Rheological study on structural transition in polyethersulfone‐modified bismaleimide resin during isothermal curing

The structural transition in the polyethersulfone (PES)‐modified bismaleimide resin, 4,4′‐bismaleimidodiphenylmethane (BDM), during isothermal curing was studied by using rheological technique, different scanning calorimetry (DSC), and time resolved light scattering (TRLS). Comparing with the cure of neat bismaleimide, two separate tan δ crossover points were observed because of the phase separation during curing the blends of PES/BDM. These two structural transitions stemmed from the fixing of phase structure of the system and the chemical crosslinking of bismaleimide, respectively. The effect of curing temperature and the PES content on structural transition was discussed and found that the occurrence of two structural transition exhibited the different dependency of curing temperature and PES content. The relaxation exponent n and gel strength S were also found to be temperature‐dependent and composition‐dependent. Moreover, the relaxation exponent n of the second structural transition is much lower than that of the first structural transition in the PES/bismaleimide blends. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3102–3108, 2006     

磁随机存储器中垂直电流驱动的磁性隧道结自由层的磁化翻转

在基于磁性隧道结(Magnetic Tunneling Junction，MTJ)的磁随机存储器(Magnetoresistantive Random Access Memory，MRAM)中利用通过MTJ的垂直电流，实现信息写入的新方法，同时给出了基于此新方法的一种新的MRAM结构和驱动原理图，并分析了它的读和写操作的可行性具体过程. 关键词： 垂直电流 磁性隧道结 磁随机存储器     

Optimal control of price and production in an assemble-to-order system

We study the optimal control of an assembly system that produces one assembled-to-order final product with multiple made-to-stock components and sells it at variable price. It is shown that a threshold control on component production, product price, and product orders maximizes total discounted profit over an infinite horizon.     

Solution to the Cosmological Constant Problem by Gauge Theory of Gravity

Based on geometry picture of gravitational gauge theory, the cosmological constant is determined theoreti-cally. The cosmological constant is related to the average energy density of gravitational gauge field. Because the energydensity of gravitational gauge field is negative, the cosmological constant is positive, which generates repulsive force onstars to make the expansion rate of the Universe accelerated. A rough estimation of it gives out its magnitude of theorder of about 10-52m-2, which is well consistent with experimental results.     

酞菁锌掺杂二氧化硅凝胶基质的光谱学特征

利用溶胶凝胶技术将四磺化酞菁锌 (ZnPcS4)成功地引入到了二氧化硅凝胶基质中 ,制备了均匀掺杂的有机 /无机复合干凝胶。研究ZnPcS4分子在溶胶凝胶过程中紫外可见吸收光谱的变化规律以探索其在复合体系中的存在状态。实验表明 ,在溶胶阶段 ,随着时间的延长 ,紫外可见吸收光谱中单体的吸收峰强度增大 ,说明凝胶中酞菁单体的浓度增大 ;而形成凝胶后 ,随着时间的延长 ,紫外可见吸收光谱中单体的吸收峰强度减小 ,二聚体的吸收峰强度增大 ,说明由于体系结构和微化学环境的变化 ,酞菁分子趋向于聚合。     

Preparation and characterizations of novel zwitterionic membranes

A novel route was proposed for preparation of zwitterionic membranes, and it comprises (1) free radical polymerization between glycidylmethacrylate (GMA) and acrylic acid (AA) monomers and (2) subsequent ring-opening of epoxide and quaternary amination with trimethylamine hydrochloride. The reaction products were confirmed by FTIR spectra. The cation-exchange capacities (CIECs) and anion-exchange capacities (AIECs) of these zwitterionic membranes are within the range of (5.4–9.3) × 10⁻² and (30.6–11.1) × 10⁻² mmol g⁻¹, respectively. In addition, the CIEC increases as AA content increases, but the AIEC generally decreases. TGA and DrTGA measurements reveal that their thermal stabilities can arrive at as high as 380 °C. The water uptake is independent of pH. As for membrane potential and streaming potential, they both suggest that these membranes possess the characteristics of anion-exchange membranes and no IEP is observed. Permeation experiments of mixed KCl and glucose solution indicate that the transport behavior of ions is dependent on the membrane’s charge density.     

Study on the effect of mechanical alloying on properties of Zn-Sb alloy

The effect of mechanical alloying on Zn-Sb alloy system is investigated with X-ray diffraction (XRD), laser grain size analysis and differential scanning calorimetry (DSC) respectively. The results of laser particle size analysis shows that the particle size decreases with increasing of the grinding time between 0 and 24 h. XRD and DSC results indicate that longer the grinding time of Zn-Sb is, the more content of Zn₄Sb₃ become in the product in this process.     

亚纯函数导数的亏量和

设ｆ（ｚ）是开平面Ｃ内的亚纯函数，Ｅ．Ｍｕｅｓ证明了对任何自然数ｋ有杨乐推广以上不等式，证明了本文推广了以上结果，证明了以下定理：设ｆ（ｚ）为亚纯函数，则对任何自然数ｋ有例子显示此不等式是精确的。     

The Degradation of Beam Quality in Large-Core Optical Fiber

The degradation of beam quality in large-core fiber is investigated experimentally. It is found that the output beam quality factor M2 is a compound tanh function ofthe fiber lengths and misalignment launch results that the beam quality degraded faster.