Molecular dynamics simulations of the surface tension of ionic liquids

We report molecular dynamics computer simulations of the surface tension and interfacial thickness of ionic liquid-vapor interfaces modeled with a soft core primitive model potential. We find that the surface tension shows an anomalous oscillatory behavior with interfacial area. This observation is discussed in terms of finite size effects introduced by the periodic boundary conditions employed in computer simulations. Otherwise we show that the thickness of the liquid-vapor interface increases with surface area as predicted by the capillary wave theory. Data on the surface tension of size-asymmetric ionic liquids are reported and compared with experimental data of molten salts. Our data suggest that the surface tensions of size-asymmetric ionic liquids do not follow a corresponding states law.     

Heavy metal analysis of rainwaters: A comparison of TXRF and ASV analytical capabilities

The aim of this work consisted on the implementation of sufficiently accurate and sensitive analytical procedure for the analysis of metal concentration in rainwater. Different sample preparation procedures were tested to achieve the required concentration prior to direct total reflection X-ray fluorescence (TXRF) analysis. TXRF and anodic stripping voltammetry (ASV) were compared in regard to achieved detection limits, precision and accuracy.     

Some remarks on the homogenization of the dam problem

The homogenization of the dam problem is discussed in the general weak formulation by means of the technique of correctors. In the two special cases of horizontal layers and of the isotropic coefficients with separated variables the problem is solved. However, in general, the unsaturated region is not stable for the homogenization, as a counterexample by Alt shows.     

Structures of daurosides A and B — New acylated coumarin glycosides fromHaplophyllum dauricum

From the roots and epigeal parts ofHaplophyllum dauricum (L.) G. Don., new acylated courmarin glycosides have been isolated: dauroside A, C₂₃H₂₈O₁₃, mp 145–147°C (ethanol), [] _D ²² – 72.7° (methanol), and dauroside B, C₃₀H₃₂O₁₄, mp 145–150°C (methanol) [] _D ²² 0° (pyridine). Their structures have been established on the basis of chemical transformations and IR, UV, mass,¹H NMR and¹³C NMR spectra.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 142–147, March–April, 1983.     

A simple device for continuous and selective detection of water vapour evolved during thermal decomposition reactions

A technique developed for the continuous and selective detection of water vapour formed during thermal decomposition reactions is described. The device can be connected to different types of thermoanalytical instruments without any difficulties. The detector can closely follow changes in the amount of water released during decomposition reactions, with negligible time delay. The signal curves obtained by the detector can be compared to the simultaneously recorded thermoanalytical curves and used to determine the step in which the water was released. The device as a free standing unit can be used to detect water plugs in different gas flows as well.     

Sensitive determination of diquat by a kinetic method using the stopped-flow mixing technique

A simple, sensitive, selective, fast and inexpensive assay for the determination of diquat is proposed. The method is based on the reduction of the herbicide to a strongly fluorescent monocation radical with sodium dithionite. The initial rate of this reaction is directly proportional to the diquat concentration. The stopped-flow mixing technique was used because the kinetic data can be obtained in only 7 s, meaning that the method can be automated. The calibration graph is linear over the range 5-500 ng ml-1 and the precision (RSD) is close to 1.2%. The applicability of the method was demonstrated by determining the herbicide in different kinds of samples.     

Activity measurements in the ternary system NaBr+NaClO4+H2O at 25°C

The activity coefficients of sodium bromide in the ternary system NaBr+NaClO₄+H₂O were determined at 25°C and constant ionic strength of 0.1, 0.5, 1, 2, and 3 mol-kg^?1 from emf of the cell without, liquid junction $$ISE - Na|NaBr(m_A ), NaClO_4 (m_B ), AgCl_{(s)} 1 Ag$$ The experimental activity coefficients were comparatively analyzed by using the Harned, Scatchard, Pitzer and Lim-HOLL treatments. All these methods are adequate for the analysis of the experimental data. The results have been compared with those of Lanier for the system: NaCl+NaClO₄+H₂O. The Gibbs excess energy of mixing was obtained and qualitatively interpreted in terms of ionic interactions.     

Elasticity and electro-magneto-elasticity of general-relativistic systems

This essay aims at demonstrating the interest for a genuine continuum mechanics and, more restrictively, elasticity of general-relativistic systems in cases where the Einsteinian gravitational picture cannot be deleted, e.g., in elastic gravitational-wave detectors and in the study of elastic oscillations of solid stars. The same foundations, constitutive theory, and methodology (superimposition of perturbations on finite initial states) apply to both cases, which also demand a generalization to comprehend electrodynamical-mechanical couplings, electroelasticity in the first case (use of piezoelectricity), and magnetoelasticity in the second case (presence of extremely intense magnetic fields).     

Heterocyclen aus α-nitroolefinen. XI . 1,2-oxazine aus α-nitroolefinen und β-dicarbonylverbindungen

Dihydro-1,2-oxazines 8 and 12-oxazines 12 are formed by the reaction of the nitronic acids of the adducts of α-nitroolefins and β-dicarbonyl compounds ( 6 ) by two ways: A ) The nitronic acids 6 are heated in a boiling solution of urea in ethanol or methanol. B ) The nitronic acids 6 are reduced with an aqueous solution of ammoniachloride and sodium sulfide. ¹H-nmr and ¹³C-nmr investigations prove the constitutions. The mechanism is discussed.