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Cationic and anionic clusters of the group-14 elements carbon, silicon, germanium, tin, and lead are produced by high-vacuum laser ablation and studied with a multi-reflection time-of-flight mass spectrometer. In-trap photodissociation is performed for cluster species in the size range n=2–10. The clusters’ production rates as well as their dissociation pathways are used to probe the nonmetal–metal transition throughout the group. Carbon clusters show neutral-trimer break-off, while those of the other elements evaporate neutral monomers and, in some cases, form specific charged fragment sizes.
Magnetooptical properties of one-dimensional aperiodic structures formed by stacking together magnetic and nonmagnetic layers according to the Kolakoski self-generation scheme are studied theoretically using the 4x4 transfer matrix method. The effect of the generation stage of the sequence, and the helicity and direction of light propagation through the magneto-photonic crystals on the transmission/reflection spectra as well as Faraday and ellipticity rotations, have been investigated. Our results reveal that this kind of aperiodic magneto-photonic crystals can be used for the fabrication of multifrequency laser cavities, and optical filters/sensors.
Mechanical properties have been proven to be a pivotal parameter to enhance our understanding of living systems. While research during the last decades focused on cells and tissues, little is known about the role of organelle mechanics in cell function. Here, mitochondria are of specific interest due to their involvement in numerous physiological and pathological processes, e.g., in the production and homeostasis of reactive oxygen species (ROS). Using real-time fluorescence and deformability cytometry, we present a microfluidic technology that is capable to determine the mechanical properties of individual mitochondria at a throughput exceeding 100 organelles per second. Our data on several thousands of viable mitochondria isolated from rat C6 glial cells yield a homogenous population with a median deformation that scales with the applied hydrodynamic stress. In two proof-of-principle studies, we investigated the impact of exogenously and endogenously produced ROS on mitochondria mechanics. Exposing C6 cells to hydrogen peroxide (H2O2) triggers superoxide production and leads to a reduction in mitochondria size while deformation is increased. In a second study, we focused on the knockout of tafazzin, which has been associated with impaired remodeling of the mitochondrial membrane and elevated levels of ROS. Interestingly, our results reveal the same mechanical alterations as observed after the exposure to H2O2, which points to a unified biophysical mechanism of how mitochondria respond to the presence of oxidative stress. In summary, we introduce high-throughput mechanical phenotyping into the field of organelle biology with potential applications for understanding sub-cellular dynamics that have not been accessible before.
We investigate local THz field generation using spintronic THz emitters to enhance the resolution for micrometer-sized imaging. Far-field imaging with wavelengths above 100 µm limits the resolution to this order of magnitude. By using optical laser pulses as a pump, THz field generation can be confined to the area of laser beam focusing. The divergence of the generated THz beam due to laser beam focusing requires the imaged object to be close to the generation spot at a distance below the THz field wavelength. We generate THz-radiation by fs-laser pulses in CoFeB/Pt heterostructures, based on spin currents, and detect them by commercial low-temperature grown-GaAs (LT-GaAs) Auston switches. The spatial resolution of THz radiation is determined by applying a 2D scanning technique with motorized stages allowing step sizes in the sub-micrometer range. Within the near-field limit, we achieve spatial resolution in the dimensions of the laser spot size on the micrometer scale. For this purpose, a gold test pattern is evaporated on the spintronic emitter separated by a 300 nm SiO2 spacer layer. Moving these structures with respect to the femtosecond laser spot, which generates THz radiation, allows for resolution determination. The knife-edge method yields a full-width half-maximum beam diameter of 4.9 +- 0.4 µm at 1 THz. The possibility to deposit spintronic emitter heterostructures on simple glass substrates makes them attractive candidates for near-field imaging in many imaging applications.
