@article{58492, abstract = {{A coupled finite plasticity ductile damage and failure model is proposed for the finite element simulation of clinch joining, which incorporates stress-state dependency and regularisation by gradient-enhancement of the damage variable. Ductile damage is determined based on a failure indicator governed by a failure surface in stress space. The latter is exemplary chosen as a combination of the Hosford–Coulomb and Cockcroft–Latham–Oh failure criteria for the high and low stress triaxiality range, respectively, to cover the wide stress range encountered in forming. Damage is coupled to elasto-plasticity to capture the damage-induced degradation of the stiffness and flow stress. This affects the material behaviour up to failure, thereby realistically altering the stress state. Consequently, especially for highly ductile materials, where substantial necking and localisation precede material fracture, the failure prediction is enhanced. The resulting stress softening is regularised by gradient-enhancement to obtain mesh-objective results. The analysis of a modified punch test experiment emphasises how the damage-induced softening effect can strongly alter the actual stress state towards failure. Moreover, the impact of successful regularisation is shown, and the applicability of the damage and failure model to clinch joining is proven.}}, author = {{Friedlein, Johannes and Mergheim, Julia and Steinmann, Paul}}, issn = {{0022-5096}}, journal = {{Journal of the Mechanics and Physics of Solids}}, keywords = {{Finite plasticity, Ductile damage, Gradient-enhancement, Stress-state dependency, Failure}}, publisher = {{Elsevier BV}}, title = {{{Modelling of stress-state-dependent ductile damage with gradient-enhancement exemplified for clinch joining}}}, doi = {{10.1016/j.jmps.2025.106026}}, volume = {{196}}, year = {{2025}}, } @article{63950, abstract = {{Sodium-ion batteries are at the forefront of new, sustainable energy systems required for the global energy transition. 23Na in situ solid-state nuclear magnetic resonance spectroscopy is capable of unraveling structures in working electrochemical cells during the charging and discharging processes. To evaluate its suitability for long-term studies, local sodium environments in sodium/sodium ion cells based on silicon carbonitride and hard carbon materials are tracked for up to 49 cycles (228.5?h). The formation of dendrites as well as the decay of a secondary metallic sodium species is observed, and local structures are analyzed up to the point of capacity degradation and cell failure. Initial points of cell breakdown are reflected in the NMR data by characteristic changes in signal intensities, whereas the degradation of the cells is reflected by a cease to periodic signal intensity fluctuations. Meanwhile, ex situ 23Na NMR spectra of the deactivated cells reveal a complex range of environments for sodium ions.}}, author = {{Egert, Sonja and Remesh, Renuka and Jusdi, Agatha Clarissa and Sugawara, Yushi and Schutjajew, Konstantin and Oschatz, Martin and Buntkowsky, Gerd and Gutmann, Torsten}}, journal = {{Batteries & Supercaps}}, keywords = {{solid-state nmr, hard carbon, in-situ, SiCN, sodium ion batteries}}, number = {{n/a}}, pages = {{e202500516}}, publisher = {{John Wiley & Sons, Ltd}}, title = {{{Long-Term Cycling Stability of Sodium/Sodium Ion Cells Probed by In Situ Solid-State NMR Spectroscopy}}}, doi = {{10.1002/batt.202500516}}, volume = {{n/a}}, year = {{2025}}, } @unpublished{63403, abstract = {{Stateful signatures like the NIST standardized signature schemes LMS and XMSS provide an efficient and mature realization of post-quantum secure signature schemes. They are recommended for long-term use cases like e.g. firmware signing. However, stateful signature schemes require to properly manage a so-called state. In stateful signature schemes like LMS and XMSS, signing keys consist of a set of keys of a one-time signature scheme and it has to be guaranteed that each one-time key is used only once. This is done by updating a state in each signature computation, basically recording which one-time keys have already been used. While this is straightforward in centralized systems, in distributed systems like secure enclaves consisting of e.g. multiple hardware security modules (HSMs) with limited communication keeping a distributed state