Institut für Physik und Astronomie
Refine
Year of publication
- 2021 (167) (remove)
Document Type
- Article (128)
- Doctoral Thesis (29)
- Postprint (7)
- Course Material (1)
- Habilitation Thesis (1)
- Master's Thesis (1)
Is part of the Bibliography
- yes (167)
Keywords
- diffusion (9)
- MHD (5)
- anomalous diffusion (5)
- cosmic rays (4)
- intergalactic medium (4)
- methods: numerical (4)
- synchronization (4)
- Synchronisation (3)
- climate change (3)
- gravitational waves (3)
- networks (3)
- organic solar cells (3)
- quasars: absorption lines (3)
- stars: massive (3)
- stars: variables: general (3)
- subdwarfs (3)
- Astrophysics (2)
- Astrophysik (2)
- Auger–Meitner (2)
- Bragg peak (2)
- Chebyshev inequality (2)
- Chromosphere (2)
- Coster–Kronig (2)
- FLASH (2)
- Gravitationswellen (2)
- Klimawandel (2)
- Kuramoto model (2)
- Laser powder bed fusion (2)
- Lasers (2)
- Lattice dynamics (2)
- Magnetism (2)
- NEXAFS (2)
- Netzwerke (2)
- Perovskites (2)
- Phonons (2)
- Photovoltaik (2)
- Residual stresses (2)
- Spectroscopy (2)
- Spektroskopie (2)
- Synchronization (2)
- Thermal effects (2)
- Thermodynamic properties (2)
- Thin films (2)
- Ultrafast X-ray diffraction (2)
- X-ray (2)
- approximate methods (2)
- astroparticle physics (2)
- binaries: close (2)
- cirrus clouds (2)
- correlations (2)
- first passage time (2)
- first-passage time (2)
- first-reaction time (2)
- hydrodynamics (2)
- large-deviation statistic (2)
- large-scale structure of Universe (2)
- lidar (2)
- neutron diffraction (2)
- nucleobases (2)
- perovskite solar cells (2)
- photoelectron (2)
- photoelectron spectroscopy (2)
- reaction cascade (2)
- shell-like geometries (2)
- stars: abundances (2)
- sulfur (2)
- systems (2)
- techniques: spectroscopic (2)
- thiouracil (2)
- time-averaged mean squared displacement (2)
- tipping cascade (2)
- white dwarfs (2)
- (PEDOT (1)
- 2D colloid ordering (1)
- 3d metals (1)
- ARPES (1)
- Actin cytoskeleton dynamics (1)
- Additive manufacturing (1)
- Aerosol (1)
- Arctic clouds (1)
- Astronomie (1)
- Astronomy (1)
- Astronomy data (1)
- Astronomy databases (1)
- Astrophotonik (1)
- Astrostatistics tools (1)
- Astroteilchenphysik (1)
- Atlantic meridional overturning circulation (1)
- Auger electron spectroscop (1)
- Azobenzene containing cationic surfactants (1)
- Bandenenergien (1)
- Bethe (1)
- Bio-Hybridsystem (1)
- Biophysik (1)
- Boltzmann distribution (1)
- Cassiopeia A (1)
- Cayley trees (1)
- Chimera (1)
- Chimäre-Zustände (1)
- Chromosphäre (1)
- Circumgalactic Medium (1)
- Content Knowledge (1)
- Coupled Systems (1)
- Curie-transition (1)
- DNA-PAINT (1)
- Datenanalyse (1)
- Datenanalyse der Galaktischen Ebene (1)
- Datenassimilation (1)
- Deeper School Knowledge (1)
- Demografie des Schwarzen Lochs (1)
- Development of Content Knowledge (1)
- Dielectric hysteresis (1)
- Dip-Dotierung (1)
- Dosimetrie (1)
- Dotierung (1)
- Drehimpulsverlust (1)
- Drude model (1)
- Dynamical Systems (1)
- Dünn film (1)
- Einbettung (1)
- Erdsystem Modellierung (1)
- European Arctic (1)
- Europäische Arktis (1)
- Experimentierkompetenz (1)
- Experimentierzyklus (1)
- Fachwissen (1)
- Fachwissensentwicklung (1)
- Faserkopplung (1)
- Filamente (1)
- Filaments (1)
- Force Field Optimization (1)
- Galactic plane data analysis (1)
- Galaxienentwicklung (1)
- Galaxy: stellar content (1)
- Gammastrahlungsastronomie (1)
- Gardner equation (1)
- Gitterdynamik (1)
- Granulation (1)
- Gravitationswellenastronomie (1)
- Grenzflächen (1)
- Gyrochronologie (1)
- H.E.S.S (1)
- H.E.S.S. (1)
- Halogenbindung (1)
