@phdthesis{Wiedenmann2018,
  author    = {Wiedenmann, Jonas},
  title     = {Induced topological superconductivity in HgTe based nanostructures},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-162782},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {This thesis describes the studies of topological superconductivity, which is predicted to emerge when pair correlations are induced into the surface states of 2D and 3D topolog- ical insulators (TIs). In this regard, experiments have been designed to investigate the theoretical ideas first pioneered by Fu and Kane that in such system Majorana bound states occur at vortices or edges of the system [Phys. Rev. Lett. 100, 096407 (2008), Phys. Rev. B 79, 161408 (2009)]. These states are of great interest as they constitute a new quasiparticle which is its own antiparticle and can be used as building blocks for fault tolerant topological quantum computing. After an introduction in chapter 1, chapter 2 of the thesis lays the foundation for the understanding of the field of topology in the context of condensed matter physics with a focus on topological band insulators and topological superconductors. Starting from a Chern insulator, the concepts of topological band theory and the bulk boundary corre- spondence are explained. It is then shown that the low energy Hamiltonian of mercury telluride (HgTe) quantum wells of an appropriate thickness can be written as two time reversal symmetric copies of a Chern insulator. This leads to the quantum spin Hall effect. In such a system, spin-polarized one dimensional conducting states form at the edges of the material, while the bulk is insulating. This concept is extended to 3D topological insulators with conducting 2D surface states. As a preliminary step to treating topological superconductivity, a short review of the microscopic theory of superconductivity, i.e. the theory of Bardeen, Cooper, and Shrieffer (BCS theory) is presented. The presence of Majorana end modes in a one dimensional superconducting chain is explained using the Kitaev model. Finally, topological band insulators and conventional superconductivity are combined to effectively engineer p-wave superconductivity. One way to investigate these states is by measuring the periodicity of the phase of the Josephson supercurrent in a topological Josephson junction. The signature is a 4π-periodicity compared to the 2π-periodicity in conventional Josephson junctions. The proof of the presence of this effect in HgTe based Josephson junction is the main goal of this thesis and is discussed in chapters 3 to 6. Chapter 3 describes in detail the transport of a 3D topological insulator based weak link under radio-frequency radiation. The chapter starts with a review of the state of research of (i) strained HgTe as 3D topological insulator and (ii) the progress of induc- ing superconducting correlations into the topological surface states and the theoretical predictions of 3D TI based Josephson junctions. Josephson junctions based on strained HgTe are successfully fabricated. Before studying the ac driven Josephson junctions, the dc transport of the devices is analysed. The critical current as a function of temperature is measured and it is possible to determine the induced superconducting gap. Under rf illumination Shapiro steps form in the current voltage characteristic. A missing first step at low frequencies and low powers is found in our devices. This is a signature of a 4π-periodic supercurrent. By studying the device in a wide parameter range - as a 147148 SUMMARY function of frequency, power, device geometry and magnetic field - it is shown that the results are in agreement with the presence of a single gapless Andreev doublet and several conventional modes. Chapter 4 gives results of the numerical modelling of the I -V dynamics in a Josephson junction where both a 2π- and a 4π-periodic supercurrents are present. This is done in the framework of an equivalent circuit representation, namely the resistively shunted Josephson junction model (RSJ-model). The numerical modelling is in agreement with the experimental results in chapter 3. First, the missing of odd Shapiro steps can be understood by a small 4π-periodic supercurrent contribution and a large number of modes which have a conventional 2π-periodicity. Second, the missing of odd Shapiro steps occurs at low frequency and low rf power. Third, it is shown that stochastic processes like Landau Zener tunnelling are most probably not responsible for the 4π contribution. In a next step the periodicity of Josephson junctions based on quantum spin Hall insulators using are investigated in chapter 5. A fabrication process of Josephson junctions based on inverted HgTe quantum wells was successfully developed. In order to achieve a good proximity effect the barrier material was removed and the superconductor deposited without exposing the structure to air. In a next step a gate electrode was fabricated which allows the chemical potential of the quantum well to be tuned. The measurement of the diffraction pattern of the critical current Ic due to a magnetic field applied perpendicular to the sample plane was conducted. In the vicinity to the expected quantum spin Hall phase, the pattern resembles