that at any point in time is consistent among all parties involved presents a challenge. This challenge is not addressed by the current standardization processes. In this paper we present a security model for the distributed key management of post-quantum secure stateful signatures like XMSS and LMS. We also present a simple, efficient, and easy to implement protocol proven secure in this security model, i.e. the protocol guarantees at any point in time a consistent state among the parties in a distributed system, like a distributed security enclave. The security model is defined in the universal composabilty (UC) framework by Ran Canetti by providing an ideal functionality for the distributed key management for stateful signatures. Hence our protocol remains secure even if arbitrarily composed with other instances of the same or other protocols, a necessity for the security of distributed key management protocols. Our main application are security enclaves consisting of HSMs, but the model and the protocol can easily be adapted to other scenarios of distributed key management of stateful signature schemes.}}, author = {{Blömer, Johannes and Bröcher, Henrik and Krummel, Volker and Porzenheim, Laurens Alexander}}, keywords = {{distributed state, hash-based signature, stateful hash-based signature, universal composability, secure enclave}}, pages = {{22}}, title = {{{Secure Distributed State Management for Stateful Signatures with a Practical and Universally Composable Protocol}}}, year = {{2025}}, } @phdthesis{56940, abstract = {{Ziel dieser Arbeit ist die Entwicklung eines modellbasierten Beobachters für eingangsaffine, nichtlineare Systeme, der trotz Modellungenauigkeiten eine hohe Schätzgüte erzielt und zusätzlich eine parametrische, physikalisch interpretierbare Darstellung dieser ermöglicht. Diese soll zur automatisierten Verbesserung des Modells verwendet werden. Die vorliegende Arbeit analysiert sowohl Techniken der hybriden Systemidentifikation wie physikalisch motivierte neuronale Netze, als auch Methoden zur Kompensation von Modellungenauigkeiten im Beobachterentwurf. Basierend auf der Analyse wird ein neuartiger, modellbasierter Beobachter entworfen, der Systemzustände und Modellungenauigkeiten gleichzeitig schätzt und insbesondere eine parametrische, physikalisch interpretierbare Darstellung der Ungenauigkeiten erzielt. Diese besteht aus einer Linearkombination von physikalisch interpretierbaren Funktionen, deren dazugehörige, dünnbesetzt modellierte Parameter mithilfe eines augmentierten Zustands parallel zu den Systemzuständen geschätzt werden. Das Novum dieser Arbeit stellt somit die echtzeitfähige Schätzung von Zuständen und Modellungenauigkeiten in physikalisch-technischer Form dar, auf deren Grundlage ein Konzept zur automatisierten Modelladaption umgesetzt wird. Die Applikation der neuartigen Methode ist in der Situation auftretender Systemveränderungen besonders vorteilhaft, da diese zur Laufzeit durch den augmentierten Beobachter geschätzt und identifiziert werden können. }}, author = {{Götte, Ricarda-Samantha}}, isbn = {{978-3-947647-42-2}}, keywords = {{state estimation, joint estimation, sparsity}}, title = {{{Online-Schätzung von Modellungenauigkeiten zur automatischen Modelladaption unter Beibehaltung einer physikalisch-technischen Interpretierbarkeit}}}, doi = {{10.17619/UNIPB/1-2066}}, volume = {{423}}, year = {{2024}}, } @article{58491, abstract = {{Similar to bulk metal forming, clinch joining is characterised by large plastic deformations and a variety of different 3D stress states, including severe compression. However, inherent to plastic forming is the nucleation and growth of defects, whose detrimental effects on the material behaviour can be described by continuum damage models and eventually lead to material failure. As the damage evolution strongly depends on the stress state, a stress-state-dependent model is utilised to correctly track the accumulation. To formulate and parameterise this model, besides classical experiments, so-called modified punch tests are also integrated herein to enhance the calibration of the failure model by capturing a larger range of stress states and metal-forming-specific loading conditions. Moreover, when highly ductile materials are considered, such as the dual-phase steel HCT590X and the aluminium alloy EN AW-6014 T4 investigated here, strong necking and localisation might occur prior to fracture. This can alter the stress state and affect the actual strain at failure. This influence is captured by coupling plasticity and damage to incorporate the damage-induced softening effect. Its relative importance is shown by conducting inverse parameter identifications to determine damage and failure parameters for both mentioned ductile metals based on up to 12 different experiments.