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The Influence of Ionic Liquid Modification on the Restructuring of Trimetallic PtNiMo/C Catalysts During Conditioning
Get PDFDuring preconditioning of PtNiMo/C catalyst metal dissolution and redeposition takes place. At slow scan rates this leads to increased steady activity for oxygen reduction reaction (ORR). Furthermore, ionic liquids (IL) influence the activity of Pt‐based catalysts and can alter the leaching of Pt‐alloy catalysts. This study investigates the influence of ILs on the preconditioning of PtNiMo/C catalysts. Therefore, preconditioning parameters as well as the IL employed were varied. ILs with long side chains like [C8fC1][BETI] resulted in a spreading of the activity development during preconditioning over a longer cycle time and with damped amplitude for the activity changes. For shorter side chains like [BMIM][BETI] the development is like the pristine catalyst. Ex‐situ and in‐situ characterization revealed that [BMIM][BETI] leached fast to the electrolyte, which was not observed for the other ILs. Nevertheless, for all ILs a strongly reduced platinum leaching was observed. Even for the leached [BMIM][BETI] a stable wetting layer influencing the leaching seems to remain. Nevertheless, only for the other ILs where an immobilized bulk phase is remaining a difference in catalyst restructuring during the preconditioning is observed and a higher number of small sized Pt clusters and a lower amount of bigger Pt clusters resulted
Cell Adhesion and Local Cytokine Control on Protein‐Functionalized PNIPAM‐co‐AAc Hydrogel Microcarriers
Get PDFAchieving adequate cell densities remains a major challenge in establishing economic biotechnological and biomedical processes. A possible remedy is microcarrier‐based cultivation in stirred‐tank bioreactors (STBR), which offers a high surface‐to‐volume ratio, appropriate process control, and scalability. However, despite their potential, commercial microcarriers are currently limited to material systems featuring unnatural mechanical properties and low adaptability. Because matrix stiffness and ligand presentation impact phenotypical attributes, differentiation potential, and genetic stability, biotechnological processes can significantly benefit from microcarrier systems tailorable toward cell‐type specific requirements. This study introduces hydrogel particles co‐polymerized from poly(N‐isopropylacrylamide) (PNIPAM) and acrylic acid (AAc) as a platform technology for cell expansion. The resulting microcarriers exhibit an adjustable extracellular matrix‐like softness, an adaptable gel charge, and functional carboxyl groups, allowing electrostatic and covalent coupling of cell adhesive and cell fate‐modulating proteins. These features enable the attachment and growth of L929 mouse fibroblast cells in static microtiter plates and dynamic STBR cultivations while also providing vital growth factors, such as interleukin‐3, to myeloblast‐like 32D cells over 20 days of cultivation. The study explores the effects of different educt compositions on cell‐particle interactions and reveals that PNIPAM‐co‐AAc microcarriers can provide both covalently coupled and diffusively released cytokine to adjacent cells
Analyzing spectral distributions of charge transfer character in ensembles: a case study on the reaction center of photosystem II
Get PDFUnderstanding the primary charge separation events in Nature's photosynthetic reaction centers is a key step toward harnessing the microscopic processes of light conversion into chemical energy. Despite intense research efforts employing state-of-the-art spectroscopic and theoretical techniques, the precise nature of energy transfer and charge separation events in these systems are still insufficiently understood. Herein, we present a computational approach that enables analysis of the charge transfer character in excited electronic states with inclusion of thermal effects in ensembles. We showcase an application of this approach to the reaction center of photosystem II, focusing on the Chl_D1Pheo_D1 and P_D1P_D2 pairs of pigments. We find that the Chl_D1Pheo_D1 pair is a more likely candidate for the primary charge separation than the P_D1P_D2 pair. Our computational approach is transferable to other biological and man-made charge separation and charge transfer systems
Comparative modelling and scenario analysis of sector-coupled island energy system optimisations
Get PDFDispatch optimisations of an off-grid island energy system were carried out. These optimisations compared a linear and piecewise linear efficiency modelling approaches for sector couplers, different Dunkelfkaute weather scenarios; and different horizon lengths over one year with an hourly resolution. Solar and wind power are complemented by battery and hydrogen storages, along with sector couplers: electrolyser, fuel cell, gas turbine and steam boiler to meet electricity and high-temperature heat loads. The unit dispatch optimisations were conducted in PyPSA. The piecewise linear model showed a concentration of the operation points at maximum efficiency for the electrolyser, which can be operated more flexibly than the other components. When modelled with constant efficiency, the gas turbine showed a significantly higher electricity output. The fuel cell and the steam boiler did not show significant differences, between the two modelling approaches. The relatively minor influence of horizon length underscored the importance of thorough pre-optimisation strategies, particularly in anticipating and managing Dunkelflaute events, where long-term foresight is crucial for system resilience. A four-week Dunkelflaute showed that the capacity of the EL in conjunction with the availability of electricity from RE in the period before the Dunkelflaute was the limiting factor for bridging the Dunkelflaute
Informational Efficiency in the Corporate Bond Market
Get PDFThis dissertation examines the informational efficiency in the corporate bond market. More precisely, it shows how new information stemming from announcements of bond issuing firms impacts the prices of these bonds. While the equity market efficiency is well examined, historically limited data quality and the complexity of bonds leave research gaps in the corporate bond market. Composed of three studies, this dissertation uses a comprehensive sample of US corporate bond trading data to close these gaps further.