that of a superconducting quantum interference device (SQUID). This shows that the current flows predominantly on the edges of the mesa. This observation is taken as a proof of the presence of edge currents. By irradiating the sample with rf, missing odd Shapiro steps up to step index n = 9 have been observed. This evidences the presence of a 4π-periodic contribution to the supercurrent. The experiment is repeated using a weak link based on a non-inverted HgTe quantum well. This material is expected to be a normal band insulator without helical edge channels. In this device, all the expected Shapiro steps are observed even at low frequencies and over the whole gate voltage range. This shows that the observed phenomena are directly connected to the topological band structure. Both features, namely the missing of odd Shapiro steps and the SQUID like diffraction pattern, appear strongest towards the quantum spin Hall regime, and thus provide evidence for induced topological superconductivity in the helical edge states. A more direct way to probe the periodicity of the Josephson supercurrent than using Shapiro steps is the measurement of the emitted radiation of a weak link. This experiment is presented in chapter 6. A conventional Josephson junction converts a dc bias V to an ac current with a characteristic Josephson frequency fJ = eV /h. In a topological Josephson junction a frequency at half the Josephson frequency fJ /2 is expected. A new measurement setup was developed in order to measure the emitted spectrum of a single Josephson junction. With this setup the spectrum of a HgTe quantum well based Josephson junction was measured and the emission at half the Josephson frequency fJ /2 was detected. In addition, fJ emission is also detected depending on the gate voltage and detection frequency. The spectrum is again dominated by half the Josephson emission at low voltages while the conventional emission is determines the spectrum at high voltages. A non-inverted quantum well shows only conventional emission over the whole gateSUMMARY 149 voltage and frequency range. The linewidth of the detected frequencies gives a measure on the lifetime of the bound states: From there, a coherence time of 0.3-4ns for the fJ /2 line has been deduced. This is generally shorter than for the fJ line (3-4ns). The last part of the thesis, chapter 7, reports on the induced superconducting state in a strained HgTe layer investigated by point-contact Andreev reflection spectroscopy. For the experiment, a HgTe mesa was fabricated with a small constriction. The diameter of the orifice was chosen to be smaller than the mean free path estimated from magne- totransport measurements. Thus one gets a ballistic point-contact which allows energy resolved spectroscopy. One part of the mesa is covered with a superconductor which induces superconducting correlations into the surface states of the topological insulator. This experiment therefore probes a single superconductor normal interface. In contrast to the Josephson junctions studied previously, the geometry allows the acquisition of energy resolved information of the induced superconducting state through the measurement of the differential conductance dI/dV as a function of applied dc bias for various gate voltages, temperatures and magnetic fields. An induced superconducting order parame- ter of about 70µeV was extracted but also signatures of the niobium gap at the expected value around Δ Nb ≈ 1.1meV have been found. Simulations using the theory developed by Blonder, Tinkham and Klapwijk and an extended model taking the topological surface states into account were used to fit the data. The simulations are in agreement with a small barrier at the topological insulator-induced topological superconductor interface and a high barrier at the Nb to topological insulator interface. To understand the full con- ductance curve as a function of applied voltage, a non-equilibrium driven transformation is suggested. The induced superconductivity is suppressed at a certain bias value due to local electron population. In accordance with this suppression, the relevant scattering regions change spatially as a function of applied bias. To conclude, it is emphasized that the experiments conducted in this thesis found clear signatures of induced topological superconductivity in HgTe based quantum well and bulk devices and opens up the avenue to many experiments. It would be interesting to apply the developed concepts to other topological matter-superconductor hybrid systems. The direct spectroscopy and manipulation of the Andreev bound states using circuit quantum electrodynamic techniques should be the next steps for HgTe based samples. This was already achieved in superconducting atomic break junctions by the group in Saclay [Science 2015, 349, 1199-1202 (2015)]. Another possible development would be the on-chip detection of the emitted spectrum as a function of the phase φ through the junction. In this connection, the topological junction needs to be shunted by a parallel ancillary junction. Such a setup would allow the current phase relation I(φ) directly and the lifetime of the bound states to be measured directly. By coupling this system to a spectrometer, which can be another Josephson junction, the energy dependence of the Andreev bound states E(φ) could be obtained. The experiments on the Andreev reflection spectroscopy described in this thesis could easily be extended to two dimensional topological insulators and to more complex geometries, like a phase bias loop or a tunable barrier at the point-contact. This work might also be useful for answering the question how and why Majorana bound states can be localized in quantum spin Hall systems.},
