Calcium Concentration Dependence of the Intergranular Film Thickness in Silicon Nitride

High-resolution electron microscopy and nano-beam analytical electron microscopy have been used to characterize both the intergranular silicate film thickness and its local composition in a series of high-purity Si₃N₄ ceramics doped with 0–450 at. ppm Ca. Calcium was detected at both two-grain junctions and triple junctions, even in the 80-ppm-Ca-doped specimen. The thickness of the intergranular film at two-grain junctions was found to depend sensitively on Ca content. In undoped material, the thickness was 1.0 ± 0.1 nm. With increasing Ca content, the thickness decreased in the dilute region (80 ppm Ca), but then increased. The variation in film thickness can be qualitatively understood in terms of the balance of three long-range forces acting normal to the film, namely the van der Waals dispersion force, a structural "steric" force, and an electrical-double-layer force. By comparing the measured thicknesses to those predicted, estimates for the structural correlation length and the inverse Debye length can be made. These estimates have values of ∼ 0.22 nm and approximately 0.3–0.5 nm, respectively, for the calcia-free and 80 ppm calcia materials.     

An Enantioselective Total Synthesis of (+)-Elenoic Acid and the Non-Natural Enantiomers of Tetrahydroalstonine,Aricine, and Reserpinine

A simple enantioselective synthesis of (+)epi-elenoic acid is reported and its transformation into (+)-elenoic acid is described. Well-established procedures transform these compounds into the antipodes of tetrahydroalstonine, aricine, and reserpinine.     

A Platform-Independent Methodology for Performance Estimation of Multimedia Signal Processing Applications

A methodological framework for performance estimation of multimedia signal processing applications on different implementation platforms is presented. The methodology derives a complexity profile which is characteristic for an application, but completely platform-independent. By correlating the complexity profile with platform-specific data, performance estimation results for different platforms are obtained. The methodology is based on a reference software implementation of the targeted application, but is, in constrast to instruction-level profiling-based approaches, fully independent of its optimization degree. The proposed methodology is demonstrated by example of an MPEG-4 Advanced Simple Profile (ASP) video decoder. Performance estimation results are presented for two different platforms, a specialized VLIW media processor and an embedded general-purpose RISC processor, showing a high accuracy of he methodology. The approach can be employed to assist in design decisions in the specification phase of new architectures, in the selection process of a suitable target platform for a multimedia application, or in the optimization stage of a software implementation on a specific platform.Hans-Joachim Stolberg received the Dipl.-Ing. degree in electrical engineering from the University of Hannover, Germany, in 1995.From 1995 to 1996, he worked at the NEC Information Technology Research Laboratories, Kawasaki, Japan, on efficient implementation of video compression algorithms. Since 1996, he has been with the Institute of Microelectronic Systems at the University of Hannover as a Research Assistant. During summer 2001, he was a Monbukagakusho Research Fellow at the Tokyo Institute of Technology, Japan. His current research interests include VLSI architectures for video signal processing, performance estimation of multimedia schemes, and profile-guided memory organization approaches for signal processing and multimedia applications.Mladen Bereković received the Dipl.-Ing. degree in electrical engineering from the University of Hannover, Germany, in 1995.Since then he has been a Research Assistant with the Institute of Microelectronic Systems of the University of Hannover. His current research interests include VLSI architectures for video signal processing, MPEG-4, System-on-Chip (SOC) designs, and simultaneously multi-threaded (SMT) processor architectures.Peter Pirsch received the Ing. grad. degree from the engineering college in Hannover, Germany, in 1966, and the Dipl.-Ing. and Dr.-Ing. degrees from the University of Hannover, in 1973 and 1979, respectively, all in electrical engineering.From 1966 to 1973 he was employed by Telefunken, Hannover, working in the Television Department. He became a Research Assistant at the Department of Electrical Engineering, University of Hannover, in 1973, a Senior Engineer in 1978. During 1979 to 1981 he was on leave, working in the Visual Communications Research Department, Bell Laboratories, Holmdel, NJ. During 1983 to 1986 he was Department Head for Digital Signal Processing at the SEL Research Center, Stuttgart, Germany. Since 1987 he is Professor in the Department of Electrical and Computer Engineering at the University of Hannover. He served as Vice President Research of the University of Hannover from 1998 to 2002.His present research includes architectures and VLSI implementations for image processing applications, rapid prototyping and design automation for DSP applications. He is the author or coauthor of more than 200 technical papers. He has edited a book on VLSI Implementations for Image Communications (Elsevier 1993) and is author of the book Architectures for Digital Signal Processing (John Wiley 1998).Dr. Pirsch is a member of the IEEE, the German Institute of Information Technology Engineers (ITG) and the German Association of Engineers (VDI). He was recipient of several awards: the NTG paper price award (1982), IEEE Fellow (1997), IEEE Circuits and Systems Golden Jubilee Medal (1999). He was member or chair of several technical program committees of international conferences and organizer of special sessions and preconference courses. He has held several administrative and technical positions with the IEEE Circuits and Systems Society and other professional organizations. Dr. Pirsch currently serves as Vice President Publications of the IEEE Circuits and Systems Society. Since 2000 he is chairman of the Accreditation Commission for Engineering and Informatics of the Accreditation Agency for Study Programs in Engineering, Informatics, Natural Science and Mathematics (ASIIN). Dr. Pirsch is chair of the VDI committee on Engineering Education.     

