General Energy Research Department

For many reactions performed in fluidized beds, the mechanical stability of particles is of major importance, and yet, despite this, previous studies have disagreed on the elutriated amount and origin of fine particles. This paper therefore investigates the attrition of particles in bubbling fluidized beds in more detail to determine whether these differences are due to electrostatic or other interparticle forces. To achieve this, the forces acting during flu-idization are mathematically derived, and two particle types (alumina and dolomite) are experimentally investigated. Based on the results obtained, a simple model is developed to describe the attrition of both particle types.

Sustainable hydrogen production through photoelectrochemical water splitting using hematite (R-Fe 2 O 3 ) is a promising approach for the chemical storage of solar energy, but is complicated by the material's nonoptimal optoelectronic properties. Nanostructuring approaches have been shown to increase the performance of hematite, but the ideal nanostructure giving high efficiencies for all absorbed light wavelengths remains elusive. Here, we report for the first time mesoporous hematite photoelectodes prepared by a solution-based colloidal method which yield water-splitting photocurrents of 0.56 mA cm -2 under standard conditions (AM 1.5G 100 mW cm -2 , 1.23 V vs reversible hydrogen electrode, RHE) and over 1.0 mA cm -2 before the dark current onset (1.55 V vs RHE). The sintering temperature is found to increase the average particle size, and have a drastic effect on the photoactivity. X-ray photoelectron spectroscopy and magnetic measurements using a SQUID magnetometer link this effect to the diffusion and incorporation of dopant atoms from the transparent conducting substrate. In addition, examining the optical properties of the films reveals a considerable change in the absorption coefficient and onset properties, critical aspects for hematite as a solar energy converter, as a function of the sintering temperature. A detailed investigation into hematite's crystal structure using powder X-ray diffraction with Rietveld refinement to account for these effects correlates an increase in a C 3v -type crystal lattice distortion to the improved optical properties.

A theoretical analysis is presented for liquid-state T 1 relaxation in a coupled two-spin system I ϭ1/2, Sϭ1 in the presence of two radio-frequency fields applied to each of the spins individually. It is demonstrated that the relaxation rate constant T 1 Ϫ1 of the spin I due to scalar relaxation sharply increases when the two radio-frequency fields are matched according to the Hartmann-Hahn condition. Relaxation measurements on the amino-protons of 3-nitroaniline show good agreement with theory.

Introduction of alternative fuels in the passenger car fleet is widely discussed in the light of emission reductions. Worldwide experiences show that the market introduction depends on the actions of many stakeholders, like car industry, fuel companies and consumers. The process demands well-timed actions and investments, whilst economic chances and risks are distributed highly unequally. Policy makers set the framework conditions, although the influence of the height and timing of subsidies, tax reductions and other stimulation policies are not well understood yet.

The market introduction of cars fueled with natural gas, a technically and economically mature option to reduce air pollution, was studied for Switzerland. Worldwide experiences have shown that the market introduction is a complex dynamical problem. The process demands well timed actions and investments of numerous stakeholder groups, from car industry to gas companies and fueling stations, whilst economic chances and risks are distributed highly unequally. Stakeholder analysis and system dynamics modeling techniques were used to characterize the system. The developed model incorporates all relevant stakeholders, and shows the consequences and indirect feedbacks of their possible actions. It enables to simulate numerous future scenarios and test different market stimulation policies, yielding a better understanding of pitfalls and success factors.