  subject      = {Quecksilbertellurid},
  language  = {en}
}
@phdthesis{Zenk2018,
  author    = {Zenk, Markus},
  title     = {On Numerical Methods for Astrophysical Applications},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-162669},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {Diese Arbeit befasst sich mit der Approximation der L{\"o}sungen von Modellen zur Beschreibung des Str{\"o}mungsverhaltens in Atmosph{\"a}ren. Im Speziellen umfassen die hier behandelten Modelle die kompressiblen Euler Gleichungen der Gasdynamik mit einem Quellterm bez{\"u}glich der Gravitation und die Flachwassergleichungen mit einem nicht konstanten Bodenprofil. Verschiedene Methoden wurden bereits entwickelt um die L{\"o}sungen dieser Gleichungen zu approximieren. Im Speziellen geht diese Arbeit auf die Approximation von L{\"o}sungen nahe des Gleichgewichts und, im Falle der Euler Gleichungen, bei kleinen Mach Zahlen ein. Die meisten numerischen Methoden haben die Eigenschaft, dass die Qualit{\"a}t der Approximation sich mit der Anzahl der Freiheitsgrade verbessert. In der Praxis werden deswegen diese numerischen Methoden auf großen Computern implementiert um eine m{\"o}glichst hohe Approximationsg{\"u}te zu erreichen. Jedoch sind auch manchmal diese großen Maschinen nicht ausreichend, um die gew{\"u}nschte Qualit{\"a}t zu erreichen. Das Hauptaugenmerk dieser Arbeit ist darauf gerichtet, die Qualit{\"a}t der Approximation bei gleicher Anzahl von Freiheitsgrade zu verbessern. Diese Arbeit ist im Zusammenhang einer Kollaboration zwischen Prof. Klingenberg des Mathemaitschen Instituts in W{\"u}rzburg und Prof. R{\"o}pke des Astrophysikalischen Instituts in W{\"u}rzburg entstanden. Das Ziel dieser Kollaboration ist es, Methoden zur Berechnung von stellarer Atmosph{\"a}ren zu entwickeln. In dieser Arbeit werden vor allem zwei Problemstellungen behandelt. Die erste Problemstellung bezieht sich auf die akkurate Approximation des Quellterms, was zu den so genannten well-balanced Schemata f{\"u}hrt. Diese erlauben genaue Approximationen von L{\"o}sungen nahe des Gleichgewichts. Die zweite Problemstellung bezieht sich auf die Approximation von Str{\"o}mungen bei kleinen Mach Zahlen. Es ist bekannt, dass L{\"o}sungen der kompressiblen Euler Gleichungen zu L{\"o}sungen der inkompressiblen Euler Gleichungen konvergieren, wenn die Mach Zahl gegen null geht. Klassische numerische Schemata zeigen ein stark diffusives Verhalten bei kleinen Mach Zahlen. Das hier entwickelte Schema f{\"a}llt in die Kategorie der asymptotic preserving Schematas, d.h. das numerische Schema ist auf einem diskrete Level kompatibel mit dem auf dem Kontinuum gezeigten verhalten. Zus{\"a}tzlich wird gezeigt, dass die Diffusion des hier entwickelten Schemas unabh{\"a}ngig von der Mach Zahl ist. In Kapitel 3 wird ein HLL approximativer Riemann L{\"o}ser f{\"u}r die Approximation der L{\"o}sungen der Flachwassergleichungen mit einem nicht konstanten Bodenprofil angewendet und ein well-balanced Schema entwickelt. Die meisten well-balanced Schemata f{\"u}r die Flachwassergleichungen behandeln nur den Fall eines Fluids im Ruhezustand, die so genannten Lake at Rest L{\"o}sungen. Hier wird ein Schema entwickelt, welches sich mit allen Gleichgewichten befasst. Zudem wird eine zweiter Ordnung Methode entwickelt, welche im Gegensatz zu anderen in der Literatur nicht auf einem iterativen Verfahren basiert. Numerische Experimente werden durchgef{\"u}hrt um die Vorteile des neuen Verfahrens zu zeigen. In Kapitel 4 wird ein Suliciu Relaxations L{\"o}ser angepasst um die hydrostatischen Gleichgewichte der Euler Gleichungen mit einem Gravitationspotential aufzul{\"o}sen. Die Gleichungen der hydrostatischen Gleichgewichte sind unterbestimmt und lassen deshalb keine Eindeutigen L{\"o}sungen zu. Es wird jedoch gezeigt, dass das neue Schema f{\"u}r eine große Klasse dieser L{\"o}sungen die well-balanced Eigenschaft besitzt. F{\"u}r bestimmte Klassen werden Quadraturformeln zur Approximation des Quellterms entwickelt. Es wird auch gezeigt, dass das Schema robust, d.h. es erh{\"a}lt die Positivit{\"a}t der Masse und Energie, und stabil bez{\"u}glich der Entropieungleichung ist. Die numerischen Experimente konzentrieren sich vor allem auf den Einfluss der Quadraturformeln auf die well-balanced Eigenschaften. In Kapitel 5 wird ein Suliciu Relaxations Schema angepasst f{\"u}r Simulationen im Bereich kleiner Mach Zahlen. Es wird gezeigt, dass das neue Schema asymptotic preserving und die Diffusion kontrolliert ist. Zudem wird gezeigt, dass das Schema f{\"u}r bestimmte Parameter robust ist. Eine Stabilit{\"a}t wird aus einer Chapman-Enskog Analyse abgeleitet. Resultate numerische Experimente werden gezeigt um die Vorteile des neuen Verfahrens zu zeigen. In Kapitel 6 werden die Schemata aus den