- Halophile Proteine (1)
- Halophilic proteins (1)
- Helium (1)
- Hertzsprung-Russell and C-M diagrams (1)
- Hertzsprung-Russell and colour-magnitude diagrams (1)
- Hilbert transform (1)
- Hilbert-Transformation (1)
- Hurricane Sandy (1)
- Integralfieldspektroskopie (1)
- Interferometer (1)
- Intergalactic Medium (1)
- Ir(111) (1)
- Kalman filter (1)
- Kalman-Filter (1)
- Kippelement (1)
- Kippkaskade (1)
- Kraftfeld Optimierung (1)
- Kuramoto-Modell (1)
- LIGO (1)
- Large-scale Structure (1)
- Lehrkräftebildung (1)
- Leitfähigkeit (1)
- Lewis acid doping (1)
- Lewis-Säure Dotierung (1)
- Lidar (1)
- Light induced diffusioosmotic flow (1)
- Lyapunov exponent (1)
- Längschnitt (1)
- Magellanic Clouds (1)
- Magnetic fields (1)
- Magnetismus (1)
- Massenaussterben (1)
- Maximum likelihood estimation (1)
- Mean first encounter time (1)
- Metal Halide Perovskites (1)
- Metal Halogenid Perowskiten (1)
- Microstructure and (1)
- Mid-temperature transition (1)
- Molecular Dynamics Simulation (1)
- Molekulardynamische Simulation (1)
- Multipolare Gravitationswellenformen (1)
- NGC 1786 (1)
- NGC 1898 (1)
- NGC 2516 (1)
- NGC 3532 (1)
- Network (1)
- Nickel-based (1)
- Non-linear dielectric spectroscopy (1)
- Oscillation (1)
- Oszillatoren (1)
- P(VDF-TrFE-CFE) (1)
- PSS)-coated porous (1)
- Paleoklimatologie (1)
- Parametric drift estimation (1)
- Partikeltransport (1)
- Perowskit Solarzellen (1)
- Phasen-Amplituden Trennung (1)
- Phasendemodulation (1)
- Phasenkopplungen höherer Ordnung (1)
- Phasenoszillatoren (1)
- Phasenraumdichte (1)
- Photometrie (1)
- Photosphere (1)
- Photovoltaics (1)
- Physics Education (1)
- Physik (1)
- Physik Lehramt (1)
- Polymer-Halbleiter (1)
- Polymeraggregation (1)
- Pre-Service (1)
- Process atmosphere (1)
- Prominences (1)
- Quiescent (1)
- Quiet (1)
- Radiation protection (1)
- Radiative transfer (1)
- Random walks (1)
- Reflexion (1)
- Rekurrenz (1)
- Rekurrenzanalyse (1)
- Relaxor-ferroelectric polymer (1)
- Röntgenbeugung (1)
- SN 1572 (1)
- STM (1)
- Scan strategies (1)
- Schwarze Löcher (1)
- Single-mode-Faser (1)
- Solar Physics (1)
- Solar chromosphere (1)
- Sonnenphysik (1)
- Spektrographen (1)
- Stochastic reaction– diffusion (1)
- Stochastisches Bursting (1)
- Strahlenarten (1)
- Strahlenbelastung (1)
- Strahlenbiologie (1)
- Strahlenschutz (1)
- Strahlungsgürtel (1)
- Strahlungtransportmodellierung (1)
- Sun (1)
- Supernovaüberreste (1)
- Survival probability (1)
- THz Spectroscopy (1)
- THz Spektroskopie (1)
- Teilchenbeschleunigung (1)
- Ti-6Al-4V (1)
- Virgo (1)
- Voronoi entropy (1)
- Wolf-Rayet (1)
- Wolken (1)
- X-ray absorption spectroscopy (1)
- X-ray and (1)
- X-ray and neutron diffractions (1)
- X-ray computed (1)
- X-ray diffraction (1)
- X-ray emission spectroscopy (1)
- X-ray imaging (1)
- X-ray spectroscopy (1)
- X-rays: binaries (1)
- X-rays: individual: 3A 1954+319 (1)
- X-rays: stars (1)
- Zirruswolken (1)
- Zustandsraumrekonstruktion/Phasenraumrekonstruktion (1)
- absorption lines (1)
- accretion (1)
- accretion discs (1)
- active galactic nuclei (1)
- active particles (1)
- active transport (1)
- adaptive Optik (1)
- adaptive optics (1)
- additive manufacturing (1)
- additive manufacturing (AM) (1)
- aerosol (1)
- aktive galaktische Kerne (1)
- aktiven Transport (1)
- all-organic (1)
- all-organic ferroelectret nanogenerator (FENG) (1)
- allgemeine Relativitätstheorie (1)
- amoeboid motion (1)
- amöboide Bewegung (1)
- analysis (1)
- angular momentum loss (1)
- astronomical instrumentation (1)
- astronomische Instrumente (1)
- astrophotonics (1)
- astrophysical plasmas (1)
