Gas tight sintered material for high temperature sublimation setups

Fine powders of WC, TaC and TaC with W and WC additives were cold-isostatically pressed to ceramic discs and pressurelessly sintered at temperatures up to 2100 °C in a second step. Afterwards, the discs were tested as crucible lid under typical AlN growth conditions. The prepared discs should be gas tight and ensure a better alignment of the thermal expansion coefficients of TaC lid and AlN.Ceramic discs densified by this method reveal a relative density up to 97%. The TaC ceramic discs without additives show a microstructure with grain sizes in the range of 10-200 μm after sintering. The grain enlargement could be reduced by W and WC additives in the range of 1-5 wt.%. The results show that the AlN boules adhere only to WC lids and tungsten containing lids with W contents higher than or equal to 3 wt.%.     

U.v. irradiation-induced crosslinking of solid poly(ethylene oxide) modified with tetraalkyl ammonium salt

Crosslinked poly(ethylene oxide) (PEO) modified with a quaternary tetraalkyl ammonium salt, ethyl methacrylate dimethyldodecylammonium bromide, was prepared by exposure of the solid blend to ultraviolet radiation from a high-pressure 150 W mercury lamp. The photochemical crosslinking of the blends proceeded in the presence of benzophenone as a hydrogen-abstracting agent. Gel fraction yield exceeded 85%, equilibrium swelling in water varied from 3.0 to 5.0, and the equilibrium swelling in chloroform from 6.5 to 12.5. The networks obtained have been characterized by elemental analysis, i.r.,¹H n.m.r., and d.s.c. measurements and their microstructure, water absorption and equilibrium swelling have been discussed.     

721型分光光度计的保养与维修

分光光度计是石油化工实验室日常分析工作中常用的仪器，文中在简介仪器基本原理和的基础上，重点讨论了仪器的光中和电路两部分的常见故障及维护，维修问题。正确地调整光源和单色器，不但是操作人员所应具备的维护技巧。     

Elektromagnetische Vorgänge im Kurzschlußringbereich großer Käfigläufermotoren

Übersicht Betrachtet werden die Verluste im Kurzschlußringbereich von großen Induktionsmaschinen im Stillstand. Berücksichtigt werden die Stromverdrängung im Ring und die inhomogene Stromeinprägung der Stabströme in eine Seite des Ringes. Zusätzlich werden die Wirbelströme aufgrund des Ringstromfeldes in den dem Ring benachbarten Konstruktionselementen berechnet. Zur Überprüfung der mittels FEM-Rechnungen gewonnenen Erkenntnisse stehen Messungen an zwei Versuchsmaschinen zur Verfügung, bei denen Ausführung und Materialeigenschaften der K-Ring Konstruktionen variiert worden sind.

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Electromagnetic effects in the rotor-overhang of large cage induction motors

Contents This article describes the losses in the end ring area of large induction motors with locked rotor. The skin-effect and the inhomogenous impression of the bar currents in only one side of the ring are considered. Additionally the eddy currents in construction elements induced by the magnetic field of the current in the end-ring are calculated. Computational predicitons using the FEM are compared with the experimental results of two machines with several variations of the material and the strucutre of the end ring construction.

     

Clock gating methodologies and tools: a survey

Clock gating (CG) is a widely used design method for reducing the dynamic power consumption in digital circuits. Although it is a mature technique, theoretical work and tools for its application are still evolving and considered a matter of ongoing research, due to its significant effect in the overall power of the designs under study. This paper introduces a detailed review of the spectrum of CG approaches, theoretical and practical, from an architectural and register transfer level to synthesis, place and route, and testing issues. Furthermore, tools availability, limitations, and requirements concerning CG are examined for each design flow step. Conclusively, an evaluation of the presented techniques and literature is provided, estimating their usefulness and identifying areas for future research, exploration, and automation. Copyright © 2015 John Wiley & Sons, Ltd.     

Unterdrückung des Einschaltstromstoßes von Dreiphasen-Leistungstransformatoren durch gesteuertes Einschalten

Übersicht Ungesteuertes Einschalten von Leistungstransformatoren führt zu Einschaltstromstößen mit großen Amplituden und langen Abklingzeiten. Eine Möglichkeit, das zu verhindern, ergibt sich durch zeitlich gesteuertes Zuschalten der einzelnen Phasen unter Beachtung der Belastung und der Remanenzflüsse. In der Arbeit werden Schaltgesetze für das sequentielle Zuschalten der einzelnen Phasen bei Drei- und Fünf-Schenkel-Transformatoren angegeben. Messungen an einem Drei-Schenkel-Transformator in Y- und Yn-Schaltung verifizieren die Schaltgesetze.

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Suppression of the inrush current of three-phase power transformers by controlled switching-on

Contents Uncontrolled switching-on of power transformers leads to inrush currents with large magnitudes and small damping coefficients. One possibility to suppress that effect is given by controlling the switching moment for each winding with taking into account the load and remanence condition. The paper gives switching rules to manage the so called sequential switching of each phase of three- and five-leg-transformers. Measurements on a three-leg-transformer with Y- and with Yn-connected primary windings verify the switching rules.

     

Information technology enhanced learning in distance andconventional education

The rapid growth of the Internet and the media-rich extensions of the World Wide Web allow new developments in the way instructors transfer knowledge to their students. There is no doubt that nothing will replace synchronous learning through face to face interaction but it is sometimes not feasible for students to attend conventional classes due to distance or time constraints. This paper presents a model for using information technology to enhance the learning experience for conventional on-campus students, as well as for those students whose circumstances require that they be asynchronous in time or space. The approach described emphasizes a solution which allows students to attend the class in real time via the Internet, or to access asynchronously digitally stored video material with hyperlinks to online training resources at any time. The proposed solution permits interaction in real-time and asynchronously among students and between students and instructor, which is a key for effective learning. In addition, the instructor maintains a significant level of spontaneity in using multimedia material prepared in advance or using conventional chalkboard or hand written materials via traditional overhead projection. The paper describes the technical issues involved and the chosen solutions to provide enhanced live and archived classes. This paper provides some comments on the evaluation of the learning experience using this method of delivery for on-campus and distance education students. Finally the authors share their vision on future trends to improve the proposed learning environment and the need for an optimal balance between expositive teaching and active learning for both synchronous and asynchronous activities