}}, author = {{Friedlein, Johannes and Böhnke, Max and Schlichter, Malte and Bobbert, Mathias and Meschut, Gerson and Mergheim, Julia and Steinmann, Paul}}, issn = {{2504-4494}}, journal = {{Journal of Manufacturing and Materials Processing}}, keywords = {{ductile damage, stress-state dependency, failure, parameter identification, punch test, clinching}}, number = {{4}}, publisher = {{MDPI AG}}, title = {{{Material Parameter Identification for a Stress-State-Dependent Ductile Damage and Failure Model Applied to Clinch Joining}}}, doi = {{10.3390/jmmp8040157}}, volume = {{8}}, year = {{2024}}, } @article{64062, abstract = {{Abstract Novel SBA-15-supported heterogeneous catalysts are synthesized and applied in the Mizoroki?Heck and the Suzuki?Miyaura cross-coupling reactions in green solvents like PEG or water. The structural properties of the products after each synthesis step are monitored by different analytics. The amount of amine/carboxyl groups and vanillin/histidine methyl ester and thermal stability are determined by TGA and elemental analysis, while ICP-OES delivered the amount of palladium of the catalysts. The morphology is investigated by SEM and XPS and confirms the presence of coordinated palladium in the zero-oxidation state. Gas adsorption analysis is conducted, which indicates the presence of palladium clusters in one of the two catalysts, which is underlined by BSE images combined with EDX. A detailed 13C ssNMR and DNP-enhanced 15N ssNMR spectral analysis is presented, which provides ultimate proof of the successful syntheses of the catalysts. The coordination of the palladium onto the carrier material is shown by combining the NMR spectral results with the results of the other analytics. First catalytic tests show for the Mizoroki?Heck reaction yields up to nearly 100% and for the Suzuki-Miyaura up to 88% in the presence of PEG and water, respectively.}}, author = {{Wissel, Till and Rösler, Lorenz and Brodrecht, Martin and Höfler, Mark V. and Herr, Kevin and Oliveira Jr., Marcos and Klimavicius, Vytautas and Ebert, Martin and Breitzke, Hergen and Hoffmann, Markus and Buntkowsky, Gerd and Gutmann, Torsten}}, issn = {{1867-3880}}, journal = {{ChemCatChem}}, keywords = {{SBA-15, Heterogeneous catalyst, Pd cross-coupling, Polyethylene glycol, Solid-state DNP NMR}}, pages = {{e202401511}}, publisher = {{John Wiley & Sons, Ltd}}, title = {{{Novel Heterogeneous Pd Catalysts for Cross-Coupling Reactions in Biocompatible Media: Structural Insights from Solid-State NMR Techniques}}}, doi = {{10.1002/cctc.202401511}}, volume = {{17}}, year = {{2024}}, } @article{63988, abstract = {{This concept summarizes recent advances in development and application of DNP enhanced multinuclear solid-state NMR to study the molecular structure and surface functionalization of cellulose and paper-based materials. Moreover, a novel application is presented where DNP enhanced 13C and 15N solid-state NMR is used to identify structure moieties formed by cross-linking of hydroxypropyl cellulose. Given these two aspects of this concept-type of article, we thus combine both, a review on recent findings already published and unpublished recent data that complement the existing knowledge in the field of characterization of functional lignocellulosic materials by DNP enhanced solid-state NMR.