开顶箱内自然气流的湍流统计特性(英文)

开顶箱内细致的湍流交换特性刻画有助于其在外场试验中的科学应用。本研究(2004 年 5 月份)使用三维超声风温仪在开顶箱内的高频观测资料细致分析了自然状态下的开顶箱内部湍流交换主要特征统计量。结果显示,与自然条件下相比,由于开顶箱的限制,其内的湍流交换表现出了十分独特的属性。开顶箱内大多数湍流统计量表现出十分清晰的日进程。湍流近似为各向同性,并在各个方向表现出很强的相关性。气团的时空结构呈现出与开顶箱形状类似的柱状结构。开顶箱内热力驱动的连续交换过程时常受到外部大尺度气团的入侵,从而表现出较强的间歇性。图3 表4 参16。

全球环境变化与中国国家安全

20世纪90年代以来,安全概念的内涵有了重大扩展。全球环境变化作为威胁人类安全的因素之一,对国家安全和社会的发展构成了新的挑战。由全球环境变化所引发的国家安全问题一方面直接与全球环境问题相联系,另一方面是通过国际事务中的冲突表现出来的。中国未来发展面临全球环境变化的严峻挑战。中国的全球环境变化人文因素研究需要关注可能对中国国家安全产生深远影响的重大环境变化问题,重视科学地评估中国自然和社会经济系统对全球环境变化影响的脆弱性,积极推动中国国家风险管理体系建设,将全球环境变化问题纳入风险管理之列,为我国可持续

Effects of ultrahigh pressure extraction conditions on yields and antioxidant activity of ginsenoside from ginseng

Ultrahigh pressure technique was employed to extract ginsenosides from roots of ginseng (Panax ginseng C.A. Meyer). The optimal conditions for ultrahigh pressure extraction (UPE) of total ginsenosides were quantified by UV-vis spectrophotometry with the ginsenoside Re as standard, the signal ginsenosides were quantified by HPLC and ELSD with ginsenosides Re, Rg(1), Rb-1, Rc and Rb-2 as standards. Orthogonal design was applied to evaluate the effects of four independent factors (extraction pressure, extraction temperature, extraction time and ethanol concentration) on the yield and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of ginsenoside, which are based on microwave extraction (ME), ultrasound extraction (UE), soxhlet extraction (SE) and heat reflux extraction (HRE) method. The results showed that UPE method can produce ginsenoside with the highest yield and the best radical scavenging activity compared to other used ones. Scanning electron microscopic (SEM) images of the plant cells after ultrahigh pressure treatment was obtained to provide visual evidence of the disruption effect.

Polyelectrolyte-functionalized ionic liquid for electrochemistry in supporting electrolyte-free aqueous solutions and application in amperometric flow injection analysis

As a green process, electrochemistry in aqueous solution without a supporting electrolyte has been described based on a simple polyelectrolyte-functionalized ionic liquid (PFIL)-modified electrode. The studied PFIL material combines features of ionic liquids and traditional polyelectrolytes. The ionic liquid part provides a high ionic conductivity and affinity to many different compounds. The polyelectrolyte part has a good stability in aqueous solution and a capability of being immobilized on different substrates. The electrochemical properties of such a PFIL-modified electrode assembly in a supporting electrolyte-free solution have been investigated by using an electrically neutral electroactive species, hydroquinone ( HQ) as the model compound. The partition coefficient and diffusion coefficient of HQ in the PFIL film were calculated to be 0.346 and 4.74 X 10(-6) cm(2) s(-1), respectively. Electrochemistry in PFIL is similar to electrochemistry in a solution of traditional supporting electrolytes, except that the electrochemical reaction takes place in a thin film on the surface of the electrode. PFILs are easily immobilized on solid substrates, are inexpensive and electrochemically stable. A PFIL-modified electrode assembly is successfully used in the flow analysis of HQ by amperometric detection in solution without a supporting electrolyte.

电极用纳米Ag_2O的电化学阻抗行为

用电化学阻抗技术(EIS)对具有不同粒径分布组成的氧化银电极进行了研究。通过建立合理的模拟等效电路,解析了各测试电极间电化学性能的差异。在充放电循环过程中,具有合适配比的混配电极A非法拉第电荷消耗减少,电极的传质传荷性能明显优于传统电极C和纯纳米粒子组成电极F,展示出可逆电极的电化学行为。通过对动电位阻抗谱的解析,发现电极反应经历了4个明显的动力学过程,对不同组成电极的动力学可控程度有了大致了解。

Analysis of norditerpenoid alkaloids extracted from Aconitum sinomantanum Nakai by electrospray ionization tandem mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) was applied simultaneously in determining norditerpenoid alkaloids from the roots of Aconitum sinomantanum Nakai ( RAS) based on molecular mass information. The tandem mass spectra (ESI-MSn) provided the alkaloidal structural information, through which the existence of these alkaloids was further confirmed. Accordingly, six known norditerpenoid alkaloids were simultaneously determined on the basis of their ESI-MSn spectra. Furthermore, based on the diagnostic fragmentation pathways of alkaloidal MSn, a rapid method for direct detection and characterization of alkaloids from an ethanolic extract of RAS was described.

