High repetition rate passively mode-locked erbium-doped fiber laser

We report a passively mode-locked high repetition rate erbium-doped femtosecond fiber laser via nonlinear polarization rotation, with a fundamental repetition rate of 101.94 MHz. The output power is 34 mW when pumped by a single mode fiber coupled laser diode at 370 mW. The spectral width is 25 nm, corresponding to a transform limited pulse width of 105 fs.     

Photonics: lasers producing tailored beams

Compact lasers that can produce a range of beam patterns are important for progress in several areas, including the improvement of optical tweezers, ultra-high-density optical memory and microfluidics. Here we engineer photonic crystals to generate semiconductor lasers that produce a range of beam patterns while maintaining stable single-mode oscillation. Our results could contribute to the realization of compact lasers that are capable of producing diverse beam patterns on demand.     

电流变液中介电颗粒在平行板电场中的运动

讨论了电流变液中介电颗粒在平行板电场中的运动。严格考虑了介电颗粒与极板的相互作用,利用特殊函数得到了封闭的积分表达式。其中偶极矩与一组无穷多个镜象偶极矩之间的相互作用严格表达式,可以方便地用来处理电流变液中颗粒与极板的作用。     

用微量汞提高测银灵敏度——玻碳电极溶出伏安法

当微量Ag~1、Hg~(2+)(10~(-7)M～10~(-9)M)共存于溶液(用HCl调pH为2的0.1MKSCN)中时,用普通极谱仪在-1.5V(VS、Ag/AgCl、盐桥联接),电解沉积2～10分钟,-0.3V～+0.2V溶出,在+0.12V出现一个很好的Ag-Hg金属间化合物溶出峰,它比Ag~+或Hg~(2+)单独存在时的溶出峰灵敏得多,并与两者的峰高、峰形、峰电位都有显著不同。当Hg~(2+)浓度一定时、峰高与Ag~+浓度呈正比,反之亦然。用标准加入外推法外延工作曲线至横轴,便能直接读出被测液中Ag~+浓度。     

湖泊水环境中湖流及其风效应研究

在不规则的三角形网格上,采用改型特征线法处理对流算子;采用集中质量的有限元法处理扩散算子,应用数值求解对流扩散方程的分步杂交法,模拟浅水型湖泊的水力特性,计算了1993年三个季度在不同风应力及入出流作用下的流态、流场分布、水位变化情况．     

基于GF集的并联机构末端运动特征分析方法

提出了一种基于GF集的机构末端运动特征分析方法,该方法简单直观,GF集是对机构末端的运动特征进行描述的集合.首先介绍了GF集的基本概念,其次提出了基于GF集的并联机构构型方法,介绍GF集的求交运算法则,而后给出了对机构末端运动特征进行分析的步骤.最后,根据该方法分析了Delta机构,得到了正确的结果.     

矢量控制的双馈电动机的功率变换过程

对矢量控制的双馈电动机的功率变换过程进行论述,并给出双馈电动机四象限运行的矢量图及功率图,从而提出将双馈电动机工业应用化的适宜性。     

Ballistic carbon nanotube field-effect transistors

A common feature of the single-walled carbon-nanotube field-effect transistors fabricated to date has been the presence of a Schottky barrier at the nanotube--metal junctions. These energy barriers severely limit transistor conductance in the 'ON' state, and reduce the current delivery capability--a key determinant of device performance. Here we show that contacting semiconducting single-walled nanotubes by palladium, a noble metal with high work function and good wetting interactions with nanotubes, greatly reduces or eliminates the barriers for transport through the valence band of nanotubes. In situ modification of the electrode work function by hydrogen is carried out to shed light on the nature of the contacts. With Pd contacts, the 'ON' states of semiconducting nanotubes can behave like ohmically contacted ballistic metallic tubes, exhibiting room-temperature conductance near the ballistic transport limit of 4e(2)/h (refs 4-6), high current-carrying capability (approximately 25 micro A per tube), and Fabry-Perot interferences at low temperatures. Under high voltage operation, the current saturation appears to be set by backscattering of the charge carriers by optical phonons. High-performance ballistic nanotube field-effect transistors with zero or slightly negative Schottky barriers are thus realized.     

一类交錯树

Ringel猜想是说,所有的树都是优美树,这个猜想至今尚未解决,是图论中的一个引人注目的难题,1979年,K.M.Koh等人提出交错树的概念,对于Ringel猜想的研究起了很大的推动作用,本文的结果是证明一类树是交错树。     

基于组块分析的路径自然语言语义角色标注方法

为了进行路径自然语言研究,首先设计了路径自然语言收集方案,主要面向室内环境收集了一定的路径自然语言语料,通过手工标注建立了一个小型的语料库.其次,对路径自然语言的特征进行了一定的分析,在此基础上概括了几种常见的语义角色,主要包括关于landmark和方位转换的语义角色.路径自然语言本身具有高度规律性,语义角色相对集中,因此语义分析采用了基于组块分析的语义角色标注方法,将语义分析问题转化为序列信号的切分和分类问题.最后,利用支持向量机进行了相关的组块标注实验.实验结果表明提出的方法具有较大的潜力.