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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.
This thesis presents the production of polyanionic clusters within two ion storage devices:
Considering a Penning trap, the accessible range of polyanionic aluminium clusters has been expanded up to the 10th charge state. In particular, abundance curves for clusters with 5 to 9 excess electrons have been measured for the first time and analysed with respect to their lifetime-dependent appearance sizes. These sizes reveal a nearly quadratic dependency on the charge state for experimentally accessible lifetimes.
Additionally, the production of polyanionic clusters has been enabled in a radiofrequency ion trap. Therefore, the transition from a harmonic to a digital 2- and 3-state guiding signal has been investigated with respect to the ion storage. The passing of electrons through the trap during field-free periods of the guiding signal led to the first production of polyanionic clusters within a radiofrequency ion trap.
In this thesis, I was able to provide answers to transport processes in lipid monolayers, which are ultimately, all of biological relevance. In particular, I was interested in lipid oxidation and dynamic compression/expansion processes of surfactant monolayers at the air-water interface:
Lipid oxidation was shown to be a consequence of the formation of a high concentration of reactive oxygen species (ROS) during cell respiration, which finally can lead to severe cell damage. It is not yet understood clearly, which part of the lipid molecules is especially prone to a ROS attack. I was particularly interested in the role of the double bonds of the acyl chains of the lipid molecules during oxidation. Further, I wanted to know the time scales of lipid interaction with the ROS.
Compared to lipid vesicles, lipid monolayers have the advantage that many parameters of the system can be adjusted easily. In our system, I made use of this by setting the lateral pressure to low values during H2O2 treatment, which facilitated the ROS to reach the double bonds in the acyl chains.
A prime example of biological systems out of thermal equilibrium was given in the alveolus surface, which is covered with a surfactant monolayer. During breathing, these monolayers undergo such a highly dynamic compression and expansion. Arising flows from breathing could disrupt a film and consequently, it would lose its protective role. One of my goals was to understand flows and their influence on domain shape. Dependent on the strength of the flows, I expected different growth regimes, with differing prevailing transport processes. Once understanding the underlying mechanisms in domain shaping would allow me to draw conclusions on biological systems.
In order to address these questions, I established two systems, both based on the compression of lipid monolayers. I used isotherms to study the phase behavior of the lipids:9 During compression, the lipids can undergo phase transitions from the gaseous phase to the liquid expanded phase (LE-phase) and further from the LE-phase to the liquid condensed phase (LC-phase). A coexistence regime is observed in between the LE-phase and the LC-phase, characterized by a flat increase of lateral pressure with decreasing molecular area. Some lipids exhibited LC-phase domains. These were further investigated with Brewster angle microscopy (BAM). The used BAM was equipped with an integrated Scheimpflug optics, enabling an overall focused image plane. Furthermore, time-resolved observation of the growth of the domains was possible by recording videos (20 frames per seconds).
The first system enabled the investigation of lipid peroxidation, when the lipids were exposed to ROS. I chose DMPC, POPC, DOPC and PLPC, since these are phospholipids differing in the number and position of double bonds in acyl chains, but not in the head group. I used a H2O2 enriched phosphate buffered saline (PBS) solution, which served as a precursor for more reactive ROS, like hydroxyls (.OH). PBS was chosen, since it resembles the cell environment best. During defined waiting times of H2O2 treatment, the ROS diffused vertically from the subphase towards the monolayer. The lipid molecules were in the LE-phase, which facilitated the ROS molecules to reach also the double bonds of the acyl chains. The oxidized monolayers were then compressed at constant compression speed. Since the corresponding isotherms could be measured with high precision, the relative area increase δA/A between oxidized and non-oxidized monolayer along the isotherm proved to be a good measure for lipid peroxidation. The area increase δA in the molecular area of the oxidized molecules was explained by the eventually added, more hydrophilic −OOH group at the position of a carbon atom adjacent to a double bond in the unsaturated acyl chain. The −OOH group is drawn to the hydrophilic head group of the lipid. This leads to a kink in the acyl chain, which increases the molecular area A by δA. A model, which explained this peroxidation process in lipid vesicles, could be adopted to monolayers.
I compared the oxidation of phospholipids, differing in the number and position of the double bonds of their acyl chains. I found that δA/A increased with the growing number of double bonds in one acyl chain. However, a comparison of DOPC with POPC also showed the importance of the position of the acyl chain. I determined a slow reaction kinetic. It could be estimated by a √t dependence of the number density N_surface, which denominates the ROS sticking on the monolayer. The transport of ROS towards the monolayer was found to be diffusive, because it was the slowest process in the reaction. This interpretation was reinforced by a comparison of the temperature dependence of the relative area increase δA/A with the Stokes-Einstein diffusion coefficient of water molecules. The initial ROS concentration c_0 in the trough could be traced back (c_0~ 50 nM), which is indeed a realistic value found in human cells.
