Two-dimensional semiconductors are a topic of intense research and very attractive materials for new developments in different elds of semiconductor technology. These materials are promising candidates to satisfy the demand for faster and more compact electronics. They make new technological possibilities feasible, such as the realization and the commercial development of exible and semitransparent electronics. For these purposes, a deep knowledge of their electronic and optical properties is required. Besides the technological interest, numerous discoveries of fundamental physics were made with many others still to come. Recently for instance, superconductivity has been achieved in twisted bilayer graphene and high-temperature exciton condensation was observed in transition metal dichalcogenide heterostructures 1. The scope of this PhD is to investigate the infrared and optical properties of different two-dimensional semiconductor systems. To this end, various spectroscopic and time-resolved investigations on transition metal dichalcogenide monolayers and few-layer InSe crystals will be presented. First of all, the fabrication of exfoliated samples and van derWaals heterostructures has been successfully carried out and is described in detail. With this knowledge, the exciton physics of MoSe2 monolayer was studied. In particular, the effects of adsorbed gas molecules on the monolayer surface is discussed. It has been demonstrated that these adsorbates can localize excitons at low temperatures and that laser irradiation can release the binding of the physisorbed gas molecules. These results are of fundamental interest for spectroscopic investigations as well as relevant for opto-electronic devices as for instance gas sensors. Thereafter, several experiments were carried out with the use of the infrared free-electron laser FELBE. The general idea was to investigate the response of transition metal dichalcogenide monolayers in the far-infrared frequency range. An effect that was observed is a redshift of the trion induced by non-resonant infrared absorption. In fact, after the absorption of infrared radiation by free carriers, the energy and the momentum of the heated electron gas are transferred to the trion population, leading to a redshift of the trion resonance. By measuring the dynamics of this process, the cooling time of the electron-hole population and the far-infrared absorption of MoSe2 monolayer were extrapolated. The experiments conducted on few-layer InSe will be also presented in this thesis. The effects of hBN-encapsulation on the optical properties of InSe are discussed. The encapsulation in hBN does not only prevent the material from degradation, but also improves the optical quality by reducing the disorder potential in the crystal. Furthermore, the photoluminescence dynamics was investigated as a function of layer thickness and temperature. A bi-exponential decay was observed and the two contributions are attributed to the direct bandgap electron-hole transition and the defect assisted radiative recombination. Because of the direct-to-indirect bandgap crossover driven by the sample thickness, the dynamics gets slower while decreasing the number of layers. In particular, the fast component, i.e. the direct bandgap recombination, tends to disappear for thin InSe samples. Moreover, the photoluminescence lifetime decreases at high temperatures as a consequence of more effcient non-radiative recombination. Finally, heterostructures of MoSe2/WSe2 monolayer were fabricated and the rst spectroscopic results are presented. The interlayer exciton was observed and its dynamics was investigated.

A defining feature of quantum many-body systems is the presence of entanglement among their constituents. Besides providing valuable insights on several physical properties, entanglement is also responsible for the computational complexity of simulating quantum systems with variational methods. This thesis explores several aspects of entanglement in many-body systems, with the primary goal of devising efficient approaches for the study of topological properties and quantum dynamics of lattice models. The first focus of this work is the development of variational wavefunctions inspired by artificial neural networks. These can efficiently encode long-range and extensive entanglement in their structure, as opposed to the case of tensor network states. This feature makes them promising tools for the study of topologically ordered phases, quantum critical states as well as dynamical properties of quantum systems. In this thesis, we characterize the representational power of a specific class of artificial neural network states, constructed from Boltzmann machines. First, we show that wavefunctions obtained from restricted Boltzmann machines can efficiently parametrize chiral topological phases, such as fractional quantum Hall states. We then turn our attention to deep Boltzmann machines. In this framework, we propose a new class of variational wavefunctions, coined generalized transfer matrix states, which encompass restricted Boltzmann machine and tensor network states. We investigate the entanglement properties of this ansatz, as well as its capability of representing physical states. Understanding how the entanglement properties of a system evolve in time is the second focus of this thesis. In this context, we first investigate the manifestation of topological properties in the unitary dynamics of systems after a quench, using the degeneracy of the entanglement spectrum as a possible signature. We then analyze the phenomenon of entanglement growth, which limits to short timescales the applicability of tensor network methods in out-of-equilibrium problems. We investigate whether these limitations can be overcome by exploiting the dependence of entanglement entropies on the chosen computational basis. Specifically, we study how the spreading of quantum correlations can be contained by means of time-dependent basis rotations of the state, using exact diagonalization to simulate its dynamics after a quench. Going beyond the case of sudden quenches, we then show how, in certain weakly interacting problems, the asymptotic value of the entanglement entropy can be tuned by modifying the velocity at which the parameters in the Hamiltonian are changed. This enables the simulation of longer timescales using tensor network approaches. We present preliminary results obtained with matrix product states methods, with the goal of studying how equilibration affects the transport properties of interacting systems at long times.

