Large-scale surface reconstruction energetics of Pt(100) and Au(100) by all-electron DFT

The low-index surfaces of Au and Pt all tend to reconstruct, a fact that is of key importance in many nanostructure, catalytic, and electrochemical applications. Remarkably, some significant questions regarding their structural energies remain even today, in particular for the large-scale quasihexagonal reconstructed (100) surfaces: Rather dissimilar reconstruction energies for Au and Pt in available experiments, and experiment and theory do not match for Pt. We here show by all-electron density-functional theory that only large enough "(5 x N)" approximant supercells capture the qualitative reconstruction energy trend between Au(100) and Pt(100), in contrast to what is often done in the theoretical literature. Their magnitudes are then in fact similar, and closer to the measured value for Pt(100); our calculations achieve excellent agreement with known geometric characteristics and provide direct evidence for the electronic reconstruction driving force.Comment: updated version - also includes EPAPS information as auxiliary file; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

Modeling of shared space with multi-modal traffic using a multi-layer social force approach

In the field of traffic road design, the shared space approach aims to develop roads from mere traffic infrastructures to public spaces, compelling higher interaction between road users. In this paper we develop the fundamentals for a micro-simulation tool based on the Social Force Model, to represent the motion of road users in such layouts. Working with the observed behavior of users in a pedestrian-friendly intersection in the city of Braunschweig (D), a multi-layer structured model is developed, in which each layer is designated to handle different situations, from free-flow movements to user interactions in crowded situations. Visibility graphs and clothoid estimations are used for designing trajectories of road users for the free flow movement. Furthermore, an enhancement of the classical Social Force Model is provided in order to model long-range collision avoidance behavior. Finally, the enhanced simulation framework is validated by two observed scenarios, which include various conflicts between pedestrians and cars.DFG/BE 2159/13-1DFG/FR 1670/13-

A multi-layer social force approach to model interactions in shared spaces using collision prediction

In shared space environments the movements of road users is not regulated by traffic rules, but is the result of spontaneous interaction between traffic users, who negotiate the priority according to social rules such as eye contact or courtesy behavior. However, appropriate micro simulation tools, which can reproduce the operation of shared spaces, are currently lacking. In this paper, a multi-layer approach for representing the movement of road users and their interaction, based on the Social Force Model, is developed. In a free-flow layer a realistic path is calculated for each user towards his destination, while a conflict layer is used for detecting possible conflict situations and computing an appropriate reaction. The novelty of this work in the field of shared space modeling is in the implementation of group dynamics and a SFM based approach for cyclists. The presented approach is qualitatively tested in different traffic situations involving cyclists, pedestrians and pedestrian groups, and shows realistic behavior. © 2017 The Authors. Published by Elsevier B.V.DFG/BE 2159/13-1DFG/FR 1670/13-

Valorization of ecosystem services through location optimization of integrated value chains for biofuel and livestock production in Brazil

Future projections indicate an increase in food and energy demands, creating a pressure on land use, while there is an urgent global need for climate change mitigation. Bioenergy is foreseen as potential option to meet future energy demands and reduce greenhouse gas (GHG) emissions. However, the sustainability of biofuels depends on availability of biomass, logistics and impacts on ecosystems, that are strictly dependent on locations and regional characteristics. This study presents a bottom-up approach to assess spatially explicit sustainability of bioenergy-livestock integrated systems (BLIS) in Brazil, to understand their contribution to future energy demands and GHG mitigation targets, and their impacts on Ecosystem Services (bioenergy production, GHG mitigation, zero direct deforestation, reduction of food competition). The proposed integration considers livestock intensification and use of biofuels by-products as animal feed supplement, taking advantage of synergies between these two value chains. Three different technological options were considered, Tech1_Sugarcane considers an autonomous sugarcane plant producing ethanol, electricity, and animal feed; in Tech2_Corn, corn is processed during sugarcane offseason, producing ethanol, corn oil and animal feed (DGS); Tech3_Soybean considers a biodiesel plant integrated with sugarcane plant. Techno-economic and environmental implications of the three BLIS technological options were modelled using the Virtual Biorefinery, developed at LNBR/CNPEM. After exclusion of biodiversity hotspots, biomes and scattered feedstock production, 18 million hectares of pasture inside Sugarcane Agroecological Zoning could be available for BLIS expansion. Tech1_Sugarcane has the highest potential for bioenergy production (89 billion liters) and GHG mitigation (139 million tonnes of CO2eq) among the technological options, and Tech3_Soybean presents the highest profits. Expansion of BLIS system in Brazil could contribute to meet future bioenergy demands and mitigation targets in the country while also alleviating pressure on land use for food and energy purposes, and without expanding on biodiversity hotspots and Pantanal and Amazon biomes. These results might help to support more assertive public policies regarding biofuel expansion in Brazil and contribute to achieve the ambitious targets assumed in the Paris Agreement