Kapiteln 4 und 5 kombiniert um das Verhalten des numerischen Schemas bei Fl{\"u}ssen mit kleiner Mach Zahl in durch die Gravitation geschichteten Atmosph{\"a}ren zu untersuchen. Es wird gezeigt, dass das Schema well-balanced ist. Die Robustheit und die Stabilit{\"a}t werden analog zu Kapitel 5 behandelt. Auch hier werden numerische Tests durchgef{\"u}hrt. Es zeigt sich, dass das neu entwickelte Schema in der Lage ist, die Dynamiken besser Aufzul{\"o}sen als vor der Anpassung. Das Kapitel 7 besch{\"a}ftigt sich mit der Entwicklung eines multidimensionalen Schemas basierend auf der Suliciu Relaxation. Jedoch ist die Arbeit an diesem Ansatz noch nicht beendet und numerische Resultate k{\"o}nnen nicht pr{\"a}sentiert werden. Es wird aufgezeigt, wo sich die Schw{\"a}chen dieses Ansatzes befinden und weiterer Entwicklungsbedarf besteht.},
  subject      = {Str{\"o}mung},
  language  = {en}
}
@phdthesis{Wannagat2018,
  author    = {Wannagat, Wienke Charlotte},
  title     = {Cognitive Processes of Discourse Comprehension in Children and Adults - Comparisons between Written, Auditory, and Audiovisual Modes of Presentation -},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-162515},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {In drei Studien wurde untersucht, wie sich unterschiedliche Darbietungsformate (schriftlich, auditiv, audiovisuell (auditiv + Bilder) auf das Verst{\"a}ndnis semantisch identischer Inhalte auswirken. Dabei interessierte insbesondere der Entwicklungsverlauf von der ersten Klasse bis zum Erwachsenenalter. Dass sich Bilder f{\"o}rderlich auf die Verst{\"a}ndnisleistung auswirken k{\"o}nnen, gilt als gut untersucht (z.B. Carney \& Levin, 2002). Anders als viele bisherige Studien erfassen wir Textverstehen mit impliziten Maßen, die differenziertere R{\"u}ckschl{\"u}sse auf die, g{\"a}ngigen Theorien zufolge, zugrundeliegenden Prozesse zulassen: Textverstehen geht mit der Konstruktion von drei Ebenen mentaler Repr{\"a}sentationen einher (vgl. Kintsch, 1998). Weiterhin bedeutet erfolgreiches Textverstehen, eine auf lokaler und globaler Ebene koh{\"a}rente mentale Repr{\"a}sentation zu konstruieren (z.B. Schnotz \& Dutke, 2004). Mit einem Satz-Rekognitionstest (vgl. Schmalhofer \& Glavanov, 1986) untersuchten wir, ob sich das Ged{\"a}chtnis f{\"u}r die Textoberfl{\"a}che, die Textbasis und das Situationsmodell bei 103 8- und 10-J{\"a}hrigen zwischen schriftlicher, auditiver und audiovisueller (Studie 1) und bei 106 7-, 9- und 11-J{\"a}hrigen zwischen auditiver und audiovisueller Darbietung narrativer Texte (Studie 2) unterscheidet. Weiterhin (Studie 3) untersuchten wir mit 155 9- und 11-J{\"a}hrigen, inwieweit sich die F{\"a}higkeit der Inferenzbildung zur Herstellung lokaler und globaler Koh{\"a}renz zwischen schriftlicher, auditiver und audiovisueller Darbietung unterscheidet. Als Indikator dienten die Reaktionszeiten auf W{\"o}rter, die mit einem {\"u}ber (global)- oder untergeordneten (lokal) Protagonistenziel assoziiert sind. Insgesamt zeigte sich, dass Sch{\"u}ler bis zu einem Alter von 11 Jahren nicht nur die Textoberfl{\"a}che besser erinnern, sondern auch besser in der Lage sind ein Situationsmodell zu konstruieren, wenn einem Text Bilder beigef{\"u}gt sind. Dies zeigte sich sowohl im Vergleich mit auditiver als auch mit schriftlicher Darbietung. Bei Erwachsenen zeigte sich kein Effekt der Darbietungsform. Sowohl 9- als auch 11-J{\"a}hrigen gelingt außerdem die Herstellung globaler Koh{\"a}renz bei audiovisueller Darbietung besser als bei auditiver. Die schriftliche Darbietung zeigte sich im Vergleich zur auditiven sowohl im Hinblick auf lokale als auch auf globale Koh{\"a}renz {\"u}berlegen.},
  subject      = {Textverstehen},
  language  = {en}
}
@phdthesis{Namal2018,
  author    = {Namal, Imge},
  title     = {Fabrication and Optical and Electronic Characterization of Conjugated Polymer-Stabilized Semiconducting Single-Wall Carbon Nanotubes in Dispersions and Thin Films},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-162393},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {In order to shrink the size of semiconductor devices and improve their efficiency at the same time, silicon-based semiconductor devices have been engineered, until the material almost reaches its performance limits. As the candidate to be used next in semiconducting devices, single-wall carbon nanotubes show a great potential due to their promise of increased device efficiency and their high charge carrier mobilities in the nanometer size active areas. However, there are material based problems to overcome in order to imply SWNTs in the semiconductor devices. SWNTs tend to aggregate in bundles and it is not trivial to obtain an electronically or chirally homogeneous SWNT dispersion and when it is done, a homogeneous thin film needs to be produced with a technique that is practical, easy and scalable. This work was aimed to solve both of these problems. In the first part of this study, six different polymers, containing fluorene or carbazole as the rigid part and bipyridine, bithiophene or biphenyl as the accompanying copolymer unit, were used to selectively disperse semiconducting SWNTs. With the data obtained from absorption and photoluminescence spectroscopy of the corresponding