A periodic array of nano‐scale parallel slats for high‐efficiency electroosmotic pumping

It is known that the eletroosmotic (EO) flow rate through a nano‐scale channel is extremely small. A channel made of a periodic array of slats is proposed to effectively promote the EO pumping, and thus greatly improve the EO flow rate. The geometrically simple array is complicated enough that four length scales are involved: the vertical period 2L, lateral period 2aL, width of the slat 2cL as well as the Debye length . The EO pumping rate is determined by the normalized lengths: a, c, or the perforation fraction of slats and the dimensionless electrokinetic width . In a nano‐scale channel, K is of order unity or less. EO pumping in both longitudinal and transverse directions (denoted as longitudinal EO pumping (LEOP) and transverse EO pumping (TEOP), respectively) is investigated by solving the Debye–Hückel approximation and viscous electro‐kinetic equation. The main findings include that (i) the EO pumping rates of LEOP for small K are remarkably improved (by one order of magnitude) when we have longer slats () and a large perforation fraction of slats (η > 0.7); (ii) the EO pumping rates of TEOP for small K can also be much improved but less significantly with longer slats and a large perforation fraction of slats. Nevertheless, it must be noted that in practice K cannot be made arbitrarily small as the criterion of for the reference potential at the channel center put lower bounds on K; in other words, there are geometrical limits for the use of the Poisson–Boltzmann equation.     

A miniaturized flow-injection analysis ( μ FIA) system with on-line chemiluminescence detection for the determination of iron in estuarine water

A miniaturized flow-injection analysis system constructed from a glass base plate and polydimethylsiloxane (PDMS) top plate was employed for the determination of iron in river water. Two designs were investigated, one utilizing a syringe pump and the other utilizing EOF pumping with a mini-filtration system incorporated. The syringe pump system was used to optimize the analytical method on chip, where the pump was used to deliver both the analyte and the reagents to the reactor chip. The highly sensitive chemiluminescence reaction between alkaline luminol (3-aminophthalhydrazide) and 0.1?M of hydrogen peroxide (H₂O₂) in the presence of iron(II) was utilized. The bright blue light (λ _max?～?440?nm) emitted was detected using a miniaturized photomultiplier tube interfaced directly under the chip. The light intensity signals were recorded, and the corresponding concentration of iron(II) concentration was determined. The calibration for iron(II) standards was linear up to 0.75?µg?mL^?1 (y?=?5.7839x?+?0.0378, r² ?=?0.9939) with a precision value of up to 3.72% RSD, for n?=?3. The limits of detection (blank?+?3s _y/x) were found to be 28?ng?mL^?1. The system which utilized EOF pumping and incorporated a minifiltration unit provided a linear calibration for 0–5?µg?mL^?1 (y?=?3.316x?+?0.1831; correlation coefficient, r ²?=?0.9996) over a working range of 0.0–0.5?µg?mL^?1. This system provided lower limits of detection 5.1?ng?mL^?1 and better repeatability (%RSD less than 0.5% for n?=?4), but problems occurred with the mini-filtration system at higher iron(II) concentrations. The EOF pumping system provided slightly higher results for the concentration of iron(II) in the Humber estuary (0.058?µg?mL^?1), but these results were in line with the results expected by the Environment Agency.     

Some theoretical and practical aspects in the separation of humic substances by combined liquid chromatography methods

Permanent need to understand nature, structure and properties of humic substances influences also separation methods that are in a wide scope used for fractionation, characterization and analysis of humic substances (HS). At the first glance techniques based on size-exclusion phenomena are the most useful and utilized for relating elution data to the molecular mass distribution of HS, however, with some limitations and exceptions, respectively, in the structural investigation of HS. The second most abundant separation mechanism is reversed-phase based on weak hydrophobic interactions beneficially combined with the step gradients inducing distinct features in rather featureless analytical signal of HS. Relatively great effort is invested to the developments of immobilized-metal affinity chromatography mimicking chelate-forming properties of HS as ligands in the environment. Surprisingly, relatively less attention is given to the ion-ion interactions based ion-exchange chromatography of HS. Chromatographic separation methods play also an important role in the examination of interactions of HS with pesticides. They allow us to determine binding constants and the other data necessary to predict the mobility of chemical pollutants in the environment. HS is frequently adversely acting in analytical procedures as interfering substance, so more detailed information is desired on manifestation of its numerous properties in analytical procedures. The article topic is covered by the review emphasizing advances in the field done in the period of last 10 years from 2000 till 2010.     

清洁、大流量真空差分系统的研制

本研究是为了设计一套大流量、清洁的真空差分系统. 计算了超重反冲核实验装置终端真空差分系统各级的真空度; 介绍了差分系统的设计和真空泵、测量设备选择; 选择能在高压强下连续运行的新型分子/增压泵作为过渡流范围内的主排气泵, 对分子增压泵进行了性能测试并对差分系统进行了模拟靶室实验, 最后对实验结果进行了分析.     

