli strain and germ-free mice. This strain, contained a severe cell wall synthesis defect leading to the inability of proliferate without external supplementation. To guarantee the tightness of our system and its similarity to the wild type strain, we tested extensively the strain properties even under extreme cell wall starvation. This tool was further adapted to Salmonella enterica Typhimurium allowing us to simulate artificially the first six hours of a natural Salmonella infection, without the actual induction of disease. Our ability of simulating the early phase of an infection led to recognition of crucial in vivo bacterial adaptations, induced by the adaptive immunity, which led to the shift from pathogenic to commensal behavior in several Salmonella strains. The mechanism of this behavioral shift was explored, leading to the recognition of a Salmonella O-antigen shift, specific IgA induction and, exclusion of a pathogenic strain combined in to protection against disease when exposed to wild type Salmonella enterica. The additive effect of the discovered mechanisms was able to only partly explain the observed behavior, suggesting that other mechanisms remain to be uncovered to fully explain the behavioral shift
Materials properties from electron density distributions: Molecular magnetism and linear optical properties
Full text linkThe general goal of this thesis is correlating observable properties of organic and metal-organic materials with their ground-state electron density distribution. In a long-term view, we expect to develop empirical or semi-empirical approaches to predict materials properties from the electron density of their building blocks, thus allowing to rationally engineering molecular materials from their constituent subunits, such as their functional groups.
In particular, we have focused on linear optical properties of naturally occurring amino acids and their organic and metal-organic derivatives, and on magnetic properties of metal-organic frameworks. For analysing the optical properties and the magnetic behaviour of the molecular or sub-molecular building blocks in materials, we mostly used the more traditional QTAIM partitioning scheme of the molecular or crystalline electron densities, however, we have also investigated a new approach, namely, X-ray Constrained Extremely Localized Molecular Orbitals (XC-ELMO), that can be used in future to extracted the electron densities of crystal subunits.
With the purpose of rationally engineering linear optical materials, we have calculated atomic and functional group polarizabilities of amino acid molecules, their hydrogen-bonded aggregates and their metal-organic frameworks. This has enabled the identification of the most efficient functional groups, able to build-up larger electric susceptibilities in crystals, as well as the quantification of the role played by intermolecular interactions and coordinative bonds on modifying the polarizability of the isolated building blocks. Furthermore, we analysed the dependence of the polarizabilities on the one-electron basis set and the many-electron Hamiltonian. This is useful for selecting the most efficient level of theory to estimate susceptibilities of molecular-based materials.
With the purpose of rationally design molecular magnetic materials, we have investigated the electron density distributions and the magnetism of two copper(II) pyrazine nitrate metal-organic polymers. High-resolution X-ray diffraction and DFT calculations were used to characterize the magnetic exchange pathways and to establish relationships between the electron densities and the exchange-coupling constants. Moreover, molecular orbital and spin-density analyses were employed to understand the role of different magnetic exchange mechanisms in determining the bulk magnetic behaviour of these materials.
As anticipated, we have finally investigated a modified version of the X-ray constrained wavefunction technique, XC-ELMOs, that is not only a useful tool for determination and analysis of experimental electron densities, but also enables one to derive transferable molecular orbitals strictly localized on atoms, bonds or functional groups. In future, we expect to use XC-ELMOs to predict materials properties of large systems, currently challenging to calculate from first-principles, such as macromolecules or polymers. Here, we point out advantages, needs and pitfalls of the technique.
This work fulfils, at least partially, the prerequisites to understand materials properties of organic and metal-organic materials from the perspective of the electron density distribution of their building blocks. Empirical or semi-empirical evaluation of optical or magnetic properties from a preconceived assembling of building blocks could be extremely important for rationally design new materials, a field where accurate but expensive first-principles calculations are generally not used. This research could impact the community in the fields of crystal engineering, supramolecular chemistry and, of course, electron density analysis
Internal and external effects on cognition: Evidence from memory training in very preterm-born children and cognition in patients with carotid artery stenosis before and after treatment
Full text linkThe present synopsis aims to integrate one study about memory training in very preterm-born children and two studies about cognition in patients with carotid artery stenosis before and after treatments.
Preterm-born children are at increased risk of cognitive deficits and behavioural problems compared with peers born at term. This thesis determined whether memory training would improve cognitive functions in school-age very preterm-born children. Memory strategy training produced significant improvements in trained and non-trained cognitive functions; a core working memory training revealed significant effects on short-term memory and working memory tasks. Six months after training, children in both training groups showed better working memory performance than children in the waiting control group. This is evidence that memory training – an external influence on cognition – induces plastic changes in very preterm-born children.
Patients with carotid artery stenosis are known to be at increased risk of cognitive impairment. We showed that patients with symptomatic or asymptomatic carotid artery stenosis were at higher risk for cognitive deficits than expected in a normative sample. This thesis seeks to link cognitive plasticity to internal factors like carotid stenosis. An external factor, which influences blood flow to the brain is the nature of the carotid artery stenosis treatment. Research on the effects of carotid artery stenosis treatment on cognition has produced inconsistent results. We found significant improvement in frontal lobe functions, visual memory and motor speed one year after treatment independent of the treatment type (best medical treatment, carotid artery stenting, carotid artery endarterectomy); providing evidence for ‘treatment-induced’ cognitive plasticity.
Baseline performance was negatively associated with improvement in various cognitive functions after training in very preterm-born children and after treatment in patients with carotid artery stenosis.
The present synopsis aims to integrate these findings into the current and relevant literature, and discuss consequences as well as methodological considerations resulting from the studies constituting the thesis at hand
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