The capability to parameterize shapes is of essential importance in biomechanics to identify cells, to track their motion, and to quantify deformation. While various shape descriptors have already been investigated to study the morphology and migration of adherent cells, little is known of how the mathematical definition of a contour impacts the outcome of rheological experiments on cells in suspension. In microfluidic systems, hydrodynamic stress distributions induce time-dependent cell deformation that needs to be quantified to determine viscoelastic properties. Here, we compared nine different shape descriptors to characterize the deformation of suspended cells in an extensional as well as shear flow using dynamic real-time deformability cytometry. While stress relaxation depends on the amplitude and duration of stress, our results demonstrate that steady-state deformation can be predicted from single cell traces even for translocation times shorter than their characteristic time. Implementing an analytical simulation, performing experiments, and testing various data analysis strategies, we compared single cell and ensemble studies to address the question of computational costs vs experimental accuracy. Results indicate that high-throughput viscoelastic measurements of cells in suspension can be performed on an ensemble scale as long as the characteristic time matches the dimensions of the microfluidic system. Finally, we introduced a score to evaluate the shape descriptor-dependent effect size for cell deformation after cytoskeletal modifications. We provide evidence that single cell analysis in an extensional flow provides the highest sensitivity independent of shape parametrization, while inverse Haralick's circularity is mostly applicable to study cells in shear flow.
We examine the turbulence driven by the ion and electron temperature gradients in selected magnetic configurations of the Wendelstein 7-X (W7-X) stellarator. The inherent flexibility in the configuration space of W7-X enables us to find candidate configurations manifesting low turbulent transport. We follow insights gained by stellarator optimization techniques, in order to identify key geometric features, which are directly related to the ion and electron heat fluxes produced by plasma turbulence. One such a feature is the flux expansion at locations where the curvature is particularly unfavourable. Starting from a configuration routinely used in the W7-X experiment, we end up with an optimized configuration. Based on this equilibrium, we select a configuration from W7-X configuration database with a similar feature as the optimized one. With the help of nonlinear gyrokinetic simulations, we show that the heat flux in this configuration is less stiff than in the initial configuration, both for ion temperature gradient and electron temperature gradient turbulence.
A hollow cathode discharge with a Ti cathode and a positively biased ring anode was operated in Ar + N2 or Ar + O2 gas mixtures. The energy distribution of plasma ions is investigated with the help of energy-resolved mass spectrometry. Singly and doubly charged Ar+ and Ar2+ ions and molecular N+2 or O+2 ions are the most abundant ionic species. The kinetic energy of all plasma ions is enhanced by a positive anode voltage.
Alterations in the organization of the cytoskeleton precede the escape of adherent cells from the framework of cell–cell and cell‐matrix interactions into suspension. With cytoskeletal dynamics being linked to cell mechanical properties, many studies elucidated this relationship under either native adherent or suspended conditions. In contrast, tethered cells that mimic the transition between both states have not been the focus of recent research. Using human embryonic kidney 293 T cells we investigated all three conditions in the light of alterations in cellular shape, volume, as well as mechanical properties and relate these findings to the level, structure, and intracellular localization of filamentous actin (F‐actin). For cells adhered to a substrate, our data shows that seeding density affects cell size but does not alter their elastic properties. Removing surface contacts leads to cell stiffening that is accompanied by changes in cell shape, and a reduction in cellular volume but no alterations in F‐actin density. Instead, we observe changes in the organization of F‐actin indicated by the appearance of blebs in the semi‐adherent state. In summary, our work reveals an interplay between molecular and mechanical alterations when cells detach from a surface that is mainly dominated by cell morphology.
The combination of the Layer-by-Layer (LbL) method, a nano-material such as carbon nanotubes (CNTs), and charged polyelectrolytes (PEs) is a reliable approach to produce highly functionalized surface coatings. These coatings are stable, controllable, ultra-thin, and most importantly, biocompatible. The ability to tune their properties by varying the preparation conditions and the terminating layer opens up a wide range of applications in the fields of biology and medicine. Here, the goal was to create electrically conductive coatings on which cells grow and proliferate. To achieve this goal, a coating with a stable conductive film structure, a suitable film surface topography, and suitable surface potential (and 𝜁-potential) must be prepared.
