ON DIRECT METHOD OF SOLUTION FOR A CLASS OF SINGULAR INTEGRAL EQUATIONS

In this article, by introducing characteristic singular integral operator and associate singular integral equations (SIEs), the authors discuss the direct method of solution for a class of singular integral equations with certain analytic inputs. They obtain both the conditions of solvability and the solutions in closed form. It is noteworthy that the method is different from the classical one that is due to Lu.     

Novel flow injection-fluorometric method for the determination of trace silicate and its application to ultrapurified water analysis

A highly sensitive fluorescence quenching method for the determination of silicate based on the formation of an ion associate between molybdosilicate and Rhodamine B (RB) in nitric acid medium was developed. A flow injection system coupled with a fluorescence detector was used for the measurement of fluorescence intensity at 560 and 580 nm as excitation and emission wavelengths, respectively. The calibration graph for Si showed a linear range of 0.1–5 ng cm⁻³ with correlation coefficient of 0.9999, and the detection limit of 0.06 ng cm⁻³. The proposed method was successfully applied to the determination of silicate in ultrapurified water with satisfactory results.     

原子发射光谱法间接测定黄连素片剂中盐酸小檗碱的研究

本文提出了离子对-原子发射光谱间接测定黄连素片剂中盐酸小檗碱的新方法。发现用1,2-二氯乙烷作萃取剂效果最佳。用此怯测定实际样品的结果与药典法一致,相对误差为0.61％,单一测定的相对标准偏差为0.67％。本法还可在盐酸普鲁卡因共存下单独测定盐酸小檗碱。方法可靠、适用,选择性较好。     

Membranes,peptides, and disease: Unraveling the mechanisms of viral proteins with solid state nuclear magnetic resonance spectroscopy

The interplay between peptides and lipid bilayers drives crucial biological processes. For example, a critical step in the replication cycle of enveloped viruses is the fusion of the viral membrane and host cell endosomal membrane, and these fusion events are controlled by viral fusion peptides. Thus such membrane-interacting peptides are of considerable interest as potential pharmacological targets. Deeper insight is needed into the mechanisms by which fusion peptides and other viral peptides modulate their surrounding membrane environment, and also how the particular membrane environment modulates the structure and activity of these peptides. An important step toward understanding these processes is to characterize the structure of viral peptides in environments that are as biologically relevant as possible. Solid state nuclear magnetic resonance (ssNMR) is uniquely well suited to provide atomic level information on the structure and dynamics of both membrane-associated peptides as well as the lipid bilayer itself; further ssNMR can delineate the contribution of specific membrane components, such as cholesterol, or changing cellular conditions, such as a decrease in pH on membrane-associating peptides. This paper highlights recent advances in the study of three types of membrane associated viral peptides by ssNMR to illustrate the more general power of ssNMR in addressing important biological questions involving membrane proteins.     

Formation of polymeric micelles with amino surfaces from amphiphilic AB‐type diblock copolymers composed of poly(glycolic acid lysine) segments and polylactide segments

Amphiphilic AB‐type diblock copolymers composed of hydrophobic poly(L ‐lactide) (PLA) segments and hydrophilic poly(glycolic acid lysine) [poly(Glc‐Lys)] segments with amino side‐chain groups self‐associated to form PLA‐based polymeric micelles with amino surfaces in an aqueous solution. The average diameter of the loose core–shell polymeric micelles for poly(Glc‐Lys) [number‐average molecular weight (M_n) = 1240]‐b‐PLA (M_n = 7000) obtained by a dimethyl sulfoxide/water dialysis method was estimated to be about 50 nm in water by dynamic light scattering measurements. The size and shape of the obtained polymeric micelles were further observed with transmission electron microscopy and atomic force microscopy. To investigate the possibility of applying the obtained PLA‐based polymeric micelles as bioabsorbable vehicles for hydrophobic drugs, we tested the entrapment of drugs in poly(Glc‐Lys) (M_n = 1240)‐b‐PLA (M_n = 7000) micelles and their release with doxorubicin as a hydrophobic drug. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1426–1432, 2002     

IR spectra,conformational lability,and intermolecular interactions in long-chain aliphatic compounds