Concluding, our results can be understood as a feasibility study. The complexity of the monolayer can be arbitrarily increased, for example by the addition of proteins, allowing the investigation of other oxidative processes occurring in the cell membrane.
The second system allowed the investigation of growth of LC domains during fast compression processes of monolayers. I chose erucic acid monolayers, due to its low line tension and a continuous nucleation phase, enabling the formation of fractal domains. The monolayers were investigated with isotherms and BAM videos. Since v_C (compression speed of the monolayer) was continuous over the whole compression time, I had a system with well-defined hydrodynamic conditions. This allowed me a complete analysis of the system, starting with descriptive features of the observed domains to a classification of the observed growth regimes by means of hydrodynamic theory, through to the distinction and quantification of different kind of flows and supersaturations, involving Ivantsov theory:
Dependent on the compression speed v_C, I observed seaweed or dendritic domains. The LE/LC phase transition pressure pi_t was slightly increased compared to pi_inf of the equilibrium isotherm. A high compression speed v_C induced a supersaturation Δc. I introduced the excess lateral pressure Δpi=pi-pi_inf as an appropriate quantity to describe the supersaturation Δc. I showed a linear behavior of Δc on Δpi. Δc is a macroscopic quantity since it is averaged over the whole monolayer area. I characterized the domains of the seaweed and dendritic regime with respect to tip radii, branch lengths, side branch separations and fractal dimensions. I calculated the growth speed of the main branches. A roughly doubling of the growth speed of dendritic domains, compared to seaweed domains was observed. This was an evidence of adjunctive (Marangoni) flow in the subphase.
For each monolayer, I observed drifts during domain growth, which I explained by an anisotropy in the LE-phase, caused by the continuous nucleation of the domains. These kind of surface flows were superimposed to bulk flows in the subphase. Since I had a well established system, I could analyze the influence of these surface flows on domain shape, in terms of magnitude, direction and duration of the surface flows. I therefore used FFT spectra and directionality histograms. At low flows, the FFT showed six-fold symmetry. Higher drifts exhibited incisions in the FFT, eventually leading to dumbbell shaped FFTs at very high drifts. The domains grew preferentially in the direction parallel to the incision.
I used directionality histograms to analyze the angular distribution of the growing domains. They showed that the drift direction always correlated with a minimum in the histogram. In order to analyze drift duration, I split the domain in downstream and upstream side. I could show that for small drift durations, downstream growth was preferred. However, for longer drift durations, the flows got more isotropic and consequently growth was more balanced then.
I could observe only a weak correlation between drift velocity v_D and compression speed v_C. However, dendrites were formed when the compression speed v_C was high, while seaweed domains were formed when v_C was small. Domain distortion occurred in the same way, independent if seaweed or dendritic domains were considered. I further showed that hydrodynamic flows in the subphase and surface flows are superimposed and scale differently. Consequently, they have different impact on domain shape: hydrodynamic flows act on μm scale and influence the domain morphology (distance between side branches, and tip radius) and the growth speed of the main branches. Surface flows act on the mm to cm scale, cause an anisotropic flow in the LE phase surrounding the domain, and thus affect the overall domain shape.
The anisotropy in the LE-phase led to a locally different degree of supersaturation. To take this into account, I introduced a local normalized supersaturation Δ, based on the Ivantsov solution. Therefore, I calculated Péclet numbers p of measured quantities of the system. I obtained values of 0.88 ≤Δ≤0.90 for the seaweed regime (p<5) and 0.93 ≤Δ≤0.96 for the dendritic regime (p>6). Since the Ivantsov solution can only be applied for purely diffusive processes, I applied a modified Ivantsov solution Δ_mod, which calculates Δ at a distance 𝛿 ahead of the dendrite tip. I was able to determine the progression of the diffusive layer 𝛿, however a quantitative determination failed.
Applying hydrodynamic theory allowed me to classify the two growth regimes with respect to the Boussinesq number Bq. Since for both growth regimes, I achieved values of Bq<1, bulk viscous losses dominated over surface viscous losses. Further, a cross-over length 𝜉 was calculated, from which one can distinguish, whether advective transport dominates over diffusion.
I further connected the two defined supersaturations Δ and Δc via the excess lateral pressure Δpi. From this, I saw differences in the seaweed and dendritic growth regimes: The local normalized supersaturation Δ of seaweed growth seemed to be quite stable for a further increase of the lateral excess pressure Δpi, whereas it reacted quite sensitive in the dendritic regime. This was found to be an indication of a non-equilibrium regime, caused by the strong coupling of the monolayer to the subphase. It reinforces therefore the theory of Marangoni-flow.