Three dimensional positron emission tomography (PET) plays an important role in cancer soil studies by enabling detection and localization of tumor cells. This thesis investigates the ClearPET measuring system. Central matter of interest is the reconstruction process. There is to be examined how accurate the ClearPET can reconstruct known interrelations between source activities. The optimization of this process is accomplished by normalizing the reconstruction image by means of a homogeneous phantom. In case of this experimental setup the phantom is a cylinder with a homogeneous activity distribution.:1 Introduction 2 Material and Methods 2.1 Measuring system 2.1.1 Measuring procedure 2.1.2 Cassettes 2.1.3 Homogeneous phantom 2.2 Physical background 2.2.1 Compton scattering 2.2.2 Attenuation coefficient 2.2.3 Types of radiation 2.2.4 Sodium-22 and related physical phenomena 2.3 Reconstruction process 2.3.1 Intensity and Beer’s law 2.3.2 Radon transform and its inverse 2.3.3 OSMAPOSL algorithm 2.4 Fourier rebinning algorithm 3 Experimental results 25 3.1 Reconstruction routine 3.2 Back projection of point sources 3.2.1 Full width half maximum analysis of the strong point source 3.2.2 Investigation of the statistical error 3.2.3 Validation of the maxima approach 3.3 Comparison of activities and quantification of spatial reconstruction behavior . 3.4 Normalization measurement 3.5 Sinogram 3.6 Reconstruction with the OSMAPOSL algorithm 3.7 Implementation of attenuation correction and multiple iterations of the OSMAPOSLalgorithm 4 Summary

Die Broschüre gibt Informationen zu natürlichen Strahlenquellen, wie wirken diese sich auf die Gesundheit des Menschen aus, welche Pflichten sind bei erhöhter natürlicher Radioaktivität zu beachten. Redaktionsschluss: 28.06.2018

In Parkinson's disease (PD), large parts of the brain transition into states of enhanced neural synchronization. These phase transitions have been associated with the death of dopaminergic neurons as well as with impaired motor function. In this thesis, we address the much-debated question of how parkinsonian synchronization depends on dopamine depletion in the basal ganglia (BG). To this end, we develop spiking neural network (SNN) models of BG circuits and study them via bifurcation analysis. First, we derive mean-field models that allow to account for various forms of short-term plasticity in SNNs. We show that such short-term plasticity mechanisms can lead to highly synchronous, periodic bursting dynamics and discuss the relevance of this bursting regime for PD. Second, we find that the external pallidum, an important part of the BG, cannot cause parkinsonian oscillations autonomously. However, our results suggest that the external pallidum may contribute to the emergence of cross-frequency coupling that has been reported for parkinsonian oscillations. Finally, we describe an open-source Python toolbox that we developed to implement and analyze mean-field models of neural dynamics. Together, this thesis provides insight into BG synchronization processes as well as the mathematical basis and software for future studies of neural synchronization.:1 Introduction 1.1 A complex systems perspective of the brain 1.2 Brain function and the phase transition to synchronized neural activity 1.3 Low-dimensional manifolds of synchronized neural activity 1.4 Phase transitions to synchronized neural activity in Parkinson’s disease 1.5 Thesis overview 2 Mathematical Models and Methods 2.1 A non-linear oscillator model of neural activity 2.2 Dynamical systems methods for the study of neural network models 2.3 Dynamics of a single QIF neuron 3 Low-Dimensional Dynamics in Spiking Neural Networks 3.1 Mean-field approaches in neuroscience 3.2 Dynamics of QIF networks with post-synaptic STP 3.3 Dynamics of QIF networks with spike-frequency adaptation 3.4 Mean-field dynamics of QIF networks with pre-synaptic STP 3.5 Discussion 4 Phase Transitions and Neural Synchronization in the External Pallidum 4.1 A new perspective on GPe structure and function 4.2 GPe model definition and analysis 4.3 Phase transitions in the GPe under static and periodic input 4.4 Discussion 5. Modeling of Neural Mean-Field Dynamics Via PyRates 5.1 Computational modeling in neuroscience 5.2 The Framework 5.3 Pre-implemented methods for neural modeling workflows 5.4 Results 5.5 Discussion 6. Conclusion and Outlook