- atmospheric effects (1)
- atmosphärische Effekte (1)
- azobenzene (1)
- binaries: general (1)
- binaries: spectroscopic (1)
- binary black holes (1)
- binäre Schwarze Löcher (1)
- bio-hybrid system (1)
- biophysics (1)
- bismuth (1)
- bismuthene (1)
- black hole demographics (1)
- black holes (1)
- cascading regime (1)
- catalogs (1)
- catalysis (1)
- cellular structures (1)
- chaos (1)
- charge selectivity (1)
- chemical (1)
- chimera states (1)
- chirality (1)
- chromospheric activity (1)
- chromospherische Aktivität (1)
- circumstellar matter (1)
- climate impacts (1)
- clouds (1)
- collective dynamics (1)
- coloured (1)
- compacton (1)
- complex networks (1)
- complex systems (1)
- computed tomography (1)
- conductivity (1)
- consecutive disasters (1)
- content analysis (1)
- convection (1)
- cool stars (1)
- correlated noise (1)
- correlation functions (1)
- cosmic ray propagation (1)
- cosmology: observations (1)
- dark ages (1)
- dark ages, reionization, first stars (1)
- data analysis (1)
- data assimilation (1)
- diaspora (1)
- dichalcogenides (1)
- diffraction-elastic constants (1)
- diffusion length (1)
- dip doping (1)
- dispersion (1)
- dispersion force (1)
- domino effect (1)
- dosis measurement (1)
- drift length (1)
- dynamical patterns (1)
- dynamische Muster (1)
- dynamische Systeme (1)
- early warning indicators (1)
- earth system modeling (1)
- economic ripple resonance (1)
- economic ripples (1)
- econophysics (1)
- electro-mechanically active polymers (1)
- electrochemistry (1)
- electronic structure (1)
- embedding (1)
- energy levels (1)
- entanglement (1)
- equation (1)
- equation of state (1)
- equivalent-circuit (1)
- exaction (1)
- exoplanets (1)
- expanded polytetrafluoroethylene (1)
- experimental competencies (1)
- experimental model (1)
- extreme weather (1)
- fabric electrodes (1)
- femtochemistry (1)
- ferroelectret (1)
- fiber coupling (1)
- fields (1)
- figure of merit (1)
- first passage (1)
- first stars (1)
- fluorescence (1)
- friction (1)
- galaxies: evolution (1)
- galaxies: formation (1)
- galaxies: halos (1)
- galaxies: individual: LMC (1)
- galaxies: interactions (1)
- galaxies: magnetic (1)
- galaxies: magnetic fields (1)
- galaxies: star clusters: individual (1)
- galaxies: starburst (1)
- galaxy evolution (1)
- gamma-ray astronomy (1)
- gekoppelte System (1)
- general relativity (1)
- geometric Brownian motion (1)
- global surface warming (1)
- globular clusters: general (1)
- graphene (1)
- gravitational-wave astronomy (1)
- green solvents (1)
- großräumige Struktur (1)
- gyrochronology (1)
- halbleitendes Polymer (1)
- halogen bonding (1)
- haptic feedback (1)
- healing (1)
- heat transfer (1)
- heterogeneous diffusion process (1)
- high-order phase coupling (1)
- hydrodynamic model (1)
- hydrogen evolution reaction (1)
- hyperbolic attractor (1)
- ice clouds (1)
- impacts (1)
- in situ monitoring (1)
- in situ thermography (1)
- information (1)
- information theory (1)
- infrared thermography (1)
- instabilities (1)
- integral field spectroscopy (1)
- integrated optics (1)
- integrierten Optik (1)
- interfaces (1)
- interfacial layers (1)
- interferometers (1)
- intergalaktisches Medium (1)
- interlayer time (1)
- international migration (1)
- interstellar matter (1)
- interstellar medium (1)
- iteration method (1)
- kind of radiation (1)
- komplexe Netzwerke (1)
- kosmische Strahlung (1)
- kühle Sterne (1)
- laser powder bed fusion (1)
- laser powder bed fusions (1)
- laser-based additive manufacturing (1)
- lattice dynamics (1)
- lattice structures (1)