At the beginning of this thesis, the focus was on the fabrication of electrically conductive multilayer films, whose electrical properties should be stable and adjustable in a controlled manner (Article 1). The combination of chemically modified CNTs as polyanions, a strong linear polycation like poly(diallyldimethylammonium chloride) (PDADMA), and the LbL-method allowed us to prepare such films. Their characterization was carried out in air at ambient conditions. Since PDADMA is non-conductive, the charge transfer within the film and thus the electrical conductivity itself depends mainly on the CNTs and their arrangement. It was found that four CNT/PDADMA bilayers (BL) were always necessary to create a lateral network structure with multiple CNT crossing points to enable and support electron transport within the film. Moreover, additional CNT/PDADMA BL resulted in decreasing sheet resistance, while the conductivity remained constant at ≈ 4 kS/m regardless of the number of bilayers. Increasing the PDADMA molecular weight (Mw) from 44.4 kDa to 322 kDa did not affect film properties such as thickness or electrical conductivity.
However, increasing the CNT concentration from 0.15 mg/ml to 0.25 mg/ml in the deposition suspension resulted in thicker and less conductive films. This is attributed to a faster adsorption process of the CNTs leading to more adsorption sites for the polycation. We found an increased PDADMA monomer/CNT ratio compared to films prepared with the lower CNT concentration in the deposition suspension. The electrical conductivity decreased by a factor of four down to 1.1 kS/m, which can be attributed to fewer contact points between the CNTs. Overall, we were able to prepare stable and electrically conductive multilayer films. Additionally, by varying the preparation conditions tuning of the electrical conductivity is possible.
To fulfill requirements regarding i.e., medical implants, film properties not only have to be stable and controllable in a dry state (described in Article 1) but also in a biological aqueous environment. Therefore, in Article 2 we immersed our coated samples in three different solutions usually employed in biological research and compared their properties with their dry state, respectively. Also, hydration/swelling effects that normally occur for polyelectrolyte multilayer films (PEMs) in solutions were investigated.
For the film preparation, PDADMA (Mw = 322 kDa) and a deposition suspension of modified CNTs with two different concentrations (0.15 mg/ml and 0.25 mg/ml), which aged for two years, were used. Independent of the CNT suspension concentration, it turned out that the film thickness of the samples, prepared from the aged suspension, decreased significantly compared to the film thickness previously measured in Article 1. As a cross-check a new and fresh CNT suspension was made, which allowed us to reproduce the film thickness described in Article 1.
These results indicated that something happened with the CNT suspension over a two-year period. An analysis via X-ray photoelectron spectroscopy (XPS) showed a decrease in the percentage of functional groups in the CNTs from the aged suspension. The loss of functional groups resulted in less negatively charged CNTs and thus in fewer adsorption sites for the polycation PDADMA. Consequently, the PDADMA monomer/CNT ratio decreased, which lowered the thickness per bilayer by a factor of three, compared to films prepared with a freshly prepared CNT suspension. The lower linear charge density of the aged CNTs also enhanced their hydrophobicity, which is, in combination with the electrostatic forces, another important factor for multilayer cohesion. In contrast to PEMs made from polycations and polyanions, no swelling of the films occurred when immersed in solutions. This can be attributed to the fact that the increased hydrophobicity of the CNTs and the hydrophobic nature of the PDADMA backbone prevent the incorporation of water into the multilayer film. In solution, the films slightly shrink (by ≈ 2 nm), which makes them even more compact. Yet they remain stable. The result is an increased electrical conductivity from 9.6 kS/m, in the dry state, up to 15.3 kS/m immersed in solutions. To summarize, we showed that by tuning the interpolyelectrolyte forces the swelling and the ensuing decrease of the electrical conductivity of the films can be prevented.
Regarding the application in biology and medicine, we must consider that long-term exposure of cells to nano-materials like CNTs could lead to damage and inflammation of adjacent tissue. Therefore, it is necessary to prevent direct contact between the electrically conductive multilayer, i.e., CNT/PDADMA film, and the cells. The solution to this problem is a biocompatible top film that covers the CNT/PDADMA multilayer completely and still provides a lateral surface structure that supports cell adhesion and proliferation. Additional layers consisting solely of PEs could provide such a top film.
In Article 3 we investigated the self-patterning of PEM films as function of deposition steps. After preparation in water, the films were dried, characterized in air, and in vacuum. The films were built with high and low molecular weight PEs. PDADMA was used as polycation and poly(styrene sulfonate) sodium salt (PSS) as polyanion. The observation via Atomic Force Microscopy (AFM) showed that films prepared with high molecular weight PEs are laterally homogeneous and form no patterns, due to the chain immobility. The flat surfaces are ineligible as a substrate for cell adhesion.
