K4CaSi6O15—Solving a 90-year-old riddle

Polycrystalline K₄CaSi₆O₁₅ was prepared from (a) solid-state reactions between stoichiometric mixtures of the corresponding oxides/carbonates and (b) combustion solution synthesis using K- and Ca-nitrates, tetraethyl orthosilicate (TEOS), and glycine (fuel component) as starting reagents. The compound was characterized by powder X-ray diffraction. Differential thermal analysis indicated that K₄CaSi₆O₁₅ melts congruently at about 956°C. On cooling down from the liquid state, a distinct glass-forming tendency was observed. Single crystals suitable for further structural investigations were obtained from sinter experiments just below the melting point. Basic crystallographic data are as follows: monoclinic symmetry, space group Pc, a = 6.9299(2) Å, b = 27.3496(9) Å, c = 12.2187(4) Å, β = 93.744(3)°, V = 2310.86(13) ų, Z = 3. The crystal structure of K₄CaSi₆O₁₅ belongs to the group of interrupted framework silicates with exclusively Q³-units. The tetrahedral network is the first inorganic representative of the so-called eth-type. Charge compensation in the structure is achieved by the incorporation of potassium and calcium cations, which are coordinated by five to nine oxygen ligands. Ninety years after its first mention the present contribution proves the existence of K₄CaSi₆O₁₅ as a stable phase in the ternary system K₂O–CaO–SiO₂.     

Optimierung des Betoniervorgangs und der Mindestbewehrung einer massiven Bodenplatte

Optimisation of Concrete Casting Procedure and the Minimum Reinforcement of a Massive Foundation Slab The early age behaviour of a massive, joint less and watertight foundation slab was investigated in detail. The investigation was performed using a numerical model considering endogenous and exogenous effects, and it was complemented by in‐situ measurements. The results showed a significant influence of in‐situ climatic conditions during concreting on the necessary reinforcement content. The deformation measurements indicate a low degree of fixity of the slab. Also, the minimum reinforcement favours a better distribution of stresses as built‐in by internal deformation gradients in the slab.     

Analysis of H2 to CO2 yield and physiological key parameters of Enterobacter aerogenes and Caldicellulosiruptor saccharolyticus

In our study two strains, Enterobacter aerogenes and Caldicellulosiruptor saccharolyticus, were chosen as model microorganisms for investigation of biohydrogen production. By using E. aerogenes, operated in repetitive batch mode, the highest cumulative volumetric hydrogen evolution rate was obtained at an initial glucose concentration of 13.7 g/L. Growing C. saccharolyticus in repetitive batch mode on xylose revealed that complex media resulted in higher volumetric hydrogen productivities but lower hydrogen yields than defined media. Chemostat culture investigations of E. aerogenes and C. saccharolyticus on glucose revealed that higher dilution rates resulted in higher biohydrogen productivities, but also in lower product yields. The highest hydrogen volumetric productivities were obtained with E. aerogenes  , while the highest product to substrate yield (Y₍H₂/s₎)$\left({\text{Y}}_{\left({\text{H}}_2\text{/s}\right)}\right)$ and hydrogen to carbon dioxide yield (Y₍H₂/CO₂₎)$\left({\text{Y}}_{\left({\text{H}}_2{\text{/CO}}_2\right)}\right)$ were obtained with C. saccharolyticus  . Y₍H₂/CO₂₎${\text{Y}}_{\left({\text{H}}_2{\text{/CO}}_2\right)}$ is an important physiological parameter, regarding a future integration of biohydrogen production into the 5th generation of biofuels.     

NV-Tree: An Efficient Disk-Based Index for Approximate Search in Very Large High-Dimensional Collections

Over the last two decades, much research effort has been spent on nearest neighbor search in high-dimensional data sets. Most of the approaches published thus far have, however, only been tested on rather small collections. When large collections have been considered, high-performance environments have been used, in particular systems with a large main memory. Accessing data on disk has largely been avoided because disk operations are considered to be too slow. It has been shown, however, that using large amounts of memory is generally not an economic choice. Therefore, we propose the NV-tree, which is a very efficient disk-based data structure that can give good approximate answers to nearest neighbor queries with a single disk operation, even for very large collections of high-dimensional data. Using a single NV-tree, the returned results have high recall but contain a number of false positives. By combining two or three NV-trees, most of those false positives can be avoided while retaining the high recall. Finally, we compare the NV-tree to Locality Sensitive Hashing, a popular method for epsilon-distance search. We show that they return results of similar quality, but the NV-tree uses many fewer disk reads.     

Analysis of boundary layer control by heat transfer strips using an asymptotic approach to the PSE

The effect of heating strips on the stability of boundary layer flow over a flat plate is investigated. Heating strips alter the flow stability through the temperature dependence of the fluid properties. A stability study is carried out using the parabolized stability equations (PSE) that calculates the effects of temperature dependent fluid properties in terms of asymptotic expansions based on the total heat input. The leading order influence is obtained as a general result and, for the particular Prandtl number taken, is independent of any special set of property laws. In a fluid for which the intrinsic viscosity increases with temperature and the density decreases with temperature (such as air) the results show that the optimal location for a heating strip to stabilise the flow is upstream of the neutral point. The optimal location moves further upstream as the total heat input level is increased. For a given heat input widening the heating strip further stabilises the flow. Finally, the potential of the asymptotic method as a tool for further analysis of the flow is discussed.