Synthesis of bis-ketene N,S-acetals with a polymethylene linkage

α-Aroyl substituted bis-ketene N,S-acetals 3–6 with a polymethylene linkage, N,N′-bis(1-methylthio-2-aroyl)vinyl polymethylene diamines, were synthesized by reactions between α-aroyl ketene dithioacetals 1 and polymethylene diamines 2 in moderate yields. © 1996 John Wiley & Sons, Inc.     

Ring-opening polymerization of macrocyclic aryl ether ketone oligomers containing the 1,2-dibenzoylbenzene moiety

Facile ring-opening polymerization of cyclic aryl ether oligomers containing the 1,2-dibenzoylbenzene moiety to form high molecular weight linear polymers in the presence of a nucleophilic initiator is described. The polymerization can be initiated in the melt in the presence of a nucleophilic initiator such as potassium carbonate, cesium fluoride, and alkali phenoxides. Various alkali phenoxides were investigated as potential nucleophilic initiators. The polymerization reaction rate in the melt increases in the order of K⁺ > Na⁺ > Cs⁺, and in the order of ⁻OPhPhO⁻ > PhO⁻ > PhOPhO⁻ > PhPhO⁻. However, the polymerization in an aprotic dipolar solvent is faster in the presence of cesium phenoxide than in the presence of potassium phenoxide. Polymerization of the cyclic oligomers in solution demonstrates that the ring-opening polymerization proceeds via a chain-growth mechanism and involves a transetherification reaction between linear and cyclic aryl ether oligomers. The ring-chain equilibrium is much more favorable towards linear polymers. Since little or no ring strain exists in the cyclic system, the transetherification reactions are indiscriminate with regards to cyclic or linear chains and the interchain equilibration is also a facile process during polymerization. This intermolecular transetherification has been demonstrated by using low molecular weight aryl ethers to control the molecular weight of the polymer formed via ring-opening polymerization. © 1996 John Wiley & Sons, Inc.     

Packing of three copies of a graph

A graph of order n is said to be 3-placeable if there are three edge-disjoint copies of this graph in K_n. An (n, n − 1)-graph is a graph of order n with n − 1 edges. In this paper we characterize all the (n, n − 1)-graphs which contain no cycles of length 3 or 4 and which are 3-placeable. © 1996 John Wiley & Sons, Inc.     

Total integrated reflection loss in a laser diode to single-mode fibre coupling system

A geometrical optics approach is used to analyse the reflection of a divergent beam falling onto a concave or convex surface. The polarisation state of a ray in the incident beam depends on the position where the ray impinges upon the surface. The distribution of transmittance over the surface for different polarisation states is determined. An integration of the transmittance distribution determines the total reflection loss of a coupling lens used in a laser diode to single-mode fibre coupling system.     

Epoxidation of styrene catalyzed by metal complexes of poly(vinylbenzyl)acetylacetonate

The epoxidation of styrene to styrene oxide at higher than 96% yield has been achieved by the catalysis by poly-(vinylbenzyl)acetylacetonate complexes of cobalt(II) or manganese(II) in the presence of isobutyraldehyde under an atmospheric pressure of molecular oxygen at room temperature. The kind of aldehyde and aldehyde/styrene molar ratio greatly influenced the reaction. The catalyst could be recycled, but after recycling for five times, the yield of styrene oxide decreased from 96.0% to 84.6%.     

Effect of Cu Ions on the Dipole Moments and Polarization of Strontium Barium Niobate Single Crystals

The crystal growth, the ferroelectric hysteresis loops, and the infrared reflectivity spectra of coppermodified strontium barium niobate (SBN) single crystals are reported. Compared with the undoped SBN crystals, the copper-modified crystals have stable hysteresis loops, the spontaneous polarization of which is about 0.30 C/m², but that of the undoped SBN crystals is only about 0.12 C/m². Their coercive field strength is all about 340 V/mm. The experimental results of the infrared spectra show that the infrared reflectivities vary as the orientations of the dipole moments owing to the copper-doping. The c-axis becomes the most stable orientation of the dipole moments, and the polarization will be locked and won't recede if the copper-modified crystals are polarized into monodomains.     

系统设计中如何节省转发器带宽的占用

本文根据村通工程中的实际情况,提出了3种节省转发器带宽的方法,并提出了不同技术适用的条件和需要注意的问题.     

无按键时代即将到来——Cypress的电容感应解决方案:界面设计的革命

从手机到汽车音响面版的传统用户界面设计,都包含了没有区别的笨拙的旋钮、拨号盘和按键.一直以来,各个消费电子产品公司的工业设计和产品营销部门都在寻找使他们的产品区别于市场上其他产品的方法,以便获得竞争优势.Cypress的电容感应解决方案迎接了这一挑战并为差异化的设计提供了无限的可能性.     

Interference suppressing for cellular MIMO system based on turbo receiver

Space-Time Coding （STC）, which combines channel coding, modulation, and multiple transmit antennas, is a powerful scheme to achieve higher data rates and combat fading in wireless systems, in this paper, we propose a soil/cancellation turbo equalization scheme to suppress Co-Channel Interference （CCI） in STC systems. The simulation results show that the proposed method significantly improves the system＇s ability of interference suppression, while preserving the space-time structure.