Zur Messung der Oberfläche von Spanplatten

Zusammenfassung Die Oberfl?chen von Spanplatten sind für deren Weiterverarbeitung von Bedeutung. Die Frage der Technik zur Messung der Oberfl?chengüte von Spanplatten wird er?rtert. Im Zusammenhang mit eigen Untersuchungen werden Vorschl?ge für die Oberfl?chenmessungen mit Hilfe des Tastschnittverfahrens gemacht. Die zur Durchführung des Verfahrens notwendige Quellung der zu prüfenden Spanplattenobertl?chen erfolgt bei Wasserlagerung rund hundertmal schneller als bei Lagerung in feuchter Luft. Eine Erh?hung des Hydrophobierungsmittel-Gehaltes der Decklagenp?ne, zeigt keinen nennenswerten Einflu? auf den Verlauf der Decklagenquellung. Mit hoher Decklagen-Spanfeuchtigkeit hergestellte Platten weisen nach 24 h Wasserlagerung eine nur geringe Rauhtiefenzunahme auf. Spanplatten, die mit Schleifpapier feinerer K?rnung geschliffen werden, zeigen auch nach einer Wasserlagerung glattere Fl?chen als mit grober K?rnung gechliffene Platten. Das Befeuchten der Spanplattenoberfl⇂hen vor dem Schleifen ergibt eine merkliche Verminderung der Rauhtiefenzunahme gegenüber nicht befeuchteten Oberfl?cher. Für die Untersuchung unbehandelter Spanplatten-oberfl?chen ist das Pastentestverfahren nach H. Flemming gut geeignet.

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Measuring of the surface of particleboard

Summary The surfaces of particleboard are of importance for their finishing. The problem of technics concerning the measurement of surface quality of particleboard is discussed. In connection with own investigations proposals for surface measurements with the tracer method are made. The swelling of the particle-board to be tested necessary for the procedure is, with watering achieed about a hundred times quicker than in humid air. An increase in the content of water-repellent agent in the outer layer does not show any significant effect on the swelling of surface layers. After 24 h of watering, boards produced with a high moisture content of the surface layers show merely a slight increase in roughness. Particleboard sanded with sandpaper of a finer grit even after watering shows a smoother surface than boards sanded with a coarser grit. The wetting of the particleboard surfaces prior to sanding yields a notable diminishing of the roughness increase as against not wetted surfaces. For the investigation of untreated particleboard surfaces the Pastentest procedure according to H. Flemming is well suited.

     

Bioinspired Intervertebral Disc with Multidirectional Stiffness Prepared via Multimaterial Additive Manufacturing

Degenerative disc disease (DDD) has become a significant public health issue worldwide. This can result in loss of spinal function affecting patient health and quality of life. Artificial total disc replacement (A-TDR) is an effective approach for treating symptomatic DDD that compensates for lost functionality and helps patients perform daily activities. However, because current A-TDR devices lack the unique structure and material characteristics of natural intervertebral discs (IVDs), they fail to replicate the multidirectional stiffness needed to match physiological motions and characterize anisotropic behavior. It is still unclear how the multidirectional stiffness of the disc is affected by structural parameters and material characteristics. Herein, a bioinspired intervertebral disc (BIVD-L) based on a representative human lumbar segment is developed. The proposed BIVD-L reproduces the multidirectional stiffness needed for the most common physiological kinematic behaviors. The results demonstrate that the multidirectional stiffness of the BIVD-L can be regulated by structural and material parameters. The results of this research deepen knowledge of the biomechanical behavior of the human lumbar disc and may provide new inspirations for the design and fabrication of A-TDR devices for both engineering and functional applications.     

Zur Prüfung der Witterungsbeständigkeit zementgebundener Holzspanplatten

The duration against weathering is of special importance when using cement bonded particleboards for structural purposes. To determine those properties cement bonded particleboards of various types, uncoated as well as coated, were tested under open air weathering conditions and with the Xenotest-weathering-apparatus. Possible qualitative changes were observed by determining bending strength and crushing strength. It could be noted, that the use of additives reduced the duration against weathering. It resulted as well, that insufficient coatings (i.e. dispersion based resins) remarkably reduce the duration as compared to more suitable coating systems.