}}, author = {{Höfler, Mark V. and Lins, Jonas and Seelinger, David and Pachernegg, Lukas and Schäfer, Timmy and Spirk, Stefan and Biesalski, Markus and Gutmann, Torsten}}, journal = {{Journal of Magnetic Resonance Open}}, keywords = {{solid-state nmr, dynamic nuclear polarization, Hydroxypropyl cellulose, Selective enhancement, Spin labelling}}, pages = {{100163}}, title = {{{DNP enhanced solid-state NMR – A powerful tool to address the surface functionalization of cellulose/paper derived materials}}}, doi = {{10.1016/j.jmro.2024.100163}}, volume = {{21}}, year = {{2024}}, } @article{63974, abstract = {{A versatile strategy for synthesizing tailored peptide based biradicals is presented. By labeling the protected amino acid hydroxyproline with PROXYL via the OH functionality and using this building block in solid phase peptide synthesis (SPPS), the obtained peptides become polarization agents for DNP enhanced solid-state NMR in biotolerant media. To analyze the effect of the radical position on the enhancement factor, three different biradicals are synthesized. The PROXYL spin-label is inserted in a collagen inspired artificial peptide sequence by binding through the OH group of the hydroxyproline moieties at specific position in the chain. This labeling strategy is universally applicable for any hydroxyproline position in a peptide sequence since solid-phase peptide synthesis is used to insert the building block. High performance liquid chromatography (HPLC) and mass spectrometry (MS) analyses show the successful introduction of the spin label in the peptide chain and electron paramagnetic resonance (EPR) spectroscopy confirms its activity. Dynamic nuclear polarization (DNP) enhanced solid-state nuclear magnetic resonance (NMR) experiments performed on frozen aqueous glycerol-d8 solutions containing these peptide radicals show significantly higher enhancement factors of up to 45 in 1H→13C cross polarization magic angle spinning (CP MAS) experiments compared to an analogous mono-radical peptide including this building block (ε ≈ 14). Compared to commercial biradicals such as AMUPol for which enhancement factors {\textgreater} 100 have been obtained in the past and which have been optimized in their structure, the obtained enhancement up to 45 for our biradicals presents a significant progress in radical design.}}, author = {{Herr, Kevin and Höfler, Mark V. and Heise, Henrike and Aussenac, Fabien and Kornemann, Felix and Rosenberger, David and Brodrecht, Martin and Oliveira, Marcos and Buntkowsky, Gerd and Gutmann, Torsten}}, journal = {{Journal of Magnetic Resonance Open}}, keywords = {{solid-state nmr, dynamic nuclear polarization, peptides, Biradicals, Spin labeling}}, pages = {{100152}}, title = {{{Biradicals based on PROXYL containing building blocks for efficient dynamic nuclear polarization in biotolerant media}}}, doi = {{10.1016/j.jmro.2024.100152}}, volume = {{20}}, year = {{2024}}, } @article{63970, abstract = {{Abstract Recent advances in solid-state nuclear magnetic resonance (NMR) spectroscopy, combined with dynamic nuclear polarization (DNP), quantum chemical DFT calculations, and gas-phase NMR spectroscopy investigating the structure and reactivity of heterogeneous catalysts are reviewed. The investigated catalysts range from classical mononuclear catalysts, like immobilized derivates of Wilkinson’s catalysts over binuclear catalysts such as the dirhodium paddlewheel catalyst to catalytic nanoparticles, employing various support materials, such as mesoporous silica gels, coordination polymers, and biomaterials such as cellulose.}}, author = {{Haro Mares, Nadia and Logrado, Millena and Kergassner, Jan and Zhang, Bingyu and Gutmann, Torsten and Buntkowsky, Gerd}}, issn = {{1867-3880}}, journal = {{ChemCatChem}}, keywords = {{solid-state nmr, heterogeneous catalysis, dynamic nuclear polarization, Nanocatalysis, Surface-reactions}}, pages = {{e202401159}}, publisher = {{John Wiley & Sons, Ltd}}, title = {{{Solid-State NMR of Heterogeneous Catalysts}}}, doi = {{10.1002/cctc.202401159}}, year = {{2024}}, } @inproceedings{57816, abstract = {{TLS-Attacker is an open-source framework for analyzing Transport Layer Security (TLS) implementations. The framework allows users to specify custom protocol flows and provides modification hooks to manipulate message contents. Since its initial publication in 2016 by Juraj Somorovsky, TLS-Attacker has been used in numerous studies published at well-established conferences and helped to identify vulnerabilities in well-known open-source TLS libraries. To enable automated analyses, TLS-Attacker has grown into a suite of projects, each designed as a building block that can be applied to facilitate various analysis methodologies. The framework still undergoes continuous improvements with feature extensions, such as DTLS 1.3 or the addition of new dialects such as QUIC, to continue its effectiveness and relevancy as a security analysis framework.