Examining architectures of photoanode-photovoltaic tandem cells for solar water splitting

Given the limitations of the materials available for photoelectrochemical water splitting, a multiphoton (tandem) approach is required to convert solar energy into hydrogen efficiently and durably. Here we investigate a promising system consisting of a hematite photoanode in combination with dye-sensitized solar cells with newly developed organic dyes, such as the squaraine dye, which permit new configurations of this tandem system. Three configurations were investigated: two side-by-side dye cells behind a semitransparent hematite photoanode, two semitransparent dye sensitized solar cells (DSCs) in front of the hematite, and a trilevel hematite/DSC/DSC architecture. Based on the current-voltage curves of state-of-the-art devices made in our laboratories, we found the trilevel tandem architecture (hematite/SQ1 dye/N749 dye) produces the highest operating current density and thus the highest expected solar-to-hydrogen efficiency (1.36% compared with 1.16% with the standard back DSC case and 0.76% for the front DSC case). Further investigation into the wavelength-dependent quantum efficiency of each component revealed that in each case photons lost as a result of scattering and reflection reduce the performance from the expected 3.3% based on the nanostructured hematite photoanodes. We further suggest avenues for the improvement of each configuration from both the DSC and the photoanode part

Identifying Reactive Sites and Surface Traps in Chalcopyrite Photocathodes

Gathering information on the atomic nature of reactive sites and trap states is key to fine tuning catalysis and suppressing deleterious surface voltage losses in photoelectrochemical technologies. Here, spectroelectrochemical and computational methods were combined to investigate a model photocathode from the promising chalcopyrite family: CuIn0.3Ga0.7S2. We found that voltage losses are linked to traps induced by surface Ga and In vacancies, whereas operando Raman spectroscopy revealed that catalysis occurred at Ga, In, and S sites. This study allows establishing a bridge between the chalcopyrite's performance and its surface's chemistry, where avoiding formation of Ga and In vacancies is crucial for achieving high activity.This work was supported by the Swiss National Science Foundation (SNSF) under the Ambizione Energy grant (PZENP2_166871) and by the Gaznat-EPFL Research Program. M.B. and U.A. were supported by the Swiss National Science Foundation Professorship Grants PP00P2_157615 and PP00P2_187185. Calculations were performed on UBELIX, the HPC cluster at the University of Bern. M.X. is grateful for the support from the China Scholarship Council (No. CSC201806160172) and the Strategic Japanese–Swiss Science and Technology program (514259). Open access funding provided by Ecole Polytechnique Federale de Lausanne

A System for Performing High Throughput Assays of Synaptic Function

Unbiased, high-throughput screening has proven invaluable for dissecting complex biological processes. Application of this general approach to synaptic function would have a major impact on neuroscience research and drug discovery. However, existing techniques for studying synaptic physiology are labor intensive and low-throughput. Here, we describe a new high-throughput technology for performing assays of synaptic function in primary neurons cultured in microtiter plates. We show that this system can perform 96 synaptic vesicle cycling assays in parallel with high sensitivity, precision, uniformity, and reproducibility and can detect modulators of presynaptic function. By screening libraries of pharmacologically defined compounds on rat forebrain cultures, we have used this system to identify novel effects of compounds on specific aspects of presynaptic function. As a system for unbiased compound as well as genomic screening, this technology has significant applications for basic neuroscience research and for the discovery of novel, mechanism-based treatments for central nervous system disorders

Peptic Ulcer Perforation as the First Manifestation of Previously Unknown Primary Hyperparathyroidism

A patient admitted for acute abdomen was incidentally found with elevated serum calcium level. In surgery, under conservative treatment of the hypercalcemia, a perforated duodenal ulcer was found and simple closure was performed. Postoperatively, calcium level continued to rise, parathyroid hormone was elevated and ultrasonographic examination showed a lesion in the right anterior neck, while serum gastrin level was normal, thus documenting the diagnosis of primary hyperparathyroidism. Conservative treatment had no effect on calcium level and the patient was subjected to emergency neck exploration, where a large parathyroid adenoma was removed. After surgery, calcium and PTH levels were normalized and the patient was discharged on the 5th postoperative day. Peptic ulcer and its complications are usual manifestations of primary hyperparathyroidism, with or without increased gastrin level. On the other hand, cases of a perforation of peptic ulcer as the first clinical manifestation of primary hyperparathyroidism are extremely rare

Identifizierung von reaktiven Zentren und Oberflächenfallen in Chalkopyrit-Photokathoden

