射线理论下的浅海环境噪声场空间相干性分析及海底声学参数反演

基于射线理论,以简化海底模型为基础,获得了浅海噪声场空间相干性在频域上的表示方法,并用于海底声学参数反演。将风关海洋噪声看作分布在无限大平面上的点源,通过计算噪声场垂直方向上的能量分布,进一步获得空间两点噪声场频域相干性表达式。利用数值仿真验证了模型对于不同海底类型的敏感性。并结合噪声场空间两点的频域相干性海上实验数据,反演得到该处海域的底质类型,进一步获得海底声速、密度和声衰减系数。结果表明,反演得到的海底参数与实际情况符合较好,文中提出采用的这种计算方法能够有效的反映海底反射对于噪声场空间相干性的影响,并且可在一定程度上提高反演海底声学参数效率。     

Flotation-spectrophotometric determination of rhodium using stannous chloride and Rhodamine 6G

Summary The conditions for the formation of a rhodium compound with tin(II) and Rhodamine 6G, in HCl medium, and their flotation with organic solvents of low polarity have been examined. The effect of the organic solvent on the flotation has been observed. The compound with Rhodamine 6G, separated and washed, is dissolved in acetone. The acetone solution is a basis of the developed sensitive and precise flotation-spectrophotometric method. The molar absorptivity in this method is 4.0×10⁵ at 530 nm. Beer's law is obeyed in the concentration range 0.04–0.5g Rh/ml. The components molar ratios in the isolated compound were determined, and the formula [(R6G⁺)₃Rh(SnCl₃ ^–)₄]·[(R6G⁺)(SnCl₃ ^–)] was proposed. The effect of the other platinum metals on the determination of rhodium with Rhodamine 6G was examined.

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Flotation und spektrophotometrische Bestimmung von Rhodium mit Zinn(II)cblorid und Rhodamin 6G

Zusammenfassung Die Bildung einer Rhodiumverbindung mit Sn(II) und Rhodamin 6G in salzsaurem Medium und deren Flotation mit organischen Lösungsmitteln geringer Polarität wurden untersucht. Der Einfluß des organischen Lösungsmittels auf die Flotation ist sicher. Die Verbindung mit Rhodamin 6G wurde abgetrennt, gewaschen und in Aceton gelöst. Diese Lösung bietet die Grundlage für die ausgearbeitete genaue spektrophotometrische Methode. Die molare Absorptivität beträgt 4,0×10⁵ bei 530 nm. Im Konzentrationsbereich 0,04–0,5g Rh/ml wird das Beersche Gesetz befolgt. Die Bestimmung des Verhältnisses der Komponenten ergab als Formel [(R6G⁺)₃Rh(SnCl₃ ^–)₄]·[(R6G⁺)(SnCl₃ ^–)]. Der Einfluß anderer Platinmetalle auf die vorgeschlagene Bestimmungsmethode wurde untersucht.

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This work was supported by Research Program MR-I-32.     

Surface remelting of 316 L + 434 L sintered steel: microstructure and corrosion resistance

This study presents arc surface remelting of three types of sintered stainless steels carried out in order to constitute a homogeneous microstructure in the surface layer which is free from open and interconnected porosity. The main aim of this treatment was to improve functional properties of the sinters analysed, especially their resistance to pitting corrosion. The sinters were obtained from powders of 316 L and 434 L steels. The PM austenitic-ferritic stainless steels are used mainly in the automotive industry, but their general application is still limited due to relatively poor corrosion properties when compared to casts or wrought components. This study used the gas tungsten arc welding (GTAW) process as a method of economical surface treatment. The effect of surface treatment was evaluated based on macro- and microstructural observations, energy-dispersive X-ray spectroscopy (EDX) analysis, X-ray phase analysis, measurements of surface roughness and electrochemical examinations. It was found that a cellular or mixed cellular and dendritic structure was formed in the remelted zone of the sinters after remelting. X-ray analysis demonstrated that application of remelting contributes to formation of the austenitic phase in the surface layer. The corrosion resistance of the remelted surface layers was evaluated using polarization tests in 0.5 M NaCl solution. It was found that arc surface remelted layers exhibit much better anticorrosive properties than sinters without surface treatment. Microstructural observations of the surface of specimens after electrochemical tests showed only a few single pits in the remelted layer, while the surface of initial sinters was much more corroded.     

