Preparation of alumina nanowires, nanorods, and nanowalls by chemical etching

Alumina (Al₂O₃) nanowires, nanorods, and nanowalls have been prepared from anodic aluminum oxide (AAO) templates by chemical etching in NaOH solution. Heating the template prior to etching is crucial to the morphology of subsequent prepared alumina nanostructures, which greatly depend on the phases of the AAO templates. It has been found that the templates with amorphous Al₂O₃, γ-Al₂O₃, and α+γ-Al₂O₃ phases will grow nanowires, nanorods, and nanowalls, respectively. A possible mechanism for forming different alumina nanostructures is proposed.     

非相干耦合的亮和暗光伏空间孤子对的偏转特性

采用数值方法研究了在一个具有扩散效应的光伏光折变晶体中的非相干耦合的亮和暗光伏空间孤子对的偏转特性.结果表明,由于非相干相互作用,晶体中的一个亮孤子和一个暗孤子互相俘获,且两个孤子的中心沿着相同的轨迹移动.发现,当亮孤子的入射峰值强度不变时,通过调节暗孤子的入射背景强度可以控制亮孤子的偏转;当暗孤子的入射背景强度处于一个特殊值时,亮孤子的偏转被抑制,而当暗孤子的入射背景强度偏离这个特殊值时,亮孤子发生偏转.同样,当暗孤子的入射背景强度不变时,其偏转可以通过调节亮孤子的入射峰值强度来控制.     

Asymmetric total synthesis of cladosporin and isocladosporin

The first asymmetric total syntheses of cladosporin and isocladosporin were accomplished in 8 steps with 8% overall yield and 10 steps with 26% overall yield, respectively. The relative configuration of isocladosporin was determined via this total synthesis.     

Construction of two Novel 2D Coordination Frameworks with the Ligand H3nbtc: Synthesis,Crystal Structures,and Luminescence

Two novel 2D coordination polymers, namely, {[Cu₂(L)₂][Cu(H₂O)₃]}_n ( 1 ) and {Pb₃(O₂N‐btb)₂}_n ( 2 ) (O₂N‐H₃btb = 5‐nitro‐benzene‐1, 2, 3‐tricarboxylic acid, L = 5‐nitro‐2‐oxidoisophthalate), were synthesized under hydrothermal conditions and characterized by elemental analysis, IR spectroscopy, X‐ray diffraction, and thermogravimetric analysis. Compound 1 is an infinite 2D layer exhibiting an extended 3D supramolecular network structure. O–H ··· O hydrogen bonding interactions play a key role in forming the final 3D supramolecular framework. It is noted that 5‐nitro‐benzene‐1, 2, 3‐tricarboxylic acid (O₂N‐H₃btb) was in situ transformed to 5‐nitro‐2‐oxidoisophthalate in 1 . Compound 2 is a 2D microporous lead‐containing metal‐organic framework made up of interconnected Pb‐carboxylate chains, involving three independent lead atoms with three different coordination arrangements. Furthermore, the solid‐state photoluminescence and lifetime characteristics of 2 reveal intense blue luminescence.     

铌酸锂晶体中飞秒激光脉冲线性电光效应及其色散补偿

针对铌酸锂晶体中飞秒激光脉冲线性电光效应, 研究了光学相位共轭 对群速度色散 以及一阶和二阶折射率色散的补偿方案. 结果发现, 在任意初始输入脉宽条件下, 这些色散基本上都能得到补偿, 输出脉冲波形基本上和输入脉冲相同. 在此方案中, 若同时在色散补偿铌酸锂晶体上对输出脉冲进行电光相位调制, 则在一定外加电场作用下, 输出脉冲的脉宽将进一步被压缩, 初始输入脉宽越小, 压缩程度越大.     

基于准周期光学超晶格的高效电光调制差频转换

为获得尽可能大的差频转换效率,基于准周期极化铌酸锂(QPPLN)光学超晶格,提出了级联电光和差频理论,用于高效的差频转换。其方法是沿QPPLN光学超晶格的y方向施加一个外加电场,用来控制能量在抽运光、信号光、o偏振的差频光和e偏振的差频光四个光波之间的转移。计算结果表明,在一个100℃,40mm长的QPPLN光学超晶格中,当1550nm信号光与1064nm抽运光光强比值r<0.324时,对光强超过特定值的任意抽运光都可以通过施加一个适当的外加电场将抽运光完全转化为1550nm信号光和3393.4nm差频光;当r≥0.324,只当抽运光光强落在一定范围内时,才可以通过施加外加电场使抽运光完全转化为信号光和差频光;超过该范围,外加电场不能增加差频光转换效率。计算结果还表明,电光调制差频转换效率对温度和畴构造误差都不敏感。     

Noncontact friction and relaxational dynamics of surface defects

The motion of a cantilever near sample surfaces exhibits additional friction even before two bodies come into mechanical contact. Called noncontact friction (NCF), this friction is of great practical importance to the ultrasensitive force detection measurements. The observed large NCF of a micron-scale cantilever found an anomalously large damping that exceeds theoretical predictions by 8-11 orders of magnitude. This finding points to a contribution beyond fluctuating electromagnetic fields within the van der Waals approach. Recent experiments reported by Saitoh et al. [Phys. Rev. Lett. 105, 236103 (2010)] also found a nontrivial distance dependence of NCF. Motivated by these observations, we propose a mechanism based on the coupling of a cantilever to the relaxation dynamics of surface defects. We assume that the surface defects couple to the cantilever tip via spin-spin coupling and their spin relaxation dynamics gives rise to the backaction terms and modifies both the friction coefficient and the spring constant. We explain the magnitude, as well as the distance dependence of the friction due to these backaction terms. Reasonable agreement is found with the experiments.     

多层线型分割法分析渐变型平板介质波导

提出了一种求解渐变折射率平板光波导的传播常数和场强分布的数值计算方法，计算了几类典型的渐变折射率波导的传播常数数值，并与其它方法进行了比较，结果表明，该方法计算的精度极高，速度较快，有实用价值。     

暗-暗与亮-暗光伏孤子相互作用

用数值方法分析了平行传播异色光伏暗孤子之间及亮-暗孤子之间的相互作用.结果表明，光伏暗孤子共轴传播能在有限的距离内保持准孤子形态，靠近传播时存在着相互吸引的作用 ，而相距较远传播时表现为一孤子暗区使另一孤子的缓变光场部分发生局部会聚作用.光伏暗孤子与亮孤子的相互作用随距离的不同可使亮孤子光强分布变尖锐或变平缓，以及使亮孤子发生能量转移.从两束信号光共同引起折射率波导这一物理机理对光伏孤子这些相互作用给出定性物理解释. 关键词： 光伏空间孤子 暗孤子 亮孤子 相互作用     

加加速度（加速度的时间变化率）——冲击、乘座舒适性、缓和曲线

介绍加加速度（加速度的时间变化率）及其在冲击、乘座舒适性和缓和曲线等问题中的应用。