Metal nano networks by potential-controlled in situ assembling of gold/silver nanoparticles

Non‐spherical Au/Ag nanoparticles can be generated by chemical reduction of silver ions in the presence of preformed gold nanoparticles. The process of particle formation can be controlled by concentrations of ligands and reducing agent. The formation of ellipsoidal, nanorod‐ and peanut‐shaped nanoparticles as well as of more complex fractal nanoassemblies can be explained by changes in particle surface state, electrochemical potential formation and particle‐internal self‐polarization effects. It is possible to create highly fractal nanoassemblies with sizes between the mid‐nanometer and the lower micrometer range. The assemblies are marked by high optical absorption and complex nano‐networks of very high surface‐to‐volume ratios and a granular base structure

Land-management strategies and the detached housing stock in shrinking municipalities: evidence from Germany

For some years, increased attention has been paid to the single-family housing stock in Germany and the further designation of building land by municipalities. A Germany-wide anonymous survey of municipalities sheds light on the municipalities' land management strategies with regard to declining populations and their anticipation of future problems for the further use of the single-family housing stock. The results of the quantitative survey are supplemented by qualitative interviews with municipal experts from case studies that were selected on the basis of criteria such as population decline, old-age dependency ratio, the share of single-family homes and vacancy rates. The aims of the survey and the interviews are to assess municipal representatives' perceptions of population decline and of the necessity of undertaking measures to deal with shrinkage. Research questions are: What measures do municipalities consider appropriate to counter population loss and falling demand for housing in shrinking regions? How important are single-family housing areas in the perception of German municipalities? The results indicate that a continued designation of building land seems to be one of the most important measures used to cope with insufficient demand. The aim is to attract new inhabitants, particularly to shrinking cities. However, this approach reinforces current problems because it lowers demand for the housing stock and increases the risk of vacancies.Seit einigen Jahren wird der Einfamilienhausbestand in Deutschland und die Praxis weiterer Baulandausweisungen von Kommunen mit erhöhter Aufmerksamkeit betrachtet. Der vorliegende Beitrag gibt Aufschluss über die Landmanagementstrategien von Kommunen vor dem Hintergrund sinkender Bevölkerungszahlen. Die Einschätzung möglicher zukünftiger Probleme für die weitere Nutzung des Einfamilienhausbestandes fußt auf einer anonymen deutschlandweiten Befragung auf der Gemeindeebene. Die Ergebnisse der quantitativen Befragung werden ergänzt durch qualitative Interviews mit Expertinnen/Experten in Fallstudiengemeinden, die nach Kriterien wie Bevölkerungsrückgang, Altenquotient, prozentualer Anteil von Einfamilienhausgebieten und Leerstandsraten ausgewählt wurden. Ziel der Befragung und der Interviews war es zu erfahren, wie die Expertinnen und Experten den Bevölkerungsrückgang einschätzen und ob sie die Notwendigkeit sehen, Maßnahmen gegen Schrumpfung zu ergreifen. Forschungsfragen sind: Welche Maßnahmen halten Kommunen für geeignet, um Bevölkerungsrückgang und rückläufiger Nachfrage bei Einfamilienhäusern entgegenzusteuern? Wie wichtig sind Einfamilienhausgebiete in der Wahrnehmung deutscher Kommunen? Die Ergebnisse deuten darauf hin, dass eine weitere Ausweisung von Bauland eine der wichtigsten Maßnahmen zu sein scheint zur Bewältigung einer unzureichenden Nachfrage, wenn das Ziel ist, neue Einwohnerinnen und Einwohner zu gewinnen, vor allem in schrumpfenden Städten. Dieses Vorgehen verstärkt jedoch die aktuellen Probleme, weil es die Nachfrage nach Bestandsgebäuden senkt und das Leerstandsrisiko erhöht

Produkt- und Technologieentwicklungen für eine nachhaltige Energieversorgung

Nicht nur die Klimakrise und die Begrenztheit fossiler Rohstoffe stellt Energieversorgungsunternehmen vor erhebliche Herausforderungen. Um zu einer nachhaltigen Energieversorgung beizutragen, sind verschiedene Ansätze notwendig