}}, author = {{Bäumer, Fabian and Brinkmann, Marcus and Erinola, Nurullah and Hebrok, Sven Niclas and Heitmann, Nico and Lange, Felix and Maehren, Marcel and Merget, Robert and Niere, Niklas and Radoy, Maximilian Manfred and Schmidt, Conrad and Schwenk, Jörg and Somorovsky, Juraj}}, booktitle = {{Proceedings of Cybersecurity Artifacts Competition and Impact Award (ACSAC ’24)}}, keywords = {{SSL, TLS, DTLS, Protocol State Fuzzing, Planning Based}}, location = {{Hawaii}}, title = {{{TLS-Attacker: A Dynamic Framework for Analyzing TLS Implementations}}}, year = {{2024}}, } @inproceedings{48352, abstract = {{Star-connected cascaded H-bridge Converters require large DC-link capacitors to buffer the second-order harmonic voltage ripple. First, it is analytically proven that the DC-link voltage ripple is proportional to the apparent converter power and does not depend on the power factor for nominal operation with sinusoidal reference arm voltages and currents. A third-harmonic zero-sequence voltage injection with an optimal amplitude and phase angle transforms the 2nd harmonic to a 4th harmonic DC-link voltage ripple. This reduces the voltage ripple by exactly 50% for all power factors at steady-state at balanced conditions. However, this requires 54% additional modules for unity power factor operation and even 100% for pure reactive power operation to account for the increased reference arm voltages due to the large amplitude of the optimal third-harmonic injection. If not enough modules are available, an adaptive discontinuous PWM is utilized to still minimize the voltage ripple for the given number of modules and power factor. With a very limited number of modules (modulation index is 1.15), the proposed method still reduces the DC-link voltage ripple by 24.4% for unity power factor operation. It requires the same number of modules as the commonly utilized 3rd harmonic injection with 1/6 of the grid voltage amplitude and achieves superior results. Simulations of a 10 kV/1 MVA system confirm the analysis.}}, author = {{Unruh, Roland and Böcker, Joachim and Schafmeister, Frank}}, booktitle = {{2023 25th European Conference on Power Electronics and Applications (EPE'23 ECCE Europe)}}, isbn = {{979-8-3503-1678-0}}, keywords = {{Cascaded H-Bridge, Solid-State Transformer, Capacitor voltage ripple, Zero sequence voltage, Third harmonic injection}}, location = {{Aalborg, Denmark}}, publisher = {{IEEE}}, title = {{{An Optimized Third-Harmonic Injection Reduces DC-Link Voltage Ripple in Cascaded H-Bridge Converters up to 50% for all Power Factors}}}, doi = {{10.23919/epe23ecceeurope58414.2023.10264313}}, year = {{2023}}, } @article{64045, abstract = {{Abstract In this work, we report on an improved cell assembly of cylindrical electrochemical cells for 23Na in-situ solid-state NMR (ssNMR) investigations. The cell set-up is suitable for using powder electrode materials. Reproducibility of our cell assembly is analyzed by preparing two cells containing hard carbon (HC) powder as working electrode and sodium metal as reference electrode. Electrochemical storage properties of HC powder electrode derived from carbonization of sustainable cellulose are studied by ssNMR. 23Na in-situ ssNMR monitors the sodiation/desodiation of a Na{\textbar}NaPF6{\textbar}HC cell (cell 1) over a period of 22?days, showing high cell stability. After the galvanostatic process, the HC powder material is investigated by high resolution 23Na ex-situ MAS NMR. The formation of ionic sodium species in different chemical environments is obtained. Subsequently, a second Na{\textbar}NaPF6{\textbar}HC cell (cell 2) is sodiated for 11?days achieving a capacity of 220?mAh/g. 23Na ex-situ MAS NMR measurements of the HC powder material extracted from this cell clearly indicate the presence of quasi-metallic sodium species next to ionic sodium species. This observation of quasi-metallic sodium species is discussed in terms of the achieved capacity of the cell as well as of side reactions of sodium in this electrode material.