- lattices (1)
- lifetime‐ mobility product (1)
- local (1)
- localization microscopy (1)
- loss propagation (1)
- magnetic field (1)
- magnetic fields (1)
- magnetism (1)
- magnetospheric waves (1)
- magnetosphärischen Wellen (1)
- mass extinctions (1)
- mass spectrometry (1)
- master (1)
- memory effects (1)
- metal optics (1)
- methods: statistical (1)
- micelles (1)
- micro-energy harvesting (1)
- migration transition (1)
- modelling (1)
- molecular doping (1)
- molekulare Dotierung (1)
- molybdenum oxide (1)
- monitoring (1)
- multi-layer systems (1)
- multipolar gravitational waves (1)
- natural disasters (1)
- neutron star mergers (1)
- nichtlineare Dynamiken (1)
- nichtlineare Oszillationen (1)
- noise (1)
- non-Gaussian (1)
- non-Gaussian distribution (1)
- non-contact heat transfer (1)
- non-equilibrium steady state (1)
- non-extensive statistics (1)
- non-geminate recombination (1)
- non-halogenated solvents (1)
- non-linear oscillators (1)
- nonergodicity (1)
- nonlinear dynamics (1)
- nonlinear lattice (1)
- nonradiative losses (1)
- nonstationary diffusivity (1)
- ocean heat uptake (1)
- offener Sternhaufen (1)
- open cluster (1)
- open-circuit voltage decay (1)
- optical fibers (1)
- optical spectroscopy (1)
- optical tomography (1)
- optische Fasern (1)
- optische Spektroskopie (1)
- optoplasmonic (1)
- organic semiconductors (1)
- organische Halbleiter (1)
- oscillations (1)
- outflows (1)
- paleoclimatology (1)
- particle acceleration (1)
- particle transport (1)
- phase demodulation (1)
- phase oscillators (1)
- phase space density (1)
- phase transitions (1)
- phase-amplitude mixing (1)
- photochemistry (1)
- photoluminescence quenching (1)
- photometry (1)
- photonic lanterns (1)
- photonische Laternen (1)
- photoswitches (1)
- photovoltaic (1)
- physics (1)
- piezoelectric nanogenerator (PENG) (1)
- planets and satellites: atmospheres (1)
- planets and satellites: composition (1)
- planets and satellites: gaseous planets (1)
- plasma instabilities (1)
- plasmonics (1)
- polarization (1)
- polymer aggregation (1)
- principal stress components (1)
- process (1)
- processing (1)
- quantifizierende Rekurrenzanalyse (1)
- quantitative Inhaltsanalyse (1)
- quantum thermodynamics (1)
- quasars: (1)
- quasars: general (1)
- quasars: supermassive black holes (1)
- quasi-particle interaction (1)
- radiation belts (1)
- radiation load (1)
- radiative transfer (1)
- radiative transfer modeling (1)
- radio continuum: galaxies (1)
- radiobiology (1)
- rate constants (1)
- recombination order (1)
- recurrence (1)
- recurrence analysis (1)
- recurrence quantification analysis (1)
- reflection (1)
- reionization (1)
- repercussion resonance (1)
- residual stress (1)
- residual stress analysis (1)
- return migration (1)
- rotation (1)
- scaled Brownian motion (1)
- screen-printed (1)
- selective laser melting (SLM) (1)
- self-organisation (1)
- semiconducting polymer (1)
- shifts (1)
- signal processing (1)
- simulation model (1)
- single-mode fiber (1)
- single-molecule (1)
- small ring systems (1)
- solitary wave (1)
- spacing (1)
- spatial (1)
- spectrographs (1)
- spectroscopy (1)
- spin-orbit interaction (1)
- stars: (1)
- stars: atmospheres (1)
- stars: chemically peculiar (1)
- stars: early-type (1)
- stars: evolution (1)
- stars: fundamental parameters (1)
- stars: horizontal-branch (1)
- stars: individual: EC 22536-5304 (1)
- stars: kinematics and dynamics (1)
- stars: mass-loss (1)
- stars: neutron (1)
- stars: winds (1)
- starspots (1)
- state space reconstruction (1)
