On Riemann surfaces with non-unique cyclic trigonal morphism

A closed Riemann surface which can be realized as a 3-sheeted covering of the Riemann sphere is called trigonal, and such a covering will be called a trigonal morphism. If the trigonal morphism is a cyclic regular covering, the Riemann surface is called cyclic trigonal Riemann surface. Accola showed that the trigonal morphism is unique for Riemann surfaces of genus greater or equal to 5. Using the characterization of cyclic trigonality by Fuchsian groups given in [3], we obtain the Riemann surfaces of low genus with non-unique trigonal morphisms. Partially supported by BFM2002-4801. Partially supported by the Swedish Research Council (VR)     

Ni(II) complexes with 8-aminoquinoline derivatives

Some Ni(II) complexes with 5,7-dicloro-8-aminoquinoline (dcaq), 5,7-dibromo-8-aminoquinoline(dbaq) and 5,7-diiodo-8-aminoquinoline(diaq) are described. The compounds are of stoichiometry NiL₂X₂(L= dcaq, dbaq, diaq; X= NO^?₃ and L= dbaq; X= Cl^?, Br^?, I^?, NCS^?) and NiLX₂·H₂O(L= dcaq, diaq; X= Cl^?). The electronic spectra and magnetic susceptibility data at room temperature, are consistent with octahedral geometry for the Ni(II) in each compound. I.r. spectra show the presence of ionic and bridging nitrate groups in the compounds NiL₂(NO₃)₂(L= dcaq, dbaq, diaq) and we assign them polymeric structures. Polymeric structures with bridging chloride are proposed for the compounds NiLCl₂·H₂O(L= dcaq, diaq) and monomeric octahedral structures for NiL₂X₂(L= dbaq; X= Cl, Br, I, NCS).     

Design of a 35 GHz gyrotron

The conceptual design of a 35 GHz gyrotron has been developed consistently with the complex formulation of the electric field longitudinal distribution in the resonant cavity. Some models of magnetron injection guns able to produce laminar beams have been investigated leading to the design of an electron gun capable of generating a current of 5 A with a perpendicular velocity dispersion of 0.5%. The device includes three magnetic systems producting flat axial magnetic induction profiles of 1.05 kG, 13.2 kG and 0.65 kG in the cathode, cavity and collector regions, respectively. The gyrotron has been designed for pulsed operation in the TE₀₂₁ mode. Under the soft self-excitation condition, the maximum attainable efficiency is 40% with an output power of 100 kW. An analysis of the collector thermal behaviour has been carried out as well as a study of the thermophysical properties of the alumina window to be used.     

Synthesis,isolation, and thermal behavior of polybutadiene grafted with poly(2,3,4,5,6‐pentafluorostyrene)

2,3,4,5,6‐Pentafluorostyrene (PFS) was copolymerized with polybutadiene (PB) in tetrahydrofuran using benzoyl peroxide as the initiator at 50, 60, and 80 °C. The copolymerizations follow typical radical polymerization kinetics and behavior. The grafting parameters were evaluated as a function of monomer conversion, initiator concentration, and/or temperature by gel permeation chromatography of directly injected copolymerization mixtures. The grafting efficiencies and grafting ratios are most consistent with a system that terminates by combination and whose graft sites are generated by hydrogen abstraction of allylic radicals by primary initiator radicals. Pure graft copolymers were isolated by extracting unreacted PB into hexanes and PPFS homopolymer into acetone. The similarity of the glass transition temperatures of the PPFS grafts and the corresponding extracted PPFS homopolymers confirms that their lengths are approximately equal. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2874–2891, 2005     

Nucleophilic Reactivity of a Nitride‐Bridged Diuranium(IV) Complex: CO2 and CS2 Functionalization

Thermolysis of the nitride‐bridged diuranium(IV) complex Cs{(μ‐N)[U(OSi(O^tBu)₃)₃]₂} ( 1 ) showed that the bridging nitride behaves as a strong nucleophile, promoting N?C bond formation by siloxide ligand fragmentation to yield an imido‐bridged siloxide/silanediolate diuranium(IV) complex, Cs{(μ‐N^tBu)(μ‐O₂Si(O^tBu)₂)U₂(OSi(O^tBu)₃)₅}. Complex 1 displayed reactivity towards CS₂ and CO₂ at room temperature that is unprecedented in f‐element chemistry, affording diverse N‐functionalized products depending on the reaction stoichiometry. The reaction of 1 with two equivalents of CS₂ yielded the thiocyanate/thiocarbonate complex Cs{(μ‐NCS)(μ‐CS₃)[U(OSi(O^tBu)₃)₃]₂} via a putative NCS^?/S^2? intermediate. The reaction of 1 with one equivalent of CO₂ resulted in deoxygenation and N?C bond formation, yielding the cyanate/oxo complex Cs{(μ‐NCO)(μ‐O)[U(OSi(O^tBu)₃)₃]₂}. Addition of excess CO₂ to 1 led to the unprecedented dicarbamate product Cs{(μ‐NC₂O₄)[U(OSi(O^tBu)₃)₃]₂}.     