dispersions, it was found out that the rigid part of the copolymer plays a primary role in determining its dispersion efficiency and electronic sorting ability. Within the two tested units, carbazole has a higher π electron density. Due to increased π-π interactions, carbazole containing copolymers have higher dispersion efficiency. However, the electronic sorting ability of fluorene containing polymers is superior. Chiral selection of the polymers in the dispersion is not directly foreseeable from the selection of backbone units. At the end, obtaining a monochiral dispersion is found to be highly dependent on the used raw material in combination to the preferred polymer. Next, one of the best performing polymers due to high chirality enrichment and electronic sorting ability was chosen in order to disperse SWNTs. Thin films of varying thickness between 18 ± 5 to 755o±o5 nm were prepared using vacuum filtration wet transfer method in order to analyze them optically and electronically. The scalability and efficiency of the integrated thin film production method were shown using optical, topographical and electronic measurements. The relative photoluminescence quantum yield of the radiative decay from the SWNT thin films was found to be constant for the thickness scale. Constant roughness on the film surface and linearly increasing concentration of SWNTs were also supporting the scalability of this thin film production method. Electronic measurements on bottom gate top contact transistors have shown an increasing charge carrier mobility for linear and saturation regimes. This was caused by the missing normalization of the mobility for the thickness of the active layer. This emphasizes the importance of considering this dimension for comparison of different field effect transistor mobilities.},
  subject      = {Feldeffekttransistor},
  language  = {en}
}
@phdthesis{PonceGarcia2018,
  author    = {Ponce Garcia, Irene Paola},
  title     = {Strategies for optimizing dynamic MRI},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-162622},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {In Magnetic Resonance Imaging (MRI), acquisition of dynamic data may be highly complex due to rapid changes occurred in the object to be imaged. For clinical diagnostic, dynamic MR images require both high spatial and temporal resolution. The speed in the acquisition is a crucial factor to capture optimally dynamics of the objects to obtain accurate diagnosis. In the 90's, partially parallel MRI (pMRI) has been introduced to shorten scan times reducing the amount of acquired data. These approaches use multi-receiver coil arrays to acquire independently and simultaneously the data. Reduction in the amount of acquired data results in images with aliasing artifacts. Dedicated methods as such Sensitivity Encoding (SENSE) and Generalized Autocalibrating Partially Parallel Acquisition (GRAPPA) were the basis of a series of algorithms in pMRI. Nevertheless, pMRI methods require extra spatial or temporal information in order to optimally reconstruct the data. This information is typically obtained by an extra scan or embedded in the accelerated acquisition applying a variable density acquisition scheme. In this work, we were able to reduce or totally eliminate the acquisition of the training data for kt-SENSE and kt-PCA algorithms obtaining accurate reconstructions with high temporal fidelity. For dynamic data acquired in an interleaved fashion, the temporal average of accelerated data can generate an artifact-free image used to estimate the coil sensitivity maps avoiding the need of extra acquisitions. However, this temporal average contains errors from aliased components, which may lead to signal nulls along the spectra of reconstructions when methods like kt-SENSE are applied. The use of a GRAPPA filter applied to the temporal average reduces these errors and subsequently may reduce the null components in the reconstructed data. In this thesis the effect of using temporal averages from radial data was investigated. Non-periodic artifacts performed by undersampling radial data allow a more accurate estimation of the true temporal average and thereby avoiding undesirable temporal filtering in the reconstructed images. kt-SENSE exploits not only spatial coil sensitivity variations but also makes use of spatio-temporal correlations in order to separate the aliased signals. Spatio-temporal correlations in kt-SENSE are learnt using a training data set, which consists of several central k-space lines acquired in a separate scan. The scan of these extra lines results in longer acquisition times even for low resolution images. It was demonstrate that limited spatial resolution of training data set may lead to temporal filtering effects (or temporal blurring) in the reconstructed data. In this thesis, the auto-calibration for kt-SENSE was proposed and its feasibility was tested in order to completely eliminate the acquisition of training data. The application of a prior TSENSE reconstruction produces the training data set for the kt-SENSE algorithm. These training data have full spatial resolution. Furthermore, it was demonstrated that the proposed auto-calibrating method reduces significantly temporal filtering in