Homopolymerization and Copolymerization of Isoprene and Styrene with a Neodymium Catalyst Using an Alkylmagnesium Cocatalyst

The catalyst system Nd(acac)₃·2 H₂O/Bu₂Mg/CHCl₃ shows a fairly high activity in both the homo‐ and copolymerization of isoprene (IP) and styrene (St) in toluene at 60°C. Copolymers obtained from various comonomer feed ratios were characterized by means of NMR spectroscopy and gel‐permeation chromatography. The polyisoprene and poly(IP‐co‐St) obtained predominantly consist of cis‐1,4 IP units. Monomer reactivity ratios were evaluated to be r_IP = 5.4 and r_St = 0.38 in the copolymerization.     

锂离子电池中固体电解质界面膜(SEI)研究进展

本文综述了锂离子电池中固体电解质界面膜(SEI膜)的研究进展.在总结SEI膜的形成机理及模型的基础上,讨论了对SEI膜可能的影响因素及其改性方法,以及各种表征技术、特别是原位分析技术在SEI膜研究中的实际应用.指出在今后的研究中,正极表面与电解液间的界面膜,以及引入水溶性粘合剂体系后正负极表面与电解液间的相互作用将成为人们关注的热点。     

二阶声低通滤波光纤水听器的声压灵敏度频响特性

信号混叠是基于光纤水听器的现代声纳系统走向应用必须解决的一个关键问题.初步的实验结果已经表明,声低通滤波光纤水听器是解决信号混叠问题的一种简单且行之有效的方案.基于电一声类比理论,建立了声低屯瞬ü庀怂鞯牡推导胁瘟磕Ｐ?利用电路分析的方法对其频响特性进行了研究.结果表明,这种光纤水听器系统与典型的二阶低通滤波电路具有相似的频响特性.为了验证理论分析的正确性,设计制作了一个简单的声低通滤波光纤水听器,并在驻波罐中对其声压灵敏度频响特性进行了测试,实验结果与数值计算的结果基本吻合.该光纤水听器低频响应非常平坦,声压灵敏度约为-141 dB,测量共振频率为985 Hz,与理论值1270 Hz基本一致.共振频率处的声压灵敏度为-126.8 dB,衰减速率约为20 dB/倍频程,3000 Hz以后的灵敏度衰减幅度大于20 dB.     

超临界流体技术制备纳米材料的研究与展望

纳米科技是人们普遍关注的重要领域,而纳米材料充当其中的基础性角色。本文介绍了在新兴绿色环保介质——超临界流体中纳米材料的合成及其制备,涉及范围包括从准零纳米微粒到三维纳米材料,从无机纳米材料到有机聚合物纳米材料。其中不仅介绍了超临界流体中纳米材料的制备方法,同时也包括制备过程中超临界流体特殊性质,如溶胀、塑化和地表面张力所起的重要作用,并对超临界流体技术在纳米材料制备中的应用前景进行展望。     

Li~+对Tb~(3+)掺杂硅酸盐玻璃闪烁性能的影响

利用高温熔融法制备了Li+掺杂Tb3+激活硅酸盐闪烁玻璃。通过Li+掺杂Tb3+激活硅酸盐玻璃的紫外可见透射光谱、发射光谱和发光衰减时间谱,研究了Li+的加入对Tb3+掺杂硅酸盐玻璃发光性能的影响。结果表明:适量Li+的加入可有效增强Tb3+激活硅酸盐玻璃的发光强度,且相比于不掺杂Li+的Tb3+掺杂硅酸盐玻璃而言,当掺入质量分数为2.0%的Li+时,Tb3+在玻璃中的最佳掺杂质量分数由12.8%提高至15.3%。其原因是Li+掺杂增加了玻璃体系中非桥氧的数量,从而有利于改善Tb3+在玻璃体中的均匀性,降低Tb3+间因非辐射跃迁而引起的能量损失,以及提高Tb3+的最佳掺杂质量分数。但当掺入Li+的质量分数超过2.0%时,会对Tb3+激活硅酸盐玻璃的闪烁光强产生负面影响,这是因为过多的非桥氧阻碍了X射线激发能达到Tb3+离子的能量传递。     

Stochastic period-doubling bifurcation analysis of a R?ssler system with a bounded random parameter

This paper aims to study the stochastic period-doubling bifurcation of the three-dimensional R?ssler system with an arch-like bounded random parameter. First, we transform the stochastic R?ssler system into its equivalent deterministic one in the sense of minimal residual error by the Chebyshev polynomial approximation method. Then, we explore the dynamical behaviour of the stochastic R?ssler system through its equivalent deterministic system by numerical simulations. The numerical results show that some stochastic period-doubling bifurcation, akin to the conventional one in the deterministic case, may also appear in the stochastic R?ssler system. In addition, we also examine the influence of the random parameter intensity on bifurcation phenomena in the stochastic R?ssler system.     