In contrast, films built with a short PSS, especially at Mw, PSS = 10.7 kDa, began to self-pattern after seven deposited PDADMA/PSS bilayers. With each additionally deposited bilayer, the surface got more and more structured, from grooves over stripes to circular domains. Increasing film thickness led to an increased lateral mean distance between the surface structures. Scanning Electron Microscopy (SEM) images showed that exposure to a vacuum resulted in a decrease in the film thickness attributed to water removal, while the mean distance between the domains increased. Thus, by using this self-pattering process we are able to prepare PEMs with a highly structured surface. By adding PDADMA/PSS bilayers, not only the CNT/PDADMA film can be covered completely, but also a suitable surface morphology for cells can be created. Controlling the number of deposited bilayers allows the preparation of suitable coatings for cells.
To further improve the interaction of the cell and coated substrate not only the lateral structure but also the interacting electrostatic forces between cells and substrate are important for the nature of cell adhesion, function, and proliferation. In Article 4 we investigated PEMs, consisting of strong PEs with a low (PDADMA) and high (PSS) linear charge density. We performed asymmetric force measurements with the help of the colloidal probe technique (CP). Here, the forces between a PEM-covered surface and a colloidal probe (silica sphere) glued to a cantilever were investigated. The colloidal probe was either bare or covered with polycation poly(ethylenimine) (PEI). The surfaces were immersed in NaCl solutions with different ionic strengths (INaCl), starting with deionized water, then enriched up to 1 mol/L NaCl. The interaction force between a CP and the surface was measured. Thus, insight into the surface potential/charge was obtained.
During film preparation, two growth regimes (parabolic and linear) exist. These regimes and the terminating layer determine the surface force of the PEM. PEMs with a terminating PSS layer are predominantly flat and negatively charged when the ion concentration is low and the film is in the parabolic growth regime (between 1 and ≈ 15 BL). This indicates charge reversal on PSS adsorption. At the transition point between the parabolic and linear growth regimes, the ratio between polyanion and polycation monomers starts to switch and some cationic monomers are neutralized not by anionic monomers but by monovalent ions. Therefore, the surface charge density in diluted NaCl solutions changed from slightly positive near the transition to positive in the linear growth regime. At the lowest ionic strengths (INaCL) the range of the surface potential goes from – 40.5 mV (9 BL, parabolic) up to + 50 mV (19 BL, linear).
In contrast, polycation (PDADMA) terminated films are overall positive in diluted NaCl solutions. At the beginning of the parabolic growth regime, the layers are more compact and flat. However, with each additional layer deposited, the film becomes less compact and the chains begin to loosen. The now more loosely bound chains start to protrude into the solution and form pseudo-brushes. This could already be observed for 10.5 BL.
It intensifies in the linear growth regime (begin at ≈ 15 BL) and results in steric surface forces. Changing the surrounding INaCl affects this behavior and the pseudo-brushes scale as polyelectrolyte brushes.
