Computersimulation of proton discharge reactions at electrocatalytic surfaces in aqueous solutions

In der vorliegenden Arbeit wird die Volmer-Reaktion, der erste Schritt der Wasserstoffentstehungsreaktion, in wässrigen Lösungen an geladenen Platinelektroden mit Hilfe von Molekulardynamiksimulationen unter Verwendung von reaktiven Kraftfeldern behandelt. Sowohl die atomaren Wechselwirkungen der klassischen Teilchen, als auch die des dynamisch wechselnden Zundelclusters werden durch Potentialkräfte abgebildet. Der verwendete EVB (Empirical Valence Bond) Ansatz ermöglicht dynamisches Brechen und Neubilden von Atombindungen zur Modellierung der strukturellen Diffusion des Grotthuss Mechanismus und der elektrochemischen Entladung eines Protons an der Metalloberfläche. Dabei werden zwei empirische Valenzzustände für den Austausch von Wasserstoffatomen innerhalb des Protonenclusters verwendet und sieben Zustände, um die Wechselwirkung mit der elektrokatalytischen Oberfläche darzustellen und die Entladung des Protons zu ermöglichen. Diese vereinfachte Herangehensweise ermöglicht ein statistisch aussagekräftiges Sampling der Volmer-Reaktion. Es kann gezeigt werden, dass bis zu vier disjunkte atomare Reaktionsmechanismen auftreten können, nach denen die Entladung stattfinden kann. Entladungsreaktionen können demnach aus der ersten Kontaktschicht des Wassers oder der zweiten Wasserschicht erfolgen. Bei Entladungen aus der ersten Kontaktschicht liegt der Zundelkomplex in einer koplanaren Orientierung vor, während bei Entladungen aus der zweiten Schicht eine oberflächennormale Ausrichtung vorliegt, durch die eine besonders schnelle Entladung möglich wird. Die verschiedenen Mechanismen tragen in verschiedenen Systemen zu unterschiedlichen Teilen zur Gesamtentladezeit bei. Neben den atomaren Reaktionsmechanismen wird der Einfluss von Elektrolyten und Oberflächenladungsdefekten auf die Volmer Reaktion untersucht und anhand des hier eingeführten Begriffes der "scheinbaren" Triebkraft klassifiziert. Diese scheinbare Triebkraft ist zu unterscheiden von der elektrostatischen Triebkraft der Oberfläche und ist ein Maß für den Antrieb in den ersten ein bis zwei Wasserschichten. Sie ist maßgeblich für die Geschwindigkeit der Entladungsreaktion und bestimmt welche Reaktionsmechanismen möglich sind. Elektrolytlösungen bewirken im Allgemeinen eine Retardierung des Transportes zur Oberfläche, jedoch weisen sie die gleichen Entlademechanismen auf wie Referenzsysteme mit reinem Wasser. Ladungsdefekte in Form von adsorbierten Anionen hingegen fördern den Transport zur Oberfläche, während sie gleichzeitig die Entladungsreaktion stark verlangsamen und die Zahl der möglichen Reaktionswege reduzieren.In the work at hand the Volmer reaction, as first step of the hydrogen evolution reaction, in aqueous solution in contact with charged platinum electrodes has been investigated. Molecular Dynamics simulations including a reactive force field approach were employed. The atomic interactions of the classical particles as well as the dynamically changing Zundel cluster are represented by conservative force potentials. The employed EVB (Empirical Valence Bond) approach enables the dynamic breaking and reformation of atomic bonds in order to model the structural diffusion of the Grotthuss mechanism and the electrochemical discharge of a proton at a metal electrode. Two empirical valence states are employed to describe the exchange of hydrogen atoms within the proton cluster. Seven states are used to describe the interaction of the proton cluster with the electrocatalytic surface in order to allow for proton discharge reactions. This simplified approach enables significant sampling of the Volmer reaction. It can be shown that up to four disjunctive atomic reaction mechanisms can be realized for the discharge. Discharge reactions can occur out of the first or second water layer. For discharges from the first water layer the Zundel complex is coplanar to the surface, whereas it is normal to the surface if it discharges from the second water layer which enables a particularly fast reaction. All reaction mechanisms contribute differently depending on the system. In addition to the atomic reaction mechanisms, the influence of electrolytes and surface charge defects on the Volmer reaction is investigated and classified using the term "apparent driving force", which is introduced herein. This apparent driving force is to be distinguished from the electrostatic driving force of the surface and is a measure for the driving force in the first and second water layer. It is relevant for the speed of the discharge reaction and specifies which reaction mechanisms are possible. In general electrolytes retard the proton transport to the surface, but the realized discharge mechanisms are similar to the system with pure water. Charge defects in form of adsorbed chlorid ions in contrast promote the transport to the surface while retarding the discharge reaction and decreasing the number of possible reaction pathways

Potential quantum advantage for simulation of fluid dynamics

Numerical simulation of turbulent fluid dynamics needs to either parameterize turbulence-which introduces large uncertainties-or explicitly resolve the smallest scales-which is prohibitively expensive. Here we provide evidence through analytic bounds and numerical studies that a potential quantum exponential speedup can be achieved to simulate the Navier-Stokes equations governing turbulence using quantum computing. Specifically, we provide a formulation of the lattice Boltzmann equation for which we give evidence that low-order Carleman linearization is much more accurate than previously believed for these systems and that for computationally interesting examples. This is achieved via a combination of reformulating the nonlinearity and accurately linearizing the dynamical equations, effectively trading nonlinearity for additional degrees of freedom that add negligible expense in the quantum solver. Based on this we apply a quantum algorithm for simulating the Carleman-linerized lattice Boltzmann equation and provide evidence that its cost scales logarithmically with system size, compared to polynomial scaling in the best known classical algorithms. This work suggests that an exponential quantum advantage may exist for simulating fluid dynamics, paving the way for simulating nonlinear multiscale transport phenomena in a wide range of disciplines using quantum computing