The findings of this thesis emphasize the importance of understanding highly dynamic compression/expansion processes arising in surfactant monolayers. Using the example of the compression of the alveolus surface, it can be seen that a more realistic model of the pulmonary alveolus is not only enabled by increasing the complexity of the surfactant monolayer (e.g. by adding specific proteins or lipid mixtures to the monolayer). Equally important is the understanding in transport processes and the consequences for the monolayer structure. By the analysis of domain shapes, I presented a method, which is suitable for such a study.
Graphene is a strictly two-dimensional honeycomb lattice of carbon atoms whose low-energy charge-carrier dynamics obey the massless pseudospin-1/2 Dirac-Weyl equation (or chiral Weyl equation) where the chiral centers (or valleys) are the corners K and K‘ of the Brillouin zone. The linear spectrum near the Dirac nodal points lends graphene its exotic and ultra-relativistic properties.
However, condensed matter systems can possess fermionic excitations with linear dispersions that have no analog in high-energy physics since the crystal space group - instead of the Poincare group - constrains the energy dispersions. Perhaps the first example in this regard is the T_3 lattice (Dice Gitter), a honeycomb-like lattice with an extra atom placed at the center of each hexagon and coupled to only one of the sublattices. The spectrum features a strictly flat band that crosses the two conical intersections of the Dirac cones at K and K' inherited from graphene. The enlarged pseudospin-1 Dirac-Weyl equation describes the low-energy dynamics. By rescaling the transfer amplitude of the additional atoms in the T_3 lattice with a parameter 0<α<1, the resulting α-T_3 lattice continously interpolates between graphene and the T_3 lattice.
In this work, we explore the behavior of generalized Dirac-Weyl quasiparticles in external magnetic and valley-dependent pseudoelectromagnetic fields induced by out-of-plane strain. First, we studied Dirac-Weyl quasiparticles in external fields confined to circular quantum dots by generalizing the infinite-mass boundary condition to the α-T_3 lattices. We verified the analytically derived valley-anisotropic eigenstates of the quantum dot by numerically solving the tight-binding lattice-model in closed (isolated) and open (contacted) systems.
Second, we considered strain fields in the α-T_3 lattices to modify the low-energy transport properties by an effective pseudo-gauge field with opposite signs at the K and K‘ valley. In particular, we showed that the inhomogeneous pseudomagnetic field generated by Gaussian out-of-plane strain at the center of a four-terminal Hall bar setup acts as a valley filter. Most interestingly, the valley polarization is most dominant when incoming electrons are excited to pseudo-Landau level subbands. These bands are linked to different iso-field orbits encircling the lobes of the pseudomagnetic field. Addittionaly, any intermediate α breaks the inversion symmetry of the α-T_3 lattice and thus splits the pseudo-Landau levels into sublattice-polarized bands.
Third, we equipped the out-of-plane strain with a time-periodic drive to induce a valley-dependent pseudoelectric field perpendicular to the pseudomagnetic field. We assessed the steady-state transport properties and found – besides the static regime for small energies – two α-dependent valley-filtering regimes due to the periodic drive. Firstly, we found an additional valley-polarization plateau at the Floquet-zone boundary between the central and first Floquet copy that also displayed a “flower”-like pattern in the local density of states. Secondly, we detected a series of transmission gaps at the center of every Floquet sideband 2mΩ related to the Floquet coupling of the flat band with the central Floquet copy. Under certain strain parameters, a novel valley-filtering regime appears near the transmission gaps where the incoming K electrons are focused through the bump by the pseudoelectric field, instead of encircling the lobes of the pseudomagnetic field. A stability analysis demonstrated that the polarization regimes are tunable by the driving frequency.
Lastly, we demonstrated that the flat band in the Haldane-dice lattice modified by a uniaxial strain along the zigzag orientation remains singular at all band crossings where the model undergoes a topological phase transition between C=+-2 and C=0. To show this, we computed the compact localized eigenstates and the quantum distance of the Bloch wave function around the band-touching points. We derived the resulting non-contractible loop states and an extended state whose components are tunabe by the system parameters.
Ion traps such as Paul traps and MR-ToF (multi-reflection time-of-flight) devices are indispensable tools at radioactive ion beam facilities for the preparation of high-quality radioactive ion beams for subsequent experiments or for precise measurements of the properties of radioactive ions, such as nuclear binding energies or nuclear charge radii.
Within the work of this thesis, Doppler- and sympathetic cooling is implemented in a linear Paul-trap cooler-buncher enabling a reduction of the longitudinal emittance of radioactive ion beams resulting in a significant improvement of the ion beam quality. Moreover, a next-generation MR-ToF device is conceptualized in order to achieve isobaric pure beams with a higher ion intensity than state-of-the-art MR-ToF devices can provide. Once fully constructed and commissioned, it will operate at an unprecedented ion beam energy of 30 keV. Both of these advances are expected to become important for a wide range of experimental programs pursued at low-energy branches of RIB facilities ranging from fundamental symmetry studies, nuclear structure, rare isotope studies with antimatter, searches of physics beyond the standard model to material science and the production of medical isotopes.
