Enhancement of ultrasonically initiated emulsion polymerization rate using aliphatic alcohols as hydroxyl radical scavengers

Ultrasonically initiated emulsion polymerization of styrene was carried out in the presence of aliphatic alcohols, e.g. methanol, ethanol, n-pronanol and n-butanol, as volatile hydroxyl radical scavengers. With the addition of methanol, the polymerization rate of styrene increased, while the molecular weight and the average particle size of the produced polystyrene decreased because more radicals were produced in the presence of methanol. This is true also for the other polymerization system using other aliphatic alcohols, such as ethanol, n-pronanol and n-butanol, suggesting that the alcohols enter into cavitation bubbles and further react with hydroxyl radicals (*OH) from the sonolysis of water to produce hydroxyalkyl radicals, so as to reduce the recombination of *H and *OH radicals, therefore more radicals will be present in the systems for initiating polymerization. Obviously, it is an effective way to enhance ultrasonically initiated emulsion polymerization rate of styrene by adding volatile hydroxyl radical scavenger.     

双包层椭圆光波导解析解

解析求解了双包层椭圆光纤中的波动方程，得到了模式精确解有模式特征方程。对基模的特征方程进行了数值计算，给出了不同椭圆比下的归一化双折射和模间色散随归一化频率的变化关系曲线，并与高斯近似解的结果进行了比较。     

Competition Between the SDW and CDW in Quasi-One-Dimensional Organic Polymer Ferromagnet

The next-nearest-neighbor hopping interactions of ρ-electrons in quasi-onedimensional organic polymer ferromagnet are considered by Peierls-Hubbard model, and a set of self-consistent equations are established to optimize the system. The competition between the SDW and CDW states, which is determined by the interplay between the electron-electron correlation and the next-nearest-neighbor hopping interaction, is studied. At the CDW state,the SDW along the main chain will be tuned by the CDW. Consequently the ferromagnetic state, in which all the spins of the unpaired electrons at side freeradicals are arranged parallelly,will be no longer a stable ground state of the system.     

综合性、设计性实验教学的探讨

综合性、设计性实验是培养学生的创新意识、创新精神和创新能力的有效措施;本文就开设综合性、设计性实验的意义、内涵、与基础实验的关系以及如何设计项目内容进行了初步的探讨。     

ON THE EXISTENCE AND UNIQUENESS OF THE SOLUTIONS OF STOCHASTIC DIFFERENTIAL EQUATIONS WITH RESPECT TO SEMIMARTINGALES

Papers [1, 2] deal with the problem of the existence and uniqueness of the solutions of two different stochastic differential equations with respect to semimarting?ales. The equation discussed in this paper unifies the equations in papers [1, 2]. This paper gives us the sufficient conditions for the existence and uniqueness of its solutions, so that the results in papers [1,2] can be obtained by theorem 1 and theorem 1; of this paper respectively.     

基于非线性偏振旋转效应的多波长光纤激光器

多波长光纤激光器是未来波分复用光通信系统的理想光源,提出和展示了一个基于非线性偏振旋转效应的多波长光纤激光器,非线性偏振旋转诱导的强度相关非均匀损耗能有效地抑制均匀加宽增益介质掺铒光纤中的模式竞争,从而使光纤激光器在室温下产生稳定的多波长输出,实验实现了最多18个波长的多波长输出.另外,此激光器没有使用传统的滤波器,而是在激光腔内插入一段保偏光纤,保偏光纤与偏振相关隔离器构成一等效Lyot双折射光纤周期性滤波器.利用这种在线型的双折射光纤滤波器简化了光纤激光器的结构,使它更易于集成.还实验研究了多波长输出随抽运功率的演化,发现抽运功率对多波长的均匀性影响很大.     

三层不对称人工电磁材料界面处表面等离子体激元的理论研究

从P和S偏振出发.研究了由常规材料/左手材料/负介电常数材料、及常规材料/左手材料/负磁导率材料这两种三层不对称结构界面上表面等离子体激元(Surface plasmon polaritons,SPPs)的存在区域、色散曲线及其激发.观察到表面等离子体激元的性质强烈地依赖于人工电磁材料的组成参量,例如介质板的厚度和等离子体的频率.最后,使用衰减全反射(Attenuated total reflection,ATR)技术,探究了激发和观察表面等离子体激元的可能性.并针对P和s偏振两种情况计算了衰减全反射光谱.     

倒V形四能级亚飞秒极化拍的三光子吸收和色散

基于孪生色锁噪声场的互相关效应,从理论上研究了倒V形(RV)四能级飞秒量级差频极化拍与极化拍中五阶非线性极化率,并提出了用一种相位敏感的方法来研究多能级原子相干造成的三光子六波混频过程.在抽泵光束为窄带末端情况下,场关联对信号和极化率的影响都很弱,在非窄带情况下,场关联会使极化强度自相干信号和极化拍信号产生关于零延时的不对称性和时域扫描上的辐射与物质失谐阻尼振荡(RDO),而极化率会产生频域扫描上的RDO振荡.参考光信号是一路传播方向和六波混频信号稍有区别的双光于非简并四波混频信号.五阶非线性响应则由享生 关键词： 外差法 吸收 色散 非线性极化     

Multisites Cr3+ in GGG and GSGG garnets

The emission and excitation spectra of Cr³⁺ -doped Gd₃Ga₅O₁₂ (GGG) and Gd₃Sc₂Ga₃O₁₂ (GSGG) are explained in the light of multisite effects. The situation is particularly complicated in the case of GSGG, where the different sites have²E energy levels near each other which overlap with the⁴A₂ ⁴T₂ absorption bands. The spectra obtained under selective excitations are interpreted on the multisite assumption.     

Effect of hydroxyl groups on Er doped Bi2O3-B2O3-SiO2 glasses

A series of Er³⁺-doped Bi₂O₃-B₂O₃-SiO₂-Na₂O glasses with different hydroxyl groups were prepared and the interaction between the Er³⁺ ions and OH groups was investigated. Infrared spectra were measured in order to calculate the exact content of OH groups in samples. The observed increase of the fluorescence lifetime with the oxygen bubbling time has been related to the reduction in the OH content concentration evidenced by infrared (IR) absorption spectra, which confirmed that the OH groups were dominant quenching centers of excited Er³⁺ and a cause of concentration quenching of 1.5 μm band emission. Various nonradiative decay rates from ⁴I_13/2 of Er³⁺ with the change of OH content were determined from the fluorescence lifetimes and radiative decay rates, which were calculated on the basis of Judd-Ofelt theory.