Investigations of the conformational lability and intermolecular interactions in long-chain aliphatic compounds (LACs), namely, in carboxylic acid derivatives (alkyl- and alkoxybenzoic acids; alkylcyclohexanecarboxylic acids and their completely or partially fluoroalkyl-substituted derivatives), 4-cyano-4-p-alkoxybiphenyls, 4-cyano-4-p-alkylbiphenyls, and cholesterol p-n-butyloxybenzoate are reviewed. Major attention is paid to experimental and theoretical IR spectroscopy data. Differential thermal analysis, polarization microscopy, and X-ray diffraction data are also taken into account. A more detailed treatment is presented on IR spectrum simulation based on data about the conformational lability of molecules and their specific (H-bonding) intermolecular interactions. The first mechanism is responsible for the conformational type of polymorphism in LACs and for the structure of the latter in solid crystal (SC) and liquid crystal (LC) states and in isotropic liquids (ILs). The second mechanism complements the structure-forming aspect of polymorphism in carboxylates, which is due to a rearrangement of hydrogen bond systems in H-complexes during polymorphic transitions to the LC and IL states. Both mechanisms are reflected in IR absorption spectra. A more adequate interpretation is possible in order to explain the many spectral features associated with the structure of LAC polymorphs and their H-complexes if these mechanisms are taken into account.Original Russian Text Copyright © 2004 by L.M. BabkovTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 389–397, May–June, 2004.     

Applications of ion associates for the microdetermination of vardenafil using atomic emission spectrometry

A simple, accurate, precise and sensitive method has been developed for the determination of Vardenafil (Vd) using direct coupled plasma atomic emission spectrometry. The ion associates formed as a result of the reaction of vardenafil with ammonium reineckate, Mn(II) and Co(II) thiocyanates and sodium cobaltinitrite are precipitated. The solubility of the solid complexes under the optimum conditions of pH and ionic strength was studied. Saturated solutions of each ion associate at different temperatures under the optimum precipitation conditions were prepared, and the metal ion content in the supernatant was determined. The solubility products were thus calculated at different temperatures, and the thermodynamic parameters ΔH, ΔG and ΔS were calculated. The method has been used for the determination of vardenafil (1.36–68.32 μg·mL⁻¹) in pure solutions and in Levitra tablets.     

Group divisible designs with three unequal groups and larger first index

We show the necessary conditions are sufficient for the existence of group divisible designs (or PBIBDs) with block size k=3 with three groups of size (n,2,1) for any n≥2 and any two indices with λ₁>λ₂.     

关联规则向量化挖掘算法及其在车险精算中的应用

本文首先回顾了关联规则的基本概念和传统的Apriori算法，然后利用关联规则的数据库是布尔型数据库的特点，在计算关联规则的支持度和置信度的时候引进向量数乘和向量内积的概念，得到关联规则向量化挖掘算法ARVDA，避免全数据库逐条记录模式匹配和属性分层，提高算法的速度．最后，本文利用提升度量关联规则的重要性，采用单独追踪和对比分析方法，衡量车险精算中风险因子的有效性．结果表明把车辆使用性质作为车险定价的分级因素是比较合理的，对于非运营车辆需要合理的费用附加．     

Ultratrace determination of phosphorus in ultrapurified water by a slope comparison method

The analytical method for the determination of phosphorus in ultrapurified water was developed. Ultrapurified water was evaporated to concentrate phosphorus and the final sample volume for analysis was 10 ml. In 0.55 mol l⁻¹ HCl, orthophosphate forms molybdophosphate, and then the molybdophosphate forms ion associate with Malachite Green (MG), which can be collected on a tiny membrane filter (diameter: 5 mm, and effective filtering diameter: 2 mm). After the ion associate on the membrane filter is dissolved together with the membrane filter in 1 ml of methyl cellosolve (MC), the absorbance of MC solution is measured at 627 nm by a flow injection-spectrophotometric detection technique. When 10 ml of the sample solution was used for the procedures and absorbance measurement, the calibration graph is linear up to about 500 ng l⁻¹ of phosphorus and the detection limit was 8 ng l⁻¹ (S/N=3). For the determination of phosphorus in an ultrapurified water, 10-40 ml of sample solutions were transferred into poly(tetrafluoroethylene) (PTFE) beaker and evaporated to 5 ml or to dryness. To them, 0.003 mol l⁻¹ HCl was added to get 10 ml of final solution, which was used as sample. Phosphate is determined by comparing the slope of the varied sample volume after evaporation/concentration with a slope of the standard calibration graph (a slope comparison method: SCM). The SCM enables to evaluate the concentration of phosphate in ultrapurified waters more sensitively and accurately.