The first study examines the power of event studies in corporate bond markets and thus sets the basis for testing informational efficiency in the bond market around any event. It shows that two market phenomena negatively impact the informative value of results: Test power decreases rapidly in the presence of event induced variance. Moreover, bond market illiquidity is problematic with samples focused on above average maturities and credit risks.
The second study specifically tests informational efficiency around dividend announcements that imply dividend payout ratio changes. It provides insights into significant, negative reactions that bondholders exhibit and highlights the complex effects that drive these bond market reactions. Additionally, it shows the explanatory power of signaling and wealth transfer hypotheses, while the information content hypothesis is refuted.
The third study analyzes the interaction effect between earnings and dividend announcements. The results of this study suggest that a strong interaction effect is present in the corporate bond market and that it is robust across several specifications. Consequently, the interaction effect of dividend and earnings announcements has to be considered when evaluating the overall contained information for the bond market
Line Defects in One-Dimensional Hexagonal Quasicrystals
Get PDFUsing the eight-dimensional framework of the integral formalism of one-dimensional quasicrystals, the analytical expressions for the displacement fields and stress functions of line defects, which are dislocations and line forces, in one-dimensional hexagonal quasicrystals of Laue class 10 are derived. The self-energy of a straight dislocation, the self-energy of a line force, the Peach–Koehler force between two straight dislocations, and the Cherepanov force between two straight line forces in one-dimensional hexagonal quasicrystals of Laue class 10 are calculated. In addition, the two-dimensional Green tensor of one-dimensional hexagonal quasicrystals of Laue class 10 is given within the framework of the integral formalism
The immunogenic potential of carbon ions and the involved mechanisms in tumor cells
Get PDFTriple-negative breast cancer and osteosarcoma are aggressive, highly metastatic, and radioresistant tumors that require innovative therapeutic approaches to improve clinical outcomes. Radiotherapy is a cornerstone of cancer treatment, used in nearly half of all cancer patients. The immunogenic signals elicited by X-ray exposure in cancer cells are relatively well-documented and form the basis for combined radiotherapy and immunotherapy approaches. Radiotherapy with charged particles, particularly carbon ions, hold promise for overcoming radioresistance due to the prevalence of direct DNA damage and the reduced dependency on oxygen, while at the same time sparing the healthy tissues to a higher extent. The impact of carbon ions on the immunogenicity of cancer cells is understudied but represents an important area of research for combinations of charged particle therapy with immunotherapy for radioresistant cancers in advanced stages.
This work addresses the limited knowledge of the immunogenic potential of carbon ions analyzing immunogenic molecules and mechanisms activated in murine triple-negative breast cancer (4T1 cells) and osteosarcoma (LM8 cells). For most of the endpoints, different doses and time points were analyzed and the results of carbon ions were compared to X-rays. The results highlighted that carbon ion irradiation effectively overcomes the radioresistance of both cell lines. In LM8 cells with a functional p53 protein, carbon ions induce more effectively regulated cell death than X-rays. In contrast, in 4T1 cells with a non-functional p53, radiation predominantly triggers mitotic catastrophe, which can delay radiation-induced cell death (in the form of apoptosis, ferroptosis, or necroptosis). Irradiation of both cell lines with carbon ions also results in an enhanced or similar release of immunostimulatory molecules, such as cytokines and chemokines, compared to X-rays. In particular, the in vitro mechanisms underlying the higher efficiency of carbon ions compared to X-rays in reducing lung metastasis in an in vivo osteosarcoma model (Helm et al., 2021) were investigated. This work revealed a higher induction of adjuvant molecules after irradiation with carbon ions of osteosarcoma cells, in the form of damage-associated molecular patterns (DAMPs), cytokines, and chemokines compared to X-rays.