核酸靶分子与苦参中生物碱成分的非共价作用研究

本文选择合成了与SARS病毒相关的DNA片段作为抗病毒药物筛选的靶分子.利用生物质谱技术,通过对该核酸分子与常见中药苦参中的两种主要生物碱成分的非共价复合作用的研究,探讨该方法作为药物筛选方法的可行性.

有机氨钙催化聚合脂肪族环酯

分别用经环氧丙烷和环氧丙烷/乙腈处理的氨钙催化剂催化聚合了ε-己内酯和L-丙交酯.研究了催化剂浓度、聚合时间、真空度、聚合温度和陈化温度等对聚合收率和聚合物粘均分子量的影响.结果表明,有机氨钙催化剂对ε-己内酯和 L-丙交酯的开环聚合有较高的催化活性 ,在较低的温度下和较短的时间内,即可获得较高的转化率和较高的分子量 ,而且具有一些“准活性聚合”的特点,分子量在一定范围内可控.陈化处理和乙腈的加入可以大大提高聚ε-己内酯的分子量 ,最大分子量达到27×104.

PEMFC催化剂的研究:自制Pt/C电催化剂的性质

研究了一种用于质子交换膜燃料电池(PEMFC)的自制Pt/C电催化剂(标记为THYT-1)的物理化学和电化学性质.将THYT-1电催化剂与E-TEK公司的同类电催化剂的组成、形态及电催化性能进行了比较.单电池测试结果显示,THYT-1的电催化性能优于E-TEK电催化剂.CV测试结果表明CO在这两种电催化剂上的电氧化性能相近;TEM分析表明两种催化剂上Pt晶粒在炭载体上呈均匀分布,平均粒径均为2～3nm;XPS和XRD测试结果表明两种催化剂中Pt主要以金属态存在.这些数据表明THYT-1催化剂的物理化学性质与E-TEK公司的相类似.

Kinetics of reactions of blocked isocyanates

Blocked isocyanates are widely used in many kinds of one-package coatings, powder coatings and adhesives. They have also been used in water-borne polyurethane. The kinetics and mechanism of the reactions of blocked isocyanates are reviewed and two urethane forming reaction mechanisms by which a blocked isocyanate can react with a nucleophile are provided. Furthermore, effects of isocyanate structure, reaction medium, catalyst and functionality on kinetics of blocked isocyanate are discussed in detail.

封闭异氰酸酯几种反应的动力学

封闭异氰酸酯广泛地应用于各种单组分涂料、粉末涂料和胶粘剂中。近年来 ,随着人们对水性聚氨酯的重视和开发 ,封闭异氰酸酯的重视和使用程度进一步加大。本文对封闭异氰酸酯的相关反应的动力学进行了综述 ,对两种不同的反应机理及其动力学的影响因素作了介绍

Modern spectral estimation of ICP-AES

The inductively coupled plasma atomic emission, spectrometry (ICP-AES) and its signal characteristics were discussed using modem spectral estimation technique. The power spectra density (PSD) was calculated using the auto-regression (AR) model of modem spectra estimation. The Levinson-Durbin recursion method was used to estimate the model parameters which were used for the PSD computation. The results obtained with actual ICP-AES spectra and measurements showed that the spectral estimation technique was helpful for the better understanding about spectral composition and signal characteristics.

Simultaneous voltammetric determination of acetophenetidin, aminopyrine, acetaminophenol and aminophenol on a glassy carbon electrode

The voltammetric behaviour of acetophenetidin(A(1)) aminopyrine(A(2)) acetaminophenol(A(3)) and aminophenol(A(4)) was investigated by linear-sweep, differential-pulse, cyclic voltammetry at a glassy carbon electrode. In a medium of 0.1 mol/L NaOH solution, 4 high sensitivity and resolution anodic peaks were obtained. Their peak potentials are about at 0.68 V, 0.51, 0.22 and - 0.06 V( vs. Ag/AgCl). They can be used for direct determination of A(1), A(2),A(3),A(4) in samples respectively. The method is simple and rapid. The mechanism of the electrode reaction was discussed.