By controlling the number of bilayers (thus the growth regime), the surrounding ionic strength, and the conformation of PEs at the PEM surface, it is possible to prepare a suitable range of surface properties i.e., for cell adhesion and proliferation. To prove that these multilayers can provide a suitable surface and have a positive effect on cell behavior, we coated in Article 5 titanium-covered samples with PEMs. Investigated was the cell interaction with the surface at different zeta(ζ) - potentials, a parameter for dynamic surface potential. Here the cell activity is measured by the mobilization of calcium (Ca2+) within the cell as a function of the ζ - potential of the substrate and the externally applied electrical potential. The cell activity indicates if the ζ - potential, provided by the sample surface, is suitable or not for the cells. The favorable interaction with the substrate is also reflected in the cell morphology and proliferation. The results showed that highly negative ζ - potentials between - 90 and - 3 mV led to a decreasing/reduced Ca2+ mobilization which correlates with reduced cell activity. Nearly neutral to moderate positive surfaces (ζ - potential + 1 to + 10 mV) i.e., PSS-terminated PEMs are able to promote cell adhesion and growth as demonstrated by an increased Ca2+ mobilization. The access to the intracellular Ca2+ stores, provided by the external stimulus, is now more effective and suggests a higher cell activity. Increasing the ζ - potentials up to ≈ + 50 mV (highly positive), i.e., PDADMA - terminated PEMs with pseudo-brushes, resulted in restricted cell viability and impaired Ca2+ mobilization, which led to a disturbed cell morphology and proliferation. In conclusion, only surfaces, terminated with i.e., PEI, with moderate positive charges (ζ - potential + 1 to + 10 mV) are able to improve the Ca2+ mobilization and thus the cell activity and proliferation. PEMs with a PSS termination provide negative 𝜁−potentials, onto which cells adhere, and proliferate. Therefore, they are a good alternative for surface functionalization for implant surfaces. In summary, the objective set at the beginning of the thesis is addressed within articles written as part of this thesis. It is possible to fabricate PEMs with modified CNTs to produce coatings that are electrically conductive with tunable sheet resistance, whether dry in air or immersed in an aqueous solution (Articles 1 and 2). Also, for pure PEMs, it is shown that with the right molecular weight of PEs and a certain number of bilayers, a suitable surface structure for cell adhesion can be produced (Article 3). Additional surface properties such as a suitable surface charge density can be provided by PEMs which can improve the cell activity as monitored with Ca2+ mobilization (Articles 4 and 5). The next step is to combine the knowledge gained from Articles 1 – 5 and link it to the application of external electrical fields to cells.
The influence of the Madden–Julian oscillation (MJO) on the middle atmosphere (MA) and particularly on MA temperature is of interest for both the understanding of MJO-induced teleconnections and research on the variability of the MA. We analyze statistically the connection of the MJO and the MA zonal mean temperature based on observations by the Microwave Limb Sounder (MLS) satellite instrument. We consider all eight MJO phases, different seasons and the state of the quasi-biennial oscillation (QBO). We show that MA temperature anomalies are significantly related to the MJO and its temporal development. The MJO signal in the zonal mean MA temperature is characterized by a particular spatial pattern in the MA, which we link to the interhemispheric coupling (IHC) mechanism, as a major outcome of this study. The signal with the largest magnitude is found in the polar MA during boreal winter with temperature deviations on the order of ±10 K when the QBO at 50 hPa is in its easterly phase. Other atmospheric conditions and locations also exhibit temperature signals, which are, however, weaker or noisier. We also analyze the change in the temperature signal while the MJO progresses from one phase to the next. We find a gradual altitude shift in parts of the IHC pattern, which can be seen more or less clearly depending on the atmospheric conditions.
The statistical link between the MJO and the MA temperature highlights illustratively the far-reaching connections across different atmospheric layers and geographical regions in the atmosphere. Additionally, it highlights close linkages of known dynamical features of the atmosphere, particularly the MJO, the IHC, the QBO and sudden stratospheric warmings (SSWs). Because of the wide coverage of atmospheric regions and included dynamical features, the results might help to further constrain the underlying dynamical mechanisms and could be used as a benchmark for the representation of atmospheric couplings on the intraseasonal timescale in atmospheric models.
The stratospheric aerosol layer plays an important role in the radiative balance of Earth primarily through scattering of solar radiation. The magnitude of this effect depends critically on the size distribution of the aerosol. The aerosol layer is in large part fed by volcanic eruptions strong enough to inject gaseous sulfur species into the stratosphere. The evolution of the stratospheric aerosol size after volcanic eruptions is currently one of the biggest uncertainties in stratospheric aerosol science. We retrieved aerosol particle size information from satellite solar occultation measurements from the Stratospheric Aerosol and Gas Experiment III mounted on the International Space Station (SAGE III/ISS) using a robust spectral method. We show that, surprisingly, some volcanic eruptions can lead to a decrease in average aerosol size, like the 2018 Ambae and the 2021 La Soufrière eruptions. In 2019 an intriguing contrast is observed, where the Raikoke eruption (48∘ N, 153∘ E) in 2019 led to the more expected stratospheric aerosol size increase, while the Ulawun eruptions (5∘ S, 151∘ E), which followed shortly after, again resulted in a reduction in the values of the median radius and absolute distribution width in the lowermost stratosphere. In addition, the Raikoke and Ulawun eruptions were simulated with the aerosol climate model MAECHAM5-HAM. In these model runs, the evolution of the extinction coefficient as well as of the effective radius could be reproduced well for the first 3 months of volcanic activity. However, the long lifetime of the very small aerosol sizes of many months observed in the satellite retrieval data could not be reproduced.
