Simulation of current pricing-tendencies in the German electricity market for private consumption

The German electricity market for private consumption is characterized by increasing prices and low participation of the consumers. This prompts us to investigate the interdependencies between the customers’ engagement in the market and the suppliers’ pricing strategies. Based on an analysis of the German retail market, an agent-based simulation model is developed. Whereas the behaviour of private customers is calibrated on field data, the suppliers learn to maximize profits with a feedback-learning heuristic. The simulation results show a tendency of rising prices, which are created without the assumption of tacit collusion among suppliers. We conclude that in Germany the current market pressure of private customers may not be a sufficient incentive for suppliers to lower electricity prices.     

Energy system aspects of hydrogen as an alternative fuel in transport

Considering the enormous ecological and economic importance of the transport sector the introduction of alternative fuels—together with drastic energy efficiency gains—will be a key to sustainable mobility, nationally as well as globally. However, the future role of alternative fuels cannot be examined from the isolated perspective of the transport sector. Interactions with the energy system as a whole have to be taken into account. This holds both for the issue of availability of energy sources as well as for allocation effects, resulting from the shift of renewable energy from the stationary sector to mobile applications. With emphasis on hydrogen as a transport fuel for private passenger cars, this paper discusses the energy systems impacts of various scenarios introducing hydrogen fueled vehicles in Germany. It identifies clear restrictions to an enhanced growth of clean hydrogen production from renewable energy sources (RES). Furthermore, it points at systems interdependencies that call for a priority use of RES electricity in stationary applications. Whereas hydrogen can play an increasing role in transport after 2030 the most important challenge is to exploit short–mid-term potentials of boosting car efficiency.     

Comprehensive study of the evolution of an annular edge flame during extinction and reignition of a counterflow diffusion flame perturbed by vortices

The structure of a time-dependent methane/enriched-air flame established in an axisymmetric, laminar counterflow configuration is investigated, as the flame interacts with two counterpropagating toroidal vortices. Computationally, the time-dependent equations are written using a modified vorticity–velocity formulation, with detailed chemistry and transport, and are solved implicitly on a nonstaggered, nonuniform grid. Boundary conditions are chosen to create local extinction and reignition in the vicinity of the axis of symmetry. Experimentally, CO planar laser-induced fluorescence (PLIF), OH PLIF, and an observable proportional to the forward reaction rate (RR) of the reaction CO+OH→CO₂+H are measured. Particle image velocimetry (PIV) is used to characterize the velocity field of the vortical structures and to provide detailed boundary conditions for the simulations. Excellent agreement is found between model and experiments to the minutest morphological details throughout the interaction. The validated model is then used to probe the dynamics of the two-dimensional extinction process with high temporal resolution. During the initial phase of the interaction, the flame is locally extinguished by the two vortices. The resulting edge flame propagates outward as an extinction front, with a structure that does not depart significantly from that of a diffusion flame. The front recedes from the axis of symmetry with a negative propagation speed that reaches a value as large as six times that of the freely propagating laminar flame with the same reactant concentrations found at the stoichiometric surface. As the front propagates outward, it transitions to an ignition front, and it reaches a positive propagation speed comparable to that of the freely propagating laminar flame. During this transition, it develops a characteristic premixed “hook,” with a lean premixed branch, a stoichiometric segment that evolves into the remnant of the original primary diffusion flame, and a much weaker secondary diffusion flame resulting from a secondary peak in heat release in the original unperturbed diffusion flame. No evidence of a distinct rich premixed flame is found. The edge flame stabilizes at a radial location where the local gaseous speed equals the propagation speed of the front. When the local perturbation has decayed below the flame propagation speed, the flame edge starts reigniting the mixing layer as an ignition wave that propagates with an essentially frozen structure along the stoichiometric surface until the original diffusion flame structure is fully recovered. Implications for flamelet modeling of turbulent flames with local extinction are discussed.     

Performance measurements from LYSO scintillators coupled to a CMOS position sensitive SSPM detector

We have designed a 5×5 mm² position sensitive solid-state photomultiplier (PS-SSPM) using a complementary metal-oxide-semiconductor (CMOS) process that provides imaging capability on the micro-pixel level. The PS-SSPM has 11,664 micro-pixels total, with each having an active area and micro-pixel pitch of 30×30 μm² and 44.3 μm, respectively. The PS-SSPM was then examined for its performance characteristics such as its energy and spatial resolution, and LYSO scintillator array imaging capabilities. When coupled to 5×5×3 mm³ LYSO, the energy resolution at 511 keV (²²Na) was measured as a function of bias, and corrected for the PS-SSPM non-linear output. The resolution is 14% (FWHM) at 511 keV with 30 V bias. The LYSO coincidence timing resolution was 9.4 ns (FWHM) at 511 keV. Spatial resolution studies were conducted using a focused (∼30 μm beam spot diameter) pulsed 635 nm diode laser. Scintillator array imaging studies were conducted at 511 keV using a 6×6 LYSO array, having 500 μm pixels (530 μm pitch) and 5 mm tall.     

Ecotoxicological evaluation of three tertiary wastewater treatment techniques via meta-analysis and feeding bioassays using Gammarus fossarum

Advanced treatment techniques, like ozone, activated carbon and TiO₂ in combination with UV, are proposed to improve removal efficiency of micropollutants during wastewater treatment. In a meta-analysis of peer-reviewed literature, we found significantly reduced overall ecotoxicity of municipal wastewaters treated with either ozone (n = 667) or activated carbon (=113), while TiO₂ and UV was not yet assessed. As comparative investigations regarding the detoxification potential of these advanced treatment techniques in municipal wastewater are scarce, we assessed them in four separate Gammarus-feeding trials with 20 replicates per treatment. These bioassays indicate that ozone concentrations of approximately 0.8 mg ozone/mg DOC may produce toxic transformation products. However, referred effects are removed if higher ozone concentrations are used (1.3 mg ozone/mg DOC). Moreover, the application of 1 g TiO₂/l and ambient UV consistently reduced ecotoxicity. Although activated carbon may remove besides micropollutants also nutrients, which seemed to mask its detoxification potential, this treatment technique reduced the ecotoxicity of the wastewater following its amendment with nutrients. Hence, all three advanced treatment techniques are suitable to reduce the ecotoxicity of municipal wastewater mediated by micropollutants and may hence help to meet the requirements of the European Water Framework Directive.     

The potential of perylene bisimide derivatives for the solubilization of carbon nanotubes and graphene

Carbon nanotubes and graphene are outstanding materials of the 21st century with a broad spectrum of applications. However, major challenges are faced such as the intrinsically low solubility of both sp2 carbon allotropes. To overcome this hurdle the potential of noncovalent functionalization is summarized with a special focus on the establishment of the perylene bisimide unit as aromatic anchor to the graphitic surface. Rational surfactant design is unmasked as the key to solubilization of the carbon allotropes, while at the same time tailoring their surface properties, or even electronic properties in a fully reversible fashion.