Hot-carrier degradation for 90nm gate length LDD-NMOSFET with ultra-thin gate oxide under low gate voltage stress

The hot-carrier degradation for 90~nm gate length lightly-doped drain (LDD) NMOSFET with ultra-thin (1.4~nm) gate oxide under the low gate voltage (LGV) (at V_g=V_th, where V_th is the threshold voltage) stress has been investigated. It is found that the drain current decreases and the threshold voltage increases after the LGV (V_g=V_th stress. The results are opposite to the degradation phenomena of conventional NMOSFET for the case of this stress. By analysing the gate-induced drain leakage (GIDL) current before and after stresses, it is confirmed that under the LGV stress in ultra-short gate LDD-NMOSFET with ultra-thin gate oxide, the hot holes are trapped at interface in the LDD region and cannot shorten the channel to mask the influence of interface states as those in conventional NMOSFET do, which leads to the different degradation phenomena from those of the conventional NMOS devices. This paper also discusses the degradation in the 90~nm gate length LDD-NMOSFET with 1.4~nm gate oxide under the LGV stress at V_g=V_th with various drain biases. Experimental results show that the degradation slopes (n) range from 0.21 to 0.41. The value of n is less than that of conventional MOSFET (0.5-0.6) and also that of the long gate length LDD MOSFET (\sim0.8).     

复合兰姆波声子晶体中超宽部分禁带

兰姆波在声子晶体薄板中的传播特性因其在无损检测、 减振技术和传感器件等领域的潜在应用价值而受到越来越多的关注. 本文采用超原胞平面波展开法和有限元法系统地研究了复合对称结构声子晶体薄板中的兰姆波超宽部分禁带. 结果表明: 对于在薄板侧面对称地嵌入双层矩形空气柱构成的复杂系统, 低阶兰姆波部分带隙结构极为丰富. 将晶格常数(L)和板厚(H) 比值具有匹配关系的兰姆波声子晶体衔接构成复合结构, 低阶兰姆波部分禁带宽度因各组分结构的部分禁带交叠而得到显著拓宽, 可在低频超宽频带内实现对特定低阶兰姆波模式良好的模式选择功能. 该研究结果对兰姆波缺陷无损检测中模式优化选择及兰姆波单向导通器件设计等方面具有重要意义.     

10-6-10-4m2/s黏度液体中靶受力学作用的测试与分析

通过自行研制的光纤传感器对不同黏度液体中材料靶后的力学作用进行研究,获得了液体黏度变化对等离子体烧蚀力、射流冲击力及空泡生存周期的影响. 实验结果表明:液体黏度相同时,靶材所受冲击力幅值随作用激光能量的增加单调上升;液体黏度增加时,靶材所受的冲击力减小,靶材的空化空蚀程度亦减小;受液体黏度增大的影响,空泡膨胀或收缩过程减缓,相应的生存周期也增大. 此外,对空泡溃灭周期公式进行修正,结果表明修正后的理论估算值与实验值的一致性较好.     

水下圆柱形Helmholtz共振器的声学特性分析

理论分析了水下圆柱形Helmholtz共振器的声学特性. 综合考虑壁面弹性和辐射阻抗的影响,基于电-声类比的基本原理,建立了较为完善的水下圆柱形Helmholtz共振器的低频集中参量模型. 利用电路分析的基本方法,得到了系统的输入阻抗和声压传递函数表达式. 仿真分析了主要结构参数对共振器声学特性的影响,得出了一些有意义的结论. 在充水驻波罐中对自制的Helmholtz共振器进行了测量,并对实验结果进行了详细地误差分析. 去除压电水听器对测量结果的影响后,实验与仿真结果基本一致,从而验证了理论分析的正确性. 关键词： Helmholtz共振器 共振频率 传递函数 辐射阻抗