Image states in metal clusters

The existence of image states in small clusters is shown, using a quantum-mechanical many-body approach. We present image state energies and wave functions for spherical jellium clusters up to 186 atoms, calculated in the GW approximation, where G is the Green's function and W is the dynamically screened Coulomb interaction, which by construction contains the dynamic long-range correlation effects that give rise to image effects. In addition, we find that image states are also subject to quantum confinement. To extrapolate our investigations to clusters in the mesoscopic size range, we propose a semiclassical model potential, which we test against our full GW results

Stabilization of semiconductor surfaces through bulk dopants

We show by employing density-functional theory (DFT) calculations (including a hybrid functional) that ZnO surfaces can be stabilized by bulk dopants. As an example, we study the bulk-terminated ZnO (0001) surface covered with half a monolayer of hydrogen. We demonstrate that deviations from this half-monolayer coverage can be stabilized by electrons or holes from bulk dopants. The electron chemical potential therefore becomes a crucial parameter that cannot be neglected in semiconductor surface studies. As one result, we nd that to form the defect-free surface with a half-monolayer coverage of hydrogen for n-type ZnO, ambient hydrogen background pressures are more conducive than high vacuum pressures

Soft-landing electrospray ion beam deposition of sensitive oligoynes on surfaces in vacuum

AbstractAdvances in synthetic chemistry permit the synthesis of large, highly functional, organic molecules. Characterizing the complex structure of such molecules with highly resolving, vacuum-based methods like scanning probe microscopy requires their transfer into the gas phase and further onto an atomically clean surface in ultrahigh vacuum without causing additional contamination. Conventionally this is done via sublimation in vacuum. However, similar to biological molecules, large synthetic compounds can be non-volatile and decompose upon heating. Soft-landing ion beam deposition using soft ionization methods represents an alternative approach to vacuum deposition. Using different oligoyne derivatives of the form of R1(CC)nR2, here we demonstrate that even sensitive molecules can be handled by soft-landing electrospray ion beam deposition. We generate intact molecular ions as well as fragment ions with intact hexayne parts and deposit them on clean metal surfaces. Scanning tunneling microscopy shows that the reactive hexayne segments of the molecules of six conjugated triple bonds are intact. The molecules agglomerate into ribbon-like islands, whose internal structure can be steered by the choice of the substituents. Our results suggest the use of ion beam deposition to arrange reactive precursors for subsequent polymerization reactions

A microfluidics-based in situ chemotaxis assay to study the behaviour of aquatic microbial communities

© 2017 The Author(s). Microbial interactions influence the productivity and biogeochemistry of the ocean, yet they occur in miniscule volumes that cannot be sampled by traditional oceanographic techniques. To investigate the behaviours of marine microorganisms at spatially relevant scales, we engineered an in situ chemotaxis assay (ISCA) based on microfluidic technology. Here, we describe the fabrication, testing and first field results of the ISCA, demonstrating its value in accessing the microbial behaviours that shape marine ecosystems