Long time dynamics of layered solutions to the shallow water equations

We study the existence of a positive connection, i.e. a stationary solution connecting the boundary data, for the initial-boundary value problem for the viscous shallow water system in a bounded interval (??, ?) of the real line. Subsequently, we investigate the asymptotic behavior of the time-dependent solutions, showing that they first develop into a layered function and then they drift towards the steady state in an exponentially long time interval. The main tool of our analysis is given by the derivation of an ODE for the interface location.     

The effects of annealing in inert atmospheres and of oxygen concentration on chemiluminescence from polypropylene

It has been shown that heating polypropylene powder under a nitrogen atmosphere leads to the significant prolongation of the oxidation induction time measured by chemiluminescence in oxygen at 130 and 140 °C. While heating in nitrogen from 0 to 4 h at 140 °C leads to the linear increase of oxidation induction time, the maximum chemiluminescence intensity I_stat increases with the time of sample annealing until 2 h; then it starts to decay. The different and sometime unknown thermal history of the sample may thus explain the scatter of induction times of oxidation observed with different PPs whether they be pure or stabilised. Maximum chemiluminescence intensity plotted vs. concentration of oxygen in the surrounding atmosphere at 130 and 140 °C also increases linearly; however, this does not correspond with very small reduction of oxidation induction time. The four-parametric “master equations” used in our earlier papers were applied to fit the chemiluminescence runs both in oxygen and in nitrogen. The equation operates with the rate constants of hydroperoxide decomposition and oxidation spreading but at the same time, it takes into account the possible effect of oxidation products on decomposition of hydroperoxides.     

Use of large-volume sample stacking in on-line solid-phase extraction-capillary electrophoresis for improved sensitivity

We present a new system for the sensitive analysis of cephalosporins by CE using both on-line SPE and large-volume sample stacking (LVSS). Sample volumes of 250 muL were loaded onto the SPE microcolumn which was then desorbed with 426 nL of ACN. The SPE elution plug was injected into the CE system via an in-line valve interface filling approximately 60% of the volume of the separation capillary. Subsequently, LVSS was performed by applying a voltage of -5 kV, which resulted in the simultaneous removal of the elution solvent and the preconcentration of the analytes in a narrow zone. This way the amount of analyte loaded into the capillary could be considerably increased without serious loss of CE separation efficiency. LODs for cefoperazone and ceftiofur were in the ng/L range which represents an improvement of a factor of 8450 and 11 450 when compared with direct CE injection. The cephalosporin test compounds presented a good linear response (corrected peak area) between 0.5 and 10 mug/L with correlation coefficients higher than 0.995. The final method is compared with previously reported LVSS-CE and SPE-CE systems for the analysis of cephalosporins.     

Enzymatic assay of marine bacterial phosphatases by capillary electrophoresis with laser-induced fluorescence detection

Microbial ectoenzyme activities in aquatic environments are important determinants of polymer hydrolysis and indicators of the state of microbial carbon, nitrogen, and phosphorus nutrition. Marine ectoenzymes are found on the cell surface or in the periplasmic space of gram-negative heterotrophic bacteria. Phosphatases, which remove phosphate groups from substrates, are one example of an ectoenzyme. Enzyme assays based on-capillary electrophoresis (CE) take advantage of CE's high-efficiency separation, extremely low sample volume requirements, and its ability to electrophoretically mix and separate zones of enzymes, substrates, and products all in one experimental run. CE has better resolving power and, when utilized with laser-induced fluorescence (LIF) detection, it is more sensitive than chromatography. CE-LIF is a promising tool for determining different phosphatases within a single microbial strain as well as the functional diversity between strains. In this study, four bacterial strains were studied (Shewanella sp., TW7, BB2AT2, and Vibrio alginolyticus) with each yielding at least one phosphatase that was kinetically characterized. K(m) values were calculated and found to be in the range of 0.0725-3.35 microM, whereas V(max) values ranged from 1.02 x 10(-3) to 1.05 x 10(-2) microM/min. The large range of values demonstrates differences among the phosphatases, suggesting different roles for each phosphatase not only between the species but also within a single bacterial species. This can have the important implications for organic matter processing in the sea.