The next-generation MR-ToF mass separator is based on MIRACLS’ 30-keV MR-ToF device for highly sensitive and high-resolution collinear laser spectroscopy. By storing the ions in the Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS), the same ion bunch is probed by a spectroscopic laser for thousands of times compared to a single passage in traditional collinear laser spectroscopy (CLS). Dedicated simulation studies show that the accuracy and resolution will be close to traditional single-passage CLS while the sensitivity is significantly enhanced. Hence, measurements of nuclear properties via fluorescence-based CLS of very rare radionuclides as well as highly sensitive and high-precision measurements of electron affinities via laser-photodetachment-threshold spectroscopy of negatively-charged (radioactive) ions will become possible.
First measurement campaigns employing MIRACLS’ 1.5-keV MR-ToF device confirm the outstanding boost in signal sensitivity and provide confidence in the application of the MIRACLS technique for the measurement of scarcely produced radioactive ions that have been so far beyond the reach of conventional techniques. Furthermore, the electron affinity of 35Cl was measured, which is in perfect agreement with the literature value. These measurements will serve as important benchmarks for modern atomic and nuclear theory, especially in its description of nuclear charge radii.
In summary, the implementation of Doppler and sympathetic cooling at RIB facilities, the conceptualization of a 30-keV MR-ToF apparatus for highly selective and high-flux mass separation as well as for highly sensitive and high-resolution fluorescence-based laser spectroscopy and the expansion of the MIRACLS technique for the study of negatively-charged ions will enable unprecedented new measurement opportunities at RIB facilities.
Polyelektrolyt-Multischichtfilme (PEMs) werden durch schichtweise (eng. Layer by Layer, LbL)
sequentielle Ablagerung von entgegengesetzt geladenen Polyelektrolyten auf einer
geladenen Oberfläche hergestellt. Die LbL Methode kann auf verschiedene Weise zur
Herstellung von PEM eingesetzt werden, z.B. durch Tauchen, Rotation, Sprühen oder
Beschichten mit elektromagnetischen und fluidischen Methoden. In allen Artikeln dieser
Dissertation wurde die Tauchmethode verwendet. Durch zyklische Wiederholung der
Abscheidungsschritte kann die Dicke der PEM leicht gesteuert werden. Die Oberflächen und
Grenzflächen des Films können mit der LbL Technik auch durch die elektrostatische
Wechselwirkung zwischen positiv und negativ geladenen Polyelektrolyten modifiziert werden.
Auf diese Weise lassen sich einige Eigenschaften des Films optimieren, beispielsweise
Oberflächenadhäsion und Biokompatibilität, z. B. in der Gewebezüchtung oder es kann
eine Monoschicht als Barriere an der Grenzfläche des Films adsorbiert werden, um die
Diffusion von Molekülen im Film zu begrenzen z.B. bei Aufnahme oder Freisetzen von
Medikamenten.
Daher wurde die Rolle einiger Faktoren, wie die molare Masse der Polyelektrolyte und das
Vorhandensein von Salzionen in der Präparationslösung auf die interne Struktur sowie die
Oberfläche der PEMs untersucht.
Für alle Untersuchungen dieser Dissertation wurde das häufig verwendete Modell-System aus
dem positiv geladenen Polyelektrolyten Polydimethyldiallylammonium (PDADMA), und dem
negativ geladenen Polyelektrolyten Polystyrolsulfonat (PSS), verwendet. Die Dicke der Filme
wurde mit Röntgenreflektometrie, Ellipsometrie, UV-Vis-NIR-Spektrometrie bestimmt die
interne Struktur mit Neutronenreflektometrie und die Oberflächentopografie mit Rasterkraftmikroskopie
(eng. AFM) und Rasterelektronenmikroskopie (eng. SEM).
In Artikel 1 wurde mit Hilfe der Neutronenreflektometrie die Struktur des Filmes und die
Diffusion des Polyanions PSS (DPSS) senkrecht zur PEM Oberfläche untersucht. Variiert wurde
die molare Masse des Polykations PDADMA und die Salzkonzentration der
Präparationslösung. PEMs wurden aus drei verschiedenen NaCl-Konzentrationen in der
Abscheidelösung hergestellt: 10 mmol/L, 100 mmol/L und 200 mmol/L. Die Salzkonzentration
in der Polyelektrolytlösung bestimmt die Konformation der Polyelektrolyte während der
Adsorption. Die Ketten werden weniger flach adsorbiert, wenn mehr Salzionen in der
Adsorptionslösung vorhanden sind und die Filme werden dicker.
