Diffusion-limited extraction of organic ions by a track-membrane interfaced vacuum inlet

Glycerol-wetted track membranes (polyethylene terephthalate) were used to interface a low-vacuum facility (approximately (10(-3) Torr) to an ambient pressure liquid analyte. High-field charge extraction conditions were routinely maintained between the liquid samples and a grid collector. The latter was positioned just near to the vacuum-facing side of such membranes. Upon establishing a steady-state charge extraction regime, the collector currents were monitored and recorded at various solute concentration levels. The collector currents, which depend on solute concentration, were found to agree with recent theoretical treatments of such processes. Both positively- and negatively-charged species from organic solutions were routinely extracted. Ion injection for the low- and the high-mobility species has favored the diffusion-limited and the evaporation-limited schemes, respectively. Variable concentrations of 1-pyrenoyl-methylpyridinium bromide as well as naphthylacetic and anthracenecarboxylic acids in glycerol were used.     

Influence of a non-uniform current density profile on quasiparticle excitations and thermally activated flux creep in YBa2Cu3O7−σ

The transport current density, flowing radially from the center of a superconducting disk to its perimeter, in a so-called Corbino geometry, results in a double action on the vortex motion when the applied magnetic field is perpendicular to the disk’s plane. First, the depinned vortices are set into a nearly circular motion in the plane of the disk. Second, the non-uniform current density profile activates the intrinsic weak links, resulting in a non negligible proximity dominated quasiparticle contribution. In turn, these intrinsic junctions impede the circular motion of vortices giving rise to a proximity influenced thermally activated flux creep. This provides a simple technique to deconvolute the flux motion and the quasiparticle induced components of the total dissipative resistivity broadening below T _c . The case for a YBaCuO disk is hereby examined and measured in this context. It is shown that such a deconvolution can be made and theoretical laws for the field dependences are also obtained and confirm the data. Furthermore, the paraconductivity region just above T _c (B) appears to be dominated by the macroscopic fluctuations accompanying the vortex core motion.     

Effect of the counterion on the steric and electronic structure of pyrylium cation

The effect of counterions on the stabilization of aromatic pyrylium cation, a heterocyclic analog of benzene, was examined by ab initio [MP2(full)/6-311++G**] method and density functional theory [B3LYP/6-311++G(d,p)(6d,10f)]. Structures of the charge-transfer molecular complexes formed by interaction of pyrylium cation with counterion are predicted. The principal role of the counterion in the stabilization of the pyrylium cation aromatic system is demonstrated. The stabilization results from both electron density transfer and covalent bonding.     

Direct mass-quantification of particulate deposits of polycyclic aromatic hydrocarbons by Fourier transform imaging microscopy

Successful coupling of imaging microscopy with Fourier transform spectrometry provides a new methodological approach. This was applied to the direct analysis of particulate deposits of polycyclic aromatic hydrocarbons (PAHs). The fluorescence signals of single microscopic particulates were found to be proportional to their mass, obtained from the corresponding HPLC results. Special fluorescence characteristics related to individual particle analysis were studied. The sensitivity of the proposed method to PAHs in soil is in the sub-ppb range, similar to HPLC results. Analysis of inhomogeneous PAH-particulates was demonstrated, as well as the resolution of photochemical products of PAHs. The effects of particulate orientation relative to the detector upon quantification are discussed.     

Steric and electronic structure of complexes of pyrylium and thiopyrylium cations with borabenzene anion

The coordination of pyrylium and thiopyrylium cations with borabenzene was studied by DFT [B3LYP/6-311++G(d,p)] calculations. The structures of charge-transfer molecular complexes formed by the aromatic ions were predicted. The stabilization is due both to electron density transfer and to covalent bonding.     

A new sono-electrochemical method for enhanced detoxification of hydrophilic chloroorganic pollutants in water

A new method for detoxification of hydrophilic chloroorganic pollutants in effluent water was developed, using a combination of ultrasound waves, electrochemistry and Fenton's reagent. The advantages of the method are exemplified using two target compounds: the common herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and its derivative 2,4-dichlorophenol (2,4-DCP). The high degradation power of this process is due to the large production of oxidizing hydroxyl radicals and high mass transfer due to sonication. Application of this sono-electrochemical Fenton process (SEF) treatment (at 20 kHz) with quite a small current density, accomplished almost 50% oxidation of 2,4-D solution (300 ppm, 1.2 mM) in just 60 s. Similar treatments ran for 600 s resulted in practically full degradation of the herbicide; sizable oxidation of 2,4-DCP also occurs. The main intermediate compounds produced in the SEF process were identified. Their kinetic profile was measured and a chemical reaction scheme was suggested. The efficiency of the SEF process is tentatively much higher than the reference degradation methods and the time required for full degradation is considerably shorter. The SEF process maintains high performance up to concentrations which are higher than reference methods. The optimum concentration of Fe²⁺ ions required for this process was found to be of about 2 mM, which is lower than that in reference techniques. These findings indicate that SEF process may be an effective method for detoxification of environmental water.     

Methods for Organization of Iteration Loops in Calculating Dynamic Modes of Large Circuits Based on Decomposition

Doklady Mathematics - A method of organizing iteration loops in calculating dynamic modes of large electronic circuits based on a decomposition of the modeled circuit into subcircuit components is...     

Photochemical study of anthracene crystallites by Fourier transform spectroscopic imaging.

Fourier transform-based spectroscopic imaging was used for direct, time-resolved, analysis of UV-irradiated anthracene crystallites. Well-resolved fluorescence spectra were obtained at a spatial resolution of 1 microm. The appearance of such photochemical by-products as dianthracene and anthraquinone was monitored throughout the irradiation experiments. Under deaerated conditions, photolysis of anthracene was accompanied by formation of dianthracene. When performed under aerated conditions, however, the spectral data indicated formation of both dianthracene and anthraquinone. Spectral features obtained for the directly monitored photolysis of anthracene are discussed in respect to the structural and compositional modifications in such crystallites. Capabilities of the spectral imaging device for the quantification of the photochemical products of anthracene are discussed.