Smoothed Particle Hydrodynamics Physically Reconsidered -- The Relation to Explicit Large Eddy Simulation and the Issue of Particle Duality

In this work we will identify a novel relation between Smoothed Particle Hydrodynamics (SPH) and explicit Large Eddy Simulation (LES) using a coarse-graining method from Non-Equilibrium Molecular Dynamics (NEMD). While the current literature points at the conclusion that characteristic SPH issues become restrictive for subsonic turbulent flows, we see the potential to mitigate these SPH issues by explicit subfilter stress (SFS) modelling. We verify our theory by various simulations of homogeneous, isotropic turbulence (HIT) at $Re=10^4$ and compare the results to a Direct Numerical Simulation (DNS) reported by Dairay et al. (2017). Although the simulations substantiate our theory, we see another issue arising, which is conceptually rooted in the particle itself, termed as Particle Duality. Finally, we conclude our work by acknowledging SPH as coarse-graining method for turbulent flows, highlighting its capabilities and limitations.Comment: Added Journal Reference & DO

Qualifying tests and economic analysis of electrolyzers for grid services

As part of the European project QualyGridS, drafts for standardized testing protocols for electrolyzers to perform electricity grid services are defined and elaborated. These protocols are designed to be used by alkaline and proton exchange membrane (PEM) electrolyzers up to the Megawatt scale. The protocols are being submitted for standardisation. Testing results using these protocols on a state-of-the-art PEM electrolyzer system of 50 kW with 1500 cm2 area stack are presented with considerations of the influence of balance of plant (BOP) components. System behaviour of 50 kW and Megawatt PEM electrolyzers are compared to determine the influence of their scale in performance and response time. An economic analysis has been conducted in the scope of the project. Today’s situation has been analyzed in a first part: the objective was to identify the best way to combine H2 supply for a primary value stream and provision of grid services. A second part of the analysis studied the potential future evolutions that could change the current pictur

Quantitative analysis of the binding affinity of poly(ADP-ribose) to specific binding proteins as a function of chain length

Poly(ADP-ribose) (PAR) is synthesized by poly(ADP-ribose) polymerases in response to genotoxic stress and interacts non-covalently with DNA damage checkpoint and repair proteins. Here, we present a variety of techniques to analyze this interaction in terms of selectivity and affinity. In vitro synthesized PAR was end-labeled using a carbonyl-reactive biotin analog. Binding of HPLC-fractionated PAR chains to the tumor suppressor protein p53 and to the nucleotide excision repair protein XPA was assessed using a novel electrophoretic mobility shift assay (EMSA). Long ADP-ribose chains (55-mer) promoted the formation of three specific complexes with p53. Short PAR chains (16-mer) were also able to bind p53, yet forming only one defined complex. In contrast, XPA did not interact with short polymer, but produced a single complex with long PAR chains (55-mer). In addition, we performed surface plasmon resonance with immobilized PAR chains, which allowed establishing binding constants and confirmed the results obtained by EMSA. Taken together, we developed several new protocols permitting the quantitative characterization of PAR–protein binding. Furthermore, we demonstrated that the affinity of the non-covalent PAR interactions with specific binding proteins (XPA, p53) can be very high (nanomolar range) and depends both on the PAR chain length and on the binding protein

Experimentelle Untersuchung der Kopplung eines H2-Alanat-Speichers mit einer Hochtemperatur- Brennstoffzelle

Die vorliegende Arbeit befasst sich mit der thermischen und stofflichen Kopplung eines Hochtemperatur Polymer Elektrolyt Membran Brennstoffzellensystems und einem komplexen Metallhydrid-Wasserstoffspeicher. Dieser komplexe Metallhydrid-Wasserstoffspeicher enthält Natriumaluminiumhydrid als Speichermaterial, welches eine Cerium-Dotierung besitzt, die als Katalysator fungiert. Zu dieser Kopplung werden theoretische Überlegungen bezüglich der energetischen Machbarkeit der Kopplung angestellt. Des Weiteren werden zum Wärmeübergang vom Wärmeträgermedium in den Speicher Berechnungen durchgeführt und Methoden vorgestellt um diesen Wärmeübergang zu verbessern. Anschließend werden die Auswertungen der experimentellen Versuche, die das Verhalten des Brennstoffzellensystems sowie das Desorptionsverhalten des Wasserstoffspeichers aufzeigen, aufgeführt. Diese Auswertungen werden auf Basis der thermischen Eigenschaften des Wasserstoffspeichers und den thermischen Eigenschaften des Wärmeträgermediums erstellt, welche durch das Brennstoffzellensystem beeinflusst werden. Abschließend erfolgt eine Zusammenfassung der in den Versuchen und den angestellten Überlegungen gewonnen Erkenntnisse

