Modifizierung des ABSE‐Polycarbosilazans mit Multi‐Walled Carbon Nanotubes zur Herstellung spinnfähiger Massen

Modification of the ABSE polycarbosilazane with multi‐walled carbon nanotubes for the creation of spinable masses An inexpensive method has been found to produce ceramic SiCN‐fibres via the precursor route consisting of five processing steps: synthesis of the polymer, preparation of the spinning mass, melt‐spinning, curing via electron beam and subsequent pyrolysis at 1100 °C in a nitrogen atmosphere. A special solid and meltable fibre polymer, the so‐called polycarbosilazane ABSE, has been developed in the last decade for this purpose. Due to its low molecular weight, an adequate catalytic and thermal aftertreatment was necessary to guarantee a stable melt‐spinning process. This article discusses an alternative way to prepare a qualified spinning mass, i.e. the addition of Multi‐Walled Carbon Nanotubes (MWCNTs) to the ABSE melt. For this purpose a homogeneous dispergation of the MWCNTs in the ABSE matrix is necessary. In this study, spinning masses were fabricated in different ways. By optical analysis and comparison of the level of dispergation in these spinning masses an optimized process for integration of the MWCNTs was identified. The influence of the addition of a dispersing agent is investigated as well. In using a dispersing agent, the level of homogeneous dispersion of the MWCNTs increases whereas the interactions between the particles and the precursor melt decrease. In first spinning experiments a good spinability of the masses were noticed. Thus the addition of MWCNTs represents a new way to modify the ABSE precursor for the melt‐spinning process.     

Ornament and function

The architects and builders in the past lacked our knowledge concerning fluid dynamics, but they exhibited a deep rooted ability to observe and reflect - thus, different cultures have developed by trial and error. The authors have produced a stimulating analysis which couples the science of fluid dynamics and a sensitive understanding of past cultures. The paper is recommended reading.     

Series resonant ZCS‐PFM DC‐DC power converter with high‐frequency high‐voltage transformer link for high‐power magnetron drive

This paper presents a single lossless inductive snubber‐assisted ZCS‐PFM series resonant DC‐DC power converter with a high‐frequency high‐voltage transformer link for industrial‐use high‐power magnetron drive. The current flowing through the active power switches rises gradually at a turned‐on transient state with the aid of a single lossless snubber inductor, and ZCS turn‐on commutation based on overlapping current can be achieved via the wide range pulse frequency modulation control scheme. The high‐frequency high‐voltage transformer primary side resonant current always becomes continuous operation mode, by electromagnetic loose coupling design of the high‐frequency high‐voltage transformer and the magnetizing inductance of the high‐frequency high‐voltage transformer. As a result, this high‐voltage power converter circuit for the magnetron can achieve a complete zero current soft switching under the condition of broad width gate voltage signals. Furthermore, this high‐voltage DC‐DC power converter circuit can regulate the output power from zero to full over audible frequency range via the two resonant frequency circuit design. Its operating performances are evaluated and discussed on the basis of the power loss analysis simulation and the experimental results from a practical point of view. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(3): 79–87, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20126     

A simplified cascade current‐source inverter interconnected to a single‐phase three‐wire distribution system and its application to electric energy storage systems with batteries

A novel current source inverter system interconnected to the single‐phase grid is proposed. It has the same construction as the conventional three‐phase current source inverter that is interconnected to the single‐phase three‐wire distribution system. Though the proposed circuit has no output transformer, it can be equivalently performed as the single‐phase double cascade inverter by diverting the pole transformer in the utility system. By controlling the appropriate scheme, the output currents can be obtained as the five‐level waveforms and their distortions can be decreased sufficiently. It is applied to the interactive electric energy storage system with batteries and the basic discharging characteristics are discussed experimentally. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(2): 50–61, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10380     

宽频带函数波形产生器的研制

本文介绍以ＭＡＸ０３８为基础而研制的宽频带函数波形产生器，它可以产生２￣２×＾７Ｈｚ频率范围的正弦波、三角波、锯齿波和矩形波以及与它们同步的ＴＴＬ脉冲信号。     

Authority updating: An expert authority evaluation algorithm considering post‐evaluation and power indices in social networks

In group assessment, the focus is on finding high‐authority experts to improve the reliability of assessment results. In this study, we propose an authority updating algorithm while considering the power and judgement reliability of an expert on the basis of social networks and post‐evaluations. A network power index is established and used to reflect the power of an expert while considering social networks. The measurement of the judgement reliability of an expert considers the post‐evaluation of the objects selected by experts, thereby more scientifically reflecting the reliability of experts. The analysis shows the following: although the social‐network structure influences the authority of experts, the influence weakens when the assessment group is a highly or even fully connected group; the network effect may increase the authority of some experts and reduce that of others, and it will weaken as the network connectivity increases; moreover, the judgement reliability and authority of an expert while considering post‐evaluation can encourage him/her to make fair assessments and strive to reduce his/her motivation and cognitive biases.     

Positive state‐bounding observer for positive interval continuous‐time systems with time delay

This paper is concerned with the problem of positive observer synthesis for positive systems with both interval parameter uncertainties and time delay. Conventional observers may no longer be applicable for such kind of systems due to the positivity constraint on the observers, and they only provide an estimate of the system state in an asymptotic way. A pair of positive observers with state‐bounding feature is proposed to estimate the state of positive systems at all times in this paper. A necessary and sufficient condition for the existence of desired observers is first established, and the observer matrices can be obtained easily through the solutions of a set of linear matrix inequalities (LMIs). Then, to reduce the error signal between the system state and its estimates, an iterative LMI algorithm is developed to compute the optimized state‐bounding observer matrices. Finally, a numerical example is presented to show the effectiveness and applicability of the theoretical results. Copyright © 2011 John Wiley & Sons, Ltd.     

高等教育服务承诺与政府规制改革

高等教育服务是一个具有时代特征的历史现象 ,在当前显露出全球化背景下经济行为与文化行为互动性特征 ,站在综合国力提升和国际竞争力增强的战略高度审视高等教育服务贸易的长远影响至关重要。通过政府规制改革 ,建立起本国能够负责任地采纳并被其他成员国创造性地适应的高等教育及其服务贸易发展模式是各国政府的重要责任     

Soap‐free emulsion copolymerization of perfluoroalkyl acrylates in the presence of a reactive surfactant

Soap‐free emulsion copolymerization of perfluoroalkyl acrylate (FA)/methyl methacrylate (MMA)/n‐butyl acrylate (n‐BA) was carried out in the presence of sodium 2‐acrylamide‐2‐methyl propanesulfonate (AMPSNa) as a reactive surfactant and potassium persulfate (KPS) as an initiator. An analysis of the effects of concentration of AMPSNa, KPS, FA as well as polymerization temperature on the kinetic features (rate of polymerization) and colloidal characteristics (mean particle diameter, particle disperse index, particle numbers, and surface charge density) was followed. NMR, FTIR, AFM, and fluorine‐selective electrode analysis were used to characterize the composition and morphology of the FA copolymers. Both AFM analysis and contact angle measurements strongly implied that the fluorinated segments migrated to the outmost surface and created films with lower surface energy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2438–2444, 2007