The book presents my PhD thesis, which is about aerosol-cloud interactions by means of a dual-field-of-view polarization lidar. Aerosol-cloud interactions (ACI) are a big challenge to quantify the overall effect of human activities on the radiative, heat, and precipitation budgets of the atmosphere. New observational capabilities are demanded. To study the influence of aerosol particles on cloud microphysics an analysis scheme composed of newly-developed arrays is introduced. The retrieval of microphysical properties of liquid-water clouds and of the aerosol particles below the clouds from lidar observations, in a practical and replicable way, is the major challenge tackled in this work. A lidar-based approach to derive liquid-water cloud microphysical properties from dual-field-of-view (DFOV) depolarization measurements is introduced. In addition, a new method to accurately obtain the aerosol properties below cloud layers was developed and implemented into the analysis infrastructure. Comparisons with alternative observational and modeling approaches corroborate the accuracy of both methods. The number concentration of cloud condensation nuclei (CCN) is derived from the aerosol particle extinction coefficient below the cloud, and in combination with the cloud-microphysics retrieval, they provide an aerosol-cloud scene, which allow us to study ACI. Long-term observations at the pristine location of Punta Arenas (PA), Chile, and at the polluted site of Dushanbe (DB), Tajikistan, were analyzed for this purpose. On average, similar values of cloud droplet and below-cloud CCN number concentrations, in the range of 10--150~cm$^{-3}$, were observed at PA. At DB, larger cloud droplet number concentrations were observed, in the order of 200--400 cm-3 but much larger CCN concentrations of about 700--900 cm-3 were found. The so-called ACI index was assessed from the collected data sets. The most robust estimate of the index was obtained when calculating monthly averages over the whole measurement periods, fourteen months at PA and seven months at DB. Values of 0.83 +/- 0.20 and 0.57+/ 0.26 were derived at PA and DB, respectively, and they were used to estimate the radiative forcing due to the Twomey effect. A radiative cooling from -0.70 to -0.17 Wm-2 for PA and between -1.89 and -0.66 Wm-2 for DB is found. These results agree with global estimates of the cloud-mediated aerosol effect but are slightly larger than those values usually found at the specific locations considered. Furthermore, the results obtained at PA show the relevance of updraft movements to trigger ACI. When considering only updraft-dominated periods, the ACI index is up to 50% larger than when no wind information is considered. The new capabilities illuminated during this work may provide a big help for estimations of the cloud-mediated radiative effect and may provide a baseline to confront models dealing with cloud microphysics in future studies.:1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 2 Aerosol, clouds and their interaction - State of the art and research questions. . 7 2.1 Aerosol and clouds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.1 Aerosol effect on liquid-water clouds . . . . . . . . . . . . . . . . . . . . . . . . .8 2.1.2 Aerosol effect on ice-containing clouds . . . . . . . . . . . . . . . . . . . . . . .9 2.1.3 Cloud processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10 2.1.4 Modeling droplet number concentration Nd . . . . . . . . . . . . . . . . . . 10 2.2 Aerosol radiative effect via ACI in liquid-water clouds . . . . . . . . . . . . . .11 2.2.1 Aerosol-cloud-interaction index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.2.2 Observational approaches for the ACI index. . . . . . . . . . . . . . . . . . . .14 2.2.3 Strategies to evaluate the ACI index from observations . . . . . . . . . . .16 2.2.4 ACI studies based on lidar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.3 Research questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3 Lidar measurements of aerosol-cloud interaction – Overview of applied methodologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 3.1 Multiple-scattering lidar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 3.2 DFOV-Raman technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.3 Single-FOV polarization lidar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25 3.3.1 Comparison between DFOV-Raman and SFOV-Depol methods . . . 27 3.4 Dual-FOV depolarization approach . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.4.1 Calibration of the lidar system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.4.2 DFOV-Depol measurement cases . . . . . . . . . . . . . . . . . . . . . . . . . . 31 3.5 Implementation of the DFOV-Depol approach into the standardized lidar sys- tem Polly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33 4 Research results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37 4.1 First publication: Polarization lidar: an extended three-signal calibration approach . . . . . . .39 4.2 Second publication: The dual-field-of-view polarization lidar technique: A new concept in monitoring aerosol effects in liquid-water clouds – Theoretical framework . . . . . . . . .59 4.3 Third publication: The dual-field-of-view polarization lidar technique: A new concept in monitoring aerosol effects in liquid-water clouds – Case studies . . . . . . . . . . . . . . . .79 5 Discussion and further applications – Long-term observations of aerosol- cloud interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101 5.1 Observations on cloud scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102 5.2 Long-term results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 5.2.1 Comparison of DFOV-Depol products with available estimations and observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108 5.3 Assessment of the ACI index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 5.4 Relevance of the ACI index for the radiative effect . . . . . . . . . . . . 112 6 Summary and outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117 Appendix A: Aerosol properties with lidar . . . . . . . . . . . . . . . . . . . .125 A.1 Lidar principles of elastic and Raman lidar . . . . . . . . . . . . . . . .125 A.2 Raman lidar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 A.2.1 Retrieval of extinction coefficient . . . . . . . . . . . . . . . . . . . . . 128 A.2.2 Retrieval of backscattering coefficient. . . . . . . . . . . . . . . . . . 128 A.2.3 Bottom-up approximation for Raman Signals . . . . .. . . . . . . 129 A.2.4 Evaluation of Raman methods. . . . . . . . . . . . . . . . . . . . . . . 130 A.3 Elastic Lidar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .132 A.3.1 Klett-Fernald Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 A.3.2 Quasi-backscattering for high resolved retrievals. . . . . . . . . 133 A.3.3 Bottom-up approximation for elastic signals . . . . . . . . . . . . 135 A.3.4 Evaluation of methods based on elastic lidar. . . . . . . . . . . . 137 A.3.5 Microphysical properties from optical properties. . . . . . . . . . 139 Appendix B Characterization of DFOV-Depol lidar . . . . . . . . . . . . 143 B.1 Transmission ratio based on long-term analysis . . . . . . . . . . . 144 Appendix C: Author’s contributions to the three publications . . . . 149 Appendix D Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .151 D.1 List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .151 D.2 List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 D.3 List of Symbols (excluding cumulative part) . . . . . . . . . . 156 D.4 List of Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