Explosive volcanic eruptions emitting large amounts of sulfur can alter the temperature of the lower stratosphere and change the circulation of the middle atmosphere. The dynamical response of the stratosphere to strong volcanic eruptions has been the subject of numerous studies. The impact of volcanic eruptions on the mesosphere is less well understood because of a lack of large eruptions in the satellite era and only sparse observations before that period. Nevertheless, some measurements indicated an increase in mesospheric mid-latitude temperatures after the 1991 Pinatubo eruption. The aim of this study is to uncover potential dynamical mechanisms that may lead to such a mesospheric temperature response. We use the Upper-Atmospheric ICOsahedral Non-hydrostatic (UA-ICON) model to simulate the atmospheric response to an idealized strong volcanic injection of 20 Tg S into the stratosphere (about twice as much as the eminent 1991 Pinatubo eruption). Two experiments with differently parameterized effects of sub-grid-scale orography are compared to test the impact of different atmospheric background states. The simulations show a significant warming of the polar summer mesopause of up to 15–21 K in the first November after the eruption. We argue that this is mainly due to intrahemispheric dynamical coupling in the summer hemisphere and is potentially enhanced by interhemispheric coupling with the winter stratosphere. This study focuses on the first austral summer after the eruption because mesospheric temperature anomalies are especially relevant for the properties of noctilucent clouds, whose season peaks around January in the Southern Hemisphere.
Carbon-cluster ions are produced by laser irradiation of glassy carbon in high vacuum. In the case of positively charged species, a bimodal cluster distribution including fullerenes with cluster-size-to-charge ratios of up to a few hundred is observed. Resolving isotopologues by use of a multireflection time-of-flight mass spectrometer allows the detection and abundance determination of multiply charged clusters. It is found that mono-, di-, and tricationic fullerenes are produced, have similar size-over-charge-state ranges, and follow log-normal distributions known to be characteristic of an underlying coalescent growth. A statistical simulation is shown to reproduce the results.
The idea of estimating stratospheric aerosol optical thickness from the twilight colours in historic paintings – particularly under conditions of volcanically enhanced stratospheric aerosol loading – is very tantalizing because it would provide information on the stratospheric aerosol loading over a period of several centuries. This idea has in fact been applied in a few studies in order to provide quantitative estimates of the aerosol optical depth after some of the major volcanic eruptions that occurred during the past 500 years. In this study we critically review this approach and come to the conclusion that the uncertainties in the estimated aerosol optical depths are so large that the values have to be considered questionable. We show that several auxiliary parameters – which are typically poorly known for historic eruptions – can have a similar effect on the red–green colour ratio as a change in optical depth typically associated with eruptions such as, for example, Tambora in 1815 or Krakatoa in 1883. Among the effects considered here, uncertainties in the aerosol particle size distribution have the largest impact on the colour ratios and hence the aerosol optical depth estimate. For solar zenith angles exceeding 80∘, uncertainties in the stratospheric ozone amount can also have a significant impact on the colour ratios. In addition, for solar zenith angles exceeding 90∘ the colour ratios exhibit a dramatic dependence on solar zenith angle, rendering the estimation of aerosol optical depth highly challenging. A quantitative determination of the aerosol optical depth may be possible for individual paintings for which all relevant parameters are sufficiently well constrained in order to reduce the related errors.