}}, author = {{Šić, Edina and Schutjajew, Konstantin and Haagen, Ulrich and Breitzke, Hergen and Oschatz, Martin and Buntkowsky, Gerd and Gutmann, Torsten}}, issn = {{1864-5631}}, journal = {{Chemsuschem}}, keywords = {{solid-state nmr, hard carbon, electrochemical cells, in-situ characterization, sodium}}, pages = {{e202301300}}, publisher = {{John Wiley & Sons, Ltd}}, title = {{{Electrochemical Sodium Storage in Hard Carbon Powder Electrodes Implemented in an Improved Cell Assembly: Insights from In-Situ and Ex-Situ Solid-State NMR}}}, doi = {{10.1002/cssc.202301300}}, volume = {{17}}, year = {{2023}}, } @article{64044, abstract = {{Abstract Polymer-derived silicon oxycarbide ceramics (SiCO) have been considered as potential anode materials for lithium- and sodium-ion batteries. To understand their electrochemical storage behavior, detailed insights into structural sites present in SiCO are required. In this work, the study of local structures in SiCO ceramics containing different amounts of carbon is presented. 13C and 29Si solid-state MAS?NMR spectroscopy combined with DFT calculations, atomistic modeling, and EPR investigations, suggest significant changes in the local structures of SiCO ceramics even by small changes in the material composition. The provided findings on SiCO structures will contribute to the research field of polymer-derived ceramics, especially to understand electrochemical storage processes of alkali metal/ions such as Na/Na+ inside such networks in the future.}}, author = {{Šić, Edina and Rohrer, Jochen and Ricohermoso, Emmanuel and Albe, Karsten and Ionescu, Emmanuel and Riedel, Ralf and Breitzke, Hergen and Gutmann, Torsten and Buntkowsky, Gerd}}, issn = {{1864-5631}}, journal = {{Chemsuschem}}, keywords = {{NMR spectroscopy, Ceramics, defects, density functional calculations, EPR spectroscopy}}, pages = {{e202202241}}, publisher = {{John Wiley & Sons, Ltd}}, title = {{{SiCO Ceramics as Storage Materials for Alkali Metals/Ions: Insights on Structure Moieties from Solid-State NMR and DFT Calculations}}}, doi = {{10.1002/cssc.202202241}}, volume = {{16}}, year = {{2023}}, } @article{27186, abstract = {{The presented paper aims to characterize the damage and fracture behavior of HX340LAD Micro-Alloyed steels using small punch test. Variations with respect to punch geometries and cutting clearance are made to describe the damage behavior of the material under different loading conditions. Experimental investigations are conducted to identify the crack initiation in the specimens. Furthermore, the numerical FEM simulations are performed to identify the stress state at crack initiation. It is shown that different stress states from shear to biaxial tension can be achieved by changing the geometries of punch and varying the cutting clearance. Moreover, it is presented how changing the configurations can influence the stress state variables: Triaxiality and lode angle parameter.}}, author = {{Otroshi, Mortaza and Meschut, Gerson}}, issn = {{1350-6307}}, journal = {{Engineering Failure Analysis}}, keywords = {{Ductile damage, stress state, small punch test, triaxiality, lode angle parameter}}, number = {{c}}, publisher = {{Elsevier}}, title = {{{Influence of cutting clearance and punch geometry on the stress state in small punch test }}}, doi = {{10.1016/j.engfailanal.2022.106183}}, volume = {{136}}, year = {{2022}}, } @inproceedings{34176, abstract = {{Cascaded H-bridge Converters (CHBs) are a promising solution in converting power from a three-phase medium voltage of 6.6 kV...30 kV to a lower DC-voltage in the range of 100 V...1 kV to provide pure DC power to applications such as electrolyzers for hydrogen generation, data centers with a DC power distribution and DC microgrids. CHBs can be interpreted as modular multilevel converters with an isolated DC-DC output stage per module, require a large DC-link capacitor for each module to handle the second harmonic voltage ripple caused by the fluctuating input power within a fundamental grid period. Without a zero-sequence voltage injection, star-connected CHBs are operated with approximately sinusoidal arm voltages and currents. The floating star point potential enables to utilize different zero-sequence voltage injection techniques such as a third-harmonic injection with 1/6 of the grid voltage amplitude or a Min-Max voltage injection. Both well-known methods have the advantage to reduce the peak arm voltage and thereby the number of required modules by 13.4 % (to √ 3 2). This paper proves analytically that the third-harmonic injection with 1/6 of the grid voltage amplitude reduces the second harmonic voltage ripple by only 15.1 % compared to no-voltage injection for unity power factor operation and balanced grid voltages. Then it is shown, that the Min-Max injection has the often overlooked advantage of reducing the second harmonic voltage ripple by even 18.8 %. By applying the here proposed zero-sequence voltage injection in saturation modulation, the second harmonic voltage ripple of the DC-link capacitors is reduced by even 24.3 %, while still requiring the same number of modules as the Min-Max injection. For a realistic number of reserve modules, the overall energy ripple in the DC-link capacitors is reduced by 40 %.