Die Diffusion nahm mit zunehmender molarer Masse von PDADMA in Filmen, die aus 10
mmol/L, 100 mmol/L und 200 mmol/L hergestellt wurden, um mindestens drei Größenordnungen
ab, denn die Zunahme der Kettenlänge, erhöht den Vernetzungsgrad im Film. Dabei zeigten Filme aus 10 mmol/L (NaCl) mit einer niedrigen molaren Masse von PDADMA
die größte Diffusion (DPSS = 4.9 × 10−20 m2/s). Der Diffusionskoeffizient DPSS als Funktion des
Polymerisationsgrades folgt zwei Potenzgesetzen mit einem Übergang bei einem
Polymerisationsgrad von 288. Bei kürzeren Ketten stimmt der Exponent des Potenzgesetzes
gut mit dem Modell der Sticky Reptation überein. Bei längeren Ketten war der Exponent viel
größer, was vermuten lässt, dass die PSS-Ketten in einem zunehmend komplexen
Polymernetzwerk gefangen sind. Wir verstehen den Übergang als Verschränkungsgrenze für
das untersuchte System.
Bei PEMs, die aus 100 mmol/L hergestellt wurden, konnte kein Potenzgesetz festgestellt
werden. DPSS nahm sprunghaft um drei Größenordnungen ab, wenn die molare Masse von
PDADMA von 45 kDa auf 72 kDa erhöht wurde.
In Artikel 2 wurden die Oberfläche von PEMs aus Polyelektrolyten unterschiedlicher molarer
Massen untersucht. Die Oberflächenrauhigkeit und die Dicke des Films wurden mit
Röntgenreflektometrie und Ellipsometrie bestimmt. Die Oberflächentopografie wurde mit AFM
und SEM aufgenommen. Alle PEMs wurden aus PE-Lösungen mit 0,1 mol/L NaCl hergestellt.
Die Oberfläche der PEM, präpariert aus langem PSS und kurzem PDADMA oder langem PSS
und langem PDADMA, war immer flach. Bei einer Filmzusammensetzung aus langen
Polykationen (Mw (PDADMAlang) = 322 kDa) und kurzen PSS Molekülen (Mw (PSSkurz) = 10,7
kDa) wurden drei Wachstumsregime identifiziert: exponentiell, parabolisch und linear. Im
exponentiellen Wachstumsregime bildet sich nach etwa sieben Beschichtungsschritten von
PDADMA/PSS (eng. bilayers, bl) eine granulare Oberflächenstruktur aus mit einer
Oberflächenrauigkeit von 1,6 nm und einer lateralen Periodizität von 70 nm. Mit zunehmender
Schichtzahl nimmt die Oberflächenrauhigkeit sowie die laterale Periodizität zu. Im
parabolischen Wachstumsbereich aggregieren die Strukturen zu Säulen, mit einer
Oberflächenrauigkeit bis zu 23 nm und einer lateralen Periodizität bis zu 210 nm. Im linearen
Wachstumsregime sind die säulenförmigen Domänen vollständig ausgebildet und die
Oberflächenstruktur ändert sich nicht mehr. Diese Strukturen wurden schon während der
Präparation, bereits vor dem Trocknen beobachtet. Dies zeigt, dass sich die Strukturen
während der Abscheidung von PDADMA/PSS bilden.
Bei Beobachtungen im Vakuum (SEM) war im linearen Bereich die Säulenstruktur bei der
PDADMA terminierten PEM ausgeprägter als bei der PSS terminierten.
Diese Strukturen bilden sich nur im Film mit anfänglichem exponentiellem Wachstum, d.h.
wenn kurzen Ketten durch den ganzen Film diffundieren können. Das legt nahe, dass es für
die Strukturbildung nicht ausreicht, dass der Polyelektrolyt kurz ist, sondern dass es auch
beweglich sein muss. Um dies näher zu untersuchen wurde in Manuskript 1 die molare Masse des PSS variiert. Es
wurden PEMs aus langem 322 kDa PDADMA und kurzem 6,5 kDa und 3,9 kDa PSS
hergestellt und mit den Messungen von PEMs aus 10,7 kDa PSS verglichen.
Die Verkürzung von PSS hat subtile Auswirkungen auf den Filmaufbau und die
Selbststrukturierung. Für PEM aus PSS mit einer molaren Masse von 6,5 kDa konnten nur
zwei Wachstumsregime ermittelt werden: ein exponentielles und ein lineares Wachstumsregime.
Der Übergang vom exponentiellen zum linearen Wachstum erfolgte bei 28
Doppelschichten. Bei PEMs, die aus 3,9 kDa PSS hergestellt wurden, wurde bis zu 29 bl nur
ein exponentielles Wachstum beobachtet. Dies zeigt, dass eine Verringerung der molaren
Masse von PSS das exponentielle Wachstum auf eine größere Anzahl von abgeschiedenen
Doppelschichten ausdehnt. Dies ist auf die zunehmende PSS-Diffusion zurückzuführen.