In previous publications [1,7] the author described the base rivalry in monotonous DNA sequences and their effect on the DNA repair mechanism. According to this theory, many base building blocks compete for the occupancy of the newly released base site in the replication of monotonous DNA sequences in the elongation phase. This gives them more and more kinetic energy from replication position k to next position. Thus, there is a probability that a tautomeric base pair is formed behind the end of the monotonic sequence because of the tunneling effect. After its replication a different, irreparable base pair develops from the tautomeric base pair, when the rivalry - energy leads to a very strong hydrogen bond. This happens, however, by chance. In the following, we will describe the 3 phenomena: The tunnel probability (section 2), the probability for coming up of a high – energy – base building block (Elitist, section 3),and the combination of both phenomena (section 4). The result of these calculations is the equation (28). It is remarkable that follows from these calculations that the length of the monotonous sequences, and also the length of DNA increases itself in the course of evolution (section 5). (Read up all detailed computations in [7].) [... from introduction]

No description available.

In this thesis, research starts by questioning Berry curvature dipole's role in electronic properties in solids. Strongly inspired by the recent studies, we discover a more profound interpretation of the Berry curvature dipole. It is demonstrated that the anomalous correction to the electron acceleration is proportional to the Berry curvature dipole and is responsible for the Non-linear Hall effect recently discovered in materials with broken inversion symmetry. This allows uncovering a deeper meaning of the Berry curvature dipole as a non-linear version of the Drude weight that serves as a measurable order parameter for broken inversion symmetry in metals. Later, we introduce the Quantum Rectification Sum Rule in time-reversal invariant materials is derived by showing that the integral over frequency of the rectification conductivity depends solely on the Berry connection and not on the band energies or relaxation rates. In the final part of the thesis, we use the Keldysch-Floquet formalism to obtain non-perturbative predictions of the optical responses in solids, mainly focusing on the clean limit response of systems with broken time-reversal symmetry.