Das Sammeln von Informationen über die atomare Natur von reaktiven Zentren und Fallenzuständen ist der Schlüssel zur Feinabstimmung der Katalyse und zur Unterdrückung schädlicher Oberflächenpotentialverluste in photoelektrochemischen Technologien. Hier wurden spektroelektrochemische und rechnerische Methoden kombiniert, um eine Modellphotokathode aus der vielversprechenden Chalkopyrit-Familie zu untersuchen: CuIn0.3Ga0.7S2. Es wurde festgestellt, dass Potentialverluste mit Fallen verbunden sind, die durch Oberflächen-Ga- und In-Leerstellen induziert werden, wohingegen Operando-Raman-Spektroskopie zeigte, dass Katalyse an Ga-, In- und S-Stellen stattfand. Diese Studie ermöglicht es, eine Brücke zwischen der Leistung des Chalkopyrits und seiner Oberflächenchemie zu schlagen, wobei die Vermeidung der Bildung von Ga- und In-Leerstellen entscheidend ist, um eine hohe Aktivität zu erzielen.Diese Arbeit wurde vom Schweizerischen Nationalfonds (SNF) im Rahmen des Ambizione Energy Grant (PZENP2_166871) und vom Gaznat-EPFL Forschungsprogramm unterstützt. M.B. und U.A. wurden durch die Förderungsprofessuren PP00P2_157615 und PP00P2_187185 des Schweizerischen Nationalfonds unterstützt. Die Berechnungen wurden auf UBELIX, dem HPC-Cluster der Universität Bern, durchgeführt. M.X. dankt dem China Scholarship Council (Nr. CSC201806160172) und dem Strategic Japanese–Swiss Science and Technology-Programm (514259) für die Unterstützung. Open access funding provided by Ecole Polytechnique Federale de Lausanne

Contribution of the Type VI Secretion System Encoded in SPI-19 to Chicken Colonization by Salmonella enterica Serotypes Gallinarum and Enteritidis

Salmonella Gallinarum is a pathogen with a host range specific to poultry, while Salmonella Enteritidis is a broad host range pathogen that colonizes poultry sub-clinically but is a leading cause of gastrointestinal salmonellosis in humans and many other species. Despite recent advances in our understanding of the complex interplay between Salmonella and their hosts, the molecular basis of host range restriction and unique pathobiology of Gallinarum remain largely unknown. Type VI Secretion System (T6SS) represents a new paradigm of protein secretion that is critical for the pathogenesis of many Gram-negative bacteria. We recently identified a putative T6SS in the Salmonella Pathogenicity Island 19 (SPI-19) of Gallinarum. In Enteritidis, SPI-19 is a degenerate element that has lost most of the T6SS functions encoded in the island. In this work, we studied the contribution of SPI-19 to the colonization of Salmonella Gallinarum strain 287/91 in chickens. Non-polar deletion mutants of SPI-19 and the clpV gene, an essential T6SS component, colonized the ileum, ceca, liver and spleen of White Leghorn chicks poorly compared to the wild-type strain after oral inoculation. Return of SPI-19 to the ΔSPI-19 mutant, using VEX-Capture, complemented this colonization defect. In contrast, transfer of SPI-19 from Gallinarum to Enteritidis resulted in transient increase in the colonization of the ileum, liver and spleen at day 1 post-infection, but at days 3 and 5 post-infection a strong colonization defect of the gut and internal organs of the experimentally infected chickens was observed. Our data indicate that SPI-19 and the T6SS encoded in this region contribute to the colonization of the gastrointestinal tract and internal organs of chickens by Salmonella Gallinarum and suggest that degradation of SPI-19 T6SS in Salmonella Enteritidis conferred an advantage in colonization of the avian host

Decoupling Feature Size and Functionality in Solution-Processed, Porous Hematite Electrodes for Solar Water Splitting

We introduce a simple solution-based strategy to decouple morphological and functional effects of annealing nanostructured, porous electrodes by encapsulation with a SiO2 confinement scaffold before high temperature treatment We demonstrate the effectiveness of this approach using porous hematite (alpha-Fe2O3) photoanodes applied for the storage of solar energy via water splitting and show that the feature size and electrode functionality due to dopant activation can be independently controlled This allows a significant increase in water oxidation photocurrent from 1 57 mA cm(-2) (in the control case) to 2 34 mA cm(-2) under standard illumination conditions in 1 M NaOH electrolyte the highest reported for a solution-processed hematite photoanode This increase is attributed to the improved quantum efficiency, especially with longer wavelength photons, due to a smaller particle size, which is afforded by our encapsulation strateg