In our study, we determine the alignment of magnetic domains in a CoFeB layer using THz radiation. We generate THz pulses by fs laser pulses in magnetized CoFeB/Pt heterostructures based on spin currents. An LT-GaAs Auston switch detects the radiation phase sensitively and allows us to determine the magnetization alignment. Our scanning technique with motorized stages, with step sizes in the sub-micrometer range, allows us to image two dimensional magnetic structures. Theoretically, the resolution is restricted to half of the wavelength if focusing optics in the far-field limit are used. By applying near-field imaging, the spatial resolution is enhanced to the single digit micrometer range. For this purpose, spintronic emitters in diverse geometric shapes, e.g., circles, triangles, squares, and sizes are prepared to observe the formation of magnetization patterns. The alignment of the emitted THz radiation can be influenced by applying unidirectional external magnetic fields. We demonstrate how magnetic domains with opposite alignment and different shapes divided by domain walls are created by demagnetizing the patterns using minor loops and imaged using phase sensitive THz radiation detection. For analysis, the data are compared to Kerr microscope images. The possibility of combining this method with THz range spectroscopic information of magnetic texture or antiferromagnets in direct vicinity to the spintronic emitter makes this detection method interesting for a much wider range of applications probing THz excitation in spin systems with high resolution beyond the Abbe diffraction limit, limited solely by the laser excitation area.
The high-latitude phenomenon of noctilucent clouds (NLCs) is characterised by a silvery-blue or pale blue colour. In this study, we employ the radiative transfer model SCIATRAN to simulate spectra of solar radiation scattered by NLCs for a ground-based observer and assuming spherical NLC particles. To determine the resulting colours of NLCs in an objective way, the CIE (International Commission on Illumination) colour-matching functions and chromaticity values are used. Different processes and parameters potentially affecting the colour of NLCs are investigated, i.e. the size of the NLC particles, the abundance of middle atmospheric O3 and the importance of multiply scattered solar radiation. We affirm previous research indicating that solar radiation absorption in the O3 Chappuis bands can have a significant effect on the colour of the NLCs. A new result of this study is that for sufficiently large NLC optical depths and for specific viewing geometries, O3 plays only a minor role for the blueish colour of NLCs. The simulations also show that the size of the NLC particles affects the colour of the clouds. Cloud particles of unrealistically large sizes can lead to a reddish colour. Furthermore, the simulations show that the contribution of multiple scattering to the total scattering is only of minor importance, providing additional justification for the earlier studies on this topic, which were all based on the single-scattering approximation.
The Mt. Pinatubo eruption in 1991 had a severe impact on the Earth system, with a well-documented warming of the tropical lower stratosphere and a general cooling of the surface. This study focuses on the impact of this event on the mesosphere by analyzing solar occultation temperature data from the Halogen Occultation Experiment (HALOE) instrument on the Upper Atmosphere Research Satellite (UARS). Previous analyses of lidar temperature data found positive temperature anomalies of up to 12.9 K in the upper mesosphere that peaked in 1993 and were attributed to the Pinatubo eruption. Fitting the HALOE data according to a previously published method indicates a maximum warming of the mesosphere region of 4.1 ± 1.4 K and does not confirm significantly higher values reported for that lidar time series. An alternative fit is proposed that assumes a more rapid response of the mesosphere to the volcanic event and approximates the signature of the Pinatubo with an exponential decay function having an e-folding time of 6 months. It suggests a maximum warming of 5.4 ± 3.0 K, if the mesospheric perturbation is assumed to reach its peak 4 months after the eruption. We conclude that the HALOE time series probably captures the decay of a Pinatubo-induced mesospheric warming at the beginning of its measurement period.
The lateral movement in lipid membranes depends on their diffusion constant within the membrane. However, when the flux of the subphase is high, the convective flow beneath the membrane also influences lipid movement. Lipid monolayers of an unsaturated fatty acid at the water–air interface serve as model membranes. The formation of domains in the liquid/condensed coexistence region is investigated. The dimension of the domains is fractal, and they grow with a constant growth velocity. Increasing the compression speed of the monolayer induces a transition from seaweed growth to dendritic growth. Seaweed domains have broad tips and wide and variable side branch spacing. In contrast, dendritic domains have a higher fractal dimension, narrower tips, and small, well-defined side branch spacing. Additionally, the growth velocity is markedly larger for dendritic than seaweed growth. The domains’ growth velocity increases and the tip radius decreases with increasing supersaturation in the liquid/condensed coexistence region. Implications for membranes are discussed.
