Photoelectron Spectra and Molecular Properties: Real-Time Gas Analysis in Flow Systems

For the analysis and optimization of numerous gas phase reactions in flow-systems, photoelectron spectroscopy has proven most valuable. This real-time measuring probe allows one to determine—with millimol quantities and within a few hours—the temperatures for different decomposition channels. Simultaneously, main products are characterized and, if need be, their yield can be improved. By careful performance of the experiment, short-lived and/or reactive molecules such as P₂, thioformaldehyde or silabenzene can be detected. PE-spectroscopic gas analysis is of particular advantage in the search for heterogeneous catalysts; they can be tested within a day using gas mixtures of varying composition over the temperature range from 300 K to 1300 K. In addition, PE-spectrometers are well-suited for on-line connection to computers; portable instruments for laboratory use are under development.     

Preparation of DSA@MNPs and application as heterogeneous and recyclable nanocatalyst for oxidation of sulfides and oxidative coupling of thiols

Research on Chemical Intermediates - Dopamine sulfamic acid-functionalized magnetic Fe3O4 nanoparticles (DSA@MNPs) were prepared by a very simple and inexpensive procedure using commercial...     

Phase relations and binary clathrate hydrate formation in the system H2-THF-H2O

Experimentally determined equilibrium phase relations are reported for the system H2-THF-H2O as a function of aqueous tetrahydrofuran (THF) concentration from 260 to 290 K at pressures up to 45 MPa. Data are consistent with the formation of cubic structure-II (CS-II) binary H2-THF clathrate hydrates with a stoichiometric THF-to-water ratio of 1:17, which can incorporate modest volumes of molecular hydrogen at elevated pressures. Direct compositional analyses of the clathrate phase, at both low (0.20 mol %) and stoichiometric (5.56 mol %) initial THF aqueous concentrations, are consistent with observed phase behavior, suggesting full occupancy of large hexakaidecahedral (51264) clathrate cavities by THF, coupled with largely complete (80-90%) filling of small dodecahedral (512) cages by single H2 molecules at pressures of >30 MPa, giving a clathrate formula of (H2) < or =2.THF.17H2O. Results should help to resolve the current controversy over binary H2-THF hydrate hydrogen contents; data confirm recent reports that suggest a maximum of approximately 1 mass % H2, this contradicting values of up to 4 mass % previously claimed for comparable conditions.     

Three-dimensional simulation of long-wavelength free-electron lasers with helical wiggler and ion-channel guiding

A three-dimensional simulation of a steady-state amplifier model of a long-wavelength free-electron laser (FEL) with realizable helical wiggler and ion-channel guiding is presented. The set of coupled nonlinear differential equations for electron orbits and fields of TE 11 mode in a cylindrical waveguide are solved numerically by the Runge-Kutta algorithm with averages calculated by the Gaussian quadrature technique. Self-fields and space-charge effects are neglected, and the electron beam is assumed to be cold and slippage is ignored. The parameters correspond to the Compton regime. Evolution of the radiation power and growth rate along the wiggler is studied. Ion-channel density is chosen to obtain optimum efficiency. Simulations are preformed for the FEL operating in the neighborhood of 35 GHz and 16.5 GHz for the electron beam energies of 250 keV and 400 keV, respectively. The result of the saturated efficiency was found to be in good agreement with the simple estimation based on the phase-trapping model.     

Hollow fiber-based liquid-liquid-liquid microextraction followed by flow injection analysis using column-less HPLC for the determination of phenazopyridine in plasma and urine

Hollow fiber-based liquid-liquid-liquid microextraction (HF-LLLME) followed by flow injection analysis and diode array detection (FIA-DAD) was applied as a simple and sensitive quantitative method for the determination of phenazopyridine in urine and plasma samples. Flow injection system included a conventional HPLC system (without a chromatographic column) and a diode array detector. The extraction of phenazopyridine was carried out using diphenyl ether as the organic phase for filling the pores of the hollow fiber wall, and 0.1 M H(2)SO(4) solution as acceptor phase in the lumen of the fiber. The factors affecting the HF-LLLME and flow injection analysis including type of organic solvent, pH of donor phase, extraction temperature, extraction time, stirring rate, and pH of mobile phase were investigated and the optimal extraction conditions were established. With the consumption of 5 mL of sample solution, the enrichment factor was about 230. The limit of detection was 0.5 μg/L with inter- and intra-day precision being (RSD%) 6.9 and 4.9, respectively. Excellent linearity was found between 5 and 200 μg/L.     

Polynomial Root-Finding Methods Whose Basins of Attraction Approximate Voronoi Diagram

Given a complex polynomial p(z) with at least three distinct roots, we first prove that no rational iteration function exists where the basin of attraction of a root coincides with its Voronoi cell. In spite of this negative result, we prove that the Voronoi diagram of the roots can be well approximated through a high order sequence of iteration functions, the Basic Family, B _m (z), m≥2. Let θ be a simple root of p(z), V(θ) its Voronoi cell, and A _m (θ) its basin of attraction with respect to B _m (z). We prove that given any closed subset C of V(θ), including any homothetic copy of V(θ), there exists m ₀ such that for all m≥m ₀, C is also a subset of A _m (θ). This implies that when all roots of p(z) are simple, the basins of attraction of B _m (z) uniformly approximate the Voronoi diagram of the roots to within any prescribed tolerance. Equivalently, the Julia set of B _m (z), and hence the chaotic behavior of its iterations, will uniformly lie to within prescribed strip neighborhood of the boundary of the Voronoi diagram. In a sense, this is the strongest property a rational iteration function can exhibit for polynomials. Next, we use the results to define and prove an infinite layering within each Voronoi cell of a given set of points, whether known implicitly as roots of a polynomial equation, or explicitly via their coordinates. We discuss potential application of our layering in computational geometry.     

Microporous silica with nanolayer structure coated with renewable organic solvent film as a novel extracting phase: A combination of solid- and liquid-phase microextraction

A new method based on combination of solid- and liquid-phase microextraction was developed. For the first time, porous flower-like silica microstructures with nanometric layers were created on the surface of the stainless steel wire by a new facile hydrothermal process. The fiber, coated with a suitable organic solvent, was applied for microextraction of some organophosphorus pesticides from aqueous samples followed by gas chromatography-nitrogen phosphorous detection. Method detection limits were between 0.6 and 3 ng L⁻¹. Relative standard deviations for intra- and inter-day precision were 4.4–7.3% and 5.1–7.8%, respectively. Fiber-to-fiber reproducibility for five prepared fibers was 6.3–8.4%. Tap, river and waste water samples were analyzed for evaluation of the method in real sample analysis. Relative recoveries for spiked tap, river and waste water samples were in the range of 94–101%, 89–97% and 82–103%, respectively. In addition, the method was compared with two commercial solid-phase microextraction (SPME) fibers, single drop microextraction (SDME) and liquid-phase microextraction (LPME). The present method showed higher extraction efficiency as compared with SDME, LPME and commercial SPME fibers.