Green change: renewable energies, policy mix and innovation

A far-reaching transformation to green, CO2–free solutions is needed to achieve the ambitious climate policy target of limiting the global temperature rise to not more than 2°C. With this in mind, the GRETCHEN project explored the impacts of the policy mix on innovation in renewable power generation technologies in Germany at three levels: the micro level, focusing on the perspective of individual companies, the meso level, examining industry structures and the innovation system, and the macro level, modelling macroeconomic effects and CO2 emissions. The impact of the policy mix was analysed at these three levels for the following aspects: political targets to expand power generation from renewable energy sources, technology push, demand pull and systemic instruments as well as their interaction within the instrument mix, and the consistency and credibility of the policy mix and the coherence of political processes. The policy mix needed for a green transformation of the energy system can be considered holistically and valuated with regard to its innovation impact based on the policy mix concept developed in the GRETCHEN project. The corresponding findings are synthesized in this report on the results of the GRETCHEN project concerning the influence of the policy mix on technological and structural change in renewable power generation technologies in Germany

Design of 280 GHz feedhorn-coupled TES arrays for the balloon-borne polarimeter SPIDER

We describe 280 GHz bolometric detector arrays that instrument the balloon-borne polarimeter SPIDER. A primary science goal of SPIDER is to measure the large-scale B-mode polarization of the cosmic microwave background in search of the cosmic-inflation, gravitational-wave signature. 280 GHz channels aid this science goal by constraining the level of B-mode contamination from galactic dust emission. We present the focal plane unit design, which consists of a 16$\times$16 array of conical, corrugated feedhorns coupled to a monolithic detector array fabricated on a 150 mm diameter silicon wafer. Detector arrays are capable of polarimetric sensing via waveguide probe-coupling to a multiplexed array of transition-edge-sensor (TES) bolometers. The SPIDER receiver has three focal plane units at 280 GHz, which in total contains 765 spatial pixels and 1,530 polarization sensitive bolometers. By fabrication and measurement of single feedhorns, we demonstrate 14.7$^{\circ}$ FHWM Gaussian-shaped beams with $<$1% ellipticity in a 30% fractional bandwidth centered at 280 GHz. We present electromagnetic simulations of the detection circuit, which show 94% band-averaged, single-polarization coupling efficiency, 3% reflection and 3% radiative loss. Lastly, we demonstrate a low thermal conductance bolometer, which is well-described by a simple TES model and exhibits an electrical noise equivalent power (NEP) = 2.6 $\times$ 10$^{-17}$ W/$\sqrt{\mathrm{Hz}}$, consistent with the phonon noise prediction.Comment: Proceedings of SPIE Astronomical Telescopes + Instrumentation 201

Accumulation of mutations in antibody and CD8 T cell epitopes in a B cell depleted lymphoma patient with chronic SARS-CoV-2 infection

Antibodies against the spike protein of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) can drive adaptive evolution in immunocompromised patients with chronic infection. Here we longitudinally analyze SARS-CoV-2 sequences in a B cell-depleted, lymphoma patient with chronic, ultimately fatal infection, and identify three mutations in the spike protein that dampen convalescent plasma-mediated neutralization of SARS-CoV-2. Additionally, four mutations emerge in non-spike regions encoding three CD8 T cell epitopes, including one nucleoprotein epitope affected by two mutations. Recognition of each mutant peptide by CD8 T cells from convalescent donors is reduced compared to its ancestral peptide, with additive effects resulting from double mutations. Querying public SARS-CoV-2 sequences shows that these mutations have independently emerged as homoplasies in circulating lineages. Our data thus suggest that potential impacts of CD8 T cells on SARS-CoV-2 mutations, at least in those with humoral immunodeficiency, warrant further investigation to inform on vaccine design

Phylogenetic Identification of Fungi Isolated from the Marine Sponge Tethya aurantium and Identification of Their Secondary Metabolites

Fungi associated with the marine sponge Tethya aurantium were isolated and identified by morphological criteria and phylogenetic analyses based on internal transcribed spacer (ITS) regions. They were evaluated with regard to their secondary metabolite profiles. Among the 81 isolates which were characterized, members of 21 genera were identified. Some genera like Acremonium, Aspergillus, Fusarium, Penicillium, Phoma, and Trichoderma are quite common, but we also isolated strains belonging to genera like Botryosphaeria, Epicoccum, Parasphaeosphaeria, and Tritirachium which have rarely been reported from sponges. Members affiliated to the genera Bartalinia and Volutella as well as to a presumably new Phoma species were first isolated from a sponge in this study. On the basis of their classification, strains were selected for analysis of their ability to produce natural products. In addition to a number of known compounds, several new natural products were identified. The scopularides and sorbifuranones have been described elsewhere. We have isolated four additional substances which have not been described so far. The new metabolite cillifuranone (1) was isolated from Penicillium chrysogenum strain LF066. The structure of cillifuranone (1) was elucidated based on 1D and 2D NMR analysis and turned out to be a previously postulated intermediate in sorbifuranone biosynthesis. Only minor antibiotic bioactivities of this compound were found so far