}}, author = {{Unruh, Roland and Schafmeister, Frank and Böcker, Joachim}}, booktitle = {{24th European Conference on Power Electronics and Applications (EPE'22 ECCE Europe)}}, isbn = {{978-9-0758-1539-9}}, keywords = {{Cascaded H-Bridge, Solid-State Transformer, Zero sequence voltage, Third harmonic injection, Capacitor voltage ripple}}, location = {{Hanover, Germany}}, publisher = {{IEEE}}, title = {{{Zero-Sequence Voltage Reduces DC-Link Capacitor Demand in Cascaded H-Bridge Converters for Large-Scale Electrolyzers by 40%}}}, year = {{2022}}, } @article{63948, abstract = {{In this work, the behavior of four different commercially available polarizing agents is investigated employing the non-ionic model surfactant 1-octanol as analyte. A relative method for the comparison of the proportion of the direct and indirect polarization transfer pathways is established, allowing a direct comparison of the polarization efficacy for different radicals and different parts of the 1-octanol molecule despite differences in radical concentration or sample amount. With this approach, it could be demonstrated that the hydrophilicity is a key factor in the way polarization is transferred from the polarizing agent to the analyte. These findings are confirmed by the determination of buildup times Tb, illustrating that the choice of polarizing agent plays an essential role in ensuring an optimal polarization transfer and therefore the maximum amount of enhancement possible for DNP enhanced NMR measurements.}}, author = {{Döller, Sonja C. and Gutmann, Torsten and Hoffmann, Markus and Buntkowsky, Gerd}}, journal = {{Solid State Nuclear Magnetic Resonance}}, keywords = {{DNP NMR, Dynamics, Low temperature NMR, Octanol, Solid state NMR, Surfactants}}, pages = {{101829}}, title = {{{A case study on the influence of hydrophilicity on the signal enhancement by dynamic nuclear polarization}}}, volume = {{122}}, year = {{2022}}, } @article{63943, abstract = {{A lithium halide exchange reaction at low-temperature, via the treatment of 2,6-di(isopropyl)phenyllithium on 1,1′-bis-(dichlorophosphino)ferrocene, resulted in the first isolated example of an aryl-substituted diphospha [2]ferrocenophane (diphospha [2]FCP) 2. Although compound 2 did not show any recognizable thermal reaction at higher temperature (up to 350 °C), its tert-butyl-substituted counterpart 1 underwent a clean selective heat-mediated P–C cleavage reaction, followed by an inter-molecular rearrangement, to produce a P–P fused bis [3]ferrocenophane 3 with all-trans oriented P-chain, which upon further heating gave a polyferrocenylphosphane tBu-[Fc’P2]n-tBu (4). Since polymer 4 is insoluble in common organic solvents, it has been characterized with solid-state techniques, including solid-state NMR. Density functional theory (DFT) has further been employed to identify possible pathways for P–C bond cleavage on 1 and 2, as well as to evaluate accessible pathways for further polymerization toward 4.}}, author = {{Dey, Subhayan and Kargin, Denis and Höfler, Mark V. and Szathmari, Balazs and Bruhn, Clemens and Gutmann, Torsten and Kelemen, Zsolt and Pietschnig, Rudolf}}, journal = {{Polymer}}, keywords = {{solid-state nmr, Ansa-ferrocene, DFT calculations, Oligophosphine, Polyphosphane, Ring-opening polymerization}}, pages = {{124589}}, title = {{{Oligo- and polymerization of phospha [2]ferrocenophanes to one dimensional phosphorus chains with ferrocenylene handles}}}, volume = {{242}}, year = {{2022}}, } @inproceedings{29938, abstract = {{Modular solid-state transformers (SSTs) are a promising technology in converting power from a 10kV three-phase medium voltage to a lower DC-voltage in the range of 100…400V to provide pure DC power to applications such as electrolyzers for hydrogen generation, data centers with a DC power distribution