熔融酯交换法合成聚碳酸酯的研究

采用熔融酯交换法,以碳酸二苯酯(DPC)和双酚A(BPA)为原料合成聚碳酸酯(PC).考察了乙酰丙酮(HACAC)类金属配合物催化剂的活性,以及催化剂活性与相应金属离子螯合配位作用的关系.以不同乙酰丙酮金属配合物为催化剂合成的PC的特性黏数([η])对相应金属离子二苯甲酰甲烷(DBM)配合物的稳定常数的对数值(lgβ1)作图,得到1个双火山型曲线,证明DPC与BPA的熔融酯交换缩聚反应是受乙酰丙酮阴离子的碱性作用和金属离子的螯合配位作用共同影响的.通过比较用各种催化剂合成的PC的性质,发现乙酰丙酮锂(LiACAC)是一种优良的催化剂,可以用来合成分子量超过40000([η]=0.710 dL.g-1)、低支化物(Fries产物)含量、低分散(PDI=2.12)的PC.以LiACAC为催化剂,考察了催化剂用量、反应物配比、酯交换阶段压力以及温度等条件对反应的影响.最佳反应条件为,LiACAC的用量为1.5×10-4mol/mol BPA、原料配比nDPC∶nBPA=1.08、酯交换阶段压力设在4000 Pa、缩聚反应阶段反应温度为260℃.     

不确定非自治混沌陀螺仪在非线性输入下的有限时间稳定性

陀螺仪是一个非常有趣,又是永恒的非线性非自治动力系统课题,它可以显示出非常复杂的动力学行为,如混沌现象.在一个给定的有限时间内,研究非线性非自治陀螺仪鲁棒稳定性问题.假设陀螺仪系统受到模型不确定的外部扰动而摄动,系统参数并不知道,同时考虑了非线性输入的影响.为未知参数提出了适当的自适应律.以自适应律和有限时间控制理论为基础,提出非连续有限时间控制理论,来研究系统的有限时间稳定性.解析证明了闭循环系统的有限时间稳定性及其收敛性.若干数值仿真结果表明,该文的有限时间控制法是有效的,同时验证了该文的理论结果.     

基于H型谐振器的Ku波段高温超导滤波器设计

高温超导滤波器已在移动通信、射电天文、雷达探测等多个领域获得了重要应用.当前高温超导滤波器的研究和应用主要集中于10GHz以下的频段,针对超高频段(>10GHz)高温超导滤波器的研究很少.本文设计优化了具有无载Q值高、耦合强、尺寸短等特点的H型阶跃阻抗谐振器,并讨论了超高频段滤波器端口激发源的电容效应对滤波器响应的影响,最后采用优化的H型谐振器,应用去嵌入(De-Embed)设计方法消除端口效应,设计了中心频率为16GHz,相对带宽12.5%的6节高温超导滤波器.研制的超导滤波器在未经调谐的情况下,测试结果与仿真结果符合得很好,插入损耗小于0.3dB,反射损耗优于-14dB,带外抑制达到了-70dB.     

Selective excitation of molecular mode in a mixture by femtosecond resonance-enhanced coherent anti-Stokes Raman scattering spectroscopy

Femtosecond time-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy is used to investigate gaseous molecular dynamics. Due to the spectrally broad laser pulses, usually poorly resolved spectra result from this broad spectroscopy. However, it can be demonstrated that by the electronic resonance enhancement optimization control a selective excitation of specific vibrational mode is possible. Using an electronically resonance-enhanced effect, iodine molecule specific CARS spectroscopy can be obtained from a mixture of iodine-air at room temperature and a pressure of 1 atm (corresponding to a saturation iodine vapour as low as about 35 Pa). The dynamics on either the electronically excited state or the ground state of iodine molecules obtained is consistent with previous studies (vacuum, heated and pure iodine) in the femtosecond time resolved CARS spectroscopy, showing that an effective method of suppressing the non-resonant CARS background and other interferences is demonstrated.     

The thermal effect in diode-end-pumped continuous-wave 914-nm Nd:YVO4 laser

The thermal effect and the heat generation in diode-end-pumped continuous-wave 914-nm Nd:YVO₄ lasers are investigated in detail. A theoretical model of a diode end-pumped solid-state laser is constructed to analyse the influence of fractional thermal loading on the thermal effect in the Nd:YVO₄ laser based on finite element analysis. The thermal focal lengths and the end-surface deformations of laser rods in Nd:YVO₄ quasi-three-level and four-level lasers are measured and compared with the results obtained by ordinary interferometry for the demonstration of higher thermal loading in 914-nm laser. Finally the fractional thermal loading in the Nd:YVO₄ quasi-three-level laser is calculated by matching the experimental and the simulated end deformations.     

带跳的Gauss积分过程幂变差的渐近行为

研究了Xt=∫t0φsdGs+ξt已实现幂变差的渐近理论,其中G为平稳增量Gauss过程,φ为随机过程,ξ为与G独立的非Gauss Lévy过程,而积分为按路径Riemann-Stietjes积分.给出了经适当规范化后已实现幂变差的概率极限定理以及相应的中心极限定理,这些结果将为处理长期记忆跳过程的统计问题提供理论基础.     

Tunable Ba0.5Sr0.5TiO3 film bulk acoustic resonators using SiO2/Mo Bragg reflectors

Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators（FBARs） based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3（BST） films at 800 C.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias（ 45 V） while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frequency is around 2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias,which can be comparable to AlN FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum（Mo） as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.     

红外光谱在线监控对二苯脲合成反应进程的研究

利用ReactIRTM4000实验室在线红外分析系统对脲和苯胺合成二苯脲反应进行在线监控,通过监测反应物脲(1 420 cm-1)和苯胺(1 270 cm-1)、中间产物苯基脲(1 339 cm-1)及产物二苯脲(1 312 cm-1)特征峰的变化,推断出反应体系中各组分浓度的变化,从而清楚地了解了该反应的进程。研究的结果证明脲和苯胺合成二苯脲的过程是脲和苯胺先生成中间产物苯基脲,苯基脲再和苯胺生成二苯脲。结果表明在线红外分析能够快速、简便、准确地确定出反应的最佳时间,从而达到对合成反应的进程进行控制的目的。     

光源稳定性对简并四波混频信噪比影响的实验研究

在碘蒸气中研究了染料激光稳定性对简并四波混频(DFWM)信噪比的影响。实验中采用多模Nd∶YAG激光器倍频的输出泵浦染料激光器(染料PM580溶于酒精)。在具有前向补偿分光系统和图像探测系统的帮助下,在常温常压条件下测得泵浦光在波长为554.013 nm时达到饱和光强为290 μJ。同时发现染料激光器的光稳定性(输出波长范围,光束质量和能量转换效率等)随使用时间,泵浦激光脉冲次数和能量的增加而逐渐减弱。另外通过对比发现在染料激光器输出不稳定时,光源单色性和指向性等指标的变化导致在同一泵浦强度不同时刻获得的DFWM信号强度相差很大,且DFWM信号信噪比低。染料激光器光源稳定性对DFWM信号影响的研究结果对物质的痕迹量探测以及无荧光物质光谱定标等方面的应用具有重要意义。     

激光感生碰撞能量转移实验

首次观察到Eu(6s6p)^P9/2至Sr(5s10s)^1So、准稳态翼为紫翼的激光感生碰撞能量转移实验现象,其荧光波长为458.42nm,峰值转移激光波长为459.75nm,并对其激发函数谱随温度和随转移激光能量改变进行实验研究,测量了激光感生碰撞能量转移谱的截面,证实了激光感生碰撞能量转移谱为非对称谱。