表面分散过程的分形研究

盐类和氧化物等活性组分在一定条件下,可在高比表面载体上自发分散。研究这些过程对多相催化剂、吸附剂的制备过程理解和控制无疑是重要的。这类分散过程已被系统地研究,并提出了单层分散模型,对CuCl_2/γ-Al_2O_3、HgCl_2/活性炭等多种体系,测定了单层分散阈值。表面化学习惯上理解为就是二维的化学。早在1931年Tayor就指出表面是不均匀的,但这种不均匀性是作为对理想二维表面的修正而引入的,如TLK模型。表面科学的这些基本概念其数学基础是欧基里德几何学,其物理背景是晶体结构,不规则性就是指晶体结     

Thermodynamics of Solvation of 18-Crown-6 and Its Alkali-Metal Complexes in Various Solvents

Heats of solution of 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) in acetonitrile, 1,2-dichloroethane, N,N-dimethylformamide, dimethyl sulfoxide, nitromethane, propylene carbonate, pyridine and water were measured at 25 °C and the enthalpies of the transfer of 18-crown-6 from waterto the aprotic solvents were derived. The thermodynamic quantities, G₁°, H₁° and T S₁°, for the formation of the[M(18-crown-6)]⁺ (M⁺ = Na⁺, K⁺, Rb⁺, Cs⁺, NH₄ ⁺) complexeswere determined by titration calorimetry in dimethyl sulfoxide containing0.1 mol dm^-3 (C₂H₅)₄NClO₄ as a constant ionic medium at 25 °C. These thermodynamic quantities suggest that the complexationof 18-crown-6 with the alkali-metal ions mainly reflects the different solvationof 18-crown-6 and also the different degree of solvent structure.     

Effect of glutaraldehyde on the activity of some DNA restriction endonucleases

The effect of the bifunctional crosslinking reagent glutaraldehyde on the activity of the restriction enzymes Bam HI,Hind III, EcoRI, and Tthlll I was investigated. The four enzymes exhibited differential sensitivity to inactivation. Tthlll I was the most sensitive, with activity losses occurring at levels of 0.0025% and above.Hind III was the most stable of the four and remained fully active at concentrations as high as 0.075%. Addition of BSA to incubation mixtures generally had a stabilizing effect. Implications of these results for the design of glutaraldehyde-based methods for the immobilization of restriction endonucleases are discussed.     

Electroanalytical sensors for nonconducting media based on electrodes supported on perfluorinated ion-exchange membranes

Electroanalytical sensors, suitable for the analysis and monitoring of electroactive analytes present in gaseous phase or low-conductive liquid media, and based on electrodes in close contact with perfluorinated ion-exchange polymers are reviewed. The basic operative mechanism of these sensors, in which ion-exchange polymers act as solid polymer electrolytes (SPE's), is thoroughly discussed, while stressing the fundamental reasons why their behavior differs from that of conventional membrane electrodes. The procedures for preparing composite working electrodes by coating one side of ion-exchange membranes with stable porous films of conductive materials are described, along with the most common strategies followed to assemble this type of sensors. Useful examples of measurements in electrolyte-free media of inorganic and organic electroactive species of interest mainly for environmental analysis are given. Future prospects for the development of these sensors are also discussed.     

流动注射萃取火焰原子吸收光谱法测定硫酸镍电解液中微量铅

本文采用流动注射在线萃取火焰原子吸收光谱法测定硫酸电解液中微量铅，考察了水相介质，共存离子，萃取装置，相比等因素的影响。分析含铅１．４ｍｇ／Ｌ和０．１６ｍｇ／Ｌ的试样，分析值的相对标准偏差（ｎ＝１０）分别为３．９％和１２．３％，方法检出限为０．０２４ｍｇ／Ｌ。     

The circular chemistry conceptual framework: A way forward to sustainability in industry 4.0

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Molecular complexes of crown ethers. Part 3. Effect of cations on charge transfer complexes with TCNE

The intermolecular charge transfer complexes (CT) of two crown ethers (CE), viz, B15C5 and DB18C6 (as donors), and tetracyanoethylene (TCNE), as acceptor, were studied in the UV-visible region in dichloroethane (DCE), at 298.2 K. The sequence of addition of the cation was varied in the case of B15C5 such that in one system the sequence was (CE+Cation)+TCNE and in the other (CE+TCNE)+cation. These two systems were found to be non-interchangeable, even under reflux conditions, giving differentK _c values which were explained as being due to the different geometries of the CE. For the first sequence, the values most affected depended on the fit of the metal cation with the ether cavity, thus in B15C5, Na⁺ showed the greatest effect, while for DB18C6 it was K⁺.     

Effect of mobile phase density gradients on efficiency in packed column supercritical fluid chromatography

Summary The efficiency of packed columns was measured as a function of flow rate, temperature, outlet density, and the density differential across the column, unsing pure carbon dioxide as the mobile phase. Although density differentials are often blamed for a serious loss in efficiency in packed column supercritical fluid chromatography, the results show that efficiency was not a function of the density differential. Peak shapes suggest that apparent loss in efficiency is actually due to inadequate solubility of the solute in carbon dioxide.     

降脂经验方降脂作用的临床观察

采用自拟的降脂方治疗血胆增高患者６３人，并与用月见草油胶丸治疗患者６１人比较，前者疗效优于后者，两组有显著性差异。     

Numerical solution of minimax problems of optimal control,part 1

This paper contains general transformation techniques useful to convert minimax problems of optimal control into the Mayer-Bolza problem of the calculus of variations [Problem (P)]. We consider two types of minimax problems: minimax problems of Type (Q), in which the minimax function depends on the state and does not depend on the control; and minimax problems of Type (R), in which the minimax function depends on both the state and the control. Both Problem (Q) and Problem (R) can be reduced to Problem (P).For Problem (Q), we exploit the analogy with a bounded-state problem in combination with a transformation of the Jacobson type. This requires the proper augmentation of the state vectorx(t), the control vectoru(t), and the parameter vector , as well as the proper augmentation of the constraining relations. As a result of the transformation, the unknown minimax value of the performance index becomes a component of the parameter vector being optimized.For Problem (R), we exploit the analogy with a bounded-control problem in combination with a transformation of the Valentine type. This requires the proper augmentation of the control vectoru(t) and the parameter vector , as well as the proper augmentation of the constraining relations. As a result of the transformation, the unknown minimax value of the performance index becomes a component of the parameter vector being optimized.In a subsequent paper (Part 2), the transformation techniques presented here are employed in conjunction with the sequential gradient-restoration algorithm for solving optimal control problems on a digital computer; both the single-subarc approach and the multiple-subarc approach are discussed.This research was supported by the National Science Foundation, Grant No. ENG-79-18667, and by Wright-Patterson Air Force Base, Contract No. F33615-80-C3000. This paper is a condensation of the investigations reported in Refs. 1–7. The authors are indebted to E. M. Coker and E. M. Sims for analytical and computational assistance.