Supraleitung in Graphit ist kein neues Thema. Dieser Effekt wurde bereits in den 1960er Jahren in Interkalationsverbindungen von Graphit gefunden. Die Supraleitung in reinem Graphit wurde bereits vor etwa 50 Jahren beschrieben. Kürzlich wurden in zweischichtigem Graphen, in dem die Graphenschichten um einen 'magischen' Winkeln um die c Achse verdreht wurden, flache Bänder in der elektronischen Bandstruktur nachgewiesen, welche mit der Entstehung von Supraleitung zusammenhängen. Wir haben die elektrischen Transporteigenschaften in Graphitproben mit unterschiedlichen Elektrodenkonfigurationen untersucht. Wir haben den elektrischen Widerstand von hochgeordnetem natürlichem und synthetischem Graphit mit Elektroden auf der Oberseite der ab Basalebene und auch parallel zur c Achse mit hoher Präzision gemessen und den Einfluss der hochleitenden Stapelfehler untersucht, an denen, eingebettet zwischen den kristallinen Graphitschichten, 2D-Grenzflächen entstehen, die ebenfalls flache Bänder aufweisen. Die Existenz einer gut geordneten rhomboedrischen Graphitphase in allen gemessenen Proben wurde durch Röntgenbeugungsmessungen nachgewiesen. Die Grenzflächen mit der hexagonalen Phase stellen laut theoretischer Vorhersagen einen möglichen Ursprung für die Hochtemperatursupraleitung dar. Die experimentellen Ergebnisse liefern eindeutige Beweise für körnige Supraleitung in diesen Materialien, z. B. einen schrittweisen Temperaturübergang bei ~ 350 K, magnetische Irreversibilität, Zeitabhängigkeit nach einer Feldänderung, die mit dem eingeschlossenen Fluss und Flusskriechen übereinstimmt, und den teilweise abgestoßenen magnetischen Fluss, welcher in Magnetisierungsmessungen beobchtet werden kann. Die Lokalisierung der körnigen Supraleitung an diesen 2D-Grenzflächen verhindert die Beobachtung widerstandsfreier elektrischer Ströme oder eines vollständigen Meißner-Zustands. Der Grund ist, dass die körnige Supraleitung in abgegrenzten Regionen an den Grenzflächen entsteht, welche in eine Multigraphen-Halbleitermatrix eingebettet sind. In dieser Arbeit wird eine detaillierte Untersuchung des Magnetowiderstands in verschiedenen Arten von Graphitproben bei niedrigen und hoch gepulsten Magnetfeldern vorgestellt. / Superconductivity in graphite is not a new topic. Its existence goes back to the 1960s when this effect was found in intercalation compounds of graphite. Superconductivity in pure graphite was reported already around 50 years ago and recently proved in bi-layer graphene, related to 'magic' angles between the graphene layers, twisted around the c axis, with the electronic band structure exhibiting flat bands. We have studied electrical transport properties in graphite samples with different electrode configurations. Measuring with high precision, the electrical resistance of highly ordered natural and synthetic graphite, with electrodes placed on the top of the ab basal plane, and also parallel to the c axis, we investigated the influence of the highly conducting stacking faults, referred as 2D interfaces, embedded between the crystalline regions of graphite, which also exhibit flat bands. The existence of well ordered rhombohedral graphite phase in all measured samples has been proved by x-ray diffraction measurements, suggesting its interfaces with the hexagonal phase as a possible origin of high-temperature superconductivity, predicted by theoretical studies. The results provide clear evidence of granular superconductivity, e.g., a step-like transition in temperature at ~ 350 K, magnetic irreversibility, time dependence after a field change, consistent with trapped flux and flux creep, and the partial magnetic flux expulsion from magnetization measurements. The localization of the granular superconductivity at these 2D interfaces prevents the observation of a zero resistance state or a full Meissner state. The reason is that the superconducting distribution is a mixture of superconducting patches at the interfaces, and they are embedded in a multigraphene semiconducting matrix. A detailed study of the magnetoresistance in different kinds of graphite samples at low and high-pulsed magnetic fields is presented in this work.