Structural Relations in the Family of Nonmetallic Filled β-Manganese Phases: The new members AGa6Te10 (A: Sn,Pb) and PbIn6Te10

Nonmetallic filled β-manganese phases form a new class of solids with a wide spaced (“eutactical”) partial structure of nonmetal atoms (Te, I), which is topologically equivalent to the arrangement of manganese atoms in cubic β-Mn (a = 6.315 Å, P4₁32, Z = 20), a manganese polymorph crystallizing in a tetrahedrally close packed structure. Different fractions of the 100 tetrahedral and 4 metaprismatic holes per unit cell of the β-Mn like arrangement of nonmetal atoms are occupied by metal atoms or pairs of covalently bonded metal atoms, leading to the different chemical compositions M₇Te₁₀, AM₆Te₁₀, Ag₂Ga₆Te₁₀, RbX₄I₅ (M: Al, Ga, In; A: Ca, Pb, Sn; X: Ag, Cu;). Basic structural properties and structural relations between the members of this new family of solids are discussed. In addition we present structural data for three new members of the family of filled β-Mn phases: SnGa₆Te₁₀ (single crystal data: a = 10.203 Å, α = 89.94°, space group R32, Z = 2) PbIn₆Te₁₀ (single crystal data: a = 10.619 Å, R32, Z = 2) and PbGa₆Te₁₀ (powder data: a = 10.237 Å, α = 89.93°, R32, Z = 2).     

Radiative emission properties of a-SiN : H based nanometric multilayers for light emitting devices

Optical and photoluminescence characterizations were performed on nanometric multilayer structures based on amorphous silicon nitrogen alloys. Evidences are shown that the radiative efficiency of multilayers increases with respect to single-layer structures. This is ascribed to a strong electron–hole pair localization and a low heterointerfaces defect density. Time-resolved photoluminescence measurements yield fast recombination with an energy-dependent lifetime due to hopping processes. Finally, the performance of an electroluminescent device based on multilayers is presented.     

Anomalous ionic transport in glassy electrolytes

Summary We discuss the dynamic structure model recently introduced by Bunde, Maass and Ingram to account for the anomalies of ionic transport in glassy ionic conductors. The model is based on the experimental evidence that ions in glass maintain their distinct local environments. Key features include a site memory effect that introduces vacancies appropriate to each kind of mobile ion, and a mismatch energy that emerges whenever an ion attempts to enter a different kind of site, the combination of both leads to the formation of fluctuating percolation pathways. The connectivity of these pathways determines the ion mobility in the glassy network. The exploration of this model by numerical methods leads i) to a power law relationship between ionic conductivity and cation content (now confirmed in the literature) and ii) to the elucidation of many facets of the mixed alkali effect. It is suggested that the model could form the basis for a comprehensive theory of vitreous electrolytes. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Controlled fed-batch fermentations of dilute-acid hydrolysate in pilot development unit scale

Inhibitors formed during wood hydrolysis constitute a major problem in fermenting dilute-acid hydrolysates. By applying a fed-batch technique, the levels of inhibitory compounds may be held low, enabling high ethanol productivity. In this study, a previously developed fed-batch strategy was modified and implemented for use in pilot development unit (PDU) scale. The rate of total gas formation, measured with a mass flow meter, was used as input variable in the control algorithm. The feed rate in the PDU-scale experiments could be properly controlled based on the gas evolution from the reactor. In fed-batch experiments utilizing TMB 3000, an inhibitor-tolerant strain of Saccharomyces cerevisiae, close to 100% of the hexoses in the hydrolysate was converted.     

光促进温和条件非贵金属催化下卤代烃与二氧化碳的羰基化反应及ESR谱研究

研究了卤代烃在光促进温和条件（常温常压）非贵金属[Co(acac)₂,Co(OAc)₂或CoCl₂]催化下与二氧化碳的羰基化反应；同时对反应过程中的ESR谱进行了研究. ESR谱研究表明，在光促进下二氧化碳参与的羰基化反应中有二氧化碳游离基负离子（CO^·-₂）[用DMPO（5,5-二甲基-1-吡咯啉-N-氧化物）捕获］生成.     

Determination of the optical second harmonic response of pharmaceutical solid–solid mixtures

We report on a new method for characterising crystallinity and polymorphism of pharmaceutical drugs and excipients in the solid state. The optical nonlinearity of certain crystalline structures allows under certain circumstances the quantitative determination of polymorphism or crystallinity. An apparatus was set up to measure the second harmonic response of powdered samples when irradiated with a pulsed laser source. Here we present experimental results from various pharmaceutically interesting materials. This rapid, novel technique has potential for industrial monitoring of pharmaceutical manufacturing processes.     

Numerical simulation of the flow field in a reactor for titanium dioxide production

A physicochemical and fluid dynamic model is formulated for the numerical simulation of the flow field in a reactor for titanium dioxide production, the turbulence motion is described by theKε equation, the governing equations are solved by the SIMPLER algorithm devised by Partankar and Spalding. The velocity, tmperature and concentration fields are obtained for three cases: A) with chemical reaction and thermal insulation on the walls; B) with chemical reaction and wall temperature is 450K; C) without chemical reaction and thermal insulation on the walls, and the physicochemical numerical simulation for the titanium dioxide production has been done. The results of the paper can be used as a theoretical guide for the engineers in the design of such reactors.     

Trapping efficiencies of various collection solvents after supercritical fluid extraction

A polarity test mix consisting of acetophenone, N, N-dimethylaniline, naphthalene, decanoic acid, 2-naphthol, and n-tetracosane was spiked onto sand, and extracted with supercritical carbon dioxide, to evaluate the collection efficiency of various solvents and solvent mixtures. Nine single collection solvent systems and four mixed collection solvent systems were studied. When one-component collection solvents were employed, quantitative (above 90%) recovery of all analytes was not possible. With mixed collection solvents, recoveries of 90% or better with all analytes studied were possible.     

New insights into the palladium-catalysed synthesis of δ-lactones from 1,3-dienes and carbon dioxide

Two-coordinate Pd(0) complexes are shown to be important intermediates in the telomerization of 1,3-dienes and CO₂ using palladium/phosphine catalysts without additives. Only one phosphorus atom is bound to palladium during the C–C bond forming steps, but the second phosphorus atom is crucial in the early stages of the catalytic cycle and for the elimination of the product. A ligand that gave an active palladium catalyst for the coupling of 1,3-butadiene and CO₂ has been designed. Use of a palladium catalyst in the reaction of isoprene with CO₂ allowed for the first time isolation and NMR spectroscopic characterization of the resulting mixture of lactones.