Towards a one‐pot synthesis of a polystyrene–PMMA block copolymer via atom‐transfer radical polymerization

The solution atom‐transfer radical copolymerization of styrene and methyl methacrylate in butyl acetate at 110 °C in the presence of Cu(II) bromide and 2,2′‐bipyride was investigated. Polystyrene was polymerized by atom‐transfer radical polymerization using benzyl bromide as initiator and MMA was then added to the system. Block copolymers were formed when MMA was added at ≤90% styrene conversion. Molecular weight distributions (M_w/M_n) of the block copolymers were ≤1.5. The possibility of end‐capping the polystyrene precursor as a means of improving its initiating efficiency towards MMA was also investigated but did not improve the system. © 2002 Society of Chemical Industry     

Fatigue crack propagation and cyclic deformation at a crack tip

The fatigue crack propagation relation da/dN = f(R)ΔK² can be derived with three assumptions: small scale yielding, material homogeneity and that crack tip stresses and strains are not strongly affected by plate thickness. f(R) is a constant at a given stress ratio, R. The effects of plate thickness and stress ratio on crack tip deformation and fatigue crack growth in 2024-T351 aluminum alloy were studied. High ΔK level in a thin specimen causes crack tip necking. Necking is more pronounced at high stress ratio. Necking causes high maximum strain near a crack tip, ε_max, and fast crack growth rate. In order to avoid the effects of crack tip necking, plates thicker than 2.5 (ΔK/σ_Y(c))² should be used.     

Effect of V2O5 and CuO additives on sintering behavior and microwave dielectric properties of BiNbO4 ceramics

The influences of V₂O₅ and CuO additives on the sintering behavior and microwave dielectric properties of BiNbO₄ ceramics were investigated. The V₂O₅ and CuO additives lowered the sintering temperature of BiNbO₄ ceramics to the range 875 °C–935 °C. All BiNbO₄ compounds with additives had the orthorhombic structure. The dielectric constant _r was not significantly changed, while the unloaded Q value was affected with additives. The Qf value was found to be a function of the sintering temperatures and the amount of additives. It varied from 4500 to 15800 (GHz) and 1000 to 8000 (GHz) with additives V₂O₅ and CuO, respectively. The _f values were increased in positive values with V₂O₅ doped, while decreased in negative values with CuO addition. V₂O₅ and CuO additives effectively improved the densification and dielectric properties of BiNbO₄ ceramics. The correlation between the microstructure and the Qf value was observed with different additives.     

浅谈材料运用与椅子设计的“骨肉”之情

随着时代的发展,工艺的进步,椅子的制作从木材的榫卯结合到金属材质的焊接再到塑料、玻璃纤维的压模成型;从皮革的缝制到棉麻布艺的胶合剂粘结……为实现椅子的种种功能,设计师们选用了各种材料,椅子也发展得千形万状。材料对于椅子来说是皮、是肉、更是骨。     

Study on laser welded heat-affected zone in new ultralow carbon bainitic steel

800 MPa grade ultralow carbon bainitic （NULCB） steel is the recently developed new generation steel, which was produced by thermo mechanical controlled processing ＆ relaxation-precipitation controlling transformation （TMCP＆RPC） tech- nique. The microstructure and the mechanical properties of the heat-affected zone （HAZ） in NULCB steel under laser welding conditions were investigated by using a Gleeble-1500 thermal simulator. The experimental results indicate that the simplex microstructure in the HAZ is granular bainite that consists of bainite-ferrite （BF） lath and M-A constituent when the cooling time from 800 to 500℃ （t8/5） is 0.3-30 s, and the M-A constituent consists of twinned martensite and residual austenite. As t8/5 increases, the hardness and tensile strength of HAZ decreases, but they are higher than that of the base metal, indicating the absence of softened zone after laser welding. The impact toughness of HAZ increases at first and then decreases when t8/5 increases. The impact energy of HAZ is much higher than that of the base metal when t8/5 is between 3 and 15 s. It indicates that excellent low temperature toughness can be obtained under appropriate laser welding conditions.     

基于AVS技术IPTV的实现

介绍宽带网络数字电视IPTV的实现方法,探讨了如何利用AVS音视频编码压缩技术使编码的视频流能够有效地适应网络带宽的波动,从而保证宽带网能传输高质量音视频信号.     

浅谈通信监理项目的绩效管理

近年来，在国家扩大内需的政策指导下，工程建设在各个行业都有较大规模的增长，这为工程监理企业提供了难得的发展机遇。但随着我国加入世界贸易组织，咨询市场进一步开放，监理企业间的竞争也日趋激烈。除了资金、技术及经营等方面的比拼，人力资源更日益成为影响企业竞争力的关键因素。[第一段]     

A Penetrating Gaze at One Open Phase: Analyzing the Polyphase Induction Motor Dilemma

Portions of the material proposed for a chapter in a new IEEE Standard (#399-the ``Brown Book') being prepared by the Power System Analysis Subcommittee of the I & CPS Committee are presented. In order to establish a library of approved analytical methods, the material provides a review of the more important basic electrical circuit analysis techniques used for determining the voltage and current relationships which describe various power system network events and operating conditions. Certain simplified circuit arrangements are examined. They illustrate the power and merit of the analytical methods that evolve, as well as the errors that can occur because of improper regard for the restraints that apply. Using the analytical methods, the classical problem of a three-phase induction motor operating with one phase of the supply line open-circuited is studied in considerable detail. Finally, important observations and conclusions are presented regarding the motor protection requirements.     

Impact of quality management practices on the knowledge creation process: The Chinese aviation firm perspective

Contemporary quality management studies describe a range of quality improvement strategies. However, these studies do not consider the impact of quality management practices on the knowledge creation process. Based on a comprehensive literature review and a field survey, this study investigates the impact of quality management practices on the knowledge creation process. A proposed model and hypotheses are presented and tested using survey data collected from aviation firms in China. The test of the structural model supports some proposed hypotheses. We find that employee training, employee involvement, product design, benchmarking, and vision statement have significant direct impacts on the knowledge creation process. We also find that some other quality management practices, such as top management support, customer focus, supplier quality management, quality information, and recognition and rewards, do not have a direct impact on knowledge creation. Suggestions for the improvement of quality management in aviation firms in China are provided. The implications of the findings for researchers and practitioners are discussed, and further research directions are offered.