Development and characterization of a biocompatible OH-modified copolymer based on polyurethane

Different polyurethanes were synthesized by varying the diol as well as the diisocyanate components and chain extenders. Polyurethanes with OH-groups were obtained by photo- and thermoinitiation of the radical polymerization of hydroxy alkyl acrylates in the presence of the polyurethanes. The polymers were evaluated with respect to their biocompatibility by measuring the cell spreading, the rates of DNA- and protein synthesis and the swelling behaviour. The differences in the surfaces and the bulks between the selected basic polyurethane and the functionalized modification were determined and characterized by XPS, FTIR-ATR and ¹³C-FT-NMR-spectroscopy. The mechanical data of Tecoflex EG 60D® and Pellethane 2363–80AE® were compared with the data of the synthesized polyurethanes.     

Membranen in der Verfahrenstechnik

Membranes in chemical engineering . In the last 10 years membranes and membrane processes have evolved from a useful laboratory tool to an industrial product of significant technical and commercial impact. In some applications membrane processes have today not only replaced some conventional separation procedures in the chemical process industry, because they are often more economical and yield better quality products, but they have also successfully been utilized to solve mass separation problems where conventional procedures failed or are too expensive. This contribution discusses the state of the art of membranes and membrane processes as well as their major applications, with the main emphasis being placed on more recent developments.     

冠带层新平台技术

子午线轮胎出现不久，就采用钢丝带束层代替了纤维带束层，这对于实现子午线轮胎提高使用寿命和改善操纵性能的潜能是必要的。     

Physical gelation of crystallizing metallocene and Ziegler-Natta ethylene-hexene copolymers

The effect of molecular architecture on the evolution of viscoelastic properties during crystallization was investigated using ethylene-hexene copolymers manufactured via metallocene (M-LLDPE) and Ziegler-Natta (ZN-LLDPE) processes. Differences in branching distribution were shown to have a drastic effect on the viscoelastic properties near the gel point. It is shown that the branching distribution rather than branch content is the determining parameter for the evolution of the rheological properties during isothermal and non-isothermal crystallization, and for the width of the solidification interval. We developed a partial melting technique for the preparation of stable critical gels of LLDPE whose viscoelastic properties correspond to the intermediate state between melt and solid. Local molecular conformation and crystallinity in these gels were characterized by Raman spectroscopy, which shows that the transition from melt-like to solid-like rheological behavior (physical gelation) in LLDPE occurs at a very low overall crystallinity of less than 5%.     

Search combinators

The ability to model search in a constraint solver can be an essential asset for solving combinatorial problems. However, existing infrastructure for defining search heuristics is often inadequate. Either modeling capabilities are extremely limited or users are faced with a general-purpose programming language whose features are not tailored towards writing search heuristics. As a result, major improvements in performance may remain unexplored. This article introduces search combinators, a lightweight and solver-independent method that bridges the gap between a conceptually simple modeling language for search (high-level, functional and naturally compositional) and an efficient implementation (low-level, imperative and highly non-modular). By allowing the user to define application-tailored search strategies from a small set of primitives, search combinators effectively provide a rich domain-specific language (DSL) for modeling search to the user. Remarkably, this DSL comes at a low implementation cost to the developer of a constraint solver. The article discusses two modular implementation approaches and shows, by empirical evaluation, that search combinators can be implemented without overhead compared to a native, direct implementation in a constraint solver.     

On preconditioning for a parallel solution of the Richards equation

In this paper, we present a class of preconditioning methods for a parallel solution of the three-dimensional Richards equation. The preconditioning methods Jacobi scaling, block-Jacobi, incomplete lower–upper, incomplete Cholesky and algebraic multigrid were applied in combination with a parallel conjugate gradient solver and tested for robustness and convergence using two model scenarios. The first scenario was an infiltration into initially dry, sandy soil discretised in 500,000 nodes. The second scenario comprised spatially distributed soil properties using 275,706 numerical nodes and atmospheric boundary conditions. Computational results showed a high efficiency of the nonlinear parallel solution procedure for both scenarios using up to 64 processors. Using 32 processors for the first scenario reduced the wall clock time to slightly more than 1% of the single processor run. For scenario 2 the use of 64 processors reduces the wall clock time to slightly more than 20% of the 8 processors wall clock time. The difference in the efficiency of the various preconditioning methods is moderate but not negligible. The use of the multigrid preconditioning algorithm is recommended, since on average it performed best for both scenarios.     

Hidden Markov model-based ensemble methods for offline handwritten text line recognition

This paper investigates various ensemble methods for offline handwritten text line recognition. To obtain ensembles of recognisers, we implement bagging, random feature subspace, and language model variation methods. For the combination, the word sequences returned by the individual ensemble members are first aligned. Then a confidence-based voting strategy determines the final word sequence. A number of confidence measures based on normalised likelihoods and alternative candidates are evaluated. Experiments show that the proposed ensemble methods can improve the recognition accuracy over an optimised single reference recogniser.