In course of the recent results from Wendelstein 7-X, stellarators are on the brink for assessing their maturity as a fusion reactor. To this end, stellarator specific transport regimes need detailed exploration both with appropriate systematic experimental investigations and models. A way to enhance the efficiency of this process is seen in an systematic evaluation of existing experimental data. We propose appropriate tools developed in information theory for examining large datasets. Information entropy calculations, that have proven to assist the systematic assessment of datasets in many other scientific fields, are used for novelty detection.
Potentially, as a first use-case of this holistic process, this thesis attempts to link and to develop approaches to examine the stellarator specific core-electron-root-confinement (CERC) regime. The specific interest for CERC emerges from the behavior of the radial electric field. While ion-root conditions exhibit negative radial electric fields, CERC’s positive field in the very core of fusion grade plasmas adds an outward thermodynamic force to high-Z impurities and could add to potential actuators to control impurity influx as to be examined for full-metal wall operation in large stellarators. Recently, this feature received revived intent for reactor scale stellarators.
Also, in this work, parameter regions close to the transition from ion-root to CERC are
examined. At lower rotational transform (a characteristic feature of the magnetic field confining fusion grade plasmas), transitions were detected when the plasma current evolved. As in smaller stellarators, it is concluded that low-order rationals and magnetic islands are related to the transitions. This is widely supported by extensive MHD simulations which finally provide indications for the role of zonal flow oscillations. As one of the outcomes, gyrokinetic instabilities are seen interacting for the first time with the neoclassical mechanisms in experiments.
In order to cope with the vast number of highly sampled spatio-temporal plasma data, new
techniques for novelty detection are required. Fundamental prerequisites for the detailed
physics investigations were the feasibility study of entropy-based data analysis techniques, and their adaptation to detect previously unrevealed transition mechanisms. These tools were applied to multivariate bulk plasma emissivity data, which allowed the exploration of large parameter spaces and provided insights in the spatio-temporal dynamics of CERC transitions.
In this manner, this research highlights the feasibility of information flow measure analysis in fusion studies. Applications of different entropy-based complexity measures are explored and this work sheds light on the capabilities, added value and limitations of these techniques. This investigation presents the integration of information flow measures to gain deeper understanding of plasma transport phenomena, by providing an approach to fast systematic data mining suited for real-time analysis. This work paves the way for further development and implementation of information-theoretic methods for plasma data analysis.
In summary, this research highlights the gained insight on CERC transitions, while showcasing the feasibility, added values and limitations of information flow measure analysis for fusion studies, to induce theory based analysis revealing new insights in fundamental, stellarator-specific transport mechanisms.
Research into nuclear physics has enjoyed a long and rich history since the earliest experiments began investigating atomic constituents. The discovery of the atomic nucleus in the early 20th century started a complex field of research that has undergone many transformations with the advancements of modern technology. Today, atomic nuclei are not only studied to advance our understanding of the strong force but also to gain more information on the synthesis of elements in the universe, to exploit nuclear decay to investigate the weak interaction, and to search for physics beyond the standard model.
In this work, we will study the strong force in atomic nuclei, i.e. the way nucleons (protons and neutrons) arrange themselves in a many-body system governed by the repulsive Coulomb interaction and the attractive strong interaction. In particular, we will focus on nuclear structure near nuclei with a "magic number" of Z protons and N neutrons, so-called doubly-magic nuclei, exhibiting a particularly stable configuration with respect to neighboring nuclei.
Within the nuclear shell model, similar to the atomic shells, the magic numbers indicate shell closures accompanied by energy gaps. Nuclei at double-shell closures and their direct vicinity provide an important playground to benchmark nuclear theories and models that aim to predict the intricate interplay of the nucleons that lead to enhanced nuclear binding energies, significant changes in charge radii and transition strengths, etc.
Of particular interest are nuclear isomers, long-lived excited states, in which the nucleon configuration with respect to its ground state is altered, resulting in a modification of their properties despite having the same number of protons and neutrons.
The main part of this work consists of three publications, which report on nuclear structure investigations through mass measurements and laser spectroscopy near the doubly magic nuclei nickel-78, tin-100, and lead-208.
The nuclides investigated in this work include neutron-deficient indium isotopes, neutron-rich zinc isotopes, and neutron-rich mercury isotopes.