Rapamycin inhibits poly(ADP-ribosyl)ation in intact cells

Rapamycin is an immunosuppressive drug, which inhibits the mammalian target of rapamycin (mTOR) kinase activity inducing changes in cell proliferation. Synthesis of poly(ADP-ribose) (PAR) is an immediate cellular response to genotoxic stress catalyzed mostly by poly(ADP-ribose) polymerase 1 (PARP-1), which is also controlled by signaling pathways. Therefore, we investigated whether rapamycin affects PAR production. Strikingly, rapamycin inhibited PAR synthesis in living fibroblasts in a dose-dependent manner as monitored by immunofluorescence. PARP-1 activity was then assayed in vitro, revealing that down-regulation of cellular PAR production by rapamycin was apparently not due to competitive PARP-1 inhibition. Further studies showed that rapamycin did not influence the cellular NAD pool and the activation of PARP-1 in extracts of pretreated fibroblasts. Collectively, our data suggest that inhibition of cellular PAR synthesis by rapamycin is mediated by formation of a detergent-sensitive complex in living cells, and that rapamycin may have a potential as therapeutic PARP inhibitor

Qualifying Tests of Electrolysers for Grid Services - System Behaviour and Scalability

As part of the European project QualyGridS, drafts for standardized testing protocols for electrolysers to perform electricity grid services are defined or elaborated. These protocols are designed to be used by alkaline and proton exchange membrane (PEM) electrolysers up to the Megawatt scale. European grid services were integrated into testing protocols for evaluation of the suitability for a certain grid service existing in the market as well as basic characterizations identifying the most relevant capabilities for this application like dynamics and stability. Testing results using these protocols on a state-of-the-art PEM electrolyzer system in 50 kW with 1500 cm2 area stack are presented with considerations of the influence of balance of plant (BOP) components. System behaviour of 10 kW, 50 kW and 1.5 MW PEM electrolysers are compared to determine the influence of their scale in performance and response time. While the stack behaviour is comparable at all scales and highly dynamic the system architecture, control strategies, volumes and dynamics of components have a strong influence on the ramping rates and the stability of the total power consumption

Quantitative Analysis of WRN Exonuclease Activity by Isotope Dilution Mass Spectrometry

Werner syndrome is a disorder characterized by a premature aging phenotype. The disease is caused by mutations in the WRN gene which encodes a DNA helicase/exonuclease which is involved in multiple aspects of DNA metabolism. Current methods mostly rely on radiometric techniques to assess WRN exonuclease activity. Here we present an alternative, quantitative approach based on non-radioactive isotope dilution mass spectrometry (LC-MS/MS). A oligoduplex substrate mimicking the telomeric sequence was used for method development. Released nucleotides, which correlate with the degree of oligoduplex degradation, were dephosphorylated, purified, and quantified by LC-MS/MS. Heavy-isotope-labeled internal standards were used to account for technical variability. The method was validated in terms of reproducibility, time-course and concentration-dependency of the reaction. As shown in this study, the LC-MS/MS method can assess exonuclease activity of WRN mutants, WRN's substrate and strand specificity, and modulatory effects of WRN interaction partners and posttranslational modifications. Moreover, it can be used to analyze the selectivity and processivity of WRN exonuclease and allows the screening of small molecules for WRN exonuclease inhibitors. Importantly, this approach can easily be adapted to study nucleases other than WRN. This is of general interest, because exonucleases are key players in DNA metabolism and aging mechanisms