- steady‐ state photoconductance (1)
- stellar activity (1)
- stellar rotation (1)
- stellare Aktivität (1)
- stellare Rotation (1)
- stilbene oxide (1)
- stochastic bursting (1)
- stochastic processes (1)
- strain-free lattice (1)
- superalloys (1)
- supermassereiche Schwarze Löcher (1)
- supermassive black holes (1)
- supernova remnants (1)
- supernovae: general (1)
- supply chains (1)
- supply network (1)
- surface hopping (1)
- surfactants (1)
- teacher education (1)
- techniques: image processing (1)
- texture (1)
- thin films (1)
- thin-film actuators (1)
- time-series analysis (1)
- tipping element (1)
- tipping interactions (1)
- tomography (XCT) (1)
- transient chaos (1)
- transit migration (1)
- triaxial residual stresses (1)
- turbulence (1)
- ultrafast (1)
- ultraschnell (1)
- ultraviolet: general (1)
- vertieftes Schulwissen (1)
- vinylidenefluoride(VDF)-based polymers (1)
- viscosity (1)
- water diffusion in the brain (1)
- wearable electronics (1)
- weather extremes (1)
- whispering gallery modes (1)
- zirkumgalaktisches Medium (1)
- иперболический аттрактор (1)
- оллективная динамика (1)
- синхронизация (1)
Institute
- Institut für Physik und Astronomie (167) (remove)
State-of-the-art organic solar cells exhibit power conversion efficiencies of 18% and above. These devices benefit from the suppression of free charge recombination with regard to the Langevin limit of charge encounter in a homogeneous medium. It is recognized that the main cause of suppressed free charge recombination is the reformation and resplitting of charge-transfer (CT) states at the interface between donor and acceptor domains. Here, we use kinetic Monte Carlo simulations to understand the interplay between free charge motion and recombination in an energetically disordered phase-separated donor-acceptor blend. We identify conditions for encounter-dominated and resplitting-dominated recombination. In the former regime, recombination is proportional to mobility for all parameters tested and only slightly reduced with respect to the Langevin limit. In contrast, mobility is not the decisive parameter that determines the nongeminate recombination coefficient, k(2), in the latter case, where k2 is a sole function of the morphology, CT and charge-separated (CS) energetics, and CT-state decay properties. Our simulations also show that free charge encounter in the phase-separated disordered blend is determined by the average mobility of all carriers, while CT reformation and resplitting involves mostly states near the transport energy. Therefore, charge encounter is more affected by increased disorder than the resplitting of the CT state. As a consequence, for a given mobility, larger energetic disorder, in combination with a higher hopping rate, is preferred. These findings have implications for the understanding of suppressed recombination in solar cells with nonfullerene acceptors, which are known to exhibit lower energetic disorder than that of fullerenes.
In contrast to the common conception that the interfacial energy-level alignment is affixed once the interface is formed, we demonstrate that heterojunctions between organic semiconductors and metal-halide perovskites exhibit huge energy-level realignment during photoexcitation. Importantly, the photoinduced level shifts occur in the organic component, including the first molecular layer in direct contact with the perovskite. This is caused by charge-carrier accumulation within the organic semiconductor under illumination and the weak electronic coupling between the junction components.