the reconstructed images compared to conventional kt-SENSE reconstructions employing low resolution training images. However, the performance of auto-calibrating kt-SENSE is affected by the Signal-to-Noise Ratio (SNR) of the first pass reconstructions that propagates to the final reconstructions. Another dedicated method used in dynamic MRI applications is kt-PCA, that was first proposed for the reconstruction of MR cardiac data. In this thesis, kt-PCA was employed for the generation of spatially resolved M0, T1 and T2 maps from a single accelerated IRTrueFISP or IR-Snapshot FLASH measurement. In contrast to cardiac dynamic data, MR relaxometry experiments exhibit signal at all temporal frequencies, which makes their reconstruction more challenging. However, since relaxometry measurements can be represented by only few parameters, the use of few principal components (PC) in the kt-PCA algorithm can significantly simplify the reconstruction. Furthermore, it was found that due to high redundancy in relaxometry data, PCA can efficiently extract the required information from just a single line of training data. It has been demonstrated in this thesis that auto-calibrating kt-SENSE is able to obtain high temporal fidelity dynamic cardiac reconstructions from moderate accelerated data avoiding the extra acquisition of training data. Additionally, kt-PCA has been proved to be a suitable method for the reconstruction of highly accelerated MR relaxometry data. Furthermore, a single central training line is necessary to obtain accurate reconstructions. Both reconstruction methods are promising for the optimization of training data acquisition and seem to be feasible for several clinical applications.},
  subject      = {Kernspintomografie},
  language  = {en}
}
@phdthesis{Narkhede2018,
  author    = {Narkhede, Yogesh},
  title     = {In silico structure-based optimisation of pyrrolidine carboxamides as Mycobacterium tuberculosis enoyl-ACP reductase inhibitors},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-152468},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {The high infection rates and recent emergence of extremely drug resistant forms of Mycobacterium tuberculosis pose a significant challenge for global health. The NADH- dependent enoyl-ACP-reductase InhA of the type II mycobacterial fatty acid biosynthesis pathway is a well-validated target for inhibiting mycobacterial growth. InhA has been shown to be inhibited by a variety of compound series. Prominent classes of InhA inhibitors from literature include diaryl ethers, pyrrolidine carboxamides and arylamides which can be subjected to further development. Despite the progress in this area, very few compounds are in clinical development phase. The present work involves a detailed computational investigation of the binding modes and structure-based optimisation of pyrrolidine carboxamides as InhA inhibitors. With substituents of widely varying bulkiness, the pyrrolidine carboxamide dataset presented a challenge for prediction of binding mode as well as affinity. Using advanced docking protocols and in-house developed pose selection procedures, the binding modes of 44 compounds were predicted. The poses from docking were used in short molecular dynamics (MD) simulations to ascertain the dominant binding conformations for the bulkier members of the series. Subsequently, an activity-based classification strategy could be developed to circumvent the affinity prediction problems observed with this dataset. The prominent motions of the bound ligand and the active site residues were then ascertained using Essential Dynamics (ED). The information from ED and literature was subsequently used to design a total of 20 compounds that were subjected to extensive in-silico evaluations. Finally, the molecular determinants of rapid-reversible binding of pyrrolidine carboxamides were investigated using long MD simulations.},
  subject      = {Tuberkelbakterium},
  language  = {en}
}
@phdthesis{Eck2018,
  author    = {Eck, Martin},
  title     = {Iron- and Copper-catalyzed Borylation of Alkyl and Aryl Halides and B-B Bond Activation and NHC Ring-expansion Reactions of the Diboron(4) Compound Bis(ethylene glycolato)diboron (B\(_2\)eg\(_2\))},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-149791},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {The purpose of the present work was, in the first part, to investigate the potential of iron-based metal complexes in catalytic borylation reactions with alkyl halides as substrates and B2pin2 as the borylation reagent. Moreover, extended studies of the recently reported, copper mediated borylation reactions of aryl halides were performed, including the screening of substrates and alkoxy bases as well as ligand-screening. Investigations were undertaken on the role of Cu-nanoparticles, which might be involved in this catalytic reaction. Furthermore, Cu-phosphine complexes were synthesized as precursors, but attempts to isolate Cu-boryl species which are intermediates in the proposed catalytic cycle were unsuccessful, although 11B NMR evidence for a Cu-boryl complex was obtained. In the second part of this work, the alternative, Lewis-acidic diboron(4) compound bis(ethylene glycolato)diboron (B2eg2) was synthesized to compare its reactivity with the reactivity of other diboron(4) compounds (e.g. B2neop2, B2cat2, B2pin2 and B2(NMe2)4). Therefore, reactions of B2eg2 with different Lewis-bases, such as NHCs and phosphines, were performed to investigate the possible formation of sp2-sp3 or sp3-sp3 adducts and ring-expansion reactions (RERs). The aim was to obtain a better general insight into the reactivity of diboron(4) compounds with Lewis-bases because they are both used as reactants in transition metal-catalyzed and metal-free borylation reactions. Understanding the B-B bond activation process promoted by Lewis-bases provides a new perspective on the reaction pathways available for various borylation reactions.},