In allen Filmen wurden Selbststrukturierungen beobachtet. Der Abstand und die Höhe der
säulenartigen Domänen nehmen mit jeder abgeschiedenen PDADMA/PSS-Doppelschicht
deutlich zu. Der durchschnittliche Domänenabstand ändert sich weniger und korreliert mit den
vertikalen Wachstumsregimen. Der Domänenabstand schwankt zwischen 70 nm und 750 nm.
Die größten lateralen Abstände und ein längeres exponentielles Wachstumsregime wurden
mit dem kürzesten PSS (3,9 kDa) erreicht, was auf die hohe Mobilität des PSS zurückgeführt
wird. Die Domänenhöhe ist immer kleiner als der Domänenabstand. Wenn die PEM mit
PDADMA terminiert ist, sind die Oberflächenrauhigkeit und der durchschnittliche Abstand
größer als bei PSS terminierten Filme in Wasser und nach dem Trocknen.
Darüber hinaus wurden zwischen den Domänen Filamente beobachtet. Die Filamente
bestehen aus PDADMA/PSS-Komplexen. Eine mögliche Vermutung ist, dass diese Komplexe
zwischen den Domänen diffundieren und ihren Abstand anpassen.
Die Oberflächenstruktur des Films aus PSS 10,7 kDa zeigt eine symmetrische gaußförmige
Höhenverteilung in allen drei Wachstumsregimen von 5 bis 40 bl. Für die kurze PSS war eine
solche Verteilung nur bis 15 bl (6,5 kDa) bzw. 20 bl (3,9 kDa) zu beobachten. Danach wurde
für 6,5 kDa schiefe Verteilung mit Ausläufern zu größeren Höhen beobachtet. 3,9 kDa PSS
zeigte dann sogar eine bimodale Höhenverteilung.
Die lineare Ladungsdichte von PDADMA ist etwa halb so groß wie die von PSS. Folglich
adsorbiert PDADMA in einer bürstenartigen Konformation. Wenn die oberste Schicht
PDADMA ist, dann ist das PDADMA-Molekül nicht fest an die Oberfläche gebunden. Daher ist
die durch die Oberflächenspannung erzeugte Kraft für PDADMA groß genug, um zu einer
Veränderung der Oberflächenmorphologie und folglich zu einer kleineren Gesamtoberfläche
zu führen.Außerdem sind die Domänen in 1 M NaCl-Lösung stabil, schrumpfen aber in 2 M NaCl enorm,
während ihr Abstand leicht zunimmt.
Diese Untersuchungen zeigten, dass die Mobilität des Polyelektrolyten PSS die
Voraussetzung für den Aufbau einer strukturierten Oberfläche in einem PEM-System aus
PDADMA/PSS ist. Diese Ergebnisse zeigten auch, dass die Verkürzung der Kette der PSS Moleküle
die Herstellung von Filmen erleichtert, deren Dicke und Selbststrukturierung je nach
dem gewünschten Zweck angepasst werden kann. Solche Filme können in der Medizin und
Biologie als geeignetes Substrat zur Optimierung der Adsorption von Zellen und anderen
Molekülen oder als Nanofilter effektiv eingesetzt werden.
In dieser Dissertation konnte ich zeigen, wie die Verkürzung der Kette der PSS-Moleküle zur
Bildung einer lateralen selbststrukturierten Oberfläche führt und wie die zunehmende Mobilität
der PSS-Moleküle die Oberflächenmorphologie signifikant beeinflusst.
In this work, 2-dimensional measurements in the THz frequency range with self-made spintronic THz emitters were presented. The STE were used to optimize the spatial resolution and determine the magnetization in geometric shapes. At the beginning, various combinations of FM and NM layers were produced and measured to achieve an optimal composition of the STE. The layer thickness of the ferromagnetic CoFeB layer and the nonmagnetic PT layer was also varied. The investigations have shown that a layer combination of 2 nm thick CoFeB and 2 nm thick Pt, applied to a fused silica glass substrate and covered with a 300 nm thick SiO2 layer, emits the highest THz amplitude. Based on these, a structured sample, consisting of an STE and an additional layer system of 5 nm Cr and 100 nm Au, was produced. Further, three wedge-shaped structures were removed from the gold layer by an etching process so that the THz radiation generated by the STE can pass through these areas. This enables the optimization of the resolution of the system. For this purpose, the sample was moved perpendicular to the laser beam by two stepping motors with a step size of 5 μm and imaged 2-dimensionally. By reducing the step size to 0.2 μm, the beam diameter could be measured at the edge of the structure using the knife-edge method. Based on this measurement, the resolution of the system could be determined as 5.1 ± 0.5 μm at 0.5 THz, 4.9 ± 0.4 μm at 1 THz, and 5.0 ± 0.5 μm at 1.5 THz. These results are confirmed by simulations considering the propagation of THz wave packets through the SiO2. The expansion of the FWHM of the waves, passing through the 300 nm thick layer, is about 1%. Only a SiO2 layer with a thickness in the μm range occurs an expansion of around 10%. This shows that it is possible to perform 2-dimensional THz spectroscopy with a resolution in the dimension of the exciting laser beam by using near-field optics. Afterward, the achieved spatial resolution was used to investigate the influence of external magnetic fields on the STE and the emitted THz radiation. By implementing a pair of coils above the sample, an external magnetic field could be applied parallel to the pattern. The used sample was designed in such a way that only certain geometric areas on the fused silica glass