We investigate the transition from incoherence to global collective motion in a three-dimensional swarming model of agents with helical trajectories, subject to noise and global coupling. Without noise this model was recently proposed as a generalization of the Kuramoto model and it was found that alignment of the velocities occurs discontinuously for arbitrarily small attractive coupling. Adding noise to the system resolves this singular limit and leads to a continuous transition, either to a directed collective motion or to center-of-mass rotations.
Noise is ubiquitous in nature and usually results in rich dynamics in stochastic systems such as oscillatory systems, which exist in such various fields as physics, biology and complex networks. The correlation and synchronization of two or many oscillators are widely studied topics in recent years.
In this thesis, we mainly investigate two problems, i.e., the stochastic bursting phenomenon in noisy excitable systems and synchronization in a three-dimensional Kuramoto model with noise. Stochastic bursting here refers to a sequence of coherent spike train, where each spike has random number of followers due to the combined effects of both time delay and noise. Synchronization, as a universal phenomenon in nonlinear dynamical systems, is well illustrated in the Kuramoto model, a prominent model in the description of collective motion.
In the first part of this thesis, an idealized point process, valid if the characteristic timescales in the problem are well separated, is used to describe statistical properties such as the power spectral density and the interspike interval distribution. We show how the main parameters of the point process, the spontaneous excitation rate, and the probability to induce a spike during the delay action can be calculated from the solutions of a stationary and a forced Fokker-Planck equation. We extend it to the delay-coupled case and derive analytically the statistics of the spikes in each neuron, the pairwise correlations between any two neurons, and the spectrum of the total output from the network.
In the second part, we investigate the three-dimensional noisy Kuramoto model, which can be used to describe the synchronization in a swarming model with helical trajectory. In the case without natural frequency, the Kuramoto model can be connected with the Vicsek model, which is widely studied in collective motion and swarming of active matter. We analyze the linear stability of the incoherent state and derive the critical coupling strength above which the incoherent state loses stability. In the limit of no natural frequency, an exact self-consistent equation of the mean field is derived and extended straightforward to any high-dimensional case.
The galactic interstellar medium is magnetized and turbulent. The magnetic field and turbulence play important roles in many astrophysical mechanisms, including cosmic ray transport, star formation, etc. Therefore, measurements of magnetic field and turbulence information are crucial for the proper interpretation of astronomical observations. Nonetheless, the magnetic field observation is quite challenging, especially, there is not universal magnetic tracer for diffuse medium. Moreover, the modelling of turbulence can be oversimplified due to the lack of observational tools to diagnose the plasma properties of the turbulence in the galactic interstellar medium. The studies presented in this thesis have addressed these challenges by bridging the theoretical studies of magnetic field and turbulence with numerical simulations and observations.
The following research are presented in this thesis. The first observational evidence of the novel magnetic tracer, ground state alignment (GSA), is discovered, revealing the three-dimensional magnetic field as well as 2 orders of magnitude higher precision comparing to previous observational study in the stellar atmosphere of the post-AGB 89 Herculis. Moreover, the application of GSA in the sub-millimeter fine-structure lines is comprehensively studied for different elements and with magnetohydrodynamic simulations. Furthermore, the influence of GSA effect on the spectroscopy is analyzed and it is found that measurable variation will be produced on the spectral line intensity and the line ratio without accounting for the optical pumping process or magnetic field.
Additionally, a novel method to measure plasma modes in the interstellar medium, Signatures from Polarization Analysis (SPA), is proposed and applied to real observations. Magneto-sonic modes are discovered in different types of interstellar medium. An explanation is provided for the long-standing mystery, the origin of γ-ray enhanced emission “Cygnus Cocoon”, based on the comparison between the outcome of SPA and multi-waveband observational data. These novel methods have strong potentials for broader observational applications and will play crucial roles in future multi-wavelength astronomy.