  language  = {en}
}
@phdthesis{Bolze2018,
  author    = {Bolze, Tom},
  title     = {Photodynamics of a fluorescent tetrazolium salt and shaping of femtosecond Laguerre-Gaussian laser modes in time and space},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-160902},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {This thesis will outline studies performed on the fluorescence dynamics of phenyl-benzo- [c]-tetrazolo-cinnolium chloride (PTC) in alcoholic solutions with varying viscosity using time-resolved fluoro-spectroscopic methods. Furthermore, the properties of femtosecond Laguerre-Gaussian (LG) laser pulses will be investigated with respect to their temporal and spatial features and an approach will be developed to measure and control the spatial intensity distribution on the time scale of the pulse. Tetrazolium salts are widely used in biological assays for their low oxidation and reduction thresholds and spectroscopic properties. However, a neglected feature in these applications is the advantage that detection of emitted light has over the determination of the absorbance. To corroborate this, PTC as one of the few known fluorescent tetrazolium salts was investigated with regard to its luminescent features. Steady-state spectroscopy revealed how PTC can be formed by a photoreaction from 2,3,5-triphenyl-tetrazolium chloride (TTC) and how the fluorescence quantum yield behaved in alcoholic solvents with different viscosity. In the same array of solvents time correlated single photon counting (TCSPC) measurements were performed and the fluorescence decay was investigated. Global analysis of the results revealed different dynamics in the different solvents, but although the main emission constant did change with the solvent, taking the fluorescence quantum yield into consideration resulted in an independence of the radiative rate from the solvent. The non-radiative rate, however, was highly solvent dependent and responsible for the observed solvent-related changes in the fluorescence dynamics. Further studies with the increased time resolution of femtosecond fluorescence upconversion revealed an independence of the main emission constant from the excitation energy, however the dynamics of the cooling processes prior to emission were prolonged for higher excitation energy. This led to a conceivable photoreaction scheme with one emissive state with a competing non-radiative relaxation channel, that may involve an intermediate state. LG laser beams and their properties have seen a lot of scientific attention over the past two decades. Also in the context of new techniques pushing the limit of technology further to explore new phenomena, it is essential to understand the features of this beam class and check the consistency of the findings with theoretical knowledge. The mode conversion of a Hermite-Gaussian (HG) mode into a LG mode with the help of a spiral phase plate (SPP) was investigated with respect to its space-time characteristics. It was found that femtosecond LG and HG pulses of a given temporal duration share the same spectrum and can be characterized using the same well-established methods. The mode conversion proved to only produce the desired LG mode with its characteristic orbital angular momentum (OAM), that is conserved after frequency doubling the pulse. Furthermore, it was demonstrated that temporal shaping of the HG pulse does not alter the result of its mode-conversion, as three completely different temporal pulse shapes produced the same LG mode. Further attention was given to the sum frequency generation of fs LG beams and dynamics of the interference of a HG and a LG pulse. It was found that if both are chirped with inverse signs the spatial intensity distribution does rotate around the beam axis on the time scale of the pulse. A strategy was found that would enable a measurement of these dynamics by upconversion of the interference with a third gate pulse. The results of which are discussed theoretically and an approach of an experimental realization had been made. The simulated findings had only been reproduced to a limited extend due to experimental limitations, especially the interferometric stability of the setup.},
  subject      = {Tetrazoliumsalze},
  language  = {en}
}
@phdthesis{Albert2018,
  author    = {Albert, Julian},