substrate were coated with an STE so that THz radiation is emitted only in those areas. The 2-dimensional images show the geometric structures for f = 1.0 THz and f = 1.5 THz clearly. By applying a permanent, positive magnetic field (+M), a positive course of the THz amplitude can be seen. A rotation of the magnetic field by 180° (-M) leads to a reversal of the orientation of the emitted THz radiation, whereby the magnetic field does not influence the corresponding frequency spectrum. By using minor loops, the sample was demagnetized by the constant reduction of the magnetic field strength with alternating magnetic field direction. The 2-dimensional representation of the pattern with a step size of 10 μm shows that the sample was demagnetized since both, positively and negatively magnetized structures, could be imaged. In addition, in the 2nd row from the top, a completely demagnetized circle and a rectangle with a division into two domains can be seen. These structures have both positive and negative magnetized areas, which are separated by a domain wall. To investigate this in more detail a 2-dimensional measurement of the divided regions was made with a step size of 2.5 μm. These images confirm the division of the structures into positive and negative domains, separated by a domain wall, which was verified by Kerr-microscope measurements. Both data show a similar course of the domains and the domain wall. However, to be able to examine the domain wall more precisely using 2-dimensional THz spectroscopy, the resolution of the system must be improved to a range of a few nm, because the expected domain wall width is between 𝑙𝑊 = 12.56 nm and 𝑙𝑊 = 125.6 nm. The improved resolution would make it possible to image foreign objects, such as microplastics in biological cells or tissue. For this purpose, different plastics, such as polypropylene, polyethylene, and polystyrene, were investigated in the THz frequency range up to 4 THz. While no specific absorption could be determined for PP, characteristic absorption peaks were found for PE and PS. The energy of the photons with a frequency of about 2.2 THz excites lattice vibrations in the PE. Therefore, this frequency is specifically absorbed, and the intensity in the transmission spectrum is lower than for other frequencies. PS absorbs especially THz radiation with a frequency of 3.2 THz. In addition, all of the investigated plastics are mostly transparent for THz radiation, which makes imaging of these materials feasible. Based on these basic properties, it will be possible to image and identify these types of plastic.
In this work, spatial distributions for reactive stable and transient species that are involved
in the reaction cycle of H2O2, a key species for biomedical applications, were
determined directly in the effluent of a kINPen-sci plasma jet. The small diameter
of cold atmospheric pressure plasma jets and their operation at atmospheric pressure
that causes strong quenching reactions make diagnostics challenging. Here, various diagnostic
techniques have been employed and adapted for the use in the effluent of a
cold atmospheric pressure plasma jet, which were laser atomic absorption spectroscopy
(LAAS) at 811.5 nm for the detection of Ar(3P2), picosecond two-photon absorption
laser-induced fluorescence spectroscopy (ps-TALIF) at 225 nm and 205 nm for the
detection of O and H atoms, respectively, and continuous wave cavity ring-down spectroscopy
(cw-CRDS) at 1.506 µm for the detection of HO2, and cw-CRDS at 8000 µm
for the detection of H2O2. All these methods provide absolute number densities. In
this work, spatial distributions within the small diameter of the effluent of a CAPJ
were obtained, which have not been reported so far literature. In order to overcome the
line-of-sight limitations of CRDS, radial scans were performed and transformed into a
spatial distribution by using Abel inversion.
Based on the determined spatial density distributions for H atoms, O atoms, HO2
radicals, and H2O2 molecules, together with the investigated impact of humidity in the
feed gas on the excitation dynamics and the production of Ar(3P2), and finally on a
comparison of the experimental results to a plasma chemical and reacting flow model,
three different zones with varying reaction kinetics were identified. The densities close
to the nozzle of the kINPen-sci plasma jet were dominated by reactions within the
plasma zone including the dissociation of H2O added to the Ar feed gas and O2 that
was presumably transferred into the plasma zone by counter-propagating ionisation
waves. Notably, also the larger molecules, such as HO2 and H2O2 were mainly formed
within the plasma zone of the plasma jet. Between 1.5 mm and 5 mm below the nozzle,
the atomic species and molecular radicals generated in the plasma zone were consumed
by chemical reactions with the surrounding gas, whose composition was controlled by
applying a gas curtain. At further distances from the nozzle, where typically biological
samples are positioned, only H2O2 and HO2 were observed.
