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.     

激光冷却气体原子研究的起步阶段

文章记述了开展激光冷却气体原子研究的起步阶段,描述了推动文章作者从原子钟研究走向激光冷却气体原子研究的动力.在研究初期阶段,文章作者着重思考了激光冷却气体原子物理机制,如:积分球红移漫反射激光冷却气体原子的设想和利用光频移效应(交流斯塔克效应)激光冷却气体原子的物理思想.文章还描述了作者所在实验室用于激光冷却原子研究的原子束实验装置,并展示了几个物理实验结果.最后,文章还总结了经验和教训,深感起步艰辛和今日可贵,期盼光辉的未来.     

Polarized He neutron spin filter program at the JCNS

Polarized neutron instruments will occupy about 80% of the Jülich Centre for Neutron Science (JCNS) instrument park. A successful polarized ³He program will be integral to many of these instruments. We have been focusing the developments on spin-exchange optical pumping (SEOP) to polarize the ³He gas in situ. Where possible, in situ polarization using the SEOP method will provide higher time averaged performance of the instruments. Further this allows a custom-built and independent source of polarized ³He to be developed optimized for each instruments demands. In this paper we will: present an argument for the advantages of in situ polarization; describe an in situ polarizer we have constructed, and initial tests of its performance; describe testing of polarization analysis for small angle neutron scattering on biological samples, and our plans for an in situ polarizer for this application.     

同带抽运高效率光纤放大器

以光纤光栅为谐振腔搭建了波长为1020 nm的光纤激光器,并通过两级级联放大获得了590 mW的最大输出功率. 利用获得的波长为1020 nm的激光进行了波长为1064 nm种子光同带抽运放大,实验研究了不同增益光纤长度时放大器的输出功率和转换效率. 当增益光纤长度为8.5 m时,放大器最大输出功率为385 mW,斜率效率为81%. 进行了波长为976 nm的半导体激光器直接抽运波长为1064 nm种子光的实验. 在增益光纤长度最优时,其斜率效率为56.4%. 实验结果表明,同带抽运方式比传统抽运方式具有更高的转换效率. 研究结果可为波长为1020 nm的激光高功率放大和波长为1064 nm的光纤激光高功率同带抽运放大提供一定的参考. 关键词： 同带抽运 光纤放大器 斜率效率     

The study of a Tm:YLF laser pumped by a Raman shifted Erbium fiber laser at 1678 nm

A Tm:YLF laser pumped by a Raman shifted Er-fiber laser at 1.678 μm was studied at two Tm³⁺ ion concentrations equal to 1.5% and 5%. At output powers up to 460 mW the measured lasing efficiency at a wavelength of ~ 1.93 μm was as high as ~ 50%. The lasing performance was compared with that obtained under pumping by a 792-nm laser diode. The temporal structure of the laser pulse was recorded and the beam propagation factor M² was measured for all pumping conditions.     

Gain assisted large-scale tunable atomic filter based on double selective optical pump induced dichroism

A gain assisted large-scale tunable optical filter scheme via double selective optical pump induced dichroism is proposed. Theoretical model predicts that the filter provides a huge gain for the weak probe light, furthermore, its tunability can reach over gigahertz while its bandwidth is only several hundred megahertz, which is important for laser communication and lidar systems subjected to large Doppler shift.     

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.     

不同加铝方式对SAPO-34分子筛合成及MTO催化性能的影响

在水热合成体系中,以三乙胺(TEA)和四乙基氢氧化铵(TEAOH)为混合模板剂,考察了在初始凝胶形成过程中铝源的加入方式对合成SAPO-34分子筛及甲醇制烯烃(MTO)催化性能的影响;通过X射线衍射(XRD)、扫描电子显微镜(SEM)、氮气等温吸附脱附(BET)、²⁹Si固体核磁(²⁹Si MAS NMR)、氨气程序升温脱附(NH₃-TPD)等方法对合成产物进行物性表征,并研究了其在甲醇转化制烯烃(MTO)反应中的催化性能。结果表明,随着首先加铝量的增加,粒径有逐渐变小的趋势,且逐渐出现板层状形貌的SAPO-34分子筛;同时,产物分子筛骨架中Si(4Al)配位结构的数量增加,强酸比例在逐渐增大,且酸密度增加;随着强酸比例和酸密度的提高,SAPO-34分子筛在MTO催化反应中的寿命逐渐延长,丙烯选择性逐渐增大而乙烯选择性逐渐减小。     

直流叠加脉冲电压下FLTD气体开关击穿特性

分析了直流叠加脉冲电压(定义为复合电压)下次级感应电压触发快脉冲直线变压器驱动源(FLTD)中气体开关击穿延时过程,给出了击穿延时的估算公式。初步实验研究了FLTD用三电极气体开关在复合电压作用下的击穿特性,结果表明:在±70kV直流充电电压叠加300kV/30ns快脉冲电压的复合电压作用下,气体开关的击穿延时小于相同工作系数下常规触发方式的击穿延时,采用SF6气体绝缘时,击穿延时较常规触发方式减小了17%~30%;采用N2绝缘时,减小了约50%,开关工作系数为55%时,击穿延时抖动小于5ns;理论估算的复合电压下击穿延时与实测结果基本吻合。