Reciprocal space slicing
(2021)
An experimental technique that allows faster assessment of out-of-plane strain dynamics of thin film heterostructures via x-ray diffraction is presented. In contrast to conventional high-speed reciprocal space-mapping setups, our approach reduces the measurement time drastically due to a fixed measurement geometry with a position-sensitive detector. This means that neither the incident (ω) nor the exit (2θ) diffraction angle is scanned during the strain assessment via x-ray diffraction. Shifts of diffraction peaks on the fixed x-ray area detector originate from an out-of-plane strain within the sample. Quantitative strain assessment requires the determination of a factor relating the observed shift to the change in the reciprocal lattice vector. The factor depends only on the widths of the peak along certain directions in reciprocal space, the diffraction angle of the studied reflection, and the resolution of the instrumental setup. We provide a full theoretical explanation and exemplify the concept with picosecond strain dynamics of a thin layer of NbO2.
Reciprocal space slicing
(2021)
An experimental technique that allows faster assessment of out-of-plane strain dynamics of thin film heterostructures via x-ray diffraction is presented. In contrast to conventional high-speed reciprocal space-mapping setups, our approach reduces the measurement time drastically due to a fixed measurement geometry with a position-sensitive detector. This means that neither the incident (ω) nor the exit (2θ) diffraction angle is scanned during the strain assessment via x-ray diffraction. Shifts of diffraction peaks on the fixed x-ray area detector originate from an out-of-plane strain within the sample. Quantitative strain assessment requires the determination of a factor relating the observed shift to the change in the reciprocal lattice vector. The factor depends only on the widths of the peak along certain directions in reciprocal space, the diffraction angle of the studied reflection, and the resolution of the instrumental setup. We provide a full theoretical explanation and exemplify the concept with picosecond strain dynamics of a thin layer of NbO2.
Surface melting of the Greenland Ice Sheet contributes a large amount to current and future sea level rise. Increased surface melt may lower the reflectivity of the ice sheet surface and thereby increase melt rates: the so-called melt-albedo feedback describes this self-sustaining increase in surface melting. In order to test the effect of the melt-albedo feedback in a prognostic ice sheet model, we implement dEBM-simple, a simplified version of the diurnal Energy Balance Model dEBM, in the Parallel Ice Sheet Model (PISM). The implementation includes a simple representation of the melt-albedo feedback and can thereby replace the positive-degree-day melt scheme. Using PISM-dEBM-simple, we find that this feedback increases ice loss through surface warming by 60 % until 2300 for the high-emission scenario RCP8.5 when compared to a scenario in which the albedo remains constant at its present-day values. With an increase of 90 % compared to a fixed-albedo scenario, the effect is more pronounced for lower surface warming under RCP2.6. Furthermore, assuming an immediate darkening of the ice surface over all summer months, we estimate an upper bound for this effect to be 70 % in the RCP8.5 scenario and a more than 4-fold increase under RCP2.6. With dEBM-simple implemented in PISM, we find that the melt-albedo feedback is an essential contributor to mass loss in dynamic simulations of the Greenland Ice Sheet under future warming.
With ongoing anthropogenic global warming, some of the most vulnerable components of the Earth system might become unstable and undergo a critical transition. These subsystems are the so-called tipping elements. They are believed to exhibit threshold behaviour and would, if triggered, result in severe consequences for the biosphere and human societies. Furthermore, it has been shown that climate tipping elements are not isolated entities, but interact across the entire Earth system. Therefore, this thesis aims at mapping out the potential for tipping events and feedbacks in the Earth system mainly by the use of complex dynamical systems and network science approaches, but partially also by more detailed process-based models of the Earth system.
In the first part of this thesis, the theoretical foundations are laid by the investigation of networks of interacting tipping elements. For this purpose, the conditions for the emergence of global cascades are analysed against the structure of paradigmatic network types such as Erdös-Rényi, Barabási-Albert, Watts-Strogatz and explicitly spatially embedded networks. Furthermore, micro-scale structures are detected that are decisive for the transition of local to global cascades. These so-called motifs link the micro- to the macro-scale in the network of tipping elements. Alongside a model description paper, all these results are entered into the Python software package PyCascades, which is publicly available on github.