With this work, it is successfully demonstrated that even for the small diameters of
cold atmospheric pressure plasma jets the determination of spatial profiles for reactive
transient and stable species is possible within the effluent. By combining the experimental
results, important insights into the formation and consumption of H2O2 and its
precursors were gained, which are essential for the understanding of use of plasmas in
biomedical applications.
The biomechanical (Young's modulus, adhesion force, deformability) properties of platelets depend on the cytoskeleton and have an undisputed influence on physiological and pathological processes such as hemostasis and thrombosis. The alterations of these biomechanical properties can be used as label-free diagnostic markers in initiation or progressive diseases such as MYH9-inherited disease. Therefore, the focus of my thesis was to investigate the relationship between the changes in platelet cytoskeleton proteins and the resulting biomechanical properties using biophysical methods.
In the first chapter of my thesis I focused on my review of the biophysical methods that are most commonly used to assess and quantify the biomechanical properties of platelets. In this review, I provide an in-depth insight into the governing principles and instrumentation setup and discuss relevant examples applied to platelet mechanics. In addition, my review also summarizes the limitations of these biophysical methods and highlight latest improvements. The review covers the following techniques: micropipette aspiration, atomic force microscopy (AFM), scanning ion conductance microscopy (SICM), tensile force microscopy on hydrogel substrates, microcolumns, and deformable 3D substrates, and real-time deformability cytometry (RT-DC). This review is directed toward clinician scientists who are interested in exploring applications of single-cell based biophysical approaches in unraveling the role of platelet biomechanics in hemostasis and thrombosis research.
In the second chapter of my thesis, I present my research paper on the influence of commonly used ex vivo anticoagulants on the intrinsic biomechanical properties and functional parameters (e.g. activation profils) of human platelets. To comprehensively assess this, platelets obtained in different ex vivo anticoagulants such as ACD-A, Na-Citrate, K2-EDTA, Li-Heparin, and r-Hirudin were used, and their biomechanical properties were determined by real-time fluorescence and deformability cytometry (RT-FDC). Flow cytometry, and confocal laser scanning fluorescence microscopy were used to determine platelet function properties. K2-EDTA and Li-Heparin were found to affect platelet biomechanics by increasing actin polymerization of non-stimulated human platelets. This increased actin polymerization results in decreased platelet deformation. It is recommended that an ex vivo anticoagulant such as ACD-A, Na-Citrate, or r-Hirudin be chosen for the study of the cytoskeleton of human platelets and, if possible, that it not be exchanged, because comparability of results is not assured. Furthermore, I demonstrate the significance of choosing correct ex vivo anticoagulants in RT-FDC by showing that platelets from a healthy donor and a MYH9 patient with the E1841K point mutation differ in their deformation. This paper is the first comprehensive investigation at the single platelet level to establish the relevance of preanalytical standardization in platelet sample preparation for biomechanical studies.
The third chapter of my thesis is focused on the biomechanical analyses of platelets and thrombi from MYH9-related disease. Here I studied three Myh9 mouse lines with a point mutation in the Myh9 gene at positions 702, 1424, or 1841. Furthermore, two MYH9 patients (MYH9 p.D1424N, MYH9 p.E1841K) were examined. MYH9-related disease (MYH9-RD) presents with macrothrombocytopenia with a moderate bleeding tendency. It is caused by mutations in the MYH9 gene that lead to alteration of non-muscle myosin heavy chains type IIA (NMMHC IIA), resulting in disruption of the platelet cytoskeleton. Western blot analysis, flow cytometry, in vitro aggregometry, and transmission electron microscopy demonstrated that Myh9 point mutant mice have comparable primary function compared to the control group. The heterozygous point mutations in the Myh9 gene resulted in decreased platelet deformation (RT-FDC), decreased platelet adhesion to collagen (single platelet force spectroscopy-SPFS), and decreased platelet-platelet interaction forces (SPFS). Decreased platelet force (Micropost Arrays) results in softer thrombi (colloidal probe Spectroscopy), impaired clot retraction, and thus prolonged bleeding time. The R702C, D1424N, and E1841K mutations have a similar effect on platelet biomechanical functions, although the E1841K mutation had less impact on thrombus formation and stiffness. MYH9-RD patients have an increased risk of bleeding, and the antifibrinolytic drug tranexamic acid (TXA) is one way to control bleeding complications in these patients. It was shown that TXA treatment significantly reduced bleeding time in the three Myh9 mouse models, confirming that the enhanced bleeding phenotype due to decreased platelet forces in Myh9 mutant mice can be compensated by the addition of TXA.
With the biophysical methods and research results presented in my thesis, it is clear that it is essential to study the altered response of the platelet cytoskeleton by cytoskeletal mutations, biochemical, physical stimuli, or by pharmacological aspects. This will provide us with an opportunity to better understand the underlying mechanisms and thus contribute to better clinical treatment.