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81.
Triphenylphosphine and tributylphosphine are excellent catalysts for Michael additions. Many β-dicarbonyl compounds and electron-poor olefins, including sterically demanding partners, react successfully. The Michael addition catalyzed by phosphines deserves attention in its own right as a useful synthetic method. 相似文献
82.
Aliquat-336 anchored on hydrophobized silica gel was used for effective separation of 237Np from soil matrices and from model solutions. Alpha spectrometry for 237Np determination was used. The interfering radionuclides present in environmental samples such as 234U, 232Th, 231Pa and 239+240Pu were removed by separation with nitric acid solutions containing formic acid and ferrous sulfamate as reducing agents.
Spiking samples with 238,234U, 232Th and 238Pu were used to check separation effectiveness. A separation yield of 237Np from soil matrices was checked by measuring of added known amount activity and was found to be about 15%. The yield of
separation for model solutions was about 56%. Different parameters of eluant on recovery of 237Np from column were studied. 相似文献
83.
Gian Paulo G. Freschi Carolina D. Freschi José A. Gomes Neto 《Mikrochimica acta》2008,161(1-2):129-135
Different kinds of modifiers and coatings on the integrated platform of transversely heated graphite atomizer (THGA) have
been tested for the simultaneous determination of two group of elements: the first, the more volatile, formed by arsenic,
bismuth, lead, antimony and selenium; the second, the less volatile, formed by cobalt, chromium, cupper, iron and manganese
in milk by electrothermal atomic absorption spectrometry. Different Rh-modifiers were studied, such as Rh-coated platforms
(Rh), carbide plus rhodium coated platforms (W-Rh, Zr-Rh), carbide-coated platforms (W and Zr) with co-injection of RhCl3, solutions and uncoated platforms with injection of solutions of Pd(NO3)2, Mg(NO3)2, and RhCl3. Milk samples were diluted 1:10 in 1.0% HNO3 and injected into the tube. The mass of modifier deposited and co-injected in the tube and the use of end capped tubes were
also evaluated in order to improve the electrothermal behavior of analytes. Integrated platform pretreated with W plus co-injection
RhCl3 for first group and pretreated with W-Rh for second group were elected. For 20 μL injected samples the analytical curves
in the 5.0–20.0 μg L−1 concentration range have good linear correlation coefficients (r > 0.998). Relative standard deviations (n = 12) are <6% and the calculated characteristic masses are between 5 pg and 62 pg.
Correspondence: Gian Paulo G. Freschi, Faculdade de Ciências Exatas e Tecnologia, Universidade Federal da Grande Dourados,
PO Box 332, 79.804-970, Dourados-MS, Brazil; Instituto de Química, Universidade Estadual Paulista, PO Box 355, 14801-970 Araraquara-SP,
Brazil 相似文献
84.
William Layton Carolina C. Manica Monika Neda Leo G. Rebholz 《Numerical Methods for Partial Differential Equations》2008,24(2):555-582
We study a computationally attractive algorithm (based on an extrapolated Crank‐Nicolson method) for a recently proposed family of high accuracy turbulence models, the Leray‐deconvolution family. First we prove convergence of the algorithm to the solution of the Navier‐Stokes equations and delineate its (optimal) accuracy. Numerical experiments are presented which confirm the convergence theory. Our 3d experiments also give a careful comparison of various related approaches. They show the combination of the Leray‐deconvolution regularization with the extrapolated Crank‐Nicolson method can be more accurate at higher Reynolds number that the classical extrapolated trapezoidal method of Baker (Report, Harvard University, 1976). We also show the higher order Leray‐deconvolution models (e.g. N = 1,2,3) have greater accuracy than the N = 0 case of the Leray‐α model. Numerical experiments for the 2d step problem are also successfully investigated. Around the critical Reynolds number, the low order models inhibit vortex shedding behind the step. The higher order models, correctly, do not. To estimate the complexity of using Leray‐deconvolution models for turbulent flow simulations we estimate the models' microscale.© 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2008 相似文献
85.
Carolina Pfaff Luis Melo Paulino Betancourt 《Reaction Kinetics and Catalysis Letters》2002,77(2):263-266
Removal of nitrates from drinking water by catalytic hydrogenation over ZSM-5 supported Pt-Cu catalysts was studied. Bimetallics Pt-Cu were prepared by ion exchange of copper on a parent monometallic platinum catalyst. Monometallic platinum catalysts are inactive for nitrate reduction, while Pt-Cu bimetallic catalysts are active for nitrate removal. In the bimetallic catalyst, the role of copper is probably to reduce nitrate according to a redox reaction. The addition of copper to Pt catalysts decreases the production of ammonium ions 相似文献
86.
87.
The ecdysial suture is the region of the arthropod exoskeleton that splits to allow the animal to emerge during ecdysis. We examined the morphology and composition of the intermolt and premolt suture of the blue crab using light microscopy and scanning electron microscopy. The suture could not be identified by routine histological techniques; however 3 of 22 fluorescein isothiocyanate-labeled lectins tested (Lens culinaris agglutinin, Vicia faba agglutinin, and Pisum sativum agglutinin) differentiated the suture, binding more intensely to the suture exocuticle and less intensely to the suture endocuticle. Back-scattered electron (BSE) and secondary electron observations of fracture surfaces of intermolt cuticle showed less mineralized regions in the wedge-shaped suture as did BSE analysis of premolt and intermolt resin-embedded cuticle. The prism regions of the suture exocuticle were not calcified. X-ray microanalysis of both the endocuticle and exocuticle demonstrated that the suture was less calcified than the surrounding cuticle with significantly lower magnesium and phosphorus concentrations, potentially making its mineral more soluble. The presence or absence of a glycoprotein in the organic matrix, the extent and composition of the mineral deposited, and the thickness of the cuticle all likely contribute to the suture being removed by molting fluid, thereby ensuring successful ecdysis. 相似文献
88.
Armandodoriano BiancoClaudia Cavarischia Angela FarinaMarcella Guiso Carolina Marra 《Tetrahedron letters》2003,44(51):9107-9109
Several naturally occurring flavonoids have been synthesised following a new proposed method based on the use of the Heck reaction. The key step involves the coupling of an aryl vinyl ketone with an aryl iodide. This procedure affords the flavonoid moiety in a single step. 相似文献
89.
We propose finitely convergent methods for solving convex feasibility problems defined over a possibly infinite pool of constraints. Following other works in this area, we assume that the interior of the solution set is nonempty and that certain overrelaxation parameters form a divergent series. We combine our methods with a very general class of deterministic control sequences where, roughly speaking, we require that sooner or later we encounter a violated constraint if one exists. This requirement is satisfied, in particular, by the cyclic, repetitive and remotest set controls. Moreover, it is almost surely satisfied for random controls.
相似文献90.
G. Daikuhara E. Truog L. Michaelis L. T. Sharp D. R. Hoogland H. A. Noyes O. Arrhenius C. B. Lipman H. R. Christensen F. W. Parker H. Kappen A. Densch A. Rippel Th. Arnd O. Schreiner G. Loges E. Ramann F. K. Cameron R. Ulbricht W. Wolf W. Jani Biéler-Chatelan E. A. Mitscherlich C. W. Davis B. S. Davisson H. Neubauer W. Schneider Fr. Czapek G. Wunder J. K. Greisenegger K. Vorbuchner H. Niklas Hirschberger Ausschuss für Boden und Düngung des Verbandes Landwirtschaftlicher Versuchs-Stationen im Deutschen Reiche 《Analytical and bioanalytical chemistry》1924,65(6-7):273-274