Pre-selectable integer quantum conductance of electrochemically fabricated silver point contacts

The controlled fabrication of well-ordered atomic-scale metallic contacts is of great interest: it is expected that the experimentally observed high percentage of point contacts with a conductance at non-integer multiples of the conductance quantum G_0 = 2e^2/h in simple metals is correlated to defects resulting from the fabrication process. Here we demonstrate a combined electrochemical deposition and annealing method which allows the controlled fabrication of point contacts with pre-selectable integer quantum conductance. The resulting conductance measurements on silver point contacts are compared with tight-binding-like conductance calculations of modeled idealized junction geometries between two silver crystals with a predefined number of contact atoms

Plankton ecology: The past two decades of progress

This is a selected account of recent developments in plankton ecology. The examples have been chosen for their degree of innovation during the past two decades and for their general ecological importance. They range from plankton autecology over interactions between populations to community ecology. The autecology of plankton is represented by the hydromechanics of plankton (the problem of life in a viscous environment) and by the nutritional ecology of phyto- and zooplankton. Population level studies are represented by competition, herbivory (grazing), and zooplankton responses to predation. Community ecology is represented by the debate about bottom- up vs. top-down control of community organization, by the PEG model of seasonal plankton succession, and by the recent discovery of the microbial food web

Grazer diversity effects in an eelgrass–epiphyte–microphytobenthos system

The dramatic loss of biodiversity and its consequences for ecosystem processes have been of considerable interest in recent ecological studies. However, the complex and interacting processes influencing diversity effects in multitrophic systems are still poorly understood. We used an experimental eelgrass system to study the effects of changing richness of three consumer species on the biomass, diversity and taxonomic composition of both epiphytic and benthic microalgal assemblages. After 1 week, consumer richness enhanced the grazing impact on epiphyte biomass relative to single consumer treatments and a positive effect of consumer richness on prey diversity was found. Moreover, strong effects of consumer species identity on taxonomic composition were found in both microalgal assemblages. However, the effects of consumer richness were not consistent over time. The consequences of high nutrient availability seemed to have masked consumer richness effects

Effects of water column nutrients and grazer diversity on a seagrass-epiphyte-microphytobenthos community within and beneath a Zostera marina meadow.

Seagrass ecosystems have experienced a dramatic decrease in recent years and high water column nutrients as well as changes in grazer diversity are regarded as major drivers of this decline. Few studies have assessed the relative importance of top-down grazer effects in combination with bottom-up nutrient effects on the entire seagrass community. In this study we used indoor mesocosms with constantly high nutrient supply and manipulated grazer diversity. We considered the seagrass habitat as a whole by including the seagrass-epiphyte community and the microphytobenthos beneath a Zostera marina bed. Nutrients significantly affected the composition and diversity of microalgal communities and on the long run eutrophication clearly took on a governing role. Grazer diversity influenced the microalgal communities on the short-term. During the course of the experiment the high food quantities boosted the grazers biomass and reproduction. However, the consumers were unable to control the strong microalgal production. This experiment provides evidence that constantly high nutrient loadings can affect seagrass communities considerably and that grazers at intermediate abundance are unable to sustain the stability at high levels of primary productivity

Solar-Driven Thermochemical Production of Sustainable Liquid Fuels from H2O and CO2 in a Heliostat Field

The technology presented has as main goal to produce for the first time fuels from concentrated sunlight, water and carbon dioxide under real-world conditions and to promote the technology to a readiness level of 5. For this purpose, a solar fuel research facility comprising a high-flux solar concentrating heliostat field and tower, a solar thermochemical reactor system, and a gas-to-liquid conversion plant have been installed at a sunny site. Ceria is used as the reactive material, which undergoes a temperature and pressure swing in a redox cycle, splitting water and carbon dioxide into hydrogen and carbon monoxide. This synthesis gas is then converted into hydrocarbons via a Fischer-Tropsch conversion plant. The customized heliostat field has been able to provide irradiances above 3000 kW/m2 onto the aperture of the 50kW reactor, producing up to 300 l/hour solar syngas subsequently converted into liquid fuel