Computer-controlled vacuum backflush for capillary GC

A vacuum-pump-operated backflush system has been developed for applications involving high-speed, repetitive GC analysis of gas streams containing ppm and ppb levels of organic vapor. The system uses an injector capable of cryofocusing and a relatively short length of 0.25-mm i.d. fused silica column for the separation of relatively simple mixtures of volatile compounds. Analysis times typically are in the 5–10 s range, and backflush times are in the 2–5 s range. Gases from the flame ionization detector are used as the backflush carrier gas, and no modification of the detector is necessary. A procedure is described which allows the average gas velocity to be measured during backflush operation. The minimum backflush time is directly proportional to the analysis time and to the square of the column length, making this system most useful with short columns and short analysis times.     

Ultrasound and microwave-assisted extraction of metals from sediment: a comparison with the BCR procedure

In this paper we investigate alternatives to mechanical stirring for the extraction of the mobile fraction of metals from sediment, and analyze whether these techniques can reduce extraction time and improve reproducibility. We compare the quantities of metal extracted from BCR601 and BCR701 certified sediments using ultrasound bath, microwave-assisted extraction and the first step in the certified BCR sequential extraction procedure. Some environmentally important not-certified metals such as As, Mn, Co, Fe and Al have been included in this study. In the case of microwave-assisted extraction, we compare tests in which samples are exposed to constant, low power irradiation with tests using pulsed high power.

In the tests using the ultrasound bath, less metal was extracted than with the other extractive techniques and standard deviations were comparable to those obtained with the BCR procedure; in assays using microwaves at constant power, extraction efficiencies were different for different metals and for different reference materials and, in some cases, standard deviations were higher than those for the reference method. In contrast, tests with microwaves and constant temperature produced encouraging results: R.S.D.s lay in the 2–4% range, both for certified and not-certified metals; these values are very low compared to those for the reference method. Extraction efficiencies for certified metals were close to 100% for Cd, Zn, Cu and Ni and around 80% for Pb and Cr.     

北黄海中部晚第四纪沉积物来源的稀土元素示踪

对北黄海中部DLC70-2孔166个沉积物样品进行了稀土元素测定,结合粒度参数研究,以探讨北黄海中部DLC70-2孔稀土元素地球化学特征和物质来源。结果表明:DLC70-2孔岩心稀土元素分布特征分别反映了末次间冰期(暖期)晚期以来北黄海海面波动以及沉积物物源的变化。判别函数和稀土元素配分模式表明北黄海DLC70-2孔沉积物物源主要为黄河源和鸭绿江源。La/Yb判别图解揭示DLC70-2孔上部0~32.10 m和下部37.60~60.72 m沉积物以黄河源为主,中部32.10~37.60 m和底部60.72~70.45 m沉积物以鸭绿江源为主。研究表明晚更新世以来黄河对北黄海中部沉积起着重要作用,而鸭绿江物质对北黄海中部沉积作用也有明显影响。     

Seepage from a channel: Solution structure and flow-rate estimation

Using functional analysis methods, problems that arise in calculating underground water seepage from an earth channel are investigated. The problem of estimating the seepage loss is considered. Novel methods which make it possible to overcome the difficulties in solving variational problems of channel seepage are proposed. An exact (unimprovable) estimate is found for the seepage loss from earth channels. The channel shape optimal among channels with a given cross-section contour length is obtained.     

Error estimation of prediction-correction legendre spectral approximation to incompressible fluid flow

1. IntroductionThere have been a lot of literatures concerning the existence, uniqueness, regularityof the solution of Navier-Stokes equation. Usually the primitive equation is considered,e.g.5 see 11,2]. Maily methods are used for its numerical simulation, e.g., see [2--7]. But wemeet several difficulties in calculation. For instance, if we use the finite difference method,then we have to evaluate the pressure at each time step. Some authors developed theartificial compressibility method or…     

The existence and uniqueness of weak solution of the flow between two concentric rotating spheres

ＩｎｔｒｏｄｕｃｔｉｏｎＩｎｔｈｉｓｐａｐｅｒ,ｗｅｓｔｕｄｙｔｈｅｕｎｓｔｅａｄｙａｘｉｓｙｍｍｅｔｒｉｃｉｎｃｏｍｐｒｅｓｓｉｂｌｅｆｌｏｗｂｅｔｗｅｅｎｔｗｏｃｏｎｃｅｎｔｒｉｃｓｐｈｅｒｅｓ．Ｔｈｉｓｆｌｏｗｉｓｃａｌｌｅｄａｓｓｐｈｅｒｉｃ...     

碱熔-水蒸气蒸馏-离子色谱法测定锌精矿中的氟

建立了一种测定锌精矿中氟含量的分析方法。通过碱熔半熔融方法,除去锌精矿中大量硫对样品前处理的影响,利用水蒸气蒸馏的方法分离了被测元素氟与矿石中其它大量重金属离子。通过碱熔-水蒸气蒸馏后离子色谱测定,最大限度排除干扰,降低测定检出限。以碳酸钠(2.5mmol/L)和碳酸氢钠(3.5mmol/L)混合溶液作为淋洗液,SH-AC-1(200mm×4.6mm ID)阴离子分析柱分离,抑制电导检测器检测。线性范围内相关系数为0.999 6,加标回收率97%~102%,相对标准偏差小于4.0%,样品检出限0.0004%。有效拓展了锌精矿中氟含量的测定范围。     

Anisotropy degree of nonlinear solids

This research aims at the generalization of the concept of anisotropy degree of linearly elastic solids which has been defined and investigated in detail by Zhang [1988] to that of nonlinear and non-elastic solids. The properties of the anisotropy degrees defined here show that they are reasonable.     

海洋沉积物中不同结合态无机碳的测定

作为全球碳的重要源与汇的海洋沉积物,在碳循环中起着重要的作用。探讨沉积物中无机碳的行为对深入了解海洋碳循环具有重要意义。本研究根据沉积物中无机碳在不同溶剂中的溶解能力不同,利用顺序浸提法,将沉积物中的无机碳分为：NaCl相(Ⅰ)、氨水相(Ⅱ)、氢氧化钠相（Ⅲ）、盐酸羟胺相（Ⅳ）和盐酸相(Ⅴ)。通过大量实验确定了不同相的最佳浸取条件。在Ⅰ～Ⅲ相,分别将浸取剂和样品加入塑料离心管中,将离心管密封后放在震荡器上震荡2h,然后离心分离,并用水洗涤残渣,将洗涤液并入浸取液,最后用容量法测定其中的无机碳;在Ⅳ,Ⅴ相,将第Ⅲ步残渣转移到锥形瓶中,加入浸取剂后用高纯N2将所产生的CO2吹出,并用饱和Ba(OH)2溶液吸收,最后用容量法测定无机碳。该方法具有较好的精密度。     

基于SCS-PRBG的数字流密码

针对单混沌系统可能会出现的动力学特性退化的缺陷,基于多混沌系统和开关技术,提出开关控制混沌伪随机比特发生器（Switch Controller Chaos ＆ Pseudo Random Bit Generalor,简称SCS—PRBG）．通过对SCS—PRBG密钥流及其性能的理论分析,表明该数字流密码具有较好的随机性与安全性,并且在硬件并行计算的环境下可以极大地提高加密速度．实验研究表明本加密算法具有较高的安全性．