Population Inversion in Monolayer and Bilayer Graphene

The recent demonstration of saturable absorption and negative optical conductivity in the Terahertz range in graphene has opened up new opportunities for optoelectronic applications based on this and other low dimensional materials. Recently, population inversion across the Dirac point has been observed directly by time- and angle-resolved photoemission spectroscopy (tr-ARPES), revealing a relaxation time of only ~ 130 femtoseconds. This severely limits the applicability of single layer graphene to, for example, Terahertz light amplification. Here we use tr-ARPES to demonstrate long-lived population inversion in bilayer graphene. The effect is attributed to the small band gap found in this compound. We propose a microscopic model for these observations and speculate that an enhancement of both the pump photon energy and the pump fluence may further increase this lifetime.Comment: 18 pages, 6 figure

Wild edible plants of Belarus : from Rostafiński's questionnaire of 1883 to the present

Background: Belarus is an Eastern European country, which has been little studied ethnobotanically. The aim of the study was to compare largely unpublished 19th century sources with more contemporary data on the use of wild food plants. Methods: The information on 19th century uses is based on twelve, mainly unpublished, responses to Józef Rostafiński’s questionnaire from 1883, and the newly discovered materials of the ethnographer Michał Federowski, who structured his data according to Rostafiński’s questionnaire and documented it with voucher specimens. Rostafiński’s questionnaire was concerned mainly with Polish territories, but for historical reasons this also encompassed a large part of Belarus, and we analyzed only the twelve responses (out of the few hundred Rostafiński obtained), which concerned the present Belarus. These data were compared with a few 20th century ethnographic sources, and our own 40 interviews and questionnaires from Belarus. Results and discussion: 58 taxa of wild food plants used in the 19th century were identified. Some of them are still used in modern Belarus, others are probably completely forgotten. In the 19th century several species of wild greens were widely used for making soups. Apart from Rumex, other wild greens are now either forgotten or rarely used. The list of species used in the 20th and 21st century encompasses 67 taxa. Nearly half of them were mentioned by Rostafiński’s respondents. The list of fruit species has not changed much, although in the 19th century fruits were mainly eaten raw, or with dairy or floury dishes, and now apart from being eaten raw, they are incorporated in sweet dishes like jams or cakes. Modern comparative data also contain several alien species, some of which have escaped from cultivation and are gathered from a semi-wild state, as well as children's snacks, which were probably collected in the 19th century but were not recorded back then. Conclusion: The responses to Rostafiński from 1883 present extremely valuable historical material as the use of wild food plants in Belarus has since undergone drastic changes, similar to those, which have taken place in other Eastern European countries

Sr2+/Ca2+ and 44Ca/40Ca fractionation during inorganic calcite formation: III. Impact of salinity/ionic strength

In order to apply Sr/Ca and 44Ca/40Ca fractionation during calcium carbonate (CaCO3) formation as a proxy to reconstruct paleo-environments, it is essential to evaluate the impact of various environmental factors. In this study, a CO2 diffusion technique was used to crystallize inorganic calcite from aqueous solutions at different ionic strength/salinity by the addition of NaCl at 25 °C. Results show that the discrimination of Sr2+ versus Ca2+ during calcite formation is mainly controlled by precipitation rate (R in μmol/m2/h) and is weakly influenced by ionic strength/salinity. In analogy to Sr incorporation, 44Ca/40Ca fractionation during precipitation of calcite is weakly influenced by ionic strength/salinity too. At 25 °C the calcium isotope fractionation between calcite and aqueous calcium ions (Δ44/40Cacalcite-aq = δ44/40Cacalcite − δ44/40Caaq) correlates inversely to log R values for all experiments. In addition, an inverse relationship between Δ44/40Cacalcite-aq and log DSr, which is independent of temperature, precipitation rate, and aqueous (Sr/Ca)aq ratio, is not affected by ionic strength/salinity either. Considering the log DSr and Δ44/40Cacalcite-aq relationship, Sr/Ca and δ44/40Cacalcite values of precipitated calcite can be used as an excellent multi-proxy approach to reconstruct environmental conditions (e.g., temperature, precipitation rate) of calcite growth and diagenetic alteration