Controlling photo-activity of solution-processed hematite electrodes for solar water splitting

Hematite is a promising material for solar energy conversion via photo-electrochemical water splitting. However, the precise control of substitutional doping and nanometer feature size is important for high photon harvesting efficiency. Doped and nanostructured hematite electrodes can be prepared by a simple solution-based colloidal approach however, a high temperature (800 degrees C) annealing is required to activate the dopant atoms. This high temperature annealing step also increases the particle size above the dimension necessary for high photon harvesting efficiencies. Here we investigate a strategy to control the two kinetic processes occurring during sintering (particle size increase and dopant diffusion/activation) by incorporating Ti dopant directly into the colloid solution and reducing the annealing time. We find that this strategy leads to porous, high-surface area hematite electrodes giving a solar photocurrent density of 1.1 mA cm(-2) at 1.23 V vs. the reversible hydrogen electrode (RHE) under standard testing conditions where only 0.56 mA cm(-2) was observed at 1.23 V vs. RHE with our previous work. In addition, scanning electron micrographs examining the morphology of the electrodes suggests that our kinetic strategy is indeed effective and that further optimization may result in higher photocurrents

1.A. Wilderness in Space

Natural and artifactual in the night sky / Alan JohnsonHumans have long regarded the night sky with awe and wonder. They have used its features for navigation, and investigated the nature of the heavens and their place in the cosmos through astronomical observation. There is substantial evidence that many other species of biota are also behaviorally or ecologically linked to features of the night sky. However, the natural appearance of the night sky has now been altered by human artifacts, including ground-based light pollution and artificial satellites. The scale of these impacts is likely to increase exponentially in the near future. I briefly review the possible significance of changes in the night sky for humans and other animals, with an emphasis on proposed satellite constellations. I raise the concern that this is an issue that requires a much broader evaluation of the aesthetic, cultural, environmental, religious and scientific values at stake. I examine the possible role of the National Environmental Policy Act (NEPA) as a legal tool for assessment of the impact of satellites on the human environment. Finally, I consider the need to for similar assessment of the lunar night sky, as humanity extends its presence to the lunar surface and cislunar orbital space. Faking biosphere / Oskari SivulaThis paper examines ecological engineering on a planetary scale from the perspective of the concept of (un)naturalness using terraformed Mars as a case study. It has been speculated that in the future it may be possible to make Mars habitable for terrestrial life. This hypothetical process is known as terraforming or planetary ecosynthesis. The possibility of establishing a planet-wide biosphere on Mars or some other celestial body opens up an interesting case of a biosphere that is in some sense unnatural. Furthermore, the concept of natural is central to many arguments in environmental ethics. For example, it has been suggested that the value of an ecosystem is dependent upon its history – it being natural of origin. Naturalness and unnaturalness discussions have centred around two questions. First, is naturalness morally relevant or should it otherwise affect decision making? Second, how naturalness should be understood in different cases? This paper addresses both questions in relation to terraforming Mars. First, I analyse in what sense the biosphere of the terraformed Mars would be unnatural. Second, I examine does its unnaturalness give us an important criterion for deciding whether we should aim to terraform Mars or not. Wilderness values in outer space / Michael LindquistThis paper critiques and develops Mark Woods’ account of wilderness as put forth in his Rethinking Wilderness (2017) with an eye towards application to extraterrestrial environs. First, I clarify Woods’ notion of wilderness and the value-adding properties he argues wildernesses tend to exemplify, namely, their being natural, wild, and free. In expanding on Woods’ work, I will demonstrate that a wilderness concept can survive extension beyond Earth’s atmosphere and that these value-adding properties thereby obtain in places such as Mars and Moon. The presence of these conceptual and normative resources allow us to theorize these places with reference to the relevant wilderness literature. Second, in light of the application of these value-adding properties to alien wilds, I will address planetary protection proposals that argue for a park-style system, such as the one argued for by Cockell and Horneck (2004; 2006). A precautionary wilderness program in a pre-settlement phase of space exploration is distinct from our current defensive wilderness protection paradigm on Earth, perhaps with a notable exception being environmental protections for Antarctica. A pre-settlement phase provides the opportunity to give primacy to wilderness values and wilderness protection in space in a way that is difficult to apply in post-settlement contexts. I will argue for such prioritization, which would thereby impose limits on the shape that future colonization projects could take, and I draw out these implications in reference to idealistic future colonial architecture and civilization-building projects on Mars or Moon