Electrodeposition of nickel/SiC composites in the presence of cetyltrimethylammonium bromide

Electrodeposition of SiC particles with nickel matrix in the presence of cetyltrimethylammonium bromide (CTAB) at two current densities was carried out. Surface chemistry (amount of acidic and basic superficial groups, surface charge, Ni²⁺ and Br⁻ adsorption) of the SiC powder in the presence of various CTAB amounts (0-1.1 mM) was studied. Cationic surfactant inhibited adsorption of cations and enhanced adsorption of anions on the positive charged carbide surface, but Br⁻/Ni²⁺ molar ratios for adsorbed ions were higher than in the bath. It was attributed to the CTAB adsorption realized predominantly by hydrophobic interactions between aliphatic chain of the molecule and SiC surface with the positive head group of CTA⁺ pointed toward the bulk solution. Increased SiC incorporation to the composite coating with CTAB addition was observed. Correlation between current efficiency and Br⁻/Ni²⁺ molar ratios for ions adsorbed on SiC was found. The influence of CTAB concentration on the cathodic polarization curves was also determined. Structure of the composite coatings was studied by microscopic observations. Microhardness of the fine-grained metal matrix composites was also determined.     

4,6-Dinitrobenzo[c]isothiazole: synthesis and 1,3-dipolar cycloaddition to azomethine ylide

1,3-Dipolar cycloaddition of 4,6-dinitrobenzo[c]isothiazole to (N-methyl-N-methylideneammonio)methanide (2 equiv.) gives 5,8-dimethyl-3b,6b-dinitrodecahydroisothiazolo[3,4-e]pyrrolo[3,4-g]isoindole, whose structure was confirmed by X-ray diffraction analysis.     

LC Determination of the Skin Exposure to Oxamyl on Greenhouse Workers and Comparison Between DAD and MS–MS Detection

An LC–DAD method was developed to determine residues of oxamyl on greenhouse workers’ skin. The wipe test was used to obtain samples from hands, forearms, neck and gloves of workers taking cactus cuttings 48 h after pesticide treatment. It was validated in a concentration range 50–5,000 ng mL^?1. The results on six workers and ten office employees indicated significant differences particularly in the hand samples. To avoid the overestimation owing to an interfering substance we proceeded to confirm these findings with LC–MS–MS, which found the pesticide only on the surface of the workers’ gloves, proving that there was indeed some UV interference.     

Gold nanoclusters protected by conformationally constrained peptides

The preparation and properties of a series of gold nanoclusters protected by thiolated peptides based on the alpha-aminoisobutyric acid (Aib) unit are described. The peptides were devised to form 0-3 C=O...H-N intramolecular hydrogen bonds, as required by their 3(10)-helical structure. The monolayer-protected clusters (MPCs) were prepared, using a modified version of the two-phase Brust-Schiffrin preparation, and fully characterized with (1)H NMR spectrometry, IR and UV-vis absorption spectroscopies, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The MPCs were obtained with core diameters in the range of 1.1-2.3 nm, depending on the reaction conditions. Structured peptides formed smaller clusters. The smallest MPC obtained is in agreement with the average formula Au(38)Pep(18). The results showed that the chemical integrity of the peptide is maintained upon monolayer formation and that the average number of peptide ligands per gold cluster is typically 75-85% the value calculated for alkanethiolate MPCs of similar sizes. The IR and NMR spectra indicated that in the monolayer the peptides are involved in both intra- and interligand C=O...H-N hydrogen bonds.     

Pesticides analysis by liquid chromatography and capillary electrophoresis

Nowadays, a wide range of pesticides are used in agricultural production, and their monitoring in samples of environmental and alimentary interest is of extreme importance to ensure, among others, the safety of consumption of foods. The aim of this work is to provide updated information about the major developments in CE and HPLC in pesticide analysis, covering relevant publications between 2004 and early 2006. The use of different sample pretreatment steps to provide a suitable extraction of these compounds from the different matrices as well as to increase the sensitivity of the determination is also discussed.