Moreover, the occurrence of cytoplasmic dsDNA and the activation of the cGAS-STING pathway, which results in immunostimulatory interferon-β release, were analyzed in triple-negative breast cancer cells based on the results of Vanpouille-Box and colleagues (Vanpouille-Box et al., 2017). The results indicate that the occurrence of cytoplasmic dsDNA is correlated with the features of mitotic catastrophe observed in 4T1 cells and that carbon ions induce more efficiently cytoplasmic dsDNA and interferon-β release than X-rays.
The influence of a fractionated irradiation scheme with X-rays was also investigated with respect to the cGAS-STING pathway and the release of interferon-β. The higher immunogenicity of a 3x8 Gy over a single high dose demonstrated by Vanpouille-Box and colleagues (Vanpouille-Box et al., 2017) could not be reproduced in this work. This points to other effects besides the immunogenic signals released by cancer cells (e.g. on the tumor microenvironment or adjacent tissues) that can additionally explain the advantages of fractionation observed in vivo (Vanpouille-Box et al., 2017).
One of the factors inducing radioresistance is intratumoral hypoxia, which is present in some solid tumors including osteosarcoma. Carbon ions, having a more direct effect on the target molecule (DNA), have the potential to reduce radioresistance but the data on their immunogenicity in reduced oxygen concentrations are limited. Therefore, the interplay between hypoxia, the linear energy transfer of the particle, and immunogenic cell death was additionally investigated in this study. The results indicate that the enhanced immunogenic potential of carbon ions may be limited by reduced oxygen levels and that increasing the linear energy transfer may not trigger a higher level of immunogenic signals.
Overall, this study integrates data on damage-associated molecular patterns, immune ligands, cytokines, and chemokine release, indicating a higher or similar immunogenicity of carbon ions compared to X-rays. These findings highlight that carbon ion radiotherapy is a powerful modality for potentially overcoming the limitations of conventional radiotherapy and its combination with immunotherapies can be an asset, particularly for the treatment of advanced and radioresistant tumors
Electric and magnetic dipole strength in ⁵⁸Ni
Get PDFThis thesis presents results on the electric and magnetic dipole strength in ⁵⁸Ni obtained with inelastic proton scattering to very forward angles. The ⁵⁸Ni(p,p') experiment was performed at the Research Center for Nuclear Physics in Osaka, Japan, using a beam energy of 295 MeV. Spectra were recorded for scattering angles between 0.40° and 5.15° covering an excitation energy range from 5 to 26 MeV.
First, a state-to-state analysis was performed on resolved transitions. A total of 116 dipole states were found. With the aid of model angular distributions, 26 were identified as M1 transitions and 11 as E1 transitions. Another 22 showed a preference for either an E1 or an M1 multipolarity. The reduced electric and the magnetic dipole transition strengths of the excited states were determined. In addition, the total isovector spin-flip M1 transition strength was extracted and compared to shell-model calculations.
The spectroscopic information from the state-to-state analysis was compared to dipole transitions measured with the ⁵⁸Ni(γ,γ') and ⁵⁸Ni(e,e') reactions and electric dipole transitions with large transverse form factors identified. Transverse electric form factors serve as a signature for the toroidal dipole mode, for which candidates were found for the first time.
The second part of the analysis involves a multipole decomposition analysis of the measured ⁵⁸Ni(p,p') cross sections. Photoabsorption cross sections from 5 to 20 MeV were extracted using the virtual photon method. High-energy contributions up to 50 MeV were estimated from QRPA+QPVC calculations leading to an electric dipole polarizability of α_D(⁵⁸Ni)=3.48(31) fm³. Further, the available experimental systematics of the dipole polarizability across the isotopic chart is presented, and approaches to extract surface and volume energies are discussed.