烟火泵浦钕玻璃激光器出光实验研究

 烟火泵浦是激光器小型化、便携化的一种解决方法。研制了一种用于钕玻璃激光器泵浦源的化学试剂,其主要成分为金属粉和碱金属含氧酸盐。设计了烟火泵浦钕玻璃激光器实验装置,激光器采用平-凹腔结构、紧包型侧面泵浦,输出镜反射率98％,钕玻璃棒尺寸f8 mm×100 mm。采用A,B两种配方的泵浦源进行出光实验,A配方得到了波长为1 053 nm能量为29 mJ的激光,B配方没有出光。分别计算了两种泵浦源的阈值辐射强度,并与测量得到的药剂辐射强度平均值比较。A配方所提供的辐射强度2.68×104 W·sr^-1,大于阈值2.37×104 W·sr^-1;B配方小于阈值,未能出光。这与实验结果吻合,证明烟火泵浦方法可行。     

高功率光子晶体光纤放大器实验研究

利用掺Yb³⁺的光子晶体光纤作为光纤放大器的增益介质,采用反向抽运方式,分别从理论和实验方面研究了不同信号的增益特性,在信号光功率为6W,抽运光功率为160W时,获得了104W的输出功率.实验发现,当抽运功率大于一定值时,放大器输出会有一定的不稳定性,并影响输出功率的进一步提高. 关键词： 光子晶体光纤 光纤放大器 反向抽运 高功率     

Electrical characterization of high-k gate dielectrics on semiconductors

This paper reviews the following electrical characterization techniques for measuring the microscopic bonding structures, impurities, and electrically active defects in advanced CMOS gate stacks: (1) inelastic electron tunneling spectroscopy (IETS), (2) lateral profiling of threshold voltages, interface-trap density, and oxide charge density distributions along the channel of a MOSFET, and (3) pulse agitated substrate hot electron injection (PASHEI) technique for measuring trapping effects in the gate dielectric at low and modest gate voltages.     

波长锁定878.9nm激光二极管抽运内腔式YVO_4/BaWO_4连续波拉曼激光器

采用波长锁定878.9 nm激光二极管共振抽运复合Nd:YV04激光晶体,改善热效应的同时提高抽运吸收率,分别以YVO_4和BaWO_4晶体作为拉曼介质,实验和理论研究了晶体性能、谐振腔结构和稳定性对内腔分体式连续波拉曼激光器性能的影响.结果表明:由于内腔分体式拉曼激光器腔长较长,谐振腔稳定性对激光器性能影响较大,选择高增益的拉曼晶体,不仅可获得高拉曼转换效率,还能一定程度上减轻热效应.而平凹腔结构中输出镜的曲率半径越小,拉曼晶体中基频光的功率密度越大,腔的动态稳定区越宽,获得的拉曼激光输出功率更高.最终以30 mm的BaWO_4晶体作为拉曼介质,在抽运功率25.1 W时,获得了3.02 W的连续拉曼激光输出,光-光转换效率达到12%.     

微腔中单量子点的激光输出特性研究

研究一个四能级量子点耦合到单模光学腔中的量子系统,利用系统的主方程作数值模拟计算微腔中单量子点的激光输出强度随非相干泵浦的变化关系.结果显示量子点在泵浦作用下激光的输出有一个阈值;且量子点和腔模耦合强度增强时,产生激光的阈值明显减小,输出激光的峰值却增大.当泵浦作用继续增强到一定程度,因激光能级间的相干性被过强的非相干泵浦所破坏,单量子点激光输出变为零----出现了淬灭现象.     

Generation of coherent blue light via bichromatic pumping in cesium vapor

Diode-pumped alkali lasers, possessing high efficiency and narrow linewidth, can provide feasible solutions for wavelength ranges difficult to reach by commercial lasers. In this study, we investigate a generation of coherent blue light (CBL) via four-wave mixing (FWM)-based up-conversion processes in cesium (Cs) vapor. A bichromatic pumping scheme with 852- and 917-nm lasers drives the Cs atoms to the 6D_5/2 excited level, followed by cascaded decay of 6D_5/2 → 7P_3/2 → 6S_1/2, producing 456-nm CBL under phase matching conditions. The fluorescence in multiple bands from blue to near- and far-infrared in the FWM process is demonstrated under different experimental conditions. To optimize the experimental parameters, we investigate the dependence of 456-nm CBL on the vapor temperature, frequency, and intensity of the two pump lasers. A maximum power of 2.94 mW is achieved with pump powers of 430 mW (for 852 nm) and 470 mW (for 917 nm). The corresponding conversion efficiency is 1.5%/W, three-fold higher than those in previous studies. Our results can contribute to fundamental research on atom−photon interactions and quantum metrology.