轴流风机叶尖泄漏流动的大涡模拟（英文）

本文采用大涡模拟(LES)的方法研究了在基于外壳直径的雷诺数为9.36×105条件下5叶片的轴流式风扇的流动特性,并且着重分析了叶尖泄漏的流动现象。本文使用了基于有限体积法和分层笛卡尔网格的可压流求解器进行数值计算,并应用了体积守恒的切割网格方法处理风扇几何结构的浸入式边界。同时开发了用于笛卡尔网格的旋转周期性边界条件,这样只需分析由2.5亿网格构造的包含一片叶片的72°区域。该研究首先对网格质量进行了分析,之后讨论了瞬态和时均流场的特性,并与使用RANS的5叶片模拟结果进行了对比。RANS和LES模拟结果的主要不同之处体现在叶尖泄漏涡尾流中的湍流动能。本文进而研究了叶尖间隙对叶尖泄漏涡的影响。研究表明,间隙的大小会影响叶尖泄漏涡的大小形状。此外,间隙中更多的分离现象和反向旋转涡会导致较低的湍流动能。     

Photo-vulcanization using thiol-ene chemistry: Film formation,morphology and network characteristics of UV crosslinked rubber latices

The photo-vulcanization with versatile thiol-ene chemistry represents an innovative approach to crosslink diene-rubber materials both in latex and in solid film state. In this work, the structure of elastomer-based thiol-ene networks and the morphology after film formation are studied in detail using electron microscopic techniques, atomic force microscopy and multiple-quantum solid-state NMR spectroscopy. Additionally, film formation properties and corresponding macroscopic properties of photo-vulcanized natural rubber (NR) latex and its synthetic counterpart, isoprene rubber (IR) latex, are determined in dependence on the curing procedure (pre- and post-vulcanization). The results reveal that thiol-ene cured elastomers comprise homogenously distributed crosslinks with a low amount of short chain defects. Whilst photochemically pre-cured NR latex particles provide coherent films, the film formation and mechanical properties of IR are strongly governed by the crosslink density of the latex particles. In film state, photo-vulcanization promotes narrow crosslink distributions and excellent tensile properties of both NR and IR.     

Lignin Impact on Fibre Degradation: 1—Quinone Methide Intermediates Formedfrom Lignin DuringIn VitroFermentation ofCorn Stover*

Experiments were conducted to determine whether formation of quinone methide intermediates from lignin occurs during ruminal fermentation of corn stover, as indicated by nucleophilic addition reaction with sulphur-containing reducing agents. Corn stover leaf and stem fractions harvested at full maturity were incubated in buffered ruminal fluid without reducing agents or with (NH₄)₂SO₄ (S-control), Na₂S.9H₂O, cysteine-HCl (cysHCl), or cysHCl plus Na₂S.9H₂O; and in only buffer with or without cysHCl plus Na₂S.9H₂O. Mixed reducing agents (cysHCl plus Na₂S.9H₂O) enhanced ( P< 0.001) in vitro fibre degradation after 48 h, tended to increase solubilisation of fibre ( P =0.07) and dry matter ( P =0.06) in buffer alone, and elevated ( P< 0.001) S-content of residual fibre. In vitro incorporation of S into the undegraded fibre was determined for corn stover fractions of varying lignin compositions that were harvested at two maturities (early dent and full maturity) in 2 years. Extent of fibre degradation was correlated with extent of S-incorporation ( r =-0.54, P< 0.001), and with lignin methoxyl content ( r =-0.84, P< 0.001). The negative association of lignin methoxyl content with digestibility is explained by the relative likelihood of quinone methide intermediate formation from guaiacyl and syringyl units in lignin.     

Apple Allergy: The cDNA Sequence of the Major Allergen of Apple,Determined by Performing PCR with a Primer Based on the N-Terminal Amino Acid Sequence,is Highly Homologous to the Sequence of the Major Birch Pollen Allergen

Considering the known N-terminal amino acid sequence of the major apple allergen, a polymerase chain reaction (PCR) primer was selected to amplify cDNA encoding this protein. A single PCR product was obtained, cloned into Escherichia coli and subsequently sequenced. The missing 5′-end of the apple cDNA sequence was obtained by a 5′-RACE method. The cDNA sequence showed 72% identity with the coding region of one of the known isoforms of Bet v 1, the major allergen of birch pollen. The deduced amino acid sequence resulted in a 158-residue protein with a calculated molecular mass of 17·5 kDa and 63% amino acid sequence identity to Bet v 1. In addition, further protein alignments showed a high degree of identity with allergens from other tree pollens and some ‘pathogenesis-related proteins’ from food plants. According to international regulations the allergen was termed Mal d 1 for this protein, it being the first major allergen discovered and characterised in fruits of apple (Malus domestica).     

Comparative X-ray scattering,microscopical, and mechanical studies on rectangular plates injection molded from different types of isotactic polypropylene

Rectangular plates were injection molded from two grades of commercial polypropylene (PP) differing in the molar mass distribution. The mold was mechanically sealed when a desired pressure p_i,max (up to 1560 bar) was reached. Samples were taken from each plate at different distances from the gate and were investigated by applying various methods. In spatially resolved wide-angle X-ray studies, the cross section of the sample was scanned with a fine X-ray beam (collimated by a Kratky small-angle camera) and the intensity of scattering was registered by a linear detector as a function of position in the cross section. The evaluation of the scattering data delivered profiles of several parameters, describing the distribution of crystallite modification β-PP and γ-PP, the degree of orientation, the size of crystallites, and interplanar spacing, depending on the distance from surface. These results and those from measurements of birefringence and elongation at break, and from polarization microscopy and transmission electron microscopy, provided details of the layered structures in the plates, at different flow lengths, and allowed far-reaching statements about the influence of molecular properties and processing conditions on the development of texture in the plates.     

Zur Stöchiometrie bei Wasserbestimmungen nach Karl Fischer

The Stoichiometry in the Determination of Water Using Karl Fischer Reagent The stoichiometry of the Karl Fischer reaction is not unambiguous. The titer of a Karl Fischer solution rises with the amount of water, because sulphur trioxide which is formed as an intermediate consumes water too. An 1:1-stoichiometry (H₂O:I₂) can be simulated by alcohols, because these solvents also react with iodine and sulphur dioxide leading to additional consumption of iodine during the titration. This interpretation of the results of Karl Fischer titrations is supported by the isolation or identification of pertinent reaction products.     

Illusion—creating a mock reality

Photorealistic computer animation sequences have become more important in recent years in visualization and presentation techniques as well as in fine arts. Some aspects of creating a photorealistic computer animation are demonstrated by the following example of the film Illusion that was created by the computer graphics team at the University of Karlsruhe. An overview of modelling methods, some special effects and details on how to administrate a large computer animation project are presented.     

Untersuchungen zu Mesityldimethylhalogensilanen als Schutzgruppenreagenzien für Alkohole

Investigation on Mesityldimethylhalosilanes as Protectiv Reagents for Alcohols The use of mesityldimethylhalosilanes as protecting reagents for steroid alcohols was investigated. The resistance of the obtained silyl ethers was tested in various media. The reaction pathway of the acidic hydrolyses of the silyl ethers is explained.