In the second part of this dissertation, the tipping element framework is first applied to components of the Earth system such as the cryosphere and to parts of the biosphere. Afterwards it is applied to a set of interacting climate tipping elements on a global scale. Using the Earth system Model of Intermediate Complexity (EMIC) CLIMBER-2, the temperature feedbacks are quantified, which would arise if some of the large cryosphere elements disintegrate over a long span of time. The cryosphere components that are investigated are the Arctic summer sea ice, the mountain glaciers, the Greenland and the West Antarctic Ice Sheets. The committed temperature increase, in case the ice masses disintegrate, is on the order of an additional half a degree on a global average (0.39-0.46 °C), while local to regional additional temperature increases can exceed 5 °C. This means that, once tipping has begun, additional reinforcing feedbacks are able to increase global warming and with that the risk of further tipping events.
This is also the case in the Amazon rainforest, whose parts are dependent on each other via the so-called moisture-recycling feedback. In this thesis, the importance of drought-induced tipping events in the Amazon rainforest is investigated in detail. Despite the Amazon rainforest is assumed to be adapted to past environmental conditions, it is found that tipping events sharply increase if the drought conditions become too intense in a too short amount of time, outpacing the adaptive capacity of the Amazon rainforest. In these cases, the frequency of tipping cascades also increases to 50% (or above) of all tipping events. In the model that was developed in this study, the southeastern region of the Amazon basin is hit hardest by the simulated drought patterns. This is also the region that already nowadays suffers a lot from extensive human-induced changes due to large-scale deforestation, cattle ranching or infrastructure projects.
Moreover, on the larger Earth system wide scale, a network of conceptualised climate tipping elements is constructed in this dissertation making use of a large literature review, expert knowledge and topological properties of the tipping elements. In global warming scenarios, tipping cascades are detected even under modest scenarios of climate change, limiting global warming to 2 °C above pre-industrial levels. In addition, the structural roles of the climate tipping elements in the network are revealed. While the large ice sheets on Greenland and Antarctica are the initiators of tipping cascades, the Atlantic Meridional Overturning Circulation (AMOC) acts as the transmitter of cascades. Furthermore, in our conceptual climate tipping element model, it is found that the ice sheets are of particular importance for the stability of the entire system of investigated climate tipping elements.
In the last part of this thesis, the results from the temperature feedback study with the EMIC CLIMBER-2 are combined with the conceptual model of climate tipping elements. There, it is observed that the likelihood of further tipping events slightly increases due to the temperature feedbacks even if no further CO$_2$ would be added to the atmosphere.
Although the developed network model is of conceptual nature, it is possible with this work for the first time to quantify the risk of tipping events between interacting components of the Earth system under global warming scenarios, by allowing for dynamic temperature feedbacks at the same time.
Constraints on the time-scales of quasar activity are key to understanding the formation and growth of supermassive black holes (SMBHs), quasar triggering mechanisms, and possible feedback effects on their host galaxies. However, observational estimates of this so-called quasar lifetime are highly uncertain (t(Q) similar to 10(4)-10(9) yr), because most methods are indirect and involve many model-dependent assumptions. Direct evidence of earlier activity is gained from the higher ionization state of the intergalactic medium (IGM) in the quasar environs, observable as enhanced Ly alpha transmission in the so-called proximity zone. Due to the similar to 30 Myr equilibration time-scale of He II in the z similar to 3 IGM, the size of the He II proximity zone depends on the time the quasar had been active before our observation t(on) <= t(Q), enabling up to +/- 0.2 dex precise measurements of individual quasar on-times that are comparable to the e-folding time-scale t(S) <= 44 Myr of SMBH growth. Here we present the first statistical sample of 13 quasars whose accurate and precise systemic redshifts allow for measurements of sufficiently precise He II quasar proximity zone sizes between similar or equal to 2 and similar or equal to 15 proper Mpc from science-grade Hubble Space Telescope (HST) spectra. Comparing these sizes to predictions from cosmological hydrodynamical simulations post-processed with 1D radiative transfer, we infer a broad range of quasar on-times from t(on) less than or similar to 1Myr to t(on) > 30 Myr that does not depend on quasar luminosity, black hole mass, or Eddington ratio. These results point to episodic quasar activity over a long duty cycle, but do not rule out substantial SMBH growth during phases of radiative inefficiency or obscuration.