and DC micro grids. Modular SSTs which can be interpreted as modular multilevel converters with an isolated DC-DC output stage per module, are designed with redundant modules to increase reliability. Usually, each of the three arms operates independently, and therefore, only a fixed number of faulty modules can be compensated in each arm, even if all modules are operational in the remaining two arms. With the proposed zero-sequence voltage injection, up to 100% more faulty modules can be compensated in an arm by employing the same hardware. In addition, module power imbalances are nearly eliminated by utilizing a fundamental frequency zero-sequence voltage. A dominant 3rd harmonic zero-sequence voltage injection in combination with the 5th, 7th and several higher order harmonics with adaptive (small) amplitudes minimize the required arm voltages at steady-state. For nominal operation or symmetrical faults, the proposed technique is equivalent to the well known Min-Max voltage injection, which already reduces the peak arm voltage by 13.4% compared to a constant star point potential. A statistical analysis proves, that the expected number of tolerable faulty modules of the 1MW SST increases by 12% without the need for additional hardware.}}, author = {{Unruh, Roland and Lange, Jarren and Schafmeister, Frank and Böcker, Joachim}}, booktitle = {{23rd European Conference on Power Electronics and Applications (EPE'21 ECCE Europe)}}, isbn = {{978-9-0758-1537-5}}, keywords = {{Solid-State Transformer, Zero sequence voltage, Fault handling strategy, Power balance control technique, Three-phase system}}, location = {{Ghent, Belgium}}, publisher = {{IEEE}}, title = {{{Adaptive Zero-Sequence Voltage Injection for Modular Solid-State Transformer to Compensate for Asymmetrical Fault Conditions}}}, doi = {{https://doi.org/10.23919/EPE21ECCEEurope50061.2021.9570542}}, year = {{2021}}, } @book{37274, abstract = {{How are activation programs for the young unemployed implemented? How do street-level bureaucrats deal with competing rationalities and demands for action? Transition policies increasingly aim at promoting self-regulation and constructing employable subjects. Stephan Dahmen explores the practical regulation of biographical transitions in activation programs for the young unemployed by focusing on the interactive accomplishment of activation work. The study reveals how the critical tensions of activation policies are continually re-interpreted and adapted to local contingencies and describes the various organisational technologies used for creating employable subjects.}}, author = {{Dahmen, Stephan}}, keywords = {{Youth, Welfare State, Transitions, Human Service Organizations, Institutional Ethnography, Activation, Sociology of Conventions, Work, Education, Educational Research, Sociology of Education, Social Pedagogy, History of Education, Bielefeld University Press}}, pages = {{312}}, publisher = {{Bielefeld University Press}}, title = {{{Regulating Transitions from School to Work. An Institutional Ethnography of Activation Work in Action}}}, doi = {{10.14361/9783839457061}}, year = {{2021}}, } @book{37273, abstract = {{How are activation programs for the young unemployed implemented? How do street-level bureaucrats deal with competing rationalities and demands for action? Transition policies increasingly aim at promoting self-regulation and constructing employable subjects. Stephan Dahmen explores the practical regulation of biographical transitions in activation programs for the young unemployed by focusing on the interactive accomplishment of activation work. The study reveals how the critical tensions of activation policies are continually re-interpreted and adapted to local contingencies and describes the various organisational technologies used for creating employable subjects.}}, author = {{Dahmen, Stephan}}, keywords = {{Youth, Welfare State, Transitions, Human Service Organizations, Institutional Ethnography, Activation, Sociology of Conventions, Work, Education, Educational Research, Sociology of Education, Social Pedagogy, History of Education, Bielefeld University Press}}, pages = {{312}}, publisher = {{Bielefeld University Press}}, title = {{{Regulating Transitions from School to Work. An Institutional Ethnography of Activation Work in Action}}}, doi = {{10.14361/9783839457061}}, year = {{2021}}, }