Finally, the nuclear level density of Jπ=1⁻ states in ⁵⁸Ni between 11 and 20 MeV is extracted by applying a fluctuation analysis
Instability and wave scattering of a compressible shear layer
Get PDFIn this thesis, the evolution of acoustic perturbations in a compressible hyperbolic tangent shear flow is studied and a framework is established to deal with the occurring singularities in the underlying differential equation. Basically, two sub-classes of problems are considered: Unstable perturbations on the one hand and neutral perturbations leading to acoustic waves in the far fields on the other hand. Both are derived as solutions of the linearized Euler equations, which, under the assumption of normal mode behavior, lead to an eigenvalue problem, in the isothermal case based on the Pridmore-Brown equation. For the non-isothermal problem under the assumption of a simplified temperature-velocity relation as well as for the consideration of 3D evolving perturbations, we find equivalence transformations to map these problems to the 2D isothermal problem. To solve this eigenvalue problem, a Frobenius power series matching algorithm is developed, which exactly takes into account the singularities arising from the inviscid consideration. All spurious modes are avoided and spectral convergence is achieved.
With this algorithm, a close connection between temporal instabilities and far-field radiating neutral waves is established. We find that the far-field radiation of sound emerges as large wavenumber neutral limit of the slow and fast mode instabilities. In addition to solving these eigenvalue problems, we extend the consideration to the scattering of far-field incident waves, thus answering the question of reflection and transmission of waves by the shear layer. We find a central connection between wave scattering and sound radiation. Waves with frequencies equal to the radiating eigenmodes are resonantly over-reflected, giving an infinite reflection coefficient, thus revealing acoustic resonance. We further observe the inverse phenomenon of so called absorbed modes which, when incident on the shear layer, lead to no reflected wave and are therefore fully absorbed by the shear layer. Again, a close link to instabilities is established, thus indicating that instability can be triggered by incident wave absorption since also absorbed modes emerge as another neutral limit of instabilities. We generally observe that the introduction of a temperature gradient within the current simplification shifts effects to lower Mach number compared to the isothermal case.
The results obtained for the shear layer are further extended to a plane-parallel jet with constant core flow constructed by two opposing shear layers. Here, the focus is on neutral far-field radiating waves, and we find two classes of modes. First, pure shear layer radiating modes arise from the radiating modes of each single shear layer. These are subsonic with respect to the core flow but supersonic with respect to the free stream and are therefore radiating. The second class of modes we describe is called leaking trapped waves. They are supersonic with respect to both the core and the free stream. The radiation is determined by a system of reflected waves trapped in the core, which partially leak into the far field and therefore give rise to noise there.
Finally, we extend the stability considerations from the purely temporal growth of a single mode to the spatial growth or decay of localized perturbations. Following Briggs' method, convective and absolute instabilities are introduced and preliminary results are shown, which serve as a preview of the applicability of the power series matching algorithm to fully determine the character of an unstable response to a pulse source excitation
A CFD ignition model to predict average-cycle combustion in SI engines with extreme EGR levels
Get PDFControl of the combustion process in Spark-Ignition (SI) engines operated with extreme dilution from exhaust gas re-circulation (EGR) represents one of the major limitations in the industrial design of such technology. Numerical approaches able to describe in detail the formation of the early flame kernel become essential to face such an ambitious task. This work presents a RANS-based multi-dimensional model of the combustion process, including an advanced description of the ignition stage to consider its stochastic re-ignitions within the average cycle prediction. The spark-channel is described as a column of Lagrangian parcels that represent early flame kernels, whose growth is controlled by the laminar flame speed and energy input from the electrical circuit. The spatial evolution of each parcel is computed according to a scaled value of the average-flow speed, to mimic the smooth but short elongation of the mean-cycle channel produced by stochastic restrikes affecting the single-cycle arcs. To clarify this phenomenon and assess the proposed CFD method, a series of experiments are performed in a single cylinder SI engine with optical access, running at a low-load cruise-speed operating condition. Increasing EGR levels are tested up to the onset of misfire, with measurements of the secondary-circuit features and of the flame evolution through high-speed imaging. Satisfactory results are achieved in terms of numerical-experimental comparison of the cycle-averaged in-cylinder pressure, discharge parameters, and spatial flame distribution, demonstrating the reliability of the proposed numerical approach