Shape-Dependent Catalytic Activity of Gold and Bimetallic Nanoparticles in the Reduction of Methylene Blue by Sodium Borohydride

In this study the catalytic activity of different gold and bimetallic nanoparticle solutions towards the reduction of methylene blue by sodium borohydride as a model reaction is investigated. By utilizing differently shaped gold nanoparticles, i.e., spheres, cubes, prisms and rods as well as bimetallic gold–palladium and gold–platinum core-shell nanorods, we evaluate the effect of the catalyst surface area as available gold surface area, the shape of the nanoparticles and the impact of added secondary metals in case of bimetallic nanorods. We track the reaction by UV/Vis measurements in the range of 190–850 nm every 60 s. It is assumed that the gold nanoparticles do not only act as a unit transferring electrons from sodium borohydride towards methylene blue but can promote the electron transfer upon plasmonic excitation. By testing different particle shapes, we could indeed demonstrate an effect of the particle shape by excluding the impact of surface area and/or surface ligands. All nanoparticle solutions showed a higher methylene blue turnover than their reference, whereby gold nanoprisms exhibited 100% turnover as no further methylene blue absorption peak was detected. The reaction rate constant k was also determined and revealed overall quicker reactions when gold or bimetallic nanoparticles were added as a catalyst, and again these were highest for nanoprisms. Furthermore, when comparing gold and bimetallic nanorods, it could be shown that through the addition of the catalytically active second metal platinum or palladium, the dye turnover was accelerated and degradation rate constants were higher compared to those of pure gold nanorods. The results explore the catalytic activity of nanoparticles, and assist in exploring further catalytic applications

Nanometer precise adjustment of the silver shell thickness during automated Au-Ag core-shell nanoparticle synthesis in micro fluid segment sequences

In this work, a wet-chemical synthesis method for gold–silver core–shell particles with nanometer precise adjustable silver shell thicknesses is presented. Typically wet-chemical syntheses lead to relatively large diameter size distributions and losses in the yield of the desired particle structure due to thermodynamical effects. With the here explained synthesis method in micro fluidic segment sequences, a combinatorial in situ parameter screening of the reactant concentration ratios by programmed flow rate shifts in conjunction with efficient segment internal mixing conditions is possible. The highly increased mixing rates ensure a homogeneous shell deposition on all presented gold core particles while the amount of available silver ions was adjusted by automated flow rate courses, from which the synthesis conditions for exactly tunable shell thicknesses between 1.1 and 6.1 nm could be derived. The findings according to the homogeneity of size and particle structure were confirmed by differential centrifugal sedimentation (DCS), scanning and transmission electron microscopy (SEM, TEM) and X-ray photoelectron spectroscopy (XPS) measurements. In UV-Vis measurements, a significant contribution of the core metal was found in the shape of the extinction spectra in the case of thin shells. These results were confirmed by theoretical calculations

Island and Indigenous systems of circularity: how Hawaiʻi can inform the development of universal circular economy policy goals

Given the dire consequences of the present global climate crisis, the need for alternative ecologically based economic models could not be more urgent. The economic and environmental concerns of the circular economy are well-developed in the literature. However, there remains a gap in research concerning the circular economy’s impact on culture and social equity. The underdeveloped social and cultural pillars of the circular economy, along with universal policy goals calling for a context- and need-based framework, makes it necessary to bridge natural and social science objectives in the circular economy. Islands can serve as model systems for studying the circular economy. We examine how Hawaiʻi, through the philosophy of aloha ʻāina, the Hawaiian ancestral circular economy, and contemporary community approaches toward advancing Indigenous economic justice can be one model system for understanding principles of circularity and policy advocacy. We introduce the concept of the ancestral circular economy and how aspects of this Indigenous institution can inform the development of universal circular economy policy goals. Furthermore, we present aloha ʻāina as a framework for reciprocal care between human–environment relations while addressing the social and cultural pillars that aid in the development of these dimensions of the circular economy