  title     = {Quantum Studies on Low-Dimensional Coupled Electron-Nuclear Dynamics},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-161512},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {In the context of quantum mechanical calculations, the properties of non-adiabatic coupling in a small system, the Shin-Metiu model, is investigated. The transition from adiabatic to non-adiabatic dynamics is elucidated in modifying the electron-nuclear interaction. This allows the comparison of weakly correlated electron-nuclear motion with the case where the strong correlations determine the dynamics. The studies of the model are extended to include spectroscopical transitions being present in two-dimensional and degenerate four-wave mixing spectroscopy. Furthermore, the quantum and classical time-evolution of the coupled motion in the complete electron-nuclear phase space is compared for the two coupling cases. Additionally, the numerically exact electron flux within the weak coupling case is compared to the Born-Oppenheimer treatment. In the last part of the thesis, the model is extended to two dimensions. The system then possesses potential energy surfaces which exhibit a typical 'Mexican hat'-like structure and a conical intersection in the adiabatic representation. Thus, it is possible to map properties of the system onto a vibronic coupling (Jahn-Teller) hamiltonian. Exact wave-packet propagations as well as nuclear wave-packet dynamics in the adiabatic and diabatic representation are performed.},
  subject      = {Theoretische Chemie},
  language  = {en}
}
@phdthesis{Kalleda2018,
  author    = {Kalleda, Nataraja Swamy},
  title     = {Spatiotemporal analysis of immune cell recruitment and Neutrophil defence functions in \(Aspergillus\) \(fumigatus\) lung infections},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-150931},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {Humans are continuously exposed to airborne spores of the saprophytic fungus Aspergillus fumigatus. In healthy individuals, local pulmonary host defence mechanisms can efficiently eliminate the fungus without any overt symptoms. In contrast, A. fumigatus causes devastating infections in immunocompromised patients. However, local host immune responses against A. fumigatus lung infections in immunocompromised conditions have remained largely elusive. Given the dynamic changes in immune cell subsets within tissues upon immunosuppressive therapy, we dissected the spatiotemporal pulmonary immune response after A. fumigatus infection to reveal basic immunological events that fail to effectively control the invasive fungal disease. In different immunocompromised murine models, myeloid but not lymphoid cells were strongly recruited upon infection. Notably, neutrophils and macrophages were recruited to infected lungs in different immunosuppressed regimens. Other myeloid cells, particularly dendritic cells and monocytes were only recruited in the corticosteroid model after infection. Lymphoid cells, particularly CD4+ or CD8+ T-cells and NK cells were highly reduced upon immunosuppression and were not recruited after A. fumigatus infection. Importantly, adoptive CD11b+ myeloid cell transfer rescued immunosuppressed mice from lethal A. fumigatus infection. These findings illustrate that CD11b+ myeloid cells are critical for anti-A. fumigatus defence under immunocompromised conditions. Despite improved antifungal agents, invasive A. fumigatus lung infections cause a high rate morbidity and mortality in neutropenic patients. Granulocyte transfusions have been tested as an alternative therapy for the management of high-risk neutropenic patients with invasive A. fumigatus infections. To increase the granulocyte yield for transfusion, donors are treated with corticosteroids. Yet, the efficacy of granulocyte transfusion and the functional defence mechanisms of granulocytes collected from corticosteroid treated donors remain largely elusive. We aimed to assess the efficacy of granulocyte transfusion and functional defence mechanisms of corticosteroid treated granulocytes using mouse models. In this thesis, we show that transfusion of granulocytes from corticosteroid treated mice did not protect cyclophosphamide immunosuppressed mice against lethal A. fumigatus infection in contrast to granulocytes from untreated mice. Upon infection, increased levels of inflammatory cytokines helped to recruit granulocytes to the lungs without any recruitment defects in corticosteroid treated and infected mice or in cyclophosphamide immunosuppressed and infected mice that have received the granulocytes from corticosteroid treated mice. However, corticosteroid treated human or mouse neutrophils failed to form neutrophil extracellular traps (NETs) in in vitro and in vivo conditions. Further, corticosteroid treated granulocytes exhibited impaired ROS production against A. fumigatus. Notably, corticosteroids impaired the β-glucan receptor Dectin-1 (CLEC7A) on mouse and human granulocytes to efficiently recognize and phagocytize A. fumigatus, which markedly impaired fungal killing. We conclude that corticosteroid treatment of granulocyte donors for increasing neutrophil yields or patients with ongoing corticosteroid treatment could result in deleterious effects on granulocyte antifungal functions, thereby limiting the benefit of granulocyte transfusion therapies against invasive fungal infections.},
  subject      = {Aspergillus fumigatus},
  language  = {en}
}