In situ observation of the reaction of scandium and carbon by neutron diffraction

The formation of scandium carbides by reaction of the elements has been investigated by in situ neutron diffraction up to 1823 K. On heating, the recrystallization of α-Sc occurs between 1000 and 1223 K. The formation of Sc₂C and ScC (NaCl-B1 type structure) phases has been detected at 1323 and 1373 K, respectively. The formation of a new orthorhombic scandium carbide phase was observed at 1473(50) K. Once the scandium carbides are formed they are stable upon heating or cooling. No other phases were detected in the present study, in which the system was always carbon saturated. The thermal expansion coefficients of all phases have been determined, they are constant throughout the temperature interval studied.     

Materials Development for Advanced Planar Solid Oxide Fuel Cells

High-power density and high durability are the main targets for solid oxide fuel cell (SOFC) development at Forschungszentrum Jülich. Power density has been further increased by variation of the material composition of perovskite-based cathodes (Sr content, Co content, substoichiometry) and by optimization of the diffusion barrier (Gd-substituted ceria) between an electrolyte and a cathode. The application of dense diffusion barrier layers significantly improved the performance. The associated avoidance of SrZrO₃ formation, however, contributed only to a small extent to the improvement of durability of SOFCs with LSCF cathodes. The redox stability of anode-supported SOFCs has been addressed in two ways: (a) conventional Ni/yttria-stabilized zirconia anode substrates have been investigated to explore the limits of re-oxidation and to determine the degree of oxidation at which no damages occur. (b) Alternative anodes and anode substrates are under development, which basically consist of mixed-conducting ceramics. Avoiding the high amount of nickel decreases the probability of failure, but does not automatically lead to redox-stable anodes. The differences in the materials' properties of such ceramics in oxidizing and reducing environment are addressed.     

Polymer‐Based Spherical Activated Carbons in Combination with TS‐1 as Efficient Epoxidation Catalysts

The heterogeneously catalyzed epoxidation of commercially available biodiesel with aqueous H₂O₂ as an oxidant was studied over composite catalysts consisting of microporous titanium silicalite‐1 (TS‐1) as reactive and polymer‐based spherical activated carbon (PBSAC) as sorptive component. The results are compared to that of a commercial TS‐1 catalyst. The polymer‐based spherical activated carbon was applied either as a support or as an exotemplate. In the composite catalyst, the active titanium sites are utilized four times more efficiently than in the commercial TS‐1.     

Importance of characterizing a reference filter test system

Standards governing the performance of air filters are there to enable comparisons to be made between different filter tests. However, measurement data from different filter test systems can vary widely, making comparisons difficult. Palas GmbH, Germany, has developed a modifed test system that it says meets the minimum requirements of a reference filter test system.     

The single-format assumption in arithmetic fact retrieval.

Current models of mental arithmetic disagree on whether the same mental representation is activated by numbers in different forms (single-format assumption). Two experiments examined if the response times in arithmetic fact retrieval from arabic digits, number words, or dice are independent of the graphical representation of the numbers. S. Sternberg's (1969) additive factors method was used to analyze which response time interactions are compatible with the single-format assumption. In accord with the assumption, additive effects of form and operation were found in Experiment 1. In contrast, Experiment 2 showed additive effects only when an operand was held in memory, but a strong Form?X?Operation interaction otherwise. The authors discuss how phonological interference and form-specific retrieval could produce these interactions and how the single-format assumption can be extended to handle the findings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Switch in Cofactor Specificity of a Baeyer–Villiger Monooxygenase

Baeyer–Villiger monooxygenases (BVMOs) catalyze the oxidation of ketones to esters or lactones by using molecular oxygen and a cofactor. Type I BVMOs display a strong preference for NADPH. However, for industrial purposes NADH is the preferred cofactor, as it is ten times cheaper and more stable. Thus, we created a variant of the cyclohexanone monooxygenase from Acinetobacter sp. NCIMB 9871 (CHMO_Acineto); this used NADH 4200‐fold better than NADPH. By combining structure analysis, sequence alignment, and literature data, 21 residues in proximity of the cofactor were identified and targeted for mutagenesis. Two combinatorial variants bearing three or four mutations showed higher conversions of cyclohexanone with NADH (79 %) compared to NADPH (58 %) as well as specificity. The structural reasons for this switch in cofactor specificity of a type I BVMO are especially a hydrogen‐bond network coordinating the two hydroxy groups of NADH through direct interactions and bridging water molecules.     

Preparation of pyridinemonocarboxylic acids by catalytic vapour phase oxidation of alkylpyridines. II. Oxidation of 2-methyl-5-ethylpyridine to niacin

The vapour phase air oxidation of 2-methyl-5-ethylpyridine (MEP) has been investigated, and the various oxidation products identified. Using a doubly promoted vanadium catalyst, V₂O₅–TiO₂–K₂O, a 98% (mole) conversion of MEP was obtained with a yield of 36% for niacin and 18% for recirculatable products (i.e. products with an intact 3-picoline skeleton) at a temperature of 413°C and a space velocity of 5500 h^?1. In a comparison of the singly promoted catalysts, varying the atom ratio V/Ti, the catalyst with V/Ti = 100/25 was found to be most active. In a comparison of different preparation temperatures for the same catalyst, 1250°C was found to be most satisfactory. A reaction scheme is proposed with the corresponding rate constants and apparent activation energies.     

COOS: a wave-function based Schrödinger–Poisson solver for ballistic nanotube transistors

This paper gives an in depth overview on a wave-function based simulation framework (called coos) for modeling ballistic nanotube transistors by solving the effective-mass Schrödinger equation. The framework considers non-parabolic electronic band structure effects, band-to-band tunneling as well as a heterojunction-like model for extended contacts to describe the injection and reception of charge carriers into and from the channel. Special emphasis is put on an efficient and reliable numerical implementation. The applicability of the simulation framework and the necessity to include the aforementioned phenomena are shown by comparing simulation results with experimental data of a \(50\hbox { nm}\) long carbon nanotube transistor (cntfet). The intrinsic transit frequencies and the output characteristics for higher drain-source voltages are predicted and analyzed.